Showing papers by "Aarhus University published in 1998"

The influence of some cations on an adenosine triphosphatase from peripheral nerves.

Abstract: Leg nerves from the shore crab (Carcinus maenas) contain an adenosine triphosphatase which is located in the submicroscopic particles. The influence of sodium, potassium, magnesium and calcium ions on this enzyme has been investigated. The presence of magnesium ions is an obligatory requirement for the activity of the enzyme. Sodium ions increase the activity when magnesium ions are present. Potassium ions increase the activity when the system contains both magnesium and sodium ions. Potassium ions in high concentration inhibit that part of the activity which is due to Na+, while the activity due to Mg++ is not affected. Calcium ions inhibit the enzyme under all conditions. When Mg++ or Mg++ + Na+ are present in the system, the optimum magnesium concentration is equal to the concentration of ATP. If potassium ions are added, the optimum magnesium concentration is doubled. If calcium ions are also added, the optimum magnesium concentration becomes still higher, and it increases with the calcium concentration. A majority of these observations may be explained by assuming (a) that the substrate most readily attacked by the enzyme is sodium-magnesium-ATP, (b) that potassium ions stimulate the enzyme directly, and (c) that an increase in the concentration of potassium ions leads to a displacement of sodium ions from the substrate and accordingly to an inhibition of the reaction. If the system contains the four cations in concentrations roughly equal to those in the crab-nerve axoplasm, an increase in the sodium concentration as well as a decrease in the potassium concentration will lead to an intensification of the enzyme activity. This observation, as well as some other characteristics of the system, suggest that the adenosine triphosphatase studied here may be involved in the active extrusion of sodium from the nerve fibre.

Helioseismic Studies of Differential Rotation in the Solar Envelope by the Solar Oscillations Investigation Using the Michelson Doppler Imager

Abstract: The splitting of the frequencies of the global resonant acoustic modes of the Sun by large-scale flows and rotation permits study of the variation of angular velocity Ω with both radius and latitude within the turbulent convection zone and the deeper radiative interior. The nearly uninterrupted Doppler imaging observations, provided by the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft positioned at the L1 Lagrangian point in continuous sunlight, yield oscillation power spectra with very high signal-to-noise ratios that allow frequency splittings to be determined with exceptional accuracy. This paper reports on joint helioseismic analyses of solar rotation in the convection zone and in the outer part of the radiative core. Inversions have been obtained for a medium-l mode set (involving modes of angular degree l extending to about 250) obtained from the first 144 day interval of SOI-MDI observations in 1996. Drawing inferences about the solar internal rotation from the splitting data is a subtle process. By applying more than one inversion technique to the data, we get some indication of what are the more robust and less robust features of our inversion solutions. Here we have used seven different inversion methods. To test the reliability and sensitivity of these methods, we have performed a set of controlled experiments utilizing artificial data. This gives us some confidence in the inferences we can draw from the real solar data. The inversions of SOI-MDI data have confirmed that the decrease of Ω with latitude seen at the surface extends with little radial variation through much of the convection zone, at the base of which is an adjustment layer, called the tachocline, leading to nearly uniform rotation deeper in the radiative interior. A prominent rotational shearing layer in which Ω increases just below the surface is discernible at low to mid latitudes. Using the new data, we have also been able to study the solar rotation closer to the poles than has been achieved in previous investigations. The data have revealed that the angular velocity is distinctly lower at high latitudes than the values previously extrapolated from measurements at lower latitudes based on surface Doppler observations and helioseismology. Furthermore, we have found some evidence near latitudes of 75° of a submerged polar jet which is rotating more rapidly than its immediate surroundings. Superposed on the relatively smooth latitudinal variation in Ω are alternating zonal bands of slightly faster and slower rotation, each extending some 10° to 15° in latitude. These relatively weak banded flows have been followed by inversion to a depth of about 5% of the solar radius and appear to coincide with the evolving pattern of torsional oscillations reported from earlier surface Doppler studies.

Design of a Surface Alloy Catalyst for Steam Reforming

Abstract: Detailed studies of elementary chemical processes on well-characterized single crystal surfaces have contributed substantially to the understanding of heterogeneous catalysis. Insight into the structure of surface alloys combined with an understanding of the relation between the surface composition and reactivity is shown to lead directly to new ideas for catalyst design. The feasibility of such an approach is illustrated by the synthesis, characterization, and tests of a high-surface area gold-nickel catalyst for steam reforming.

Growth hormone and bone.

Abstract: It is well known that GH is important in the regulation of longitudinal bone growth. Its role in the regulation of bone metabolism in man has not been understood until recently. Several in vivo and in vitro studies have demonstrated that GH is important in the regulation of both bone formation and bone resorption. In Figure 9 a simplified model for the cellular effects of GH in the regulation of bone remodeling is presented (Fig. 9). GH increases bone formation in two ways: via a direct interaction with GHRs on osteoblasts and via an induction of endocrine and autocrine/paracrine IGF-I. It is difficult to say how much of the GH effect is mediated by IGFs and how much is IGF-independent. GH treatment also results in increased bone resorption. It is still unknown whether osteoclasts express functional GHRs, but recent in vitro studies indicate that GH regulates osteoclast formation in bone marrow cultures. Possible modulations of the GH/IGF axis by glucocorticoids and estrogens are also included in Fig. 9. GH deficiency results in a decreased bone mass in both man and experimental animals. Long-term treatment (> 18 months) of GHD patients with GH results in an increased bone mass. GH treatment also increases bone mass and the total mechanical strength of bones in rats with a normal GH secretion. Recent clinical studies demonstrate that GH treatment of patients with normal GH secretion increases biochemical markers for both bone formation and bone resorption. Because of the short duration of GH treatment in man with normal GH secretion, the effect on bone mass is still inconclusive. Interestingly, GH treatment to GHD adults initially results in increased bone resorption with an increased number of bone-remodeling units and more newly produced unmineralized bone, resulting in an apparent low or unchanged bone mass. However, GH treatment for more than 18 months gives increased bone formation and bone mineralization of newly produced bone and a concomitant increase in bone mass as determined with DEXA. Thus, the action of GH on bone metabolism in GHD adults is 2-fold: it stimulates both bone resorption and bone formation. We therefore propose "the biphasic model" of GH action in bone remodeling (Fig. 10). According to this model, GH initially increases bone resorption with a concomitant bone loss that is followed by a phase of increased bone formation. After the moment when bone formation is stimulated more than bone resorption (transition point), bone mass is increased. However, a net gain of bone mass caused by GH may take some time as the initial decrease in bone mass must first be replaced (Fig. 10). When all clinical studies of GH treatment of GHD adults are taken into account, it appears that the "transition point" occurs after approximately 6 months and that a net increase of bone mass will be seen after 12-18 months of GH treatment. It should be emphasized that the biphasic model of GH action in bone remodeling is based on findings in GHD adults. It remains to be clarified whether or not it is valid for subjects with normal GH secretion. A treatment intended to increase the effects of GH/IGF-I axis on bone metabolism might include: 1) GH, 2) IGF, 3) other hormones/factors increasing the local IGF-I production in bone, and 4) GH-releasing factors. Other hormones/growth factors increasing local IGF may be important but are not discussed in this article. IGF-I has been shown to increase bone mass in animal models and biochemical markers in humans. However, no effect on bone mass has yet been presented in humans. Because the financial cost for GH treatment is high it has been suggested that GH-releasing factors might be used to stimulate the GH/IGF-I axis. The advantage of GH-releasing factors over GH is that some of them can be administered orally and that they may induce a more physiological GH secretion. (ABSTRACT TRUNCATED)

An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group

Abstract: It is suggested that the GRIP Greenland ice-core should constitute the stratotype for the Last Termination. Based on the oxygen isotope signal in that core, a new event stratigraphy spanning the time interval from ca. 22.0 to 11.5 k GRIP yr BP (ca. 19.0-10.0 k 14 C yr BP) is proposed for the North Atlantic region. This covers the period from the Last Glacial Maximum, through Termination 1 of the deep-ocean record, to the Pleistocene-Holocene boundary, and encompasses the Last Glacial Late-glacial of the traditional northwest European stratigraphy. The isotopic record for this period is divided into two stadial episodes, Greenland Stadials 1 (GS-1) and 2 (GS-2), and two interstadial events, Greenland Interstadials 1 (GI-1) and 2 (GI-2). In addition, GI-1 and GS-2 are further subdivided into shorter episodes. The event stratigraphy is equally applicable to ice-core, marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon-dated chronostratigraphy that has been used hitherto. © 1998 John Wiley & Sons, Ltd.

The Danish Medical Birth Registry.

Abstract: The Danish Medical Birth Registry (MBR) was established in 1968 and has been computerized since 1973. The primary purpose of the registration is to monitor the health of the newborns and of the quality of the antenatal and delivery care services but the registry is increasingly being used in research.... The paper describes the content and usage of the MBR over time and suggests research topics for the future. (EXCERPT)

Log Gaussian Cox Processes

Abstract: Planar Cox processes directed by a log Gaussian intensity process are investigated in the univariate and multivariate cases. The appealing properties of such models are demonstrated theoretically as well as through data examples and simulations. In particular, the first, second and third-order properties are studied and utilized in the statistical analysis of clustered point patterns. Also empirical Bayesian inference for the underlying intensity surface is considered.

The Risk of a Diagnosis of Cancer after Primary Deep Venous Thrombosis or Pulmonary Embolism

Abstract: Background Several small studies have indicated an association between deep venous thrombosis or pulmonary embolism and a subsequent diagnosis of cancer, but the subject is controversial Methods We conducted a nationwide study of a cohort of patients with deep venous thrombosis or pulmonary embolism that was drawn from the Danish National Registry of Patients for the years 1977 through 1992 The occurrence of cancer in the cohort was determined by linkage to the Danish Cancer Registry The expected number of cancer cases was estimated on the basis of national age-, sex-, and site-specific incidence rates Results A total of 15,348 patients with deep venous thrombosis and 11,305 patients with pulmonary embolism were identified We observed 1737 cases of cancer in the cohort with deep venous thrombosis, as compared with 1372 expected cases (standardized incidence ratio, 13; 95 percent confidence interval, 121 to 133) Among the patients with pulmonary embolism, the standardized incidence ratio was 13,

Direct immunogold labeling of aquaporin-4 in square arrays of astrocyte and ependymocyte plasma membranes in rat brain and spinal cord

Abstract: Aquaporin (AQP) water channels are abundant in the brain and spinal cord, where AQP1 and AQP4 are believed to play major roles in water metabolism and osmoregulation. Immunocytochemical analysis of the brain recently revealed that AQP4 has a highly polarized distribution, with marked expression in astrocyte end-feet that surround capillaries and form the glia limitans; however, the structural organization of AQP4 has remained unknown. In freeze-fracture replicas, astrocyte end-feet contain abundant square arrays of intramembrane particles that parallel the distribution of AQP4. To determine whether astrocyte and ependymocyte square arrays contain AQP4, we employed immunogold labeling of SDS-washed freeze-fracture replicas and stereoscopic confirmation of tissue binding. Antibodies to AQP4 directly labeled ≈33% of square arrays in astrocyte and ependymocyte plasma membranes in rat brain and spinal cord. Overall, 84% of labels were present beneath square arrays; 11% were beneath particle clusters that resembled square arrays that had been altered during fixation or cleaving; and 5% were beneath the much larger areas of glial plasma membrane that were devoid of square arrays. Based on this evidence that AQP4 is concentrated in glial square arrays, freeze-fracture methods may now provide biophysical insights regarding neuropathological states in which abnormal fluid shifts are accompanied by alterations in the aggregation state or the molecular architecture of square arrays.

Interpretation of measured concentration profiles in sediment pore water

Abstract: A robust numerical procedure for biogeochemical interpretation and analysis of measured concentration profiles of solutes in sediment pore water has been developed. Assuming that the concentration-depth profile represents a steady state, the rate of net production or consumption as a function of depth can be calculated, together with the flux across the sediment-water interface. Three kinds of vertical transport can be included in the analysis: molecular diffusion, bioturbation, and irrigation. The procedure involves finding a series of least square fits to the measured concentration profile, followed by comparisons of these fits through statistical F-testing. This approach leads to an objective selection of the simplest production-consumption profile that reproduces the concentration profile. Because the numerical procedure is optimized with respect to speed, one prediction can typically be done in a few minutes or less on a personal computer. The technique has been tested successfully against analytical solutions describing the transport and consumption of 0, in sediment pore water. In other tests, measured concentration profiles of O,, NO;, , NH:, and ZCO, have been interpreted using the new procedure.

Solar fusion cross sections

Abstract: We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates.

Aquaporin-4 Water Channel Protein in the Rat Retina and Optic Nerve: Polarized Expression in Müller Cells and Fibrous Astrocytes

Abstract: The water permeability of cell membranes differs by orders of magnitude, and most of this variability reflects the differential expression of aquaporin water channels. We have recently found that the CNS contains a member of the aquaporin family, aquaporin-4 (AQP4). As a prerequisite for understanding the cellular handling of water during neuronal activity, we have investigated the cellular and subcellular expression of AQP4 in the retina and optic nerve where activity-dependent ion fluxes have been studied in detail. In situ hybridization with digoxigenin-labeled riboprobes and immunogold labeling by a sensitive postembedding procedure demonstrated that AQP4 and AQP4 mRNA were restricted to glial cells, including Muller cells in the retina and fibrous astrocytes in the optic nerve. A quantitative immunogold analysis of the Muller cells showed that these cells exhibited three distinct membrane compartments with regard to AQP4 expression. End feet membranes (facing the vitreous body or blood vessels) were 10–15 times more intensely labeled than non-end feet membranes, whereas microvilli were devoid of AQP4. These data suggest that Muller cells play a prominent role in the water handling in the retina and that they direct osmotically driven water flux to the vitreous body and vessels rather than to the subretinal space. Fibrous astrocytes in the optic nerve similarly displayed a differential compartmentation of AQP4. The highest expression of AQP4 occurred in end feet membranes, whereas the membrane domain facing the nodal axolemma was associated with a lower level of immunoreactivity than the rest of the membrane. This arrangement may allow transcellular water redistribution to occur without inducing inappropriate volume changes in the perinodal extracellular space.

Bacterial Biogeochemistry: The Ecophysiology of Mineral Cycling

Abstract: Preface. Introduction. General Considerations: Bacterial Metabolism. Bioenergetics of Microbial Metabolism. Transport Mechanisms and Structure of Microbial Communities. Mineral Cycles: Hydrolysis of Organic Polymers. Comparison of Element Cycles. The Water Column: Prokaryotic Primary Producers. Water Column Bacteria and Mineralisation. Biogeochemical Cycling in Soils: Soil Water as a Master Variable. Responses to Plant Organic Matter. Responses of Soil Biogeochemistry to Disturbance and Change. Aquatic Sediments: Comparison of Freshwater and Marine Sediments. The Carbon Cycle. The Nitrogen Cycle. The Phosphorus Cycle. Manganese and Iron. Microbial Mats and Stratified Water Columns: Mats Based on Colourless Sulfur Bacteria. Cyanobacterial Mats. Other Types of Mats. Stratified Water Columns. Symbiotic Systems: The Role of Symbiosis in the Biosphere. Symbiotic Polymer Degradation. Symbiotic Nitrogen Fixation. Autotrophic Bacteria as Symbionts. Biogeochemistry and Extreme Environments. Microbial Biogeochemical Cycling and the Atmosphere: The Atmosphere as an Elemental Reservoir. Atmospheric Structure and Evolution. Synopsis of Trace Gas Biogeochemistry and Linkages to Climate Change. Trace Gas Dynamics and Climate Change: An Analysis of Methane Production and Consumption. Summary and Conclusion. Origins and Evolution of Biogeochemical Cycles: Biogeochemical Cycles and Thermodynamics. Pre-Biotic Earth and Mineral Cycles. Theoretical Perspectives on the Origin of Life. Evolution of Biogeochemical Cycles. Appendix: Thermodynamics and Calculation of Energy Yields of Metabolic Processes.

The practitioner's guide to coloured Petri nets

Abstract: Coloured Petri nets (CP-nets or CPNs) provide a framework for the design, specification, validation, and verification of systems. CP-nets have a wide range of application areas and many CPN projects have been carried out in industry, e.g., in the areas of communication protocols, operating systems, hardware designs, embedded systems, software system designs, and business process re-engineering. Design/CPN is a graphical computer tool supporting the practical use of CP-nets. The tool supports the construction, simulation, and functional and performance analysis of CPN models. The tool is used by more than four hundred organisations in forty different countries – including one hundred commercial companies. It is available free of charge, also for commercial use. This paper provides a comprehensive road map to the practical use of CP-nets and the Design/CPN tool. We give an informal introduction to the basic concepts and ideas underlying CP-nets. The key components and facilities of the Design/CPN tool are presented and their use illustrated. The paper is self-contained and does not assume any prior knowledge of Petri nets and CP-nets nor any experience with the Design/CPN tool.

Quantum Superposition States of Bose-Einstein Condensates

Abstract: We propose a scheme to create a macroscopic ``Schr\"odinger-cat'' state formed by two interacting Bose condensates. In analogy with quantum optics, where the control and engineering of quantum states can be maintained to a large extent, we consider the present scheme to be an example of quantum atom optics at work.

Aquaporins in complex tissues: distribution of aquaporins 1–5 in human and rat eye

Abstract: Multiple physiological fluid movements are involved in vision. Here we define the cellular and subcellular sites of aquaporin (AQP) water transport proteins in human and rat eyes by immunoblotting,...

Elemental Sulfur and Thiosulfate Disproportionation by Desulfocapsa sulfoexigens sp. nov., a New Anaerobic Bacterium Isolated from Marine Surface Sediment

Abstract: A mesophilic, anaerobic, gram-negative bacterium, strain SB164P1, was enriched and isolated from oxidized marine surface sediment with elemental sulfur as the sole energy substrate in the presence of ferrihydrite. Elemental sulfur was disproportionated to hydrogen sulfide and sulfate. Growth was observed exclusively in the presence of a hydrogen sulfide scavenger, e.g., ferrihydrite. In the absence of a scavenger, sulfide and sulfate production were observed but no growth occurred. Strain SB164P1 grew also by disproportionation of thiosulfate and sulfite. With thiosulfate, the growth efficiency was higher in ferrihydrite-supplemented media than in media without ferrihydrite. Growth coupled to sulfate reduction was not observed. However, a slight sulfide production occurred in cultures incubated with formate and sulfate. Strain SB164P1 is the first bacterium described that grows chemolithoautotrophically exclusively by the disproportionation of inorganic sulfur compounds. Comparative 16S rDNA sequencing analysis placed strain SB164P1 into the delta subclass of the class Proteobacteria. Its closest relative is Desulfocapsa thiozymogenes, and slightly more distantly related are Desulfofustis glycolicus and Desulforhopalus vacuolatus. This phylogenetic cluster of organisms, together with members of the genus Desulfobulbus, forms one of the main lines of descent within the delta subclass of the Proteobacteria. Due to the common phenotypic characteristics and the phylogenetic relatedness to Desulfocapsa thiozymogenes, we propose that strain SB164P1 be designated the type strain of Desulfocapsa sulfoexigens sp. nov.

Effects of naturally-occurring flavonoids and biflavonoids on epidermal cyclooxygenase and lipoxygenase from guinea-pigs

Abstract: Although there have been numerous topical applications of plant extracts having flavonoids known as anti-inflammatory compounds, only a few studies were reported concerning effects of flavonoids on epidermal cyclooxygenase/lipoxygenase. In this investigation, effects of naturally occurring flavonoids on epidermal cyclooxygenase/lipoxygenase were studied using five selected derivatives: flavanone, apigenin (flavone), quercetin (flavonol), amentoflavone and ginkgetin (biflavone) because eicosanoids generated in the epidermis are believed to be involved in various biological activities of the skin. Microsomal and cytosolic fractions were obtained from guinea-pig epidermal homogenate by centrifugation and used as a source for cyclooxygenase and lipoxygenase. It was found that quercetin inhibited both cyclooxygenase and lipoxygenase, being more potent against lipoxygenase, while flavanone and apigenin did not show any inhibition. Amentoflavone, one of the biflavones tested, showed potent and selective inhibitory activity on cyclooxygenase (IC50 = 3 microM) which was comparable to indomethacin (IC50 = 1 microM). In contrast, structurally similar ginkgetin possessed weak inhibitory activity on cyclooxygenase. The in vivo effects of these flavonoids on the normal and diseased skin remain to be studied.

Contribution of bedrock nitrogen to high nitrate concentrations in stream water

Abstract: Concentrations of nitrate in stream water throughout the world are reported to be elevated relative to natural background levels. This enrichment is commonly attributed to anthropogenic activities such as atmospheric emissions1, livestock feeding2, agricultural runoff3,4, timber harvesting practices5 and domestic/industrial effluent discharge4,6. Here we show that bedrock containing appreciable concentrations of fixed nitrogen contribute a surprisingly large amount of nitrate to surface waters in certain California watersheds,o an extent that even small areas of these rocks have a profound influence on water quality. As 75% of the rocks now exposed at the Earth's surface are sedimentary in origin7, and as these rocks contain about 20% of the global nitrogen inventory8, ‘geological’ nitrogen may be a large and hitherto unappreciated source of nitrate to surface waters. Such a natural nitrate source may be especially significant given that nitrate contamination at very low levels can contribute to surface water eutrophication9, may cause infant methaemoglobinaemia (‘blue baby’ syndrome)6 and has been implicated in certain cancers6. In addition, geological nitrogen may be a source of the ‘missing’ nitrogen noted in several biogeochemical studies of ecosystem nitrogen budgets1.