A numerical assessment of the load bearing capacity of externally pressurized moderately thick tubes

The collapse behavior of cylindrical shells pressurized from outside is examined. Attention is focused on tubes of moderate thickness, as required by very deep water pipelines or some innovative nuclear power plant proposals. Their collapse is expected to be dominated by yielding but, because of the decreasing nature of the post-collapse evolution, interaction with instability is likely to be significant enough to demand consideration. At present, no quantitative assessment of such effect is available, because little study has been devoted to tubes in this thickness range.Plasticity–instability interaction is activated by imperfections and to assess their influence on a systematic numerical study is undertaken. Computations produce a meaningful measure of the collapse pressure and it is proposed that the allowable pressure be determined on its basis, by introducing a suitable safety factor. This is chosen so that results reproduce those provided by presently accepted procedures in the well explored and reliable range of medium-thin tubes. When the same factor is applied to thicker tubes, the resulting allowable pressure is significantly higher than the values suggested by codes, which apparently react to the present lack of knowledge by assuming an extremely conservative attitude.     

Kinetic theory of geodesic acoustic modes in toroidal plasmas: a brief review

Geodesic acoustic modes(GAM) are oscillating zonal structures unique to toroidal plasmas,and have been extensively studied in the past decades due to their potential capabilities of regulating microscopic turbulences and associated anomalous transport.This article reviews linear and nonlinear theories of GAM;with emphases on kinetic treatment,system nonuniformity and realistic magnetic geometry,in order to reflect the realistic experimental conditions.Specifically,in the linear physics,the resonant wave–particle interactions are discussed,with the application to resonant excitation by energetic particles(EPs).The theory of EP-induced GAM(EGAM) is applied to realistic devices for the interpretation of experimental observations,and global effects due to coupling to GAM continuum are also discussed.Meanwhile,in the nonlinear physics,the spontaneous GAM excitation by microscale turbulences is reviewed,including the effects of various system nonuniformities.A unified theoretical framework of GAM/EGAM is then constructed based on our present understandings.The first-principle-based GAM/EGAM theories reviewed here,thus,provide the tools needed for the understanding and interpretation of experimental/numerical results.     

Modeling Lac du Bonnet granite using a discrete element model

A discrete element method code developed by the authors is used to model Lac du Bonnet granite in triaxial compression. The paper first presents the features of the model and the algorithms used to identify the micro deformability and strength parameters. With these identification algorithms, the model was calibrated to match experimental triaxial test data on Lac du Bonnet granite. With the calibrated model, investigation on failure evolution was then performed. The monitored evolution of the number and type of contact failures (micro cracks) reveals that at micro level tensile failures occur first, followed by mobilization of residual friction. Three distinct stages of stress–strain curve can be well identified by the accumulated number of contact failures and the mode of contact failures.     

Polymerization of bicyclic ethers

Summary Structure of copolymers obtained by ring opening cationic polymerization from 7-oxabicyclo[ 2.2.1] heptane and ethylene oxide has been recently reported. This study about the spin lattice relaxation times and Nuclear Overhauser enhancement factor in the carbon-13 NMR spectra was performed and the results interpreted in terms of different internal mobility of the units in the copolymer chain.Previous papers in this series are: G. CECCARELLI, F.ANDRUZZI, Makromol. Chem. 180, 1371(1979); F.ANDRUZZI, G.CECCARELLI, M.PACI Polymer 21, 1180(1980); and ref (M.PACI et al. 1981).     

Thermoelectric performance of disordered and nanostructured graphene ribbons using Green’s function method

The thermoelectric properties of defected graphene nanoribbons (GNRs) and multi-junction (MJ) GNRs coupling periodic armchair sections of different width are analyzed by means of Green’s function techniques to simulate electron and phonon transport. Among the different strategies likely to enhance the thermoelectric performance, the effects of edge disorder and random vacancies are shown to be small since they lead to the concomitant degradation of the phonon thermal conductance and of the electronic conductance, which finally reduces the thermoelectric factor ZT. However, the periodic distribution of vacancies and the structuring of GNRs in MJ-GNRs both lead to the enhancement of the figure of merit ZT. In the latter case, in addition to the strong reduction of the phonon thermal conductance, an effect of resonant tunneling of electrons allows retaining high electronic conductance and enhancing significantly the thermopower. Finally, by introducing a periodic distribution of vacancies in the MJ-GNR, the maximum value ZT=0.4 is reached at room temperature.     

Mixed micelles containing lipophilic gadolinium complexes as MRA contrast agents

Mixed micelles for MRA are multicomponent systems containing a phospholipid, a biocompatible non-ionic surfactant (e.g. Synporonic^(k) F-108) and a lipophilic gadolinium complex. A variety of lipophilic gadolinium complexes were designed taking into account features such as: (i) nature of ligand (cyclic versus acyclic); (ii) lipophilic moiety; (iii) global charge of the complex; and (iv) nature of bond connecting the complex to the lipophilic moiety. All the lipophilic gadolinium complexes after formulation as mixed micelles show high relaxivities in water and in blood (rat). Mixed micelles containing gadolinium complexes bearing only one aliphatic chain cannot be used as MRA contrast agents because they have a high haemolytic effect. Furthermore, in rats they are quickly eliminated from the blood stream. These drawbacks are completely circumvented using gadolinium complexes bearing two aliphatic chains. Mixed micelles containing such complexes show high relaxivities. no haemolytic effect and long blood permanence. This makes them promising candidates as MRA contrast agents. However, elimination, which occurs exclusively through the liver, is not complete, even after 7 days. Complexes containing labile (e.g. ester) bonds between the lipophilic moieties and the chelate subunit are eliminated through both the liver and the kidneys. However, elimination is stiil not complete after 7 days.     

Effects of Sectorization on Cellular Radio Systems Capacity with Different Traffic Loads

The application of cell sectorization as a mean to improve a cellular radiosystem Signal-to-Interference Ratio (SIR), and hence capacity, is investigated.To assess the usefulness of sectorization, a lower bound to the Shannoncapacity of the uplink channel of a cellular systemis evaluated, with perfect channel state information (CSI) at the receiver,versus the reuse distance and the traffic loading. In the paper, two different rules for the use of sectored antennasare presented and analyzed in terms of their effect on system capacity.The sectorized system performance is compared with the performance ofa conventional system using omni-directional antennas at the base stations (BS).     

DOGeye: Controlling your home with eye interaction

Nowadays home automation, with its increased availability, reliability and with its ever reducing costs is gaining momentum and is starting to become a viable solution for enabling people with disabilities to autonomously interact with their homes and to better communicate with other people. However, especially for people with severe mobility impairments, there is still a lack of tools and interfaces for effective control and interaction with home automation systems, and general-purpose solutions are seldom applicable due to the complexity, asynchronicity, time dependent behavior, and safety concerns typical of the home environment. This paper focuses on user-environment interfaces based on the eye tracking technology, which often is the only viable interaction modality for users as such. We propose an eye-based interface tackling the specific requirements of smart environments, already outlined in a public Recommendation issued by the COGAIN European Network of Excellence. The proposed interface has been implemented as a software prototype based on the ETU universal driver, thus being potentially able to run on a variety of eye trackers, and it is compatible with a wide set of smart home technologies, handled by the Domotic OSGi Gateway. A first interface evaluation, with user testing sessions, has been carried and results show that the interface is quite effective and usable without discomfort by people with almost regular eye movement control.