Recently in applied physics Category

A flurry (pun intended) of articles in today's issue of The Wall Street Journal prompted me to drop another post about the controversy surrounding climate change research and efforts to curb global warming. Readers who have followed my posts here and in the Ask Charlie blog I wrote for Control Engineering know that I'm no fan of the IPCC report upon which most of the current nonsense is based. It's not that I think that there's anything wrong with the basic thesis that dumping loads of carbon dioxide into the atmosphere will likely ratchet up global temperatures, my problem is that so much of the so-called research, and especially the conclusions drawn therefrom, are prima facie so much politically motivated dreck (or to use the proper Yiddish spelling drek).

As I see it, there are two basic problems. First, the conclusions are based on a sophmoric physical model. Second, who ever said that higher global temperatures would be a bad thing, anyway?

The theory of global warming is based on a simple physical model - the greenhouse model - which is, in turn, based on the solid physics of radiative heat transfer. Specifically, it starts with the observation that the opacity of most atmospheric gasses is wavelength dependent. That is, while most of these gasses appear transparent to visible light, they are more opaque (sometimes very opaque) to infrared wavelengths.

So, the radiative power flux of sunlight, a large fraction of which comes at visible wavelengths, gets through the atmosphere to warm the ground. The warm ground tries to radiate that power back out at lower wavelengths (basically, the color temperature of sunlight is about 6,000 K, while that of radiation from the ground is about 300 K). The infrared, however, is absorbed by the dense lower atmosphere. Ergo, the ground and lower atmosphere, which are roughly in thermal equilibrium, get warmer. Increasing the density of the more infrared-absorbtive gasses, especially carbon dioxide, (so the theory goes) will necessarily increase the infrared absorbtion, and lead to higher temperatures.

We teach this model as an example in second-semester freshman physics. It's simple, easy to understand, and illustrates the mathematics of radiative heat transfer (which is what we're trying to do in freshman physics). The only problem is that the model is dead wrong. The real world is vastly more complicated. The difference is so extreme that any conclusions drawn from the greenhouse model are unlikely to correspond to anything in the real world.

One of the biggest problems is that meteorologists have known for decades that the weather system is chaotic. Weather patterns cannot be reliably predicted for a time scale longer than about a week. Weather, of course, is critical to radiative heat transfer, so asking a climate model that uses radiative heat transfer to predict anything beyond about a week is simply stupid. Other parts of the climate system are similarly chaotic, such as solar flux variability, making the prediction of future climate via computer models an exercise in futility. It is of academic interest, but of academic interest only.

Moving on to the second problem, who says global warming is a bad thing, anyway? The medieval warm period (look it up) ushered in an age of prosperity, cultural advancement, and generally really good times. It was followed by the the Little Ice Age, which brought with it famine, plague, and death. Who th' heck wants that?

Lessons from history, and prehistory uniformly lead to the syllogism:

cooler = bad;

warmer = good.

You do the math.

During the 1970s, I conducted an (unpublished) meta-analysis of data Charles Greeley Abbot collected from various sources in the early 20th Century to look for cross correlations between his solar irradiance measurements, sunspot index measurements, and weather patterns in various cities. The meta-analysis showed a significant positive correlation between solar irradiance and sunspot data, and a partial correlation between them and the temperature data.

Abbot, like nearly all astronomers and astrophysicists of his time, firmly believed in a negative correlation between sunspot index and solar irradiance, rather than the positive one his data showed. He noted the partial correlation between sunspot index and temperatures, but his prejudice about the correlation between index and irradiance led him to reject the effect as spurious.

By the end of the 1980s, the positive correlation between solar irradiance variations and sunspot index variations had been confirmed by satellite measurements, overturning astrophysicists' previous view. This allowed partial explanation of historically observed climatic variations, specifically the so-called "Little Ice Age" in the latter half of the second millennium, by reduction of solar activity observed through anomalies in the sunspot index, specifically the Sporer, Maunder, and Dalton minima. This research strongly indicates that solar variability is also an important input to the climate system that is certainly not under human control.

Now, it is becoming clear that the climate system is highly complex, with multiple positive and negative feedback loops, as well as a large number of independent forcing inputs, only a few of which are under human control (see "Aerosols Cloud Climate Picture," Science News, v. 176, n. 11., pp. 5-6 for a brief synopsis). These are characteristics of a chaotic system

Paleontologists and geologists have pieced together a fairly complete, though not necessarily detailed, picture of Earth's climate over the 4.5 billion years of the planet's existence. This picture shows a chaotic climate capable of varying over a wide temperature range. On short time scales, weather patterns are now acknowledged to be chaotic, with a horizon of predictability on the order of a week.

Taken together, these bits of information lead one to the conclusion that Earth's climate exhibits chaotic behavior on all time scales. It is, basically, a chaotic system.

Now, let's look at efforts to control climate change. We are attempting to use a chaotic system (global politics) to harness a second chaotic system (social, economic, and technical institutions) to control a third chaotic system (Earth's climate), when not all the forcing variables (e.g., solar irradiance, geology) are in our hands, anyway.

This sounds like a fool's errand.

I suggest that we could much more effectively apply our energies to developing means to react to climate change that is inevitable, than to the fool's errand of trying to direct it. Climate change, in any direction, has both positive and negative affects. It would be far better to direct our efforts toward engineering social systems, laws, and technologies to take advantage of the positive effects, and ameliorate the negative effects.

Buried at the end of Section B (Marketplace) in today's issue of  The Wall Street Journal was a one-sixth-page article (blown up to nearly a half page by an enormous photo of a pretty Japanese lady wearing the modern version of 3-D glasses) discussing the the hurdles 3-D television faces to becoming a commercial success. According to the article, television manufacturers in Korea and Japan (specifically, Samsung Electronics, LG Electronics, Sony, and Panasonic) "... see 3-D as the next big technological breakthrough...." The article intimates that the technology's biggest hurdle is getting consumers to upgrade so soon after paying up for the transition to HDTV.

It fails to mention the possibility that the technology might turn out to be as useless for television as the proverbial enhanced mammary glands on a male Bos taurus.

True 3-D visual experience relies on solving the technical problem of presenting separate images to the viewer's left and right eyes. The two images must differ slightly to allow the viewer to subconciously solve the parallax problem locating the objects in the scene relative to the presumed camera position along the third spatial dimension (range).

An elegant technical solution became commercially available a couple of decades ago, when electron-microscope maker Cambridge Instrument Company introduced a scanning electron microscope (SEM) featuring a display system using circular polarization. Images for one eye were displayed using light with left-handed circular polarization while images for the other eye used right-handed circularly polarized light. The viewer wore glasses with circularly polarized lenses. The lenses on one side passed left-handed light, while the other passed right-handed light. Circular polarization has two advantages as a coding scheme:

• polarization is, in general, color neutral, so full-color images can be displayed;
• circular polarization is maintained during reflection and transmission of light, so the system is harder to accidentally spoof.

So, while the technical challenge is pretty much a thing of the past, there's a big issue with utility. You see, parallax is not the only way to signal range information. More importantly, parallax only works at short distances.

Because human eyes are necessarily spaced only a few inches apart (baseline). Other creatures may enhance parallax perception by mounting their eyes on stalks protruding from the sides of their heads, but humans obviously don't. This limited eye separation combines with the eye's finite angular resolution to restrict the effectiveness of parallax as a range cue to distances smaller than the order of 100 feet. In fact, other means of judging distance become more important at ranges beyond a few tens of feet.

Leonardo Da Vinci pointed out the importance of creating a 3D illusion by depicting distant objects as seen through an intervening mist. While he noticed the related illusion that objects appear magnified when seen through a fog, he missed (no pun intended) the explanation that the fog causes the brain to overestimate the distance to the object. It then solves the resulting cognitive dissonance by percieving a larger object located at the overestimated distance.

Walt Disney solved the problem of portraying distance on a flat screen in his 1942 film Bambi (not to be confused with Marv Newland's 1969 Bambi Meets Godzilla, which I couldn't resist linking to) by the simple expedient of introducing parallax while moving the assumed camera's point of view. He showed nearer objects moving more as the camera dollyed (moved along a track at right angles to the line of sight) than more distant objects.

Both solutions arise naturally in live-action video. These solutions become even more powerful when combined with the immersive experience of wide-screen HDTV.

So, adding parallax through circularly polarized stereoscopic projection gives a realistic 3D effect only for objects that are a few tens of feet from the camera. Anything farther away, and other range cues are far more important.

I haven't done the study, and I don't know if anyone else has, but it would be interesting to know what percentage of scenes in motion pictures or TV mainly include objects less than, say, 30 feet from the camera.

Photographers making images for the stereoscopic viewers popular in the late 19th Century were fond of creating cityscape views with points of view separated along a baseline many times that of human eyes. Nobody would percieve parallax when visiting the actual scene. All they really accomplished was to make the scene look like a miniature model, reduced in scale by a factor equal to the ratio of the camera baseline to the distance between the viewer's eyes!

Trying to enhance the stereo effect of video content by recording with an overly long baseline will have the same effect for TV. You'd make Jaws look like a 3 foot sand shark. The Grand Canyon would look like a drainage ditch.

In the final analysis, how much extra would you pay for 3D TV? How much would it enhance your enjoyment of sports, for example? If your sport is chess, it might do a lot. If your sport is, say, football, or baseball, or motor racing, or sail boating, on the other hand, not so much.

Whether 3D TV will be a commercial success in the long run has nothing to do with market-introduction timing, or whether folks have already gone through a recent upgrade to HDTV. It's about whether the marginal enhancement of their viewing experience is enough to make folks give a rotten dingo's kidney about it.

Chevrolet leads off the content at its website for the Volt electric car with a cryptic explanation of the test conditions that allow them to claim 230 mpg fuel economy for an electric car. That's good, because nobody in their right mind would accept such an outlandish figure without at least a stab at knowing the test conditions. It's bad because fuel economy figures for an electric vehicle are meaningless, since an electric vehicle does not run on fuel.

Hybrid automotive propulsion systems run primarily on fuel (gasoline, diesel, liquified natural gas, etc.) with a means of capturing energy generated when the car's propulsion demand is lower than the engine's available output, then delivering it back when propulsion demand is high. That allows the vehicle to have an undersized engine and still deliver bursts of performance equivalent to a car with a much more powerful engine.

As an example of how this works in practice, some Formula One race cars use a similar technology called the kinetic energy recovery system (KERS). While braking for a corner, the KERS system captures some of the energy that would be burned off as heat in the brakes and stores it in a battery. The driver has a push button that pours that energy back through the drive train, delivering some 80 HP in excess of the engine's maximum output.

Two anecdotes are available from this experiment. First, it is said that KERS equipped cars are nearly impossible for non-KERS cars to pass under acceleration. Does that surprise anyone? The second bit of information is that the leader in this year's F1 constructors championship does not use KERS. What that really means, and what the standings will be at the end of the season are valid topics for beer hall debates.

Electric vehicles - the Volt included - are primarily driven by electric motors. From an engineering standpoint, there's a lot to be said for this architecture. It's well understood. It vastly simplifies the mechanical drive train. Leaving out the battery pack, it reduces the powerplant weight by a lot. Consequently, it will likely reduce the energy cost of getting the payload from A to B. It probably will reduce maintenance requirements as well, since the components are few, quite robust, and don't suffer much wear.

I said that the technology is well understood. It is and has been for a very long time. Some of the earliest experiments in automotive technology were electric vehicles. I drove an electric forklift during the 1960s. My grandson has owned and operated a series of electric go karts for most of his life. Electric golf carts dot the fairways of America. Electric vehicle technology has been under development for at least as long as the internal combustion engine. What we know about it is a lot!

The problem, which I sidestepped above, is that battery technology is such that storing the energy needed to get that payload from A to B is enormously bulky and heavy. If A and B are significantly far apart, the size and weight of the battery becomes impractical.

The problem is storing enough energy in electric form to run the thing a reasonable distance. The Volt gets around this problem by installing an auxiliary power unit (APU) to provide power when the driver has been foolish enough to drive past the vehicle's point of no return on battery power, and wants to get back by, say, 3:45 PM for a meeting. The APU kicks in, providing enough juice to get you home.

Altogether, I have no problem with the Volt itself. It looks great - or at least as good as allowed by the inaesthetic drech that passes for automobile styling today. Not having driven one myself, yet, I can't answer for its performance, but electric vehicles generally can be made to go as fast as you want (for a while). From my comments above, you can tell that I like the concept from an engineering standpoint - especially for short trips with long recharge spells in between.

My problem is with the idea of assigning a miles per gallon performance figure. It makes sense for hybrid vehicles because the whole driving experience is energized by fuel from a tank. For an electric vehicle, with the bulk of the energy theoretically supplied by an electric outlet, it is rediculous.

So what if the current test protocol returns a result of 230 mpg? I can double that just by jiggering the test protocol for shorter trips so the horse gets back to the barn for more oats before having to limp the last few furlongs. If the car is good for 40 mi on battery power, I can jack the fuel economy rating to infinity just by allowing test trips of 39.5 mi.

It's just soooo bogus!

With all the hoopla around alternative-propulsion vehicles (e.g., electric cars and hybrids), not too much gets into the mass media about the efficiency of rail transport. Those of us who've lived in the Far West don't need to be reminded of railroad transportation. Running individual truckloads of goods along highways one-by-one seems kinda silly next to mile-long freight trains.

BNSF Railway Company recently announced two free tools for shippers and carriers to be able to directly compare the cost and transit times of intermodal service to the highway alternative. The company says that shipping by intermodal rather than solely by highway provides important environmental, safety and security benefits.

In the late 1949s, when then Gen. Dwight Eisenhower became impressed with the German Autobahn system, rail cars had to be individually loaded and unloaded at each end of any transportation run. So, a shipment of barbell weights cast in China would have been loaded on a ship, sailed across the Pacific Ocean, unloaded in, say, San Pedro, Calif., then unpacked from the freighter and repacked into boxcars. After making the rail trip to, say, Erie, Penn., they'd have been unpacked from the train, and repacked into freight trucks for delivery to wherever they were finally to go. All that packing and unpacking took a lot of time and labor.

A few years later, when elected President of the United States, Eisenhower took the opportunity to reproduce the Autobahn system on a grand scale in the Interstate Highway system.

Figure 1: Movement of a truck through the atmosphere builds high air pressure ahead and pulls low pressure behind. Both effects create retarding forces on the truck. This effect is called induced drag. (Click to expand)

Since then, however, we've developed the intermodal transportation system. With intermodal, everything destined for that Erie location from that China starting point would be packed in ISO shipping containers, which are exactly the size and shape of the boxy trailers that long-haul trucks pull, sans the wheels. At the Chinese port, these containers would be tightly packed into cavernous holds of dry-shipping freighters headed for the U.S. port. Once there, the containers would be lifted out of the holds, and stacked two-to-three high on railroad flatcars made for the purpose. The flatcars would be made up into trains for the transcontinental passage. In Erie, each container would be lifted from the rail cars onto an individual truck for final delivery. That makes the system time and labor efficient.

I won't go into the safety and security benefits, as they are not basic technology issues. The environmental aspects, however, stem from basic physics and engineering. Specifically, high-speed rail transport can be (should be) more fuel efficient than highway transport.

There are two main forces that cause vehicles to burn fuel at high speeds: aerodynamic drag and rolling friction. I'll start with rolling friction.

The main cause of rolling friction is deformation of the wheels as they generate reaction forces to support the vehicle's gross weight. These deformations convert kinetic energy of the rolling wheel to heat. The more deformation and the faster the wheel rotates, the greater the heat. That is why truck tires are so large in diameter (fewer revolutions per mile) and why they run at very high pressures (less deformation). Rail cars, on the other hand, have steel tires, rather than pneumatically supported rubber tires, so they hardly deform at all, even when carrying the enormous gross weight of a fully loaded rail car. Thus, rolling friction per unit weight in railroad transport is a fraction of that for highway transport.

Aerodynamic drag arises from the need to elbow air out from in front of the vehicle, then suck it back to fill the hole in the atmosphere after it passes. Figure 1 shows how high pressure builds up in front of a highway freight truck, and low pressure forms behind it. These high and low pressure regions create forces that hold the truck back - aerodynamic drag.

Figure 2: Running two trucks in tandem dangerously close together neutralizes the low pressure region behind the first truck and the high pressure region in front of the second, reducing the aerodynamic drag by nearly half. (Click to expand)

Drag forces increase as the square of the vehicle's speed, so they rapidly become the dominant energy-loss mechanism.

Truckers soon learned that the best way to reduce aerodynamic drag is to run trucks nose-to-tail close enough so the high-pressure zone in front of the following truck overlaps the low-pressure zone behind the truck ahead. As Figure 2 shows, the two pressure zones cancel each other out, effectively cutting the net aerodynamic drag in half. This so-called drafting technique has been used for decades by truck "convoys" to lower operating expenses by saving fuel. The more trucks in the convoy, the more fuel saved.

Figure 3: Because they are physically coupled together, railroad cars can run safely with very little spacing between them, providing huge aerodynamic drag advantages. This drafting phenomenon effectively neutralizes induced drag for all but the lead and last cars. It does not, however, reduce viscous drag caused by sliding of air past the cars tops and sides. (Click to expand)

The same effect improves aerodynamic efficiency of railroad transport, except that the trains are very much longer and the cars can be safely run very much closer.

These two effects boosting overland transport efficiency makes maximizing use of rail transport good energy policy. What we, as ordinary citizens, can do is raise the volume of voices calling for increased use of rail transport as part of energy policy. Since the same phenomena apply to passenger transport compared to individual cars, we should also clamor for upgrading commuter rail as an alternative to commuting via cars.