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排序方式: 共有810条查询结果,搜索用时 578 毫秒
111.
研究了双共焦波导回旋行波管高频结构的电磁特性。根据惠根斯原理的光衍射理论,分析得出双共焦波导中的两类本征模式(叠加模和环形模)对应的截止频率和场分布情况。理论分析结果与商用仿真软件CST的仿真结果一致。其中用作回旋行波管工作模式的“反相叠加TE06模”的损耗明显小于其他模式,这种不同模式损耗不同的特性将有效抑制竞争模式带来的寄生振荡。双共焦波导的模式密度略大于传统单共焦波导的模式密度,但是明显小于圆波导的模式密度,因此双共焦波导适合用作回旋行波管的高频结构。 相似文献
112.
A Nanostructuring Method to Decouple Electrical and Thermal Transport through the Formation of Electrically Triggered Conductive Nanofilaments
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![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
José Ramón Durán Retamal Chen‐Fang Kang Der‐Hsien Lien Wei‐Cheng Kuo Zhen‐Yu Juang Meng‐Lin Tsai Chih‐Hsiang Ho Jenh‐Yih Juang Vincent K. S. Hsiao Ying‐Hao Chu Lain‐Jong Li Yue Wu Jr‐Hau He 《Advanced materials (Deerfield Beach, Fla.)》2018,30(28)
Transforming thermal energy into electric energy and vice versa needs the decoupling of electrical transport from thermal transport. An innovative strategy is proposed by forming/disrupting electrically triggered conductive nanofilaments within semiconducting thin films to switch thermoelectric properties between two states without further material modification and manufacturing processes. It can also controllably adjust the degree of decoupling, providing a potential resolution and performance adjustability for heat/coldness control or power consumption reduction on demand. 相似文献
113.
Hao Wu Hui Ling Tan Cui Ying Toe Jason Scott Lianzhou Wang Rose Amal Yun Hau Ng 《Advanced materials (Deerfield Beach, Fla.)》2020,32(18):1904717
Photocatalytic and photoelectrochemical processes are two key systems in harvesting sunlight for energy and environmental applications. As both systems are employing photoactive semiconductors as the major active component, strategies have been formulated to improve the properties of the semiconductors for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Although there are universal strategies applicable to improve the performance of photoactive semiconductors, similarities and differences exist when the semiconductors are to be used differently. Here, considerations on selected typical factors governing the performances in photocatalytic and photoelectrochemical systems, even though the same type of semiconductor is used, are provided. Understanding of the underlying mechanisms in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a general guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuel generation. 相似文献
114.
Shuyu Bao Yue Wang Khaw Lina Li Zhang Bing Wang Wardhana Aji Sasangka Kenneth Eng Kian Lee Soo Jin Chua Jurgen Michel Eugene Fitzgerald Chuan Seng Tan Kwang Hong Lee 《半导体学报》2021,42(2):83-102
The heterogeneous integration of Ⅲ-Ⅴ devices with Si-CMOS on a common Si platform has shown great promise in the new generations of electrical and optical systems for novel applications,such as HEMT or LED with integrated control cir-cuitry.For heterogeneous integration,direct wafer bonding(DWB)techniques can overcome the materials and thermal mis-match issues by directly bonding dissimilar materials systems and device structures together.In addition,DWB can perform at wafer-level,which eases the requirements for integration alignment and increases the scalability for volume production.In this paper,a brief review of the different bonding technologies is discussed.After that,three main DWB techniques of single-,double-and multi-bonding are presented with the demonstrations of various heterogeneous integration applications.Mean-while,the integration challenges,such as micro-defects,surface roughness and bonding yield are discussed in detail. 相似文献
115.
Nuclear Magnetic Resonance Investigation of the Effect of pH on Micelle Formation by the Amino Acid‐Based Surfactant Undecyl l‐Phenylalaninate
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Gabriel A. Rothbauer Elisabeth A. Rutter Chelsea Reuter‐Seng Simon Vera Eugene J. Billiot Yayin Fang Fereshteh H. Billiot Kevin F. Morris 《Journal of surfactants and detergents》2018,21(1):139-153
Micelle formation by the anionic amino acid‐based surfactant undecyl l ‐phenylalaninate (und‐Phe) was investigated as a function of pH in solutions containing either Na+, l ‐arginine, l ‐lysine, or l ‐ornithine counterions. In each mixture, the surfactant's critical micelle concentration (CMC) was the lowest at low pH and increased as solutions became more basic. Below pH 9, surfactant solutions containing l ‐arginine and l ‐lysine had lower CMC than the corresponding solutions with Na+ counterions. Nuclear magnetic resonance (NMR) diffusometry and dynamic light scattering studies revealed that und‐Phe micelles with Na+ counterions had hydrodynamic radii of approximately 15 Å throughout the investigated pH range. Furthermore, l ‐arginine, l ‐lysine, and l ‐ornithine were found to bind most strongly to the micelles below pH 9 when the counterions were cationic. Above pH 9, the counterions became zwitterionic and dissociated from the micelle surface. In und‐Phe/l ‐arginine solution, counterion dissociation was accompanied by a decrease in the hydrodynamic radius of the micelle. However, in experiments with l ‐lysine and l ‐ornithine, micelle radii remained the same at low pH when counterions were bound and at high pH when they were not. This result suggested that l ‐arginine is attached perpendicular to the micelle surface through its guanidinium functional group with the remainder of the molecule extending into solution. Contrastingly, l ‐lysine and l ‐ornithine likely bind parallel to the micelle surface with their two amine functional groups interacting with different surfactant monomers. This model was consistent with the results from two‐dimensional ROESY (rotating frame Overhauser enhancement spectroscopy) NMR experiments. Two‐dimensional NMR also showed that in und‐Phe micelles, the aromatic rings on the phenylalanine headgroups were rotated toward the hydrocarbon core of micelle. 相似文献
116.
Oligomeric Composition of Polyols From Fatty Acid Methyl Ester: The Effect of Ring‐Opening Reactants of Epoxide Groups
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![点击此处可从《Journal of the American Oil Chemists](/ch/ext_images/free.gif)
Tuan Noor Maznee Tuan Ismail Nor Azowa Ibrahim Mohd Azmil Mohd Noor Seng Soi Hoong Kosheela Devi Poo Palam Shoot Kian Yeong Zainab Idris Christi M. Schiffman Ibrahim Sendijarevic Emilia Abd Malek Norhazlin Zainuddin Vahid Sendijarevic 《Journal of the American Oil Chemists' Society》2018,95(4):509-523
Commercial availability of fatty acid methyl ester (FAME) from palm oil targeted for biodiesel offers a good feedstock for the production of structurally well‐defined polyols for polyurethane applications. The effect of molecular weight (MW), odd and even carbon numbers, and the linear and branched structure reactants used in the ring‐opening reaction of epoxidized fatty acid methyl ester (E‐FAME) on the properties of polyols was investigated. Conversions of E‐FAME to PolyFAME polyols were confirmed by Fourier transform infrared analysis, oxirane oxygen content, and hydroxyl number. Gel permeation chromatography (GPC) calibrated against polyether polyols as a standard and vapor pressure osmometry were used for MW determination. GPC chromatograms of PolyFAME polyols clearly demonstrated the formation of oligomers during ring‐opening reactions. MW, and odd and even carbon numbers in a structure of linear diols and branched diol used in the syntheses of PolyFAME polyols did not have an effect on crystallinity, glass transition, or melt temperatures measured using Differential scanning calorimetry (DSC). PolyFAME polyols ring‐opened with water, methanol, and 1,2‐propanediol contained secondary hydroxyl groups, whereas PolyFAME polyols ring‐opened with linear diols contained a mixture of primary and secondary hydroxyl groups. It was found that the concentration of primary hydroxyl groups increased significantly by increasing the number of carbons from C2 to C3 in the linear diols. The viscosity of PolyFAME polyols also increased with the MW of linear diols used in the E‐FAME ring‐opening reaction. These findings would be beneficial for formulators in choosing the most cost effective polyols for polyurethane formulations. 相似文献
117.
Physicochemical stability of calcium alginate beads immobilizing TiO2 nanoparticles for removal of cationic dye under UV irradiation
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Recently, there have been considerable interests to immobilize photocatalyst in alginate beads for removing pollutants from water sources. However, the feasibility of using alginate beads in industry largely depends on its long‐term stability during operation. This study investigated the physicochemical stability of alginate/titanium dioxide beads (Alg/TiO2) when exposed to UV irradiation in aqueous environment. The degradation of Alg/TiO2 beads was evident because the diameter and mass of the beads was reduced by 12% and 40%, respectively, after 120 h of irradiation. A substantial amount of TiO2 was leached into the external medium. Consequently, the removal efficiency of model cationic dye was found to reduce after every process cycle. Morphological analysis showed the formation of cavities on the surface of the Alg/TiO2 beads. Interestingly, the blank alginate beads degraded more rapidly than the Alg/TiO2 beads, confirming the UV‐shielding effect of TiO2. Nevertheless, this study reveals the need to improve the UV stability of alginate‐based beads before they can be considered for practical application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45002. 相似文献
118.
Dr. Christina Haußner Dominik Damm Sandra Nirschl Anette Rohrhofer Prof. Dr. Barbara Schmidt Prof. Dr. Jutta Eichler 《Chembiochem : a European journal of chemical biology》2017,18(7):647-653
The broadly neutralizing HIV‐1 antibody b12 recognizes the CD4 binding site of the HIV‐1 envelope glycoprotein gp120 and efficiently neutralizes HIV‐1 infections in vitro and in vivo. Based on the 3D structure of a b12 ? gp120 complex, we have designed an assembled peptide (b12‐M) that presents the parts of the three heavy‐chain complementarity‐determining regions (CDRs) of b12, which contain the contact sites of the antibody for gp120. This b12‐mimetic peptide, as well as a truncated peptide presenting only two of the three heavy‐chain CDRs of b12, were shown to recognize gp120 in a similar manner to b12, as well as to inhibit HIV‐1 infection, demonstrating functional mimicry of b12 by the paratope mimetic peptides. 相似文献
119.
An experimental study was undertaken to determine the effects of administering shock loads of sucrose to a laboratory-scale anaerobic effluent treatment plant (UASB reactor) treating diluted landfill leachate. Administration of shock loads of 10 g l− sucrose caused accumulations of up to 7 g l−1 of l-lactate and the resultant acidity caused the pH value of the reactor effluent to drop from 7.2 to 4.7 which inhibited methanogenesis.Major disturbances in the composition of the biogas also occurred and, under the severest conditions, the biogas contained up to 30% (v/v) hydrogen. 相似文献
120.