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981.
Low‐order density expansions cannot adequately describe recombination reactions. Therefore, the usefulness of an exact quantum virial expansion truncated at the order of ?5/2 is limited to the deeper interior of the Sun, where the plasma is nearly fully ionized. Here, intermediate steps towards full‐fledged solar modeling are presented. They are (i) a smooth numerical representation of the quantum virial expansion and (ii) the construction of a smooth transition to the low‐temperature regime (below 50,000 K), where the virial expansions breaks down due to H recombination. These technical steps are realized for a simplified H‐only plasma; the extension to He and heavier elements will be dealt with later. Ultimately, the outcome will be that solar observations can be used to test the accuracy of the virial equation of state and to compare it with current more phenomenological formalisms (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
982.
Yuki Yamamoto Jun‐ya Hasegawa Yoshikatsu Ito 《Journal of Physical Organic Chemistry》2012,25(3):239-247
The kinetics of carbamate formation from the reaction of carbon dioxide with α‐amino acids in D2O was first investigated by means of nuclear magnetic resonance spectroscopy. Potassium carbonate was used as the CO2 source. For each amino acid, the maximum carbamate yield, the apparent rate constant for the carbamate formation kapp, and the rate constants for the formation k1 and the breakdown k?1 of the carbamate were estimated. Plots of log k1 or log k?1 versus pKa of amino acids indicated that the formation rate k1 increased with the basicity (pKa) of amino acid, while the decomposition rate k?1 decreased. A Br?nsted β value of 0.39 was obtained from the former plot, being in good agreement with the previously reported ones (0.26–0.43). The observed negative pKa dependence of log k?1 (Br?nsted α = 0.34) is reasonable, because the carbamate decomposition is acid‐catalyzed and the steady‐state concentration of H+ should be higher for weaker basic amines. The charge (σ) and the lone‐pair energy (EN) at the nitrogen atom of the amino group were calculated. Although log k1 correlated with σ and EN, log k?1 was unrelated with both of these parameters. Considering that the carbamate formation (k1) is not only base‐catalyzed but should also be promoted by the nucleophilicity of the amino nitrogen, its correlation with σ and EN in addition to pKa is rational. The irrelevance of log k?1 to σ and EN is not surprising, because σ and EN are not a direct measure of [H+] of the solution. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
983.
Juan Bory Reyes Ricardo Abreu Blaya Martín P. Árciga Alejandre Yudier Peña Pérez 《Complex Analysis and Operator Theory》2018,12(5):1369-1382
In this paper we are interested in finding solvability conditions for Riemann and Dirichlet type boundary value problems with generalized Hölder-continuous boundary data in the case of hyperanalytic functions defined in a domain of the complex plane bounded by an h-summable closed curve. 相似文献
984.
Yi Zhang Senfu ZhangCaiqin Luo Juan DongQingfang Liu Jianbo Wang 《Journal of magnetism and magnetic materials》2012
An easy method of tuning the response of maximum magnetoimpedance (MI) ratio in Fe75.5Si13.5B7Nb3Cu1 amorphous ribbons was investigated by laser ablation. In order to obtain different GMI peak positions, the stripes were ablated by laser with different separations on the surface layer of the ribbon. When the stripes were parallel (or perpendicular) to the applied magnetic field, the peak location of maximum MI ratio would drift to larger (or smaller) external field. And the shift was correlated with the spaces between stripes. The applied fields corresponding to the minimum and maximum values of peak location are 13 Oe and 49 Oe at the frequency of 15 MHz, respectively. The phenomenon can be explained by the anisotropy field induced by demagnetizing field after the laser ablation. 相似文献
985.
Hédy Attouch Juan Peypouquet Patrick Redont 《Journal of Mathematical Analysis and Applications》2018,457(2):1095-1117
In this paper, we study the backward–forward algorithm as a splitting method to solve structured monotone inclusions, and convex minimization problems in Hilbert spaces. It has a natural link with the forward–backward algorithm and has the same computational complexity, since it involves the same basic blocks, but organized differently. Surprisingly enough, this kind of iteration arises when studying the time discretization of the regularized Newton method for maximally monotone operators. First, we show that these two methods enjoy remarkable involutive relations, which go far beyond the evident inversion of the order in which the forward and backward steps are applied. Next, we establish several convergence properties for both methods, some of which were unknown even for the forward–backward algorithm. This brings further insight into this well-known scheme. Finally, we specialize our results to structured convex minimization problems, the gradient-projection algorithms, and give a numerical illustration of theoretical interest. 相似文献
986.
987.
988.
Jian Dong Zhihao Zhuang Feng Song Debra Dunaway‐Mariano Paul R. Carey 《Journal of Raman spectroscopy : JRS》2012,43(1):65-71
4‐Hydroxybenzoyl‐CoA (4‐HB‐CoA) thioesterase from Arthrobacter is the final enzyme catalyzing the hydrolysis of 4‐HB‐CoA to produce coenzyme A and 4‐hydroxybenzoic acid in the bacterial 4‐chlorobenzoate dehalogenation pathway. Using a mutation E73A that blocks catalysis, stable complexes of the enzyme and its substrate can be analyzed by Raman difference spectroscopy. Here we have used Raman difference spectroscopy, in the non‐resonance regime, to characterize 4‐HB‐CoA bound in the active site of the E73A thioesterase. In addition, we have characterized complexes of the wild‐type enzyme complexed with the unreactive substrate analog 4‐hydroxyphenacyl‐CoA (4‐HP‐CoA). Both sets of complexes show evidence for two forms of the ligand in the active site: one population has the 4‐hydroxy group protonated, 4‐OH; while the second has the group as the hydroxide, 4‐O−. For bound 4‐HP‐CoA, X‐ray data show that glutamate 78 is close to the 4‐OH in the complex and it is likely that this is the proton acceptor for the 4‐OH proton. Although the pKa of the 4‐OH group on the free substrate in aqueous solution is 8.6, the relative populations of ionized and neutral 4‐HB‐CoA bound to E73A remain invariant between pH 7.3 and 9.8. The invariance with pH suggests that the 4‐OH and the ‐COO− of E78 constitute a tightly coupled pair where their separate pKa ‘s lose their individual qualities. Narrow band profiles are seen in the CO double bond and C‐S regions, suggesting that the hydrolyzable thioester group is rigidly bound in the active site in a syn gauche conformation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
989.
Mehdi Asghari‐Khiavi Bayden R. Wood Pejman Hojati‐Talemi Andrew Downes Don McNaughton Adam Mechler 《Journal of Raman spectroscopy : JRS》2012,43(2):173-180
Tip‐enhanced Raman scattering (TERS) spectroscopy is a promising technique for nanoscale chemical analysis. However, there are several challenges preventing widespread application of this technology, including reproducible fabrication of efficient TERS probes. These problems reflect a lack of clear understanding of the origins of, and the parameters influencing TERS. It is believed that the coating characteristics at the apex of the tip have a major effect on the near‐field optical enhancement and thus the TERS activity of a metalized probe. Here we show that the aspect ratio of the tip can play a significant role in the efficiency of TERS probes. We argue that the electrostatic field arising from the lightning‐rod effect has a substantial role in the observed TERS effect. This argument is supported by ‘edge‐enhanced Raman scattering’ which is shown for a noble metal film. Furthermore, it is reported that an associated tip‐surface‐enhanced Raman scattering effect can be achieved by using a TERS‐inactive metalized probe on a surface‐enhanced Raman spectroscopy‐inactive roughened surface. This observation can be explained by an interparticle enhancement of the electromagnetic field. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
990.
Extremal solutions for a nonlinear impulsive differential equations with multi-orders fractional derivatives 下载免费PDF全文
In this paper, by employing the lower and upper solutions method, we give an existence theorem for the extremal solutions for a nonlinear impulsive differential equations with multi-orders fractional derivatives and integral boundary conditions. A new comparison result is also established. 相似文献