排序方式: 共有25条查询结果,搜索用时 31 毫秒
11.
Amel Boudjemaa Aline Auroux Souhila Boumaza Mohamed Trari Ouiza Cherifi Rabah Bouarab 《Reaction Kinetics and Catalysis Letters》2009,98(2):319-325
The effect of the structure of the achiral primary amine additive on the enantioselective heterogeneous catalytic hydrogenation
of (E)-2-methyl-2-butenoic acid over cinchonidine modified Pd/Al2O3 was studied. It was found that a variety of amines increase the enantioselectivity, which was always accompanied by decrease
in the initial rate of the hydrogenations. Based on these results, the participation of the amine additive in the formation
of the intermediate complex responsible for enantioselection was suggested. A decrease in the reaction temperature resulted
in further increase in the optical purity of the product up to 67%, the highest value reported in the hydrogenation of unsaturated
aliphatic acids in this heterogeneous catalytic system so far. 相似文献
12.
R. Engel-Herbert A. Locatelli S. Cherifi D.M. Schaadt J. Mohanty K.H. Ploog E. Bauer R. Belkhou S. Heun A. Pavlovska T. Leo T. Hesjedal 《Applied Physics A: Materials Science & Processing》2006,84(3):231-236
We studied the magnetic coupling of ferromagnetic, submicron-sized stripes in the material system MnAs on GaAs. A specific coupling state, determined by stripe period and stripe width, can be tuned via film thickness and temperature, respectively. Micromagnetic imaging – in combination with micromagnetic simulations – reveals two coupling regimes. Strong magnetic coupling between the stripes creates micromagnetic domains extending across several stripes, whereas weak coupling allows for demagnetization within individual stripes. This behavior is observed for all investigatedfilm thicknesses, since a stripe geometry leading to a given coupling scenario is a function of temperature. PACS 68.37.Rt; 68.35.Rh; 75.70.-i; 75.70.Kw 相似文献
13.
K. Bachari A. Touileb N. Tahir A. Saadi D. Halliche O. Cherifi 《Kinetics and Catalysis》2011,52(1):48-54
A series of chromium-containing mesoporous silicas with different Cr contents were prepared and characterized with chemical
analysis, N2 adsorption measurements (BET equation and BJH theory), X-ray diffraction, diffuse reflectance UV-visible and H2-temperature programmed reduction techniques. Excellent results in benzylation of benzene and substituted benzenes employing
benzyl chloride as the alkylating agent were obtained. The mesoporous chromium-containing materials showed both high activity
and high selectivity for benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic
compounds is in the following order: benzene > toluene > p-xylene > anisole. Kinetics of the benzene benzylation over these catalysts has also been investigated. 相似文献
14.
Many web platforms now include recommender systems. Network representation learning has been a successful approach for building these efficient recommender systems. However, learning the mutual influence of nodes in the network is challenging. Indeed, it carries collaborative signals accounting for complex user-item interactions on user decisions. For this purpose, in this paper, we develop a Mutual Interaction Graph Attention Network “MIGAN”, a new algorithm based on self-supervised representation learning on a large-scale bipartite graph (BGNN). Experimental investigation with real-world data demonstrates that MIGAN compares favorably with the baselines in terms of prediction accuracy and recommendation efficiency. 相似文献
15.
A new method of contrast enhancement based on steerable pyramid transform is presented in this work. The use of steerable
filters is motivated by the fact that the images are to be observed by human and therefore it would be better to incorporate
some knowledge on the Human Visual System in the design of the image processing tool. Here, the frequency and directional
selectivity of the HVS is modeled by the steerable filters. The contrast is amplified using a selective nonlinear function
which simulates the nonlinearity response of the HVS to the luminance stimuli. So the basic idea is to enhance the luminance
signal irrespective of the two chrominance components using a multidirectional and multiscale decorrelation color transform.
Initially the rgb (red, green and blue) color image is converted to lab (luminance and chrominance) color image. Only the luminance component
is transformed by the steerable pyramid transform, so that the luminance component is independently decomposed into different
scale and orientation sub-bands. The contrast in each sub-band is enhanced using a nonlinear mapping function. Finally the
rgb color image is obtained from the enhanced luminance component along with the original chrominance components. The performance
of the proposed method is objectively evaluated using spectrum energy analysis and a visibility map based on a perceptual
filtering model. The obtained results confirm the efficiency of the method in enhancing subtle details without affecting color
balance and without the usual noise amplification and edge ringing effect. 相似文献
16.
N. Cherifi A. BenAboura M. Save L. Billon 《Journal of polymer science. Part A, Polymer chemistry》2012,50(19):3976-3985
In this work, we describe the “in situ” synthesis of “all‐acrylic” copolymer (n‐butyl acrylate‐co‐methyl methacrylate)/clay materials at different low contents of raw and modified Montmorillonite (1–4 wt % versus monomer). The cationic 2,2′ azobis‐(amidinopropane)dihydrochloride initiator was used to modified the clay by cation exchange in combination with the N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] (SG1) nitroxide to synthesize the polymer/clay nanocomposite via nitroxide mediated controlled radical polymerization. All synthesized materials are characterized by proton nuclear magnetic resonance, size exclusion chromatography, thermogravimetric analysis and differential scanning calorimetry techniques. The thermo‐mechanical properties of the synthesized materials are also reported. The results show that a decrease in molar masses and/or slight changes in molar compositions of poly (n‐butyl acrylate‐ co‐methyl methacrylate)/clay systems can be balanced by clay loading in polymer matrix, and consequently compensated or masked clay effects on physical properties of obtained materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
17.
Mohammed El Hassouni Hocine Cherifi Driss Aboutajdine 《IEEE transactions on image processing》2006,15(3):572-581
In this paper, a new spatiotemporal filtering scheme is described for noise reduction in video sequences. For this purpose, the scheme processes each group of three consecutive sequence frames in two steps: 1) estimate motion between frames and 2) use motion vectors to get the final denoised current frame. A family of adaptive spatiotemporal L-filters is applied. A recursive implementation of these filters is used and compared with its nonrecursive counterpart. The motion trajectories are obtained recursively by a region-recursive estimation method. Both motion parameters and filter weights are computed by minimizing the kurtosis of error instead of mean squared error. Using the kurtosis in the algorithms adaptation is appropriate in the presence of mixed and impulsive noises. The filter performance is evaluated by considering different types of video sequences. Simulations show marked improvement in visual quality and SNRI measures cost as well as compared to those reported in literature. 相似文献
18.
Cherifi T. Abouchi N. Guo-Neng Lu Bouchet-Fakri L. Quiquerez L. Sorli B. Chateaux J.-F. Pitaval M. Morin P. 《IEEE transactions on circuits and systems. I, Regular papers》2005,52(12):2576-2583
For improving sensitivity of nuclear magnetic resonance (NMR) measurements, an in-field preamplifier in a low-cost CMOS process is presented. It is based on a second-generation positive current conveyor (CCII+), with an impedance-matching output stage. The circuit has been designed with optimization of key performances, such as bandwidth, noise, and offset voltage. There have also been precautions taken against potential effect of strong magnetic field under which the circuit should operate. The designed preamplifier has a voltage gain of 15 dB and a bandwidth of 100 MHz. After fabrication of the circuit, we have carried out testing work, including in-field circuit test and characterization of MOS transistors. Under 2-T magnetic field, there have not been substantial changes in overall circuit performances compared to results obtained by post-layout simulations. For an experiment of NMR measurements with and without in-field preamplifier, the circuit is coupled with a receiver micro-coil. The experiment has been to detect protons at 85.13-MHz resonance frequency under 2-T magnetic field with water sample. The obtained results have shown a 14-dB signal-to-noise ratio improvement when the preamplifier is associated with the receiver coil. 相似文献
19.
20.
Iqra Erum Rauf Ahmed Shams Malick Ghufran Ahmed Hocine Cherifi 《Entropy (Basel, Switzerland)》2022,24(8)
News reports in media contain news about society’s social and political conditions. With the help of publicly available digital datasets of events, it is possible to study a complex network of mass violations, i.e., Mass Killings. Multiple approaches have been applied to bring essential insights into the events and involved actors. Power law distribution behavior finds in the tail of actor mention, co-actor mention, and actor degree tells us about the dominant behavior of influential actors that grows their network with time. The United States, France, Israel, and a few other countries have been identified as major players in the propagation of Mass Killing throughout the past 20 years. It is demonstrated that targeting the removal of influential actors may stop the spreading of such conflicting events and help policymakers and organizations. This paper aims to identify and formulate the conflicts with the actor’s perspective at a global level for a period of time. This process is a generalization to be applied to any level of news, i.e., it is not restricted to only the global level. 相似文献