37,772 research outputs found
Production of thermal photons in viscous fluid dynamics with temperature-dependent shear viscosity
We compute the spectrum of thermal photons created in Au+Au collisions at
GeV, taking into account dissipative corrections in
production processes corresponding to the quark--gluon plasma and hadronic
phases. To describe the evolution of the fireball we use a viscous fluid
dynamic model with different parametrizations for the temperature--dependence
of . We find that the spectrum significantly depends on the values of
in the QGP phase, and is almost insensitive to the values in the
hadronic phase. We also compare the influence of the temperature--dependence of
on the spectrum of thermal photons to that of using different
equations of state in the fluid dynamic simulations, finding that both effects
are of the same order of magnitude.Comment: 16 pages, 4 figures. Accepted for publication in Mod. Phys. Lett.
Chaotic behavior of the Compound Nucleus, open Quantum Dots and other nanostructures
It is well established that physical systems exhibit both ordered and chaotic
behavior. The chaotic behavior of nanostructure such as open quantum dots has
been confirmed experimentally and discussed exhaustively theoretically. This is
manifested through random fluctuations in the electronic conductance. What
useful information can be extracted from this noise in the conductance? In this
contribution we shall address this question. In particular, we will show that
the average maxima density in the conductance is directly related to the
correlation function whose characteristic width is a measure of energy- or
applied magnetic field- correlation length. The idea behind the above has been
originally discovered in the context of the atomic nucleus, a mesoscopic
system. Our findings are directly applicable to graphene.Comment: 10 pages, 5 figures. Contribution to: "4th International Workshop on
Compound-Nuclear Reactions and Related Topics (CNR*13)", October 7-11, 2013,
Maresias, Brazil. To appear in the proceeding
Obtaining a class of Type N pure radiation metrics using invariant operators
We develop further the integration procedure in the generalised invariant
formalism, and demonstrate its efficiency by obtaining a class of Petrov type N
pure radiation metrics without any explicit integration, and with comparatively
little detailed calculations. The method is similar to the one exploited by
Edgar and Vickers when deriving the general conformally flat pure radiation
metric. A major addition to the technique is the introduction of non-intrinsic
elements in generalised invariant formalism, which can be exploited to keep
calculations manageable.Comment: This work was presented in July 2004, in the Gr17 meeting held in
Dublin-Irelan
Modelling a layer for real-time management of interactions in web based distance learning
In the last few years, the University of Aveiro, Portugal, has been offering several distance learning courses
over the Web, using e-learning platforms.
Experience showed that different editions of a same course, using the same contents and structure, and having
similar target learners, had different success rates. What would be the reason for that?
A hypothesis was considered: The level of success could be directly related with the remote follow-up of the
learners’ participation in the courses; the best results usually occur when the follow-up is closer.
The existing e-learning platforms offer and the standardization works being developed by organizations and
consortiums like IMS (IMS Global Learning Consortium, Inc), ADL SCORM (Advanced Distributed Learning
Sherable Content Object Reference Model), IEEE LTSC LOM (Institute of Electrical and Electronic Engineers
Learning Technologies Standard Committee Learning Object Metadata), ARIADNE (ARIADNE Foundation
for the European Knowledge Pool), AICC CMI (Aviation Industry CBT Committee Computer Managed
Instruction), etc, don’t cover the course monitorization concerns mentioned. Those projects were focused on
aspects like contents and its delivery in the context of the execution of the courses’ activities. This is even
true in the SCORM project that doesn’t include any reference to the management of the e-learning processes.
Recently, in the context of the IMS Global Consortium, a new project designated IMS LD (Learning Design) is
under development, providing a framework for the description of learning units under a three level model. In
the most recently defined level, the C level, some functionalities related to notifications were proposed,
expressing similar concerns to the ones that triggered our research. However, the extent at which IMS LD
takes the functionalities is, from our point of view, not complete.
This article describes a proposal of a reference model and functionalities towards a specification of a layer for
real-time management of user interactions on LMSs, and its possible integration with the ADL SCORM
standard proposal. The paper includes a discussion of the management metadata model for the LMS
sub-system and how the integration of the management module under SCORM may be achieved
Enhancing web supported learning in higher education by adding a management layer to LMSs
There are many situations in the e-Learning experiences
that can compromise the success of the courses. Many
times simple reasons are great enough to motivate people
to abandon them. For example, if someone does not
execute a programmed activity inside the defined window
of time, it can compromise the rest of the course to that
person. In such situations it would be important that the
teacher knew about the situation in useful time, to be able
to take any corrective action.
Another example could be presented, involving the
professor and the learners. Let us assume that an activity
A2 is programmed to be executed by the learners and that
it depends on the previous knowledge of the result of the
evaluation of a work submitted by the learners to the
teacher (activity A1). If the teacher doesn’t inform the
learners about their classification in useful time, that can
compromise the execution of the activity A2.
It seems to be necessary to use mechanisms of automatic
management, in real time, of the envolvement of each
participant in a distance learning course using LMS
(Learning Management System). Such a functionality
allows the detection of deviations to the scheduled
activities planned for each actor. If it is the case, the
referred mechanism can initiate the process of sending
notifications to the relevant entities, enabling the
correction of these deviations.
Several organizations and consortiuns, involving the
industry, governmental institutions and universities, are
developing projects of standardization. It seemed
important to us to see how the referred aspects were
covered by those projects, and to perceive how it could be
possible to articulate our work with the ones that are
available from these organizations and consortiuns.
This article describes the work that the authors are
developing towards the specification of a layer for
real-time management of user interactions with LMSs,
during the operationalization of a course, and also
includes a management meta-data model, related to that
management layer
A note on the predictions of models with modular flavor symmetries
Models with modular flavor symmetries have been thought to be highly predictive. We point out that these predictions are subject to corrections from non–holomorphic terms in the Lagrangean. Specifically, in the models discussed in the literature, the Kähler potential is not fixed by the symmetries, for instance. The most general Kähler potential consistent with the symmetries of the model contains additional terms with additional parameters, which reduce the predictive power of these constructions. We also comment on potential ways of how one may conceivably retain the predictivity
Generalized enthalpy model of a high pressure shift freezing process
High-pressure freezing processes are a novel emerging technology in food processing, offering significant improvements to the quality of frozen foods. To be able to simulate plateau times and thermal history under different conditions, in this work we present a generalized enthalpy model of the high-pressure shift freezing process. The model includes the effects of pressure on conservation of enthalpy and incorporates the freezing point depression of non-dilute food samples. In addition the significant heat transfer effects of convection in the pressurizing medium are accounted for by solving the two-dimensional Navier-Stokes equations. We run the model for several numerical tests where the food sample is agar gel, and find good agreement with experimental data from the literature
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