170,196 research outputs found
L’Autorità nazionale anticorruzione: storia, competenze e principali ambiti di attività
No full textHigh temperature tribological behaviour and microstructural modifications of the low temperature carburised AISI 316L austenitic stainless steel
No full textThe influence of low-temperature carburizing (LTC) on the room- and high-temperature dry sliding tribological behaviour of AISI 316L was investigated and discussed along with microstructural modifications of the carburized layer (expanded austenite or S-Phase). The wear tests were carried out by a ball-on-disk testing device at temperatures up to 600°C, by using alumina balls as the counterface material. The significant hardness increase induced by the LTC treatment, due to S-phase formation, significantly enhanced the tribological behaviour of the AISI 316L at room temperature. However, the wear resistance of the LTC-treated steel strongly decreased with increasing temperature, becoming comparable to that of the non-treated AISI 316L already at 150 °C. Such tribological properties can be explained by considering the presence of a continuous and protective oxide layer in the non-treated AISI 316L steel, whose formation is prevented in the LTC one by a thin amorphous carbon layer covering the S-phase. Thermal stability of the S-phase was studied by static annealing in the temperature range 150-600 °C for 2 hours. Temperature increase led to carbon diffusion from the S phase to the matrix, but a remarkable effect with consequent weakening of the surface hardened layer occurs only above the treatment temperature . The high temperature involved in the sliding tests and further frictional heating induced by the tribological contact enhanced the tendency towards structural modifications in the carburized layer
Mechanical spectroscopy investigation of liquid Pb-Bi alloys
No full textLiquid Pb–Bi eutectic alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system (ADS). The alloy has been characterized in liquid state from melting (125 °C) to 650 °C by mechanical spectroscopy (MS). Experiments have been carried out using hollow reeds of austenitic stainless steel filled with the Pb-Bi alloy and sealed at the extremities. From 350 °C to 520 °C modulus shows a remarkable drop accompanied by a broad Q-1 maximum. In the same temperature range radial distribution functions (RDFs), determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The anelastic phenomena have been attributed to a structural re-arrangement of liquid metal.
For comparison, other alloys of the Pb-Bi system with hypo-eutectic composition have been investigated
Decellularization and tissue engineering. Viable therapeutic prospects for transplant patients and infertility?
No full textDecellularization and tissue engineering: Viable therapeutic prospects for transplant patients and infertility
Liquid Pb-Bi eutectic alloy: Study of short-range order
No full textLiquid Pb-Bi eutectic (LBE) alloy has been selected as a coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system (ADS). This new reactor type might be one of the possible solutions for the nuclear waste problem because it is able to transmute high level radioactive waste and long lived actinides. The ADS technology however requires special operating conditions. The materials need to resist temperatures ranging between 200-550°C under a high energy neutron flux and in contact with the LBE. This condition increases liquid metal corrosion and embrittlement, in fact the limitation of ADS life is due to the relatively low corrosion resistance of structural materials in the LBE environment. The compatibility of structural materials with liquid LBE at high temperature is one of the key issues for the commercialization of such fast reactors. Possible structural changes of the liquid may affect the interaction of LBE with structural materials. Therefore, in previous works LBE was investigated by internal friction (IF) and dynamic modulus measurements far above the eutectic temperature (125 °C) by using a new method developed by us. After melting the alloy exhibits a steady modulus decrease up to 350 °C, here a remarkable drop is observed covering a temperature range of about 170 °C. Finally, above 520°C, modulus continues to decrease with slope very close to the initial one. In correspondence of the modulus drop two IF maxima were detected: The first centered at -350 °C, the second at -460 °C. Anomalies of the liquid metal have been evidenced by other investigators as well. It is believed that the structure of the alloys is heterogeneous after melting, with residual minor crystals still existing and, when the critical temperature is reached, the residual conglomerates are broken and the uniform structure appears. To better understand the nature of LBE structural evolution vs. temperature High Temperature X-Ray Diffraction (HT-XRD) measurements have been carried out up to 720 °C; from diffraction patterns the radial distribution function (RDF) has been calculated (some G(r) curves are reported in Fig. 1). RDF provides information about possible changes of liquid metal. The average distance rt between the 1st nearest neighbour atoms is of particular relevance: The position (Fig. 2) and shape of 1st RDF peak progressively change as temperature increases with strict correspondence with the dynamic modulus drop previously observed by us. The trend of the ratio r2 / r1 vs. temperature (Fig. 3) showed that just after melting r2 /r1 is ~ 1.41, increases till to reach the value of -1.61 at 720 °C. The result indicates that the short-order of liquid LBE gradually changes from a cuboctahedral configuration (the ratio is ) just after melting to an icosahedral one (the ratio corresponds to the golden ratio φ = 1.618 ) at 720 °C. The two structures of the liquid are shown in Fig. 4. To describe structural re-arrangement of atoms in the liquid from cuboctahedral to icosehedral configuration a model has been realized (Fig. 5). The fitting of the first RDF peak by pair functions Pij(r) permitted to identify and determine the single contributions at increasing temperature. From melting up to 350 °C, the mixed Pb-Bi pairs are not present. They appear at 350 °C and their contribution to RDF 1st peak becomes more important as temperature increases. In fact, the increasing number of Pb-Bi pairs corresponds to a more homogeneous elemental distribution in the alloy
Physiological response of eight Mediterranean maquis species to low air temperatures during winter
No full textWe analyzed the physiological response of the Mediterranean evergreen species (Arbutus unedo L., Cistus incanus L., Erica arborea L., Erica multiflora L., Phillyrea latifolia L., Pistacia lentiscus L., Quercus ilex L., and Rosmarinus officinalis L.) to winter low air temperatures. In occasion of two cold events, in February 2005 (Tmin = 1.8 °C), and January 2006 (Tmin = 3.1 °C and minimum Tair = –0.40 °C during the nights preceding the measurements), R. officinalis, C. incanus, and E. multiflora had the highest net photosynthetic rate (PN) decrease (73 %, mean value) with respect to the winter PN maximum, followed by A. unedo (62 %), P. latifolia and P. lentiscus (54 %, mean value), E. arborea (49 %), and Q. ilex (44 %). Among the considered species, Q. ilex was able to maintain PN near the maximum for 150 min during the day, A. unedo, P. lentiscus, E. arborea, P. latifolia, E. multiflora, and R. officinalis for 60 min, and C. incanus for 30 min. The calculated mean winter daily PN ranged from 7.9±0.6 (Q. ilex) to 2.8±0.5 (R. officinalis) μmol(CO2) m–2 s–1. During the study period, chlorophyll (Chl) content decreased by 36 % on an average in the two cold events, and the carotenoid (Car) to Chl ratio increased by 133 % in Q. ilex, having the highest value in January 2006. Principal component analysis underlined the highest cold resistance of Q. ilex by high PN and high Car/Chl ratio. On the contrary, R. officinalis and C. incanus had the lowest cold resistance by the highest PN decrease and the lowest Car/Chl (C. incanus). Thus, winter stress could be an additional limitation to Mediterranean evergreen species production, and the capacity of the species to maintain PN near 90–100 % during winter is determinant for biomass accumulation
Uterus transplant and controversial assisted reproductive technologies: can the right to parenthood clash with ethical precepts?
No full text: Fast-developing assisted reproductive techniques based on innova- tive technologies have given rise to incredibly consequential ethical challenges of unprecedented scope. The development of innovative assisted reproductive technologies (ARTs) has steadily risen since the late 1970s. Until just over 20 years ago, those who sought to become parents had no way to overcome their infertility or sterility issues, but can now achieve parenthood and have children with at least a partial genetic and/or biological relationship. Treatments aimed at ovarian stimulation, artificial insemination, either by using the sperm of a husband or of an unrelated donor, in vitro fertilization with embryo transfer, gamete and zygote intrafallopian transfers, and intracyto- plasmic sperm injection are among the options currently available. A major ethical quandary linked to ARTs is the one arising from unused embryos, i.e. supernumerary embryos which were not implanted. Still, aside from ethical concerns stemming from embryo rights, in such a fast-evolving field, a solid ethical foundation is absolutely necessary to provide guidance for regulations and legislation. This is especially true considering how assisted reproductive practices such as surrogacy and uterus transplant (UTx) are even more controversial, hence the need to rely on a broadly acknowledged and shared set of principles for their regulation, by virtue of their unique distinctive traits which challenge our ethical and moral compass at its very core
Plant crown traits and carbon sequestration capability by Platanus hybrida Brot. in Rome
No full textMeasurements of carbon dioxide (CO2) concentration carried out in the city of Rome in the period January-December 2005 showed a mean yearly CO2 concentration of 414 +/- 45 ppm; polluted sites (P sites) had 21% higher CO2 concentration than control sites (C sites). The significant (p < 0.01) correlation analysis between CO2 concentration and traffic density measured during the study period at P sites showed that traffic density explained 51% of the CO2 variation. The CO2 trend during the traffic limitation days (provision imposed by ordinance of the City Council) did not show significant differences as regards regular traffic days, suggesting the ineffectiveness of this provision. Leaf area index (LAI) of Platanus hybrida Brot. was on an average 11% lower at P sites than at C ones associated with a lower total photosynthetic leaf surface area (SPT, 34% lower at P sites than at C ones). P. hybrida had a total carbon sequestration of 117 +/- 13 kg year(-1) (mean value of P and C sites) playing an important role in sequestering CO2. Thus, the choice of plant species for urban areas may be set out taking into account their own air amelioration capability. Plant traits of each species may be used for urban tree planting programs to ameliorate urban air pollution. (c) 2007 Elsevier B.V. All rights reserved
Daily and seasonal variation of CO2 in the city of Rome in relationship with the traffic volume
No full textMeasurements of carbon dioxide (CO2) concentration carried out in the city of Rome showed an increase from 1995 (367 +/- 29 ppm mean yearly value) to 2004 (477 +/- 30 ppm, mean yearly value). The annual trend showed a peak in winter, 18% greater than the summer one correlated to traffic density (35 +/- 4 and 29 +/- 3 cars min(-1) mean winter and summer value, respectively). The weekly trend had the lowest values (414 +/- 19 ppm) during the weekends when traffic density was 72% reduced. The daily trend had a peak in the early morning when traffic was the highest and the atmosphere was more stable. The critical zones of the city (B zones) had 3.5% CO2 concentration higher than the park (D zone) and 18% more than the control zones (E zones). An increase of air temperatures from the surrounding zones (20.0 +/- 4.1 degrees C) to the centre of the city (28.9 +/- 1.2 degrees C, mean between A and B zones) was observed
Variazioni spaziali della struttura della macchia mediterranea e cambiamento climatico
No full textGli ecosistemi di tipo mediterraneo sono caratterizzati da un’elevata diversità di specie, che riflette le differenti strategie adattative, in risposta ai fattori di stress. Lo scopo della presente ricerca è stato quello di analizzare la struttura ed il modello di aggregazione delle specie della Macchia mediterranea, che si sviluppa lungo il tratto di costa presente all’interno della Tenuta di Castelporziano (S – SW di Roma). Lo studio è stato condotto in aree campione (ciascuna di 100 m2). In ciascuna area sono stati considerati i seguenti parametri: altezza e volume dei cespugli, volume della corona fotosintetizzante e indice di area fogliare (LAI). A livello di specie è stata analizzata la superficie fogliare totale per ciascun individuo e per ciascuna specie, la superficie fogliare specifica (SLA, data dal rapporto fra la superficie fogliare e il peso secco), la massa fogliare specifica (LMA, data dal rapporto fra il peso secco e la superficie fogliare), l’LTD (dal rapporto fra il peso secco e il volume fogliare) e la longevità fogliare. I risultati dell’analisi strutturale hanno permesso di suddividere i cespugli in tre classi dimensionali (piccoli, medi e grandi), di cui l’86 % è formato da un minimo di due ad un massimo di 10 specie. Tra le specie costituenti C. incanus è quella più frequente ed è presente in tutte le classi dimensionali, mentre E. arborea è quella a più bassa frequenza ed è esclusiva dei cespugli grandi. A livello fogliare sono stati osservati i valori più elevati di LMA e di LTD in E. multiflora, seguita da Q. ilex, P. latifolia, P. lentiscus e R. officinalis ed i più bassi in A. unedo, C. incanus ed E. arborea. Il cambiamento climatico in atto, potrebbe determinare un aumento dello stress da aridità, variando i rapporti inter ed intraspecifici, con ripercussioni sulla presenza e densità delle specie, che potrebbero essere messe precocemente in evidenza attraverso il monitoraggio strutturale degli arbusti della macchia
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