1,721,268 research outputs found
On the apparent viscosity of granular soils during liquefaction tests
No full textLiquefaction is a phenomenon marked by a rapid loss of soil strength and stiffness, which generally occurs in loose saturated sandy deposit during earthquake because of the generation of excess pore water pressure. Several experimental researches concluded that liquefied soil behaves as a fluid during ground movement, but after the earthquake motion ceases, due to the dissipation of excess pore water pressure and soil dilatancy, the liquefied soil recovers its initial stiffness and returns to behave as a solid. Such a change of state can be analysed by considering the soil as an equivalent visco-plastic material, characterized by an apparent viscosity (η) that changes during the cyclic loading. Following this approach, the authors analysed the results of some cyclic undrained triaxial tests carried out on reconstituted and undisturbed (frozen) specimens of sandy and gravelly soils in terms of apparent viscosity decay law (η-Ncyc), highlighting the relevance of η as physically based parameter for the correct identification of the liquefaction triggering. The experimental results confirm that the apparent viscosity decreases with the increase of the shear strain rate and highlight that the flow characteristics of liquefied soils (consistency coefficient and liquidity index) are affected by both grain size distributions and soil state conditions (relative density and confining stress)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
General Approach to Model the Surface Charge Induced by Multiple Surface Chemical Reactions in Potentiometric FET Sensors
Full text linkWe propose a general methodology to calculate the individual sensitivity and the cross-sensitivities of potentiometric sensor devices (e.g., ion sensitive FETs (ISFETs), CHEMFETs) with an arbitrary number of non-interacting receptors binding to ionic species or analytes in the electrolyte. The surface charge generated at the (bare or functionalized) interface with the electrolyte is described by the Poisson equation coupled to a linear system of equations for each type of receptor, where the unknowns are the fractions of sites binding with a given ion/analyte. Our general model encompasses in a unique framework a few simple special cases so far separately reported in the literature and provides for them closed-form expressions of the average site occupation probability. Detailed procedural description of the usage and benefits of the model is shown for specific cases with concurring surface chemical reactions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Soil Liquefaction: From mechanisms to effects on the built environment
No full textThe analysis of soil liquefaction phenomenon and its consequences on built environment remains one of the more active research areas in geotechnical engineering around the world. In many major earthquakes, liquefaction induced ground failures (sand boils, ground settlements, cracks and lateral spreading, flow failure) caused extensive damages to shallow-founded buildings and other engineering facilities. An accurate liquefaction hazard analysis can be done if all factors governing the liquefaction triggering and its effects are included, in a consistent way, into the assessment procedure. Given the complexity of the phenomenon itself and the variety of ground failure mechanisms, the evaluation of liquefaction hazard at large scale is necessarily done by means of simplified procedures that in some major earthquakes gave a misprediction of liquefaction effects on the built environment, highlighting the limits of their predictive capability. The development of more accurate methods to quantify liquefaction hazard and the associated consequences for buildings and infrastructures is the challenge on which the research is ongoing
Liquefaction triggering of non-saturated sandy soils
No full textIn saturated sandy soils liquefaction triggering is generally well-identified according to stress or strain criteria. On the contrary, the attainment of liquefaction in non-saturated sandy soils is still a cause of discussion in the scientific community. Even if the liquefaction resistance of non-saturated soils is higher than that of saturated ones, these soils may liquefy, as well. The increasing interest for cyclically mechanical behaviour of non-saturated sandy soils is due to the fact that desaturation or induced partial saturation can be used as useful mitigation techniques against soil liquefaction. Therefore, it is important to define, as accurately as possible, the attainment of liquefaction, on which depends the estimation of liquefaction resistance. The relevance of the apparent viscosity as a physically based parameter for the correct identification of the liquefaction triggering for fully saturated soils has been already demonstrated. In this paper, the viscous triggering approach has been used for non-saturated soils, processing some cyclic triaxial tests carried out on different sandy soils. The results confirm the reliability of the apparent viscosity as a liquefaction triggering parameter, showing a tight correlation with the strain liquefaction triggering criterion. Therefore, strain criterion should be preferred in non-saturated sandy soils
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
On the prediction of liquefaction resistance of unsaturated sands
No full textThe increasing interest in the undrained cyclic behaviour of unsaturated soils is justified by the evidence of the beneficial effect of desaturation on liquefaction resistance and is thus strictly connected with the need to put forth sound tools to be used in the design of Induced Partial Saturation (IPS)interventions. IPS is still far from being a routine technology because of the lack of such design tools, as well as of simple technologies to obtain and preserve it on site. This paper offers a contribution to the first issue, based on the energetic interpretation of laboratory results that highlights the role of the volumetric and deviatoric components of the specific energy spent during undrained cycling on the liquefaction mechanism. Independent experimental results taken from the literature are successfully simulated using this interpretation. Then, stemming from the theoretical and experimental considerations reported in the first part of the paper, two possible approaches to calculate the desired degree of saturation of a loose sand (design goal for IPS)are introduced and discussed
General model and equivalent circuit for the chemical noise spectrum associated to surface charge fluctuation in potentiometric sensors
Full text linkThis paper firstly reports a general and powerful approach to evaluate the power spectral density (PSD) of the surface charge fluctuations, so-called “chemical noise”, from a generic set of reactions at the sensing surface of potentiometric sensors such as, for instance, Ion-Sensitive Field Effect Transistors (ISFETs). Starting from the master equation, the spectral noise signature of a reaction set is derived as a function of the reaction kinetic parameters and of the interface concentration of the ionic species. Secondly, we derive an equivalent surface admittance, whose thermal noise PSD produces a noise PSD equal to that of the surface charge fluctuations. We also show how to expand this surface admittance into stair-case RC networks, with a number of elementary cells equal to the number of surface reactions involved. This admittance can be included in circuit simulations coupled with a SPICE compact model of the underlying FET, to enable the physically based modelling of frequency dispersion and noise of the sensing layer when simulating the sensor and the read-out. Validation with existing models and literature results as well as new application examples are provided. The proposed methodology to compute the PSD from rate equations is amenable to use in different contexts where fluctuations are generated by random transitions between discrete states with given exchange rates
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