Characterization of the functionally graded shear modulus of a half-space

In this article, a method is proposed for determining parameters of the exponentialy varying shear modulus of a functionally graded half-space. The method is based on the analytical solution of the problem of pure shear of an elastic functionally graded half-space by a strip punch. The half-space has the depth-wise exponential variation of its shear modulus, whose parameters are to be determined. The problem is reduced to an integral equation that is then solved by asymptotic methods. The analytical relations for contact stress under the punch, displacement of the free surface outside the contact area and other characteristics of the problem are studied with respect to the shear modulus parameters. The parameters of the functionally graded half-space shear modulus are determined (a) from the coincidence of theoretical and experimental values of contact stresses under the punch and from the coincidence of forces acting on the punch, or (b) from the coincidence of theoretical and experimental values of displacement of the free surface of the half-space outside the contact and coincidence of forces acting on the punch, or (c) from other conditions. The transcendental equations for determination of the shear modulus parameters in cases (a) and (b) are given. By adjusting the parameters of the shear modulus variation, the regions of "approximate-homogeneous" state in the functionally graded half-space are developed

Очистка околоземного космического пространства от космического мусора

The article deals with issues related to the removal of man-made space debris (SD) from the near-Earth space. SD is divided into observed (a typical size of over 100 mm) and unobserved ones. When encountering the observed SD, a spacecraft takes evasive maneuvers by changing the height. The International Space orbital station used to commit this maneuver more than once. Panels protect a spacecraft from unobserved debris. SD has emerged from the former used satellites, vehicle stages, and boosters still available on orbit, as well as a result of their destruction in case of explosion and collision. A large number of projects on removal of the near-Earth space from both the observed and the unobserved fragments of SD have been recently under development. There are offerings to remove SD via grapple fixtures, mesh-works, harpoons, etc. All anti-debris means are placed in the spacecraft (SC) and boosted into an orbit, and vehicle stages and boosters still remain on the orbit. Russia has set a Standard, which specifies the SD counter-measures. It gives recommendation for choosing the way of its disposal and dimensioning the fuel mass required for disposal in the dumping area. Selection of the dumping area depends on the altitude of a SD fragment. For high orbits the dumping area is selected according to GOST formulas. From the low orbits the fragments should be taken away to the Earth's atmosphere where they should be burned up. The calculations presented in the article show that with dumping area chosen properly the fuel mass required for maneuver is 10 - 15%. However, given the high cost of the spacecraft and its launch into orbit it is advisable to use the shuttle type vehicles similar to "Buran" and "Space Shuttle" to retrieve the spacecraft from the orbit. Space Shuttles were used to do similar work. This will allow preventing from near-Earth’s space debris due to available final vehicle stages and boosters, and, what is most important, after modernization and renovation the shuttle-retrieved spacecraft can be re-launched into space by the Space Shuttle. The special devices decelerate unobserved space debris of small size, which is moved to the low orbits and then into the Earth's atmosphere.В статье рассмотрены вопросы, связанные с очисткой околоземного космического пространства от фрагментов космического мусора (КМ) техногенного происхождения. КМ подразделяются на наблюдаемый (характерный размер более 100 мм) и не наблюдаемый. При встрече с наблюдаемым космическим мусором работающий космический аппарат совершает уклонение, переходя на другую высоту. Этот маневр неоднократно совершала Международная космическая орбитальная станция. От не наблюдаемого космического мусора космические аппараты защищаются с помощью панелей. Космический мусор возник в результате оставления на орбите отработавших свой срок космических аппаратов, ступеней ракет носителей и разгонных блоков, а также в результате разрушений этих объектов при взрывах и столкновениях. В последнее время разрабатывается большое количество проектов очистки околоземного космического пространства как от наблюдаемых, так и не наблюдаемых фрагментов КМ. Предлагают удалять КМ с помощью: захватов, сетей, гарпунов и др. Все средства борьбы с мусором размещаются на космических аппаратах (КА) и выводятся на орбиту, при этом на орбите остаются ступени ракет-носителей и разгонных блоков. В России существует ГОСТ в котором оговорены меры по борьбе с КМ. В нем рекомендуется на этапе проектирования КА выбирать способ его захоронения и закладывать массу топлива, необходимого для увода в зону захоронения. Выбор зоны захоронения зависит от высоты полета фрагмента КМ. Для высоких орбит зона захоронения выбирается по формулам, приведенным в ГОСТ. С низких орбит фрагменты следует уводить в атмосферу Земли, где они должны сгорать. Расчеты, приведенные в статье, показывают, что при правильном выборе зоны захоронения масса топлива, необходимая для выполнения маневра составит 10-..15% . Однако, учитывая высокую стоимость КА и их выведения на орбиту целесообразно снимать их с орбиты с помощью много разовых транспортных космических кораблей (МТКК), аналогичных «Бурану» и «Спейс Шаттл». Подобные работы проводились с использованием МТКК «Спейс Шаттл». Это позволит избежать засорения околоземного космического пространства последними ступенями ракет-носителей и разгонных блоков, а главное доставленный на Землю КА после модернизации и ремонта может быть снова выведен в космос с помощью МТКК. Мелкий, не наблюдаемый космический мусор тормозится специальными устройствами, которые переводят их на низкие орбиты, а затем в атмосферу Земли

Hydrophilic molecularly imprinted phenol-amine-formaldehyde resins

Hydrophilic molecularly imprinted resins (MIR), which are produced using hydrophilic monomers such as phenols, aldehydes, melamine or urea, have recently attracted increasing attention for use in separation and preconcentration. Among their obvious advantages are good sorption capacity, high recovery and selectivity, as well as their reusability in aqueous solutions. In this work we applied the bulk molecular imprinting method to produce quercetin-imprinted phenol-amino-formaldehyde resin. For this purpose, phloroglucinol and melamine solutions were mixed with formaldehyde and then polyethylene glycol and quercetin (Qu) were added to the obtained solution as a porogen and a template, respectively. The mixture was stirred under heating, then left in the thermostat for a continuous time. The optimum ratio of phloroglucinol to melamine was 3:1. The average molecular mass of porogen (Mw) varied between 4000–10000 Da. The obtained MIR were eluted with ethanol-water mixture (4:1, v/v) in the Soxhlet extractor for 36 h to remove the template. The MIR were characterized by FTIR-spectroscopy, laser diffraction spectroscopy and differential thermal analysis. The maximum recovery and sorption capacity of MIR synthesized in the presence of a porogen with Mw 10000 were 47% and 4.7 μmol Qu/g, respectively. The maximum imprinting factor was 1.41. The sorption kinetics of quercetin by a non-imprinted resin (NIR) is best described by a pseudo-second-order model, while MIR has a mixed pseudo-first-second-order mechanism

Analysis of a variant of current regulation with two regulators in high-power thyristor electric drives of rolling mills

Представленный материал посвящен анализу качества регулирования координат (тока, момента, скорости) в мощных тиристорных электроприводах постоянного тока (мощностью более 2000 кВт), выполненных с использованием эквивалентных 12-пульсных тиристорных преобразователей при параллельном включении вентильных секций через токоограничивающие дроссели и трехобмоточный силовой трансформатор. Рассмотрен вариант с индивидуальными регуляторами тока для каждой вентильной секции. В результате моделирования в среде Simulink и анализа, приведена оценка динамических показателей рассматриваемой системы. Даны рекомендации по применению варианта с индивидуальными регуляторами для каждой вентильной секции контуров регулирования тока (момента) электроприводов для прокатных станов.The presented material is devoted to the analysis of the quality of coordinate regulation (current, torque, speed) in high-power DC thyristor electric drives (with a capacity of more than 2000 kW), made using equivalent 12-pulse thyristor converters with parallel switching of valve sections through current-limiting chokes and a three-winding power transformer. A variant with individual current regulators for each valve section is considered. As a result of Simulink modeling and analysis, an assessment of the dynamic indicators of the system under consideration is given. Recommendations are given on the use of a variant with individual regulators for each valve section of the current (torque) control circuits of electric drives for rolling mills

Claisen-Umlagerung im Ruehr- und Durchflussbetrieb : Verstaendnis des Mechanismus und Steuerung der Einflussgroessen : the Claisen rearrangement in flow and batch processing : mechanism exploration and control over influencing factors.

Die Claisen-Umlagerung wurde in über 100 Jahren durch zahlreiche Forscher äußerst eingehend im Rührbetrieb untersucht. Insbesondere der Reaktionsmechanismus wurde in allen Details erforscht. Quantenmechanische Modellierung und moderne Kurzzeit-Spektroskopie haben hier ganz neue Impulse gegeben. Auch wurden schon erste Erfahrungen im Durchflussbetrieb in Mikroreaktoren gesammelt. Wie für viele andere Reaktionen so konnte eine massive Beschleunigung in neuen Prozessfenstern erreicht werden. Dieser Übersichtsartikel zeigt, dass das wahre Potenzial dennoch darauf wartet, für den Mikroreaktorbetrieb entdeckt zu werden. The Claisen rearrangement has been extensively studied over the past 100 years in batch mode. Especially the reaction mechanism has been determined in all details. Quantum-mechanical modelling and ultrashort pulse spectroscopy have recently provided entirely new insight. First experiments were carried out in microreactors using flow chemistry. An enhancement of the yield and selctivity in the new processing windows has been observed. This review shows, that the true and full potential has still not been fully explored for the microreactor processing

PLM-COMPETENCE FORMATION USING COMPUTATIONAL-GRAPHICAL PRACTICE

The description of a new kind of learning activity “Computational - graphical practice” is presented. This practice aimed at consolidating the knowledge and skills acquired by students in the study of the basic engineering disciplines and bridge the gap in the training of students in the field of PLM-technology. The goals, objectives, program practices and competencies, which should have a student after passing the training practice, are liste

Influence of anionic surfactant on stability of nanoparticles in aqueous solutions

Dispersion and aggregation of nanoparticles in aqueous solutions are important factors for safe and effective application of nanoparticles, for instance, in the oil industry. As conventional oil reserves are depleted, it is necessary to advance chemical enhanced oil recovery (cEOR) techniques to develop unconventional oil reservoirs. Nanoparticles modified by surfactants can be a promising reagent in cEOR. These nanomaterials can reduce interfacial tension and change the wettability of reservoir rock, which leads to an increase in oil recovery. However, the application of nanoparticles is limited by their substantial aggregation in aqueous solutions. The purpose of this work is to select nanoparticles for obtaining stable sols in water in the presence of an anionic surfactant and to optimize the conditions (pH) for further modifying the nanoparticles with the anionic surfactant. Sodium dodecyl sulfate (SDS) is used as an anionic surfactant. The aggregation of oxide and carbon nanoparticles in water and anionic surfactant solutions was studied by laser diffraction, dynamic and electrophoretic light scattering methods. Most of the studied nanoparticles in water form aggregates with bi-, three- and polymodal particle size distributions. TiO2 nanoparticles obtained by plasma dynamic synthesis form the most stable sols in anionic surfactant solutions. The range of 5–7 pH is defined as optimal for their modification with surfactants. The stability of carbon nanoparticles in aqueous solutions increases significantly in the presence of a surfactant. The obtained results form the basis for further research on the modification of marked nanoparticles in surfactant solutions