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排序方式: 共有833条查询结果,搜索用时 15 毫秒
121.
Armin Veitl 《中国照明》2009,(9):82-82
LED的散热问题将是限制它未来能否在市场上取得更大成功的主要因素。目前业界的很多研究都集中在散热器上,但对LED和散热表面之间的隔层研究较少。 相似文献
122.
He Q Tian Y Küller A Grunze M Gölzhäuser A Lil J 《Journal of nanoscience and nanotechnology》2006,6(6):1838-1841
The fabrication of lipid-modified molecular patterns by Chemical Lithography combined with interfacial chemical reactions is reported. In this method, self-assembled monolayers (SAMs) of 4'-nitro-1,1'-biphenyl-4-thiol (NBT) were structured by Chemical Lithography which produced cross-linked 4'-amino-1,1'-biphenyl-4-thiol (cABT) monolayers within a nitro-terminated (NBT) matrix. The terminal amino groups in the cABT monolayer were diazotized to create diazo cations, and the lipid monolayer with negative charge was assembled on the diazo regions by electrostatic attraction. Under the exposure of UV light, the photoreaction occurs. The diazonium groups interacting with the lipid headgroups via electrostatic attraction decompose and release N2 which leads to the lipid monolayer covalently attaching to the cABT region. The presence of phosphorus in X-ray photoelectron spectra (XPS) reveals the binding of the phospholipid layer to the cABT surface. Atomic force microscopy (AFM) images display that lipid-modified molecular patterns with different sizes and shapes and with a thickness of ca. 2.5 nm have been formed. The resulting lipid-modified molecular patterns are considered to be a first step towards obtaining stable biointerfacing patterns and studying biomolecular recognition. 相似文献
123.
Nick Anthony Eaves Armin Veshkini Christian Riese Qingan Zhang Seth Benjamin Dworkin Murray John Thomson 《Combustion and Flame》2012,159(10):3179-3190
A numerical study is conducted of ethane–air coflow diffusion flames at pressures from 2 to 15 atm. The model employed uses a detailed gas phase chemical kinetic mechanism that includes PAH formation and growth, and is coupled to a detailed sectional soot particle dynamics model. The model is able to accurately predict the trends observed experimentally with increasing pressure without any tuning of the model for different pressures. The model shows good agreement with the experimental data on both the flame wings and centerline regions. Peak wing and centerline soot volume fractions are found to scale with P2.49 and P2.02 respectively. This scaling compares well to that observed experimentally for methane–air and ethylene–air flames. As pressure is increased, the flame cross-sectional area decreases according to P?1.0 due to a constant mass flux and a thinning of the flame, which is consistent with experimental observations. Soot formation along the wings is seen to be surface growth dominated, while PAH condensation dominates centerline soot formation. Surface growth and PAH condensation increase with increasing pressure primarily due to both of these processes being a function of surface area. This causes increases in soot volume fraction to further accelerate surface growth and PAH condensation, acting in a positive feedback manner. This positive feedback mechanism is initiated by increases in reaction rates caused by increases in gas phase density. Additionally, the significance of surface growth decreases with increasing pressure, while the role of PAH condensation increases. 相似文献
124.
Zhitomirsky D Kramer IJ Labelle AJ Fischer A Debnath R Pan J Bakr OM Sargent EH 《Nano letters》2012,12(2):1007-1012
The size-effect tunability of colloidal quantum dots enables facile engineering of the bandgap at the time of nanoparticle synthesis. The dependence of effective bandgap on nanoparticle size also presents a challenge if the size dispersion, hence bandgap variability, is not well-controlled within a given quantum dot solid. The impact of this polydispersity is well-studied in luminescent devices as well as in unipolar electronic transport; however, the requirements on monodispersity have yet to be quantified in photovoltaics. Here we carry out a series of combined experimental and model-based studies aimed at clarifying, and quantifying, the importance of quantum dot monodispersity in photovoltaics. We successfully predict, using a simple model, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using this same experimentally tested model the implications of a broadened quantum dot population on device performance. We report that present-day colloidal quantum dot photovoltaic devices with typical inhomogeneous linewidths of 100-150 meV are dominated by surface traps, and it is for this reason that they see marginal benefit from reduction in polydispersity. Upon eliminating surface traps, achieving inhomogeneous broadening of 50 meV or less will lead to device performance that sees very little deleterious impact from polydispersity. 相似文献
125.
Hybrid passivated colloidal quantum dot solids 总被引:1,自引:0,他引:1
AH Ip SM Thon S Hoogland O Voznyy D Zhitomirsky R Debnath L Levina LR Rollny GH Carey A Fischer KW Kemp IJ Kramer Z Ning AJ Labelle KW Chou A Amassian EH Sargent 《Nature nanotechnology》2012,7(9):577-582
Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electron-hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device. 相似文献
126.
127.
In a mixed-model assembly line, different models of a common base product can be manufactured in intermixed production sequences. A famous solution approach for the resulting short-term sequencing problem is the so-called level scheduling problem, which aims at evenly smoothing the material requirements over time in order to facilitate a just-in-time supply. However, if materials are delivered in discrete quantities, the resulting spread of material usages implies that issued cargo carriers of a respective material remain at a station for a longer period of time. In practical applications with many materials required per station, this procedure might lead to bottlenecks with respect to the scarce storage space at stations. This paper investigates level scheduling under the constraint that the induced part usage patterns may not violate given storage constraints. The resulting sequencing problem is formalised and solved by suitable exact and heuristic solution approaches. 相似文献
128.
Noppadol Charbkaew Thanapong Suwanasri Teratam Bunyagul Armin Schnettler 《IEEJ Transactions on Electrical and Electronic Engineering》2012,7(1):13-22
Nowadays, the goals of electrical supply utilities are to reduce equipment failures, extend service life, increase equipment reliability, and reduce their related operating and maintenance costs. The high‐voltage circuit breaker is an important element in the electrical network. In order to determine or to detect abnormal conditions inside a circuit breaker, powerful vibration analytical techniques have been proposed. In this paper, a vibrational analysis is carried out by analyzing the signal in the time–frequency domain under no‐load switching operations with a commercially available high‐voltage puffer‐type circuit breaker without opening its major parts. Vibration of the circuit breaker poles, operating mechanism, and various monitored parameters were recorded under normal and variable operating conditions. Moreover, a synthetic mechanical damage introduced deliberately is also investigated. The experimental result indicates that mechanical defects can be detected by analyzing the vibration signal. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. 相似文献
129.
Araz Bidari Mohammad Reza Ganjali Yaghoub Assadi Armin Kiani Parviz Norouzi 《Food Analytical Methods》2012,5(4):695-701
In this work, we have developed a sensitive and cost-effective preconcentration and quantification methodology for total mercury (Hg) at trace levels in food supplements of marine origin. Dispersive liquid–liquid microextraction was successfully employed for the preconcentration of mercury at trace levels prior to inductively coupled plasma atomic emission spectrometry. The mercury was extracted as mercury-1, 5-diphenyl-3-formazathiol complex, at pH 1.0 mediated by multidroplet formation of microextraction solvent assisted by disperser solvent. The lower limit of detection obtained under the optimal conditions was 0.24 μg L−1. The calibration graphs were linear up to 500 μg L−1. The precision of the method in terms of relative standard deviation was 4.8% for the concentration of 100 μg L−1. In order to validate the proposed method, a certified reference material RTC-QCI-049 was analyzed with the proposed procedure. Moreover, potential interference by 20 species was also evaluated. 相似文献
130.
Two‐photon laser scanning microscopy as a useful tool for imaging and evaluating macrophage‐, IL‐4 activated macrophage‐ and osteoclast‐based In Vitro degradation of beta‐tricalcium phosphate bone substitute material 下载免费PDF全文
Daniela F. Duarte Campos Michael Vogt Markus Lindner Armin Kirsten Michael Weber Remco T. A. Megens Jürgen Pyta Martin Zenke Marc Van Zandvoort Horst Fischer 《Microscopy research and technique》2014,77(2):143-152
Two‐photon microscopy is an innovative technology that has high potential to combine the examination of soft and hard tissues in vitro and in vivo. Calcium phosphates are widely used substitutes for bone tissue engineering, since they are degradable and consequently replaced by newly formed tissue. It is well known that osteoclasts are responsible for the resorption processes during bone remodelling. We hypothesize that also macrophages are actively involved in the resorption process of calcium phosphate scaffolds and addressed this question in in vitro culture systems by two‐photon laser scanning microscopy. Beta‐tricalcium phosphate specimens were incubated with (1) macrophages, (2) interleukin‐4 activated macrophages, and (3) osteoclasts for up to 21 days. Interestingly, macrophages degraded beta‐tricalcium phosphate specimens in an equivalent fashion compared to osteoclasts and significantly more than IL‐4 activated macrophages. An average of ~32% of the macrophages was partially filled with ceramic material while this was 18% for osteoclasts and 9% for IL‐4 activated macrophages. For the first time by applying two‐photon microscopy, our studies show the previously unrecognized potential of macrophages to phagocytose ceramic material, which is expected to have implication on osteoconductive scaffold design. Microsc. Res. Tech. 77:143–152, 2014. © 2013 Wiley Periodicals, Inc. 相似文献