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Modeling and Measuring Friction of the Leighton 10m Telescope

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Research in Astronomy and Astrophysics 2022年第12期22卷 311-321页

作者： Yongwei Guo David Woody nicolas Matinez Chinese Academy of Sciences South America Center for Astronomy Camino El Observatorio 1515Las CondesSantiagoChile national Astronomical Observatories Chinese Academy of SciencesBeijing 100101China California Institute of Technology Owens Valley Radio ObservatoryBig PineCA 93513USA Universidad de Concepcion Facultad de Ciencias Físicas y MatematicasConcepcion403000Chile

Estimating and identifying friction are important aspects of simulating a mechanical drive system. Accurate friction modeling helps to improve a telescope's performance. However, the friction conditions inside are complex and hard to measure. We did simulations with mathematical transfer functions for the Leighton 10 m Telescope and employed a polyline model to identify sources of friction. We made a two-stage model for the Leighton 10 m Telescope. Based on measurements of the motor's currents and speeds, we constructed a curve containing the friction information of the transmission elements. We simulated the system using a step function input under many combinations of friction parameters. By comparing simulation results with the measured ones, we determined the various friction components. This model accurately reproduced the telescope performance including the nonlinearities.

关键词： astronomical instrumentation methods and techniques telescopes methods:analytical

A practical path guiding method for participating media

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Computational Visual Media 2020年第1期6卷 37-51页

作者： Hong Deng Beibei Wang Rui Wang nicolas Holzschuch nanjing University of Science and Technology Nanjing 210094China State Key Lab of CAD&CG Zhejiang UniversityHangzhou 310058China Univ.grenoble-Alpes InriaCNRSGrenoble INPLJK38000 GrenobleFrance

Rendering translucent materials is costly:light transport algorithms need to simulate a large number of scattering events inside the material before reaching *** cost is especially high for materials with a large albedo or a small mean-freepath,where higher-order scattering effects *** simple terms,the paths get lost in the *** guiding has been proposed for surface rendering to make convergence faster by guiding the sampling *** this paper,we introduce a path guiding solution for translucent *** learn an adaptive approximate representation of the radiance distribution in the volume and use it to sample the scattering direction,combining it with phase function sampling by resampled importance *** proposed method significantly improves the performance of light transport simulation in participating media,especially for small lights and media with refractive *** method can handle any homogeneous participating medium,with high or low scattering,with high or low absorption,and from isotropic to highly anisotropic.

关键词： Monte Carlo ray tracing path guiding volume light transport participating media rendering

Tribological behaviour of Ti_(3)C_(2)T_(x) nano-sheets: Substrate-dependent tribo-chemical reactions

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Friction 2023年第8期11卷 1522-1533页

作者： Alberto ROTA nicolas BELLInA Bo WAnG Andreas ROSEnKRAnZ Dipartimento di Scienze Fisiche Informatiche e MatematicheUniversitàdi Modena e Reggio EmiliaModena 41125Italy CnR-Istituto di nanoscienze Centro S3Modena 41125Italy Centro Interdipartimentale per la Ricerca Applicata e i Servizi nel settore della Meccanica Avanzata e della Motoristica Universitàdi Modena e Reggio EmiliaModena 41125Italy Key Laboratory of Marine new Materials and Related Technology Zhejiang Key Laboratory of Marine Materials and Protection TechnologyNingbo Institute of Material Technology&EngineeringChinese Academy of SciencesNingbo 315201China Department of Chemical Engineering Biotechnology and MaterialsUniversity of ChileSantiago 8370456Chile

MXenes,a newly emerging class of layered two dimensional(2D)materials,are promising solid lubricants due to their 2D structure consisting of weakly-bonded layers with a low shear strength and ability to form beneficial *** work aims at evaluating for the first time MXenes lubrication performance and tribofilm formation ability on different metallic substrates(mirror-lapped Fe and Cu discs).After depositing MXenes via ethanol(1 wt%)on the substrates,pronounced differences in the resulting substrate-dependent frictional evolution are *** MXenes are capable to reduce friction for both substrates after the full evaporation of ethanol,MXenes lubricating effect on Cu is long-lasting,with a 35-fold increased lifetime compared to *** spectra acquired in the wear-tracks of the substrates and counter-bodies reveal notable differences in the friction-induced chemical changes depending on the substrate *** case of Fe,the progressive failure of MXenes lubrication generates different Fe oxides on both the substrate and the ball,resulting in continuously increasing friction and a poor lubrication *** Cu,sliding induces the formation of a Ti_(3)C_(2)-based tribofilm on both rubbing surfaces,enabling a long-lasting lubricating *** work boosts further experimental and theoretical work on MXenes involved tribo-chemical processes.

关键词： Mxenes Ti_(3)C_(2)T_(x) nano-sheets coefficient of friction Raman spectroscopy tribochemistry

A detail preserving neural network model for Monte Carlo denoising

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Computational Visual Media 2020年第2期6卷 157-168页

作者： Weiheng Lin Beibei Wang Lu Wang nicolas Holzschuch School of Computer Science and Engineering Nanjing University of Science and TechnologyNanjing210094China School of Computer Science and Technology Shandong UniversityJinan250100China Univ.grenoble-Alpes InriaCNRSGrenoble INPLJK38000GrenobleFrance

Monte Carlo based methods such as path tracing are widely used in movie production. To achieve low noise, they require many samples per pixel,resulting in long rendering time. To reduce the cost,one solution is Monte Carlo denoising, which renders the image with fewer samples per pixel(as little as128) and then denoises the resulting image. Many Monte Carlo denoising methods rely on deep learning:they use convolutional neural networks to learn the relationship between noisy images and reference images,using auxiliary features such as position and normal together with image color as inputs. The network predicts kernels which are then applied to the noisy input. These methods show powerful denoising ability,but tend to lose geometric or lighting details and to blur sharp features during *** this paper, we solve this issue by proposing a novel network structure, a new input feature—light transport covariance from path space—and an improved loss function. Our network separates feature buffers from the color buffer to enhance detail effects. The features are extracted separately and then integrated into a shallow kernel predictor. Our loss function considers perceptual loss, which also improves detail *** addition, we use a light transport covariance feature in path space as one of the features, which helps to preserve illumination details. Our method denoises Monte Carlo path traced images while preserving details much better than previous methods.

关键词： deep learning light transport covariance perceptual loss Monte Carlo denoising

A Charge Preserving Scheme for the numerical Resolution of the Vlasov-Ampere Equations

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Communications in Computational Physics 2011年第9期10卷 1001-1026页

作者： nicolas Crouseilles Thomas Respaud InRIA-nancy-Grand Est CALVI ProjectStrasbourgFrance IRMA Universite de Strasbourg and INRIA-Nancy-Grand EstCALVI ProjectStrasbourgFrance

In this report,a charge preserving numerical resolution of the 1D VlasovAmp`ere equation is achieved,with a forward Semi-Lagrangian method introduced in[10].The Vlasov equation belongs to the kinetic way of simulating plasmas evolution,and is coupled with the Poisson’s equation,or equivalently under charge conservation,the Amp`ere’s one,which self-consistently rules the electric field *** order to ensure having proper physical solutions,it is necessary that the scheme preserves charge numerically.B-spline deposition will be used for the interpolation *** solving of the characteristics will be made with a Runge-Kutta 2 method and with a Cauchy-Kovalevsky procedure.

关键词： Semi-Lagrangian method charge conservation Runge-Kutta Cauchy-Kovalevsky B-spline deposition

On the estimation of ship’s fuel consumption and speed curve:A statistical approach

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Journal of Ocean Engineering and Science 2016年第2期1卷 157-166页

作者： nicolas Bialystocki Dimitris Konovessis Technical Department Antares Shipping Ltd.Israel School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore

When fuel efficiency is at stake,along with the reduction of the environmental foot print of air pollution,a need is presented to estimate a ship’s fuel consumption for a forthcoming voyage,and means for decision making and for cost *** paper suggests an operational approach for obtaining an accurate fuel consumption and speed curve,on the basis of major factors affecting it,namely,ship’s draft and displacement,weather force and direction,hull and propeller roughness.A statistical analysis on 418 noon reports of a Pure Car and Truck Carrier case ship is carried out and the influence of the above factors is *** expected,stronger wind and head weather increases the fuel consumption,and the difference between several weather conditions could be quantified.A simple and accurate algorithm is proposed in order for ship owners,managers and operators to be in a position to apply the suggested method on their ***,applications of the structured algorithm are introduced with examples,in estimating the fuel consumption of the case ship for a future voyage,and also the same for a sister ***,voyage planning in several scenarios is proposed in order to assist the stakeholders with decision making aimed to fuel saving and environmental friendliness of their ships.

关键词： Fuel consumption Ship’s noon report Weather Hull and propeller roughness Service performance Decision-making

Evaluation of renal function in patients with cirrhosis:Where are we now?

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World Journal of Gastroenterology 2014年第10期20卷 2533-2541页

作者： nicolas Rognant Sandrine Lemoine nephrology Department Hospices Civils de Lyon France and University Claude Bernard Lyon I F-69008 Lyon France School of Biochemistry University of BristolUniversity Walk Medical Sciences Building Bristol BS8 1TDUnited Kingdom

In the clinical context of the patients with liver cirrhosis, accurate evaluation of the renal function is potentially crucial. Indeed, it can lead to early diagnosis of both acute kidney injury and chronic kidney disease and to reliable characterization of the renal status of the patient before performing a liver transplantation. Despite some limitations, the assay of serum creatinine (SCr) is universally used to estimate glomerular filtration rate (GFR) because of its wide availability, its simplicity and because it is inexpensive. nevertheless, several reports show that the value of this assay to estimate GFR is strongly challenged in cirrhotic patients, especially in patients with liver failure and/or severely impaired renal function. This has led to seek new alternatives to estimate more reliably the GFR in these patients. Although the reference methods, based on the utilization of exogenous markers, allow measuring GFR and thereby constitute the “gold standard” to evaluate renal function, they are not feasible in routine clinical practice. Several studies have shown that a cystatin C (CysC) based formula perform better than the SCr-based estimates in cirrhotic patients and the estimation of GFR by these formulas could therefore lead to optimize the management of the patients. A new estimate based on CysC has been recently developed using a large number of patients and the first results regarding the evaluation of its performance are promising, making this new formula the best candidate for a reference estimate of the renal function in cirrhotic patients.

关键词： Cirrhosis Glomerular filtration rate Formula Estimation Agreement Plasma creatinine Cystatin C

Wright-Fisher-like models with constant population size on average

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International Journal of Biomathematics 2017年第6期10卷 51-72页

作者： nicolas Grosjean Thierry Huillet Laboratoire de Physique Theorique et Modelisation CnRS-UMR 8089 et Universite de Cergy-Pontoise 2 Avenue Adolphe Chauvin 95302 Cergy-Pontoise France

We first recall some basic facts from the theory of discrete-time Markov chains arising from two types neutral and non-neutral evolution models of population genetics with constant size. We then define and analyze a version of such models whose fluctuating total population size is conserved on average only. In our model, the population of interest is seen as being embedded in a frame process which is a critical Galton Watson process. In this context, we address problems such as extinction, fixation, size of the population at fixation and survival probability to a bottleneck effect of the environment.

关键词： Markov chain population dynamics Wright-Fisher-like models constant pop-ulation size on average critical Galton-Watson process extinction/fixation.

Slow and steady wins the race: contrasted phylogeographic signatures in two Alpine amphibians

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Integrative Zoology 2022年第1期17卷 181-190页

作者： Christophe DUFRESnES nicolas RODRIGUES Romain SAVARY LASER College of Biology and EnvironmentNanjing Forestry UniversityNanjingChina Department of Ecology&Evolution University of LausanneLausanneSwitzerland Laboratory for Biological Geochemistry School of ArchitectureCivil and Environmental EngineeringEcole Polytechnique Fédérale de Lausanne(EPFL)LausanneSwitzerland

A deeper phylogeographic structure is expected for slow-dispersing habitat specialists compared to widespread adaptable species,especially in topographically complex *** tested this classic assumption by comparing the genomic(RAD-sequencing)phylogeographies of 2 amphibians inhabiting the Swiss Alps:the mobile,cosmopolitan common frog(Rana temporaria)against the stationary,mountain endemic Alpine salamander(Salamandra atra).Our results ran opposite of predictions:the frog displayed significantly higher genetic divergences and lower within-population variation compared to the *** implies a prominent role for their distinctive glacial histories in shaping intraspecific diversity and structure:diversification and recolonization from several circum-Alpine micro-refugia for the frog versus a single refugium for the salamander,potentially combined with better population connectivity and *** striking differences emphasize the great variability of phylogeographic responses to the Quaternary glaciations,hence the complexity to predict general patterns of genetic diversity at the regional scale,and the forces that underlie them.

关键词： Alps comparative phylogeography dispersal RAD-sequencing Rana temporaria Salamandra atra