Pressure limited sustained off-resonance irradiation for collision-activated dissociation in Fourier transform mass spectrometry

A theoretical evaluation of the sustained off-resonance irradiation of ions (SORI) in the presence of a collisional buffer gas in a Fourier transform ion cyclotron resonance mass spectrometer is presented. It is shown that there is an optimal pressure for a given set of irradiation parameters corresponding to the most effective dissociation. Theoretical predictions are compared with experimental results for the dissociation of electrosprayed biopolymer ions and with previously accepted view of the SORI process.     

Adaptation of Decoy Fusion Strategy for Existing Multi-Stage Search Workflows

A number of proteomic database search engines implement multi-stage strategies aiming at increasing the sensitivity of proteome analysis. These approaches often employ a subset of the original database for the secondary stage of analysis. However, if target-decoy approach (TDA) is used for false discovery rate (FDR) estimation, the multi-stage strategies may violate the underlying assumption of TDA that false matches are distributed uniformly across the target and decoy databases. This violation occurs if the numbers of target and decoy proteins selected for the second search are not equal. Here, we propose a method of decoy database generation based on the previously reported decoy fusion strategy. This method allows unbiased TDA-based FDR estimation in multi-stage searches and can be easily integrated into existing workflows utilizing popular search engines and post-search algorithms.

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Effect of ion irradiation on the structure and luminescence characteristics of porous silicon impregnated with tungsten-telluride glass doped by Er and Yb impurities

Using transmission electron microscopy and elemental analysis, it has been shown that tungsten telluride glass (TTG) containing erbium and ytterbium as impurities penetrates into pores of porous silicon (PS) when melted in vacuum at 500°C. It has been found that the intensity of photoluminescence (PL) of erbium at the wavelength of 1.54 μm in PS: TTG layers increases by a factor of up to 5 in the layers irradiated by P⁺ and Ar⁺ ions. This is assigned to ion mixing which favors interaction among the Er ions and PS-embedded Si nanocrystals initiating sensitization of the PL, as well as to broadening of the glass-impregnated PS region. Implantation of the lighter Ne⁺ ions affects only weakly the PL of erbium ions.     

Emission of photoexcited charge carriers from InAs/GaAs quantum dots grown by gas-phase epitaxy

A model describing the emission of photoexcited electrons and holes from an array of InAs quantum dots into the GaAs matrix is suggested. The analytical expression obtained for the emission efficiency takes into account the thermal emission of charge carriers into the GaAs matrix and two-dimensional states of the InAs wetting layer, tunneling and thermally activated tunneling escape, and electron transitions between the quantum-confinement levels in the conduction band of InAs. The temperature dependences of the photosensitivity in the regions of the ground-state and first excited-state optical transitions in InAs/GaAs quantum dots grown by gas-phase epitaxy are investigated experimentally. A number of quantum dot parameters are determined by fitting the results of a theoretical calculation to the experimental data. Good agreement between the theoretical and experimental results is obtained in this way.     

Monte Carlo simulation of brain sensing by optical diffuse spectroscopy

We report on development of adapted Monte Carlo based algorithm and code for simulation of light propagation in turbid media with complex geometry aimed for simulation of optical diffuse spectroscopy signal in noninvasive brain sensing. Simulation will allow to determine optimal characteristics of a prototype device for optical diffuse brain sensing. The developed Monte Carlo code can be efficiently parallelized both for SMP and distributed memory systems. We show that the speed-up of the developed algorithm almost linearly depends on the number of nodes/threads in a utilized system.     

Effect of physical and chemical nonequilibrium processes on the parameters of the near wake downstream of a spacecraft

The axisymmetric laminar flowfield and heat transfer characteristics of the RAM-C experimental spacecraft moving in the Earth’s atmosphere at an altitude of 61 km and a velocity of 7.65 km/s are investigated on the basis of a numerical solution of the Navier-Stokes equations. In studying the effect of the physical and chemical nonequilibrium processes on the flow parameters two approximations are employed for describing the gas properties, namely, that of a perfect gas with a constant adiabatic exponent and a model of dissociating and vibrationally-relaxing air. Emphasis is placed on the study of the spacecraft’s near-wake parameters. The results obtained are compared with experimental data on the electron concentration in the shock layer on the lateral surface and the calculated results of other authors.     

Thin triangular blunt-nosed plate in a viscous hypersonic flow

The effect of a small blunt nose on the hypersonic flow past a thin, high-sweep and high-aspect-ratio plate at small incidence is investigated. The analysis is made by means of numerical simulation within the framework of the parabolized Navier-Stokes equations and the Euler equations in combination with approximate methods for calculating the heat transfer. The results are compared with the data of experiments in which some nontrivial features of the heat flux distributions over the thin plate surface were revealed.     

A dynamic ion cooling technique for FTICR mass spectrometry

A fast dynamic ion cooling technique based upon the adiabatic invariant phenomenon for Fourier transform ion cyclotron resonance mass spectrometry (FTICR) is presented. The method cools ions in the FTICR trap more efficiently, within a few hundred milliseconds without the use of a buffer gas, and results in a substantial signal enhancement. All performance aspects of the FTICR spectrum, e.g., peak intensities, mass resolution, and mass accuracy, improve significantly compared with cooling based on ion-ion interactions. The method may be useful in biological applications of FTICR, such as in proteomic studies involving extended on-line liquid chromatography (LC) separations, in which both the duty cycle and mass accuracy are crucially important.     

Anomalous Phenomena in Zirconium,Hafnium, and Titanium Salt Solutions,Studied by Capillary Isotachophoresis

Capillary isotachophoresis was used to separate mixtures of solutions containing zirconium, hafnium, titanium, and aluminum salts with various anions. Anomalous phenomena occurring in separation of mixtures in solutions with medium and high concentrations are described and analyzed.