692 research outputs found
Infinite slabs and other weird plane symmetric space-times with constant positive density
We present the exact solution of Einstein's equation corresponding to a
static and plane symmetric distribution of matter with constant positive
density located below . This solution depends essentially on two
constants: the density and a parameter . We show that this
space-time finishes down below at an inner singularity at finite depth. We
match this solution to the vacuum one and compute the external gravitational
field in terms of slab's parameters. Depending on the value of , these
slabs can be attractive, repulsive or neutral. In the first case, the
space-time also finishes up above at another singularity. In the other cases,
they turn out to be semi-infinite and asymptotically flat when .
We also find solutions consisting of joining an attractive slab and a
repulsive one, and two neutral ones. We also discuss how to assemble a
"gravitational capacitor" by inserting a slice of vacuum between two such
slabs.Comment: 8 page
Resonance saturation in the odd-intrinsic parity sector of low-energy QCD
Using the large N_C approximation we have constructed the most general chiral
resonance Lagrangian in the odd-intrinsic parity sector that can generate low
energy chiral constants up to O(p^6). Integrating out the resonance fields
these O(p^6) constants are expressed in terms of resonance couplings and
masses. The role of eta' is discussed and its contribution is explicitly
factorized. Using the resonance basis we have also calculated two QCD Green
functions of currents: and and found, imposing high energy
constraints, additional relations for resonance couplings. We have studied
several phenomenological implications based on these correlators from which let
us mention here our prediction for the pi0-pole contribution to the muon g-2
factor: .Comment: 42 pages, 3 figure
The Surname Space of the Czech Republic: Examining Population Structure by Network Analysis of Spatial Co-Occurrence of Surnames
In the majority of countries, surnames represent a ubiquitous cultural attribute inherited from an individual's ancestors and predominantly only altered through marriage. This paper utilises an innovative method, taken from economics, to offer unprecedented insights into the “surname space” of the Czech Republic. We construct this space as a network based on the pairwise probabilities of co-occurrence of surnames and find that the network representation has clear parallels with various ethno-cultural boundaries in the country. Our inductive approach therefore formalizes a simple assumption that the more frequently the bearers of two surnames concentrate in the same locations the higher the probability that these two surnames can be related (considering ethno-cultural relatedness, common co-ancestry or genetic relatedness, or some other type of relatedness). Using the Czech Republic as a case study this paper offers a fresh perspective on surnames as a quantitative data source and provides a methodology that can be easily incorporated within wider cultural, ethnic, geographic and population genetics studies already utilizing surnames.</p
On Orbits of the Ring Zmn under Action of the Group SL(m, Zn)
We consider the action of the finite matrix group SL(m,Zn ) on the ring Zmn. We determine orbits of this action for n arbitrary natural number. It is a generalization of the task which was studied by A. A. Kirillov for m = 2 and n prime number
Understanding the Josephson current through a Kondo-correlated quantum dot
We study the Josephson current 0- transition of a quantum dot tuned to
the Kondo regime. The physics can be quantitatively captured by the numerically
exact continuous time quantum Monte Carlo method applied to the single-impurity
Anderson model with BCS superconducting leads. For a comparison to an
experiment the tunnel couplings are determined by fitting the normal-state
linear conductance. Excellent agreement for the dependence of the critical
Josephson current on the level energy is achieved. For increased tunnel
couplings the Kondo scale becomes comparable to the superconducting gap and the
regime of the strongest competition between superconductivity and Kondo
correlations is reached; we predict the gate voltage dependence of the critical
current in this regime.Comment: 5 pages, 3 figure
Renormalizacija tenzorske svojstvene energije u rezonantnoj kiralnoj teoriji
We study the problems related to the renormalization of propagators in resonance chiral theory, concentrating on the case of vector resonances in the antisymmetric tensor formalism. The general form of the propagators for antisymmetric tensor fields contains not only the resonance states but also the states that are ghosts or tachyons which decouple in the free-field limit. However, when the interaction terms are taking into account they are dynamically generated through the renormalization procedure.Proučavamo probleme oko renormalizacije propagatora u rezonantnoj kiralnoj teoriji, usredotočivši se na vektorske rezonancije u formalizmu antisimetričnih tenzora. Opći oblik propagatora antisimetričnih tenzorskih polja sadrži pored rezonantnih stanja i duhove i tahione koji se odvajaju u granici slobodnog polja. Međutim, ako se članovi međudjelovanja uzmu u obzir, oni se stvaraju dinamički renormalizacijskim postupkom
Measurement of Two Phase Flow
This paper presents the results of experiments with moist wet steam. The aim of the experiment was to measure the velocity of the growth of a condensing nucleus in wet steam dependent on the velocity of condensation. For the experiments in wet steam an experimental setup was designed and constructed, which generated superheated steam at lowered pressure and a temperature of 50 °C. Low pressure and temperature of the hot vapour was chosen in order to minimize the risk of accidental disruption of the wall. The size of the condensing nucleus was measured by the method of Interferometric Particle Imaging (IPI). The IPI method is a technique for determining the particle size of transparent and spherical particles based on calculating the fringes captured on a CCD array. The number of fringes depends on the particle size and on the optical configuration. The experimental setup used is identical with the setup for measuring flow by the stereo PIV method. The only difference is the use of a special camera mount comprising a transparent mirror and enabling both cameras to be focused to one point. We present the results of the development of the growth of a condensing nucleus and histograms of the sizes of all measured particles depending on position and condensation velocity.
Evaluation of a Reflection Method on an Open-Ended Coaxial Line and its Use in Dielectric Measurements
This paper describes a method for determining the dielectric constant of a biological tissue. A suitable way to make a dielectric measurement that is nondestructive and noninvasive for the biological substance and broadband at the frequency range of the network analyzer is to use a reflection method on an open ended coaxial line. A coaxial probe in the frequency range of the network analyzer from 17 MHz to 2 GHz is under investigation and also a calibration technique and the behavior of discrete elements in an equivalent circuit of an open ended coaxial line. Information about the magnitude and phase of the reflection coefficient on the interface between a biological tissue sample and a measurement probe is modeled with the aid of an electromagnetic field simulator. The numerical modeling is compared with real measurements, and a comparison is presented.
Support for Expert Estimations in Transportation Projects
This paper deals with risk analysis as a part of the financial assessment of transportation projects. Two approaches to risk assessment are discussed. A risk can be evaluated either directly in terms of the probabilistic distribution of the assessment criterion; or an indirect determination of the risk can be applied without constructing the probability distribution, but by determining the characteristic features of the project.
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