omenti

lessons

Recently Om wrote an excellent piece on Derek Jeter’s career and some lessons one might draw from it. Even if you don’t like baseball, it’s worth reading.

 

Consistency, finding opportunity, leading by example .. and the ultimate goal.

 

One of my heroes is Ray Davis. I got to know him when I was a grad student and postdoc at Brookhaven National Laboratories. He was an experimental physical chemist who was doing some interesting solar physics. He was also of those people who mentored those more junior by example. I sailed with him on his homemade sailboat and joined him on numerous nature walks around the BNL installation as he photographed almost everything. He’d show up on Mondays with bandages from whatever home repair he had attempted. 

 

It’s worth reading a personal statement he made in 2002

 

also check out how people recognized him at the bottom. I’m sure he didn’t put that in himself. He was exceptionally humble.

 

His statement doesn’t go into the controversy and drama of the Homestake Gold Mine experiment. By 1960 physicists had a good idea how fusion took place in the Sun. It’s a somewhat complicated multistep process and different from how manmade fusion machines or bombs work. Some of the energy is released in the form of neutrinos. You may have head about neutrinos. They have a very small mass and barely interact with matter. A standard comment is more than half the neutrinos that strike a piece of lead a light year thick will travel though as if it didn’t exist. But the Sun was making a lot of electron neutrinos and a few will interact. In the late 60s Ray decided to count them and nail down what was going on in the Sun’s core.

 

He was exceptionally careful. Every month he was able to count about three dozen argon37 atoms They started out as chlorine37 but were turned into argon37 when an electron neutrino struck them. Ray spent years making sure hhis results were accurate. His numbers were very consistent… and about a third of what everyone knew was required for the Sun to shine like we see it. It seemed eithre Ray was wrong or the solar models were wrong. Ray persisted. People were in awe of how careful he was. The solar models were also holding up in other tests.

 

It turned out new physics was afoot. Ray was only sensitive to one type of neutrino - the electron neutrino - the type the Sun had to generate. What they found, when another observatory was built that detected another type was neutrinos oscillated from one type to another as they sped along. It was as if your Ford changed into a Chevy and then a Toyota regularly. You owned a “car” that was an admixture of these different brands. Startling new physics. Ray had peered into the core of the Sun with a tank of chlorine about a mile underground in South Dakota and by not giving up when the numbers seemed wrong, found Nature was answering with a new question

 

Ray was sprinkled with Swedish holy water in 2002 for his work.

 

It is remarkable that his institution - BNL - gave him that level of freedom. It’s also remarkable how he stuck with it and impressed all of us with the beauty of his work.

 

lessons…

connecting the titanic, sputnik and dealing with forgetfulness

1955, Fred Whipple had just been appointed to head the Smithsonian Astrophysical Observatory in Cambridge.  The International Geophysical Year was less than two years away and he wanted to involve citizen scientists as much as possible.  Whipple was one of the few who realized a satellite was likely and set about creating a web of radio operators to monitor and relay transmissions from satellites along with groups of amateur astronomers who could optically track their orbits.  Operation Moonwatch was formed and by Sputnik's launch over 200 teams were in place. 

 

Tracking a satellite was done with a clock and a low power telescopes that could read azimuth and declination.  The National Bureau of Standards time signal broadcast on WWV in Fort Collins, Colorado used as the reference clock and most people into amateur astronomy had a shortwave radio. Readings from stations separated by hundreds of miles were sent by amateur radio operators to a computer at MIT that gave the project a bit of its precious time.  More clusters of readings would come in from around the world and a model of the satellite's orbit generated an ephemerides - predictions of where it would be. Later specialized cameras were developed by Bell Labs to automatically generate satellite ephemerides as well as tracking ICBM tests, but Moonwatch was a success and lit the imagination of a few people.  

 

In physics it's common to turn a problem on its head to gain a bit of insight.  Operation Moonwatch used known positions on earth and an accurate clock to measure a position in orbit.  What if you put synchronized clocks in space and measured how long it took radio signals to reach a position on earth?  With enough satellites with synchronized clocks you could triangulate a position anywhere on the Earth's surface.  The technical details were difficult details, but the basic idea was simple.  

 

It turns out accurate navigation is very difficult and expensive and a limiting factor in fighting the cold war.  It was so difficult that as technology progressed ARPA decided to push ahead with a satellite based global positioning system - the inverse of Operation Moonwatch.  It was a bargain for what it gave to the military.  Finally a good enough signal was made available to civilians and navigation changed.¹ 

 

GPS doesn't work everywhere.  It would be nice to track things indoors and at a lower cost. Bluetooth and WiFi are currently used -  usually measuring signal strength from several transmitting beacons and triangulate a position.  Sometimes it's just proximity to a single beacon - a lighthouse model.   The approaches aren't very accurate - three to ten meters is common.  Good enough to track your phone as you move around, say, in a mall or subway, but doing better would be nice.

 

This is where the Titanic comes in..

 

On April 15, 1912 the Titanic struck an iceberg.  Frantic radio signals went out, but there was confusion among rescue vessels and people on land trying to coordinate the rescue effort.  Sometimes it takes a disaster to create order and an effort to regulate radio frequencies began soon after. Transmitters were assigned narrow swaths of the electromagnetic spectrum that were large enough to effectively communicate with receivers that could tune to those frequencies. Regulations changed as larger chunks of this resource were needed - AM radio required more than Morse Code, FM radio even more and television much more. Government would parcel out these increasingly scarce resources, but power was also regulated and it was possible to give much larger chunks to low power short range communications - WiFi and Bluetooth are examples.  Most of radio engineering tried to pack as much information into as little spectrum as possible and to build transmitters and receivers that could be accurately tuned to specific frequency ranges  If you waited for some technology to catch up there was another way (actually several, but I'll only mention one) way to do radio.

 

You may have heard about ultrawideband (UWB).  In the mid 2000s it was supposed to be a good way to send large amounts of information over short distances.  Cheaper and higher bandwidth than the WiFi of the day. Often existing technologies are improved with scale and an embedded base making it difficult for new players.  Sophisticated coding technologies and enormous penetration (WiFi has greater penetration than smartphones) cemented WiFi as the prime high bandwidth low range wireless connection.  In a few years UWB went from redundant to lagging. Many thought it was dead, but it had a few advantages in some use cases.   

 

Here's how it works.  Rather than sending out a precisely tuned narrow band frequency, UWB sends out narrow (in time) digital pulses that "splash" over a very wide frequency range.  The signals are usually only one or two billionths of a second long and aren't sent that often - a hundred thousand to ten million a second are common rates. The frequency range is so wide that usually at least some of it can pass through objects that block signals like GPS and WiFi.  It's also so weak that narrowband communication can't detect it.²

 

 Imagine scattering a few UWB transmitters around where you know their location with some accuracy.  Now start transmitting synchronized pulses.  A receiver notices the time of arrival of each signal and, using the fact that light travels about 30 centimeters in a billionth of a second, can triangulate it's own position.  Accuracy is about ten centimeters - about four inches.

 

A use case I'm familiar with is finding the locations of players in a beach volleyball game.  In international FIVB games a very small (less than a half ounce) UWB device goes in the back of each player's  shirt or sports bra.  Their positions are tracked within ten centimeters about a hundred times a second and accelerometers and a compass send out rotation and orientation information on the UWB signal that the announcers, coaches and sports science people use.  Four transmitters are used and all four players are easily tracked.

 

It would also be useful for augmented reality and Apple has included an UWB chip in every iPhone 11 - the greatest deployment of the technology so far.  For now it's being used for data transfer, but wait a bit.  Someone could also make very cheap ($10 or less) postage stamp devices that might be powered by available light that could be location tags.  Put them on your keys, glasses, remote control .. anything you tend to lose track of.  We went through trying to manage dementia with my mother.  I would have paid a lot for this capability.  And thousands of other uses from amateur sports to tracking boxes accurately in warehouses.

 

There are probably some bad things that can be done with it.  We need to be thinking these things through, but our track record isn't exactly good. 

__________

¹ It also gives a very good frequency standard and a timing signal.  Without this our mobile phone system, high frequency trading and a host of other core technologies we depend on would break.  This is an issue as GPS is vulnerable to attack and we've done almost nothing on backup technologies. 

² The FCC defines it as taking up at least 500 MHz of spectrum somewhere from 3.1 to 10.6 GHz.  Power is under -41.3 dBm/MHz .. or 75 nanowatts.  Since it only deposits a tiny bit of power in any narrowband frequency, it's just below the noise floor of a narrowband receiver.  Fortunately it's straightforward to build a receiver that can detect the signal. 

a bolt down the track

A pre-Olympics minipost

 

Competing in the 2009 Berlin World Championships, Usain Bolt set the 100 meter sprint world record at 9.58 seconds.  A few of us have analyzed his performance using position and speed data taken every tenth of a second by a laser tracking system. The exercise gave me a deeper appreciation for what's going on in this type of performance.

 

Physics suggests world class sprinters should be taller than world class distance runners, but at 195cm, Bolt is extremely tall even for a sprinter.  Aerodynamic drag is where most of a runner's effort goes in sprinting as the power required to overcome drag goes as the cube of your speed relative to the wind.  Part of sorting out what's going on requires knowing the effective area he presents running. The coefficient of drag (C_d) is multiplied times the cross sectional area of a body moving through a fluid (air in this case) to give an effective area - C_dA.  A very streamlined body is going to present much less drag than a brick of the same area.   A human runner has a C_d of about 1.2 ..  most cars are 0.3 to 0.4 and a bike racer is about 0.8, so you can see he's not very streamlined. And being so tall increases only makes matters worse by increasing the area he presents.  

 

But he makes up for it. 

 

Usain pushed off the starting blocks with about 830 Newtons of force, about the same as his weight, giving an initial acceleration of 9.5 meters per second. Around 0.9 seconds out he's delivering about 2600 watts of power.  That peak falls off rapidly, but the number needs to be put into perspective.  When you're riding a bike at a comfortable speed you're delivering between 50 and 150 watts.  A world class bike racer can supply about 400 watts for an hour.  A horsepower is 746 watts.  

 

From one to four seconds he's supplying a roughly constant force, but his acceleration slows as he fights drag. His speed continues to build - at this point his moving 4 meters per second or about 9 miles per hour.  Four seconds out he's reached a maximum speed of nearly 12.2 m/s - 27.3 mph.  The force from drag is now equal to the force he can generate.  He's reached an effective terminal velocity.  Bolt manages to maintain about 99 percent of that speed for the remainder of the race.

 

Now for the part that shocked me. The total energy that goes to motion is about 1.8 watt-hours, but since he's applying a nearly constant force you can work out the total energy he needs to run and overcome drag  - about 22.6 watt-hours. Ninety-two percent of his energy goes into overcoming air resistance!  He's almost entirely relying on anaerobic metabolism which can supply these enormous power bursts for short amounts of time (under 30 seconds) He jokes he couldn't run a mile at any speed.  Anaerobic metabolism is inefficient and the waste heat needs to go somewhere. The core body temperature of these sprinters rises quickly and would be a limiting factor (eg - they'd pass out or die) if they could maintain their pace for longer periods.

 

So why the picture?  The world record has dropped over the decades, but people have calculated the impact of better tracks (world record tracks have a special harder surface so less energy is lost during the run), better shoes, and starting blocks.  Given the same technical changes, Jessie Owens' best performance falls in the high 9.60s - about a tenth of a second difference between the two great athletes.  Of course we don't have time machines, but ...

 

Why is riding a bike so much more efficient than running?  That's for another time...

 

 

 

making sense of it

Some of you are probably using smartwatches and fitness sensors for long standing exercise routines or perhaps new routines that began with a resolution a few days ago.  Since regular exercise is considered one of the most powerful and safest medicines known, anything that encourages it can be a terrific investment. There's evidence that competition with yourself or others based on feedback from these devices is motivational for some people. 

 

But what do the readings mean?  

 

Regular exercise is great, but no one knows how much is enough or even too much as there's variation from person to person and careful studies are very difficult. Even the understanding of metabolism is general - it is important to forget the concept of a total energy budget (calories eaten - calories burned) as that requires very careful lab measurements.   What is known is a few hours a week at moderate intensity is a great start.  A heart rate monitor can give feedback on intensity, but there are other effective non-technical methods too.  As the ad says - just do it using whatever works for you.  But what if you are an amateur or professional athlete - do these technical aides give an edge?

 

For four hundred dollars a smartwatch gives you information it would have cost thousands of dollars twenty years ago. The problem is you need to understand what it's reporting in context.  For most of us that's somewhere between very difficult and impossible. An elite runner or cyclist might have access a to multi-million dollar support effort with specialists who try to understand information from a variety of sources in context for that elusive one percent performance gain, but even then they regularly fail.  Generally these tools  are most successful used in training as the complexity of understanding the information changes during competition.  In recent years telemetry from athletes in team sports became possible.  A coach could see the condition of each of their players on the field as well as track how much and how fast they moved. It became popular in football, soccer, rugby and a few other sports, but is being set aside by many as understanding context during competition difficult and it had led to some dramatic coaching errors. 

 

Besides wearables video analysis can make a big difference for amateurs.  Usually a coach or trainer who understands what they're watching and how to make changes is needed - you're not going to find great personalized information on youtube.  A few sports like baseball, golf, tennis and gymnastics are making use of motion capture.  I'm guessing we'll see that make its way to smartphones one of these days (there have been a couple of so-so efforts already).

 

I'll cut it short as probably only a few of you are interested in diving in (for those that are feel free to get in touch - I have an interest in sports science and sports tech)  For everyone else the message is use whatever it takes to find the motivation for regular exercise.  It may be a smartwatch or fitness tracker, but you're probably in the minority if those work over the long term. Find what works for you.  And if you're an amateur athlete the lowest hanging fruit may well be a few hours with a trainer working on form.  There's a tendency to use tech for that one percent where a simple change in form might buy much more.  And an added befit of a few sessions with a trainer is they might be able to spot and correct bad habits that might lead to injury. 

 

There's a message for anyone who relies on numbers for their work.  Where did they come from and what exactly do they mean?   Perfect understanding is rarely possible, but understanding what is good enough and how to find and understand context is essential.  One of the reasons why much of what is being done with big data and machine learning frightens me.  They can inspire false confidence.