Localized Flow Research Articles

Investigation of blade design parameters for performance improvement of hydraulic cross flow turbine

Micro hydro power plant offers the cheapest renewable as well as a clean energy resource having abundant room for development. Cross flow turbine is easy to manufacture and maintain, operable in off-grid remote areas with negligible civil work requirement leading to its high popularity in developing countries. The present study numerically investigates the effect of different blade design parameters on the performance of hydraulic cross flow turbine using Ansys-CFX®. Firstly, a comparative analysis of the full turbine and half turbine model is performed. Then, the blade leading and trailing edge is varied considering four distinct geometric profiles with varying rotational speeds of 100–240 rpm. Moreover, the blade exit angle is varied from 50° to 100°, keeping a consistent rotational speed of 180 rpm. The results are presented in terms of the torque generated, and the turbine efficiency. In addition, the localized flow around the blades is elaborated using the flow velocity contours and streamlines. The geometric combination with a circular profile for the blade leading edge followed by a sharp trailing edge transpired maximum turbine efficiency. Moreover, the optimal blade exit angle lies between 55° and 60° contrary to the general practice of radial exit.

The flood reduction and water quality impacts of watershed-scale natural infrastructure implementation in North Carolina, USA

Natural infrastructure as a mitigation measure for flooding has received increased attention following recent extreme rainfall and flood events in North Carolina. While natural infrastructure (e.g., wetlands, floodplain expansion, reforestation, etc.) has been shown to reduce runoff and mitigate peak flows, it is difficult to predict the aggregate impacts of widespread implementation at the watershed scale for a given location. The primary objectives of this study were to identify suitable areas for natural infrastructure implementation on the landscape to reduce flooding and to use the Soil & Water Assessment Tool (SWAT) model to simulate the flood reduction and water quality impacts for three subwatersheds (~150 sq. km each) of the Neuse River Basin. Model results indicated that substantial localized annual maximum flow reduction (up to 30–40%) was possible, mostly correlated to the area of natural infrastructure implementation in the subbasin, but flood reduction benefits declined at the subwatershed-scale (1–16%). On a per hectare basis, wetlands sized and designed strategically for flood control had a greater impact on peak flow reduction than reforestation. The implementation of reforestation and flood control wetlands produced substantial nutrient and sediment load reductions, which also correlated with the area of natural infrastructure implementation. Total nitrogen load reduction ranged from 6 to 18% and total phosphorus load reductions from 4 to 17% for the most intensive implementation of wetlands restoration and reforestation. Sediment load reductions ranged from 16 to 30%. The results of this study illustrate that while flood reduction benefits can be realized at local scales (i.e., subbasin), a substantial area would need to be converted to natural infrastructure to provide flood reduction benefits at the watershed scale.

Estimating Canopy-Scale Evapotranspiration from Localized Sap Flow Measurements

The results reported in this work are based in part on measurements of sap flow in a few select trees on a representative riparian forest plot coupled with a forest-wide randomized sampling of tree sapwood area in a watershed located along the Pacific coast in Santa Cruz County, California. These measurements were upscaled to estimate evapotranspiration (ET) across the forest and to quantify groundwater usage by dominant phreatophyte vegetation. Canopy cover in the study area is dominated by red alder (Alnus rubra) and arroyo willow (Salix lasiolepis), deciduous phreatophyte trees from which a small sample was selected for instrumentation with sap flow sensors on a single forest plot. These localized sap flow measurements were then upscaled to the entire riparian forest to estimate forest ET using data from a survey of sapwood area on six plots scattered randomly across the entire forest. The estimated canopy-scale ET was compared to reference ET and NDVI based estimates. The results show positive correlation between sap flow based estimates and those of the other two methods, though over the winter months, sap flow-based ET values were found to significantly underestimate ET as predicted by the other two methods. The results illustrate the importance of ground-based measurements of sap flow for calibrating satellite based methods and for providing site-specific estimates and to better characterize the ET forcing in groundwater flow models.

An Experimental Model of Unconfined Bubbly Lava Flows: Importance of Localized Bubble Distribution

AbstractMost lava flows carry bubbles and crystals in suspension. From earlier works, it is known that spherical bubbles increase the effective viscosity while bubbles deformed by rapid flow decrease it. Changes in the spatial distribution of bubbles can lead to variable rheology and flow localization and thus modify the resulting lava flow structure and morphology. To understand the roles of bubble and solid phase crystal distributions, we conducted a series of analog experiments of high bubble fraction suspensions. We poured the analog lava on an inclined slope, observed its shape, calculated the velocity field, and monitored its local thickness. A region of localized rapid flow and low vesicularity, whose thickness is thinner than the surrounding area, develops at the center of the bubbly flows. These features suggest that the locally higher liquid fraction decreases the effective viscosity, increases the fluid density, and accelerates the flow. We also found that a halted particle‐bearing bubbly flow can resume flowing. We interpret this to result from the upward vertical separation of bubbles, which generates a liquid‐rich layer at the bottom of the flow. In our experiment, bubbles are basically spherical and decrease the flow velocity, while our estimate suggests that bubbles in natural lava flows could increase or decrease flow velocity. Downstream decreases in flow velocity stops the bubble deformation and can cause a sudden increase of effective viscosity. The vertical segregation of the liquid phase at the slowed flow front may be a way to generate a cavernous shelly paho’eho’e.

Long Term Vortex Flow Evolution around a Magnetic Island in Tokamaks.

We present a gyrokinetic analysis of the vortex flow evolution in a magnetic island in collisionless tokamak plasmas. In a short term ω[over ¯]_{D}t<1, where ω[over ¯]_{D} is the secular magnetic drift of the orbit center, initial monopolar vortex flow approaches to its residual level determined by the neoclassical enhancement of polarization shielding after collisionless relaxation. The residual level depends on the location inside an island and is higher than the Rosenbluth-Hinton level [M.N. Rosenbluth and F.L. Hinton, Phys. Rev. Lett. 80, 724 (1998)PRLTAO0031-900710.1103/PhysRevLett.80.724] due to finite island width. In a long term ω[over ¯]_{D}t>1, the residual vortex flow evolves to a dipolar zonal-vortex flow mixture due to toroidicity-induced breaking of a helical symmetry. The mixture forms localized flow shear layers near the island separatrix away from X points. The deviation of the streamlines of the mixture flows from magnetic surfaces allows turbulence advection across the island. We expect a small island w≲qρ_{Ti}/s[over ^] provides a favorable condition for this mixture flow formation, while the monopolar vortex flow persists for a larger island.

Non-Invasive Rheo-MRI Study of Egg Yolk-Stabilized Emulsions: Yield Stress Decay and Protein Release.

A comprehensive understanding of the time-dependent flow behavior of concentrated oil-in-water emulsions is of considerable industrial importance. Along with conventional rheology measurements, localized flow and structural information are key to gaining insight into the underlying mechanisms causing time variations upon constant shear. In this work, we study the time-dependent flow behavior of concentrated egg-yolk emulsions with (MEY) or without (EY) enzymatic modification and unravel the effects caused by viscous friction during shear. We observe that prolonged shear leads to irreversible and significant loss of apparent viscosity in both emulsion formulations at a mild shear rate. The latter effect is in fact related to a yield stress decay during constant shearing experiments, as indicated by the local flow curve measurements obtained by rheo-MRI. Concurrently, two-dimensional D-T2 NMR measurements revealed a decrease in the T2 NMR relaxation time of the aqueous phase, indicating the release of surface-active proteins from the droplet interface towards the continuous water phase. The combination of an increase in droplet diameter and the concomitant loss of proteins aggregates from the droplet interface leads to a slow decrease in yield stress.

Comparison of fluid dynamics changes due to physical activity in 3D printed patient specific coronary phantoms with the Windkessel equivalent model of coronary flow

Background3D printing (3DP) used to replicate the geometry of normal and abnormal vascular pathologies has been demonstrated in many publications; however, reproduction of hemodynamic changes due to physical activities, such as rest versus moderate exercise, need to be investigated. We developed a new design for patient specific coronary phantoms, which allow adjustable physiological variables such as coronary distal resistance and coronary compliance in patients with coronary artery disease. The new design was tested in precise benchtop experiments and compared with a theoretical Windkessel electrical circuit equivalent, that models coronary flow and pressure using arterial resistance and compliance.MethodsFive phantoms from patients who underwent clinically indicated elective invasive coronary angiography were built from CCTA scans using multi-material 3D printing. Each phantom was used in a controlled flow system where patient specific flow conditions were simulated by a programmable cardiac pump. To simulate the arteriole and capillary beds flow resistance and the compliance for various physical activities, we designed a three-chamber outlet system which controls the outflow dynamics of each coronary tree. Benchtop pressure measurements were recorded using sensors embedded in each of the main coronary arteries. Using the Windkessel model, patient specific flow equivalent electrical circuit models were designed for each coronary tree branch, and flow in each artery was determined for known inflow conditions. Local flow resistances were calculated through Poiseuille’s Law derived from the radii and lengths of the coronary arteries using CT angiography based multi-planar reconstructions. The coronary stenosis flow rates from the benchtop and the electrical models were compared to the localized flow rates calculated from invasive pressure measurements recorded in the angio-suites.ResultsThe average Pearson correlations of the localized flow rates at the location of the stenosis between each of the models (Benchtop/Electrical, Benchtop/Angio, Electrical/Angio) are 0.970, 0.981, and 0.958 respectively.Conclusions3D printed coronary phantoms can be used to replicate the human arterial anatomy as well as blood flow conditions. It displays high levels of correlation when compared to hemodynamics calculated in electrically-equivalent coronary Windkessel models as well as invasive angio-suite pressure measurements.

THROUGHGOING FLUID-CONDUCTING STRUCTURES: CONCEPTUALIZATION, TERMINOLOGY, TYPES, PROPERTIES, AND THE ROLE IN FLUID CIRCULATION

In this paper the review and analysis of global data on throughgoing fluid-conducting structures is performed, the problematic issues of related concepts and terminology are considered, typification of structures by various criteria is proposed and their role in fluid circulation and in lithogenesis and evolution of sedimentary basins is accessed. Such structures are ubiquitous and are an integral part of the drainage system of the upper crust, although the intensity of their distribution and impact on fluid circulation vary widely and increase drastically in certain geological and geodynamic conditions. At the local and subregional scales, throughgoing structures and related phenomena show uneven, clustered distribution. The key role of throughgoing structures in fluid circulation, including the migration of hydrocarbons and pollutants, is determined by their intersecting and throughgoing nature with respect to layered inhomogeneities, including sealing (low permeability) horizons, and by usually much higher permeability than that of the host rocks. The vertical nature of structures and localized vertical fluid flow across lateral lithological and hydrodynamic boundaries cause the formation of thermal and geochemical anomalies and disequilibrium of the water-rock system, accompanied by the interaction of conduit fluids with host rocks and reservoirs and by alteration of the rocks that contain them. This determines the leading role of throuhgoing structures in superimposed lithogenesis and ore mineralization. The fluid conductivity of throughgoing structures is variable over time because it depends on their origin, stages of their formation and secondary changes. In this regard, the comparison of this ability between morphogenetic varieties of throughgoing structures is generally difficult, although the most effective in this respect are structures of karstic origin. For structures of fluidodynamic type, the greatest permeability and intensity of fluid flows through the conduits are characteristic of the periods of their formation and immediately after them, as well as of the periods of activation, which are usually associated with tectonic events.

Soft machining-induced surface and edge chipping damage in pre-crystalized lithium silicate glass ceramics

Soft machining is a key procedure in fabrication of high-strength lithium-based silicate glass ceramic (LS) restorations. This paper reports on the diamond machining-induced surface and edge chipping damage in two pre-crystalized LS materials: pre-crystallized lithium metasilicate/orthophosphate glass ceramic (Pre-LS, IPS e.max CAD) and pre-crystallized zirconia-containing lithium metasilicate glass ceramic (Pre-ZLS, Vita Suprinity). Indentation techniques were used to measure the material mechanical properties. Soft machining was conducted using a robotic controlled apparatus mimicking dental CAD/CAM machining processes at different removal rates and enabling in-process force measurement. Machined surface roughness was assessed using 3D confocal optical profilometry in terms of the average and maximum surface heights. Scanning electron microscopy was used to assess diamond tool and machined surface and edge morphology. Soft machining of both materials was dominated by brittle fracture mixed with localized ductile flow. However, the higher brittleness index of Pre-ZLS than Pre-LS yielded higher degrees of machining-induced conchoidal fractures in Pre-ZLS in comparison with irregular fractures in Pre-LS. Thus, much larger surface roughness and deeper edge chipping damage were produced in Pre-ZLS than Pre-LS. Machining forces for Pre-ZLS were significantly smaller than Pre-LS, due to the lower machinability index associated with a complex relation of the mechanical properties as well as less debris adhesion for Pre-ZLS than Pre-LS. Further, increased material removal rates resulted in significantly increased machining forces, maximum surface roughness and fracture, and edge chipping damage in both Pre-ZLS and Pre-LS materials. Therefore, optimization of soft machining processes needs to be practiced to achieve accepted surface and edge quality at balanced removal rates.

Bio‐Micromotor Tweezers for Noninvasive Bio‐Cargo Delivery and Precise Therapy (Adv. Funct. Mater. 16/2022)

Bio-Micromotor Tweezers In article number 2111038, Hongbao Xin, Baojun Li, and co-workers construct bio-micromotor tweezers for noninvasive bio-cargo delivery and precise therapy based on two optically trapped living microalgae cells. The rotating cells generate highly localized flow fields, which can trap and drive bio-cargos along controllable trajectories in different biological media in a noncontact and noninvasive manner, and further for targeted drug delivery into single cancer cell for precise therapy.

Design of Experiments to Support VTR Core Design

To support the development of the U.S. Department of Energy (DOE) Versatile Test Reactor (VTR), a new set of experiments has been established at Argonne National Laboratory (ANL). Driven in part by the validation needs for code calculations and simulations of the reference VTR core design, three unique test facilities have been designed, or are in the process of being designed, to allow measurement of the phenomena and behavior prototypic to the full-scale VTR core. The Pressure drop Experimental Loop for Investigations of Core Assemblies in Nuclear reactors (PELICAN) facility, recently constructed and currently operational, is capable of producing full-scale flow rates for measurement of the pressure drop across a prototypic fuel assembly, including axial reflectors, fuel, and plenum components. The REDuced Scale Hydraulic Inlet Plenum (REDSHIP) experiment, beginning construction, will provide measurements of phenomena within the inlet plenum, including flow distributions through the core assembly ducts, pressure losses across the assembly receptacles, and localized velocity flow fields. A separate-effects-test experiment, called Parallel HEated ASsemblies for Advanced Nuclear Tests (PHEASANT), which is in the early stages of design, is being developed to examine the mixing of exiting core assembly jet streams within the upper plenum. As each of the test facilities becomes operational, they will begin generating timely, reliable, and qualified empirical data suitable for verification and validation of computational tools. In collaboration with other efforts across the DOE complex, the ANL experimental programs are well poised to provide continuous support for the advancement of the VTR design.

Monazite record for the Paleoproterozoic Svecofennian orogeny, SE Finland: An over 150-Ma spread of monazite dates

The Svecofennian orogeny in Fennoscandia is an example of a long-lived orogeny characterised by low pressure, high temperature (LP–HT) metamorphism. In this paper, we present new LA-ICP-MS age data on monazite from fifteen paragneiss samples and two granitoid samples from the southeastern part of the Svecofennian orogen, including the Sulkava granulite complex. The high-grade rocks in the study area were metamorphosed at ca. 750–800 °C and 5–6 kbar, followed by near-isothermal decompression down to 3–4 kbar. The analysed monazites yielded 207Pb/206Pb dates from 1953 to 1737 Ma. The youngest dates are typically yielded by rims and overgrowths of monazites and by younger domains in patchy monazite grains. Psammitic and pelitic layers from the same outcrop display differences in monazite date distributions, with younger dates being more common in pelitic layers. Both detrital and metamorphic origins are possible for the ≥1.91 Ga monazite grains found in some samples. For the younger (<1.91 Ga) monazite grains, we found three main age peaks. The peak at 1.89–1.86 Ga fits well with the high-grade metamorphic event at 1.89–1.88 Ga observed elsewhere in southern and central Finland. The 1.87–1.86 Ga interval dates a near-isothermal decompression stage. The age peak at 1.83–1.82 Ga records the age of younger high-grade metamorphism in the study area. The age peak at 1.80–1.77 Ga is interpreted to represent isotopic resetting due to fluid-induced alteration during a shield-wide exhumation stage, when waning magmatism, leucosome crystallisation and a change towards brittle-ductile deformation led to localised fluid flow before cratonisation. The dates between the age peaks could be explained in part by mixed isotopic ages in patchy grains without clear growth zones.

Controls on Larsen C Ice Shelf Retreat From a 60‐Year Satellite Data Record

AbstractRapid retreat of the Larsen A and B ice shelves has provided important clues about the ice shelf destabilization processes. The Larsen C Ice Shelf, the largest remaining ice shelf on the Antarctic Peninsula, may also be vulnerable to future collapse in a warming climate. Here, we utilize multisource satellite images collected over 1963–2020 to derive multidecadal time series of ice front, flow velocities, and critical rift features over Larsen C, with the aim of understanding the controls on its retreat. We complement these observations with modeling experiments using the Ice‐sheet and Sea‐level System Model to examine how front geometry conditions and mechanical weakening due to rifts affect ice shelf dynamics. Over the past six decades, Larsen C lost over 20% of its area, dominated by rift‐induced tabular iceberg calving. The Bawden Ice Rise and Gipps Ice Rise are critical areas for rift formation, through their impact on the longitudinal deviatoric stress field. Mechanical weakening around Gipps Ice Rise is found to be an important control on localized flow acceleration and the propagation of two rifts that caused a major calving event in 2017. Capturing the time‐varying effects of rifts on ice rigidity in ice shelf models is essential for making realistic predictions of ice shelf flow dynamics and instability. In the context of the Larsen A and Larsen B collapses, we infer a chronology of destabilization processes for embayment‐confined ice shelves, which provides a useful framework for understanding the historical and future destabilization of Antarctic ice shelves.

Predictive environmental hydrogen embrittlement on fracture toughness of commercial ferritic steels with hydrogen-modified fracture strain model

In this work, a practical numerical model with few parameters was proposed for the prediction of environmental hydrogen embrittlement. The proposed method adopts hydrogen enhanced plasticity-based mechanism in a fracture strain model to describe hydrogen embrittlement. Fracture toughness degradation of three commercial steels SA372J70, AISI4130 and X80 in high pressure hydrogen environment were investigated. Firstly, governing equations for hydrogen distribution and material damage evolution was established. Hydrogen enhanced localized flow softening effect was coupled within fracture strain dependency on stress triaxiality. Then, the numerical implementation and identification process of model parameters was described. Model parameters of the investigated steels were determined based on experiment results from literatures. Finally, with the calibrated model, fracture toughness reduction of the steels was predicted in a wide range of hydrogen pressure. The prediction results were compared with experimental results. Reasonable accuracy was reached. The proposed method is an attempt to reach balance between physical accurate prediction and engineering practicality. It is promising to provide a simplified numerical tool for the design and fit for service evaluation of hydrogen storage vessels. • Hydrogen embrittlement prediction model with few parameters was proposed. • Identification of model parameters with a few support of experiments. • Simplified Fracture toughness prediction model with acceptable accuracy.

Population Genomics of Microbial Biostalactites: Non-recombinogenic Genome Islands and Microdiversification by Transposons.

Intrapopulation genetic variability in prokaryotes is receiving increasing attention thanks to improving sequencing methods; however, the ability to distinguish intrapopulation variability from species clusters or initial stages of gene flow barrier development remains insufficient. To overcome this limitation, we took advantage of the lifestyle of Ferrovum myxofaciens, a species that may represent 99% of prokaryotic microbiome of biostalactites growing at acid mine drainage springs. We gained four complete and one draft metagenome-assembled F. myxofaciens genomes using Oxford Nanopore and Illumina sequencing and mapped the reads from each sample on the reference genomes to assess the intrapopulation variability. We observed two phenomena associated with intrapopulation variability: hypervariable regions affected by mobilome expansion called “scrapyards,” and variability in gene disruptions caused by transposons within each population. Both phenomena were previously described in prokaryotes. However, we present here for the first time scrapyard regression and the development of a new one. Nearly complete loss of intrapopulation short sequence variability in the old scrapyard and high variability in the new one suggest that localized gene flow suppression is necessary for scrapyard formation. Concerning the variable gene disruptions, up to 9 out of 41 occurrences per sample were located in highly conserved diguanylate cyclases/phosphodiesterases. We propose that microdiversification of life strategies may be an adaptive outcome of random diguanylate cyclase elimination. The mine biostalactites thus proved as a unique model system for describing genomic intrapopulation processes, as they offer easily sampleable units enriched in a single microbial species.

Study of Drain Injected Breakdown Mechanisms in AlGaN/GaN-on-SiC HEMTs

Breakdown mechanism in 0.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu } \text{m}$ </tex-math></inline-formula> gate length AlGaN/GaN-on-SiC iron doped high electron mobility transistors (HEMTs) with background carbon is investigated through the drain current injection technique. The measurement results reveal that it can be divided into two distinct stages according to the gate voltage levels. The first stage of the measured drain injected breakdown is mainly due to the initiation of the punchthrough process under the gate, and the second stage of breakdown is associated with the potential barrier between the unintentionally doped (UID) GaN and the Fe doped p-type GaN buffer layer which also has a higher carbon density. The electroluminescence (EL) results suggest that the first stage shows uniform punchthrough current flow, but localized leakage current flow associated with a snapback breakdown mechanism replaces the uniform punchthrough current flow and dominates the second stage. A 2D-TCAD simulation has been implemented and shows the current paths under uniform flow conditions.

Haemodynamic Analysis of Branched Endografts for Complex Aortic Arch Repair.

This study aims to investigate the haemodynamic response induced by implantation of a double-branched endograft used in thoracic endovascular aortic repair (TEVAR) of the aortic arch. Anatomically realistic models were reconstructed from CT images obtained from patients who underwent TEVAR using the RelayPlus double-branched endograft implanted in the aortic arch. Two cases (Patient 1, Patient 2) were included here, both patients presented with type A aortic dissection before TEVAR. To examine the influence of inner tunnel branch diameters on localised flow patterns, three tunnel branch diameters were tested using the geometric model reconstructed for Patient 1. Pulsatile blood flow through the models was simulated by numerically solving the Navier–Stokes equations along with a transitional flow model. The physiological boundary conditions were imposed at the model inlet and outlets, while the wall was assumed to be rigid. Our simulation results showed that the double-branched endograft allowed for the sufficient perfusion of blood to the supra-aortic branches and restored flow patterns expected in normal aortas. The diameter of tunnel branches in the device plays a crucial role in the development of flow downstream of the branches and thus must be selected carefully based on the overall geometry of the vessel. Given the importance of wall shear stress in vascular remodelling and thrombus formation, longitudinal studies should be performed in the future in order to elucidate the role of tunnel branch diameters in long-term patency of the supra-aortic branches following TEVAR with the double-branched endograft.

Temperature field of metal structures of transport facilities with a thin protective coating

A study of the temperature field in metal structures of transport facilities with corrosion-resistant coating under the conditions of changes in ambient temperature has been conducted. The results of experimentally determined temperature distribution in the surface vicinity of a galvanized metal sheet are presented. The data were obtained over the day at positive and negative surface temperatures. Given a generalized boundary condition for the heat conduction problem, with a solid heated by a localized heat flow through a thin coating, there has been obtained and analyzed a temperature field. The temperature distribution across the surface outside the heating region during heat propagation along the coating was analyzed. Experimental data and model calculations, as well as temperature calculations allowing for the coating and not, have been compared. It has been established that the effect of coating on the temperature distribution in the metal structure, when the solid is heated by a localized heat flow through a thin coating, is insignificant.

Preferential Energization of Lower‐Charge‐State Heavier Ions in the Near‐Earth Magnetotail

AbstractO+ ions make a significant contribution to plasma pressure in the inner magnetosphere during magnetic storms. The storm‐time O+ enhancements are primarily caused by enhanced supply from the ionosphere and preferential energization in the magnetotail. In order to characterize the magnetotail process that dominates the energization, we examine differences in energy spectra of energetic 10–180 keV/q ions between different ion species, namely H+, He++, He+. O++, and O+. We use observations made by the MEP‐i instrument on the Arase (ERG) spacecraft on the nightside in the radial distance range of ∼5–∼7 Re during the main and early recovery phases of the May and July 2017 storms. The comparisons of energy spectra show that, for the same charge states, heavier ions are more energized than lighter ions. For the same mass, lower‐charge‐state ions are more energized than higher‐charge‐state ions. The spectra exhibit a sharp decrease at high energies for all ion species, while the spectra for more energized ions were shifted toward higher energies, compared to those for less energized ions. The results suggest that the preferential energization is due to temperature increases rather than the generation of energetic ions in the high‐energy tail. Considering temporal and spatial scales of heavy ion kinetic motions, we conclude that the preferential energization of lower‐charge‐state heavier ions occurs during the course of dipolarization, likely due to non‐adiabatic heating in the near‐Earth plasma sheet, effective trapping during transport by localized flow channels, and/or non‐adiabatic acceleration within the near‐Earth flow‐braking region.

Morphology of fibrous structures formed in the course of superplastic deformation of the 01420T alloy with the original bimodal grain structure

The morphology of the fibrous structures formed in the working parts of the 01420T alloy samples with the initial bimodal grain structure, deformed to fracture under optimal conditions of superplastic deformation at a temperature Т = 520°С and flow stress σ = 4,5 MPa is investigated. The maximum elongation of specimens deformed to failure δ is 670%. It has been suggested that the specific type of fibrous structures found in the specimens of the investigated alloy 01420T probably depends on the volume of the metastable liquid-solid phase, which was concentrated in the form of inclusions at some grain boundaries and made a viscous flow during superplastic deformation, its shear viscosity , the characteristics of its surface tension, the degree of dynamic oxidation of the melt, and the kinetics of the development of this process. The final view of the fibers and their shape, likely, depends not only on the nature of the viscous flow of the liquid-solid material, but also on the process of its crystallization during the cooling of the specimen in air to room temperature after mechanical tests. It was found that in view, all fibrous structures found in the working parts of the specimens can be conditionally divided into the following: cylindrical fibers; tapered fibers; cylindrical fibers on which there is a thickening or one or more drop-like formations; ribbon-like fibers; fibers that look like stalactites or stalagmites. The reasons for the formation of cracks on ribbon-like fibers are considered. It is assumed that they were formed as a result of relaxation of internal stresses, which were not fully minimized in the course of recrystallization, which was carried out when the sample was cooled. The reasons for the formation of droplets on the fibers are considered. It has been suggested that fibrous structures similar to stalactites and stalagmites were formed from a viscous material, which, in the course of superplastic deformation, as a result of crystallization, occured in local microvolumes of fibers, gradually turned from liquid-solid to solid-liquid. This led to the fact that in the crystallized microvolume of this fiber, the viscous homogeneous flow of the material probably turned into a localized flow, which is characteristic of the plastic flow carried out as a result of displacement of dislocations in the solid phase, and leads to the formation of stalagmitic fibers.