Initial Rate Of Change Research Articles

THERMAL CYCLIC DEFORMATION AND DEGRADATION OF SHAPE MEMORY EFFECT IN Ti-Ni ALLOY

Abstract The most basic single axial cyclic motion (i.e. fatigue) tests by the alternative heating up and cooling down of shape memory Ti-Ni50.2at%wires were performed. Heating up was done by direct current method or temperature controllable water-bath and the characteristics on the cyclic motion and its degradation in shape memory effect (SME) are discussed. The degradation of SME can be divided into two factors; the cyclic deformation by thermoelastic transformation ΔD and the gradual inelasatic elongation U of Ti-Ni wire. The stress dependency of each SME degradation factor, ΔD or ΔU, and the variation of transformation temperature with thermal cycles are discussed. Lastly, nondestructive estimation of total thermal fatigue life of wire is tried from the view point of the initial changing rate of these degradation parameters.

Measurement of pH to quantify urease activity

The rate of change of pH caused by the hydrolysis of urea was measured for urease solutions of 18 different concentrations. Concentrations were converted into an activity, A (measured in IU/cm 3), by using a titrimetric method to assay the urease sample. For activities in the range 0.6–38 IU/cm 3, A was related to the initial rate of change of pH, ( dpH/ dt) 0 , (measured in s −1) by the empirical relationship: A = 549( dpH/ dt) 0 − 1423( dpH/ dt) 0 2 . Values of ( dpH/ dt) 0 were sensitive to changes in the urease activity of about 0.6 IU/cm 3.

Water permeability of ventricular cell membrane in choroid plexus epithelium from Necturus maculosus.

1. The osmotic water permeability Lp and the relations between the flows of H2O, K+ and Cl- were studied in the ventricular membrane of the epithelium from the choroid plexus of Necturus maculosus. 2. The flows were induced by abrupt changes in external osmolarity of the ventricular solution. Solution changes were convective and no effects of unstirred layers could be detected on measured parameters. 3. The initial rate of change in intracellular concentrations of K+ and Cl- was monitored by double-barrelled ion-selective microelectrodes. 4. The initial rate of flux of H2O could be monitored as the changes in the concentration of intracellular choline ions (Ch+i). When 0.5 mmol l-1 of choline chloride was added to the external solutions, Ch+i attained values of 1-5 mmol l-1. The dilution or concentration of Ch+i could be recorded by K+ electrodes since the sensitivity of these to Ch+ is more than 50 times greater than to K+. 5. The Lp of the ventricular membrane of the epithelium was 1.4-2.1 x 10(-4) cm s-1 (osmol l-1)-1 and independent of the direction of the induced water flux. Lp was unchanged in tissues adapted to osmolarities of half the physiological value. 6. The efflux of H2O induced by mannitol was associated with an instantaneous efflux of K+ which was inhibited by furosemide. The fluxes had a ratio of 40 mmol l-1. The influx of H2O induced by the removal of NaCl from the ventricular solution was associated with an instantaneous influx of K+. The H2O influx had a ratio to the flux of K+ of 70 mmol l-1. 7. The efflux of H2O induced by mannitol was associated with an efflux of Cl- which was inhibited by furosemide. The ratio of the two fluxes was in the range 15-44 mmol l-1. 8. The conclusion is that the Ch+ method gives a reliable measure of the movement of H2O across the ventricular membrane. The magnitude of the Lp and its relevance to transepithelial transport are discussed. The osmotically induced H2O movement is accompanied by furosemide-sensitive fluxes of K+ and Cl- of the same magnitude. This suggests that co-transport between H2O and KCl can take place in the membrane.

Diffusion and deactivation characteristics in Be-implanted GaAs

In this work, we have observed for the first time that irreversible changes in the sheet hole concentration of the rapid thermally annealed Be-implanted GaAs samples occurred during subsequent heat treatments. The hole concentration is found to decrease with annealing time. Also, the rate of decrease in the hole concentration increases with increasing annealing temperature. By determining the initial rate of change of the carrier concentration during subsequent heat treatments, an activation energy of around 1 eV has been identified. It is concluded that the rate dependent process for this irreversible reaction is the out-diffusion of beryllium atoms. The electrical profiles of the Be implanted samples have also been modified during the annealing processes. These modifications in the electrical properties could lead to deleterious effects to transistor operations if Be is used as a dopant.

Simultaneous kinetic determination of epinephrine and norepinephrine by the stopped-flow technique

A stopped-flow method for the simultaneous determination of epinephrine and norepinephrine, two catecholamines with a wide spectrum of biological activity, is proposed. The method is based on the oxidation of these compounds with 1,10-phenanthroline-iron(III) complex, which is monitored by measuring the initial rate of change of the absorbance of the ferroin formed at 510 nm. The difference in kinetic behaviour between the two species was exploited by applying a modified version of the proportional-equation method for the resolution of epinephrine-norepinephrine mixtures at the micrograms ml-1 level over the ratio range 1:10-10:1, with an error of less than 5% and an average precision of about 2.5%. The method was successfully applied to the determination of the two catecholamines in pharmaceuticals.

Efficiency of nitrogen utilization by pregnant West African dwarf goats fed various levels of crude protein in the diet

Twenty pregnant West African dwarf ( Fouta djallon) goats, with mean live weights of 26.3 ± 0.6 kg, were used in a crude protein (CP) utilization study to ascertain optimal dietary levels. Does were randomized into five groups of four animals each. Five supplements with 5, 10, 15, 20 and 25% CP were prepared from cassava flour, dried brewer's grain, molasses and urea. Each animal group was fed one of the protein supplements to basal grass ( Cynodon nlemfluensis) hay. Nitrogen intake (NI), apparently absorbed nitrogen (AAN), faecal nitrogen (FN), urinary nitrogen (UN) and retained nitrogen (RN) increased significantly ( P<0.05) with increasing CP in the diets. Over 70% of daily dry matter (DM) intake was from concentrate supplements. Changes in the rate of NI and AAN with increasing CP in the supplement were described by exponential equations which showed that the initial rate of change was 0.097, which declined at 0.012 per unit increase of CP in the concentrate. Corresponding values of 0.116 and 0.017 were obtained for AAN. Both NI and AAN increased exponentially ( P<0.01) with increasing CP in the supplement. By differentiating regression equations of NI and AAN, peak rate of change per unit change of CP in the concentrate occurred at 20 and 17% CP, respectively. Results showed that it would be uneconomical to go beyond 20% CP in the concentrate as supplement for pregnant West African dwarf goats.

The one-dimensional kinetic Ising model: A series expansion study

Exact power series expansions (through eight terms) in the time are derived for relaxation in the one-dimensional Ising model with nearest-neighbor interactions for a general rate parameter where the activation energy is a variable fraction of the energy required to break nearest-neighbor bonds. It is found that the qualitative nature of the relaxation is very dependent on this parameter, varying from nearly simple exponential decay (as with Glauber dynamics) for an intermediate value of this parameter, to an initial rate of change that is either much slower or faster than a simple exponential at the extremes of the range of variation of the parameter. The rate equations for the limit of rapid internal diffusion (internal equilibration) are integrated for several special values of the rate parameter. In general the internal equilibration approximation is not a good representation of the relaxation except when the relaxation is similar to Glauber dynamics.

Neonatal rabbit juxtamedullary proximal convoluted tubule acidification.

The present in vitro microperfusion study examined apical membrane Na+/H+ antiporter and basolateral membrane Na(HCO3)3 symporter activity in newborn and adult juxtamedullary proximal convoluted tubules. Proton fluxes were determined from the initial rate of change of intracellular pH after a change in the luminal or bathing solution, buffer capacity, and tubular volume of newborn and adult tubules. Intracellular pH (pHi) was measured fluorometrically using the pH-sensitive dye (2',7')-bis (carboxyethyl)-(5,6)-carboxyfluorescein (BCECF). Apical Na+/H+ antiporter proton flux, assayed by the effect of sodium removal (147----0 meq/liter) on pHi, was one-third the adult level for the first 2 wk and doubled in the 3rd wk of life. Adult levels were achieved by 6 wk of age. Na+/H+ antiporter activity was not detected on the basolateral membrane of 1-wk-old newborns, indicating that polarity of this transporter was already present. Basolateral membrane Na(HCO3)3 proton flux, assayed by the effect of a bath bicarbonate change (25----5 meq/liter) and by a bath sodium change (147----0 meq/liter) on pHi, was 50-60% of adult values in 1-wk-old newborns. Basolateral membrane Na(HCO3)3 proton flux assayed by a bath bicarbonate change (25----5 meq/liter) remained at 50-60% of adult values for the 1st mo of life and increased to adult levels by 6 wk of age. This transporter not only plays a role in net acidification, but is an important determinant of cell pH in newborn juxtamedullary proximal convoluted tubules.

The influence of heat treatment on the electrical characteristics of selenium-implanted GaAs

The effects of subsequent heat treatments on the electrical properties of ion-implanted layers in GaAs have received little attention. This is of paramount importance as far as both the industrial applications and the understanding of the physics behind the incorporation of dopants in GaAs are concerned. In this work, we have observed reversible changes in the sheet carrier concentration of the rapid thermally annealed Se-implanted GaAs samples during subsequent heat treatments. The carrier concentration is observed to reach a limit for a certain temperature at sufficiently long annealing times. By noting the initial rate of change of the carrier concentration during subsequent heat treatments, an activation energy in the range of 1.6–2.5 eV has been identified for these samples. It is concluded that the rate dependent process for such reversible reactions is the diffusion of gallium atoms/vacancies. The electrical profiles of the Se-implanted samples have also been modified during the annealing processes.

Kinetic determination of sulphonamides at the millimolar level by the continuous addition of reagent technique

A kinetic method for the determination of sulphonamides by the continuous addition of reagent (CAR) technique is reported. The method involves the formation of an azo dye between 1-naphthol and a diazonium salt, which is in turn obtained on reaction between the free primary aryl amine of the sulphonamide and sodium nitrite in a weak acid medium. The reaction is monitored via the initial rate of change of the absorbance of the azo dye formed at 470 nm, which is proportional to the sulphonamide concentration. Practical problems associated with this type of reaction for the determination of sulphonamides were readily avoided by using the CAR technique. Sulphonamides can be determined in the range 3 × 10 −6 −3 × 10 −5 M with a relative standard deviation of about 1% and a sampling frequency of 25 h −1 (triplicate runs). The proposed method is simple and rapid and insensitive to the presence of excipients; it proved useful for the determination of sulphonamides in pharmaceutical samples.

Temperature-induced changes in cold tolerance of Lolium perenne

SUMMARYResponses of cultivars of Lolium perenne with contrasting winter hardiness to hardening and dehardening at different temperatures were studied in controlled-environment experiments in 1984/85. After hardening at 2 °C, the hardy cultivars Premo and S23 had faster initial rates of change of LT50 (lethal temperature at which 50% of plants were killed), measured on seedlings in an artificial freezing test, and achieved a greater degree of cold tolerance than the susceptible cultivar Grasslands Ruanui. When acclimated at higher temperatures (4–10 °C), the hardier cultivars were better able to develop increased cold tolerance than Grasslands Ruanui. Plants of Premo and S23, previously hardened at 2 °C, maintained their cold tolerance when transferred to warmer temperatures (4–12 °C) better than Grasslands Ruanui, which dehardened even at 4 °C.The responses of the cultivars to hardening and dehardening temperatures under controlled-environment conditions were reflected in seasonal changes in hardiness, measured as cold tolerance of tillers sampled during fluctuating temperatures of a typical maritime winter (1977/78) at Aberystwyth, UK.

Osmotic water permeability of Necturus gallbladder epithelium.

An electrophysiological technique that is sensitive to small changes in cell water content and has good temporal resolution was used to determine the hydraulic permeability (Lp) of Necturus gallbladder epithelium. The epithelial cells were loaded with the impermeant cation tetramethylammonium (TMA+) by transient exposure to the pore-forming ionophore nystatin in the presence of bathing solution TMA+. Upon removal of the nystatin a small amount of TMA+ is trapped within the cell. Changes in cell water content result in changes in intracellular TMA+ activity which are measured with intracellular ion-sensitive microelectrodes. We describe a method that allows us to determine the time course for the increase or decrease in the concentration of osmotic solute at the membrane surface, which allows for continuous monitoring of the difference in osmolality across the apical membrane. We also describe a new method for the determination of transepithelial hydraulic permeability (Ltp). Apical and basolateral membrane Lp's were assessed from the initial rates of change in cell water volume in response to anisosmotic mucosal or serosal bathing solutions, respectively. The corresponding values for apical and basolateral membrane Lp's were 0.66 x 10(-3) and 0.38 x 10(-3) cm/s.osmol/kg, respectively. This method underestimates the true Lp values because the nominal osmotic differences (delta II) cannot be imposed instantaneously, and because it is not possible to measure the true initial rate of volume change. A model was developed that allows for the simultaneous determination of both apical and basal membrane Lp's from a unilateral exposure to an anisosmotic bathing solution (mucosal). The estimates of apical and basal Lp with this method were 1.16 x 10(-3) and 0.84 x 10(-3) cm/s.osmol/kg, respectively. The values of Lp for the apical and basal cell membranes are sufficiently large that only a small (less than 3 mosmol/kg) transepithelial difference in osmolality is required to drive the observed rate of spontaneous fluid absorption by the gallbladder. Furthermore, comparison of membrane and transepithelial Lp's suggests that a large fraction of the transepithelial water flow is across the cells rather than across the tight junctions.

Axial heterogeneity of rabbit proximal tubule luminal H+ and basolateral HCO3- transport

The present in vitro microperfusion study examined whether the rates of the apical membrane Na+-H+ antiporter and basolateral membrane Na(HCO3)3 symporter vary along the length of the proximal tubule. Initial proximal convoluted tubules (PCT obtained within 0.5 mm from the glomerulus), mid-PCT (PCT without glomerular attachments) and cortical proximal straight tubules were examined. The rate of either the apical or basolateral membrane acidification mechanism was measured from the initial rate of change of intracellular pH after a change in either the luminal or bathing solution. Intracellular pH was measured fluorometrically using the pH-sensitive dye (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein. The rate of bicarbonate exit across the basolateral membrane was examined by imposing either a sodium or bicarbonate gradient. There was no difference between initial and mid-PCT, but the rate of change in cell pH was 30% slower in PST in both series. The rate of sodium-dependent apical proton secretion was examined by changing the sodium concentration in the lumen. There was no difference in sodium-dependent apical proton secretion in initial vs. mid-PCT, but the rate fell by 70% in the proximal straight tubule (PST). These differences were not due to a difference in buffer capacity in these segments. These data are consistent with a homogeneous rate of apical Na+-H+ antiporter and basolateral Na(HCO3)3 activity along the rabbit PCT, but a lower rate in the PST.

Stopped-flow kinetic determination of acetaminophen by oxidation with a 1,10-phenanthroline/iron(III)complex

A stopped-flow method for the determination of acetaminophen based on its oxidation with a 1,10-phenanthroline/iron (III) complex is described. The reaction is followed by measuring the initial rate of change of the absorbance of the ferroin formed at 510 nm, which is proportional to the acetaminophen concentration. The linear range of the determination is 0.25–25.0 μg ml −1 and the relative standard deviation is 2.6%. Sample throughput is 60 h −1 (triplicate runs). The method is simple and rapid and unaffected by the presence of most other drugs and excipients. Analysis of pharmaceutical samples showed excellent correlation with the nominal values.

Thermal Stability of Zinc and Selenium Implanted GaAs

ABSTRACTWe have observed for the first time reversible changes in the sheet carrier concentration of the rapid thermally annealed Se and Zn implanted GaAs samples during subsequent heat treatments. The electrical profiles of the implanted samples have also been modified during the annealing processes. By observing the initial rate of change in the carrier concentration, an activation energy of about 2 eV is obtained which is thought to correspond to the diffusion of gallium atoms/vacancies.

Intracellular chloride regulation in amphibian dorsal root ganglion neurones studied with ion-selective microelectrodes.

1. Intracellular Cl- activity (aiCl) and membrane potential (Em) were measured in frog dorsal root ganglion neurones (DRG neurones) using double-barrelled Cl- -selective microelectrodes. In standard Ringer solution buffered with HEPES (5 mM), equilibrated with air or 100% O2, the resting membrane potential was -57.7 +/- 1.0 mV and aiCl was 23.6 +/- 1.0 mM (n = 53). The value of aiCl was 2.6 times the activity expected for an equilibrium distribution and the difference between Em and ECl was 25 mV. 2. Removal of external Cl- led to a reversible fall in aiCl. Initial rates of decay and recovery of aiCl were 4.1 and 3.3 mM min-1, respectively. During the recovery of aiCl following return to standard Ringer solution, most of the movement of Cl- occurred against the driving force for a passive distribution. Changes in aiCl were not associated with changes in Em. Chloride fluxes estimated from initial rates of change in aiCl when external Cl- was removed were too high to be accounted for by electrodiffusion. 3. The intracellular accumulation of Cl- was dependent on the extracellular Cl- activity (aoCl). The relationship between aiCl and aoCl had a sigmoidal shape with a half-maximal activation of about 50 mM-external Cl-. 4. The steady-state aiCl depended on the simultaneous presence of extracellular Na+ and K+. Similarly, the active reaccumulation of Cl- after intracellular Cl- depletion was abolished in the absence of either Na+ or K+ in the bathing solution. 5. The reaccumulation of Cl- was inhibited by furosemide (0.5-1 x 10(-3) M) or bumetanide (10(-5) M). The decrease in aiCl observed in Cl- -free solutions was also inhibited by bumetanide. 6. Cell volume changes were calculated from the observed changes in aiCl. Cells were estimated to shrink in Cl- -free solutions to about 75% their initial volume, at an initial rate of 6% min-1. 7. The present results provide direct evidence for the active accumulation of Cl- in DRG neurones. The mechanism of Cl- transport is electrically silent, dependent on the simultaneous presence of external Cl-, Na+ and K+ and inhibited by loop diuretics. It is suggested that a Na+:K+:Cl- co-transport system mediates the active transport of Cl- across the cell membrane of DRG neurones.

Chronic metabolic acidosis causes an adaptation in the apical membrane Na/H antiporter and basolateral membrane Na(HCO3)3 symporter in the rat proximal convoluted tubule.

The effect of chronic dietary acid on the apical membrane Na/H antiporter and basolateral membrane Na(HCO3)3 symporter was examined in the in vivo microperfused rat proximal tubule. Transporter activity was assayed with the epifluorescent measurement of cell pH using the intracellular, pH-sensitive fluorescent dye, (2'7')-bis(carboxyethyl)-(5,6)-carboxy-fluorescein (BCECF). BCECF was calibrated intracellularly, demonstrating similar pH-sensitivity of the dye in control and acidotic animals. In subsequent studies, lumen and peritubular capillaries were perfused to examine Na/H and Na(HCO3)3 transporter activity in the absence of contact with native fluid. The initial rate of change in cell pH (dpHi/dt) was 97, 50, and 44% faster in tubules from acidotic animals when peritubular [HCO3] was changed from 25 to 10 mM in the presence or absence of chloride, or peritubular [Na] was changed from 147 to 50 mM, respectively. dpHi/dt was 57% faster in tubules from acidotic animals when luminal [Na] was changed from 152 to 0 mM. Buffer capacities, measured using NH3/NH+4 addition, were similar in the two groups. The results demonstrate that chronic metabolic acidosis causes an adaptation in the intrinsic properties of both the apical membrane Na/H antiporter and basolateral membrane Na(HCO3)3 symporter.

Cell membrane water permeabilities and streaming currents in Ambystoma proximal tubule.

An electrophysiological approach is used to analyze the possible routes of osmotically driven water flow across the isolated perfused Ambystoma proximal tubule. The minimum hydraulic conductivities (Lp) of the cell membranes were estimated from the initial rate of change of intracellular activities of Na+ and K+ in response to a step gradient of 50 or 100 mosmol/kg sucrose. The Lp of the apical membrane is 1.30 X 10(-4) cm.s-1.osM-1 referred to the luminal epithelial surface and 2.45 X 10(-6) cm.s-1.osM-1 when corrected for amplification of the brush border (n = 8). The Lp of the basolateral membrane is 1.42 X 10(-4) cm.s-1.osM-1 referred to the basement membrane surface and 6.39 X 10(-6) cm.s-1.osM-1 when corrected for the amplification of the basal and lateral membranes (n = 5). Transepithelial water flows were generated in either direction by a unilateral step increase of osmolality with 100 mosmol sucrose. Bath-to-lumen flow increased paracellular transepithelial resistance (R3) by 48%; lumen-to-bath flow decreased R3 by only 3%. A bilateral increase in the osmolality of both solutions by 50 mosM had no significant effect on R3. Streaming potentials were observed during trans-epithelial water flow induced by unilateral gradients of sucrose; their polarity, magnitude, site of generation, and insensitivity to change of paracellular resistance are all indicative of water flow through paracellular structures, especially the lateral intercellular spaces. Contrary to earlier suggestions (J. M. Diamond, J. Membr. Biol. 51: 195-216, 1979), these potentials are not primarily diffusion potentials across anion-selective tight junctions resulting from solute polarization in the unstirred layers. Instead, a true electrokinetic basis for these streaming potentials is indicated by their continued presence after deletion of all Cl-. Thus water moves through both cellular and paracellular pathways in this epithelium.

A microelectrode study of the mechanisms of L-lactate entry into and release from frog sartorius muscle.

1. Changes in intracellular pH and intracellular anion levels were monitored in frog sartorius muscle fibres during exposure to extracellular L-lactate, using ion-sensitive microelectrodes. 2. Resting intracellular pH (pHi) in 20 mmol l-1 HEPES buffer was 7.18 +/- 0.015 (S.E. of mean, n = 62). Exposure to an extracellular solution at pH 6.5 buffered with 20 mmol l-1 3-(N-morpholino)propanesulphonic acid (MOPS) resulted in a slow intracellular acidification. 3. A reversible decrease in pHi and an increase in intracellular anion levels was observed when L-lactate replaced chloride in equimolar amounts. The increase in intracellular anion level is consistent with intracellular accumulation of L-lactate ion. 4. The rate and steady-state change in pHi and anion level was a function of both extracellular pH and L-lactate concentration, providing evidence for the coupled movement of lactate and proton equivalents. 5. The initial rate of uptake of L-lactate, as measured by the change of pHi, was a non-linear function of the extracellular L-lactate concentration at extracellular pH 6.8 and 7.35. 6. No saturation was observed with concentrations of L-lactate between 5 and 60 mmol l-1 at pH 7.35 and 2.5 and 40 mmol l-1 at pH 6.8. 7. The non-linear relationship between the initial rate of change in pHi and extracellular L-lactate was well fitted by a curve defining uptake as the sum of a carrier process displaying Michaelis-Menten kinetics and a passive diffusion component. The apparent Km of the carrier was 10 mmol l-1 at pHo 7.35 and 4 mmol l-1 at pHo 6.8. 8. The initial rate of change of pHi in the presence of L-lactate was significantly inhibited 39.1 +/- 6.2% by 2-5 mmol l-1 alpha-cyano-4-hydroxycinnamate (n = 9; P less than 0.05, paired t test). 9. alpha-Cyano-4-hydroxycinnamate had no detectable effect on the initial rate of change of pHi induced by propionate exposure. 10. The initial rate of change of pHi induced by L-lactate was not affected by 20-100 mumol l-1 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS). 11. We conclude that L-lactate crosses the membrane of the frog sartorius muscle with proton equivalents via (1) a carrier-mediated process, and (2) passive diffusion of lactic acid. In the physiological range of L-lactate concentrations and pH the transport process dominates.

Use of a microbial fuel cell for the rapid enumeration of bacteria

The detection of bacteria using a thionine mediated microbial fuel cell was examined. On addition of bacteria to the anode compartment of a fuel cell, a rapid increase in the current output was observed. Both the total change in the steady state current (ΔmA) and the initial rate of change of current were proportional to the numbers of bacteria added. Regression analysis of plots of log10 ΔmA against log10 bacteria ml-1 (final concentration) upon the addition of E. coli K12, Lactococcus lactis, coliform sp. A1, Micrococcus sp. M3 but not Pseudomonas sp. P5 gave reasonable correlation coefficients. Determination of the rates of respiration and thionine reduction by E. coli indicated that the transfer of metabolic electrons from the bacteria to the mediator was reasonably efficient (approx. 50%). These results are discussed with respect to the potential application of this technique for the rapid estimation of the bacterial contamination of foods.