Solid solution GaSe1−xSx single crystals for THz generation

A table top source of coherent Terahertz (30-1000 µm) radiation, which is high power, narrow bandwidth, and broadly tunable, is high desired for applications in imaging, non-destructive testing (NDT), quantum, security and biomedical technologies. In spite of intensive research over many decades such a device remains elusive. Sulpher doped Gallium Selenide (GaSex−1Sx) solid solution ε-polytype crystals are an outstanding candidate for the efficient generation of radiation and tunability throughout the majority of the Terahertz (THz) regime; thanks to the prodigious linear and nonlinear optical properties of the Gallium Selenide (GaSe) parent crystal. Close control of doping and the crystal growth process enable the manufacture of superior quality nonlinear crystals, where the optical properties may be engineered and the mechanical properties vastly improved. Thus overcoming many of the physical issues that, despite its exceptional optical properties, have frustrated the widespread adoption of GaSe for laser frequency down conversion to the THz regime. In order to fully exploit the potential of GaSex−1Sx crystals and successfully design efficient sources for THz generation the optical properties of these crystals must be accurately determined and their transformation with doping well understood. The work in this thesis aims to accurately determine the optical properties of GaSe, Gallium Sulphide (GaS) and GaSex−1Sx crystals in the Far-Infrared and THz regimes to enable this exploitation. In the first phase of investigation we determine the linear refractive index (n) and absorption (α) coefficient for both the o and e waves in the THz regime (0.14.5 THz) using Terahertz - Time Domain Spectroscopy (THz-TDS) for GaSe, and a dense set of GaSex−1Sx crystals (x = 0.05 0.11 0.22 0.29 0.44). Measurements of THz dispersion and absorption properties of GaS crystals are performed for the first time. The transformation of the optical properties of the crystals and their phonon structure is studied. We examine the sources of inaccuracy in the THzTDs measurements of high refractive index birefringent crystals and propose a set of criteria for the selection of adequate data. The nonlinear Figure of Merit (FOM) of available high quality GaSex−1Sx crystals is found to be an order of magnitude less than that predicted in the literature, with FOM = 19.8 for GaSe, FOM = 17 for GaSex−1Sx, on the other hand estimates for double doping with Sulphur and Aluminium predict significant enhanced of these FOM values, up to 5-10 times. In the second phase of investigation we examine the phonon band of the GaSe, GaS and GaSex−1Sx by FTIR and Raman spectroscopy. For the first time we determine the absorption coefficients of the main phonon peak in the set of GaSex−1Sx crystals. The transformation of the phonon band with doping is studied. In the third phase of investigation we attempt to determine the nonlinear optical properties deff and n2 of GaSe and GaSex−1Sx in the Far Infra-Red (FIR) and THz regimes using the Maker fringe and Z-scan methods on the FELIX free electron laser

Detection of metal vapor atoms in bubbles at room temperature

One of the largest obstacles in miniaturizing traditional atomic spectroscopic sources is the need for a thermal/electrical source for free atom production. A single article in the literature has demonstrated atomic absorption detection of Ag, Cu, and Pd in aqueous solution at room temperature for atoms in the gas phase, which may ultimately permit miniaturization. Unfortunately, several laboratories have found that reproducing the phenomenon has been difficult. Without a sound fundamental explanation of the processes leading to the signal, one must conclude that it can be done, but some unsuspected and unknown design/methodological nuances are responsible for only a single reported success. Gas phase atoms could exist at room temperature “in solution” if the atoms were trapped in very small bubbles. A simpler system containing Hg vapor within a single 500 µL bubble was first studied using atomic absorption measurements. The use of experimental data and computer simulations revealed that metal transport out of bubbles suffers from slow diffusion through solution and limited solubility of the elemental species. Absorption signals for Hg vapor decayed over thousands of seconds, with slower decay rates associated with solutions higher in metal concentration and reducing power. Submicron sized bubbles were created in a flow-through cell during mixing of a 20% ethanol solution containing a reducing agent with Pd in 2% HCl. A repeatable atomic absorption signal was produced using this method. Replacement of ethanol with 1-propanol and use of a surfactant enhanced the signal through generation of more bubbles with lower internal pressures present. Limits of detection of ca. 100 ppb in Pd were achieved, although it is estimated that about 0.4% of the Pd initially added is contained within the bubbles as gaseous atoms. Further discussion includes exploration of the fundamental processes present in a procedure that delivers a repeatable signal.ChemistryChemistry and Biochemistr

Model based predictive control of a drum-type boiler

High fuel costs, stringent safety and pollution standards and the need to increase plant life-time have all driven the search for better boiler control. Traditional PID control cannot achieve the best possible results as it does not account for the strong interactions between the controlled variables. Much work has been done in the area of optimal control, but the improvements gained in performance have been lost to some extent by the difficulties involved in tuning such controllers. A linear predictive controller is presented in this paper, which is both fully multivariable and computationally efficient. It is also easy to tune as the controller tuning parameters are physically meaningful

Effect of Collector Configuration on Test Section Turbulence Levels in an Open-Jet Wind Tunnel

Flow quality studies in the Langley 14- by 22-Foot Subsonic Tunnel indicated periodic flow pulsation at discrete frequencies in the test section when the tunnel operated in an open-jet configuration. To alleviate this problem, experiments were conducted in a 1/24-scale model of the full-scale tunnel to evaluate the turbulence reduction potential of six collector configurations. As a result of these studies, the original bell-mouth collector of the 14- by 22-Foot Subsonic Tunnel was replaced by a collector with straight walls, and a slot was incorporated between the trailing edge of the collector and the entrance of the diffuser

Neural network modelling of a boiler combustion system

Boiler combustion systems represent highly nonlinear systems with associated lags and delays which depend on operating point. Such systems represent a significant challenge to the control engineer. In this paper, we present a model typical of a medium-size industrial boiler, which highlights the difficulties associated with such systems. As a starting point for nonlinear control design, we demonstrate how a neural network may be used to obtain a concise functional description of the system, initially for fixed operating points and then for variation over the full range of operation

Long-Term Capital Gains Tax Strategies: Correlated Protective Put Strategy

A reduction in the long-term capital gains tax rate provides investors with new strategies to minimize taxes and protect investment gains.  One such opportunity exists when an investor decides to sell a profitable stock with a holding period of less than one-year, resulting in short-term ordinary taxes.  The investor would find it more beneficial to sell the stock after one-year lapses, resulting in lower long-term capital gain taxes, although the longer holding period exposes the investor to the uncertainty of stock price movement.  A strategy to extend the holding period without excess risk would be to use the protective put option strategy, sometimes referred to as “investment insurance”.  The strategy involves the purchase of a put option to protect against the possible decline in the stock price, to take advantage of the lower long-term capital gains tax rate, and to preserve the upside potential of the stock.  Pursuant to IRS Publication 550, the IRS does not allow the use of a protective put to extend the holding period on the same security considered for sale.  Since the IRS does not allow a direct protective put hedge, this study will explore an alternative strategy involving the purchase of a put on a highly correlated investment to extend the holding period to recognize lower capital gains tax rates.  The paper presents example situations when an investor benefits from utilizing the correlated protective put option strategy

DDR とCOIN : 不確実な収束

PDF/A formatsAccess: via World Wide Web東京外国語大学大学院総合国際学研究科博士 (学術) 論文 (2013年7月)Author's thesis (Ph.D)--Tokyo University of Foreign Studies, 2013博甲第170号Bibliography: p. 306-321Summaries in Japanese and in English東京外国語大学 (Tokyo University of Foreign Studies)博士 (学術

LATE DEVONIAN-TOURNAISIAN CONODONTS FROM THE EASTERN KHYBER REGION, NORTH-WEST PAKISTAN

Conodonts (62 species and subspecies) from acid-leaching of 226 samples from four sections through the Ali Masjid Formation west of Misri Khel in the former South Khyber Agency, north-west Pakistan, are documented by illustrations and distributional data. These indicate that most of this unit, at least in that area, spans the interval Middle crepida Zone (low in the Famennian) to at least Early crenulata Zone (mid-Tournaisian), though a fauna from low in one of the sections produced conodonts indicative of the Late falsiovalis Zone (early Frasnian). Two major hiatuses are inferred: between the Late falsiovalis and Middle crepida zones, and between the Late expansa and Early duplicata zones. Coherence of the conodont biostratigraphy accords with lithologic alignments between the sections. &nbsp