The electrical activity of Saharan dust as perceived from surface electric field observations

We report on the electric field variations during Saharan dust advection over two atmospheric remote stations in Greece, using synergistic observations of the vertical atmospheric electric field strength (Ez) at ground level and the lidar-derived particle backscatter coefficient profiles. Both parameters were monitored for the first time with the simultaneous deployment of a ground-based field mill electrometer and a multi-wavelength polarization lidar. The field mill time series are processed to extract the diurnal variations of the global electric circuit and remove fast field perturbations due to peak lightning activity. In order to identify the influence of the elevated dust layers on the ground Ez, we extract a localized reference electric field from the time series that reflects the local fair-weather activity. Then, we compare it with the reconstructed daily average behaviour of the electric field and the Saharan dust layers' evolution, as depicted by the lidar. The observed enhancement of the vertical electric field (up to ∼100 V m−1), for detached pure dust layers, suggests the presence of in-layer electric charges. Although higher dust loads are expected to result in such an electric field enhancement, episodic cases that reduce the electric field are also observed (up to ∼60 V m−1). To quantitatively approach our results, we examine the dependency of Ez against theoretical assumptions for the distribution of separated charges within the electrified dust layer. Electrically neutral dust is approximated by atmospheric conductivity reduction, while charge separation areas within electrically active dust layers are approximated as finite-extent cylinders. This physical approximation constitutes a more realistic description of the distribution of charges, as opposed to infinite-extent geometries, and allows for analytical solutions of the electric field strength so that observed variations during the monitored dust outbreaks can be explained.

Study of the Structural, Morphological and Electrical Properties of WO3 Nanopowders which Use as Gas Sensors

nanopowders of tungsten oxide (WO3) have been prepared by high energy ball-milling for various spans of mill time (1-18 h). The crystal structure, surface morphology of the prepared WO3 nanopowder were characterized by X-ray diffraction and scanning electron microscope. Thick films of WO3 nanopowders were prepared by printing painting chemical method to use them as gas sensors for methanol vapor at different operating temperatures, Their I-V characteristics were studied by using devices KEITHLEY 237. The effect of the milling time on the crystal structure, surface morphology, and electrical properties are reported.

Effect of Sintering Temperature on Aluminium Chip Recycling (Al7075) by Powder Metallurgy Process

Al7075 was recycled using the powder metallurgy technique to determine the effect of particle size distribution on the mechanical and microstructure of materials. Analysis of the microstructure, green density and microhardness was conducted to evaluate the performance of the recycled aluminium. The Al7075 was added with 4% of alumina and Al2O3 (3-4μm). The results showed that the green density of recycled Al7075 was lower than the pure Al7075. The average size distribution of the aluminium powder decreased with the increase in the ball mill time. As the temperature of sintering process increased, the green density decreased. The alloy’s microstructure sintered at 650°C has the lowest density, indicating a larger and more frequent porosity. The hardness of the samples with the addition of alumina was higher than the samples without the alumina. Sintering at 650°C also caused the hardness of the sample to increase in the range of approximately 50-62 Hv.

Microstructure and thermoelectric properties of Ga-DOPED SiGe alloys prepared by mechanical alloying and induction hot pressing

Ga -doped SiGe alloys were prepared by high energy ball milling followed by induction hot pressing. The grain size decreases dramatically with increasing mill time, and nanostructured features in the range 3–500 nm were introduced after extensive ball milling for 2–12 h. The bulk alloys hot pressed from 2 h and 6 h dry-milled powders consist of different compositions of micron- to nanosized Si y Ge 100-y, where Ga prefers to locate in the submicron- and nanosized Ge -rich phase and form a modulation-doping structure. The samples hot pressed from 12 h wet-milled powders are more homogeneous in microstructure and composition. Property characterization shows that although Ga -doping leads to p-type conduction, only part of Ga atoms is incorporated as dopant in the SiGe solid solution phase. Samples hot pressed from 2 h and 6 h dry-milled powders have higher power factors, while those hot pressed from 12 h wet-milled powders posses much lower thermal conductivity. The maximum figure of merit (ZT) is 0.51 at 805°C for the 6 h dry-milled and hot pressed sample with the nominal composition Si 80 Ge 18 Ga 2.

Hydrogen Storage Properties of LiNH2/MgH2 Complex Materials with Ti Catalyst by Mechanical Alloying

A LiNH2/MgH2 (1:1) complex was prepared by mechanical alloying and the effects of Ti and TiF3 on the characteristics of hydrogen storage were investigated. It was found that LiMgN and Li2NH phases exist as the main phases in the LiNH2/MgH2 (1:1) complex and that Mg (NH2)2 and NH4HF2 phases appear when TiF3 is added. The onset temperature of hydrogen desorption was reduced with increasing mill time, and the hydrogen saturation absorption temperature for the LiNH2/MgH2 complex decreased about 30°C with the addition of Ti and TiF3. Ti and TiF3 as catalysts are favorable for reducing the dehydrogenation temperature. The addition of TiF3 can also facilitate the increase of hydrogen desorption for the LiNH2/MgH2 (1:1) complex.

Mechanochmical Synthesis of a Mg-Al-H Complex Hydrides

Magnesium hydride is considered as one of the most interesting alternatives for the reversible storage of hydrogen. In this study,The feasibility and reaction process of different materials（Mg and pretreated Al powders(mainly composed of Al and Ni)）were discussed and investigated by thermodynamic calculation. The effects of material proportioning, mill time, mill energy density were also investigated by XRD analysis and TG-DSC technique, and analyzed the essence mechanism. The results show that nano-sized MgH2 and Mg(AlH4)2 could be directly synthesized by pure Mg and pretreated Al powder, The product composite hydrides release 2.7wt% H2 through multi-step decompositions, of which the starting endothermic peaks are as low as 265°C.

Synthesis of Fine Co/ WC Composite and Application to Supersonic Plasma Spraying

Co/ WC composite powders (with 10 wt% content of Co) were synthesized by direct mechanical grinding in a rotary-vibration mill. The powders with different mill time were evaluated. WC and WC/Co composite coatings were prepared by supersonic plasma spraying. The results showed that the milled powders consist of composite particles that were formed in the first 2h of milling. Longer milling times improve the distribution of phases inside the composite particles. The formation of the composite particles involves sequential steps of deformation, fragmentation, cold welding, work hardening and piercing of particles of the hard phase in the soft phase. X-ray spectra of the sprayed coating are shown that only very weak W2C and Co6W6C peaks are observed. Compared with WC coating, the Co/ WC coating is denser, and less large pores within composite coating.

The Effect of Temperature and Mean Cumulative Daily Light Intensity on Fruiting Behavior of Greenhouse-grown Tomato

Determinations were made of the effect of mean daily temperature and cumulative daily light intensity related to planting date on fruiting behavior of greenhouse-grown tomato (Lycopersicon esculentum Mill.). Time to first flowering (FT), flower bud number per cluster (BN/C), fruit number per cluster (FN/C), mean fruit weight, fruit growth period (FGP), and fruit production rate (FPR) in tomato were plotted against mean daily temperature (11 to 28 °C) and mean cumulative daily light intensity (2 to 8 MJ·m−2·d−1) obtained from different planting dates. The FT was negatively related to mean daily temperature at any given mean cumulative daily light intensity. Mean cumulative daily light intensity had a negative sharp and slight curvilinear relationship to FT at lower and higher mean daily temperatures, respectively. At the highest cumulative daily light intensity, BN/C was the greatest at the lowest mean daily temperature, whereas at lower cumulative daily light intensities, BN/C was curvilinearly related to mean daily temperature with the optimum mean daily temperature for BN/C between 13 and 19 °C. Mean cumulative daily light intensity had a positive curvilinear relationship to BN/C at any given mean daily temperature. FN/C increased linearly with mean cumulative daily light intensity with a steeper slope at low mean daily temperatures. At each cumulative daily light intensity, FN/C declined curvilinearly with mean daily temperature. Mean fruit weight was curvilinearly related to mean daily temperature at all mean cumulative daily light intensities. Mean fruit weight was greatest at the highest mean cumulative daily light intensities. There was a curvilinear relationship between mean cumulative daily light intensity and FGP at all mean daily temperatures. The FGP increased curvilinearly as mean daily temperature and mean cumulative light intensity increased. There was a curvilinear increase in FPR with mean cumulative daily light intensity at any given mean daily temperatures. Mean daily temperature also had a curvilinear effect on FPR such that FPR increased up to 25 °C for the lowest cumulative daily light intensity and 22 °C for the highest cumulative daily light intensity and declined thereafter as mean daily temperature increased. Optimum mean daily temperatures for FPR declined as mean cumulative daily light intensity rose. It can be said that the relationships produced in this study can be incorporated into the climate control and fertigation programs of greenhouse tomatoes.

ASSESSING THE EFFECT OF ARMOURSTONE SHAPE AND WEAR

Impacts, abrasion and physico-chemical weathering which sometimes result in rapid changes of armour shape and size can have disastrous consequences for armour stability. This paper draws together the background ideas and some new techniques which have been developed to tackle the prediction of weight loss and shape change of rock armourstone during the life of a coastal structure. The framework proposed is to measure separately the wear resisting material properties of a rock type using a tumbling mill simulation of prototype block degradation. Time on the structure is then related to mill time by a factor which accounts for initial block size and the site specific environmental conditions. A field site in Scotland is used to demonstrate the new image analysis methods for measuring rounding of prototype blocks. The shape analysis results can also be used to calibrate the equivalent wear factor for conditions at that site. Discussion of this framework is extended to dynamically stable design concepts where abrasion losses are faster. Preliminary flume testing in collaboration with H. R. Wallingford indicates that losses in stability due to rounding could be considerable.