How about a skin control pad?

Sensors turn skin into gadget control pad

The sensors can spot many different locations on the arm
Tapping your forearm or hand with a finger could soon be the way you interact with gadgets.

US researchers have found a way to work out where the tap touches and use that to control phones and music players.

Coupled with a tiny projector the system can use the skin as a surface on which to display menu choices, a number pad or a screen.

Early work suggests the system, called Skinput, can be learned with about 20 minutes of training.

"The human body is the ultimate input device," Chris Harrison, Skinput's creator, told BBC News.

Sound solution

He came up with the skin-based input system to overcome the problems of interacting with the gadgets we increasingly tote around.

Gadgets cannot shrink much further, said Mr Harrison, and their miniaturisation was being held back by the way people are forced to interact with them.

The size of human fingers dictates, to a great degree, how small portable devices can get. "We are becoming the bottleneck," said Mr Harrison.

A finished device would be far smaller than the bulky prototype


To get around this Mr Harrison, a PhD student in computer science at Carnegie Mellon and colleagues Desney Tan and Dan Morris from Microsoft Research, use sensors on the arm to listen for input.

A tap with a finger on the skin scatters useful acoustic signals throughout the arm, he said. Some waves travel along the skin surface and others propagate through the body. Even better, he said, the physiology of the arm makes it straightforward to work out where the skin was touched.

Differences in bone density, arm mass as well as the "filtering" effects that occur when sound waves travel through soft tissue and joints make many of the locations on the arm distinct.

Software coupled with the sensors can be taught which sound means which location. Different functions, start, stop, louder, softer, can be bound to different locations. The system can even be used to pick up very subtle movements such as a pinch or muscle twitch.

"The wonderful thing about the human body is that we are familiar with it," said Mr Harrison. "Proprioception means that even if I spin you around in circles and tell you to touch your fingertips behind your back, you'll be able to do it."

"That gives people a lot more accuracy then we have ever had with a mouse," he said.

Early trials show that after a short amount of training the sensor/software system can pick up a five-location system with accuracy in excess of 95%.

Accuracy does drop when 10 or more locations are used, said Mr Harrison, but having 10 means being able to dial numbers and use the text prediction system that comes as standard on many mobile phones.

The prototype developed by the research team sees the sensors enclosed in a bulky cuff. However, said Mr Harrison, it would be easy to scale them down and put them in a gadget little bigger than a wrist watch.

Mr Harrison said he envisages the device being used in three distinct ways.

The sensors could be coupled with Bluetooth to control a gadget, such as a mobile phone, in a pocket. It could be used to control a music player strapped to the upper arm.

Finally, he said, the sensors could work with a pico-projector that uses the forearm or hand as a display surface. This could show buttons, a hierarchical menu, a number pad or a small screen. Skinput can even be used to play games such as Tetris by tapping on fingers to rotate blocks.

Mr Harrison would not be drawn on how long it might take Skinput to get from the lab to a commercial product. "But," he said, "in the future your hand could be your iPhone and your handset could be watch-sized on your wrist."

Superchilly chemistry

PORTLAND, Ore. — Researchers have been able to stop and start chemical reactions between molecules at temperatures colder than the depths of outer space. And new theoretical descriptions help explain the quantum mechanical details of these ultracold chemical reactions.

The details, presented March 17 at a meeting of the American Physical Society, offer glimpses into the burgeoning field of ultracold physics, which enables the creation of strange new states of matter and has potential applications in quantum computers and precision measurement devices (SN: 12/20/08, p. 22). At temperatures this low, the molecules no longer obey everyday rules, but instead are governed by quantum mechanics.

Deborah Jin and Jun Ye, both of the University of Colorado at Boulder and the JILA research center in Boulder, led experiments which used precisely tuned lasers and electric fields to deftly start and stop reactions between ultracold potassium-rubidium molecules.

“It’s a beautiful demonstration of how quantum mechanics works,” said Jeremy Hutson, a chemist at the University of Durham in England who studies ultracold reactions. The new studies reveal the existence of strange quantum effects “in a very simple regime that’s never been explored before.”

The University of Colorado researchers used lasers to cool the potassium-rubidium molecules, halting all the frenetic motion that usually characterizes the jittery molecules. Held in this chilly “ground state” at around 200 nanokelvin, the molecules moved incredibly slowly, Ye said. But after a second or so, the molecules started to disappear by twos.

“What’s going on here is chemistry,” Jin says. The potassium-rubidium molecules interact with each other to form molecules made up of two potassium atoms and two rubidium atoms. These results also appeared February 12 in Science.

At the meeting, Jin and Ye presented new preliminary results showing that not only do these chemical reactions occur, but that they can be sped up and halted. Potassium-rubidium molecules have slight electric charges at each end — slightly negative at the potassium atom and slightly positive at the rubidium atom. These dipole moments can act like small handles, giving researchers a way to manipulate the molecules. When the team turned up an electric field around the ultracold molecules, the chemical reaction rate went up dramatically by a factor of 20 or 30, Jin said. The positive rubidium atom on one molecule was hungrier for the negative potassium atom on another molecule.

In a second set of experiments, Jin and Ye showed that the molecules’ chemical reactions also could be suppressed. Since these chemical reactions happen only when the molecules line up head to tail, researchers could lock the molecules into a conformation that prevents the molecules from reacting. The team used a laser to slice a big glob of ultracold molecules into 20 or so very thin, pancakelike shapes. This tight conformation prevented the molecules from lining up head to tail, and the chemical reactions were suppressed, the team found. The ability to stop these chemical reactions — which can be bothersome, depending on the experiment — is important, Jin says. “Chemical reactions are great and fun,” until an experiment requires the original molecules themselves, Jin says. “Then those chemical reactions are kind of a problem.”

The experimental results highlight how scientists can control the reactions of the molecules under different conditions, but new theoretical results reported at the meeting illuminate how the ultracold molecules find each other in the first place. Paul Julienne, a theoretical physicist at the National Institute of Standards and Technology in Gaithersburg, Md., presented a quantum mechanical description of the molecules’ reaction rates. At temperatures this cold, the molecules behave more like diffuse waves rather than discrete spots. Julienne and his collaborator Zbigniew Idziaszek of the University of Warsaw in Poland found that under ultracold conditions, long-range effects of these waves, which can reach hundreds of nanometers, influence how the molecules close in on each other.

Once the molecules are within one nanometer or so of each other, they “react with great certainty,” Julienne said. “The reaction rates turn out to depend entirely on how the long-range forces work.” The theoretically predicted reaction rates, which will appear soon in Physical Review Letters, agree very well with the rates observed by Jin and Ye in their experiments, Julienne said.

Collections of ultracold, polar molecules might lead to new forms of matter, as well as technological applications, the researchers said. An internal property of the molecule called spin could hold quantum information and form the basis of a quantum computer, for instance.

“The beautiful thing is that we’ve got full quantum control over all degrees of freedom of the particles,” Julienne says. “I’m hoping that we can do some really neat things with these molecules.”

Why add acid to water when diluting?

Whether you add acid to the water or water to the acid is one of those things I know it's important to remember, but always have to puzzle out. Sulfuric acid (H2SO4) reacts very vigorously with water, in a highly exothermic reaction. If you add water to concentrated sulfuric acid, it can boil and spit and you may get a nasty acid burn.

If you spill some sulfuric acid on your skin, you want to wash it off with copious amounts of running cold water as soon as possible. Water is less dense than sulfuric acid, so if you pour water on the acid, the reaction occurs on top of the liquid. If you add the acid to the water, it sinks and any wild and crazy reactions have to get through the water or beaker to get to you.

How Solar Cells work?

Solar (or photovoltaic) cells convert the sun’s energy into electricity. Whether they’re adorning your calculator or orbiting our planet on satellites, they rely on the the photoelectric effect: the ability of matter to emit electrons when a light is shone on it.

Silicon is what is known as a semi-conductor, meaning that it shares some of the properties of metals and some of those of an electrical insulator, making it a key ingredient in solar cells. Let’s take a closer look at what happens when the sun shines onto a solar cell.

Sunlight is composed of miniscule particles called photons, which radiate from the sun. As these hit the silicon atoms of the solar cell, they transfer their energy to loose electrons, knocking them clean off the atoms. The photons could be compared to the white ball in a game of pool, which passes on its energy to the coloured balls it strikes.

Freeing up electrons is however only half the work of a solar cell: it then needs to herd these stray electrons into an electric current. This involves creating an electrical imbalance within the cell, which acts a bit like a slope down which the electrons will flow in the same direction.

Creating this imbalance is made possible by the internal organisation of silicon. Silicon atoms are arranged together in a tightly bound structure. By squeezing small quantities of other elements into this structure, two different types of silicon are created: n-type, which has spare electrons, and p-type, which is missing electrons, leaving ‘holes’ in their place.

When these two materials are placed side by side inside a solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in the p-type silicon. This means that the n-type silicon becomes positively charged, and the p-type silicon is negatively charged, creating an electric field across the cell. Because silicon is a semi-conductor, it can act like an insulator, maintaining this imbalance.

As the photons smash the electrons off the silicon atoms, this field drives them along in an orderly manner, providing the electric current to power calculators, satellites and everything in between.

 

Introduction

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