A bouncing oil droplet in a stratified liquid and its sudden death

Droplets can self-propel when immersed in another liquid in which a concentration gradient is present. Here we report the experimental and numerical study of a self-propelling oil droplet in a vertically stratified ethanol/water mixture: At first, the droplet sinks slowly due to gravity, but then, before having reached its density matched position, jumps up suddenly. More remarkably, the droplet bounces repeatedly with an ever increasing jumping distance, until all of a sudden it stops after about 30 min. We identify the Marangoni stress at the droplet/liquid interface as responsible for the jumping: its strength grows exponentially because it pulls down ethanol-rich liquid, which in turn increases its strength even more. The jumping process can repeat because gravity restores the system. Finally, the sudden death of the jumping droplet is also explained. Our findings have demonstrated a type of prominent droplet bouncing inside a continuous medium with no wall or sharp interface.Comment: 6 pages, 4 figure

Self-Identifying Sensor Data

Public-use sensor datasets are a useful scientific resource with the unfortunate feature that their provenance is easily disconnected from their content. To address this we introduce a technique to directly associate provenance information with sensor datasets. Our technique is similar to traditional watermarking but is intended for application to unstructured datasets. Our approach is potentially imperceptible given sufficient margins of error in datasets, and is robust to a number of benign but likely transformations including truncation, rounding, bit-flipping, sampling, and reordering. We provide algorithms for both one-bit and blind mark checking. Our algorithms are probabilistic in nature and are characterized by a combinatorial analysis.Engineering and Applied Science

Equations for solar tracking

Direct Sun light absorption by trace gases can be used to quantify them and investigate atmospheric chemistry. In such experiments, the main optical apparatus is often a grating or a Fourier transform spectrometer. A solar tracker based on motorized rotating mirrors is also needed to direct the light along the spectrometer axis, correcting for the apparent rotation of the Sun. Calculating the Sun azimuth and altitude for a given time and location can be achieved with high accuracy but different sources of angular offsets appear in practice when positioning the mirrors. A feedback on the motors, using a light position sensor closed to the spectrometer is almost always needed. This paper aims to gather the main geometrical formulas necessary for the use of a widely used kind of solar tracker, based on two 45{\deg} mirrors in altazimuthal set-up with a light sensor on the spectrometer, and to illustrate them with a tracker developed for atmospheric research by our group.Comment: 14 pages, 7 figures. Second version of the paper as published in Sensors. Main correction: a rotation matrix converted to a reflection matrix. Main addition: a discussion on how the control theory applies to this kind of tracking syte

Spectroscopic Ellipsometry Study of Spark Plasma Sintered Nano Silver

International audienceSpark Plasma Sintered (SPS) silver layers were studied by Spectroscopic Ellipsometry (SE) using an M-2000V spectroscopic ellipsometer from J. A. Woollam Co., Inc. which operate in rotating compensator mod

Expert recommendations for the diagnosis and treatment of iron-deficiency anemia during pregnancy and the postpartum period in the Asia-Pacific region

Anemia during pregnancy and the postpartum period is commonly caused by iron deficiency and is a significant worldwide issue with severe consequences for both mother and developing fetus. From a worldwide perspective, iron-deficiency anemia (IDA) during pregnancy is highest in the Asia-Pacific region; however, there has been little guidance in this region for safe and effective treatment. An expert panel was convened to develop a concise and informative set of recommendations for the treatment of IDA in pregnant and postpartum women in the Asia-Pacific region. This manuscript provides these recommendations and aims to reduce the morbidity and mortality associated with IDA in pregnant and postpartum women in the Asia-Pacific region. The consensus recommendations define anemia as a hemoglobin (Hb) level <10.5g/dL during pregnancy and <10g/dL during the postpartum period, and provide cut-off Hb levels to initiate therapy with oral iron, intravenous iron or red blood cell transfusio

Prototipo inalámbrico para carga de vehículos

La transferencia inalámbrica de potencia (WPT) es una solución atractiva para cargar vehículos eléctricos, cuya demanda aumentará con la Estrategia Nacional de Movilidad Eléctrica en Panamá. Sin embargo, un factor que la afecta negativamente es el desalineamiento entre las bobinas transmisora y receptora, pues provoca la disminución de la potencia transferida. Buscando mitigar este problema, se presenta el diseño y construcción de un prototipo de cargador inalámbrico para caracterizar los efectos del desalineamiento, empleando un inversor medio puente y bobinas con compensación serie-serie. Un microcontrolador es utilizado para suplir y monitorear señales de alta frecuencia. Se utilizó una resistencia como carga. Los resultados muestran que, al operar el sistema a la frecuencia de resonancia, se maximiza la transferencia de potencia y no existe desfase entre las ondas de voltaje y corriente. Por otro lado, al crear desalineamientos controlados en las bobinas, hay un cambio en la frecuencia de resonancia del sistema y se origina un desfase proporcional en las ondas mencionadas