1,960 research outputs found
Riemannian Geometry of Noncommutative Surfaces
A Riemannian geometry of noncommutative n-dimensional surfaces is developed
as a first step towards the construction of a consistent noncommutative
gravitational theory. Historically, as well, Riemannian geometry was recognized
to be the underlying structure of Einstein's theory of general relativity and
led to further developments of the latter. The notions of metric and
connections on such noncommutative surfaces are introduced and it is shown that
the connections are metric-compatible, giving rise to the corresponding Riemann
curvature. The latter also satisfies the noncommutative analogue of the first
and second Bianchi identities. As examples, noncommutative analogues of the
sphere, torus and hyperboloid are studied in detail. The problem of covariance
under appropriately defined general coordinate transformations is also
discussed and commented on as compared with other treatments.Comment: 28 pages, some clarifications, examples and references added, version
to appear in J. Math. Phy
Deconfinement transition in protoneutron stars: analysis within the Nambu-Jona-Lasinio model
We study the effect of color superconductivity and neutrino trapping on the
deconfinement transition of hadronic matter into quark matter in a protoneutron
star. To describe the strongly interacting matter a two-phase picture is
adopted. For the hadronic phase we use different parameterizations of a
non-linear Walecka model which includes the whole baryon octet. For the quark
matter phase we use an Nambu-Jona-Lasinio effective model which
includes color superconductivity. We impose color and flavor conservation
during the transition in such a way that just deconfined quark matter is
transitorily out of equilibrium with respect to weak interactions. We find that
deconfinement is more difficult for small neutrino content and it is easier for
lower temperatures although these effects are not too large. In addition they
will tend to cancel each other as the protoneutron star cools and deleptonizes,
resulting a transition density that is roughly constant along the evolution of
the protoneutron star. According to these results the deconfinement transition
is favored after substantial cooling and contraction of the protoneutron star
Statistical models of mixtures with a biaxial nematic phase
We consider a simple Maier-Saupe statistical model with the inclusion of
disorder degrees of freedom to mimic the phase diagram of a mixture of rod-like
and disc-like molecules. A quenched distribution of shapes leads to the
existence of a stable biaxial nematic phase, in qualitative agreement with
experimental findings for some ternary lyotropic liquid mixtures. An annealed
distribution, however, which is more adequate to liquid mixtures, precludes the
stability of this biaxial phase. We then use a two-temperature formalism, and
assume a separation of relaxation times, to show that a partial degree of
annealing is already sufficient to stabilize a biaxial nematic structure.Comment: 11 pages, 2 figure
Virtual environments to cope with anxiety situations: Two case-studies
Anxiety is a growing problem in modern societies. Virtual reality has been widely adopted to treat anxiety and more severe psychological problems. We have been working on an approach that involves compelling virtual environments (VE) to treat anxiety. These VE recreate a particular situation and support in real-time the intervention of the therapist. Public domain software tools and a simple projection screen have been used. This paper describes two interactive applications that simulate VE to help people coping with particular anxiety situations. One of the applications is developed in Blender and is dedicated to the fear of talking in front of an audience; the other application is developed in OpenSim and is devoted to the fear of driving inside a tunnel.info:eu-repo/semantics/acceptedVersio
Shelf life extension of Ricotta cheese using coatings of galactomannans from nonconventional sources incorporating nisin against Listeria monocytogenes
Shelf life extension of Ricotta cheese was evaluated at 4 °C upon the use of edible coatings made of galactomannans from Gleditsia triacanthos incorporating nisin against Listeria monocytogenes. Three different treatments were tested in cheese: samples without coating; samples with coating without nisin; and samples with coating containing 50 IU·g−1 of nisin. To test the effectiveness of the treatments against L. monocytogenes, the surface of the cheese was inoculated with a suspension of the microorganism. Microbiological and physical−chemical analyses of the cheese samples were performed during 28 days. Results showed that the cheese coated with nisin-added galactomannan film was the treatment presenting the best results in terms of microbial growth delay (p < 0.05). The addition of nisin also affects (p < 0.05) the physical and mechanical properties of the films: O2 permeability decreased from 1.84 to 1.35 × 10−12 cm3·(Pa·s·m)−1; CO2 permeability increased from 1.96 to 6.31 × 10−12 cm3·(Pa·s·m)−1; opacity increased from 3.68 to 4.59%; tensile strength ranged from 0.84 to 1.46 MPa; and elongation at break improved from 50.93 to 68.16%. These results demonstrate that novel galactomannan-based edible coatings, when combined with nisin, may provide consumer-friendly alternatives to reduce L. monocytogenes postcontamination on cheese products during storage.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil)Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/32566/2006, SFRH/BD/23897/200
Effect of the application of a galactomannan coating incorporating nisin on the growth of Listeria monocytogenes on Ricotta cheese
Antimicrobial packaging, besides protecting the product from the external environment, inhibits
or delays microorganism growth in foods and meets the actual demand of consumers for
healthier foods, containing less additives (Lopez‐Rubio, Gavara, & Lagaron, 2006).
Cheese is a ready‐to‐eat type of food that has been associated with foodborne listeriosis. Listeria
monocytogenes is an important ubiquitous foodborne pathogen which may contaminate foods at
pre‐ and post‐harvest stages of production. To overcome this problem bacteriocins could be
entrapped in a suitable edible coating applied to food. Nisin is an antimicrobial peptide produced
by Lactococcus lactis subsp. lactis. and research studies have revealed its ability to inhibit the
growth of some pathogenic bacteria (Sobrino‐López, & Martín‐Belloso, 2008).
The aim of this study was to evaluate the antimicrobial activity of coatings of galactomannans
from Gleditsia triacanthos incorporating nisin against L. monocytogenes during storage of Ricotta
cheese at 4 °C.
Three different treatments were tested: a control with no coating; a sample with coating
containing no nisin and a coating with 50 IU.g‐1 of nisin. Samples of cheese (20 g) were immersed
in 0.5 % w/v galactomannan solution containing glycerol (as plasticizer) (1.5 % v/v). To test the
effectiveness of the treatments Ricotta cheese samples were surface‐inoculated with a solution
containing approximately 1×106 CFU.ml‐1 of L. monocytogenes. Microbiological and physicalchemical
parameters (color change, pH, moisture content and weight loss) were monitored over
28 days for cheese stored at 4 ºC.
Among the three treatments, the combination of coating and nisin showed the best results,
followed by the coating containing no nisin. Counts of L. monocytogenes were lower (p<0.05) in
nisin‐containing coating that in no‐coated cheese. The nisin‐containing coating presented a
reduction from 5.1 to 4.4 log CFU.g‐1 after 2 days of storage. For samples coated with nisin,
reductions of 2.2 log CFU.g‐1 were achieved for samples after 7 days of storage.
These results suggest that the application of these coatings could be a potential food packaging
solution for the release of nisin in view of the control of L. monocytogenes spoilage in cheese
Volume Fractions of the Kinematic "Near-Critical" Sets of the Quantum Ensemble Control Landscape
An estimate is derived for the volume fraction of a subset in the neighborhood
of the critical set
of the kinematic quantum ensemble control landscape J(U) = Tr(U\rho U' O),
where represents the unitary time evolution operator, {\rho} is the initial
density matrix of the ensemble, and O is an observable operator. This estimate
is based on the Hilbert-Schmidt geometry for the unitary group and a
first-order approximation of . An upper bound on these
near-critical volumes is conjectured and supported by numerical simulation,
leading to an asymptotic analysis as the dimension of the quantum system
rises in which the volume fractions of these "near-critical" sets decrease to
zero as increases. This result helps explain the apparent lack of influence
exerted by the many saddles of over the gradient flow.Comment: 27 pages, 1 figur
A serious game-based solution to prevent bullying
This paper presents a Serious Game with the main purpose of inducing attitude changes as a way to prevent bullying, in a target audience of young people between 10 and 12 years old. The rationale for prevention is: first, to help victims of these aggressive episodes to acquire or improve competencies in avoiding or dealing with future real bullying situations; and, second, to promote empathy towards the victims in bystanders. A back office application complements the game, providing substantial assistance to psychologists while using the game with patients in therapy or in research work. Both components, the game and the back office, were evaluated with volunteers. The user study lead us to the conclusion that the current version of the game holds good potential in bullying prevention: the young people that played the game in a continuous time span, at the end of this testing process have expressed improvements in their bullying prevention strategies. The back office application was positively assessed by the psychologists who tested it.
The game deals with strong social features, such as number of friends and invitations to social events (e.g. a birthday party), to which young people give much importance. Additionally, it offers a variability of scenarios and consequences of actions, taking into account the user's performance in the game. The main factors that make the presented solution stand out in comparison with other similar bullying prevention solutions are mainly the following: it includes a back office application to assist therapists with data management features; the role of the player in the game can be chosen accordingly to his own profile; it is possible to play even outside a therapy session (e.g. at home) and it is a portable solution.info:eu-repo/semantics/acceptedVersio
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