上海魔都后花园

A sloppy light system may be just what a squid needs to hide from predators. Bioluminescent cells in some glass squid work in a surprisingly inefficient way — leaking a lot of light rather than fully channeling it, a new study suggests.

Glass squid have largely transparent bodies, helpful for inconspicuous swimming in deep open water. Marine predators often scan the waters above them for the telltale silhouettes of prey blocking sunlight, but there’s little to betray a glass squid — except for a few notable features such as the shadow-making eyes on its head.
Underneath those eyes, squid in the genus Galiteuthis grow silvery patches of cells that act as undersurface bioluminescence, a camouflage technique that has evolved in various marine creatures, making their shadows less conspicuous to hunters below.

Biophysicist Alison Sweeney of the University of Pennsylvania in Philadelphia had hypothesized that the cells, called photophores, act like microscopic cables that channel the bioluminescent glow of the squid down or out in a specific direction. The skinny, cablelike cells are surrounded by thin, protein-dense layers that create a silver tube that reminds Sweeney of Saran Wrap. But in the first detailed look at these structures, Sweeney and Pennsylvania colleague Amanda Holt found that the channels performed poorly, letting most of the light leak away sideways. That efficiency, it turns out, could be useful, Sweeney and Holt report June 8 in the Journal of the Royal Society Interface.
“We always expect that the most ‘perfect’ or efficient mechanism will be the pinnacle of evolution, but this study shows that there are many ways to solve challenges imposed by the environment,” says marine biologist Steven Haddock of Monterey Bay Aquarium Research Institute in California.

Inefficiency might sound like an improbable scenario for success. But, says visual ecologist Justin Marshall of the University of Queensland in Brisbane, Australia, “I believe it.”

Other researchers had discussed the idea that certain sea creatures show a great deal of subtlety in disguising their silhouettes, but Sweeney knew of no other study trying to figure out how supposed cables work.
It turns out that the squid structures were “really bad at being fiber-optic cables,” Sweeney says. The cells are about 50 micrometers long, longish for a cell but short for a cable. And the cells couldn’t guide light even over that short distance without losing much of it. Looking at the cross sections of the photophores under a microscope showed big, uneven gaps in the layers. When she first recognized this, she expected to write “a boring paper that’s, ‘Gee, squid cells kind of sort of guide light, but not really.’”

Then came the “of course” moment for Sweeney and her puzzling measurements. “The lesson that keeps coming back to us,” she says, “is that these things are meaningless until you consider the habitat.” After calculating the light environment where wild squid swim, the researchers realized that the overall effect of the leaking tubes created a plausible approximation for the twilightlike haze in which the squid live. A glowing blur might actually make the eyes less conspicuous to predator approaching from a variety of angles.

Irregularities in the sheathing and shapes of the leaky cables might even make the living cables more remarkable, Sweeney speculates. Dividing them into five rough types, the researchers investigated the kinds of light effects each produced and matched those effects with ocean conditions at two locations off Hawaii. If squid can pick which cable doodads to use and when, the animals could improve the match between their under-eye shine and conditions in the ocean.

Other squid with opaque skin flicker, darken and quick-change their tiny color-making structures, she points out. So, the suggestion that eye-glow structures might change, too, “is not crazy,” Sweeney says.

Spoiler alert: Scientists can gauge a film’s emotional tenor from the gasps of its audience. Sure, the audible sounds are a cue, but so are the chemicals exhaled with each sigh and scream. These gases could point the way to a subtle form of human communication.

“There’s an invisible concerto going on,” says Jonathan Williams, an atmospheric chemist at the Max Planck Institute for Chemistry in Mainz, Germany. “You hear the music and see the pictures, but you don’t realize there are chemical signals in the air.”
Williams started out measuring the air in a soccer stadium to see if human breath had a noticeable impact on the concentration of greenhouse gases in the atmosphere. The answer was no, at least on a small scale. But he noticed that levels of carbon dioxide and other gases fluctuated wildly whenever the crowd cheered. That got him wondering: Maybe humans’ emissions are influenced by emotions. So he went to the movies.

Williams and colleagues measured air samples collected over six weeks in two movie theaters in Germany. Overall, 9,500 moviegoers watched 16 films — a mix of comedy, romance, action and horror that included The Hunger Games: Catching Fire, Walking With Dinosaurs and Carrie. The researchers classified scenes from the movies using such labels as “suspense,” “laughter” and “crying.” Then they looked for associations between movie scenes and hundreds of compounds in the air.

Certain scenes, primarily those that had people laughing or on the edge of their seats, had distinct chemical fingerprints, the researchers write May 10 in Scientific Reports. During screenings of The Hunger Games: Catching Fire, CO2 and isoprene emissions consistently peaked at two suspenseful moments. Williams and colleagues attribute the spikes in CO2 to increased pulse and breathing rate. The spikes in isoprene — a chemical associated with muscle action — were probably due to tense movie moments.

The researchers had to account for chemicals wafting into the air that may not have been a reaction to onscreen action. People emit chemicals from their perfume, shampoo and even the snacks they munch such as popcorn or beer. During screenings of The Secret Life of Walter Mitty, for instance, the researchers noticed a spike in ethanol corresponding with a scene in which Mitty orders a beer. Williams speculates that the scene reminded movie-goers to take a swig of their own alcoholic beverages.

Scientists need more data to make robust connections between human emotion and chemical emissions. But Williams sees potential practical applications. Marketers, for example, could quickly measure the air during consumer testing to see how people feel about products. He envisions future studies involving heart rate, body temperature and other physiological measurements.

“We have scratched the surface and it’s made a funny smell,” he says. “It’s something to investigate.”

SAN DIEGO — While astrophysicists celebrate the second detection of ripples in spacetime (SN Online: 6/15/16), they are also looking ahead to figuring out what led to these cosmic quakes. Black holes colliding in remote galaxies sent the gravitational waves our way. But how these duos ended up in an ill-fated embrace in the first place is unknown.

With only two clear detections from the Advanced Laser Interferometer Gravitational-Wave Observatory, and a third marginal candidate, there isn’t enough information to figure out for sure how these binary black holes formed. But there are two leading ideas.

One is that two heavyweight stars, each more than roughly 20 times as massive as the sun, are born, live and detonate together. Their deaths would leave behind a pair of black holes snuggled up to one another. They would eventually spiral together in a spectacular collision (SN: 3/19/16, p. 5).

Another idea is that the black holes find each other in the hustle and bustle of a dense star cluster. Within these crowded clusters, stars and black holes gravitationally shove each other around. “My graduate student calls it a black hole mosh pit,” Frederic Rasio, an astrophysicist at Northwestern University in Evanston, Ill., said June 15 during a news briefing at a meeting of the American Astronomical Society.

Rasio and colleagues developed computer simulations that investigate how denizens of these clusters interact with one another. Black holes settle into the center of the cluster, where some get caught in another’s gravitational embrace. Continued run-ins with other wandering black holes fling these pairings from the cluster, leaving the couple to soar across the galaxy and eventually merge into a single black hole.

There’s no way to tell if the two black hole pairs found by LIGO formed as stellar siblings or cluster cousins. But tests could be done as more are found.

Measuring the spins of the black holes could distinguish between formation scenarios, says Rasio. Black holes from previously paired stars will be spinning the same way; those that hooked up in a star cluster are more likely to be spinning in random directions. While LIGO researchers report that one of the black holes in the latest detection was twirling, they can’t tell which one it was or which way its spin axis was pointing.
Another test requires finding collisions over a range of distances from Earth. Because it takes time for gravitational waves to reach us, more distant impacts happened earlier in cosmic history. If astronomers notice an uptick in collisions happening around the same time that star formation peaked in the early universe, then pairings of massive stars are the more likely culprit, says Vicky Kalogera, an astrophysicist also at Northwestern.

“This has great potential to tell us how binary black holes formed,” she says. “But we need a larger sample.”

With improved detectors, researchers could eventually listen in on the entire observable universe — and all of cosmic history back to the first wave of star formation. “Big black holes come from big stars,” says Jonah Kanner, a Caltech astrophysicist. And the first stars are thought to have been hundreds of times more massive than our sun. If LIGO had 10 times its current sensitivity, he says, “we could learn about the first generation of stars. That’s exciting astrophysics.”

Such a leap would require a much more ambitious facility, such as a souped-up LIGO with 40-kilometer-long arms, says Kanner (today’s LIGO is one-tenth that size). “That’s the kind of concept where I can daydream,” he says. It’s just a pipedream for now, but over the coming years, new observatories will come online and bring with them incremental improvements in how far researchers can probe.

LIGO itself is undergoing an upgrade, and will be switched back on this fall. The VIRGO detector in Italy should return to service in early 2017 after five-plus years of refurbishment. In Japan, the KAGRA facility is under construction with plans to begin operation in 2018. And the Indian government recently gave the go-ahead to build a third LIGO facility.

“This is just the beginning of gravitational wave astronomy,” said VIRGO spokesperson Fulvio Ricci, a physicist at the Sapienza University of Rome. “We did it, then we did it again, and we will do it again in the future.”

Lightning seen as cause of puzzling chondrules — Lightning flashes in the huge cloud of primeval dust and gas from which the planets in the solar system condensed may have caused formation of the puzzling objects known as chondrules … the tiny, rounded granules about the size of poppy seeds found in stony meteorites…. Dry lightning flashes could have been the source of the fast heating that, followed by quick cooling, [explains] the glassy structure of chondrules. — Science News, July 16, 1966

Update
Chondrules are among the oldest pieces of planetary building blocks, formed roughly 4.6 billion years ago during the solar system’s first few million years. How they formed is still up for debate. But the lightning hypothesis has mostly fallen out of favor. One leading idea is that chondrules emerged in the wake of shock waves that rippled through the planet nursery. Those shock waves may have been triggered by collisions of embryonic planets, gas waves spiraling around the sun or strong solar flares.