Bascule de Schmitt | EPFL Graph Search

Une bascule de Schmitt, aussi appelée trigger de Schmitt ou bascule à seuil, est un circuit logique inventé en 1934 par Otto Schmitt, ingénieur américain. Principe C'est une bascule à trois entrées V, SB et SH et une sortie Q. Contrairement aux autres bascules, qui sont commandées en appliquant des signaux logiques à leurs entrées, la bascule de Schmitt est conçue pour être pilotée par une tension analogique, c'est-à-dire qu'il peut prendre n'importe quelle valeur (dans l'intervalle 0 - Vcc afin de ne pas dégrader le circuit). Les entrées SB et SH (seuil bas, seuil haut, ce dernier étant à un potentiel supérieur à SB) sont maintenues à des potentiels fixes ; ceci peut se faire par exemple grâce à un diviseur de tension composé de 3 résistances placées en série entre Vcc et la masse ; SH et SB sont reliés aux points intermédiaires du diviseur. Fonctionnement Le fonctionnement est le suivant :

supposons qu'au départ, V soit à 0 ; Q est alors à 0 ;
quand

Thermal Responsive Silk Composite Membrane for Magnetic Field Triggered Controllable Drug Delivery

Ya Wang

Drug delivery implant which provides localized and controlled drug release is beneficial for the therapies of chronic diseases and tumors. This dissertation aims to develop thermal responsive composite membranes that can be utilized as smart drug release implants. Magnetic field is chosen as the external trigger due to its harmlessness and spatio-temporal control. A fully biodegradable composite membrane is prepared to prevent the risk of secondary damages caused by surgery to take out non-biodegradable implants after the treatment. The membrane is made from silk fibroin and MNPs, and its stability in water can be prolonged up to several months by increasing the content of ß-sheet structures through ethanol annealing. The thermal degradation of the composite membrane starts consistently at around 200 °C, which is independent of membrane thickness, ethanol post-processing, and the existence of magnetic nanoparticles. The membrane can be remotely triggered by an alternating magnetic field (16 mT, 111 kHz) to open nanopores inside, through which a liquid can then diffuse. The controllable release of the Rhodamine B (Rh.B) model drug is achieved by adjusting the exposure time to the magnetic field. A longer exposure time, which results in more nanopore sites, increases the release rate eventually. Another composite membrane consisting of silk fibroin, MNPs, and poly(N-isopropylacrylamide) (PNIPAM) microgels (MGs) is prepared to be utilized as on-demand drug delivery implant, which can realize repeated, multiple releases according to the real-time needs of patients. PNIPAM-based thermal and pH dual sensitive microgel particles are fabricated by copolymerization of three monomers including N-isopropylacrylamide, isopropylmethacrylamide, and methacrylic acid. The dried microgels are uniform spheres with core-shell structures, and the diameter is around 1 µm with a core diameter of 800 nm and shell thickness of 160 nm respectively. It has been found that the microgel shrinks when the temperature increases, whereby its volume phase transition temperature (VPTT) depends also on the pH value. Both parameters are adjusted to be in the physiological relevant window. The measured VPTT is around 38 °C at pH 5.0 and increases to 44 °C at pH 7.4. The controlled release of the Rh.B model drug has been shown by changing the environmental temperature or pH. With higher temperature and more acidic pH, the release rate is faster. Additionally, a higher content of MGs and smaller thickness of the membrane facilitate the release of Rh.B. Furthermore, an alternating magnetic field of 16 mT at 111 kHz is applied to trigger the release of Rh.B remotely. The on/off switching of the magnetic field induces the shrinking/swelling of the microgels, changes reversibly the membrane permeability, and precisely controls the release of the model drug. A control over two orders of magnitude of the release rate (0.01 to 5.0 µg min-1) is achieved by tuning the content of microgels and magnetic nanoparticles, and the thickness of the membrane. In addition, it is found that a higher content of magnetic nanoparticles and a larger thickness contribute to a faster release rate of Rh.B due to the higher heating efficiency. Lastly, the observed much higher release rate of Rh.B in the acidic condition with respect to the physiological one represents a potentially important feature for spatially selective treatment of cancer.

EPFL2020

Caching (Bivariate) Gaussians

Michael Christoph Gastpar, Guillaume Jean Op 't Veld

Caching is a technique that alleviates networks during peak hours by transmitting partial information before a request for any is made. In a lossy setting of Gaussian databases, we study a single-user model in which good caching strategies minimize the data still needed on average once the user requests a file. The encoder decides on a caching strategy by weighing the benefit from two key parameters: the prior preference for a file and the correlation among the files. Considering uniform prior preference but correlated files, caching becomes an application of Wyner's common information and Watanabe's total correlation. We show this case triggers a split: caching Gaussian sources is a non-convex optimization problem unless one spends enough rate to cache all the common information between files. Combining both correlation and user preference we explicitly characterize the full trade-off when the encoder uses Gaussian codebooks in a database of two files: we show that as the size of the cache increases, the encoder should change strategy and increasingly prioritize user preference over correlation. In this specific case we also address the loss in performance incurred if the encoder has no knowledge of the user's preference and show that this loss is bounded.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2020

Thermal Responsive Silk Composite Membrane for Magnetic Field Triggered Controllable Drug Delivery

Ya Wang

EPFL2020