On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events

We describe and analyze Hubble Space Telescope (HST) observations of transient emission near 4680 {\AA} in Eta Car, reported earlier by Steiner & Damineli (2004). If, as seems probable, this is He II $\lambda$4687, then it is a unique clue to Eta Car's 5.5-year cycle. According to our analysis, several aspects of this feature support a mass-ejection model of the observed spectroscopic events, and not an eclipse model. The He II emission appeared in early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and then abruptly disappeared. It did not appear in any other HST spectra before or after the event. The peak brightness was larger than previously reported, and is difficult to explain even if one allows for an uncertainty factor of order 3. The stellar wind must provide a temporary larger-than-normal energy supply, and we describe a special form of radiative amplification that may also be needed. These characteristics are consistent with a class of mass-ejection or wind-disturbance scenarios, which have implications for the physical structure and stability of Eta Car.Comment: 47 pages (including all appendices, tabs, & figs), 9 figures, 3 tables; submitted to Astrophysical Journal (2005 March 29), accepted for publication in Ap

Inflation and nonequilibrium renormalization group

We study de spectrum of primordial fluctuations and the scale dependence of the inflaton spectral index due to self-interactions of the field. We compute the spectrum of fluctuations by applying nonequilibrium renormalization group techniques.Comment: 6 pages, 1 figure, submitted to J. Phys.

Self-assembled dynamic perovskite composite cathodes for intermediate temperature solid oxide fuel cells

Electrode materials for intermediate temperature (500–700 ∘C) solid oxide fuel cells require electrical and mechanical stability to maintain performance during the cell lifetime. This has proven difficult to achieve for many candidate cathode materials and their derivatives with good transport and electrocatalytic properties because of reactivity towards cell components, and the fuels and oxidants. Here we present Ba0.5Sr0.5(Co0.7Fe0.3)0.6875W0.3125O3−δ (BSCFW), a self-assembled composite prepared through simple solid state synthesis, consisting of B-site cation ordered double perovskite and disordered single perovskite oxide phases, as a candidate cathode material. These phases interact by dynamic compositional change at the operating temperature, promoting both chemical stability through the increased amount of W in the catalytically active single perovskite provided from the W-reservoir double perovskite, and microstructural stability through reduced sintering of the supported catalytically active phase. This interactive catalyst-support system enabled stable high electrochemical activity through the synergic integration of the distinct properties of the two phases

The Binarity of Eta Carinae and its Similarity to Related Astrophysical Objects

I examine some aspects of the interaction between the massive star Eta Carinae and its companion, in particular during the eclipse-like event, known as the spectroscopic event or the shell event. The spectroscopic event is thought to occur when near periastron passages the stellar companion induces much higher mass loss rate from the primary star, and/or enters into a much denser environment around the primary star. I find that enhanced mass loss rate during periastron passages, if it occurs, might explain the high eccentricity of the system. However, there is not yet a good model to explain the presumed enhanced mass loss rate during periastron passages. In the region where the winds from the two stars collide, a dense slow flow is formed, such that large dust grains may be formed. Unlike the case during the 19th century Great Eruption, the companion does not accrete mass during most of its orbital motion. However, near periastron passages short accretion episodes may occur, which may lead to pulsed ejection of two jets by the companion. The companion may ionize a non-negligible region in its surrounding, resembling the situation in symbiotic systems. I discuss the relation of some of these processes to other astrophysical objects, by that incorporating Eta Car to a large class of astrophysical bipolar nebulae.Comment: Updated version. ApJ, in pres

The UV Scattering Halo of the Central Source Associated with Eta Carinae

We have made an extensive study of the UV spectrum of Eta Carinae, and find that we do not directly observe the star and its wind in the UV. Because of dust along our line of sight, the UV light that we observe arises from bound-bound scattering at large impact parameters. We obtain a reasonable fit to the UV spectrum by using only the flux that originates outside 0.033". This explains why we can still observe the primary star in the UV despite the large optical extinction -- it is due to the presence of an intrinsic coronagraph in the Eta Carinae system, and to the extension of the UV emitting region. It is not due to peculiar dust properties alone. We have computed the spectrum of the purported companion star, and show that it could only be directly detected in the UV spectrum preferentially in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectral region (912-1175 Ang.). However, we find no direct evidence for a companion star, with the properties indicated by X-ray studies and studies of the Weigelt blobs, in UV spectra. This might be due to reprocessing of the companion's light by the dense stellar wind of the primary. Broad FeII and [FeII] emission lines, which form in the stellar wind, are detected in spectra taken in the SE lobe, 0.2" from the central star. The wind spectrum shows some similarities to the spectra of the B & D Weigelt blobs, but also shows some marked differences in that high excitation lines, and lines pumped by Ly-alpha, are not seen. The detection of the broad lines lends support to our interpretation of the UV spectrum, and to our model for Eta Carinae.Comment: To appear in ApJ. 57 pages with 18 figure

Factors affecting mechanical (nociceptive) thresholds in piglets

AbstractObjectiveTo evaluate the stability and repeatability of measures of mechanical (nociceptive) thresholds in piglets and to examine potentially confounding factors when using a hand held algometer.Study designDescriptive, prospective cohort.AnimalsForty-four piglets from four litters, weighing 4.6 ± 1.0 kg (mean ± SD) at 2 weeks of age.MethodsMechanical thresholds were measured twice on each of 2 days during the first and second week of life. Data were analyzed using a repeated measures design to test the effects of behavior prior to testing, sex, week, day within week, and repetition within day. The effect of body weight and the interaction between piglet weight and behaviour were also tested. Piglet was entered into the model as a random effect as an additional test of repeatability. The effect of repeated testing was used to test the stability of measures. Pearson correlations between repeated measures were used to test the repeatability of measures. Variance component analysis was used to describe the variability in the data.ResultsVariance component analysis indicated that piglet explained only 17% of the variance in the data. All variables in the model (behaviour prior to testing, sex, week, day within week, repetition within day, body weight, the interaction between body weight and behaviour, piglet identity) except sex had a significant effect (p < 0.04 for all). Correlations between repeated measures increased from the first to the second week.Conclusions and Clinical relevanceRepeatability was acceptable only during the second week of testing and measures changed with repeated testing and increased with increasing piglet weight, indicating that time (age) and animal body weight should be taken into account when measuring mechanical (nociceptive) thresholds in piglets. Mechanical (nociceptive) thresholds can be used both for testing the efficacy of anaesthetics and analgesics, and for assessing hyperalgesia in chronic pain states in research and clinical settings