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1.
Conductance measurements are reported for s-alkylisothiouronium bromide, iodide and picrate salts in the dipolar aprotic solvent DMSO at 25°C. The data were analysed by Fuoss's equation (1975–1980) for 1:1 electrolytes, from which the values of Λ0, the Gurney's cosphere diameter R and KA are obtained. The results are discussed in the light of the recorded values of the constants KR and KS and the free energy term Gs. 相似文献
2.
Kubat M. Hafez A. Raghavan V.V. Lekkala J.R. Wei Kian Chen 《Knowledge and Data Engineering, IEEE Transactions on》2003,15(6):1522-1534
Association mining techniques search for groups of frequently co-occurring items in a market-basket type of data and turn these groups into business-oriented rules. Previous research has focused predominantly on how to obtain exhaustive lists of such associations. However, users often prefer a quick response to targeted queries. For instance, they may want to learn about the buying habits of customers that frequently purchase cereals and fruits. To expedite the processing of such queries, we propose an approach that converts the market-basket database into an itemset tree. Experiments indicate that the targeted queries are answered in a time that is roughly linear in the number of market baskets, N. Also, the construction of the itemset tree has O(N) space and time requirements. Some useful theoretical properties are proven. 相似文献
3.
Golestaneh S. Hafez H.M. Mahmoud S.A. 《Vehicular Technology, IEEE Transactions on》1994,43(4):946-954
In FDMA cellular radio systems, the adjacent channel interference (ACI) is suppressed by the IF filter and also by a distance factor. Channels immediately adjacent to each other in frequency are assigned to different cells and, as such, the distance plays a role in reducing their mutual interference. The authors study the feasibility of optimizing the frequency spacing between carriers such that the combined effect of distance and IF filter will be enough to control the interference while allowing the maximum number of channels in a given bandwidth. They also study the decision feedback equalizer (DFE) as a means to reduce any excess ACI that results from reducing the channel spacing. The paper starts with a model that estimates the cumulative probability density of the signal to adjacent channel interference ratio (SIR) as a function of the channel spacing. They then present the results of a computer simulation study to estimate the performance of DFE in mitigating the effect of ACI. The results indicate that, under the conditions of slow flat fading and selection diversity, the DFE is very effective in reducing the effect of excess ACI interference which allows for a considerable reduction in the frequency spacing 相似文献
4.
Automatic onset detection and picking algorithm has been proposed by applying the spectro-ratio on time–frequency sub-band. The proposed algorithm does not need any parameter settings as it will work on data generated by either short or very broad band seismometers. Our algorithm is applied on local events from Cairo region recorded by three stations of the Egyptian National Seismic Network (ENSN). Maximum standard deviation is observed to be 0.113 s of the corresponding manual picks made by analysts. 相似文献
5.
A. H. Abdul Hafez Manpreet Arora K. Madhava Krishna C. V. Jawahar 《Advanced Robotics》2016,30(1):50-67
Crowded urban environments are composed of different types of dynamic and static elements. Learning and classification of features is a major task in solving the localization problem in such environments. This work presents a gradual learning methodology to learn the useful features using multiple experiences. The usefulness of an observed element is evaluated by a scoring mechanism which uses two scores – reliability and distinctiveness. The visual features thus learned are used to partition the visual map into smaller regions. The robot is efficiently localized in such a partitioned environment using two-level localization. The concept of active map (AM) is proposed here, which is a map that represents one partition of the environment in which there is a high probability of the robot existing. High-level localization is used to track the mode of the AMs using discrete Bayes filter. Low-level localization uses a bag-of-words model to retrieve images and accurately localize the robot. The pose of the robot is the one retrieved from the AM that has maximum a posteriori. Experiments have been conducted on a unique highly crowded data-set collected from Indian roads. The results support the proposed method due to speed and localization accuracy. 相似文献
6.
7.
The patent-pending integrated waste-to-energy system comprises both a novel biohydrogen reactor with a gravity settler (Biohydrogenator), followed by a second stage conventional anaerobic digester for the production of methane gas. This chemical-free process has been tested with a synthetic wastewater/leachate solution, and was operated at 37 °C for 45 d. The biohydrogenator (system (A), stage 1) steadily produced hydrogen with no methane during the experimental period. The maximum hydrogen yield was 400 mL H2/g glucose with an average of 345 mL H2/g glucose, as compared to 141 and 118 mL H2/g glucose for two consecutive runs done in parallel using a conventional continuously stirred tank reactor (CSTR, System (B)). Decoupling of the solids retention time (SRT) from the hydraulic retention time (HRT) using the gravity settler showed a marked improvement in performance, with the maximum and average hydrogen production rates in system (A) of 22 and 19 L H2/d, as compared with 2–7 L H2/d in the CSTR resulting in a maximum yield of 2.8 mol H2/mol glucose much higher than the 1.1–1.3 mol H2/mol glucose observed in the CSTR. Furthermore, while the CSTR collapsed in 10–15 d due to biomass washout, the biohydrogenator continued stable operation for the 45 d reported here and beyond. The methane yield for the second stage in system (A) approached a maximum value of 426 mL CH4/gCOD removed, while an overall chemical oxygen demand (COD) removal efficiency of 94% was achieved in system (A). 相似文献
8.
Hisham Hafez George Nakhla M. Hesham El. Naggar Elsayed Elbeshbishy Bita Baghchehsaraee 《International Journal of Hydrogen Energy》2010
This study investigated the impact of six organic loading rates (OLR) ranging from 6.5 gCOD/L-d to 206 gCOD/L-d on the performance of a novel integrated biohydrogen reactor clarifier systems (IBRCSs) comprised a continuously stirred reactor (CSTR) for biological hydrogen production, followed by an uncovered gravity settler for decoupling of solids retention time (SRT) from hydraulic retention time (HRT). The system was able to maintain a high molar hydrogen yield of 2.8 mol H2/mol glucose at OLR ranging from 6.5 to 103 gCOD/L-d, but dropped precipitously to approximately 1.2 and 1.1 mol H2/mol glucose for the OLRs of 154 and 206 gCOD/L-d, respectively. The optimum OLR at HRT of 8 h for maximizing both hydrogen molar yield and volumetric hydrogen production was 103 gCOD/L-d. A positive statistical correlation was observed between the molar hydrogen production and the molar acetate-to-butyrate ratio. Biomass yield correlated negatively with hydrogen yield, although not linearly. Analyzing the food-to-microorganisms (F/M) data in this study and others revealed that, both molar hydrogen yields and biomass specific hydrogen rates peaked at 2.8 mol H2/mol glucose and 2.3 L/gVSS-d at F/M ratios ranging from 4.4 to 6.4 gCOD/gVSS-d. Microbial community analysis for OLRs of 6.5 and 25.7 gCOD/L-d showed the predominance of hydrogen producers such as Clostridium acetobutyricum, Klebsiella pneumonia, Clostridium butyricum, Clostridium pasteurianum. While at extremely high OLRs of 154 and 206 gCOD/L-d, a microbial shift was clearly evident due to the coexistence of the non-hydrogen producers such as Lactococcus sp. and Pseudomonas sp. 相似文献
9.
Synthesis of Novel Series of Benzothieno [2,3-d] Pyrimidine Derivatives, Promising Anticancer Agents
Omer Khalid AI-Duaij Hend Nagah Hafez Abdel-Rhman Barakat Ahmed EI-Gazzar 《化学与化工:英文版》2013,(8):725-742
An extension of the authors' previous discovery of in vitro antitumor activity of substituted thino [2,3-d] prymidine derivatives is reported. The synthesis of some new spirothino [2,3-d] prymidine (4a-f), imidazolidin, substituted prymidinyl and substituted thiazolidine thino [2,3-d] prymidine derivatives have been described. Thirteen of the obtained compounds were selected by the NCI and evaluated for their in vitro anticancer activity. Seven of the investigated compounds, 4a, 8a, 9a, (12a, b), 14a and 15a, displayed high anticancer activity in the primary assay. These compounds have been selected for a full anticancer screening against a 60-cell panel assay where they showed non-selective broad spectrum and promising activity against all cancer cell lines. Compounds 12a and 12b proved to be the active members in this study compared to 5-fluorouracil and cyclophosphamide as reference drugs, respectively. Compounds 12a and 12b were identified as promising lead compounds, evaluated for their in-vitro antitumor activity. 相似文献
10.