Author: uc24

This article originally appeared in the Yale Scientific magazine.

Picture a bike ride along the seaside. Your T-shirt has a built-in heart rate monitor to track your activity. Floating up from the picturesque water are dozens, maybe hundreds of balloons that feed into a charging station on the beach, where you can recharge your phone to take a photo of the incredible scene. This is the future that Carter Haines, associate research professor at the University of Texas in Dallas, envisions. Haines and his collaborators have figured out a way to turn mechanical energy into electricity with the help of carbon nanotube yarns.

At the heart of the method is a capacitor. The archetypal capacitor is called a parallel-plate electrostatic capacitor, and it consists of a positive and a negative electrode with some dielectric medium in between. This dielectric is a material that stores charge well; the electrodes, by contrast, are conductors through which charge is quickly removed as a current. You can charge a capacitor to a high voltage and then harvest the energy inside it at a later time.

“You take a piece of rubber, coat carbon grease on both sides to get electrodes, and as you stretch and release this rubber you can change the capacitance and get energy out,” Haines said. However, the trouble with electrostatic capacitors is two-fold. First, of course, you have to charge them up with an electronic circuit to start with. Second, a human body, with its high conductivity, probably shouldn’t be near, let alone touching, high voltages.

This is the beauty of electrochemical capacitors. Virtually all electrochemical capacitors today have electrodes made of carbon allotropes—different forms of carbon with its atoms interacting in different ways—with high surface areas. Carbon nanotubes are one class of such allotropes. First discovered by Soviet scientists Radushkevich and Lukyanovich in 1952, they are incredibly strong and stiff, with length-to-diameter ratios of up to 100 million. They are grown upright in what is called a forest, then pulled out into fibers and twisted into yarns. “The nanotubes are no longer in the yarn axis, but are following helical paths, just as you’d have with any yarn that you twist,” Haines said. If you continue to twist the yarn under pressure, it will actually form coils; you’ve probably discovered this phenomenon while playing with your shoelaces. With the right amount of tension on the ends of the yarn during the twisting process, you can get neatly packed coils.

The dielectric in an electrochemical capacitor is an electrolyte, a solution of charged ions in a liquid. “Because there’s so much surface area on the surface of the nanotubes, the ions can just come and hang out on the surface,” Haines said. “When we compress the yarn, we’re actually getting rid of surface area.” By pulling one strand (one electrode) and tightening the twist, the ions on it pack closer together, increasing the voltage. Since the ions all have the same sign, they repel each other and are eager to escape. Even a small voltage on the surface area of the nanotubes will collect a large charge—much larger than the charge on their conventional parallel plate counterparts. Thus, electrochemical capacitors have earned the alternate name of “supercapacitors,” and their low voltage means no electrocuted humans.

The most interesting application is the potential for embedding the yarns into clothing. The group has already tracked breathing, which Haines says is just the beginning. “You can measure things like pulse, heart rate and all sorts of things about the way the body is moving just by having different yarns embedded in the textile,” Haines said. The biggest roadblock to a commercial-scale use of energy-harvesting yarns is the production cost of the carbon nanotubes. The search is on for cheaper alternatives that have the same ability to host ions from an electrolyte on an easily changeable surface area.

In the lab and in the fabrics, the electrolyte is some kind of synthetic gel. But it turns out that seawater, with its high salt concentration, also works well. Haines’ collaborators in South Korea did indeed attach a balloon to one end of the yarn and hold the other down to the seabed with a rock. “They can see the voltage coming out of the yarn as the waves are moving the balloon around,” Haines said. Harvesting the mechanical energy of ocean waves has been an open challenge, and one that these yarns may rise to meet—if scientists succeed in finding a way to affordably produce them on the industrial scale.

This article originally appeared in the Yale Scientific magazine.

Take a moment to appreciate how powerful your immune system is. Over millions of years, evolution has selected for specimens with the ability to identify an essentially infinite number of foreign objects, or antigens, in our bodies, and develop antibodies to attack them. This is why we are able to survive over 200 types of the common cold.

But with great power, notes Peter Parker’s Uncle Ben, comes great responsibility. To successfully attack our bodies, antigens must be relatively similar to our own cells. Your immune system has to carefully identify which agents in the body are foreign; sometimes, it can be too good. This is the basis of autoimmune disease:  when the body misidentifies its own cells as pathogens and attacks them.

“Myasthenia gravis” (MG) literally translates to grave muscle weakness. “For the longest time, it was thought to be like a muscular dystrophy, in that it was chronic, typically progressive and with no available disease-modifying treatment ” said Professor Richard J. Nowak, a physician-scientist, in the Department of Neurology at the Yale School of Medicine. In the 1970s, it was discovered to be an autoimmune disease.  This was a “major game changer” said Dr. Nowak.

Take another moment to appreciate your physical body. Each time you take a step or move your eye across a page to read a sentence, you make a decision. Your brain relays that decision to your muscles and induces their compliance. This communication occurs at a neuromuscular junction (NMJ).

The neuron contains neurotransmitters in synaptic vesicles, which are released at the NMJ and make their way to receptors on the surface of the muscle in question. In fact, there are so many of these receptors that the muscle surface is folded up into small villi to accommodate all of them. The neurotransmitter and receptor fit like pieces in a puzzle: something clicks, and the muscle knows to contract or release, causing motion.

In MG, the immune system mistakes one these critical components, the acetylcholine receptor, for a pathogen. B-cells, crucial agents of the immune system, flood the body with autoantibodies, which attach to the acetylcholine receptors on the muscle surface. The receptors no longer can bind the acetylcholine, and the neuromuscular communication fails. Movement becomes difficult and weakness results.

MG has traditionally been treated with immunosuppressants, like steroids. These treatments globally suppress the immune system, resulting in fewer life threatening attacks of the acetylcholine receptors. The sometimes chronic and continuous attack by the autoantibodies eventually takes its toll. “After a long period of active and unchecked autoimmunity, the architecture of the muscle surface is flattened,” said Nowak. The villi close up, leaving ever fewer receptors accessible to the neurotransmitter. “It was not uncommon for patients to die from [MG] in the past, because their respiratory muscles weaken, their diaphragm weakens and they can’t breathe on their own.”  Current immunosuppressive strategies are not targeted and can result in significant side effects when used chronically along with the fact that about 15% of patients do not respond to standard treatments.

But what if you could attack only the rogue B-cells, that ones that produce the autoantibodies and remove them completely? Nowak’s group is studying such a drug.

Rituximab was developed about twenty years ago in the treatment of non-Hodgkin’s lymphoma, which is a cancer of B-cells. One unfortunate patient also had MG and showed dramatic improvement in those symptoms. “Rituximab targets the CD20 antigen, which is expressed on B-cells that are antibody producing,” said Nowak. “It is administered intravenously once a week for four weeks.” The cycle is repeated six months later. The clinical benefits show several weeks to months later, so long-term follow-up is key.

Nowak’s team followed a group of 16 patients up to 8 years. After a year, most were able to reduce, or completely stop, their use of other immunosuppressants. The mean time until relapse was three years after treatment was completed. “This is the longest relapse time recorded in any treatment for MG,” remarked Nowak.

Affecting up to 100,000 individuals in the U.S., myasthenia gravis is considered a rare disease and as such there is a paucity of large interventional clinical trials.  Many treatments currently in use are based on small studies or anecdotal experience and do not have an FDA-approved indication.  Most health insurance companies are resistant to covering these treatments as a result.
Careful studies are necessary to ensure the treatment’s validity, notes Nowak and further explains that “everyone wants a prospective, placebo-controlled trial”. The team has already begun such a trial: BeatMG Study. “We anticipate results in late 2017.”

This article originally appeared in the Yale Scientific magazine.

Almost every observed galaxy has a giant black hole at its center. Clues lead us to believe that these monsters, weighing as much a billion suns, eat copious amounts of gas from their environment and occasionally send some of it back as powerful jets, bubbles or heat. How exactly they do this, however, has been a mystery.

For over half a century, said Grant Tremblay, postdoctoral researcher at Yale, “people have simplified supermassive black hole accretion as a smooth spherical inflow of very hot plasma.” And this wasn’t necessarily a bad idea: gas that falls into a gravitational field gets heated up—the stronger the gravity, the higher the temperature. For a dense region like a cluster of galaxies, this temperature is over a hundred million Kelvin, ten times the temperature of the Sun’s core. So far, warm accretion sounds like a credible explanation.

But then there is thermal bremsstrahlung, or braking radiation. In hot plasma, electrons zoom freely around until they come close to positively charged ions; then they change trajectories and lose energy. We observe this lost energy as X-ray emission. “The cluster had to lose energy to give us this photon,” said Tremblay. “Every X-ray observation of a galaxy cluster is actually a direct measurement of galaxy cooling.” If a gas is both hot and dense, in summary, it won’t stay hot for very long. There isn’t a long-term reservoir of warm gas to feed the black hole.

In fact, Professor Megan Donahue of Michigan State University, who is a co-author on the paper, explained that we now have the opposite problem. “The gas near the centers of galaxies is very dense, and the cooling rate of a gas goes as density squared”. The more gas there is at the center, the easier it should be for electrons to find positive ions to brake against, emitting X-ray radiation and cooling down. The cluster cores should be brimming with cold gas, which in turn should form lots of stars. Instead, astronomers found them warm and star-less. This discovery motivated theorists to propose a new model: central black holes are Active Galactic Nuclei (AGN), and spit energy back into their environment in what is known as feedback.

So if hot gas doesn’t feed the AGN, what does? Donahue says the key is realizing that the gas is not all the same: “it’s like this big rain cloud that can produce raindrops that cool very rapidly.” In this model, neither uniformly warm nor uniformly cold gas feeds the black hole; rather, cold clouds precipitate out of the warm gas, and these clouds can then rain down on the black hole. Just like raindrops, on their way to the Earth through the atmosphere, don’t heat up and evaporate, so the cold clouds can maintain their structure all the way from where they formed to the cluster core. Donahue’s team designed the model by observing galaxy clusters, but they could not detect the drops —until now.

In a paper published in Nature this June, the team reported observations of the elusive drops in the Atacama Large Millimeter Array (ALMA), a collection of telescopes located in the Atacama Desert. ALMA can accurately measure both positions and speeds of any object it sees, and has such great angular resolution that it could see a dime held up in New Haven from where it stands in Chile. The team was trying to observe the cold, star-forming gas in the galaxy cluster Abell 2597, which is a tad further – one billion light years away.

The central supermassive black hole (SMBH) is accreting a lot of matter – but a black hole can only eat so fast, and so the in-falling matter settles in a large accretion disk around it. Different layers of the rotating disk generate friction as they rub against each other, which they release as heat. The cluster center should have been bright as a light bulb. “But you also have, between the observer and the light bulb, something eclipsing the light bulb and creating a shadow,” said Tremblay. These shadows were the elusive cold gas clumps, absorbing the light in certain parts of the spectrum. “This is one of the first really big pieces of unambiguous evidence for cold molecular clouds that are falling towards a supermassive black hole,” says Tremblay.

What wavelengths of the light from the black hole the clouds absorbed depended on how fast they were moving with respect to it. Tremblay saw that they were moving inwards towards the SMBH at about 300 km/s, or 67,000 miles an hour. “These things are basically on ballistic trajectories falling towards the black hole.”

Perhaps the best part is that this Nature paper was just a by-product of asking a different question—how is the cold, star-forming gas distributed in galaxies, and clusters of galaxies, and how is that shaped by AGN? We saw above that it lives in little clouds, but there’s one last fascinating detail – the clouds themselves are arranged in extended filaments, as long as the cluster itself. Megan Donahue pictures it as “not like a squid… It’s got these little tentacles.”

Tremblay thinks pasta is a better way to understand the underlying physics. After the first round of cold gas falls into the black hole, the AGN releases jets and bubbles of energy. These ejecta, he says, “drag cold gas out of the center of the galaxy, like pulling spaghetti out of hot water.” Your best bet, then, is to imagine a perpetual fountain of pasta, jetting out of the cluster center towards its outskirts, dragging little bubbles of cold gas along with it.

And so, looking for the tiniest, coldest clumps of gas everywhere in a cluster of galaxies, astronomers confirmed a model for the how the largest, hot object at its very core feeds and responds to its environment.