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Showing papers by "University of Antwerp published in 1980"


Journal ArticleDOI
TL;DR: A relationship between parallel rewriting systems and two-way machines is investigated, finding restrictions on the “copying power” of these devices endow them with rich structuring and give insight into the issues of determinism, parallelism, and copying.

181 citations


Journal ArticleDOI
TL;DR: The main theorem is a result on the combinatorial structure of graph languages generated by NLC grammars; it resembles the pumping theorem for context-free string languages.

163 citations


OtherDOI
TL;DR: In this paper, the effects of temperature on different functional components of the blood vessel wall were analyzed, and role in the intact organism of the human body was discussed, including the role of light and photorelaxation.
Abstract: The sections in this article are: 1 Temperature 1.1 Effect of Temperature on Isolated Blood Vessel Wall 1.2 Analysis of Effects of Temperature on Different Functional Components of Blood Vessel Wall 1.3 Role in the Intact Organism 2 Light 2.1 Photoactivated Contraction 2.2 Photorelaxation 2.3 Summary 3 Vibration

98 citations


Journal ArticleDOI
TL;DR: Despite the important contribution of high‐resolution electron microscopy to materials science, the use of computer simulation as a reliable tool for the interpretation of the structure images in complex crystals or disordered solids has been limited seriously by the high computer demands of the available computational techniques.
Abstract: SUMMARY Despite the important contribution of high-resolution electron microscopy to materials science, the use of computer simulation as a reliable tool for the interpretation of the structure images in complex crystals or disordered solids has been limited seriously by the high computer demands of the available computational techniques.

96 citations


Journal ArticleDOI
TL;DR: In this paper, the distribution patterns of aliphatic and polyaromatic hydrocarbons as a function of molecular weight or carbon number are reported for typical summer and winter samples collected under the most frequently occurring stable meteorological conditions, at two urban and one rural site in Belgium, the Netherlands and Bolivia.

95 citations


Journal ArticleDOI
TL;DR: Very simple languages are introduced which play the same role for the class of recursively enumerable languages that the Dyck languages play for theclass of context-free languages.
Abstract: Fixed point languages and equality languages of homomorphisms and dgsm mappings are consid- ered. Some basic properties of these classes of languages are proved, and it is shown how to use them to represent recursively enumerable sets. In particular, very simple languages are introduced which play the same role for the class of recursively enumerable languages that the Dyck languages play for the class of context-free languages. Finally, a new type of acceptor for defining equality languages is introduced. KEY WOADS AND PHRASES: equality language, fLxed point language, recursively enumerable language, determin- istic sequential machine, Turing machine, Post correspondence problem, shuffle, AFL generator, representation of languages

93 citations


Journal ArticleDOI
TL;DR: Three topics are investigated quite thoroughly: (1) the role of the connection relation in an NLC grammar, (2) “context-freeness” of NLC grammars, and (3) the ability of N LC grammARS to generate string languages.

85 citations


Journal ArticleDOI
TL;DR: The reproducibility of the PIXE analysis, as determined by analyzing up to 20 targets from the same material, was of the order of 10% or better as mentioned in this paper, indicating that PIXe can yield data which are accurate to within 10%.

81 citations


Journal ArticleDOI
TL;DR: In this article, the effect of exchange effects in the dielectric function of the homogeneous electron gas was studied, and the Hartree-Fock ground state energy was tested for its internal consistency.
Abstract: By making the dynamical-exchange decoupling in the equation of motion for the Wigner distribution function, exchange effects in the dielectric function of the homogeneous electron gas were, in an earlier derivation, described by a frequency-dependent local-field correction $G(q,\ensuremath{\omega})$. In paper I, details were provided how the sixfold integral for $G(q,\ensuremath{\omega})$ can be reduced analytically into a double integral, adapted for numerical purposes. In this paper, the consequences of dynamical-exchange effects are studied, and the theory is tested for its internal consistency. The evaluation of the pair correlation function $g(r)$ at the origin from both the static limit and the high-frequency limit of the frequency-dependent local-field correction $G(q,\ensuremath{\omega})$ leads to the same value $g(0)=\frac{1}{2}$, in contrast to other theories where, from both limits, different results are obtained. Also, the compressibility, calculated from the dielectric function including exchange, agrees with the Hartree-Fock result. Furthermore, it is shown that the high-frequency limit of $G(q,\ensuremath{\omega})$ satisfies the general properties implied by the third-frequency-moment sum rule, resulting again in $g(0)=\frac{1}{2}$ and leading to the Hartree-Fock ground-state energy. This consistency between the static and high-frequency behavior of $G(q,\ensuremath{\omega})$ cannot be fulfilled by any static approximation to $G(q,\ensuremath{\omega})$, because an adequate treatment of dynamical-exchange effects involves excited states that are consistent with the Hartree-Fock ground state. In the static limit, $G(q,\ensuremath{\omega})$ exhibits a relatively sharp peak near $q=2{k}_{F}$. This peak induces an instability of the homogeneous electron gas, quite similar to and in the same density range as the instability of the spin susceptibility discussed by Hamann and Overhauser. For ${r}_{s}\ensuremath{\ge}10.6$, a supplementary instability relative to charge-density deformations occurs. The frequency dependence of $G(q,\ensuremath{\omega})$ is examined, and numerical values for $\mathrm{Re}G(q,\ensuremath{\omega})$ and $\mathrm{Im}G(q,\ensuremath{\omega})$ are presented. The real part of the dielectric function and the imaginary part of the inverse dielectric function are plotted for several densities in the metallic range. Compared to the random-phase approximation (RPA), the frequencies of the maxima in the structure factor obtained in the present work (i.e., with dynamical-exchange decoupling) are shifted to lower frequencies. The plasmon dispersion is considerably closer to recent experimental data in aluminium than with RPA. Finally, it turns out that the inclusion of frequency-dependent exchange effects results in the natural occurrence of spin- and charge-density waves. These are the dynamical extension of the instability relative to magnetic perturbations, found in the static limit at low densities.

60 citations


Journal ArticleDOI
TL;DR: In this paper, the 6-oxo-prostaglandin F1α (6oxoPGF1α) degradation product of prostacyclin was measured in arterial blood from anaesthetized rabbits, befor and after intravenous (i.v) administration of endotoxin (Lipopolysaccharide W.E. coli 0111:B4, 5 mg/kg).

55 citations


Journal ArticleDOI
TL;DR: The use of a gas-liquid chromatograph in combination with a graphite-furnace atomic absorption spectrometer is described for the determination of tetraalkyllead compounds.

Journal ArticleDOI
TL;DR: In this paper, a detailed study of energy-dispersive X-ray spectra is undertaken, where a method for a systematic and accurate description of the K and L spectra; a digital correction for the peak profile is evaluated.
Abstract: A detailed study of energy-dispersive X-ray spectra is undertaken. Considerable attention is given to a method for a systematic and accurate description of the K and L spectra; a digital correction for the peak profile is evaluated. The following second order effects and spectral artefacts are investigated: radiative Auger transitions, spectral background components, Raman scattering of X-rays, silicon escape, fluorescence of the detector materials, and sum peaks.

Journal ArticleDOI
TL;DR: In this article, a procedure for the sequential determination of arsenite and arsenate in samples of natural waters is described, based on the extraction of arsenic(III) with ammonium sec-butyl dithiophosphate and measurement, after re-extraction into water, by graphitefurnace atomic absorption spectrometry.

Journal ArticleDOI
TL;DR: It is demonstrated that anoxia can cause constriction of large coronary arteries and that lidoflazine depresses both anoxic and normoxic contractions of coronary smooth muscle.


Journal ArticleDOI
TL;DR: Electronic analysis of the response to rapid small sinusoidal perturbations gave a continuous measurement of the elastic and viscous components of total stiffness, implying that hypoxic contracture unlike reoxygenation contracture is not due solely to a rise in intracellular calcium, but is associated with a component of stiffness not participating an active force development, for example rigor.
Abstract: Isolated rat papillary muscle preparations were used to study hypoxic contracture, and cat papillary muscle preparations with ouabain to study reoxygenation contracture. Electronic analysis of the response to rapid small sinusoidal perturbations gave a continuous measurement of the elastic and viscous components of total stiffness. Increased resting force during hypoxic contracture was characterised by an increase in resting elastic and viscous stiffness relative to the control stiffness-active force relationships. During reoxygenation contracture the stiffness-force relationships followed those of active force development. The linear active force-elastic stiffness relationship (dt/dl=kT+c) was also reversibly altered during hypoxic contracture, predominantly by an increase in intercept c. These data imply that hypoxic contracture unlike reoxygenation contracture is not due solely to a rise in intracellular calcium, but is associated with a component of stiffness not participating an active force development, for example rigor.

Journal ArticleDOI
01 Aug 1980-Talanta
TL;DR: Two commercially available systems for the determination of selenium by hydride-generation and atomic-absorption spectrometry were compared and both systems evaluated with respect to performance and applicability to determination of traces of Selenium.

Journal ArticleDOI
TL;DR: The direct determination of arsenic by graphite-furnace atomic absorption spectrometry is critically examined in this article, where it is shown that matrix stabilization by nickel salts is effective for preventing charring losses of arsenic.

Journal ArticleDOI
TL;DR: Aerosols were collected with a high-volume sampler for 8-20 day periods from July 1975 to August 1977 at a remote mountain location near La Paz, Bolivia as discussed by the authors.

Journal ArticleDOI
TL;DR: The adrenergic neuro-effector interaction undergoes a diverging long-term adaptation in the heart and the blood vessels of hypertensive animals, and tends to increase, but in the latter to reduce, the efficiency of sympathetic nervous control.
Abstract: 1. The ability of the blood vessel wall to synthesize noradrenaline is augmented at the early stages of genetic hypertension in animals. It usually is normal, or reduced in chronic hypertension. 2. The exocytotic release of noradrenaline is greater than normal, in the early stages of a number of experimental models of hypertension. 3. Postjunctional receptors for noradrenaline are not uniform throughout the vascular tree. Their sensitivity changes during the development of high blood pressure. 4. In chronic hypertension neuronal uptake and the extraneuronal disposition of released noradrenaline is depressed in the heart, but accelerated in the blood vessel wall. 5. The adrenergic neuro-effector interaction undergoes a diverging long-term adaptation in the heart and the blood vessels of hypertensive animals. In the former this tends to increase, but in the latter to reduce, the efficiency of sympathetic nervous control.

Journal ArticleDOI
TL;DR: A characteristic tomaculous neuropathy was discovered in hereditary pressure-sensitive neuropathy, which is autosomal dominant with total penetrance but variable expression.

Book ChapterDOI
TL;DR: This report summarizes the accumulated evidence which implicates both a glycoprotein and a ganglioside in the structure and function of the TSH receptor.
Abstract: Recent studies (1, 2, 28–30, 33–35) have implicated ganglio-sides in the receptor recognition process for thyrotropin (TSH) and have led to the hypothesis (15–17, 19) that the TSH receptor is structurally and functionally related to receptors for other ligands which interact with gangliosides in vitro, ie, cholera toxin, tetanus toxin, and interferon This report summarizes the accumulated evidence which implicates both a glycoprotein (4, 38–40, 43) and a ganglioside in the structure and function of the TSH receptor In the context of this symposium, particular attention will be addressed to the role of the ganglioside

Journal ArticleDOI
TL;DR: A selected ion monitoring method for the determination of 6-oxo-PGF1 alpha, the stable end-product of prostacyclin, in biological fluids has been developed.
Abstract: A selected ion monitoring method for the determination of 6-oxo-PGF1 alpha, the stable end-product of prostacyclin, in biological fluids has been developed. In this method, biosynthetically prepared [2H6]-6-oxo-PGF1 alpha is used as internal standard. The method involves extraction, thin-layer chromatography purification and derivatization into the methyl ester, methoxime, trimethylsilyl ether derivatives by carrying out the methoximation first. Quantitative gas chromatographic mass spectrometric analysis is performed in the electron impact mode by monitoring the [M - (TMSOH + CH3O)]+ fragment ions. The use of this method in the measurement of 6-oxo-PGF1 alpha in serous fluids and in incubation media of serous tissues is described.

Journal ArticleDOI
TL;DR: The electron diffraction data for gaseous cyclohexanone, collected at 371 K, combined with microwave rotational constants, can be explained by a single chair conformation as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, chemical ionization desorption mass spectrometry was used for a series of original pyridinium nucleoside salts, together with some purine and pyrimidine nucleo(t)sides.
Abstract: Promising results were obtained by chemical ionization desorption mass spectrometry for a series of original pyridinium nucleoside salts, together with some purine and pyrimidine nucleo(t)sides. They were recorded using ammonia as reagent gas and tungsten wires. Principal ions correspond to protonated or cationized ([NH4]+) forms of the molecular ion or the free base depending upon the compound under investigation.

Journal ArticleDOI
TL;DR: A data acquisition system and processing software for spark-source mass spectrometry (s.m.s.s.) with photographic detection with off-line software that renders the system suitable for research purposes as well as for routine analysis.

Journal ArticleDOI
TL;DR: The complete set of vacuum solutions for the metric tensor of a static spherically symmetric field is given, some of these solutions showing the remarkable feature of not agreeing with the classically well-known weak-field solutions of the Brans-Dicke (B.D.) equations as discussed by the authors.
Abstract: The complete set of vacuum solutions for the metric tensor of a static spherically symmetric field is given, some of these solutions showing the remarkable feature of not agreeing-even in first order-with the classically well-known weak-field solutions of the Brans-Dicke (B.D.) equations. The existence of a particular two-parameter family of solutions raises severe doubts about the so-called Machian aspect of B.D. theory.

Journal ArticleDOI
TL;DR: The relationship between adrenergic nerve activity and neuronal uptake was investigated in this article, where a rat tail artery was mounted in organ chambers and isometric contractions were recorded, and the results indicated that spontaneous activity of rat tail arteries is related to the leakage of norepinephrine from nerve endings.
Abstract: The relationship between adrenergic nerve activity and neuronal uptake was investigated. Helically cut strips of rat tail artery were mounted in organ chambers and isometric contractions were recorded. Spontaneous contractions were occasionally observed and these contractions were blocked by phentolamine. Cumulative addition of cocaine produced contractions of the strips. These contractions were blocked by phentolamine and reduced after denervation with 6-hydroxydopamine. Cocaine potentiated the contractile responses to exogenous norepinephrine and caused a shift to the left in the concentration--response curve. Contractions in response to low-frequency field stimulation were potentiated by cocaine; contractions produced by high frequencies were not altered by the drug. Cocaine had no effect on contractions produced by depolarization of the prejunctional membrane with high potassium. The relative rates of relaxation following high- and low-frequency stimulation were increased similarly by cocaine. The results indicate (1) the spontaneous activity of rat tail artery is related to the leakage of norepinephrine from nerve endings; (2) contraction in response to cocaine alone probably results from inhibition of neuronal uptake and the release of endogenous norepinephrine; and (3) the amine uptake mechanism is not operative during depolarization of prejunctional membrane.

Journal ArticleDOI
TL;DR: The accessory nidamental glands of the cuttlefish, Sepia officinalis L. show an intense orange-red coloration in mature females, due to carotenoid pigments which occur in symbiotic bacteria.
Abstract: 1. 1. The accessory nidamental glands of the cuttlefish, Sepia officinalis L. show an intense orange-red coloration in mature females. This colour is due to carotenoid pigments which occur in symbiotic bacteria. 2. 2. Six different pigmented strains of bacteria were isolated. 3. 3. The main pigment in five of these strains is β-carotene. 4. 4. The main pigment in the sixth strain is the keto carotenoid, adonixanthin.

Journal ArticleDOI
H. Nullens1, G. De Roy1, P. Van Espen1, F. C. Adams1, Etienne F. Vansant1 
TL;DR: In this paper, a non-linear least-squares program for the analysis of Mossbauer spectra is presented, which is capable of resolving very complex spectra and can be used on a minicomputer system, with regard to both calculation time and memory requirements.