416 research outputs found
Hadronic Weak Decays of Hyperons in a Soliton Model
We study the parity violating hyperon non-leptonic weak decays in the three
flavor Skyrme model. We follow the approach in which the symmetry breaking
terms in the action are diagonalized exactly within the collective coordinate
approximation. We show that although this method introduces some configuration
mixing, the rule is numerically well satisfied. In addition,
and in contrast to previous calculations, we show that not only the relative
amplitudes are in good agreement with the empirical values but also their
absolute values. The issue of whether the strong interaction enhancement
factors should be included in soliton calculations is also addressed.Comment: 8 pages, LaTeX, no figure
An efficient finite-difference scheme for computation of electron states in free-standing and core-shell quantum wires
The electron states in axially symmetric quantum wires are computed by means
of the effective-mass Schroedinger equation, which is written in cylindrical
coordinates phi, rho, and z. We show that a direct discretization of the
Schroedinger equation by central finite differences leads to a non-symmetric
Hamiltonian matrix. Because diagonalization of such matrices is more complex it
is advantageous to transform it in a symmetric form. This can be done by the
Liouville-like transformation proposed by Rizea et al. (Comp. Phys. Comm. 179
(2008) 466-478), which replaces the wave function psi(rho) with the function
F(rho)=psi(rho)sqrt(rho) and transforms the Hamiltonian accordingly. Even
though a symmetric Hamiltonian matrix is produced by this procedure, the
computed wave functions are found to be inaccurate near the origin, and the
accuracy of the energy levels is not very high. In order to improve on this, we
devised a finite-difference scheme which discretizes the Schroedinger equation
in the first step, and then applies the Liouville-like transformation to the
difference equation. Such a procedure gives a symmetric Hamiltonian matrix,
resulting in an accuracy comparable to the one obtained with the finite element
method. The superior efficiency of the new finite-difference (FDM) scheme is
demonstrated for a few rho-dependent one-dimensional potentials which are
usually employed to model the electron states in free-standing and core-shell
quantum wires. The new scheme is compared with the other FDM schemes for
solving the effective-mass Schroedinger equation, and is found to deliver
energy levels with much smaller numerical error for all the analyzed
potentials. Moreover, the PT symmetry is invoked to explain similarities and
differences between the considered FDM schemes
Giant strongly connected component of directed networks
We describe how to calculate the sizes of all giant connected components of a
directed graph, including the {\em strongly} connected one. Just to the class
of directed networks, in particular, belongs the World Wide Web. The results
are obtained for graphs with statistically uncorrelated vertices and an
arbitrary joint in,out-degree distribution . We show that if
does not factorize, the relative size of the giant strongly
connected component deviates from the product of the relative sizes of the
giant in- and out-components. The calculations of the relative sizes of all the
giant components are demonstrated using the simplest examples. We explain that
the giant strongly connected component may be less resilient to random damage
than the giant weakly connected one.Comment: 4 pages revtex, 4 figure
The Multidimensional Study of Viral Campaigns as Branching Processes
Viral campaigns on the Internet may follow variety of models, depending on
the content, incentives, personal attitudes of sender and recipient to the
content and other factors. Due to the fact that the knowledge of the campaign
specifics is essential for the campaign managers, researchers are constantly
evaluating models and real-world data. The goal of this article is to present
the new knowledge obtained from studying two viral campaigns that took place in
a virtual world which followed the branching process. The results show that it
is possible to reduce the time needed to estimate the model parameters of the
campaign and, moreover, some important aspects of time-generations relationship
are presented.Comment: In proceedings of the 4th International Conference on Social
Informatics, SocInfo 201
Measurement report: In situ observations of deep convection without lightning during the tropical cyclone Florence 2018
Hurricane Florence was the sixth named storm in the Atlantic hurricane season 2018. It caused dozens of deaths and major economic damage. In this study, we present in situ observations of trace gases within tropical storm Florence on 2 September 2018, after it had developed a rotating nature, and of a tropical wave observed close to the African continent on 29 August 2018 as part of the research campaign CAFE Africa (Chemistry of the Atmosphere: Field Experiment in Africa) with HALO (High Altitude and LOng Range Research Aircraft). We show the impact of deep convection on atmospheric composition by measurements of the trace gases nitric oxide (NO), ozone (O), carbon monoxide (CO), hydrogen peroxide (HO), dimethyl sulfide (DMS) and methyl iodide (CHI) and by the help of color-enhanced infrared satellite imagery taken by GOES-16. While both systems, i.e., the tropical wave and the tropical storm, are deeply convective, we only find evidence for lightning in the tropical wave using both in situ NO measurements and data from the World Wide Lightning Location Network (WWLLN)
Parity Violation in gamma proton Compton Scattering
A measurement of parity-violating spin-dependent gamma proton Compton
scattering will provide a theoretically clean determination of the
parity-violating pion-nucleon coupling constant . We
calculate the leading parity-violating amplitude arising from one-loop pion
graphs in chiral perturbation theory. An asymmetry of ~5 10^{-8} is estimated
for Compton scattering of 100 MeV photons.Comment: 6 pages, 1 figure, latex. Reference adde
Ferroelectric and Dipolar Glass Phases of Non-Crystalline Systems
In a recent letter [Phys. Rev. Lett. {\bf 75}, 2360 (1996)] we briefly
discussed the existence and nature of ferroelectric order in positionally
disordered dipolar materials. Here we report further results and give a
complete description of our work. Simulations of randomly frozen and
dynamically disordered dipolar soft spheres are used to study ferroelectric
ordering in non-crystalline systems. We also give a physical interpretation of
the simulation results in terms of short- and long-range interactions. Cases
where the dipole moment has 1, 2, and 3 components (Ising, XY and XYZ models,
respectively) are considered. It is found that the Ising model displays
ferroelectric phases in frozen amorphous systems, while the XY and XYZ models
form dipolar glass phases at low temperatures. In the dynamically disordered
model the equations of motion are decoupled such that particle translation is
completely independent of the dipolar forces. These systems spontaneously
develop long-range ferroelectric order at nonzero temperature despite the
absence of any fined-tuned short-range spatial correlations favoring dipolar
order. Furthermore, since this is a nonequilibrium model we find that the
paraelectric to ferroelectric transition depends on the particle mass. For the
XY and XYZ models, the critical temperatures extrapolate to zero as the mass of
the particle becomes infinite, whereas, for the Ising model the critical
temperature is almost independent of mass and coincides with the ferroelectric
transition found for the randomly frozen system at the same density. Thus in
the infinite mass limit the results of the frozen amorphous systems are
recovered.Comment: 25 pages (LATEX, no macros). 11 POSTSCRIPT figures enclosed.
Submitted to Phisical Review E. Contact: [email protected]
Modification of a conventional photolytic converter for improving aircraft measurements of NO via chemiluminescence
Nitrogen oxides (NOâĄNO+NO) are centrally involved in the photochemical processes taking place in the Earth\u27s atmosphere. Measurements of NO, particularly in remote areas where concentrations are of the order of parts per trillion by volume (pptv), are still a challenge and subject to extensive research. In this study, we present NO measurements via photolysisâchemiluminescence during the research aircraft campaign CAFE Africa (Chemistry of the Atmosphere â Field Experiment in Africa) 2018 around Cabo Verde and the results of laboratory experiments to characterize the photolytic converter used. We find the NO reservoir species MPN (methyl peroxy nitrate) to produce the only relevant thermal interference in the converter under the operating conditions during CAFE Africa. We identify a memory effect within the conventional photolytic converter (type 1) associated with high NO concentrations and rapidly changing water vapor concentrations, accompanying changes in altitude during aircraft measurements, which is due to the porous structure of the converter material. As a result, NO artifacts, which are amplified by low conversion efficiencies, and a varying instrumental background adversely affect the NO measurements. We test and characterize an alternative photolytic converter (type 2) made from quartz glass, which improves the reliability of NO measurements in laboratory and field studies
Further progress in the study of epsilon iron oxide in archaeological baked clays
The occurrence of Δ-Fe2O3 in archaeological samples that have been subjected to high temperatures is gradually being detected by the use of micrometric structural characterization techniques. This work provides new information by revealing that the Δ-Fe2O3 is formed as a response to temperature, the aggregation state and the position within the baked clay with respect to the nearest heat source. In addition, depending mainly on the atmospheric environment, the temperature reached by the combustion structure, the distance from the heating source and the particle aggregation, other iron oxide magnetic phases are produced. In the baked clay studied here, hematite is found over the whole range of samples studied but its magnetic contribution is negligible. Magnetite is observed at the sample surface, probably due to local atmospheric environment closest to the combustion source. Maghemite is found at all depths up to 6âŻcm below the sample surface. Δ-Fe2O3 has a limited distribution, found within 2â3âŻcm of the sample surface. Furthermore, the viability of this compound as a palaeofield marker has been evaluated in both archaeological and synthetic samples. The results indicate that Δ-Fe2O3 is able to register the direction of the magnetic field. Linear palaeointensity plots have been obtained in synthetic samples, although the value of the palaeofield could be, sometimes, overestimated
Parity nonconserving cold neutron-parahydrogen interactions
Three pion dominated observables of the parity nonconserving interactions
between the cold neutrons and parahydrogen are calculated. The transversely
polarized neutron spin rotation, unpolarized neutron longitudinal polarization,
and photon-asymmetry of the radiative polarized neutron capture are considered.
For the numerical evaluation of the observables, the strong interactions are
taken into account by the Reid93 potential and the parity nonconserving
interactions by the DDH model along with the two-pion exchange.Comment: 17 pages, 2 figure
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