omenti

a shot echoed in the dark

   Our guide, the Director of Development for The Cleveland Orchestra, noted how difficult it was to find matching marble for the lavatories.   There were only two of us and we wanted to set up in the main hall, but impressions must be made and little was being spared in the big three year remodeling job. 

 

Cleveland's Severance Hall is a remarkable place.  A odd mash-up of Art Deco and Egyptian Revival architecture, it was finished during the Great Depression and became home to The Cleveland Orchestra.  Like many symphony halls the acoustics were bad boarding on terrible.  Remodeling a few decades later partly fixed the problem, but in addition to rendering the pipe organ unusable,  was architecturally "wrong."  The work underway when we visited would address all of those issues and make the space one of the best concert halls in the world. 

 

Our company was doing quite a bit with digital music at the time.  There was a relationship with the Rock and Roll Hall of Fame and another with the Oberlin Conservatory.  Two of us who were doing much of the Oberlin work developed a relationship with The Cleveland Orchestra and Telarc Records on the side.¹  At the same time work on sound field reproduction was a serious research topic.

 

The idea behind sound field reproduction sounds simple enough. If you've ever been around live music - or even in a recording studio - you've probably noticed your home equipment can't begin to reproduce the acoustic experience.  The problem stems from the fact that the wavelengths of the sounds we hear range over three orders of magnitude and much of it is similar in size to musicians, audience members, seats, curtains, the room itself, etc etc.  These sounds are reflected, refracted and absorbed.  Moving anything causes a change.  It's a difficult problem that the music industry and Hollywood would love to see solved.  Plus it's an interesting problem!

 

The approach we were using had a microphone array on a tripod.  One up, one down and an odd number between them in the same plane as the floor.  Severance was undergoing acoustic tuning and we were going to set up the array to record some music to compare it with other techniques.

 

We were left alone in the open hall. It was very quiet so I did the obvious thing and clapped my hands once.  There was a lovely echo coming from everywhere at slightly different times.   If we recorded an even better "clap" - an impulse function - we could mathematically play with it and create a signature of the room.²  Armed with this we could have some fun.  We needed to create a good enough impulse.

 

Severance Hall is on the grounds of Case Western Reserve University - a lovely area with good restaurants and a lot of art and music.  (if you ever stay in the area get a room in Glidden House - fantastic little hotel).  I figured the school probably had an athletic department and quickly found a track coach.  I was able to talk him into lending me a starter's pistol.

 

Later that night in the darkened hall a shot rang out - only to be captured digitally.  Then a few more just to make sure there was enough.

 

Back at the Labs we had a special acoustically isolated room - an acoustically neutral room (these are rare and not cheap!)   Using the same microphone array that was used in Severance Hall we recorded some live music with musicians in the area.  The music was convolved with Severance Hall's signature and then mixed down to six channels for playback in the room.  

 

It was fairly convincing..  close your eyes and it really felt like the place the shot rang out in the great hall.   Of course you can do better, but it was a great excuse to have a bit of fun.

 

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¹ Over the years I’d spent some time worrying about image and sound quality. At one point I thought better was - well - better. My epiphany came in the a perfectly restored 66 red Mustang. It was near Cleveland with the head recording engineer from Telarc Records and a seriously good musician from the Oberlin Conservatory. We were talking about where music reproduction might go with sound field reconstruction and dramatically more information than CDs could provide when a favorite Beatles tune came up on the 8 track (gasp! - it *was* an authentically restoration). The volume came up and the two of them were singing along to the music in pure delight. There is something transcendent about the music - even with awful reproduction in that noisy environment. Portable music players with cheap headphones would be good enough for most. As long as there's a personal touchstone.

²  take its Fourier Transform.

the third wave

Electric cars are beginning to take off.  If you need to replace your old car they may be a good choice as maintanence is potentially much less expensive.  They're usually a bit more environmentally friendly than a conventional car of the same size, but not by much. There are much more cost effective ways to lower your carbon footprint. One is replacing local commutes and errands with a bicycle. 

 

We may be at the beginning of a third wave of bicycling in the US.  This time it's a bit different with pedestrian, human powered, and human-electric hybrid bicycles in a category that's called active transportation.  I'm not so sure it will take hold in the US this time - after all, our second wave fizzled in the 70s.

 

The first wave came with the invention of the safety bicycle in the 1880s.  Suddenly cheap transport that could extend your walking range by a factor of three or four appeared and bicycle fever swept the US and much of Europe.  I've written about it a few times and won't say much other than it was an important component of women's suffrage in England. It also lead to widespread mass production and engineering leading directly to the automobile and airplane.  

 

The second wave began in the late 1960s - first in the Netherlands, followed by the US, and slightly later by Denmark.  None shared a common trigger.  The Netherlands was a reaction against the beginning of affluence that came in the mid 60s that flooded the streets with cars.  The narrow streets, children playing and cars were a nasty combination and people reacted strongly closing streets and going back to the bicycles they had used since the war.  The US boom was fueled by the green movement - particularly in university towns.  Denmark's was a reaction to the oil crisis.  The Netherlands and Denmark stayed the course building physical and social infrastructure that favored cycling in cities and small towns. Progress was slow, but by the early 90s the bicycle had become an important piece of transportation.

 

The US started much more aggressively, but fizzled for a number of reasons shortly after the mid 70s. Carlton Reid wrote a piece on the US boom that failed - a short recommended read!

 

Now something has changed - the ebike.

 

A first ride is astonishing.  They're not motorbikes - you pedal and an electric motor adds power to your muscle power.  You can set the level of added power to levels better than any Olympic bike racer. Hills flatten and the distance you're willing to ride doubles on average.  The efficiency of a person on a regular bike is amazingly high - an ebike typically improves it by a factor of two. You're still get exercise and it's much more practical than a Peloton if exercise is the goal.  Currently there are more customers than bicycles..  

 

So they make sense for you?  Probably the most important consideration is safety. Women and children are usually seen as the two indicator species - when at least half of the adult riders are women and most of the children walk or bike to school..   Women and children already dominate bike riding in the Netherlands and Denmark.  Bicycle racks were removed from schools in my New Jersey town as bike riding was considered too dangerous by the school board.  They were afraid of lawsuits if they encouraged bicycle use.  Some of you live in areas with very low traffic densities and safe conditions. For others the question is how to build a safe transportation infrastructure. 

 

You don't want to share the road with drivers who aren't aware of you, don't know what it's like to be on a bike, and may have more legal protections than you.  A variety of approaches can create safe cycling - certainly European counties have taken differing approaches.  A commonality is traffic calming.. speed limits should be 20 mph or less if bikes and cars share a lane.  Bikes on more heavily traveled streets should have physically separated lanes.  Paris has shown this isn't difficult or expensive.  The most cost effective way to come up with real estate for separate bike lanes is to eliminate car parking and the experiment has been very popular to the point where the changes are becoming permanent.  The city is on its way to removing about 70 percent of parking.  

 

Assuming the risk of cycling is low enough for you, it's important to find a good ride as there are a lot of poorly built bikes out there.  A good ebike that should last a decade will set you back at least $2.5k.  These usually have a similar design to a conventional bike  They're great for commuting and just riding around, but consider a cargo bike if you're serious about replacing a car on local trips.  The past few years has seen a revolution in properly engineered  and practical electric cargo bikes.  Good bikes in this class tend to be spendy starting around $4k.  I have a favorite, but these are individual choice and spening time at a good bike shop is important.  

 

a promotion video of a very good cargo bike illustrating some use cases - you can easily carry two hundred pounds of cargo without worrying about balance, power or overloading.

 

Back to that third wave - will it continue or just fade?  Many regions in Europe already see a lot of cycling and the trend will only increase as automobile use is minimized in the cities.   North America is more difficult as the infrastructure and expectation supporting cars and city layouts are somewhat rigid.   Emerging cities, mostly outside of North America and Europe,  have a choice of city layout and transportation infrastructure.  It will be fascinating to see how and where active transportation fits in.  And there are other practical but non-conventional transportation modes - and I'm not talking about self driving vehicles...  

 

 

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...

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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.

 

a meltdown between two brownies

You need to read Om’s blog post Why iPhone is today’s Kodak Brownie Camera  It reminded me of my home-brew digital camera about 35 years ago (the Meltdown the ferret photo is in this post - probably the first digital image of a ferret).   

 

 

Digital photography - at least how we usually think of photography (more on that later) - was invented in 1975 by Steve Sasson at Kodak.  (a fun NY Times piece)  Charged coupled devices (CCDs) used to capture the image, had been invented at Bell Labs a few years earlier.  Sasson used one made by Fairchild for his experiments.  I had read a bit about digital cameras when I built mine, but decided to used a modified DRAM memory chip because I could get one for nothing and it seemed like a reasonable thing to try.  It was just that - fooling around with some hardware and writing a bit of software for fun.  The fact that it captured my only record of my ferret Meltdown made it special.

 

 

But there’s another form of digital image making.  Experimental particle physics people moved from detecting events with regular photography (bubble chambers and film emulsions) to electronic counters.  Around 1968 the multiwire proportional chamber revolutionized the field and set the stage for dramatic discoveries that lead to the Standard Model - still the best description of three of the four fundamental forces.  A MWPC consists of many planes of parallel wires.  They’re assembled in a chamber filled with a gas that ionizes when a charged particle flies by.  The wire closest to the passing particle detects the event and a signal is read out. These arrays are arranged at right angles in tightly spaced pairs so it’s possible to calculate a position in two coordinates.  As the particle passes through the chamber its x and y position is registered along its track.  A computer calculates a trajectory for each particle and all of the particles that registered form a 3d image of the event.  This information is then processed to reveal the physics of the event.   This type of photography has become more sophisticated and MWPCs have largely been replaced by more capable detectors, but it's still the same idea - just a fancy camera.    The people  who use these exotic cameras use their smartphones like everyone else for all kinds of personal images. 

 

 

Over the years I’d spent some time worrying about image and sound quality.  At one point I thought better was - well - better.  My epiphany came in the a perfectly restored 66 red Mustang.  It was near Cleveland with the head recording engineer from Telarc Records and a seriously good musician from the Oberlin Conservatory.  We were talking about where music reproduction might go with sound field reconstruction and dramatically more information than CDs could provide when a favorite Beatles tune came up on the 8 track (gasp! - it *was* an authentically restoration).  The volume came up and the two of them were singing along to the music in pure delight.  There is something transcendent about the music - even with awful reproduction in that noisy environment.   Portable music players with cheap headphones would be good enough for most.  As long as there's a personal touchstone.

 

 

Om points out there is a market for high end photography.  Perhaps the real distinction is high end photography is more of a verb than a noun.  You do it to learn how to see images as much as to capture them.   Hopefully it will never go out of fashion.

 

you're here because dinosaurs didn't have good telescopes

Sixty six million years ago - the end of the Cretaceous period  - an asteroid or comet struck the Earth near what is now Chicxulub, Mexico creating a crater 150 kilometers in diameter.  Huge tsunamis that rose hundreds of feet as they approached coastlines.  Worse, firestorms swept the planet and the oceans underwent a sudden and deep acidification.  Food chains collapsed on land and in the oceans and with them three quarters of plant and animal species vanished.  

Arguably it was a bad day.

If the non-avian dinosaurs only had evolved larger brains perhaps they would have made it to the point where they had good astronomy and a good enough space program.   But nature keeps moving on and the massive change allowed other lifeforms to evolve including us.  In retrospect it was a great day for the human race.

 

Could it happen again?  That one's easy -  100 percent probability.  Fortunately we're at the point where we have astronomy and a space program so it makes sense to think about risk and mitigation efforts.   

 

In 1994 a comet called Shoemaker-Levy 9 broke into 21 major pieces and struck Jupiter.  It had been captured by Jupiter's gravity and had been orbiting the planet for about three decades it put on a show that would have devastated life on Earth.

 

An Earth strike would be different and Jupiter's large size makes it a more likely target it did ring alarms and people started thinking about the probability of something big enough to do serious damage hitting the Earth as well as what could be done about it.  After all - we had telescopes to figure out likelihoods and rockets to do something about it. 

 

On the 1^st of July, 1770 we came very close to a major extinction event - one that probably would have included humanity among the erased.  Lexell's comet came with six times the distance between the Earth and the Moon. Cosmically speaking that's a near miss.  New comets tend to appear anywhere between a few months to a year before they could be dangerous.  But there's much more than just comets out there. 

 

NEOs - Near Earth Objects - are comets or asteroids that come close to or pass through Earth's orbit.   They range in size from a few meters to several kilometers.  Small ones are common and tend to fragment or disintegrate leaving only small pieces for collectors and scientists.  Moving up the size scale you pass through city killers to objects capable of global devastation.  Fortunately the big ones are fairly easy to spot, but over ninety percent of the estimated city killers have yet to be cataloged.

 

A program to funding the construction and operation of new survey telescopes along with retrofitting existing observatories was kicked off about ten years ago with the US and EU taking part.  It's relatively inexpensive and has made some progress, but the Trump Administration cut funding.  

 

So what can you do?  With enough advance warning you can evacuate regions for objects in the city killer size range.  Moving up the size scale means using rockets to intercept the threatening NEO.  What to do with it is non-trivial and depends a lot on its composition and size.  That's an interesting subject for a future post if there's interest (hint: you probably don't want to nuke it) , but an important step would be expanding missions to asteroids of various sizes to learn about their makeup.  In addition to insurance there are technical and scientific benefits that are probably justification enough.  

 

Perhaps it would help us think about preparation and mitigation - the next pandemic and global warming will both make their presence known with much higher probabilities in the next few decades.  

 

 

 

 

where simple beats "ai"

minipost

A friend complained about his new rice cooker.  It's a very expensive model with programmable features and claimed to use "ai" for "perfectly cooked rice" every time.  After a dozen or so attempts he called their help line and spent a half hour using their smartphone app that talked to the cooker.  It passed the diagnostics with flying colors.  He isn't happy.  

 

Simple rice cookers tend to work well every time.  They rely on two bits of physics that give clear signals.  The first is how water responds as you heat it.  The energy needed to raise the temperature of liquid water by one degree is very nearly the same from room temperature until it's right at the boiling point.  Adding more heat at the boiling point just turns the water into water vapor - the remaining liquid water stays at 100°C.  

 

The next clever bit was discovered by Pierre Curie who probably never thought of its rice cooker use. 

 

The cooker I use has a spring at the bottom of the pot and a strong permanent magnet.  You put rice and water into a smaller cooking pot and push it down a bit until the magnet attracts and grabs a piece of special metal.   Then the heating element engages and cooking begins. The rice is cooked as the water heats and continues to cook as it boils.  The rice temperature stays below 100°C until just enough of the water starts boiling.  When most of the water has boiled away the rice temperature starts rising again.  Now the discover of Madame Curie's husband takes over.  At around about 105° C, the Curie temperature of the metal, the metal is no longer attracted by the magnet.¹  The spring pushes up and turns off the heating element and a power light.  On mine it is also connected to a mechanical bell and turns off a power light.  The rice is always great.

 

I looked at a repair takedown of an expensive rice cooker.  The construction was better, but it was complex with a microprocessor, control panel, barometer, humidity sensor, thermometer and Bluetooth chip (they have a smartphone app:-). Presumably it has some sort of table that rice is perfectly cooked when all of those signals reach a certain values, although it could be more complex.   I'll stick with simple.

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¹ Magnets lose their magnetism when heated at a specific temperature called the Curie Point.  In this case the permanent magnet stays magnetic at 105° C, but the special metal used here suddenly loses its ability to be attracted by a magnet.

 

frogs, pots of water and the slow application of heat

A few weeks ago Om posted a piece on Apple's new laptop based on their M1 chip.  It's one of those huge transitions that gives Apple a much higher starting point  for desktop and laptop machines - machines that are still very important to many of us. They've been working on this for at least ten years as part of their smartphone silicon effort. People like Horace Dediu and Om (and even a non-technologist like me) have noted the progression of Apple silicon and wondered if it would be deadly to Intel.  For me the biggest surprise has been the software effort - writing was all over the place for on the silicon side. 

 

Zoom's emergence represents a pot that had been slowly warming for decades coming to a sudden boil with pandemic-fueled heat.  It's frustrating with a terrible UX and UI, can be iffy on highly asymmetrical Internet connections that are slow upstream (cable modems for example), causes enormous frustration for many, but it's better than other tools and works well enough.  Last week I described it as the modern equivalent of the <blink> markup in html during the early days of web browsers like Mosaic.  People think it's cool at the time, but it will be laughably primitive down the road.   

 

Remote video tools will get better and may change some habits. At the same time others are recognizing the importance of face to face. One university I work with just completed a survey that found 0% of 1600 students said they'd prefer in-class instruction to remote leaning when the pandemic quiets down.  Already there's a lot of experimentation on campuses and in some businesses.  An animation company saw productivity crater and is working on a better than Zoom suite of tools for internal use. The university I mentioned has found messaging apps like Discord excel in spaces that Zoom handles poorly.  And perhaps we'll get better Internet connectivity.  Price to performance in the US is abysmal, 5G is a largely marketing joke, cable modems are too asymmetrical (upstream is slow) to support serious video conferencing, and the digital divide has widened the already huge education gap.  There's a lot to fix.  It's like cycling - you need to sort out infrastructure and culture along with adding bikes.  

 

I'm confident tool improvements will come but serious leaps need to be taken and I don't have great confidence in the major players.  What I'm more worried about, at least in the US and Canada, is infrastructure. A friend is moving from Colorado to North Carolina and needs a very solid Internet connection.  The only advice I could give was to find cities that offered good fiber connections that we're from telcos.  That mostly narrowed it down to Ting, which left only a few cities. The movement of people from cities to rural and suburban areas is constrained by many forces - this is one. 

 

On to something else..

 

I've argued that virtual reality wasn't very important and augmented reality meant much more than projecting information in your field of view - and that Apple had just introduced their first AR product. 

 

In a way glasses are AR devices - they help you see more than you normally would. The same for microscopes, telescopes, stethoscopes, I have built bat detectors that let me augment my world by adding a bit of theirs, ... the list is long.  But back to my comment about Apple.   I have to admit I was wrong.  Apple's first AR product was the Apple watch, although they didn't know it at the time.  At first it was more of a fashion statement with a weird assortment of apps.  After a few years they learned what it was for.  People saw it as something for improving their health and fitness. Exercise, heart monitoring, and even the state of your body. Jutta has an app that interfaces with other hardware for diabetes management.  We're talking about life altering AR.   The area is growing rapidly and we won't even think of it as AR because we're used to its Hollywood manifestation.  Of course Alexa, Siri and other voice driven interfaces are AR.  They augment our local information space.  Apple's EarPods are just a portal you wear.  There's still a place to visual AR, but the pot's already boiling.  AR is here now.

 

Of course we should think about how these things fit into our lives. That's a serious area I'm not terribly confident about - at least if tech is making the design choices.

 

 

green flight

Two years ago the Environmental Protection Agency reported aviation accounted for about three percent of the nation's CO₂ emissions, or about twelve percent of transportation.  The international figure is about two point five percent.  These may not seem huge, but they've been growing steadily and, post pandemic, should continue their growth.  Making matters worse is the global warming contribution from the cloud-like contrails produced by the jet engines at altitude.   It's difficult to study, but indications are the contribution may double the global warming impact. 

 

A number of approaches have been suggested and are in various stages of testing.  Moving to bio-fuels isn't the greatest solution as growing and producing biofuels has issues and you're still producing contrails.  In the short term some airlines will move to it, but that may be part a PR and carbon credits game as much as anything. 

 

Electric airplanes exist and there are even a few (very) sort haul commercial flights.  The problem is the specific energy of the battery - how heavy is a battery per unit of energy storage.   Turbine fuel stores about eighty times as much energy as a safe lithium-ion battery of the same weight.  Airplanes frequently carry large amounts of fuel - the weight of fuel burned on a cross country trip is greater than that of the the passengers and crew.  The range of a battery powered airplane is severely limited even after accounting for the great efficiency of an electric motor.   We could get a lot closer with exotic batteries that aren't anywhere close to reality, but even then you're talking about a propeller driven (slower) aircraft. 

 

Hydrogen often comes up as the perfect clean fuel - the combustion product is just water.   Although it's the most common element in the universe and accounts for most of your body's atoms, we need hydrogen gas and that's extremely rare on Earth.  Hydrogen gas (H₂) must to be produced and it takes a lot of energy to create it - more than you can get out of it.  Most of it is produced from a petrochemical process that involves carbon emissions.  This is called black or grey hydrogen and, if you manage to capture most of the carbon emissions it's called blue hydrogen.  What you want is green hydrogen - hydrogen produced using electrolysis with electricity from wind, solar or nuclear power.  That seems like a nice use of excess intermittent power. 

 

It's important to think of hydrogen as an energy storage medium - a non-rechargeable battery of sorts.  It has a very low - essentially unusable energy density at atmospheric pressure.  You'd need impossibly large tanks (think about Hindenburg sized tanks) or you can compress it or liquify it and shrink your tanks to something more manageable.  In gas form at a very high but probably safe pressure it needs about five to ten times the volume of  jet fuel. Liquid hydrogen gets you down to about three and a half times the volume.  

 

Engineering is all about finding an optimal solution to several problems that generally interact.  You could convert a turboprop or turbofan to burn hydrogen and see where that takes you.  Turboprops seem to be workable on short haul routes (1,000 km or less) with small passenger loads (under 100 passengers).  They'd be slow and fly at lower altitudes than today's jets.  Turbofans present a number of problems - at altitude they're making contrails and the range and payload isn't great.  One needs to think a bit out of the box.   

 

You might use a hybrid jet fuel/hydrogen engine that climbs to cruising altitude on jet fuel as fuel consumption is much greater in that phase. Then the switch to hydrogen fuel is made when the engines are throttled back at cruise altitude.  You could also design a lifting body aircraft that has a lot of internal volume for liquid hydrogen fuel tanks without being too large for conventional airports.  Tricks might get you across the US with a few hundred passengers, but flights across the Atlantic or Pacific would require something more. 

 

The prop-driven airplanes present other opportunities. A fuel cell converts hydrogen to electricity and electric motors are more efficient that jet engines.  There are a number of little problems that can be overcome, but a fuel cell propeller airliner may just be a short to medium range solution.

 

I didn't go into the NOx problem.  The high heat of combustion in a jet engine creates nitrous oxides when the nitrogen in the air is heated to high temperatures.  That's a problem - particularly at the high altitudes jets fly at and burning hydrogen won't fix it.  The way around it is to use fuel cells and electric motors, but that's for lower altitudes and slower speeds.  There isn't an ideal solution - you just hope to reduce as much as you can.  

 

Airbus is working on the problem - or at least they were before the pandemic.  I can believe the target date for the propeller aircraft, the lifting body is probably more than fifteen years out.

There may be a near term niche for hydrogen powered flying vehicles.  Agricultural and inspection drones are much larger than hobbyist drones.  They're limited to half hour flight times with batteries, but new fuel cell drones with small high pressure hydrogen tanks have appeared in Korea.  They can fly for hours and that may be the first practical opening for aerial hydrogen.

 

moving from noun to verb

About a week ago Apple announced its latest Watch.  While it isn't a major leap, Horace and Om wrote great pieces about something more significant - namely what it does.¹  The first few iterations were a bit muddled - now it has become a wearable assistive technology.  That's significant.

 

Assistive technology invokes images of wheelchairs, braces, crutches and so on..  adaptations to make life easier for those people with physical problems.  It's a mistake to think that way.  All of us use these technologies  (I'll ignore the distinction between assistive and adaptive) ..  utensils, chairs, shoes, door knobs, screw drivers - all of these count.  Many of us wear eye glasses - a technology that compensates for a deficiency that would be a serious handicap if not corrected.  Some people have artificial joints and pacemakers - implantable assistive technologies that are always worn.   It begs the question of who gets to be called normal and who makes the decision.  I've written about that, so back to the Apple Watch.

 

At the beginning of the nineteenth century town clocks were an adaptive technology that gave people in emerging industrial cities a sense of common time to allow for synchronized work.  Less expensive models for the home became a necessity for workers who could afford them.  People who couldn't employed a variety of other techniques including "knocker-uppers" - people you would pay to make sure you got up in time.  Towards the end of the century the need for standards and a more global time synchronization emerged - railroads were the first big driver.

 

Railroad time is to the time of the future. The Sun is no longer to boss the job. People—all 55,000,000 of them—must eat, sleep and work as well as travel by railroad time. It is a revolt, a rebellion. The sun will be requested to rise and set by railroad time. The planets must, in the future, make their circuits by such timetables as railroad magnates arrange. People will have to marry by railroad time, and die by railroad time. Ministers will be required to preach by railroad time—banks will open and close by railroad time—in fact, the Railroad Convention has taken charge of the time business, and the people may as well set about adjusting their affairs in accordance with its decree… . We presume the sun, moon and stars will make an attempt to ignore the orders of the Railroad Convention, but they, too, will have to give in at last.
—Indianapolis Sentinel, 21 November 1883

 

Synchronizing clocks turns out to be an interesting technical problem. A Swiss patent clerk named Albert Einstein specialized in clock synchronization patents by day while thinking about time more deeply after hours.  

 

With atomic clocks - some orbiting in GPS satellites - we now have very accurate time synchronization available anywhere on Earth.  It's available in your smartphone and your Apple Watch with much better accuracy than the display requires .. very accurate time is much more central to communication and location determination. 

 

So just how important is a watch as something you wear to tell you the time - the watch as a simple noun?

 

There are still synchronizations for connecting with people, transport, broadcasts and so on.  Some of that requires less synchronization.  Some of the most creative work is poorly synchronized much of the time.  Television has become streaming video at your convenience and much of radio has turned into podcasts and streaming audio.  So why wear a thick $400 piece of hardware on your wrist?

 

You wear it because it is becoming a verb.  It's stuffed full of sensors and watches you.  A growing list of health, exercise and motivation related functions.  Complex computations turn thousands of dollar of tech in a doctor's office or researcher's lab into a few one dollar sensors and software.  And all of this can be networked.  I'll mention Happy Bob - a Type 1 Diabetes app by one of you (Jutta Haaramo) that is making the lives of thousands of diabetics easier.   This is only the beginning.    The Watch overlaps a bit with the iPhone, but they mostly fill very different functions - wearable is a big deal.  It's important to note the Watch still has a lot of headroom for growth. 

 

We humans have been expanding and augmenting the basic human body for over ten thousand years and the process is accelerating.   It's exciting, but we should be thinking more deeply about what it means as well as who is normal and who decides.

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¹ Oxygen saturation wasn't difficult to add - it exists elsewhere.  What is important is the watch can keep a record.  A General Practitioner friend is currently testing one. If it takes good readings he's going to recommend it to patients who are in the at risk categories for Covid-19 - cheap insurance. 

That said I think the major improvement was the addition of an ultra-wideband chip. I wouldn't buy a device just for that as this is preliminary work for something that could be very big, but it's good to know new iPhones and Apple Watches have the capability now.

your partner in efficiency

As an undergrad I developed a serious bicycling habit.  Our club would take longish sixty to one hundred mile rides on weekends. These were tours rather than anything approaching racing so we talked along the way.   One of the members was obsessed with the idea of human powered flight.  His spirt was contagious and several of us volunteered labor and calculations helping to build the first prototype in quest of the Kremer Prize.  It was one of those rare challenges where the goal was just barely possible. 

 

My involvement wasn't that deep, but I quickly learned to appreciate the efficiencies required. Questions arose.  What sort of athlete would be required?  How would power move from muscles to where it could be useful?  What kind of aerodynamic design would be most efficient and what was the flight envelope?    

We knew bicycles were efficient.  A good chain drive was almost 99% efficient and you could match the power output curve of the pilot to the requirements of a propeller. That's when I learned only the pilot's legs would be used... using arms and legs wouldn't work for a couple of reasons.  And what about the nature of the leg motion?  Lots of interesting issues and answers.

 

A bit earlier an article on the cost of transportation appeared in Scientific American.  This is the famous piece that Steve Jobs loved to refer to when he pointed out a person by themselves isn't incredibly efficient, but on a bike they're spectacular.  But why?

 

There are a number of ways to approach the problem, but I'll ask a slightly different question and hopefully cover a bit more ground.  

"Why can you go faster on a bicycle than you can run?"

We have two basic models of bipedal motion: walking and running.  When you walk you straighten your knee which lifts you just a bit as your heel comes up shifting weight to the front of the foot. The other leg swings forward, staying close to the ground most of the time.  One foot doesn't lift completely until the other has landed. You don't move up and down much and most of the work is done by muscles in the upper part of your leg.

 

Running is very different.  Your body lifts further and lower leg muscles become important as the motion makes you rise up on the forward part of your foot.  Runners will go into great detail on what's happening, but basically you're launching yourself with quite a bit of force using more muscles and force than when you walk.  When a foot lands some of the energy used to break the fall is stored in tendons for release during the next launch -  a mechanical battery. Optimizing efficiency is the work of training and genetics. [ An odd thing about the efficiency of running and walking is that walking is most efficient over a very narrow speed range, while running has a much flatter efficiency curve.¹ ]

 

You can go faster running by increasing the length of your strides (or leaps), but there are limits. Your leg is a kind of double pendulum.   It takes energy to accelerate it forward and some energy to brake that motion as it starts to reach its forward limit.  It's worse if your leg is heavy.²

 

Rather than swinging legs a cyclist spins a crank.  The crank's motion is a circle about a third of a meter in diameter. A much smaller distance than walking or running strides.   Circular motion means the cyclist isn't having to waste the kinetic energy of their moving lower leg by slowing it (it does waste a some energy, but not nearly as much). The knees and thighs still need to be stopped and started, but the motion is much smaller.  The end result is less wasted energy from leg motion.³

 

Like running there's an upper limit to how fast a cyclist can move their legs and still generate their greatest power.  That's where gears come into play.  The gears and large rear wheel allow the bike to move a longer distance forward than the distance your feet travel in one revolution of the crank.  And different gear ratios allow you tailor your effort to the conditions - speed, head wind, hills ...

 

On a smooth flat road your speed is usually limited by wind resistance and the power your muscles can develop.  It's amazingly efficient.  With very little effort you can sustain a pace that no marathon runner can keep pace with.   

 

note:  I've skipped over a lot.  Human motion is a rich and not completely understood science, but hopefully this is good enough.

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¹ without going into great detail I show a chart here.

² To think about this consider the leg's moment of inertia and the fact that all parts of the leg aren't moving at the same speed. The upper leg moves slower - this is why fast running animals have their muscle concentrated in the upper leg.  Carbon fiber lower legs can make partial amputees faster than an otherwise similar runner with an intact leg.

Note the power your muscles generate increases as cross sectional area, while the weight increases as the volume.  Larger muscles increase in power more slowly than their weight increases.  This is why most competitive distance runners are of average height and very lean. 

³ The cyclist's center of gravity isn't moving as much either and that saves energy.