Quasi-pinning and entanglement in the lithium isoelectronic series

The Pauli exclusion principle gives an upper bound of 1 on the natural occupation numbers. Recently there has been an intriguing amount of theoretical evidence that there is a plethora of additional generalized Pauli restrictions or (in)equalities, of kinematic nature, satisfied by these numbers. Here for the first time a numerical analysis of the nature of such constraints is effected in real atoms. The inequalities are nearly saturated, or quasi-pinned. For rank-six and rank-seven approximations for lithium, the deviation from saturation is smaller than the lowest occupancy number. For a rank-eight approximation we find well-defined families of saturation conditions.Comment: 22 pages, 6 figures, minor changes, references adde

Una clase especial de Hipersuperficies parametrizadas por líneas de curvatura en R4

In this paper we study hypersurfaces in R4 parametrized by lines of curvature with three distinct principal curvatures and with Laplace invariants mji = mki = 0; mjik 6= 0 for i; j; k distinct fixed indices. We characterize locally a generic family of such hypersurfaces in terms of the principal curvatures and three vector valued functions of one variable, this family includes a classe of Dupin hypersurfaces. Moreover, weshow that these vector valued functions are invariant under inversions and homotheties.En este artículo estudiamos hipersuperficies en R4 parametrizadas por líneas de curvatura con tres curvaturas principales distintas y con invariantes de Laplace mji = mki = 0; mjik 6= 0 para índices fijos i; j; k distintos. Caracterizamos localmente una familia genérica de tales hipersuperficies en términos de las curvaturas principales y tres funciones vectoriales de una variable, esta familia incluye una clase de hipersuperficies de Dupin. Ademas, mostramos que estas funciones vectoriales son invariantes por inversiones y dilataciones

Quasipinning and selection rules for excitations in atoms and molecules

Postulated by Pauli to explain the electronic structure of atoms and molecules, the exclusion principle establishes an upper bound of 1 for fermionic natural occupation numbers {ni }. A recent analysis of the pure N-representability problem provides a wide set of inequalities for the {ni}, leading to constraints on these numbers. This has a strong potential impact on reduced density matrix functional theory as we know it. In this work we continue our study of the nature of these inequalities for some atomic and molecular systems. The results indicate that (quasi)saturation of some of them leads to selection rules for the dominant configurations in configuration interaction expansions, in favorable cases providing means for significantly reducing their computational requirements

Apropa't a la ciencia

Presentamos una propuesta didáctica que permite contextualizar la ciencia en la sociedad: el taller ¿Cómo será la ciencia del futuro? realizado durante la exposición “Apropa’t a la ciència”, realizada en el Palau Robert de Barcelona entre abril y junio del 2007. El taller promueve la creatividad y la reflexión sobre la actividad científica, así como el debate sobre la relación entre la ciencia y la sociedad, mediante la discusión de noticias que sean portada de periódico en el año 2060, creadas por grupos de estudiantes después de su visita a la exposición. Analizamos la percepción social de ciencia, la inclusión de aspectos sociales y los temas les resultan más atractivos a partir de sus producciones e ideas previas. Simultáneamente nos interesa indagar la existencia o no de diferencias atribuibles al género en las visiones del alumnado

Ecuación de Helmholtz generalizada

In this paper we introduce the generalized Helmholtz equation and present explicit solutions to this generalized Helmholtz equation, these solutions depend on three holomorphic functions. As an application we present explicit solutions to the Helmholtz equation. We note that these solutions are not necessarily limited to certain domains of the complex plane C.En este artículo introducimos la ecuación de Helmholtz generalizada y presentamos soluciones explícitas para esta ecuación de Helmholtz generalizada, estas soluciones dependen de tres funciones holomorfas. Como aplicación presentamos soluciones explícitas para la ecuación de Helmholtz. Observamos que estas soluciones nonecesariamente estan limitadas a ciertos dominios del plano complejo C

Hipersuperficies con líneas de curvatura planas en espacios euclideanos

In this work, we present explicit parameterizations of hypersurfaces parameterized by lines of curvature with prescribed Gauss map and we characterize the hypersurfaces with planar curvature lines. As an applicationwe obtain a classification of isothermic surfaces with respect to the third fundamental form with two planar curvature lines. Also, we present a class of surfaces with one family of planar curvature lines and generalize these results to present classes of hypersurfaces with families of planar curvature lines.En este trabajo, presentamos parametrizaciones explícitas de hipersuperficies parametrizadas por líneas de curvatura con aplicación de Gauss prescrita y caracterizamos las hipersuperficies con líneas de curvatura planas. Como aplicación obtenemos una clasificación de superficies isotérmicas con respecto a la tercera forma fundamental con dos líneas de curvatura planas. También, presentamos una clase de superficiescon una familia de líneas de curvatura plana y generalizamos estos resultados para presentar clases de hipersuperficies con familias de líneas de curvatura planas.

lean H2 and NH3 large production in Paraguay by the 14 GW Itaipu hydroelectric facility

This paper aims to present a feasibility study for clean production, storage and distribution of large amounts of hydrogen, starting from low-cost available renewable electrical energy. Paraguay and Brazil own equally the binational company ITAIPU Hydroelectric Plant (14 GW, about 96,000 GWh/year of production). 50% of this energy corresponds to Paraguay: however, since its energy demand is quite low, a large amount of this energy is sold to Brazil, receiving a compensation of 10 $/MWh. In this context, seeking for ways of adding value to generated electricity, this paper assesses the potential of clean H2 production by water electrolysis, simulating the use of one generator unit of the mentioned company (700 MW) and discussing two alternatives for the produced hydrogen: a) using it for ammonia production as base for fertilizers; b) using it for passenger cars. A detailed thermo-economic analysis is performed using a dedicated software developed by the authors. The results show that production is economically feasible for both cases, moreover the process is completely clean and significant amounts of oxygen are produced, potentially representing an additional revenue for the process