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SpaceX Rocket Explosion Is Latest in Space Station Resupply Failures

A SpaceX resupply mission to the International Space Station ended prematurely when the Falcon 9 rocket exploded just minutes after launch. The rocket failure won’t likely change NASA's planned reliance on private spaceflight contractors such as SpaceX, but it represents the latest in a string of failed attempts to resupply the space station.

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Formula E Ends First Season Wheel-to-Wheel

Formula E, the electric version of Formula One racing, completed its first season this weekend in London with back-to-back races. NextEV driver Nelson Piquet Jr. came from behind to win the series driver championship and Virgin Racing driver Sam Bird also came from behind to win Sunday's tight race.

Spectators cheered whenever drivers tried to pass, but few drivers succeeded. At Sunday’s race first-time Formula E spectator Fred Turrettini, already a Formula One fan, said he liked that the leafy Battersea Park circuit was so narrow. His wife Laura added that she liked that the race was electric.

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Femtosecond Lasers Create 3-D Midair Plasma Displays You Can Touch

Science fiction has promised us three-dimensional midair displays since at least the first Star Wars movie. We’ve seen a few holographic technologies that have come close; they rely on optical tricks of one sort or another to make it seem like you’re seeing an image hovering in front of you.

There’s nothing wrong with such optical tricks (if you can get them to work), but the fantasy is to have true midair pixels that present no concerns about things like viewing angles. This technology does exist, and has for a while, in the form of laser-induced plasma displays that ionize air molecules to create glowing points of light. If lasers and plasma sound like a dangerous way to make a display, that's because it is. But Japanese researchers have upped the speed of their lasers to create a laser plasma display that’s touchably safe.

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New Mode of Transmission May Double Fiber Optic Capacity

A new approach to transmitting data signals could more than double the amount of data that optical fibers can carry, claim scientists at the University of California, San Diego. The researchers suggest their work, which was published in in the June 26 issue of the journal Science, could "completely redefine the economy on which the present data traffic rests." 

Data signals traveling as laser pulses through an optical fiber are vulnerable to optical distortions resulting from interference among multiple signals of different wavelengths traveling down the same fiber.

These nonlinear wave interactions mean that data signals can degrade over great distances unless they regularly get regenerated along the way — that is, converted to electrical signals, subjected to computer analysis to weed out any distortions, and then converted back to optical signals. This process not only slows data traffic, but also accounts for most of the cost of setting up new optical network infrastructure.

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What Does “Responsible Innovation” Mean?

This is a guest post. The views expressed here are solely those of the author and do not represent positions of IEEE Spectrum or the IEEE.

We might say that in doing their work, and through the innovation processes that they are part of, engineers are writing history. In so doing, they take on a huge responsibility. As more and more voices lend their weight to the call for “responsible innovation,” and a community of scholars and practitioners adopt the “RI” cause, what role should engineers and their professional organizations play in this debate?

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Next-Gen Pacemakers May Be Powered by the Beating of a Heart

It sounds almost like a perpetual motion machine: A pacemaker that’s powered by the very beating of the heart that it’s regulating. Of course, such a device wouldn’t really be a fantasy of engineering, as the heart would receive energy to power its beats from both the pacemaker and the body’s natural systems. But it’s still a nifty idea.

The idea for a piezoelectric-powered pacemaker, which generates electricity in response to mechanical stress, comes from M. Amin Karami, an assistant professor of mechanical engineering at the University of Buffalo. He’s working on two prototypes, and tells IEEE Spectrum that he’s talking to device-makers about collaborating on a commercial product. “I would guess that in two years we will have the animal tests done, and be ready for human tests” as part of the FDA approval process, he says. 

Today’s typical pacemaker is a small flat device that fits easily in the palm of a hand, yet it could be smaller still, Karami said earlier this month in a talk at the MD&M medical device conference. Only about 40 percent of a pacemaker consists of the pulse generator and related electronics, he said; about 60 percent is devoted to the battery. And because the battery eventually gives out, surgeons have to swap out the whole device every seven to ten years. Doing away with the battery would do away with the inconvenience, medical risks, and costs of those replacement surgeries, Karami said. 


Karami’s first design is for an energy-harvesting module that could replace the batteries on a conventional pacemaker, which sits in the chest cavity and connects to the heart via insulated wires called leads. His second idea takes the work a step further, and would power a tiny lead-less pacemaker that nestles inside the heart itself. Such miniature devices are just starting to make it to market in Europe. 

To power a conventional pacemaker, Karami designed a flat ceramic piezoelectric structure that oscillates in response to the vibrations in the chest cavity, which are generated with every heartbeat. He has tested his device with heartbeat rates ranging from 7 to 700 beats per minute, and found that it generated more than enough power to keep a pacemaker running. 

But Karami told Spectrum that powering leadless pacemakers would be the best use of his technology. “Conventional pacemakers are a very mature technology,” he says. “But with leadless pacemakers, power is still a big challenge.” To design the piezoelectric power source for these tiny devices, Karami had to come up with a 3D structure that would fit inside the lozenge-shaped device. 

A leadless pacemaker doesn’t require surgeons to open up the chest cavity, but can instead be delivered to the heart’s interior through a catheter in a vein. “It’s a simple surgery that can be done easily in developing countries,” Karami notes. Getting rid of the leads also removes a potential point of failure (various cardiac leads have been recalled over the years when their insulation eroded or cracked). “Every time the heart moves, it pulls on the leads,” he says. “And the heart moves significantly. You would be awestruck to see the heart in motion.” 

Flashristors: Getting the Best of Memristors and Flash Memory

Memristors, devices that contain conductors that 'remember' the current that has passed through them by changing their resistance, are being extensively investigated for potential application in memory cells.   

The advantage of memristor memory is that it is nonvolatile, so it does not require continuous power to retain data, as DRAMs do.  Also, memristors have proven to be a possible candidate for multistate memory cells, opening the way for their use in bionic brains. One drawback is that memristors’ repeatability, or the number of times a memristor state can be switched on and off, is limited. 

A team of researchers at Bingöl University in Bingöl and Bilkent University in Ankara, both in Turkey, reported on 12 June in Applied Physics Letters that they’ve developed a 'flashristor,' a device that combines both the properties of a memristor and a flash-memory cell. Unlike existing devices, the memristor effect in their flashristor is not a local effect (such as a change on an atomic scale in crystalline structure), but a distributed effect in a larger area of the device, explains Aykutlu Dâna, one of the paper’s authors.  “This way you can switch on and off with a high precision and repeatability,” he adds.

Dana's team, which has been researching flash memories for some time, realized that a field-effect transistor could behave like a memristor if instead of varying the voltage of the gate via an external terminal, you charge it with electrons that remain trapped by changing the drain voltage only.  The apparent resistance of the channel (which connects the source with the drain) would then depend on the charge in this "floating gate."

This floating gate—called "storage layer" in the paper—needed to have three properties: 1) it had to be able to store electrons; 2) it had to be well insulated so that it retains the charge; and 3) there had to be a path that allows electrons to easily reach this layer.  To create the flashristor device, they used a structure similar to that of a thin-film flash memory. 

The channel consists of a zinc oxide layer connected to the source and drain via aluminum contacts. A 15-nanometer-thick hafnium oxide tunnel barrier allows the passage of electrons from the channel to the storage layer—a 5-nm-thick layer of silicon nitride. The storage layer is separated from the p-silicon substrate (which acts as a gate) by a control layer of aluminum oxide. 

The device differs from a flash memory cell in that the source is connected to the p-silicon gate. When, for example, a negative 5-volt pulse is sent to the drain, the electric field causes electrons from the channel to pass through the tunneling layer and become trapped in the storage layer.  When the pulse stops, the channel "sees" the charge in the storage layer, and its apparent resistance is changed into a different memristor state.  The resistance of the channel can be read out with a 0.1-volt pulse; but this voltage is too low to affect the electron population in the storage layer.  The flashristor can be reset by a positive 5-volt pulse, which gives the electrons in the storage layer sufficient energy to return to the channel through the tunnel barrier.

The researchers demonstrated four memristor states. But the uniformity and repeatability of the charge is better than a few percent, so it’s possible in principle to generate with 10 different states, explains Dâna.

Currently the write and erasing times are too long (about one second), admits Dana, who reiterates that the experiment was just a proof of principle.

Harika Manem, an electrical engineer at SUNY Polytechnic Institute’s Colleges of Nanoscale Science and Engineering, agrees that the device, which is CMOS compatible, needs to record memory states more quickly. “I liked that their analysis and modeling backed up their experimental results, but I don't think it is very applicable for neural circuits or other applications; you need much faster writing times,” she says.   

Improvement should be possible, says Dâna. “We have some preliminary results that show an extremely high performance of graphene as a storage layer,” he says. “The conduction band of graphene sits right in the middle of the valence and conduction bands of the channel, and it can more efficiently capture the tunneling electrons from the channel, so it can be written in very short times. We have some initial devices that can be charged below a microsecond; this is better than conventional flash," says Dâna. But the road to practical applications might still be long. "Maybe if we come up with devices that can be operated with nanosecond write/read pulses, then industry will become interested,” concludes Dâna.

A Second Life for Charge Pumping

An international research group has given new life to charge pumping, a former mainstay of semiconductor testing that had been nearly abandoned when its sensitivity failed to keep pace with ever-shrinking chips.

A handful of single-atom defects in a semiconductor chip—a few holes in the lattice, dangling bonds, an single foreign atom impurity, or even an extra interstitial silicon atom shoe-horned in to disrupt the structure—can degrade the chip’s performance. When they occur at the junction of a transistor gate and the dielectric layer, these “interface traps” badly distort the device’s response as applied electrons fill and drain from these backwater pools.

Finding such defects in metal-oxide field effect transistors quickly and inexpensively is essential to maintaining quality.

In traditional charge pumping, testers apply a square-wave input signal to the transistor gate, cycling the voltage to change the gap bias and generate a signal that can be measured on the far side of the substrate (which is also connected to the source and drain).

In a normal transistor, the output signal echoes the input in a consistent way. In a defective chip, though, the electrons eddying in the interface traps degrade the response. A single input signal won’t find all of the defects, though: Different traps fill and empty at different rates, so the engineers repeat the test with a number of different input signal frequencies.

The test is further complicated by current leaking through the dielectric layer, which adds a leakage current to the charge pumping signal. This was a negligible problem at first; leakage through the relatively thick dielectric layers of earlier transistors was relatively small. But chips got smaller, and so did the charge pumping signal; but the leakage current grew. And about a decade ago, the usable signal vanished almost completely amid the leakage noise. Charge pumping ceased to be a reliable technique for evaluating the most advanced devices.

In IEEE Transactions on Electron Devices, researchers at NIST in Gaithersburg, Md.—with colleagues from Peking University in Beijing, IBM Research in Albany, N.Y., and TSMC in Hsinchu, Taiwan—report on a revision of the technique that both revives charge pumping’s utility and simplifies the measurements.

Traditional charge-pumping applied a square wave input at a single frequency and measured a direct current output. Individual measurements at multiple frequencies were needed, and output data had to be manipulated off-line to subtract out the leakage signal.

NIST researchers Jason T. Ryan and Kin P. Cheung (the corresponding author) and their collaborators have developed an elegant solution that both cancels the leakage current error and generates results directly, without manipulation. They have replaced the series of single-frequency square waves with a frequency modulated input signal that combines two alternating test frequencies in a single input. If the higher first input signal is f1 and the second is f2, the output frequency, f3, is the difference between them (f3=f1-f2, the familiar “beat” of musical notes that are not quite in tune). The combination cancels the leakage current, so that the combined AC output current reflects the charge pumping alone.

In the process, the researchers also found a systematic error in the traditional test. The classical method assumed that leakage current did not vary with the input frequency, while the charge pumping output did. The earlier chip-testers plotted total output signal against the multiple input frequencies, extrapolated the curve to zero frequency, took that value to be the leakage current, and subtracted it from their other results to find the true charge pumping output.

Ryan, Huang, and their collaborators found that while it is technically true that leakage current is independent of the input frequency of an ideal square wave, in the real world, the leakage current does, in fact, change with frequency. Because square waves are, of course, not absolutely square, there is a finite time during which the voltage is rising, and another during which it is falling. These intervals do slightly alter the amount of current flowing through the dielectric.

Illustrations: NIST

This article was edited 21 June 2015 to include NIST’s Kin P. Cheung as corresponding author, rather than the last author, Peking University’s Ru Huang.

Using Light to Activate a Mouse's Happy Memory Protects It from Stress

This is one of the joys of writing about neuroscience: finding a press release image like the one above with the caption, “Cross section of a happy memory.” 

Need a little more explanation? The image shows neurons in a mouse brain that were active when the rodent formed a happy memory. And that memory had therapeutic value: When researchers artificially reactivated those neurons while the mouse was under stress, the mouse exhibited fewer depression-like behaviors. The research was published this week in Nature

There’s still a lot to unpack here: What’s a happy memory for a mouse? Why was it so stressed out? And how can you tell if a mouse is depressed? 

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