Simultaneous analysis of elastic scattering and transfer/breakup channels for the 6He+208Pb reaction at energies near the Coulomb barrier

The elastic and alpha-production channels for the 6He+208Pb reaction are investigated at energies around the Coulomb barrier (E_{lab}=14, 16, 18, 22, and 27 MeV). The effect of the two-neutron transfer channels on the elastic scattering has been studied within the Coupled-Reaction-Channels (CRC) method. We find that the explicit inclusion of these channels allows a simultaneous description of the elastic data and the inclusive alpha cross sections at backward angles. Three-body Continuum-Discretized Coupled-Channels (CDCC) calculations are found to reproduce the elastic data, but not the transfer/breakup data. The trivially-equivalent local polarization potential (TELP) derived from the CRC and CDCC calculations are found to explain the features found in previous phenomenological optical model calculations for this system.Comment: 7 pages, 6 figures (replaced with updated version

On the security of a new image encryption scheme based on chaotic map lattices

This paper reports a detailed cryptanalysis of a recently proposed encryption scheme based on the logistic map. Some problems are emphasized concerning the key space definition and the implementation of the cryptosystem using floating-point operations. It is also shown how it is possible to reduce considerably the key space through a ciphertext-only attack. Moreover, a timing attack allows the estimation of part of the key due to the existent relationship between this part of the key and the encryption/decryption time. As a result, the main features of the cryptosystem do not satisfy the demands of secure communications. Some hints are offered to improve the cryptosystem under study according to those requirements.Comment: 8 pages, 8 Figure

Laser beam properties and microfluidic confinement control thermocavitation

Thermocavitation, the creation of a vapor bubble by heating a liquid with a continuous-wave laser, has been studied for a wide range of applications. Examples include the development of an actuator for needle-free jet injectors, as the pumping mechanism in microfluidic channels and nanoparticle synthesis. Optimal use in these applications requires control over the bubble dynamics through the laser power and beam radius. However, the influence of the laser beam radius on the bubble characteristics is not fully understood. Here, we present a way to control the beam radius from an optical fiber by changing the distance from the glass-liquid interface. We show that the increase in the beam size results in a longer nucleation time. Numerical simulations of the experiment show that the maximum temperature at nucleation is 237 ± 5 °C and independent of laser parameters. Delayed nucleation for larger beam sizes results in more absorbed energy by the liquid at the nucleation instant. Consequently, a larger beam size results in a faster growing bubble, producing the same effect as reducing the laser power. We conclude that the bubble energy only depends on the amount of absorbed optical energy and it is independent of the beam radius and laser power for any amount of absorbed energy. This effect contrasts with pulsed lasers, where an increase in the beam radius results in a reduction of bubble energy. Our results are of relevance for the use of continuous-wave laser-actuated cavitation in needle-free jet injectors as well as other applications of thermocavitation in microfluidic confinement.</p

Laser beam properties and microfluidic confinement control thermocavitation

Thermocavitation, the creation of a vapor bubble by heating a liquid with a continuous-wave laser, has been studied for a wide range of applications. Examples include the development of an actuator for needle-free jet injectors, as the pumping mechanism in microfluidic channels and crystallization or nanoparticle synthesis. Optimal use in these applications require control over the dynamics of the laser-generated bubble through the laser power and beam radius. In contrast to pulsed lasers, for continuous-wave lasers the influence of the laser beam radius on the bubble characteristics is not fully understood. Here, we present a novel way to control the size of the beam from an optical fiber by changing the distance from the glass-liquid interface. We show that the increase in beam size results in a longer nucleation time. Numerical simulations of the experiment show that the maximum temperature at the moment of nucleation is 237$\pm$5{\deg}C and independent of laser parameters. Due to delayed nucleation for larger beam sizes, more energy is absorbed by the liquid at the nucleation instant. Consequently, a larger beam size results in a faster growing bubble, producing the same effect as reducing the laser power. We conclude that the total bubble energy only depends on the amount of absorbed optical energy and it is independent of the beam radius and laser power for any amount of absorbed energy. This effect contrasts with pulsed lasers, where an increase in beam radius results in a reduction of bubble energy. Our results are of relevance for the use of continuous-wave laser-actuated cavitation in needle-free jet injectors as well as other applications of thermocavitation in microfluidic confinement

Assessing the operating temperature of multi-junction solar cells with novel rear side layer stack and local electrical contacts

Sub-bandgap sunlight provides a source of heat generation in solar cells that is detrimental to performance, especially in space applications where heat dissipation is limited. In this work we assess the impact that an advanced rear-side contact scheme for multi-junction solar cells has on the cell temperature. Our results show that this scheme reduces the optical power absorption below the bandgap of germanium by 81% compared to a standard, full metallization design. Measurements of the electrical and thermal power fluxes performed in vacuum demonstrate that this lower near-infrared light absorption results in 8% less heat dissipated in the cell with the novel rear-side contact scheme when operating at 25 ºC. Modelling of the operating temperature for both cells when fully encapsulated with glass indicates that this effect will also result in a reduction of the operating temperature of 9 ºC for the novel design

Synthesis of temperature-responsive Dextran-MA/PNIPAAm particles for controlled drug delivery using superhydrophobic surfaces

Purpose: To implement a bioinspired methodology using superhydrophobic surfaces suitable for producing smart hydro- gel beads in which the bioactive substance is introduced in the particles during their formation. Methods: Several superhydrophobic surfaces, including polystyrene, aluminum and copper, were prepared. Polymeric solutions composed by photo-crosslinked dextran-methacrylated and thermal responsive poly(N-isopropylacrylamide) mixed with a protein (insulin or albumin) were dropped on the superhydrophobic surfaces, and the obtained millimetric spheres were hardened in a dry environment under UV light. Results: Spherical and non-sticky hydrogels particles were formed in few minutes on the superhydrophobic surfaces. The proteins included in the liquid formulation were homogeneously distributed in the particle network. The particles exhibited temperature-sensitive swelling, porosity and protein release rate, with the responsiveness tunable by the dextran-MA/PNIPAAm weight ratio.Conclusions: The proposed method permitted the preparation of smart hydrogel particles in one step with almost 100% encapsulation yield. The temperature-sensitive release profiles suggest that the obtained spherical-shaped biomaterials are suitable as protein carriers. These stimuli-responsive beads could have potential to be used in pharmaceutical or other biomedical applications, including tissue engineering and regenerative medicine.The authors acknowledge funding from the project: PTDC/QUI/68804/2006 (FCT), IBEROMARE-Procept, FEDER and MICINN (SAF2008-01679). The research leading to these results has also received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement #NMP4-SL-2009-229292. The authors are grateful to project DISC REGENERATION, Collaborative Project-Large-scale integrating project, NMP3-LA-2008-213904 for the use of the UV lamp

Silica Inverse Opal Nanostructured Sensors for Enhanced Immunodetection of Extracellular Vesicles by Quartz Crystal Microbalance with Dissipation Monitoring

Extracellular vesicles (EVs) are nanosized circulating assemblies that contain biomarkers considered promising for early diagnosis within neurology, cardiology, and oncology. Recently, acoustic wave biosensors, in particular based on quartz crystal microbalance with dissipation monitoring (QCM-D), have emerged as a sensitive, label-free, and selective EV characterization platform. A rational approach to further improving sensing detection limits relies on the nanostructuration of the sensor surfaces. To this end, inorganic inverse opals (IOs) derived from colloidal self-assembly present a highly tunable and scalable nanoarchitecture of suitable feature sizes and surface chemistry. This work systematically investigates their use in two-dimensional (2D) and three-dimensional (3D) for enhanced QCM-D EV detection. Precise tuning of the architecture parameters delivered improvements in detection performance to sensitivities as low as 6.24 × 107 particles/mL. Our findings emphasize that attempts to enhance acoustic immunosensing via increasing the surface area by 3D nanostructuration need to be carefully analyzed in order to exclude solvent and artifact entrapment effects. Moreover, the use of 2D nanostructured electrodes to compartmentalize analyte anchoring presents a particularly promising design principle

Thermophysical properties of functionalized graphene nanoplatelet dispersions for improving efficiency in a wind turbine cooling system

A new generation of heat transfer fluids, nanofluids, can play a major role in the development of today’s renewable energies. In the particular case of wind turbines, an undesirable overheating of electrical and mechanical components can provoke a noticeable reduction of overall efficiency due to the temperature is a limiting factor to the electricity generation or even very expensive repair cost because of an unexpected crash of generators, or others turbine components. Dispersions of multiple-layer graphene nanostructures with high thermal conductivity in conventional working fluids are a promising type of new heat transfer fluids due to the excellent performance of nanoadditives in heat transference. Hence, determining the thermophysical properties of these nanomaterials under different conditions is the first step and key issue for analysing and optimizing the dispersions. Although water-based graphene nanoplatelet nanofluids have been investigated and some correlations can be found in the literature, scarce studies were conducted using other industrial working fluids as base fluids. The purpose of this study is to carry out a thorough thermophysical characterization of different loaded samples of functionalized graphene nanoplatelet dispersions in an industrial heat transfer fluid, Havoline XLC Pre-mixed 50/50. Four different nanofluids at mass concentrations (0.25, 0.50, 0.75 and 1.0) wt.% of functionalized graphene nanoplatelets powder were produced. In order to obtain improved long-term stabilities, sodium dodecyl benzene sulphonate was added to the samples at a mass concentration of 0.125 % in relation to the base fluid without appreciable variations in the pH value. Stability was assessed through zeta potential and dynamic light scattering measurements. Tests for determining thermal conductivity were conducted with a transient hot wire technique in a wide temperature range. In addition, densities, dynamic viscosities and specific heat capacities of the samples were experimentally determined at different temperatures in order to carry out further studies such as experimental convective heat transfer coefficients and pressure drops. Increases in thermal conductivity up to 7.3 % were found with not very high viscosity rises.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers