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排序方式: 共有573条查询结果,搜索用时 531 毫秒
61.
Phase transformations have been studied in glasses related in composition to Li2O-MgO-SiO2 (930° C) eutectic glass modified by replacement on a cation per cation basis. Crystallization processes and changes in the solid solutions of the mineral phases developed during the controlled heating of the glasses have been followed using X-ray and microscopic techniques.Solid solutions of lithia aluminosilicate phases (B-eucryptite and/or B-spodumene s.s.) are the essential minerals that crystallize in glasses through most of the heat treatment applied. Lithium metasilicate, disilicate, clinoenstatite and cordierite are also encountered.B-eucryptite s.s. is formed in early stage of crystallization of the glass which transforms into B-spodumene s.s. at higher temperature (800° C). However, in some cases, it persists at temperatures as high as 1000° C.Metastable B-eucryptite-B-quartz s.s. can accomodate considerable amounts of Mg2+ and Al3+ ions in its lattice especially at lower temperature. At higher temperature for long duration, a redistribution of the elements takes place, and the cordierite phase then developed. 相似文献
62.
A design is described which enables the accurate alignment of high voltage plane parallel electrodes used in an ultra-high vacuum assembly. The main features of this design are that it effectively overcomes the eccentricities which are present in both the glass-to-metal graded seal used in the housing envelope and in the linear motion drives employed to vary the gap separation between the electrodes, as well as being relatively simple to fabricate. The present design has been successfully tested in two large chambers at applied voltages of up to 100 kV and at a background pressure of better than 10?9 torr. 相似文献
63.
Wael Salman 《Chemical engineering science》2006,61(20):6653-6666
The formation of Taylor bubbles and resulting bubble lengths were studied in a ID vertical tube for air-water and air-octane systems. In the co-flow tube/nozzle arrangement two nozzle sizes were used as gas inlets. Superficial velocities varied between 0.001- for the liquid and 0.002- for the gas. Three different mechanisms of initial bubble formation were observed. Of the three mechanisms, mechanism 3 is periodic (with period consisting of a bubble and a liquid slug), reproducible and can be simply modelled. After initial bubble formation further modifications may occur in the formed bubble size by coalescence or pairing. Bubble pairing is encouraged by smaller nozzles and liquid flow rates, while coalescence is observed only for cases where non-Taylor bubbles form initially.Two simple models have been proposed, the first predicts the size of the Taylor bubbles formed by mechanism 3 while the second attempts to predict the condition for bubble pairing to occur. Reasonable agreement with experimental results validates the predictions of the first model for a strong dependence of the volume of Taylor bubbles formed on the gas and liquid flow rates, a moderate dependence on nozzle diameter and a weak dependence (if at all) on the surface tension of the liquid used. Mismatch with the experimental results is caused (at least in part) by the experimental setup where there was no perfect axial alignment of the gas inlet. The experiments also suffered from problems at the outlet at low flow rates where smooth bubble disengagement could not be ensured for long Taylor bubbles. The second model for pairing predicts its occurrence for concentric tube/nozzle arrangements as a function of flow rates and channel diameters. The model over-predicted the range of liquid flow rates at which pairing was observed experimentally, but it captured the form of the boundary between different bubble volume modification mechanisms when represented on superficial velocity graphs. 相似文献
64.
Salman E. Jakushokas R. Friedman E.G. Secareanu R.M. Hartin O.L. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2009,17(10):1405-1418
A methodology is proposed to efficiently analyze substrate noise coupled to a sensitive block due to an aggressor digital block in large-scale mixed-signal circuits. The methodology is based on identifying voltage domains on the substrate by exploiting the small spatial voltage differences on the ground distribution network of the aggressor circuit. Specifically, similarly biased regions on the substrate short-circuited by the ground network are determined, and each of these regions is represented by a single equivalent input port to the substrate. The remaining ports within that domain are ignored to reduce the computational complexity of the extraction process. An algorithm with linear time complexity is proposed to merge those substrate contacts exhibiting a voltage difference smaller than a specified value, identifying a voltage domain. An equivalent contact is placed at the geometric mean of the merged contacts, ignoring all of the remaining ports such as the source/drain junctions of the devices. The ground network impedance is updated for each merged contact based on the proposed algorithm to maintain sufficient accuracy of the noise voltage. The substrate with reduced input ports is extracted using an existing extraction tool to analyze the noise at the sense node. As compared to the full extraction of an aggressor circuit, the methodology achieves a reduction of more than four orders of magnitude in the number of extracted substrate resistors with a peak-to-peak error of 24%. 相似文献
65.
Anees A. Ansari M. A. M. Khan M. Naziruddin Khan Salman A. Alrokayan M. Alhoshan M. S. Alsalhi 《半导体学报》2011,32(4):043001-6
This paper reports the optical and electrical properties of electrochemically deposited polyaniline (PANI)-cerium oxide (CeO2) hybrid nano-composite film onto indium-tin-oxide (ITO) glass substrate. UV–visible spectroscopy and I-V characteristic were performed to study the optical and electrical parameters of the electrochemically deposited film. The film exhibited a strong absorption below 400 nm (3.10 eV) with a well defined absorbance peak at around 285nm (4.35 eV). The estimated band gap of the CeO2 sample was 3.44 eV and this value is higher than bulk CeO2 powder (Eg = 3.19 eV) due to quantum confinement effect. 相似文献
66.
In this paper, a self-tuning fuzzy PI controller (STFPIC) is proposed for thyristor-controlled series capacitor (TCSC) to improve power system dynamic performance. In a STFPIC controller, the output-scaling factor is adjusted on-line by an updating factor (α). The value of α is determined from a fuzzy rule-base defined on error (e) and change of error (Δe) of the controlled variable. The proposed self-tuning controller is designed using a very simple control rule-base and the most natural and unbiased membership functions (MFs) (symmetric triangles with equal base and 50% overlap with neighboring MFs). The comparative performances of the proposed STFPIC and the standard fuzzy PI controller (FPIC) have been investigated on two multi-machine power systems (namely, 4 machine, 2 area system and 10 machine 39 bus system) through detailed non-linear simulation studies using MATLAB/SIMULINK. From the simulation studies it has been found out that for damping oscillations, the performance of the proposed STFPIC is better than that obtained by the standard FPIC. Moreover, the proposed STFPIC as well as the FPIC have been found to be quite effective in damping oscillations over a wide range of operating conditions and are quite effective in enhancing the power carrying capability of the power system significantly. 相似文献
67.
Sami D. Salman 《亚洲传热研究》2019,48(8):3749-3762
This article presents the computational fluid dynamic simulation of the heat transfer characteristics induced by a swap swirl air‐jet generator on the impingement surface. The study was carried out for conventional and swap twist tape inserts of twisted ratio y = 2.93 with various swap angles (α = 30°, 60°, 90°) at a constant distance of nozzle diameter impingement plate (L = 2D). The results show that the Nusselt number of the swirl impingement air‐jet depends on the twisted tape swap angles and airflow rate. The results also showed that the swap angle of 90° gave notable uniform local heat transfer distribution compared with the typical twist tape and other swap twist tapes (α = 30°, 60°). In addition, the predicted results of the local heat transfer coefficient help explain the local turbulence intensity and generation to assist the industrial applications of swirl impingement air‐cooling jet. 相似文献
68.
69.
Salman Khan Mukhtaj Khan Nadeem Iqbal Mohd Amiruddin Abd Rahman Muhammad Khalis Abdul Karim 《计算机、材料和连续体(英文)》2022,72(2):2243-2258
Piwi-interacting Ribonucleic acids (piRNAs) molecule is a well-known subclass of small non-coding RNA molecules that are mainly responsible for maintaining genome integrity, regulating gene expression, and germline stem cell maintenance by suppressing transposon elements. The piRNAs molecule can be used for the diagnosis of multiple tumor types and drug development. Due to the vital roles of the piRNA in computational biology, the identification of piRNAs has become an important area of research in computational biology. This paper proposes a two-layer predictor to improve the prediction of piRNAs and their function using deep learning methods. The proposed model applies various feature extraction methods to consider both structure information and physicochemical properties of the biological sequences during the feature extraction process. The outcome of the proposed model is extensively evaluated using the k-fold cross-validation method. The evaluation result shows that the proposed predictor performed better than the existing models with accuracy improvement of 7.59% and 2.81% at layer I and layer II respectively. It is anticipated that the proposed model could be a beneficial tool for cancer diagnosis and precision medicine. 相似文献
70.
Xiaojun Wang Yaqiong Su Guorui Yang Guodong Chai Zhicheng Xu Muhammad Salman Nasir Xing Zheng Caiyun Wang Wei Yan 《International Journal of Hydrogen Energy》2021,46(21):11621-11635
The production of new solar fuel through CO2 photocatalytic reduction has aroused tremendous attention in recent years because of the increased demand of global energy sources and global warming caused by the mass concentration of CO2 in the earth's atmosphere. In this work, UiO-66-NH2 was co-modified by the Au nanoparticles (Au-NPs) and Graphene (GR). The resultant nanocomposite exhibits a strong absorption edge in visible light owing to the surface plasmon resonance (SPR) of Au-NPs. More attractively, Au/UiO-66-NH2/GR displays much higher photocatalytic activity (49.9 μmol) and selectivity (80.9%) than that of UiO-66-NH2/GR (selectivity: 71.6%) and pure UiO-66-NH2 (selectivity: 38.3%) for the CO2 reduction under visible light. The enhanced photocatalytic performance is primarily dued to the surface plasmon resonance (SPR) of Au-NPs, which could enhance the visible light absorption. The GR sheets could play as an electron acceptor with superior conductivity and thus suppress the recombination of electrons and holes. Besides, the GR could also improve the dispersibility of UiO-66-NH2 so as to expose more active sites and strengthen the capture of CO2. The contact effect and synergy effect among different samples are strengthened in the ternary composites and the photocatalytic performance is therefore improved. This study demonstrates a MOF based hybrid composite for efficient photocatalytic CO2 reduction, the findings not only prove great potential for the design and application of MOFs-based materials but also bring light to novel chances in the development of new high performance photocatalysts. 相似文献