Co(en)3][Sb12S19]: a new antimony sulfide with a zeolite-like structure containing one-dimensional channels

Solvothermal synthesis affords access to the first truly three-dimensional antimony-sulfide framework which contains one-dimensional circular channels.     

Traveling fronts in an array of coupled symmetric bistable units

Traveling fronts are shown to occur in an array of nearest-neighbor coupled symmetric bistable units. When the local dynamics is given by the Lorenz equations we observe the route: standing-->oscillating-->traveling front, as the coupling is increased. A key step in this route is a gluing bifurcation of two cycles in cylindrical coordinates. When this is mediated by a saddle with real leading eigenvalues, the asymptotic behavior of the front velocity is found straightforwardly. If the saddle is focus-type instead, the front's dynamics may become quite complex, displaying several oscillating and propagating regimes and including (Shil'nikov-type) chaotic front propagation. These results stand as well for other nearest-neighbor coupling schemes and local dynamics.     

Excess molar volumes of (ethyl formate or ethyl acetate + an isomer of hexanol) at 298.15 K

Excess molar volumes V_m^E were determined over the entire composition range at 298.15 K for ethyl formate or ethyl acetate + hexan-1-ol, +2-methylpentan-1-ol, +3-methylpentan-2-ol, +2-methylpentan-3-ol, +3-methylpentan-3-ol, +2-methylpentan-2-ol, +4-methyl-pentan-2-ol, and +hexan-2-ol. Excess volumes were determined from density measurements made with a vibrating-tube densimeter. The V_m^E values were all positive, decreasing with the n value of the ester: C_n?1H_2n?1CO₂C₂H₅.     

Ternary uranium oxides from thermal decomposition of uranyl butyrates with divalent cations

In order to make DTA accessible to a larger group of interested people a new simple DTA concept was developed. Without large-scale electronics linear changes of temperature in the range of + 20 to + 1000°C are realized. The system seems to be suitable for both laboratory courses and research. Constructional features, the mode of operation and a selection of different DTA curves are reported.     

A Formalism to Study the Propagation of the Four-Wave Mixing Signal in a Strongly Driven Two-Level System Immersed in a Thermal Reservoir

We analyze two analytical solutions for the study of the propagation of the four-wave mixing (FWM) signal in a strongly driven two-level system, when the stochastic effects of the solvent are explicitly considered. The first solution is valid only for a constant pump intensity, while the second solution considers pump propagation explicitly. In both cases, we were able to derive analytical expressions for the FWM nonlinear intensity signal in terms of the field amplitude and thermal noise parameters. Copyright 2000 Academic Press.     

Heterodimetallic germanium(IV) complex structures with transition metals

The hydrothermal synthesis and structural characterization of a number of complex compounds containing the divalent tris(oxalato-O,O')germanate anion, [Ge(C2O4)3]2-, or the neutral bis(oxalate-O,O')germanium fragment, [Ge(C2O4)2], with transition-metal (M) cationic complexes of 1,10'-phenanthroline (phen) is reported: [M(phen)3][Ge(C2O4)3].xH2O [where M2+ = Cu2+ (1a and 1b), Fe2+ (2a and 2b), Ni2+ (3), Co2+ (4); x = 0.2 for 2b], [MGe(phen)2(mu2-OH)2(C2O4)2] [where M2+ = Cd2+ (5) and Cu2+ (6)]. The isolation of two polymorphs with Cu2+ (1a and 1b) and other pseudo-polymorphs for Fe2+ (2a and 2b) was rationalized based on slightly different molar ratios for the starting materials. All compounds have been characterized using EDS, SEM, vibrational spectroscopy (FT-IR and FT-Raman), thermogravimetry, and CHN elemental composition and their structure determined on the basis of single-crystal X-ray diffraction studies. The crystal packing of the different chemical moieties for each series of compounds was discussed on the basis of the various intermolecular interactions present (strong C-H...pi and weak C-H...O hydrogen-bonding interactions, C-H...pi and pi-pi contacts).     

The Euclidean Bottleneck Steiner Path Problem and Other Applications of (α,β)-Pair Decomposition

We consider a geometric optimization problem that arises in network design. Given a set P of n points in the plane, source and destination points s, t∈P, and an integer k>0, one has to locate k Steiner points, such that the length of the longest edge of a bottleneck path between s and t is minimized. In this paper, we present an O(nlog² n)-time algorithm that computes an optimal solution, for any constant k. This problem was previously studied by Hou et al. (in Wireless Networks 16, 1033–1043, 2010), who gave an O(n ²logn)-time algorithm. We also study the dual version of the problem, where a value λ>0 is given (instead of k), and the goal is to locate as few Steiner points as possible, so that the length of the longest edge of a bottleneck path between s and t is at most λ. Our algorithms are based on two new geometric structures that we develop—an (α,β)-pair decomposition of P and a floor (1+ε)-spanner of P. For real numbers β>α>0, an (α,β)-pair decomposition of P is a collection $\mathcal{W}=\{(A_{1},B_{1}),\ldots,(A_{m},B_{m})\}$ of pairs of subsets of P, satisfying the following: (i) For each pair $(A_{i},B_{i}) \in\mathcal {W}$ , both minimum enclosing circles of A _i and B _i have a radius at most α, and (ii) for any p, q∈P, such that |pq|≤β, there exists a single pair $(A_{i},B_{i}) \in\mathcal{W}$ , such that p∈A _i and q∈B _i , or vice versa. We construct (a compact representation of) an (α,β)-pair decomposition of P in time O((β/α)³ nlogn). In some applications, a simpler (though weaker) grid-based version of an (α,β)-pair decomposition of P is sufficient. We call this version a weak (α,β)-pair decomposition of P. For ε>0, a floor (1+ε)-spanner of P is a (1+ε)-spanner of the complete graph over P with weight function w(p,q)=?|pq|?. We construct such a spanner with O(n/ε ²) edges in time O((1/ε ²)nlog² n), even though w is not a metric. Finally, we present two additional applications of an (α,β)-pair decomposition of P. In the first, we construct a strong spanner of the unit disk graph of P, with the additional property that the spanning paths also approximate the number of substantial hops, i.e., hops of length greater than a given threshold. In the second application, we present an O((1/ε ²)nlogn)-time algorithm for computing a one-sided approximation for distance selection (i.e., given k, $1 \le k \le{n \choose2}$ , find the k’th smallest Euclidean distance induced by P), significantly improving the running time of the algorithm of Bespamyatnikh and Segal.     

Semicarbazones from N-hydroxyureas and amines: a novel entry in the reactivity of the acyl nitroso group

The condensation of carbamoyl nitroso compounds, obtained by oxidation of N-hydroxyureas, with amines unexpectedly afforded semicarbazones (aka carbamoyl hydrazones). Although the substitution of the nitrosyl moiety might compete to afford the corresponding urea, an excess of amine led to the semicarbazone as the major product, which is presumably formed via isomerization of an initially generated acyl azo compound.     

Microcalorimetric study on the growth and metabolism of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Microcalorimetry is an experimental technique which allows us to precisely measure the energy released as a consequence of any transformation process. All organisms produce heat as a consequence of metabolism. The rate of heat production is an adequate measurement of metabolic activity of organisms and their constituent parts, cells and sub-cellular levels. Microorganisms produce small amounts of heat, in the order of 1–3 pW per cell. Despite the low quantity of heat produced by bacteria, their exponential replication in culture medium allows their detection using microcalorimetry. This study is a microcalorimetric study of the growth and metabolism of the bacterium Pseudomonas aeruginosa, using the heat liberated as a consequence of bacterial metabolism. With this aim, we used a Calvet microcalorimeter, inside which two Teflon screw-capped stainless steel cells were located (sample and reference). Experiments were carried out at final concentrations of 10⁶, 10⁵, 10³ and 10 CFU/mL, and a constant temperature of 309.65 K was maintained within the microcalorimeter. Recording the difference in calorific potential over time we obtained P. aeruginosa’s growth curves. The shape of these curves is characteristic and has a single phase. Thus, the heat flow curves were mathematically studied to calculate the growth constant and generation time of this bacterium.