Showing papers by "Université libre de Bruxelles published in 1978"
972 citations
TL;DR: It is shown that nonequilibrium may become a source of order and that irreversible processes may lead to a new type of dynamic states of matter called "dissipative structures" and the thermodynamic theory of such structures is outlined.
Abstract: Fundamental conceptual problems that arise from the macroscopic and microscopic aspects of the second law of thermodynamics are considered. It is shown that nonequilibrium may become a source of order and that irreversible processes may lead to a new type of dynamic states of matter called "dissipative structures." The thermodynamic theory of such structures is outlined. A microscopic definition of irreversible processes is given, and a transformation theory is developed that allows one to introduce nonunitary equations of motion that explicitly display irreversibility and approach to thermodynamic equilibrium. The work of the group at the University of Brussels in these fields is briefly reviewed. In this new development of theoretical chemistry and physics, it is likely that thermodynamic concepts will play an ever-increasing role.
864 citations
TL;DR: In this article, the universe is conceived as the response of matter and the gravitational field to a spontaneous point-like disturbance, and the history unfolds in two stages, creation and free expansion.
440 citations
TL;DR: Several extreme thermophilic Gram negative bacteria found in a thermally polluted river in Belgium have been compared with Thermus strains isolated from widely distant geographical areas, finding them to be morphologically identical with strain YT-1 of Thermus aquaticus.
Abstract: Several extreme thermophilic Gram negative bacteria found in a thermally polluted river in Belgium have been compared with Thermus strains isolated from widely distant geographical areas. This analysis has become possible after the design of a new culture medium (162). All strains examined (including the isolate successively denominated Flavobacterium thermophilum and Thermus thermophilus) were found to be morphologically identical with strain YT-1 of Thermus aquaticus. The cells are immotile, rod-like, strictly aerobic, catalase and oxidase positive. They produce amylase, hydrolyze gelatin and are confirmed to be highly sensitive towards penicillin. The nutritional pattern of all strains has been analysed extensively, by testing a broad spectrum of possible substrates. The strains display a uniform response to the microbiological tests applied and most probably belong to the same species: Thermus aquaticus.
309 citations
TL;DR: An automatic procedure which generates possible modes of protein-protein association is developed and applied to the bovine pancreatic trypsin inhibitor-trypsin complex, suggesting that the major contributions to the free energy of dissociation are taken into account by the selection procedure.
268 citations
TL;DR: In this article, a diagenetic model simulating the concentration profile of ammonium and nitrate in the interstitial water of the North Sea sediments of the Belgian coast is presented.
223 citations
TL;DR: Fractions containing desmosome- ton ofilament complexes were invariably dominated by the nonmembranous proteins of the tonofilaments which appeared as five major polypeptide bands which indicate that the desmosomal membrane is complex in protein and lipid composition and has a typical plasma membrane character.
Abstract: Complexes of plasma membrane segments with desmosomes and attached tonofilaments were separated from the stratum spinosum cells of calf muzzle by means of moderately alkaline buffers of low ionic strength and mechanical homogenization. These structures were further fractionated by the use of various treatments including sonication, sucrose gradient centrifugation, and extraction with buffers containing high concentrations of salt, urea, citric acid, or detergents. Subfractions enriched in desmosome-tonofilament-complexes and tonofilament fragments were studied in detail. The desmosome structures such as the midline, the trilaminar membrane profile, and the desmosomal plaque appeared well preserved and were notably resistant to the various treatments employed. Fractions containing desmosome-tonofilament complexes were invariably dominated by the nonmembranous proteins of the tonofilaments which appeared as five major polypeptide bands (apparent molecular weights: 48,000; 51,000; 58,000; 60,000; 68,000) present in molar ratios of approx. 2:1:1:2:2. Four of these polypeptide bands showed electrophoretic mobilities similar to those of prekeratin polypeptides from bovine hoof. However, the largest polypeptide (68,000 mol wt) migrated significantly less in polyacrylamide gels than the largest component of the hoof prekeratin (approximately 63,000 mol wt). In addition, a series of minor bands, including carbohydrate-containing proteins, were identified and concluded to represent constituents of the desmosomal membrane. The analysis of protein-bound carbohydrates (total 270 microgram/mg phospholipid in desmosome-enriched subfractions) showed the presence of relatively high amounts of glucosamine, mannose, galactose, and sialic acids. These data as well as the lipid composition (e.g., high ratio of cholesterol to phospholipids, relatively high contents of sphingomyelin and gangliosides, and fatty acid pattern) indicate that the desmosomal membrane is complex in protein and lipid composition and has a typical plasma membrane character. The similarity of the desmosome-associated tonofilaments to prekeratin filaments and other forms of intermediate-sized filaments is discussed.
172 citations
TL;DR: Single motor units were recorded from the masseter, soleus and first dorsal interosseous muscles of normal adult man and an analysis of discharge patterns was carried out either during slow ramp voluntary contractions, or during self‐initiated isolated ballistic voluntarycontractions.
Abstract: 1 Single motor units were recorded from the masseter, soleus and first dorsal interosseous muscles of normal adult man An analysis of discharge patterns was carried out either during slow ramp voluntary contractions, or during self-initiated isolated ballistic voluntary contractions The isometric myogram was simultaneously recorded2 Each motor unit was only recruited when the peak force of a brisk contraction exceeded a certain value and a ;ballistic force threshold' (in kg) was estimated for the unit from a large series of brisk contractions of different strengths For each muscle, the ranking order for recruitment of different motor units recorded from one electrode position was virtually identical in slow ramp versus brisk ballistic contractions of different force (Kendall rank correlation coefficient = 091-10) There was no evidence for any consistent selective activation of fast twitch motor units in ballistic contractions3 The ballistic force threshold is considerably reduced with respect to the slow ramp force threshold for the motor units of the soleus muscle This drop is also marked for the units of the first interosseous and tibialis anterior muscles, whereas it is only small for the units of the masseter muscle These data have been validated after consideration of the complicating factor related to the possible differential involvement of synergic muscles in ramp or ballistic contractions4 In the masseter and first interosseous muscles, the time to peak is about 80 msec in small ballistic voluntary contractions and it increases to about 150 msec in strong contractions This effect appears related to repetitive discharges of single motor units when their force threshold is exceeded By contrast, in the soleus muscle, the time to peak remains at about 150 msec both in small and in strong ballistic contractions and most soleus motor units fire only one spike in the ballistic burst5 Brisk ballistic contractions are graded in force by the recruitment of additional motor units according to their usual rank order The importance of rate gradation through the repetitive firing of motor units varies in the different human muscles investigated, being quite significant in isometric brisk contractions of the masseter and first interosseous muscles but much less so in the soleus muscle in which little repetitive firing of single motor units was observed over the range of ballistic forces studied
164 citations
TL;DR: With these simple rules, one can often predict the essential features of the behaviour of complex systems, just by reducing them to simpler “homologous” systems whose behaviour is known.
159 citations
TL;DR: The parameters of presynaptic inhibition of the Ia spindle afferents from soleus muscle by vibration have been investigated and the inhibitory effects increase with the amplitude of vibration, but decrease when the vibration frequency is increased.
Abstract: 1. The parameters of presynaptic inhibition of the Ia spindle afferents from soleus muscle by vibration have been investigated. The inhibitory effects increase with the amplitude of vibration, but decrease when the vibration frequency is increased.2. The monosynaptic reflex threshold of twenty-one single soleus motor units activated in the H (Hoffmann) reflex by a single electrical stimulus to the posterior tibial nerve was estimated quantitatively and expressed in relation to the size of the simultaneously recorded H reflex.3. A parametric study of the effects of various Achilles tendon vibrations on the reflex threshold of the single soleus motor units indicated that their order of derecruitment is concordant with their rank order for activation in the phasic reflexes of the soleus. The last recruited motoneurones are the most susceptible to being silenced by steady vibration.4. Muscle vibration progressively recruits single motor units according to the motoneurone size principle through polysynaptic proprioceptive pathways. However the presynaptic inhibition of Ia spindle afferents simultaneously induced by the vibration works in reverse on the same rank order of motoneurones of the soleus spinal pool, thereby limiting the polysynaptic recruitment of units in the tonic vibration reflex while depressing the autogenic phasic proprioceptive reflexes. These mechanisms elucidate the so-called vibration paradox and extend the size principle of Henneman to presynaptic inhibitory effects.
156 citations
TL;DR: In this paper, the authors present a derivation of the noise properties of linear two-ports in terms of noise waves, which leads to a convenient measurement method in distributed systems.
Abstract: Noise temperature or noise factor are important parameters for many microwave devices. Their dependence on source characteristics is classically established using low-frequency concepts such as impedance, admittance, voltage, and current sources. This paper presents a derivation of the noise properties of linear two-ports in terms of noise waves, which leads to a convenient measurement method in distributed systems.
TL;DR: It is found that the condition of "mixing" is necessary and the property of being K-flow is sufficient for the existence of a Lyapounov variable, and this support and sharpen the view that the thermodynamical and the dynamical descriptions of classical systems could be consistently reconciled as being complementary descriptions analogous to the complementary descriptions encountered in quantum mechanics.
Abstract: We discuss the problem of defining (nonequilibrium) entropy in terms of the concepts of mechanics and of reconciling its monotonic increase with the Hamiltonian evolution of the dynamical system. This leads to investigating necessary and sufficient conditions for the existence of monotonically increasing quantities or the so-called Lyapounov variables of classical systems. It is found that the condition of “mixing” is necessary and the property of being K-flow is sufficient for the existence of a Lyapounov variable. The significance of the study of Lyapounov variables for the elucidation of the fundamental questions of statistical mechanics is briefly discussed. It is seen that every Lyapounov variable must fail to commute with at least some of the operators of multiplication by phase space functions. The uncertainty relations implied by this necessary noncommutativity would then set a limit on the simultaneous determination of entropy and trajectories in phase space. These considerations thus support and sharpen the view that the thermodynamical and the (microscopic) dynamical descriptions of classical systems could be consistently reconciled as being complementary descriptions analogous to the complementary descriptions encountered in quantum mechanics.
TL;DR: The photo-oxidation of polystyrene irradiated at 253.7 nm at a pressure of 600 Torr oxygen has been studied quantitatively as mentioned in this paper, and it has been shown that only about 4% of the oxygen absorbed ultimately results in chain scissions.
TL;DR: The specificity of binding sites for vasoactive intestinal peptide was established, and in this class of nucleotides GTP was 6-fold more potent than guanosine 5′-[β,γ-imido]triphosphate.
Abstract: 1
The interaction of the vasoactive intestinal peptide family of hormones with synaptic membranes from guinea pig brain was examined using 125I-labeled vasoactive intestinal peptide as a tracer molecule. Binding of this peptide was rapid and temperature-dependent, as well as reversible and saturable. Scatchard plots were compatible with the existence of two classes of binding sites, the first class with an apparent Kd of 36 nM and a low binding capacity (4 pmol vasoactive intestinal peptide/mg membrane protein) and a second class of binding sites with a lower affinity (apparent Kd of 285 nM) and a higher capacity (20 pmol vasoactive intestinal peptide/mg membrane protein).
2
The specificity of binding sites for vasoactive intestinal peptide was established from the fact that binding of the 125I-labeled peptide was inhibited by the unlabeled peptide and by higher concentrations of unlabeled secretin but not by the parent hormone glucagon or by the neuropeptides somatiostatin, bombesin, C-terminal octapeptide of pancreozymin, Leu-enkephalin, and substance P.
3
Na+, K+, Ca2+, Mg2+ and EDTA reduced the amount of 125I-labeled vasoactive intestinal peptide bound at equilibrium. The monovalent and divalent cations decreased the binding rate constant, whereas EDTA increased the dissociation rate constant of binding.
4
Nucleoside triphosphates and diphosphates decreased binding of the 125I-labeled peptide at equilibrium and increased the rate constant of dissociation of membrane-bound vasoactive intestinal peptide. Guanyl nucleotides were the most potent and in this class of nucleotides GTP was 6-fold more potent than guanosine 5′-[β,γ-imido]triphosphate.
TL;DR: In this paper, an H-function suitable for a system of dense hard spheres satisfying the nonlinear Enskog equation was constructed and the equality sign holds only when the system has reached absolute equilibrium, in which case S = − kBH becomes the exact equilibrium entropy of the hard-sphere fluid.
Abstract: We construct anH-function suitable for a system of dense hard spheres satisfying the (modified) nonlinear Enskog equation and we show that∂tH ⩽ 0. The equality sign holds only when the system has reached absolute equilibrium, in which caseS=− kBH becomes the exact equilibrium entropy of the hard-sphere fluid.
TL;DR: In this article, the authors describe a very sensitive method for the evaluation of nitrification rates requiring only short incubation times (3-6 h) and applicable to all aquatic media.
TL;DR: The distribution and concentration of dissolved aluminum in a vertical hydrographic profile in the Mediterranean Sea near Corsica are controlled by biological activity and support the hypothesis that the silicon and aluminum cycles in the oceans are linked through the activity of diatoms.
Abstract: The distribution and concentration of dissolved aluminum in a vertical hydrographic profile in the Mediterranean Sea near Corsica are controlled by biological activity. The concentrations of dissolved silica and aluminum covary in the profile and exhibit minima coincident with the seasonal thermocline, a nitrate minimum, and an oxygen maximum. These observations support the hypothesis that the silicon and aluminum cycles in the oceans are linked through the activity of diatoms.
TL;DR: In this article, the parent magma of the andesine-type massifs has a jotunitic (hypersthene-monzodioritic) composition characterized by variable K/Rb ratios (from 480 to 1700), by the absence of an Eu anomaly, by variable rare earth elements (REE) contents (from 50 to 220 for La chondrite-normalized content) and by La/Yb ratios almost constant (from 6 to 12), as well as by high Ti and Fe contents, by transition elements indicating calc-alkaline
TL;DR: In this article, a model is developed in which the change in the population distribution of a region is linked to the employment pattern, and this latter in turn to population distribution through the concepts of Central Place Theory.
TL;DR: In the patients remaining euthyroid while taking amiodarone or after its withdrawal, but still under its influence as shown by the iodine overload, a ‘low‐T3 syndrome’ is observed.
Abstract: Cardiac patients treated with the iodine-containing drug 'amiodarone' undergo a significant iodine overload which can last for months after the drug has been withdrawn. Some patients develop hyperthyroidism and others hypothyroidism. In the hyper- or hypothyroid patients, the indices of thyroid function are modified as usually observed in these situations. In the patients remaining euthyroid while taking amiodarone or after its withdrawal, but still under its influence as shown by the iodine overload, a 'low-T3 syndrome' is observed, this state being characterized by a high total T4, a low free T4, a normal T3 resin uptake, a low total T3, a normal free T3, a high r-T3 and a relative TSH-unresponsiveness to TRH.
TL;DR: The stability of HeLa cell poly (A)-free histone mRNAs injected into Xenopus oocytes is studied, and the effect of 3′-OH polyadenylation on this stability is studied.
Abstract: WE have shown that, when injected into Xenopus oocytes, poly (A) free globin messenger RNA is translated for a short period of time and then rapidly degraded1–3, while, under the same conditions, native mRNA shows a marked stability1,2,4 The poly (A) segment itself is responsible for the stability of native globin mRNA, since its readdition to previously de-adenylated mRNA restores the stability of the message5 We have shown also that the poly (A) stretch must contain a minimum number of adenylate residues to ensure its protective function6 It was interesting to see whether the concept of the stabilisation of eukaryotic mRNAs by 3′-OH polyadenylation is general This can be done by looking at the effect of the presence of a 3′-OH poly (A) segment on the stability of various mRNAs Here we study the stability of HeLa cell poly (A)-free histone mRNAs injected into Xenopus oocytes, and the effect of 3′-OH polyadenylation on this stability
TL;DR: It is likely that some elements of RNA evolution are independent of the structural needs of the RNA itself and of the translated protein product.
Abstract: The non-random distribution of degenerate code words in Bacteriophage MS2 RNA can be explained partially by considerations of the stability of the codon-anticodon complex in prokaryotic systems. Supporting this hypothesis we note that wobble codons are positively selected in codons having G and/or C in the first two positions. In contrast, wobble codons are statitically less likely in codons composed of A and U in the first two positions. Analyses of nucleotides adjacent to 5′ and 3′ ends of codons indicate a nonrandom distribution as well. It is thus likely that some elements of RNA evolution are independent of the structural needs of the RNA itself and of the translated protein product.
TL;DR: Serum prolactin, LH, FSH, and estradiol were measured in single blood samples collected from 465 nursing mothers in Central Africa during the first 2 postpartum years and there was a significant association of hyperprolactinemia with amenorrhea.
TL;DR: Stepwise discriminant analyses between tertile III and tertile I introducing psychological, social and bioclinical variables showed that the ‘obese’ subjects (tertile III) are less frequently cigarette smokers, are less neurotic, are of a lower occupational class, are more frequently living in Wallonia (south of Belgium) and are more extravert compared to the ’lean’Subjects.
TL;DR: In this article, the Glauber distribution function of the field emitted by a laser with a saturable absorber was considered and the role of terms with derivatives of order higher than second was investigated.
Abstract: We consider the time-evolution equation for the Glauber distribution function of the field emitted by a laser with saturable absorber and investigate the role of the terms with derivatives of order higher than second. It is found that the main effect of these terms is the following: When the relative saturability of the passive atoms with respect to the active atoms is very high, the (first-order-like) transition is much sharper than predicted by the Fokker-Planck equation.
TL;DR: It is proposed that the A function directly concerns the insertion of the phage and the B gene codes for a replication function, indicating that Mu gene expression is required for these rearrangements.
Abstract: THE temperate iphage Mu-1 not only integrates at any location in the chromosome of its host Escherichia coli1 but also provokes different types of chromosomal aberrations: insertions of extrachromosomal circular DNA2–4, translocations, deletions and inversions of chromosomal segments (refs 5, 6, Howe and Bukhari, unpublished results and M.F., in preparation). Immunity to phage Mu prevents the induction of such events, indicating that Mu gene expression is required for these rearrangements. Furthermore, the direct participation of Mu DNA in the generation of chromosomal aberrations is demonstrated by the observations that one entire Mu genome is always adjacent to the site of the deletions, two entire Mu genomes in the same orientation flank the inserted and translocated DNA fragments, and inverted chromosomal segments are surrounded by two entire Mu genomes in opposite orientations (ref. 22 and M.F., in preparation). Dependence of such Mu-induced alteration on the A and B early phage functions was investigated. A− mutants of Mu are unable to mediate all the events tested, while B− mutants still promote deletion. Based on the results presented here, and on other data, we propose that the A function directly concerns the insertion of the phage and that the B gene codes for a replication function.
TL;DR: Six infants in whom thyroid insufficiency was detected in the early days of life and disappeared spontaneously after a few weeks are discussed.
TL;DR: The data suggest the presence of an abnormal extrathyroidal T4 metabolism as well as a pituitary defect in euthyroid patients with severe diabetic ketoacidosis, and caution is recommended in the interpretation of thyroid‐function tests during and several days after the treatment of diabetic ketOacidosis.
Abstract: The pituitary-thyroid axis was investigated in nineteen euthyroid patients with severe diabetic ketoacidosis. A 'low T3 syndrome' was found, with the following characteristics: lowered serum concentrations of triiodothyronine (T3), increased reverse triiodothyronine (rT3), slightly low thyroxine (T4), normal thyrotrophin (TSH), slightly increased triiodothyronine uptake (RT3U) values, and a blunted TSH response to thyrotrophin-releasing hormone (TRH). These disturbances in thyroid-function tests required several days good control of the diabetes to be corrected, at least partially. The data suggest the presence of an abnormal extrathyroidal T4 metabolism as well as a pituitary defect. Caution is recommended in the interpretation of thyroid-function tests during and several days after the treatment of diabetic ketoacidosis.
TL;DR: In this paper, metal mobility in soils and availability to plants in both calcareous and non-calcareous situations were investigated in relation to the development of genetical heavy metal tolerance in plant populations.
Abstract: SUMMARY
The development of vegetation (mainly the Violetum calaminariae Schwick.) in heavy metal-contaminated areas depends on the metals mobility in soils and on metal availability for plants. Moreover, the ability of plant populations to evolve metal tolerance is one of the most important characters which determines the structure, density and development of the vegetation in such areas. In this work, metal mobility in soils and availability to plants in both calcareous and non-calcareous situations were investigated in relation to the development of genetical heavy metal tolerance in plant populations.
In soils, exchangeable metals amounts are linearly related to total amounts. Availability of metals for plants depends on soil pH and on organic matter contents. High calcium content in soils reduced lead toxicity more than zinc toxicity and generally reduced metal uptake but some exceptions were found. The structure and the density of the vegetation colonizing calcareous and non-calcareous places is related to the interaction between lead, zinc and exchangeable non-toxic cations. A relationship between exchangeable Pb++/Ca++ in soils and the lead tolerance level of plant populations was found. The relation between exchangeable Zn++/Ca++ and zinc tolerance level was not satisfactory.