排序方式: 共有56条查询结果,搜索用时 584 毫秒
21.
In this paper we prove that any Riemannian surface, with no restriction of curvature at all, can be decomposed into blocks belonging just to some of these types: generalized Y-pieces, generalized funnels and halfplanes. 相似文献
22.
M. Galvan-Sosa J. Portilla J. Hernandez-Rueda J. Siegel L. Moreno A. Ruiz de la Cruz J. Solis 《Applied Physics A: Materials Science & Processing》2014,114(2):477-484
Femtosecond laser pulse temporal shaping techniques have led to important advances in different research fields like photochemistry, laser physics, non-linear optics, biology, or materials processing. This success is partly related to the use of optimal control algorithms. Due to the high dimensionality of the solution and control spaces, evolutionary algorithms are extensively applied and, among them, genetic ones have reached the status of a standard adaptive strategy. Still, their use is normally accompanied by a reduction of the problem complexity by different modalities of parameterization of the spectral phase. Exploiting Rabitz and co-authors’ ideas about the topology of quantum landscapes, in this work we analyze the optimization of two different problems under a deterministic approach, using a multiple one-dimensional search (MODS) algorithm. In the first case we explore the determination of the optimal phase mask required for generating arbitrary temporal pulse shapes and compare the performance of the MODS algorithm to the standard iterative Gerchberg–Saxton algorithm. Based on the good performance achieved, the same method has been applied for optimizing two-photon absorption starting from temporally broadened laser pulses, or from laser pulses temporally and spectrally distorted by non-linear absorption in air, obtaining similarly good results which confirm the validity of the deterministic search approach. 相似文献
23.
A new aluminosilicate molecular sieve with a system of pores between those of ZSM-5 and beta zeolite
Moliner M González J Portilla MT Willhammar T Rey F Llopis FJ Zou X Corma A 《Journal of the American Chemical Society》2011,133(24):9497-9505
A new aluminosilicate zeolite (ITQ-39) has been synthesized. This is an extensively faulted structure with very small domains that makes the structure elucidation very difficult. However, a combination of adsorption spectroscopy and reactivity studies with selected probe molecules suggests that the pore structure of ITQ-39 is related to that of Beta zeolite, with a three-directional channel system with large pores (12-MR), but with an effective pore diameter between those of Beta and ZSM-5, or a three-directional channel system with interconnected large (12-MR) and medium pores (10-MR). The pore topology of ITQ-39 is very attractive for catalysis and shows excellent results for the preparation of cumene by alkylation of benzene, while it can be a promising additive for FCC. 相似文献
24.
J. de Oñate Martínez C. Díaz Aguila J. Fernández Bertrán E. Reguera Ruíz C. Portilla Vergara R. Roque Malherbe 《Hyperfine Interactions》1992,73(3-4):371-375
The tribochemical reactions between Na-LTA and natural erionite with Fe2(SO4)3·5H2O were studied by Mössbauer spectroscopy, X-ray powder diffraction, IR spectroscopy and NH3 adsorption experiments. The reactions occur with the consequent zeolite dealumination and the formation of a crystalline compound, a product of the extracted aluminum and the sulfate. 相似文献
25.
Joan Josep Ferrando Juan Antonio Morales Miquel Portilla 《General Relativity and Gravitation》1990,22(9):1021-1032
The paper contains the necessary and sufficient conditions for a given energy tensor to be interpreted as a sum of two perfect fluids. Given a tensor of this class, the decomposition in two perfect fluids (which is determined up to a couple of real functions) is obtained. 相似文献
26.
A series of 5-amino-1-aroylpyrazoles 3 are synthesized directly by the reaction of β-aminocrotononitrile 1 with some structures containing the hydrazine moiety (X-NHNH2) 2 by refluxing ethanol in presence of sodium acetate. When semicarbazide 3i was used (X = CONH2), the reaction afforded the unexpected 7-aminopyrazolo[1,5-a]pyrimidine 4. 相似文献
27.
Díaz E Barrios H del Río Portilla F Guzmán A Aguilera JL Becerril R Jankowski CK Reynolds WF 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(11):2191-2201
The reaction of substituted diarylidene acetones with hydroxylamine hydrochloride affords isomeric N-hydroxy diaryl piperidinone oximes as main products. The structures as well as conformational equilibria of these products were established by 1H and 13C NMR spectroscopy and further studied by variable temperature NMR. It was found that the cis/trans ratio of 2,6-substituted piperidine derivatives depended on the position of the substituent on the aromatic ring. 相似文献
28.
Rivera OM Torrado AM Moldes AB Domínguez JM 《Applied biochemistry and biotechnology》2009,152(2):262-274
This work deals with the nutritional evaluation of grape marc hydrolyzates as fermentation medium for Lactobacillus pentosus. Usually, the fermentation of xylose and arabinose in the presence of glucose remains a primary obstacle for economical biomass
conversion. The few microorganisms that can grow simultaneously on both pentose and hexose sugars contained in lignocellulosic
feedstocks typically grow slowly and demonstrate marginal yields and productivities. Moreover, lignocellulosic hydrolyzates
contain phenolic compounds and other components originated by the degradation of sugars that can inhibit lactic acid fermentation.
However, in this case, grape marc hydrolyzates not only did not need a detoxification stage, but it also improved the xylose
consumption by Lactobacillus pentosus with a faster and more efficient conversion of hemicellulosic sugars compared with synthetic media. After analysis of grape
marc hydrolyzates, it was observed that minerals such as K (2,707 mg/L), Ca (3,681 mg/L), and Mg (198.5 mg/L) are present
in higher concentration than those found in the general medium of Lactobacillus (1,705 mg/L of K, 58.3 mg/L of Ca, and 27.0 mg/L of Mg). Moreover, grape marc hydrolyzates contain an additional source of
nitrogen (9.2 g/L) which, together with their elevated mineral concentration, improved lactic acid fermentation compared with
synthetic media. 相似文献
29.
30.
Jaime Portilla Jairo Quiroga Justo Cobo John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(8):o458-o461
In both 2,5‐dimethyl‐6,7‐dihydrobenzo[h]pyrazolo[1,5‐a]quinazoline, C16H15N3, (I), and 2‐tert‐butyl‐5‐methyl‐6,7‐dihydrobenzo[h]pyrazolo[1,5‐a]quinazoline, C19H21N3, (II), which crystallizes with Z′ = 2 in the space group P, the non‐aromatic carbocyclic rings adopt screw‐boat conformations. The molecules of (I) are linked into chains of rings by a combination of C—H...N and C—H...π(arene) hydrogen bonds, while in (II) there are no hydrogen bonds of any kind. 相似文献