Some Thoughts on Energy Conditions and Wormholes

This essay reviews some of the recent progress in the area of energy conditions and wormholes. Most of the discussion centers on the subject of ``quantum inequality'' restrictions on negative energy. These are bounds on the magnitude and duration of negative energy which put rather severe constraints on its possible macroscopic effects. Such effects might include the construction of wormholes and warp drives for faster-than-light travel, and violations of the second law of thermodynamics. Open problems and future directions are also discussed.Comment: 24 pages; to appear in the Proceedings of the Tenth Marcel Grossmann Meeting on General Relativity and Gravitatio

A New Galactic Wolf-Rayet Star in Centaurus

In this work I communicate the detection of a new Galactic Wolf-Rayet star (WR60a) in Centaurus. The H- and K-band spectra of WR60a, show strong carbon near-infrared emission lines, characteristic of Wolf-Rayet stars of the WC5-7 sub-type. Adopting mean absolute magnitude M$_K$ and mean intrinsic ($J-K_S$) and ($H-K_S$) colours, it was found that WR60a suffer a mean visual extinction of 3.8$\pm$1.3 magnitudes, being located at a probable heliocentric distance of 5.2$\pm$0.8 Kpc, which for the related Galactic longitude (l=312) puts this star probably in the Carina-Sagittarius arm at about 5.9 kpc from the Galactic center. I searched for clusters in the vicinity of WR60a, and in principle found no previously known clusters in a search radius region of several tens arc-minutes. The detection of a well isolated WR star induced us to seek for some still unknown cluster, somewhere in the vicinity of WR60a. From inspection of 5.8$\mu$m and 8.0$\mu$m Spitzer/IRAC GLIMPSE images of the region around the new WR star, it was found strong mid-infrared extended emission at about 13.5 arcmin south-west of WR60a. The study of the the H-K$_S$ colour distribution of point sources associated with the extended emission, reveals the presence of a new Galactic cluster candidate probably formed by at least 85 stars.Comment: 5 pages, 2 tables and 4 figures. Figure 4 is in low-resolution mode. The published on-line version of the paper can be obtained at http://www.isrn.com/journals/astro/2011/632850

Knowing How: A Computational Approach

With advances in Artificial Intelligences being achieved through the use of Artificial Neural Networks, we are now at the point where computers are able to do tasks that were previously only able to be accomplished by humans. These advancements must cause us to reconsider our previous understanding of how people come to know how to do a particular task. In order to unpack this question, I will first look to an account of knowing how presented by Jason Stanley in his book Know How. I will then look towards criticisms of this view before using evidence presented by the existence of Artificial Neural Networks to present a new view that addresses the problems present in Stanley’s work. Finally, I will argue that knowing how to do something is a matter of heuristics, or knowing certain shortcuts which approximate a solution to the task one is trying to accomplish

Discovery of two Galactic Wolf-Rayet stars in Circinus

I report the discovery of two new Galactic Wolf-Rayet stars in Circinus via detection of their C, N and He Near-Infrared emission lines, using ESO-NTT-SOFI archival data. The H- and K-band spectra of WR67a and WR67b, indicate that they are Wolf-Rayet stars of WN6h and WC8 sub-types, respectively. WR67a presents a weak-lined spectrum probably reminiscent of young hydrogen rich main-sequence stars such as WR25 in Car OB1 and HD97950 in NGC3603. Indeed, this conclusion is reinforced by the close morphological match of the WR67a H- and K-band spectra with that for WR21a, a known extremely massive binary system. WR67b is probably a non-dusty WC8 Wolf-Rayet star that has a estimated heliocentric distance of 2.7(0.9) kpc, which for its Galactic coordinates, puts the star probably in the near portion of the Scutum-Centaurus arm.Comment: 6 pages, 3 figures, accepted for publication on MNRA