1,743 research outputs found
Effect of Self-Interaction on Charged Black Hole Radiance
We extend our previous analysis of the modification of the spectrum of black
hole radiance due to the simplest and probably most quantitatively important
back-reaction effect, that is self-gravitational interaction, to the case of
charged holes. As anticipated, the corrections are small for low-energy
radiation when the hole is well away from extremality, butbecome qualitatively
important near extremality. A notable result is that radiation which could
leave the hole with mass and charge characteristic of a naked singularity,
predicted in the usual approximation of fixed space-time geometry, is here
suppressed. We discuss the nature of our approximations, and show how they work
in a simpler electromagnetic analogue problem.Comment: 13 pages in Latex, no figure
Hawking Radiation as Tunneling
We present a short and direct derivation of Hawking radiation as a tunneling
process, based on particles in a dynamical geometry. The imaginary part of the
action for the classically forbidden process is related to the Boltzmann factor
for emission at the Hawking temperature. Because the derivation respects
conservation laws, the exact spectrum is not precisely thermal. We compare and
contrast the problem of spontaneous emission of charged particles from a
charged conductor.Comment: LaTeX, 10 pages; v2. journal version, added section on relation of
black hole radiation to electric charge emission from a charged conducting
sphere; v3. restored cut referenc
Self-Interaction Correction to Black Hole Radiance
We consider the modification of the formulas for black hole radiation, due to
the self-gravitation of the radiation. This is done by truncating the coupled
particle-hole system to a small set of modes, that are plausibly the most
significant ones, and quantizing the reduced system. In this way we find that
the particles no longer move along geodesics, nor is the action along the rays
zero for a massless particle. The radiation is no longer thermal, but is
corrected in a definite way that we calculate. Our methods can be extended in a
straightforward manner to discuss correlations in the radiation, or between
incoming particles and the radiation.Comment: 20 pages, no figures, uses Phyzzx, IASSNS-HEP 94/6
Test validation, method comparison and reference range for the measurement of β-hydroxybutyrate in peripheral blood samples
Introduction: The measurement of β-hydroxybutyrate (βOHB) concentrations is a corner stone of the diagnosis of diabetic ketoacidosis and other ketonic states. The aim of this study was to perform a validation of a peripheral blood βOHB assay (Randox) on a Roche cobas c502 analyser and to establish a βOHB reference range for the validated assay.
Materials and methods: Precision, linearity and limit of detection and blank (LoD, LoB) were determined according to Clinical and Laboratory
Standards Institute (CLSI) EP05-A3, EP 06-A and EP17-A2 guidelines, using commercial control material and residual patient sample pools. As method comparison, for 190 semi-quantitative measurements of urine ketones we determined the corresponding βOHB blood concentration. The reference range was based on the CLSI C28-A3 guideline, using 304 randomly selected serum samples from population based German National Cohort (GNC) study.
Results: Coefficients of variation for the validated assay ranged from 1.5% for high concentrations (3.1 mmol/L) to 6.5% for low concentrations (0.1 mmol/L). Detection capacity was LoB = 0.011 mmol/L and LoD = 0.037 mmol/L. Linearity of the assay ranged from 0.10 to 3.95 mmol/L. The agreement between the semi-quantitative urine ketone test and the βOHB blood test was moderate (Kappa = 0.66). The obtained 95% serum reference range was estimated as 0.02 to 0.28 mmol/l βOHB.
Conclusions: The Ranbut βOHB assay showed good precision and analytical performance. Our results confirm that βOHB measurement in peripheral blood is indeed a preferable alternative to the semi-quantitative measurement of urine ketones
Differential analysis of matrix convex functions
We analyze matrix convex functions of a fixed order defined on a real
interval by differential methods as opposed to the characterization in terms of
divided differences given by Kraus. We obtain for each order conditions for
matrix convexity which are necessary and locally sufficient, and they allow us
to prove the existence of gaps between classes of matrix convex functions of
successive orders, and to give explicit examples of the type of functions
contained in each of these gaps. The given conditions are shown to be also
globally sufficient for matrix convexity of order two. We finally introduce a
fractional transformation which connects the set of matrix monotone functions
of each order n with the set of matrix convex functions of order n+1
Modelling Vibrational Dissociation of [H2âHCO]+
The [H2âHCO]+ complex is likely to be one of the most important complexes in interstellar space, as it is a complex of the most abundant interstellar species. In the current work, we investigate the interaction energy and potential surface of the complex using a range of computational methods. The dynamics of the complex are investigated by incorporating an external time-dependent field into Car-Parrinello molecular dynamics (CPMD) and inducing a vibrationally activated dissociation. This excitation method is compared to a normal-mode excitation from the equilibrium structure. The results agree well with the available experimental data: an excitation to the first vibrationally-excited state of either of the high-frequency HCO+ modes (ν2, ν3) causes a dissociation of the complex on picosecond timescales
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Precipitate number density determination in microalloyed steels by complementary atom probe tomography and matrix dissolution
Particle number densities are a crucial parameter in the microstructure engineering of microalloyed steels. We introduce a new method to determine nanoscale precipitate number densities of macroscopic samples that is based on the matrix dissolution technique (MDT) and combine it with atom probe tomography (APT). APT counts precipitates in microscopic samples of niobium and niobium-titanium microalloyed steels. The new method uses MDT combined with analytical ultracentrifugation (AUC) of extracted precipitates, inductively coupled plasmaâoptical emission spectrometry, and APT. We compare the precipitate number density ranges from APT of 137.81 to 193.56 Ă 1021Â mâ3 for the niobium steel and 104.90 to 129.62 Ă 1021Â mâ3 for the niobium-titanium steel to the values from MDT of 2.08 Ă 1021Â mâ3 and 2.48 Ă 1021Â mâ3. We find that systematic errors due to undesired particle loss during extraction and statistical uncertainties due to the small APT volumes explain the differences. The size ranges of precipitates that can be detected via APT and AUC are investigated by comparison of the obtained precipitate size distributions with transmission electron microscopy analyses of carbon extraction replicas. The methods provide overlapping resulting ranges. MDT probes very large numbers of small particles but is limited by errors due to particle etching, while APT can detect particles with diameters below 10Â nm but is limited by small-number statistics. The combination of APT and MDT provides comprehensive data which allows for an improved understanding of the interrelation between thermo-mechanical controlled processing parameters, precipitate number densities, and resulting mechanical-technological material properties. Graphical abstract: [Figure not available: see fulltext.
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