Dewetting experiments on molten spherulites, previously grown at Tc = 120 °C in thin films of isotactic polypropylene (iPP), revealed two kinds of instabilities of the dewetting rims, namely a ...fingering instability and a fracture instability for dewetting temperatures Ts above and below ca. 165 °C, respectively. For Ts ≥ 165 °C, the dynamics of growing dewetting holes on slippery substrates was governed by viscous dissipation, causing undulations leading to a fingering instability of the rims. However, for 160 °C < Ts < 165 °C, the dewetting rims exhibited a fracture instability, which was related to the release of elastic energy stored in the rim. From the dewetting dynamics of the molten polymers, we derived the non-equilibrium viscosity ηnon-equ(Ts) and equilibrated viscosity ηequ(Ts) as a function of Ts. The values of ηnon-equ(Ts) were significantly larger than ηequ(Ts), with differences decreasing for increasing Ts. Interestingly, extrapolation of ηnon-equ(Ts) to the cross-over point ηnon-equ = ηequ yielded Ts,cross ≈ 166 °C. We relate Ts,cross with the maximum melting temperature of crystalline domains which existed within iPP spherulites. Below Ts,cross, not all crystallites were molten and the melt contained crystalline seeds. Above Ts,cross, the melt was homogeneous and free of any seeds. Our approach opens up a new possibility for determining the maximum melting temperature of polymer crystals.
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•The fingering instability and fracture instability were respectively observed in homogeneous melt and heterogeneous melt.•The rim instability changed from fingering to fracture at 165 °C was revealed by dewetting of iPP films.•The non-equilibrium viscosity extrapolated to the equilibrium viscosity at a cross-over temperature Ts,cross ≈ 166 °C.•The Ts,cross was considered as the maximum melting temperature of crystalline domains within iPP spherulites.
B4C‐TiB2 ceramics (TiB2 ranging 5~70 vol%) with Mo‐Co‐WC as the sintering additive were prepared by spark plasma sintering. In comparison with B4C‐TiB2 without additive, the enhanced densification ...was evident in the sintered specimen with Mo‐Co‐WC additive. Core‐rim structured grain was observed around TiB2 grains. The interface of the rim between TiB2 and B4C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B4C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B2 rim around the TiB2 core may occur as a result of the solid solution and dissolution‐precipitation between TiB2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB2 content increased, alongside the decreased hardness. B4C‐30 vol% TiB2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m1/2.
Introduction
Most classification systems for lateral discoid meniscus do not evaluate instability of the meniscal peripheral rim. Considerable variability in the prevalence of peripheral rim ...instability has been published, and it appears that instability is underestimated. The purpose of this study was: first, to evaluate the prevalence of peripheral rim instability and its location in the symptomatic lateral discoid meniscus, and second, to investigate if patient age or type of discoid meniscus are possible risk factors for instability.
Methods
A cohort of 78 knees that underwent operative treatment due to symptomatic discoid lateral meniscus was analyzed retrospectively for the rate and location of peripheral rim instability.
Results
Out of the 78 knees, 57.7% (45) had a complete and 42.3% (33) had an incomplete lateral meniscus. The prevalence of peripheral rim instability in symptomatic lateral discoid menisci was 51.3%, and with 32.5%, the anterior attachment was most commonly affected, followed by the posterior (30%) and central (10%) attachment. 27.5% of the tested menisci were unstable anteriorly and posteriorly. There was no significant difference in the prevalence of rim instability between the type of discoid menisci (complete vs. incomplete), nor was there a significant correlation for age as a risk factor for instability.
Conclusion
The discoid lateral meniscus has a high prevalence and variable location of peripheral rim instability. Meniscal rim stability must be tested and addressed cautiously in all parts and in all types of discoid lateral menisci during operative treatment.
In this paper, multiband antennas based on a single ring slot are proposed for 4G/5G smartphone applications. The basic structure of the antenna is consisted of a large metal ground and an unbroken ...metal rim, in which a single 2 mm-wide ring slots is realized between the metal ground and rim. Here, a reconfigurable 4G antenna (820-960 and 1710-2690 MHz) is initially devised by loading multiple grounded stubs and a simple dc controlling circuit with varactor diode into the upper section of the ring slot. To further cover the sub-6 GHz spectrum (3400-3600 MHz) for future 5G communications, a four-element multi-input multi-output (MIMO) slot antennas configuration is designed by utilizing the lower section of the ring slot. A prototype antenna was fabricated, and good agreement is shown between the measured and simulated results. Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and compact structure, the proposed antenna design is attractive for 4G/5G smartphones.
The object of research in the paper is the technology of manufacturing segments of the rotor rim of large hydrogenerators-motors. The subject of study is the design and geometrical state of the rotor ...rim during the operation of hydraulic units. The goal is to make a three-dimensional mechanical calculation of the rotor segment for the further determination of the most optimal technology for the rotor rim manufacturing. The following tasks are set: to study the peculiarities of the manufacturing technology of the rotor rim segments; to perform an analytical calculation and a three-dimensional calculation with the determination of the average values of stresses and deformations in the rotor segment. The used methods are: finite element method of mathematical modeling of the thermal stress state of nodes. The following results were obtained: a description of the two main manufacturing technologies of the rotor rim segments, namely the stamping method and the laser cutting method, was provided. The advantages and disadvantages of each technological process were analyzed, and it was determined that the laser cutting method should be used in the production of powerful small-scale hydrogenerators. Three-dimensional models of the rotor segment were developed and a three-dimensional mechanical calculation of this model was performed, as a result of which the value of the displacement of the rotor of the hydrogenerator at the nominal frequency of rotation, as well as the average values of the stresses in the spoke and the rim of the rotor, were obtained. Based on the results of calculations, it was established that significant tolerances in the manufacture of rotor segments can lead to changes in the shape of the rotor during its further operation, the appearance of additional vibrations and further affect the performance of the hydraulic unit. The scientific novelty consists in a combined approach to the estimation of the average values of stresses and deformation of the rotor rim, taking into account the technology of its manufacture, which includes elements of analytical mechanical calculation and calculation in a three-dimensional setting.
Abstract
The microstructural and textural characteristics of a spinel corona that formed around a faceted corundum xenocrystal by reaction with the hosting basaltic melt in the Siebengebirge volcanic ...field demonstrate that the crystallographic and shape preferred orientation of spinel is influenced by the orientation of the reaction interface with respect to the corundum crystal lattice. The spinel roughly shows the common topotactic orientation relationships with corundum, where one of the $\{111\}_{Spl}$ planes is parallel to the (0001)$_{Crn}$ plane, and three of the $\{110\}_{Spl}$ planes are parallel to the $\{10\overline {1}0\}_{Crn}$ planes. In detail, there are subtle but systematic deviations from this topotactic relationship due to small rotations about the c-axis and/or an a-axis of corundum. The former is observed when the corundum c-axis is closely parallel to the interface plane, while the latter require a corundum a-axis orientation perpendicular to the interface. In this case, the preferred sense of rotation depends on the sign of the a-axis direction, irrespective of the spinel growth direction being parallel or antiparallel to this axis. Additionally, the selection of either one or both of two spinel twin variants that equally fulfill the topotactic orientation relationship depends on the orientation of the corundum-spinel interface with respect to the lattices of both the corundum and the spinel. Finally, also the grain boundary character is controlled by the interface orientation and the corundum lattice. Despite the differences between corona segments, the nature of these textures are persistent along and across each segment. We emphasize that all these microstructural and textural features are ascribed to the period of spinel growth in magmatic environment. The extent to which prominent slip planes in spinel are aligned parallel with the corundum-spinel interface seems to be of crucial importance for the nature of the spinel texture and microstructure, indicating that the activity of dislocations pertaining to these slip systems ease the accommodation of lattice misfit across the corundum-spinel interface. By comparison with experimentally grown spinel layers, we infer predominantly interface reaction controlled growth of the studied spinel corona.
A Doença Renal Crônica (DRC) é uma afecção caracterizada por causar lesões estruturais e funcionais nos rins, provocando perda irreversível da função renal, uremia e falência renal. Essa doença é ...classificada pela Sociedade Internacional de Interesse Renal (IRIS) em quatros estágios distintos, diferenciados através de parâmetros específicos. Tendo em vista a prevalência da DRC no que se refere a causa de óbito em gatos, é de suma importância estabelecer seu diagnóstico, tratamento e posterior progressão em pacientes acometidos. A ultrassonografia surge assim como um exame essencial para proporcionar análise completa dos rins, e acompanhamento de animais com DRC, por ser mais acessível e não invasiva. Desse modo, essa revisão de literatura tem o intuito de ressaltar a significância da ultrassonografia como importante meio para monitorar de forma não invasiva a DRC em gatos, proporcionando assim menos estresse a esses pacientes, além de auxiliar o médico veterinário quanto a progressão da DRC.
As a common condition in train operation, the out‐of‐roundness (OOR) of wheels may have a great influence on the life of cracked wheels. In this study, the I–II mixed‐mode crack growth rate of ...different angles was tested, finite element analysis was carried out by using the test results, and the influence of different wheel roundness conditions on the life of cracked wheels was revealed. The results show that the mode II stress intensity factor of mixed‐mode cracks is the main driving force for crack propagation in the process of wheel rim crack growth. With an increase in the wheel scar length and the order of the wheel polygon, the crack propagation life decreases significantly.
Highlights
Fracture mechanical properties are obtained for different crack deflection angles.
The wheel‐rail contact model for out‐of‐round wheel with crack submodel is constructed.
The remaining life of the wheel decreases as the crack angle and flat scar length increase.
The polygon phenomenon of the wheel will greatly reduce the remaining life of the wheel.
Chlorite rims have been of interest to petroleum geologists over the past several decades, as a significant number of abnormal high-porosity sandstone reservoirs at great depths have been related to ...chlorite rims. To clarify the contribution of chlorite rims to porosity preservation in sandstones, the relationship between chlorite rims and porosity evolution in Chang 7 sandstones of the Upper Triassic Yanchang Formation in the Ordos Basin in north-central China was investigated using thin sections, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analyses. Based on the detrital composition and diagenetic evolution pathway analyses, it was concluded that chlorite rims inhibited the formation of quartz cementation. However, in addition to quartz cementation, compaction and other cements (commonly carbonates and clays) also control the porosity evolution of sandstones. In sandstones in which porosity reduction is largely controlled by compaction or other cements, chlorite rims may have a limited effect on porosity preservation. Thus, chlorite rims can play an important role in porosity preservation only in sandstones in which quartz cementation is the main process of porosity destruction. The results of this study indicate that the development of high-porosity sandstones is often controlled by many factors, and the effects of chlorite rims on porosity preservation are not always significant.
•Chlorite rims have a limited effect on porosity preservation in sandstones in which porosity destruction is mainly caused by compaction.•Even if compaction and quartz cement are both inhibited, other late-stage cements may destroy porosity.•Chlorite rims play an important role in porosity preservation in sandstones in which porosity destruction is mainly caused by quartz cementation.
