1,300 research outputs found
Quasilocal Conservation Laws: Why We Need Them
We argue that conservation laws based on the local matter-only
stress-energy-momentum tensor (characterized by energy and momentum per unit
volume) cannot adequately explain a wide variety of even very simple physical
phenomena because they fail to properly account for gravitational effects. We
construct a general quasi}local conservation law based on the Brown and York
total (matter plus gravity) stress-energy-momentum tensor (characterized by
energy and momentum per unit area), and argue that it does properly account for
gravitational effects. As a simple example of the explanatory power of this
quasilocal approach, consider that, when we accelerate toward a freely-floating
massive object, the kinetic energy of that object increases (relative to our
frame). But how, exactly, does the object acquire this increasing kinetic
energy? Using the energy form of our quasilocal conservation law, we can see
precisely the actual mechanism by which the kinetic energy increases: It is due
to a bona fide gravitational energy flux that is exactly analogous to the
electromagnetic Poynting flux, and involves the general relativistic effect of
frame dragging caused by the object's motion relative to us.Comment: 20 pages, 1 figur
Dirac versus Reduced Quantization of the Poincar\'{e} Symmetry in Scalar Electrodynamics
The generators of the Poincar\'{e} symmetry of scalar electrodynamics are
quantized in the functional Schr\"{o}dinger representation. We show that the
factor ordering which corresponds to (minimal) Dirac quantization preserves the
Poincar\'{e} algebra, but (minimal) reduced quantization does not. In the
latter, there is a van Hove anomaly in the boost-boost commutator, which we
evaluate explicitly to lowest order in a heat kernel expansion using zeta
function regularization. We illuminate the crucial role played by the gauge
orbit volume element in the analysis. Our results demonstrate that preservation
of extra symmetries at the quantum level is sometimes a useful criterion to
select between inequivalent, but nevertheless self-consistent, quantization
schemes.Comment: 24 page
The horizon and its charges in the first order gravity
In this work the algebra of charges of diffeomorphisms at the horizon of
generic black holes is analyzed within first order gravity. This algebra
reproduces the algebra of diffeomorphisms at the horizon, (Diff(S^1)), without
central extension
Properties of the symplectic structure of General Relativity for spatially bounded spacetime regions
We continue a previous analysis of the covariant Hamiltonian symplectic
structure of General Relativity for spatially bounded regions of spacetime. To
allow for near complete generality, the Hamiltonian is formulated using any
fixed hypersurface, with a boundary given by a closed spacelike 2-surface. A
main result is that we obtain Hamiltonians associated to Dirichlet and Neumann
boundary conditions on the gravitational field coupled to matter sources, in
particular a Klein-Gordon field, an electromagnetic field, and a set of
Yang-Mills-Higgs fields. The Hamiltonians are given by a covariant form of the
Arnowitt-Deser-Misner Hamiltonian modified by a surface integral term that
depends on the particular boundary conditions. The general form of this surface
integral involves an underlying ``energy-momentum'' vector in the spacetime
tangent space at the spatial boundary 2-surface. We give examples of the
resulting Dirichlet and Neumann vectors for topologically spherical 2-surfaces
in Minkowski spacetime, spherically symmetric spacetimes, and stationary
axisymmetric spacetimes. Moreover, we show the relation between these vectors
and the ADM energy-momentum vector for a 2-surface taken in a limit to be
spatial infinity in asymptotically flat spacetimes. We also discuss the
geometrical properties of the Dirichlet and Neumann vectors and obtain several
striking results relating these vectors to the mean curvature and normal
curvature connection of the 2-surface. Most significantly, the part of the
Dirichlet vector normal to the 2-surface depends only the spacetime metric at
this surface and thereby defines a geometrical normal vector field on the
2-surface. Properties and examples of this normal vector are discussed.Comment: 46 pages; minor errata corrected in Eqs. (3.15), (3.24), (4.37) and
in discussion of examples in sections IV B,
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The visibility of environmental rights in the EU legal order: eurolegalism in action?
The current article responds to a key puzzle and a question. First, why, given the potential for ârights talkâ that has been seen in other countries and other policy areas, have environmental rights in the EU legal order been relatively invisible until recently? And second, with Daniel Kelemenâs influential work on Eurolegalism arguing that the EU has become much more reliant on US-style adversarial legalism, including a shift towards rights-based litigation, do EU environmental rights fit the picture Kelemen has painted, or are they an exception? The article explores the visibility of EU environmental rights at EU level and then seeks to explain the possible reasons for visibility/invisibility
Selected Topics in High Energy Semi-Exclusive Electro-Nuclear Reactions
We review the present status of the theory of high energy reactions with
semi-exclusive nucleon electro-production from nuclear targets. We demonstrate
how the increase of transferred energies in these reactions opens a complete
new window in studying the microscopic nuclear structure at small distances.
The simplifications in theoretical descriptions associated with the increase of
the energies are discussed. The theoretical framework for calculation of high
energy nuclear reactions based on the effective Feynman diagram rules is
described in details. The result of this approach is the generalized eikonal
approximation (GEA), which is reduced to Glauber approximation when nucleon
recoil is neglected. The method of GEA is demonstrated in the calculation of
high energy electro-disintegration of the deuteron and A=3 targets.
Subsequently we generalize the obtained formulae for A>3 nuclei. The relation
of GEA to the Glauber theory is analyzed. Then based on the GEA framework we
discuss some of the phenomena which can be studied in exclusive reactions,
these are: nuclear transparency and short-range correlations in nuclei. We
illustrate how light-cone dynamics of high-energy scattering emerge naturally
in high energy electro-nuclear reactions.Comment: LaTex file with 51 pages and 23 eps figure
Feynman Graphs and Generalized Eikonal Approach to High Energy Knock-Out Processes
The cross section of hard semi-exclusive reactions for fixed
missing energy and momentum is calculated within the eikonal approximation.
Relativistic dynamics and kinematics of high energy processes are unambiguously
accounted for by using the analysis of appropriate Feynman diagrams. A
significant dependence of the final state interactions on the missing energy is
found, which is important for interpretation of forthcoming color transparency
experiments. A new, more stringent kinematic restriction on the region where
the contribution of short-range nucleon correlations is enhanced in
semi-exclusive knock-out processes is derived. It is also demonstrated that the
use of light-cone variables leads to a considerable simplification of the
description of high-energy knock-out reactions.Comment: 24 pages, LaTex, two Latex and two ps figures, uses FEYNMAN.tex and
psfig.sty. Revisied version to appear in Phys. Rev.
Predictive markers and risk factors in canine pyometra
Pyometra is a common and life-threatening disease in intact female dogs, which is generally treated by surgery. Early identification of dogs with high risk of complications or poor prognosis is valuable for optimising treatment and increase survival. The objectives of this thesis were to detect predictive markers for prognosis and outcome of pyometra by investigating clinical and pathophysiological responses and to explore the breed-dependent risk for pyometra and mammary tumours (MTs).
Leucopaenia was the most important predictive variable, associated with an 18-fold increased risk for peritonitis (present in 13% of the dogs) and an over 3.5-fold increased risk for prolonged postoperative hospitalisation. Fever or hypothermia was linked with an increased risk for peritonitis and dogs with moderate to severely depressed general condition or pale mucous membranes had an increased risk for prolonged postoperative hospitalisation. These results show that commonly explored clinical variables may be helpful for predicting prognosis.
Blood concentrations of the acute phase proteins, C-reactive protein and serum amyloid A (SAA) were found to be increased in dogs with pyometra, whereas concentrations of albumin, insulin-like growth factor-I, and iron were decreased. Importantly, SAA concentrations were higher in the dogs that also suffered from sepsis. Though unspecific, SAA could therefore be a potential marker for identifying more severely affected dogs. The neuroendocrine protein chromogranin A was measured by its breakdown products catestatin and vasostatin. Catestatin concentrations were decreased in pyometra whereas vasostatin concentrations did not differ compared to healthy dogs. None of these investigated inflammatory mediators or chromogranin A were useful for outcome prediction as measured by postoperative hospitalisation.
The incidence of pyometra in 110 different breeds was studied using insurance data. Before 10 years of age, 19% of all female dogs had suffered from the disease. Breed greatly affected the risk of both pyometra and MTs.
In summary, these findings show that clinical and laboratory data and analysis of inflammatory variables can be helpful for predicting prognosis and assessing severity in dogs with pyometra. Breed considerably affects the risk of pyometra and MTs, and the information presented in this thesis will be valuable for evaluating possible health benefits of spaying in individual dogs, based on the risk of developing these diseases
Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules
This paper gives an account of our progress towards performing femtosecond
time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe
setup combining optical lasers and an X-ray Free-Electron Laser. We present
results of two experiments aimed at measuring photoelectron angular
distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and
dissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss
them in the larger context of photoelectron diffraction on gas-phase molecules.
We also show how the strong nanosecond laser pulse used for adiabatically
laser-aligning the molecules influences the measured electron and ion spectra
and angular distributions, and discuss how this may affect the outcome of
future time-resolved photoelectron diffraction experiments.Comment: 24 pages, 10 figures, Faraday Discussions 17
DEVELOPMENT OF A TESTING FACILITY FOR EXPERIMENTAL INVESTIGATION OF MEMS DYNAMICS
Abstract Dynamic characteristics of overhung and/or moving components play a pivotal role in determining the overall performance and reliability of microsystems (MEMS). In addition to the structural dynamics of the components, the response is very sensitive to multi-physics phenomena such as electrostatics, gas damping, and friction. Therefore, the ability to experimentally analyze linear and nonlinear dynamics of microsystems under varying environmental conditions is very important. This paper describes a facility for experimental investigation and validation of linear and nonlinear dynamic response of microsystems under varying environmental conditions. A detailed account of the facility components and software developed for excitation and data collection is given. Experimental results and discussion for various MEMS structures are included to illustrate the effectiveness of the experimental facility
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