Моделирование и тепловой анализ теплоотводящих слоев многослойной платы

Issues of heat dissipation in multilayer printed circuit boards (PCB) are very important due to the increasing density of installation of electronic components. There are many approaches to solving the problem of reducing the temperature of electronic components from conductive and convective heat removal in vacuum and normal operating conditions prior to the use of fans and cooling radiators. In multilayer printed circuit boards, the most efficient is the removal of heat using heat-removing layers made of materials with a high degree of heat transfer: copper, aluminium, magnesium, etc., and of sufficient thickness for efficient heat dissipation. At the same time, as experience shows, an unjustified increase in the thickness of the heat-removing layers in multilayer printed circuit boards leads to a deterioration in the weight characteristics of multilayer boards with an inefficient heat sink. Therefore, the study of the effective thickness of the heat-removing layers and the materials used in this process is an important and urgent problem. Mathematical modelling of the module of an aircraft instrument containing a multilayer printed circuit board with heat-removing layers of various materials has been carried out. The convergence of the calculation results is checked by reducing the mesh of the finite element mesh. Heat removal was taken into account at different thicknesses of the heat-removing layer. The dependence of the heat sink on the thickness of the heat sink layer of the multilayer printed circuit board was revealed. This dependence was nonlinear in nature: with an increase in the thickness of the heat sink layer, the relative value of the heat sink decreased. As a result, the optimum thickness of the heat sink layer was obtained, at which an increase in thickness slightly affected the heat removal.Проблемы рассеивания тепла в многослойных печатных платах имеют большое значение в связи с увеличением плотности монтажа электронных компонентов. Существует много подходов к решению проблемы снижения температуры электронных компонентов от кондуктивного и конвективного отвода тепла в вакууме и нормальных условиях эксплуатации до использования вентиляторов и радиаторов охлаждения. В многослойных печатных платах наиболее эффективным является отвод тепла с использованием теплоотводящих слоев, изготовленных из материалов с высокой степенью теплопередачи: меди, алюминия, магния и т. д. и достаточной толщины для эффективного отвода тепла. В то же время, как показывает опыт, необоснованное увеличение толщины теплоотводящих слоев в многослойных печатных платах приводит к ухудшению весовых характеристик многослойных плат с неэффективным теплоотводом. Поэтому изучение эффективной толщины теплоотводящих слоев и материалов, используемых в этом процессе, является важной и актуальной проблемой. Проведено математическое моделирование модуля авиационного прибора, содержащего многослойную печатную плату с теплоотводящими слоями из различных материалов. Сходимость результатов расчета проверяется путем уменьшения ячейки сетки конечных элементов. Отвод тепла учитывался при разных толщинах теплоотводящего слоя. Была выявлена зависимость теплоотвода от толщины теплоотводящего слоя многослойной печатной платы. Эта зависимость носила нелинейный характер: с увеличением толщины теплоотводящего слоя относительная величина теплоотвода уменьшалась. В результате была получена оптимальная толщина теплоотводящего слоя, при которой увеличение толщины незначительно повлияло на отвод тепла

Robotic systems: optimization of stiffness characteristics

Optimization methods of structure are considered. Methods have been developed for modeling robotic structure made of a multilayer composite material, including a three-layer one, consisting of external bearing layers and lightweight aggregate between the bearing layers. It is necessary to arrange the basis of the composite material along the lines of maximum stresses to obtain the most stiffness composite structure. The structure of a homogeneous material under operating loads was calculated to determine the lines of maximum stresses at the first stage, and the trajectories of the maximum tensile and compressive stresses were determined. The structure was modeled by composite materials at the second stage, and the basis of the composite material was located along the found paths of maximum stresses. The trajectories arrangement of the basis of the composite material were adjusted according to the results of the composite structure calculation at the third stage. The process continued until the true location of the composite base along the maximum stress paths was achieved. A multi-stage dynamic stand was considered as a robotic system designed for semi-natural modeling. The technique is proposed for approximating parts of robotic systems containing ring gears, motors, reduction gear, and bearing supports. The essence of the method was to determine the stiffness of ring gears, motors, reduction gear, bearing supports based on analytical methods. The resulting stiffness were assigned to the rod systems in the future, replacing the elements under consideration. Methods and algorithms for the frequency analysis and the optimization of the semi-natural modeling stands designed to simulate the flight characteristics in laboratory conditions have been developed. The developed methodology and algorithms allow you the following: to determine the frequency characteristics of the stand; to optimize the stands’ characteristics of various structures that have great technical, scientific and applied value. The analysis was carried out using finite element and analytical methods. The convergence of the calculation results was checked by increasing the number of finite elements, i.e. the thickening of the approximation grid. The last partition was considered sufficient to obtain reliable calculation results when the partition results of the previous and subsequent, the smaller ones do not differ by more than 3%. The data obtained as a result of the study for test problems were compared with the available experimental data. The good agreement was observed between theoretical and experimental results. The discrepancy was not more than 10%. The good agreement between theoretical and experimental results was observed. The discrepancy was not more than 10%

Моделирование тепловых режимов радиоэлектронного блока кассетной конструкции

The modelling and study of the thermal conditions of the electronic unit of the cassette design installed in the open compartment of the spacecraft on a thermal stabilization platform operated in a vacuum is considered. One of the main issues of heat removal from electronic components is the effect of the characteristics of the intermediate layers of a multilayer printed circuit board on effective heat dissipation. Effective heat removal means determining the thickness of the intermediate copper layer, which significantly affects the heat removal and determination of the thickness of which does not lead to heat removal, but only increases the mass characteristics of the electronic device, which is one of the main parameters in aerospace engineering. The problem is solved by the finite element method. The convergence of the results was checked by thickening the grid of finite elements. If the results of the previous and subsequent, partitions differ by no more than 2-3%, then it is considered that the results of the calculations are valid. Thermal calculation of the cassette, performed by the finite element method, and analysis of the results showed that the thickness of the intermediate copper layers nonlinearly affects the temperature distribution in electronic components, with the greatest effect being observed when the thickness of the intermediate copper layer less than 175 microns. When the thickness of the intermediate copper layer is more than 175 μm, heat removal is ineffective in terms of weight characteristics. The calculation results illustrated by the figures of the distribution of the temperature field during module operation are presented.Рассмотрено моделирование и исследование теплового режима электронного блока конструкции кассеты, установленного в открытом отсеке космического аппарата на платформе термостабилизации, работающей в вакууме. Одним из основных вопросов отвода тепла от электронных компонентов является влияние характеристик промежуточных слоев многослойной печатной платы на эффективное рассеяние тепла. Эффективный отвод тепла означает определение толщины промежуточного медного слоя, который существенно влияет на отвод тепла, и определение толщины которого не приводит к отводу тепла, а лишь увеличивает массовые характеристики электронного устройства, которое является одним из основных параметров в аэрокосмической технике. Задача решается методом конечных элементов. Сходимость результатов проверялась путем сгущения сетки конечных элементов. Если результаты предыдущего и последующих разбиений различаются не более чем на 2-3%, то считается, что результаты расчетов являются действительными. Тепловой расчет кассеты, выполненный методом конечных элементов, и анализ результатов показали, что толщина промежуточных слоев меди нелинейно влияет на распределение температуры в электронных компонентах, причем наибольший эффект наблюдается при толщине промежуточного слоя меди. менее 175 мкм. Когда толщина промежуточного медного слоя составляет более 175 мкм, отвод тепла неэффективен с точки зрения весовых характеристик. Представлены результаты расчетов, иллюстрируемые рисунками распределения температурного поля при работе модуля

Synthesis, characterization and biological evaluation of a new photoactive hydrogel against Gram-positive and Gram-negative bacteria

In 2013, the World Health Organization reported that 884 million people lack access to clean potable water. Photodynamic antimicrobial chemotherapy (PACT) is a very promising alternative to conventional antibiotics for the efficient inactivation of pathogenic microorganisms. We report the synthesis, characterization and antibacterial activity of a polyacrylamide-based hydrogel (7), with a new photoactive phenothiazinium compound (6) immobilized on it, to be used as a novel water-sterilizing device. The hydrogel was characterized by IR and scanning electron microscopy and incorporation of the dye confirmed by UV-visible spectroscopy. Antibacterial tests using the recombinant bioluminescent Gram-positive Staphylococcus aureus RN4220 and Gram-negative Escherichia coli DH5α were performed to assess the ability of the hydrogel to inactivate bacterial strains in solution. The hydrogel is characterized by a non-ordered microporous structure and is able to generate reactive oxygen species. The hydrogel is able to inactivate planktonic cells of the S. aureus and E. coli (3.3 log and 2.3 log killing, respectively) after 25 min of irradiation with white light at 14.5 mW cm−2. The contact surface does not influence the kill rates while the killing rate increased by increasing the total amount of the hydrogel (0.27 log drop to 1.65 log drop with 0.5 mg cm−3 to 2.5 mg cm−3 of total amount of dye). The hydrogel was found to be active for four cycles, suggesting the possibility of reuse and it was shown to be active against both Gram-positive and Gram-negative species with no leaching of the active molecule

Forecasting natural rubber price in Malaysia using Arima

This paper contains introduction, materials and methods, results and discussions, conclusions and references. Based on the title mentioned, high volatility of the price of natural rubber nowadays will give the significant risk to the producers, traders, consumers, and others parties involved in the production of natural rubber. To help them in making decisions, forecasting is needed to predict the price of natural rubber. The main objective of the research is to forecast the upcoming price of natural rubber by using the reliable statistical method. The data are gathered from Malaysia Rubber Board which the data are from January 2000 until December 2015. In this research, average monthly price of Standard Malaysia Rubber 20 (SMR20) will be forecast by using Box-Jenkins approach. Time series plot is used to determine the pattern of the data. The data have trend pattern which indicates the data is non-stationary data and the data need to be transformed. By using the Box-Jenkins method, the best fit model for the time series data is ARIMA (1, 1, 0) which this model satisfy all the criteria needed. Hence, ARIMA (1, 1, 0) is the best fitted model and the model will be used to forecast the average monthly price of Standard Malaysia Rubber 20 (SMR20) for twelve months ahead

The prediction of suspended solids of river in forested catchment using artificial neural network

This study presents an artificial neural network (ANN) model that is able to predict suspended solids concentrations in forested catchment namely Berring River, Kelantan, Malaysia.The network was trained using data collected during a period of 13 days in April 2001. The sampling location was established in the middle section of the river for collecting water samples. The study was carried out for a duration of two weeks in April 2001. The water sample was collected at 60% of the total depth from the river bed for every two hours starting from 6:00 am to 12:00 midnight for the whole duration of the study period. In this study five parameters were selected as input parameter for the network which are turbidity, flow velocity, depth, width, and weather condition of during the sampling period, while suspended solids as desire output. The data fed to the neural network were divided into two set: a training set and testing set. 116 of the data were used in training set and 24 remained as testing set. A network of the model was detected automatically by the network to give good predictions for both training and testing data set. A partitioning method of the connection weights of the network was used to study the relative percentage contribution of each of the input variables. It was found that turbidity and river width gives 73.03% and 24.73% each. The performance of the neural network model was measured by computing the correlation coefficient which gives the value of 0.93. It’s shown that the neural network gives superior predictions. Based on the results of this study, ANN modeling appears to be a promising technique for the prediction of suspended solids. Dynamic Metadata(s

Resistance of Human Cytomegalovirus to Cyclopropavir Maps to a Base Pair Deletion in the Open Reading Frame of \u3cem\u3eUL97\u3c/em\u3e

Human cytomegalovirus (HCMV) is a widespread pathogen in the human population, affecting many immunologically immature and immunocompromised patients, and can result in severe complications, such as interstitial pneumonia and mental retardation. Current chemotherapies for the treatment of HCMV infections include ganciclovir (GCV), foscarnet, and cidofovir. However, the high incidences of adverse effects (neutropenia and nephrotoxicity) limit the use of these drugs. Cyclopropavir (CPV), a guanosine nucleoside analog, is 10-fold more active against HCMV than GCV (50% effective concentrations [EC50s] = 0.46 and 4.1 μM, respectively). We hypothesize that the mechanism of action of CPV is similar to that of GCV: phosphorylation to a monophosphate by viral pUL97 protein kinase with further phosphorylation to a triphosphate by endogenous kinases, re- sulting in inhibition of viral DNA synthesis. To test this hypothesis, we isolated a CPV-resistant virus, sequenced its genome, and discovered that bp 498 of UL97 was deleted. This mutation caused a frameshift in UL97 resulting in a truncated protein that lacks a kinase domain. To determine if this base pair deletion was responsible for drug resistance, the mutation was engineered into the wild-type viral genome, which was then exposed to increasing concentrations of CPV. The results demonstrate that the engineered virus was approximately 72-fold more resistant to CPV (EC50 = 25.8 ± 3.1 μM) than the wild-type virus (EC50 = 0.36 ± 0.11 μM). We conclude, therefore, that this mutation is sufficient for drug resistance and that pUL97 is involved in the mechanism of action of CPV

Second T = 3/2 state in 9^9B and the isobaric multiplet mass equation

Recent high-precision mass measurements and shell model calculations~[Phys. Rev. Lett. {\bf 108}, 212501 (2012)] have challenged a longstanding explanation for the requirement of a cubic isobaric multiplet mass equation for the lowest $A = 9$ isospin quartet. The conclusions relied upon the choice of the excitation energy for the second $T = 3/2$ state in $^9$B, which had two conflicting measurements prior to this work. We remeasured the energy of the state using the $^9{\rm Be}(^3{\rm He},t)$ reaction and significantly disagree with the most recent measurement. Our result supports the contention that continuum coupling in the most proton-rich member of the quartet is not the predominant reason for the large cubic term required for $A = 9$ nuclei