126 research outputs found
Chalcogenide-based phase-change metamaterials
No full textPhase-change metamaterials combine the sharp resonant dispersions afforded by metamaterials with the optical switching characteristics of phase-change chalcogenides to create a high-contrast, non-volatile planar optical modulator. Spectroscopic ellipsometry was used to accurately determine the highly-contrasting complex dielectric functions of the amorphous and crystalline states of GST, an amorphous chalcogenide. This data was then used to model a phase-change metamaterial hybrid device in both phases,which showed a large wavelength shift in resonant spectral features on crystallisation of the chalcogenide layer. Femtosecond pulse-induced crystallisation and amorphisation of thin films of GST was shown to be possible, and the crystalline fraction in the material was shown to be continuously tunable. Femtosecond pulses were then used to reversibly switch a phase-change metamaterial device to modulate the trapped mode resonance. Modelling of an all-dielectric phase-change metamaterial structure indicated that larger optical modulation may be realised by changing the phase of the resonant structure itself
All-optical, non-volatile, chalcogenide phase-change meta-switch
No full textWe show experimentally that bistable, optically-induced phase switching in germanium antimony telluride (GST) - a member of the Te-based chalcogenide alloy family upon which all of today's re-writable optical disc and phase-change RAM technologies are based - provides a platform for the engineering of non-volatile metamaterial transmission/reflection modulators (Fig. 1) for near- to mid-infrared wavelengths with thicknesses down to 1/27 of the operating wavelength. These hybrid materials provide a robust and versatile platform for a new generation of optical switching and memory devices
2D cognitive optical data processing with phase change materials
No full textWe demonstrate high-density, multi-level crystallization of a Ge2Sb2Te5 thin film using tightly focused femtosecond laser pulses. The optical reflectivity in each distinct phase states level is characterized for applications in ultra-fast cognitive parallel data processing
Femtosecond multi-level phase switching in chalcogenide thin films for all-optical data and image processing
No full textWe report on the non-volatile switching of amorphous chalcogenide glass thin films to the crystalline phase through a through a number of reproducible, discrete, optically distinguishable intermediate states, and on the re-amorphization of these films using femtosecond laser pulses. Potential applications lie in high-base (>binary) all-optical signal modulation, high-density data storage, image processing and non-Von Neuman computing. Chalcogenide phase-change media such as Ge2Sb2Te5 (GST) are commercially established as a platform for both optical and electronic data storage (re-writable CDs, DVDs and Blu-Ray discs; Phase-change RAM). These technologies harness non-volatile amorphous-crystalline (binary) transitions in the chalcogenide induced by nanosecond optical or electronic excitations, which have also recently been applied to the realization of metamaterial electro- and all-optical transmission/reflection modulators for near- to mid-IR wavelengths providing switching high-contrast in device structures only a fraction of a wavelength thick. But chalcogenides offer a much richer pallet of transitional behaviours that can be exploited to enhance all of these functionalities and to open up new computational and image processing paradigms: They retain a 'memory' of sub-threshold excitations, such that transitions ordinarily initiated by single excitation pulses can be reproducibly stimulated by sequences of arbitrarily timed shorter/lower energy pulses cumulatively delivering the required energy. Here we demonstrate multi-level switching of GST films down to 30 nm thick using femtosecond optical pulses. Domains ranging in size from 200 down to 1 µm2 are progressively converted through at least eight distinct partially crystalline states using 85 fs pulses. Intermediate states are distinguished and their progressively changing optical properties characterised using white light reflectivity, transmission/reflection microspectrophotometry and spectroscopic ellipsometry measurements. Applications potential is demonstrated to high-density data storage - encoding/read-out of multiple bits per (semi-)crystalline mark with micron-level pixellation, the performance of optical arithmetic operations, and progressive tuning of chalcogenide hybrid metamaterial resonance
Phase-change and optomechanical functionalities in photonic metamaterials
No full textSwitchable and nonlinear metamaterials, with properties surpassing those of natural media, will underpin the next stage of the photonic technological revolution, providing a functional platform for nanoscale ‘meta-devices’. We report here on recent advances in the development of versatile, planar photonic metamaterial solutions to provide a new generation of nanoscale optical switching and memory devices: We demonstrate that optically-induced phase transitions in germanium antimony telluride (GST) – a member of the chalcogenide alloy family upon which re-writable optical disc and phase-change RAM technologies are based - provide for the engineering of non-volatile metamaterial transmission/reflection modulators for the near- to mid-infrared range with thicknesses down to 1/27 of the operating wavelength.And we introduce all-dielectric optomechanical metamaterials, wherein optical forces drive changes in structural configuration, as a new paradigm (inherently free of Joule losses) for achieving strong optical nonlinearity, optical bistability and asymmetric transmission at intensity levels of only a few hundred µW/µm2
Volatile and non-volatile switching in dielectric metamaterials
No full textThe next phase of the photonic technological revolution will be driven by the development of nanoscale/nanostructured switchable and nonlinear materials as functional platforms for integrated nanophotonics. We report here on recent advances in the development of versatile, planar photonic metamaterial solutions to provide a new generation of nanoscale all-optical switching and memory 'meta-devices'
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WATERBUD: A SPREADSHEET-BASED MODEL OF THE WATER BUDGET AND WATER MANAGEMENT SYSTEMS OF THE UPPER SAN PEDRO RIVER BASIN, ARIZONA
No full textThis report describes the development and application of a spreadsheet -based model of the water budget and water management systems of the Upper San Pedro River Basin in southeastern Arizona. The model has been given the name, WATERBUD.This report is revised from a thesis of the same title by the senior author prepared
in the Department of Hydrology and Water Resources at the University of Arizona. The
thesis committee consisted of Dr. William B. Lord and Dr. Thomas Maddock III,
directors, and Dr. Randy Bassett. The research was funded in part by the Cochise
County, Arizona, Flood Control District, who supported an Upper San Pedro
Interdisciplinary Study Team during 1990 and 1991 through the University of Arizona,
Water Resources Research Center. Dr. Lord and Dr. Maddock also served as directors of
the Study Team. The contents of this report express the views of the authors and do not
necessarily reflect the views or policies, either expressed or implied, of Cochise County;
nor does the mention of trade names or commercial products constitute their endorsement
by Cochise County or the University of Arizona.
All of the students and staff on the Upper San Pedro Interdisciplinary Study Team
contributed to the work leading up to this report. The senior author especially wishes to
thank Ali Aljamal, Rick Dorrance, Dave Gillilan, Edella Schlager, Souad Sherif, Scott
Summerside, Leticia Vionnet, and Mary Wallace for their insights and assistance.See also related thesis at: http://hdl.handle.net/10150/291643This title from the Hydrology & Water Resources Technical Reports collection is made available by the Department of Hydrology & Atmospheric Sciences and the University Libraries, University of Arizona. If you have questions about titles in this collection, please contact [email protected]
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Flow model for the Bingham cienega area, San Pedro river basin, Arizona: a management and restoration tool
No full textA finite element groundwater flow model was used to support a hydrologic assessment for a study area in the Lower San Pedro River Basin which contains the Bingham Cienega. Consolidated sedimentary rocks associated with an extension of the Catalina Core Complex truncate the floodplain aquifer system in the study area. The elevated water table produced by this "hardrock" results in spring discharge at the cienega and a locally gaining reach of the San Pedro River. The steady -state model suggests that recharge (and discharge) components for the floodplain aquifer sum to 3.10 cfs. Mountain front recharge, underflow, and stream leakage are the primary recharge mechanisms, while stream leakage, evapotranspiration, spring flow, and underflow out are sources for groundwater discharge. A steady -oscillatory model was used to account for seasonal periodicity in the system's boundary conditions. Monthly variation in the evapotranspiration rate was offset primarily by storage changes in the aquifer. Due to a lack of measured hydrologic data within the study area, results from the model simulations are only preliminary. Model development and the subsequent sensitivity analyses have provided insight into what type of data needs to be collected. Head measurements are most needed in the area just downstream from Bingham Cienega. The mountain front recharge and evapotranspiration rates are shown to be highly sensitive parameters in the model; improved estimation of these values would be helpful. Spring discharge would be a valuable calibration tool if it could be accurately measured. A more extensive record of stream baseflow in the San Pedro River should be established. After more hydrologic data is collected, the model could be recalibrated so as to better represent the system. Eventually, this tool may be used in direct support of management and/or restoration decisions.Research and development for this project was funded in part by the Arizona
Chapter of The Nature Conservancy. The views and conclusions reported are those of the
author and are not necessarily shared by The Nature Conservancy.
We would like to give special thanks to Robert Mac Nish, Kate Baird and Kevin
Lansey for their thoughtful comments on this document.This title from the Hydrology & Water Resources Technical Reports collection is made available by the Department of Hydrology & Atmospheric Sciences and the University Libraries, University of Arizona. If you have questions about titles in this collection, please contact [email protected]
Long-term Patterns in Australia’s Terms of Trade
Get PDFWe examine two important aspects of Australia’s terms of trade using 135 years of annual data up to 2003/04. Since Australia predominantly exports commodities and imports manufactures, the Prebisch-Singer hypothesis suggests that there should be a negative trend in the terms of trade. But the trend is no more than –0.1 per cent per annum, less than the trend decline in world commodity prices relative to manufactured goods prices. The weaker trend appears to be the result of Australia exporting, and importantly diversifying toward, commodities with faster price growth. Extending the sample using projections for the terms of trade for the two years to 2005/06 based on commodity price movements to date, the apparent downward trend disappears. Indeed, based on these projections, the terms of trade will have increased by around 50 per cent over the period 1987–2006, unwinding the decline over the preceding 30 years. We also investigate the volatility of the terms of trade and demonstrate that it was significantly higher between 1923 and 1952. This is attributable to substantially higher volatility in the export prices of a few key commodity exports. Volatility declined after 1952 due to smaller shocks to the prices of these goods. The diversification in Australia’s export base since then means that the terms of trade are less susceptible to shocks to prices of individual commodity exports.terms of trade; commodity prices; Prebisch-Singer
The florist's directory : or, A treatise on the culture of flowers ; to which is added a supplementary dissertation on soils, manures, &c. / by James Maddock.
No full textvii, 272 p., 6 leaves of plates
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