Links for February 2017

  • If you are a high school student, or know one, who would be interested in the SPARC summer camp, the deadline is March 1.

    SPARC helps talented high school students apply their quantitative thinking skills to their lives and the world.

    SPARC will be hosted in the San Francisco Bay Area from August 6 – 17, with students arriving the evening of the 6th and leaving the morning of the 17th. Room and board are provided free of charge.

    The curriculum covers topics from causal modeling and probability to game theory and cognitive science. But the focus of SPARC is on applying the same quantitative and rigorous spirit outside of the classroom. How can we understand our own reasoning and behavior? How can we think more clearly and better achieve our goals?

  • Indian Space Research Organisation’s Polar Satellite Launch Vehicle successfully launched 104 satellites into orbit on the same mission. Onboard video of the deployment:
    Pictures of some of the cubesats, including Planet‘s 88 imagining satellites for continuous Earth monitoring.
  • What is a ‘Shavers Only’ Electrical Outlet?
  • A possible rare shake-up of the GiveWell list: temporary subsidies for migrant workers in India.
  • How to think about cell walls:

    I most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength. The apparent rigidity of primary plant tissues is enabled by cell walls, but is not due to the walls’ stiffness. Hydraulic turgor pressure creates this rigidity, along with the wall structure. The flexibility of the cell walls is seen when plants wilt, so that the stems and leaves begin to droop, or in seaweeds that bend in water currents. As John Howland explains:

    Think of the cell wall as a wicker basket in which a balloon has been inflated so that it exerts pressure from the inside. Such a basket is very rigid and resistant to mechanical damage. Thus does the prokaryote cell (and eukaryotic cell that possesses a cell wall) gain strength from a flexible plasma membrane pressing against a rigid cell wall.

    The apparent rigidity of the cell wall thus results from inflation of the cell contained within. This inflation is a result of the passive uptake of water.

  • Good post by Holden Karnofsky about the costs of transparency, with good discussion. My summary of both: As you gain expertise and notability, the value you get directly by publicly writing up your findings (e.g., critical feedback) goes down, and the costs go up. However, the value others get from your writing go up.
  • The Juno mission to Jupiter has given up on ever moving into the tighter, 14-day orbit. If they are extending the mission, I’m curious as to why they don’t try doing the maneuver later (after collecting as much data as is useful at this orbit).
  • Good HN discussion of NASA announcement regarding the nearby system with seven Earth-like planets.
  • A selection of “milestone” papers (1-5 each year) from Physical Review Letters.
  • Excerpt from background material from a hearing at the US International Trade Commission:

    Hawaii did not develop the pineapple industry until 1899 (Dole), and by 1960 was supplying 80% of the world’s pineapples. Today, Hawaii exports are zero, Thailand and the Philippines are #1 and #2. There is a little cultivation in Hawaii for local consumption, and some dried pineapple for trailmix.

    (H/t Commissioner Meredith Broadbent.)

  • Sarah Constantin: improvements in image identification with machine learning, measured in negative log error rate, appear to be linear over the past 5 years.
  • What analysts, associates, VPs, and MDs really do in investment banks“.

    Goldman Sachs, for example, only promotes around 400 people to managing director every two years and has 12,000 vice presidents in total…

  • What do wild animals do when they encounter a mirror?
  • The Gates Foundation has long, popular summary of the tremendous progress is reducing poverty, illness, and death in the developing world over the past three decades.But do we really have to pretend this letter is intended for Warren Buffett?…)a  

  • “The Train Inspection Monorail (TIM)…is a chain of wagons, sensors and cameras that snake along a track bolted to the LHC tunnel’s ceiling.”:
  • Franklin Chang-Díaz’s plasma rocket:

    This has long been the promise of Chang-Díaz’s plasma-based rocket engine, Vasimr. From a theoretical physics standpoint, Vasimr has always seemed a reasonable proposition: generate a plasma, excite it, and then push it out a nozzle at high speed. But what about the real-world engineering of actually building such an engine—managing the plasma and its thermal properties, then successfully firing it for a long period of time? That has proven challenging, and it has led many to doubt Vasimr’s practicality.

    …Speaking almost no English at the time, he immigrated to the United States from Costa Rica in 1969 to finish high school. Chang-Díaz then earned a doctoral degree in plasma physics from Massachusetts Institute of Technology. Later, as an astronaut, Chang-Díaz flew seven Space Shuttle missions, tying Jerry Ross’ record for most spaceflights by anyone, ever.

    …The rocket engine starts with a neutral gas as a feedstock for plasma, in this case argon. The first stage of the rocket ionizes the argon and turns it into a relatively “cold” plasma. The engine then injects the plasma into the second stage, the “booster,” where it is subjected to a physics phenomenon known as ion cyclotron resonance heating. Essentially, the booster uses a radio frequency that excites the ions, swinging them back and forth.

    As the ions resonate and gain more energy, they are spun up into a stream of superheated plasma. This stream then passes through a corkscrew-shaped nozzle and is accelerated out of the back of the rocket, producing a thrust….

    The Sun powers both the production of plasma and the booster exciting the plasma, and the extent to which it does either can be shifted. When a spacecraft needs more thrust, more power can be put into making plasma. This process uses more propellant, but it provides the thrust needed to move out of a gravity well, such as Earth orbit. Later, when the vehicle is moving quickly, more power can be shifted to the booster, providing a higher specific impulse and greater fuel economy.

  • Mammoth Steppe:

    At the last deglaciation Earth’s largest biome, mammoth-steppe, vanished….Analyzes of fossils 14C dates and reconstruction of mammoth steppe climatic envelope indicated that changing climate wasn’t a reason for extinction of this ecosystem. We calculate, based on animal skeleton density in frozen soils of northern Siberia, that mammoth-steppe animal biomass and plant productivity, even in these coldest and driest of the planet’s grasslands were close to those of an African savanna.

    Now’s a good time to read up on this, since Mammoths may be on the revived in just a few years. (Nevermind.) Obtaining DNA from more than a few million years ago is still impossible but the some proteins and other soft tissue from 100M+ year-old fossils can be recovered [Nature article].

  • Need to get oriented about those geological time scales? They are divided at the largest level into eons, which are progressively subdivided into eras, periods, epochs, and ages. Each level is generally subdivided into 2-6 parts. The definition of the divisions is often as much geological and biological as temporal. Here is a video of the trajectories taken by continents over the past few billion years:
  • Henry Ford’s utopia:

    …I boarded a riverboat this year in Santarém, an outpost at the confluence of the Amazon and Tapajós rivers, and made the six-hour trip to the place where Ford, one of the world’s richest men, tried turning a colossal swath of Brazilian jungle into a Midwest fantasyland.

  • Advantages of underwater data centers. Except in tropical locations where the surface temperature can get very warm, I don’t see why it wouldn’t be better to have them float on the surface for easier access. (Obstructing ocean traffic? Maybe, but trawling accidents would be rarer.)
  • Weird symbiosis:

    What makes the pom-pom crab …so special is [its pincers, which] are shaped like forceps, with which it always holds a pair of stinging sea anemones…The crabs use the sea anemones like nets, to catch food; the crabs also use the anemones to ward off larger animals that would prey on the crabs. The sea anemones, for their efforts, get fed scraps….“Every single crab we’ve ever found was found holding an anemone, but we’ve never found a free-living anemone”…if crabs lacked two full anemone bouquets, the crabs would force the tentacled creatures to divide into clones…

    The scientists caught a few dozen crabs and removed some of their anemones; wild crabs are rarely if ever found without the symbiotic poms in claw. “Laboratory observations showed that the removal of one anemone from a crab induces a ‘splitting’ behavior, whereby the crab tears the remaining anemone into two similar parts, resulting in a complete anemone in each claw after regeneration”…

    Something similar happened after the scientists removed the anemones completely from one crab, and then put it in a cage with a fully endowed partner. The crabs fought — not causing mortal damage but “almost always leading to the ‘theft’ of a complete anemone or anemone fragment by the crab without them,” wrote the researchers. “Following this, crabs ‘split’ their lone anemone into two.” DNA analysis of the anemones in the wild confirmed that the wild poms were genetic clones, indicating that similar splits may occur in the ocean.

    The pom-pom crab, the scientists speculated, is perhaps the only animal on the planet that controls another species’ growth, feeding and asexual reproduction.

    Another pretty video here (but no fighting/splitting).

  • Fast 3D models of the human skeleton. Plays nicely with touch screens. Gives you a much better sense of, say, the layout of the bones in the wrist than you can get from flat diagrams.
  • Matt Levine’s Money Stuff daily email newsletter is a firehose of humorous, and occasionally really clarifying, analysis of finance. I doubt it would be a good use of my time to read it on a daily basis, but it’s impressive. Relatedly, here’s a service for converting email newsletters into RSS feeds you can read on a feed reader. Works well with Gmail.
  • Operation Solomon:

    Operation Solomon was a covert Israeli military operation to airlift Ethiopian Jews to Israel in 1991. Non-stop flights of 35 Israeli aircraft, including Israeli Air Force C-130s and El Al Boeing 747s, transported 14,325 Ethiopian Jews to Israel in 36 hours.

    In 1991, the sitting Ethiopian government of Mengistu Haile Mariam was close to being toppled with the military successes of Eritrean and Tigrean rebels, threatening Ethiopia with dangerous political destabilization. World Jewish organizations and Israel were concerned about the well-being of the Ethiopian Jews, known as Beta Israel, residing in Ethiopia. Also, the Mengistu regime had made mass emigration difficult for Beta Israel and the regime’s dwindling power presented an opportunity for those wanting to immigrate to Israel. In 1990, the Israeli government and Israeli Defense Forces, aware of Mengistu’s worsening political situation, made covert plans to airlift the Jews to Israel….

    In order to accommodate as many people as possible, airplanes were stripped of their seats and up to 1,122 passengers were boarded on a single plane. Many of the immigrants came with nothing except their clothes and cooking instruments, and were met by ambulances, with 140 frail passengers receiving medical care on the tarmac. Several pregnant women gave birth on the plane, and they and their babies were rushed to the hospital. The operation set a world record for single-flight passenger load on May 24, 1991, when an El Al 747 carried 1,122 passengers to Israel (1,087 passengers were registered, but dozens of children hid in their mothers’ robes). “Planners expected to fill the aircraft with 760 passengers. Because the passengers were so light, many more were squeezed in.”

  • Electronics robust enough for Venus: A silicon carbide circuit lasted more than three weeks in a laboratory simulation of the caustic conditions that prevail on the planet’s surface.” More on the device used to simulate these conditions, the Glenn Extreme Environments Rig: 1, 2, 3.
  • Gastric bypass surgery is dramatic in strategy and effectiveness. The topology of the GI tract is changed, and dramatic weight loss is achieved through a (still poorly understood) combination of mechanical limitations and a new hormonal response to food.
  • Planetary Resources claim that the same observational tech for assessing the mineral composition of asteroids is applicable to Earth-observing satellites, which is marketable on a much closer time horizon:
    It’s not clear to me how true this is, versus just an inspiring story for a normal satellite company. Similar criticisms can be leveled at SpaceX (Mars colonization) and PayPal (decentralized, nation-state-independent currency).
  • Scientists finally figured out why whales leap into the air“:

    Their findings…show breaching is far more common when pods of humpback whales are far apart (at least 4,000 meters or 2.5 miles), and fin or tail slapping is more frequent as groups split or come together. The authors say these patterns suggest breaching and slapping play a role in both long-distance and close-range communication. By slamming their massive bodies into the water, the resulting sounds, like a drum, can travel enormous distances.

    (H/t Tyler Cowen.)

  • Tuberculosis-resistant cows developed for the first time using CRISPR technology“.

    We used a novel version of the CRISPR system called CRISPR/Cas9n to successfully insert a tuberculosis resistance gene, called NRAMP1, into the cow genome. We were then able to successfully develop live cows carrying increased resistance to tuberculosis. Importantly, our method produced no off target effects on the cow genetics meaning that the CRISPR technology we employed may be better suited to producing transgenic livestock with purposefully manipulated genetics.

    [Journal article.]
  • Why Don’t We Have a General Purpose Tree Editor?
  • The most NYC news story ever.
  • Many of the earliest settlers of Madagascar came by out-rigger canoe from the island of Borneo which is between Malaysia and Indonesia, and more than 4,000 miles away.
  • Reconstruction of a Train Wreck: How Priming Research Went off the Rails“. (H/t Gwern.)
  • New from Boston Dynamics:
  • AI beats humans at heads-up no-limit Hold ’em. (H/t Steve Hsu.)
  • Trajectory of New Horizons after Pluto, headed for an object of interest in the Kuiper belt.
  • Four Column ASCII.


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  1. But do we really have to pretend this letter is intended for Warren Buffett?…)
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