Negative thermal expansion of MgB2_{2} in the superconducting state and anomalous behavior of the bulk Gr\"uneisen function

The thermal expansion coefficient $\alpha$ of MgB$_2$ is revealed to change from positive to negative on cooling through the superconducting transition temperature $T_c$. The Gr\"uneisen function also becomes negative at $T_c$ followed by a dramatic increase to large positive values at low temperature. The results suggest anomalous coupling between superconducting electrons and low-energy phonons.Comment: 5 figures. submitted to Phys. Rev. Let

Aceite de linaza: Caracterización y estudio de su degradación oxidativa

This paper proposes to characterize and monitor the degradation of linseed oil under two oxidation conditions using some traditional oxidative and quality parameters. The experimental section of this study was divided into 2 stages. In the first one, three commercial linseed oil samples (OL1, OL2, and OL3) were characterized according to oxidative stability (90 °C) and fatty acid composition. In the second stage, the OL1 sample, selected due to its availability, was subjected to the following oxidation procedures: storage at room temperature conditions with exposure to light and air (temperature ranging from 7 to 35 °C) for 140 days and accelerated oxidation at 100 °C for 7h. Samples were collected at different time intervals and analyzed for oxidative stability (90 °C), peroxide value, and acid value. The results showed that all the samples presented a similar fatty acid profile and that the OL3 sample showed a higher induction period (p < 0.05). Regarding the oxidative degradation, the induction period of the OL1 sample reduced from 9.7 to 5.7 and 9.7 to 6.3 during 140 days of storage under room temperature and 7 h of accelerated oxidation, respectively. The end of induction period of the OL1 sample is expected to occur within 229 days according to an exponential mathematical model fitted to the induction period values at different temperatures. In addition, the OL1 sample met the limits proposed by Codex and Brazilian regulations for peroxide and acid values during the oxidation time intervals.Este trabajo propone caracterizar y monitorear la degradación del aceite de linaza en dos condiciones de oxidación utilizando algunos parámetros oxidativos y de calidad tradicionales. La sección experimental de este estudio se dividió en 2 etapas. En la primera, se caracterizaron tres muestras comerciales de aceite de linaza (OL1, OL2 y OL3) a través de la estabilidad oxidativa (90 °C) y la composición de ácidos grasos. En la segunda etapa, la muestra OL1 se seleccionó por su disponibilidad y se sometió a los siguientes procedimientos de oxidación: almacenamiento en condiciones ambientales con exposición a la luz y al aire (temperatura que varía de 7 a 35 °C) durante 140 días y oxidación acelerada a 100 °C durante 7 h. Las muestras se recogieron a diferentes intervalos de tiempo y se analizaron mediante estabilidad oxidativa (90 °C), índice de peróxido e índice de acidez. Los resultados mostraron que todas las muestras presentaron un perfil de ácidos grasos similar y también que la muestra OL3 mostró un período de inducción más alto (

Ceras utilizadas como agentes estructurantes para organogeles de alimentos – Revisión:

Lipids are key ingredients in the human diet. Because of the manipulation and modification of lipids in the food industry, the amount of trans and saturated fat has been substantially increasing in industrialized products. At the same time, the number of studies demonstrating the harmful effects of these foods on human health has increased. Organogels arise as a promising alternative for replacing trans and saturated fat in processed foods. Among the main challenges of preparing an organogel is the difficulty of finding compatible and viable structuring agents in the food industry. Waxes have been studied for this purpose and are one of the most promising organogelators. This article brings a bibliographical review on the recent studies regarding the use of waxes as structuring agents for edible vegetable oils.Los lípidos son ingredientes clave en la dieta humana. Debido a la manipulación y modificación de estos lípidos en la industria alimentaria, la cantidad de grasas trans y las saturadas ha aumentado sustancialmente en los productos industrializados. Al mismo tiempo, ha aumentado la cantidad de estudios que demuestran los efectos nocivos de estos alimentos en la salud humana. Los organogeles surgen como una alternativa prometedora para reemplazar las grasas trans y las saturadas en los alimentos procesados. Entre los principales desafíos de preparar un organogel está la dificultad de encontrar agentes estructurantes compatibles y viables en la industria alimentaria. Las ceras se han estudiado para este propósito y son uno de los organogeladores más prometedores. Este artículo presenta una revisión bibliográfica de los estudios recientes sobre el uso de ceras como agentes estructurantes para aceites vegetales comestibles

Effective electronic response of a system of metallic cylinders

The electronic response of a composite consisting of aligned metallic cylinders in vacuum is investigated, on the basis of photonic band structure calculations. The effective long-wavelength dielectric response function is computed, as a function of the filling fraction. A spectral representation of the effective response is considered, and the surface mode strengths and positions are analyzed. The range of validity of a Maxwell-Garnett-like approach is discussed, and the impact of our results on absorption spectra and electron energy-loss phenomena is addressed.Comment: 15 pages, 6 figures, to appear in Phys. Rev.

Malaria pigment hemozoin impairs gm-csf receptor expression and function by 4-hydroxynonenal

Malarial pigment hemozoin (HZ) generates the lipoperoxidation product 4-hydroxynonenal (4-HNE), which is known to cause dysregulation of the immune response in malaria. The inhibition of granulocyte macrophage colony-stimulating factor (GM-CSF)-dependent differentiation of dendritic cells (DC) by HZ and 4-HNE was previously described in vitro, and the GM-CSF receptor (GM-CSF R) was hypothesised to be a primary target of 4-HNE in monocytes. In this study, we show the functional impact of HZ on GM-CSF R in monocytes and monocyte-derived DC by (i) impairing GM-CSF binding by 50 ± 9% and 65 ± 14%, respectively (n = 3 for both cell types); (ii) decreasing the expression of GM-CSF R functional subunit (CD116) on monocyte’s surface by 36 ± 11% (n = 6) and in cell lysate by 58 ± 16% (n = 3); and (iii) binding of 4-HNE to distinct amino acid residues on CD116. The data suggest that defective DC differentiation in malaria is caused by GM-CSF R dysregulation and GM-CSF R modification by lipoperoxidation product 4-HNE via direct interaction with its CD116 subunit

In Silico Assembly And Nanomechanical Characterization Of Carbon Nanotube Buckypaper

Carbon nanotube sheets or films, also known as 'buckypaper', have been proposed for use in actuating, structural and filtration systems, based in part on their unique and robust mechanical properties. Computational modeling of such a fibrous nanostructure is hindered by both the random arrangement of the constituent elements as well as the time- and length-scales accessible to atomistic level molecular dynamics modeling. Here we present a novel in silico assembly procedure based on a coarse-grain model of carbon nanotubes, used to attain a representative mesoscopic buckypaper model that circumvents the need for probabilistic approaches. By variation in assembly parameters, including the initial nanotube density and ratio of nanotube type (single- and double-walled), the porosity of the resulting buckypaper can be varied threefold, from approximately 0.3 to 0.9. Further, through simulation of nanoindentation, the Young's modulus is shown to be tunable through manipulation of nanotube type and density over a range of approximately 0.2–3.1 GPa, in good agreement with experimental findings of the modulus of assembled carbon nanotube films. In addition to carbon nanotubes, the coarse-grain model and assembly process can be adapted for other fibrous nanostructures such as electrospun polymeric composites, high performance nonwoven ballistic materials, or fibrous protein aggregates, facilitating the development and characterization of novel nanomaterials and composites as well as the analysis of biological materials such as protein fiber films and bulk structures.National Science Foundation (U.S.) (MRSEC Program under award number DMR- 0819762

A Fast Algorithm for Robust Regression with Penalised Trimmed Squares

The presence of groups containing high leverage outliers makes linear regression a difficult problem due to the masking effect. The available high breakdown estimators based on Least Trimmed Squares often do not succeed in detecting masked high leverage outliers in finite samples. An alternative to the LTS estimator, called Penalised Trimmed Squares (PTS) estimator, was introduced by the authors in \cite{ZiouAv:05,ZiAvPi:07} and it appears to be less sensitive to the masking problem. This estimator is defined by a Quadratic Mixed Integer Programming (QMIP) problem, where in the objective function a penalty cost for each observation is included which serves as an upper bound on the residual error for any feasible regression line. Since the PTS does not require presetting the number of outliers to delete from the data set, it has better efficiency with respect to other estimators. However, due to the high computational complexity of the resulting QMIP problem, exact solutions for moderately large regression problems is infeasible. In this paper we further establish the theoretical properties of the PTS estimator, such as high breakdown and efficiency, and propose an approximate algorithm called Fast-PTS to compute the PTS estimator for large data sets efficiently. Extensive computational experiments on sets of benchmark instances with varying degrees of outlier contamination, indicate that the proposed algorithm performs well in identifying groups of high leverage outliers in reasonable computational time.Comment: 27 page

Feasibility of Noninvasive Positive Pressure Ventilation in the Treatment of Oxygen-Dependent COVID-19 Patients in Peru

Intensive care is expensive, and availability is limited. Low- and middle-income countries in particular have struggled to cope with the large influx of critically ill patients during the COVID-19 pandemic. Noninvasive respiratory support devices delivering continuous positive airways pressure (CPAP) require less resource and staff expertise compared with invasive mechanical ventilators and can be routinely used outside of intensive care units. This study assessed the use of the UCL-Ventura Wayrachi CPAP device in hospitalized patients with COVID-19 in Peru. A secondary analysis of data collected for a feasibility study commissioned by the Peruvian Ministry of Health was conducted. Data were collected from three hospitals, including patient demographics, clinical data, and outcomes. Forty-five patients were enrolled from July 16 to September 1, 2020. Eight patients (18%) were intolerant of the CPAP mask. Of the remainder, 18 (48.7%) improved and were discharged from hospital after 6 days. Eight (21.6%) died while on CPAP and 11 (29.7%) were eventually intubated, of whom two died. In total, 27 (60%) survived to hospital discharge. Participating physicians noted the device was easy to use and provided patient benefit, though voiced concerns about the strain on hospital oxygen supplies. In conclusion, the UCL Ventura Wayrachi CPAP device proved feasible in COVID-19 patients in Peru, and offered a bridging therapy for patients who required a ventilator when none were available

Evolución de la oxidación en el aceite de soja y su biodiesel en las condiciones del test de estabilidad a la oxidación

The objective of this study was to know the evolution of the oxidation of soybean oil and biodiesel under the conditions of the oxidation stability test (110 °C) using the Rancimat apparatus. Samples were analyzed at different periods of time until the end of the induction period. The analytical determinations related to the changes in oxidation include peroxide value, anisidine value, natural tocopherols and polar compounds. Acid value, kinematic viscosity, polymers and ester content were also analyzed because of their relevance in the evaluation of biodiesel quality. Results showed that only peroxide value and the group of polar compounds including hydroperoxides, i.e. oxidized monomeric TAG in the oil and oxidized monomeric FAME in the biodiesel increased significantly during the early oxidation stage. The end of the induction period was marked by a rapid increase in polymerization compounds and the exhaustion of tocopherols. Significant changes in acid value, viscosity and ester content were only observed after the end of the induction period.El objetivo de este estudio fue conocer la evolución de la oxidación del aceite de soja y de su biodiesel a 110 °C en las condiciones del método estándar para la determinación de la estabilidad oxidativa, usando el aparato Rancimat. Las muestras se analizaron en diferentes períodos de tiempo hasta que el período de inducción fue sobrepasado. Se determinaron los índices de peróxidos y anisidina, los tocoferoles y los compuestos polares cuyos cambios están relacionados con el desarrollo de la alteración oxidativa. Además, fueron determinados el índice de acidez, la viscosidad y el contenido en ésteres, de interés en el análisis de la calidad del biodiesel. Los resultados indicaron que sólo el índice de peróxidos y el grupo de compuestos polares que incluye los hidroperóxidos (triglicéridos oxidados monómeros en el aceite y ésteres metílicos oxidados monómeros en el biodiesel) aumentaron durante todo el periodo de inducción. El final del período de inducción fue determinado por el marcado aumento de los compuestos de polimerización y la pérdida total de los tocoferoles. Sólo se observaron cambios significativos en el índice de acidez, viscosidad y contenido de ésteres al final del periodo de inducción