1,721,137 research outputs found
From geotechnical and hydraulic researches to use of natural materials in mitigation works for river embankments: A case study
No full textIn rivers, a hydraulic hazard is the result of natural or human factors, or both. The first step in addressing the problem is to establish hydraulic security measures; the work undertaken must allow for improving hydraulic characteristics of the river in order to create a section compatible with the maximum predictable height and flow. The logic of the mitigation works for the hydraulic hazard usually doesn’t coincide with river redevelopment measures because some actions are obviously conflicting. These questions are faced with a geotechnical and hydraulic research and with the use of natural materials in mitigation works. The study consists of a diagnosis about the conditions of functionality of the fluvial embankments (in particular in the urban section), to suggest guidelines for measures with low environmental impact and with a “friend of nature” engineering approach. In this paper the geotechnical and hydraulic problem of the existing embankments is analysed in two areas that are particularly important to the Aterno River (L’Aquila, Italy). The aims of the studies are to find the most suitable solutions of correction and restoration works. This paper illustrates the methodology to define the map of hydraulic hazard and to determine the maximum heights of the flow. Moreover, it shows the results of many in-situ tests by flat dilatometer (DMT) and laboratory geotechnical tests performed in the river alluvium soils in order to perform a stability analysis of embankments and for settlements prediction. Finally, it gives guidelines for measures with low environmental impact and with an eco-friendly engineering approach
On the experimental assessment of De Marchi’s discharge coefficient for inclined side weirs: transfer functions for the application of alternative methods
No full textThe use of De Marchi’s approach, solving the 1D dynamic equation of spatially varied steady flow with non-uniform discharge, is commonly accepted in the design of side weirs. A key issue in applying De Marchi’s formula is the assessment of the discharge coefficient CM. However, no explicit equation for the experimental determination of CM can be derived for inclined side weirs, due to the longitudinal change of crest’s height. In this context, the present study analyzes the feasibility of using alternative methods for the estimation of the discharge coefficient (i.e. Dominguez’s, Schimdt’s or other approaches), which may be suitable to be used in De Marchi’s equation also for inclined side weirs. However, this solution necessarily yields an additional error in the estimation of CM, due to the different modelling assumptions underlying these other methods. Therefore, in this study, the magnitude of this error is first quantified using a 1D numerical model for different tested hydraulic conditions and geometric configurations of the side weir, including: Froude number (only subcritical flows), channel and friction slope, crest angle, water depth/weir height and weir length/channel width ratios. Results indicate that error factors (i.e. observed/predicted ratio) in the assessment of De Marchi’s coefficient can range from 0.57 to 15.60 for inclined lateral weirs, depending on the selected modelling approach. As a second step, a Multilayer Perceptron Neural network is applied to derive transfer functions from the discharge coefficients calculated using the different methods to the corresponding values of CM to be used in De Marchi’s weir equation
Effects of protuberances on surface loads on the vega-c launch vehicle
No full textThe need to meet the demands of the aerospace market in terms of payload capability, mission flexibility, and cost reduction has led the European Space Agency to develop Vega-C as an evolution of the original Vega launcher. The design of a modern launch vehicle like the Vega-C requires accurate evaluation of the thermal and mechanical loads on its surface under conditions as close as possible to real flight conditions. Despite its apparently simple aeroshape, the Vega-C surface is characterized by the presence of antennas, wiring ducts, flanges, and retrorockets. These protuberances interact with the external supersonic stream during the launcher's flight, giving rise to locally complex flows that can impose stresses on the launcher structure through the generation of severe mechanical and thermal loads. The present work focuses on an in-depth aerothermal analysis of Vega-C protuberances under specific flight conditions. Numerical computations are carried out using the commercial solver CFD++ on multiblock structured Chimera grids to assess which protuberances are subject to the most severe surface loads. Particular emphasis is placed on the role of boundary-layer thickness in the heat flux and pressure peaks that occur on the protuberances
An anatomical review of spinal cord blood supply
No full textKnowledge of the spinal cord (SC) vascular supply is important in patients undergoing procedures that involve the thoracic and thoracoabdominal aorta. However, the SC vasculature has a complex anatomy, and teaching is often based only on anatomical sketches with highly variable accuracy; historically, this has required a "leap of faith" on the part of aortic surgeons. Fortunately, this "leap of faith" is no longer necessary given recent breakthroughs in imaging technologies and postprocessing software. Imaging methods have expanded the non-invasive diagnostic ability to determine a patient's SC vascular pattern, particularly in detecting the presence and location of the artery of Adamkiewicz. CT is the imaging modality of choice for most patients with thoracic and thoracoabdominal aortic disease, proving especially useful in the determination of feasibility and planning of endovascular treatment. Thus the data set required for analysis of SC vascular anatomy is usually already available. We have concentrated our efforts on CT angiography, which offers particularly good imaging capabilities with state-of-the-art multidetector scanners. Multidetector row helical CT provides examinations of an extensive range in the craniocaudal direction with thin collimation in a short time interval, giving excellent temporal and spatial resolution. This paper provides examples of the SC vasculature imaging quality that can be obtained with 64 row scanners and appropriate postprocessing. Knowledge of the principal anatomical features of the SC blood supply of individual patients undergoing open or endovascular thoracoabdominal procedures has several potential benefits. For open surgery, analysis of the SC vasculature could tell us the aortic region that feeds the Adamkiewicz artery and thus needs to be reimplanted. For endovascular procedures, we can determine whether the stent-graft will cover the Adamkiewicz artery, thus avoiding unnecessary coverage. CT data can also be used to stratify risk of SC ischemia and guide the selective use of spinal cord injury prevention strategies
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
Investigation of hydraulic, geotechnical, and planning aspects for the environmental safety of the new sport facilities in L'Aquila
No full textThe earthquake of L’Aquila (on 6 April 2009) has resulted in a pressing need to provide the city with hospitality areas and new structures for the population. In the territory of L’Aquila, the lack of space and the inhabitability of sport facilities make the case study below compelling. In rivers, hydraulic hazards are the result of either natural or human factors. The first step in addressing the problem is to establish hydraulic safety measures: this work must include the improvement of the hydraulic characteristics of rivers in order to create a section compatible with the maximum predictable height and flow. The logic of mitigation works for hydraulic hazards usually does not coincide with river redevelopment measures because some actions are obviously conflicting. The issues dealing with mitigation works are related to geotechnical and hydraulic research, and the use of natural materials. This paper aims to illustrate a diagnostic functionality of the embankments of the Aterno River (L’Aquila, Italy) and its surrounding areas. The definition of hydraulic and geotechnical properties allows the integration of hydraulic safety measures with extra-agricultural use of the territory. In fact, in this area, mitigation works are combined with the plan of the city and of sports and leisure time, applying measures that have a different environmental impact. The river embankments, for example, are embedded in the spatial and functional organization of the planned sport facilities
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
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