Effect of imperfect salt rejection on concentration polarization in reverse osmosis systems

A study of the two-dimensional boundary layer equations describing reverse osmosis in a flat membrane duct reveals the existence of maximum concentration polarization phenomenon corresponding to a particular value of salt rejection ratio, which is contrary to the common belief that the extent of concentration polarization always increases as membranes become more perfect. A one-dimensional model is used to analyze the same problem and explicit relationship between membrane characteristics, operating variables and the presence of maximum concentration polarization is presented.     

Radiation from a uniformly moving distribution of electric charge in an anisotropic, compressible plasma

The radiation characteristics of a linear distribution of electric charge moving with a uniform velocity in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform static magnetic field is impressed externally throughout the medium. The linear distribution of charge and its direction of motion are assumed to be parallel and perpendicular, respectively, to the direction of the external magnetic field. Of the two possible modes of waves of small amplitude, namely, the modified electromagnetic mode and the modified electron plasma mode, the uniformly moving charge distribution excites the modified electron plasma mode. The emitted radiation has no frequencies less than the plasma frequency. For a particular value of the ratio of the gyrotropic to the plasma frequency of the electrons, the frequency and the angular spectrum of the emitted radiation are determined for two values of the velocity of the charge.     

Surface waves on a grounded anisotropic plasma slab

The dispersion relations of the plane surface waves supported by a grounded magnetoplasma slab immersed in free space are discussed for the case in which the magnetostatic field is parallel to both the direction of propagation and the vacuum-plasma interface. The dependence of the surface-wave characteristics on the thickness of the plasma slab and the strength of the magnetostatic field is also examined.     

On three-dimensional nonlinear analysis of concrete structures

Solution capabilities for three-dimensional geometric and material nonlinear finite element analysis of concrete structures are presented. The concrete material is modeled including triaxial nonlinear stress-strain behavior, tensile cracking, compression crushing and strain-softening. The objective in this work was the development of a practical nonlinear concrete analysis capability. The material model can also be employed to represent some rock materials. The results of various sample analyses are given, in which the stability and accuracy of the finite element representations have been studied.     

Investigation of (Cr,Co)7C3-fcc-graphite equilibrium in the temperature interval 1373 to 1473 K

In the current study, the phase equilibria between fcc, graphite and M₇C₃ (M = Cr,Co) have been studied at 1373 °K, 1423 °K, and 1473 °K. The solubility of Co in the M₇C₃ phase and the solubility of Cr and C in the fcc phase have been determined by the high-temperature equilibration and quenching technique. Appropriate mixtures of Cr₇C₃ + Co or M₇C₃ + Co + C were equilibrated and subsequently quenched in liquid nitrogen. The quenched samples were characterized by X-ray diffraction and by metallographic examination. The studies were carried out on the samples to determine the homogeneity of the sample as well as the phases and their composition. From the results, the compositional regions of the three-phase triangle M₇C₃ + fcc + graphite could be accurately determined. The results show that the Co solubility in the Cr₇C₃ in the experimental temperature interval is higher than previous investigations performed at higher temperatures.     

Turbo processing in transmit antenna diversity systems

We consider turbo-trellis-coded transmission over fading multiple-input-multiple-output (M1M0) channels with transmit diversity using space-time block codes. We give a new view on space-time block codes as a transformation of the fading MIMO channel towards a Gaussian single-input-single-output (siso) channel and provide analytical results on the BER of space-time block codes. Furthermore, we describe the concatenation of Turbo-TCM with a space-time block code and show that in addition to the transmit diversity substantial benefits can be obtained by turbo iterations as long as the channel is time-varying during transmission of a coded block or frequency hopping is applied. Finally, a double iterative scheme for turbo equalization and turbo decoding of the concatenation of Turbo-TCM and space-time block code in frequency-selective MIMO channels is described.     

Synthesis and characterization of electrodeposited Ni-Pd alloy electrodes for methanol oxidation

A wide compositional range of Ni-Pd alloy catalysts were prepared by electrodeposition for use as anode materials for methanol oxidative fuel cells in alkaline conditions. Structural characterization of the electrocatalysts in their as-plated condition revealed that the Ni-Pd catalysts synthesized were nanocrystalline, single phase, face centered cubic materials, indicating the formation of complete solid solution in the alloy. Compositional analysis of the alloys indicated that the palladium composition of the alloy increased with decrease in current density. This change in the composition of the alloy resulted in a shift in the X-ray diffraction peaks. The percentage shift in the d-spacing calculated from X-ray diffraction is in good agreement with percentage of palladium in the alloy. The electrocatalysts prepared are active for methanol oxidation in alkaline medium.     

Gas diffusion layer with PTFE gradients for effective water management in PEM fuel cells

Experimental procedures to establish in-plane and through plane polytetrafluroethylene (PTFE) gradient in Gas Diffusion Layer (GDL) used in proton exchange membrane fuel cells (PEMFC) are presented in this work. In-plane PTFE gradients were obtained by exploiting capillary wicking of PTFE suspension. The through plane PTFE gradients were obtained by changing the drying temperature employed in PTFE loading procedure. The samples were characterized for fluorine distribution using energy dispersive spectrum (EDS) to gauge the PTFE distribution and change in hydrophobicity after PTFE treatment. The results indicate that manipulation of PTFE gradients are expected to result in effective water management in PEMFC.     

The Pyreno-Triazinyl Radical – Magnetic and Sensor Properties

We report the first example of a stable pyrenotriazinyl radical, 1,3-diphenyl-1,2,4-pyrenotriazin-4-yl ( PyT ). Magnetic susceptibility measurements of the radical PyT show a transition from a paramagnetic state to an antiferromagnetic state. The pyrene moiety has a strong influence via π π interactions in 1D chain stacks that result in the observed magnetic properties. Unexpectedly, the pyrene unit has essentially no effect on the electronic structure of the triazinyl core. Chemical sensing studies on various nitrophenol-based compounds showed that the radical PyT exclusively senses picric acid ( PA ), as a pH sensor, with a detection limit of 5.0×10⁻⁶ M.     

A study on the occurrence of N-triacontanol,a plant growth regulator,in tea

The compound n -triacontanol, reported to have exceptional plant growth promoting properties, has now been identified as a constituent of tea. Tea wastes from instant tea processing, green tea and black tea have decreasing quantities of this compound in that order. This may be attributed to the higher firing temperatures in the case of green tea and black tea. Polyphenol oxidase does not seem to have any effect as shown byin vitroexperiments.