Simultaneous Q-switching and mode-locking in a diode-pumped Nd:YVO4-Cr4+:YAG laser

Parametric studies of passive Q-switching and mode-locking in a Nd ³⁺:YVO₄-Cr⁴⁺:YAG laser were theoretically carried out. Simultaneous mode-locking and Q-switching was also experimentally studied. It was found that over 90% of the output power could be mode-locked in a diode-pumped passively Q-switched Nd³⁺:YVO₄-Cr⁴⁺:YAG laser. The average pulse duration of the mode-locked pulse train was estimated to he around 110~150 ps. The highest peak power of a single pulse near the maximum of the Q-switched envelope was greater than 100 kW     

Ho arrangement in the Zn6Mg3Ho icosahedral quasicrystal studied by atomic-resolution Z-contrast STEM

The atomic structure of the Zn6Mg3Ho icosahedral quasicrystal has been studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast (Z: atomic number). We demonstrate that in particular Z-contrast imaging is quite powerful for specifying heavy atom positions in the quasicrystalline compound, as shown by a comparison with high-resolution phase-contrast imaging. It is confirmed that the observed Z-contrast images are fairly well explained by the projected potential of only the Ho atomic arrangement, which was recently proposed by X-ray diffraction analysis; Ho occupies an even-body-center site of the 3-dimensional Penrose lattice. Consequently, the present direct structural observation strongly supports the validity of the proposed Ho site.     

Antibacterial activity of shrimp chitosan against Escherichia coli

The effects of cell age, reaction temperature, pH value, and salts on the inhibitory activity of shrimp chitosan (98% deacetylated) against Escherichia coli were investigated. The age of a bacterial culture affected its susceptibility to chitosan, with cells in the late exponential phase being most sensitive to chitosan. Higher temperature (25 and 37 degrees C) and acidic pH increased the bactericidal effects of chitosan. Sodium ions (100 mM Na+) might complex with chitosan and accordingly reduce chitosan's activity against E. coli. Divalent cations at concentrations of 10 and 25 mM reduced the antibacterial activity of chitosan, in the order of Ba2+ > Ca2+ > Mg2+. Chitosan also caused leakage of glucose and lactate dehydrogenase from E. coli cells. These data support the hypothesis that the mechanism of chitosan antibacterial action involves a cross-linkage between the polycations of chitosan and the anions on the bacterial surface that changes the membrane permeability.     

Growth of epitaxial Si1-xGex layers at 750° C by VLPCVD

Silicon-germanium epitaxial layers have been grown on (100) silicon at 750° C by very low pressure chemical vapor deposition (VLPCVD). Pure SiH₄ and GeH₄ were used as the processing gases. Commensurate films of Si_1-x withx < 0.13 have been deposited up to a critical thickness about 2-4 times larger than the equilibrium value. Interrupted growth, controlled by gas switching, was employed to improve interfacial abruptness. The films have been characterized as a function of SiH₄ and GeH₄ flow rates and germanium content. Growth rate and germanium incorporation as a function of GeH₄:SiH₄ input ratio and total gas flow rate have been studied. We observed that the growth rate of the Si_1-x Ge _x layer decreases as the germanium content in the film or the GeH₄:SiH₄ ratio increases at 750° C using VLPCVD. We also found that, for a given GeH₄:SiH₄ ratio, the germanium incorporated in the solid is independent of the total gas flow rate.     

Analysis of passively Q-switched lasers with simultaneous modelocking

Simultaneous Q-switching and modelocking in a diode-pumped Nd:YAG/Cr⁴⁺:YAG laser is experimentally demonstrated. A general recurrence is derived for the analysis of the temporal shape of a single Q-switched envelope with mode locked pulse trains. With the developed model, the modelocked pulse energy and the total Q-switched pulse energy can be calculated. Excellent agreement was found between the present results and detailed theoretical computations     

Design of the QoS framework for the IEEE 802.16 mesh networks

IEEE 802.16 (WiMax) technology is designed to support broadband speeds over wireless networks for the coming era of broadband wireless access (BWA). IEEE 802.16 is expected to provide transmission of high‐rate and high‐volume multimedia data streams for fixed and mobile applications. As an extension of point‐to‐multipoint (PMP) configuration, the IEEE 802.16 mesh mode provides a quicker and more flexible approach for network deployment. Multimedia networking requires quality‐of‐service (QoS) support, which demands elaborate mechanisms in addition to the four service types defined in the specification. By examining standard centralized and distributed scheduling/routing schemes in the mesh mode from QoS aspect, a BS‐controlled and delay‐sensitive scheduling/routing scheme is proposed in the paper. Associate mechanisms including admission control, flow setup and link state monitoring are also proposed. Integration of the proposed mechanisms is presented as a complete QoS framework. Simulation study has demonstrated that the average delay as well as the delay jitters per hop in the proposed scheme is smaller than that of the distributed scheme and much smaller than that of the centralized scheme. Furthermore, proposed mechanisms can also achieve higher throughput than the contrasts and generate much smaller signaling overhead, making the proposed framework a promising scheme for multimedia support in the IEEE 802.16 mesh network. Copyright © 2009 John Wiley & Sons, Ltd.     

Iterative multiuser detector-decoding for nonbinary LDPC coded multicarrier MFSK systems

Telecommunication Systems - This paper investigates an iterative multiuser detection for nonbinary low density parity check (LDPC) coded multicarrier multiple level frequency shift keying system to...     

Thermal measurements and analyses of low-cost high-power LED packages and their modules

The thermal behaviors of high-power light emitting diode (LED) chip-on-plate (COP) package and module are investigated by experimental measurements (with LED junction temperature (T_j) tester, thermocouples, and thermal imager), a thermal resistance circuit (TRC) method, a commercial finite element code (ANSYS), and a computational fluid dynamics code (CFdesign). Based on the experimental results, the thermal resistance of the COP package was found to be comparable to those for the commercial packages. Furthermore, it was also found that the T_j and thermal resistances of the COP package and module, calculated from 2D ANSYS, 3D TRC and 3D CFdesign, are consistent well with those from the experiments. Besides, the uncertain equation-based convection coefficients used in ANSYS and TRC for the thermal analysis of the COP module were closely examined and discussed in detail by comparing with those from CFdesign analysis. Moreover, the validated ANSYS and CFdesign models were used for parametric studies of the COP module and further provided useful design parameters. Finally, the COP module under natural and forced convection conditions was studied, and the results showed that the junction-to-air thermal resistances are sensitive to the flow conditions, but not for thermal resistances from the junction to aluminum substrate and to heat sink.     

Field enhancement of omega-shaped-gated poly-Si TFT SONOS memory fabricated by a simple sidewall spacer formation

A novel omega-shaped-gated (Ω-Gate) poly-Si thin-film-transistor (TFT) silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memory devices fabricated with a simple process have been proposed for the first time. The Ω-Gate structure inherently covered two sharp corners manufactured simply via a sidewall spacer formation. Due to the sharp corner geometry, the local electric fields across the tunneling oxide could be enhanced effectively, thus improving the memory performance. Based on this field enhanced scheme, the Ω-Gate TFT SONOS revealed excellent program/erase (P/E) efficiency and larger memory window as compared to the conventional planar (CP) counterparts. In addition, owing to the better gate controllability, the Ω-Gate TFT SONOS also exhibited superior transistor performance with a much higher on-current, smaller threshold voltage, and steeper subthreshold swing. Therefore, such an Ω-Gate TFT SONOS memory is very promising for the embedded flash on the system-on-panel applications.     

Influence of bias-temperature stressing on the electrical characteristics of SiOC:H film with Cu/TaN/Ta-gated capacitor

Experiments on bias-temperature stressing, capacitance-voltage measurements, current-voltage characteristics, and time-dependent dielectric breakdown were performed to evaluate the reliability of Cu and low-k SiOC:H integration. A high leakage current of ∼8 × 10⁻¹⁰ to 2 × 10⁻⁸ A/cm² at 1 MV/cm in SiOC:H dielectrics in a Cu-gated capacitor, and a lower 2 × 10⁻¹⁰ to 5 × 10⁻¹⁰ A/cm² at 1 MV/cm in a Cu/TaN/Ta-gated capacitor, were observed at evaluated temperatures. The drift mobility of the Cu⁺ ions in the Cu/TaN/Ta-gated capacitor was lower than that in a Cu-gated capacitor. A physical model was developed to explain the observed kinetics of Cu⁺ ions that drift in Cu-gated and Cu/TaN/Ta-gated capacitors. The electric field in the Cu-gated MIS capacitor in the cathode region is believed to be increased by the accumulation of positive Cu⁺ ions, which determines the breakdown acceleration. Good Cu⁺ ions drift barrier layers are required as reliable interconnects using thin TaN and Ta layers. Additionally, Schottky emission dominates at low electric fields, E<1.25 MV/cm, and Poole-Frenkel emission dominates at high fields, E>1.5 MV/cm.