Science News

Headlines
 
. New sulphur for better batteries
. Why corals pulse
. Computers decoding dreams 
. A 'live' switch!
. Hiding under the sonar

New sulphur for better batteries
What are the most difficult challenges in designing batteries? One is developing small, heavy-duty batteries (those that hold a really big charge). The other is being able to recharge such batteries hundreds of times without their losing the ability to hold a lot of energy. A team of scientists reports having achieved both feats, mainly adding sulphur to their battery’s recipe.
This might make you look sceptical. Aren't sulphur-based batteries unsafe, prone to explode? Not these, say the scientists.
Batteries, especially those for powering portable electronics, need to store a lot of energy in a small space. This trait lets people use devices longer before needing to recharge the battery. Material science has suggested the answer to this problem. (This is the study of how the atomic and molecular structure of a material relates to its overall properties.) 
Sulfur is a very attractive battery material. Just a small amount of this inexpensive yellow element can pack a lot of energy. But past attempts to use it in batteries have proven difficult. The reason: each time you charge a sulphur-based battery, bad byproducts form.
What makes them bad? These byproducts — known as polysulphides — take up more room than the starting sulphur. In some cases, they can take up almost double the volume of the original sulphur. And an increase that large could make a battery explode.
Another problem: These byproducts readily dissolve in the fluids found inside most batteries. That, in turn, makes it increasingly harder to recharge the battery back to full power.
First, the scientists developed bits of sulphur that were each 800 nanometers across. Nano is a prefix meaning a billionth. So each of these particles was about 800 billionths of a meter wide. (They are so small that 20 sitting side by side wouldn’t be as wide as the diameter of the thinnest human hair!) The scientists then gave each bit a 15-nanometer-thick coating. That thin coat was made from titanium dioxide. This inexpensive material is used in a range of products, including paints. 
Finally, the researchers dunked the coated particles in a solution that could pass through the titanium dioxide layer and into the sulphur. Once inside, the solution dissolved some of the sulphur and then washed it through the coating. This process washed out enough sulphur to leave room for the fat polysulphides that would form as the battery charged. That means that the battery shouldn’t blow up, say the researchers.
A second benefit of the coating: the tiny holes in it are too small to let any dissolved polysulphides escape. That means the battery can stay strong and be recharged more times than batteries made from other compounds.
Still, some problems may remain. For instance, the coating itself fattens the sulphur nanoparticles a little. So it wastes space that could have gone to adding even more energy-holding sulphur. And the air between the particles is an even bigger waste of space. (Think of a jar of small chocolate spheres in a jar, and the space in between individual spheres. If the toffee weren’t separated into lots of small pieces, you could fit a lot more chocolate into the jar.)
Nevertheless, tests show that even after 100 cycles of use and recharging, the new batteries can still hold almost 97 percent of their initial energy capacity. That’s much better than most lithium-ion batteries used in today’s cell phones.
These findings were published earlier this year in "Nature Communications".

Why corals pulse
Come on, here is a new dance for you to do. Waving your arms slowly in the air, and while waving, gently bring all of your fingertips on each hand together. Then spread them out again. Then bring them in again. Keep going, opening and closing, every few seconds, all the time ....
There is a catch: you have to do this underwater! This is a dance called "Pulsing Coral", since that's exactly what corals do.
Certain corals known as xeniids (zee-nee-idz) do this day and night with only a few breaks. One interesting question has been why corals do this. Scientists have now uncovered a clue: their motion mixes the water. And that helps in two ways. It sweeps in nutrient-rich water. It also flushes away excess oxygen.
Many corals owe their survival to photosynthesis. This process uses light to transform carbon dioxide and water into food. But the corals don’t perform photosynthesis — algae living inside them do. And they give a share of the food they produce to their coral hosts. In fact, pulsing corals appear to get all of their food from these in-house algae. (These types of algae are single-celled organisms that can photosynthesize like a green plant but live inside the bodies of corals.)
Photosynthesis also produces oxygen. Previous studies — not on pulsing corals — found that too much oxygen can mess up photosynthesis. An excess can limit a coral’s access to carbon dioxide, which its algae need to photosynthesize. Scientists suspected the xeniid corals’ pulsing swishes away some of the oxygen. This would bring in water rich in carbon dioxide. But this would help xeniids only if a buildup of extra oxygen was a problem for them, too.
To find out, the scientists grew xeniids in tanks with very high levels of oxygen. As predicted, photosynthesis slowed in these corals (compared with corals exposed to normal oxygen levels). So swishing the water indeed helped xeniids remove excess oxygen, the scientists say. That motion also may bring in more food for the corals, they conclude.

Computers decoding dreams 
All of us dream, but do we *understand* them? Interpreting dreams has held humanity's interest for thousands of years. Now a new tool has come to our aid in this: computers, of course.
In a recent experiment reported in {\em Science}, a computer program successfully identified some contents of people’s dreams. The program compared people’s brain activity when they were both awake and asleep. It identified that seeing a certain object produced a particular pattern of brain activity. And it found that pattern was similar for an object whether it was seen in waking life or dreamy slumber.
Neuroscientists want to understand how our brains produce the images we see in a dream. Scientists have only a very slight understanding of this, and the new study adds just a little to that knowledge. Comparing sleeping and waking brain activity could also help scientists understand other brain states, such as those of people in a coma.
Dreams aren’t easy to study. Previous experiments on mice have helped scientists understand some aspects of dreaming, such as how memories are formed. These studies can go only so far — after all, mice can’t describe their dreams to researchers.
Dream experiments on people are limited, too. The dream-filled part of adult sleep takes 90 minutes to get going. So researchers have to settle in and wait. And the machine they use to scan participants’ brains — called an fMRI — is noisy. It can prevent some people from falling asleep.
This time, researchers found a different way to study dreams. They cut out the wait by recording the brain activity of people in the early stages of sleep. Their experiment involved three adult males who volunteered to sleep for science. The participants were in for a rough night.
The scientists recorded the brain activity of the men as they fell asleep in an fMRI. Shortly after the volunteers dozed off, the researchers awakened them. Each time, the men had to describe what they had just seen in their dreams. The scientists took careful notes of the volunteers’ descriptions. Over and over, the volunteers fell asleep for a short while before being woken up and asked to describe their dreams.
Later, the scientists asked the same volunteers to look at images while awake. Their brain activity was recorded during this exercise, too. Some of the pictures showed objects the participants had reported seeing in their dreams.
The scientists then added the new brain activity data — along with the corresponding images — to the computer program. At this point, the program analyzed both waking and sleeping data. It then linked certain patterns in brain activity to particular images. Using those links, the program analyzed a sleeping patient’s brain activity. More often than not, the program correctly picked which of two objects had appeared in a dream — for example, a girl, and not a book.
The study suggests that the brain experiences real and dreamed images in similar ways. So if seeing is believing, then the brain is giving us another good reason to believe in our dreams.

A 'live' switch!
You watch out for live wires, they are dangerous. But it makes no sense to have live switches, right? Not if the switch was made of DNA!
Computers are lifeless. They’re ordinarily built from metal, silicon, plastic and other materials. Those components work together to shuttle around the electricity needed to surf the Internet, watch videos or even do homework.
But why stick to the ordinary? Scientists are finding that computer parts can also be built from DNA. This long molecule contains genetic material and is found inside almost every living cell. It tells each cell which molecules to make. In March, researchers published a study that shows how DNA also can be used to build an important computer component, called a transistor.
In a computer, a transistor acts like a tiny switch that can be turned on or off. Computer processors or “chips” use hundreds of millions — and often billions — of transistors to keep information flowing. They’re used for memory, too. For example, a photograph on a memory card is saved as a series of switches in specific positions.
DNA can be used to build those switches, too, say scientists who worked on the new study. They call their *bio-switch* a transcriptor. And it could be used with other DNA devices to build biological computers.
These "bio-engineers" say that a DNA switch could be used to turn a germ — like the bacteria found in buttermilk — into a disease-hunting detective. Scientists could use the DNA switch to program the germ to look for signs of cancer. If it found such signs, the germ would send out warning signals. These signals would be hard to miss.
Transistors work by controlling the flow of electricity. In one position, they let the electricity pass. In the other position, they stop the flow. A DNA switch wouldn’t affect electricity. Instead, such a device would work by either making a molecule called a protein or not.
A DNA-based computer would also work in places that ordinary computers can’t — like deep inside a person’s body.
So, who knows, we might be working with "wet computers" in some years!

Hiding under the sonar
Can sound waves track you? Better still, if there are such waves, can you hide from them? It would be easy to mistake this recent device for a trinket. The plastic gadget is a mere 17 centimeters long and looks like a cross between a bird-cage and a slightly large egg. But appearances can be deceiving. This little device achieves something never done before: it hides a solid object from sound waves. Essentially, it’s a "cloaking" device.
The device makes objects invisible to `sonar'. Sonar devices send out sound waves in search of objects in the dark or too far away to be seen. An object is detected when the sound waves bounce off of it and return to their source, like an echo. The new invention is the first acoustic cloak (acoustic relates to sound) that can hide a three-dimensional object. Of course, the only thing it hides right now is a sphere about the size of a table tennis ball. But with some modifications, an improved version of the cloak could help cities reduce noise pollution.
Such a cloaking device might also help submarines cruise through enemy waters without being detected. Submarines use sonar to see who else is in the water. The new device could prevent sound waves that bounce off of a sub from returning to their source.
In the last 10 years, engineers have been figuring out new ways to hide things. They have developed an invisibility cloak for light waves. Light, like sound, travels through space as a wave. In 2007, the idea of a similar cloak to hide objects from sonar was proposed.
A light wave scatters when it hits an object. That means the wave breaks, with each splintered signal travelling in a different direction. We can see things only when some of this scattered light makes it to our eyes. To build invisibility cloaks, engineers use complex materials that prevent scattered light from reaching our eyes.
In a similar way, these scientists wanted to prevent sound waves from scattering, using simple materials. They used a computer program to design the cloak and a 3-D printer to print it. The device has 60 parallel rings of different sizes that encircle the object to be cloaked. Arriving sound waves scatter off the cloaking device itself and the cloaked sphere. The cloak is so designed that when the scattered waves from the cloaked sphere collide with the scattered waves from the cloaking device, they cancel each other out. Then, the scattered sonar signal can’t be detected — because the scattered waves have vanished.
It’s like a tug-of-war. You can drag a rope if no one is pulling on the other end. But if someone else pulls with an equal force on the other end, the rope won’t go anywhere. The reason: the action on one side cancels out the action on the other.
Researchers tested their device in a small, insulated chamber. They found that it didn’t work for most pitches of sound. Pitch refers to how high or low a sound is. But it did work for a particular high-pitched note. And it only worked when that sound arrived from one particular direction. Sound waves coming from other directions would not be canceled out.
This is only a start, but even this first step can be useful. It might reduce the noise coming from one area, like a busy road.
Ready to hide your submarine, anyone?