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排序方式: 共有126条查询结果,搜索用时 31 毫秒
1.
Fattaruso J.W. Kiriaki S. De Wit M. Warwar G. 《Solid-State Circuits, IEEE Journal of》1993,28(12):1216-1223
Design techniques for self-calibration of the digital-to-analog converter DAC in a multibit sigma-delta modulator are described. When used in conjunction with dynamic element matching, self-calibration provides linearity performance suitable for digital audio applications. The dynamic element matching circuitry provides the mechanism of determining device mismatch for self-calibration. Practical circuit details and an effective calibration method are discussed. Test results from a l-μm CMOS test chip are presented. In this test system, a second-order loop with a 3-b quantizer achieves an 89-dB dynamic range and -91-dB harmonic distortion after calibration. In addition, a new method of detecting the presence of tones is described, using the entropy of the spectrum of the decimation filter output 相似文献
2.
In this paper we consider the following problem of computing a map of geometric minimal cuts (called MGMC problem): Given a graph G=(V,E) and a planar rectilinear embedding of a subgraph H=(V H ,E H ) of G, compute the map of geometric minimal cuts induced by axis-aligned rectangles in the embedding plane. The MGMC problem is motivated by the critical area extraction problem in VLSI designs and finds applications in several other fields. In this paper, we propose a novel approach based on a mix of geometric and graph algorithm techniques for the MGMC problem. Our approach first shows that unlike the classic min-cut problem on graphs, the number of all rectilinear geometric minimal cuts is bounded by a low polynomial, O(n 3). Our algorithm for identifying geometric minimal cuts runs in O(n 3logn(loglogn)3) expected time which can be reduced to O(nlogn(loglogn)3) when the maximum size of the cut is bounded by a constant, where n=|V H |. Once geometric minimal cuts are identified we show that the problem can be reduced to computing the L ∞ Hausdorff Voronoi diagram of axis aligned rectangles. We present the first output-sensitive algorithm to compute this diagram which runs in O((N+K)log2 NloglogN) time and O(Nlog2 N) space, where N is the number of rectangles and K is the complexity of the Hausdorff Voronoi diagram. Our approach settles several open problems regarding the MGMC problem. 相似文献
3.
The reduction of NO by propene in the presence of excess oxygen over mechanical mixtures of Au/Al2O3 with a bulk oxide has been investigated. The oxides studied were: Co3O4, Mn2O3, Cr2O3, CuO, Fe2O3, NiO, CeO2, SnO2, ZnO and V2O5. Under lean C3H6-SCR conditions, these oxides (with the exception of SnO2) convert selectively NO to NO2. When mechanically mixed with Au/Al2O3, the Mn2O3 and Co3O4 oxides and, to a much greater extent, CeO2 act synergistically with this catalyst greatly enhancing its SCR performance. It was found that their synergistic action is not straightforwardly related to their activity for NO oxidation to NO2. The exhibited catalytic synergy may be due to the operation of either remote control or a bifunctional mechanism. In the later case, the key intermediate must be a short-lived compound and not the NO2 molecule in gas-phase. 相似文献
4.
E. Papadopoulou D. Delimaris A. Denis A. Machocki T. Ioannides 《International Journal of Hydrogen Energy》2012
Co–MnO catalysts have been prepared by pyrolytic decomposition of the corresponding fumarate or gluconate salts and examined in the reactions of methanol and ethanol reforming. The synthesis parameters were the type of organic salt, the Co:Mn ratio and the temperature of decomposition. The decomposition pathway depends on the type of carboxylate, with the fumarate group being more stable than the gluconate. In-situ XRD measurements of salt decomposition showed that the reducing atmosphere prevailing during thermal treatment, as well as the presence of solid carbon, facilitates reduction of cobalt oxides towards metallic cobalt at temperatures above ∼500 °C. Thus, the reduced form of the catalyst, consisting mainly of metallic cobalt and MnO dispersed in a carbonaceous matrix can be prepared in a single step. It was found that reforming of both methanol and ethanol proceeds under comparable reaction conditions and hydrogen yield is maximized at temperatures of 400–450 °C. The activity of catalysts prepared under an inert atmosphere was considerably higher than the one of catalysts prepared through oxidative pre-treatment. 相似文献
5.
Biological treatment of groundwater with a high hexavalent chromium content under anaerobic and anoxic conditions
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6.
P. Papadopoulou N. Georgoulas L. Georgopoulos A. Thanailakis 《Electrical Engineering (Archiv fur Elektrotechnik)》2001,83(4):203-211
Contents This paper presents an analytical model for the dc electrical behavior of bulk barrier diodes (BBD's). The proposed model
extends previously published models, and includes analytical expressions for all significant quantities of the device dc performance,
i.e. barrier height, current density and ideality factor, with respect to the technological parameters and the applied voltage
in both bias conditions. The analytical results have been compared with those obtained using the 2-D device simulator S-PISCES,
which takes into account the drift–diffusion theory, as well as a concentration and field dependent mobility, the Shockley–Read–Hall
and Auger carrier recombination, and the band gab narrowing. Good agreement was obtained between theory and simulation. The
device simulation played a very important role in best understanding BBD's behavior, because it could easily take into account
parameters strongly affecting the behavior of BBD's, e.g. the free carrier presence in depletion layers, which was very difficult
for the analytical model to include.
Received: 15 January 2001 相似文献
7.
Kiriaki Marnasidou George Takidis Michael Stamatoudis 《Chemical Engineering Communications》2001,187(1):149-159
Fourteen generalized equations of state were compared on the ability to predict gas-phase fugacity of pure compounds. The equations were tested using 30254 literature data points. The accuracy of the prediction varied with the equation and the range of temperature and pressure. 相似文献
8.
Haris Doukas Alexandra G. Papadopoulou Christos Nychtis John Psarras Nicole van Beeck 《Renewable & Sustainable Energy Reviews》2009,13(3):682-688
The European Union (EU) from the beginning of 2007 has focused its emphasis on the development of a new policy that puts energy back at the heart of EU action. Indeed, it has very often been stated that the difficulty and complexity of achieving green energy targets in the EU will require strengthened measures to promote implementation of new energy technologies (NET), as well as measures to support the related energy Research and Technology Development (R&TD). Often forgotten is the fact, that most of all, a European-wide co-ordinated forum is needed to continuously develop and sophisticate the monitoring and methodology results, bringing together specialised statisticians, energy researchers and experts on energy socio-economics. Today a nebulous picture prevails on the existence of categorized data with regards to energy Research and Technology Development (R&TD) expenditure. In this context, aim of this paper is the presentation of energy R&TD data collection strategies, as well as the related findings for the Greek energy market. 相似文献
9.
Sotirios Paraschos Prokopios Magiatis Panagiota Gousia Vangelis Economou Hercules Sakkas Chrissanthy Papadopoulou Alexios-Leandros Skaltsounis 《Food chemistry》2011
Mastic water is a commercial flavouring obtained during the steam distillation of mastic resin (the resin of Pistacia lentiscus var. chia) for the production of mastic oil. The mastic water extracts were analysed by GC−MS. The major compounds identified were verbenone, α-terpineol, linalool and trans-pinocarveol. Overall the composition was found to be very different from that of mastic oil. Additional GC−MS revealed the enantiomeric ratio of the chiral constituents of mastic water. The antimicrobial activity of mastic water extract, as well as that of its major constituents, was examined against Escherichia coli, Staphylococcus aureus and Candida spp. including ATCC wild clinical and food-borne strains. Linalool and α-terpineol were found to be the most potent antimicrobial constituents. Finally the stability of mastic water at different temperatures was studied, showing no change in the GC−MS profile of the organic extract for a period of 4 months at storage temperatures up to 4 °C. 相似文献
10.
MA Dimopoulos M Papadopoulou E Andreopoulou C Papadimitriou N Pavlidis G Aravantinos A Aspropotamitis A Anagnostopoulos G Fountzilas S Michalas D Pectacides 《Canadian Metallurgical Quarterly》1998,70(1):70-74
The effect of pretreatment of human polymorphonuclear leukocites (PMNs), for 30 min with fluconazole (0.1, 1, 5 and 50 microgram/ml) and itraconazole (0.05, 0.5 and 5 microgram/ml) on phagocytosis and generation of free radicals (superoxide anion and hydrogen peroxide) was studied in vitro. Phorbol miristate acetate (200 nM) was used as a stimulant. The mean amount of superoxide anion generated by 2.5 x 10(5) PMNs per hour was 4.39 +/- 1.13 nmol for fluconazole-treated PMNs and 4.56 +/- 1.2 nmol for itraconazole, and that of hydrogen peroxide was 11.19 +/- 2.18 and 11.28 +/- 3.61 nmol, respectively. The phagocytosis percentages were 83.8% for the control group and 88. 7% in antifungal agent- treated PMNs; the phagocytosis index was 3.0 yeasts per PMN for both groups. The differences between the control and treated PMNs were not statistically significant at any of the tested concentrations. 相似文献