Comparison of Howland and General Impedance Converter (GIC) circuit based current sources for bio-impedance measurements

The current source is a key component in bio-impedance measurement systems. The accuracy of the current source can be measured in terms of its output impedance together with other parameters, with certain applications demanding extremely high output impedance. This paper presents an investigation and comparison of different current source designs based on the Enhanced Howland circuit combined with a General Impedance Converter (GIC) circuit using both ideal and non-ideal operational amplifiers. Under differing load conditions two different settings of the GIC are evaluated and the results are compared to show its performance settings. Whilst the study has shown that over a wide bandwidth (i.e. 100Hz-100MHz) the output impedance is limited, operation over a more limited range offers output impedance in the Giga-ohm range, which can be considered as being infinite

Effect of gastro-esophageal reflux symptoms on the risk of Barrett's esophagus: A systematic review and meta-analysis

Background and Aim Gastro-esophageal reflux (GER) is the main predisposing factor for Barrett's esophagus (BE). A more precise estimate of the association of GER symptoms with the risk of BE would be important to prioritize endoscopic screening. We conducted a systematic review and meta-analysis to examine this issue. Methods MEDLINE, EMBASE, and EMBASE Classic were searched to identify cross-sectional studies that reported the prevalence of BE based on presence of GER symptoms. The prevalence of BE was compared according to presence or absence of GER symptoms using an odds ratio (OR), with a 95% confidence interval (CI). Specificity and sensitivity of GER symptoms for predicting BE was calculated. Results Of 10,463 citations evaluated, 19 studies reported the prevalence of BE in 43,017 subjects. The pooled OR among individuals with weekly GER symptoms compared with those without was 1.67 (95% CI 1.30-2.15) for endoscopically suspected BE, and 2.42 (95% CI 1.59-3.68) for histologically confirmed BE. No significant association was found between weekly GER symptoms and the presence of short segment BE (OR 1.30; 95% CI 0.86-1.97), whereas a strong association was present with long segment BE, with an OR of 6.30 (95% CI 2.26-17.61). Conclusions Gastro-esophageal reflux symptoms are associated with an increased odds of BE, with a further increase when weekly symptoms are present. Overall, GER symptoms showed low sensitivity and specificity for predicting BE; however, a strong association was found between weekly GER symptoms and long segment BE, but not short segment BE, suggesting that it may be worth considering screening individuals with weekly GER symptoms to rule out long segment BE

Mass Transport in “Water-in-Polymer Salt” Electrolytes

“Water-in-polymer salt” electrolytes (WiPSEs) based on potassium polyacrylate (PAAK) belong to a new family of “water-in-salt” electrolytes that is envisioned as a potential solution for large-scale supercapacitors to balance the electric grid at short time scales. The WiPSEs display a broad electrochemical stability window up to 3 V, yet they are nonflammable and provide high ionic conductivity (100 mS/cm) as required in high-power devices. However, the transport of matter in PAAK-based WiPSEs has not been studied. In this work, we have extensively characterized PAAK by spectroscopic methods such as Raman spectroscopy and NMR diffusometry to determine the state of water and elucidate the mechanism of ionic transport as well as its interplay with water and polymer chain dynamics, which reveals that a significant proportion of the transport in WiPSEs is attributed to hydrated cations. The results are further supported by molecular dynamics (MD) simulations. Finally, the potential of WiPSEs based on PAAK is demonstrated in an activated carbon-based supercapacitor operating up to 2 V with reasonable self-discharge. This proof of concept shows promise for low-cost and large-scale supercapacitors

Metodología alternativa para el tratamiento de problemas de programación entera usando programación no lineal

Este trabajo propone una alternativa de solución a los problemas de Programación Entera, dejando de lado la idea de la enumeración implícita y sus consecuentes dificultades a la vez que aprovecha información matemática de la función objetivo y de las funciones que determinan el espacio de soluciones. Tal alternativa de solución es posible gracias a una sencilla transformación de las restricciones de integralidad usando un polinomio que permite tratar el problema con Programación No Lineal (PNL

Metodología alternativa para el tratamiento de problemas de programación entera usando programación no lineal

Este trabajo propone una alternativa de solución a los problemas de Programación Entera, dejando de lado la idea de la enumeración implícita y sus consecuentes dificultades a la vez que aprovecha información matemática de la función objetivo y de las funciones que determinan el espacio de soluciones. Tal alternativa de solución es posible gracias a una sencilla transformación de las restricciones de integralidad usando un polinomio que permite tratar el problema con Programación No Lineal (PNL

Metodología alternativa para el tratamiento de problemas de programación entera usando programación no lineal

Este trabajo propone una alternativa de solución a los problemas de Programación Entera, dejando de lado la idea de la enumeración implícita y sus consecuentes dificultades a la vez que aprovecha información matemática de la función objetivo y de las funciones que determinan el espacio de soluciones. Tal alternativa de solución es posible gracias a una sencilla transformación de las restricciones de integralidad usando un polinomio que permite tratar el problema con Programación No Lineal (PNL

The fluorescence explorer (FLEX) mission:imaging spectroscopy in very high spectral resolution

The FLuorescence EXplorer (FLEX) mission was selected in 2015, by the European Space Agency, as the 8th ESA Earth Explorer, to be launched in 2025. The key scientific objective of the mission is the quantitative mapping of actual photosynthetic activity of terrestrial ecosystems, at a global scale and with a spatial resolution adequate to resolve land processes associated to vegetation dynamics. To accomplish such objective, the FLEX satellite carries the Fluorescence Imaging Spectrometer (FLORIS). FLEX will fly in tandem with Copernicus Sentinel-3 (same orbit at 815 km, 27 days repeat cycle). Together with FLORIS, the OLCI and SLSTR instruments on Sentinel-3 provide all the necessary information to retrieve the emitted vegetation fluorescence, including compensation for atmospheric effects and the derivation of the additional biophysical information needed to map the spatial and temporal dynamics of vegetation photosynthesis from such global measurements

Remarks on quiver gauge theories from open topological string theory

We study effective quiver gauge theories arising from a stack of D3-branes on certain Calabi-Yau singularities. Our point of view is a first principle approach via open topological string theory. This means that we construct the natural A-infinity-structure of open string amplitudes in the associated D-brane category. Then we show that it precisely reproduces the results of the method of brane tilings, without having to resort to any effective field theory computations. In particular, we prove a general and simple formula for effective superpotentials