E- and Z-vinyloxyboranes (alkenyl borinates): stereoselective formation and aldol condensation

Vinyloxyboranes, intermediates of Hooz' reaction, are almost exclusively $\text{E}$-isomers which can be isomerized to the $\text{Z}$-isomers. Both isomers undergo stereoselective aldol condensations.     

Analysis of a tandem network model of a single-router Network-on-Chip

We study a single-router Network-on-Chip modelled as a tandem queueing network. The first node is a geo ^K /D/1 queue (K fixed) representing a network interface, and the second node is a ./G/1 queue representing the packet switch. If K>1 we have train arrivals at the second node. If K=1 the arrival process of the second node reduces to a Bernoulli process. In the latter case, routers have been studied extensively as part of ATM and LAN networks under the assumption that the number of input ports N tends to infinity. In Networks-on-Chips N is usually 4 or 5 and results for ATM and LAN routers lead to inaccurate results. We introduce a new approximation scheme that yields accurate results for small switches. In addition to this we analyse the tandem network, both for K=1 and K>1, and we approximate the mean sojourn time in the switch and the mean end-to-end delay. If N=4 our approximation has a relative error of only 4.5% if K=6 and 1% if K=1.     

A review of induction and attachment times of wetting thin films between air bubbles and particles and its relevance in the separation of particles by flotation

Bubble-particle attachment in water is critical to the separation of particles by flotation which is widely used in the recovery of valuable minerals, the deinking of wastepaper, the water treatment and the oil recovery from tar sands. It involves the thinning and rupture of wetting thin films, and the expansion and relaxation of the gas-liquid-solid contact lines. The time scale of the first two processes is referred to as the induction time, whereas the time scale of the attachment involving all the processes is called the attachment time. This paper reviews the experimental studies into the induction and attachment times between minerals and air bubbles, and between oil droplets and air bubbles. It also focuses on the experimental investigations and mathematical modelling of elementary processes of the wetting film thinning and rupture, and the three-phase contact line expansion relevant to flotation. It was confirmed that the time parameters, obtained by various authors, are sensitive enough to show changes in both flotation surface chemistry and physical properties of solid surfaces of pure minerals. These findings should be extended to other systems. It is proposed that measurements of the bubble-particle attachment can be used to interpret changes in flotation behaviour or, in conjunction with other factors, such as particle size and gas dispersion, to predict flotation performance.     

Characterization and aging effect study of nitrogen-doped ZnO nanofilm

The influence of sputtering and annealing conditions and aging effect on properties of sputtered ZnO:N thin films were investigated. Achieved results confirmed a planar growth of nitrogen-doped ZnO film with a high uniform and smooth surface morphology. Incorporation of nitrogen in the ZnO films made new Raman shifts. X-ray diffraction spectra showed only the ZnO (0 0 2) diffraction peak, which was slightly shifted toward lower angels, compared to pure ZnO, which is the result of incorporating nitrogen in the ZnO films. The amount of this shift was proportional to N concentration. In addition, annealed samples showed better crystallinity with lower shift due to dramatically reduction of N atoms during the annealing. The Hall effect measurements exhibited p-type behaviour on annealed ZnO:N thin films while the un-annealed samples showed n-type conductivity. Aging effect studies demonstrated that the N content of thin films decreased dramatically as time passed. The reduction of N concentration in annealed samples was lower than un-annealed ones after 6 months.     

Effect of interactions, disorder and magnetic field in the Hubbard model in two dimensions

The effects of both interactions and Zeeman magnetic field in disordered electronic systems are explored in the Hubbard model on a square lattice. We investigate the thermodynamic (density, magnetization, density of states) and transport (conductivity) properties using determinantal quantum Monte Carlo and inhomogeneous Hartree Fock techniques. We find that at half filling there is a novel metallic phase at intermediate disorder that is sandwiched between a Mott insulator and an Anderson insulator. The metallic phase is highly inhomogeneous and coexists with antiferromagnetic long-range order. At quarter filling also the combined effects of disorder and interactions produce a conducting state which can be destroyed by applying a Zeeman field, resulting in a magnetic field-driven transition. We discuss the implication of our results for experiments.     

The acquisition queue

We propose a new queueing model named the acquisition queue. It differs from conventional queueing models in that the server not only serves customers, but also performs acquisition of new customers. The server has to divide its energy between both activities. The number of newly acquired customers is uncertain, and the effect of the server’s acquisition efforts can only be seen after some fixed time period δ (delay). The acquisition queue constitutes a (δ+1)-dimensional Markov chain. The limiting queue length distribution is derived in terms of its probability generating function, and an exact expression for the mean queue length is given. For large values of δ the numerical procedures needed for calculating the mean queue length become computationally cumbersome. We therefore complement the exact expression with a fluid approximation. One of the key features of the acquisition queue is that the server performs more acquisition when the queue is small. Together with the delay, this causes the queue length process to show a strongly cyclic behavior. We propose and investigate several ways of planning the acquisition efforts. In particular, we propose an acquisition scheme that is designed specifically to reduce the cyclic behavior of the queue length process. This research was financially supported by the European Network of Excellence Euro-NGI. The work of the second author was supported in part by a TALENT grant from the Netherlands Organisation for Scientific Research (NWO).     

Effect of substrate temperature on gold-catalyzed silicon nanostructures growth by hot-wire chemical vapor deposition (HWCVD)

The effect of substrate temperature on the structural property of the silicon nanostructures deposited on gold-coated crystal silicon substrate by hot-wire chemical vapor deposition (HWCVD) was studied. The uniformity and size of the as-grown silicon nanostructures is highly influenced by the substrate temperature. XRD, Raman and HRTEM measurements show the silicon nanostructures consist of small crystallites embedded within amorphous matrix. The crystallite size of the as-grown silicon nanostructures decreases with increases in substrate temperature. FTIR shows that these silicon nanostructures are highly disordered for sample prepared at substrate temperature above 250 °C. The correlation of crystallinity and structure disorder of the silicon nanostructures growth at different substrate temperature was discussed.     

A factored implicit scheme for numerical weather prediction

The nonlinear partial differential equations of atmospheric dynamics govern motion on two time scales, a fast one and a slow one. Only the slow-scale motions are relevant in predicting the evolution of large weather patterns. Implicit numerical methods are therefore attractive for weather prediction, since they permit a large time step chosen to resolve only the slow motions. To develop an implicit method which is efficient for problems in more than one spatial dimension, one must approximate the problem by smaller, usually one-dimensional problems. A popular way to do so is to approximately factor the multidimensional implicit operator into one-dimensional operators. The factorization error incurred in such methods, however, is often unacceptably large for problems with multiple time scales. We propose a new factorization method for numerical weather prediction which is based on factoring separately the fast and slow parts of the implicit operator. We show analytically that the new method has small factorization error, which is comparable to other discretization errors of the overall scheme. The analysis is based on properties of the shallow water equations, a simple two-dimensional version of the fully three-dimensional equations of atmospheric dynamics.     

A.C. susceptibility and magnetisation measurements on polysulphur nitride, (SN)x

Measurements of the complex A.C. susceptibility and magnetization of crystals of polysulphur nitride, (SN)_x, are reported. At temperatures near 0.2K both the in-phase and quadrature components of the A.C. susceptibility show a marked change which can be related to the onset of superconductivity. However, changes in the sample magnetization could not be detected.     

An oxovanadium(IV) complex containing a pentacoordinate Schiff-base ligand: synthesis and crystal and molecular structure of N,N′-(3,3′-dipropylamine)bis (3-methoxysalicylideneiminato)oxovanadium(IV) dihydrate

Crystals ofN,N-(3,3-dipropylamine)bis(3-methoxysalicylideneiminato) oxovanadium(IV) dihydrate are monoclinic, space groupP2₁/n (No. 14) with four molecules in the unit cell of dimensionsa=8.667(4),b=20.617(4),c=12.744(3) Å,=91.48(3)°. The structure was solved by the heavy-atom method and refined by block diagonal least-squares calculations with anisotropic thermal parameters for nonhydrogen atoms.R=0.038 for 1457 reflections withI>3(I). This structure is the first reported for an oxovanadium(IV) complex involving complexation of a pentacoordinate Schiff-base ligand. The coordination polyhedron is based on a distorted octahedron. Three nitrogen and one oxygen atom from the ligand form an equatorial plane around vanadium with V-N(1) 2.096(4), V-N(2) 2.180(4), V-N(3) 2.088(4), V-O(2) 1.961(3) Å, and octahedral coordination is completed by the vanadyl oxygen [V-O(1) 1.617(3) Å] and the remaining ligand oxygen [V-O(3) 2,098(3) Å]. The relatively long V-O(1) distance correlates well with the low value ofv(V=O) of 919 cm^–1. The molecules of the complex are linked by water molecules of crystallization to form infinite hydrogen-bonded chains parallel toa.