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排序方式: 共有413条查询结果,搜索用时 31 毫秒
31.
We propose a new approach for catalyst development that combines different scientific disciplines: experimental design, surface
science, reaction kinetics and simulations with the objective of accelerating catalyst development. In this paper we present
a study of the possibilities of using small data sets in microkinetic modeling, and studies of the required precision of temperature
measurement. 相似文献
32.
Surface Cleanliness Effect on Lunar Soil Shear Strength 总被引:1,自引:0,他引:1
Lunar soil consists of dry silty sand. Observations and measurements conducted during Surveyor, Apollo, and Luna missions indicated that the lunar soil is unusually cohesive. This is attributable to the fact that thick layers of adsorbed gases, which coat and lubricate soil particles on Earth, are absent in the ultrahigh vacuum on the Moon. “Surface cleanliness” is introduced as a new parameter for describing soils in different planetary environments. It is defined as the dimensionless inverse of adsorbate thickness on solid surfaces. By this definition, the ultrahigh vacuum on the Moon is associated with high surface cleanliness, while Earth's atmosphere is associated with low surface cleanliness. A model is developed to calculate surface cleanliness and its effect on shear strength in any planetary environment. Results obtained from the model compare well with data from previous ultrahigh vacuum and variable temperature laboratory experiments on Earth soils. It is shown that surface cleanliness is an important parameter with respect to lunar soil shear strength. 相似文献
33.
Marta Carballa Wim Moerman Wim De Windt H Grootaerd Willy Verstraete 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(1):63-68
BACKGROUND: Owing to more stringent phosphate discharge requirements and the increasing prices of fertilizers, beneficial recovery and reuse of phosphate from industrial anaerobic effluents is becoming an important issue. Phosphate recovery by struvite or magnesium ammonium phosphate (MAP) permits its recycling in the fertilizer industry because struvite is a valuable slow release fertilizer. Two different approaches to MAP crystallization depending on initial levels of phosphate in the wastewaters were tested and compared. RESULTS: For low‐phosphate‐containing anaerobic effluents (<30 mg PO43?‐P L?1), a novel approach using ureolytic induced MAP formation with MgO addition appeared to be suitable. The residual phosphate concentrations in the effluent ranged from 5 to 7 mg PO43?‐P L?1 and the separated matter contained residual amounts of Mg(OH)2. High‐phosphate‐containing anaerobic effluents (100 to 120 mg PO43?‐P L?1) were treated efficiently using air stripping combined with MgCl2 and NaOH reagents, yielding residual phosphate levels of 8 to 15 mg PO43?‐P L?1 and spherical pure MAP crystals of 0.5 to 2 mm. CONCLUSION: Results show that depending on the initial phosphate concentrations in the wastewaters and the ammonium and magnesium levels, the strategy selected for struvite crystallization is a determinative factor in achieving a cost effective technology. Copyright © 2008 Society of Chemical Industry 相似文献
34.
Xiaofeng Chen Fangguo Zhang Haibo Tian Baodian Wei Willy Susilo Yi Mu Hyunrok Lee Kwangjo Kim 《Information Sciences》2008,178(21):4192-4203
The “hash–sign–switch” paradigm was firstly proposed by Shamir and Tauman with the aim to design an efficient on-line/off-line signature scheme. Nonetheless, all existing on-line/off-line signature schemes based on this paradigm suffer from the key exposure problem of chameleon hashing. To avoid this problem, the signer should pre-compute and store a plenty of different chameleon hash values and the corresponding signatures on the hash values in the off-line phase, and send the collision and the signature for a certain hash value in the on-line phase. Hence, the computation and storage cost for the off-line phase and the communication cost for the on-line phase in Shamir–Tauman’s signature scheme are still a little more overload. In this paper, we first introduce a special double-trapdoor hash family based on the discrete logarithm assumption and then incorporate it to construct a more efficient generic on-line/off-line signature scheme without key exposure. Furthermore, we also present the first key-exposure-free generic on-line/off-line threshold signature scheme without a trusted dealer. Additionally, we prove that the proposed schemes have achieved the desired security requirements. 相似文献
35.
Geert Lissens Helene Klinke Willy Verstraete Birgitte Ahring Anne Belinda Thomsen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(8):889-895
Woody yard waste with high lignin content (22% of dry matter (DM)) was subjected to wet oxidation pre‐treatment for subsequent enzymatic conversion and fermentation. The effects of temperature (185–200 °C), oxygen pressure (3–12 bar) and addition of sodium carbonate (0–3.3 g per 100 g DM biomass) on enzymatic cellulose and hemicellulose (xylan) convertibility were studied. The enzymatic cellulose conversion was highest after wet oxidation for 15 min at 185 °C with addition of 12 bars of oxygen and 3.3 g Na2CO3 per 100 g waste. At 25 FPU (filter paper unit) cellulase g?1 DM added, 58–67% and 80–83% of the cellulose and hemicellulose contained in the waste were converted into monomeric sugars. The cellulose conversion efficiency during a simultaneous saccharification and fermentation (SSF) assay at 10% DM was 79% for the highest enzyme loading (25 FPU g?1 DM) while 69% conversion efficiency was still reached at 15 FPU g?1 DM. Total carbohydrate recoveries were high (91–100% for cellulose and 72–100% for hemicellulose) and up to 49% of the original lignin and 79% of the hemicellulose could be solubilized during wet oxidation treatment and converted into carboxylic acids mainly (total carboxylic acids = 3.1–7.4% on DM basis). Copyright © 2004 Society of Chemical Industry 相似文献
36.
A New and Efficient Fail-stop Signature Scheme 总被引:4,自引:0,他引:4
37.
Raf Schoofs Michiel S. J. Steyaert Willy M. C. Sansen 《IEEE transactions on circuits and systems. I, Regular papers》2007,54(1):209-217
A third-order continuous-time delta-sigma (DeltaSigma) analog-to-digital converter (ADC) is presented for the conversion of an input signal bandwidth of 10 MHz. Design optimization towards minimal power consumption is demonstrated for the high-speed low-power building blocks of the DeltaSigma modulator. From this point of view, it is shown that GmC integrators are preferred over RC integrators in the low-pass filter of the modulator because they show a better tradeoff between power, speed, and accuracy. A new single-bit quantizer topology is presented that incorporates a local feedback path that improves stability using a switched-voltage technique. Finally, a design methodology for the single-bit digital-to-analog converter (DAC) in the feedback loop is proposed, focusing on the impact of high sampling rates on the stability of the converter. The presented continuous-time ADC achieves a simulated dynamic range of 72 dB and a signal-to-noise-and-distortion-ratio of 66 dB in a 10-MHz signal bandwidth. Therefore, it can be applied for WLAN broadband communication. The power consumption of the DeltaSigma modulator is limited to 7.5 mW. The chip is designed in a 0.18-mum triple-well CMOS technology 相似文献
38.
Desloover J De Clippeleir H Boeckx P Du Laing G Colsen J Verstraete W Vlaeminck SE 《Water research》2011,45(9):2811-2821
New Activated Sludge (NAS®) is a hybrid, floc-based nitrogen removal process without carbon addition, based on the control of sludge retention times (SRT) and dissolved oxygen (DO) levels. The aim of this study was to examine the performance of a retrofitted four-stage NAS® plant, including on-line measurements of greenhouse gas emissions (N2O and CH4). The plant treated anaerobically digested industrial wastewater, containing 264 mg N L−1, 1154 mg chemical oxygen demand (COD) L−1 and an inorganic carbon alkalinity of 34 meq L−1. The batch-fed partial nitritation step received an overall nitrogen loading rate of 0.18-0.22 kg N m−3 d−1, thereby oxidized nitrogen to nitrite (45-47%) and some nitrate (13-15%), but also to N2O (5.1-6.6%). This was achieved at a SRT of 1.7 d and DO around 1.0 mg O2 L−1. Subsequently, anammox, denitrification and nitrification compartments were followed by a final settler, at an overall SRT of 46 d. None of the latter three reactors emitted N2O. In the anammox step, 0.26 kg N m−3 d−1 was removed, with an estimated contribution of 71% by the genus Kuenenia, which constituted 3.1% of the biomass. Overall, a nitrogen removal efficiency of 95% was obtained, yielding a dischargeable effluent. Retrofitting floc-based nitrification/denitrification with carbon addition to NAS® allowed to save 40% of the operational wastewater treatment costs. Yet, a decrease of the N2O emissions by about 50% is necessary in order to obtain a CO2 neutral footprint. The impact of emitted CH4 was 20 times lower. 相似文献
39.
Kerwin Rakness Gilbert Gordon Bruno Langlais Willy Masschelein Nobuo Matsumoto Yves Richard 《臭氧:科学与工程》1996,18(3):209-229
A joint meeting of members of the Quality Assurance Committees of the International Ozone Association Pan American Group (PAG), European-African Group (EAG), and Nippon Islands Group (NIG) was held in Oxford, Ohio on November 8 and 9, 1995. The purpose of the meeting was to establish a single, shared guideline for ozone concentration measurement in the gas phase and, in particular, from commercial ozone generators. 相似文献
40.
Stijn Wyffels Pascal Boeckx Kris Pynaert Willy Verstraete Oswald Van Cleemput 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(4):412-419
A membrane‐assisted bioreactor (MBR) for sustained nitrite accumulation is presented, treating a synthetic wastewater with total ammonium nitrogen (TAN) concentrations of 1 kg N m?3 at a hydraulic retention time down to 1 day. Complete biomass retention was obtained by microfiltration with submerged hollow fibre membranes. A membrane flux up to 189.5 dm3 day?1 m?2 could be maintained at a suction pressure below 100 kPa. Nitrification was effectively blocked at the nitrite stage (nitritation), and nitrate concentration was less than 29 g N m?3. The rate of aeration was reduced to obtain a mixture of ammonium and nitrite, and after adjusting this rate the TAN/NO2‐N ratio in the reactor effluent was kept around unity, making it suitable for further treatment by anaerobic oxidation of ammonium with nitrite. After increasing again the rate of aeration, complete nitrification to nitrate recovered after 11 days. It is suggested that nitrite accumulation resulted from a combination of factors. First, the dissolved oxygen (DO) concentration in the reactor was always limited with concentrations below 0.1 g DO m?3, thereby limiting nitrification and preventing significant nitrate formation. The latter is attributed to the fact that ammonium‐oxidising bacteria cope better with low DO concentrations than nitrite oxidisers. Second, the MBR was operated at a high ammonia concentration of 7–54 g N m?3, resulting in ammonia inhibition of the nitrite‐oxidising microorganisms. Third, a temperature of 35 °C was reported to yield a higher maximum growth rate for ammonium‐oxidising bacteria than for nitrite‐oxidising bacteria. Nitrite oxidisers were always present in the MBR but were out‐competed under the indicated process conditions, which is reflected in low concentrations of nitrate. Oxygen limitation was shown to be the most important factor to sustain nitrite accumulation. Nevertheless, nitritation was possible at ambient temperature (22–24 °C), lower ammonia concentration (<7 g N m?3) and when using raw nitrogenous wastewater containing some biodegradable carbon. Overall, application of the MBR for nitritation was shown to be a reliable technology. © 2003 Society of Chemical Industry 相似文献