RESUMO
SrAl2O4:Eu2+,Dy3+ long afterglow phosphors with one-dimensional nanostructures were synthesized by a hydrothermal method followed by post-annealing, and subsequently CdS was uniformly coated on their surfaces by a sol-gel approach. The nanocomposite system can significantly enhance the photocatalytic activity for the degradation of methyl orange and hexavalent chromium under ultraviolet and visible light irradiation. After the modification treatment with a 1 : 2 molar ratio of CdS to SrAl2O4:Eu2+,Dy3+ nanophosphors, the degradation rate of methyl orange can increase by 2.5 times and reach a maximum of 96.3% under visible light illumination for 30 min. The enhancement of photocatalytic activity originates from the improvement of light usage efficiency due to the hole migration from SrAl2O4:Eu2+,Dy3+ phosphors to the CdS semiconductor and the reutilization of SrAl2O4:Eu2+,Dy3+ luminescence.
RESUMO
Hybrid nanostructures can show enormous potential in different areas because of their unique structural configurations. Herein, Fe@Al2O3 hybrid nanotubes are constructed via a homogeneous coprecipitation method followed by subsequent annealing in a reducing atmosphere. The introduction of zero band gap Fe nanocrystals in the wall of ultrawide band gap Al2O3 insulator nanotubes results in the formation of charge trap centers, and correspondingly a single hybrid nanotube-based two-terminal device can show reversible negative resistive switching (RS) characteristics with symmetrical negative differential resistance (NDR) at relatively high operation bias voltages. At a large bias voltage, holes and electrons can be injected into traps at two ends from electrodes, respectively, and then captured. The bias voltage dependence of asymmetrical filling of charges can lead to a reversible variation of built-in electromotive force, and therefore the symmetrical negative RS with NDR arises from two reversible back-to-back series bipolar RS. At a low readout voltage, the single Fe@Al2O3 hybrid nanotube can show an excellent nonvolatile memory feature with a relatively large switching ratio of â¼30. The bias-governed reversible negative RS with superior stability, reversibility, nondestructive readout, and remarkable cycle performance makes it a potential candidate in next-generation erasable nonvolatile resistive random access memories.
RESUMO
miR-34a is a conserved microRNA highly expressed in the brain. It is thought to play critical roles in regulating many aspects of brain development and function, such as neural stem cell proliferation and differentiation, neuronal migration and apoptosis, fear memory consolidation, etc. However, the assessment of its function was mainly conducted through vector-mediated overexpression and miRNA sponge or antagomir-mediated functional suppression, therefore may suffer from nonspecific off-target effects or incomplete inactivation. We thus analyzed mouse model with a targeted deletion of miR-34a which completely abolishes its expression. To our surprise, loss of miR-34a led to neither an obvious change in brain size, morphology or cortical lamination, nor impaired marker gene expression in major excitatory and inhibitory neuron types in the neocortex. In addition, miR-34a ablation did not affect fear memory formation or consolidation, as well as the anxiety or depression related behavior. However, the performance of mice in rotarod assay was significantly affected, suggesting a defect in motor activity in miR-34a deficient mice. As neocortical parvalbumin (PV) neurons are known for high level miR-34a expression, we also tested the effect of PV-Cre-mediated conditional miR-34a deletion. Similar as germline deletion, PV neuron specific miR-34a deletion did not affect cortical lamination or PV expression in the neocortex. Our studies suggest that, although miR-34a may be involved in regulating certain aspects of brain development or function, such as motor activity, it does not play a significant role in regulating brain morphogenesis, cortical lamination or neocortical neuron subtype specification, and it is also dispensable for fear memory formation, expression and consolidation.