7,655 research outputs found
On 3+1 anti-de Sitter and de Sitter Lie bialgebras with dimensionful deformation parameters
We analyze among all possible quantum deformations of the 3+1 (anti)de Sitter
algebras, so(3,2) and so(4,1), which have two specific non-deformed or
primitive commuting operators: the time translation/energy generator and a
rotation. We prove that under these conditions there are only two families of
two-parametric (anti)de Sitter Lie bialgebras. All the deformation parameters
appearing in the bialgebras are dimensionful ones and they may be related to
the Planck length. Some properties conveyed by the corresponding quantum
deformations (zero-curvature and non-relativistic limits, space isotropy,...)
are studied and their dual (first-order) non-commutative spacetimes are also
presented.Comment: 7 pages. Communication presented in the XIII Int.Colloq. Integrable
Systems and Quantum Groups, June 17-19, 2004, Prague, Czech Republic. Some
misprints and dimensions of parameters have been fitte
Non-commutative relativistic spacetimes and worldlines from 2+1 quantum (anti-)de Sitter groups
The -deformation of the (2+1)D anti-de Sitter, Poincar\'e and de
Sitter groups is presented through a unified approach in which the curvature of
the spacetime (or the cosmological constant) is considered as an explicit
parameter. The Drinfel'd-double and the Poisson-Lie structure underlying the
-deformation are explicitly given, and the three quantum kinematical
groups are obtained as quantizations of such Poisson-Lie algebras. As a
consequence, the non-commutative (2+1)D spacetimes that generalize the
-Minkowski space to the (anti-)de Sitter ones are obtained. Moreover,
noncommutative 4D spaces of (time-like) geodesics can be defined, and they can
be interpreted as a novel possibility to introduce non-commutative worldlines.
Furthermore, quantum (anti-)de Sitter algebras are presented both in the known
basis related with 2+1 quantum gravity and in a new one which generalizes the
bicrossproduct one. In this framework, the quantum deformation parameter is
related with the Planck length, and the existence of a kind of "duality"
between the cosmological constant and the Planck scale is also envisaged.Comment: 25 pages. Updated version with more content, comments and reference
Self-assembly of triblock copolymers in aqueous solution
Indexación: ScieloThe aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072008000200013&lng=es&nrm=is
Benchmarking some Portuguese S&T system research units: 2nd Edition
The increasing use of productivity and impact metrics for evaluation and
comparison, not only of individual researchers but also of institutions,
universities and even countries, has prompted the development of bibliometrics.
Currently, metrics are becoming widely accepted as an easy and balanced way to
assist the peer review and evaluation of scientists and/or research units,
provided they have adequate precision and recall.
This paper presents a benchmarking study of a selected list of representative
Portuguese research units, based on a fairly complete set of parameters:
bibliometric parameters, number of competitive projects and number of PhDs
produced. The study aimed at collecting productivity and impact data from the
selected research units in comparable conditions i.e., using objective metrics
based on public information, retrievable on-line and/or from official sources
and thus verifiable and repeatable. The study has thus focused on the activity
of the 2003-06 period, where such data was available from the latest official
evaluation.
The main advantage of our study was the application of automatic tools,
achieving relevant results at a reduced cost. Moreover, the results over the
selected units suggest that this kind of analyses will be very useful to
benchmark scientific productivity and impact, and assist peer review.Comment: 26 pages, 20 figures F. Couto, D. Faria, B. Tavares, P.
Gon\c{c}alves, and P. Verissimo, Benchmarking some portuguese S\&T system
research units: 2nd edition, DI/FCUL TR 13-03, Department of Informatics,
University of Lisbon, February 201
Multi-q Pattern Classification of Polarization Curves
Several experimental measurements are expressed in the form of
one-dimensional profiles, for which there is a scarcity of methodologies able
to classify the pertinence of a given result to a specific group. The
polarization curves that evaluate the corrosion kinetics of electrodes in
corrosive media are an application where the behavior is chiefly analyzed from
profiles. Polarization curves are indeed a classic method to determine the
global kinetics of metallic electrodes, but the strong nonlinearity from
different metals and alloys can overlap and the discrimination becomes a
challenging problem. Moreover, even finding a typical curve from replicated
tests requires subjective judgement. In this paper we used the so-called
multi-q approach based on the Tsallis statistics in a classification engine to
separate multiple polarization curve profiles of two stainless steels. We
collected 48 experimental polarization curves in aqueous chloride medium of two
stainless steel types, with different resistance against localized corrosion.
Multi-q pattern analysis was then carried out on a wide potential range, from
cathodic up to anodic regions. An excellent classification rate was obtained,
at a success rate of 90%, 80%, and 83% for low (cathodic), high (anodic), and
both potential ranges, respectively, using only 2% of the original profile
data. These results show the potential of the proposed approach towards
efficient, robust, systematic and automatic classification of highly non-linear
profile curves.Comment: 12 pages, 7 figure
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