Feedback enhanced Dyakonov-Shur instability in graphene field-effect transistors.

Graphene devices are known to have the potential to operate THz signals. In particular, graphene field-effect transistors (gFETs) have been proposed as devices to host plasmonic instabilities in the THz realm; for instance, Dyakonov-Shur (DS) instability which relies upon dc excitation. In this work, starting from a hydrodynamical description of the charge carriers, we extend the transmission line description of gFETs to a scheme with a positive feedback loop, also considering the effects of delay, which leads to the transcendental Laplace-transform transfer function, with complex frequencys, with terms of the forme-assechk(s)/s, for a givena∈R0+arising from the delay time and withk∈N. Applying the conditions for the excitation of DS instability, we report an enhanced voltage gain in the linear regime that is corroborated by our simulations of the nonlinear hydrodynamic model for the charge carriers. This translates to both greater saturation amplitude-often up to 50% increase-and faster growth rate of the self-oscillations. Thus, we bring forth a prospective concept for the realization of a THz oscillator suitable for future plasmonic circuitry.

Prenatal sonographic diagnosis of isolated fetal ascites in cri-du-chat (5p-) syndrome: A case report.

Isolated fetal ascites and cri-du-chat syndrome (CdCS; OMIM #123450) are two very rare conditions that, to our best knowledge, have never been reported together. Here, we describe a case of isolated fetal ascites detected in the first trimester ultrasound, with no other remarkable signs. After an extensive work-up (fetal ultrasound, serologies, Coombs test, and NIPT), an amniocentesis was performed and revealed an abnormal karyotype of 46,XX,del(5)(p15.2), characteristic of CdCS. We hypothesize that isolated fetal ascites has to be considered an antenatal ultrasonographic marker for CdCS, a finding that should be confirmed in further cases.

Los contaminantes atmosféricos urbanos son factores de riesgo significativos para el asma y la neumonía en niños: influencia del lugar de medición de los contaminantes / Urban Air Pollutants are Significant Risk Factors for Asthma and Pneumonia in Children: The Influence of Location on the Measurement of Pollutants

Antecedentes: La contaminación atmosférica se asocia a una carga sustancial para la salud humana; sin embargo, los contaminantes de mayor importancia pueden variar según el lugar. Es necesaria una monitorización adecuada para determinar el efecto de dichos contaminantes sobre la salud respiratoria. Objetivos: Este estudio se diseñó para evaluar el papel de la exposición en el exterior, en el interior y personal a los contaminantes derivados de la combustión NO2 y O3 sobre la salud respiratoria de los niños en una zona urbana económicamente poco favorecida de São Paulo (Brasil). Métodos: Se determinaron de forma continua los niveles de NO2 y O3 en el aire del exterior, el interior, y también en la exposición personal, durante 30 días con el empleo de aparatos de medición pasiva. Se evaluó la salud respiratoria con una versión en brasileño del cuestionario ISAAC. Resultados: Se dispuso de datos completos de 64 niños de 6 a 10 años de edad. La morbilidad respiratoria fue alta, con 43 (67,2%) niños en los que había habido sibilancias en alguna ocasión, 27 (42,2%) con sibilancias en el mes anterior, 17 (26,6%) con asma en alguna ocasión y 21 (32,8%) con neumonía en alguna ocasión. Las correlaciones entre los niveles de NO2 y O3 determinados en las 3 localizaciones evaluadas fueron bajas. Los niveles de NO2 en el área de interior y la exposición personal a O3 mostraron una asociación independiente con el asma (p=0,02 en ambos casos), la neumonía (O3, p=0,02) y la presencia de sibilancias en alguna ocasión (p<0,01 en ambos casos). No se observaron asociaciones entre el NO2 y el O3 del exterior y la salud respiratoria(AU)

Conclusiones: La exposición a niveles más elevados de NO2 y O3 se asoció a un aumento del riesgo de asma y neumonía en los niños; sin embargo, el lugar en el que se determinan los contaminantes influye en los resultados. Las determinaciones realizadas en el interior y las determinaciones personales fueron las más exactas(AU)

Background: Air pollution is associated with a substantial burden on human health; however, the most important pollutants may vary with location. Proper monitoring is necessary to determine the effect of these pollutants on respiratory health. Objectives: This study was designed to evaluate the role of outdoor, indoor and personal exposure to combustion-related pollutants NO2 and O3 on respiratory health of children in a non-affluent urban area of São Paulo, Brazil. Methods: Levels of NO2 and O3 were continuously measured in outdoor and indoor air, as well as personal exposure, for 30 days using passive measurement monitors. Respiratory health was assessed with a Brazilian version of the ISAAC questionnaire. Results: Complete data were available from 64 children, aged 6-10 years. Respiratory morbidity was high, with 43 (67.2%) reporting having had wheezing at any time, 27 (42.2%) wheezing in the last month, 17 (26.6%) asthma at any time and 21 (32.8%) pneumonia at any time. Correlations between levels of NO2 and O3 measured in the three locations evaluated were poor. Levels of NO2 in indoor air and personal exposure to O3 were independently associated with asthma (both cases P=0.02), pneumonia (O3, P=0.02) and wheezing at any time (both cases P<0.01). No associations were seen between outdoor NO2 and O3 and respiratory health. Conclusions: Exposure to higher levels of NO2 and O3 was associated with increased risk for asthma and pneumonia in children. Nonetheless, the place where the pollutants are measured influences the results. The measurements taken in indoor and personal exposure were the most accurate(AU)