Excitation and spectral dependence of the rise and decay time responses of Eu2+- and Dy3+-doped strontium aluminates

Journal of Materials Science: Materials in Electronics - In this paper, we study the phosphorescence rise and decay time responses of Eu2+- and Dy3+-doped strontium aluminates prepared by different...     

High efficiency of methylene blue removal using a novel low-cost acid treated forest wastes,Cupressus semperirens cones: Experimental results and modeling

The removal of methylene blue (MB) from aqueous solutions using sulfuric acid modified Cupressus semperirens cones (H₂SO₄-CSC), was investigated. Results showed that a pH value of 12 was favorable for the adsorption of MB and that the moisture and ash yields are suitable for industrial exploitation. A high porosity value was found, 68.1%. In agreement with its low content of basicity compared to its acidity, the H₂SO4-CSC absorbent had an acidic behavior. Rate constants of pseudo-first-order, pseudo-second-order, and nth kinetic model were determined to analyze the dynamic of the biosorption process; they showed that adsorption kinetics followed a pseudo-second-order and nth kinetic models. Ionic strength was shown to have a negative impact on the biosorption of MB onto H₂SO₄-CSC. The Sips isotherm model was found to be the most relevant to describe MB biosorption onto H₂SO₄-CSC with a correlation factor R²?>?0.999. The biosorption capacity of H₂SO₄-CSC was found to be 460?mg?g^?1 at 10°C and 590?mg?g^?1 at 25°C, confirming biosorbent efficiency for the removal of MB dye from aqueous solutions. Thermodynamic parameters indicated that the biosorption process of MB was endothermic and more effective at high temperatures. The values of ΔG° and ΔH° confirmed that the biosorption of MB onto H₂SO₄-CSC was spontaneous and endothermic in nature. An irregular increase in randomness at the H₂SO₄-CSC–solution interface during the biosorption process was suggested by the positive values of ΔS°.     

An experimental investigation on the rate of CO<Subscript>2</Subscript> absorption into aqueous methyldiethanolamine solutions

In this paper, the CO₂ absorption rates into aqueous solutions of Methydiethanolamine (MDEA) at various concentrations of 1, 2, 3 and 4 M and temperatures varying from 293 to 323 K were measured by using a laboratory stirred reactor. The kinetics experiments were conducted under a pseudo first order regime. The data were analyzed by means of chemical absorption theory and the kinetic parameters associated with the reaction, such as the reaction order and the reaction rate constants, were evaluated. The effect of temperature on the reaction rate constant was assessed and the activation energy was evaluated at about 44.12 kJoule/mol.     

Flocculation and viscoelastic behavior of industrial papermaking suspensions

The effects of the surface charge type and density C496, C492 and A130LMW polyacrylamides (PAMs) on the rheological behavior of real industrial papermaking suspensions were quantitatively related to the degree of flocculation for the same industrial papermaking suspensions. The floc sizes were larger but less dense when anionic PAM was used, and this due to the repulsive forces between the anionic PAM and colloidal particles, leading to the development of open structure flocs of less density. On the other hand, rheological measurements showed that the papermaking suspension is thixotropic with a measurable yield stress. The results showed that the magnitude of the critical stress, τ _c , complex viscosity, η*, elastic modulus, G′, and viscous modulus, G″, depend on the number of interactions between the PAM chains and particle surface and the strength of those interactions. Cationic PAM showed higher values of η*, G′, G″ and τ _c compared to anionic PAM. This behavior is in good agreement with Bingham yield stress, τ _B , adsorption and effective floc density results. Similar to oscillatory measurements, creep measurements also showed that the deformation was much lower for the cationic PAM based suspensions than for the anionic PAM based suspensions. Furthermore, the results revealed that increasing the cationic PAM surface charge decreases the floc size but increases the adsorption rate, elasticity and effective floc density proposing differences in the floc structures, which are not revealed clearly in the Bingham yield stress measurements.     

Kinetic of CO2 absorption and carbamate formation in aqueous solutions of diethanolamine

The absorption rates of CO₂ into aqueous solutions of Diethanolamine (DEA) with varying concentrations from 0.2 to 4M and temperature range from 293 to 323 K were measured by using a laboratory stirred reactor. The CO₂ partial pressure was varied in a range that the reaction would occur in pseudo first order regime. Experimental data were analyzed and the kinetic parameters associated with the reaction were determined. The activation energy for the deprotonation of the intermediate zwitterion was estimated at about 11.4 kcal/mol. The contribution of carbamate formation to the overall absorbed CO₂ was experimentally evaluated and found to be of the order of 100%.     

IARP: An Intelligent ACO-Based Routing Protocol with Multiple Mobile Sinks Support for Wireless Sensor Networks

Wireless Personal Communications - Using a single fixed sink in wireless sensor networks (WSNs) creates the hotspot problem. Recently, the mobile sink technique is considered as a good solution to...     

ECRP: an energy-aware cluster-based routing protocol for wireless sensor networks

Energy conservation is the main issue in wireless sensor networks. Many existing clustering protocols have been proposed to balance the energy consumption and maximize the battery lifetime of sensor nodes. However, these protocols suffer from the excessive overhead due to repetitive clustering resulting in high-energy consumption. In this paper, we propose energy-aware cluster-based routing protocol (ECRP) in which not only the cluster head (CH) role rotates based on energy around all cluster members until the end of network functioning to avoid frequent re-clustering, but also it can adapt the network topology change. Further, ECRP introduces a multi-hop routing algorithm so that the energy consumption is minimized and balanced. As well, a fault-tolerant mechanism is proposed to cope up with the failure of CHs and relay nodes. We perform extensive simulations on the proposed protocol using different network scenarios. The simulation results demonstrate the superiority of ECRP compared with recent and relevant existing protocols in terms of main performance metrics.

     

Interaction of Surface Radiation With Laminar and Turbulent Natural Convection in Tall Vertical Cavities: Analysis and Heat Transfer Correlations

The interaction of surface radiation with laminar and turbulent natural convection in differentially heated vertical cavities, filled with air and of large aspect ratio (greater than 10), is analyzed in this study. The k ? ωSST turbulence model is used for the formulation of the convection fluid flow and heat transfer, while the governing equations are discretized by the finite-volume method. As an extension of the scarce previous studies, more realistic conditions with a wide range of parameters are considered in the performed simulations. The presented results show the effect of surface radiation on streamlines, isotherms, turbulent kinetic energy, and temperature and vertical velocity profiles, as well as on local and on average convective and radiative heat transfer. Globally, it is found that surface radiation has a weak effect on the dynamic and thermal fields in the major part of the cavity; however, some influence in the upper and lower zones of the cavity is observed. For design purposes, accurate correlations are developed for average convective and radiative Nusselt numbers that cover emissivity of surfaces between 0 and 1, cold wall temperature ranging from 263 K to 303 K, temperature difference between vertical walls ranging from 5 K to 40 K, width of the cavity between 2.5 cm and 7.5 cm, and height of the cavity between 0.25 m and 6 m (this leads to a Rayleigh number ranging from 10³ to 2 × 10⁶ and an aspect ratio between 10 and 80).     

Platinum degradation mechanisms in proton exchange membrane fuel cell (PEMFC) system: A review

Proton Exchange Membrane Fuel Cells (PEMFCs) have the perspective to intensely decrease global emission through environmentally-friendly potential. This review paper summarizes the degradation of platinum catalyst layer that has become a significant issue in the improvement of PEMFCs. The review intends to categorise and provide a clear understanding between disintegration and agglomerate that occurs during platinum degradation. In each process, different degradation mechanisms and their migration processes are presented. The improvement in platinum degradation as a function of increasing the performance of PEMFC is established. Prospects for addressing platinum degradation through the exploration of further experimental and numerical research are recommended. Lastly, this paper through recommendation attempts to prevent platinum degradation and reduces high costs associated with the replacement of catalysts in the PEMFCs.     

Properties of flowable sand concretes reinforced by polypropylene fibers

This paper presents an experimental research on fresh and hardened properties of flowable sand concretes (FSC) reinforced by polypropylene fibers (PF). Tests were conducted on both plain and fiber-reinforced FSC. The fresh properties are tested for viscosity using a programmable DV-II?+?viscometer. For the physical and mechanical properties, drying shrinkage, flexural, and compressive strengths, as well as micro-structural analyses have been studied. Results indicate that all studied mixtures have a pseudo-plastic behavior in fresh state and can be well fitted using power law model. Results also confirmed that PF incorporation increases the viscosity and reduces free shrinkage of FSC. In terms of mechanical strength, results show that incorporating PF would enhance flexural strength. However, a reduction in compressive strength is observed.