Texas Fertilizer Plant Explosion Shakes the Ground

Posted on April 18, 2013 | Leave a comment

Another quick post of some interesting data concerning the explosion at the fertilizer plant in Texas.  Yesterday (4/17/13) there was a large explosion at approximately 7:50 pm local time.  As of early this morning reports showed around 179 people hospitalized, 24 in critical condition, and 5-15 fatalities.  Currently 3-5 firefighters and one law enforcement officer are unaccounted for.  Over 60 homes were damaged by the very large blast.

The best video I've seen so far is attached below, the explosion happens around 30 seconds in.  Also below is the initial emergency services traffic.

 

Finally, we can look at data from the Amarillo seismic station (US.AMTX).  I've pulled down the data and filtered it to show all frequencies above 1Hz.  We expect the explosion to produce mostly high frequency signals and attenuate, or lose strength, quickly (why I didn't see the explosion on any other stations such as US.WMOK in Oklahoma).  It looks like there are 6 main pulses of energy (possibly tanks failing?) very quickly and the large explosion in a period of around 10 seconds.

If you want to look at the data yourself I've made the SAC file available here or you can download the data from IRIS and duplicate the filtering with the following OBSPy code:

EDIT: The USGS posted a transportable array station that was closer to the event (seismogram below) that shows both the fast ground waves and the slower air blast.  They classify this as a magnitude 2.1 event on the event page, but it's really a larger explosion than that hints at as magnitude is only based upon ground motion.

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April 2013 Oklahoma Earthquakes

Posted on April 16, 2013 | 2 comments

This morning Oklahoma experienced another small sequence of earthquakes.  (There was also a large earthquake with an estimated magnitude of 7.8 in Iran over night.)  While I'm preparing for a conference very soon I'm a bit crunched for time, but thought a short post would be in order.  I would like to write a few posts concerning what magnitude is, how we calculate it, and other common questions I get asked at some point in the near future.

Okay, here's the synopsis of the most recent events. Early this morning at 01:56:29.875 CDT a magnitude 4.7 earthquake occurred centered northeast of the Oklahoma City metro area.  There have been a few significant aftershocks at magnitude 3.0, 3.6, and 4.6.  It is notable that there was a higher number of seismic events (though all small) beginning yesterday.  All these numbers are from the Oklahoma Geological Survey, the USGS estimates are lower with the largest events at 4.3, 4.2, and 3.3.  These magnitudes are computed on slightly different scales, but either way the largest earthquake released over 10 times LESS energy than the earthquakes last year.

The USGS did you feel it program has already collected around 1600 responses and the shaking reported matches very well with what was expected, probably due to the DYFI scale being pretty accurately calibrated after the large earthquake sequence last year.  It was striking that the vast majority of the responses came within 90 minutes of the quakes indicating the people actually got up and reported as soon as the event was over.  These responses really help the folks at the national earthquake information center (NEIC) and if you felt the earthquake but didn't go fill one out you should!

The moment tensor solution of the earthquake shows a strike slip solution meaning that the rock moved laterally past each other, not up and down.  This is shown by the "beachball" below with the colored regions indicating areas of compression.  There isn't enough information from one earthquake alone to tell if the fault runs SW to NE or SE to NW, but based upon the distribution of the large aftershocks it would be an okay initial guess that the fault trends to the NW.  Also notice the solution isn't perfectly strike-slip.  There is a small amount of oblique motion with a thrusting sense.  
After inspecting the infrasound instrument I have in my office I didn't see the earthquake, but the ground motion wasn't really detectable on the seismic station in Standing Stone, PA either.  It looks like the infrasound may have recorded the Iran earthquake, but I need to move it to a less noisy location.
Just for fun I've thrown in a seismograph below from a station in the Wichita Mountains in SW Oklahoma.  It would be fun to calculate the different arrivals and plot, but that's more fun for another time! I've made the trimmed .SAC file is available here in case you want to download it and try.

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Seismic Evidence From the Russian Meteorite Explosion

Posted on February 22, 2013 | Leave a comment

Today we're going to follow up on the last blog post about the explosion of a meteorite over Chelyabinsk, Russia.  The process of figuring out precise infrasound arrival times is quite a tricky process, the travel times depend on winds, humidity, and many other atmospheric variables that are hard to constrain over such a long travel path.  I've had several fantastic discussions with Dr. Charles Ammon here at Penn State to try to obtain the infrasound data that was collected near the blast, but so far we have not been able to get it.  When/if we do, expect another posting.

The focus of this post will actually be the seismic data near the blast.  There are many seismometers all over the Earth that record the motion of the ground many times a second.  After some discussion of the infrasound and seismic data available with Dr. Ammon, we found some really nice, simple results that would make a great laboratory assignment for an introductory seismology or geoscience class.  The activity could range from reading times of arrivals on provided graphs for a non-majors class, to filtering and grid searching to estimate the precise detonation location for a more advanced class.  I've provided the data and some thoughts on it below.

We'll consider data from five seismic observatories, the station names are ARU, BRVK, KURK, OBN, and ABKAR.  Below is a map showing the station location, distance to the blast (red star), and a seismogram from that station.  The seismogram shows how the ground is moving through time, in this case I'm showing the "Z" component.   This really just means we're looking at how the ground is moving up and down, though these stations also record North/South and East/West movement.  What we see is ground motion caused by the shock wave hitting the ground and that ground motion propagating away.

Fig. 1 - Map view of the seismic stations used.  Distance from the explosion, time after the explosion to a phase arrival, and arrival order (rank) are shown along with the seismogram.  All seismograms begin at the instant of the explosion.

It's common sense to expect the energy from the explosion to arrive at a later time at stations further away, which it does.  Notice how the sharp peak corresponds to distance? We can actually make a plot of this and learn some more from the data.  To do this, pick a feature that is easily identified in each waveform (we used the first trough) and record how many seconds after the blast it arrives at the instrument.  We then plot that on the x-axis of a graph and the distance of the station from the blast on the y-axis.  The result should be something like that shown in figure 2.  Now we can use some basic math to figure out how fast this energy was traveling.  The red line on the figure is the "best fit line" to the data.  We use some basic statistics (a linear regression) to make this line, but any plotting program will do it for you.  A line has a slope (how steep it is) and a y-intercept (where it touches the y-axis when x is zero).  The slope of a line is how much the y values change per a certain change on the x axis, often taught as "rise over run" in the classroom.  The slope of this line turns out to be about 3km/s.  That's a pretty reasonable speed for surface waves (which these are) through the ground!

Fig. 2 - The distance from the blast against arrival times.  This data indicates the surface waves traveled about 3km/s, a reasonable speed.

If we could pick out a "p-wave" in the data (difficult for reasons we will discuss), the intercept of the line would be the height above the ground that the blast happened.  I haven't seen a really good estimate of the height, probably because the p-wave is hard to find and the speed of the meteorite. The meteorite was traveling about 40,000 mph when it exploded.  It's hard to imagine something moving that fast, so let's change around the units: that's something like 11 miles every second!

The p-wave could be hard to see because 1) it's going to be relatively small, and 2) there are waves from an earthquake in Tonga arriving about the same time as the meteorite explosion.  We know the waves we picked aren't from the tonga event, those would have arrived at all the stations at almost the same time because they were reflecting off the Earth's core.  It would be an interesting project to play with trying to pick p-waves and/or estimate their arrival window by guessing the height of detonation.

We don't have to stop here though.  This morning I saw this youtube video, a compilation of people recording the shockwave.  The meteorite had streaked past, exploded, and they were recording this when the shock wave hit.  Shockwaves behave in a funny way, but luckily it's been studied a lot by the government.  Why? Nuclear weapons! Seismologists are commonly employed to determine if a nuclear test has taken place, and estimate it's size, location, etc.  A lot of very interesting information on air-blast and it's interaction with buildings can be found in the book "The Effects of Nuclear Weapons".  The book has lots of formulas and relations that could make many interesting lab exercises, but we'll just discuss reflection in this post.

A shock wave is really a front of very high air pressure that is propagating through some material.  The high pressure is followed (in a developed shock wave) by a small, longer, suction, then a small overpressure.    I've tried to locate meteorological observations and so far have only found hourly observations.  If we can find short term observations we would expect to see wind rushing away from the blast, then more weakly towards it, then very weakly away from the blast.  By knowing those wind velocities we could estimate the pressure differential that caused the shock.  The local airport (station USCC) does report hourly average winds (data here).  There is a small bump in the average winds between 9-10am local time, when the meteorite entered.  The lack of a gust report though makes this observation a bit too shaky to use for a pressure estimate.  

Shock waves move faster than the speed of sound if they are a high enough "overpressure", or the pressure above atmospheric.  Shock waves will reflect off the ground when they reach it, as shown in figure 3.  The overpressure in the region of "regular reflection" is much higher than the overpressure of the shock wave due to a combined stacking effect.  There can also be complicating patterns such as "Mach Reflections".  

Fig.3 - The initial pressure wave (solid lines) and the reflected shock (dashed lines).  Image from "The Effects of Nuclear Weapons"

What's interesting about all this is the audio of the clips at about 20 and 40 seconds into the YouTube video.  Notice these clips contain two bangs.  The first clip with two shocks could be reflection off the building behind the camera, the second shock follows the first very close and is very loud.  The next clip has a significant delay though.  At any height above the surface the initial reflection occurred on, there will be a delay between the initial and reflected shock.  If we knew the location of this video it would help constrain the shock location.  (After some google searching I can't locate the "Assorty" store in the footage anywhere.)

Overall with the observations of glass breaking over such a large area, we can assume the reflected pressure was probably in the area of 1psi.  This means the initial overpressure was very small at the ground.  Could you work backwards from the estimate of 500 kiltons TNT? Sure! That's a topic for another day or for your students in lab! Be sure to check out the book "The Effects of Nuclear Weapons", many campus libraries have it, Penn State has it online even.

Below is a link to a zip file that contains the .SAC files for the seismic stations (starting at detonation time and low pass filtered as well as raw data) and high quality figures.  If I end up writing up a lab from the event, expect the data and lab to be on my academic website.  A review of literature on the Tunguska event may be helpful as well!

Zip file of data.

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Chelyabinsk Meteorite - Infrasound, Seismic, and Satellites oh my!

Posted on February 16, 2013 | 1 comment

Just as Earth was about to have a close encounter with asteroid 2012 DA14, the people of Chelyabinsk, Russia had a personal experience.  Before we talk about both 2012 DA14 and the Chelyabinsk event some terminology needs to be set out.  A meteoroid is a small chunk of debris in space, generally anything from a fleck of dust to a small boulder.  A larger space bit of debris is termed an asteroid.  A meteor is when some of this debris enters our atmosphere, heating up due to friction.  A meteor is called a meteorite if it actually reaches the surface of the Earth and survives impact.  Everyday we are pelted with many tiny meteors, but few reach the surface.  Most meteorites are never discovered as they are statistically much more likely to land in the ocean due to it's coverage of Earth's surface.  Sometimes meteorites are found on land, in fact it is common for scientists to go to Antarctica to look for the dark rocks on the surface of a white sheet of ice.  There are many pages on hunting meteorites  and a book as well, it's worth reading about if your curious how we find rocks that landed a long time ago.

It's worth saying that there are different kinds of space debris, some more stony, some made of almost solid metal, and some of ice.  While it's worth discussing, I'd rather focus on the current events in this post, so if you are curious there is a nice page at geology.com that gives the basics.

To begin, lets talk about 2012 DA14, or the non-intuitive name that we gave a near Earth asteroid that is about 160 feet in diameter and weighs a massive 190,000 metric tons.  This asteroid could do some serious damage and was scheduled to have a close call with Earth on February 15th.  How close? Well, it would be about 17,200 miles from the surface, which seems like a long way.  It's not.  The moon is 250,000 miles away (roughly) and we've been there and back in a matter of a few days.  In fact, the geosynchronous satellites that beam TV and weather data down to Earth orbit about 22,236 miles above the surface to rotate at the same rate the Earth does.  As shown in the figure below, 2012 DA14 passed between us and the geostationary satellite band; a very close call.

Why talk about 2012 DA14 in a post about a meteor over Russia? To say they are not related in any way.  They approached from entirely different directions and it just happened to be a coincidence of space and time.

Now for the event in Russia.  At 3:20:26 UTC on Feburary 15th a large meteor about the size of a schoolbus entered the atmosphere.  The 49-55 foot estimated diameter object probably weighed about 7000-10000 tons.  While heating up upon atmospheric entry the meteor "detonated" or exploded in mid-air.  This has happened before, a list of historic airbursts can be found here.  The most famous being a large explosion (also over Russia) in 1908 called the Tunguska event.  That explosion released the energy of 10-15 million tons of TNT, leveling forests and destroying an area of about 830 square miles.  The event that just occurred was about 500 kilotons of TNT equivalent, or roughly 20 times smaller.  Shock waves from the event still managed to send around 1500 people to local hospitals with shards of glass and building materials in their faces/skin from rushing to a window too see what was happening.  Videos of the entry are all over the web, in several you can hear the detonation and shock wave.

So how do we know so much about this object considering we didn't know anything about it until it exploded overhead? Well, remote sensing helps us.  When a meteor entered over Wisconsin in 2010, I wrote about following the trail on the US Doppler Radar Network (here).  This time we could see the meteor from weather satellites (Meteosat 10 image below) as well as on seismic and infrasound stations.  Another meteosat also captured several frames that have been made into a video here.  Current estimates of the entry speed are in the area of 40,000 mph with a very shallow entry angle.

First the seismic observations.  So far I've seen reports of the Borovoye, Kazakhstan station seeing a gorgeous signal (thanks to Luke Zoet on this one). The station details, and even a photo are available at the USGS network operations page.  Below is a filtered (0.15 Hz low-pass) seismogram from BRVK.  This would be a result of the shock wave rattling the ground and seismic station.

Next, and rather interesting, are the infrasound observations.  Infrasound is very low frequency sound (below 20Hz) that we can't hear, but can record as air pressure variations.  It so happens that Steve Piltz of the Tulsa National Weather Service has a microbarograph.  Upon seeing his data from an earlier earthquake (yes, ground movement causes air pressure waves), I immediately bought a unit from Infiltec and set it up in the office at Penn State.  Below is a picture of the station.

Infrasound propagation is incredibly complex and difficult to predict over such long distances, so I've done a simple calculation that is very likely going to be revised upon some discussions with seismologists this week.  First, I wanted to know how long the sound would have to travel.  To find the shortest travel distance between a latitude and longitude set you can assume a spherical Earth (not too bad for such a back of the envelope calculation) and some math.  Remember trigonometry? Well when it's modified to work on a sphere instead of in a plane it's creatively called 'spherical trigonometry' and consists of a strange function called the haversin.  If you are curious about how I calculated the travel path of the sound waves checkout the wikipedia page on the Haversine formula, but I've included the formula below.  Below is the result of the calculation, a great circle path between Chelyabinsk and State College, PA.
d = 2 r \arcsin\left(\sqrt{\operatorname{haversin}(\phi_2 - \phi_1) + \cos(\phi_1) \cos(\phi_2)\operatorname{haversin}(\lambda_2-\lambda_1)}\right)

The distance the wave would travel would be something like 8670 kilometers.  Sound travels at 340.29 m/s at sea level, but since we're making assumptions we'll say 300 m/s is a nice number.  So the wave would take somewhere in the 7-8 hour range to reach State College (assuming it's non-dispersive and many other likely not so great assumptions).  Luckily for us, the event and the arrivals are overnight.  During the day my infrasound station is swamped by signals from office doors opening and closing amongst other things.  The meteor entered the atmosphere at 10:20 pm local time, so I've plotted the infrasound from 10 minutes before the meteor entered to well after the energy should arrive.  There is a large increase in the noise shortly after entry, but this is too soon.  Could it be seismic energy or arrival of a faster shock path? Maybe, that's a point for some discussion and revision later.  The big thing to notice is the noise increase at about 7-8 hours after the entry.  It's still early in the morning, so it is doubtful that this is people coming into work.

I've made a .SAC (seismic analysis code) file of the raw data for about 24 hours around the event available to download here.  Download the file (~19Mb) and play with it! The data is collected at 50Hz, but all that is in the meta-data (as well as location details).  I use ObsPy to do most of my analysis in Python, but you could use SAC or other codes meant for seismic event analysis.

Steve's station in Oklahoma recorded similar signatures.  His data over a slightly shorter time span (5:21-11:42 UTC) is below, showing similar signatures.

Infrasound is actually what allows us to determine the energy release from the explosion.  As it turns out seismic stations and infrasound have been used to monitor nuclear testing for years (a relevant topic currently considering the recent tests by North Korea).

Overall, I'd say stay tuned for any updates.  Eventually the infrasound station I have will be setup for live streaming.  I'm sure after discussion with some folks more versed in infrasound travel we can clean up the data and maybe do some more back of the envelope energy/rate calculations for demonstation purposes.

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"The 4-Hour Work Week" - Thoughts on the Best Selling Book

Posted on December 30, 2012 | Leave a comment

In a best selling book "The 4-Hour Work Week", author Tim Ferriss argues for working less and experiencing life more.  While this concept is intriguing and what many corporate types long for, I was curious if and how Mr. Ferriss' ideas could convert over to academia.

In academics, many of us (myself included) enjoy what we do and spend much much more than 40 hours a week "working".  While we may not always be in the lab or in the office, we generally think about problems all day, all night, etc.  Why do we do this? Is it because we are addicted to work? Not really, we do it because of an intense interest and desire to solve problems.  You may think that this automatically throws the concepts of the book entirely out the door, which is incorrect! Tim Ferriss admits that he really does work more than 4 hours a week, but his main argument is cutting unnecessary things out of your schedule.

The concept of "work for work's sake" is hammered throughout the book as something to instantly eliminate.  Do you have items that you do to avoid tackling the big projects? For example, sending out a dozen "check up" emails that don't really need to be sent or could be addressed with a short face-to-face kills an hour or so and helps you avoid doing real items that are important but difficult.  This concept can come right on over to academics and graduate students are famous for ninja like procrastination skills.

To achieve the freedom described in the book , Ferriss outlines a plan on starting a business, automating it, and letting it produce income with minimum input from you... Sound too good to be true? It probably is and certainly doesn't sound like academia, but with some adapting I think we can focus it down and maybe consider a few of the sub-points in detail.

Starting a business to market a product: not so applicable to graduate students, we make ideas and concepts that can't be outsourced or sold. Later if your idea becomes a product, instrument, etc? Maybe. Overall I'd say this part isn't very applicable and you'll never have to worry about distribution houses and merchant accounts.

Automation: YES! This is something that many graduate students, professors, and even undergraduates can use more of.  My motto is "if you have to do it more than 10 times, write a program".  In some cases that is overkill, but a few simple things like automating your email rules, writing a data plotting routine instead of pointing and clicking to make the same plots, or even automating bill pay can save you enormous amounts of time.

First off for email: my personal plan follows the David Allen "Getting Things Done" philosophy of inbox zero.  At the end of everyday when I leave for home my inbox (electronic and physical) has exactly zero items in it.  If the item takes less than 2 minutes I do it immediately, if it takes more it gets clipped into OmniFocus and the email archived or deleted.  You can also improve your spam filters and use smart labeling/smart inbox depending your email setup.  All my inboxes (about half a dozen addresses) forward to a gmail account because I think they are the most versatile provider.  I use Sparrow as a client, but the web interface is fine as well.  Check out the wealth of information including Gmail Ninja.

Ferriss encourages readers to check email only twice a day and then cut down from there: this simply isn't possible in my field.  Ferriss even recommends paying personal assistant services to do things like check email, make basic appointments/decisions, etc.  Assistants aren't really useful for more than business type emails though and as a graduate student I live in the world of mostly non-FAQ style messages. Could I check email less than I do currently? You bet, and I'm working on that.  Checking email the first thing in the morning, while discouraged by many experts is still essential for me.  I want to know what's flying my way for the day that I need to add to the schedule.  Playing with timers that shut down my email for 30-90 minute focus sessions is an experiment I plan to try in the coming year.  (Ferriss would call this a "lifestyle experiment", which is an excellent term in the eyes on an experimentalist.)  Use a stats service to track your email response time, length, thread length, etc.  If you're sending an email every 20 minutes thats in a long thread of long messages just pick-up the phone and call or Skype the parties involved.  I know, I hate phone calls as well, but it saves massive amounts of time.

Further automation (some from Ferriss and some I've picked up) includes Amazon auto shipment of essential items and automatic bill pay.  The automatic shipment of Amazon products on a schedule not only saves me money directly, but time.  I no longer run to at 8:30 pm several times a year to pickup essentials I've forgotten.  Things like deodorant, toilet paper, toothpaste, printer paper, ink, toner, juice, snacks, and just about anything non-perishable can be scheduled to ship at a given interval.  I see the email that a shipment is on the way and leave a note to drop the package at my door instead of the office for the UPS delivery man/woman.  It sounds silly, but it really does save me trips and thinking about repetitive tasks.  Options to request and additional shipment and skip a shipment exists if you over/under estimated how often you use a product.  Automatic bill pay is a similar process: the computer does it and I just supervise by looking at my online banking site every week and noting account action emails. (If you happen to be in the area, PNC bank has great online tools.)

Meetings: Ferriss advises us to avoid these at all costs.  While that may be a good bit of advice, spending time with fellow scientists is how new projects emerge, so cutting isn't as easy as in business.  I do like the idea of having someone requesting a meeting (be it a student or colleague) send some discussion points ahead of time to the group.  This means everyone knows what's on the table and conversation is less likely to drift.  Hit the points, write down new points, but try not to chase them.  Save the idea batting for my favorite meeting idea: agree to meet later for a drink and bring notebooks.  Geologists are famous for their love of beer and having a beer is a relaxed environment that allows ideas to flow onto paper and doesn't eat into the "business hours" of trying to knock off action items.

While there are more points in the book, I want to mention just one more: mini-retirements.  Ferriss says why retire? just take breaks from the work and spread experiences throughout your lifetime.  This is a great idea and very easy to do in academics.  We get mini breaks with semester schedules, but it's not uncommon to go on a research trip or go to a conference overseas and spend an extra week or two.  Several people in our department end up living overseas for months at a time to do their work and get new experiences.  This concept is on my list of experiments to try, but I've noticed working in intense sessions and then really taking small breaks during the day/week has already helped.

In the end, I recommend you read the book.  Maybe grab it from your library and see what you think.  Ferriss seems like a rather abrasive personality, but you don't have to be to adopt a few of the concepts in the book.  It really boils down to the same idea though: make a get of goals, get to them in the best way possible, and don't waste time, recreation or work.

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Fluxgate Magnetometer Wrap-Up (For now)

Posted on December 26, 2012 | 6 comments

Per lots of emails and requests I’m going to post what I have from the design of the fluxgate magnetometer mentioned in several previous posts (like this one).  The schematic attached at the bottom is a rough draft, but should provide some guidelines for designing and building a version of this instrument.  I’ve also attached links to several PDFs that I found very helpful when building this demo.

It should be noted that this design doesn’t have a plain readout with XXXXXX nT magnetic field, but displays a waveform on the oscilloscope.  Could one be made? Absolutely! Since this was more of a demonstration of the underlying physics I didn’t bother, but it would be a good weekend project.

First off let me list a few things I would build differently were I building this again:

-       Use shielded lead wires to reduce crosstalk to the coil.

-       Use a simple Analog-to-Digital converter so this output is projected from a laptop to the classroom screen (much easier than gathering students around an oscilloscope).  I think an Arduino might do the trick.  Raspberry Pi would be a good choice too.

-       Add gain adjustment knobs to the control panel.

-       I would again use the Velleman kit for the signal generator instead of re-designing the wheel.

When using this in the classroom I laid it alongside commercial magnetometers on the table.  We discussed the physical principles behind the instrument, and then students would use the demo fluxgate to generate an output wave.  Afterwards we used the commercial magnetometers to do simple tasks like finding conduits and keys. 

It would also be nice to have a first-principles proton-precession magnetometer.  There is a book “Signals from the Subatomic World: How to Build a Proton PrecessionMagnetometer” that describes one such instrument, but significant improvements in the instrument could be made with modern programming languages and ADC devices. 

I still welcome questions on the fluxgate and will probably update the instrument next time I teach an Intro Geophysics course (undetermined).  Thank you for all the interest and if you build one, please send your results and we’ll put them up here for all to benefit.  

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Fun With Office Supplies - Geometric Cohesion and Staples

Posted on October 28, 2012 | 2 comments

After the small rash of tape theft resulting from my suggestion at a talk that the audience go home and unroll scotch tape to see the resulting electrical dischange (which deserves a blog post soon) it's time for another attempt to make Swingline Co. stock soar.

In a recent Physics Today article "Geometric Cohesion in Granular Materials", Scott Franklin of the Rochester Institute of Technology showed some very interesting data regarding how the shape of a material effects how likely it is to stay together as a coherent mass.  Before we delve into the article though, let's talk about cohesion in general.  Then we can come up with a couple of fun experiments that you can do at home.

Cohesion is just the tendency of a material to stick together.  This is different than adhesion though.  Consider a water drop on a dish in your dish drainer.  The water drop is sticking to another material (the ceramic) which is adhesion.  The water drop is also a coherent mass; water molecules are sticking together to form a raised droplet on the surface of the plate.  In essence the water is 'sticking to itself', which is due to electrostatic forces of water being a polar molecule.  Electrostatic forces give water a property of surface tension that causes lots of wonderful things that can make up a whole other post at some point.

Other things can cause a material to stick to itself though.  Remember playing the old pickup sticks game as a kid? The object was to extract a stick from a pile of sticks on the table without disturbing other sticks.  This turns out to be pretty challenging.  Your pile of sticks appeared to be stuck together or interconnected, which is cohesion in a macroscopic or broad sense.  In the case of the sticks electrostatic forces certainly aren't the cause.  Electrostatics forces are relatively weak, and the sticks don't have enough mass for their gravitational attraction to cause this cohesiveness of the pile.  What is the mysterious factor then? It's just their shape. When objects act cohesive because of their geometry or shape it's called geometric cohesion.

First grab a couple of tablespoons of sugar, place it in a small container (an old medicine bottle works great) and turn the container upside down on the table.  Now remove the container... the sugar spreads out in a small pile.  The roughly spherical grains of the sugar don't stick together that well and the pile isn't very tall.  The angle of the pile from horizontal is called the angle of repose, and is around 30-35 degrees for lots of things.  My pile of sugar sat at about 30 degrees.  The angle of repose really tells us how hard it is for the grains to slide past one another.  If it's easy, the pile is a very low angle, and if the pile is made of large, angular hunks of rock, it becomes more steep.

The angle of repose can even be thought of as a proxy for the coefficient of static friction, or how hard it is for the grains to move past each other from a dead stop.  A mathematical relationship can be derived from some geometry, but it turns out the tangent of the angle is about the coefficient of friction. So the tangent of 30 degrees is about 0.6, which is the general number for static friction of lots of materials.  This result means all is well in the world of static newtonian physics and we can think about something more interesting than approximate spheres of sugar.

What about rods? Going back to our game of pickup sticks, the shape of the long, narrow rods seems to be the main factor holding things together.  It's easy for lots of objects to interact and become 'locked together'.  Who cares about rods locking together? Manufacturers often have automated assembly machinery that may have large hoppers of screws, and when things get locked together it costs money.  The long narrow shape of screws can jam hoppers in seconds and hold up the entire line.  While not many people have a pile of tiny screws at home, I bet you have staples.

Staples are a funny shape really.  Standard office staples are about 7mm along the long upper shank and  around 5mm at the two barbs.  These measurements give the staple a barb to shank ratio of about 0.7, which as it turns out, is a governing number describing how well staples can stick together.  Franklin's group did a whole series of experiments with staples of different barb ratios and found that staples with a ratio near 0.4 were the most cohesive.  Even though our staples aren't the ideal ratio let's repeat the sugar experiment.

Using a stapler, eject a bunch of staples into the same container (or one with a slightly larger mouth if you have it).  Now shake the container up for a bit, turn it upside down, and remove the container.  This time the mass didn't spread like the sugar, but retained the relatively sharp edges of the container shape.  Retention of shape tells us that the staples are cohesive, and their high angle of repose means that the coefficient of static friction is very very high.  Franklin's group is currently seeing how strong these piles are by pulling on the ends, but they are actually pretty robust.

The big question is why does any of this matter other than being interesting? Well, cohesion is a big deal when we study soils.  Cohesion can determine if the ground can support a building, if a landslide is due, or if the machine powder coating your morning doughnuts gives you a plain doughnut.  While some of these are more life threatening that others, it's import to study cohesion to keep tabs of impending disasters, especially avalanches and landslides. I know that there aren't that many staples in soils generally, but there are clays which are shaped like plates.  Different minerals/materials in the soil with different shapes can greatly change the strength of the soil and how likely it is to slide as a mass.

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Posted in Education Opportunity, Geology, Geophysics, Rock Mechanics

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3D Printing in the Lab - Will Lab Hardware Follow Software into Open-Source?

Posted on September 15, 2012 | Leave a comment

Today I read the article "Building Research Equipment with Free, Open-Source Hardware" by Joshua Pearce from a recent Science Perspectives section.  I'd like to share some thoughts on the article as I thought it introduced what may be the next "want" item in many labs.

In the modern scientific lab there is a large assortment of sophisticated hardware necessary to conduct increasingly complex research.  Generally scientific hardware is some combination of turn-key or off the shelf equipment and equipment designed and built in house.  In recent years laboratory software has progressively become part of the free and open-source software (FOSS) movement; hardware is now following the same trend with the advent of open-source 3D printers from the hobbyist community.

Open-source hardware became popular in the late 90’s with the basic stamp “board of education” microcontroller circuit boards, but the Arduino has taken over the hobby market with its $30 price tag.  Arduino has a number of modules, or shields as they are called, ready built with significant code libraries available.  With the Arduino circuit boards scientists can perform basic hardware control with digital and analog outputs in addition to basic analog-to-digital conversion.  

The RepRap open-source 3D printer is driven by the Arduino and can be constructed for <$1000.  The machine prints the parts required to make another RepRap printer, so building a machine is approached by entering the RepRap community with a parts request.  Users also post 3D designs on Thingiverse for download and printing by anyone.  A sufficient amount of laboratory equipment from test tube racks and filter wheels to Dremel tool adapters are already online.  

Printing laboratory equipment may not only reduce the cost of research, but allow the same flexibility, innovation, and rapid development cycle enjoyed by scientific software.  Being able to create a custom bracket, holder, mold, or sample jig could be advantageous to almost any laboratory and allow research to be conducted more efficiently with less focus on coordinating development with engineers at commercial manufacturers.  The open-source nature of the parts library will reduce duplication of work between those in a common field of research and allow cross-lab standardization of sample preparation techniques.  

There are limitations to what can be easily constructed in the lab, such as 3D printing with metal.  The technology to do this exists, but is too complex and expensive at the present time for individual applications.  While working at Oak Ridge National Laboratory I got the opportunity to see 3D printing with titanium.  The video below is a titanium ball... bouncing. (Apologies for the portrait video and quality, this was taken several years ago with an early iPhone.)




Like all community projects, the RepRap is being updated to have greater capabilities.  According to the project website a major milestone will be printing with electrical conductors to manufacture rapid prototype circuit boards without milling away copper clad board material.  

Just as sometimes labs must use commercial software, it is likewise not expected that all lab hardware will become open source.  Some tolerances are too tight for the parts to be constructed by simple printers and some materials are not practical to print in the lab.  With all this in mind it is worthwhile to monitor the progress of open-source hardware such as the RepRap, Arduino, and the new RaspberryPi single board computer.  These tools may provide teaching support also as controlling and displaying data from classroom demonstrations is easier than ever and does not require the resolution/precision of research grade instruments.

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Posted in Education Opportunity, Electronics, Hardware, Open Source

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The Scientific Workspace

Posted on September 9, 2012 | Leave a comment

Today I'd like to discuss the evolution of the scientific workspace, but before that I need to address a few comments and recent happenings.  The fluxgate magnetometer project is done, I decided to not build a bandpass filter in the unit.  Hopefully I can get the schematic drawn up nicely and post a PDF on my website content section.  Website, oh yes, there is a new website for my academic life.  I'll still be doing blog posts here, but the website will have all my static content, research, etc.



Awhile back I read an interview with Adam Savage of the popular discovery show Mythbusters.  This interview was mostly getting at how Adam works and the productivity tools he utilizes.  The question/answer that caught my attention was the following:

Q: What's your workspace setup like?
A: I have several desks: One at home, one at work, and one in my own shop. I spend little time at any of them. My workplace is wherever I'm making something, which could be in a field in gold country, or in an abandoned warehouse on a military base.

The part of the statement in bold is what I want to discuss.  Scientists are often viewed as working hard in their lab with test tubes, beakers, and bunson burners (as evidenced by a colleague asking his geoscience intro class to draw a scientist on their first day of class).  This view is really valid for only a small sector of the sciences; as geologists we are often making a workspace in the field on an outcrop of rock, working on a laptop in the office or at a coffee shop, or doing an experiment in the lab. So what is the workspace and how has it changed? 



First: Do people (not just scientists or geologists) view the workspace differently than they did in the 1960's? I think so.  With the advent of mobile computing and being able to walk around with 1000+ PDF files and books on an iPad the office is becoming less and less important.  Until the late 90's the office was the place where all your paper lived, without this support it was impossible to do much work.  Now that this isn't the case, I believe the office is becoming occupied more infrequently and being replaced with the mobile office.  The internet is also making telecommuting easier each year.  While in Houston I could occasionally see updates to spacecraft flight software coming into the repository from a colleague who programed at a Starbucks frequently.   Just a few years ago that was impossible and during the Apollo days out of the question.

Next, can the creative (yes, scientists are creatives that won't admit it) work in a single workspace like an office or lab? While they could this is a severely limiting strategy.  There are several times I've found it useful to go into the shop or lab and tinker with things and setup a laptop and work there.  Sometimes I spend the majority of the week at the desk, but sometimes I'll setup for a paper reading or programming marathon in another building or at a restaurant.  

Why would you want to work somewhere that doesn't have the big monitor and files you enjoy at your desk? Chance encounters.  While working in the traditional office should still be a component of our days, some of the most useful conversations I've had occurred with people in other buildings on campus or at a coffee shop.  

For example: in December of last year I was working in a tea shop near Denver programming an image analysis code (for the laser cave mapper).  While coding away the owner of the shop (Damon) came over to refill my glass and noticed I was writing software on a Mac.  He inquired about what I did, asked if I could answer a Mac question for him, and then from the view of an outsider to the geosciences made a comment that ended up making me think a lot about other applications for this technology.  These kind of chance encounters have happened several times and even ended up in some good professional relationships being formed.

The physics rock star Richard Feynman would have loved this notion of many workspaces I believe.  Feynman loved new ways to look at things and could be looking at a complex problem from a new angle while in the outdoors, at a blackboard, or submerged in a tub of water on hallucinogenic drugs (to see Feynman's unique mind I highly suggest his book Surely You're Joking Mr. Feynman).  

I suppose the biggest point I want to make with these examples and from the quote is that as scientists it's easy to get comfy in our office surrounded by a couple of giant computer screens and full of distractions.  We shouldn't throw that office out, but be sure to go into the lab (even if you're not an experimentalist) and tinker, go into the field and observe connections, or go to a coffee shop and make that a temporary office.  Anywhere can be your workspace and it's enriching to switch between them and look at the same problem with another set of tools and surroundings. 


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Posted in Productivity

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Teaching Field Camp - Starry Nights

Posted on June 10, 2012 | Leave a comment

The geophysics students have given their final presentations and gone home.  I'll be finishing up a couple of posts (mostly waiting on graphics) about their last weeks of work and a few interesting study areas, but for now we will break from geology.  The geologists will be doing geophysics for the next few days (hence I'll still be in Cañon City), but now I'll have slightly more free time to do some photo experiments!

Saturday night another TA rushed in to tell me that the milky way was out and nicely visible.  I grabbed my camera, but sadly the moon was rising and it was hard to get great shots.  The wind was gusty, but a moon shot turned out okay, and we staged a photo with the dining hall, OU vans, and star trails.  Look for more geology posts in the next few days before I depart for my desert loop on the way to Arkansas.

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Posted in Photography, Space

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