Weakly Nonlinear Convection in a Porous Layer with Multiple Horizontal Partitions

We consider convection in a horizontally uniform fluid-saturated porous layer which is heated from below and which is split into a number of identical sublayers by impermeable and infinitesimally thin horizontal partitions. Rees and Genç (Int J Heat Mass Transfer 54:3081–3089, 2010) determined the onset criterion by means of a detailed analytical and numerical study of the corresponding dispersion relation and showed that this layered system behaves like the single-sublayer constant-heat-flux Darcy–Bénard problem when the number of sublayers becomes large. The aim of the present work is to use a weakly nonlinear analysis to determine whether the layered system also shares the property of the single-sublayer constant-heat-flux Darcy–Bénard problem by having square cells, as opposed to rolls, as the preferred planform for convection.     

A structural investigation of the alkali metal site distribution within bioactive glass using neutron diffraction and multinuclear solid state NMR

The atomic-scale structure of Bioglass and the effect of substituting lithium for sodium within these glasses have been investigated using neutron diffraction and solid state magic angle spinning (MAS) NMR. Applying an effective isomorphic substitution difference function to the neutron diffraction data has enabled the Na-O and Li-O nearest-neighbour correlations to be isolated from the overlapping Ca-O, O-(P)-O and O-(Si)-O correlations. These results reveal that Na and Li behave in a similar manner within the glassy matrix and do not disrupt the short range order of the network former. Residual differences are attributed solely to the variation in ionic radius between the two species. Successful simplification of the 2 < r (?) < 3 region via the difference method has enabled all the nearest neighbour correlations to be deconvolved. The diffraction data provides the first direct experimental evidence of split Na-O nearest-neighbour correlations in these melt quench bioactive glasses, and an analogous splitting of the Li-O correlations. The observed correlations are attributed to the metal ions bonded either to bridging or to non-bridging oxygen atoms. (23)Na triple quantum MAS (3QMAS) NMR data corroborates the split Na-O correlations. The structural sites present will be intimately related to the release properties of the glass system in physiological fluids such as plasma and saliva, and hence to the bioactivity of the material. Detailed structural knowledge is therefore a prerequisite for optimizing material design.     

Models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes: salts and zwitterions from 1-dimethylamino-naphthalene-8-carbaldehyde

The X-ray crystal structures of salts and zwitterionic Knoevenagel products from 1-dimethylamino-naphthalene-8-carbaldehyde show long N-C bonds between peri-groups which provide models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes respectively. For the salts the N-C bonds lie in the range 1.625-1.638 ? with C-OH bonds intermediate in length between single and double bonds, while for the zwitterions the N-C bonds lie in the range 1.612-1.660 ?. The structural assignment of the former is supported by solid state (13)C and (15)N NMR studies on doubly isotopically-labelled material. Several zwitterions were converted to naphtha[1,8-bc]azepines by a mechanism involving the tertiary amino effect.     

Onset of Convection in a Porous Layer with Continuous Periodic Horizontal Stratification. Part I. Two-Dimensional Convection

The onset of convection in a horizontal porous layer is investigated theoretically. The permeability of the porous medium is a continuous periodic function of the horizontal x coordinate. Floquet theory has been employed to determine the favoured two-dimensional mode of convection. For a wide range of periods of the permeability variation, a matrix eigenvalue technique with eighth order accuracy has been employed to find the critical Darcy– Rayleigh number. This is supplemented by a multiple-scales analysis of the large-period limit, and a brief consideration of the anisotropic limit for very short periods.     

Prediction of natural convection flow using network model and numerical simulations inside enclosure with distributed solid blocks

Steady state natural convection of a fluid with Pr ≈ 1 within a square enclosure containing uniformly distributed, conducting square solid blocks is investigated. The side walls are subjected to differential heating, while the top and bottom ones are kept adiabatic. The natural convection flow is predicted employing the nondimensional volumetric flow rate (Q_max^* Q_{\max }^{*} ) by using a network model and also using numerical simulations. For identical solid and fluid thermal conductivities (i.e. k _s  = k _f ), a parametric study of the effect of number of blocks (N ²), gap size (δ) and enclosure Rayleigh number (Ra) on Q_max^* Q_{\max }^{*} is performed using the two approaches. Network model predictions are observed to agree well with that from the simulations until Raδ³ ~ 12. Considering the enclosure with blocks as a porous medium, for a fixed enclosure Ra number, increasing the number of blocks for a fixed volumetric porosity leads to a decrease in enclosure permeability, which in turn reduces the flow rate. When the number of blocks is fixed, and for a given Ra number, the flow rate increases as the porosity increases by widening the gap between the blocks.     

Pulsed‐laser polymerization‐gel permeation chromatographic determination of the propagation‐rate coefficient for the methyl acrylate dimer: A sterically hindered monomer

The methyl acrylate dimer (MAD) is a sterically hindered macromonomer, and the propagating radical can fragment to an unsaturated end group. The propagation‐rate coefficient (k_p) for MAD was obtained by pulsed‐laser polymerization (PLP). The Mark–Houwink–Sakaruda parameters required for the analysis of the molecular weight distributions (MWDs) were obtained by multiple‐detector gel permeation chromatography (GPC) with on‐line viscometry. The small radical created by the fragmentation results in a short‐chain polymer that means the MWD may no longer be given by that expected for “ideal” PLP conditions; simulations suggest that the degree of polymerization required for “ideal” PLP conditions can be obtained from the primary point of inflection provided the GPC traces also show a clear secondary inflection point (radicals terminated by the second, rather than the first, pulse subsequent to initiation). Over the temperature range of 40–75 °C, the data can be best fitted by k_p/dm³ mol^?1 s^?1 = 10^6.1 exp(?29.5 kJ mol^?1), with a moderately large joint confidence interval for the Arrhenius parameters. The data are consistent with an increased activation energy and reduced frequency factor as compared with acrylate or methacrylate; both of these changes can be ascribed to hindrance. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3902–3915, 2001     

Necroptosis Induced by Ruthenium(II) Complexes as Dual Catalytic Inhibitors of Topoisomerase I/II

Inducing necroptosis in cancer cells is an effective approach to circumvent drug‐resistance. Metal‐based triggers have, however, rarely been reported. Ruthenium(II) complexes containing 1,1‐(pyrazin‐2‐yl)pyreno[4,5‐e][1,2,4]triazine were developed with a series of different ancillary ligands ( Ru1 ‐ 7 ). The combination of the main ligand with bipyridyl and phenylpyridyl ligands endows Ru7 with superior nucleus‐targeting properties. As a rare dual catalytic inhibitor, Ru7 effectively inhibits the endogenous activities of topoisomerase (topo) I and II and kills cancer cells by necroptosis. The cell signaling pathway from topo inhibition to necroptosis was elucidated. Furthermore, Ru7 displays significant antitumor activity against drug‐resistant cancer cells in vivo. To the best of our knowledge, Ru7 is the first Ru‐based necroptosis‐inducing chemotherapeutic agent.     

Road traffic sound level distributions

A microprocessor-controlled instrument has been used to form a traffic noise level histogram with a resolution better than 0·1 dB per channel. The instrument calculates the mean, standard deviation, skewness and kurtosis of the distribution, along with L_N and L_eq values. The results of over 200 measurements, of 400 s duration, are shown to be in disagreement with predictions based on the commonly assumed Gaussian distribution. Skewness values ranging from +1 to ?1 have been observed, while kurtosis can exceed 4. Measurements taken near freely flowing, pulsed and banked traffic have been used to describe the “typical” distribution shape, it being observed that banked traffic noise has markedly different characteristics from other types of traffic. Simultaneous measurements taken on each side of the road have been related to the position of the traffic on the road and these data have led to a simple model for estimating the distribution shape and statistical parameters.     

The equivalence of certain equidistant binary codes and symmetric bibds

We study equidistant codes of length 4k + 1 having (constant) weight 2k, and (constant) distance 2k between codewords. The maximum number of codewords is 4k; this can be attained if and only ifk = (u ² +u)/2 (for some integeru) and there exists a ((2u ² + 2u + 1,u ², (u ² −u)/2) — SBIBD. Also, one can construct such a code, with 4k − 1 codewords, from a (4k − 1, 2k − 1,k − 1) — SBIBD. Supported, in part by NSERC grants U0217 (D. R. Stinson), A3558 (G. H. J. van Rees).