87,017 research outputs found
Thermal degradation of polystyrene
No full textThermal degradation of plastic wastes offers the possibility of recovering energy and useful chemicals. Polyethylene and polypropylene pyrolysis have been discussed already in previous works (E. Ranzi, M. Dente, T. Faravelli, G. Bozzano, S. Fabini, R. Nava, V. Cozzani, L. Tognotti, J. Anal. Appl. Pyrol., 40–41 (1997) 305–319 and T. Faravelli, G. Bozzano, C. Scassa, M. Perego, S. Fabini, E. Ranzi, M. Dente, J. Anal. Appl. Pyrol., 52 (1999) 87–103). This paper aims to develop a detailed kinetic model of polystyrene thermal degradation. The predictions of overall rates of degradation and volatile product distribution are compared with experimental results obtained by different authors at different pressure and temperature conditions. In order to reduce the computing times required by the numerical integration of the kinetic model, a flexible lumping procedure has also been introduced
Impact of Methanol Synthesis Kinetics on Bulk Production Prediction: an In-Silico Assessment
No full textKinetic modelling covers a key role in process simulation and design. Recently the methanol sector is assisting a remarkable enhancement due to its applications as fuel, solvent, and precursor as shown in Bozzano and Manenti (2016). The increasing number of patents, the market prospects, and recent research witness this renewed interest. However, despite this rate in developing and improving technologies, the kinetics modelling does not follow these trends. The methanol synthesis chemical paths, the intermediates, and the real role of the active sites are nowadays still unclear. However, process engineering requires reliable models to estimate the methanol synthesis rate, hence, to design and size the reactor and downstream equipment. Currently, the most used kinetics are Graaf and Vanden Bussche - Froment’s models which in any case show some shortcomings and weaknesses. Starting from these premises, the need for updated kinetics is clear. This work aims at comparing and highlighting the impact of different kinetic models (1) original Graaf (or-GR), (2) Vanden Bussche - Froment (VBF), and (3) refitted Graaf (ref-GR) on the methanol synthesis configuration for different feedstocks through an in-silico assessment. The general simulation flowsheet includes the single-stage PFR for the methanol synthesis, the condensation step, and recycle loop for the unreacted syngas. The comparison with industrial data proves that the ref-GR model predicts better than the original Graaf model as in Graaf et al. (1988), while the VBF, Vanden Bussche and Froment (1997), tends to overestimate methanol production. The validation exploits industrial data published in the literature
Mathematical and Statistical Approaches for Anaerobic Digestion Feedstock Optimization
No full textThis book examines biomass mixture modeling and optimization.
The book discusses anaerobic digestion and related fermentative processes and explains their compositional dynamics. Early chapter examine macromolecules, elemental fractions, and their direct influence on methane production. Supported by an extensive data bank of substrates obtained from research, the book points out correlations that enable the estimation of global methane production for diverse biomass mixtures. Furthermore, it provides valuable insights into discerning the optimal composition capable of yielding the utmost methane output.
The book integrates cutting-edge machine learning techniques and shows how the programming language Python and Julia can be used for analysis and to optimize processes. It has many graphs, figures, and visuals
Du fascisme à la République : la transition dans les entreprises publiques italiennes, 1943-1950. L'Institut Luce : un cas exemplaire
No full textEvaluation of landslide reactivation: a modified rainfall threshold model based on historical records of rainfall and landslides
No full textThis study proposes a modification of the conventional threshold model for assessing the probability of rainfall-induced landslide reactivation. The modification is based on the consideration that exceedance of a pre-determined rainfall threshold is a necessary but not sufficient condition to reactivate a landslide. The proposed method calculates the probability of reactivation as a function of the probability of exceedance of a pre-determined rainfall threshold, as well as the probability of occurrence of a landslide after such exceedance. The data for the calculation were obtained from historical records of landslides and rainfall.
The method was applied to two complex landslides (“San Donato” and “La Salsa”) involving fine-grained debris in the southern section of the Apennine foredeep. The minimumrainfall threshold triggering landslide reactivation on the two slopes was determined by examining rainfall patterns during the 180 days preceding the slide events. For the San Donato and La Salsa landslides, the minimum triggering threshold consists of rainfall events lasting 15 days,with cumulated rainfall exceeding 150 and 180mm, respectively. Based on hydrological and statistical analyses, the annual probabilities of exceeding the thresholds were estimated to be 0.38 and 0.25, respectively. During the period from 1950 to 1987, the minimum threshold was exceeded 14 times, and four reactivations occurred at San Donato; whereas, the threshold was exceeded 10 times and three reactivations occurred at La Salsa. Hence, the probabilities of landsliding after exceedance of theminimumrainfall threshold are 4/14 and 3/10, respectively. Finally, annual reactivation probabilitieswere calculated to be 0.11 and 0.08, respectively. The reliability of the minimumrainfall threshold was tested by: i) simulating variations in the stress–strain behavior of the slopes as a result of fluctuations in the water table from normal to extreme values; and ii) analyzing the results of continuous multi-year monitoring of pore pressure and rainfall variations on a slope composed of dominantly fine-grained debris
Gender gaps in education
No full textThis chapter reviews the growing body of research in economics which concentrates on the education gender gap and its evolution, over time and across countries. The survey first focuses on gender differentials in the historical period that roughly goes from 1850 to the 1940s and documents the deep determinants of the early phase of female education expansion, including preindustrial conditions, religion, and family and kinship patterns. Next, the survey describes the stylized facts of contemporaneous gender gaps in education, from the 1950s to the present day, accounting for several alternative measures of attainment and achievement and for geographic and temporal differentiations. The determinants of the gaps are then summarized, while keeping a strong emphasis on an historical perspective and disentangling factors related to the labor market, family formation, psychological elements, and societal cultural norms. A discussion follows of the implications of the education gender gap for multiple realms, from economic growth to family life, taking into account the potential for reverse causation. Special attention is devoted to the persistency of gender gaps in the STEM and economics fields
Chronostratigraphic and lithologic features of the Tiber River sediments (Rome, Italy): Implications on the post-glacial sea-level rise and Holocene climate
No full textRapid and permanent granulometric changes within the clastic sedimentary deposits of the Tiber River are directly linked to changes in sediment transport capacity and give insight on climate fluctuations and related sea-level oscillations during Late Pleistocene-Holocene times. In this work, we investigate the stratigraphic features of the sedimentary fill of the Tiber River channel as far as 30km from the coast, and of one tributary, the Grottaperfetta stream. Through direct observation and core sampling of ten, 30 to 80m deep boreholes, and the analysis of a large number of stratigraphic log data, we reconstruct a series of transverse sections and correlate them along a longitudinal profile of the Tiber River course. We provide geochronologic constraints to the deposition of distinct lithostratigraphic units by means of 8 newly acquired 14C ages and 21 previously reported ages of intercalated peat layers and wood fragments. Moreover, we review and select 28 radiocarbon ages from literature on the deposits of the Tiber River in the coastal plain, in order to reconstruct the aggradational history throughout the distal portion of the basin. Finally, we provide curves of sediment aggradation vs. time during the last 19,000yr for the different investigated portions of the Tiber River course. We compare them to sea-level curves from the literature. To perform this comparison, we use a rigorous geotechnical approach to estimate the subsidence due to sediment compaction, and we apply a correction to the Present-day elevation of the dated samples of organic material interbedded with the sedimentary deposits.Two significant sedimentary events at around 13,800. yr. BP and 7500. yr. BP, marked by sharp stratigraphic and granulometric changes, are recognized and correlate to important variations in the rate of sea-level rise. Moreover, we show evidence of an erosional event coupled to a reversal of the granulometry (increase in gain size of sediments) affecting the whole investigated tract of the Tiber River channel between 5500 and 3500. yr. BP and discuss its possible causes. In particular, we discuss whether besides the change in capacity of transport due to a climatic change, also a drop in sea level, in the order of 2-3 meters, may have occurred in this time span, either in response to an increase in global ice volume, glacial isostatic adjustment, or local tectonic uplift. © 2013 Elsevier B.V
Thermodynamic Equilibrium Study of Anaerobic Digestion through Helmholtz Equation of State
No full textThe growing attention regarding a more sustainable future, and thus into energy recovery and waste reduction technologies, has intensified the interest towards processes which allow to exploit waste and biomasses to generate energy, such as the anaerobic digestion. Improving the efficiency of this industrial application is crucial to increase methane production, and is essential from the economic, environmental and safety point of view. This study focuses on the thermodynamic modelling of a steady-state reactor as a flash unit, in order to determine the best operating conditions to produce the maximum amount of pure bio-methane. To this purpose, a new hybrid approach based on the Peng–Robinson cubic equation of state and on the Multi-Parameter Helmholtz-Energy EoS has been proposed. The simulations, performed using the developed algorithm at temperatures between 20 and 55 °C and at pressure values between 0.3 atm and 1.5 atm, point out that the fugacity of the mixture evaluated with the proposed technique is much more accurate and reliable than the one calculated with the PR EoS. In addition, this research has shown not only that the purity and the production of the biogas can be optimised by working at mesophilic conditions and at pressure between 1 atm and 1.5 atm, but also that it is not convenient to operate in a temperature range of 42 °C–45 °C, since about 20 % more H2S goes into the exiting biogas, reducing the CH4 amount and raising the post-treatment costs. Lastly, it has been seen that there is a significant water content in the vapour phase (∼5 %wt.), and this is a factor to be taken into account in order to improve the process
IMMUNOLOGY OF TUBERCULOSIS
No full textMTB ranks as the first worldwide pathogen latently infecting one third of the population and the second leading cause of death from a single infectious agent, after the human immunodeficiency virus (HIV). The development of vigorous and apparently appropriate immune response upon infection with M.tuberculosis in humans and experimental animals conflict with failure to eradicate the pathogen itself and with its ability to undergo clinical latency from which it may exit. From a clinical standpoint, our views on MTB infection may take advantage from updating the overall perspective, that has quite changed over the last decade, following remarkable advances in our understanding of the manipulation of the immune system by M.tuberculosis and of the role of innate components of the immune response, including macrophages, neutrophils, dendritic cells and NK cells in the initial spread of MTB and in its exit from latency. Scope of this review is to highlight the the major mechanisms of MTB escape from immune control and to provide a supplementary translational perspective for the interpretation of innate immune mechanisms with particular impact on clinical aspects
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