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Constant Value (constant + value)
Kinds of Constant Value Selected AbstractsInfluence of in-stream diel concentration cycles of dissolved trace metals on acute toxicity to one-year-old cutthroat trout (Oncorhynchus clarki lewisi)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2007David A. Nimick Abstract Extrapolating results of laboratory bioassays to streams is difficult, because conditions such as temperature and dissolved metal concentrations can change substantially on diel time scales. Field bioassays conducted for 96 h in two mining-affected streams compared the survival of hatchery-raised, metal-näive westslope cutthroat trout (Oncorhynchus clarki lewisi) exposed to dissolved (0.1-,m filtration) metal concentrations that either exhibited the diel variation observed in streams or were controlled at a constant value. Cadmium and Zn concentrations in these streams increased each night by as much as 61 and 125%, respectively, and decreased a corresponding amount the next day, whereas Cu did not display a diel concentration cycle. In High Ore Creek (40 km south of Helena, MT, USA), survival (33%) after exposure to natural diel-fluctuating Zn concentrations (range, 214,634 ,g/L; mean, 428 ,g/L) was significantly (p = 0.008) higher than survival (14%) after exposure to a controlled, constant Zn concentration (422 ,g/L). Similarly, in Dry Fork Belt Creek (70 km southeast of Great Falls, MT, USA), survival (75%) after exposure to diel-fluctuating Zn concentrations (range, 266,522 ,g/L; mean, 399 ,g/L) was significantly (p = 0.022) higher than survival (50%) in the constant-concentration treatment (392 ,g/L). Survival likely was greater in these diel treatments, both because the periods of lower metal concentrations provided some relief for the fish and because toxicity during periods of higher metal concentrations was lessened by the simultaneous occurrence each night of lower water temperatures, which reduce the rate of metal uptake. Based on the present study, current water-quality criteria appear to be protective for streams with diel concentration cycles of Zn (and, perhaps, Cd) for the hydrologic conditions tested. [source] On the mechanism of fatigue failure in the superlong life regime (N>107 cycles).FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2000Part II: influence of hydrogen trapped by inclusions High cycle fatigue fracture surfaces of specimens in which failure was initiated at a subsurface inclusion were investigated by atomic force microscopy and by scanning electron microscopy. The surface roughness Ra increased with radial distance from the fracture origin (inclusion) under constant amplitude tension,compression fatigue, and the approximate relationship: Ra,,,C,K,2I holds. At the border of a fish-eye there is a stretched zone. Dimple patterns and intergranular fracture morphologies are present outside the border of the fish-eye. The height of the stretch zone is approximately a constant value around the periphery of the fish-eye. If we assume that a fatigue crack grows cycle-by-cycle from the edge of the optically dark area (ODA) outside the inclusion at the fracture origin to the border of the fish-eye, we can correlate the crack growth rate da/dN, stress intensity factor range ,KI and Ra for SCM435 steel by the equation and by da/dN proportional to the parameter Ra,. Integrating the crack growth rate equation, the crack propagation period Np2 consumed from the edge of the ODA to the border of the fish-eye can be estimated for the specimens which failed at Nf,>,107. Values of Np2 were estimated to be ,1.0,×,106 for the specimens which failed at Nf,,,5,×,108. It follows that the fatigue life in the regime of Nf >107 is mostly spent in crack initiation and discrete crack growth inside the ODA. [source] Modelling of GPR waves for lossy media obeying a complex power law of frequency for dielectric permittivityGEOPHYSICAL PROSPECTING, Issue 1 2004Maksim Bano ABSTRACT The attenuation of ground-penetrating radar (GPR) energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies (absorption) with increasing traveltime and causes also a distortion of wavelet phase (dispersion). The attenuation is often expressed by the quality factor Q. For GPR studies, Q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity. We consider a complex power function of frequency for the dielectric permittivity, and show that this dielectric response corresponds to a frequency-independent- Q or simply a constant- Q model. The phase velocity (dispersion relationship) and the absorption coefficient of electromagnetic waves also obey a frequency power law. This approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only, for example Q and the phase velocity at an arbitrary reference frequency. This simplicity makes it practical for any inversion technique. Furthermore, by using the Hilbert transform relating the velocity and the absorption coefficient (which obeys a frequency power law), we find the same dispersion relationship for the phase velocity. Both approaches are valid for a constant value of Q over a restricted frequency-bandwidth, and are applicable in a material that is assumed to have no instantaneous dielectric response. Many GPR profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes. Changes in water content are believed to be the origin of this reflectivity. We model the radar reflections from the bottom of a dry aeolian dune using the 1D wavelet modelling method. We discuss the choice of the reference wavelet in this modelling approach. A trial-and-error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site. Additionally, by combining the complex refractive index method (CRIM) and/or Topp equations for the bulk permittivity (dielectric constant) of moist sandy soils with a frequency power law for the dielectric response, we introduce them into the expression for the reflection coefficient. Using this method, we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling. [source] Selective Zinc(II)-Ion Fluorescence Sensing by a Functionalized Mesoporous Material Covalently Grafted with a Fluorescent Chromophore and Consequent Biological ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Krishanu Sarkar Abstract A highly ordered 2D-hexagonal mesoporous silica material is functionalized with 3-aminopropyltriethoxysilane. This organically modified mesoporous material is grafted with a dialdehyde fluorescent chromophore, 4-methyl-2,6-diformyl phenol. Powder X-ray diffraction, transmission electron microscopy, N2 sorption, Fourier transform infrared spectroscopy, and UV-visible absorption and emission have been employed to characterize the material. This material shows excellent selective Zn2+ sensing, which is due to the fluorophore moiety present at its surface. Fluorescence measurements reveal that the emission intensity of the Zn2+ -bound mesoporous material increases significantly upon addition of various concentrations of Zn2+, while the introduction of other biologically relevant (Ca2+, Mg2+, Na+, and K+) and environmentally hazardous transition-metal ions results in either unchanged or weakened intensity. The enhancement of fluorescence is attributed to the strong covalent binding of Zn2+, evident from the large binding constant value (0.87,×,104M,1). Thus, this functionalized mesoporous material grafted with the fluorescent chromophore could monitor or recognize Zn2+ from a mixture of ions that contains Zn2+ even in trace amounts and can be considered as a selective fluorescent probe. We have examined the application of this mesoporous zinc(II) sensor to cultured living cells (A375 human melanoma and human cervical cancer cell, HeLa) by fluorescence microscopy. [source] Comparative study of the least squares approximation of the modified Bessel functionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 8 2008Jianguo XinArticle first published online: 14 DEC 200 Abstract The least squares problem of the modified Bessel function of the second kind has been considered in this study with the Fourier series, Tchebycheff and Legendre approximation. Numerical evidence shows that the Gibbs phenomenon exists in the approximation with the truncated Fourier series, thus, giving poor convergence results compared with the other polynomial bases. For the latter two cases, the Legendre series perform better than Tchebycheff series in terms of the ,2 norm of the relative errors for each order of the polynomial approximation, and the ratio of the ,2 norm of the relative errors from the corresponding approximation seems to be a constant value of 1.3. Copyright © 2006 John Wiley & Sons, Ltd. [source] The performance of natural draft dry cooling towers under crosswind: CFD studyINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2004Rafat Al-Waked Abstract The thermal performance of a natural draft dry cooling tower (NDDCT) under a crosswind has been investigated using a general-purpose CFD code. A three-dimensional study using the standard k,, turbulence model to simulate airflow in and around an NDDCT has been conducted. A parametric study has been carried out to examine the effect of crosswind velocity profile and air dry-bulb temperature on the thermal performance of an NDDCT. Two approaches have been considered in this study to quantify the crosswind effect. Firstly, simulations have been conducted at the nominal conditions and crosswind effect has been represented by thermal effectiveness parameter. Secondly, the ejected heat from the NDDCT has been maintained at a constant value (285 MW) and the crosswind effect has been represented by the change in the cooling tower approach parameter. After quantifying the effect of the crosswind on the thermal performance, windbreak walls have been introduced as a means of reducing this effect. The results in this paper show the importance of considering the crosswind velocity profile. Moreover, the introduction of windbreak walls has indicated an improvement in reducing the thermal performance losses due to the crosswind. Copyright © 2004 John Wiley & Sons, Ltd. [source] Estimation of apparent thermal conductivity of carrot purée during freezing using inverse problemINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 7 2009Viviana Cocco Mariani Summary This article presents an inverse problem to determine the apparent thermal conductivity of carrot purée during the freezing process. The heat diffusion equation with the enthalpy model is solved to estimate the thermal conductivity. A modern meta-heuristic of evolutionary computation field called Differential Evolution (DE) is applied for the solution of inverse problem. Experiments were performed to estimate the thermal conductivity of the carrot purée as a function of temperature, using two piecewise functions. A best least square fitting between the experimental and predicted temperature curves during freezing conditions is obtained using DE. Statistical analysis are considered with Gaussian error of 0.05 and zero mean showing than the results for one piecewise function are more stable than with another piecewise function. Good agreement between the reported and estimated temperature curves was obtained. The apparent thermal conductivity was observed to decrease asymptotically with temperature in the range [,40 °C, 0 °C] and stay approximately a constant value for temperatures bigger than 0 °C. [source] Matching network design using non-Foster impedancesINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2006*Article first published online: 8 FEB 200, Stephen E. Sussman-Fort Abstract Non-Foster synthesis bypasses the gain-bandwidth limitations of conventional LC matching and achieves superior broadband performance by employing negative circuit elements, which are realized via negative impedance converters. The idea is to construct a negative-image model of an antenna, which cancels the antenna's parasitic reactance and transforms its frequency-dependent radiation resistance to a constant value. Successful implementation of negative-image modeling requires the realization of stable, low-loss negative elements. After a discussion of the basic ideas of non-Foster matching, we present experimental results for broadband, stable, high- Q, grounded negative capacitance. Next, in the first experimental confirmation of non-Foster impedance matching for signal reception, we use a floating negative capacitor to cancel a substantial portion of the reactance of a 6-in. monopole antenna. Over 20,110 MHz, the signal-to-noise ratio improved by up to 6 dB as compared to the same antenna with no matching, or to a lossy-matched blade antenna of twice the size. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [source] Soil N dynamics in relation to leaf litter quality and soil fertility in north-western Patagonian forestsJOURNAL OF ECOLOGY, Issue 2 2003Patricia Satti Summary 1We examined the relationships among soil N dynamics, soil chemistry and leaf litter quality in 28 forest stands dominated by conifers, woody broad-leaf deciduous species or broad-leaf evergreens. Potential net N mineralization, net nitrification and microbial biomass N were used as indicators of soil N dynamics; pH, organic C, total N, exchangeable cations and extractable P as indicators of soil chemistry and N concentration, lignin concentration, C : N ratio and lignin : N ratio in senescent leaves as indicators of leaf litter quality. N dynamics were assessed in two consecutive years with contrasting precipitation. 2Net N mineralization was lower in stands of the three conifers and one of three broad-leaf evergreen species than in stands of the other six broad-leaf species (40,77 vs. 87,250 mg N kg,1 after 16-week incubations) and higher in the wetter year. 3The proportion of N nitrified was high beneath most species regardless of mineralization rates, soil N fertility and leaf litter quality, and was significantly higher for the wetter year. Ammonium was the predominant form of N in three sites affected by seasonal waterlogging and in two sites the predominant form changed from ammonium in the drier year to nitrate during the wetter year, probably due to differences in soil texture affecting soil moisture. 4Net N mineralization was linearly related to microbial biomass N, implying that the microbial activity per biomass unit was quite similar beneath all species. Constant microbial biomass during the wetter year suggested that as mineralization/nitrification increased, there was a higher potential risk of N losses. 5Although the litter lignin : N ratio allowed differentiation of soil N dynamics between broad-leaf species and conifers, its constant value (23,28) in all broad-leaf species made it a poor predictor of the differences found within this group. Across all sites and between broad-leaf species, soil N dynamics were best explained by a combination of leaf litter lignin and soil chemistry indicators, particularly soil total N for net N mineralization and net nitrification, and soil organic C for microbial biomass N. [source] Hydrogen response in liquid propylene polymerization: Towards a generalized modelAICHE JOURNAL, Issue 5 2006M. Al-haj Ali Abstract Liquid propylene batch experiments in the absence of a gas phase have been carried out using a highly-active MgCl2/TiCl4/phthalate/silane/AlR3 catalyst at varying temperatures (60-80°C) and molar hydrogen-monomer ratios of 0-10 mmol/mol. With increasing hydrogen concentration the polymerization rate increases rapidly, reaching a constant value at concentrations above 1.4 mmol/mol; pseudo-first-order catalyst deactivation constant increases; molecular weight decreases; polydispersity decreases slightly; but average molecular weight and polydispersity increase with increasing temperature. Polymerization rate, deactivation constant, and average molecular weight can be modeled based on a consistent dormant site mechanism assuming an (averaged) quasi-single-site model. © 2006 American Institute of Chemical Engineers AIChE J,2006 [source] Simulation of binary mixture adsorption of methane and CO2 at supercritical conditions in carbonsAICHE JOURNAL, Issue 3 2006Yohanes Kurniawan Abstract Knowledge of the adsorption behavior of coal-bed gases, mainly under supercritical high-pressure conditions, is important for optimum design of production processes to recover coal-bed methane and to sequester CO2 in coal-beds. Here, we compare the two most rigorous adsorption methods based on the statistical mechanics approach, which are Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) simulation, for single and binary mixtures of methane and carbon dioxide in slit-shaped pores ranging from around 0.75 to 7.5 nm in width, for pressure up to 300 bar, and temperature range of 308-348 K, as a preliminary study for the CO2 sequestration problem. For single component adsorption, the isotherms generated by DFT, especially for CO2, do not match well with GCMC calculation, and simulation is subsequently pursued here to investigate the binary mixture adsorption. For binary adsorption, upon increase of pressure, the selectivity of carbon dioxide relative to methane in a binary mixture initially increases to a maximum value, and subsequently drops before attaining a constant value at pressures higher than 300 bar. While the selectivity increases with temperature in the initial pressure-sensitive region, the constant high-pressure value is also temperature independent. Optimum selectivity at any temperature is attained at a pressure of 90-100 bar at low bulk mole fraction of CO2, decreasing to approximately 35 bar at high bulk mole fractions. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Distributed midpoint chain scission in ultrasonic degradation of polymersAICHE JOURNAL, Issue 9 2004G. Sivalingam Abstract The ultrasonic degradation of poly(bisphenol A carbonate), poly(,-caprolactone), and poly(vinyl acetate) was investigated with various solvents such as benzene, monochlorobenzene, and dichlorobenzene. The time evolution of molecular weight was determined using gel permeation chromatography. A limiting molecular weight was observed for all the systems and was a function of solvent properties. The degradation rates increased with increase in viscosity and decrease in vapor pressure. The polydispersity reached a maximum before reaching a constant value at longer times. The experimental data indicate that the breakage of the polymer is around midpoint, with a distribution rather than an ideal midpoint scission. A continuous distribution model with a stoichiometric kernel based on Lorentzian probability distribution function was developed to satisfactorily model the experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2258,2265, 2004 [source] Semibatch emulsion polymerization of methyl methacrylate using different polyurethane particlesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2005ebenik Abstract Aqueous acrylic-polyurethane (AC,PU) hybrid emulsions were prepared by semibatch emulsion polymerization of methyl methacrylate (MMA) in the presence of four polyurethane (PU) dispersions. The PU dispersions were synthesized with isophorone diisocyanate (IPDI), 1000 and 2000 molecular weight (MW) poly(neopentyl) adipate, 1000 MW polytetramethyleneetherglycol, butanediol (BD), and dimethylol propionic acid (DMPA). MMA was added in the monomer emulsion feed. We studied the effect of the use of different PU seed particles on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The PU rigidity was controlled by varying the polyol chemical structure, the polyol MW (Mn), and by adding BD. The monomer feed rate was varied to study its influence on the process. It was observed that the PU particles that had been prepared with a higher MW polyol swelled better with MMA before the monomer-starved conditions occurred. There seemed to be no significant discrepancies between the series with different PU seeds in the monomer-starved conditions. The overall conversion depended on the monomer addition rate, and the polymerization rate acquired a constant value that was comparable to the value of the monomer addition rate. The instantaneous conversion increased slightly. The average particle size increased, and the total particle number in the reactor was constant and similar to the number of PU particles in the initial charge. The average number of radicals per particle increased. The differences between the system with a constant particle number and average number of radicals per particle and the system with a fixed radical concentration are discussed. The semibatch emulsion polymerization of MMA in the presence of PU particles studied was better compared to the system with a fixed radical concentration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 844,858, 2005 [source] Chemical Synthesis of Nanocrystalline Strontium Bismuth Tantalate Powders Using Tantalum,Tartarate ComplexJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Asit Baran Panda Nanocrystalline strontium bismuth tantalate (SrBi2Ta2O9; SBT) powders have been synthesized through complete dehydration of an aqueous solution mixture of tantalum tartarate, strontium salt of ethylenediaminetetraacetic acid, and bismuth,triethanolamine complex. Single-step calcination of the fluffy, mesoporous, carbonaceous dehydrated precursor mass at 700°C/2 h results in nanosized SBT powders, with average particle size ,15 nm. When palletized and sintered at 950°C/4 h these powders show a relative density of 97.6% of theoretical value, and a maximum dielectric constant value of 1387 at Tc (Curie temperature)=279°C, when measured at 100 kHz. [source] The oxygen vacancy in Ga2O3: a double resonance investigation,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005H. J. Kümmerer Abstract When produced under reducing conditions, ,-Ga2O3 is transformed into an n -type semiconductor with delocalized conduction electrons that exhibit a very strong electron spin resonance (ESR) and a strong hyperfine coupling to the gallium nuclei of the host lattice. We apply the Overhauser-shift technique to investigate single crystals of this compound. With extension to the high magnetic field of a W-band spectrometer, we were able to resolve all spectral lines that were recorded and to assign them to their corresponding electronic and nuclear states. This separate analysis was the basis to access additional sample characteristics: the hyperfine coupling that is actually averaged out in the ESR signal, as well as the nuclear relaxation rates could be analyzed. Systematic measurements by varying the microwave power revealed the Overhauser shift in thermal equilibrium. The signal could be tracked to very small microwave saturation parameters, at which the deviation from the usual linear relation between power and shift becomes evident and the shift clearly approaches a constant value. This value in equilibrium was determined directly from a fit to a sequence of measurements, whereas standard X-band experiments only provided indirect conclusions. The probability densities of the electrons at the nuclei in the two nonequivalent crystallographic positions,the lattice sites with octahedral and tetrahedral coordination,could also be determined directly. The enhanced resolution revealed an otherwise hidden substructure in the nuclear resonance signals. On the basis of a microscopic model, this structure could be used to probe the environment of the oxygen vacancy more precisely and to determine the extension of the electronic wave function of the donor electrons. Copyright © 2005 John Wiley & Sons, Ltd. [source] Cosmology and cluster halo scaling relationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009Pablo A. Araya-Melo ABSTRACT We explore the effects of dark matter and dark energy on the dynamical scaling properties of galaxy clusters. We investigate the cluster Faber,Jackson (FJ), Kormendy and Fundamental Plane (FP) relations between the mass, radius and velocity dispersion of cluster-sized haloes in cosmological N -body simulations. The simulations span a wide range of cosmological parameters, representing open, flat and closed Universes. Independently of the cosmology, we find that the simulated clusters are close to a perfect virial state and do indeed define an FP. The fitted parameters of the FJ, Kormendy and FP relationships do not show any significant dependence on ,m and/or ,,. One outstanding effect is the influence of ,m on the thickness of the FP. Following the time evolution of our models, we find slight changes of FJ and Kormendy parameters in high-,m universe, along with a slight decrease of FP fitting parameters. We also see an initial increase of the FP thickness followed by a convergence to a nearly constant value. The epoch of convergence is later for higher values of ,m, while the thickness remains constant in the low- ,m , models. We also find a continuous increase of the FP thickness in the standard cold dark matter cosmology. There is no evidence that these differences are due to the different power spectrum slopes at cluster scales. From the point of view of the FP, there is little difference between clusters that quietly accreted their mass and those that underwent massive mergers. The principal effect of strong mergers is to significantly change the ratio of the half-mass radius rhalf to the harmonic mean radius rh. [source] A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula SpectrographMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006H. R. Merrett ABSTRACT We present a catalogue of positions, magnitudes and velocities for 3300 emission-line objects found by the Planetary Nebula Spectrograph in a survey of the Andromeda galaxy, M31. Of these objects, 2615 are found likely to be planetary nebulae (PNe) associated with M31. The survey area covers the whole of M31's disc out to a radius of . Beyond this radius, observations have been made along the major and minor axes, and the Northern Spur and Southern Stream regions. The calibrated data have been checked for internal consistency and compared with other catalogues. With the exception of the very central, high surface brightness region of M31, this survey is complete to a magnitude limit of m5007, 23.75, 3.5 mag into the PN luminosity function. We have identified emission-line objects associated with M31's satellites and other background galaxies. We have examined the data from the region tentatively identified as a new satellite galaxy, Andromeda VIII, comparing it to data in the other quadrants of the galaxy. We find that the PNe in this region have velocities that appear to be consistent with membership of M31 itself. The luminosity function of the surveyed PNe is well matched to the usual smooth monotonic function. The only significant spatial variation in the luminosity function occurs in the vicinity of M31's molecular ring, where the luminosities of PNe on the near side of the galaxy are systematically ,0.2 mag fainter than those on the far side. This difference can be explained naturally by a modest amount of obscuration by the ring. The absence of any difference in luminosity function between bulge and disc suggests that the sample of PNe is not strongly populated by objects whose progenitors are more massive stars. This conclusion is reinforced by the excellent agreement between the number counts of PNe and the R -band light. The number counts of kinematically selected PNe also allow us to probe the stellar distribution in M31 down to very faint limits. There is no indication of a cut-off in M31's disc out to beyond four scalelengths, and no signs of a spheroidal halo population in excess of the bulge out to 10 effective bulge radii. We have also carried out a preliminary analysis of the kinematics of the surveyed PNe. The mean streaming velocity of the M31 disc PNe is found to show a significant asymmetric drift out to large radii. Their velocity dispersion, although initially declining with radius, flattens out to a constant value in the outer parts of the galaxy. There are no indications that the disc velocity dispersion varies with PN luminosity, once again implying that the progenitors of PNe of all magnitudes form a relatively homogeneous old population. The dispersion profile and asymmetric drift results are shown to be mutually consistent, but require that the disc flares with radius if the shape of its velocity ellipsoid remains invariant. [source] Optical absorption, paramagnetic resonance and depolarisation currents in MgAl2O4 spinelPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007Roberto Paiva Abstract Optical Absorption (OA), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarisation Currents (TSDC) techniques were applied to study the effects of irradiation and thermal treatments in the formation, aggregation and destruction processes of dipole defects in MgAl2O4 spinel. Irradiated MgAl2O4 crystals present two OA bands centred at 3.4 eV and 5.1 eV. The 3.4 eV band increases with the irradiation-dose, stabilizes its maximum height for doses near 10 kGy and is completely destroyed for thermal treatments above 500 K. This same band decays when the sample is maintained at room temperature reaching a constant value after a few weeks. The EPR spectrum is composed by two superimposed bands at g = 2.011. The gamma dose dependence, the thermal treatments between 370 K and 500 K and the thermal decay of the two bands at room temperature, show that each band behaves in a different way thus indicating that they are associated with two different defects. Gamma dose of 10 kGy produces a TSDC band at 245 K. When the sample is maintained at room temperature, after the gamma irradiation, for several weeks, a displacement in the peak position to 290 K, is observed. Thermal treatments above 500 K destroy the 290 K band. This band is associated to at least two V-type centres. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Evaluation of instant light-response curves of chlorophyll fluorescence parameters obtained with a portable chlorophyll fluorometer on site in the fieldPLANT CELL & ENVIRONMENT, Issue 12 2000U. Rascher ABSTRACT Miniaturized pulse-amplitude modulated photosynthesis yield analysers are primarily designed for measuring effective quantum yield (,F/Fm,) of photosystem II under momentary ambient light conditions in the field. Although this provides important ecophysiological information, it is often necessary to learn more about the potential intrinsic capacities of leaves by measuring light-response curves. Thus, instruments provide light-curve programmes, where light intensities are increased in short intervals and instant light-response curves are recorded within a few minutes. This method can be criticized because photosynthesis will most likely not be in steady state. This technical report shows that with the appropriate precautions instant light curves can nevertheless provide reliable information about cardinal points of photosynthesis. First, the geometry of the light source of the instrument in relation to the quantum sensor must be considered and quantum sensor readings must be corrected. Second, the measurements of the light-response curves must be compared with readings of effective quantum yield of photosystem II under ambient light conditions where photosynthesis is in steady state. This may show that in the critical range of the light curves either both measurements perfectly coincide or are offset against each other by a constant value (examples are given here). In the first case results of light curves can be taken at face values, and in the second case a simple correction can be applied. With these precautions and careful interpretations instant light-response curves can be an enormous advantage in ecophysiological field work. [source] Effect of photo-initiators on melt degradation of polypropylene and starch-filled polymer,POLYMER INTERNATIONAL, Issue 10 2002Rouhallah Bagheri Abstract Six series of the processed polypropylene (pp) samples containing 0.25,1,wt% photo-initiators (PIs, four aromatic carbonyl, two ferric compounds) and also a series of 6,wt% corn-starch-filled pp containing 0.5,wt% of each PI, were prepared using a mixer in a closed system at 180,°C for 5,min. The melt flow index (MFI) and apparent viscosity measurments of the processed pp,PI samples showed a large increase in MFI/or decrease in apparent viscosity at 0.25,wt% of the PIs. Further increase in the amounts of PIs led these properties to reach a constant value at 0.5,wt% of the PIs. The presence of corn starch in the samples corresponded to a much lower increase in the MFI or decrease in the apparent viscosity. Ferric stearate and Irgacure 184 amoung the PIs showed the highest and lowest melt degradation effects, respectively. Carbonyl measurments of all the film samples showed good correlations between chemical changes in the pp structure and variations in the flow properties during processing. UV absorption of the films also evidenced the presence of the aromatic carbonyl PIs in the pp matrix after melt processing. © 2002 Society of Chemical Industry [source] A Discussion of the Kamlet-Jacobs Formula for the Detonation PressurePROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2006Luc Kazandjian Abstract The main features of the Kamlet-Jacobs formula for the detonation pressure of CHNO explosives are analytically derived from a BKW (Becker-Kistiakowsky-Wilson) equation of state of the detonation products. In the derivation, well-known typical values at the Chapman-Jouguet state, in particular the nearly constant value of the relative volume of the detonation products, are used. [source] Simulations of Bubble Column Reactors Using a Volume of Fluid Approach: Effect of Air DistributorTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007M. Abid Akhtar Abstract Two- and three-dimensional numerical simulations have been performed on a laboratory scale bubble column reactor using a volume-of-fluid approach. The effect of hole-size and superficial gas velocity on the bubble size distribution and their trajectories has been investigated on a 20 cm diameter and 1 m high cylindrical reactor. All simulations were performed in a transient manner using a FLUENT solver. Surface tension between two phases has been modelled as a body force with a constant value. Turbulence was modelled using the k-, turbulence approach. A comparison between simulation predictions and the reported experimental studies has shown a good agreement. On a effectué des simulations numériques bi et tridimensionnelles dans un réacteur à colonne à bulles à l'échelle de laboratoire à l'aide d'une approche volume-de-fluide. L'effet de la taille du trou et de la vitesse de gaz superficielle sur la distribution de tailles des bulles et leurs trajectoires a été étudié dans un réacteur cylindrique de 20 cm de diamètre et de 1 m de hauteur. Toutes les simulations ont été réalisées selon un mode transitoire à l'aide du logiciel FLUENT. La tension de surface entre deux phases a été modélisée comme une force volumique avec une valeur constante. La turbulence a été modélisée par la méthode de turbulence k-,. Une comparaison entre les prédictions des simulations et les études expérimentales mentionnées montre un bon accord. [source] Ca2+ -independent hypoxic vasorelaxation in porcine coronary arteryTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Min Gu To demonstrate a Ca2+ -independent component of hypoxic vasorelaxation and to investigate its mechanism, we utilized permeabilized porcine coronary arteries, in which [Ca2+] could be clamped. Arteries permeabilized with ,-escin developed maximum force in response to free Ca2+ (6.6 ,m), concomitant with a parallel increase in myosin regulatory light chain phosphorylation (MRLC-Pi), from 0.183 ± 0.023 to 0.353 ± 0.019 MRLC-Pi (total light chain),1. Hypoxia resulted in a significant decrease in both force (,31.9 ± 4.1% prior developed force) and MRLC-Pi (from 0.353 to 0.280 ± 0.023), despite constant [Ca2+] buffered by EGTA (4 mm). Forces developed in response to Ca2+ (6.6 ,m), Ca2+ (0.2 ,m) + GTP,S (1 mm), or in the absence of Ca2+ after treatment with ATP,S (1 mm), were of similar magnitude. Hypoxia also relaxed GTP,S contractures but importantly, arteries could not be relaxed after treatment with ATP,S. Permeabilization with Triton X-100 for 60 min also abolished hypoxic relaxation. The blocking of hypoxic relaxation after ATP,S suggests that this Ca2+ -independent mechanism(s) may operate through alteration of MRLC-Pi or of phosphorylation of the myosin binding subunit of myosin light chain phosphatase. Treatment with the Rho kinase inhibitor Y27632 (1 ,m) relaxed GTP,S and Ca2+ contractures; but the latter required a higher concentration (10 ,m) for consistent relaxation. Relaxations to N2 and/or Y27632 averaged 35% and were not additive or dependent on order. Our data suggest that the GTP-mediated, Rho kinase-coupled pathway merits further investigation as a potential site of this novel, Ca2+ -independent O2 -sensing mechanism. Importantly, these results unambiguously show that hypoxia-induced vasorelaxation can occur in permeabilized arteries where the Ca2+ is clamped at a constant value. [source] Enhancement of oil droplet removal from o/w emulsion by adding methylated milk casein in flotation techniqueASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009Hideo Maruyama Abstract To clarify oil-in-water (o/w) emulsion, flotation experiments were conducted by adding methylated milk casein (MeCS), which is a biodegradable flocculant. Emulsion used in this study was prepared by ultrasonic emulsification of heavy oil (bunker-A) and sodium dodecyl sulfate (SDS) solution. It was found that addition of MeCS enhanced clarification of oil droplets from o/w emulsion solution due to floc formation by adding MeCS. An optimum dosage of MeCS to form effective floc was determined by the relative turbidity in a clarification experiment. In flotation experiments, clarification ability was evaluated by removal rate constant, k, obtained by fitting of turbidity data to a pseudo-first-order kinetic equation. In case of varying dosage of MeCS and keeping superficial gas velocity, Ug, at constant value (5.48 × 10,2 cm/s), removal rate was greatly influenced by amount of MeCS dosage. The maximum value of k was also obtained at the most optimum dosage of MeCS, and k decreased with adding lesser or larger amount of MeCS than the optimum dosage. On the other hand, in case of keeping the dosage of MeCS at the optimum dosage, and varying superficial gas velocity, up to Ug < ca. 0.2 cm/s, k was increased with increasing superficial gas velocity, and increase in removal rate of oil droplets was mostly proportional with increase in bubble surface area production rate. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Dynamic culture of droplet-confined cell arraysBIOTECHNOLOGY PROGRESS, Issue 1 2010Elisa Cimetta Abstract Responding to the need of creating an accurate and controlled microenvironment surrounding the cell while meeting the requirements for biological processes or pharmacological screening tests, we aimed at designing and developing a microscaled culture system suitable for analyzing the synergic effects of extracellular matrix proteins and soluble environments on cell phenotype in a high-throughput fashion. We produced cell arrays deposing micrometer-scale protein islands on hydrogels using a robotic DNA microarrayer, constrained the culture media in a droplet-like volume and developed a suitable perfusion system. The droplet-confined cell arrays were used either with conventional culture methods (batch operating system) or with automated stable and constant perfusion (steady-state operating system). Mathematical modeling assisted the experimental design and assessed efficient mass transport and proper fluidodynamic regimes. Cells cultured on arrayed islands (500 ,m diameter) maintained the correct phenotype both after static and perfused conditions, confirmed by immunostaining and gene expression analyses through total RNA extraction. The mathematical model, validated using a particle tracking experiment, predicted the constant value of velocities over the cell arrays (less than 10% variation) ensuring the same mass transport regime. BrdU analysis on an average of 96 cell spots for each experimental condition showed uniform expression inside each cell island and low variability in the data (average of 13%). Perfused arrays showed longer doubling times when compared with static cultures. In addition, perfused cultures showed a reduced variability in the collected data, allowing to detect statistically significant differences in cell behavior depending on the spotted ECM protein. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Pharmacological and functional characterization of the guinea-pig B2 bradykinin receptor stably expressed in CHO-K1 cell lineBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2002C Robert In the present study, pharmacological properties of a bradykinin B2 receptor amplified either from guinea-pig ileum or lung and homologous to the previously reported sequence except two amino-acid changes L124,P and N227,Y in the receptor protein were characterized. Tritiated bradykinin ([3H]-BK) specifically bound to the cloned guinea-pig B2 bradykinin receptor stably expressed in Chinese hamster ovary cells (CHO-K1) with a KD value of 0.29±0.07 nM. In competition experiments, bradykinin (BK) affinity constant value was 0.21±0.05 nM while the two specific kinin B1 ligands, des-Arg9 -bradykinin (DBK) and des-Arg9 -Leu8 -bradykinin (DLBK) were unable to compete with [3H]-BK. As the specific peptide antagonist D -Arg-[Hyp3,Thi5,D -Tic7,Oic8]-bradykinin (HOE140), (E)-3-(6-acetamido-3-pyridil)-N-[-N-[2,4-dichloro-3-[(2-methyl-8-quinolinyl)oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide (FR173657) and 1-[[3-[2,4-dimethylquinolin-8-yl)oxymethyl] - 2,4 - dichloro - phenyl]sulfonyl] - 2(S) - [[4-[4-(aminoiminomethyl)-phenylcarbonyl]piperazin-1-yl]carbonyl]pyrrolidine (LF16-0335C) exhibited a high affinity for this receptor with Ki values of 7.34±2.45 nM and 8.54±1.55 nM respectively. BK and kallidin (KD) increased inositol phosphates (IPs) levels with EC50 values of 0.44±0.12 nM and 6.88±0.28 nM, respectively. Neither DLBK nor DBK (0.01 nM to 10 ,M) stimulated or inhibited IPs turnover and as expected HOE140 did not raise IPs production. HOE140 (0.1 ,M) and LF 16-0335c (1 ,M) right shifted the BK response curve with pKB values of 9.2±0.4 and 8.4±0.3, respectively. The results indicate that this cloned guinea-pig receptor displayed typical pharmacological properties of a bradykinin B2 receptor and support the existence of a single B2 receptor in this species. British Journal of Pharmacology (2002) 135, 462,468; doi:10.1038/sj.bjp.0704494 [source] Studies on Regime Transition, Operating Range and System Stability in a Liquid-Solid Circulating Fluidized BedCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2009P. Natarajan Abstract In the present work, the variations in the solids circulation rate and solids holdup were analyzed to study the behavior of a liquid-solid circulating fluidized-bed (LSCFB) regime. The results confirm the existence of two regions in the regime of LSCFB. A new concept of critical liquid velocity, jlc, is proposed in the present work for demarcation between region,1 and region,2, which is found to be a constant value of about 1.3,ut for all particles considered. The operating range of the LSCFB regime is obtained for the various particles and a correlation is developed from the data to estimate the maximum total liquid velocity. The predicted maximum liquid velocity was compared with the experimental values and found to be in good agreement within ±9,%. The effects of total liquid velocity, particle size and density on the stable operating range are discussed. Analysis of the experimental results shows that stable operation prevails both in region,1 and region,2. [source] Ion and pH Sensing with Colloidal Nanoparticles: Influence of Surface Charge on Sensing and Colloidal PropertiesCHEMPHYSCHEM, Issue 3 2010Feng Zhang Dr. Abstract Ion sensors based on colloidal nanoparticles (NPs), either as actively ion-sensing NPs or as nanoscale carrier systems for organic ion-sensing fluorescent chelators typically require a charged surface in order to be colloidally stable. We demonstrate that this surface charge significantly impacts the ion binding and affects the read-out. Sensor read-out should be thus not determined by the bulk ion concentration, but by the local ion concentration in the nano-environment of the NP surface. We present a conclusive model corroborated by experimental data that reproduces the strong distance-dependence of the effect. The experimental data are based on the capability of tuning the distance of a pH-sensitive fluorophore to the surface of NPs in the nanometer (nm) range. This in turn allows for modification of the effective acid dissociation constant value (its logarithmic form, pKa) of analyte-sensitive fluorophores by tuning their distance to the underlying colloidal NPs. [source] Combined use of chiral ionic liquid and CD for MEKC: Part II.ELECTROPHORESIS, Issue 16 2009Determination of binding constants Abstract A competitive inhibition mechanism is proposed to investigate the interactions among 2,3,6-tri- O -methyl-,-CD (TM-,-CD), cationic ionic liquid type surfactants, N -undecenoxy-carbonyl- L -leucinol bromide (L -UCLB) and profens using affinity CE. The apparent binding constant of TM-,-CD to L -UCLB was estimated by nonlinear and linear plotting methods. The binding constants of one representative profen (e.g. fenoprofen) to TM-,-CD and L -UCLB were estimated by a secondary plotting approach. The R - and S -fenoprofens have different binding constant values, resulting in the enantioseparation due to the synergistic effect of the two chiral selectors, TM-,-CD and L -UCLB. [source] Kinetic Studies of the Oxidative Addition and Transmetallation Steps Involved in the Cross-Coupling of Alkynyl Stannanes with Aryl Iodides Catalysed by ,2 -(Dimethyl fumarate)(iminophosphane)palladium(0) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2004Bruno Crociani Abstract The complexes [Pd(,2 -dmfu)(P,N)] {dmfu = dimethyl fumarate; P,N = 2-(PPh2)C6H4,1-CH=NR, R = C6H4OMe-4 (1a), CHMe2 (2a), C6H3Me2 -2,6 (3a), C6H3(CHMe2)2 -2,6 (4a)} undergo dynamic processes in solution which consist of a P,N ligand site exchange through initial rupture of the Pd,N bond at lower energy and an olefin dissociation-association at higher energy. According to equilibrium constant values for olefin replacement, the complex [Pd(,2 -fn)(P,N)] (fn = fumaronitrile, 1b) has a greater thermodynamic stability than its dmfu analogue 1a. The kinetics of the oxidative addition of ArI (Ar = C6H4CF3 -4) to 1a and 2a lead to the products [PdI(Ar)(P,N)] (1c, 2c) and obey the rate law, kobs = k1A + k2A[ArI]. The k1A step involves oxidative addition to a reactive species [Pd(solvent)(P,N)] formed from dmfu dissociation. The k2A step is better interpreted in terms of oxidative addition to a species [Pd(,2 -dmfu)(solvent)(,1 -P,N)] formed in a pre-equilibrium step from Pd,N bond breaking. The complexes 1c and 2c react with PhC,CSnBu3 in the presence of an activated olefin (ol = dmfu, fn) to yield the palladium(0) derivatives [Pd(,2 -ol)(P,N)] along with ISnBu3 and PhC,CAr. The kinetics of the transmetallation step, which is rate-determining for the overall reaction, obey the rate law: kobs = k2T[PhC,CSnBu3]. The k2T values are markedly enhanced in more polar solvents such as CH3CN and DMF. The solvent effect and the activation parameters suggest an associative SE2 mechanism with substantial charge separation in the transition state. The kinetic data of the above reactions in various solvents indicate that, for the cross-coupling of PhC,CSnBu3 with ArI catalysed by 1a or 2a, the rate-determining step is represented by the oxidative addition and that CH3CN is the solvent in which the highest rates are observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] | |||||||||||||||||||||||||||||||||||||||||||