Wikipedia:Reference desk/Archives/Science/2015 January 27

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January 27

What kind of bird?

What kind of bird is this? (I photographed it on the coast of Georgia, USA.)

I asked someone who should know, and they said anhinga. But the beak looks too different (among other things). Anyhow, that article led me to Cormorant, which has about the same kind of beak. Bubba73 ^{You talkin' to me?} 06:39, 27 January 2015 (UTC)

Yup, definitely a cormorant, and a very good photo of one, in a typical pose (drying its wings). They are common and widespread.--Shantavira|^{feed me} 08:23, 27 January 2015 (UTC)

Thanks, I was out taking some photos (e.g. Jekyll Island Club#Gallery) and I suddenly had the opportunity to take aome photos of the bird. Bubba73 ^{You talkin' to me?} 08:38, 27 January 2015 (UTC)

LH & FSH produced by negative or positive feedback?

5.28.171.15 (talk) 15:00, 27 January 2015 (UTC)

OK - I give up. You're going to have to expand your question a bit. What does FH and FSH stand for in this context? It's really hard to guess and our disambiguation pages for those two acronyms don't show up anything that helps!

(If someone here can guess from the context - please add the expansion into those two dab pages!) SteveBaker (talk) 15:30, 27 January 2015 (UTC)

I suspect the OP may have intended to ask about FSH and LH, not FSH and FH. I.E. follicle-stimulating hormone and luteinizing hormone. Nil Einne (talk) 16:57, 27 January 2015 (UTC)

[you're right, I correct it. 149.78.26.195 (talk) 19:51, 27 January 2015 (UTC)]

Assuming you meant LH and FSH, you can read about endocrine feedback loops at Hypothalamic–pituitary–gonadal axis. --Mark viking (talk) 17:10, 27 January 2015 (UTC)

The Original Poster really needs to come back and provide more info; otherwise mēdeís may hat it. An' then non of us will discover the real question nor answer--Aspro (talk) 19:07, 27 January 2015 (UTC)

Thank you, I meant to LH& FSH - hormones. Sorry 149.78.26.195 (talk) 19:51, 27 January 2015 (UTC)

I read the article that mentioned above and I didn't understand a clear answer for my question. 149.78.26.195 (talk) 19:57, 27 January 2015 (UTC)

Well we don't understand your question. Please now explain what you mean by negative and positive feedback in this context.--Shantavira|^{feed me} 11:16, 28 January 2015 (UTC)

We also have articles on positive feedback and negative feedback, both are common in biological systems for signaling and control. This page from a class at UC Berkeley [1] seems to say that estrogen in females can trigger both positive and negative feedback to FSH and LH. SemanticMantis (talk) 14:43, 28 January 2015 (UTC)

What is the antonym of "conspecific"?

If 2 organisms are from different species, is there an adjective that can describe this?
Thanks.

Heterospecific. See biological specificity for relations among the types of specificity. --Mark viking (talk) 17:16, 27 January 2015 (UTC)

But I personally would go out of my way to avoid using either of those words, even in a scientific paper. It's so easy to say "same species" and "different species" without resorting to Latinish gobbldygook. Looie496 (talk) 19:54, 28 January 2015 (UTC)

I absolutely agree. There's no reason to resort to Latin when perfectly good English words exist, unless the intention is to deliberately try to hide the meaning from the common man. StuRat (talk) 20:11, 28 January 2015 (UTC)

Sorry, this is nonsense. Of course you are both entitled to your opinions. But let me offer a contrary view to the OP and anyone else who happens to read:

Shall we never talk about intramural sports, and instead speak of "sports played by teams within the same school or organization"? Looie, shall we not speak of dendrites in scientific papers on neuroscience, and instead prefer "the branching part at the end of a neuron"? What about the hippocampus or the amygdala? Are all those terms gobbledegook Latin/Greek? No, they are English words that have simple meanings, and most high school graduates know them. You would be laughed out of the review process if you submitted a paper talking about the "seahorse-shaped part of the brain". These words are English words, as are "heterospecific", "conspecific", as well as "interspecific" and "intraspecific". We also have heterogenous and heterosexual and heterozygous -- all English words. As are "confluence" and "congenital", "converge", "congregation", "congener" etc. I won't even bother listing the many common words that start with "intra-" or "inter-".

The simple fact of the matter is that these terms for biological specificity (as well as their derivatives, e.g. "confamilial", etc) are highly useful for science writing, especially in the fields of evolution, ecology, and organismal biology. If I had to write "competition between two individuals that are not of the same species" instead of "interspecific competition", I'd never be able to fit abstracts into the word limits, let alone the appalling sentences that would result. I do appreciate the desire for clarity and simplicity in science writing, and I also try to avoid five dollar words where a simple one would suffice. But heterospecific and conspecific are basic terms with simple definitions, that use the same standard prefixes as dozens (if not hundreds) of other words. It's not too much to expect people to know them if they are reading science papers in these fields. SemanticMantis (talk) 22:34, 28 January 2015 (UTC)

You've missed the point entirely. It's only where there are widely understood simple English words or phrases that they should be used in place of arcane Latin terms. Obviously long-winded English descriptions don't qualify. The English phrase shouldn't be much longer than the Latin. Of course, where you have a Latin phrase, like a writ of habeas corpus (literally meaning a written order to "produce the body"), then an English phrase, like an "order to bring the prisoner to court" would be far easier to understand. As for people laughing, I imagine many laughed when church services were first performed in English instead of Latin, too. StuRat (talk) 04:43, 31 January 2015 (UTC)

I'm just speaking as someone who's published several research articles in the field of ecology. If you think "conspecific" is an arcane Latin word, then I can't help you. I'm telling you that it's an English word that is widely used in science, and fits the same basic format as many English words. But please, don't take my word for it - write however you like when you submit your next manuscript for peer review. SemanticMantis (talk) 19:26, 2 February 2015 (UTC)

Off Center Thrust in Spacecraft

If a rocket motor on a spacecraft is not perfectly aligned with the center of mass of said spacecraft, how much of the thrust will become rotary motion, and how much will become linear motion? If some of the thrust becomes linear motion, what direction would that motion take? I imagine that the spacecraft would follow a curved trajectory, much like the depictions in old spaceship cartoons. While we are at it, aligning a rocket motor with the center of mass of a craft with a mobile payload, like the shuttle, would be a bit of a trick. How is it done? 50.43.56.168 (talk) 20:04, 27 January 2015 (UTC)

Over sufficiently long time the average velocity of the spacecraft will tend to a constant, while the rotation will be continuously accelerating. Ruslik_Zero 20:26, 27 January 2015 (UTC)

If I am not mistaken this constant velocity limit will (in case the mass of fuel is negligible and rotation is about a fixed axis) be

$v={\sqrt {\frac {\pi }{2}}}{\frac {1}{m}}{\sqrt {\frac {FI}{r_{0}}}}$,

where m is the mass of the spacecraft, I is its inertia moment, r₀ is displacement of the thrust relative to the center of mass and F is the thrust. This constant velocity will be directed some 45 degrees from the initial trust direction. Ruslik_Zero 20:56, 27 January 2015 (UTC)

It's never possible to align a rocket motor perfectly with the center of mass, so spacecraft have a number of ways to counteract the torque induced by poor alignment. Some rocket engines have gimbaled thrust, so they can change their thrust vector slightly. Reaction wheels resist changes in orientation due to torque. Reaction control systems use small thrusters to actively change the spacecraft's orientation. In Earth orbit, spacecraft can also use magnetorquers for stabilization by taking advantage of the Earth's magnetic field. For orbital launches, rockets often carry ballast so that their mass distribution is exactly what their designers intended. Cubesats take advantage of this to get a cheap ride into orbit--rather than carry dead weight, why not carry some cubesats? --Bowlhover (talk) 10:19, 28 January 2015 (UTC)

S-IC S-II cutoff on Apollo 13

The previous question got me to wondering something. During the launch of Apollo 13, the center engine of the S-IC first stage S-II second stage shut down prematurely. The decision was made to burn the outboard engines longer to compensate. But what if it was one of the outboard engines that shut down? How would the imbalance have been dealt with?    → Michael J Ⓣ Ⓒ Ⓜ 21:45, 27 January 2015 (UTC)

It was actually the S-II second stage that had the problem with pogo oscillation. If one of the outboard engines had shut down as well (and presuming that it wasn't immediately catastrophic), the spacecraft would have jettisoned the second stage and performed a COI (Contingency Orbit Insertion) burn with the S-IVB for an Earth-orbit mission. See Apollo abort modes. Tevildo (talk) 23:17, 27 January 2015 (UTC)

I believe that Michael J was not asking about it losing a second engine, but wondered if thrust vectoring could have compensated if the engine which shut down was one of the outboard ones. -- ToE 00:15, 28 January 2015 (UTC)

According to the flight rules for Apollo 11 (here, page 102), BOOSTER would call an abort if three of the S-II engines were out, or two were out and the commanded gimbal angles on the remaining engines were greater than 40° off nominal. So, it was presumably capable of a full mission if it had lost one of the outboard engines, and even losing two wouldn't have required an immediate abort. Tevildo (talk) 01:22, 28 January 2015 (UTC)

You are correct, it was the S-II, not the S-IC. Oops.    → Michael J Ⓣ Ⓒ Ⓜ 01:31, 28 January 2015 (UTC)

For that matter, if it was okay to fly with 3 out of 5 engines, then if an outboard engine failed and it wasn't certain that the gimbals could compensate well enough for the off-center thrust, they could have chosen to shut down the opposite outboard engine. --65.94.50.4 (talk) 02:25, 28 January 2015 (UTC)

"...gimbal angles on the remaining engines were greater than 40° off nominal." I would be surprised if the engines could be angled more than 10 degrees.50.43.56.168 (talk) 03:29, 28 January 2015 (UTC)

Yes, it sounded like a lot to me, as well. According to the user manual (page 83), the S-II gimbal range was ±7°. The verbatim text of the flight rules is "[Abort] if the difference in commanded angles and gimbal angles exceeds 40 deg in pitch or yaw", so it may refer to the attitude error of the spacecraft itself rather than the engine. The important point is that it could keep going with two engines out in most circumstances, and I'm sure the people at Houston (who _were_ rocket scientists) could be trusted to make the right decision. Tevildo (talk) 21:36, 29 January 2015 (UTC)