Showing papers by "University of Bremen published in 1991"

Chlorofluoromethane and oxygen in the Eastern Mediterranean

Abstract: CFM-12 (chlorofluoromethane, CCl2F2) data from the 1987 expedition of the F.S. Meteor in the Eastern Mediterranean are presented and discussed in the context of simultaneous oxygen and hydrographic measurements. Taken together, these data strongly suggest that the Adriatic is the only substantial source of bottom and deep water for the Eastern Mediterranean, in that no signatures of Aegean-derived water are found in the Levantine and Ionian Basins below about 1200 m depth. On the basis of a CFM-12 budget, the time-averaged inflow rate of Adriatic deep water into the Ionian is estimated to be 0.3 ± 0.1 Sv. The lowest CFM-12 and oxygen concentrations are found in the deep water between 2800 and 1200 m depth. This water mass is considered the oldest water in the Eastern Mediterranean and appears to be renewed by upwelling of bottom water. A lens of high CFM-12 water centered near 700 m depth is observed at a single station (Sta. 756) south of Crete. According to multi-parameter water analysis this water originates in the Aegean (about 300 m depth). The form of the θ-S relation and the fact that the anomalous water was only observed at one station suggest that inflow of Aegean water occurs in the form of isolated lenses. The salinity distribution in 700 m depth, together with the anomaly at Sta. 756, indicates that water from the Aegean spreads out in the western Levantine and the Ionian between about 500 and 1200 m depth. We propose to denote this water mass Cretan Intermediate Water. Atlantic Water has CFM-12 concentrations in equilibrium with 1987 atmospheric concentrations everywhere in the Eastern Mediterranean, and oversaturations for both CFM-12 and oxygen are found in the seasonal thermocline above it. In contrast, Levantine Intermediate Water (LIW) is undersaturated for both oxygen and CFM-12, even in the presumed formation areas in the northeast Levantine.

Parallelism and concurrency in high-level replacement systems

Abstract: High-level replacement systems are formulated in an axiomatic algebraic framework based on categories pushouts. This approach generalizes the well-known algebraic approach to graph grammars and several other types of replacement systems, especially the replacement of algebraic specifications which was recently introduced for a rule-based approach to modular system design.in this paper basic notions like productions, derivations, parellel and sequential independence are introduced for high-level replacement syetms leading to Church-Rosser, Parallelism and concurrency Theorems previously shown in the literature for special cases only. In the general case of high-level replacement systems specific conditions, called HLR1- and HLR2-conditions, are formulated in order to obtain these results.Several examples of high-level replacement systems are discussed and classified w.r.t. HLR1- and HLR2-conditions showing which of the results are valid in each case.

Effects of ice coverage and ice-rafted material on sedimentation in the fram strait

Abstract: As little is known about pelagic sedimentation processes in Arctic environments1, the interpretation of biological and chemical processes, as well as the reconstruction of ancient conditions, including those in the glacial North Atlantic, is difficult. Here we provide sediment-trap results, which show that the position of the sea-ice boundary significantly influences the particle flux. The seasonal variability of the particle flux differed markedly in the various sediment-trap sites in Fram Strait, depending on the behaviour of the sea ice. Under complete ice cover, sedimentation is very low, whereas maximum sedimentation is found at the ice margin. The highest particle flux observed, showing a large lithogenic component, was observed at the ice edge where the water was warmer (>2 °C). We find that high biogenic opal fluxes are characteristic of the summer ice margin, indicating that the sedimentary record of opal fluxes may allow the position of ice margins in the past to be reconstructed.

Numerical computation of an analytic singular value decomposition of a matrix valued function

Abstract: This paper extends the singular value decomposition to a path of matricesE(t). An analytic singular value decomposition of a path of matricesE(t) is an analytic path of factorizationsE(t)=X(t)S(t)Y(t) T whereX(t) andY(t) are orthogonal andS(t) is diagonal. To maintain differentiability the diagonal entries ofS(t) are allowed to be either positive or negative and to appear in any order. This paper investigates existence and uniqueness of analytic SVD's and develops an algorithm for computing them. We show that a real analytic pathE(t) always admits a real analytic SVD, a full-rank, smooth pathE(t) with distinct singular values admits a smooth SVD. We derive a differential equation for the left factor, develop Euler-like and extrapolated Euler-like numerical methods for approximating an analytic SVD and prove that the Euler-like method converges.

Short-term variations in particulate matter sedimentation off Kapp Norvegia, Weddell Sea, Antarctica: relation to water mass advection, ice cover, plankton biomass and feeding activity

Abstract: A multi-cup sediment trap was deployed at 250m in the shelf area off Kapp Norvegia, Weddell Sea (630 m water depth) to determine the relative importance of water mass advection, sea ice movement, phytoplankton biomass and plankton feeding. Short-term fluctuations in sedimentation were determined using a sampling frequency of 2.7 days over 54 days during January and February 1988. Three periods of enhanced sedimentation were associated with water mass exchange, settling of diatoms following break-up of ice cover and release of fecal matter by krill feeding on particulate matter derived from phytoplankton and ice algae. An initial sedimentation pulse (28 Jan) was mainly due to sinking pelagic diatoms and krill fecal strings containing algae released from sea ice passing over the trap position. The δ13C-composition of the sedimented organic carbon was about-24‰. The isotope ratio decreased sharply by about 5.5‰ at the end of the first pulse indicating the source of sinking matter becoming pelagic diatoms of the retreating ice-edge. At this time the diatom Corethron criophilum contributed a very high proportion of the organic flux causing an increase of the opal/Corg ratios. The second pulse (6 Feb) was due to empty diatom frustules, minipellets and small planktonic aggregates. Much of the organic carbon was transported by round fecal pellets. During the third pulse (14 Feb), round fecal pellets transported even more; the percentage of C. criophilum to the diatom organic carbon flux was more than 80% (>2mg C m−2 day−1).

Characterization of Sp-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole- 3',5'-monophosphorothioate (Sp-5,6-DCl-cBiMPS) as a potent and specific activator of cyclic-AMP-dependent protein kinase in cell extracts and intact cells.

Abstract: A newly designed cyclic AMP (cAMP) analogue, Sp-5,6-dichloro-1-beta-D- ribofuranosylbenzimidazole-3',5'-monophosphorothioate (Sp-5,6-DCl-cBiMPS), and 8-(p-chlorophenylthio)-cAMP (8-pCPT-cAMP) were compared with respect to their chemical and biological properties in order to assess their potential as activators of the cAMP-dependent protein kinases (cAMP-PK) in intact cells. Sp-5,6-DCl-cBiMPS was shown to be both a potent and specific activator of purified cAMP-PK and of cAMP-PK in platelet membranes, whereas 8-pCPT-cAMP proved to be a potent activator of cAMP-PK and cyclic-GMP-dependent protein kinase (cGMP-PK) both as purified enzymes and in platelet membranes. Sp-5,6-DCl-cBiMPS was not significantly hydrolysed by three types of cyclic nucleotide phosphodiesterases, whereas 8-pCPT-cAMP (and 8-bromo-cAMP) was hydrolysed to a significant extent by the Ca2+/calmodulin-dependent phosphodiesterase and by the cGMP-inhibited phosphodiesterase. The apparent lipophilicity, a measure of potential cell-membrane permeability, of Sp-5,6-DCl-cBiMPS was higher than that of 8-pCPT-cAMP. Extracellular application of Sp-5,6-DCl-cBiMPS to intact human platelets reproduced the pattern of protein phosphorylation induced by prostaglandin E1, a cAMP-increasing inhibitor of platelet activation. In intact platelets, Sp-5,6- DCl-cBiMPS was also more effective than 8-pCPT-cAMP in inducing quantitative phosphorylation of the 46/50 kDa vasodilator-stimulated phosphoprotein (VASP), a major substrate of cAMP-PK in platelets. As observed with prostaglandin E1, pretreatment of human platelets with Sp-5,6-DCl-cBiMPS prevented the aggregation induced by thrombin. The results suggest that Sp-5,6-DCl-cBiMPS is a very potent and specific activator of cAMP-PK in cell extracts and intact cells and, in this respect, is superior to any other cAMP analogue used for intact-cell studies. In contrast with 8-pCPT-cAMP, Sp-5,6-DCl-cBiMPS can be used to distinguish the signal-transduction pathways mediated by cAMP-PK and cGMP-PK.

Inhibition of Sarcoplasmic Reticulum Ca2+-ATPase Activity by Cadmium, Lead and Mercury

Abstract: The effect of Cd2+, Pb2+ and Hg2+ on the Ca(2+)-ATPase activity of sarcoplasmic reticulum from rabbit muscle was studied. The concentration of relevant free and complex species for the assay conditions have been computed. As a result, ATP hydrolysis was found to be inhibited with an IC50 value of 950 nmol/l free Cd2+ or 95 nmol/l free Pb2+. Although calculation of the free Hg2+ was not possible, the comparison of the IC50 values for total metal ions show that Hg2+ is the strongest inhibitor of enzyme activity. The inhibition by Cd2+ seems to be independent of substrate concentration, whereas the inhibitory effect of Pb2+ is lowered in the presence of higher MgATP concentrations. Our data illustrate that the three heavy metals are potent inhibitors of the Ca2+ pump. Therefore low concentrations of these metal ions may disturb intracellular Ca2+ homeostasis and act on Ca(2+)-mediated cell functions.

Alcohol, smoking, and occupational factors in cancer of the larynx: a case-control study.

Abstract: A hospital-based case-control study of laryngeal cancer was conducted in Bremen in 1986 and 1987 with 100 prevalent male laryngeal cancer patients and 100 male hospital controls with diseases not considered to be related to smoking, alcohol, or occupational exposures, who were frequency matched by age. The odds ratio for heavy smoking (more than 30 pack-years) reached a value of 3.5 (95% confidence limits (CL) 1.1, 7.9). Ex-smokers showed a significant decrease in risk; this reached the level of those who had never smoked about 15 years after smoking cessation. For daily consumers of alcohol an odds ratio of 3.2 (95% CL 1.4, 7.5) was observed. Among the 17 occupations in which at least ten subjects had worked, excess risks were observed for stock keeping and transportation workers, and for leather and textile workers. The odds ratio was significantly increased for the latter (p less than 0.05). Among all those persons ever employed in a priori defined-risk occupations, an odds ratio of 2.74 (95% CL 1.23, 6.06) was observed. Considering responses to an exposure check-list, no increased risks could be shown for exposure to asbestos, coal tar, or welding fumes. On the other hand, excess risks were observed for exposures to diesel oil, gasoline, and mineral oil, controlling for smoking and alcohol. The findings in occupational and exposure subgroups were based on small numbers of cases and controls and, consequently, were subject to large sampling errors. Many of the results are consistent, however, with occupational risk factors reported from other studies.

Ultrafast low-angle RARE: U-FLARE.

Abstract: The subsecond application of the RARE technique is described. Two possible methods of implementation are discussed, one in which T2 contrast is manipulated by temporal reordering of the phase-encoding gradient, and the other in which the phase-encoding order is held constant and the contrast is manipulated by means of a spin-echo preparation experiment. In vivo images obtained with the latter method are presented and applications of the sequence discussed.

Productivity of the glacial ocean: Discussion of the iron hypothesis

Abstract: An increase in the productivity of the glacial-age Southern Ocean has been postulated to explain the decrease in pC0, of the atmosphere observed in ice cores. A plausible mechanism has been proposed elsewhere that productivity is limited by the availability of Fe in this region and that the greater supply of eolian dust during glacial time removed this limit. Recently published evidence from cores from the Southern Ocean suggests that in fact there was no change in productivity in the assumed manner. Glacial-age productivity was indeed greatly increased in the equatorial Pacific and in the eastern boundary upwelling systems. The cause, presumably, was the mechanical action of glacial-age winds rather than a greater supply of Fe. However, a role of increased supply of micronutrients from the continents in the increase of equatorial productivity during glacial time cannot be excluded. Such enhancement from increased supply of dust would have the interesting corollary of more efficient export transfer to depth, possibly contributing to nutrient depletion in glacial-age, deep intermediate waters. There is some indication, as well, of a general decrease in nutrient content in the tropical thermocline in the western Pacific during the last several million years, a depletion that may have been fostered by increasing supply of dust from emerging Asian highlands. Alternative explanations are available. The case for Fe as a major modifier of productivity and biogenic sedimentation on geological time scales cannot be made in the absence of criteria diagnostic for Fe supply as opposed to stirring and upwelling.

Development of Arctic sea-ice organisms under graded snow cover

Abstract: In 1988, the short-term response of sea-ice organisms to manipulated changes in snow cover (no snow cover, natural snow cover, natural snow cover + black foil) was investigated in one ice floe located in the East Greenland Current northwest of Svalbard over a period of three weeks. Autotrophic organisms (flagellates and diatoms) were concentrated in the lowermost 30 cm of the floe. In the field without snow cover, the highest diatom concentrations were observed, consisting nearly entirely of pennate forms, together with a maximum bacterial abundance. The community of larger protozoa and smaller metazoa was dominated by ciliates. Under natural conditions the flora consisted of both flagellates and diatoms, while turbellaria were the dominating animals. In the darkened field, the organism concentrations decreased with time. The results indicate that brine drainage, induced by changes in ice temperature, can reduce concentrations of ice organisms over short time scales.

Crossing the Border: The Social and Engineering Design of Computer Integrated Manufacturing Systems

Abstract: 1 The Work-Oriented Shaping Perspective: The Problem Setting and Perspectives- 11 Do We Need a New Paradigm- 12 The Technique-Oriented Approach- 121 Background and Assumptions- 122 Example- 123 "Weaknesses" in the Practical Implementation- 13 The Sociotechnical Approach- 131 Background and Assumptions- 132 Examples- 133 "Weaknesses" in the Practical Implementation- 14 The Human-Centred Approach- 141 Background and Assumptions- 142 Examples- 143 Possible Limitations and Challenges of the Human-Centred Approach- 15 Towards a Work-Oriented Shaping Approach- 16 Summary- 2 The Interdisciplinary Design of Computer-Integrated Manufacturing Systems: ESPRIT Project 1217 (1199) Part One- 21 Introduction- 22 Experiences of Interdisciplinary Collaboration During the First Year of the Project- 221 TheUK CAM Group- 222 The Danish CAD Group- 223 The German CAP Group- 23 Evaluation of the First-Year Experiences in the Three National Groups- 231 National Differences- 232 Critical Evaluation of Interdisciplinary Collaboration During the First Year of the Project- 24 The "Shaping Paper" - Intentions, Reactions and Influence- 241 Intentions: The International Social Science Group (ISSG)- 242 The Social Shaping of Technology and Work- A Introduction- B The Concept of Technological Shaping- B1 Introduction- B2 The Role of Technological Rationality- B3 Technological Rationality and the Mechanistic World Picture- B4 Work and Personality from a Holistic Perspective- B41 The Search for a New Paradigm- B42 The Concept of "Life-World" and "System"- B43 The Concept of "Praxis"- B44 The Relation Between Mind and Body- B45 The Relationship between Working Conditions and the Personality- B5 Fields of Technology Shaping- C Dimensions of Human-Centred Work- C1 Introduction- C2 The Relationship of Work and Technology- C3 Work and Communication- C4 Work and Learning- C41 The Relationship Between Cultivation (Bildung) and Qualification- D Methods for Evaluating and Shaping Computer-Aided Technology and Work- D1 Introduction- D2 A Scenario- D21 Range of Products- D22 The Factory- D23 The Production Island- D24 The Workplace- 3 The Scenario Related to the Dimensions and Criteria of Experiencing, Shaping and Evaluating Work- D31 The Normative Perspective of the Shaping Process- D32 Dimensions of Work- D33 Example of How to Use the Dimensions of Work in the Shaping and Evaluation Process- D34 Criteria for Human-Machine Interface Design- D35 Summary- D4 How to Shape and Evaluate Computer-Aided Technology and Work- D41 Typical Shortcomings of Conventional Methods of System Development- D42 The Search after Methods in Accordance with the New Paradigm- E References- 243 Reactions of the Engineers to the Shaping Paper- 244 The Influence of the Shaping Paper on the Project- Interdisciplinary Collaboration in the Second Half of ESPRIT Project 1217 (1199)- 31 Experiences of Interdisciplinary Collaboration at the National Level- 311 The British CAM Group- 312 The Danish CAD Group- 313 The German CAP Group- 32 Experiences of Collaboration at the International Level- 321 The International Data Management Group- 33 Lessons Learned- 331 Constraints on Interdisciplinary Collaboration- 332 Experiences of Improved Collaboration During the Project- 4 Crossing the Border- 41 Crossing the Border - A Tentative Definition- 411 Fields of Action- 412 Agents Involved in the Shaping Process- 413 Shaping Competence- 42 Participatory Systems Development- 421 Hierarchic-Sequential Design Tradition- 422 The Limitations of Traditional Design- 423 Technology Shaping- 43 The Shaping Process- 44 Prospective Example of the Shaping Process as a Rolling Development- 441 Preparation of the Shaping Process- 442 Future-Creating Workshops- 443 Shaping Workshops- 444 Coordination of the Results of the Shaping Workshops- 445 The Second Shaping Workshop- 446 Seminar with Outside Experts- 447 Conclusion- 45 Summary and Conclusions- References

Organic Solar Cells

Abstract: Solar cells are devices that utilize the light energy of the sun and convert it into electrical energy, which is needed for powering any electronic device. While organic solar cells(OSC) have the same fundamental structure as traditional or inorganic solar cells(ISC), OSCs use polymers instead of semiconductors, such as silicon or gallium arsenide, which are used in ISCs. While the efficiencies of OSCs are still somewhat low in relation to other solar cells, their advantages, such as being light in weight, flexible, low in material and processing costs, failure resistant, and relatively environmentally friendly make them a worthy competitor of ISCs. Considering fossil fuels are limited and alternate forms of energy need to be considered, OSCs will play a major role in supplying power to people around the world.

Relevance of polycyclic aromatic hydrocarbons as environmental carcinogens

Abstract: All emissions from incomplete combustion contain polycyclic aromatic hydrocarbons (PAH) which are a well-known class of carcinogens. The question whether additional carcinogenic compounds do exist in these emissions can be answered by separating the emission condensate into a PAH-containing and a PAH-free part. These parts have been tested in an animal experiment by means of a carcinogen-specific test system such as topical application onto the skin of mice or injection into the lung of rats. The investigation on the contribution of PAH-fractions and of benzo(a)pyrene to the carcinogenic potential of emission condensate from gasoline driven engines, Diesel engines, coal combustion in domestic furnaces and sidestream smoke of cigarettes shows that the carcinogenic effect of the particle phase of these pyrolytic condensates is predominantly caused by polycyclic aromatic compounds such as PAH. In all cases investigated the PAH-fraction containing 4 and more rings accounted for more than 75% of the total carcinogenic effect resulting from the implantation into the lung of rats or from the topical application onto mouse skin. The contribution of benzo(a)pyrene to the carcinogenic potency of various condensates, however, is minor in all cases investigated and accounts for only 0.17% to 4% of the total carcinogenicity as evaluated from implantation into the lung of rats (Table 1).

Phytoplankton maxima in the tidal freshwater reaches of two coastal plain estuaries

Abstract: Seasonal and spatial patterns of phytoplankton biomass are found to be very similar in the tidal freshwater reaches of the Weser and Elbe estuaries. The phytoplankton communities are dominated by riverine populations in spring and early summer, introduced from upstream into the tidal freshwater reaches, with seaward-decreasing chlorophyll a concentrations minimizing within the turbidity maximum region. During late summer and autumn a chlorophyll a maximum occurs in both estuaries within the tidal freshwater reaches, formed mainly by the autochthonous species Actinocyclus normanii . Peak abundance clearly occurs upstream of the turbidity maximum. Phytoplankton biomass in the estuaries of the Weser and Elbe during this time is higher in the tidal freshwater reaches in the river than in the middle and outer reaches of the estuaries. The suspected controlling mechanisms of these maxima are discussed. It is concluded that river discharge and water residence time are key factors. The tidal freshwater reaches are considered to be important sites of biogeochemical reactions and should be integrated into estuarine definitions and estuarine ecological research.

Molecular mechanisms of brainstem plasticity. The vestibular compensation model.

Abstract: Vestibular compensation is the process of behavioral recovery that occurs following unilateral deafferentation of the vestibular nerve fibers (unilateral labyrinthectomy, UL). Since UL results in a permanent loss of vestibular input from the ipsilateral vestibular (VIIIth) nerve, vestibular compensation is attributed to CNS plasticity and has been used as a general model of lesion-induced CNS plasticity. Behavioral recovery from the ocular motor and postural symptoms of UL is correlated with a partial return of resting activity to neurons in the vestibular nucleus (VN) on the deafferented side (the “deafferented VN”), and lesions to the deafferented VN prevent compensation; therefore, the regeneration of resting activity within the deafferented VN is believed to have a causal role in vestibular compensation. The biochemical mechanisms responsible for the adaptive neuronal changes within the deafferented VN are poorly understood. Neuropeptide hormone fragments, such as adrenocorticotrophic hormone (ACTH)-4–10, have been shown to accelerate vestibular compensation and can act directly on some VN neurons in vitro. Antagonists for theN-methyl-D-aspartate (NMDA) receptor have been shown to inhibit vestibular compensation if administered early in the compensation process. Biochemical studies in frog indicate marked alterations in the phosphorylation patterns of several proteins during compensation, and the in vitro phosphorylation of some of these proteins is modulated by ACTH-(1–24), calcium (Ca2+), and calmodulin or protein kinase C. It is therefore possible that ACTH fragments and NMDA antagonists (via their effects on NMDA receptor-mediated Ca2+ channels) modulate vestibular compensation through their action on Ca2+-dependent pathways within VN neurons. Recent studies have shown that some Ca2+-channel antagonists and the Ca2+-dependent enzyme inhibitor calmidazolium chloride facilitate vestibular compensation. How the regulation of Ca2+ may be related to the neuronal changes responsible for vestibular compensation is unclear at present.

Boron-containing thiouracil derivatives for neutron-capture therapy of melanoma.

Abstract: Boron-containing derivatives of 2-thiouracil and 2,4-dithiouracil and the corresponding 6-propyl compounds, containing a dihydroxyboryl group in the 5-position, have been prepared. These compounds accumulate in B16 melanoma in mice in concentrations up to 30 micrograms of boron per gram tissue. The uptake persists. The toxicity of both 2-thiouracil derivatives is low. These compounds are therefore good candidates for boron neutron-capture therapy of malignant melanoma.

Correlation of stable oxygen isotope temperature record with light attenuation profiles in reef-dwelling Tridacna shells

Abstract: Molluscs are known to record environmental changes in their carbonate shells in detail. This paper reports the findings of a high-resolution analysis of stable oxygen isotopic compositions and light transmission properties of a shell of the reef-dwelling Pacific giant clamTridacna gigas. Our findings reveal that the annual growth rates and the longevity ofTridacna specimens can be readily determined by measuring the annual light attenuation pattern within the shell. Annual seasonal changes in water temperature are reflected with high resolution in the stable oxygen isotope ratios and in the light attenuation values of the aragonite shell. The inner shell ofT. gigas deposited below the pallial line revealing undisturbed shell accretion with high growth rates shows the maximum seasonal oxygen isotope range and the highest resolution in light attenuation changes. We suggest that this is the best part of the shell to reconstruct former seasonal surface water temperatures in tropical environments. Scanning electron microscopy (SEM) studies suggest that the annual growth patterns observed in transmitted light are generated by a complex pattern of daily growth increments with varying sizes of skeletal crystallites and varying amounts of organic carbon.