7,783 research outputs found
Nuclear interactions with modern three-body forces lead to the instability of neutron matter and neutron stars
It is shown that the neutron matter interacting through Argonne V18
pair-potential plus modern variants of Urbana or Illinois three-body forces is
unstable. For the energy of neutrons , which interact through these
forces, we prove mathematically that ,
where is a constant. This means that: (i) the energy per particle and
neutron density diverge rapidly for large neutron numbers; (ii) bound states of
neutrons exist for large enough. The neutron matter collapse is
possible due to the form of the repulsive core in three-body forces, which
vanishes when three nucleons occupy the same site in space. The old variant of
the forces Urbana VI, where the phenomenological repulsive core does not vanish
at the origin, resolves this problem. We prove that to prevent the collapse one
should add a repulsive term to the Urbana IX potential, which should be larger
than 50 MeV when 3 nucleons occupy the same spatial position
Multimedia transcription of think-aloud data on the L2 reading process
Es geht um die methodologische Frage, wie sich Laut-Gedachtes transkribieren lĂ€sst, wenn Fremdsprachensprecher englischsprachige Texte lesen. Obwohl hĂ€ufig angewendet, scheint dieses Verfahren nicht grĂŒndlich ausgearbeitet zu sein; allzu oft wird es gar den Standards der schriftlichen Mitteilung angepasst. Anhand dreier Beispiele geht dieser Text auf die Besonderheiten ein, die Videoaufzeichnungen in diesem Kontext mit sich bringen. Am Ende steht der Vorschlag, nicht nur verbale und non-verbale Kommunikation aufzuzeichnen, sondern zusammen damit weitere AktivitĂ€ten wĂ€hrend des Lesens in einem multimedialen Transkript zu erfassen.This paper focuses on the methodological problem of precisely and concisely transcribing think-aloud data on the EFL reading process. Although the use of think-aloud protocols is widely spread in L2 reading strategy research, the respective methods of transcription do not seem to be refined to the necessary degree. All too often, transcripts of think-aloud during L2 reading have been produced according to standards of written language only. Using three empirical examples from a study on the EFL reading process as mental action (Schramm 2001), this paper explores the specific transcription challenges posed by videotaped think-aloud data on L2 reading. From a discourse analytical position, it suggests to not only transcribe verbal communication, but to also document aspects of non-verbal communication (e.g. gesturing and pointing) and actional activities (e.g. underlining and writing) during reading. In particular, it proposes to integrate related materials such as the read texts or the ctsâ notes as well as videos of gestures and recordings of voices into a multimedia transcript
Quark core impact on hybrid star cooling
In this paper we investigate the thermal evolution of hybrid stars, objects
composed of a quark matter core, enveloped by ordinary hadronic matter. Our
purpose is to investigate how important are the microscopic properties of the
quark core to the thermal evolution of the star. In order to do that we use a
simple MIT bag model for the quark core, and a relativistic mean field model
for the hadronic envelope. By choosing different values for the microscopic
parameters (bag constant, strange quark mass, strong coupling constant) we
obtain hybrid stars with different quark core properties. We also consider the
possibility of color superconductivity in the quark core. With this simple
approach, we have found a set of microscopic parameters that lead to a good
agreement with observed cooling neutron stars. Our results can be used to
obtain clues regarding the properties of the quark core in hybrid stars, and
can be used to refine more sophisticated models for the equation of state of
quark matter.Comment: 8 pages, 10 figures. Accepted for publication in Physical Review
Stationarity of SLE
A new method to study a stopped hull of SLE(kappa,rho) is presented. In this
approach, the law of the conformal map associated to the hull is invariant
under a SLE induced flow. The full trace of a chordal SLE(kappa) can be studied
using this approach. Some example calculations are presented.Comment: 14 pages with 1 figur
Rotating Neutron Stars in a Chiral SU(3) Model
We study the properties of rotating neutron stars within a generalized chiral
SU(3)-flavor model. The influence of the rotation on the inner structure and
the hyperon matter content of the star is discussed. We calculate the Kepler
frequency and moments of inertia of the neutron star sequences. An estimate for
the braking index of the associated pulsars is given.Comment: 14 pages, 9 figure
Neutrino degeneracy and cosmological nucleosynthesis, revisited
A reexamination of the effects of non-zero degeneracies on Big Bang Nucleosynthesis is made. As previously noted, non-trivial alterations of the standard model conclusions can be induced only if excess lepton numbers L sub i, comparable to photon number densities eta sub tau, are assumed (where eta sub tau is approx. 3 times 10(exp 9) eta sub b). Furthermore, the required lepton number densities (L sub i eta sub tau) must be different for upsilon sub e than for upsilon sub mu and epsilon sub tau. It is shown that this loophole in the standard model of nucleosynthesis is robust and will not vanish as abundance and reaction rate determinations improve. However, it is also argued that theoretically (L sub e) approx. (L sub mu) approx. (L sub tau) approx. eta sub b is much less than eta sub tau which would preclude this loophole in standard unified models
From FAIR to RHIC, hyper clusters and an effective strange EoS for QCD
Two major aspects of strange particle physics at the upcoming FAIR and NICA
facilities and the RHIC low energy scan will be discussed. A new distinct
production mechanism for hypernuclei will be presented, namely the production
abundances for hypernuclei from 's absorbed in the spectator matter in
peripheral heavy ion collisions. As strangeness is not uniformly distributed in
the fireball of a heavy ion collision, the properties of the equation of state
therefore depend on the local strangeness fraction. The same, inside neutron
stars strangeness is not conserved and lattice studies on the properties of
finite density QCD usually rely on an expansion of thermodynamic quantities at
zero strange chemical potential, hence at non-zero strange-densities. We will
therefore discuss recent investigations on the EoS of strange-QCD and present
results from an effective EoS of QCD that includes the correct asymptotic
degrees of freedom and a deconfinement and chiral phase transition.Comment: Talk given at the international conference on Strangeness in Quark
Matter 2011 in Krako
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