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Recent experiments suggest that the Ising pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 display qualitative properties of the nearest-neighbor "spin ice" model. We discuss the dipolar energy scale present in both these materials and discuss how spin-ice behavior can occur despite the presence of long-range dipolar interactions. We present results of numerical simulations and a mean field analysis of Ising pyrochlore systems. Based on our quantitative theory, we suggest that the spin-ice behavior in these systems is due to long-range dipolar interactions, and that the nearest-neighbor exchange in Dy2Ti2O7 is antiferromagnetic. 相似文献
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We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR
2 in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the
FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein
field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity.
Some new and interesting potentials are noted in the presence of R
2 term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover
approximation. 相似文献
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We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum. 相似文献
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AbstractA series of seven coumarinyl-amino acid ester conjugates have been synthesized and characterized by NMR (1H and 13C) and mass spectra. Further, the compounds were investigated for their therapeutic applications such as anti-inflammatory and antioxidant activities. Among the synthesized compounds most of the analogs showed good efficiency compared with the standard. 相似文献
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Martin SF Follows BC Hergenrother PJ Franklin CL 《The Journal of organic chemistry》2000,65(15):4509-4514
The phospholipase C (PLC) isozymes catalyze the hydrolysis of phospholipids to provide diacylglycerol (DAG) and a phosphorylated headgroup. Because DAG has been implicated in cellular signal transduction cascades in mammalian systems, there has been considerable interest in the development of inhibitors of these enzymes. Toward this end, we have discovered that the cyclic N,N'-dihydroxyureas 6-10 inhibit the phosphatidylcholine preferring PLC from Bacillus cereus (PLCBc). This class of inhibitors is believed to function by the bidentate chelation of the N,N'-dihydroxyurea array to one or more of the zinc ions at the active site of the enzyme. Because the affinities of these compounds correlate with the pKaS of the N-OH hydroxyl groups, it is apparent that one or both of the hydroxyl groups must be ionized for effective coordination to the zinc ions. It is also apparent that there may be rather strict steric requirements for these inhibitors. 相似文献
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