Choice of Metrics used in Collaborative Filtering and their Impact on Recommender Systems

The capacity of recommender systems to make correct predictions is essentially determined by the quality and suitability of the collaborative filtering that implements them. The common memory-based metrics are Pearson correlation and cosine, however, their use is not always the most appropriate or sufficiently justified. In this paper, we analyze these two metrics together with the less common mean squared difference (MSD) to discover their advantages and drawbacks in very important aspects such as the impact when introducing different values of k-neighborhoods, minimization of the MAE error, capacity to carry out a sufficient number of predictions, percentage of correct and incorrect predictions and behavior when attempting to recommend the n-best items. The paper lists the results and practical conclusions that have been obtained after carrying out a comparative study of the metrics based on 135 experiments on the MovieLens database of 100,000 ratios

Alteraciones funcionales de la conjunción gastroesofágica en la escoliosis

Las posibles alteraciones funcionales de la conjunción gastroesofágica frecuentes en la escoliosis son de mecanismo no bien conocido. Con el objeto de conocer su incidencia y relación con las características de la curva escoliótica, posible origen y sus modificaciones con la corrección quirúrgica, se ha realizado un estudio radiológico de tránsito esofagogástrico, manometría esofágica y TAC en tres grupos de paciente escolióticos y un grupo control. En un grupo de 96 pacientes jóvenes con escoliosis existía un 27% de trastornos funcionales de la unión gastroesofágica frente a un 0% en el grupo control de 25 casos. El estudio estadístico de relación de variables más significativos demostró una mayor incidencia de estas alteraciones en las escoliosis torácicas que afectaban al segmento T7-T12 y cuando mayor era el ángulo de Cobb. En un grupo de 24 pacientes con escoliosis la corrección quirúrgica eliminó el reflujo gastroesofágico en 6 de los 7 casos sin modificaciones de los parámetros de estudio manométrico. El estudio con TAC en un grupo de 25 pacientes escolióticos, reveló una importante deformidad de los pilares diafragmáticos pero sin relación con el grado de rotación vertebral ni con las alteraciones digestivas estudiadas.Since the possible functional alterations of the gastroesophageal junction that are frecuent in scoliosis are not well known, Radiologic studies of the gastroesophageal passageway, esophageal manometric studies, and C. T. Scan Studies wer e perfomed in three groups of scoliotic patients and in one control group in order to determine the possible origin of the alterations, their incidenc e and the relationship with the characteristics of the scoliotic curve, and the modifications produced after surgical correction. Functional disorders of the gastroesophageal junction occur in 27% of the-96 young patients with scoliosis compared to 0% in the control group of 25 young individuals. The statiscal study of the most significant variables demonstrated a greater incidenc e of thes e gastroesophageal alterations in thoracic scoliosis that affected the vertebral segment T7-T12 and when the Angle of Cobb wa s larger. In a group of 24 scoliotic patients, the surgical correction of the scoliosis eliminated the GER (gastroesophageal Reflux) in 7 cases, without modifying the parametres of the manometri c study. In the C. T. Scan study, a group of 25 scoliotic patients showed an important distortion in the diaphragmatic crura, but no relationship wa s found between this and the degree of vertebral rotation nor with the digestive alterations which have been studied

Modeling long term Enhanced in situ Biodenitrification and induced heterogeneity in column experiments under different feeding strategies

Enhanced In situ Biodenitrification (EIB) is a capable technology for nitrate removal in subsurface water resources. Optimizing the performance of EIB implies devising an appropriate feeding strategy involving two design parameters: carbon injection frequency and C:N ratio of the organic substrate nitrate mixture. Here we model data on the spatial and temporal evolution of nitrate (up to 1.2 mM), organic carbon (ethanol), and biomass measured during a 342 day-long laboratory column experiment (published in Vidal-Gavilan et al., 2014). Effective porosity was 3% lower and dispersivity had a sevenfold increase at the end of the experiment as compared to those at the beginning. These changes in transport parameters were attributed to the development of a biofilm. A reactive transport model explored the EIB performance in response to daily and weekly feeding strategies. The latter resulted in significant temporal variation in nitrate and ethanol concentrations at the outlet of the column. On the contrary, a daily feeding strategy resulted in quite stable and low concentrations at the outlet and complete denitrification. At intermediate times (six months of experiment), it was possible to reduce the carbon load and consequently the C:N ratio (from 2.5 to 1), partly because biomass decay acted as endogenous carbon to respiration, keeping the denitrification rates, and partly due to the induced dispersivity caused by the well developed biofilm, resulting in enhancement of mixing between the ethanol and nitrate and the corresponding improvement of denitrification rates. The inclusion of a dual-domain model improved the fit at the last days of the experiment as well as in the tracer test performed at day 342, demonstrating a potential transition to anomalous transport that may be caused by the development of biofilm. This modeling work is a step forward to devising optimal injection conditions and substrate rates to enhance EIB performance by minimizing the overall supply of electron donor, and thus the cost of the remediation strategy.Peer ReviewedPostprint (author's final draft

What are the main factors influencing the presence of faecal bacteria pollution in groundwater systems in developing countries?

Groundwater is the major source of drinking water in most rural areas in developing countries. This resource is threatened by the potential presence of faecal bacteria coming from a variety of sources and pollution paths, the former including septic tanks, landfills, and crop irrigation with untreated, or insufficiently treated, sewage effluent. Accurately assessing the microbiological safety of water resources is essential to reduce diseases caused by waterborne faecal exposure. The objective of this study is to discern which are the most significant sanitary, hydrogeological, geochemical, and physical variables influencing the presence of faecal bacterial pollution in groundwater by means of statistical multivariate analyses. The concentration of Escherichia coli was measured in a number of waterpoints of different types in a rural area located in the coast of Kenya, assessing both a dry and a wet season. The results from the analyses reaffirm that the design of the well and their maintenance, the distance to latrines, and the geological structure of the waterpoints are the most significant variables affecting the presence of E. coli. Most notably, the presence of faecal bacteria in the study area correlates negatively with the concentration of ion Na+ (being an indirect indicator of fast recharge in the study site), and also negatively with the length of the water column inside the well.Peer ReviewedPostprint (author's final draft

Fractura luxación posterior de cadera asociada a fractura parcelar de la cabeza femoral: a propósito de un caso

La asociación de luxación posterior traumática de cadera con fractura de la cabeza femoral, es relativamente poco frecuente. Presentamos un varón de 33 años de edad que sufrió un accidente vial con resultado de luxación posterior asociada a fractura de la cabeza femoral craneal a la fovea centralis (tipo II de la clasificación de Pipkin). El tratamiento realizado fue una reducción abierta sin osteosíntesis, dentro de las seis primeras horas. A los dos años el paciente camina con mínina claudicación y sin dolor. El ultimo estudio radiográfico realizado no muestra signos de necrosis cefálica. Pensamos que en estas lesiones, cuando la reducción cerrada no es posible, la realización de una reducción abierta puede ser suficiente para la aposición del fragmento sin necesidad de llevar a cabo ninguna osteosíntesis.The posterior traumatic dislocation of the hip associated to femoral head fracture is an unfrequent lesion. The present report describe a 33-year-old man who sustained a traffic accident with posterior dislocation of the hip associated to a marginal fracture of the femoral head located cranealy to the fovea centralis (tipe two of Pipkin's clasification). Open reduction and inmovilization was performed. At 2-year follow-up the patient is walking with slight limp and no pain. At this time, radiographic evaluation showed no signs of cephalic necrosis. In this tipe of traumatic lesions, when closed reduction is unsuccesfull, open reduction can be an adequate alternative treatment to reduce the cephalic fragment without any osteosinthesis

El codo flotante en el niño: opciones terapéuticas y complicaciones

La fractura simultánea ipsilateral del húmero y de uno o ambos huesos del antebrazo, llamada también "codo flotante", es una entidad poco frecuente, siendo escasa la literatura al respecto. En este artículo se describe nuestra experiencia con este tipo de lesiones en el paciente pediátrico, así como sus complicaciones asociadas y las distintas opciones de tratamiento. El tratamiento del codo flotante es actualmente controvertido en cuanto a su indicación y la técnica quirúrgica a emplear. También existe controversia con respecto a la mayor incidencia de complicaciones en este tipo de lesiones.Simultaneous ipsilateral fracture of the humerus and one or both bones of the forearm, also called "floating elbow" is a rare entity, with little literature. This article describes our experience with this type of injury in the pediatric patient and their associated complications and treatment options. The floating elbow treatment is currently controversial in terms of indications and surgical technique to use. There is also controversy over the increased incidence of complications in this type of injury

Fracturas de la extremidad distal del fémur: tratamiento quirúrgico versus tratamiento ortopédico

Se estudiaron los resultados obtenidos en 72 fracturas de la extremidad distal del fémur según el tipo de tratamiento (quirúrgico o conservador) en 70 pacientes. De ellos, 23 fueron mujeres y 47 varones, con una edad media de 50 años. El tipo más frecuente fue la supracondílea no conminuta (42%). En 40 casos (56%) se registraron lesiones concomitantes, con un total de 48 fracturas asociadas. En 2 casos la fractura fue bilateral. Veinticuatro fracturas fueron tratadas en forma ortopédica (sistema de tracción-suspensión o vendaje enyesado) y 48 mediante cirugía. La técnica quirúrgica realizada consistió en reducción abierta y fijación interna en 47 casos (21 casos placa atornillada, 17 con placa AO y 9 con placa DCS). Los resultados se valoraron según los criterios de Schatzker, Horne y Wadell. Hubo un 71% de resultados excelente y bueno, con diferencia significativa entre ambos tratamientos (54% para el tratamiento ortopédico y 74% para el quirúrgico, p < 0,01). Se produjeron un total de 17 complicaciones: infección profunda en 6 casos, deformidad residual en 6, anquilosis en 4 y fracaso de la osteosíntesis en 2. El tratamiento quirúrgico tiene mejores resultados que el tratamiento ortopédico, que debe quedar limitado a fracturas clavadas en pacientes osteoporóticos o en aquellos casos, en los que se contraindique la cirugía.The results obtained in 72 fractures of the distal femur in 70 patients were assessed with regard to the treatment type, surgical or conservative. There were 23 women and 47 men, with a 50 year-old mean age. The most frequent type of fracture was the supracondylar non-comminuted (42%). In 40 cases (56%) concomitant lesions were registered, with a total of 48 associate fractures. In two cases the fracture was bilateral. Twenty-four fractures were treated by orthopaedic means (traction-suspension system or plaster cast) and 48 by surgery. The surgical technique consisted on open reduction and internal fixation in 47 cases (plate and screws 21 cases, 17 with the AO plate and 9 with the DCS plate). The results were evaluated according to the classification of Schatzker, Horne and Wadell. There was 71% excellent and good results, with a significant difference between the treatment modalities (54% for orthopaedic treatment and 74% for surgical treatment, p < 0.01). A total of 17 complications was registered (24%): deep infection in 5 cases, residual deformity in 6, anquilosis in 4, and failed fixation in 2 cases. In summary, surgical treatment of distal femoral fractures shows better results than the orthopaedic treatment. Non-surgical treatment should be reserved for fractures in osteoporotic patients or in those cases with surgical contraindications

Experimental evaluation of the CO2-based mixtures CO2/R32, CO2/R1234yf and CO2/R1270 in a transcritical refrigerating plant considering the effect of the internal heat exchanger (IHX)

Using CO2 mixtures results in a simple but effective solution to increase the critical temperature of CO2 and reduce its working pressures. However, the overall effect of these mixtures on the global performance of the cycle has yet to be explored experimentally in detail. Accordingly, this work tests three CO2-binary blends with R32, R1270 and R1234yf in a small-capacity vapour compression test rig considering the same working conditions of heat rejection temperature and cooling demand. These mixtures were compared with pure CO2 in two-cycle arrangements without and with the internal heat exchanger (IHX). The results without IHX provided COP enhancements of 6.4%, 9.7% and 15.3% with CO2/R1270, CO2/R1234yf and CO2/R32, respectively, compared to CO2 without IHX. Using the IHX and taking CO2 without IHX as a reference, the COP increments ranged from 6.7% with R744, 12.1% with CO2/R1270, 16.1% with CO2/R1234yf and 22.2% with CO2/R32

A risk assessment methodology to evaluate the risk failure of managed aquifer recharge in the Mediterranean Basin

Managed aquifer recharge (MAR) can be affected by many risks. Those risks are related to different technical and non-technical aspects of recharge, like water availability, water quality, legislation, social issues, etc. Many other works have acknowledged risks of this nature theoretically; however, their quantification and definition has not been developed. In this study, the risk definition and quantification has been performed by means of "fault trees" and probabilistic risk assessment (PRA). We defined a fault tree with 65 basic events applicable to the operation phase. After that, we have applied this methodology to six different managed aquifer recharge sites located in the Mediterranean Basin (Portugal, Spain, Italy, Malta, and Israel). The probabilities of the basic events were defined by expert criteria, based on the knowledge of the different managers of the facilities. From that, we conclude that in all sites, the perception of the expert criteria of the non-technical aspects were as much or even more important than the technical aspects. Regarding the risk results, we observe that the total risk in three of the six sites was equal to or above 0.90. That would mean that the MAR facilities have a risk of failure equal to or higher than 90 % in the period of 2–6 years. The other three sites presented lower risks (75, 29, and 18 % for Malta, Menashe, and Serchio, respectively).Peer ReviewedPostprint (published version

El clavo gamma en las fracturas pertrocantéreas de cadera. Revisión de 400 casos

Las fracturas de la extremidad proximal del fémur son las más incapacitantes del organismo, siendo de ellas las más frecuentes las fracturas pertrocantéreas. Establecemos un estudio retrospectivo de 400 fracturas tratadas en nuestro Servicio mediante clavo Gamma, destacando nuestros resultados tanto clínicos como radiológicos, pérdida sanguínea, complicaciones médicas, quirúrgicas y radiológicas. Consideramos el clavo Gamma como el método de osteosíntesis idóneo para el tratamiento de fracturas pertrocantéreas por asocial una implantación endomedular con el deslizamiento del tornillo cefálico, condiciones imprescindibles para una movilización y carga precoz tan importante en estos pacientes.Fractures of the proximal femur are the most invalidating type of fractures affecting the skeleton and the most frequently found is the pertrochanteric variant. We have studied 400 pertrochanteric fractures treated with the standard gamma nail, showing our clinical and radiological results, blood loss, medical and surgical complications. We consider the gamma nail as the "gold standard" in the surgical treatment of petrochanteric fractures because it combines the endomedullary position with the sliding screw allowing an early mobilization and weight bearing, limited only by the patient's general conditions