Posts Tagged physics

Would you like something scanned with an electron microscope? Aimee Whitcroft Feb 22

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Of course you would!  Who wouldn’t?

SEM pollen

And have it you can.  As I came into the work this morning, blearily clearing emails as I attempted to mainline some caffeine, I came upon an email most arresting.

From an American company, ASPEX, it said that the company in question had a bit of an offer going at the moment: anyone who sent them a sample could have it photographed, for free, using a scanning electron microscope* (SEM).  The campaign, entitled Send Us Your Sample, takes your sample, makes stunning pictures using said sample, and posts them online for the whole world to see.  And marvel at.

And they’ll send you an email as well, just so you know it’s up.

Now, for those of us in New Zealand, I’d suggest being a little careful in choosing your sample – I have a sneaking suspicion that anything plant/animal-related might get stopped.  For obvious reasons. Luckily, biological stuff isn’t the only thing that looks brilliant under SEM: just about anything does.

Extra: boring anecdote about personal use of SEM

Sadly, I have lost the images I took during my degree’s third year.  Well, I haven’t lost them, but they’re in a book (probably) in Dubai.  Probably.  Anyway, it was great good fun to play with.  We were looking at actinomycetes, and in particular, were hoping to to find a novel antitubercular one.  We didn’t.

For the uninitiated, actinomycetes are found in soils, generally floating about, and on your bread when it goes a little postal.  That blue fluffy mould stuff?  That’s actually a type of bacteria:  the actinomyctes.  They come in a range of different flavours, though, and I had great fun watching the wars that broke out between competing groups on my petri dishes.  I think my favourites were the black fluffy colonies which hung out, alone, at the fringe of the petri dish.  Apparently, goth-like behaviour isn’t limited to human beings…

And as for the antitubercular bit?  Well, actinomycetes are most famous for their ability to produce antibiotics.  Like penicillin (that blue bread mould again).  And antibiotic-resistant tuberculosis is a major issue in Africa.  Hence looking for a new one.

Anyway, at the end of it all we needed to take pictures of our chosen actinomycete, with an SEM.  This was quite an interesting challenge, as we were trying to take nice clear pictures of the tiiiiiiiny filaments which make up the structure thereof.  The only problem being, that focusing too intently on a filament would destroy it – they’re actually fragile enough that a beam of electrons would destroy them!  Fun stuff.

* If you’d like to see what  cool machines look like in real life, have a look at some of ASPEX’s Scanning Electron Microscope range.

Stunning science imagery Pt I Aimee Whitcroft Feb 03

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Presents for your visual systems today… And we’ll be presenting two different people who’re merging science and visuals in new, and quite effective, ways.

xkcd: Fourier

xkcd: Fourier

I know I have a previous post somewhere (probably on my old blog) about engineering photos as well, but I thought I’d start afresh.

So, first up (because I saw it first), is this fantastic imagery, generated by acoustics engineer Mark Fischer (article here).

Fourier Transform (FT) maths is normally used to analyse sound.  It has its limitations, however: it doesn’t handle more complex sounds very well, often turning elements into noise.

And a perfect example of these kind of complex sounds are the calls of whales and dolphins.  And birds.  So Fischer has begun using another method: wavelets.  This is great – not only does it give a far more accurate and detailed map of the sounds/elements in the calls, but the pictures are perdy.  Seriously.  So perdy, in fact, that he’s able to sell them as art.

Hooray for interdisciplinarianism.

Up next is this.  Again, one of those almost ‘duh’ moments, except you have to be a mathematician, a photograher, and a little bit on the artsy side to have the thought.

Still, it works.  Nikki Graziano overlays graphs and their corresponsing questions onto photographs she’s taken which illustrate the equation/graph in question.  Of course, the cool thing about being a mathematician is that she doesn’t need to draw the graph and then prowl the streets looking for an analogous image – instead, she’s able to take photos and then fit the maths to them.

Interesting stuff.  I continue to be unimpressed that I’m not one of Nature’s mathematicians…

If I was a running shoe manufacturer, I would be worried… Aimee Whitcroft Jan 28

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This is brilliant.  I’ve heard intimations of it on various websites for the last few months, but it’s always good to see a published paper backing it up.

running shoes

In short, it says that running shoes are not actually necessary for runners.  In fact, they may do more to cause damage than to protect.

So, the paper, published in Nature, says something along the following lines:

Man has evolved as a creature capable of running.  For long distances, on often very hard (and by that I mean the opposite of squishy) terrain.  If you don’t believe me, simply look at the runners in, well, large parts of Africa.

People running barefoot generally land one of two ways – either on the front/balls of their feet, or else using a ‘mid-foot strike’ in which both ball and heel land simultaneously.  This allows the complex feat of structural engineering that is the human body to absorb most of the shock of this impact – the moment when, apparently, running can cause the most injury.

However, running shoes change the gait of a runner substantially.  By lifting and cushioning the heel, they elongate a runner’s stride, meaning that the impact of striking is the ground is borne by the runner’s heel. and then ricochets upward.  This, in turn, leads to a huge amount of jarring – some 1.5-3 times the weight of the runner, much of which happens to the lower leg.  This could help account for the impact-related injuries which are experienced by many runners these days, including tibial stress fractures and plantar fasciitis.

(Also, the arches of one’s feet, whose primary purpose is shock absorption, apparently flatten over time.  Everyone who wears heels often will be familiar with this problem.)

In order to come to this determination, the researchers looked at three primary groups of people – those who have always undertaken endurance running using athletic footwear (1), those who grew up running either barefoot or minimally shod but now use running shoes (2), and those who grew up using running shoes but now run barefoot or minimally shod (3).   They also compared two other groups of people – those who have never worn running shoes (4), and those who have grown up habitually wearing them (5).

What they found was this:

Groups 1 and 5 (the habitually heavily shod, as it were) generally hit the ground with their heels, both when running with and without shoes.

Groups 2 and 4 (the originally unshod) generally landed on the balls of their feet in both situations, and occasionally used mid-foot strikes (when shod in group 2, and unshod in group 4)…

barefoot

Credit: Benton et. al.*

“This image compares two Kenyan runners from our study at the moment just prior to foot strike plus representative force traces below. The subject on the left has been shod most of his life and lands on his heel (a rear-foot strike)l, causing an impact transient: a rapid, large collisional force within a few milliseconds of impact (not unlike being hit on the heel with a hammer with a force several times one’s body weight). The subject on the right has never worn shoes and lands on outer the ball of her foot before bringing down the heel (a fore-foot strike). This kind of landing is comfortable without shoes because it avoids any collision. The paper explains why forefoot and some mid-foot strikes avoid collision forces at impact.“

The upshot of all of this, after looking at all the maths and stuff, is this: your body has been designed, through the millenia, to run either barefoot or with just enough of a sole to protect your feet from the glass shards and goodness-knows-what-else that is such a feature of the modern urban landscape.  Wearing running shoes could, in fact, lead to stress injuries.

A caveat, however: for those of who count yourselves as being amongst the habitually-shod, don’t simply throw your shoes away and begin your new, natural regime immediately – you will need some time for your body and gait to readjust to this new (yet very old) way of doing things.  As with all sports, take it slowly.

And, of course, the money you were saving for that very expensive pair of [insert name here]-branded shoes can now be used for something else.  Like sending me a real cocktail, across teh interweb, to say thanks.

For more details, I’d suggest having a look at the paper.  If nothing else, it has plenty of pictures of differently flexed feet and ankles, and maths, for those who’re into that kind of thing…

Reference:

* Lieberman, D., Venkadesan, M., Werbel, W., Daoud, A., D’Andrea, S., Davis, I., Mang’Eni, R., & Pitsiladis, Y. (2010). Foot strike patterns and collision forces in habitually barefoot versus shod runners Nature, 463 (7280), 531-535 DOI: 10.1038/nature08723

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Stunning visions of Mars Aimee Whitcroft Jan 26

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Humanity is now the proud owner of some 13,000 photos of Mars taken by NASA’s Mars Reconnaissance Orbiter.

HiRise polar capMonitoring Seasonal Albedo Patterns on South Polar Residual Cap (ESP_014405_0945)
Credit: NASA/JPL/University of Arizona

The photos were taken by the most powerful camera of any on NASA’s spacecraft – the aptly (if dryly) named High Resolution Imaging Science Experiment (HiRISE).  The HiRISE site not only lets you amble through the collection, but also offers wallpapers (for the particularly geeky amongst us) and gives some great detail about each photo, including exactly where (as hosted, amusingly, by Google Maps), and what the local time was…

Of course, for those not as interested in the thought of hours spent wandering the archives, have a look at Wired’s ‘best of’ to see some of the strangest and most beautiful.

And, best of all, NASA wants to hear what you, the public, would like photographed next…

On the matter of time, and how the past crystallises out of the future Aimee Whitcroft Jan 20

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Yes, you read the title correctly.

u block sml

In a fascinating paper written by George Ellis, of me ol’ alma mater the University of Cape Town and Tony Rothman, from Princeton University in New Jersey, they posit that the place where this crystallisation occurs is, interestingly, the present. Not as in gift (although the present is a gift, yes), but as in the now.  This moment. No, this one. Kinda (but on to that later).

But wait – this sounds a little bit like that whole ‘yes, time technically has no meaning in relative physics, but try saying that to the real world’ issue.  Or maybe that’s just me.

Apparently, cosmologists can, being the amazingly abstract people they are, think of the universe as a sort of block in which space and time are merged.  A static block in which, as the paper says:

“…Time does not ‘roll on’ in this picture. All past and future times are equally present, and the present ‘now’ is just one of an infinite number.”

Confused so far?  Excellent, so was I.  But wait, dear readers, there is more.

Up until now, this blockheaded (sorry) approach hasn’t yielded much of use, but now!  Ah! Something useful – or at least very interesting, which in this area is enough, I think – has come of it.

Our two eminent scientists have developed a new sort of block universe, one into which they’ve introduced the mind-shattering madness that is quantum mechanics.   That wonderful state in which things can be in two places at once, or pop in and out of existence, or be connected across vast distances in such a way that what affects one, affects the other, instantly.  That state.  And they’ve found something interesting.

Firstly, it tends to make the block rather less static. Time does have significance now.  And when one does this, it seems that the future is driven by quantum, and the past by relativity, with the present sitting, as expected, inbetween. For some reason, I keep having in my mind the potentiality of a good or bad cup of coffee, the present experience of a mediocre cup of coffee, and the dried grounds (wormfood) thereafter as my mental image of it.

crystallising block universeThe third graph in the paper, the block universes here take into account quantum mechanics, and show that small pockets of potentiality* can remain even when most of it has stabilised into the present (the wavy lines).  In this way, time acts something like a mixture which is crystallising – the process isn’t entirely uniform.

They also propose that this model may offer a solution for the unidirectional nature of time as we experience it – often called the ‘arrow of time’.  Apparently, it’s because the future does not, in actual fact, really exist yet (yes, yes, I know, but still)…

“One can be influenced at the present time from many causes lying in our past, as they have already taken place and their influence can thereafter be felt.  One cannot be influenced by causes coming from the future, for they have not yet come into being.”

The arxiv blog is of the opinion that the model needs a bit more work (and, of course, some testable predictions would also be super) – I’m simply of the opinion that it’s a really fun idea.

And, as usual, I’m extremely grateful to the arxiv blog for their immensely useful cribnotes.

Finally…

I contacted George Ellis in early December about the paper, and here’s the quotation he kindly provided for me.  Let’s hope that the above explanation makes this a little easier to understand :) Thanks, Prof Ellis!

“Our paper looks at the idea that, contrary to what many physicists claim,  time really matters: time is not an illusion, things really do take place! But in looking at this, one has to fully take into account `quantum weirdness’ as evidenced by many experiments, and in particular by Wheeler’s delayed choice experiments.

“This leads us to the idea of a Crystallizing Block Universe: a space time which `grows’ as time evolves, but does so in such a way that one can still to a small degree influence the `past’, as in those quantum experiments.  Thus spacetime is like a Crystallizing material, where the transition from the uncertainty of the future to the certainty of the past (Quantum weirdness changes to classical certainty) takes place almost everywhere at a time we can call “the present’, but with small remnants of uncertainty remaining that crystallize out later.”

*Basically, the process isn’t completely uniform or simultaneous – apparently, say the authors:

“Quantum physics appears to allow some degree of influence of the present on the past, as indicated by such effects as Wheeler’s delayed choice experiments and Scully’s quantum eraser.”

Nano ho-ho Aimee Whitcroft Dec 15

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In the spirit of Christmas, I’d like to share with you all the world’s smallest snowman.

(Click on image for link to site)

Credit: NPL site
The snowman was developed by the UK’s National Physical Laboratory, and is a marvel of festivity-inspired nano-jollity.

According to the website, it’s 10 µm across, which equates to roughly 1/5th the width of a human hair.

It wasn’t made out of snowballs, of course, as these on average measure about half an inch, and we have yet to develop the ability to do the whole ‘Honey, I shrunk the snowflake’ thing.

Instead, it was made out of two tiny little tin balls. hilariously, they’re normally used to correct microscope astigmatism, which brings to mind wonderful images of a microscope with glasses, peering at the objects/tissues it needs to focus on.

I’m looking forward to tiny Christmas trees with even tinier tinsel. Of course, a treetop angel on this scale might also bring whole new answers to the classic question involving angels and the heads of a pin…

The LHC’s first collisions Aimee Whitcroft Nov 25

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Woohoo! I couldn’t, personally, be more thrilled.


No doubt, people who actually understand properly the physics and true awesomeness behind the LHC couldn’t be more thrilled either. Even more so than I.

Because, * fanfare *, the first collisions in the new, better-than-broken, up-and-running, ghost-in-the-machine lacking LHC have been observed!

A brief history lesson – the LHC, or Large Hadron Collider, is a truly gobsmacking feat of engineering which has taken a decade to build, billions of euros, and, no doubt, the sanity (or at least youth) of a number of engineers who’ve had to fight various problems, including errant baguette-bearing birds, to finally get it up and running. Properly.

And why has this wonderfully photogenic machine been built? Why, to find new particles! Amongst other things, of course. Of particular interest is the possibility that our scientists may be able to spot the elusive Higgs boson. (I have a fantastic image in my head of scientists in khaki, with binoculars, and a David Attenborough voice-over). The Higgs boson, or ‘god particle’, has thus far only been theorised, but it’s thought that it could be what gives everything in the universe mass.

Basically, it works like this (there’s a better explanation here):

The Higgs boson (or particle) carries the Higgs field, which imparts mass to objects as they move through the field, kinda like this…

People evenly distributed in a room, akin to the Higgs field (CERN)

Then Thatcher (yes, yes, I know!) enters the room, people gather, mass increases (CERN)

Of course, the LHC has also lead to howls and terrors from various quarters about its potentially causing the end of the world, or a huge black hole, or something. Amusingly, some physicists even suggested that it (well, the universe) could be sabotaging itself from the future.

But I digress. The news here is that the first collisions have been observed, and they look like this!

The green lines denote changed particles (following the collision), which are, apparently, generally pions (not peons, although those can also be unstable during changing circumstances).

[Pions] are unstable particles consisting of an up quark and an anti-down (or an anti-up and a down). Though they are unstable, they live long enough to nearly always leave tracks in the detector.

Then, the yellow bits denote the silicon strip detectors responsible for recording our particles

After that, it all gets quite technical. A far more knowledgeable account of it, and the source of the quote above, can be found here (which, by the way, is a great blog).

Mostly, I’m just happy she’s started up, and I’d like to raise a toast to her: we’re happy to have you back with us, dear gal, and we look forward to the show!

There’s also a lovely Nat Geog article on it. I love the subheading ‘happy physicists’ – it’s a warm and fluffy thought.

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The teapot effect, end of Aimee Whitcroft Nov 12

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So apparently, there’s something called the teapot effect. Or, rather, there was.


No, it’s not what you might first imagine it is. At least, it’s not what I first imaged it was. Instead, it’s apparently the name used for the phenomenon whereby the spouts of teapots dribble, and even English women who’ve been pouring tea for posh friends for decades are unable to pour that perfect, immaculate cup of tea.

“Previous studies have shown that dribbling is the result of flow separation where the layer of fluid closest to the boundary becomes detached from it. When that happens, the fluid flows smoothly over the lip. But as the flow rate decreases, the boundary layer re-attaches to the surface causing dribbling.”

And here’s where fluid dynamicists have stepped up, donned their superhero cloaks, and sorted the problem. Huzzah!

The factors involved?

“Previous studies have shown that a number of factors effect this process such as the radius of curvature of the teapot lip, the speed of the flow and the “wettability” of the teapot material. But a full understanding of what’s going on has so far eluded scientists.

“Now Cyril Duez at the University of Lyon in France and a few amis, have identified the single factor at the heart of the problem and shown how to tackle it. They say that the culprit is a “hydro-capillary” effect that keeps the liquid in contact with the material as it leaves the lip. The previously identified factors all determine the strength of this hydro-cappillary effect.”

The solution is two-fold: make the lip of the teapot as thin as possible, and and coat it with superhydrophobic materials (materials, in other words, that really, really, really, really don’t like water).

Even more fun, apparently there are materials in which the superhydrophobicity can be turned on and off electronically. Meaning that to dribble or not to dribble would no longer be hypothetical…

And, because there’s no better way to end things than with wry, physics-based sarcasm, there was this comment, as well:

“(Of course, there are one or two other potential applications in shaping the fluid flow in microfluidic machines but these pale into insignificance compared with the teapot revolution in hand.)”

On another teapot-related note, I had not idea, but apparently teapot-blowing (again, not what you think) is something of an artform!

p.s. Yes, I know the original arXiv post isn’t that new – sadly, life has perforce distracted me somewhat of recent.

PostNote (1 March 2010): the paper’s now been officially published!  Reference:

Cyril Duez, Christophe Ybert, Christophe Clanet, and Lyderic Bocquet (2010). Wetting Controls Separation of Inertial Flows from Solid Surfaces Physical Review Letters : 10.1103/PhysRevLett.104.084503

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