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排序方式: 共有920条查询结果,搜索用时 46 毫秒
911.
M. Saeed Abaee Somayeh CheraghiSomayeh Navidipoor Mohammad M. Mojtahedi Soodabeh Forghani 《Tetrahedron letters》2012,53(33):4405-4408
An efficient synthesis of β-aryl-β-mercapto ketones is achieved via a tandem aldol condensation-thia-Michael addition process using an aqueous medium and diethylamine. Addition of different thiols to α,β-unsaturated ketones, formed in situ from the condensation of acetophenone derivatives with aldehydes, led to a rapid and high yielding synthesis of the products under very mild conditions using no expensive additive or catalyst. Products which precipitated spontaneously in the reaction mixtures were separated by simple filtration and purified by recrystallization. 相似文献
912.
Ali Keivanloo Mohammad Bakherad Hossein Nasr-Isfahani Somayeh Esmaily 《Tetrahedron letters》2012,53(25):3126-3130
A highly efficient one-pot synthesis of 5,6-disubstituted-5H-pyrrolo[2,3-b]pyrazine-2,3-dicarbonitriles is presented. The reaction of 5-(alkyl-arylamino)-6-chloropyrazine-2,3-dicarbonitriles with phenylacetylene, catalyzed by Pd–Cu, in the presence of SDS as the surfactant in water, leads to the desired products in good-to-high yields. 相似文献
913.
Gerhard Post Samad Ahmadi Sophia Daskalaki Jeffrey H. Kingston Jari Kyngas Cimmo Nurmi David Ranson 《Annals of Operations Research》2012,194(1):385-397
The High School Timetabling Problem is amongst the most widely used timetabling problems. This problem has varying structures
in different high schools even within the same country or educational system. Due to lack of standard benchmarks and data
formats this problem has been studied less than other timetabling problems in the literature. In this paper we describe the
High School Timetabling Problem in several countries in order to find a common set of constraints and objectives. Our main
goal is to provide exchangeable benchmarks for this problem. To achieve this we propose a standard data format suitable for
different countries and educational systems, defined by an XML schema. The schema and datasets are available online. 相似文献
914.
Omran Ahmadi 《Designs, Codes and Cryptography》2006,38(3):395-397
Joseph Yucas and Gary Mullen conjectured that there is no self-reciprocal irreducible pentanomial of degree n over
if n is divisible by 6. In this note we prove this conjecture for the case n ≡ 0, and disprove the conjecture for the case n ≡
6 (mod 12)
AMS Classifications: 11T55 相似文献
915.
Sepideh Khoee Somayeh Zamani Masoumeh Tajik 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,72(5):1054-1061
Several diamines with remarkable different polarities were used to produce photoactive poly(amide–imide)s (PAI)s in a quantitative yield. The absorption, fluorescence and photophysical properties of series of poly(amide–imide)s containing fused aromatic systems as energy donor and energy acceptor with different diamines cores are described. Poly(amide–imide)s exhibit broad fluorescent characteristic, and its fluorescent intensity is related to the intermolecular chain–chain or chain–solvent interaction. The fluorescence spectra confirmed an efficient singlet–singlet energy transfer between fused aromatic systems. The self-quenching mechanism was studied according to the specific behavior of these polymers in different solvents. The self-quenching rate constant for the association reaction in the excited state (Kq) could be measured from the Stern–Volmer equation. The kind of fused system and diamines show different electron migration mechanisms and photoluminescent properties in the singlet-excited states. By using the exothermic energy transfer as a function of diamine polarity, the electron transfer mechanism was evaluated for aromatic poly(amide–imide)s. In principle, the fluorescence energy is absorbed by different (PAI)s and raises the molecules to one of its excited states. Afterwards this excitation energy transfers through the different relaxation channels, i.e. columbic or exchange energy transfer. 相似文献
916.
The aim of this paper is to investigate the entropy properties of current records. Several characterizations are obtained based on the entropy of these statistics. It is proved that the equality of the entropy of the endpoints of record coverage is a characteristic property of symmetric distribution. It is shown that the parent distribution can be identified uniquely by the entropy properties of the endpoints of record coverage. Considering the records coming from distribution with decreasing (increasing) density, the monotonicity of entropy of current records is discussed. We also prove that the dispersive ordering of the parent distributions implies the entropy ordering of their respective current records. 相似文献
917.
Mohammad Reza Aziziyan Narjes Moghadam Davood Fathi Vahid Ahmadi 《Applied Physics A: Materials Science & Processing》2012,109(2):481-488
The effects of uniaxial and torsional strains on the double-lightly doped MOSCNT (DLD-MOSCNT) performances are investigated, using the non-equilibrium Green function (NEGF) formalism in mode space approach. The Hamiltonian of the device is obtained by a tight-binding approximation assuming that only p z orbitals are contributing in carrier transport. In all simulation processes, one mode with the lowest subband is considered. DLD-MOSCNT has a small band-to-band tunneling and almost eliminates the ambipolar behavior of I DS–V GS characteristics because of the band engineering. We use a modified model to demonstrate the strain effects on such a low OFF-current device. The results show that the strain effects mainly depend on the chiral vector and diameter of CNT. The strain causes band gap and carrier velocity changes, which result in variation of ON- or OFF-current. In addition, the subthreshold swing of this device under uniaxial strain is calculated, which is about 61 mV/Dec for 2 % tensile strain in (16,0) and for ?2 % compressive strain in (17,0). Under the uniaxial strain, in the case that the energy band gap increases, the variation of DIBL is very small. 相似文献
918.
919.
Dr. Raju Bej Dr. Chuanxiong Nie Dr. Kai Ludwig Dr. Vahid Ahmadi Dr. Jakob Trimpert Julia M. Adler Dr. Tatyana L. Povolotsky Dr. Katharina Achazi Marten Kagelmacher Ricardo Martin Vidal Dr. Jens Dernedde Dr. Benedikt B. Kaufer Prof. Dr. Rainer Haag 《Angewandte Chemie (International ed. in English)》2023,62(29):e202304010
Mucins are the key component of the defensive mucus barrier. They are extended fibers of very high molecular weight with diverse biological functions depending strongly on their specific structural parameters. Here, we present a mucin-inspired nanostructure, produced via a synthetic methodology to prepare methacrylate-based dendronized polysulfates ( MIP-1 ) on a multi gram-scale with high molecular weight (MW=450 kDa) and thiol end-functionalized mucin-inspired polymer ( MIP ) via RAFT polymerization. Cryo-electron tomography (Cryo-ET) analysis of MIP-1 confirmed a mucin-mimetic wormlike single-chain fiber structure (length=144±59 nm) in aqueous solution. This biocompatible fiber showed promising activity against SARS-CoV-2 and its mutant strain, with a remarkable low half maximal (IC50) inhibitory concentration (IC50=10.0 nM). Additionally, we investigate the impact of fiber length on SARS-CoV-2 inhibition by testing other functional polymers ( MIPs ) of varying fiber lengths. 相似文献
920.
Electrochemical determination of melatonin in the presence of tryptophan is a challenge because of the coincidence of voltammetric signals of these compounds when executing a voltammetric technique. The new method for selective determination of melatonin based on the square wave anodic stripping voltammetry determination of an electroactive product of melatonin was suggested here. This product is produced by previously applied positive pre-potential to a carbon paste electrode, immersed in the test solution. By this means, the electrochemical signal of melatonin was separated effectively from that of tryptophan, making it possible to determine melatonin in the presence of a high concentration of tryptophan. The effect of important parameters on electrode performance was studied and optimized. The optimum response was obtained at pH=2 and utilizing the pre-potential magnitude of +0.8 V, applied for 10 s. A linear relationship was found between peak current intensity and melatonin concentrations over the range of 5.00×10−7 to 8.00×10−5 mol L−1. A detection limit of 8.30×10−8 mol L−1 was calculated for the method (S/N=3). The selectivity of the method was considerably high, because of the independence of melatonin signal to the presence of higher amounts of some potentially interfering agents such as ascorbic acid, tryptophane glucose, etc. As an analytical application, the proposed sensor was used for the determination of melatonin in pharmaceutical and food samples. 相似文献