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991.
A spectrophotometer system for spectral characterization of materials in the infrared has been built around a bench-top Fourier transform instrument. Its capabilities include the measurement of directional-hemispherical reflectance from 1 to 18 μm. The spectral reflectance measurement is performed with an integrating sphere with an incidence angle of 8°. Both relative and absolute measurements can be made. Several methods can be used to determine the absolute value of the directional-hemispherical reflectance of samples. The primary method used is independent of the integrating sphere theory and the requisite assumptions associated with its use. The calibration of a standard reference material (SRM) is described. This SRM has a reflectance value near 0.9 over the complete calibration range 2–18 μm. As part of the calibration procedure the spatial uniformity of the sphere throughput and the bi-directional reflectance distribution function (BRDF) of the SRM material are evaluated. 相似文献
992.
Any solid state X-ray photoelectron spectrum (XPS) contains contributions due to multiple inelastic scattering in the bulk, surface excitations, energy losses originating from the screening of the final state hole (intrinsic losses), and, for non-monochromatized incident radiation, ghost lines originating from the X-ray satellites. In the present paper it is shown how all these contributions can be consecutively removed from an experimental spectrum employing a single general deconvolution procedure. Application of this method is possible whenever the contributions mentioned above are uncorrelated. It is shown that this is usually true in XPS to a good approximation. The method is illustrated on experimental non-monochromatized MgK spectra of Au acquired at different detection angles but for the same angle of incidence of the X-rays. 相似文献
993.
The Drivers, Pressures, State, Impact and Response or DPSIR framework has been with us for over a decade now and it is widely used as a means to assess and measure and, eventually provide a guide to managing the environment. With its repertoire of diagnostic and analytical components the DPSIR can be argued to be a Problem Structuring Method or PSM. Criticisms of the framework abound but it has a resilience which is noteworthy. Some argue that DPSIR, by its nature, is a narrowly formulated, engineering device, incompatible with the multiple perspectives which human interaction in global ecology requires. Is there a value in DPSIR being more flexible in expression and experience of users? In this article it is shown how the DPSIR framework was applied within a multi-methodology approach called Imagine in a number of coastal management projects around the Mediterranean and in other contexts. The article argues that DPSIR, whilst admittedly limited in its scope and approach can, if applied in a participatory and systemic multi-methodology, combine with other tools and help to create outcomes of value to local populations. 相似文献
994.
995.
Stephen M. Lipson Ashley J. Cadby Paul A. Lane Diarmuid F. O’Brien Anna Drury Donald D. C. Bradley Werner J. Blau 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):151-158
Summary. We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer
poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50% when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert
atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces
polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption.
It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and
non-radiative quenching routes, thus resulting in increased PL efficiency.
Received June 23, 2000. Accepted (revised) August 3, 2000 相似文献
996.
Seref Kalem Peter Werner Vadim Talalaev 《Applied Physics A: Materials Science & Processing》2013,112(3):561-567
We present the room-temperature near-infrared (NIR) photoluminescence (PL) properties of Si/Ge nanowire (NW)-grown silicon wafers which were treated by vapor of HF:HNO3 chemical mixture. This treatment activates or enhances the PL intensity in the NIR region ranging from 1000 nm to 1800 nm. The PL consists of a silicon band-edge emission and a broad composite band which is centered at around 1400–1600 nm. The treatment modifies the wafer surface particularly at defect sites especially pits around NWs and NW surfaces by etching and oxidation of Si and Ge. This process can induce spatial confinement of carriers where band-to-band (BB) emission is the dominant property in Si-capped strained Si/Ge NW-grown wafers. Strong signals were observed at sub-band-gap energies in Ge-capped Si/Ge NW-grown wafers. It was found that NIR PL is a competitive property between the Si BB transition and deep-level emission, which is mainly attributable to Si-related defects, Ge dots and strained Ge layers. The enhancement in BB and deep-level PL is discussed in terms of strain, oxygen-related defects, dot formation and carrier-confinement effects. The results demonstrate the effectiveness of this method in enhancing and tuning NIR PL properties for possible applications. 相似文献
997.
Stuart C. Wimbush Dominic Walsh Simon R. Hall 《Physica C: Superconductivity and its Applications》2010,470(7-8):373-377
We have recently demonstrated that through a sol–gel route, superconductor crystallization in the presence of simple biopolymers results in a drastic alteration of morphology, producing technologically useful nanowires and porous architectures. Morphological control is of the utmost importance to bulk high-temperature superconductors, as grain boundaries act as weak links in limiting the achievable critical current density (Jc). Here we show that, as expected, the incorporation of nanoparticulate barium zirconate (BaZrO3) species into a biopolymer-mediated synthetic protocol for YBa2Cu3O7?δ (Y123) leads to a significantly improved in-field Jc compared to that observed in a sample without BaZrO3 additions. To ameliorate degradation of the BaZrO3 species in this protocol, we demonstrate that by drawing the precursor sol into fibers, a microtape architecture is able to be formed, leading to lengthy, anisotropic structures having enhanced Jc through the retention of the BaZrO3 species. 相似文献
998.
Simon E. Gant 《Flow, Turbulence and Combustion》2010,84(2):325-335
Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES) and Scale-Adaptive Simulation (SAS) are increasingly being used
as engineering tools to predict the behaviour of complex industrial flows. Often the flows studied have not been examined
previously and the required grid resolution is unknown. Industrial users studying these flows tend to be using commercial
CFD codes and do not usually have access to high-performance computing facilities. Due to the significant computing times
required, it is difficult to undertake systematic grid-dependence studies. There is therefore a risk that LES, DES and SAS
will be performed using overly coarse grids which may lead to unreliable predictions. The present work surveys a number of
practical techniques that provide a means of assessing the quality of the grid resolution in large-eddy simulations and related
approaches. To examine the usefulness of these techniques, a gas release in a ventilated room is examined using DES and SAS.
The grid resolution measures indicate that overall the grids used are relatively coarse. Both DES and SAS model predictions
are found to be in poor agreement with experimental data compared to steady and unsteady Reynolds-averaged Navier–Stokes (RANS)
results using the SST model. The SAS model also shows the greatest grid sensitivity of the four models tested. The work highlights
the need for grid-dependence studies and the potential problems of using coarse grids. 相似文献
999.
1000.