6,082 research outputs found
Stranded Structure Development in Thermally Produced Protein Concentrate Gel
Scanning electron micrographs of thermally induced whey protein concentrate gels were taken. Sample preparation was accomplished by glutaraldehyde fixation, osmium tetroxide post fixation and critical point dehydration. Stranded or beaded gel structures were observed on the external surface of a gas bubble, suggesting that a string-of-beads gel microstructure may result from bubble formation during thermal treatment
Efficient nonlinear room-temperature spin injection from ferromagnets into semiconductors through a modified Schottky barrier
We suggest a consistent microscopic theory of spin injection from a
ferromagnet (FM) into a semiconductor (S). It describes tunneling and emission
of electrons through modified FM-S Schottky barrier with an ultrathin heavily
doped interfacial S layer . We calculate nonlinear spin-selective properties of
such a reverse-biased FM-S junction, its nonlinear I-V characteristic, current
saturation, and spin accumulation in S. We show that the spin polarization of
current, spin density, and penetration length increase with the total current
until saturation. We find conditions for most efficient spin injection, which
are opposite to the results of previous works, since the present theory
suggests using a lightly doped resistive semiconductor. It is shown that the
maximal spin polarizations of current and electrons (spin accumulation) can
approach 100% at room temperatures and low current density in a nondegenerate
high-resistance semiconductor.Comment: 7 pages, 2 figures; provides detailed comparison with earlier works
on spin injectio
Evaluation of bait uptake by ricefield rats using Rhodamine B as a bait marker under enclosure conditions
Tung, T.T., Henry, S., Cowan, D., Sudarmaji, M.P., Hinds, L.A
Head-on collisions of binary white dwarf--neutron stars: Simulations in full general relativity
We simulate head-on collisions from rest at large separation of binary white
dwarf -- neutron stars (WDNSs) in full general relativity. Our study serves as
a prelude to our analysis of the circular binary WDNS problem. We focus on
compact binaries whose total mass exceeds the maximum mass that a cold
degenerate star can support, and our goal is to determine the fate of such
systems. A fully general relativistic hydrodynamic computation of a realistic
WDNS head-on collision is prohibitive due to the large range of dynamical time
scales and length scales involved. For this reason, we construct an equation of
state (EOS) which captures the main physical features of NSs while, at the same
time, scales down the size of WDs. We call these scaled-down WD models
"pseudo-WDs (pWDs)". Using pWDs, we can study these systems via a sequence of
simulations where the size of the pWD gradually increases toward the realistic
case. We perform two sets of simulations; One set studies the effects of the NS
mass on the final outcome, when the pWD is kept fixed. The other set studies
the effect of the pWD compaction on the final outcome, when the pWD mass and
the NS are kept fixed. All simulations show that 14%-18% of the initial total
rest mass escapes to infinity. All remnant masses still exceed the maximum rest
mass that our cold EOS can support (1.92 solar masses), but no case leads to
prompt collapse to a black hole. This outcome arises because the final
configurations are hot. All cases settle into spherical, quasiequilibrium
configurations consisting of a cold NS core surrounded by a hot mantle,
resembling Thorne-Zytkow objects. Extrapolating our results to realistic WD
compactions, we predict that the likely outcome of a head-on collision of a
realistic, massive WDNS system will be the formation of a quasiequilibrium
Thorne-Zytkow-like object.Comment: 24 pages, 14 figures, matches PRD published version, tests of HRSC
schemes with piecewise polytropes adde
Evaluating quasilocal energy and solving optimal embedding equation at null infinity
We study the limit of quasilocal energy defined in [7] and [8] for a family
of spacelike 2-surfaces approaching null infinity of an asymptotically flat
spacetime. It is shown that Lorentzian symmetry is recovered and an
energy-momentum 4-vector is obtained. In particular, the result is consistent
with the Bondi-Sachs energy-momentum at a retarded time. The quasilocal mass in
[7] and [8] is defined by minimizing quasilocal energy among admissible
isometric embeddings and observers. The solvability of the Euler-Lagrange
equation for this variational problem is also discussed in both the
asymptotically flat and asymptotically null cases. Assuming analyticity, the
equation can be solved and the solution is locally minimizing in all orders. In
particular, this produces an optimal reference hypersurface in the Minkowski
space for the spatial or null exterior region of an asymptotically flat
spacetime.Comment: 22 page
The microcanonical ensemble of the ideal relativistic quantum gas with angular momentum conservation
We derive the microcanonical partition function of the ideal relativistic
quantum gas with fixed intrinsic angular momentum as an expansion over fixed
multiplicities. We developed a group theoretical approach by generalizing known
projection techniques to the Poincare' group. Our calculation is carried out in
a quantum field framework and applies to particles with any spin. It extends
known results in literature in that it does not introduce any large volume
approximation and it takes particle spin fully into account. We provide
expressions of the microcanonical partition function at fixed multiplicities in
the limiting classical case of large volumes and large angular momenta and in
the grand-canonical ensemble. We also derive the microcanonical partition
function of the ideal relativistic quantum gas with fixed parity.Comment: 38 pages; minor corrections to the formulae for the published versio
Spectral perturbation by rank- matrices
Let and designate matrices with coefficients in a field
. In this paper, we completely answer the following question: For fixed,
what are the possible characteristic polynomials of , where ranges
over matrices of rank ?Comment: Comments are welcom
Discrete Symmetries in the Weyl Expansion for Quantum Billiards
We consider two and three-dimensional quantum billiards with discrete
symmetries. We derive the first terms of the Weyl expansion for the level
density projected onto the irreducible representations of the symmetry group.
As an illustration the method is applied to the icosahedral billiard. The paper
was published in J. Phys. A /27/ (1994) 4317-4323Comment: 8 printed pages Latex fil
Electron surface layer at the interface of a plasma and a dielectric wall
We study the potential and the charge distribution across the interface of a
plasma and a dielectric wall. For this purpose, the charge bound to the wall is
modelled as a quasi-stationary electron surface layer which satisfies Poisson's
equation and minimizes the grand canonical potential of the wall-thermalized
excess electrons constituting the wall charge. Based on an effective model for
a graded interface taking into account the image potential and the offset of
the conduction band to the potential just outside the dielectric, we
specifically calculate the potential and the electron distribution for
magnesium oxide, silicon dioxide and sapphire surfaces in contact with a helium
discharge. Depending on the electron affinity of the surface, we find two
vastly different behaviors. For negative electron affinity, electrons do not
penetrate into the wall and an external surface charge is formed in the image
potential, while for positive electron affinity, electrons penetrate into the
wall and a space charge layer develops in the interior of the dielectric. We
also investigate how the electron surface layer merges with the bulk of the
dielectric.Comment: 15 pages, 9 figures, accepted versio
Properties of the symplectic structure of General Relativity for spatially bounded spacetime regions
We continue a previous analysis of the covariant Hamiltonian symplectic
structure of General Relativity for spatially bounded regions of spacetime. To
allow for near complete generality, the Hamiltonian is formulated using any
fixed hypersurface, with a boundary given by a closed spacelike 2-surface. A
main result is that we obtain Hamiltonians associated to Dirichlet and Neumann
boundary conditions on the gravitational field coupled to matter sources, in
particular a Klein-Gordon field, an electromagnetic field, and a set of
Yang-Mills-Higgs fields. The Hamiltonians are given by a covariant form of the
Arnowitt-Deser-Misner Hamiltonian modified by a surface integral term that
depends on the particular boundary conditions. The general form of this surface
integral involves an underlying ``energy-momentum'' vector in the spacetime
tangent space at the spatial boundary 2-surface. We give examples of the
resulting Dirichlet and Neumann vectors for topologically spherical 2-surfaces
in Minkowski spacetime, spherically symmetric spacetimes, and stationary
axisymmetric spacetimes. Moreover, we show the relation between these vectors
and the ADM energy-momentum vector for a 2-surface taken in a limit to be
spatial infinity in asymptotically flat spacetimes. We also discuss the
geometrical properties of the Dirichlet and Neumann vectors and obtain several
striking results relating these vectors to the mean curvature and normal
curvature connection of the 2-surface. Most significantly, the part of the
Dirichlet vector normal to the 2-surface depends only the spacetime metric at
this surface and thereby defines a geometrical normal vector field on the
2-surface. Properties and examples of this normal vector are discussed.Comment: 46 pages; minor errata corrected in Eqs. (3.15), (3.24), (4.37) and
in discussion of examples in sections IV B,
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