10,827 research outputs found
Spontaneous exciton dissociation in carbon nanotubes
Simultaneous photoluminescence and photocurrent measurements on individual
single-walled carbon nanotubes reveal spontaneous dissociation of excitons into
free electron-hole pairs. Correlation of luminescence intensity and
photocurrent shows that a significant fraction of excitons are dissociating
during their relaxation into the lowest exciton state. Furthermore, the
combination of optical and electrical signals also allows for extraction of the
absorption cross section and the oscillator strength. Our observations explain
the reasons for photoconductivity measurements in single-walled carbon
nanotubes being straightforward despite the large exciton binding energies.Comment: 4 pages, 3 figure
Fabrication and characterization of Si3N4 ceramics without additives by high pressure hot pressing
High pressure hot-pressing of Si3N4 without additives was performed using various kinds of Si3N4 powder as starting materials, and the relation between densification and alpha-beta phase transformation was studied. The temperature dependences of Vickers microhardness and fracture toughness were also examined. Densification of Si3N4 was divided into three stages, and it was found that densification and phase transformation of Si3N4 under pressure were closely associated. The results of the temperature dependence of Vickers microhardness indicated that the high-temperature hardness was strongly influenced not only by the density and microstructure of sintered body but also by the purity of starting powder. The fracture toughness values of Si3N4 bodies without additives were 3.29-4.39 MN/m to the 3/2 power and independent of temperature up to 1400 C
Time-reversal focusing of an expanding soliton gas in disordered replicas
We investigate the properties of time reversibility of a soliton gas,
originating from a dispersive regularization of a shock wave, as it propagates
in a strongly disordered environment. An original approach combining
information measures and spin glass theory shows that time reversal focusing
occurs for different replicas of the disorder in forward and backward
propagation, provided the disorder varies on a length scale much shorter than
the width of the soliton constituents. The analysis is performed by starting
from a new class of reflectionless potentials, which describe the most general
form of an expanding soliton gas of the defocusing nonlinear Schroedinger
equation.Comment: 7 Pages, 6 Figure
Gate-controlled generation of optical pulse trains using individual carbon nanotubes
We report on optical pulse-train generation from individual air-suspended
carbon nanotubes under an application of square-wave gate voltages.
Electrostatically-induced carrier accummulation quenches photoluminescence,
while a voltage sign reversal purges those carriers, resetting the nanotubes to
become luminescent temporarily. Frequency domain measurements reveal
photoluminescence recovery with characteristic frequencies that increase with
excitation laser power, showing that photoexcited carriers quench the emission
in a self-limiting manner. Time-resolved measurements directly confirm the
presence of an optical pulse train sychronized to the gate voltage signal, and
flexible control over pulse timing and duration is demonstrated.Comment: 4 pages, 4 figure
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The Operation of Mitigation under Japanese and English Commercial Law: A Comparative Analysis
A commercial contract is intended to lead to the mutual satisfaction of both parties to that contract. If there is dissatisfaction and such dissatisfaction is caused by a breach of the contract, then, except in rare cases, the dissatisfied will seek a remedy—either a commercially agreed one or a formal remedy in damages—as a monetary expression of loss, but the extent of damages has the potential to cause dispute; how much money is it appropriate for the court to award? In considering this, we should bear in mind that it is often the case that the breach will arise because the party, although having the capability to fulfil its obligation, notes that at the time of discharge there are changed economic circumstances which offer more lucrative returns, and it has been tempted into breach in order to obtain greater economic benefit. There is a very important debate among academics and jurists as to the way that such a default should be viewed. When considering the benefit and utility of breach in preference to performance, the “breaching” party needs to know the extent of likely damages; likewise, the “non-breaching” party needs to know its entitlement to redress. Quantifying the amount of damages has concentrated minds through the ages and in all countries, and the task is not an easy one. We propose to consider the issues related to limiting damages from the perspective of two of the legal regimes found in two commercially sophisticated countries: Japan and England & Wales
Interminiband Rabi oscillations in biased semiconductor superlattices
Carrier dynamics at energy level anticrossings in biased semiconductor
superlattices, was studied in the time domain by solving the time-dependent
Schroedinger equation. The resonant nature of interminiband Rabi oscillations
has been explicitly demonstrated to arise from interference of intrawell and
Bloch oscillations. We also report a simulation of direct Rabi oscillations
across three minibands, in the high field regime, due to interaction between
three strongly coupled minibands.Comment: 13 pages, 16 figure
Nonequilibrium Microscopic Distribution of Thermal Current in Particle Systems
A nonequilibrium distribution function of microscopic thermal current is
studied by a direct numerical simulation in a thermal conducting steady state
of particle systems. Two characteristic temperatures of the thermal current are
investigated on the basis of the distribution. It is confirmed that the
temperature depends on the current direction; Parallel temperature to the
heat-flux is higher than antiparallel one. The difference between the parallel
temperature and the antiparallel one is proportional to a macroscopic
temperature gradient.Comment: 4 page
Slow Radiation-Driven Wind Solutions of A-Type Supergiants
The theory of radiation-driven winds succeeded in describing terminal
velocities and mass loss rates of massive stars. However, for A-type
supergiants the standard m-CAK solution predicts values of mass loss and
terminal velocity higher than the observed values. Based on the existence of a
slow wind solution in fast rotating massive stars, we explore numerically the
parameter space of radiation-driven flows to search for new wind solutions in
slowly rotating stars, that could explain the origin of these discrepancies. We
solve the 1-D hydrodynamical equation of rotating radiation-driven winds at
different stellar latitudes and explore the influence of ionization's changes
throughout the wind in the velocity profile. We have found that for particular
sets of stellar and line-force parameters, a new slow solution exists over the
entire star when the rotational speed is slow or even zero. In the case of slow
rotating A-type supergiant stars the presence of this novel slow solution at
all latitudes leads to mass losses and wind terminal velocities which are in
agreement with the observed values. The theoretical Wind Momentum-Luminosity
Relationship derived with these slow solutions shows very good agreement with
the empirical relationship. In addition, the ratio between the terminal and
escape velocities, which provides a simple way to predict stellar wind energy
and momentum input into the interstellar medium, is also properly traced.Comment: 7 Pages, 3 figures, Astrophysical Journal, Accepte
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