Last week I went to an astronaut's speech on the future of commercial space flight. The astronaut, Steve Smith, worked on the Hubble Space Telescope while it was in orbit. I got to meet and talk with him personally for a few minutes, and loved every second of it.
He had a lot of interesting anecdotes, but the one that I'm still thinking about is this: the space program rejected him as an astronaut candidate four times before being accepting him. You can only apply once every two years, so he was living in a state of space-program rejection for eight years before being accepted. I wish I had had the foresight to ask him whether this was normal for astronaut candidates, or if he was an exception. Either way, the fact that he keep reaching for his dream, even after eight years of rejection, is amazing and inspiring to me.
2009-11-21
2009-11-07
Chip
My 2.5 by 2 mm^2 integrated circuit design was finalized yesterday. Maybe now I can stop stressing out so much?
Probably not.
2009-11-04
Bleg: Books
These are the books I'm thinking of buying for myself, with the up-coming holiday season discounts:
Non-Fiction:
Non-Fiction:
The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom
Violence: A Micro-sociological Theory
Everyday Practice of Science: Where Intuition and Passion Meet Objectivity and Logic
American Homicide
Codes of the Underworld: How Criminals Communicate
The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature
Spent: Sex, Evolution, and Consumer Behavior
Wild Justice: The Moral Lives of Animals
The End of Overeating: Taking Control of the Insatiable American Appetite
The Addict: One Patient, One Doctor, One Year
The Science of Fear: Why We Fear the Things We Shouldn't--and Put Ourselves in Greater Danger
The Marriage-Go-Round: The State of Marriage and the Family in America Today
The Invisible Hook: The Hidden Economics of Pirates
The Overflowing Brain: Information Overload and the Limits of Working Memory
2009-11-02
Randomizing a Coin Toss
Way to report only the problem, Freakonomics blog:
Mathematically, if the probability of landing heads is P, then:
Since the probability of HT is the same as TH, taking the first element removes the bias.
Mad props to von Neumann for inventing this trick (publication was "Various techniques used in connection with random digits"), along with fundamental portions of the theory for quantum mechanics, cryptography, and game theory. They don't make mathematicians like they used to.
But it may be that the the random coin toss isn’t so random. A 2007 study found that a vigorously flipped coin is likely to land on the same side it started on at least 51 percent of the time, possibly more depending on the person doing the flipping.Say you have a coin with a bias that doesn't change from flip to flip. You can remove the bias by flipping the coin twice, and taking the first result if the second result differs from the first or repeating if it lands the same way both times.
Mathematically, if the probability of landing heads is P, then:
P^2 = Prob[HH]
P*(1-P) = Prob[HT]
(1-P)*P = Prob[TH]
(1-P)^2 = Prob[TT]
Since the probability of HT is the same as TH, taking the first element removes the bias.
Mad props to von Neumann for inventing this trick (publication was "Various techniques used in connection with random digits"), along with fundamental portions of the theory for quantum mechanics, cryptography, and game theory. They don't make mathematicians like they used to.
2009-10-14
Temper
I don't normally blog about personal things, because I think they're lame and I really hate putting personal information onto the interweb. But I figured I've got to try most things once and see how it turns out.
I lost my temper today. It was pretty bad. If you know me, I may not seem like the kind of person who loses it very easily, and in general I think I keep my cool pretty well. Today just wasn't my day.
Today at work, one of my officemates made a passing remark about gay people and how they were decreed to be killed in his home country. He was talking to another person at the time (not me), but I thought the way he phrased it was completely inappropriate. What I thought I heard was a statement supporting violence against people based on their sexual preference. What he probably said or intended to say was a factual statement about what happens in his home country because of the laws. In retrospect, as he isn't a native English speaker, the intention of the statement and what were said were probably different. I think the words "should," "could" and "would" are particularly difficult for non-native speakers to grasp. Even native speakers aren't clear with their intentions in everyday conversation.
Anyways, I then asked him if he would please keep the hate speech out of this country.
A large fight ensued where I lost my cool. He claimed the remark wasn't for public consumption, but at the same time I heard it and pointed out that other people use our room. When he makes remarks like the one he made, other people listen and he implicitly represents our group, and hence me in such remarks. We ended up taking the issue to our adviser, who as head of our group is mostly responsible for our group image.
My adviser agreed with me about our room and our remarks being public. My adviser warned my colleague to be more careful with his words in the future. My adviser told me I needed to be less strict in my interpretations of what people, especially non-native speakers, say, and that I shouldn't assume their intentions from their speech. He also said not to overreact so much. I think I agree with him on all statements. I lost my cool, and need to be more understanding of the slipperiness in communications.
I would be lying if I said there hasn't been a build-up to this, or to the other times I've lost my cool. The way my officemate structures his speech would be extremely rude in Iowa. I've tried explaining it, but so far without much success. Maybe the problem is with me? I don't know. Things aren't really great between us. He accused me of being a spy today (I don't think he knows what the word means), and I think I've burned too many bridges to try and explain to him how he is subtly insulting me. He probably wouldn't believe me anyways - I'm a spy, right?
I'm been having some problems with my temper lately (when I say lately, I mean over the past two years, since leaving university). At my last job, I had pretty big issues with how long it took to accomplish things. I'm a prettylazyefficient person, and when I do work I want it to matter. I get angry when it doesn't, or if I did unnecessary work. Making sure I take the right approach to getting things working is very important to me, and I think it makes me a good engineer. I know I can focus my anger when things don't go well. I distinctly remember times in middle school when I did poorly on a test and studied non-stop because I was angry about it, and the next tests always came back with high marks. At the same time, it seems over the past few years my temper has starting to get in the way of getting things done in the most efficient manner. I should have asked my officemate to clarify his statement, not immediately assumed a bigoted intention. I should have known that getting things done quickly is different for a very constrained university assignment than for work in the corporate world.
I thought I'd share this moment of anger with you. While writing about it has been a bit cathartic, I'll still be fuming for the next few days.
I lost my temper today. It was pretty bad. If you know me, I may not seem like the kind of person who loses it very easily, and in general I think I keep my cool pretty well. Today just wasn't my day.
Today at work, one of my officemates made a passing remark about gay people and how they were decreed to be killed in his home country. He was talking to another person at the time (not me), but I thought the way he phrased it was completely inappropriate. What I thought I heard was a statement supporting violence against people based on their sexual preference. What he probably said or intended to say was a factual statement about what happens in his home country because of the laws. In retrospect, as he isn't a native English speaker, the intention of the statement and what were said were probably different. I think the words "should," "could" and "would" are particularly difficult for non-native speakers to grasp. Even native speakers aren't clear with their intentions in everyday conversation.
Anyways, I then asked him if he would please keep the hate speech out of this country.
A large fight ensued where I lost my cool. He claimed the remark wasn't for public consumption, but at the same time I heard it and pointed out that other people use our room. When he makes remarks like the one he made, other people listen and he implicitly represents our group, and hence me in such remarks. We ended up taking the issue to our adviser, who as head of our group is mostly responsible for our group image.
My adviser agreed with me about our room and our remarks being public. My adviser warned my colleague to be more careful with his words in the future. My adviser told me I needed to be less strict in my interpretations of what people, especially non-native speakers, say, and that I shouldn't assume their intentions from their speech. He also said not to overreact so much. I think I agree with him on all statements. I lost my cool, and need to be more understanding of the slipperiness in communications.
I would be lying if I said there hasn't been a build-up to this, or to the other times I've lost my cool. The way my officemate structures his speech would be extremely rude in Iowa. I've tried explaining it, but so far without much success. Maybe the problem is with me? I don't know. Things aren't really great between us. He accused me of being a spy today (I don't think he knows what the word means), and I think I've burned too many bridges to try and explain to him how he is subtly insulting me. He probably wouldn't believe me anyways - I'm a spy, right?
I'm been having some problems with my temper lately (when I say lately, I mean over the past two years, since leaving university). At my last job, I had pretty big issues with how long it took to accomplish things. I'm a pretty
I thought I'd share this moment of anger with you. While writing about it has been a bit cathartic, I'll still be fuming for the next few days.
2009-10-12
How are Our Children Going to Get Out of Bathrooms?
It was roughly 2 am on a standard night at MIT. Pacing the hallways with my trusty football, I asked a few people if they wanted to hit up a local shop for some late night chocolate milk and Italian subs. Receiving an affirmative, I told them I'd be back in a moment. I really had to go to the bathroom.
Having finished my business and washed my heads, I went to unlock the bathroom door. The knob turned, but the latch did not retract. I looked at my football. We were stuck in the bathroom.
After yelling and attracting the attention of some local residents, I asked if they had any bright ideas. One suggested re-locking and unlocking the door, which had allowed her to escape a similar situation several days ago. Alas, it did not work. I looked at my football again. Still stuck in the bathroom.
But wait! I had my trusty Gerber multi-tool with me! Holding my football a bit steadier, I whipped out the mini-screwdriver, took off the doorknob casing, had some friends help take apart the rest of the doorknob, pulled out the latch, and escaped the clutches of the bathroom (EDIT: this sentence was modified to properly attribute work to people missed on the initial post).
Today, the NYTimes ran an article on schools punishing children for carrying multi-tools. I want to know from these multi-tool nay-sayers: Who is going to get our children out of the bathrooms at 2 am? Because I don't think it is going to be you.
Having finished my business and washed my heads, I went to unlock the bathroom door. The knob turned, but the latch did not retract. I looked at my football. We were stuck in the bathroom.
After yelling and attracting the attention of some local residents, I asked if they had any bright ideas. One suggested re-locking and unlocking the door, which had allowed her to escape a similar situation several days ago. Alas, it did not work. I looked at my football again. Still stuck in the bathroom.
But wait! I had my trusty Gerber multi-tool with me! Holding my football a bit steadier, I whipped out the mini-screwdriver, took off the doorknob casing, had some friends help take apart the rest of the doorknob, pulled out the latch, and escaped the clutches of the bathroom (EDIT: this sentence was modified to properly attribute work to people missed on the initial post).
Today, the NYTimes ran an article on schools punishing children for carrying multi-tools. I want to know from these multi-tool nay-sayers: Who is going to get our children out of the bathrooms at 2 am? Because I don't think it is going to be you.
The Invention of Google Wave: A Play in One Act
Date: roughly one year ago. Two twenty-something google engineers (both decked out in blue google t-shirts and jeans) sit on their fitness balls. One sips some strange coffee-like concoction while the other downs an Odwalla drink. Engineer one checks his e-mail.
One: That jerk Larry from HR keeps top-replying to my emails. Seriously. Who the h#** uses top-reply these days?
Two: Everyone but nerds uses top-reply. Didn't you talk with new girl? She was an M$ intern last year, and apparently M$ mandates top-reply in their emails.
One: And what if you want to respond to multiple points in the e-mail?
Two: I think Outlook would have crashed by then.
One: Seriously, this is non-sense. We need to get some giant conspiracy going to make bottom-reply the default.
Two: I have an idea. How about we claim we're merging IM functionality with e-mail. But in reality we'll just be forcing people to use the indent-reply conventions nerds have been using for the past 40 years, and give people too stupid to setup IM notifications of email events the chance to get e-mail instantly.
One: That sounds awesome. We'll dress it up to look fancy, so people aren't so intimidated by the less than signs that would normally occupy the start of the line.
Two: I know. Heaven forbid people learn how to use conventions, or look at plain text.
One: Oh, and we can put in annoying features that geeks would hate! Maybe we can have it immediately show the person's reply, while they're typing! Heaven forbid people think before they respond, like us introverted nerds do with emails, so the hundreds of people getting our emails don't have to sit through our mistakes. We can cut out the subject line, too - it isn't like people use that to its potential.
Two: Those sound like exactly the sorts of nerd-hating features that'll launch this project into the big time! Let's get coding.
Curtains close as furious keyboard pounding commences.
One: That jerk Larry from HR keeps top-replying to my emails. Seriously. Who the h#** uses top-reply these days?
Two: Everyone but nerds uses top-reply. Didn't you talk with new girl? She was an M$ intern last year, and apparently M$ mandates top-reply in their emails.
One: And what if you want to respond to multiple points in the e-mail?
Two: I think Outlook would have crashed by then.
One: Seriously, this is non-sense. We need to get some giant conspiracy going to make bottom-reply the default.
Two: I have an idea. How about we claim we're merging IM functionality with e-mail. But in reality we'll just be forcing people to use the indent-reply conventions nerds have been using for the past 40 years, and give people too stupid to setup IM notifications of email events the chance to get e-mail instantly.
One: That sounds awesome. We'll dress it up to look fancy, so people aren't so intimidated by the less than signs that would normally occupy the start of the line.
Two: I know. Heaven forbid people learn how to use conventions, or look at plain text.
One: Oh, and we can put in annoying features that geeks would hate! Maybe we can have it immediately show the person's reply, while they're typing! Heaven forbid people think before they respond, like us introverted nerds do with emails, so the hundreds of people getting our emails don't have to sit through our mistakes. We can cut out the subject line, too - it isn't like people use that to its potential.
Two: Those sound like exactly the sorts of nerd-hating features that'll launch this project into the big time! Let's get coding.
Curtains close as furious keyboard pounding commences.
2009-10-11
Tape-Out
If you've talked with me lately, I've probably told you how stressed out I am about something called a "tape-out." The phrase refers to production of an integrated circuit. According to my adviser, 20 or 30 years ago, before the internet was around, circuit designers would send physical tapes to the chip manufacturers. Hence the term tape-out. Thus when an electrical engineer is creating an integrated circuit, (s)he uses the term tape-out to describe the process.
Today I thought I'd share a little bit of the designer process, so you can understand what I'm talking about when I say I've been staring at colored polygons all day. Circuits perform a lot of tasks, from the main processing in our computers, to capturing images in some of our cameras, or detecting events in the world around us.
To create circuits to do all these things, engineers start simple and build up. The basic unit in an integrated circuit is the transistor, which acts as a switch in digital logic. The switch is on or off depending on the electrical signals we send to the transistor. I've taken public domain pictures from Wikipedia that shows the behavior when the transistor is off (first picture) or on (second picture).
The basis for transistor construction is the placement of materials with different characteristics. The "n" and "p" labels above are on materials with different elements. Placing these materials at proper distances from one another is critical to proper operation of the switches.
When electrical engineers create circuits, we need ways to control where the materials go, and then we can control the behavior of the circuit. Thus when I talk about colored polygons, I am talking about visualizing the locations of different types of material that determine a circuit's operation. I've labeled the drawings above with the colors of the layers, and including a screenshot of what I look at when I am using software to "create" a transistor. The wikipedia images are from the side, whereas engineers view things from the top.
The red polygon, representing the gate, interfaces with the control signal for the transistor. The green layer represents the 'n' implant into the 'p' type silicon. The blue layer is a metal routing layer on top - there are other metal layers for routing, along with via layers such as the teal layer above that connect metal layers to other layers.
You'll notice I don't specify all the layers. The silicon dioxide layer, dashed in the figure, doesn't have a corresponding polygon. Some layers are auto-generated from other layers; this can create problems when you want to do something fancy.
Starting from these simple layers, we can quickly build up complicated devices. I didn't mention this before, but there are actually two types of complementary transistors on most integrated circuits. This is the basis for the term CMOS, or complementary metal oxide semiconductor. The next picture shows both types of transistors. You can check out the CMOS Wikipedia page if you're interested in the two types.
The structure you're looking at is an inverter, as it outputs the opposite of the input signal after some time. If you're confused by the layers, follow the red polygon (the gate) to the green areas - the overlap area would be the two transistors. The yellow and white dotted layers help describe which type of transistor is to be created. The big orange box around the top portion would change the material in a large area, and is required for one of the two transistor types. The teal / cyan squares are vias that connect the metal to other material. Though vias only connect to the green layers in the transistor I showed above, they can also connect to other layers.
There are additional metal routing layers than the metal one I've shown so far. The next picture shows a custom structure I have made. This structure includes yellow and white polygons, which represent metals at different heights than the metal in the previous images.
The purple and orange squares represent vias between the various metal layers. The structure that you're looking at is a variable-delay buffer. It takes a control signal and an input signal, and outputs the input signal after a delay which is set by the control signal.
I've included measurements on the side of the structure in microns, or one-thousandth of a millimeter. A micron is also one-millionth of a meter. When you hear people talk about different integrated circuits production processes, they'll usually use the minimum accuracy of the gate size as a first-order statement of how advanced the process is. This is a 0.35 micron process, meaning that the minimum gate size is 0.35 microns, or 350 nanometers. The current processor in your computer is probably a 45, 90 or 130 nanometer process.
You might ask why people care about the construction of the circuit - don't we really just care about the behavior? Digital engineers do tend to care more about the behavior than the construction itself, and they usually don't lay out circuits by hand. They usually specify the behavior using some type of code, and run this code through a bunch of fancy tools to get the material locations.
However, if you work with sensors, it is often more difficult to specify the exact characteristics of the structures than simply laying out the structures by hand. This is the case for most of the work my group does.
There is the additional problem that messing up means the entire circuit might not work. This is why I'm constantly stressed out - while one mistake can cost a software person months of their life, simple things are enough to easily prevent this. This often isn't the case in hardware, as creating the circuit takes months, and you're stuck with the circuit.
Well, I hope you enjoyed my post on tape-outs. I cannot post pictures of my more complex structures, as a lot of the cells I work with are proprietary, and the man would come after me. I'm finished with this tape-out in early November, and then it will be a few months before I know whether it was a waste of time. I'll probably be drinking a lot of egg nog at xmas time.
Today I thought I'd share a little bit of the designer process, so you can understand what I'm talking about when I say I've been staring at colored polygons all day. Circuits perform a lot of tasks, from the main processing in our computers, to capturing images in some of our cameras, or detecting events in the world around us.
To create circuits to do all these things, engineers start simple and build up. The basic unit in an integrated circuit is the transistor, which acts as a switch in digital logic. The switch is on or off depending on the electrical signals we send to the transistor. I've taken public domain pictures from Wikipedia that shows the behavior when the transistor is off (first picture) or on (second picture).
The basis for transistor construction is the placement of materials with different characteristics. The "n" and "p" labels above are on materials with different elements. Placing these materials at proper distances from one another is critical to proper operation of the switches.
When electrical engineers create circuits, we need ways to control where the materials go, and then we can control the behavior of the circuit. Thus when I talk about colored polygons, I am talking about visualizing the locations of different types of material that determine a circuit's operation. I've labeled the drawings above with the colors of the layers, and including a screenshot of what I look at when I am using software to "create" a transistor. The wikipedia images are from the side, whereas engineers view things from the top.
The red polygon, representing the gate, interfaces with the control signal for the transistor. The green layer represents the 'n' implant into the 'p' type silicon. The blue layer is a metal routing layer on top - there are other metal layers for routing, along with via layers such as the teal layer above that connect metal layers to other layers.
You'll notice I don't specify all the layers. The silicon dioxide layer, dashed in the figure, doesn't have a corresponding polygon. Some layers are auto-generated from other layers; this can create problems when you want to do something fancy.
Starting from these simple layers, we can quickly build up complicated devices. I didn't mention this before, but there are actually two types of complementary transistors on most integrated circuits. This is the basis for the term CMOS, or complementary metal oxide semiconductor. The next picture shows both types of transistors. You can check out the CMOS Wikipedia page if you're interested in the two types.
The structure you're looking at is an inverter, as it outputs the opposite of the input signal after some time. If you're confused by the layers, follow the red polygon (the gate) to the green areas - the overlap area would be the two transistors. The yellow and white dotted layers help describe which type of transistor is to be created. The big orange box around the top portion would change the material in a large area, and is required for one of the two transistor types. The teal / cyan squares are vias that connect the metal to other material. Though vias only connect to the green layers in the transistor I showed above, they can also connect to other layers.
There are additional metal routing layers than the metal one I've shown so far. The next picture shows a custom structure I have made. This structure includes yellow and white polygons, which represent metals at different heights than the metal in the previous images.
The purple and orange squares represent vias between the various metal layers. The structure that you're looking at is a variable-delay buffer. It takes a control signal and an input signal, and outputs the input signal after a delay which is set by the control signal.
I've included measurements on the side of the structure in microns, or one-thousandth of a millimeter. A micron is also one-millionth of a meter. When you hear people talk about different integrated circuits production processes, they'll usually use the minimum accuracy of the gate size as a first-order statement of how advanced the process is. This is a 0.35 micron process, meaning that the minimum gate size is 0.35 microns, or 350 nanometers. The current processor in your computer is probably a 45, 90 or 130 nanometer process.
You might ask why people care about the construction of the circuit - don't we really just care about the behavior? Digital engineers do tend to care more about the behavior than the construction itself, and they usually don't lay out circuits by hand. They usually specify the behavior using some type of code, and run this code through a bunch of fancy tools to get the material locations.
However, if you work with sensors, it is often more difficult to specify the exact characteristics of the structures than simply laying out the structures by hand. This is the case for most of the work my group does.
There is the additional problem that messing up means the entire circuit might not work. This is why I'm constantly stressed out - while one mistake can cost a software person months of their life, simple things are enough to easily prevent this. This often isn't the case in hardware, as creating the circuit takes months, and you're stuck with the circuit.
Well, I hope you enjoyed my post on tape-outs. I cannot post pictures of my more complex structures, as a lot of the cells I work with are proprietary, and the man would come after me. I'm finished with this tape-out in early November, and then it will be a few months before I know whether it was a waste of time. I'll probably be drinking a lot of egg nog at xmas time.
2009-10-10
2009-10-05
Architecture around TU Delft
The weather was nice a few weekends ago, so I went out and snapped a few photos. Enjoy!
This is a picture from the window of my new apartment. I now have a view of the canal. Sorry for the tilt, my head isn't on straight so it looks normal to me.
TNO is a large defense contractor in Delft.
A south view from my building.
A west view from my building, towards the part of town with the high-rise apartment buildings.
I've circled a bunch of the high rise buildings. As I've previously described, most of the development in Delft occurs on the outskirts of town. This preserves the town center as is.
You can see that along the canal there are a lot of industrial type buildings. A lot of heavy freight is shipped along the canals instead of roads, which means that the roads require less maintainence.
Some apartments near the university. You can see part of my building in the background.
Some apartments near the university. They stand over a pond.
Due to all of the bicycle traffic, it can be difficult to know whether a bicycle is supposed to go on a path or not. The people who designed the park in the middle of campus included environmental cues to help. First, the rocks are close enough together that a bicycle would have trouble going between them. Next, the gray sections of the path are rough; riding over the alternating path sections feels unnatural on a bicycle. The path goes down a few steps out of sight, so it is important that bicyclists don't go on this path. People don't seem to like signs here, Delft has a lot of these environmental cues around the city to help bicyclists with whether or not they belong in certain places.
The main bicycle path next to the mechanical engineering building. Exposed stairwells are very common here, I think architects like them.
My building.
The civil engineering building, which also contains administrative offices. Another building with exposed stairwells.
A set of dorm rooms are by my building.
Two Hogeschools (or vocational schools) have opened up next to TUDelft. When they were building this school, they had water in the lot that is now under construction. This building looked like one of those beach buildings on stilts. The empty lot will soon contain housing.
Another vocational school. This one is interesting because it contains a parking lot on the roof!
This is a picture from the window of my new apartment. I now have a view of the canal. Sorry for the tilt, my head isn't on straight so it looks normal to me.
TNO is a large defense contractor in Delft.
A south view from my building.
A west view from my building, towards the part of town with the high-rise apartment buildings.
I've circled a bunch of the high rise buildings. As I've previously described, most of the development in Delft occurs on the outskirts of town. This preserves the town center as is.
You can see that along the canal there are a lot of industrial type buildings. A lot of heavy freight is shipped along the canals instead of roads, which means that the roads require less maintainence.
Some apartments near the university. You can see part of my building in the background.
Some apartments near the university. They stand over a pond.
Due to all of the bicycle traffic, it can be difficult to know whether a bicycle is supposed to go on a path or not. The people who designed the park in the middle of campus included environmental cues to help. First, the rocks are close enough together that a bicycle would have trouble going between them. Next, the gray sections of the path are rough; riding over the alternating path sections feels unnatural on a bicycle. The path goes down a few steps out of sight, so it is important that bicyclists don't go on this path. People don't seem to like signs here, Delft has a lot of these environmental cues around the city to help bicyclists with whether or not they belong in certain places.
The main bicycle path next to the mechanical engineering building. Exposed stairwells are very common here, I think architects like them.
My building.
The civil engineering building, which also contains administrative offices. Another building with exposed stairwells.
A set of dorm rooms are by my building.
Two Hogeschools (or vocational schools) have opened up next to TUDelft. When they were building this school, they had water in the lot that is now under construction. This building looked like one of those beach buildings on stilts. The empty lot will soon contain housing.
Another vocational school. This one is interesting because it contains a parking lot on the roof!
2009-09-28
Dracthen
The town of Drachten in the northern part of the Netherlands took its main traffic intersection and changed it drastically in 2003 -- all traffic signs and lights were removed! Below are pictures from before and after the rebuilding of the city square.
My favorite note from the summarizing report is that respondents think the traffic situation is less safe now (appendix 6c from the report), whereas the number of accidents has fallen to under 20% of previous levels. I think something called the Peltzman effect is behind the discrepancy between the increased safety but decreased view of safety. When human beings feel safe, they might engage in riskier behavior. By playing on the fears of people, the intersection has (so far) been much safer. I have previously blogged about this effect in a post on condoms.
Oddly enough, people ranked the "quality" of the re-designed space much better than before, even though they thought the re-design was less safe. In addition, the transit times across the intersection improved.
I think this effect has strong implications for how we can misunderstand our own rationality, and helps explain why it is important to study information objectively by examining accident rates and transit times, getting a full picture of how our emotions steer us in all situations.
Tip of the hat to reddit for still providing signal, even though most of your links are now noise.
Copyright note - the publication with these pictures didn't include explicit copyright information, but did contain a logo for a sponsoring institution, a Gemeente, meaning they should be in the public domain. If you are a random visitor with more information, please let me know if you are aware of the copyright situation of these photographs.
My favorite note from the summarizing report is that respondents think the traffic situation is less safe now (appendix 6c from the report), whereas the number of accidents has fallen to under 20% of previous levels. I think something called the Peltzman effect is behind the discrepancy between the increased safety but decreased view of safety. When human beings feel safe, they might engage in riskier behavior. By playing on the fears of people, the intersection has (so far) been much safer. I have previously blogged about this effect in a post on condoms.
Oddly enough, people ranked the "quality" of the re-designed space much better than before, even though they thought the re-design was less safe. In addition, the transit times across the intersection improved.
I think this effect has strong implications for how we can misunderstand our own rationality, and helps explain why it is important to study information objectively by examining accident rates and transit times, getting a full picture of how our emotions steer us in all situations.
Tip of the hat to reddit for still providing signal, even though most of your links are now noise.
Copyright note - the publication with these pictures didn't include explicit copyright information, but did contain a logo for a sponsoring institution, a Gemeente, meaning they should be in the public domain. If you are a random visitor with more information, please let me know if you are aware of the copyright situation of these photographs.
2009-09-20
Drawing the US
As a follow-up to my earlier post, I drew the U.S. today. I managed to get all the states, though a few have some major issues. I colored in what I meant to draw, and I'm not really sure what happened at the MO / IL / KY border...hmmm...
If you think you can do better you should give it a shot!
If you think you can do better you should give it a shot!
2009-09-13
Farewell, Norman Borlaug
Norman Borlaug has died:
There are a lot of slow, dangerous effects that we hear about every now and then - I think that people, myself included, don't think enough about the drastic increases in population that will come with better health-care and nourishment in every part of the world.
Norman E. Borlaug, the plant scientist who did more than anyone else in the 20th century to teach the world to feed itself and whose work was credited with saving hundreds of millions of lives, died Saturday night. He was 95 and lived in Dallas.In high school biology class, we had a population unit that included articles on Borlaug. As a fellow Iowan, Norman Borlaug was the center of several important discussions, especially his premonition that "If the world population continues to increase at the same rate, we will destroy the species."
There are a lot of slow, dangerous effects that we hear about every now and then - I think that people, myself included, don't think enough about the drastic increases in population that will come with better health-care and nourishment in every part of the world.
2009-09-08
High SNR Sentences: Identifying You in Data
It was found that 87% (216 million of 248 million) of the population in the United States had reported characteristics that likely made them unique based only on {5-digit ZIP, gender, date of birth}.The sentence was from a CMU researcher working in 2000 on 1990 census data. Unfortunately the paper is behind a wall, but a different, available paper with a decent methodology puts the number at 63%. I was not comforted by the lower estimate. Tip of the hat to Ars Technica for an interesting discussion on "anonymizing" data.
2009-09-06
Drawing the US from Memory
I used to challenge people to draw the US from memory, it was usually hilarious when people who weren't from the mid-west tried to draw the region. I can do a respectable job, I almost always hit all the states and the shapes aren't too bad...but holy cow, Al Franken, you're my hero.
2009-08-30
Timing Properties of SPADs
I've gotten requests for more technical material, so here ya go:
Today I'm going to talk about some applications of SPADs. If you want a reminder of the basics of SPADs, you can read my introductory post or my post on noise. SPADs are single-photon detectors that use feedback systems in conjunction with one another to accurately time the arrival of single-photons. Accurately timing a photon's arrival time is important in many applications, but today I'll be talking about rangefinding.
In rangefinding applications, such as laser-based rangefinding for land surveying, a laser fires a pulse of photons and a detector times the difference between the pulse and the photon detection time. Photons, being light, travel at the speed of light. You'll usually here the speed of light quoted as 300,000,000 meters per second, but optics people prefer to quote the speed of light as
Anyways, we have to accurately time this photon arrival so we can determine the time of flight. The timing inaccuracy is termed jitter; we use various metrics to quantify the jitter, but most of these metrics just capture the usual case. For SPADs, the jitter depends on a few things.
First, the temperature is very important. In a silicon integrated circuit, increasing the temperature increases the ambient energy available to electrons, the main information carriers in the circuit. The introduction of additional energy modifies a carrier's behavior, and thus changing the temperature will change the characteristics of both the fast and slow feedback loops in SPADs.
Next, the color of the light is also important. Different colors of light have different wavelengths. The wavelength describes how frequently the energy moves around in space. Since silicon has a repeating structure, the wavelengths will help determine how likely it is that the light interacts with the crystal, producing the primary electron that could cause an avalanche. It turns out that blue light is optimal for the current generation of SPADs - the optimal wavelength is a balance between how far light usually penetrates into the silicon and where the avalanche region is (remember that we moved the region away from the surface to avoid the noise-causing irregularities at the surface).
Within the avalanche region, the build-up time of the avalanche is obviously important. During the initial portion of the positive feed-back loop, when there are very few carriers active, the variation in each carrier can change the build-up time. Current understanding is that it takes between 0 and 15 picoseconds to generate enough carriers to average out these variations, though this build-up process depends on characteristics like the temperature and strength of the applied force (the electric field).
So what is the end result? Well it depends on what you need and what you have available. If you have a lot of area available on a silicon chip, you can use more complex current detectors to get the jitter as low as 15 or 20 picoseconds. On the other hand, if you're short on area you can raise the jitter as much as you like, but you'd be hard-pressed to raise it above nanoseconds and still have a viable application. Keep in mind that you'll be changing how close the SPADs are, so the cross-talk will change.
When you're making a range-finder, you might care only about one specific range, or you might be trying to acquire a bunch of ranges to get a 3D pictures. If you only care about one range, you can use a lot of area to achieve the 20 picosecond resolution. This corresponds to an uncertainty in space around 6 millimeters. If you have an array of SPADs and timing circuitry, you're more likely to have an error in the 100 picosecond range. 100 picoseconds corresponds to an error of 3 cm in space. You can lower this uncertainty by taking multiple measurements, and since the measurements are so fast the accuracy can easily be one millimeter or less.
Anyways, I hope this post helped you understand about the timing uncertainty in SPADs. The uncertainty affects other applications besides rangefinding, things like quantum-based encryption algorithms, biological imaging, and cancer detection, but those applications are a bit more complicated to explain! I'll be attempting in future posts, and we'll see how it goes.
Today I'm going to talk about some applications of SPADs. If you want a reminder of the basics of SPADs, you can read my introductory post or my post on noise. SPADs are single-photon detectors that use feedback systems in conjunction with one another to accurately time the arrival of single-photons. Accurately timing a photon's arrival time is important in many applications, but today I'll be talking about rangefinding.
In rangefinding applications, such as laser-based rangefinding for land surveying, a laser fires a pulse of photons and a detector times the difference between the pulse and the photon detection time. Photons, being light, travel at the speed of light. You'll usually here the speed of light quoted as 300,000,000 meters per second, but optics people prefer to quote the speed of light as
- 30 centimeters per nanosecond
- 300 millimeters per nanosecond
- 300 micrometers (microns) per picosecond
- 30 millimeters per 100 picoseconds
Anyways, we have to accurately time this photon arrival so we can determine the time of flight. The timing inaccuracy is termed jitter; we use various metrics to quantify the jitter, but most of these metrics just capture the usual case. For SPADs, the jitter depends on a few things.
First, the temperature is very important. In a silicon integrated circuit, increasing the temperature increases the ambient energy available to electrons, the main information carriers in the circuit. The introduction of additional energy modifies a carrier's behavior, and thus changing the temperature will change the characteristics of both the fast and slow feedback loops in SPADs.
Next, the color of the light is also important. Different colors of light have different wavelengths. The wavelength describes how frequently the energy moves around in space. Since silicon has a repeating structure, the wavelengths will help determine how likely it is that the light interacts with the crystal, producing the primary electron that could cause an avalanche. It turns out that blue light is optimal for the current generation of SPADs - the optimal wavelength is a balance between how far light usually penetrates into the silicon and where the avalanche region is (remember that we moved the region away from the surface to avoid the noise-causing irregularities at the surface).
Within the avalanche region, the build-up time of the avalanche is obviously important. During the initial portion of the positive feed-back loop, when there are very few carriers active, the variation in each carrier can change the build-up time. Current understanding is that it takes between 0 and 15 picoseconds to generate enough carriers to average out these variations, though this build-up process depends on characteristics like the temperature and strength of the applied force (the electric field).
So what is the end result? Well it depends on what you need and what you have available. If you have a lot of area available on a silicon chip, you can use more complex current detectors to get the jitter as low as 15 or 20 picoseconds. On the other hand, if you're short on area you can raise the jitter as much as you like, but you'd be hard-pressed to raise it above nanoseconds and still have a viable application. Keep in mind that you'll be changing how close the SPADs are, so the cross-talk will change.
When you're making a range-finder, you might care only about one specific range, or you might be trying to acquire a bunch of ranges to get a 3D pictures. If you only care about one range, you can use a lot of area to achieve the 20 picosecond resolution. This corresponds to an uncertainty in space around 6 millimeters. If you have an array of SPADs and timing circuitry, you're more likely to have an error in the 100 picosecond range. 100 picoseconds corresponds to an error of 3 cm in space. You can lower this uncertainty by taking multiple measurements, and since the measurements are so fast the accuracy can easily be one millimeter or less.
Anyways, I hope this post helped you understand about the timing uncertainty in SPADs. The uncertainty affects other applications besides rangefinding, things like quantum-based encryption algorithms, biological imaging, and cancer detection, but those applications are a bit more complicated to explain! I'll be attempting in future posts, and we'll see how it goes.
Another Airbrushing Site
I stumbled across a really interesting airbrushing site today...I can never click through enough of these to remind me how much people are mis-represented in print and online media. (earlier post)
2009-08-27
Question
Why are TVs and computer monitors horizontally long, but paper is vertically long? I suppose it makes sense that monitors and TVs are horizontal, as this matches our visual field, but then why is paper tall, rather than wide?
2009-08-17
Firsts
It has been a year! Here are some of the things I've done in the past year:
1) Forgot / lost passport, had to travel 3 hours to get it back
2) Setup an experiment using somewhat dangerous radiation while I was suffering a headache from lack of sleep
3) Was the last person on a plane, having nearly missed it (this experience is over-rated)
4) Laid out a portion of an integrated ciricuit that (if it works, crosses fingers!) will have 5.12 GBps going through it
5) Lost PhD topic
5.5) Lost PhD topic
6) Found PhD topic (errrr.....I think?)
7) Went all-in and won a poker pot, went all-in and lost a poker pot, successfully spotted a bluff at a poker table, successfully set a trap at a poker table
8) Gone to one of those fancy European clubs in Paris (it was worse than I thought and I will not be returning)
9) Bought plane tickets, booked a hotel, flew on plane and checked into hotel within 5 hours of one another
10) Successfully found apartment in a foreign country and moved into it from another apartment
11) Gotten a first-hand view of how difficult it is to be an immigrant
12) Earned the title Expatriate
Things I haven't done:
1) Successfully had a conversation in Dutch (I haven't had many successful ones in English over here, either)
2) Joined a choir
3) Written a paper (I'm working on one right now, and I have two in various stages of the paper pipeline)
4) Used tools to go from VHDL to ASIC
By the numbers:
Guitars purchased - 1
Bicycles purchased - 1
Haircuts - 2
"Original" research ideas that someone else had actually tried but adviser didn't know about - 3
Canned hot dogs consumed - 4
Moose seen - 4 (two real, two mascots)
Shoes purchased - 6
Countries book was purchased in - 5 (6 if you separate England and Scotland, 7 if you include online purchases)
Countries "visited" - 7 (Scotland, US, Canada, Switzerland, Ghana, France, Belgium)
Passport resources used - 27 boxes from stamps, 2 pages from visas
Train tickets purchased - ~100 (I go through about 8 a month)
PB&J Sandwichs consumed - ~150 (they have this awesome sour cherry jam over here)
Emails sent - 2,088 (more than I thought, 25 were to myself)
Emails received - 2,698 (fewer than I thought)
Most lines of code written in a single day - ~3,200 (most of it was test code...firmware test code can be pretty massive to go through the appropriate states)
Lines of code written overall - ~16,000 (again, around 14,000 lines are test code)
Heartbeats - ~37,000,000 (the heart is a work of art)
And finally:
Dutch postcards sent - 0 (yeeeeeeeah...I still owe a lot of people postcards.....)
1) Forgot / lost passport, had to travel 3 hours to get it back
2) Setup an experiment using somewhat dangerous radiation while I was suffering a headache from lack of sleep
3) Was the last person on a plane, having nearly missed it (this experience is over-rated)
4) Laid out a portion of an integrated ciricuit that (if it works, crosses fingers!) will have 5.12 GBps going through it
5) Lost PhD topic
5.5) Lost PhD topic
6) Found PhD topic (errrr.....I think?)
7) Went all-in and won a poker pot, went all-in and lost a poker pot, successfully spotted a bluff at a poker table, successfully set a trap at a poker table
8) Gone to one of those fancy European clubs in Paris (it was worse than I thought and I will not be returning)
9) Bought plane tickets, booked a hotel, flew on plane and checked into hotel within 5 hours of one another
10) Successfully found apartment in a foreign country and moved into it from another apartment
11) Gotten a first-hand view of how difficult it is to be an immigrant
12) Earned the title Expatriate
Things I haven't done:
1) Successfully had a conversation in Dutch (I haven't had many successful ones in English over here, either)
2) Joined a choir
3) Written a paper (I'm working on one right now, and I have two in various stages of the paper pipeline)
4) Used tools to go from VHDL to ASIC
By the numbers:
Guitars purchased - 1
Bicycles purchased - 1
Haircuts - 2
"Original" research ideas that someone else had actually tried but adviser didn't know about - 3
Canned hot dogs consumed - 4
Moose seen - 4 (two real, two mascots)
Shoes purchased - 6
Countries book was purchased in - 5 (6 if you separate England and Scotland, 7 if you include online purchases)
Countries "visited" - 7 (Scotland, US, Canada, Switzerland, Ghana, France, Belgium)
Passport resources used - 27 boxes from stamps, 2 pages from visas
Train tickets purchased - ~100 (I go through about 8 a month)
PB&J Sandwichs consumed - ~150 (they have this awesome sour cherry jam over here)
Emails sent - 2,088 (more than I thought, 25 were to myself)
Emails received - 2,698 (fewer than I thought)
Most lines of code written in a single day - ~3,200 (most of it was test code...firmware test code can be pretty massive to go through the appropriate states)
Lines of code written overall - ~16,000 (again, around 14,000 lines are test code)
Heartbeats - ~37,000,000 (the heart is a work of art)
And finally:
Dutch postcards sent - 0 (yeeeeeeeah...I still owe a lot of people postcards.....)
$500 for a Bicycle
The Freakonomics blog has a great post on the cost of bicycles in bicycle-crazy Portland:
I bought an inexpensive, new bicycle in Delft for just over $500, though the university reimbursed most of the cost through a travel program. I was expecting to find a nice, new one for around $250.
We don't have CostCo here, and sadly Ikea doesn't sell bicycles. I'll just keep dreaming.
Yeah, the bike guy answered, he had something super-cheap for me ... I could have it, he said, for $475.
So I went to another store. Same deal, more or less. There was one bike for $275, but it was a girl’s Raleigh from the 1960’s with a wicker basket.
...
At Portland’s Costco, meanwhile — on the outskirts of the city — you can buy a brand-new Schwinn Midtown city bike with Shimano shifters for around $200. But, according to the clerk there, those Schwinns aren’t moving.
I bought an inexpensive, new bicycle in Delft for just over $500, though the university reimbursed most of the cost through a travel program. I was expecting to find a nice, new one for around $250.
We don't have CostCo here, and sadly Ikea doesn't sell bicycles. I'll just keep dreaming.
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