Stationary point approach to the phase transition of the classical XY chain with power-law interactions

The stationary points of the Hamiltonian H of the classical XY chain with power-law pair interactions (i.e., decaying like r^{-{\alpha}} with the distance) are analyzed. For a class of "spinwave-type" stationary points, the asymptotic behavior of the Hessian determinant of H is computed analytically in the limit of large system size. The computation is based on the Toeplitz property of the Hessian and makes use of a Szeg\"o-type theorem. The results serve to illustrate a recently discovered relation between phase transitions and the properties of stationary points of classical many-body Hamiltonian functions. In agreement with this relation, the exact phase transition energy of the model can be read off from the behavior of the Hessian determinant for exponents {\alpha} between zero and one. For {\alpha} between one and two, the phase transition is not manifest in the behavior of the determinant, and it might be necessary to consider larger classes of stationary points.Comment: 9 pages, 6 figure

Nonlinear dielectric response at the excess wing of glass-forming liquids

We present nonlinear dielectric measurements of glass-forming glycerol and propylene carbonate applying electrical fields up to 671 kV/cm. The measurements extend to sufficiently high frequencies to allow for the investigation of the nonlinear behavior in the regime of the so-far mysterious excess wing, showing up in the loss spectra of many glass formers as a second power law at high frequencies. Surprisingly, we find a complete lack of nonlinear behavior in the excess wing, in marked contrast to the alpha-relaxation where, in agreement with previous reports, a strong increase of dielectric constant and loss is found.Comment: 8 pages (including 3 pages Supplementary Information), 4 + 1 figures. Revised according to suggestions of referee

Physical Structure of the Planetary Nebula NGC 3242 from the Hot Bubble to the Nebular Envelope

One key feature of the interacting stellar winds model of the formation of planetary nebulae (PNe) is the presence of shock-heated stellar wind confined in the central cavities of PNe. This so-called hot bubble should be detectable in X-rays. Here we present XMM-Newton observations of NGC 3242, a multiple-shell PN whose shell morphology is consistent with the interacting stellar winds model. Diffuse X-ray emission is detected within its inner shell with a plasma temperature ~2.35\times10^6 K and an intrinsic X-ray luminosity ~2\times10^30 ergs s^(-1) at the adopted distance of 0.55 kpc. The observed X-ray temperature and luminosity are in agreement with "ad-hoc" predictions of models including heat conduction. However, the chemical abundances of the X-ray-emitting plasma seem to imply little evaporation of cold material into the hot bubble, whereas the thermal pressure of the hot gas is unlikely to drive the nebular expansion as it is lower than that of the inner shell rim. These inconsistencies are compounded by the apparent large filling factor of the hot gas within the central cavity of NGC 3242. Subject headings: planetary nebulae: individual (NGC 3242)Comment: Accepted the publication in Astronomical Journa

Electronic Properties of Charged Centers in Si0₂-like Glasses

Contains report on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020

Songs of sand and grit : a collection of narrative literary journalism

Includes bibliographical references (leaves 87-92).The introduction explicates the nature of narrative literary journalism and situates the four stories within this edifice. This body of work experiments with the classical form of narrative literary journalism. The Soul Searcher tells the story of the ethnomusicologist John Turest-Swartz who wants to promote the little known rural musician Louisa Steenkamp. It traces the development of an indigenous South African band over a period of one year. Thumeka in the Dunes is a career portrait in the context of urban nature conservation. The protagonist Thumeka Mdlazi is both part of the obstacle - the community threatening the nature reserve - and its solution, as a protector of the dunes. A Place to Live under the Rainbow deals with the repeated attacks against Somali refugees in South Africa portraying victims and perpetrators alike. On a meta-level, the story also reflects on the topic of xenophobia in a more discursive style. A Runner's Mind is a first-person creative non-fiction narrative. The core of the story is the motivation for ultra-marathon runner Randall Turner to keep running. This account is framed by my own personal reflections on running and non-running. All stories are anchored in a South African social setting and reflect people's struggles and small achievements in overcoming seemingly hopeless situations

Pinpointing the Position of the Post-AGB Star at the Core of RAFGL 2688 using Polarimetric Imaging with NICMOS

We have used infrared polarimetric imaging with NICMOS to determine precisely the position of the star that illuminates (and presumably generated) the bipolar, pre-planetary reflection nebula RAFGL 2688 (the Egg Nebula). The polarimetric data pinpoint the illuminating star, which is not detected directly at wavelengths less than or equal to 2 microns, at a position well within the dark lane that bisects the nebula, 0.55" (about 550 AU) southwest of the infrared peak which was previously detected at the southern tip of the northern polar lobe. The inferred position of the central star corresponds to the geometric center of the tips of the four principle lobes of near-infrared H2 emission; identifying the central star at this position also reveals the strong point symmetric structure of the nebula, as seen both in the intensity and polarization structure of the polar lobes. The polarimetric and imaging data indicate that the infrared peak directly detected in the NICMOS images is a self-luminous source and, therefore, is most likely a distant binary companion to the illuminating star. Although present theory predicts that bipolar structure in pre-planetary and planetary nebulae is a consequence of binary star evolution, the separation between the components of the RAFGL 2688 binary system, as deduced from these observations, is much too large for the presence of the infrared companion to have influenced the structure of the RAFGL 2688 nebula.Comment: 15 pages, 6 figures, to appear in The Astrophysical Journa