3,924 research outputs found
Water and Alanine: From Puddles(32) to Ponds(49)
The solvation of alanine is investigated, with a focus on adding a sufficient number of discrete water molecules to determine the first solvation shell for both the nonionized (N) and zwitterionic (Z) forms to converge the enthalpy of solvation and the enthalpy difference for the two forms of alanine. Monte Carlo sampling was employed using the generalized effective fragment potential (EFP) method to determine the global minimum of both conformers, with the number of EFP water molecules ranging from 32−49. A subset of sampled geometries were optimized with second-order perturbation theory (MP2) using the 6-31++G(d,p) basis set. Single point energies were calculated at these geometries using the polarizable continuum model (PCM). The predicted 298.15 K enthalpy of solvation ranges for MP2/6-31++G(d,p) and MP2+PCM//MP2/6-31++G(d,p) are 10.0−13.2 kcal/mol and 10.1−12.6 kcal/mol, respectively
Absence of Fragmentation in Two-Dimensional Bose-Einstein Condensation
We investigate the possibility that the BEC-like phenomena recently detected
on two-dimensional finite trapped systems consist of fragmented condensates. We
derive and diagonalize the one-body density matrix of a two-dimensional
isotropically trapped Bose gas at finite temperature. For the ideal gas, the
procedure reproduces the exact harmonic-oscillator eigenfunctions and the Bose
distribution. We use a new collocation-minimization method to study the
interacting gas in the Hartree-Fock approximation and obtain a ground-state
wavefunction and condensate fraction consistent with those obtained by other
methods. The populations of the next few eigenstates increase at the expense of
the ground state but continue to be negligible; this supports the conclusion
that two-dimensional BEC is into a single state.Comment: 6 pages, 1 figur
Exclusion Statistics in a two-dimensional trapped Bose gas
We briefly explain the notion of exclusion statistics and in particular
discuss the concept of an ideal exclusion statistics gas. We then review a
recent work where it is demonstrated that a {\em two-dimensional} Bose gas with
repulsive delta function interactions obeys ideal exclusion statistics, with a
fractional parameter related to the interaction strength.Comment: 10 pages, RevTeX. Proceedings of the Salerno workshop "Theory of
Quantum Gases and Quantum Coherence", to appear in a special issue of J.Phys.
B, Dec. 200
Embedding the affine complement of three intersecting lines in a finite projective plane
An (r, 1)–design is a pair (V, F) where V is a ν–set and F is a family of non-null subsets of V (b in number) which satisfy the following. (1) Every pair of distinct members of V is contained in precisely one member of F. (2) Every member of V occurs in precisely r members of F. A pseudo parallel complement PPC(n, α) is an (n+1, 1)–design with ν=n2−αn and b≦n2+n−α in which there are at least n−α a blocks of size n. A pseudo intersecting complement PIC(n, α) is an (n+1, 1)–design with ν=n2−αn+α−1 and b≦n2+n−α in which there are at least n−α+1 blocks of size n−1. It has previously been shown that for α≦4, every PIC(n, α) can be embedded in a PPC(n, α−1) and that for n>(α4−2α3+2α2+α−2)/2, every PPC(n, α) can be embedded in a finite projective plane of order n. In this paper we investigate the case of α=3 and show that any PIC(n, 3) is embeddable in a PPC(n,2) provided n≧14
Classification of phase transitions of finite Bose-Einstein condensates in power law traps by Fisher zeros
We present a detailed description of a classification scheme for phase
transitions in finite systems based on the distribution of Fisher zeros of the
canonical partition function in the complex temperature plane. We apply this
scheme to finite Bose-systems in power law traps within a semi-analytic
approach with a continuous one-particle density of states for different values of and to a three dimensional harmonically
confined ideal Bose-gas with discrete energy levels. Our results indicate that
the order of the Bose-Einstein condensation phase transition sensitively
depends on the confining potential.Comment: 7 pages, 9 eps-figures, For recent information on physics of small
systems see "http://www.smallsystems.de
Imperfect Homoclinic Bifurcations
Experimental observations of an almost symmetric electronic circuit show
complicated sequences of bifurcations. These results are discussed in the light
of a theory of imperfect global bifurcations. It is shown that much of the
dynamics observed in the circuit can be understood by reference to imperfect
homoclinic bifurcations without constructing an explicit mathematical model of
the system.Comment: 8 pages, 11 figures, submitted to PR
Anisotropic Spin Diffusion in Trapped Boltzmann Gases
Recent experiments in a mixture of two hyperfine states of trapped Bose gases
show behavior analogous to a spin-1/2 system, including transverse spin waves
and other familiar Leggett-Rice-type effects. We have derived the kinetic
equations applicable to these systems, including the spin dependence of
interparticle interactions in the collision integral, and have solved for
spin-wave frequencies and longitudinal and transverse diffusion constants in
the Boltzmann limit. We find that, while the transverse and longitudinal
collision times for trapped Fermi gases are identical, the Bose gas shows
diffusion anisotropy. Moreover, the lack of spin isotropy in the interactions
leads to the non-conservation of transverse spin, which in turn has novel
effects on the hydrodynamic modes.Comment: 10 pages, 4 figures; submitted to PR
Fluid Restriction Dehydration Increase Core Temperature During Endurance Exercise Compared to Exercise Induced Dehydration
International Journal of Exercise Science 15(2): 166-176, 2022. This study aimed to evaluate the difference in heart rate and core temperature during aerobic exercise between two forms of dehydration: exercise-induced (EI) and fluid restricted (FR). Twenty-two subjects (N = 22; 83.35 ± 13.92 kg) completed the current study, performing a familiarization session, a pre-experimental exercise session, and two exercise testing sessions. The EI exercise trial (81.52 ± 13.72 kg) was conducted after performing exercise in a hot environment to lose three to four percent of body weight and partial rehydration. The FR exercise trial (81.53 ± 14.14 kg) was completed after 12 hours of fluid restriction. During both exercise sessions, subjects pedaled against a set resistance of 130 watts for 30 minutes. The main effect of hydration on Tc was significant, F(1, 18) = 4.474, p = .049, ηp2 = .199 (Figure 2) with core temperature being greater during the FR trial compared to the EI trial (FR = 37.58 ± .06°C vs. EI = 37.31 ± .11°C). No significant interaction was found between hydration and time for HR, F(2, 42) = 0.120, p = .887, ηp2 = .006. The main effect of time on HR was significant, F(2, 42) = 119.664, p \u3c .001, ηp2 = .851. Fluid restriction was associated with an increase in core temperature. An increased core temperature may negatively influence performance, and care should be taken to ensure proper hydration
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