Advanced Electron Beam (EB) Wastewater Treatment System with Low Background X-ray Intensity Generation

Electron beam wastewater treatment is a very effective method for the destruction of organic and microbiological pollutants. The technology was implemented for municipal and textile industry wastewater treatment. Availability of electron accelerators characterized with different operation parameters make the technology applicable for different end-users and also for installation in confined spaces. In such a case, the design of wastewater irradiation room has to take into account the limited space available for shielding construction, which must restrict X-ray emission. Considering construction of an irradiation room for water treatment facility, it is important to focus not only on a stream formation for irradiation to achieve the desired electron penetration, but also on the reduction in x-ray generation. In the presented work, the X-ray field was tested, using modelling and experimental methods. The final results gave an advanced solution, which can be used in the installation of wastewater treatment, ballast and other types of origin, providing low cost shield and good radiation protection measures.

A new argument against cooling by convective air eddies formed above sunlit zebra stripes

There is a long-lasting debate about the possible functions of zebra stripes. According to one hypothesis, periodical convective air eddies form over sunlit zebra stripes which cool the body. However, the formation of such eddies has not been experimentally studied. Using schlieren imaging in the laboratory, we found: downwelling air streams do not form above the white stripes of light-heated smooth or hairy striped surfaces. The influence of stripes on the air stream formation (facilitating upwelling streams and hindering horizontal stream drift) is negligible higher than 1–2 cm above the surface. In calm weather, upwelling air streams might form above sunlit zebra stripes, however they are blown off by the weakest wind, or even by the slowest movement of the zebra. These results forcefully contradict the thermoregulation hypothesis involving air eddies.

The role of sliding in ice stream formation

Ice streams are bands of fast-flowing ice in ice sheets. We investigate their formation as an example of spontaneous pattern formation, based on positive feedbacks between dissipation and basal sliding. Our focus is on temperature-dependent subtemperate sliding, where faster sliding leads to enhanced dissipation and hence warmer temperatures, weak- ening the bed further, and on a similar feedback driven by basal melt water production. Using a novel thermomechanical model, we show that formation of a steady pattern of fast and slow flow can occur through the downstream amplification of noise in basal conditions. This process can lead to the establishment of a clearly defined ice stream separated from slowly flowing, cold-based ice ridges by narrow shear margins. Our model is also able to predict the downstream widening of ice streams due to dissipation and heat transport in these margins. We also show that downward advection of cold ice induced by accelerated sliding is the primary stabilizing mechanism that can suppress ice steam formation altogether, and give an approximate, analytical criterion for pattern formation.

Ice stream formation

<div>Ice streams are the arteries through which a large fraction of the ice lost from Antarctica is discharged. With the introduction of "higher order" mechanics, the representation of ice streams in ice sheet models appears to have become more robust, eliminating previously ubiquitous grid effects. The detailed processes that control ice stream formation --- and the minimal ingredients that a model requires to represent them faithfully --- remain incompletely explored. Here we focus on "pure" ice streams, not confined to topographic troughs. We study two mechanisms that can cause their formation through feedbacks between enhanced dissipation and faster sliding, and study the minimal model capable of reproducing both mechanisms. In the first mechanism, increased dissipation raises basal temperature before the melting point is reached, and subtemperate sliding is in turn facilitated by these higher temperatures, leading to yet more dissipation. This mechanism has received very limited attention in the literature, and is not fully incorporated in at least some commonly used ice sheet model. The second, better-studied mechanism involves basal effective pressure rather than temperature as the degree of freedom that creates a positive feedback: increased dissipation produces additional meltwater. Draining that excess water requires a lower effective pressure in typical "distributed" draiange ssytems. Reduced effective pressure in turn leads to faster sliding, and yet more dissipation. The two mechanisms are distinct and one can operate in the absence of the other, but both can cause the formation of ice streams whose trunks have very similar features. Using a novel, hybrid `shallow/"full Stokes" flow' model derived from first principles, we show how accelerated flow due to either feedback leads to advection of cold ice to the bed, and demonstrate that this is the key negative feedback that controls ice steam formation due to its role in cooling the bed. Downward advection occurs both along the axis of the incipient ice stream, and in the transverse plane. There, a significant secondary flow towards the ice stream centre develops, which is of equal importance to along-flow advection in controlling heat transport. Our model is unique in its ability to fully resolve that secondary flow while still using the "shallowness" of the flow to simplify computations of ice stream physics. The formation of ice streams can be understood as "spatial" instabilities in which small-scale structure is amplified in the downflow direction, for which we derive an analytical criterion. Our model self-consistently predicts the formation of a sharply-defined ice stream margin and very cold-bedded ice ridges over a relatively short downstream distance from the onset of patterning for both mechanisms. The model also shows how basal dissipation in the margin leads to appreciable stream widening in the downstream direction, while englacial dissipation in combination with advection can lead to a pronounced peak in basal water supply some distance inside the margins. We demonstrate additionally that the emergent patterns can be unstable in time, and identify the properties required of a model that can handle such temporal instabilities.</div>

Self-organization in brain tumors: how cell morphology and cell density influence glioma pattern formation

Modeling cancer cells is essential to better understand the dynamic nature of brain tumors and glioma cells, including their invasion of normal brain. Our goal is to study how the morphology of the glioma cell influences the formation of patterns of collective behavior such as flocks (cells moving in the same direction) or streams (cells moving in opposite direction) referred to as oncostream. We have observed experimentally that the presence of oncostreams correlates with tumor progression. We propose an original agent-based model that considers each cell as an ellipsoid. We show that stretching cells from round to ellipsoid increases stream formation.A systematic numerical investigation of the model was implemented in ℝ2. We deduce a phase diagram identifying key regimes for the dynamics (e.g. formation of flocks, streams, scattering). Moreover, we study the effect of cellular density and show that, in contrast to classical models of flocking, increasing cellular density reduces the formation of flocks. We observe similar patterns in ℝ3 with the noticeable difference that stream formation is more ubiquitous compared to flock formation.Author summarySelf-organization is the formation of large-scale multicellular patterns that result exclusively from the interactions amongst constituent single cells. To establish the existence of self-organization in brain tumors we used agent-based modeling based on data extracted from static and dynamic genetically engineered mouse glioma models. Implementation of our model in ℝ2 identifies the dynamics that lead to formation of flocks (cells moving in a single direction), streams (cells moving in two directions), and cells moving as swarms or scattering. Increasing cellular density reduced formation of flocks and increased the formation of streams both in ℝ2 and in ℝ3. These results demonstrate the detailed mechanism leading to self-organization in brain tumors. As increasing density of oncostreams correlates with tumor malignancy, we establish a pathophysiological link between self-organization of glioma tumors and glioma malignancy. We propose the dismantling of oncostreams as a new therapeutic approach to the treatment of brain tumors.

Long-term observations of supraglacial streams on an Arctic glacier

Supraglacial streams are a significant part of the glacial hydrological system and important for understanding glacial hydrology and dynamics. Here we infer factors that influence the long-term development of perennial supraglacial streams, particularly in reference to canyon, incised and surface stream formation. Orthophotos and digital elevation models generated from high-resolution aerial imagery taken with unmanned aerial vehicles or piloted helicopters between 2010 and 2017 were used to compare seven streams on Fountain Glacier, Bylot Island, Canada over time. Results show canyon formation occurs from a combination of fluvial processes and the impact of solar radiation. The greater the discharge or slope, the faster the incision and higher the sinuosity. With greater sinuosity, the distance between the top of the valley banks increases, and cutoffs cause trapezoidal canyon-like valleys to form. Solar radiation causes the backward migration of the valley walls, further enhancing canyon area. Canyons are less likely to occur in areas of low discharge and slope. Less incised channels are also more likely to have water flow jumping the channel banks, changing the channel path. The presence of medial moraines and crevasses also increases rerouting of small streams. Lastly, windblown created snow-plugs may lead to stream diversion.