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Citizen scientists air quality results are in

27 October 2014 - Mobile data

ispex results.PNGLast year we reported on a novel experiment in citizen science (iSPEX) involving a smart phone and a measurement of atmospheric dust levels (here). The official results are now published in Geophysical Research Letters (open access!) and the article has no less than 3203 authors! Must be a world record. OK, that figure is not entirely honest: the article has 16 named authors and mention is made of another 3187 iSPEX citizen scientists. On three sunny measurement days each several thousands of submissions were collected. Basically a measurement involved attaching a small plastic optical device to the camera of the smart phone, taking several photo's of the blue sky at different angles and upload them to the research group.

The aerosol optical thickness results were collected on a map of the Netherlands and compared to that of satellite data provided by MODIS (niche use: tracking wildland fires). Compared to MODIS the resolution of iSPEX was larger (2 km compared to 10-20 km) and overall the researchers state they are happy with agreement between the two methods. A comparison with the AERONET network was also deemed favourable.
On July 8 2013 (measurement day 1) the main source of aerosols in The Netherlands were North-American forest fires. The formation of Cirrus clouds did not help but later in the afternoon wind from the sea started to provide fresh air at least to the northern provinces.

The tunable mirror

25 October 2014 - Gadgets

A tunable mirror.PNGWouldn't that be nice. A mirror that you can switch between a reflective mode and a transparent mode with a push of a button. A nice gadget that would make. For some reason police interrogation rooms come to mind. Devices exist based on silver electrodeposition backed by an electrolyte solution (called 'reversible electrochemical mirror' or REM). However, because the silver slowly dissolves, the device requires a continuous voltage. Cracking of the silver mirror is also an issue. Ideally the reflective mode would not have to require a voltage and one way to accomplish this as detailed recently by a group of Korean researchers (Park et al. DOI) is making dissolution of the silver mirror less straightforward.

Here is how they did it. One piece of an ITO glass electrode was treated with an oxygen plasma leaving a surface covered with hydroxyl groups. This surface was further treated with (3-mercaptopropyl) trimethoxysilane (MPTMS) forming a self-assembled monolayer. The second ITO electrode remained bare. The electrolyte solution in between consisted of silver nitrate, copper chloride, tetrabutylammonium bromide, polyvinyl butyral and DMSO. By applying a voltage across both electrodes a bimetallic Ag/Cu nanoparticle film formed predominantly on the surface-treated side. Reversing the voltage quickly dissolved the film, forming a soluble AgBr salt.

Thanks to the surface treatment it now takes 60 seconds for the metallic film to dissolve after switching off the power (as opposed to immediate for untreated film). But 60 seconds is still disappointing and the fast dissolution is due to the presence of halides in the electrolyte. In current thinking silver is oxidised (the article does not explain how) and then carried of by halide ions to form species such as AgBrn(1-n). In this way high halide concentrations speed up silver dissolution.

The researchers then found a way to slow silver dissolution to two hours by replacing some of the DMSO by an ionic liquid. The idea behind it is that the ionic liquid assists in forming an electrical double layer with the positive ions of the ionic liquid occupying the surface where the halide ions have no longer have any businesses.


Opening a can of worms

10 October 2014 - Biochemical

molecular dynamics plasma membrane.PNGThe image of the week is the result of a molecular dynamics simulation of a mammalian plasma membrane (DOI). It looks like a can of worms has opened but the piece of cell wall depicted (a bilayer) consists of a complex mixture of 63 different worm-like lipids (phosphatidylcholines, sphingomyelin and gangliosides for the inside and hosphatidylethanolamine and phosphatidylserine for the outside) with additional cholesterol and water thrown in. This process is called computational microscopy.

The details: simulations were performed using MARTINI and using a tool called INSANE (INSert membrANE), around half a million particles (lipids, water molecules and counter ions) were crammed into a box measuring 70 by 70 by 11 nm and monitored for 40 microseconds. Initially all players are distributed randomly but phase-separation takes place instantly with cholesterol congregating and also aliphatic lipid tails in general. The gangliosides were also found to form clusters.

The simulation reveals how cholesterol-rich regions flip-flop between the in- and outside. In the accompanying video these regions are like waves in an ocean. Not able to find: the amount of time the computations took, hours?, days?, weeks?. The 40 microseconds were not enough for everything to equilibrate. Hence the curiosity.

Meanwhile in the Whitesides lab (V)

04 October 2014 - Nobel Prize predictions

Meanwhile in the Whitesides lab. This blog continues to cover George Whitesides in the run up to the Nobel Prize in Chemistry 2014 announcement. See earlier episodes I, II, III and IV. This year we have already been covering a new use of the Maglev here but the big breakthrough this year must have been the inventive use of bubble wrap in analytical chemistry (DOI). The publication describing it all attracted some media attention for example from NPR and newscientist. Basically, bubble wrap can be used as a cheap replacement for essay plates in places with poor medical infrastructure.

What else is new? Click-e-Bricks (DOI, Newscientist) are the next evolutionary step in soft-robots. The robots are built up from Lego pieces and can do amazing stuff. See vid below.
And how to move a ball on a flat surface? Many ways exists but in one of them the surface is covered with pneumatic pins (think pinball machine) that are operated by a Braille display (DOI).