20,716 research outputs found
Evidence of Skyrmion excitations about in n-Modulation Doped Single Quantum Wells by Inter-band Optical Transmission
We observe a dramatic reduction in the degree of spin-polarization of a
two-dimensional electron gas in a magnetic field when the Fermi energy moves
off the mid-point of the spin-gap of the lowest Landau level, . This
rapid decay of spin alignment to an unpolarized state occurs over small changes
to both higher and lower magnetic field. The degree of electron spin
polarization as a function of is measured through the magneto-absorption
spectra which distinguish the occupancy of the two electron spin states. The
data provide experimental evidence for the presence of Skyrmion excitations
where exchange energy dominates Zeeman energy in the integer quantum Hall
regime at
Has foreign bank entry led to sounder banks in Latin America?
Policymakers continue to debate the merits of opening emerging market financial sectors to foreign ownership. A comparison of the 1995-2000 performance of foreign and domestic banks in select Latin American countries reveals that while foreign banks differed little from their domestic counterparts in overall financial condition, they showed more robust loan growth, a more aggressive response to asset quality deterioration, and a greater ability to absorb losses_characteristics that could help to strengthen the financial systems of their host countries.Banks and banking - Latin America ; Banks and banking, Foreign ; Economic development - Latin America
Exciton mediated one phonon resonant Raman scattering from one-dimensional systems
We use the Kramers-Heisenberg approach to derive a general expression for the
resonant Raman scattering cross section from a one-dimensional (1D) system
explicitly accounting for excitonic effects. The result should prove useful for
analyzing the Raman resonance excitation profile lineshapes for a variety of 1D
systems including carbon nanotubes and semiconductor quantum wires. We apply
this formalism to a simple 1D model system to illustrate the similarities and
differences between the free electron and correlated electron-hole theories.Comment: 10 pages, 6 figure
Dynamics of electromagnetic waves in Kerr geometry
Here we are interested to study the spin-1 particle i.e., electro-magnetic
wave in curved space-time, say around black hole. After separating the
equations into radial and angular parts, writing them according to the black
hole geometry, say, Kerr black hole we solve them analytically. Finally we
produce complete solution of the spin-1 particles around a rotating black hole
namely in Kerr geometry. Obviously there is coupling between spin of the
electro-magnetic wave and that of black hole when particles propagate in that
space-time. So the solution will be depending on that coupling strength. This
solution may be useful to study different other problems where the analytical
results are needed. Also the results may be useful in some astrophysical
contexts.Comment: 15 Latex pages, 4 Figures; Accepted for publication in Classical and
Quantum Gravit
Relativistic three-body recombination with the QED vacuum
Electron-positron pair annihilation into a single photon is studied when a
second free electron is present. Focussing on the relativistic regime, we show
that the photon emitted in the three-lepton interaction may exhibit distinct
angular distributions and polarization properties. Moreover, the process can
dominate over two-photon annihilation in relativistic electron-positron plasmas
of few-MeV temperature. An analogy with three-body recombination of electrons
with ions is drawn.Comment: 5 pages, 4 figure
Design of a fault tolerant airborne digital computer. Volume 2: Computational requirements and technology
This final report summarizes the work on the design of a fault tolerant digital computer for aircraft. Volume 2 is composed of two parts. Part 1 is concerned with the computational requirements associated with an advanced commercial aircraft. Part 2 reviews the technology that will be available for the implementation of the computer in the 1975-1985 period. With regard to the computation task 26 computations have been categorized according to computational load, memory requirements, criticality, permitted down-time, and the need to save data in order to effect a roll-back. The technology part stresses the impact of large scale integration (LSI) on the realization of logic and memory. Also considered was module interconnection possibilities so as to minimize fault propagation
Chirality dependence of the radial breathing phonon mode density in single wall carbon nanotubes
A mass and spring model is used to calculate the phonon mode dispersion for
single wall carbon nanotubes (SWNTs) of arbitrary chirality. The calculated
dispersions are used to determine the chirality dependence of the radial
breathing phonon mode (RBM) density. Van Hove singularities, usually discussed
in the context of the single particle electronic excitation spectrum, are found
in the RBM density of states with distinct qualitative differences for zig zag,
armchair and chiral SWNTs. The influence the phonon mode density has on the two
phonon resonant Raman scattering cross-section is discussed.Comment: 6 pages, 2 figures, submitted to Phys. Rev.
Behaviour of spin-1/2 particle around a charged black hole
Dirac equation is separable in curved space-time and its solution was found
for both spherically and axially symmetric geometry. But most of the works were
done without considering the charge of the black hole. Here we consider the
spherically symmetric charged black hole background namely Reissner-Nordstrom
black hole. Due to presence of the charge of black-hole charge-charge
interaction will be important for the cases of incoming charged particle (e.g.
electron, proton etc.). Therefore both gravitational and electromagnetic gauge
fields should be introduced. Naturally behaviour of the particle will be
changed from that in Schwarzschild geometry. We compare both the solutions. In
the case of Reissner-Nordstrom black hole there is a possibility of
super-radiance unlike Schwarzschild case. We also check this branch of the
solution.Comment: 8 Latex pages and 4 Figures; RevTex.style; Accepted for Publication
in Classical and Quantum Gravit
A New Approach to Black Hole Microstates
If one encodes the gravitational degrees of freedom in an orthonormal frame
field there is a very natural first order action one can write down (which in
four dimensions is known as the Goldberg action). In this essay we will show
that this action contains a boundary action for certain microscopic degrees of
freedom living at the horizon of a black hole, and argue that these degrees of
freedom hold great promise for explaining the microstates responsible for black
hole entropy, in any number of spacetime dimensions. This approach faces many
interesting challenges, both technical and conceptual.Comment: 6 pages, 0 figures, LaTeX; submitted to Mod. Phys. Lett. A.; this
essay received "honorable mention" from the Gravity Research Foundation, 199
Multi-objective evolutionary–fuzzy augmented flight control for an F16 aircraft
In this article, the multi-objective design of a fuzzy logic augmented flight controller for a high performance fighter jet (the Lockheed-Martin F16) is described. A fuzzy logic controller is designed and its membership functions tuned by genetic algorithms in order to design a roll, pitch, and yaw flight controller with enhanced manoeuverability which still retains safety critical operation when combined with a standard inner-loop stabilizing controller. The controller is assessed in terms of pilot effort and thus reduction of pilot fatigue. The controller is incorporated into a six degree of freedom motion base real-time flight simulator, and flight tested by a qualified pilot instructor
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