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Search Results: 1 - 10 of 655894 matches for " J. A. White "
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Is there Ornstein-Zernike equation in the canonical ensemble?
J. A. White,S. Velasco
Physics , 2000, DOI: 10.1209/epl/i2001-00270-x
Abstract: A general density-functional formalism using an extended variable-space is presented for classical fluids in the canonical ensemble (CE). An exact equation is derived that plays the role of the Ornstein-Zernike (OZ) equation in the grand canonical ensemble (GCE). When applied to the ideal gas we obtain the exact result for the total correlation function h_N. For a homogeneous fluid with N particles the new equation only differs from OZ by 1/N and it allows to obtain an approximate expression for h_N in terms of its GCE counterpart that agrees with the expansion of h_N in powers of 1/N.
Equivalence of two approaches for the inhomogeneous density in the canonical ensemble
J. A. White,S. Velasco
Physics , 2000, DOI: 10.1103/PhysRevE.62.4427
Abstract: In this article we show that the inhomogeneous density obtained from a density-functional theory of classical fluids in the canonical ensemble (CE), recently presented by White et al [Phys. Rev. Lett. 84 (2000) 1220], is equivalent to first order to the result of the series expansion of the CE inhomogeneous density introduced by Gonzalez et al [Phys. Rev. Lett. 79 (1997) 2466].
Monte Carlo methods and applications for the nuclear shell model
D. J. Dean,J. A. White
Physics , 1998, DOI: 10.1063/1.59542
Abstract: The shell-model Monte Carlo (SMMC) technique transforms the traditional nuclear shell-model problem into a path-integral over auxiliary fields. We describe below the method and its applications to four physics issues: calculations of sdpf- shell nuclei, a discussion of electron-capture rates in pf-shell nuclei, exploration of pairing correlations in unstable nuclei, and level densities in rare earth systems.
Fast supersymmetry phenomenology at the Large Hadron Collider using machine learning techniques
A. Buckley,A. Shilton,M. J. White
Physics , 2011, DOI: 10.1016/j.cpc.2011.12.026
Abstract: A pressing problem for supersymmetry (SUSY) phenomenologists is how to incorporate Large Hadron Collider search results into parameter fits designed to measure or constrain the SUSY parameters. Owing to the computational expense of fully simulating lots of points in a generic SUSY space to aid the calculation of the likelihoods, the limits published by experimental collaborations are frequently interpreted in slices of reduced parameter spaces. For example, both ATLAS and CMS have presented results in the Constrained Minimal Supersymmetric Model (CMSSM) by fixing two of four parameters, and generating a coarse grid in the remaining two. We demonstrate that by generating a grid in the full space of the CMSSM, one can interpolate between the output of an LHC detector simulation using machine learning techniques, thus obtaining a superfast likelihood calculator for LHC-based SUSY parameter fits. We further investigate how much training data is required to obtain usable results, finding that approximately 2000 points are required in the CMSSM to get likelihood predictions to an accuracy of a few per cent. The techniques presented here provide a general approach for adding LHC event rate data to SUSY fitting algorithms, and can easily be used to explore other candidate physics models.
Baryonic Signatures in Large-Scale Structure
A. Meiksin,Martin White,J. A. Peacock
Physics , 1998, DOI: 10.1046/j.1365-8711.1999.02369.x
Abstract: We investigate the consequences of a non-negligible baryon fraction for models of structure formation in Cold Dark Matter dominated cosmologies, emphasizing in particular the existence of oscillations in the present-day matter power spectrum. These oscillations are the remnants of acoustic oscillations in the photon-baryon fluid before last scattering. For acceptable values of the cosmological and baryon densities, the oscillations modulate the power by up to 10%, with a `period' in spatial wavenumber which is close to Delta k approximately 0.05/ Mpc. We study the effects of nonlinear evolution on these features, and show that they are erased for k > 0.2 h/ Mpc. At larger scales, the features evolve as expected from second-order perturbation theory: the visibility of the oscillations is affected only weakly by nonlinear evolution. No realistic CDM parameter combination is able to account for the claimed feature near k = 0.1 h/ Mpc in the APM power spectrum, or the excess power at 100 Mpc/h wavelengths quoted by several recent surveys. Thus baryonic oscillations are not predicted to dominate existing measurements of clustering. We examine several effects which may mask the features which are predicted, and conclude that future galaxy surveys may be able to detect the oscillatory features in the power spectrum provided baryons comprise more than 15% of the total density, but that it will be a technically challenging achievement.
Teachers, Are They Really Needed?  [PDF]
Bader A. Alomary, Cris I. Nunn, Bobby J. White, Shelley L. Williams, M. Diane Clark
Creative Education (CE) , 2017, DOI: 10.4236/ce.2017.813147
Abstract: Beginning in the mid-20th century, traditional educational models were challenged by educational experts. The traditional model of instruction is what is known as teacher guided instruction or direct instruction. The current focus in education moved to student centered learning or problem based learning (PBL). Given these pedagogical discussions, SugataMitra asked the question, “Do we need teachers?” and developed the term Self-Organized Learning Environments (SOLE) to describe self-directed learning. The idea behind a SOLE is independent learning among students as they work at their own pace, while satisfying their own goals and objectives. One doctoral level class, composed of deaf students, used this strategy for a beginning level course. Findings showed that students needed a bit more structure in the beginning of the course, but then they were able to direct their own learning in ways that went beyond the bounds of traditional learning. This strategy is suggested as a possible motivational one for deaf students who often employ more passive learning strategies.
The HPV Vaccination Strategy: Could Male Vaccination Have a Significant Impact?
V. Brown,K. A. J. White
Computational and Mathematical Methods in Medicine , 2010, DOI: 10.1080/17486700903486613
Abstract: We investigate the potential success of the human papilloma virus (HPV) vaccine, taking into consideration possible waning immunity and the influence of behavioural parameters. We use a compartmental, population-level ordinary differential equation (ODE) model. We find the effective reproductive value for HPV, R 0 e , which measures the threshold for infection outbreak in a population that is not entirely susceptible, together with infection prevalence. We study the effects of different parameters on both of these quantities. Results show that waning immunity plays a large part in allowing infection to persist. The proportion of the population not sexually active when vaccination occurs affects R 0 e , as does the rate at which individuals become sexually active. In several cases, infection persists as a result of an infection reservoir in the male cohort. To explore this further, we introduce male vaccination and find the conditions for which vaccination of males could be considered appropriate.
Construct Validity of the Holistic Complementary and Alternative Medicines Questionnaire (HCAMQ)—An Investigation Using Modern Psychometric Approaches
Paula Kersten,P. J. White,A. Tennant
Evidence-Based Complementary and Alternative Medicine , 2011, DOI: 10.1093/ecam/nep141
Abstract: The scientific basis of efficacy studies of complementary medicine requires the availability of validated measures. The Holistic Complementary and Alternative Medicine Questionnaire (HCAMQ) is one such measure. This article aimed to examine its construct validity, using a modern psychometric approach. The HCAMQ was completed by 221 patients (mean age 66.8, SD 8.29, 58% females) with chronic stable pain predominantly from a single joint (hip or knee) of mechanical origin, waiting for a hip (40%) or knee (60%) joint replacement, on enrolment in a study investigating the effects of acupuncture and placebo controls. The HCAMQ contains a Holistic Health (HH) Subscale (five items) and a CAM subscale (six items). Validity of the subscales was tested using Cronbach alpha's, factor analysis, Mokken scaling and Rasch analysis, which did not support the original two-factor structure of the scale. A five-item HH subscale and a four-item CAM subscale (worded in a negative direction) fitted the Rasch model and were unidimensional (2=8.44, =0.39, PSI=0.69 versus 2=17.33, =0.03, PSI=0.77). Two CAM items (worded in the positive direction) had significant misfit. In conclusion, we have shown that the original two-factor structure of the HCAMQ could not be supported but that two valid shortened subscales can be used, one for HH Beliefs (four-item HH), and the other for CAM Beliefs (four-item CAM). It is recommended that consideration is given to rewording the two discarded positively worded CAM questions to enhance construct validity.
Creation of maximally entangled photon-number states using optical fiber multiports
G. J. Pryde,A. G. White
Physics , 2003, DOI: 10.1103/PhysRevA.68.052315
Abstract: We theoretically demonstrate a method for producing the maximally path-entangled state (1/Sqrt[2]) (|N,0> + exp[iN phi] |0,N>) using intensity-symmetric multiport beamsplitters, single photon inputs, and either photon-counting postselection or conditional measurement. The use of postselection enables successful implementation with non-unit efficiency detectors. We also demonstrate how to make the same state more conveniently by replacing one of the single photon inputs by a coherent state.
Observational Constraints on the Formation and Evolution of Binary Stars
R. J. White,A. M. Ghez
Physics , 2001, DOI: 10.1086/321542
Abstract: We present a high spatial resolution UV to NIR survey of 44 young binary stars in Taurus with separations of 10-1000 AU. The primary results include: (1) The relative ages of binary star components are more similar than the relative ages of randomly paired single stars, supporting coeval formation. (2) Only one of the companion masses is substellar, and hence the apparent overabundance of T Tauri star companions relative to main-sequence star companions can not be explained by a wealth of substellar secondaries that would have been missed in main-sequence surveys. (3) Roughly 10% of T Tauri binary star components have very red NIR colors (K-L > 1.4) and unusually high mass accretion rates. This phenomenon does not appear to be restricted to binary systems, however, since a comparable fraction of single T Tauri stars exhibit the same properties. (4) Although the disk lifetimes of single stars are roughly equal to their stellar ages, the disk lifetimes of binary stars are an order of magnitude less than their ages. (5) The accretion rates for both single and binary T Tauri stars appear to be moderately mass dependent. (6) Although most classical T Tauri star binaries retain both a circumprimary and a circumsecondary disk, there are several systems with only a circumprimary disk. Together with the relative accretion rates, this suggests that circumprimary disks survive longer, on average, than circumsecondary disks. (7) The disk lifetimes, mass ratios, and relative accretion signatures of the closest binaries (10-100 AU) suggest that they are being replenished from a circumbinary reservoir with low angular momentum. Overall, these results support fragmentation as the dominant binary star formation mechanism.
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