Protabit (United States)

In the past decades significant improvement of the performance of III-V Geiger-mode APDs (GmAPD) has been achieved in Near Infrared (NIR) and Short Wavelength Infrared (SWIR) wavelengths. In order to meet the challenge to GmAPDs in visible wavelength for some special military and space applications, Acqubit developed a GaAs-based InGaP APD with a substrate removal structure. With a proprietary mesa passivation process, very low dark current, ~0.5 nA in a 50 um diameter device or 25 uA/cm2, was demonstrated just before breakdown at room temperature. Sufficient device thickness ensured an external quantum efficiency (QE) about 50% at 532 nm without a bottom reflector. The combination of mesa structure and substrate removal process greatly suppressed the array pixel crosstalk and afterpulsing while maintaining a high QE and photon detection efficiency (PDE). In this paper we will report the progress of the GmAPD detectors and arrays with low DCR and high PDE at 532 µm.

A molecular mechanics model, previously validated in applications to structure prediction, is shown to reproduce experiment in predictions of protein ionization state, and in predictions of sequence and pH dependence of protein stability. Over a large dataset, 1876 values of ΔΔG of folding, the RMSD is 1.34 kcal/mol. Using an alternative measure of accuracy, either the sign of the calculated ΔΔG agrees with experiment or the absolute value of the deviation is less than 1.0 kcal/mol, 1660 of 1876 data points (88.5%) pass the condition. Relative to models used previously in computer-aided protein design, the concept, we propose, most responsible for the performance of our model, and for the extensibility to non-neutral values of pH, is the treatment of electrostatic energy. The electronic structure of the protein is modeled using distributed atomic multipoles. The structured liquid state of the solvent is modeled using a dielectric continuum. A modification to the energetics of the reaction field, induced by the protein in the dielectric continuum, attempts to account for preformed multipoles of solvent water molecules and ions. An adjustable weight (with optimal value.141) applied to the total vacuum energy accounts implicitly for electronic polarization. A threshold distance, beyond which pairwise atomic interactions are neglected, is not used. In searches through subspaces of sequences and conformations, efficiency remains acceptable for useful applications.