Neurons have the remarkable ability to polarize even in symmetrical in vitro environments. Although recent studies have shown that asymmetric intracellular signals can induce neuronal polarization, it remains unclear how these polarized signals are organized without asymmetric cues. We describe a novel protein, named shootin1, that became up-regulated during polarization of hippocampal neurons and began fluctuating accumulation among multiple neurites. Eventually, shootin1 accumulated asymmetrically in a single neurite, which led to axon induction for polarization. Disturbing the asymmetric organization of shootin1 by excess shootin1 disrupted polarization, whereas repressing shootin1 expression inhibited polarization. Overexpression and RNA interference data suggest that shootin1 is required for spatially localized phosphoinositide-3-kinase activity. Shootin1 was transported anterogradely to the growth cones and diffused back to the soma; inhibiting this transport prevented its asymmetric accumulation in neurons. We propose that shootin1 is involved in the generation of internal asymmetric signals required for neuronal polarization.
Structural and electrical properties of Al‐doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD‐AZO films exhibit a unique layer‐by‐layer structure consisting of a ZnO matrix and Al2O3 dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al2O3 dopant layer deposited during one ALD cycle could provide ≈4.5 × 1013 cm−2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD‐AZO films when the interval between the Al2O3 layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD‐AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.
Ge – Sb – Te alloys are widely used for data recording based on the rapid and reversible amorphous-to-crystalline phase transformation that is accompanied by increases in the optical reflectivity and the electrical conductivity. However, uncertainties about the optical band gaps and electronic transport properties of these phases have persisted because of inappropriate interpretation of reported data and the lack of definitive analytical studies. In this paper we characterize the most widely used composition, Ge2Sb2Te5, in its amorphous, face-centered-cubic, and hexagonal phases, and explain the origins of inconsistent or unphysical results in previous reports. The optical absorption in all of these phases follows the relationship αhν∝(hν−Egopt)2, which corresponds to the optical transitions in most amorphous semiconductors as proposed by Tauc, Grigorovici, and Vancu [Tauc et al., Phys. Status Solidi 15, 627 (1966)], and to those in indirect-gap crystalline semiconductors. The optical band gaps of the amorphous, face-centered-cubic, and hexagonal phases are 0.7, 0.5, and 0.5eV, respectively. The subgap absorption in the amorphous phase shows an exponential decay with an Urbach slope of 81meV. We measured the photoconductivity of amorphous Ge2Sb2Te5 and determined a mobility-lifetime product of 3×10−9cm2∕V. The spectral photoconductivity shows a threshold at about 0.7eV, in agreement with our analysis of the optical band gap. The face-centered-cubic and hexagonal phases are highly conductive and do not show freeze-out; even at 5K the density of free carriers remains at 1019–1020cm−3, so these are degenerate semiconductors in which the Fermi level resides inside a band. In the hexagonal phase, the effect of free electrons on the Hall coefficient is significant at high temperatures. When the Hall data are fitted using the two-carrier analysis, the hole mobility is found to decrease slowly with temperature, as expected. The considerations discussed in this paper can be readily applied to study related chalcogenide materials.
Mesenchymal stem cells (MSCs) may hold great promise for treating diabetic wounds. However, it is difficult for a clinician to use MSCs because they have not been commercialized. Meanwhile, a new commercial drug that contains adipose-derived stem cells (ASCs) has been developed. The purpose of this study was to examine the potential of allogeneic ASC sheets for treating diabetic foot ulcers. Fifty-nine patients with diabetic foot ulcers were randomized to either the ASC treatment group (n = 30) or a control group treated with polyurethane film (n = 29). Either an allogeneic ASC sheet or polyurethane film was applied on diabetic wounds weekly. These wounds were evaluated for a maximum of 12 weeks. Complete wound closure was achieved for 73% in the treatment group and 47% in the control group at week 8. Complete wound closure was achieved for 82% in the treatment group and 53% in the control group at week 12. The Kaplan-Meier median times to complete closure were 28.5 and 63.0 days for the treatment group and the control group, respectively. There were no serious adverse events related to allogeneic ASC treatment. Thus, allogeneic ASCs might be effective and safe to treat diabetic foot ulcers.
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