Morphological variations in cadmium sulfide nanocrystals without phase transformation

A very novel phenomenon of morphological variations of cadmium sulfide (CdS) nanorods under the transmission electron microscopy (TEM) beam was observed without structural phase transformation. Environmentally stable and highly crystalline CdS nanorods have been obtained via a chemical bath method. The energy of the TEM beam is believed to have a significant influence on CdS nanorods and may melt and transform them into smaller nanowires. Morphological variations without structural phase transformation are confirmed by recording selected area electron diffraction at various stages. The prepared CdS nanorods have been characterized by X-ray powder diffraction, TEM, UV-Vis spectroscopy, and photoluminescence spectroscopy. The importance of this phenomenon is vital for the potential application for CdS such as smart materials

Cerrando la brecha entre la teoría y el aprendizaje activo: un estudio de caso de aprendizaje basado en proyectos en el curso introducción a ciencia e ingeniería de materiales

La presente investigación es un estudio de caso de la metodología de aprendizaje basado en proyectos (ABP) aplicada a uno de los cursos básicos de ingeniería más difundidos: introducción a la ciencia e ingeniería de materiales. El proyecto se realizó con estudiantes de primer año de la carrera de Ingeniería Mecánica. Para esto, parte de la clase teórica se redujo al 40 % de un proyecto multidisciplinario que requería producir bastones y muletas para personas con movilidad limitada utilizando materiales económicos y materiales de desecho sólido. Los estudiantes que participaron en este proyecto diseñaron, probaron y evaluaron el producto final de los demás. Además, los alumnos presentaron un informe técnico con una revisión bibliográfica ampliada que incluía información de la pieza fabricada. A diferencia de otros estudios de ABP, el instructor evaluó el progreso de los estudiantes en cuatro momentos diferentes a lo largo del semestre, a través de un proceso de evaluación sumativa en el que se certificó, a través de una calificación, de acuerdo con el aprendizaje desarrollado durante el proceso de mediación con los estudiantes. Se realizó una encuesta a estudiantes, miembros de la facultad, profesionales y expertos locales en las piezas fabricadas para evaluar la estética y la innovación de las piezas fabricadas. Una organización sin fines de lucro también participó en la sensibilización de los estudiantes para brindar mejores soluciones a las personas con varias presentaciones orales durante el tiempo de clase. Para evaluar la efectividad del método ABP, se comparó el curso de Ingeniería Mecánica con otro de enseñanza tradicional, donde la comparación se basó en los mismos exámenes administrados a ambos grupos de estudio. El método implementado en este estudio ha demostrado ser una buena estrategia para la enseñanza de cursos de ingeniería de materiales, permitiendo a los estudiantes participar en proyectos interdisciplinarios. A partir de esta experiencia, se concluye que es factible implementar métodos activos como alternativa a los cursos impartidos utilizando únicamente métodos tradicionales

Fricción interna y comportamiento anelástico en sólidos

Se presentan los conceptos de Fricción Interna (FI), anelasticidad y espectroscopia mecánica, como una técnica potente para la determinación de las propiedades mecánicas dinámicas en sólidos. Se comentan algunos de los logros de la técnica, fundamentalmente en el campo de la física del estado sólido

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI <18·5 kg/m2) and obesity (BMI ≥30 kg/m2). For schoolaged children and adolescents, we report thinness (BMI <2 SD below the median of the WHO growth reference) and obesity (BMI >2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesit

Mechanical Behavior and Thermal Stability of Acid-Base Phosphate Cements and Composites Fabricated at Ambient Temperature

This dissertation presents the study of the mechanical behavior and thermal stability of acid-base phosphate cements (PCs) and composites fabricated at ambient temperature. These materials are also known as chemically bonded phosphate ceramics (CBPCs). Among other advantages of using PCs when compared with traditional cements are the better mechanical properties (compressive and flexural strength), lower density, ultra-fast (controllable) setting time, controllable pH, and an environmentally benign process. Several PCs based on wollastonite and calcium and alumino phosphates after thermal exposure up to 1000�C have been investigated.First, the thermo-mechanical and chemical stability of wollastonite-based PC (Wo-PC) exposed to temperatures up to 1000�C in air environment were studied. The effects of processing conditions on the curing and shrinkage of the wollastonite-based PC were studied. The chemical reactions and phase transformations during the fabrication and during the thermal exposure are analyzed in detail using scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermo-gravimetric analysis (TGA Then, the thermo-mechanical and chemical stability of glass, carbon and basalt fiber reinforced Wo-PC composites, were studied using SEM, XRD, TGA. The flexural strength and Weibull statistics were analyzed. A significant strength degradation in the composites were found after the thermal exposure at elevated temperatures due to the interdifusion and chemical reactions across the fibers and the matrix at temperatures over 600�C. To overcome this barrier, we have developed a new PC based on calcium and alumino-phosphates (Ca-Al PCs). The Ca-Al PCs were studied in detail using SEM, XRD, TGA, curing, shrinkage, Weibull statistics, and compression tests. Our study has confirmed that this new composite material is chemically and mechanically stable at temperatures up to 1000�C. Moreover, the compression strength increases after exposure to 1000�C. This is a significant result since phosphates typically show strength degradation at temperatures over 500�C.In addition, other PCs materials were developed during this research with their current and potential applications. These include a new PC based on fly ash (Fly ash-PC) as raw material; and PC-based on boron (B-PC), which can be used in shielding neutron irradiation and infrastructure for nuclear facilities

Alkaline activation of brick waste with partial addition of ordinary Portland cement (OPC) for reducing brick industry pollution and developing a feasible and competitive construction material

This study shows an alkaline activated cement (AAC), also known as geopolymer, made from red brick waste with partial addition of Ordinary Portland Cement (OPC). This is a sustainable material since incorporates waste from the brick industry to make cements, therefore increasing the materials circularity and this reducing pollution. The material was cured at room temperature. The brick residue was activated with sodium hydroxide and sodium silicate in aqueous solution to form the hybrid cement. Several mixtures were made with different amounts of waste and proportions of alkaline activator. The mechanical properties of the materials were studied to determine their feasibility to be used in the construction sector. Three contents of OPC were used: 10, 20, and 30 wt%, which were added to improve the mechanical behavior and post-curing time. The activated hybrid cement was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), compression, and flexural tests. The main results show that the addition of OPC to the brick derived AAC produces an increased compressive strength of 106 MPa when 30 wt% OPC was added, a very significant result since the control sample found was 33 MPa in compression strength, an improvement for more than 3 times. The data were corroborated by statistical analysis

Alkali-activated cement manufactured by the alkaline activation of demolition and construction waste using brick and concrete wastes

This study examines the mechanical and materials science properties of a novel Alkali-activated cement (AAC) cured at room temperature and using construction and demolition waste (CDW), which was obtained from brick and concrete waste from a landfill in Medellín, Colombia. The cement was activated with an aqueous solution of sodium hydroxide and sodium silicate. Different mixtures were tested to determine the optimum amount of CDW and the proportion of alkaline activator. The formulations were characterized by compressive and flexural strength tests, X-ray diffraction, scanning electron microscopy, and water absorption tests. Results indicate that the mechanical properties of the developed cement are strongly influenced by both the type of activated residue and the activator ratio. The AAC with the best mechanical properties is the one based on brick waste, which has a mean compressive strength of 33 MPa

Failure Analysis of a Pellet-Mill Die

One of the most important parts for pellet-mills is the die, since the die transforms raw materials in small cylinders called pellets. In this paper, a failure analysis was conducted for a pellet-mill die that had not reached its service life expectancy. The failure analysis consist of a characterization of the material using atomic emission spectroscopy, hardness measurements, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy by SEM. Additionally, visual inspection and fractography of the fracture surfaces and FE analysis were performed. It was found that the die material was a CA40 alloy, which microstructure consists of a martensitic matrix with finely dispersed carbides of the type M23C6. Also, a non-common level of inclusion type Al2O3 was found on the microstructure of the die material. According to the fractographic analysis, the crack initiation was located in a high-stress concentration region on the counterbored holes of the die, and also aided by the inclusions on the structure. Crack propagated along the material as an intergranular brittle fracture

Calcium Silicate Phosphate Cement with Samarium Oxide Additions for Neutron Shielding Applications in Nuclear Industry

A simple method to obtain calcium silicate phosphate with samarium oxide (Sm2O3) admixtures is presented. Samples were produced by mixing mineral wollastonite (CaSiO3) and Sm2O3 powders with an aqueous acidic formulation of phosphoric acid (H3PO4) at room temperature. Microstructural, mechanical, and neutron attenuation properties of phosphate pastes with Sm2O3 additions between 1 and 10 wt% were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results revealed that the composites were made of remaining CaSiO3 and Sm2O3 and newly created silica (SiO2) and brushite (CaHPO4⋅2H2O) phases. The highest compressive strength (37 MPa) was achieved for phosphates pastes with 1 wt% Sm2O3 loading, representing 15% improvement over the reference sample (32 MPa). Composites with 10 wt% Sm2O3 (27 MPa) showed a reduction of 15% in compressive strength over the reference paste. Finally, the effect of Sm2O3 concentration on the neutron shielding properties was studied. For additions of 10 wt % Sm2O3 an improvement of more than 1000% in linear attenuation coefficient for thermal and epithermal neutrons was measured. Based on the overall results from this study, it is concluded that the optimum interval of Sm2O3 content in wollastonite phosphate cement for neutron shielding in nuclear systems ranged between 1 and 5 wt%