Failure-mechanism models for conductive-filament formation

This tutorial illustrates design and qualification situations where conductive filament formation, a failure mechanism that can occur in laminates, can affect product performance. Empirical models to design against this failure mechanism are presented in this paper. Examples illustrate the use of these models for design and qualification tests in electronic packaging     

A random walk down the genomes: DNA evolution in Valis

The authors propose a new software system that incorporates biological data and domain-specific knowledge and show how biologists can use it to model, analyze, and experiment with genomic evolutionary processes. A better understanding of biology will come through information-theoretic studies of genomes that provide insights into DNA's role in governing metabolic and regulatory pathways. Understanding the evolutionary processes that act on these "codes of life" requires the ability to analyze vast amounts of continually generated genomic data. Researchers in the emerging bioinformatics discipline require more complex mechanisms to investigate the full ensemble of available biological facts. To meet this challenge, New York University's Bioinformatics Group is creating a computational environment called Valis, the vast active living intelligent system. Valis is designed to solve the immediate genomic and proteomic problems that the biological community currently faces, while remaining flexible enough to adapt to the maturing bioinformatics field     

Biological removal of arsenic pollution by soil fungi

Fifteen fungal strains were isolated from arsenic contaminated (range 9.45-15.63 mg kg^− 1) agricultural soils from the state of West Bengal, India. Five fungal strains were belonged to the Aspergillus and Trichoderma group each, however, remaining five were identified as the Neocosmospora, Sordaria, Rhizopus, Penicillium and sterile mycelial strain. All these fungal strains were cultivated on medium supplemented with 100, 500, 1000, 5000 and 10,000 mg l^− 1 of sodium arsenate. After 30-day cultivation under laboratory conditions, radial growth of these strains was determined and compared with control. Toxicity and tolerance of these strains to arsenate were evaluated on the basis of tolerance index. Out of fifteen, only five fungal strains were found resistant and survived with tolerance index pattern as 0.956 (sterile mycelial strain) > 0.311 (Rhizopus sp.) > 0.306 (Neocosmospora sp.) > 0.212 (Penicillium sp.) > 0.189 (Aspergillus sp.) at 10,000 mg l^− 1 of arsenate. The arsenic removal efficacy of ten fungal strains, tolerant to 5000 mg l^− 1 arsenate, was also assayed under laboratory conditions for 21 days. All these strains were cultivated individually on mycological broth enriched with 10 mg l^− 1 of arsenic. The initial and final pH of cultivating medium, fungal biomass and removal of arsenic by each fungal strain were evaluated. Fungal biomass of ten strains removed arsenic biologically from the medium which were ranged from 10.92 to 65.81% depending on fungal species. The flux of biovolatilized arsenic was determined indirectly by estimating the sum of arsenic content in fungal biomass and medium. The mean percent removal as flux of biovolatilized arsenic ranged from 3.71 to 29.86%. The most effective removal of arsenic was observed in the Trichoderma sp., sterile mycelial strain, Neocosmospora sp. and Rhizopus sp. fungal strains. These fungal strains can be effectively used for the bioremediation of arsenic-contaminated agricultural soils.     

In(Al)GaAs–AlGaAs Wafer Fused VCSELs Emitting at 2- μm Wavelength

We demonstrate 2-mum wavelength, wafer-fused In(Al)GaAs-InP-AlGaAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) emitting single-mode power of 0.5 mW at room temperature with a threshold current of 4 mA and sidemode suppression ratio of over 30 dB. These devices can be continuously tuned with current by 5 nm without mode hopping, with a tuning rate of 0.31 nm/mA. These features demonstrate the potential of these long wavelength VCSELs for gas sensing and other optical spectroscopy applications.     

DX centers in Sn-doped Ga0.7Al0.3As

We have measured and analyzed the extended fine structure on the Sn K-shell x-ray absorption spectra of GaAs and Ga_0.7Al_0.3As doped with ∼5 x 10¹⁸ cm⁻³ Sn. Our results and their implications for the atomic structure of DX centers are discussed.     

Self-formation of hexagonal nanotemplates for growth of pyramidal quantum dots by metalorganic vapor phase epitaxy on patterned substrates

We demonstrate the self-formation of hexagonal nanotemplates on GaAs (111)B substrates patterned with arrays of inverted tetrahedral pyramids during metal-organic vapor phase epitaxy and its role in producing high-symmetry, site-controlled quantum dots (QDs). By combining atomic force microscopy measurements on progressively thicker GaAs epitaxial layers with kinetic Monte Carlo growth simulations, we demonstrate self-maintained symmetry elevation of the QD formation sites from three-fold to six-fold symmetry. This symmetry elevation stems from adatom fluxes directed towards the high-curvature sites of the template, resulting in the formation of a fully three-dimensional hexagonal template after the deposition of relatively thin GaAs layers. We identified the growth conditions for consistently achieving a hexagonal pyramid bottom, which are useful for producing high-symmetry QDs for efficient generation of entangled photons.

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Velocity-dependent dynamic curvature gain for redirected walking

Redirected walking techniques allow people to walk in a larger virtual space than the physical extents of the laboratory. We describe two experiments conducted to investigate human sensitivity to walking on a curved path and to validate a new redirected walking technique. In a psychophysical experiment, we found that sensitivity to walking on a curved path was significantly lower for slower walking speeds (radius of 10 m versus 22 m). In an applied study, we investigated the influence of a velocity-dependent dynamic gain controller and an avatar controller on the average distance that participants were able to freely walk before needing to be reoriented. The mean walked distance was significantly greater in the dynamic gain controller condition, as compared to the static controller (22 m versus 15 m). Our results demonstrate that perceptually motivated dynamic redirected walking techniques, in combination with reorientation techniques, allow for unaided exploration of a large virtual city model.     

Direct numerical simulation of ignition of syngas (H2/CO) mixtures with temperature and composition stratifications relevant to HCCI conditions

In this paper, ignition characteristics of syngas (H₂/CO) under homogeneous charge compression ignition environment have been studied using direct numerical simulation (DNS) and detailed reaction mechanism with temperature stratification. 2D DNS are performed by varying several parameters such as fuel composition, temperature fluctuation $\left(T^{\prime }\right)$ and with different temperature and composition correlations. Results show that high H₂ content syngas mixture exhibits increase in peak mean heat release rate (HRR) and decrease in spreading of mean HRR. Also, for large $T^{\prime }$, deflagration mode of ignition becomes dominant source of HRR and reduces the effects of fuel composition on peak mean HRR. On the contrary, spontaneous mode of ignition becomes dominant source of HRR and occurs more homogenously for small $T^{\prime }$, and this phenomenon becomes significant for low H₂ content syngas mixture. The effect of different correlations between temperature and composition on ignition in syngas illustrate that HRR occurs from mixed mode of deflagration and spontaneous ignition for uncorrelated cases, whereas spontaneous mode of ignition occurring homogeneously is the major source of HRR for negatively correlated cases.