Gifford-McMahon refrigerator with split cold head

Leybold-Heraeus Co. have developed, built and successfully tested a Gifford-McMahon cryocooler with splitted cold head for cooling a cryopump. The refrigerating part of the cold head and the gas flow control device have been separated (splitted cold head) and the distance between them is bridged by only two thin lines for carrying the working gas. Due to this separation the size of the refrigerating part is virtually defined only by the size of the displacers whilst the gas flow control device can be of any desired design. It has been shown that dimensioning of the connecting lines and the corresponding losses became less critical with increasing size of the expander, but additional cooling in proportion to the refrigerating capacity is required

A unified projection formalism for the Al-Pd-Mn quasicrystal Xi-approximants and their metadislocations

The approximants xi, xi' and xi'_n of the quasicrystal Al-Mn-Pd display most interesting plastic properties as for example phason-induced deformation processes (Klein, H., Audier, M., Boudard, M., de Boissieu, M., Beraha, L., and Duneau, M., 1996, Phil. Mag. A, 73, 309.) or metadislocations (Klein, H., Feuerbacher, M., Schall, P., and Urban, K., 1999, Phys. Rev. Lett., 82, 3468.). Here we demonstrate that the phases and their deformed or defected states can be described by a simple projection formalism in three-dimensional space - not as usual in four to six dimensions. With the method we can interpret microstructures observed with electron microscopy as phasonic phase boundaries. Furthermore we determine the metadislocations of lowest energy and relate them uniquely to experimentally observed ones. Since moving metadislocations in the xi'-phase can create new phason-planes, we suggest a dislocation induced phase transition from xi' to xi'_n. The methods developed in this paper can as well be used for various other complex metallic alloys.Comment: 25 pages, 12 figure

Workers' Compensation Insurance In North America: Lessons for Victoria?

Among the issues we will consider here are the following. Who carries the underwriting(insurance) risk for workers' compensation benefits? How is workers' compensation insuranceprices, and by whom? What fundamental principles guide the insurance pricing system? Whomonitors benefits for compliance with statutory requirements? Are the availability of coverageand the payment of insurers' claims obligations guaranteed? Is self-insurance allowed and, if so, for whom? How are incentives for prevention of accidents, and resulting workers' compensation claims, maintained? What is the performance of the overall system? In summary, how are these questions answered and what so the answers reveal about how these responsibilities are allocated among government agencies, other public entities and private firms

Interplay of Fulde-Ferrell-Larkin-Ovchinnikov and Vortex states in two-dimensional Superconductors

Clean superconductors with weakly coupled conducting planes have been suggested as promising candidates for observing the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We consider here a layered superconductor in a magnetic field of arbitrary orientation with respect to the conducting plane. In this case there is competition of spin-pair-breaking and orbital-pair-breaking effects. In previous work, phase boundaries characterized by Landau quantum numbers n > 0 have been predicted. Here, we calculate the actual structure of the stable states below Hc2 by minimizing the free energy. We find several new order parameter structures differing from both the traditional Abrikosov and FFLO solutions. Some interesting unsolved questions appear in the limit of large n.Comment: 13 pages, 3 figure

Tritiated alumina serves as reagent for self-labeling analysis

Tritiated alumina, prepared by exchange of the surface hydroxyl groups with tritiated water, is a suitable reagent for exchange-labeling of specific compounds in low concentrations prior to chromatographic analysis. In a chromatographic column, it detects and measures submicrogram quantities of material

Volume Dependence of the Pion Mass from Renormalization Group Flows

We investigate finite volume effects on the pion mass and the pion decay constant with renormalization group (RG) methods in the framework of a phenomenological model for QCD. An understanding of such effects is important in order to interpret results from lattice QCD and extrapolate reliably from finite lattice volumes to infinite volume. We consider the quark-meson-model in a finite Euclidean 3+1 dimensional volume. In order to break chiral symmetry in the finite volume, we introduce a small current quark mass. In the corresponding effective potential for the meson fields, the chiral O(4)-symmetry is broken explicitly, and the sigma and pion fields are treated individually. Using the proper-time renormalization group, we derive renormalization group flow equations in the finite volume and solve these equations in the approximation of a constant expectation value. We calculate the volume dependence of pion mass and pion decay constant and compare our results with recent results from chiral perturbation theory in finite volume.Comment: 9 pages, 3 figures, talk given at "Hadronic Physics 2004 - Joint meeting Heidelberg-Liege-Paris-Rostock", to appear in the proceedings, AIP conference serie

Mechanical detection of nuclear spin relaxation in a micron-size crystal

A room temperature nuclear magnetic resonance force microscope (MRFM), fitted in a $^1$Tesla electromagnet, is used to measure the nuclear spin relaxation of $^1$H in a micron-size (70ng) crystal of ammonium sulfate. NMR sequences, combining both pulsed and continuous wave r.f. fields, have allowed us to measure mechanically $T_2$ and $T_1$, the transverse and longitudinal spin relaxation times. Because two spin species with different $T_1$ values are measured in our $7\mu{\rm m}$ thick crystal, magnetic resonance imaging of their spatial distribution inside the sample section are performed. To understand quantitatively the measured signal, we carefully study the influence of the spin-lattice relaxation and the non-adiabaticity of the c.w. sequence on the intensity and time dependence of the detected signal.Comment: latex drafteps.tex, 13 files, 12 pages [SPEC-S00/010], submitted to Eur. Phys. J.