1,721,163 research outputs found
Symmetry energy and the isoscaling properties of the fragments in multifragmentation of 40Ca+58Ni, 40Ar+58Ni, and 40Ar+58Fe reactions
Full text linkThe symmetry energy and the isoscaling properties of the fragments produced in
multifragmentation of 40Ar, 40Ca + 58Fe, 58Ni reactions at 25, 33, 45 and 53
MeV/nucleon were investigated within the framework of a statistical multifragmentation
model. The isoscaling parameter, ������ from the hot primary and cold secondary fragment
yield distributions, was studied as a function of the excitation energy, isospin (neutronto-
proton asymmetry), and fragment symmetry energy.
Through changing the symmetry energy in the statistical multifragmentation
model to describe the experimental data, it is observed that the isoscaling parameter ������
decreases with increasing excitation energy and decreases with decreasing symmetry
energy. The parameter ������ is also observed to increase with increasing difference in the
isospin of the fragmenting system. The sequential decay of the primary fragments into
secondary fragments show very little influence on the isoscaling parameter when studied
as a function of excitation energy. However, the symmetry energy has a strong
influence on the isospin properties of the hot fragments. The results indicate that the
isospin properties of the fragments produced at high excitation energy and reduced
density in multifragmentation reactions are sensitive to the symmetry energy, indicating that the properties of hot nuclei at excitation energies, densities, and isospin away from
normal ground state nuclei are significantly different than those of normal (cold) nuclei
at saturation density
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Initial Conditions from Color Glass Condensate
Full text linkNuclei at very high energy, characterized by a saturation scale, can be described by an e���ective theory of Quantum ChromoDynamics (QCD) called Color Glass Condensates. The earliest phase of the collision of two nuclei is modeled as the collision of two sheets of color glass. The classical ���eld resulting from the collision then decays and equilibrates to a plasma of quarks and gluons. Using a recursive solution of the Yang-Mills equations, we calculate analytic expressions for the gluon ���eld created in ultra-relativistic heavy ion collisions at small times ��. We have worked out explicit solutions for the ���elds and the energy momentum tensor up to 4^th order in an expansion in �� . We generalize the existing calculations to go beyond the limit of large homogenous nuclei. This allows us to calculate radial and elliptic ���ow of gluon ���elds. The resulting transverse and longitudinal structure of the Poynting vector ���eld has a rich phenomenology. Besides the well known radial and elliptic ���ow in transverse direction, classical quantum chromodynamics predicts a rapidity-odd transverse ���ow that tilts the ���reball for non-central collisions, and it implies a characteristic ���ow pattern for collisions of non-symmetric systems A + B. The rapidity-odd transverse ���ow translates into a directed particle ���ow v_1 which has been observed at RHIC and LHC. The global ���ow ���elds in heavy ion collisions could be a powerful check for the validity of classical Yang-Mill dynamics in high energy collisions. We also propose a procedure to calculate the energy momentum tensor of gluon ���elds on an event-by-event basis. The matching of the initial ���eld energy momentum tensor to viscous hydrodynamic initial conditions is discussed and some preliminary results of a subsequent hydrodynamic evolution are shown. Our results can provide event-by-event initial conditions for hydrodynamic simulations of nuclear collisions that include initial flow and initial shear stress
Microscopic Nucleon-Nucleus Optical Potentials from Chiral Effective Field Theory
Full text linkIn this dissertation I focus on my work in the development of nucleon-nucleus optical potentials
calculated in the framework of many-body perturbation theory with nuclear forces from chiral
effective field theory. Building upon previous calculations of the nucleon optical potential in nuclear matter my goal was to construct a global nucleon-nucleus optical potential, suitable for nuclei across the nuclear chart. In the first two works, neutron- and proton-calcium optical potentials are calculated and analyzed. Comparisons are made to experimental data, phenomenology, and other microscopic approaches. The next step was constructing the first microscopic global optical potential. Comparisons are again made, and we find key departures from phenomenology that support the idea that microscopic calculations are better suited for exotic nuclei for which there are no experimental data. Fermi liquid theory, a related many-body topic, is discussed. I end with brief outlines of applications of the optical potential including nucleon spectral functions and effective masses
Superallowed β-Decay Branching Ratio Measurement of 26Si
Full text linkAs part of the continued effort to test the unitarity of the Cabbibo-Kobayashi-Maskawa
matrix, the branching ratio for the Tvz = -1 superallowed 0^+ → 0^+ positron-emitter ^26Si was
measured precisely for the first time. Since the QvEC value, 4840.86(10) keV, and half-life,
2245.3(7) ms, are known precisely, the branching ratio is all that is required to obtain a
precise ft value. This completes the second pair of mirror superallowed transitions, ^26Si → ^26mAl and 26mAl → ^26Mg. A previous measurement of the mirror transitions, ^38Ca → ^38mK
and ^38mK → ^38Ar, showed that the ratio of mirror ft-values is very sensitive to the model
used to calculate the small isospin symmetry-breaking corrections required to extract Vvud. In
calculating this correction, both Woods-Saxon and Hartree-Fock radial wave functions have
been used, with the experimental results from the first pair favoring Woods-Saxon. The
result for the A = 26 mirror pair demonstrates that this conclusion can be generalized
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fusion Reactions in Laser Produced Plasma
Full text linkThe investigation of fusion reactions in laser produced plasma has become of great interest since the development of ultra-short pulse lasers technique, which can enable the measurement of not well known fusion cross sections in plasmas and energy production via nuclear fusion reactions on a larger scale. Also, the direct measurement of fusion cross sections at low plasma temperatures might reveal some role for instance of electron screening. For all these reasons, the investigation of ion energy spectra to better understand the nuclear fusion process in a plasma plays a very important role. For a long period of time, however, only light elements such as Deuterium, Tritium, and 3^He have been studied for these applications because of the higher efficiency. In particular, the first generation fusion reactors built on Earth were based on the d-t system, in which the 80% of the fusion energy goes into the neutrons. Nevertheless, recent advances in this particular field of physics and the availability of high intensity laser facilities capable of delivering Petawatts of power into small volumes has opened the possibility to fuels based on neutron-less fusion reactions, like for example p-^11B. In this fusion reaction, energy is released mainly in charged alpha particles rather than neutrons, which makes easier the actual conversion and final utilization through various methods (i.e., induction or electrostatic effects). Such methods might be also of guidance for experiments where the plasma is highly compressed and heated such as at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (USA), and at the Omega facility at the Laboratory for Laser Energetics (LLE) of the University of Rochester (USA)
Measurement of the Michel parameter rho in muon decay
No full textThe TWIST Collaboration has measured the Michel parameter rho in normal muon
decay,u+ -> e+VeVu. In the standard model of particle physics,rho = 3/4. Deviations
from this value require mixing of left- and right-handed muon and electron couplings in
the muon-decay Lagrangian. We find rho = 0:75080+-0:00032(stat.)+-0:00097(syst.) +- 0:00023, where the last uncertainty represents the dependence of rho on the Michel
parameter n. This result sets new limits on the WL - WR mixing angle in left-right
symmetric models
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