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271.
Peter Bürgisser Felipe Cucker Martin Lotz 《Foundations of Computational Mathematics》2005,5(4):351-387
In [8] counting complexity classes #PR and #PC in the Blum-Shub-Smale (BSS) setting of
computations over the real and complex numbers, respectively,
were introduced. One of the main results of [8] is that the problem
to compute the Euler characteristic of a semialgebraic set
is complete in the class FPR#PR.
In this paper, we prove that the corresponding result is true
over C, namely that the computation of the Euler characteristic
of an affine or projective complex variety is complete
in the class FPC#PC. We also obtain a corresponding
completeness result for the Turing model. 相似文献
272.
Rather recently equations of Lax type defined by a double commutator, the so-called Brockett equations, have received considerable
attention. In this paper we prove that a supersymmetric version of a Brockett hierarchy is an infinite dimensional integrable
gradient system. As far as we know, this is the only graded system of this type existing in the literature.
Received: 9 February 2000 / Accepted: 18 January 2001 相似文献
273.
274.
Panel sound absorbers are typically used to absorb low-frequency noise in concert halls, auditoriums, recording studios, and other architectural applications. These systems are composed of flexible panels mounted over an air space that can be either partly or completely filled with a porous material. In this paper, a theoretical model is derived for predicting the sound-absorption coefficient of a cylindrical low-frequency absorber made of a circular plate. The theory takes into account the mass, bending stiffness, damping loss and the elastic boundary condition of the circular plate. The effects of the stiffness of an air-back cavity and of partially adding a porous material into the cavity are also considered. It is observed that the low-frequency resonances of such a system are dependent upon the clamping condition, the width of the air-back cavity, and mechanical properties of the plate. There is good agreement between theoretical and experimental results. 相似文献
275.
García F Less RJ Naseri V McPartlin M Rawson JM Sancho Tomas M Wright DS 《Chemical communications (Cambridge, England)》2008,(7):859-861
The two products obtained from the reaction of 1,2-(PH(2))(2)C(6)H(4) with the mixed-metal base (n)BuLi-Sb(NMe(2))(3) in the presence of 12-crown-4, [Li(12-crown-4)(2)]+[C(6)H(4)P(3)]- (1) and {[Li(12-crown-4)(2)]+}3[Sb(11)]3- (2), represent thermodynamic sinks in which P-P and Sb-Sb bonding are maximized at the expense of P-Sb bonding, providing access to the 1,2,3-[C(6)H(4)P(3)]- phospholide anion. 相似文献
276.
Hernández DM de Moura MA Valencia DP González FJ González I de Abreu FC da Silva Júnior EN Ferreira VF Pinto AV Goulart MO Frontana C 《Organic & biomolecular chemistry》2008,6(18):3414-3420
In this work, the electrochemical behaviour of an antitumoral nitro o-quinone derivative obtained from 3-bromo-nor-beta-lapachone was studied. Cyclic voltammetric experiments, in acetonitrile solution, revealed that both quinone and nitro functions are reduced independently as quasi-reversible one-electron transfer processes in this order. Depending on the reduction potential, a radical anion or a biradical dianion is obtained. The formation of these paramagnetic species was confirmed by performing in situ Electrochemical-Electron Spin Resonance (E-ESR) experiments. Analysis of the kinetics of electron transfer associated to those electron uptake processes, in terms of the Marcus-Hush-Levich model, revealed differences in the reorganization energy (lambda((k))) for both steps (lambda((I)): 1.07-1.11 eV; lambda((II)): 1.21-1.30 eV). By evaluating the conformations of the radical and biradical systems by calculations at the BLYP//TZVP level of theory, it was found that the inner component, for the second reduction process (lambda((II))) was approximately 72% of lambda((II)), reflecting modifications in the molecular structure during the radical anion-biradical dianion transition. This change is also reflected in the differences presented by line widths of the ESR signals of both electrogenerated radical and diradical species. 相似文献
277.
García F Less RJ Naseri V McPartlin M Rawson JM Wright DS 《Dalton transactions (Cambridge, England : 2003)》2008,(8):997-999
The reaction of 1,2-(NH(2))(2)C(6)H(4) with Sb(NMe(2))(3)/(n)BuLi gives the formally-aromatic heterocyclic anion [C(6)H(4)N(2)Sb](-) which oligomerises into a cyclic tetrameric arrangement in the complex [C(6)H(4)N(2)SbLi.PMDETA](4) () (PMDETA = {Me(2)NCH(2)CH(2)}(2)NMe) using a donor-acceptor bonding mode that is unique in related main group heterocyclic anions. 相似文献
278.
Kevin M. Siniard Dr. Meijia Li Dr. Shi-Ze Yang Dr. Junyan Zhang Dr. Felipe Polo-Garzon Dr. Zili Wu Dr. Zhenzhen Yang Dr. Sheng Dai 《Angewandte Chemie (International ed. in English)》2023,62(20):e202214322
The development of facile methodologies to afford robust supported metal nanocatalysts under mild conditions is highly desirable yet challenging, particularly via strong metal-support interactions (SMSI) construction. State-of-the-art approaches capable of generating SMSI encapsulation mainly focus on high temperature annealing in reductive/oxidative atmosphere. Herein, ultra-stable metal nanocatalysts based on SMSI construction were produced by leveraging the instantaneous high-energy input from ultrasonication under ambient conditions in H2O, which could rapidly afford abundant active intermediates, Ti3+ ions, and oxygen vacancies within the scaffolds to induce the SMSI overlayer formation. The encapsulation degree could be tuned and controlled via the reducibility of the solvents and the ultrasonication parameters. This facile and efficient approach could be further extended to diverse metal oxide supports and noble metal NPs leading to enhanced performance in hydrogenation reactions and CO2 conversion. 相似文献
279.
Felipe T. Martins I. Camps Antônio C. Doriguetto Marcelo H. dos Santos Javier Ellena Luiz C. A. Barbosa 《Helvetica chimica acta》2008,91(7):1313-1325
Garciniaphenone (=rel‐(1R,5R,7R)‐3‐benzoyl‐4‐hydroxy‐8,8‐dimethyl‐1,7‐bis(3‐methylbut‐2‐en‐1‐yl)bicyclo[3.3.1]non‐3‐ene‐2,9‐dione; 1 ), a novel natural product, was isolated from a hexane extract of Garcinia brasiliensis fruits. The crystal structure of 1 as well as the selected geometrical and configurational features were compared with those of known related polyprenylated benzophenones. Garciniaphenone is the first representative of polyprenylated benzophenones without a prenyl substituent at C(5). Notably, the absence of a 5‐prenyl substituent has an impact on the molecular geometry. The tautomeric form of 1 in the solid state was readily established by a residual‐electronic‐density map generated by means of a difference Fourier analysis, and there is an entirely delocalized six‐membered chelate ring encompassing the keto–enol moiety. The configuration at C(7) was used to rationalize the nature of the keto–enol tautomeric form within 1 . The intermolecular array in the network is maintained by nonclassical intermolecular H‐bonds. 相似文献
280.
Caseli L Crespilho FN Nobre TM Zaniquelli ME Zucolotto V Oliveira ON 《Journal of colloid and interface science》2008,319(1):100-108
The immobilization of enzymes in organized two-dimensional matrices is a key requirement for many biotechnological applications. In this paper, we used the Langmuir-Blodgett (LB) technique to obtain controlled architectures of urease immobilized in solid supports, whose physicochemical properties were investigated in detail. Urease molecules were adsorbed at the air-water interface and incorporated into Langmuir monolayers of the phospholipid dipalmitoyl phosphatidyl glycerol (DPPG). Incorporation of urease made DPPG monolayers more flexible and caused the reduction of the equilibrium and dynamic elasticity of the film. Urease and DPPG-urease mixed monolayers could be transferred onto solid substrates, forming LB films. A close packing arrangement of urease was obtained, especially in the mixed LB films, which was inferred with nanogravimetry and electrochemistry measurements. From the blocking effect of the LB films deposited onto indium tin oxide (ITO) substrates, the electrochemical properties of the LB films pointed to a charge transport controlled by the lipid architecture. 相似文献