Repost: Microwave Unsafe or Unsafe Microwave June 22, 2012Posted by mareserinitatis in electromagnetics, engineering, food/cooking, science.
Tags: cooking, engineering, food, microwaves
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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.
Musings on research June 13, 2012Posted by mareserinitatis in career, engineering, grad school, papers, research, science.
Tags: engineering, engineering research, research, scooped
I made an interesting observation today. It’s funny that I should’ve noticed this before, but I didn’t.
I have finally come to the realization that the question, “How’s your research going?” is really a euphemism for, “How long until you’ve finished your PhD?” I’m not sure why it didn’t hit me before. My usual response to the question is to ask ‘which research?’ because I work in two totally different areas of research, both of which I find pretty fascinating. I thought the person asking the question was actually interested in what I was doing.
Nope. I realized today that they always say, “Why, your PhD work, of course!” And, when it comes down to it, only a handful of people who ask really are interested in the research itself. Most are just interested in how close that completion date is.
The reason I should’ve realized this before is because my husband got the question all the time. It didn’t occur to me until this line of thought became clear that once he’d graduated, people started asking, “How’s work?” (And usually, they aren’t interested in his research, either.)
If there isn’t a PhD comic strip devoted to this topic yet, there ought to be.
I got scooped. (A work related project – not my dissertation.) It was a small side project that I’d worked on here and there but had really not had any significant time to commit to. I’d gotten started on it and looked at things here and there. In part, I was waiting for someone else to finish some of his software development. (Of course, he was laid off earlier this year…so I imagine I’ll be waiting a while.)
Anyway, I am kicking myself because I obviously had a good idea (given someone else published exactly. the. same. thing.), but there was just no time to flesh it out. Did I make the right choice by focusing on other things or did I miss the boat? On the other hand…hey! I had a good idea. I, of course, have a couple of ideas of things that can be done based on the original project, but it’s disappointing that I won’t have the paper that gives the original idea. Of course, at the rate that particular project is going (because it’s so low priority…just some ideas I had playing around in the lab), I’m not sure I’ll ever get those other papers out.
This makes me wonder…is it good to focus on the ‘next big thing’? Or should one keep trying to work on those little things in the meantime? How do you prioritize? I think I made the right decision…but it’s easy to second-guess yourself.
How I saved a caterpillar from certain doom May 22, 2012Posted by mareserinitatis in pets, science, younger son.
Tags: caterpillar, younger son
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On Sunday evening, the family got together with the local astronomy club to watch the annular eclipse. The younger boy stayed interested for about 10 minutes before deciding to go play with some other kids near the trees. One of the girls found a caterpillar but wasn’t allowed to bring it with her, so the younger boy asked if he could bring it home.
“Sure,” I said. I hoped this would give me a slight reprieve from his constantly begging for yet another pet. (We have two cats and a dog…but I’m constantly fielding requests for birds, rodentia, fish…and even a gecko.) I figured that, in terms of pets, a caterpillar was probably going to be fairly low on the required maintenance scale. Also, the whole life cycle thing is interesting to watch.
Said caterpillar is now residing in a large plastic cup with a lid in younger boy’s room. He’s been talking non-stop about caterpillars since he got it. But this morning, he came out and the first thing he said was, “My caterpillar is dead.” He then walked quite slowly over to the garbage in the kitchen and put the cup in there. I asked what had happened, and he said it was broken into a bunch of little pieces. Now, even if it had died immediately after we brought it home, it shouldn’t have desiccated that quickly. I fished the cup out of the garbage and opened it up. Sure enough, there was black stuff at the bottom, but the caterpillar was sitting there clinging to a stick. I pulled it out and showed the younger son, who couldn’t see it at first because it was nearly the same color as the stick. I also explained that the black stuff in the bottom was caterpillar feces.
“So caterpillars have privates like us?” Well…sort of. They certainly have digestive systems and whatever they eat is going to have to come out. Pretty soon the younger son was babbling about caterpillar poo.
Anyway, I felt pretty good about having a second look until I went online to find out what kind of caterpillar it is. Chances are pretty good that it’s an eastern tent caterpillar…and it’s probably going to be a nasty looking moth. Blech. (Did I mention I don’t like moths?)
Permanent position April 24, 2012Posted by mareserinitatis in education, research, science.
Tags: academia, funding, science funding, soft money
The other day, I was talking with a professor who was asking about my employment situation. After clarifying where I was at, he said, “But your husband has a permanent position, right?”
“Permanent insofar as he’s on soft money, too.”
One thing that’s become fairly obvious is that there has been a bit of confusion about our research center. A lot of people don’t realize we run entirely on soft money, which is a very uncomfortable situation to be in. It’s even more uncomfortable when both members of a couple are in that situation.
I recently read this article about the money trail in academia, and it got me thinking: what would happen if PIs were in the same situation as some of the rest of us. That is, what if they not only had no tenure, but also had to bring in their own salary? (I say this is the realization that, in some places, this is the case.)
I have a lot of thoughts on what may happen, but I’m going to put them in a separate post. In fact, by the time this post has been published, I will already have my post written so as to be untainted by potential comments. In the meantime, however, I’m curious what you think. Do you think this sort of system would help or hurt academia? Encourage or discourage competition, quality, efficiency? Do you think this would motivate the system to change or would it just be more of the same?
Famous April 11, 2012Posted by mareserinitatis in career, research, science, solar physics.
Tags: famous, publicity
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I’m not sure if it’s because I live in a small town, but I had something odd happen yesterday. There is a wonderful bakery in town which has things like sandwiches and soup. It’s also the only place in town (that I know of) with no internet, so I go there when I have things to do like grading.
Yesterday, as I was buying some lunch, one of the people working there came up and said he’d seen the profile of my research in the paper a couple weeks ago and asked me some questions about it. Given it’s been a couple of weeks, I’m surprised he remembered seeing it. On the other hand, because I’m in there fairly often, I wondered if he recognized me when he saw the article. But it was kind of cool to be recognized.
The Brain Drain March 22, 2012Posted by mareserinitatis in education, Fargo, grad school, research, science, societal commentary.
Tags: fargo, higher education, north dakota, politics, universities
Yesterday, I was getting into my car when I noticed something on my windshield.
My neighbor had seen the article about me in yesterday’s paper and left me a message about it. In fact, it hit three of major newspapers in the state. (If you care to read it, one copy is located here.)
When I was asked by the public relations person at NDSU if she could feature my research as part of an effort to promote the supercomputing facilities on campus, I was certainly glad to do so. First, from a simply pragmatic point of view, it’s not a good idea to bite the hand that feeds you. (Although, to be honest, they have a lot of other projects they could’ve featured.) Second, and more important in my mind, is that this type of thing counters some of the negative attitude about the state universities in the western part of the state.
People from out of state (probably the 4 of my 5 readers) are probably not aware that there is a bit of a divide in state politics, and it can be roughly framed by drawing a vertical line down the center of the state. The eastern part of the state has the major universities and sees the benefits of having them. The western part of the state thinks the universities are sucking all of their hard-earned money, and worse yet – children, away from them.
Growing up in the 80s and 90s all I heard about was the ‘brain drain’ that the state was suffering: all of those bright, hard-working, born-in-North-Dakota kids were being educated at a low cost and then leaving the state. The people in the western part of the state seemed to think we just ought not to spend so much money educating them. I don’t think they understood that the likely result of that would not be to prevent brain drain but to accelerate it as those students would end up leaving for colleges out of state. On the other hand, the eastern part of the state was asking for more and more money to fund already seriously underfunded universities which were teaching a lot more kids than they could realistically accommodate. And we won’t even talk about research. The universities are supposed to be there to serve the students from the state…what does research have to do with anything?
I was one of those kids that left straight out to go to college, and I really had no intention of returning. I wanted to do research, and I knew that coming out of high school. I knew that because I’d gotten involved in research through a state-sponsored program at NDSU as a high school student, and I also knew that I likely couldn’t do what I wanted here. And why should I, when I could go someplace better?
If you fast forward to about 2000 (when I came back to return to school), there were some significant changes happening. Great Plains software was bought out by Microsoft, making it the second largest Microsoft campus in the world. There were companies in town doing engineering. There was a way to stay in North Dakota with a technical degree. And about that same time, NDSU started to make some aggressive moves to increase the size and reputation of its campus.
In the past ten years (even before the oil boom in the western part of the state), this significantly slowed the population loss the state was suffering. However, the western part of the state was still shrinking, and this was probably aggravating the divide. The eastern part of the state is right, though, IMO. If you want to keep people from leaving, you need to find a way to create jobs, and not just any jobs: they have to be jobs that bright, educated people will want to do. Universities are very often centers of creativity and entrepreneurship, and so bringing in more money to the universities will likely do a lot to create jobs and businesses. Bright, educated people will start businesses to hire those that may not necessarily have the advanced degrees but are still hard workers. The state is finally starting to see that, and they’re also using some of the money from the oil and gas taxes to create incentives for businesses to operate here.
Going back to the article, I was excited to do this as I see this as a way to communicate to the skeptics that the universities are good for the state. Here is a project that I would likely have to do somewhere else if it weren’t for the fact that we have the facilities here and they are easily accessible. Part of the reason I think my research was featured is not only the coolness factor, but the fact that I’m a native of the state and one of the people who, ostensibly, you don’t want leaving for a better job elsewhere. So yes, the universities are doing something to keep people here, even if not in the western part of the state. (On the other hand, it sounds like they have more people there now than they really know what to do with, which is another story altogether.)
My only disappointment in all this is that my hometown paper, the Bismarck Tribune, didn’t run the story. I can’t help but wonder if that is a result of the fact that the divide still obviously exists.
Tags: fargo, flood, red river
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Scientist, with kids February 19, 2012Posted by mareserinitatis in career, education, engineering, family, feminism, grad school, homeschooling, older son, personal, physics, research, science, societal commentary.
Tags: feminism, gender equity, kids, parenting, role models, sexism
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FSP has a post asking about the Local Mom Effect. That is, she wonders if being in a department with more women professors who have kids affects the outlook of younger women in the field. I find this post interesting…but also, I hate to say it, irrelevant.
Let’s put it this way: what women?!
When I started school at Caltech, I knew of two women professors out of all of math, physics, and astronomy. I only ever met one of them, knew she had no kids. I knew nothing about the other professor. When I decided to go back to school a few years later, I ended up in a physics dept. where the professors were all men. Later, I ended up in an electrical engineering department where the professors were all men.
I guess that, in my mind, the notion of being one of the few women in the department was no different than being one of the few women with kids in the department. When I went back to school, I had a kid already, so it wasn’t like I really had a choice about whether or not to be a childless woman in physics or engineering.
I will say that when I originally got pregnant as an undergrad at Caltech, I was told by my advisor that women couldn’t do calculus while pregnant and that I should drop out. Of course, he was a guy, so I seriously doubted he understood how women’s brains work while pregnant. (And it turns out that I can do calculus great while pregnant…I just can’t speak a full sentence coherently.) However, I guess I never took it as a message that women with kids don’t belong in science…I inferred that he meant it more personally, and that I myself was not a good fit for science. (Fortunately, major hopping got boring after a while, I ended up back in physics.)
When I went back to school, however, I felt that being the only woman or one of a few was very advantageous for several reasons. First, if I was the only woman or one of a very small number, I was already an oddity. A woman with kids is probably not much more odd than a woman without, and there was really no one to compare myself to (or say that I was doing it wrong). Second, I went back to school in North Dakota, and it really seems like people here more or less expect you to have kids no matter what you’re doing. I know that grates on some people, but for me, it was a blessing: having kids is just another part of life, and most people here learn to do their jobs while having them. (Also, I can’t recall anyone having a fit if I said I couldn’t make it to something because of kid-related issues.) Third, I was older than the average undergraduate or even grad student, so I think people assumed that it was pretty normal for someone my age to have kids. The fact that the younger students didn’t have kids was simply a function of age and never made me feel self-conscious that I did have kids. Finally, when I started my MS, my advisor was fine with the fact that I was homeschooling the older boy and would only be doing my degree part-time. He said this was really no different than other students in the department who were working full-time and pursing their degree part-time, as well.
I have been told, especially when doing my PhD classes, that it was “really cool to see a woman in science with kids”, especially by some fellow grad students. Until I started my PhD, I really hadn’t expected it to be a big deal. It had never occurred to me that I might be a “role model”…but I keep hearing it more than I ever expected to. I also suspect it’s because I often had kids with me or family issues that were more apparent to fellow grad students. Many professors try to maintain a more professional relationship with their students, and it doesn’t surprise me that many grad students don’t see how having kids affects the lives of the professors or that they don’t realize some professors have kids at all.
Realistically, I only got here because I didn’t really know that what I was doing was unusual in any way. If I had been surrounded by women who had kids but never let it on or didn’t have kids, I might have felt self-conscious about being a mom already. With no one to compare to, however, I just assumed that it wasn’t any more abnormal than a woman without kids.
My theory on the Big Bang Theory January 30, 2012Posted by mareserinitatis in humor, physics, science, science fiction, societal commentary.
Tags: Big Bang Theory, physics, stories, suspension of disbelief, TV
I really don’t watch much TV, but I do own all of the Big Bang Theory that’s available on DVD. Most of my friends really enjoy it, too, and I have a theory why that is: I think that it’s one of the few TV shows that nerds can stand to watch because it is far more factually correct than most TV shows.
Most of the nerds I know are the ones who annoy everyone else at movies by making commentary throughout about the impossibility or improbability of what they’re witnessing. (In particular, my older son is this way. Of course, he also likes to tell you what’s going to happen next, so he’s been banned from speaking during movies.) Suspension of disbelief becomes a little harder when you’re faced with something you know cannot possibly happen.
I think this became obvious to me in one scene where Sheldon was waxing (un)poetic about how great Isaac Newton was. Leonard made some comment meant in sarcasm, and Sheldon’s response was to say that Leonard disputed Newton’s claim that he invented calculus so Leonard wanted to put Leibniz at the top of the Christmas tree.
Most people who have no clue about calculus would probably laugh at this scene because Sheldon missed the point of the sarcasm. On the other hand, those of us who know anything about calculus might have been laughing because we knew exactly to what he was referring. And it made me ponder…would I want Newton at the top of my tree, or Leibniz? For the record, I would have been fine with Newton at the top of the tree because he did a lot more than invent calculus…but I still am glad for Leibniz’s wonderful notation. Either way, you couldn’t have just thrown any mathematician or physicist’s name out. It HAD to be Leibniz because the rivalry is so historic and well-known among mathophiles.
As I go through the show, I find little details like that a lot, and I really enjoy them. Whether or not I want to, I tend to pay attention to those points and letting them go is tough. Sometimes they even draw me in more than just the storyline does. In the episode where Sheldon is attempting to teach Penny physics, I kept thinking, “There’s better ways to explain that.” And when she was supposed to answer a question, it felt like sitting in a classroom and wanting to blurt out the answer.
It’s a real treat to watch a show that doesn’t use science as some sort of nifty backdrop to the story, where the science actually is important to the story or at least makes it more fun. And better yet, it still manages to entertain all the non-physicists out there, too.