Effects Of Concentrations Research Articles

Epithelial modulation of preterm airway smooth muscle contraction.

To determine if epithelium from immature airways can modulate the responsiveness of smooth muscle, we studied paired trachealis muscle strips from preterm sheep. The epithelium was removed from one strip and left undisturbed in the other. Concentration-effect (CE) curves to acetylcholine (ACh), KCl, and isoproterenol were obtained. To evaluate maturational effects, responses to ACh and isoproterenol were studied in trachealis strips from adult airways. Maximal stress (Po) to ACh increased after epithelium removal in preterm (P < 0.05) but not adult strips. Epithelium removal caused a leftward shift of the ACh CE curves in both preterm and adult strips (P < 0.001) and a decrease in the dose required to achieve a one-half maximal response (ED50) in both preterm (P < 0.005) and adult strips (P < 0.05). The magnitude of the change in Po as well as in the ED50 for ACh between preterms and adults was similar. Epithelium removal did not alter either the Po or the CE curves of preterm strips stimulated by KCl. Response to isoproterenol in precontracted strips was enhanced in the presence of an intact epithelium in both groups (P < 0.05). These data demonstrate that preterm airway epithelium is able to modulate the responsiveness of smooth muscle. Additionally, the magnitude of the effect is unchanged with maturation. We speculate that damage of airway epithelium from mechanical ventilation may contribute to the increased incidence of airway hyperreactivity observed in preterm infants.

Absence of denervation supersensitivity to neurokinin A in the rat vas deferens

1. 1. Unilateral denervation of the rat vas deferens (RVD) was performed under anesthesia. The animals were allowed to recover 4 or 10 days and then concentration-effect (C-E) curves to noradrenaline (NA) and neurokinin A (NKA) were constructed in denervated and control RVD. 2. 2. Tissues denervated 4 or 10 days produced NA responses shifted 20-fold to the left with maxima 130% of control. 3. 3. NKA C-E curves in denervated RVD were not significantly different from control. 4. 4. Phenylephrine exhibited a 6-fold increase in tissue sensitivity after denervation. 5. 5. Chronic denervation of the vas deferens resulted in significant postsynaptic supersensitivity to α 1-adrenoceptor agonists but not to NKA.

Concentration, Unionism, and Labor Earnings: A Sample Selection Approach

Using a simultaneous equations model of wages and union membership, the elasticity of the wage with respect to market concentration is estimated to be approximately 0.2. The estimate uses a large data set and extensive controls to measure concentration's direct effect on the wage, an indirect effect through unionization, and a feedback effect. The indirect effect represents the majority of concentration's effect. Copyright 1988 by MIT Press.

Industrial Concentration and Interindustry Wage Determination

THE hypothesis that firms with market power pay higher wages than competitive industries has implications that are important to many areas of policy. If firms with market power do pay higher wages, the excessive portion of those wages would be a rather large addition to the social costs of monopoly. In addition, wages that are inconsistent with labor market characteristics and not uniformly sensitive to business cycles will hamper the implementation of macroeconomic stabilization programs. Previous studies in this area have usually tested the market power hypothesis by determining the relationship between industry concentration and industry wages.' In addition, studies focusing upon other aspects of interindustry wages, such as the effect of unions2 and plant size3 have included concentration as an explanatory variable in their models. Results of these studies have differed with respect to their findings on the importance of concentration. Some studies found concentration to be important in the wage determination process while others did not. The research reported in this article indicates that the concentrationwage relationship changes significantly over the business cycle making cross sectional studies sensitive to the year used for the analysis. This finding is consistent with the results of models developed to describe the wage determination process over time. The method of analysis used here focuses upon the concentration-wage relationship at two points in the business cycle. A cross sectional test of a model of interindustry wage determinants in manufacturing is presented for the years 1958 and 1967. The results of these tests indicate that six independent variables can explain over 72% of the variation in wages found in each of the two test years, with each of the six coefficients statistically significant in both years. However, the impact of the independent variables change considerably over the business cycle. Of particular interest are findings that support the hypotheses (1) that concentration's effect upon wages appears to change over the business cycle, thus providing support for the spillover hypothesis and (2) that the wage-concentration relationship is not linear.

The Study of The Effect of Concentration of The Agar-Agar Solution on The Rheological and Thermo Rheological Behavior

The purpose of this work is to study the effect of concentration and temperature of agar agar solution on the rheological behavior of a complex fluid (agar agar solution) used on a capillary rheometer. The rheological properties of agar solution were studied, in particular the concentration's effect (0.1%, 0.15%, 0.17% and 0.2%), and temperature (20°C, 30°C, 40°C, 50°C, 60°C and 70 °C) on the rheological behaviour of the agar agar solution. A comparative study of various rheological laws (Herschel-Buckley, Cross, Oswald De Waele, Bingham) was made, to etablish a model that presents the rheological behavior which applies to different samples of agar agar solution, based on the coefficient of correlation. Results indicated that the rheological behavior of agar agar solution depends on the range of shear rate used : for low shear rate (lower than 6.2 s-1) the solution of agar agar can be modeled by an Ostwald-De Waele-type power-law, but for the high shear rate (higher than 6.2 s-1) the solution of agar agar can be described by Bingham's model. The concentration's and temperature's effect of agar agar solution on the two models studies's parameters (Ostwald-De Waele, Bingham) was studied.We observe a decrease of consistency index 'k' as a function of temperature, this decrease is more accentuated for temperatures ranging from 20 to 40 °C. On the other hand, above 40°C the decrease in the consistency index with temperature is less sensitive. The consistency index increases a function of concentration. the increase in the concentration of agar agar has a positive effect on the critical stress and plastic viscosity and the critical constraint ?_c and plastic viscosity ?p at high shear rates, decrease with increasing temperature.