Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical

We present an experimental study of the {\em nonlinear} susceptibility of Mn$_{12}$ single-molecule magnets. We investigate both their thermal-equilibrium and dynamical nonlinear responses. The equilibrium results show the sensitivity of the nonlinear susceptibility to the magnetic anisotropy, which is nearly absent in the linear response for axes distributed at random. The nonlinear dynamic response of Mn$_{12}$ was recently found to be very large and displaying peaks reversed with respect to classical superparamagnets [F. Luis {\em et al.}, Phys. Rev. Lett. {\bf 92}, 107201 (2004)]. Here we corroborate the proposed explanation -- strong field dependence of the relaxation rate due to the detuning of tunnel energy levels. This is done by studying the orientational dependence of the nonlinear susceptibility, which permits to isolate the quantum detuning contribution. Besides, from the analysis of the longitudinal and transverse contributions we estimate a bound for the decoherence time due to the coupling to the phonon bath.Comment: 13 pages, 8 figures, resubmitted to Phys. Rev. B with minor change

Large quantum nonlinear dynamic susceptibility of single-molecule magnets

The nonlinear dynamical response of Mn$_{12}$ single-molecule magnets is experimentally found to be very large, quite insensitive to the spin-lattice coupling constant, and displaying peaks reversed with respect to classical superparamagnets. It is shown that these features are caused by the strong field dependence of the relaxation rate due to the detuning of energy levels between which tunneling takes place. The nonlinear susceptibility technique, previously overlooked, is thus proposed as a privileged probe to ascertain the occurrence of quantum effects in mesoscopic magnetic systems.Comment: 4 pages, 4 figure

Temperature dependence of antiferromagnetic susceptibility in ferritin

We show that antiferromagnetic susceptibility in ferritin increases with temperature between 4.2 K and 180 K (i. e. below the N\'{e}el temperature) when taken as the derivative of the magnetization at high fields ($30\times10^4$ Oe). This behavior contrasts with the decrease in temperature previously found, where the susceptibility was determined at lower fields ($5\times10^4$ Oe). At high fields (up to $50 \times10^4$ Oe) the temperature dependence of the antiferromagnetic susceptibility in ferritin nanoparticles approaches the normal behavior of bulk antiferromagnets and nanoparticles considering superantiferromagnetism, this latter leading to a better agreement at high field and low temperature. The contrast with the previous results is due to the insufficient field range used ($< 5 \times10^4$ Oe), not enough to saturate the ferritin uncompensated moment.Comment: 7 pages, 7 figures, accepted in Phys. Rev.

Eficacia de finasterida en el tratamiento de la hematuria asociada a la hiperplasia protática benigna

La hematuria es una complicación de la hiperplasia benigna de próstata (HBP), tanto en su evolución natural como durante el seguimiento post cirugía prostática. En el estudio de Mebust et al., de 3000 pacientes sometidos a prostactectomía por Hiperplasia prostática benigna (HBP), en el 12 % la presencia de hematuria fue la causa de esta indicación quirúrgica (1). Existen escasas referencias de la acción de la finasterida ante dicho síntoma (2-7), aunque los resultados publicados hasta el momento demuestran un efecto terapéutico precoz y estable mientras dura el tratamient

Characterizing sampling and quality screening biases in infrared and microwave limb sounding

This study investigates orbital sampling biases and evaluates the additional impact caused by data quality screening for the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and the Aura Microwave Limb Sounder (MLS). MIPAS acts as a proxy for typical infrared limb emission sounders, while MLS acts as a proxy for microwave limb sounders. These biases were calculated for temperature and several trace gases by interpolating model fields to real sampling patterns and, additionally, screening those locations as directed by their corresponding quality criteria. Both instruments have dense uniform sampling patterns typical of limb emission sounders, producing almost identical sampling biases. However, there is a substantial difference between the number of locations discarded. MIPAS, as a mid-infrared instrument, is very sensitive to clouds, and measurements affected by them are thus rejected from the analysis. For example, in the tropics, the MIPAS yield is strongly affected by clouds, while MLS is mostly unaffected. The results show that upper-tropospheric sampling biases in zonally averaged data, for both instruments, can be up to 10 to 30 %, depending on the species, and up to 3 K for temperature. For MIPAS, the sampling reduction due to quality screening worsens the biases, leading to values as large as 30 to 100 % for the trace gases and expanding the 3 K bias region for temperature. This type of sampling bias is largely induced by the geophysical origins of the screening (e.g. clouds). Further, analysis of long-term time series reveals that these additional quality screening biases may affect the ability to accurately detect upper-tropospheric long-term changes using such data. In contrast, MLS data quality screening removes sufficiently few points that no additional bias is introduced, although its penetration is limited to the upper troposphere, while MIPAS may cover well into the mid-troposphere in cloud-free scenarios. We emphasize that the results of this study refer only to the representativeness of the respective data, not to their intrinsic quality

Capital social y democracia: explorando normas, valores y redes sociales en el Perú

Propone estudiar el funcionamiento de la sociedad civil peruana desde la perspectiva del capital social, concepto cuyo uso se ha conocido durante la última década tanto en el campo académico como en el de los organismos multilaterales. Contiene cuatro capítulos. En el primero, se examina críticamente la compleja trayectoria que ha seguido el concepto de capital social desde que comenzó a ser empleado en las Ciencias Sociales. El segundo capítulo, analiza las características y limitaciones más importantes de un tipo de organizaciones voluntarias que encuentran en los valores religiosos de la caridad cristiana su principal fuente de inspiración. El tercero estudia las estrategias colectivas y el tipo de liderazgo que desarrollan las organizaciones vecinales en su búsqueda por conseguir una vivienda digna. El cuarto capítulo intenta identificar los principales obstáculos que enfrentan las Comunidades Locales de Administración de Salud para conseguir que la población participe y esté adecuadamente representada en la gestión de este tipo de establecimientos. Finalmente, se formulan algunas reflexiones a la luz de los capítulos anteriores

Deformidad vertebral y mielomeningocele: actitud terapéutica y resultados

Presentamos nuestra experiencia en el tratamiento quirúrgico de la deformidad vertebral relacionada con el mielomeningocele entre los años 1972 y 1995. En ese período un total de 48 pacientes fueron intervenidos. Se han evaluado las condiciones generales previas, el estado prequirúrgico, las diversas modalidades de instrumentación y el resultado de las mismas, así como el tipo y número de complicaciones. Durante el período posquirúrgico inmediato hemos encontrado un porcentaje de infecciones del 68%. Sin embargo, el resultado final, tanto del equilibrio pélvico como del vertebral conseguido, no estuvo influenciado significativamente por esta complicación. El tipo de patología, las complicaciones generales derivadas de la misma, el tiempo quirúrgico empleado y las pérdidas sanguíneas, son condiciones estrechamente relacionadas con el número de infecciones encontradas.We present our experience on the surgical treatment of myelomeningocelelinked vertebral deformity between 1972 and 1995. We evaluated the previous general condition, the presurgical status, the instrument modalities and their outcome, as well as the type and number of complications in a series of 48 patients. During the immediate postoperative period, we found a 68% infection rate. However, the end result for pelvic as well as vertebral balance was not influenced significantly by this complication. The number of infections found is closely linked to the specific pathology, the complications, duration of operation, and blood loss