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A rigorous solution aimed at accounting for the superposition and flow rule assumptions in the assessment of the bearing capacity of shallow strip footings under plane strain conditions has been developed using the method of characteristics and the finite element method. With reference to the Hill and Prandtl failure mechanisms, a bearing capacity factor Nγq and a superposition corrective coefficient μ that allow to directly obtain the actual bearing capacity of shallow strip foundations have been proposed. The geometry of the plastic volume involved in the failure mechanism has been also investigated, highlighting the influence of the superposition and flow rule assumptions. Starting from the numerical results obtained using the method of characteristics, several empirical relationships have been proposed for an accurate estimate of Nγq and μ as well as for the lateral extension and depth of the plastic volume. The accuracy of the numerical results has been checked through finite element analyses under the assumption of associated and non-associated flow rule showing that the proposed superposition corrective coefficient μ is not influenced by the flow rule assumption. Thus, a general bearing capacity equation for shallow strip footings has been provided which accounts for superposition approximation and non-associated flow rule. [ABSTRACT FROM AUTHOR]

Abstract: The static and seismic sliding limit equilibrium condition of retaining walls is investigated, and analytical solutions for the angle of the active slip surface, the critical acceleration coefficient and the coefficient of active earth pressure are provided for different surcharge conditions. In particular, walls retaining a horizontal backfill without surcharge, walls supporting an extended uniform surcharge applied at different distances from the wall and walls supporting a limited uniform surcharge or linear uniform surcharge parallel to the wall are considered in the analysis. The solutions have been derived in the framework of the limit equilibrium approach, considering the effect of the wall through its weight, and accounting for the shear resistance at the base of the wall and the inertia force arising in the wall under seismic conditions. For the wall without surcharge the effect of the vertical component of the seismic acceleration as well as the effects of the inclination of the wall internal face and of the soil–wall friction were also investigated. The angle of the slip plane, the critical seismic acceleration coefficient and the coefficient of active earth pressure are given as functions of dimensionless parameters and the boundary conditions for the applicability of each solution are specified. The influence of soil weight, surcharge conditions and inertia forces on the active earth pressure coefficient is analysed. [Copyright &y& Elsevier]

Abstract: The response of an earth dam to seismic loading is studied through displacement-based analyses and finite element, effective stress dynamic analyses. Displacement-based analyses are carried out using both empirical relationships and the decoupled approach in which the deformable response of the soil is accounted for through ground response analyses, and the resulting accelerograms are used in the sliding block analysis. The FE analyses are carried out using a constitutive model capable to reproduce soil non-linearity, calibrated against laboratory measurements of the stiffness at small strains. The influence of the assumed input motion and bedrock depth on the seismic response of the dam is also studied. The FE analyses permitted evaluation of the overall patterns of the dam behaviour in terms of displacements and of stress, strain and acceleration fields. For any of the seismic scenarios considered in the analyses the performance of the dam was satisfactory in that maximum computed settlements at the crest were considerably smaller than the service freeboard of the dam and limited shear strains were obtained within the dam during earthquake loading. Comparison of FE dynamic analyses with displacement-based analyses allowed predictions from different approaches to be compared. A fair agreement was obtained provided that ground response analysis was accounted for when using the displacement-based approach. [Copyright &y& Elsevier]

The effects of earthquake induced pore pressure on seismic and post seismic stability conditions of cohesionless slopes are investigated with reference to the infinite slope scheme. In cohesionless slopes the shear strength reduction caused by pore pressure build-up may lead the slope to a deformation failure or to a flow failure if liquefaction conditions are approached. Two critical values of the seismic induced pore pressure ratio are introduced to evaluate the effect of shear strength reduction on the slope failure mechanism. The results are given in the form of stability charts and a procedure for the evaluation of the seismic stability condition is described. The procedure gives useful information about the failure mechanism that slopes may exhibit and the displacement analysis which should be carried out. [Copyright &y& Elsevier]

A rigorous and practical solution aimed at accounting for the effect of groundwater in the assessment of bearing capacity of shallow strip footings in plane strain conditions has been developed using the method of characteristics. A steady water table in the foundation soil is considered and a bearing capacity factor N γw to be used in the classical trinomial bearing capacity equation is introduced. The proposed bearing capacity factor depends on the angle of shear strength, on the footing roughness and on the water table depth and is also influenced by the soil unit weight. Normalizing N γw with respect to the bearing capacity factor N γ computed for the case of dry foundation soil, a corrective coefficient has been introduced for which best-fit empirical relationships have been proposed for both smooth and rough foundations. The size of the plastic mechanism under the footing has also been investigated and equations allowing to evaluate its relevant dimensions have been provided. The proposed solutions have been checked against results obtained via finite element analyses, finding a perfect agreement in terms of both corrective coefficients and shape and size of the soil plastic volume. Finally, the actual bearing capacity problem was solved showing that the trinomial formula, even in presence of a steady water table, still yields conservative values of the bearing capacity. [ABSTRACT FROM AUTHOR]

The method of characteristics has been used to develop a rigorous solution for the evaluation of seismic bearing capacity of shallow foundations resting on homogenous fully submerged soil accounting for the effect of earthquake-induced pore water pressures. The solution, derived with reference to both the Hill and Prandtl plastic mechanisms, is essentially referred to the bearing capacity factor N γ , is of general validity and has been checked against finite element analysis results. An original empirical expression providing the corrective coefficient to be introduced in the usual trinomial bearing capacity formula has been proposed, accounting for the reduction in bearing capacity due to combined effect of soil inertia and earthquake-induced pore water pressures. It has also been demonstrated that, even considering earthquake-induced excess pore pressures, the soil and superstructure inertial effects are still decoupled. This allowed introducing an overall corrective coefficient accounting for both the inertial (soil and superstructure) and excess pore pressure effects, computed as the product of the corresponding corrective coefficients. Finally, original simple equations were derived giving a threshold value of the excess pore pressure ratio required to trigger a bearing capacity failure in the static post-seismic conditions because of the soil shear strength reduction. • A novel seismic bearing capacity solution with excess pore pressures is described. • The method of characteristics was used to integrate plastic equilibrium equations. • It is shown inertia effect are decoupled even in presence of excess pore pressures. • An original corrective coefficient accounting for excess pore pressure is provided. [ABSTRACT FROM AUTHOR]

Isotactic poly(3-hydroxybutyrate) (P3HB) is an aliphatic polyester obtained by bacterial fermentation. This truly biodegradable polymer has been widely investigated, mainly with the aim to replace conventional plastics, which cause environmental pollution. To improve its properties, extensive studies have been conducted to modify it properly by copolymerization or blending with other polymers. Macroscopic properties of polymers, particularly of polymer blends, are strongly affected by their microstructure, especially by the allocation of different phases and their level of dispersion and adhesion. In nonreactive blends, the adhesion level is mainly determined by the similarity between the chemical structure of the components, and the arrangement of the phases is remarkably controlled by the crystallization conditions. The superstructure of the crystalline phases accounts for the mechanical resistance of the blend, but the composition and the distribution of the amorphous phases also play an important role, especially with respect to toughness properties. This article reviews data on thermal properties and the crystallization process of P3HB and its copolymers, both alone and in the presence of other polymers. In particular, copolymers of 3-hydroxybutyrate with 3-hydroxyvalerate and with 4-hydroxybutyrate and blends of P3HB and the copolymers with atactic poly(3-hydroxybutyrate), poly(vinyl acetate), poly(vinyl alcohol), poly(ethylene oxide), poly(methylene oxide), poly(epichlorohydrin), and poly(methyl methacrylate) are considered. Major attention is directed toward the influence of miscibility and composition on solidification kinetics and crystal structure with the objective to provide an overview of the current state of the art. *Dedicated to Prof. Francisco J. Baltá Calleja on the occasion of his 65th birthday. [ABSTRACT FROM AUTHOR]

Aims. HD 142527 is one of the most frequently studied Herbig Ae/Be stars with a transitional disk that hosts a large cavity that is up to about 100 au in radius. For this reason, it has been included in the guaranteed time observation (GTO) SpHere INfrared survey for Exoplanets (SHINE) as part of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT) in order to search for low-mass companions that might explain the presence of the gap. SHINE is a large survey within about 600 young nearby stars are observed with SPHERE with the aim to constrain the occurrence and orbital properties of the giant planet population at large (> 5 au) orbital separation around young stars. Methods. We used the IRDIFS observing mode of SPHERE (IRDIS short for infrared dual imaging and spectrograph plus IFS or integral field spectrograph) without any coronagraph in order to search for and characterize companions as close as 30 mas of the star. Furthermore, we present the first observations that ever used the sparse aperture mask (SAM) for SPHERE both in IRDIFS and IRDIFS_EXT modes. All the data were reduced using the dedicated SPHERE pipeline and dedicated algorithms that make use of the principal component analysis (PCA) and reference differential imaging (RDI) techniques. Results. We detect the accreting low–mass companion HD 142527B at a separation of 73 mas (11.4 au) from the star. No other companions with mass greater than 10 MJ are visible in the field of view of IFS (∼100 au centered on the star) or in the IRDIS field of view (∼400 au centered on the star). Measurements from IFS, SAM IFS, and IRDIS suggest an M6 spectral type for HD 142527B, with an uncertainty of one spectral subtype, compatible with an object of M = 0.11 ± 0.06 M⊙ and R = 0.15 ± 0.07 R⊙. The determination of the mass remains a challenge using contemporary evolutionary models, as they do not account for the energy input due to accretion from infalling material. We consider that the spectral type of the secondary may also be earlier than the type we derived from IFS spectra. From dynamical considerations, we further constrain the mass to 0.26+0.16−0.14 0. 26 − 0.14 + 0.16 $ 0.26^{+0.16}_{-0.14} $ M⊙, which is consistent with both our spectroscopic analysis and the values reported in the literature. Following previous methods, the lower and upper dynamical mass values correspond to a spectral type between M2.5 and M5.5 for the companion. By fitting the astrometric points, we find the following orbital parameters: a period of P = 35 − 137 yr; an inclination of i = 121 − 130°, a value of Ω = 124 − 135° for the longitude of node, and an 68% confidence interval of ∼18 − 57 au for the separation at periapsis. Eccentricity and time at periapsis passage exhibit two groups of values: ∼0.2–0.45 and ∼0.45–0.7 for e, and ∼2015–2020 and ∼2020–2022 for T0. While these orbital parameters might at first suggest that HD 142527B is not the companion responsible for the outer disk truncation, a previous hydrodynamical analysis of this system showed that they are compatible with a companion that is able to produce the large cavity and other observed features. [ABSTRACT FROM AUTHOR]

The recent discovery of an earth-like planet around Proxima Centauri has drawn much attention to this star and its environment. We performed a series of observations of Proxima Centauri using Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), the planet-finder instrument installed at the European Southern Observatory (ESO) Very Large Telescope (VLT) UT3, using its near-infrared modules, InfraRed Dual-band Imager and Spectrograph (IRDIS) and IFS. No planet was detected directly, but we set upper limits on the mass up to 7 au by exploiting the AMES-COND models. Our IFS observations reveal that no planet more massive than ∼6–7 MJup can be present within 1 au. The dual-band imaging camera IRDIS also enables us to probe larger separations than other techniques such as radial velocity or astrometry. We obtained mass limits of the order of 4 MJup at separations of 2 au or larger, representing the most stringent mass limits at separations larger than 5 au available at the moment. We also made an attempt to estimate the radius of possible planets around Proxima using the reflected light. Since the residual noise for the observations is dominated by photon noise and thermal background, longer exposures in good observing conditions could improve the achievable contrast limit further. [ABSTRACT FROM AUTHOR]

In this paper, a method for generating samples of a fully non-stationary zero-mean Gaussian process, having a target acceleration time-history as one of its own samples, is presented. The proposed method requires the following steps: i) divide the time axis of the target accelerogram in contiguous time intervals in which a uniformly modulated process is introduced as the product of a deterministic modulating function per a stationary zero-mean Gaussian sub-process, whose power spectral density (PSD) function is filtered by two Butterworth filters; ii) estimate, in the various time intervals, the parameters of modulating functions by least-square fitting the expected energy of the proposed model to the energy of the target accelerogram; iii) estimate the parameters of the PSD function of the stationary sub-process, once the occurrences of maxima and of zero-level up-crossings of the target accelerogram, in the various intervals, are counted; iv) obtain the evolutionary spectral representation of the fully non-stationary process by adding the various contribution evaluated in the various intervals. • The generation of artificial accelerograms consistent with real seismic records is addressed. • Main characteristics of target accelerograms are used to define fully non-stationary processes. • The target accelerogram is considered a sample of the fully non-stationary process. • The proposed method is suitable for selecting input motion for dynamic analyses of structural and geotechnical systems. • The proposed procedure is characterised by accuracy and computational efficiency. [ABSTRACT FROM AUTHOR]