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排序方式: 共有321条查询结果,搜索用时 15 毫秒
311.
Rahim Hekmatshoar Ghodsieh Nanva Kenary Sodeh Sadjadi Yahya S. Beheshtiha 《合成通讯》2013,43(13):2007-2013
An efficient method for the synthesis of 4-amino-5-pyrimidinecarbonitriles by three-component reaction of malononitrile, aldehydes, and N-unsubstituted amidines, under aqueous conditions, using ZnO nanoparticles as catalyst is reported. The catalyst exhibited remarkable activity and is recyclable. 相似文献
312.
Ultrasonic assisted extraction-dispersive liquid-liquid microextraction (UAE-DLLME) coupled with gas chromatography (GC) was applied for extraction and determination of essential oil constituents of the plant Oliveria decumbens Vent. Scanning electron microscopy (SEM) was used to see the effect of ultrasonic radiation on the extraction efficiency. By comparison with hydrodistillation, UAE-DLLME is fast, low cost, simple, efficient and consuming small amount of plant materials (~1.0 g). The effects of various parameters such as temperature, ultrasonication time, volume of disperser and extraction solvents were investigated by a full factorial design to identify significant variables and their interactions. The results demonstrated that temperature and ultrasonication time had no considerable effect on the results. In the next step, a central composite design (CCD) was performed to obtain the optimum levels of significant parameters. The obtained optimal conditions were: 0.45 mL for disperser solvent (acetonitrile) and 94.84 μL for extraction solvent (chlorobenzene). The limits of detection (LODs), linear dynamic range and determination coefficients (R(2)) were 0.2-29 ng mL(-1), 1-2100 ng mL(-1) and 0.995-0.998, respectively. The main components of the essential oil were: thymol (47.06%), carvacrol (23.31%), gamma-terpinene (18.94%), p-cymene (8.71%), limonene (0.76%) and myristicin (0.63%). 相似文献
313.
We introduce directed versions of the Shannon Switching Game. In the Directed Shannon Switching Game two players, BLACK and WHITE, alternatively direct edges of a graph with two distinguished vertices x0, x1. WHITE wins if he connects x0 to x1 by a directed path. In the One-Way Game, WHITE is allowed to use edges directed by BLACK. Several related other games are also considered. All these games are particular cases of games played on oriented matroids. The main results of the paper yield complete classifications of directed switching games on graphic and cographic oriented matroids. 相似文献
314.
Abdo Mohammed Al‐Fakih Zakariya Yahya Algamal Muhammad Hisyam Lee Hassan H. Abdallah Hasmerya Maarof Madzlan Aziz 《Journal of Chemometrics》2016,30(7):361-368
A new quantitative structure–activity relationship (QSAR) of the inhibition of mild steel corrosion in 1 M hydrochloric acid using furan derivatives was developed by proposing two‐stage sparse multiple linear regression. The sparse multiple linear regression using ridge penalty and sparse multiple linear regression using elastic net (SMLRE) were used to develop the QSAR model. The results show that the SMLRE‐based model possesses high predictive power compared with sparse multiple linear regression using ridge penalty‐based model according to the mean‐squared errors for both training and test datasets, leave‐one‐out internal validation (Q2int = 0.98), and external validation (Q2ext = 0.95). In addition, the results of applicability domain assessment using the leverage approach reveal a reliable and robust SMLRE‐based model. In conclusion, the developed QSAR model using SMLRE can be efficiently used in the studies of corrosion inhibition efficiency. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
315.
Yahya Badran 《The Journal of the Operational Research Society》1987,38(11):1031-1037
The aim of the paper is to show how Shannon's entropy may be used for optimal grouping of state spaces of discrete stochastic systems. Compositions (ordered partitions) of discrete state spaces and their entropic optimality have been defined, and optimal compositions were computed as solutions of a dynamic programme. Uniform and binomial systems were used for illustrations. Sturges' rule was reinterpreted. 相似文献
316.
Yahya S. Al-Degs 《Chromatographia》2009,69(9-10):1137-1140
The resolving power of liquid chromatography and partial least-square (PLS-1) calibration has been compared for simultaneous analysis of three leachable pesticides, atrazine, methidathion, and propoxur, in groundwater. The chromatographic method outperformed PLS-1 for analysis of the pesticides, for which spectral overlap is substantial (30–75%). After application of a liquid–liquid extraction step, both methods could be used to quantify 500 ng L?1 of the pesticides with recovery in the ranges 92.8–95.6% for PLS-1 and 97.6–99.3% for chromatography, and RSD in the ranges 6.9–8.6% for PLS-1 and 1.9–3.4% for chromatography. The better performance of the chromatographic method was attributed to separation of groundwater constituents from the pesticides before quantification, which was not possible with the PLS-1 method. Despite the superiority of the chromatographic method, PLS-1 seems a reasonable and inexpensive substitute for chromatography. 相似文献
317.
Suhaina Mohd Ibrahim Abdul Kadir Masrom Babak Mazinani Shahidan Radiman Farinaa Md Jamil Ali Beitollahi Nobuaki Negishi Noorhana Yahya 《Research on Chemical Intermediates》2013,39(3):1003-1014
Mesoporous TiO2 has been synthesized by the sol–gel method, using a nonionic triblock copolymer P123 as surfactant template under acidic conditions. The as-prepared samples were characterized by thermogravimetry–differential thermal analysis (TG–DTA), nitrogen absorption–desorption (BET), field emission scanning electron microscopy, and transmission electron microscopy. The photocatalytic activity of the mesoporous TiO2 was evaluated by degradation of methylene blue under high-intensity UV light irradiation; the amount of methylene blue was measured by UV–visible spectroscopy. TG–DTA analysis revealed that the surfactant had been removed partly in as-synthesized samples. BET analysis proved that all the samples retained mesoporosity with a narrow pore-size distribution (4.5–6.3 nm) and high surface area (103–200 m2/g). All calcined mesoporous TiO2 had high photocatalytic activity in the photodegradation of methylene blue. 相似文献
318.
The n-step mixed integer rounding (MIR) functions generate n-step MIR inequalities for MIP problems and are facets for the infinite group problems. We show that the n-step MIR functions also directly generate facets for the finite master cyclic group polyhedra especially in many cases where the breakpoints of the n-step MIR function are not necessarily at the elements of the group (hence the linear interpolation of the facet coefficients obtained has more than two slopes). 相似文献
319.
Babak Mazinani Ali Beitollahi Abdul Kadir Masrom Noorhana Yahya Thomas S. Y. Choong Suhaina Mohd Ibrahim Jafar Javadpour 《Research on Chemical Intermediates》2012,38(8):1733-1742
TiO2?CSiO2 mesoporous materials were synthesised by deposition of TiO2 nanoparticles prepared by the sol?Cgel method on to the internal pore surface of wormhole-like mesoporous silica. In this work we synthesised wormhole-like mesoporous silica of different surface area by changing the hydrothermal temperature (70, 100, or 130?°C). Subsequent to this, titania solution was deposited on to the inner surface of the pores and this was followed by calcination at different temperatures (400, 600, or 800?°C). The effect of different hydrothermal and calcination temperature on the photocatalytic properties was evaluated. The samples were characterized by N2-sorption, X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The effect of different hydrothermal and calcination temperatures on the photocatalytic properties was evaluated by measuring the degradation of methylene blue in aqueous solution under UV light irradiation (mercury lamp, 125?W). The results indicated that appropriate surface area and degree of crystallinity are two important factors for obtaining high photocatalytic efficiency. Samples prepared at a hydrothermal temperature of 100?°C and calcined at 800?°C had the best photocatalytic performance, because of the highest surface area and high crystallinity. 相似文献
320.
We consider the problem of finding the nearest point in a polyhedral cone C={x∈R
n
:D
x≤0} to a given point b∈R
n
, where D∈R
m×n
. This problem can be formulated as a convex quadratic programming problem with special structure. We study the structure
of this problem and its relationship with the nearest point problem in a pos cone through the concept of polar cones. We then
use this relationship to design an efficient algorithm for solving the problem, and carry out computational experiments to
evaluate its effectiveness. Our computational results show that our proposed algorithm is more efficient than other existing
algorithms for solving this problem. 相似文献