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排序方式: 共有542条查询结果,搜索用时 131 毫秒
101.
F van Swol SR Challa JA Shelnutt 《Physical chemistry chemical physics : PCCP》2012,14(38):13309-13318
Producing nanostructures with high surface area that are stable is important to accomplish sustained use of catalytic materials in practical settings. Avoiding the processes of ripening and sintering that typically hinder stability has long been recognized as a significant challenge and much research is focused on addressing these issues. In this article, we investigate a Pt nanostructure-a holey nanosheet-that exhibits high surface area and stability. The findings from lattice gas simulations produce a stability diagram that relates a critical hole diameter to sheet thickness. The stability is now addressed from a thermodynamic point of view, and, in particular, the crucial role of curvature is considered. We find that the stability of certain sized holes is due to the near zero mean curvature of the surface of the holes and of the surrounding flat sheet. Molecular dynamics simulations of Pt (using an embedded atom potential) are reported for small nanoclusters and model holes in sheets to illustrate the strong effects of curvature on thermodynamic properties such as the lowering of melting and surface melting temperatures. 相似文献
102.
Smith JD Meuler AJ Bralower HL Venkatesan R Subramanian S Cohen RE McKinley GH Varanasi KK 《Physical chemistry chemical physics : PCCP》2012,14(17):6013-6020
Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for deep-sea oil and gas operations. Current methods for hydrate mitigation are expensive and energy intensive, comprising chemical, thermal, or flow management techniques. In this paper, we present an alternate approach of using functionalized coatings to reduce hydrate adhesion to surfaces, ideally to a low enough level that hydrodynamic shear stresses can detach deposits and prevent plug formation. Systematic and quantitative studies of hydrate adhesion on smooth substrates with varying solid surface energies reveal a linear trend between hydrate adhesion strength and the practical work of adhesion (γ(total)[1 + cos?θ(rec)]) of a suitable probe liquid, that is, one with similar surface energy properties to those of the hydrate. A reduction in hydrate adhesion strength by more than a factor of four when compared to bare steel is achieved on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the practical work of adhesion is minimized. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and could lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations. 相似文献
103.
Sekharan S Katayama K Kandori H Morokuma K 《Journal of the American Chemical Society》2012,134(25):10706-10712
Eyes gather information, and color forms an extremely important component of the information, more so in the case of animals to forage and navigate within their immediate environment. By using the ONIOM (QM/MM) (ONIOM = our own N-layer integrated molecular orbital plus molecular mechanics) method, we report a comprehensive theoretical analysis of the structure and molecular mechanism of spectral tuning of monkey red- and green-sensitive visual pigments. We show that interaction of retinal with three hydroxyl-bearing amino acids near the β-ionone ring part of the retinal in opsin, A164S, F261Y, and A269T, increases the electron delocalization, decreases the bond length alternation, and leads to variation in the wavelength of maximal absorbance of the retinal in the red- and green-sensitive visual pigments. On the basis of the analysis, we propose the "OH-site" rule for seeing red and green. This rule is also shown to account for the spectral shifts obtained from hydroxyl-bearing amino acids near the Schiff base in different visual pigments: at site 292 (A292S, A292Y, and A292T) in bovine and at site 111 (Y111) in squid opsins. Therefore, the OH-site rule is shown to be site-specific and not pigment-specific and thus can be used for tracking spectral shifts in any visual pigment. 相似文献
104.
Single crystals of the nonlinear material γ-glycine have been grown in the presence of lithium nitrate by slow-evaporation method. Structural characterization of the grown crystals was carried out by powder and single crystal X-ray diffraction (XRD) methods and it is observed that the samples crystallize in hexagonal system with non-centrosymmetric space groups. The modes of vibrations of different molecular groups present in glycine have been identified by spectral analyses. UV–visible transmittance study was performed to analyze optical transparency of γ-glycine crystals and found that the crystal was transparent in the entire visible-NIR region. Second harmonic generation (SHG) conversion efficiency has been estimated as 62 mV and the output power by the crystal was 1.72 times that of potassium dihydrogen phosphate (KDP) crystal. The thermal stability and decomposition of the sample have been studied by thermal analysis and it is observed that the γ-glycine crystal have good thermal stability. 相似文献
105.
The authors revisit the notion of a row monotone matrix and obtain new results that establish relationships with certain specific types of splittings of the matrix concerned. Among other results, analogous results for range monotone matrices are also obtained. 相似文献
106.
P. Sivakumar S. Meenakshi R. V. Subba Rao 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(2):603-608
A new process for the partitioning of plutonium and uranium during the reprocessing of spent fuel discharged from fast reactor
was optimised using hydroxyurea (HU) as a reductant. Stoichiometric ratio of HU required for the reduction of Pu(IV) was studied.
The effect of concentration of uranium, plutonium and acidity on the distribution ratio (Kd) of Pu in the presence of HU was
studied. The effect of HU in further purification of Pu such as solvent extraction and precipitation of plutonium as oxalate
was also studied. The results of the study indicate that Pu and U can be separated from each other using HU as reductant. 相似文献
107.
P. Sivakumar S. Meenakshi R. V. Subba Rao 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(3):763-767
Spent fuel discharged from Fast Breeder Test Reactor (FBTR) in Kalpakkam is being reprocessed by modified plutonium uranium
reduction extraction (PUREX) process using 30% TBP (tributylphosphate) as extractant in the presence of heavy normal paraffin
(HNP) as diluent. Partitioning of uranium (U) and plutonium (Pu) is carried out using oxalate precipitation method. Uranium
oxide product obtained by this method contains appreciable amount of plutonium which has to be recovered. Recovery of plutonium
from this uranium oxide product is carried out by reducing Pu to inextractable Pu(III) using hydroxyurea (HU) and then uranium
is extracted into 30% TBP. A small amount of Pu which is extracted in the organic phase is stripped back to aqueous phase
by scrubbing with scrubbing agent containing 0.1 M HU in 4 M nitric acid. Similarly U and Pu are co-extracted into 30% TBP
and then Pu is removed by scrubbing with 0.1 M HU in 4 M nitric acid. Further decontamination from Pu is obtained in the stripping
stages. By this method Pu contamination in the uranium oxide is brought from 7300 ppm to 0.4–3 ppm (wt/wt). This uranium product
obtained can be handled on table top. 相似文献
108.
We develop a stochastic formulation of cosmology in the early universe, after considering the scatter in the redshift-apparent
magnitude diagram in the early epochs as an observational evidence for the non-deterministic evolution of early universe.
We consider the stochastic evolution of density parameter in the early universe after the inflationary phase qualitatively,
under the assumption of fluctuating w factor in the equation of state, in the Fokker-Planck formalism. Since the scale factor for the universe depends on the energy
density, from the coupled Friedmann equations we calculated the two variable probability distribution function assuming a
flat space geometry. 相似文献
109.
R. V. Krishnakumar M. Subha Nandhini S. Natarajan K. Sivakumar Babu Varghese 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(10):1149-1150
The glycine molecule in the title compound, Na(NO3)·C2H5NO2, exists in the zwitterionic form. The Na atom exhibits eightfold coordination and the polyhedron may be visualized as a distorted hexagonal bipyramid. The glycine molecules are linked through head-to-tail hydrogen bonds and are found `sandwiched' between the Na(NO3) layers. 相似文献