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Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements

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Research in Astronomy and Astrophysics 2013年第11期13卷 1363-1380页

作者： Tapas Baug Thyagarajan chandrasekhar Physical Research Laboratory

A lunar occultation （LO） technique in the near-infrared （NIR） provides angular resolution down to milliarcseconds for an occulted source, even with ground- based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio （S/N ~40） for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant imorovement in S/N.

关键词： methods: analytical -- techniques: high angular resolution -- methods:lunar occultation -- infrared: stars -- stars: late type

Multi-objective simultaneous optimal planning of electric vehiclefast charging stations and DGs in distribution system

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Journal of Modern Power Systems and Clean Energy 2019年第4期7卷 923-934页

作者： Gurappa BATTAPOTHULA chandrasekhar YAMMANI Sydulu MAHESWARAPU National Institute of Technology WarangalIndia

The large-scale construction of fast charging stations(FCSs)for electric vehicles(EVs)is helpful inpromoting the *** creates a significant challenge for the distribution system operator to determine the optimal planning,especially the siting and sizing of FCSs in the electrical distribution *** planning of fast EV charging stations(EVCSs)cause a negative impact on the distribution *** paper presented a multiobjective optimization problem to obtain the simultaneous placement and sizing of FCSs and distributed generations(DGs)with the constraints such as the number of EVs in all zones and possible number of FCSs based on the road and electrical network in the proposed *** problem is formulated as a mixed integer non-linear problem(MINLP)to optimize the loss of EV user,network power loss(NPL),FCS development cost and improve the voltage profile of the electrical distribution ***-dominated sorting genetic algorithmⅡ(NSGA-Ⅱ)is used for solving the *** performance of the proposed technique is evaluated by the 118-bus electrical distribution system.

关键词： Electric vehicles(EVs) Fast charging stations(FCSs) Non-dominated sorting genetic algorithmⅡ(NSGA-Ⅱ) Renewable energy sources

Evaluation of unconstrained and constrained mathematical functions to model girth growth of rubber trees (Hevea brasiliensis) using young agemeasurements

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Journal of Forestry Research 2012年第3期23卷 365-375页

作者： T.R.chandrasekhar Rubber Research Institute of India Hevea Breeding Sub StationKadaba-574221DK DistrictKarnatakaIndia

No attempt has been made to date to model growth in girth of rubber tree （Hevea brasiliansis）. We evaluated the few widely used growth functions to identify the most parsimonious and biologically reasonable model for describing the girth growth of young rubber trees based on an incomplete set of young age measurements. Monthly data for girth of immature trees （age 2 to 12 yearsi from two locations were sub- jected to modelling. Re-parameterized, unconstrained and constrained growth functions,of Richards （RM）, Gompertz （GM） and the monomo- lecular ＇model ^（MM） were fitted to data. Duration of growth was the firsf constraint introduced. In the stagel We attempted a population aver- age （PA） model to capture the trend in growth. The best PA model was fitted as a subject specific （SS） model. We used appropriate error vari- ance-covariance structure to account for correlation due to repeated measurements over time. Unconstrainecl functions underestimated the asymptotic maximum that did not reflective carrying capacity of the locations. Underestimafions were attributed to the partial set＇ of meas- urements made during the early growth phase of the trees. MM proved superior to RM and GM. In the randomcoefficient models, both Gf and Go appeared to be influenced by tree level effects. Inclusion of diagonal definite positive matrix removed the correlation between random effects. The results were similar at both locations. In the overall assessment MM appeared as the candidate model for studying the girth-age relationships in Hevea trees. Based on the fitted model we conclude that, in Hevea trees, growth rate is maintained at maximum value at to, then decreases until the final state at dG/dt 〉 0, resulting in yield curve with no period of accelerating growth. One physiological explanation is that photosynthetic activity in Hevea trees decreases as girth increases and constructive metabolism is larger than destructive metabolism.

关键词： natural rubber Hevea Brasiliensis growth modelling un-constrained functions constrained functions mixed model

Parameter identification through mode isolation for reaction-diffusion systems on arbitrary geometries

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International Journal of Biomathematics 2018年第4期11卷 149-178页

作者： Laura Murphy chandrasekhar Venkataraman Anotida Madzvamuse School of Mathematical and Physical SciencesUniversity of Sussex Department of Mathematics Brighton BNI 9QH UK School of Mathematics and StatisticsUniversity of St Andrews St Andrews UK School of Mathematical and Physical SciencesUniversity of Sussex Department of Mathematics Brighton BN1 9QH UK

We present a computational framework for isolating spatial patterns arising in the steady states of reaction-diffusion systems. Such systems have been used to model many nat- ural phenomena in areas such as developmental and cancer biology, cell motility and material science. In many of these applications, often one is interested in identifying parameters which will lead to a particular pattern for a given reaction-diffusion model. To attempt to answer this, we compute eigenpairs of the Laplacian on a variety of domains and use linear stability analysis to determine parameter values for the system that will lead to spatially inhomogeneous steady states whose patterns correspond to particular eigenfunctions. This method has previously been used on domains and surfaces where the eigenvalues and eigenfunctions are found analytically in closed form. Our contribution to this methodology is that we numerically compute eigenpairs on arbitrary domains and surfaces. Here we present examples and demonstrate that mode isolation is straightforward especially for low eigenvalues. Additionally, we show that in some cases the inhomogeneous steady state can be a linear combination of eigenfunctions. Finally,we show an example suggesting that pattern formation is robust on similar surfaces in cases that the surface either has or does not have a boundary.

关键词： Reaction diffusion systems finite elements parameter identification eigen-value problem.

On the Urbach's formula for evaluation of electron trapping parameter:The case of persistent luminescent materials

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Journal of Rare Earths 2017年第8期35卷 733-738页

作者： Ngangbam chandrasekhar K.Bishal Singh R.K.Gartia Department of Physics Manipur University Imphal-795003 Manipur India

Urbach’s formula for evaluation of electron trapping parameter that happens to be the earliest has emerged as a popular method amongst researchers of persistent luminescence. In this study, we analysed the thermoluminescence curves of glow-in-the-dark phosphors. Those included some curves recorded by us and others that solely used the Urbach’s formula. Using the parameter obtained by rigorous analysis by fitting the whole TL curves, we presented a comprehensive picture of the potentialities and limitations of the simple Urbach’s relation E=T_m/500, where E is the trap-depth and T_m the peak temperature in absolute scale, first proposed by Urbach in 1930. Some simple thumb rules on the use of the formula were presented for beginners as well as non-specialists so that entry of physically unrealistic data into the literature was prevented.

关键词： Urbach’s formula electron-trapping parameter glow-in-the-dark phosphor afterglow rare earths

Experimental repetitive mild traumatic brain injury induces deficits in trabecular bone microarchitecture and strength in mice

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Bone Research 2017年第4期5卷 357-366页

作者： chandrasekhar Kesavan Nikita M Bajwa Heather Watt Subburaman Mohan Musculoskeletal Disease Center VA Loma Linda Healthcare SystemLama LindaCAUSA Department of Medicine Loma DndaCAUSA Department of Orthopedic Surgery Loma Linda UniversityLoma LindaCAUSA

To evaluate the long-term consequence of repetitive mild traumatic brain injury （mTBI） on bone, mTBI was induced in 10-week-old female C57BL/6J mice using a weight drop model, once per day for 4 consecutive days at different drop heights （0.5, 1 and 1.5 m） and the skeletal phenotype was evaluated at different time points after the impact. In vivo micro-CT （μ-CT） analysis of the tibial metaphysis at 2, 8 and 12 weeks after the impact revealed a 5%-32% reduction in trabecular bone mass. Histomorphometric analyses showed a reduced bone formation rate in the secondary spongiosa ofl.5 m impacted mice at 12 weeks post impact. Apparent modulus （bone strength）, was reduced by 30% （P 〈 0.05） at the proximal tibial metaphysis in the 1.5 m drop height group at 2 and 8 weeks post impact. Ex vivo μ-CT analysis of the fifth lumbar vertebra revealed a significant reduction in trabecular bone mass at 12 weeks of age in all three drop height groups. Serum levels of osteocalcin were decreased by 22%, 15%, and 19% in the 0.5, 1.0 and 1.5 m drop height groups, respectively, at 2 weeks post impact. Serum IGF-I levels were reduced by 18%-32% in mTBI mice compared to control mice at 2 weeks post impact. Serum osteocalcin and IGF-I levels correlated with trabecular BV/TV （r2 = 0.14 and 0.16, P 〈 0.05）. In conclusion, repetitive mTBI exerts significant negative effects on the trabecular bone microarchitecture and bone mechanical properties by influencing osteoblast function via reduced endocrine IGF-I actions.

关键词： IGF TBI Experimental repetitive mild traumatic brain injury induces deficits in trabecular bone microarchitecture and strength in mice

Hybrid IWD-DE:A Novel Approach to Model Cooperative Navigation Planning for Multi-robot in Unknown Dynamic Environment

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Journal of Bionic Engineering 2019年第2期16卷 235-252页

作者： Degal chandrasekhar Rao Manas Ranjan Kabat Pradipta Kumar Das Prabir Kumar Jena Department of Information Technology VSSUTBurlaOdisha 768018India Department of Computer Science&Engineerings VSSUT、Burla Odisha 76801&India Department of Mechanical Engineering VSSUTBurlaOdisha 76801&India

The current study emphasizes inadequacies of earlier research findings on multi-robot navigation and offers a robust approach to guide the robots in an unknown dynamic *** attain the objective,the Intelligent Water Drop(IWD)algorithm is combined with Differential Evolution(DE)in a new conceptual fashion to optimize the navigation path of multiple mobile *** hybrid IWD-DE,basic IWD and DE algorithms are then explored for multi-robot navigation in a dynamic workspace through *** simulation outcomes demonstrate the competency of the proposed method to guide the robot in predicting the nature of the obstacle and to generate an optimal and safe trajectory in a dynamic *** potency of the proposed algorithm is further validated through experimentation with fire bird robot in a real *** outcomes of the simulation and experimentation,by employing IWD-DE algorithm are compared with those of basic IWD and DE *** error estimated for Average Navigation Path Travelled(ANPT),Aggregate Navigation Path Deviation(ANPD)and number of turns between simulation and experimental results by employing IWD-DE is 8.96,9.09,and 11.13,respectively while reaching 16.43,28.61,29.15 for IWD,and 6.66,10.20,14.28 for *** efficiency of the proposed approach is further verified with the state-of-the-art in a dynamic *** outcomes reveal the efficiency and flexibility of the proposed approach in resolving the multi-robot navigation problem as compared to the state-of-the-art in a dynamic workspace.

关键词： multi-robot dynamic environment intelligent water drop differential evolution navigation planning waypoints fire bird robot

A Robust and Efficient Adaptive Multigrid Solver for the Optimal Control of Phase Field Formulations of Geometric Evolution Laws

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Communications in Computational Physics 2017年第1期21卷 65-92页

作者： FengWei Yang chandrasekhar Venkataraman Vanessa Styles Anotida Madzvamuse Department of Mathematics University of SussexUK School of Mathematics&Statistics University of St AndrewsUK.

We propose and investigate a novel solution strategy to efficiently and accurately compute approximate solutions to semilinear optimal control problems,focusing on the optimal control of phase field formulations of geometric evolution *** optimal control of geometric evolution laws arises in a number of applications in fields including material science,image processing,tumour growth and cell *** this,many open problems remain in the analysis and approximation of such *** the current work we focus on a phase field formulation of the optimal control problem,hence exploiting the well developed mathematical theory for the optimal control of semilinear parabolic partial differential *** of the resulting optimal control problemis computationally challenging,requiring massive amounts of computational time and memory *** main focus of this work is to propose,derive,implement and test an efficient solution method for such *** solver for the discretised partial differential equations is based upon a geometric multigrid method incorporating advanced techniques to deal with the nonlinearities in the problem and utilising adaptive mesh *** in-house twogrid solution strategy for the forward and adjoint problems,that significantly reduces memory requirements and CPU time,is proposed and investigated ***,parallelisation as well as an adaptive-step gradient update for the control are employed to further improve *** with a detailed description of our proposed solution method together with its implementation we present a number of computational results that demonstrate and evaluate our algorithms with respect to accuracy and efficiency.A highlight of the present work is simulation results on the optimal control of phase field formulations of geometric evolution laws in 3-D which would be computationally infeasible without the solution strategies proposed in the present work.

关键词： Optimal control geometric evolution law phase field multigrid parallel mesh adaptivity two-grid solution strategy

Study of residual stresses and distortions from the Ti6Al4V based thinwalled geometries built using LPBF process

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Defence Technology（防务技术） 2023年第10期28卷 33-41页

作者： Jagatheeshkumar S Raguraman M Siva Prasad AVS Nagesha B K chandrasekhar U Indian Institute of Information Technology Design and Manufacturing KancheepuramChennai 600127India Gas Turbine Research Establishment DRDOBengaluru 560093India Wipro3D Bengaluru560058India

The current paper focuses on the prediction of residual stresses and distortions in the Laser Powder Bed Fusion(LPBF)built Ti6Al4V thin-walled geometries using Ansys Additive Print(AAP)software which employs a layer-by-layer accumulation of inherent strain to calculate the *** and anisotropic strain scaling factors were calibrated initially within the APP software for the Ti6Al4V based single cantilever beam ***,the numerical simulations were performed in APP software and computed the residual stresses and distortions for the varied process parameters including laser power,scan speed and hatch distance while maintaining the layer thickness constant for all the design *** numerical predictions were compared;they were found to match reasonably well with the XRD measurements within the calibrated regime.

关键词： Ti6Al4V Thin-walled geometry Residual stress Inherent strain XRD Ansys additive print