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Tunable Optoelectronic Properties of Triply Bonded Carbon Molecules with Linear and Graphyne Substructures
No full textIn this paper we present a detailed computational study of the electronic structure and optical properties of triply bonded hydrocarbons with linear and graphyne substructures, with the aim of identifying their potential in optoelectronic device applications. For this reason, we employed a correlated electron methodology based upon the Pariser-Parr-Pople model Hamiltonian, coupled with the configuration interaction (CI) approach, and studied structures containing up to 42 carbon atoms. Our calculations, based upon large-scale CI expansions, reveal that the linear structures have intense optical absorption at the HOMO-LUMO gap, while the graphyne ones have those at higher energies. Thus, the optoelectronic properties depend on the topology of the graphyne substructures, suggesting that they can be tuned by means of structural modifications. Our results are in very good agreement with the available experimental data
Fe-Dy Nanogranular Thin Films: Investigation of Structural, Microstructural and Magnetic Properties
No full textA series of Few(100) Dy-x(x) thin films with the concentration range x = 6 to 35 were fabricated by dc magnetron sputtering process. X-ray diffraction and TEM studies revealed that films have separate Fe and Dy nanograins and that there is no intermixing of Fe and Dy thus forming nanogranular films. This unmixed behaviour in our thin films is very different from the bulk Fe-Dy alloys where several stoichiometric compounds can be formed. Magnetic properties of the films have been systematically studied. The contribution to the total magnetization is due to the Fe grains and the Dy grains are paramagnetic down to 4 K. The saturation magnetization of all the samples is significantly lower than that of bulk Fe due to the existence of superparamagnetic Fe grains. Upon increasing x, the in-plane magnetic anisotropy is found to decrease and the samples become isotropic. The zero field cooled and field cooled magnetization measurements also confirmed the presence of the superparamagnetic Fe grains
Comments on "High strain rate response of nanofiber interlayered structural composites" [Compos. Struct. 168 (2017) 47-55]
No full textField evaluation of low-cost particulate matter sensors in high-and low-concentration environments
No full textLow-cost particulate matter (PM) sensors are promising tools for supplementing existing air quality monitoring networks. However, the performance of the new generation of low-cost PM sensors under field conditions is not well understood. In this study, we characterized the performance capabilities of a new low-cost PM sensor model (Plan-tower model PMS3003) for measuring PM2.5 at 1 min, 1 h, 6 h, 12 h, and 24 h integration times. We tested the PMS3003 sensors in both low-concentration suburban regions (Durham and Research Triangle Park (RTP), NC, US) with 1 h PM2.5 (mean +/- SD) of 9 +/- 9 and 10 +/- 3 mu g m(-3), respectively, and a high-concentration urban location (Kanpur, India) with 1 h PM2.5 of 36 +/- 17 and 116 +/- 57 mu g m(-3) during monsoon and post-monsoon seasons, respectively. In Durham and Kanpur, the sensors were compared to a research-grade instrument (environmental beta attenuation monitor, E-BAM) to determine how these sensors perform across a range of PM2.5 concentrations and meteorological factors (e.g., temperature and relative humidity, RH). In RTP, the sensors were compared to three Federal Equivalent Methods (FEMs) including two Teledyne model T640s and a Thermo Scientific model 5030 SHARP to demonstrate the importance of the type of reference monitor selected for sensor calibration. The decrease in 1 h mean errors of the calibrated sensors using univariate linear models from Durham (201 %) to Kanpur monsoon (46 %) and post-monsoon (35 %) seasons showed that PMS3003 performance generally improved as ambient PM2.5 increased. The precision of reference instruments (T640: +/- 0.5 mu g m(-3) for 1 h; SHARP: +/- 2 mu g m(-3) for 24 h, better than the E-BAM) is critical in evaluating sensor performance, and beta-attenuation-based monitors may not be ideal for testing PM sensors at low concentrations, as underscored by (1) the less dramatic error reduction over averaging times in RTP against optically based T640 (from 27% for 1 h to 9% for 24 h) than in Durham (from 201% to 15 %); (2) the lower errors in RTP than the Kanpur post-monsoon season (from 35% to 11 %); and (3) the higher T640-PMS3003 correlations (R-2 >= 0.63) than SHARP-PMS3003 (R-2 >= 0.25). A major RH influence was found in RTP (1 h RH = 64 +/- 22 %) due to the relatively high precision of the T640 measurements that can explain up to similar to 30% of the variance in 1 min to 6 h PMS3003 PM2.5 measurements. When proper RH corrections are made by empirical nonlinear equations after using a more precise reference method to calibrate the sensors, our work suggests that the PMS3003 sensors can measure PM2.5 concentrations within similar to 10% of ambient values. We observed that PMS3003 sensors appeared to exhibit a nonlinear response when ambient PM2.5 exceeded similar to 125 mu g m(-3) and found that the quadratic fit is more appropriate than the univariate linear model to capture this nonlinearity and can further reduce errors by up to 11 %. Our results have substantial implications for how variability in ambient PM2.5 concentrations, reference monitor types, and meteorological factors can affect PMS3003 performance characterization
From waste to wealth: High recovery of nutraceuticals from pomegranate seed waste using a green extraction process
No full textWaste pomegranate seed (WPS) from the pomegranate juice industry is an interesting substrate for the food processing industry as it contains high quality oil which is rich in conjugated fatty acids, high quality proteins and dietary fibres. However, the majority of the work reported extraction of only oil and employed organic solvents which decrease the nutritional quality of pomegranate seed protein and fibres. Therefore, in this study, a one pot enzymatic green process was investigated for recovery of high quality oil, food-grade proteins and fibres from WPS. The WPS were treated with protease followed by centrifugation to recover the oil, protein and insoluble fibres in different phases. The mechanism of extraction was confirmed by FTIR-imaging and scanning electron microscopy analysis of WPS. The highest oil recovery of 22.9% (out of which 97.4% in free form) and protein recovery of 13.2% (out of which 90.2% in free form) were obtained, when WPS was incubated with protease at a concentration of 50 U/g for 14 h, at 45 degrees C and pH 7.2. The remaining WPS residue was rich in insoluble fibres (97.6 g per 100 g WPS residue). The protease-derived oil had 2.3% higher content of conjugated fatty acids and 1.4 times higher total phenolic content than the hexane-extracted oil. Moreover, the protease derived oil displayed 4% higher antioxidant activity than the hexane-extracted oil. The extracted free proteins were in protein hydrolysate form and had high values of the essential amino acid index (91.6%), protein efficiency ratio (5) and biological value (88.5) confirming their high quality. The insoluble fibre rich WPS residue possessed improved water and oil holding capacity, glucose absorption capacity and glucose dialysis retardation index compared to raw WPS
Application of kinetic bioluminescence inhibition assay using live cultures of Aliivibrio fischeri for determination of zinc toxicity
No full textVariation in zinc toxicity with variation in environmental conditions was studied using the kinetic bioluminescence inhibition assay conducted with live cultures of Aliivibrio fischeri. A good correlation was observed between the static assay and flash assay for colorless non-turbid samples. Color and turbidity had negligible impact on the flash assay results while the static assay caused artifacts. Naturally occurring water samples showed wide variation in the toxicity profiles. Change in zinc toxicity was determined in response to variation in hardness, alkalinity and other coexisting cations/anions in model lake water and in the presence of a solid matrix. The presence of other anions and cations in model lake water reduced and enhanced zinc toxicity, respectively, due to changes in zinc speciation, and bioluminescence inhibition was well correlated with free zinc ion concentration. Increase in alkalinity and sulfate in model lake water lowered zinc toxicity, whereas increase in ammonium ions enhanced the toxicity. Variation in toxicity with hardness was dependent on the Ca: Mg hardness ratio in the samples. The presence of solid matrix decreased toxicity of the aqueous extracts, and toxicity of the matrix was found to increase with decreasing grain size. Speciation pattern of zinc in the respective fractions, however, revealed no direct relationship between zinc associated with fraction that are considered bioavailable to higher organism and the observed toxicity. This assay may be recommended for toxicity analysis of environmental samples since most of the results obtained correlate well with observations reported in toxicity studies with higher organisms
Superconvergence of a class of expanded discontinuous Galerkin methods for fully nonlinear elliptic problems in divergence form
No full textFor fully nonlinear elliptic boundary value problems in divergence form, improved error estimates are derived in the frame work of a class of expanded discontinuous Galerkin methods. It is shown that the error estimate for the discrete flux in L-2-norm is of order k+1, when piecewise polynomials of degree k >= 1 are used to approximate both potential as well as flux variables. Then, solving a discrete linear elliptic problem in each element locally, a suitable post-processing of the discrete potential is proposed and it is proved that the resulting post-processed potential converges with order of convergence k + 2 in L-2-norm. By choosing stabilizing parameters appropriately, similar results are derived for the expanded HDG methods for nonlinear elliptic problems. (C) 2017 Elsevier B.V. All rights reserved
Experimental study of heat transfer in rarefied gas flow in a circular tube with constant wall temperature
No full textThis paper presents an experimental study of heat transfer in a slightly rarefied gas flowing in a circular tube with constant wall temperature boundary condition. Local temperature measurements are carried out for the first time in rarefied gas flows to investigate into the anomalous values of Nusselt number (Nu) obtained by a previous experimental study (Demsis et al., 2009). The present measurements agree well with the low Nu reported by Demsis et al. (2009) when the Nu is obtained using their procedure; additionally, the measurements reveal the importance of end effects in determining the Nusselt number in rarefied gases. The Nusselt number obtained in the present experiments tends to zero with increasing axial conduction. Nu shows a weak dependence on Knudsen number for the range investigated here (0.001 < Kn < 0.012)
Development of robust extended Kalman filter and moving window estimator for simultaneous state and parameter/disturbance estimation
No full textSimultaneous occurrence of gross errors (outliers/biases/drifts) in the measured signals, and drifting disturbances/parameter variations affecting the system dynamics can lead to biased state estimates, and, in turn, can lead to deterioration in the performance of model-based monitoring and control schemes. In this work, robust recursive and moving window based Bayesian state and parameter estimators are developed that are robust w.r.t. gross errors in the measurements and can simultaneously estimate non-additive unmeasured disturbance/parameter variations. Using Bayes' rule, the update step of Kalman filter (KF) is recast as an optimization problem. The optimization is then modified by replacing the likelihood term in the objective function with cost function defined by an M-estimator. The M-estimators considered in this work are Huber's Fair function and Hampel's redescending estimator. The reformulated KF is then used as a basis for reformulating extended Kalman filter (EKF). This re-formulated EKF is then used for developing robust simultaneous state and parameter estimation schemes. In particular, a robust version of recently proposed moving window based state and parameter estimator [1] has been developed. The resulting formulation can be viewed as a hybrid approach, in which the gross errors in the measurements are dealt with in a passive manner, with an active elimination of model plant mismatch by estimating unmeasured disturbance/parameter variations simultaneously. The efficacy of the proposed robust state and parameter estimators is demonstrated by conducting simulation studies and experimental studies. Analysis of the simulation and experimental results reveal that the proposed robust recursive and moving window based state and parameter estimators significantly reduce or completely nullify the effect of gross errors on the state estimates while simultaneously estimating drifting unmeasured disturbances/parameters. The simulation study also underscores the importance of simultaneous estimation of unmeasured disturbances/parameters while achieving robustness using the M-estimators. Moreover, Hampel's redescending estimator is found to be a better choice of M-estimator than the popular Huber's Fair function, as the redescending estimator can completely nullify the effect of gross errors on the state and parameter estimates. (C) 2018 Elsevier Ltd. All rights reserved
Induction of quiescence (GO) in bone marrow stromal stem cells enhances their stem cell characteristics
No full textSeveral studies have suggested that bone marrow stromal steam cells (BMSC) exist in a quiescent state (GO) within the in vivo niche; however, an explicit analysis of the biology of GO state-BMSC has not been reported. We hypothesized that induction of GO in BMSC might enhance their stem cell properties. Thus, we induced quiescence in BMSC in vitro by (a) suspension culture in a viscous medium or (b) culture on soft polyacrylamide substrate; and examined their molecular and functional phenotype. Induction of GO was confirmed by bromodeoxyuridine (BrdU) labelling and analysis of cell cycle gene expression. Upon reactivation and re-entry into cell cycle, GO state-BMSC exhibited enhanced clonogenic self-renewal, preferential differentiation into osteoblastic rather than adipocytic cells and increased ectopic bone formation when implanted subcutaneously in vivo in immune-deficient mice, compared to asynchronous proliferating (pre-GO) BMSC. Global gene expression profiling revealed reprogramming of the transcriptome during GO state including significant alterations in relevant pathways and expression of secreted factors, suggesting altered autocrine and paracrine signaling by GO state-BMSC and a possible mechanism for enhanced bone formation. GO state-BMSC might provide a clinically relevant model for understanding the in vivo biology of BMSC