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排序方式: 共有152条查询结果,搜索用时 31 毫秒
1.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
2.
Alberti G Brunet E Dionigi C Juanes O de La Mata MJ Rodríguez-Ubis JC Vivani R 《Angewandte Chemie (International ed. in English)》1999,38(22):3351-3353
The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space. 相似文献
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Summary Spot tests have been described for calcium sulphate, lead sulphate, silver, thallium and formaldehyde based on the reaction with selenosulphate. In these reactions either red elemental selenium (CaSO4, CH2O) or black metal selenide (PbSO4 Tl, Ag) is formed. The limits of identification are: 0.2 mg of PbS04 or CaSO4, 2 g of Ag, 10 g of Tl, 0.2 g of CH2O.
This paper has been dedicated to Prof. Dr.Fritz Wessely, Vienna, on the occasion of his 70th birthday. 相似文献
Zusammenfassung Für Calciumsulfat, Bleisulfat, Silber, Thallium und Formaldehyd werden Tüpfelproben beschrieben, die auf Umsetzungen mit Selenosulfat beruhen. Hierbei -wird entweder rotes elementares Selen abgeschieden (CaSO4 CH2O) oder schwarze Selenide werden gebildet (PbSO4, Tl, Ag). Die Nachweisgrenzen betragen: 0,2 mg PbSO4 oder CaSO4, 2 g Ag, 10 g Tl, 0,2 g CH2O.
This paper has been dedicated to Prof. Dr.Fritz Wessely, Vienna, on the occasion of his 70th birthday. 相似文献
6.
V. Caldas G. R. Brown R. S. Nohr J. G. MacDonald 《Journal of Polymer Science.Polymer Physics》1996,34(12):2085-2098
The double melting endotherm of spunbonded isotactic polypropylene (iPP) fabrics was investigated by monitoring changes in the solid-state NMR spectrum that result from thermal annealing. The DSC melting thermogram was found to change from a double to a single endotherm at anneal temperatures ≥156°C, with a concomitant increase in percent crystallinity. All of the carbon resonances in the CP/MAS NMR spectrum of the purely crystalline phase of iPP were found to be composed of multiple peaks with relative intensities that depend on anneal temperature. By monitoring the changes in the distribution of intensity among the various peaks of a given resonance, a transition temperature of 156°C was identified. Arguments are presented that this redistribution of intensity within a given carbon resonance characterizes the transformation from the α1 to the α2 monoclinic crystal form. The exothermicity associated with this transformation is responsible for the observation of a double melting endotherm by DSC. The splitting patterns observed in the NMR spectrum are discussed in terms of interlayer distances between layers of isochiral helices and the density of exposed methyls at the contact faces of these interlayers. © 1996 John Wiley & Sons, Inc. 相似文献
7.
Beatriz Werneck Lopes Santos Daniel Carneiro Moreira Tatiana Karla dos Santos Borges Eloisa Dutra Caldas 《Molecules (Basel, Switzerland)》2022,27(8)
Banisteriopsis caapi is used to prepare the psychoactive beverage ayahuasca, and both have therapeutic potential for the treatment of many central nervous system (CNS) conditions. This study aimed to isolate new bioactive compounds from B. caapi extract and evaluate their biological activity, and that of the known β-carboline components of the plant (harmine, harmaline, and tetrahydroharmine), in BV-2 microglial cells, the in vivo activation of which is implicated in the physiopathology of CNS disorders. B. caapi extract was fractionated using semipreparative liquid chromatography (HPLC-DAD) and the exact masses ([M + H]+ m/z) of the compounds in the 5 isolated fractions were determined by high-resolution LC-MS/MS: F1 (174.0918 and 233.1289), F2 (353.1722), F3 (304.3001), F4 (188.1081), and F5 (205.0785). Harmine (75.5–302 µM) significantly decreased cell viability after 2 h of treatment and increased the number of necrotic cells and production of reactive oxygen species at equal or lower concentrations after 24 h. F4 did not impact viability but was also cytotoxic after 24 h. Most treatments reduced proinflammatory cytokine production (IL-2, IL-6, IL-17, and/or TNF), especially harmaline and F5 at 2.5 µM and higher concentrations, tetrahydroharmine (9.3 µM and higher), and F5 (10.7 µM and higher). The results suggest that the compounds found in B. caapi extract have anti-inflammatory potential that could be explored for the development of treatments for neurodegenerative diseases. 相似文献
8.
Plasmas confined in tokamaks with non-symmetric perturbations are surrounded by a chaotic layer of magnetic field lines that guide charged particles to the tokamak wall. We use an analytical two-dimensional symplectic mapping to study the resulting fractal patterns of field line escape. However, particles may experience several collisions before escaping toward the tokamaks wall. We add a random collisional term to the field line mapping to investigate how the particle collisions modify their escape patterns. 相似文献
9.
10.
J. S.E. Portela I. L. Caldas R. L. Viana 《The European physical journal. Special topics》2008,165(1):195-210
The magnetic field line structure in a tokamak can be obtained by direct numerical integration of the field line equations.
However, this is a lengthy procedure and the analysis of the solution may be very time-consuming. Otherwise we can use simple
two-dimensional, area-preserving maps, obtained either by approximations of the magnetic field line equations, or from dynamical
considerations. These maps can be quickly iterated, furnishing solutions that mirror the ones obtained from direct numerical
integration, and which are useful when long-term studies of field line behavior are necessary (e.g. in diffusion calculations).
In this work we focus on a set of simple tokamak maps for which these advantages are specially pronounced. 相似文献