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Spatially heterogeneous stressors can alter the performance of indicators of regime shifts
No full textMathematical models together with empirical tests suggest that it may be possible to detect leading indicators, or early warnings, of approaching shifts in ecosystems. Previous studies have often relied on ecological systems where the stressor (e.g. temperature, precipitation) is assumed to act homogeneously in space. Many ecological systems are, however, prone to spatially heterogeneous stresses (or `spatial stressors'), such as grazing, whose strength varies as a function of local vegetation patchiness. Here, we employed three well-studied spatially explicit ecological models to investigate how spatial stressors influence (a) the dynamics and resilience of ecosystems and (b) the robustness of early warnings of approaching ecosystem shifts. Mean-field and numerical simulations of the models suggested that spatial stressors could affect the stability and the number of equilibria of the system. Trends of spatial and temporal indicators were broadly consistent with the theory, i.e. they exhibited increasing trends as the system approached ecosystem shifts. However, in two of the three models, at high levels of spatial stress, spatial indicators could either exhibit trends opposite to those expected by the theory, or show no signals at all. Our results suggest that spatial stressors can interfere with the spatial patterns and thereby with the theoretically expected trends of early warning signals of ecosystem shifts. This highlights, once again, the importance of having a good knowledge of the ecosystem under study to be able to accurately interpret the indicator trends observed
Post-collisional talc-alkaline lamprophyres from the Kadiri greenstone belt: Evidence for the Neoarchean convergence-related evolution of the Eastern Dharwar Craton and its schist belts
No full textLamprophyres from the greenstone belts play a crucial role in deciphering tectonic and geodynamic processes operating during the Archean. This study presents a comprehensive mineralogical and geochemical study of three lamprophyre dykes with talc-alkaline to shoshonitic affinities from the Neoarchean Kadiri schist belt, eastern Dharwar craton, southern India. These rocks display porphyritic-panidiomorphic texture, typical of the lamprophyres with amphibole (magnesio-hornblende) as phenocrysts, biotite as microphenocrysts and feldspar, epidote, titanite and apatite confined to the groundmass. Alteration of biotite to chlorite is observed along with mild deformation in the amphibole phenocrysts. Based on mineralogy and major oxide geochemistry, these rocks are classified as the talc-alkaline lamprophyres. Higher Ba/Nb and low Nb/La points to their derivation from an enriched lithospheric mantle source and higher Th/Yb ratio along with negative TNT (Ti-Nb-Ta) and Zr-Hf anomalies on the primitive mantle (PM) normalized multi-element diagram indicates dehydrated fluids from the foundering slab could be the possible metasomatic agent. Fractionated HREE ratios (Gd-N/Yb-N >1.9) and higher Sm-N/Yb-N suggests that the source region lies in the garnet stability field. Higher than PM Rb/Sr along with positive correlation between K/La and Rb/La reveals presence of metasomatic phlogopite in the source region. Strong negative initial epsilon Nd along with radiogenic (87) Sr/(86) Sr ratios further support an enriched mantle reservoir involved in their genesis. Non-modal batch melting (1-5%) of a mixed source (phlogopite-garnet peridotite) assuming 5% mixing of subducted sediment with ambient mantle wedge (depleted mantle) satisfies the multi-element concentration pattern shown by the Kadiri lamprophyres. The source enrichment can be linked to the accretion-related growth of Dharwar craton and its schist belts during Neoarchean. Our study shows that a majority of lamprophyres associated with the Archean greenstone belts display a shoshonitic character; this highlights the role of subduction-related processes in the growth and evolution of the greenstone belts (C) 2018 Elsevier B.V. All rights reserved
Frequency, Damping, and Flutter Prediction from Aircraft Flight Data Using Autoregressive Model
No full textDemonstration of flutter stability over the design envelope and identification of a safe flight envelope is a prerequisite for operational clearance of any new aircraft design. Generally, in all the flight flutter-testing programs, frequency and modal damping ratios are estimated at each flight-test point, and the trend of variation of frequency and damping is established. Frequencies and damping value estimations have to be as accurate as possible to define the aircraft flutter margin at each test point. In this study, stability parameters are estimated directly from the flight flutter-test time response data using an autoregressive (AR) model, which in turn is used to estimate the frequency and damping. In this paper, the focus is on determining an optimized AR model to ensure the accuracy of the model so that the estimation of stability parameters as well as frequency and damping parameters will be more accurate. Toward that, model order estimation techniques such as Akaike's information criteria and final prediction error were used to predict the model order efficiently. Studies have been presented for different data lengths to prove the capability of this method to produce an accurate spectral estimate even with short data records. This will enable a quick evaluation of spectral estimate and flutter stability parameter using the same AR model, facilitating a quick flight envelope expansion
High Contrast Grating based Intrinsic Fluorescence Enhancing Substrates for Water Contamination Detection
No full textWater quality monitoring has become important in today's scenario due to severe chemical and bacterial contamination in urban and rural water bodies. However, current monitoring methods do not provide fast and reliable results. By using intrinsic fluorescence, microbial contamination and industrial pollutants in water can be monitored in real-time, continuously and at very low concentrations. Intrinsic fluorescence can be enhanced by using High Contrast Gratings (HCGs) spectrally tuned to the fluorescence signatures of pollutants. Compared to metallic gratings which suffer from higher losses especially at lower wavelengths and are easily prone to oxidation, an all dielectric approach can overcome these limitations. HCGs using silicon nitride as grating material on a glass substrate are optimized to detect the presence of tryptophan (a bio-chemical marker for bacterial contamination) and phenanthrene (chemical contaminant) Tryptophan and phenanthrene have a fluorescence emission wavelength of 340 nm and 420 nm respectively. HCGs are optimized to enhance fluorescence emission at both of these wavelengths. The optimized grating parameters for tryptophan are: period: 206 nm, duty cycle: 0.8 and thickness: 226 nm and for phenanthrene are: period: 262 nm, duty cycle: 0.8 and thickness: 265 nm. The optimized HCGs show an electric field enhancement of four and eight times for tryptophan and phenanthrene respectively, concentrated in the air region between the gratings which would result in enhanced fluorescence
Electromechanical Properties and Electric Field Induced Strain of BNT-BT Piezoceramic Material at the MPB Region
No full textCharacterization of the electromechanical properties of (1-x)(Bi0.5Na0.5)TiO3-xBaTiO(3) was attempted over a range of composition near the morphotropic phase boundary (MPB) region. A complete set of electromechanical properties were determined using the results of impedance resonance spectroscopy carried out for the thickness-extension and length-extension modes of the piezoceramic resonators. Room temperature properties depicted a strong compositional dependence while the coupling and piezoelectric properties reaching maxima at x = 0.07 for both the resonance modes. Strain-field hysteresis loops traced at room temperature for the composition x = 0.07 under moderate electric fields revealed high values of recoverable strain and inverse piezoelectric coefficient. (C) 2018 Elsevier Ltd. All rights reserved
Exploring Synergy Effect of Plasma with Lignite Ash on NOx Abatement in a Biofuel Exhaust
No full textThe paper focuses on treating the oxides of nitrogen (NOx) present in a biofuel exhaust in a non-conventional way. The biofuel or biodiesel is obtained from pongamia pinnata, a native Indian plant. While the biodiesel emissions have lesser amount of carbon-monoxide and hydrocarbons, it has increased concentration of NOx which needs to be addressed. Dielectric barrier discharges energized by high voltage repetitive pulses were used to cause the chemical reactions in the plasma reactor. The plasma reactor is a dielectric glass reactor with a concentrically placed screw type electrode. To enhance removal of NOx the plasma treatment reactor was connected in cascade with an adsorbent reactor. Pellets made out of lignite fly ash, an industrial waste product, were used as adsorbents. This is a first-time attempt to study plasma-lignite synergistic effect on exhaust gas treatment. Results indicate significant removal of NOx under the laboratory conditions in the cascaded plasma-adsorbent treatment. (C) 2018 Elsevier Ltd. All rights reserved
The Effect of Introducing Redundancy in a Probabilistic Forwarding Protocol
No full textThis paper is concerned with the problem of broadcasting information from a source node to every node in an ad-hoc network. Flooding, as a broadcast mechanism, involves each node forwarding any packet it receives to all its neighbours. This results in excessive transmissions and thus a high energy expenditure overall. Probabilistic forwarding or gossiping involves each node forwarding a received packet to all its neighbours only with a certain probability p. In this paper, we study the effect of introducing redundancy, in the form of coded packets, into a probabilistic forwarding protocol. Specifically, we assume that the source node has k data packets to broadcast, which are encoded into n >= k coded packets, such that any k of these coded packets are sufficient to recover the original k data packets. Our interest is in determining the minimum forwarding probability p for a ``successful broadcast'', which we take to be the event that the expected fraction of network nodes that receive at least k of the n coded packets is close to 1. We examine, via simulations and analysis of a number of different network topologies (e.g., trees, grids, random geometric graphs), how this minimum forwarding probability, and correspondingly, the expected total number of packet transmissions varies with the amount of redundancy added. Our simulation results indicate that over network topologies that are highly connected, the introduction of redundancy into the probabilistic forwarding protocol is useful, as it can significantly reduce the expected total number of transmissions needed for a successful broadcast. On the other hand, for trees, our analysis shows that the expected total number of transmissions needed increases with redundancy
MRN complex-dependent recruitment of ubiquitylated BLM helicase to DSBs negatively regulates DNA repair pathways
No full textMutations in BLM in Bloom Syndrome patients predispose them to multiple types of cancers. Here we report that BLM is recruited in a biphasic manner to annotated DSBs. BLM recruitment is dependent on the presence of NBS1, MRE11 and ATM. While ATM activity is essential for BLM recruitment in early phase, it is dispensable in late phase when MRE11 exonuclease activity and RNF8-mediated ubiquitylation of BLM are the key determinants. Interaction between polyubiquitylated BLM and NBS1 is essential for the helicase to be retained at the DSBs. The helicase activity of BLM is required for the recruitment of HR and c-NHEJ factors onto the chromatin in S-and G1-phase, respectively. During the repair phase, BLM inhibits HR in S-phase and c-NHEJ in G1-phase. Consequently, inhibition of helicase activity of BLM enhances the rate of DNA alterations. Thus BLM utilizes its pro- and anti-repair functions to maintain genome stability
State dependent Girsanov's controls in time variant reliability estimation in randomly excited dynamical systems
No full textThe problem of time variant reliability estimation of structural dynamical systems subjected to nonstationary, Gaussian, random excitations is considered. The system equations are cast in the form of Ito's stochastic differential equations and the problem of reliability estimation is tackled based on Monte Carlo simulations with a Girsanov transformation based sampling variance reduction scheme. The problem of time variant reliability analysis is first cast as an equivalent problem in series system reliability analysis. Novel contribution of the work lies in proposing procedures to arrive at state dependent (closed loop) Girsanov's controls. Suboptimal Girsanov's controls for estimating the time variant reliability are derived based on component level ideal controls, which are exactly obtainable for linear systems, and, via a local linearization step for nonlinear systems. It is shown that a simplified version of the above closed loop controls, that avoids linearization step for nonlinear systems, can be deduced by minimizing a distance measure similar to what has been done for arriving at open loop controls. Illustrations on multi-degree of freedom linear/nonlinear systems demonstrate the superior performance of the proposed method vis-a-vis the existing open loop control based methods. Limited largescale Monte Carlo simulations are used to verify the acceptability of solutions based on the proposed scheme. (C) 2017 Elsevier Ltd. All rights reserved
Control of vortex state in cobalt nanorings with domain wall pinning centers
No full textMagnetic rings at the mesoscopic scale exhibit new spin configuration states and switching behavior, which can be controlled via geometrical structure, material composition and applied field. Vortex states in magnetic nanorings ensure flux closure, which is necessary for low stray fields in high packing density in memory devices. We performed magnetoresistance measurements on cobalt nanoring devices and showthat by attaching nanowires to the ring, the vortex state can be stabilized. When a square pad is attached to the free end of the wire, the domain wall nucleation field in the nanowire is reduced. In addition, the vortex state persists over a larger range of magnetic fields, and exists at all in-plane orientations of the magnetic field. These experimental findings are well supported by our micromagnetic simulations. (c) 2017 Author(s)