4,874 research outputs found
SO(4,C)-covariant Ashtekar-Barbero gravity and the Immirzi parameter
An so(4,C)-covariant hamiltonian formulation of a family of generalized
Hilbert-Palatini actions depending on a parameter (the so called Immirzi
parameter) is developed. It encompasses the Ashtekar-Barbero gravity which
serves as a basis of quantum loop gravity. Dirac quantization of this system is
constructed. Next we study dependence of the quantum system on the Immirzi
parameter. The path integral quantization shows no dependence on it. A way to
modify the loop approach in the accordance with the formalism developed here is
briefly outlined.Comment: 14 pages, LATEX; minor changes; misprints corrected; commutator of
two secondary second class constraints correcte
The Husain-Kuchar Model: Time Variables and Non-degenerate Metrics
We study the Husain-Kuchar model by introducing a new action principle
similar to the self-dual action used in the Ashtekar variables approach to
Quantum Gravity. This new action has several interesting features; among them,
the presence of a scalar time variable that allows the definition of geometric
observables without adding new degrees of freedom, the appearance of a natural
non-degenerate four-metric and the possibility of coupling ordinary matter.Comment: LaTeX, 22 pages, accepted for publication in Phys. Rev.
The structure of the distortion free-energy density in nematics: second-order elasticity and surface terms
Alignment transition in a nematic liquid crystal due to field-induced breaking of anchoring
We report on the alignment transition of a nematic liquid crystal from
initially homeotropic to quasi-planar due to field-induced anchoring breaking.
The initial homeotropic alignment is achieved by Langmuir-Blodgett monolayers.
In this geometry the anchoring strength can be evaluated by the Frederiks
transition technique. Applying an electric field above a certain threshold
provokes turbulent states denoted DSM1 and DSM2. While DSM1 does not affect the
anchoring, DSM2 breaks the coupling between the surface and the liquid crystal:
switching off the field from a DSM2 state does not immediately restore the
homeotropic alignment. Instead, we obtain a quasi-planar metastable alignment.
The cell thickness dependence for the transition is related to theComment: 7 pages, LaTeX2e article, 4 figures, 7 EPS files, added references,
accepted for publication in Europhysics Letter
Design for Healthcare Sustainability: Ethical implications of eco-design research
The growing interest in environmental sustainability is the result of a new cultural awareness focused on the holistic conceptions of wellbeing and justice. However, this attention is also moved by economic considerations. The increasing awareness of the environmental impacts of medical treatments is a prompting example: the optimization of resource consumption and the reduction of wastes can lead to huge economic and environmental benefits. However, sustainable solutions might arise problems with regard to the patients’ well- being. When talking about eco-sustainability, the ethics of design is usually considered as implicit; however this carries the risk of not being able to create a system that is ethically right.
This study aimed to examine a practice-based approach to ethics in design projects addressing environmental sustainability in the healthcare field. Combining different theoretical approaches from bioethics, environmental and design ethics, this research determined a set of practical guidelines for the implementation and assessment of ethics into design practice.
We investigated the responsibilities of design towards all the stakeholders involved, on the basis of the Bivins’ bioethical obligation items. Then, the ethical implications were analysed by the definition of possible scenarios, starting from the Triple Bottom Line theory. Starting from these scenarios, the design team was involved in internal brainstorming sessions to define the personal motivations and ethical limits within the project. This enabled the creation of a detailed set of guidelines in the form of open questions. This approach has been applied to a case study on hemodialysis sustainability, that allowed to test this ethical approach
Reality Conditions and Ashtekar Variables: a Different Perspective
We give in this paper a modified self-dual action that leads to the
-ADM formalism without having to face the difficult second class
constraints present in other approaches (for example if one starts from the
Hilbert-Palatini action). We use the new action principle to gain some new
insights into the problem of the reality conditions that must be imposed in
order to get real formulations from complex general relativity. We derive also
a real formulation for Lorentzian general relativity in the Ashtekar phase
space by using the modified action presented in the paper.Comment: 22 pages, LATEX, Preprint CGPG-94/10-
Nuclear masses, deformations and shell effects
We show that the Liquid Drop Model is best suited to describe the masses of
prolate deformed nuclei than of spherical nuclei. To this end three Liquid Drop
Mass formulas are employed to describe nuclear masses of eight sets of nuclei
with similar quadrupole deformations. It is shown that they are able to fit the
measured masses of prolate deformed nuclei with an RMS smaller than 750 keV,
while for the spherical nuclei the RMS is, in the three cases, larger than 2000
keV. The RMS of the best fit of the masses of semi-magic nuclei is also larger
than 2000 keV. The parameters of the three models are studied, showing that the
surface symmetry term is the one which varies the most from one group of nuclei
to another. In one model, isospin dependent terms are also found to exhibit
strong changes. The inclusion of shell effects allows for better fits, which
continue to be better in the prolate deformed nuclei regionComment: 10 pages, 8 tables, Proc. of the XXXIV Nuclear Physics Symposium,
January 4-7 2011, Cocoyoc, Morelos, Mexico. IOP Journal of Physics:
Conference Series (in press
Minisuperspace Examples of Quantization Using Canonical Variables of the Ashtekar Type: Structure and Solutions
The Ashtekar variables have been use to find a number of exact solutions in
quantum gravity and quantum cosmology. We investigate the origin of these
solutions in the context of a number of canonical transformations (both complex
and real) of the basic Hamiltonian variables of general relativity. We are able
to present several new solutions in the minisuperspace (quantum cosmology)
sector. The meaning of these solutions is then discussed.Comment: 23 pages, latex, 3 figures (uuencoded, separate file
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