Comprehensive modeling of mat density effect on duckweed (Lemna minor) growth under controlled eutrophication

The effect of mat density on duckweed (Lemna minor) growth was studied under controlled conditions: 12.5h a day light exposure and 342 mol m(-2) s(-1) light intensity at 20 degrees C. The plant growth was carried out in Hoagland medium for 7 days without harvesting. The results revealed a maximal biomass growth rate of 88 g-dry m(-2) (1,470 g-wet m(-2)) at an optimal initial mat density of 45 g-dry m(-2) (750 g-wet m(-2)), with removal rates for nitrogen (N) and phosphorus (P) of 483 mg-Nm(-2) d(-1) and 128 mg-Pm(-2) d(-1), respectively. A mathematical model that takes into account the mat density was developed in order to simulate the growth of Lemna minor under controlled eutrophication. Based on experiments carried out, the model exhibits a reliability of 89% . The model remains to be validated at the full-scale level.     

Intrinsic growth rate: a new approach to evaluate the effects of temperature, photoperiod and phosphorus-nitrogen concentrations on duckweed growth under controlled eutrophication

A comprehensive model based on a new approach was developed to simulate the duckweed growth under controlled conditions. Contrary to other approaches which use the specific growth rate, this approach uses the intrinsic growth rate which permits to differentiate the effect of duckweed mat density from that of temperature, photoperiod and phosphorus-nitrogen concentrations. The model was calibrated using data from laboratory experiments carried out during the present study and validated using other data from two literature sources. In both cases, the results demonstrated that the model was capable of predicting duckweed growth with a reliability of 95%.     

Global characterization of soft magnetic materials under rotating flux density conditions

Although several authors have proposed different devices to measure the iron loss in magnetic sheets used in the building of electrical machines, few of them take into account the real electromagnetic working context. This paper deals with the possibility of determining the iron loss and the apparent magnetic permeability from the measurement of the flux density in the air gap with the use of the Maxwell's tensor and an analog computer. We propose new methods to obtain the power loss and the magnetic permeability of magnetic samples.     

Stopping of 0.3-1.2 MeV/u protons and alpha particles in Si

The stopping cross sections ε(E) of silicon for protons and alpha particles have been measured over the velocity range 0.3-1.2 MeV/u from a Si//SiO₂//Si (SIMOX) target using the Rutherford backscattering spectrometry (RBS) with special emphasis put on experimental aspects. A detection geometry coupling simultaneously two solid-state Si detectors placed at 165° and 150° relative to each side of the incident beam direction was used to measure the energies of the scattered ions and determine their energy losses within the stopping medium. In this way, the basic energy parameter, E_x, at the Si/SiO₂ interface for a given incident energy E₀ is the same for ions backscattered in the two directions off both the Si and O target elements, and systematic uncertainties in the ε(E) data mainly originating from the target thickness are significantly minimized. A powerful computer code has been elaborated for extracting the relevant ε(E) experimental data and the associated overall uncertainty that amounts to less than 3%. The measured ε(E) data sets were found to be in fair agreement with Paul’s compilation and with values calculated by the SRIM 06 computer code. In the case of ⁴He⁺ ions, experimental data for the γ effective charge parameter have been deduced by scaling the measured stopping cross sections to those of protons crossing the same target with the same velocity, and compared to the predictions of the SRIM 06 computer code. It is found that the γ-parameter values generated by the latter code slightly deviate from experiment over the velocity region around the stopping cross section maximum where strong charge exchanges usually occur.     

Achievement in hydrogen storage on adsorbents with high surface-to-bulk ratio – Prospects for Si-containing matrices

In hydrogen storage, the concept of the reversible capture still remains a major issue to be addressed. The advances in chemical storage provide useful data that demonstrate that purely physical adsorption offer promising prospects, even though the hydrogen uptakes barely attain 11 wt%. The emerging nanotubes, fullerenes, metal-organic frameworks are sophisticated structures that display weak affinity toward hydrogen, and require complex synthesis procedures. Adsorption rather consists of a gas condensation at low temperatures and/or high pressures. That is why the present review is devoted to the most recent achievements in developing novel microporous materials with emphasis on silicon-based structures, aluminosilicates and related materials. Their large availability and low production costs open promising prospects. On aluminosilicates, low Si:Al ratio, high porosity and specific surface area, along with alkali or alkaline-earth exchangeable cations are essential requirements for effective hydrogen adsorption even at room temperature.     

Intrinsic affinity of acid-activated bentonite towards hydrogen and carbon dioxide

The effect of acid activation on bentonite affinity toward carbon dioxide (CO₂) and hydrogen (H₂) was investigated at ambient conditions. Characterization through X-ray diffraction and fluorescence, thermal gravimetric analysis, nitrogen adsorption-desorption isotherms, Fourier Transform Infrared spectroscopy and differential scanning calorimetry allowed correlating newly induced textural and structural features with adsorptive properties. Optimum acid treatment improved the specific surface area and porosity. The resulting decrease in dehydration temperature indicates decay in hydrophilic character. The affinity improvement towards hydrogen was due to Brønsted acidity suppression and surface basicity attenuation, which are essential requirements for adsorption on aluminosilicates (AS) via weak Lewis Acid-Base interactions, but excessive acid attack was detrimental. Low Si/Al surfaces should be suitable for CO₂ capture, while moderately acid-treated clays should be interesting candidates as hydrogen adsorbents. This allows envisaging promising prospects for low-cost AS-based materials intended for selective CO₂-free capture and storage of hydrogen without energy and safety constraints.     

Improvement of flux pinning ability by tungsten oxide nanoparticles added in YBa2Cu3Oy superconductor

In this study, series of superconductor-tungsten oxide (WO₃) nanoparticles composites, YBa₂Cu₃O_7-δ/(WO₃)_x, were produced via the solid-state reaction process. The structural, morphological, chemical compositions, electrical and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) along with EDX system and physical properties measurement system (PPMS), respectively. The XRD, SEM and EDX analyses showed the successful formation of the Y-123 orthorhombic phase. The electrical resistivity measurements proved the occurrence of superconductivity in different samples. The magnetic results showed an improvement of critical current density (J_c) and pinning ability in WO₃ nanoparticles added Y-123 products. The dominant pinning mechanisms and the strength of pinning centers in various sintered products were examined and discussed. The measurements of zero-field-cooled (ZFC) and field-cooled (FC) magnetization versus temperature (M-T) indicated an increase in the magnitude of diamagnetic signal with the addition of WO₃ nanoparticles in the Y-123 superconductor.     

Flux pinning mechanisms of (YBa2Cu3Oy-d)1−x/(Dy2O3)x superconductors (x=0.1 and 0.5 wt%)

Polycrystalline (YBa₂Cu₃O_y-d)_1?x/(Dy₂O₃)_x superconductor samples were produced through the solid-state reaction route and by adding amounts of x = 0.1 and 0.5 wt% of Dy₂O₃ nanoparticles (NP-Dy₂O₃ with a size of about 10 nm) during the second stage of heat treatment. The structural, microstructural, critical current density and pinning properties were investigated using x-ray diffraction, scanning electron microscope, and DC magnetization at various temperatures ranging from 77 down to 10 K and under an applied magnetic field varying between ?6 and +6 Tesla. Both samples crystallize in the orthorhombic structure. It was found that the Dy₂O₃ nanoparticles reside in the grain boundaries. Although the sample with 0.5 wt% NP-Dy₂O₃ is characterized by a low zero resistive temperature of about 78 K that is close to the useful temperature for technological applications, it showed the highest J_c values and the excellent flux pinning capacity. The addition of an appropriate amount of NP-Dy₂O₃ up to 0.5 wt% extends the single bundle pinning regime and retards the liquid vortex regime.