Current rectification in a single molecule diode: the role of electrode coupling

We demonstrate large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 10^5 A/cm^2. By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes

Numerical simulation of strongly nonlinear and dispersive waves using a Green-Naghdi model

We investigate here the ability of a Green-Naghdi model to reproduce strongly nonlinear and dispersive wave propagation. We test in particular the behavior of the new hybrid finite-volume and finite-difference splitting approach recently developed by the authors and collaborators on the challenging benchmark of waves propagating over a submerged bar. Such a configuration requires a model with very good dispersive properties, because of the high-order harmonics generated by topography-induced nonlinear interactions. We thus depart from the aforementioned work and choose to use a new Green-Naghdi system with improved frequency dispersion characteristics. The absence of dry areas also allows us to improve the treatment of the hyperbolic part of the equations. This leads to very satisfying results for the demanding benchmarks under consideration

Profilaxis antibiótica en cirugía

Existe una abundantísima documentación en la literatura acerca de la eficacia de los antibióticos utilizados profilácticamente en cirugía (1-10). Probablemente lo más útil para el trabajo diario de un hospital sea la adopción de pautas concretas que permitan ser evaluadas periódicamente a través de la colaboración, entre otros, de anestesistas, cirujanos y microbiólogos (11,12). En esta línea hemos revisado, de una manera intencionadamente esquemática, diversas facetas relativas a la profilaxis antibiótica en cirugía. Para ello comentaremos algunos aspectos generales de profilaxis de la infección postquirúrgica, unas breves normas para la utilización profiláctica de antibióticos y resumiremos determinadas indicaciones en función del tipo de intervención

Trasplante pancreático

Diabetes mellitus is a health concern of the first order, given the high level of associated morbidity and mortality. The objective, in order to slow down the advance of its complications before they become irreversible, is based on correct metabolic control. The high rate of morbidity associated with the surgery of the vascularized pancreas transplant and the high index of rejection have for three decades formed an obstacle to this being considered a valid alternative in the treatment of these patients. Nowadays the pancreas transplant has come to occupy a key position, thanks to the new regimes of immunosuppression and to the perfection of surgical techniques. In this article we review the evolution of the pancreas transplant from its beginnings to its present state

Hydrochemical characterization of a mine water geothermal energy resource in NW Spain

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behavior of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22 °C) and increases with depth, so, considering the available flow (> 100 L s− 1), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use

Magnetite mineralization inside cross-linked protein crystals

Crystallization in confined spaces is a widespread process in nature that also has important implications for the stability and durability of many man-made materials. It has been reported that confinement can alter essential crystallization events, such as nucleation and growth and, thus, have an impact on crystal size, polymorphism, morphology, and stability. Therefore, the study of nucleation in confined spaces can help us understand similar events that occur in nature, such as biomineralization, design new methods to control crystallization, and expand our knowledge in the field of crystallography. Although the fundamental interest is clear, basic models at the laboratory scale are scarce mainly due to the difficulty in obtaining well-defined confined spaces allowing a simultaneous study of the mineralization process outside and inside the cavities. Herein, we have studied magnetite precipitation in the channels of cross-linked protein crystals (CLPCs) with different channel pore sizes, as a model of crystallization in confined spaces. Our results show that nucleation of an Fe-rich phase occurs inside the protein channels in all cases, but, by a combination of chemical and physical effects, the channel diameter of CLPCs exerted a precise control on the size and stability of those Fe-rich nanoparticles. The small diameters of protein channels restrain the growth of metastable intermediates to around 2 nm and stabilize them over time. At larger pore diameters, recrystallization of the Fe-rich precursors into more stable phases was observed. This study highlights the impact that crystallization in confined spaces can have on the physicochemical properties of the resulting crystals and shows that CLPCs can be interesting substrates to study this process

Acceso venoso central mediante cápsulas de inyección subcutáneas. Serie de 124 dispositivos

Presentamos una serie de 111 pacientes (límites: 9 meses - 78 años) en los que se colocaron 124 dispositivos como modalidad de acceso venoso central. Se analizan las complicaciones aparecidas durante su utilización, que actualmente sobrepasa los 1.100 meses, y se comentan aspectos técnicos de colocación con influencia sobre la morbilidad del sistema. La media actual de funcionamiento se sitúa en 9,9 meses por persona, con una tasa de complicaciones del 19 %

Sistemas de acceso venoso central (SAVC) en pacientes pediátricos. Experiencia de seis años

The need for an access to the venous system, in order to infuse chemotherapeutic treatments or parenteral nutrition, has increased the number of central venous access systems (CVAS) implanted in the past years. Between February 1985 and December 1990, 87 devices were implanted in 76 patients (from 11 months to 15 years of age), with a median function time of 349 days (range: 7 to 1887 days). The overall incidence of complications was 0.10 per 10 days of catheterization, with complication rates for infection and thrombosis of 0.02 and 0.03, respectively. Nineteen systems were removed because of complications and 11 because of completion of the treatment. Of the cases, 97.7% included a follow-up period. The present study confirms the advantages of these devices, with a long working life and a low complication rate, being a good alternative for chronically ill children requiring long-term and/or cyclic intravenous therapy

Totally Laparoscopic Roux-en-Y Duct-to-Mucosa Pancreaticojejunostomy After Middle Pancreatectomy A Consecutive Nine-case Series at a Single Institution

To present the results of a series of laparoscopic middle pancreatectomies with roux-en-Y duct-to-mucosa pancreaticojejunostomy. SUMMARY OF BACKGROUND DATA: Middle pancreatectomy makes it possible to preserve pancreatic parenchyma in the resection of lesions that traditionally have been treated by distal splenopancreatectomy or cephalic duodenopancreatectomy. The laparoscopic approach could minimize the invasiveness of the procedure and enhance the benefits of middle pancreatectomy. METHODS: From March 2005 to October 2007, 9 consecutive patients with benign or low malignant potential lesions in the pancreatic neck or body underwent surgery. Laparoscopic middle pancreatectomy with a roux-en-Y duct-to-mucosa pancreaticojejunostomy was planned on all of them. In the first 2 patients, the pancreas was transected by endostapler; in the last 7, the staple line was reinforced with absorbable polymer membrane. RESULTS: The intervention was concluded laparoscopically in every case except 1 (laparoscopic-assisted) in which pancreaticojejunostomy was performed by means of minilaparotomy. Mortality was 0% and perioperative morbidity was 33%, (fistula of the cephalic stump in the first 2 patients (22%)). The pancreaticojejunostomy fistula rate was 0%. The median postoperative hospital stay was 5 days (range, 3-41). In the last 7 patients, in which pancreas was transected with staple line reinforcement material there were no stump fistulas; morbidity decreased to 14% and the median hospital stay was 4 days (range, 3-30). CONCLUSIONS: Laparoscopic middle pancreatectomy is feasible and safe. Duct-to-mucosa pancreaticojejunostomy can be performed safely using this approach. The method of pancreatic transection seems to be decisive in the incidence of cephalic stump fistulas