48,902 research outputs found
NRQCD results on the MILC extra coarse ensemble
We present preliminary results using NRQCD to describe heavy quarks on the
MILC 2+1 flavour dynamical extra coarse ensemble. We calculate the spectra of
low lying states in bottomonium to complement earlier results on the finer MILC
ensembles. We then exploit the coarseness of the lattices to calculate charm
propagators using NRQCD. These are used to examine the charmonium spectrum and
to calclate the mass of the using NRQCD. Finally we look breifly at the
and systems using the imporoved staggered formalism to describe the
light valence quarks.Comment: 6 pages, Talk presented at Lattice 2005 (Heavy Quarks), Dublin, 25-30
July 200
Are There Magnetars in High Mass X-ray Binaries? The Case of SuperGiant Fast X-Ray Transients
In this paper we survey the theory of wind accretion in high mass X-ray
binaries hosting a magnetic neutron star and a supergiant companion.
We concentrate on the different types of interaction between the inflowing
wind matter and the neutron star magnetosphere that are relevant when accretion
of matter onto the neutron star surface is largely inhibited; these include the
inhibition through the centrifugal and magnetic barriers. Expanding on earlier
work, we calculate the expected luminosity for each regime and derive the
conditions under which transition from one regime to another can take place. We
show that very large luminosity swings (~10^4 or more on time scales as short
as hours) can result from transitions across different regimes.
The activity displayed by supergiant fast X-ray transients, a recently
discovered class of high mass X-ray binaries in our galaxy, has often been
interpreted in terms of direct accretion onto a neutron star immersed in an
extremely clumpy stellar wind. We show here that the transitions across the
magnetic and/or centrifugal barriers can explain the variability properties of
these sources as a results of relatively modest variations in the stellar wind
velocity and/or density. According to this interpretation we expect that
supergiant fast X-ray transients which display very large luminosity swings and
host a slowly spinning neutron star are characterized by magnetar-like fields,
irrespective of whether the magnetic or the centrifugal barrier applies.
Supergiant fast X-ray transients might thus provide a new opportunity to
detect and study magnetars in binary systems.Comment: Accepted for publication in ApJ. 16 pages, 6 figure
Eddington limited starbursts in the central 10pc of AGN, and the Torus in NGC1068
We present results from a survey of nearby AGN using the near infrared
adaptive optics integral field spectrograph SINFONI. These data enable us to
probe the distribution and kinematics of the gas and stars at spatial
resolutions as small as 0.085arcsec. We find strong evidence for recent but
short lived starbursts residing in very dense nuclear disks. On scales of less
than 10pc these would have reached Eddington-limited luminosities when active,
perhaps accounting for their short duration. In addition, for NGC1068 at a
resolution of 6pc, we present direct observations of molecular gas close around
the AGN which we identify with the obscuring torus.Comment: Conference proceedings to appear in "The Central Engine of Active
Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP
The effect of stellar-mass black holes on the structural evolution of massive star clusters
We present the results of realistic N-body modelling of massive star clusters
in the Magellanic Clouds, aimed at investigating a dynamical origin for the
radius-age trend observed in these systems. We find that stellar-mass black
holes, formed in the supernova explosions of the most massive cluster stars,
can constitute a dynamically important population. If a significant number of
black holes are retained (here we assume complete retention), these objects
rapidly form a dense core where interactions are common, resulting in the
scattering of black holes into the cluster halo, and the ejection of black
holes from the cluster. These two processes heat the stellar component,
resulting in prolonged core expansion of a magnitude matching the observations.
Significant core evolution is also observed in Magellanic Cloud clusters at
early times. We find that this does not result from the action of black holes,
but can be reproduced by the effects of mass-loss due to rapid stellar
evolution in a primordially mass segregated cluster.Comment: Accepted for publication in MNRAS Letters; 2 figures, 1 tabl
Doppler lidar observations of sensible heat flux and intercomparisons with a ground-based energy balance station and WRF model output
This is an open access article - Copyright @ 2009 E. Schweizerbart'sche VerlagsbuchhandlungDuring the Convective and Orographically induced Precipitation Study (COPS), a scanning Doppler lidar was deployed at Achern, Baden-Wüttemberg, Germany from 13th June to 16th August 2007. Vertical velocity profiles ('rays') through the boundary layer were measured every 3 seconds with vertical profiles of horizontal wind velocity being derived from performing azimuth scans every 30 minutes. During Intense Observation Periods radiosondes were launched from the site. In this paper, a case study of convective boundary layer development on 15th July 2007 is investigated. Estimates of eddy dissipation rate are made from the vertically pointing lidar data and used as one input to the velocity-temperature co-variance equation to estimate sensible heat flux. The sensible heat flux values calculated from Doppler lidar data are compared with a surface based energy balance station and output from the Weather Research and Forecasting (WRF) model.Funding is obtained from NER
Control networks for the Galilean satellites, November 1979
Pictures of the four Galilean satellites taken as the two Voyager spacecraft approached Jupiter during March and July 1979 are presented. Control nets of the Galilean satellites, computed photogrammetrically, and measurements of the mean radii are presented. The pictures in the control nets are identified, the coordinates of the control points are given, and identifications of some of the control points are shown on figures. The use of star field pictures to compute the focal lengths of the camera is discussed and the geometric relationship between the narrow and wide and angle cameras is reported. A description of the coordinate systems of the Galilean satellites is presented and the status of the control net computations is reported
Range safety signal propagation through the SRM exhaust plume of the space shuttle
Theoretical predictions of plume interference for the space shuttle range safety system by solid rocket booster exhaust plumes are reported. The signal propagation was calculated using a split operator technique based upon the Fresnel-Kirchoff integral, using fast Fourier transforms to evaluate the convolution and treating the plume as a series of absorbing and phase-changing screens. Talanov's lens transformation was applied to reduce aliasing problems caused by ray divergence
Heavy meson masses and decay constants from relativistic heavy quarks in full lattice QCD
We determine masses and decay constants of heavy-heavy and heavy-charm
pseudoscalar mesons as a function of heavy quark mass using a fully
relativistic formalism known as Highly Improved Staggered Quarks for the heavy
quark. We are able to cover the region from the charm quark mass to the bottom
quark mass using MILC ensembles with lattice spacing values from 0.15 fm down
to 0.044 fm. We obtain f_{B_c} = 0.427(6) GeV; m_{B_c} = 6.285(10) GeV and
f_{\eta_b} = 0.667(6) GeV. Our value for f_{\eta_b} is within a few percent of
f_{\Upsilon} confirming that spin effects are surprisingly small for heavyonium
decay constants. Our value for f_{B_c} is significantly lower than potential
model values being used to estimate production rates at the LHC. We discuss the
changing physical heavy-quark mass dependence of decay constants from
heavy-heavy through heavy-charm to heavy-strange mesons. A comparison between
the three different systems confirms that the B_c system behaves in some ways
more like a heavy-light system than a heavy-heavy one. Finally we summarise
current results on decay constants of gold-plated mesons.Comment: 16 pages, 12 figure
Entanglement quantification by local unitaries
Invariance under local unitary operations is a fundamental property that must
be obeyed by every proper measure of quantum entanglement. However, this is not
the only aspect of entanglement theory where local unitaries play a relevant
role. In the present work we show that the application of suitable local
unitary operations defines a family of bipartite entanglement monotones,
collectively referred to as "mirror entanglement". They are constructed by
first considering the (squared) Hilbert-Schmidt distance of the state from the
set of states obtained by applying to it a given local unitary. To the action
of each different local unitary there corresponds a different distance. We then
minimize these distances over the sets of local unitaries with different
spectra, obtaining an entire family of different entanglement monotones. We
show that these mirror entanglement monotones are organized in a hierarchical
structure, and we establish the conditions that need to be imposed on the
spectrum of a local unitary for the associated mirror entanglement to be
faithful, i.e. to vanish on and only on separable pure states. We analyze in
detail the properties of one particularly relevant member of the family, the
"stellar mirror entanglement" associated to traceless local unitaries with
nondegenerate spectrum and equispaced eigenvalues in the complex plane. This
particular measure generalizes the original analysis of [Giampaolo and
Illuminati, Phys. Rev. A 76, 042301 (2007)], valid for qubits and qutrits. We
prove that the stellar entanglement is a faithful bipartite entanglement
monotone in any dimension, and that it is bounded from below by a function
proportional to the linear entropy and from above by the linear entropy itself,
coinciding with it in two- and three-dimensional spaces.Comment: 13 pages, 3 figures. Improved and generalized proof of monotonicity
of the mirror and stellar entanglemen
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