Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry

We have performed precision electrostatic calibrations in the sphere-plane geometry and observed anomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was found to be smaller than expected on the basis of the pure Coulombian contribution and the residual potential found to be distance dependent. We argue that these findings affect the accuracy of the electrostatic calibrations and invite reanalysis of previous determinations of the Casimir force.Comment: 4 pages, 4 figure

Spin polarized neutron matter within the Dirac-Brueckner-Hartree-Fock approach

The relation between energy and density (known as the nuclear equation of state) plays a major role in a variety of nuclear and astrophysical systems. Spin and isospin asymmetries can have a dramatic impact on the equation of state and possibly alter its stability conditions. An example is the possible manifestation of ferromagnetic instabilities, which would indicate the existence, at a certain density, of a spin-polarized state with lower energy than the unpolarized one. This issue is being discussed extensively in the literature and the conclusions are presently very model dependent. We will report and discuss our recent progress in the study of spin-polarized neutron matter. The approach we take is microscopic and relativistic. The calculated neutron matter properties are derived from realistic nucleon-nucleon interactions. This makes it possible to understand the nature of the EOS properties in terms of specific features of the nuclear force model.Comment: 6 pages, 11 figures, revised/extended calculation

Thermal and dissipative effects in Casimir physics

We report on current efforts to detect the thermal and dissipative contributions to the Casimir force. For the thermal component, two experiments are in progress at Dartmouth and at the Institute Laue Langevin in Grenoble. The first experiment will seek to detect the Casimir force at the largest explorable distance using a cylinder-plane geometry which offers various advantages with respect to both sphere-plane and parallel-plane geometries. In the second experiment, the Casimir force in the parallel-plane configuration is measured with a dedicated torsional balance, up to 10 micrometers. Parallelism of large surfaces, critical in this configuration, is maintained through the use of inclinometer technology already implemented at Grenoble for the study of gravitationally bound states of ultracold neutrons, For the dissipative component of the Casimir force, we discuss detection techniques based upon the use of hyperfine spectroscopy of ultracold atoms and Rydberg atoms. Although quite challenging, this triad of experimental efforts, if successful, will give us a better knowledge of the interplay between quantum and thermal fluctuations of the electromagnetic field and of the nature of dissipation induced by the motion of objects in a quantum vacuum.Comment: Contribution to QFEXT'06, appeared in special issue of Journal of Physics

The flying radiation case

The Los Alamos foil implosion program has the goal of producing an intense, high-energy density x-ray source by converting the energy of a magnetically imploded plasma into radiation and material energy. One of the methods for converting the plasma energy into thermal energy and radiation and utilizing it for experiments is called the flying radiation case (FRC). In this paper the authors shall model the FRC and provide a physical description of the processes involved. An analytic model of a planar FRC in the hydrodynamic approximation is used to describe the assembly and shock heating of a central cushion by a conducting liner driver. The results are also used to benchmark a hydrodynamics code for modeling an FRC. They then use a radiation-hydrodynamics computational model to explore the effects of radiation production and transport when a gold plasma assembles on a CH cushion. Results are presented for the structure and evolution of the radiation hohlraum

A zeta function approach to the relation between the numbers of symmetry planes and axes of a polytope

A derivation of the Ces\`aro-Fedorov relation from the Selberg trace formula on an orbifolded 2-sphere is elaborated and extended to higher dimensions using the known heat-kernel coefficients for manifolds with piecewise-linear boundaries. Several results are obtained that relate the coefficients, $b_i$, in the Shephard-Todd polynomial to the geometry of the fundamental domain. For the 3-sphere we show that $b_4$ is given by the ratio of the volume of the fundamental tetrahedron to its Schl\"afli reciprocal.Comment: Plain TeX, 26 pages (eqn. (86) corrected

Preparation for a comprehensive assessment of North Pacific sei whales.

The last assessment of North Pacific sei whales was performed by Tillman (1977), and seems to have been accepted by the Scientific Committee in 1974 (Gambell, 1974). The exploitable stock (440ft) is estimated to have declined from 42,000 in 1963 to 8,600 in 1974, during a period of intensive pelagic whaling

Magnetothermal instability in laser plasmas including hydrodynamic effects

The impact of both density gradients and hydrodynamics on the evolution of the field compressing magnetothermal instability is considered [J. J. Bissell et al., Phys. Rev. Lett. 105, 175001 (2010)]. Hydrodynamic motion is found to have a limited effect on overall growth-rates; however, density gradients are shown to introduce an additional source term corresponding to a generalised description of the field generating thermal instability [D. Tidman and R. Shanny, Phys. Fluids 17, 1207 (1974)]. The field compressing and field generating source terms are contrasted, and the former is found to represent either the primary or sole instability mechanism for a range of conditions, especially those with Hall parameter v > 101. The generalised theory is compared to numerical simulation in the context of a recent nano-second gas-jet experiment [D. H. Froula et al., Phys. Rev. Lett. 98, 135001 (2007)] and shown to be in good agreement: exhibiting peak growth-rates and wavelengths of order 10 ns1 and 50 lm, respectively. The instability’s relevance to other experimental conditions, including those in inertial confinement fusion (I.C.F.) hohlraums, is also discussed

Semantic fluency in deaf children who use spoken and signed language, in comparison to hearing peers

Background Deafness has an adverse impact on children’s ability to acquire spoken languages. Signed languages offer a more accessible input for deaf children, but because the vast majority are born to hearing parents who do not sign, their early exposure to sign language is limited. Deaf children as a whole are therefore at high risk of language delays. Aims We compared deaf and hearing children’s performance on a semantic fluency task. Optimal performance on this task requires a systematic search of the mental lexicon, the retrieval of words within a subcategory, and, when that subcategory is exhausted, switching to a new subcategory. We compared retrieval patterns between groups, and also compared the responses of deaf children who used British Sign Language (BSL) to those who used spoken English. We investigated how semantic fluency performance related to children’s expressive vocabulary and executive function skills, and also re-tested semantic fluency in the majority of the children nearly two years later, in order to investigate how much progress they had made in that time. Methods and procedures Participants were deaf children aged 6-11 years (N=106, comprising 69 users of spoken English, 29 users of BSL and 8 users of Sign Supported English) compared to hearing children (N=120) of the same age who used spoken English. Semantic fluency was tested for the category “animals”. We coded for errors, clusters (e.g., “pets”, “farm animals”) and switches. Participants also completed the Expressive One-Word Picture Vocabulary Test and a battery of six non-verbal executive function tasks. In addition, we collected follow-up semantic fluency data for 70 deaf and 74 hearing children, nearly 2 years after they were first tested. Outcomes and results Deaf children, whether using spoken or signed language, produced fewer items in the semantic fluency task than hearing children, but they showed similar patterns of responses for items most commonly produced, clustering of items into subcategories and switching between subcategories. Both vocabulary and executive function scores predicted the number of correct items produced. Follow-up data from deaf participants showed continuing delays relative to hearing children two years later. Conclusions and implications We conclude that semantic fluency can be used experimentally to investigate lexical organisation in deaf children, and that it potentially has clinical utility across the heterogeneous deaf population. We present normative data to aid clinicians who wish to use this task with deaf children

Gesture Production in Language Impairment:It's Quality, Not Quantity, That Matters

PURPOSE: The aim of this study was to determine whether children with language impairment (LI) use gesture to compensate for their language difficulties. Method: The present study investigate d gesture accuracy and frequency i n children with LI (n = 21 ) across gesture imitation, gesture elicitation , spontaneous narrative and interactive problem solving tasks, relative to typically developing (TD) peers (n = 18 ) and peers with low language (LL) and educational concerns (n=21). RESULTS: C hildren with LI showed weaknesses in gesture accuracy (imitation and gesture elicitation ) in comparison to TD peers , but no differences in gesture rate . Children with LL only showed weaknesses in gesture imitation and used significantly more gest ures than TD peers during parent - child interaction. Across the whole sample, motor abilities were significantly related to gesture accuracy but not gesture rate. In addition, children with LI produce d proportionately more extending gestures, suggesting that they may use gesture to replace words that they are unable to articulate verbally. CONCLUSION: The results support the notion that gesture and language form a tightly linked communication system in which gestured eficits are seen alongside difficulties with spoken communication. Furthermore, it is the quality, not quantity of gestures that distinguish children with LI from typical peers