Dale Peterson

Mode shapes and modal decomposition

luke — Wed, 07 Dec 2011 08:55:40 +0000

I recently did a lecture in a mechanical vibrations course on mode shapes and modal decomposition. I made a handout for the material to summarize the main ideas.

Sad

luke — Sat, 26 Nov 2011 04:28:29 +0000

Success in court

luke — Wed, 23 Nov 2011 22:08:16 +0000

I pleaded not guilty to a bicycle stop sign violation in Yolo county today. The judge found there to be reasonable doubt, and I was found not guilty.

I was cited for failure to stop at the stop sign while headed eastbound at the intersection of East 8th street and J street, Davis, CA. The citation occurred at 9:05am on a weekday. The officer stated the indisputable facts of the case, and the key to my argument was that he was on the west side of J street, about 100 feet north of E 8th street, facing south. I was coming to the intersection from the officers right, but I was in the bike lane next to the cars, so his view of me would be obstructed by automobile traffic had there been any. I asked him if he recalled there being traffic at the intersection at the time of the incident. He responded that he didn’t recall there being any. I asked him also whether he would be able to see through the cars to see whether I stopped. He responded that he couldn’t testify whether or not he could. I then presented my case, which is as follows.

I commute by bicycle and pass through this intersection 2-4 times per day. I know the stop signs are there and I know that I stop for them. In the particular day in question, I recall there being traffic and being adjacent to cars (on the south side of eastbound traffic) as I approached the intersection. I recall stopping, as I always do at that intersection. I disputed the officer’s testimony that he could see me approach the intersection without slowing down and that I went through the intersection without stopping. I argued that he couldn’t have seen me not stop because there were cars in between him and I. I also reemphasized that I frequent this intersection a lot and that I always stop. The officer responded by repeating his original statements but didn’t really add anything new to what he originally testified. I responded by emphasizing that I know for a fact that there was traffic since it was 9:05am, and that there was no way he could have seen whether or not I stopped from his position, and that I pass through that intersection frequently and always stop.

The judge stated that he found there to be reasonable doubt of my guilt and that since there was no further evidence, I was found not guilty.

So, it was worth making 2 trips to the Yolo courthouse because I saved myself $200 and also avoided points being added to my DMV record.

Feynman Lectures Exercise Challenge

luke — Mon, 14 Nov 2011 10:17:06 +0000

I noticed that the editors/publshers of the revised Feynman Lectures on Physics posted a challenge problem, so I decided to work out a solution. In doing so, I took the time to learn TikZ. The result was a pretty nice (I think) drawing of the pendulum system described in that problem. My solution is available here.

The price of a single stitch

luke — Sun, 30 Oct 2011 18:26:18 +0000

About 2 months ago on a Saturday evening, I was working on my bike and cut the middle joint of my index finger. The cut was deep enough, and the hacksaw was dirty enough, that I knew that I needed get it looked by a doctor. I looked up my health benefits on my insurance card and tried to find a clinic that was open at 9pm on a Saturday night. Nothing was open anywhere. So, my options were to wait until Monday, or go to the ER. I choose to go to the ER. They weren’t busy and I was in and out in less than 45 minutes. They cleaned the wound and put a single stitch in it, then put a bit of neosporin on it and put a band aid on it.

The total cost? $1060.71. Seriously? Luckily I am insured, and I am only responsible for $100 of that. I don’t know what the cost would have been if I had gone to a clinic during normal business hours (8am-5pm on a weekday).

If I didn’t have insurance, would I have gone? I don’t think so. With national unemployment at 9.1% it is a safe bet that at least 1 in 10, probably 1 in 5, either don’t have health insurance or have insurance that wouldn’t cover enough for them to be able to afford such a trip to the hospital to get a relatively minor finger injury taken care of properly. So 1 in 5 wouldn’t get such a serious injury taken care of. Imagine if it were a more serious injury. This system is broken.

Matlab function syntax is abysmal

luke — Wed, 12 Oct 2011 00:40:14 +0000

Today I was helping some undergraduates in a mechanical vibrations course to use ode45. The way you specify the right hand side of the ode’s must fit Matlab’s particular form (using an @ before the function name, which must be contained in a file of the same name, with a ‘.m’ extension). Looking at the documentation, I found this gem that really made me want to suck start a shotgun:
One way to provide additional parameters to a functional argument of a function function is to write a file that: -- Accepts the additional parameters as inputs -- Invokes the function function -- Contains the function called by the function function as a nested function
That last one is a real doozy. Try saying that 5 times real fast, then explain what the hell it means to an undergrad. I’d rather explain what a pointer to pointer to char is, personally.

MathJax test

luke — Wed, 11 May 2011 23:32:13 +0000

I’ve been using $\LaTeX$ for about 7 years now, and have always been impressed with its ability to make math and text look amazing. Obviously, a serious shortfall of the web has been to be able to incorporate math directly into web pages. There have been lots of approaches, but most of them have been ugly hacks that just can’t replace $\LaTeX$. Until now. MathJax looks amazing! Here is a quick example:
\[
\begin{aligned}
P_\nu^{-\mu}(z)&=\frac{\left(z^2-1\right)^{\frac{\mu}{2}}}{2^\mu \sqrt{\pi}\Gamma\left(\mu+\frac{1}{2}\right)}\int_{-1}^1\frac{\left(1-t^2\right)^{\mu -\frac{1}{2}}}{\left(z+t\sqrt{z^2-1}\right)^{\mu-\nu}}dt\\
&=42\\
&=\boldsymbol{b}_1
\end{aligned}
\]

Notice that you can click on the math, view the source that created it, and copy and paste it!!!

This is really going to help science make better use of the web.

High speed voltage level translators

luke — Wed, 01 Dec 2010 01:09:50 +0000

My robotic bike has several 5.0V devices (encoders and motor controllers, and a 5.0V Arduino Mega), as well as several 3.3V logic level devices (Vector Nav VN-100 IMU, SST SPI Flash). For high speed voltage level conversion, I found these products from Maxim-IC:

http://www.maxim-ic.com/datasheet/index.mvp/id/3672

They will convert from 1.2V to 5.5V, or 5.5V to 1.2V and are specifically designed for high speed digital I/O (like SPI and I2C). I ordered some samples and I’ll be testing them out as soon as they come in.

I also found a place that sells a ton of breakout boards for all different types of SMT devices:

http://www.proto-advantage.com/store/

The prices range from $3-5, and they have detailed specs of every board, so you can be sure you get the board that fits your physical package.

Animation of the motion of the bicycle

luke — Sun, 06 Jun 2010 05:41:19 +0000

New VPS

luke — Sun, 06 Jun 2010 01:49:28 +0000

My VPS host just upgraded their servers to Ubuntu 10.04, so I just spent today saving all my old stuff, wiping my VPS, and reinstalling everything. I was using nginx as my webserver previously, but now I’m using lighttpd, and it was pretty easy to setup. I’m still ironing out the bugs, but I was able to get most everything up in running in several hours, so I hope to have the rest dialed in very soon.