Showing papers by "Aarhus University published in 1982"

Mineralization of organic matter in the sea bed—the role of sulphate reduction

Abstract: The bacterial reduction of sulphate to sulphide at the sea bed is a key process in the oceanic sulphur cycle, and is responsible for the oxidation of organic matter which becomes buried below the oxic and sub-oxic zones of the sea bed. The oxic surface layer of the sea bed varies in thickness from a few millimetres in sheltered coastal areas to ⩾1 m in pelagic sediments1,2. Below this layer, organic matter is mineralized mainly by fermenting, denitrifying, sulphate-reducing and methane-producing bacteria. Sulphate reduction is the predominant terminal step in the mineralization processes of sulphate-rich shelf sediments where the sulphate reducers inhibit the methanogens by competing with them for common substrates3–5. Sulphate reduction may therefore have a quantitatively important role in the overall oxidation of organic matter in the sea bed. Recently, concurrent measurements of oxygen uptake and sulphate reduction in a coastal sediment6 have demonstrated the importance of the sulphate-reducing bacteria in the mineralization of organic carbon. I present here the first comparative survey of aerobic and anaerobic mineralization in the sea bed based on direct rate measurements of the two processes. The results demonstrate a surprisingly high contribution from the sulphate-reducers. In coastal sediments, this specialized group of bacteria oxidized as much organic matter to CO2 as did all the aerobic organisms. Their relative contribution decreased three fold over the continental shelf from the shore to a depth of 200 m.

Results on the Propositional µ-Calculus

Abstract: We define a propositional version of the Μ-calculus, and give an exponential-time decision procedure, small model property, and complete deductive system. We also show that it is strictly more expressive than PDL. Finally, we give an algebraic semantics and prove a representation theorem.

Reduction of ferric iron in anaerobic, marine sediment and interaction with reduction of nitrate and sulfate.

Abstract: Studies were carried out to elucidate the nature and importance of Fe3+ reduction in anaerobic slurries of marine surface sediment. A constant accumulation of Fe2+ took place immediately after the endogenous NO3− was depleted. Pasteurized controls showed no activity of Fe3+ reduction. Additions of 0.2 mM NO3− and NO2− to the active slurries arrested the Fe3+ reduction, and the process was resumed only after a depletion of the added compounds. Extended, initial aeration of the sediment did not affect the capacity for reduction of NO3− and Fe3+, but the treatments with NO3− increased the capacity for Fe3+ reduction. Addition of 20 mM MoO42− completely inhibited the SO42− reduction, but did not affect the reduction of Fe3+. The process of Fe3+ reduction was most likely associated with the activity of facultative anaerobic, NO3−-reducing bacteria. In surface sediment, the bulk of the Fe3+ reduction may be microbial, and the process may be important for mineralization in situ if the availability of NO3− is low.

Covalent effects in the effective-medium theory of chemical binding: Hydrogen heats of solution in the 3 d metals

Abstract: The effective-medium-theory estimate of the binding energy of an atom to a host (another atom, molecule, or solid) from the host electron density, and the binding energy of the atom in a homogeneous electron gas has been extended to include covalent effects. The covalent term involves the difference in the one-electron energies between the atom in the host and the atom in homogeneous electron-gas systems. The scheme is tested for helium impurities in several transition metals and for hydrogen impurities in all the metals from potassium to copper. For helium all available binding energies are well reproduced and all the observed trends in the hydrogen heat of solution can be accounted for.

Results on the Propositional µ-Calculus

Abstract: We define a propositional version of the µ-calculus, and give an exponential-time decision procedure, small model property, and complete deductive system. We also show that it is strictly more expressive than PDL. Finally we give an algebraic semantics and prove a representation theorem.

Ecology of the bacteria of the sulphur cycle with special reference to anoxic-oxic interface environments

Abstract: H $\_2$ S is produced as a main end-product of anaerobic mineralization in anoxic, sulphate-rich environments by a diverse population of sulphate-reducing bacteria. The sulphate reducers can carry out an almost complete oxidation of detrital organic matter to CO $\_2$ . The H $\_2$ S consequently becomes an important electron carrier from the anoxic to the oxic world. Thiobacilli and other colourless sulphur bacteria have the potential to oxidize the H $\_2$ S at the oxic-anoxic interface in sediments or stratified waters, but their role is still poorly understood. A comparison of sulphide oxidation processes in the chemoclines of the Black Sea, the Solar Lake and in a Beggiatoa mat indicated that depth scales and retention times of coexisting O $\_2$ and H $\_2$ S regulate the bacterial involvement in the sulphide oxidation. The H $\_2$ S specialists, Beggiatoa and Thiovulum, are optimally adapted to compete with the autocatalytic oxidation of H $\_2$ S by O $\_2$ . Microelectrode measurements show retention times of O $\_2$ -H $\_2$ S in the bacterial mats or veils of less than 1 s. In photic chemoclines of stratified waters or sulfureta, the phototrophic sulphur bacteria or cyanobacteria interact with the sulphide oxidation at the O $\_2$ -H $\_2$ S interface. Short cycles between H $\_2$ S and intermediate oxidation products, S $^0$ or S $\_2$ O $^{2-}\_3$ , are created. The bacteria of the sulfuretum are highly adapted to the diurnal rhythm of light, O $\_2$ and H $\_2$ S.

High-Level Petri Nets

Abstract: This paper combines two closely related net models, predicate/transition nets and coloured Petri nets, into a new net model called high-level Petri nets. The new model is intended to combine the qualities of the two old models into a single formalism, and we propose in future to use high-level Petri nets instead of both predicate/transition nets and coloured Petri nets.

Event Structure Semantics for CCS and Related Languages

Abstract: We give denotational semantics to a wide range of parallel programming languages based on the idea of Milner’s CCS [Mil80a], that processes communicate by events of mutual synchronization. Processes are denoted by labeled event structures. Event structures represent concurrency rather directly, as in net theory [Bra80]. The semantics does not simulate concurrency by non-deterministic interleaving. We first define a category E of event structures [NPW79, NPW81, Win80] appropriate to synchronized communication. The category bears a natural relation to a subcategory of trees though an interleaving functor; so results transfer to trees neatly. Then we introduce the concept of a synchronization algebra (S.A.) on labels by adopting an idea of Milner [Mil80b]. An S.A. specifies how two processes synchronize via labels on their events. From each S.A., L, we derive a category EL of labeled event structures with natural operations for composing labeled event structures. In particular the parallel composition L is derived from the product in E. We obtain semantics for a class of CCS-like languages by varying the S.A.. Synchronization algebras are very general so the class is very broad, handling synchrony and asynchrony in a common framework. As a corollary we get an event structure semantics for CCS. When interleaved our semantics is Milner’s synchronization/communication tree semantics [Mil80a]. However our semantics distinguishes more terms as it reflects concurrency. Event structure semantics is at a rather basic level of abstraction but should support all abstract notions of equivalence (see [Mil80a] for examples), including those which take concurrency into account.

A flexible approach to interprocedural data flow analysis and programs with recursive data structures

Abstract: A new approach to data flow analysis of procedural programs and programs with recursive data structures is described. The method depends on simulation of the interpreter for the subject programming language using a retrieval function to approximate a program's data structures.

Exogenous selenium in the brain. A histochemical technique for light and electron microscopical localization of catalytic selenium bonds.

Abstract: Transcardial perfusion or intraperitoneal injections with sodium selenite result in the creation of selenium bonds that can be visualized by physical development. The present paper describes how these catalytic bonds are made visible in the tissues by surrounding them with shells of metallic silver. Based on experiments with chelating agents, the possibility that selenium-metal bonds are the catalysts is discussed. In the brain, the selenium pattern is delicate and highly laminated, the grains of silver being orderly arranged corresponding with the neuropil morphology. The precipitate is most densely packed in cortical regions. The difference in staining intensity seen in different regions of the CNS reflects the density of selenium reactive terminals. The visualized selenium bonds are predominantly located within boutons, and examination in the electron microscope reveals accumulation in the presynaptic regions. In a few places precipitates can also be found in axons, but have not been observed in perikarya or dendrites. The only non-neuronal locations of selenium were sparsely scattered, astrocyte-like neuroglia, predominantly found in the cerebellum and the hypothalamus; infrequently a few blood vessels were also stained. Sections from kidney and liver are presented as examples of localizations outside the CNS of exogenous selenium.

Seed production and outbreaks of non-cyclic rodent populations in deciduous forests.

Abstract: In a 10-year study period, outbreaks of the bank vole, Clethrionomys glareolus, Schreber only occurred in years following huge seed production of European beech, Fagus sylvatica Intensive winter reprodution preceded the outbreaks, in contrast to a normal breeding season from April through September No winter reproduction occurred in nearby populations from habitats without mast production During the winter, the average weight of C glareolus remained high in the mast forests and the age structure resembled that of a summer breeding population Despite excess energy requirements of winter breeding, survival rates were similar to that of non-breeding winter populations In mast years, rodent consumption in the beech forest was estimated as 10–103% of endosperm production available to postdispersal seed predators Between mast years rodent consumption made up 30–100% of endosperm production available Mast years occurred at irregular intervals and seed production seems to be synchronized between individual trees over large areas and induced by climatic events These phenomena lead to seed predator satiation

Seasonal dynamics of elemental sulfur in two coastal sediments

Abstract: A spectrophotometric method for elemental sulfur (S0) analysis without interference from other reduced sulfur compounds was adapted for the use in reducing sediments. The S0 distribution in two coastal sediments was studied regularly from summer to winter and compared to factors regulating the S0 accumulation, such as redox potentials, the rate of bacterial sulfide production and the general sulfur chemistry. Dense coatings of sulfur bacteria developed on the sediment surface of a sulfuretum which had an S0 concentration of up to 41 μmol S cm−3. The 2·5-mm thick bacterial coating contained 40% of all S0 in the sediment. A more typical marine sediment with a few cm thick oxidized surface layer had an S0 maximum of 1–3 μmol S cm−3 at 2–4 cm depth. The S0 maximum in both sediments increased from summer to winter as the sediments gradually became more oxidized. The deeper layers maintained a low S0 concentration. Most of the S0 in the upper few mm of a laboratory sulfuretum was present inside sulfur bacteria and actively migrated up and down with the bacteria depending upon the changing light and oxygen conditions.

The Gordon phenomenon induced by the eosinophil cationic protein and eosinophil protein X

Abstract: Cerebellar Purkinje cell degeneration after intracerebral injection of eosinophil granulocytes or extracts thereof is known as the Gordon phenomenon. The reaction is said to be highly selective. An eosinophil-derived neurotoxin (EDN) has recently been reported to induce the Gordon phenomenon. However, we report here that two eosinophil-derived proteins, eosinophil cationic protein (ECP) and eosinophil protein X (EPX), may induce the Gordon phenomenon after intraventricular injection. The potency of ECP is far greater than that of EPX and the latter is possibly identical to EDN. The Fink-Heimer staining for degenerating nerve fibers and boutons, however, indicated that the selectivity of the Gordon phenomenon is not as specific as was previously thought, since this method revealed degeneration of all brain areas in proximity to the ventricular system.

The primary structures of two leghemoglobin genes from soybean.

Abstract: We present the complete nucleotide sequences of two leghemoglobin genes isolated from soybean DNA. Both genes contain three intervening sequences which interrupt the two coding sequences in identical positions. The 5' and 3' flanking sequences in both genes contain conserved sequences similar to those found in corresponding positions in other eukaryotic genes. Thus, the general DNA sequence organization of these plant genes is similar to that of other eukaryotic genes.

Age at menarche, urine estrogens and breast cancer risk.

Abstract: In 511 nulliparous women aged 15-19 years and 347 aged 30-39, an analysis has been undertaken of the relationship of urine concentrations of the three principal estrogens to age, age at menarche and Quetelet's index of adiposity. The analysis was undertaken by means of multiple regression, controlling for each of the 12 centers from which the data originated, as well as for the other study variables. In the younger women, age was strongly and positively related to concentrations of E1 and E2 and less so to E3. In the age group 30-39, follicular phase specimens showed positive relationships with age for all three fractions but luteal specimens did not. Age at menarche showed inverse relationships to levels of E1 and E2 which were significant in the younger but not in the older age group. The associations of estrogens with Quetelet's index were weak and not statistically significant. The data suggest that women whose menarche occurs early not only have a longer duration of exposure to estrogens during years which are probably important in the initiation of breast cancer but, in addition, their exposures are at a higher level during those years and probably at later ages also. These observations support the hypothesis that the mechanism of the association of early menarche with breast cancer risk is via the association of both with estrogen stimulus.

Turnover of 14C-labelled acetate in marine sediments

Abstract: A method for the determination of volatile fatty acids (VFA) in coastal marine sediments is presented. Acidified porewater was vacuum distilled to extract the VFA and the distillate was analysed by gas chromatography (Porapak QS column and flame ionization detection). The limit of detection was 2 μM in the samples, but was increased tenfold by lyophilization. In the upper 10 cm of the sediments 2–70 nmol acetate cm-3 sediment was found. Uniformly labelled 14C-acetate (0.02 nmol, 10-3 μci) was injected at 1- to 2-cm intervals through silicone-stoppered holes in the tubing of undisturbed sediment cores. Turnover rate constants were determined from semilogrithmic plots of the 14C-acetate radioactivity versus the incubation time. The 14C-acetate was shown to be distributed in at least three sediment pools: a porewater pool, an adsorbed pool which was displaced by excess acetate, and an adsorbed pool which was not displaced by excess acetate. The rate constants ranged from 1.5–13 h-1 in the investigated sediments. The turnover rates of acetate were calculated from the turnover rate constants and the acetate concentrations in the porewater. The rate of acetate turnover calculated from the NH4*turnover and the N:C ratio of the sediment organic matter was only 16% of the measured rate of acetate turnover. The apparent overstimation of the acetate turnover was most likely due to an overestimation of the degradable acetate pool. A gel filtration of 14C-acetate-containing porewater showed that the fractions which contained the tracer had only 25% of the total acetate. This implied that a large fraction of the acetate in the porewater was unavailable to the microbes. This was also indicated by the fact that the measured acetate pool in porewater incubated with 14C-acetate did not decrease, when the added 14C-acetate was oxidized.

Age at menarche, probability of ovulation and breast cancer risk.

Abstract: An analysis is undertaken of the frequency of ovulation in 17 groups of women aged 15 to 19 who had been the subjects of other studies. A urine specimen of at least 8 h accumulation had been provided on the 20th or 21st day of a menstrual cycle by 681 women. Analysis is restricted to 431 specimens which had been collected between 11 and 3 days prior to the onset of the subsequent menstrual period. A pregnanediol concentration of less than 1 mg per litre in such a specimen was taken as evidence that the cycle was anovular. The probability of a cycle being anovular was inversely and significantly related to the number of years since menarche, and, with years since menarche held constant, was positively but not significiantly associated with age at menarche. This observation indicates that women with early menarche do not have a longer duration of exposure to anovular cycles than do those whose menarche is delayed, and that variation in the duration of exposure to post-menarcheal anovular cycles does not explain the association of breast cancer risk with early age at menarche. The 17 groups of women were classified into four categories according to ethnic origin and breast cancer incidence in the populations from which they derived. Anovular cycles were not more common in the high-risk groups; indeed, the two centers in the lowest risk category had the highest proportion of anovular cycles.

Gill ventilation and O 2 extraction during graded hypoxia in two ecologically distinct species of flatfish, the flounder ( Platichthys flesus ) and the plaice ( Pleuronectes platessa )

Abstract: Gill ventilation, breathing frequency, breath volume, oxygen extraction from the ventilatory water current and oxygen uptake through the gills were measured in flounder, Platichthys flesus, and plaice, Pleuronectes platessa, at water O2 tensions ranging from 35 to 155 mm Hg at 10° C. Ventilation volumes were similar in the two species at high water O2 tension. Exposure to hypoxic water elicited a larger increase in ventilation in the flounder. The per cent extraction of O2 from water decreased slightly in both species as water O2 tension was lowered. At comparable levels of ventilation O2 extraction was higher in flounder. At the higher levels of water O2 tension, O2 uptake across the gills of flounder was stable, the critical O2 tension being between 60 and 100 mm Hg. The plaice behaved as an oxygen conformer over the entire range of O2 tensions investigated. The superior ability of the flounder in maintaining OZ uptake across the gills during a reduction in water O2 tension may in part explain why the species, unlike plaice, inhabits very shallow waters with large fluctuations in dissolved oxygen.