omenti

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   This type of photography has become more sophisticated and MWPCs have largely been replaced by more capable detectors, but it's still the same idea - just a fancy camera.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.

 

checking out your neighborhood

minipost and recommendation

The books you wore out when you were fourteen or fifteen are probably serious hints about your dreams and direction.  One of the two I wore out was a Norton's Star Atlas and Reference Handbook.   Beautiful, wonderful star charts to find your way around the night sky.  The graphical design was (and still is) stunning and it just works.  It cost a fortune in the day, but so wonderful.

 

Every now and again someone publishes a survey that claims only a small fraction of Americans under 30 or 35 have seen the Milky Way. That's a shame.  On a sufficiently clear dark night it's about as beautiful as anything I've seen in Nature.  Light pollution has largely taken it from us.

 

But even in suburban areas you can still see some stars and planets and the Fall in much of Europe and North America offers crisp clear skies.  Checking out our stellar neighborhood is much more inspiring than watching TV, but you need a guide to make any progress. Although I still love my Norton's (I've been through several editions), the better entryway is to use an app.  At least a dozen exist.  My clear favorite on iOS is Sky Safari at about three dollars on the App Store.  (they also have an Android version, but I haven't used it).  Go for the low-end version - currently Sky Safari 6 AR - the more expensive versions are used to drive computerized telescopes.

 

The beauty of apps like this is they know location and the time of day.  Then, using the phone or pad's compass and gyroscope, they calculate and display the section of sky you're pointed at.   Change the display magnification to roughly match the sky and it's sort of augmented reality. You can identify stars and planets as well as search for them and learn the constellations. Playing around with the settings is useful (particularly turning off the background music), but the defaults for star brightnesses displayed roughly matches the human eye in a semi-dark area.  You can also turn off the compass and gyros and explore the sky indoors.

 

If you get hooked the next thing would be a good pair of binoculars .. stay away from telescopes for awhile. 

 

 

 

remote learning laboratory kits

a mini-post you can have fun with

 

I managed to survive a bit of remote online instruction.  While it doesn't fit my teaching style, it seems clear it's going to be with us for awhile.  Labs are a big issue for science and engineering courses. Watching videos and running simulations isn't a rich experience, but what is?  A few of us have been thinking about that recently.  The fact that most students have access to a smartphone opens up some real possibilities.  A smartphone is basically a computer with a lot of sensors and a network connection.  The trick is to get raw data from the sensors and devise experiments students can run or - better yet - design on their own.  You need an app with a good interface. 

 

I know of a  few projects working on apps to get at sensor data.  They tend to fill different niches, but  there are some existing apps.  

recommendation

Get phyphox from Apple's AppStore or GooglePlay.  (if you have a choice I recommend the iPhone version as the variety and quality of sensors is well-defined).  It's a free download from Bergische Universität Wuppertal.  Their webpage (English and German) has some experiments including some videos and forums. It's a great starting point.  

 

Chemistry seems more difficult and I think biology needs real samples if you're going to get serious, but I'm confident we'll see some inventiveness.    We'll probably see other sensors and adaptors that attach to phones.  Microscopes are naturals and I have an ultrasound adaptor that is a dandy bat detector.  Some would be easy - like a simple  spectrograph and others would take some design and manufacture.  Many could be vastly cheaper than current lab gear if enough units were sold. A school system or university could just give them to students.  Also old smartphones can be donated to kids who don't have one - you don't need a network connection for most of this. 

 

Engineering has huge possibilities with Arduino kits and simple sensors and actuators. So much exists - it's a question of crafting projects and instruction. 

 

I would love to see inexpensive, easy to calibrate environmental sensors.  Environmental work would be a lot of fun and could engage students socially and politically.  Imagine mapping out toxic substances at the block level around the country. Collaborative student science. 

 

And all of this works for the amateur at home.  Perhaps someone needs to restart SciAm's old Amateur Scientist column or create and Amateur Technologist... and I'm particularly interested in the intersection of this and art (folks like Shuli would probably be or already are all over it as she's already in the space).  

 

And I'm working on an amateur project of my own. (although that's usually the case)

 

exciting times

 

 

the problem of where

a minipost

 

Wandering around in a field we seem to know roughly where we are and can make a plan to get from here to there.  This sense of location takes place deep in the hippocampus and the neighboring entorhinal cortex (full disclosure - I couldn't remember that one and had to look it up).  The hippocampus has place cells that fire individually at different locations.  Grid cells and head direction cells are in the entorhinal cortex and create a virtual map of triangles that provide the hippocampus with additional information of location and heading.  It's a full navigation system that receives additional sensory information from sight and hearing.  

 

Some of us make better use than others.

 

I've been wondering about the "court sense" seen in some elite athletes where it's important to know the position and motion of the ball as well other relevant players at any moment.  Soccer, hockey, rugby and beach volleyball come to mind. Using beach volleyball as an example the best players create an evolving mental map of the other three players including one that may be behind you.  They can't take the time to think about it.   It's interesting talking to a player.  They may be unaware of the uniform or other details of the other players, but are very aware of a few pieces of dynamic spatial information. 

 

Toddlers often take indirect paths getting distracted by any number of interesting waypoints on their path.  As adults we tend to take what we think is the easy path from A to B and these days that information comes from the GPS in our phone or car.  GPS navigation isn't infallible, but the same is true for human navigation.  Are we getting worse at human navigation by relying on these satellite consultations so much or is it just a computational extension of our brain?

 

fMRI experiments have been done with people navigating virtual cities and forests with and without GPS.¹   Compared to those who navigated using their own mental maps there was much less hippocampus activity in those who navigated by following external directions.   The virtual map generated by the hippocampus seems to appear only when you are actively engaged in the act of navigation.  It's like we're bypassing part of our brain when we use a GPS.  It has also been shown that enhanced use of personal active navigation increases the size of the hippocampus while inactivity causes atrophy.²  

 

Make it a game to turn off your GPS and navigation on your own for awhile.  There are numerous natural signs and signals that help you find your orientation and path.  Which side of the tree has moss? What is the sun angle and shadow direction?  Which direction is North at night? .. and hundreds more.  Try it in a city too.  If you get lost you can always pull out your phone for a quick look.  You might even find the fun of discovery that a toddler gets by observing their surroundings more carefully.    There's even some evidence that exercising the hippocampus by building up rich maps through cafeful observation lower dramatic stress.  Perhaps give up the GPS function, but sketch or carefully photograph was you see.  Straight up play and you might be doing your brain a favor. 

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¹ Several studies exist.  Here's a fascinating fMRI study taking place in virtual London.

² London taxi drivers have to spend a large amount of time building a mental virtual map of much of the city.  Brain scans show highly developed hippocampus regions.  Some preliminary work with people genetically disposed to early onset dementia has found people with highly developed hippocampuses may be protected from decline. 

beyond birding

There are a number of ways to learn about systems, but you're usually stuck with observation and modeling when it comes to complex systems.  Every now and again systems you're interested in get a large wack. Fires in California are an example of localized system perturbations.  Reactions may or may not be what you had expected, but you can learn if you observe carefully.

 

COVID-19 has given a lot of systems that involve humans a major wack.  There has been a major drop in transportation and the power production curves have shifted.  Online education with a large variety of techniques will result in some failures and perhaps some successes. How effective are different appraoches and in what context?  How effective is telemedicine?  What happens when you delay elective surgery?  What is the outcome of delaying treatment for a variety of conditions?  What approaches work for dealing with pandemics?  What forms of government are effective for restoring economies? How much socialization do children and adults require? 

 

We live in a suburban area, but normally crepuscular animals are wandering around in daylight.  Which ones and why?  The sound levels in the woods are very different.  I'll be recording and labeling sound ambient sound levels and seeing how they change as this goes on and as we come out of it.  Many animal populations have been hurt by human activity.  Will some make a comeback and how quickly will they fade as we go back to business as usual.

 

It's easy to make long lists.  If you're so inclined there are any number of activities where amateur observation can be effective. Carefully recorded observations will be important even if you don't know what to do with them now.   Bird watching and amateur astronomy could be a model - amateur observations have turned out to be very important over time.  

 

Some of these activities could be great for curious kids and others may give business and life changing insights to adults.  And it's a lot more fun than sitting back and watching tv.

 

 

 

the sandman and the songs of the sand

Om's fine sand dune images took me back to a spring break during my undergrad days.  I had heard about singing sands and managed to talk someone with a car into an expedition to the Mojave Desert.  First towards Barstow and then onto a short dirt road before we got out and two hours of hiking to the Kelso Dune Field.  

Some of the dunes are several hundred feet high and climbing is something you do when you're young or crazy.  We were both and found a long leeward slope to slide down.  I highly recommend sliding down dunes and this one was special.  As we slid it made a satisfying rumble. I don't have a good sense of pitch, but would judge it somewhere between middle C and the C an octave higher.    Over and over we slid just enjoying the effect.  I poured some of it into a bag and we made it back to the car just around sunset.

 

There are perhaps two dozen examples of singing sands in the world. The effect hasn't been studied carefully enough to sort out exactly what's going on, but the common thread is you need very round grains of silica sand of similar size averaging about a quarter millimeter in diameter.  One hypothesis is these clean, round equally sized grains act as layers that jiggle up and down as the shear force causes them to slide against each other.  There are several other plausible ideas.  Sadly it's been observed that even a little pollution can silence a dune. The Kelso Dunes are apparently a faint whisper of what they once were. 

 

Singing sand is a different animal from the sand you tend to find on beaches and river beds. A few years ago it struck me that the sand found on great beach volleyball beaches doesn't stick to the athletes .. at least not that much.  Sarah told me about - the official sand consultant for the Olympics and other major events Hutcheson Sand and Mixes in Huntsville, Ontario.  Curious, I got in touch with their sandman and asked a few questions. You send them a kilo of your sand from layers down to about a half meter and they'll tell you if it meets the specification or find a source.   The size and shape requirements of the grains (mostly between a half and one millimeter in diameter and naturally weathered to a sub-angular to rounded shape) insure it drains easily and doesn't compact like more angular sands.  Size distribution and shape largely keep it from sticking to bare skin.  The sand used in the London games came from a quarry near Surrey, Copacabana beach sand passed muster as do most Southern California beaches, but China had to import 17,000 tonnes from an island in the South China sea.

 

Much of the sand we normally see has a large distribution of size and tends to look more angular than round.  The angular bits allow it to compact and, with a small bit of water, clump together and stick to skin.  The binding force comes from the surface tension of small amounts of water than form little bridges between angular pieces.  Not good for beach volleyball, but great for making concrete.  A side note is demand has been so great that construction grade sand is getting rare and there are sand pirates.  Desert sand doesn't cut muster, so all of those highrises in the Mideast require imported sand.

 

There are any number of interesting properties of sand, but one one you've probably seen.  You may have noticed walking on sand can dry it out.  Walking on wet sand applies pressure.  The grains push against each other and, if they are angular,  rotate into a new position. The sand had been fairly well packed by the force of wind and water, but many of these rotations force the grains apart a bit. This new configuration has a bit more empty volume and water the drains into it. It's called Reynold's dilatancy - here's a little video showing a simple experiment you can try at home.  

 

head and tailwinds

Today a friend said he was having a difficult time concentrating - ".. like running in circles, but with headwinds."   After hanging up I found myself thinking about running or cycling on a closed course in a wind.  Just how much does a wind cost if you have an equal amount of head and tailwind?   A bit of high school physics is required.

 

Here's a simple model.  Consider a square closed course with the wind blowing at a constant speed w from the left..

 

Let's make it easy.  Rather than thinking about what speed you can run on each leg, imagine a constant speed - say v - on each leg of the course and calculate the amount of power you need to generate to overcome the aerodynamic drag force. Everything else you do running should be the same.  

 

Power is force times velocity. Since your mass isn't changing, just look at what power is proportional to.  Tricks like these are common in physics - just leave out terms that stay constant where we only care about the comparison rather than a number.   The very quick answer would be since the power increases as the cube of the effective wind speed you will never gain as much from a trailing wind as you'll loose going into the wind.   Calling wind speed s

 

sorting it out:

 

for leg 1   required power proportional to (v + s)³

for leg 2   required power proportional to  (v - s)³

 

the crosswind terms are the same:  v(v² + as²)  where a is some constant showing how much extra force you need to use to deal with the crosswind.  It could be very low or high depending..  For now consider the simple case where a is 0 and expand the expressions.

 

leg 1: v³ + 3s²v + 3sv² + s³

leg 3:  v³ + 3s²v - 3sv² - s³

leg 2 = leg 4: v³

 

So if we add these up (we're just doing a comparison) we get 4v³ + 6s²v  (you can get away with this as the running speed v is constant).

 

With no wind the power around the course is proportional to 4v³, so having a wind always requires you to generate more power.  What you gain from the tailwind never compensates for what you lose from the headwind and letting the crosswind term a be greater than zero (it will be) only makes things worse.

 

Perhaps a simpler way to think about it is to consider just the drag force from air resistance.  Let's say you're running at 10 mph and have a 3 mph wind.  Going into the wind you're feeling 13 mph of effective windspeed so the drag force will scale as the square of that or 169. With the tailwind you're feeling 7 mph so the drag force scales as 49.  With zero windspeed the force scales like 100.    You lose 69 going into the wind and pick up 51 running with the wind.  

 

So you want to draft behind other racers going into the wind and try to make sure no one is right behind you when you have tailwind. And if you're worried about record setting it's best not to have a wind on a closed course.  

 

 

a dive into pizza pt. 2

Now that we know why we hold pizza the way we do, it's time to move on making a great pie.  There are dozens of varieties. I'll stick with one I have some (perhaps too much) experience with - Neapolitan.  A few  other thin crust styles like New York (which has a higher fat content in the dough) will be somewhat similar, but deep dish and other types have dramatically different baking requirements.

 

Folklore and my experience suggests a brick oven does the best job.  These are usually a set around 330°C (about 625°F).  The cooking surface is brick with a large brick dome covering the space.  Many of these use burn gas, but wood is sometimes used to impart a bit of a smokey flavor.  Much more common are commercial steel electric or gas ovens.  Chain pizza shops? I'm not a fan.

 

There are three heat transfer mechanisms: conduction, radiation, and convection.  Conduction is heat transfer by direct contact between the oven and pizza bottom. Radiation is infrared energy that largely comes from the rest of the oven - the broiler element in your oven uses this trick. Finally convection is the transfer of heat from the oven to the pie by the air.

 

Convection turns out to play only a minor role so we'll skip it.  Conduction is another matter.  In our 330°C brick oven the interface between the pizza and brick is about 210°C (410°F).¹  In about two minutes the bottom cooks nicely and the temperature at the top of a half centimeter thick pizza approaches the boiling temperature of water.

 

Most pizzerias use steel pizza ovens.  Steel is a much better conductor of  heat than brick.  With the oven set at the same 330°C,  the temperature at the bottom of the pizza is now much higher - about 300°C (570°F) and the bottom burns quickly.  Dropping the steel oven's temperature to 230°C (445°F) will give you the good 210°C crust cooking temperature, but there's another problem - what about the top of the pie?  For both brick and steel ovens we need to look at radiative heat transfer..

 

Infrared radiation from the 330°C brick walls quickly raises the temperature of the top of the pie to the boiling point of water allowing water in the cheese and toppings to evaporate so they can cook properly.  For a simple Margherita pie two minutes gives a nearly perfect "balance" with everything cooked just right.  The cooler 230°C steel oven has a much lower radiative heat transfer.  So low the top of the pie doesn't reach boiling by the time the bottom cooks  Cooking the top requires another 90 seconds or so leaving the crust overcooked.

 

You can partly get around these problems by adjusting the dough (New York style pies have a higher fat content), using a broiler element (some steel ovens have them) or physically lifting the pie from the oven floor with a wooden pizza spade for a minute or so.  A good pizza cook with a brick oven will also use the spade on a Neapolitan pie if there are a extra toppings.

 

If you're lucky enough to visit a shop with a brick oven and good cook, try to go when they aren't busy.  It's common to raise the temperature to at least 390°C during busy hours to increase throughput by turning around pies in about eighty seconds.  These fast and hot pies are difficult to judge and frequently have slightly burned crusts.  It's even harder if you want anything more than the simplest pie.

 

You can get a ceramic or brick pizza stone if you want to back a pie a home.  Set your oven as high as it will go and experiment - it will take more cooking time.  I've tried with lackluster results .. I tend to wait and visit real pizzerias.  Alternatively you can work on types of pizza that have very different cooking techniques. 

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¹ You can calculate this with a differential equation using the thermal properties of the brick and pizza. It gets a little messy and the 210° figure could be off by a couple of degrees, but it's in the right ballpark and that's a good temperature for baking the crust.

 

a dive into pizza pt.1

Sarah and I were talking and the subject of pizza came up.  It turns out she's a big fan - particularly of Hawaiian pizza.  Rather than getting mired in the cultural war of pizza types, let's go for the basics - the mathematics of pizza.  You'll only need a piece of paper, a ball (Sarah recommends a volleyball), and a marker. 

 

Take a piece of paper and lay it flat on something.  It's flat with zero curvature everywhere.  if you draw a triangle on it and sum the angles, you get 180°.  A circle will have a circumference of 2π times the radius - 2πr - and an area of πr². All is well. Now fold it along an axis - say the long one if it's a rectangular piece.  You've introduced some curvature.   Now grab it by a corner and let it flop. Again there's curvature, but notice which one is stronger and save that thought.

 

Here's where the math comes in.  Exploring what curvature means, Carl Friedrich Gauss wondered if there was anything intrinsic about the curvature of a surface.  The sheet of paper - what is the relation between its flat shape and when you fold it?  His approach was to consider the paths you can take along the surface.    Imagine you're tiny and walking on the sheet of paper.  You can take any path you want.  When it's folded state there are a lot of paths that are concave (he called these negative curvature) and others, along the axis of the fold, with no curvature.  Gauss defined the curvature at any point on the surface as the product of the two most extreme curvatures running through that point.  In this case the red one that runs along the axis has zero curvature and the most curved green path has some negative value.  The total curvature for that point is zero times a negative number or zero.  The beautiful part is the curvature for all points on the paper are zero if it's flat or folded in such a way that doesn't stretch or tear it.  

 

Now try a ball.  The surface is convex everywhere and the curvature is always positive in any direction.  The Gaussian curvature for any point - the product of the curvature of the two extreme paths - is always a positive number times positive number or positive. (for now just consider the sign of the curvature - the actual measure is a bit beyond this post).  This is why you can't perfectly wrap a sheet of paper - or pizza - around a ball.  The paper always has zero curvature and the ball is always positive.   This also explains why can't make an accurate flat map of the Earth and have to rely on projections with distortions.

 

Many surfaces are more complicated. For fun explore points on bagel or bananas, but for now back to the pizza.  If you let it flop it still has zero curvature, but no strength.  Putting a fold down an axis gives it rigidity.  You find this throughout nature and engineering. An empty Coke can should hold your weight if you put it on the ground upright and carefully stand on it.   Lay it on its side and will crush flat under your weight. The fold in a surface of zero curvature gives a lot of rigidity in one direction.   Next go somewhere that is easy to clean and try to break an egg by squeezing it in your hand.  The positive curvature everywhere makes it surprisingly strong.  If the shell has an imperfection or if you tap it with the edge of a knife or fork while squeezing, you'll have a mess. The positive curvature was distorted and the surface failed.

 

Assuming you didn't make a mess, go back to the ball.  Draw an equator and then mark a North pole. Drawing an arc at a right angle to the equator, you'll always intersect the North pole - it's a line of longitude.  Next pick another point on the equator and make another arc at a right angle.  You've made a spherical triangle. Sum up the angles.  If you started with the points close together the sum will be just over 180° and if you go all the way around it will be nearly 540°. Our old rules of trig don't work on this non-flat surface.¹  A neat thing you can do is measure the shape of the Universe in a way that is similar to making these trigonometric measurements.  So far it looks extremely flat and that's a deep result about the structure and evolution of the Universe.

 

So get some pizza to celebrate the Remarkable Theorem its explanation of why we hold pizza the way we do. 

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¹ If you draw and measure some circles on the sphere you'll notice the circumference is less than 2πr and the area is less than πr².  If you try it on a surface with negative curvature - a saddle shape or the inner part of a bagel for example - the circumference is greater than 2πr and the area is greater than πr².

 

puzzling symmetries

A mini-post

A friend sent a short video of her seven year old asking about mirrors.  Mirrors were a huge puzzle for me at that age.  They would swap left and right, but not up and down.  How did they know?  You could rotate a mirror, but it was always the left and right swapping.  I worried about it on and off for a few months. My parents couldn't help and my teacher couldn't either.  

 

I won't spell it out as it's a neat problem to think about if you haven't already.  After puzzling about it for a few months and then mostly forgetting about it, I was helping my mother wash the dishes.  Finishing, I pulled off a rubber glove and watched it go inside-out.  Suddenly I had the answer. Without realizing it I had learned a bit about symmetry and I also had the thrill of working out something by myself. It was worth the time I spent befuddled and all of the silly drawings I made. 

 

Later I learned you can ask deeper questions about mirrors and that symmetry was a big thing. I also learned you have to pick your questions - why does a mirror switch left and right, but not top and bottom is one I could work out.  How does a mirror work is seriously more involved, but I'd get there with time and work.   In a way the mirror puzzle was a gateway drug.  What were your gateway questions?  I think they can appear at any age.