Electromagnetically Induced Transparency with an Ensemble of Donor-Bound Electron Spins in a Semiconductor

We present measurements of electromagnetically induced transparency with an ensemble of donor- bound electrons in low-doped n-GaAs. We used optical transitions from the Zeeman-split electron spin states to a bound trion state in samples with optical densities of 0.3 and 1.0. The electron spin dephasing time T* \approx 2 ns was limited by hyperfine coupling to fluctuating nuclear spins. We also observe signatures of dynamical nuclear polarization, but find these effects to be much weaker than in experiments that use electron spin resonance and related experiments with quantum dots.Comment: 4 pages, 4 figures; Improved analysis of data in Fig. 3, corrected factors of 2 and p

Stabilizing nuclear spins around semiconductor electrons via the interplay of optical coherent population trapping and dynamic nuclear polarization

We experimentally demonstrate how coherent population trapping (CPT) for donor-bound electron spins in GaAs results in autonomous feedback that prepares stabilized states for the spin polarization of nuclei around the electrons. CPT was realized by excitation with two lasers to a bound-exciton state. Transmission studies of the spectral CPT feature on an ensemble of electrons directly reveal the statistical distribution of prepared nuclear spin states. Tuning the laser driving from blue to red detuned drives a transition from one to two stable states. Our results have importance for ongoing research on schemes for dynamic nuclear spin polarization, the central spin problem and control of spin coherence.Comment: 5 pages, 4 figure

Two-laser dynamic nuclear polarization with semiconductor electrons:Feedback, suppressed fluctuations, and bistability near two-photon resonance

Feedback control is a powerful tool to stabilize systems for which precision control is difficult to impose directly, such as the environment of an open quantum system. Reduction of noise from the environment is a major challenge on the road to harnessing delicate quantum effects such as superposition and entanglement. In particular, spin states of defects and quantum dots in semiconductors display promising coherence properties for future applications, often being limited by disturbance from disordered nuclear spins in their environment. Here we show how optical coherent population trapping (CPT) of the spin of localized semiconductor electrons stabilizes the surrounding nuclear spins via feedback control. We find distinct control regimes for different signs of laser detuning and examine the transition from an unpolarized, narrowed state to a polarized state possessing a bistability. The narrowing of the state protects the electron spin against dephasing and yields self-improving CPT. Our analysis is relevant for a variety of solid-state systems where hyperfine-induced dephasing is a limitation for using electron spin coherence

Automated discrimination of psychotropic drugs in mice via computer vision-based analysis

Cataloged from PDF version of article.We developed an inexpensive computer vision-based method utilizing an algorithm which differentiates drug-induced behavioral alterations. The mice were observed in an open-field arena and their activity was recorded for 100 min. For each animal the first 50 min of observation were regarded as the drug-free period. Each animal was exposed to only one drug and they were injected (i.p.) with either amphetamine or cocaine as the stimulant drugs or morphine or diazepam as the inhibitory agents. The software divided the arena into virtual grids and calculated the number of visits (sojourn counts) to the grids and instantaneous speeds within these grids by analyzing video data. These spatial distributions of sojourn counts and instantaneous speeds were used to construct feature vectors which were fed to the classifier algorithms for the final step of matching the animals and the drugs. The software decided which of the animals were drug-treated at a rate of 96%. The algorithm achieved 92% accuracy in sorting the data according to the increased or decreased activity and then determined which drug was delivered. The method differentiated the type of psychostimulant or inhibitory drugs with a success ratio of 70% and 80%, respectively. This method provides a new way to automatically evaluate and classify drug-induced behaviors in mice. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved

Middle interhemispheric holoprosencephaly with subdural hematoma

Background: A 4-month-old boy with prenatal sonography findings consistent with corpus callosum agenesis and ventriculomegaly presented. Patient was born at 37-weeks from 18-yearold woman, gravida 1 para 1. There was no history of teratogen exposure in utero such as radiation, alcohol, drug or postnatal trauma. There was no family history of brain malformations nor chromosomal abnormalities. Clinically no facial abnormality was observed. The mother had gestational diabetes during pregnancy. The baby was delivered by means of cesarean section because of severe eclampsia at 37 weeks. Postnatal routine physical examination of patient was normal

Foreign market entry, upstream market power, and endogenous mode of downstream competition

In a differentiated duopoly model of trade and FDI featuring both horizontal and ver tical product differentiation, we examine whether globalization and trade policy mea sures can generate welfare gains by leading firms to change their mode of competition. We show that when a high-quality foreign variety is manufactured under large frictions due to upstream monopoly power, a foreign firm can become a Bertrand competitor against a Cournot local rival in equilibrium, especially when the relative product quality of the foreign variety is sufficiently high and trade costs are sufficiently low (implying higher input price distortions due to double marginalization). Our results suggest that such strategic asymmetry is welfare improving and that the availability of FDI as an alternative to trade can make welfare-enhancing strategic asymmetry even more likely, especially when both input trade costs and fixed investment costs are sufficiently low and trade costs in final goods are sufficiently large

An extended mixed-integer programming formulation and dynamic cut generation approach for the stochastic lot sizing problem

We present an extended mixed-integer programming formulation of the stochastic lot-sizing problem for the static-dynamic uncertainty strategy. The proposed formulation is significantly more time efficient as compared to existing formulations in the literature and it can handle variants of the stochastic lot-sizing problem characterized by penalty costs and service level constraints, as well as backorders and lost sales. Also, besides being capable of working with a predefined piecewise linear approximation of the cost function-as is the case in earlier formulations-it has the functionality of finding an optimal cost solution with an arbitrary level of precision by means of a novel dynamic cut generation approach

Procurement Risk Management in Beef Supply Chains

Procurement risk management in beef supply chain