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Today in science explained by Tim F, a breaking study in Proceedings of the National Academy of Sciences.

[A]ll mammals above 3 kg in weight empty their bladders over nearly constant duration of 21 ± 13 s.

They went to a zoo and watched animals piss. It takes the same time because larger mammals have larger urethras, more help from gravity and less viscosity to slow down flow.

This has been another edition of science explained by Tim F.

***Update***

If you see an impossible headline in an original research journal that you want to see me [attempt to] explain with simple words and inappropriate analogies, feel free to email me. There is a non-zero chance that I might give it a try.






58 replies
  1. 1
    dmsilev says:

    “Nearly constant” with a standard deviation that’s 66% of the mean? One could equally well say the majority showed durations between 8 and 34 seconds, and that’s a pretty big variation for “nearly constant”. Now, granted, the size range of the animals is vastly greater than that, so OK.

    Also, I had to laugh at this sentence from the full paper: “We filmed the urination of 16 animals and obtained 28 videos of urination from YouTube.” Science!

  2. 2
    Shakezula says:

    No offense to the other writers here or other blogs, but this is my new favorite thing on this blog and a close second to Confused Cats Against Feminism, which is still the best thing on the internet.

    Would you be willing to tackle psych/soc. studies?

  3. 3
    dmsilev says:

    I will also note, in a somewhat more serious vein, this:
    “Fig. 1H shows the urination time for 32 animals across six orders of magnitude of body mass from 0.03 to 8,000 kg. Despite this wide range in mass, urination time remains constant, T = 21 ± 13 s (n = 32), for all animals heavier than 3 kg. This invariance is noteworthy, considering that an elephant’s bladder, at 18 L, is nearly 3,600 times larger in volume than a cat’s bladder at 5 mL. Using the method of least squares, we fit the data to a clear scaling law shown by the dashed line: T~ M^0.13”

    The interesting thing, to me, is the last sentence, that the variation is a power law (time proportional to a power of the mass). Power laws are ubiquitous in nature (Wiki), and generally are an indication of some underlying universal principle driving the variation.

  4. 4
    max says:

    It takes the same time because larger mammals have larger urethras, more help from gravity and less viscosity to slow down flow.

    Didn’t they have a study a few years ago claiming that all (male, I think) humans pee for the same length of time? I assume this is some kind of knock-on study.

    max
    [‘Otherwise, what dmsilev said.’]

  5. 5

    Here’s one:

    The Dissemination of Mass in the United States: Results and Implications of Recent BIPM Calibrations of US National Prototype Kilograms

  6. 6
    Shortstop says:

    Much-needed laugh. Thanks.

  7. 7
    HelloRochester says:

    PNAS: The journal you publish in if you either have grey hairs on your balls or are owed a favor by a scientist with grey hairs on his balls.

  8. 8
    Blanche says:

    Here is one I find hard to believe:

    Children’s drawings indicate later intelligence, study shows
    http://www.sciencedaily.com/re.....204114.htm

  9. 9
    dmsilev says:

    @HelloRochester: That’s actually not the case for most of the articles published there now. The bulk of the research reports go through a normal peer-review referring process, and typically you don’t even get to choose which Academy member serves as the editor for your manuscript (you suggest a few candidates, but the journal can and will pick someone else if they feel like it).

    (I have a couple of papers published there, and one that’s currently wending its way through the review process)

  10. 10
    maurinsky says:

    My daughter was at the Beardsley Zoo in Bridgeport once when a tiger decided to piss all over the people outside his cage.

    @Blanche, when I was 1 1/2, I drew a picture of my family which looked like some of those more abstract 4 year old drawings, and I can tell you that I am only slightly above average intelligence.

  11. 11
    dmsilev says:

    @Southern Beale: Ah, the fundamental unit of mass. There’s a long story there. Basically, once upon a time, all of our units of measure (length, time, mass, etc.) were based on physical artifacts. There was a standard meter which served as the reference for all other meters (and the foot was a certain fraction of a standard meter), a standard kilogram kept in a vault in Paris, etc. Over the years, we got better and better at measuring natural phenomena, and one by one, we’ve replaced the physical artifacts with fundamental natural constants. The second is defined in terms of the period of a particular oscillation associated with a specific type of atom. We define the meter by measuring the speed of light and from our definition of the second. And so forth.

    There’s now only one physical artifact left: the standard kilogram. And what concerns the authors of that paper is how do you take the standard kilogram in Paris and duplicate it with sufficient precision that the US’s copy of the standard is _the same_ as the original reference. And that it _stays_ the same over the years.

  12. 12
    soonergrunt says:

    And now I can die.

  13. 13
    RSA says:

    Funny. Friends and I were talking about this last year when it showed up on arvix.

  14. 14
    Amir Khalid says:

    @dmsilev:
    Why does the mass of the standard Kg creep upward over time?

  15. 15
    MattF says:

    @dmsilev: There’s actually a somewhat… odd story that was going around a couple of years ago– try googling ‘standard kilogram losing mass.’

  16. 16
    Gin & Tonic says:

    So by that meaning of “nearly constant”, 5k run times from 14 min to 58 min are pretty much the same. Kind of stretches that “nearly constant”, wouldn’t you say?

  17. 17
    Gin & Tonic says:

    @Amir Khalid: Dust.

  18. 18
    Mnemosyne says:

    I’m assuming this study will be eligible for an IgNobel?

  19. 19
    MattF says:

    @MattF: I should probably note that at least part of the oddity is that ‘standard kilogram losing mass’ is impossible, by definition.

  20. 20
    dmsilev says:

    @Amir Khalid: It shouldn’t, but that’s the problem with using physical artifacts as standards. You do your best to keep it in a controlled environment and prevent spurious stuff from sticking to the mass and so forth, but that’s not perfect.

    It’s not really my field, but my understanding is that the state of the art is almost good enough to switch away from the reference kg and instead go to mass units defined by “x number of carbon-12 atoms” (or possibly silicon instead). You have to be very good at counting atoms for that to work…

  21. 21

    PNAS paper, much smart, so science
    @MattF: Shouldn’t it be standard American gaining mass.

  22. 22
    Face says:

    Wait….+/- 13 seconds on a 24 sec mean? That’s an ENORMOUS variation.

    Callin’ shenanigans.

  23. 23
    Scamp Dog says:

    @dmsilev: I wonder if that 0.13 exponent is an approximation of 1/8, nature favoring whole number exponents (or roots in this case) in many contexts.

  24. 24
    Jerzy Russian says:

    @HelloRochester:

    PNAS: The journal you publish in if you either have grey hairs on your balls or are owed a favor by a scientist with grey hairs on his balls.

    They do a ball check? What if you don’t have balls?

  25. 25

    @dmsilev:

    OK if you say so.

    I thought a kilogram in Paris would be a kilogram in Nashville. But I guess not? Oh my God. All this time ….

  26. 26
    Missouri Buckeye says:

    This sounds like a sure bet to win a Ig Nobel Prize.

  27. 27
    Roger Moore says:

    @Southern Beale:
    Layman’s summary: using a physical artifact as an international standard sucks.

  28. 28
    Roger Moore says:

    @dmsilev:
    They really ought to use gold instead of carbon or silicon. Gold has two big advantages:

    1) It is essentially inert, so you don’t have to worry about the mass changing from atmospheric oxidation

    2) It has a single naturally occurring isotope, so you don’t have to worry about the isotopic composition as part of your calculations.

  29. 29
    Scuffletuffle says:

    WHOOSH! (The sound of this entire thread and its comments going right over my head.)

  30. 30
    dmsilev says:

    @Roger Moore: My understanding is that a key requirement is being able to make a perfect single-crystal sphere. Growing large single crystals of silicon is something we know how to do very well; the semiconductor industry has spent umpteen billion dollars developing that particular skill-set.

  31. 31
    Cervantes says:

    @HelloRochester: You seem resentful.

  32. 32
    Cervantes says:

    @dmsilev:

    And what concerns the authors of that paper is how do you take the standard kilogram in Paris and duplicate it with sufficient precision that the US’s copy of the standard is _the same_ as the original reference. And that it _stays_ the same over the years.

    Not only the US’s platinum copy of the platinum original in France but also the US’s stainless-steel copies of its platinum copy.

  33. 33
    Cervantes says:

    @Southern Beale: Do you have a specific question about it?

    (That isn’t already answered above, I mean.)

  34. 34
    HelloRochester says:

    It’s not resentment it’s just that PNAS has historically been a place where a paper lands when it can’t land in a better journal and you know a guy in the Academy who will sherpa the manuscript past the initial gatekeepers. If they’ve changed that policy, then hurray. Not sure that reputation is gone within science. That being said, peer review is a hot mess and the reform process is gaining momentum. I’m looking forward to the day where the style of scientific papers is radically reformed as well. The standard format is stale and unnecessary in the post-paper world.

  35. 35
    HelloRochester says:

    It’s not resentment it’s just that PNAS has historically been a place where a paper lands when it can’t land in a better journal and you know a guy in the Academy who will sherpa the manuscript past the initial gatekeepers. If they’ve changed that policy, then hurray. Not sure that reputation is gone within science. That being said, peer review is a hot mess and the reform process is gaining momentum. I’m looking forward to the day where the style of scientific papers is radically reformed as well. The standard format is stale and unnecessary in the post-paper world.

  36. 36
    Cervantes says:

    @HelloRochester: Good points — a long discussion, not limited to PNAS by any means.

    About this in particular:

    I’m looking forward to the day where the style of scientific papers is radically reformed as well. The standard format is stale and unnecessary in the post-paper world.

    Care to elaborate? (Thanks.)

  37. 37
    Roger Moore says:

    @Southern Beale:

    I thought a kilogram in Paris would be a kilogram in Nashville.

    In theory, yes. The problem is that the only way we have yet come up with to define a kilogram is to have an actual chunk of metal that’s defined as The Kilogram. Because there’s only one absolute standard, there are practical problems. Ordinary people can’t bring their stuff all the way to Paris to compare against the absolute reference, and even if they could there are worries about physical changes to the reference, either from accumulation of dirt making it heavier or wear making it lighter, that get worse the more you take it out and use it.

    The practical solution is to make secondary reference kilograms that are distributed to other countries. The ones in the USA are kept by NIST, and in practice they’re used to make and calibrate tertiary standards in much the same way the primary reference kilogram is used to make and calibrate them. NIST may wind up using additional levels of standard, with the tertiary standards being used to make quaternary standards that are sold to manufacturers, who use them to calibrate their own products that are eventually distributed to end users. And that’s for really demanding applications. Your household scale may be separated from the standard in Paris by six or eight layers of replication.

    Because the kilograms are physical objects, the only way to make sure that they’re still good is to physically transport them back to Paris and compare them to The Kilogram. What happens if all the secondary standards appear to be gaining weight relative to the primary standard? Is that a sign that the secondary standards are used more and pick up more dust and dirt, or is it a sign that the primary is losing weight? It’s an essentially unsolvable problem as long as the only standard is a physical object.

  38. 38
    dmsilev says:

    @HelloRochester: The articles in PNAS are tagged depending on what review track they followed. If the header of the article says “contributed by …”, that means that one of the authors is an Academy member and the paper didn’t really get refereed. If the header says “Pre-arranged editor”, that means that the authors called in a favor from an Academy member. Those articles do go through blind peer review, but the person picking the reviewers is a friend of at least one of the authors… Finally, if there is no such notation, the editor was chosen by the journal staff, and the review process is more or less comparable to other journals. The last of these categories makes up the majority of articles. Basically, the first two categories (and especially the first) should cause you to be a tad suspicious of the paper, but the normal submission track is run-of-the-mill peer review.

    Edit: Apparently the “Pre-arranged Editor” track is getting axed in the next couple of months. So, two tracks, one which should be taken with a grain of salt and one which is normal review.

  39. 39
    Bill Arnold says:

    Only vaguely related, my current favorite paper figure, Agency/Experience. (Prune url for link to paper. Might need an account to read anything other than the abstract.)

  40. 40
    I'mNotSureWhoIWantToBeYet says:

    @dmsilev: Yup.

    Redefining the Kilo from 2007.

    Silicon was chosen because it can be grown into large single crystals. The purest 28Si was produced in Russia’s Nuclear Ministry in St Petersburg, by centrifugation of SiF4, before conversion into SiH4, and finally silicon itself, at the Institute for Ultrapure Materials in Nishni-novgorod.

    The Institute of Crystal Growth in Berlin, Germany, then repeatedly melted and solidified this material over six months to remove contaminants. The resulting 5kg crystal has now been sent to the Australian Centre for Precision Optics (ACPO) at the CSIRO in Sydney, Australia, the only lab in the world that can shape the crystal into two almost perfectly round spheres.

    Making each sphere is a 12-week process. ‘We make the spheres by grinding the silicon with progressively finer abrasive powders,’ said Katie Green, an optical engineer at ACPO. The best spheres the ACPO team have produced are perfectly spherical to within 35 nm.

    Once the spheres are finished, around the end of 2007, the sphere’s volume and mass will be measured, along with the volume that each silicon atom takes up (measured by x-ray). Crucial mass spectrometry experiments will measure the levels of 29Si and 30Si in the spheres, which make up 0.006 per cent of the material. Previous efforts to define the Avogadro number using spheres of natural silicon, which includes around 5 per cent 29Si and 3 per cent 30Si, failed to attain the required accuracy, primarily due to limitations in the mass spectrometry experiments, says Robinson. This uncertainty decreases as the ratio of the other isotopes falls, hence the use of virtually pure 28Si.

    It’s still not good enough to be the de-jure standard, last I checked. More here.

    Cheers,
    Scott.

  41. 41
    Roger Moore says:

    @dmsilev:
    What I’m wondering is what the key problem is. As I understand it, the idea of making a sphere with a specific number of atoms in it has several challenges:

    1) Physically making a sphere as perfect (shape and purity) as possible
    2) Measuring its size so you know its volume exactly
    3) Measuring the lattice spacing so you can calculate how many atoms would fit in the volume
    4) Measuring the isotopic masses of the different isotopic species present
    5) Measuring the isotopic ratios of the different isotopic species present

    Each one of these things will have some kind of error bar that will contribute to imprecision in the final measurement. I know from my background in mass spec that 4) can be done with very high precision (low ppb or high ppt range), and I’m willing to accept that 2) is unlikely to be the biggest problem. I just don’t know enough about the rest of the issues involved to know the relative difficulties of 1), 3), and 5) and how 1) and 3) differ between silicon and gold. What I do know is that 5) can be quite challenging when necessary, but that it’s completely unnecessary for gold because it has only a single isotope. That makes me lean toward gold as the solution, and I know that other people have thought about going in that direction, too.

  42. 42
    Julia Grey says:

    @Roger Moore: But pure gold is (relatively) SOFT, hence more vulnerable to abrasion and distortion when in use, right?

    And on the Experience/Agency chart, ha ha, but what’s a PVS man?

  43. 43
    dmsilev says:

    @Bill Arnold: Oh God, that graph. I’ve had a copy of that on my office door for the last few years.

  44. 44
    MattF says:

    @Roger Moore: Since gold is metallic, it’s really (to a first approximation) just a pile of atoms bound together in an isotropic soup of electrons. Silicon, in contrast, has directional covalent bonding. Very different sorts of critters from a solid-state point of view, and I’d imagine there’s much less variance in Si-Si distances compared to Au-Au distances.

  45. 45

    @Cervantes:

    Nah you know, math ain’t my thing. And I guess that applies to weights and measures, too.

  46. 46
    dmsilev says:

    My favorite entry on the preprint server is this:
    “Difficult Sudoku Puzzles Created by Replica Exchange Monte Carlo Method”

    The abstract originally read “We adopt the replica exchange Monte Carlo method with simultaneous temperature adjustments to search lower energy states efficiently, and we succeed in creating a puzzle which is the world hardest ever created in our definition, to our best knowledge.” but a day later, an additional bit was added: “the created puzzle can be solved easily by hand. Our definition of the difficulty is inappropriate.”

    Never mind…

    (I saw the abstract in its original form, and forwarded to some folks. Later that day, I was told that a friend of a friend solved the purported worlds-hardest-Sudoku in about 20 minutes. He was probably not alone, and the author of that paper probably got a whole bunch of snarky responses from around the world. Hey, at least people read his paper…)

  47. 47
    Comrade Mary says:

    Alternate title: last October on Quirks and Quarks! Canadians listening to the CBC while doing Saturday chores got an, um, earful about this field last fall.

    Mammal Micturition Reel. May not be safe for all workplaces. Rule 34 may apply, especially with the slo-mo effects and lighting.

  48. 48
    askew says:

    @Blanche:

    Well that explains everything. Damn it.

  49. 49
    Uncle Cosmo says:

    So you’re saying that PNAS has now (d)evolved into a pee-reviewed urinal? (As the French might put it, wee wee…)

  50. 50
    Roger Moore says:

    @MattF:

    Since gold is metallic, it’s really (to a first approximation) just a pile of atoms bound together in an isotropic soup of electrons.

    Metals do form crystals, though. It’s hard to grow large single crystals of metal, but it can be done; some applications requiring ultra-high strength (IIRC, turbine blades for airplane engines are an example) involve metal single crystals.

  51. 51
    dmsilev says:

    @Roger Moore: See, this is something I do know a bit about since I do enough X-ray scattering work to care about single crystals. A bulk single crystal of a metal is hard to grow. That’s especially true for something as ductile as gold; the energetic cost of a grain boundary or a dislocation fault is pretty small, so trying to anneal out imperfections is very very tedious. Less ductile materials, such as silicon, are easier to grow fault-free crystals. Not _easy_, but easier.

  52. 52
    Bill Arnold says:

    @Julia Grey:

    And on the Experience/Agency chart, ha ha, but what’s a PVS man?

    From the paper: “man in a persistent vegetative state”.

  53. 53
    Cervantes says:

    @Julia Grey: Persistent Vegetative State.

  54. 54
    Roger Moore says:

    @dmsilev:

    Less ductile materials, such as silicon, are easier to grow fault-free crystals. Not _easy_, but easier.

    Sure, but purifying ultra-high isotopic purity 28Si is obviously no picnic, either. No matter how you try to solve this problem, you’re going to encounter something god awful difficult. If it were well within our technological capabilities to make a better standard than the current one, we would have done it already. That’s generally true of any ultra-high precision endeavor.

  55. 55
    henqiguai says:

    @Amir Khalid (14):

    Why does the mass of the standard Kg creep upward over time?

    Because, what with global warming and the general overall increase of suckitude on this here planet, the Earth is beginning to suck even harder.

    What, you thought ‘gravity’ was all mystically difficult and stuff?

  56. 56
    John M. Burt says:

    @Uncle Cosmo: Your comment reminds me when my father, displeased to find that the majestic bathtub-sized Edwardian urinals in the men’s room at his workplace had been replaced with conventional little modern ones, wrote a memo asking that any future changes in the restrooms be submitted “to a jury of peers”.

  57. 57
    bruceJ says:

    It should be submitted to the ‘Annals of Improbable Research’ for consideration of next year’s Ig-Nobels

  58. 58
    Aaron Evan Baker says:

    I’m sure the question we’re all asking ourselves is: why do larger mammals have less viscosity?

Comments are closed.