313 research outputs found
Tevatron Beam Halo Collimation System: Design, Operational Experience and New Methods
Collimation of proton and antiproton beams in the Tevatron collider is
required to protect CDF and D0 detectors and minimize their background rates,
to keep irradiation of superconducting magnets under control, to maintain
long-term operational reliability, and to reduce the impact of beam-induced
radiation on the environment. In this article we briefly describe the design,
practical implementation and performance of the collider collimation system,
methods to control transverse and longitudinal beam halo and two novel
collimation techniques tested in the Tevatron.Comment: 25 p
Veterinary drug therapies used for undesirable behaviours in UK dogs under primary veterinary care
Undesirable behaviours (UBs) in dogs are common and important issues with serious potential welfare consequences for both the dogs and their owners. This study aimed to investigate the usage of drug therapy for UBs in dogs and assess demographic risk factors for drug-prescribed UBs within the dog population under primary-care veterinary care in the UK in 2013. Dogs receiving drug therapy for UB were identified through the retrospective analysis of anonymised electronic patient records in VetCompass™. Risk factor analysis used multivariable logistic regression modelling. The study population comprised 103,597 dogs under veterinary care in the UK during 2013. There were 413 drug-prescribed UBs recorded among 404 dogs. The prevalence of dogs with at least one UB event treated with a drug in 2013 was 0.4%. Multivariable modelling identified 3 breeds with increased odds of drug-prescribed UB compared with crossbred dogs: Toy Poodle (OR 2.75), Tibetan Terrier (OR 2.68) and Shih-tzu (OR 1.95). Increasing age was associated with increased odds of drug-prescribed UB, with dogs ≥ 12 years showing 3.1 times the odds compared with dogs < 3 years. Neutered males (OR 1.82) and entire males (OR 1.50) had increased odds compared with entire females. The relatively low prevalence of dogs with at least one UB event that was treated with a drug in 2013 could suggest that opportunities for useful psychopharmaceutical intervention in UBs may be being missed in first opinion veterinary practice. While bodyweight was not a significant factor, the 3 individual breeds at higher odds of an UB treated with a behaviour modifying drug all have a relatively low average bodyweight. The current results also support previous research of a male predisposition to UBs and it is possible that this higher risk resulted in the increased likelihood of being prescribed a behaviour modifying drug, regardless of neuter status
Thin accretion disc with a corona in a central magnetic field
We study the steady-state structure of an accretion disc with a corona
surrounding a central, rotating, magnetized star. We assume that the
magneto-rotational instability is the dominant mechanism of angular momentum
transport inside the disc and is responsible for producing magnetic tubes above
the disc. In our model, a fraction of the dissipated energy inside the disc is
transported to the corona via these magnetic tubes. This energy exchange from
the disc to the corona which depends on the disc physical properties is
modified because of the magnetic interaction between the stellar magnetic field
and the accretion disc. According to our fully analytical solutions for such a
system, the existence of a corona not only increases the surface density but
reduces the temperature of the accretion disc. Also, the presence of a corona
enhances the ratio of gas pressure to the total pressure. Our solutions show
that when the strength of the magnetic field of the central neutron star is
large or the star is rotating fast enough, profiles of the physical variables
of the disc significantly modify due to the existence of a corona.Comment: Accepted for publication in Astrophysics & Space Scienc
The rms-flux relations in different branches in Cyg X-2
In this paper, the rms-flux (root mean square-flux) relation along the
Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data
of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e.
positive, negative, and 'arch'-like correlations are found in different
branches. The rms is positively correlated with flux in normal branch (NB), but
anti-correlated in the vertical horizontal branch (VHB). The rms-flux relation
shows an 'arch'-like shape in the horizontal branch (HB). We also try to
explain this phenomenon using existing models.Comment: Accepted for publication in Astrophysics & Space Scienc
Ruling out four-neutrino oscillation interpretations of the LSND anomaly?
Prompted by recent solar and atmospheric data, we re-analyze the
four-neutrino description of current global neutrino oscillation data,
including the LSND evidence for oscillations. The higher degree of rejection
for non-active solar and atmospheric oscillation solutions implied by the SNO
neutral current result as well as by the latest 1489-day Super-K atmospheric
neutrino data allows us to rule out (2+2) oscillation schemes proposed to
reconcile LSND with the rest of current neutrino oscillation data. Using an
improved goodness of fit (gof) method especially sensitive to the combination
of data sets we obtain a gof of only 1.6 times 10^{-6} for (2+2) schemes.
Further, we re-evaluate the status of (3+1) oscillations using two different
analyses of the LSND data sample. We find that also (3+1) schemes are strongly
disfavoured by the data. Depending on the LSND analysis we obtain a gof of 5.6
times 10^{-3} or 7.6 times 10^{-5}. This leads to the conclusion that all
four-neutrino descriptions of the LSND anomaly, both in (2+2) as well as (3+1)
realizations, are highly disfavoured. Our analysis brings the LSND hint to a
more puzzling status.Comment: 21 pages, 7 figure
Global analysis of neutrino oscillation data in four-neutrino schemes
We present an analysis of the global neutrino oscillation data in terms of four-neutrino mass schemes. We find that the strong preference of oscillations into active neutrinos implied by the latest solar as well as atmospheric neutrino data allows to rule out (2+2) mass schemes, whereas (3+1) schemes are strongly disfavoured by short-baseline experiments. Our analysis shows that four-neutrino oscillations do not provide a satisfactory description of the global neutrino oscillation data including the LSND result
Jet disc coupling in black hole binaries
In the last decade multi-wavelength observations have demonstrated the
importance of jets in the energy output of accreting black hole binaries. The
observed correlations between the presence of a jet and the state of the
accretion flow provide important information on the coupling between accretion
and ejection processes. After a brief review of the properties of black hole
binaries, I illustrate the connection between accretion and ejection through
two particularly interesting examples. First, an INTEGRAL observation of Cygnus
X-1 during a 'mini-' state transition reveals disc jet coupling on time scales
of orders of hours. Second, the black hole XTEJ1118+480 shows complex
correlations between the X-ray and optical emission. Those correlations are
interpreted in terms of coupling between disc and jet on time scales of seconds
or less. Those observations are discussed in the framework of current models.Comment: Invited talk at the Fifth Stromlo Symposium: Disks, Winds & Jets -
from Planets to Quasars. Accepted for publication in Astrophysics & Space
Scienc
Physics, Topology, Logic and Computation: A Rosetta Stone
In physics, Feynman diagrams are used to reason about quantum processes. In
the 1980s, it became clear that underlying these diagrams is a powerful analogy
between quantum physics and topology: namely, a linear operator behaves very
much like a "cobordism". Similar diagrams can be used to reason about logic,
where they represent proofs, and computation, where they represent programs.
With the rise of interest in quantum cryptography and quantum computation, it
became clear that there is extensive network of analogies between physics,
topology, logic and computation. In this expository paper, we make some of
these analogies precise using the concept of "closed symmetric monoidal
category". We assume no prior knowledge of category theory, proof theory or
computer science.Comment: 73 pages, 8 encapsulated postscript figure
Highly Charged Ions in Rare Earth Permanent Magnet Penning Traps
A newly constructed apparatus at the National Institute of Standards and
Technology (NIST) is designed for the isolation, manipulation, and study of
highly charged ions. Highly charged ions are produced in the NIST electron-beam
ion trap (EBIT), extracted through a beamline that selects a single mass/charge
species, then captured in a compact Penning trap. The magnetic field of the
trap is generated by cylindrical NdFeB permanent magnets integrated into its
electrodes. In a room-temperature prototype trap with a single NdFeB magnet,
species including Ne10+ and N7+ were confined with storage times of order 1
second, showing the potential of this setup for manipulation and spectroscopy
of highly charged ions in a controlled environment. Ion capture has since been
demonstrated with similar storage times in a more-elaborate Penning trap that
integrates two coaxial NdFeB magnets for improved B-field homogeneity. Ongoing
experiments utilize a second-generation apparatus that incorporates this
two-magnet Penning trap along with a fast time-of-flight MCP detector capable
of resolving the charge-state evolution of trapped ions. Holes in the
two-magnet Penning trap ring electrode allow for optical and atomic beam
access. Possible applications include spectroscopic studies of one-electron
ions in Rydberg states, as well as highly charged ions of interest in atomic
physics, metrology, astrophysics, and plasma diagnostics.Comment: Proceedings of CDAMOP-2011, 13-16 Dec 2011, Delhi, India. To be
published by Springer Verla
- …