Showing papers by "Aarhus University published in 1979"

Petri Nets, Event Structures and Domains

Abstract: The general aim of the paper is to find a theory of concurrency combining the approaches of Petri and Scott (and other workers) [Pet 1,2],ESeo ~,3],[Sto]. To connect the abstract ideas of events and domains of information, we show how causal nets induce certain kinds of domains where the information points are certain sets of events. This allows translations between the languages of net theory and domain theory. Following the idea that events of causal nets are occurrences we generalise causal nets to occurrence nets, by adding forwards conflict; just as infinite flow chartsunfold finite ones [Sco 2], so transition nets can be unfolded into occurrence nets. Next we extend the above connections between nets and domains to these new nets. Event structures, which are intermediate between nets and domains play an important part in all our work.

The depth resolution of sputter profiling

Abstract: It is shown that the bulk radiation damage accompanying sputtering events sets ultimate limits to the depth resolution attainable in sputter profiling. These limits have been reached in a few cases but most published experimental resolutions are dominated either by instrumental effects or deterioration of depth resolution caused by surface-topography changes. The radiation-damage induced mixing is called “cascade mixing”. Guidelines for selection of projectile species and energies to minimize such mixing are given and numerical estimates for attainable depth resolutions are presented. Finally, the influence of cascade mixing is assessed relative to that of recoil implantation.

Somatostatin cell processes as pathways for paracrine secretion

Abstract: Somatostatin is produced by gastrointestinal endocrine cells that have long, nonluminal, cytoplasmic processes. Such processes terminate on other cell types, including gastrin-producing and hydrochloric acid-producing cells, whose functions are profoundly affected by somatostatin. The findings suggest that somatostatin cells control the functions of other cells through local release of the peptide by way of cytoplasmic processes. Also, certain other types of gastrointestinal endocrine cells have similar cytoplasmic prolongations, which may have analogous local (paracrine) regulatory functions.

Descriptions of exchange and correlation effects in inhomogeneous electron systems

Abstract: Starting from a formula relating the exchange-correlation (XC) energy of the Kohn-Sham density-functional formalism to the XC hole, we discuss some general but approximate descriptions of XC effects in inhomogeneous electron systems, in particular valence electrons, using homogeneous-electron-gas data as input. The new descriptions have all the virtues of the local-density (LD) approximation, including the computational simplicity of a local XC potential, and it reduces to the latter in the proper limit. In addition, they have a physically motivated nonlocal dependence on the electron density, which results in such desirable features as an asymptotical ${r}^{\ensuremath{-}1}$ behavior far away from, e.g., atoms and a ${z}^{\ensuremath{-}1}$ behavior of the potential outside solid surfaces. We present two explicit forms of the XC energy functional, one which is exact for a system with almost constant density but with possibly spatially rapid variations, and another which is exact in some simple limits. Illustrations on atoms show them to reduce the error in the total energy by about one order of magnitude compared with the LD approximation. Applications to surfaces show a reasonable modeling of the image-potential effect but also illustrate shortcomings of the approximations. We also point out shortcomings of two earlier methods to extend the LD approximation, the gradient expansion, and the expansion to second order in the density variations, when they are applied to inhomogeneous systems.

Determination of membrane thickness distribution from orthogonal intercepts

Abstract: This report deals with the reconstruction of the distribution of membrane thickness T from that of orthogonal length Lo, measured in random section planes. In such planes the membrane appears as a band and the linear distance from one of its boundaries perpendicular to the opposite one is the length of the orthogonal intercept. Using a membrane model, an integral equation relating the probability density functions of orthogonal intercept length f(lo) and membrane thickness g(tau) is derived. Relations between moments are derived and the analytic solution to the problem of reconstructing g(tau) from f(lo) is given. The parametric approach by which it assumed that g(tau) has some known analytic form with unknown parameters is considered, and the use of a suggested analytic form for describing the thickness distribution of the human glomerular basement membrane is discussed.

Commissural and intrinsic connections of the rat hippocampus.

Abstract: The commissural and intrinsic connections of the hippocampus were studied using the Fink-Heimer method and the horseradish peroxidase (HRP) uptake technique. A conspicuous septo-temporal gradient was found of the density of the commissural projection that passes through the psalterium ventrale to the Ammon's horn. The degeneration resulting from transection of the psalterium ventrale was most dense in the septal tip and decreased towards the temporal tip. The commissural and ipsilateral connections from the hilus fasciae dentatae (CA4) and regio inferior (CA3/CA2) were found to terminate in different parts of the hippocampus. The hilus fasciae dentatae gave rise to ipsilateral and commissural projections to the dentate area only. The regio inferior has ipsilateral and commissural projections to the Ammon's horn. A specific termination pattern was found of the projection from regio inferior to stratum radiatum of both the ipsilateral and contralateral regio superior (CA1) and regio inferior (CA2/CA3). At levels temporal to the lesion, the projection is primarily to the superficial part of stratum radiatum, while at levels septal to the lesion the terminal zone occupies the deep part of the layer. This pattern was not related to the position of the cells of origin, along the septotemporal or subiculo-dentate axes. In general, the commissural projections showed the same degree of septotemporal divergence as the ipsilateral projections. The only major difference in the terminal fields of the two sets of projections to the Ammon's horn was that the terminal zone of the commissural projection to stratum oriens was always more dense than that of the ipsilateral projection to this layer, while an inverse gradient was seen in stratum radiatum. The projections from the septal and middle dorso-ventral parts of regio inferior differed. The temporal spread of the projections from the septal part was large while that from the projections arising at middle dorso-ventral levels was more restricted. Moreover, a longitudinal association path interconnecting different parts of the regio inferior along the septo-temporal axis was seen to arise only from the cells in the septal parts of the regio inferior. Each part of the regio inferior projected to all parts of stratum radiatum and oriens of the contralateral Ammon's horn. However, the projection to the contralateral regio inferior was most dense at the site homotopic to that lesioned. The ventricular part of regio inferior projected primarily to the contralateral stratum oriens of the Ammon's horn, while the part adjacent to the dentate area mostly supplied stratum radiatum.

A comparison of oxygen, nitrate, and sulfate respiration in coastal marine sediments.

Abstract: Aerobic respiration with oxygen and anaerobic respiration with nitrate (denitrification) and sulfate (sulfate reduction) were measured during winter and summer in two coastal marine sediments (Denmark). Both aerobic respiration and denitrification took place in the oxidized surface layer, whereas sulfate reduction was most significant in the deeper, reduced sediment. The low availability of nitrate apparently limited the activity of denitrification during summer to less than 0.2 mmoles NO 3 − m−2 day−1, whereas activities of 1.0–3.0 mmoles NO 3 − m−2 day−1 were measured during winter. Sulfate reduction, on the contrary, increased from 2.6–7.6 mmoles SO 4 2− m−2 day−1 during winter to 9.8–15.1 mmoles SO 4 2− m−2 day−1 during summer. The aerobic respiration was high during summer, 135–140 mmoles O2 m−2 day−1, as compared to estimated winter activities of about 30 mmoles O2 m−2 day−1. The little importance of denitrification relative to aerobic respiration and sulfate reduction is discussed in relation to the availability and distribution of oxygen, nitrate, and sulfate in the sediments and to the detritus mineralization.

Microbial Transformations of Sulfur-Compounds in a Stratified Lake (Solar Lake, Sinai)

Abstract: Microbiological and chemical aspects of the sulfur cycle were studied in the chemocline of a tropical salt lake. Oxygen and sulfide coexisted in a O-lo-cm layer which migrated up and down during a diurnal cycle. Sulfide was rapidly oxidized by oxygen, with a half-life of 5-10 min, to produce mainly sulfate and thiosulfate. Thiosulfate and elemental sulfur had concentration maxima in the chemocline while polysulfide was abundant throughout the sulfide zone. Radiotracer experiments showed that the elemental sulfur was produced by anoxygenic photosynthesis in cyanobacteria. The elemental sulfur was further oxidized or again reduced, depending on the presence or absence of oxygen. Cyanobacteria in the che- mocline shifted between anoxygenic photosynthesis in the morning and oxygenic photosyn- thesis in the afternoon. A high dark CO, fixation was found in the chemocline which could be stimulated by sulfide, elemental sulfur, and thiosulfate. The oxidation rate of sulfide in the chemocline was dependent on the presence of bacteria.

Method for Measuring Rates of NH(4) Turnover in Anoxic Marine Sediments, Using a N-NH(4) Dilution Technique.

Abstract: A method is described for the determination of the net and total rates of NH(4) production and NH(4) incorporation at different depths in an anoxic marine sediment. N-NH(4) was added to the sediment NH(4) pool, and the N content was assayed after 0, 2, and 5 days of incubation. The pool size changed during incubation; this change in pool size is incorporated into a model which predicts the dynamics of N-NH(4) dilution. A simple microdiffusion of NH(3) was followed by an emission spectrometry analysis of N content. This procedure avoided all problems of cross-contamination. The model was tested and rates were measured in four sediment cores, at seven different depths. The high correlation coefficients (mean, 0.96 for the 0- to 2-, 2- to 4-, 4- to 6-, and 6- to 8-cm sediment fractions) indicated that the model was correct and that the measured rates were valid. The immediate distribution of N-NH(4) between interstitial and exchangeable NH(4) pools indicated that it was the combined pool that was turning over. In the 0- to 2-cm fraction at 17 degrees C the net rate of NH(4) production was 274 (standard deviation, 31) nmol cm day, and the mean total rate of NH(4) production was 309 (standard deviation, 39) nmol cm day; both rates decreased to <1% of these values in the 12- to 14-cm fractions.

Distribution and quantitative development of aquatic macrophytes in relation to sediment characteristics in oligotrophic Lake Kalgaard, Denmark

Abstract: SUMMARY. The distribution and quantitative development of aquatic macrophytes have been studied in oligotrophic Lake Kalgaard, Denmark. The vegetation is dominated by isoetid species, which are widely distributed (about 40% of the lake bottom) compared to emergent and floating-leaved macrophytes (about 4%). Littorella uniflora dominates at depths of 0–2 m and Isoetes lacustris from 2.0 to 4.5m. Within the colonization area the mean midsummer biomass of Littorella is 112g organic dry weight m−2 and that of Isoetes, 66 gm−2. The total biomass of these two species constitutes 99% of the biomass of submerged macrophytes. The perennial Littorella shows only small seasonal biomass variations. The vegetational biomass, the above-ground fraction of the biomass, and the weight of individual plants all increased with the organic content of the sediment at water depths from 0 to 0.75 m. At the same time the interstitial concentrations of carbon dioxide, extractable inorganic nitrogen, and exchangeable inorganic phosphorus increased, thus supporting the hypothesis that an increasing organic content of the sediments at this low level creates a physiologically richer medium for the plants. The isoetid growth form is discussed in relation to the chemical environment of oligotrophic, softwater lakes.

Met- and Leu-enkephalin immunoreactivity in separate neurones.

Abstract: A pair of pentapeptides, Met- and Leu-enkephalin were recently isolated from brain tissue. The two peptides seem to represent endogenous opiate receptor ligands and have by immunocytochemical and radioimmunoassay studies been shown to occur in an extensive system of cerebral and peripheral nerves. The relative proportions between Met- and Leu-enkephalin varies between different brain regions and also between different species, suggesting the existence of separate populations of Met- and Leu-enkephalin nerves. Until now, however, immunocytochemistry has given no support for this notion. We report here evidence of separate populations of Met- and Leu-enkephalin nerves.

Combined effects of adrenaline and insulin on active electrogenic Na + –K + transport in rat soleus muscle

Abstract: Both β2-adrenoreceptor stimulants (such as adrenaline and salbutamol) and insulin can increase active Na+–K+ transport1–6 and hyperpolarise skeletal muscle cells1,2,7–9. Thus, adrenaline and insulin, which are otherwise antagonistic regulators of several metabolic processes, have one action in common, namely, stimulation of active ion translocation. This is especially interesting as cyclic AMP stimulates Na+–K+ transport2, whereas a lowering of the cytoplasmic concentration of cyclic AMP has been proposed as an early signal in the action of insulin10,11. Here we report the results of experiments in which the active Na+–K+ transport and membrane potential (EM) of rat soleus muscles were studied during the action of supramaximal doses of insulin and β2-adrenoreceptor stimulants, alone and in combination. We conclude that the stimulant action of insulin on active electrogenic Na+–K+ transport is unlikely to be evoked by a lowering of the intracellular concentration of cyclic AMP.

Time-temperature relationship th hyperthermic treatment of malignant and normal tissue in vivo

Abstract: The effect of hyperthermia on normal and tumor tissue was studied following water bath heating of a methylcholanthrene-induced fibrosarcoma (FSaI) isotransplanted into the feet of C3H mice. The time-temperature relation for the 50% tumor control dose over the temperature range of 41.5--45.5 degrees showed a log linear relationship which followed a biphasically modified Arrhenius plot. At temperatures above 43 degrees, there was a 50% reduction in heating time to obtain the 50% tumor control dose for each 1 degree increase in temperature, corresponding to an activation energy of 140 kcal/mol. At temperatures below 43 degrees, the curve was steeper, with a tendency to double the treatment time for each 0.5 degree reduction in temperature (activation energy, approximately 230kcal/mol). Normal tissue damage in the tumor-bearing foot was estimated at two levels with a 50% response dose assay. Severe normal tissue damage showed a time-temperature relationship similar to the tumor response, thus indicating no variation in therapeutic ratio at different temperatures. However, for slight tissue damage, the therapeutic ratio increased with decreasing temperatures, yielding a better therapeutic ratio at lower temperatures. The time-temperature relationship obtained in the FSaI fibrosarcoma is supported by other studies and points to a general time-temperature relationship for hyperthermic tumor destruction.

Projections from the subiculum to the deep layers of the ipsilateral presubicular and entorhinal cortices in the guinea pig.

Abstract: Projections from the subiculum to retrohippocampal areas were studied by reduced silver impregnation of anterograde degeneration and by autoradiographic tracing of transported proteins following injections of radioactive amino acids. The subiculum was found to project to the presubiculum and to the medial and lateral parts of the entorhinal area. The projections are exclusively ipsilateral, and arranged in a dorso-ventral topographical order with the terminations confined to the deep cortical layers. The projections form part of multisynaptic chains within the hippocampal region and must also be implicated in output routes for hippocampal activity additional to the fimbria-fornix system.

Structure of the backbone in myosin filaments of muscle.

Abstract: New X-ray data suggest how myosin rods, themselves α-helical coiled coils, form the thick filament backbone of crustacean muscles by additional supercoiling. Natural transformations of this structure may describe the myosin backbone in many other animals also.