23,313 research outputs found
Transients in the Synchronization of Oscillator Arrays
The purpose of this note is threefold. First we state a few conjectures that
allow us to rigorously derive a theory which is asymptotic in N (the number of
agents) that describes transients in large arrays of (identical) linear damped
harmonic oscillators in R with completely decentralized nearest neighbor
interaction. We then use the theory to establish that in a certain range of the
parameters transients grow linearly in the number of agents (and faster outside
that range). Finally, in the regime where this linear growth occurs we give the
constant of proportionality as a function of the signal velocities (see [3]) in
each of the two directions. As corollaries we show that symmetric interactions
are far from optimal and that all these results independent of (reasonable)
boundary conditions.Comment: 11 pages, 4 figure
Subband structure of II-VI modulation-doped magnetic quantum wells
Here we investigate the spin-dependent subband structure of newly-developed
Mn-based modulation-doped quantum wells. In the presence of an external
magnetic field, the s-d exchange coupling between carriers and localized d
electrons of the Mn impurities gives rise to large spin splittings resulting in
a magnetic-field dependent subband structure. Within the framework of the
effective-mass approximation, we self-consistently calculate the subband
structure at zero temperature using Density Functional Theory (DFT) with a
Local Spin Density Approximation (LSDA). We present results for the
magnetic-field dependence of the subband structure of shallow ZnSe/ZnCdMnSe
modulation doped quantum wells. Our results show a significant contribution to
the self-consistent potential due to the exchange-correlation term. These
calculations are the first step in the study of a variety of interesting
spin-dependent phenomena, e.g., spin-resolved transport and many-body effects
in polarized two-dimensional electron gases.Comment: 3 pages, 3 postscript figures, submitted to the proceedings of the
10th Brazilian Workshop on Semiconductor Physics (BWSP10
The Abell 85 BCG: a nucleated, core-less galaxy
New high-resolution r band imaging of the brightest cluster galaxy (BCG) in
Abell 85 (Holm 15A) was obtained using the Gemini Multi Object Spectrograph.
These data were taken with the aim of deriving an accurate surface brightness
profile of the BCG of Abell 85, in particular its central region. The new
Gemini data show clear evidence of a previously unreported nuclear emission
that is evident as a distinct light excess in the central kiloparsec of the
surface brightness profile. We find that the light profile is never flat nor
does it present a downward trend towards the center of the galaxy. That is, the
new Gemini data show a different physical reality from the featureless,
"evacuated core" recently claimed for the Abell 85 BCG. After trying different
models, we find that the surface brightness profile of the BCG of Abell 85 is
best fit by a double Sersic model.Comment: Gemini web feature: Supermassive black hole that wasn't -
http://gemini.edu/node/1247
Many-body effects on the ringlike structures in two-subband wells
The longitudinal resistivity of two-dimensional electron gases
formed in wells with two subbands displays ringlike structures when plotted in
a density--magnetic-field diagram, due to the crossings of spin-split Landau
levels (LLs) from distinct subbands. Using spin density functional theory and
linear response, we investigate the shape and spin polarization of these
structures as a function of temperature and magnetic-field tilt angle. We find
that (i) some of the rings "break" at sufficiently low temperatures due to a
quantum Hall ferromagnetic phase transition, thus exhibiting a high degree of
spin polarization (%) within, consistent with the NMR data of Zhang
\textit{et al.} [Phys. Rev. Lett. {\bf 98}, 246802 (2007)], and (ii) for
increasing tilting angles the interplay between the anticrossings due to
inter-LL couplings and the exchange-correlation (XC) effects leads to a
collapse of the rings at some critical angle , in agreement with the
data of Guo \textit{et al.} [Phys. Rev. B {\bf 78}, 233305 (2008)].Comment: 4 pages, 3 figure
Diffusion of muonium and hydrogen in diamond
Jump rates of muonium and hydrogen in diamond are calculated by quantum
transition-state theory, based on the path-integral centroid formalism. This
technique allows us to study the influence of vibrational mode quantization on
the effective free-energy barriers Delta F for impurity diffusion, which are
renormalized respect to the zero-temperature classical calculation. For the
transition from a tetrahedral (T) site to a bond-center (BC) position, Delta F
is larger for hydrogen than for muonium, and the opposite happens for the
transition from BC to T. The calculated effective barriers decrease for rising
temperature, except for the muonium transition from T to BC sites. Calculated
jump rates are in good agreement to available muon spin rotation data.Comment: 4 pages, 3 figure
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