Low temperature dielectric relaxation in ordinary perovskite ferroelectrics: enlightenment from high-energy x-ray diffraction

Ordinary ferroelectrics exhibit a second order phase transition that is characterized by a sharp peak in the dielectric permittivity at a frequency-independent temperature. Furthermore, these materials show a low temperature dielectric relaxation that appears to be a common behavior of perovskite systems. Tetragonal lead zirconate titanate is used here as a model system in order to explore the origin of such an anomaly, since there is no consensus about the physical phenomenon involved in it. Crystallographic and domain structure studies are performed from temperature dependent synchrotron x-ray diffraction measurement. Results indicate that the dielectric relaxation cannot be associated with crystallographic or domain configuration changes. The relaxation process is then parameterized by using the Vogel–Fulcher–Tammann phenomenological equation. Results allow us to hypothesize that the observed phenomenon is due to changes in the dynamic behavior of the ferroelectric domains related to the fluctuation of the local polarization.Postprint (author's final draft

Brainstem lesions are associated with sleep apnea in multiple sclerosis

Background: Studies linking MRI findings in MS patients with obstructive sleep apnea severity are limited. Objective: We conducted a retrospective study to assess MRI abnormalities associated with obstructive sleep apnea (OSA) in patients with multiple sclerosis (MS). Methods: We performed retrospective chart review of 65 patients with multiple sclerosis who had undergone polysomnography (PSG) for fatigue as well as brain MRI. We measured the number of lesions in the brainstem and calculated the standardized third ventricular width (sTVW) as a measure of brain atrophy, and subsequently performed correlation analyses of the apnea-hypopnea index (AHI) with brainstem lesion location, sTVW, and Expanded Disability Status Scale (EDSS). Results: MS Patients with OSA were significantly older and had a higher body mass index (BMI) and higher AHI measures than patients without OSA. After adjustment for covariates, significant associations were found between AHI and lesion burden in the midbrain (p \u3c 0.01) and pons (p = 0.05), but not medulla. Conclusions: Midbrain and pontine lesions burden correlated with AHI, suggesting MS lesion location could contribute to development of OSA

Underwater Optical Wireless Communications Link for Short-Range Data Transmission: A Proof of Concept Study

Gemstone Team OPTICThe purpose of this thesis is to lay the groundwork for the development of a cost-effective Underwater Optical Wireless Communications system. Currently, one of the largest barriers to the expansion of underwater enterprise and research is a lack of high-speed wireless communication systems. Wireless communication underwater is essential for safety, improving aquatic technology, and many other marine ventures, yet it is still technologically limited. Current methods, such as acoustic communication, are often power inefficient, cumbersome, and expensive. The proposed system would enable scuba divers and researchers to bridge the technological gaps in available underwater data transmission systems. This paper proposes using visible light to wirelessly transmit data underwater. Visible light is an effective carrier wave underwater due to its large bandwidth and low absorption coefficient. Using light emitting diodes, silicon PIN photodetectors, waterproof enclosures, and consumer-grade microcontrollers, a model for the development of a wireless optical communications system is proposed. The system also adopts a modular design which allows each component to evolve as needed. The proposed system can transmit and receive audio and vitals signals underwater, illustrating the potential of a technology that could make diving and other underwater endeavors safer and more efficient. Furthermore, the proposed data link shows the potential for this technology to be used in other underwater applications that were previously limited by data speeds or mobility. Above all, this technology seeks to build upon existing knowledge of optical wireless communication and advance the field of underwater science and technology

Panel One

Introduction - Janet K. Levit, Dean & Dean John Rogers Endowed Chair, and Robert Spoo, Chapman Distinguished Chair in Law, The University of Tulsa College of LawModerator – Stephen Galoob, Assistant Professor of Law, The University of Tulsa College of Law Christopher Buccafusco, Associate Professor and Co-Director of the Center for Empirical Studies of Intellectual Property, Kent College of Law - “Informal Norms, Moral Intuitions, and Creativity” Catherine Fisk, Chancellor’s Professor of Law, University of California, Irvine School of Law - “The Rules of Art in Television Writing: The Significance of the Writer’s Self-Conception as Union Labor” Lior Jacob Strahilevitz, Sidley Austin Professor of Law, University of Chicago Law School - “Don’t Ask, Must Tell – and Other Combinations

International Law Colloquia, Spring 2007 Series

Spring 2007 Presenters: February 9: Curtis A. Bradley (Duke Law School), Unratified Treaties, Domestic Politics and the U.S. Constitution February 16: Melissa A. Waters (Washington & Lee University School of Law), “Foreign Authority” Through a Narrow Lens: Interpretive Incorporation of Treaties February 23: Joost Pauwelyn (Duke Law School), Optimal Protection of International Law: Navigating between ‘European Absolutism’ and ‘American Voluntarism’ March 2: Jacob Katz Cogan (University of Cincinnati College of Law), Competition and Control in International Adjudication March 23: Janet Koven Levit (University of Tulsa College of Law), A Bottom-Up Approach to International Lawmaking: The Tale of Three Trade Finance Instruments April 13: Derek Jinks (University of Texas School of Law), Hamdan and the Law of War: The Applicability of the Geneva Conventions to the “Global War on Terrorism” April 20: Diane Marie Amann (University of California-Davis School of Law): Slave Trafficking, Crimes against Humanit

Low temperature dielectric relaxation in ordinary perovskite ferroelectrics: enlightenment from high-energy x-ray diffraction

Ordinary ferroelectrics exhibit a second order phase transition that is characterized by a sharp peak in the dielectric permittivity at a frequency-independent temperature. Furthermore, these materials show a low temperature dielectric relaxation that appears to be a common behavior of perovskite systems. Tetragonal lead zirconate titanate is used here as a model system in order to explore the origin of such an anomaly, since there is no consensus about the physical phenomenon involved in it. Crystallographic and domain structure studies are performed from temperature dependent synchrotron x-ray diffraction measurement. Results indicate that the dielectric relaxation cannot be associated with crystallographic or domain configuration changes. The relaxation process is then parameterized by using the Vogel–Fulcher–Tammann phenomenological equation. Results allow us to hypothesize that the observed phenomenon is due to changes in the dynamic behavior of the ferroelectric domains related to the fluctuation of the local polarization