Dang Nguyen - LAGA

Dang Nguyen
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Dang Nguyen

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Pub Categories

Mathematics - Probability (6)
Quantum Physics (5)
Mathematics - Algebraic Topology (4)
Mathematics - Commutative Algebra (4)
Quantitative Biology - Populations and Evolution (4)
Physics - Atomic Physics (3)
Mathematics - Numerical Analysis (2)
Computer Science - Information Retrieval (2)
Physics - Chemical Physics (2)
Computer Science - Computation and Language (2)
Mathematics - Dynamical Systems (1)
Computer Science - Digital Libraries (1)
Mathematics - Combinatorics (1)
Physics - Fluid Dynamics (1)
Mathematics - Spectral Theory (1)
Computer Science - Learning (1)
Mathematics - Algebraic Geometry (1)
Computer Science - Robotics (1)
Mathematics - Analysis of PDEs (1)
Mathematics - Functional Analysis (1)
Mathematical Physics (1)
Mathematics - Mathematical Physics (1)

Publications Authored By Dang Nguyen

This paper is devoted to the analysis of a simple Lotka-Volterra food chain evolving in a stochastic environment. It can be seen as the companion paper of Hening and Nguyen `17 where we have characterized the persistence and extinction of such a food chain under the assumption that there is no intraspecific competition among predators. In the current paper we focus on the case when all the species experience intracompetition. Read More

In recent years there has been a growing interest in the study of the dynamics of stochastic populations. A key question in population biology is to understand the conditions under which populations coexist or go extinct. Theoretical and empirical studies have shown that coexistence can be facilitated or negated by both biotic interactions and environmental fluctuations. Read More

We study the persistence and extinction of species in a simple food chain that is modelled by a Lotka-Volterra system with environmental stochasticity. There exist sharp results for deterministic Lotka-Volterra systems in the literature but few for their stochastic counterparts. The food chain we analyze consists of one prey and $n-1$ predators. Read More

Let $I$ and $J$ be nonzero ideals in two Noetherian algebras $A$ and $B$ over a field $k$. We study algebraic properties and invariants of symbolic powers of the ideal $I+J$ in $A\otimes_k B$. Our main technical result is the binomial expansion $(I+J)^{(n)} = \sum_{i+j = n} I^{(i)} J^{(j)}$ for all $n > 0$. Read More

In this paper, we consider the patient similarity matching problem over a cancer cohort of more than 220,000 patients. Our approach first leverages on Word2Vec framework to embed ICD codes into vector-valued representation. We then propose a sequential algorithm for case-control matching on this representation space of diagnosis codes. Read More

While autonomous multirotor micro aerial vehicles (MAVs) are uniquely well suited for certain types of missions benefiting from stationary flight capabilities, their more widespread usage still faces many hurdles, due in particular to their limited range and the difficulty of fully automating their deployment and retrieval. In this paper we address these issues by solving the problem of the automated landing of a quadcopter on a ground vehicle moving at relatively high speed. We present our system architecture, including the structure of our Kalman filter for the estimation of the relative position and velocity between the quadcopter and the landing pad, as well as our controller design for the full rendezvous and landing maneuvers. Read More

In practice many problems related to space/time fractional equations depend on fractional parameters. But these fractional parameters are not known a priori in modelling problems. Hence continuity of the solutions with respect to these parameters is important for modelling purposes. Read More

In this paper, we discuss the possibility of imaging molecular orbitals from photoelectron spectra obtained via Laser Induced Electron Diffraction (LIED) in linear molecules. This is an extension of our work published recently in Physical Review A \textbf{94}, 023421 (2016) to the case of the HOMO-1 orbital of the carbon dioxide molecule. We show that such an imaging technique has the potential to image molecular orbitals at different internuclear distances in a sub-femtosecond time scale and with a resolution of a fraction of an Angstr\"om. Read More

The fringe pattern that allows geometrical and orbital structure information to be extracted from LIED spectra of symmetric molecules is shown to reflect a symmetry conservation principle. We show that under a field polarization which preserves certain symmetry elements of the molecule, the symmetry character of the initial wave function is conserved during its time-evolution. We present a symmetry analysis of a deviation from a perfect alignment by decomposing the field into a major, symmetry-determining part, and a minor, symmetry breaking, part. Read More

Since the first online demonstration of Neural Machine Translation (NMT) by LISA, NMT development has recently moved from laboratory to production systems as demonstrated by several entities announcing roll-out of NMT engines to replace their existing technologies. NMT systems have a large number of training configurations and the training process of such systems is usually very long, often a few weeks, so role of experimentation is critical and important to share. In this work, we present our approach to production-ready systems simultaneously with release of online demonstrators covering a large variety of languages (12 languages, for 32 language pairs). Read More

Imaging structures at the molecular level is a fast developing interdisciplinary research field that spans across the boundaries of physics and chemistry. High spatial resolution images of molecules can be obtained with photons or ultrafast electrons. In addition, images of valence molecular orbitals can be extracted via tomographic techniques based on the coherent XUV radiation emitted by a molecular gas exposed to an intense ultra-short infrared laser pulse. Read More

In the 1980's, the magic properties of the cohomology of elementary abelian groups as modules over the Steenrod algebra initiated a long lasting interaction between topology and modular representation theory in natural characteristic. The Adams-Gunawardena-Miller theorem in particular, showed that their decomposition is governed by the modular representations of the semi-groups of square matrices. Applying Lannes' T functor on the summands L P := Hom Mn(Fp) (P, H * (F p) n) defines an intriguing construction in representation theory. Read More

This work is devoted to studying the dynamics of a population subject to the combined effects of stochastic environments, competition for resources, and spatio-temporal heterogeneity and dispersal. The population is spread throughout $n$ patches whose population abundances are modeled as the solutions of a system of nonlinear stochastic differential equations living on $[0,\infty)^n$. We prove that $\lambda$, the stochastic growth rate of the system in the absence of competition, determines the long-term behaviour of the population. Read More

Convolving the output of Discontinuous Galerkin (DG) computations using spline filters can improve both smoothness and accuracy of the output. At domain boundaries, these filters have to be one-sided. Recently, position-dependent smoothness-increasing accuracy-preserving (PSIAC) filters were shown to be a superset of the top-of-the-line one-sided RLKV and SRV filters. Read More

We report about an intriguing boiling regime occurring for small heaters embedded on the boundary in subcooled water. The microheater is realized by focusing a continuous wave laser beam to about $10\,\mu$m in diameter onto a 165\,nm-thick layer of gold, which is submerged in water. After an initial vaporous explosion a single bubble oscillates continuously and repeatably at several $100\,$kHz. Read More

This work derives sufficient conditions for the coexistence and exclusion of a stochastic competitive Lotka-Volterra model. The conditions obtained are close to the necessary conditions. In addition, convergence in distribution of positive solutions of the model is also established. Read More

Convolving the output of Discontinuous Galerkin (DG) computations with symmetric Smoothness-Increasing Accuracy-Conserving (SIAC) filters can improve both smoothness and accuracy. To extend convolution to the boundaries, several one-sided spline filters have recently been developed. We interpret these filters as instances of a general class of position-dependent spline filters that we abbreviate as PSIAC filters. Read More

This note gives a new construction of Takayasu's cofibrations. Read More

This note is devoted to some questions about the representation theory over the finite field $\mathbb{F}_2$ of the general linear groups $\mathbb{GL_n(F_2)}$ and Poincar\'e series of unstable modules. The first draft was describing two conjectures. They were presented during talks made at VIASM in summer 2013. Read More

We explore the laser-induced ionization dynamics of N2 and CO2 molecules subjected to a few-cycle, linearly polarized, 800\,nm laser pulse using effective two-dimensional single active electron time-dependent quantum simulations. We show that the electron recollision process taking place after an initial tunnel ionization stage results in quantum interference patterns in the energy resolved photo-electron signals. If the molecule is initially aligned perpendicular to the field polarization, the position and relative heights of the associated fringes can be related to the molecular geometrical and orbital structure, using a simple inversion algorithm which takes into account the symmetry of the initial molecular orbital from which the ionized electron is produced. Read More

In this paper, we study different generalizations of the notion of squarefreeness for ideals to the more general case of modules. We describe the cones of Hilbert functions for squarefree modules in general and those generated in degree zero. We give their extremal rays and defining inequalities. Read More

We characterize the toric face rings that are normal (respectively seminormal). Extending results about local cohomology of Brun, Bruns, Ichim, Li and R\"omer of seminormal monoid rings and Stanley toric face rings, we prove the vanishing of certain graded parts of local cohomology of seminormal toric face rings. The combinatorial formula we obtain generalizes Hochster's formula. Read More

Toric face rings is a generalization of the concepts of affine monoid rings and Stanley-Reisner rings. We consider several properties which imply Koszulness for toric face rings over a field $k$. Generalizing works of Laudal, Sletsj\o{}e and Herzog et al. Read More

We address the feasibility of imaging geometric and orbital structure of a polyatomic molecule on an attosecond time-scale using the laser induced electron diffraction (LIED) technique. We present numerical results for the highest molecular orbitals of the CO2 molecule excited by a near infrared few-cycle laser pulse. The molecular geometry (bond-lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital. Read More

The necessary of buiding the searching system being able to support users expressing their searching by natural language queries is very important and opens the researching direction with many potential. It combines the traditional methods of information retrieval and the researching of Question Answering (QA). In this paper, we introduce a searching system built by us for searching courses on the Vietnam OpenCourseWare Program (VOCW). Read More

In the objective of building intelligent searching systems for Elibraries or online bookstores, we have proposed a searching system model based on a Vietnamese language query processing component. Such document searching systems based on this model can allow users to use Vietnamese queries that represent content information as input, instead of entering keywords for searching in specific fields in database. To simplify the realization process of system based on this searching system model, we set a target of building a framework to support the rapid development of Vietnamese language query processing components. Read More

One constructs minimal injective resolutions for certain unstable modules that appears to be the mod 2 cohomology of Thom spectra. The terms of the resolution are tensor products of Brown-Gitler modules and Steinberg modules introduced by S. Mitchell and S. Read More