The Gentlest Ascent Dynamics

Dynamical systems that describe the escape from the basins of attraction of stable invariant sets are presented and analyzed. It is shown that the stable fixed points of such dynamical systems are the index-1 saddle points. Generalizations to high index saddle points are discussed. Both gradient and non-gradient systems are considered. Preliminary results on the nature of the dynamical behavior are presented

Ab initio study of electron transport in dry poly(G)-poly(C) A-DNA strands

The bias-dependent transport properties of short poly(G)-poly(C) A-DNA strands attached to Au electrodes are investigated with first principles electronic transport methods. By using the non- equilibrium Green's function approach combined with self-interaction corrected density functional theory, we calculate the fully self-consistent coherent I-V curve of various double-strand polymeric DNA fragments. We show that electronic wave-function localization, induced either by the native electrical dipole and/or by the electrostatic disorder originating from the first few water solvation layers, drastically suppresses the magnitude of the elastic conductance of A-DNA oligonucleotides. We then argue that electron transport through DNA is the result of sequence-specific short-range tunneling across a few bases combined with general diffusive/inelastic processes.Comment: 15 pages, 13 figures, 1 tabl

Metamaterials: optical activity without chirality

We report that the classical phenomenon of optical activity, which is traditionally associated with chirality (helicity) of organic molecules, proteins, and inorganic structures, can be observed in artificial planar media which exhibit neither 3D nor 2D chirality. We observe the effect in the microwave and optical parts of the spectrum at oblique incidence to regular arrays of nonchiral subwavelength metamolecules in the form of strong circular dichroism and birefringence indistinguishable from those of chiral three-dimensional media

Block-based feature adaptive compressive sensing for video

This paper focuses on the problem of feature adaptive reconstruction of Compressive Sensing (CS) captured video. In CS, sparse signals can be recovered with high probability of success from very few random samples. Utilizing the temporal correlations between video frames, it is possible to exploit improved CS reconstruction algorithms. Features that relate to the changes between frames are one of the options to benefit reconstruction. However, to choose the optimal feature for every particular region in each frame is difficult, as the true images are unknown in a CS framework. In this paper, we propose two systems for block-based feature adaptive CS video reconstruction, i.e., a Cross Validation (CV) based system and a classification based system. The CV based system achieves the selection of the optimal feature by applying the techniques of CV to the results of extra reconstructions and the classification based system reduces complexity by classifying the CS samples directly, where the optimal feature for the particular class is employed for the reconstruction. Simulations demonstrate that both of our systems work appropriately and their performance is better than uniformly using any single feature for the whole video reconstruction.This work is supported by EPSRC Research Grant (EP/K033700/1); the Natural Science Foundation of China (61401018); Beijing Jiaotong University; the Fundamental Research Funds for the Central Universities (2014JBM149).This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/CIT/IUCC/DASC/PICOM.2015.25

Mapping the magneto-structural quantum phases of Mn3O4

We present temperature-dependent x-ray diffraction and temperature- and field-dependent Raman scattering studies of single crystal Mn3O4, which reveal the novel magnetostructural phases that evolve in the spinels due to the interplay between strong spin-orbital coupling, geometric frustration, and applied magnetic field. We observe a structural transition from tetragonal to monoclinic structures at the commensurate magnetic transition at T2=33K, show that the onset and nature of this structural transition can be controlled with an applied magnetic field, and find evidence for a field-tuned quantum phase transition to a tetragonal incommensurate or spin glass phase.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Lett; typos correcte

Variable-Frequency QPOs from the Galactic Microquasar GRS 1915+105

We show that the galactic microquasar GRS 1915+105 exhibits quasi-periodic oscillations (QPOs) whose frequency varies continuously from 1-15 Hz, during spectrally hard dips when the source is in a flaring state. We report here analyses of simultaneous energy spectra and power density spectra at 4 s intervals. The energy spectrum is well fit at each time step by an optically thick accretion disk plus power law model, while the power density spectrum consists of a varying red noise component plus the variable frequency QPO. The features of both spectra are strongly correlated with one another. The 1-15 Hz QPOs appear when the power law component becomes hard and intense, and themselves have an energy spectrum consistent with the power law component (with root mean square amplitudes as high as 10%). The frequency of the oscillations, however, is most strikingly correlated with the parameters of the thermal disk component. The tightest correlation is between QPO frequency and the disk X-ray flux. This fact indicates that the properties of the QPO are not determined by solely a disk or solely a corona.Comment: Accepted to ApJ Letters, 12 pages, 3 figures, AASTEX forma

Sparsity-fused Kalman filtering for reconstruction of dynamic sparse signals

This article focuses on the problem of reconstructing dynamic sparse signals from a series of noisy compressive sensing measurements using a Kalman Filter (KF). This problem arises in many applications, e.g., Magnetic Resonance Imaging (MRI), Wireless Sensor Networks (WSN) and video reconstruction. The conventional KF does not consider the sparsity structure presented in most practical signals and it is therefore inaccurate when being applied to sparse signal recovery. To deal with this issue, we derive a novel KF procedure which takes the sparsity model into consideration. Furthermore, an algorithm, namely Sparsity-fused KF, is proposed based upon it. The method of iterative soft thresholding is utilized to refine our sparsity model. The superiority of our method is demonstrated by synthetic data and the practical data gathered by a WSN.This work is supported by EPSRC Research Grant (EP/K033700/1); the Natural Science Foundation of China (61401018, U1334202); the State Key Laboratory of Rail Traffic Control and Safety (RCS2014ZT08), Beijing Jiaotong University; the Fundamental Research Funds for the Central Universities (2014JBM149); the Key Grant Project of Chinese Ministry of Education (313006); the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/ICC.2015.724938