Ultraviolet semiconductor lasers are widely used for applications in photonics, information storage, biology and medical therapeutics. Although the performance of gallium nitride ultraviolet lasers has improved significantly over the past decade, demand for lower costs, higher powers and shorter wavelengths has motivated interest in zinc oxide (ZnO), which has a wide direct bandgap and a large exciton binding energy. ZnO-based random lasing has been demonstrated with both optical and electrical pumping, but random lasers suffer from reduced output powers, unstable emission spectra and beam divergence. Here, we demonstrate electrically pumped Fabry-Perot type waveguide lasing from laser diodes that consist of Sb-doped p-type ZnO nanowires and n-type ZnO thin films. The diodes exhibit highly stable lasing at room temperature, and can be modelled with finite-difference time-domain methods.

The carrier recombination processes in ZnO quantum dots ͑ϳ4 nm in diameter͒, ZnO nanocrystals ͑ϳ20 nm in diameter͒ and bulk ZnO crystal have been studied using photoluminescence ͑PL͒ spectroscopy in the temperature range from 8.5 to 300 K. The obtained experimental data suggest that the ultraviolet PL in ZnO quantum dots originates from recombination of the acceptor-bound excitons for all temperatures. In the larger size ZnO nanocrystals, the recombination of the acceptor-bound excitons is the dominant contribution to PL only at low temperature ͑T Ͻ 150 K͒. For higher temperatures ͑T Ͼ 150 K͒, PL is mostly due to recombination of the donor-bound excitons. Recombination processes in ZnO quantum dots and nanocrystals differ from those in bulk ZnO mainly because of the large surface-to-volume ratio in both types of nanoparticles and, consequently, a large number of acceptor defects near the surface. No strong inhomogeneous broadening has been observed in ultraviolet PL from ZnO quantum dots. Our results shed light on the carrier-recombination processes in ZnO quantum dots and nanocrystals, and can be used for the ZnO nanostructure optimization for the proposed optoelectronic and spintronic applications.

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The water strider is an insect that lives on the surface of ponds, slow streams, marshes, and other quiet waters. [1][2][3][4] Trying to understand the physical mechanism behind its ability to float on the water surface has become a very interesting area for bio-inspired research. [5,6] Hu et al. have demonstrated that there are two kinds of upward forces to support the water strider's weight: the curvature force and the buoyancy force. Through theoretical analysis, they have concluded that the curvature force produced by the insect's legs is much larger than the buoyancy force. [7,8] Furthermore, Cheng, [9] Andersen, [10,11] and Gao and Jiang [12] have discovered that the legs of water striders have superhydrophobic coatings that bear hierarchical structures of many oriented tiny hairs with fine nanogrooves. The superhydrophobic coatings were believed to be responsible for the water striders' floating. However, since many other kinds of insects, such as mosquitoes, can float on the water surface with only normal hydrophobic coatings, it is not clear why superhydrophobic coatings are required for the water strider's legs. In the work reported here, using gold threads that are modified with normal hydrophobic or superhydrophobic coatings as model systems, we studied to what extent the hydrophobicity contributes to the gold thread's floating and movement on the water surface. In addition, combining experimental results and theoretical force analysis, we report, for the first time, that deformation of the gold thread contributes to the total supporting force of the water on the floating gold thread. For easily deformed floating objects, such as very thin gold threads or legs of water striders, the contribution of deformation is significant compared to the other components of the supporting force. Our results suggest that the superhydrophobic coating of a water strider's legs can not only provide a larger supporting force, but also help to decrease the insect's total density beneath the water surface and allow it to move faster on the water surface. Therefore the superhydrophobic coating is indispensable, although the normal hydrophobic coating provides enough supporting force for the water strider merely to float. We anticipate that our results provide a deeper understanding of the mechanism of aquatic insects' floating, and hope that it may lead to further research on drag-reducing materials and rapid underwater motion.In an attempt to understand why a surperhydrophobic surface is needed by water striders, we modified gold threads with superhydrophobic coatings (contact angle > 150°) or normally hydrophobic coatings (contact angle ≈ 110°).[13] By comparing these two kinds of gold threads, we expected to obtain some information on how the supporting force is enhanced by superhydrophobicity. Several techniques have been developed to prepare superhydrophobic coatings; [14][15][16][17][18] however, here we needed a new technique to fabricate superhydrophobic coatings on curved surfaces such as gold threads. In our prev...

Electrically pumped ZnO quantum well diode lasers are reported. Sb-doped p-type ZnO/Ga-doped n-type ZnO with an MgZnO/ZnO/MgZnO quantum well embedded in the junction was grown on Si by molecular beam epitaxy. The diodes emit lasing at room temperature with a very low threshold injection current density of 10 A / cm 2. The lasing mechanism is exciton-related recombination and the feedback is provided by close-loop scattering from closely packed nanocolumnar ZnO grains formed on Si.

Surface microstructures of solids play a significant role in producing superhydrophobic surfaces. In the present paper, the Cassie-Baxter and Wenzel models on a rough substrate are examined from the viewpoints of geometry and energy. The result shows that if the air beneath a droplet on a sinusoidal substrate is open to the atmosphere, the superhydrophobic state can exist only when the substrate is hydrophobic, and that the geometric parameters of the microstructure have a great influence on the wetting behavior. Two mechanisms that may lead to a superhydrophobic property from a hydrophilic substrate are addressed. Firstly, for closed or airproof microstructures (e.g. honeycomb structures), a negative Laplace pressure difference caused by the trapped air under the drop can keep the balance of the liquid/vapor interface. Secondly, some special topologies of surface structures satisfying a certain geometric condition may also lead to the formation of a Cassie-Baxter state even if the microstructures are open to the air. Therefore, some surface morphologies may be designed to obtain superhydrophobic properties on hydrophilic surfaces. The present study is also helpful to understand some superhydrophobic phenomena observed in experiments and in nature.

Oral squamous cell carcinoma (OSCC), with high potential for metastasis, is the most common malignant tumor of the head and neck. Cancer-associated fibroblasts (CAFs) are the main stromal cells in the microenvironment and aggravate tumor progression. However, whether CAFs are associated with the progression of OSCC remains unknown and the underlying mechanism remains unclear. In the present study, the role of CAFs in mediating OSCC cell migration and invasion was investigated, and the participation of exosomal miR-382-5p in this process was elucidated. In this study, according to the α-SMA staining with immunohistochemistry, 47 OSCC patients were divided into CAFs-rich and CAFs poor groups, and association of CAF density and clinicopathologic features of the OSCC patients were analyzed with Pearson χ 2 test. Transwell assay was used for evaluating cell migration and invasion ability of OSCC cells after being co-cultured with NFs or CAFs, or after added exosomes. qPCR was used to detect the expression of miR-382-5p. Western blot analysis was used to measure the expression of migration and invasion-associated proteins. In the present study, the CAF density in tumor tissues was found to be relevant to OSCC lymph node metastasis and TNM stage. Furthermore, we revealed that miR-382-5p was overexpressed in CAFs compared with that in fibroblasts of adjacent normal tissue and miR-382-5p overexpression was responsible for OSCC cell migration and invasion. Finally, we demonstrated that CAF-derived exosomes transported miR-382-5p to OSCC cells. The present study confirmed a new mechanism of CAF-facilitated OSCC progression and may be beneficial for identifying new cancer therapeutic targets.

Ponseti clubfoot treatment has become more popular during the last decade because of its high initial correction rate. But the most common problem affecting the long-term successful outcome is relapse of the deformity. Non-compliance with Ponseti brace protocol is a major problem associated with relapse. Although more comfortable braces have been reported to improve the compliance, they all have the same design and no significant changes have been made to the protocols. After refinement in the Ponseti method and emphasizing the importance of brace to parents, the relapse rate has been markedly decreased. Nevertheless, there are patients who do not have any recurrence although they are not completely compliant with the brace treatment, whereas other patients have a recurrence even though they are strictly compliant with the brace treatment. The aim of this article is to review the relapse of clubfoot and the function of the brace and to develop an individualized brace protocol for each patient by analyzing the mechanism of the brace and the biomechanical properties of muscles, tendons, and ligaments.