omenti

leaps of faith

minipost

Yesterday I had my first jab of a Covid-19 vaccine - specifically the Pfizer mRNA vaccine.  Despite political, production, and distribution issues several vaccines appeared and more are coming.  Going from decoding the SARS-CoV-2 genome to first injections took only about a half year and a year later a few hundred million doses have been produced. While some corners were safely cut, the real story - at least for the new mRNA vaccines - began nearly thirty years earlier.  

 

Katalin Karikó's work will certainly win her a Nobel Prize next year.   Here's a good telling of the story.  A major point is the work was judged unworthy and finding support was nearly impossible.  After about ten years another player, Drew Weissman, entered and the two of them managed to crack the final bits of the problem.  He'll certainly be sprinkled with the Swedish holy water too. The mRNA approach is important well beyond the current pandemic - it may mark a fundamental change in medicine.  It wouldn't have happened - at least not as soon as it did - without a certain type of reserch.  

 

Curiosity-driven fundamental research requires a certain type of scientist, time and resources.  While much of it fails to produce an immediately useful result,  it has an established track record of changing the world.  Industries don't do this kind of work anymore.  Most universities shy from it - there's a tendency to want results-focused work.  When it's funded you usually find it in physics and astronomy  rather than the biological sciences and that's a problem.   These leaps are driven by hope and curiosity.  They open doors that often require more than a decade of work - usually by other people in different organizations.   Expanding this work is how you create radical change.  I'd never argue results-driven research should be cut - after all, that's where the next five to twenty years come from.  But I'd love to see the Katalin Karikós of the world given more of a space.  And then there are the spin-offs - a good deal of the instrumentation used in medicine came out of  fundamental physics - but that's another set of stories.

 

my that's a big watch you have

 

That watch you're wearing - what does it do?

Sarah always wears the same watch.  A large round face that must be 60mm across and a simple band.  I was curious.

It tells time and it's easy to read at a glance.  She replied

That's about what I expected - just a simple analog watch.  About the farthest athing from a fitness tracker or wearable computer.  As a world champion Olympian on the hunt for gold, Sarah doesn't leave much to chance. But before going into why she doesn't use wearables, it's probably best to backtrack a bit.

 

For the majority of people fitness trackers can be useful.  If you give them to people, about three out of five increase their activity levels for at least a few months.  If they buy on their own it goes up to about four out of five.  It's generally agreed that physical exercise of any kind is healthy and many MDs and medical researchers consider exercise a powerful drug with few negative side effects (you can always injure yourself if you aren't careful).  It is possible that these devices will have a positive long term impact on the population.

 

Less known is what kind of exercise is best for a given person.  Here we get into personal tastes and capabilities.  My undergrad school had a physical education requirement.  These were once more common with roots in the muscular Christianity movement of the late 19^th century.  I'm far from an athlete, but was surprised to find the first meetings were a series of one on one tests and a discussion of what seemed right.  The teacher was more of a physical trainer than anything.  Half joking he told us the college wanted people to be healthy so they could live long productive lives and leave a lot of money to the school.  His job was to find a few activities that we might enjoy enough to continue for decades.   He was trying to help us figure out our own internal version of a fitness tracker.   For me it came down to cycling and rowing.

 

More than a few people buy expensive exercise kit only to quit after a few months.  Everything from simple treadmills to Pelotons.  I'd go with what I learned in college - hire a personal trainer for a couple of sessions to (a) find out what kind of exercise you like, (b) learn some proper form, and (c) learn how to set and keep goals.  Some people respond well to online sessions, but they're often only one-way without analysis of your form.  Some personal trainers consult via video chat and may be the best choice in a pandemic.  Of course that's if you're serious.  If you're the type who responds to closing circles, you can get good results with a fitness tracker or Apple Watch.  Or you can use your bicycle. 

 

What about more serious athletes?  There are a number of tools available to amateurs and pros.  I've had chats with some serious sports science people - the type who work with elite athletes.  They'll tell you it boils down to measurement:

What do you measure?
How do you measure it?
What does it mean?

Basically the same things I worry about in physics and probably many of you do in yours.

 

Much of this goes beyond what a smartwatch can do.  Power ergometers on bicycles and rowing machines, gps tracking at the team level, heart rate analysis, enzyme measurements, muscle fatigue tests, and much more. Sometimes movements are analyzed with thousand frame per second photography.  Many of these reading are combined in an attempt to measure something.  In many sports it's been counter productive (again at the elite level) there aren't direct measurements of what you'd really like to measure - whatever it takes to create the best performance.  You start out not knowing exactly what you're doing and from there it only gets worse - often the advice is about as good as a coin-flip. 

 

Elite athletes also have access to excellent coaches who know what to measure and how to use it in context. This can vary wildly from sport to sport and even from athlete to athlete in the same sport.  These people can answer those three questions for the technologies they use. 

 

Beyond tech the mental game is often decisive.  Humans have dozens of internal senses (we have way more than five senses).  Our interoceptive system has this fantastically powerful neural network in our skull for analyzing complex information from around our body in real time. Some athletes train themselves to be aware of and learn how to read this information.  It's part of the mental game that separates the best from everyone else.  There are a variety of ways to get there including mindfulness and it's an active area of exploration.

 

Watching Sarah is fun.  In a match she's performing some experiments on the other side early on while having an intense conversation with her teammate Melissa. at some point a switch seems to come on and she's playing at another level.   She says she really doesn't notice it - much of it is in a state of flow.  She manages to do this even under intense pressure and knowing how to adjust to whatever state her body is in.  Of course the other top players are doing something similar, which is what makes the sport interesting. 

 

It took her years and years to get to this point.  Fortunately none of us have to do anything like that as we're usually more interested in health and feeling good rather than crushing the competition.  Go with whatever motivates you.  Even brisk walking is great.  Get a fitness tracker if that's a positive motivation.   But maybe the best spent money is a few sessions with a physical trainer to explore the space.

 

Or you can get a dog that you have to walk and enjoy extra mental health benefits along with the exercise.

 

The impact of tech in sport is another long conversation I'm only learning a bit about. 

 

power different

Recently a friend sent a piece on an energy harvesting device that coverts some of your body's waste heat into electricity.  The description was sparse, but it mentioned the average person produces about one hundred watts of waste heat and went on to say that is enough to power a laptop.  

 

umm..  Both true, but there are some problems ...

 

The average adult metabolizes about 100 watts on average to stay alive.  That's about the same as eating 2000 calories of food a day.   The average adult has about 1.7 square meters of skin area.¹  This means we need to get rid of about 0.006 watts per square centimeter of skin area.  Six milliwatts of power per square centimeter.  The photo of the device showed a ring like affair with some fins - maybe two square centimeters of radiator area.  Let's round that to about ten milliwatts for the device - hardly enough to deal with a laptop, which are on the order of 20 watts or even a smartphone which are a few watts.  That assumes all of the waste heat can be harvested with one hundred percent efficiency.  Here things begin to go down hill quickly.

 

A thermoelectric converter on human skin has a theoretical efficiency of about 5% at room temperature.²  This reduces the six milliwatts per square centimeter down to 0.3 mw/cm².  Even if you covered your entire body, you'd only harvest five watts and you'd be shivering.   And that's unrealistically optimistic as these devices rarely have more than single digit efficiencies on top of their thermal efficiency in this temperature range.  Even optimistically we're down to about 0.03 mw/cm² or 30 microwatts/cm².  Something like an armband might have 100 cm² giving us 3 milliwatts.

 

This isn't reason to abandon hope.  There are hardware devices with sub-milliwatt power requirements. Small energy harvesting devices that harvest mechanical or solar energy also exist and make it practical to put tiny sensors with tiny transmitters nearly anywhere as long as your receiver is nearby. The micro part of the Internet of Things (which has its own issues).  It turns out this is a rich area for college engineering projects.

 

But what about larger power demands where it's inconvenient to change batteries?  Spacecraft that travel past the orbit of Mars generally rely on radioisotope thermoelectric generators (RTGs) because the Sun is too dim to make solar power practical.  An RTG puts a thermoelectric converter on something hot - a radioactive material that decays rapidly.  Ideally it's an alpha emitter so you don't need heavy shielding.  There are a number of candidates, but Plutonium-238 (Pu-238) is the most common American choice with a half life of about 88 years. Not only do these generators produce electricity, the extra heat is used to warm the spacecraft's warm.   The current generation of Martian rover is RTG powered. 

 

There are a number of RTG stories.³  I don't want to go on forever, but the nuclear powered pacemaker and artificial heart are among the more interesting.  

 

A problem with early pacemakers was longevity. Batteries had to be replaced every eighteen months or so necessitating expensive and risky surgery.  In the late 60s and early 70s two types of tiny radioisotope generators were manufactured for use by several pacemaker manufacturers. They had enough shielding to be very safe and would last longer than even very young patients.  They were also very cost effective and a few thousand patients received them. Then, in the mid 70s, the practice suddenly halted.   The worry was devices might not be removed before cremation from patients who had died.  This would destroy the shielding and turn an area in and around the crematorium into a radioactive hot zone requiring evacuation and a very expensive cleanup.  

 

The radioactive heart implant never made it into a patient.  To make enough power to run the heart, the RTG generated about 50 watts of waste heat adding to a normal person's 100 watts.  It wouldn't be bad if it could be spread over a skin sized area, but that would be impractical.  It would be like holding an incandescent light bulb.   One of those interesting ideas that you wonder about afterwards...

_________

¹ The approximation medical researchers usually use is from Mosteller:  (height[cm] * weight[kg]/3600)^0.5  a

² The theoretical maximum efficiency of a heat engine is 1 - Tc/Th  where Te is the temperature of the environment - the air around the device in this case - and Th is the temperature of the radiator - the skin temperature.  We have to use an absolute temperate scale so Th = 310°K and Tc ~ 295°K.  So about 4.8% efficient.. let's call it 5, although it is probably half that with poor coupling to the skin and air. 

³ One could go on for a long time .. the CIA's RTG in the Himalayas is particularly interesting.  And then there's the Apollo 13 RTG that required last minute maneuvers as the limping spacecraft approached the Earth.   The very hot RTG is somewhere on the floor of the Pacific.

 

frozen bubbles

a minipost

 

First a short video

You can make this yourself.  You'll need a chilly day and a cold surface.  I had success as a teenager in Montana with outdoor temperatures ranging from -25°C up to about -10°C.  Colder worked but the effect wasn't as dramatic and warmer just didn't work. Some of you are in areas that are still seeing chilly weather. You could probably do it in a very cold home freezer if you opened it slowly enough that the warm room air didn't mix in very much.  Use a drinking straw to blow bubbles from a soap mixture onto a cold surface.  Then watch in amazement.  Some of the best views I had were at night using a light to illuminate just the area around the bubble.   Children's soap bubble soap works, but I've found better and you might experiment   My favorite recipe created a bit stronger bubble:  

200g water
35g corn syrup
35g dish soap
25g white sugar

Stir and set aside for awhile so the turbulence from stirring settles down.  The corn syrup makes a more robust bubble. The sugar  was based on a hunch that it would create nucleation sites.

 

Here's a piece on some people who looked into the underlying physics.  My basic toy model back then that was sort of on the right track but missed a central insight and lacked the experimental analysis.  Physics gives tools to understand a variety of phenomena.  The underlying physics is very well understood, but much of what happens around us isn't deeply understood as it hasn't been studied or the math is just too difficult.  Sand, for example, is extremely difficult at the fundamental level. 

 

Bubbles have had an important role in physics.  Newton was fascinated by their formation and optical properties.  Faraday (one of the three great scientific minds of the 19^th century and the last physicist who didn't use sophisticated mathematics) used bubbles in a creative measurement that a led him to develop the idea of field theory - something that James Clerk Maxwell (one of the other great 19^th century scientists) used to explain one of the four fundamental forces.  Fields are central to fundamental physics.  They were also part of particle physics experiments for about thirty years in the form of some of the most sophisticated and exotic photographic cameras ever made - including an early test that used beer. 

 

Probably things I should write about down the road, but for now try to freeze some bubbles if you have the opportunity!