Science desk
< January 20	<< Dec \| January \| Feb >>	January 22 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 21

Old French mechanical signals

How exactly did the mechanical ralentissement (slow 30) signal work? Was the mechanical vane operated from the signal box via the lever frame, or was it directly linked to the switch and the associated rappel de ralentissement signal? Also, how exactly did it produce the two yellow lights in the closed position, and the single green in the open? Were there two (or three) separate color lamps, or only one lamp fitted with movable color filters linked to the vane? Thanks in advance! 67.169.83.209 (talk) 03:37, 21 January 2014 (UTC)[reply]

I forwarded this query to Clive Feather, who has kindly replied as follows:

From http://www.carreweb.fr/stfr/sl_en.html and other pages (found by searching for "French railway signalling" or similar), it is clear that Ralentissment 30 is an aspect shown at the running signal (like "Medium to Clear" in North American practice). For the mechanical layout, you have a Carré above a Ral30. If the lever for the main route is pulled, only the Carré rotates. If the lever for the diverging route is pulled, both rotate.

If you asked me to implement this, I'd use an inverted slot mechanism. You have three bars that are centre pivoted on the same axis. A weight holds the left side down by default. The wire from the main lever pulls on the right end of bar 1. The wire from the diverging lever runs through the Ral30 rotation mechanism and pulls on the right end of bar 3. Bars 1 and 3 each have a short bar at right angles that crosses over to bar 2. So if either lever is pulled, the right end of bar 2 is pushed down by the relevant short bar; this in turn pulls the Carré rotation mechanism. When the lever is replaced, the weight on bar 2 rotates the Carré back again. (It's an "inverted" slot because the standard slot is an "and" gate, not an "or".)

Rappel de ralentissment is like the UK double yellow; it's a preliminary warning used when the signals are closer togther. The mechanical version would be driven from the same lever or from the equivalent of a distant signal lever.

It's clear from the images that there are three separate lamps.

-- Clive D.W. Feather

Forwarded (and lightly copedited/wikified) by: --50.100.193.107 (talk) 21:28, 22 January 2014 (UTC)[reply]

Thanks! So it is operated from the lever frame and not linked directly to the switch mechanism, right? 67.169.83.209 (talk) 03:50, 23 January 2014 (UTC)[reply]

"Correct", says Clive. --50.100.193.107 (talk) 06:59, 26 January 2014 (UTC)[reply]

what is the difference between chemistry and biochemistry in the blood test

I have noticed that there are two kinds of blood tetsts. One is chemistry, and the two is biochemistry. So what is the different between the two? which kinds of tests are included in the chemistry or biochemistry blood tests. 194.114.146.227 (talk) 05:53, 21 January 2014 (UTC)[reply]

See Blood test#Types of blood tests. Red Act (talk) 07:02, 21 January 2014 (UTC)[reply]

thank you. But it doesn't answer on my question: What does define a bihemiemical blood test as biochemical test? 194.114.146.227 (talk) 09:43, 21 January 2014 (UTC)[reply]

Chemical tests relate to things like simple ions (e.g. Na+, K+) and pH. Biochemical tests look for larger molecules, for example certain serum proteins e.g. serum albumin. --—Cyclonenim | Chat 09:27, 21 January 2014 (UTC)[reply]

Thank you. So I can understand that the chemical blood test is looking for the elements or the ions of them in the blood while the biochemical tests is looking for molecule. Am I right? 194.114.146.227 (talk) 09:43, 21 January 2014 (UTC)[reply]

Not quite. Biochemical tests are a subset of chemical tests. A biochemical test is a chemical test that detects or quantifies a biomolecule. If you want to reserve the name "chemical test" to "chemical tests that are not biochemical tests", they would still include ions composed of several atoms, such as phosphate, and dissolved gases such as ammonia. --NorwegianBlue^talk 20:46, 21 January 2014 (UTC) — Preceding unsigned comment added by 109.189.65.217 (talk) [reply]

Identify this animal

What animal is this? [1] — Preceding unsigned comment added by Bobatnet (talk • contribs) 10:17, 21 January 2014‎

a monitor lizard? —Tamfang (talk) 11:00, 21 January 2014 (UTC)[reply]

A legavaan? A white-throated Rock_monitor. 196.214.78.114 (talk) 13:14, 21 January 2014 (UTC)[reply]

A bengal monitor, I think. Mikenorton (talk) 21:09, 21 January 2014 (UTC)[reply]

Goanna? HiLo48 (talk) 06:04, 22 January 2014 (UTC)[reply]

Looks like a Lace Monitor (varanus varius) to me, quite a big one. There's not many monitors that have those spots. Tom duF (talk) 07:01, 22 January 2014 (UTC)[reply]

"Alabama Rot" in the UK

The BBC reports that 17 dogs across Britain have been killed by "Alabama Rot". However an article mentioning Alabama rot says that it is "Idiopathic cutaneous and renal glomerular disease", affects only Greyhounds, and is associated with them eating raw meat. What makes them think that the cases in the UK are the same disease, it sounds quite different. -- Q Chris (talk) 10:59, 21 January 2014 (UTC)[reply]

The BBC report does not say that, but maybe it has been updated since you read it. Suggest you read it again.--Shantavira|^{feed me} 11:47, 21 January 2014 (UTC)[reply]

You're right it changed! -- Q Chris (talk) 13:29, 21 January 2014 (UTC)[reply]

The BBC article says it's "similar to Alabama rot" - not that it is that. Both diseases involve skin lesions in the early stages, Idiopathic just means that the cause is unknown, and "renal glomerular disease" means it affects the kidneys (see Glomerulus), which probably means it leads to renal (kidney) failure, like the disease in the BBC article. The second article says Alabama rot has "only been reported in greyhounds". That doesn't mean it only affects greyhounds - only they it hasn't been seen in other breeds yet. Richerman (talk) 13:21, 21 January 2014 (UTC) [reply]

Not to be confused with the live concert CD: Alabama Rot in the UK —(sorry, couldn't resist. 71.20.250.51 (talk) 18:53, 21 January 2014 (UTC)}[reply]

Metric expansion of space 2

So, as I seen from the graphic, the recession velocity didn't change too much with the time. My final question is: if there wasn't that difference, how is possible that the limit of our observable universe is 46 billion light-years, where the recession speed is three times c (the light's speed)? This would mean that the recession velocity would have at least triplied from the time the radiation that reacht us was emitted, a thing that according to the graphic is impossible (the highest difference isn't more than 20%). Thanks for answering and excuse me for my insistence. 93.45.32.204 (talk) 12:56, 21 January 2014 (UTC)[reply]

It doesn't mean that at all. Suppose that 6 billion years ago, the universe was 50% its current size, so a=0.5. A photon travels for 1 year across the universe. That one light-year would be two light-years today, giving the impression that the ancient photon traveled at 2c.

Mathematically, a photon travels a distance c*dt in time dt. But this distance corresponds to a distance of c*dt/a(t) in today's universe, because the universe has since expanded by a factor of 1/a. To find the size of the observable universe, we integrate c*dt/a from t=0 to t=13.7 billion years:

R=\int _{0}^{t_{age}}c{\frac {dt}{0.72*sinh^{2/3}(1.28H_{0}t)}}

\approx {\frac {3.45c}{H_{0}}}

where $c/H_{0}$ is very close to 13.6 billion light-years. Multiplying that by 3.45 gives 47 billion light-years. You can see the result of the integral here. --Bowlhover (talk) 21:02, 21 January 2014 (UTC)[reply]

The recession speed was generally higher in the past, not lower, which makes sense since gravitational attraction slows expansion down. If it weren't for the cosmological constant, the recession speed would always decrease. The speed goes to infinity at the big bang (in the standard radiation-dominated model without inflation).

The image on the right shows visually what's going on with the distances. Light travels at a "45° angle" relative to the local metric. The earth (brown, left) and a distant quasar (yellow, right) have gone from a few billion light years apart to 28 billion light years apart in 13 billion years, which is an average recession speed of about 2c over that time, but light (red) traveling at a local speed of c can get from one to the other regardless. The geometry just works out that way. It's often said that the distance the light travels early on "counts for more" because the distance it has covered later expands. I'm not sure how much I like that explanation, but it's probably fine if you find it helpful. -- BenRG (talk) 20:47, 21 January 2014 (UTC)[reply]

Ancient Mesopotamian units of measurement

Dear Sirs

Regarding mesopotanian measurement standards the talk section describes a potential problem

In the table of values the length of the Cubit and smaller values seens to be consistant but the values fro the larger standards appear to be rounded off

the talk section describes a possinle solution which seems correct to me

IT IS VERY IMPORTANT to researchers like myself to have accurate data

I have been critized for using this Wikepedia reference but am convinced that you are correct in stating the length of the cubit at 497 mm

can you help me overcome my rejection of by reviewers on this single issue

Roland Boucher — Preceding unsigned comment added by Roland Boucher (talk • contribs) 16:33, 21 January 2014 (UTC)[reply]

For convenience, this question seems to be about our article Ancient_Mesopotamian_units_of_measurement. That article gives no source for the claim 1 cubit=497mm. Cubit gives some examples of ancient metrology standards that have been recovered, with a range of 518 to 529 mm. It then states that 450mm is an estimate used by biblical scholars.

If I were reviewing your article, I would not allow you to publish 1cubit=497mm based on only a citation to Wikipedia. I looked quickly on google scholar, and found this paper, which is probably citable, [2] and this manuscript [3], which is not citable, though it does have some good references for several types of cubits and metric equivalents that you can read/cite for a peer-reviewed article. If you cannot get access to these articles, I suggest you ask at WP:REX. Finally, if you are seeking to be a good researcher in this field, then you are in the best position to improve these WP articles! You can add the citations that you need for your research to support our articles, and everyone then can benefit from your work! SemanticMantis (talk) 17:45, 21 January 2014 (UTC)[reply]

Finding the value for the cubit at the particular time and space that you're researching is essential. For example, the Olympias was a super-carefully researched reconstruction of a Greek trireme (an oared vessel). They spent a small fortune building the thing - and only after they tried putting a crew into it to row it did they discover that they'd used "the wrong cubit" and the ship was much more cramped than it should have been. Given the massive amount of work they put into doing this - this minor catastrophy is a measure of how easy it is to get the wrong cubit. It's really not an easy question to answer - and there is no single answer that's correct over more than a small interval of time and a small geographical region. Worse still, researchers can only really relate these ancient cubit measures to modern units by physically measuring some historical artifact who's dimensions were documented in cubits. We know the dimensions of things like the great pyramid in cubits - and we can measure the real thing and know what size the pyramid builder's cubit was...but if you want to know the size of cubit used by a trireme builder, you're right out of luck because there are no surviving vessels of that kind still around. (I don't recall how the Olympias people figured out how they'd screwed up). SteveBaker (talk) 21:04, 21 January 2014 (UTC)[reply]

The other way of finding out is by finding extant physical standard cubits. Our cubit article has photos of a few, and says "Fourteen such rods, including one double cubit rod, were described and compared by Lepsius in 1865" -- so at least some cubits can be "rigorously" converted to metric. As you say though, it really depends on time and place, and those known samples won't necessarily say much about the cubits that Roland needs. I think he could probably dig through the refs I gave above and find an estimate that is at least vaguely for the right time and place. For something this subtle, I think that's far better than relying on the authority of Wikipedia! SemanticMantis (talk) 22:06, 21 January 2014 (UTC)[reply]

Hmmm, our article on the trireme doesn't cover the cubit mix-up. I'm reminded of a film This Is Spinal Tap which came out just a year afterward -- I'm not seeing any hits to document a connection, but my nose knows. :) Wnt (talk) 22:40, 23 January 2014 (UTC)[reply]

I'm not sure what your nose knows...but it's all described in their book "The Athenian Trireme" by Morrison, Coates and Rankov (an excellent book BTW) - with the relevant passage starting on page 245 & 246. "...excavations at Philon's naval storehouse in the Piraeus in 1989 revealed that this building of the mid-fourth century had been constructed using a foot of 0.327m in length and therefore a cubit (= 1.5 feet) of 0.49m. This discovery suggested that the longer cubit could have been used contemporaneously in other naval contexts, such as ship construction. If so, then the two-cubit (rowing space) room of an Athenian trieres could have been as much as 0.98 meter, an invaluable 9 centimeters longer than that of the Olympias." ...I'm not going to quote it all because the explanation runs on for most of the chapter, but it eventually emerges that this error in the choice of 'which cubit' meant that the rowers in their reconstructed ship were too cramped to do their work efficiently - and that this more or less invalidated much of the data they collected over the speed and acceleration rate of the vessel compared to the real thing.

I know all this because I spent a long time conversing with the authors because they were interested in a video-game I was writing that involved Greek sea battles with triremes. I managed (for example) to prove to them that their theory that the ships would have communicated using flag signals from on deck would be impossible due to how low the deck is to the ocean - and the curvature of the earth! The greeks de-masted their ships before battle - so they couldn't haul flags up to the mast-heads - and practical experiments with the Olympias made it quite clear that using drums or trumpets to communicate would have been impossible given the deafening amount of noise made by the rowers and their oars. They couldn't have sent out smaller ships as messengers because the trireme was the fastest vehicle known to mankind at the time and the messengers would have been unable to catch them once battle had commenced. This inability to communicate orders once the action had started has severe implications for how the Greek commanders ran large scale battles - which in turn casts doubt on modern interpretations of several historic naval battles! SteveBaker (talk) 15:02, 24 January 2014 (UTC)[reply]

Hmmmm, smoke signals, kites, flaming arrows? But quite interesting! Wnt (talk) 17:54, 24 January 2014 (UTC)[reply]

Trouble is, there is no historical account of them doing any of those things. Fire was a really feared thing on wooden ships - so it's unlikely that they'd want to be loosing flaming arrows right in the middle of a bunch of friendly ships! (Yes, I know you're going to mention "Greek fire" - but that didn't start to appear until long after the heyday of Greek naval power - it was really a Byzantine invention). Kites were not known in Europe until the end of the 13th century - so that's extremely unlikely. (Hint: Read more articles before speculating!) It's known that triremes carried both trumpets and drums - and that had long been thought to be used to pass on orders between ships - but the Olympias study strongly suggested that they were instead used to relay orders to the rowers and used to carry a beat that would determine the pace of the rowers (especially during acceleration and turning). The "discovery" that triremes are incredibly noisy places was not obvious until someone tried to get one moving quickly under oars. SteveBaker (talk) 03:07, 25 January 2014 (UTC)[reply]

Hey, I was asking, not speculating. I'm very surprised to see from kite (and more than a little skeptical) that it took 2000 years for the idea to spread from China to Europe! While flaming arrows would certainly be a terrifying thing to play with aboard ship... is there anything they ever did on board a trireme that wasn't terrifying or at least utterly miserable? Soldiers know how to take a risk when needed, especially if just a few arrows could change the course of a battle. Wnt (talk) 19:10, 27 January 2014 (UTC)[reply]

Actually, looking online, I'm seeing references to Archytas, who made some kind of flying device, and a pottery image which at least various Greek bloggers say is a girl flying a kite (search for kite in [4]). Wnt (talk) 19:23, 27 January 2014 (UTC)[reply]