Narrow bandwidth, low-emittance positron beams from a laser-wakefield accelerator.

The rapid progress that plasma wakefield accelerators are experiencing is now posing the question as to whether they could be included in the design of the next generation of high-energy electron-positron colliders. However, the typical structure of the accelerating wakefields presents challenging complications for positron acceleration. Despite seminal proof-of-principle experiments and theoretical proposals, experimental research in plasma-based acceleration of positrons is currently limited by the scarcity of positron beams suitable to seed a plasma accelerator. Here, we report on the first experimental demonstration of a laser-driven source of ultra-relativistic positrons with sufficient spectral and spatial quality to be injected in a plasma accelerator. Our results indicate, in agreement with numerical simulations, selection and transport of positron beamlets containing N e + ≥ 10 5 positrons in a 5% bandwidth around 600 MeV, with femtosecond-scale duration and micron-scale normalised emittance. Particle-in-cell simulations show that positron beams of this kind can be guided and accelerated in a laser-driven plasma accelerator, with favourable scalings to further increase overall charge and energy using PW-scale lasers. The results presented here demonstrate the possibility of performing experimental studies of positron acceleration in a laser-driven wakefield accelerator.

Observation of Monoenergetic Electrons from Two-Pulse Ionization Injection in Quasilinear Laser Wakefields.

The generation of low emittance electron beams from laser-driven wakefields is crucial for the development of compact x-ray sources. Here, we show new results for the injection and acceleration of quasimonoenergetic electron beams in low amplitude wakefields experimentally and using simulations. This is achieved by using two laser pulses decoupling the wakefield generation from the electron trapping via ionization injection. The injection duration, which affects the beam charge and energy spread, is found to be tunable by adjusting the relative pulse delay. By changing the polarization of the injector pulse, reducing the ionization volume, the electron spectra of the accelerated electron bunches are improved.

Automation and control of laser wakefield accelerators using Bayesian optimization.

Laser wakefield accelerators promise to revolutionize many areas of accelerator science. However, one of the greatest challenges to their widespread adoption is the difficulty in control and optimization of the accelerator outputs due to coupling between input parameters and the dynamic evolution of the accelerating structure. Here, we use machine learning techniques to automate a 100 MeV-scale accelerator, which optimized its outputs by simultaneously varying up to six parameters including the spectral and spatial phase of the laser and the plasma density and length. Most notably, the model built by the algorithm enabled optimization of the laser evolution that might otherwise have been missed in single-variable scans. Subtle tuning of the laser pulse shape caused an 80% increase in electron beam charge, despite the pulse length changing by just 1%.

Evaluation of single and stack membraneless enzymatic fuel cells based on ethanol in simulated body fluids.

The purpose of this work is to evaluate single and double-cell membraneless microfluidic fuel cells (MMFCs) that operate in the presence of simulated body fluids SBF, human serum and blood enriched with ethanol as fuels. The study was performed using the alcohol dehydrogenase enzyme immobilised by covalent binding through an array composed of carbon Toray paper as support and a layer of poly(methylene blue)/tetrabutylammonium bromide/Nafion and glutaraldehyde (3D bioanode electrode). The single MMFC was tested in a hybrid microfluidic fuel cell using Pt/C as the cathode. A cell voltage of 1.035V and power density of 3.154mWcm-2 were observed, which is the highest performance reported to date. The stability and durability were tested through chronoamperometry and polarisation/performance curves obtained at different days, which demonstrated a slow decrease in the power density on day 10 (14%) and day 20 (26%). Additionally, the cell was tested for ethanol oxidation in simulated body fluid (SBF) with ionic composition similar to human blood plasma. Those tests resulted in 0.93V of cell voltage and a power density close to 1.237mWcm-2. The double cell MMFC (Stack) was tested using serum and human blood enriched with ethanol. The stack operated with blood in a serial connection showed an excellent cell performance (0.716mWcm-2), demonstrating the feasibility of employing human blood as energy source.

Copper-palladium core-shell as an anode in a multi-fuel membraneless nanofluidic fuel cell: toward a new era of small energy conversion devices.

A membraneless nanofluidic fuel cell with flow-through electrodes that works with several fuels (individually or mixed): methanol, ethanol, glycerol and ethylene-glycol in alkaline media is presented. For this application, an efficient Cu@Pd electrocatalyst was synthesized and tested, resulting outstanding performance until now reported, opening the possibility of power nano-devices for multi-uses purposes, regardless of fuel re-charge employed.

Infección por el virus de la hepatitis C en individuos transfundidos antes de 1994 en Antioquia, Colombia / Hepatitis C Infections among Individuals who Received Transfusions prior to 1994 in Antioquia, Colombia

Introducción: la infección por el virus de la hepatitis C es un problema de salud pública. Según datos de la Organización Mundial de la Salud, se estiman 184 millones de casos de infección por VHC en el mundo. El principal factor de riesgo en países en desarrollo corresponde a la transfusión de componentes sanguíneos. En Colombia, en 1993, se reglamentó el tamizaje serológico en los bancos de sangre para diferentes agentes infecciosos, incluido el VHC; sin embargo, los datos de infección por VHC en la población transfundida antes de esta fecha es limitada. Objetivo: describir la frecuencia de infección por el VHC en una población de individuos transfundidos antes de 1994 en Antioquia. Materiales y Métodos: un total de 166 individuos transfundidos antes de 1994 aceptaron participar en el estudio. A partir de las muestras de suero se realizó la detección de anticuerpos totales contra el VHC (anti-VHC) mediante prueba de ELISA y en las muestras positivas se determinó la presencia del genoma viral por RT-PCR de la región no codificante 5’. Resultados y conclusiones: en el población de estudio se encontró una frecuencia de anticuerpos anti-VHC de 6,6% (11/166) y presencia del genoma del VHC en 7/11 de las muestras; el genotipo 1 se identificó en 4 de las muestras. No se encontró asociación de otros factores de riesgo diferentes a transfusión en los individuos con marcadores de infección por el VHC. Este estudio aporta datos a la epidemiología de la infección por el VHC en Colombia.

Introduction: Infection with the hepatitis C virus is a public health problem. According to the World Health Organization there are an estimated 184 million cases of HCV infection around the world. The main risk factor in developing countries is transfusion of blood components. In 1993, Colombian regulations began requiring serological screening by blood banks for infectious agents including HCV. Nevertheless, data about HCV infections in the population transfused before this date is limited. Objective: The objective of this study is to describe the frequency of HCV infection in the population of individuals transfused before 1994 in Antioquia. Materials and Methods: A total of 166 individuals transfused before 1994 agreed to participate in the study. ELISA tests for antibodies to HCV were performed on these patients’ serum samples. Samples that were positive were tested for the presence of the viral genome by RT-PCR of non-coding region 5. Results and Conclusions: The frequency of anti-HCV antibodies in study population was 6.6% (11/166) while the HCV genome was present in seven of these eleven individuals. Genotype 1 was identified in four of the samples. No associations of different risk factors for transfusion in individuals with markers of HCV infection were found. This study provides data on the epidemiology of HCV infection in Colombia.

A nanofluidic direct formic acid fuel cell with a combined flow-through and air-breathing electrode for high performance.

The use of three-dimensional flow-through nanoporous electrodes and the merging of a flow-through and air-breathing cathode were explored and successfully applied in a formic acid air-breathing nanofluidic fuel cell. The effects of fuel concentration, reaction stoichiometry and catalyst mass loading were investigated, resulting in power densities ranging from 28 to 100 mW cm(-2).

Hybrid microfluidic fuel cell based on Laccase/C and AuAg/C electrodes.

A hybrid glucose microfluidic fuel cell composed of an enzymatic cathode (Laccase/ABTS/C) and an inorganic anode (AuAg/C) was developed and tested. The enzymatic cathode was prepared by adsorption of 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and Laccase on Vulcan XC-72, which act as a redox mediator, enzymatic catalyst and support, respectively. The Laccase/ABTS/C composite was characterised by Fourier Transform Infrared (FTIR) Spectroscopy, streaming current measurements (Zeta potential) and cyclic voltammetry. The AuAg/C anode catalyst was characterised by Transmission electron microscopy (TEM) and cyclic voltammetry. The hybrid microfluidic fuel cell exhibited excellent performance with a maximum power density value (i.e., 0.45 mW cm(-2)) that is the highest reported to date. The cell also exhibited acceptable stability over the course of several days. In addition, a Mexican endemic Laccase was used as the biocathode electrode and evaluated in the hybrid microfluidic fuel cell generating 0.5 mW cm(-2) of maximum power density.

AuPd/polyaniline as the anode in an ethylene glycol microfluidic fuel cell operated at room temperature.

AuPd/polyaniline was used for the first time, for ethylene glycol (EG) electrooxidation in a novel microfluidic fuel cell (MFC) operated at room temperature. The device exhibits high electrocatalytic performance and stability for the conversion of cheap and fully available EG as fuel.

Presence of a radioactive gas in archaeological excavations, determination and mitigation.

During recent archaeological discovery and excavation of a tunnel build approximately 2000 years ago by the Teotihuacans under the feathered serpent temple, in Mexico, abnormal radon concentrations up to 700 Bq m(-3) were measured at several excavation stages. The tunnel is at 15m below the earth surface with a vertical rectangular entrance of 4×4 m(2), a semi cylindrical shape of 3m in diameter, with a probable length of 100 m. This study supports the assumption that at the opening of the tunnel radon concentration was around 5500 Bq m(-3); however, although natural convection in the tunnel atmosphere naturally pups radon out, it build up to a maximum concentration of 2000 Bq m(-3). This paper presents the identification of the radon problem in this archaeological site, dose determination, and the mitigation actions that reduced the radon concentration down to 40 Bq m(-3) that ensure a negligible radon risk for archaeologist.

Radon monitoring in sites of economical importance in Jamaica.

The main task was to evaluate possible radon risk to the public and workers in four caves of economical importance. Green Grotto Cave is a large labyrinthine limestone cave, open to the tourism; kept Rn concentration in the range 30-40 Bq m(-3). Xtabil a coral limestone sea cave is part of a beach resort resulted in very low radon concentration of 10 Bq m(-3). Windsor is an intricate limestone cave system showed Rn concentration in the range 250-350 Bq m(-3). Whereas the Oxford caves, is situated in a region of high radioactivity in soil due to the bauxite mines, reached a maximum of 2592 Bq m(-3).

Analysis of Ag nanoparticles synthesized by bioreduction.

Based on a green chemistry mechanism, small silver clusters were obtained by using biosynthesis with alfalfa (medicago sativa), controlling the size of the nanoparticles base don different pH conditions. The analysis of the samples was made with help of transmission electron microscopy methods, mainly with high angle annular dark field and high resolution transmission electron microscopy. The optimal conditions were identified when the sample was obtained at pH10, which allowed obtaining an average size of 4.09 nm and a standard deviation of 1.59, mainly based on cubic like structures.

Dosimetric assessment of radon in a vegetable system.

An alpha-dose calculation due to radon uptake in anthers of Tradescantia, clone 4430, has been performed. Probability distribution density of the dose in the pollen mother cells was calculated by means of a model that simulates the interaction of separate alpha-particles with these cells. It is shown that alpha-radiation from either radon or its decay products surrounding the buds does not reach pollen mother cells because of the short-range alpha-particles. However, it is suggested that radon diffuses through the gap structure of the bud to the anther from which a radon-gas adsorption process takes place. Absorbed-dose calculations in the anther are discussed as well as their relationship to the experimental results of micronucleus induction in pollen mother cells. The radon concentration interval used (0.85 kBq m(-3)-98.16 kBq m(-3)) is equivalent to the exposure to an average environmental radon concentration (40 Bq m(-3)) for 2.3 months or 22.1 years, respectively. The lowest radon concentration to induce micronuclei was 12.1 kBq m(-3), which is 15 times in excess of that adopted for old buildings in Canada.

Heavy metal concentrations in water and bottom sediments of a Mexican reservoir.

Metal concentrations have been measured in water and sediments of the Jose Antonio Alzate Reservoir, Mexico, using EDXRF and ICP techniques. Spatial and temporal distributions of total metal levels have been identified; no organised pattern was detected for any particular metal concentration. Temporal variations of metal concentrations show evidence of the water self-cleaning capacity of the reservoir, despite the high-level metal contamination determined.

Genetic effects observed in tetrads of Tradescantia induced by radon.

Inflorescences of Tradescantia clone 4430 were exposed to different concentrations of radon (Rn) gas (0.85, 12.10, 36.50 and 98.16 kBq/m3) from plants placed in an acrylic chamber that received radon from a container with pitchblende (containing uranium mineral). The exposure time was 24 h, afterwards the plants were left for 6 h in water and constantly aerated. Positive control plants were irradiated with gamma rays (0.8 Gy) and negative control plants received ambient air only (the background measurement had a mean of 0.38 kBq/m3). Micronuclei (MCN) in the tetrads induced by alpha particles emitted from Rn were tabulated and a linear concentration response was obtained. The potency of radon to induce MCN from the slope of the regression line was 0.13 MCN/kBq/m3 of alpha-radiation. Radon could reach the anthers by diffusion through the aerial spaces within the buds.

SOS induction by low activity alpha sources: microdosimetric considerations.

The SOS response to alpha-radiation was measured using two Escherichia coli strains with differential repair capabilities. Monolayers of exponentially growing cells, placed on cellulose acetate filters, were exposed to an electrodeposited 252Cf alpha source to total doses from 46 to 165 cGy at a dose-rate of 0.8 cGy/min. A mean alpha energy of 2.9 MeV, with a corresponding LET of 133 keV/micrometer (for water) was attained by means of a filter placed between the bacterial culture and the radioactive source. Owing to the low fluences ranging from 0.013 to 0.037 alpha-particles/cell and short irradiation times, calculations of the estimated number of irradiated cells were done to obtain the total absorbed doses by the culture. The results show that in spite of the low doses, the damage was sufficient to induce the SOS function in one of the strains used (PQ37). Nevertheless in another strain IN88, lacking double strand break repair and which should be more sensitive, SOS induction could not be observed, probably due to the killing effect of the high LET radiation.