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排序方式: 共有190条查询结果,搜索用时 31 毫秒
81.
82.
Fabrice Onofri Thierry Girasole Grard Grhan Grard Gouesbet Günter Brenn Joachim Domnick Tian-Hua Xu Cameron Tropea 《Particle & Particle Systems Characterization》1996,13(2):112-124
The principle of the dual burst technique (DBT) based on phase-Doppler anemometry (PDA) is proposed for simultaneous particle refractive index, size and velocity measurements. This technique used the trajectory effects in PDA systems to separate the two contributions of the different scattering processes. In the case of forward scattering and refracting particles, it is shown that from the phase of the reflected contribution, the particle diameter can be deduced, whereas from the refracted contribution the particle refractive index and velocity can be obtained. Furthermore, the intensity ratio of these two scattering processes can be used for absorption measurements. Simulations based on generalized Lorenz-Mie theory and experimental tests using monodispersed droplets of different refractive indices and absorption coefficients have validated this technique. 相似文献
83.
Khwaja M. Rahman Cam Nguyen 《International Journal of Infrared and Millimeter Waves》1994,15(7):1297-1314
Coplanar waveguide has found increasing use in microwave and millimeter-wave integrated circuits, and a knowledge of its eigenmodes is very useful for circuit design. In this paper, we determine the dispersion properties of the eigenmodes in a shielded multilayer coplanar waveguide using the spectral domain approach. Numerical results of the propagation constants for different combinations of dielectric materials are presented to illustrate the behaviors of the eigenmodes. 相似文献
84.
G. C. Galletti Paola Bocchini Darinn Cam Giuseppe Chiavari Rocco Mazzeo 《Fresenius' Journal of Analytical Chemistry》1997,357(8):1211-1214
A black crust sample from the stony central portal of the abbey of St. Denis, France, was analyzed by chromatographic and
spectroscopic techniques to determine whether it was due to atmospheric pollution or to the degradation of a past restoration
treatment. Stratigraphic surveys by optical microscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron
microscopy/energy dispersive X-ray fluorescence (SEM/EDX) and pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS) were
consistent in ascribing the bulk of the crust to gypsum (CaSO4 ⋅ 2H2O) with inclusion of carbon particulate. The organic fraction was a minor constituent of the black crust. Hence, the deterioration
by an organic substance used in the past to restore the building was ruled out.
Received: 23 May 1996/Revised: 29 July 1996/Accepted: 1 August 1996 相似文献
85.
Ricardo J. N. Bettencourt da Silva Maria João Lino Júlia Ribeiro Santos M. Filomena G. F. C. Camões 《Accreditation and quality assurance》2002,7(5):195-201
Food chemical control, particularly control involving the analysis of pesticide residues in fruits and vegetables, is routinely
performed on composite samples. This sample design is adequate for the control of the majority of pesticides which have only
long-term effects. However, from the viewpoint of consumer risk assessment, this sample design is inadequate for pesticides
with relevant acute toxicity, when their residues occur in large food items the consumption of which may represent an important
fraction of a single meal or an important fraction of the consumption in 24 h. This work presents the results of the Portuguese
official pesticide residue control authority concerning the variability of methamidophos concentration in sweet pepper units,
collected from the market, in the framework of the EU 1999 co-ordinated programme for the official control of pesticides in
products of vegetable origin. The results were expressed with uncertainty and the conclusion was that the observed dispersion
cannot be allocated to the method precision. The studied samples presented a variability factor (ratio between the maximum
and the mean concentration of the units) ranging from 1.8 to 3.5 supporting the need to consider a variability factor representing
the potential unit-to-unit variation in residues concentration for the purpose of consumer risk assessment.
Received: 8 December 2001 Accepted: 25 February 2001 相似文献
86.
The erosion process of a stably stratified light gas layer by a vertical turbulent fountain of denser fluid inside a generic containment – for which experimental reference data are available – is studied computationally using large eddy simulation (LES). In addition, various Reynolds averaged Navier–Stokes (RANS) models are applied aiming at a comparative assessment of different computational approaches for the considered case. With the LES methodology included into the present modelling study, a novelty to date is established for fountain-stratification interaction inside generic containments. The high Reynolds number RANS models applied in the framework of this study include both the realisable k–? eddy viscosity model (EVM) as well as the basic Reynolds stress model (RSM). Furthermore, we show that certain regimes of the present configuration can be predicted using an analytically derived scaling approach. Various data beyond the experimentally obtained ones are computationally provided in order to facilitate the calibration of less costly statistical turbulence models and lumped parameter codes, since the presently considered configuration is regarded to be a valuable small-scale equivalent for containment flow applications. 相似文献
87.
Dr. William M. Hewitt Dr. George T. Lountos Dr. Katherine Zlotkowski Samuel D. Dahlhauser Dr. Lindsey B. Saunders Danielle Needle Dr. Joseph E. Tropea Chendi Zhan Dr. Guanghong Wei Dr. Buyong Ma Dr. Ruth Nussinov Dr. David S. Waugh Dr. John S. Schneekloth Jr. 《Angewandte Chemie (International ed. in English)》2016,55(19):5703-5707
Conjugation of the small ubiquitin‐like modifier (SUMO) to protein substrates is an important disease‐associated posttranslational modification, although few inhibitors of this process are known. Herein, we report the discovery of an allosteric small‐molecule binding site on Ubc9, the sole SUMO E2 enzyme. An X‐ray crystallographic screen was used to identify two distinct small‐molecule fragments that bind to Ubc9 at a site distal to its catalytic cysteine. These fragments and related compounds inhibit SUMO conjugation in biochemical assays with potencies of 1.9–5.8 mm . Mechanistic and biophysical analyses, coupled with molecular dynamics simulations, point toward ligand‐induced rigidification of Ubc9 as a mechanism of inhibition. 相似文献
88.
Gerbaux P Dechamps N Flammang R Nam PC Nguyen MT Djazi F Berruyer F Bouchoux G 《The journal of physical chemistry. A》2008,112(24):5418-5428
The C2H4NO(+) system has been examined by means of quantum chemical calculations using the G2 and G3B3 approaches and tandem mass spectrometry experiments. Theoretical investigation of the C2H4NO(+) potential-energy surface includes 19 stable C2H4NO(+) structures and a large set of their possible interconnections. These computations provide insights for the understanding of the (i) addition of the nitrosonium cation NO(+) to the ethylene molecule, (ii) skeletal rearrangements evidenced in previous experimental studies on comparable systems, and (iii) experimental identification of new C2H4NO(+) structures. It is predicted from computation that gas-phase nitrosation of ethylene may produce C2H4(*)NO(+) adducts, the most stable structure of which is a pi-complex, 1, stabilized by ca. 65 kJ/mol with respect to its separated components. This complex was produced in the gas phase by a transnitrosation process involving as reactant a complex between water and NO(+) (H2O.NO(+)) and the ethylene molecule and fully characterized by collisional experiments. Among the other C 2H 4NO (+) structures predicted by theory to be protected against dissociation or isomerization by significant energy barriers, five were also experimentally identified. These finding include structures CH3CHNO(+) (5), CH 3CNOH (+) ( 8), CH3NHCO(+) (18), CH3NCOH(+) (19), and an ion/neutral complex CH2O...HCNH(+) (12). 相似文献
89.
90.
Suad Jakirlić Björn Kniesner Gisa Kadavelil Markus Gnirß Cameron Tropea 《Flow, Turbulence and Combustion》2009,83(3):425-448
A complementary experimental and computational study of the flow and mixing in a single annular gas turbine combustor has
been carried out. The object of the investigation is a generic mixing chamber model, representing an unfolded segment of a
simplified Rich-Quick-Lean (RQL) combustion chamber operating under isothermal, non-reacting conditions at ambient pressure.
Two configurations without and with secondary air injection were considered. To provide an appropriate reference database
several planar optical measurement techniques (time-resolved flow visualisation, PIV, QLS) were used. The PIV measurements
have been performed providing profiles of all velocity and Reynolds-stress components at selected locations within the combustor.
Application of a two-layer hybrid LES/RANS (HLR) method coupling a near-wall k − ε RANS model with conventional LES in the core flow was the focus of the computational work. In addition to the direct comparison
with the experimental results, the HLR performance is comparatively assessed with the results obtained by using conventional
LES using the same (coarser) grid as HLR and two eddy-viscosity-based RANS models. The HLR model reproduced all important
flow features, in particular with regard to the penetrating behaviour of the secondary air jets, their interaction with the
swirled main flow, swirl-induced free recirculation zone evolution and associated precessing-vortex core phenomenon in good
agreement with experimental findings. 相似文献