Showing papers by "Utrecht University published in 1976"

Polymers at Interfaces and the Interactions in Colloidal Dispersions

Abstract: Solutions of different polymers in the same solvent are incompatible as a rule and show phase separation when they are mixed. If incompatibility is also to be observed in systems where one of the polymer components is replaced by colloidal particles, sterically stabilized by a cover of polymer chains, will be discussed in this lecture. After a discussion of the applicability of statistical thermodynamical criteria for colloid stability we focus attention on the potential of average force between two particles, V(r), and the second virial coefficient, B2. First it is shown from general arguments that V(r) and B2 always decrease in magnitude upon addition of particles identical to the particle pair considered. The decrease is particularly large for high molecular weight polymers. Subsequently, the analysis is extended, with the help of simple models, to mixtures of polymer colloid and polymer. It is predicted that B2 should decrease and may become negative when the molecular weight and concentration of the polymer are sufficiently large. For high molecular weight polymer this is of the order of a per cent or less. More polymer is needed for low molecular weights. The destabilization is intimately connected with the expulsion of polymer from the interstitial spaces between approaching particles because of “volume restriction”- and “osmotic” effects. The predictions are in accordance with some experiments that were available. Finally the applicability of light scattering as an experimental tool in these stability problems is stressed. Results are also given of the incompatibility of two polymers in a single solvent in which one of the polymers is masked i.e. does not scatter light.

Local structure of movement parallax of the plane

Abstract: The movement parallax field due to the translation of an observer relative to a plane surface is studied in an infinitesimal neighborhood of a visual direction. The parallax field is decomposed into elementary transformations: a translation, a rigid rotation, a similarity, and a deformation. A topologically invariant classification based on critical-point analysis is also obtained. It is shown that the field is either that of a node or that of a saddle point. Numerical results for a general case are offered as illustration. We discuss the relevance of the local, as opposed to the global structure of the parallax field for visual perception and the visual space sense.

Pressure equilibrium and energy balance of small photospheric fluxtubes

Abstract: Field configurations and temperature distributions of axially symmetric fluxtubes are determined on the basis of pressure equilibrium and energy balance of the tubes. The description concentrates on layers below ≈ 600 km above the photosphere; a magnetostatic field, and energy transport by a diffusion process are assumed. It is assumed also that the magnetic field of the tubes prevents convective flow across the field lines, so that only radiative energy exchange between the tube and the convection zone is present. A set of model tubes is presented ranging in size from facular points (150 km) to small pores (1000 km), for different values of the field amplitude and the asymptotic energy flux F 0 flowing along the tube from the deeper layers. Radial influx of heat into the tube at the photospheric level influences the temperature in the tube strongly for all these models. For a pore-like tube f 0 = 0.25 (similar to the flux from a spot umbra) seems appropriate (F 0 in units of the normal photospheric flux). If in the smallest fluxtubes F 0 is also 0.25, a comparison of the intensity contrast with observations of facular points indicates that the radius of tubes corresponding to facular points is 50–100 km. In the continuum the structure looks like a depression in the photosphere (similar to the Wilson depression of spots). The magnitude of this depression is ≈ 200 km for pores of 1000 km diameter and ≈ 100 km for facular points. The walls of the hole created by the depression contribute considerably to the contrast of structures observed near the solar limb. It is shown how this contribution may explain the centre to limb behaviour of facular contrast as seen in the continuum, and why the continuum CLV differs so strongly from that in line cores. Over the first 400 km above the photosphere the tube expands by a factor of ≈ 2 for all the tubes calculated.

Anaerobic metabolism in bivalvia (Mollusca) Characteristics of anaerobic metabolism

Abstract: 1. 1. The role of carbohydrates (glycogen, trehalose, glucose), lipids and proteins as forms of energy storage during aerobiosis and anaerobiosis is discussed. 2. 2. Fatty acid and amino acid conversions cannot be ruled out during anaerobiosis, but this is accompanied by a simultaneous mobilization of carbohydrates. 3. 3. Carbohydrates are therefore the main energy reserve stores under this condition. A Pasteur effect has been shown only in a few studies. The consumed carbohydrates form only a fraction of the pool size. This may be the result of a reduction of the metabolic rate during anaerobiosis. 4. 4. Calculations of ATP production and consumption reveal that the lowest possible energy demand is far below that of the standard rate. 5. 5. Anaerobiosis may lead to the accumulation of pyruvate, lactate, octopine, succinate, alanine, acetate, propionate and CO 2 . The ratio in which these compounds accumulate alters with time. Alanine and lactate are probably initial end products. 6. 6. Stoichiometric studies between consumed fuel substrates and accumulated compounds are discussed. 7. 7. There is a relationship between pH changes and shell movements. During shell closure there is a gradual decrease in pH. 8. 8. ATP levels decrease during anaerobiosis.

ACTH, cyclic nucleotides, and brain protein phosphorylation in vitro

Abstract: Endogenous phosphorylation of proteins from rat brain synaptosomal plasma membranes was studied in vitro. Cyclic AMP (cAMP) markedly stimulated(32)P incorporation in three protein bands with molecular weights of 75,000, 57,000, and 54,000, respectively. The effect of the behaviorally active peptide ACTH1-24 on this endogenous phosphorylation in vitro was studied using peptide concentrations from 10(-10) to 10(-4) M. In a number of protein bands, a biphasic effect of ACTH1-24 was observed: in concentrations of 10(-4)-10(-5) M, a reduced amount of(32)P was found; in concentrations of 10(-6)-10(-7) M, hardly any effect could be detected, whereas consistently at concentrations around 10(-8) M, a significant decrease was again observed. The phosphoprotein bands affected by in vitro addition of ACTH1-24 were of a smaller molecular weight than those affected by in vitro addition of cAMP.

Fermion-Boson Puzzle in a Gauge Theory

Abstract: It is argued that magnetic monopoles in an SU(2) gauge theory may bind with an ordinary boson with isospin, to give bound states with spin. If the isospin of the free boson is integer or half-odd-integer, the total angular mometum of the bound state is integer or half-odd-integer, respectively. According to the spin-statistics theorem we can obtain fermions this way in a theory that started off with bosons only.

Vasopressin and memory consolidation

Abstract: Publisher Summary The hypothalamic-neurohypophyseal system possibly makes use of (a) the general circulation for peripheral effects of posterior pituitary hormones; (b) the portal vessel system for the regulation of anterior pituitary function; and (c) the cerebrospinal fluid for CNS activities. Evidence is presented in the chapter that vasopressin and its analogues facilitate the consolidation of learned behavior patterns. Under certain conditions, these peptides facilitate the acquisition of active avoidance behavior and increase the resistance to the extinction of active and passive avoidance behavior and of sexually motivated approach behavior as well. Intraventricular administration of minute amounts of vasopressin analogues facilitates memory consolidation. This supports the idea that the behavioral effect of these polypeptides is centrally mediated. Vasopressin antibodies, which are assumed to neutralize in situ vasopressin released into the cerebrospinal fluid (CSF), prevent memory consolidation. Studies on paradoxical sleep in diabetes insipidus rats reveal disturbances in hippocampal theta frequencies and strengthen the hypothesis that memory consolidation is under the influence of vasopressin analogues. The development of resistance to the analgesic action of narcotic analgesics is facilitated by the administration of vasopressin analogues and markedly retarded in diabetes insipidus rats. These and other results suggest that the memory consolidating effects of vasopressin analogues are of a more general nature.

Reactions involving singlet oxygen and the superoxide anion

Abstract: IN discussing reactions involving the superoxide anion O2−, it is generally considered that the radical itself or singlet oxygen generated from O2− is harmful to molecules of biological importance1,2. Since the demonstration that singlet oxygen participates in reactions is technically difficult, conclusions about its effects are rather speculative. I show here, on thermo-dynamic grounds, in which reactions singlet oxygen can be formed from O2− and in which reactions this is improbable.

Induction of excessive grooming in the rat by fragments of lipotropin.

Abstract: CURRENT research reveals the existence of endogenous peptides in brain1,2 and pituitary tissue3,4, which are presumably derived from lipotropin (LPH) and which have opiate like effects and affinity for opiate receptors (enkephalin1, endorphins5, C-Fragment6). N-terminal peptides of ACTH also have measurable, although much lower, affinity for rat brain receptors in vitro7,8, ACTH and congeners are known to play a crucial role in the acquisition and maintenance of a variety of behaviours in animals and man9,10. Intraventricular but not systematic administration of these peptides elicits a stretching and yawning syndrome11,12. In rats this syndrome is preceded by a display of excessive grooming13,14 and this grooming response can be suppressed by peripheral administration of specific opiate antagonists (naloxone, naltrexone)15. Morphine also induces grooming15 and this observation prompted us to study the effect of LPH fragments on excessive grooming in the rat in the absence and presence of an opiate antagonist.

Hydrolysis-precipitation studies of aluminum (III) solutions. 2. A kinetic study and model

Abstract: The hydrolysis-precipitation process of Al(OH)3 from acidified aluminum nitrate and chloride solutions was studied with a homogeneous alkali injection technique. In these studies the total Al(III) concentration (CAl) varied from 5 × 10−5 to 0.5 M, the ionic strength from about 10−4 (no added salt) to 2.8 M; and the temperature from 25 to 90°C. Continuous and discontinuous kinetic experiments with both alkali and acid suggest that different processes occur below and above an OH/Al ratio = 2.5 in solutions with cAl3+ > 5 × 10−4 M. At very low concentration the reaction proceeds solely via monomeric species. Light scattering measurements are used to determine the average degree of polymerization, Nz. It is observed that over the range 0 < OH/Al < 2.5 the average degree of polymerization changes in the order 0 < Nz < 15. The reactivity of these polynuclear complexes with acid suggests that the hydroxyl ions form bridges between the Al3+ cations up to an OH/Al ratio of 2.5. A model, which is based upon the structure of the solid, is postulated for the hydrolysis process. This model appears to be in qualitative agreement with experiment.

An ethological analysis of types of agonistic interaction in a captive group of Java-monkeys ( Macaca fascicularis ).

Abstract: The primate literature provides many indications not only that the nature of dyadic interactions is to a large extent determined by the relations of the interacting animals with others and between these others, but also of the existence of polyadic interactions in which more than two individuals are simultaneously involved. The objectives of the present study are to obtain a quantitative categorization of the agonistic interaction types of captive Java-monkeys and an analysis of their dynamics. After having described the agonistic behaviour patterns of Java-monkeys we shall discuss the categorization of agonistic interaction types (depending on the number of involvees: “dyads”, “triads” and “polyads”), the way in which these types can be further differentiated on the basis of the nature and the direction of the behaviours shown (e.g., different types of alliances), and the existence of so-called “sub-directed” behaviours (i.e., non-agonistic behaviours which are shown towards a dominant third animal more or less simultaneously with aggressive behaviour directed towards an opponent). The analysis indicates that agonistic behaviour is different both in its form and its regulation in interactions of different complexity.

Centrally induced hypotension and bradycardia after administration of alpha-methylnoradrenaline into the area of the nucleus tractus solitarii of the rat.

Abstract: 1 In anaesthetized rats, bilateral injections of alpha-methylnoradrenaline, noradrenaline or adrenaline into the area of the nucleus tractus solitarii (NTS) of the brain stem caused dose-dependent decreases of systemic arterial blood pressure and heart rate. The effects of alpha-methylnoradrenaline were most pronounced and lasted longest. 2 The cardiovascular effects of alpha-methylnoradrenaline appeared to be restricted to the medio-caudal part of the NTS. 3 Prior administration of the alpha-adrenoceptor blocking agent, phentolamine, reversed the fall in blood pressure and heart rate induced by alpha-methylnoradrenaline into an increase. 4 Systemic administration of atropine combined with vagotomy potentiated the inhibitory effects of alpha-methylnoradrenaline on the cardiovascular system.

Induction of tolerance to the analgesic action of lipotropin in C-fragment.

Abstract: THE C-Fragment of β-lipotropin (lipotropin 61-91), was first discovered as an intact peptide in the pituitary gland1,2 and it has recently been shown to be present in brain3. The peptide binds strongly to brain opiate receptors in vitro4,5 and has potent opiate-like actions on the guinea pig ileum and mouse vas deferens15. Reports from our laboratory described the potent analgesic properties of C-Fragment when injected into the cerebral ventricles of the cat4–6, and in subsequent studies its analgesic effects have been demonstrated in rodents7–9. The results reported here confirm the analgesic potency of C-Fragment administered intracerebrally in the rat, and show that chronic administration of the peptide leads to the development of tolerance to its analgesic actions.

Array analysis of seismic surface waves: Limits and possibilities

Abstract: The dispersion of higher modes of surface waves over a region covered by an array of stations can be measured by applying a frequency-wavenumber transform to segments of the signals in these stations, centered at a number of group-velocities. Thus, at a fixed period, modes appear as separate maxima in a display of the power spectrum on a phase-velocity vs. group velocity plane.

Adenosine phosphates and energy charge in different tissues ofMytilus edulis L. under aerobic and anaerobic conditions

Abstract: 1. Concentrations of AMP, ADP and ATP are determined in total tissue and in posterior adductor muscle, hepatopancreas, mantle and residue ofMytilus edulis, in order to calculate the energy charge. This parameter was the highest in posterior adductor muscle (0.91) and the lowest in the hepatopancreas (0.69). 2. During exposure to air minimum levels of about 60% of the normal ATP content were determined in total mussel and the various tissues. The decrease in ATP could be accounted for by the increase in concentrations of AMP plus ADP and therefore the total adenylate pool was hardly affected. 3. The energy charge decreased in total animal during the initial days of anoxia, but raised again at the 7th day to a value equal to that in dead animals. The shift after 3 days of anoxia was highest in the posterior adductor muscle (0.24) and lowest in the hepatopancreas (0.14). 4. The energy charge was nearly the same in both “fed” and “starved” mussels and changed within the same range (0.85–0.6) during anaerobiosis. In “starved” animals, however, the minimum value was reached at an earlier stage. 5. Within this range key enzymes are highly sensitive to regulation by the energy charge according to the theory of Atkinson (1968).

Second Threshold in Weak Interactions

Abstract: The point of view that weak interactions must have a second threshold below 300 — 600 GeV is developed. Above this threshold new physics must come in. This new physics may be the Higgs system, or some other nonperturbative system possibly having some similarities to the Higgs system. The limit of large Higgs mass is thought to be relevant in this context. Radiative corrections proportional to m 2 and ln m 2 , m being the Higgs mass, are calculated. Contemplation of the theory in the limit of large Higgs mass suggests that the “new physics„ may contain breakdown of μ- e universality and other than V–A neutrino interactions already at relatively low energies.