Revisiting the asymptotic dynamics of General Relativity on AdS3_3

The dual dynamics of Einstein gravity on AdS$_3$ supplemented with boundary conditions of KdV-type is identified. It corresponds to a two-dimensional field theory at the boundary, described by a novel action principle whose field equations are given by two copies of the "potential modified KdV equation". The asymptotic symmetries then transmute into the global Noether symmetries of the dual action, giving rise to an infinite set of commuting conserved charges, implying the integrability of the system. Noteworthy, the theory at the boundary is non-relativistic and possesses anisotropic scaling of Lifshitz type.Comment: 18 page

Quasi-Exactly Solvable Spin 1/2 Schr\"odinger Operators

The algebraic structures underlying quasi-exact solvability for spin 1/2 Hamiltonians in one dimension are studied in detail. Necessary and sufficient conditions for a matrix second-order differential operator preserving a space of wave functions with polynomial components to be equivalent to a \sch\ operator are found. Systematic simplifications of these conditions are analyzed, and are then applied to the construction of several new examples of multi-parameter QES spin 1/2 Hamiltonians in one dimension.Comment: 32 pages, LaTeX2e using AMS-LaTeX packag

Performance and ownership in the governance of urban water

In this paper the differences in terms of performance between public and the private governance in urban water management are investigated. A statistical ranking is implemented to determine programmatic efficiency differences in DEA, using an incomplete panel data that gathers information on 20 water utilities in Andalusia, in Southern Spain. In the model, labour and operational costs are considered as inputs. The volume of revenue water, the number of connections and the network length are used as outputs. The analysis indicates that private management is more efficient. The efficiency indicators adjusted by a variable related to quality are estimated and demonstrate that privatization of the service does not mean any loss in terms of quality. However, there are no significant differences between both types of management including as a desirable input hydraulic yield as a proxy of the degree of network renovation. A lower hydraulic efficiency in private management would suggest that the need to make significant investments could be an important factor when making the decision to privatize the management of the urban water service: Water supply; Management; Local government;

AERODYNAMICS PERFORMANCES IN SPORTS

Aerodynamic forces are important in many racing sports and all those which use projectiles or any kind of ball. For all of them, the wind tunnel becomes one of the most efficient tools to improve the athlete performances and to coach as well. Coaching demands a lot of time wind tunnel occupancy, so its operating cost is very relevant. Advantages of specifically developed wind tunnels and possibilities of tests are discussed

On form-preserving transformations for the time-dependent Schr\"odinger equation

In this paper we point out a close connection between the Darboux transformation and the group of point transformations which preserve the form of the time-dependent Schr\"odinger equation (TDSE). In our main result, we prove that any pair of time-dependent real potentials related by a Darboux transformation for the TDSE may be transformed by a suitable point transformation into a pair of time-independent potentials related by a usual Darboux transformation for the stationary Schr\"odinger equation. Thus, any (real) potential solvable via a time-dependent Darboux transformation can alternatively be solved by applying an appropriate form-preserving transformation of the TDSE to a time-independent potential. The preeminent role of the latter type of transformations in the solution of the TDSE is illustrated with a family of quasi-exactly solvable time-dependent anharmonic potentials.Comment: LaTeX2e (with amsmath, amssymb, amscd, cite packages), 11 page

The cyclical trend of local public service governance: evidence from urban water management in Spain

The level of public and private involvement in economic activity in societies has changed over time. One may talk about the existence of a cyclical trend in which the most important periods of public governance are replaced by periods in which private management dominates the situation. This phenomenon may also be observed in local areas. Some authors have pointed out the existence of an alternation in the provision of municipal services, resulting in periods dominated by governance compared to other stages dominated by private management. In order to illustrate this cyclical trend at local level, this paper intends to analyze the evolution of the governance of the Spanish water supply since the mid-nineteenth century to the present day. Recent evidence from the industry suggests the possibility that we may currently be witnessing a further change in the trend.: Local Government, urban water supply, privatization, municipalization

CEO turnover in public and private organizations: analysis of the relevance of different performance horizons

Purpose – This paper investigates how past performance changes, prior CEO replacements and changes in the chairperson impact CEO turnover in public and large private businesses. Design/methodology/approach – We analyze 1,679 CEO replacements documented in a sample of 1,493 Spanish public and private firms during 1998–2004 by computing dynamic binary choice models that control for endogeneity in CEO turnovers. Findings – The results reveal that different performance horizons (short- and long-term) explain the dissimilar rate of CEO turnover between public and private firms. Private firms exercise monitoring patience and path dependency characterizes the evaluation of CEOs, while public companies’ short-termism leads to higher CEO turnover rates as a reaction to poor short-term economic results, and alternative controls—ownership and changes in the chairperson—improve the monitoring of management. Originality/value – Our results show the importance of controlling for path dependency to examine more accurately top executives’ performance. The findings confirm that exposure to market controls affects the functioning of internal controls in evaluating CEOs and shows a short-term performance horizon that could be behind the recent moves of public firms going private or restraining shareholders’ power.Peer ReviewedPostprint (published version

Modeling bone healing by boundary element method

El proceso de curación de fracturas es iniciado y regulado principalmente por los factores de crecimiento y por el entorno mecánico en el callo. Este fenómeno ha sido analizado desde un punto de vista biomecánico. La mayoría de los modelos computacionales están basados en el método de los elementos finitos y muchos de ellos estudian los niveles de tensiones y deformaciones producidos en los diferentes tejidos como el principal estímulo mecánico que afecta la diferenciación celular y el patrón de osificación ósea. En este trabajo se incorporó esa hipótesis en un entorno basado en el método de los elementos de contorno (BEM) para problemas axialmente simétricos. La idea principal es proponer el método de elementos de contorno como una alternativa atractiva a los métodos de dominio comúnmente utilizados en esta clase de problemas: diferencias finitas y elementos finitos. Los resultados obtenidos fueron cotejados con los reportados por la literatura comprobando la versatilidad y efectividad del método numérico propuesto. Como una primera aproximación, se realizó un análisis elástico-lineal para modelar los efectos de estimulación e inhibición que ejerce el estado de deformación sobre el proceso de diferenciación tisular, siguiendo la metodología propuesta por Claes and Heigele. Luego, en un modelo bifásico poroelástico en régimen estacionario, se incorpora la presión de poro como variable adicional dentro de la hipótesis, lo que permitió complementar las conclusiones hechas por Claes and Heigele. De esta manera, existe una nueva correlación de valores que permitirán a los modelos actuales comparar la evolución de propiedades tales como el modulo de elasticidad (E) y relación de Poisson (À), en base al estado de deformación presente en el modelo en análisis poroelásticos.Peer Reviewe