Observing femtosecond orbital dynamics in ultrafast Ge melting with time-resolved resonant X-ray scattering.

Photoinduced nonequilibrium phase transitions have stimulated interest in the dynamic interactions between electrons and crystalline ions, which have long been overlooked within the Born-Oppenheimer approximation. Ultrafast melting before lattice thermalization prompted researchers to revisit this issue to understand ultrafast photoinduced weakening of the crystal bonding. However, the absence of direct evidence demonstrating the role of orbital dynamics in lattice disorder leaves it elusive. By performing time-resolved resonant X-ray scattering with an X-ray free-electron laser, we directly monitored the ultrafast dynamics of bonding orbitals of Ge to drive photoinduced melting. Increased photoexcitation of bonding electrons amplifies the orbital disturbance to expedite the lattice disorder approaching the sub-picosecond scale of the nonthermal regime. The lattice disorder time shows strong nonlinear dependence on the laser fluence with a crossover behavior from thermal-driven to nonthermal-dominant kinetics, which is also verified by ab initio and two-temperature molecular dynamics simulations. This study elucidates the impact of bonding orbitals on lattice stability with a unifying interpretation on photoinduced melting.

Poller (blocking) screw with intramedullary femoral nailing for subtrochanteric femoral non-unions: clinical outcome and review of concepts.

INTRODUCTION: Surgery to treat nonunion resulted from malalignment is challenging since correction and bone union should be achieved simultaneously. To report the clinical outcomes achieved through reconstruction of sub-trochanteric femoral fractures by femoral nailing using a poller screw and to review the current concepts. MATERIALS AND METHODS: Fourteen patients (11 men and 3 women; mean age 56.4 years) who were diagnosed with non-union of subtrochanteric femoral fractures and who underwent intramedullary nailing with blocking screws between August 2013 and March 2019, with at least 1 year follow-up, were analyzed retrospectively. The preoperative and postoperative Centrum-Collum-Diaphyseal angle and anterior angulation angle were measured. Bone union time, position and number of poller screws used, and complications were analyzed. Functional assessment was performed by evaluating the Harris hip score. The related literature was searched, and 14 clinical studies on the treatment of sub-trochanteric non-union were analyzed. RESULTS: Bone union was achieved in 12/14 cases (85.7%) at the final follow-up within a mean of 6.52 (3-12) months. Bone union was also achieved in two patients lacking bone union at the final follow-up through bone grafting and augmented plating. No cases developed complications, including infection and bone necrosis, and the varus deformity and anterior angulation significantly improved from a preoperative mean of 12.4° and 9.4° to postoperative mean 3.8° and 2.4°, respectively. The mean Harris hip score at the final follow-up was 87.07 (73-98) points. Analysis of published literature revealed high rates of bone union (78-100%) through various fixation methods. CONCLUSION: Correction with blocking screws and rigid fixation with intramedullary nailing to treat sub-trochanteric-non-union-caused malalignment can yield good clinical and radiological outcomes.

Matched Comparison of Bone Transport Using External Fixator Over a Nail Versus External Fixator Over a Plate for Segmental Tibial Bone Defects.

OBJECTIVE: To compare the outcomes and complications of bone transport over a nail (BTON) with those of bone transport over a plate (BTOP) for segmental tibial bone defects. DESIGN: Retrospective matched study design. SETTING: A major metropolitan tertiary referral trauma center. PATIENTS: Thirty-six patients with segmental tibial bone defects of >4 cm were included in this study. INTERVENTION: Either BTON or BTOP was performed on 18 patients. MAIN OUTCOME MEASUREMENTS: We compared the healing of the distraction process and of the docking site between the techniques. Distraction parameters including external fixator (EF) time, external fixation index, and healing index were compared. Bone and functional results were compared according to the Paley-Maar classification. Complications associated with each procedure were compared. RESULTS: Both BTON and BTOP achieved similar rates of primary union (83% vs. 89%) at the distraction or docking site. Significantly less time wearing an EF was needed for BTOP than for BTON (2.8 vs. 5.4 months; P < 0.01). The external fixation index was significantly lower for BTOP than for BTON (0.45 vs. 0.94 mo/cm; P < 0.01), whereas the healing indexes were similar. The final outcomes and complication incidences were not significantly different. CONCLUSIONS: The EF time was significantly shorter for BTOP than for BTON; however, the final outcomes were similar. Therefore, BTOP could be considered an attractive option for bone transport in patients with segmental tibial defects. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Conventional bicortical pin substitution with a novel unicortical pin in external fixation: A biomechanical study.

INTRODUCTION: As most patients with polytrauma or open fractures are converted from temporary external fixation to definite stabilization, the prevention of complications such as infection is especially important. To overcome the high risk of infection associated with the use of the conventional bicortical pin for temporary external fixation, the authors developed a novel unicortical pin and analyzed it in a biomechanical study. METHODS: The unicortical pin consisted of an inner screw, purchasing the cortical bone, and an outer sleeve with 6 spikes. A bicortical pin was used for the purpose of comparison. A fracture gap model was stabilized using a monoplanar configuration. Both the unicortical pins (Uni group) and bicortical pins (Bi group) underwent axial compressive and torsional load testing using a servo-hydraulic testing machine. Stiffness, load to failure, and mode of failure were documented. RESULTS: Stiffness and load to failure of the Uni group (average, 40.5 N/mm and 1098.4 N, respectively) were greater than that of the Bi group (average, 33.7 N/mm and 968.6 N, respectively) in the axial compressive load test (P = 0.008 and 0.032). Stiffness and load to failure of the Uni group (average, 1.2 Nm/degree and 1.7 Nm, respectively) were also significantly higher than those of the Bi group (average, 0.8 Nm/degree and 0.6 Nm, respectively) in the torsional load test (P = 0.008 and 0.016). All pins in the Bi group were bent at the pin-synthetic bone interface without synthetic bone failure. Contrarily, the Uni group did not show any pin bending or failure. However, in the axial compression test, partial cracks in the synthetic bone were found at the interface with spikes in the outer shell. In addition, in the torsion test, incomplete fractures were seen through the inner screws' holes. CONCLUSION: Compared with the conventional bicortical pin, the newly designed unicortical pin significantly increased fracture stability under both axial compressive and torsional loads. The unicortical pin can be considered an alternative biomechanical solution to obtain adequate stability when performing external fixation of fractures.

Correlation between structural phase transition and surface chemical properties of thin film SrRuO3/SrTiO3 (001).

The correlation between the structural phase transition (SPT) and oxygen vacancy in SrRuO3 (SRO) thin films was investigated by in situ X-ray diffraction (XRD) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In situ XRD shows that the SPT occurs from a monoclinic SRO phase to a tetragonal SRO phase near ∼200 °C, regardless of the pressure environment. On the other hand, significant core level shifts in both the Ru and Sr photoemission spectra are found under ultrahigh vacuum, but not under the oxygen pressure environment. The directions and behavior of the core level shift of Ru and Sr are attributed to the formation of oxygen vacancy across the SPT temperature of SRO. The analysis of in situ XRD and AP-XPS results provides an evidence for the formation of metastable surface oxide possibly due to the migration of internal oxygen atoms across the SPT temperature, indicating the close relationship between oxygen vacancy and SPT in SRO thin films.

Crosslinking Effect on Thermal Conductivity of Electrospun Poly(acrylic acid) Nanofibers.

The thermal conductivity (k) of poly(acrylic acid) (PAA) nanofibers, which were electrospun at various electrospinning voltages, was measured using suspended microdevices. While the thermal conductivities of the as-spun PAA nanofibers varied depending on the electrospinning voltages, the most pronounced 3.1-fold increase in thermal conductivity in comparison to that of bulk PAA was observed at the electrospinning voltage of 14 kV. On the other hand, a reduction in the thermal conductivity of the nanofibers was observed when the as-spun nanofibers were either thermally annealed at the glass transition temperature of PAA or thermally crosslinked. It is notable that the thermal conductivity of crosslinked PAA nanofibers was comparable to that of crosslinked bulk PAA. Polarized Raman spectroscopy and Fourier transform infrared spectroscopy verified that the k enhancement via electrospinning and the k reduction by the thermal treatments could be attributed to the conformational changes between gauche and trans states, which may be further related to the orientation of molecular chains. In contrast, hydrogen bonds did not contribute significantly to the k enhancement. Additionally, the suppression of k observed for the crosslinked PAA nanofibers might result from the shortening of single molecular chains via crosslinking.

Real-Time Structural and Electrical Characterization of Metal-Insulator Transition in Strain-Modulated Single-Phase VO2 Wires with Controlled Diameters.

Single-crystal VO2 wires have gained tremendous popularity for enabling the study of the fundamental properties of the metal-insulator transition (MIT); however, it remains tricky to precisely measure the intrinsic properties of the transitional phases with controlled wire-growth properties, such as diameter. Here, we report a facile method for growing VO2 wires with controlled diameters by separating the formation of the liquidus V2O5 seed droplets from the evolution of the VO2 wire using oxygen gas. The kinetic analyses suggest that the growth proceeds via the VS (vapor-solid) mechanism, whereas the droplet determines the size and the location of the wire. In situ Raman spectroscopy combined with analyses of the electrical properties of an individual wire allowed us to construct a diameter-temperature phase diagram from three initial phases (i.e., M1, T, and M2), which were created by misfit stress from the substrate and were preserved at room temperature. We also correlated this relation with resistivity-diameter and activation energy-diameter relations supported by theoretical modeling. These carefully designed approaches enabled us to elucidate the details of the phase transitions over a wide range of stress conditions, offering an opportunity to quantify relevant thermodynamic and electronic parameters (including resistivities, activation energies, and energy barriers of the key insulating phases) and to explain the intriguing behaviors of the T phase during the MIT.