Methods of increasing the dielectric strength of the accelerating gap in an electron source with a plasma cathode

This work represents the investigations for decreasing acceleration gap breakdown probability of plasma source of electrons SOLO, with grid stabilization of the boundaries of the arc cathode plasma. We increased the distance to the treated target, bent the transportation channel of the electron beam, created additional plasma in the anode space, and increased the beam front. The effect of the above measures on the breakdown probability when the target is exposed of a low-energy electron beam with a power density of up to 0.5 MW/cm2 with a diameter of 2.5 cm was investigated separately. Beam deflection is most effective at relatively long pulse durations of 150 μs and accelerating voltage of 20 kV, rather than a lower one. It was possible to double the maximum power for the same beam transport length applied to a low-melting target. Preionization in the anode proved to be effective for relatively short beams of 15 μs duration.

Experimental Investigation On a Thin Loop Heat Pipe with New Evaporator Structure

This paper presents thin loop heat pipes (tLHPs) with evaporator thickness of 1 mm and a one-way transport length of 200 mm. Grooves and liquid cores are mounted on the evaporator case in the design of a flat evaporator. Liquid cores play a critical role in reducing the pressure drop in the wick and in increasing the path length for heat transfer. A one-dimensional steady model was applied to the design of the tLHP. New tLHPs with thin evaporator (26 × 24 × t1 mm) was fabricated by a three-dimensional printer. Firstly, two kinds of tLHP systems were (type-1) fabricated with different wick materials - micro glass paper and Shirasu porous glass (SPG). Ethanol was selected as a working fluid. The experimental results showed the both LHPs can transport heat up to 12 W. Secondary, the evaporator structure was modified based on the experimental results with the type-1 tLHP, and the tLHP with SPG wick (type-2) was fabricated. The experimental results demonstrated the stable operation. The operation temperature was 83 °C, and the thermal resistance became 1.98 °C/W. The power cycle test at the range of a heat load from 5 to 10 W was also conducted. No temperature hysteresis was observed during three cycles.

Quantitative texture analysis of alluvial gold: primary and secondary signatures

<p>The origin of gold nuggets (Au‐Ag alloys) is not completely understood. They crop out in placer deposits, potentially derived from a primary source (hydrothermal/magmatic). Meteorization, erosion and transport of primary gold deposits result in the liberation of a variety of particle size. Recent investigations suggest that both primary and secondary microstructural features may be preserved and could be related to deformation during transport, recrystallization and primary formation. Besides, the contribution of biological mechanisms (biomineralization) may have played an important role during secondary growth in some nuggets. In many cases, there is no clear evidence to distinguish between supergenic and hypogenic gold, so texture information could be excellent information to constrain the origin. Besides, it has been demonstrated that crystallography controls the de‐alloying processes in gold nuggets. This mechanism, that transforms the primary Au–Ag alloys into pure gold by preferential dissolution of Ag along crystal boundaries, could be determined by variations on texture, a factor never explored before, which may explain the dispersion in de‐alloying values in the same deposit.</p><p> </p><p>In this case we have explored a selection of gold nuggets collected in the W sector of the Iberian Massif (Spain), representing the principal morphological types. As a non-destructive technique neutron diffraction appears as the technique of choice in this case. Beside, neutrons absorption is very low so that large samples could be investigated. Samples were analyzed in transmission at ILL (Grenoble) for texture. Quantitative texture and gold crystallinity was calculated using Rietveld method as implemented in Maud software (EWIMV). Mono- and polycrystalline nuggets and alloy composition were clearly identified in each particle with this technique. Our results show a close correlation between the morphology (i.e. transport length) of the particle and the crystallographic results, particularly for fibrous and discoid shapes (i.e. Zingg, Corey shape factor), what could be used to develop better transport models (distance-to-bedrock sources) and understand multisource gold placer assemblages. </p>

Non-Equilibrium Carrier Transport in Strongly Coupled Quantum Dot Solids and Heterostructures

Understanding and controlling carrier dynamics in colloidal quantum dot (CQD) solids is crucial for unlocking their full potential for optoelectronic applications. The recent development of solution-processing methods to incorporate CQDs into high-mobility semiconducting matrices opens new routes to control simultaneously electronic coupling and packing uniformity in CQD solids. However, the fundamental nature of carrier transport in such systems remains elusive. Here we report the direct visualisation of carrier propagation in metal-halide exchanged PbS CQD solids and quantum-dot-in-perovskite (QDiP) heterostructures via transient absorption microscopy. We reveal three distinct transport regimes: an initial band-like transport persisting over hundreds of femtoseconds, an Auger-assisted sub-diffusive transport before thermal equilibrium is achieved, and a final hopping regime at longer times. The band-like transport was observed to correlate strongly with the extent of carrier delocalisation and the degree of energetic disorder. By tailoring the perovskite content in heterostructures, we obtained a band-like transport length of 90 nm at room temperature and an equivalent diffusivity of up to 106 cm2 s-1 – which is four orders of magnitude higher than the steady-state values obtained for PbS CQD solids. These findings not only shed light on the non-equilibrium dynamics in CQD solids and their influence on carrier transport, but also introduce promising strategies to harness non-equilibrium transport phenomena for more efficient optoelectronic devices.

Eolian megaripple stripes

We present observations, measurements, and modeling of an enigmatic eolian bedform pattern of cross-wind alternating, wind-parallel corridors of megaripples and smaller bedforms (“megaripple stripes”). Megaripple corridors have taller bedforms, longer wavelengths, and coarser surface sediment than intervening smaller bedform corridors. We document examples from Earth (Argentina, Namibia, United States, Iran, Peru, and China) and Mars. Using a reduced complexity model, we show that megaripples and megaripple stripes initiate under the influence of two eolian transport length scales: long-hop saltons and short-hop reptons. The self-organizing stripe pattern manifests in a narrow range of repton concentrations and develops into more typical megaripples as the surface repton concentration increases. We show that the three-dimensional topography of simulated megaripple stripes closely resembles natural megaripple stripes at Oceano Dunes, California, USA. By tracking repton surface concentration and spatial autocorrelation during simulations, we show that the striped pattern initiates from local repton concentrations of sufficient size to serve as megaripple nuclei that seed the striped pattern. Results suggest that megaripple stripes may have a simple and robust formation mechanism.

Direct Numerical Simulations on Jets during the Propagation and Break down of Internal Solitary Waves on a Slope

Jet flows often have an important role in the water environment. The aim of this research is to study the dilution of jets due to complex velocity fields induced by internal solitary waves in stratified water. Direct numerical simulations are used to study vertical jet flows during the propagation and breaking of internal solitary waves (ISWs) with elevation type on a slope. Energy analysis shows that the internal interface is able to absorb kinetic energy from the jet and that for Re < 10,000 with Ri > 3.7, the ISWs can stay stable during the propagation within the presence of jet flows. The vortices jointly induced by the jets and the ISWs are observed at the bottom behind the ISW’s crest. The transport of the jet’s emitted scalar by the ISWs can be divided into two parts; some is transported by the moving interface and the rest by the bottom vortices. The ultimate transport length scales of two types are defined, and it is found that when the center of the jet inlet approaches the slope, the extension of the bottom vortices into the slope will lead to strong mixing. That causes increasing scalar concentration over the slope of the scalar that originated from the jet.

Assessment of arrangements for the detection of radon emanating from soil

CR-39 solid state nuclear track detectors were used to measure radon (222Rn) concentration in the soil near ground surface. The measurements were performed in the campus of the University of Ioannina, using PVC tubes at 0.25 m intervals down to depths of 1.25 m. The track detectors were etched in 7N NaOH solutions at 80°C. The tracks were counted using a microscope - camera - computer system, developed for automatic counting. The results provide evidence for the non-diffusive transport of radon in soils. A transport length of (46.9 ± 3.2) cm was estimated for radon transport near ground surface. Also the variation of soil's radon was correlated to meteorological variations.