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Mechanically Induced Nucleation Improves Crystalline Quality During Melt Growth of Semiconductors

Significantly lower supercooling results in the ideal growth condition of single crystal nucleation. Marshall Space Flight Center, Alabama For certain semiconductors with important applications, the existing bulk crystal growth technique from the melt usually results in poor-quality multi-crystalline ingots that cause the typically low yield of the commercial growth process. The low-quality, multi-grained crystal growth is mainly caused by the large supercool of the melt, which prohibits the ideal growth condition that a small, single-crystal nucleus forms at the very tip and grows into a large single crystal. For instance, semi-insulating cadmium zinc telluride (CdZnTe) crystal is a highly promising material for room-temperature x-ray and gamma ray detectors. However, the major hurdle in using the CdZnTe crystals is its cost. The ability to pack many data acquisition channels (hundreds) with the stopping power for high-energy radiation requires large single crystals of CdZnTe.

Posted in: Briefs

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Fabrication of a Nanopipette Array for Biosensing

Ames Research Center, Moffett Field, California Development of biosensors is an active field due to a wide range of applications in lab-on-a-chip, diagnostics of infectious diseases, cancer diagnostics, environment monitoring, biodetection, and others. One of the strategies used for selective identification of a target is to preselect a probe that has a unique affinity for the target, or can uniquely interact or hybridize with the target — a lock and key approach. In this approach, one then needs a platform to support the probe and a recognizing element that can recognize the said interaction between the probe and the target. Electrical readout biosensors have gained much attention because, in principle, they can be made more compact than optical technologies.

Posted in: Briefs

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Fabrication of a Nanopipette Array for Biosensing

Ames Research Center, Moffett Field, California Development of biosensors is an active field due to a wide range of applications in lab-on-a-chip, diagnostics of infectious diseases, cancer diagnostics, environment monitoring, biodetection, and others. One of the strategies used for selective identification of a target is to preselect a probe that has a unique affinity for the target, or can uniquely interact or hybridize with the target — a lock and key approach. In this approach, one then needs a platform to support the probe and a recognizing element that can recognize the said interaction between the probe and the target. Electrical readout biosensors have gained much attention because, in principle, they can be made more compact than optical technologies.

Posted in: Briefs, Sensors

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Predictive Computations of Single-Phase Turbulent Flows

Explicitly filtered large-eddy simulation is used. NASA’s Jet Propulsion Laboratory, Pasadena, California This software computes a single-phase turbulent flow. The solution is independent of the grid spacing on which it is computed, and on the discretization order used for the differential equations. Grid spacing and discretization-order independence can be achieved by reformulating the large-eddy simulation (LES) equations. Previous software followed the conventional LES equations, whereas the present one follows the explicitly filtered formulation (EFLES).

Posted in: Briefs, Simulation Software

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Predictive Computation of Two-Phase Turbulent Flows with Phase Change

Explicitly filtered large-eddy simulation is used. NASA’s Jet Propulsion Laboratory, Pasadena, California This software computes two-phase turbulent flows with phase change, and the solution is independent of the grid spacing on which it is computed and on the discretization order used for the differential equations. Grid spacing and discretization-order independence can be achieved by reformulating the large-eddy simulation (LES) equations. Previous software followed the conventional LES equations, whereas the present one follows the explicitly filtered formulation (EFLES).

Posted in: Briefs, Simulation Software

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Physics-Model-Based Wiring Fault Detection Toolbox for MATLAB

Ames Research Center, Moffett Field, California This software provides a toolbox of MATLAB functions for detecting precursor wiring faults, such as chafing, in shielded impedance-controlled cable using measurements from off-the-shelf time domain reflectometry or vector network analyzer hardware. It advances the state-of-the-art in wiring fault detection, currently limited to the detection of hard opens or shorts, by combining high-fidelity analytical physics models for signal propagation on faulty cable with fast Bayesian inference algorithms for intrinsic cable and fault parameter retrieval. The overall approach is robust to noisy operating conditions, and does not require fixed baseline measurements. More information about this software can be found at: http://ti.arc.nasa.gov/project/wiring.

Posted in: Briefs

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PEGASUS 5.2: Automated Pre-Processing of Overset CFD Grids

Ames Research Center, Moffett Field, California The Pegasus software is used as a pre-processor for overset-grid computational fluid dynamic (CFD) simulations. The main features of the software include: automated hole cutting algorithms; a projection scheme for fixing small discretization errors in overset surfaces; efficient interpolation search methods; hole-size optimization based on adding additional layers of fringe points; and an automatic restart capability. The code can be run in parallel using the Message-Passing Interface standard. The parallelization performance provides efficient speed-up of the execution time capable of utilizing dozens or even hundreds of processors.

Posted in: Briefs, Simulation Software

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