Synthesis and characterization of [MCl2(nPr-N(Ph2P)2] (M?=?Pt, Pd) complexes and hydroformylation of 1-octene using [PtCl2(R-N(Ph2P)2)] (R?=?benzyl, 2-picolyl, nPr) complexes

The synthesis and characterization of platinum(II) and palladium(II) complexes of the type [PtX₂( ⁿ Pr-N(Ph₂P)₂)] (X = Cl, I) and [PdCl₂(R-N(Ph₂P)₂)] {R =  ⁿ Pr, p-OMe(C₆H₄)} containing aminodiphosphine P,P-bidentate ligands is described. Complexes of the type [PtCl₂(R-N(Ph₂P)₂)] (where R = benzyl, 2-picolyl and ⁿ Pr) catalyzed the hydroformylation of 1-octene, albeit at low activities and slightly elevated regioselectivities toward the linear aldehyde, when compared with analogous compounds containing small bite angles.     

Constraints on the fundamental string coupling from B-mode experiments

We study signatures of cosmic superstring networks containing strings of multiple tensions and Y junctions, on the cosmic microwave background (CMB) temperature and polarization spectra. Focusing on the crucial role of the string coupling constant g(s), we show that the number density and energy density of the scaling network are dominated by different types of string in the g(s) ~ 1 and g(s) ? 1 limits. This can lead to an observable shift in the position of the B-mode peak--a distinct signal leading to a direct constraint on g(s). We forecast the joint bounds on g(s) and the fundamental string tension μ(F) from upcoming and future CMB polarization experiments, as well as the signal to noise in detecting the difference between B-mode signals in the limiting cases of large and small g(s). We show that such a detectable shift is within reach of planned experiments.     

Investigation of slow light enhanced nonlinear transmission for all-optical regeneration in silicon photonic crystal waveguides at 10 Gbit/s

We demonstrate bit error rate improvement, corroborated by eye diagram measurements, of a (10 MHz) amplitude distorted 10 Gbit/s data signal in silicon photonic crystal waveguides. This demonstration exploits a power clamping nonlinear transfer function, provided by slow light enhancement of nonlinear absorption in these waveguides.     

Group invariant solution for a pre-existing fluid-driven fracture in impermeable rock

The propagation of a two-dimensional fluid-driven fracture in impermeable rock is considered. The fluid flow in the fracture is laminar. By applying lubrication theory a partial differential equation relating the half-width of the fracture to the fluid pressure is derived. To close the model the PKN formulation is adopted in which the fluid pressure is proportional to the half-width of the fracture. By considering a linear combination of the Lie point symmetries of the resulting non-linear diffusion equation the boundary value problem is expressed in a form appropriate for a similarity solution. The boundary value problem is reformulated as two initial value problems which are readily solved numerically. The similarity solution describes a preexisting fracture since both the total volume and length of the fracture are initially finite and non-zero. Applications in which the rate of fluid injection into the fracture and the pressure at the fracture entry are independent of time are considered.     

Group invariant solution for a pre-existing fluid-driven fracture in impermeable rock

The propagation of a two-dimensional fluid-driven fracture in impermeable rock is considered. The fluid flow in the fracture is laminar. By applying lubrication theory a partial differential equation relating the half-width of the fracture to the fluid pressure is derived. To close the model the PKN formulation is adopted in which the fluid pressure is proportional to the half-width of the fracture. By considering a linear combination of the Lie point symmetries of the resulting non-linear diffusion equation the boundary value problem is expressed in a form appropriate for a similarity solution. The boundary value problem is reformulated as two initial value problems which are readily solved numerically. The similarity solution describes a preexisting fracture since both the total volume and length of the fracture are initially finite and non-zero. Applications in which the rate of fluid injection into the fracture and the pressure at the fracture entry are independent of time are considered.     

Human neuronal stargazin-like proteins, γ2, γ3 and γ4; an investigation of their specific localization in human brain and their influence on CaV2.1 voltage-dependent calcium channels expressed in Xenopus oocytes.

Background  

Stargazin (γ₂) and the closely related γ₃, and γ₄ transmembrane proteins are part of a family of proteins that may act as both neuronal voltage-dependent calcium channel (VDCC) γ subunits and transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazoleproponinc (AMPA) receptor regulatory proteins (TARPs). In this investigation, we examined the distribution patterns of the stargazin-like proteins γ₂, γ₃, and γ₄ in the human central nervous system (CNS). In addition, we investigated whether human γ₂ or γ₄ could modulate the electrophysiological properties of a neuronal VDCC complex transiently expressed in Xenopus oocytes.     

Stability of underexpanded supersonic jet flames burning H2-CO mixtures

It has been established experimentally that both natural gas and hydrogen discharges, through circular orifices larger than a critical diameter, sustain stable lifted flames irrespective of the reservoir pressure driving the release. At smaller diameters, however, stable burning will only be achieved at operating pressures higher than a particular, diameter-dependent, threshold. This latter is strongly fuel-type dependent but empirical correlations have been developed to describe such behaviour. Given the wide disparity of critical diameters depending upon the fuel type considered, the behaviour of multi-component gaseous mixtures involving hydrogen is much less predictable than the correlations for pure fuels might indicate. A series of experiments has been undertaken in which H₂-CO mixtures are discharged from a high pressure reservoir to ambient through convergent circular nozzles, varying in diameter from 1.3 to 5 mm. A wide range of driving pressures has been investigated, from 3 to 50 bar, embracing fuel mixtures containing up to 20% CO by volume. Stability curves have been derived that identify the region where stable burning is sustained relative to the pressure ratio (reservoir pressure/ambient pressure) and the CO concentration in the fuel mixture. The present experimental data are compared with existing correlations (Kalghatgi 1981), derived from subsonic releases, and Birch et al. (1988a), applied to underexpanded supersonic methane jet flames. Although these correlations reproduce the general trend observed experimentally, they appear to significantly over-estimate the stability region. Furthermore, they do not account for the high sensitivity of the diluent concentration on the blowout stability. A thorough investigation is carried out in order to determine the source of discrepancies observed between the empirical correlations and the present measurements. Differential diffusion between the fuel components is shown to be negligible. The introduction of additional information on the turbulent flowfield from numerical simulation of the isothermal underexpanded jet, immediately upstream of the flame stabilisation region, does not appear to yield discriminating evidence for incipient blow-off instability. The maximum burning velocity alone, a widely employed characterising parameter, does not appear to describe accurately the complex interactions between the turbulent flowfield and the chemical kinetics.     

The identification of two distinct laminar to turbulent transition modes in pipe flows accelerated from rest

A study was undertaken to investigate transition in a pipe flow accelerated from rest. Experiments were carried out on a vertical tube under a constant head of liquid: flow was initiated by opening a solenoid valve. A wall shear stress probe used in the role of an event recorder identified two transition events, separated by the passage of a turbulent to laminar front and a period of laminar flow. Evidence suggests that the first comprises a laminar to turbulent interface arising from a natural stable/unstable front moving up the tube as local conditions become met, while the second is consequent upon the formation of a continuous turbulent structure carried down the tube from the inlet by the bulk flow. The paper provides a formal explanation of a phenomenon which is typical of that which is observed in starting pipe flows with a disturbed inlet.     

Raman spectroscopic investigation on the microenvironment of the liver tissues of Zebrafish (Danio rerio) due to titanium dioxide exposure

Nano titanium dioxide (nTiO₂), generally considered to be toxicologically inert, is manufactured in large quantities and extensively applied in consumer products. The small size and large surface area endow them with an active group or intrinsic toxicity. Advances in instrumentation are making Raman spectroscopy the tool of choice for an increasing number of (bio) chemical applications. One of the great advantages of this technique is its ability to provide information on the concentration, structure and interaction of biochemical molecules in their microenvironments within intact cells and tissues, non-destructively. Zebrafish (Danio rerio), one of the most important vertebrate model organisms used in developmental biology, are increasingly used in biomedical research, particularly as a model of human disease. In the present work, an attempt is made to study the effect of titanium dioxide, both nano and bulk, on the microenvironment of the liver tissues of Zebrafish using FT-Raman spectroscopy. The results of the present study suggest that TiO₂ exposure demonstrate a marked influence on the microenvironments of the liver tissues of Zebrafish. A shift to a higher wavenumber and an increase in the intensity of the band at ∼1087 cm⁻¹ in the TiO₂ exposed tissues suggest that some of the conformational changes resulting from the alkali recovery process takes place due to TiO₂ exposure. The decreased intensity ratio (I₃₂₂₀/I₃₄₀₀) observed in the titanium-exposed tissues suggests a decreased water domain size, which could be interpreted in terms of weaker hydrogen-bonded molecular species of water in the TiO₂ exposed tissues. The observed shift of COO⁻ bands to higher frequencies shows the disruption of salt bridges as a result of a change in the oppositely charged partners and due to the enhanced random coil conformation. The variation in the intensity ratio of the tyrosyl doublet (I₈₅₈/I₈₂₅) indicates variation in the hydrogen bonding of the phenolic hydroxyl group due to TiO₂ exposure. The results further suggest that the microenvironments are greatly altered due to titanium nano exposure when compared to titanium bulk. In conclusion, the results indicate that FT-Raman spectroscopy might be a useful tool for rapid assessment of nano particle biological interactions.     

Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis, characterization and catalytic oligomerisation of ethylene

New N-functionalised 2-phosphinobenzaldimino (P^N) ligands bearing 3-picolyl, furfuryl, thiophene-2-methyl, thiophene-2-ethyl, and benzyl groups have been prepared in good yield. The 2-phosphinobenzaldimino ligands were reacted with PdCl₂(COD) to give the corresponding metal complexes of the type Pd(L)Cl₂ (L = 2-phosphinobenzaldimino (P^N) ligand). All compounds were fully characterized using spectroscopic and analytical techniques, including ¹H, ¹³C, and ³¹P NMR and IR spectroscopies, mass spectrometry and elemental analysis. Selected neutral palladium complexes were evaluated as catalyst precursors in ethylene oligomerisation reactions, after activation with a co-catalyst (MMAO, EtAlCl₂, or Et₂AlCl).