2,702 research outputs found
What does an observed quantum system reveal to its observer ?
The evolution of a quantum system under observation becomes retarded or even
impeded. We review this ``quantum Zeno effect'' in the light of the criticism
that has been raised upon a previous attempt to demonstrate it, of later
reexaminations of both the projection postulate and the significance of the
observations, and of the results of a recent experiment on an individual cold
atom. Here, the micro-state of the quantum system gets unveiled with the
observation, and the effect of measurement is no longer mixed up with dephasing
the object's wave function by the reactive effect of the detection. A procedure
is outlined that promises to provide, by observation, an upper limit for the
delay of even an exponential decay.Comment: 9 pages, 4 figures. Published version: Section VII sligthly change
The radio-far infrared correlation: Spiral and blue compact dwarf galaxies opposed
The recently established correlation between radio continuum and far infrared emission in galaxies was further investigated by comparing normal spiral and blue compact dwarf galaxies. The puzzling result is that the ratio of radio to far infrared luminosity and its dispersion is the same for both samples, although their ratios of blue to far infrared luminosity, their radio spectral indices and their dust temperatures exhibit markedly different mean values and dispersions. This suggests that the amount of energy radiated in the two regimes is enhanced in the same way although the mechanisms responsible for the two components are rather different and complex. The fact that the blue light does not increase at the same proportion shows that both the radio and the far infrared emission are connected with the recent star formation history
Estimating Health Care Costs Among Fragile and Conflict Affected States: an Elastic Net-Risk Measures Approach
Fragile and conflict affected states (FCAS) are those in which the government lacks the political will and/or capacity to provide the basic functions necessary for poverty reduction, economic development, and the security of human rights of their populations.Until recent history, unfortunately, the majority of research conducted and universal health care debates have been centered around middle income and emerging economies. As a result, FCAS have been neglected from many global discussions and decisions. Due to this neglect, many FCAS do not have proper vaccinations and antibiotics. Seemingly, well estimated health care costs are a necessary stepping stone in improving the health of citizens among FCAS. Fortunately, developments in statistical learning theory combined with data obtained by the WBG and Transparency International make it possible to accurately model health care cost among FCAS. The data used in this paper consisted of 35 countries and 89 variables. Of these 89 variables, health care expenditure (HCE) was the only response variable. With 88 predictor variables, there was expected to be multicollinearity, which occurs when multiple variables share relatively large absolute correlation. Since multicollinearity is expected and the number of variables is far greater than the number of observations, this paper adopts Zou and Hastie\u27s method of regularization via elastic net (ENET). In order to accurately estimate the maximum and expected maximum HCE among FCAS, well-known risk measures, such as Value at Risk and Conditional Value at Risk, and related quantities were obtained via Monte Carlo simulations. This paper obtained risk measures at 95 security level
Radio continuum, far infrared and star formation
A very tight correlation was found between the radio emission and the far infrared emission from galaxies. This has been found for various samples of galaxies and is explained in terms of recent star formation. The tight correlation would imply that the total radio emission is a good tracer of star formation. The correlation between the radio power at 5 GHz and the far infrared luminosity is shown. The galaxies are of various morphological types and were selected from the various IRAS circulars, hence the sample is an infrared selected sample. The far infrared luminosities were corrected for the dust temperature. This is significant because it decreases the dispersion in the correlation
Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system
We report the experimental observation of the spin-Hall effect in a
two-dimensional (2D) hole system with Rashba spin-orbit coupling.
The 2D hole layer is a part of a p-n junction light-emitting diode with a
specially designed co-planar geometry which allows an angle-resolved
polarization detection at opposite edges of the 2D hole system. In equilibrium
the angular momenta of the Rashba split heavy hole states lie in the plane of
the 2D layer. When an electric field is applied across the hole channel a non
zero out-of-plane component of the angular momentum is detected whose sign
depends on the sign of the electric field and is opposite for the two edges.
Microscopic quantum transport calculations show only a weak effect of disorder
suggesting that the clean limit spin-Hall conductance description (intrinsic
spin-Hall effect) might apply to our system.Comment: 4 pages, 3 figures, paper based on work presented at the Gordon
Research Conference on Magnetic Nano-structures (August 2004) and Oxford Kobe
Seminar on Spintronics (September 2004); accepted for publication in Physical
Review Letters December 200
Low-dimensional light-emitting transistor with tunable recombination zone
We present experimental and numerical studies of a light-emitting transistor
comprising two quasi-lateral junctions between a two-dimensional electron and
hole gas. These lithographically defined junctions are fabricated by etching of
a modulation doped GaAs/AlGaAs heterostructure. In this device electrons and
holes can be directed to the same area by drain and gate voltages, defining a
recombination zone tunable in size and position. It could therefore provide an
architecture for probing low-dimensional devices by analysing the emitted light
of the recombination zone.Comment: 12 Pages, to be published in Journal of Modern Optic
Study of ambiguities in scattering amplitudes
Amplitudes for the reaction are reconstructed from
data on the differential cross section , the recoil
polarization , and on the spin rotation parameter . At low energies,
no data on exist, resulting in ambiguities. An approximation using
and waves leads only to a fair description of the data on
and ; in this case, there are two sets of amplitudes. Including waves,
the data on and are well reproduced by the fit but now,
there are several distinct solutions which describe the data with identical
precision. In the range where the spin rotation parameter was measured,
a full and unambiguous reconstruction of the partial wave amplitudes is
possible. The energy-independent amplitudes are compared to the energy
dependent amplitudes which resulted from a coupled channel fit (BnGa2011-02) to
a large data set including both pion and photo-induced reactions. Significant
deviations are observed. Consistency between energy dependent and energy
independent solutions by choosing the energy independent solution which is
closest to the energy dependent solution. In a second step, the {\it known}
energy dependent solution for low (or high) partial waves is imposed and only
the high (or low) partial waves are fitted leading to smaller uncertainties
- …