Showing papers by "Université libre de Bruxelles published in 1981"
01 Jan 1981
TL;DR: For more complex systems, as far as one can tell, the presence of at least one negative loop in the logical structure appears as a necessary (but not sufficient) condition for a permanent periodic behaviour, and the absence of a positive loop is not a necessary condition for multiple steady states.
Abstract: Simple feedback loops behave in two essentially different ways depending on whether they contain an odd number of inhibitory elements (“negative” loops) or an even number of inhibitory elements (“positive” loops); for proper values of parameters or delays, the former generate sustained oscillations, the latter, multiple steady states. For more complex systems, as far as one can tell, the presence of at least one negative loop in the logical structure appears as a necessary (but not sufficient) condition for a permanent periodic behaviour, and the presence of at least one positive loop as a necessary (but not sufficient) condition for multiple steady states.
397 citations
TL;DR: The changes associated with normal aging have been confirmed and extended and a new widespread component N18 was identified and shown to be generated below the cortex.
388 citations
TL;DR: The question asked was whether bias occurred only with fusion, as is predicted by some accounts of reactions to discordance, and the answer could not be answered for auditory bias of visual localization, which, although significant, was very small in Experiment 1 and fell below significance under the conditions of Experiment 2.
Abstract: Investigations of situations involving spatial discordance between auditory and visual data which can otherwise be attributed to a common origin have revealed two main phenomena:cross-modal bias andperceptual fusion (or ventriloquism). The focus of the present study is the relationship between these two. The question asked was whether bias occurred only with fusion, as is predicted by some accounts of reactions to discordance, among them those based on cuesubstitution. The approach consisted of having subjects, on each trial, both point to signals in one modality in the presence of conflicting signals in the other modality and produce same-different origin judgments. To avoid the confounding of immediate effects with cumulative adaptation, which was allowed in most previous studies, the direction and amplitude of discordance was varied randomly from trial to trial. Experiment 1, which was a pilot study, showed that both visual bias of auditory localization and auditory bias of visual localization can be observed under such conditions. Experiment 2, which addressed the main question, used a method which controls for the selection involved in separating fusion from no-fusion trials and showed that the attraction of auditory localization by conflicting visual inputs occurs even when fusion is not reported. This result is inconsistent with purely postperceptual views of cross-modal interactions. The question could not be answered for auditory bias of visual localization, which, although significant, was very small in Experiment 1 and fell below significance under the conditions of Experiment 2.
367 citations
TL;DR: A survey of multicriteria analysis can be found in this paper, where the authors present a survey of the different directions in which multi-attribute utility analysis has developed: multiattribute utility theory, outranking relations, interactive methods, and the methodology recently proposed by B. Roy.
308 citations
TL;DR: In this article, the Fokker-Planck equation corresponding to a zero-dimensional climatic model showing bistable behavior is analyzed and a climatic potential function is introduced, whose variational properties determine the most probable states of the stationary probability distribution.
Abstract: The Fokker-Planck equation corresponding to a zero-dimensional climatic model showing bistable behavior is analyzed. A climatic potential function is introduced, whose variational properties determine the most probable states of the stationary probability distribution. A study of the time-dependent properties leads to the identification of the characteristic time scales of evolution.
273 citations
TL;DR: The use of 14 simultaneous recordings including a series of pre- and post-vertebral electrodes clearly identified two distinct generators for the spinal SEP components to median nerve stimulation: a presynaptic generator which ascends the dorsal column (N 11 ) and a postsynaptic fixed generator in the dorsal horn of the cervical spinal cord (N 13 -P 13).
269 citations
TL;DR: In this article, a dynamical model of a central place system is described which, derived from the concepts underlying dissipative structures, takes into account the self-organizing aspects of urban evolution, and s...
Abstract: A dynamical model of a central place system is described which, derived from the concepts underlying dissipative structures, takes into account the self-organizing aspects of urban evolution, and s...
225 citations
TL;DR: The present results on human fibroblasts with reported differential sensitivity to ionizing radiation and patients with ataxia telangiectasia and retinoblastoma support the first hypothesis and fail to substantiate the second since the second hypothesis is not substantiated.
Abstract: SummaryWe recently showed (Scott and Zampetti-Bosseler 1980) that X-ray sensitive mouse lymphoma cells sustain more chromosome damage, mitotic delay and spindle defects than X-ray resistant cells. We proposed that (a) chromosome aberrations contribute much more to lethality than spindle defects, and (b) that DNA lesions are less effectively repaired in the sensitive cells and give rise to more G2 mitotic delay and chromosome aberrations. Our present results on human fibroblasts with reported differential sensitivity to ionizing radiation (i.e. normal donors and patients with ataxia telangiectasia and retinoblastoma) support the first hypothesis since we observed a positive correlation between chromosome aberration frequencies and cell killing and no induced spindle defects. Our second hypothesis is however not substantiated since X-ray sensitive fibroblasts from the ataxia patient suffered less mitotic delay than cells from normal donors. A common lesion for mitotic delay and chromosome aberrations can st...
222 citations
TL;DR: Motor commands in human interosseous muscle appear to be patterned in terms of movements rather than muscles and to involve different connectivities to the motoneuron pool of a muscle executing movements in different directions.
Abstract: Single motor units in human interosseous muscle are recruited in order from small to large in slow or brisk voluntary abduction of the index finger. When the same muscle acts as a synergist as opposed to a prime mover, about 8 percent of the unit pairs consistently reversed their recruitment order. Motor commands appear to be patterned in terms of movements rather than muscles and to involve different connectivities to the motoneuron pool of a muscle executing movements in different directions.
192 citations
TL;DR: This study presents a unitary scheme for the structural organization of the small ribosomal subunit RNAs and concludes that the evolutionary constraints on both primary and secondary structures most likely reveal the basic role of some restricted RNA regions in the function of the ribosome.
Abstract: A consensus on the folding of the Escherichia coli 16-S ribosomal RNA is emerging and several complete nucleotide sequences of small ribosomal subunit RNAs, covering diverse types of organisms and organelles, are now available. We therefore investigated the extent of both nucleotide sequence and secondary structure conservation that may exist between the E. coli 16-S RNA and other ribosomal RNAs. All the RNA molecules examined could be folded into secondary structure schemes that illustrated remarkable preservation of many structural motifs as well as striking nucleotide sequence conservation compared with the E. coli molecule. This study presents a unitary scheme for the structural organization of the small ribosomal subunit RNAs. The evolutionary constraints on both primary and secondary structures most likely reveal the basic role of some restricted RNA regions in the function of the ribosome.
144 citations
TL;DR: In this paper, an asymptotic method of analysis of fluctuations in systems far from equilibrium is developed, using singular perturbative expansion of the equation for the generating function, using as smallness parameter the inverse of the size of the system.
TL;DR: In this article, it was shown that non-unitary equivalence between stochastic Markov processes and non-isomorphic K flows is intrinsically random, and the connection of intrinsic randomness with local instability of motion is briefly discussed.
Abstract: We discuss the problem of nonunitary equivalence, via positivity-preserving similarity transformations, between the unitary groups associated with deterministic dynamical evolution and semigroups associated with stochastic processes. Dynamical systems admitting such nonunitary equivalence with stochastic Markov processes are said to be intrinsically random. In a previous work, it was found that the so-called Bernoulli systems (discrete time) are intrinsically random in this sense. This result is extended here by showing that a more general class of dynamical systems---the so-called K systems and K flows---are intrinsically random. The connection of intrinsic randomness with local instability of motion is briefly discussed. We also show that Markov processes associated through nonunitary equivalence to nonisomorphic K flows are necessarily nonisomorphic.
TL;DR: During a recrudescence of meningococcal disease mainly due to serogroup B, 1913 notified cases were investigated in Belgium from 1971 to 1976, and the attack rates were significantly higher than the incidence rates in the corresponding age-groups in the general community, indicating the need for prophylaxis in these contacts.
TL;DR: It is reported here that this additional copy of the living trypanosome is in a chromatin configuration highly sensitive to pancreatic deoxyribonuclease, suggesting that it is the transcribed one.
Abstract: The antigenic specificity of the living trypanosome seems to be determined by the protein component of a unique glycoprotein species covering the whole surface of the parasite. During chronic infection, a single clone of trypanosomes may successively express a large repertoire of different variable antigen types (VATs). There are probably as many genes as variant-specific antigens (VSAs) (see refs 1-3 for reviews). The expression of the genes coding for the synthesis of these antigens is linked to genomic rearrangements involving duplication of the coding sequence and transposition of the additional copy. The regulation of the expression of the VSA genes is operated at the transcriptional level. It can thus be supposed that their transcription depends on the presence of the additional, transposed copy. We report here that this additional copy is in a chromatin configuration highly sensitive to pancreatic deoxyribonuclease, suggesting that it is the transcribed one.
TL;DR: The protease inhibitors puromycin and bacitracin, the metal chelator 1,10-phenanthroline, and the sulphydryl blocking agents N-ethylmaleimide and p-chloromercuribenzoate greatly reduced the release of tryptophan from CCK-8.
TL;DR: The dose-effect curves of stimulation of adenylate cyclase by VIP and parent peptides were compatible with the existence of two classes of VIP receptor, the relative peptide potencies being identical with their ability to compete with 125I-labelled VIP for binding.
TL;DR: It is concluded that the stabilization effect of t6A occurs on U · A and U · G base pairs adjacent to the 5′ side of the modified nucleoside, most probably by stacking.
Abstract: The effect of N-[9-(β-d-ribofuranosyl) purin-6-ylcarbamoyl]threonine (t6A) adjacent to anticodon U*-C-U of yeast tRNAArgIII (where U* is a modified U), compared to its unmodified adenosine counterpart, has been evaluated by three independent methods: (a) the polynucleotide-directed binding of tRNA on ribosomes, (b) the ribosome-free trinucleotide binding to the anticodon. (c) the anticodon-anticodon binding test.
The results obtained by these three methods indicate a small but significant stabilization effect of t6A on the binding of yeast tRNAArgIII with (a) poly(A,G) in the presence of Escherichia coli ribosomes, (b) free A-G-A triplet, and (c) E.coli tRNAServ (anticodon G-G-A).
We therefore conclude that the stabilization effect of t6A occurs on U · A and U · G base pairs adjacent to the 5′ side of the modified nucleoside, most probably by stacking.
TL;DR: In this article, the rotational and translational motions of single diatomic molecules in the liquid state are investigated for both the homo- and heteronuclear cases using computer simulations using the method of molecular dynamics.
Abstract: The coupling between the translational and rotational motions of single diatomic molecules in the liquid state is investigated for both the homo- and heteronuclear cases. ‘Experimental’ data are provided by computer simulations using the method of molecular dynamics. Their analysis is made in terms of low order time correlation functions of the translational velocity V of the centre of mass and the rotational velocity ω; these correlation functions are defined in two different ways: (a) with respect to the fixed laboratory axis and (b) with respect to a moving reference frame attached to the molecule itself. It is observed, at the level of the correlation matrix {V, ω}, that the rotation-translation coupling appears only indirectly in presentation (a) while direct evidence is provided in presentation (b). Further, this second presentation displays qualitative differences between homo- and heteronuclear molecules. These results should help in clarifying the validity of various stochastic equations modellin...
TL;DR: In this article, fixed-bed hydropyrolysis has been investigated by treating 100 g coal up to 900°C and 10 MPa, and it has been shown that the benzene content of the oil rises with temperature.
TL;DR: In this article, it was shown that chiral symmetry breaking is a property of strong-coupling lattice theories both in the case where quark color is confined, and also when it is screened by gauge field fluctuations.
TL;DR: In this article, the trace element geochemistry of the early formed anorthositic orthocumulates largely depends upon the amount of a trapped intercumulus liquid in the exposed levels of the Hidra massif.
TL;DR: Fructose 2,6-bisphosphate was identified in Saccharomyces cerevisiae grown on glucose both by its property to be an acid-labile stimulator of 6-phosphofructo 1-kinase and by its ability to be quantitatively converted into fructose 6- phosphate under mild acid conditions.
01 Jan 1981
TL;DR: The development of sensitive radioimmunoassays and of high frequency blood sampling techniques has made possible to measure accurately the variations in plasma levels of pituitary and other hormones over the 24-h cycle and introduced the notion that time of sampling is an important factor in defining normal and pathological levels.
Abstract: The development of sensitive radioimmunoassays and of high frequency blood sampling techniques has made possible to measure accurately the variations in plasma levels of pituitary and other hormones over the 24-h cycle. Data generated challenged the concept of hormonal homeostasis and introduced the notion that time of sampling is an important factor in defining normal and pathological levels. The investigators of hormonal rhythms are faced with the interpretation of data of a new type, namely, time series where at least two types of temporal variation are present: (1) a circadian periodicity (low frequency variation); and (2) short-term, episodic fluctuations (high frequency variation). Because of the complexity of the data and of their dependence upon time, classical statistical methods currently used in clinical investigation cannot be generally applied. The majority of reports on the 24-h profile of blood constituents have therefore been largely descriptive. The determination of possible correlations between hormonal variations and sleep stages has also been often based on visual examination of the data. The sophistication of the sampling procedures and of the biochemical determinations in plasma is thus far greater than that of the quantitative interpretation of the observations.
TL;DR: In this article, a mechanism enabling nonequilibrium systems to select spatially asymmetric solutions is proposed, which operates when a macroscopic mode undergoing a symmetry-breaking bifurcation can interact with a polar or a chiral field.
Abstract: A mechanism enabling nonequilibrium systems to select spatially asymmetric solutions is outlined. It operates when a macroscopic mode undergoing a symmetry-breaking bifurcation can interact with a polar or a chiral field not explicitly involved in the bifurcation. The perturbation of the bifurcation induced by the field allows the system to capture the external asymmetry and build patterns of preferred polarity or preferred chirality. The chemical and biological implications of forming such an asymmetric medium are discussed.
TL;DR: In this paper, the authors investigated the reorientation transition of two distinct monolayers of isoquinoline molecules by using the single-potential step and the doublepotential-step methods under various experimental conditions.
TL;DR: Comparison of two isotypes of variant surface glycoproteins belonging to different serodemes showed almost complete nucleotide homology in the coding sequence of the C-terminal 115 amino acids, indicating that this extension is a universal feature in T. brucei VSGs.
Abstract: Gene duplication and transposition are known to be involved in the mechanism of antigenic variation in Trypanosoma brucei1–3. However, the structure of the antigens in question—the variant surface glycoproteins (VSGs)—is poorly defined. Limited sequencing data show extensive variation between the N-terminal amino acid sequences of different VSGs4,5, although serological studies indicate common antigenic determinants in the C-terminal portion (refs 6, 7 and N. Van Meirvenne, personal communication). More recently, the existence of a C-terminal hydrophobic tail, which is absent from the isolated glycoprotein, was reported8. We have now compared the messenger RNA sequences corresponding to the C-terminal 115 amino acids of two serologically different variants belonging to the same serodeme and report a 35% lack of homology (52% of amino acid positions). However, there is a large homologous area of 33 amino acids making up the C-terminus, which includes the 23-amino acid hydrophobic tail. Our data indicate that this extension is a universal feature in T. brucei VSGs. In addition, comparison of two isotypes (serologically similar VSGs) belonging to different serodemes showed almost complete nucleotide homology in the coding sequence of the C-terminal 115 amino acids.
TL;DR: The synthesis of 1,4,5,8,9,12-hexaazatriphenylene (HAT), a new ligand for low-valent transition metals, is described; it gives mono-, bis- and tris-chromium tetracarbonyl complexes as mentioned in this paper.
TL;DR: In this article, the spherical Skyrme Hartree-fock formalism has been used to derive an effective A -nucleon interaction of the Skyrmes type, which is required to fit the ground-state binding energies of 5ΛHe, 13ΛC and 16ΛO as well as the energy difference between the 16ΞO ground state and its excited state at BΛ = 2.5 MeV where the Λ-particle is assumed to be excited from the s- to the p-shell.