Typology Selection of Retaining Walls Based on Multicriteria Decision-Making Methods

This research received no external funding.In civil engineering and construction, in the selection of the most adequate and sustainable alternative, all of the alternatives and selection criteria, such as the requirements of the construction process (which are often overlooked) and the preferences of designers, clients, or contractors, are not always taken into account. The purpose of this article is to suggest a methodology that may allow studying all of the possible alternatives to find the most ideal solution among all of the existing possibilities for the selection of retaining walls to be built in infrastructures in different environments. For this purpose, all typologies of retaining walls and selection criteria (external requirements, construction requirements, characteristics of the natural land and economic criteria) are first identified. Subsequently, a simple methodological method is proposed, allowing the relative importance of each criterion to be established and allowing us to select the most suitable solution for each situation by successively applying different multicriteria decision-making methods. Finally, the methodology developed is applied to two projects in different locations with different constraints. The results obtained provide a set of compromise solutions that remain as best-rank alternatives when the weights of the criteria change. Therefore, the methodology developed can be applied to the selection of typologies of other structures in future projects

Uncertainty analysis methods to select the optimal alternative in the design of parking facilities

The selection of the preferred alternative in a parking facility project is usually made in a state of uncertainty. Decision-making methods are a useful tool to systematically arrive at a final decision between different alternatives and reduce subjectivity in decision making by creating a series of filters. However, the selection of the appropriate variables to be considered in the analysis may be problematic as well. Performing sensitivity analyses on entry variables is a key feature to ensure that the final choice is stable when initial conditions experience changes. This paper suggests a methodology to select the best alternative when considering parking facilities. The methodology compares the results from two different sensitivity analyses techniques. The changes in preference experienced as the applied weights change through the process are analyzed and the most critical criteria are identified

Interpocket polarization model for magnetic structures in rare-earth hexaborides

The origin of peculiar magnetic structures in cubic rare-earth (R) hexaborides RB_6 is traced back to their characteristic band structure. The three sphere-like Fermi surfaces induce interpocket polarization of the conduction band as a part of a RKKY-type interaction. It is shown for the free-electron-like model that the interpocket polarization gives rise to a broad maximum in the intersite interaction I(q) around q=(1/4,1/4,1/2) in the Brillouin zone. This maximum is consistent with the superstructure observed in R=Ce, Gd and Dy. The wave-number dependence of I(q) is independently extracted from analysis of the spin-wave spectrum measured for NdB_6. It is found that I(q) obtained from fitting the data has a similarly to that derived by the interpocket polarization model, except that the absolute maximum now occurs at (0,0,1/2) in consistency with the A-type structure. The overall shape of I(q) gives a hint toward understanding an incommensurate structure in PrB_6 as well.Comment: 5 pages, 3 figures, submitted to J.Phys.Soc.Jp

Contribution to the knowledge of early geotechnics during the twentieth century: Ralph Peck

Ralph B. Peck (1912–2008), graduate and doctor of philosophy in civil engineering (1934 and 1937 respectively) from the Rensselaer Polytechnic Institute, was one of the major contributors to the development of geotechnics in the twentieth century. Born in Winnipeg (Manitoba) as an American national, he was influenced from childhood by the world of civil engineering through his father, Orwin K. Peck, who was a civil engineer, mainly as a structural engineer in the railway sector. In the absence of job offers as a structural engineer, Ralph Peck arrived at Harvard University in 1938 to attend the soil mechanics courses taught by Arthur Casagrande, which guided Peck's professional career towards geotechnics. In addition to Casagrande, Peck had the opportunity to meet and work with other very important people related to geotechnics: Albert E. Cummings, Laurits Bjerrum, Alec W. Skempton and especially Karl Terzaghi, with whom he established a great friendship, in addition to providing support, professional advice and performing important work, such as the Chicago Subway Works. Peck actively dedicated himself to consulting work, which led him to visit 44 states within the United States and 28 countries on five continents. In addition, he also participated in research work where he was asked and was a committed lecturer at the University of Illinois, where he was a professor for 32 years. The objective of this paper is to analyse, through Peck's biography, his contribution to the field of geotechnics based on his research, teaching and consultancy work, and through the influence of Peck on other important people in the field, such as Karl Terzaghi.</p

Contribution to the knowledge of early geotechnics during the twentieth century: Arthur Casagrande

Arthur Casagrande (1902–1981) is one of the main people responsible for the geotechnics that we know today. Born in Haidenschaft, now Slovenia, he went to the United States in 1926 to participate in major civil engineering projects: he graduated in 1924 from the Technische Hochschule in Vienna, Austria. On this visit to the USA he met Karl Terzaghi (1883–1963), the father of soil mechanics and geotechnology, who taught him the basic concepts of this discipline to which Casagrande dedicated the rest of his life.In his early years of work with Terzaghi, Casagrande focused on research studies, such as the development on the limits of Atterberg published in 1932, and the development of equipment for soil trials, such as the Casagrande spoon also developed in 1932. Casagrande not only dedicated himself to research in his early years, but he also carried out studies throughout his professional career, such as those carried out on liquefaction, which he began in 1937 and continued throughout his life.Casagrande not only made important contributions in the field of geotechnology, but also lectured at Harvard University, which he joined in 1932. He also consulted and was involved in several projects for the Army Corps of Engineers of the United States. In addition, Casagrande made an important contribution to the 1st International Conference of Soil Mechanics and Foundations Engineering that took place at Harvard University in 1936.The aim of this paper is to analyze, through the biography of Casagrande, his contribution to the field of geotechnics, based on his research, teaching, and consulting work. Moreover, Casagrande influenced other important people in the field, such as Terzaghi, Peck, and even the work with his brother Leo, and, of course, the influence of these people on Casagrande's team.</p

On determining spectral parameters, tracking jitter, and GPS positioning improvement by scintillation mitigation

A method of determining spectral parameters p (slope of the phase PSD) and T (phase PSD at 1 Hz) and hence tracking error variance in a GPS receiver PLL from just amplitude and phase scintillation indices and an estimated value of the Fresnel frequency has been previously presented. Here this method is validated using 50 Hz GPS phase and amplitude data from high latitude receivers in northern Norway and Svalbard. This has been done both using (1) a Fresnel frequency estimated using the amplitude PSD (in order to check the accuracy of the method) and (2) a constant assumed value of Fresnel frequency for the data set, convenient for the situation when contemporaneous phase PSDs are not available. Both of the spectral parameters ( p, T ) calculated using this method are in quite good agreement with those obtained by direct measurements of the phase spectrum as are tracking jitter variances determined for GPS receiver PLLs using these values. For the Svalbard data set, a significant difference in the scintillation level observed on the paths from different satellites received simultaneously was noted. Then, it is shown that the accuracy of relative GPS positioning can be improved by use of the tracking jitter variance in weighting the measurements from each satellite used in the positioning estimation. This has significant advantages for scintillation mitigation, particularly since the method can be accomplished utilizing only time domain measurements thus obviating the need for the phase PSDs in order to extract the spectral parameters required for tracking jitter determination

In situ observation of stress relaxation in epitaxial graphene

Upon cooling, branched line defects develop in epitaxial graphene grown at high temperature on Pt(111) and Ir(111). Using atomically resolved scanning tunneling microscopy we demonstrate that these defects are wrinkles in the graphene layer, i.e. stripes of partially delaminated graphene. With low energy electron microscopy (LEEM) we investigate the wrinkling phenomenon in situ. Upon temperature cycling we observe hysteresis in the appearance and disappearance of the wrinkles. Simultaneously with wrinkle formation a change in bright field imaging intensity of adjacent areas and a shift in the moire spot positions for micro diffraction of such areas takes place. The stress relieved by wrinkle formation results from the mismatch in thermal expansion coefficients of graphene and the substrate. A simple one-dimensional model taking into account the energies related to strain, delamination and bending of graphene is in qualitative agreement with our observations.Comment: Supplementary information: S1: Photo electron emission microscopy and LEEM measurements of rotational domains, STM data of a delaminated bulge around a dislocation. S2: Movie with increasing brightness upon wrinkle formation as in figure 4. v2: Major revision including new experimental dat

Magnetic Phase Diagram of GdNi2B2C: Two-ion Magnetoelasticity and Anisotropic Exchange Couplings

Extensive magnetization and magnetostriction measurements were carried out on a single crystal of GdNi2B2C along the main tetragonal axes. Within the paramagnetic phase, the magnetic and strain susceptibilities revealed a weak anisotropy in the exchange couplings and two-ion tetragonal-preserving alpha-strain modes. Within the ordered phase, magnetization and magnetostriction revealed a relatively strong orthorhombic distortion mode and rich field-temperature phase diagrams. For H//(100) phase diagram, three field-induced transformations were observed, namely, at: Hd(T), related to the domain alignment; Hr(T), associated with reorientation of the moment towards the c-axis; and Hs(T), defining the saturation process wherein the exchange field is completely counterbalanced. On the other hand, For H//(001) phase diagram, only two field-induced transformations were observed, namely at: Hr(T) and Hs(T). For both phase diagrams, Hs(T) follows the relation Hs[1-(T/Tn)^2]^(1/2)kOe with Hs(T-->0)=128.5(5) kOe and Tn(H=0)=19.5 K. In contrast, the thermal evolution of Hr(T) along the c-axis (much simpler than along the a-axis) follows the relation Hr[1-T/Tr]^(1/3) kOe where Hr(T-->0)=33.5(5) kOe and Tr(H=0)=13.5 K. It is emphasized that the magnetoelastic interaction and the anisotropic exchange coupling are important perturbations and therefore should be explicitly considered if a complete analysis of the magnetic properties of the borocarbides is desired

Tackling ionospheric scintillation threat to GNSS in Latin America

Scintillations are rapid fluctuations in the phase and amplitude of transionospheric radio signals which are caused by small-scale plasma density irregularities in the ionosphere. In the case of the Global Navigation Satellite System (GNSS) receivers, scintillation can cause cycle slips, degrade the positioning accuracy and, when severe enough, can even lead to a complete loss of signal lock. Thus, the required levels of availability, accuracy, integrity and reliability for the GNSS applications may not be met during scintillation occurrence; this poses a major threat to a large number of modern-day GNSS-based applications. The whole of Latin America, Brazil in particular, is located in one of the regions most affected by scintillations. These effects will be exacerbated during solar maxima, the next predicted for 2013. This paper presents initial results from a research work aimed to tackle ionospheric scintillation effects for GNSS users in Latin America. This research is a part of the CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project, co-funded by the EC Seventh Framework Program and supervised by the GNSS Supervisory Authority (GSA), which aims to develop and test ionospheric scintillation countermeasures to be implemented in multi-frequency, multi-constellation GNSS receivers