Droplet mixer based on siphon-induced flow discretization and phase shifting

We present a novel mixing principle for centrifugal microfluidic platforms. Siphon structures are designed to disrupt continuous flows in a controlled manner into a sequence of discrete droplets, displaying individual volumes as low as 60 nL. When discrete volumes of different liquids are alternately issued into a common reservoir, a striation pattern of alternating liquid layers is obtained. In this manner diffusion distances are drastically decreased and a fast and homogeneous mixing is achieved. Efficient mixing is demonstrated for a range of liquid combinations of varying fluid properties such as aqueous inks or saline solutions and human plasma. Volumes of 5 muL have been mixed in less than 20 s to a high mixing quality. One-step dilutions of plasma in a standard phosphate buffer solution up to 1:5 are also demonstrated

Conditions for the onset of the current filamentation instability in the laboratory

Current Filamentation Instability (CFI) is capable of generating strong magnetic fields relevant to explain radiation processes in astrophysical objects and lead to the onset of particle acceleration in collisionless shocks. Probing such extreme scenarios in the laboratory is still an open challenge. In this work, we investigate the possibility of using neutral $e^{-}$ $e^{+}$ beams to explore the CFI with realistic parameters, by performing 2D particle-in-cell simulations. We show that CFI can occur unless the rate at which the beam expands due to finite beam emittance is larger than the CFI growth rate and as long as the role of competing electrostatic two-stream instability (TSI) is negligible. We also show that the longitudinal energy spread, typical of plasma based accelerated electron-positron fireball beams, plays a minor role in the growth of CFI in these scenarios

A flat-topped leaky-wave source for phased arrays with reduced scan losses

International audienceThis paper describes the design of a planar Fabry-Perot leaky wave antenna generating a flat-topped radiation pattern. The flat-topped pattern is achieved by exciting various leaky-wave modes between a metallic ground plane and a superstrate. Two configurations for the superstrate structure are proposed and analyzed: i) dielectric layers; ii) impedance sheets. In all cases, the antennas are fed by a small waveguide opening in the ground plane. An in-house optimization tool based on a Green's function spectral approach is used to derive the appropriate arrangement for the generation of the required flat-topped pattern. The proposed approach is validated numerically for an antenna generating a flat topped pattern in an angular range of ±25°. The proposed flat-topped antenna may be used for the design of phased arrays with reduced scan losses over a given angular range

Erodibilidade do solo nos tabuleiros costeiros.

Para determinar perdas de solo por erosão hídrica, em diferentes situações, são utilizados modelos de predição de erosão, como a Equação Universal de Perdas de Solo (EUPS). A aplicação destes modelos, no planejamento agrícola e ambiental, depende da determinação dos fatores da EUPS, dentre estes a erodibilidade (fator K). Este estudo teve como objetivo determinar a erodibilidade, para as principais classes de solos da região dos Tabuleiros Costeiros, em Aracruz (ES). O experimento foi instalado nos seguintes solos: Argissolo Amarelo textura média/argilosa (PA1), Plintossolo Háplico (FX) e Argissolo Amarelo moderadamente rochoso (PA2). Para o cálculo da erodibilidade, foram utilizados dados de erosividade e de perdas de solo de novembro de 1997 a maio de 2004. As coletas de perdas de solo foram realizadas para cada evento de chuva considerada erosiva. Os valores de erodibilidade foram 0,007 Mg h MJ-1 mm-1; 0,017 Mg h MJ-1 mm-1; e 0,0004 Mg h MJ-1 mm-1, para PA1, FX e PA2, respectivamente

Monoenergetic proton beams accelerated by a radiation pressure driven shock

High energy ion beams (> MeV) generated by intense laser pulses promise to be viable alternatives to conventional ion beam sources due to their unique properties such as high charge, low emittance, compactness and ease of beam delivery. Typically the acceleration is due to the rapid expansion of a laser heated solid foil, but this usually leads to ion beams with large energy spread. Until now, control of the energy spread has only been achieved at the expense of reduced charge and increased complexity. Radiation pressure acceleration (RPA) provides an alternative route to producing laser-driven monoenergetic ion beams. In this paper, we show the interaction of an intense infrared laser with a gaseous hydrogen target can produce proton spectra of small energy spread (~ 4%), and low background. The scaling of proton energy with the ratio of intensity over density (I/n) indicates that the acceleration is due to the shock generated by radiation-pressure driven hole-boring of the critical surface. These are the first high contrast mononenergetic beams that have been theorised from RPA, and makes them highly desirable for numerous ion beam applications

High Repetition-Rate Wakefield Electron Source Generated by Few-millijoule, 30 femtosecond Laser Pulses on a Density Downramp

We report on an experimental demonstration of laser wakefield electron acceleration using a sub-TW power laser by tightly focusing 30-fs laser pulses with only 8 mJ pulse energy on a 100 \mu m scale gas target. The experiments are carried out at an unprecedented 0.5 kHz repetition rate, allowing "real time" optimization of accelerator parameters. Well-collimated and stable electron beams with a quasi-monoenergetic peak in excess of 100 keV are measured. Particle-in-cell simulations show excellent agreement with the experimental results and suggest an acceleration mechanism based on electron trapping on the density downramp, due to the time varying phase velocity of the plasma waves.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Design of a Rotman lens operating in the full K/Ka band using ridge waveguide technology

Several services associated with satellite on the move and 5G applications are populating the K and Ka frequency bands. Beam forming networks are crucial components for achieving the necessary beam flexibility and agility of these systems. The Rotman lens is being widely investigate as a cost-effective solution for overcoming the main limitations of other types of beam forming networks, namely bandwidth, complexity, and size. One of the main design challenges is obtaining broadband transitions for the array and beam ports. In this work, we used a standard K/Ka double ridge (WRD180) for interfacing with the Rotman Lens. The main motivation for this choice is the wide bandwidth, compatible with the K/Ka satcom frequency bands, and the use of air/vacuum propagation medium in the parallel plate waveguide section to avoid dielectric losses associated with microstrip implementations. We present a design capable of fully exploiting the ridge waveguide bandwidth with wide beam scanning, outperforming previous works. The presented design consists of a 13×7 Rotman Lens with a scanning range of ±50 degrees operating between 16 and 40 GHz, validated through full-wave simulations.info:eu-repo/semantics/acceptedVersio

Predicting the output dimensions, porosity and elastic modulus of additive manufactured biomaterial structures targeting orthopedic implants

This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the grant FRH/BD/128657/2017, the projects PTDC/EMS-TEC/5422/2014_ADAPTPROSTHESIS, POCI-01-0145-FEDER-030353 (SMARTCUT), NORTE 010145_FEDER-000018-HAMaBICo and UID/EEA/04436/2019.SLM accuracy for fabricating porous materials is a noteworthy hindrance when aiming to obtain biomaterial cellular structures owing precise geometry, porosity, open-cells dimension and mechanical properties as outcomes. This study provides a comprehensive characterization of seventeen biomaterial Ti6Al4V-based structures in which experimental and numerical investigations (compression stress-strain tests) were carried out. Monomaterial Ti6Al4V cellular structures and multi-material Ti6Al4V-PEEK cellular structures were designed, produced by SLM and characterized targeting orthopedic implants. In this work, the differences between the CAD design and the as-produced Ti6Al4V-based structures were obtained from image analysis and were used to develop predictive models. The results showed that dimensional deviations inherent to SLM fabrication are systematically found for different dimensional ranges. The present study proposes several mathematical models, having high coefficients of determination, that estimate the real dimensions, porosity and elastic modulus of Ti6Al4V-based cellular structures as function of the CAD model. Moreover, numerical analysis was performed to estimate the octahedral shear strain for correlating with bone mechanostat theory limits. The developed models can help engineers to design and obtain near-net shape SLM biomaterials matching the desired geometry, opencells dimensions, porosity and elastic modulus. The obtained results show that by using these AM structures design it is possible to fabricate components exhibiting a strain and elastic modulus that complies with that of bone, thus being suitable for orthopedic implants.info:eu-repo/semantics/publishedVersio

Dual-band dual linear to circular polarization converter in transmission mode-application to K/Ka-band satellite communications

Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications, the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm ×5.3 mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer.info:eu-repo/semantics/acceptedVersio