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  • Springer  (19)
  • 1985-1989  (15)
  • 1970-1974  (4)
  • 1910-1914
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 22 (1985), S. 1-9 
    ISSN: 1432-1416
    Keywords: Oscillations ; phaselocking ; phase models ; all-to-all coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract An exact solution to a model of mutually interacting sinusoidal oscillators is found. Limits on the variation of the native frequencies are determined in order for synchronization to occur. These limits are computed for different distributions of native frequencies.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 197 (1988), S. 513-517 
    ISSN: 1432-041X
    Keywords: Cell adhesion ; Condensation ; Mechanism ; Somitogenesis ; Traction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This paper suggests that chick somites form because presomitic cells exert tractional forces on one another. These forces derive from the increase in cell adhesion and density that occurs as N-CAM and N-cadherin are laid down by the motile cells of the presomitic mesoderm, well before the somites form. Harris et al. (1984) have shown that adhesive and motile cells in an appropriate environment in vitro can spontaneously form aggregates under the influence of the tractional forces that they exert. Presomitic mesodermal cells may behave similarly: as CAM production increases local adhesivity, the tractional forces between the cells should become sufficiently strong for groups of cells to segment off the mesenchyme as somites. The successive expression of CAMs down the presomitic mesoderm will thus lead to the formation of an anterior-posterior sequence of somites. This mechanism can explain several aspects of somitogenesis that models generating a repetitive pre-pattern through gating cohorts of cells find hard to explain: first, mesodermal segregation occurs among highly adherent cells; second, that multiple rows of somites can form in embryos cultured on highly adherent substrata; third, that stirred mesoderm will still form normal somites; and, fourth, how somite size can be altered in heat-shocked embryos and elsewhere. Suggestions are given as to how the mechanism may be tested and where else in the embryo it could apply.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 28 (1970), S. 117-134 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract This paper attempts to illustrate the chemical variations of metamorphic hornblendes regarding host rocks and prograde variations. Changes related to bulk chemistry (orthoamphibolites) mainly concern Si, Al, Mg, Fetot and Ca. The Mg, Fe2+ and Fe3+ contents of hornblendes are, however, not strictly related to host rook compositions and Mg enrichments are correlated with increasing Fe3+ contents in the amphiboles. Thus, variations of oxygen fugacity may control the Mg contents of the Ca amphiboles studied but this does not show clear relations with the prograde metamorphism. The most sensitive but irregular variation related to the metamorphic conditions is the prograde enrichment of the alkalis into the “A” vacant position and an increase of the (Na+K)tot/Na+K+Ca ratios of the amphiboles. Increasing Ti and AlIV contents as well as decreasing AlVI concentrations are also, but much less evidently, related to increasing T and P. A variation trend from tschermakitic to edenitic hornblendes may be drawn using Shido's end members calculation; this tendency and the relative deficiency of AlVI contents in the low-grade members suggests that the amphiboles studied were subjected to conditions of a low-pressure metamorphism type. Such a conclusion is in agreement with the occurrence of andalusite-cordierite/sillimanite-cordierite associations in the metapelitic rocks, and the absence of Fe-rich garnet and epidote from the orthoamphibolites of the amphibolite facies at Aracena. Comparisons with Ca amphiboles from other metamorphic areas show, in agreement with various authors, that “Abukuma” hornblendes are similar to those encountered in high-grade thermal aureoles and tonalitic intrusives but different from the hornblendes of “Barrovian” metamorphism types.
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  • 4
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Bioturbation acts as a low-pass filter in displacing and reducing the amplitudes of stratigraphic signals. This often leads to a loss of high-frequency events in the stratigraphic record. In addition, when considering an isotopic signal δ18O,14C measured in stratigraphic “carriers”, such as foraminifera, bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record. We presenthere a model in which bioturbationis treated as a time-invariant filter whose impulse response function (IRF) is like that of a first-order system. The method involves first deconvoluting the abundance curves of the carriers and then the isotopic signals using the restored “carrier” abundances. This analysis was initially used to artificially generate ideal curves, with the aim of qualitatively modelling the effects of bioturbation. Following this, deconvolved curves were obtained using data from the core CH73-139C using δ18O, A. M. S. C-14 ages, and abundances of two planktonic foraminifera:G. bulloides andN. pachyderma left-coiling. A comparison of the data with the unmixed curves enables separation of the bioturbation artifacts and the construction of a common deglaciation curve based on the restored signals. Importantly, the model emphasizes some severe limitations of mathematical analysis of stratigraphic signals.
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  • 5
    ISSN: 1432-1041
    Keywords: simvastatin ; hypercholesterolaemia ; HMG-CoA reductase inhibitor ; cholesterol ; apolipoproteins ; lipoprotein particles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of treatment with simvastatin, a new HMG-CoA reductase inhibitor, has been investigated in 27 patients with primary hypercholesterolaemia. It produced a significant decrease of cholesterol and phospholipids in plasma, LDL and apolipoprotein B-containing lipoproteins. Plasma apolipoproteins B, C-III and E were also significantly lowered. The concentration of lipoprotein particles recognized by monoclonal antibodies (BL3, BL5 and BL7), associated with atherosclerotic disease, was also lowered by the treatment. Lipoproteins LpA-II:A-I were not changed, while LpA-I, which has been suggested to be the protective fraction of the apo A-I-containing lipoproteins, was slightly and inconsistently increased.
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  • 6
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The construction of copper/Nafion electrodes (solid polymer electrolyte structures) by an electroless plating method is described. These electrodes were used for the gas phase electrochemical reduction of CO2 to hydrocarbon products, including CH4 and C2H4. The faradaic efficiencies of the electrodes under ambient conditions with a counter solution of 1 mM H2SO4 at a potential of −2.00 V vs. SCE reached a steady-state value of about 20% after 30 min of electrolysis. This corresponded to a rate of total hydrocarbon production of approximately 9.8×10−7 mole h−1 cm−2. Increasing the potential of the electrode to more negative potentials, or increasing the proton concentration of the counter solution, caused a decrease in the faradaic efficiencies due to a relative increase in the rate of proton reduction vs. that of CO2 reduction. If the proton concentration of the counter solution was decreased to an alkaline pH, hydrocarbon production quickly ceased because of proton starvation.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Genetica 44 (1973), S. 16-24 
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Kernels of Zea mays L. occur in pairs in adjacent rows. Fifty-six paired kernels from $$\frac{{Ws_3 Lg_1 Gl_2 }}{{ws_3 lg_1 gl_2 }} \times ws_3 lg_1 gl_2$$ were selected from each of 24 ears. The resulting 1334 plants, 662 pairs and 10 individual survivors, were classified and expected frequencies of different categories of pairs determined. Analysis by chi-square disclosed no significant deviation from overall random distribution of crossovers and non-crossovers in paired plants. Accordingly, crossing-over is not related to the ontogeny of spikelets in pairs from a single protuberance on the young ear. Substances affecting crossingover in maize have been postulated. Any such substances thus appear to be formed late in development. Variation in recombination was observed among the small samples from the different ears. Six ears with presumptive high recombination and six with presumptive low recombination were chosen for further study, and 244 more kernels planted from each ear. The resulting data were pooled with that previously obtained to produce two equivalent-sized populations with presumptive high and low recombination frequencies for comparison. An eight-fold increase in double crossovers in the high recombination population was associated with a significant increase in single crossovers for the ws 3−lg 1 interval, region 1, and a highly significant increase in single crossovers for region 2. Coefficients of coincidence were determined for the two populations and diselosed that interference was greater in the low recombination population in addition to the reduced occrroence of single crossovers.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The environmentalist 6 (1986), S. 89-104 
    ISSN: 1573-2991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Summary The parable of the tribes offers a theory of social evolution to explain why civilization has developed as it has, in particular, why its major transformations of human life have not better served human needs. It challenges the commonsense view that people have freely chosen among the many cultural options. Another selective process has operated, one not under human control and not a function of human nature. Before civilization, all life was governed by a complex, biologically-evolved order. For a creature to develop culture to the point that it can invent its way of life appears to offer freedom, but this freedom is a trap. For what is freedom for any single society is anarchy in an interactive system of such societies. Anarchy — unprecedented in the history of life — makes inevitable a struggle for power amongst societies. This ceaseless competition, combined with open-ended possibilities for cultural innovation, inevitably drives social evolution in an unchosen direction: ways of life that do not confer sufficient power, regardless of how humane intrinsically, are eliminated, while the ways of power are inexorably spread throughout the system.
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  • 9
    ISSN: 1432-0878
    Keywords: Kupffer cells ; Liver endothelial cells ; Cultures ; Surface receptors ; Percoll ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary This paper presents a study on the structure and function of Kupffer cells (KC) and liver endothelial cells (LEC) isolated by a simple and rapid technique involving 1) perfusion of the liver with collagenase; 2) cell separation by means of density centrifugation in Percoll; and 3) cell culture, taking advantage of the fact that KC and LEC differ in their preferences for growth substrate. The KC, which attach and spread under serum-free conditions on surfaces of glass or plastic during the first 15 min in culture exhibit a typical macrophage-like morphology including membrane ruffling and a heterogenous content of vacuoles. Moreover, these cells express (a) Fc receptors (FcR) for binding and phagocytosis of erythrocytes covered with immune globulin G (E-IgG), and (b) complement receptors (CR) for binding and serum dependent phagocytosis of erythrocytes covered with either human C3b or mouse inactivated C3b (iC3b). The cells also bind fluid phase fluoresceinated C3b. Approximately 30% of the KC express immune response-associated (Ia)-antigens. The LEC attach and spread on fibronectin coated surfaces, but not on glass or plastic surfaces, during the first two hours in culture with or without serum, and are morphologically distinct from KC. Cultured LEC are well spread out with no membrane ruffling and with numerous large vesicles surrounding the regularly shaped nucleus. These cells bind, but do not ingest E-IgG via the FcR, but no binding of fluid phase C3b or particle fixed C3b or iC3b can be observed. Incubation of LEC with fluorescein amine conjugates of ovalbumin or formaldehyde treated serum albumin, but not with fluoresceinated native serum albumin, results in accumulation of fluorescence specifically localized in the large perinuclear vesicles. Neither KC nor any other cell types tested have the ability to accumulate fluorescence upon incubation with these compounds. Iaantigens are not present on the LEC. Cytochemical demonstration of unspecific esterase, acid phosphatase, and peroxidase reveals different patterns and intensities of staining in KC as compared to LEC.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Human evolution 2 (1987), S. 175-183 
    ISSN: 1824-310X
    Keywords: Chimpanzees ; Observational Learning ; Tool-Use
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the current study two groups of young chimpanzees (4–6 and 8–9 years old) were given a T-bar and a food item that could only be reached by using the T-bar. Experimental subjects were given the opportunity to observe an adult using the stick as a tool to obtain the food; control subjects were exposed to the adult but were given no demonstration. Subjects in the older group did not learn to use the tool. Subjects in the younger group who were exposed to the demonstrator learned to use the stick as a tool much more readily than those who were not. None of the subjects demonstrated an ability to imitatively copy the demonstrator's precise behavioral strategies. More than simple stimulus enhancement was involved, however, since both groups manipulated the T-bar, but only experimental subjects used it in its function as a tool. Our findings complement naturalistic observations in suggesting that chimpanzee tool-use is in some sense «culturally transmitted» — though perhaps not in the same sense as social-conventional behaviors for which precise copying of conspecifics is crucial.
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