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Beautiful, elegant models March 27, 2014

Posted by mareserinitatis in engineering, geology, physics, research.
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I’m interested in the different uses of the word model.  Of course, the most common reference (outside of science and engineering) is to someone who wears expensive clothes.  Upon encountering such a model, most of us in the sciences and engineering wonder how they could charge so much for so little fabric.

In science and engineering, however, I’m discovering that I don’t like the use of the word because it’s ubiquitous and therefore nearly useless.  The problem I’ve run into is that everyone uses it but not necessarily for the same things.  In one field (or to one person), it means the equations describing a phenomenon.  In another field, it’s a computational model incorporating those equations in a specific configuration.  In yet a third field, it can describe a computational framework.  Then there are models that are simple calculations to describe inputs and outputs of a system.  And finally, I’ve also heard someone refer to it as a non-quantitative description of a process.

I’m slowly realizing that a model depends on what you and your field emphasize.  It’s used to describe an abstraction or an idea of the process, but what you’re describing as a model is extremely dependent on your training.

I think I may go back to using it to describe the walking mannequin.


The moment you’ve all been waiting for… February 21, 2014

Posted by mareserinitatis in engineering, feminism.
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Before I make a small announcement, I’m going to provide a wonderful piece of advice.  If you plan to marry an engineer, add a whiteboard and some markers to the registry.  You’ll need them in case you ever have an argument with your soon to be spouse.

Now that that’s out of the way (and you’ve waited for a moment, so that the title of this post is appropriate…although I have to admit waiting much longer than that), I wanted to thank the folks at Engineering Commons for inviting me as a guest on their podcast.  I discussed the issue of women in engineering (among several other things), and it was quite a bit of fun.  If you’d like to listen, you can find it here: http://theengineeringcommons.com/episode-49-women-in-engineering/

Please let me know what you have any thoughts on the conversation!

Wordless Wednesday: The engineering section January 29, 2014

Posted by mareserinitatis in engineering, photography.
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I think you have the wrong engineer December 12, 2013

Posted by mareserinitatis in engineering, papers.
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Every few weeks, I get a request to review papers for a conference.  (For those who are sciencey types, a lot of engineering conferences require full, peer-reviewed papers rather than abstracts.)  At first, this was rather cool and accepted the first half dozen that came to me.  Then I started realizing that it was a bad idea, but not simply because, as you expect, it required a decent amount of time.

I started realizing I had no business reviewing some of those papers.  The reviews often request that you assess your own knowledge and expertise in the area.  Unfortunately, many of them didn’t have an option that was similar to, “Ignorant dolt.”  The best I could do was say I had a passing knowledge and try to make constructive comments on the lack of legible text in the legend and poor grammar here and there.  Oh…and finding out that half of their text was copied and pasted from another document.

I have to wonder why they aren’t more careful about screening potential reviewers given most of my requests come from a service which describes my qualifications.  After all, there are several subdisciplines within electrical engineering, and I don’t imagine too many people are knowledgeable about the state of the art for all of them.  Beyond that, my undergrad is in physics, so my knowledge of EE is probably even more limited than your standard engineer.

I guess I’m probably a decent reviewer as long as as you’re only looking for someone who can point out when something is undecipherable.  Maybe I should add that to my skills: unenlightening critiques.

Falling to pieces August 1, 2013

Posted by mareserinitatis in engineering, photography.
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Yesterday, I posted a picture of a textbook I use as a reference.  The picture showed pages detaching from the glue binding.  Sadly, the problem is worse than it appears:


I’m beginning to think a lot of textbook manufacturers aren’t really using glue but maybe teflon in their binding.  Or something along those lines.  My husband has an older edition of this book that’s held up better than this one.  I would like to replace it with an ebook, but my brain has a hard time handling technical information on a computer screen.  Paper seems to be best.

Better find the duct tape.

Wordless Wednesday: Coming unglued July 31, 2013

Posted by mareserinitatis in electromagnetics, engineering, photography.
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Whom to believe December 5, 2012

Posted by mareserinitatis in engineering, research, work.
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I went to conference earlier this year in Tucson, Arizona.  While there, I saw a lot of cool presentations, but one in particular really got me interested.  I knew we’d done some work similar to this presentation, and it was obvious that there was some interest in the area.  However, I wanted to come up with a different application so as not to be competing with work  already being done.

When I came back, we did a lot of brainstorming, but couldn’t quite come up with anything.  Or rather, it’s not that we didn’t come up with anything but that the practicalities of applying this solution to the application in mind had some serious issues.  The idea sat for months in the back of my head, churning.  Finally, about 3 months ago, I came up with a method to deal with the problems.  I got together some people whose skills were required, convinced them my crazy idea might have some merit, and we started writing out proposals and white papers.

(Note: coming up with an idea less than two weeks before the opening of proposal windows for major funding agencies is NOT a good idea.)

Of the few people who have heard about this idea, they generally liked it and thought it was clever as well as pragmatic.  (And here I feel like I’m doing well if I manage to hit one of those!)  However, there was one person who really did NOT like the idea.  In meeting with this person, they spent a good chunk of our meeting dismissing it and pointing out its flaws.  I was feeling, after talking with this person, that maybe I’d made a mistake and the idea wasn’t terribly good.  In fact, I really felt like they were suggesting the project was a waste of time.

Four days later, I got an email saying that the letter of intent submitted to one funding agency had been reviewed: they want a full proposal.  I felt considerably better after that.  However, rather than feeling entirely vindicated, I think I might want to sit down and take notes on the drawbacks and flaws that were pointed out.  Hopefully, this will contribute to a better final proposal.

After that email, however, I’m not sure I believe that the idea is a total loss.  I guess the funding agencies will let me know one way or the other.

Students finding their direction June 23, 2012

Posted by mareserinitatis in education, engineering, geology, geophysics, physics, research, teaching.
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The younger son’s birthday was this week, and we opted to host a pool party at a local hotel.  (IMO, pool parties are the best for the elementary school age group: they keep themselves busy and then go home exhausted.)  I was checking in when I noticed a young man standing at the other end of the counter.  He looked familiar, so I asked if I knew him.

“I took your class last fall.”

“Oh great!  How did the rest of the school year go for you?”

“Great.  I actually switched to business and am really liking it.”

“Really?  Why did you switch?”

“I just figured I liked business a lot better.”

“That’s why they have you take those early major classes – so that you find out you don’t like it before you get too far into it.”

I think the poor kid thought I would be mad that he had switched.  But I wasn’t mad at all.  If he feels like he’d be better off in a different major, then he ought to go for it.  And that is part of what I’m trying to set out in the class – this is what engineers do.  If it doesn’t look fun, then you ought to think about a different major.  That’s a perfectly valid choice, and no one should judge a student for it.

(Yeah, I know…I sit here and wring my hands because older son gets these obnoxiously high scores in math and science but wants to be a writer…I’m one to talk.)

But seriously, I actually think it’s sort of silly to make students choose a major really early on in school.  I think it’s a good idea to try to take a lot of classes in different fields before you really choose.  I say this as someone who major hopped a lot during undergrad.  I spent some time in physics, chemistry, journalism, and graphic arts.  I finally decided that I liked physics after all, but what got me excited was geophysics.  I happened to take a geology class when I was at Caltech because I had to take a lab course, and everyone told me geology was the easiest.  Turns out, I really liked it and did very well in the course.  (Of course, later on, I found that geology feels too qualitative and prefer geophysics, so it all worked out.  On the other hand, I think I would’ve liked geology better if it had all been field courses.)  🙂

I have run into people who got upset with me for this type of thing.  I was doing research with a professor in undergrad, but I felt like the research wasn’t going well and got sort of excited about a math project that I’d seen a professor give a talk about.  I talked to that professor to see if he’d be interested in having me as a student, which he was.   When I told the other professor that I was going to work with the math professor, all hell broke loose.  (I still think I made the right choice, though, especially since the first project really never did go anywhere.)  I have yet to figure out why the first professor got upset, though, and did some petty stuff, like kicking me out of the student office (despite no one needing a spot) and having the secretary take away my mailbox.  (This was silly, BTW, as I was president of the Society of Physics Students, so she ended up giving it back to me a month later so I could get SPS mail.)

And what did this do?  Certainly reinforced that I didn’t want to work with this person, but I could also see it making a student feel like this person is representative of a particular field.  Wouldn’t you wonder if a student would not want to go into a major because of the way the professors treat him or her?  I can (and did!), and it just shows how ridiculous the whole thing was.

No, students need  some time to explore their interests and getting mad at them for not doing what you think they should do is silly.  They are the ones who have to deal with the consequences of their choices, and if a student takes my class and decides they don’t want to spend the next five to ten years of their life studying engineering, then I think they’ve learned something very important and just as valid as anything else I have to teach them.

Repost: Microwave Unsafe or Unsafe Microwave June 22, 2012

Posted by mareserinitatis in electromagnetics, engineering, food/cooking, science.
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(Note: this is from the old blog, back when living in Minneapolis)

There’s nothing like a nice, hot cup of English Breakfast or Earl Grey in the morning…until you reach into the microwave and burn your hand on your mug.

I’ve noticed something very irritating. Since I moved into my new place, all of my dishes get hot and some of them have cracking glaze after use in the microwave. The most irritating thing, aside from the pain, is that I’ve noticed my favorite mug is expanding and shrinking. It expands when heated and then contracts as it cools. This, unfortunately, has caused my tea basket to get physically stuck in the mug, which never happened with my old microwave (thus eliminating the notion that heating of the basket causes it to expand and get stuck).

Traditionally, this means that my dishes are not “microwave safe”. In other words, there is something in the dishes that heats up when put in the microwave. That means that you can destroy the dishes and burn yourself.

It wouldn’t be that big an issue except that all of these dishes worked fine in my other microwave back in Fargo.


This has led me to look into what might be causing the problem. Hypothetically, if something is microwave safe in one microwave, it should be that way in all microwaves.


There are lots of places that give you the basics of how a microwave works. A brief overview is that it emits electromagnetic waves which cause water molecules in food to rotate. The frequency of most commercial microwaves for the home is around 2.45 GHz, which is apparently a good frequency to get water molecules to “flip”. Flipping, rotating, shaking are all ways that molecules move, and molecular movement translates into heat. So the microwave makes all these water molecules do their jig because it excites them at just the right tempo. If you try exciting them at a different frequency or tempo, the water molecules won’t respond as well.

It’s harder to find information about how microwaves create these fields. It turns out that they generate electromagnetic waves with something called a magnetron. (An excellent and quite detailed description of how they work can be found here. According to The Art of Electronics, magnetrons fall under the category of “exotic devices”. This is probably code for “uses an electromagnetic field in a non-obvious way” or maybe “doesn’t always use silicon to do its job”. Interestingly enough, these are the same devices used to create fields for radar, including the Doppler radar that is used to look at cloud cover and precipitation. (If you’re a Wunderground nerd, like me, you spend a lot of time looking at images generated by Doppler radar.)

Again, I’ll summarize. There is a cathode (something which generates electrons) running down the middle of a cylindrical chamber. The chamber is subdivided into resonant chambers. Resonant chambers are areas where electromagnetic energy creates a standing wave. (A good though not exact analogy from sound, which is also a wave, would be an organ pipe.) The electrons formed around the cathode form into groups which spin and sweep past the resonant chamber openings. Because moving charge creates an electromagnetic wave which becomes a standing wave in the resonant chambers. This wave then creates a current in a wire or “feed”, which conducts a current to a waveguide. A waveguide is basically a replacement for a wire. It conducts an electromagnetic field when the power is too high or you could easily lose too much power through a wire. (Wires can be awfully lossy.) All it looks like is a rectangular tube, but the size of the tube is important because this will determine the frequency of the waves it can carry. (Remember, we want to have things pretty sharply focused at 2.45 GHz.) This tube leads into the microwave chamber which is tada! a Faraday cage. This is something that will contain electromagnetic energy inside of it without letting it escape as well as keep electromagnetic energy from your surroundings out. In this case, we want the energy inside. Waves which don’t hit our food will hit the side of the chamber and bounce around until it hits the food.

That metal screen is part of the Faraday cage and is keeping your brains from being baked when you’re pressing your nose to the glass going, “When will it be done?!”

Many microwaves contain things that look like fans but are actually “mixers” or “stirrers”. They cause the waves to bounce more randomly and create a more even distribution of the waves for heating. When the waves hit your food, they can only penetrate to about an inch. How far the wave goes into the food is quantified by something called a “skin depth”. Because your food isn’t a good conductor (like copper) which has pretty much no penetration depth, you will often notice that things get hot on the outside but not on the inside, like often happens to me when I reheat lasagna.

Food is also not a pure dielectric (like air or styrofoam) where the wave passes through and can’t generate a current inside. Food which is more conductive (which will likely have more water) will tend to heat up better or faster (as well as internally distribute that heat better) than food that doesn’t. Conductive food will also tend to have more water. In this case, you may be heating up a fruit-filled pie. The pie filling has a lot of water and will heat up fast, but the crust doesn’t and doesn’t seem to get as warm. You bite in, expecting the filling to be the same temp as the crust but end up getting burned instead.

People who design fast food meals ought to consult with microwave engineers on optimal heating set up. 🙂

As I mentioned before, microwave safe dishes don’t contain anything that will heat up when exposed to microwaves. Dishes which aren’t microwave safe contain some molecules that will be able to rotate, twist or vibrate in some way similar to water, causing the dish to heat up.

Sometimes you have dishes which are “thermally conductive”…that is, they transfer heat well. While you’re heating up your food, the dish is pulling a lot of that heat away from the food and into itself, causing the dish to get hot.

However, that doesn’t seem to be my situation. My previous microwave was much a higher power and seemed to heat up the food fine without heating up the dishes. My current one seems to do nearly the opposite. And since these are the same dishes, I have to conclude that it is in fact the microwave with the issue.

My first guess is one that doesn’t seem plausible. I don’t think it has anything to do with the size/shape of the magnetron or waveguide. Those are fairly large objects that can be mass constructed well within tolerances. I could be wrong, but that’s my initial guess. This also minimizes the chance that there may be some sort of mismatch between the magnetron and the waveguide.

Looking at the remaining possibilities, I’ve come up with three.

The first is that my microwave is poorly designed in the sense that it doesn’t direct electromagnetic energy well. This may be part of the problem as it seems to heat the dishes in areas away from the food. I don’t think that this is the entire issue because, if designed poorly, the wave should just bounce around until it hits something with high water content. However, I can’t say it’s not doing this.

There are two other possibilities. It turns out that magnetron frequency can change both with the temperature and the current through the cathode. Although the cathode temperatures get pretty high, I doubt that it would be that huge a change from a prototype once it gets over the initial change.

The last option seems most likely to me: the cathode isn’t working exactly the way it’s supposed to (which can be characterized by something called a “pushing curve”). If the current from the cathode is too high or too low, this will change the way the electrons behave, which will alter the frequency of the wave being generated by the magnetron.

In doing some research on my microwave, it turns out to have a horrid reputation. They die a lot, like within a year. Unfortunately, they’re so cheap that it’s not worth it to send them in for repairs because you have to pay for shipping to and from. When microwaves die like this, a lot of times it can be due to power problems, and thus the design of the controlling electronics or the high voltage power system can come into play. (Did I mention that magnetrons require huge voltages to operate???)

It appears that perhaps this line of microwaves may not have the best electronics design, and for whatever reason, the power into the magnetron isn’t quite right. This is causing my dishes to heat and expand while not heating my food optimally.

I guess I’ll be using oven mitts to take everything out of there until it decides to kick the bucket.

Friday Fun: How dogs keep cool & cool things with control theory June 22, 2012

Posted by mareserinitatis in engineering, Friday Fun, pets.
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A friend posted the following video on facebook.  I think I may use this with my class this fall, so they can get a good handle on the cool things you can do with control theory:

This is based on the following video created with computer animation.  (I find it amusing that for so many  years, we’ve been trying to master creating animation that looks real, and now Intel tried to make something real that mimicked an animation.)

Once you’ve finished watching those, you’ll want to check out the latest cartoon featuring Gigadog.  (I think all Newf owners understand this one…)

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