Self-Healing Rubber Keeps on Stretching, Rip after Rip

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A new synthetic rubber fixes itself when torn ends are touched together.
Francois Tournilhac and Ludwik Leibler ESPCI/CNRS, Paris (France)

Talk about bouncing back from adversity. A new stretchy material can be cut and rejoined at the same spot just by pressing the broken ends together for a few minutes. The self-healing rubber stays stretchy even after being severed five or six times, or cut and left on the countertop overnight, French researchers say. A chemical manufacturer is already working to create large batches of the material for still hypothetical applications such as sealants and self-healing rubber duckies.

The material's secret is its molecular structure, which resembles a plate of spaghetti, says physicist Ludwik Leibler of the National Center for Scientific Research (CNRS) in Paris, who led the research team. The strands straighten out when pulled, but they relax back to their tangled shape when the tension is released. The result is a rubber that can stretch to six times its resting length, the group reports in the journal Nature.

The self-mending occurs because each strand consists of numerous small molecules of vegetable fat linked to each other and to far-flung neighbors via relatively weak hydrogen bonds, the same chemical bonds that give water molecules their cohesiveness. When the material was cut or ripped, the severed bonds remained chemically sticky for each other.

Leibler recalls the first time his group ripped the material and pressed the torn ends together gingerly. "It was unbelievable, because after few seconds you could take the sample and the pieces would not fall apart," he says. "And it worked again and again and again." They called the sample "Miracle 1."

A full repair required up to six hours of bonding, the researchers report. They note that a ripped sample could be left overnight before being repaired, although it would not stretch as far, because some of the severed bonds had linked to their neighbors. Recycling a sample into a new shape is easy, Leibler adds—just heat it so the bonds break and reform.

The demonstration does have "a touch of magic about it," biochemists Justin Mynar and Takuzo Aida wrote in an editorial accompanying the paper. Prior self-healing materials relied on embedded capsules of sealant that opened during a break and then had to be replenished, or polymers that required high heat to rebond, they note.

Leibler says the Philadelphia-based chemical maker Arkema, Inc., is working on scaling up the synthesis process, "so that people can play with and dream about it." Among his own dreams are self-healing toys, pipe seals and pavement as well as plastic medical pouches that can be punctured and reused.

NASA images reveal mystery figure on Mars

A Chinese website has reportedly posted the first sighting of Martian life in the form of a mysterious figure caught on camera by the Spirit rover:

According to the Mail on Sunday, the sighting came after alien hunters spent "years" scouring NASA images for evidence of little green men before unearthing this example.

In fact, the Red Planet's first confirmed inhabitant features in this panorama snapped by Spirit back in November last year. We've marked the approximate position of the extraterrestrial with an arrow:

And before you all going running off to the NASA website to get the highest-res snap possible, here's our Martian as seen in the biggest file we could find - the 133 meg tiff.

Well, the jury's out on this one. NASA has the above false colour panorama available here, or you might try the slightly less colourful version here, or stereo representation here. Happy hunting

Frequency counters

The measurement of energy used by your home is an application to which digital metering
is well suited. It’s easier to read the drum type, digital kilowatt-hour meter than
to read the pointer type meter. When measuring frequencies of signals, digital metering
is not only more convenient, but far more accurate.
The frequency counter measures by actually counting pulses, in a manner similar
to the way the utility meter counts the number of turns of a motor. But the frequency
counter works electronically, without any moving parts. It can keep track of thousands,
millions or even billions of pulses per second, and it shows the rate on a digital display
that is as easy to read as a digital watch. It measures frequency directly by tallying up
the number of pulses in an oscillating wave, even when the number of pulses per second
is huge.
The accuracy of the frequency counter is a function of the lock-in time. Lock-in is
usually done in 0.1 second, 1 second or 10 seconds. Increasing the lock-in time by a factor
of 10 will cause the accuracy to be good by one additional digit. Modern frequency
counters are good to six, seven or eight digits; sophisticated lab devices will show frequency
to nine or ten digits.

Digital readout meters

Increasingly, metering devices are being designed so that they provide a direct readout,
and there’s no need (or possibility) for interpolation. The number on the meter is the indication.
It’s that simple. Such a meter is called a digital meter.
The advantage of a digital meter is that it’s easy for anybody to read, and there is no
chance for interpolation errors. This is ideal for utility meters, clocks, and some kinds of
ammeters, voltmeters and wattmeters. It works very well when the value of the quantity
does not change very often or very fast.
But there are some situations in which a digital meter is a disadvantage. One good
example is the signal-strength indicator in a radio receiver. This meter bounces up and
down as signals fade, or as you tune the radio, or sometimes even as the signal modulates.
A digital meter would show nothing but a constantly changing, meaningless set of
numerals. Digital meters require a certain length of time to “lock in” to the current, voltage,
power or other quantity being measured. If this quantity never settles at any one
value for a long enough time, the meter can never lock in.
Meters with a scale and pointer are known as analog meters. Their main advantages
are that they allow interpolation, they give the operator a sense of the quantity
relative to other possible values, and they follow along when a quantity changes. Some
engineers and technicians prefer the “feel” of an analog meter, even in situations where
a digital meter would work just as well.
One problem you might have with digital meters is being certain of where the decimal
point goes. If you’re off by one decimal place, the error will be by a factor of 10.
Also, you need to be sure you know what the units are; for example, a frequency indicator
might be reading out in megahertz, and you might forget and think it is giving you
a reading in kilohertz. That’s a mistake by a factor of 1000. Of course this latter type of
error can happen with an analog meter, too.