omenti

finding the best physical user interface - mini post

The photo shows Katie at a seminar yesterday afternoon. A question came up and in answering it, she's doing some hell-for-leather astrophysics.   Usually scientists in cartoons,  television or movies are depicted as working at a whiteboard filled with either gibberish or something out of a textbook.   Sometimes science advisors bring a bit of authenticity, but generally there's a gap between reality and what's shown (I'm sure the same is probably true for any field depicted by outsiders).   The television show Big Bang Theory is a partial exception.  A particle physicist from UCLA consults to add a bit of reality to the dialog as well as most of that goes up on their whiteboards or posters.  But it doesn't capture reality and that's interesting.

 

 

 

Physics and astrophysics have periods of rather intense play.  You try out ideas and follow them for awhile.  This is usually done with paper and pencil or, particularly in collaborations, on a slate blackboard with chalk.    There are a number of shorthands you just can't quickly produce on a computer in a satisfying manner.  Sometimes when you're following an idea a four by eight foot blackboard isn't enough. Some of the markings get erased almost immediately while others may be important and live for months or longer.  White boards and magic markers fail on the long term ..  they just don't erase easily enough as the markings tend to permanence.  The markers lack the artistic expressiveness of a quality chalk like Hagoromo Fulltouch Chalk and their solvents smell bad if you're standing at the board all day.  There are only a few companies in the US that sell quality slate boards and most of their business comes from physics and math departments.  And, like a quality pencil on good paper, there's the feel.

 

I understand why others don't like chalk or pencil and paper, but slate and chalk appears to be a nearly optimal technology for the sport of physics.  It raises the question of what is best suited for a given field and how good it really is.  I find it necessary to decouple the frontal cortex a bit to let the imagination flow. This just seems to work better with paper and pencil and slate and chalk for me.   Even young mathematicians and physicists appear to follow the same convention.  It may well be that something better will come along..  I've seen people try artificial realities where you can add computer simulations, but the jury is still out as the tech is primitive.   My experiences with augmented and virtual realities have been disappointing.  

 

But what about your field?  Have people found an optimal interface or are they still looking?  There's a subfield of human computer interaction that looks at that - it's particularly important for remote work. It turns out most of us communicate person to person with much more than audio and just our faces.  We adapt and use what's around, but can we do better?  

 

Art and photography are highly dependent on interface and experience ..  I'll probably write about some very unusual cameras that might surprise you.  My sister is an artist and photographer and will tell you about her frustrations with the computational tools she uses.  It's very difficult to get into a state of flow with many.

 

Pianos, cellos, drums, beat boxes...  auto-tuners?  Sometimes it's in the ear of the beholder.

 

And sports...  it strikes me as interesting that so much of the planet's attention is focused on moving a ball between two contestants or groups of contestants.  An invention that independently arose in many cultures.  Here the interfaces and experiences are often highly tuned.  Although computer gaming is large and growing, there's something lacking.

 

 

the basic reproduction number - minipost

Measles turns out to be wickedly contagious and an outbreak is currently underway in the Northwest US.  It's the result of too few people being vaccinated.  It turns out there's a simple way think about herd immunity.

 

R_o (r-nought) is the basic reproduction number:  the average number of people an infected person will infect while he's contagious.  It's a threshold.  If it's less than 1.0, the disease will eventually die out.  If greater than 1.0 it will spread and can become an epidemic.  A lot goes into R_o - how contagious the disease is, how long it is contagious, social factors, variable latencies and so on.  There are models for calculating it, but each disease tends to fall into a range making it easy for a non-epidemiologist to think about.  

 

Measles had an R_o range between 12 and 18, smallpox 5 to 7, mumps 4 to 7, HIV/AIDs 2 to 6, the 1918 influenza 2.0  to 3.0,  and Ebola  between 1.2 and 2.5.    We tend to be afraid of Ebola and flues like the 1918 variety as the mortality rate is very high.  Even so, before vaccinations measles killed about two million people a year in a world with forty percent the current population.  It is fair to say measles vaccines save about five million people a year.

 

The proportion of a population that needs to be vaccinated must exceed 1 - 1/Ro.  To understand how it works consider a disease like smallpox with an R_o of 5.  With no vaccination one infected person infects five others, but if four out of the five are vaccinated, only one will contract the disease. This make the effective R_o for the disease 1 (one person manages to infect one other).  In this case if the faction of the population is greater than eighty percent, the disease won't become an epidemic.  

 

To really protect the population from measles you need to have more than 1 - 1/18 or 0.944 of the population immunized .. 95% would be a minimum for the most infectious measles, 1 -  1/12 or about 92% for the least infectious.  There are regions in the US with immunization rates under 80%.  They are tempting an epidemic and are ground zero for the current epidemic. 

 

When not enough people vaccinated (in some cases vaccines don't exist) and you lack effective treatments, quarantine is about the only option.  Nigeria effectively did this in the Ebola outbreak a few years ago.

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You can talk about the spread of other things.  People have done serious work on the R_o for ideas.  Years ago two of us wrote an (ahem) April 1 math paper on how part of our corporate headquarters structure was a fairly efficient vaccine:-)  

 

 

northward and beyond!

Yesterday a friend asked for comments on a piece about the recent movement of the magnetic north pole.  The article referred to an update to officially published information about the Earth's magnetic field.  Unfortunately it was both confusing and inaccurate so I typed out a reply on my iPhone.  He suggested I turn it into a blog post.  I'm leaving it unedited and adding a bit on the North Star.

 

This is poorly written. The model is not used for GPS, but rather for compasses… smartphones and cars have compasses, but the accuracy is poor- a few degrees.. this wander is, at middle latitudes, only a fraction of a degree. There are folks who need very accurate compasses (submarines for example) and using them at high latitudes demands a very accurate map. Also GPS denial is a major worry of the military.

The standard model for the planet’s magnetic field is fairly well accepted, but some aspects are not well known.

It’s exceptionally important.. our form of life certainly wouldn’t exist without it as it builds a shield that keeps energetic particles largely from the Sun from reaching the surface. The core of the Earth is mostly iron and a few other heavy elements. It’s about the size of the moon and very hot - about 5700°C if memory serves - but under enormous pressure so it’s a solid. . Just outside is a 1500 or so thick liquid that is mostly iron with a good deal of nickel. This is also a hot zone, although not quite as hellish, and the pressure is now low enough that it’s a non-homogeneous fluid. There’s a lot of movement - in very very slow motion - with slightly warmer plumes rising and the cooling and falling and getting mixed put into circular motions as from the Earth’s rotation (the Coriolis force). The flow of the hot liquid iron generates huge electric currents which, in turn, make magnetic fields. These separate magnetic field regions roughly align along the Earth’s spin axis and produce the planet’s magnetic field.

The motion of the poles is caused by large scale flows going on deep below. To our time scale it appears slow, but it’s been going since the formation of the planet.

Something dramatic takes place every half million years or so although the timing is statistically random. The poles swap. The last was about 700 or 800k years ago (I could be wrong… the number sticks with me) and probably happened very quickly — in a few hundred years or less. There have been short lived reversals since then.. one was during the last glacial period and only lasted for a few hundred years. The Earth’s field dropped to a very low level - like under 10% of the current level - and filled for awhile before going back to something stable.

The strength of the field has been dropping for a few hundred years and there is speculation it might lead to one of these mini events or perhaps even a complete reversal. There are people who feel it is very likely in the “near” future — like the next 5,000 or 10,000 years.

 

On dark and starry nights most people can find Ursa Major - the constellation know as The Big Dipper.  Fewer can find Polaris - the North Star.  The trick is to use the outermost stars of the Little Dipper's bowl as a pointer.  Extend the end of the bowl upwards five times its length and the bright star is Polaris.  It's close to the north celestial pole - the point in the sky you'd find if you extended the axis the Earth spins on straight up.  Polaris is within a degree - roughly the width of your little finger at arm's length and close enough for simple navigation.¹ 

 

Finding North is fundamentally important to navigation.  If you want to be accurate with a compass you need the magnetic corrections.  And to navigate  by the stars you need the celestial north pole.   Literature is full of references.

But I am constant as the northern star,
Of whose true-fixed and resting quality
There is no fellow in the firmament.  (Julius Caesar III i)

A guiding star is mentioned in Iceland sagas 800 years ago.  But it hasn't always been Polaris.  

 

You've probably played with toy gyroscopes.  Spin one up and points in one direction even when you move it around.  But perturb it you  and it can wobble in a circle.  Its spin axis is said to be precessing. The Earth's slightly  non-spherical shape and the gravitational influence of the Sun and Moon conspire to give the Earth a wobble that takes about 25,800 years to complete.   Polaris has been roughy the north star for about a thousand years and is currently about as close to the celestial pole as it gets.  Vikings were navigating in the 8th and 9th century used Polaris even though it was about seven degrees off - enough for large errors if they didn't make corrections.  At the time of Christ a collection of stars in the Little Dipper was used and it was about three degrees off for Columbus.   Shakespeare's Julius Caesar was using a bad metaphor - the North Star isn't North over time.   But it's even less reliable in another way and that makes it fascinating.

 

Polaris is a bright and fat yellow star about two thousand times brighter than the Sun and nearly fifty times the Sun's diameter.  There are two smaller companion stars making it wobble back and forth a bit..  If you can make accurate position measurements it isn't steady.  Even more dramatic is the fact that its brightness changes on a regular basis . well, sort of regular. (did I mention it was fascinating?)

 

A bit over a hundred years ago Henrietta Swan Leavitt made a discovery that revolutionized astrophysics and astronomy.  She showed the intrinsic brightness of a certain type of variable stars called Cepheids was directly related to the time it took to change brightness.  She ha given astronomers an important method to measure stellar distances.  The fact she didn't receive a Nobel Prize is an astonishing example of sexism. As Nobels go this would have been one of the more important.

 

Polaris is about 450 light years away - the closest Cepheid.  Think of it as a nuclear powered internal combustion reciprocating engine (although technically there isn't any combustion).  In Cepheids a carbon core is surround by thin shells of fusing helium and hydrogen.  The cycle starts with the helium  being singly ionized - the temperature is such that one electron is missing (He^-) . Gravity pulls the shell inward compressing and heating it.  Enough heat that the second electron is stripped away.  Doubly ionized helium  (He^{- -}) is more opaque to heat transfer than the singly ionized variety so it heats up in a hurry.  As it heats it expands beginning to cool in the process.  Finally it's cold enough that electrons from the plasma soup in the layer re-attach and He^{- -} is becoming the He^- variety. Radiation now flows more easily and the star gets brighter as it expands.  But now enough radiation is getting through that gravity begins to pull in the He^- and the cycle repeats.  A huge engine chugging away.  When the largest engines on Earth were at around ten thousand horsepower, Henrietta had worked out the secret of vastly larger engines.

 

Polaris isn't exactly your garden variety Cepheid.  In addition it's getting brighter - ten percent brighter in the last century.  (this would be a true disaster if it happened to the Sun..  most life would be snuffed out in a hundred years and the oceans would boil away a hundred years later)  To make things more interesting the change in brightness throughout the star's period got much weaker almost vanishing in the 1990s - but now it's returning. There are some interesting hints and more than a few conjectures, but it's still a mysterious object. Curiously it was discovered to be emitting X-rays.  That usually implies a super hot atmosphere driven by an extremely strong magnetic field.  Where it would come from is still a mystery,.

 

It's humbling to realize how much we can learn by looking at these tiny points of light in the sky and asking really good questions.

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¹ As seen from Earth the Moon is about thirty minutes of arc in diameter - a half degree.  Here are some rules of thumb that are close enough for most people.  If you're really tall with long arms your hands and fingers are usually a bit larger.  If you like you can calibrate your hand.  These are all at arms length

1 degree - the width of your little finger

5 degrees - the width of your three middle fingers side by side

10 degrees - make a fist and hold it with the back of your hand facing you.  

25 degrees -  stretch your thumb and little finger as far away from each other as they'll go. Tip to tip is about 25 degrees

15 degrees - a bit out of order .. like the 25 degree measurement, but between your index and middle finger.

 

little quakes - making the earth shake

Some of you live in areas prone to earthquakes.  The USGS map is a great resource for checking out what's been shaking in the past day.  It goes down to magnitude 2.5 - close to the smallest you'd notice if you were in the vicinity.  You'll notice that smaller quakes are much more common than larger ones.  But how small can you go?

 

We're conditioned to think "Richter Scale" when we hear earthquake. It's a measure of the amount of shaking recorded on a specific seismometer Charles Frances Richter built at Caltech in the mid 1930s to standardize measurements around the world. Richter's seismometers gave a measure in short order and the media quickly latched on.

 

Geophysicists have learned a lot since the thirties and Richter Scale was obsoleted decades ago.  The problem was new measures were more difficult to describe.  For awhile Richter numbers were given, but then one of the new measures was  normalized to give similar numbers as the old scale for garden vanity mid-sized quakes.  These days you'll just hear the term magnitude..  if the reporter says "on the Richter Scale.."  well .. 

 

There's an issue of what it really means.  We're used to 3.0 being mostly benign, 4 causing some damage, 5 getting into real damage and 6 and about being severe.. depending on a lot of things, of course.  The scale is logarithmic.  A magnitude 5 quake has ten times the shaking of the seismometer needle as a 4 and just a tenth of a 6.  The energy released goes a bit more dramatically.¹ These numbers are still a bit abstract.  So let's consider smaller shakings..

 

Modern seismometers record down to about magnitude 2.0 or 1.5 . Below that more sensitive instruments called geophones are used. It's common practice to prospect for minerals by setting off a blast (a bit of TNT or dynamite) and "listening" to how the ground shakes  These blasts are in the magnitude 1 range.  You can keep going down. Let's consider the world at a human scale.

 

There was a big football game recently.  If one team ran as fast as they could into a brick wall the energy released would be about the same as a magnitude 0 quake.²  A high school wide receiver running flat out into your tree (I've seen something like that) would be a -1.   If Puff jumps to the top of the tall newly waxed dresser and skids off, you have the equivalent of a -2 quake when she hits the floor.  Puff glares menacingly and appears to be plotting a cat scheme.  Later she jumps up and pushes off your iPhone.  It strikes the hardwood floor at about magnitude -3 and probably needs a new screen.  You can keep going.. snowflakes hitting the ground, your voice striking a microphone.  Things shake. 

 

Back to football and shaking at our scale.  The first recorded football earthquake came in 1988 when LSU scored a last minute winning touchdown against Auburn sending the fans leaping for joy and then jumping in place for about a minute

If the jumping gets coordinated it can be dangerous and arena sections have collapsed.   Here's an example of cheering in a Frankfurt football match that caused structural damage.

For completeness something on the other end of the scale.  The energy required to break the Earth apart is roughly magnitude 15.  Logarithmic scales are compressed and very handy if you want to look at something that changes a lot in scale.  Some of our senses are logarithmic, but that's for a different post.

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¹ The energy released goes as the 3/2 power of the amplitude. A magnitude 6 quake releases 1000 times the energy of a 4 and 31.6 times that of a 5.

² These are just to get a sense of scale - approximations of energy transferred in the collision.  The amount of shaking would be much more complex and depend on the dynamics of the collision.

 

the polar vortex and global warming - probably not what you think

When I was a kid we had to walk miles through snow drifts up to our necks and below zero weather..

Yeah, you say, cutting me off and there's that part about running from the dinosaurs too..

 

Part of it turns out to be true. Winters in Montana were much colder when I was young than they are now.  We saw -30° F (about -34°C) at least once a year and I remember a few excursions beyond -40° (F or C).  When I was in high school one Winter produced a few weeks where the daytime highs stayed below zero F.  It became something of a point of pride with more than a few people cheering as the all time record was broken.  It was part of our cultural identity. (Jeri will probably remember the "we want a Chinook" chants)

 

 Winters were colder in most of the world.  The dramatic increase and acceleration of global temperatures has given us shorter and warmer Winters - much warmer in the higher latitudes.  Weather is complex and dynamic giving excursions up and down.  Some very warm almost Springlike days and periods of bitter cold give us some variety.  In the past few years parts of the US has been visited by the dreaded Polar Vortex (the Beast from the East in Western Europe and real Winter in Siberia). Some sources have been telling us global warming is responsible for these plunges and suggest we can expect intense periods of the most extreme cold weather from here on out.  

 

A nice story - more extreme events all around.  The problem is that isn't correct.

 

The Polar Vortex is nothing new.  It's a technical term used to describe a wind pattern in the Arctic that has been used for about eighty years.  We had them in the past -- really brutal ones.  A few years ago a paper hypothesized that the extreme warmth in the Arctic could weaken the vortex and send cold air plunging South.  Its publication coincided with one of the coldest Winters in the Northeastern US in a decade along with very cold weather in Western Europe - again - very cold, but nothing spectacularly cold.  There may be a connection, but the evidence is not strong and the temperature excursions would not be record breaking in any event.

 

The lows of last week were the coldest in two decades in much of the Midwestern US.  Cold, but far from absolute records.  So far this year a few dozen record warm days have been recorded in the US and no record cold.  On average it's getting warmer.  The town I grew up in just doesn't see the extreme cold anymore. Sure it's dangerous and interesting to talk about, but extremes now and going forward are going to be on the hotter side.  We'll see blasts of cold, but they're getting lamer and lamer decade by decade.  The last really cold deep Winters occurred in the early 1980s. Unless something dramatic happens like huge volcanic eruptions or a nuclear war we won't see that again in any of our lives.

 

What will probably happen for areas like the mid-Atlantic and New England states is more intense Winter precipitation.  Most of the heat trapped by the extra carbon dioxide we've pumped into the atmosphere goes into the oceans - water has a much great heat capacity and land.  Without that it would be much hotter than it is. The added heat represents extra energy for pumping moisture into the atmosphere.  Depending on the air it intersects you'll get snow, ice or rain.  The effect has been dramatic in the Northeastern US and Maritime Canada in the past decade.

 

It's frustrating when the real science is misinterpreted, but perhaps there's a silver lining.  The media, some politicians, and environmental groups are missing the point by claiming global warming brought the temperature plunge.   But I'm all for it if it moves people and governments towards taking real steps to fight global warming.   Sometimes people will do the right thing based on a misconception.

 

Endnote

 

I'm biased.  I love Winter.  Some of the readers are Montanans, Canadians and from the Nordics and may well agree.   Even when I lived in Pasadena the few days where it froze and a few flakes were in the area got me excited. The light and how it plays with ice crystals in the air - sun dogs, halos, light pillars.  Knowing the certain squeaking sound really cold snow makes.   All kinds of sound for that matter.  The special light of February.  That feeling when you've nailed the wax and the skis move with so little effort. Animal tracks.  The sound of an ice storm.  Those quiet still nights with huge flakes tumbling down through the light and those moonless clear nights in the country with fresh snow fields reflecting the playing with the starlight like millions of diamonds.  Tolkein had a word to describe it:  tingilinde. 

 

a tip of the hat to the always wonderful xkcd for the image