295 research outputs found
Lignin, Cellulose and Crude Fiber Changes in Maturing Western Wheatgrass: (Agropyron smithii Rybd.)
It can be said from observations that plants become more woody as they mature. A young plant is relatively tender and supple, whereas an older plant is tougher and has greater strength structure. The nature of this woodiness and its effect upon the digestibility of plants and plant products by animals is of some concern
The two-fluid model with superfluid entropy
The two-fluid model of liquid helium is generalized to the case that the
superfluid fraction has a small entropy content. We present theoretical
arguments in favour of such a small superfluid entropy. In the generalized
two-fluid model various sound modes of HeII are investigated. In a
superleak carrying a persistent current the superfluid entropy leads to a new
sound mode which we call sixth sound. The relation between the sixth sound and
the superfluid entropy is discussed in detail.Comment: 22 pages, latex, published in Nuovo Cimento 16 D (1994) 37
Bose-Einstein Condensation in a Harmonic Potential
We examine several features of Bose-Einstein condensation (BEC) in an
external harmonic potential well. In the thermodynamic limit, there is a phase
transition to a spatial Bose-Einstein condensed state for dimension D greater
than or equal to 2. The thermodynamic limit requires maintaining constant
average density by weakening the potential while increasing the particle number
N to infinity, while of course in real experiments the potential is fixed and N
stays finite. For such finite ideal harmonic systems we show that a BEC still
occurs, although without a true phase transition, below a certain
``pseudo-critical'' temperature, even for D=1. We study the momentum-space
condensate fraction and find that it vanishes as 1/N^(1/2) in any number of
dimensions in the thermodynamic limit. In D less than or equal to 2 the lack of
a momentum condensation is in accord with the Hohenberg theorem, but must be
reconciled with the existence of a spatial BEC in D=2. For finite systems we
derive the N-dependence of the spatial and momentum condensate fractions and
the transition temperatures, features that may be experimentally testable. We
show that the N-dependence of the 2D ideal-gas transition temperature for a
finite system cannot persist in the interacting case because it violates a
theorem due to Chester, Penrose, and Onsager.Comment: 34 pages, LaTeX, 6 Postscript figures, Submitted to Jour. Low Temp.
Phy
COUPLED NETWORK APPROACH TO PREDICTABILITY OF FINANCIAL MARKET RETURNS AND NEWS SENTIMENTS
Breakdown of Fermi-liquid theory in a cuprate superconductor
The behaviour of electrons in solids is remarkably well described by Landau's
Fermi-liquid theory, which says that even though electrons in a metal interact
they can still be treated as well-defined fermions, called ``quasiparticles''.
At low temperature, the ability of quasiparticles to transport heat is strictly
given by their ability to transport charge, via a universal relation known as
the Wiedemann-Franz law, which no material in nature has been known to violate.
High-temperature superconductors have long been thought to fall outside the
realm of Fermi-liquid theory, as suggested by several anomalous properties, but
this has yet to be shown conclusively. Here we report on the first experimental
test of the Wiedemann-Franz law in a cuprate superconductor,
(Pr,Ce)CuO. Our study reveals a clear departure from the universal law
and provides compelling evidence for the breakdown of Fermi-liquid theory in
high-temperature superconductors.Comment: 7 pages, 3 figure
Study of solid 4He in two dimensions. The issue of zero-point defects and study of confined crystal
Defects are believed to play a fundamental role in the supersolid state of
4He. We report on studies by exact Quantum Monte Carlo (QMC) simulations at
zero temperature of the properties of solid 4He in presence of many vacancies,
up to 30 in two dimensions (2D). In all studied cases the crystalline order is
stable at least as long as the concentration of vacancies is below 2.5%. In the
2D system for a small number, n_v, of vacancies such defects can be identified
in the crystalline lattice and are strongly correlated with an attractive
interaction. On the contrary when n_v~10 vacancies in the relaxed system
disappear and in their place one finds dislocations and a revival of the
Bose-Einstein condensation. Thus, should zero-point motion defects be present
in solid 4He, such defects would be dislocations and not vacancies, at least in
2D. In order to avoid using periodic boundary conditions we have studied the
exact ground state of solid 4He confined in a circular region by an external
potential. We find that defects tend to be localized in an interfacial region
of width of about 15 A. Our computation allows to put as upper bound limit to
zero--point defects the concentration 0.003 in the 2D system close to melting
density.Comment: 17 pages, accepted for publication in J. Low Temp. Phys., Special
Issue on Supersolid
Condensation Energy and Spectral Functions in High Temperature Superconductors
If high temperature cuprate superconductivity is due to electronic
correlations, then the energy difference between the normal and superconducting
states can be expressed in terms of the occupied part of the single particle
spectral function. The latter can, in principle, be determined from angle
resolved photoemission (ARPES) data. As a consequence, the energy gain driving
the development of the superconducting state is intimately related to the
dramatic changes in the photoemission lineshape when going below Tc. These
points are illustrated in the context of the "mode" model used to fit ARPES
data in the normal and superconducting states, where the question of kinetic
energy versus potential energy driven superconductivity is explored in detail.
We use our findings to comment on the relation of ARPES data to the
condensation energy, and to various other experimental data. In particular, our
results suggest that the nature of the superconducting transition is strongly
related to how anomalous (non Fermi liquid like) the normal state spectral
function is, and as such, is dependent upon the doping level.Comment: 10 pages, revtex, 4 encapsulated postscript figure
Collective excitations of a two-dimensional interacting Bose gas in anti-trap and linear external potentials
We present a method of finding approximate analytical solutions for the
spectra and eigenvectors of collective modes in a two-dimensional system of
interacting bosons subjected to a linear external potential or the potential of
a special form , where is the chemical
potential. The eigenvalue problem is solved analytically for an artificial
model allowing the unbounded density of the particles. The spectra of
collective modes are calculated numerically for the stripe, the rare density
valley and the edge geometry and compared with the analytical results. It is
shown that the energies of the modes localized at the rare density region and
at the edge are well approximated by the analytical expressions. We discuss
Bose-Einstein condensation (BEC) in the systems under investigations at and find that in case of a finite number of the particles the regime of BEC
can be realized, whereas the condensate disappears in the thermodynamic limit.Comment: 10 pages, 2 figures include
Review of the Application of Modern Cytogenetic Methods (FISH/GISH) to the Study of Reticulation (Polyploidy/Hybridisation).
The convergence of distinct lineages upon interspecific hybridisation, including when accompanied by increases in ploidy (allopolyploidy), is a driving force in the origin of many plant species. In plant breeding too, both interspecific hybridisation and allopolyploidy are important because they facilitate introgression of alien DNA into breeding lines enabling the introduction of novel characters. Here we review how fluorescence in situ hybridisation (FISH) and genomic in situ hybridisation (GISH) have been applied to: 1) studies of interspecific hybridisation and polyploidy in nature, 2) analyses of phylogenetic relationships between species, 3) genetic mapping and 4) analysis of plant breeding materials. We also review how FISH is poised to take advantage of nextgeneration sequencing (NGS) technologies, helping the rapid characterisation of the repetitive fractions of a genome in natural populations and agricultural plants.This work was supported by NSF grant DEB-0922003
Vortex stabilization in Bose-Einstein condensate of alkali atom gas
A quantized vortex in the Bose-Einstein condensation (BEC), which is known to
be unstable intrinsically, is demonstrated theoretically to be stabilized by
the finite temperature effect. The mean-field calculation of Popov
approximation within the Bogoliubov theory is employed, giving rise to a
self-consistent solution for BEC confined by a harmonic potential. Physical
origin of this vortex stabilization is investigated. An equivalent effect is
also proved to be induced by an additional pinning potential at the vortex
center produced by a focused laser beam even at the lowest temperature. The
self-consistent solutions give detailed properties of a stable vortex, such as
the spatial profiles of the condensate and non-condensate, the particle current
density around the core, the whole excitation spectrum, and their temperature
dependences.Comment: 11 pages, 17 eps figure
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