Ab Initio Study of Doping Mechanisms in BaTiO3-BiYO3

A density functional plane-wave pseudopotential method is used to study the doping mechanisms of impurity defects（BiBa, YTi） in BaTiO3- BiYO3. Single BiBa and YTi impurities have little structure distortion. Bi forms ionic bond with nearby O atom in single Bi impurity, Y formed [YO6] octahedral in single Y impurity. However, in the co-doped BiB~ and Yr~ structure, Bi formed three valence bonds with nearby O atom, which causes the large structure distortion. The doped ion makes the mobile of Ti4~ difficult and loss local ferroelectricity, which will broaden the dielectric constant temperature curve and increase the temperature stability of BaTiO3 ceramic matrix.

Longitudinal bending stiffness does not affect running economy in Nike Vaporfly Shoes

Purpose This study aimed to determine the independent effect of the curved carbon-fiber plate in the Nike Vaporfly 4%shoe on running economy and running biomechanics.Methods Fifteen healthy male runners completed a metabolic protocol and a biomechanics protocol.In both protocols participants wore 2 different shoes,an intact Nike Vaporfly 4%(VF_(intact))and a cut Nike Vaporfly 4%(VF_(cut)).The VF_(cut) had 6 medio-lateral cuts through the carbon-fiber plate in the forefoot to reduce the effectiveness of the plate.In the metabolic protocol,participants ran at 14 km/h for 5 min,twice with each shoe,on a force-measuring treadmill while we measured metabolic rate.In the biomechanics protocol,participants ran across a runway with embedded force plates at 14 km/h.We calculated running economy,kinetics,and lower limb joint mechanics.Results Running economy did not significantly differ between shoe conditions(on average,0.55%±1.77%(mean±SD))worse in the VF_(cut) compared to the VF_(intact);95%confidence interval(-1.44%to 0.40%).Biomechanical differences were only found in the metatarsophalangeal(MTP)joint with increased MTP dorsiflexion angle,angular velocity,and negative power in the VF_(cut).Contact time was 1%longer in the VF_(intact).Conclusion Cutting the carbon-fiber plate and reducing the longitudinal bending stiffness did not have a significant effect on the energy savings in the Nike Vaporfly 4%.This suggests that the plate's stiffening effect on the MTP joint plays a limited role in the reported energy savings,and instead savings are likely from a combination and interaction of the foam,geometry,and plate.

Optical and defect properties of S-doped and Al-doped GaSe crystals

S-doped and Al-doped GaSe crystals are promising materials for their applications in nonlinear frequency conversion devices. The optical and defect properties of pure, S-doped, and Al-doped GaSe crystals were studied by using photoluminescence（PL） and Fourier transform infrared spectroscopy（FT-IR）. The micro-topography of（0001） face of these samples was observed by using scanning electron microscope（SEM） to investigate the influence of the doped defects on the intralayer and interlayer chemical bondings. The doped S or Al atoms form the SSe^0 or AlGa^＋1） substitutional defects in the layer GaSe structure, and the positive center of AlGa-^＋1 could induce defect complexes. The incorporations of S and Al atoms can change the optical and mechanical properties of the GaSe crystal by influencing the chemical bonding of the layer structure. The study results may provide guidance for the crystal growth and further applications of S-doped and Al-doped GaSe crystals.