In a recent study, scientists at Cornell University propose a novel method by which nanoscale light can be manipulated and transported. These special modes of light transport are known to arise at finely tuned interfaces between slightly different nanomaterials. Minwoo Jung, lead researcher on this study, illustrates this concept through a simple analogy: “A floating tube has a hole in the middle, but a normal balloon doesn’t. No matter how you squeeze the round balloon, it cannot be reshaped like a donut-at least not without popping the balloon, re-knitting the rubber, and re-injecting the air. Thus, a tube and a balloon are distinct in their topology because they are not connected through a smooth deformation.”

Jung further explains that physicists have been interested in gluing two topologically distinct materials side by side so that one of them acts like a balloon and the other like a tube. This means that, at their interface, a process that connects these two materials must occur, much like the poking/popping/re-knitting/re-injecting from a balloon to a tube. Under the right conditions, this process can give rise to a strong channel for transmitting energy or information along the interface. Because this process can be applied to light (which acts as a carrier of energy or information), this branch of physics is called topological photonics.

Jung and his team combined the fascinating concept of topological photonics with an innovative technique that traps light in an atomically thin material. This method brought together two rapidly emerging fields in applied and fundamental physics: graphene nanolight and topological photonics. Jung says, “Graphene is a promising platform for storing and controlling nanoscale light and could be key in the development of on-chip and ultracompact nanophotonic devices, such as waveguides and cavities.”

The research team ran simulations involving a graphene sheet layered on a nanopatterned material that functions as a metagate. This honeycomb-like metagate consists of a solid layer of material with holes of different sizes, centered at the vertices of the hexagons. The varying radii of these holes affect the way in which the photons pass through the material. The scientists found that strategically “gluing” together two different metagates creates a topological effect that confines photons at their interface in a predictable, controllable manner.

Different choices of metagate designs demonstrate the dimensional hierarchy of the device’s topology. Specifically, depending on the metagate geometry, nanolight can be made to flow along one-dimensional edges of the topological interface or can be topologically stored at zero-dimensional (point-like) vertices. Moreover, the metagate allows for on-and-off electric switching of these waveguides or cavities. Such battery-operated topological effects can benefit the technological adoption of topological photonics in practical devices.

Jung’s team is optimistic that the synergistic combination of graphene nanolight and topological photonics will spur advances in relevant research areas, like optics, material sciences, and solid-state physics. Their graphene-based material system is simple, efficient, and suitable for nanophotonic applications: a step forward in harnessing the full potential of light.

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Materials provided by SPIE–International Society for Optics and Photonics. Note: Content may be edited for style and length.

Researchers found that air pollution was a “risk factor for a risk factor” that contributed to the common soil of other fatal problems like heart attack and stroke. Similar to how an unhealthy diet and lack of exercise can lead to disease, exposure to air pollution could be added to this risk factor list as well.

“In this study, we created an environment that mimicked a polluted day in New Delhi or Beijing,” said Sanjay Rajagopalan, MD, first author on the study, Chief of Cardiovascular Medicine at University Hospitals Harrington Heart and Vascular Institute, and Director of the Case Western Reserve University Cardiovascular Research Institute. “We concentrated fine particles of air pollution, called PM_2.5 (particulate matter component < 2.5 microns). Concentrated particles like this develop from human impact on the environment, such as automobile exhaust, power generation and other fossil fuels.”

These particles have been strongly connected to risk factors for disease. For example, cardiovascular effects of air pollution can lead to heart attack and stroke. The research team has shown exposure to air pollution can increase the likelihood of the same risk factors that lead to heart disease, such as insulin resistance and type 2 diabetes.

In the mouse model study, three groups were observed: a control group receiving clean filtered air, a group exposed to polluted air for 24 weeks, and a group fed a high-fat diet. Interestingly, the researchers found that being exposed to air pollution was comparable to eating a high-fat diet. Both the air pollution and high-fat diet groups showed insulin resistance and abnormal metabolism — just like one would see in a pre-diabetic state.

These changes were associated with changes in the epigenome, a layer of control that can masterfully turn on and turn off thousands of genes, representing a critical buffer in response to environmental factors. This study is the first-of-its-kind to compare genome-wide epigenetic changes in response to air pollution, compare and contrast these changes with that of eating an unhealthy diet, and examine the impact of air pollution cessation on these changes.

“The good news is that these effects were reversible, at least in our experiments” added Dr. Rajagopalan. “Once the air pollution was removed from the environment, the mice appeared healthier and the pre-diabetic state seemed to reverse.”

Dr. Rajagopalan explains that if you live in a densely polluted environment, taking actions such as wearing an N95 mask, using portable indoor air cleaners, utilizing air conditioning, closing car windows while commuting, and changing car air filters frequently could all be helpful in staying healthy and limiting air pollution exposure.

Next steps in this research involve meeting with a panel of experts, as well as the National Institutes of Health, to discuss conducting clinical trials that compare heart health and the level of air pollution in the environment. For example, if someone has a heart attack, should they be wearing an N95 mask or using a portable air filter at home during recovery?

Dr. Rajagopalan and his team believe that it is important to address the environment as a population health risk factor and continue to diligently research these issues. The authors also note that these findings should encourage policymakers to enact measures aimed at reducing air pollution.

Affirmative action is a contentious issue across the globe, hotly debated in countries such as India, Sri Lanka, Malaysia, Nigeria and Brazil, as well as in the United States. While the direct effects of affirmative action on college admissions are well known, new evidence from India shows that affirmative action has indirect benefits on the behavior of underrepresented high school students, who tend to stay in school longer when they know higher education is within reach.

In a new University of California San Diego study published in the Review of Economics and Statistics, researchers find minority students attain 0.8 additional years of education where affirmative action policies are in place. The study underscores previous theoretical work on affirmative action that shows the opportunity to be admitted to college may motivate students to graduate from high school, according to the study’s author, Gaurav Khanna, assistant professor of economics at UC San Diego’s School of Global Policy and Strategy.

“In the policy space, people have made claims that affirmative action lowers standards and the learning gains for underrepresented students who will ‘no longer work as hard.’ My research suggests the opposite,” Khanna said. “Affirmative action makes going to a good college much more attainable, and actually encourages minority groups to work harder to get into such schools. Without affirmative action, many colleges may not appear attainable, and it may discourage students from even trying.”

India’s federal government instituted affirmative action policies in 1993, reserving 27% of government jobs that are highly sought after for Other Backward Classes (OBCs) — a collective term used by the country’s government to classify castes which are educationally or socially disadvantaged. In 2006, reservations in colleges were implemented.

Other research shows how these affirmative action policies in India increased the representation of minority groups in top colleges, and how the graduates went on to perform well in college and in the subsequent labor market. However, the UC San Diego study explores if affirmative action incentivizes students to stay in school by looking at the educational attainment at pre-collegiate levels.

To answer the question, Khanna compiled a number of data sources, including the Indian National Sample Survey (NSS) to map the trends in educational attainment by birth cohort and social group. Those born before 1976 would be over the age of 18 by the time the federal government policy was implemented in 1994. Thus, he looked at education levels of minority students in this cohort and compared them to education levels attained by OBCs before the affirmative action policies were enacted.

The results show that after affirmative action policies were implemented, there was a marked increase in OBCs’ educational attainment. While non-minorities were still more likely to pursue more education, wide-scale affirmative action helped bridge the education gap by about 40% over a decade and a half.

“The evidence suggests that aspirations respond to such laws and additional research also shows that if peers are seen to benefit from this policy, then a role model effect may encourage educational attainment,” Khanna writes.

While affirmative action is a federal law in India, each state chooses a different level of application. This is defined by the fraction of seats reserved at universities and government job openings reserved for minorities, compared to their population in that state. For example, in the state of Karnataka the policy is stronger with more seats reserved in jobs and colleges, relative to the OBC population. Conversely, in the state of Madhya Pradesh fewer jobs and college seats are reserved for OBCs, as a fraction of their population. Khanna finds that states that had a higher intensity of affirmative action, in terms of the fraction of seats reserved per OBC, saw a sharper increase in the educational attainment of minorities.

Affirmative action: a contentious policy both at home and abroad

Today, in India these policies are an integral part of political platforms and election campaigns; the media covers the policies extensively, and any policy change is met with protests from different factions.

Similarly, in the U.S., the issue is divisive. For example, the Trump administration announced in 2018 that it was abandoning the Obama administration policies that called on universities to consider race as a factor in diversifying campuses. Education Secretary Betsy DeVos stated that “schools should continue to offer equal opportunities for all students.”

Given the debate in both countries, the other question Khanna sought to answer: is this educational response from the minority groups rational in terms of the expected costs and benefits?

With education levels being important for the qualification criteria for government jobs in India, Khanna found that between 2000 and 2005, the fraction of OBCs in public sector jobs rose from 22% to 27%. These jobs are extremely lucrative, especially in rural areas, where they guarantee benefits and job security. As such, increases in the likelihood of getting such jobs can greatly influence the decision made by minority groups.

Khanna writes, “Yet even for members of the minority group who do not get government jobs, an increase in education may translate into benefits (like better health) and high wages as the estimated returns to education in developing countries are between 6% and 13%.”

He concluded, “Indeed, lowering educational inequalities — and possibly wealth inequalities — may be intrinsically valuable to policymakers. In light of these results, policymakers should consider the externalities of affirmative action policies when designing them.”