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Friday, July 5, 2019
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A new way of making complex structures in thin films
Self-assembling materials called block copolymers, which are known to form a variety of predictable, regular patterns, can now be made into much more complex patterns that may open up new areas of materials design, a team of MIT researchers say.
The new findings appear in the journal Nature Communications, in a paper by postdoc Yi Ding, professors of materials science and engineering Alfredo Alexander-Katz and Caroline Ross, and three others.
“This is a discovery that was in some sense fortuitous,” says Alexander-Katz. “Everyone thought this was not possible,” he says, describing the team’s discovery of a phenomenon that allows the polymers to self-assemble in patterns that deviate from regular symmetrical arrays.
Self-assembling block copolymers are materials whose chain-like molecules, which are initially disordered, will spontaneously arrange themselves into periodic structures. Researchers had found that if there was a repeating pattern of lines or pillars created on a substrate, and then a thin film of the block copolymer was formed on that surface, the patterns from the substrate would be duplicated in the self-assembled material. But this method could only produce simple patterns such as grids of dots or lines.
In the new method, there are two different, mismatched patterns. One is from a set of posts or lines etched on a substrate material, and the other is an inherent pattern that is created by the self-assembling copolymer. For example, there may be a rectangular pattern on the substrate and a hexagonal grid that the copolymer forms by itself. One would expect the resulting block copolymer arrangement to be poorly ordered, but that’s not what the team found. Instead, “it was forming something much more unexpected and complicated,” Ross says.
There turned out to be a subtle but complex kind of order — interlocking areas that formed slightly different but regular patterns, of a type similar to quasicrystals, which don’t quite repeat the way normal crystals do. In this case, the patterns do repeat, but over longer distances than in ordinary crystals. “We’re taking advantage of molecular processes to create these patterns on the surface” with the block copolymer material, Ross says.
This potentially opens the door to new ways of making devices with tailored characteristics for optical systems or for “plasmonic devices” in which electromagnetic radiation resonates with electrons in precisely tuned ways, the researchers say. Such devices require very exact positioning and symmetry of patterns with nanoscale dimensions, something this new method can achieve.
Katherine Mizrahi Rodriguez, who worked on the project as an undergraduate, explains that the team prepared many of these block copolymer samples and studied them under a scanning electron microscope. Yi Ding, who worked on this for his doctoral thesis, “started looking over and over to see if any interesting patterns came up,” she says. “That’s when all of these new findings sort of evolved.”
The resulting odd patterns are “a result of the frustration between the pattern the polymer would like to form, and the template,” explains Alexander-Katz. That frustration leads to a breaking of the original symmetries and the creation of new subregions with different kinds of symmetries within them, he says. “That’s the solution nature comes up with. Trying to fit in the relationship between these two patterns, it comes up with a third thing that breaks the patterns of both of them.” They describe the new patterns as a “superlattice.”
Having created these novel structures, the team went on to develop models to explain the process. Co-author Karim Gadelrab PhD ’19, says, “The modeling work showed that the emergent patterns are in fact thermodynamically stable, and revealed the conditions under which the new patterns would form.”
Ding says “We understand the system fully in terms of the thermodynamics,” and the self-assembling process “allows us to create fine patterns and to access some new symmetries that are otherwise hard to fabricate.”
He says this removes some existing limitations in the design of optical and plasmonic materials, and thus “creates a new path” for materials design.
So far, the work the team has done has been confined to two-dimensional surfaces, but in ongoing work they are hoping to extend the process into the third dimension, says Ross. “Three dimensional fabrication would be a game changer,” she says. Current fabrication techniques for microdevices build them up one layer at a time, she says, but “if you can build up entire objects in 3-D in one go,” that would potentially make the process much more efficient.
These findings “open new pathways to generate templates for nanofabrication with symmetries not achievable from the copolymer alone,” says Thomas P. Russell, the Silvio O. Conte Distinguished Professor of Polymer Science and Engineering at the University of Massachusetts, Amherst, who was not involved in this work. He adds that it “opens the possibility of exploring a large parameter space for uncovering other symmetries than those discussed in the manuscript.”
Russel says “The work is of the highest quality,” and adds “The pairing of theory and experiment is quite powerful and, as can be seen in the text, the agreement between the two is remarkably good.”
The research was funded by the Office of General Sciences of the U.S. Department of Energy. The team also included graduate student Hejin Huang.
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Thursday, July 4, 2019
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Louisiana experiences major drop in new HIV cases, its lowest in a decade
Louisiana diagnosed 989 people with HIV last year, its lowest number of new HIV cases in at least a decade in a state with a heavy number of infections within the African American community.
Although Louisiana ranked in the top 10 states to register the highest number of new HIV cases in 2017, the latest numbers from 2018 are a welcome decline that state officials hope reflect a new trend, according to NOLA.com.
READ MORE: Ex-Florida cop gets eight-year sentence for knowingly exposing woman to HIV
Overall, new HIV transmissions have declined by 12 percent over the past three years, according to the Louisiana Department of Health. State officials attribute the decrease to the state’s Medicaid expansion, which provided greater access to medication like PrEP, a daily pill that prevents HIV and increased screenings.
“This provides even more support for the importance of knowing your status and taking control of your infection to suppress the virus in the body,” Dr. Alexander Billioux, assistant secretary for the state’s Office of Public Health, told NOLA.com. “As we have said before, undetectable equals untransmittable.”
Out of the state’s 989 new transmissions, roughly three-quarters of these cases were male and African-American. Blacks accounted for 70% of the new diagnoses, while whites made up 23%, Hispanics 6%, and Asians 1%.
READ MORE: The importance of World AIDS Day as a person living with HIV
Health professionals found Louisiana’s news hopeful and possibly indicative of what’s to come.
“I feel as though we will actually see the end of HIV in our lifetime,” Fran Lawless, director of the Office of Health Policy & AIDS Funding, within the New Orleans Health Department, told Nola.com. “I think that’s just on the horizon. This year is the first that I felt that might actually come to fruition. Things were pretty bleak when I first entered this area.”
Billioux agreed that Louisiana has battled HIV and other health challenges that have at times felt “insurmountable.” But she pointed to the Medicaid expansion as proof that it works in bringing access to treatment to vulnerable populations. Billioux also compared other southern states, like Georgia, which did not expand Medicaid, and how its numbers continue to rank among the highest in the nation. According to Nola.com, Georgia saw 2,698 new HIV diagnoses in 2017, the most recent year data was available, which translates to a rate of 30 people per 100,000. By comparison, Louisiana’s rate dropped from 28.9 in 2016 to 26.6 in 2017.
The post Louisiana experiences major drop in new HIV cases, its lowest in a decade appeared first on theGrio.
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Bail denied for Mississippi man charged with murdering 21-year-old pregnant woman
A Mississippi man, who is the son of a judge, was denied bail on charges that he murdered a young woman and her unborn child.
The Holmes County district attorney said a special appointed judge had to be called in because two justice court judges in the county know the suspect, Terrence K. Sample’s mother, who works as a judge in neighboring Attala County, reported the Jackson Clarion-Ledger. The two judges recused themselves.
Sample, 33, is charged with two counts of murder and one count of kidnapping in the killing of 21-year-old Makayla Winston, whose body was found Monday on a deserted road in the county a few days after her family first reported her missing. She was nine months pregnant, and Mississippi is one of 38 states with a fetal homicide law in place that allows murder charges to be levied against suspects for the death of an unborn child.
READ MORE: D.A. makes decision on Alabama woman charged with manslaughter when she lost baby after being shot
Police believe Winston was Sample’s girlfriend, but he reportedly denies this, and also denies having any connection with Winston. Holmes County Sheriff Willie March said police are questioning another woman, from Attala County, who is also believed to have been in a romantic relationship with Sample. This second woman has not been identified.
According to Holmes County District Attorney Akille Malone-Oliver, one of Sample’s relatives found Winston’s body near his property. Her body was found on State Park Road. Winston’s family told police that she was last seen Thursday night. She told family members that she was going to show the baby’s sonogram to the father but that she never returned. Her due date was Thursday.
In a bail hearing this week, Yazoo County Justice Court Judge Bennie Warrington denied bond for Sample. The next court appearance will likely be for a preliminary hearing, something Sample’s attorney, Richard Carter would have to request, Oliver said.
Sample is being held at the Holmes-Humphreys County Regional Correctional Facility.
March told reporters on Tuesday that he expects that a charge of capital murder will be added against Sample.
The post Bail denied for Mississippi man charged with murdering 21-year-old pregnant woman appeared first on theGrio.
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Did Kamala Harris backpedal a bit on the issue of school busing?
Sen. Kamala Harris appears to have slightly dialed back a comment made at the Democratic presidential debate regarding school busing.
On Wednesday, Harris said she thinks busing should be a decision made by local school districts attempting to desegregate their locations. At the debate, she seemed to support federal intervention to force districts to utilize busing, and sharply criticized former Vice President Joe Biden for his record on the issue.
READ MORE: New 2020 Democratic poll reveals Harris and Warren tied for third place
When reporters asked Harris point blank whether she favors federally mandated busing, after a Democratic Party picnic Wednesday in West Des Moines, Iowa, she responded: “I think of busing as being in the toolbox of what is available and what can be used for the goal of desegregating America’s schools,” according to the Associated Press.
During the debate last week, Harris zinged Biden for opposing federally mandated school busing when he was a senator in the 1970s. Harris told the audience that she was bused in the 1970s as an elementary school student growing up in Berkeley, California, and that busing provided her a great education.
“That’s where the federal government must step in,” Harris said passionately, while eyeing a surprised Biden. The crowd burst in applause.
But on Wednesday, she stated that busing should be an option for local school districts to make.
READ MORE: Kamala Harris scores endorsement from freshman Congresswoman Jahana Hayes
When reporters asked her whether she agrees with federally mandated busing, Harris replied, “I believe that any tool that is in the toolbox should be considered by a school district.”
Biden’s campaign took no time bashing Harris’ comment.
Kate Bedingfield, Biden’s deputy campaign manager, tweeted that Harris isn’t being consistent.
“It’s disappointing that Senator Harris chose to distort Vice President Biden’s position on busing — particularly now that she is tying herself in knots trying not to answer the very question she posed to him!” Bedingfield said.
READ MORE: Biden lands 2020 endorsement from Atlanta Mayor Keisha Lance Bottoms
For his part, Biden insists that he is not against busing, but thinks it should be a decision made by the districts and not forced on them.
During an appearance at a conference last week in Chicago, Biden told the audience he “never, never, never, ever opposed voluntary busing.”
In the 1970s and 80s, Biden was an outspoken critic of federally mandated busing. Back then, he even sponsored a congressional measure that would have imposed funding limits for federal busing.
The post Did Kamala Harris backpedal a bit on the issue of school busing? appeared first on theGrio.
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