New research indicates that leaf growth may not be as complicated as it seems. When compared species to species, shorter trees exhibit a greater variety of leaf sizes than taller ones, with the tallest trees all having leaves that measure 10 to 20 centimeters in length.

The scientists published their findings in the journal Physical Review Letters⊃1;. The narrow size range may be simply explained in the inner workings of trees. If this is correct, this could also explain why the tallest trees can only attain about 100 meters.

The team only considered angiosperms like maples and oaks, not gymnosperms, like pines and redwoods. They reviewed data for 1925 species and found that among angiosperms shorter than 30 meters, leaf length varies enormously, from 3 cm all the way up to 60 cm. The range narrows as the trees become taller.

The flow of sap and energy throughout the tree is what explains this. A leaf of an angiosperm produces a sugary sap that flows into a network of cells called the phloem, which transports the sap down to the tree’s trunk and through the roots. While it’s in transit, the tree metabolizes the sugar. The flow is driven by the difference in concentration in the sugars, which generates osmotic pressure.

The scientists modeled a tree as a pair of cylindrical tubes. A short, permeable tube, which represented the phloem in the leaf, was attached to a long, impermeable tube, the phloem in the trunk. Sap diffuses into the leave phloem and travels down into the trunk phloem. The longer the permeable leaf tube is, the more the surface area it has, so the more easily sap can enter. In the trunk phloem, the longer the tube is, the more resistance it offers to flow.

The scientists then considered how the total flow of sap and energy varies with leaf length. If the leaves are big, the resistance from the trunk limits the flow and making the leaves bigger than a certain maximum length yields no additional flow or benefit. On the other hand, if the leaves are very small, their resistance limits the flow. And if the leaf is shorter than a certain minimum length, the sap would flow through the phloem more slowly than it could diffuse through the entire tree.

Trees taller than 100 meters simply could not produce leaves that obey both length limits, setting a limit for tree height. Other scientists think that the uniformity of leaf size amongst the tallest trees could come from the comparable environments and conditions that produce them.

One way to test how the flow speed varies with the height of a tree and the length of its leaves would be to directly measure it in different species of tall trees, but that might require taking an MRI machine into a rain forest canopy.

Want to wirelessly upload hundreds of movies to a mobile device in a few seconds? Researchers at Georgia Tech have drawn up blueprints for a wireless antenna made from atom-thin sheets of carbon, or graphene, that could allow terabit-per-second transfer speeds at short ranges.

“It’s a gigantic volume of bandwidth. Nowadays, if you try to copy everything from one computer to another wirelessly, it takes hours. If you have this, you can do everything in one second—boom,” says Ian Akyildiz, director of the broadband wireless networking laboratory at Georgia Tech.

A terabit per second could be done at a range of about one meter using a graphene antenna, which would make it possible to obtain 10 high-definition movies by waving your phone past another device for one second. Akyildiz and colleagues have also calculated that at even shorter ranges, such as a few centimeters, data rates of up to 100 terabits per second are theoretically possible.

Graphene is a sheet of carbon just one atom thick, in a honeycomb structure, and it has many desirable electronic properties. Electrons move through graphene with virtually no resistance—50 to 500 times faster than they do in silicon. To make an antenna, the group says, graphene could be shaped into narrow strips of between 10 and 100 nanometers wide and one micrometer long, allowing it to transmit and receive at the terahertz frequency, which roughly corresponds to those size scales. Electromagnetic waves in the terahertz frequency would then interact with plasmonic waves—oscillations of electrons at the surface of the graphene strip—to send and receive information.  

“This points out and provides a set of classical calculations on estimates of sizes and performance: it points out that there is something worthwhile here,” says Phaedon Avouris, an IBM fellow who leads graphene and other nanometer-scale technology at IBM Research in Yorktown Heights, New York. “It doesn’t solve the whole problem, but points out an opportunity.”

As well as facilitating high-speed communication between devices, graphene antennas could enable faster wireless connections between nanoscale components on chips. “Antennas made of graphene can be made much smaller in all dimensions than a metal wire antenna. It can be made to be on the order of a micrometer or a few nanometers,” Avouris says. “The significance is that the antenna can be incorporated in a very small object.”

Of course, myriad challenges lie ahead. Antennas don’t work alone; they rely on many other components—such as signal generators and detectors, amplifiers, and filters—all of which would have to be fabricated at similar scales and with similar speeds in order to make a complete device. 

Researchers also need to work out how to do the manufacturing. Working with the material is extremely tricky, because its properties change when it comes in contact with other materials. 

However, the Georgia Tech group hopes to make a prototype of an antenna within a year, Akyildiz added, and other components after that.  

A new experiment simulating conditions in deep space reveals that the complex building blocks of life could have been created on icy interplanetary dust and then carried to Earth, jump-starting life.

Chemists from the University of California, Berkeley, and the University of Hawaii, Manoa, showed that conditions in space are capable of creating complex dipeptides – linked pairs of amino acids – that are essential building blocks shared by all living things. The discovery opens the door to the possibility that these molecules were brought to Earth aboard a comet or possibly meteorites, catalyzing the formation of proteins (polypeptides), enzymes and even more complex molecules, such as sugars, that are necessary for life.

“It is fascinating to consider that the most basic biochemical building blocks that led to life on Earth may well have had an extraterrestrial origin,” said UC Berkeley chemist Richard Mathies, coauthor of a paper published online last week and scheduled for the March 10, 2013 print issue of The Astrophysical Journal.

While scientists have discovered basic organic molecules, such as amino acids, in numerous meteorites that have fallen to Earth, they have been unable to find the more complex molecular structures that are prerequisites for our planet’s biology. As a result, scientists have always assumed that the really complicated chemistry of life must have originated in Earth’s early oceans.

In an ultra-high vacuum chamber chilled to 10 degrees above absolute zero (10 Kelvin), Seol Kim and Ralf Kaiser of the Hawaiian team simulated an icy snowball in space including carbon dioxide, ammonia and various hydrocarbons such as methane, ethane and propane. When zapped with high-energy electrons to simulate the cosmic rays in space, the chemicals reacted to form complex, organic compounds, specifically dipeptides, essential to life.

At UC Berkeley, Mathies and Amanda Stockton then analyzed the organic residues through the Mars Organic Analyzer, an instrument that Mathies designed for ultrasensitive detection and identification of small organic molecules in the solar system. The analysis revealed the presence of complex molecules – nine different amino acids and at least two dipeptides – capable of catalyzing biological evolution on earth.

A study partially funded by NASA finds evidence of ocean salt on Europa's surface.

If you could lick the surface of Jupiter's icy moon Europa, you would actually be sampling a bit of the ocean beneath. A new paper by Mike Brown, an astronomer at the California Institute of Technology in Pasadena, Calif., and Kevin Hand from NASA's Jet Propulsion Laboratory, also in Pasadena, details the strongest evidence yet that salty water from the vast liquid ocean beneath Europa's frozen exterior actually makes its way to the surface.

The finding, based on some of the best data of its kind since NASA's Galileo mission (1989 to 2003) to study Jupiter and its moons, suggests there is a chemical exchange between the ocean and surface, making the ocean a richer chemical environment. The work is described in a paper that has been accepted for publication in the Astronomical Journal.

The exchange between the ocean and the surface, Brown said, "means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you'd like to know what's in the ocean, you can just go to the surface and scrape some off."

Europa's ocean is thought to cover the moon's whole globe and is about 60 miles (100 kilometers) thick under a thin ice shell. Since the days of NASA's Voyager and Galileo missions, scientists have debated the composition of Europa's surface. The infrared spectrometer aboard Galileo was not capable of providing the detail needed to identify definitively some of the materials present on the surface. Now, using the Keck II Telescope on Mauna Kea, Hawaii, and its OSIRIS spectrometer, Brown and Hand have identified a spectroscopic feature on Europa's surface that indicates the presence of a magnesium sulfate salt, a mineral called epsomite, that could have formed by oxidation of a mineral likely originating from the ocean below.

Brown and Hand started by mapping the distribution of pure water ice versus anything else. The spectra showed that even Europa's leading hemisphere contains significant amounts of non-water ice. Then, at low latitudes on the trailing hemisphere—the area with the greatest concentration of the non-water ice material—they found a tiny, never-before-detected dip in the spectrum.

The two researchers tested everything from sodium chloride to Drano in Hand's lab at JPL, where he tries to simulate the environments found on various icy worlds. At the end of the day, the signature of magnesium sulfate persisted.

The magnesium sulfate appears to be generated by the irradiation of sulfur ejected from the Jovian moon Io and, the authors deduce, magnesium chloride salt originating from Europa's ocean. Chlorides such as sodium and potassium chlorides, which are expected to be on the Europa surface, are in general not detectable because they have no clear infrared spectral features. But magnesium sulfate is detectable. The authors believe the composition of Europa's ocean may closely resemble the salty ocean of Earth.

Europa is considered a premier target in the search for life beyond Earth, Hand said. A NASA-funded study team led by JPL and the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., has been working with the scientific community to identify options to explore Europa further. "If we've learned anything about life on Earth, it's that where there's liquid water, there's generally life," Hand said. "And of course our ocean is a nice, salty ocean. Perhaps Europa's salty ocean is also a wonderful place for life."