Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Insectes sociaux 46 (1999), S. 348-360 
    ISSN: 1420-9098
    Keywords: Key words:Apis mellifera, honey bee, swarm, communication, house-hunting, decision-making.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary: Thousands of individuals in a house-hunting honey bee swarm make a collective decision for one among many nest sites discovered. We recorded the dances on swarms in a forested area, where one swarm's search encompassed about 150 km2 and many different sites. We then analyzed swarms in a desert area with only nest sites that we provided and monitored, to study how the swarm winnows multiple finds to a single site over the course of a few days. Most bees did not visit any site, very few visited more than one. Apparently choices were made with little or no direct comparison, through the interaction of two mechanisms: positive feedback through recruitment leading to growth in the number of scouts visiting good nest sites, and attrition reducing activity and recruitment for non-chosen sites. Individual differences between bees substantially affected these dynamics. Scouts varied considerably in amount of dancing and persistence, but most that danced did so vigorously after their first few visits, and then dropped out, ceasing their dancing though continuing to visit the nest site. Dances were nearly twice as long as reported for nectar and pollen. Scouts followed dances of others, and occasionally visited alternative sites, but rarely switched their dancing. When unanimity is reached, the bees must recognize that a decision has been made, break up the swarm cluster, and fly to the nest site. Buzz-running (Schwirrlaufen) probably plays a role here, but we observed less buzz-running than previously reported, and this occurred even early in the process; it might function as a chain-reaction effect triggering the end of the house-hunting process. Our results suggest that the choice among nest sites relies less on direct comparison of nest sites, and more on inherent processes of positive feedback and attrition by dancers dropping out.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 132 (1998), S. 453-460 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Total sulfur (STOT), elemental sulfur (S°) and sulfur-isotope compositions (δ34S) of marine animals were analyzed to determine whether these chemical characteristics could help distinguish animals with a sulfur-based, thiotrophic nutrition from animals whose nutrition is based on methanotrophy or on more normal consumption of phytoplankton-derived organic matter. The presence of S° was almost entirely confined to the symbiont-containing tissues of thiotrophs, but was sometimes undetectable in thiotrophic species where sulfide availability was probably low. When S° contents were subtracted, the remaining tissue-sulfur concentrations were similar for all nutritional groups. δ34S values were typically lower for thiotrophs than for other groups, although there was overlap in methanotroph and thiotroph values at some sites. Field evidence supported the existence of small to moderate (1 to 10‰)34S fractionations in the uptake of sulfides and metabolism of thiosulfate. In general, a total sulfur content of 〉3% dry weight, the presence of elemental sulfur, and δ34S values less than +5‰ can be used to infer a thiotrophic mode of nutrition.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 13
    ISSN: 1573-4919
    Keywords: atria ; thyroid hormones ; β-adrenergic effect ; sarcoplasmic reticulum ; phospholamban
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This paper discusses the mechanisms of two basic effects of thyroid hormones on atrial responses to β-adrenergic agonists, i.e. increased inotropic sensitivity and decreased maximal contractile responsiveness. The increased sensitivity of atria to β-adrenergic agonists under thyroid hormones appears to be related to increases in β-adrenoceptor density and Gs/Gi protein ratio, leading to activation of Gs-mediated pathway, but suppression of Gi-mediated pathway of adenylate cyclase regulation. Therefore, the i/c concentrations of cAMP and corresponding inotropic responses achieve their maximums at lower doses of β-adrenergic agonist. Thyroid hormones also decrease the expression of phospholamban, but increase the expression of sarcoplasmic reticulum Ca+2-pump. As a result, the basal activity of sarcoplasmic reticulum Ca+2-pump increases, but its β-adrenergic activation through phosphorylation of phospholamban decreases. It is suggested that these changes are causal for decreased maximal inotropic and lusitropic responses of atria to β-adrenergic agonists.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 14
    ISSN: 1435-1803
    Keywords: Cardiac Na+/Ca2+ exchanger ; expression and function ; postnatal development ; cadiac hypertrophy and failure ; Ca+ overload ; arrhythmogenic potential ; reversed mode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The diastolic and systolic dysfunction in the failing heart appear to be related to the altered Ca2+ handling of the cardiac myocyte. Disturbed Ca2+ handling might also affect influx and efflux of other ions, including Na+. In this context, the cardiac sarcolemmal Na+/Ca2+ exchanger represents an important exchange mechanism of Ca2+ versus Na+ transport across the sarcolemma. Expression and function of cardiac Na+/Ca2+ exchanger is highest in newborn rats and declines gradually in postnatal development. In pressure overload-induced hypertrophy, expression of cardiac Na+/Ca2+ exchanger is increased and translated into increased Na+/Ca2+ exchanger activity similar to the early phase of postnatal development in the rat. This suggests a common underlying mechanism in the control of Na+/ Ca2+ exchanger expression in the immature and the hypertrophied myocardium. Similar to experimental-induced hypertrophy, mRNA, protein and activity of Na+/Ca2+ exchanger is increased in the failing human heart suggesting an increase in the number of functional exchanger molecules rather than an enhanced exchange rate by preexisting exchanger molecules. The potential functional implications of an increased cardiac Na+/Ca2+ exchanger activity in human heart failure may be limitation of diastolic intracellular Ca2+ overload. However, this may increase the arrhythmogenic potential of the failing heart, since additional Na+ influx via Na+/Ca2+ exchanger may affect the membrane potential.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 30 (1995), S. 6209-6217 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The process of removing a multicomponent binder from a metal powder compact has been investigated. Model experiments of debinding were performed on compounds consisting of less than 40 vol% binders (low molecular weight polyethylene, paraffin and Carnauba waxes) and more than 60 vol% metal content. As typical representatives for injection moulding morphology and meeting all other requirements for optimal powder characteristics, elemental powders of the Fe-Al system were used. Viscosity results over a wide range of shear rates for various plastisols are presented as functions of binder system composition and metal powder content. Based on the rheological response, an optimization of plastisol formulation was performed. Results are reported on three series of debinding modes using heat and fluid wicking in air and in nitrogen. The time dependence of fractional debinding, x(t), during wicking has been estimated using a model. Direct observation by SEM of binder distribution and pore structure evolution at different stages of the debinding process was made. Wick-assisted thermal debinding in nitrogen proved to be an effective debinding method in terms of shape preservation and the absence of defects in the studied material.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 165 (1995), S. 46-55 
    ISSN: 1432-136X
    Keywords: Citrate synthase ; Enzyme characteristics ; Temperature adaptation ; Isopod crustacea ; Euphausiid crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The characteristics and properties chromatographically purified citrate synthase from the euphausiids Euphausia superba (Antarctica) and Meganyctiphanes norvegica (Scandinavian Kattegat and Mediterranean Sea) and from the isopods Serolis polita (Antarctica) and Idotea baltica (Baltic Sea) were used to elucidate biochemical mechanisms of temperature adaptation. Additionally, maintenance experiments were carried out on the euphausiids to determine mechanisms of short term acclimation. Temperature optima (between 37 and 45°C) were unrelated to genotypic cold adaptation, but the activation energy of the Antarctic krill E. superba (10.9 kJ · mol-1) was only a quarter of that in other species (41.8–45.1 kJ · mol-1). The minima of apparent Michaelis constants (total range: 4–20 μmol · 1-1 oxaloacetate; 7–45 μmol · 1-1 acetyl-coenzyme A) showed no relation to natural conditions, and no distinct pH optimum occurred at ambient temperatures. In contrast, apparent Michaelis constants and specific enzyme activities were related to maintenance temperatures in M. norvegica, but not in E. superba. The differences between M. norvegica and E. superba can be interpreted as adaptations to the changes in ambient temperature with regard to the respective steno- and eurythermic tolerances of these crustaceans.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 165 (1995), S. 56-61 
    ISSN: 1432-136X
    Keywords: Citrate synthase ; Enzyme regulation ; Temperature adaptation ; ATP inhibition ; Crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Citrate synthase is a regulatory enzyme of the energy metabolism pathway controlling the citric acid cycle. It was studied in order to determine modes of enzyme regulation with regard to the life-style of the investigated species. Citrate synthase from crustaceans with different life-styles were compared: the pelagic euphausiids Euphausia superba from the Antarctic and Meganyctiphanes norvegica from the Scandinavian Kattegat and the Mediterranean were compared to the benthic isopods Serolis polita from the Antarctic and Idotea baltica from the Baltic. Citrate synthase was partly purified chromatographically and the influence of adenosine 5′-triphosphate on enzyme activity was examined. Mechanisms of inhibition and inhibitor constants were determined. Two different mechanisms of enzyme regulation by ATP were found. Citrate synthase from isopods was only competitively inhibited, while citrate synthase from euphausiids showed not only competitive inhibition but also activation by low concentrations of ATP. This activation is equivalent to the reversed methanism of uncompetitive inhibition. The ecophysiological relevances of the coupling of these mechanisms are discussed. The degree of competitive inhibition was different in the two groups of investigated crustaceans. Inhibitor constants were similar within the euphausiids but not in isopods, which showed higher or lower inhibition depending on the climatic zone: the colder the ambient temperature the lower the ATP inhibition. A possible mechanism of temperature adaptation through effects of varying inhibition constants is concluded.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 18
    ISSN: 1573-9686
    Keywords: Cardiovascular system ; Autonomic nervous system ; Subband decomposition ; Wavelet filter bank ; Multidimensional linear modeling ; Subband modeling ; Cardiovascular regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We present a new approach to cardiovascular analysis based on a well-known signal processing technique, namely, the frequency subband decomposition. The subbands are chosen in accordance with physiological standards: (1) 0–0.04 Hz, (2) 0.04–0.15 Hz, (3) 0.15–0.4 Hz. It is shown that such a pre-processing drastically improves the accuracy of the analysis and introduces a new direction in the understanding of the relationships between cardiovascular signals. © 1998 Biomedical Engineering Society. PAC98: 8710+e
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...