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One of the most vexing topics for fluid dynamicists and their audiences is the subject of how wings generate lift. As discussed in the video above, there are a number of common but flawed explanations for this. Perhaps the most common one argues that the shape of the wing requires air moving over the top to move farther in the same amount of time, therefore moving faster. The flaw here, as my advisor used to say, is that there is no Conservation of Who-You-Were-Sitting-Next-To-When-You-Started. Nothing requires that air moving over the top and bottom of a wing meet up again. In fact, the air moving over the top of the wing outpaces air moving underneath it. 

In the Sixty Symbols video, the conclusion presented is that any complete explanation requires use of three conservation principles: mass, momentum, and energy. In essence, though, this is like saying that airplanes fly because the Navier-Stokes equations say they do. It’s not a terribly satisfying answer to someone uninterested in the mathematics. 

Part of the reason that so many explanations exist – here’s one the video didn’t touch on using circulation – is that no one has presented a simple, intuitive, and complete explanation. This is not to say that we don’t understand lift on fixed wings – we do! It’s just tough to simplify without oversimplifying. 

Here’s the bottom line, though: the shape of the wing forces air moving around it to change direction and move downward. By Newton’s 3rd law (equal and opposite reactions), that means the air pushes the wing up, thereby creating lift. (Video credit: Sixty Symbols)

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Is zero a number? Was it always a number?

Today, zero has two roles: First, as a placeholder within our number system, representing an absence of a value. It allows us to create huge numbers without extra digits. Its second role is as a number in its own right, in between -1 and 1. We can subtract, add, multiply by 0… but dividing gets tricky. I mean, you can’t divide 1 chicken by 0 chickens:

(You might think the answer would be infinity chickens, but it’s not, as infinity is a concept, not a number)

Most ancient civilisations developed some sort of number system to keep track of things, and they are all thought to have had a general concept of zero.

And when the Indians began developing a number system (the one that evolved into what we use today), zero was first explicitly born, with 9 number symbols and a dot to represent the absence of a number.

In the 7th Century, Brahmagupta developed terms for zero in addition, subtraction and division… though he struggled a bit with that last one.

Over time, the mathematics of India matured and spread outwards. But it found resistance in Europe, in particular against the established Roman numeral system.

But by the 13th century academics like Fibonacci were championing zero, helping it gain a solid foothold across Europe:

Zero went on to form the cornerstone of calculus, which allowed anyone to break down dynamic systems into smaller and smaller units approaching zero, but never quite getting there, avoiding the tricky problem of dividing by zero.

More recently, the binary numerical system formed the basis of the computer system and zero’s importance shone once more.

So maybe it really is possible to get something from nothing. Watch the full animation on our YouTube channel here.

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The experts at Brookhaven National Lab have put together a graphic to explain electromagnetic radiation (which is light) by comparing its wavelength to things found in the ocean. Radio waves “wave” at a length of about 10 meters, the size of a giant octopus. X-rays “wave” at a length of about 1 nanometer, the size of a double helix of DNA.

The waves between 0.1 and 1 micrometers are the kind that, when they pour into your eyes, allow you to see. It’s such a tiny part of the “spectrum” but it serves us well. 

We can’t be the only ones disappointed that the Internet fails to provide a beautiful electromagnetic spectrum, right? So we enlisted the aid of our graphic design team to put together this lovely ocean-inspired image, which covers everything from blue whales to oxygen atoms. Look at that pygmy seahorse!

Electromagnetic radiation—including radio waves, visible light, and x-rays—rises and falls as it travels through space, like waves rippling across the ocean. The length of these waves, measured from peak to peak or valley to valley, helps define their properties and potential uses.

At Brookhaven, we specialize in exploring the ultra-small right end of the spectrum using ultra-bright x-rays, electron microscopes, and other fantastic tools. Investigating materials at that scale allows fundamental discoveries that can revolutionize our understanding of biology, energy technology, and even the cosmos.

Learn more here and grab the poster-size, high-res version on our Flickr.

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A recent photo of the Clear Science staff working on batteries on a Friday afternoon. Have a great weekend, Clear Scientists!

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A paper was recently published in Nature, highlighting a new type of battery cathode. (An ultrafast rechargeable aluminium-ion battery by Lin et al.) The popular press write-up of the paper has followed the lead of the paper’s (possibly misleading) title, suggesting the promise of cell phone batteries charging in less than a minute.

Extrapolating scientific results from a small thing to a large thing always requires some critical thinking. Dimensional analysis tells you why a matchstick model of a cathedral can’t give you information about a real cathedral. The same goes for batteries. Scaling up a battery, like the aluminum-ion battery in the paper, will involve thickening the electrodes, shown above. We will call this increasing L.

The dimensionless number δ, or John Newman’s number, tells you how balanced the reactions in a battery electrode are. When L increases, it tells you that something else has to decrease, like current I. This means, in general, a small battery will charge fast and a large battery will charge slowly. So if a paper reports a fast battery, the first thing to do is check the size. If the battery is small, it might get slower when you make it big.

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To understand scaling of battery electrodes, let’s pause and talk about scaling of anything. Dimensional analysis is the engineering concept used to understand the scale or size of something, and was discovered by Galileo. Basically, to make size not matter, you have to eliminate all dimensionality in a problem. To do this you multiply/divide the important constants in the problem to make the dimensions cancel out. 

Up above is a dimensionless number for a structure, which involves: the yield strength and density of the structure materials, the gravitational constant (gravity pulls down on the structure), and the structure size, which is L, a length like the height. Consider this: is a matchstick model of Notre Dame Cathedral a fair model of the real Notre Dame cathedral? And if so, why not make the real Cathedral out of wood too? Also consider: if you tilted both structures, would they act the same?

The answer is no. The matchstick model is not at all like the real Cathedral, because while size does change, gravity does not. A successful matchstick model would mean you could build the real Cathedral out of wood ... only on a smaller planet with a lower value of g.

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When you’re doing research on a battery (or most things) you have to stick to small sizes, and that’s why the aluminum-ion battery we talked about yesterday is small. As the battery is further developed it will be redesigned in bigger versions, to reach the size desired. (This size is given in mAh or milliamp-hours, which you’ll find written on your cell phone battery.)

There are two ways to go about this kind of scale-up. First you could just repeat the small battery over and over, all connected (shown on the right). This keeps the electrodes inside all the same size, but results in a larger battery, because you get redundant amounts of electrolyte, seals, containers, and wiring. 

Second, you could make the electrodes themselves bigger, inside one battery container (shown on the left). This is the route usually taken because it makes the most design sense: the final battery ends up smaller.

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In their paper An ultrafast rechargeable aluminium-ion battery, Lin and co-workers describe the innovative aluminum-ion battery illustrated above. Like all batteries, it is a system designed to drive current in a circuit. The current moves as electrons (electricity!) in one part of the circuit, and as charged chemicals or ions in another part of the circuit. The ion in question is AlCl4-, which is an aluminum ion.

What’s really new is the cathode, which is a graphitic foam (a type of carbon). The AlCl4- ions go to the cathode and insert themselves between the carbon atoms. This is called intercalation, and it’s also how the lithium-ion battery in your cell phone or laptop works.

The battery in the paper is very small: about 10,000 times smaller than a regular cell phone battery. It lasts more than 7500 cycles (this would be twenty years if you charge it once a day) and can charge up in less than a minute. But the reason it can charge so fast is because of its size. When the battery is scaled up to, say, cell phone size, it will slow things down. We’ll talk about why next.

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The Clear Science staff is going to tackle the question of the fast-charging aluminum battery in the first headline above. Meng-Chang Lin and co-workers published an account in Nature last week called An ultrafast rechargeable aluminium-ion battery.

The paper describes an innovative new cathode design for batteries. (A cathode is one of the two battery electrodes.) However, most reports of the paper in the mainstream and scientific press have focused on the idea that a real-world battery developed using this cathode will charge in less than 60 seconds.

The laws of physics make this idea dubious, and we’re going to explain why. It turns out the press write-ups are breaking a fundamental rule of engineering, promising something that probably cannot happen.  

This Week in Chemistry: A fast-charging aluminium battery, fracking air pollution concerns, and more: http://goo.gl/LyZT5F

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It’s a good point. However, if the battery is discharged at a sufficiently slow rate (20 hours or slower) you do observe the well-formed spinel structure of Mn3O4. Opening the battery and using a standard XRD will result in a collection of products that are difficult to distinguish. By using a synchrotron beam to do diffraction through the battery without opening it, a good Mn3O4 structure is observed. The Clear Science staff will have a paper out about this soon … our preliminary paper on the technique is here.

We aren’t the first people to identify Mn3O4 as the slow-rate product. The Handbook of Batteries gives the same reaction as we have written above. (Wikipedia lists a different reaction, which is not well supported by the literature.)

A battery scientist’s trivial dilemma

You may find yourself hunting through all the batteries at the drugstore, trying to find an LR44 to buy instead of a 303/357. All because you want to be ‘faithful’ to MnO2. (By the way, this particular day you won’t find one.)

Functionally, these button cells are essentially interchangeable, but they have different active materials inside them. The LR44 is an “alkaline” battery which has the overall reaction:

3 MnO2 + 2 Zn = Mn3O4 + 2 ZnO

The 303/357 is a silver oxide battery having the overall reaction:

Zn + Ag2O = 2 Ag + ZnO

They both give you a potential of about 1.5 V. Actually, the silver oxide battery voltage is a little higher, and its capacity is a bit bigger. But if you’ve been concentrating on MnO2 for a couple years in your work … you know … your loyalty might kick in.

[clearscience]

A battery scientist's trivial dilemma

You may find yourself hunting through all the batteries at the drugstore, trying to find an LR44 to buy instead of a 303/357. All because you want to be ‘faithful’ to MnO2. (By the way, this particular day you won’t find one.)

Functionally, these button cells are essentially interchangeable, but they have different active materials inside them. The LR44 is an “alkaline” battery which has the overall reaction:

3 MnO2 + 2 Zn = Mn3O4 + 2 ZnO

The 303/357 is a silver oxide battery having the overall reaction:

Zn + Ag2O = 2 Ag + ZnO

They both give you a potential of about 1.5 V. Actually, the silver oxide battery voltage is a little higher, and its capacity is a bit bigger. But if you’ve been concentrating on MnO2 for a couple years in your work … you know … your loyalty might kick in.

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Could you possibly provide a source the endangered elements it's got me curious :)

Sure thing, it can be found here in the MRS Bulletin. (Full citation is MRS Bulletin / Volume 37 / Issue 04 / April 2012 , pp 405-410.)

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A while back Clear Science used the example of tellurium (Te, element 52) to illustrate how obtaining enough of a specific material can be challenging.

"Of the 118 elements that make up everything—from the compounds in a chemists arsenal to consumer products on the shelf—44 will face supply limitations in the coming years. These critical elements include rare earth elements, precious metals, and even life essentials like Phosphorus. Research into more abundant alternatives, more efficient uses, recycling and recovery will help mitigate risks and move industry us towards sustainable supply chains." Via.

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A crate of oranges hastily filled at the orchard can be more efficiently packed if vigorously shaken a few times to eliminate waste space. In a similar way, atoms loosely collected or disordered in space can become more energetically stable by bonding together into an ordered crystal structure.

Introduction to Crystal Chemistry, by Howard W. Jaffe

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In a first for laser-driven fusion, scientists at a US lab say they have reached a key milestone called fuel gain: they are producing more energy than the fuel absorbed to start the reaction.

Laser-sparked fusion power passes key milestone  |  New Scientist

Okay, okay, okay, okay, guys. Scientists at the National Ignition Facility have taken the first itty bitty baby steps towards fusion and I’m having trouble containing my excitement.

First of all, they’re using 192 laser beams, which are pointed at a gold chamber that converts the lasers into X-ray pulses, which then squeeze a small fuel pellet and make it implode and undergo fusion. That anyone ever figured out even how to do this is completely nutso.

Secondly, the lead researcher is named Omar Hurricane. I have never in my life heard a better name. He sounds like a comic book character. Please someone write a comic starring Omar Hurricane and his band of laser-wielding scientists.

And then there’s what it actually means. So far, they’ve been able to get 15 kilojoules of energy out of a fuel pellet that was blasted with 10 kilojoules. But, as The Guardian points out, much more energy is delivered by the lasers (and lost in the conversion to X-rays): “The lasers unleash nearly two megajoules of energy on their target, the equivalent, roughly, of two standard sticks of dynamite.” 

Even so, this is a hugely significant tiny step forward toward recreating the clean energy production that happens in the heart of stars.

(via chels)

Due to a peculiarity of nuclear physics, you can release energy either by 1) breaking apart heavy atoms, or 2) forcing together light atoms. Breaking apart is called fission and forcing together is called fusion. We already know how to generate energy by man-made fission, but generating energy by man-made fusion remains an aspiration. (Of course, we know how to build bombs both ways. Nuclear and thermonuclear bombs respectively.)

Essentially, solar power is fusion, though. Because the sun is a fusion reactor, and its light lands on our planet and makes everything happen. 

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Richard Wool from the University of Delaware won the 2013 Presidential Green Chemistry Challenge Award. His research group works to develop replacements for energy and pollution intensive materials. Leather is one example. In this video he talks about ecoleather, which is made from soybean oil and natural fibers derived from chicken feathers and flax.

Goals like this are good for people who like science and want to work with material and chemistry. People have used leather for thousands of years because it has a lot of properties that make it useful and valuable. But it's also a material with a significant environmental impact (for example the chemicals used for tanning). Coming up with more sustainable replacement materials is not always easy. So maybe some young Clear Scientists should think about how to do more of that.

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Oxides form on the surfaces of metals because in the atmosphere they are in contact with oxygen. The nature of these oxides affect how we think of the metals themselves. For example everyone knows that if you leave iron laying around, it will get rusty.

The oxide layer on aluminum is very thin and adheres to the aluminum, insulating it from air and protecting it from oxidizing further. This is why we think of aluminum as a material that doesn't corrode. (By the way, this aluminum oxide is the same compound that many gems are made of.)