6,839 research outputs found
Temperature and size-dependent suppression of Auger recombination in quantum-confined lead salt nanowires
Auger recombination (AR) of the ground biexciton state in quantum-confined
lead salt nanowires (NWs) with a strong coupling between the conduction and the
valence bands is shown to be strongly suppressed, and only excited biexciton
states contribute to Auger decay. The AR rate is predicted to be greatly
reduced when temperature or the NW radius are decreased, and the effect is
explained by decrease in both the population of excited biexciton states and
overlap of phonon-broadened single- and biexciton states. Suppression of AR of
multiexciton states exhibiting strong radiative decay makes obviously lead salt
NWs a subject of special interest for numerous lasing applications.Comment: 4 pages, 3 figure
New Types of Thermodynamics from -Dimensional Black Holes
For normal thermodynamic systems superadditivity , homogeneity \H and
concavity \C of the entropy hold, whereas for -dimensional black holes
the latter two properties are violated. We show that -dimensional black
holes exhibit qualitatively new types of thermodynamic behaviour, discussed
here for the first time, in which \C always holds, \H is always violated
and may or may not be violated, depending of the magnitude of the black
hole mass. Hence it is now seen that neither superadditivity nor concavity
encapsulate the meaning of the second law in all situations.Comment: WATPHYS-TH93/05, Latex, 10 pgs. 1 figure (available on request), to
appear in Class. Quant. Gra
Impact Excitation by Hot Carriers in Carbon Nanotubes
We investigate theoretically the efficiency of intra-molecular hot carrier
induced impact ionization and excitation processes in carbon nanotubes. The
electron confinement and reduced screening lead to drastically enhanced
excitation efficiencies over those in bulk materials. Strong excitonic coupling
favors neutral excitations over ionization, while the impact mechanism
populates a different set of states than that produced by photoexcitation. The
excitation rate is strongly affected by optical phonon excitation and a simple
scaling of the rate with the field strength and optical phonon temperature is
obtained.Comment: 5 pages 4 figure
Gedanken experiments on nearly extremal black holes and the Third Law
A gedanken experiment in which a black hole is pushed to spin at its maximal
rate by tossing into it a test body is considered. After demonstrating that
this is kinematically possible for a test body made of reasonable matter, we
focus on its implications for black hole thermodynamics and the apparent
violation of the third law (unattainability of the extremal black hole). We
argue that this is not an actual violation, due to subtleties in the absorption
process of the test body by the black hole, which are not captured by the
purely kinematic considerations.Comment: v2: minor edits, references added; v3: minor edits to match published
versio
Molecular kinetic analysis of a finite-time Carnot cycle
We study the efficiency at the maximal power of a
finite-time Carnot cycle of a weakly interacting gas which we can reagard as a
nearly ideal gas. In several systems interacting with the hot and cold
reservoirs of the temperatures and , respectively,
it is known that which
is often called the Curzon-Ahlborn (CA) efficiency . For the
first time numerical experiments to verify the validity of
are performed by means of molecular dynamics simulations and reveal that our
does not always agree with , but
approaches in the limit of .
Our molecular kinetic analysis explains the above facts theoretically by using
only elementary arithmetic.Comment: 6 pages, 4 figure
Heavy doping effects in high efficiency silicon solar cells
A model for bandgap shrinkage in semiconductors is developed and applied to silicon. A survey of earlier experiments, and of new ones, give an agreement between the model and experiments on n- and p-type silicon which is good as far as transport measurements in the 300 K range. The discrepancies between theory and experiment are no worse than the discrepancies between the experimental results of various authors. It also gives a good account of recent, optical determinations of band gap shrinkage at 5 K
Universal restrictions to the conversion of heat into work derived from the analysis of the Nernst theorem as a uniform limit
We revisit the relationship between the Nernst theorem and the Kelvin-Planck
statement of the second law. We propose that the exchange of entropy uniformly
vanishes as the temperature goes to zero. The analysis of this assumption shows
that is equivalent to the fact that the compensation of a Carnot engine scales
with the absorbed heat so that the Nernst theorem should be embedded in the
statement of the second law.
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Se analiza la relaci{\'o}n entre el teorema de Nernst y el enunciado de
Kelvin-Planck del segundo principio de la termodin{\'a}mica. Se{\~n}alamos el
hecho de que el cambio de entrop{\'\i}a tiende uniformemente a cero cuando la
temperatura tiende a cero. El an{\'a}lisis de esta hip{\'o}tesis muestra que es
equivalente al hecho de que la compensaci{\'o}n de una m{\'a}quina de Carnot
escala con el calor absorbido del foco caliente, de forma que el teorema de
Nernst puede derivarse del enunciado del segundo principio.Comment: 8pp, 4 ff. Original in english. Also available translation into
spanish. Twocolumn format. RevTe
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