4,452 research outputs found
Antiferromagnetic Alignment and Relaxation Rate of Gd Spins in the High Temperature Superconductor GdBa_2Cu_3O_(7-delta)
The complex surface impedance of a number of GdBaCuO
single crystals has been measured at 10, 15 and 21 GHz using a cavity
perturbation technique. At low temperatures a marked increase in the effective
penetration depth and surface resistance is observed associated with the
paramagnetic and antiferromagnetic alignment of the Gd spins. The effective
penetration depth has a sharp change in slope at the N\'eel temperature, ,
and the surface resistance peaks at a frequency dependent temperature below 3K.
The observed temperature and frequency dependence can be described by a model
which assumes a negligibly small interaction between the Gd spins and the
electrons in the superconducting state, with a frequency dependent magnetic
susceptibility and a Gd spin relaxation time being a strong function
of temperature. Above , has a component varying as , while below it increases .Comment: 4 Pages, 4 Figures. Submitted to Phys. Rev.
Data base management system analysis and performance testing with respect to NASA requirements
Several candidate Data Base Management Systems (DBM's) that could support the NASA End-to-End Data System's Integrated Data Base Management System (IDBMS) Project, later rescoped and renamed the Packet Management System (PMS) were evaluated. The candidate DBMS systems which had to run on the Digital Equipment Corporation VAX 11/780 computer system were ORACLE, SEED and RIM. Oracle and RIM are both based on the relational data base model while SEED employs a CODASYL network approach. A single data base application which managed stratospheric temperature profiles was studied. The primary reasons for using this application were an insufficient volume of available PMS-like data, a mandate to use actual rather than simulated data, and the abundance of available temperature profile data
Noether’s theorem for dissipative quantum dynamical semi-groups
Noether's Theorem on constants of the motion of dynamical systems has
recently been extended to classical dissipative systems (Markovian semi-groups)
by Baez and Fong. We show how to extend these results to the fully quantum
setting of quantum Markov dynamics. For finite-dimensional Hilbert spaces, we
construct a mapping from observables to CP maps that leads to the natural
analogue of their criterion of commutativity with the infinitesimal generator
of the Markov dynamics. Using standard results on the relaxation of states to
equilibrium under quantum dynamical semi-groups, we are able to characterise
the constants of the motion under quantum Markov evolutions in the
infinite-dimensional setting under the usual assumption of existence of a
stationary strictly positive density matrix. In particular, the Noether
constants are identified with the fixed point of the Heisenberg picture
semigroup.Comment: 8 pages, no figure
PKS 1830-211: A Possible Compound Gravitational Lens
Measurements of the properties of gravitational lenses have the power to tell
us what sort of universe we live in. The brightest known radio Einstein
ring/gravitational lens PKS 1830-211 (Jauncey et al., 1991), whilst obscured by
our Galaxy at optical wavelengths, has recently been shown to contain
absorption at the millimetre waveband at a redshift of 0.89 (Wiklind and
Combes, 1996a). We report the detection of a new absorption feature, most
likely due to neutral hydrogen in a second redshift system at z = 0.19.
Follow-up VLBI observations have spatially resolved the absorption and reveal
it to cover the NE compact component and part of the lower surface brightness
ring. This new information, together with existing evidence of the unusual VLBI
radio structure and difficulties in modeling the lensing system, points to the
existence of a second lensing galaxy along our line of sight and implies that
PKS 1830-211 may be a compound gravitational lens.Comment: 8 pages, 2 figures, LaTeX (aasms4.sty). Accepted for publication in
ApJ Letters. Preprint also available at
http://kerr.phys.utas.edu.au/preprints
Promoting Mental Health and Wellbeing with Men and Boys: What Works?
In May 2014 the Movember Foundation commissioned the Centre for Men’s Health, Leeds Beckett University, in collaboration with the Men’s Health Forum (England & Wales), to gather the current research evidence and practical (‘tacit’) knowledge about the core elements that make for successful work with boys and men around mental health promotion, early intervention and stigma reduction
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