2 results
Microwave Volumetric Probe Measurements of Field localization, Zero and Negative Index within Photonic Bandgap Metamaterial Structures
- Eric Kuster, Ricky L. Moore, Stephen Blalock, Brian Cieszynski, John Swarner, Matthew Habib
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1343 / 2011
- Published online by Cambridge University Press:
- 08 September 2011, mrss11-1343-w04-04
- Print publication:
- 2011
-
- Article
- Export citation
-
Electromagnetic mode localization within photonic bandgap (PBG) crystals has been evidenced by external measurement of enhanced optical emission from quantum dots or photoemissive polymers that are placed within the structure. In this paper wavelength is decreased and photonic crystal dimensions increased to allow insertion of a loop probe in the PBG to directly measure volumetric electromagnetic fields; thereby producing a volume -frequency map of field amplitude and phase within the PBG. The unit cells of the PBG are formed from arrays of Alumina strips which are supported by surrounding acrylic supports. Electromagnetic fields of single, two and three layer PBGs are predicted and these compare well with measurement.
Field localization within the PBG and transmission coefficients of the PBG, with and without electrical perturbations, are presented. Predictions assume layered unit cells formed from sections in which translational invariance along the Z-axis is assumed for zn-1 ≤ z ≤ zn for the nth section. Periodicity implies that field X dependence can be represented as a sum of Floquet modes and field solutions are found by mode matching techniques in combination with multimode cascade matrix formalism.
Transmission coefficient is measured using a focused beam, network analyzer based system and volumetric fields within the PBG are measured using a loop probe antenna inserted between Alumina strips and moved to different positions. Measurements at 1600 frequencies over the 4-18 GHz band at each of 100 positions are made. PBG fields are calibrated to probe measurements at identical positions and frequencies but absent the PBG.
Both electromagnetic model and measurement shows field localization and effective negative or zero indexes at multiple frequencies within the 4 to 18 GHz band. Volumetric field magnitudes increase by at least one order of magnitude and local field phase-frequency derivatives are negative or near zero near localization frequencies. Field localizations and transmission are sensitive to small perturbations of electrical properties or geometry. Wideband measurements of PBGs, perturbed by small cylindrical inserts placed at high field locations, allow precision measurements of an insert’s electromagnetic properties.
6 - Anxiety disorders and HIV disease
-
- By Andrew C. Blalock, Ph.D., Department of Psychology, Georgia State University, Atlanta, GA, USA, Sanjay M. Sharma, M.D., M.B.A., Assistant Professor, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, USA, J. Stephen McDaniel, M.D., Clinical Professor of Psychiatry and Behavioral Sciences, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, USA
- Edited by Kenneth Citron, Marie Josée Brouillette, McGill University, Montréal, Alexandra Beckett, Harvard University, Massachusetts
-
- Book:
- HIV and Psychiatry
- Published online:
- 06 August 2009
- Print publication:
- 07 July 2005, pp 120-127
-
- Chapter
- Export citation
-
Summary
Introduction
Anxiety disorders may occur any time in the course of HIV disease and are most likely to become manifest at pivotal points in disease progression (Elliott, 1998). Most people with HIV respond adequately to the stress of living with the disease and are able to limit the impact of disease-related anxiety on their daily functioning and quality of life. They cope with medical problems, employment changes, family struggles, relationship difficulties, financial hardship, and the uncertainty of the disease process itself. In these circumstances, anxiety is often considered a normal psychological response to stress (American Psychological Association, 1999).
For some patients, however, the anxiety is so severe and persistent that it can significantly impair their ability to function and would be diagnosed as a disorder. In the USA, prevalence rates for anxiety disorders among patients with HIV disease range from 5–40% (McDaniel and Blalock, 2000). The estimates vary widely for two reasons:
anxiety is often part of a complex symptom picture that frequently includes concurrent mood disorders and psychoactive substance use disorders
prevalence data often come from retrospective, cross-sectional studies that do not address whether anxiety preceded or followed HIV infection.
Despite this wide range in prevalence estimates, a pattern has emerged over the last 5 years. According to several recent studies, the point prevalence of anxiety disorders in HIV-seropositive patients is not significantly different from that of HIV-seronegative clinical comparison groups.