loc nguyen - Academia.edu (original) (raw)

Papers by loc nguyen

The aim of this paper is to propose for the first time a reconstruction scheme and a stability re... more The aim of this paper is to propose for the first time a reconstruction scheme and a stability result for recovering from acoustic-optic data absorption distributions with bounded variation. The paper extends earlier results in [3] and [5] on smooth absorption distributions. It opens a door for a mathematical and numerical framework for imaging, from internal data, parameter distributions with high contrast in biological tissues.

This paper studies a possible connection between the way the time averaged electromagnetic power ... more This paper studies a possible connection between the way the time averaged electromagnetic power dissipated into heat blows up and the anomalous localized resonance in plasmonic structures. We show that there is a setting in which the localized resonance takes place whenever the resonance does and moreover, the power is always bounded and might go to 0. We also provide another setting in which the resonance is complete and the power goes to infinity whenever resonance occurs; as a consequence of this fact there is no localized resonance. This work is motivated from recent works on cloaking via anomalous localized resonance. * EPFL SB MATHAA CAMA, Station 8

This paper is devoted to establishing results for semilinear elliptic boundary value problems whe... more This paper is devoted to establishing results for semilinear elliptic boundary value problems where the solvability of problems subject to No Flux boundary conditions follows from the solvability of related Dirichlet boundary value problems. Throughout it is assumed that the nonlinear perturbation terms are gradient dependent. An extension of No-Flux problems is discussed, as well.

The aim of this paper is to propose an optimal control optimization algorithm for reconstructing ... more The aim of this paper is to propose an optimal control optimization algorithm for reconstructing admittivity distributions (i.e., both conductivity and permittivity) from multi-frequency micro-electrical impedance tomography. A convergent and stable optimization scheme is shown to be obtainable from multi-frequency data. The results of this paper have potential applicability in cancer imaging, cell culturing and differentiation, food sciences, and biotechnology.

The aim of this paper is to tackle the nonlinear optical reconstruction problem. Given a set of a... more The aim of this paper is to tackle the nonlinear optical reconstruction problem. Given a set of acousto-optic measurements, we develop a mathematical framework for the reconstruction problem in the case where the optical absorption distribution is supposed to be a perturbation of a piecewise constant function. Analyzing the acousto-optic measurements, we establish a new equation in the sense of distributions for the optical absorption coefficient. For doing so, we introduce a weak Helmholtz decomposition and interpret in a weak sense the cross-correlation measurements using the spherical Radon transform. We next show how to find an initial guess for the unknown coefficient and finally construct the true coefficient by providing a Landweber type iteration and proving that the resulting sequence converges to the solution of the system constituted by the optical diffusion equation and the new equation mentioned above. Our results in this paper generalize the acousto-optic process proposed in for piecewise smooth optical absorption distributions.

ABSTRACT The aim of this paper is to develop an efficient reconstruction algorithm for ultrasound... more ABSTRACT The aim of this paper is to develop an efficient reconstruction algorithm for ultrasound-modulated diffuse optical tomography. In diffuse op-tical imaging, the resolution is in general low. By mechanically perturbing the medium, we show that it is possible to achieve a significant resolution en-hancement. When a spherical acoustic wave is propagating inside the medium, the optical parameter of the medium is perturbed. Using cross-correlations of the boundary measurements in the perturbed medium and in the unperturbed one, we provide an iterative algorithm for reconstructing the optical absorp-tion coefficient. Using a spherical Radon transform inversion, we first establish an equation that the optical absorption satisfies. This equation together with the diffusion model constitutes a nonlinear system. Then, solving iteratively such a nonlinear coupled system, we obtain the true absorption parameter. We prove the convergence of the algorithm and present numerical results to illustrate its resolution and stability performances.

Bounds are obtained on the volume fraction in a two-dimensional body containing two elastically i... more Bounds are obtained on the volume fraction in a two-dimensional body containing two elastically isotropic materials with known bulk and shear moduli. These bounds use information about the average stress and strain fields, energy, determinant of the stress, and determinant of the displacement gradient, which can be determined from measurements of the traction and displacement at the boundary. The bounds are sharp if in each phase certain displacement field components are constant. The inequalities we obtain also directly give bounds on the possible (average stress, average strain) pairs in a two-phase, two-dimensional, periodic or statistically homogeneous composite

Journal of Traumatic Stress, 1993

The current study of Vietnamese refugee students revealed that the majority had experienced multi... more The current study of Vietnamese refugee students revealed that the majority had experienced multiple traumatic events and reported moderate to severe PTSD symptomatology. A stress intervention module (SIT), designed to treat rape victims, was introduced to determine its efficacy for the treatment of Vietnamese refugees with PTSD symptoms. Postintervention PTSD symptomatology was significantly reduced contrasted to virtually no change in symptomatology for the control subjects. Serious methodological concerns, e.g., selection bias, sample size, are highlighted in the paper. The current inquiry is essentially a pilot study. The paper is intended for heuristic value. Clinical literature is extant for culturally sensitive intervention approaches for this vulnerable population.

Physical chemistry chemical physics : PCCP, Jan 21, 2012

A selective co-sensitization approach to increase photon conversion effi ciency and electron life... more A selective co-sensitization approach to increase photon conversion effi ciency and electron lifetime in dye-sensitized solar cells Ruthenium-based C106 and organic D131 sensitizers have been judicially chosen for co-sensitization due to their complementary absorption properties and different molecular sizes. Co-sensitization yields a higher light-harvesting efficiency as well as better dye coverage to passivate the surface of TiO 2 . The co-sensitized devices C106 + D131 showed significant enhancement in the performance (g = 11.1%), which is a marked improvement over baseline devices sensitized with either D131 (g = 5.6%) or C106 (g = 9.5%). The improved performance of the co-sensitized cell is attributed to the combined enhancement in the short circuit current, open circuit voltage, and the fill-factor of the solar cells. J sc is improved because of the complementary absorption spectra and favorable energy level alignments of both dyes; whereas, V oc is improved because of the better surface coverage helping to reduce the recombination and increase the electron life time. The origins of these enhancements have been systematically studied through dye desorption, absorption spectroscopy, and intensity modulated photovoltage spectroscopy investigations. 33115 w Electronic supplementary information (ESI) available: Detailed device fabrication, photovoltaic measurements and dispersion in the values of J-V characteristics for individual as well as co-sensitized devices. See

American journal of public health, 2014

The sharing of data, particularly health data, has been an important tool for the public health c... more The sharing of data, particularly health data, has been an important tool for the public health community, especially in terms of data sharing across systems (i.e., interoperability). Child maltreatment is a serious public health issue that could be better mitigated if there were interoperability. There are challenges to addressing child maltreatment interoperability that include the current lack of data sharing among systems, the lack of laws that promote interoperability to address child maltreatment, and the lack of data sharing at the individual level. There are waivers in federal law that allow for interoperability to prevent communicable diseases at the individual level. Child maltreatment has a greater long-term impact than a number of communicable diseases combined, and interoperability should be leveraged to maximize public health strategies to prevent child maltreatment.

Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, 1992

This paper presents some experimental results from applying an input shaping algorithm for vibrat... more This paper presents some experimental results from applying an input shaping algorithm for vibration reduction in a flexible beam. The theory of input shaping is reviewed, along with the mathematical formulation and the sofrware implementation. The experimental hardware is described and some experimental results are presented. The experimental results show that input shaping can successfully reduce vibration in flexible beams

2013 IEEE Power & Energy Society General Meeting, 2013

This paper presents a method to operate a grid connected hybrid system. The hybrid system compose... more This paper presents a method to operate a grid connected hybrid system. The hybrid system composed of a Photovoltaic (PV) array and a Proton exchange membrane fuel cell (PEMFC) is considered. The PV array normally uses a maximum power point tracking (MPPT) technique to continuously deliver the highest power to the load when variations in irradiation and temperature occur, which

2009 International Conference on Computational Science and Engineering, 2009

ABSTRACT

2014 International Conference on Interactive Collaborative Learning (ICL), 2014

Nowadays modern society requires every citizen always updates and improves her / his knowledge an... more Nowadays modern society requires every citizen always updates and improves her / his knowledge and skills necessary to working and researching. E-learning or distance learning gives everyone a chance to study at anytime and anywhere with full support of computer technology and network. Adaptive learning, a variant of e-learning, aims to satisfy the demand of personalization in learning. The adaptive learning system (ALS) is defined as the computer system that has ability to change its action to provide learning content and pedagogic environment/method for every student in accordance with her/his individual characteristics. Therefore, the ultimate goal of this research is to give the best support to learners in their learning path and this is an enthusiastic contribution to research community. Learners’ information and characteristics such as knowledge, goal, experience, interest, background, etc are the most important to adaptive system. These characteristics are organized in structure so-called learner model (or user model) and the system or computer software that builds up and manipulates learner model is called user modeling system (or learner modeling system). This research proposes a learner model that consists of three essential kinds of information about learners such as knowledge, learning style and learning history. Such three characteristics form a triangle and so this learner model is called Triangular Learner Model (TLM). The ideology of TLM is that user characteristics are various and only some information is really necessary to adaptive learning and an optimal user modeling system should choose essential information relating to user’s study to build up learner model. Keywords: User Modeling System, E-learning, Triangular Learner Model.

Studies in Computational Intelligence, 2010

ABSTRACT

Journal of Data Analysis and Information Processing, 2014

User model which is the representation of information about user is the heart of adaptive systems... more User model which is the representation of information about user is the heart of adaptive systems. It helps adaptive systems to perform adaptation tasks. There are two kinds of adaptations: 1) Individual adaptation regarding to each user; 2) Group adaptation focusing on group of users. To support group adaptation, the basic problem which needs to be solved is how to create user groups. This relates to clustering techniques so as to cluster user models because a group is considered as a cluster of similar user models. In this paper we discuss two clustering algorithms: k-means and k-medoids and also propose dissimilarity measures and similarity measures which are applied into different structures (forms) of user models like vector, overlay, and Bayesian network.

2009 3rd IEEE International Conference on Digital Ecosystems and Technologies, 2009

ABSTRACT

The aim of this paper is to propose for the first time a reconstruction scheme and a stability re... more The aim of this paper is to propose for the first time a reconstruction scheme and a stability result for recovering from acoustic-optic data absorption distributions with bounded variation. The paper extends earlier results in [3] and [5] on smooth absorption distributions. It opens a door for a mathematical and numerical framework for imaging, from internal data, parameter distributions with high contrast in biological tissues.

This paper studies a possible connection between the way the time averaged electromagnetic power ... more This paper studies a possible connection between the way the time averaged electromagnetic power dissipated into heat blows up and the anomalous localized resonance in plasmonic structures. We show that there is a setting in which the localized resonance takes place whenever the resonance does and moreover, the power is always bounded and might go to 0. We also provide another setting in which the resonance is complete and the power goes to infinity whenever resonance occurs; as a consequence of this fact there is no localized resonance. This work is motivated from recent works on cloaking via anomalous localized resonance. * EPFL SB MATHAA CAMA, Station 8

This paper is devoted to establishing results for semilinear elliptic boundary value problems whe... more This paper is devoted to establishing results for semilinear elliptic boundary value problems where the solvability of problems subject to No Flux boundary conditions follows from the solvability of related Dirichlet boundary value problems. Throughout it is assumed that the nonlinear perturbation terms are gradient dependent. An extension of No-Flux problems is discussed, as well.

The aim of this paper is to propose an optimal control optimization algorithm for reconstructing ... more The aim of this paper is to propose an optimal control optimization algorithm for reconstructing admittivity distributions (i.e., both conductivity and permittivity) from multi-frequency micro-electrical impedance tomography. A convergent and stable optimization scheme is shown to be obtainable from multi-frequency data. The results of this paper have potential applicability in cancer imaging, cell culturing and differentiation, food sciences, and biotechnology.

The aim of this paper is to tackle the nonlinear optical reconstruction problem. Given a set of a... more The aim of this paper is to tackle the nonlinear optical reconstruction problem. Given a set of acousto-optic measurements, we develop a mathematical framework for the reconstruction problem in the case where the optical absorption distribution is supposed to be a perturbation of a piecewise constant function. Analyzing the acousto-optic measurements, we establish a new equation in the sense of distributions for the optical absorption coefficient. For doing so, we introduce a weak Helmholtz decomposition and interpret in a weak sense the cross-correlation measurements using the spherical Radon transform. We next show how to find an initial guess for the unknown coefficient and finally construct the true coefficient by providing a Landweber type iteration and proving that the resulting sequence converges to the solution of the system constituted by the optical diffusion equation and the new equation mentioned above. Our results in this paper generalize the acousto-optic process proposed in for piecewise smooth optical absorption distributions.

ABSTRACT The aim of this paper is to develop an efficient reconstruction algorithm for ultrasound... more ABSTRACT The aim of this paper is to develop an efficient reconstruction algorithm for ultrasound-modulated diffuse optical tomography. In diffuse op-tical imaging, the resolution is in general low. By mechanically perturbing the medium, we show that it is possible to achieve a significant resolution en-hancement. When a spherical acoustic wave is propagating inside the medium, the optical parameter of the medium is perturbed. Using cross-correlations of the boundary measurements in the perturbed medium and in the unperturbed one, we provide an iterative algorithm for reconstructing the optical absorp-tion coefficient. Using a spherical Radon transform inversion, we first establish an equation that the optical absorption satisfies. This equation together with the diffusion model constitutes a nonlinear system. Then, solving iteratively such a nonlinear coupled system, we obtain the true absorption parameter. We prove the convergence of the algorithm and present numerical results to illustrate its resolution and stability performances.

Bounds are obtained on the volume fraction in a two-dimensional body containing two elastically i... more Bounds are obtained on the volume fraction in a two-dimensional body containing two elastically isotropic materials with known bulk and shear moduli. These bounds use information about the average stress and strain fields, energy, determinant of the stress, and determinant of the displacement gradient, which can be determined from measurements of the traction and displacement at the boundary. The bounds are sharp if in each phase certain displacement field components are constant. The inequalities we obtain also directly give bounds on the possible (average stress, average strain) pairs in a two-phase, two-dimensional, periodic or statistically homogeneous composite

Journal of Traumatic Stress, 1993

The current study of Vietnamese refugee students revealed that the majority had experienced multi... more The current study of Vietnamese refugee students revealed that the majority had experienced multiple traumatic events and reported moderate to severe PTSD symptomatology. A stress intervention module (SIT), designed to treat rape victims, was introduced to determine its efficacy for the treatment of Vietnamese refugees with PTSD symptoms. Postintervention PTSD symptomatology was significantly reduced contrasted to virtually no change in symptomatology for the control subjects. Serious methodological concerns, e.g., selection bias, sample size, are highlighted in the paper. The current inquiry is essentially a pilot study. The paper is intended for heuristic value. Clinical literature is extant for culturally sensitive intervention approaches for this vulnerable population.

Physical chemistry chemical physics : PCCP, Jan 21, 2012

A selective co-sensitization approach to increase photon conversion effi ciency and electron life... more A selective co-sensitization approach to increase photon conversion effi ciency and electron lifetime in dye-sensitized solar cells Ruthenium-based C106 and organic D131 sensitizers have been judicially chosen for co-sensitization due to their complementary absorption properties and different molecular sizes. Co-sensitization yields a higher light-harvesting efficiency as well as better dye coverage to passivate the surface of TiO 2 . The co-sensitized devices C106 + D131 showed significant enhancement in the performance (g = 11.1%), which is a marked improvement over baseline devices sensitized with either D131 (g = 5.6%) or C106 (g = 9.5%). The improved performance of the co-sensitized cell is attributed to the combined enhancement in the short circuit current, open circuit voltage, and the fill-factor of the solar cells. J sc is improved because of the complementary absorption spectra and favorable energy level alignments of both dyes; whereas, V oc is improved because of the better surface coverage helping to reduce the recombination and increase the electron life time. The origins of these enhancements have been systematically studied through dye desorption, absorption spectroscopy, and intensity modulated photovoltage spectroscopy investigations. 33115 w Electronic supplementary information (ESI) available: Detailed device fabrication, photovoltaic measurements and dispersion in the values of J-V characteristics for individual as well as co-sensitized devices. See

American journal of public health, 2014

The sharing of data, particularly health data, has been an important tool for the public health c... more The sharing of data, particularly health data, has been an important tool for the public health community, especially in terms of data sharing across systems (i.e., interoperability). Child maltreatment is a serious public health issue that could be better mitigated if there were interoperability. There are challenges to addressing child maltreatment interoperability that include the current lack of data sharing among systems, the lack of laws that promote interoperability to address child maltreatment, and the lack of data sharing at the individual level. There are waivers in federal law that allow for interoperability to prevent communicable diseases at the individual level. Child maltreatment has a greater long-term impact than a number of communicable diseases combined, and interoperability should be leveraged to maximize public health strategies to prevent child maltreatment.

Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, 1992

This paper presents some experimental results from applying an input shaping algorithm for vibrat... more This paper presents some experimental results from applying an input shaping algorithm for vibration reduction in a flexible beam. The theory of input shaping is reviewed, along with the mathematical formulation and the sofrware implementation. The experimental hardware is described and some experimental results are presented. The experimental results show that input shaping can successfully reduce vibration in flexible beams

2013 IEEE Power & Energy Society General Meeting, 2013

This paper presents a method to operate a grid connected hybrid system. The hybrid system compose... more This paper presents a method to operate a grid connected hybrid system. The hybrid system composed of a Photovoltaic (PV) array and a Proton exchange membrane fuel cell (PEMFC) is considered. The PV array normally uses a maximum power point tracking (MPPT) technique to continuously deliver the highest power to the load when variations in irradiation and temperature occur, which

2009 International Conference on Computational Science and Engineering, 2009

ABSTRACT

2014 International Conference on Interactive Collaborative Learning (ICL), 2014

Nowadays modern society requires every citizen always updates and improves her / his knowledge an... more Nowadays modern society requires every citizen always updates and improves her / his knowledge and skills necessary to working and researching. E-learning or distance learning gives everyone a chance to study at anytime and anywhere with full support of computer technology and network. Adaptive learning, a variant of e-learning, aims to satisfy the demand of personalization in learning. The adaptive learning system (ALS) is defined as the computer system that has ability to change its action to provide learning content and pedagogic environment/method for every student in accordance with her/his individual characteristics. Therefore, the ultimate goal of this research is to give the best support to learners in their learning path and this is an enthusiastic contribution to research community. Learners’ information and characteristics such as knowledge, goal, experience, interest, background, etc are the most important to adaptive system. These characteristics are organized in structure so-called learner model (or user model) and the system or computer software that builds up and manipulates learner model is called user modeling system (or learner modeling system). This research proposes a learner model that consists of three essential kinds of information about learners such as knowledge, learning style and learning history. Such three characteristics form a triangle and so this learner model is called Triangular Learner Model (TLM). The ideology of TLM is that user characteristics are various and only some information is really necessary to adaptive learning and an optimal user modeling system should choose essential information relating to user’s study to build up learner model. Keywords: User Modeling System, E-learning, Triangular Learner Model.

Studies in Computational Intelligence, 2010

ABSTRACT

Journal of Data Analysis and Information Processing, 2014

User model which is the representation of information about user is the heart of adaptive systems... more User model which is the representation of information about user is the heart of adaptive systems. It helps adaptive systems to perform adaptation tasks. There are two kinds of adaptations: 1) Individual adaptation regarding to each user; 2) Group adaptation focusing on group of users. To support group adaptation, the basic problem which needs to be solved is how to create user groups. This relates to clustering techniques so as to cluster user models because a group is considered as a cluster of similar user models. In this paper we discuss two clustering algorithms: k-means and k-medoids and also propose dissimilarity measures and similarity measures which are applied into different structures (forms) of user models like vector, overlay, and Bayesian network.

2009 3rd IEEE International Conference on Digital Ecosystems and Technologies, 2009

ABSTRACT