A constant factor approximation algorithm for boxicity of circular arc graphs

Boxicity of a graph G(V, E) is the minimum integer k such that G can be represented as the intersection graph of k-dimensional axis parallel boxes in Rk. Equivalently, it is the minimum number of interval graphs on the vertex set V such that the intersection of their edge sets is E. It is known that boxicity cannot be approximated even for graph classes like bipartite, co-bipartite and split graphs below O(n0.5-ε)-factor, for any ε > 0 in polynomial time unless NP = ZPP. Till date, there is no well known graph class of unbounded boxicity for which even an nε-factor approximation algorithm for computing boxicity is known, for any ε < 1. In this paper, we study the boxicity problem on Circular Arc graphs - intersection graphs of arcs of a circle. We give a (2+ 1/k)-factor polynomial time approximation algorithm for computing the boxicity of any circular arc graph along with a corresponding box representation, where k ≥ 1 is its boxicity. For Normal Circular Arc(NCA) graphs, with an NCA model given, this can be improved to an additive 2-factor approximation algorithm. The time complexity of the algorithms to approximately compute the boxicity is O(mn+n2) in both these cases and in O(mn+kn2) which is at most O(n3) time we also get their corresponding box representations, where n is the number of vertices of the graph and m is its number of edges. The additive 2-factor algorithm directly works for any Proper Circular Arc graph, since computing an NCA model for it can be done in polynomial time.

Channel estimation using minimum bit error rate framework for BPSK signals

We consider the design of a linear equalizer with a finite number of coefficients in the context of a classical linear intersymbol-interference channel with additive Gaussian noise for channel estimation. Previous literature has shown that Minimum Bit Error Rate(MBER) based detection has outperformed Minimum Mean Squared Error (MMSE) based detection. We pose the channel estimation problem as a detection problem and propose a novel algorithm to estimate the channel based on the MBER framework for BPSK signals. It is shown that the proposed algorithm reduces BER compared to an MMSE based channel estimation when used in MMSE or MBER detection.

Spectral-envelope and group-delay models for transient signals—applications to castanets and stop consonants

We present a novel approach to represent transients using spectral-domain amplitude-modulated/frequency -modulated (AM-FM) functions. The model is applied to the real and imaginary parts of the Fourier transform (FT) of the transient. The suitability of the model lies in the observation that since transients are well-localized in time, the real and imaginary parts of the Fourier spectrum have a modulation structure. The spectral AM is the envelope and the spectral FM is the group delay function. The group delay is estimated using spectral zero-crossings and the spectral envelope is estimated using a coherent demodulator. We show that the proposed technique is robust to additive noise. We present applications of the proposed technique to castanets and stop-consonants in speech.

Frequency detection from multiplexed compressed sensing of noisy signals

Signal acquisition under a compressed sensing scheme offers the possibility of acquisition and reconstruction of signals sparse on some basis incoherent with measurement kernel with sub-Nyquist number of measurements. In particular when the sole objective of the acquisition is the detection of the frequency of a signal rather than exact reconstruction, then an undersampling framework like CS is able to perform the task. In this paper we explore the possibility of acquisition and detection of frequency of multiple analog signals, heavily corrupted with additive white Gaussian noise. We improvise upon the MOSAICS architecture proposed by us in our previous work to include a wider class of signals having non-integral frequency components. This makes it possible to perform multiplexed compressed sensing for general frequency sparse signals.

Interferon-gamma- and glucocorticoid-mediated pathways synergize to enhance death of CD4(+) CD8(+) thymocytes during Salmonella enterica serovar Typhimurium infection

Thymic atrophy is known to occur during infections; however, there is limited understanding of its causes and of the cross-talk between different pathways. This study investigates mechanisms involved in thymic atrophy during a model of oral infection by Salmonella enterica serovar Typhimurium (S.typhimurium). Significant death of CD4+CD8+ thymocytes, but not of single-positive thymocytes or peripheral lymphocytes, is observed at later stages during infection with live, but not heat-killed, bacteria. The death of CD4+CD8+ thymocytes is Fas-independent as shown by infection studies with lpr mice. However, apoptosis occurs with lowering of mitochondrial potential and higher caspase-3 activity. The amounts of cortisol, a glucocorticoid, and interferon- (IFN-), an inflammatory cytokine, increase upon infection. To investigate the functional roles of these molecules, studies were performed using Ifn/ mice together with RU486, a glucocorticoid receptor antagonist. Treatment of C57BL/6 mice with RU486 does not affect colony-forming units (CFU), amounts of IFN- and mouse survival; however, there is partial rescue in thymocyte death. Upon infection, Ifn/ mice display higher CFU and lower survival but more surviving thymocytes are recovered. However, there is no difference in cortisol amounts in C57BL/6 and Ifn/ mice. Importantly, the number of CD4+CD8+ thymocytes is significantly higher in Ifn/ mice treated with RU486 along with lower caspase-3 activity and mitochondrial damage. Hence, endogenous glucocorticoid and IFN--mediated pathways are parallel but synergize in an additive manner to induce death of CD4+CD8+ thymocytes during S.typhimurium infection. The implications of this study for host responses during infection are discussed.

A generalized Stein's estimation approach to speech enhancement based on perceptual criteria

We address the problem of speech enhancement using a risk- estimation approach. In particular, we propose the use the Stein’s unbiased risk estimator (SURE) for solving the problem. The need for a suitable finite-sample risk estimator arises because the actual risks invariably depend on the unknown ground truth. We consider the popular mean-squared error (MSE) criterion first, and then compare it against the perceptually-motivated Itakura-Saito (IS) distortion, by deriving unbiased estimators of the corresponding risks. We use a generalized SURE (GSURE) development, recently proposed by Eldar for MSE. We consider dependent observation models from the exponential family with an additive noise model,and derive an unbiased estimator for the risk corresponding to the IS distortion, which is non-quadratic. This serves to address the speech enhancement problem in a more general setting. Experimental results illustrate that the IS metric is efficient in suppressing musical noise, which affects the MSE-enhanced speech. However, in terms of global signal-to-noise ratio (SNR), the minimum MSE solution gives better results.

A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1 center dot 5 M lead (II) methanesulfonate and 0 center dot 9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min (-aEuro parts per thousand 1). During the charge cycle, pure lead (Pb) and lead dioxide (PbO2) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO2 are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g (-aEuro parts per thousand 1) at a load current-density of 20 mA cm (-aEuro parts per thousand 2) with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.

Surface morphology, optical properties and conductivity changes of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) by using additives

The optical properties and electrical conductivity of highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) are reported as a function of the processing additive conditions. The addition of dimethyl sulfoxide (DMSO) increases the conductivity and modifies the dielectric response as observed from the ellipsometric studies. Also the surface roughness and morphology change with the composition of PEDOT: PSS: DMSO and film deposition conditions. The real part of the dielectric function becomes negative in highly conducting samples, indicating the presence of delocalized charge carriers. The real and imaginary parts of the refractive index were determined as a function of wavelength. The results are consistent with the increase in conductivity upon the addition of DMSO.

SARAS: a precision system for measurement of the cosmic radio background and signatures from the epoch of reionization

SARAS is a correlation spectrometer purpose designed for precision measurements of the cosmic radio background and faint features in the sky spectrum at long wavelengths that arise from redshifted 21-cm from gas in the reionization epoch. SARAS operates in the octave band 87.5-175 MHz. We present herein the system design arguing for a complex correlation spectrometer concept. The SARAS design concept provides a differential measurement between the antenna temperature and that of an internal reference termination, with measurements in switched system states allowing for cancellation of additive contaminants from a large part of the signal flow path including the digital spectrometer. A switched noise injection scheme provides absolute spectral calibration. Additionally, we argue for an electrically small frequency-independent antenna over an absorber ground. Various critical design features that aid in avoidance of systematics and in providing calibration products for the parametrization of other unavoidable systematics are described and the rationale discussed. The signal flow and processing is analyzed and the response to noise temperatures of the antenna, reference termination and amplifiers is computed. Multi-path propagation arising from internal reflections are considered in the analysis, which includes a harmonic series of internal reflections. We opine that the SARAS design concept is advantageous for precision measurement of the absolute cosmic radio background spectrum; therefore, the design features and analysis methods presented here are expected to serve as a basis for implementations tailored to measurements of a multiplicity of features in the background sky at long wavelengths, which may arise from events in the dark ages and subsequent reionization era.

Role of electrolyte chemistry on electronic and in vitro electrochemical properties of micro-arc oxidized titania films on Cp Ti

The primary objective of the present work was to study the electronic and in vitro electrochemical properties of micro-arc oxidized titania films on Cp Ti, fabricated independently in various electrolyte solutions consisting of anions such as phosphate (PO43-), borate (B4O72-), citrate (C6H5O73-) and silicate (SiO32-). Further the role of anions on the structural, morphological and compositional properties of the fabricated films was studied. All the titania films were developed by micro-arc oxidation (MAO) technique for a fixed treatment time of 8 min under constant current mode. The surface morphology, elemental distribution, composition and structural characteristics of the films were assessed by scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The thermodynamic and kinetic corrosion properties of the films were studied under simulated body fluid (SBF) conditions (pH 7.4 and 37 degrees C) by conducting chronopotentiometric and potentiodynamic polarization tests. Electrochemical impedance spectroscopy (EIS) coupled with equivalent circuit modelling was carried out to analyse the frequency response and Mott-Schottky analysis was performed to study the semiconducting (electronic) properties of the films. Salt spray fog accelerated corrosion test was conducted for 168h as per ASTM B117 standard to corroborate the corrosion and semiconducting properties of the samples based on the visual examination. The XRD results showed that the transformation from the metastable anatase phase to the thermodynamically stable rutile phase and the crystalline growth of the respective phases were strongly influenced by the addition of anions. The SEM-EDS results demonstrated that the phosphorous (P) content in the films varied from 2.4 at% to 5.0 at% indicating that the amount of P in the films could be modified by adding an appropriate electrolyte additive. The electrochemical corrosion test results showed that the film fabricated in citrate (C6H5O73-) containing electrolyte is thermodynamically and kinetically more stable compared to that of all the others. The results of the Mott-Schottky analysis indicated that all the fabricated films showed an n-type semiconducting behaviour and the film developed in citrate (C6H5O73-) containing electrolyte exhibited the lowest donor concentration and the most negative flat band potential that contributed to its highest corrosion resistance in SBF solution. The results of the salt spray accelerated corrosion tests were in agreement with those obtained from the electrochemical and Mott-Schottky analysis.

Employing synergistic interactions between few-layer WS2 and reduced graphene oxide to improve lithium storage, cyclability and rate capability of Li-ion batteries

The aim of the contribution is to introduce a high performance anode alternative to graphite for lithium-ion batteries (LiBs). A simple process was employed to synthesize uniform graphene-like few-layer tungsten sulfide (WS2) supported on reduced graphene oxide (RGO) through a hydrothermal synthesis route. The WS2-RGO (80:20 and 70:30) composites exhibited good enhanced electrochemical performance and excellent rate capability performance when used as anode materials for lithium-ion batteries. The specific capacity of the WS2-RGO composite delivered a capacity of 400-450 mAh g(-1) after 50 cycles when cycled at a current density of 100 mA g(-1). At 4000 mA g(-1), the composites showed a stable capacity of approximately 180-240 mAh g(-1), respectively. The noteworthy electrochemical performance of the composite is not additive, rather it is synergistic in the sense that the electrochemical performance is much superior compared to both WS2 and RGO. As the observed lithiation/delithiation for WS2-RGO is at a voltage 1.0 V (approximate to 0.1 V for graphite, Li* /Li), the lithium-ion battery with WS2-RGO is expected to possess high interface stability, safety and management of electrical energy is expected to be more efficient and economic. (C) 2013 Elsevier Ltd. All rights reserved.

A Nearly Exact Reformulation of the Girsanov Linearization for Stochastically Driven Nonlinear Oscillators

The Girsanov linearization method (GLM), proposed earlier in Saha, N., and Roy, D., 2007, ``The Girsanov Linearisation Method for Stochastically Driven Nonlinear Oscillators,'' J. Appl. Mech., 74, pp. 885-897, is reformulated to arrive at a nearly exact, semianalytical, weak and explicit scheme for nonlinear mechanical oscillators under additive stochastic excitations. At the heart of the reformulated linearization is a temporally localized rejection sampling strategy that, combined with a resampling scheme, enables selecting from and appropriately modifying an ensemble of locally linearized trajectories while weakly applying the Girsanov correction (the Radon-Nikodym derivative) for the linearization errors. The semianalyticity is due to an explicit linearization of the nonlinear drift terms and it plays a crucial role in keeping the Radon-Nikodym derivative ``nearly bounded'' above by the inverse of the linearization time step (which means that only a subset of linearized trajectories with low, yet finite, probability exceeds this bound). Drift linearization is conveniently accomplished via the first few (lower order) terms in the associated stochastic (Ito) Taylor expansion to exclude (multiple) stochastic integrals from the numerical treatment. Similarly, the Radon-Nikodym derivative, which is a strictly positive, exponential (super-) martingale, is converted to a canonical form and evaluated over each time step without directly computing the stochastic integrals appearing in its argument. Through their numeric implementations for a few low-dimensional nonlinear oscillators, the proposed variants of the scheme, presently referred to as the Girsanov corrected linearization method (GCLM), are shown to exhibit remarkably higher numerical accuracy over a much larger range of the time step size than is possible with the local drift-linearization schemes on their own.

Versatility of azide in serendipitous assembly of Copper(II) Magnetic Polyclusters

Engineering at the molecular level is one of the most exciting new developments for the generation of functional materials. However, the concept of designing polynuclear extended structures from bottom up is still not mature. Although progress has been made with secondary building units (SBUs) in metal organic frameworks (MOFs), the control seems to be just an illusion when it comes to bridging ligands such as the azide ion. When we say that the azido ligand is versatile in its bridging capabilities, what we mean is that it would be difficult to predict or control its bridging properties. However, this kind of serendipity is not always bad news. For example, scientists have shown that the azido ligand can mediate magnetic exchanges between paramagnetic metals in a predictable fashion (usually depending upon the bonding geometries). Therefore, it is a well-respected ligand in polynuclear assemblies. Serendipitous assemblies offer new magnetic structures that we may not otherwise even think about synthesizing. The azido ligand forms a variety of complexes with copper(II) using different blocking amines or pyridine based ligands. Its structural nature changes upon changing the substitution on amine, as well as the amount of blocking ligand. In principle, if we take any of these complexes and provide more coordination sites to the bridging azido ligands by removing a fraction of the blocking ligands, we can get new complexes with intricate structural networks and therefore different magnetic properties with the same components as used for the parent complex. In this Account, we mainly discuss the development of a number of new topological and magnetic exchange systems synthesized using this concept. Not all of these new complexes can be grouped according to their basic building structures or even by the ratio of the metal to blocking ligand. Therefore, we divided the discussion by the nuclearity of the basic building structures. Some of the complexes with the same nuclearities have very similar or even almost identical basic structures. However, the way these building units are joined together (by the azido bridges) to form the overall extended structures differ almost in every case. The complexes having the Cu-6 core are particularly interesting from a structural point of view. Although they have almost identical basic structures, some of them are extended in three dimensions, but two of them are extended in two dimensions by two different bridging networks. In the complexes having linear Cu-4 basic units, we find that using similar ligands does not always give the same bridging networks even within the basic building structures. These complexes have also enriched the field of molecular magnetism. One of the complexes with a Cu-3 building unit has provided us with the opportunity to study the competing behavior of two different kinds of magnetic exchange mechanism (ferromagnetic and antiferromagnetic) acting simultaneously between two metal ions. Through density functional theory calculations, we showed how they work independently and their additive nature to produce the overall effect. The exciting methodology for the generation of copper(II) polyclusters presented in this Account will provide the opportunity to explore analogous serendipitous assembly of diverse structures with interesting magnetic behavior using other transition metal ions having more than one unpaired electrons.

Epoch extraction based on integrated linear prediction residual using plosion index

Epoch is defined as the instant of significant excitation within a pitch period of voiced speech. Epoch extraction continues to attract the interest of researchers because of its significance in speech analysis. Existing high performance epoch extraction algorithms require either dynamic programming techniques or a priori information of the average pitch period. An algorithm without such requirements is proposed based on integrated linear prediction residual (ILPR) which resembles the voice source signal. Half wave rectified and negated ILPR (or Hilbert transform of ILPR) is used as the pre-processed signal. A new non-linear temporal measure named the plosion index (PI) has been proposed for detecting `transients' in speech signal. An extension of PI, called the dynamic plosion index (DPI) is applied on pre-processed signal to estimate the epochs. The proposed DPI algorithm is validated using six large databases which provide simultaneous EGG recordings. Creaky and singing voice samples are also analyzed. The algorithm has been tested for its robustness in the presence of additive white and babble noise and on simulated telephone quality speech. The performance of the DPI algorithm is found to be comparable or better than five state-of-the-art techniques for the experiments considered.

Excellent Performance of Few-Layer Borocarbonitrides as Anode Materials in Lithium-Ion Batteries

Borocarbonitrides (BxCyNz) with a graphene-like structure exhibit a remarkable high lithium cyclability and current rate capability. The electrochemical performance of the BxCyNz materials, synthesized by using a simple solid-state synthesis route based on urea, was strongly dependent on the composition and surface area. Among the three compositions studied, the carbon-rich compound B0.15C0.73N0.12 with the highest surface area showed an exceptional stability (over 100cycles) and rate capability over widely varying current density values (0.05-1Ag(-1)). B0.15C0.73N0.12 has a very high specific capacity of 710mAhg(-1) at 0.05Ag(-1). With the inclusion of a suitable additive in the electrolyte, the specific capacity improved drastically, recording an impressive value of nearly 900mAhg(-1) at 0.05Ag(-1). It is believed that the solid-electrolyte interphase (SEI) layer at the interface of BxCyNz and electrolyte also plays a crucial role in the performance of the BxCyNz .