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Recursive properties of Dirac and Metriplectic Dirac brackets with Applications
Sonnet Q H Nguyen,Lukasz A Turski
Physics , 2009, DOI: 10.1016/j.physa.2008.09.026
Abstract: In this article, we prove that Dirac brackets for Hamiltonian and non-Hamiltonian constrained systems can be derived recursively. We then study the applicability of that formulation in analysis of some interesting physical models. Particular attention is paid to the feasibility of implementation code for Dirac brackets in Computer Algebra System and analytical techniques for inversion of triangular matrices.
Canonical description of incompressible fluid -- Dirac brackets approach
Sonnet H. Q. Nguyen,Lukasz A. Turski
Physics , 2010, DOI: 10.1016/S0378-4371(99)00194-6
Abstract: We present a novel canonical description of the incompressible fluid dynamics. This description uses the dynamical constraints, in our case reflecting "incompressibility" assumption, and leads to replacement of usual hydrodynamical Poisson brackets for density and velocity fields with Dirac brackets. The resulting equations are then known nonlinear, and non-local in space, equations for incompressible fluid velocity.
On the Dirac Approach to Constrained Dissipative Dynamics
Sonnet Q H Nguyen,Lukasz A Turski
Physics , 2001, DOI: 10.1088/0305-4470/34/43/312
Abstract: In this paper, we propose a novel algebraic and geometric description for the dissipative dynamics. Our formulation bears some similarity to the Poisson structure for non-dissipative systems. We develop a canonical description for constrained dissipative systems through an extension of the Dirac brackets concept, and we present a new formula for calculating Dirac brackets. This formula is particularly useful in the description of dynamical systems with many second-class constraints. After presenting the necessary formal background we illustrate our method on several examples taken from particle dynamics, continuum media physics and wave mechanics.
Campus Mobility for the Future: The Electric Bicycle  [PDF]
I. V. McLoughlin, I. K. Narendra, L. H. Koh, Q. H. Nguyen, B. Seshadri, W. Zeng, C. Yao
Journal of Transportation Technologies (JTTs) , 2012, DOI: 10.4236/jtts.2012.21001
Abstract: Sustainable and practical personal mobility solutions for campus environments have traditionally revolved around the use of bicycles, or provision of pedestrian facilities. However many campus environments also experience traffic congestion, parking difficulties and pollution from fossil-fuelled vehicles. It appears that pedal power alone has not been sufficient to supplant the use of petrol and diesel vehicles to date, and therefore it is opportune to investigate both the reasons behind the continual use of environmentally unfriendly transport, and consider potential solutions. This paper presents the results from a year-long study into electric bicycle effectiveness for a large tropical campus, identifying barriers to bicycle use that can be overcome through the availability of public use electric bicycles.
Sub-50 mK electronic cooling with large-area superconducting tunnel junctions
H. Q. Nguyen,M. Meschke,H. Courtois,J. P. Pekola
Physics , 2014,
Abstract: In electronic cooling with superconducting tunnel junctions, the cooling power is counterbalanced by the interaction with phonons and by the heat flow from the overheated leads. We study aluminium-based coolers that are equipped with a suspended normal metal and an efficient quasi-particle drain. At intermediate temperatures, the phonon bath of the suspended normal metal is cooled. At lower temperatures, by adjusting the junction transparency, we control the injection current, and thus the superconductor temperature. The device shows a strong cooling from 150 mK down to about 30 mK, a factor of five in temperature. We suggest that spatial non-uniformity in the superconductor gap limits the cooling toward lower temperatures.
Non-equilibrium and proximity effects in superconductor-normal metal junctions
V. J. Kauppila,H. Q. Nguyen,T. T. Heikkil?
Physics , 2013, DOI: 10.1103/PhysRevB.88.075428
Abstract: We study the consequences of non-equilibrium heating and inverse proximity effect in normal metal - insulator - superconductor - insulator - normal metal (NISIN) junctions with a simple quasi-one-dimensional model. We especially focus on observables and parameter regions that are of interest in the design of SINIS coolers with quasiparticle traps. We present numerical results calculated by solving the Usadel equation and also present analytical approximations in two limiting cases: a short junction with a non-negligible resistance in both ends and a long junction with a transparent contact at one end.
An induction theorem and nonlinear regularity models
Phan Q. Khanh,Alexander Y. Kruger,Nguyen H. Thao
Mathematics , 2014,
Abstract: A general nonlinear regularity model for a set-valued mapping $F:X\times R_+\rightrightarrows Y$, where $X$ and $Y$ are metric spaces, is considered using special iteration procedures, going back to Banach, Schauder, Lusternik and Graves. Namely, we revise the induction theorem from Khanh, J. Math. Anal. Appl., 118 (1986) and employ it to obtain basic estimates for studying regularity/openness properties. We also show that it can serve as a substitution of the Ekeland variational principle when establishing other regularity criteria. Then, we apply the induction theorem and the mentioned estimates to establish criteria for both global and local versions of regularity/openness properties for our model and demonstrate how the definitions and criteria translate into the conventional setting of a set-valued mapping $F:X\rightrightarrows Y$.
Depth Reconstruction from Sparse Samples: Representation, Algorithm, and Sampling
Lee-Kang Liu,Stanley H. Chan,Truong Q. Nguyen
Computer Science , 2014,
Abstract: The rapid development of 3D technology and computer vision applications have motivated a thrust of methodologies for depth acquisition and estimation. However, most existing hardware and software methods have limited performance due to poor depth precision, low resolution and high computational cost. In this paper, we present a computationally efficient method to recover dense depth maps from sparse measurements. We make three contributions. First, we provide empirical evidence that depth maps can be encoded much more sparsely than natural images by using common dictionaries such as wavelets and contourlets. We also show that a combined wavelet-contourlet dictionary achieves better performance than using either dictionary alone. Second, we propose an alternating direction method of multipliers (ADMM) to achieve fast reconstruction. A multi-scale warm start procedure is proposed to speed up the convergence. Third, we propose a two-stage randomized sampling scheme to optimally choose the sampling locations, thus maximizing the reconstruction performance for any given sampling budget. Experimental results show that the proposed method produces high quality dense depth estimates, and is robust to noisy measurements. Applications to real data in stereo matching are demonstrated.
Adaptive Image Denoising by Targeted Databases
Enming Luo,Stanley H. Chan,Truong Q. Nguyen
Computer Science , 2014, DOI: 10.1109/TIP.2015.2414873
Abstract: We propose a data-dependent denoising procedure to restore noisy images. Different from existing denoising algorithms which search for patches from either the noisy image or a generic database, the new algorithm finds patches from a database that contains only relevant patches. We formulate the denoising problem as an optimal filter design problem and make two contributions. First, we determine the basis function of the denoising filter by solving a group sparsity minimization problem. The optimization formulation generalizes existing denoising algorithms and offers systematic analysis of the performance. Improvement methods are proposed to enhance the patch search process. Second, we determine the spectral coefficients of the denoising filter by considering a localized Bayesian prior. The localized prior leverages the similarity of the targeted database, alleviates the intensive Bayesian computation, and links the new method to the classical linear minimum mean squared error estimation. We demonstrate applications of the proposed method in a variety of scenarios, including text images, multiview images and face images. Experimental results show the superiority of the new algorithm over existing methods.
Influence of Replacement of Concentrate by Beer By-product on Performance of Broilers in Central Vietnam
L.Q. Nguyen,T.Q. Vui,H.T. Hue,D.T. Hang
International Journal of Poultry Science , 2004,
Abstract: In an attempt to lower feed costs of small-holder broiler production in the area of Hue City, Central Vietnam, we replaced part of the commercial concentrate component of the diet by locally available wheat brewing by-product. There were three experimental diets containing either 5, 10 or 15% brewing by-product. The three diets were fed on five small-holder farms to groups of 20 broilers each. The results show that beer by-product enhanced growth and improved feed efficiency. Slaughter carcass traits and the weights of breast and drumstick were enhanced by the feeding of beer by-product. The inclusion of 10% beer by-product in the diet increased the antibody titre against Newcastle disease when the birds were aged 9 weeks, but not when they were aged either 4 or 12 weeks. It is concluded that substitution of brewers` wheat for part of the concentrate component can render broiler diets less expense and more efficient.
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