548 research outputs found
Criticality and Superfluidity in liquid He-4 under Nonequilibrium Conditions
We review a striking array of recent experiments, and their theoretical
interpretations, on the superfluid transition in He in the presence of a
heat flux, . We define and evaluate a new set of critical point exponents.
The statics and dynamics of the superfluid-normal interface are discussed, with
special attention to the role of gravity. If is in the same direction as
gravity, a self-organized state can arise, in which the entire sample has a
uniform reduced temperature, on either the normal or superfluid side of the
transition. Finally, we review recent theory and experiment regarding the heat
capacity at constant . The excitement that surrounds this field arises from
the fact that advanced thermometry and the future availability of a
microgravity experimental platform aboard the International Space Station will
soon open to experimental exploration decades of reduced temperature that were
previously inaccessible.Comment: 16 pages, 9 figures, plus harvard.sty style file for references
Accepted for publication in Colloquia section of Reviews of Modern Physic
Liquid 4He near the superfluid transition in the presence of a heat current and gravity
The effects of a heat current and gravity in liquid 4He near the superfluid
transition are investigated for temperatures above and below T_lambda. We
present a renormalization-group calculation based on model F for the Green's
function in a self-consistent approximation which in quantum many-particle
theory is known as the Hartree approximation. The approach can handle a zero
average order parameter above and below T_lambda and includes effects of
vortices. We calculate the thermal conductivity and the specific heat for all
temperatures T and heat currents Q in the critical regime. Furthermore, we
calculate the temperature profile. Below T_lambda we find a second correlation
length which describes the dephasing of the order parameter field due to
vortices. We find dissipation and mutual friction of the superfluid-normal
fluid counterflow and calculate the Gorter-Mellink coefficient A. We compare
our theoretical results with recent experiments.Comment: 26 pages, 9 figure
BCS-BEC crossover at finite temperature in the broken-symmetry phase
The BCS-BEC crossover is studied in a systematic way in the broken-symmetry
phase between zero temperature and the critical temperature. This study bridges
two regimes where quantum and thermal fluctuations are, respectively,
important. The theory is implemented on physical grounds, by adopting a
fermionic self-energy in the broken-symmetry phase that represents fermions
coupled to superconducting fluctuations in weak coupling and to bosons
described by the Bogoliubov theory in strong coupling. This extension of the
theory beyond mean field proves important at finite temperature, to connect
with the results in the normal phase. The order parameter, the chemical
potential, and the single-particle spectral function are calculated numerically
for a wide range of coupling and temperature. This enables us to assess the
quantitative importance of superconducting fluctuations in the broken-symmetry
phase over the whole BCS-BEC crossover. Our results are relevant to the
possible realizations of this crossover with high-temperature cuprate
superconductors and with ultracold fermionic atoms in a trap.Comment: 21 pages, 15 figure
Dobrushin states in the \phi^4_1 model
We consider the van der Waals free energy functional in a bounded interval
with inhomogeneous Dirichlet boundary conditions imposing the two stable phases
at the endpoints. We compute the asymptotic free energy cost, as the length of
the interval diverges, of shifting the interface from the midpoint. We then
discuss the effect of thermal fluctuations by analyzing the \phi^4_1-measure
with Dobrushin boundary conditions. In particular, we obtain a nontrivial limit
in a suitable scaling in which the length of the interval diverges and the
temperature vanishes. The limiting state is not translation invariant and
describes a localized interface. This result can be seen as the probabilistic
counterpart of the variational convergence of the associated excess free
energy.Comment: 34 page
A First-Landau-Level Laughlin/Jain Wave Function for the Fractional Quantum Hall Effect
We show that the introduction of a more general closed-shell operator allows
one to extend Laughlin's wave function to account for the richer hierarchies
(1/3, 2/5, 3/7 ...; 1/5, 2/9, 3/13, ..., etc.) found experimentally. The
construction identifies the special hierarchy states with condensates of
correlated electron clusters. This clustering implies a single-particle (ls)j
algebra within the first Landau level (LL) identical to that of multiply filled
LLs in the integer quantum Hall effect. The end result is a simple generalized
wave function that reproduces the results of both Laughlin and Jain, without
reference to higher LLs or projection.Comment: Revtex. In this replacement we show how to generate the Jain wave
function explicitly, by acting with the generalized ls closed-shell operator
discussed in the original version. We also walk the reader through a
classical 1d caricature of this problem so that he/she can better understand
why 2s+1, where s is the spin, should be associated with the number of
electrons associated with the underlying clusters or composites. 11 page
Stability of condensate in superconductors
According to the BCS theory the superconducting condensate develops in a
single quantum mode and no Cooper pairs out of the condensate are assumed. Here
we discuss a mechanism by which the successful mode inhibits condensation in
neighboring modes and suppresses a creation of noncondensed Cooper pairs. It is
shown that condensed and noncondensed Cooper pairs are separated by an energy
gap which is smaller than the superconducting gap but large enough to prevent
nucleation in all other modes and to eliminate effects of noncondensed Cooper
pairs on properties of superconductors. Our result thus justifies basic
assumptions of the BCS theory and confirms that the BCS condensate is stable
with respect to two-particle excitations
Surprising flowering response to photoperiod: Preliminary characterization of West and Central African pearl millet germplasm
Pearl millet (Pennisetum glaucum) is considered to be a
short-day species that flowers, or flowers earlier, when
day lengths are short. A few studies with two to six
planting dates and few selected entries have been
conducted in USA (Burton 1965), Senegal (Ramond
1968), and India (Patil et al. 1978, Das 1991). However,
there is no known research on the flowering response of
pearl millet to photoperiod changes over the entire year.
Likewise, knowledge about the photoperiod-sensitivity
in West and Central African pearl millets is insufficient
The association between age and telomere length is age‐dependent: Evidence for a threshold model of telomere length maintenance
This is the final version. Available on open access from Wiley via the DOI in this record. Data availability statement: The data that supports the findings of this study are available in the Supporting Information material of this articleTelomere length and dynamics are commonly used biomarkers of somatic state, yet the role of telomeres underlying the aging process is still debated. Indeed, to date, empirical evidence for an association between age and telomere length is mixed. Here, we test if the age‐dependency of the association between age and telomere length can provide a potential explanation for the reported inconsistencies across studies. To this end, we quantified telomere length by telomere restriction fragment analysis in two groups of Japanese quail (Coturnix japonica) that differed in their age distribution. One group consisted of young adults only, whereas the second group consisted of adults across a wide range of ages. In the young adults group, there was a highly significant negative association between telomere length and age, whereas no association between age and telomere length was found in the all‐ages adults group. This difference between groups was not due to telomere length‐dependent selective disappearance. Our results shows that the association between telomere length and age is age‐dependent and suggest that the costs and benefits associated with telomere maintenance are dynamic across an individual's life course.European Union Horizon 2020Swiss National Science FoundationUniversity of Castilla‐
La ManchaThe Company of Biologists limite
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