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11.
A. I. D’Souza M. G. Stapelbroek P. N. Dolan P. S. Wijewarnasuriya R. E. DeWames D. S. Smith J. C. Ehlert 《Journal of Electronic Materials》2003,32(7):633-638
The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit
sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms
of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of
1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The
1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors
at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density
in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth
in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under
illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias,
with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if
this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps
are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as
a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular
bias. The 1/f noise was not a direct function of the applied bias. 相似文献
12.
Mobile ad hoc networks rely on the co-operation of devices that route for each other. This immediately presents security problems.
Each device's data passes through the not so friendly hands of other devices. Forwarding devices must use their processing
power and battery power to route packets for others. When bandwidth is limited they must also use bandwidth that they might
want to use for themselves. These are not great issues with the first incarnations of ad hoc networks — military systems or
others where all the devices are owned by a single organisation. However, if ad hoc networks are to be generally deployed
and become an alternative or adjunct to future cellular systems, then ways to encourage co-operation are required.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
14.
van Dick Rolf; Wagner Ulrich; Pettigrew Thomas F.; Christ Oliver; Wolf Carina; Petzel Thomas; Castro Vanessa Smith; Jackson James S. 《Canadian Metallurgical Quarterly》2004,87(2):211
Furthering G. W. Allport's (1954) contentions for optimal contact, the authors introduce a new construct: the perceived importance of contact. They propose that perceived importance is the best proximal predictor of contact's reduction of prejudice. If individuals have opportunities for contact at work or in the neighborhood, their chances to have intergroup acquaintances and friends increase. Intergroup contact among acquaintances and friends can be perceived as more or less important, which in turn determines intergroup evaluations. A 1st study shows that the new measure of perceived importance is indeed distinct from established quantity and quality indicators. The results are cross-validated in a 2nd study that also sheds light on the meaning of importance. In 3rd and 4th studies, structural equation analyses and a meta-analysis support the hypotheses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
15.
Z Abbas AH Khan SM Jafri SS Hamid SH Shah S Abid JA Qureshi 《Canadian Metallurgical Quarterly》1997,12(11):703-706
The authors compared in a controlled clinical study two groups of patients after a first renal transplantation treated by triple drug immunosuppressive therapy. In a group of 31 patients the triple combination comprised Sandimmune Neoral. In the control group there were 30 patients who received Sandimmune. No differences were found between the two groups as regards the effectiveness of this treatment and the authors did not confirm a lower incidence of rejections described in patients treated with Sandimmune Neoral. They confirmed, however, a lower interindividual variability of Cy-A levels assessed specifically in patients treated with Sandimmune Neoral. 相似文献
16.
LJ Huang K Durick JA Weiner J Chun SS Taylor 《Canadian Metallurgical Quarterly》1997,94(21):11184-11189
Subcellular localization directed by specific A kinase anchoring proteins (AKAPs) is a mechanism for compartmentalization of cAMP-dependent protein kinase (PKA). Using a two-hybrid screen, a novel AKAP was isolated. Because it interacts with both the type I and type II regulatory subunits, it was defined as a dual specific AKAP or D-AKAP1. Here we report the cloning and characterization of another novel cDNA isolated from that screen. This new member of the D-AKAP family, D-AKAP2, also binds both types of regulatory subunits. A message of 5 kb pairs was detected for D-AKAP2 in all embryonic stages and in all adult tissues tested. In brain, skeletal muscle, kidney, and testis, a 10-kb mRNA was identified. In testis, several small mRNAs were observed. Therefore, D-AKAP2 represents a novel family of proteins. cDNA cloning from a mouse testis library identified the full length D-AKAP2. It is composed of 372 amino acids which includes the R binding fragment, residues 333-372, at its C-terminus. Based on coprecipitation assays, the R binding domain interacts with the N-terminal dimerization domain of RIalpha and RIIalpha. A putative RGS domain was identified near the N-terminal region of D-AKAP2. The presence of this domain raises the intriguing possibility that D-AKAP2 may interact with a Galpha protein thus providing a link between the signaling machinery at the plasma membrane and the downstream kinase. 相似文献
17.
18.
Conflicting results have been reported in literature about the influence of beta-adrenergic stimulation on the fast cardiac sodium current (INa+). To elucidate these mechanisms in multicellular preparations we used the loose-patch-clamp technique to evaluate the effect of the beta-adrenergic agonist isoproterenol 1-1000 nmol/l. Isoproterenol enhanced INa+ at all membrane potentials by elevation of the maximal available INa+ . Only at the high concentration of 1 micromol/l was INa+ slightly depressed after depolarizing conditioning clamps. The most marked increase of the maximal available INa+ was 30+/-9% after application of 100 nmol/l isoproterenol. To learn about the mechanisms in view of sodium channel modulation we combined isoproterenol with the sodium channel blocker lidocaine (47 micromol/l). Under these circumstances the effects of both drugs were completely independent. This investigation shows clearly that low concentrations of isoproterenol increase INa+ in multicellular preparations by a gating-independent mechanism. 相似文献
19.
The paper presents the findings of a survey that investigated the level of quality management practice within some 150 UK companies from a sample of 500. It provides a snapshot of practice at the time of the survey, and assesses the impact of government quality initiatives particularly, the TickIT scheme at that time. The survey methodology is described, together with the results and conclusions. The sample has been graded by size of company, which the authors consider to have a significant effect upon the adoption of quality practices. The survey highlights the need to encourage small companies to adopt quality practices and to assist them with the short-term costs incurred. 相似文献
20.
FT-Raman spectroscopy proves to be a powerful technique to study surface reactions on bioactive glasses and it eliminates the fluorescence of the organic phase of whole bone, thereby making it possible to compare the reaction layers formed on bioactive glasses with the mineral phase of bone. The spectrum of hydroxycarbonate apatite (HCA) developed on the bioactive glasses is closer to that of bone than synthetic hydroxyapatite (HA) and closely matches that of bone mineral obtained by deproteination of whole human femoral cortical bone. 相似文献