Electronic states in semiconductor nanostructures and upscaling to semi-classical models

In semiconductor devices one basically distinguishes three spatial scales: The atomistic scale of the bulk semiconductor materials (sub-Angstroem), the scale of the interaction zone at the interface between two semiconductor materials together with the scale of the resulting size quantization (nanometer) and the scale of the device itself (micrometer). The paper focuses on the two scale transitions inherent in the hierarchy of scales in the device. We start with the description of the band structure of the bulk material by kp Hamiltonians on the atomistic scale. We describe how the envelope function approximation allows to construct kp Schroedinger operators describing the electronic states at the nanoscale which are closely related to the kp Hamiltonians. Special emphasis is placed on the possible existence of spurious modes in the kp Schroedinger model on the nanoscale which are inherited from anomalous band bending on the atomistic scale. We review results of the mathematical analysis of these multi-band kp Schroedinger operators. Besides of the confirmation of the main facts about the band structure usually taken for granted, key results are conditions on the coefficients of the kp Schroedinger operator for the nanostructure, which exclude spurious modes and an estimate of the size of the band gap. Using these results, we give an overview of properties of the electronic band structure of strained quantum wells. Further, the assumption of flat-band conditions across the nanostructure allows for upscaling of quantum calculations to state equations for semi-classical models. We demonstrate this approach for parameters such as the quantum corrected band-edges, the effective density of states, the optical response, and the optical peak gain. Further, we apply the kp Schroedinger theory to low gap quantum wells, a case where a proper rescaling of the optical matrix element is necessary to avoid spurious modes. Finally, we discuss the application of the kp Schroedinger models to biased quantum wells, the operation mode of electro-optic modulators

Un estudio comparativo de actuadores Piezoeléctricos y Magnetoestrictivos para estructuras inteligentes

[EN] This paper introduces a comparative analysis of Piezoelectric (PZ) and Magnetostrictive (MS) actuators as components in smart structures. There is an increasing interest in functional structures which are able to adapt to external or internal perturbations, i.e. changes in loading conditions or ageing. Actuator technologies must perform concomitantly as sensors and actuators to be applicable in smart structures. In this paper we will comparatively analyze the possibility of using PZ and MS actuators in smart structures and in so doing their capability to act concomitantly as sensors and of modifying their material characteristics. We will also focus on the analysis of how them can be integrated in structures and on the analysis of the most appropriate structures for each actuator. The operational performance of PZ (Stacks) and MS actuators will be compared and eventually some conclusions will be drawn.[ES] Este artículo presenta un estudio comparativo de actuadores Piezoeléctricos (PZ) y Magnetoestrictivos (MS) como elementos integrantes de estructuras inteligentes. Existe un interés creciente en estructuras activas que puedan adaptarse a perturbaciones tanto internas como externas, por ejemplo, ante cambios en carga estructural o ante su envejecimiento. Para que un actuador forme parte de una estructura inteligente, debe poder actuar también como sensor. Este artículo presenta un estudio comparativo del uso de actuadores PZ y MS en estructuras inteligentes y, como consecuencia, de su habilidad para actuar y medir simultáneamente así cómo para modificar sus características mecánicas. Nos centraremos también en el análisis de como pueden integrase en estructuras y cuales son las más indicadas para cada actuador. Se compararán las características operacionales de los actuadors PZ multicapa y los MS.Peer reviewe

Гидроимпульсный силовой механизм сваебойной машины в условиях обустройства месторождений

AbstractObjectivesThis study sought to evaluate whether objective assessment of the myocardial functional reserve, using strain rate imaging (SRI), allows accurate detection of viable myocardium.BackgroundStrain rate imaging is a new echocardiographic modality that allows quantitative assessment of segmental myocardial contractility.MethodsIn 37 patients (age 58 ± 9 years) with ischemic left ventricular dysfunction, myocardial viability was assessed using low-dose (10 μg/kg body weight per min) two-dimensional dobutamine stress echocardiography (DSE), tissue Doppler imaging, SRI and 18F-fluorodeoxyglucose (18FDG) positron emission tomography (PET). The peak systolic tissue Doppler velocity and peak systolic myocardial strain rate were determined at baseline and during low-dose dobutamine stress from the apical views.ResultsA total of 192 segments with dyssynergy at rest were classified by 18FDG PET as viable in 94 and nonviable in 98. An increase of peak systolic strain rate from rest to dobutamine stimulation by more than −0.23 1/s allowed accurate discrimination of viable from nonviable myocardium, as determined by 18FDG PET with a sensitivity of 83% and a specificity of 84%. Receiver operating characteristic (ROC) curve analysis showed an area under the curve for prediction of nonviable myocardium, as determined by 18FDG PET using SRI, of 0.89 (95% confidence interval [CI] 0.88 to 0.90), whereas the area under the ROC curve using tissue Doppler imaging was 0.63 (95% CI 0.61 to 0.65).ConclusionsThe increase in the peak systolic strain rate during low-dose dobutamine stimulation allows accurate discrimination between different myocardial viability states. Strain rate imaging is superior to two-dimensional DSE and tissue Doppler imaging for the assessment of myocardial viability

Технология сборки и сварки теплообменника аммиачной холодильной установки

Объектом является технологический процесс изготовления аммиачного теплообменника с использованием средств механизации и автоматизации сборочно-сварочных процессов. Цель работы – технология сборки и сварки теплообменника аммиачной холодильной установки. В процессе работы производился выбор методов сварки, сварочных материалов и оборудования. Разработка технологического процесса изготовления изделия с использованием средств механизации и автоматизации сборочно-сварочных процессов. Проведен технико–экономический анализ разработки технологии сборки и сварки теплообменника аммиачной холодильной установки. По оценке ресурсоэфективности проекта, можно сделать выводы, что она выше для технологического процесса автоматической сварки под флюсом, по сравнению с другими способами сварки.The object of the study is a technological process for the production of an ammonia heat exchanger using mechanization and automation equipment for assembly and welding processes. The purpose of the work is to increase the productivity of welding operations in the manufacture of the coolant shell of ammonia OA-1080. During the work he made a choice of welding methods, welding materials and equipment. Development of the technological process of manufacture using means of mechanization and automation of assembly and welding processes. The carried out technical and economic analysis of the development of technologies for assembling and welding the heat exchanger of an ammonia refrigeration plant. According to the project's resource efficiency

Design of virtual polygon in Unity3D

The paper is devoted to research and designing of autonomous car - a self-governing car in which artificial intelligence will take the role of driver. In today's world, the present invention is necessary because today humanity cannot imagine being without any types of transport