排序方式: 共有72条查询结果,搜索用时 0 毫秒
21.
马丽娜 《纯粹数学与应用数学》2007,23(4):549-555
通过构造两个非负鞅证明了一个强极限定理,然后把它应用到本文所定义的广义Bethe树上的奇偶马尔可夫链场上,从而获得了此马氏链场上的一类强极限定理. 相似文献
22.
The pair correlation function of an expanding gas is investigated with an emphasis on the BEC-BCS crossover of a superfluid Fermi gas at zero temperature. At unitarity quantum Monte Carlo simulations reveal the occurrence of a sizable bunching effect due to interactions in the spin up-down channel which, at short distances, is larger than that exhibited by thermal bosons in the Hanbury-Brown-Twiss effect. We propose a local equilibrium ansatz for the pair correlation function which we predict will remain isotropic during the expansion even if the trapping potential is anisotropic, in contrast with the behavior of the density. The isotropy of the pair correlation function is an experimentally accessible signature, which makes a clear distinction with respect to the case of noninteracting gases and can be understood as a consequence of the violation of scaling. 相似文献
23.
Nicola Monti Stefano Zacchini Massimiliano Massi Alejandro Hochkoeppler Loris Giorgini Valentina Fiorini Alessandra Stefan Stefano Stagni 《应用有机金属化学》2020,34(9):e5806
Herein, we describe a new family of tris chelate homoleptic Ru (II) complexes, [Ru(N^N) 3 ] 2+ , where the role of the diimine-type ligands (N^N) was fulfilled by 2-pyridyl (PTZ) or 2-quinolyl tetrazole (QTZ) derivatives decorated with various alkyl substituents at the N-2 position of the tetrazole ring. The new Ru (II) complexes with general formula [Ru (PTZ-R) 3 ] 2+ and [Ru (QTZ-R) 3 ] 2+ , were obtained as mixtures of facial (fac) and meridional (mer) isomers, as suggested by NMR (1H, 13C) experiments, and confirmed in the case of mer-[Ru (QTZ-Me) 3 ] 2+ , by X-ray crystallography. The photophysical behavior of the tetrazole-based [Ru(N^N) 3 ] 2+ type species was investigated by UV–vis absorption spectroscopy, providing trends typical of polypyridyl Ru (II) complexes. The new homoleptic complexes fac/mer- [Ru (PTZ-R) 3 ] 2+ and fac/mer- [Ru (QTZ-R) 3 ] 2+ have been assessed for any eventual antimicrobial activity towards two different bacteria such as Gram-negative Escherichia coli and Gram-positive Deinococcus radiodurans. Whereas being inactive toward E. coli, the response of agar disks diffusion tests suggested that some of the new fac/mer Ru (II) complexes could inhibit the growth of D. radiodurans. This effect was further investigated by determining the growth kinetics in liquid medium of D. radiodurans exposed to the fac/mer- [Ru (PTZ-R) 3 ] 2+ and fac/mer- [Ru (QTZ-R) 3 ] 2+ complexes at different concentrations. The outcome of these experiments highlighted that the turn-on of the growth inhibitory effect took place as the linear hexyl chain was appended to the PTZ or QTZ scaffold, suggesting also how the inhibitory activity appeared more pronouncedly exerted by the facial isomers fac- [Ru (PTZ-Hex) 3 ] 2+ and fac- [Ru (QTZ-Hex) 3 ] 2+ (MIC = ca. 3.0 μg/ml) with respect to the corresponding meridional isomers (MIC = ca. 6.0 μg/ml). 相似文献
24.
M. Baccaredda M. Giorgini A. Lucchesi F. Morelli R. Tartarelli 《Journal of polymer science. Part A, Polymer chemistry》1969,7(1):209-216
Trioxane–1,3-dioxolane copolymers of high molecular weights and good thermal stability are obtained with high yields by a crystallization-polymerization method. The feed consists of concentrated solutions of trioxane in cyclohexane in the presence of dissolved 1,3-dioxolane. The 1,3-dioxolane/trioxane molar ratio in the feed lies in the range 2 to 10%. The results are compared with those obtained from isothermal copolymerizations. 相似文献
25.
Bose gases confined in highly elongated harmonic traps are investigated over a wide range of interaction strengths using quantum Monte Carlo techniques. We find that the properties of a Bose gas under tight transverse confinement are well reproduced by a 1D model Hamiltonian with contact interactions. We point out the existence of a unitary regime, where the properties of the quasi-1D Bose gas become independent of the actual value of the 3D scattering length a(3D). In this unitary regime, the energy of the system is well described by a hard-rod equation of state. We investigate the stability of quasi-1D Bose gases with positive and negative a(3D). 相似文献
26.
We calculate the equation of state of a two-component Fermi gas with attractive short-range interspecies interactions using the fixed-node diffusion Monte Carlo method. The interaction strength is varied over a wide range by tuning the value a of the s-wave scattering length of the two-body potential. For a>0 and a smaller than the inverse Fermi wave vector our results show a molecular regime with repulsive interactions well described by the dimer-dimer scattering length a(m)=0.6a. The pair correlation functions of parallel and opposite spins are also discussed as a function of the interaction strength. 相似文献
27.
Luigi Angiolini Tiziana Benelli Loris Giorgini Francesco Mauriello Elisabetta Salatelli 《Macromolecular Symposia》2006,234(1):68-75
The synthesis by radical homopolymerization of a novel optically active methacrylic polymer containing a side-chain chiral moiety linked to a photochromic bisazoaromatic chromophore has been carried out starting from the related monomer (S)-3-methacryloyloxy-1-[4′-phenylazo-(4-azobenzene)]-pyrrolidine [(S)- MPAAP ]. The polymeric derivate has been fully characterized and its spectroscopic properties compared to those of the monomer and of the corresponding homopolymer bearing only one azoaromatic chromophore in the side chain. The optical activity displayed by the bisazo polymer is discussed in terms of extent of chiral conformation assumed by the macromolecules as a consequence of dipole-dipole interactions between the bisazoaromatic chromophores. 相似文献
28.
29.
Barberá J Giorgini L Paris F Salatelli E Tejedor RM Angiolini L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(35):11209-11221
The synthesis of chiral liquid-crystalline polymers of well-controlled structure (linear and three-armed star-shaped) with distinct average chain lengths and low polydispersity was achieved by atom transfer radical polymerisation (ATRP) of a new optically active monomer (S)-4-[6-(2-methacryloyloxypropanoyloxy)hexyloxy)]-4'-ethoxyazobenzene [(S)-ML6A], containing the L-lactic residue of one absolute configuration in the side-chain. All the obtained polymeric samples, characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarised optical microscopy (POM), exhibit a smectic A(1/2) (fully interdigitated) liquid-crystalline phase and high cleaning points, with transition temperatures dependent on the average polymerisation degree and the macromolecular structure. The chirality originated at the molecular level by the asymmetric functionality of the L-lactic acid residue provides the polymers, in the smectic phase, of highly homogeneous conformations with a prevailing chirality related to the presence of H-aggregates having conformational dissymmetry of one prevailing screw-sense. By irradiating with circularly polarised light (CPL), it is possible to photomodulate the chiroptical properties of these intrinsically chiral polymeric thin films. Upon irradiation with left-handed CPL (l-CPL), the circular dichroism (CD) spectra of the films show enhancement of ellipticity and a net inversion of sign. The effect is reversible and the mirror image of the CD spectrum can be restored by pumping with right-handed CPL radiation (r-CPL). The results show the ability of l-CPL to invert the supramolecular chirality of the materials and demonstrate the essential role of azoaromatic aggregates. 相似文献
30.
The C=O stretching [nu(C=O)] Raman bands of the carbonyl solvents, S (acetone and acetophenone), in some electrolytic solutions of lithium and sodium salts (M(+)X(-)) are analyzed. The large and negative values of the noncoincidence effect (NCE=nu(ani)-nu(iso)) measured for the component of this band generated by the solvent-ion interactions are interpreted in the light of the results of ab initio quantum chemical calculations performed for clusters of type (S)nM(+) and also on the basis of the transition dipole coupling mechanism between pairs of nu(C=O) oscillators. The effects of the size of the ion M(+) and of the solvation number n on the NCE are analyzed. It is shown that the decrease of the NCE resulting from the change in the size of the ion M(+) from Li(+) to Na(+) is appreciably counterbalanced by the increase of the NCE arising form the change in the ion solvation number n from 4 for Li(+) to 6 for Na(+). 相似文献