Photogeneration,optical absorption and transport in hydrogenated sputtered amorphous silicon

By combining direct optical transmission with steady state photocurrent and photoconductivity gain measurements we evaluated the optical absorption constant of sputtered hydrogenated a-Si between 10⁵ to 10^?1cm^?1. The photogeneration process involves excitation from the valence band or from defect states in the middle of the gap to the conduction band, with the electrons making the major contribution to the photocurrent. The electron drift mobility, determined from the photoconductivity studies, is considerably smaller than that determined from the time of flight technique, due to trapping at deep centers.     

Anomalous thermoelectric power of some liquid chalcogenide systems

In some liquid chalcogenide systems, the activation energy derived from thermopower is larger than that derived from the temperature dependence of conductivity. This anomaly is accounted for with an asymmetric density of states model in which an electronic contribution to thermopower increases exponentially with temperature.     

Dependence of avidity on linker length for a bivalent ligand-bivalent receptor model system

This paper describes a synthetic dimer of carbonic anhydrase, and a series of bivalent sulfonamide ligands with different lengths (25 to 69 ? between the ends of the fully extended ligands), as a model system to use in examining the binding of bivalent antibodies to antigens. Assays based on analytical ultracentrifugation and fluorescence binding indicate that this system forms cyclic, noncovalent complexes with a stoichiometry of one bivalent ligand to one dimer. This dimer binds the series of bivalent ligands with low picomolar avidities (K(d)(avidity) = 3-40 pM). A structurally analogous monovalent ligand binds to one active site of the dimer with K(d)(mono) = 16 nM. The bivalent association is thus significantly stronger (K(d)(mono)/K(d)(avidity) ranging from ~500 to 5000 unitless) than the monovalent association. We infer from these results, and by comparison of these results to previous studies, that bivalency in antibodies can lead to associations much tighter than monovalent associations (although the observed bivalent association is much weaker than predicted from the simplest level of theory: predicted K(d)(avidity) of ~0.002 pM and K(d)(mono)/K(d)(avidity) ~ 8 × 10(6) unitless).     

Preparation of highly photoconductive amorphous silicon by rf sputtering

The photoconductivity of hydrogenated rf sputtered amorphous Si has been determined as a function of the partial pressure of hydrogen in the sputtering gas and of deposition temperatures up to 450°C. The data can be used to choose conditions for preparing material with large photoresponse and small defect state density.     

Optimum transimpedance broadband optical preamplifier design

We consider in this paper the optimum design of a broadband transimpedance optical preamplifier which utilizes a GaAs MESFET first stage. An alternative configuration to the feedback cascode is suggested which offers significant improvement in the noise performance. This configuration employs a common-source FET first stage followed by a shunt feedback bipolar second stage.     

Plasmon-enhanced light emission based on lattice resonances of silver nanocylinder arrays

Diffractive arrays of silver nanocylinders are used to increase the radiative efficiency of InGaN/GaN quantum wells emitting at near-green wavelengths. Large enhancements in luminescence intensity (up to a factor of nearly 5) are measured when the array period exceeds the emission wavelength in the semiconductor material. The experimental results and related numerical simulations indicate that the underlying mechanism is a strong resonant coupling between the light-emitting excitons in the quantum wells and the plasmonic lattice resonances of the arrays. These excitations are particularly well suited to light-emission-efficiency enhancement, compared to localized surface plasmon resonances at similar wavelengths, due to their larger scattering efficiency and larger spatial extension across the sample area.     

Crossover from conserving to lossy transport in circular random-matrix ensembles

In a quantum dot with three leads, the transmission matrix t12 between two of these leads is a truncation of a unitary scattering matrix S, which we treat as random. As the number of channels in the third lead is increased, the constraints from the symmetry of S become less stringent and t12 becomes closer to a matrix of complex Gaussian random numbers with no constraints. We consider the distribution of the singular values of t12, which is related to a number of physical quantities.     

Development and validation of a modular, extensible docking program: DOCK 5

We report on the development and validation of a new version of DOCK. The algorithm has been rewritten in a modular format, which allows for easy implementation of new scoring functions, sampling methods and analysis tools. We validated the sampling algorithm with a test set of 114 protein-ligand complexes. Using an optimized parameter set, we are able to reproduce the crystal ligand pose to within 2 A of the crystal structure for 79% of the test cases using our rigid ligand docking algorithm with an average run time of 1 min per complex and for 72% of the test cases using our flexible ligand docking algorithm with an average run time of 5 min per complex. Finally, we perform an analysis of the docking failures in the test set and determine that the sampling algorithm is generally sufficient for the binding pose prediction problem for up to 7 rotatable bonds; i.e. 99% of the rigid ligand docking cases and 95% of the flexible ligand docking cases are sampled successfully. We point out that success rates could be improved through more advanced modeling of the receptor prior to docking and through improvement of the force field parameters, particularly for structures containing metal-based cofactors.