6,326 research outputs found
Jet Trimming
Initial state radiation, multiple interactions, and event pileup can
contaminate jets and degrade event reconstruction. Here we introduce a
procedure, jet trimming, designed to mitigate these sources of contamination in
jets initiated by light partons. This procedure is complimentary to existing
methods developed for boosted heavy particles. We find that jet trimming can
achieve significant improvements in event reconstruction, especially at high
energy/luminosity hadron colliders like the LHC.Comment: 20 pages, 11 figures, 3 tables - Minor changes to text/figure
Optimal jet radius in kinematic dijet reconstruction
Obtaining a good momentum reconstruction of a jet is a compromise between
taking it large enough to catch the perturbative final-state radiation and
small enough to avoid too much contamination from the underlying event and
initial-state radiation. In this paper, we compute analytically the optimal jet
radius for dijet reconstructions and study its scale dependence. We also
compare our results with previous Monte-Carlo studies.Comment: 30 pages, 11 figures; minor corrections; published in JHE
The mass area of jets
We introduce a new characteristic of jets called mass area. It is defined so
as to measure the susceptibility of the jet's mass to contamination from soft
background. The mass area is a close relative of the recently introduced
catchment area of jets. We define it also in two variants: passive and active.
As a preparatory step, we generalise the results for passive and active areas
of two-particle jets to the case where the two constituent particles have
arbitrary transverse momenta. As a main part of our study, we use the mass area
to analyse a range of modern jet algorithms acting on simple one and
two-particle systems. We find a whole variety of behaviours of passive and
active mass areas depending on the algorithm, relative hardness of particles or
their separation. We also study mass areas of jets from Monte Carlo simulations
as well as give an example of how the concept of mass area can be used to
correct jets for contamination from pileup. Our results show that the
information provided by the mass area can be very useful in a range of
jet-based analyses.Comment: 36 pages, 12 figures; v2: improved quality of two plots, added entry
in acknowledgments, nicer form of formulae in appendix A; v3: added section
with MC study and pileup correction, version accepted by JHE
V803 Centauri: Helium Dwarf Nova Mimicking a WZ Sge-Type Superoutburst
We observed long-term behavior of the helium dwarf nova V803 Cen, and
clarified the existence of at least two distinct states (state with 77-d
supercycles and standstill-like state) which interchangeably appeared with a
time-scale of 1--2 yr. We also conducted a time-resolved CCD photometry
campaign during the bright outburst in 2003 June. The overall appearance of the
outburst closely resemble that of the late stage of the 2001 outburst of WZ
Sge, consisting of the initial peak stage (superoutburst plateau), the dip, and
the oscillating (rebrightening) states. During the initial peak stage, we
detected large-amplitude superhump-type variation with a period of 0.018686(4)
d = 1614.5(4) s, and during the oscillation stage, we detected variations with
a period of 0.018728(2) d = 1618.1(2) s. We consider that the former period
better represents the superhump period of this system, and the latter
periodicity may be better interpreted as arising from late superhumps. The
overall picture of the V803 Cen outburst resembles that of a WZ Sge-type
outburst, but apparently with a higher mass-transfer rate than in hydrogen-rich
WZ Sge-type stars. We suggest that this behavior may be either the result of
difficulty in maintaining the hot state in a helium disk, or the effect of an
extremely low tidal torque resulting from the extreme mass ratio.Comment: 13 pages, 11 figures, to appear in PAS
Reactivation and Precise IPN Localization of the Soft Gamma Repeater SGR1900+14
In 1998 May, the soft gamma repeater SGR1900+14 emerged from several years of
quiescence and emitted a series of intense bursts, one with a time history
unlike any previously observed from this source. Triangulation using Ulysses,
BATSE, and KONUS data give a 1.6 square arcminute error box near the galactic
supernova remnant G42.8+0.6. This error box contains a quiescent soft X-ray
source which is probably a neutron star associated with the soft repeater.Comment: Accepted for publication in the Astrophysical Journal Letter
Priorities for the professional development of registered nurses in nursing homes: a Delphi study
Objective: to establish a consensus on the care and professional development needs of registered nurses (RNs) employed by UK care homes.
Design: two-stage, online modified Delphi study. Setting and participants: a panel (n = 352) of individuals with experience, expertise or interest in care home nursing: (i) care home nurses and managers; (ii) community healthcare professionals (including general practitioners, geriatricians, specialist and district nurses); and (iii) nurse educators in higher education. Results: RNs employed by nursing homes require particular skills, knowledge, competence and experience to provide high-quality care for older residents. The most important responsibilities for the nursing home nurse were: promoting dignity, personhood and wellbeing, ensuring resident safety and enhancing quality of life. Continuing professional development priorities included personal care, dementia care and managing long-term conditions. The main barrier to professional development was staff shortages. Nursing degree programmes were perceived as inadequately preparing nurses for a nursing home role. Nursing homes could improve by providing supportive learning opportunities for students and fostering challenging and rewarding careers for newly RNs. Conclusion: if nurses employed by nursing homes are not fit for purpose, the consequences for the wider health and social-care system are significant. Nursing homes, the NHS, educational and local authorities need to work together to provide challenging and rewarding career paths for RNs and evaluate them. Without well-trained, motivated staff, a high-quality care sector will remain merely an aspiration
Quasars: a supermassive rotating toroidal black hole interpretation
A supermassive rotating toroidal black hole (TBH) is proposed as the
fundamental structure of quasars and other jet-producing active galactic
nuclei. Rotating protogalaxies gather matter from the central gaseous region
leading to the birth of massive toroidal stars whose internal nuclear reactions
proceed very rapidly. Once the nuclear fuel is spent, gravitational collapse
produces a slender ring-shaped TBH remnant. These events are typically the
first supernovae of the host galaxies. Given time the TBH mass increases
through continued accretion by several orders of magnitude, the event horizon
swells whilst the central aperture shrinks. The difference in angular
velocities between the accreting matter and the TBH induces a magnetic field
that is strongest in the region of the central aperture and innermost
ergoregion. Due to the presence of negative energy states when such a
gravitational vortex is immersed in an electromagnetic field, circumstances are
near ideal for energy extraction via non-thermal radiation including the
Penrose process and superradiant scattering. This establishes a self-sustaining
mechanism whereby the transport of angular momentum away from the quasar by
relativistic bi-directional jets reinforces both the modulating magnetic field
and the TBH/accretion disk angular velocity differential. Quasar behaviour is
extinguished once the BH topology becomes spheroidal. Similar mechanisms may be
operating in microquasars, SNe and GRBs when neutron density or BH tori arise.
In certain circumstances, long-term TBH stability can be maintained by a
negative cosmological constant, otherwise the classical topology theorems must
somehow be circumvented. Preliminary evidence is presented that Planck-scale
quantum effects may be responsible.Comment: 26 pages, 14 figs, various corrections and enhancements, final
versio
An updated assessment of the Agulhas sole resource, Austroglossus pectoralis
This analysis updates that of Butterworth and Glazer (2014), which considered two hypotheses of decreasing catchability and of decreasing productivity to account for a recent large drop in CPUE. Two further years of data reflect some increase in CPUE. For the most pessimistic scenario (a decrease in productivity, which remains at its current reduced level into the future), projections are somewhat more positive than previously, with recent biomasses estimated higher and projected to decrease more slowly if the 2013 effort level is maintained
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