Decoration of Graphitic Surfaces with Sn Nanoparticles through Surface Functionalization Using Diazonium Chemistry

Composites of tin nanoparticles (Sn NP) and graphene are candidate materials for high capacity and mechanically stable negative electrodes in rechargeable Li ion batteries. A uniform dispersion of Sn NP with controlled size is necessary to obtain high electrochemical performance. We show that the nucleation of Sn particles on highly ordered pyrolitic graphite (HOPG) from solution can be controlled by functionalizing the HOPG surface by aryl groups prior to Sn deposition. On the contrary, we observe heterogeneous deposition of micrometer sized Sn islands on HOPG subjected to oxidation prior to deposition in the same conditions. We demonstrate that functional groups act as nucleation sites for Sn NP nucleation, and that homogeneous nucleation of small particles can be achieved by combining surface functionalization with diazonium chemistry and appropriate stabilizers in solution.     

Efficient preparation of proline N-carboxyanhydride using polymer-supported bases

[Structure: see text] A procedure for the preparation of proline N-carboxyanhydride in high yield and purity is described using polymer-supported tertiary amines. The polymer-supported amine can be recycled with a basic wash and filtration of the resin. The procedure facilitates the access to the efficient preparation of the polyproline polymer with potential therapeutic interest.     

Palladium-catalyzed [3 + 2] intramolecular cycloaddition of alk-5-enylidenecyclopropanes

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.     

The nature of associates of 1,4-dinitrobenzene dianion with 1-butyl-3-methylimidazolium and 1-butyl-2,3-dimethylimidazolium cations

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.     

Computer simulations of dynamic crossover phenomena in nanoconfined water

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.     

Optimal control of a vector borne disease with horizontal transmission

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.     

Effective-field theory with the differential operator technique for a kinetic Blume–Capel model with random diluted single-ion anisotropy

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$M$) 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.     

Effects of the Quenched Random Crystal Field on the Dynamic Spin-1 Blume-Capel Model

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.     

Two photon absorption characteristics of bulk GaTe crystal

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.     

Computational research on memory effects in AlPO4-5 nanoporous material

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.