Archive for category Science
Transparent solar cells
Posted by bumscientist in Engineering, Science on December 23, 2009
Can a solar cell be transparent?
The answer is yes, but you wouldn’t particularly want to unless you have some application like solar windows. The sun is a black body radiator at 5777 K. For a solar to be transparent it has to allow the visible spectrum (380 to 750 nm) through, but absorb the rest.
If we look at where the energy from the sun lies, you get
- 10% in the short wavelength
- 44% in the visible
- 46% in the long wavelength
So there is about just as much energy in the infrared and longer as there is in the visible, but the peak energy is in the visible. The way inorganic solar cells work is that they start absorbing at a certain wavelength and lower wavelengths with less efficiency.
MIT is working on solar cells that can be integrated into windows. Here’s a treehugger article.
One thing that decreases long wavelength energy production is that molecules in the atmosphere absorb certain frequencies as vibrational modes.
Waste Heat
Posted by bumscientist in Science on November 29, 2009
I’ve read of pools built next to data centers to make use of the heat generated by the racks of servers, but what about in one’s own home. I have a 750 W/1500 W space heater. Would I get the same amount of heat if I ran 750 W work of computers? The energy has to go somewhere, so I would think that those 750 W would be more useful if they were spent on computation in addition to heating up my room on a cold cold San Francisco night. I’ve noticed a room being warm when I turn on a bunch of pumps and electronics, but I never tried this in my own room. I only have about 300 W of electronics (PS3, KPC, MBP, 24″ LCD) to operate at one time in my effort to reduce how much electricity I use. I think the LCD doesn’t contribute to heat since it gives off light.
Astrolabe
Posted by bumscientist in Musings, Science on November 24, 2009
I love watching TED videos, because they are always so inspiring. This latest one about the astrolabe is conjuring all types of images of early explorers and old school science and astronomy. I’m tempted to design on and build it through ponoko, but unfortunately it seems it will be quite expensive and they can not etch brass, only cut. I might try to make it out of acrylic depending on costs.
Efficiency
Posted by bumscientist in Engineering, Science on November 11, 2009
“I’ve always been a bit of an energy efficiency nut.
I’ve made it my mission to cut the utility bills at every home we’ve owned. Long before I learned about the risks of climate change, I was fanatical about energy efficiency because I’m cheap.” – Steven Chu, from a facebook post.
I think we can put a band-aid over some of the problems with energy and water by conserving and increasing efficiency. Things are inefficient, because people are lazy. People don’t conserve, because it doesn’t cost them enough to conserve. When gasoline increased in price near $5, people are changing their habits. The problem is that it may be too late for the free market to take its course, before people can change their habits. I previously wrote that sometimes making the sandbox smaller can lead to more creative ideas. Making things efficient is like a game along the lines of tuning your car for better performance. I think the #1 use for energy was heating, so properly insulating your home will reduce energy usage dramatically.
Maybe I’ll go over one of the 14 engineering challenges each day and try to advance my knowledge of the area bit by bit. Then I’ll reduce it to 7, so I can do one a day. Then continue to reduce the challenges until I find one that I wish to pursue after I graduate.
Reporting Accidents
Posted by bumscientist in Health, Science on October 5, 2009
The question is whether to report an accident and risk having your experiment being shutdown or not reporting an accident. This is why it is always important to follow proper safety procedures.
Powerpoint in Education
Posted by bumscientist in Musings, Science on July 26, 2009
I used to detest powerpoint slides and preferred copying things written on the whiteboard. This practice was drilled into me in high school. I would have notebooks and notebooks filled with notes. All information conveniently at my finger tips. As I went to undergrad, I continued this practice and occasionally computerized the notes, since my handwriting is less than legible. This was satisfactory for my own learning, but now I in addition to learning something myself, I also need to be able to explain it to other people. I find myself a very visual learner. I like looking at pictures and equations and don’t really pay attention to words. This makes powerpoint presentations nice since I can use minimal text and put images up. One thing powerpoint is great for is for highlighting things and showing changes between slides. I think powerpoint slides are perfect for displaying equations and how these equations change as you begin to solve it. You can also circle things and work them out. Now with tablets, you can draw on your powerpoint slides in real time and save what you drew. Some people even include blank slides to draw out things in class.
Powerpoint slides remind me of creating the figures for a research paper first and then writing the text. You want to show something, the text is there merely to highlight the journey, but the figures are the tourist destinations that you want to guide your reader through. When you make powerpoint slides, the goal is to distill complex information in its simplest form. I’m moving into the simple many slides school of thought, rather than few dense slides.
This all occurred to me as I was writing some LaTeX to go over an explanation. I found the writing tedious, I already had some slides that did a perfectly good job of explaining. For a course, I think it is best to have as many ways for the student to learn as possible: LaTeX lecture notes with lots of text, simple powerpoint slides, which go over derivations step by step and convey the main points, recorded video of someone going over the powerpoint slides, live demos to drive the point home, and visual breaks, because my hacker graphics professor likes putting in visual breaks. I think technology is going to make learning a lot easier. I think people are interested in learning, because they want to learn specific things. Rather than going over an entire course, people can pick what exactly they want to hear about if it is all documented and recorded.
Space
Posted by bumscientist in Science on July 20, 2009
In celebration of the apollo moon landing, I’m going to go over space travel.
A surprising number of people doubt the moon landing. Maybe that number of people is close to the number of people who believe in god. Maybe I should capitalize God. Since it’s been a while since I did any mechanics, let’s look at it from a physics point of view.
G, gravitational constant = 6.67300 × 10-11 m3 kg-1 s-2
m_earth, Mass of Earth = 5.9742 × 1024 kilograms
r_earth, Radius of Earth = 6378.1 kilometers
The potential energy of something on the surface of the earth is P = GM_earth/r_earth or 62.504 MJ/kg.
Let’s take gasoline as an example, 1 gallon of gasoline is 114,000 BTU or 120,276,367 J. If we were able to harness all the energy in gasoline to send a 1 kg piece of turd up in space, we totally could. The only problem is that we also have to send the fuel up there at the same time. A gallon of gasoline weighs a little less than 3 kg, so that means it takes 180 MJ to send the gallon of gasoline up, but you only get 120 MJ from it. This is why sending stuff into space is a pain. You spend most of the fuel getting the fuel into space.
What you want to do is impart most of the energy on the ground. The Navy is developing railguns in the MJ range, so their claims about shooting something into space and have it fall back down on targets hundreds of miles from the coast seem entirely plausible.