Slope Of Ln Research Articles

The effect of benzotriazole on mass transfer in the corrosion of a copper rotating disk electrode

The effect of benzotriazole, BTA, on mass transfer in dissolution-corrosion of the copper rotating disk electrode in 0.02 M Fe(III)–0.5 M H2SO4 has been studied by means of atomic absorption spectrometry. The mass transfer coefficient, K, was determined from the slope of ln(C0/C)Fe(III) vs. time plots. In the absence of BTA the corrosion process can be described by the correlation Sh = KR/D = 4.47Re0.5. The difference in values between Sh and ShLevich, and the change in slope in the Arrenhius plot points to mixed control for the cathodic process Fe3+ + 1e− → Fe 2+ and charge transfer control for the anodic process, Cu → Cu2+ + 2e. The average activation energies were 7.7 kJ mol−1 and 19.5 kJ mol−1 at (500–1500) and (2000–3000) rpm, respectively. At low concentration of BTA the inhibiting action of BTA increases with concentration and with rotation speed. For [BTA] ≥ 5 × 10−3 M, the K value, 10−4 cm s−1, remains constant and is independent of rotation rate. The morphology of the copper rotating disk after corrosion in the absence and presence of BTA was examined using scanning electron microscopy (SEM).

Kinetics and free energy profiles of spermine transport in liver mitochondria.

In the present study, the voltage-dependent mechanism of spermine transport in liver mitochondria [Toninello, A., Dalla Via, L., Siliprandi, D., and Garlid, K. D. (1992) J. Biol. Chem. 267, 18393-18397] was further characterized by determining the rate constants J(max) and K(m) as functions of membrane potential. An increase in mitochondrial membrane potential from 150 to 210 mV promoted spermine transport, as reflected by an approximate 4-fold increase in J(max) and 25% decrease in K(m). The mechanism for the voltage dependence of transport was examined using the beta value, i. e., the slope of ln(flux) vs FDeltaPsi/RT plots. Flux-voltage analyses performed at very high and very low spermine concentrations yielded beta values of 0.125 and 0.25, for J(max) and J(max)/K(m), respectively. The physical significance of these beta values was analyzed by means of a theory relating the enzyme reaction rate to the free energy profiles [Yagisawa, S. (1985) Biochem. J. 303, 305-311]. Depending on the nature of K(m), two possible models could be proposed to describe the location and shape of the barriers in the membrane. Analysis of previous data concerning spermine binding [Dalla Via, L., Di Noto, V., Siliprandi, D., and Toninello, A. (1996) Biochim. Biophys. Acta 1284, 247-252] by a new rationale provided evidence for an asymmetrical energy profile composed of two peaks with the binding site near the membrane surface followed by a rate-determining energy barrier for the movement of the bound spermine toward the internal region of the membrane.

Characterization of recycled cellulose by dynamic and isothermal thermogravimetry investigations

Isothermal thermogravimetric measurements were performed on recycled cellulosic materials. The kinetic parameters were determined with the Avrami-Erofe'ev equation from two different ways. The first one consists of the determination of n from the slope of the variations of ln(–ln(1–α)) versus ln(t) and apparent activation energy ΔE from the slope of ln(k(T)) versus 1/T. The second one also gives the values of n and ΔE from a numerical fit of the experimental data. Both methods lead to the same results and show that the reaction order of the degradation process of the cellulose is close to unity. The value of this reaction order allows the interpretation of the dynamic thermogravimetry data with the Broido method. Using this method on a series of recycled cellulose with different content of chemical and mechanical paper pulps, we show that the apparent activation energies depend linearly onto paper pulp ratio.

Is Arginine a Zwitterion in the Gas Phase?

Is Arginine a Zwitterion in the Gas Phase?

Kinetic studies of intermetallic compound formation by resistance measurements

Measurements of electrical resistance provide the easiest way to assess the evolution of reactions leading to the formation (by reaction or phase transition) of a new solid phase. Measurements carried out in situ during heating allow one to see at once that evolution is a function of temperature. The relationship between the measured resistance and the amount of the new phase formed is not direct so the derivation of kinetic data from resistance measurements is not obvious. This paper is an attempt to correctly relate sheet resistance measurements to the amounts of phase formed, and furthermore obtain the activation energy for phase growth. Exact relationships are complex and rather difficult to use, so simplifications have to be made which are justified either through mathematical derivation or actual numerical calculations. Two examples are considered: (1) the diffusion limited planar growth of a phase, and (2) the transformation of a film from one phase to another, assuming that the nuclei are pre-existent and that the film is sufficiently thin for the transformation to occur entirely via the lateral growth of the nuclei. For this latter case, it is shown that there is no linear relation between the sheet resistance and the evolution of the transformation. Using the results obtained from in situ measurements at different heating rates m and taking equivalent values of the sheet resistance, i.e. for equal amounts of the newly grown phase let us say 50% or 80% transformation, the activation energy can be obtained as the slope of ln m/ T 2 versus 1/ T.

Low-temperature Si(001) epitaxy using low-energy (〈E 〉≂18 eV) Si atoms

The use of energetic (average energy ≂18 eV), rather than thermal (≂0.2 eV), Si beams during deposition at R=1 Å s−1 was found to increase the Si(001) epitaxial thickness te (100 Å–1.2 μm) by up to an order of magnitude over the growth temperature range Ts=80–300 °C. The overall increase in te is attributed primarily to a more effective filling of interisland trenches which form during growth in the low adatom mobility two-dimensional multilayer mode and provide preferential sites for the nucleation of the terminal amorphous phase. In addition, the behavior of te(Ts) at constant R and te(R) at constant Ts is quite different than that reported for films grown by molecular-beam epitaxy. A decrease in the slope of ln(te) versus −1/Ts at Ts<225 °C indicates an additional increase in the epitaxial thickness at very low growth temperatures while at constant Ts, 150 °C, te increases with decreasing R, reaches a maximum, and then decreases. These latter effects are explained in terms of changes in average island sizes giving rise to corresponding changes in interlayer mass transport.

The transition from nondispersive to dispersive charge transport in vapor deposited films of 1-phenyl-3- p-diethylamino-styryl-5- p-diethylphenylpyrazoline (DEASP)

Hole mobilities have been measured for vapor deposited glassy films of DEASP as a function of: (i) temperature encompassing the glass transition temperature; (ii) electric field; and (iii) sample thickness. Time-of-flight photocurrent transients become dispersive below a temperature T c at which ln μ versus T −2 plots, μ being the operationally defined mobility, reveal a break. Both the decrease of T c with sample thickness and the slope of ln μ( T< T c) versus T −2 plots are in quantitative agreement with model predictions for charge transport in materials with energetic disorder yet devoid of polaron effects. The μ( T, E) behavior for T> T g is rationalized in terms of a temperature-induced increase in the quasi-static disorder.

Low-temperature behavior of oxygen ordering in YBa 2Cu 3O 6+2 c: calculation of length of O (1)-Cu (1)-O (1) chains at T < 100 K

Oxygen ordering in the basal plane of YBa 2Cu 3O 6+2 c is investigated in terms of the two-dimensional Ising model with the repulsive nearest-neighbor OO bond ( V 1) and the second-neighbor OO bond ( V 3), while OO interaction through Cu ( V 2) is attractive. The phase diagram is calculated using the modified cluster field model (MCFM) for values of interactions obtained by the linear muffin-tin orbital (LMTO) first-principle calculations. The analytic closed-form expression, based on the cluster variation method (CVM), for the length of O (1)Cu (1)O (1) chains l at arbitrary low temperatures, is derived and compared with MCFM calculations for T > 100 K. The agreement with the MCFM calculations is excellent. We found that the slope of ln ( l) versus inverse temperature plot practically equals 2 | V 2 | for all values of oxygen content c and temperatures below room temperature.

Optical Measurements during Gelation Process of Muscle Protein under High Pressure

The dynamical properties of the pressure-induced gelation process of the muscle protein was investigated by observing the evolution of the turbidity spectra in the pressure-jump experiments. In the pressure-induced gelation process, time dependence of the slope of ln (τ d ) vs. ln λ (τ : turbidity, d : the thickness of the specimen and λ : wavelength) showed quite different behavior compared with the heat-induced one. Namely, as the time passed, the slope once decreased and then increased, suggesting that the depolymerization of F-actin takes place before the gelation process. Also, the surfaces of the pressure-treated products examined with a scanning electron microscope revealed the more smooth structure than that of the heat-induced gel.

Stomatal Response to Humidity in Common Bean (Phaseolus vulgaris): Implications for Maximum Transpiration Rate, Water-Use Efficiency and Productivity

Twelve common bean (Phaseolus vulgaris L.) cultivars were grown under greenhouse conditions to study the response of net photosynthesis (A) and transpiration (E) to variation in the leaf-to-air humidity gradient (v). Large differences were observed between cultivars in maximum rates of A and E. The variation in A correlated with both leaf nitrogen content and specific leaf area. Thin leaves had higher nitrogen contents per unit dry weight, but thick leaves had higher nitrogen content per unit surface area. Photosynthetic nitrogen-use efficiency did not correlate with nitrogen content on either a mass or a surface area basis. Very little variation was found between cultivars in the sensitivity of total leaf conductance (g) to increasing v, when sensitivity was defined as the slope of ln(g) versus v (δln(g)/δv). No significant correlation existed between δln(g)/δv and variation in maximum conductance values. Much steeper slopes (greater sensitivity) were found in the response of stomatal conductance alone (gs) to the leaf-leaf surface humidity gradient (vs). The sensitivity of stomatal response correlated positively with variation in maximum conductance among cultivars, and, since stomatal conductance was in series with a fixed boundary layer conductance, this positive correlation made possible the uniform sensitivity of g(total) with respect to v(leaf-air) despite the wide variation in gmax. All cultivm reached their maximum E at very similar v values, and all showed a relatively constant E over a wide range of high v. The implications of this relative homeostasis in E are discussed in the context of possible hydraulic limitations on E. Considerable recent interest has focussed on the use of carbon isotope discrimination (Δ) as a useful screening character in crop breeding programmes, and Δ has been found to correlate positively with yield in P. vulgaris. We found that Δ measured on bulk leaf tissue, positively correlated with both Amax and gmax between bean cultivars, but did not correlate with instantaneous measures of intercellular CO2 (cI) when v was held constant across all measurements. This apparent discrepancy may be due, at least in part, to variation in leaf temperatures among cultivars under normal growing conditions. Leaf-energy-budget simulations indicated that the observed range of maximum leaf conductance at low v would generate up to 3.0�C variation in leaf temperatures under field conditions of low to moderate windspeed. Given the strong stomatal response to v, this variation in leaf temperature could cause variation in carbon isotope discrimination, which reflects long-term cI values. Such a mechanism of producing variation in cI would not be apparent in cI measurements taken under cuvette conditions where leaf temperature was held constant.

CONDUCTIVITIES OF POLY(2-VINYLPYRIDINE) MATRIX COMPOSITES

Poly(2-Vinylpyridine) and composites (with Zn and Hg as conductive components and Poly(2-Vinylpyridine) as a matrix polymer) have been synthesized to study the electrical behaviour of these materials. The current values have been monitored at different voltages and temperatures. On the basis of different current-voltage and current-temperature curves, it is suggested that the conduction mechanism in these materials is of Poole-Frenkel type. The activation energy value determined from the slope of ln I versus (kT)−1 is approximately 0.65 eV.

Theoretical and experimental aspects of the thermal dependence of electron capture coefficients

The thermal activation of the capture coefficient c is very often treated in a semiclassical way, resulting from a simple energy barrier. Experimentally, this activation energy Eb is said to be the slope of ln[c(T)] vs 1/T kT. Unfortunately, many experimental evidences deny this analysis and suggest that a single energy barrier is not enough to reproduce the physical behavior of a point defect. Here we propose a more complete approach to the problem of nonradiative carrier capture assisted by phonons, which is based on a less restrictive hypothesis and leads to a compact formulation of the capture coefficient. This formula reproduces the previous asymptotic forms at high temperature in the strong coupling limit, but remains valid over the whole temperature range and for any strength of the coupling between the lattice and the defect. This point is illustrated for typical cases and the accuracy of the new formula is shown in the case of the so-called B level in GaAs, whose capture coefficient does exhibit a nonexponential behavior with temperature. Our wish is to put the theoretical point of view previously developed by Passler under a form allowing more extensive use in order to extract physical parameters from the experimental c(T) curves with better accuracy.

Incorporation probabilities and depth distributions of aluminum co-evaporated during Si(100) molecular beam epitaxy

The incorporation probabilities σA1 and dopant depth distributions CA1 (x) of aluminum co-evaporated during growth of Si(100) films by molecular beam epitaxy (silicon flux approximately 1.2×1015 cm−2 s−1 were investigated as a function of growth temperature Ts between 525 and 975°C. σA1 varied exponentially and ranged from approximately 0.2 at Ts = 525°C to approximately 9 × 10−5 with an increase in the slope of ln(σA1)vs. 1/Ts for Ts> 800°C because of desorption from a surface-accumulated aluminum overlayer. Surface-segregation-induced profile broadening resulted in profile width ΔA1∼625 nm per concentration-decade for Ts≈775°C. Increasing to values of Ts⩾900°C greatly reduced aluminum surface accumulation because of rapid desorption but introduced bulk-diffusion broadening resulting in ΔA1∼90 nm per concentration-decade. Relatively abrupt profiles, ΔA1<60 nm per concentration-decade, were obtained at intermediate growth temperatures near 875°C or at lower Ts combined with rapid thermal desorption at the end of each doped layer. The maximum achievable aluminum concentration in films grown at 675°C was approximately 1 ×1018 cm−3.

Spin Density and Magnetic Susceptibility of Charge‐Transfer Complexes with Chalkogenanthrene Donors

AbstractSpin densities n of CT‐complexes Vn2E2·TCNQ and Vn2E2·DDQ [Vn2E2 = 2,3,7,8‐Tetramethoxychalkogenanthrene (“5,10‐Dichalkogena‐cyclo‐diveratrylene”) with E = S, Se; TCNQ = 7,7,8,8‐Tetracyanoquinodimethane; DDQ = 2,3‐dichloro‐5,6‐dicyanoquinone] are evaluated from EPR measurements in the temperature range of 5–400 K. Three temperature regions with different slopes of ln n vs. 1/T are found. Correlations between donor/acceptor combinations, electrical, magnetic and structural properties are discussed.

Strain broadening of EPR linewidths in Cr/MgO single crystals and powders

The EPR linewidths of the M = + 12 ↔ − 12 transition of the Cr3+ spectrum of Cr/MgO single crystals and powders have been measured at 9 GHz before and after annealing. The nominal chromium concentrations ranged from 800 to 15 000 ppm. Specimens were annealed at 500°C in oxygen for up to 150 h. Annealing produced reductions in peak-to-peak linewidth (ΔHpp) which occured in two stages. Each followed an exponential [ΔHpp]t = [ΔHpp]0exp(− αt) and the initial (α1) and final (α2) decay rates were determined from the slopes of ln[ΔHpp] vs. time plots. For single crystals all the values of α1 were about 0.04 h-1; the smaller values of α2 were concentration dependent ranging from 0.9 × 10-3 to 1.25 × 10-3 h-1 of the two sources of strain. The rapid decay rate is associated with cationic vacancy strain relief and the slower decay with removal of lattice distortion brought about when the Mg2+ ions are replaced by Cr3+ dopant ions. Similar effects were observed with powders but in these both types of lattice strain were relieved at a slower rate in the powder than in the corresponding single crystal, e.g. for 3600 ppm Cr, α1 = 0.016 h-1 and α2 = 1.0 × 10-3h-1.

Rate of increase in pulmonary distensibility in a longitudinal study of smokers.

To examine the hypothesis that an abnormally rapid increase in pulmonary distensibility occurs in cigarette smokers, 39 adult smokers (24 men), mean age 47 (SD 8) years, who were not disabled were studied on two occasions over a mean interval of 3.5 (SD 0.5) years. Exponential analysis of static pressure-volume data obtained during deflation of the lungs gave the exponent K, an index of distensibility. Total lung capacity (TLC) was measured in a body plethysmograph. At entry into the longitudinal study means values for K and static recoil pressure in the 39 smokers available for follow up were similar to those obtained in the original group of 101 smokers (73 men), mean age 42 (SD 11) years, in the cross sectional study. Over the interval of the study, ln K and TLC increased and FEV1 decreased at rates greater than those found in a previous longitudinal study of 34 non-smokers (24 men), mean age 42 (SD 15) years. In the longitudinal study of smokers the observed changes in K and in recoil pressure over the interval of study were greater than the values obtained from the regression slopes found in the cross sectional study of smokers. On the basis of the regression model used previously in the longitudinal study of non-smokers, the age coefficient for ln K was greater than that found in the non-smokers (p less than 0.01). The regression model also showed that the slope of ln K on age increased in older subjects. Because K is related to peripheral airspace size, a rapid rate of increase in K identifies smokers in whom airspace size is increasing abnormally rapidly. In this study the rate of increase in K and the variation between subjects was sufficient to explain the magnitude of the increased pulmonary distensibility found in cigarette smokers who present with emphysema.

Diffusion coefficient of dye in a polymer using multiple-sheet arrangements with a step profile of the initial concentration.

A method to obtain the diffusion coefficient D of a diffusant in a polymer substrate is described. It basically applies the multiple-sheets, in which an amount α of the diffusant was initially distributed within the central sheet, giving a concentration distribution of a step function. After a diffusion interval t, the broadened concentration distribution across the stacked sheets, C(x, t), was determined spectroscopically and analysed by the following equation. D was calculated from the slope of ln C vs. x2/4t plots. The applicability of this method was demonstrated for the diffusion of p-aminoazobenzene into a nylon 6 sheet at 90°C where the diffusion interval, the thickness of the polymer sheet and the initial concentration of the diffusant in the central sheet were varied. In contrast to experimental setups where diffusion of a dye into a polymer is measured in the presence of solution of the dye, the described method yields diffusion coefficients of dyes in polymers which are not influenced by the simultaneous diffusion of the solvent.

Use of acetylcholine to measure total vascular pressure-volume relationship in dogs.

To define total vascular capacitance, we used acetylcholine to arrest the heart and measured mean circulatory filling pressure (MCFP) during controlled hemorrhage and volume loading in 12 splenectomized dogs after ganglion blockade with hexamethonium. We also examined the gross pathological and histological changes in the lungs. Controlled hemorrhage (n = 12) of 5 and 10 ml/kg decreased MCFP from 6.8 +/- 0.1 to 4.9 +/- 0.3 and 3.6 +/- 0.2 mmHg, respectively. Volume loading of 5 (n = 8) and 10 ml/kg (n = 4) increased MCFP to 9.3 +/- 0.2 and 12.1 +/- 0.1 mmHg, respectively. At MCFPs below 5 mmHg, the pressure (P)-volume (V) relationship was not linear [(P = P0ekV, where k is slope of ln (MCFP) vs. V, k = 0.061, R2 = 0.998]. At MCFPs between 5 and 12 mmHg, the pressure-volume relationship was linear (slope = 0.479 mmHg.ml-1.kg-1, R2 = 0.992) and total vascular compliance was 2.09 ml.mmHg-1.kg-1. There were no changes in heart rate, cardiac output, right atrial, pulmonary artery, and pulmonary artery wedge pressures when values at base line were compared with those measured 15 min after each arrest. There were no changes in arterial gas measurements or acid-base balance, and there was no evidence of atelectasis or interstitial or intra-alveolar edema. We conclude that the total body pressure-volume relationship in the presence of ganglion blockade had a nonlinear configuration. The use of acetylcholine to arrest the heart, four times with hexamethonium in reflex-blocked animals, did not result in changes in hemodynamics or pulmonary function.

Space-resolved determination of electron temperature from x-ray continuum radiation

A method to obtain the electron temperature Te in plasmas from the chordal measurement of x-ray continuum radiation is described. The maximum value of Te along the line of observation can be derived from the slope of ln E1/2I vs E plot, where I is the chordal x-ray intensity and E is photon energy. The method is applied to obtain the value of Te from the soft x-ray measurement on ST tokamak.

Determination of the conduction-band discontinuity between In0.53Ga0.47As/In0.52Al0.48As using n+-InGaAs/InAlAs/n−-InGaAs capacitors

The conduction-band discontinuity (ΔEc) between In0.53Ga0.47As and In0.52Al0.48As is determined by current-voltage measurements on n+-InGaAs/InAlAs/n−-InGaAs capacitors. Current is found to be dominated by thermionic emission conduction down to 180 K. Barrier heights are determined from the slope of ln(J/T2) vs 1/T where good straight-line fits are obtained in the thermionic emission range. After correcting for the Fermi level a conduction-band discontinuity of 0.51±0.04 eV is obtained representing 70% of the total band-gap discontinuity. Furthermore, capacitance-voltage measurements are fit to classical capacitance-voltage theory and show that no charge is present in the InAlAs insulating layer.