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排序方式: 共有49条查询结果,搜索用时 15 毫秒
1.
Mollah A.K.M.K. Rosales R. Tabatabaei S. Cicalo J. Ivanov A. 《IEEE transactions on circuits and systems. I, Regular papers》2007,54(12):2669-2682
Timing measurements such as jitter and skew in the range of picoseconds, for circuits with multigigahertz clocks or multigigabit-per-second serial communication interfaces are common. A Vernier-oscillator-based time-to-digital converter (TDC) is a circuit that allows picosecond-timing measurements by means of two tunable oscillators. In such a circuit, the oscillator jitter, tuning response, start-up transient, and frequency switching transient play an important role in the TDCs measurement time and accuracy. In this work, we discuss the design of an optimized, differential CML-based ring oscillator and its impact on a TDC design. Simulation results from the new oscillator show that the oscillator's short start-up and frequency switching transients have negligible effects on the accuracy of the TDC measurements. TDC simulation results show that, using two of these oscillators, accurate timing measurements in the range of 10 to 900 ps can be achieved with best-case accuracy of ~2 ps. 相似文献
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3.
The long-term effects on solidification/stabilization (S/S) of As5+-bearing oxyanions (AsO4(3)-) in Portland cement type-V (OPC) have been investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) techniques. The results of this study confirm our previous results that the early hydration of cement is inhibited by the presence of AsO4(3)-, and that the inhibition is mainly caused by the formation of highly insoluble Ca3(AsO4)2 on the surface of hydrating cement particles. Arsenate analog of ettringite [Ca6(Al2O6)(SO4)3 x 32H2O] was identified in the early stages of hydration of pure Portland cement and As(V)-treated Portland cement [OPC-As(V)], but not in 10-year-old similar samples. The XRD and FT-IR results indicated interactions of oxyanions and cement particles to produce minor quantities of As5+-bearing compounds in fresh as well as in 10-year-old samples. New As5+-bearing phases, NaCaAsO4 x 7.5H2O and Ca5(AsO4)3OH were identified in the 10-year-old OPC-As(V) samples by XRD analyses. Based on these results it is concluded that Portland cement may be considered as a potential matrix to immobilize As5+-bearing wastes. 相似文献
4.
Pentachlorophenol adsorption and desorption characteristics of granular activated carbon-I. Isotherms 总被引:1,自引:0,他引:1
The adsorption/desorption of pentachlorophenol (PCP) with Calgon F300 granular activated carbon (GAC) was studied and modelled. A modified Radke-Prausnitz (1972) isotherm model, incorporating a temperature- and pH-dependent proportionality constant, was found to best describe the observed PCP adsorption and desorption. The modified isotherm is valid in the ranges 4 ≤ pH ≤ 11 and 10 ≤ T ≤ 60°C. The activation energy of PCP adsorption was calculated to be 5.2 kJ/mol. At 30°C, PCP adsorbed strongly, and the rate of subsequent desorption was very low. However, the amount of PCP desorbed could be increased significantly by increasing the temperature to 60°C. 相似文献
5.
Large quantities of iron oxide nanowires are rapidly synthesized at room temperature by pulsed-laser (248?nm) ablation of iron powder under methanol. By introducing a stream of methanol, a continuous flow of nanoscale products is collected. Through control of the flow rate, and hence the residence time of the products within the growth vessel, their morphology can be controlled. At high collection rates a lamellate 'nanobelt' morphology is observed, whereas at low collection rates nanowires dominate. Chemical and structural characterization suggests that the as-synthesized products have the stoichiometry of the goethite [FeO(OH)] phase. Annealing at temperatures above 400?°C crystallizes the products as hematite (α-Fe(2)O(3)). 相似文献
6.
Richard L Davies D Robin Baigent Malcolm S Levitt Yasin Mollah Carl J Rayner Alison B Frensham 《Journal of the science of food and agriculture》1992,59(4):423-436
Five laboratories collaborated in a two-part study to improve and measure the accuracy and precision of amino acid analysis. The results of the unpublished first part allowed each laboratory the opportunity to optimise their own procedure. In the second part of the study reported here, three purified and six conventional proteins were analysed, each after three different preparation procedures (normal and extended acid hydrolysis, and following preliminary oxidation). Preparative effects reported in the literature were confirmed though not uniformly, and there were other, often unique, preparative effects. Well documented preparative effects are essential in matching analytical work to differing requirements. Results from one laboratory were excluded from further statistical analysis because of high replicate variation. The repeatability (within laboratory) coefficient of variation was 4.1% and for reproducibility (between laboratory) it was 13.1%. Discrepancies between best amino acid estimates for purified proteins and estimates calculated from published sequences (P < 0.01) provided evidence of bias in five amino acids from one laboratory and in one from another. When P < 0.01 was used as the discard threshold for conventional protein results, a total of 9.9% of best estimates were discarded: 8.1% were biased, 3.2% were outliers and 1.3% were both biased and outliers. When these values were discarded, 19 of 96 mean values changed by up to 4%, nine changed by 4-8%, eight changed by larger amounts and the pooled coefficient of variation fell from 8.2% to 5.4%. At this threshold between zero and 31% of each laboratory's data on conventional proteins was discarded. A lower threshold (P < 0.05) doubled the discard rate but had marginal effects on mean values and residual variation. At P < 0.01 less than 20% of biased estimates were also outliers and less than half the outliers were also biased. This means that only studies which examine both accuracy and precision will achieve maximum improvement in either. 相似文献
7.
Asfak Ali Mollah Dilip Kumar Pratihar 《The International Journal of Advanced Manufacturing Technology》2008,37(9-10):937-952
Input-output relationships of tungsten inert gas (TIG) welding and abrasive flow machining (AFM) processes were determined using radial basis function networks (RBFNs). A batch mode of training was adopted to implement the principle of back-propagation (BP) algorithm (which works based on a steepest descent algorithm) and a genetic algorithm (GA), separately. The performances of RBFN tuned by a BP algorithm and that trained by a GA were compared, on some test cases related to the above two manufacturing processes. The GA-optimized RBFN was found to perform slightly better than the BP-tuned RBFN. The back-propagation algorithm works based on the principle of a steepest descent method, whose solutions have the chance of getting stuck at the local minima, whereas the probability of the GA-solutions for being trapped at the local minima is less. However, their performances may depend on the nature of the deviation (error) function. 相似文献
8.
Many estimation methods for independent component analysis (ICA) requires prewhitening of observed signals. This paper proposes
a new method of prewhitening named β-prewhitening by minimizing the empirical β-divergence over the space of all the Gaussian distributions. The value of the tuning parameter β plays the key role in the performance of our current proposal. An attempt is made to propose an adaptive selection procedure
for the tuning parameter β for this algorithm. At last, a measure of performance index is proposed for assessing prewhitening procedures. Simulation
results show that β-prewhitening efficiently improves the performance over the standard prewhitening when outliers exist; it keeps equal performance
otherwise. Performance of the proposed method is compared with the standard prewhitening by both FastICA and our proposed
performance index. 相似文献
9.
This investigation reports the experimental results of neutron transport and shielding properties of heavy concretes made from locally available ilmenite and magnetite sand. The experiment has been carried out with a 252Cf source and a BF3 detector as a long counter. The thickness dependent removal cross section has been investigated and found to vary from 0.0936 cm−1 at 5 cm to 0.0346 cm−1 at 100 cm and 0.0990 cm−1 at 5 cm to 0.0366 cm−1 at 100 cm for ilmenite and magnetite concretes respectively. The results illustrate the effectiveness of ilmenite and magnetite heavy concretes so far as their sheilding properties are concerned. These materials may be used as a neutron shield in reactors, accelerators and neutron sources. 相似文献
10.
Mechanical properties development of sodium alginate films with additives by UV‐radiation processing
To improve mechanical properties of polymer films; sodium alginate (SA) films was prepared with ethylene glycol (EG) and photocured. The formulation was prepared at various concentration with EG and photoinitiator (2%) in methanol. The mechanical properties were optimized in case of monomer (EG) concentration, soaking time, and radiation dose of intensities. The highest polymer loading (PL) was 7.1% and tensile strength (TS) of the film was 37.9 MPa were found for 3 min soaking in 5% EG containing formulation at 20th pass of UV radiation; the highest value (22%) of elongation at break (Eb) was obtained at 1 min soaking time at 15th passes of UV doses. The mechanical properties improvement of the films varied acrylic monomers; such as 2‐ethylhexylacrylate (EHA), 1,4‐butanediol diacrylate (BDDA), and trimethylpropane triacrylate (TMPTA) were used as additives (2%) in the optimized formulation. The highest PL (12.7%) and TS (42.2 MPa) of the films are at 5% EG, 2% TMPTA, and 2% photoinitiator in methanol at 3 min soaking time at 20th pass of UV radiation. The highest Eb (25%) was obtained using additives 2% EHA additives in 5% EG and 2% photoinitiator in methanol at 3 min soaking time. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献