998 research outputs found
Tracking Black Holes in Numerical Relativity
This work addresses and solves the problem of generically tracking black hole
event horizons in computational simulation of black hole interactions.
Solutions of the hyperbolic eikonal equation, solved on a curved spacetime
manifold containing black hole sources, are employed in development of a robust
tracking method capable of continuously monitoring arbitrary changes of
topology in the event horizon, as well as arbitrary numbers of gravitational
sources. The method makes use of continuous families of level set viscosity
solutions of the eikonal equation with identification of the black hole event
horizon obtained by the signature feature of discontinuity formation in the
eikonal's solution. The method is employed in the analysis of the event horizon
for the asymmetric merger in a binary black hole system. In this first such
three dimensional analysis, we establish both qualitative and quantitative
physics for the asymmetric collision; including: 1. Bounds on the topology of
the throat connecting the holes following merger, 2. Time of merger, and 3.
Continuous accounting for the surface of section areas of the black hole
sources.Comment: 14 pages, 16 figure
Block-Transitive Designs in Affine Spaces
This paper deals with block-transitive - designs in affine
spaces for large , with a focus on the important index case. We
prove that there are no non-trivial 5- designs admitting a
block-transitive group of automorphisms that is of affine type. Moreover, we
show that the corresponding non-existence result holds for 4- designs,
except possibly when the group is one-dimensional affine. Our approach involves
a consideration of the finite 2-homogeneous affine permutation groups.Comment: 10 pages; to appear in: "Designs, Codes and Cryptography
Steiner t-designs for large t
One of the most central and long-standing open questions in combinatorial
design theory concerns the existence of Steiner t-designs for large values of
t. Although in his classical 1987 paper, L. Teirlinck has shown that
non-trivial t-designs exist for all values of t, no non-trivial Steiner
t-design with t > 5 has been constructed until now. Understandingly, the case t
= 6 has received considerable attention. There has been recent progress
concerning the existence of highly symmetric Steiner 6-designs: It is shown in
[M. Huber, J. Algebr. Comb. 26 (2007), pp. 453-476] that no non-trivial
flag-transitive Steiner 6-design can exist. In this paper, we announce that
essentially also no block-transitive Steiner 6-design can exist.Comment: 9 pages; to appear in: Mathematical Methods in Computer Science 2008,
ed. by J.Calmet, W.Geiselmann, J.Mueller-Quade, Springer Lecture Notes in
Computer Scienc
Modelling residential habitability and human displacement for tsunami scenarios in Christchurch, New Zealand
Noise parametric identification and whitening for LIGO 40-meter interferometer data
We report the analysis we made on data taken by Caltech 40-meter prototype
interferometer to identify the noise power spectral density and to whiten the
sequence of noise. We concentrate our study on data taken in November 1994, in
particular we analyzed two frames of data: the 18nov94.2.frame and the
19nov94.2.frame.
We show that it is possible to whiten these data, to a good degree of
whiteness, using a high order whitening filter. Moreover we can choose to
whiten only restricted band of frequencies around the region we are interested
in, obtaining a higher level of whiteness.Comment: 11 pages, 15 figures, accepted for publication by Physical Review
The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant
We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at
Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young
oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the
resultant data cube, we have been able to reconstruct the full 3D structure of
the system of [O III] filaments. The majority of the ejecta form a ring of
~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We
conclude that SNR N132D is approaching the end of the reverse shock phase
before entering the fully thermalized Sedov phase of evolution. We speculate
that the ring of oxygen-rich material comes from ejecta in the equatorial plane
of a bipolar explosion, and that the overall shape of the SNR is strongly
influenced by the pre-supernova mass loss from the progenitor star. We find
tantalizing evidence of a polar jet associated with a very fast oxygen-rich
knot, and clear evidence that the central star has interacted with one or more
dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8
figure
Impact of triaxiality on the rotational structure of neutron-rich rhenium isotopes
A number of 3-quasiparticle isomers have been found and characterised in the odd-mass, neutron-rich, 187Re, 189Re and 191Re nuclei, the latter being four neutrons beyond stability. The decay of the isomers populates states in the rotational bands built upon the 9/2-[514] Nilsson orbital. These bands exhibit a degree of signature splitting that increases with neutron number. This splitting taken together with measurements of the M1/E2 mixing ratios and with the changes observed in the energy of the gamma-vibrational band coupled to the 9/2-[514] state, suggests an increase in triaxiality, with γ values of 5°, 18° and 25° deduced in the framework of a particle-rotor model
Academic freedom: in justification of a universal ideal
This paper examines the justification for, and benefits of, academic freedom to academics, students, universities and the world at large. The paper surveys the development of the concept of academic freedom within Europe, more especially the impact of the reforms at the University of Berlin instigated by Wilhelm von Humboldt. Following from this, the paper examines the reasons why the various facets of academic freedom are important and why the principle should continue to be supported
Effect of denosumab on osteolytic lesion activity after total hip arthroplasty: a single-centre, randomised, double-blind, placebo-controlled, proof of concept trial
Background
Osteolysis causes recurrent pain and disability after total hip arthroplasty. We investigated the effect of the human monoclonal antibody denosumab on osteolytic lesion activity in patients undergoing revision total hip arthroplasty surgery to show the biological proof of concept for a non-surgical treatment for the disease.
Methods
We did a phase 2, randomised, double-blind, placebo-controlled, proof of concept superiority trial at Sheffield Teaching Hospitals, Sheffield, UK. Eligible patients aged 30 years or older and scheduled for revision surgery for symptomatic, radiographically confirmed osteolysis were randomly allocated (1:1) to subcutaneous denosumab (60 mg single-dose) or placebo by an independent pharmacist using a random number table. The primary outcome was the between-group difference in osteoclast number per mm of bone surface of biopsies taken from the osteolytic membrane–bone interface at surgery 8 weeks later, measured by quantitative histomorphometry in all patients who underwent revision surgery. Adverse events were analysed in all randomly assigned participants. This trial is registered with the EU Clinical Trials Register (EudraCT 2011-000541-20).
Findings
Between Dec 12, 2012, and June 24, 2018, 51 patients were assessed for eligibility, of whom 24 were randomly assigned to study treatment. Two patients had their revision surgery cancelled for unrelated reasons, leaving 22 patients (ten in the denosumab group) for analysis of the primary outcome. There were 83% fewer osteoclasts at the osteolysis membrane–bone interface in the denosumab versus the placebo group (median 0·05 per mm [IQR 0·11] vs 0·30 mm [0·40], p=0·011). No deaths or treatment-related serious adverse events occurred. Seven adverse events, including one severe adverse event, occurred in four (36%) of 11 patients in the denosumab group. In the placebo group ten adverse events, including three severe adverse events, occurred in five (38%) of 13 patients.
Interpretation
To our knowledge, this is the first clinical trial of an investigational drug for osteolysis that shows tissue-specific biological efficacy. These results justify the need for future trials that target earlier-stage disease to test for clinical efficacy in reducing the need for revision surgery.
Funding
Amgen
Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas
Several seemingly unrelated effects in Alcator C-Mod ohmic L-mode plasmas are shown to be closely connected: non-local heat transport, core toroidal rotation reversals, energy confinement saturation and up/down impurity density asymmetries. These phenomena all abruptly transform at a critical value of the collisionality. At low densities in the linear ohmic confinement regime, with collisionality ν[subscript *] ≤ 0.35 (evaluated inside of the q = 3/2 surface), heat transport exhibits non-local behaviour, core toroidal rotation is directed co-current, edge impurity density profiles are up/down symmetric and a turbulent feature in core density fluctuations with k[subscript θ] up to 15 cm[superscript −1] (k[subscript θ]ρ[subscript s] ~ 1) is present. At high density/collisionality with saturated ohmic confinement, electron thermal transport is diffusive, core rotation is in the counter-current direction, edge impurity density profiles are up/down asymmetric and the high k[subscript θ] turbulent feature is absent. The rotation reversal stagnation point (just inside of the q = 3/2 surface) coincides with the non-local electron temperature profile inversion radius. All of these observations suggest a possible unification in a model with trapped electron mode prevalence at low collisionality and ion temperature gradient mode domination at high collisionality.United States. Dept. of Energy (Contract DE-FC02-99ER54512)United States. Dept. of Energy. Office of Fusion Energy Sciences (Postdoctoral Research Program
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