Regression In Function Research Articles

An Experimental Study of Saturated and Unsaturated Permeabilities in Resin Transfer Molding Based on Unidirectional Flow Measurements

Resin transfer molding (RTM) is a manufacturing process of composite parts that consists of injecting a fluid resin through a fibrous reinforcement. Permeability of the fiber bed is a key parameter that governs the flow, together with the viscosity of the resin. In this paper, the saturated and unsaturated permeabilities of a glass-woven fabric are studied for different injection pressures and porosities of the fibrous reinforcement. Unidirectional injection experiments are carried out to evaluate the unsaturated permeability of the reinforcement during the injection and the saturated permeability that governs the permanent flow established after filling of the cavity. The unsaturated permeability is evaluated by a linear regression in function of the position of the resin front during transient flow experiments performed at constant injection pressure. For each position of the resin front in the test mold, a transient permeability can be calculated by application of Darcy’s law. This transient permeability depends on the injection pressure, position of the resin front in the mold, and porosity of the reinforcement. After a certain flow length called the convergence length, the transient permeability converges to a value that is independent of the flow rate and of the injection pressure. This limit value is called here the unsaturated permeability. The convergence length is related to a maximum flow rate or average particle velocity below which Darcy’s law holds. The saturated permeability is measured after all air bubbles have been evacuated from the cavity. As a result of this experimental investigation, three parameters can be identified that are characteristic of the pore structure of the fibrous reinforcement: (1) a maximum average resin velocity can be identified below which the transient permeability remains constant; (2) the saturated and unsaturated permeabilities differ by a value that remains constant within the injection pressure range used in this study and that is independent of the fiber volume content; (3) the new notion of convergence length proposed here, namely the flow length necessary to ensure convergence of the transient permeability, depends on the two-scale pore structure of the fibrous reinforcement. This study corroborates the findings of several other investigators, who have shown that the saturated permeability is always higher than the unsaturated permeability. The difference between these two permeability values is also related to the pore structure of the fiber bed. It is hoped that this work will contribute to define a much-needed standard on permeability measurements.

The Relationship between Q-wave Regression and Improvement in the Left Ventricular Systolic Function after an Anterior Wall Acute Myocardial Infarction

Background and Objectives:An abnormal Q wave, after an acute myocardial infarction, has been considered an indicator of myocardial necrosis. However, in some cases this Q wave partially or completely disappears during the evolution of the myocardial infarction. The clinical significance of Q wave regression remains to be established. Accordingly, this study was conducted to evaluate the relationship between Q wave regression, after an anterior wall acute myocardial infarction, and the improvements of the regional wall motion abnormality and left ventricular ejection fraction in echocardiography. Subjcets and Methods:A total of 80 patients, who presented with a first anterior wall acute myocardial infarction, managed successfully with direct intervention, were divided into two groups according to the regression (group A) or presence (group B) of abnormal Q waves. Regression of an abnormal Q wave was defined as the disappearance of the Q wave and reappearance of the R wave ≥0.1 mV, in at least two of the I, aVL, and V1 to V6 leads. Results:Of the 80 patients, 26 (32.5 %) had an abnormal Q wave regression within 12 months. The peak creatine kinase-MB activity was lower in group A than B (277.3±202.6 vs. 521.3±284.4 ng/dL, p<0.01). Group A had better left ventricular regional wall motion than group B in the initial echocardiograms. The degree of improvement of the left ventricular ejection fraction and regional wall motion between the initial and follow-up echocardiographies were significantly greater in group A than B. Conclusion:Patients with an anterior wall acute myocardial infarction, showing Q wave regression, tended towards a smaller amount of necrotic myocardium and a significantly larger amount of stunned myocardium. (Korean Circulation J 2004;34(4):356-361)

Alterations in Left Ventricular Diastolic Filling Patterns after Aortic Valve Replacement in Patients with Aortic Stenosis: Relation to Functional Class

To determine the changes in left ventricular diastolic filling velocity profiles after aortic valve replacement and their relation to clinical functional status, 48 consecutive patients with severe aortic stenosis underwent preoperative cardiac catheterization and Doppler échocardiographie assessment before and 3 months after surgery. The patients were divided into two groups according to the functional class. Group I included 15 patients in New York Heart Association functional class I or II, and group II consisted of 33 patients in functional class III or IV. Before the operation, the left ventricular peak early filling velocity was higher, and the later atrial filling velocity was lower in group II than in group I. The ratio early/late filling velocities was higher and the deceleration time was shorter in group II patients. For overall 48 patients, the Dopplerderived left ventricular filling variables correlated significantly with functional class, pulmonary artery pressure, and left ventricular systolic function. After aortic valve replacement, early filling velocity (71 ± 22 vs. 85 ± 22 cm/s; p < 0.001) and early-to-late filling velocity ratio (0.70 ± 0.14 vs. 0.88 ± 0.23; p < 0.001 ) increased in group I, but decreased in group II (early filling velocity 92 ± 26 vs. 80 ± 25 cm/s; early-to-late filling velocity ratio 1.60 ± 0.90 vs. 0.90 ± 0.30; all p < 0.001). The improvement in functional class was closely related to changes in early-to-late filling velocity ratio (p < 0.02), but did not correlate with myocardial mass regression and changes in left ventricular systolic function. This prospective study indicates that left ventricular diastolic filling is often impaired in patients with aortic stenosis and contributes to the reduced functional capacity. Aortic valve replacement alters favorably the left ventricular diastolic function and, therefore, the patients' symptomatology.

Endocrine and Testicular Changes Associated with Season, Artificial Photoperiod, And the Peri-Pubertal Period in Stallions

The seasonal reproductive cycle of stallions is characterized by an annual regression and recrudescence in testicular function and concentrations of LH, FSH, and testosterone in serum. Maximum reproductive capacity occurs during the increasing day lengths of spring and summer. The annual cycle in LH secretion may reflect a seasonally associated and photosensitive reduction and replenishment in pituitary content of LH. Similar to other seasonal breeders, it appears that stallions may possess an endogenous circannual rhythm in reproductive function that is subject to manipulation by altering the light:dark ratio, i.e., photoperiod. The application of a long-day photoperiod (16 hours light:8 hours dark) in December, following 20 weeks of short days (8 hours light:16 hours dark), was effective in hastening the seasonal sexual recrudescence of stallions but was not effective in prolonging the interval of heightened reproductive capacity. The infantile period in colts lasts approximately 32 weeks and is characterized by low gonadotropin concentrations and little gonadal activity. The start of the pre-pubertal period is marked by changes in the hypothalamic-pituitary axis which result in increased amounts of LH and FSH secretion between 32 and 40 weeks of age. Testosterone concentrations in serum exhibit a dramatic increase at 75 to 80 weeks of age, with puberty (defined as the age when the first ejaculate was obtained containing a minimum of 50 x 10(6) sperm with greater than or equal to 10% progressive motility) occurring at 83 weeks of age.

Communication and Oral‐Motor Function in Rett Syndrome

The communication skills, oral-motor function and respiration patterns of 20 girls with Rett syndrome were studied. Loss of communication has been previously recognized as a sign of the onset of Rett syndrome, but oral-motor dysfunction has not been reported. All the girls showed a regression in speech and language function by the onset of stage II Rett syndrome. Changes in oral-motor function and respiration correlated with the progression of the disease from stages II to IV.

Effects of glyceryl trinitrate on functionally regressed newly developed collateral vessels in conscious dogs.

The effects of glyceryl trinitrate on collateral blood flow and regional myocardial function during a 2 min coronary occlusion were evaluated in 10 conscious dogs with well developed collateral vessels. Collateral growth was promoted by brief, repeated, reversible coronary occlusions. After partial regression in collateral function a small dose of glyceryl trinitrate (5 micrograms.kg-1) was injected intravenously 1 min before coronary occlusion. After pretreatment with glyceryl trinitrate the collateral blood flow velocity (mean[SD]) increased from 3.0(0.9) to 4.4(1.4) cm.s-1 (p less than 0.05). After 2 min of occlusion the percentage systolic subendocardial segment shortening in the collateral dependent zone increased from 7.8(6.1) to 12.6(6.7)% (p less than 0.05). The blood flow debt repayment after release of the occlusion decreased from 122(41) to 68(34%) (p less than 0.05). Thus in conscious dogs with regressed newly developed collaterals a major component of the beneficial effects of glyceryl trinitrate on collateral circulation is dilatation of collateral vessels, as evidenced by a pronounced increase in collateral blood flow and myocardial function during a transient period of coronary occlusion.

Effect of five years' ageing on ventilatory capacity and physical work capacity in elderly people.

Abstract. The effect of five years' ageing on the ventilatory capacity and physical work capacity is studied on a sample of apparently healthy individuals of ages 57–71 years, representative of the population. The physiological functional regression for maximal expiratory volume per 1.0 second and maximal voluntary ventilatory capacity was about 6–9% for both sexes, and for physical work capacity somewhat greater, viz. 9–13% for the men and about 10–25% for the women. This finding is assumed to be due to the fact that the regression in physiological function takes place more rapidly for the circulatory than for the respiratory system. In this series a correlation, which has not been reported previously, was found between work load at a given pulse rate and age.