Spectral Zero-Crossings: Localization Properties and Applications

We present an analysis of the rate of sign changes in the discrete Fourier spectrum of a sequence. The sign changes of either the real or imaginary parts of the spectrum are considered, and the rate of sign changes is termed as the spectral zero-crossing rate (SZCR). We show that SZCR carries information pertaining to the locations of transients within the temporal observation window. We show duality with temporal zero-crossing rate analysis by expressing the spectrum of a signal as a sum of sinusoids with random phases. This extension leads to spectral-domain iterative filtering approaches to stabilize the spectral zero-crossing rate and to improve upon the location estimates. The localization properties are compared with group-delay-based localization metrics in a stylized signal setting well-known in speech processing literature. We show applications to epoch estimation in voiced speech signals using the SZCR on the integrated linear prediction residue. The performance of the SZCR-based epoch localization technique is competitive with the state-of-the-art epoch estimation techniques that are based on average pitch period.

Lower bounds on Ricci flow invariant curvatures and geometric applications

We consider Ricci flow invariant cones C in the space of curvature operators lying between the cones ``nonnegative Ricci curvature'' and ``nonnegative curvature operator''. Assuming some mild control on the scalar curvature of the Ricci flow, we show that if a solution to the Ricci flow has its curvature operator which satisfies R + epsilon I is an element of C at the initial time, then it satisfies R + epsilon I is an element of C on some time interval depending only on the scalar curvature control. This allows us to link Gromov-Hausdorff convergence and Ricci flow convergence when the limit is smooth and R + I is an element of C along the sequence of initial conditions. Another application is a stability result for manifolds whose curvature operator is almost in C. Finally, we study the case where C is contained in the cone of operators whose sectional curvature is nonnegative. This allows us to weaken the assumptions of the previously mentioned applications. In particular, we construct a Ricci flow for a class of (not too) singular Alexandrov spaces.

Halogen bonds in some dihalogenated phenols: applications to crystal engineering

3,4-Dichlorophenol (1) crystallizes in the tetragonal space group I4(1)/a with a short axis of 3.7926 (9) angstrom. The structure is unique in that both type I and type II Cl.....Cl interactions are present, these contact types being distinguished by the angle ranges of the respective C-Cl....Cl angles. The present study shows that these two types of contacts are utterly different. The crystal structures of 4-bromo-3-chlorophenol (2) and 3-bromo-4-chlorophenol (3) have been determined. The crystal structure of (2) is isomorphous to that of (1) with the Br atom in the 4-position participating in a type II interaction. However, the monoclinic P2(1)/c packing of compound (3) is different; while the structure still has O-H....O hydrogen bonds, the tetramer O-H.....O synthon seen in (1) and (2) is not seen. Rather than a type I Br....Br interaction which would have been mandated if (3) were isomorphous to (1) and (2), Br forms a Br....O contact wherein its electrophilic character is clearly evident. Crystal structures of the related compounds 4-chloro-3-iodophenol (4) and 3,5-dibromophenol (5) were also determined. A computational survey of the structural landscape was undertaken for (1), (2) and (3), using a crystal structure prediction protocol in space groups P2(1)/c and I4(1)/a with the COMPASS26 force field. While both tetragonal and monoclinic structures are energetically reasonable for all compounds, the fact that (3) takes the latter structure indicates that Br prefers type II over type I contacts. In order to differentiate further between type I and type II halogen contacts, which being chemically distinct are expected to have different distance fall-off properties, a variable-temperature crystallography study was performed on compounds (1), (2) and (4). Length variations with temperature are greater for type II contacts compared with type I. The type II Br....Br interaction in (2) is stronger than the corresponding type II Cl....Cl interaction in (1), leading to elastic bending of the former upon application of mechanical stress, which contrasts with the plastic deformation of (1). The observation of elastic deformation in (2) is noteworthy; in that it finds an explanation based on the strengths of the respective halogen bonds, it could also be taken as a good starting model for future property design. Cl/Br isostructurality is studied with the Cambridge Structural Database and it is indicated that this isostructurality is based on shape and size similarity of Cl and Br, rather than arising from any chemical resemblance.

Studies on RF Magnetron Sputtered HfO2 Thin Films for Microelectronic Applications

We investigated the effect of oxygen flow rate during the reactive magnetron sputtering on the compositional, structural, optical and electrical properties of HfO2 films. We also studied the influence of annealing temperature on the structural and electrical properties of optimized HfO2 films of 25 to 30 nm thick. X-ray photoelectron study reveals that the films deposited at 15 SCCM of oxygen flow rate are stoichiometric and have an optical band gap of 5.86 eV. X-ray diffraction indicates that films without oxygen flow are amorphous, and beyond an oxygen flow rate of 5 SCCM exhibit polycrystalline monoclinic structure. At an annealing temperature of 600 degrees C, tetragonal phase was observed besides the monoclinic phase. The dielectric constant of 11 and low leakage currents of 1 x 10(-7) A/cm(2) were achieved for the stoichiometric films. As-deposited films show significant frequency dispersion due to the presence of defect states at the HfO2/Si interface, and it reduces after annealing.

Investigation of orographic features influencing spatial distribution of rainfall over the Western Ghats of India using satellite data

Using remotely sensed Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall and topographic data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM), the impact of oroghraphical aspects such as topography, spatial variability of elevation and altitude of apexes are examined to investigate capacious summer monsoon rainfall over the Western Ghats (WG) of India. TRMM 3B42 v7 rainfall data is validated with Indian Meteorological Department (IMD) gridded rainfall data at 0.5 degrees resolution over the WG. The analysis of spatial pattern of monsoon rainfall with orography of the WG ascertains that the grade of orographic precipitation depends mainly on topography of the mountain barrier followed by steepness of windward side slope and altitude of the mountain. Longer and broader, i.e. cascaded topography, elevated summits and gradually increasing slopes impel the enhancement in precipitation. Comparing topography of various states of the WG, it has been observed that windward side of Karnataka receives intense rainfall in the WG during summer monsoon. It has been observed that the rainfall is enhanced before the peak of the mountain and confined up to the height about 800m over the WG. In addition to this, the spatial distribution of heavy and very heavy rainfall events in the last 14 years has also been explored. Heavy and very heavy rain events on this hilly terrain are categorized with a threshold of precipitation (R) in the range 150>R>120mmday(-1) and exceeding 150mmday(-1) using probability distribution of TRMM 3B42 v7 rainfall. The areas which are prone to heavy precipitation are identified. The study would help policy makers to manage the hazard scenario and, to improve weather predictions on mountainous terrain of the WG.

Multifarious facets of sugar-derived molecular gels: molecular features, mechanisms of self-assembly and emerging applications

The remarkable capability of nature to design and create excellent self-assembled nano-structures, especially in the biological world, has motivated chemists to mimic such systems with synthetic molecular and supramolecular systems. The hierarchically organized self-assembly of low molecular weight gelators (LMWGs) based on non-covalent interactions has been proven to be a useful tool in the development of well-defined nanostructures. Among these, the self-assembly of sugar-derived LMWGs has received immense attention because of their propensity to furnish biocompatible, hierarchical, supramolecular architectures that are macroscopically expressed in gel formation. This review sheds light on various aspects of sugar-derived LMWGs, uncovering their mechanisms of gelation, structural analysis, and tailorable properties, and their diverse applications such as stimuli-responsiveness, sensing, self-healing, environmental problems, and nano and biomaterials synthesis.

Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides

A novel and highly sensitive sensing strategy for the detection of organophosphorus compounds (OPs) based on the catalytic reaction of acetylcholinesterase (AChE) and acetylcholine (ATCh) during the modulated synthesis of silver nanoparticles (AgNPs) has been developed. The enzymatic hydrolysis of ATCh by AChE yields thiocholine (TCh), which induces the aggregation of AgNPs during synthesis, and the absorption peak at 382 nm corresponding to AgNPs decreases. The enzymatic reaction can be regulated by OPs, which can covalently bind to the active site of AChE and decrease the TCh formation, thereby decreasing the aggregation and significantly enhancing the absorption peak at 382 nm. The proposed system achieved good linearity and limits of detection of 0.078 nM and 2.402 nM for trichlorfon and malathion, respectively, by UV-visible spectroscopy. Further, the sensitivity of the proposed system was demonstrated through the determination of OPs in different spiked real samples. The described work shows the potential application for further development of a colorimetric sensor for other OP pesticide detection during the synthesis of AgNPs using enzyme-based assays.

Bolaamphiphiles as carriers for siRNA delivery: From chemical syntheses to practical applications

In this study we have investigated a new class of cationic lipids - ``bolaamphiphiles'' or ``bolas'' - for their ability to efficiently deliver small interfering RNAs (siRNAs) to cancer cells. The bolas of this study consist of a hydrophobic chain with one or more positively charged head groups at each end. Recently, we reported that micelles of the bolas GLH-19 and GLH-20 (derived from vernonia oil) efficiently deliver siRNAs, while having relatively low toxicities in vitro and in vivo. Our previous studies validated that; bolaamphiphiles can be designed to vary the magnitude of siRNA shielding, its delivery, and its subsequent release. To further understand the structural features of bolas critical for siRNAs delivery, new structurally related bolas (GLH-58 and GLH-60) were designed and synthesized from jojoba oil. Both bolas have similar hydrophobic domains and contain either one, in GLH-58, or two, in GLH-60 positively charged head groups at each end of the hydrophobic core. We have computationally predicted and experimentally validated that GLH-58 formed more stable nano sized micelles than GLH-60 and performed significantly better in comparison to GLH-60 for siRNA delivery. GLH-58/siRNA complexes demonstrated better efficiency in silencing the expression of the GFP gene in human breast cancer cells at concentrations of 5 mu g/mL, well below the toxic dose. Moreover, delivery of multiple different siRNAs targeting the HIV genome demonstrated further inhibition of virus production. Published by Elsevier B.V.

A semi-automated, field-portable microscopy platform for clinical diagnostic applications

Clinical microscopy is a versatile diagnostic platform used for diagnosis of a multitude of diseases. In the recent past, many microfluidics based point-of-care diagnostic devices have been developed, which serve as alternatives to microscopy. However, these point-of-care devices are not as multi-functional and versatile as clinical microscopy. With the use of custom designed optics and microfluidics, we have developed a versatile microscopy-based cellular diagnostic platform, which can be used at the point of care. The microscopy platform presented here is capable of detecting infections of very low parasitemia level (in a very small quantity of sample), without the use of any additional computational hardware. Such a cost-effective and portable diagnostic device, would greatly impact the quality of health care available to people living in rural locations of the world. Apart from clinical diagnostics, it's applicability to field research in environmental microbiology has also been outlined. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

One pot auto-ignition based synthesis of novel Sr2CeO4: Ho3+ nanophosphor for photoluminescent applications

Ho3+ (0.25-7 mol%) doped Sr2CeO4 nanophosphors were synthesized by solution combustion method using urea as fuel. The structural properties of the nanophosphors were investigated by powder X-ray diffraction studies (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. UV-Visible and photoluminescence (PL) spectroscopic techniques were used for analysing the optical properties of the nanoparticles. PXRD and TEM results revealed the formation of Sr2CeO4: Ho3+ nanocrystalline particles with orthorhombic crystal structure. From the UV-Vis studies the optical band gap energy found to decrease from 5.9 to 5.74 eV with increase in dopant concentration. The PL spectra exhibit the broad excitation band from 200 to 400 nm which concurs well with the commercial near UV LED. The PL spectra vary with the dopant content due to energy transfer from the host to the activator. In this present work we demonstrate that color tuning of phosphor can be achieved by merely varying the Ho3+ ions concentration. The CIE and CCT chromaticity coordinates suggests Sr2CeO4: Ho3+ nanophosphors may be potentially applicable as promising single - phased phosphors for lighting applications. (C) 2015 Elsevier B.V. All rights reserved.

Synthesis of Eu3+-activated BaMoO4 phosphors and their Judd-Ofelt analysis: Applications in lasers and white LEDs

Eu3+-activated BaMoO4 phosphors were synthesized by the nitrate citrate gel combustion method. The Rietveld refinement analysis confirmed that all the compounds were crystallized in the scheelite-type tetragonal structure with I4(1)/a (No. 88) space group. Photoluminescence (PL) spectra of BaMoO4 phosphor reveals broad emission peaks at 465 and 605 nm, whereas the Eu3+-activated BaMoO4 phosphors show intense 615 nm (D-5(0) -> F-7(2)) emission peak. Judd-Ofelt theory was applied to evaluate the intensity parameters (Omega(2), Omega(4)) of Eu3+-activated BaMoO4 phosphors. The transition probabilities (A(T)), radiative lifetime (tau(rad)), branching ratio (beta), stimulated emission cross-section (sigma(e)), gain bandwidth (sigma(e) x Delta lambda(eff)) and optical gain (sigma(e) x tau(rad)) were investigated by using the intensity parameters. CIE color coordinates confirmed that the BaMoO4 and Eu3+-activated BaMoO4 phosphors exhibit white and red luminescence, respectively. The obtained results revealed that the present phosphors can be a potential candidate for red lasers and white LEDs applications. (C) 2015 Elsevier B.V. All rights reserved.

Review on Tin (II) Sulfide (SnS) Material: Synthesis, Properties, and Applications

Tin (II) sulphide (SnS), a direct band gap semiconductor compound, has recently received great attention due to its unique properties. Because of low cost, absence of toxicity, and good abundance in nature, it is becoming a candidate for future multifunctional devices particularly for light conversion applications. Although the current efficiencies are low, the cost-per-Watt is becoming competitive. At room temperature, SnS exhibits stable low-symmetric, double-layered orthorhombic crystal structure, having a = 0.4329, b = 1.1192, and c = 0.3984nm as lattice parameters. These layer-structured materials are of interest in various device applications due to the arrangement of structural lattice with cations and anions. The layers of cations are separated only by van der Waals forces that provide intrinsically chemically inert surface without dangling bonds and surface density of states. As a result, there is no Fermi level pinning at the surface of the semiconductor. This fact leads to considerably high chemical and environmental stability. Further, the electrical and optical properties of SnS can be easily tailored by modifying the growth conditions or doping with suitable dopants without disturbing its crystal structure.In the last few decades, SnS has been synthesized and studied in the form of single-crystals and thin-films. Most of the SnS single-crystals have been synthesized by Bridgeman technique, whereas thin films have been developed using different physical as well as chemical deposition techniques. The synthesis or development of SnS structures in different forms including single-crystals and thin films, and their unique properties are reviewed here. The observed physical and chemical properties of SnS emphasize that this material could has novel applications in optoelectronics including solar cell devices, sensors, batteries, and also in biomedical sciences. These aspects are also discussed.

Corrosion behaviour of creep-resistant AE42 magnesium alloy-based hybrid composites developed for powertrain applications

The corrosion behaviour of AE42 magnesium alloy and its composites reinforced with Saffil short fibres and SiC particles in various combinations was investigated. The corrosion rate of the unreinforced alloy was the lowest. The composite reinforced with Saffil short fibre alone exhibited slightly lower corrosion rate than the hybrid composites containing both Saffil short fibres and SiC particles. However, there was no specific trend observed in the corrosion rate of the hybrid composites with respect to the SiC particle content. The degradation of corrosion resistance of the composites was mainly attributed to the irregular and loose surface films.

Handling large variations in mechanics: Some applications

There is a need to use probability distributions with power-law decaying tails to describe the large variations exhibited by some of the physical phenomena. The Weierstrass Random Walk (WRW) shows promise for modeling such phenomena. The theory of anomalous diffusion is now well established. It has found number of applications in Physics, Chemistry and Biology. However, its applications are limited in structural mechanics in general, and structural engineering in particular. The aim of this paper is to present some mathematical preliminaries related to WRW that would help in possible applications. In the limiting case, it represents a diffusion process whose evolution is governed by a fractional partial differential equation. Three applications of superdiffusion processes in mechanics, illustrating their effectiveness in handling large variations, are presented.

Dispersible crystalline nanobundles of YPO4 and Ln (Eu, Tb)-doped YPO4: rapid synthesis, optical properties and bio-probe applications

Undoped and Ln(3+) (Eu and Tb)-doped crystalline nanobundles of YPO4 were prepared by a facile microwave-assisted route with water as a solvent and without using any surfactant. TEM investigations reveal that the as-prepared powder consists of lenticular-shaped nanobundles (similar to 100 nm in diameter) made of very small nanorods with diameter less than 10 nm and length varying from 20 to 50 nm. Each nanorod in turn is single crystalline, as revealed by HRTEM imaging. The as-prepared nanobundles are easily dispersible in various solvents, especially water, without any surface functionalization, which is critical for various bio-probe applications like cell and tissue imaging. The Eu- and Tb-doped YPO4 nanobundles show good photoluminescence properties and were further evaluated for their use as fluorescent biolabels. Our results show that HeLa cells labelled with Eu- and Tb-doped YPO4 nanobundles show bright red (Eu) and green (Tb) intracellular luminescence under a confocal microscope. Concentration-and time-dependent MTT cell viability assays show that the nanobundles show low toxicity towards cells which makes them promising in bioimaging field.