Grafts vs. flaps: a comparative study of Bracka repair and staged transverse preputial island flap urethroplasty for proximal hypospadias with severe ventral curvature.

Introduction: Bracka repair and staged transverse preputial island flap urethroplasty are both significant methods in treating proximal hypospadias. They utilize the flap and graft techniques, respectively, to achieve a satisfactory success rate. This study aimed to compare the outcomes of these 2 methods in the treatment of proximal hypospadias with severe ventral curvature. Methods: We retrospectively analyzed 117 cases of proximal hypospadias with severe ventral curvature who had undergone either Bracka repair (n = 62) or staged transverse preputial island flap urethroplasty (n = 55). All operations were performed by a single surgeon, and the choice of method was determined by the surgeon's preference based on his experience. Cosmetic outcome was evaluated with Pediatric Penile Perception Score (PPPS). Patients' characteristics including age, penis length, glans diameter, length of the urethral defect and ventral curvature degree, cosmetic outcomes, and complication rates were all compared. Results: There was no significant difference in age, penis length, glans diameter, length of the urethral defect, or ventral curvature degree. In the Bracka group, there were 5 patients with fistula, 1 patient with stricture, and 1 case of dehiscence. In the staged transverse preputial island flap urethroplasty group, there were 4 patients with fistula, 1 with stricture, and 2 with diverticulum. The scores of shaft skin and general appearance were consistently higher in the Bracka group than in the staged transverse preputial island flap urethroplasty group. The differences in complication rate and cosmetic outcome were not statistically different (P > 0.05). Conclusions: Bracka repair and staged transverse preputial island flap urethroplasty are both satisfactory staged surgical options for proximal hypospadias with severe ventral curvature and have similar complication rates. Bracka repair may create a better appearance, but more studies are needed to confirm this finding. Pediatric surgeons should consider additional factors, such as the patient's specific condition, parents' inclination, and personal experience, rather than safety, to make the best choice between the 2 methods.

Self-supervised learning and prediction of microstructure evolution with convolutional recurrent neural networks.

Microstructural evolution is a key aspect of understanding and exploiting the processing-structure-property relationship of materials. Modeling microstructure evolution usually relies on coarse-grained simulations with evolution principles described by partial differential equations (PDEs). Here we demonstrate that convolutional recurrent neural networks can learn the underlying physical rules and replace PDE-based simulations in the prediction of microstructure phenomena. Neural nets are trained by self-supervised learning with image sequences from simulations of several common processes, including plane-wave propagation, grain growth, spinodal decomposition, and dendritic crystal growth. The trained networks can accurately predict both short-term local dynamics and long-term statistical properties of microstructures assessed herein and are capable of extrapolating beyond the training datasets in spatiotemporal domains and configurational and parametric spaces. Such a data-driven approach offers significant advantages over PDE-based simulations in time-stepping efficiency and offers a useful alternative, especially when the material parameters or governing PDEs are not well determined.

Dynamics of Lithium Insertion in Electrochromic Titanium Dioxide Nanocrystal Ensembles.

Nanocrystalline anatase TiO2 is a robust model anode for Li insertion in batteries. The influence of nanocrystal size on the equilibrium potential and kinetics of Li insertion is investigated with in operando spectroelectrochemistry of thin film electrodes. Distinct visible and infrared responses correlate with Li insertion and electron accumulation, respectively, and these optical signals are used to deconvolute bulk Li insertion from other electrochemical responses, such as double-layer capacitance, pseudocapacitance, and electrolyte leakage. Electrochemical titration and phase-field simulations reveal that a difference in surface energies between anatase and lithiated phases of TiO2 systematically tunes the Li-insertion potentials with the particle size. However, the particle size does not affect the kinetics of Li insertion in ensemble electrodes. Rather, the Li-insertion rates depend on the applied overpotential, electrolyte concentration, and initial state of charge. We conclude that Li diffusivity and phase propagation are not rate limiting during Li insertion in TiO2 nanocrystals. Both of these processes occur rapidly once the transformation between the low-Li anatase and high-Li orthorhombic phases begins in a particle. Instead, discontinuous kinetics of Li accumulation in TiO2 particles prior to the phase transformations limits (dis)charging rates. We demonstrate a practical means to deconvolute the nonequilibrium charging behavior in nanocrystalline electrodes through a combination of colloidal synthesis, phase field simulations, and spectroelectrochemistry.

Effects of catalyst droplets on wire growth and the resulting branched structures during VLS growth.

The vapor-liquid-solid (VLS) method is vastly employed to grow hierarchical structures with unique properties. However, key questions remain, such as what controls the branched structures and what the roles of the catalyst droplet size are during the growth. Here, an in-depth understanding of the kinetics of the nucleation, growth, and subsequent coalescence processes of Bi liquid catalyst droplets is provided by direct observation of PbSe branched wire growth in an environmental transmission electron microscope. This brings a kinetic control of the branch density by varying the parameters, such as temperature. In addition, the dependence of the wire growth rate on the catalyst droplet size is revealed, i.e., the smaller the catalyst size the larger the wire growth rate, unlike the wire growth controlled by the Gibbs-Thomson effect, possibly due to different mass transport pathways and atomic surface diffusion. These results extend the fundamental understanding of the VLS growth mechanism of branched structures and benefit the structure design of hierarchical materials with tailored properties.

Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr0.1Bi2Se3.

Superconductivity mediated by phonons is typically conventional, exhibiting a momentum-independent s-wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions. Here, by performing inelastic neutron scattering measurements on a superconducting single crystal of Sr0.1Bi2Se3, a prime candidate for realizing topological superconductivity by doping the topological insulator Bi2Se3, we find that there exist highly anisotropic phonons, with the linewidths of the acoustic phonons increasing substantially at long wavelengths, but only for those along the [001] direction. This observation indicates a large and singular electron-phonon coupling at small momenta, which we propose to give rise to the exotic p-wave nematic superconducting pairing in the MxBi2Se3 (M = Cu, Sr, Nb) superconductor family. Therefore, we show these superconductors to be example systems where electron-phonon interaction can induce more exotic superconducting pairing than the s-wave, consistent with the topological superconductivity.

Spin-Wave Excitations Evidencing the Kitaev Interaction in Single Crystalline α-RuCl_{3}.

Kitaev interactions underlying a quantum spin liquid have long been sought, but experimental data from which their strengths can be determined directly, are still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality single crystals of α-RuCl_{3}, we observe spin-wave spectra with a gap of ∼2 meV around the M point of the two-dimensional Brillouin zone. We derive an effective-spin model in the strong-coupling limit based on energy bands obtained from first-principles calculations, and find that the anisotropic Kitaev interaction K term and the isotropic antiferromagnetic off-diagonal exchange interaction Γ term are significantly larger than the Heisenberg exchange coupling J term. Our experimental data can be well fit using an effective-spin model with K=-6.8 meV and Γ=9.5 meV. These results demonstrate explicitly that Kitaev physics is realized in real materials.