Abstract The reaction products of PCl5 with 2,6-dimesityl-aniline and with naphthalene-1,5-diamine are 4-chloro-2,6-dimesityl-aniline and (2,4,6,8-tetrachloronaphthalene-1,5-diyl)bis(phosphorimidic trichloride), respectively, and were characterized by X-ray crystallographic analyses. The phosphazene shows π-stacking, extremely large C–N–P angles, and extremely short P–N distances. 相似文献
We have realized a p-type ZnO surface layer by N+ ion implantation of a high quality ZnO wafer and subsequent annealing. The conduction type of this surface layer was revealed by scanning capacitance microscopy. Rectifying current–voltage characteristics for processed devices were coherent with the existence of an internal pn junction. Deep donor- and acceptor-like defects were investigated by junction deep level transient spectroscopy. The donor-like levels correspond to those commonly observed for E1 and E3 defects. The acceptor states resolved have thermal activation energies of about 150 meV and 280 meV, respectively. 相似文献
Severe acute respiratory syndrome (SARS) is a rapidly spreading infectious disease which was transmitted in late 2002 and early 2003 to more than 28 countries through the medium of international travel. The evolution and spread of SARS has resulted in an international effort coordinated by the World Health Organization (WHO).
We have formulated a discrete mathematical model to investigate the transmission of SARS and determined the basic reproductive number for this model to use as a threshold to determine the asymptotic behavior of the model. The dependence of the basic reproductive number on epidemic parameters has been studied. The parameters of the model have been estimated on the basis of statistical data and numerical simulations have been carried out to describe the transmission process for SARS in China. The simulation results matches the statistical data well and indicate that early quarantine and a high quarantine rate are crucial to the control of SARS. 相似文献
The conformation and structural dynamics of cellobiose, one of the fundamental building blocks in nature, its C4' epimer, lactose, and their microhydrated complexes, isolated in the gas phase, have been explored through a combination of experiment and theory. Their structures at low temperature have been determined through double resonance, IR-UV vibrational spectroscopy conducted under molecular beam conditions, substituting D(2)O for H(2)O to separate isotopically, the carbohydrate (OH) bands from the hydration (OD) bands. Car-Parrinello (CP2K) simulations, employing dispersion corrected density functional potentials and conducted "on-the-fly" from ~20 to ~300 K, have been used to explore the consequences of raising the temperature. Comparisons between the experimental data, anharmonic vibrational self-consistent field calculations based upon ab initio potentials, and the CP2K simulations have established the role of anharmonicity; the reliability of classical molecular dynamics predictions of the vibrational spectra of carbohydrates and the accuracy of the dispersion corrected (BLYP-D) force fields employed; the structural consequences of increasing hydration; and the dynamical consequences of increasing temperature. The isolated and hydrated cellobiose and lactose units both present remarkably rigid structures: their glycosidic linkages adopt a "cis" (anti-? and syn-ψ) conformation bound by inter-ring hydrogen bonds. This conformation is maintained when the temperature is increased to ~300 K and it continues to be maintained when the cellobiose (or lactose) unit is hydrated by one or two explicitly bound water molecules. Despite individual fluctuations in the intra- and intermolecular hydrogen bonding pattern and some local structural motions, the water molecules remain locally bound and the isolated carbohydrates remain trapped within the cis potential well. The Car-Parrinello dynamical simulations do not suggest any accessible pathway to the trans conformations that are formed in aqueous solution and are widespread in nature. 相似文献
Functional Analysis and Its Applications - In a recent paper, given an arbitrary homogeneous cohomological field theory ( CohFT), Rossi, Shadrin, and the first author proposed a simple formula for... 相似文献
Cationic, chiral arene ruthenium complexes of the type [Ru(η6-cym)(PPh3){κ2N,S-PhNC(S)R}]BPh4 were prepared in high yields by refluxing a mixture containing [(η6-cym)RuCl2]2, Ph3P, PhNHC(S)R, NaBPh4 and Et3N in MeOH. A series of seven complexes with different thioamide ligands was prepared and fully characterised by spectroscopic methods including NMR spectroscopy and electrospray mass spectrometry. The solid-state structures of two complexes were determined by single crystal X-ray diffraction. 相似文献