Refractory multi-element alloys (RMEA) with body-centered cubic (bcc) structure have been the subject of much research over the last decade due to their high potential as candidate materials for ...high-temperature applications. Most of these alloys display a remarkable strength at temperatures above 1000 ∘C, which cannot be explained by the standard model of bcc plasticity dominated by thermally-activated screw dislocation motion. Recent research on Nb-Mo-Ta-W alloys points to a heightened role of edge dislocations during mechanical deformation, which is generally attributed to atomic-level chemical fluctuations in the material and their interactions with dislocation cores during slip. However, while this effect accounts for levels of strength that are larger than what might be found in a pure metal, it is not sufficient to explain the high yield stress found at elevated temperatures, particularly in the so-called strength ‘plateau’ region. In this work, we propose a strengthening mechanism based on the existence of thermal super-jogs in edge dislocations that act as strong obstacles to dislocation motion. The basis for the formation of these super-jogs is found in the unique properties of RMEA, which display vacancy formation energy distributions with tails that extend to almost zero energy. This facilitates vacancy formation at dislocation cores, which subsequently relax into atomic-sized super-jogs. While these super-jogs result in alloy strengthening in a wide temperature range, they can also displace diffusively along the glide direction, relieving with their motion some of this extra stress and eventually leading to strength softening above 2000 K. We implement these mechanisms into a specially-designed hybrid kinetic Monte Carlo/Discrete Dislocation Dynamics approach (kMC/DD) parameterized with vacancy formation and migration energy distributions obtained with machine-learning potentials designed specifically for the Nb-Mo-Ta-W system. The kMC module sets the timescale dictated by thermally-activated events, while the DD module relaxes the dislocation line configuration in between events in accordance with elastic forces and the applied stress. We find that the balance between super-jog pinning and super-jog diffusion confers an extra strength to edge dislocations at intermediate-to-high temperatures which is consistent with the experimental observation of a strength plateau in equiatomic Nb-Mo-Ta-W. We derive an analytical model based on the computational results that captures this improved understanding of plastic processes in these alloys and could help to partially explain the strength measurements at high temperatures.
The second international consensus conference on the scapula was held in Lexington Kentucky. The purpose of the conference was to update, present and discuss the accumulated knowledge regarding ...scapular involvement in various shoulder injuries and highlight the clinical implications for the evaluation and treatment of shoulder injuries. The areas covered included the scapula and shoulder injury, the scapula and sports participation, clinical evaluation and interventions and known outcomes. Major conclusions were (1) scapular dyskinesis is present in a high percentage of most shoulder injuries; (2) the exact role of the dyskinesis in creating or exacerbating shoulder dysfunction is not clearly defined; (3) shoulder impingement symptoms are particularly affected by scapular dyskinesis; (4) scapular dyskinesis is most aptly viewed as a potential impairment to shoulder function; (5) treatment strategies for shoulder injury can be more effectively implemented by evaluation of the dyskinesis; (6) a reliable observational clinical evaluation method for dyskinesis is available and (7) rehabilitation programmes to restore scapular position and motion can be effective within a more comprehensive shoulder rehabilitation programme.
It is important to be knowledgeable about the latest information on the diagnosis and the evidence-based management of developmental hip dysplasia and dislocation from birth through adolescence. The ...focus should be on the effect of the problem; normal growth and development of the hip joint; and the pathoanatomy, natural history, and long-term outcomes of developmental dysplasia of the hip, hip subluxation, and dysplasia. Many controversies exist in the management of this complex spectrum of disorders.
In the presented work, the mechanism of evolution of defects in the crystalline structure after irradiation with 1500 kGy and 3000 kGy absorption dose at room temperature in a 60Co gamma source was ...studied, using 43 nm sized ZrB2 crystals. The crystals were characterized by a purity of 99.9%, a powder density of 0.23 g/cm3, a specific surface area of 80 to 120 m2/g, and a hexagonal P6/mmm spatial structure. The dose rate applied was 6.05 Gy/s, with 1.17 and 1.37 MeV energy lines. The effect of particles resulting from the decay of 22Naradioactive isotope β+ with an activity of 10.5 μCi, as well as gamma quanta with an energy of 1.27 MeV, on the core and valence electrons and vacancies in the crystal structure was studied using Positron Annihilation Lifetime Spectroscopy (PALS) and Doppler broadening analysis methods. Additionally, the changes in the S and W parameters, which characterize the distribution of defects within the volume of the ZrB2 crystal, were studied using the Doppler broadening method. For unannealed material, the positron lifetime τ1 component varied between 174±2 ps and 181±1 ps. After annealing, the positron lifetime component τ2 was decreased from 290±3 ps to 226±3 ps, and the intensity component I2 increased from 17.49% to 40% depending on the radiation dose. The calculated values of the positron lifetime τ for one boron vacancy from ABINIT and MIKA packages were found to be 172 ps and 145 ps, respectively. The material was observed to satisfy the necessary functional conditions at gamma doses not exceeding 3000 kGy.
White‐beam X‐ray topography has been performed to provide direct evidence of micro‐voids in dislocation‐free high‐purity germanium single crystals. The voids are visible because of a dynamical ...diffraction contrast. It is shown that voids occur only in dislocation‐free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.
White beam X‐ray topography has been performed to provide direct evidence of micro‐voids in dislocation‐free high‐purity germanium single crystals. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.
Progressive peritalar subluxation (PTS) is part of adult acquired flatfoot deformity (AAFD). We investigated the use of the middle facet as an indicator of PTS using standing, weight-bearing computed ...tomography (CT) images. We hypothesized that weight-bearing CT would be an accurate method of measuring increased subluxation ("uncoverage") and incongruence of the middle-facet among patients with AAFD.
We included 30 patients with stage-II AAFD (20 female and 10 male; mean age, 57.4 years range, 24 to 78 years) and 30 matched controls (20 female and 10 male; mean age, 51.8 years range, 19 to 81 years) who underwent standing, weight-bearing CT. Two independent and blinded fellowship-trained foot and ankle surgeons measured the amount of subluxation (percentage of uncoverage) and the incongruence angle of the middle facet at the midpoint of its longitudinal length, using coronal-plane, weight-bearing, cone-beam CT images. Intraobserver and interobserver reliabilities were assessed using intraclass correlation coefficients (ICCs). Comparisons were performed using independent t tests or Wilcoxon tests. P values of <0.05 were considered significant.
Substantial to almost perfect intraobserver and interobserver reliability was observed for both measurements. We found that the middle facet demonstrated significantly increased PTS in patients with AAFD, with a mean value for joint uncoverage of 45.3% (95% confidence interval CI, 38.5% to 52.1%) compared with 4.8% (95% CI, 3.2% to 6.4%) in controls (p < 0.0001). A significant difference was also found for the incongruence angle, with a mean value of 17.3° (95% CI, 14.7° to 19.9°) in the AAFD group and 0.3° (95% CI, 0.1° to 0.5°) in controls (p < 0.0001). A joint incongruence angle of >8.4° was found to be diagnostic for symptomatic stage-II AAFD.
We investigated the use of the middle facet of the subtalar joint as a marker for PTS in patients with AAFD. We confirmed that standing, weight-bearing CT images allowed accurate measurements and that significant differences were found in the percentage of joint uncoverage and the incongruence angle compared with controls.
The assessment of the amount of subluxation and incongruence of the middle facet of the subtalar joint represents an accurate diagnostic tool for symptomatic adult acquired flatfoot deformity.
Horizontally stacked pure-Ge-nanosheet gate-all-around field-effect transistors (GAA FETs) were developed in this study. Large lattice mismatch Ge/Si multilayers were intentionally grown as the ...starting material rather than Ge/GeSi multilayers to acquire the benefits of the considerable difference in material properties of Ge and Si for realising selective etching. Flat Ge/Si multilayers were grown at a low temperature to preclude island growth. The shape of Ge nanosheets was almost retained after etching owing to the excellent selectivity. Additionally, dislocations were observed in suspended Ge nanosheets because of the absence of a Ge/Si interface and the disappearance of the dislocation-line tension force owing to the elongation of misfit dislocation at the interface. Forming gas annealing of the suspended Ge nanosheets resulted in a significant increase in the glide force compared to the dislocation-line tension force; the dislocations were easily removed because of this condition and the small size of the nanosheets. Based on this structure, a new mechanism of dislocation removal from suspended Ge nanosheet structures by annealing was described, which resulted in the structures exhibiting excellent gate control and electrical properties.
Thermophotovoltaic (TPV) devices based on GaInAsSb lattice matched to GaSb (100) substrates have demonstrated high external quantum efficiencies (EQEs) in the mid-infrared spectral range, making them ...promising candidates for waste heat recovery from high temperature “blackbody” sources. In this work, the GaInAsSb alloy has been integrated onto more cost-effective GaAs (100) substrates by using advanced metamorphic buffer layer techniques in molecular beam epitaxy (MBE), which included an interfacial misfit (IMF) array at the GaSb/GaAs interface followed by GaInSb/GaSb dislocation filtering layers. The threading dislocations in the GaInAsSb region can be efficiently supressed, resulting in high quality materials for TPV applications. To determine the performance of the GaInAsSb TPV on GaAs it was compared with a cell grown lattice matched onto GaSb substrate having the same structure. The resulting TPV on GaAs exhibited similar dark current-voltage characteristics with that on GaSb. Under illumination from an 800 °C silicon nitride emitter, the short circuit current density (Jsc) from the GaInAsSb TPVs on GaAs reached more than 90% of the control cell on GaSb, and the open circuit voltage (Voc) exceeded 80% of the cell on GaSb. The EQE from the TPV on GaAs reached around 62%, the highest value reported from this type of TPV on GaAs. With improved TPV structure design, large area GaInAsSb TPV panels on GaAs substrates can be realized in the future for waste heat energy recovery applications.
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•GaInAsSb material was integrated onto GaAs substrates with advanced buffer layer, resulting in low dislocation densities.•GaInSb/GaSb dislocation filtering layers can effectively reduce the threading dislocations.•The GaInAsSb thermophotovoltaic (TPV) on GaAs achieved similar performance as the one on lattice matched GaSb substrate.•Highest external quantum efficiency of 62% was reported from the GaInAsSb TPV on GaAs.
We investigated the impact of dislocations on the UV photodetection device performance. The existence of screw dislocations leads towards augmenting the dark current from the fabricated devices which ...limits the overall photocurrent generation from the device illuminated by a UV Laser source having wavelength of 325 nm. A sharp and stable transient current can be acquired from the device developed with reduced dislocation density film. Upon quantifying the performance, detection ability of the photodetectors decreases with increased dislocation density because it created leakage paths that develop trap states which enhances the possibility of recombination process of photo-generated electron-hole pairs. Thus, by restraining the screw dislocations via better growth conditions, the increment in dark current can be controlled which results in better device performance.
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•Dislocation-assisted charge-carrier transport & effective photocurrent generation.•Increment in the dark current is triggered by the existence of screw dislocations.•A direct correlation between screw dislocation density & device performance.•Results implicate persistent photoconductivity upon turning-OFF Laser source.•Fall in dislocation density will effectively enrich optoelectronic properties.
We analyze the dislocation-assisted charge carrier transport and effective photocurrent generation in the photodetection devices. Specifically, the impact of screw dislocations on the performance of GaN based metal–semiconductor-metal ultraviolet photodetector is investigated. The experiments reveal that reducing screw dislocations had a strong impact on dark current (~3x decrement) of the devices as well as on the photo-generated current (~20x enhancement) upon illumination (ultraviolet, 325 nm). The responsivity of the photodetection device has been increased from 85.05 mA/W to 130.17 mA/W with decreasing dislocation density. Because, higher dislocations created leakage paths that develop trap states which enhances the possibility of recombination process of photo-generated electron-hole pairs leading to lower charge collection. Further, the external quantum efficiency increases from 32.51% to 49.76% by reducing dislocation density. The work in this study proposes that reduction of defects/dislocations will be an effective approach to enrich the III-nitride semiconductor system for advancement in optoelectronic devices.
Hypothesis Type IIA, IIB, and V lateral clavicular fractures (Craig modification of the Neer classification) are characterized by a constant displacement and are associated with a high rate of ...nonunion. The aim of this study is to verify whether the reduction and arthroscopic stabilization of these clavicular fractures with coracoclavicular cerclage provide stable fixation to allow for bone healing. To date, the treatment of these fractures is still controversial in young active patients in whom functional requirements are to be met. Methods Fourteen male patients, with type IIA, IIB, and V lateral clavicular fractures (2 type IIA, 10 type IIB, and 2 type V) had been treated arthroscopically with a TightRope (Arthrex, Naples, FL, USA) and had a radiologic/clinical follow-up of at least 2 years. Results All fractures were confirmed to have healed without limitations in range of motion or loss of reduction. The acromioclavicular joint and the coracoclavicular interspace were restored to the level of the healthy site in all but 1 patient, in whom a reduction was observed because of hypercorrection of the fracture. The mean Constant score was 95, and all patients had a Simple Shoulder Test score of 12 points. Healing was delayed up to 20 days in 1 patient because of a skin infection, and the coracoid bone tunnel was too marginal in another patient, in whom the coracoid button broke the lateral side of the tunnel during fixation. Conclusions The arthroscopic procedure with the TightRope allows for fracture healing with no loss of reduction in the acromioclavicular joint and full return to everyday activities.
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