341 research outputs found
Asymptotic channels and gauge transformations of the time-dependent Dirac equation for extremely relativistic heavy-ion collisions
We discuss the two-center, time-dependent Dirac equation describing the
dynamics of an electron during a peripheral, relativistic heavy-ion collision
at extreme energies. We derive a factored form, which is exact in the
high-energy limit, for the asymptotic channel solutions of the Dirac equation,
and elucidate their close connection with gauge transformations which transform
the dynamics into a representation in which the interaction between the
electron and a distant ion is of short range. We describe the implications of
this relationship for solving the time-dependent Dirac equation for extremely
relativistic collisions.Comment: 12 pages, RevTeX, 2 figures, submitted to PR
Enhancement of photoelectrochemical and optical characteristics using a TiO2 nanoparticles interlayer in MEH-PPV heterojunction devices
International audienc
Stellar granulation as seen in disk-integrated intensity. II. Theoretical scaling relations compared with observations
A large set of stars observed by CoRoT and Kepler shows clear evidence for
the presence of a stellar background, which is interpreted to arise from
surface convection, i.e., granulation. These observations show that the
characteristic time-scale (tau_eff) and the root-mean-square (rms) brightness
fluctuations (sigma) associated with the granulation scale as a function of the
peak frequency (nu_max) of the solar-like oscillations. We aim at providing a
theoretical background to the observed scaling relations based on a model
developed in the companion paper. We computed for each 3D model the theoretical
power density spectrum (PDS) associated with the granulation as seen in
disk-integrated intensity on the basis of the theoretical model. For each PDS
we derived tau_eff and sigma and compared these theoretical values with the
theoretical scaling relations derived from the theoretical model and the Kepler
measurements. We derive theoretical scaling relations for tau_eff and sigma,
which show the same dependence on nu_max as the observed scaling relations. In
addition, we show that these quantities also scale as a function of the
turbulent Mach number (Ma) estimated at the photosphere. The theoretical
scaling relations for tau_eff and sigma match the observations well on a global
scale. Our modelling provides additional theoretical support for the observed
variations of sigma and tau_eff with nu_m max. It also highlights the important
role of Ma in controlling the properties of the stellar granulation. However,
the observations made with Kepler on a wide variety of stars cannot confirm the
dependence of our scaling relations on Ma. Measurements of the granulation
background and detections of solar-like oscillations in a statistically
sufficient number of cool dwarf stars will be required for confirming the
dependence of the theoretical scaling relations with Ma.Comment: 12 pages, 6 figures,accepted for publication in A&
AI in Education: Improving Quality for Both Centralized and Decentralized Frameworks
Education is essential for achieving many Sustainable Development Goals (SDGs). Therefore, the education system focuses on empowering more educated people and improving the quality of the education system. One of the latest technologies to enhance the quality of education is Artificial Intelligence (AI)-based Machine Learning (ML). As a result, ML has a significant influence on the education system. ML is currently widely applied in the education system for various tasks, such as creating models by monitoring student performance and activities that accurately predict student outcomes, their engagement in learning activities, decision-making, problem-solving capabilities, etc. In this research, we provide a survey of machine learning frameworks for both distributed (clusters of schools and universities) and centralized (university or school) educational institutions to predict the quality of students\u27 learning outcomes and find solutions to improve the quality of their education system. Additionally, this work explores the application of ML in teaching and learning for further improvements in the learning environment for centralized and distributed education systems
Stellar turbulence and mode physics
An overview of selected topical problems on modelling oscillation properties
in solar-like stars is presented. High-quality oscillation data from both
space-borne intensity observations and ground-based spectroscopic measurements
provide first tests of the still-ill-understood, superficial layers in distant
stars. Emphasis will be given to modelling the pulsation dynamics of the
stellar surface layers, the stochastic excitation processes and the associated
dynamics of the turbulent fluxes of heat and momentum.Comment: Proc. HELAS Workshop on 'Synergies between solar and stellar
modelling', eds M. Marconi, D. Cardini, M. P. Di Mauro, Astrophys. Space
Sci., in the pres
Synthesis of benzimidazole-cyclohexanone derivatives
This work reports the synthesis and characterization of new benzimidazole-cyclohexanone derivatives 3a-d, 4a-d and 5a-d under different reaction conditions. The intermediates and final compounds were purified and their chemical structures were elucidated using 1H-NMR, 13C-NMR and mass spectral data.Keywords: Benzimidazole, Cyclohexanone, NMR, Reaction intermediate
A Calculation of Baryon Diffusion Constant in Hot and Dense Hadronic Matter Based on an Event Generator URASiMA
We evaluate thermodynamical quantities and transport coefficients of a dense
and hot hadronic matter based on an event generator URASiMA (Ultra-Relativistic
AA collision Simulator based on Multiple Scattering Algorithm). The statistical
ensembles in equilibrium with fixed temperature and chemical potential are
generated by imposing periodic boundary condition to the simulation of URASiMA,
where energy density and baryon number density is conserved. Achievement of the
thermal equilibrium and the chemical equilibrium are confirmed by the common
value of slope parameter in the energy distributions and the saturation of the
numbers of contained particles, respectively. By using the generated ensembles,
we investigate the temperature dependence and the chemical potential dependence
of the baryon diffusion constant of a dense and hot hadronic matter.Comment: 15 pages, 5 figures, LaTeX2
Microscopic Models for Ultrarelativistic Heavy Ion Collisions
In this paper, the concepts of microscopic transport theory are introduced
and the features and shortcomings of the most commonly used ansatzes are
discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics
(UrQMD) transport model is described in great detail. Based on the same
principles as QMD and RQMD, it incorporates a vastly extended collision term
with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin
is explicitly treated for all hadrons. The range of applicability stretches
from GeV/nucleon, allowing for
a consistent calculation of excitation functions from the intermediate energy
domain up to ultrarelativistic energies. The main physics topics under
discussion are stopping, particle production and collective flow.Comment: 129 pages, pagestyle changed using US letter (8.5x11 in) format. The
whole paper (13 Mb ps file) could also be obtained from
ftp://ftp.th.physik.uni-frankfurt.de/pub/urqmd/ppnp2.ps.g
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Capture from pair production as a beam loss mechanism for heavy ions at RHIC
Electron capture from electron-positron pair production is predicted to be a major source of beam loss for the heaviest ions at RHIC. Achieving the highest luminosity thus requires an understanding of the capture process. The authors report measurements of this process at Brookhaven National Laboratory`s AGS using 10.8 GeV/nucleon Au{sup 79+} projectiles on Au targets. Capture from pair production is a process in which the very high electromagnetic field involved in the collision of two relativistic heavy ions results in the production of an electron-positron pair with the capture of the electron by one of the ions. There are many theoretical papers published on capture from pair production with discrepancies between predicted cross sections. The experimental results are compared to theory and to previous experiments at 1 GeV/nucleon. The implications of extrapolations to RHIC energies are presented
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