DOA estimation of LFM signal based on Krylov subspace method

Telecommunication Systems - Direction of arrival estimation of LFM signal is an essential task in radar, sonar, acoustics and biomedical. In this paper, a short time Fourier transform multi-step...     

Bifurcation of limit cycles in small perturbations of a hyper-elliptic Hamiltonian system with two nilpotent saddles

In this paper we study the first-order Melnikov function for a planar near-Hamiltonian system near a heteroclinic loop connecting two nilpotent saddles. The asymptotic expansion of this Melnikov function and formulas for the first seven coefficients are given. Next, we consider the bifurcation of limit cycles in a class of hyper-elliptic Hamiltonian systems which has a heteroclinic loop connecting two nilpotent saddles. It is shown that this system can undergo a degenerate Hopf bifurcation and Poincarè bifurcation, which emerges at most four limit cycles in the plane for sufficiently small positive ε. The number of limit cycles which appear near the heteroclinic loop is discussed by using the asymptotic expansion of the first-order Melnikov function. Further more we give all possible distribution of limit cycles bifurcated from the period annulus.     

Evaluation of UiO‐66 metal organic framework as an effective sorbent for Curcumin's overdose

Metal organic frameworks (MOFs) UiO‐66 (UiO stands for University of Oslo) and NH₂‐UiO‐66 were prepared and characterized as sorbent (antidotal agents) for curcumin (CUR) adsorption. The structure of products were characterized by X‐ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Attenuated Total Reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR), and N₂ adsorption–desorption measurements. FESEM showed NH₂‐UiO‐66 displayed symmetrical crystals with triangular base pyramid morphology, with the particle size around 100 nm and uniform size distribution. Adsorption capacities of CUR/MOFs with different mass ratios in the feed were investigated in the present study, and this investigation revealed that when the CUR/MOFs with mass ratio was around 0.4, the absorption capacity of NH₂‐UiO‐66 had tended to maximum. Although, functionalization reduced the specific surface area and free volume, introducing polar amine groups could improve the affinity of NH₂‐UiO‐66 respect to CUR. Kinetic studies showed that the kinetic data are well fitted with the pseudo‐ second‐order model. MTT assay revealed that MOFs at the concentration range of 0–560 μg/ml had no cytotoxic effect on the Human Foreskin Fibroblast normal cell line (HFF‐2). These results suggest that these MOFs could be safe as sorbent for adsorb CUR from the body.     

Study of acoustic bubble cluster dynamics using a lattice Boltzmann model

The search for the development of a reliable mathematical model for understanding bubble dynamics behavior is an ongoing endeavor.A long list of complex phenomena underlies the physics of this problem.In the past decades,the lattice Boltzmann method has emerged as a promising tool to address such complexities.In this regard,we have applied a 121-velocity multiphase lattice Boltzmann model to an asymmetric cluster of bubbles in an acoustic field.A problem as a benchmark is studied to check the consistency and applicability of the model.The problem of interest is to study the deformation and coalescence phenomena in bubble cluster dynamics,as well as the screening effect on an acoustic multibubble medium.It has been observed that the LB model is able to simulate the combination of the three aforementioned phenomena for a bubble cluster as a whole and for every individual bubble in the cluster.     

Incorporation of twinning into a crystal plasticity finite element model: Evolution of lattice strains and texture in Zircaloy-2

A crystal plasticity finite element code is developed to model lattice strains and texture evolution of HCP crystals. The code is implemented to model elastic and plastic deformation considering slip and twinning based plastic deformation. The model accounts for twinning reorientation and growth. Twinning, as well as slip, is considered to follow a rate dependent formulation. The results of the simulations are compared to previously published in situ neutron diffraction data. Experimental results of the evolution of the texture and lattice strains under uniaxial tension/compression loading along the rolling, transverse, and normal direction of a piece of rolled Zircaloy-2 are compared with model predictions. The rate dependent formulation introduced is capable of correctly capturing the influence of slip and twinning deformation on lattice strains as well as texture evolution.     

Photodegradation of methyl orange catalyzed by nanoscale zerovalent iron particles supported on natural zeolite

A nanoscale catalyst Fe⁰(FeNPs) supported on the natrolite zeolite nanoparticles (NANPs) is successfully synthesized and characterized by FT-IR, X-ray diffraction (XRD) and scanning electron microscopy (SEM) and thermogravimetric-differential thermal analysis (TG-DTA). The photodegradation of methyl orange (MO) is studied in aqueous suspension containing the catalyst under UV irradiation and H₂O₂. The effect of various reaction parameters such as initial dye concentration, irradiation time, pH, H₂O₂ concentration and catalyst dosage on the decolorization of methyl orange is investigated. The degradation study reveals that the reactivity of the catalysts is in order of: photo-NANPs–FeNPs–H₂O₂ > photo-NANPs–H₂O₂ > photo-NANPs–FeNPs > photo-H₂O₂ > NANPs–FeNPs–H₂O₂. The results show that methyl orange can be effectively decolorized by NANPs–FeNPs via the pseudo-first-order kinetic model.     

What does shape a topological atom?

In this pedagogical communication after demonstrating the legitimacy for using the quantum theory of atoms in molecules (QTAIM) to non-Coulombic systems, Hookean H₂ ⁺/H₃ ²⁺ species are used for AIM analysis. In these systems, in contrast to their Coulombic counterparts, electron density is atom-like and instead of expected two/three topological atoms, just a single topological atom emerges. This observation is used to demonstrate that what is really “seen” by the topological analysis of electron densities is the clustering of electrons. The very trait of monotonic decay of electron density around the “centers” of clustering guarantees the appearance of topological atoms as basin of attraction of the gradient vector field of the electron density. Although observations with Hookean molecules may seem disappointing at first glance, a careful reasoning points to the fact that the QTAIM methodology is extendable to novel domains, by a knowledge of the morphology of underlying densities, beyond the typical Coulombic systems.     

Adaptive low‐energy clustering in slotted beacon‐enabled IEEE 802.15.4 networks

We present, model, and evaluate a novel clustering algorithm running on top of IEEE 802.15.4 wireless sensor networks operating in slotted, beacon‐enabled mode. The adaptive low‐energy clustering algorithm provides randomized sleep and randomized rotation of the cluster‐head role so as to maximize the useful lifetime of the network by improving efficiency and balancing the lifetime of individual nodes. We model the adaptive low‐energy clustering algorithm through probabilistic analysis and show that its parameters can be tuned to extend the network lifetime and reduce the delay and energy overhead imposed by clustering. Copyright © 2014 John Wiley & Sons, Ltd.