Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Atomic spectrometry update: Review of advances in the analysis of metals, chemicals and materials

There has been a large increase in the number of papers published that are relevant to this review over this review period. The growth in popularity of LIBS is rapid, with applications being published for most sample types. This is undoubtedly because of its capability to analyse in situ on a production line (hence saving time and money) and its minimally destructive nature meaning that both forensic and cultural heritage samples may be analysed. It also has a standoff analysis capability meaning that hazardous materials, e.g. explosives or nuclear materials, may be analysed from a safe distance. The use of mathematical algorithms in conjunction with LIBS to enable improved accuracy has proved a popular area of research. This is especially true for ferrous and non-ferrous samples. Similarly, chemometric techniques have been used with LIBS to aid in the sorting of polymers and other materials. An increase in the number of papers in the subject area of alternative fuels was noted. This was at the expense of papers describing methods for the analysis of crude oils. For nanomaterials, previous years have seen a huge number of single particle and field flow fractionation characterisations. Although several such papers are still being published, the focus seems to be switching to applications of the nanoparticles and the mechanistic aspects of how they retain or bind with other analytes. This is the latest review covering the topic of advances in the analysis of metals, chemicals and materials. It follows on from last year's review1-6 and is part of the Atomic Spectrometry Updates series

Thick film screen printed environmental and chemical sensor array reference electrodes suitable for subterranean and subaqueous deployments

Purpose - Thick film environmental and chemical sensor arrays designed for deployment in both subterranean and submerged aqueous applications are reported.Design/methodology/approach - Various choices of materials for reference electrodes employed in these different applications have been evaluated and the responses of the different sensor types are compared and discussed. Findings - Results indicate that the choice of binder materials is critical to the production of sensors capable of medium term deployment (e.g. several days) as the binders not only affect the tradeoff between hydration time and drift but also have a significant bearing on device sensitivity and stability. Sensor calibration is shown to remain an issue with long term deployments (e.g. several weeks) but this can be ameliorated in the medium term with the use of novel device fabrication and packaging techniques.Originality/value – The reported results indicates that is possible through careful choice of materials and fabrication methods to achieve near stable thick film reference electrodes that are suitable for use in solid state chemical sensors in variety of different application areas

A theoretical and experimental investigation of accelerometer design using thick-film technology

This thesis describes research undertaken to develop a low-cost accelerometer using thick-film strain gauge transduction elements. A systematic design process was adopted, including a study of substrate materials, evaluation of the fatigue life of the transducer, investigations of the mechanical and thermal properties of thick-film inks, and an assessment of the limits on resolution imposed by the intrinsic noise characteristics of thick-film resistors.The research has shown that fatigue is unlikely to be a problem for thick-film transducers and has led to a new explanation of the nature of thermally-induced resistance changes observed in thick-film resistors. It has also been shown that since the thick-film resistor noise exhibits a 1/f characteristic the resolution of the transducer is frequency dependant.The accelerometer design adopted uses thick-film strain gauges in a novel 'z-axis' configuration, which confers a number of advantages on the design. Firstly, the thick-film transducers are kept in a state of compressive stress, which is varied by the acceleration in a manner which allows the strain gauges to only experience tensile stress. This makes the design very rugged, and allows the use of ceramic substrates. Secondly, the use of the z-axis technique gives a higher gauge factor than all other methods, thus enhancing the sensitivity of the sensor and simplifying the signal conditioning required

An explanation of thermal behaviour of thick film strain gauges

Earlier study shows that resistor thickness of the thick film strain gauge can affect its temperature characteristic, which is usually a roughly parabolic curve. Thicker resistors tend to exhibit a higher positive temperature coefficient of resistance (TCR) and a lower T&min;, the temperature at which the TCR changes to zero in the curve. This paper presents a possible explanation of this observation based on an analysis of strain profiles and resistivity behaviour difference in resistors with different thicknesses subjected to temperature variation

An investigation of the effect of poling conditions on the characteristics of screen-printed piezoceramics

A study of the effect of poling conditions on screen-printed piezoceramics was undertaken. Printable pastes were produced, using a commercially available lead zirconate titanate (PZT) powder, mixed with two types of binder, lead (II) oxide and a lead borosilicate glass. Sample devices were fabricated using the two paste types and processed, using standard thick film techniques, before being poled under varying conditions. Samples were compared by measurement of piezoelectric charge constant, d33 and using scanning electron microscopy techniques. Temperature and time are shown to increase poling efficiency, while poling field reaches an optimum at 2-3 MV m-1. The PZT layers start to fail through a process of dielectric breakdown at fields of 3.5 MV m-1 and above

Investigation of the fabrication parameters of thick film oxide-PVC pH electrodes using experimental designs

This paper describes a study into the development of an optimum fabrication process for the batch production of thick film titanium oxide-PVC pH electrodes. Multi-factorial experimental plans are used to explore the effect of fabrication parameters on the average sensitivity of sensors and their batch variability. Analysis of the results indicates that a number of the factors have a small effect on the sensitivity. Factors of particular importance are identified and TiO2 in a PVC binder is examined in detail. The optimal values for these fabrication values are identified and examined. Mechanisms for the experimentally observed sub-Nernstian responses and immersion-time variations in sensor behaviour are discussed