Rate Of Change In Concentration Research Articles

Linearization of the relationship between postmortem plasma chloride concentration and postmortem interval in rats

A potentiometric titration procedure was employed for measurement of plasma chloride concentrations during the 0–96 h postmortem period in rats. The data revealed antemortem absolute values and postmortem rate of decrease in plasma chloride concentration (P Cl) which were almost identical to those in dogs and in man. Expression of the data in the form of a double logarithmic plot of P Cl versus postmortem interval (PMI) yielded a linear relationship of high correlation ( r = −0.97; P < 0.001). Attention is drawn to the possibility of utilizing postmortem rate of change in plasma chloride concentration as a means of estimating time elapsed since death.

Predicting changes in hypolimnetic oxygen concentrations with phosphorus retention, temperature, and morphometry

A statistical analysis of the rate of change in oxygen concentrations (VOD, mg O2 m−3 d−1) in 1‐m‐thick strata in the hypolimnia of 29 lakes suggests that these rates can be predicted from a knowledge of the annual retention of phosphorus by the lake sediments, the mean summer temperature of the stratum, and the morphometry of the stratum. VOD values increased as temperature and phosphorus retention increased. Rates were inversely proportional to the ratio of the volume of the stratum divided by the area of sediments that are contiguous to the stratum. The statistical model was tested by measuring VOD values in an independent group of 12 lakes. Predictions agreed well with the measured values. An analysis of the combined data explained 91% of the variance in VOD values. The regression correctly predicted the vertical variation in VOD values in lakes that exhibited negative heterograde, orthograde, and clinograde oxygen profiles. After further testing, this model should provide a method of predicting changes in oxygen concentrations in lakes that are subject to perturbations such as changes in temperature or nutrient loading.

Reaction rate analysis of complex kinetic systems

AbstractUsing the elementary sensitivity densities, a reaction rate sensitivity gradient is obtained which is the derivative of the rate of species concentration change with respect to the rate coefficient. The dimensionless (log‐normalized) form of the reaction rate sensitivity gradient is the ratio of the rate of concentration change of species i due to elementary reaction j and the net rate of concentration change of species i. This result provides a mathematical basis for the use of various forms of reaction rate analyses in the study of complex reaction mechanisms. The kinetic information inherent in the relative reaction rate matrix is extracted by principal component analysis. The method is used to analyze the mechanism of high‐temperature formaldehyde oxidation and high‐temperature propane pyrolysis. Ranking of the elementary reactions allowed us to reduce significantly the original mechanisms and a detailed study of the results revealed the reaction structures and the major reaction paths of the species.

Simultaneous evaluation of insulin secretion and action using a model

For the simultaneous evaluation of insulin secretion and insulin sensitivity, a glucose regulation model has been developed. In order to estimate the parameters of the model, an intravenous glucose infusion test (GIT, 100 mg/kg · min × 2 min and 10 mg/kg · min × 118 min) was carried out on 15 healthy subjects (N), 12 subjects with impaired glucose tolerance (IGT), 20 non-insulin-dependent diabetics (NIDDM) and 13 patients with chronic pancreatitis (CP). The coefficient (μU/mg) for insulin secretion depending on blood glucose concentration in IGT, NIDDM and CP were lower (35.9 ± 2.7, 24.5 ± 3.3, 43.1 ± 3.1) than in N (77.5 ± 7.9). The coefficients (μU · min/mg) for insulin secretion depending on rate of change in blood glucose concentration in IGT and NIDDM were significantly lower (6.5 ± 2.1, 3.8 ± 1.2) than in N (52.8 ± 8.8). The insulin sensitivity index (ISI; 10 −2 mg/(μU/ml) · kg · min) in NIDDM was lower (4.98 ± 0.75) than in N (11.37 ± 1.08). Administration of exogenous insulin did not significantly affect the value of ISI in N and NIDDM. ISI showed a tendency to increase (15.09 ± 1.92) in CP. It was demonstrated that the proposed model which estimates both insulin secretory ability and insulin sensitivity simultaneously is quite useful for analyzing the mechanism of impaired glucose tolerance.

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.

Dynamic Moisture Vapor Transfer through Textiles

Cotton, polyester, and a blend in plain woven, pure finish fabrics were studied to determine their influence on dynamic surface wetness and moisture transfer through textiles. A simulated sweating skin was used, over which were placed test fabrics incorporating a clothing hygrometer to continuously measure dynamic surface wetness. Moisture vapor concentration and its rate of change at both inner and outer fabric surfaces was determined. At the inner fabric surface facing the sweating skin, all-cotton fabric exhibited the slowest buildup of moisture vapor concentration, followed by the cotton/polyester blend. The all-polyester fabric showed the highest rate of change in moisture vapor concentration. These dynamic moisture changes differ from reports of little or no fiber effect when tested at equilibrium moisture transfer conditions. Indeed the equilibrium moisture vapor transfer also showed no significant fiber differences in this work. It is the short time, dynamic moisture vapor transfer that is believed to hold most promise for explaining wetness and moisture-related subjective sensations in human comfort of worn clothing. The newly modified clothing hygrometer provides a sensitive method for ascertaining dynamic surface wetness on both fabrics and clothing as worn.

Relationship between the concentration and rate of change of calcium and serum intact parathyroid hormone levels in normal humans.

We employed variable rates of infusion of EDTA or calcium gluconate to examine the relationships between the concentration and rate of change of serum total and plasma ionized calcium and serum immunoreactive intact PTH concentrations in normal subjects. Use of a sensitive immunoradiometric assay specific for PTH-(1-84) made it possible to determine the full range of PTH responses to perturbations in the extracellular calcium concentration. By progressively increasing the rate of administration of calcium gluconate or EDTA during rapid or slow infusions, linear rates of change in the serum calcium concentration were achieved in eight men. The slopes were 2-fold greater during the rapid infusions. Both the calcium infusions decreased serum PTH-(1-84) levels from a mean of 23.2 +/- 2.0 (+/- SE) to 6.4 +/- 1.0 and 5.6 +/- 1.0 ng/L for the rapid and slow infusions, respectively, with no obvious rate dependence. The rapid or slow EDTA infusions increased serum PTH levels to the same maximal extent (95.0 +/- 20.2 and 99.9 +/- 14.5 ng/L, respectively), also with no significant rate dependence. Thus, there was no effect of the rate of change of calcium on the PTH response, which was reflected in similar inverse sigmoidal relationships between PTH and serum total and plasma ionized calcium when the data for the slow and rapid infusions were pooled separately. Similar sigmoidal curves were found in normal women. These data suggest the feasibility of using calcium and EDTA infusions combined with an intact PTH assay to define the relationships between circulating levels of PTH-(1-84) and calcium in states of normal and deranged parathyroid physiology.

A high‐precision respirometer for measuring small rates of change in the oxygen concentration of natural waters

A computer‐controlled system is described that can detect very low respiration rates of planktonic organisms in unconcentrated samples of ocean water. The polarographic sensor used consumed &lt; 10−4 µmol O2 h−1 and thus required little stirring. Estimates of community respiration of −2.23±0.06 and −0.19±0.04 µM O2 h−1 were made during short‐term incubations of the waters of the middle and outer continental shelf of Georgia.

An assessment of the depletion technique for comparative measurement of phosphorus uptake in plants

This paper examines the depletion of a standard 32P solution by 221 plants, either cereals or clovers, as a means of determining the recognized parameters, Vmax, Km and Cmin, in the kinetics of phosphorus uptake, and attempts to relate them to comparative phosphorus uptake by the plants, with a view to recognizing the more efficient ones.No single depletion curve was found. The data were grouped into six distinct curve types, based on the change in solution concentration (C) with time (t) and the rate of change in concentration (dC/dt) with concentration. The six types were part of one general curve which could be separated into 3 phases.In Phase 1, solution concentration was non-limiting, and plant performance was the principal determinant in depleting the solution. In the second and third phases, plant performance became progressively less dominant and the solution concentration more dominant in determining the concentration of the remaining solution.For comparative phosphorus uptake purposes, it is suggested that only the initial rate of uptake (Phase 1) is worth measuring and that this has attendant difficulties; the issue whether these kinetic parameters are real, or measurements of the model selected, is raised and discussed.No relation was found between these kinetic parameters and the efficiency of phosphorus use by subterranean clover plants grown in soil. Despite these practical shortcomings, variability in uptake capability between individual plants, even of the same line, was demonstrated. This plant variability offers a new area of plant nutrition for exploitation.

THE EFFECT OF DEEP LEVEL TRAP ON PHOTO-TRANSIENT CHARACTERISTICS, EQUIVALENT NOISE CURRENT AND INCREMENT OF DRAIN CURRENT FOR FET

In this paper, based on the differential equations of Change rate of hole concentration for deep acceptor trap and excess hole located below quasi-Fermi level under equilibrium or non-equilibrium state (with light illumination), an exponential attenuation equation has been deduced. It is capable of explaining the effect of deep level trap on photo-pulse transient characteristics, satisfactorily. We indicate chat the deep trap is the primary cause of producing the long tail of attenuation curve. The photo-pulse transient characteristic curves of GaAs MESFET, GaAl-As TEGFET and Si JFET were measured. The experimental results could check the exactness of the theory. The effect of deep level depth ET, concentration NT and so on attenuation curves has also been discussed. The dependence of equivalent noise voltage Eeq on frequence for the above three devices were measured. The relations between equivalent noise current Ieq and f, and between Ieq and effect deep level concentration NT,eff were obtained using the equations in ref. (6). In this way, the effect of deep level trap on noise may be obtained. The relation between △NT,eff and drift of drain current △ID could be calculated. They were in well agreement with the experimental results. Hence, the increase of △ID also results from the deep level trap.

In vivo lipid peroxidation in man as measured by the respiratory excretion of ethane, pentane, and other low-molecular-weight hydrocarbons

A method for the collection and measurement of low-molecular-weight volatile hydrocarbons exhaled in human breath as a result of lipid peroxidation in vivo is described. Subjects breathed in a closed-circiut rebreathe system and samples were taken over a 2-h period, extracted, and analyzed by gas-liquid chromatography isothermally on a 3-m column of n-octane/Porasil-C. Immediately, prior to rebreathing subjects were equilibrated with scrubbed air containing very low ambient levels of hydrocarbons to eliminate the effects of previous exposure to hydrocarbon-contaminated environments. Only under these conditions could hydrocarbon exhalation be measured. In the rebreathe system C 3-C 5 hydrocarbon concentrations increased linearly initially but reached a steady state after 1.5 h while ethane did not approach equilibrium even after 2 h. The steady-state equilibrium was demonstrated to be due to tissue uptake and metabolism of the hydrocarbon gases. Ethane metabolism was slow, allowing calculation of the endogenous production from the initial rate of change in concentration and an experimentally determined total body solubility coefficient. Similar calculations for pentane were not valid as metabolism was rapid; therefore production was estimated from the equilibrium value reached after 2 h. Ethane production in six healthy subjects was calculated to be 95.1 ± 19.0 pmol/kg/h while equilibrium values for pentane were 120 ± 50 pmol/liter. This method now allows the quantitation in man of lipid peroxidation in vivo.

The dynamic property of glucagon secretion in response to blood glucose--analysis with the aid of the control theory using an artificial endocrine pancreas

The precise dynamic property of glucagon secretion in response to glucose concentration has not yet been elucidated, since in in vitro studies using pancreatic islets, the co-existence of pancreatic B cells modifies the mode of glucagon secretion, and in vivo studies, the exogenous insulin administration greatly affects pancreatic A cell function. In this study, to clarify the dynamic property of glucagon secretion in response to glucose concentration and the ability of glucagon to raise hepatic glucose production, an artificial endocrine pancreas was employed as a research tool. Our originally developed artificial endocrine pancreas prepared the glucagon and/or glucose infusion algorithm as the counterregulatory system. The principle of glucagon and glucose infusion algorithm is set as the proportional plus derivative modes of action to blood glucose concentration with time delay constant, as follows; Gn.I.R.(t) = Gp[BGp - BG(t - tau)] + Gd[-delta BG(t - tau)] + Gc G.I.R.(t) = Cp[BGp - BG(t - tau)] + Cd[-delta BG(t - tau)] where Gn.I.R.(t) and G.I.R.(t) are glucagon infusion rate and glucose infusion rate, respectively. BGp is the projected value of blood glucose concentration, and BG(t) and delta BG are blood glucose concentrations and the rate of change in blood glucose concentration at time t respectively. Gp and Gd are coefficients for glucagon infusion, and Cp and Cd are those for glucose infusion. Gc is the constant for basal glucagon supplementation. tau(min) is the time delay constant for glucagon and glucose infusion. In a depancreatized dog, the blood glucose concentration was maintained at the normoglycemic level with intraportal insulin infusion using this artificial endocrine pancreas for at least one hour, then hypoglycemia was induced by iv bolus insulin injection (0.1 U/kg). Glucagon was infused intraportally or glucose was infused into the peripheral vein when the counterregulatory system was operated according to each of these algorithm by variously changing the parameters. In the intraportal glucagon infusion algorithm, with the optimal parameters based on proportional plus derivative modes of action with a 10-min time delay (Gp/Gd/Gc/tau = 0.2/0.4/0.6/10), both the blood glucose response curves and plasma glucagon profiles simulated those seen in normal dogs. On the other hand, glucagon infusion based only on the proportional action failed to simulate the blood glucose response and plasma glucagon profile of normal dogs. When glucose was infused on the basis of the proportional action with a 20-min time delay (Cp/Cd/tau - 0.2/0/20), the insulin-induced hypoglycemia in depancreatized dogs could be restored to normoglycemia in the sa

A mathematical insulin-secretion model and its validation in isolated rat pancreatic islets perifusion

A mathematical insulin-secretion model was constructed by analyzing the glucose-induced insulin secretion using a control theory. To validate the model, experimental data obtained in the isolated rat pancreatic islet perifusion system were compared with the simulation results. The simulation study of the model was found to fit quite well to insulin responses under various experimental conditions. A glucose-induced insulin secretion from pancreatic islets' β cell was found to be expressed as a function of proportional plus derivative response to glucose input with the first order time lag. And the negative rate of change in glucose concentration was found to suppress insulin secretion to the extent of the negative stimuli, regardless of glucose concentration. This model would be useful as a research tool for analysis of physiological significance of insulin secretory dynamics and clinical investigation of insulin secretion.

Rate of Dust Decay as Affected by Relative Humidity, Ionization and Air Movement

ABSTRACT THE rate of change in airborne dust concentration was investigated for the effects of various air-circulation rates, ionization levels with and without charged collection plates, and humidity levels in an environmental chamber. An increase in air circulation rate and ionization levels showed a significant increase in the removal of airborne dust. Relative humidity showed little effect on dust-removal efficiency.

Handling of inspired vaporized ethanol in the airways and lungs (with comments on forensic aspects)

Collections of expired air and chemical determinations of ethanol concentrations in inspired and expired air showed that during prolonged inspiration of ethanol (vapour)-containing air about 55% was absorbed by adult human subjects. The fractional absorption was not detectably affected by variations in tidal volume (0.7–2.1 liters), nor was it significantly reduced in experiments where, due to preceding oral intake, the ethanol concentration of systemic blood was up to 50 times higher than that of inspired air. In these experiments the difference between the rates of change in blood alcohol concentration ( β 60) during and before ethanol inhalation agreed well with values calculated from measured respiratory absorptions. Mass spectrometric recordings of ethanol concentration in expired air vs. expired volume, taken in a state of steady uptake, also gave absorption fractions of about 0.55, and showed that the concentration in end-expiratory air did not fall below some 30% of that of the inspired air. These and other findings show that a large part of ethanol being inspired is deposited in the airway linings to be released again to ethanol-free alveolar air expired through the airways. It is concluded that inspired ethanol deserves consideration as a source of elevations of blood alcohol concentrations.

The development of a counterregulatory system for an artificial endocrine pancreas--invention of glucose and glucagon infusion algorithms

To accomplish an artificial endocrine pancreas system by adding a glucose and glucagon infusion mechanism in the artificial beta cell developed originally in the First Department of Medicine, Osaka University Medical School, glucose and glucagon infusion algorithms were invented.The principle of glucose or glucagon infusion algorithm is determined as the proportional plus derivative modes of action to blood glucose concentration with a time delay constant, as follows : GIR (t) = Cp [BGp - BG (t-T)] + Cd [-_??_BG (t-T)]GnIR (t) = Gp [BGp - BG (t-T)] + Gd [-ABG (t-T)] + Gc where GIR (t) and GnIR (t) are the glucose infusion rate (mg·kg-1min 1) and glucagon infusion rate (ng.kg-1.min-1), respectively. BGp is the projected value of blood glucose concentration (mg/100ml), and BG (t) and _??_BG (t) are blood glucose concentration at time t (mg/ 100ml) and the rate of change in blood glucose concentration at time t (mg·100ml-1), respectively. Cp and Cd are coefficients for glucose infusion, and Gp and Gd are those for glucagon infusion. Gc is the constant for basal glucagon infusion supplementation. T (min) is the time delay constant for glucose and glucagon infusion.The validation of these algorithms were attempted in depancreatized dogs. In dogs, hypoglycemias were induced by iv bolus insulin injections, then a counterregulatory system was operated according to each of these algorithms.The following results were obtained : 1) When glucose was infused on the basis of the proportional action with a 20-min time delay (Cp/Cd/T = 0.2/0/20), the insulin-induced hypoglycemia in depancreatized dogs could be restored to normoglycemia in the same manner as seen in normal dogs.2) A speedier and less fluctuating restoration to normoglycemia could be obtained when the glucose was infused on the basis of a proportional plus derivative mode of action with a 4-min time delay (Cp/Cd/T = 0.5/0.5/4).3) In glucagon infusion algorithm, with the optimal parameters based on proportional plus derivative modes of action with a 10-min time delay (Gp/Gd/Gc/T = 0.2/0.4/0.4/10), both the blood glucose response curves and plasma glucagon profiles simulated perfectly those seen in normal dogs.4) When glucagon was infused on the basis of proportional plus derivative modes of action without the time delay (Gp/Gd/Gc/T = 0.5/0.5/0.4/0), hypoglycemias rarely occurred in spite of iv insulin injections with the least glucagon infusion amount.These results clearly indicate that an artificial endocrine pancreas system characterized with glucose or glucagon infusion algorithm constitutes a clinically useful device not only as a safety control against hypoglycemia, but it also enables adaptive and optimal glycemic controls. In addition, by applying these algorithms, an artificial endocrine pancreas system becomes a powerful research tool for such investigations as the dynamic property of the pancreatic a cell in glucagon secretion against blood glucose, the analysis of the effects of hormones on the glucoregulatory system and for the glucose clamp method.

Permeation of nitrogen and oxygen into polymer gas- sampling bags

An expression is derived for the rate of change in gas concentration within a polymer bag caused by permeation through the walls of gases from the surrounding air. The rates of permeation of nitrogen and oxygen into such bags have been measured by gas chromatography and fitted to the theoretical expression to give an estimte of the permeation coefficients. These coefficients are compared with known values for the polymers involved. The significance of the results is discussed with regard to the purity of samples stored in gas-sampling bags.

Effects of lung inflation on alveolar epithelial solute and water transport properties.

Paired hollow bullfrog lungs (Rana catesbeiana) were used to study the effects of lung inflation on alveolar epithelial transport of water and hydrophilic solutes. Frogs were double pithed and the lungs were removed after bronchial placement of a Lucite plug. Three openings in the plug accommodated the insertion of two agar-Ringer bridges (for electrical potential measurement and passage of direct current) and the injection and removal of alveolar bathing fluid. Ringer solution containing a tracer quantity of radioactive solute was instilled into the lung sacs (5 ml or 50 ml) and the lungs were suspended in baths of Ringer solution containng appropriate cold solutes (5 mM). Permeability properties of each solute (and water) were determined from the rate of radiotracer concentration change in the bath. The spontaneous potential difference, tissue resistance, and solute permeability properties determined in these experiments showed no significant differences between the 5- and 50-ml lungs. Assuming homogeneous, cylindrical water-filled pores to be present in the tissue, the equivalent pore radii estimated from the rates of solute and water fluxes were 1.1 (for 5-ml lungs) and 0.9 nm (for 50-ml lungs). After overinflation of the lung (to greater than 80 ml), experiments at 50 ml yielded a pore radius of 3.4 nm. These data suggest that passive alveolar epithelial transport properties do not change with degrees of lung inflation normally encountered in vivo but that overinflation can lead to increased leakiness of the barrier.

Effects of interruption of the enterohepatic circulation of bile acids on the transport of very low density-lipoprotein triglycerides

An increase in plasma very low density lipoprotein-triglycerides (VLDL-TG) is seen frequently during treatment with bile acid-binding resins. The purpose of this study was to determine whether this increment in VLDL-TG is due mainly to an increase in synthesis of VLDL, or to an enhanced catabolism. Three types of patients were studied: (1) 7 normotriglyceridemic subjects. (2) 4 obese patients, and (3) 9 hypertriglyceridemic patients. Before treatment they underwent a study of VLDL-TG kinetics that employed multicompartmental analysis of specific activity curves following injection of 3H-glycerol. The patients were then treated with a bile acid-binding resin, either cholestyramine or colestipol, for several weeks to several months. At the end of the treatment period, they were readmitted to the hospital for a second study of VLDL-TG kinetics. The patients showed a variable response to resin therapy. Many had an increase in concentrations of VLDL-TG, but others had no change or even a slight decrease. However, analysis of the data showed a high correlation between change in production rates of VLDL-TG and change in concentration. Also, when the data for the 20 patients were combined, there was a statistically significant increase in both synthetic rates and concentrations of VLDL-TG; in contrast, the fractional catabolic rate (FCR) was unchanged by therapy. Therefore, our data show that when treatment with bile acid sequestrants causes an increase in plasma VLDL-TG, the increase is due to an increment in production and not to a decrease in catabolism.

The Chemistry of Flames

Combustion scientists are primarily concerned with the fuels most often burned as energy sources (coal, petroleum products, and natural gas), with the goal of learning to burn them as efficiently, intensely, and cleanly as possible. Discovering those slight rearrangements of chemical bonds that together account for the net chemical transformation is the key to understanding how combustion proceeds. Once these reactions have been defined, the chemist can determine the rate coefficient of each reaction as a function of temperature and assemble the information into flame models. The computer programs that use these models to predict experimental results combine two sets of equations describing (1) the diffusive and reactive rates of change in concentration of all the molecules in the flame and (2) the flow of the reacting gases. Although the details of hydrocarbon-flame models are still disputed, many of their general features are clear and the basic reactions well-known; computer models for methane combustion already include over 100 elementary reactions. Experimental data on NO/sub x/ formation have led to ingenious methods for purifying postcombustion gases. Currently, the two most actively studied processes in combustion chemistry are the formation and oxidation of soot. The synthetic fuels most likely to replace fossilmore » ones will probably contain less hydrogen, making them more prone to produce soot. How to understand and overcome this problem will be the next challenge for combustion chemists and engineers.« less