Behavior of Porewater Pressures in an Earth Dam by Principal Component Analysis

This study deals with the utilization of the pore pressure meter for evaluating the stability of a dam through the correlation between the porewater pressure installed in the fill dam and the water level of the dam. To this end, principal components analysis was performed on a total of 18 porewater pressure meters, and the main components were classified into three groups: internal (Group A), external (Group B), and upper (Group C), on the basis of the seepage line formed within the dam body. The coefficient of correlation between the porewater pressure and water level was found to be 0.86 to 1.00, indicating a strong positive linear relationship. This means that the maintenance of the dam is possible through the pore pressure meter present in Group A. Furthermore, the regression analysis for porewater pressures and water levels resulted in a linear regression model with the coefficient of determination (R2) of Group A being between 0.74 and 0.99. In particular, R2 between the power water pressure installed at the base of the dam and the water level was more than 0.99. Therefore, it was shown that the prediction of the porewater pressure is possible by using the relationships with the water level, making it possible to determine the safety of the dam by comparing it with the currently measured values

Behavior of Porewater Pressures in an Earth Dam by Principal Component Analysis

This study deals with the utilization of the pore pressure meter for evaluating the stability of a dam through the correlation between the porewater pressure installed in the fill dam and the water level of the dam. To this end, principal components analysis was performed on a total of 18 porewater pressure meters, and the main components were classified into three groups: internal (Group A), external (Group B), and upper (Group C), on the basis of the seepage line formed within the dam body. The coefficient of correlation between the porewater pressure and water level was found to be 0.86 to 1.00, indicating a strong positive linear relationship. This means that the maintenance of the dam is possible through the pore pressure meter present in Group A. Furthermore, the regression analysis for porewater pressures and water levels resulted in a linear regression model with the coefficient of determination (R2) of Group A being between 0.74 and 0.99. In particular, R2 between the power water pressure installed at the base of the dam and the water level was more than 0.99. Therefore, it was shown that the prediction of the porewater pressure is possible by using the relationships with the water level, making it possible to determine the safety of the dam by comparing it with the currently measured values

Transmission electron microscopy and thermodynamic studies of CaO-added AZ31 Mg alloys

We investigated the microstructural evolution of Mg-3Al-1Zn (AZ31) alloy systems, with Ca or CaO added, by carrying out microstructural characterizations in conjunction with thermodynamic calculations. A calculated phase diagram of the Mg-Ca-O ternary system showed that CaO can be dissolved in liquid Mg so as to have 12.6 wt.% Ca content in the liquid Mg at 700 degrees C. Therefore, for a 0.3 wt.% CaO-added AZ31 alloy, our thermodynamic calculation predicted a similar precipitation pathway to that of a 0.3 wt.% Ca-added AZ31 alloy during the solidification process. In fact, a thermodynamic analysis of the precipitation pathway assuming the Scheil model showed that the major precipitates in both alloys were Al8Mn5, CaMgSi, Laves C15 and Laves C36, in good agreement with our experimental observation. However, a microstructural characterization of the as-cast alloys using transmission electron microscopy revealed that the spatial distribution of the precipitates was significantly different in the two alloy systems; unlike in the Ca-added AZ31 alloy, the Ca-containing precipitates in the CaO-added AZ31 alloy exhibited strong agglomeration tendencies. Moreover, in an alloy solidified at a faster cooling rate, undissolved CaO particles were observed in the precipitate agglomerates that were connected to the other Ca-containing precipitates. These results suggest that an incomplete dissolution of CaO particles in the liquid results in the agglomeration of precipitates, as the undissolved CaO particles can act as local sources, supplying Ca to the liquid, and can thus act as preferential nucleation sites for the Ca-containing precipitates forming during the solidification of the alloy. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X112723sciescopu

Reversible cyclic deformation mechanism of gold nanowires by twinning-detwinning transition evidenced from in situ TEM

Mechanical response of metal nanowires has recently attracted a lot of interest due to their ultra-high strengths and unique deformation behaviours. Atomistic simulations have predicted that face-centered cubic metal nanowires deform in different modes depending on the orientation between wire axis and loading direction. Here we report, by combination of in situ transmission electron microscopy and molecular dynamic simulation, the conditions under which particular deformation mechanisms take place during the uniaxial loading of [110]-oriented Au nanowires. Furthermore, by performing cyclic uniaxial loading, we show reversible plastic deformation by twinning and consecutive detwinning in tension and compression, respectively. Molecular dynamics simulations rationalize the observed behaviours in terms of the orientation-dependent resolved shear stress on the leading and trailing partial dislocations, their potential nucleation sites and energy barriers. This reversible twinning-detwinning process accommodates large strains that can be beneficially utilized in applications requiring high ductility in addition to ultra-high strength.open114361sciescopu

In-situ observation of the initiation of plasticity by nucleation of prismatic dislocation loops

The elastic-to-plastic transition during the deformation of a dislocation-free nanoscale volume is accompanied by displacement bursts associated with dislocation nucleation. The dislocations that nucleate during the so-called "pop-in" burst take the form of prismatic dislocation loops (PDLs) and exhibit characteristic burst-like emission and plastic recovery. Here, we report the in-situ transmission electron microscopy (TEM) observation of the initial plasticity ensued by burst-like emission of PDLs on nanoindentation of dislocation-free Au nanowires. The in-situ TEM nanoindentation showed that the nucleation and subsequent cross slip of shear loop(s) are the rate-limiting steps. As the indentation size increases, the cross slip of shear loop becomes favored, resulting in a transition from PDLs to open half-loops to helical dislocations. In the present case of nanoindentation of dislocation-free volumes, the PDLs glide out of the indentation stress field while spreading the plastic zone, as opposed to the underlying assumption of the Nix-Gao model. Prismatic dislocation loops (PDLs) form during the elastic-to-plastic transition of a dislocation-free volume under nanoindentation. Here the authors observe the initial plasticity and burst-like emission of PDLs in Au nanowires by in-situ transmission electron microscopy, elucidating fundamental aspects of the formation process.11Ysciescopu

High performance gas sensors with an array of TiO2nano-helixesfabricatedbyobliqueangledeposition

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A near single crystalline TiO2 nanohelix array: enhanced gas sensing performance and its application as a monolithically integrated electronic nose

We present high performance gas sensors based on an array of near single crystalline TiO2 nanohelices fabricated by rotating oblique angle deposition (OAD). The combination of large surface-to-volume ratio, extremely small size (<30 nm) comparable to the Debye length, a near single crystallinity of TiO2 nanohelices, together with the unique top-and-bottom electrode configuration hugely improves the H-2-sensing performance, including similar to 10 times higher response at 50 ppm, approximately a factor of 5 lower detection limit, and much faster response time than the conventional TiO2 thin film devices. Beyond such remarkable performance enhancement, the excellent compatibility of the OAD method compared with the conventional micro-fabrication technology opens a new avenue for monolithic integration of high-performance chemoresistive sensors to fabricate a simple, low cost, reliable, yet fully functional electronic nose and multi-functional smart chips for in situ environmental monitoring.close9

Proposition of Adaptive Read Bias: A Solution to Overcome Power and Scaling Limitations in Ferroelectric‐Based Neuromorphic System

Abstract Hardware neuromorphic systems are crucial for the energy‐efficient processing of massive amounts of data. Among various candidates, hafnium oxide ferroelectric tunnel junctions (FTJs) are highly promising for artificial synaptic devices. However, FTJs exhibit non‐ideal characteristics that introduce variations in synaptic weights, presenting a considerable challenge in achieving high‐performance neuromorphic systems. The primary objective of this study is to analyze the origin and impact of these variations in neuromorphic systems. The analysis reveals that the major bottleneck in achieving a high‐performance neuromorphic system is the dynamic variation, primarily caused by the intrinsic 1/f noise of the device. As the device area is reduced and the read bias (VRead) is lowered, the intrinsic noise of the FTJs increases, presenting an inherent limitation for implementing area‐ and power‐efficient neuromorphic systems. To overcome this limitation, an adaptive read‐biasing (ARB) scheme is proposed that applies a different VRead to each layer of the neuromorphic system. By exploiting the different noise sensitivities of each layer, the ARB method demonstrates significant power savings of 61.3% and a scaling effect of 91.9% compared with conventional biasing methods. These findings contribute significantly to the development of more accurate, efficient, and scalable neuromorphic systems