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Monday, August 6th, 2018
| Time |
Event |
| 12:30p |
Study: Hole in ionosphere is caused by sudden stratospheric warming Forecasting space weather is even more challenging than regular meteorology. The ionosphere — the upper atmospheric layer containing particles charged by solar radiation — affects many of today’s vital navigation and communication systems, including GPS mapping apps and airplane navigation tools. Being able to predict activity of the charged electrons in the ionosphere is important to ensure the integrity of satellite-based technologies.
Geospace research has long established that certain changes in the atmosphere are caused by the sun’s radiation, through mechanisms including solar wind, geomagnetic storms, and solar flares. Coupling effects — or changes in one atmospheric layer that affect other layers — are more controversial. Debates include the extent of connections between the layers, as well as how far such coupling effects extend, and the details of processes involved with these effects.
One of the more scientifically interesting large-scale atmospheric events is called a sudden stratospheric warming (SSW), in which enormous waves in the troposphere — the lowermost layer of the atmosphere in which we live — propagate upward into the stratosphere. These planetary waves are generated by air moving over geological structures such as large mountain ranges; once in the stratosphere, they interact with the polar jet streams. During a major SSW, temperatures in the stratosphere rise dramatically over the course of a few days.
SSW-induced changes in the ionosphere were once thought to be daytime events. A recent study led by Larisa Goncharenko of MIT Haystack Observatory, available online and in the forthcoming issue of the Journal of Geophysical Research: Space Physics, examined a major SSW from January 2013 and its effect on the nighttime ionosphere. Decades of data from the MIT Millstone Hill geospace facility in Westford, Massachusetts; Arecibo Observatory in Puerto Rico; and the Global Navigation Satellite System (GNSS) was used to measure various parameters in the ionosphere and to separate the effect of the SSW from other, known effects.
The study found that electron density in the nighttime ionosphere was dramatically reduced by the effects of the SSW for several days: A significant hole was formed that stretched across hemispheres from latitudes 55 degrees S to 45 degrees N. They also measured a strong downward plasma motion and a decrease in ion temperature after the SSW.
“Goncharenko et al. show clearly that lower atmospheric forcing associated to the large meteorological event called an SSW can also influence the low- and mid-latitude ionosphere,” says Jorge L. Chau, head of the Radar Remote Sensing Department at the Leibniz Institute of Atmospheric Physics. “In a way the connection was expected, given the strong connectivity between regions; however, due to other competing factors, lack of proper data, and — more important — lack of perseverance to search for such nighttime connections, previous studies have not shown such connections — at least not as clear. The new findings open new challenges as well of opportunities to improve the understanding of lower atmospheric forcing in the ionosphere.”
These significant results from Goncharenko and colleagues are also featured as an AGU research highlight in EOS.
Understanding how events far away and in other layers of the atmosphere affect the ionosphere is an important component of space weather forecasting; additional work is needed to pin down the precise mechanisms by which SSWs affect the nighttime ionosphere and other coupling effects.
“The large depletions in the nighttime ionosphere shown in this study are potentially important for near-Earth space weather as they may impact how the upper atmosphere responds to geomagnetic storms and influence the occurrence of ionosphere irregularities,” says Nick Pedatella, scientist at the High Altitude Observatory of the National Center for Atmospheric Research. “The observed depletions in the nighttime ionosphere provide another point of reference for testing the fidelity of model simulations of the impact of SSWs on the ionosphere.” | | 2:59p |
A targeted approach to treating glioma Glioma, a type of brain cancer, is normally treated by removing as much of the tumor as possible, followed by radiation or chemotherapy. With this treatment, patients survive an average of about 10 years, but the tumors inevitably grow back.
A team of researchers from MIT, Brigham and Women’s Hospital, and Massachusetts General Hospital hopes to extend patients’ lifespan by delivering directly to the brain a drug that targets a mutation found in 20 to 25 percent of all gliomas. (This mutation is usually seen in gliomas that strike adults under the age of 45.) The researchers have devised a way to rapidly check for the mutation during brain surgery, and if the mutation is present, they can implant microparticles that gradually release the drug over several days or weeks.
“To provide really effective therapy, we need to diagnose very quickly, and ideally have a mutation diagnosis that can help guide genotype-specific treatment,” says Giovanni Traverso, an assistant professor at Brigham and Women’s Hospital, Harvard Medical School, a research affiliate at MIT’s Koch Institute for Integrative Cancer Research, and one of the senior authors of the paper.
The researchers are also working ways to identify and target other mutations found in gliomas and other types of brain tumors.
“This paradigm allows us to modify our current intraoperative resection strategy by applying molecular therapeutics that target residual tumor cells based on their specific vulnerabilities,” says Ganesh Shankar, who is currently completing a spine surgery fellowship at Cleveland Clinic prior to returning as a neurosurgeon at Massachusetts General Hospital, where he performed this study.
Shankar and Koch Institute postdoc Ameya Kirtane are the lead authors of the paper, which appears in the Proceedings of the National Academy of Sciences the week of Aug. 6. Daniel Cahill, a neurosurgeon at MGH and associate professor at Harvard Medical School, is a senior author of the paper, and Robert Langer, the David H. Koch Institute Professor at MIT, is also an author.
Targeting tumors
The tumors that the researchers targeted in this study, historically known as low-grade gliomas, usually occur in patients between the ages of 20 and 40. During surgery, doctors try to remove as much of the tumor as possible, but they can’t be too aggressive if tumors invade the areas of the brain responsible for key functions such as speech or movement. The research team wanted to find a way to locally treat those cancer cells with a targeted drug that could delay tumor regrowth.
To achieve that, the researchers decided to target a mutation called IDH1/2. Cancer cells with this mutation shut off a metabolic pathway that cells normally use to create a molecule called NAD, making them highly dependent on an alternative pathway that requires an enzyme called NAMPT. Researchers have been working to develop NAMPT inhibitors to treat cancer.
So far, these drugs have not been used for glioma, in part because of the difficulty in getting them across the blood-brain barrier, which separates the brain from circulating blood and prevents large molecules from entering the brain. NAMPT inhibitors can also produce serious side effects in the retina, bone marrow, liver, and blood platelets when they are given orally or intravenously.
To deliver the drugs locally, the researchers developed microparticles in which the NAMPT inhibitor is embedded in PLGA, a polymer that has been shown to be safe for use in humans. Another desirable feature of PLGA is that the rate at which the drug is released can be controlled by altering the ratio of the two polymers that make up PLGA — lactic acid and glycolic acid.
To determine which patients would benefit from treatment with the NAMPT inhibitor, the researchers devised a genetic test that can reveal the presence of the IDH mutation in approximately 30 minutes. This allows the procedure to be done on biopsied tissue during the surgery, which takes about four hours. If the test is positive, the microparticles can be placed in the brain, where they gradually release the drug, killing cells left behind during the surgery.
In tests in mice, the researchers found that treatment with the drug-carrying particles extended the survival of mice with IDH mutant-positive gliomas. As they expected, the treatment did not work against tumors without the IDH mutation. In mice treated with the particles, the team also found none of the harmful side effects seen when NAMPT inhibitors are given throughout the body.
“When you dose these drugs locally, none of those side effects are seen,” Traverso says. “So not only can you have a positive impact on the tumor, but you can also address the side effects which sometimes limit the use of a drug that is otherwise effective against tumors.”
The new approach builds on similar work from Langer’s lab that led to the first FDA-approved controlled drug-release system for brain cancer — a tiny wafer that can be implanted in the brain following surgery.
“I am very excited about this new paper, which complements very nicely the earlier work we did with Henry Brem of Johns Hopkins that led to Gliadel, which has now been approved in over 30 countries and has been used clinically for the past 22 years,” Langer says.
An array of options
The researchers are now developing tests for other common mutations found in brain tumors, with the goal of devising an array of potential treatments for surgeons to choose from based on the test results. This approach could also be used for tumors in other parts of the body, the researchers say.
“There’s no reason this has to be restricted to just gliomas,” Shankar says. “It should be able to be used anywhere where there’s a well-defined hotspot mutation.”
They also plan to do some tests of the IDH-targeted treatment in larger animals, to help determine the right dosages, before planning for clinical trials in patients.
“We feel its best use would be in the early stages, to improve local control and prevent regrowth at the site,” Cahill says. “Ideally it would be integrated early in the standard-of-care treatment for patients, and we would try to put off the recurrence of the disease for many years or decades. That’s what we’re hoping.”
The research was funded by the American Brain Tumor Association, a SPORE grant from the National Cancer Institute, the Burroughs Wellcome Career Award in the Medical Sciences, the National Institutes of Health, and the Division of Gastroenterology at Brigham and Women’s Hospital. | | 11:59p |
Mass timber: Thinking big about sustainable construction The construction and operation of all kinds of buildings uses vast amounts of energy and natural resources. Researchers around the world have therefore been seeking ways to make buildings more efficient and less dependent on emissions-intensive materials.
Now, a project developed through an MIT class has come up with a highly energy-efficient design for a large community building that uses one of the world’s oldest construction materials. For this structure, called “the Longhouse,” massive timbers made of conventional lumber would be laminated together like a kind of supersized plywood.
The design will be presented this October at the Maine Mass Timber Conference, which is dedicated to exploring new uses of this material, which can be used to build safe, sound high-rise buildings, if building codes permit them.
John Klein, a research scientist in MIT’s architecture department who taught a workshop called Mass Timber Design that came up with the new design, explains that “in North America, we have an abundance of forest resources, and a lot of it is overgrown. There’s an effort to find ways to use forest products sustainably, and the forests are actively undergoing thinning processes to prevent forest fires and beetle infestations.”
People tend to think of wood as a suitable material for structures just a few stories high, but not for larger structures, Klein says. But already some builders are beginning to use mass timber products (a term that basically applies to any wood products much larger than conventional lumber) for bigger structures, including medium-rise buildings of up to 20 stories. Even taller buildings should ultimately be practical with this technology, he says. One of the largest mass timber buildings in the U.S. is the new 82,000-square-foot John W. Olver Design Building at the University of Massachusetts at Amherst.
One of the first questions people raise when they hear of such construction has to do with fire. Can such tall wooden structures really be safe? In fact, Klein says, tests have demonstrated that mass timber structures can resist fire as well or better than steel. That’s because wood exposed to fire naturally produces a layer of char, which is highly insulating and can protect the bulk of the wood for more than two hours. Steel, in contrast, can fail suddenly when heat softens it and causes it to buckle.
Klein explains that this natural fire resistance makes sense when you think about dropping a lit match onto a pile of wood shavings, versus dropping it onto a log. The shavings will burst into flames, but on the log a match will simply sputter out. The greater the bulk of the wood, the better it resists ignition.
The structure designed by the class uses massive beams made from layers of wood veneers laminated together, a process known as laminated veneer lumber (LVL), made into panels 50 feet long, 10 feet wide, and more than 6 inches thick These are cut to size and used to make a series of large arches, 40 feet tall to the central peak and spanning 50 feet across, made of sections with a triangular cross-section to add structural strength. A series of these arches is assembled to create a large enclosed space with no need for internal structural supports. The pleated design of the roof is designed to accommodate solar panels and windows for natural lighting and passive solar heating.
“The structural depth achieved by building up the triangular section helps us achieve the clear span desired for the communal space, all while lending a visual language on both the interior and the exterior of the structure,” says Demi Fang, an MIT architecture graduate student who was part of the design team. “Each arch tapers and widens along its length, because not every point along the arch will be subject to the same magnitude of forces, and this varying cross-section depth both expresses structural performance while encouraging materials savings,” she says.
The arches would be factory-built in sections, and then bolted together on site to make the complete building. Because the building would be largely prefabricated, the actual on-site construction process would be greatly streamlined, Klein says.
“The Longhouse is a multifunctional building, designed to accommodate a range of event scenarios from co-working, exercise classes, social mixers, exhibitions, dinner gatherings and lectures,” Klein says, adding that it builds on a long tradition of such communal structures in cultures around the world.
Whereas the production of concrete, used in most of the world’s large buildings, involves large releases of greenhouse gases from the baking of limestone, construction using mass timber has the opposite effect, Klein says. While concrete adds to the world’s burden of greenhouse gases, timber actually lessens it, because the carbon removed from the air while trees grow is essentially sequestered for as long as the building lasts. “The building is a carbon sink,” he says.
One obstacle to greater use of mass timber for large structures is in current U.S. building codes, Klein says, which limit the use of structural wood to residential buildings up to five stories, or commercial buildings up to six stories. But recent construction of much taller timber buildings in Europe, Australia, and Canada — including an 18-story timber building in British Columbia — should help to establish such buildings’ safety and lead to the needed code changes, he says.
Steve Marshall, an assistant director of cooperative forestry with the U.S. Forest Service, who was not involved in this project, says “Longhouse is a wonderfully creative and beautifully executed example of the design potential for mass timber.” He adds that “mass timber is poised to become a significant part of how America builds. The sustainability implications for the places we live, work, and play are huge. In addition to the well-known ramifications such as the sequestration of carbon within the buildings, there are also community benefits such as dramatically reduced truck traffic during the construction process.”
The Longhouse design was developed by a cross-disciplinary team in 4.S13 (Mass Timber Design), a design workshop in MIT’s architecture department that explores the future of sustainable buildings. The team included John Fechtel, Paul Short, Demi Fang, Andrew Brose, Hyerin Lee, and Alexandre Beaudouin-Mackay. It was supported by the Department of Architecture, BuroHappold Engineering and Nova Concepts. |
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