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431.
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
432.
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
433.
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
434.
435.
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
436.
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
437.
Valerio?Bertolasi Shasta?Lee?Mosher Keith?VaughanEmail author 《Journal of chemical crystallography》2005,35(2):119-124
1,4-Di-[2-phenyl-1-diazenyl]perhydro-1,4-diazepine (1) has been synthesized by reaction of benzenediazonium chloride with homopiperazine (perhydro-1,4-diazepine). The crystal structure of 1 has been determined by single crystal X-ray diffraction analysis. The bis-triazene (1) adopts an extended conformation which precludes any close intramolecular interaction of the phenyl rings. The heterocyclic seven-membered ring adopts a chair conformation, with the triazene side chains occupying alternate axial and equatorial positions consistent with cis-geometry. Internal torsion angles of the seven-membered ring have been measured. The crystal packing is determined by short contacts between C=H groups of phenyl rings and nitrogens of triazene moieties and by van der Waals interactions, with no evidence for intermolecular – interactions. This work establishes the structure of the product of diazonium coupling with homopiperazine as 1,4-di[(E)-2-phenyl-1-diazenyl]perhydro-1,4-diazepine. Crystal data: 1 C17H20N6, monoclinic, space group P21/n, a = 9.1838(5) Å, b = 12.1095(6) Å, c = 15.0081(8) Å, = 101.320(2), V = 1636.6(2) Å,3 for Z = 4. 相似文献
438.
Valerio Fasano Nils Winter Adam Noble Varinder K. Aggarwal 《Angewandte Chemie (International ed. in English)》2020,59(22):8502-8506
There is considerable interest in incorporating fluorine into agrochemicals and pharmaceuticals to improve their biological properties. Whilst a number of methods have been reported for installing CH2F and CHF2 groups, they are mainly limited to radical reactions, which are invariably racemic. Herein, we report the divergent, stereospecific reaction of fluoroiodomethyllithium with boronic esters to give α‐fluoro‐boronic esters. These unique intermediates can be readily transformed into the corresponding mono‐ or difluoromethylated compounds through proto‐ or fluorodeboronation, respectively. The use of the highly unstable fluoroiodomethyllithium was key to allowing rapid 1,2‐migration over competing decomposition of the carbanion. DFT calculations informed and supported the experimental findings. 相似文献
439.
Mariangela Lopreiato Rossana Cocchiola Susanna Falcucci Martina Leopizzi Michele Cardone Valeria Di Maio Umberto Brocco Valerio D'Orazi Stefano Calvieri Roberto Scandurra Federico De Marco Anna Scotto d'Abusco 《Photochemistry and photobiology》2020,96(1):74-82
The ultraviolet (UV) component of solar radiation is the driving force of life on earth, but it can cause photoaging and skin cancer. In this study, we investigated the effects of the glucosamine-derivative 2-(N-Acetyl)-L-phenylalanylamido-2-deoxy-β-D-glucose (NAPA) on human primary fibroblasts (FBs) stimulated in vitro with environmental levels of UVB radiation. FBs were irradiated with 0.04 J cm−2 UVB dose, which resulted a mild dosage as shown by the cell viability and ROS production measurement. This environmental UVB dose induced activation of MAP kinase ERK 1/2, the stimulation of c-fos and at lower extent of c-jun, and in turn AP-1-dependent up-regulation of pro-inflammatory factors IL-6 and IL-8 and suppression of collagen type I expression. On the contrary, 0.04 J cm−2 UVB dose was not able to stimulate metalloprotease production. NAPA treatment was able to suppress the up-regulation of IL-6 and IL-8 via the inhibition of MAP kinase ERK phosphorylation and the following AP-1 activation, and was able to attenuate the collagen type I down-regulation induced by the UVBs. Taken together, our results show that NAPA, considering its dual action on suppression of inflammation and stimulation of collagen type I production, represents an interesting candidate as a new photoprotective and photorepairing agents. 相似文献
440.
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