7,706 research outputs found
Paper-based chromatic toxicity bioassay by analysis of bacterial ferricyanide reduction
Water quality assessment requires a continuous and strict analysis of samples to guarantee compliance with established standards. Nowadays, the increasing number of pollutants and their synergistic effects lead to the development general toxicity bioassays capable to analyse water pollution as a whole. Current general toxicity methods, e.g. Microtox®, rely on long operation protocols, the use of complex and expensive instrumentation and sample pre-treatment, which should be transported to the laboratory for analysis. These requirements delay sample analysis and hence, the response to avoid an environmental catastrophe. In an attempt to solve it, a fast (15 min) and low-cost toxicity bioassay based on the chromatic changes associated to bacterial ferricyanide reduction is here presented. E. coli cells (used as model bacteria) were stably trapped on low-cost paper matrices (cellulose-based paper discs, PDs) and remained viable for long times (1 month at -20 °C). Apart from bacterial carrier, paper matrices also acted as a fluidic element, allowing fluid management without the need of external pumps. Bioassay evaluation was performed using copper as model toxic agent. Chromatic changes associated to bacterial ferricyanide reduction were determined by three different transduction methods, i.e. (i) optical reflectometry (as reference method), (ii) image analysis and (iii) visual inspection. In all cases, bioassay results (in terms of half maximal effective concentrations, EC50) were in agreement with already reported data, confirming the good performance of the bioassay. The validation of the bioassay was performed by analysis of real samples from natural sources, which were analysed and compared with a reference method (i.e. Microtox). Obtained results showed agreement for about 70% of toxic samples and 80% of non-toxic samples, which may validate the use of this simple and quick protocol in the determination of general toxicity. The minimum instrumentation requirements and the simplicity of the bioassay open the possibility of in-situ water toxicity assessment with a fast and low-cost protocolPostprint (author's final draft
Comparison between measured and predicted turbulence frequency spectra in ITG and TEM regimes
The observation of distinct peaks in tokamak core reflectometry measurements
- named quasi-coherent-modes (QCMs) - are identified as a signature of
Trapped-Electron-Mode (TEM) turbulence [H. Arnichand et al. 2016 Plasma Phys.
Control. Fusion 58 014037]. This phenomenon is investigated with detailed
linear and nonlinear gyrokinetic simulations using the \gene code. A Tore-Supra
density scan is studied, which traverses through a Linear (LOC) to Saturated
(SOC) Ohmic Confinement transition. The LOC and SOC phases are both simulated
separately. In the LOC phase, where QCMs are observed, TEMs are robustly
predicted unstable in linear studies. In the later SOC phase, where QCMs are no
longer observed, ITG modes are identified. In nonlinear simulations, in the ITG
(SOC) phase, a broadband spectrum is seen. In the TEM (LOC) phase, a clear
emergence of a peak at the TEM frequencies is seen. This is due to reduced
nonlinear frequency broadening of the underlying linear modes in the TEM regime
compared with the ITG regime. A synthetic diagnostic of the nonlinearly
simulated frequency spectra reproduces the features observed in the
reflectometry measurements. These results support the identification of core
QCMs as an experimental marker for TEM turbulenc
Design and realization of a sputter deposition system for the \textit{in situ-} and \textit{in operando-}use in polarized neutron reflectometry experiments
We report on the realization of a sputter deposition system for the in situ-
and in operando-use in polarized neutron reflectometry experiments. Starting
with the scientific requirements, which define the general design
considerations, the external limitations and boundaries imposed by the
available space at a neutron beamline and by the neutron and vacuum
compatibility of the used materials, are assessed. The relevant aspects are
then accounted for in the realization of our highly mobile deposition system,
which was designed with a focus on a quick and simple installation and
removability at the beamline. Apart from the general design, the in-vacuum
components, the auxiliary equipment and the remote control via a computer, as
well as relevant safety aspects are presented in detail.Comment: Submitted for publication in Nuclear Inst. and Methods in Physics
Research, A. (1st revised version
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Distributed Strain Sensing Using Electrical Time Domain Reflectometry With Nanocomposites
Soft X-ray reflectivity: from quasi-perfect mirrors to accelerator walls
Reflection of light from surfaces is a very common, but complex phenomenon
not only in science and technology, but in every day life. The underlying basic
optical principles have been developed within the last five centuries using
visible light available from the sun or other laboratory light sources. X-rays
were detected in 1895, and the full potential of soft- and hard-x ray radiation
as a probe for the electronic and geometric properties of matter, for material
analysis and its characterisation is available only since the advent of
synchrotron radiation sources some 50 years ago. On the other hand
high-brilliance and high power synchrotron radiation of present-days 3rd and
4th generation light sources is not always beneficial. Highenergy machines and
accelerator-based light sources can suffer from a serious performance drop or
limitations due to interaction of the synchrotron radiation with the
accelerator walls, thus producing clouds of photoelectrons (e-cloud) which in
turn interact with the accelerated beam. Thus the suitable choice of
accelerator materials and their surface coating, which determines the x-ray
optical behaviour is of utmost importance to achieve ultimate emittance. Basic
optical principles and examples on reflectivity for selected materials are
given here.Comment: 11 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Italy; CERN Yellow Report CERN-2013-002, pp.105-11
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