4,338 research outputs found
A critical approach to the concept of a polar, low-altitude LARES satellite
According to very recent developments of the LARES mission, which would be
devoted to the measurement of the general relativistic Lense--Thirring effect
in the gravitational field of the Earth with Satellite Laser Ranging, it seems
that the LARES satellite might be finally launched in a polar, low--altitude
orbit by means of a relatively low--cost rocket. The observable would be the
node only. In this letter we critically analyze this scenario.Comment: LaTex2e, 11 pages, 4 figures, 1 table. Accepted for publication in
Classical and Quantum Gravit
Min-Max Theorems for Packing and Covering Odd -trails
We investigate the problem of packing and covering odd -trails in a
graph. A -trail is a -walk that is allowed to have repeated
vertices but no repeated edges. We call a trail odd if the number of edges in
the trail is odd. Let denote the maximum number of edge-disjoint odd
-trails, and denote the minimum size of an edge-set that
intersects every odd -trail.
We prove that . Our result is tight---there are
examples showing that ---and substantially improves upon
the bound of obtained in [Churchley et al 2016] for .
Our proof also yields a polynomial-time algorithm for finding a cover and a
collection of trails satisfying the above bounds.
Our proof is simple and has two main ingredients. We show that (loosely
speaking) the problem can be reduced to the problem of packing and covering odd
-trails losing a factor of 2 (either in the number of trails found, or
the size of the cover). Complementing this, we show that the
odd--trail packing and covering problems can be tackled by exploiting
a powerful min-max result of [Chudnovsky et al 2006] for packing
vertex-disjoint nonzero -paths in group-labeled graphs
Conservative evaluation of the uncertainty in the LAGEOS-LAGEOS II Lense-Thirring test
We deal with the test of the general relativistic gravitomagnetic
Lense-Thirring effect currently ongoing in the Earth's gravitational field with
the combined nodes \Omega of the laser-ranged geodetic satellites LAGEOS and
LAGEOS II.
One of the most important source of systematic uncertainty on the orbits of
the LAGEOS satellites, with respect to the Lense-Thirring signature, is the
bias due to the even zonal harmonic coefficients J_L of the multipolar
expansion of the Earth's geopotential which account for the departures from
sphericity of the terrestrial gravitational potential induced by the
centrifugal effects of its diurnal rotation. The issue addressed here is: are
the so far published evaluations of such a systematic error reliable and
realistic? The answer is negative. Indeed, if the difference \Delta J_L among
the even zonals estimated in different global solutions (EIGEN-GRACE02S,
EIGEN-CG03C, GGM02S, GGM03S, ITG-Grace02, ITG-Grace03s, JEM01-RL03B, EGM2008,
AIUB-GRACE01S) is assumed for the uncertainties \delta J_L instead of using
their more or less calibrated covariance sigmas \sigma_{J_L}, it turns out that
the systematic error \delta\mu in the Lense-Thirring measurement is about 3 to
4 times larger than in the evaluations so far published based on the use of the
sigmas of one model at a time separately, amounting up to 37% for the pair
EIGEN-GRACE02S/ITG-Grace03s. The comparison among the other recent GRACE-based
models yields bias as large as about 25-30%. The major discrepancies still
occur for J_4, J_6 and J_8, which are just the zonals the combined
LAGEOS/LAGOES II nodes are most sensitive to.Comment: LaTex, 12 pages, 12 tables, no figures, 64 references. To appear in
Central European Journal of Physics (CEJP
Perspectives in measuring the PPN parameters beta and gamma in the Earth's gravitational fields with the CHAMP/GRACE models
The current bounds on the PPN parameters gamma and beta are of the order of
10^-4-10^-5. Various missions aimed at improving such limits by several orders
of magnitude have more or less recently been proposed like LATOR, ASTROD,
BepiColombo and GAIA. They involve the use of various spacecraft, to be
launched along interplanetary trajectories, for measuring the effects of the
solar gravity on the propagation of electromagnetic waves. In this paper we
investigate what is needed to measure the combination nu=(2+2gamma-beta)/3 of
the post-Newtonian gravitoelectric Einstein perigee precession of a test
particle to an accuracy of about 10^-5 with a pair of drag-free spacecraft in
the Earth's gravitational field. It turns out that the latest gravity models
from the dedicated CHAMP and GRACE missions would allow to reduce the
systematic error of gravitational origin just to this demanding level of
accuracy. In regard to the non-gravitational errors, the spectral noise density
of the drag-free sensors required to reach such level of accuracy would amounts
to 10^-8-10^-9 cm s^-2 Hz^-1/2 over very low frequencies. Although not yet
obtainable with the present technologies, such level of compensation is much
less demanding than those required for, e.g., LISA. As a by-product, an
independent measurement of the post-Newtonian gravitomagnetic Lense-Thirring
effect with a 0.9% accuracy would be possible as well. The forthcoming Earth
gravity models from CHAMP and GRACE will further reduce the systematic
gravitational errors in both of such tests.Comment: LaTex2e, 14 pages, 3 tables, no figures, 75 references. To appear in
Int. J. Mod. Phys.
On a new observable for measuring the Lense-Thirring effect with Satellite Laser Ranging
In this paper we present a rather extensive error budget for the difference
of the perigees of a pair of supplementary SLR satellites aimed to the
detection of the Lense-Thirring effect.Comment: LaTex2e, 14 pages, 1 table, no figures. Some changes and additions to
the abstract, Introduction and Conclusions. References updated, typos
corrected. Equation corrected. To appear in General Relativity and
Gravitatio
On the trace identity in a model with broken symmetry
Considering the simple chiral fermion meson model when the chiral symmetry is
explicitly broken, we show the validity of a trace identity -- to all orders of
perturbation theory -- playing the role of a Callan-Symanzik equation and which
allows us to identify directly the breaking of dilatations with the trace of
the energy-momentum tensor. More precisely, by coupling the quantum field
theory considered to a classical curved space background, represented by the
non-propagating external vielbein field, we can express the conservation of the
energy-momentum tensor through the Ward identity which characterizes the
invariance of the theory under the diffeomorphisms. Our ``Callan-Symanzik
equation'' then is the anomalous Ward identity for the trace of the
energy-momentum tensor, the so-called ``trace identity''.Comment: 11 pages, Revtex file, final version to appear in Phys.Rev.
Many-core applications to online track reconstruction in HEP experiments
Interest in parallel architectures applied to real time selections is growing
in High Energy Physics (HEP) experiments. In this paper we describe performance
measurements of Graphic Processing Units (GPUs) and Intel Many Integrated Core
architecture (MIC) when applied to a typical HEP online task: the selection of
events based on the trajectories of charged particles. We use as benchmark a
scaled-up version of the algorithm used at CDF experiment at Tevatron for
online track reconstruction - the SVT algorithm - as a realistic test-case for
low-latency trigger systems using new computing architectures for LHC
experiment. We examine the complexity/performance trade-off in porting existing
serial algorithms to many-core devices. Measurements of both data processing
and data transfer latency are shown, considering different I/O strategies
to/from the parallel devices.Comment: Proceedings for the 20th International Conference on Computing in
High Energy and Nuclear Physics (CHEP); missing acks adde
An isolated, blood-perfused, feline heart preparation for evaluating pharmacological interventions during myocardial ischemia
A preparation is described in which feline hearts were perfused with arterial blood drawn from a blood-donor cat. Ventricular function was measured with a fluidfilled latex balloon within the left ventricle. Left ventricular developed pressure, maximum left ventricular dP/dt, ventricular compliance, and coronary blood flow changed only slightly during two hours of perfusion at a constant pressure of 75 mmHg. Water, sodium, potassium, and calcium contents, and creatine kinase activity of isolated hearts did not differ from the values obtained for intact hearts from the blood-donor cats. Isolated hearts subJected to 40 minutes of normothermic global ischemia with one hour of reperfusion exhibited significantly decreased contractility, but no change in ventricular compliance. Myocardial water and sodium contents were increased after 40 minutes of ischemia and reperfusion. Hearts subJected to 60 minutes of ischemia with reperfusion exhibited decreases in both contractility and compliance. A prolonged reactive hyperemic response was maintained throughout the hour of reperfusion. Myocardial sodium content increased more than could be accounted for by edema formation; decreases were observed in potassium content and creatine kinase activity while calcium content was increased. The applicability of this model for evaluating the effects of pharmacological interventions on myocardial ischemic injury are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23096/1/0000015.pd
An Algebraic Criterion for the Ultraviolet Finiteness of Quantum Field Theories
An algebraic criterion for the vanishing of the beta function for
renormalizable quantum field theories is presented. Use is made of the descent
equations following from the Wess-Zumino consistency condition. In some cases,
these equations relate the fully quantized action to a local gauge invariant
polynomial. The vanishing of the anomalous dimension of this polynomial enables
us to establish a nonrenormalization theorem for the beta function ,
stating that if the one-loop order contribution vanishes, then will
vanish to all orders of perturbation theory. As a by-product, the special case
in which is only of one-loop order, without further corrections, is
also covered. The examples of the N=2,4 supersymmetric Yang-Mills theories are
worked out in detail.Comment: 1+32 pages, LaTeX2e, typos correcte
Quantum Holonomy in Three-dimensional General Covariant Field Theory and Link Invariant
We consider quantum holonomy of some three-dimensional general covariant
non-Abelian field theory in Landau gauge and confirm a previous result
partially proven. We show that quantum holonomy retains metric independence
after explicit gauge fixing and hence possesses the topological property of a
link invariant. We examine the generalized quantum holonomy defined on a
multi-component link and discuss its relation to a polynomial for the link.Comment: RevTex, 12 pages. The metric independence of path integral measure is
justified and the case of multi-component link is discussed in detail. To be
published in Physical Review
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