35,815 research outputs found
Coexistence Curve Singularities at Critical End Points
We report an extensive Monte Carlo study of critical end point behaviour in a
symmetrical binary fluid mixture. On the basis of general scaling arguments,
singular behaviour is predicted in the diameter of the liquid-gas coexistence
curve as the critical end point is approached. The simulation results show
clear evidence for this singularity, as well as confirming a previously
predicted singularity in the coexistence chemical potential. Both singularities
should be detectable experimentally.Comment: 9 pages Revtex, 3 figures. To appear in Phys. Rev. Let
Redshift-Space Distortions and the Real-Space Clustering of Different Galaxy Types
We study the distortions induced by peculiar velocities on the redshift-space
correlation function of galaxies of different morphological types in the
Pisces-Perseus redshift survey. Redshift-space distortions affect early- and
late-type galaxies in different ways. In particular, at small separations, the
dominant effect comes from virialized cluster cores, where ellipticals are the
dominant population. The net result is that a meaningful comparison of the
clustering strength of different morphological types can be performed only in
real space, i.e., after projecting out the redshift distortions on the
two-point correlation function xi(r_p,pi). A power-law fit to the projected
function w_p(r_p) on scales smaller than 10/h Mpc gives r_o =
8.35_{-0.76}^{+0.75} /h Mpc, \gamma = 2.05_{-0.08}^{+0.10} for the early-type
population, and r_o = 5.55_{-0.45}^{+0.40} /h Mpc, \gamma =
1.73_{-0.08}^{+0.07} for spirals and irregulars. These values are derived for a
sample luminosity brighter than M_{Zw} = -19.5. We detect a 25% increase of r_o
with luminosity for all types combined, from M_{Zw} = -19 to -20. In the
framework of a simple stable-clustering model for the mean streaming of pairs,
we estimate sigma_12(1), the one-dimensional pairwise velocity dispersion
between 0 and 1 /h Mpc, to be 865^{+250}_{-165} km/s for early-type galaxies
and 345^{+95}_{-65} km/s for late types. This latter value should be a fair
estimate of the pairwise dispersion for ``field'' galaxies; it is stable with
respect to the presence or absence of clusters in the sample, and is consistent
with the values found for non-cluster galaxies and IRAS galaxies at similar
separations.Comment: 17 LaTeX pages including 3 tables, plus 11 PS figures. Uses AASTeX
macro package (aaspp4.sty) and epsf.sty. To appear on ApJ, 489, Nov 199
Multicanonical Study of the 3D Ising Spin Glass
We simulated the Edwards-Anderson Ising spin glass model in three dimensions
via the recently proposed multicanonical ensemble. Physical quantities such as
energy density, specific heat and entropy are evaluated at all temperatures. We
studied their finite size scaling, as well as the zero temperature limit to
explore the ground state properties.Comment: FSU-SCRI-92-121; 7 pages; sorry, no figures include
Vectorial Loading of Processive Motor Proteins: Implementing a Landscape Picture
Individual processive molecular motors, of which conventional kinesin is the
most studied quantitatively, move along polar molecular tracks and, by exerting
a force on a tether, drag cellular cargoes, {\em in
vivo}, or spherical beads, {\em in vitro}, taking up to hundreds of
nanometer-scale steps. From observations of velocities and the dispersion of
displacements with time, under measured forces and controlled fuel supply
(typically ATP), one may hope to obtain insight into the molecular motions
undergone in the individual steps. In the simplest situation, the load force
may be regarded as a scalar resisting force, , acting
parallel to the track: however, experiments, originally by Gittes {\em et al.}
(1996), have imposed perpendicular (or vertical) loads, , while more
recently Block and coworkers (2002, 2003) and Carter and Cross (2005) have
studied {\em assisting} (or reverse) loads, , and also sideways (or
transverse) loads
Isospin fractionation and isoscaling in dynamical nuclear collisions
Isoscaling is found to hold for fragment yields in the antisymmetrized
molecular dynamics (AMD) simulations for collisions of calcium isotopes at 35
MeV/nucleon. This suggests the applicability of statistical considerations to
the dynamical fragment emission. The observed linear relationship between the
isoscaling parameters and the isospin asymmetry of fragments supports the above
suggestion. The slope of this linear function yields information about the
symmetry energy in low density region where multifragmentation occurs.Comment: 11 pages, 6 figure
Asymmetric Fluid Criticality I: Scaling with Pressure Mixing
The thermodynamic behavior of a fluid near a vapor-liquid and, hence,
asymmetric critical point is discussed within a general ``complete'' scaling
theory incorporating pressure mixing in the nonlinear scaling fields as well as
corrections to scaling. This theory allows for a Yang-Yang anomaly in which
\mu_{\sigma}^{\prime\prime}(T), the second temperature derivative of the
chemical potential along the phase boundary, diverges like the specific heat
when T\to T_{\scriptsize c}; it also generates a leading singular term,
|t|^{2\beta}, in the coexistence curve diameter, where t\equiv
(T-T_{\scriptsize c}) /T_{\scriptsize c}. The behavior of various special loci,
such as the critical isochore, the critical isotherm, the k-inflection loci, on
which \chi^{(k)}\equiv \chi(\rho,T)/\rho^{k} (with \chi = \rho^{2}
k_{\scriptsize B}TK_{T}) and C_{V}^{(k)}\equiv C_{V}(\rho,T)/\rho^{k} are
maximal at fixed T, is carefully elucidated. These results are useful for
analyzing simulations and experiments, since particular, nonuniversal values of
k specify loci that approach the critical density most rapidly and reflect the
pressure-mixing coefficient. Concrete illustrations are presented for the
hard-core square-well fluid and for the restricted primitive model electrolyte.
For comparison, a discussion of the classical (or Landau) theory is presented
briefly and various interesting loci are determined explicitly and illustrated
quantitatively for a van der Waals fluid.Comment: 21 pages in two-column format including 8 figure
Radial Redshift Space Distortions
The radial component of the peculiar velocities of galaxies cause
displacements in their positions in redshift space. We study the effect of the
peculiar velocities on the linear redshift space two point correlation
function. Our analysis takes into account the radial nature of the redshift
space distortions and it highlights the limitations of the plane parallel
approximation. We consider the problem of determining the value of \beta and
the real space two point correlation function from the linear redshift space
two point correlation function. The inversion method proposed here takes into
account the radial nature of the redshift space distortions and can be applied
to magnitude limited redshift surveys that have only partial sky coverage.Comment: 26 pages including 11 figures, to appear in Ap
IRAS versus POTENT Density Fields on Large Scales: Biasing and Omega
The galaxy density field as extracted from the IRAS 1.2 Jy redshift survey is
compared to the mass density field as reconstructed by the POTENT method from
the Mark III catalog of peculiar velocities. The reconstruction is done with
Gaussian smoothing of radius 12 h^{-1}Mpc, and the comparison is carried out
within volumes of effective radii 31-46 h^{-1}Mpc, containing approximately
10-26 independent samples. Random and systematic errors are estimated from
multiple realizations of mock catalogs drawn from a simulation that mimics the
observed density field in the local universe. The relationship between the two
density fields is found to be consistent with gravitational instability theory
in the mildly nonlinear regime and a linear biasing relation between galaxies
and mass. We measure beta = Omega^{0.6}/b_I = 0.89 \pm 0.12 within a volume of
effective radius 40 h^{-1}Mpc, where b_I is the IRAS galaxy biasing parameter
at 12 h^{-1}Mpc. This result is only weakly dependent on the comparison volume,
suggesting that cosmic scatter is no greater than \pm 0.1. These data are thus
consistent with Omega=1 and b_I\approx 1. If b_I>0.75, as theoretical models of
biasing indicate, then Omega>0.33 at 95% confidence. A comparison with other
estimates of beta suggests scale-dependence in the biasing relation for IRAS
galaxies.Comment: 35 pages including 10 figures, AAS Latex, Submitted to The
Astrophysical Journa
Renormalization Group for Large N Strongly Commensurate Dirty Boson Model
The large N sigma model, in D<4 space-time dimensions, with disorder a
function of d space dimensions, is analyzed via a renormalization group
treatment. Critical exponents for average quantities are calculated, first to
lowest order and then to all orders, in . In particular, it
is found that . When D=d+1, this model is equivalent to a large N
limit of the strongly commensurate dirty boson problem.Comment: 16 pages, 4 figures, to be published in PR
Dynamical Quantum Phase Transitions in the Transverse Field Ising Model
A phase transition indicates a sudden change in the properties of a large
system. For temperature-driven phase transitions this is related to
non-analytic behavior of the free energy density at the critical temperature:
The knowledge of the free energy density in one phase is insufficient to
predict the properties of the other phase. In this paper we show that a close
analogue of this behavior can occur in the real time evolution of quantum
systems, namely non-analytic behavior at a critical time. We denote such
behavior a dynamical phase transition and explore its properties in the
transverse field Ising model. Specifically, we show that the equilibrium
quantum phase transition and the dynamical phase transition in this model are
intimately related.Comment: 4+4 pages, 4 figures, Appendix adde
- âŠ