Agneta M. Balint

The growth of a single crystal filament and of a sheet with pre-established piece-wise constant diameter cross-section and half-thickness, respectively, from the melt in a vacuum by EFG method

Abstract In this paper we give a model based proof of the fact that it is possible to grow from the melt in a vacuum by EFG method single crystal filament and sheet with pre-established piece-wise constant diameter cross-section and constant thicknesses d 1 , d 2 ,…, d n , respectively of lengths l 1 , l 2 ,…, l n , changing adequately during the growth, the melt temperature T m at the meniscus basis and the pulling rate v .

The effect of a periodic movement on the die of the bottom line of the melt/gas meniscus in the case of edge-defined film-fed growth system

Abstract In this paper the usual model which permits to describe the evolution of the radius r = r ( t ) and of the meniscus height h = h ( t ) in the case of filament growth from the melt by edge-defined film-fed growth method is considered. What is specific is that the bottom line of the melt/gas meniscus is movable on the die. The main objective is to show that a periodic movement of the bottom line leads to a periodic change of the crystal radius (as it was observed by practical crystal growers) and to show that this effect can be compensated for example by an adequate periodic change of the pulling rate.

A modified Chang–Brown model for the determination of the dopant distribution in a Bridgman–Stockbarger semiconductor crystal growth system

Abstract In this paper, we start from the Chang–Brown model which allows computation of flow, temperature and dopant concentration in a vertical Bridgman–Stockbarger semiconductor growth system. The modifications made by us concern the melt/solid interface. Namely, we assume that the phase transition does not take place on a flat mathematical surface, but in a thin region (the so-called precrystallization-zone), masking the crystal, where both phases, liquid and solid, co-exist. We deduce for this zone new effective equations which govern flow, heat and dopant transport and make the coupling of these equations with those governing the same phenomena in the pure melt. We compute flow, temperature and dopant concentration for crystal and melt with thermophysical properties similar to gallium-doped germanium using the modified Chang–Brown model and compare the results to those obtained using the Chang–Brown model.

Oscillation Susceptibility Analysis of the ADMIRE Aircraft along the Path of Longitudinal Flight Equilibriums in Two Different Mathematical Models

The oscillation susceptibility of the ADMIRE aircraft along the path of longitudinal flight equilibriums is analyzed numerically in the general and in a simplified flight model. More precisely, the longitudinal flight equilibriums, the stability of these equilibriums, and the existence of bifurcations along the path of these equilibriums are researched in both models. Maneuvers and appropriate piloting tasks for the touch-down moment are simulated in both models. The computed results obtained in the models are compared in order to see if the movement concerning the landing phase computed in the simplified model is similar to that computed in the general model. The similarity we find is not a proof of the structural stability of the simplified system, what as far we know never been made, but can increase the confidence that the simplified system correctly describes the real phenomenon.

The effect of the initial dopant distribution in the melt on the axial compositional uniformity of a thin doped crystal grown in strictly zero-gravity environment by Bridgman–Stockbarger method

Abstract The objective of this paper is to show (numerically in the framework of a mathematical model) that using a nonuniform initial dopant repartition, given by an explicit formula, the prescribed constant axial dopant concentration c cr =1 can be achieved on the solidified fraction 0–0.7 in a thin doped crystal, grown in strictly zero-gravity by Bridgman–Stockbarger method. It is also shown that the magnitude of the axial compositional nonuniformities of the crystal is small on the solidified raction 0–0.7.

The axial and radial segregation due to the thermo-convection, the decrease of the melt in the ampoule and the effect of the precrystallization-zone in the semiconductor crystals grown in a Bridgman–Stockbarger system in a low gravity environment

Abstract In this paper, we give a model based simulation of the evolution of axisymmetric flow, heat transport and Ga dispersion in the melt and we predict the axial and radial Ga distribution in a Ga-doped Ge semiconductor crystal grown in a low gravity environment using the Bridgman–Stockbarger growth method.

The Concepts of Well-Posedness and Stability in Different Function Spaces for the 1D Linearized Euler Equations

This paper considers the stability of constant solutions to the 1D Euler equation. The idea is to investigate the effect of different function spaces on the well-posedness and stability of the null solution of the 1D linearized Euler equations. It is shown that the mathematical tools and results depend on the meaning of the concepts “perturbation,” “small perturbation,” “solution of the propagation problem,” and “small solution, that is, solution close to zero,” which are specific for each function space.

Homology Modeling and Validation of the Human M1 Muscarinic Acetylcholine Receptor.

One of the major targets of available drugs on the market is the family of G-protein coupled receptors (GPCR). In practice 14 % (earlier 30 %) of the available pharmaceutical compounds develops its effect on this site of action. Although these receptors themselves are important targets, drugs developed with other therapeutic aim can also act on these receptors and cause adverse side effects. Therefore these targets are antitargets as well and the screening for the possible side effects is very important in the early phase of drug development. From the point of view of the GPCRs, the main antitargets are as follows (in paranthesis the action of the compounds and their main adverse effect is enumerated): adrenergic a1a (antagonist, orthostatic hypotension, dizziness and fainting spells), dopaminergic D2 (antagonist, extrapyramidal syndrome, tardive dyskinesia), serotonin 5-HT2C (antagonist, weight gain, obesity), serotonin 5-HT2B (agonist, valvular heart disease) and muscarinic M1 (antagonist, attention deficits, hallucinations and memory deficits). Nowadays the accurate structure-based description of the GPCR ligand interaction is more feasible due to the increased number of available crystal structures. Experimental structures of the aforementioned GPCRs are not available, therefore the initial structure has to be built up using a homology modeling (HM) approach and the structure obtained should be submitted for validation (structural and ligand recognition). In the past several years a few 3D structures of the human M1 muscarinic acetylcholine receptor (hM1acr) have been developed using various methods. Recently Haga et al. solved the crystal structure of the human M2 muscarinic acetylcholine receptor (hM2acr), which can be used as the most appropriate template for the 3D structure generation of other muscarinic receptors. The aim of our study was to build a relevant 3D structure (Model#1) of the hM1acr using the most appropriate reference structure, the crystallographic structure of hM2acr as a template. This model was compared to the model developed by McRobb et al.(a b2 adrenergic receptor based structure, Model#2) from structural and enrichment factor point of views (using the recently developed GPCR ligand library (GLL) and GPCR decoy database (GDD) set). These sets of active and decoy compounds were prepared in order to obtain chemically diverse molecules with similar physical properties (molecular weight, formal charge, number of rotatable bonds, number of hydrogen bond acceptors and donors, octanol-water partition coefficient, and topological polar surface area) which resulted in unbiased enrichment compared to random selection. The structure obtained from HM was analyzed in order to verify its 3D structure from structural points of view. On the Ramachandran surface we did not find any residue in the disallowed region (see Supporting Information, Figure S1) and outliers were not found in the angle and torsional angle space either. Between Model#1 and Model#2, structural comparison was performed regarding the overall structural similarity/ dissimilarity (backbone root-mean square deviation (RMSD) calculations) and the binding pocket forming residues (all atom RMSD calculations). The per residue RMSD values as well as the segment RMSD values were calculated (see Supporting Information, Figure S2). In these cases the two structures were aligned along the backbone forming atoms (C, CA and N) and the RMSD values were calculated only for these atoms. The overall RMSD between the two models is 2.8 , which suggests an overall similarity between these models. As it was expected, larger deviation was obtained for the extra(EC) and intracellular (IC) loops compared to the transmembrane (TM) segments. Among the more flexible and variable part of the receptors the largest difference was obtained for the IC2 and EC2 loops (see Supporting Information, Figure S3). The intracellular part of the receptor does not take part in the ligand recognition process; therefore this structural difference has no impact on the docking results. In contrast the extracellular part, especially the EC2

Existence of oscillatory solutions in the non simplified model

The purpose of this paper is a numerical investigation of the existence of oscillatory movement of an unmanned aircraft whose automatic flight control system fails at a moment when the aircraft is not in equilibrium and the value of the angle of attack is high. This investigation is made in the framework of the non simplified mathematical model.

Avoiding oscillations by using an alternative flight controller

In this paper we present an alternative flight control system for an unmanned aircraft whose flight control system, during a longitudinal flight with constant forward velocity, fails in a moment when the value of the angle of attack is high. The new controller is conceived using the non simplified system of differential equations, which governs the movement of the aircraft around its center of mass. Numerical simulation is given.