Mitigation of lower order harmonics in a grid-connected single-phase PV inverter

In this paper, a simple single-phase grid-connected photovoltaic (PV) inverter topology consisting of a boost section, a low-voltage single-phase inverter with an inductive filter, and a step-up transformer interfacing the grid is considered. Ideally, this topology will not inject any lower order harmonics into the grid due to high-frequency pulse width modulation operation. However, the nonideal factors in the system such as core saturation-induced distorted magnetizing current of the transformer and the dead time of the inverter, etc., contribute to a significant amount of lower order harmonics in the grid current. A novel design of inverter current control that mitigates lower order harmonics is presented in this paper. An adaptive harmonic compensation technique and its design are proposed for the lower order harmonic compensation. In addition, a proportional-resonant-integral (PRI) controller and its design are also proposed. This controller eliminates the dc component in the control system, which introduces even harmonics in the grid current in the topology considered. The dynamics of the system due to the interaction between the PRI controller and the adaptive compensation scheme is also analyzed. The complete design has been validated with experimental results and good agreement with theoretical analysis of the overall system is observed.

Ultranarrow and Widely Tunable Mn2+-Induced Photoluminescence from Single Mn-Doped Nanocrystals of ZnS-CdS Alloys

Extensively studied Mn-doped semiconductor nanocrystals have invariably exhibited photoluminescence over a narrow energy window of width <= 150 meV in the orange-red region and a surprisingly large spectral width (>= 180 meV), contrary to its presumed atomic-like origin. Carrying out emission measurements on individual single nanocrystals and supported by ab initio calculations, we show that Mn PL emission, in fact, can (i) vary over a much wider range (similar to 370 meV) covering the deep green-deep red region and (ii) exhibit widths substantially lower (similar to 60-75 meV) than reported so far, opening newer application possibilities and requiring a fundamental shift in our perception of the emission from Mn-doped semiconductor nanocrystals.

Integrated higher-order pulse-width modulation filter-transformer structure for single-phase static compensator

A power filter is necessary to connect the output of a power converter to the grid so as to reduce the harmonic distortion introduced in the line current and voltage by the power converter. Many a times, a transformer is also present before the point of common coupling. Magnetic components often constitute a significant part of the overall weight, size and cost of the grid interface scheme. So, a compact inexpensive design is desirable. A higher-order LCL-filter and a transformer are increasingly being considered for grid interconnection of the power converter. This study proposes a design method based on a three-winding transformer, that generates an integrated structure that behaves as an LCL-filter, with both the filter inductances and the transformer that are merged into a single electromagnetic component. The parameters of the transformer are derived analytically. It is shown that along with a filter capacitor, the transformer parameters provide the filtering action of an LCL-filter. A single-phase full-bridge power converter is operated as a static compensator for performance evaluation of the integrated filter transformer. A resonant integrator-based single-phase phase locked loop and stationary frame AC current controller are employed for grid frequency synchronisation and line current control, respectively.

Cantilever resonator with integrated actuation and sensing fabricated using a single step lithography

Micro- and nano-mechanical resonators have been proposed for a variety of applications ranging from mass sensing to signal processing. Often their actuation and/or detection involve external subsystems that are much larger than the resonator itself. We have designed a simple microcantilever resonator with integrated sensor and actuator, facilitating the integration of large arrays of resonators. This unique design can be manufactured with a low-cost fabrication process, involving just a single step of lithography. The bilayer cantilever of gold and silicon dioxide is used as piezoresistive sensor as well as thermal bimorph actuator. The ac current used for actuation and the dc current used for piezoresistive detection are separated in the frequency-domain using a bias-tee circuit configuration. The resonant response is measured by detecting the second harmonic of the actuation current using a lock-in amplifier.

Modeling of temperature and field-dependent electron mobility in a single-layer graphene sheet

In this paper, we address a physics-based analytical model of electric-field-dependent electron mobility (mu) in a single-layer graphene sheet using the formulation of Landauer and Mc Kelvey's carrier flux approach under finite temperature and quasi-ballistic regime. The energy-dependent, near-elastic scattering rate of in-plane and out-of-plane (flexural) phonons with the electrons are considered to estimate mu over a wide range of temperature. We also demonstrate the variation of mu with carrier concentration as well as the longitudinal electric field. We find that at high electric field (>10(6) Vm(-1)), the mobility falls sharply, exhibiting the scattering between the electrons and flexural phonons. We also note here that under quasi-ballistic transport, the mobility tends to a constant value at low temperature, rather than in between T-2 and T-1 in strongly diffusive regime. Our analytical results agree well with the available experimental data, while the methodologies are put forward to estimate the other carrier-transmission-dependent transport properties.

Transverse single spin asymmetry in e plus p(up arrow) -> e plus J/psi plus X and transverse momentum dependent evolution of the Sivers function

We extend our analysis of transverse single spin asymmetry in electroproduction of J/psi to include the effect of the scale evolution of the transverse momentum dependent (TMD) parton distribution functions and gluon Sivers function. We estimate single spin asymmetry for JLab, HERMES, COMPASS, and eRHIC energies using the color evaporation model of charmonium production, using an analytically obtained approximate solution of TMD evolution equations discussed in the literature. We find that there is a reduction in the asymmetry compared with our predictions for the earlier case considered by us, wherein the Q(2) dependence came only from DGLAP evolution of the unpolarized gluon densities and a different parametrization of the TMD Sivers function was used.

Generation of extended light-sheets for single and multi-photon fluorescence microscopy

We theoretically propose and computationally demonstrate the generation of extended light-sheet for fluorescence microscopy. This is made possible by the introduction of a specially designed double-window spatial filter that allows the light to pass through the periphery and center of a cylindrical lens. When illuminated with a plane wave, the proposed filter results in an extended depth-of-focus along with side-lobes which are due to other interferences in the transverse focal plane. Computational studies show a maximum extension of light-sheet by 3.38 times for single photon excitation and 3.68 times for multiphoton excitation as compared to state-of-art single plane illumination microscopy system. This technique may facilitate the study of large biological specimens (such as Zebrafish embryo and tissue) with high spatial resolution and reduced photobleaching. (C) 2013 AIP Publishing LLC.

Single electron transfer-driven multi-dimensional signal read-out function of TCNQ as an ``off-the-shelf'' detector for cyanide

Herein we report the first applications of TCNQ as a rapid and highly sensitive off-the-shelf cyanide detector. As a proof-of-concept, we have applied a kinetically selective single-electron transfer (SET) from cyanide to deep-lying LUMO orbitals of TCNQ to generate a persistently stable radical anion (TCNQ(center dot-)), under ambient condition. In contrast to the known cyanide sensors that operate with limited signal outputs, TCNQ(center dot-) offers a unique multiple signaling platform. The signal readability is facilitated through multichannel absorption in the UV-vis-NIR region and scattering-based spectroscopic methods like Raman spectroscopy and hyper Rayleigh scattering techniques. Particularly notable is the application of the intense 840 nm NIR absorption band to detect cyanide. This can be useful for avoiding background interference in the UV-vis region predominant in biological samples. We also demonstrate the fabrication of a practical electronic device with TCNQ as a detector. The device generates multiorder enhancement in current with cyanide because of the formation of the conductive TCNQ(center dot-).

Kinetic proofreading at single molecular level: aminoacylation of tRNA(Ile) and the role of water as an editor

Proofreading/editing in protein synthesis is essential for accurate translation of information from the genetic code. In this article we present a theoretical investigation of efficiency of a kinetic proofreading mechanism that employs hydrolysis of the wrong substrate as the discriminatory step in enzyme catalytic reactions. We consider aminoacylation of tRNA(Ile) which is a crucial step in protein synthesis and for which experimental results are now available. We present an augmented kinetic scheme and then employ methods of stochastic simulation algorithm to obtain time dependent concentrations of different substances involved in the reaction and their rates of formation. We obtain the rates of product formation and ATP hydrolysis for both correct and wrong substrates (isoleucine and valine in our case, respectively), in single molecular enzyme as well as ensemble enzyme kinetics. The present theoretical scheme correctly reproduces (i) the amplitude of the discrimination factor in the overall rates between isoleucine and valine which is obtained as (1.8x10(2)).(4.33x10(2)) = 7.8x10(4), (ii) the rates of ATP hydrolysis for both Ile and Val at different substrate concentrations in the aminoacylation of tRNA(Ile). The present study shows a non-michaelis type dependence of rate of reaction on tRNA(Ile) concentration in case of valine. The overall editing in steady state is found to be independent of amino acid concentration. Interestingly, the computed ATP hydrolysis rate for valine at high substrate concentration is same as the rate of formation of Ile-tRNA(Ile) whereas at intermediate substrate concentration the ATP hydrolysis rate is relatively low. We find that the presence of additional editing domain in class I editing enzyme makes the kinetic proofreading more efficient through enhanced hydrolysis of wrong product at the editing CP1 domain.

Growth and characterization of L-histidinium 2-nitrobenzoate single crystals: A new NLO material

Crystals of a new nonlinear optical (NLO) material, viz., L-histidinium 2-nitrobenzoate (LHNB) (1) were grown by slow evaporation of an aqueous solution containing equimolar concentrations of L-histidine and 2-nitrobenzoic acid. The structure of the title compound which crystallizes in the non-centrosymmetric monoclinic space group P2(1) was elucidated using single crystal X-ray intensity data. The UV-Vis-NIR spectrum of 1 reveals its transparent nature while the vibrational spectra confirm the presence of the functional groups in 1. The thermal stability and second harmonic generation (SHG) conversion efficiency of 1 were also investigated. (C) 2012 Elsevier GmbH. All rights reserved.

Block Sparse Estimator for Grid Matching in Single Snapshot DoA Estimation

In this work, the grid mismatch problem for a single snapshot direction of arrival estimation problem is studied. We derive a Bayesian Cramer-Rao bound for the grid mismatch problem with the errors in variables model and propose a block sparse estimator for grid matching and sparse recovery.

Single-step synthesis of internally functionalizable hyperbranched polyethers

Radical catalyzed thiol-ene reaction has become a useful alternative to the Huisgen-type azide-yne click reaction as it helps expand the variability in reaction conditions as well as the range of clickable entities. In this study, the direct generation of a hyperbranched polyether (HBPE) having decyl units at the periphery and a pendant allyl group on every repeat unit of the polymer backbone is described; the allyl groups serve as a reactive handle for postpolymerization modifications and permits the generation of a variety of internally functionalized HBPEs. In this design, the AB(2) monomer carries two decylbenzyl ether units (B-functionality), an aliphatic OH (A-functionality) and a pendant allyl group within the spacer segment; polymerization of the monomer readily occurs at 150 degrees C via melt transetherification process by continuous removal of 1-decanol under reduced pressure. The resulting HBPE has a hydrophobic periphery due to the presence of numerous decyl chains, while the allyl groups that remain unaffected during the melt polymerization provides an opportunity to install a variety of functional groups within the interior; thiol-ene click reaction with two different thiols, namely 3-mercaptopropionic acid and mercaptosuccinic acid, generated interesting amphiphilic structures. Preliminary field emission scanning electron microscope (FESEM) and Atomic Force Microscopy (AFM) imaging studies reveal the formation of fairly uniform spherical aggregates in water with sizes ranging from 200 to 400 nm; this suggests that these amphiphilic HBPs is able to reconfigure to generate jellyfish-like conformations that subsequently aggregate in an alkaline medium. The internal allyl functional groups were also used to generate intramolecularly core-crosslinked HBPEs, by the use of dithiol crosslinkers; gel permeation chromatography traces provided clear evidence for reduction in the size after crosslinking. In summary, we have developed a simple route to prepare core-clickable HBPEs and have demonstrated the quantitative reaction of the allyl groups present within the interior of the polymers; such HB polymeric systems that carry numerous functional groups within the core could have interesting applications in analyte sequestration and possibly sensing, especially from organic media. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4125-4135

Generation of Ligand Specificity and Modes of Oligomerization in beta-Prism I Fold Lectins

beta-Prism I fold lectins constitute one of the five widely occurring structural classes of plant lectins. Each single domain subunit is made up of three Greek key motifs arranged in a threefold symmetric fashion. The threefold symmetry is not reflected in the sequence except in the case of the lectin from banana, a monocot, which carries two sugar-binding sites instead of the one in other lectins of known three-dimensional structure, all from dicots. This is believed to be a consequence of the different evolutionary paths followed by the lectin in monocots and dicots. The galactose-specific lectins among them have two chains produced by posttranslational proteolysis and contain three aromatic residues at the binding site. The extended binding sites of galactose- and mannose-specific lectins have been thoroughly characterized. Ligand binding at the sites involves both conformational selection and induced fit. Molecular plasticity of some of the lectins in the family has been characterized. The plasticity appears to be such as to promote variability in quaternary association which could be dimeric, tetrameric, or octameric. Structural and evolutionary reasons for the variability have been explored, and the relation of oligomerization to ligand binding and conformational selection investigated.

Exploration of deleterious single nucleotide polymorphisms in the components of human P bodies: An in silico approach

P bodies are 100-300 nm sized organelles involved in mRNA silencing and degradation. A total of 60 human proteins have been reported to localize to P bodies. Several human SNPs contribute to complex diseases by altering the structure and function of the proteins. Also, SNPs alter various transcription factors binding, splicing and miRNA regulatory sites. Owing to the essential functions of P bodies in mRNA regulation, we explored computationally the functional significance of SNPs in 7 P body components such as XRN1, DCP2, EDC3, CPEB1, GEMIN5, STAU1 and TRIM71. Computational analyses of non-synonymous SNPs of these components was initiated using well utilized publicly available software programs such as the SIFT, followed by PolyPhen, PANTHER, MutPred, I-Mutant-2.0 and PhosSNP 1.0. Functional significance of noncoding SNPs in the regulatory regions were analysed using FastSNP. Utilizing miRSNP database, we explored the role of SNPs in the context that alters the miRNA binding sites in the above mentioned genes. Our in silico studies have identified various deleterious SNPs and this cataloguing is essential and gives first hand information for further analysis by in vitro and in vivo methods for a better understanding of maintenance, assembly and functional aspects of P bodies in both health and disease. (C) 2013 Elsevier B.V. All rights reserved.

Optimisation of an asymmetric polymerase chain reaction assay for the amplification of single-stranded DNA from Wuchereria bancrofti for electrochemical detection

Single-stranded DNA (ssDNA) is a prerequisite for electrochemical sensor-based detection of parasite DNA and other diagnostic applications. To achieve this detection, an asymmetric polymerase chain reaction method was optimised. This method facilitates amplification of ssDNA from the human lymphatic filarial parasite Wuchereria bancrofti. This procedure produced ssDNA fragments of 188 bp in a single step when primer pairs (forward and reverse) were used at a 100:1 molar ratio in the presence of double-stranded template DNA. The ssDNA thus produced was suitable for immobilisation as probe onto the surface of an Indium tin oxide electrode and hybridisation in a system for sequence-specific electrochemical detection of W. bancrofti. The hybridisation of the ssDNA probe and target ssDNA led to considerable decreases in both the anodic and the cathodic currents of the system's redox couple compared with the unhybridised DNA and could be detected via cyclic voltammetry. This method is reproducible and avoids many of the difficulties encountered by conventional methods of filarial parasite DNA detection; thus, it has potential in xenomonitoring.