Bibliothek

Notizen: The stability of equilibrium configurations of a capillary liquid in a circular cylindrical container with planar ends is investigated. The liquid is under zero gravity conditions, and its wetting angle is constant over the entire solid surface. Attention is focused on the case for which the free surface consists of two disconnected pieces (connectivity components) that bound the connected liquid domain. First we outline the method used to determine critical states with disconnected free surfaces when each connectivity component is axisymmetric. Then we examine the stability of disconnected surfaces for the simple cases that arise when each connectivity component represents a closed sphere or a part of a sphere. Ten configurations were considered that represent all possible combinations of the following connectivity components: A closed sphere (that bounds a gas bubble), a spherical cap in contact with the lateral wall of a cylinder; a spherical cap in contact with a cylinder endwall, and a portion of a sphere (that does not cross the cylinder's axis of symmetry) bounded by a cylindrical wall and a flat endwall. © 2000 American Institute of Physics.

Notizen: Results are presented on the control of a zero-pressure gradient Mach 8 boundary layer using low-momentum helium injection through a transverse slot. The boundary layer structure was visualized in three orthogonal planes using planar filtered Rayleigh scattering. Sequential images of the boundary layer were obtained using a new MHz imaging system and employed to construct three-dimensional representations of the instantaneous boundary layer behavior. The results indicate that low levels of helium injection into transitional and turbulent boundary layers can have a substantial effect on the boundary layer structure. Longitudinal structures develop downstream of the slot and persist for long times. They appear to be streamwise vortices, and it is speculated that they are formed near the injection slot due to local streamline concave curvature. The results may be important for aero-optic applications. © 2001 American Institute of Physics.

Notizen: The stability of weightless axisymmetric liquid bridge equilibrium configurations to "large" disturbances is examined by calculating the stability margin. For bridges held between coaxial equidimensional circular disks (radius R0) separated by a distance H, the stability to infinitesimal perturbations (linear stability) has been thoroughly investigated and the stability region is constructed in the (Λ,V) plane. Here, the slenderness Λ (=H/2R0) and the relative volume V (ratio of the actual liquid volume to that of a cylinder with radius R0 and height H) are the parameters that define the system. To assess stability with respect to finite amplitude disturbances we use a potential energy analysis based on the concepts of a potential energy well and the equilibrium stability margin introduced by Myshkis [USSR Comput. Math. Math. Phys. 5, 193 (1965); Math. Notes Acad. Sci. USSR 33, 131 (1983); Introduction to the Dynamics of a Body Containing a Liquid Under Zero-Gravity Conditions (Vychisl. Tsentr Akad. Nauk SSSR, Moscow, 1968)]. The stability margin represents the height of a local potential energy barrier adjacent to the well of a given stable equilibrium. Wherever a linearly stable equilibrium is nonunique equilibrium, the stability margin corresponds to the smallest among the heights of saddle points on the potential energy surface that are adjacent to the well. The saddle point that determines the stability margin is the point of emergence from the well and leads to the energy wells corresponding to other equilibria or to infinity. Unless the total energy of perturbations exceeds the stability margin for a given stable equilibrium, the liquid bridge will return to that equilibrium state. In this work we determined the stability margin in part of the stability region where axisymmetric bridges that are already unstable to small axisymmetric perturbations coexist with stable ones. The domains of existence of a variety of unstable axisymmetric bridges are constructed using previous results concerning the bifurcation structure. This enabled us to construct contours of the dimensionless stability margin within the linear stability region not only in the vicinity of the stability boundary, but also far from it. The stability margins for bridges with fixed values of the slenderness, as well as for cylindrical and catenoidal bridges, are also calculated. © 2002 American Institute of Physics.

Notizen: An emotion-modulated acoustic startle paradigm for inducing positive and negative affect was used to address pregoal and postgoal affect. Participants played a computerized lottery task in which they chose digits that could match a subsequently displayed, random set of numbers. In the positive conditions, matches led to monetary rewards. In the negative condition, matches led to an aversive noise blast. In three experiments, we found eyeblink startle magnitude was potentiated just prior to feedback concerning reward outcome, suppressed following the feedback that a monetary reward was won, and potentiated when threatened with an aversive noise. When presented with a 0%, 45%, 90%, or 100% chance of winning, higher probabilities suppressed startle response after feedback whereas the 45% trials did not. These data indicate that postgoal positive affect (winning reward) reliably suppressed the startle response whereas pregoal positive affect did not.

Notizen: Single crystals of z-cut 0.05% Fe:doped lithium niobate (Fe:LiNbO3), have been etched in a mixture of HF and HNO3 acids, under simultaneous illumination from a ∼100 mW 488 nm wavelength Ar ion laser light source, focused to power densities of ∼50 W cm−2 at the crystal surface exposed to the etchant. Etching is partially inhibited in illuminated regions, and the degree of inhibition shows a systematic latency: sites illuminated early in the etch run resist further etching even after the light is removed. Etched structures additionally exhibit regular periodic features of ∼0.5 μm scale length. Details of these structures are shown, and the latent etching effect is discussed. © 2000 American Institute of Physics.

Notizen: Electromigration results have provided clear evidence of a short or "Blech" length effect in dual- damascene, Cu/oxide, multilinked interconnects. The test structure incorporates a repeated chain of Blech-type line elements and is amenable to failure analysis tools such as focused ion beam imaging. This large interconnect ensemble provides a statistical representation of electromigrationinduced damage in the regime where steady-state interconnect stress is manifest. Statistical analysis yields a critical length of 90 μm for interconnects with line width 0.5 μm at j=1.0×106 A/cm2 and T=325 °C. © 2001 American Institute of Physics.

Notizen: Using data from a nationally representative sample of telecommunications establishments, this study finds that HR practices and workforce unionization influence managerial pay levels and the ratio of manager-to-worker pay. High performance HR practices, including investment in the skills of the workforce, in computer-based technologies and in performance-based worker pay practices, are all positively related to managerial pay; but the use of workforce teams, which shift some managerial responsibilities to workers, has the opposite association. High performance HR practices also are associated with lower manager-to-worker pay differentials. In addition, workforce unionization is positively associated with managerial pay levels, with worker base pay mediating the relationship between managers' pay and unionization.

Notizen: Bedforms and associated sedimentary structures, formed under supercritical water flow over an aggrading sand bed, were studied in a laboratory flume. Although the geometry and hydraulic characteristics of these bedforms (antidunes, chutes-and-pools) are well known, their internal structures are not. The objectives of the study were to: (1) describe the three-dimensional geometry of the sedimentary structures and examine their mode of origin; (2) develop a relationship between the geometries of the sedimentary structures and the formative bedforms and; (3) identify criteria that distinguish these sedimentary structures from similar types, such as hummocky and swaley cross-strata. Sedimentary structures associated with antidunes are primarily lenticular laminasets with concave-upward erosional bases (troughs) in which laminae generally dip upstream or fill the troughs symmetrically. These laminasets are associated with growth and upstream migration of water-surface waves and antidunes, and with surface-wave breaking and filling of antidune troughs respectively. In addition, sets of downstream-dipping laminae are produced by rapid migration of asymmetrical bedwaves immediately after wave breaking. Rare convex-upward laminae define the shape of antidunes that developed under stationary water-surface waves. The laminasets and internal laminae extend across the width of the flume, but vary in thickness and inclination, indicating that the antidunes have some degree of three dimensionality. The length and maximum thickness of the lenticular laminasets are approximately half of the length and height of formative antidunes, providing a potentially useful tool for palaeohydraulic reconstructions. The sets of downstream-dipping laminae formed under antidunes are distinctive and do not occur in hummocky and swaley cross-strata. Sedimentary structures associated with chutes-and-pools are sets of upstream-dipping laminae and structureless sand.

Notizen: Aims  To incorporate a psychosocial model of tobacco smoking into a behaviour genetic design to examine genetic and environmental influences on variation in smoking involvement.Design  Longitudinal twin study.Setting and participants  Twins initially aged between 13 and 18 years and registered with the Australian Twin Registry were surveyed three times between 1988 and 1996. A total of 414 pairs of identical and same-sex fraternal twin pairs participated in all three surveys, aged between 20 and 25 at wave 3. Biometric modelling estimated the influence of genetic and environmental factors in determining variation in smoking at each wave, both before and after adjusting for perceived smoking behaviours of peers and parents.Measurements  Twins answered a questionnaire on their own smoking status and reported on the use of tobacco by parents and friends as they perceived it, at each survey wave.Findings  At all three surveys, current smokers were more likely to have parents who smoked and to have smokers among their peers. Genes and environmental factors, both common and unique, contributed to variation in smoking behaviours. However, after controlling for the smoking behaviours of peers and parents, the role of genes in determining variation in smoking involvement was reduced by 100% at wave 1 and by 30% at wave 2. Friends’ smoking reduced the magnitude of the common environment variance by 11%, 30% and 40% at waves 1, 2 and 3, respectively. Parents’ smoking behaviours explained part of the common environment. Biometric modelling of the covariation between smoking involvement and peer smoking suggested that genes might influence smoking involvement at wave 1 by influencing choice of peers.Conclusion  Environmental factors play the greatest role in determining variation in tobacco smoking among adolescents and young adults. Among adolescents, genes may influence variation in smoking behaviours indirectly by influencing choice of peers. However, genes seem to have a direct influence on variations in the smoking behaviours of young adults.