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排序方式: 共有417条查询结果,搜索用时 15 毫秒
111.
Claeyssens F Ranaghan KE Manby FR Harvey JN Mulholland AJ 《Chemical communications (Cambridge, England)》2005,(40):5068-5070
Multiple profiles for the reaction from chorismate to prephenate in the enzyme chorismate mutase calculated with hybrid density functional combined quantum mechanics/molecular mechanics methods (B3LYP/6-31G(d)-CHARMM27) agree well with experiment, and provide direct evidence of transition-state stabilization by this important enzyme, which is at the centre of current debates about the nature of enzyme catalysis. 相似文献
112.
Divenyi PL Stark PB Haupt KM 《The Journal of the Acoustical Society of America》2005,118(2):1089-1100
A group of 29 elderly subjects between 60.0 and 83.7 years of age at the beginning of the study, and whose hearing loss was not greater than moderate, was tested twice, an average of 5.27 years apart. The tests measured pure-tone thresholds, word recognition in quiet, and understanding of speech with various types of distortion (low-pass filtering, time compression) or interference (single speaker, babble noise, reverberation). Performance declined consistently and significantly between the two testing phases. In addition, the variability of speech understanding measures increased significantly between testing phases, though the variability of audiometric measurements did not. A right-ear superiority was observed but this lateral asymmetry did not increase between testing phases. Comparison of the elderly subjects with a group of young subjects with normal hearing shows that the decline of speech understanding measures accelerated significantly relative to the decline in audiometric measures in the seventh to ninth decades of life. On the assumption that speech understanding depends linearly on age and audiometric variables, there is evidence that this linear relationship changes with age, suggesting that not only the accuracy but also the nature of speech understanding evolves with age. 相似文献
113.
A. Cunsolo A. Foti G. Immè G. Pappalardo G. Raciti N. Saunier B.T. Kim 《Nuclear Physics A》1981,355(1):261-268
Angular distributions of the charge exchange reaction 14C(6Li, 6He)14N leading to the 1+ ground state and 3.95 MeV 1+, and 5.20 MeV 2? excited states at the 34 MeV incident beam energy were analyzed and measured. The 62 MeV data of Goodman et al. were also reanalyzed. The direct one-step charge exchange caused by the spin-isospin dependent term in the two-body interaction can account well for the observed data. The strength of spin-isospin dependent effective interaction (gaussian form with a range parameter of 1.8 fm) was extracted to be 18.5 MeV. 相似文献
114.
The molar entropies (or heats) of transport of dilute aqueous alkali bromide solutions have been measured by the potentiometric method using the silver, silver bromide thermocell at a mean temperature of 25°C and over a concentration range of 5×10–4 to 0.1M. Experimental results were extrapolated to infinite dilution to obtain the standard molar entropies of transport. The limiting behavior observed is compared with theory based on the electrostatic model.The standard transported entropy of Br– was also derived by extrapolating the steady-state thermoelectric powers to infinite dilution. The absolute ionic entropies of transport of alkali metal ions have been estimated based on Gurney's scale. The results obtained are compared with that derived f1/om the previous work on alkali chlorides. 相似文献
115.
Yaln Elerman Hülya Kara Sabahat
zcan Engin Kendi 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(8):950-951
The crystal structure of the title compound, chloro(1,10‐phenanthroline‐N,N′)(1‐phenyl‐1,3‐butanedionato‐O,O′)copper(II), [CuCl(C10H9O2)(C12H8N2)], has been determined. The CuII ion displays a distorted square‐pyramidal coordination, being linked to the two O atoms of the benzoylacetonate ligand and the two N atoms of the 1,10‐phenanthroline ligand in the basal plane, and the Cl atom in the apical site. TheCu—N, Cu—O and Cu—Cl bond lengths are 2.043 (2)/2.025 (2), 1.914 (2)/1.941 (2) and 2.485 (1) Å, respectively. 相似文献
116.
Asl Genolu Sarkaya Bilgen Osman Ali Kara Nurdan Pazarlioglu Necati Beirli 《Biomedical chromatography : BMC》2016,30(2):88-96
In this study, antimicrobial pigment cinnabarinic acid (CA) was produced from Pycnoporus cinnabarinus in laboratory‐scale batch cultures. Magnetic poly(ethylene glycol dimethacrylate‐N‐methacryloyl‐l‐tryptophan methyl ester) [m‐poly(EGDMA‐MATrp)] beads (average diameter = 53–103 µm) were synthesized by copolymerizing of N‐methacryloyl‐l‐tryptophan methyl ester (MATrp) with ethylene glycol dimethacrylate (EGDMA) in the presence of magnetite (Fe3O4) and used for the adsorption of CA. The m‐poly(EGDMA‐MATrp) beads were characterized by N2 adsorption/desorption isotherms (Brunauer Emmet Teller), X‐ray photoelecron spectroscopy, scanning electron microscopy, infrared spectroscopy, thermal gravimetric analysis, electron spin resonance and swelling studies. The efficiency of m‐poly(EGDMA‐MATrp) beads for separation of CA from culture fluid was evaluated. The effects of pH, initial concentration, contact time and temperature on adsorption were analyzed. The maximum CA adsorption capacity of the m‐poly(EGDMA‐MATrp) beads was 272.9 mg g−1 at pH 7.0, 25 °C. All the isotherm data can be fitted with the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The adsorption process obeyed pseudo‐second‐order kinetic model. Thermodynamic parameters ΔH = 5.056 kJ mol−1, ΔS = 52.44 J K−1 mol−1 and ΔG = −9.424 kJ mol−1 to ‐11.27 kJ mol−1 with the rise in temperature from 4 to 40 °C indicated that the adsorption process was endothermic and spontaneous. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
117.
Stephanie Y. Lee Casey R. Christopher Kara J. Manke Tyson R. Vervoort 《Molecular physics》2014,112(18):2424-2432
The diatomic molecule tantalum hydride (TaH) and its isotopologue tantalum deuteride (TaD) have been detected for the first time by laser excitation spectroscopy. The gas-phase molecules were produced in a hollow cathode discharge. Two red-degraded bands, one arising from TaH at 636 nm and the other from TaD at 635 nm, have been recorded at sub-Doppler resolution by intermodulated fluorescence spectroscopy. A rotational analysis shows that both bands are Ω = 2←2 in character, with well-resolved Ω-doubling in the upper state of TaH. Analysis of the 181Ta magnetic dipole and electric quadrupole hyperfine structure reveals that the lower X3Φ2 electronic state of the two transitions arises from a σ2πδ electronic configuration, in agreement with previous theoretical calculations. The bond length in the TaH X3Φ2 (v = 0) level is found to be 1.756960(4) Å. 相似文献
118.
Khalid Sbiaai Yahia Boughaleb M'hammed Mazroui Abdelkader Kara 《Surface and interface analysis : SIA》2013,45(11-12):1702-1708
The authors aimed to investigate the diffusion of Cu monomer, dimer and trimer on Ag (110) (1×2) missing‐row surface. This problem is addressed through molecular dynamic simulation based on semi‐empirical many‐body potential, derived from the embedded atom method. Within this approach, we have identified and calculated the activation energy of each microscopic mechanism. Thus, for Cu monomer, the diffusion process occurs essentially by simple hopping between nearest‐neighbor sites. While for the Cu dimer, three processes have been identified such as dissociation–reassociation (DR), concerted jump (CJ) and leapfrog mechanisms (LF) with a slight predominance of DR process and a dual competition between CJ and LF processes. But, in the case of small one‐dimensional cluster such as trimer on (110)(1×2) missing‐row reconstructed surface, the main diffusion mechanism is the LF process. These results shed light on the diffusion processes on missing‐row reconstructed surfaces, especially for heterogeneous systems. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
119.
Kara E. Humanski Santanna D. Patterson Paul J. Pecorin Madeline M. Perfitt Janet Romero William R. Sassack 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):709-717
AbstractNovel trisubstituted ethylenes, ring-substituted propyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO2C3H7 (where R is 4-chloro-3-fluoro, 2-fluoro-5-iodo, 2-fluoro-6-iodo, 2-trifluoromethyl, 3-trifluoromethyl, 4-trifluoromethyl, 2-trifluoromethoxy, 3-trifluoromethoxy, and 4-trifluoromethoxy) were prepared and copolymerized with styrene. The ethylenes were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and propyl cyanoacetate and characterized by CHN analysis, FTIR, 1H and 13C NMR. All the ethylenes were copolymerized with styrene in solution with radical initiation (ABCN) at 70?°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by FTIR, 1H and 13C NMR. Decomposition of the copolymers in nitrogen (TGA) occurred in two steps, first in the 250–500?°C range with residue (0.5–3.1% wt.), which then decomposed in the 500–700?°C range. 相似文献
120.
Merve Kara Sajjad Dadashi‐Silab Yusuf Yagci 《Macromolecular rapid communications》2015,36(23):2070-2075
A new phenacyl‐type photoinitiator based on ethyl carbazole as a long wavelength photoinitiator is developed for free radical polymerization. Phenacyl ethyl carbazolium hexafluoroantimonate (PECH) photoinitiator is synthesized in a two‐step, one‐pot manner by quaternizing ethyl carbazole with phenacyl bromide and subsequent ion exchange reaction with potassium hexafluoroantimonate. Under irradiation, PECH tends to undergo homolytic bond cleavage bringing about initiating free radicals. However, as evidenced by cyclic voltammetry and real‐time photobleaching studies, formation of initiating cationic species is highly unlikely as the photochemically formed charged carbazole units tend to couple.