2,694 research outputs found

    What does an observed quantum system reveal to its observer ?

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    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

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    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

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    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

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    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

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    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

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    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 πpΛK0\pi^-p\to \Lambda K^0 scattering amplitudes

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    Amplitudes for the reaction πpΛK0\pi^-p\to \Lambda K^0 are reconstructed from data on the differential cross section dσ/dΩd\sigma/d\Omega, the recoil polarization PP, and on the spin rotation parameter β\beta. At low energies, no data on β\beta exist, resulting in ambiguities. An approximation using SS and PP waves leads only to a fair description of the data on dσ/dΩd\sigma/d\Omega and PP; in this case, there are two sets of amplitudes. Including DD waves, the data on dσ/dΩd\sigma/d\Omega and PP 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 β\beta 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
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