Puzzlers: Optimization Prime

(Microsoft Clip Art Image)

Imagine that you had 12 coins. One of the coins, being fake, weighs less than the other 11. You have one balance that will break if you make more than 3 measurements. How do you determine which coin is fake?

(Inspiration for this comes from http://www.scientificpsychic.com/mind/mind1.html)

How is this relevant? Experiments (and anything, really) cost time and money. In order to be a good steward of the resources we are given, it is important to minimize waste and unnecessary experiments. Sometimes, due to the amount of time required to do an experiment, you can only do a certain number of experiments before a deadline. You also have a limited budget. Similarly, when making a product, you want to keep the production costs low, so you don't want to do excessive experiments and tests that add to the product cost without really improving product quality.

An answer is given in the comments section.

Can you go further? Try finding the one fake coin in a bag of 18 coins.

Puzzlers: Robinhood and the Boolean Question

(Assembled using Microsoft Clip Art images)

Robinhood arrives at an crossroads, where he comes across two of the King's guards. One of the guards is loyal to the king's brother, Prince John, who will do anything that he can to stop Robinhood and his merry men, and the other is loyal to the king. The guard loyal to Prince John always lies to Robinhood and the guard loyal to the king always tells him the truth. The two guards agree to give Robinhood a 'yes' or 'no' answer to any one question that Robin asks either one of them. What question should Robin ask to determine which guard is which?

(Note: inspiration drawn from http://www.scientificpsychic.com/mind/mind1.html , which does not provide an answer that logically follows).

How is this relevant? This is logic. In digital circuit design, you often have to check that what you are reading is real. You don't know if something went wrong earlier in the calculation. You have to do something to check that what you are reading is real. This property is called parity. Similarly, when doing a science experiment and gathering data, it is not always clear that the data you are gathering is telling the truth. Odd things can interfere with measurements and give misleading data. You need to find techniques that can distinguish whether the data you are gathering tells the truth or not.

Note: An answer is provided in the comments. There are definitely others, as well (I can think of several different ones). Feel free to post your thoughts on additional answers.

Now, if only we had an answer to this question.

Source: XKCD comic 246 (Note: no link provided since not all comics are appropriate for children)

Why do you investigate Cu2ZnSnS4 (CZTS) for solar cells. Why not use silicon or other competing technologies?

Many competing technologies are currently more efficient and cheaper to produce than CZTS solar cells. We are investigating CZTS because it is very interesting and also promising. Why is it promising?

 

L.M. Peters, Phil. Trans. R. Soc. A 369 [2011] 1840-1856

• All elements are pretty non-toxic. This isn't a major issue for solar cells because they are encased in other materials and it is unlikely toxic parts will get out, but it is definite plus!
• All elements are easy to find (they are abundant). Unlike many competing technologies, there is more than enough of these elements on the planet than are needed to supply our current and growing energy needs. For example, CdTe cells are inexpensive, but there isn't enough of those elements on the planet to fulfill current energy demands.
• It is likely that the materials used to make the cells will stay cheap.
• Competing technologies often use an element called Indium, which is also needed to make new lights (LEDs) and displays, which may make cells made using it more expensive as the solar industry competes with other industries for a limited resource.

• It is easier to make CZTS solar cells than competing technologies, lowering their cost and reducing the amount of energy required to produce the cells. It tends to be less bothered by imperfections (mistakes) in the material. 
• Silicon solar cells must be made of extremely (~99.999 %) pure materials and don't perform well around defects. CZTS cells are less affected by these things.
• There is a lot of room for improvement! A lot about CZTS is unknown. Further research is needed! Processes can be optimized. 

Stay tuned to learn why CZTS is interesting!

Who cares about solar cells? Why do materials matter?

Solar cells are pretty cool! They take energy from the sun and convert that energy into electricity (the stuff that powers your lights and computers). In previous posts, we have talked about energy and charge. We have shown you a video describing how solar cells work and allowed you to play with a simulated solar cell to learn about light (photons, the basic unit of light) absorption. If you have any question about what words mean, check out our glossary page or message us.

We care about solar cells. Solar cells may be used to reduce our reliance on fossil fuels like coal or gasoline, which may become more scarce and therefore expensive in the future. They can be made in ways the pollute the environment little. They can provide energy to regions of the world where it isn't practical to string wires to power plants. They are used in war zones and in space. They are used to power homes and businesses. 

Why do materials matter? The materials play a major role in determining the efficiency of the cells. Efficiency describes how much of the energy you get out of a cell that has a certain amount of energy from the sun coming in. You want to get a lot of energy out of the cell. Solar cells using the photovoltaic effect must include semiconducting materials to operate. Not all semiconductors are created equal. Some have favorable defects and some have unfavorable defects. Some absorb more light than others. Some absorb light of the sun's energy more efficiently than others. Some materials are more expensive or abundant than others. The techniques used to produce the material impact the number and types of defects found in a material. These techniques can also add cost to the cells, making people less willing to buy them.

The material that our group researches absorbs light really well and is composed of some pretty abundant and inexpensive elements. It is also more tolerant of defects than many competing technologies. However, devices using this material, so far, are not as efficient as cells built with some other materials like silicon, CdTe, or CIGS. This is why we research it. We need to better understand the fundamental materials science of this material (thermodynamics and kinetics) in order to better design techniques to produce the material. We do this by both experiment and computational modeling. We also need to better understand how solar cells can better be used.

What do you think? Can you think of other times when the material something is made of matters? How? Have you ever thought of the sun as an energy source? Have you ever seen a solar cell? Many calculators have them.

What are atoms?

All matter (anything with mass, so basically everything except for light/energy) is made of atoms. They are the basic building blocks that make everything up. What makes one material different from another? It's the atoms and how they are arranged. How small is an atom (hint: pretty tiny--you can't see them)? Check out this video to learn about atoms.

Atoms are the basis of chemistry. They also play a major role in physics. We frequently talk about atoms in our research all the time. Atoms are cool!

Meet the Researchers: Chris Muzzillo

Have you ever wanted to talk to and meet a scientist? We wanted to introduce ourselves to our readers. Please ask us a question/share ideas using the form on the left side of the page.

The fourth researcher we would like to introduce is Chris Muzzillo of the University of Florida.

•What is your name?

–Chris Muzzillo

•Describe your research.

–We look at ways to better understand thin film photovoltaic materials, so that they can cheaply be made available to everyone

•How did you get interested in what you are researching?

–Luck.  I'm so happy I found it (or did it find me?)...

•How did you get to where you are today?

–Mostly hard work, but also by ceaselessly questioning everything

•What hobbies do you have?

–I dabble in all kinds of things.  Remember that divisions between disciplines are artificial...

•Do you have any funny stories from when you were a young scientist?

–No!  There's no room for humor in science! ;)

•What were some of your favorite activities as a kid?

–Playing sports; making up games with friends

•Do you have any advice for the next generation?

–Develop your unique perspective enough to give me some advice!  And clichés don't count!

Meet the Researchers: Hankook Kim

Have you ever wanted to talk to and and meet a scientist? We wanted to introduce ourselves to our readers. Please ask us a question/share ideas using the form on the left side of the homepage.

The third researcher we would like to introduce is Hankook Kim of the University of Florida.

• State your name.
• Hankook Kim. I'm from South Korea
• Describe your research.
• I'm interested in improving photovoltaic (solar cell) efficiency by using buffer layers.
• How did you get interested in what you are researching?
• I have always enjoyed making something new and I think making new energy is pretty cool!!!
• How did you get where you are today?
• I majored in chemical engineering at Seoul National University. I realized that I could learn more if I went to graduate school. I got a master's degree and worked for LG for more than 5 years. I felt that I needed to study more to make better things so I came to the University of Florida to pursue my dream.
• What hobbies do you have?
• I like watching movies, especially scifi movies.
• Do you have any funny stories from when you were a young scientist?
• I can not forget when I first made my research system. I spent a lot of time there...survey[ing] my research field. Starting something can be scary. However, it makes people stronger.
• What were some of your favorite activities as a kid?
• When I was a kid, I liked drawing cartoons. I still draw some characters when I feel bored. 
• Do you have any advice for the next generation?
• Get experiences as much as you can. That will be super helpful for solving problems.