The assessment of the damage probability of storage tanks in domino events triggered by fire

An approach aimed to the quantitative assessment of the risk caused by escalation scenarios triggered by fire was developed. Simplified models for the estimation of the vessel time to failure (ttf) with respect to the radiation intensity on the vessel shell were obtained using a multi-level approach to the analysis of vessel wall failure under different fire conditions. Each vessel “time to failure” calculated by this approach for the specific fire scenario of concern was compared to a reference time required for effective mitigation actions and related to the escalation probability. The failure probability of each vessel was correlated to the probability of scenarios involving multiple vessel failure as a consequence of the primary fire, thus allowing a comprehensive assessment of domino scenarios triggered by fire. The application of the methodology to the analysis of several case-studies allowed the estimation of the quantitative contribution of escalation events triggered by fire to the overall individual and societal risk indexes.     

The quantitative assessment of domino effects caused by overpressure. Part I. Probit models

Accidents caused by domino effect are among the more severe that took place in the chemical and process industry. However, a well established and widely accepted methodology for the quantitative assessment of domino accidents contribution to industrial risk is still missing. Hence, available data on damage to process equipment caused by blast waves were revised in the framework of quantitative risk analysis, aiming at the quantitative assessment of domino effects caused by overpressure. Specific probit models were derived for several categories of process equipment and were compared to other literature approaches for the prediction of probability of damage of equipment loaded by overpressure. The results evidence the importance of using equipment-specific models for the probability of damage and equipment-specific damage threshold values, rather than general equipment correlation, which may lead to errors up to 500%.     

Forensic analysis of poly(ethylene terephthalate) fibers by infrared spectroscopy

Poly(ethylene terephthalate) (PET) is one of the most commonly employed polymers in the textile industry. Its relevance as a source of evidence in the reconstruction of criminal cases is nevertheless very limited because the properties and morphologies of fibers from different producers tend to be very similar. By integrating bands, obtained on single fibers by infrared (IR) microscopy, associated with trans and gauche conformation and to the O-H end-groups of the molecules, a method is proposed that can discriminate otherwise similar PET fibers. The absorbancies at 1370 and at 846 cm(-1) relative, respectively, to the gauche and trans conformation, were measured and ratioed. The end-group content was evaluated by ratioing the absorbancies of the signals at 3440 and at 874 cm(-1). Relative standard deviation (R. S. D.) was 1% for repetitive analyses on the same location of the same single fiber. Precision was reduced if the ratios were measured along the length of a single fiber (R. S. D. = 3%) and even further when different fibers of the same sample were examined (R. S. D. varied from 2 to 10%). This simple method can greatly enhance the evidential value of PET fibers by subclassifying them, thus helping the Court to better assess their significance.     

Input-output statistical independence in divisive normalization models of V1 neurons

Simoncelli and co-workers have proposed statistically-derived nonlinear divisive normalization models of the primary visual cortex (V1) that are consistent with the hypothesis that sensory systems are adapted to the signals to which they are exposed. In this paper, we present a more rigorous mathematical formulation and analysis of these statistically-derived models in terms of mutual information as a metric for statistical independence. We prove that the ad hoc choice of divisive normalization parameters proposed by Simoncelli and co-workers does not guarantee statistical independence between the output responses, but interestingly such choice does guarantee that each output response is statistically independent of almost all the linear inputs. This holds for the two different models of natural image statistics analysed theoretically, and is consistent with empirical results obtained on a set of natural images.     

Multisensory cues capture spatial attention regardless of perceptual load.

We compared the ability of auditory, visual, and audiovisual (bimodal) exogenous cues to capture visuo-spatial attention under conditions of no load versus high perceptual load. Participants had to discriminate the elevation (up vs. down) of visual targets preceded by either unimodal or bimodal cues under conditions of high perceptual load (in which they had to monitor a rapidly presented central stream of visual letters for occasionally presented target digits) or no perceptual load (in which the central stream was replaced by a fixation point). The results of 3 experiments showed that all 3 cues captured visuo-spatial attention in the no-load condition. By contrast, only the bimodal cues captured visuo-spatial attention in the high-load condition, indicating for the first time that multisensory integration can play a key role in disengaging spatial attention from a concurrent perceptually demanding stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Production and characterization of pure and Cr<Superscript>3+</Superscript>-doped hydroxyapatite for biomedical applications as fluorescent probes

Pure and Cr³⁺-doped hydroxyapatite (HAP) were prepared via chemical precipitation route. The XRD measurements revealed that the typical HAP powder pattern was obtained. SEM analysis indicated that aggregates of nanoparticles were formed. EDX analysis indicates that the [Ca]/[P] concentration ratio was higher than the expected values but can be explained by the presence of carbonate groups as dopants. The optical absorption spectra of the doped samples presented absorption bands typical of Cr³⁺ occupying to different crystalline sites. From the position of the bands, it was possible to estimate the crystal field parameters for both sites of Cr³⁺ in the HAP matrix. The emission spectra of the Cr-doped samples were also investigated and typical transitions of the dopant ion, in trivalent state, were identified. The potential use of the Cr³⁺-HAP as fluorescent probes for medical applications was discussed.