Correlations Beyond the Nearest-Neighbor Level in Grain Boundary Networks

Correlations among \u27special\u27 and \u27general\u27 grain boundaries are studied on two-dimensional networks, by examining the configurational entropy of boundary structures as well as percolation thresholds. Consideration of crystallographic constraints at various length scales reveals that higher-order constraints play a role in boundary connectivity and network structure. Implications for grain boundary engineering are discussed and directions for future work highlighted

Diffusion of tungsten in chromium: Experiments and atomistic modeling

The solute diffusion of tungsten at low concentrations in chromium has been investigated both by experiments and computational methods. From finite-source diffusion experiments measured with an Electron Probe Micro Analyzer at temperatures from 1526 to 1676 K, it was found that the diffusivity of tungsten in chromium follows the Arrhenius relationship D=D[subscript 0]exp(-Q[over]RT), where the activation energy was found to be Q = 386 ± 33 kJ/mol. Diffusion of tungsten in chromium was investigated computationally with both the activation–relaxation technique (ART) and molecular dynamics (MD) using a hybrid potential. From ART, the effective diffusion activation energy was determined to be Q = 315 ± 20 kJ/mol based on a multi-frequency model for a monovacancy mechanism. From MD, the square displacement of tungsten was analyzed at temperatures between 1200 and 1700 K, and the diffusion activation energy was determined to be Q = 310 ± 18 kJ/mol. In spite of possible complications arising due to experimental compositions away from the dilute limit, the agreement between experiments and simulations falls within the calculated uncertainties, supporting a monovacancy mechanism for diffusion of tungsten in chromium.United States. Defense Threat Reduction Agency (Grant No. HDTRA1-11-1-0062)United States. Army Research Office (Grant No. W911NF-09-1-0422)Kwanjeong Educational Foundation (Korea)United States. Dept. of Energy (DOE Computational Science Graduate Fellowship, Grant No. DE-FG02-97ER25308)Hertz Foundatio

Cryopyrin-associated periodic fever syndrome manifesting as Tolosa-Hunt syndrome

Background Tolosa-Hunt syndrome (THS) is characterized by unilateral orbital pain, ipsilateral oculomotor paresis and a prompt response to treatment with corticosteroids. Several reports have demonstrated that the clinical features of THS are not specific to one causal aetiology and can lead to misdiagnosis. Case report We report the case of a patient diagnosed with THS after an episode of unilateral orbital pain and diplopia with demonstration of granulomatous inflammation of both cavernous sinus on cerebral magnetic resonance imaging and an immediate response to treatment with corticosteroids. Progression of the disease over the following years, accompanied by increasing signs of inflammation on cerebral magnetic resonance imaging and cerebrospinal fluid pleocytosis, led to further diagnostic tests. Genetic analyses revealed a heterozygote low-penetrance mutation (Q703K) of the cryopyrin/NLRP3 gene compatible with a cryopyrin-associated periodic fever syndrome. Discussion This case report demonstrates that THS can be a central nervous system manifestation of cryopyrin-associated periodic fever syndrome, which therefore represents a differential diagnosis of THS, even in elderly patients

Protease inhibitors prevent plasminogen-mediated, but not pemphigus vulgaris-induced, acantholysis in human epidermis

Pemphigus is an autoimmune blistering disease of the skin and mucous membranes. It is caused by autoantibodies directed against desmosomes, which are the principal adhesion structures between epidermal keratinocytes. Binding of autoantibodies leads to the destruction of desmosomes resulting in the loss of cell-cell adhesion (acantholysis) and epidermal blisters. The plasminogen activator system has been implicated as a proteolytic effector in pemphigus. We have tested inhibitors of the plasminogen activator system with regard to their potential to prevent pemphigus-induced cutaneous pathology. In a human split skin culture system, IgG preparations of sera from pemphigus vulgaris patients caused histopathologic changes (acantholysis) similar to those observed in the original pemphigus disease. All inhibitors that were tested (active site inhibitors directed against uPA, tPA, and/or plasmin; antibodies neutralizing the enzymatic activity of uPA or tPA; substances interfering with the binding of uPA to its specific cell surface receptor uPAR) failed to prevent pemphigus vulgaris IgG-mediated acantholysis. Plasminogen-mediated acantholysis, however, was effectively antagonized by the synthetic active site serine protease inhibitor WX-UK1 or by p-aminomethylbenzoic acid. Our data argue against applying anti-plasminogen activator/anti-plasmin strategies in the management of pemphigus

Micropatterned Electrostatic Traps for Indirect Excitons in Coupled GaAs Quantum Wells

We demonstrate an electrostatic trap for indirect excitons in a field-effect structure based on coupled GaAs quantum wells. Within the plane of a double quantum well indirect excitons are trapped at the perimeter of a SiO2 area sandwiched between the surface of the GaAs heterostructure and a semitransparent metallic top gate. The trapping mechanism is well explained by a combination of the quantum confined Stark effect and local field enhancement. We find the one-dimensional trapping potentials in the quantum well plane to be nearly harmonic with high spring constants exceeding 10 keV/cm^2.Comment: 21 pages, 6 figures, submitted to Phys. Rev.

Direct Observation of Controlled Coupling in an Individual Quantum Dot Molecule

We report the direct observation of quantum coupling in individual quantum dot molecules and its manipulation using static electric fields. A pronounced anti-crossing of different excitonic transitions is observed as the electric field is tuned. Comparison of our experimental results with theory shows that the observed anti-crossing occurs between excitons with predominant spatially \emph{direct} and \emph{indirect} character. The electron component of the exciton wavefunction is shown to have molecular character at the anti-crossing and the quantum coupling strength is deduced optically. In addition, we determine the dependence of the coupling strength on the inter-dot separation and identify a field driven transition of the nature of the molecular ground state.Comment: 11 pages, 4 figures submitted to Physical Review Letter

Predicting Higher Education Graduation Rates from Institutional Characteristics and Resource Allocation

This study incorporated institutional characteristics (e.g., Carnegie type, selectivity) and resource allocations (e.g., instructional expenditures, student affairs expenditures) into a statistical model to predict undergraduate graduation rates. Instructional expenditures, library expenditures, and a number of institutional classification variables were significant predictors of graduation rates. Based on these results, recommendations as well as warranted cautions are included about allocating academic financial resources to optimize graduation rate

Quantum interference and phonon-mediated back-action in lateral quantum dot circuits

Spin qubits have been successfully realized in electrostatically defined, lateral few-electron quantum dot circuits. Qubit readout typically involves spin to charge information conversion, followed by a charge measurement made using a nearby biased quantum point contact. It is critical to understand the back-action disturbances resulting from such a measurement approach. Previous studies have indicated that quantum point contact detectors emit phonons which are then absorbed by nearby qubits. We report here the observation of a pronounced back-action effect in multiple dot circuits where the absorption of detector-generated phonons is strongly modified by a quantum interference effect, and show that the phenomenon is well described by a theory incorporating both the quantum point contact and coherent phonon absorption. Our combined experimental and theoretical results suggest strategies to suppress back-action during the qubit readout procedure.Comment: 25 pages, 8 figure

Spin dephasing and photoinduced spin diffusion in high-mobility 110-grown GaAs-AlGaAs two-dimensional electron systems

We have studied spin dephasing and spin diffusion in a high-mobility two-dimensional electron system, embedded in a GaAs/AlGaAs quantum well grown in the [110] direction, by a two-beam Hanle experiment. For very low excitation density, we observe spin lifetimes of more than 16 ns, which rapidly decrease as the pump intensity is increased. Two mechanisms contribute to this decrease: the optical excitation produces holes, which lead to a decay of electron spin via the Bir-Aranov-Pikus mechanism and recombination with spin-polarized electrons. By scanning the distance between the pump and probe beams, we observe the diffusion of spin-polarized electrons over more than 20 microns. For high pump intensity, the spin polarization in a distance of several microns from the pump beam is larger than at the pump spot, due to the reduced influence of photogenerated holes.Comment: 4 pages, 3 figure