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排序方式: 共有3433条查询结果,搜索用时 15 毫秒
41.
Dejan Reljic Vladimir Katic Veran Vasic 《电力电子》2005,3(2):59-62,75
因为人们越来越多地使用非线性负载,电网中就存在电源质量问题。在交流传动系统中广泛使用功率变换器,由于其非线性的工作运行状态,导致电压发生畸变,从而影响敏感设备的性能。本文试图分析由功率变换器供电的电梯交流传动系统对电源质量的影响。敏感电气设备和电梯交流传动系统都连接到0.4kV输电线路上。因功率逆变器导致的电压畸变能够导致系统故障甚至电气设备中部分元件的损坏。 相似文献
42.
Maxim L. Kulygin Gregory G. Denisov Vladimir V. Kocharovsky 《Journal of Infrared, Millimeter and Terahertz Waves》2010,31(1):31-40
Problems of high-power microwaves penetrating into and reflecting from a semiconductor (silicon) plate with non-stationary
processes are investigated. The plate is the basis of switches activated by laser-driven photoconductivity which changes its
properties when heated by the switched microwave power. Analytical criteria for the stationary solutions of the activated
(quasi-metallic) and deactivated (dielectric) states of the switch under the conditions of high-power microwave heating and
external cooling are found. Results of numerical simulations are also given for the problems of the switch activation by microwave
heating initiated by pulsed laser radiation, which increases the carrier density rapidly. Numerical simulations are carried
out using the finite-difference time-domain method with the unsplit perfectly matched layer absorbing boundary conditions.
We demonstrate various types of solutions depending on the basic parameters of the problems - microwave field intensity, laser
pulse energy and semiconductor doping. 相似文献
43.
Venema B Blanik N Blazek V Gehring H Opp A Leonhardt S 《IEEE transactions on bio-medical engineering》2012,59(7):2003-2010
Pulse oximetry is a well-established, noninvasive photoplethysmographic method to monitor vital signs. It allows us to measure cardiovascular parameters, such as heart rate and arterial oxygen saturation, and is considered an essential monitoring tool in clinical routine. However, since many of the conventional systems work in transmission mode, they can only be applied to the thinner or peripheral parts of the body, such as a finger tip. This has the major disadvantage that, in case of shock-induced centralization and a resulting drop in perfusion, such systems cannot ensure valid measurements. Therefore, we developed a reflective in-ear sensor system that can be worn in the ear channel like a headphone. Because the sensor is integrated in an ear mold and positioned very close to the trunk, reliable measurement is expected even in case of centralization. An additional advantage is that the sensor is comfortable to wear and has considerable resistance to motion artifacts. In this paper, we report on hypoxia studies with ten healthy participants which were performed to analyze the system with regard to the detection of heart rate and arterial oxygen saturation. It was shown earlier that, due to the high signal quality, heart rate can easily be detected. Using the conventional calculation principle, based on Beer-Lambert's law combined with a single-point calibration method, we now demonstrate that the detection of arterial oxygen saturation in the human ear canal is possible using reflective saturation sensors. 相似文献
44.
Evidence for biotic control of Australian reservoir phytoplankton communities and the potential for applied biomanipulation 总被引:1,自引:0,他引:1
Vladimir Matveev 《Lakes & Reservoirs: Research and Management》1998,3(2):105-111
Although some concerns have been expressed with respect to the applicability of biomanipulation to Australian reservoirs and other inland waters, no major obstacles were found in this review. The previous doubts stimulated research, which has provided evidence for unexpected mechanisms of food web interactions, such as positive effects of small copepods on planktonic algae, higher than usual grazing potential of cladoceran communities, and direct positive effects of planktivores on phytoplankton. Further research into zooplankton-cyanobacteria interactions should indicate how widespread is the previously reported ability of some southern hemisphere crustaceans to benefit at a population level from feeding on cyanobacteria. Quantitative fisheries acoustics, which has not been widely used in biomanipulation trials before, is a promising new tool in the assessment of the biomass of planktivorous fish in the pelagic zone of reservoirs. 相似文献
45.
Ggoch Ddeul Han William R. Collins Trisha L. Andrew Vladimir Bulović Timothy M. Swager 《Advanced functional materials》2013,23(24):3061-3069
New tetraalkylcyclobutadiene–C60 adducts are developed via Diels–Alder cycloaddition of C60 with in situ generated cyclobutadienes. The cofacial π‐orbital interactions between the fullerene orbitals and the cyclobutene are shown to decrease the electron affinity and thereby increase the lowest unoccupied molecular orbital (LUMO) energy level of C60 significantly (ca. 100 and 300 meV for mono‐ and bisadducts, respectively). These variations in LUMO levels of fullerene can be used to generate higher open‐circuit voltages (VOC) in bulk heterojunction polymer solar cells. The tetramethylcyclobutadiene–C60 monoadduct displays an open‐circuit voltage (0.61 V) and a power conversion efficiency (2.49%) comparable to the widely used P3HT/PCBM (poly(3‐hexylthiophene/([6,6]‐phenyl‐C61‐butyric acid methyl ester) composite (0.58 V and 2.57%, respectively). The role of the cofacial π‐orbital interactions between C60 and the attached cyclobutene group was probed chemically by epoxidation of the cyclobutene moiety and theoretically through density functional theory calculations. The electrochemical, photophysical, and thermal properties of the newly synthesized fullerene derivatives support the proposed effect of functionalization on electron affinities and photovoltaic performance. 相似文献
46.
Vladimir Svrcek Katerina Dohnalova Davide Mariotti Minh Tuan Trinh Rens Limpens Somak Mitra Tom Gregorkiewicz Koiji Matsubara Michio Kondo 《Advanced functional materials》2013,23(48):6051-6058
Substantial improvements of the absolute photoluminescence quantum yield (QY) for surfactant‐free silicon nanocrystals (Si‐ncs) by atmospheric pressure microplasma 3‐dimensional surface engineering are reported. The effect of surface characteristics on carrier multiplication mechanisms is explored using transient induced absorption and photoluminescence QY. Surface engineering of Si‐ncs is demonstrated to lead to more than 120 times increase in the absolute QY (from 0.1% up to 12%) within an important spectral range of the solar emission (2.3–3 eV). The Si‐ncs QY is shown to be stable when Si‐ncs are stored in ethanol at ambient conditions for three months. 相似文献
47.
Srinivasa R Raghavan Vladimir Ladik Klemens B Meyer 《IEEE transactions on information technology in biomedicine》2005,9(2):229-238
The complexity, variability, quantitative nature, and data density of treatment for chronic kidney failure make dialysis information systems excellent candidates for computerized decision support. We describe the development of an intelligent system building on existing knowledge and susceptible to reconfiguration on the basis of knowledge acquired during the use of the system. Various decision support techniques were used to design and develop the decision support modules. This paper briefly reviews the literature on clinical decision support, discusses some of the problems faced by practitioners in managing chronic kidney failure (end-stage renal disease) patients, and sets forth the decision support techniques used in developing a dialysis decision support system. 相似文献
48.
Chloride and Indium‐Chloride‐Complex Inorganic Ligands for Efficient Stabilization of Nanocrystals in Solution and Doping of Nanocrystal Solids 下载免费PDF全文
Vladimir Sayevich Chris Guhrenz Maria Sin Volodymyr M. Dzhagan Alexander Weiz Daniel Kasemann Eike Brunner Michael Ruck Dietrich R. T. Zahn Karl Leo Nikolai Gaponik Alexander Eychmüller 《Advanced functional materials》2016,26(13):2163-2175
Here, the surface functionalization of CdSe and CdSe/CdS core/shell nanocrystals (NCs) with compact chloride and indium‐chloride‐complex ligands is reported. The ligands provide not only short interparticle distances but additionally control doping and passivation of surface trap states, leading to enhanced electronic coupling in NC‐based arrays. The solids based on these NCs show an excellent electronic transport behavior after heat treatment at the relatively low temperature of 190 °C. Indeed, the indium‐chlorido‐capped 4.5 nm CdSe NC based thin‐film field‐effect transistor reaches a saturation mobility of μ = 4.1 cm2 (V s)?1 accompanied by a low hysteresis, while retaining the typical features of strongly quantum confined semiconductor NCs. The capping with chloride ions preserves the high photoluminescence quantum yield ( ≈ 66%) of CdSe/CdS core/shell NCs even when the CdS shell is relatively thin (six monolayers). The simplicity of the chemical incorporation of chlorine and indium species via solution ligand exchange, the efficient electronic passivation of the NC surface, as well as their high stability as dispersions make these materials especially attractive for wide‐area solution‐processable fabrication of NC‐based devices. 相似文献
49.
50.
James S. Bendall Marzia Paderi Francesca Ghigliotti Nello Li Pira Vitoguido Lambertini Vladimir Lesnyak Nikolai Gaponik Giuseppe Visimberga Alexander Eychmüller Clivia M. Sotomayor Torres Mark E. Welland Christina Gieck Leonardo Marchese 《Advanced functional materials》2010,20(19):3298-3302
A novel all‐inorganic electroluminescent device is demonstrated based on highly luminescent CdTe nanocrystals intercalated within a laminar hydrotalcite‐like structure. The laminar scaffold acts to both support and distribute the CdTe nanocrystals. The device is synthesized using simple wet chemical processes at room temperature in ambient conditions. It has high thermal stability, operating continuously up to 90 °C, and a maximum efficiency at J = 0.12 A cm?2. The device is targeted at the automotive industry. 相似文献