home-made plasma cleaner

July 23, 2014 at 12:52 pm | | everyday science, hardware, science@home, stupid technology

I really want a plasma cleaner, for cleaning coverslips and activating glass for PDMS bonding, but they cost thousands of dollars. I thought that was a lot of money for a glorified microwave. So I made my own.

Drill a few holes in glass:

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Make a PDMS seal (thanks Kate):

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Glue the chamber:

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We’re ready to go!

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Fill the chamber with argon, evacuate it, turn on the microwave oven, and … voila! … a plasma:

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Below are slides before and after (right) plasma treatment. You can see the contact angle of water is dramatically reduced.

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It works!

Well, not really. I found that the plasma really only stays lit with argon. When I flow air in, it extinguishes, but also burns some of the rubber hoses. That adds more dirt to my slides than I want.

Conclusion: don’t do this at home. :)

(Well, that might be a little harsh. It does work well to bond PDMS to glass. And I’ll try a longer etch sometime to see if it will ever clean the coverslips.)

DIY spectrometer

August 30, 2012 at 1:44 pm | | hardware, science@home, wild web

A Kickstarter project is aiming to make a kit for simple DIY spectroscopy. For spectra-nerds, this is pretty cool.

(Hat tip Austin.)

walking with coffee

May 23, 2012 at 8:40 am | | literature, nerd, science@home

I love this paper: H. C. Mayer and R. Krechetnikov. Walking with coffee: Why does it spill? Phys. Rev. E 2012, 85, 046117.

In our busy lives, almost all of us have to walk with a cup of coffee. While often we spill the drink, this familiar phenomenon has never been explored systematically. Here we report on the results of an experimental study of the conditions under which coffee spills for various walking speeds and initial liquid levels in the cup. These observations are analyzed from the dynamical systems and fluid mechanics viewpoints as well as with the help of a model developed here. Particularities of the common cup sizes, the coffee properties, and the biomechanics of walking proved to be responsible for the spilling phenomenon. The studied problem represents an example of the interplay between the complex motion of a cup, due to the biomechanics of a walking individual, and the low-viscosity-liquid dynamics in it.

Genius. Here’s a great figure from the paper:

Fun stuff. It would be especially cool if they designed a new cup shape to minimize coffee oscillations.

chemicals ad campaign

May 16, 2012 at 9:41 am | | science and the public, science@home

Paul has a good first draft of a chemicals ad campaign. But I was more inspired by Klaas Wynne‘s “We love … eat … live chemicals” poster:

The reason I like it is that it points out that “chemical-free” is a stupid label, and that not all chemicals are bad (at the right doses). This type of poster could be also applied to “chemical-free” shampoos, by listing what’s in natural coconut and mint oils. I also think it would be cool to draw all those chemicals (make the size of the structure correspond to the relative amount in the apple), and repeat for several “natural” and man-made products.

I think that the “We love chemicals” posters could be combined with a set of “Natural isn’t aways safe” posters. For instance, Andrea writes about an example of dangerous natural foodstuffs. And there’s always Jim Collman’s book Naturally Dangerous.

Here are my quick drafts:

I’m moderately satisfied with them.

UPDATE: MRW posted his really cool posters:

Very cool. I like them, MRW!

405 nm laser fun

May 26, 2011 at 5:39 pm | | nerd, science and the public, science@home

I bought a 10 mW (30 mW, actually, according to our lab’s power meter) 405 nm laser from Amazon. No this pointer isn’t for presentations, for reasons I have already stated. This pointer is for fun.

For instance, I’ve enjoyed shooting the beam through tonic water and seeing the fluorescence from quinine. Here’s some total internal reflection:

Any other ideas for cool “experiments”?

(Note, please be careful with this or any laser pointer. Although the purple light emanating from this pointer doesn’t look bright, it can damage your eye or skin. Even if your eyes aren’t sensitive to 405 nm, that doesn’t mean they can’t be damaged by 405 nm. This pointer is dangerous to be viewed even in diffuse reflections.)

(P.S. The sorta shitty photo credited to E.Y.L.)

UPDATE: It turns out that urine is also fluorescent:

Especially after taking a multivitamin.

why is the left bike pedal left-hand threaded?

April 18, 2011 at 10:06 am | | hardware, science@home

Any cyclist knows that the left bike pedal is left-hand (i.e. reverse) threaded. This is so the pedal doesn’t unscrew itself while you’re pedaling. But go grab a bike and spin the pedal and crank around and you might be a little confused. Last time I did this, I thought, Wait why isn’t the right pedal reverse threaded? When you spin the pedal and crank forward, as if you’re actually powering the bike, the effective spinning of the pedal around its axle (AKA the spindle) should actually unscrew both pedals: lefty-loosey on the right pedal and righty-loosey on the left. Did every bike manufacturer get this wrong?!?

Of course not, and the real answer blew my mind. (Probably because I’m not a mechanical engineer.)

It is not, not mind you, because of the effective unscrewing force from the non-zero friction of the ball bearings. Instead, it is an effect that works in the opposite direction (in this case): mechanical precession:

“Precession is the process of a round part in a round hole rotating with respect to that hole because of clearance between them and a radial force on the part that changes direction. The direction of rotation of the inner part is opposite to the direction of rotation of the radial force.”

The source of the screwing/unscrewing force is thus radial on the spindle—the downward force you put on the pedal—instead of the twisting force from the ball bearing friction. This radial force translates into a screwing/unscrewing force because there is a small amount of clearance between the spindle and the threaded hole in the crank. I picture it like a pencil in a toilet-paper tube: crank the end of the pencil around, and there is a force that wants it to rotate on its long axis (from friction with the wall of the tube).

The screwing force from precession (on a reverse-thread on the right pedal) is much stronger than the unscrewing force from friction of ball bearings, so bike manufacturers ignore the latter.

I wish I could find an animated gif of mechanical precession, but I haven’t found one. Anyone have a book on “advanced thread theory” and want to make an animation?

UPDATE: Here’s a nice animated figure from Wikipedia:


Animation of mechanical precession” by Chris ShannonOwn work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

great escape

March 24, 2011 at 10:49 am | | literature, science@home

Fun paper:

Harvey, A.; Zukoff, S. Wind-Powered Wheel Locomotion, Initiated by Leaping Somersaults, in Larvae of the Southeastern Beach Tiger Beetle (Cicindela dorsalis media). PLoS ONE 20116(3), e17746. http://dx.doi.org/10.1371/journal.pone.0017746

Escape mechanisms in the animal kingdom can be pretty cool. Or just downright entertaining. This little guy does a somersault, grabs his tail, and rolls away in the wind (see Video 1). Check out Video 4 for a slo-mo version.

dangerous laser pointers

August 11, 2010 at 9:36 am | | lab safety, science and the public, science@home, stupid technology

NIST is warning us that some cheapo green laser pointers might be unfiltered and dangerous. Some manufacturers skip installing the IR filter, thus making a laser pointer that has a high-power invisible beam along with the green light.

The “green” of green laser pointers is 532 nm, doubled frequency of the 1064 nm emission from a neodymium (e.g. Nd:YAG, Nd:YLF, or Nd:YVO4) laser. A diode (e.g. 800 nm) pumps the neodymium laser, which emits 1064 nm light; a doubling crystal produces the green 532 nm light. But the doubling crystal is not 100% efficient, so an IR filter is necessary to block the remaining 1064 nm light that isn’t doubled (as well as block the 800 nm pumping light). The plot above shows how much 1064 nm light escapes if the filter is removed: it’s much more than the green light—if the 532 nm is 20 mW, the IR might be as high as 100 mW, certainly potentially damaging to the eye!

IR is especially dangerous laser light. First, it is invisible, so it is more difficult to identify and avoid stray beams. In this case, that’s less of a worry, because the green beam coaligned is visible. However, the second reason IR is dangerous is that, because it is invisible, you can’t tell how bright it is (see below). The final reason IR is dangerous is the biology of the eye, which is transparent to IR light, and focuses it to the retina (the nerves). IR can easily burn the retina permanently (causing blindness), or burn other parts of the eye or skin.

The simple method NIST suggests we can use to test our laser pointers is described in the announcement. Basically, they use a CD as a diffraction grating and a cheap webcam. The sensor of a digital camera is sensitive to IR light, but usually has a filter to see only visible; it is simple to remove the IR filter of a cheap webcam to make an IR sensitive detector. (Unfortunately, the sensitivity cuts out before 1064 nm, so the camera can only see the 800 nm pump light). The picture above shows the diffraction of the visible light with a normal digital camera; the bottom image is using the IR webcam. You can see the extra diffraction spots from the 800 nm light. Note also how much brighter the IR light is from the laser: even though you can’t see it with your eyes, it is very bright and dangerous.

By the way, my favorite line in the NIST report is the following: “The infrared light spreads out beyond the green, which could be injurious, for example, to a cat closely chasing a spot of green light.” Actually, that’s kinda sad: I hope the NIST folks didn’t discover this problem after they blinded their pet.

what the heck is permanent press?

July 10, 2010 at 9:47 pm | | nerd, open thread, science@home

OK, what the heck is the “permanent press” cycle on my washer? On the dryer, I think it just adds a cool tumble to the end to avoid wrinkles. But what about for the washer?

Wiki says that some machines might spray a little water during the spin, but I’m fairly sure that my cheap washer does not have that feature. From what I can tell, the perm press wash cycle is 2 min shorter than the “normal” setting, and the second rinse is a “cool down” rinse. However, my washer make the second rinse cold anyway, so I don’t think this makes perm press special. I wonder if the agitation is weaker (or stronger) for perm press compared to normal, but I sorta doubt it.

So, in conclusion, I have no idea what the “permanent press” settings on my washer are for. Maybe they just had extra space on the settings knob, so they added some fictional settings?

UPDATE: I called GE to ask them this question about their washer. The woman at the technical service said, “I have no idea.” And sorta laughed. No help there.

food carbon

July 23, 2009 at 1:42 pm | | science@home

This is sorta old news, but I found this paper again. What are the best diet choices to minimize your carbon (and entropy) footprint? Many say that buying local goods is essential, to minimize transportation. This is true, but the type of food is far more important in reducing greenhouse gases (GHG).

Or, as the authors state: “Shifting less than one day per week’s worth of calories from red meat and dairy products to chicken, fish, eggs, or a vegetable-based diet achieves more GHG reduction than buying all locally sourced food.”


Bottom line: cows produce a lot of GHG. It is obvious that growing meat is less efficient than plants (animals must be fed plants, and they are inefficient at converting plant matter into meat. Every extra rung of a food latter loses energy). What is not as obvious is that cows produce a lot of methane, which is a more potent GHG than carbon dioxide.

Red meat produces the most CO2 equivalents per calorie, more than twice dairy or fruits and vegetables. Another reason to go veg… and buy local!

looking forward to wolfram|alpha

May 15, 2009 at 12:35 pm | | news, science and the public, science@home, wild web

Wolfram|alpha search engine goes live on Monday. I can’t wait. Here’s a demo. I’m sure they selected the queries very carefully. But for the queries they ran, Wolfram|alpha looks awesome!

There will be a live broadcast of them trying to go online, starting at 8 PM EST (5 PM Pacific).

UPDATE: Try using the site for chemistry.

fluorescent cognac

February 16, 2009 at 1:45 pm | | nerd, science@home

I was watching bad TV the other day, and I got bored and started playing with a cool LED pen Thorlabs gave me. I was also drinking some VS (the cheap stuff) Courvoisier cognac. I was surprised to see fluorescence coming from the cognac when illuminated with the blue LED (the fluorescence is the greenish glow):


I suppose that it shouldn’t be surprising, given that cognac is so aromatic! But a visible absorption and green fluorescence isn’t from benzene or something—it’s from a real fluorophore. Cool.


So I wonder what fluorophore is in cognac. I know that coumarin (general structure above) is found in some plants, such as cinnamon, and some coumarins absorb in the blue. And there are a lot of tannins in wooden barrels.


I found these fluorescence spectra of brandy (B), whisky (W), slivovice (S), and juniper spirit (J). Note that the brandy—cognac is a brandy—does fluoresce in the blue/green.

DIY oobleck on a speaker

February 10, 2009 at 11:34 am | | nerd, science@home

Remember those Oobleck fingers in PRL? I finally got around to trying it at home.


And a video (more below):

My cousin and I bought a crappy old speaker to $3, tore off the cover, and spread a thin polyethylene bag (like the bags you put vegetables in at the grocery store). We used a free waveform generating software to apply sinusoidal waves at a range of frequencies—anywhere from 10-200 Hz had an effect. The oobleck was just a mixture of corn starch and water.

I was totally surprized that we actually saw those strange finger things! They weren’t as cool as in the PRL paper, but ours was a fairly ghetto setup. I couldn’t get those persistent holes to form, but whatev.

Here are the rest of the videos.

make your science sexy

January 7, 2009 at 7:15 pm | | crazy figure contest, hardware, literature, science and the public, science@home

This machine is the closest some graduate students get to the Real Thing:


“Finally, theories proposed for the mechanism of breakage were investigated on a laboratory coital model.”

Source: White, N.; Hill, D.; Bodemeier, S. Male condoms that break in use do so mostly by a “blunt puncture” mechanism. Contraception 2008, 77, 360-365. (Also reported in Nature’s news section here.)

vit D and time of year

November 3, 2008 at 2:26 pm | | literature, science@home

With the shorter days of winter fast approaching (in my hemisphere, at least), we should all be concerned with getting enough vitamin D.

In a recent paper (Kazantzidis, et al. Calculations of the human vitamin D exposure from UV spectral measurements at three European stationsPhotochem. Photobiol. Sci. 2009), some scientists measured the UV doses in some European cities. The plot below looks at seasonal UV doses—converted to vitamin D effective dose (VDED)—averaged over 10-15 years.

Note the log scale on the y axis.

The blue line is somewhere in Greece, lattitude around 41 ºN, which is north of San Francisco. That means I get the most vitamin D in the summer, and more than an order of magnitude less in the winter.

So maybe I should take a supplement?

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