Power Scaling of High Power Solid State Lasers.

The solid-state laser is one of the most widely used lasers in scientific research and industrial applications. This thesis describes detailed investigations of two modern architectures of high power cw solid-state lasers, a 20 W diode-pumped Yb:YAG thin disc laser and 300 W diode-pumped Nd:YAG rod laser. With the thin disc laser architecture, the signal beam must fit to the pump area on the disc defined by the multi-pass diode pump configuration. The beam propagation, beam diameter, phase and thermal effects for various cavity configurations are investigated theoretically and experimentally. In addition, the internal loss, small signal gain, and thermal lensing effect are essential properties to construct the laser system but usually unknown. The theories and methodologies to obtain these properties are presented and the experimental results are compared. In a second phase of the project, the multi-mode and single-mode operation of a high power diode-pumped rod laser system are examined and compared to the thin disc system. Thermal effects on the phase, beam quality and brightness are examined and future applications and improvements considered

Optimal Length of Hybrid Metal???Semiconductor Nanorods for Photocatalytic Hydrogen Generation

Hybrid metal???semiconductor nanostructures have been utilized as attractive model catalysts for understanding photocatalytic reactions because each geometrical factor is precisely controllable. Herein, we prepared Pt-tipped CdSe nanorods and tailored their length. The maximum hydrogen-evolution rates were obtained in the length of 15???20 nm for the single-tipped nanorods and 30 nm for the double-tipped nanorods. By means of time-resolved spectroscopic analysis and kinetic modeling, we revealed that the hydrogen-evolution rate was directly proportional to the amount of long-lived charge-transfer state dominated by the interplay between the carrier diffusion to the metal center and recombination. As the length increased, the absorption cross section increased, whereas the dissociation rate of excitons decreased. As a result, the number of carriers migrating to the metal tips was maximized with the 15???20 nm nanorods per tip. This information provides a direct guideline to design the optimal geometrical configuration of metal???semiconductor hybrid catalysts

Identification and profiling of novel microRNAs in the <it>Brassica rapa</it> genome based on small RNA deep sequencing

Abstract Background MicroRNAs (miRNAs) are one of the functional non-coding small RNAs involved in the epigenetic control of the plant genome. Although plants contain both evolutionary conserved miRNAs and species-specific miRNAs within their genomes, computational methods often only identify evolutionary conserved miRNAs. The recent sequencing of the Brassica rapa genome enables us to identify miRNAs and their putative target genes. In this study, we sought to provide a more comprehensive prediction of B. rapa miRNAs based on high throughput small RNA deep sequencing. Results We sequenced small RNAs from five types of tissue: seedlings, roots, petioles, leaves, and flowers. By analyzing 2.75 million unique reads that mapped to the B. rapa genome, we identified 216 novel and 196 conserved miRNAs that were predicted to target approximately 20% of the genome’s protein coding genes. Quantitative analysis of miRNAs from the five types of tissue revealed that novel miRNAs were expressed in diverse tissues but their expression levels were lower than those of the conserved miRNAs. Comparative analysis of the miRNAs between the B. rapa and Arabidopsis thaliana genomes demonstrated that redundant copies of conserved miRNAs in the B. rapa genome may have been deleted after whole genome triplication. Novel miRNA members seemed to have spontaneously arisen from the B. rapa and A. thaliana genomes, suggesting the species-specific expansion of miRNAs. We have made this data publicly available in a miRNA database of B. rapa called BraMRs. The database allows the user to retrieve miRNA sequences, their expression profiles, and a description of their target genes from the five tissue types investigated here. Conclusions This is the first report to identify novel miRNAs from Brassica crops using genome-wide high throughput techniques. The combination of computational methods and small RNA deep sequencing provides robust predictions of miRNAs in the genome. The finding of numerous novel miRNAs, many with few target genes and low expression levels, suggests the rapid evolution of miRNA genes. The development of a miRNA database, BraMRs, enables us to integrate miRNA identification, target prediction, and functional annotation of target genes. BraMRs will represent a valuable public resource with which to study the epigenetic control of B. rapa and other closely related Brassica species. The database is available at the following link: http://bramrs.rna.kr [1].</p

Pt cocatalyst morphology on semiconductor nanorod photocatalysts enhances charge trapping and water reduction

In photocatalysis, metal-semiconductor hybrid structures have been proposed for ideal photocatalytic systems. In this study, we investigate the effect of morphology and surface nature of Pt cocatalysts on photocatalytic hydrogen evolution activity in Pt-tipped CdSe nanorods. Three distinct morphologies of Pt cocatalysts were synthesized and employed as visible light photocatalysts. The rough tips exhibit the highest activity, followed by the round and cubic tips. Kinetic investigations using transient absorption spectroscopy reveal that the cubic tips exhibit lower charge-separated states feasible for reacting with water and water reduction rates due to their defectless surface facets. In contrast, the rough tips show a similar charge-separation value but a two-fold higher surface reaction rate than the round tips, resulting in a significant enhancement of hydrogen evolution. These findings highlight the importance of rational design on metal cocatalysts in addition to the main semiconductor bodies for maximizing photocatalytic activities

Pt cocatalyst morphology on semiconductor nanorod photocatalysts enhances charge trapping and water reduction

In photocatalysis, metal-semiconductor hybrid structures have been proposed for ideal photocatalytic systems. In this study, we investigate the effect of morphology and surface nature of Pt cocatalysts on photocatalytic hydrogen evolution activity in Pt-tipped CdSe nanorods. Three distinct morphologies of Pt cocatalysts were synthesized and employed as visible light photocatalysts. The rough tips exhibit the highest activity, followed by the round and cubic tips. Kinetic investigations using transient absorption spectroscopy reveal that the cubic tips exhibit lower charge-separated states feasible for reacting with water and water reduction rates due to their defectless surface facets. In contrast, the rough tips show a similar charge-separation value but a two-fold higher surface reaction rate than the round tips, resulting in a significant enhancement of hydrogen evolution. These findings highlight the importance of rational design on metal cocatalysts in addition to the main semiconductor bodies for maximizing photocatalytic activities

Paper-Based Bimodal Sensor for Electronic Skin Applications

We present the development of a flexible bimodal sensor using a paper platform and inkjet printing method, which are suited for low-cost fabrication processes and realization of flexible devices. In this study, we employed a vertically stacked bimodal device architecture in which a temperature sensor is stacked on top of a pressure sensor and operated on different principles, allowing the minimization of interference effects. For the temperature sensor placed in the top layer, we used the thermoelectric effect and formed a closed-loop thermocouple composed of two different printable inks (conductive PEDOT:PSS and silver nanoparticles on a flexible paper platform) and obtained temperature-sensing capability over a wide range (150 °C). For the pressure sensor positioned in the bottom layer, we used microdimensional pyramid-structured poly­(dimethylsiloxane) coated with multiwall carbon nanotube conducting ink. Our pressure sensor exhibits a high-pressure sensitivity over a wide range (100 Pa to 5 kPa) and high-endurance characteristics of 10⁵. Our 5 × 5 bimodal sensor array demonstrates negligible interference, high-speed responsivity, and robust sensing characteristics. We believe that the material, process, two-terminal device, and integration scheme developed in this study have a great value that can be widely applied to electronic skin