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451.
Gulías M García R Delgado A Castedo L Mascareñas JL 《Journal of the American Chemical Society》2006,128(2):384-385
Readily accessible alk-5-enylidenecyclopropanes undergo [3 + 2] intramolecular cycloaddition reactions upon treatment with appropriate palladium complexes. The method allows the rapid and efficient assembly of a variety of bicyclo[3.3.0]octane systems with up to three stereocenters. Preliminary theoretical calculations uncovered previously unsuspected mechanistic possibilities based on either a concerted pallada-ene-like rearrangement or a stepwise process involving zwitterionic intermediates. 相似文献
452.
Arpita Banerjee Pali Maiti Tanmay Chattopadhyay Kazi Sabnam Banu Manami Ghosh Eringathodi Suresh Ennio Zangrando Debasis Das 《Polyhedron》2010
Four new coordination polymers of cadmium(II) with hexamethylenetetramine (htm) have been synthesized and characterized by routine physicochemical techniques as well as by X-ray single crystal structure analysis. They are [CdBr(htm)(SCN)(H2O)2·CH3OH]n (1), [CdI(htm)(SCN)(H2O)2·0.5(CH3OH)]n (2), [Cd2(htm)3(SCN)4(H2O)]n·nH2O (3) and [Cd3Br6(htm)2(H2O)5·(htm)(H2O)6]n (4). Complexes 1, 2 and 3 exhibit 1D polymeric structure and complex 4 shows a 2D undulated layered arrangement, containing Cd6(htm)6 hexagonal units as building block, which extended to a 3D supramolecular architecture through hydrogen bonding. Thorough thermal investigation suggest that as far as the thermal stability of Cd(II)-htm bond is concerned it attains the maximum in complex 1 and minimum in complex 4. In case of complex 3 the thermal study inferred that CdS end product was obtained at ∼730 °C, whereas in case of other complexes the thermally stable end product remained unidentified. Solid state fluorescence study shows that all the complexes are luminescent at room temperature except complex 3. 相似文献
453.
Syroeshkin M. A. Mendkovich A. S. Mikhal’chenko L. V. Gul’tyai V. P. 《Russian Chemical Bulletin》2009,58(8):1688-1693
Association of 1,4-dinitrobenzene (1,4-DNB) dianion (DA) with 1-butyl-3-methylimidazolium (bmim+) and 1-butyl-2,3-dimethylimidazolium (bdmim+) cations, whose salts are widely used as ionic liquids, was studied by cyclic voltammetry. In 0.1 M solution of Bu4NClO4 in DMF, associates with the number of coordinated cations up to four in the case of bmim+ and two in the case of bdmim+ are formed. The partial stability constant values for the associates of bmim+ are 40, 20, 5, and 3.2 L mol−1, of bdmim+ − 24 and 1.9 L mol−1. The higher number of coordinated bmim+ cations is attributed to the formation of, along with ion pairs, hydrogen bonds between
1,4-DNB DA and bmim+ due to the labile hydrogen atom at position 2 of the imidazole ring, in contrast to bdmim+, which is involved only into the ion-pair interactions. 相似文献
454.
In order to study dynamic crossover phenomena in nanoconfined water we performed a series of molecular dynamics (MD) computer simulations of water clusters adsorbed in zeolites, which are microporous crystalline aluminosilicates containing channels and cavities of nanometric dimensions. We used a sophisticated empirical potential for water, including the full flexibility of the molecule and the correct response to the electric field generated by the cations and by the charged atoms of the aluminosilicate framework. In addition, the full flexibility of the aluminosilicate framework was included in the calculations. Previously reported and new simulations of water confined in a number of different types of zeolites in the temperature range 100-300 K and at various coverage are discussed in connection with the experimental data. Dynamic crossover phenomena are found in all the considered cases, in spite of the different shape and size of the clusters, even when the confinement hinders the formation of tetrahedral hydrogen bonds for water molecules. Hypotheses about the possible dynamic crossover mechanisms are proposed. 相似文献
455.
The paper presents the optimal control applied to a vector borne disease with direct transmission in host population. First, we show the existence of the control problem and then use both analytical and numerical techniques to investigate that there are cost effective control efforts for prevention of direct and indirect transmission of disease. In order to do this three control functions are used, one for vector-reduction strategies and the other two for personal (human) protection and blood screening, respectively. We completely characterize the optimal control and compute the numerical solution of the optimality system using an iterative method. 相似文献
456.
Suman Kumar Nath Kazi Hanium Maria Saroaut Noor S.S. Sikder S.Manjura Hoque M.A. Hakim 《Journal of magnetism and magnetic materials》2012
A series of Ni1−xCdxFe2O4 (0.0≤x≤0.8) were prepared by conventional double sintering ceramic method and sintered at 1200 °C for 6 h. X-ray diffraction results confirmed the single-phase spinel structures of all the samples. The Curie temperature decreases linearly with increasing Cd content, which is explained due to the weakening of the A–B exchange interaction. The sample with x=0.7 shows re-entrant type of spin glass phase transitions. The magnetic moment and saturation magnetization at 20 K are found to increase with Cd content up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice (A- and B-sublattice) collinear models according to which the magnetic moment is the vector sum of the lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x>0.3 indicates the increased tendency for triangular spin arrangements on B-sites. This suggests the existence of a canted spin structure in the ferrite system with higher content of Cd. 相似文献
457.
We present the dynamical phase diagrams of the kinetic Blume–Capel model with random diluted single-ion anisotropy in a square lattice under the presence of a time-varying (oscillating) external magnetic field calculated by an analytical method, the effective-field theory (EFT). The kinetics is modeled with the formalism of a master equation. The time-averaged magnetization (M) acts as the order parameter and divides the temperature–field plane into three regions: ferromagnetic, paramagnetic, and coexistence of ferromagnetic and paramagnetic phases. In addition, the hysteresis loop area and the dynamic correlation function are calculated. It is observed that the inclusion of spin–spin correlations suppress the first-order transition lines and dynamical tricritical points for all values of the crystal-field concentration. 相似文献
458.
In this study, we have analyzed the dynamical phase transitions of spin-1 Blume-Capel model with quenched random crystal field
under the effect of a time dependent oscillating magnetic field. We have obtained the magnetic field, temperature (h,T) cross sections of the global phase diagram for constant values of the concentration and the amplitude of the single-ion
anisotropy within mean field approximation. There are regions of the phase space where both ordered and disordered phases
coexist. In addition, the dynamic phase transition from one regime to the other can be a first- or a second-order depending
on the region in the phase diagram. Hence, the system exhibits a number of interesting phenomena and a rich variety of phase
diagrams with type being according to the concentration p of active local crystal fields. 相似文献
459.
Mustafa Yüksek Hüseyin Ertap Ayhan Elmali H. Gul Yaglioglu Gasan M. Mamedov Mevlüt Karabulut Mustafa K. Öztürk 《Optics & Laser Technology》2012,44(7):2178-2181
We have investigated the structural and optical properties of bulk GaTe crystal grown by vertical Bridgman method. Two photon absorption (TPA) properties of GaTe crystal have been investigated by the open aperture Z-scan technique under 1064 nm wavelength with 4 ns or 65 ps pulse durations. The TPA coefficients are greater in ns regime than that of ps regime. Upon increasing intensity of incident light from 5.02×107 W/cm2 to 1.07×108 W/cm2, the TPA coefficients increased from 3.47×10?6 cm/W to 8.53×10?6 cm/W for nanosecond excitation. Similarly, when intensity of incident light was increased from 6.81×108 W/cm2 to 9.94×108 W/cm2 the TPA coefficients increased from 3.53×10?7 cm/W to 6.83×10?7 cm/W for picosecond excitation. Measured TPA coefficient of GaTe crystal is larger than that of GaSe and GaS layered crystals. 相似文献
460.
J. Gulín-González P. Demontis E. Navas Conyedo G.B. Suffritti 《Journal of Physics and Chemistry of Solids》2012,73(6):797-802
Reversible amorphization and memory effects of both dense and open frameworks have received a great attention due to their prospective industrial applications. In this paper, the results of a computational study related to phase transition and memory effects in AlPO4-5 nanoporous material at high external pressure is presented. The behavior of the AlPO4-5 unit cell at high external pressures was studied by energy minimization techniques using classical potentials. A combination of interatomic potentials was used to describe the crystalline structure of the aluminophosphate. According to simulation's result a decrease of crystalline order is observed at a pressure about 3.5 GPa. The behavior of the simulated infrared spectra of compressed structures is an unambiguous evidence of structural disorder. Also, an abrupt change in the slope of the unit cell volume vs. pressure curve was obtained. At P≤3.5 GPa the process was found reversible. Contrary to what has been reported in other aluminosilicate systems the final crystalline state of AlPO4-5 at the highest simulated pressure was not amorphous. According to our knowledge this is the first evidence of a reversible first-order crystal-crystal phase transition in AlPO- family materials. This result could be important in future industrial and catalytic applications of these materials. 相似文献