3,317 research outputs found
Gap solitons in spatiotemporal photonic crystals
We generalize the concept of nonlinear periodic structures to systems that
show arbitrary spacetime variations of the refractive index. Nonlinear pulse
propagation through these spatiotemporal photonic crystals can be described,
for shallow nonstationary gratings, by coupled mode equations which are a
generalization of the traditional equations used for stationary photonic
crystals. Novel gap soliton solutions are found by solving a modified massive
Thirring model. They represent the missing link between the gap solitons in
static photonic crystals and resonance solitons found in dynamic gratings.Comment: 3 figures, submitte
Predicting Shannon’s information for genes in finite populations: new uses for old equations
This study provides predictive equations for Shannon’s information in a finite population, which are intuitive and simple enough to see wide scale use in molecular ecology and population genetics. A comprehensive profile of genetic diversity contains three complementary components: numbers of allelic types, Shannon’s information and heterozygosity. Currently heterozygosity has greater resources than Shannon’s information, such as more predictive models and integration into more mainstream genetics software. However, Shannon’s information has several advantages over heterozygosity as a measure of genetic diversity, so it is important to develop Shannon’s information as a new tool for molecular ecology. Past efforts at making forecasts for Shannon’s information in specific molecular ecology scenarios mostly dealt with expectations for Shannon’s information at genetic equilibrium, but dynamic forecasts are also vital. In particular, we must be able to predict loss of genetic diversity when dealing with finite populations, because they risk losing genetic variability, which can have an adverse effect on their survival. We present equations for predicting loss of genetic diversity measured by Shannon’s information. We also provide statistical justification for these models by assessing their fit to data derived from simulations and managed, replicated laboratory populations. The predictive models will enhance the usefulness of Shannon’s information as a measure of genetic diversity; they will also be useful in pest control and conservation
Recommended from our members
Increasing Play and Decreasing the Challenging Behavior of Children With Autism During Recess With Activity Schedules and Task Correspondence Training
This article examines the effects of a teacher-implemented playground intervention consisting of activity schedules and task correspondence training on the challenging behaviors and play of three school-age children with moderate to severe autism. Researchers used a multiple-baseline design across participants to evaluate the intervention effects. Results indicated that each of the participants learned to use an activity schedule to follow a schedule of play activities and demonstrated improved play. Moreover, challenging behavior decreased for two participants during the intervention and remained at low levels for the third participant. The findings from this study provide support for the use of activity schedules and task correspondence training to reinforce appropriate play and decrease challenging behaviors during recess.Educatio
Dynamics of light propagation in spatiotemporal dielectric structures
Propagation, transmission and reflection properties of linearly polarized
plane waves and arbitrarily short electromagnetic pulses in one-dimensional
dispersionless dielectric media possessing an arbitrary space-time dependence
of the refractive index are studied by using a two-component, highly symmetric
version of Maxwell's equations. The use of any slow varying amplitude
approximation is avoided. Transfer matrices of sharp nonstationary interfaces
are calculated explicitly, together with the amplitudes of all secondary waves
produced in the scattering. Time-varying multilayer structures and
spatiotemporal lenses in various configurations are investigated analytically
and numerically in a unified approach. Several new effects are reported, such
as pulse compression, broadening and spectral manipulation of pulses by a
spatiotemporal lens, and the closure of the forbidden frequency gaps with the
subsequent opening of wavenumber bandgaps in a generalized Bragg reflector
Women\u27s preferences for selective estrogen reuptake modulators: an investigation using the time trade off technique
PurposeSelective Estrogen Receptor Modulators (SERMs) reduce the risk of breast cancer for women at increased risk by 38%. However, uptake is extremely low and the reasons for this are not completely understood. The aims of this study were to utilize time trade-off methods to determine the degree of risk reduction required to make taking SERMs worthwhile to women, and the factors associated with requiring greater risk reduction to take SERMs. MethodsWomen at increased risk of breast cancer (N = 107) were recruited from two familial cancer clinics in Australia. Participants completed a questionnaire either online or in pen and paper format. Hierarchical multiple linear regression analysis was used to analyze the data. ResultsOverall, there was considerable heterogeneity in the degree of risk reduction required to make taking SERMs worthwhile. Women with higher perceived breast cancer risk and those with stronger intentions to undergo (or who had undergone) an oophorectomy required a smaller degree of risk reduction to consider taking SERMs worthwhile. ConclusionWomen at increased familial risk appear motivated to consider SERMs for prevention. A tailored approach to communicating about medical prevention is essential. Health professionals could usefully highlight the absolute (rather than relative) probability of side effects and take into account an individual’s perceived (rather than objective) risk of breast cancer
Charge and Orbital Ordering in Pr_{0.5} Ca_{0.5} MnO_3 Studied by ^{17}O NMR
The charge and orbital ordering in Pr_{0.5} Ca_{0.5} MnO_3 is studied for the
first time by ^{17}O NMR. This local probe is sensitive to spin, charge and
orbital correlations. Two transitions exist in this system: the charge and
orbital ordering at T_{CO} = 225 K and the antiferromagnetic (AF) transition at
T_N = 170 K. Both are clearly seen in the NMR spectra measured in a magnetic
field of 7T. Above T_{CO} there exists only one NMR line with a large isotropic
shift, whose temperature dependence is in accordance with the presence of
ferromagnetic (FM) correlations. This line splits into two parts below T_{CO},
which are attributed to different types of oxygen in the charge/orbital ordered
state. The interplay of FM and AF spin correlations of Mn ions in the charge
ordered state of Pr_{0.5} Ca_{0.5} MnO_3 is considered in terms of the hole
hopping motion that is slowed down with decreasing temperature. The developing
fine structure of the spectra evidences, that there still exist
charge-disordered regions at T_{CO} > T > T_N and that the static (t >
10^{-6}s) orbital order is established only on approaching T_N. The CE-type
magnetic correlations develop gradually below T_{CO}, so that at first the AF
correlations between checkerboard ab-layers appear, and only at lower
temperature - CE correlations within the ab-planes
Structural, electronic, and dynamical properties of amorphous gallium arsenide: a comparison between two topological models
We present a detailed study of the effect of local chemical ordering on the
structural, electronic, and dynamical properties of amorphous gallium arsenide.
Using the recently-proposed ``activation-relaxation technique'' and empirical
potentials, we have constructed two 216-atom tetrahedral continuous random
networks with different topological properties, which were further relaxed
using tight-binding molecular dynamics. The first network corresponds to the
traditional, amorphous, Polk-type, network, randomly decorated with Ga and As
atoms. The second is an amorphous structure with a minimum of wrong (homopolar)
bonds, and therefore a minimum of odd-membered atomic rings, and thus
corresponds to the Connell-Temkin model. By comparing the structural,
electronic, and dynamical properties of these two models, we show that the
Connell-Temkin network is energetically favored over Polk, but that most
properties are little affected by the differences in topology. We conclude that
most indirect experimental evidence for the presence (or absence) of wrong
bonds is much weaker than previously believed and that only direct structural
measurements, i.e., of such quantities as partial radial distribution
functions, can provide quantitative information on these defects in a-GaAs.Comment: 10 pages, 7 ps figures with eps
On the Analysis of Simple Genetic Programming for Evolving Boolean Functions
This work presents a first step towards a systematic time and space complexity analysis of genetic programming (GP) for evolving functions with desired input/output behaviour. Two simple GP algorithms, called (1+1) GP and (1+1) GP*, equipped with minimal function (F) and terminal (L) sets are considered for evolving two standard classes of Boolean functions. It is rigorously proved that both algorithms are efficient for the easy problem of evolving conjunctions of Boolean variables with the minimal sets. However, if an extra function (i.e. NOT) is added to F, then the algorithms require at least exponential time to evolve the conjunction of n variables. On the other hand, it is proved that both algorithms fail at evolving the difficult parity function in polynomial time with probability at least exponentially close to 1. Concerning generalisation, it is shown how the quality of the evolved conjunctions depends on the size of the training set s while the evolved exclusive disjunctions generalize equally badly independent of s
- …