MIT Research News' Journal
[Most Recent Entries]
[Calendar View]
Tuesday, April 2nd, 2019
| Time |
Event |
| 1:30p |
Researchers tune material’s color and thermal properties separately The color of a material can often tell you something about how it handles heat. Think of wearing a black shirt on a sweltering summer’s day — the darker the pigment, the warmer you’re likely to feel. Likewise, the more transparent a glass window, the more heat it can let through. A material’s responses to visible and infrared radiation are often naturally linked.
Now MIT engineers have made samples of strong, tissue-like polymer material, the color and heat properties of which they can tailor independently of the other. For instance, they have fabricated samples of very thin black film designed to reflect heat and stay cool. They’ve also made films exhibiting a rainbow of other colors, each made to reflect or absorb infrared radiation regardless of the way they respond to visible light.
The researchers can specifically tune the color and heat properties of this new material to fit the requirements for a host of wide-ranging applications, including colorful, heat-reflecting building facades, windows, and roofs; light-absorbing, heat-dissipating covers for solar panels; and lightweight fabric for clothing, outerwear, tents, and backpacks — all designed to either trap or reflect heat, depending on the environments in which they would be used.
“With this material, everything could look more colorful, because then you wouldn’t be concerned with what color does to the thermal balance of, say, a building, or a window, or your clothing,” says Svetlana Boriskina, a research scientist in MIT’s Department of Mechanical Engineering.
Boriskina is author of a study that appears today in the journal Optical Materials Express, outlining the new material-engineering technique. Her MIT co-authors are Luis Marcelo Lozano, Seongdon Hong, Yi Huang, Hadi Zandavi, Yoichiro Tsurimaki, Jiawei Zhou, Yanfei Xu, and Gang Chen, the Carl Richard Soderberg Professor of Power Engineering, along with Yassine Ait El Aoud and Richard Osgood III, both of the Combat Capabilities Development Command Soldier Center, in Natick, Massachusetts.
Polymer conductors
For this work, Boriskina was inspired by the vibrant colors in stained-glass windows, which for centuries have been made by adding particles of metals and other natural pigments to glass.
“However, despite providing excellent visual transparency, glass has many limitations as a material,” Boriskina notes. “It is bulky, inflexible, fragile, does not spread heat well, and is obviously not suitable for wearable applications.”
She says that while it’s relatively simple to tailor the color of glass, the material’s response to heat is difficult to tune. For instance, glass panels reflect room-temperature heat and trap it inside the room. Furthermore, if colored glass is exposed to incoming sunlight from a particular direction, the heat from the sun can create a hotspot, which is difficult to dissipate in glass. If a material like glass can’t conduct or dissipate heat well, that heat could damage the material.
The same can be said for most plastics, which can be engineered in any color but for the most part are thermal absorbers and insulators, concentrating and trapping heat rather than reflecting it away.
For the past several years, Chen’s lab has been looking into ways to manipulate flexible, lightweight polymer materials to conduct, rather than insulate, heat, mostly for applications in electronics. In previous work, the researchers found that by carefully stretching polymers like polyethylene, they could change the material’s internal structure in a way that also changed its heat-conducting properties.
Boriskina thought this technique might be useful not just for fabricating polymer-based electronics, but also in architecture and apparel. She adapted this polymer-fabrication technique, adding a twist of color.
“It’s very hard to develop a new material with all these different properties in it,” she says. “Usually if you tune one property, the other gets destroyed. Here, we started with one property that was discovered in this group, and then we added a new property creatively. All together it works as a multifunctional material.”
Hotspots stretched away
To fabricate the colorful films, the team started with a mixture of polyethylene powder and a chemical solvent, to which they added certain nanoparticles to give the film a desired color. For instance, to make black film, they added particles of silicon; other red, blue, green, and yellow films were made with the addition of various commercial dyes.
The team then attached each nanoparticle-embedded film onto a roll-to-roll apparatus, which they heated up to soften the film, making it more pliable as the researchers carefully stretched the material.
As they stretched each film, they found, unsurprisingly, that the material became more transparent. They also observed that polyethylene’s microscopic structure changed as it stretched. Where normally the material’s polymer chains resemble a disorganized tangle, similar to cooked spaghetti, when stretched these chains straighten out, forming parallel fibers.
When the researchers placed each sample under a solar simulator — a lamp that mimics the visible and thermal radiation of the sun — they found the more stretched out a film, the more heat it was able to dissipate. The long, parallel polymer chains essentially provided a direct route along which heat could travel. Along these chains, heat, in the form of phonons, could then shoot away from its source, in a “ballistic” fashion, avoiding the formation of hotspots.
The researchers also found that the less they stretched the material, the more insulating it was, trapping heat, and forming hotspots within polymer tangles.
By controlling the degree to which the material is stretched, Boriskina could control polyethylene’s heat-conducting properties, regardless of the material’s color. She also carefully chose the nanoparticles, not just by their visual color, but also by their interactions with invisible radiative heat. She says researchers can potentially use this technique to produce thin, flexible, colorful polymer films, that can conduct or insulate heat, depending on the application.
Going forward, she plans to launch a website that offers algorithms to calculate a material’s color and thermal properties, based on its dimensions and internal structure.
In addition to films, her group is now working on fabricating nanoparticle-embedded polyethylene thread, which can be stitched together to form lightweight apparel, designed to be either insulating, or cooling.
“This is in film factor now, but we’re working it into fibers and fabrics,” Boriskina says. “Polyethylene is produced by the billions of tons and could be recycled, too. I don’t see any significant impediments to large-scale production.”
This research was supported, in part, by the Combat Capabilities Development Command Soldier Center. | | 5:00p |
Keeping genetic engineering localized Genetic engineering tools that spread genes within a target species have the potential to humanely control harmful pests as well as eradicate parasitic diseases such as malaria.
The tools, known as gene drives, ensure that engineered organisms transmit desired genetic variants to their offspring. These variants could ensure, for example, that the organisms only produce male offspring, or sterile females.
In this way, gene drives could be used to exterminate insects such as mosquitoes that carry pathogens, and that can spread malaria, dengue, and the Zika virus. Gene drives could also be used to control invasive species such as rodents that can threaten the survival of native animals.
However, previously described versions of gene drives based on the CRISPR genome editing system have the potential to spread far wider than their intended local population — to affect an entire species. The affects could also spread across international boundaries, potentially leading to disputes between countries where no prior agreement had been made.
These types of concerns could significantly delay, if not altogether prevent, the safe testing and introduction of the technology.
Now, in a paper published today in the Proceedings of the National Academy of Sciences, researchers at MIT and Harvard University describe a gene drive system with in-built controls.
The CRISPR-based drive consists of a series of genetic elements arranged in a so-called daisy chain, according to Kevin Esvelt, an assistant professor of media arts and sciences and head of the Sculpting Evolution research group at the MIT Media Lab who co-led the research.
One link within the daisy-drive system encodes the CRISPR gene editing system itself, while each of the other links encode guide RNA sequences. These guide sequences tell the CRISPR system to cut and copy the next link in the chain, Esvelt says.
Adding more links allows the daisy drive system to spread for additional generations within the population.
“Imagine you have a chain of daisies, and at each generation you remove the one on the end. When you run out, the daisy chain drive stops," Esvelt explains.
In this way, a small number of genetically-engineered organisms could be released into the wild to spread the daisy-drive within the local population, and then stop when programmed to.
“We’re programming the organism to do CRISPR genome editing on its own, within its reproductive cells, in each generation,” Esvelt says.
Esvelt developed the system in collaboration with George Church, a professor of genetics at Harvard Medical School, visiting professor at the Media Lab, and a senior associate member at the Broad Institute of MIT and Harvard. Co-first authors Charleston Noble and John Min, both graduate students at Harvard Medical School, led the modelling and the molecular biology experiments designed to ensure the system is evolutionarily stable, respectively.
“If the world is to benefit from new gene-drive technologies, we need to be very confident that we can reverse it and contain it, both theoretically and via controlled tests,” Church says.
“Many of the applications of gene drives involve islands and other geographical isolations, at least for initial tests, including invasive species and Lyme disease,” he noted. “It would be great if these highly motivated local governments can do tests that do not automatically affect adjacent islands or mainlands. The daisy-chain drives offer this.”
The research suggests that for every 100 wild counterpart, releasing just one engineered organism with a weak 3-link daisy-drive system, once per generation, should be enough to edit the entire population in about two generations — roughly a year in a fast-reproducing insect. That compares with existing systems that must release at least as many organisms as are already present in a local population, and sometimes 10 or 100 times as many.
The process could take several years in species that reproduce more slowly, such as mice, but would be more humane than the existing use of rodenticides, which can also harm people and predator species, Esvelt says.
In 2014, Esvelt and his colleagues first suggested that CRISPR-Cas9 could be used in gene-drive systems, and he has felt a moral responsibility to develop an alternative to self-propagating systems, he says. “Ideally, localization will let each community make decisions about its own environment, without forcing those decsions on others.
According to Professor Luke Alphey, head of arthropod genetics at The Pirbright Institute in the UK, self-propagating drive systems can spread rapidly through target populations. However, such drive systems are also thought likely to spread to all connected populations of the target species — which is desirable if you want to modify the entire species, undesirable if you do not, he says.
“Daisy-drives potentially provide a means to get much of the benefit of this type of gene drive, while constraining spread and also limiting persistence of the gene drive even in the target population,” Alphey says. “That is likely to be highly desirable when one wants to affect one population but not another of the same species, perhaps affecting an invasive pest population but not populations of the same species in its native range.”
Alphey was not involved in the initial daisy-drive research, but is now collaborating with Esvelt, including work on the use of daisy-drives in mosquitoes.
Esvelt and the Sculpting Evolution group are also beginning to explore the possible use of this technology to heritably immunize white-footed mice, the primary reservoir of the bacteria responsible for Lyme disease in North America. They are also setting up a research collaboration to explore the use of daisy-drives in Cochliomyia, also known as the New World screwworm, a parasitic fly that produces larvae that eat the living tissue of warm-blooded animals, causing considerable suffering.
In addtition, the researchers are also investigating this technology for use in nematode worms, microscopic creatures that reproduce every three days. This will allow them to carry out laboratory-based evolutionary studies of the daisy-drive engineered organisms, with the goal of ensuring the systems cannot become self-propagating. | | 11:59p |
Advance boosts efficiency of flash storage in data centers MIT researchers have designed a novel flash-storage system that could cut in half the energy and physical space required for one of the most expensive components of data centers: data storage.
Data centers are server farms that facilitate communication between users and web services, and are some of the most energy-consuming facilities in the world. In them, thousands of power-hungry servers store user data, and separate servers run app services that access that data. Other servers sometimes facilitate the computation between those two server clusters.
Most storage servers today use solid-state drives (SSDs), which use flash storage — electronically programmable and erasable memory microchips with no moving parts — to handle high-throughput data requests at high speeds. In a paper being presented at the ACM International Conference on Architectural Support for Programming Languages and Operating Systems, the researchers describe a new system called LightStore that modifies SSDs to connect directly to a data center’s network — without needing any other components — and to support computationally simpler and more efficient data-storage operations. Further software and hardware innovations seamlessly integrate the system into existing data center infrastructure.
In experiments, the researchers found a cluster of four LightStore units, called storage nodes, ran twice as efficiently as traditional storage servers, measured by the power consumption needed to field data requests. The cluster also required less than half the physical space occupied by existing servers.
The researchers broke down energy savings by individual data storage operations, as a way to better capture the system’s full energy savings. In “random writing” data, for instance, which is the most computationally intensive operation in flash memory, LightStore operated nearly eight times more efficiently than traditional servers.
The hope is that, one day, LightStore nodes could replace power-hungry servers in data centers. “We are replacing this architecture with a simpler, cheaper storage solution … that’s going to take half as much space and half the power, yet provide the same throughput capacity performance,” says co-author Arvind, the Johnson Professor in Computer Science Engineering and a researcher in the Computer Science and Artificial Intelligence Laboratory. “That will help you in operational expenditure, as it consumes less power, and capital expenditure, because energy savings in data centers translate directly to money savings.”
Joining Arvind on the paper are: first author Chanwoo Chung, a graduate student in the Department of Electrical Engineering and Computer Science; and graduate students Jinhyung Koo and Junsu Im, and Professor Sungjin Lee, all of the Daegu Gyeongbuk Institute of Science and Technology (DGIST).
Adding “value” to flash
A major efficiency issue with today’s data centers is that the architecture hasn’t changed to accommodate flash storage. Years ago, data-storage servers consisted of relatively slow hard disks, along with lots of dynamic random-access memory circuits (DRAM) and central processing units (CPU) that help quickly process all the data pouring in from the app servers.
Today, however, hard disks have mostly been replaced with much faster flash drives. “People just plugged flash into where the hard disks used to be, without changing anything else,” Chung says. “If you can just connect flash drives directly to a network, you won’t need these expensive storage servers at all.”
For LightStore, the researchers first modified SSDs to be accessed in terms of “key-value pairs,” a very simple and efficient protocol for retrieving data. Basically, user requests appear as keys, like a string of numbers. Keys are sent to a server, which releases the data (value) associated with that key.
The concept is simple, but keys can be extremely large, so computing (searching and inserting) them solely in SSD requires a lot of computation power, which is used up by traditional “flash translation layer.” This fairly complex software runs on a separate module on a flash drive to manage and move around data. The researchers used certain data-structuring techniques to run this flash management software using only a fraction of computing power. In doing so, they offloaded the software entirely onto a tiny circuit in the flash drive that runs far more efficiently.
That offloading frees up separate CPUs already on the drive — which are designed to simplify and more quickly execute computation — to run custom LightStore software. This software uses data-structuring techniques to efficiently process key-value pair requests. Essentially, without changing the architecture, the researchers converted a traditional flash drive into a key-value drive. “So, we are adding this new feature for flash — but we are really adding nothing at all,” Arvind says.
Adapting and scaling
The challenge was then ensuring app servers could access data in LightStore nodes. In data centers, apps access data through a variety of structural protocols, such as file systems, databases, and other formats. Traditional storage servers run sophisticated software that provides the app servers access via all of these protocols. But this uses a good amount of computation energy and isn’t suitable to run on LightStore, which relies on limited computational resources.
The researchers designed very computationally light software, called an “adapter,” which translates all user requests from app services into key-value pairs. The adapters use mathematical functions to convert information about the requested data — such as commands from the specific protocols and identification numbers of the app server — into a key. It then sends that key to the appropriate LightStore node, which finds and releases the paired data. Because this software is computationally simpler, it can be installed directly onto app servers.
“Whatever data you access, we do some translation that tells me the key and the value associated with it. In doing so, I’m also taking some complexity away from the storage servers,” Arvind says.
One final innovation is that adding LightStore nodes to a cluster scales linearly with data throughput — the rate at which data can be processed. Traditionally, people stack SSDs in data centers to tackle higher throughput. But, while data storage capacity may grow, the throughput plateaus after only a few additional drives. In experiments, the researchers found that four LightStore nodes surpass throughput levels by the same amount of SSDs. |
|