An automatic data system for vibration modal tuning and evaluation

A digitally based automatic modal tuning and analysis system developed to provide an operational capability beginning at 0.1 hertz is described. The elements of the system, which provides unique control features, maximum operator visibility, and rapid data reduction and documentation, are briefly described; and the operational flow is discussed to illustrate the full range of capabilities and the flexibility of application. The successful application of the system to a modal survey of the Skylab payload is described. Information about the Skylab test article, coincident-quadrature analysis of modal response data, orthogonality, and damping calculations is included in the appendixes. Recommendations for future application of the system are also made

Filaments as Possible Signatures of Magnetic Field Structure in Planetary Nebulae

We draw attention to the extreme filamentary structures seen in high-resolution optical images of certain planetary nebulae. We determine the physical properties of the filaments in the nebulae IC 418, NGC 3132, and NGC 6537, and based on their large length-to-width ratios, longitudinal coherence, and morphology, we suggest that they may be signatures of the underlying magnetic field. The fields needed for the coherence of the filaments are probably consistent with those measured in the precursor circumstellar envelopes. The filaments suggest that magnetic fields in planetary nebulae may have a localized and thread-like geometry.Comment: 26 pages with 7 figures. To be published in PASP. For full resolution images see http://physics.nyu.edu/~pjh

Zeta-Functions for Non-Minimal Operators

We evaluate zeta-functions $\zeta(s)$ at $s=0$ for invariant non-minimal 2nd-order vector and tensor operators defined on maximally symmetric even dimensional spaces. We decompose the operators into their irreducible parts and obtain their corresponding eigenvalues. Using these eigenvalues, we are able to explicitly calculate $\zeta(0)$ for the cases of Euclidean spaces and $N$-spheres. In the $N$-sphere case, we make use of the Euler-Maclaurin formula to develop asymptotic expansions for the required sums. The resulting $\zeta(0)$ values for dimensions 2 to 10 are given in the Appendix.Comment: 26 pages, additional reference

X-ray emission from Planetary Nebulae. I. Spherically symmetric numerical simulations

(abridged) The interaction of a fast wind with a spherical Asymptotic Giant Branch (AGB) wind is thought to be the basic mechanism for shaping Pre-Planetary Nebulae (PPN) and later Planetary Nebulae (PN). Due to the large speed of the fast wind, one expects extended X-ray emission from these objects, but X-ray emission has only been detected in a small fraction of PNs and only in one PPN. Using numerical simulations we investigate the constraints that can be set on the physical properties of the fast wind (speed, mass-flux, opening angle) in order to produce the observed X-ray emission properties of PPNs and PNs. We combine numerical hydrodynamical simulations including radiative cooling using the code FLASH with calculations of the X-ray properties of the resulting expanding hot bubble using the atomic database ATOMDB. In this first study, we compute X-ray fluxes and spectra using one-dimensional models. Comparing our results with analytical solutions, we find some agreements and many disagreements. In particular, we test the effect of different time histories of the fast wind on the X-ray emission and find that it is determined by the final stage of the time history during which the fast wind velocity has its largest value. The disagreements which are both qualitative and quantitative in nature argue for the necessity of using numerical simulations for understanding the X-ray properties of PNs.Comment: 17 pages, accepted for publication in ApJ (July 27, 2006), uses emulateap

Gauge Independent Trace Anomaly for Gravitons

We show that the trace anomaly for gravitons calculated using the usual effective action formalism depends on the choice of gauge when the background spacetime is not a solution of the classical equation of motion, that is, when off-shell. We then use the gauge independent Vilkovisky-DeWitt effective action to restore gauge independence to the off-shell case. Additionally we explicitly evaluate trace anomalies for some N-sphere background spacetimes.Comment: 19 pages, additional references and title chang

A CO Survey of Young Planetary Nebulae

We report the results of a sensitive survey of young planetary nebulae in the CO J=2-1 line that significantly increases the available data on warm, dense, molecular gas in the early phases of planetary nebula formation. The observations were made using the IRAM 30 m telescope with the 3 by 3 pixel Heterodyne Receiver Array (HERA). The array provides an effective means of discriminating the CO emission of planetary nebulae in the galactic plane from contaminating emission of interstellar clouds along the line of sight. 110 planetary nebulae were observed in the survey and 40 were detected. The results increase the number of young planetary nebulae with known CO emission by approximately a factor of two. The CO spectra yield radial velocities for the detected nebulae, about half of which have uncertain or no velocity measurements at optical wavelengths. The CO profiles range from parabolic to double-peaked, tracing the evolution of structure in the molecular gas. The line widths are significantly larger than on the Asymptotic Giant Branch, and many of the lines show extended wings, which probably result from the effects on the envelopes of high velocity jets.Comment: 29 pages, 2 figures (with multiple panels), to be published in Astrophysical Journal Supplement Serie

Interactive radio’s promising role in climate information services: Farm Radio International concept paper

This paper focuses on how interactive radio programming can increase the reach of weather and seasonal climate information and related advisory services. In doing so, they can enhance small-scale farmers’ capacity to make optimal decisions and manage risks based on a better understanding of probabilistic seasonal forecasts. The objective is to outline strategy that could vastly and affordably expand the number of small-scale farmers that are reached by and benefit from weather and climate information and related advisory services. Building on Farm Radio International’s (FRI) pioneering African Farm Radio Research Initiative (AFRRI), we assess the opportunities for interactive radio to provide integrated climate and advisory information while increasing farmers’ equitable access to salient and legitimate programming. We describe a number of practical strategies that can be used to make radio-based climate communication interactive, outline elements of a successful interactive radio service targeting rural communities, and discuss costs and other issues required for sustainability

Radio continuum properties of young planetary nebulae

We have selected a small sample of post-AGB stars in transition towards the planetary nebula and present new Very Large Array multi-frequency high-angular resolution radio observations of them. The multi-frequency data are used to create and model the targets' radio continuum spectra, proving that these stars started their evolution as very young planetary nebulae. In the optically thin range, the slopes are compatible with the expected spectral index (-0.1). Two targets (IRAS 18062+2410 and 17423-1755) seem to be optically thick even at high frequency, as observed in a handful of other post-AGB stars in the literature, while a third one (IRAS 20462+3416) shows a possible contribution from cold dust. In IRAS 18062+2410, where we have three observations spanning a period of four years, we detect an increase in its flux density, similar to that observed in CRL 618. High-angular resolution imaging shows bipolar structures that may be due to circumstellar tori, although a different hypothesis (i.e., jets) could also explain the observations. Further observations and monitoring of these sources will enable us to test the current evolutionary models of planetary nebulae.Comment: 8 pages, 3 figures, accepted for publication in MNRA

Jets and the shaping of the giant bipolar envelope of the planetary nebula KjPn 8

A hydrodynamic model involving cooling gas in the stagnation region of a collimated outflow is proposed for the formation of the giant parsec-scale bipolar envelope that surrounds the planetary nebula KjPn 8. Analytical calculations and numerical simulations are presented to evaluate the model. The envelope is considered to consist mainly of environmental gas swept-up by shocks driven by an episodic, collimated, bipolar outflow. In this model, which we call the ``free stagnation knot'' mechanism, the swept-up ambient gas located in the stagnation region of the bow-shock cools to produce a high density knot. This knot moves along with the bow-shock. When the central outflow ceases, pressurization of the interior of the envelope stops and its expansion slows down. The stagnation knot, however, has sufficient momentum to propagate freely further along the axis, producing a distinct nose at the end of the lobe. The model is found to successfully reproduce the peculiar shape and global kinematics of the giant bipolar envelope of KjPn 8.Comment: 20 pages + 8 figures (in 1 tar-file 0.67 Mb

We must become gatekeepers : editing indigenous writing

With the proliferation of Indigenous texts currently published by specialist and mainstream publishers, non-Indigenous editors increasingly find themselves negotiating the uncomfortable territories of race, politics and power for which current training (in an Australian context) leaves them poorly prepared. Indigenous writer Anita Heiss advocates the employment of Indigenous editors as an \u27ideal\u27 solution, though few are currently working in the Australian industry. Margaret McDonell, an experienced non-Indigenous editor of Indigenous texts, suggests non-Indigenous editors need to \u27undertake a journey of learning\u27 during which \u27assumptions, biases, tastes and preconceptions\u27 are examined. Yet this presents a difficult task within a postcolonial society, when, as identified by Clare Bradford, even the classification of texts into genres such as fiction and the short story represents an entirely Eurocentric construct, \u27not readily correspond[ing] with Aboriginal schemata\u27. The Australian Society of Authors\u27 discussion paper \u27Writing about Indigenous Australia: Some Issues to Consider and Protocols to Follow\u27 provides practical guidelines that may be adapted for editorial use. This article canvasses these and other ideas with a focus on establishing an ethical and appropriately sensitive cross-cultural approach to editing Indigenous writing.<br /