Showing papers by "Katholieke Universiteit Leuven published in 1974"

Thermoelasticity, pseudoelasticity and the memory effects associated with martensitic transformations

Abstract: The pertinent thermodynamic relations, nucleation and growth and the influence of stress are considered and applied to thermoelasticity and the memory effects.

The rheological properties of suspensions of fibres in Newtonian fluids subjected to extensional deformations

Abstract: Data are presented for the extensional flow of suspensions containing 0.1−1 % of fibres by volume. The aspect ratio of the fibres was varied from 280 to 1260. The observed stress levels were between one and two orders of magnitude greater than in shearing flow, in agreement with the a priori predictions of Batchelor (1971).

Heat conduction model for the calculation of the volume of molten metal in electric discharges

Abstract: The craters obtained by electric sparks in electro-discharge machining are numerically calculated by use of a thermal model. The computational procedure is based on the exact solution of the related two-dimensional transient heat conduction problem in a finite or semi-infinite body subjected to a stepwise or time-dependent uniform heat flux over a small circular part of its upper surface. Optimal geometrical conditions, relative to a fast convergence and negligible influence of the boundaries, are demonstrated. By superposition of rectangular heat flux pulses over circular parts with different diameters, the influence of the channel widening can be investigated. It is shown that a theoretical model should include the possibility of accounting for the plasma channel widening in order to obtain acceptable agreement with experimental data or to predict the optimal operating conditions.

Viral Infection and Host Defense

Abstract: Double-stranded RNA, made as an intermediary substance in the replication of most, if not all, viruses, may play a much more important role in the pathogenesis and the recovery from virus infections than has hitherto been suspected. Apparently, dsRNA is used by both the challenge virus and the host cell in an attempt to gain "molecular control." Double-stranded RNA exerts a set of effects, which may be well balanced, not only at the level of the individual cell but also at the complex assemblage of these cells termed the organism (Fig. 1). In the cell, interferon synthesis is triggered, although interferon mRNA translation may not occur if dsRNA shuts off protein synthesis too quickly. In the whole organism, the disease severity will depend on how certain toxic reactions evoked by infection (such as cell necrosis and fever) are counterbalanced by an increase in the host defense mechanisms (for example, immune responsiveness and interferon production). Many aspects of the response, relating to either progress of, or recovery from, the disease, can be explained on the basis of a dsRNA. In addition to drawing attention to the biodynamic role of dsRNA, our hypothesis suggests specific experimental vectors designed to enhance our information on the molecular basis of the morbid process which occurs with viral infection. Finally, we suggest that, although the dsRNA molecule may be viewed as a rather simple unit structure, the opportunity for further diversity in the biological activity of a given dsRNA molecule always exists. Namely, each deviation from a perfectly double-helical arrangement introduces the possibility for emphasizing one biological reactivity at the expense of another. This latter structure-activity property may partially account for the extreme apparent diversity, commonly encountered, in the presentations of virologic illness. Appendix note added in proof. Subsequent to submission of this text, we have found that the potent mitogen effect of dsRNA for lymphocytes (murine and human) is also exquisitively sensitive to the fidelity in base pairing of the input polymer pair (59). For example, infrequent "loops" (one nucleotide per 20 base pairs) in an otherwise perfectly helical rI(n) (.) rC(n) molecule [for example, rI(n) (.) r(C(19,)U)(n)] strongly changes its mitogenic properties. This observation, which supports our thesis that a "fine structure" term can be developed for other reactions triggered by dsRNA's in biological systems, emphasizes that diverse biological effects may be encountered with an ostensibly uniform family of dsRNA's.

Electrogenic sodium pump in arterial smooth muscle cells.

Abstract: 1. The membrane potential, the tension development and the42K-efflux were studied in the ear artery of the rabbit under different experimental conditions. 2. K-free solution depolarized the cells. Readmission of K in the external medium caused a transient hyperpolarization. 3. Ouabain 10−5 M also depolarized the cells. On washing out the ouabain the membrane potential gradually returned to its control value. 4. Tension development appeared simultaneously with the depolarization, but it subsided during prolonged depolarization. 5. K-free solution and ouabain induced a small increase of the rate coefficient of K-efflux from the ear artery. This effect appeared later than the depolarization or the tension development. These changes of42K-efflux make a rapid change of (Na)i unlikely. 6. It is concluded that the electrogenic Na-pump plays an important role in maintaining the membrane potential of arterial smooth muscle cells. All procedures which inhibit this pump, induce a depolarization of the cells and thereby a tension development. There is no experimental evidence in favour of the hypothesis that the inhibition of a Na−Ca exchange system would be the primary event in inducing contraction under our experimental conditions.

Parathyroid Function in Patients with Hyper- or Hypothyroidism

Abstract: The function of the parathyroid glands was assessed in 5 hypothyroid patients, 5 hyperthyroid patients and 13 controls before as well as during and after an infusion of disodium EDTA. Serum calcium levels are significantly higher in hyperthyroid patients than in hypothyroid patients, normal controls having intermediary values. Serum phosphorus values, both in basal conditions and during or after EDTA infusion, are increased in hyperthyroid patients compared with hypothyroid or control patients. Serum parathyroid hormone levels, measured with two different antisera, are significantly lower in hyperthyroid than in hypothyroid patients. It is suggested that functional hypoparathyroidism prevails in hyperthyroidism, while parathyroid function is normal or increased in myxedema.

Influence of interferon on virus-particle synthesis in oncornavirus-carrier lines. II. Evidence for a direct effect on particle release.

Abstract: Interferon treatment of murine C-type oncornavirus carrier lines results in a drastic inhibition of extracellular virus formation. When such cells are subcultured in the presence of interferon, synthesis of extracellular C-type virus remains depressed until the interferon treatement is discontinued. Cell-associated virus as seen in the electron microscope or as detected by uridine incorporation is not proportionally inhibited. Several possibilities to explain this discrepancy are tested. The most likely hypothesis is that interferon treatment primarily inhibits virus release.

Synthetic interferon inducers.

Abstract: 4. Structural Requirements for Interferon Induction by Synthetic Interferon Inducers . . . . . . . . . . . . . . . . . 183 4.1. Polycarboxylates . . . . . . . . . . . . . . . . 183 4.2. Polynucleotides . . . . . . . . . . . . . . . . . 184 4.2.1. Sufficiently High Molecular Weight . . . . . . . . 184 4.2.2. Stable, Highly Ordered Secondary Structure . . . . . 186 4. 2.3. Differential Importance of Constituent Homopolymers in Poly(I). Poly(C) . . . . . . . . . . . . . . 188 4.2.4. Adequate Resistance to Nucleolytic Degradation 190 4.2.5. Presence of 2'-Hydroxyl Groups . . . . . . . . . 192 4.3. Low Molecular Weight Compounds . . . . . . . . . . 194

Crystallization of poly(ethylene terephthalate) induced by inorganic compounds. I. Crystallization behavior from the glassy state in a low‐temperature region

Abstract: The kinetics of isothermal crystallization from the glassy state at low temperatures and the morphology of poly(ethylene terephthalate) (PET) filled with additives are reported. Talc, kaolin, silicon oxide, and titanium oxide have been used as fillers; they act as effective nucleating agents for PET. The overall rate of crystallization depends on the volume concentration, the size distribution, and the nucleating ability of the additives. An electron microscopic study reveals a transcrystalline morphology at the surface of the filler particles. The occurrence of transcrystallinity is attributed to extensive heterogeneous nucleation induced at the filler surface. From the shape of the crystallization isotherms, it can be concluded that the crystallization mechanism depends on the type of filler.

Subcutaneous adipose tissue and lipids in blood in growth hormone deficiency before and after treatment with human growth hormone.

Abstract: Extract: This study was undertaken to evaluate adipose cell size and number and subcutaneous fat and blood lipids composition in hypopituitary patients before and daring treatment with human growth hormone (HGH). The investigations were performed in 14 prepubertal children 6–17 11/12 years of age, with idiopathic hypopituitarism. Human growth hormone was administered successfully to 6 of these 14 patients for at least 1 year. Before HGH treatment there was a significant reduction of adipose tissue cell number according to chronologic age and to skeletal age. The average adipose cell size was significantly larger than normal. A significant correlation between subcutaneous adipose cell mean weight and tricipital and subscapular skin fold thickness, similar to that observed in normal children, was observed. The distribution of fatty acids in the subcutaneous fat and in the blood lipid composition was normal. During the 1st and 2nd year of HGH treatment, the total number of adipose cells increased rapidly. There was also a highly significant reduction of the average adipose cell size after the 1st year. A significant reduction of the fatty acids unsaturated fraction was observed after the 1st year without further changes after the 2nd year of treatment. The blood lipid composition did not change significantly after either 1 or 2 years of HGH treatment. Speculation: The striking increase in total number of adipose cells observed during HGH administration in hypopituitary patients tends to prove that the adipose tissue organogenesis is not limited to a finite period ending after the 1st year of life. The modifications in composition of adipose tissue triglycerides induced by long term treatment with HGH would mean that the several components of the fatty acid pool are differentially liberated.

Formation and regeneration of Penicillium chrysogenum protoplasts

Abstract: 1. High yields of protoplasts from Penicillium chrysogenum Wisc. 49,2105 were obtained by using a combined enzyme system containing either Cellulase from Oxoporus plus an extract of Helix pomatia gut juice, or cellulase plus an enzyme preparation from the culture filtrate of Streptomyces graminofaciens ATCC 12,705. When 15 h old mycelium was incubated with one of these enzyme systems in 0.55 M NaCl at pH 5.6 nearly all of the mycelium was transformed into protoplasts within 4–5 h. 2. The process of protoplast regeneration was studied both on solid and in liquid media. Approximately 50% of the protoplasts regenerated within 8–10 h. Addition of yeast extract to the medium accelerated the speed of regeneration. Microscopically, 3 patterns were seen by which protoplasts could regenerate to normal mycelium.

Triple Crossover Study on Absorption and Excretion of Ampicillin, Pivampicillin, and Amoxycillin

Abstract: Talampicillin and amoxycillin were shown to be absorbed twice as well as ampicillin in a triple crossover experiment.

Induction of polyoma tumors in athymic nude mice.

Abstract: We verified the oncogenic effect ofpolyoma virus in gnotobiotic nude (nu/nu) mice compared to their gnotobiotic normal counterparts (nu/+). The nude mice were found to be much more sensitive to the oncogenic activity of the virus than were their heterozygote counterparts. This increased sensitivity is illustrated by the short latent period and by the high incidence of polyoma tumors in the nude mice inoculated with the virus several weeks after birth at a time when the nu/+ mice are completely resistant to polyoma oncogenesis. Moreover, the cytolytic lesions observed in the kidney and in the salivary glands were also much more conspicuous in the nude mice. The results are discussed in relation to the role of immune surveillance in oncogenesis.

Development of teratomas from displaced visceral yolk sac.

Abstract: A surgical procedure for the induction of extra-uterine teratomas in pregnant R rats is described. These teratomas originate from the visceral yolk sac and are characterized by the presence of a variety of well-differentiated tissues. The tumors have the histological and ultrastructural morphology as well as the biological characteristics of benign teratomas. Their origin and development are discussed in relation to the multipotentiality of yolk-sac cells.

Immunochemical quantitation of human transcortin.

Abstract: Serum transcortin levels were measured by single radial immunodiffusion using a monospecific antihuman transcortin rabbit serum. The results of this direct determination closely correlate with those obtained indirectly by assessing the cortisol-binding properties of transcortin. This immunochemical method allows transcortin quantitation in the presence of cortisol excess and has the additional advantage of being temperature independent.

Effects of octanoate and oleate on energy metabolism in the perfused rat liver

Abstract: The effects of octanoate and oleate were studied in the isolated fasted rat liver perfused without substrate and were compared with the effects of lactate. Measurements were made of hepatic adenine nucleotide content, formation of ketone bodies, urea and glucose and uptake of fatty acids, lactate and oxygen. Calculations of the Krebs cycle activity and the flux through the oxidation at C-3 were carried out. Comparing the extra oxygen consumption with extra ATP needs after addition of the fatty acids or lactate, ADP: O ratios were estimated for fatty acid oxidation and lactate gluconeogenesis. 1. Octanoate as well as oleate induced a net decrease in ATP and an increase in AMP content of the liver. Total adenine nucleotides were unaltered. ATP:ADP ratios were lowered while the adenylate kinase mass-action ratio increased. 2. The Krebs cycle activity was suppressed by both fatty acids and enhanced by lactate. Oxidation at C-3 was strongly stimulated by the fatty acids and was unaffected by lactate. 3. An apparent ADP:O ratio of 2.7 was obtained after lactate addition, indicating a tightly coupled oxidative phosphorylation for the liver preparations used. Octanoate and oleate gave extremely low ratios of near one and near zero respectively. 4. Perfusion with oligomycin caused a severe drop in oxygen uptake by the liver, which was unaltered after addition of fatty acids. Oligomycin added after the fatty acids caused an immediate fall in oxygen uptake to the level observed with oligomycin alone. 2,4-Dinitrophenol was able to stimulate the oligomycin-depressed respiration, both in the absence and in the presence of fatty acids. These results indicate that under our experimental conditions the fatty acids had no uncoupling effect and that microsomal fatty acid oxidation had to be minimal. 5. Incorporation of [3H]leucine into proteins in liver and medium remained unchanged after addition of fatty acids, indicating that the low apparent ADP:O ratios are not the result of an enhanced synthesis of proteins. 6. The possible relationship between fatty acid transport, energy-wasting futile cycles and the low apparent ADP:O ratios observed during fatty acid oxidation is discussed.