Galileo dust data from the jovian system: 2000 to 2003

The Galileo spacecraft was orbiting Jupiter between Dec 1995 and Sep 2003. The Galileo dust detector monitored the jovian dust environment between about 2 and 370 R_J (jovian radius R_J = 71492 km). We present data from the Galileo dust instrument for the period January 2000 to September 2003. We report on the data of 5389 particles measured between 2000 and the end of the mission in 2003. The majority of the 21250 particles for which the full set of measured impact parameters (impact time, impact direction, charge rise times, charge amplitudes, etc.) was transmitted to Earth were tiny grains (about 10 nm in radius), most of them originating from Jupiter's innermost Galilean moon Io. Their impact rates frequently exceeded 10 min^-1. Surprisingly large impact rates up to 100 min^-1 occurred in Aug/Sep 2000 when Galileo was at about 280 R_J from Jupiter. This peak in dust emission appears to coincide with strong changes in the release of neutral gas from the Io torus. Strong variability in the Io dust flux was measured on timescales of days to weeks, indicating large variations in the dust release from Io or the Io torus or both on such short timescales. Galileo has detected a large number of bigger micron-sized particles mostly in the region between the Galilean moons. A surprisingly large number of such bigger grains was measured in March 2003 within a 4-day interval when Galileo was outside Jupiter's magnetosphere at approximately 350 R_J jovicentric distance. Two passages of Jupiter's gossamer rings in 2002 and 2003 provided the first actual comparison of in-situ dust data from a planetary ring with the results inferred from inverting optical images.Comment: 59 pages, 13 figures, 6 tables, submitted to Planetary and Space Scienc

An optical lattice on an atom chip

Optical dipole traps and atom chips are two very powerful tools for the quantum manipulation of neutral atoms. We demonstrate that both methods can be combined by creating an optical lattice potential on an atom chip. A red-detuned laser beam is retro-reflected using the atom chip surface as a high-quality mirror, generating a vertical array of purely optical oblate traps. We load thermal atoms from the chip into the lattice and observe cooling into the two-dimensional regime where the thermal energy is smaller than a quantum of transverse excitation. Using a chip-generated Bose-Einstein condensate, we demonstrate coherent Bloch oscillations in the lattice.Comment: 3 pages, 2 figure

Professor A. J. H. van der Walt- 'n Waardering

My kennismaking met prof. Andries van der Walt dateer vanaf Februarie1925, nou een-en-dertig jaar gelede

Die betekenis van die teologiese skool vir ons kerklike lewe.

Die grondslag is van huis uit Gereformeerd. Dieselfde bodem dus waarop die Kerk van die Skool gefondeer is. Nader verklaar, beteken dit, dat ons Teologiese Skool staan op die beginsels van die Bybel, soos dit in die drie Formuliere van Enigheid vertolk en vasgelê is deur die Nasionale Sinode van Dordrecht, in die jaar 1619

Ons erfenis van driehonderd jaar

Waar ons tans die stigting van die blanke volksplanting aan die Kaap driehonderd jaar gelede herdenk, gaan dit nie om bloot in die herinnering terug te roep ’n eenmalige gebeurtenis van April 1652 nie, maar veel meer die uitwerking en gevolge daarvan, soos sigbaar in die Unie van Suid-Afrika vandag

Quantum Phase Transitions in Spin Systems

We discuss the influence of strong quantum fluctuations on zero-temperature phase transitions in a two-dimensional spin-half Heisenberg system. Using a high-order coupled cluster treatment, we study competition of magnetic bonds with and without frustration. We find that the coupled cluster treatment is able to describe the zero-temperature transitions in a qualitatively correct way, even if frustration is present and other methods such as quantum Monte Carlo fail.Comment: 8 pages, 12 Postscipt figures; Accepted for publication in World Scientifi

Pacifying the Fermi-liquid: battling the devious fermion signs

The fermion sign problem is studied in the path integral formalism. The standard picture of Fermi liquids is first critically analyzed, pointing out some of its rather peculiar properties. The insightful work of Ceperley in constructing fermionic path integrals in terms of constrained world-lines is then reviewed. In this representation, the minus signs associated with Fermi-Dirac statistics are self consistently translated into a geometrical constraint structure (the {\em nodal hypersurface}) acting on an effective bosonic dynamics. As an illustrative example we use this formalism to study 1+1-dimensional systems, where statistics are irrelevant, and hence the sign problem can be circumvented. In this low-dimensional example, the structure of the nodal constraints leads to a lucid picture of the entropic interaction essential to one-dimensional physics. Working with the path integral in momentum space, we then show that the Fermi gas can be understood by analogy to a Mott insulator in a harmonic trap. Going back to real space, we discuss the topological properties of the nodal cells, and suggest a new holographic conjecture relating Fermi liquids in higher dimensions to soft-core bosons in one dimension. We also discuss some possible connections between mixed Bose/Fermi systems and supersymmetry.Comment: 28 pages, 5 figure

Risk factors for violence among long-term psychiatric in-patients: a comparison between violent and non-violent patients

Objective: The problem of the prediction of violence in psychiatric patients has led to a proliferation of research over the last decade. This study focuses on enduring patient related risk factors of violence, and investigates which long-term patients in Weskoppies Hospital (a specialist psychiatric hospital) are the most likely to commit violent acts. Method: Nursing statistics on violent incidents and other security breaches were collected for 262 long-term in-patients over a six month period (April – September 2007). The 41 patients who committed violent acts were compared to the 221 non-violent patients in terms of demographic and clinical variables, using two-way tables and Chi-Square or Fisher’s Exact Tests. Results: The prevalence of violence among the long-term patients was 16%. Fighting among patients was the most common form of violence (58%). The most significant risk factors of violence among the long-term patients are: A diagnosis of mental retardation; first hospital admission before the age of 40 years; total hospital stay >12 years; current accommodation in a closed ward; habitual verbal aggression; absence of disorganised behaviour; and being clinically evaluated as unsuitable for community placement. Conclusion: The findings will help to identify those long-term patients most at risk of violence. The subgroup of patients with mental retardation is responsible for a disproportionately large number of violent acts in the hospital. The risk lies not so much in their psychiatricsymptoms, but more in their cognitive ability, coping skills and  inappropriate admission circumstances. Efforts should be directed– at a provincial level – towards their community placement.Key words: Violence; Risk factors; Inpatients; Mental disorders; South Afric

Trap-tubs as a means of vole-damage reduction in afforestations

Krüger, F., Jarchow, D