388 research outputs found
Numerical versus analytical accuracy of the formulas for light propagation
Numerical integration of the differential equations of light propagation in
the Schwarzschild metric shows that in some situations relevant for practical
observations the well-known post-Newtonian solution for light propagation has
an error up to 16 microarcsecond. The aim of this work is to demonstrate this
fact, identify the reason for this error and to derive an analytical formula
accurate at the level of 1 microarcsecond as needed for high-accuracy
astrometric projects (e.g., Gaia).
An analytical post-post-Newtonian solution for the light propagation for both
Cauchy and boundary problems is given for the Schwarzschild metric augmented by
the PPN and post-linear parameters , and . Using
analytical upper estimates of each term we investigate which
post-post-Newtonian terms may play a role for an observer in the solar system
at the level of 1 microarcsecond and conclude that only one post-post-Newtonian
term remains important for this numerical accuracy. In this way, an analytical
solution for the boundary problem for light propagation is derived. That
solution contains terms of both post-Newtonian and post-post-Newtonian order,
but is valid for the given numerical level of 1 microarcsecond. The derived
analytical solution has been verified using the results of a high-accuracy
numerical integration of differential equations of light propagation and found
to be correct at the level well below 1 microarcsecond for arbitrary observer
situated within the solar system. Furthermore, the origin of the
post-post-Newtonian terms relevant for the microarcsecond accuracy is
elucidated. We demonstrate that these terms result from an inadequate choice of
the impact parameter in the standard post-Newtonian formulas
The cost and risk impacts of rerouting railroad shipments of hazardous materials
Cataloged from PDF version of article.Rail shipments of hazardous materials expose the population near the routes to the possibility of an accident resulting in a spill. Rail routes are
determined by economic concerns such as route length and the revenue generated for the originating carrier. In this paper we consider an alternate
routing strategy that takes accident risks into account. We employ a model to quantify rail transport risk and then use a weighted combination of
cost and risk and generate alternate routes. In some cases the alternate routes achieve significantly lower risk values than the practical routes at a
small incremental cost. While there are generally fewer rerouting alternatives for rail than for road transport, considering the possible consequences
of a train derailment we argue that risk should be taken into account when selecting rail routes and that the cost–risk tradeoffs should be evaluated.
© 2007 Elsevier Ltd. All rights reserved
An International Classification of Inherited Metabolic Disorders (ICIMD)
Several initiatives at establishing a classification of inherited metabolic disorders have been published previously, some focusing on pathomechanisms, others on clinical manifestations, while yet another attempted a simplified approach of a comprehensive nosology. Some of these classifications suffered from shortcomings, such as lack of a mechanism for continuous update in light of a rapidly‐evolving field, or lack of widespread input from the metabolic community at large. Our classification – the International Classification of Inherited Metabolic Disorders, or ICIMD – includes 1,450 disorders, and differs from prior approaches in that it benefited from input by a large number of experts in the field, and was endorsed by major metabolic societies around the globe. Several criteria such as pathway involvement and pathomechanisms were considered. The main purpose of the hierarchical, group‐based approach of the ICIMD is an improved understanding of the interconnections between many individual conditions that may share functional, clinical and diagnostic features. The ICIMD aims to include any primary genetic condition in which alteration of a biochemical pathway is intrinsic to specific biochemical, clinical and/or pathophysiological features. As new disorders are discovered, we will seek the opinion of experts in the advisory board prior to inclusion in the appropriate group of the ICIMD, thus guaranteeing the continuing relevance of this classification via regular curation and expert advice
Impact of Nucleon Mass Shift on the Freeze Out Process
The freeze out of a massive nucleon gas through a finite layer with time-like
normal is studied. The impact of in-medium nucleon mass shift on the freeze out
process is investigated. A considerable modification of the thermodynamical
variables temperature, flow-velocity, energy density and particle density has
been found. Due to the nucleon mass shift the freeze out particle distribution
functions are changed noticeably in comparison with evaluations, which use
vacuum nucleon mass.Comment: submitted to Physical Review
Direction of light propagation to order G^2 in static, spherically symmetric spacetimes: a new derivation
A procedure avoiding any integration of the null geodesic equations is used
to derive the direction of light propagation in a three-parameter family of
static, spherically symmetric spacetimes within the post-post-Minkowskian
approximation. Quasi-Cartesian isotropic coordinates adapted to the symmetries
of spacetime are systematically used. It is found that the expression of the
angle formed by two light rays as measured by a static observer staying at a
given point is remarkably simple in these coordinates. The attention is mainly
focused on the null geodesic paths that we call the "quasi-Minkowskian light
rays". The vector-like functions characterizing the direction of propagation of
such light rays at their points of emission and reception are firstly obtained
in the generic case where these points are both located at a finite distance
from the centre of symmetry. The direction of propagation of the
quasi-Minkowskian light rays emitted at infinity is then straightforwardly
deduced. An intrinsic definition of the gravitational deflection angle relative
to a static observer located at a finite distance is proposed for these rays.
The expression inferred from this definition extends the formula currently used
in VLBI astrometry up to the second order in the gravitational constant G.Comment: 19 pages; revised introduction; added references for introduction;
corrected typos; published in Class. Quantum Gra
ost in promiscuity? An evolutionary and biochemical evaluation of HSD10 function in cardiolipin metabolism
Multifunctional proteins are challenging as it can be difficult to confirm pathomechanisms associated with disease-causing genetic variants. The human 17β-hydroxysteroid dehydrogenase 10 (HSD10) is a moonlighting enzyme with at least two structurally and catalytically unrelated functions. HSD10 disease was originally described as a disorder of isoleucine metabolism, but the clinical manifestations were subsequently shown to be linked to impaired mtDNA transcript processing due to deficient function of HSD10 in the mtRNase P complex. A surprisingly large number of other, mostly enzymatic and potentially clinically relevant functions have been attributed to HSD10. Recently, HSD10 was reported to exhibit phospholipase C-like activity towards cardiolipins (CL), important mitochondrial phospholipids. To assess the physiological role of the proposed CL-cleaving function, we studied CL architectures in living cells and patient fibroblasts in different genetic backgrounds and lipid environments using our well-established LC–MS/MS cardiolipidomic pipeline. These experiments revealed no measurable effect on CLs, indicating that HSD10 does not have a physiologically relevant function towards CL metabolism. Evolutionary constraints could explain the broad range of reported substrates for HSD10 in vitro. The combination of an essential structural with a non-essential enzymatic function in the same protein could direct the evolutionary trajectory towards improvement of the former, thereby increasing the flexibility of the binding pocket, which is consistent with the results presented here
Evidence for the absence of regularization corrections to the partial-wave renormalization procedure in one-loop self energy calculations in external fields
The equivalence of the covariant renormalization and the partial-wave
renormaliz ation (PWR) approach is proven explicitly for the one-loop
self-energy correction (SE) of a bound electron state in the presence of
external perturbation potentials. No spurious correctio n terms to the
noncovariant PWR scheme are generated for Coulomb-type screening potentia ls
and for external magnetic fields. It is shown that in numerical calculations of
the SE with Coulombic perturbation potential spurious terms result from an
improper treatment of the unphysical high-energy contribution. A method for
performing the PWR utilizing the relativistic B-spline approach for the
construction of the Dirac spectrum in external magnetic fields is proposed.
This method is applied for calculating QED corrections to the bound-electron
-factor in H-like ions. Within the level of accuracy of about 0.1% no
spurious terms are generated in numerical calculations of the SE in magnetic
fields.Comment: 22 pages, LaTeX, 1 figur
Rho - Omega Splitting and Mixing in Nuclear Matter
We investigate the splitting and mixing of and mesons in
nuclear matter. The calculations were performed on the basis of QCD sum rules
and include all operators up to mass dimension-6 twist-4 and up to first order
in the coupling constants. Special attention is devoted to the impact of the
scalar 4-quark condensates on both effects. In nuclear matter the Landau
damping governs the mass splitting while the scalar 4-quark
condensates govern the strenght of individual mass shifts. A strong in-medium
mass splitting causes the disappearance of the mixing.Comment: 28 pages, 8 figures, Phys. Rev. C 70 (2004) 03520
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