Additions to fused-fluoride lubricant coatings for reduction of low-temperature friction

Additions to fused-fluoride lubricant coatings for reduction of low temperature frictio

Recoiling from a kick in the head-on collision of spinning black holes

Recoil ``kicks'' induced by gravitational radiation are expected in the inspiral and merger of black holes. Recently the numerical relativity community has begun to measure the significant kicks found when both unequal masses and spins are considered. Because understanding the cause and magnitude of each component of this kick may be complicated in inspiral simulations, we consider these effects in the context of a simple test problem. We study recoils from collisions of binaries with initially head-on trajectories, starting with the simplest case of equal masses with no spin and then adding spin and varying the mass ratio, both separately and jointly. We find spin-induced recoils to be significant relative to unequal-mass recoils even in head-on configurations. Additionally, it appears that the scaling of transverse kicks with spins is consistent with post-Newtonian theory, even though the kick is generated in the nonlinear merger interaction, where post-Newtonian theory should not apply. This suggests that a simple heuristic description might be effective in the estimation of spin-kicks.Comment: 12 pages, 10 figures. Replaced with published version, including more discussion of convergence and properties of final hol

The bloodstream differentiation - division of Trypanosoma brucei studied using mitochondrial markers

In the bloodstream of its mammalian host, the African trypanosome Trypanosoma brucei undergoes a life cycle stage differentiation from a long, slender form to a short, stumpy form. This involves three known major events: exit from a proliferative cell cycle, morphological change and mitochondrial biogenesis. Previously, models have been proposed accounting for these events (Matthews & Gull 1994a). Refinement of, and discrimination between, these models has been hindered by a lack of stage-regulated antigens useful as markers at the single-cell level. We have now evaluated a variety of cytological markers and applied them to investigate the coordination of phenotypic differentiation and cell cycle arrest. Our studies have focused on the differential expression of the mitochondrial enzyme dihydrolipoamide dehydrogenase relative to the differentiation-division of bloodstream trypanosomes. The results implicate a temporal order of events: commitment, division, phenotypic differentiation

Text Type And Text Structure: An Analysis Of Three Secondary Informal Reading Inventories

Reading educators (Cheek & Cheek, 1983; Roe, Stoodt, & Burns, 1978) urge secondary teachers to use informal reading inventories (IRIs) in order to diagnose students\u27 reading problems and to place students in textbooks at appropriate levels to optimize instruction. Advice of this nature is surely well-intended; nevertheless, educators have reservations about the merits of available IRIs. For example, readability levels of IRI passages (Gerke, 1980), passage dependency of questions (Marr & Lyon, 1980; Tuinman, 1971), classification of questions (Shell & Hanna, 1981), scoring criteria (Bormuth, 1969), validity (Cooper, 1952; Powell, 1971), and allowable errors or miscues (Ekwall, 1971; Harris & Sipay, 1980) have been the focus of serious questions by reading researchers

Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission

Particle-hole (p-h) mixing is a fundamental consequence of the existence of a pair condensate. We present direct experimental evidence for p-h mixing in the angle-resolved photoemission (ARPES) spectra in the superconducting state of Bi_2Sr_2CaCu_2O_{8+\delta}. In addition to its pedagogical importance, this establishes unambiguously that the gap observed in ARPES is associated with superconductivity.Comment: 3 pages, revtex, 4 postscript figure

Nonlinear dynamics, rectification, and phase locking for particles on symmetrical two-dimensional periodic substrates with dc and circular ac drives

We investigate the dynamical motion of particles on a two-dimensional symmetric periodic substrate in the presence of both a dc drive along a symmetry direction of the periodic substrate and an additional circular ac drive. For large enough ac drives, the particle orbit encircles one or more potential maxima of the periodic substrate. In this case, when an additional increasing dc drive is applied in the longitudinal direction, the longitudinal velocity increases in a series of discrete steps that are integer multiples of the lattice constant of the substrate times the frequency. Fractional steps can also occur. These integer and fractional steps correspond to distinct stable dynamical orbits. A number of these phases also show a rectification in the positive or negative transverse direction where a non-zero transverse velocity occurs in the absence of a dc transverse drive. We map out the phase diagrams of the regions of rectification as a function of ac amplitude, and find a series of tongues. Most of the features, including the steps in the longitudinal velocity and the transverse rectification, can be captured with a simple toy model and by arguments from nonlinear maps. We have also investigated the effects of thermal disorder and incommensuration on the rectification phenomena, and find that for increasing disorder, the rectification regions are gradually smeared and the longitudinal velocity steps are no longer flat but show a linearly increasing velocity.Comment: 14 pages, 17 postscript figure

An Experimental Study of Decisions in Dynamic Optimization Problems.

In this paper we use an experimental approach to study the decisions of human subjects who are given cash incentives to solve a particular representative agent dynamic model widely studied in macroeconomics. In a representative agent dynamic model, an economy is modelled as a single decision maker, who maximizes the discounted utility of consumption over the appropriate time horizon. The assupmtion of a single decision maker in the economy removes complications resulting from the existence of multiple agents, such as inefficiencies resulting from strategic behavior or externalities, and technical difficulties arising from the aggregation of preferences.OPTIMIZATION ; DECISION MAKING ; MACROECONOMICS

Resonant Charge Transfer In Symmetric Alkali-ion Alkali-atom Collisions

Resonant charge transfer in alkali-ion alkali-atom collisions is investigated by using the molecular-orbital expansion method incorporating the use of electron translation factors. Molecular wave functions and eigen energies are obtained by the pseudopotential method. Molecular properties, Re, De, and e, obtained in the present calculation are in good accord with other recent theoretical results, as well as spectroscopic measurements. Three-state close-coupling calculations reproduce the positions of the maxima and minima in the oscillatory structure seen experimentally in the resonant-charge-transfer cross sections for the Li2 + and Cs2 + systems. The magnitude of the total cross sections and their velocity dependence are in agreement with experimental measurements. © 1986 The American Physical Society

Outflows and Jets from Collapsing Magnetized Cloud Cores

Star formation is usually accompanied by outflow phenomena. There is strong evidence that these outflows and jets are launched from the protostellar disk by magneto-rotational processes. Here, we report on our three dimensional, adaptive mesh, magneto-hydrodynamic simulations of collapsing, rotating, magnetized Bonnor-Ebert-Spheres whose properties are taken directly from observations. In contrast to the pure hydro case where no outflows are seen, our present simulations show an outflow from the protodisk surface at ~ AU and a jet at ~ 0.07 AU after a strong toroidal magnetic field build up. The large scale outflow, which extends up to ~ AU at the end of our simulation, is driven by toroidal magnetic pressure (spring), whereas the jet is powered by magneto-centrifugal force (fling). At the final stage of our simulation these winds are still confined within two respective shock fronts. Furthermore, we find that the jet-wind and the disk-anchored magnetic field extracts a considerable amount of angular momentum from the protostellar disk. The initial spin of our cloud core was chosen high enough to produce a binary system. We indeed find a close binary system (separation ~ 3 R_sol) which results from the fragmentation of an earlier formed ring structure. The magnetic field strength in these protostars reaches ~ 3 kG and becomes about 3 G at 1 AU from the center in agreement with recent observational results.Comment: revised version, accepted for publication in ApJ, a higher resolution version of this paper can be downloaded at http://www.physics.mcmaster.ca/~banerjee/outflows.pd

Comparison of Measured and Calculated Specific Resistances of Pd/Pt Interfaces

We compare specific resistances (AR equals area A times resistance R) of sputtered Pd/Pt interfaces measured in two different ways with no-free-parameter calculations. One way gives 2AR(Pd/Pt) of 0.29 (0.03) fohm-m(2) and the other 0.17 (0.13) fohm-m(2). From these we derive a best estimate of 2AR(Pd/Pt) of 0.28 (0.06) fohm-m(2), which overlaps with no-free-parameter calculations: 2AR(predicted) of 0.30 (0.04) fohm-m(2) for flat, perfect interfaces, or 0.33 (0.04) fohm-m(2) for interfaces composed of 2 monolayers of a 50percent-50percent PdPt alloy. These results support three prior examples of agreement between calculations and measurements for pairs of metals having the same crystal structure and the same lattice parameter to within 1 percent. We also estimate the spin-flipping probability at Pd/Pt interfaces as 0.13 (0.08).Comment: 3 pages, 3 figures, submitted for publication New version has corrected value of delta(Pd/Pt