701 research outputs found
Catalytic and non-catalytic chemical kinetics of hydrocarbons cracking for hydrogen and carbon materials production
No full textIn the perspective of decarbonizing the chemical and energy industries, the production of hydrogen from the thermal and thermo-catalytic pyrolysis of hydrocarbons has been highlighted as a potentially effective route. Indeed, the "turquoise" hydrogen pathway enables to fixate the carbon content of the feedstock in high-performance, durable and recyclable materials entirely avoiding CO2 emissions. Such multiphase processes include chemical vapor deposition (CVD) and infiltration (CVI), diamond synthesis and the catalytic production of carbon nanotubes (CNTs). All the above involve a homogeneous gas-phase environment where feedstock cracking occurs together with heterogeneous interactions between gas-phase fragments and an active carbon (preform) or catalyst surface.
Mechanistic models provide insights into gas-phase product distribution, untangling the competition between amorphous carbon formation (soot) in the gas-phase and structured carbon deposition. Once the models are developed and validated, kinetic analyses allow the identification of optimal conditions by relating process parameters (temperature, pressure, feedstock, catalyst morphology, etc.) to feedstock conversion, product yields and quality.
This chapter provides an overview of relevant chemical kinetics aspects starting systematically from the description of reaction classes and reference rate parameters used to describe homogeneous gas-phase cracking. Then the formation mechanisms of polycyclic aromatic hydrocarbons and soot is addressed. The latter is a critical aspect as soot formation competes with the synthesis of highly structured and organized carbon materials through heterogeneous mechanisms. These are then discussed specifically focusing on CVD/CVI processes, diamond growth mechanisms and carbon nanotubes synthesis
Pessimi poeti: tradizione antica e criteri di selezione
No full textAuthors, whose works are available to us just in a fragmentary form, raise a most central issue: why are they pre-served only in fragments? With respect to some poets it is possible to find an answer in their reputation as pessimi poetae, already attested in antiquity. I intend to approach this topic by considering a revealing passage in Philode-mus’ De Poematis (Tractatus A, col. XXV Sbordone, from book 2 in Janko’s reconstruction, from 3 in Dorandi’s), which has been curiously neglected by the critics. There, models of good poetry are opposed to examples of bad poetry: for instance, Euripides in opposed to Carcinus and Cleaenetus for what concern tragedy, and Homer to Choerilus and Anaximenes with respect to epic poetry. It is not hard to recognise in their bad reputation the reason why their works have not been transmitted to us. Carcinus, Cleaenetus, Choerilus and Anaximenes represent in fact a blatant case of literature preserved only in fragments.
In this paper, I aim therefore to consider the tradition related to the pessimi poetae, starting from Philodemus’ pas-sage. I shall have this achieved by elaborating on their bad reputation, which would be impossible to reconstruct without Philodemus’ testimony. For Cleaenetus (TrGF 84), I will reconsider a fragment by Alexis (fr. 268 K.-A.). I will then focus on the tradition about Carcinus: in this case, it is necessary to establish if the author cited by Philo-demus is Carcinus I (TrGF 21) or rather Carcinus II (70). Lastly, I will dwell on Choerilus (from Iasus: SH 333) and Anaximenes (from Lampsacus: SH 31). Both are to be identified with the homonymous poets that accompa-nied Alexander the Great on his Asiatic expedition. Even if Horace corroborates Choerilus’ bad reputation, details are to be added to his depiction; also for Anaximenes new evidences need to be taken into account.
Thanks to such a reconstruction of the tradition concerned with the pessimi poetae, it is possible to focus on an ex-tremely early selection in the transmission of ancient literature, otherwise ignored. Thanks to Philodemus’ passage we can understand how the neglect concerning a number of poets, far from being casual, reflects the standpoint adopted by ancient critics
Evaluating process safety at conceptual stage: A stream-based index approach
No full textIncorporating safety indexes during the conceptual design stage is essential for ensuring the safety and efficiency of chemical processes. Despite many advances in the field, there are still areas that can be improved. Here we present a new Stream Safety Index: a fully automated, stream-based safety index coupled with a process simulator. The index ranges over a simple scale from 0 to 10 and provides immediate feedback on safety performance, facilitating safer design decisions. It is constructed starting from various sub-indexes, based on continuous, optimized functions. The index is tested on a methanol production process flowsheet and compared to two existing indexes, Process Stream Index (PSI) and Comprehensive Inherent Safety Index (CISI). Stream Safety Index (SSI) identifies the same sensitive zones as CISI, but its calculation is automatized and almost instantaneous. While Stream Safety Index does not completely eliminate subjectivity, it can be easily adapted to fit the specific parameters of the end user
The rise and fall in menopausal hormone therapy and breast cancer incidence
No full textStudies conducted in different areas of North America and Europe showed a 5-10% decline in the incidence of breast cancer following reductions up to 70% in menopause hormone therapy (HT) use after 2002. The observation that the decline was larger in (or limited to) women aged ≥50 years weighs in favour of an effect of reduced HT use on breast cancer incidence. However, changes in screening are also likely to play a role in the decreasing incidence of breast cancer observed in several countries. In particular, the technical improvements and the increased effectiveness of breast cancer screening and detection during the 1990s led to a decreased number of pre-clinical cases found by screening in subsequent years. Further, disentangling the effects of HT use and screening is difficult, as women who stop using HT may also undergo mammography screening less frequently. Thus, the reasons of the falls in incidence remain open to discussion
Methane pyrolysis for hydrogen production: Modeling of soot deposition by computational fluid dynamics and experimental validation
No full textMethane pyrolysis is an attractive technology to reduce greenhouse gas emissions, since the carbonaceous part of the hydrocarbon is captured into a solid, easier to store than carbon dioxide. In this framework, computational fluid dynamics (CFD) is an excellent tool to simulate the catalyst deactivation and the complex phenomena arising on the carbon surface. We investigated thermal and catalytical pyrolysis of methane in a tubular quartz reactor with an internal diameter of 3.8 cm. We modeled soot deposition and added a new surface mass balance that parametrize bed porosity as time-dependent variable. Our model predicts occlusion (clogging) time for empty and packed bed reactor: operating at 1373 K, an empty bed clogs in 15 d, which is coherent with industrial operations. The model well predicts methane conversion in the empty reactor even after 24 h time on stream. When a packed bed is used, the experimental conversion follow the predicted activity decay, with deviations due to the size distribution of the carbon during experiments. Radiation is the main heat transfer mechanism (86 % of the total heat absorbed by the system), compared to the others involved in this system, i.e., conduction, which is more than 50 times smaller, natural convection, more than 18 times smaller, and forced convection, more than 300 times smaller
Hearing loss and facial palsy as presenting symptoms of Schwannoma of the jugular foramen
No full textA schwannoma (or neurilemmoma) of the jugular foramen is a rare tumour of the head and neck region arising from the cranial nerve sheaths and/or the sympathetic chain. Due to its location, in the early stages of growth there is usually a lack of symptoms. Furthermore, it tends to grow slowly, and progressively involves adjacent cranial nerves so that the nerve in which the tumour originated may be difficult to identify. Appropriate imaging techniques such as computed tomography (CT) and magnetic resonance (MR) allow accurate differential diagnosis and surgical planning. Schwannomas of the jugular foramen appear as sharply demarcated, contrast-enhancing tumours, which are typically centred or based in an enlarged jugular foramen having sharp and round bony borders with a sclerotic rim. Intraosseus extension may be marked. The authors report a case associated with rapid progression leading to death, and review the English literatur
GLI EPIGRAMMI 'DI PLATONE'. EDIZIONE, COMMENTO, FORTUNA
No full textThis thesis provides a new critical edition and full commentary of the epigrams transmitted under Plato's name. The edition includes for the first time all the epigrams assigned to 'Plato' by the ancient tradition and offers a critical text based on a review of the manuscript tradition and philological work. The commentary provides an in-depth analysis of the epigrams, from both the philological and the literary and exegetical points of view. An introductory study addresses the problem of the epigrams' authenticity by reviewing the scholarly debate on the topic. It also traces the history of Plato's epigrams in antiquity, proposing a reconstruction of relevant context and possible reasons why the epigrams were composed and assigned to Plato
Combining Metadynamics and Mean Force Integration for studying chemical reactions in solution: an application to backbiting of poly-Butyl Acrylate.
No full textFree radical polymerization (FRP) and pyrolysis processes are fundamental technologies with wide-ranging applications in fields such as material synthesis and recycling. Understanding the underlying reaction mechanisms and considering the effect of solvents is crucial for the design and scale-up of such processes. However, since pyrolysis lacks selectivity and radical intermediates are hard to measure due to their extremely short lifetimes, rate coefficients from experimental campaigns on this subject are scarce. Nevertheless, experiments on free radical polymerization have been a flourishing field of study in past two decades. Knowledge of rate parameters of elementary reactions in solution or in bulk is key for formulating a valid kinetic mechanism. To this day, individual kinetic rate parameters of radical chain propagations, depropagations as well as isomerizations (backbiting) can be accessed experimentally through Pulsed Laser Polymerization technique (PLP) coupled with Size Exclusion Cromatography (SEC) [1] as well as semibatch solution polymerization coupled with Nuclear Magnetic Resonance (NMR) [2]. The resulting rate coefficients are gathered in the IUPAC Database for standard monomers which represents the gold standard for the validation of theoretical calculations. In particular, the experimental studies taken as reference [1-2] report the propagation, backbiting and beta-scission rate coefficients for poly-Butyl Acrylate in bulk and in solvent (mainly a mixture of ortho/meta/para-xylene). In this work, accelerated molecular dynamics in conjunction with Mean Force Integration (MFI) have been employed for exploring the free energy landscape of the backbiting of poly-Butyl Acrylate (PBA) in gas phase as well as in solution with non-polar (o-/m-/p-xylene) and polar (water) solvent
The rice StMADS11-like genes OsMADS22 and OsMADS47 cause floral reversions in Arabidopsis without complementing the svp and agl24 mutants
No full textDuring floral induction and flower development plants undergo delicate phase changes which are under tight molecular control. MADS-box transcription factors have been shown to play pivotal roles during these transition phases. SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) are important regulators both during the transition to flowering and during flower development. During vegetative growth they exert opposite roles on floral transition, acting as repressor and promoter of flowering, respectively. Later during flower development they act redundantly as negative regulators of AG expression. In rice, the orthologues of SVP and AGL24 are OsMADS22, OsMADS47, and OsMADS55 and these three genes are involved in the negative regulation of brassinosteroid responses. In order to understand whether these rice genes have maintained the ability to function as regulators of flowering time in Arabidopsis, complementation tests were performed by expressing OsMADS22 and OsMADS47 in the svp and agl24 mutants. The results show that the rice genes are not able to complement the flowering-time phenotype of the Arabidopsis mutants, indicating that they are biologically inactive in Arabidopsis. Nevertheless, they cause floral reversions, which mimic the SVP and AGL24 floral overexpressor phenotypes. Yeast two-hybrid analysis suggests that these floral phenotypes are probably the consequence of protein interactions between OsMADS22 and OsMADS47 and other MADS-box proteins which interfere with the formation of complexes required for normal flower development
Gratitude, Forgiveness, and Anger: Resources and Risk Factors for Italian Prison Inmates
No full textThe adjustment of prison inmates is recently becoming a social concern. In the current study we focused on the role of gratitude, interpersonal forgiveness, and anger, which have been widely addressed as likely to influence people’s health and adaptive behaviors, in shaping prison inmates’ psychological wellbeing and criminal attitudes. Participants were 104 male prison inmates aged between 24 and 75 (Mage = 46.63, SD = 11.38) imprisoned in Northern Italy who were asked to fill in an anonymous self-report questionnaire. Results highlighted that all dimensions considered play an important, albeit different and highly specific, role; Gratitude is a promotional factor that enhances psychological wellbeing, whereas interpersonal forgiveness appears to be a protective factor against the adoption of a criminal attitude as violence or antisocial intent. Finally, anger is a risk factor toward both psychological wellbeing and violent behaviors. Implications of these results and further developments of the study are discussed
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