Wear and Friction Behavior of Pressure Infiltration Cast Copper-Carbon Composites

Metal matrix composites, prepared by pressure infiltration casting of copper base alloy into 2 types of microporous carbon preforms, one with 100% amorphous carbon and the other containing 40 wt pct. graphite and 60 wt pct. amorphous carbon, have been examined for their wear and friction behavior under ambient conditions using a pin-on-plate reciprocating wear tester. Micro-structural characterization of tribo-surfaces has been carried out. The thin carbon films formed on the tribo-surface reduced the friction coefficient and wear for the composites, especially at low loads on the pin. Adhesive wear observed on the tribo-surface promoted wear and friction at high loads. The wear and friction were observed to be very sensitive to the size and distribution of the microstructural constituents

Elastic electron deuteron scattering with consistent meson exchange and relativistic contributions of leading order

The influence of relativistic contributions to elastic electron deuteron scattering is studied systematically at low and intermediate momentum transfers ($Q^2\leq 30$ fm$^{-2}$). In a $(p/M)$-expansion, all leading order relativistic $\pi$-exchange contributions consistent with the Bonn OBEPQ models are included. In addition, static heavy meson exchange currents including boost terms and lowest order $\rho\pi\gamma$-currents are considered. Sizeable effects from the various relativistic two-body contributions, mainly from $\pi$-exchange, have been found in form factors, structure functions and the tensor polarization $T_{20}$. Furthermore, static properties, viz. magnetic dipole and charge quadrupole moments and the mean square charge radius are evaluated.Comment: 15 pages Latex including 5 figures, final version accepted for publication in Phys.Rev.C Details of changes: (i) The notation of the curves in Figs. 1 and 2 have been clarified with respect to left and right panels. (ii) In Figs. 3 and 4 an experimental point for T_20 has been added and a corresponding reference [48] (iii) At the end of the text we have added a paragraph concerning the quality of the Bonn OBEPQ potential

Four years of Ulysses dust data: 1996 to 1999

The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse ($i = 79^{\circ}$, perihelion distance 1.3 AU, aphelion distance 5.4 AU). Between January 1996 and December 1999 the spacecraft was beyond 3 AU from the Sun and crossed the ecliptic plane at aphelion in May 1998. In this four-year period 218 dust impacts were recorded with the dust detector on board. We publish and analyse the complete data set of both raw and reduced data for particles with masses $\rm 10^{-16} g$ to $\rm 10^{-8}$ g. Together with 1477 dust impacts recorded between launch of Ulysses and the end of 1995 published earlier \cite{gruen1995c,krueger1999b}, a data set of 1695 dust impacts detected with the Ulysses sensor between October 1990 and December 1999 is now available. The impact rate measured between 1996 and 1999 was relatively constant with about 0.2 impacts per day. The impact direction of the majority of the impacts is compatible with particles of interstellar origin, the rest are most likely interplanetary particles. The observed impact rate is compared with a model for the flux of interstellar dust particles. The flux of particles several micrometers in size is compared with the measurements of the dust instruments on board Pioneer 10 and Pioneer 11 beyond 3 AU (Humes 1980, JGR, 85, 5841--5852, 1980). Between 3 and 5 AU, Pioneer results predict that Ulysses should have seen five times more ($\rm \sim 10 \mu m$ sized) particles than actually detected.Comment: accepted by Planetary and Space Science, 22 pages, 8 figures (1 colour figure

Wear and Friction Behavior of Pressure Infiltration Cast Copper-Carbon Composites

Metal matrix composites, prepared by pressure infiltration casting of copper base alloy into 2 types of microporous carbon preforms, one with 100% amorphous carbon and the other containing 40 wt pct. graphite and 60 wt pct. amorphous carbon, have been examined for their wear and friction behavior under ambient conditions using a pin-on-plate reciprocating wear tester. Micro-structural characterization of tribo-surfaces has been carried out. The thin carbon films formed on the tribo-surface reduced the friction coefficient and wear for the composites, especially at low loads on the pin. Adhesive wear observed on the tribo-surface promoted wear and friction at high loads. The wear and friction were observed to be very sensitive to the size and distribution of the microstructural constituents