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?

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.

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.)

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

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.

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].

…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.

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).

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.”

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.)

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.