Wikipedia:Reference desk/Archives/Science/2012 March 22

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March 22

Orbital borrowing

Sodium oxide. To demonstrate my visualisation of MO theory, I need to confirm that sodium oxide is a linear, not a bent molecule. Plasmic Physics (talk) 07:53, 22 March 2012 (UTC)

Sodium Oxide is an ionic crystal. It doesn't have molecules to speak of, at least in the solid state. The oxygen ions in the crystal are cubically coordinated, while the sodium ions have a tetrahedral coordination. I can't find any information about the compound in the gas phase, but it wouldn't be hard (with the proper tools) to run some calculations to approximate the bond angle. Why do you believe the molecule should be linear, and not bent? Buddy431 (talk) 15:42, 22 March 2012 (UTC)

OK, this does indicate a linear molecule. They aren't really good about saying where this came from - I think it's from calculation (the rotational constants are calculated). Buddy431 (talk) 15:52, 22 March 2012 (UTC)

Good. According to orbital borrowing, when oxygen is bonded to both sodiums via sigma orbitals, the sodiums have unoccupied AOs. Oxygen has two non-bonding MOs. It should be energetically favourable for oxygen to borrow the empty sodium orbitals and drop its non-bonding MOs to a lower GS, forming two new coordinate bonds. There are now no non-bonding valence MO orbitals, there is a double bond to each sodium where oxygen contributes three eletrons to each double bond.

Oxygen is borrowing an orbital from sodium, because it's not a fair trade - sodium is not contributing any of it's own electrons. Plasmic Physics (talk) 20:26, 22 March 2012 (UTC)

Ceftriaxone

It says in the article on Ceftriaxone that it is sometimes given to babies for an ear infection as a single intramuscular injection. In theory could it also be used to treat an adult ear infection in a single dose injection? --64.38.197.217 (talk) 09:41, 22 March 2012 (UTC)

My guess would be yes. I assume babies can't be given oral antibiotics, and IM seems to be a cheaper alternative to intravenous injection, what could be the rational behind the use of it. IM may be painful with some antibiotics though. ... 84.197.178.75 (talk) 12:17, 22 March 2012 (UTC)

wood homes

How come in North America they build homes out of wood. It seems kind of stupid to build something that susceptible to mold, rot, fire and water damage. It makes sense to build your home something like concrete or brick. This is what they do in many other countries why don't they do that in North America. — Preceding unsigned comment added by 92.48.194.174 (talk) 09:44, 22 March 2012 (UTC)

Treated wood can last a very long time, and can be better in a fire than steel. In a fire, wood beams will often last longer than steel, as they burn on the outside, yet remain unburned in the middle. The advantage is that they don't sag like steel does in high temperatures. Wood is a cheap, easy to acquire resource, and is easier to work with and transport. Having lived in North America, I've watched houses with wooden frames erected in a couple of days, with no massive lifting equipment. I'm guessing that these factors are what make it a popular choice. 217.158.236.14 (talk) 09:48, 22 March 2012 (UTC)

If your house is made of steel, what is it that's burning, exactly? --Trovatore (talk) 00:49, 23 March 2012 (UTC)

Even if a home doesn't use a timber frame, there is still likely to be at least wood paneling on the walls and floors, as well as wooden siding on the outside. In addition, you also have to think of furniture, clothing, and just about anything else humans own and use that is flammable. See, for example, Collapse of the World Trade Center. Evanh2008 (talk) (contribs) 01:01, 23 March 2012 (UTC)

The WTC doesn't count — it had just been doused with enough jet fuel to fly coast-to-coast. Are those other things really enough fuel to melt steel girders? --Trovatore (talk) 01:40, 23 March 2012 (UTC)

Well, actually "melting" the steel (in other words, reducing it to a liquid state), is not really necessary to destroy a steel structure. The frame only needs to be just malleable enough that its own weight brings it down. Re jet fuel in the WTC, most of the fuel actually burned up within a few minutes of the plane impact and didn't serve to do much damage to the structure beyond starting other fires. The definition of "destroy" is also an issue here. If we're talking about causing a total immolation of the structure, to where it no longer exists in any meaningful sense, then fire alone isn't likely to do that in a totally steel structure. However, as I said, very few structures are composed solely of steel and glass. A significant uncontrolled fire in a steel-framed building is going to, at least, gut the structure and destroy everything that makes the structure usable for human purposes (floors, for example). That could certainly be considered a form of destruction Evanh2008 (talk) (contribs) 02:36, 23 March 2012 (UTC)

Agreed. The problem with steel is that it conducts heat well, and has a significant coefficient of thermal expansion, so quickly twists and buckles, popping out of it's brackets, etc. Wood, on the other hand, is a good thermal insulator, even when charred, so it takes many hours for heat to reach the interior and for it to twist and buckle. If you've ever burned a large log in the fireplace, you know how long it takes. StuRat (talk) 05:26, 23 March 2012 (UTC)

Houses with timber frames are much easier to build than those other types of buildings you mentioned. Given the choice between a big house made of timber, or a smaller house made of brick, Americans will usually choose the bigger home. (We like things that are huge.)

Properly cared for timber homes can last a century with no problem, often more. In USA that pretty much passes for "permanent".

And, of course, in earthquake-prone areas, there are obvious advantages to building materials with a little "give" in them. APL (talk) 09:54, 22 March 2012 (UTC)

In New Zealand, houses are built almost exclusively, from wood. Clay bricks are expensive, and are only used as a veneer on the outside of buildings. The only problem with wooden constructions would be those suffering as a result of the Leaky homes crisis. Plasmic Physics (talk) 10:06, 22 March 2012 (UTC)

A lot of Europeans seem shocked that wooden homes are common in some areas. They seem convinced that wood is flimsy and should only be used for temporary structures. However, used properly wood is an excellent building material. Many homes built during the USA's colonial period are still rock solid.

Like user:PlasmicPhysics says, they are vulnerable to water damage, but if water is leaking into your house you have a serious potential health problem anyway. APL (talk) 10:45, 22 March 2012 (UTC)

Wood is also a much better thermal insulator than concrete or brick. Lowering heating costs is big factor in home design in the northern parts of NA.Anonymous.translator (talk) 11:46, 22 March 2012 (UTC)

The problem is that in New Zealand, wooden homes have hollow walls, and there is big money to be made in selling thermal insulation, like the locally famous Pink Bats. Plasmic Physics (talk) 11:50, 22 March 2012 (UTC)

The suggestion that mammals of the order Chiroptera were used as insulation in NZ intrigued me, though sadly Google revealed the more prosaic truth - 'Pink Batts' insulation. [1] AndyTheGrump (talk) 20:24, 22 March 2012 (UTC)

Here in North America we use mammals of the genus Panthera for that purpose. Same color, though. APL (talk) 23:23, 22 March 2012 (UTC)

Da dah. Da dah. Da dah da dah da dah d.d.d.d.daaaaah -- dadadadadaah. --Trovatore (talk) 00:45, 23 March 2012 (UTC)

In case anyone missed the reference, Owens Corning insulation uses The Pink Panther as it's mascot: [2]. StuRat (talk) 05:15, 23 March 2012 (UTC)

I think it's a question of resources. Whatever can be found locally, clay for bricks or big trees for wood. 84.197.178.75 (talk) 12:23, 22 March 2012 (UTC)

You are right. On the east cost of Australia, brick veneer construction is the norm. This is a type of construction that has timber framing, plaster clad timber framed internal walls and brick exterior surfaces. This gives reasonably cheap construction as it minimises the use of relatively expensive brickwork, good thermal performance, and is low in maintenance cost because the outside is brick - extremely durable and no painting every few years required as would be the case with all-timber construction. But on the west coast of Australia, clay bricks from local clay have been historically very cheap, and most houses are "double brick" - that is external walls are two brick layers separated by an air space, and all internal walls are brick. Thermal performance is not as good as brick veneer, but this matters less in the west coast's warmer climate. You can't beat double brick for durability, quietness & livability though - the teenagers can be having a wild party in one room, and Dad can be asleep in another room in total ignorance. Ratbone124.178.149.160 (talk) 15:48, 22 March 2012 (UTC)

Wood has another advantage in that it's easy to modify. You can take out a wall and/or add on without needing a huge diamond cutter to remove masonry. Need to route a wire through a wall ? All you need is a drill. StuRat (talk) 17:19, 22 March 2012 (UTC)

Gee, I've cut holes in brick walls lots of times. Nothing difficult about it. Need to route a cable thru a brick wall? All you need is a masonry drill bit. Bricks are mainenance free for 100 years or more when used for outside surfaces, and they are immune to children's accidental damage. But bricks are not actually that strong. A few good wallops with a sledgehammer will bring a brick wall down. I have demolished a brick fence with a hand hammer far quicker than I could demolish a timber fence. Ratbone124.178.138.138 (talk) 00:37, 23 March 2012 (UTC)

The bricks may last, but the mortar doesn't. Even the bricks seem to suffer from the frost/freeze cycle, with pieces popping off each winter. Last time I tried a masonry bit it was quite difficult to cut straight through, as it kept changing direction and overheating. Breathing brick dust wasn't fun, either. StuRat (talk) 02:58, 23 March 2012 (UTC)

I think that there's a matter of natural selection involved, also availability of materials. For example, in Chicago in the 1800s, not only were the homes made of wood - even the sidewalks were made of wood! Then came the Great Chicago Fire and downtown Chicago became a city of brick and stone. I think, in general, that the older an American neighborhood is the more buildings are made from stone. Of course, the oldest American neighborhoods tend to be recent by European standards. Wnt (talk) 04:59, 23 March 2012 (UTC)

respirator safety

I bought a 3M respirator and the cartridges feel itchy like when I used to work with fiberglass insulation. How likely is it these are made of fiberglass and isn't that harmful to hold this up right in front of my face and breathe Through it. Wouldn't you basically be breathing in glass dust and small glass fibers? I handled the cartridges and when I held my hands up to the light and it looked like there was glass dust on them--69.5.89.70 (talk) 11:20, 22 March 2012 (UTC)

I would consider ringing the 3M helpline (Your IP address is in the US, so this would be the number: 1-888-3M HELPS) and asking them about it, it doesn't sound right. Perhaps the filter has become damaged? 217.158.236.14 (talk) 12:04, 22 March 2012 (UTC)

Yes, fiberglass is used in filters. But loose particles on the outside would not normally go through the filter. Unless you see fiberglass particles on the inside of the cartridge (the outlet so to speak) it could be ok. However, it seems a bit strange that it's shedding particles at all. 84.197.178.75 (talk) 12:37, 22 March 2012 (UTC)

Yes, I'd return them, they sound defective. StuRat (talk) 17:14, 22 March 2012 (UTC)

Just to ask the obvious: Is the one-way valve on the front operating properly? Does the mask seal on your face properly? Either one could let fibres by-pass the filters. And how many editors have started to scratch their suddenly itchy face whilst reading this through this section?--Aspro (talk) 19:57, 22 March 2012 (UTC)

LEDA 074886 discovery date

I'm puzzled by the wording in the discovery report of LEDA 074886: "The unusual shape of LEDA 074886 was discovered by us in deep i′-band exposures acquired with the SuprimeCam imager (Miyazaki et al. 2002)..." How to reconcile 2002 with March 2012? The report itself contains two dates: 16 March and 19 March, 2012, so I can't figure out the actual discovery date. Brandmeister^talk 12:25, 22 March 2012 (UTC)

That's a reference to a publication in 2002, presumably one about the SuprimeCam imager or deep band exposures. See the reference list at the end.

There are some confusing refs I must admit, for example: "At a distance of 21 Mpc (Spolaor et al. 2008)" Nevermind, the group of galaxies was discovered before, so these shared properties would be known already ...84.197.178.75 (talk) 12:42, 22 March 2012 (UTC)

They didn't really discover the galaxy but noticed its peculiar shape. "Discoveries" of things that have been observed before are not such a rare occurrence. For instance, Galilei saw Neptune and recorded the observation, but did not realize that what he saw was a planet. The gravitationally lensed giant arc in Abell 370 was discovered in 1987 although it is clearly visible in earlier photographs. The 2002 paper [3] is actually a description of the camera, not of these exposures. They don't seem to say when the Subaru image was taken, but the galaxy had been known before as evidenced by the LEDA number and the references for distance and magnitudes. --Wrongfilter (talk) 13:05, 22 March 2012 (UTC)

They explicitly state "we report the discovery" and then "we have discovered". There would have been earlier reports had it been realized before. Brandmeister^talk 13:25, 22 March 2012 (UTC)

Considering where they are located: Centre for Astrophysics and Supercomputing, and Astronomisches Rechen-Institut, they may have done a lot of image processing to enhance the details so the shape became visible 84.197.178.75 (talk) 12:42, 22 March 2012 (UTC)

Here is the table from the paper by Trentham, Tully & Mahdavi (2006). LEDA 074886 is right there, at number 25. Its apparent brightness is R=14.3, which is not very faint at all. NED lists references that go back to 1990. It is, however, true that the rectangular shape seems to become apparent only at large radii, where the surface brightness is low. This may be why it took a 10m class telescope to discover that this galaxy is actually quite interesting. --Wrongfilter (talk) 15:23, 22 March 2012 (UTC)

Others have addressed the details of this specific case very well above, but to enlarge the general point, it quite often takes many years for the relatively few working astronomers to examine all the very many photos, or other non-pictorial data, they obtain using various instruments – in fact, a frequent problem of scientific funding is that particular projects may run out of money (or their personnel move on) and can't finish making even a first inspection of much of their data, which they may come back to, or which may be looked at by someone else, years later.

Then again (as Wrongfilter mentions above), when a new class of object is discovered, photos (etc) years or decades old will be re-examined and instances quite often found because when the photos were first inspected no-one was looking for those as-yet-unknown objects. Similarly, when a newly discovered Solar system body, fast-moving star, variable star and so on is identified and its orbit/motion/period calculated, it can often then be identified on much earlier photos where it was just another faint dot or smudge among millions, and so not recognised - such pre-discovery images can then be used to refine the accuracy of the orbital/whatever calculations and find even older images, and so on.

In summary, long delays between the original obtainment of an image/datum and a discovery being made using it, or at least additional data being taken from it, are quite common in Astronomy, and all old images/data are carefully retained and when possible re-examined in the light of current research. {The poster formerly known as 87.81.230.195} 90.197.66.73 (talk) 18:24, 22 March 2012 (UTC)

Thanks, that preprint was indeed confusing. Brandmeister^talk 18:27, 22 March 2012 (UTC)

Help: Identify the Bird

Please help in identifying the bird in picture File:Bird (Brown) - Unidentified.JPG

Rajenver (talk) 14:25, 22 March 2012 (UTC)

The location and season in which you saw the bird would be useful information. But assuming it was in India, it seems likely to be a Brown Rock Chat. - Cucumber Mike (talk) 15:05, 22 March 2012 (UTC)

Agree, the only confusable is female Indian Robin but that has a longer tail and a brown vent. Shyamal (talk) 04:51, 23 March 2012 (UTC)

I have spotted this bird in Khajuraho, Madhaya Pradesh, India, in March (Summer Season). The size of bird was small, somewhat closer to sparrow. Rajenver (talk) 06:14, 23 March 2012 (UTC)

Looks quite closer to Brown Rock Chat as suggested by Cucumber Mike

Rajenver (talk) 06:24, 23 March 2012 (UTC)

Help: Identify the Bird (Black)

Please help in identifying this bird.

File:Bird (Black - Unidentified).JPG

Rajenver (talk) 14:26, 22 March 2012 (UTC)

I'm not even remotely a bird expert but love a good challenge...Is it a Black Drongo? From the WIkipedia link they don't look that alike but a google image search shows up photos that closely resemble yours (http://www.google.co.uk/search?hl=en&q=Black%20Drongo&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=_WxrT-nvMIfR8gPG3_jdBg&biw=1122&bih=632&sei=E21rT8K3Hcf_8QPWpcnyBg) ny156uk (talk) 18:20, 22 March 2012 (UTC)

(Here's one that looks particularly like yours http://www.birding.in/birds/Passeriformes/Corvidae/black_drongo.htm) ny156uk (talk) 18:21, 22 March 2012 (UTC)

One pic in our Black_Drongo#Description section does resemble the tail feathers. It's the one labeled "Typical silhouette". StuRat (talk) 03:02, 23 March 2012 (UTC)

Good identification. Have changed the taxobox image on the Black Drongo article. Shyamal (talk) 04:11, 23 March 2012 (UTC)

I have spotted this bird in Khajuraho, Madhaya Pradesh, India, in March (Summer Season). The size of bird was small, somewhat closer to sparrow. Body of bird was approx (4-5 inches) and Tail of the bird was approx 6 inches. The body diameter approx 1 to 1.5 inches. The bird was quite small and doesn't looks from a CROW Family. Rajenver (talk) 06:17, 23 March 2012 (UTC)

World Trade Center, height with old antenna

Hello. Does anyone know how tall the World Trade Centers North Tower was by total height after completion? The big antenna with a total height of almost 1,727 feet (527m) was installed in 1978. By watching this video from 1973 there is a shorter mast visiable (around 1:00 minutes). How tall was the tower by pinnacle height with this mast. I would like to know if it was taller than the antenna mast of the Empire State Building that rises up to 448.7m (until 1984 when it was decreased). Thanks in advance, --92.226.131.154 (talk) 19:51, 22 March 2012 (UTC)

Did you read the information table in the article (WTC) you linked to? All the stats are right there. Plasmic Physics (talk) 20:30, 22 March 2012 (UTC)

Not the stat he's looking for, actually. APL (talk) 23:09, 22 March 2012 (UTC)

• I am looking for the old mast, not the new. The 1,728ft height figure is the new mast that was put in place in 1978; the old mast that can be seen in this video from 1973 is even shorter. --92.226.205.225 (talk) 08:34, 24 March 2012 (UTC)