Refractive index of a transparent liquid measured with a concave mirror

This paper describes the spherical concave mirror method for measuring the index of refraction of transparent liquids. We derived the refractive index equation using Snell's law and the small-angle approximation. We also verified the validity of this method using the traditional spherical mirror and thin-lens Gaussian equations.Comment: IOPart, 8 pages, 4 figure

Neutron-Proton Correlations in an Exactly Solvable Model

We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double beta decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton QRPA (RQRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller beta+ strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an N=Z core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar side of the phase transition.Comment: 13 pages + 11 postscript figures, in RevTe

Image Storage in Hot Vapors

We theoretically investigate image propagation and storage in hot atomic vapor. A $4f$ system is adopted for imaging and an atomic vapor cell is placed over the transform plane. The Fraunhofer diffraction pattern of an object in the object plane can thus be transformed into atomic Raman coherence according to the idea of ``light storage''. We investigate how the stored diffraction pattern evolves under diffusion. Our result indicates, under appropriate conditions, that an image can be reconstructed with high fidelity. The main reason for this procedure to work is the fact that diffusion of opposite-phase components of the diffraction pattern interfere destructively.Comment: 11 pages, 3 figure

Uncovering the (un-)occupied electronic structure of a buried hybrid interface

The energy level alignment at organic/inorganic (o/i) semiconductor interfaces is crucial for any light-emitting or -harvesting functionality. Essential is the access to both occupied and unoccupied electronic states directly at the interface, which is often deeply buried underneath thick organic films and challenging to characterize. We use several complementary experimental techniques to determine the electronic structure of p-quinquephenyl pyridine (5P-Py) adsorbed on ZnO(10-10). The parent anchoring group, pyridine, significantly lowers the work function by up to 2.9 eV and causes an occupied in-gap state (IGS) directly below the Fermi level $E_\text{F}$. Adsorption of upright-standing 5P-Py also leads to a strong work function reduction of up to 2.1 eV and to a similar IGS. The latter is then used as an initial state for the transient population of three normally unoccupied molecular levels through optical excitation and, due to its localization right at the o/i interface, provides interfacial sensitivity, even for thick 5P-Py films. We observe two final states above the vacuum level and one bound state at around 2 eV above $E_\text{F}$, which we attribute to the 5P-Py LUMO. By the separate study of anchoring group and organic dye combined with the exploitation of the occupied IGS for selective interfacial photoexcitation this work provides a new pathway for characterizing the electronic structure at buried o/i interfaces

Numerical renormalization group calculation of near-gap peaks in spectral functions of the Anderson model with superconducting leads

We use the numerical renormalization group method (NRG) to investigate a single-impurity Anderson model with a coupling of the impurity to a superconducting host. Analysis of the energy flow shows, in contrast to previous belief, that NRG iterations can be performed up to a large number of sites, corresponding to energy differences far below the superconducting gap. This allows us to calculate the impurity spectral function very accurately for frequencies near the gap edge, and to resolve, in a certain parameter regime, sharp peaks in the spectral function close to the gap edge.Comment: 18 pages, 7 figures, accepted for publication in Journal of Physics: Condensed Matte

Airglow observations of dynamical (wind shear-induced) instabilities over Adelaide, Australia, associated with atmospheric gravity waves

While several observations have been made in recent years of instability features in airglow images of atmospheric gravity waves (AGWs), such measurements are still rare. To date, these features are characterized by appearing to be aligned perpendicular to the AGW wave fronts. Multi-instrument observations confirm the theoretical prediction that such features are caused by convective instabilities where the AGW-induced temperature variation causes the total lapse rate to exceed the adiabatic lapse rate. In February 2000, airglow observations were obtained at Buckland Park, Australia, which showed instability features with a different characteristic. These images showed small-scale (less than 10 km horizontal wavelength) features aligned parallel to the larger scale AGW wave fronts. These features were only seen in OH images, not in O2A images, indicating that they originate below 90 km altitude. Simultaneous MF radar wind data reveal the presence of a mean wind shear which, during the period of the small-scale features, was aligned nearly in the direction of AGW propagation. In addition, the larger scale AGW approached a critical level near 90 km altitude. While the wind shear itself is not large enough to cause an instability, an analysis of the data suggests that the small-scale features are the result of a dynamic (wind shear-induced) instability in the 87–90 km altitude region. The instability was due to a combination of the background wind shear and the large shear induced by the passage of the larger scale AGW as it approached the critical level.J. H. Hecht, R. L. Walterscheid and R. A. Vincen

Mass and Spin of Poincare Gauge Theory

We discuss two expressions for the conserved quantities (energy momentum and angular momentum) of the Poincar\'e Gauge Theory. We show, that the variations of the Hamiltonians, of which the expressions are the respective boundary terms, are well defined, if we choose an appropriate phase space for asymptotic flat gravitating systems. Furthermore, we compare the expressions with others, known from the literature.Comment: 16 pages, plain-tex; to be published in Gen. Rel. Gra

Deterministic spatio-temporal control of nano-optical fields in optical antennas and nano transmission lines

We show that pulse shaping techniques can be applied to tailor the ultrafast temporal response of the strongly confined and enhanced optical near fields in the feed gap of resonant optical antennas (ROAs). Using finite-difference time-domain (FDTD) simulations followed by Fourier transformation, we obtain the impulse response of a nano structure in the frequency domain, which allows obtaining its temporal response to any arbitrary pulse shape. We apply the method to achieve deterministic optimal temporal field compression in ROAs with reduced symmetry and in a two-wire transmission line connected to a symmetric dipole antenna. The method described here will be of importance for experiments involving coherent control of field propagation in nanophotonic structures and of light-induced processes in nanometer scale volumes.Comment: 5 pages, 5 figure

The Conceptualization and Communication of Risk Among Rural Appalachian Adolescents

This study employs a meta-theoretical perspective for examining risk perceptions and behavior in the rural, Appalachian cultural context, an area that remains largely unexplored. In-depth interviews were conducted with 113 rural adolescents to describe how youth conceptualize risk and how risk is communicated in the rural environment. Analyses revealed adolescents viewed behavior as risky when they had personal or vicarious experiences resulting in a loss of control or physical harm. Elements of the rural Appalachian culture including activities, familism, and community ties can both prevent and promote adolescent risk-taking in various forms. This study demonstrates the conceptualization of risk and messages about risk are culturally-situated and communicatively devised and enacted. The implications of these findings for adolescent risk prevention programs are discussed