Science desk
< July 9	<< Jun \| July \| Aug >>	July 11 >

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.

July 10[edit]

Elevation of the Cajon Pass in San Bernardino County, CA[edit]

Wikipedia states the summit elevation to be 4190 Ft and the coordinates to be 34deg 18.7 & 117Deg 28.5.. Google Earth shows this location to be right at the CA 138 junction, and the elevation at 3111 ft.

Is the Wikipedia article incorrect, or is Google Earth just a fun toy, not to be used for data?

Other search hits verify the 4190 elevation! —Preceding unsigned comment added by Chipscom (talk • contribs) 02:35, 10 July 2010 (UTC)[reply]

I think you can trust the elevations shown in Google Earth, although sometimes the surface features are drawn at the wrong spot because of incorrect handling of the satellite photos -- for example you can sometimes see rivers flowing along the walls of canyons, which looks pretty weird. But it is less reliable about putting labels at the right places. Looie496 (talk) 05:02, 10 July 2010 (UTC)[reply]

The reason for rivers flowing up the sides of canyons in Google Earth is that the source elevation data is sampled as some regular interval (say, every 50 meters). If the bottom of a 50m wide canyon is at (say) 15m above sea level - and there are vertical cliffs either side of the canyon bottom that rise to 65m above sea level. The regular 50m sampling might say something like 65m,65m,15m,65m,65m - but the Google Earth software can't tell from those elevation numbers whether there is a 45 degree slope slope from 65m down to 15m and back up again (a V-shaped valley) - or whether there is a vertical cliff-face somewhere between one 50m sample point and the next (a U-shaped valley, perhaps). If the river happens to run somewhere other than through the dead-center of the 50m-wide canyon then the software has no way to know whether it actually runs along the top of the cliff, the bottom of the cliff - or whether there is a 45 degree slope with a river running along halfway up it on a narrow ledge. Now, you and I both know that rivers almost always run along the bottoms of canyons - not the tops or the sides - but remember that Google Earth doesn't necessarily know that there is a river there - all there is to represent it are some pixels in a photograph. A typical muddy river is really hard for software to pick out from the similarly colored dirt that's nearby - especially if there are overhanging trees, rocks and white-water in the river, etc. So the software makes a guess at how to draw the slope - and the river ends up flowing along a 45 degree slope! Looking like a really good place to go water skiing without a boat! (An old joke amongst people like me who have to actually solve these kinds of problems for a living!) SteveBaker (talk) 07:13, 10 July 2010 (UTC)[reply]

Well, no doubt that's part of the story, but from looking at the actual pattern of errors, I suspect a more important factor is that the satellite photos are often taken at an angle, and the software has problems in shifting points correctly to compensate for differences in ground elevation. In other words, my impression is that the software projects the photos onto a flat surface and then warps the surface according to the topographic data, rather than taking the theoretically correct approach of warping the surface first and then projecting the satellite photos onto the warped surface. Looie496 (talk) 16:50, 10 July 2010 (UTC)[reply]

I doubt that. The process of 'orthorectification' (which fixes those problems) is well understood and there is a mountain of free/OpenSourced software produced by various US government agencies that can perform that task. It's really unlikely that Google would be getting that wrong given how easy it is to fix. I work in this very area of computer graphics technology - and the 'sloping rivers' problem is well known - even when orthorectification has been optimally performed. The bottom line is that the terrain photography is almost always provided at a much higher resolution than the elevation data. In effect, the imagery 'samples' the elevation data to determine how it should be drawn - and the Nyquist sampling limit isn't close to being met. So you get all sorts of weird-looking artifacts as a result. SteveBaker (talk) 04:19, 11 July 2010 (UTC)[reply]

The AAA Road Atlas, 1996 edition, shows on its Los Angeles area map that after the route 138 interchange as you go north on I-15, the road turns right, then more sharply right, and then left in the space of a few miles, and Cajon Pass is marked near the end of the left turn, with an elevation of 4,190 feet. Nearby is Summit Lookout, 4,260 feet.

The National Geographic Road Atlas, 1999 edition, shows a pass symbol at very nearly the same place on the road, but labeled Cajon Summit, 4,259 feet. The American Map Road Atlas, 2006 edition, appears to have used maps from the same source and agrees with this.

The Rand McNally Road Atlas, 2001 edition, renders the road differently, showing a left turn between the two right turns. But it puts the pass symbol in the same place and labels it Cajon Pass, 4,260 feet. Unlike the others, this one also marks the pass on its main Southern California map, but this time the label is Cajon Summit and the elevation is given as 4,257 feet! (The location looks farther south, too, nearer the route 138 interchange, but I assume that's due to the limitations of the map scale.)

In view of all this I am inclined to believe that the AAA atlas has it right with 4,190 feet, while the others are confusing locations on and just off the Interstate, and that the elevation that was found in Google Maps is probably the elevation of the route 138 interchange, not the pass.

--Anonymous, 05:40 UTC, July 10, 2010.

Some old US maps used a different measure of a 'foot' called a 'survey foot' - but I don't think the difference is enough to account for this much error. SteveBaker (talk) 07:13, 10 July 2010 (UTC)[reply]

That's a red herring; it's only different by a couple of parts per million. See Foot (length)#Survey foot. --Anonymous, 11:40 UTC, July 13, 2010.

I've adjusted the coordinates a bit in the article. Anonymous, can you confirm that they now match the location shown in the atlases? Deor (talk) 12:07, 10 July 2010 (UTC)[reply]

Sorry, I only just now got back to this and have now viewed the area in Google Maps for the first time. It seems clear to me that all of the road atlases are showing the elevation of the high point on I-15; after all, they are road atlases. They aren't interested in the exact location of the saddle point of the pass as a landform, or the location of the high point on a minor road like 138 or on the railway. Further, I see from Google Maps that the northbound and southbound lanes of I-15 are widely separated in that area. I now think this accounts both for the different shape of the road in the Rand McNally vs. the other road atlases, and also the difference in elevation between the road atlases. From Google Maps it appears that the high point in the southbound lanes is about 34.34954,-117.44664, right next to the lookout parking lot. This must be at about elevation 4,257 to 4,260 feet. But in the northbound lanes the high point would be about 34.35193,-117.43861 and at a lower elevation, maybe the 4,190 feet although from the contour lines it looks a bit higher. Note where the article says "Some maps may show the Cajon Pass as a feature on SR 138, which crosses I-15 south of the summit between West Cajon Valley and Summit Valley. The highest point on I-15 between Los Angeles and Victorville is thus sometimes identified as Cajon Summit. However, the entire area, including Cajon Summit, is often called Cajon Pass"; I think this explains the terminological confusion. --Anonymous, 11:40 UTC, July 13, 2010.

Now I'm really confused. The USGS topographic map of the region, which one would expect to be definitive, has the label "Cajon Pass" at a point on California State Route 138 (34°19′32″N 117°25′43″W / 34.3255°N 117.4286°W), at what looks to be an altitude of only a little over 3,800 feet. Perhaps this whole thread should be copied to the article's talk page, so that those interested in the article can work out the best-sourced location and altitude to include in it. Deor (talk) 16:59, 10 July 2010 (UTC)[reply]

As far as I can tell, the railroad tracks occupy the pass's lowest high point (if that makes sense), while the road winds along somewhat higher slopes. The U.S. Geological Survey Geographic Names Information System: Cajon Pass page gives an elevation of 3835 feet, but the GNIS database is not always to be trusted, especially with elevation. This page, about the railroad tracks, says that the pass "crests the summit at 3872 feet", but also that in 1972 the Santa Fe Railway decided to "reconstruct the summit of Cajon Pass". The "summit was lowered by 50 feet to 3822 feet". The section of track is known as the "Big Cut". Pfly (talk) 17:11, 11 July 2010 (UTC)[reply]

Also I just discovered that the article, Cajon Pass, puts its location at 34.349,-117.447, which according to USGS topo maps is not Cajon Pass but "Cajon Summit": USGS topographic map of article coords. Interstate 15 doesn't cross Cajon Pass. Perhaps the confusion arises from the assumption that it does? Perhaps it is common to say I-15 crosses Cajon Pass, but to be precise, the pass is about a mile southeast of I-15.Pfly (talk) 17:20, 11 July 2010 (UTC)[reply]

submitting an article for review.[edit]

I have tried numerous times to submit an article for review but I can not seem to get it to post. I have reviewed the process on many of the pages available and just can't figure out what I am doing wrong. I have several articles I could submit. I am currently taking online courses towards the acquistion of my Masters Degree in the Science of Higher Education. Each term I am required to submit a course project, all of which I have received an A grade on. I am more than willing to submit these papers to Wiki, however, I must first figure out how to do so. If I could get some assistance, it would be great. Thank you in advance for your help and I hope to get a reply soon. My new term just started and I have a little bit of extra time at the present. Once the term gets into full swing I will not be able to do any extracurriular activities such as submission of articles for Wiki. So the sooner you can reply, the better. —Preceding unsigned comment added by Patter lake (talk • contribs) 02:41, 10 July 2010 (UTC)[reply]

Questions about Wikipedia itself are best directed to the Wikipedia Help Desk - where I'm sure they'll be happy to help you. SteveBaker (talk) 03:50, 10 July 2010 (UTC)[reply]

Try following the instructions on WP:PR --Chemicalinterest (talk) 12:40, 11 July 2010 (UTC)[reply]

Night sky on Mars[edit]

I've been wondering what the night sky looks like on Mars. My hypothesis is that all the constellations would look the same as here, but that since the axial tilt of Mars is different from that of Earth, the North Star isn't directly above the Martian North Pole, and therefore there is some other point in the Martian Northern Hemisphere about which the stars appear to rotate. Can anyone confirm or deny? +An gr 13:11, 10 July 2010 (UTC)[reply]

Celestia is a good tool to find the night sky on other planets. I'm not sure about the exact axial tilt, but even on Earth, precession plays a role in which star becomes the North Star more than any variations in tilt (22-24°). As for the planets on Mars, they would have different positions across the constellations and different brightnesses than seen on Earth. ~A H 1^(TCU) 14:25, 10 July 2010 (UTC)[reply]

I should have checked the links before posting. I meant: since Polaris isn't the North Star on Mars, there is some other point in the Martian Northern Hemisphere about which the stars appear to rotate. Likewise the apparent point of rotation in Earth's Southern Hemisphere is different from that in Mars's Southern Hemisphere. I suppose not only the planets but also the Sun would have different positions across the constellations, so that the Martian Zodiac would be different from ours. +An gr 14:55, 10 July 2010 (UTC)[reply]

Well, for the Southern hemisphere of earth, there is no southern "pole star" that's visible to the naked eye. The two stars Acrux and Gacrux in the Southern cross constellation are the closest thing we have - but they aren't as exact as Polaris is for the Northern hemisphere. SteveBaker (talk) 15:08, 10 July 2010 (UTC)[reply]

Okay, but this isn't answering my question. Am I correct in thinking that the constellations would look the same on Mars as on Earth but that their point of apparent rotation would be different? And here's a related question: would the smaller circumference of Mars play a role in the appearance of the night sky? +An gr 15:20, 10 July 2010 (UTC)[reply]

Yes, the constellations would look the same on Mars as they do on Earth, at least with the naked eye (astronomers could take very precise measurements and see very small differences). The point in the sky that they rotate around would be different, although there is no actual (visible) star at that point(see here). Mars' axial tilt is actually quite similar to Earth's (25.2 compared to 23.5, see here, but points in a different direction.

24.150.18.30 (talk) 15:39, 10 July 2010 (UTC)[reply]

The reduced diameter of Mars would result in the horizon being closer - which might allow you to see more stars closer to the horizon than here on Earth - but aside from that, the only noticable difference would be the point about which the stars rotate. Constellations would look essentially identical. Earth and Mars are very close together compared to the distance to even the nearest stars. Even out as far as Pluto, you'd need some rather precise measurements with a big telescope to see a measurable difference. SteveBaker (talk) 04:12, 11 July 2010 (UTC)[reply]

According to Astronomy on Mars, "The orientation of Mars's axis is such that its north celestial pole is in Cygnus at R.A. 21h 10m 42s Decl. +52° 53.0′. The top two stars in the Northern Cross, Sadr and Deneb, point to the north celestial pole of Mars. The pole is about halfway between Deneb and Alpha Cephei." The article also mentions that the Martian north celestial pole lies only a few degrees from the Milky Way, which therefore is always visible. Looie496 (talk) 16:40, 10 July 2010 (UTC)[reply]

As for the Zodiac question, this is determined by the planet's orbital plane. As it says in the Mars article under "inclination", the orbital plane of Mars is only 1.85° different from that of the Earth (which we call the ecliptic). So the Sun's path through the constellations would be almost the same as we see here. --Anonymous, 17:01 UTC, July 10, 2010.

One more thing worth noting: All the modern photos from Mars show a hazy pink sky. The sky itself is blue there (product of the atmosphere), but it gets very dusty and windy so there is always a haze, ~~and that will make nighttime viewing a bit problematic. However, I haven't read up on this too much so this may be completely oversimplistic~~. SamuelRiv (talk) 19:20, 10 July 2010 (UTC) EDIT from article Extraterrestrial skies: "The sky is thus rather bright during the daytime and stars are not visible" SamuelRiv (talk) 16:31, 11 July 2010 (UTC)[reply]

Thanks to everyone for the informative answers and especially to Looie496 for directing my attention to Astronomy on Mars, a topic I never imagined we would have an article on. That and Extraterrestrial skies are going to make interesting reading I think. (Next we need an article on Astrology on Mars!) +An gr 20:45, 10 July 2010 (UTC)[reply]

WP:WHAAOE (nearly). CS Miller (talk) 21:35, 10 July 2010 (UTC)[reply]

Hollow core concrete slabs[edit]

How are hollow core concrete slabs manufactured? —Preceding unsigned comment added by 113.199.149.217 (talk) 14:59, 10 July 2010 (UTC)[reply]

I you're referring to the things in the picture - they just pour concrete into molds. SteveBaker (talk) 15:04, 10 July 2010 (UTC)[reply]

those are blocks not slabs.. eg I think these are meant http://www.concretec.ae/products/Home_Img/DSC00703_2_26_200802_39_164071250.JPG

According to Hollow-core slab they are extruded.

eg http://www.mabeton.com/products3.htm

For more info try google books and search for "concrete extrusion slab hollow" or similar eg [1] 87.102.85.197 (talk) 15:41, 10 July 2010 (UTC)[reply]

Actually youtube is very useful here eg http://www.youtube.com/watch?v=wEDPtSK1RLw&feature=related there are several videos showing hollow core slab manufacturing from a variety of manufacturers and sources.87.102.85.197 (talk) 18:02, 10 July 2010 (UTC)[reply]

I know those things as besa blocks, however googling it seems like this might not be as common a name for them as I assumed, might be an Australian thing.. Vespine (talk) 00:59, 12 July 2010 (UTC)[reply]

According to Concrete masonry unit you are right, but the spelling is different.Sf5xeplus (talk) 01:21, 12 July 2010 (UTC)[reply]

Funny! I wasn't sure of the spelling, i don't think i've ever had to write it before, so i googled besa blocks and it had more then enough results to convince me that I had the right spelling. :) Vespine (talk) 05:56, 12 July 2010 (UTC)[reply]

DRI and RDA intake[edit]

What are the DRI and RDA intake for carbohydrate, protein, total fat, saturated fat, fiber, sodium and calcium? —Preceding unsigned comment added by 74.14.117.187 (talk) 15:12, 10 July 2010 (UTC)[reply]

You can find the Reference Daily Intake at Reference Daily Intake which are based on RDA.

The DRI's can be found at Dietary Reference Intake

The figures are for specific conditions (age sex), for the general picture try the external links in those articles. 87.102.85.197 (talk) 15:45, 10 July 2010 (UTC)[reply]

Recharging the unrechargeable Issue[edit]

Of course, rechargeable batteries are meant to be recharged, but others are dry cell, the type we use once and then simply throw them away. Is it possible that all, cells, even those not build to be recharged, i.e. the ones we use-up and then throw away can be somehow recharged ? Of course it's implausible, but some one thinks it can be done → http://shopping.rediff.com/product/maxis-green-magic-alkaline-battery-charger/10471140 Check it out, boys... Jon Ascton (talk) 18:10, 10 July 2010 (UTC)[reply]

Non-rechargeable batteries drop their available voltage with further use, regardless of how long they are charged for. Furthermore, there is a risk of explosion if they are recharged unsuitably, so I'd advise against it. Regards, --—Cyclonenim | Chat 18:40, 10 July 2010 (UTC)[reply]

All reactions are reversible, but there are many examples were the reverse reaction is not feasible. Recharging alkaline batteries is one such case. When the cell discharges zinc is converted to zinc ions; to recharge one would usually reverse the potential to re-deposit zinc. However since the cell is alkaline the anode reaction is this:

Zn + 4OH^- > Zn(OH)₄^2- + 2e^-    (A)

The problem is that the zincate ion (Zn(OH)₄^2-) is negatively charged (unlike normal Zn²⁺ ions), so when the 'anode' is made negative in an attempt to recharge the zincate ion actually moves away from the 'anode' rather than moving towards as it would be if it where Zn²⁺. This means that the alternative reaction which is basically electrolosis of water occurs:

H₂O + e- > 1/2H₂ + OH^-    (B)

H₂ is hydrogen gas - production of this increases the pressure inside the cell hence the warning "Do not attempt to recharge, Danger of leak or explosion" , usually the battery does not explode since there is a pressure releasing valve built in - instead the high pressure can force out the electrolyte which is corrosive and caustic Potassium hydroxide which can damage people and electrical equipment.

The hydrogen produced may be able to reduce zincate to zinc in fact this isn't likely - not a strong enough reductant - but there is no guarantee that this will happen at the electrode - which means that it may not be available to the battery:

H₂ + Zn(OH)₄^2- > Zn + 2OH^- + 2H₂O    (C)

Similar but less problematic processes happen at the cathode, which can also result in the production of oxygen gas.

That's why attempting to recharge alkaline batteries is neither realistic nor a good idea.

(How they work) Devices that attempt to recharge non-rechargable alkaline batteries use on-off pulses of electricity: The on pulse causes reaction B. During the off pulse reaction C can occur which should prevent build up of pressure.87.102.85.197 (talk) 18:54, 10 July 2010 (UTC)[reply]

I remember hearing that those chargers can only be used for about 5 times before the voltage drops so low it is essentially useless. --Chemicalinterest (talk) 20:33, 10 July 2010 (UTC)[reply]

Medically pure tin[edit]

How can I make pure tin? I want to make it convert into the alpha form and pewter does not convert. --Chemicalinterest (talk) 20:31, 10 July 2010 (UTC)[reply]

Possibilities:

a. Electroplate from a tin(II) solution

b. Electrorefine a tin solder.

If you decide to try either of these further advice could be given depending on what you're working from.87.102.85.197 (talk) 20:46, 10 July 2010 (UTC)[reply]

Out of curiosity, isn't a tin(II) solution going to have cation impurities anyway, some of which will inevitably deposit on electroplating? I suppose on could set up two cathode-anode structures, with one tin terminal on each attracting all things with higher electronegativity and all things with lower, respectively, right? Or how would one purify, say, from a tin can? SamuelRiv (talk) 16:35, 11 July 2010 (UTC)[reply]

(from a solution of the metal ions) the deposition of more electropositive metals can be avoided by using a deposition voltage lower than their deposition voltage see Standard electrode potential (data page) - so a solution of tin(II) can be deposited to tin in the precense of Fe(ii) etc.

Conversely less electropositive metals (eg Ag+) can be deposited out first, using the method above.

Electrorefining (ie starting from metal) is more complex since the net reaction is metal > metal (accross electrodes) and technically EMF=0 (excluding effects due to impurities) .. in practice it also works, there's a good introduction here [2] 178.78.64.206 (talk) 18:49, 11 July 2010 (UTC)[reply]

(Separating tin from iron using electrorefining I think will be tricky though).178.78.64.206 (talk) 19:22, 11 July 2010 (UTC)[reply]

Stoichiometry[edit]

How many mL of 0.3M KMnO₄ is required to titrate 0.02 moles of sodium oxalate.

Isn't the answer 100 mL?--478jjjz (talk) 20:47, 10 July 2010 (UTC)[reply]

Have you got the reaction? It's given at [3] 1 mole permanganate reacts with 2.5 moles of oxalate.

From Sodium oxalate:

5H₂C₂O₄ + 2KMnO₄ + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 10CO₂ + 8H₂O

87.102.85.197 (talk) 20:50, 10 July 2010 (UTC)[reply]

I have

Na₂C₂O₄ + 2KMnO₄ → 2 NaMnO₄ + K₂C₂O₄

--478jjjz (talk) 20:56, 10 July 2010 (UTC)[reply]

Reduction to manganate(VI) is right for alkaline conditions. But your equation is wrong - the oxalate needs to be oxidised, and the permanganate reduced.87.102.85.197 (talk) 20:59, 10 July 2010 (UTC)[reply]

My instructor has given the following answer

[0.02 x (2/5) /0.3] x 1000 = 26.67 mL

He doesn't explain a diddly-squat, so I am baffled.

I am supposed to use 16 H⁺ + 2 MnO₄⁻ + 5 C₂O₄^2-→ 2 Mn²⁺ + 8 H₂O + 10 CO₂

, but I don't understand why.--478jjjz (talk) 21:18, 10 July 2010 (UTC)[reply]

That's the reaction: Permanganate is reduced to manganese 2+ ions, and oxalate is oxidised to carbon dioxide

These are called redox reactions. Didn't you get a class about them? There's an introduction here http://www.chemtutor.com/redox.htm I think you need to understand anout redox reactions first - then you'll understand the equation you were given.87.102.85.197 (talk) 21:26, 10 July 2010 (UTC)[reply]

This was on a lab quiz in the 1st semester of my general chemistry course. Redox reactions will be studied in detail in the next semester. The lab manual was written by my college professors who cover the topics in a different order than my acutal textbook. The lab manual keeps jumping back and forth in terms of the topics covered in the textbook.--478jjjz (talk) 21:31, 10 July 2010 (UTC)[reply]

It appears that 87's reaction works for this example. If there is 0.02 moles of oxalate, and the ratio of oxalate to permanganate is 5·2, then there needs to be 0.02 · 2 ÷ 5 moles of permanganate, or 0.008M. The concentration is 0.3M per liter and there is 0.008M; divide 0.3 ÷ 0.008 = 37.5. 1000 mL in a liter ÷ 37.5 = 26.66(repeating). The last problem could also be a proportion; 0.3M over 0.008M = 1000 ml over ??? ml. Hope this helps. --Chemicalinterest (talk) 22:20, 10 July 2010 (UTC)[reply]

Molniya orbit[edit]

Does this table make sense? Within a range of 500 to 39,900 km above the Earth, 1.5 to 10.0 km/s?--Email4mobile (talk) 15:20, 11 July 2010 (UTC)[reply]

It doesn't make sense, actually. Some of these orbital speeds are calculated with respect to the tangential speed at the surface of the Earth (8km/s), and some are calculated with respect to a stationary frame. I'll have to fix this. SamuelRiv (talk) 17:09, 11 July 2010 (UTC)[reply]

Aircraft tails[edit]

If the vertical stabilizers on an aircraft are tilted outward (e.g. Lockheed Martin F-22 Raptor) or inward (e.g. Lockheed Have Blue), does this make any difference in maneuverability or drag? Also, is there a name for this tilt? --The High Fin Sperm Whale 20:50, 10 July 2010 (UTC)[reply]

That would be the dihedral of the vertical stabilizer(s). This certainly impacts drag, lift, and maneuverability, especially because the rudder or rudders serve as elevators) as well. The exact parameters are complex, of course, because the airframe and the rest of the aircraft dynamics are all interconnected. Nimur (talk) 16:25, 11 July 2010 (UTC)[reply]

Following on that, as one gets to very steeply angled vertical stabilizers it becomes possible to discard the elevators entirely, leading to ruddervators which combine the function of rudder and elevator in the same control surfaces. TenOfAllTrades(talk) 16:32, 11 July 2010 (UTC)[reply]

So I'm assuming that tails that point out from the centre are more maneuverable since they are used on many fighter aircraft (e.g. McDonnell Douglas F/A-18 Hornet, Lockheed Martin F-22 Raptor, Lockheed Martin F-35 Lightning II)? --The High Fin Sperm Whale 16:35, 11 July 2010 (UTC)[reply]

They also reduce the radar signature of the aircraft by avoiding the right angle between the horizontal and vertical fins that acts like a corner reflector for the radar. But I'm not sure whether that is the dominant reason for using them. When you have a computer flying the plane, it's easy to have the software decode simple left/right and up/down commands from the pilot into the complicated mix of flapperons (aileron/flaps) and ruddervators needed to make the plane do that. In the past, when those controls were essentially connected directly to the joystick with cables and push-rods, the various control surfaces had to map onto the pilot's inputs directly and simply. SteveBaker (talk) 16:58, 11 July 2010 (UTC)[reply]

This page discusses several examples, and the reasoning behind them. Canted vertical stabilizers were first added to military aircraft in the 1960s to reduce radar cross-section (the SR-71 spy plane may be the first example, with its unique inward-canted tails), more recent aircraft also definitely take advantage of the canted stabilizers to increase manoeuverability and performance. (The link I provided discusses some of the specific benefits in the F-18, as one example.) As SteveBaker notes, the advent of fully fly-by-wire craft made it much easier for aircraft designers to take advantage of 'non-traditional' control surface orientation and placement. TenOfAllTrades(talk) 17:19, 11 July 2010 (UTC)[reply]

How does it affect the areodynamics if an airplane's tail is canted inward (Lockheed SR-71 Blackbird and Lockheed Have Blue)? --The High Fin Sperm Whale 21:26, 11 July 2010 (UTC)[reply]

Diatomaceous earth[edit]

I have just produced a very large image of diatomaceous earth, a powdery rock made up of the skeletons of dead diatoms. Does anyone know much about diatoms and can help identify some of the classes of diatoms present in this sample? - Zephyris _Talk 21:59, 10 July 2010 (UTC)[reply]

Probably they are deformed and compacted so much that they are unrecognizable. --Chemicalinterest (talk) 12:36, 11 July 2010 (UTC)[reply]

They probably aren't too compressed/distorted (the rock has not been greatly compacted as you can tell its the low density and absorbency), and there are definately fairly complete shells (look, for example, at the centre bottom). I'm sure some general level of classification would be possible... - Zephyris _Talk 14:40, 11 July 2010 (UTC)[reply]