Search Results (129)

Wave propagation in periodic media is governed by energy–momentum relations and geometric phases characterizing band topology, such as Zak phase in one-dimensional lattices. We demonstrate that, in the off-diagonal trimer lattices, Zak phase carries quantized screw-type dislocations winding around degeneracies in parameter space. If the lattice evolves in time periodically, as in adiabatic Thouless pumps, the corresponding closed trajectory in parameter space is characterized by a Chern number equal to the negative total winding number of Zak phase dislocations enclosed by the trajectory. We discuss the correspondence between bulk Chern numbers and the edge states in a finite system evolving along various pumping cycles. Full article

Background: Acromioclavicular joint (ACJ) injuries frequently result from trauma to the shoulder girdle and are particularly common among young, physically active individuals. These injuries account for approximately 9% of all traumatic shoulder girdle injuries and often lead to functional impairment and pain. The TightRope^® system, LARS™ band, and Bosworth screw are among over 160 currently described surgical techniques for managing ACJ dislocations. However, there is no consensus regarding the optimal surgical approach, particularly for the management of moderate Rockwood Type III ACJ dislocations. Materials and Methods: In this retrospective study, data from 246 patients who underwent surgery for ACJ dislocation between 2010 and 2018 at the Department of Orthopedics and Trauma Surgery, Medical University of Vienna, were analyzed. Patients were divided into four cohorts based on the surgical technique used: Bosworth screw, LARS (acute), LARS (chronic), and TightRope. Clinical and radiological outcomes were assessed pre- and postoperatively using the Visual Analog Scale (VAS), Constant, Disability of the Arm, Shoulder and Hand Score (DASH), Simple Shoulder Test (SST), University of California—Los Angeles Shoulder Score (UCLA), Short Form Health Survey (SF-36), and American Shoulder and Elbow Surgeons score (ASES), as well as radiographic analysis. Radiological measurements of the acromioclavicular (AC) and coracoclavicular (CC) joint spaces were taken on both the injured and uninjured shoulders to analyze and compare the reduction in joint gaps. Results: All surgical methods resulted in significant reductions in AC and CC joint gaps. The TightRope and LARS acute groups showed the greatest reductions, with minimal complication rates. Complication analysis revealed significant differences in clavicular elevation (p < 0.001) and CC-ligament ossification (p = 0.006), which were most frequent in the Bosworth group and least common in TightRope^® patients, with LARS showing intermediate values. AC joint arthrosis was uncommon in all four groups and did not differ significantly (p = 0.13). Overall, TightRope^® was associated with the most favorable complication profile. The postoperative VAS score in the TightRope group was 1.52 ± 2.06, and the Constant score was 96.83 ± 5.41, reflecting high patient satisfaction. Conclusions: All systems led to satisfactory radiological and clinical outcomes, with the LARS™ band showing particular effectiveness in chronic ACJ dislocations. While all techniques provided good results, the TightRope^® system demonstrated the most favorable overall profile in our cohort and may therefore be considered a promising contemporary option. Further studies are needed to determine the optimal treatment for moderate ACJ dislocations and to assess the cost-effectiveness of these surgical techniques. Full article

This study investigates the strain hardening and dislocation structure in the surface layers of C45 steel subjected to precision grinding at various depths. The aim was to assess how different grinding conditions influence the mechanical response and defect structure of ferrite. Nanoindentation was used to evaluate mechanical properties, while X-ray diffraction analysis provided data on the microstrain, crystallite size, and residual stress. The character and density of dislocations were further examined using modified Williamson–Hall and q-parameter analysis. The results revealed that the sample ground to a depth of 2 μm exhibited the highest density of statistically stored dislocations, as well as the lowest dislocation mobility. This condition also corresponded to the highest residual stresses and the greatest share of screw dislocations, indicating intense strain localization. In contrast, deeper grinding depths resulted in lower dislocation densities and reduced the strain energy. The observed trends highlight the formation of a dislocation-rich nanostructured layer in the shallowest ground region. These findings provide new insights into the mechanisms of surface hardening in ferritic steels and demonstrate how the depth of material removal during grinding governs the subsurface microstructure and strengthening effects. Full article

Background: Greater tuberosity fracture–dislocations (GTFDs) represent a distinct subset of proximal humerus fractures, occurring in up to 57% of anterior glenohumeral dislocations. Malreduction may result in impingement, instability, and functional limitation. Treatment is influenced by the displacement magnitude and direction, bone quality, and patient activity level. Methods: This narrative review was based on a comprehensive search of PubMed, Scopus, and Web of Science for English-language articles published between January 2000 and March 2025. Studies on pathomechanics, classification, diagnosis, treatment, and outcomes of GTFDs in adult and pediatric populations were included. Data were analyzed to summarize the current evidence and identify clinical trends. Results: A displacement ≥ 5 mm is the standard surgical threshold, though superior or posterosuperior displacement ≥ 3 mm—and ≥2 mm in overhead athletes—may justify surgery. Conservative treatment remains appropriate for minimally displaced fractures but is associated with up to 48% subacromial impingement and 11% delayed surgery. Surgical options include arthroscopic repair for small or comminuted fragments and open reduction and internal fixation (ORIF) with screws or plates for larger, split-type fractures. Locking plates and double-row suture constructs demonstrate superior biomechanical performance compared with transosseous sutures. Reverse shoulder arthroplasty (RSA) is reserved for elderly patients with poor bone stock, cuff insufficiency, or severe comminution. Pediatric cases require physeal-sparing strategies. Conclusions: GTFDs management demands an individualized approach based on fragment displacement and direction, patient age and activity level, and bone quality. While 5 mm remains the common threshold, lower cutoffs are increasingly adopted in active patients. A tiered treatment algorithm integrating displacement thresholds, fracture morphology, and patient factors is proposed to support surgical decision making. The incorporation of fracture morphologic classifications further refines fixation strategy. Further prospective and pediatric-specific studies are needed to refine treatment algorithms and validate outcomes. Full article

This study investigates the coupling mechanism between a parabolic notch and dislocations in one-dimensional (1D) hexagonal piezoelectric quasicrystals (PQCs) based on the theory of complex variable functions. By applying perturbation techniques and the Cauchy integral, analytical solutions for complex potentials are derived, yielding closed-form expressions for the phonon–phason stress field and electric displacement field. Numerical examples reveal several key findings: significant stress concentration occurs at the notch root, accompanied by suppression of electric displacement; interference patterns between dislocation cores and notch-induced stress singularities are identified; the J-integral quantifies distance-dependent forces, size effects, and angular force distributions reflecting notch symmetry; and the energy-driven dislocation slip toward free surfaces leads to the formation of dislocation-free zones. These results provide new insights into electromechanical fracture mechanisms in quasicrystals. Full article

This study investigates the deformation and fracture mechanisms of a Ti₆₁Al₁₆Cr₁₀Nb₈V₅ multi-principal element alloy (Ti61V5 alloy) under quasi-static and dynamic compression. The alloy comprises an equiaxed BCC matrix (~35 μm) with uniformly dispersed nano-sized B2 precipitates and a ~3.5% HCP phase along grain boundaries, exhibiting a density of 4.82 g/cm³, an ultimate tensile strength of 1260 MPa, 12.8% elongation, and a specific strength of 262 MPa·cm³/g. The Ti61V5 alloy exhibits a pronounced strain-rate-strengthening effect, with a strain rate sensitivity coefficient (m) of ~0.0088 at 0.001–10/s. Deformation activates abundant {011} and {112} slip bands in the BCC matrix, whose interactions generate jogs, dislocation dipoles, and loops, evolving into high-density forest dislocations and promoting screw-dominated mixed dislocations. The B2 phase strengthens the alloy via dislocation shearing, forming dislocation arrays, while the HCP phase enhances strength through a dislocation bypass mechanism. At higher strain rates (960–5020/s), m increases to ~0.0985. Besides {011} and {112}, the BCC matrix activates high-index slip planes {123}. Intensified slip band interactions generate dense jogs and forest dislocations, while planar dislocations combined with edge dislocation climb enable obstacle bypassing, increasing the fraction of edge-dominated mixed dislocations. The Ti61V5 alloy shows low sensitivity to adiabatic shear localization. Under forced shear, plastic-flow shear bands form first, followed by recrystallized shear bands formed through a rotational dynamic recrystallization mechanism. Microcracks initiate throughout the shear bands; during inward propagation, they may terminate upon encountering matrix microvoids or deflect and continue when linking with internal microcracks. Full article

Background/Objectives: Patellar instability in adolescents is a significant cause of short- and long-term morbidity and disability. Traditionally, patients with first-time patellar dislocation are managed nonoperatively, although most studies are not focusing on the adolescent athletic population. The primary objective of the current study was to compare patient-reported outcomes and complications in adolescent athletes who underwent surgery either after the first patellar dislocation or after the recurrence of the dislocation with a minimum postoperative follow-up of 48 months (48–75 months). Methods: A total of 39 adolescent athletes who underwent medial patellofemoral ligament (MPFL) reconstruction (Group A, after the first dislocation, and Group B, recurrent patella dislocation) were included in this study. In all the patients, the same MPFL reconstruction technique was applied using a semitendinosus autograft. The graft was fixed on the patella using a transverse tunnel and adjustable loop button fixation and, in the femur, using a tunnel and absorbable screw fixation. The tunnel was drilled obliquely to prevent penetration of the distal femoral physis. The preoperative and postoperative clinical and functional evaluations of the patients were conducted via the visual analog scale (VAS), the Lysholm Knee Scoring System, the Kujala Anterior Knee Pain Scale, and the Pediatric International Knee Documentation Committee (Pedi-IKDC), and the return to sports score was assessed via the Tegner Activity Scale (TAS). Results: At the latest follow-up, both groups demonstrated significant improvement in the Lysholm scores, with Group A achieving a mean of 92.57 ± 6.21 and Group B achieving a mean of 90.53 ± 8.21 (p = 0.062). Postoperatively, Group A achieved a mean Kujala score of 94.21 ± 9.23, whereas Group B reached 92.76 ± 12.39, with no statistically significant difference (p = 0.08). The Pedi-IKDC score improved postoperatively in both groups. In Group A, it increased from 67.98 ± 12.29 to 93.65 ± 4.1, and in Group B, from 56.21 ± 13.6 to 91.67 ± 6.21 (p = 0.067). The preoperative visual analog scale (VAS) score for pain was significantly lower in Group A (3.1 ± 1.13) than in Group B (4.2 ± 3.01, p < 0.01). At the latest follow-up, the VAS scores improved in both groups, with Group A reporting a mean score of 0.47 ± 1.01 and Group B 0.97 ± 1.32 (p = 0.083). The Tegner activity scores were similar between the groups preoperatively, with Group A at 7.72 ± 1.65 and Group B at 7.45 ± 2.09 (p = 0.076). Postoperatively, Group A had a mean score of 7.28 ± 2.15, whereas Group B had a mean score of 6.79 ± 3.70 (p = 0.065). The mean time to return to sports was significantly shorter in Group A (5.1 ± 1.3 months) than in Group B (7.6 ± 2.1 months) (p < 0.01). Overall, 84.61% of the patients returned to their previous activity level. Specifically, 95.2% (20/21) of patients in Group A achieved this outcome, whereas 72.22% (13/18) achieved it in Group B. Patient satisfaction was generally high, with 76% (16/21) of patients in Group A reporting being satisfied or very satisfied, compared with 77% (14/18) in Group B. Conclusions: MPFL reconstruction is a safe and effective procedure for both acute and recurrent patellar dislocation in adolescent athletes. While patients who underwent acute reconstruction returned to sport more quickly and showed higher absolute postoperative scores, the greatest overall improvement from preoperative to final follow-up was observed in those treated for recurrent instability. Both surgical approaches demonstrated high satisfaction rates and minimal complications, supporting MPFL reconstruction as a reliable option in both acute and recurrent cases. Full article

Body-centered cubic (BCC) metals, extensively utilized in low-alloy high-strength steels and heat-resistant alloys, exhibit a pronounced ductile–brittle transition (DBT) at cryogenic temperatures, marked by a well-defined yet narrow ductile–brittle transition temperature (DBTT) window. This paper overviews the research progress regarding the DBT mechanism of BCC metals. This mechanism was recently found to be related to the mobility of screw dislocation relative to edge dislocation, a decrease in which can induce a critical drop in the proliferation efficiency of dislocation sources. Furthermore, this paper summarizes the current research on the dilute solution softening effect of BCC metals, which has been frequently observed and studied in refractory alloys. The mechanism of this effect involves the low-temperature mobility of screw dislocations that could be promoted by specific solute atoms through kink pair nucleation. This offers a potential strategy for reducing the DBTT of low-alloy steels using a dilute solution, namely microalloying in metallurgy. However, the current understanding of the relationship between the macroscopic ductility of BCC alloys and the dilute solution softening effect is limited. This review aimed to draw attention to this relationship and strengthen related research. Full article

The origin of homochirality by rotational magnetoelectrochemistry was theoretically examined. Electrochemical reductions in a rotating solution under a static vertical magnetic field were concluded to yield microscopic vortices with L-activity for enantiomeric reagents, whereas D-active vortices arise from electrochemical oxidation. The reduction case was experimentally verified by rotational magnetoelectrodeposition (RMED) of copper films using an electrolysis cell rotating in a magnetic field, where L-active screw dislocations were created by L-active microscopic vortices. In all the cases of the directions of magnetic polarity and system rotation, the RMED films exhibited L-activity for the enantiomeric reactions of amino acids. Full article

Mg alloys are highly attractive for biodegradable surgical clips because of their low density and good biocompatibility; however, their limited strength and ductility restrict their widespread application. To overcome this limitation, this study employed screw rolling (SR) to produce a Mg–3Zn–0.2Ca alloy with a fine microstructure and an average grain size of 1.6 µm. Experimental results showed that the SR process improved the comprehensive tensile properties of the alloy, increasing the yield strength, ultimate tensile strength, and elongation from 192.6, 234.4 MPa, and 21.7% for the pre-extruded alloy to 252.3, 289 MPa, and 39.5%, respectively. Quantitative analysis of the strengthening behaviour identified grain refinement as the primary strengthening mechanism, along with considerable contributions from Orowan and dislocation strengthening. The ultra-high-tensile ductility was primarily attributed to the low internal stress, nano-sized precipitates, texture weakening, and activation of multiple slip systems. These findings provide a strategy for simultaneously increasing the ductility and strength of Mg alloys and lay a foundation for applying them as biodegradable clips. Full article

Two-dimensional transition metal dichalcogenides have attracted considerable attention in electrocatalytic hydrogen evolution due to their unique layered structures and tunable electronic properties. However, prior research has predominantly focused on the intrinsic catalytic activity of planar few-layer structures, which offer limited exposure of edge-active sites due to their restricted two-dimensional geometry. Moreover, van der Waals interactions between layers impose substantial barriers to electron transport, significantly hindering charge transfer efficiency. To overcome these limitations, this study presents the innovative synthesis of high-quality single-screw WS₂ with a 5° dislocation angle via physical vapor deposition. Second harmonic generation measurements revealed a pronounced asymmetric polarization response, while the selected area electron diffractionand atomic force microscopy elucidated the material’s distinctive screwed dislocation configuration. In contrast to planar monolayer WS₂, the conical/screw-structured WS₂—formed through screw-dislocation-mediated growth—exhibits a higher density of exposed edge-active catalytic sites and enhanced electron transport capabilities. Electrochemical performance tests revealed that in an alkaline medium, the screwed WS₂ nanosheets exhibited an overpotential of 310 mV at a current density of −10 mA/cm², with a Tafel slope of 204 mV/dec. Additionally, under a current density of 18 mA/cm², the screwed WS₂ can sustain this current density for at least 30 h. These findings offer valuable insights into the design of low-cost, high-efficiency, non-precious metal catalysts for hydrogen evolution reactions. Full article

A comprehensive X-ray topography analysis of two selected aluminum nitride (AlN) bulk crystals is presented. We compare surface inspection X-ray topography in back-reflection geometry with high-energy transmission topography in the Lang and Laue configuration using the monochromatic K_α1 excitation wavelength of copper, silver, and tungsten, respectively. A detailed comparison of the results allows the assessment of both the high- and low-energy X-ray topography methods with respect to performance and structural information, giving essential feedback for crystal growth. This is demonstrated for two selected AlN freestanding faceted crystals up to 8 mm in thickness grown in all directions using the physical vapor transport (PVT) method. Structural defects of all facets of the crystals are determined using the X-ray topography in back-reflection geometry. The mean threading dislocation densities are 480 ± 30 cm⁻² for both crystals of either the Al- or N-face. Clustering of dislocations could be observed. The m-facets show the presence of basal plane dislocations and their accumulation as clusters. The integral transmission topographs of the $10\overline{1}0$ (m-plane) reflection family show that basal plane dislocations of the screw type in ${\displaystyle \frac{1}{3}}⟨\overline{1}2\overline{1}0⟩$ directions decorate threading dislocation clusters. Three-dimensional section transmission topography reveals that the basal plane dislocation clusters mainly originate at the seed boundary and propagate in the ${\displaystyle \frac{1}{3}}⟨\overline{1}2\overline{1}0⟩$ direction along the growth front. In newly laterally grown material, the Borrmann effect has been observed for the first time in PVT-grown bulk AlN, indicating very high structural perfection of the crystalline material in this region. This agrees with a low mean FWHM of 10.6 arcsec of the $10\overline{1}0$ reflection determined through focused high-energy Laue transmission mappings. The latter method also opens the analysis of the $∆2\theta$-shift correlated to the residual stress distribution inside the bulk crystal, which is dominated by dislocation clusters. Contrary to Lang transmission topography, the de-focused high-energy Laue transmission penetrates the 8 mm-thick crystal enabling a defect analysis in the bulk. Full article

Anteroinferior shoulder dislocations require surgical intervention when related to critical glenoid bone loss. Scapular spine bone blocks have emerged as a promising alternative to traditional bone augmentation techniques. However, limited data exist on their biomechanical stability when using different suture-based fixation techniques. This study aimed to evaluate primary stability and micromotion after glenoid augmentation using a scapular spine bone block. A total of 31 fresh-frozen human shoulder specimens underwent bone block augmentation. The specimens were randomized into three groups: double-screw fixation (DSF), single-suture bone block cerclage (SSBBC), and double-suture bone block cerclage (DSBBC). Biomechanical testing was conducted using cyclic loading (5000 cycles at 1 Hz) and micromotion was analyzed using an optical 3D measurement system. Statistical analysis showed that medial irreversible displacement was significantly greater in the SSBBC group compared to DSF (p = 0.0386), and no significant differences were found in anterior or inferior irreversible displacements. A significant difference was noted in posterior reversible displacement (p = 0.0035), while no differences were found in inferior or medial reversible displacements. Between DSF and DSBBC, no significant differences were found in irreversible or reversible displacements in any direction. DSBBC provided stability comparable to DSF while offering a viable metal-free alternative. In contrast, SSBBC displayed inferior biomechanical properties, raising concerns about its clinical reliability. Full article

Coronoid process fractures in the pediatric population are rare and often misdiagnosed, leading to chronic elbow instability. We aim to evaluate the surgical management of two adolescent cases of inveterate coronoid fractures using autologous bone grafting. Both patients, with a history of recurrent elbow dislocations, presented with pseudoarthrosis and were initially misdiagnosed due to minor or subtle fractures. Comprehensive imaging, including computed tomography (CT) and magnetic resonance imaging (MRI), confirmed the presence of significant coronoid defects. The surgical intervention involved employing autografts from the iliac wing to reconstruct the coronoid process, followed by fixation with screws. Both patients underwent postoperative rehabilitation via physiotherapy, resulting in full functional recovery. At their one-year follow-ups, both patients regained full elbow function, achieving range-of-motion measurements of 0–0–130° flexion–extension and 90–0–90° pronation–supination; no recurrence of instability was reported, with no complications at the yearly follow-ups. This approach demonstrates the efficacy of autograft reconstruction in restoring elbow stability, particularly in cases with substantial bone loss or pseudoarthrosis. Our study highlights the importance of advanced imaging and individualized treatment strategies, emphasizing that early surgical intervention can prevent long-term disability in pediatric patients with chronic coronoid fractures. Full article

Uranium mononitride (UN) is a promising advanced nuclear fuel due to its high thermal conductivity and high fissile density. However, many aspects of its mechanical behavior, particularly at reactor-relevant conditions, remain unclear. In this study, molecular dynamics (MD) simulations were employed to investigate the deformation behavior and dislocation motion in UN. We found that the Kocevski potential predicts the principal slip system as ${\displaystyle \frac{1}{2}}⟨110⟩\left\{110\right\}$, aligning with experimental data. On the other hand, the Tseplyaev potential predicts slip to primarily occur on ${\displaystyle \frac{1}{2}}⟨110⟩\left\{111\right\}$. MD simulations of stress–strain behavior were used to estimate the nanoindentation hardness, revealing that the Kocevski potential accurately predicts hardness even though it fails to model dynamic plasticity. Complete dislocation mobility functions have been fitted for the edge and screw dislocations in both the thermally activated and phonon-drag regimes. The 300 K linear mobility of the edge dislocation using the Tseplyaev potential was found to be 817 ${\mathrm{Pa}}^{-1}·{\mathrm{s}}^{-1}$, whereas that of the screw dislocation using the Kocevski potential was found to be 4546 ${\mathrm{Pa}}^{-1}·{\mathrm{s}}^{-1}$. At intermediate stresses, we observed that the subsonic steady-state motion of the edge dislocation in UN is intermittently interrupted by velocity jumps, reaching the average sound velocity. Finally, the threshold Schmid stress is calculated as 179–197 MPa, which gives an upper-limit estimate of the uniaxial yield stress of polycrystalline UN of 548–603 MPa. These findings, including the fitted dislocation mobility function, provide essential input for future plasticity and dislocation dynamics models of nuclear fuels. Full article