Investigation of the use of microwave image line integrated circuits for use in radiometers and other microwave devices in X-band and above

Program results are described in which the use of a/high permittivity rectangular dielectric image waveguide has been investigated for use in microwave and millimeter wavelength circuits. Launchers from rectangular metal waveguide to image waveguide are described. Theoretical and experimental evaluations of the radiation from curved image waveguides are given. Measurements of attenuation due to conductor and dielectric losses, adhesives, and gaps between the dielectric waveguide and the image plane are included. Various passive components are described and evaluations given. Investigations of various techniques for fabrication of image waveguide circuits using ceramic waveguides are also presented. Program results support the evaluation of the image line approach as an advantageous method for realizing low loss integrated electronic circuits for X-band and above

Far-flung Filaments of Ejecta in the Young Supernova Remnant G292.0+1.8

New optical images of the young SNR G292.0+1.8, obtained from the 0.9-m telescope at CTIO, show a more extensive network of filaments than had been known previously. Filaments emitting in [O III] are distributed throughout much of the 8 arcmin diameter shell seen in X-ray and radio images, including a few at the very outermost shell limits. We have also detected four small complexes of filaments that show [S II] emission along with [OIII]. In a single long-slit spectrum we find variations of almost an order of magnitude in the relative strengths of oxygen and sulfur lines, which must result from abundance variations. None of the filaments, with or without [S II], shows any evidence for hydrogen, so all appear to be fragments of pure SN ejecta. The [S II] filaments provide the first evidence for undiluted products of oxygen burning in the ejecta from the supernova that gave rise to G292.0+1.8. Some oxygen burning must have occurred, but the paucity of [S II]-emitting filaments suggests that either the oxygen burning was not extensive or that most of its products have yet to be excited. Most of the outer filaments exhibit radial, pencil-like morphologies that suggest an origin as Rayleigh-Taylor fingers of ejecta, perhaps formed during the explosion. Simulations of core-collapse supernovae predict such fingers, but these have never before been so clearly observed in a young SNR. The total flux from the SNR in [OIII] 5007 is 5.4 * 10**-12 ergs/cm**2/s. Using a distance of 6 kpc and an extinction correction corresponding to E(B-V) = 0.6 (lower than previous values but more consistent both with our data and radio and X-ray estimates of NH), this leads to a luminosity of 1.6 * 10**35 ergs/s in the 5007 Ang. line.Comment: 32 pages including 10 figures, and 3 tables, accepted for publication in AJ. Vol 132, July 2006. Higher resolution versions of the figures and a pdf of the manuscript can be found at http://www-int.stsci.edu/~long/papers/g292_optical

Low-Surface-Brightness Galaxies in the Sloan Digital Sky Survey. I. Search Method and Test Sample

In this paper we present results of a pilot study to use imaging data from the Sloan Digital Sky Survey (SDSS) to search for low-surface-brightness (LSB) galaxies. For our pilot study we use a test sample of 92 galaxies from the catalog of Impey et al. (1996) distributed over 93 SDSS fields of the Early Data Release (EDR). Many galaxies from the test sample are either LSB or dwarf galaxies. To deal with the SDSS data most effectively a new photometry software was created, which is described in this paper. We present the results of the selection algorithms applied to these 93 EDR fields. Two galaxies from the Impey et al. test sample are very likely artifacts, as confirmed by follow-up imaging. With our algorithms, we were able to recover 87 of the 90 remaining test sample galaxies, implying a detection rate of $\sim$96.5%. The three missed galaxies fall too close to very bright stars or galaxies. In addition, 42 new galaxies with parameters similar to the test sample objects were found in these EDR fields (i.e., $\sim$47% additional galaxies). We present the main photometric parameters of all identified galaxies and carry out first statistical comparisons. We tested the quality of our photometry by comparing the magnitudes for our test sample galaxies and other bright galaxies with values from the literature. All these tests yielded consistent results. We briefly discuss a few unusual galaxies found in our pilot study, including an LSB galaxy with a two-component disk and ten new giant LSB galaxies.Comment: 36 pages, 16 figures, accepted for publication by AJ, some figures were bitmapped to reduce the siz

A Machian Model of Dark Energy

Einstein believed that Mach's principle should play a major role in finding a meaningful spacetime geometry, though it was discovered later that his field equations gave some solutions which were not Machian. It is shown, in this essay, that the kinematical $\Lambda$ models, which are invoked to solve the cosmological constant problem, are in fact consistent with Mach's ideas. One particular model in this category is described which results from the microstructure of spacetime and seems to explain the current observations successfully and also has some benefits over the conventional models. This forces one to think whether the Mach's ideas and the cosmological constant are interrelated in some way.Comment: Received an Honorable mention in the Essay Contest-2002 sponsored by the Gravity Research Foundation; A paragraph added on how the model can explain the CMB anisotropy observations; To appear in the Classical and Quantum Gravit

Modeling Extragalactic Foregrounds and Secondaries for Unbiased Estimation of Cosmological Parameters From Primary CMB Anisotropy

Using the latest physical modeling and constrained by the most recent data, we develop a phenomenological parameterized model of the contributions to intensity and polarization maps at millimeter wavelengths from external galaxies and Sunyaev-Zeldovich effects. We find such modeling to be necessary for estimation of cosmological parameters from Planck data. For example, ignoring the clustering of the infrared background would result in a bias in n_s of 7 sigma. We show that the simultaneous marginalization over a full foreground model can eliminate such biases, while increasing the statistical uncertainty in cosmological parameters by less than 20%. The small increases in uncertainty can be significantly reduced with the inclusion of higher-resolution ground-based data. The multi-frequency analysis we employ involves modeling 46 total power spectra and marginalization over 17 foreground parameters. We show that we can also reduce the data to a best estimate of the CMB power spectra, and just two principal components (with constrained amplitudes) describing residual foreground contamination.Comment: 17 pages, 7 figures, submitted to Ap

Exact treatment of exciton-polaron formation by Diagrammatic Monte Carlo

We develop an approximation-free Diagrammatic Monte Carlo technique to study fermionic particles interacting with each other simultaneously through both an attractive Coulomb potential and bosonic excitations of the underlying medium. Exemplarily we apply the method to the long-standing exciton-polaron problem and present numerically exact results for the wave function, ground-state energy, binding energy and effective mass of this quasiparticle. Focusing on the electron-hole pair bound-state formation, we discuss various limiting cases of a generic exciton-polaron model. The frequently used instantaneous approximation to the retarded interaction due to the phonon exchange is found to be of very limited applicability. For the case of a light electron and heavy hole the system is well approximated by a particle in the field of a static attractive impurity.Comment: 5 pages, 5 figure

Far Ultraviolet Observations of the Dwarf Nova VW Hyi in Quiescence

We present a 904-1183 A spectrum of the dwarf nova VW Hydri taken with the Far Ultraviolet Spectroscopic Explorer during quiescence, eleven days after a normal outburst, when the underlying white dwarf accreter is clearly exposed in the far ultraviolet. However, model fitting show that a uniform temperature white dwarf does not reproduce the overall spectrum, especially at the shortest wavelengths. A better approximation to the spectrum is obtained with a model consisting of a white dwarf and a rapidly rotating ``accretion belt''. The white dwarf component accounts for 83% of the total flux, has a temperature of 23,000K, a v sin i = 400 km/s, and a low carbon abundance. The best-fit accretion belt component accounts for 17% of the total flux, has a temperature of about 48,000-50,000K, and a rotation rate Vrot sin i around 3,000-4,000 km/s. The requirement of two components in the modeling of the spectrum of VW Hyi in quiescence helps to resolve some of the differences in interpretation of ultraviolet spectra of VW Hyi in quiescence. However, the physical existence of a second component (and its exact nature) in VW Hyi itself is still relatively uncertain, given the lack of better models for spectra of the inner disk in a quiescent dwarf nova.Comment: 6 figures, 10 printed page in the journal, to appear in APJ, 1 Sept. 2004 issue, vol. 61

The Yellow Excitonic Series of Cu2O Revisited by Lyman Spectroscopy

We report on the observation of the yellow exciton Lyman series up to the fourth term in Cu2O by time-resolved mid-infrared spectroscopy. The dependence of the oscillator strength on the principal quantum number n can be well reproduced using the hydrogenic model including an AC dielectric constant, and precise information on the electronic structure of the 1s exciton state can be obtained. A Bohr radius a_{1s}=7.9 A and a 1s-2p transition dipole moment \mu_{1s-2p}= 4.2 eA were found

Spontaneous emission from large quantum dots in nanostructures: exciton-photon interaction beyond the dipole approximation

We derive a rigorous theory of the interaction between photons and spatially extended excitons confined in quantum dots in inhomogeneous photonic materials. We show that, beyond the dipole approximation, the radiative decay rate is proportional to a non-local interaction function, which describes the interaction between light and spatially extended excitons. In this regime, light and matter degrees of freedom cannot be separated and a complex interplay between the nanostructured optical environment and the exciton envelope function emerges. We illustrate this by specific examples and derive a series of important analytical relations, which are useful for applying the formalism to practical problems. In the dipole limit, the decay rate is proportional to the projected local density of optical states and we obtain the strong and weak confinement regimes as special cases.Comment: 14 pages, 4 figure