10,039 research outputs found
The Theory of Generalised Hydrodynamics for the One-dimensional Bose Gas
This article reviews the recent developments in the theory of generalised
hydrodynamics (GHD) with emphasis on the repulsive one-dimensional Bose gas. We
discuss the implications of GHD on the mechanisms of thermalisation in
integrable quantum many-body systems as well as its ability to describe
far-from-equilibrium behaviour of integrable and near integrable systems in a
variety of quantum quench scenarios. We outline the experimental tests of GHD
in cold-atom gases and its benchmarks with other microscopic theoretical
approaches. Finally, we offer some perspectives on the future direction of the
development of GHD.Comment: 13 pages, 10 figure
Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars
In more than four years of observation the Large Area Telescope on board the
Fermi satellite has identified pulsed -ray emission from more than 80
young pulsars, providing light curves with high statistics. Fitting the
observations with geometrical models can provide estimates of the magnetic
obliquity and aspect angle , yielding estimates of the
radiation beaming factor and luminosity. Using -ray emission geometries
(Polar Cap, Slot Gap, Outer Gap, One Pole Caustic) and radio emission geometry,
we fit -ray light curves for 76 young pulsars and we jointly fit their
-ray plus radio light curves when possible. We find that a joint radio
plus -ray fit strategy is important to obtain (, )
estimates that can explain simultaneous radio and -ray emission. The
intermediate-to-high altitude magnetosphere models, Slot Gap, Outer Gap, and
One pole Caustic, are favoured in explaining the observations. We find no
evolution of on a time scale of a million years. For all emission
geometries our derived -ray beaming factors are generally less than one
and do not significantly evolve with the spin-down power. A more pronounced
beaming factor vs. spin-down power correlation is observed for Slot Gap model
and radio-quiet pulsars and for the Outer Gap model and radio-loud pulsars. For
all models, the correlation between -ray luminosity and spin-down power
is consistent with a square root dependence. The -ray luminosities
obtained by using our beaming factors not exceed the spin-down power. This
suggests that assuming a beaming factor of one for all objects, as done in
other studies, likely overestimates the real values. The data show a relation
between the pulsar spectral characteristics and the width of the accelerator
gap that is consistent with the theoretical prediction for the Slot Gap model.Comment: 90 pages, 80 figures (63 in Appendices), accepted for publication in
Astronomy and Astrophysic
Nonnegatively curved homogeneous metrics obtained by scaling fibers of submersions
We consider invariant Riemannian metrics on compact homogeneous spaces G/H
where an intermediate subgroup K between G and H exists, so that the
homogeneous space G/H is the total space of a Riemannian submersion. We study
the question as to whether enlarging the fibers of the submersion by a constant
scaling factor retains the nonnegative curvature in the case that the
deformation starts at a normal homogeneous metric. We classify triples of
groups (H,K,G) where nonnegative curvature is maintained for small
deformations, using a criterion proved by Schwachh\"ofer and Tapp. We obtain a
complete classification in case the subgroup H has full rank and an almost
complete classification in the case of regular subgroups.Comment: 23 pages; minor revisions, to appear in Geometriae Dedicat
The economics of rabbit control in Central Otago: A preliminary analysis
With contributions by J.M. Williams, J. Bell and T.M. Broad, Agricultural Research Division, Ministry of Agriculture and Fisheries.
Prepared under contract for Agricultural Research Division Ministry of Agriculture and Fisheries, WellingtonThis paper reports a preliminary examination of the economic efficiency and equity implications of recent rabbit control policies and programmes. The Alexandra Pest Destruction Board in Central Otago was used as a case study.
Public and private expenditure data on rabbit control were collected and analysed for the period 1974-75 through 1981-82. Control programme benefits were estimated using data obtained in a survey of runholders and from historical production records. Programme costs were developed from actual expenditure data on control operations and administration based on Board records. While the estimated benefits are much less precise in comparison to programme costs, the results of the cost-benefit analysis suggest that significant cost savings can be achieved in meeting the stated objectives of current pest management policies. In particular, the level of annual expenditure in recent years on those lands which can be regarded as good natural habitat for the feral rabbit does not appear to be warranted, since such land types have an inherently low productive capacity and could not sustain the present level of control input on a 'user pays' basis. Although certain public benefits (e.g., land and water conservation) were not estimated, such benefits would have to be quite large to justify recent levels of annual taxpayer input into APDB control operations. The incidence of programme costs under present policy shows that most of the burden is borne by the tax-paying public. The report concludes with some suggestions to appraise these implications more accurately for regional and national public policy
Magneto-optical Kerr Effect Studies of Square Artificial Spin Ice
We report a magneto-optical Kerr effect study of the collective magnetic
response of artificial square spin ice, a lithographically-defined array of
single-domain ferromagnetic islands. We find that the anisotropic inter-island
interactions lead to a non-monotonic angular dependence of the array coercive
field. Comparisons with micromagnetic simulations indicate that the two
perpendicular sublattices exhibit distinct responses to island edge roughness,
which clearly influence the magnetization reversal process. Furthermore, such
comparisons demonstrate that disorder associated with roughness in the island
edges plays a hitherto unrecognized but essential role in the collective
behavior of these systems.Comment: Physical Review B, Rapid Communications (in press
Kerr-Schild Symmetries
We study continuous groups of generalized Kerr-Schild transformations and the
vector fields that generate them in any n-dimensional manifold with a
Lorentzian metric. We prove that all these vector fields can be intrinsically
characterized and that they constitute a Lie algebra if the null deformation
direction is fixed. The properties of these Lie algebras are briefly analyzed
and we show that they are generically finite-dimensional but that they may have
infinite dimension in some relevant situations. The most general vector fields
of the above type are explicitly constructed for the following cases: any
two-dimensional metric, the general spherically symmetric metric and
deformation direction, and the flat metric with parallel or cylindrical
deformation directions.Comment: 15 pages, no figures, LaTe
G328.4+0.2 : A large and luminous Crab-like supernova remnant
We report on radio continuum and HI observations of the radio source
G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm
G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing
significant linear polarization and an almost flat spectral index. These
results lead us to conclude that G328.4+0.2 is a Crab-like, or ``plerionic'',
supernova remnant (SNR), presumably powered by an unseen central pulsar. HI
absorption towards G328.4+0.2 puts a lower limit on its distance of 17.4 +/-
0.9 kpc, making it the largest (D=25 pc) and most luminous (L_R = 3e35 erg/s)
Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than
the Crab Nebula, but powered by a pulsar which is fast spinning (P<20 ms) and
which has a comparatively low magnetic field (B<1e12 G). We propose G328.4+0.2,
G74.9+1.2 and N157B as a distinct group of large-diameter, high-luminosity
Crab-like SNRs, all powered by fast-spinning low-field pulsars.Comment: 7 pages, 3 embedded EPS figures, uses emulateapj.sty. Accepted to
ApJ. Abstract corrected so that distance is now in kpc, not pc
Two Large HI Shells in the Outer Galaxy near l=279 degrees
As part of a survey of HI 21-cm emission in the Southern Milky Way, we have
detected two large shells in the interstellar neutral hydrogen near l=279 deg.
The center velocities are +36 and +59 km/s, which puts the shells at kinematic
distances of 7 and 10 kpc. The larger shell is about 610 pc in diameter and
very empty, with density contrast of at least 15 between the middle and the
shell walls. It has expansion velocity of about 20 km/s and swept up mass of
several million solar masses. The energy indicated by the expansion may be as
high as 2.4 X 10^53 ergs. We estimate its age to be 15 to 20 million years. The
smaller shell has diameter of about 400 pc, expansion velocity about 10 km/s
and swept up mass of about 10^6 solar masses.
Morphologically both regions appear to be shells, with high density regions
mostly surrounding the voids, although the first appears to have channels of
low density which connect with the halo above and below the HI layer. They lie
on the edge of the Carina arm, which suggests that they may be expanding
horizontally into the interarm region as well as vertically out of the disk. If
this interpretation is correct, this is the first detection of an HI chimney
which has blown out of both sides of the disk.Comment: 21 pages, 14 jpeg figures, accepted for publication in A
Design Considerations for Efficient and Effective Microarray Studies
This paper describes the theoretical and practical issues in experimental design for gene expression microarrays. Specifically, this paper (1) discusses the basic principles of design (randomization, replication, and blocking) as they pertain to microarrays, and (2) provides some general guidelines for statisticians designing microarray studies
Grazing Collisions of Black Holes via the Excision of Singularities
We present the first simulations of non-headon (grazing) collisions of binary
black holes in which the black hole singularities have been excised from the
computational domain. Initially two equal mass black holes are separated a
distance and with impact parameter . Initial data are
based on superposed, boosted (velocity ) solutions of single black
holes in Kerr-Schild coordinates. Both rotating and non-rotating black holes
are considered. The excised regions containing the singularities are specified
by following the dynamics of apparent horizons. Evolutions of up to are obtained in which two initially separate apparent horizons are present
for . At that time a single enveloping apparent horizon forms,
indicating that the holes have merged. Apparent horizon area estimates suggest
gravitational radiation of about 2.6% of the total mass. The evolutions end
after a moderate amount of time because of instabilities.Comment: 2 References corrected, reference to figure update
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