Wikipedia:Reference desk/Archives/Science/2013 June 10

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June 10

Can time really be depicted with space in continuum?

What is the spatial distance between the two positions of a stationary object separated by one second in its world line and how this can be represented geometrically in the light cone? 74.200.19.65 (talk) 01:04, 10 June 2013 (UTC)Eclectic Eccentric Kamikaze

Time and space can be depicted in many ways. Physicists commonly use a graph to represent position versus time. A stationary object, as observed in some reference frame, would have zero spatial distance between its start- and end- positions over time. That is the definition of stationarity. It could be drawn as a stationary point or as a line with constant position on the space-axis, depending on how you visually represent time and space in a diagram. Do you need help finding introductory articles to these subjects? I recommend starting with Galilean transforms first, to develop familiarity with the use of algebraic geometry to represent time and position. Nimur (talk) 01:35, 10 June 2013 (UTC)

Also relevant is Minkowski space, which provides the geometric underpinning for the concept of space-time. --Jayron32 01:40, 10 June 2013 (UTC)

(ec) Your two questions (the one in the section heading and the other in the text) are not the same question, so I'll answer both.

1. Space and time must be regarded together as part of the same spacetime continuum to maintain consistency. To try to separate them is no different from separating the x-axis from the y-axis on a geometric plane, due to the arbitrariness of the direction in which you can choose to draw them. The relationship between the t-axis and the x-axis is slightly different, but in this respect it is the same. If you have a mathematical bent, articles like Minkowski space may be interesting.
2. The word-line of an object stationary with respect to the observer is depicted as a vertical line in a spacetime diagram, parallel to the time axis in the top diagram in Minkowski space and Special relativity. Any given time may be depicted by a horizontal plane in the diagram (as for this observer – planes representing an instant in time for other moving observers will be seen as tilted from the horizontal by the first observer). Planes one second apart will intersect the object's world line, defining two points (or "events"), one straight above the other in the diagram. The spatial distance between these two points (as seen by this observer) is the horizontal separation between these points, and is hence zero. Any moving observer will see the object's world line as tilted, and hence the spatial separation of two distinct points on the object's world line as seen by such an observer will be non-zero.

— Quondum 01:54, 10 June 2013 (UTC)

I think the OP is asking if there is any meaningful correlation between distance in space and "distance" in time. I've always assumed that 1 second equates to 1 light-second in the other three axes, but I don't know if this is at all justified. Rojomoke (talk) 14:53, 10 June 2013 (UTC)

The ratio between distance in space and "distance" in time is called speed. As quondum said above, if an oject is stationary, its speed is zero and so is the distance traveled. Dauto (talk) 20:43, 10 June 2013 (UTC)

speed of aurora video

Are these videos in real time or are they sped up? Bubba73 ^{You talkin' to me?} 02:09, 10 June 2013 (UTC)

Thanks for asking this. I've often wondered about the same thing. HiLo48 (talk) 02:13, 10 June 2013 (UTC)

If you take a few seconds to click the links on the APOD page, you find the author's website. That video is made from a time-lapse sequence of few hundred frames, each with an exposure of 3 to 6 seconds, or, played back at about 100x natural speed. Nimur (talk) 02:17, 10 June 2013 (UTC)

Thanks. Would that be the case for all videos of auroras? They all seem similarly fast. Having never seen a real aurora, it would be nice if they all carried some explanation. HiLo48 (talk) 02:23, 10 June 2013 (UTC)

Here are viewing tips from University of Alaska's Geophysical Institute, providing guidance on what real aurora observations are like for the average enthusiast. Actual aurora are often quite dim; brightness varies widely based on geomagnetic activity. The speed that the aurora move through the sky is also quite slow. At least from a purely aesthtetic perspective, aurora are similar to clouds: somewhat slow and boring. Of course the physical process is totally different from clouds, and if you've never seen an aurora, the novelty is greater; but there are many natural novelties in the polar regions. Personally, I found the novelty of midnight sun more fascinating; when I was in Fairbanks, (which is not even above the Arctic circle), the late sunsets were very unusual to me. There were several days that we remained outside and actively working well past midnight, because without a clock to tell us otherwise, it seemed like late afternoon. Of course we understand the science quite well, but there is an aesthetic quality that perhaps must be experienced.

Ideal aurora-viewing is of course during the winter months, because it is darker more often; but the aurora can occur at any time of year, and even at any time of the day. The vanishing daytime E-layer may make aurora slightly more common at night. Nimur (talk) 02:52, 10 June 2013 (UTC)

I have seen real-life auroral displays that appear to move at a similar rate to that shown in the time-lapse video linked above, but usually affecting only smallish regions at a time, not sweeping across the whole sky as we see there. Part of the fun of watching aurorae is the suddenness with which the character or behaviour of a display can change from moment to moment.—Odysseus1479 02:50, 10 June 2013 (UTC)

(Edit Conflict) Actually, the first two or three segments of that video are not speeded up to the same extent as the latter few: this is evident from the differing speeds at which the background stars can be seen moving: such visible movement is a crude indication of time lapse having been employed, but could not be measured to calculate the degree of speeding up unless parameters of the lenses used were known.

Obviously different aurora videos may be sped up to different degrees (or may be in real time). As one who used to observe them regularly in Scotland (while studying Astronomy at University) where they're more frequent than most people realise, I can say that although the gross movement of the green curtains in that video are obviously sped up, occasionally some details in some auroras can be seen moving almost as quickly as in the opening segments. I agree that it would be useful if the degree of speed-up were more frequently mentioned in such videos. {The poster formerly known as 87.81.230.195} 5.66.247.129 (talk) 02:56, 10 June 2013 (UTC)

Resolved

Thank you. Bubba73 ^{You talkin' to me?} 02:32, 10 June 2013 (UTC)

Birds as pest control

Is it feasible to use insectivorous birds as a supplementary (not primary) method of broad-spectrum insect control? This source says no, but many wiki articles suggest otherwise (for example, the article about the sand martin suggests that it eats many harmful insects). So which of these is right? 24.23.196.85 (talk) 05:36, 10 June 2013 (UTC)

One can find many sources which show that people build houses for purple martins because they believe them to keep down insects, but this paper which reviews much of the literature indicates that mosquitoes are not one of the insects that it eats; mosquitoes being one of the most harmful insects. --Jayron32 05:40, 10 June 2013 (UTC)

Yes, this makes sense because mosquitoes mostly fly at night, and martins hunt only in daylight. But what about nightjars -- do they eat a lot of mosquitoes? 24.23.196.85 (talk) 05:54, 10 June 2013 (UTC)

And the armchair speculation continues... even published studies have similar issues. Bats eat an enormous amount of insects, but the endemic mosquito population in malaria zones is probably not gonna change anytime soon. Shadowjams (talk) 09:32, 10 June 2013 (UTC)

That martins eat lots of insects is undisputed. It is true that they don't eat many mosquitoes, but they they can generally suppress insect populations, including plant pest species. Also, the goal of control is not always eradication, often you just want to reach the economic threshold. So don't dismiss martins as pest control just because they don't eat mosquitoes. SemanticMantis (talk) 16:08, 10 June 2013 (UTC)

It really depends on what you mean by control, and how you classify "harmful insects." For the agricultural side of things, here's some refs: "Sustainable pest regulation in agricultural landscapes: a review on landscape composition, biodiversity and natural pest control" [1], which says "In 74% ... of the studies reviewed ... natural enemy populations were higher and pest pressure lower in complex landscapes versus simple landscapes." (Natural enemy includes insectivorous birds) There's also a review article on the topic, "Past and Current Attempts to Evaluate the Role of Birds as Predators of Insect Pests in Temperate Agriculture" [2]. The former article is basically about how insectivorous birds can reduce pest loads in agriculture. However, rather than trying to put birds in fields directly, the strategy is to attract them by having structurally and biologically diverse landscapes. The birds will naturally come and eat insects if the habitat is right. If you want to do more searching on the idea, this is known in academia as integrated pest management. So - though it is tough to get specific numbers to quantify exactly how effective they are, there is plenty of evidence that insectivorous birds can help manage pests. SemanticMantis (talk) 15:56, 10 June 2013 (UTC)

• Guinea fowl are ground birds bought specifically for pest control, see google and University of Connecticut. μηδείς (talk) 18:25, 10 June 2013 (UTC)

Geese are quite popular for pest control in vinyards and orchards.[3][4][5] -- Roger (Dodger67) (talk) 20:22, 10 June 2013 (UTC)

Geese shit constantly from their high-fiber diets and are considered a major pest of lawns in the U.S. Northeast Canada_goose#Relationship_with_humans. μηδείς (talk) 00:41, 11 June 2013 (UTC)

And they cause plane crashes... 24.23.196.85 (talk) 00:45, 12 June 2013 (UTC)

Mosquitos simply do not make much of a meal. I suspect it's just not worth the effort to catch them, except passivley, like a spider's web. They would be just as hard if not harder catch then many other insects and a single moth, beetle or fly would weigh as much as dozens of mosquitos. Vespine (talk) 00:39, 11 June 2013 (UTC)

Which is why I asked if whippoorwills catch them on a regular basis -- from what I know about whippoorwills, they can fly through a swarm of mosquitos (or other bugs) with open mouth and just suck them in, like a whale swallowing krill. That would be a fairly efficient way to catch mosquitos, which would allow whippoorwills to at least supplement their menu with mosquitos. (Not to mention that whippoorwills are nocturnal birds, so they hunt precisely when mosquitos are active.) 24.23.196.85 (talk) 00:45, 12 June 2013 (UTC)

Greater blue-ringed octopus size

How big is the greater blue-ringed octopus? The article doesn't address the size, so I decided to find it via Google and add it; I've found several pages with size information, such as 1, 2, and 3, but none of them appear to be reliable sources. I don't know where to find reliable sources on cephalapods. Nyttend (talk) 15:28, 10 June 2013 (UTC)

According to Aquarium of the Pacific (Online Learning Center Species Print Sheet), "the body of H. lunulata is about the size of a grape seed at birth and that of a golf ball at maturity. Adults are usually less than 5 cm (1.97 in) long with arms to 7 cm (2.8 in) when extended. They weigh 10-100 g, avg. 55 g (0.35-3.5 oz, avg. 1.9 oz). Females are slightly larger than males". Brandmeister^talk 16:00, 10 June 2013 (UTC)

The Australian Museum website at http://www.australianmuseum.net.au/ may be of assistance. --220 of ^Borg 18:10, 10 June 2013 (UTC)

Yep ! "Size range: Body to 5cm, arms to 10cm." from above website at Southern-Blue-lined-Octopus-Hapalochaena-fasciata ---220 of ^Borg 18:14, 10 June 2013 (UTC)

Why Dewar flask cannot be considered a truly isolated system?

Since, according to isolated system, "truly isolated systems cannot exist in nature". 93.174.25.12 (talk) 15:49, 10 June 2013 (UTC)

Have you answered your own question here? — Preceding unsigned comment added by 217.158.236.14 (talk) 16:01, 10 June 2013 (UTC)

The Dewar flask is well-insulated, but not perfectly so. Even if it were sealed after filling so that it were entirely surrounded by vacuum, and kept in space where the inside would need no point of support, no mirror is perfectly reflective. Wnt (talk) 16:14, 10 June 2013 (UTC)

Yes, and no vacuum is perfect. SemanticMantis (talk) 18:02, 10 June 2013 (UTC)

Actually, I am a little unsure about that. You'd think that you could literally remove every single light isotope atom period from a container ... with enough skill. Now, true, I suppose that even if you make an evacuated container out of tungsten, there will be a chance of individual stray atoms in a vapor phase - is it possible though to somehow measure the container and prove that, for some moments, none are present? Wnt (talk) 06:49, 14 June 2013 (UTC)

It is often still possible to do measurements involving perfectly isolated systems, even though they don't exist. What you then use is that they exist in some ideal limit; you can do experiments in better and and better isolated systems and extrapolate the results to the ideal limit. Count Iblis (talk) 18:46, 10 June 2013 (UTC)

Dopamine chemistry

I've been working on our article on dopamine, and I can handle the biological aspects, but my weakness at chemistry is causing me difficulties. I'd be grateful if anybody can help me with these two questions:

• The solubility of dopamine is listed as 60g/100ml. Is it appropriate to describe that as "moderately soluble"? Would there be sources that tell whether there are factors that affect the solubility (pH, or example)? Is it possible to find out the solubility in substances other than water?

• When dopamine in solution is mixed with hydrochloric acid, it becomes protonated and forms a highly soluble hydrochloride salt. That means that dopamine is a base, right? Is it an organic base? Is there any way of finding out its alkalinity?

Thanks for any responses. Looie496 (talk) 17:06, 10 June 2013 (UTC)

Dopamine is a by definition of "that which reacts with acid", but also as usual for most amines. And this property causes there to be an effect of pH on solubility (also discussed in the section I linked). The key parameter to report would be the pKa value, and there is a chembox field for it. A solubility of 60g/mL in water at room temp is 50% more by mass than what NaCl does (but only a little over half compared to NaCl by moles).

I'm not sure what other properties you have in mind, but temperature always affects solubility, but that's not a notable detail for most chemicals (unless it's strongly altered at near physiologic conditions or during storage/transport to affect product formulation, for example). There may be other solubility data available (temperature or solvent); anyone can predict them computationally, but that would not meet WP:RS unless published/validated in the scientific literature. DMacks (talk) 17:25, 10 June 2013 (UTC)

Hmm. The literature says that dopamine is usually supplied as a hydrochloride salt because it is much more soluble than the unreacted form. I wonder whether that number actually refers to the hydrochloride salt? I'll see what I can find out -- anyway your information has already been very helpful, thanks. (Basically I want the article to contain everything that is important to large numbers of readers and supported by good sources.) Looie496 (talk) 17:36, 10 June 2013 (UTC)

If it's going to be administered orally, it doesn't make any difference, since your stomach acid will turn it into the hydrochloride salt anyways. --Jayron32 23:37, 10 June 2013 (UTC)

As far as I know the only direct medical use for dopamine is intravenous injection. It's useful for emergency treatment of heart failure or shock, especially in infants. Looie496 (talk) 04:48, 11 June 2013 (UTC)

Did he say anything about eating it? I don't know what would happen - I know dopamine solutions tend to be unstable (akin to melanin...) if you keep them at room temperature. Wnt (talk) 03:36, 11 June 2013 (UTC)

Turtles

What is the ideal sand porosity for sea turtle nesting? Does the ideal sand porosity vary between species? — Preceding unsigned comment added by 99.146.124.35 (talk) 18:53, 10 June 2013 (UTC)

This article:

• FOLEY, ALLEN M., SUE A. PECK, and GLENN R. HARMAN. "Effects Of Sand Characteristics And Inundation On The Hatching Success Of Loggerhead Sea Turtle (Caretta Caretta) Clutches On Low-Relief Mangrove Islands In Southwest Florida." Chelonian Conservation & Biology 5.1 (2006): 32-41. Academic Search Premier. Web. 10 June 2013.

states that "sand porosity [was] negatively related to sand water salinity," and that "hatching success decreased as inundations, sand water content, and sand water salinity increased" in clutches that were inundated by sea water, but in clutches that were not inundated sand water content and salinity were not related to hatching success. The mean sand porosity the study found at 47 nest sites was 42%, with a range of 30.2 to 60.1%.

This one:

• Yalçin-Ozdilek, Şükran, Hasan Göksel Ozdilek, and F. Sancar Ozaner. "Possible Influence Of Beach Sand Characteristics On Green Turtle Nesting Activity On Samandağ Beach, Turkey." Journal Of Coastal Research 23.6 (2007): 1379-1390. Science Full Text Select (H.W. Wilson). Web. 10 June 2013.

says "Green turtles are noted to prefer nesting in areas with uniform sand grain sorting. Good sand packing appears to prevent nesting of this species because of a number of reasons, such as porosity and specific yields."

I also found this article:

• Brock, Kelly A., Joshua S. Reece, and Llewellyn M. Ehrhart. "The Effects Of Artificial Beach Nourishment On Marine Turtles: Differences Between Loggerhead And Green Turtles." Restoration Ecology 17.2 (2009): 297-307. Academic Search Premier. Web. 10 June 2013.

It says "artificial beach nourishment projects modify ecosystem components," including porosity, but doesn't directly relate sand porosity to nesting success. All three articles are pretty high level (a little over my head, really) and all have their own lists of references that may provide additional information. If you can track them down online or at your library, they may be worth a look to you. --some jerk on the Internet (talk) 20:59, 10 June 2013 (UTC)

Does switching to a different diet require extra energy in humans?

When you cultivate bacteria like E.coli, and switch from one carbon source to the other, growth lags. This is because new proteins need to be synthesized to deal with the new carbon source. Does something similar happen in humans? For instance, recently I became a vegetarian. I felt a bit weak the first 3 days. After that I was fine. I wonder if my body had to make large changes to adapt to my diet.137.224.239.102 (talk) 19:54, 10 June 2013 (UTC)

Your gut flora will have changed. But I don't know the answer to your main question. Thincat (talk) 22:47, 10 June 2013 (UTC)

Things like the Atkins diet depend on changing one's metabolism and blood chemistry. Just changing from meat and plants to plants as the source of one's sugars, fats and amino acids in a normal balance shouldn't have any effect on a healthy person's body's metabolism, since it is much more complex than a bacterium's and is already digesting those things.

But we have absolutely no knowledge of your health concerns, actual diet, or metabolism. It's quite possible you may have a disorder, need or missing nutrient we don't know about, so you should seek professional medical advice. μηδείς (talk) 00:35, 11 June 2013 (UTC)

I'd say it differently: "The body's digestion process is less efficient for some time after switching to a new diet". This explains why many diets work, at first, but very few are successful in the long run. Once your body adjusts, you can get just as many calories out of a variety of sources. StuRat (talk) 02:13, 11 June 2013 (UTC)

I agree. I think in part (or even mostly) it is due to the gut flora not having had time to optimise towards efficiently fermenting undigested carbohydrates in the new food mix. Thincat (talk) 07:58, 11 June 2013 (UTC)

Of course if someone changes to a weight-loss diet they may be highly motivated to start with and so initially eat less and lose weight more rapidly. However, that is not what the original poster was asking about nor what any of the answers have been dealing with. Thincat (talk) 08:08, 11 June 2013 (UTC)

Thanks for the answers guys! This wasn't a medical question btw. Just interested. [OP on another PC] 137.224.252.10 (talk) 14:04, 11 June 2013 (UTC)

Heat storage

I believe more porous sands would hold less heat then less porous sands. Is this true? — Preceding unsigned comment added by 99.146.124.35 (talk) 20:05, 10 June 2013 (UTC)

Heat per mass? heat per volume? heat per surface area? Dauto (talk) 20:35, 10 June 2013 (UTC)

Besides, it's the fluids that count. Are you concerned with total thermal flow, or only thermal conductivity by the solid substrate? Nimur (talk) 20:47, 10 June 2013 (UTC)

It depends on what's in the pores. --Jayron32 23:27, 10 June 2013 (UTC)

Bufotenine - Medicinal Uses in China?

Extracts of toad venom, containing bufotenin and other bioactive compounds, have been used in some traditional medicines such as ch’an su (probably derived from Bufo gargarizans), which has been used medicinally for centuries in China according:

http://en.wikipedia.org/wiki/Bufotenin

but is NOT native to China so any suggestions on how that is possible? Sincere curiosity.

http://en.wikipedia.org/wiki/Colorado_River_toad

I came here after a search for the word Bufotenine which I came across in a novel I am reading:

"American Gods: The Tenth Anniversary Edition authored by Neil Gaiman.

On the Kindle, this word appears at location 927 but does not appear in the Kindle dictionary. A web search led me here.

Learning is my passion, a day without learning something new is a day wasted.

After reading the pages listed above I am now curious as to how this toad, which is native to a small portion of the US, could have been used for medicinal uses as stated centuries in China. Or

Also stated in the book is this: 'A character in the book is smoking synthetic toad-skins and inquires of the main character, Shadow, if he is aware that its possible to synthesize bufotenine now?'

True or author's fiction?

Thanks for your time, greatly appreciated. — Preceding unsigned comment added by Not1knowsme (talk • contribs) 20:07, 10 June 2013 (UTC)

You should read the article!  :) Seriously, it points to Asiatic toad, native to China. I should emphasize that it is important to distinguish between authentic traditional medicine and modern revivals with a different focus. (Just consider the difference between kava kava as pounded and extracted with water in the Pacific islands and its hazards when entrepreneurs put undesirable parts of the plant in a capsule to be swallowed because they have a high concentration of the "active ingredient"; or between native Americans who used tobacco to positively reinforce the rituals of their religion, and Westerners who seized on the dope and managed to kill themselves by the hundred million!) Wnt (talk) 00:40, 11 June 2013 (UTC)

citronella oil

Is citronella oil still usable and effective in burning torches if there is no yellow color to it?```` — Preceding unsigned comment added by 173.80.150.188 (talk) 21:06, 10 June 2013 (UTC)

Think it would help if you rephrased this. Citronella oil will, on flagration, produce sooty partials in the flame that iridesse at about 1,00 deg. C. I.e, Yellow. Try kerosene – its cheaper.--Aspro (talk) 22:19, 10 June 2013 (UTC)

But citronella oil smells a lot better, and also may have insect-repelling properties. 24.23.196.85 (talk) 23:25, 10 June 2013 (UTC)

I think the OP is asking about the color of the oil, not the flame. Citronella oil that I've seen for sale (and just double-checked with a quick google image search) usually has a yellow or amber color. I do not know if there are clear variants. I do think "effective" needs to be clarified. Effective at what? Just burning, or as an insect repellent as well? Citronella oil is commonly sold as a "tiki torch" fuel with the claim of it repelling insects, but our article only has information on it being used as a topical repellent. 209.131.76.183 (talk) 15:51, 11 June 2013 (UTC)

How spacecrafts estimate moon's and planet's internal structure

I thought once the spacecraft studies planet's and moon's surface they suppose to be able to tell what is inside a moon and planets. Do spacecraft not able to track all the information like how thick is the ice layers on gas giant's moons when trying to look at its interior? I thought once Galileo spacecraft went to Jupiter's four famous moons they have a special electric signals sends details to tell us what their moon's interior looks like. Then how spacecrafts measure how the celestial bodies interior looks like. Density? Chemical (Spectograph). When Cassini spacecraft went to Saturn do they use electric signal lighting to model what Titan have in interior, or they just build a variables to estimate what Titan might have inside. When Messenger went to Mercury did Messenger actually study its surface in detail?--69.233.254.115 (talk) 21:30, 10 June 2013 (UTC)

These interplanetary gizmos all employ variations of Remote sensing. --Aspro (talk) 22:55, 10 June 2013 (UTC)

Oh. And before anybody reminds me that the Huygens probe actually made 'physical' contact with the surface of Titan, let them tell me first, if the probe was able to transmit back, that it had landed on a vanilla, or a strawberry flavored crème brûlée. --Aspro (talk) 23:12, 10 June 2013 (UTC)

Per my favorite planetary science book, de Pater and Lissauer, geoscientists can use orbital parameters to determine moment of inertia and gravitational anomaly of a large celestial object. Then, they invert for a plausible geological internal substructure. This is why your usual model of a planetary interior is perfectly radially symmetric! In the book I linked (Planetary Sciences), an entire chapter is devoted to these techniques. Nimur (talk) 23:00, 10 June 2013 (UTC)