2,563 research outputs found
Bottlenose Dolphins, Tursiops truncatus, Removing By-catch from Prawn-trawl Codends During Fishing in New South Wales, Australia
During a fishing trip to record video footage of fish escaping from a by-catch reducing device located in a commercial prawn trawl, two bottlenose dolphins, Tursiops truncatus, were observed to actively manipulate the codend at the seabed, removing and consuming components of catch (mostly juvenile whiting, Sillago spp.). The observed feeding pattern suggests a well established behavioral response to trawling activities and is discussed with
respect to (1) the potential nutritional benefit that dolphins may derive from such activities and (2) the effects that scavenging may have on selectivity of the gear
Multi-Phenomena Modeling of the New Bullet Cluster, ZwCl008.8+52, using N-body/hydrodynamical Simulations
We use hydrodynamical/N-body simulations to interpret the newly discovered
Bullet-cluster-like merging cluster, ZwCl 0008.8+5215 (ZwCl 0008 hereafter),
where a dramatic collision is apparent from multi-wavelength observations. We
have been able to find a self-consistent solution for the radio, X-ray, and
lensing phenomena by projecting an off-axis, binary cluster encounter viewed
just after first core passage. A pair radio relics traces well the leading and
trailing shock fronts that our simulation predict, providing constraints on the
collision parameters. We can also account for the observed distinctive
comet-like X-ray morphology and the positions of the X-ray peaks relative to
the two lensing mass centroids and the two shock front locations. Relative to
the Bullet cluster, the total mass is about 70% lower, ( Msun, with a correspondingly lower infall velocity, km/s,
and an impact parameter of kpc. As a result, the gas component of
the infalling cluster is not trailing significantly behind the associated dark
matter as in the case of the Bullet cluster. The degree of agreement we find
between all the observables provides strong evidence that dark matter is
effectively collisionless on large scales calling into question other claims
and theories that advocate modified gravity.Comment: 9 pages, 3 figures, and 1 table, submitted to the Astrophysical
Journal for publicationon on December 18. Coments are welcom
Shocks and Tides Quantified in the "Sausage" Cluster, CIZA J2242.8+5301, using N-body/hydro-dynamical Simulations
The colliding cluster, CIZA J2242.8+5301, displays a spectacular, almost 2
Mpc long shock front with a radio based Mach number M ~ 5, that is puzzlingly
large compared with the X-ray estimate of M ~ 2.5. The extent to which the
X-ray temperature jump is diluted by cooler unshocked gas projected through the
cluster currently lacks quantification. Thus, here we apply our self-consistent
N-body/hydro-dynamical code (based on FLASH) to model this binary cluster
encounter. We can account for the location of the shock front and also the
elongated X-ray emission by tidal stretching of the gas and dark matter between
the two cluster centers. The required total mass is Msun
with a 1.3:1 mass ratio favoring the southern cluster component. The relative
velocity we derive is km/s initially between the two main cluster
components, with an impact parameter of 120 kpc. This solution implies that the
shock temperature jump derived from the low angular resolution X-ray satellite
SUZAKU is underestimated by a factor of two, due to cool gas in projection,
bringing the observed X-ray and radio estimates into agreement. We propose that
the complex southern relics in CIZA J2242.8+5301, have been broken up as the
southerly moving "back" shocked gas impacts the gas still falling in along the
collision axis. Finally, we use our model to generate Compton-y maps to
estimate the reduction in radio flux caused by the thermal Sunyaev-Zel'dovich
(SZ) effect. At 30 GHz, this amounts to mJy/arcmin
and mJy/arcmin at the locations of the northern and
southern shock fronts respectively. Our model estimate agrees with previous
empirical estimates that have inferred the measured radio spectra can be
significantly affected by the SZ effect, with implications for charged particle
acceleration models of the radio relics.Comment: 8 pages, 7 figures and 1 table, submitted to the Astrophysical
Journal for publication on March
A Hydrodynamical Solution for the "Twin-Tailed" Colliding Galaxy Cluster "El Gordo"
The distinctive cometary X-ray morphology of the recently discovered massive
galaxy cluster "El Gordo" (ACT-CT J0102-4915; z=0.87) indicates that an
unusually high-speed collision is ongoing between two massive galaxy clusters.
A bright X-ray "bullet" leads a "twin-tailed" wake, with the SZ centroid at the
end of the Northern tail. We show how the physical properties of this system
can be determined using our FLASH-based, N-body/hydrodynamic model, constrained
by detailed X-ray, Sunyaev-Zel'dovich (SZ), and Hubble lensing and dynamical
data. The X-ray morphology and the location of the two Dark Matter components
and the SZ peak are accurately described by a simple binary collision viewed
about 480 million years after the first core passage. We derive an impact
parameter of ~300 kpc, and a relative initial infall velocity of ~2250 km/sec
when separated by the sum of the two virial radii assuming an initial total
mass of 2.15x10^(15) Msun and a mass ratio of 1.9. Our model demonstrates that
tidally stretched gas accounts for the Northern X-ray tail along the collision
axis between the mass peaks, and that the Southern tail lies off axis,
comprising compressed and shock heated gas generated as the massive component
plunges through the main cluster. The challenge for LCDM will be to find out if
this physically extreme event can be plausibly accommodated when combined with
the similarly massive, high infall velocity case of the "Bullet cluster" and
other such cases being uncovered in the new SZ based surveys.Comment: 9 pages, 5 Figures and 1 Table, accepted for publication in the
Astrophysical Journa
Determinations of rational Dedekind-zeta invariants of hyperbolic manifolds and Feynman knots and links
We identify 998 closed hyperbolic 3-manifolds whose volumes are rationally
related to Dedekind zeta values, with coprime integers and giving for a manifold M
whose invariant trace field has a single complex place, discriminant ,
degree , and Dedekind zeta value . The largest numerator of the
998 invariants of Hodgson-Weeks manifolds is, astoundingly,
; the largest denominator is merely
b=9. We also study the rational invariant a/b for single-complex-place cusped
manifolds, complementary to knots and links, both within and beyond the
Hildebrand-Weeks census. Within the censi, we identify 152 distinct Dedekind
zetas rationally related to volumes. Moreover, 91 census manifolds have volumes
reducible to pairs of these zeta values. Motivated by studies of Feynman
diagrams, we find a 10-component 24-crossing link in the case n=2 and D=-20. It
is one of 5 alternating platonic links, the other 4 being quartic. For 8 of 10
quadratic fields distinguished by rational relations between Dedekind zeta
values and volumes of Feynman orthoschemes, we find corresponding links.
Feynman links with D=-39 and D=-84 are missing; we expect them to be as
beautiful as the 8 drawn here. Dedekind-zeta invariants are obtained for knots
from Feynman diagrams with up to 11 loops. We identify a sextic 18-crossing
positive Feynman knot whose rational invariant, a/b=26, is 390 times that of
the cubic 16-crossing non-alternating knot with maximal D_9 symmetry. Our
results are secure, numerically, yet appear very hard to prove by analysis.Comment: 53 pages, LaTe
Evaluations of k-fold Euler/Zagier sums: a compendium of results for arbitrary k
Euler sums (also called Zagier sums) occur within the context of knot theory
and quantum field theory. There are various conjectures related to these sums
whose incompletion is a sign that both the mathematics and physics communities
do not yet completely understand the field. Here, we assemble results for
Euler/Zagier sums (also known as multidimensional zeta/harmonic sums) of
arbitrary depth, including sign alternations. Many of our results were obtained
empirically and are apparently new. By carefully compiling and examining a huge
data base of high precision numerical evaluations, we can claim with some
confidence that certain classes of results are exhaustive. While many proofs
are lacking, we have sketched derivations of all results that have so far been
proved.Comment: 19 pages, LaTe
Leptonic contribution to the effective electromagnetic coupling constant up to three loops
In this note the leptonic contribution to the running of the electromagnetic
coupling constant is discussed up to the three-loop level. Special emphasize is
put on the evaluation of the double-bubble diagrams.Comment: 5 pages (Latex) 2 figure
Capturing the scale and pattern of recurrent care proceedings: initial observations from a feasibility study
This article reports the initial findings of a feasibility study that has captured the scale and pattern of recurrent care proceedings. Although frontline professionals have reported long-standing concerns about the repeat clients of public law proceedings, prior to the study we report, the scale of the problem has been unknown. With funding from the Nuffield Foundation and support from the Child and Family Court Advisory Service (CAFCASS) and the President of the Family Division, the research team has arrived at a first estimate of prevalence, confirming that recurrence is a sizeable problem for the English family court. Based on cases that completed during the observational window 2007-2013 (calendar years), 7,143 birth mothers appeared in 15,645 recurrent care applications concerning 22,790 infants and children. Moreover, the study most likely underestimates recurrence, because reliable data concerning completed cases is not available before 2007. Initial observations are that the spacing between recurrent care proceedings is very short, which raises searching questions about prevention. Where episodes of care proceedings follow in swift succession, most likely prompted by the birth of another infant, this affords mothers little opportunity to effect change. Unless, this ‘status quo’ is tackled, it is difficult to envisage how vulnerable birth mothers can exit this cycle. Preliminary recommendations are made in respect of policy and practice change
Two-loop two-point functions with masses: asymptotic expansions and Taylor series, in any dimension
In all mass cases needed for quark and gluon self-energies, the two-loop
master diagram is expanded at large and small , in dimensions, using
identities derived from integration by parts. Expansions are given, in terms of
hypergeometric series, for all gluon diagrams and for all but one of the quark
diagrams; expansions of the latter are obtained from differential equations.
Pad\'{e} approximants to truncations of the expansions are shown to be of great
utility. As an application, we obtain the two-loop photon self-energy, for all
, and achieve highly accelerated convergence of its expansions in powers of
or , for .Comment: 25 pages, OUT--4102--43, BI--TP/92--5
Three-loop non-diagonal current correlators in QCD and NLO corrections to single-top-quark production
The non-diagonal correlators of vector and scalar currents are considered at
three-loop order in QCD. The full mass dependence is computed in the case where
one of the quarks is massless and the other one carries the mass . As
applications we consider the single-top-quark production via the process
and the decay rate of a charged Higgs into hadrons. In
both cases the computed NLO corrections are shown to be numerically much less
important than the leading ones.Comment: 13 page
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