Standard General Relativity from Chern-Simons Gravity

Chern-Simons models for gravity are interesting because they provide with a truly gauge-invariant action principle in the fiber-bundle sense. So far, their main drawback has largely been the perceived remoteness from standard General Relativity, based on the presence of higher powers of the curvature in the Lagrangian (except, remarkably, for three-dimensional spacetime). Here we report on a simple model that suggests a mechanism by which standard General Relativity in five-dimensional spacetime may indeed emerge at a special critical point in the space of couplings, where additional degrees of freedom and corresponding "anomalous" Gauss-Bonnet constraints drop out from the Chern-Simons action. To achieve this result, both the Lie algebra g and the symmetric g-invariant tensor that define the Chern-Simons Lagrangian are constructed by means of the Lie algebra S-expansion method with a suitable finite abelian semigroup S. The results are generalized to arbitrary odd dimensions, and the possible extension to the case of eleven-dimensional supergravity is briefly discussed.Comment: 6 pages, no figures; v2: published versio

Euler Chern Simons Gravity from Lovelock Born Infeld Gravity

In the context of a gauge theoretical formulation, higher dimensional gravity invariant under the AdS group is dimensionally reduced to Euler-Chern-Simons gravity. The dimensional reduction procedure of Grignani-Nardelli [Phys. Lett. B 300, 38 (1993)] is generalized so as to permit reducing D-dimensional Lanczos Lovelock gravity to d=D-1 dimensions.Comment: 6 pages, no figures, accepted for publication in Phys. Lett.

Osteocondroma intra-raquideo con afectación neurológica

Se presenta el caso de un varón de 16 años con lumbalgia consecutiva a traumatismo vertebral, sin hallazgo s radiológicos, que no mejoraba con tratamient o conservador, y que a las 5 semanas desarrolló un cuadro de paraparesia e incontinencia de esfínteres indicativo de afectación del cono medular. En el estudio mielográfico se objetivó bloqueo completo a nivel de Ll. La tomografía axial mostró una imagen sugestiva de osteocondroma intraraquídeo, que s e confirmó quirúrgicamente . Dos año s tras la intervención, se logró la total recuperación neurológica. Se destaca la rareza de la lesión, la dificultad diagnóstica, y la probable etiología traumática de la tumoración.A 16-year-old man with no improvement of low back pain after vertebral trauma conservatively treated and without radiological findings is presented. Five weeks after trauma, the patient developed paraparesia and fecal and urinary incontinence indicating compression of the medullary conus. A complet e stop of the contrast at Ll level wa s found in the myelographi c study. The CT-Scan showed an image suggesting osteochondroma whic h wa s confirmed a r surgery. Complet e neurogical recover y w a s achieved 2 year s after surgical treatment. The rare character of the lesion, the dificulty for diagnosis and the probable traumatic etiology of this tumor is discussed

Report of the NAFO Precautionary Approach Working Group (PA-WG)

The meeting was opened by the co-Chairs Fernando González-Costas and Steven Cadrin at 09:00 hours (Atlantic Daylight Time in Halifax, Nova Scotia) on Thursday, 19 May 2022

Report of the NAFO Joint Commission-Scientific Council Working Group on Risk-Based Management Strategies (WG-RBMS) Meeting

The meeting was opened by the co-Chairs Fernando González-Costas (European Union) and Ray Walsh (Canada) at 09:30 hours (UTC/GMT -3 hours in Halifax, Nova Scotia) on Wednesday, 17 August 2022

Quality of the Surveys Information in Relation with the Greenland Halibut Assessment of Subarea 2 and Divisions 3KLMNO

The aim of this paper is to provide a study of the quality of the surveys information in relation with the Greenland halibut assessment of the NAFO Subarea 2 and Divisions 3KLMNO. The surveys abundance correlation within surveys, between surveys and XSA showed that the surveys had many difficulties to track ages older than 6 years. For Flemish Cap survey and Canadian Spring Survey, the problem to track these ages could be principally the depth coverage of the surveys, but for the other surveys this lack of tracking could be due to different reasons as age reading inconsistencies and changes in catchability of these ages in the surveys

Effect of intrinsic defects on the thermal conductivity of PbTe from classical molecular dynamics simulations

Despite being the archetypal thermoelectric material, still today some of the most exciting advances in the efficiency of these materials are being achieved by tuning the properties of PbTe. Its inherently low lattice thermal conductivity can be lowered to its fundamental limit by designing a structure capable of scattering phonons over a wide range of length scales. Intrinsic defects, such as vacancies or grain boundaries, can and do play the role of these scattering sites. Here we assess the effect of these defects by means of molecular dynamics simulations. For this we purposely parametrize a Buckingham potential that provides an excellent description of the thermal conductivity of this material over a wide temperature range. Our results show that intrinsic point defects and grain boundaries can reduce the lattice conductivity of PbTe down to a quarter of its bulk value. By studying the size dependence we also show that typical defect concentrations and grain sizes realized in experiments normally correspond to the bulk lattice conductivity of pristine PbTe

Achieving NAFO Convention Objectives with a Precautionary Approach Framework

The Precautionary Approach Working Group (PA-WG) developed recommendations for designing a Precautionary Approach Framework that is expected to meet the objectives of the NAFO Convention. The objectives and general principles of the NAFO Convention can be achieved by a Precautionary Approach Framework in addition to other NAFO processes to minimize bycatch, catch by lost/abandoned gear, pollution and waste from fishing. The PA-WG recommends that the Precautionary Approach Framework should: 1) promote rebuilding of depleted stocks toward the stock biomass associated with maximum sustainable yield (BMSY), 2) account for scientific uncertainty through buffer reference points or other risk-based approaches, 3) develop limit reference points for stock biomass (Blim) and fishing mortality (Flim) that are consistent with each other, 4) Blim should be based on sustainability and reduced productivity where possible, and 5) reference points should be re-evaluated when the available information on productivity substantially changes, there is evidence of a productivity regime shift, or management procedures based on re-evaluated reference points are demonstrated to perform better for meeting NAFO’s objectives. All options considered for a revised Precautionary Approach Framework should be simulation tested to determine if management measures set in accordance with the framework are expected to achieve the following objectives: a very low risk of stock depletion (i.e., B<Blim), effectively rebuild stocks to BMSY, maintain stocks above BMSY more often than not, and maintain average catches of approximately MSY in the long-term

Report of the Scientific Council Meeting 27 July 2022

Scientific Council reviewed and finalized the working paper drafted by the Precautionary Approach Working Group (PA-WG). The final draft of this working paper, which will be presented to the Precautionary Approach workshop (15-16 August 2022) and WG-RBMS (17-19 August 2022), is attached to this report as Appendix I

Serial No. N7262 NAFO COM-SC Doc. 22-01 Northwest Atlantic Fisheries Organization Report of the NAFO Working Group on Improving Efficiency of NAFO Working Group Process (E-WG) Meeting, 22 February 2022

Report of the NAFO Working Group on Improving Efficiency of NAFO Working Group Process (E-WG) Meeting held by WebEx 22 February 2022Versión del editor