660 research outputs found
Static and Dynamic Properties of Dissipative Particle Dynamics
The algorithm for the DPD fluid, the dynamics of which is conceptually a
combination of molecular dynamics, Brownian dynamics and lattice gas automata,
is designed for simulating rheological properties of complex fluids on
hydrodynamic time scales. This paper calculates the equilibrium and transport
properties (viscosity, self-diffusion) of the thermostated DPD fluid explicitly
in terms of the system parameters. It is demonstrated that temperature
gradients cannot exist, and that there is therefore no heat conductivity.
Starting from the N-particle Fokker-Planck, or Kramers' equation, we prove an
H-theorem for the free energy, obtain hydrodynamic equations, and derive a
non-linear kinetic equation (the Fokker-Planck-Boltzmann equation) for the
single particle distribution function. This kinetic equation is solved by the
Chapman-Enskog method. The analytic results are compared with numerical
simulations.Comment: 22 pages, LaTeX, 3 Postscript figure
Density fluctuations and single-particle dynamics in liquid lithium
The single-particle and collective dynamical properties of liquid lithium
have been evaluated at several thermodynamic states near the triple point. This
is performed within the framework of mode-coupling theory, using a
self-consistent scheme which, starting from the known static structure of the
liquid, allows the theoretical calculation of several dynamical properties.
Special attention is devoted to several aspects of the single-particle
dynamics, which are discussed as a function of the thermodynamic state. The
results are compared with those of Molecular Dynamics simulations and other
theoretical approaches.Comment: 31 pages (in preprint format), 14 figures. Submitted to Phys. Rev.
Sneutrino Mixing Phenomena
In any model with nonzero Majorana neutrino masses, the sneutrino and
antisneutrino of the supersymmetric extended theory mix. We outline the
conditions under which sneutrino-antisneutrino mixing is experimentally
observable. The mass-splitting of the sneutrino mass eigenstates and sneutrino
oscillation phenomena are considered.Comment: 12 pages, revtex + axodraw, 1 figure included. Minor change
Genetic Risk Factors for Atypical Femoral Fractures (AFFs): A Systematic Review
Atypical femoral fractures (AFFs) are uncommon and have been associated particularly with long-term antiresorptive therapy, including bisphosphonates. Although the pathogenesis of AFFs is unknown, their identification in bisphosphonate-naĂŻve individuals and in monogenetic bone disorders has led to the hypothesis that genetic factors predispose to AFF. Our aim was to review and summarize the evidence for genetic factors in individuals with AFF. We conducted structured literature searches and hand-searching of conference abstracts/reference lists for key words relating to AFF and identified 2566 citations. Two individuals independently reviewed citations for (i) cases of AFF in monogenetic bone diseases and (ii) genetic studies in individuals with AFF. AFFs were reported in 23 individuals with the following 7 monogenetic bone disorders (gene): osteogenesis imperfecta (COL1A1/COL1A2), pycnodysostosis (CTSK), hypophosphatasia (ALPL), X-linked osteoporosis (PLS3), osteopetrosis, X-linked hypophosphatemia (PHEX), and osteoporosis pseudoglioma syndrome (LRP5). In 8 cases (35%), the monogenetic bone disorder was uncovered after the AFF occurred. Cases of bisphosphonate-naĂŻve AFF were reported in pycnodysostosis, hypophosphatasia, osteopetrosis, X-linked hypophosphatemia, and osteoporosis pseudoglioma syndrome. A pilot study in 13 AFF patients and 268 controls identified a greater number of rare variants in AFF cases using exon array analysis. A whole-exome sequencing study in 3 sisters with AFFs showed, among 37 shared genetic variants, a p.Asp188Tyr mutation in the GGPS1 gene in the mevalonate pathway, critical to osteoclast function, which is also inhibited by bisphosphonates. Two studies completed targeted ALPL gene sequencing, an ALPL heterozygous mutation was found in 1 case of a cohort of 11 AFFs, whereas the second study comprising 10 AFF cases did not find mutations in ALPL. Targeted sequencing of ALPL, COL1A1, COL1A2, and SOX9 genes in 5 cases of AFF identified a variant in COL1A2 in 1 case. These findings suggest a genetic susceptibility for AFFs.
Constraints on the SU(3) Electroweak Model
We consider a recent proposal by Dimopoulos and Kaplan to embed the
electroweak SU(2)_L X U(1)_Y into a larger group SU(3)_W X SU(2) X U(1) at a
scale above a TeV. This idea is motivated by the prediction for the weak mixing
angle sin^2 theta_W = 1/4, which naturally appears in these models so long as
the gauge couplings of the high energy SU(2) and U(1) groups are moderately
large. The extended gauge dynamics results in new effective operators that
contribute to four-fermion interactions and Z pole observables. We calculate
the corrections to these electroweak precision observables and carry out a
global fit of the new physics to the data. For SU(2) and U(1) gauge couplings
larger than 1, we find that the 95% C.L. lower bound on the matching (heavy
gauge boson mass) scale is 11 TeV. We comment on the fine-tuning of the high
energy gauge couplings needed to allow matching scales above our bounds. The
remnants of SU(3)_W breaking include multi-TeV SU(2)_L doublets with electric
charge (+-2,+-1). The lightest charged gauge boson is stable, leading to
cosmological difficulties.Comment: 17 pages, LaTeX, 4 figures embedded, uses JHEP.cl
Creating a low-dimensional quantum gas using dark states in an inelastic evanescent-wave mirror
We discuss an experimental scheme to create a low-dimensional gas of
ultracold atoms, based on inelastic bouncing on an evanescent-wave mirror.
Close to the turning point of the mirror, the atoms are transferred into an
optical dipole trap. This scheme can compress the phase-space density and can
ultimately yield an optically-driven atom laser. An important issue is the
suppression of photon scattering due to ``cross-talk'' between the mirror
potential and the trapping potential. We propose that for alkali atoms the
photon scattering rate can be suppressed by several orders of magnitude if the
atoms are decoupled from the evanescent-wave light. We discuss how such dark
states can be achieved by making use of circularly-polarized evanescent waves.Comment: 8 pages, 4 figure
Evidence of two viscous relaxation processes in the collective dynamics of liquid lithium
New inelastic X-ray scattering experiments have been performed on liquid
lithium in a wide wavevector range. With respect to the previous measurements,
the instrumental resolution, improved up to 1.5 meV, allows to accurately
investigate the dynamical processes determining the observed shape of the the
dynamic structure factor, . A detailed analysis of the lineshapes
shows the co-existence of relaxation processes with both a slow and a fast
characteristic timescales, and therefore that pictures of the relaxation
mechanisms based on a simple viscoelastic model must be abandoned.Comment: 5 pages, 4 .PS figure
Collective dynamics of liquid aluminum probed by Inelastic X-ray Scattering
An inelastic X-ray scattering experiment has been performed in liquid
aluminum with the purpose of studying the collective excitations at wavevectors
below the first sharp diffraction peak. The high instrumental resolution (up to
1.5 meV) allows an accurate investigation of the dynamical processes in this
liquid metal on the basis of a generalized hydrodynamics framework. The
outcoming results confirm the presence of a viscosity relaxation scenario ruled
by a two timescale mechanism, as recently found in liquid lithium.Comment: 8 pages, 7 figure
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