Interaction of SN Ib 2004dk with a Previously Expelled Envelope.

The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong Hα-emitting point source on narrowband Hα images. We present follow-up optical spectroscopy that reveals the presence of a broad Hα component with full width at half maximum of ~ 290 km s-1 in addition to the narrow Hα+[N ii] emission features from the host galaxy. Such a broad component is a clear sign of an ejecta-CSM interaction. We also present observations with the XMM-Newton Observatory, the Swift satellite, and the Chandra X-ray Observatory that span 10 days to 15 years after discovery. The detection of strong radio, X-ray, and Hα emission years after explosion allows various constraints to be put on pre-SN mass-loss processes. We present a wind-bubble model in which the CSM is "pre-prepared" by a fast wind interacting with a slow wind. Much of the outer density profile into which the SN explodes corresponds to no steady-state mass-loss process. We estimate that the shell of compressed slow wind material was ejected ~1400 yr prior to explosion, perhaps during carbon burning, and that the SN shock had swept up about 0.04 M ⊙ of material. The region emitting the Hα has a density of order 10-20 g cm-3.

Bacterial bioluminescence, bioelectromagnetics and function.

The biological functions of light emission in bacterial bioluminescence are not always obvious, especially if the bacteria are in a free-living mode. Experimental evidence suggests that light emission confers benefit to the bacteria themselves such as through photoreactivation and involves as much as 20% of cell energy metabolism. A theoretical model shows if the effect is mediated solely by light then cells should be luminescent at both high and low cell densities, therefore raising doubt over the photoreactivation hypothesis and suggesting that another cofactor is involved. It has been postulated that bioelectromagnetics may be involved in biological processes and be involved with coordinated activity in quorate cells. The cell densities associated with autoinduction coincide with a large change in coupling efficiency in the millimeter and submillimeter spectral region. In this paper it is suggested that one function of bioluminescence is as a pump, involving millimeter and submillimeter wave coupling that is of benefit to the quorum. This may be related to the observation that millimeter wave radiation exposure has been reported to induce changes in DNA conformation and possibly gene expression. Agents that change DNA conformation in bioluminescent bacteria can cause increases in light emission. This work may have implications for electromagnetic fields as quorum-quenching agents.

Globular cluster x-ray sources.

Globular clusters and x-ray astronomy have a long and fruitful history. Uhuru and OSO-7 revealed highly luminous (> 10(36) ergs(-1)) x-ray sources in globular clusters, and Einstein and ROSAT revealed a larger population of low-luminosity (< 10(33) ergs(-1)) x-ray sources. It was realized early on that the high-luminosity sources were low-mass x-ray binaries in outburst and that they were orders of magnitude more abundant per unit mass in globular clusters than in the rest of the galaxy. However, the low-luminosity sources proved difficult to classify. Many ideas were put forth--low-mass x-ray binaries in quiescence (qLMXBs), cataclysmic variables (CVs), active main-sequence binaries (ABs), and millisecond pulsars (MSPs)--but secure identifications were scarce. In ROSAT observations of 55 clusters, about 25 low-luminosity sources were found. Chandra has now observed over 80 Galactic globular clusters, and these observations have revealed over 1,500 x-ray sources. The superb angular resolution has allowed for many counterpart identifications, providing clues to the nature of this population. It is a heterogeneous mix of qLMXBs, CVs, ABs, and MSPs, and it has been shown that the qLMXBs and CVs are both, in part, overabundant like the luminous LMXBs. The number of x-ray sources in a cluster correlates very well with its encounter frequency. This points to dynamical formation scenarios for the x-ray sources and shows them to be excellent tracers of the complicated internal dynamics. The relation between the encounter frequency and the number of x-ray sources has been used to suggest that we have misunderstood the dynamical states of globular clusters.

Continuous culture of photobacterium.

The design and performance characteristics of a small volume (20 ml) continuous culture device for the cultivation of luminous bacteria are described. This simply constructed device can be used to supply luminescent bacteria with constant properties for either laboratory use or the assay of environmental pollutants. Furthermore, bacteria can be deployed to make sensitive (<1 nM) oxygen measurements. The culture device may be configured, alone or in combination, as a chemostat, turbidostat or a "bioluminostat" where bacterial bioluminescence becomes the controlling variable. Over extended periods (>1 week) it was possible to maintain steady-state luminescence within 5% of a pre-set value, although occasionally a non-bioluminescent "mutant" became dominant; in this case light emission was irreversibly lost. A secondary chamber provided additional flexibility and easy manipulation of the cultivated bacteria for testing. The continuous culture system is also suitable for the growth of recombinant microorganisms that either constitutively express luciferase, or do so in response to stress promoter activity. The non-standard control methodologies reported may have important research and industrial applications, for example in providing immediate process control or as an inferential method to optimize biomass: product yield ratios.