10,948 research outputs found
Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity
Large-grain Nb has become a viable alternative to fine-grain Nb for the
fabrication of superconducting radio-frequency cavities. In this contribution
we report the results from a heat treatment study of a large-grain 1.5 GHz
single-cell cavity made of "medium purity" Nb. The baseline surface preparation
prior to heat treatment consisted of standard buffered chemical polishing. The
heat treatment in the range 800 - 1400 C was done in a newly designed vacuum
induction furnace. Q0 values of the order of 2x1010 at 2.0 K and peak surface
magnetic field (Bp) of 90 mT were achieved reproducibly. A Q0-value of
(5+-1)1010 at 2.0 K and Bp = 90 mT was obtained after heat treatment at 1400 C.
This is the highest value ever reported at this temperature, frequency and
field. Samples heat treated with the cavity at 1400 C were analyzed by
secondary ion mass spectrometry, secondary electron microscopy, energy
dispersive X-ray, point contact tunneling and X-ray diffraction and revealed a
complex surface composition which includes titanium oxide, increased carbon and
nitrogen content but reduced hydrogen concentration compared to a non
heat-treated sample
Emergence of Order in Textured Patterns
A characterization of textured patterns, referred to as the disorder function
\bar\delta(\beta), is used to study properties of patterns generated in the
Swift-Hohenberg equation (SHE). It is shown to be an intensive,
configuration-independent measure. The evolution of random initial states under
the SHE exhibits two stages of relaxation. The initial phase, where local
striped domains emerge from a noisy background, is quantified by a power law
decay \bar\delta(\beta) \sim t^{-{1/2} \beta}. Beyond a sharp transition a
slower power law decay of \bar\delta(\beta), which corresponds to the
coarsening of striped domains, is observed. The transition between the phases
advances as the system is driven further from the onset of patterns, and
suitable scaling of time and \bar\delta(\beta) leads to the collapse of
distinct curves. The decay of during the initial phase
remains unchanged when nonvariational terms are added to the underlying
equations, suggesting the possibility of observing it in experimental systems.
In contrast, the rate of relaxation during domain coarsening increases with the
coefficient of the nonvariational term.Comment: 9 Pages, 8 Postscript Figures, 3 gif Figure
The Molonglo Galactic Plane Survey: I. Overview and Images
The first epoch Molonglo Galactic Plane Survey (MGPS1) is a radio continuum
survey made using the Molonglo Observatory Synthesis Telescope (MOST) at 843
MHz with a resolution of 43" X 43" cosec |delta|. The region surveyed is 245
deg < l < 355 deg, |b| < 1.5 deg. The thirteen 9 deg X 3 deg mosaic images
presented here are the superposition of over 450 complete synthesis
observations, each taking 12 h and covering 70' X 70' cosec |delta|. The
root-mean-square sensitivity over much of the mosaiced survey is 1-2 mJy/beam
(1 sigma), and the positional accuracy is approximately 1" X 1" cosec |delta|
for sources brighter than 20 mJy. The dynamic range is no better than 250:1,
and this also constrains the sensitivity in some parts of the images. The
survey area of 330 sq deg contains well over 12,000 unresolved or barely
resolved objects, almost all of which are extra-galactic sources lying in the
Zone of Avoidance. In addition a significant fraction of this area is covered
by extended, diffuse emission associated with thermal complexes, discrete H II
regions, supernova remnants, and other structures in the Galactic interstellar
medium.Comment: Paper with 3 figures and 1 table + Table 2 + 7 jpg grayscales for Fig
4. Astrophysical Journal Supplement (in press) see also
http://www.astrop.physics.usyd.edu.au/MGP
Coevolution of religious and political authority in Austronesian societies
Authority, an institutionalized form of social power, is one of the defining features of the large-scale societies that evolved during the Holocene. Religious and political authority have deep histories in human societies and are clearly interdependent, but the nature of their relationship and its evolution over time is contested. We purpose-built an ethnographic dataset of 97 Austronesian societies and used phylogenetic methods to address two long-standing questions about the evolution of religious and political authority: first, how these two institutions have coevolved, and second, whether religious and political authority have tended to become more or less differentiated. We found evidence for mutual interdependence between religious and political authority but no evidence for or against a long-term pattern of differentiation or unification in systems of religious and political authority. Our results provide insight into how political and religious authority have worked synergistically over millennia during the evolution of large-scale societies
Role of the dielectric constant of ferroelectric ceramic in enhancing the ionic conductivity of a polymer electrolyte composite
The dispersal of high dielectric constant ferroelectric ceramic material
Ba(0.7)Sr(0.3)TiO(3) (Tc~30 C) and Ba(0.88)Sr(0.12)TiO(3) (Tc~90 C) in an ion
conducting polymer electrolyte (PEO:NH4I) is reported to result in an increase
in the room temperature ionic conductivity by two orders of magnitude. The
conductivity enhancememt "peaks" as we approach the dielectric phase transition
of the dispersed ferroelectric material where the dielectric constant changes
from ~ 2000 to 4000. This establishes the role of dielectric constant of the
dispersoid in enhancing the ionic conductivity of the polymeric composites.Comment: 10 pages, 2 figure
First determination of the strange and light quark masses from full lattice QCD
We compute the strange quark mass and the average of the and
quark masses using full lattice QCD with three dynamical quarks
combined with experimental values for the pion and kaon masses. The simulations
have degenerate and quarks with masses as low as
, and two different values of the lattice spacing. The bare lattice
quark masses obtained are converted to the \msbar scheme using perturbation
theory at . Our results are: m_s^\msbar(2 GeV) = 76(0)(3)(7)(0)
MeV, \hat m^\msbar(2 GeV) = 2.8(0)(1)(3)(0) MeV and =
27.4(1)(4)(0)(1), where the errors are from statistics, simulation,
perturbation theory, and electromagnetic effects, respectively.Comment: 5 pages, revtex, 2 figures. v2: New ms/hat(m) discussion and
reference, v3: slight change in discussion of referenc
On directed information theory and Granger causality graphs
Directed information theory deals with communication channels with feedback.
When applied to networks, a natural extension based on causal conditioning is
needed. We show here that measures built from directed information theory in
networks can be used to assess Granger causality graphs of stochastic
processes. We show that directed information theory includes measures such as
the transfer entropy, and that it is the adequate information theoretic
framework needed for neuroscience applications, such as connectivity inference
problems.Comment: accepted for publications, Journal of Computational Neuroscienc
- âŠ