Dynamic fault trees resolution: A conscious trade-off between analytical and simulative approaches

Safety assessment in industrial plants with ‘major hazards’ requires a rigorous combination of both qualitative and quantitative techniques of RAMS. Quantitative assessment can be executed by static or dynamic tools of dependability but, while the former are not sufficient to model exhaustively time-dependent activities, the latter are still too complex to be used with success by the operators of the industrial field.In this paper we present a review of the procedures that can be used to solve quite general dynamic fault trees (DFT) that present a combination of the following characteristics: time dependencies, repeated events and generalized probability failure.Theoretical foundations of the DFT theory are discussed and the limits of the most known DFT tools are presented. Introducing the concept of weak and strong hierarchy, the well-known modular approach is adapted to study a more generic class of DFT. In order to quantify the approximations introduced, an ad-hoc simulative environment is used as benchmark.In the end, a DFT of an accidental scenario is analyzed with both analytical and simulative approaches. Final results are in good agreement and prove how it is possible to implement a suitable Monte Carlo simulation with the features of a spreadsheet environment, able to overcome the limits of the analytical tools, thus encouraging further researches along this direction.     

Saturated patterned excitation microscopy--a concept for optical resolution improvement

The resolution of optical microscopy is limited by the numerical aperture and the wavelength of light. Many strategies for improving resolution such as 4Pi and I5M have focused on an increase of the numerical aperture. Other approaches have based resolution improvement in fluorescence microscopy on the establishment of a nonlinear relationship between local excitation light intensity in the sample and in the emitted light. However, despite their innovative character, current techniques such as stimulated emission depletion (STED) and ground-state depletion (GSD) microscopy require complex optical configurations and instrumentation to narrow the point-spread function. We develop the theory of nonlinear patterned excitation microscopy for achieving a substantial improvement in resolution by deliberate saturation of the fluorophore excited state. The postacquisition manipulation of the acquired data is computationally more complex than in STED or GSD, but the experimental requirements are simple. Simulations comparing saturated patterned excitation microscopy with linear patterned excitation microscopy (also referred to in the literature as structured illumination or harmonic excitation light microscopy) and ordinary widefield microscopy are presented and discussed. The effects of photon noise are included in the simulations.     

MDA improvement technique for lung counter measurements of uranium workers

A practical and simple method was employed to improve the minimum detectable activity (MDA) for lung counting measurements by summing several accumulated spectra. The method was checked for natural uranium, which produces peaks due to photon energies of 63.3, 92.6 and 185.7 keV. By combining nine measurements, an overall improvement of the MDA by a factor of about 3 was achieved. Uranium contamination levels lower than the MDA of a single spectrum could be detected with acceptable accuracy when analyzing the sum spectra. Specific results are given for four workers occupationally exposed to natural uranium.     

An improvement to the space resolution of charged tracks

A simple tracking method is to look for the U, X and V triple coincidences in a wire chamber, but the space resolution is in general not satisfactory. In this paper, we consider the use of space correction for the inclined planes in a chamber. The resolution can be much improved for both the proportional chamber and the drift chamber. For proportional chambers, the combination of this method and the wire-spacing “drift distance” technique, further improved the resolution.     

Nitric oxide microsensor for high spatial resolution measurements in biofilms and sediments

Nitric oxide (NO) is a ubiquitous biomolecule that is known as a signaling compound in eukaryotes and prokaryotes. In addition, NO is involved in all conversions of the biogeochemical nitrogen cycle: denitrification, nitrification, and the anaerobic oxidation of ammonium (Anammox). Until now, NO has not been measured with high spatial resolution within microbial communities, such as biofilms, sediments, aggregates, or microbial mats, because the available sensors are not robust enough and their spatial resolution is insufficient. Here we describe the fabrication and application of a novel Clark-type NO microsensor with an internal reference electrode and a guard anode. The NO microsensor has a spatial resolution of 60-80 microm, a sensitivity of 2 pA microM-1, and a detection limit of approximately 30 nM. Hydrogen sulfide (H2S) was found to be a major interfering compound for the electrochemical detection of NO. The application of the novel NO microsensor to nitrifying biofilms and marine sediments revealed dynamic NO concentration profiles with peaks in the oxic parts of the samples. The local concentrations suggested that NO may be an important bioactive compound in natural environments. The consumption and production of NO occurs in separate regions of stratified microbial communities and indicates that it is linked to distinct biogeochemical cycles.     

The effective resolution measurements in scope of sine-fit test

This paper presents a detailed analysis of the effective resolution (efr) measurements in scope of the IEEE Standard 1057 sine-fit test. The results explain not only a poor repeatability in the efr measurement but also give some hints how to improve it. The two-point method proposed here enables the compensation of the inherent bias influence on the efr accuracy. The idea is accomplished by using the correct standard deviation in the efr definition. The standard deviation depends on the amplitude V and dc bias C of a pure sine wave stimulus     

High resolution spectral measurements of Raman shifts in barium nitrate

High resolution spectral measurements of the first, second, and third Stokes shifts in barium nitrate are reported. The laser source for the experiment is a frequency-doubled, injection-seeded Nd:YAG laser. Spectra for both single-pass conversion and for a Raman oscillator are compared. Significant gain narrowing of the spectrum is observed.     

Determination of the depth resolution in Auger depth profiling measurements

The depth resolution Δz of the Auger depth profiling method was studied in multilayer thin films comprising alternate layers of nickel and molybdenum or of cobalt and molybdenum. The composition-depth profiles of several interfaces located at different depths within the same film were compared. Thus changes which depended on the sputtering depth z could be distinguished from effects which were independent of z. According to a statistical theory the profiles of the interfaces can be described by a gaussian error function. An empirical formula $\text{Δz = αz}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ β}$ was determined from the width of the profiles. The first term agrees with the statistical theory and the constant term is explained by the roughness of the interface. The order of magnitude of β (≈ 3 nm) suggests that the depth resolution in the films is not limited by the escape depth of the Auger electrons (? 1.5 nm). The relative depth resolution $\text{Δz}\text{z}$ improves with increasing sputtering depth.     

Postacquisition mass resolution improvement in time-of-flight secondary ion mass spectrometry

Good mass resolution can be difficult to achieve in time-of-flight secondary ion mass spectrometry (TOF-SIMS) when the analysis area is large or when the surface being analyzed is rough. In most cases, a significant improvement in mass resolution can be achieved by postacquisition processing of raw data. Methods are presented in which spectra are extracted from smaller regions within the original analysis area, recalibrated, and selectively summed to produce spectra with higher mass resolution than the original. No hardware modifications or specialized instrument tuning are required. The methods can be extended to convert the original raw file into a new raw file containing high mass resolution data. To our knowledge, this is the first report of conversion of a low mass resolution raw file into a high mass resolution raw file using only the data contained within the low mass resolution raw file. These methods are applicable to any material but are expected to be particularly useful in analysis of difficult samples such as fibers, powders, and freeze-dried biological specimens.     

Elastographic axial resolution criteria: an experimental study

In elastography, window size has been typically used synonymously with resolution. Strain is estimated by computing the gradient of the displacement estimates, which have a direct dependence on the window size. However, the resolution is also dependent on the separation between these windows. The intricate relationship between the window size, window shift, and resolution has not previously been explored. In this article, we perform a controlled simulation experiment to evaluate the relationship among elastographic axial resolution, window size, and window shift. We conclude that the axial resolution can be expressed as a bilinear function of window size and window shift, the latter having a much larger weight.     

Sensitivity study of two high-throughput resolution metrics for photoresists

The resolution of chemically amplified resists is becoming an increasing concern, especially for lithography in the extreme ultraviolet (EUV) regime. Large-scale screening is currently under way to identify resist platforms that can support the demanding specifications required for EUV lithography. Current screening processes would benefit from the development of metrics that can objectively quantify resist resolution in a high-throughput fashion. Here we examine two high-throughput metrics for resist resolution determination. After summarizing their details and justifying their utility, we characterize the sensitivity of both metrics to known uncertainties in exposure tool aberrations and focus control. For an implementation at EUV wavelengths, we report aberration and focus-limited error bars in extracted resolution of approximately 1.25 nm rms for both metrics, making them attractive candidates for future screening and downselection efforts.     

Scanning electrochemical cell microscopy: theory and experiment for quantitative high resolution spatially-resolved voltammetry and simultaneous ion-conductance measurements

Scanning electrochemical cell microscopy (SECCM) is a high resolution electrochemical scanning probe technique that employs a dual-barrel theta pipet probe containing electrolyte solution and quasi-reference counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochemical cell. The substrate can be an electrical conductor, semiconductor, or insulator. The main focus here is on the general case where the substrate is a working electrode, and both ion-conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice, a small perpendicular oscillation of the probe with respect to the substrate is employed, so that an alternating conductance current (ac) develops, due to the change in the dimensions of the electrolyte contact (and hence resistance), as well as the direct conductance current (dc). It is shown that the dc current can be predicted for a fixed probe by solving the Nernst-Planck equation and that the ac response can also be derived from this response. Both responses are shown to agree well with experiment. It is found that the pipet geometry plays an important role in controlling the dc conductance current and that this is easily measured by microscopy. A key feature of SECCM is that mass transport to the substrate surface is by diffusion and, for charged analytes, ion migration which can be controlled and varied quantifiably via the bias between the two QRCEs. For a working electrode substrate this means that charged redox-active analytes can be transported to the electrode/solution interface in a well-defined and controllable manner and that relatively fast heterogeneous electron transfer kinetics can be studied. The factors controlling the voltammetric response are determined by both simulation and experiment. Experiments demonstrate the realization of simultaneous quantitative voltammetric and ion conductance measurements and also identify a general rule of thumb that the surface contacted by electrolyte is of the order of the pipet probe dimensions.     

Problem of improvement of the system of provision for unity in measurements in the country

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 5–6, October, 1992.     

Four archetypes of process improvement: a Q-methodological study

This paper explores the process improvement approaches of organisations. It seeks to identify process redesign principles and the combinations of these principles that are used successfully in industry. We use Q-methodology to explore the viewpoints of a range of highly experienced process experts about the success of 16 improvement practices. Q-methodology enables the examination of the similarities and differences in the success of the improvement principles used by organisations in order to inform archetypes of process improvement. Overall, our findings suggest that process improvement is determined through the application of two foundational principles combined with one of four archetypes. ‘Remove non-value-adding tasks’ and ‘re-sequence tasks’ are described as foundational principles of process improvement, whilst outsourcing needs to be approached with caution. Furthermore, we articulate four distinctive archetypes comprising unique configurations of improvement principles that can be used to redesign operational processes. Based on this evidence we propose a typology of process improvement. This work suggests that rather than adopting generic improvement frameworks, managers should consult the typology to determine the archetype in closest proximity to their specific requirements. This study has several limitations including the small number of items populating the concourse and the fact that implementation problems are not taken into account.     

Absolute high spectral resolution measurements of surface solar radiation for detection of water vapour continuum absorption

Solar-pointing Fourier transform infrared (FTIR) spectroscopy offers the capability to measure both the fine scale and broadband spectral structure of atmospheric transmission simultaneously across wide spectral regions. It is therefore suited to the study of both water vapour monomer and continuum absorption behaviours. However, in order to properly address this issue, it is necessary to radiatively calibrate the FTIR instrument response. A solar-pointing high-resolution FTIR spectrometer was deployed as part of the 'Continuum Absorption by Visible and Infrared radiation and its Atmospheric Relevance' (CAVIAR) consortium project. This paper describes the radiative calibration process using an ultra-high-temperature blackbody and the consideration of the related influence factors. The result is a radiatively calibrated measurement of the solar irradiation at the ground across the IR region from 2000 to 10?000?cm(-1) with an uncertainty of between 3.3 and 5.9 per cent. This measurement is shown to be in good general agreement with a radiative-transfer model. The results from the CAVIAR field measurements are being used in ongoing studies of atmospheric absorbers, in particular the water vapour continuum.     

Inversion of light-scattering measurements for particle size and optical constants: theoretical study

We invert the Fredholm equation representing the light scattered by a single spherical particle or a distribution of spherical particles to obtain the particle size distribution function and refractive index. We obtain the solution by expanding the distribution function as a linear combination of a set of orthonormal basis functions. The set of orthonormal basis functions is composed of Schmidt-Hilbert eigenfunctions and a set of supplemental basis functions, which have been orthogonalized with respect to the Schmidt-Hilbert eigenfunctions by using the Gram-Schmidt orthogonalization procedure. We use the orthogonality properties of the basis functions and of the eigenvectors of the kernel covariance matrix to obtain the solution that minimizes the residual errors subject to a trial function constraint. The inversion process is described, and results from the inversion of several simulated data sets are presented.     

An information-theoretic methodology for the resolution of pure component spectra without prior information using spectroscopic measurements

The resolution of pure component spectra based on spectroscopic measurements from a reaction system is a challenging task for chemometric systems in the absence of a priori knowledge about the reaction components involved. A popular approach in the literature is based on constrained entropy minimization of the second-order derivative of the resolved pure component spectra. Using an analytical information theoretic framework, it can however be shown that minimization of this cost function is not sufficient to completely separate the underlying components from a set of mixture spectra. Instead, an augmented objective function derived from this analysis is proposed for complete minimization of the mutual information between separated components. The final optimization approach is further shown to be analog to independent component analysis (ICA), a signal processing technique successfully applied to biomedical and speech data to separate linear source mixtures in the absence of a priori information. The developed theoretical insights and proposed methodologies in this paper are illustrated in a simulation study on the separation of three component spectra based on absorbance data acquired from a first-order kinetic reaction system.     

In-plane permeability measurements: a nordic round-robin study

Three methods to measure the in-plane permeability are compared. The methods are based on the wetting and saturated parallel flow techniques and the wetting radial flow technique. It is found that the stability of all three methods is very good. The best repeatability in the results is obtained with the wetting parallel flow technique. A main drawback of this method is, however, that the samples are not saturated hence, the saturated parallel flow method is suggested for continued evaluation. The standard deviation from repeatable measurements of this method is 14 and 20% for the two fabrics tested. By a round-robin comparison at three laboratories it is found that the reproducibility of the saturated parallel flow technique is in the same range as the repeatability of the method. Furthermore, it is shown that the liquid tested and the pressure applied have very small influence on the results. It is clear that most of the scatter is due to the sample preparation and variations in the material. Accordingly, a continued work should be concentrated on improvements of the sample preparation, and development of methods to reduce the influence, from small errors, in sample preparation on the results.