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41.
Nouali Fatiha Kibou Zahira Boukoussa Bouhadjar Choukchou-Braham Noureddine Bengueddach Abdelkader Villemin Didier Hamacha Rachida 《Research on Chemical Intermediates》2020,46(6):3179-3191
Research on Chemical Intermediates - An efficient and green procedure for the synthesis of 2-aminopyridines derivatives via four-component reaction of acetophenone, malononitrile, triethoxymethane... 相似文献
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C. Bru-Chevallier H. Chouaib A. Bakouboula T. Benyattou 《Applied Surface Science》2006,253(1):194-199
Photoreflectance (PR) spectroscopy has proven to be a very efficient non-destructive tool to get information on various semiconducting epitaxial structures as it is very sensitive to every direct optical transitions in semiconducting quantum structures and allows as well to optically measure internal electric fields in space charge layers, through Franz-Keldysh oscillation (FKO) analysis. We have developed an experimental setup to get micro-PR spectra on epitaxial structures or devices on a few micrometer size spots. Due to very low signal intensity, experimental conditions have to be very carefully controlled: the signal/noise ratio strongly depends on the pump-probe power ratio.We give experimental micro-PR results recorded on antimonide-based heterojunction bipolar transistors (HBTs), which give the local electric field at the emitter-base junction under different biasing conditions. A second part of the paper is devoted to micro-PR analysis performed on tuneable vertical cavity surface emitting layers (VCSELs) with InP/air Bragg mirrors. In such VCSELs, both the cavity Fabry-Perot peak and the active region quantum well ground state are giving transitions in the micro-PR spectrum. This is very useful in the case of a tuneable structure. Feasibility of micro-PR analysis at the device scale is demonstrated. 相似文献
44.
Marie Thérèse Aimar Abdelkader Intissar Jean Martin Paoli 《Communications in Mathematical Physics》1993,156(1):169-177
We consider a closed densely defined linear operatorT in a Hilbert spaceE, and assume the existence of
0 (T) such thatK = (T -
0
I)-1 is compact and the existence ofp>0 such thats
n
(K)=o((n
–1/p)), whereS
n
(K) denotes the sequence of non-zero eigenvalues of the compact hermitian operator
. In this work, sufficient conditions (announced in [1]) are introduced to assure that the closed subspace ofE spanned by the generalized eigenvectors ofT coincides withE. These conditions are in particular verified by a family of non-self-adjoint operators arising in reggeon's field theory. 相似文献
45.
Abdelkader Intissar 《Communications in Mathematical Physics》1987,113(2):263-297
In this paper, we study a few spectral properties of a non-symmetrical operator arising in the Gribov theory. The first and second section are devoted to Bargmann's representation and the study of general spectral properties of the operator: $$\begin{gathered} H_{\lambda ',\mu ,\lambda ,\alpha } = \lambda '\sum\limits_{j = 1}^N {A_j^{ * 2} A_j^2 + \mu \sum\limits_{j = 1}^N {A_j^ * A_j + i\lambda \sum\limits_{j = 1}^N {A_j^ * (A_j + A_j^ * )A_j } } } \hfill \\ + \alpha \sum\limits_{j = 1}^{N - 1} {(A_{j + 1}^ * A_j + A_j^ * A_{j + 1} ),} \hfill \\ \end{gathered}$$ whereA* j andA j ,j∈[1,N] are the creation and annihilation operators. In the third section, we restrict our study to the case of nul transverse dimension (N=1). Following the study done in [1], we consider the operator: $$H_{\lambda ',\mu ,\lambda } = \lambda 'A^{ * 2} A^2 + \mu A^ * A + i\lambda A^ * (A + A^ * )A,$$ whereA* andA are the creation and annihilation operators. For λ′>0 and λ′2≦μλ′+λ2. We prove that the solutions of the equationu′(t)+H λ′, μ,λ u(t)=0 are expandable in series of the eigenvectors ofH λ′,μ,λ fort>0. In the last section, we show that the smallest eigenvalue σ(α) of the operatorH λ′,μ,λ,α is analytic in α, and thus admits an expansion: σ(α)=σ0+ασ1+α2σ2+..., where σ0 is the smallest eigenvalue of the operatorH λ′,μ,λ,0. 相似文献
46.
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Cycloaddition reactions are an integral and weighty part of organic chemistry in pedagogy and research as well. The wealthy literature on cycloaddition reactions from their birth up to now, unequivocally witnesses to their leading chemistry. The so-called “conventional solvents” are organic solvents that have indubitably promoted their success. Yet, the toxicity facet of these solvents impedes their use freely and with no fear. Not only is the operating chemist uncomfortable while experimenting, but also the environment is equally threatened. Working out the cycloaddition reactions and other organic ones in aqueous systems would certainly bring some relief to the chemist and to the environment as well. Unusual outcomes in terms of yield, reactivity and selectivity compared to those performed in organic solvents were commonly observed, and have overwhelmed the chemists with surprise indeed. In this review, homo Diels–Alder reactions in aqueous media include those involving the following dienophiles: maleimides, α,β-unsaturated esters, p-benzoquinones, vinyl ketones, phenyl-1-(2-pyridyl)-2-propen-1-one, α,β-unsaturated esters. A special case is the organocatalysis of Diels–Alder cycloaddition of α,β-unsaturated ketones (aldehydes). Of no less importance, some hetero Diels–Alder cycloaddition reactions in water systems are delineated. The impact of additives (salts, organic and inorganic chemicals), micellar catalysis and Lewis/Brønstëd acid catalysis on outcomes of such cycloaddition reactions is discussed. The 1,3-dipolar cycloaddition methodology applied to aqueous media has brought forth a number of heterocyclic compounds, usually with a regio- and stereoselectivity pecularity. These heterocycles include triazoles, tetrazoles, pyrazoles, isoxazoles, isoxazolidines, pyrroles and pyrrolidines. The superiority of copper(I) catalysis in the azide-alkyne cycloaddition (Huisgen cycloaddition) in water is endorsed by a number of examples. 相似文献
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Tabti Hadja Alia Adjdir Mehdi Ammam Abdelkader Mdjahed Baghdad Guezzen Brahim Ramdani Amina Benddedouche Choukry Kamel Bouchikhi Noria Chami Nadir 《Research on Chemical Intermediates》2020,46(12):5377-5390
Research on Chemical Intermediates - A range of Cu-LDHs has been synthesized by co-precipitation using metal nitrate precursors and sodium carbonate under varying molar ratios Cu/Al... 相似文献
50.
Imene Terrab Rachida Ouargli Bouhadjar Boukoussa Kamel Ghomari Rachida Hamacha René Roy Abdelkrim Azzouz Abdelkader Bengueddach 《Research on Chemical Intermediates》2017,43(7):3775-3786
Three mesoporous silica, SBA-16, SBA-15 and MCM-41, with different structures and porosities were synthesized via a hydrothermal method and their interactions with carbon dioxide (CO2) were investigated through thermal programmed desorption (TPD) and differential scanning calorimetry. TPD measurements provided precise assessments of the intrinsic affinity towards CO2, without the influence of moisture. All silica materials were found to exhibit intrinsic affinity towards carbon dioxide, but the surface basicity, expressed in terms of retained CO2 amount, is markedly influenced by increases in pore size and framework structures. SBA-15 displayed the highest CRC values, explained in terms of larger pore size, lower numbers of acidic out-of plane Si–OH and higher numbers of much less acidic in-plane silanols. These findings provide valuable information for a better understanding of the role of the silica structure in the intrinsic basicity, prior to further modifications for improving the affinity towards CO2 or merely for catalysis purposes involving CO2 as reagents, intermediates or products. 相似文献