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排序方式: 共有1093条查询结果,搜索用时 46 毫秒
41.
Showkat A. Bhawani Othman Sulaiman Ziya A. Khan Rokiah Hashim Mohamad N. M. Ibrahim 《Journal of surfactants and detergents》2011,14(2):301-305
The mutual separation of a mixture of cetyltrimethyl ammonium chloride (CTAC), methyl trioctyl ammonium bromide (MTOB), dodecyltrimethyl
ammonium chloride (DTAC), benzyltrimethyl ammonium chloride (BTAC) and tetrabutyl ammonium bromide (TBAB), was achieved on
silica high performance thin layer chromatographic plates using dimethyl sulfoxide with aqueous sodium-l-tartrate dibasic dihydrate as the solvent system. The effect of concentration of sodium-l-tartrate dibasic dihydrate on the mobility of all the five quaternaries was examined. The limit of detection of CTAC, MTOB,
DTAC, BTAC and TBAB was estimated as 0.6, 0.6, 0.3, 0.6 and 0.3 μg/zone, respectively. The method developed was utilized to
identify these surfactants in different spiked water samples after their preliminary separation. 相似文献
42.
Li Wan Yoon Gek Cheng Ngoh Adeline Seak May Chua Mohd. Ali Hashim 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(10):1342-1348
BACKGROUND: Much attention has been given to applying ionic liquids (ILs) as an alternative pretreatment method for lignocellulosic biomass. This study aims to select the most suitable type of IL for pretreating sugarcane bagasse (SCB). The potential of ILs for pretreatment was evaluated and compared with conventional pretreatment media, acids and alkalis. The performance of the pretreatment media was evaluated based on the amount of reducing sugar produced from enzymatic saccharification, the energy requirement, and changes in the chemical structure and crystallinity index of the pretreated bagasse. RESULTS: 1‐ethyl‐3‐methylimidazolium acetate [EMIM]oAc was selected as the most suitable IL for SCB pretreatment. The optimum yields of reducing sugar obtained from [EMIM]oAc‐, alkali‐, and acid‐pretreated SCB were 69.5%, 92.8% and 41.3%, respectively. Although a lower yield of reducing sugar was obtained, [EMIM]oAc pretreatment required the least energy to pretreat 1 kg of SCB. Moreover, the percentage of SCB loss during [EMIM]oAc pretreatment was the lowest. [EMIM]oAc‐pretreated SCB also had the lowest crystallinity index (CI) with the most amorphous structure. CONCLUSION: [EMIM]oAc appears to be another option for pretreating SCB, and other issues such as the recyclability of [EMIM]oAc is worth investigating. Copyright © 2011 Society of Chemical Industry 相似文献
43.
44.
The transient switching delay in a micro/nano-scale circuit containing resistive and reactive elements are sternly affected by the surge in the resistance arising from sub-linear current-voltage (I-V) characteristics limited by the velocity and current saturation. The saturation arises due to the realignment of randomly oriented velocity vectors to the unidirectional streamlined ones in a high electric field when voltage applied across a resistor exceeds its decreasing critical value with reduced channel length. The frequency response f = 1/2πτt is affected by a transit time delay τt is lower than that predicted from the application of Ohm’s law. The resistance surge dramatically boosts the RC time constant and switching delay and attenuates the L/R time constant and switching delay. 相似文献
45.
Analysis of Heuristic Graph Partitioning Methods for the Assignment of Packet Control Units in GERAN
Matías Toril Iñigo Molina-Fernández Volker Wille Chris Walshaw 《Wireless Personal Communications》2011,60(4):611-633
Over the last few years, graph partitioning has been recognized as a suitable technique for optimizing cellular network structure.
For example, in a recent paper, the authors proposed a classical graph partitioning algorithm to optimize the assignment of
cells to Packet Control Units (PCUs) in GSM-EDGE Radio Access Network. Based on this approach, the quality of packet data
services in a live environment was increased by reducing the number of cell re-selections between different PCUs. To learn
more about the potential of graph partitioning in cellular networks, in this paper, a more sophisticated, yet computationally
efficient, partitioning algorithm is proposed for the same problem. The new method combines multi-level refinement and adaptive
multi-start techniques with algorithms to ensure the connectivity between cells under the same PCU. Performance assessment
is based on an extensive set of graphs constructed with data taken from a live network. During the tests, the new method is
compared with classical graph partitioning approaches. Results show that the proposed method outperforms classical approaches
in terms of solution quality at the expense of a slight increase in computing time, while providing solutions that are easier
to check by the network operator. 相似文献
46.
The stability of PVDF hollow fibre membranes in sodium hydroxide (NaOH) aqueous solutions were investigated in this study. PVDF hollow fibre membranes were prepared from each of the three commercial raw PVDF materials (Kynar 761, Solef 1015 and Solef 6010) from two major suppliers (Atofina Chemicals Inc., USA and Solvay, Belgium) for comparison purposes. The effect of NaOH concentration, treatment time and temperature on mechanical properties, thermal properties and crystalline structure of the PVDF hollow fibre membranes were investigated through mechanical strength measurement, surface area analysis, XRD, FTIR and DSC analyses. The obtained results indicate that the reaction between PVDF and NaOH was initiated even at low concentrations of NaOH and was aggravated with the extended treatment time, resulting in the decrease in mechanical strength and crystallinity of PVDF hollow fibre membranes. The reaction was accelerated and intensified by increasing the concentration of NaOH and/or treatment temperature. At 70 °C, the mechanical integrity of the PVDF membranes was completely destroyed in 4 wt% NaOH solution within 24 h or in 10 wt% NaOH solution within 8 h. The deterioration of stability in NaOH solutions is considered universal for all PVDF employed in this study, irrespective of the raw materials or the corresponding hollow fibre membranes. 相似文献
47.
O. Šolcová L. Matějová P. Topka Z. Musilová P. Schneider 《Journal of Porous Materials》2011,18(5):557-565
Argon(87 K) and nitrogen(77 K) adsorption of three types of porous samples (microporous, microporous-mesoporous and mesoporous)
was evaluated. The shapes of isotherms, specific surface areas, mesopore-, micropore- and net pore volumes, pore-size distributions
(PSD) and positions of micropore and mesopore PSD’s maxima were compared to ascertain the credibility of individual adsorbates
for the texture information estimation. The shapes of adsorption isotherms for Ar and N2 of all samples are similar and the adsorbed amounts at relative pressure x = 0.975 differ slightly. For mesoporous samples some differences are observed between specific mesopore surface areas derived
from nitrogen and argon isotherms. Radii of pore size maxima from Ar(87 K) PSD’s are on average systematically lower than
from N2(77 K) for all samples. The Saito-Foley approach for ZSM-5 samples gives consistently lower mean pore radius from N2(77 K) adsorbate than from Ar(87 K). This difference probably arises from the multiplication factor, Ω, in the Saito-Foley
equation which includes physical properties (magnetic susceptibility, polarizability etc. at 77 and 87 K) and is not easy to obtain with sufficient precision. The use of both adsorbates Ar(87 K) and N2(77 K) possesses some advantages as well some disadvantages and the comparison of textural properties of individual samples
must be evaluated with respect to adsorbate. 相似文献
48.
Abbas Mehdizadeh Fazirulhisyam Hashim Raja Syamsul Azmir Raja Abdullah Borhanuddin Mohd. Ali 《Wireless Personal Communications》2014,77(3):2195-2212
Group key management is one of the key security issues in multicast networks. The main challenge is to provide a secure group key management method which avoids high key update cost in terms of the number of transmitted keys. In order to achieve low key update cost for group key management, most of the existing methods increase their encryption/decryption cycles which requires a strong cryptographic function. In this paper, a cost-effective key management method is proposed to address the problem of high key update cost without increasing the encryption/decryption cycles. We evaluated our proposed method with existing tree-based methods by using Markov chain and Poisson Arrival Process. Results indicate the efficiency of our proposed method in reducing the key update cost significantly compared to the existing tree-based key management methods. 相似文献
49.
Muhammad Aizat Noor Ismail Mansor Hashim Abdollah Hajalilou Ismayadi Ismail Muhammad Misbah M. Zulkimi Norhapishah Abdullah Wan Norailiana A. Rahman Mutia Suhaibah Abdullah Masni Manap 《Journal of Superconductivity and Novel Magnetism》2014,27(5):1293-1298
In this work, the physical and the magnetic properties of cobalt-zinc ferrite nanoparticles, synthesized via high-energy ball milling (HEBM), were examined. X-Ray diffraction (XRD), field emission scanning electron microscopy (FeSEM), and scanning transmission electron microscopy (STEM) were used to study changes of the powder structure and morphology analyses. Hysteresis and permeability measurement were carried out using a BH hysteresisgraph system and an impedance analyzer, respectively. The results suggested improved magnetic properties of Co0.5Zn0.5Fe2O4 with increasing sintering temperature from 950 °C up to 1200 °C. However, the variations of the magnetic responses were consistent with the varying volume concentration of the ferrite composites. Unlike the highly crystalline pure ferrite which showed magnetic resonance within the measured frequency, the crystallineamorphous composites showed no visible resonance peak. This proved that the resonance peak shifted to higher frequency as a result of the single domain spin behavior in the absence of domain walls movement. 相似文献
50.
Natália Tomašovičová Milan Timko Vlasta Závišová Anežka Hashim Jan Jadzyn Xavier Chaud Eric Beaugnon Peter Kopčanský 《International Journal of Thermophysics》2014,35(11):2044-2053
We have studied the influence of electric and magnetic fields on the orientational structure of ferronematics based on a thermotropic nematic 4-trans-4 \(^{\prime }\) -n-hexylcyclohexyl-isothiocyanato-benzene (6CHBT). The 6CHBT liquid crystal has been dissolved in phenyl isothiocyanate and doped with rod-like or chain-like magnetic particles. In such a mixture, the phase transition from an isotropic to a nematic phase is via a droplet state, i.e., coexistence of nematic and isotropic phases. The obtained results showed that a combination of the electric and magnetic fields can change the character of a phase transition from the isotropic to the nematic phase via the droplet state in such systems. Moreover, magneto-dielectric measurements of structural transitions showed the magnetic field induced a shift of the phase transition temperature from the isotropic to the droplet state. 相似文献