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排序方式: 共有458条查询结果,搜索用时 31 毫秒
421.
The phase diagram of a 2D Josephson junction array with large substrate resistance, described by a quantum XY model, is studied by means of Fourier path-integral Monte Carlo. A genuine Berezinskii-Kosterlitz-Thouless transition is found up to a threshold value g( small star, filled ) of the quantum coupling, beyond which no phase coherence is established. Slightly below g( small star, filled ) the phase stiffness shows a reentrant behavior with temperature, in connection with a low-temperature disappearance of the superconducting phase, driven by strong nonlinear quantum fluctuations. 相似文献
422.
We show that weak measurements with postselection, proposed in the context of the quantum theory of measurement, naturally appear in the everyday physics of fiber optics telecom networks through polarization-mode dispersion (PMD) and polarization-dependent losses (PDL). Specifically, the PMD leads to a time-resolved discrimination of polarization; the postselection is done in the most natural way: one postselects those photons that have not been lost because of the PDL. The quantum formalism is shown to simplify the calculation of optical networks in the telecom limit of weak PMD. 相似文献
423.
Di Marco VB Bombi GG Tubaro M Traldi P 《Rapid communications in mass spectrometry : RCM》2003,17(18):2039-2046
Electrospray ionization mass spectrometry (ESI-MS) has been applied to the study of solution equilibria between Al(III) and the two ligands 4-hydroxy-3-pyridinecarboxylic acid (4H3P) and 3-hydroxy-4-pyridinecarboxylic acid (3H4P). The results compare well with the speciation data obtained from potentiometric, UV-visible spectroscopy, and NMR measurements. This agreement suggests the applicability of ES-MS to the study of more complicated aluminium-ligand systems. 相似文献
424.
425.
Tetrabutyl-1,3-diacyloxydistannoxanes, (RCOO)Bu2SnOSnBu2(OOCR) (A) and/or tetrabutyl-1-acyloxy-3-hydroxydistannoxanes, (RCOO)Bu2SnOSnBu2(OH) (B), can be prepared from equimolecular amounts of dibutyldiallyltin and carboxylic acid, RCOOH (R = H, CH3, CH2Cl, CHCl2, CCl3, CF3) in moist methanol or acetone/water (50/50, v/v). Isolation of compounds (A) or (B) depends upon the hydrolyzing power of the medium and the nature of R. 相似文献
426.
C.E.A. Grigorescu E. Valerio L. Tortet G. Pavelescu C. Ducu H.J. Trodahl N. Strickland W.R. Branford 《Applied Surface Science》2007,253(19):8102-8106
Thin films of nonstoichiometric Heusler alloys Co2MnSbxSn1−x (x = 0.2; 0.4; 0.6; 0.8) have been grown by pulsed laser deposition (double-target/double beam configuration) on Si (1 0 0) substrates using a KrF excimer laser (λ = 248 nm, τ = 20 ns). The substrate temperature was held at 300 K in all experiments to prevent interface interdiffusion of the species. A comparison between the compositions of films and corresponding targets has been done through energy dispersive X-ray spectroscopy (EDS) analysis showing a very satisfactory match. Scanning electron microscopy (SEM) imaging served to investigate the morphology of the films in order to determine the size and density of droplets which may influence the optical data. Optical conductivity derived from reflectivity measurements shows absorption onsets close to 1 eV, which corresponds to the onset of valence-to-conduction transitions in the minority spin bands theoretically predicted. The values of the saturation magnetisation measured at 300 K on the quaternary alloys are very close to those of ternary ones for which either half-metallic properties or high spin polarisation were theoretically predicted. 相似文献
427.
Branciard C Ling A Gisin N Kurtsiefer C Lamas-Linares A Scarani V 《Physical review letters》2007,99(21):210407
Bell's theorem guarantees that no model based on local variables can reproduce quantum correlations. Also, some models based on nonlocal variables, if subject to apparently "reasonable" constraints, may fail to reproduce quantum physics. In this Letter, we introduce a family of inequalities, which use a finite number of measurement settings, and which therefore allow testing Leggett's nonlocal model versus quantum physics. Our experimental data falsify Leggett's model and are in agreement with quantum predictions. 相似文献
428.
Alkyl thio-, phenyl seleno-, and phenyl thioglycosides can be prepared through short synthetic sequences based on the generation of glycosyl iodides as versatile intermediates. In addition, a novel cheap combined system (stoichiometric NBS and catalytic Bi(OTf)3) has been developed for rapid and efficient activation of a wide variety of thio- and selenoglycoside donors. 相似文献
429.
Simůnek P Lusková L Svobodová M Bertolasi V Lycka A Machácek V 《Magnetic resonance in chemistry : MRC》2007,45(4):330-339
The reaction of 3-phenylaminocyclopent-2-en-1-one with 4-methyl, 4-methoxy and 4-chlorobenzenediazonium tetrafluoroborates was used to prepare the azo coupling products 3a-c. It was found that these compounds are present in both CDCl(3) solution and solid phase practically exclusively as (E)-3-phenylamino-2-(4-subst.phenyldiazenyl)cyclopent-2-en-1-ones with N--H...N intramolecular hydrogen bond. The substitution of the phenyl residue of the diazonium salt has no effect on the position of the tautomeric equilibrium. On the other hand, the compounds 4a, b formed by the reaction of 3-phenylamino-1H-inden-1-one with 4-methylbenzene- or benzenediazonium tetrafluoroborates exist in CDCl(3) solution and in solid phase as hydrazone compounds. In the solution they occur as a mixture of three forms, out of which two were identified as E/Z isomers with different types of hydrogen bonds. Compound 5 formed by the reaction of 3-amino-5,5-dimethylcyclohex-2-en-1-one with 4-methoxybenzenediazonium tetrafluoroborate is converted into a stable hydrochloride 5.HCl on standing in CHCl(3) solution; this product exhibits a high degree of delocalization of the positive charge. Its structure was studied by means of X-ray. 相似文献
430.
Mandal D Bertolasi V Aromí G Ray D 《Dalton transactions (Cambridge, England : 2003)》2007,(20):1989-1992
The Ni(4) inverse metallacrown (NHEt(3)) [Ni(4)(bmo)4(Hael)2(ael)2](ClO(4))3 [(NHEt(3)).1.(ClO(4))3], with the inverse 12-MC-4 motif, has been assembled via simultaneous chelation and bridging of butan-2,3-dionemonoxime (Hbmo) and 2-amino ethanol (Hael). 相似文献