A two-dimensional domain decomposition technique for the simulation of quantum-scale devices

The simulation of realistically sized devices under the Non-Equilibrium Greens Function (NEGF) formalism typically requires prohibitive amounts of memory and computation time. In order to meet the rising computational challenges associated with quantum-scale device simulation we offer a 2-D domain decomposition technique. This technique is applicable to a large class of atomistic and spatial simulation problems. Considering a decomposition along both the cross section and length of the device, the framework presented in this work ensures efficient distribution of both memory and computation based upon the underlying device structure. As an illustration we stably generate the density of states and transmission, under the NEGF formalism, for the atomistic-based simulation of square 5 nm cross section silicon nanowires consisting of over one million atomic orbitals.     

The ac conductivity and complex impedance of CuO-doped (Ba0.5Sr0.5)TiO3 ceramic

The AC conductivity and complex impedance spectroscopy of CuO-doped (Ba_0.5Sr_0.5)TiO₃ ceramic were investigated. X-ray diffraction analysis showed that CuO-doped (Ba_0.5Sr_0.5)TiO₃ has a perovskite structure without any pyrochlore phase. Frequency dependent dielectric permittivity was discussed at a different temperature range. The activation energy was calculated and discussed through the Arrehnius equation from the ac conductivity with different frequency plots. CuO-doped (Ba_0.5Sr_0.5)TiO₃ ceramics have a negative temperature coefficient of resistivity. Dependence of impedance spectroscopy on frequency and temperature showed that the conduction process in the CuO-doped (Ba_0.5Sr_0.5)TiO₃ ceramic follows the thermally activated conduction mechanism.     

Phase equilibrium measurements and the tuning behavior of new sII clathrate hydrates

We suggest two types of new amine-type sII formers: pyrrolidine and piperidine. These guest compounds fail to form clathrate hydrate structures with host water, but instead have to combine with light gaseous guest molecules (methane) for enclathration. First, two binary clathrate hydrates of (pyrrolidine + methane) and (piperidine + methane) were synthesized at various amine concentrations. ¹³C NMR and Raman analysis were done to identify the clathrate hydrate structure and guest distribution over sII-S and sII-L cages. XRD was also used to find the exact structure and corresponding cell parameters. At a dilute pyrrolidine concentration of less than 5.56 mol%, the tuning phenomenon is observed such that methane molecules surprisingly occupy sII-L cages. At the critical guest concentration of about 0.1 mol%, the cage occupancy ratio reaches the maximum of approximately 0.5. At very dilute guest concentration below 0.1 mol%, the methane molecules fail to occupy large cages on account of their rarefied distribution in the network. Direct-release experiments were performed to determine the actual guest compositions in the clathrate hydrate phases. Finally, we measured the clathrate hydrate phase equilibria of (pyrrolidine + methane) and (piperidine + methane).     

Structures and Chromaticity of Extremal 3-Colourable Sparse Graphs

 Assume that G is a 3-colourable connected graph with e(G) = 2v(G) −k, where k≥ 4. It has been shown that s ₃(G) ≥ 2 ^{k −3}, where s _r (G) = P(G,r)/r! for any positive integer r and P(G, λ) is the chromatic polynomial of G. In this paper, we prove that if G is 2-connected and s ₃(G) < 2 ^{k −2}, then G contains at most v(G) −k triangles; and the upper bound is attained only if G is a graph obtained by replacing each edge in the k-cycle C _k by a 2-tree. By using this result, we settle the problem of determining if W(n, s) is χ-unique, where W(n, s) is the graph obtained from the wheel W _n by deleting all but s consecutive spokes. Received: January 29, 1999 Final version received: April 8, 2000     

Relative Topological Pinsker Factors and Entropy Pairs

 A relative version of the topological m-Pinsker factor is given and its relationships with other notions of relative Pinsker factors are investigated. Relative topological Pinsker factors (of various kinds) of relative products are described. (Received 4 December 2000; in revised form 1 June 2001)     

Kinetics of nanoconfined benzyl methacrylate radical polymerization

The effect of nanoconfinement on the kinetics of benzyl methacrylate radical polymerization is investigated using differential scanning calorimetry. Controlled pore glass (CPG), ordered mesoporous carbons, and mesoporous silica are used as confinement media with pore sizes from 2 to 8 nm. The initial polymerization rate in CPG and mesoporous silica increases relative to the bulk and increases linearly with reciprocal pore size; whereas, the rate in the carbon mesopores decreases linearly with reciprocal pore size; the changes are consistent with the rate being related to the ratio of the pore surface area to pore volume. Induction times are longer for nanoconfined polymerizations, and in the case of CPG and carbon mesopores, autoacceleration occurs earlier, presumably due to the limited diffusivity and lower termination rates for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The equilibrium conversion under nanoconfinement decreases with decreasing temperature and with confinement size, exhibiting what appears to be a floor temperature at low temperatures.     

Vector mesons and magnetic moments of hyperons

We calculate hyperon magnetic moments by using the bound-state approach to the SU(3) Skyrme model. We analyze the role of the vector mesons as ω and meson in the calculation of the magnetic moment. Inclusion of an ω vector meson, instead of the Skyrme term, shows a net improvement of the nonstrange part of the isoscalar current. Taking account of the vector meson, although only treated approximately in the SU(2) sector, does not give a meaningful improvement in isoscalar or isovector current, if we fix the physical input of the model to fit the hyperon masses. Importance of the heavy vector mesons is argued, not only in the hyperfine mass splitting but also in the magnetic moment. It is also argued that the treatment of the gauged Wess-Zumino action in the SU(2) sector is crucial in reproducing the experimental results.     

Modification chimique de polyalcadiènes par les composés du type CX3POZ2—II: Modification des polybutadiènes-1,2 par le dichlorure de trichlorométhyl-phosphonyle catalysée par le dichlorure de tris(triphénylphosphine)ruthénium II

The catalytic influence of dichlorotris (triphenylphosphine) ruthenium II, Cl₂Ru (PPh₃)₃ (I), on chemical modification of 1,2-polybutadienes ($\text{M}{}_{\mathrm{<mtext>n</mtext>}}\text{< 10,000}$) by trichloromethylphosphonyl dichloride, CCl₃POCl₂ (II) has been studied. The catalytic activity of (I) has been compared with those of redox systems, CuCl₂/Et₃NHCl, FeCl₃/Et₃NHCl/benzoïn. In addition to good solubility in the usual solvents, the polymers modified with (I) contain a higher percentage of DTMP and side reactions, including HCl elimination, are fewer. The influences of various parameters on the yield of the reaction catalysed by (I) have been examined. (Reaction temperature, nature and quantity of solvent, reagent and catalyst concentrations, reaction time, surrounding atmosphere.)     

Toluene solvent system for the headspace gas chromatographic determination of styrene monomer in polystyrene

The use of toluene as a solvent to dissolve polystyrene for the determination of styrene monomers is studied. Compared with the modified solution headspace method using dimethylacetamide as solvent, with toluene the system is slightly less sensitive. However, there appeared to be minimal matrix effect when toluene is used, so a simpler external calibration method can be applied.