50175 research outputs found
Sort by
Trajectory based Deep Policy Search for Quadrupedal Walking
No full textIn this paper, we explore a specific form of deep reinforcement learning (D-RL) technique for quadrupedal walking - trajectory based policy search via deep policy networks. Existing approaches determine optimal policies for each time step, whereas we propose to determine an optimal policy for each walking step. We justify our approach based on the fact that animals including humans use 'low' dimensional trajectories at the joint level to realize walking. We will construct these trajectories by using Bézier polynomials, with the coefficients being determined by a parameterized policy. In order to maintain smoothness of the trajectories during step transitions, hybrid invariance conditions are also applied. The action is computed at the beginning of every step, and a linear PD control law is applied to track at the individual joints. After each step, reward is computed, which is then used to update the new policy parameters for the next step. After learning an optimal policy, i.e., an optimal walking gait for each step, we then successfully play them in a custom built quadruped robot, Stoch 2, thereby validating our approach. © 2019 IEEE
External flow choking at the landing phase of aircraft and re-entry vehicles
No full textIn this paper 3D numerical studies have been carried out for improving the aerodynamic performance of aerospace vehicles at ground effect during takeoff and landing through a prudent design modification of the conventional fuselage. In this pilot work, using a validated 3D double precision density-based implicit standard k-ε turbulence model, the parametric analytical studies have been carried out to examine the external flow features of aircraft and re-entry spacecraft at ground effect. In the numerical study, a fully implicit finite volume scheme of the compressible, Navier�Stokes equations is employed. The validation and calibration of the 3D k-ε model is carried out based on the unique exact solution of boundary layer displacement thickness at the Sanal flow choking condition for 3D adiabatic flows (V.R.Sanal Kumar et al., AIP Advances, 8, 025315, 2018). We observed that facilitating a divergent channel effect at the bottom surface of the fuselage will be more beneficial for negating the external flow choking at ground effect during the close proximity flying. We inferred that under the identical flying conditions the chances of external flow choking at craft-in-ground (CIG) effect is less while comparing with the similar flying vehicles having the convectional fuselage. The fact is that if the ground clearance height to the chord length of the craft is too small, the developing boundary layers from either side of the surface (ground and the moving wing) can interact and develop a transient fluid-throat, leading to a choked flow, which will be delayed or negated for aircraft and re-entry space craft having fuselage bottom surface facilitated with diffuser channel shape. This study is a pointer towards for the fuselage and wings integrated geometry optimization for improving the overall aerodynamic performance of any flying craft at ground effect
Engineering Order and Cooperativity in a Disordered Protein
No full textStructural disorder in proteins arises from a complex interplay between weak hydrophobicity and unfavorable electrostatic interactions. The extent to which the hydrophobic effect contributes to the unique and compact native state of proteins is, however, confounded by large compensation between multiple entropic and energetic terms. Here we show that protein structural order and cooperativity arise as emergent properties upon hydrophobic substitutions in a disordered system with non-intuitive effects on folding and function. Aided by sequence-structure analysis, equilibrium, and kinetic spectroscopic studies, we engineer two hydrophobic mutations in the disordered DNA-binding domain of CytR that act synergistically, but not in isolation, to promote structure, compactness, and stability. The double mutant, with properties of a fully ordered domain, exhibits weak cooperativity with a complex and rugged conformational landscape. The mutant, however, binds cognate DNA with an affinity only marginally higher than that of the wild type, though nontrivial differences are observed in the binding to noncognate DNA. Our work provides direct experimental evidence of the dominant role of non-additive hydrophobic effects in shaping the molecular evolution of order in disordered proteins and vice versa, which could be generalized to even folded proteins with implications for protein design and functional manipulation
Fast Adaptive Bilateral Filtering
No full textIn the classical bilateral filter, a fixed Gaussian range kernel is used along with a spatial kernel for edge-preserving smoothing. We consider a generalization of this filter, the so-called adaptive bilateral filter, where the center and width of the Gaussian range kernel are allowed to change from pixel to pixel. Though this variant was originally proposed for sharpening and noise removal, it can also be used for other applications, such as artifact removal and texture filtering. Similar to the bilateral filter, the brute-force implementation of its adaptive counterpart requires intense computations. While several fast algorithms have been proposed in the literature for bilateral filtering, most of them work only with a fixed range kernel. In this paper, we propose a fast algorithm for adaptive bilateral filtering, whose complexity does not scale with the spatial filter width. This is based on the observation that the concerned filtering can be performed purely in range space using an appropriately defined local histogram. We show that by replacing the histogram with a polynomial and the finite range-space sum with an integral, we can approximate the filter using analytic functions. In particular, an efficient algorithm is derived using the following innovations: the polynomial is fitted by matching its moments to those of the target histogram (this is done using fast convolutions), and the analytic functions are recursively computed using integration-by-parts. Our algorithm can accelerate the brute-force implementation by at least 20x, without perceptible distortions in the visual quality. We demonstrate the effectiveness of our algorithm for sharpening, JPEG deblocking, and texture filtering
Interpretation of surface degradation on polymeric insulators
No full textSilicone rubber based polymeric insulators are being used widely used as outdoor insulation for high voltage applications. However, their long-term service life performance is highly dependent on local environmental conditions that cause deterioration of material properties of the insulators. In the present work, tracking and erosion studies are conducted on silicone rubber samples using. Inclined Plane Tracking (IPT) and Erosion method based on IEC 60587. The contaminants used to simulate different environmental conditions are as per standard and in addition acidic rain composition is used. Leakage current flowing through samples was continuously monitored and recorded over the experimental duration. The consequence of leakage current variation is analyzed using. Recurrent Plot (RP) Analysis and this resulted in variation of quantitative parameters Recurrence Rate (RR), Determinism (DET), Entropy (ENT) and Length (L) these are used to interpret the tracking and erosion performance of silicone rubber samples. Further, physico-chemical analysis is conducted using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX) and Fourier Transform Infra-Red (FTIR) spectroscopy to observe surface morphology and chemical changes happened in the samples. Thermo-Gravimetric Analysis (TGA) is performed to observe thermal stability and presence of Aluminum Tri-hydrate (ATH) fillers before and after experiments. The investigations show RP method as a potential tool for detection and diagnostic of polymeric insulators
Globularization using heat treatment in additively manufactured Ti-6Al-4V for high strength and toughness
No full textA bimodal globularized microstructure in contrast to martensitic laths is known to impart high strength and toughness in Ti-6Al-4V. Heat treatment for the phase transformation of the laths to the globularized microstructure must be preceded by plastic deformation. This work reports an innovative strategy to obtain the bimodal microstructure consisting of globular alpha in additively manufactured Ti-6Al-4V alloy by heat treatment alone. The heat treatment schedule involves repeated thermal cycling close to but below the beta transus temperature to form globular alpha eliminating the need for plastic deformation prior to heat treatment. A new mechanism of globularization other than known in literature is proposed to explain the formation of globular alpha. The inherent dislocation sub-structure of the martensitic laths initiates globularization by thermal grooving and boundary splitting but is unable to completely globularize the microstructure. Mechanisms such as cylinderization and edge spheroidization also do not lead to globularization. The purposefully designed thermal cycling causes oscillations in the volume fractions of alpha and beta phases that in synergism with the slow cooling segments of the cycle globularize the a phase by epitaxial growth. The bimodal microstructure thus produced led to a significant improvement in the ductility by 80% and the toughness by 66%, which are desirable for structural applications. Furthermore, beneficial compressive stresses were generated in the alloy because of cyclic heat treatment. It is envisaged that the exceptional combination of mechanical properties observed here will lead to the fabrication of SLM printed Ti-6Al-4V parts that could leverage the advantages of additive manufacturing with material properties that are comparable to those obtained by conventional fabrication routes. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Effects of termite foraging activity on topsoil physical properties and water infiltration in Vertisol
No full textIn the tropics, termites are key litter decomposers and soil bioturbators. Termite foraging activity involves the production of sheetings and galleries that influence the physical, chemical and hydraulic properties of soils. The functional impacts of these biogenic structures and biopores have been acknowledged for a long time in soils dominated by 1:1 minerals. Less is known, however, on their functional impacts in soils dominated by 2:1 minerals, such as vertisol which represent 22% of the land surface in India. Therefore, an experiment was carried out in a vertisol in southern India where elephant (Elephas maximus) dung pats (ED) and Lantana camara twigs (LT) were applied on the ground and protected (+) or not (-) from termite activity. Termite activity was only measured below ED-, showing a clear preference for organic matter derived from elephant dung. Soil sheetings had similar properties to the surrounding topsoil, with the exception of their C content that was reduced. This result raised the question of the origin of the soil used by termites for covering ED. ED - was also associated with the presence of effective macropores up to 5 cm depth and a significant increase in water hydraulic conductivity (12-fold). However, the utilization of the coefficient of linear extensibility showed that these galleries were unstable and most likely short-lived. In conclusion, this study confirmed that the structure of soils dominated by 2:1 minerals is mainly controlled by physical processes (i.e., the shrinking and swelling of soils). This study also stresses the need to better understand the dynamic of termite galleries in soil and to quantify the origin and fate of organic matter in soil sheetings
A faster scheme to generate multimodal dispersion plots for Rayleigh wave propagation
No full textA faster computational scheme is proposed to determine multimodal dispersion plots using the stiffness matrix method (SMM) for Rayleigh wave propagation in horizontally layered ground media. The scheme decomposes the governing stiffness matrix (K) into a product of unit lower triangular matrix (L) and the upper triangular matrix (U). Accordingly, the determinant of K, which is needed for obtaining the required solution, becomes the product of all the diagonal terms in U. An algorithm is introduced to write all the diagonal terms in U. By considering the special structure of the stiffness matrix, the determinant of K is evaluated directly in a single step avoiding all the computationally expensive loops. The solution is then obtained by using the root search method (RSM). No approximation is involved in this scheme which involves hyperbolic and transcendental functions, and there is no need to discretize different strata further into a number of thin layers. The efficacy of the proposed scheme is demonstrated by using different examples both for regular and irregular dispersive layered media. The proposed computational scheme is found to be highly time efficient in obtaining multimodal dispersion plots
DNA methylation regulates Microtubule-associated tumor suppressor 1 in human non-small cell lung carcinoma
No full textMicrotubule associated tumor suppressor 1 (MTUS1) has been recognized as a tumor suppressor gene in multiple cancers. However, the molecular mechanisms underlying the regulation of MTUS1 are yet to be investigated. This study aimed to clarify the significance of DNA methylation in silencing MTUS1 expression. We report that MTUS1 acts as tumor suppressor in non-small cell lung carcinoma (NSCLC). Analysis of in silica database and subsequent knockdown of DNMT1 suggested an inverse correlation between DNMT1 and mars]. function. Interestingly, increased methylation at MTUS1 promoter is associated with low expression of MTUS1. Treatment with DNA methyltransferases (DNMTs) inhibitor, 5-aza-2'-deoxycytidine (AZA) leads to both reduced promoter methylation accompanied with enrichment of H3K9Ac and enhanced MTUS1 expression. Remarkably, knockdown of MTUS1 showed increased proliferation and migration of NSCLC cells in contrast to diminished proliferation and migration, upon treatment with AZA. We concluded that low expression of MTUS1 correlates to DNA methylation and histone deacetylation in human NSCLC
