196,447 research outputs found
Interpretation, validation and segmentation of preference mapping models
No full textIn this paper we discuss an extension to preference mapping of the method proposed in [Endrizzi, I., Menichelli, E., Johansen, S. B., Olsen, N. V., & Næs, T. (2011). Handling of individual differences in rating-based conjoint analysis. Food Quality and Preference, 22, 241-254 ] for accommodating both population averages and individual differences in the same model. The method, based on average estimates and residuals, is a combination of ANOVA, PCA and PLS-DA, which are well-known techniques that can be run in almost all statistical software packages. Main attention is given to the relation between the double-centred residual matrix which highlights differences between consumers in their relative position as compared to the average consumer values and the standard centring in preference mapping. This approach has been found particularly useful for highlighting differences in preference pattern among the consumers. Furthermore, the interpretation and the segmentation, that is here taking place based on differences in acceptance pattern, are graphically oriented. In addition, some possible alternatives to the generally used validation method in PCA are suggested. The approach is then illustrated using two data-sets from consumer studies of apple and raspberry juice, showing that when individual differences are analysed by the present method, interesting results regarding individual differences in response pattern are detected
Application of an expectation maximization method to the reconstruction of X-ray-tube spectra from transmission data
No full textAn expectation maximization method is applied to the reconstruction of
X-ray tube spectra from transmission measurements in the energy range
7 − 40 keV. A semiconductor single-photon counting detector, ionization
chambers and a scintillator-based detector are used for the experimental
measurement of the transmission. The number of iterations required to reach
an approximate solution is estimated on the basis of the measurement error,
according to the discrepancy principle. The effectiveness of the stopping rule
is studied on simulated data and validated with experiments. The quality
of the reconstruction depends on the information available on the source
itself and the possibility to add this knowledge to the solution process is
investigated. The method can produce good approximations provided that
the amount of noise in the data can be estimated
X-ray spectra reconstruction from analysis of attenuation data: A Back Scattering Thomson source application
No full textIt is known that useful information about the spectral distribution of an X-ray beam can be extracted by measuring and analyzing its transmission curve. This kind of approach to the characterization of the distribution in energy of photons is justified when the direct measurements of the energy of a single photon becomes too expensive or cannot just be performed. Thomson Scattering sources can produce up to 10(8) photons within a pulse 10 ps long. Hence the rate of incidence of photons is too high to apply traditional X-ray spectroscopy methods while methods based on the transmission curve can still be used. In order to propose an application of these techniques in the characterization of a Thomson Scattering source we studied an iterative statistical algorithm (Expectation-Maximization) used as a regularization method on simulated measurement computed starting from a calculated energy distribution with peak energy of 20 keV. Results show that this method can give good approximations in the low energy range (approximately 20 keV) and that it is at least sensible to a small amount of radiation in the higher part of the energy range (approximately 70 keV). The robustness of the method against non-ideal experimental conditions is also considered. (C) 2009 Elsevier B.V. All rights reserved
Laboratory implementation of edge illumination X-ray phase-contrast imaging with energy-resolved detectors
No full textEdge illumination (EI) X-ray phase-contrast imaging (XPCI) has potential for applications in different fields of research, including materials science, non-destructive industrial testing, small-animal imaging, and medical imaging. One of its main advantages is the compatibility with laboratory equipment, in particular with conventional non-microfocal sources, which makes its exploitation in normal research laboratories possible. In this work, we demonstrate that the signal in laboratory implementations of EI can be correctly described with the use of the simplified geometrical optics. Besides enabling the derivation of simple expressions for the sensitivity and spatial resolution of a given EI setup, this model also highlights the EI’s achromaticity. With the aim of improving image quality, as well as to take advantage of the fact that all energies in the spectrum contribute to the image contrast, we carried out EI acquisitions using a photon-counting energy-resolved detector. The obtained results demonstrate that this approach has great potential for future laboratory implementations of EI. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Application of an expectation maximization method to the reconstruction of X-ray-tube spectra from transmission data
No full text
Invasive Crayfish moving Northwards: management challenges and policy implications at the local scale
No full textFreshwater ecosystems in Italy, as most European countries, have been severely impacted by the invasion of alien crayfish. The two most widespread species in Trentino (NE Italy) are Procambarus clarkii and Faxionus limosus; for both species, the high elevation and cold climate of most of the Trentino territory represent a climatic barrier to their northwards spread. Procambarus clarkii is present in one small lake at 950 m asl, and Faxionus limosus in a group of 5 lakes at 450 m asl, over an area of about 80km2. the introduction of both species is associated with fish restocking, and lead to the extinction of existing populations of the native stone crayfish Austropotamobius pallipes. The Management Plan of Austropotamobius pallipes in Trentino listed the eradication/containment of these IAS populations among the conservation priorities for the native populations. The eradication campaigns of P. clarkii started in 2018 with a release/recapture campaign aimed at assessing the abundance of the populations, and continued in 2020, 2021, 2022. As a result, the capture efficiency decreased, suggesting a population reduction trend. The containment of Faxionus limosus is more difficult, given its presence in a higher number of lakes, three of which are hydrologically connected. A first containment campaign to prevent its spread in the river network is planned for summer 2023. The financial support to these activities has been granted by the local Nature 2000 networks and by the local administrations, which have also promoted the communication with citizens and stakeholders to raise consensus and collaboratio
Preventing the spread of Faxonius limosus in Trentino: management challenges, experimental protocols and new threats
No full textTwo Alien Invasive crayfish species are present in Trentino (NE Italy): Procambarus clarkii and Faxonius limosus. Both species were accidentally introduced in the first decade of this century with fish restocking; their introduction caused the extinction of populations of the native Austropotamobius pallipes. Procambarus clarkii was so far recorded only in one small lake at 950 m asl, whereas Faxionus limosus has colonized a group of 5 lakes at 450 m asl, over an area of about 80km2. The containment of Faxionus limosus is therefore difficult, given its presence in a high number of lakes, three of which are hydrologically connected. The first containment campaign to prevent its spread was conducted in summer 2023 in the downstream-most of the three connected lakes, Costa Lake, a small lake of about 1 hectare surface area. The efficiency of traps with different mesh size was tested in a 10-day campaign in mid-June, a more extensive one-week campaign was conducted in July. The use of small size (1 cm) mesh was the most efficient trapping system, as the small body size of the individuals probably allows them to escape from the standard, larger size (3x2 cm) mesh; crayfish were collected mainly in the canal which acts as the emissary of the lake, connecting it to the main river network. Unexpectedly and unluckily, individuals of Procambarus clarkii were collected in the NW part of the lake, suggesting a recent, point introduction, of unknown origin, which represent a further threat for the area
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