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  • 1
    Electronic Resource
    Electronic Resource
    A polygynous nest ofVespula pensylvanica from California with a discussion of possible factors influencing the evolution of polygyny inVespula (1996)
    Springer
    Insectes sociaux 43 (1996), S. 401-410 
    Details
    ISSN: 1420-9098
    Keywords: Vespula pensylvanica ; polygyny ; Vespidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A thriving, polygynous, and probably overwintered colony of the western yellowjacket,Vespula pensylvanica, was collected on 2 November 1994 in Riverside, southern California, and examined in detail. The colony had 14 combs, of combined area 1.30 m2 containing 55,704 small and 10,266 large cells. There were 17 functional, physogastric queens, 70 newly emerged non-reproductive queens, 7300 adult workers, 685 adult males, and c. 17,600 capped cells containing pupae or fully-fed larvae. Dissections of 200 workers showed that none had well-developed ovaries. Hypotheses for the rarity of polygyny inVespula are put forward and evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01258412
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  • 2
    Electronic Resource
    Electronic Resource
    House-hunting by honey bee swarms: collective decisions and individual behaviors (1999)
    Springer
    Insectes sociaux 46 (1999), S. 348-360 
    Details
    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
    URL: http://dx.doi.org/10.1007/s000400050156
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  • 3
    Electronic Resource
    Electronic Resource
    Sulfur contents and sulfur-isotope compositions of thiotrophic symbioses in bivalve molluscs and vestimentiferan worms (1998)
    Springer
    Marine biology 132 (1998), S. 453-460 
    Details
    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
    URL: http://dx.doi.org/10.1007/s002270050411
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  • 4
    Electronic Resource
    Electronic Resource
    Cs(6D3/2)+H2→CsH+H reaction. IV. Rotationally resolved total cross sections (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3428-3436 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Cs(6D3/2)+H2→CsH [X 1Σ+(v″=0,1; J″)]+H photochemical reaction has been studied in a crossed-beam experiment with electronic excitation of Cs atoms and laser-induced fluorescence detection of CsH products. The reactive cross section is measured at a collision energy of 0.09 eV: σ(6D3/2)=0.04×10−16 cm2. The rotational distributions of CsH products measured on v″=0 for 0≤J″≤23 and on v″=1 for 0≤J″≤15 are close to statistical ones with 16% of products in v″=1. A quasi-classical 3D trajectory calculation of this reaction yields both rotational and vibrational distributions of CsH products and their angular scattering probability. The reactive cross section measured with Cs(6D3/2) excitation is an order of magnitude smaller than the cross section σ(7P1/2)=0.6×10−16 cm2, which is re-evaluated in this article. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478209
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  • 5
    Electronic Resource
    Electronic Resource
    Stereodynamics and Active Controls in Chemical Reactions (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 13569-13570 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100037a600
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  • 6
    Electronic Resource
    Electronic Resource
    Bound states and time-dependent dynamics of the N2H+ molecular ion in its ground electronic state. I. 2D treatment (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2930-2941 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground-state potential energy surface (PES) for linear arrangements of the N2H+ molecular ion is numerically computed by the multireference single- and double-excitation configuration interaction (MRD-CI) technique. An analytical representation of the potential energy function is obtained by fitting a power series in the Simons–Parr–Finlan coordinates to the numerical data. For investigating the intramolecular dynamics we describe the nuclear motion by a Gaussian wave packet located initially in the strong interaction region of the PES. The vibrational eigenvalue spectrum is calculated by Fourier transforming the time autocorrelation function. The spectrum is then analyzed statistically in the light of random matrix theory (RMT) to understand the nature of the intramolecular dynamics. We examine the short-range correlation in the spectrum through the nearest neighbor level spacing distribution P(s) and the long-range correlation through Δ3 and Σ2 statistics. The spectrum in the time domain is analyzed by computing the ensemble averaged survival probability 〈〈P(t)〉〉. The above four quantities obtained from the spectrum are compared with the distribution predicted for regular, irregular, and mixed (intermediate) spectra by the RMT. We find the system is of mixed type and the fractional irregularity is 0.7±0.05. In order to reveal a possible correspondence to the classical dynamics, we have carried out the spectral analysis of the dynamical variables for classical trajectories over a wide range of internal energies. In addition the classical dynamics of proton collisions with N2 molecules has also been preliminarily studied on the same PES, in particular the dependence of the final vibrational action nf on the initial vibrational phase φi of N2 and, furthermore, the Poincaré surface-of-section superimposed with the zero-order separatrix; we find a large number of trapped trajectories. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474651
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  • 7
    Electronic Resource
    Electronic Resource
    Photodissociation of NH2: Two-dimensional potential energy surfaces for the dissociation into NH and H (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5558-5571 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Extensive multireference configuration interaction calculations were carried out in order to obtain complete two-dimensional (2D) potential energy surfaces for the amidogen (NH2) radical as functions of both N–H bond lengths keeping the bond angle fixed at its experimental ground state equilibrium value. The eight lowest-lying states (four of each symmetry, A′ and A″) were treated mainly for the purpose of using these surfaces in subsequent studies of the photodissociation dynamics. In analogy with the neighboring dihydrides CH2 and H2O the photodissociation of NH2 into NH+H (hydrogen abstraction) takes place preferentially after excitation of the first two Rydberg s states (3 2A′/2 2A1 and 2 2A″/2 2B1) found closely together at about 7.6 eV. The transition dipole moments connecting the ground state with these two states are large (0.44 a.u. and 0.66 a.u.) in the Franck–Condon region, but the behavior of the potentials in the dissociation channel is quite different. The 3 2A′/2 2A1 state is weakly repulsive whereas the 2 2A″/2 2B1 state is strongly repulsive. This will result in differences in the dissociation dynamics for the two states.The next higher state which should play a role in the NH2 photodissociation is the 4 2A″/3 2B1 Rydberg s state at 9.4 eV, because of its large transition dipole moment with the ground state (0.36 a.u.). Close to this state, many Rydberg p states were found. Due to the high density of states in the region above 9.0 eV, interactions of these states are expected and should lead to complicated dissociation dynamics. Contrary to CH2, the two low-lying valence states for NH2 are found at lower energies [2.2 eV (1 2A1) and 6.5 eV (1 2B2)], well separated from the first members of the Rydberg series. These states are less important for the photodissociation of NH2, compared with CH2, because the first state is bound and the transition to the other is dipole-forbidden in C2v symmetry. For H2O, the valence states are missing. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471796
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  • 8
    Electronic Resource
    Electronic Resource
    Tunneling through the potential barrier of the B1Πu state of 7Li–7Li (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1926-1936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A sub-Doppler experiment involving an effusive beam of lithium dimers and a continuous wave (cw) tunable dye laser is used to record the absorption spectrum of the B–X system. Predissociation due to tunneling through the potential barrier of the B state is studied in a small range of energy above the Li(2p)+Li(2s) dissociation limit by analyzing the shape of homogeneously broadened absorption lines and by measuring the fluorescence intensity of Li atoms. Experimental data are interpreted in the frame of a semiclassical dynamical model involving the shape of the potential barrier. Their accuracy should address an improvement of the potential shape through a full quantal dynamical model. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479461
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  • 9
    Electronic Resource
    Electronic Resource
    Expression and function of the cardiac Na+/Ca2+ exchanger in postnatal development of the rat, in experimentaliduced cardiac hypertrophy and in the failing human heart (1997)
    Springer
    Basic research in cardiology 92 (1997), S. 53-58 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00794068
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  • 10
    Electronic Resource
    Electronic Resource
    Overview of powder injection molding (1996)
    Springer
    Advanced performance materials 3 (1996), S. 121-151 
    Details
    ISSN: 1572-8765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Powder injection molding is a near net-shape technique suitable for the production of moderate to large volumes of small complex components of a wide range of materials such as ceramics, metals and hard metals. It combines the plastics injection molding technique with the power sintering techniques to produce high density parts at close tolerances. The technology has been known for more than 40 years, but it is only for the last decade that it became a commercial reality. Thanks to recent economical and technological developments the business outlook is positive with parts being produced for a wide field of applications. Still, in order to become truly a great commercial success researchers and producers have to overcome numerous technical and economical challenges and increase the awareness among designers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00136742
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