Evaluation of the COSMO model (v5.1) in polarimetric radar space – impact of uncertainties in model microphysics, retrievals and forward operators

Sensitivity experiments with a numerical weather prediction (NWP) model and polarimetric radar forward operator (FO) are conducted for a long-duration stratiform event over northwestern Germany to evaluate uncertainties in the partitioning of the ice water content and assumptions of hydrometeor scattering properties in the NWP model and FO, respectively. Polarimetric observations from X-band radar and retrievals of hydrometeor classifications are used for comparison with the multiple experiments in radar and model space. Modifying the critical diameter of particles for ice-to-snow conversion by aggregation (Dice) and the threshold temperature responsible for graupel production by riming (Tgr), was found to improve the synthetic polarimetric moments and simulated hydrometeor population, while keeping the difference in surface precipitation statistically insignificant at model resolvable grid scales. However, the model still exhibited a low bias (lower magnitude than observation) in simulated polarimetric moments at lower levels above the melting layer (−3 to −13 ∘C) where snow was found to dominate. This necessitates further research into the missing microphysical processes in these lower levels (e.g. fragmentation due to ice–ice collisions) and use of more reliable snow-scattering models to draw valid conclusions.

Biocrude Production from Hydrothermal Liquefaction of Chlorella: Thermodynamic Modelling and Reactor Design

Hydrothermal liquefaction can directly and efficiently convert wet biomass into biocrude with a high heating value. We developed a continuous hydrothermal liquefaction model via Aspen Plus to explore the effects of moisture content of Chlorella, reaction pressure and temperature on thermodynamic equilibrium yields, and energy recoveries of biocrude. We also compared the simulated biocrude yield and energy recoveries with experiment values in literature. Furthermore, vertical and horizontal transportation characteristics of insoluble solids in Chlorella were analyzed to determine the critical diameters that could avoid the plugging of the reactor at different flow rates. The results showed that the optimum moisture content, reaction pressure, and reaction temperature were 70–90 wt%, 20 MPa, and 250–350 °C, respectively. At a thermodynamic equilibrium state, the yield and the energy recovery of biocrude could be higher than 56 wt% and 96%, respectively. When the capacity of the hydrothermal liquefaction system changed from 100 to 1000 kg·h−1, the critical diameter of the reactor increased from 9 to 25 mm.

Aggravated stress fluctuation and mechanical size effects of nanoscale lamellar bone pillars

The size effects of mechanical properties influence the microdeformation behaviors and failure mechanisms of hierarchical lamellar bones. Investigations of the continuous deformation behaviors and structure–behavior–property relationships of nanoscale lamellar bones provide essential data for reducing the risk of fracture. Here, five pillars with diameters ranging from 640 to 4971 nm inside a single lamella were fabricated. In situ pillar compressive tests inside a scanning electron microscope directly revealed the diameter-dependent enhanced strength, ductility, and stress fluctuation amplitude. Real-time observations also revealed the segmented deformation and morphological anisotropy of pillars with smaller diameters and the slight elastic recovery of pillars with larger diameters. The critical diameter leading to the brittle-to-ductile transition was confirmed. The “analogous to serrated flow” stress fluctuation behaviors at the nanoscale exhibited a significant size effect, with coincident fluctuation cycles independent of diameter, and each cycle of the fluctuation manifested as a slow stress increase and a rapid stress release. The discontinuous fracture of collagen fibrils, embedded enhancement of hydroxyapatite crystals, and layered dislocation movement on the basis of strain gradient plasticity theory were expected to induce cyclical stress fluctuations with different amplitudes.

Bone Fracture-Treatment Method: Fixing 3D-Printed Polycaprolactone Scaffolds with Hydrogel Type Bone-Derived Extracellular Matrix and β-Tricalcium Phosphate as an Osteogenic Promoter

Bone formation and growth are crucial for treating bone fractures. Improving bone-reconstruction methods using autologous bone and synthetic implants can reduce the recovery time. Here, we investigated three treatments using two different materials, a bone-derived decellularized extracellular matrix (bdECM) and β-tricalcium phosphate (β-TCP), individually and in combination, as osteogenic promoter between bone and 3D-printed polycaprolactone scaffold (6-mm diameter) in rat calvarial defects (8-mm critical diameter). The materials were tested with a human pre-osteoblast cell line (MG63) to determine the effects of the osteogenic promoter on bone formation in vitro. A polycaprolactone (PCL) scaffold with a porous structure was placed at the center of the in vivo rat calvarial defects. The gap between the defective bone and PCL scaffold was filled with each material. Animals were sacrificed four weeks post-implantation, and skull samples were preserved for analysis. The preserved samples were scanned by micro-computed tomography and analyzed histologically to examine the clinical benefits of the materials. The bdECM–β-TCP mixture showed faster bone formation and a lower inflammatory response in the rats. Therefore, our results imply that a bdECM–β-TCP mixture is an ideal osteogenic promoter for treating fractures.

Effects of Plate Edge Thickness On Droplet Generation Caused by Water Film Breakup At the Plate Edge

Droplets generated at trailing edges of low-pressure steam turbines strike the leading edge of moving blades, resulting in severe damage by erosion. In this study, water film flows on a plate set in a parallel airflow and breakup patterns are observed and measured to investigate the breakup behavior of the water film at the plate edge and the effect of the plate edge thickness. Profiles of frequency distribution of the droplet diameters exhibit on approximately linear in a semilog graph. The gradient of those distributions becomes steeper when the air flow velocity increases. Coarse droplets are generated from the deformation of ligaments, as shown in the end stage of a sheet-type breakup, and will result in a secondary breakup. Meanwhile fine droplets whose diameters are similar to the critical diameter remain in the high airflow velocity region; they are assumed to contribute significantly to erosion damage. The plate edge thickness does not affect the frequency distributions of the droplet diameter and Sauter mean diameter. However, it affects the intermittency of discharge water. The discharged water period becomes longer when the plate edge thickness increases. This discharged water frequency is smaller than the wave frequency of the water film flow on the plate when the airflow velocity is high. Based on an experiment involving the highest airflow velocity, the discharged water frequency is similar to that generated by a general turbine rotation speed.

About the mass of combustible dust deposited in the room

Темой данной статьи является рассмотрение расчетного метода оценки пыленакопления в помещении с оборудованием, содержащим дисперсные материалы, а задача заключается в его совершенствовании на основании современных представлений. Витающие в воздухе мелкие пылинки постепенно осаждаются на горизонтальных поверхностях, создавая угрозу внезапного перехода в состояние аэровзвеси и взрывообразного сгорания с образованием волны давления. Для определения категории помещения по взрывопожарной и пожарной опасности и разработки профилактических противопожарных мероприятий необходимо иметь математический инструмент, позволяющий оценивать количество пыли, которое может участвовать во взрыве. В статье предлагается определять критический диаметр частиц пыли, исходя из равенства скорости осаждения частиц и скорости распространения пламени. При этом скорость осаждения частиц следует определять по известному соотношению Стокса, а скорость распространения пламени принимать или по данным эксперимента, или среднестатистическую, равную 3 м/с. The dust that settles on the horizontal surfaces of equipment and building structures is inevitably contained in the premises in which technological process is carried out with the presence of combustible dispersed materials. The amount of dust deposited in a room can be determined in several ways. 1. Weighing the dust collected during cleaning. 2. Experimentally by placing dust collectors on different surfaces for a certain period of time. It should be considered the incompleteness of the previous dust collection, which depends on the dust collection method when determining the amount of dust deposited in the room. The amount of the remaining uncollected dust is estimated as 10 % of the detected dust if the cleaning was carried out by a mechanized method (dust extraction coefficient K = 0.9, and insufficient decontamination coefficient n = 0.1). The amount of remaining uncollected dust is estimated as 40% of the detected dust if cleaning was carried out manually using a dry method (dust extraction coefficient K = 0.6 and insufficient decontamination coefficient n = 0.4). The amount of remaining uncollected dust is estimated as 30% of the detected dust if the cleaning is carried out manually with a wet method (K coefficient = 0.7, and insufficient decontamination coefficient n = 0.3). Dust factor is the ratio of amount of dust suspended in the airspace to the total amount of dust in the room. It should be taken equal to 0.5, if the diameter of dust particles is more critical, and equal to 1, if the diameter of dust particles is less than the critical diameter. The diameter of the dust particles is critical, above which the dust ceases to spread the flame. The critical diameter can be determined based on the following considerations. Flame propagation through the air suspension will not occur if the particle deposition rate exceeds the flame propagation rate from bottom to top. The deposition rate is easily determined by the Stokes coefficient. The flame propagation rate can be determined experimentally or estimated as slightly higher than the average for most industrial dusts. The authors obtain a formula for calculating the critical diameter of dust particles equating the terminal velocity to flame propagation rate (3 m/s) and solving the Stokes equations of the particle diameter. The critical particle diameter of air suspension of combustible materials in most cases does not exceed 300 microns at flame propagation speed of 3 m/s. The obtained calculated values of the critical diameters are in satisfactory agreement with the literature data, and also confirm the correctness of the choice of dust formation coefficient K = 1 for dust with dispersion of less than 350 mkm. The air suspension ready for a secondary explosion is formed when combustible particulate material leaves the equipment as a result of an internal explosion. The aerosol with a high concentration of solid phase is formed in case of free precipitation from the device or from damaged packaging located above the floor level of the room. In this case, the amount of fuel capable for explosive combustion is determined by the amount of oxygen in the cloud, since the diffusion supply of oxygen from the outside does not have time to ensure complete combustion of the fuel. When the product spills unhindered, the resulting cloud has the shape of a volumetric cone with a base diameter equal to the height of the cone. It is possible to determine the amount of burned dust knowing the stoichiometric concentration of dust (%) required for its combustion per unit of air volume, as well as the volume of the dust cloud (V). The Pc value can be determined by the combustion reaction if the chemical composition of the dust is known. There are proposed refined equations for determining the critical diameter of combustible dust, the stoichiometric concentration during its combustion in a unit of air volume as well as the mass of dust deposited in the room. It is recommended to estimate the value of the stoichiometric concentration according to the combustion heat of dust for dusts of indeterminate chemical composition.

Approximate estimation of the critical diameter in Koenen tests

A simple correlation between computed detonation parameters and the critical diameter obtained using the Koenen (steel-sleeve) test is reported. This correlation is not meant to replace a proper Koenen test, but rather, to act as an aid to help to know which orifice diameter to start testing with.

Magnetic reversal modes in cylindrical nanostructures: from disks to wires

Cylindrical magnetic nanowires are key elements of fast-recording and high-density 3D-storage devices. The accurate tuning of the magnetization processes at the nanoscale is crucial for the development of future nano-devices. Here, we analyzed the magnetization of Ni nanostructures with 15–100 nm in diameter and 12–230 nm in length and compared our results with experimental data for periodic arrays. Our modelling led to a phase diagram of the reversal modes where the presence of a critical diameter (d ≈ 30 nm) triggered the type of domain wall (DW) formed (transverse or vortex); while a critical length (L ≈ 100 nm) determined the number of DWs nucleated. Moreover, vortex-DWs originated from 3D skyrmion tubes, reported as one of the best configurations for storage devices. By increasing the diameter and aspect-ratio of nanowires with L > 100 nm, three reversal modes were observed: simultaneous propagation of two vortex-DWs; propagation of one vortex-DW; or spiral rotation of both DWs through “corkscrew” mechanism. Only for very low aspect-ratios (nanodisks), no skyrmion tubes were observed and reversal occurred by spiral rotation of one vortex-DW. The broad range of nanostructures studied allowed the creation of a complete phase diagram, highly important for future choice of nanoscaled dimensions in the development of novel nano-devices.

Effect of Alloying Additives and Microadditives on Hardenability Increase Caused by Action of Boron

The presented work was aimed at evaluating influence of boron on hardenability of steel quantitatively and evaluating this effect during complex use of boron with other alloying additives like chromium, vanadium and titanium. For this purpose, eight melts with variable chemical compositions were prepared. From the ingots, cylindrical specimens with normalized dimensions according to EN ISO 642:1999 were cut out and subjected to full annealing at 1200 °C and to normalizing at 900 °C. Such specimens were subjected to the hardenability Jominy test. In order to distinguish the influence of boron on hardenability of a given melt and thus to eliminate the differences resulting from its chemical composition, grain size and austenitizing temperature, the obtained ideal critical diameter was corrected and the boron effectiveness factor was determined. The performed examinations and analyses showed that inadequate quantities of microadditives result in losing the benefits coming from introduction of boron as the hardenability-improving element and can even result in a reduction of hardenability of the boron-containing steel.