Effect of cations in solution on the oxidation of methanol on the surface of platinum electrode

The effect of metal cations in solution on the oxidation of methanol on the electrode surface of platinum is a neglected aspect to direct methanol fuel cell (DMFC). In this paper, a smooth platinum electrode absorbing metal cations as the working electrode was applied to investigate the methanol oxidation with the cyclic voltammetry (CV) in 1.0 mol L-1 H2SO4. From the analysis of experiment, it is found that the cations, Li+, Ce4+, Mn2+, Ni2+, Cu2+, have some negative effect on the catalytic oxidation of methanol on the surface of platinum. The degree of the effect from different cations was analyzed.

The influence of nucleating agent on crystallization behavior and properties of polypropylene and its copolymer with ethylene

The influences of nucleating agent EDBS on crystallization behavior and properties of polypropylene UP) and its copolymer with a small amount (4. 48 %, molar fraction) of ethylene (CPP) were studied. DSC results indicated that the crystallization temperature of iPP and CPP samples with 0.5 % (mass fraction) EDBS obviously increased and the degree of crystallinity of these samples became higher. In addition, adding small amount of EDBS enhanced the crystallization of the low isotacticity and low molecular weight segments of the CPP. PLM results showed that their spherulite size decreased markedly, and as a result, the transmittance and haze of the films were all improved.

Studies on the nature of the macromolecular condensed state of "nascent" ultra high molar mass polyethylene

Ultra high molar mass polyethylene (UHPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC, effect of annealing the recrystallized specimen at 120 similar to 130 degreesC, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC, possibly higher than 300 degreesC, the exact temperature is however not sue because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120 similar to 130 degreesC.

The influence of heat treatment on structures of the aggregated state of polyamide-1010

The structural parameters of the aggregated state of polyamide (PA)-1010 annealed at various temperatures were computed by means of the desmearing intensity from Smalt Angle X-ray Scattering (SAXS) measurements and by using the concept of the distance distribution function. The results indicated that the structural parameters of the aggregated state were strongly dependent upon heat treatment conditions and the maximum values of the structural parameters were obtained for the samples annealed at T = 175 degrees C. The particle size Z annealed at different temperature was ranged between 8.1-12.8nm, and the values of the distance distribution function P-max(Z) were obtained when Z = 4.0-6.8 nm. Using one dimension electron density correlation function (1D EDCF) method long period (L) and thickness of the lamellar (d(0)) were estimated and were found to increase with the increase of the degree of crystallinity.

The determination of ethylene-propylene copolymer-grafted-glycidyl methacrylate by the contact angle method

The contact angles theta of some liquids on ethylene-propylene copolymer-grafted-glycidyl methacrylate (EPM-g-GMA) were measured. The critical surface tensions r(c) of EPM-g-GMA were evaluated by the Zisman Plot (cos theta versus r(L)), Young-Dupre-Good-Girifalco plot (1 + cos theta versus 1/r(L)(0.5)) and log (1 + cos theta) versus log(r(L)) plot. The following results were obtained: the r(c) values varied significantly with the estimation methods. The critical surface tension r(c) decreased with the increase of the degree of grafting of EPM-g-GMA.

Crystal structure of the blend of polyamide 1010 with a bismaleimide by WAXD and SAXS

The blend polyamide 1010/N,N'-(diphenylmethane-4,4'-diyl)bismaleimide (PA1010/ BMI) has been investigated by means of WAXD and SAXS. The results obtained with the help of the Ruland, variance and 1D EDCF analysis showed that the degree of crystallinity (W-c,W-x), crystallite size (L(hikl)), long period (L) and thickness of average crystal lamellae (d) decrease with BMI content. Experimental and calculated density values (rho(c)) are in good agreement. Addition of BMT to PA1010 causes an increase in structural distortion. The results from SAXS analysis also supported that a crystalline amorphous interphase exists in the lamellae of semicrystalline polymers, so that a three-phase model instead of the traditional two-phase model should be used.

THE INFLUENCE OF GAMMA-RADIATION ON POLYAMIDE-1010 AGGREGATE STRUCTURES

The influence of gamma-radiation on polyamide 1010 aggregate structures and crystal damage were examined by using wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The results revealed that some structural parameters of the aggregated state, the density differences and the degree of crystallinity W-c,W-x, essentially decreased with increasing radiation dose, but the specific surface O-s increased. Crosslinking and scission of irradiated polyamide 1010 samples occurred mainly in amorphous and interphase regions, and crystal damage and amorphization induced by gamma-radiation spread from the interphase and extended into the crystal phase with increasing radiation dose. This result also indicated that the (010) reflection with the hydrogen bond was more susceptible to the action of radiation.

THE EFFECT OF RADIATION-INDUCED CROSS-LINKING ON THE RELAXATION OF TAUT TIE MOLECULES DURING ANNEALING OF DRAWN LDPE

Shrinkage, retractive stress, and infrared dichroism of the drawn low-density polyethylene (LDPE) as-drawn and irradiated by Co-60-ray have been measured under different annealing conditions. The shrinkage and the disorientation of the irradiated sample was undergone more rapidly than that of unirradiated one as the temperature was continuously increased, surpassing a certain value, and a higher degree of shrinkage and disorientation was achieved finally for the irradiated sample when the samples were annealed with free ends. For the samples heated isothermally with fixed ends, the retractive stress went through a maximum and then attenuated to a limited value, and the degree of such a stress attenuation for the unirradiated sample was much more than that for the irradiated sample. These results show that the taut tie molecules (TTMs) in drawn PE can relax by the pulling of chain segments out of crystal blocks that they anchored in at elevated temperatures higher than the a transition and also by the displacing of microfibrils if the samples were annealed with free ends. The cross-links produced by irradiation prohibit the former process. It was further observed that the dependence of the average extinction coefficient of the band at 2016 cm-1 on that of the band at 1894 cm-1 is related to irradiation and annealing conditions, which has also been explained by the relaxation of TTMs and the function of irradiation-induced cross-linking on the relaxation.

The effects of spring-neap tide on the phytoplankton community development in the Jiaozhou Bay, China

The development of the phytoplankton community was studied in the Jiaozhou Bay during the spring to neap tide in August 2001, through three cruises and a 15 d continuous observation. This investigation indicates that diatom cell abundance increased sharply following the end of a spring tide, from 9 cells/cm(3) to a peak of 94 cells/cm(3). The dominant species composition and abundance show a quick species sequence from spring to neap tide, and the dominant species at the start phase is Skeletomena costatum, then changes to Chaetoceros curvisetus, finally it changes to Eucampia zodiacus. Silicate concentration increases during spring tide, as a result of nutrient replenishment from the water-sediment interface, its initial average concentration in neap tide is 1.39 mumol/dm(3) and reached the peak average concentration of 8.40 mumol/dm(3) in spring tide. But the nitrogen concentration dropped due to dilution by the low nitrogen seawater from the Huanghai Sea, its initial average concentration in neap tide is 67 mumol/dm(3) and decreased to the average concentration of 54 mumol/dm(3) in spring tide. The degree of silicon limitation was decreased and phytoplankton, especially diatoms, responds immediately after nutrient replenishment in the water column. Skeletonmea costatum, as one of the dominant species in the Jiaozhou Bay, shows a quicker response to nutrient availability than Eucampia zodiacus and Chaetoceros curvisetus. It is proposed that dominant species composition and water column stability synchronously determine the development of phytoplankton summer blooms in the Raozhou bay.

Influence of polarization orientation of violet light on the diffraction efficiency of bacteriorhodopsin

When a grating is recorded in a bacteriorhodopsin film by two linear parallel polarized beams together with anauxiliary violet light, the diffraction efficiency has a dependence on the polarization orientation of the violet light as well as its intensity. A method for calculating the diffraction efficiency of gratings in bacteriorhodopsin is proposed based on the two-state photochromic model, considering the saturation effect and the polarization status of all the involved lights. It is found that the polarization orientation of the violet light produces an approximate-cosine and an approximate-sine modulation on the steady-state diffraction efficiency separately at low and high intensities, respectively. The parallel polarized violet light can improve the steady-state diffraction efficiency to a larger degree than the perpendicularly polarized violet light when both are at their optimal intensities. The optimal intensity for the parallel polarized violet light is lower than that of the perpendicular polarized one. Thus, the improvement of the steady-state diffraction efficiency is less sensitive to the intensity of perpendicular polarized violet light than to that of parallel polarized violet light. (C) 2008 Optical Society of America.

Electro-optic modulation of light propagating near the optic axis with any polarization in uniaxial crystals

The electro-optic effect in uniaxial crystals for light propagating near the optic axis with any polarization has been analyzed. The passive and the electrically induced birefringences and the rotation of polarization direction in crystals have been calculated, and the conoscopic interference figures under orthogonal polariscopes for different polarizer directions have been plotted. The extinction areas caused by the rotation of polarization direction in crystals change with the polarizer direction, but the two heads of the induced optical axes do not vary, which are always on the induced principal axis with bigger refractive index. The directions of polariscopes are always extinction, and the +/- 45 degrees directions with polarizer are always complete transmission. The conoscopic interference figures for LiNbO3 crystals have been demonstrated experimentally by rotating polariscopes directions, which accord with the theoretically calculating plots. (c) 2006 Elsevier GmbH. All rights reserved.

Design of high polarization and single-mode photonic crystal laser

The dipole mode in triangular photonic crystal single defect cavity is degenerate. By deforming the lattice in photonic crystal we can obtain non-degenerate dipole modes. Lattice deforming in the whole photonic crystal destroys the characteristic of symmetry, so the distribution of the electromagnetic field is affected and the polarization of the electromagnetic field is also changed. Lattice deforming divides the degenerate dipole mode into the x-dipole mode and the y-dipole mode. It is found that the non-degenerate modes have better properties of polarization. So the high polarization and single dipole mode photonic crystal laser can be achieved by deforming the lattice of photonic crystal. In this paper, we simulated the cavity in photonic crystal slab and mainly calculated the quality factor of x-dipole mode under different deforming conditions and with different filling factors. The properties of polarization of x-dipole and y-dipole modes are also calculated. It is found that the ratio of intensities of E-x to E-y in x-dipole mode and that of E-y to E-x in y-dipole mode are 44 and 27, respectively.

Impact of polarization on quasi-two-dimensional exciton and barrier-width dependence of the exciton associated transition in wurtzite III-V nitride quantum wells

Excitonic states in AlxGa1-xN/GaN quantum wells (QWs) are studied within the framework of effective-mass theory. Spontaneous and piezoelectric polarizations are included and their impact on the excitonic states and optical properties are studied. We witnessed a significant blue shift in transition energy when the barrier width decreases and we attributed this to the redistribution of the built-in electric field between well layers and barrier layers. For the exciton the binding energies, we found in narrow QWs that there exists a critical value for barrier width, which demarcates the borderline for quantum confinement effect and the quantum confined Stark effect. Exciton and free carrier radiative lifetimes are estimated by simple argumentation. The calculated results suggest that there are efficient non-radiative mechanisms in narrow barrier QWs. (C) 2002 Elsevier Science Ltd. All rights reserved.

Effect of reconstruction beam polarization on the kinetics of anisotropic gratings in bacteriorhodopsin

Anisotropic gratings are recorded on bacteriorhodopsin films by two parallelly polarized beams, and the effect of the polarization orientation of the reconstructing beam on the diffraction efficiency kinetics is studied. A theoretical model for the diffraction efficiency kinetics of the anisotropic grating is developed by combining Jones-matrix and photochromic two-state theory. It is found that the polarization azimuth of the reconstructing beam produces a cosine modulation on the kinetics of the diffraction efficiency, being positive at the peak efficiency and negative for steady state. By adding auxiliary violet light during grating formation, the saturation of the grating can be restrained. As a result, the negative cosine modulation for the steady-state diffraction efficiency changes to a positive one. In addition, the steady-state diffraction efficiency is increased appreciably for all reconstructing polarization orientations. (c) 2008 Optical Society of America.