5,094 research outputs found
Matrix Big Brunch
Following the holographic description of linear dilaton null Cosmologies with
a Big Bang in terms of Matrix String Theory put forward by Craps, Sethi and
Verlinde, we propose an extended background describing a Universe including
both Big Bang and Big Crunch singularities. This belongs to a class of exact
string backgrounds and is perturbative in the string coupling far away from the
singularities, both of which can be resolved using Matrix String Theory. We
provide a simple theory capable of describing the complete evolution of this
closed Universe.Comment: 15 pages, no figures. References adde
Developing student competence through peer assessment: the role of feedback, self-regulation and evaluative judgement
© 2019, The Author(s). How can students’ competence be developed through peer assessment? This paper focuses on how relevant variables such as participation, evaluative judgement and the quality of the assessment interact and influence peer assessment. From an analysis of 4 years of data from undergraduate classes in project management, it develops a model of causal relationships validated using the PLS-SEM method. It demonstrates relationships between these variables and considerers the influence of students’ competence and the mediating nature of feedback and self-regulation on the process. It points to how peer assessment practices can be improved whilst highlighting how evaluative judgement and feedback are two key elements that can be addressed to deliver the effective development of students’ competence
Chiral perturbation theory for nonzero chiral imbalance
We construct the most general low-energy effective lagrangian including local parity violating terms parametrized by an axial chemical potential or chiral imbalance mu (5), up to O mml:mfenced close=")" open="("p4 ml:mfenced> order in the chiral expansion for two light flavours. For that purpose, we work within the Chiral Perturbation Theory framework where only pseudo-NGB fields are included, following the external source method. The O mml:mfenced close=")" open="("p2 mml:mfenced> lagrangian is only modified by constant terms, while the O mml:mfenced close=")" open="("p4 mml:mfenced one includes new terms proportional to mu 52 and new low-energy constants (LEC), which are renormalized and related to particular observables. In particular, we analyze the corrections to the pion dispersion relation and observables related to the vacuum energy density, namely the light quark condensate, the chiral and topological susceptibilities and the chiral charge density, providing numerical determinations of the new LEC when possible. In particular, we explore the dependence of the chiral restoration temperature T-c with mu (5). An increasing T-c(mu (5)) is consistent with our fits to lattice data of the ChPT-based expressions. Although lattice uncertainties are still large and translate into the new LEC determination, a consistent physical description of those observables emerges from our present work, providing a theoretically robust model-independent framework for further study of physical systems where parity-breaking effects may be relevant, such as heavy-ion collisions
The Magnetic Field of the H~II Region NGC 6334A
We have studied the polarization characteristics and Faraday rotation of the
extragalactic radio source J172043554, that appears projected on the north
lobe of the galactic H II region NGC 6334A. From observations made with the
Very Large Array at 6.0 and 3.6 cm in three different epochs (1994, 1997, and
2006), we estimate a rotation measure of +5100900 rad m for the
extragalactic source. This large rotation measure implies a line-of-sight
average magnetic field of G, the largest
obtained by this method for an H II region. NGC 6334A is significantly denser
than other H II regions studied and this larger magnetic field is expected on
the grounds of magnetic flux conservation. The ratio of thermal to magnetic
pressure is 5, in the range of values determined for more diffuse H II
regions.Comment: 5 pages, 0 figure
Composition operators on the algebra of Dirichlet series
The algebra of Dirichlet series consists on
those Dirichlet series convergent in the right half-plane and
which are also uniformly continuous there. This algebra was recently introduced
by Aron, Bayart, Gauthier, Maestre, and Nestoridis. We describe the symbols
giving rise to bounded composition
operators in and denote this
class by . We also characterise when the operator
is compact in . As a
byproduct, we show that the weak compactness is equivalent to the compactness
for . Next, the closure under the local uniform convergence
of several classes of symbols of composition operators in Banach spaces of
Dirichlet series is discussed. We also establish a one-to-one correspondence
between continuous semigroups of analytic functions in the class
and strongly continuous semigroups of composition
operators , ,
. We conclude providing examples showing the
differences between the symbols of bounded composition operators in
and the Hardy spaces of Dirichlet series
and
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