135,567 research outputs found
Lo straniero e i marziani. Istituzioni e pentiti di mafia tra appartenenza ed estraneità.
No full textStudy on the effects of cooling phase and construction technology on the fire performance of R/C tunnels
No full textFire performance of tunnels can represent a critical issue in the design phase, even more than for other structures and infrastructures, due to some inherent features such as (a) the fire compartment geometry often leading to very high temperature (also making difficult the intervention of fire brigades), (b) the structural redundancy caused by soil restraint fostering the development of relevant indirect actions, and (c) the high compression state in the lining (all the more during the fire exposure) that increases the spalling propensity and severity. Within this context, the role played by key parameters such as lining thickness and stiffness are investigated by comparing the fire performance of two different technological solutions for the lining: (1) traditional cast-in-situ lining and (2) pre-cast segmental tunnel lining. The fire scenario also considers the cooling phase, in order to discuss the main critical points to be solved when facing the final stage of the fire. 3D finite element analyses have been performed, proving that (I) higher thickness and stiffness does not necessarily correspond to a higher safety factor due to the indirect actions, and (II) fire cooling phase (if any) can be even more critical than the heating phase
Geotechnical engineering practice and the implementation of Eurocode approach in Italy
No full textSince 2003 several efforts have been done in Italy by the Italian Government to modify Technical Standards, abandoning the conventional allowable stress approach and introducing the limit state approach, according to Eurocodes. More specifically in the paper the following aspects are discussed: a) the intrinsic incompatibility between the Eurocode approach and the Italian Legislation as far as the responsibilities of practising engineers are concerned; b) resistance of practising engineers and geologists to abandon conventional design methods together with a generalized reluctance in Italy towards continuous education programs; c) intrinsic incompatibility between EC7 (2004) and "structural" Eurocodes (more specifically EC8 (2004)). Eventually the difficulties of introducing the limit state approach in conventional education programs are discussed. © 2008 Taylor & Francis Group, London
Toward Optimal Cross-layer Solutions for Cognitive Radio Wireless Networks
No full textCognitive radio (CR) networks have been proposed as a viable solution to spectrum scarcity problems. In CR networks, CR nodes exploit spectrum holes in space, time and/or frequency to transmit on licensed frequency bands without affecting primary users. In such a dynamic and unpredictable environment, CR networks require the ability to gather information on the surrounding available spectrum and to exploit this information to maximize CR nodes performance. In a companion paper we deal with sensing architecture and protocols. In this paper, instead, we derive a cross-layer scheme for cognitive radio networks which jointly optimize the sources flow rates, routing and medium access control while accounting for and exploiting the available spectrum resources. The proposed scheme builds on important recent results on close to optimal fully distributed CSMA-based scheduling algorithms, which allows us to derive a fully distributed solution
Crystal structures of a bis(cyclopentadienyl)(Z)-enyne framed manganese(I)-rhenium(I) complex and its [Co2(CO)8] adduct
No full textThe X-ray structural determination of the manganese(I)-rhenium(I) complex [(OC)3Mn{eta-5-C5H4)(Z)CH = CHC = C(eta-5-C5H4)}Re(CO)3] 1 has been carried out. The structural data show that the (Z)-enyne linkage between the two cyclopentadienyl rings, despite the conjugation that would keep the ligand framework coplanar, allows twisting of the two cyclopentadienylmetal units. Because of this characteristic the Mn Re interatomic distance (6.1 angstrom) is much shorter than in similar bis(cyclopentadienyl)-linked heterobimetallic complexes. Reaction of 1 with [Co2(CO)8] affords quantitatively the corresponding dicobalt tetragonal pyramidal adduct [(OC)3Mn{eta-5-C5H4)(Z)CH = CHC-(OC)3Co-Co(CO)3-C-(eta-5-C5H4)}Re(CO)3]2 the X-ray structure of which has been determined. The presence of the dicobalt unit on the triple bond heavily affects the carbon chain connecting the two cyclopentadienyl rings, and the metal centres are at a larger distance than in 1. Crystal data: 1, triclinic, space group P1BAR, a = 6.546(1), b = 11.066(2), c = 13.451 (3) angstrom, alpha = 96.06(2), beta = 100.46(2), gamma = 96.31 (1)-degrees, R(F) = 0.0466, R'(F) = 0.0542 for 2710 observed reflections with F > 4.0-sigma(F); 2, triclinic, space group P1BAR, a = 9.825(3), b = 11.853(4), c = 13.662(3) angstrom, alpha = 109.41 (2), beta = 1 04.36(2), gamma = 99.16(2)-degrees, Z = 2, R(F) = 0.0325, R'(F) = 0.0352 for 5913 observed reflections with F > 4.0-sigma(F)
Vitamin C against cancer.
No full textAbstract: The selective anticancer properties of vitamin C are known since at least four decades.
However, only recently in vitro studies have shown that vitamin C, in high enough concentrations,
can efficiently and selectively kill a number of different human tumor cell
lines, and these data have been confirmed in experimental animal tumor models. The
first human clinical trials revealed that high doses of vitamin C administered by intravenous
injection are not only very well tolerated but also substantially improve the quality
of life of patients with clinically advanced cancer. However, the clinical evidence of the
effectiveness of vitamin C in fighting off cancer is still controversial. The present chapter
outlines the importance of vitamin C for a number of physiological functions, within the
human body, and shows that there is a solid rationale for its use in the routine treatment
of cancer, either alone or in combination with conventional treatment
Indirectly-supported one-way R/C slabs: Durability and safety issues
No full textSimply-supported one-way R/C slabs are commonly used in the covers of small and medium underground facilities, where durability is the main issue face with rather limited service loads and short spans (2-4 m [6.5-13.0 ft]). The structural performance, however, should not be underrated, as being the slab in a roundabout does not prevent a heavy truck from straying off the right lane! To have fresh information on durability and cracking (working loads), and on the bearing capacity and failure mode (ultimate loads), displacement-controlled tests have been recently performed in Milan on four typical rectangular R/C slabs suspended along their short sides via corbels (dapped ends; size: 1.3×2.2×0.15 m [51×87×6 in.]). A transversely-distributed or concentrated load was applied either at mid-span (in the bending tests), or at 1/10 of the span (in the shear tests). The two slabs Type A are provided with longitudinal bent-up bars in the main body and hooks in the corbels. On the contrary, the slabs type B are reinforced via two continuous layers of longitudinal straight bars. Under the working loads, cracking never occurred, neither in bending nor in shear - to the advantage of durability - while above the working loads rather complex crack patterns formed in the D zones close to the corbels, particularly under the concentrated load, which brought in 3-D effects, with a limited reduction in the bearing capacity. Refining the reinforcement layout is shown - once more - to markedly improve slab performance, with little or no extra cost
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