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排序方式: 共有367条查询结果,搜索用时 968 毫秒
251.
Navid Khani Mir Masoud Seyyed Fakhrabadi Mohammad Vahabi Babak Kamkari 《Applied Physics A: Materials Science & Processing》2014,116(4):1687-1694
This article discusses the vibrational properties of silicon carbide nanotubes with various dimensions, chiralities and boundary conditions. The molecular mechanics-based finite element method is applied to study the mode shapes and natural frequencies of the silicon carbide nanotubes. The results reveal that the natural frequencies of the nanotubes increase with decreasing length, but they do not show monotone behaviors vs. diameter changes. The reasons are discussed in detail. 相似文献
252.
253.
An efficient one-pot method has been developed for the synthesis of α-oxycarbanilinophosphonates via a one-pot reaction of an aldehyde with diethyl phosphite in the presence of magnesium oxide followed by reaction with an isocyanate under solvent-free conditions using ultrasonic irradiation. This method is simple, rapid and good yielding. 相似文献
254.
Yip HL Ma H Jen AK Dong J Parviz BA 《Journal of the American Chemical Society》2006,128(17):5672-5679
Strong hydrogen bonding and pi-pi stacking between 1-pyrylphosphonic acid (PYPA) molecules were exploited to create self-assembled two-dimensional supramolecular structures. Polycrystalline films of these laminate crystalline PYPA bilayers were easily deposited onto the solid supports through a simple spin-coating technique. Atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption, and fluorescence spectroscopy reveal that processing parameters, such as solvent, concentration, and surface of the substrate, are critical factors in determining the final morphology of the stacked film. Robust laminate structures could be obtained only when short alkyl chain protic solvents (methanol or ethanol) and a nonhydrophobic substrate surface were used. Polycrystalline films were formed through the nucleation and growth of PYPA molecules into laminate structures at the air/solvent interface before they land on the substrate during the spin-coating process. These films possess good mechanical properties and were easily transferred onto a SiO2/Si substrate that was patterned with Au electrodes without breaking their crystalline structures. The successful transfer of the laminate crystals allows us to probe their electrical properties through a field effect transistor device. A gating effect on the charge transport of the stacked films indicates that PYPA laminate crystal possesses p-typed semiconductor characteristics. 相似文献
255.
Physicochemical properties of low molecular weight alkylated chitosans: a new class of potential nonviral vectors for gene delivery 总被引:3,自引:0,他引:3
Ercelen S Zhang X Duportail G Grandfils C Desbrières J Karaeva S Tikhonov V Mély Y Babak V 《Colloids and surfaces. B, Biointerfaces》2006,51(2):140-148
Low molecular weight chitosans grafted with N-/2(3)-(dodec-2-enyl)succinoyl groups (HM-LMW-chitosans) with a mean molecular mass of 5 kDa, a degree of acetylation of 3% and a degree of tetradecenoyl substitution (TDC) of 3–18 mol% have been synthesized. These molecules are monodisperse and soluble in water at neutral pH. Using tensiometry and Nile Red fluorescence, the HM-LMW-chitosans were found to form micelles through hydrophobic interactions involving their tetradecenoyl chains and nonprotonated glucosamine monomers. Their critical micelle concentration decreases with increasing TDC values but varies little with pH and salt. Interaction with large unilamellar vesicles taken as model membranes indicated that HM-LMW-chitosans interact mainly with vesicles mimicking the inner leaflet of biomembranes both through electrostatic and hydrophobic interactions. This preferential interaction may destabilize endosomal membranes and favor the DNA release into the cytoplasm in gene delivery applications. Moreover, since this interaction significantly decreased the membrane fluidity of these vesicles, the HM-LMC-chitosans are thought to exhibit limited lateral mobility and flip-flop ability, and thus, limited cytotoxicity. These properties suggest that the HM-LMW-chitosans may constitute a promising new class of nonviral vectors for gene therapy. 相似文献
256.
Wang XB Woo HK Wang LS Minofar B Jungwirth P 《The journal of physical chemistry. A》2006,110(15):5047-5050
The electronic structure and electron affinity of the acetyloxyl radical (CH3COO) were investigated by low-temperature anion photoelectron spectroscopy and ab initio calculations. Photoelectron spectra of the acetate anion (CH3COO-) were obtained at two photon energies (355 and 266 nm) and under three different temperatures (300, 70, and 20 K) with use of a new low-temperature ion-trap photoelectron spectroscopy apparatus. In contrast to a featureless spectrum at 300 K, a well-resolved vibrational progression corresponding to the OCO bending mode was observed at low temperatures in the 355 nm spectrum, yielding an accurate electron affinity for the acetyloxyl radical as 3.250 +/- 0.010 eV. This experimental result is supported by ab initio calculations, which also indicate three low-lying electronic states observed in the 266 nm spectrum. The calculations suggest a 19 degrees decrease of the OCO angle upon detaching an electron from acetate, consistent with the vibrational progression observed experimentally. 相似文献
257.
Gallai conjectured that every 4-critical graph on n vertices has at least 5/3n-2/3 edges. We prove this conjecture for 4-critical graphs in which the subgraph induced by vertices of degree 3 is connected. 相似文献
258.
Russian Physics Journal - The article describes circuit schematics, features and design methodology of microwave integrated digital step attenuators (DSAs) based on SiGe technology (SiGe BiCMOS).... 相似文献
259.
260.
Babak Jabarnejad 《Journal of Pure and Applied Algebra》2018,222(7):1906-1910
In this paper we describe the defining equations of the multi-Rees algebra over a Noetherian ring R when I is an ideal of linear type. This generalizes a result of Ribbe and recent work of Lin–Polini and Sosa. 相似文献