23,020 research outputs found
Charge and momentum transfer in supercooled melts: Why should their relaxation times differ?
The steady state values of the viscosity and the intrinsic ionic-conductivity
of quenched melts are computed, in terms of independently measurable
quantities. The frequency dependence of the ac dielectric response is
estimated. The discrepancy between the corresponding characteristic relaxation
times is only apparent; it does not imply distinct mechanisms, but stems from
the intrinsic barrier distribution for -relaxation in supercooled
fluids and glasses. This type of intrinsic ``decoupling'' is argued not to
exceed four orders in magnitude, for known glassformers. We explain the origin
of the discrepancy between the stretching exponent , as extracted from
and the dielectric modulus data. The actual width of the
barrier distribution always grows with lowering the temperature. The contrary
is an artifact of the large contribution of the dc-conductivity component to
the modulus data. The methodology allows one to single out other contributions
to the conductivity, as in ``superionic'' liquids or when charge carriers are
delocalized, implying that in those systems, charge transfer does not require
structural reconfiguration.Comment: submitted to J Chem Phy
Analytic Solutions to the Constraint Equation for a Force-Free Magnetosphere around a Kerr Black Hole
The Blandford-Znajek constraint equation for a stationary, axisymmetric
black-hole force-free magnetosphere is cast in a 3+1 absolute space and time
formulation, following Komissarov (2004). We derive an analytic solution for
fields and currents to the constraint equation in the far-field limit that
satisfies the Znajek condition at the event horizon. This solution generalizes
the Blandford-Znajek monopole solution for a slowly rotating black hole to
black holes with arbitrary angular momentum. Energy and angular momentum
extraction through this solution occurs mostly along the equatorial plane. We
also present a nonphysical, reverse jet-like solution.Comment: 6 pages, accepted for publication in Ap
Inter-band magnetoplasmons in mono- and bi-layer graphene
Collective excitations spectrum of Dirac electrons in mono and bilayer
graphene in the presence of a uniform magnetic field is investigated.
Analytical results for inter-Landau band plasmon spectrum within the
self-consistent-field approach are obtained. SdH type oscillations that are a
monotonic function of the magnetic field are observed in the plasmon spectrum
of both mono- and bi-layer graphene systems. The results presented are also
compared with those obtained in conventional 2DEG. The chiral nature of the
quasiparticles in mono and bilayer graphene system results in the observation
of and Berry's phase in the SdH- type oscillations in the plasmon
spectrum.Comment: 9 pages, 2 figure
The Influence of Formulation, Buffering, pH and Divalent Cations on the Activity of Endothall on Hydrilla.
Endothall has been used as an aquatic herbicide for more
than 40 years and provides very effective weed control of
many weeds. Early research regarding the mechanism-of-action
of endothall contradicts the symptomology normally associated
with the product. Recent studies suggest endothall
is a respiratory toxin but the mechanism-of-action remains
unknown. To further elucidate the activity of endothall, several
endothall formulations were evaluated for their effects
on ion leakage, oxygen consumption and photosynthetic oxygen
evolution from hydrilla shoot tips. The influence of pH,
buffering and divalent cations was also evaluated. (PDF contains 6 pages.
J Fluorescence
The scope of this paper is to illustrate the need for an improved quality assurance in fluorometry. For this purpose, instrumental sources of error and their influences on the reliability and comparability of fluorescence data are highlighted for frequently used photoluminescence techniques ranging from conventional macro- and microfluorometry over fluorescence microscopy and flow cytometry to microarray technology as well as in vivo fluorescence imaging. Particularly, the need for and requirements on fluorescence standards for the characterization and performance validation of fluorescence instruments, to enhance the comparability of fluorescence data, and to enable quantitative fluorescence analysis are discussed. Special emphasis is dedicated to spectral fluorescence standards and fluorescence intensity standards
The effect of overconfidence and underconfidence on consumer value
Although the effect of knowledge miscalibration (i.e., the inaccuracy in subjective knowledge relative to objective knowledge) on consumer purchase decisions has been investigated, its effect in the usage stage of consumption is little understood. This paper examines the effect of knowledge miscalibration in terms of both overconfidence (i.e., when subjective knowledge is inflated) and underconfidence (i.e., when subjective knowledge is deflated) on the dimensions of consumer value (i.e., efficiency, excellence, play and aesthetics). We make the case that overconfidence and underconfidence should be treated separately as they trigger different consumption consequences. Several hypotheses are tested through two studies: a co-variance based study (Study 1) and an experimental study (Study 2). In Study 1, overconfidence and underconfidence are measured, while in Study 2 they are experimentally manipulated. Findings of both studies show that underconfidence negatively influences efficiency, excellence and aesthetics, and overconfidence negatively influences play. Also, Study 1 finds a negative effect of underconfidence on play and Study 2 finds a negative effect of overconfidence on excellence and aesthetics. Findings reveal that knowledge miscalibration negatively impacts consumers’ usage experiences. This implies that in designing product or service experiences, suppliers benefit from ensuring that consumers achieve a reduced level of knowledge miscalibration
From electrons to Janskys: Full stokes polarized radiative transfer in 3D relativistic particle-in-cell jet simulations
The underlying plasma composition of relativistic extragalactic jets remains
largely unknown. Relativistic magnetohydrodynamic (RMHD) models are able to
reproduce many of the observed macroscopic features of these outflows. The
nonthermal synchrotron emission detected by very long baseline interferometric
(VLBI) arrays, however, is a by-product of the kinetic-scale physics occurring
within the jet, physics that is not modeled directly in most RMHD codes. This
paper attempts to discern the radiative differences between distinct plasma
compositions within relativistic jets using small-scale 3D relativistic
particle-in-cell (PIC) simulations. We generate full Stokes imaging of two PIC
jet simulations, one in which the jet is composed of an electron-proton
(-) plasma (i.e., a normal plasma jet), and the other in which
the jet is composed of an electron-positron (-) plasma (i.e., a
pair plasma jet). We examined the differences in the morphology and intensity
of the linear polarization (LP) and circular polarization (CP) emanating from
these two jet simulations. We find that the fractional level of CP emanating
from the - plasma jet is orders of magnitude larger than the
level emanating from an - plasma jet of a similar speed and
magnetic field strength. In addition, we find that the morphology of both the
linearly and circularly polarized synchrotron emission is distinct between the
two jet compositions. We also demonstrate the importance of slow-light
interpolation and we highlight the effect that a finite light-crossing time has
on the resultant polarization when ray-tracing through relativistic plasma.Comment: 21 pages, 13 figures; accepted for publication in A&
Skyrme Crystal In A Two-Dimensional Electron Gas
The ground state of a two-dimensional electron gas at Landau level filling
factors near is a Skyrme crystal with long range order in the
positions and orientations of the topologically and electrically charged
elementary excitations of the ferromagnetic ground state. The lowest
energy Skyrme crystal is a square lattice with opposing postures for
topological excitations on opposite sublattices. The filling factor dependence
of the electron spin-polarization, calculated for the square lattice Skyrme
crystal, is in excellent agreement with recent experiments.Comment: 3 pages, latex, 3 figures available upon request from
[email protected]
Anomalous Fisher-like zeros for the canonical partition function of noninteracting fermions
Noninteracting fermions, placed in a system with a continuous density of
states, may have zeros in the -fermion canonical partition function on the
positive real axis (or very close to it), even for a small number of
particles. This results in a singular free energy, and instability in other
thermal properties of the system. In the context of trapped fermions in a
harmonic oscillator, these zeros are shown to be unphysical. By contrast,
similar bosonic calculations with continuous density of states yield sensible
results.Noninteracting fermions, placed in a system with a continuous density
of states yield sensible results.Comment: 5 pages and 5 figure
Exact results for interacting electrons in high Landau levels
We study a two-dimensional electron system in a magnetic field with a fermion
hardcore interaction and without disorder. Projecting the Hamiltonian onto the
n-th Landau level, we show that the Hartree-Fock theory is exact in the limit n
\rightarrow \infty, for the high temperature, uniform density phase of an
infinite system; for a finite-size system, it is exact at all temperatures. In
addition, we show that a charge-density wave arises below a transition
temperature T_t. Using Landau theory, we construct a phase diagram which
contains both unidirectional and triangular charge-density wave phases. We
discuss the unidirectional charge-density wave at zero temperature and argue
that quantum fluctuations are unimportant in the large-n limit. Finally, we
discuss the accuracy of the Hartree-Fock approximation for potentials with a
nonzero range such as the Coulomb interaction.Comment: RevTex, 12 pages with figures included in same file; to appear in
Physical Review
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