nhgri_melanoma_class this series represents group of cutaneous malignant melanomas and unrelated controls which were clustered based on correlation coefficients calculated through comparison of gene expression


cerebellar development the affymetrix genechip mu11k was used to analyze the gene expression profile in developing mouse cerebellum two genechips per e18 p7 p14 p21 and p56 to assist in the understanding of the genetic basis of cerebellar development in mice


renal cell carcinoma differential expression we investigated the changes in gene expression accompanying the development and progression of kidney cancer using 500 element complementary dna arrays we measured expression profiles for paired neoplastic and non cancerous renal epithelium samples from individuals using an experimental design optimized for factoring out technological and biological noise and an adapted statistical test we find differentially expressed cdnas with an expected number of false positives functional annotation of these genes provided views of the changes in the activities of specific biological pathways in renal cancer cell adhesion signal transduction and nucleotide metabolism were among the biological processes with large proportion of genes overexpressed in renal cell carcinoma downregulated pathways in the kidney tumor cells included small molecule transport ion homeostasis and oxygen and radical metabolism our expression profiling data uncover gene expression changes shared with other epithelial tumors as well as unique signature for renal cell carcinoma expression data for the differentially expressed cdnas are available in the web supplement


diurnal and circadian regulated genes in arabidopsis plants respond to day night cycling in number of physiological ways at the mrna level the expression of some genes changes during the hr period to identify novel genes regulated in this way we used microarrays containing 521 arabidopsis expressed sequence tags representing an estimated unique genes to determine gene expression levels at hr intervals throughout the day eleven percent of the genes encompassing genes expressed at both high and low levels showed diurnal expression pattern approximately cycled with circadian rhythm by clustering microarray data from additional unrelated experiments we identified groups of genes regulated only by the circadian clock these groups contained the already characterized clock associated genes lhy cca1 and gi suggesting that other key circadian clock genes might be found within these clusters


global profile of germline gene expression in elegans we used dna microarrays to profile gene expression patterns in the elegans germline and identified germline enriched transcripts that define three groups the sperm enriched group contains an unusually large number of protein kinases and phosphatases the oocyte enriched group includes potentially new components of embryonic signaling pathways the germline intrinsic group defined as genes expressed similarly in germlines making only sperm or only oocytes contains family of piwi related genes that may be important for stem cell proliferation finally examination of the chromosomal location of germline transcripts revealed that sperm enriched and germline intrinsic genes are nearly absent from the chromosome but oocyte enriched genes are not


genetic diversity among helicobacter pylori strains helicobacter pylori colonizes the stomach of half of the world population causing wide spectrum of disease ranging from asymptomatic gastritis to ulcers to gastric cancer although the basis for these diverse clinical outcomes is not understood more severe disease is associated with strains harboring pathogenicity island to characterize the genetic diversity of more and less virulent strains we examined the genomic content of pylori clinical isolates by using whole genome pylori dna microarray we found that full of pylori genes are dispensable in one or more strains thus defining minimal functional core of pylori genes while the core genes encode most metabolic and cellular processes the strain specific genes include genes unique to pylori restriction modification genes transposases and genes encoding cell surface proteins which may aid the bacteria under specific circumstances during their long term infection of genetically diverse hosts we observed distinct patterns of the strain specific gene distribution along the chromosome which may result from different mechanisms of gene acquisition and loss among the strain specific genes we have found class of candidate virulence genes identified by their coinheritance with the pathogenicity island


tryptophan metabolism response in coli dna microarray analysis of gene expression in response to physiological and genetic changes that affect tryptophan metabolism in escherichia coli


topoisomerase function in coli replication fork movement analysis of topoisomerase function in bacterial replication fork movement use of dna microarrays


uv exposure in wild type and sos deficient coli uv irradiation of the wild type and lexa mg1655 escherichia coli cells were irradiated at 2x10 cells ml in the davis medium by germicidal lamp nm 66j sec set also includes respective controls for unirradiated cells collected at and min time points comparison between lexa mutant and the isogenic wild type prior the uv treatment is also included as part of the set


eye sage human retinal and rpe sage libraries


leon bailey or federico cheisa


the study of the equation of state ( eos ) , transport properties , and mixing rules of hydrogen ( h ) and helium ( he ) under extreme condition of high pressure and temperature is not only of fundamental interest but also of essential practical applications for astrophysics @xcite .
for instance , giant planets such as jupiter and saturn require accurate eos as the basic input into the respective interior models in order to solve hydrostatic equation and investigate the solubility of the rocky core @xcite . on the other side , the evolution of stars and the design of thermal protection system is assisted by high precision transport coefficients of h - he mixtures at high pressure @xcite . in addition ,
the viscosity and mutual diffusion coefficients are also important input properties for hydrodynamic simulations in modelling the stability of the hot spot - fuel interfaces and the degree of fuel contamination in inertial confinement fusion ( icf ) @xcite .    since direct experimental access such as shock wave experiments
is limited in the mbar regime @xcite , the states deep in the interior of jupiter ( @xmath2 mbar ) and saturn ( @xmath3 mbar ) @xcite can not be duplicated in the laboratory . as a consequence ,
theoretical modelling provides most of the insight into the internal structure of giant planets .
the eos of h - he mixtures have been treated by a linear mixing ( lm ) of the individual eos via fluid perturbation theory @xcite and monte carlo simulations @xcite . recently , several attempts have been made to calculate eos of h - he mixtures by means of quantum molecular dynamic ( qmd ) simulations .
@xcite applied local density approximation of density functional theory ( lda - dft ) calculations for solid h - he mixtures , implying demixing for jupiter and saturn at 15000 k for a he fraction of @xmath4 .
@xcite , lorenzen _ et al . _
@xcite , and militzer @xcite performed qmd simulations by using generalized gradient expansion ( gga ) instead of the lda in order to evaluate the accuracy of the lm approximation and study the demixing of h - he at mbar pressures .
@xcite introduced car - parrinello molecular dynamics ( cpmd ) simulations to calculate the excess gibbs free energy of mixing at a lower temperature compared to that set in the work of lorenzen _ et al .
_ @xcite and militzer @xcite .    considering the transport properties , qmd @xcite and orbital - free molecular dynamics ( ofmd ) @xcite simulations
have been introduced to study hydrogen and its isotropic deuterium ( d ) and tritium ( t ) .
self - diffusion coefficients in the pure h system and mutual diffusion for d - t mixtures were determined for temperatures @xmath51 to 10 ev and equivalent h mass densities 0.1 to 8.0 g / cm@xmath1 @xcite .
qmd and ofmd simulations of self - diffusion , mutual diffusion , and viscosity have recently been performed on heavier elements ( fe , au , be ) @xcite and on mixtures of li and h @xcite .
the present work selects h - he mixture as a representative system and examines some of the standard mixing rules with respect to the eos and transport properties ( viscosity , self and mutual diffusion coefficients ) in the warm dense regime that covers standard extreme condition as reached in the interiors of jupiter and saturn .
the thermophysical properties of the full mixture and the individual species have been derived from qmd simulations , where the electrons are quantum mechanically treated through finite - temperature ( ft ) dft and ions move classically . in the next section , we present the formalism for qmd and for determining the static and transport properties .
then , eos , viscosity , and diffusion coefficients for h - he mixtures are presented , and the qmd results are compared with the results from reduced models and qmd based linear mixing models . finally , concluding remarks are given .
in this section , a brief description of the fundamental formalism employed to investigate h - he mixtures is introduced .
the basic quantum mechanical density functional theory forms the basis of our simulations .
the implementation of schemes in determining diffusion and viscosity is discussed . mixing rules that combine pure species quantities to form composite properties
is also presented .
qmd simulations have been performed for h - he mixtures by using vienna _
ab initio _ simulation package ( vasp ) @xcite . in these simulations , the electrons are treated fully quantum mechanically by employing a plane - wave ft - dft description , where the electronic states follow the fermi - dirac distribution .
the ions move classically according to the forces from the electron density and the ion - ion repulsion .
simulations have been performed in the nvt ( canonical ) ensemble where the number of particles @xmath7 and the volume are fixed .
the system was assumed to be in local thermodynamic equilibrium with the electron and ion temperatures being equal ( @xmath8 ) . in these calculations ,
the electronic temperature has been kept constant according to fermi - dirac distribution , and ion temperature is controlled by noe thermostat @xcite .    at each step during md simulations , a set of electronic state functions [ @xmath9 for each * k*-point
are determined within kohn - sham construction by @xmath10 with @xmath11 in which the four terms respectively represent the kinetic contribution , the electron - ion interaction , the hartree contribution and the exchange - correlation term . the electronic density is obtained by @xmath12 then by applying the velocity verlet algorithm , based on the force from interactions between ions and electrons , a new set of positions and velocities are obtained for ions .
all simulations are performed with 256 atoms and 128 atoms for pure species of h and he , and as for the case of the h - he mixture , a total number of 245 atoms ( 234 h atoms and 11 he atoms ) for a mixing ratio @xmath13 ( corresponding to the h - he immiscibility region determined in the work of morales _ et al . _
@xcite ) has been adopted , where a cubic cell of length @xmath14 ( volume @xmath15 ) is periodically repeated .
the simulated densities range from 1.0 to 4.0 g / cm@xmath1 for pure h system . as for pure
he and h - he mixture , the size of the supercell is chosen to be the same as that for pure h to secure a constant electron number density ( in the range @xmath0/m@xmath1 ) . the temperature from 4000 k to 20000 k
has been selected to highlight the conditions in the interiors of jupiter and saturn .
the convergence of the thermodynamic quantities plays an important role in the accuracy of qmd simulations . in the present work ,
a plane - wave cutoff energy of 1200 ev is employed in all simulations so that the pressure is converged within 2% .
we have also checked out the convergence with respect to a systematic enlargement of the * k*-point set in the representation of the brillouin zone . in the molecular dynamic simulations ,
only the @xmath16 point of brillouin zone is included .
the dynamic simulation is lasted 20000 steps with time steps of 0.2 @xmath17 0.7 fs according to different densities and temperatures . for each pressure and temperature ,
the system is equilibrated within 0.5 @xmath17 1 ps .
the eos data are obtained by averaging over the final 1 @xmath17 3 ps molecular dynamic simulations .
the self - diffusion coefficient @xmath18 can either be calculated from the trajectory by the mean - square displacement @xmath19 or by the velocity autocorrelation function @xmath20 where @xmath21 is the position and @xmath22 is the velocity of the @xmath23th nucleus . only in the long - time limit , these two formulas of @xmath18 are formally equivalent .
sufficient lengths of the trajectories have been generated to secure contributions from the velocity autocorrelation function to the integral is zero , and the mean mean - square displacement away from the origin consistently fits to a straight line .
the diffusion coefficient obtained from these two approaches lie within 1 % accuracy of each other .
here , we report the results from velocity autocorrelation function .
we have also computed the mutual - diffusion coefficient @xmath24 from the autocorrelation function @xmath25 with @xmath26 where the concentration and particle number of species @xmath27 are denoted by @xmath28 and @xmath29 , respectively , and the total number of particles in the simulation box @xmath30 .
the quantity @xmath31 is the thermodynamic factor related to the second derivation of the gibbs free energy with respect to concentrations @xcite . in the present simulations ,
@xmath31 value has been adopted equal to unity since studies with leonard - jones and other model potentials have shown that for dissimilar constituents the @xmath31-factor departs from unity by about 10% @xcite .
the viscosity @xmath32 has been computed from the autocorrelation function of the off - diagonal component of the stress tensor @xcite @xmath33 the results are averaged from the five independent off - diagonal components of the stress tensor @xmath34 , @xmath35 , @xmath36 , @xmath37 , and @xmath38 .
different from the self - diffusion coefficient , which involves single - particle correlations and attains significant statistical improvement from averaging over the particles , the viscosity depends on the entire system and thus needs very long trajectories so as to gain statistical accuracy . to shorten the length of the trajectory , we use empirical fits @xcite to the integrals of the autocorrelation functions .
thus , extrapolation of the fits to @xmath39 can more effectively determine the basic dynamical properties .
both of the @xmath18 and @xmath40 have been fit to the functional in the form of @xmath41 $ ] , where @xmath42 and @xmath43 are free parameters .
reasonable approximation to the viscosity can be produced from the finite time fitting procedure , which also serves to damp the long - time fluctuations .
the fractional statistical error in calculating a correlation function @xmath44 for molecular - dynamics trajectories @xcite can be given by @xmath45 where @xmath43 is the correlation time of the function , and @xmath46 is the length of the trajectory .
in the present work , we generally fitted over a time interval of [ 0 , @xmath47 .      here
, we examine two representative mixing rules .
the first , termed density - matching rule ( mrd ) with the inspiration of a two - species ideal gas .
the second , termed pressure - matching rule ( mrp ) , which follows from two interacting immiscible fluids .    in the mrd
, the volume of the individual species is set equal to that of the mixture ( @xmath48 ) , and qmd simulations are performed for h at a density of @xmath49 and he at @xmath50 at a temperature @xmath51 .
then , pressure predicted by mrd is determined by simply adding the individual pressures from the pure species h and he simulations .
other transport coefficients , such as mutual diffusion and viscosity , follow the same prescription and are summarized as @xmath52 the superscript is used to denote values predicted from mrd .
the derived pressure based on density mixing rule generally follows from the ideal noninteracting h and he gas in a volume @xmath53 .
the mrp has a more complicated construction compared to mrd .
mrp can be characterized as the following prescription : @xmath54 in this case , we have performed a series of qmd simulations on the individual species h and he , where the volumes change under a constraint @xmath55 until the individual pressures equal to each other @xmath56 .
the total pressure becomes the predicted value .
here , we use the excess or electronic pressure @xmath57 to evaluate this mrp mixing rule .
composite properties such as mutual diffusion and viscosity are evaluated by combining the individual species results via volume fractions @xmath58 .
finally , we also derive properties of the mixture from a slightly more complex mixing rule @xcite , as so - called binary ionic mixture ( bim ) : @xmath59 with @xmath60 the predicted mutual - diffusion coefficient or the viscosity .
the subscript @xmath61 denotes the mixture and @xmath23 the pure species .
in this section , the wealth of information derived from qmd calculations are mainly presented through figures , and the general trends of the eos as well as transport coefficients are concentrated in the text .
it is , therefore , interesting to explore not only to get insight into the interior physical properties of giant gas planets but also to examine a series of mixing rules for hydrogen and helium .
additionally , one can consider the influence of helium on the eos and transport coefficients of mixing .
high precision eos data of hydrogen and helium are essential for understanding the evolution of jupiter and target implosion in icf .
experimentally , the eos of hydrogen and helium in the fluid regime have been studied through gas gun @xcite , chemical explosive @xcite , magnetic driven plate flyer @xcite , and high power laser @xcite . since these experiments were limited by the conservation of mass , momentum , and energy , the explored density of warm dense matter
were limited within @xmath62 times of the initial density .
recently , a new technique combined diamond anvil cell ( dac ) and high intensity laser pulse has successfully been proved to provide visible ways to generate shock huguniot data of hydrogen over a significantly broader density - temperature regime than previous experiments @xcite
. however , the density therein was still restricted within 1 g / cm@xmath1 .        in our simulations , wide range eos for h
, he , and h - he mixtures have been determined according to qmd method .
the eos can be divided into two parts that is , contributions from the noninteracting motion of ions ( @xmath63 ) and the electronic term ( @xmath64 ) , @xmath65 where @xmath64 is calculated directly through dft . in fig .
[ fig_eos1 ] ( a ) , we have compared our results of @xmath64 with that of holst _ et al . _
@xcite , where the electronic pressure is expressed as a smooth function in terms of density and temperature , and the results agree with each other with a very slight difference ( accuracy within 5% ) . in the simulated density and temperature regime
, we do not find any signs indicating a liquid - liquid phase transition ( @xmath66 ) or plasma phase transition ( @xmath67 ) , which are characterized by molecular dissociation and ionization of electrons , respectively . with considering the mixing of he into h ,
the electronic pressure is effectively reduced , as has been shown in fig .
[ fig_eos1 ] ( b ) .
mrd accounts for contribution from noninteracting h and he subsystems in the volume of the mixtures . in mrd ,
the pressure contributed from noninteracting ions is the same as that of the mixture , but the electronic pressure is much lower due to the low electronic density in the pure species simulations .
it is indicated that the electronic pressure is underestimated by mrd model at about 8% @xmath17 9% ( see fig .
[ fig_eos2 ] ) . for mrp model
, we have firstly performed a series of pure species simulations at a wider density ( temperature ) regime compared to h - he mixtures .
then , the simulated eos data are fitted into smooth functions in terms of density and temperature . under the constraint of @xmath68
, we have predicted the electronic pressures @xmath69 according to mrp model by solving pure species eos function at certain densities and temperatures , as shown in fig .
[ fig_eos2 ] .
it is indicated that the mrp model agrees better with direct qmd simulations ( accuracy within 3% ) , the difference mainly come from the ionic interactions between h and he species after mixing .       and 8 g / cm@xmath1 , respectively .
( a ) self - diffusion coefficient ; ( b ) viscosity .
the direct qmd simulated results are presented by black crosses , while the fitted results are denoted by blue dashed lines . ]
qmd simulations have been performed within the framework of ft - dft to benchmark the dynamic properties of h , he , and h - he mixture in the wdm regime .
illustrations for the self - diffusion coefficients and viscosity ( for h and he at densities of 2.0 g / cm@xmath1 and 8.0 g / cm@xmath1 , respectively ) at a temperature 12000 k , as well as their fits are shown in fig . [ fig_dandeta ] .
the trajectory of the present simulations lasts 4.0 @xmath17 14.0 ps , and correlation times between 1.0 and 15.0 fs . as a consequence ,
the computational error for the viscosity lies within 10% .
after accounting for the fitting error and extrapolation to infinite time , a total uncertainty of @xmath17 20% can be estimated .
the uncertainty in the self - diffusion coefficients is smaller than 1% , due to the additional @xmath70 advantage given by particle average .    .
for helium , the density is 8 g / cm@xmath1 .
the electron number density for pure species ( h and he ) is @xmath71/m@xmath1 .
]    dynamic properties of wdm are generally governed by two dimensionless quantities , namely , ionic coupling ( @xmath16 ) and electronic degenerate ( @xmath72 ) parameter .
the former one is defined by the ratio of the potential to kinetic energy @xmath73 , with @xmath74 the ionic charge , and @xmath75 the ion - sphere radius ( @xmath76 is the number density ) . the latter one @xmath77 , where @xmath78 is fermi temperature .
it has been reported that dynamic properties such as diffusion coefficients and viscosity can be represented purely in terms of ionic coupling parameter @xmath16 according to molecular dynamics or monte carlo simulations based on one component plasma ( ocp ) model @xcite , where ions move classically in a neutralizing background of electrons .
for instance , hansen _
@xcite introduced a memory function to analyze the velocity autocorrelation function , and obtain the diffusion coefficient in terms of @xmath79 with the plasma frequency @xmath80 .
based on classical molecular dynamic simulations , bastea @xcite has fitted the viscosity into the following form @xmath81 with @xmath82 , @xmath83 , @xmath84 , and @xmath85 .
since ocp model is restricted to a fully ionized plasma , we use @xmath74=1.0 ( or 2.0 ) for hydrogen ( or helium ) to compute the self - diffusion coefficient and viscosity . in fig .
[ fig_qmd_ocp ] ( a ) , we show comparison between qmd and ocp model @xcite for hydrogen and helium at densities of 2 g / cm@xmath1 and 8 g / cm@xmath1 .
the general tendency for the self - diffusion coefficient with respect to temperature is similar for qmd and ocp model , however , the difference up to @xmath1760 % is observed between the two results . for the viscosity [ fig .
[ fig_qmd_ocp ] ( b ) ] , ocp @xcite predicts smaller ( larger ) values for hydrogen ( helium ) compared to qmd simulations .
the viscosity is governed by interactions between particles and ionic motions , contribution from the former one decrease with the increase of temperature , while , it increases for the latter one . as a consequence
, the viscosity may have local minimum along temperature . for hydrogen
, the local minimum locates around 10000 k and 14000 k indicated by qmd and ocp model , respectively . while in the case of helium
, we do not observe any signs for the local minimum in the simulated regime .
/m@xmath1 and temperature from 4000 @xmath17 20000 k. ]    in fig .
[ fig_mix ] , we have shown the mutual diffusion coefficient @xmath86 and viscosity @xmath87 for h - he mixture with an electron number density of @xmath88/m@xmath1 , and results from mixing models are also provided .
the transport coefficients predicted by mrd can be directly evaluated through eq .
( [ eq_mrd ] ) . for mrp model ,
we have firstly fitted the self - diffusion coefficients and viscosity in terms of density and temperature , after determining the volume for each species under the constraint of @xmath89 , the transport coefficients are then obtained . in bim model , we have used @xmath90 and @xmath91 , then , the transport coefficients are determined by eq .
( [ eq_bim ] ) . here
we would like to stress that in some mixture studies based on average atom models , the properties of pure species are derived from perturbed - atom models , where boundary conditions are introduced from the surrounding medium by treating a single atom within a cell . in the present work ,
the dynamic properties of different mixing rules originate from qmd calculations of the individual species . despite divorced of the h -
he interactions , the pure species calculations still contain complex intra - atomic interactions based on large samples of atoms .
the mutual diffusion coefficient of h - he mixture shows a linear increase with respect of temperature , as indicated in fig .
[ fig_mix](a ) .
the data from mrp and bim models have a better agreement with qmd simulations compared with that of the mrd model , where ion densities are reduced and results in a larger diffusion coefficient .
the viscosity of h - he mixture has a more complex behavior than pure species under extreme condition . as shown in fig .
[ fig_mix ] ( b ) , mrd is valid at low temperature , while mrp works at higher temperature .
bim rule moves the results into better agreement with the h - he mixture , leaving within 30% or better for the simulated conditions .
in summary , we have performed systematic qmd simulations of h , he , and h - he mixture in the warm dense regime for electron number density ranging from @xmath0/m@xmath1 and for temperatures from 4000 to 20000 k. the present study concentrated on thermophysical properties such as the eos , diffusion coefficient , and viscosity , which are of crucial interest in astrophysics and icf .
various mixing rules have been introduced to predict dynamical properties from qmd simulations of the pure species and compare with direct calculations on the fully interacting mixture .
we have shown that mrd and mrp rules produce pressures within about 10 % of the h - he mixture , however , the mutual diffusion coefficients are as different as 75 % and it is 50 % for the viscosity .
bim rule generally gives better agreement with the mixture results .
we have also compared our qmd results with ocp model for the pure species .
this work was supported by nsfc under grants no .
11275032 , no . 11005012 and no . 51071032 , by the national basic security research program of china , and by the national high - tech icf committee of china .
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 thermophysical properties of hydrogen , helium , and hydrogen - helium mixtures have been investigated in the warm dense matter regime at electron number densities ranging from @xmath0/m@xmath1 and temperatures from 4000 to 20000 k via quantum molecular dynamics simulations .
 we focus on the dynamical properties such as the equation of states , diffusion coefficients , and viscosity . mixing rules ( density matching , pressure matching , and binary ionic mixing rules )
 have been validated by checking composite properties of pure species against that of the fully interacting mixture derived from qmd simulations .
 these mixing rules reproduce pressures within 10% accuracy , while it is 75 % and 50 % for the diffusion and viscosity , respectively .
 binary ionic mixing rule moves the results into better agreement .
 predictions from one component plasma model are also provided and discussed .


kouveliotou ( 1993 ) showed that the durations of gamma ray bursts ( grbs ) have a bimodal distribution , with roughly a third of the observed bursts corresponding to a short duration ( @xmath6 s ) population , and the remaining two - thirds belonging to a long duration ( @xmath7 s ) population .
searches for transient x - ray , optical and radio afterglow emission have so far been largely limited to long duration bursts .
this is because the italian - dutch bepposax satellite and other presently active instruments , which have been used to obtain well - determined grb coordinates , are sensitive only to bursts longer than a few seconds .
most of the x - ray follow - ups of long grbs have been successful , and 35 x - ray afterglows have been detected so far ( mid-2001 ) .
the success rate of optical searches has been somewhat less ( lazzati , covino & ghisellini 2001 ; fynbo 2001 ) , and 23 optical afterglows have been detected ; the majority of optical afterglows have yielded redshifts .
the success rate in radio has been comparable to that in the optical .    among short grbs , optical and radio searches for afterglows
have so far been carried out for only four sources that happened to be well localized by the interplanetary network ( hurley 2001 ) .
no afterglow emission was detected , but the sensitivity of the searches was not very high .
more searches will be carried out in the future when rapid arc - minute localizations of short grbs become routinely available from the upcoming hete ii and swift satellites .    in this _
, we make reasonable assumptions about the physical parameters of short grbs and estimate the broadband afterglow emission to be expected from these bursts .
the results may be useful for designing search strategies for afterglows of short grbs .
the predictions for the light - curves of the afterglows depend on some key parameters .
we attempt to estimate the relative magnitudes of these parameters in short and long grbs using observational data and some theoretical ideas .
studies of the temporal and spectral properties of short and long grbs have revealed that the burst duration is anticorrelated with the spectral hardness ( kouveliotou 1993 ) .
the peak frequency of the @xmath8 spectrum increases with the bulk lorentz factor of the grb in the external shock model for producing @xmath0-ray emission ( rees & mszros 1992 ; piran , shemi & narayan 1993 ; katz 1994 ) , however the relationship is complicated in the internal shock model ( see piran 1999 for a review ) .
fortunately , the lorentz factor ( lf ) of the late - time grb remnant which produces the afterglow is practically independent of the lf during the early grb phase , and so it is unlikely that any difference in the initial lf for the long and the short duration grbs will have any effect on the afterglow flux .
we note , however , that if the initial jet opening angle @xmath9 for short duration grbs were larger than longer lasting grbs , it will cause the afterglows of short grbs to become considerably dimmer since the jet transition time ( see  3 ) varies as @xmath10 .    by analysing a sample of over 400 grbs , and allowing for observational bias against detecting weak and long bursts with peak fluxes below the detection threshold ,
lee & petrosian ( 1997 ) showed that there is a highly significant positive correlation between the burst fluence and duration . in another study ,
mukherjee ( 1998 ) used two multivariate clustering methods to show that most of the structure in the multidimensional space of burst observations is contained in three fundamental quantities : duration , fluence , and spectral hardness . according to their analysis , short / hard grbs have a 25 kev1 mev fluence @xmath11 ( in cgs units ) of approximately @xmath12 , while long / soft grbs have @xmath13 .
short bursts thus have about 20 times less fluence than long bursts ( see also mao et al . 1994 , piran 1996 ) .
figure 1 shows the 25 kev1mev fluences @xmath11 and the durations @xmath14 of 34 long grbs for which afterglows have been observed .
the average duration for these grbs is @xmath15 , similar to that of the 486 long bursts analyzed by mukherjee ( 1998 ) from the third batse catalog ( meegan 1996 ) .
the average fluence of long grbs with afterglows is @xmath16 , implying that these bursts are , on average , approximately twice as bright as the long bursts analyzed by mukherjee et al .
( 1998 ) and 40 times more energetic than the 203 short bursts analyzed by them .
the grb energy output is determined by the kinetic energy of the relativistic outflow and the efficiency with which dissipative and radiative mechanisms convert some of the energy into @xmath0-ray emission . assuming that grbs arise from internal shocks in unsteady winds , the dissipation efficiency is determined by the magnitude of the fluctuations in the ejection lorentz factors of various parts of the outflow .
our present understanding of the properties of grb progenitors does not allow us to establish a correlation between the grb duration and efficiency .
it is possible that short grbs are somewhat less efficient than long grbs because the radius at which internal shocks occur in short grbs is closer to the photospheric radius ( kumar 1999 ) , so that some of the emission may be degraded by multiple scattering . ignoring this effect
, we expect the ratio of the kinetic energies of short and long grbs to be the ratio of their fluences , i.e. , a factor of about 20 .
we finally discuss the environments in which short and long bursts take place .
the existence of these two clearly distinct populations of grbs probably implies different physical origins .
most models of grbs  mergers of binary neutron stars ( ns  ns ) , black hole ( bh)ns , or bh  white dwarf ( wd ) , and failed supernovae / collapsars  involve the formation of a bh surrounded by a disk of debris .
the spin energy of the hole and the gravitational , thermal , and rotational energy of the disk represent the available reservoirs to power the @xmath17 ergs required for the grb .
the bh spin may be tapped by the blandford - znajek process ( 1977 ) , and the disk energy may be extracted either via neutrino annihilation ( eichler et al . 1989 ) or via magnetic fields / flares ( narayan , paczyski & piran 1992 ; see mszros , rees & wijers 1999 for a review ) .    the burst duration is determined both by the timescale for ejecting the relativistic outflow , and by the processes that @xmath18 shape the outflow dynamics until the gas reaches the region where the @xmath0-ray photons are emitted , such as the penetration of the grb jet through the envelope of a collapsed star , and @xmath19 convert the outflow kinetic energy into @xmath0-rays . in those bursts where the high energy emission arises as the outflow energy is dissipated through interaction with the circumburst medium , grbs of long duration can be obtained even if the initial ejection is impulsive .
however , the general absence of signatures of an external shock in the temporal structure of grbs ( sari & piran 1997 ; ramirez - ruiz & fenimore 2000 ) indicates that the grb emission is produced in internal shocks over a small range of distances . if this is the case , then the grb duration is a direct measure of the time interval during which the `` central engine '' is active .    if grbs originate in ns
ns or ns - bh mergers ( goodman 1986 ; eichler 1989 ; paczyski 1991 ; narayan 1992 ; mszros & rees 1992 ; katz & canel 1996 ) , enough mass reaches the resulting bh to power the grb , provided the disk is sufficiently small and accretion is driven by neutrino cooling ( narayan , piran & kumar 2001 ) .
the expected duration of the relativistic wind ( and thus the grb ) is under 1 s. thus these progenitors can naturally produce short grbs .
the collapse of the iron core of a massive star ( collapsar model : woosley 1993 ; paczyski 1998 ) with intermediate angular momentum leads to the formation of a disk with a sufficient accretion rate to power a relativistic outflow lasting for 1020 s ( macfadyen & woosley 1999 ) .
the collapsar model is thus more appropriate for long grbs .
if the core collapse produces a ns and an out - going shock , the bh and the torus form when the ejected matter , lacking sufficient momentum , falls back ( macfadyen , woosley & heger 2001 ) . in this model
the grb duration is set by the dynamics of the fallback , and most likely would accommodate only the longest grbs , lasting for more than 100 s. long grbs could also arise from wd  bh ( fryer 1999 ) or helium star  bh mergers ( zhang & fryer 2001 ) , which lead to the formation of larger disks with accretion times above 10 s. however , it is likely that the gas will accrete via a convection - dominated accretion flow in these systems , in which case the flow is likely to be rather inefficient at extracting the disk energy ( narayan 2001 ) .    according to these ideas ,
then , there is a clear association between the type of grb progenitor and the burst duration .
short grbs are likely to involve merging ns binaries ( ns  ns or ns  bh ) , which should occur predominantly in the low density halo of the host galaxy , given the velocities of a few hundred @xmath20 acquired by the ns at birth and the binary coalescence time of about 100 myr .
long grbs , on the other hand , are likely to be associated with massive stars that at the end of their evolution ( a few myr ) are still within the cloud where they formed .
we note that bloom , kulkarni & djorgovski ( 2001 ) have identified the host galaxies of 20 afterglows of long duration grbs and have found grb  host offsets lower than those expected for merging ns binaries ( bloom , sigurdsson & pols 1999 ; bulik , belczyski & zbijewski 1999 ; fryer , woosley & hartmann 1999 ) .
furthermore , the high column densities identified by owens ( 1998 ) and galama & wijers ( 2001 ) from the absorption of the x - ray afterglow emission indicate that long - duration grbs occur in giant molecular clouds , yielding further support for the massive star collapse model for long bursts .
if the above arguments are correct , we expect the afterglows of short grbs to occur in a more tenuous medium compared to the afterglows of long - duration grbs .
the difference in the density of the medium is likely to be a few orders of magnitude .
given the kinetic energy @xmath21 of the relativistic outflow and the number density @xmath22 of the ambient external medium , plus a few other dimensionless parameters described below , the afterglow light - curves in various bands may be theoretically estimated ( e.g. , sari , piran & narayan 1998 ; panaitescu & kumar 2001a , and references therein ) . if we consider early times , when the radio emission is below the peak frequency @xmath23 of the afterglow spectrum , and if we assume that the cooling frequency @xmath24 is between the optical and x - ray bands , then the analysis of panaitescu & kumar ( 2001a ) shows that f_radio ^-2/3 ^1/3 e^5/6 n^1/2 , [ radio ] f_optical ^p-1 ^(p+1)/4 e^(p+3)/4 n^1/2 , [ optic ] f_x - ray ^p-1 ^(p-2)/4 e^(p+2)/4 .
[ xray ] here , @xmath21 is the isotropic equivalent kinetic energy of the outflow , @xmath25 is the fractional energy in electrons , @xmath26 is the index of the power - law distribution of the electron lorentz factor @xmath27 , and @xmath28 is the fraction of the post - shock thermal energy in magnetic field ( see panaitescu & kumar 2001a for details ) .
the break frequencies satisfy @xmath29 , @xmath30 for synchrotron - dominated electron cooling , and @xmath31^{1/(4-p)}$ ] when inverse compton losses exceed synchrotron cooling .
the above equations show that for @xmath32 , which is the average value for this parameter determined by panaitescu & kumar ( 2001b ) from numerical modeling of eight grb afterglows , the afterglow flux is roughly proportional to the kinetic energy @xmath21 .
since short grbs have a fluence on average @xmath2 times smaller than that of long grbs , other parameters being equal , we expect the afterglows of short grbs to be @xmath2 times dimmer than the afterglows of long grbs .
the equations show that the afterglow flux in short bursts would be further suppressed if these bursts occur in a lower density medium compared to long bursts .
the expressions for the radio and optical flux have an explicit dependence on @xmath22 .
even though the formula for the x - ray flux does not have an explicit dependence , this flux is also suppressed since , for low @xmath22 , the cooling frequency @xmath24 moves above the x - ray band and so the x - ray afterglow light - curve is described by equation ( [ optic ] ) rather than equation ( [ xray ] ) .    finally , if the breaks observed at one to a few days in the optical emission of several grb afterglows are due to collimation of the outflow ( rhoads 1999 ; sari et al .
1999 ; kumar & panaitescu 2000 ) , then the @xmath2 times smaller kinetic energy of the jets in short grbs will cause the jet break time @xmath33 to occur @xmath34 times earlier in these bursts compared to long grbs .
this will further diminish the brightness of short - grb afterglows ( at a fixed observing time ) by a factor of about @xmath35 .
these conclusions are illustrated in figure 2 , which compares the radio , optical , and x - ray emission of a typical long - grb afterglow with that predicted for short - grb afterglows with lower values of @xmath21 and @xmath22 .
the numerical calculations of the afterglow dynamics and emission of radiation were done by the methods described in panaitescu & kumar ( 2000 ) .
the parameters for the long - grb afterglow were chosen such that at one day after the burst the model yields a radio flux of @xmath36 mjy , an optical brightness of @xmath37 and a 210 kev x - ray flux of @xmath38 , in rough agreement with observations .
we see from fig .
2 that the radio emission from a typical short - grb afterglow will most likely be very difficult to detect . the same is true also for the optical emission , where only early ( @xmath39 day ) observations as deep as the measurements made by groot ( 1998 ) for grb 970828 and by fynbo ( 2001 ) for grb 000630 are likely to be successful . the best chance for detecting the afterglow of a short grb is with x - ray observations .
bepposax will need to observe earlier than @xmath40 day , and cxo , hete ii and swift earlier than @xmath41 days .
such observations are quite feasible .    because of the roughly linear dependence of the afterglow brightness on the kinetic energy @xmath21 , any difference in the average redshifts of short and long grbs will not alter the above conclusions .
the redshift enters into the estimate of @xmath21 , and through it in the estimate of the afterglow luminosity , but it factors out when the luminosity is converted to the observed flux .
the fluences above 25 kev of grbs detected by batse are positively correlated with the durations of these bursts ; long bursts ( durations longer than a few seconds ) are on average 20 times more energetic than short bursts .
moreover , the @xmath42 three dozen long grbs for which afterglows have been detected so far ( following their accurate localization by bepposax and the interplanetary network ) are on average 40 times brighter ( in fluence ) than typical short grbs .
thus we expect the relativistic outflow of a long grb to have about 20 times the kinetic energy of the outflow from a short grb .
if the other parameters that influence the dynamics of the grb remnant and the emission of radiation are roughly the same , we predict that the afterglows of short grbs should be a factor of 10 or more dimmer than the afterglows of long grbs .    if short grbs arise from merging ns  ns or ns  bh binaries which may have traveled upto or beyond the very tenuous outskirts of their host galaxies , and if long grbs are due to the core collapse of massive stars which die in the dense molecular clouds where they were formed , then the densities @xmath22 of the media surrounding these two types of grbs may differ by a few orders of magnitude .
this could further seriously diminish the prospects of detecting radio and optical afterglows of short grbs since the afterglow brightness in these bands is proportional to @xmath43 .
we conclude that the best chance of detecting afterglows of short grbs is with early x - ray observations within 1 day after the grb .
rapid and deep optical follow - up within a few hours after the main event may also lead to a detection .
radio observations appear the least promising ( fig .
2 ) .    of course
, short grbs significantly brighter than average could be as energetic as some of the long grbs for which afterglows have been seen ( fig .
the afterglows of such unusually bright short grbs could be detected even beyond a day , particularly if the magnetic field strength is close to equipartition ( @xmath44 ) .
but such bursts should be in the minority .
on the other hand , if future observations indicate that the afterglows of most short grbs are as bright as those of long grbs , it would imply that one or more of the assumptions we have made in our analysis is invalid .
one possibility is that the @xmath0-efficiency is significantly lower in short bursts than in long bursts , as disussed in kumar ( 1999 ) , and another is that the efficiency spans a wide range in both types of bursts , indicating a highly inhomogeneous outflow ( kumar & piran 2000 ) .
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, apj , 523 , l113 kumar , p. & piran , t. 2000 , apj , 535 , 152 kumar , p. & panaitescu , a. 2000 , apj , 541 , l9 lazzati , d. , covino , s. & ghisellini , g. 2001 , a&a , submitted ( astro - ph/0011443 ) lee , t. & petrosian , v. 1997 , apj , 474 , 37 macfadyen , a. & woosley , s. 1999 , apj , 524 , 262 macfadyen , a. , woosley , s. & heger , a. 2001 , apj , 550 , 410 mao , s. , narayan , r. , and piran , t. , 1994 , apj , 420 , 171 meegan , c. 1996 , apj , s106 mszros , p. & rees , m. 1992 , apj , 397 , 570 mszros , p. , rees , m.j . & wijers , r. 1999 , new ast , 4 , 303 mukherjee , s. 1998 , apj , 508 , 314 narayan , r. , paczyski , b. & piran , t. 1992 , apj , 395 , l83 narayan , r. , piran , t. & kumar , p. 2001 , apj , in press ( astro - ph/0103360 ) paczyski , b. 1991 , acta ast , 41 , 257 paczyski , b. 1998 , apj , 494 , l45 panaitescu , a. & kumar , p. 2000 , apj , 543 , 66 panaitescu , a. & kumar , p. 2001a
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 if the efficiency for producing @xmath0-rays is the same in short duration ( @xmath1 s ) gamma - ray bursts ( grbs ) as in long duration grbs , then the average kinetic energy of short grbs must be @xmath2 times less than that of long grbs .
 assuming further that the relativistic shocks in short and long duration grbs have similar parameters , we show that the afterglows of short grbs will be on average 1040 times dimmer than those of long grbs .
 we find that the afterglow of a typical short grb will be below the detection limit ( @xmath3 ) of searches at radio frequencies
 . the afterglow would be difficult to observe also in the optical , where we predict @xmath4 a few hours after the burst
 . the radio and optical afterglow would be even fainter if short grbs occur in a low - density medium , as expected in ns  ns and ns  bh merger models .
 the best prospects for detecting short - grb afterglows are with early ( @xmath5 day ) observations in x - rays .    3


the conception and construction of systems of well - defined coupled macrospins underpins both the fields of artificial frustrated magnetism@xcite and nanomagnetic logic.@xcite the two communities however remain largely separate , balanced at the fundamental and applied ends of the same physical problem : the predictable and controlled evolution of magnetic configurations in patterns of nanomagnets .
a carefully - designed balance of field scales allows for the manipulation of well - defined defects or `` frustrations '' in the local ground state ( gs ) macrospin order , forming the basis of interesting and useful operations . quenched disorder ( qd ) , the distribution in properties between the coupled components inherent from nanopatterning
, however acts to disrupt these processes.@xcite    antiferromagnetic ising lattices@xcite and ice models@xcite have been realized from patterned elements possessing well - defined bi - stable dipolar behavior , in which competing interactions control collective ordering .
propagation of charge defects has generated substantial interest@xcite due to a qualitative analogy with `` monopole '' excitations in rare - earth pyrochlore materials.@xcite magnetic islands and multilayer heterostructures have also been employed for information processing , in the form of logic gates , shift registers and ratchets.@xcite a domain wall `` soliton''@xcite at the boundary between two gs ordered phases can be unidirectionally field - driven along a conduit given underlying symmetries are appropriately broken .    in this work ,
we introduce a novel system which exemplifies the equality of such contemporary works in nanomagnetism , and explore its potential in executing reliable and repeatable operations .
the system is a circular ring of radially - aligned evenly - spaced ising - like spin moments .
crucially , the number of moments @xmath0 is fixed to be odd , which , as we will show , forces the system to possess a frustrated topological soliton defect@xcite in its gs and form an approximate realization of a magnetic mbius loop.@xcite the curvature of the ring imposes chirality under the application of a rotating constant - amplitude magnetic field , and we use numerical simulations to show how this allows for a soliton to be driven around the system . with experimental realization in mind ,
we make various assumptions appropriate for patterned nanomagnets to build the model and further test for robustness against qd .
furthermore , we discuss the application of the system as a multiturn counter.@xcite     spin ring systems for ( a ) @xmath1  3 , and ( b ) @xmath1  5 .
the ring radius @xmath2 .
spins are number from @xmath3  1 to @xmath0 .
an intrinsic ground state defect can take positions p@xmath4 as indicated by circles .
the defect position for the given ground state configuration is emboldened in red at p@xmath5 .
@xmath6 is the initial applied field used in simulations .
the spin ring is illustrated in fig .
[ fig1 ] for @xmath0 = 3 and 5 spins .
the ising - like spins @xmath7 , represented by arrows numbered @xmath8 = 1 to @xmath0 anticlockwise , are radially - aligned and equally spaced by an angle @xmath9 on a ring of radius @xmath10 .
spin @xmath8 experiences a net point - dipolar field from its neighbors @xmath11    @xmath12/{|\bm{\mathrm{x}}}_{ij}|^{3 }   \label{eqno1}\ ] ]    where * * x**@xmath13 is the vector displacement from spin * * s**@xmath4 to spin * * s**@xmath14 .
we work in normalized units , and set all @xmath15 = 1 .
it is instructive to first consider the ground state ( gs ) of the system . to minimize the dominant pairwise interaction which exists between first nearest neighbors , an `` in - out '' relative configuration
must be adopted for a given pair .
further neighbor interactions , whilst not necessarily insignificant , will not alter this ordering rule . because @xmath0 is odd , if one attempts to propagate the rule around a ring , a defect must always be ultimately formed , consisting of a frustrated `` in - in '' or `` out - out '' arrangement , resembling a magnetic soliton defect,@xcite as illustrated in fig .
the frustrated defect can hence exist at positions p@xmath4 , as indicated by circles , and we will refer to spins which constitute a soliton as `` defected spins '' .
it is important to note that the system can generally support only odd numbers of solitons    similar solitons are found in linear 1d chains of ising spins where two domains of opposite phase meet,@xcite a result of a two - fold degenerate antiferromagnet - like gs . in our ring system , the gs possesses an _ intrinsic _ local frustration , much like a 1d ising chain with periodic boundary conditions where setting @xmath0 = odd imposes this `` twist '' in the local order parameter .
there are also @xmath0 possible soliton positions .
calculation of the net zeeman energy @xmath16 shows that this is the gs , which is hence 2@xmath0-fold degenerate .
an interesting analogy exists here between the spin ring system and the mbius loop , a planar strip possessing only one side due a twisted topology.@xcite following the antiferromagnetic order parameter around the ring , one finds it must invert once each cycle at the defect , which represents the topological kink of the mbius loop .
( this analogy would only stand completely true for a spin ring possessing only 1@xmath17 nearest neighbor interactions , however , as we will show , this is the dominant interaction defining the system s behavior , hence the same qualitative behavior is expected . )    for now , we simply consider that each spin possesses an intrinsic switching astroid of a given type . as for a linear 1d chain system,@xcite it is anticipated that dipolar interactions result in a local instability at a frustrated defect , its two constituent spins being more willing to flip their orientations than non - defected spins , and local stability elsewhere .
flipping an unstable spin , e.g. by applying a suitable magnetic field ( not large enough to reverse any stabilized spins ) , acts only to move the soliton , creating an energetically equivalent gs if the applied field is subsequently removed .
however , for identical spins on the linear 1d chain , an applied field can not preferentially flip one defected spin over the other , due to symmetry , hence a directional `` pressure '' can not be established in the system . whilst qd
, e.g. in the intrinsic switching fields of the spins , can locally break the symmetry , this produces no net directionality in the system . as can be seen by simple geometrical considerations , the employment of a curved chain , as for the ring system , potentially overcomes both of these issues , by imposing asymmetry when a uniform global applied field is present .
it is hence possible to favour the switching of one defected spin over the other , given qd is not too strong . under a uniform applied field , two defect spins
are now generally inequivalent , and their angular offset may be exploited .
a field sequence may hence be applied to propagate the soliton defect as desired . due to its simplicity in both experiment and simulation
, we consider a uniform applied field @xmath18 of constant magnitude , rotating at a constant rate.@xcite three field regimes must exist .
there are two trivial regimes , one in which the applied field magnitude @xmath19 is too small to ever reconfigure the system , and one in which the field is so large that it only acts to polarizes the system . in between there
exists a non - trivial field window in which meaningful dynamics should be possible , exploiting the local instability / stability of defected / non - defected spins imparted by the dipolar interactions and the form of the spins intrinsic switching astroid .
our simulations are similar to those recently presented in studies of artificial spin ice systems.@xcite we set @xmath10 = @xmath0/3 , which keeps the first nearest neighbor interaction approximately constant at @xmath20  0.1 as a function of @xmath0 ( an approximation which improves as @xmath0 increases ) . for a given @xmath0
, the system is primed from a gs configuration , as shown in fig .
[ fig1 ] , with a defect existing at position p@xmath21 .
a field @xmath18 is applied at an initial angle @xmath22 , aligned with the initial net moment of the ring , taking field angle @xmath23 to be aligned with spin @xmath24 and the anti - clockwise sense as positive .
the field is incremented in anticlockwise angular steps of @xmath25 : this allows for a sufficient angular resolution , and for even division of the @xmath26 range , maintaining symmetry between @xmath27 and @xmath28 . for a given simulation step
, a spin @xmath7 is selected at ( pseudo-)random and an attempt is made to flip its orientation .
spin @xmath7 experiences a total field    @xmath29    to represent realistic reversal behavior , a stoner - wolfarth ( sw ) switching criterion is implemented.@xcite even for elongated ferromagnetic nanowires which reverse via nucleation and propagation of a domain wall , nucleation often occurs within a coherently rotating sub - volume.@xcite spin @xmath7 flips given two inequalities are satisfied :    @xmath30    and    @xmath31    where @xmath32 is the angle between spin @xmath7 and @xmath33 .
this allows for reversal given the projection of @xmath33 onto @xmath7 is antiparallel with @xmath7 ( equation ( 3 ) ) , and that @xmath33 lies outside the sw astroid of spin @xmath7 ( equation ( 4 ) ) .
the sw astroid varies between @xmath34 and @xmath35 at its maxima and minima respectively , occurring at and halfway between integer multiples of @xmath36/2 respectively , where @xmath34 is a constant .
this random selection and test process is repeated until no further spins can flip , upon which the step ends .
note that this is a zero - temperature simulation hence the system only ever makes downward transitions in energy .
this is an appropriate starting point when considering nanomagnets which are robustly thermally stable at remanence@xcite and which will reverse their magnetization state effectively instantaneously relative to the applied field rotation rate.@xcite
to illustrate the ideal behavior of the system , we first consider the case in which @xmath37  1 for all @xmath8 , @xmath1  5 and @xmath38  0.55 .
an animation of a simulation realization is shown in the supplemental material,@xcite and we follow the initial behavior schematically in figures [ fig1](b ) and [ fig2](a - d ) . figure [ fig2](e ) shows a plot of the simulated soliton position p@xmath4 as a function of applied field angle @xmath27 . in the initial configuration ,
the soliton exists at position p@xmath21 , as illustrated in fig .
[ fig1](b ) , with spins @xmath39 defected . whilst @xmath40 is anti - aligned with @xmath41
, @xmath41 is unable to flip , experiencing an opposing net field of 0.3 along its axis ( @xmath42  1 , at @xmath43 ) .
this is true even as @xmath40 rotates , as @xmath44 remains within the sw astroid of spin @xmath41 .
as @xmath40 approaches @xmath45 , spin @xmath46 is allowed to flip , destabilized by its neighboring spin @xmath24 , forming the state shown in fig .
[ fig2](a ) .
it is worth re - emphasizing that the shape of the sw astroid allows for reversal at such a value of @xmath47.@xcite the reversal of @xmath46 propagates the soliton from position p@xmath21 to position p@xmath48 , as shown in fig .
[ fig2 ] ( e ) , acting to stabilize(destabilize ) @xmath49 .
spins @xmath50 remain stabilized by their nearest neighbors . as @xmath40 continues to rotate , fig .
[ fig2 ] ( b ) , no spin flips occur until @xmath51 ( fig .
[ fig2](c ) ) , at which spin @xmath52 reverses , further incrementing the position of the soliton to position p@xmath53 .    5 and @xmath38  0.55 , as the applied field @xmath40 is swept anti - clockwise from its initial orientation .
@xmath54 is large enough to sequentially flip defected spins , indicated by lightened gray arrows , but not large enough to polarize the system .
the soliton , represented by an emboldened circle , increments its position p@xmath4 every @xmath55 rotation of @xmath40 , as plotted in ( e ) . the red / blue color scheme in ( a - e )
represents the out / in polarity of a soliton at a given position , as do the square / circular data points in ( e ) .
the angular position of the spin flips in ( a ) , ( c ) , and ( d ) are indicated in ( e ) .
[ fig2 ] ]    continued rotation of @xmath40 continues to propagate the soliton in this manner ( fig .
[ fig2](d , e ) ) every @xmath56 rotation of @xmath40 , equal to @xmath57 for @xmath1  5 .
note that the net `` in / out '' polarity of the defect changes with each increment ( indicated by blue / red emboldened circles in figure [ fig2 ] ( a - d ) ) , and that the defect position rotates with the opposite sense to that of @xmath40 .
once the defect completes a full circuit of the system , the whole system has undergone a global spin flip transformation from its initial configuration , as the order parameter `` twist '' is swept around .
a total rotation of @xmath58 is required to achieve this .
we find the same non - trivial behavior throughout the range of @xmath59 , the phase of the spin flipping decreasing(increasing ) as @xmath54 increases(decreases ) due to the profile of the sw astroid .
below @xmath38  0.43 , no dynamics occur as the net field @xmath33 is never large enough to satisfy equation ( 3 ) for all @xmath8 and @xmath32 . above @xmath38  0.675 ,
the applied field is strong enough to satisfy equation ( 3 ) even for non - defected spins , hence the net polarization of the system tracks @xmath40 ; whilst multiple soliton defects form under such conditions ( for @xmath60 ) , their motion is trivial , dominated by the zeeman energy .
the non - trivial interval has a width @xmath61 indicating how the operation of the system relies crucially on 1@xmath17 nearest neighbor coupling .
we have hence established that such a spin ring system may be used for the manipulation of a well - defined soliton defect . whilst the system possesses symmetry in its interactions , as for a linear chain , the _ anticlockwise _ rotating applied field provides the required chirality for unidirectional angular soliton propagation with a _ clockwise _ sense .
it is of course possible to set the initial applied field angle @xmath62 to any direction and , in particular , a direction that first favors reversal of spin @xmath24 , rather than @xmath46 , from the initial spin configuration of fig .
[ fig1](b ) .
in such a case , the soliton will initially take a single step with the _ same _ sense as @xmath40 from position p@xmath21 to position p@xmath63 , however , as @xmath40 continues to rotate the behavior previously described is resumed .
furthermore , reversing the sense of rotation of @xmath40 to clockwise produces a complementary reversal in the sense of propagation of the soliton , which can be understood by symmetry .
hence , the soliton may be translated to any position in any angular direction .
the scheme also works for alternative switching models and has been tested using an ising switching astroid .
fundamentally , the scheme requires that spins possess switching astroids which vary as a function of net field direction , that are also offset in angle from each other such that switching can be accessed for individual spins in turn .
hence , the scheme should work experimentally for any realisable bistable nanomagnet type .
this is particularly important when considering that the switching astroid of a sw nanomagnet loses four - fold rotational symmetry at finite temperature , the switching threshold for applied fields approaching the easy axis becoming reduced relative to that along the hard axis.@xcite the same qualitative behavior is hence expected .
next we consider a more realistic situation in which quenched disorder qd is present in the system .
we follow similar model studies and implement this as a distribution in the spins switching behavior.@xcite for a given realization , we generate the values @xmath34 from a psuedo - gaussian distribution with mean = 1 and standard deviation @xmath64 .
studies show that this provides a good approximation for the behavior of coupled nanomagnet vertex systems , accounting for a combination of possible property distributions.@xcite we explore the behavior of the system as a function of both @xmath54 and @xmath64 . to further characterize the system
, we define the system as `` working '' if the single soliton is able to make a full circuit of the system , as previously described . over @xmath65 realizations for each parameter set ,
we build a map of the probability @xmath66 that the system operates as designed .
this map is shown in fig .
[ fig3 ] for @xmath1  5 and @xmath67  150 . cross - sectional profiles from fig .
[ fig3 ] are shown in fig .
[ fig4 ] for select values of ( a ) @xmath54 , and ( b ) @xmath64 . a clear triangular region with @xmath68  1 exists spanning the interval @xmath59 at @xmath69  0 ( as previously discussed ) , converging linearly to a point at @xmath70  0.55 and @xmath71  0.1 .
@xmath70 0.55 is an optimal field magnitude , allowing for the greatest robustness against qd . on moving out of this region
, @xmath66 falls abruptly .
the size and shape of this triangular region of @xmath68  1 is defined by the size of @xmath72  0.1 .    5 system , @xmath66 ( see colour key ) , as a function of applied field magnitude @xmath54 and switching astroid constant standard deviation @xmath64 .
[ fig3 ] ]    for given values of @xmath54 and @xmath64 , the behavior within the phase diagram can be understood in terms of spins which are `` pinned '' , possessing sufficiently high values of @xmath34 to prevent their reversal even when defected , and spins which are `` loose '' , possessing sufficiently low values of @xmath34 such that they can flip even when not defected.@xcite for @xmath38  0.45 and @xmath69  0.1 , there is a significant probability of failure due to at least one spin being unable to flip . upon meeting a pinned spin ,
the soliton enters a trapped `` resonant '' behavior mode , taking one step back then one step forward within each rotation of @xmath54 .
failure can also occur if both @xmath46 and @xmath24 are pinned , preventing the soliton from ever moving .
as @xmath64 increases , more erratic behavior can occur , with an increased chance of finding loose spins in a given realization .    for @xmath38  0.65 and @xmath69  0.1
, failure is likely for a given realization due to the increased probability of spins that are loose , which behave trivially under @xmath54 .
typically , a loose spin is allowed to flip when not defected by interactions , nucleating an additional pair of solitons in the system .
the evolution of the system then appears as the trivial high field regime discussed in section 3.1 . as @xmath64 increases the probability of such behavior increases .
for @xmath69  0.4 , there often exists increasing numbers of pinned spins too : the combination of loose and pinned spins can result in erratic behavior in which soliton pairs are periodically nucleated and annihilated on the ring , with no meaningful evolution . for @xmath38  0.55 and @xmath69  0.4 , the most erratic behavior is found , due to an average balance of pinned and loose spins , resulting in a balanced probability of various different failure modes . it should be noted that for @xmath73  0.4 , realizations become increasing unphysical , with negative values of @xmath34 becoming common , hence we do not explore this range .    within the @xmath68  1 region in fig .
[ fig3 ] , finite qd acts to modify the number of field steps the soliton spends at each position , which depends on the specific realization , however , given the defect can make a full circuit in the desired sequence , this is still a `` successful '' soliton .
-map of fig .
[ fig3 ] , taken along the ( a ) @xmath54 , and ( b ) @xmath64 axes at the labeled values of @xmath64 and @xmath54 respectively .
note , due the symmetry of the phase diagram , ( b ) shows data for @xmath74 only .
[ fig4 ] ]    the results shown @xmath75 are representative of all @xmath60 studied ( up to 11 ) , possessing the same form of triangular phase diagram defined by @xmath76 . for @xmath77 , no high - field failure phase is present , as both the trivial high - field regime and non - trivial regime possess a full polarization and a single soliton ( fig .
[ fig1](a ) ) .
the @xmath77 system is incompatible with the generation of multiple defects under a uniform applied magnetic field .    regarding experimental realization ,
the simulations show that the limit imposed by qd on the system s successful operation is a value of @xmath78 , for an optimal @xmath19 .
keeping within such a limit is in principle experimentally achievable and compares well with recently presented estimates in patterned artificial spin ice systems built from elongated highly - anisotropic bistable nife nanomagnets of @xmath79  100  nm dimensions spaced edge - to - edge by @xmath79  40  nm.@xcite qd is however not a straight - forward phenomenon to quantify.@xcite    in order to first generate the required single - defect ground state , it is possible to reset an initial state in an experimental nanomagnet system via various methods currently being developed by the nanomagnetism community .
patterns tailored to allow `` on / off '' switching of thermal dynamics e.g. via volume@xcite or material@xcite , allow for thermal equilibration of the magnetic macrospins towards their gs , which would remove all but one soliton from any given initial configuration as they undergo a random walk around the ring
. it may also be possible to field - anneal the system , using the correct field sequence.@xcite
as an example of a practical application , the macrospin ring is a multiturn counter .
a full @xmath26 motion of the soliton requires @xmath80 complete applied field rotations . as the soliton must travel around the system twice to reset the system ,
the system can count up to @xmath81 .
magnetic nano - systems have been shown to be highly applicable for such contactless powerless operation.@xcite this spin ring can potentially be realized experimentally by patterning of radially - aligned single - domain nanomagnets , as discussed , which experience the field of a rotating permanent magnet .
each gs soliton state represents a unique macrospin configuration , which could be directly read by incorporation of giant magnetoresistance - based sensing .
there is no need to inject soliton defects as for spiral domain wall conduit counters,@xcite which also require a fixed rotational sense to operate and are limited to a maximum number of turns , domain walls eventually `` falling out '' of the ends .
the spin ring will count up to @xmath0 cyclically : each soliton step counts an angle @xmath82 , which = @xmath83 for @xmath84 , and converges to @xmath85 as @xmath0 increases .
the spin ring bares similarity to closed - loop conduit devices@xcite and perpendicular magnetic anisotropy shift register loops@xcite recently presented , always possessing at least one local defect , which may be used to count field oscillations .
a spin ring system built of highly anisotropic single - domain nanomagnets may also present further benefits , minimising switching time between states relative to extended nanowires .
furthermore , combining @xmath86 spin rings of different spin number @xmath87 allows for a total of @xmath88 rotations to be counted in a coprime scheme .
the odd - numbered macrospin ring demonstrates an unexplored means of imposing chirality in systems of coupled single - domain nanomagnet chains , as utilized in conventional magnetic logic and mqca architectures.@xcite the scheme is simple to implement using nanopatterned thin films and more general systems of curved spin chains may be designed .
it is further an example of a user - designed artifical geometrically frustrated system , possessing an _ intrinsic _ soliton defect , which can be manipulated in a well - defined way and potentially employed for useful operations , exemplified here as a simple multiturn counter .
it further represents a building block for the study of more complex coupled systems.@xcite whilst a small handful of reports exists in the field of molecular magnetism on such `` magnetic mbius loops'',@xcite built from odd - numbered spin-@xmath85 rings , our work highlights the possibility of exploring such physics in nanopatterned systems via real - space real - time microscopy.@xcite    we thank c. h. marrows , z. budrikis , r. mansell , and a. fernandez - pacheco for useful discussions and careful proof - readings .
we acknowledge research funding from the ( uk ) epsrc , and the european community under the seventh framework programme contract no .
247368 : 3spin .
this work has been partly carried out within the joint research project exl04 ( spincal ) , funded by the european metrology research programme .
the emrp is jointly funded by the emrp participating countries within euramet and the european union .
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 we report simulations of a frustrated odd - numbered macrospin ring system , with full point dipolar interactions , driven by a rotating uniform applied magnetic field of constant magnitude .
 the system is designed with equally - spaced radially - aligned macrospins , which must carry a frustrated soliton defect in its ground state .
 it is shown how correctly tuning the applied field magnitude can allow for non - trivial unidirectional propagation of the soliton , the required directional pressure acquired via the curvature of the ring .
 furthermore , the system , which may be employed as a multiple rotation counter , is tested for robustness against quenched disorder as would be present in an experimental realization .


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<newsArticle>


I think we should be able to play in a sport if we have a grade C. I think i would be not fear for student that have a good grade like c to play in a sport. If we had a D or an F i would understand that but a C i nothing. Not a lot of kid get A or Bs and if we do. Some of those kids don't like to play a sport they like to do all there homework not that i am saying that a bad C grade people do there homework to. If there is only 1 out of 4 percent of student that get A and B, They all don't like the same sports and some don't like to do sports so it wouldn't be a hole team in that sport. that means you would have to cancel all the sport teams in the school. That why you should let C student play an a sport.Some schools require summer projects for students; these projects need to be student designed. When teachers plan a project some students don't enjoy completing the assigned task. For students to learn they have to be interested in what they are doing. There are many ways to assign a school project, it could be hands on, writing, individually, in groups etc. Each student has different skills, they should do a project that best fits that skill to succeed. Summer projects need to be student designed so that they are more motivated to complete the assignment, to have fun with the assignment and to have interest in the task.


Summer projects need to be student designed to enhance motivation. When students are motivated this encodes the topic in their memory. When students are motivated they get better grades, the project is better quality and students do the project to their best ability. As a student when a project gets assigned and I am not interested in the assignment I try to get it done as quickly as possible and put no effort into it. I end up getting a lower grade. Students will also want to keep working on the project if they are motivated to complete it. With more time spent on the project this equals better quality and higher grades. Students won't procrastinate if the project interests them and will be motivated to start the project early. As a student in High School lots of students procrastinate when given a project. If projects were student designed this would motivate them to learn about the topic.


Summer projects need to be student designed so that they have fun with it. If they had fun with the assignment then they would have a memory of their experience. If schools made learning fun they are more likely to remember the topic of the project. If students were in a group for the project this would enhance team work skills if they had fun. As a student I found out that if I had fun learning about a certain topic I remember it more clearly and can connect it to other things in life.


Summer projects need to be student designed to have students have interest in the topic. This would help students explore their interests that they never knew they were interested in. This may help students what they want to do after graduation. Chances are if a student is really interested in what they learned in class then they might explore that topic outside of school. When I had a project assigned to me that I was interested in I enjoyed completing the project and continued to learn more about it outside of school. Summer projects that have students interested is a key to success in their academic career.


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Context: Since the IPCC does not carry out its own research, it operates on the basis of scientific papers and independently documented results from other scientific bodies, and its schedule for producing reports requires a deadline for submissions prior to the report's final release. In principle, this means that any significant new evidence or events that change our understanding of climate science between this deadline and publication of an IPCC report cannot be included. In an area of science where our scientific understanding is rapidly changing, this has been raised as a serious shortcoming in a body which is widely regarded as the ultimate authority on the science. However, there has generally been a steady evolution of key findings and levels of scientific confidence from one assessment report to the next.[citation needed]

Question: Who is seen as the ultimate climate change authority?


Context: After al-Nimeiry was overthrown in 1985 the party did poorly in national elections, but in 1989 it was able to overthrow the elected post-al-Nimeiry government with the help of the military. Turabi was noted for proclaiming his support for the democratic process and a liberal government before coming to power, but strict application of sharia law, torture and mass imprisonment of the opposition, and an intensification of the long-running war in southern Sudan, once in power. The NIF regime also harbored Osama bin Laden for a time (before 9/11), and worked to unify Islamist opposition to the American attack on Iraq in the 1991 Gulf War.

Question: What did the NIF try to unify Islamist opposition against?

American attack on Iraq
the American attack on Iraq
American attack on Iraq


Context: For the first time, the Super Bowl 50 Host Committee and the NFL have openly sought disabled veteran and lesbian, gay, bisexual and transgender-owned businesses in Business Connect, the Super Bowl program that provides local companies with contracting opportunities in and around the Super Bowl. The host committee has already raised over $40 million through sponsors including Apple, Google, Yahoo!, Intel, Gap, Chevron, and Dignity Health.

Question: How much money has been raised by the host committee?

$40 million
over $40 million
$40 million


Context: In December 1901, Marconi successfully transmitted the letter S from England to Newfoundland, terminating Tesla's relationship with Morgan.[improper synthesis?] Over the next five years, Tesla wrote over 50 letters to Morgan, pleading for and demanding additional funding to complete the construction of Wardenclyffe. Tesla continued the project for another nine months. The tower was erected to its full 187 feet (57 m). In July 1903, Tesla wrote to Morgan that in addition to wireless communication, Wardenclyffe would be capable of wireless transmission of electric power. On 14 October 1904, Morgan finally replied through his secretary, stating, "It will be impossible for [me] to do anything in the matter," after Tesla had written to Morgan when the financier was meeting with the Archbishop of Canterbury in an attempt to appeal to his Christian spirit.

Question: How much correspondence did Tesla send Morgan in the five years following 1901?

over 50 letters
over 50 letters
50 letters


Context: European Union law is a body of treaties and legislation, such as Regulations and Directives, which have direct effect or indirect effect on the laws of European Union member states. The three sources of European Union law are primary law, secondary law and supplementary law. The main sources of primary law are the Treaties establishing the European Union. Secondary sources include regulations and directives which are based on the Treaties. The legislature of the European Union is principally composed of the European Parliament and the Council of the European Union, which under the Treaties may establish secondary law to pursue the objective set out in the Treaties.

Question: What is European Union Law?


Context: If the input size is n, the time taken can be expressed as a function of n. Since the time taken on different inputs of the same size can be different, the worst-case time complexity T(n) is defined to be the maximum time taken over all inputs of size n. If T(n) is a polynomial in n, then the algorithm is said to be a polynomial time algorithm. Cobham's thesis says that a problem can be solved with a feasible amount of resources if it admits a polynomial time algorithm.

Question: Whose thesis states that the solution to a problem is solvable with reasonable resources assuming it allows for a polynomial time algorithm?


Context: In addition to those actors who have headlined the series, others have portrayed versions of the Doctor in guest roles. Notably, in 2013, John Hurt guest-starred as a hitherto unknown incarnation of the Doctor known as the War Doctor in the run-up to the show's 50th anniversary special "The Day of the Doctor". He is shown in mini-episode "The Night of the Doctor" to have been retroactively inserted into the show's fictional chronology between McGann and Eccleston's Doctors, although his introduction was written so as not to disturb the established numerical naming of the Doctors. Another example is from the 1986 serial The Trial of a Time Lord, where Michael Jayston portrayed the Valeyard, who is described as an amalgamation of the darker sides of the Doctor's nature, somewhere between his twelfth and final incarnation.

Question: What actor played the Valeyard?

Michael Jayston
Michael Jayston
Michael Jayston


Context: The development of plate tectonics provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries. Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, were explained as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes were explained as convergent boundaries, where one plate subducts under another. Transform boundaries, such as the San Andreas fault system, resulted in widespread powerful earthquakes. Plate tectonics also provided a mechanism for Alfred Wegener's theory of continental drift, in which the continents move across the surface of the Earth over geologic time. They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.

Question: The lithosphere moves over which mantle n the theory of plate tectonics?

the convecting mantle
convecting mantle
convecting
convecting


Context: Tesla read many works, memorizing complete books, and supposedly possessed a photographic memory.:33 He was a polyglot, speaking eight languages: Serbo-Croatian, Czech, English, French, German, Hungarian, Italian, and Latin.:282 Tesla related in his autobiography that he experienced detailed moments of inspiration. During his early life, Tesla was repeatedly stricken with illness. He suffered a peculiar affliction in which blinding flashes of light would appear before his eyes, often accompanied by visions.:33 Often, the visions were linked to a word or idea he might have come across; at other times they would provide the solution to a particular problem he had encountered. Just by hearing the name of an item, he would be able to envision it in realistic detail.:33 Tesla would visualize an invention in his mind with extreme precision, including all dimensions, before moving to the construction stage, a technique sometimes known as picture thinking. He typically did not make drawings by hand but worked from memory. Beginning in his childhood, Tesla had frequent flashbacks to events that had happened previously in his life.:33

Question: What other visual phenomena accompanied Tesla's visions?

flashbacks
blinding flashes of light
blinding flashes of light


hypothesis: Al Rashi is an executive of the police. premise: Sunday's explosion outside the Al-Rashi police station in the Al-Mashtel neighbourhood in the southeast of Baghdad, left a huge crater in the street.


hypothesis: Everglades National Park is located in Florida. premise: Many hopes are riding on the sale of Talisman's holdings in Palm Beach and Hendry counties, which Vice President Al Gore announced with much fanfare last year at the 50th anniversary of Everglades National Park.


hypothesis: The introduction of the euro has been opposed. premise: The most recent poll carried out by NOP market research in January revealed that 61% of Britons are opposed to joining the euro.


hypothesis: The Istiqlal Mosque is one of the largest mosques in Southeast Asia. premise: The Istiqlal Mosque, in the northeast corner of Medan Merdeka opposite Lapangan Banteng, is one of the largest mosques in Southeast Asia.


hypothesis: Nike said orders for footwear and apparel for delivery totaled $4.9 billion, including a 12 percent increase in U.S. orders. premise: Nike Inc. said, Monday, that its first-quarter profit grew 32 percent, as the world's largest sneaker and athletic apparel company posted broad gains in sales and orders.


hypothesis: Italian director is awarded an honorary Oscar. premise: Oscar-winning director Franco Zeffirelli has been awarded an honorary knighthood for his "valuable services to British performing arts".


hypothesis: The literacy rate in Cuba is 90%. premise: By 1979, the literacy rate in Cuba was higher than 90%, comparable to the rates in the United States and other developed countries.


hypothesis: The government of Ecuador aims to prevent trafficking in persons. premise: Exercising the powers referred to in article 15, paragraph 3, of the protocol to suppress and punish trafficking in persons, especially women and children, the government of Ecuador makes a reservation with regard to article 15, paragraph 2, relating to the settlement of disputes.


hypothesis: The abbreviation GIA stands for Armed Islamic Group. premise: Government forces killed the head of the Armed Islamic Group, or GIA, which has claimed responsibility for killing 61 foreigners in the last year.


hypothesis: Tom Online earned US$42.78 mn in three months. premise: Tom Online revenues for the three months ended June 30, 2005 were US$42.78 mn, an increase of 38.5% over the same period in 2004.


EU rejects German call to boycott British lamb .


The European Commission said on Thursday it disagreed with German advice to consumers to shun British lamb until scientists determine whether mad cow disease can be transmitted to sheep .


Germany 's representative to the European Union 's veterinary committee Werner Zwingmann said on Wednesday consumers should buy sheepmeat from countries other than Britain until the scientific advice was clearer .


" We do n't support any such recommendation because we do n't see any grounds for it , " the Commission 's chief spokesman Nikolaus van der Pas told a news briefing .


He said further scientific study was required and if it was found that action was needed it should be taken by the European Union .


He said a proposal last month by EU Farm Commissioner Franz Fischler to ban sheep brains , spleens and spinal cords from the human and animal food chains was a highly specific and precautionary move to protect human health .


Fischler proposed EU-wide measures after reports from Britain and France that under laboratory conditions sheep could contract Bovine Spongiform Encephalopathy ( BSE ) -- mad cow disease .


But Fischler agreed to review his proposal after the EU 's standing veterinary committee , mational animal health officials , questioned if such action was justified as there was only a slight risk to human health .


Inside Out (2015)


Mean Dreams (2017)


Captain America: Civil War (2016)


The Jungle Book (2016)


Happy Death Day (2017)


The Martian (2015)


Captain Fantastic (2016)


Nightcrawler (2014)


Big Hero 6 (2014)


Jumanji: Welcome to the Jungle (2017)


Contraceptive Forms for High School Students

How do you propose the school will fund your program? Condoms cost money and checking an "opt out" list before handing them out takes time away from staff members whenever they could be doing their actual jobs. Your "opt out" option is only be a token to parental authority and would be easily subverted. If everyone in school except a handful of students had access to free condoms, do you not think those students would simply ask their friends to provide them with condoms?

Question: which way would you fund the contraceptive program?


Question: how to grant free contraception to school students


Question: how can you fund condoms


Schools have no compelling interest in providing contraceptives to students. The purpose of schools is not to provide healthcare nor to provide any other service except insofar as it relates to the furtherance of education [1,2,3], though I do not contest that individual districts ought to have this option if they so choose. As an educator, I do feel that adequate sexual education is a necessary. [1] tinyurl.com/z786mww[2] tinyurl.com/jafrt2n[3] tinyurl.com/zbkwkz6

Question: do schools provide contraception


Question: is sexual education necessary


Question: what are the main purposes of contraception in public schools


As a senior at my school. My group and I are focusing on teenage pregnancy; we are determined to have high school districts provide contraceptive forms to students to be safe about sex. This focus isn't for us to encourage to have sex, but if teenagers decide to have sex to please be safe about it. In addition. if parents do not agree to this we want to have an opt out form where their child/children will not be receiving this form.

Question: what are the best types of contraception for girls


i start to feel emotional


i believe feeling duality suffering soul growth tells of an ending or a decline or a change of direction often one associated with emotions and it offers one possible response to that decline or change moving on


i hostage negotiator on her case has her feeling hopeful about her future


im feeling a little dirty


i can cope with his presence without feeling distressed if i can force myself into a quiet and resigned friendship


i had the feeling that it might not have been taken as the truthful and sincere compliment it would have been


i asked some girls what it meant to them to be valued and for the most part the response was that they felt valued when the people around them made them feel valued and treated them in a loving and caring manner


i feel if i completely hated things i d exercise my democratic right speak my mind in what ever ways possible and try to enact a change


i could almost feel her gentle touch in the moonbeam she sent to shine over me he added touching his face dreamily


i woke up very early this morning feeling joyful


This is so cool. It's like, 'would you want your mother to read this??' Really great idea, well done!