Dielectric Breakdown in Chemical Vapor Deposited Hexagonal Boron Nitride

Insulating films are essential in multiple electronic devices because they can provide essential functionalities, such as capacitance effects and electrical fields. Two-dimensional (2D) layered materials have superb electronic, physical, chemical, thermal, and optical properties, and they can be effectively used to provide additional performances, such as flexibility and transparency. 2D layered insulators are called to be essential in future electronic devices, but their reliability, degradation kinetics, and dielectric breakdown (BD) process are still not understood. In this work, the dielectric breakdown process of multilayer hexagonal boron nitride (h-BN) is analyzed on the nanoscale and on the device level, and the experimental results are studied via theoretical models. It is found that under electrical stress, local charge accumulation and charge trapping/detrapping are the onset mechanisms for dielectric BD formation. By means of conductive atomic force microscopy, the BD event was triggered at several locations on the surface of different dielectrics (SiO2, HfO2, Al2O3, multilayer h-BN, and monolayer h-BN); BD-induced hillocks rapidly appeared on the surface of all of them when the BD was reached, except in monolayer h-BN. The high thermal conductivity of h-BN combined with the one-atom-thick nature are genuine factors contributing to heat dissipation at the BD spot, which avoids self-accelerated and thermally driven catastrophic BD. These results point to monolayer h-BN as a sublime dielectric in terms of reliability, which may have important implications in future digital electronic devices.Fil: Jiang, Lanlan. Soochow University; ChinaFil: Shi, Yuanyuan. Soochow University; China. University of Stanford; Estados UnidosFil: Hui, Fei. Soochow University; China. Massachusetts Institute of Technology; Estados UnidosFil: Tang, Kechao. University of Stanford; Estados UnidosFil: Wu, Qian. Soochow University; ChinaFil: Pan, Chengbin. Soochow University; ChinaFil: Jing, Xu. Soochow University; China. University of Texas at Austin; Estados UnidosFil: Uppal, Hasan. University of Manchester; Reino UnidoFil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lu, Guangyuan. Chinese Academy of Sciences; República de ChinaFil: Wu, Tianru. Chinese Academy of Sciences; República de ChinaFil: Wang, Haomin. Chinese Academy of Sciences; República de ChinaFil: Villena, Marco A.. Soochow University; ChinaFil: Xie, Xiaoming. Chinese Academy of Sciences; República de China. ShanghaiTech University; ChinaFil: McIntyre, Paul C.. University of Stanford; Estados UnidosFil: Lanza, Mario. Soochow University; Chin

BACTERIAL FLORA IN THE DIGESTIVE TRACT OF HELIX ASPERSA MÜLLER SNAILS UNDER TWO BREEDING SYSTEMS

El objetivo del estudio fue comparar la flora bacteriana de intestino y hepatopáncreas del caracol Helix aspersa Müller criados en dos sistemas de producción: intensivo y extensivo. Se colectaron 30 caracoles adultos aparentemente sanos por cada sistema de producción, en seis criaderos ubicados en la provincia de Lima. Se tomó muestras de mucosa intestinal y parénquima del hepatopáncreas de cada individuo, empleando protocolos de aislamientos establecidos para bacterias aerobias y aerobias facultativas. Se aisló bacterias de 15 géneros: Escherichia, Citrobacter, Klebsiella, Enterobacter, Serratia, Hafnia, Proteus, Providencia, Aeromonas, Staphylococcus, Streptococcus, Enterococcus, Micrococcus, Pseudomonas, Acinetobacter; y bacilos gramnegativos no fermentadores (BNF). Se obtuvo 193 cepas en las muestras de caracoles del sistema extensivo, donde el género Escherichia fue el de mayor frecuencia (17.1%, 33/193); mientras que en caracoles del sistema intensivo se aisló 183 cepas, donde el género Klebsiella fue el de mayor frecuencia (17.5%, 32/183). Por otro lado, el género más frecuentemente aislado en intestino y hepatopáncreas fue Klebsiella (13.6%, 25/184 y 17.2%, 33/192, respectivamente). Bacterias de los géneros Providencia y Micrococcus solo se encontraron en el hepatopáncreas. Hubo diferencias estadísticas en la frecuencia de algunas bacterias aisladas dentro de cada tipo de muestra por efecto del sistema de crianza.El objetivo del estudio fue comparar la flora bacteriana de intestino y hepatopáncreas del caracol Helix aspersa Müller criados en dos sistemas de producción: intensivo y extensivo. Se colectaron 30 caracoles adultos aparentemente sanos por cada sistema de producción, en seis criaderos ubicados en la provincia de Lima. Se tomó muestras de mucosa intestinal y parénquima del hepatopáncreas de cada individuo, empleando protocolos de aislamientos establecidos para bacterias aerobias y aerobias facultativas. Se aisló bacterias de 15 géneros: Escherichia, Citrobacter, Klebsiella, Enterobacter, Serratia, Hafnia, Proteus, Providencia, Aeromonas, Staphylococcus, Streptococcus, Enterococcus, Micrococcus, Pseudomonas, Acinetobacter; y bacilos gramnegativos no fermentadores (BNF). Se obtuvo 193 cepas en las muestras de caracoles del sistema extensivo, donde el género Escherichia fue el de mayor frecuencia (17.1%, 33/193); mientras que en caracoles del sistema intensivo se aisló 183 cepas, donde el género Klebsiella fue el de mayor frecuencia (17.5%, 32/183). Por otro lado, el género más frecuentemente aislado en intestino y hepatopáncreas fue Klebsiella (13.6%, 25/184 y 17.2%, 33/192, respectivamente). Bacterias de los géneros Providencia y Micrococcus solo se encontraron en el hepatopáncreas. Hubo diferencias estadísticas en la frecuencia de algunas bacterias aisladas dentro de cada tipo de muestra por efecto del sistema de crianza

Thermal biology of mosquito-borne disease

Mosquito-borne diseases cause a major burden of disease worldwide. The vital rates of these ectothermic vectors and parasites respond strongly and nonlinearly to temperature and therefore to climate change. Here, we review how trait-based approaches can synthesise and mechanistically predict the temperature dependence of transmission across vectors, pathogens, and environments. We present 11 pathogens transmitted by 15 different mosquito species – including globally important diseases like malaria, dengue, and Zika – synthesised from previously published studies. Transmission varied strongly and unimodally with temperature, peaking at 23–29ºC and declining to zero below 9–23ºC and above 32–38ºC. Different traits restricted transmission at low versus high temperatures, and temperature effects on transmission varied by both mosquito and parasite species. Temperate pathogens exhibit broader thermal ranges and cooler thermal minima and optima than tropical pathogens. Among tropical pathogens, malaria and Ross River virus had lower thermal optima (25–26ºC) while dengue and Zika viruses had the highest (29ºC) thermal optima. We expect warming to increase transmission below thermal optima but decrease transmission above optima. Key directions for future work include linking mechanistic models to field transmission, combining temperature effects with control measures, incorporating trait variation and temperature variation, and investigating climate adaptation and migration

The everchanging epidemiology of meningococcal disease worldwide and the potential for prevention through vaccination.

Neisseria meningitidis is a major cause of bacterial meningitis and septicaemia worldwide and is associated with high case fatality rates and serious life-long complications among survivors. Twelve serogroups are recognised, of which six (A, B, C, W, X and Y) are responsible for nearly all cases of invasive meningococcal disease (IMD). The incidence of IMD and responsible serogroups vary widely both geographically and over time. For the first time, effective vaccines against all these serogroups are available or nearing licensure. Over the past two decades, IMD incidence has been declining across most parts of the world through a combination of successful meningococcal immunisation programmes and secular trends. The introduction of meningococcal C conjugate vaccines in the early 2000s was associated with rapid declines in meningococcal C disease, whilst implementation of a meningococcal A conjugate vaccine across the African meningitis belt led to near-elimination of meningococcal A disease. Consequently, other serogroups have become more important causes of IMD. In particular, the emergence of a hypervirulent meningococcal group W clone has led many countries to shift from monovalent meningococcal C to quadrivalent ACWY conjugate vaccines in their national immunisation programmes. Additionally, the recent licensure of two protein-based, broad-spectrum meningococcal B vaccines finally provides protection against the most common group responsible for childhood IMD across Europe and Australia. This review describes global IMD epidemiology across each continent and trends over time, the serogroups responsible for IMD, the impact of meningococcal immunisation programmes and future needs to eliminate this devastating disease

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Efecto de la desnutrición pre y posnatal y la exposición posnatal a vapores de tolueno sobre el desempeño en campo abierto en ratas

El objetivo, del presente estudio fue investigar los efectos de la desnutrición prenatal y posnatal, y la exposición posnatal a vapores de tolueno, sobre la actividad conductual en campo abierto en ratas wistar. Material y métodos: se desnutrieron ratas hembras vírgenes, con el 50% del alimento que consumían las ratas nutridas. Esta dieta se inició desde tres semanas antes de la cruza y se mantuvo durante la gestación, lactancia y hasta los 60 días de vida posnatal de los críos. La inhalación de tolueno en los críos se llevó a cabo de los 40 a los 60 días de edad. La dosis de tolueno fue de 0.4 ml y el cual se colocó en una cámara de cristal con capacidad de 3.7 l durante 15 minutos por día. Se formaron 6 grupos con 10-14 animales, tres grupos bien nutridos, el mantenido en condiciones de laboratorio (N), expuesto a vapores de tolueno (NT) y control de manejo (NM), y tres grupos desnutridos, el mantenidos en condiciones de laboratorio (D), expuesto a vapores de tolueno (DT) y control de manejo (DM). Los animales de cada uno de los grupos se sometieron a una prueba de desempeño en campo abierto en la que se filmó su desplazamiento en una caja de madera de 100 x 100 x 45 cm durante 5 minutos. Se calculó la distancia total recorrida por medio de un monitor. El peso y recorrido fueron analizados con Bonferroni, bolos fecales U de Mann-Witney y acicalamiento con ANOVA. Resultados: la desnutrición y la exposición mostraron acción aditiva reduciendo significativamente el peso corporal de las ratas. Las ratas de los grupos nutridos y desnutridos, que se introdujeron en la cámara de inhalación pero sin el solvente (NM y DM), desplegaron mayor actividad en el campo abierto en tanto que los grupos sometidos al solvente mostraron menor actividad. Discusión: la desnutrición y el manejo por separado indujeron mayor actividad motora comparada con el grupo control sano; la exposición al solvente redujo la actividad

Electrical Homogeneity of Large-Area Chemical Vapor Deposited Multilayer Hexagonal Boron Nitride Sheets

Large-area hexagonal boron nitride (h-BN) can be grown on polycrystalline metallic substrates via chemical vapor deposition (CVD), but the impact of local inhomogeneities on the electrical properties of the h-BN and their effect in electronic devices is unknown. Conductive atomic force microscopy (CAFM) and probe station characterization show that the tunneling current across the h-BN stack fluctuates up to 3 orders of magnitude from one substrate (Pt) grain to another. Interestingly, the variability in the tunneling current across the h-BN within the same substrate grain is very low, which may enable the use of CVD-grown h-BN in ultra scaled technologies. Keywords: hexagonal boron nitride; chemical vapor deposition; electrical homogeneity; conductive AFM; polycrystallineNational Science Foundation (U.S.) (Grant DMR/ECCS–1509197