18,761 research outputs found
Possible magnetic-field-induced voltage and thermopower in diluted magnetic semiconductors
In diluted magnetic semiconductors, the carrier concentration and the
magnetization of local moments are strongly coupled, since the magnetic
interaction is mediated by the carriers. It is predicted that this coupling
leads to an electric polarization due to an applied magnetic-field gradient and
to the appearance of a magnetic-field-dependent voltage. An expression for this
voltage is derived within Landau theory and its magnitude is estimated for
(Ga,Mn)As. Furthermore, a large contribution to the thermopower based on the
same mechanism is predicted. The role of fluctuations is also discussed. These
predictions hold both if the magnetization is uniform and if it shows
stripe-like modulations, which are possible at lower temperatures.Comment: 6 pages revtex, 5 figure
The Fall of Emily Grierson: a Jungian Analysis of a Rose for Emily
This paper discusses the tragic life of Faulkner\u27s Emily Grierson, a life dominated by patriarchy and traditional Southern social values, which concludes with her living as a lonely recluse in her family\u27s decaying aristocratic house for more than forty years until her death. The key of the tragedy is her father, who isolates Emily from the outside world and tortures her with traditional patriarchal rules and Southern family duty. Emily is expected to lead a life like other girls; however, under the burden of old-fashioned, patriarchal responsibilities, her inner world collapses. This study uses the Jungian concepts of archetypes, persona and shadow, anima and animus to interpret Emily\u27s transitions and her fall. By examining the process through the lens of Jungian theories, the aspects that affect her fall in the patriarchal, aristocratic society, as well as the inherited social values, can be revealed and specified
Self-injection-locked magnetron as an active ring resonator side coupled to a waveguide with a delayed feedback loop
The theoretical analysis and numerical simulations of the magnetron operation
with a feedback loop were performed assuming that the delay of the
electromagnetic wave propagating in the loop is constant whereas the phase of
the complex feedback reflection coefficient is varied. Results of simulations
showed that by a proper adjustment of values of the time delay and phase of
reflection coefficient that determines phase matching between the waves in the
resonator and feedback loop, one can increase the magnetron's output power
significantly without any other additional measures.Comment: 12 pages, 4 figure
Where are the Walls?
The reported spatial variation in the fine-structure constant at high
redshift, if physical, could be due to the presence of dilatonic domains, and
one or more domain walls inside our horizon. An absorption spectrum of an
object in a different domain from our own would be characterized by a different
value of alpha. We show that while a single wall solution is statically
comparable to a dipole fit, and is a big improvement over a weighted mean
(despite adding 3 parameters), a two-wall solution is a far better fit (despite
adding 3 parameters over the single wall solution). We derive a simple model
accounting for the two-domain wall solution. The goodness of these fits is
however dependent on the extra random error which was argued to account for the
large scatter in most of the data. When this error is omitted, all the above
solutions are poor fits to the data. When included, the solutions that exhibit
a spatial dependence agree with the data much more significantly than the
Standard Model; however, the Standard Model itself is not a terrible fit to the
data, having a p-value of ~ 20 %
Exact-exchange kernel of time-dependent density functional theory: Frequency dependence and photoabsorption spectra of atoms
In this work we have calculated excitation energies and photoionization cross
sections of Be and Ne in the exact-exchange (EXX) approximation of
time-dependent density functional theory (TDDFT). The main focus has been on
the frequency dependence of the EXX kernel and on how it affects the spectrum
as compared to the corresponding adiabatic approximation. We show that for some
discrete excitation energies the frequency dependence is essential to reproduce
the results of time-dependent Hartree-Fock theory. Unfortunately, we have found
that the EXX approximation breaks down completely at higher energies, producing
a response function with the wrong analytic structure and making inner-shell
excitations disappear from the calculated spectra. We have traced this failure
to the existence of vanishing eigenvalues of the Kohn-Sham non-interacting
response function. Based on the adiabatic TDDFT formalism we propose a new way
of deriving the Fano parameters of autoionizing resonances.Comment: 14 pages, 7 figure
On Quantum Nature of Black-Hole Spacetime: A Possible New Source of Intense Radiation
Atoms and the planets acquire their stability from the quantum mechanical
incompatibility of the position and momentum measurements. This incompatibility
is expressed by the fundamental commutator [x, p_x]=i hbar, or equivalently,
via the Heisenberg's uncertainty principle Delta x Delta p_x sim hbar. A
further stability-related phenomenon where the quantum realm plays a dramatic
role is the collapse of certain stars into white dwarfs and neutron stars.
Here, an intervention of the Pauli exclusion principle, via the fermionic
degenerate pressure, stops the gravitational collapse. However, by the
neutron-star stage the standard quantum realm runs dry. One is left with the
problematic collapse of a black hole. This essay is devoted to a concrete
argument on why the black-hole spacetime itself should exhibit a quantum
nature. The proposed quantum aspect of spacetime is shown to prevent the
general-relativistic dictated problematic collapse. The quantum nature of
black-hole spacetime is deciphered from a recent result on the universal
equal-area spacing [=lambda_P^2 4 ln(3)] for black holes. In one interpretation
of the emergent picture, an astrophysical black hole can fluctuate to
sqrt{pi/ln(3)} approx 1.7 times its classical size, and thus allow radiation
and matter to escape to the outside observers. These fluctuations I conjecture
provide a new source, perhaps beyond Hawking radiation, of intense radiation
from astrophysical black holes and may be the primary source of observed
radiation from those galactic cores what carry black hole(s). The presented
interpretation may be used as a criterion to choose black holes from black hole
candidates.Comment: This essay received an "honorable mention" in the 1999 Essay
Competition of the Gravity Research Foundation - Ed. Int. J. Mod. Phys. D
(1999, in press). For Joseph Knech
Sensitive linear response of an electron-hole superfluid in a periodic potential
We consider excitons in a two-dimensional periodic potential and study the
linear response of the excitonic superfluid to an electromagnetic wave at low
and high densities. It turns out that the static structure factor for small
wavevectors is very sensitive to a change of density and temperature. It is a
consequence of the fact that thermal fluctuations play a crucial role at small
wavevectors, since exchanging the order of the two limits, zero temperature and
vanishing wavevector, leads to different results for the structure factor. This
effect could be used for high accuracy measurements in the superfluid exciton
phase, which might be realized by a gated electron-hole gas. The transition of
the exciton system from the superfluid state to a non-superfluid state and its
manifestation by light scattering are discussed.Comment: 9 pages, 5 figure
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