Application of the Trace Formula in Pseudointegrable Systems

We apply periodic-orbit theory to calculate the integrated density of states $N(k)$ from the periodic orbits of pseudointegrable polygon and barrier billiards. We show that the results agree so well with the results obtained from direct diagonalization of the Schr\"odinger equation, that about the first 100 eigenvalues can be obtained directly from the periodic-orbit calculations in good accuracy.Comment: 5 Pages, 4 Figures, submitted to Phys. Rev.

Examining the Relationship Between Math Scores and English Language Proficiency

Multiple studies propose that English proficiency dictates English language learners’ (ELLs) performances on mathematics assessments. The current study investigates the predictive power of English proficiency on mathematics scores, while controlling for gender, socioeconomic status (SES), and grade level among ELLs at a south Florida elementary school. Krashen’s theory of comprehensible input as a precursor to second language acquisition provides the framework for this quantitative, correlation study. Mathematics scores from the Florida Comprehensive Assessment Test for Grade 3–5 ELLs (N = 177) were analyzed using multiple linear regression. Analysis reveals English proficiency as a statistically significant predictor of mathematics scores. Mathematics scores increase simultaneously with English proficiency but inversely with grade level. Grade level moderates the influence of English proficiency on mathematics scores. Gender and SES have no significant moderating influence

Social Mobility Through Mathematics Proficiency for English Language Learners

College admission is contingent upon students’ high school performances, especially mathematics proficiency that is crucial in qualifying for the projected science, technology, engineering, and mathematics professions of the future. This paper reviews some concerns that hinder the efforts of English language learners (ELLs), often the children of immigrants, to achieve social mobility through a college education. ELLs consistently fail to achieve proficiency on mathematics assessments as measured by the National Assessment for Educational Progress and local assessments such as the Florida Comprehensive Assessment Test. Consequently, many ELLs do not attend college. The article examines implications for educators and policymakers for resolving some of the issues that impede transforming ELLs into academic and societal achievers. Actions taken by educators and policymakers might assist ELLs in navigating the challenges encountered in their pursuit of a college education

Quantal Consequences of Perturbations Which Destroy Structurally Unstable Orbits in Chaotic Billiards

Non-generic contributions to the quantal level-density from parallel segments in billiards are investigated. These contributions are due to the existence of marginally stable families of periodic orbits, which are structurally unstable, in the sense that small perturbations, such as a slight tilt of one of the segments, destroy them completely. We investigate the effects of such perturbation on the corresponding quantum spectra, and demonstrate them for the stadium billiard

The Generation of Successive Unmarked Mutations and Chromosomal Insertion of Heterologous Genes in Actinobacillus pleuropneumoniae Using Natural Transformation

We have developed a simple method of generating scarless, unmarked mutations in Actinobacillus pleuropneumoniae by exploiting the ability of this bacterium to undergo natural transformation, and with no need to introduce plasmids encoding recombinases or resolvases. This method involves two successive rounds of natural transformation using linear DNA: the first introduces a cassette carrying cat (which allows selection by chloramphenicol) and sacB (which allows counter-selection using sucrose) flanked by sequences to either side of the target gene; the second transformation utilises the flanking sequences ligated directly to each other in order to remove the cat-sacB cassette. In order to ensure efficient uptake of the target DNA during transformation, A. pleuropneumoniae uptake sequences are added into the constructs used in both rounds of transformation. This method can be used to generate multiple successive deletions and can also be used to introduce targeted point mutations or insertions of heterologous genes into the A. pleuropneumoniae chromosome for development of live attenuated vaccine strains. So far, we have applied this method to highly transformable isolates of serovars 8 (MIDG2331), which is the most prevalent in the UK, and 15 (HS143). By screening clinical isolates of other serovars, it should be possible to identify other amenable strains

Attractive Casimir Forces in a Closed Geometry

We study the Casimir force acting on a conducting piston with arbitrary cross section. We find the exact solution for a rectangular cross section and the first three terms in the asymptotic expansion for small height to width ratio when the cross section is arbitrary. Though weakened by the presence of the walls, the Casimir force turns out to be always attractive. Claims of repulsive Casimir forces for related configurations, like the cube, are invalidated by cutoff dependence.Comment: An updated version to coincide with the one published December 2005 in PRL. 4 pages, 2 figure

Density of states of helium droplets

Accurate analytical expressions for the state densities of liquid He-4 droplets are derived, incorporating the ripplon and phonon degrees of freedom. The microcanonical temperature and the ripplon angular momentum level density are also evaluated. The approach is based on inversions and systematic expansions of canonical thermodynamic properties.Comment: 20 pages, 5 figure

The relationship between self‐reported received and perceived social support: A meta‐analytic review

Social support is broad term encompassing a variety of constructs, including support perceptions (perceived support) and receipt of supportive behaviors (received support). Of these constructs, only perceived support has been regarded as consistently linked to health, and researchers have offered differing assessments of the strength of the received‐perceived support relationship. An overall estimate of the received‐perceived support relationship would clearly further the dialogue on the relationship between received and perceived support and thus assist in the theoretical development of the field. This study evaluated all available studies using the Inventory of Socially Supportive Behaviors (ISSB; Barrera, Sandler, & Ramsey, 1981, American Journal of Community Psychology, 9, 435–447) and any measure of perceived social support. Using effect sizes from 23 studies, we found an average correlation of r = .35, p < .001. Implications of this estimate for further development of models of social support as well as interventions to enhance social support are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117157/1/ajcp9100.pd

Quantum Chaos of Bogoliubov Waves for a Bose-Einstein Condensate in Stadium Billiards

We investigate the possibility of quantum (or wave) chaos for the Bogoliubov excitations of a Bose-Einstein condensate in billiards. Because of the mean field interaction in the condensate, the Bogoliubov excitations are very different from the single particle excitations in a non-interacting system. Nevertheless, we predict that the statistical distribution of level spacings is unchanged by mapping the non-Hermitian Bogoliubov operator to a real symmetric matrix. We numerically test our prediction by using a phase shift method for calculating the excitation energies.Comment: minor change, 4 pages, 4 figures, to appear in Phys. Rev. Let

Chaotic Scattering in the Regime of Weakly Overlapping Resonances

We measure the transmission and reflection amplitudes of microwaves in a resonator coupled to two antennas at room temperature in the regime of weakly overlapping resonances and in a frequency range of 3 to 16 GHz. Below 10.1 GHz the resonator simulates a chaotic quantum system. The distribution of the elements of the scattering matrix S is not Gaussian. The Fourier coefficients of S are used for a best fit of the autocorrelation function if S to a theoretical expression based on random--matrix theory. We find very good agreement below but not above 10.1 GHz