Persistence of entanglement in thermal states of spin systems

We study and compare the persistence of bipartite entanglement (BE) and multipartite entanglement (ME) in one-dimensional and two-dimensional spin XY models in an external transverse magnetic field under the effect of thermal excitations. We compare the threshold temperature at which the entanglement vanishes in both types of entanglement. We use the entanglement of formation as a measure of the BE and the geometric measure to evaluate the ME of the system. We have found that in both dimensions in the anisotropic and partially anisotropic spin systems at zero temperatures, all types of entanglement decay as the magnetic field increases but are sustained with very small magnitudes at high field values. Also we found that for the same systems, the threshold temperatures of the nearest neighbour (nn) BEs are higher than both of the next-to-nearest neighbour BEs and MEs and the three of them increase monotonically with the magnetic field strength. Thus, as the temperature increases, the ME and the far parts BE of the system become more fragile to thermal excitations compared to the nn BE. For the isotropic system, all types of entanglement and threshold temperatures vanish at the same exact small value of the magnetic field. We emphasise the major role played by both the properties of the ground state of the system and the energy gap in controlling the characteristics of the entanglement and threshold temperatures. In addition, we have shown how an inserted magnetic impurity can be used to preserve all types of entanglement and enhance their threshold temperatures. Furthermore, we found that the quantum effects in the spin systems can be maintained at high temperatures, as the different types of entanglements in the spin lattices are sustained at high temperatures by applying sufficiently high magnetic fields.Comment: 20 pages, 17 figure

Uncertainty propagation in a multiscale model of nanocrystalline plasticity

We characterize how uncertainties propagate across spatial and temporal scales in a physicsbased model of nanocrystalline plasticity of fcc metals. Our model combines molecular dynamics (MD) simulations to characterize atomic level processes that govern dislocation basedplastic deformation with a phase field approach to dislocation dynamics (PFDD) that describes how an ensemble of dislocations evolve and interact to determine the mechanical response of the material. We apply this approach to a nanocrystalline Ni specimen of interest in micro-electromechanical (MEMS) switches. Our approach enables us to quantify how internal stresses that result from the fabrication process affect the properties of dislocations (using MD) and how these properties, in turn, affect the yield stress of the metallic membrane (using the PFMM model). Our predictions show that, for a nanocrystalline sample with small grain size (4 nm), a variation in residual stress of 20 MPa (typical in today’s microfabrication techniques) would result in a variation on the critical resolved shear yield stress of approximately 15 MPa, a very small fraction of the nominal value of approximately 9 GPa

A fermentation-powered thermopneumatic pump for biomedical applications

We present a microorganism-powered thermopneumatic pump that utilizes temperature-dependent slow-kinetics gas (carbon dioxide) generating fermentation of yeast as a pressure source. The pump consists of stacked layers of polydimethylsiloxane (PDMS) and a silicon substrate that form a drug reservoir, and a yeast-solution-filled working chamber. The pump operates by the displacement of a drug due to the generation of gas produced via yeast fermentation carried out at skin temperatures. The robustness of yeast allows for long shelf life under extreme environmental conditions (50 degrees C, \u3e250 MPa, 5-8% humidity). The generation of carbon dioxide is a linear function of time for a given temperature, thus allowing for a controlled volume displacement. A polymeric prototype (dimensions 15 mm x 15 mm x 10 mm) with a slow flow rate o

Peptide ormosils as cellular substrates

Peptide-functionalized thin films exhibit significant potential for integration into implantable devices and cell-based technologies. A new type of neuroactive peptide-modified silica was developed using sol-gel reaction chemistry to produce thin films from four different peptide silane precursors. Peptide silanes containing binding sequences from laminin ( YIGSR and KDI), fibronectin ( RGD), and EGF repeats from laminin and tenascin ( NID) were produced using standard solid-state FMOC peptide synthesis conditions and the covalent attachment of 3\u27-( aminopropyl) trimethoxysilane ( APTMS), using carbonyldiimadazole ( CDI) as a linking molecule. Precursor formation was confirmed with MALDI- MS. Thin films were produced by dip-coating using the peptide precursors combined with hydrolyzed tetramethoxysilane. Atomic force microscopy indicated that the surface topography was not affected by low concentrations of peptide precursor ( 0.0025 mol%), but higher concentrations of peptide precursor ( 0.01 mol%) resulted in features that were 50 - 75 nm in height. The height features observed were consistent in size with previously determined topographical morphology supportive of neuronal cell lines. The surfaces were biologically active and modulated the phenotype of the embryonic carcinoma stem cell line, P19. Combinations of the peptide silanes resulted in altered cell types after retinoic acid treatment. More neurons were observed on RGD/YIGSR and RGD/YIGSR/NID surfaces compared to tetramethoxysilane ( TMOS) controls. More supporting cells were observed compared to collagen coated tissue culture plates. In addition, neurites were significantly longer on the peptide ormosils compared to controls. This work demonstrates a novel method for producing biologically active peptide ormosils using peptide-modified precursors

Study of Ultra-Scaled SiGe/Si Core/Shell Nanowire FETs for CMOS Applications

SiGe/Si core/shell nanowire (NW) devices are promising candidates for the future generation MOSFETs providing better channel control and hole mobility [1-4]. These core-shell devices can be exploited both as p- and n-type devices [3]. The Si shell improves the semiconductor-oxide interface and enhances the device performances [1, 3]. The Germanium condensation technique [4] is able to provide high Ge content (\u3e50%) channel with Si as capping layer. In this work we investigate the viability of using these core/shell NWFETs for CMOS application

Nanopatterned contacts to GaN

The effect of nanoscale patterning using a self-organized porous anodic alumina (PAA) mask on the electrical properties of ohmic and Schottky contacts to n-GaN was investigated with the aim of evaluating this approach as a method for reducing the specific contact resistance of ohmic contacts to GaN. The electrical characteristics of contacts to these nanopatterned GaN samples were compared with contacts to planar, chemically prepared ( as-grown ) GaN samples and reactive ion etched (RIE) GaN films without any patterning. The specific contact resistivities to unintentionally doped n-GaN using a Ti/Al bilayer metallization were determined to be 7.4 x 10(-3) Omega cm(2) for the RIE sample and 7.0 x 10(-4) Omega cm(2) for the PAA patterned sample. Schottky metal contacts with Pt and Ni were prepared on the three samples to validate the effects of RIE and nanopatterning on electrical behavior. The effective barrier height was decreased and the reverse current was increased significantly in the PAA patterned sample. The radius of curvature of the nanoscale corrugation in the patterned interface was smaller than the depletion width. The reduction of the depletion width at sharp corners enhanced the local tunneling current, reducing the specific contact resistivity and decreasing the effective barrier height. These results suggest that nanopatterning with PAA on GaN can significantly lower the contact resistance

Automated Grid-Probe System to Improve End-To-End Grid Reliability for a Science Gateway

In 2010, the science gateway nanoHUB.org, the world’s largest nanotechnology user facility, hosted 9,809 simulation users who performed 372,404 simulation runs. Many of these jobs are compute-intensive runs that benefit from submission to clusters at Purdue, TeraGrid, and Open Science Grid (OSG). Most of the nanoHUB users are not computational experts but end-users who expect complete and uninterrupted service. Within the ecology of grid computing resources, we need to manage the grid submissions of these users transparently with the highest possible degree of user satisfaction. In order to best utilize grid computing resources, we have developed a grid probe protocol to test the job submission system from end to end. Beginning in January 2009, we have collected a total of 1.2 million probe results from job submissions to TeraGrid, OSG, Purdue, and nanoHUB compute clusters. We then utilized these results to intelligently submit jobs to various grid sites using a model for probability of success based in part on probe test history. In this paper we present details of our grid probe model, results from the grid probe runs, and a discussion of data from production runs over the same time period. These results have allowed us to begin assessing our utilization of grid resources while providing our users with satisfactory outcomes