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81.
Performance scaling of passively mode-locked ultrashort-pulse fiber oscillators in terms of average power, peak power, and pulse energy is demonstrated. A very-large-mode-area fiber laser in an all-positive group-velocity-dispersion ring cavity configuration with intracavity spectral filter, mode-locked by nonlinear polarization evolution, emits 66 W of average power at 76 MHz repetition rate, corresponding to 0.9 μJ pulse energy. The pulses are dechirped to 91 fs outside the cavity with an average power of 60 W remaining after the compressor. The generated pulse peak power is as high as 7 MW. 相似文献
82.
Abdo A Saeed F Hamza H Ahmed A Salim N 《Journal of computer-aided molecular design》2012,26(3):279-287
Query expansion is the process of reformulating an original query to improve retrieval performance in information retrieval
systems. Relevance feedback is one of the most useful query modification techniques in information retrieval systems. In this
paper, we introduce query expansion into ligand-based virtual screening (LBVS) using the relevance feedback technique. In
this approach, a few high-ranking molecules of unknown activity are filtered from the outputs of a Bayesian inference network
based on a single ligand molecule to form a set of ligand molecules. This set of ligand molecules is used to form a new ligand
molecule. Simulated virtual screening experiments with the MDL Drug Data Report and maximum unbiased validation data sets
show that the use of ligand expansion provides a very simple way of improving the LBVS, especially when the active molecules
being sought have a high degree of structural heterogeneity. However, the effectiveness of the ligand expansion is slightly
less when structurally-homogeneous sets of actives are being sought. 相似文献
83.
Mohamed Ali Mahjoub Samia Ammar Kaouther Majouli Zine Mighri 《Chemistry of Natural Compounds》2012,47(6):955-958
Two new alkaloid derivatives of the 3-benzazocine skeleton (cotuzine A and B) and a new polyphenolic substance (3-(1,3-dihydroxyprop-2-yl)-4-hydroxyanisol)
(corimen) have been isolated from the aerial part (stems, leaves) of the plant Cotula coronopifolia (L.). These three new
structures were established by spectroscopic procedures (1H, 13C, one- and two-dimensional NMR). The stereochemistry of the new alkaloids was established based on different NOE effects
revealed on the NOESY spectrum. Mass spectrometry and IR spectroscopy were used to confirm these structures. 相似文献
84.
Houcine Ammar Fatma Abdelkafi Souhir Abid Bouchra Benjelloum-Mlayah Rachid El Gharbi Michel Delmas 《Chemistry of Natural Compounds》2012,48(1):99-102
Alfa grass pulping was successfully performed in hydro-organic acid medium under mild conditions (107°C, atmospheric pressure, cooking
time: 3 h). Use of an acetic acid/formic acid/water mixture as pulping liquor was perfectly suitable for selective isolation
of pulp, lignin, and hemicelluloses. The unbleached pulp obtained in good yield was first delignified by peroxyacids in organic
acid medium and then bleached with hydrogen peroxide in a basic medium to give pulp offering good physico-chemical and mechanical
characteristics. 相似文献
85.
Chakroune N Viau G Ammar S Poul L Veautier D Chehimi MM Mangeney C Villain F Fiévet F 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6788-6796
Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline. 相似文献
86.
Y. A. Ammar A. M. Sh. El‐Sharief A. G. Al‐Sehemi Y. A. Mohamed M. A. Senussi M. S. A. El‐Gaby 《中国化学会会志》2005,52(3):553-558
Ketene dithioacetal 3 , aminopyrazole 5 , tetrazine 7 , benzoazole 9 and pyridone 11 , 12 , 13 and 16 derivatives were prepared from cyanoacetanilide 1 as a starting material. 相似文献
87.
M. E. Kassem A. M. El-Khatib E. A. Ammar M. M. Denton 《Journal of Thermal Analysis and Calorimetry》1991,37(3):533-540
Thermodynamic studies of (LixK1?x)2SO4, LKS, mixed crystals have been made in the concentration range (x=0.1, 0.2, ...,x=0.5). The thermal behaviour has been investigated by differential thermal analysis, DTA, and differential scanning calorimeter, DSC, in the vicinity of high temperature phases. Also, the effect of the thermal neutron irradiations on the thermal properties of mixed crystals was studied. The results showed a change in the transition temperatureT c, as well as the value of specific heatC p at transition temperature, due to the change of stoichiometric ratio and radiation doses. The change of enthalpy and entropy of mixed crystals have been estimated numerically. 相似文献
88.
Binary 3-point scheme, developed by Hormann and Sabin [Hormann, K. and Sabin, Malcolm A., 2008, A family of subdivision schemes with cubic precision, Computer Aided Geometric Design, 25, 41-52], has been modified by introducing a tension parameter which generates a family of C1 limiting curves for certain range of tension parameter. Ternary 3-point scheme, introduced by Siddiqi and Rehan [Siddiqi, Shahid S. and Rehan, K., 2009, A ternary three point scheme for curve designing, International Journal of Computer Mathematics, In Press, DOI: 10.1080/00207160802428220], has also been modified by introducing a tension parameter which generates family of C1 and C2 limiting curves for certain range of tension parameter. Laurent polynomial method is used to investigate the continuity of the subdivision schemes. The performance of modified schemes has been demonstrated by considering different examples along with its comparison with the established subdivision schemes. 相似文献
89.
Ammar Mustafa N. M. Mikhailova N. S. Prostakov 《Chemistry of Heterocyclic Compounds》1996,32(1):65-67
9-Phenacylidene-4-azaf luorene and 9-bromo-9-(-bromophenacyl)-4-azafluorene have been used in the synthesis of spiro compounds with fragments of substituted pyrazolines. 1-Methyl-2-oxo-5 phenacylidene-indeno[2, 3-e]-1,2-dihydropyridine and hydrazine gave 1-methyl-2-oxo-3 phenylspiro[indeno(2, 3-e)-1,2-dihydropyridine-5,5-pyrazoline-2]. 相似文献
90.
Summary Glass layers of (V2O5)1−x
(P2O5)
x
were prepared by melting appropriate mixtures of V2O5 and P2O5 powders. The measurements ofI–V characteristic curves show three regions of conduction, namely high-resistance state, turnover point with zero-differential
resistance region (∂V/∂I=0) and differential negative-resistance region. The turnover point is strongly dependent on composition, sample thickness
and temperature. It is found that the increase of the ratio of phosphorus/vanadium reduces conductance as well as it raises
the field required to produce turnover behaviour. The data in the range up to the turnover point are discussed on the basis
of an electrothermal process. Results of the negative-resistance state could be explained in terms of a hopping mechanism. 相似文献