排序方式: 共有74条查询结果,搜索用时 15 毫秒
41.
An experimental apparatus was built to measure the time constant of fine wet-bulb thermocouples in air. Rapid response solenoid valves (15 msec response time) were used to control airflow through tubing into which wet-bulb thermocouples were placed. Wet-bulb thermocouples (type T, 0.005 cm diameter) with the tip (bead) covered with a moistened wick were tested. Experiments were performed for air velocities ranging from 1.50 to 2.5 m sec?1 (Reynolds number of 2,500 to 4,500) and wet-bulb temperature ranging from 12.5 to 17.4°C. Experimental conditions were selected to simulate human respiratory conditions. Correlation between airflow velocity and wet-bulb thermocouple time constants was not significant at all levels. 相似文献
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A quantum ring based intersubband photodetector is designed and its optical performance is studied based on a developed theoretical model. Intersubband absorption of quantum rings is numerically calculated for two transitions, from ground state to first excited state and to continuum energy and the effects of broadening mechanisms are studied. Device show responsivity about 0.2 A/W at T = 80 K and V = 2 V. Dark current of structure with and without the resonant tunneling barriers is calculated. Specific detectivity \((D^*)\) is studied at different temperatures and peak values about \(3\times 10^{12}\,\hbox {cm Hz}^{1/2}/\hbox {W}\) is obtained at T = 50 K. Results show that inclusion of resonant tunneling barriers leads to improvement in \(D^*\) about one order of magnitude. 相似文献
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Journal of Thermal Analysis and Calorimetry - This investigation provides a review on the applications of nanofluids in porous media. The transport phenomena in porous media have been of continuing... 相似文献
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Kambiz Abedi Vahid Ahmadi Mohammad Kazem Moravvej-Farshi 《Optical and Quantum Electronics》2009,41(10):719-733
The finite difference method is exploited for a full-vectorial analysis of mushroom-type waveguides for traveling wave electroabsorption
modulators (TWEAM) based on asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQW). In this analysis,
the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as
the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type
TWEAM based on AICD-SQW and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The
important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and
transverse mode confinement factor are calculated. Then, the transmission line microwave properties (microwave index, microwave
loss, and characteristic impedance) of TWEAMs are obtained. The modulation response of mushroom-type TWEAM is calculated using
circuit model by considering interaction between microwave and optical fields in waveguide and compared with conventional
ridge-type TWEAM. It is found that increasing the width of p-cladding layer with the same i-layer to reduce the resistance
in p-i-n mushroom-type waveguide of TWEAM based on AICD-SQW can improve the microwave propagation loss and thus the high-speed
electro-optical response. 相似文献
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Highly Regioselective and Diastereoselective,One‐Pot,Four‐Component Synthesis of Novel Spiroindenoquinoxalineindolizidine Derivatives 下载免费PDF全文
Mehdi Moemeni Hamid Arvinnezhad Saadi Samadi Farbod Salahi Khosrow Jadidi Behrouz Notash 《Journal of heterocyclic chemistry》2015,52(3):944-948
A one‐pot, four‐component procedure for the synthesis of novel spiroindenoquinoxalineindolizidines with high regioselectivity and diastereoselectivity from the 1,3‐dipolar cycloaddition of azomethine ylides, generated from indenoquinoxalines and pipecolinic acid, and chalcones is described. The reaction occurs under reflux of ethanol as a green solvent and in the absence of any catalyst. The cycloadducts are obtained purely without future purification. The regiochemistry and stereochemistry of resultant cycloadducts have been determined by several 2D‐NMR spectroscopic techniques and X‐ray single crystal diffraction. 相似文献
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To acquire accurate structural and dynamical information on complex biomolecular machines using single-molecule fluorescence resonance energy transfer (sm-FRET), a large flux of donor and acceptor photons is needed. To achieve such fluxes, one may use higher laser excitation intensity; however, this induces increased rates of photobleaching. Anti-oxidant additives have been extensively used for reducing acceptor's photobleaching. Here we focus on deciphering the initial step along the photobleaching pathway. Utilizing an array of recently developed single-molecule and ensemble spectroscopies and doubly labeled Acyl-CoA binding protein and double-stranded DNA as model systems, we study these photobleaching pathways, which place fundamental limitations on sm-FRET experiments. We find that: (i) acceptor photobleaching scales with FRET efficiency, (ii) acceptor photobleaching is enhanced under picosecond-pulsed (vs continuous-wave) excitation, and (iii) acceptor photobleaching scales with the intensity of only the short wavelength (donor) excitation laser. We infer from these findings that the main pathway for acceptor's photobleaching is through absorption of a short wavelength photon from the acceptor's first excited singlet state and that donor's photobleaching is usually not a concern. We conclude by suggesting the use of short pulses for donor excitation, among other possible remedies, for reducing acceptor's photobleaching in sm-FRET measurements. 相似文献
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Manuel Figueroa Kambiz Pourrezaei Somdev Tyagi 《Journal of Raman spectroscopy : JRS》2012,43(4):588-591
One of the most widely used methods for surface‐enhanced Raman scattering (SERS) employs silver or gold nanoparticles either in colloidal suspension or in the dry‐drop form. In such substrates the SERS amplification factors depend critically on the interparticle distances. Here, we report that microwave absorption as a function of temperature in dry‐drop substrates can be used as a probe to demarcate temperature regions for thermal annealing to produce SERS substrates with very high amplification factors. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Ding R Katebzadeh K Roman L Bergquist KE Lindström UM 《The Journal of organic chemistry》2006,71(1):352-355
[reaction: see text] Significant rate acceleration of metal-catalyzed Michael addition reactions in water was observed upon addition of small, dibasic ligands. Ytterbium triflate and TMEDA was the most effective combination leading to a nearly 20-fold faster reaction than in the absence of ligand. 相似文献