803 research outputs found
Particle on the Innermost Stable Circular Orbit of a Rapidly Spinning Black Hole
We compute the radiation emitted by a particle on the innermost stable
circular orbit of a rapidly spinning black hole both (a) analytically, working
to leading order in the deviation from extremality and (b) numerically, with a
new high-precision Teukolsky code. We find excellent agreement between the two
methods. We confirm previous estimates of the overall scaling of the power
radiated, but show that there are also small oscillations all the way to
extremality. Furthermore, we reveal an intricate mode-by-mode structure in the
flux to infinity, with only certain modes having the dominant scaling. The
scaling of each mode is controlled by its conformal weight, a quantity that
arises naturally in the representation theory of the enhanced near-horizon
symmetry group. We find relationships to previous work on particles orbiting in
precisely extreme Kerr, including detailed agreement of quantities computed
here with conformal field theory calculations performed in the context of the
Kerr/CFT correspondence.Comment: 15 pages, 4 figures, v2: reference added, minor changes, matches
published versio
The Shape of the Black Hole Photon Ring: A Precise Test of Strong-Field General Relativity
We propose a new test of strong-field general relativity (GR) based on the
universal interferometric signature of the black hole photon ring. The photon
ring is a narrow ring-shaped feature, predicted by GR but not yet observed,
that appears on images of sources near a black hole. It is caused by extreme
bending of light within a few Schwarzschild radii of the event horizon and
provides a direct probe of the unstable bound photon orbits of the Kerr
geometry. We show that the precise shape of the observable photon ring is
remarkably insensitive to the astronomical source profile and can therefore be
used as a stringent test of GR. We forecast that a tailored space-based
interferometry experiment targeting M87* could test the Kerr nature of the
source to the sub-sub-percent level.Comment: 20 pages, 9 figures. v2: minor change
Electromagnetic self-forces and generalized Killing fields
Building upon previous results in scalar field theory, a formalism is
developed that uses generalized Killing fields to understand the behavior of
extended charges interacting with their own electromagnetic fields. New notions
of effective linear and angular momenta are identified, and their evolution
equations are derived exactly in arbitrary (but fixed) curved spacetimes. A
slightly modified form of the Detweiler-Whiting axiom that a charge's motion
should only be influenced by the so-called "regular" component of its
self-field is shown to follow very easily. It is exact in some interesting
cases, and approximate in most others. Explicit equations describing the
center-of-mass motion, spin angular momentum, and changes in mass of a small
charge are also derived in a particular limit. The chosen approximations --
although standard -- incorporate dipole and spin forces that do not appear in
the traditional Abraham-Lorentz-Dirac or Dewitt-Brehme equations. They have,
however, been previously identified in the test body limit.Comment: 20 pages, minor typos correcte
Thrombolyse der Arteria cerebri media
Zusammenfassung: In den ersten 3h nach Eintritt eines akuten ischämischen Hirninfarkts ist die intravenöse Thrombolyse (IVT) die evidenzbasierte Therapie (IVT 3-4,5h: "off-label use" mit Einverständnis des Patienten). Die intraarterielle Thrombolyse (IAT) führt in der A.cerebri media (ACM) allerdings häufiger zur Rekanalisation als die IVT. Daher ist die IAT in dafür ausgerüsteten Kliniken ergänzend oder alternativ zur IVT bis zu 6h nach Symptombeginn zu erwäge
Oral vinorelbine and cisplatin with concomitant radiotherapy in stage III non-small cell lung cancer (NSCLC): A feasibility study
Background: Concurrent chemoradiotherapy has improved survival in inoperable stage III non-small cell lung cancer (NSCLC). This phase I trial was performed in order to establish a dose recommendation for oral vinorelbine in combination with cisplatin and simultaneous radiotherapy. Patients and Methods: Previously untreated patients with stage IIIB NSCLC received concurrent chemoradiotherapy with 66 Gy and 2 cycles of cisplatin and oral vinorelbine which was administered at 3 different levels (40, 50 and 60 mg/m(2)). This was to be followed by 2 cycles of cisplatin/vinorelbine oral consolidation chemotherapy. The study goal was to determine the maximal recommended dose of oral vinorelbine during concurrent treatment. Results: 11 stage IIIB patients were entered into the study. The median radiotherapy dose was 66 Gy. Grade 3-4 toxicity included neutropenia, esophagitis, gastritis and febrile neutropenia. The dose-limiting toxicity for concurrent chemoradiotherapy was esophagitis. 9 patients received consolidation chemotherapy, with neutropenia and anemia/thrombocytopenia grade 3 being the only toxicities. The overall response was 73%. Conclusion: Oral vinorelbine 50 mg/m(2) (days 1, 8, 15 over 4 weeks) in combination with cisplatin 20 mg/m2 (days 1-4) is the recommended dose in combination with radiotherapy (66 Gy) and will be used for concurrent chemoradiotherapy in a forthcoming phase III trial testing the efficacy of consolidation chemotherapy in patients not progressing after chemoradiotherapy
Effective source approach to self-force calculations
Numerical evaluation of the self-force on a point particle is made difficult
by the use of delta functions as sources. Recent methods for self-force
calculations avoid delta functions altogether, using instead a finite and
extended "effective source" for a point particle. We provide a review of the
general principles underlying this strategy, using the specific example of a
scalar point charge moving in a black hole spacetime. We also report on two new
developments: (i) the construction and evaluation of an effective source for a
scalar charge moving along a generic orbit of an arbitrary spacetime, and (ii)
the successful implementation of hyperboloidal slicing that significantly
improves on previous treatments of boundary conditions used for
effective-source-based self-force calculations. Finally, we identify some of
the key issues related to the effective source approach that will need to be
addressed by future work.Comment: Invited review for NRDA/Capra 2010 (Theory Meets Data Analysis at
Comparable and Extreme Mass Ratios), Perimeter Institute, June 2010, CQG
special issue - 22 pages, 8 figure
The Atacama Cosmology Telescope: CO(J = 3 - 2) mapping and lens modeling of an ACT-selected dusty star-forming galaxy
We report Northern Extended Millimeter Array (NOEMA) CO()
observations of the dusty star-forming galaxy ACT-S\,J020941+001557 at , which was detected as an unresolved source in the Atacama Cosmology
Telescope (ACT) equatorial survey. Our spatially resolved spectral line data
support the derivation of a gravitational lens model from 37 independent
velocity channel maps using a pixel-based algorithm, from which we infer a
velocity-dependent magnification factor with a
luminosity-weighted mean \left\approx 13. The resulting
source-plane reconstruction is consistent with a rotating disk, although other
scenarios cannot be ruled out by our data. After correction for lensing, we
derive a line luminosity , a cold gas mass , a dynamical mass , and a gas mass
fraction . The line brightness
temperature ratio of relative to a Green Bank Telescope
CO() detection may be elevated by a combination of external heating of
molecular clouds, differential lensing, and/or pointing errors.Comment: 8 pages, 5 figures, accepted to Ap
A new concurrent chemotherapy with vinorelbine and mitomycin C in combination with radiotherapy in patients with locally advanced squamous cell carcinoma of the head and neck
Objective: The purpose of this pilot study was to evaluate the feasibility and toxicity of concurrent chemotherapy with vinorelbine and mitomycin C in combination with accelerated radiotherapy (RT) in patients with locally advanced cancer of the head and neck. Patients and Methods: Between January 2003 and March 2004, 15 patients with T4/N2-3 squamous cell carcinoma (12/15) and with N3 cervical lymph node metastases of carcinoma of unknown primary (3/15) were treated with chemotherapy and simultaneous accelerated RT. Results: 11 patients completed therapy without interruption or dose reduction. Grade 3 - 4 acute mucosal toxicity was observed in 9/15 patients, grade 4 hematologic toxicity in 6/15 patients. At a median follow-up of 7.5 months, 2 patients have died of intercurrent disease, 2 patients have experienced local relapse; 5 patients are alive with no evidence of disease at the primary tumor site. Discussion: The described regimen is highly effective, but led to remarkable side effects
- …