Numerical simulation of hydrogen dispersion in the vicinity of a cubical building in stable stratified atmospheres

A computational fluid dynamics (CFD) approach using the standard k-ε turbulence model was applied to simulate hydrogen and methane dispersion around a cubical building. Model results were compared against towing-tank data and other numerical results. The relative impact between hydrogen and methane releases on the building and its surroundings under several stable atmospheric stratifications was assessed. The computed dispersion patterns show a greater risk potential of hydrogen in comparison to methane when released in the vicinity of a building. However, since hydrogen rapidly rises, the impact of a release on the surrounding buildings promptly diminishes. The results also depict complex interactions of hydrogen dispersion patterns due to strong buoyant forces.     

Broadband electroluminescence from reverse breakdown in individual suspended carbon nanotube pn-junctions

Nano Research - There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral emission characteristics that provide important information...     

Mapping wheat response to variations in N,P, Zn,and irrigation using an unmanned aerial vehicle

ABSTRACT

The ability to identify the vulnerable regions within the crop fields assist the farmers in executing the counter plans precisely. In this regard, the unmanned aerial vehicles (UAVs) equipped with red-green-blue and multispectral sensors have added a new dimension in precision agriculture for a broad range of applications. In this study, we present the transformation of an off-the-shelf quadrotor platform into an aerial-crop-observer by adding customized payload capable of delivering high-resolution multispectral imagery. The main objective of the study was to aerially quantify the response of wheat crop under the influence of different elements critical to crop health, i.e. nitrogen (N), phosphorus, zinc, irrigation levels (I), and agro-climatological conditions. Two different experimental plots with different varieties of wheat crop were selected for the study. The vegetation indices were derived after all the necessary radiometric and geometrical corrections. The linear estimation models were developed to assess the grain yield, aboveground biomass, and leaf area index. Our results indicate that high-resolution multispectral imagery acquired through lightweight UAVs offers a standing potential for quantifying aerial observations of wheat crop under a variety of field-inputs. The study is characterized through respective soil analysis, applied field inputs, calibration of aerial image sensors, the agro-climatological observations, and derivations of vegetation indices.     

Concomitant field compensation of spiral turbo spin-echo at 0.55 T

Magnetic Resonance Materials in Physics, Biology and Medicine - Diagnostic-quality neuroimaging methods are vital for widespread clinical adoption of low field MRI. Spiral imaging is an efficient...     

Joint parameter estimation and decoding in a distributed receiver

This paper presents an algorithm for iterative joint channel parameter (carrier phase, Doppler shift, and Doppler rate) estimation and decoding of transmission over channels affected by Doppler shift and Doppler rate using a distributed receiver. This algorithm is derived by applying the sum-product algorithm (SPA) to a factor graph representing the joint a posteriori distribution of the information symbols and channel parameters given the channel output. In this paper, we present two methods for dealing with intractable messages of the SPA. In the first approach, we use particle filtering with sequential importance sampling for the estimation of the unknown parameters. We also propose a method for fine-tuning of particles for improved convergence. In the second approach, we approximate our model with a random walk phase model, followed by a phase tracking algorithm and polynomial regression algorithm to estimate the unknown parameters. We derive the Weighted Bayesian Cramer-Rao Bounds for joint carrier phase, Doppler shift, and Doppler rate estimation, which take into account the prior distribution of the estimation parameters and are accurate lower bounds for all considered signal-to-noise ratio values. Numerical results (of bit error rate and the mean-square error of parameter estimation) suggest that phase tracking with the random walk model slightly outperforms particle filtering. However, particle filtering has a lower computational cost than the random walk model-based method.     

QoS and resource management in distributed interactive multimedia environments

Quality of Service (QoS) is becoming an integral part of current ubiquitous Distributed Interactive Multimedia Environments (DIMEs) because of their high resource and real-time interactivity demands. It is highly influenced by the management techniques of available resources in these cyber-physical environments. We consider QoS and resource management influenced by two most important resources; the computing (CPU) and networking resources. In this paper, we survey existing DIME-relevant QoS and resource management techniques for these two resources, present their taxonomy, compare them, and show their impacts on DIMEs. Finally, we discuss appropriateness of those techniques in a sample DIME scenario.     

Numerical analysis of a magnetic nanoparticle-enhanced microfluidic surface-based bioassay

An innovative magnetic nanoparticle (MNP)-based strategy for enhancing the dynamics and kinetics of surface-based antigen–antibody binding in a microfluidic platform is presented in this study. Finite element technique was employed for quantifying the effect of convection, diffusion, reaction and magnetic field on the detection performance of surface-based bio-assay. It was identified that diffusion is rate limiting when compared with reaction and convection. In order to reduce the detection time, increasing diffusion transport or in general bringing more target antigen towards the surface-bound antibody will be most effective. A novel and simple strategy based on tagging the antigen with MNPs was demonstrated using the numerical model. It was found that local concentration of antigen–MNP complex in the vicinity of sensing surface was increased when magnetic field was used. Different configurations of magnetic field around the microchannel for focusing target antigen towards the sensing surface were simulated and the most optimized configuration was identified. Furthermore, it was quantitatively demonstrated that MNP enhanced the surface-binding kinetics and reduced the detection time of target antigen by almost 42%. Moreover, when compared with physical means of reducing diffusion barrier, MNP-based detection was 35% more efficient. Overall, MNPs enhanced the mass transport of target antigen towards sensing surface which resulted in considerable reduction in detection time. The simulations performed using the developed model will not only help to investigate a wide range of design parameters but also provide generic strategy that can be exploited at the concept stage for designing, optimizing and developing efficient and fast small-scale surface-based bioassays.     

Citric acid modified waste cigarette filters for adsorptive removal of methylene blue dye from aqueous solution

Waste cigarette filters (CFs) were recycled and modified with a nontoxic and low-cost citric acid (CA). The modified CFs were employed in the adsorptive removal of methylene blue (MB) dye from aqueous medium. The influence of pH, contact time, initial dye concentration, and adsorbent dose on adsorption of MB dye was evaluated. The adsorption studies were conducted by employing linear and nonlinear Langmuir and Freundlich isotherm models. The adsorption capacity of CF obtained through linear and nonlinear Langmuir model were 88.02 and 94 mg g⁻¹, which improved up to 163.93 and 168.81 mg g⁻¹, respectively, after the introduction of functional groups in CF-CA. The adsorption kinetics data were well fitted by pseudo-second order kinetics with coefficient of regression (R²) closed to unity. The removal efficiency of CF-CA was 97% at equilibrium time of 4 h. Desorption studies indicated that CF-CA could be regenerated by using HCl (0.1 M) and desorption efficiency was up to 82% upon second cycle of reusability experiment. This study proposed a green and economical use of recycled CFs in dyes wastewater treatment, simultaneously reducing the negative environmental impact due to their improper disposal.     

Aerodynamic response of structures with parametric uncertainties

Uncertainties associated with the load effects and dynamic characteristics of wind-excited structures have been identified and discussed. Based on the available experimental data from laboratory and field study measurements the variability of the parameter space categorized as wind environment and meteorological data, wind-structure interaction and structural properties has been assessed. The probabilistic dynamic response of a wind-excited structyre has been expressed in terms of uncertain parameters. The influence of uncertainty in these parameters has been propagated in accordance with the functional relationships that relate them to the structural response. In this study, the propagation of uncertainty has been obtained by employing the Second-Moment and Monte Carlo simulation techniques. The dynamic response of a chimney subjected to aerodynamic loads is presented to illustrate the treatment of uncertainty in the parameter space. The mean and coefficient of variation of the peak chimney response, in terms of top deflections and associated base bending moments, exhibit close agreement between the Second-Moment and simulation techniques. A sensitivity analysis has been conducted which delineates the relative significance of uncertainty in the several parameters, related to both load effects and structural characteristics, on the overall uncertainty in the aerodynamic response of a chimney. The uncertainty associated with both response components suggests a need for further improvement in the modeling of wind-structure interaction, prediction of natural frequencies and damping, and reduction in the variability of extreme wind estimates. There are immediate applications of the procedures discussed in this paper for a variety of wind-sensitive structures.     

Disproportionation of Q m (0 ≤ m ≤ 4) species in partially devitrified Li2Si2O5 glasses with small amounts of P2O5

The effect of addition of small amounts of P₂O₅ in the lithium disilicate glasses results in the scavenging of lithium metal ions by a phosphate group, Li₃PO₄. As a consequence of the scavenging, the silicate network partially repolymerises. The phosphate group remains intact during heat treatment of the optically clear, X-ray amorphous and slightly nucleated base glasses. However, the relative amounts of the silicate species, Q_m (0 ≤ m ≤ 4), are dependent on the state of the glasses. These amounts, in the optically clear and X-ray amorphous, do not change with heat treatment but they do change, i.e. disproportionation occurs in the slightly nucleated and milky coloured glasses. The disproportionation follows the relation 2Q₃ → Q₂ + Q₄ which is evident from the relative intensity of the different peaks.