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排序方式: 共有87条查询结果,搜索用时 15 毫秒
1.
Co-directional and bi-directional, co-polarized and cross-polarized characteristics of a lossless, matched four-port transmission network have been examined. For example, an arbitrary-inclined dielectric plate in a circular or square waveguide supporting dual-orthogonal linearly polarized modes has been analyzed, and a coordinate system is defined to apply for co-directional and bi-directional propagating circularly polarized waves. The matrix elements are polarization state and network dependent. Instead of using the terms network reciprocity and matrix symmetry, the matrix elements are discussed in terms of ratios to describe co-directional, bi-directional, co-polarized, cross-polarized, and polarization discrimination properties. Some of the ratios are equal to 1∠0° and others 1∠180°. Applications of this analysis are described. If the properties of the four-port network are frequency dependent and integrated over a bandwidth, and/or time dependent and integrated temporally, the scattering matrix formulation is not valid due to the presence of a randomly polarized component; in these cases a Mueller matrix is used to characterize the network 相似文献
2.
Numerical computations were made for a low-sidelobe-level 20-element symmetrical linear array whose equal-amplitude elements were spaced mostly equally (but some unequally) to yield aperture illumination densities along the array that approximate a truncated Gaussian distribution. It is argued that this design approach of using both equal and unequal interelement spacings and variations from the array analyzed should be investigated for large arrays and optimized for low sidelobe performance. Another design alternative for a large array is to have different size clusters of equally space elements with the intercluster spacings varied to attain desired tapered average illumination densities 相似文献
3.
Kentaro Yanagihara Jumpei Taketsugu Kiyoshi Fukui Shigeru Fukunaga Shinsuke Hara Ken-ichi Kitayama 《Wireless Personal Communications》2007,40(3):401-415
In this paper, we propose a new energy efficient clustering scheme with transmission power control named “EACLE” (Energy-Aware
CLustering scheme with transmission power control for sEnsor networks) for wireless sensor networks, which are composed of
the following three components; “EACLE clustering” is a distributed clustering method by means of transmission power control,
“EACLE routing” builds a tree rooted at a sink node and sets the paths from sensor nodes taking energy saving into consideration,
and “EACLE transmission timing control” changes the transmission timing with different levels of transmission power to avoid
packet collisions and facilitates packet binding.
With an indoor wireless channel model which we obtained from channel measurement campaigns in rooms and corridors and an energy
consumption model which we obtained from a measurement of a chipset, we performed computer simulations to investigate the
performance of EACLE in a realistic environment. Our simulation results indicate that EACLE outperforms a conventional scheme
such as EAD (Energy-Aware Data-centric routing) in terms of communication success rate and energy consumption. Furthermore,
we fully discuss the impact of transmission power and timing control on the performance of EACLE. 相似文献
4.
S. Y. Kim M. Harada H. Tomiyasu Y. Ikeda Y. Y. Park 《Progress in Nuclear Energy》2000,37(1-4):399-404
The structural and kinetic studies of U(VI) complex with benzamidoxime(Hba) as ligand in CD3COCD3 have been studied by means of 1H and 13C NMR. The Hba molecule was found to coordinate to UO22+ in the form of anionic benzamidoximate (ba), and the number of ba coordinated to UO22+ was determined to be 3 by analyzing the chemical shift of 13C NMR signal for Hba in the presence of UO22+. The exchange rate constants(kex) of ba in [UO2(ba)3] were determined by the NMR line-broadening method. The kinetic parameters were obtained as follows: kex(25°C) = 3.1 × 103s−1, ΔH≠ = 35.8 ± 3.5 KJ mol−1, and ΔS≠ = −65 ± 13.7 J K−1 mol−1. The UV-visible absorption spectra of solutions containing UO22+ and Hba were also measured. The molar extinction coefficient of the complex was found to be extremely large compared with those of UO2(L)52+ (L = unidentate oxygen donor ligands) complexes. This is due to the strong electron withdrawing of UO22+ from Hba and suggests that an interaction between UO22+ and Hba is very strong. Such a high affinity of monomeric amidoxime to UO22+ reasonably explains the high adsorptibility of amidoxime resin to U(VI) species, and is considered to result in the high recovery of U(VI) species from sea water using amidoxime resin. 相似文献
5.
Shan Liu Jumpei Washio Satoko Sato Yuki Abiko Yuta Shinohara Yuri Kobayashi Haruki Otani Shiori Sasaki Xiaoyi Wang Nobuhiro Takahashi 《International journal of molecular sciences》2022,23(2)
Metformin is a metabolic disruptor, and its efficacy and effects on metabolic profiles under different oxygen and nutrient conditions remain unclear. Therefore, the present study examined the effects of metformin on cell growth, the metabolic activities and consumption of glucose, glutamine, and pyruvate, and the intracellular ratio of nicotinamide adenine dinucleotide (NAD+) and reduced nicotinamide adenine dinucleotide (NADH) under normoxic (21% O2) and hypoxic (1% O2) conditions. The efficacy of metformin with nutrient removal from culture media was also investigated. The results obtained show that the efficacy of metformin was closely associated with cell types and environmental factors. Acute exposure to metformin had no effect on lactate production from glucose, glutamine, or pyruvate, whereas long-term exposure to metformin increased the consumption of glucose and pyruvate and the production of lactate in the culture media of HeLa and HaCaT cells as well as the metabolic activity of glucose. The NAD+/NADH ratio decreased during growth with metformin regardless of its efficacy. Furthermore, the inhibitory effects of metformin were enhanced in all cell lines following the removal of glucose or pyruvate from culture media. Collectively, the present results reveal that metformin efficacy may be regulated by oxygen conditions and nutrient availability, and indicate the potential of the metabolic switch induced by metformin as combinational therapy. 相似文献
6.
Transfer RNA (tRNA) is an essential component of the cell's translation apparatus. These RNA strands contain the anticodon for a given amino acid, and when "charged" with that amino acid are termed aminoacyl-tRNA. Aminoacylation, which occurs exclusively at one of the 3'-terminal hydroxyl groups of tRNA, is catalyzed by a family of enzymes called aminoacyl-tRNA synthetases (ARSs). In a primitive translation system, before the advent of sophisticated protein-based enzymes, this chemical event could conceivably have been catalyzed solely by RNA enzymes. Given the evolutionary implications, our group attempted in vitro selection of artificial ARS-like ribozymes, successfully uncovering a functional ribozyme (r24) from an RNA pool of random sequences attached to the 5'-leader region of tRNA. This ribozyme preferentially charges aromatic amino acids (such as phenylalanine) activated with cyanomethyl ester (CME) onto specific kinds of tRNA. During the course of our studies, we became interested in developing a versatile, rather than a specific, aminoacylation catalyst. Such a ribozyme could facilitate the preparation of intentionally misacylated tRNAs and thus serve a convenient tool for manipulating the genetic code. On the basis of biochemical studies of r24, we constructed a truncated version of r24 (r24mini) that was 57 nucleotides long. This r24mini was then further shortened to 45 nucleotides. This ribozyme could charge various tRNAs through very simple three-base-pair interactions between the ribozyme's 3'-end and the tRNA's 3'-end. We termed this ribozyme a "flexizyme" (Fx3 for this particular construct) owing to its flexibility in addressing tRNAs. To devise an even more flexible tool for tRNA acylation, we attempted to eliminate the amino acid specificity from Fx3. This attempt yielded an Fx3 variant, termed dFx, which accepts amino acid substrates having 3,5-dinitrobenzyl ester instead of CME as a leaving group. Similar selection attempts with the original phenylalanine-CME and a substrate activated by (2-aminoethyl)amidocarboxybenzyl thioester yielded the variants eFx and aFx (e and a denote enhanced and amino, respectively). In this Account, we describe the history and development of these flexizymes and their appropriate substrates, which provide a versatile and easy-to-use tRNA acylation system. Their use permits the synthesis of a wide array of acyl-tRNAs charged with artificial amino and hydroxy acids. In parallel to these efforts, we initiated a crystallization study of Fx3 covalently conjugated to a microhelix RNA, which is an analogue of tRNA. The X-ray crystal structure, solved as a co-complex with phenylalanine ethyl ester and U1A-binding protein, revealed the structural basis of this enzyme. Most importantly, many biochemical observations were consistent with the crystal structure. Along with the predicted three regular-helix regions, however, the flexizyme has a unique irregular helix that was unexpected. This irregular helix constitutes a recognition pocket for the aromatic ring of the amino acid side chain and precisely brings the carbonyl group to the 3'-hydroxyl group of the tRNA 3'-end. This study has clearly defined the molecular interactions between Fx3, tRNA, and the amino acid substrate, revealing the fundamental basis of this unique catalytic system. 相似文献
7.
Enhanced Light Storage of SrAl2O4 Glass‐Ceramics Controlled by Selective Europium Reduction 下载免费PDF全文
Takayuki Nakanishi Kazune Watanabe Jumpei Ueda Koji Fushimi Setsuhisa Tanabe Yasuchika Hasegawa 《Journal of the American Ceramic Society》2015,98(2):423-429
A luminescent Eu, Dy: SrAl2O4 glass‐ceramics with high transparency in the visible region was successfully synthesized using the frozen sorbet technique with the control of O2 partial pressure () for the oxidation of Eu2+ ions. The glass‐ceramics include Eu2+, Eu3+, and Dy3+ ions, and thus exhibits three characteristic types of emission bands, 4f–5d at around 520 nm (Eu2+ ions), 4f–4f at 610 nm (Eu3+ ions), and 480 nm (Dy3+ ions). The Eu, Dy: SrAl2O4 glass‐ceramics provide remarkable long‐persistent luminescence under dark condition. The glass‐ceramics also exhibits color‐changing luminescence in the visible region based on their remarkable light storage properties. The luminescent Eu, Dy: SrAl2O4 glass‐ceramics using the frozen sorbet technique with control of are promising materials for application in novel photonic and light storage materials. 相似文献
8.
Tomoo Yamamura Tomonori Mori Ki Chul Park Yasuhiko Fujii Hiroshi Tomiyasu 《The Journal of Supercritical Fluids》2009,51(1):43-49
Catalytic reduction gasification in the presence of ruthenium(IV) dioxide (RuO2) in supercritical water was used to decompose intractable biomass. The gasification of model biomass samples (glucose, cellulose, and heterocyclic compounds), and low-purity biomass samples obtained from a paper-recycling facility (paper sludge) and from a sewage treatment plant (sewage sludge) were studied. In clear contrast to another catalysts, the RuO2 catalyst completely gasified cellulose to produce mainly hydrogen, methane, and carbon dioxide under various conditions (e.g., 673 K at 30 MPa and 773 K at 50 MPa). As for heterocyclic compounds, nitrogen compounds did not deactivate the RuO2 catalyst; the gasification of carbazole proceeded completely. Furthermore, paper sludge was almost completely decomposed in supercritical water with RuO2 at 723 K. 相似文献
9.
Lütke-Eversloh T Fischer A Remminghorst U Kawada J Marchessault RH Bögershausen A Kalwei M Eckert H Reichelt R Liu SJ Steinbüchel A 《Nature materials》2002,1(4):236-240
The development of non-petrochemical sources for the plastics industry continues to progress as large multinationals focus on renewable resources to replace fossil carbon. Many bacteria are known to accumulate polyoxoesters as water-insoluble granules in the cytoplasm. The thermoplastic and/or elastomeric behaviour of these biodegradable polymers holds promise for the development of various technological applications. Here, we report the synthesis and characterization of microbial polythioesters (PTEs), a novel class of biopolymers of general technological relevance. Biosynthesis of PTE homopolymers was achieved using a recombinant strain of Escherichia coli that expressed a non-natural pathway consisting of a butyrate kinase, a phosphotransbutyrylase, and a PHA synthase. Different homopolymers were produced, consisting of either 3-mercaptopropionate, 3-mercaptobutyrate, or 3-mercaptovalerate repeating units, if the respective mercaptoalkanoic acids were provided as precursor substrates to the fermentative process. The PTEs contributed up to 30% (w/w) of the cellular dry weight and were identified as hydrophobic inclusions in the cytoplasm. The chemical and stereochemical homogeneity of the purified PTEs were identified by different methods, and the estimated physical properties were compared to the oxypolyester equivalents, revealing low crystalline order and, for the poly(3-mercaptopropionate) improved thermal stability. The ability to produce PTEs through a biosynthetic route opens up new avenues in the field of biomaterials. 相似文献
10.
laser bibliography, compiled during the period from July through December, 1965, contains 644 references which are divided into 25 subject categories and listed chronologically. Brief annotations are added to many references. 相似文献