Wikipedia:Reference desk/Archives/Science/2010 January 24

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January 24

Maps of Australia

G'day! I'm looking forward to a drive across the Outback later this year. I will have a GPS and a road atlas, but as far as I can make out, Australia has no national grid reference system like I have in the UK. Are the reference grids on their maps just arbitrary or are they consistent from one publisher to another? Do the road atlases give any indication of latitude and longitude?--Shantavira|^{feed me} 10:49, 24 January 2010 (UTC)

Possibly. Quoting from page 3 of the 2008 "StreetSmart" Perth Street Directory (bold is added by me for emphasis) - which is Perth metro area, not the outback!

“ The black coordinates located at the corners of each map refer to the Australian Map Grid (AGD84). The pink coordinates ... refer to the Map Grid of Australia, Geocentric Datum of Australia (GDA94). The coordinates on the Regional Centres maps refer to the Map Grid of Australia (MGA94). For more information about GDA94 please refer to: http://www.landgate.wa.gov.au/corporate.nsf/web/Geodetic+Data. ”

I am not a cartographer so I don't know if this is what you are looking for, but perhaps it will help. Mitch Ames (talk) 11:41, 24 January 2010 (UTC)

Thanks, that's interesting. Looks like we need an article on that system. My GPS supports UTM, but I guess that is different. Does anyone know if I might be able to download the Aussie system to my Garmin GPS? Their website is not very informative. Maybe I should just buy a new GPS in Oz?--Shantavira|^{feed me} 12:34, 24 January 2010 (UTC)

Don't know about downloading, but a spare GPS, if you are going to rely on them a great deal, would be a very good idea. Are you for example planning to go off paved/marked roads? Our A$ is high at them moment so buying it here will be more expensive, though I have seen them for less than ≈$A150. 220.101.28.25 (talk) 13:41, 24 January 2010 (UTC)

Nah, probably only on paved roads, so the GPS is only for location rather than navigation. Your dollar is really low at the moment compared to the GBP [1]. I was amazed to discover that Google Street View now includes a lot of the Outback, including some dirt roads.--Shantavira|^{feed me} 14:43, 24 January 2010 (UTC)

You're reading the chart backwards, that graph shows GBP is low against AUD. The pound is only buying AUD $1.70, one year ago it was much stronger buying AUD$2.20. Vespine (talk) 22:14, 24 January 2010 (UTC)

Oops, thank you! Someone told me it was low. Looks like I'm not going to have quite the luxury holiday I was expecting!--Shantavira|^{feed me} 10:33, 25 January 2010 (UTC)

You have to watch those exchange rates! Petrol/fuel/gas isn't cheap here either, probably(?) cheaper then the UK. (In the Outback I imagine it will be VERY expensive, compared to city prices). Possibly add several Jerry cans to your list of necessities? --220.101.28.25 (talk) 18:33, 25 January 2010 (UTC)

Some Australian road maps (example (PDF)) include latitude and longtitude. Mitch Ames (talk) 06:51, 26 January 2010 (UTC)

Garmin GPSs are sold here, and your map provider should also have Australian maps - mine has UK/europe maps, so I don't see why the reverse wouldn't be true! Mattopaedia ^{Have a yarn} 02:18, 30 January 2010 (UTC)

Hypochondria paradox

If hypochondriacs have a tendency to self-diagnose themselves with many diseases, why do they fail to self-diagnose themselves with hypochondria, and thus realise that they actually probably don't have those diseases? Also, is this related to the Dunning-Kruger effect? --Mark PEA (talk) 14:52, 24 January 2010 (UTC)

Hypochondria is a tendency to channel anxiety into worries about one's own body health. Perceived evidence of disease is given more weight than evidence of health or reassurance from other sources of health information. I do not consider hypochondria very closely related to the Dunning-Kruger effect. alteripse (talk) 15:16, 24 January 2010 (UTC)

Hypochondria isn't deadly or debilitating. Hypochondriacs have more to worry about than hypochondria. Even if they do diagnose themselves with it, it's not important enough to bother a doctor about when they've got so many other things that could be far more harmful. Vimescarrot (talk) 15:46, 24 January 2010 (UTC)

This is the difference between psychology and physiology. Vranak (talk) 22:55, 24 January 2010 (UTC)

live jasmin

how can i block live jasmin.com from my computer —Preceding unsigned comment added by 67.246.254.35 (talk) 14:58, 24 January 2010 (UTC)

1. This question really belongs on the Computing ref desk...and they'll also want to know...
2. You need to tell us what operating system you use and what browser/email client(s) you use.
3. Do you mean to block email from that domain? Or prevent people who use your computer from browsing that web site? What precisely?

SteveBaker (talk) 16:50, 24 January 2010 (UTC)

nb: livejasmine.com is an adult webcam site that pops up (I guess from ad links or partnership links) when browsing many porn sites. I guess the original-poster wants to be able to block these popups. I don't know how to do that, but running Firefox's "flashblock" extension means that the popup window doesn't have a live webcam feed. Googling for "livejasmine popup block" finds lots of threads about how to block the popup itself. 87.114.29.120 (talk) 16:57, 24 January 2010 (UTC)

Presuming the popups need to access livejasmine.com and don't use an IP or have different domains that they continually vary, a simple (and common) solution that will work in most OSes (albeit you'll need to find out how to do it in each) would be to put livejasmine.com in the hosts file and point it to 127.0.0.1 or something similar. This will not block the popups windows from opening, it will simple mean you'll get an webserver doesn't respond message (unless you actually have a webserver locally or wherever you point it to) and as I've said will not help if the websites start using popups from an IP or they cycle between domains. And it's obviously not an effective way of stopping all software from accessing the domain, they could query a hardcoded domain name server or query the defined DNS themselves bypassing the OS DNS subsystem (if the DNS is a router you control you may be able to do something similar on the router) but it should work for browsers. Nil Einne (talk) 04:27, 25 January 2010 (UTC)

Expression of ratios

The title makes this sound like a mathematics question. I have never been able to understand an answer - or, to be fair, most of the questions- on the mathematics desk, however, so I am hoping someone with a science background will have the same information. (I sometimes understand science answers.)

I had always understood that ratios are expressed using a ":" in the form "A:B", and represent a mathematical relatipnship between A and B. In the article Vaccination controversy is the following sentence:

In the U.S. during the year 2001, routine childhood immunizations against seven diseases were estimated to save over $40 billion per birth-year cohort in overall social costs including $10 billion in direct health costs, and the societal benefit-cost ratio for these vaccinations was estimated to be 16.5.

(The emphasis is mine.) Thinking this was merely a typo for "16:5", I went to the footnoted source which contains the following sentence:

Direct and societal benefit-cost ratios for routine childhood vaccination were 5.3 and 16.5, respectively.

Thus the "ratio" presented in the WP article is correctly transcribed, but I still don't know how a ratio can be a single number. Is anyone willing to explain? Bielle (talk) 18:37, 24 January 2010 (UTC)

It's 16.5:1. The one's implied in a ratio when they only show one number like that. For every dollar spent on vaccinating kids, $16.50 is saved in health care costs down the road. You can also check out Benefit-cost ratio for information about this specific type of ratio, and cost-benefit analysis for more general information on the subject. Buddy431 (talk) 18:53, 24 January 2010 (UTC)

When the ':' and the second number is missing, it's generally accepted that ':1' is intended. So 5.3 and 16.5 really mean 5.3:1 and 16.5:1 respectively. In other words, the benefit is 5.3 times the cost or 16.5 times the cost. SteveBaker (talk) 18:54, 24 January 2010 (UTC)

Really, this is just a matter of different ways of thinking about the same thing. The ratio 14:4 is equivalent to the ratio 7:2, just as the fraction 14/4 is equivalent to the fraction 7/2. The value of the fraction as a number is 3.5 and the fraction can also be written as 3.5/1, just as the ratio can also be written as 3.5:1. But if you had the fraction 3.5/1, you would normally simplify it to just 3.5 (well, you might write 7/2 if you considered that simpler). Well, in the same way, the ratio 3.5:1 can be written as just 3.5. A ratio (of two nonzero terms) and a fraction -- or for that matter a quotient, like 7÷2 -- are really pretty much equivalent, and it's common to see a ratio expressed as a single number.

Incidentally, 7:2 is actually the way they write 7÷2 in many countries; they don't use what we call a division sign at all. --Anonymous, 19:01 UTC, January 24, 2010.

Your division sign ÷ is an Obelus. It is commonly seen today representing minus in Norway, for example in advertisements proclaiming "Opptil 30% på salgsvare" (= Up to 30% reduction on goods in sale). Pity the plight of little Norwegians who must use pocket calculators with buttons + - x ÷ while their math teacher teaches them to write + - . : for the same functions. With luck the little ones may grow up to be programmers who use + - * / respectively. Cuddlyable3 (talk) 22:20, 24 January 2010 (UTC)

Ummm... there's no obelus is that quotation... --Tango (talk) 02:42, 25 January 2010 (UTC)

Unfortunately the ratio article doesn't discuss this normalised format for expressing ratio; if this usage is as common as the above implies, then it clearly should. I did try to find a reliable source to back up this usage, but searching for "normalised ratio" and the like only finds specific ratios, rather than this general style of expressing as a ratio:1 and then omitting the :1 -- Finlay McWalter • Talk 19:10, 24 January 2010 (UTC)

Doesn't any number qualify as a ratio that can have a /1 or ÷1 or :1 or whatever done to it without it really meaning anything? --Neptunerover (talk) 19:18, 24 January 2010 (UTC)

Yes, any number can be a ratio. Ratios don't, as you say in your original question, denote any kind of relationship between the two numbers. "The ratio of X to Y is A:B" means "For every A of X you have B of Y". It's a relationship between X and Y, not between A and B. --Tango (talk) 19:37, 24 January 2010 (UTC)

You mean that's not the same difference? --Neptunerover (talk) 19:48, 24 January 2010 (UTC)

I suppose it is, but the fact that a particular (ordered) pair of numbers happens to be the ratio of something isn't very interesting. For any pair of numbers you will be able to find infinitely many things that it is the ratio of. The fact that the ratio of a particular thing is some pair of numbers is far more interesting. --Tango (talk) 20:01, 24 January 2010 (UTC)

I have a feeling you are on a topic far removed from this page and this question, and from which you already bid farewell. There's no sense confusing the OP here because of something unrelated. --Neptunerover (talk) 21:12, 24 January 2010 (UTC)

Thank you all. I understand the protocol that has emitted the ":1" when something is called a "ratio" but is expressed as a single number. I am sure, after another read or two, I will also understand the point about A of X and B of Y. Bielle (talk) 19:44, 24 January 2010 (UTC)

It would probably be clearer if I didn't state it so generally and instead gave an example. "The ratio of boys to girls in the class is 3:2" means "For every 3 boys there are 2 girls". --Tango (talk) 20:01, 24 January 2010 (UTC)

I expect to see two numbers in a ratio, even if the divisor is one. There should be an antecedent and a consequent. A number, by itself, is not a ratio. Saying "The ratio is 5.3" is unnecessarily confusing. How hard is it to say "The ratio is 5.3:1?" As a college teacher, or as a journal editor, I would have questioned such a usage. Edison (talk) 04:35, 25 January 2010 (UTC)

Well, what one expects and what actually happens are often two very different things! It is very common to drop the ":1", whether we like it or not. --Tango (talk) 06:08, 25 January 2010 (UTC)

One as a divisor is assumed, even if it isn't always written fully out. --Neptunerover (talk) 08:14, 25 January 2010 (UTC)

Incidentally, is a differential equation basically the same thing as a ratio? --Neptunerover (talk) 15:14, 25 January 2010 (UTC)

No. Not even a little bit. Algebraist 15:16, 25 January 2010 (UTC)

When ":1" is omitted, we are using a factor (as in multiple), not a ratio, but the usage seems to be widely abused. Do scientific journals really say "cost-benefit ratio" when they mean "cost-benefit factor", or is it just second-hand reporting that makes the error? Dbfirs 15:38, 25 January 2010 (UTC)

I've never heard anyone say "cost-benefit factor". I think we just have to accept that this is a meaning of the word "ratio". The English language is defined entirely by how it is used. --Tango (talk) 20:44, 25 January 2010 (UTC)

Yes, I agree I've only ever heard "ratio", but then I would expect, like Edison, to see a ratio. I suppose we have to accept that the "to one" is just understood in the context. I've made a few minor edits to our article on Ratio, but it really needs a major re-write. Dbfirs 14:17, 26 January 2010 (UTC)

Use of Enoxaparin sodium in aortic dissection.

Is there any indication of use of Enoxaparin sodium in aortic dissection? Maybe it prevents the formation of thrombi in the false lumen (thrombi could migrate and induce arteries occlusion in brain, coronaries ...) or what else? Or Enoxaparin sodium just aggravates dissection by inhibiting coagulation? Thansk so much for replies. --62.98.29.51 (talk) 21:40, 24 January 2010 (UTC)

I've just checked the article on enoxaparin sodium -- it says that this stuff is indicated for prevention of blood clots during dialysis and abdominal and orthopedic surgery and for treatment of deep vein thrombosis and some kinds of heart attack. Nothing at all about aortic dissection or any other kind of open-heart surgical procedure. I'm not an expert on surgery, but my guess is that it would be contraindicated for open-heart surgery because it could aggravate bleeding and possibly cause a dangerous hemorrhage. Clear skies to you 24.23.197.43 (talk) 03:37, 25 January 2010 (UTC)

Aortic dissection is not a procedure. It's a real quick way to get dead. I suppose the only way to save you is with a surgical procedure, so maybe that was what you meant. --Trovatore (talk) 03:40, 25 January 2010 (UTC)

The first plausible-sounding answer is a great example of why we forbid medical advice here! DMacks (talk) 06:48, 25 January 2010 (UTC)

Speaking of which, I should retract part of my answer — according to the article, surgery is not always the treatment for aortic dissection. It depends on the details. Not that I think anyone's going to say: Doc, I have to have surgery! Some guy on the refdesk said so! But you never know. --Trovatore (talk) 08:05, 25 January 2010 (UTC)

Sorry, I really thought aortic dissection was a procedure where they open up the aorta to take out some kind of blockage and then sew it shut again. (Well, I told y'all that I'm not a medical expert!) Anyway, now that we all know what aortic dissection really is, I can say with certainty that enoxaparin sodium would ABSOLUTELY, DEFINITELY be contraindicated in that case cause all it would do is to make you bleed out faster. See, my answer was right after all, even though it was for all the wrong reasons! 146.74.230.82 (talk) 01:09, 26 January 2010 (UTC)

Quick seagull question

If there were no people to give them an incentive to venture inland to scavenge, would gulls be restricted only to coastal areas? --95.148.109.223 (talk) 22:45, 24 January 2010 (UTC)

I've seen seagulls in Colorado (far away from any coast). I'm not sure if they migrated there because of people. --Neptunerover (talk) 05:01, 25 January 2010 (UTC)

Of course, my reference to 'Colorado' seagulls may be irrelevant, as who knows when the species may have last seen an ocean. Where I saw them just happened to be at the dump as well. I suppose inland seagulls have lakes instead of oceans, where they might very well stay, if it weren't for the local dump. --Neptunerover (talk) 05:44, 25 January 2010 (UTC)

I can testify to them congregating around lakes, and not just seas. Here in Vermont we have quite a few near Lake Champlain and at least a good 10 or so miles in the parking lot at my workplace. Dismas|^(talk) 11:56, 25 January 2010 (UTC)

They're a menace, I say! (jokingly; I like live seagulls) --Neptunerover (talk) 16:38, 25 January 2010 (UTC)

But not the dead ones? Seems an interesting distinction to point out. Dismas|^(talk) 20:15, 25 January 2010 (UTC)

Interesting perhaps, but I felt it was necessary just in case someone wanted to come back with "where do you like them, on your dinner plate?" Sadly, it appears many hunters have this point of view when they speak about how much they love animals. The Native Americans were not like that at all. Hunting is a natural part of life on Earth though, so I'm not going to point fingers (hey, I used to have a BB gun, and I'm not proud of having used it to shoot things that would've kept living had I not shot them, but I was a kid seeking fun in a misguided way. When people grow up, hopefully by that time they realise that killing things isn't really any fun, assuming they ever might have at some point thought that killing is or might be fun, say from a video game.) --Neptunerover (talk) 13:11, 27 January 2010 (UTC)

Here on the Wikipedia Ref desk, we have physicists, chemists, biologists, mathematicians, computer scientists - and a seagull expert. I'm sure User:Kurt Shaped Box will be along in a moment to help. SteveBaker (talk) 05:06, 25 January 2010 (UTC)

As far as I know (and to echo Dismas), gulls will hang around/breed near lakes, inland seas and areas of marshland too, without human encouragement. If I'm remembering correctly, there are huge colonies to be found inland in Central Asia in these habitats. Gulls, being the tough, adaptable little generalists that they are, don't strictly *need* to be around accumulations of water in order to eke out a living - but they seem to be 'drawn' to it. --Kurt Shaped Box (talk) 19:57, 25 January 2010 (UTC)

I was thinking about this on my morning commute and I think that Life After People mentions what would (will?) become of gulls. Yep, just checked the article and it says that there is a large die-off but that populations come back once fish populations start to rebound. Dismas|^(talk) 20:15, 25 January 2010 (UTC)

Incidentally, the book Jonathan Livingston Seagull is very enlightening as to the life of a 'seagull', although the reliability of the book's perspective, at least on this desk, is not verifiable. (still a good book though, and short too) --Neptunerover (talk) 13:11, 27 January 2010 (UTC)