Electronic linewidth narrowing method for single axial mode operation of Q-switched Nd: YAG lasers

Electronic control of the Q-switch is used to obtain single axial mode output from an unstable resonator Nd: YAG oscillator. Controlled opening of the Q-switch following prespiking pulses provides over 10 MW of peak power in a single axial mode without significant output power reduction.     

A model for the plane to plane variations in catalytic activity seen during nitric oxide decomposition on platinum

Previous work has shown that the reactivity of platinum for nitric oxide decomposition varies significantly with the geometry of the exposed surface of the platinum. Here, the available data are compared to the predictions of a model, which is based on conservation of orbital symmetry and a simplified picture of the band structure of the surface. The model predicts that the (100) face of platinum should be more active than either the (111) or the (110). The (410) should be more active still. These predictions agree with recent experiment. The model makes several other predictions which need to be tested experimentally. These results suggest that symmetry conservation methods, similar to the ones developed by Woodward and Hoffmann for organic reactions, could yield many valuable insights into the relative activity of various catalyst structures.     

Congruential Inventory Model for Two-Echelon Distribution Systems

Large-scale inventory-distribution systems typically comprise a hierarchy of warehouses that stock goods for distribution to retailers at which demand for these goods originates. This paper develops an inventory model for two-echelon distribution systems under the assumption that the central warehouse and retailers order periodically. Characteristics of the optimal policy are described. An iterative solution procedure is presented to find optimal or near optimal operating-policy variables. Solutions of the model to a large number of test examples show that the model outperforms other existing models in the literature without sacrificing the computation time. Tested against the lower bounds on the optimal average annual variable cost obtained by removing some of the ordering costs, the solutions of the present model are found to be near optimal.     

Discretely tunable erbium-doped fiber ring laser selecting ITU-T grids of 273 channels × 50-GHz spacing in <Emphasis Type="Italic">C</Emphasis>- and <Emphasis Type="Italic">L</Emphasis>-band regions

We report the fabrication of a discretely tunable erbium-doped fiber ring laser with a novel scheme that can select ITU-T grids of 50-GHz spacing in both C and L bands. Wavelength selections of 273 channels are demonstrated with a signal to source spontaneous emission ratio of 60 dB/nm and excellent power flatness over 111-nm bandwidth. This was realized by incorporating both a solid Fabry–Pérot interferometer and a fiber Fabry–Pérot tunable filter into the ring laser. To our knowledge, our experimental result has the widest tuning range ever reported for a discretely tunable fiber laser with 50-GHz channel spacing that matches the ITU-T grids and is the first equipment that can operate in both C and L bands. PACS 42.55.Wd; 42.60.Da; 42.60.-v     

Multichannel transceiver dual-tuned RF coil for proton/sodium MR imaging of knee cartilage at 3 T

Sodium magnetic resonance (MR) imaging is a promising technique for detecting changes of proteoglycan (PG) content in cartilage associated with knee osteoarthritis. Despite its potential clinical benefit, sodium MR imaging in vivo is challenging because of intrinsically low sodium concentration and low MR signal sensitivity. Some of the challenges in sodium MR imaging may be eliminated by the use of a high-sensitivity radiofrequency (RF) coil, specifically, a dual-tuned (DT) proton/sodium RF coil which facilitates the co-registration of sodium and proton MR images and the evaluation of both physiochemical and structural properties of knee cartilage. Nevertheless, implementation of a DT proton/sodium RF coil is technically difficult because of the coupling effect between the coil elements (particularly at high field) and the required compact design with improved coil sensitivity. In this study, we applied a multitransceiver RF coil design to develop a DT proton/sodium coil for knee cartilage imaging at 3 T. With the new design, the size of the coil was minimized, and a high signal-to-noise ratio (SNR) was achieved. DT coil exhibited high levels of reflection S11 (～-21 dB) and transmission coefficient S12 (～-19 dB) for both the proton and sodium coils. High SNR (range 27-38) and contrast-to-noise ratio (CNR) (range 15-21) were achieved in sodium MR imaging of knee cartilage in vivo at 3-mm(3) isotropic resolution. This DT coil performance was comparable to that measured using a sodium-only birdcage coil (SNR of 28 and CNR of 20). Clinical evaluation of the DT coil on four normal subjects demonstrated a consistent acquisition of high-resolution proton images and measurement of relative sodium concentrations of knee cartilages without repositioning of the subjects during the same MR scanning session.     

Removal of nanoparticles on silicon wafer using a self-channeled plasma filament

The effective removal of nanoparticles from a silicon wafer surface was demonstrated using the self-channeled plasma filament excited by a femtosecond (130?fs) Ti:sapphire laser (?? _p=790?nm). The photoinduced self-channeled plasma filament in air reached a length of approximately 110?C130?mm from the first focal spot with diameters ranging from 40 to 50???m at input intensities of more than 1.0×10¹⁴?W/cm². By the scan of wafer using the X?CY?CZ stage during self-channeled plasma filament, the removal variation of nanoparticles on surface was observed in situ before and after the plasma filament occurred. The cleaning efficiency was strongly dependent on the gap distance between the plasma filament and the surface. The removal efficiency of nanoparticles reached 96?% with no damage to the surface when the gap was 150???m.