The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Olivier Dulieu - One of the best experts on this subject based on the ideXlab platform.
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Electronic structure of the magnesium hydride molecular ion
Journal of Physics B: Atomic Molecular and Optical Physics, 2009Co-Authors: Mireille Aymar, Romain Guérout, Mohamed Sahlaoui, Olivier DulieuAbstract:In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, Gaussian basis sets and effective Core polarization potentials, we investigate the electronic properties of the MgH+ ion. We first determine potential energy curves for several states using different basis sets and discuss their predicted accuracy by comparing our values of the well depths and position with other available results. We then calculate permanent and transition dipole moments for several transitions. Finally, for the first time, we calculate the static dipole polarizability of MgH+ as a function of the interatomic distance. This study represents the first step towards the modelling of collisions between trapped cold Mg+ ions and H2 molecules.
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Systematic trends in electronic properties of alkali hydrides
arXiv: Atomic Physics, 2009Co-Authors: Mireille Aymar, Johannes Deiglmayr, Olivier DulieuAbstract:Obtaining ultracold samples of dipolar molecules is a current challenge, which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. Alkali hydride molecules have permanent dipole moments significantly larger than those of mixed alkali species, and, as pointed out by Taylor-Juarros et al. (Eur. Phys. J. D, 31, 213 (2004)) and by Juarros et al. (Phys. Rev. A, 73, 041403 (2006)), are thus good candidates for cold molecule forma- tion. In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, large Gaussian basis sets, and effective Core polarization potential, we systematically investigate the electronic properties of the alkali hydrides LiH to CsH, to discuss general trends of their behavior. We computed (for the first time for NaH, KH, RbH, and CsH) the variation of their static polarizability with the internuclear distance. Moreover, in addition to po- tential curves, we determine accurate values of permanent and transition dipole moments for ground and excited states de- pending on the internuclear distance. The electronic properties of all alkali hydrides are compared with one another, in the light of the numerous other data available in the literature. Finally, the influence of the quality of the Representation of the hydrogen electronic affinity in the approach on the results is discussed.
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Systematic trends in electronic properties of alkali hydridesThis article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.
Canadian Journal of Physics, 2009Co-Authors: Mireille Aymar, Johannes Deiglmayr, Olivier DulieuAbstract:Obtaining ultracold samples of dipolar molecules is a current challenge, which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. Alkali hydride molecules have permanent dipole moments significantly larger than those of mixed alkali species, and, as pointed out by Taylor-Juarros et al. (Eur. Phys. J. D, 31, 213 (2004)) and by Juarros et al. (Phys. Rev. A, 73, 041403 (2006)), are thus good candidates for cold molecule formation. In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, large Gaussian basis sets, and effective Core polarization potential, we systematically investigate the electronic properties of the alkali hydrides LiH to CsH, to discuss general trends of their behavior. We computed (for the first time for NaH, KH, RbH, and CsH) the variation of their static polarizability with the internuclear distance. Moreover, in addition to potential curves, we determine accurate values of permanent...
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Calculations of static dipole polarizabilities of alkali dimers. Prospects for alignment of ultracold molecules
The Journal of chemical physics, 2008Co-Authors: Johannes Deiglmayr, Mireille Aymar, Roland Wester, Matthias Weidemüller, Olivier DulieuAbstract:The rapid development of experimental techniques to produce ultracold alkali molecules opens the ways to manipulate them and to control their dynamics using external electric fields. A prerequisite quantity for such studies is the knowledge of their static dipole polarizabilities. In this paper, we computed the variations with internuclear distance and with vibrational index of the static dipole polarizability components of all homonuclear alkali dimers including Fr$_2$, and of all heteronuclear alkali dimers involving Li to Cs, in their electronic ground state and in their lowest triplet state. We use the same quantum chemistry approach than in our work on dipole moments (M. Aymar and O. Dulieu, J. Chem. Phys. 122, 204302 (2005)), based on pseudopotentials for atomic Core Representation, Gaussian basis sets, and effective potentials for Core polarization. Polarizabilities are extracted from electronic energies using the finite-field method. For the heaviest species Rb$_2$, Cs$_2$ and Fr$_2$ and for all heteronuclear alkali dimers, such results are presented for the first time. The accuracy of our results on atomic and molecular static dipole polarizabilities is discussed by comparing our values with the few available experimental data and elaborate calculations. We found that for all alkali pairs, the parallel and perpendicular components of the ground state polarizabilities at the equilibrium distance $R_e$ scale as $(R_e)^3$, which can be related to a simple electrostatic model of an ellipsoidal charge distribution. Prospects for possible alignment and orientation effects with these molecules in forthcoming experiments are discussed.
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Calculations of transition and permanent dipole moments of heteronuclear alkali dimers NaK, NaRb and NaCs
Molecular Physics, 2007Co-Authors: Mireille Aymar, Olivier DulieuAbstract:Obtaining ultracold samples of dipolar molecules is a current challenge which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. In this paper, we calculate permanent dipole moments and transition dipole moments for excited states for alkali dimers NaK, NaRb and NaCs using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, Gaussian basis sets, and effective terms for Core polarization effects. We provide an extensive set of data concerning transitions among the first seven molecular states of each symmetry 1Σ+, 3Σ+, 1Π, 3Π. The accuracy of our results is generally improved compared to previous similar calculations on NaK, while they are found to be in good agreement with the few NaRb states calculated with other methods. Results for NaCs transition dipole moments are given here for the first time.
Derek Hoiem - One of the best experts on this subject based on the ideXlab platform.
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Aligned Image-Word Representations Improve Inductive Transfer Across Vision-Language Tasks
arXiv: Computer Vision and Pattern Recognition, 2017Co-Authors: Tanmay Gupta, Kevin J. Shih, Saurabh Singh, Derek HoiemAbstract:An important goal of computer vision is to build systems that learn visual Representations over time that can be applied to many tasks. In this paper, we investigate a vision-language embedding as a Core Representation and show that it leads to better cross-task transfer than standard multi-task learning. In particular, the task of visual recognition is aligned to the task of visual question answering by forcing each to use the same word-region embeddings. We show this leads to greater inductive transfer from recognition to VQA than standard multitask learning. Visual recognition also improves, especially for categories that have relatively few recognition training labels but appear often in the VQA setting. Thus, our paper takes a small step towards creating more general vision systems by showing the benefit of interpretable, flexible, and trainable Core Representations.
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ICCV - Aligned Image-Word Representations Improve Inductive Transfer Across Vision-Language Tasks
2017 IEEE International Conference on Computer Vision (ICCV), 2017Co-Authors: Tanmay Gupta, Kevin J. Shih, Saurabh Singh, Derek HoiemAbstract:An important goal of computer vision is to build systems that learn visual Representations over time that can be applied to many tasks. In this paper, we investigate a vision-language embedding as a Core Representation and show that it leads to better cross-task transfer than standard multitask learning. In particular, the task of visual recognition is aligned to the task of visual question answering by forcing each to use the same word-region embeddings. We show this leads to greater inductive transfer from recognition to VQA than standard multitask learning. Visual recognition also improves, especially for categories that have relatively few recognition training labels but appear often in the VQA setting. Thus, our paper takes a small step towards creating more general vision systems by showing the benefit of interpretable, flexible, and trainable Core Representations.
Frédéric Pascal - One of the best experts on this subject based on the ideXlab platform.
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New Insights Into the Statistical Properties of $M$ -Estimators
IEEE Transactions on Signal Processing, 2018Co-Authors: Gordana Draskovic, Frédéric PascalAbstract:This paper proposes an original approach to better understanding the behavior of robust scatter matrix $M$ -estimators. Scatter matrices are of particular interest for many signal processing applications since the resulting performance strongly relies on the quality of the matrix estimation. In this context, $M$ -estimators appear as very interesting candidates, mainly due to their flexibility to the statistical model and their robustness to outliers and/or missing data. However, the behavior of such estimators still remains unclear and not well understood since they are described by fixed-point equations that make their statistical analysis very difficult. To fill this gap, the main contribution of this work is to prove that these estimators distribution is more accurately described by a Wishart distribution than by the classical asymptotical Gaussian approximation. To that end, we propose a new “Gaussian-Core” Representation for complex elliptically symmetric distributions and we analyze the proximity between $M$ -estimators and a Gaussian-based sample covariance matrix, unobservable in practice and playing only a theoretical role. To confirm our claims, we also provide results for a widely used function of $M$ -estimators, the Mahalanobis distance. Finally, Monte Carlo simulations for various scenarios are presented to validate theoretical results.
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New insights into the statistical properties of M-estimators
IEEE Transactions on Signal Processing, 2018Co-Authors: Gordana Draskovic, Frédéric PascalAbstract:This paper proposes an original approach to better understanding the behavior of robust scatter matrix M-estimators. Scatter matrices are of particular interest for many signal processing applications since the resulting performance strongly relies on the quality of the matrix estimation. In this context, M-estimators appear as very interesting candidates, mainly due to their flexibility to the statistical model and their robustness to outliers and/or missing data. However, the behavior of such estimators still remains unclear and not well understood since they are described by fixed-point equations that make their statistical analysis very difficult. To fill this gap, the main contribution of this work is to prove that these estimators distribution is more accurately described by a Wishart distribution than by the classical asymptotical Gaussian approximation. To that end, we propose a new "Gaussian-Core" Representation for Complex Elliptically Symmetric (CES) distributions and we analyze the proximity between M-estimators and a Gaussian-based Sample Covariance Matrix (SCM), unobservable in practice and playing only a theoretical role. To confirm our claims we also provide results for a widely used function of M-estimators, the Maha-lanobis distance. Finally, Monte Carlo simulations for various scenarios are presented to validate theoretical results.
Tanmay Gupta - One of the best experts on this subject based on the ideXlab platform.
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Aligned Image-Word Representations Improve Inductive Transfer Across Vision-Language Tasks
arXiv: Computer Vision and Pattern Recognition, 2017Co-Authors: Tanmay Gupta, Kevin J. Shih, Saurabh Singh, Derek HoiemAbstract:An important goal of computer vision is to build systems that learn visual Representations over time that can be applied to many tasks. In this paper, we investigate a vision-language embedding as a Core Representation and show that it leads to better cross-task transfer than standard multi-task learning. In particular, the task of visual recognition is aligned to the task of visual question answering by forcing each to use the same word-region embeddings. We show this leads to greater inductive transfer from recognition to VQA than standard multitask learning. Visual recognition also improves, especially for categories that have relatively few recognition training labels but appear often in the VQA setting. Thus, our paper takes a small step towards creating more general vision systems by showing the benefit of interpretable, flexible, and trainable Core Representations.
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ICCV - Aligned Image-Word Representations Improve Inductive Transfer Across Vision-Language Tasks
2017 IEEE International Conference on Computer Vision (ICCV), 2017Co-Authors: Tanmay Gupta, Kevin J. Shih, Saurabh Singh, Derek HoiemAbstract:An important goal of computer vision is to build systems that learn visual Representations over time that can be applied to many tasks. In this paper, we investigate a vision-language embedding as a Core Representation and show that it leads to better cross-task transfer than standard multitask learning. In particular, the task of visual recognition is aligned to the task of visual question answering by forcing each to use the same word-region embeddings. We show this leads to greater inductive transfer from recognition to VQA than standard multitask learning. Visual recognition also improves, especially for categories that have relatively few recognition training labels but appear often in the VQA setting. Thus, our paper takes a small step towards creating more general vision systems by showing the benefit of interpretable, flexible, and trainable Core Representations.
Mireille Aymar - One of the best experts on this subject based on the ideXlab platform.
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Electronic structure of the magnesium hydride molecular ion
Journal of Physics B: Atomic Molecular and Optical Physics, 2009Co-Authors: Mireille Aymar, Romain Guérout, Mohamed Sahlaoui, Olivier DulieuAbstract:In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, Gaussian basis sets and effective Core polarization potentials, we investigate the electronic properties of the MgH+ ion. We first determine potential energy curves for several states using different basis sets and discuss their predicted accuracy by comparing our values of the well depths and position with other available results. We then calculate permanent and transition dipole moments for several transitions. Finally, for the first time, we calculate the static dipole polarizability of MgH+ as a function of the interatomic distance. This study represents the first step towards the modelling of collisions between trapped cold Mg+ ions and H2 molecules.
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Systematic trends in electronic properties of alkali hydrides
arXiv: Atomic Physics, 2009Co-Authors: Mireille Aymar, Johannes Deiglmayr, Olivier DulieuAbstract:Obtaining ultracold samples of dipolar molecules is a current challenge, which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. Alkali hydride molecules have permanent dipole moments significantly larger than those of mixed alkali species, and, as pointed out by Taylor-Juarros et al. (Eur. Phys. J. D, 31, 213 (2004)) and by Juarros et al. (Phys. Rev. A, 73, 041403 (2006)), are thus good candidates for cold molecule forma- tion. In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, large Gaussian basis sets, and effective Core polarization potential, we systematically investigate the electronic properties of the alkali hydrides LiH to CsH, to discuss general trends of their behavior. We computed (for the first time for NaH, KH, RbH, and CsH) the variation of their static polarizability with the internuclear distance. Moreover, in addition to po- tential curves, we determine accurate values of permanent and transition dipole moments for ground and excited states de- pending on the internuclear distance. The electronic properties of all alkali hydrides are compared with one another, in the light of the numerous other data available in the literature. Finally, the influence of the quality of the Representation of the hydrogen electronic affinity in the approach on the results is discussed.
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Systematic trends in electronic properties of alkali hydridesThis article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.
Canadian Journal of Physics, 2009Co-Authors: Mireille Aymar, Johannes Deiglmayr, Olivier DulieuAbstract:Obtaining ultracold samples of dipolar molecules is a current challenge, which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. Alkali hydride molecules have permanent dipole moments significantly larger than those of mixed alkali species, and, as pointed out by Taylor-Juarros et al. (Eur. Phys. J. D, 31, 213 (2004)) and by Juarros et al. (Phys. Rev. A, 73, 041403 (2006)), are thus good candidates for cold molecule formation. In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, large Gaussian basis sets, and effective Core polarization potential, we systematically investigate the electronic properties of the alkali hydrides LiH to CsH, to discuss general trends of their behavior. We computed (for the first time for NaH, KH, RbH, and CsH) the variation of their static polarizability with the internuclear distance. Moreover, in addition to potential curves, we determine accurate values of permanent...
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Calculations of static dipole polarizabilities of alkali dimers. Prospects for alignment of ultracold molecules
The Journal of chemical physics, 2008Co-Authors: Johannes Deiglmayr, Mireille Aymar, Roland Wester, Matthias Weidemüller, Olivier DulieuAbstract:The rapid development of experimental techniques to produce ultracold alkali molecules opens the ways to manipulate them and to control their dynamics using external electric fields. A prerequisite quantity for such studies is the knowledge of their static dipole polarizabilities. In this paper, we computed the variations with internuclear distance and with vibrational index of the static dipole polarizability components of all homonuclear alkali dimers including Fr$_2$, and of all heteronuclear alkali dimers involving Li to Cs, in their electronic ground state and in their lowest triplet state. We use the same quantum chemistry approach than in our work on dipole moments (M. Aymar and O. Dulieu, J. Chem. Phys. 122, 204302 (2005)), based on pseudopotentials for atomic Core Representation, Gaussian basis sets, and effective potentials for Core polarization. Polarizabilities are extracted from electronic energies using the finite-field method. For the heaviest species Rb$_2$, Cs$_2$ and Fr$_2$ and for all heteronuclear alkali dimers, such results are presented for the first time. The accuracy of our results on atomic and molecular static dipole polarizabilities is discussed by comparing our values with the few available experimental data and elaborate calculations. We found that for all alkali pairs, the parallel and perpendicular components of the ground state polarizabilities at the equilibrium distance $R_e$ scale as $(R_e)^3$, which can be related to a simple electrostatic model of an ellipsoidal charge distribution. Prospects for possible alignment and orientation effects with these molecules in forthcoming experiments are discussed.
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Calculations of transition and permanent dipole moments of heteronuclear alkali dimers NaK, NaRb and NaCs
Molecular Physics, 2007Co-Authors: Mireille Aymar, Olivier DulieuAbstract:Obtaining ultracold samples of dipolar molecules is a current challenge which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. In this paper, we calculate permanent dipole moments and transition dipole moments for excited states for alkali dimers NaK, NaRb and NaCs using a standard quantum chemistry approach based on pseudopotentials for atomic Core Representation, Gaussian basis sets, and effective terms for Core polarization effects. We provide an extensive set of data concerning transitions among the first seven molecular states of each symmetry 1Σ+, 3Σ+, 1Π, 3Π. The accuracy of our results is generally improved compared to previous similar calculations on NaK, while they are found to be in good agreement with the few NaRb states calculated with other methods. Results for NaCs transition dipole moments are given here for the first time.