Thursday, May 24, 2007
Tuesday, May 22, 2007
Last month I complained about the difficulty of upgrading a PC's primary hard-drive (i.e the one holding your primary Windows XP and/or Linux system partitions) without having to reinstall Windows and all its software by hand (and without buying commercial Windows-centric software) to the new drive.
Well, I eventually worked out how to do it with rdiff-backup after several weekends (and many weekday evenings) of experimentation and much frustration.
As I haven't seen all the necessary steps laid out together anywhere on the web, I've put together a page on my website entitled "Using rdiff-backup to restore Windows XP and Linux to a new disk." So that is the place to go if you need to know how.
Posted by Dave Strickland at 9:02 PM
Monday, May 21, 2007
[Image credit: Mandel-Wilson, http://www.galaxyimages.com/UNP_IFNebula.html. The image shows a snapshot of one small part of the IFN nebulosity near M81 (largest elliptical blob) and M82 (smaller blob to the right and slightly up from M81).]
APOD (astronomy picture of the day) is often spectacular, but rarely presents something a professional astronomer won't already have heard of.
But Integrated Flux Nebulae (IFN) were something I'd never heard of before. Basically these are large (in angular extent) Milky-Way reflection nebulae near or associated with the North Polar Spur (itself an interesting topic, most probably part of a very nearby supernova remnant, although some have argued that it is a much larger, more distant, part of the Milky Way's disk/halo interface. If I have time I will discuss this in a another post). They are visible in the optical via the scattering of starlight by the dust grains contained within the gas clouds making up the nebula. Apparently the dust clouds were already known from the IR-based dust maps of Schlegel, Finkbeiner and Davis (1998), but the first optical images of them were obtained by the amateur astronomers behind the Mandel-Wilson Catalogue of Unexplored Nebulae, of which the IFN website is a part.
That there is a lot of dust and optical nebulosity associated with the NPS is perhaps not too surprising, but what what hit me was that these objects were right in the vicinity of M81 and M82, objects whose environment I thought I knew everything about given the large amount of professional study of M82's wind and the M81/M82/NGC 3077 tidal streamers. These results raise the question of whether some of the nebulosity associated with the M81 group and M82's wind may be confused foreground emission from the NPS IFN... Note how much structure there is even in the dust images shown at the IFN website. The foreground extinction toward the M81 group is clearly not going to be uniform.
Here I will post a very rough initial attempt at answering the issue of whether IFN-related gunk is actually responsible for what are currently thought to be very extended parts of M82's wind. Of specific interest is the M82 northern ridge or cap, seen in H-alpha, UV and X-ray emission (Devine & Bally 1999, Lehnert Heckman & Weaver 1999, Hoopes et al 2005). The image below is the GALEX NUV (red) and FUV (blue) color composite of M82 from Hoopes et al (2005).
The heliocentric velocity of M82's nucleus is ~200 km/s (redshifted with respect to us), although the warm ionized gas associated with the inner wind has velocities of ~ 50 km/s and ~350 km/s. Thus the near-side (blue-shifted with respect to M82) H-alpha emission is already close in line-of-sight velocity to the velocities expected of material within our Galaxy. Devine & Bally (1999) show that the cap exhibits a monotonic trend in LOS velocity from ~0 to ~150 km/s (i.e. blueshifted by 200 to 50 km/s w.r.t M82).
If the cap were instead Galactic and associated with the NPS then its angular length of 3 arcminutes would correspond to a physical extent of about ~0.8 pc (d/1 kpc), where d is the assumed distance between us and the NPS material. Typical estimates of the distance to the NPS are only 50 to 200 pc, the cap would be < 0.2 pc in length if it were this close. To have a 200km/s velocity change in a gaseous cloud over a distance of only <1 pc would highly unusual (and rather unphysical for a small cloud within a supernova remnant).
Although I do not know the exact line of sight velocity of the NPS or IFN in this region, Savage et al (1997) find the LOS velocities for UV absorption lines in the NPS toward 3D 273 to be ~-60 to ~-5 km/s w.r.t. heliocentric, quite different from the LOS velocity of the cap.
Furthermore, the cap displays behaviour very similar to the rest of the superwind, specifically simultaneous soft X-ray, H-alpha and NUV/FUV emission, with a soft X-ray/H-alpha flux ratio ~1 which is typical of superwinds (e.g. see Strickland et al 2002). Material associated with a cool dusty or photoionized cloud that is part of the NPS would not be expected to be detected as soft X-ray source or similar surface brightness to the superwind (although the presence of more widely-distributed lower surface brightness X-ray emission from the NPS might be expected), nor have that particular wind-like SX/H-alpha flux ratio.
This leads me to conclude that the Cap is very unlikely to be associated with the Galactic NPS, and most likely to be a genuine feature of M82's wind.
Nevertheless, I'm pleasantly surprised to learn something new about the M81/M82 region. It is also another nice example of the genuinely valuable contribution that amateur astronomers can still make.
- Devine, David; Bally, John, 1999, The Astrophysical Journal, Volume 510, Issue 1, pp. 197-204.
- Hoopes, C, et al, 2005, The Astrophysical Journal, Volume 619, Issue 1, pp. L99-L102.
- Lehnert, Matthew D.; Heckman, Timothy M.; Weaver, Kimberly A., 1999, The Astrophysical Journal, Volume 523, Issue 2, pp. 575-584.
- Sembach, Kenneth R.; Savage, Blair D.; Tripp, Todd M., 1997, Astrophysical Journal v.480, p.216.
- Schlegel, David J.; Finkbeiner, Douglas P.; Davis, Marc, 1998, The Astrophysical Journal v.500, p.525.
- Strickland, David K.; Heckman, Timothy M.; Weaver, Kimberly A.; Hoopes, Charles G.; Dahlem, Michael, 2002, The Astrophysical Journal, Volume 568, Issue 2, pp. 689-716.
Posted by Dave Strickland at 1:38 PM
Friday, May 18, 2007
The BBC reports that in a partial victory for rationality and progress, the UK government has agreed to allow the creation of "human animal hybrid embryos" for research purposes only (damn, cancel that cat-woman order!), after initially wanting to ban all such research.
Note that actually true hybridization is still banned - effectively what is allow is the creation of a chimera. Still, even restricted in this manner, humanity will benefit.
Public Health Minister Caroline Flint denied that the government had staged a climbdown, saying they had always wanted to "leave the door open" for this type of research to be allowed on a case-by-case basis.
She said scientists had put forward more evidence about the importance of using hybrid embryos.
"We saw this was an area where these could be used for scientific benefit."
The draft bill allows the creation of human embryos that have been physically mixed with one or more animal cells. However, true animal-animal hybrids, made by the fusion of sperm and eggs, remain outlawed.
Scientists say their work could help find cures for devastating diseases, such as Alzheimer's.
Professor Robin Lovell-Badge, head of the division of Developmental Genetics at the MRC National Institute for Medical Research, said: "This research has many potential benefits for the understanding of disease and for treatments and should not be feared."
As usual, the argument against such research is largely based on nebulous claims about "ethics" and "morality," as if research that may lead to actually helping people isn't moral, and as if scientists can not say anything about morals or ethics.
But Josephine Quintavalle, of the campaign group Comment on Reproductive Ethics, disagreed, saying: "It is appalling that the government has bowed to pressure from the random collection of self-interested scientists and change its prohibitive stance.
"This is a highly controversial and terrifying proposal, which has little justification in science and even less in ethics.
As always, what is really happening is that people with religous beliefs about human embryos, beliefs not supported in any way by science, are trying to impose their beliefs on everyone, while under the cover of calling it ethics and morals (and only the religous are allowed to comment on morals in this brave new world we live in).
Note the absurd statement that the Government should take into consideration and act on the best scientific advice ("pressure from a self-interested scientists"), but of course they should bow to pressure from a tiny group of non-qualified, ignorant Luddites.
And as for terrifying, what is terrifying about it? There is nothing terrifying about chimerism (its actually surprisingly common in nature), hybridization or stem cell research. Terrifying is hundreds of millions of children starving or dying of disease each year. Terrifying is overpopulation and climate damage. Terrifying is religious fundamentalism and the brutality it so eagerly incites.
Anyway, hooray for the Labour government in stepping back from uninformed knee-jerk legislating and actually listening to the experts. Its a step in the right direction...
The politically astute will remember that the current US President (GWB) spent time in one of his State of the Nation speeches (normally reserved for such important things as talking about [faked] claims that Saddam was working on getting Uranium from Niger, and also the threat to civilization caused by athletes taking performance enhancing drugs) complaining about "manimals" and how such research would be banned.
Also note that right-wing reactionary "author" (deliberately put in quotes) and anti-science bigot Michael Crichton's novel "Next" contains a subplot about chimerism.
[update: fixed one obvious typo. Added labels. Credit for Cheetara picture: http://www.cheezey.org/thundercats/gallery/cheetaragallery.html].
Posted by Dave Strickland at 9:44 AM
Monday, May 14, 2007
See today's Pharyngula [14/05/2007]. Ditto to what PZ said.
Apart from that, its been quite a while since I've had the time to post, what with a superwind theory paper in the works, a trip to Arizona to see my astronomer friend Jason and Haiyin get married, a cold, allergies (worst allergy season in MD for many years), and the near endless struggle to fix my home PC (now done, info to follow at some point when I write up the techniques and the what-not-to-dos).
Posted by Dave Strickland at 9:53 AM