Jeff Danner

The Birthday Problem

You may have heard that if you are in a room with 23 people, there is a greater than 50% chance that two people in the room have the same birthday. This is commonly known as the “Birthday Problem.” Most people presented with this information are, at least initially, quite skeptical. Typically what throws people off is that they approach the problem with an incorrect perspective.

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3D Printing Part I: The Technology

For the past several years, 3D printing technology has been garnering quite a few headlines. Unfortunately, as is common for the main-stream media, many of the interesting science elements are left out of these stories. So I figured it was time for a Common Science treatment of this fascinating technology. This week I will discuss what 3D printing is, and next week I will speculate on its potential. The printing process starts by creating a digital 3D model of the object to be assembled in computer code. Next, you decide what material you want to build your object from. This choice leads me to the first key element that the mass media usually leaves out. Most stories which one encounters about 3D printers exude boundless optimism about them being able to make just about anything. While 3D printing is quite amazing, there are some limits which are important to understand. Generally speaking, there are three classes of starting materials which can be used by 3D printers: metal powders, plastic powders, or liquids which rapidly polymerize. Once the material is selected, the computer model guides an extremely precise nozzle to spray successive layers, each approximately 20-100 microns thick. For reference, 100 microns is about the thickness of a human hair. Each layer needs to be fused together using one of the following techniques: • Plastic powders are melted with a...

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China, The Canary in the Coal Mine

When I started writing Common Science in 2011, I did not envision devoting so many columns to resource constraint issues. However, every time I listen to the news or read the paper I am assaulted with warning signs of rapidly approaching resource scarcity issues. Many of these stories are set in China. Let me give you some examples. In my column iPads, Priuses, and Neodymium, I discussed the growing importance of rare earth metals(1) in electronic devices and advanced battery technologies. Deposits of these valuable metals are few and far between. Any reasonable assessment of the situation suggests that supplies of these key metals are soon going to become tight. China, which currently controls over 80% of the world market for rare earth metals, has apparently reached this conclusion and is preparing. In September of 2013, China purchased 10,000 tons of rare earths to bolster its strategic metals reserve. In January of 2014, the largest mining company in China purchased nine rare earth mining companies from Mongolia, further consolidating their grip on world supply. Last year, I wrote a five part series on food in which I discussed how land supply and land degradation was imperiling global supply. In December of 2013, the Chinese government declared that eight million acres of farmland were unsuitable for farming due to pollution of the soil by heavy metals.(2) For reference, this is...

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Checking In On Peak Oil

In last week’s column, The Case of the Missing Propane, I explained how the widespread use of hydraulic fracturing (fracking) of shale oil deposits since 2008 has led to a 30% increase in the production of crude petroleum in the United States. While that statistic makes for snappy headlines, it is not particularly meaningful to the overall world oil supply or the phenomenon known as Peak Oil. If you are not familiar with Peak Oil, I published a column in June of 2011 called Peak Oil in Five Paragraphs or Less. Here are the key points: • Peak Oil refers to the time at which we reach the global maximum rate of oil production, which is followed by decades of declining rates of production. • Due to oil’s pivotal role as a transportation fuel and (as I explained in Everything Comes from Oil) the key raw material for most consumer goods, the global economy can only grow if oil supply continues to grow. • In order to keep producing more and more oil, you must keep discovering more and more and more. This is not possible. Eventually you are exhausting oil fields at a rate faster than the new ones can be discovered. • The global peak for conventional oil sources occurred in approximately 2005, requiring us to turn to unconventional sources such as shale oil and oil sands. These...

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The Case of the Missing Propane

Over the past few weeks, I have seen many stories about propane shortages in the United States. As a result of these shortages, prices for propane have nearly doubled from around $2.20 per gallon at the end of last year to over $4.00 per gallon this week. This situation struck me as quite odd. We should be nearly drowning in propane at the moment. So I decided to try to figure out what was going on. As usual, let’s start with the background. Propane is a small, simple hydrocarbon with the chemical formula C3H8. At normal temperatures and pressures, propane is a gas. By applying a modest amount of pressure you can induce it to liquefy, which is what comes in the propane tank you may be using for the grill on the back porch. Three quarters of propane production in the U.S. comes from the refining of natural gas. The primary component of natural gas is methane (CH4). Mixed in with the methane are larger hydrocarbons such as ethane (C2H6), propane and butane (C4H10). Before natural gas can be put through a pipeline (the only economical way that it can be transported long distances), most of the propane and butane must be removed, thus resulting in most of our supply of propane and butane. Butane is what is used in most cigarette lighters. The other 25% of propane...

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A Tale of Two Spills

On February 2, 2014, a storm water drain at a retired coal-fired power plant near the North Carolina-Virginia border ruptured, which allowed more than 80,000 tons of coal ash to spill into the Dan River. The Dan River is the drinking water source for many communities and is a primary feeder to Kerr Lake Reservoir. This event comes closely on the heels of another coal-industry-related accident, the spill of 4-methylcyclohexane methanol (MCHM) into the Elk River in West Virginia. (Follow this link to my recent column on the events in West Virginia.) These two spills share an important connection: toxic heavy metals. So what is coal ash? The easiest way to understand it is to consider a fireplace. The sticks and logs you use in a fireplace are flammable, but some parts don’t burn and are left as ash in the bottom. Burning coal in a power plant works the same way; most of it burns but some is left behind as ash. Coal contains small amounts of a number of heavy metals including arsenic, cadmium, selenium, uranium, lead, and mercury. These metals do not burn and are thus left behind in the coal ash. Among toxins which are harmful to human health, heavy metals are some of the most pernicious. Once they enter the body, be it from breathing in contaminated dusts, ingesting liquids in which heavy metals...

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Keystone Pipeline Update

With the recent release of the State Department’s report on the Keystone XL pipeline, I thought would review some of the key issues for this topic. The Keystone XL pipeline is intended to transport diluted bitumen, a low-grade, impure form of crude petroleum, from the oil sands in Alberta, Canada to refineries in Oklahoma and Texas. The essence of the State Department report is that the pipeline project would not have a negative environmental impact because, in its absence, the oils sands would be exploited anyway and transported via railcar. The report further stated, correctly, that rail transport is less safe for people and the environment than pipeline transport. In 2012, I wrote about the science and climate change implications of the oil sands in Keystone Controversy. Last spring, I noticed a shift in focus of opponents to this project from potential climate impacts towards the possibility of pipeline leaks. I explained why I thought this was a bad idea in Advice for Opponents of the Keystone Pipeline. My main point in this second column was that focusing on the safety and environmental aspects of the transport of the dilbit distracts from what is truly important. The underlying question on the oil sands and the Keystone XL pipeline is, “How high can the carbon dioxide concentration in the atmosphere get before climate change has a dramatic, negative consequence on...

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My First PC Weighed 25 Pounds

My children like to make comparisons between the technology I had growing up and what they have today. In the course of a recent conversation on this topic, it occurred to me that, having been born in 1966, I have lived through the entire evolution of the personal computer and the internet. The internet got its start in the 1960s with government funding through an organization called the Advanced Research Project Agency (ARPA), whose original network was called ARPANet. In time, the project was taken over by the Department of Defense, which changed the name to DARPANet. Advances in DARPANet continued until, in 1983, it was split into military and civilian networks. At first the civilian network was restricted to non-commercial uses such as research. These restrictions were eased over time, allowing the internet to weave its way into nearly every aspect of our lives. In the fall of 1983, I started my senior year at State College Area High School, which is effectively the Chapel Hill High School of Pennsylvania. This was the first year that the school had a computer lab. We used Apple computers, which look substantially like the one shown here.   We learned word processing and computer programming in both BASIC and Pascal. It’s hard to convey to my children how fascinating this was for me, since I had never used a personal computer before....

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West Virginia Chemical Spill

On January the 9th, 2014, 7,500 gallons of a chemical called 4-methylcyclohexane methanol (MCHM) leaked from a Freedom Industries storage tank into the Elk River near Charleston, West Virginia, polluting the drinking water supply for over 300,000 people. The tank had not been inspected by regulators since the early 1990s. The other day a friend asked me if I planned to write a column about this incident. I told her that the whole sad story seemed unremarkable to me, and that I had yet to find an aspect of it to which I thought I could provide a meaningful contribution. Then I read the comment below from a Los Angeles Times story about the events, and I changed my mind. “Federal inspections are not required because ‘atmospheric tanks’ like the one operated by Freedom Industries are exempt under federal safety inspections because they are not under pressure, cooled or heated — and are not involved in chemical processing, according to the U.S. Chemical Safety Board.” (Los Angeles Times, 1/17/14) Before I explain why this comment from the LA Times inspired this column, let me provide you with a little more background. MCHM is used in the processing of coal, specifically for a step called froth flotation. I will resist the temptation to provide you with a lengthy dissertation on froth flotation and skip to the point: it removes minerals...

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We Can Afford More Math Textbooks

As an engineer, I have had a lot of math education in my life, everything from multiplication tables to systems of partial differential equations.  I was quite successful in these classes due in part to the good fortune of innate ability, but also, I firmly believe, because for every class I had a textbook of my own filled with helpful explanations and examples. I frequently tutor my children and my friends’ children in math and have being doing so for years. As such, I believe I have sufficient data to make a few valid conclusions. I have no doubt that having a textbook increases understanding and improves performance for every student, irrespective of ability. The value of a textbook is amplified for students who either do not have an adult or older sibling at home to help out or (and this is a big one) do not have the fine motor skills required to transcribe a large volume of detailed notes during class. If my observations are correct, then there is an easy solution to improving math scores in North Carolina: buy more textbooks. Consider Chapel Hill – Carrboro City Schools, the best funded and highest performing school district in North Carolina. To be diplomatic, our supply of math textbooks is deplorably bad. My children have been provided with their own textbook at most 50% of the time. Sometimes...

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