Search results for "35"

A Bayesian Multilevel Random-Effects Model for Estimating Noise in Image Sensors

2020

Sensor noise sources cause differences in the signal recorded across pixels in a single image and across multiple images. This paper presents a Bayesian approach to decomposing and characterizing the sensor noise sources involved in imaging with digital cameras. A Bayesian probabilistic model based on the (theoretical) model for noise sources in image sensing is fitted to a set of a time-series of images with different reflectance and wavelengths under controlled lighting conditions. The image sensing model is a complex model, with several interacting components dependent on reflectance and wavelength. The properties of the Bayesian approach of defining conditional dependencies among parame…

Unbiased Inference for Discretely Observed Hidden Markov Model Diffusions

2021

We develop a Bayesian inference method for diffusions observed discretely and with noise, which is free of discretisation bias. Unlike existing unbiased inference methods, our method does not rely on exact simulation techniques. Instead, our method uses standard time-discretised approximations of diffusions, such as the Euler--Maruyama scheme. Our approach is based on particle marginal Metropolis--Hastings, a particle filter, randomised multilevel Monte Carlo, and importance sampling type correction of approximate Markov chain Monte Carlo. The resulting estimator leads to inference without a bias from the time-discretisation as the number of Markov chain iterations increases. We give conver…

Fixed angle inverse scattering for sound speeds close to constant

2021

We study the fixed angle inverse scattering problem of determining a sound speed from scattering measurements corresponding to a single incident wave. The main result shows that a sound speed close to constant can be stably determined by just one measurement. Our method is based on studying the linearized problem, which turns out to be related to the acoustic problem in photoacoustic imaging. We adapt the modified time-reversal method from [P. Stefanov and G. Uhlmann, Thermoacoustic tomography with variable sound speed, Inverse Problems 25 (2009), 075011] to solve the linearized problem in a stable way, and use this to give a local uniqueness result for the nonlinear inverse problem.

Integrability and non integrability of some n body problems

2015

We prove the non integrability of the colinear $3$ and $4$ body problem, for any masses positive masses. To deal with resistant cases, we present strong integrability criterions for $3$ dimensional homogeneous potentials of degree $-1$, and prove that such cases cannot appear in the $4$ body problem. Following the same strategy, we present a simple proof of non integrability for the planar $n$ body problem. Eventually, we present some integrable cases of the $n$ body problem restricted to some invariant vector spaces.

Quantum Toda Lattice: a Challenge for Representation Theory

2021

Quantum Toda lattice may solved by means of the Representation Theory of semisimple Lie groups, or alternatively by using the technique of the Quantum Inverse Scattering Method. A comparison of the two approaches, which is the purpose of the present review article, sheds a new light on Representation Theory and leads to a number of challenging questions.

The temporal analogue of diffractive couplers

2020

International audience; Based on the space-time duality of light, we numerically demonstrate that temporal dispersion grating couplers can generate from a single pulse an array of replicas of equal amplitude. The phase-only profile of the temporal grating is optimized by a genetic algorithm that takes into account the optoelectronic bandwidth limitations of the setup.

Fluctuacions quàntiques en cavitats òptiques no lineals

2011

Aquesta tesi doctoral tracta sobre alguns aspectes de la generació de llum comprimida en cavitats no lineals tipus Kerr. La llum comprimida és un dels tipus de "llum quàntica", un tipus de llum que posseeix propietats relatives a les fluctuacions en els valors esperats dels seus observables de les què no es pot donar compte si no és mitjançant l'ús de la teoria quàntica de la radiació. L'estat buit del camp electromagnètic posseeix fluctuacions d'acord amb el principi d'incertitud d'Heisenberg. En aquest context, denominem llum comprimida a un tipus de radiació que presenta en algun dels seus observables fluctuacions menors que les corresponents a l'estat buit. Aquest tipus especial de radi…

Internationalisation level, Distribution of Decision-Making Power and Alliance Formation: Evidence from the Italian Machine Tool Industry

2011

We explore how internationalization-orientation and family business-configuration influence the propensity of Italian Machine Tool (MT) firms to sign strategic alliances. Starting from the industry sector analysis and literature review we propose a conceptual framework explaining alliance formation determinants. Our study uses the information provided by a representative sample of Italian MT firms. We argue and our data validate that the centralization of decision-making power acts as a moderator enhancing the positive effect of the internationalization on the firm inclination in signing agreements with other companies.

Farmaci dermatologici e cosmetici in gravidanza.

2009

Binder and Mixture Fatigue Performance of Plant-Produced Road Surface Course Asphalt Mixtures with High Contents of Reclaimed Asphalt

2019

The aged properties of Reclaimed Asphalt (RA) binders are one of the main factors working against their utilisation in high-RA content (&gt