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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
3.
Zhang H Paulsen ES Walker KA Krakowiak KE Dearden DV 《Journal of the American Chemical Society》2003,125(31):9284-9285
Cucurbit[6]uril forms a doubly charged complex with 1,4-butanediammonium cation that is observed using electrospray ionization Fourier transform mass spectrometry. Such 1:1 complexes are not observed for the smaller cucurbit[5]uril, which forms a 2:1 ammonium:cucurbituril complex instead. The 1:1 complex with cucurbit[6]uril is difficult to fragment via collisional activation; when it does fragment, both breakup of the cucurbituril cage and loss of the amine are observed. Further, the complex reacts with tert-butylamine via slow adduction. In contrast, nonrotaxane analogues (such as doubly charged 2:1 complexes of either protonated 1,4-butanediamine or protonated ethylenediamine with cucurbit[6]uril) fragment via easy loss of the intact amine upon collisional activation and react with tert-butylamine via rapid displacement of the original amine. On the basis of stoichiometry, fragmentation behavior, and reactivity, we conclude that the doubly charged complex of cucurbit[6]uril with 1,4-butanediammonium is a gas-phase pseudorotaxane. 相似文献
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Three new (+)-sparteine-like diamines were prepared from (-)-cytisine and evaluated as sparteine surrogates in the alpha-lithiation rearrangement of cyclooctene oxide and the palladium(II)/diamine catalyzed oxidative kinetic resolution of 1-indanol. The new diamines exhibited opposite enantioselectivity to that observed with (-)-sparteine but increasing the steric hindrance of the N-alkyl group beyond N-Et had a detrimental effect on enantioselectivity. The optimal N-Me diamine was evaluated with much success in five other (-)-sparteine-mediated processes involving different metals (lithium, magnesium, and copper) and different types of reaction mechanisms. 相似文献
10.
Geronikaki A Vicini P Theophilidis G Lagunin A Poroikov V Dearden JC 《SAR and QSAR in environmental research》2003,14(5-6):485-495
On the basis of computer prediction of biological activity by PASS and toxicity by DEREK, the most prospective 18 alkylaminoacyl derivatives of 3-amino-benzo-[d]-isothiazole were selected. Their local anesthetic action was assessed using an in vitro preparation of the isolated peroneal nerve of the frog. The local anesthetics action of the compounds was assessed according to the time required for each compound to reduce the amplitude of the evoked compound action potential (CAP). Lidocaine was used as the control compound. The results show that the tested compounds can be divided into three groups: (a) compounds with action similar to lidocaine, (b) compounds with action lower than lidocaine and (c) compounds which block completely the evoked CAP, but after the compound was removed and replaced with normal saline showed no recovery of the potential at all. QSAR studies showed that polarizability, polarity and presence of five-membered rings in molecules have a positive influence on local anesthetic activity, while contributions of aromatic CH and singly bonded nitrogen are negative. Since estimations from PASS probabilities to find local anesthetic activity in the most active compounds were less than 50%, these compounds may be considered as new chemical entities (NCEs). 相似文献