12,444 research outputs found
Superconducting re-entrant cavity transducer for a resonant bar gravitational radiation antenna
Copyright @ American Institute of PhysicsA 10‐GHz superconducting niobium re‐entrant cavity parametric transducer was developed for use in a cryogenic 1.5‐tonne Nb resonant bar gravitational radiation antenna. The transducer has a very high electrical Q (6×105 at 4.2 K), and was operated at high cavity fields without degrading the Q. A very high electromechanical coupling between the antenna and the transducer was therefore achieved. The highest coupling attained, constrained by the available pump power, was 0.11. If the transducer were to be operated in conjunction with a wideband impedance matching element, an antenna bandwidth comparable to the frequency of the antenna would be attained. The temperature dependence of the Q of the transducer was in good agreement with theory. At temperatures above about 6 K the Q was degraded by the increase in the BCS surface resistance, while at lower temperatures the Q was limited by radiative losses
Sparticle Mass Spectrum in Grand Unified Theories
We carry out a detailed analysis of sparticle mass spectrum in supersymmetric
grand unified theories. We consider the spectroscopy of the squarks and
sleptons in SU(5) and SO(10) grand unified theories, and show how the
underlying supersymmetry breaking parameters of these theories can be
determined from a measurement of different sparticle masses. This analysis is
done analytically by integrating the one-loop renormalization group equations
with appropriate boundary conditions implied by the underlying grand unified
gauge group. We also consider the impact of non-universal gaugino masses on the
sparticle spectrum, especially the neutralino and chargino masses which arise
in supersymmetric grand unified theories with non-minimal gauge kinetic
function. In particular, we study the interrelationships between the squark and
slepton masses which arise in grand unified theories at the one-loop level,
which can be used to distinguish between the different underlying gauge groups
and their breaking pattern to the Standard Model gauge group. We also comment
on the corrections that can affect these one-loop results.Comment: 19 pages, 6 figure
The Magellanic System: What have we learnt from FUSE?
I review some of the findings on the Magellanic System produced by the Far
Ultraviolet Spectroscopic Explorer (FUSE) during and after its eight years of
service. The Magellanic System with its high-velocity complexes provides a
nearby laboratory that can be used to characterize phenomena that involve
interaction between galaxies, infall and outflow of gas and metals in galaxies.
These processes are crucial for understanding the evolution of galaxies and the
intergalactic medium. Among the FUSE successes I highlight are the coronal gas
about the LMC and SMC, and beyond in the Stream, the outflows from these
galaxies, the discovery of molecules in the diffuse gas of the Stream and the
Bridge, an extremely sub-solar and sub-SMC metallicity of the Bridge, and a
high-velocity complex between the Milky Way and the Clouds.Comment: A contributed paper to the FUSE Annapolis Conference "Future
Directions in Ultraviolet Spectroscopy.", 5 pages. To appear as an AIP
Conference Proceedin
A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds
(ABRIDGED) We present a Far-Ultraviolet Spectroscopic Explorer survey of
highly ionized high-velocity clouds (HVCs) in 66 extragalactic sight lines. We
find a total of 63 high-velocity O VI absorbers, 16 with 21 cm-emitting H I
counterparts and 47 ``highly ionized'' absorbers without 21 cm emission. 11 of
these high-velocity O VI absorbers are positive-velocity wings (broad O VI
features extending asymmetrically to velocities of up to 300 km/s). The highly
ionized HVC population is characterized by =38+/-10 km/s and <log
N_a(O VI)>=13.83+/-0.36. We find that 81% (30/37) of high-velocity O VI
absorbers have clear accompanying C III absorption, and 76% (29/38) have
accompanying H I absorption in the Lyman series. The lower average width of the
high-velocity H I absorbers implies the H I lines arise in a separate, lower
temperature phase than the O VI. We find that the shape of the wing profiles is
well reproduced by a radiatively cooling, vertical outflow. However, the
outflow has to be patchy and out of ionization equilibrium. An alternative
model, consistent with the observations, is one where the highly ionized HVCs
represent the low N(H I) tail of the HVC population, with the O VI formed at
the interfaces around the embedded H I cores. Though we cannot rule out a Local
Group explanation, we favor a Galactic origin. This is based on the recent
evidence that both H I HVCs and the million-degree gas detected in X-ray
absorption are Galactic phenomena. Since the highly ionized HVCs appear to
trace the interface between these two Galactic phases, it follows that highly
ionized HVCs are Galactic themselves. However, the non-detection of
high-velocity O VI in halo star spectra implies that any Galactic high-velocity
O VI exists at z-distances beyond a few kpc.Comment: 36 pages, 14 figures (3 in color), accepted to ApJS. Some figures
downgraded to limit file siz
On transversally elliptic operators and the quantization of manifolds with -structure
An -structure on a manifold is an endomorphism field
\phi\in\Gamma(M,\End(TM)) such that . Any -structure
determines an almost CR structure E_{1,0}\subset T_\C M given by the
-eigenbundle of . Using a compatible metric and connection
on , we construct an odd first-order differential operator ,
acting on sections of , whose principal symbol is of the
type considered in arXiv:0810.0338. In the special case of a CR-integrable
almost -structure, we show that when is the generalized
Tanaka-Webster connection of Lotta and Pastore, the operator is given by D
= \sqrt{2}(\dbbar+\dbbar^*), where \dbbar is the tangential Cauchy-Riemann
operator.
We then describe two "quantizations" of manifolds with -structure that
reduce to familiar methods in symplectic geometry in the case that is a
compatible almost complex structure, and to the contact quantization defined in
\cite{F4} when comes from a contact metric structure. The first is an
index-theoretic approach involving the operator ; for certain group actions
will be transversally elliptic, and using the results in arXiv:0810.0338,
we can give a Riemann-Roch type formula for its index. The second approach uses
an analogue of the polarized sections of a prequantum line bundle, with a CR
structure playing the role of a complex polarization.Comment: 31 page
Sand in the wheels, or oiling the wheels, of international finance? : New Labour's appeal to a 'new Bretton Woods'
Tony Blair’s political instinct typically is to associate himself only with the future. As such, his explicit appeal to ‘the past’ in his references to New Labour’s desire to establish a “new Bretton Woods” is sufficient in itself to arouse some degree of analytical curiosity (see Blair 1998a). The fact that this appeal was made specifically in relation to Bretton Woods is even more interesting. The resonant image of the international economic context established by the original Bretton Woods agreements invokes a style and content of policy-making which Tony Blair typically dismisses as neither economically nor politically consistent with his preferred vision of the future (see Blair 2000c, 2001b)
Wide area protection and fault location : review and evaluation of PMU-based methods
Wide area protection (WAP) systems use multiple sources of information to improve trip times and reduce the complexity of protection settings. Therefore, such communications-enhanced schemes have the potential to replace conventional transmission system backup protection. Through review and assessment of the present state-of-the-art relating to WAP systems, this paper demonstrates how multiple synchrophasor data sources, and the associated communications systems, can be leveraged to enable new forms of supervisory protection. Two case studies are presented: a scalable WAP architecture for future decentralised power systems, and the validation a prototype WAP system, using the principle of distributed photonic sensing, highlighting how new tools can provide cost-effective solutions to emerging protection challenges
Validity and practical utility of accelerometry for the measurement of in-hand physical activity in horses
Background:
Accelerometers are valid, practical and reliable tools for the measurement of habitual physical activity (PA). Quantification of PA in horses is desirable for use in research and clinical settings. The objective of this study was to evaluate a triaxial accelerometer for objective measurement of PA in the horse by assessment of their practical utility and validity.
Horses were recruited to establish both the optimal site of accelerometer attachment and questionnaire designed to explore owner acceptance. Validity and cut-off values were obtained by assessing PA at various gaits. Validation study- 20 horses wore the accelerometer while being filmed for 10 min each of rest, walking and trotting and 5 mins of canter work. Practical utility study- five horses wore accelerometers on polls and withers for 18 h; compliance and relative data losses were quantified.
Results:
Accelerometry output differed significantly between the four PA levels (P <0•001) for both wither and poll placement. For withers placement, ROC analyses found optimal sensitivity and specificity at a cut-off of <47 counts per minute (cpm) for rest (sensitivity 99.5 %, specificity 100 %), 967–2424 cpm for trotting (sensitivity 96.7 %, specificity 100 %) and ≥2425 cpm for cantering (sensitivity 96.0 %, specificity 97.0 %). Attachment at the poll resulted in optimal sensitivity and specificity at a cut-off of <707 counts per minute (cpm) for rest (sensitivity 97.5 %, specificity 99.6 %), 1546–2609 cpm for trotting (sensitivity 90.33 %, specificity 79.25 %) and ≥2610 cpm for cantering (sensitivity 100 %, specificity 100 %) In terms of practical utility, accelerometry was well tolerated and owner acceptance high.
Conclusion:
Accelerometry data correlated well with varying levels of in-hand equine activity. The use of accelerometers is a valid method for objective measurement of controlled PA in the horse
A Comparison of Ultraviolet, Optical, and X-Ray Imagery of Selected Fields in the Cygnus Loop
During the Astro-1 and Astro-2 Space Shuttle missions in 1990 and 1995, far
ultraviolet (FUV) images of five 40' diameter fields around the rim of the
Cygnus Loop supernova remnant were observed with the Ultraviolet Imaging
Telescope (UIT). These fields sampled a broad range of conditions including
both radiative and nonradiative shocks in various geometries and physical
scales. In these shocks, the UIT B5 band samples predominantly CIV 1550 and the
hydrogen two-photon recombination continuum. Smaller contri- butions are made
by emission lines of HeII 1640 and OIII] 1665. We present these new FUV images
and compare them with optical Halpha and [OIII], and ROSAT HRI X-ray images.
Comparing the UIT images with those from the other bands provides new insights
into the spatial variations and locations of these different types of emission.
By comparing against shock model calculations and published FUV spectroscopy at
select locations, we surmise that resonance scattering in the strong FUV
permitted lines is widespread in the Cygnus Loop, especially in the bright
optical filaments typically selected for observation in most previous studies.Comment: 21 pages with 10 figures. See http://www.pha.jhu.edu/~danforth/uit/
for full-resolution figure
Dense, Fe-rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?
We present observations of two LMC supernova remnants (SNRs), DEM L238 and
DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central
emission, surrounded by a faint shell, is present in both remnants. The central
emission has an entirely thermal spectrum dominated by strong Fe L-shell lines,
with the deduced Fe abundance in excess of solar and not consistent with the
LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and
DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission
originates in gas swept up and heated by the blast wave. A standard Sedov
analysis implies about 50 solar masses in both swept-up shells, SNR ages
between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and
subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich
supernova ejecta are close to collisional ionization equilibrium. Their
presence is unexpected, because standard Type Ia SNR models predict faint
ejecta emission with short ionization ages. Both SNRs belong to a previously
unrecognized class of Type Ia SNRs characterized by bright interior emission.
Denser than expected ejecta and/or a dense circumstellar medium around the
progenitors are required to explain the presence of Fe-rich ejecta in these
SNRs. Substantial amounts of circumstellar gas are more likely to be present in
explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar
SNRs could be remnants of ``prompt'' Type Ia explosions with young (~100 Myr
old) progenitors.Comment: 24 pages, 8 figures, ApJ, in pres
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