288 research outputs found
Complementary Speckle Patterns : deterministic interchange of intrinsic vortices and maxima through Scattering Media
Intensity minima and maxima of speckle patterns obtained behind a diffuser
are experimentally interchanged by applying a spiral phase delay of charge to the impinging coherent beam. This transform arises from the intuitive
expectation that a tightly focused beam is so-changed into a vortex beam and
vice-versa. The statistics of extrema locations and the intensity distribution
of the so-generated "complementary" patterns are characterized by numerical
simulations. It is demonstrated experimentally that the incoherent
superposition of the three "complementary speckle patterns" yield a synthetic
speckle grain size enlarged by a factor . A cyclic permutation of
optical vortices and maxima is unexpectedly observed and discussed.Comment: 9 pages, 9 figure
Topological transformations of speckles
Deterministic control of coherent random light is highly important for
information transmission through complex media. However, only a few simple
speckle transformations can be achieved through diffusers without prior
characterization. As recently shown, spiral wavefront modulation of the
impinging beam allows permuting intensity maxima and intrinsic -charged
optical vortices. Here, we study this cyclic-group algebra when combining
spiral phase transforms of charge , with - and -point-group
symmetry star-like amplitude modulations. This combination allows statistical
strengthening of permutations and controlling the period to be 3 and 4,
respectively. Phase saddle-points are shown to complete the cycle. These
results offer new tools to manipulate critical points in speckles.Comment: 14 pages, 10 figures, 4 table
Reference-less complex wavefields characterization with a high-resolution wavefront sensor
Wavefront sensing is a widely-used non-interferometric, single-shot, and
quantitative technique providing the spatial-phase of a beam. The phase is
obtained by integrating the measured wavefront gradient. Complex and random
wavefields intrinsically contain a high density of singular phase structures
(optical vortices) associated with non-conservative gradients making this
integration step especially delicate. Here, using a high-resolution wavefront
sensor, we demonstrate experimentally a systematic approach for achieving the
complete and quantitative reconstruction of complex wavefronts. Based on the
Stokes' theorem, we propose an image segmentation algorithm to provide an
accurate determination of the charge and location of optical vortices. This
technique is expected to benefit to several fields requiring complex media
characterization.Comment: 7 page
Understanding and Integrating Resolution, Accuracy and Sampling Rates of Temperature Data Loggers Used in Biological and Ecological Studies
International audienceDuring the 5 th Workshop about Temperature-Dependent Sex Determination held in the 38 th International Sea Turtles Symposium (16-22 February 2018) in Kobe, Japan, we discussed the uncertainty of temperatures recorded by data logger and their calibration. We report here an extension of this discussion. First, we propose a way to estimate the uncertainty of the average temperature recorded using data loggers considering the accuracy of the data logger (repeatability of measurements), resolution of the data logger (resolution of its indicating device) and period of sampling temperature. Second, a general procedure of calibration is described. Functions to perform the estimates are provided in R package embryo growth freely available
Analyzing the evolution of deterioration patterns: A first step of an image-based approach for comparing multitemporal data sets
International audienceWhen documenting and analyzing cultural heritage, the monument states can be described by multitemporal data sets, which however present a complication for the elaboration and examination process. This difficulty leads to the necessity to improve the analyze process in order to expand the documentation process and help experts to enrich and share information about the historical buildings. Therefore an approach of change measurement, which supports the chronical comprehension of a building by visualizing and quantifying the dimensional temporal effects was elaborated, where the analyze process of a multitemporal data set was based on the interpretation of depth map images. These maps were obtained by generating ortho images of an object that was created on purpose by setting up an experimentation to acquire a multitemporal data set. This approach is the first step of a wider ongoing research about change detection processes on multitemporal data sets. Index Terms-Change measurements, multitemporal data set, depth map, ortho image, evolution of deterioration patterns
MatiĂšre altĂ©rĂ©e, couleurs modifiĂ©es : apports des techniques analytiques et dâimagerie pour la comprĂ©hension des dĂ©cors originaux sur les plafonds peints mĂ©diĂ©vaux, lâexemple de la maison du viguier Ă Puisserguier
Le plafond Ă la française de lâancienne maison du viguier Ă Puisserguier (HĂ©rault) montre dâintĂ©ressants restes de polychromies datant du tout dĂ©but du XVIe siĂšcle. LâĂ©tat de dĂ©gradation avancĂ© de la matiĂšre picturale est cependant Ă lâorigine de certaines modifications chromatiques qui ont pu ĂȘtre mises en Ă©vidence par le biais dâanalyses physico-chimiques et de lâimagerie scientifique. Nous verrons comment ces outils technologiques ont permis la comprĂ©hension des processus dâaltĂ©ration de la matiĂšre mais aussi comment ils ont jouĂ© un rĂŽle fondamental dans la connaissance du dĂ©cor original et des modifications quâil a subi depuis sa crĂ©ation jusquâĂ nos jours.The French-style ceiling of the former house of the medieval judge in Puisserguier (HĂ©rault) has interesting remains of paintings from the early 16th century. However, advanced ageing of the pictorials is causing chromatic changes which were highlighted by means of physicochemical analysis and technical imaging. We will see how these techniques have constituted a very useful tool for the understanding of material degradation processes and helped to figure out how the original decoration was without the climate modifications it has been subjected to since its creation
Dispersion en milieux poreux insaturés (modélisations et mesures RMN de distributions de vitesse)
La dispersion dans des milieux poreux homogĂšnes (empilements de grains) a Ă©tĂ© Ă©tudiĂ©e par des mesures par rĂ©sonance magnĂ©tique nuclĂ©aire (RMN) et des simulations de marches alĂ©atoires dans un rĂ©seau de pores. La RMN permet de mesurer l ensemble des dĂ©placements des molĂ©cules d eau durant un temps t , et d obtenir propagateurs et moments caractĂ©ristiques. L Ă©volution temporelle du second moment ( 2 ta ) permet de caractĂ©riser de maniĂšre prĂ©cise le rĂ©gime de dispersion des molĂ©cules (Gaussien ou anormal). Des mesures pour des Ă©coulements de 15 < Pe < 45 dans un empilement de grains de 30 m ont permis d observer une dispersion anormale faiblement super-dispersive (a = 1.17) en Ă©coulement saturĂ© et une augmentation progressive du caractĂšre super-dispersif avec la diminution de la saturation en eau (jusqu Ă a = 1.5 pour 42 %)lors d une co-injection stationnaire eau-huile. En Ă©coulement saturĂ©, les propagateurs et courbes de percĂ©e sont quasi-gaussiennes, tandis qu en Ă©coulement insaturĂ©, les propagateurs sont asymĂ©triques et les courbes de percĂ©e prĂ©sentent des trainĂ©es aux grands temps. Dans ces conditions, on montre que la dispersion anormale observĂ©e est mieux dĂ©crite par des lois stables de LĂ©vy que par des lois gaussiennes. Des simulations de marche alĂ©atoire ont Ă©tĂ© rĂ©alisĂ©es dans un rĂ©seau de pores extrait d un milieu poreux rĂ©el par imagerie microscanner.Elles permettent d obtenir les mĂȘmes informations que la RMN, les marcheurs se dĂ©plaçant par advection et diffusion. Ces simulations montrent l existence d une stagnation non observĂ©e dans les expĂ©riences, montrant que la simplification du rĂ©seau poreux est trop importante et empĂȘche de reproduire certains aspects du champ de vitesses dĂ©tectĂ© par la RMN. Toutefois, l Ă©volution temporelle du second moment a Ă©galement un caractĂšre super-dispersif Ă temps long Ă 100 % de saturationWe investigated dispersion in homogeneous porous media (grain packs) by nuclear magnetic resonance (NMR) measurements and random walk simulations in pore networks. We measured water molecules displacements during a time interval t by NMR measurements, which allows us to obtain propagators and charateristic cumulants of displacements such as the mean square displacement . The evolution of the cumulant as a function of time t ( 2 ta ) is a very sensitive test of Gaussian behaviour compared to the analysis of the shape of propagators. In a homogeneous 30 m grain pack and low Peclet numbers (15 < Pe < 45), we observed weak super dispersion in saturated conditions (a = 1.17) and gradually stronger super-dispersionas the water saturation decreases (up to a = 1.5 for 42 %) during steady-state oil-water two phase flow. Insaturated conditions, propagators and breakthrough curves are Gaussian or nearly Gaussian, whereas in two phase conditions, propagators are non symmetric and breakthrough curves show thick tails at long time. Weshow that the anomalous dispersion observed is better explained by LĂ©vy stable laws (asymetric for longitudina ldispersion, and symetric for transverse dispersion) than by Gaussian laws. Random walk simulations were performed in a pore network constructed using high resolution images of the grain pack. They allow us to obtain the same informations than the NMR, with walkers submitted to diffusive and advective effects. The simulations show the existence of an anomalous stagnation not observed in experiments, highlighting the oversimplification of the pore network that prevent reproducing some aspects of the velocity field detected by NMR. However, the simulations indicate similarly a super-dispersion at long time in saturated conditionsAVIGNON-Bib. numĂ©rique (840079901) / SudocSudocFranceF
Imagerie numĂ©rique et conservation-restauration : Ă©tat de lâart et perspectives
Lâimagerie scientifique est un outil incontournable des sciences de la conservation-restauration. La modification du support de la photographie, devenu numĂ©rique, le dĂ©veloppement du rendu tridimensionnel qualitatif et quantitatif de lâimage ont transformĂ© la photographie technique en un outil dâinvestigation non destructif Ă part entiĂšre, indispensable et complĂ©mentaire des approches physiques et physico-chimiques classiques et en un outil-support de documentation. Lâensemble des dĂ©veloppements et travaux menĂ©s en imagerie scientifique et sur lâintĂ©gration dans des plateformes collaboratives dâannotation sĂ©mantique 3D permet, outre une production plus facile de documents, de mettre en synergie les rĂ©sultats provenant de diffĂ©rentes techniques dâanalyse. Elle va modifier, dans un futur proche, lâapproche sur le terrain des acteurs de la conservation et conduire Ă une meilleure synergie interprofessionnelle. Ils auront ainsi la possibilitĂ© de mieux mettre en cohĂ©rence leurs observations, leurs conclusions quant aux analyses faites Ă diffĂ©rentes Ă©chelles, dans une dynamique temporelle qui intĂšgre les donnĂ©es de la restauration, de son histoire passĂ©e. Ă terme, et par lâintĂ©gration des donnĂ©es environnementales, ces plateformes seront un outil de suivi de lâĂ©volution de lâĂ©tat matĂ©riel du bien culturel et aussi de transmission des connaissances vers un public large.Technical imaging has always been an essential tool in conservation science. Thanks to todayâs digital photography and its quantitative and qualitative tridimensional aspects, this imaging has become an autonomous and vital nondestructive instrument that complements classic physical and chemical analyses. It is also an essential tool for documentation purposes. Results coming from different techniques of analysis can now be synthesized by means of new developments in technical imaging and their insertion into collaborative 3D semantic annotation platforms. Technical imaging can modify the infield approach of conservation professionals and will help lead to better interprofessional dialogue in the future. Conservation professionals will have the assurance of better consistency in their observations, which can cover different time frames for restoration projects and historical data and conclusions drawn from analyses made at different scales. In the long term and after integration of environmental data, these platforms will become monitoring tools dedicated to following the state of conservation of cultural heritage objects and a tool for transmitting knowledge about these objects to a wider audience
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