Gravitational Lensing by Asymptotically Flat Wormholes

Natural wormholes and its astrophysical signatures have been sugested in various oportunities. By applying the strong field limit of gravitational lensing theory, we calculate the deflection angle and magnification curves produced by Morris-Thorne wormholes in asimptotically flat space-times. The results show that wormholes act like convergent lenses. Therefore, we show that it is hard to distinguish them from black holes using the deflection's angle of the gravitational lens effect, in contrast with the results reported by Cramer et.al. and Safanova et.al. However, we also show that it is possible, in principle, distinguish them by the magnification curves, in particular, by observing the position of the peak of the Einstein's ring.Comment: 9 pages, 14 figure

Decision-making Tools and Memetic Algorithms in Management and Linear Programming Problems

Operational Research uses a set of tools based on scientific research principles to achieve rational and meaningful management decisions. This article tries to give solution to a highly complex Linear Programming problem by using Simplex method, Solver and a hybrid prototype which combines the theories of Genetic Algorithms with a new local search heuristic technique. Hybridization of these two techniques is becoming known as Memetic Algorithm. Additionally, this article tries to present different techniques to support management decision-making, with the intention of being used increasingly in the business environment sustaining, thus, decisions by mathematics or artificial intelligence and not only by experience.quantitative management; quantitative methods; decision-making; linear programming; operational research; heuristics; hybrid methods; memetic algorithms.

El accionar del Estado en la construcción de mercados hortícolas no formales de la Agricultura Familiar como estrategia de comercialización y desarrollo local/ O papel do Estado na construção de mercados informais de hortaliças basados na agricultura familiar como estratégia de comercialização e desenvolvimento local

En la región periurbana de la ciudad de Bahía Blanca (Provincia de Buenos Aires), a lo largo de la cuenca baja del río Sauce Chico, hay un cinturón hortícola compuesto por productores con diferentes características tecnológicas y sociales (lugar de origen, suministro de productos, área de producción, nivel tecnológico, experiencia en el campo), que distingue diferentes tipos sociales agrarios. En este contexto, el presente estudio se centra en los pequeños agricultores que practican la agricultura familiar y que comercializan su producción a través de diferentes canales según sus posibilidades (acceso al lugar de comercialización, volumen y diversidad de productos, capacidad de negociación). El objetivo de este trabajo (un avance de tesis doctoral) es describir y comprender la lógica operativa de los diferentes canales de comercialización utilizados por los respectivos agricultores, con énfasis en los mercados no formales, analizando el papel del Estado en ellos, a través de las instituciones públicas. o mediante políticas orientadas a este sector productivo. El objetivo es estudiar cómo las acciones estatales pueden promover la producción y ofrecer alternativas de comercialización a los agricultores familiares. El marco conceptual que se aborda corresponde a las diferentes teorías de estado, políticas públicas, teoría de redes de institucionalización, entre otras. La metodología utilizada consiste en estudios cualitativos, a través de entrevistas semiestructuradas realizadas con técnicos de campo, funcionarios de instituciones públicas, agentes municipales, y mapeando la red de los protagonistas involucrados en este espacio. Además, hay una revisión y análisis de la documentación bibliográfica recopilada hasta el momento, que complementa la información obtenida durante el trabajo de camp

Enthalpy and the Mechanics of AdS Black Holes

We present geometric derivations of the Smarr formula for static AdS black holes and an expanded first law that includes variations in the cosmological constant. These two results are further related by a scaling argument based on Euler's theorem. The key new ingredient in the constructions is a two-form potential for the static Killing field. Surface integrals of the Killing potential determine the coefficient of the variation of the cosmological constant in the first law. This coefficient is proportional to a finite, effective volume for the region outside the AdS black hole horizon, which can also be interpreted as minus the volume excluded from a spatial slice by the black hole horizon. This effective volume also contributes to the Smarr formula. Since the cosmological constant is naturally thought of as a pressure, the new term in the first law has the form of effective volume times change in pressure that arises in the variation of the enthalpy in classical thermodynamics. This and related arguments suggest that the mass of an AdS black hole should be interpreted as the enthalpy of the spacetime.Comment: 21 pages; v2 references adde

An International Perspective on Chronic Multimorbidity: Approaching the Elephant in the Room

Multimorbidity is a common and burdensome condition that may affect quality of life, increase medical needs, and make people live more years of life with disability. Negative outcomes related to multimorbidity occur beyond what we would expect from the summed effect of single conditions, as chronic diseases interact with each other, mutually enhancing their negative effects, and eventually leading to new clinical phenotypes. Moreover, multimorbidity mirrors an accelerated global susceptibility and a loss of resilience, which are both hallmarks of aging. Due to the complexity of its assessment and definition, and the lack of clear evidence steering its management, multimorbidity represents one of the main current challenges for clinicians, researchers, and policymakers. The authors of this article recently reflected on these issues during two twin international symposia at the 2016 European Union Geriatric Medicine Society (EUGMS) meeting in Lisbon, Portugal, and the 2016 Gerontological Society of America (GSA) meeting in New Orleans, USA. The present work summarizes the most relevant aspects related to multimorbidity, with the ultimate goal to identify knowledge gaps and suggest future directions to approach this condition

Leprosy & gangrene: A rare association; role of anti phospholipid antibodies

BACKGROUND: Leprosy still remains an important public health problem for many parts of the world. An association of gangrene with leprosy is a rare one & can have a number of causative mechanisms. We present a case with Leprosy & gangrene with positive anti phopholipid antibody titers. CASE PRESENTATION: A 50-year-old non-diabetic, non-hypertensive lady presented with 2 months history of progressive gangrene of bilateral toes. She was found to have madarosis & hypopigmented, hypoaesthetic macular lesions on the upper limb & thighs. Bilateral ulnar & popliteal nerves were thickened. A skin biopsy of the lesions revealed borderline tuberculoid leprosy, slit skin smears revealed a bacteriological index of 1+. She did not have any evidence of thromboembolic episode or atherosclerosis. ACLA was positive at presentation & also on another occasion 6 weeks later. ACLAs were of the IgM type on both occasions. Lupus Anticoagulant & β2 GPI antibody were negative. DOPPLER of the lower limb arteries did not reveal any abnormality. Patient was successfully treated with multi-drug antileprotics & anticoagulants. CONCLUSION: Infectious APLAs should be recognized as a cause of thrombosis in Leprosy. Appropriate anticoagulation can salvage limb function

Strong field gravitational lensing in scalar tensor theories

Strong field gravitational lensing in the Brans-Dicke theory has been studied. The deflection angle for photons passing very close to the photon sphere is estimated for the static spherically symmetric space-time of the theory and the position and magnification of the relativistic images are obtained. Modeling the super massive central object of the galaxy by the Brans-Dicke space-time, numerical values of different strong lensing observable are estimated. It is found that against the expectation there is no significant scalar field effect in the strong field observable lensing parameters. This observation raises question on the potentiality of the strong field lensing to discriminate different gravitational theories.Comment: 20 pages, accepted in Class. Quantum Grav., final versio

Geometrothermodynamics of the Kehagias-Sfetsos Black Hole

The application of information geometric ideas to statistical mechanics using a metric on the space of states, pioneered by Ruppeiner and Weinhold, has proved to be a useful alternative approach to characterizing phase transitions. Some puzzling anomalies become apparent, however, when these methods are applied to the study of black hole thermodynamics. A possible resolution was suggested by Quevedo et al. who emphasized the importance of Legendre invariance in thermodynamic metrics. They found physically consistent results for various black holes when using a Legendre invariant metric, which agreed with a direct determination of the properties of phase transitions from the specific heat. Recently, information geometric methods have been employed by Wei et al. to study the Kehagias-Sfetsos (KS) black hole in Horava-Lifshitz gravity. The formalism suggests that a coupling parameter in this theory plays a role analogous to the charge in Reissner-Nordstrom (RN) black holes or angular momentum in the Kerr black hole and calculation of the specific heat shows a singularity which may be interpreted as a phase transition. When the curvature of the Ruppeiner metric is calculated for such a theory it does not, however, show a singularity at the phase transition point. We show that the curvature of a particular Legendre invariant ("Quevedo") metric for the KS black hole is singular at the phase transition point. We contrast the results for the Ruppeiner, Weinhold and Quevedo metrics and in the latter case investigate the consistency of taking either the entropy or mass as the thermodynamic potential.Comment: v2: some references adde