Misure del Fattore di Qualità di Cavità a Microonde alla Temperatura dei Millikelvin

Si presentano le misure del fattore di qualità di una cavità risonante cilindrica alla temperatura di 4.2 K. Si descrive la procedura per ottenere una temperatura di circa 19 mK per mezzo di un refrigeratore a diluizione 3He-4He. Sono riportati i dati della calibrazione delle resistenze di un termometro di RuO2 con le temperature di transizione di un termometro a punti fissi.ope

Misure del Fattore di Qualità di Cavità a Microonde alla Temperatura dei Millikelvin

Si presentano le misure del fattore di qualità di una cavità risonante cilindrica alla temperatura di 4.2 K. Si descrive la procedura per ottenere una temperatura di circa 19 mK per mezzo di un refrigeratore a diluizione 3He-4He. Sono riportati i dati della calibrazione delle resistenze di un termometro di RuO2 con le temperature di transizione di un termometro a punti fissi

Motion control of water droplets by means of optical patterns imprinted on Fe:LiNbO3 crystals

Chemical and morphological surface patterning is very common in micro uidic devices to control the ow. In this project, the dynamics of water droplets moving on a iron-doped lithium niobate (Fe:LiNbO3) crystal which has been exposed to optical patterns produced by lenses will be studied. This optowetting technique will exploit the photovoltaic eect of lithium niobate, that creates surface charges upon illumination and enables the control of droplets without xed electrodes. To reduce the friction, the crystal surfaces will be covered with a micrometric lubricant lm (LIS) made of octadecyltrichlorosilane (OTS) impregnated with silicone oil that acts as hydrophobic dielectric layer. The behaviour of the LIS will be investigated by droplet sliding on glass and Fe:LiNbO3 substrates and compared with results from literature. The interaction between charged regions at the Fe:LiNbO3 surface and water will be proved by analyzing pendant droplets falling on the substrates due to the dielectrophoretic force. In the nal experiments, the motion of drops with dierent volumes on straight lines with dierent inclinations imprinted on samples tilted at dierent angles will be observed by means of video recordings

Oscillatory motion of viscoelastic drops on slippery lubricated surfaces

The introduction of slippery lubricated surfaces allows for the investigation of the flow of highly viscous fluids, which otherwise will hardly move on standard solid surfaces. Here we present the study of the gravity induced motion of small drops of polymeric fluids deposited on inclined lubricated surfaces. The viscosity of these fluids decreases with increasing shear rate (shear thinning) and, more importantly, they exert normal forces on planes perpendicular to shear directions (elasticity). Despite the homogeneity of the surface and of the fluids, drops of sufficiently elastic fluids move downward with an oscillating instantaneous speed whose frequency is found to be directly proportional to the average speed and inversely to the drop volume. The oscillatory motion is caused by the formation of a bulge at the rear of the drop, which will be dragged along the drop free contour by the rolling motion undergone by the drop. This finding can be considered as a kind of new Weissenberg effect applied to moving droplets that combines dynamic wetting and polymer rheology

Air Embolism after Central Venous Catheter Removal: Fibrin Sheath as the Portal of Persistent Air Entry

Central venous catheterization is of common practice in intensive care units; despite representing an essential device in various clinical circumstances, it represents a source of complications, sometimes even fatal, related to its management. We report the removal of a central venous catheter (CVC) that had been wrongly positioned through left internal jugular vein. The vein presented complete thrombosis at vascular ultrasonography. An echocardiogram performed 24 hours after CVC removal showed the presence, apparently unjustified, of microbubbles in right chambers of the heart. A neck-thorax CT scan showed the presence of air bubbles within the left internal jugular vein, left innominate vein, and left subclavian vein. A vascular ultrasonography, focused on venous catheter insertion site, disclosed the presence of a vein-to-dermis fistula, as portal of air entry. Only after air occlusive dressing, we documented echographic disappearance of air bubbles within the right cardiac cavity. This report emphasizes possible air entry even many hours after CVC removal, making it mandatory to perform 24–72-hour air occlusive dressing or, when inadequate, to perform a purse string

Microfluidic Strategies for Extracellular Vesicle Isolation: Towards Clinical Applications

Extracellular vesicles (EVs) are double-layered lipid membrane vesicles released by cells. Currently, EVs are attracting a lot of attention in the biological and medical fields due to their role as natural carriers of proteins, lipids, and nucleic acids. Thus, they can transport useful genomic information from their parental cell through body fluids, promoting cell-to-cell communication even between different organs. Due to their functionality as cargo carriers and their protein expression, they can play an important role as possible diagnostic and prognostic biomarkers in various types of diseases, e.g., cancers, neurodegenerative, and autoimmune diseases. Today, given the invaluable importance of EVs, there are some pivotal challenges to overcome in terms of their isolation. Conventional methods have some limitations: they are influenced by the starting sample, might present low throughput and low purity, and sometimes a lack of reproducibility, being operator dependent. During the past few years, several microfluidic approaches have been proposed to address these issues. In this review, we summarize the most important microfluidic-based devices for EV isolation, highlighting their advantages and disadvantages compared to existing technology, as well as the current state of the art from the perspective of the use of these devices in clinical applications

Halide-driven formation of lead halide perovskites: insight from ab initio molecular dynamics simulations

Controlling the crystallization mechanism of metal halide perovskites is of utmost importance to grow defect-less perovskite layers for efficient solar cells and optoelectronic devices. Despite its relevance, there is a lack of microscopic understanding of the nucleation and crystallization processes during the formation of the perovskite phase from its precursors. To unveil the electronic and atomistic features of this process we carry out ab initio molecular dynamics simulations on a model system which consists of a stoichiometric layered lead iodide (PbI2)·methylammonium iodide (MAI) structure, characteristic of intermediate phases observed in sequential deposition methods. Our results show clear evidence of halide-driven chemistry: MAI iodine ions attack lead ions in the PbI2 layers and cause a nucleophilic substitution of Pb–I bonds with a subsequent breaking of the PbI2 layer. Undercoordinated [PbIn]2−n complexes are initially formed which create the 3D perovskite framework mediated by additional nucleophilic attacks. The relatively fast rearrangement of [PbIn]2−n complexes followed by motion of MA cations limits the perovskite growth. Our results provide insight into the key steps of the perovskite formation on a microscopic scale, providing hitherto inaccessible details on the factors limiting the perovskite growth and on the effect of different halides on the kinetics of crystal formation

Determination of the Dielectrophoretic Force Induced by the Photovoltaic Effect on Lithium Niobate

The actuation of droplets on a surface is extremely relevant for microfluidic applications. In recent years, various methodologies have been used. A promising solution relies on iron-doped lithium niobate crystals that, when illuminated, generate an evanescent electric field in the surrounding space due to the photovoltaic effect. This field can be successfully exploited to control the motion of water droplets. Here, we present an experimental method to determine the attractive force exerted by the evanescent field. It consists of the analysis of the elongation of a pendant droplet and its detachment from the suspending syringe needle, caused by the illumination of an iron-doped lithium niobate crystal. We show that this interaction resembles that obtained by applying a voltage between the needle and a metallic substrate, and a quantitative investigation of these two types of actuation yields similar results. Pendant droplet tensiometry is then demonstrated to offer a simple solution for quickly mapping out the force at different distances from the crystal, generated by the photovoltaic effect and its temporal evolution, providing important quantitative data for the design and characterization of optofluidic devices based on lithium niobate crystals

Shaking Device for Homogeneous Dispersion of Magnetic Beads in Droplet Microfluidics

Magnetic beads (or particles) having a size between 1 and 5 µm are largely used in many biochemical assays devoted to both purification and quantification of cells, nucleic acids, or proteins. Unfortunately, the use of these beads within microfluidic devices suffers from natural precipitation because of their size and density. The strategies applied thus far to cells or polymeric particles cannot be extended to magnetic beads, mainly due to their magnetization and their higher densities. We report an effective shaking device capable of preventing the sedimentation of beads that are stored in a custom PCR tube. After the characterization of the operating principle, the device is validated for magnetic beads in droplets, leading to an equal distribution between the droplets, barely affecting their generation