19,270 research outputs found
Understanding Confinement From Deconfinement
We use effective magnetic SU(N) pure gauge theory with cutoff M and fixed
gauge coupling g_m to calculate non-perturbative magnetic properties of the
deconfined phase of SU(N) Yang-Mills theory. We obtain the response to an
external closed loop of electric current by reinterpreting and regulating the
calculation of the one loop effective potential in Yang-Mills theory. This
effective potential gives rise to a color magnetic charge density, the
counterpart in the deconfined phase of color magnetic currents introduced in
effective dual superconductor theories of the confined phase via magnetically
charged Higgs fields. The resulting spatial Wilson loop has area law behavior.
Using values of M and g_m determined in the confined phase, we find SU(3)
spatial string tensions compatible with lattice simulations in the temperature
interval 1.5T_c < T < 2.5T_c. Use of the effective theory to analyze
experiments on heavy ion collisions will provide applications and further tests
of these ideas.Comment: 18 pages, 5 figures, v2: fixed archive title (only
Kinetic cross coupling between non-conserved and conserved fields in phase field models
We present a phase field model for isothermal transformations of two
component alloys that includes Onsager kinetic cross coupling between the
non-conserved phase field and the conserved concentration field. We also
provide the reduction of the phase field model to the corresponding macroscopic
description of the free boundary problem. The reduction is given in a general
form. Additionally we use an explicit example of a phase field model and check
that the reduced macroscopic description, in the range of its applicability, is
in excellent agreement with direct phase field simulations. The relevance of
the newly introduced terms to solute trapping is also discussed
Differences in nitrate uptakeamong benthic algal assemblages in a mountain stream
We evaluated how benthic algal assemblages that vary in composition, richness, and other diversity metrics remove NO 3 -N from the water column of a mountain stream. Ecological theory and empirical studies suggest that ecosystem process rates should increase as richness increases because of niche separation or activity of dominant taxa. Accordingly, we predicted that algal assemblages with highest richness would show the highest rates of NO 3 -N uptake. To test this prediction, we transplanted 225 rocks representing 3 patch types (green, yellow, and brown) that differed macroscopically in algal composition from a lake outflow stream to a lake inflow stream where an experimental release of 15 N-NO 3 was ongoing. We measured 15 N uptake in each patch type during the stable isotope release. Benthic algal richness varied from 28 genera in the green patch type and 26 genera in the yellow patch type to 22 genera in the brown patch type. Without accounting for differences in chlorophyll a content, NO 3 -N uptake (2.1–3.3 3 10 4 /d) was highest in the green patch type, lowest (0.3–0.6 3 10 4 /d) in the yellow patch type, and intermediate (1.2–1.5 3 10 4 /d) in the brown patch type. NO 3 -N uptake normalized to chlorophyll a increased in concert with algal richness in the 3 patch types. This result supports the hypothesis that increased assemblage diversity leads to higher rates of community processes. Aside from diversity differences per se, lower rates of NO 3 -N uptake in the brown patch type might be the consequence of differences in functional characteristics of the taxa present. Approximately 29% of algal biovolume in the brown patch type consisted of taxa capable of N 2 -fixation, a result that suggests that algae in this patch type might be capable of meeting N needs via N 2 -fixation rather than via removal from the water column
Improved Quantum Hard-Sphere Ground-State Equations of State
The London ground-state energy formula as a function of number density for a
system of identical boson hard spheres, corrected for the reduced mass of a
pair of particles in a sphere-of-influence picture, and generalized to fermion
hard-sphere systems with two and four intrinsic degrees of freedom, has a
double-pole at the ultimate \textit{regular} (or periodic, e.g.,
face-centered-cubic) close-packing density usually associated with a
crystalline branch. Improved fluid branches are contructed based upon exact,
field-theoretic perturbation-theory low-density expansions for many-boson and
many-fermion systems, appropriately extrapolated to intermediate densities, but
whose ultimate density is irregular or \textit{random} closest close-packing as
suggested in studies of a classical system of hard spheres. Results show
substantially improved agreement with the best available Green-function Monte
Carlo and diffusion Monte Carlo simulations for bosons, as well as with ladder,
variational Fermi hypernetted chain, and so-called L-expansion data for
two-component fermions.Comment: 15 pages and 7 figure
Four-nucleon scattering: Ab initio calculations in momentum space
The four-body equations of Alt, Grassberger and Sandhas are solved for \nH
scattering at energies below three-body breakup threshold using various
realistic interactions including one derived from chiral perturbation theory.
After partial wave decomposition the equations are three-variable integral
equations that are solved numerically without any approximations beyond the
usual discretization of continuum variables on a finite momentum mesh. Large
number of two-, three- and four-nucleon partial waves are considered until the
convergence of the observables is obtained. The total \nH cross section data
in the resonance region is not described by the calculations which confirms
previous findings by other groups. Nevertheless the numbers we get are slightly
higher and closer to the data than previously found and depend on the choice of
the two-nucleon potential. Correlations between the deficiency in \nd
elastic scattering and the total \nH cross section are studied.Comment: Corrected Eq. (10
Spermatogenesis and sertoli cell activity in mice lacking Sertoli cell receptors for follicle stimulating hormone and androgen
Spermatogenesis in the adult male depends on the action of FSH and androgen. Ablation of either hormone has deleterious effects on Sertoli cell function and the progression of germ cells through spermatogenesis. In this study we generated mice lacking both FSH receptors (FSHRKO) and androgen receptors on the Sertoli cell (SCARKO) to examine how FSH and androgen combine to regulate Sertoli cell function and spermatogenesis. Sertoli cell number in FSHRKO-SCARKO mice was reduced by about 50% but was not significantly different from FSHRKO mice. In contrast, total germ cell number in FSHRKO-SCARKO mice was reduced to 2% of control mice (and 20% of SCARKO mice) due to a failure to progress beyond early meiosis. Measurement of Sertoli cell-specific transcript levels showed that about a third were independent of hormonal action on the Sertoli cell, whereas others were predominantly androgen dependent or showed redundant control by FSH and androgen. Results show that FSH and androgen act through redundant, additive, and synergistic regulation of spermatogenesis and Sertoli cell activity. In addition, the Sertoli cell retains a significant capacity for activity, which is independent of direct hormonal regulation
The Parameterized Post-Friedmann Framework for Theories of Modified Gravity: Concepts, Formalism and Examples
A unified framework for theories of modified gravity will be an essential
tool for interpreting the forthcoming deluge of cosmological data. We present
such a formalism, the Parameterized Post-Friedmann framework (PPF), which
parameterizes the cosmological perturbation theory of a wide variety of
modified gravity models. PPF is able to handle spin-0 degrees of freedom from
new scalar, vector and tensor fields, meaning that it is not restricted to
simple models based solely on cosmological scalar fields. A direct
correspondence is maintained between the parameterization and the underlying
space of theories, which allows us to build up a `dictionary' of modified
gravity theories and their PPF correspondences. In this paper we describe the
construction of the parameterization and demonstrate its use through a number
of worked examples relevant to the current literature. We indicate how the
formalism will be implemented numerically, so that the dictionary of modified
gravity can be pitted against forthcoming observations.Comment: 24 pages, updated to match version published in PRD. Discussion of
section 4 extended. Suggestions for the busy reader are given at the end of
section
Renormalized couplings and scaling correction amplitudes in the N-vector spin models on the sc and the bcc lattices
For the classical N-vector model, with arbitrary N, we have computed through
order \beta^{17} the high temperature expansions of the second field derivative
of the susceptibility \chi_4(N,\beta) on the simple cubic and on the body
centered cubic lattices. (The N-vector model is also known as the O(N)
symmetric classical spin Heisenberg model or, in quantum field theory, as the
lattice
O(N) nonlinear sigma model.) By analyzing the expansion of \chi_4(N,\beta) on
the two lattices, and by carefully allowing for the corrections to scaling, we
obtain updated estimates of the critical parameters and more accurate tests of
the hyperscaling relation d\nu(N) +\gamma(N) -2\Delta_4(N)=0 for a range of
values of the spin dimensionality N, including
N=0 [the self-avoiding walk model], N=1 [the Ising spin 1/2 model],
N=2 [the XY model], N=3 [the classical Heisenberg model]. Using the recently
extended series for the susceptibility and for the second correlation moment,
we also compute the dimensionless renormalized four point coupling constants
and some universal ratios of scaling correction amplitudes in fair agreement
with recent renormalization group estimates.Comment: 23 pages, latex, no figure
Chiral Quasicrystalline Order and Dodecahedral Geometry in Exceptional Families of Viruses
On the example of exceptional families of viruses we i) show the existence of
a completely new type of matter organization in nanoparticles, in which the
regions with a chiral pentagonal quasicrystalline order of protein positions
are arranged in a structure commensurate with the spherical topology and
dodecahedral geometry, ii) generalize the classical theory of quasicrystals
(QCs) to explain this organization, and iii) establish the relation between
local chiral QC order and nonzero curvature of the dodecahedral capsid faces.Comment: 8 pages, 3 figure
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