Communication Roles, Perceived Effectiveness, and Satisfaction in an Environmental Management Program

Earlier research has shown a relationship between various forms of structural centrality and perceived leadership and role satisfaction in small experimental groups. The limited amount of research on this topic in naturally occurring social networks has yielded results that often conflict with one another. Different results have generally been attributed to possible differences in task environments. This paper examines the relationship between two types of structural centrality and perceived influence, role satisfaction, and perceived effectiveness in an environmental resource management program. Findings in this paper suggest that the observed differences in relationships between the network and other variables is partly a function of global network properties (e.g., marginality of subgroups) and related task environments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pulsed fluorescence measurements of trapped molecular ions with zero background detection

Sensitive methods have been developed to measure laser-induced fluorescence from trapped ions by reducing the detection of background scattering to zero levels during the laser excitation pulse. The laser beam diameter has been reduced to approximately 150 microm to eliminate scattering on trap apertures and the resulting laser-ion interaction is limited to a volume of approximately 10(-5) cm which is approximately 0.03-0.15 of the total ion cloud volume depending on experimental conditions. The detection optics collected fluorescence only from within the solid angle defined by laser-ion interaction volume. Rhodamine 640 and Alexa Fluor 350 ions, commonly used as fluorescence resonance energy transfer (FRET) fluorophores, were generated in the gas phase by using electrospray ionization and injected into a radiofrequency Paul trap where they were stored and exposed to Nd:YAG laser pulses at 532 and 355 nm for times up to 10 m. Fluorescence emitted by these ions was investigated for several trap q(z) values and ion cloud temperatures. Analysis of photon statistics indicated an average of approximately 10 photons were incident on the PMT detector per 15 ns pulse for approximately 10(3) trapped ions in the interaction volume. Fluorescence measurements displayed a dependence on trapped ion number which were consistent with calculations of the space charge limited ion density. To investigate the quantitative capability of these fluorescence techniques, the laser-induced fragmentation of trapped Alexa Fluor 350 ions was measured and compared with a rate equation model of the dynamics. Decay of the fluorescence signal as well as the parent ion number compared closely with quantitative predictions of the photofragmentation model.     

Photoelectron spectroscopy of isolated multiply negatively charged oligonucleotides

Ultraviolet photoelectron spectroscopy in an ion beam was used to investigate the electronic properties of isolated DNA oligonucleotides [dA(5)-4H](4-) and [dT(5)-4H](4-), carrying four excess negative charges. We find the fourth adiabatic electron affinity to be slightly negative for [dA(5)-4H](4-), while it is positive for [dT(5)-4H](4-). This implies a significant influence of the base composition on energetics, which is in turn relevant for analytic applications and also for charge transport properties.     

Nickel cluster structure determined from the adsorption of molecular nitrogen: Ni49-Ni71

The geometrical structures of nickel clusters in the size range from 49 to 71 atoms are studied by the chemical probe method. Saturation coverages of molecular nitrogen are determined for each cluster and from this data specific structures are proposed (except for Ni₆₆ and Ni₆₇). The results indicate that icosahedral packing is the dominant structural configuration throughout this size range, in agreement with earlier results based on water and ammonia adsorption. In addition, it seems that for clusters larger than Ni₅₄ the excessive strain in the surface of the 55-atom regular icosahedron often leads to rear-rangements of the surface atoms to relieve that strain. Ni₅₅, in particular, is found to have two isomers, the regular icosahedron and a structure in which a single apex atom is displaced to the center of an opposite face. Ni₇₁ occurs as a 55-atom regular icosahedron with a 16-atom cap. The results suggest that the atoms in the cap adopt an ABA configuration relative to the underlying icosahedron rather than an icosahedral arrangement. For some clusters the saturation with nitrogen causes a small degree of surface reconstruction that leads to the adsorption of additional nitrogen molecules.Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under Contract No. W-31-109-Eng-38     

Reactions of cobalt clusters with deuterium

The kinetics of chemical reactions of cobalt clusters Co_n with deuterium are described. Absolute rate constants have been measured in the size range n=7–68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by a factor of 400. This size dependence is most prominent for n=7 to 25: Co₁₅ is the most reactive cluster, and Co_7–9 and Co_19–20 are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n=25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size.