Lead and other toxic components of ammunition are crucial in establishing the presence of gunshot residue, or GSR, at crime scenes. However, heavy metals like lead aren’t present in new “green” ammunitions that are changing the rules for GSR analysis, according to Tatiana Trejos, associate professor in the Eberly College of Arts and Sciences Department of Forensic and Investigative Science.

“A major forensics discovery was that, when you fire a gun, a cloud of particles is produced by the primer, the material that explodes and causes a bullet to eject. The primer contains, among other things, inorganic compounds, heavy metals like lead, barium, antimony,” Trejos said.

“When this cloud touches our skin, tiny particles remain there. The composition of those particles is specific to firearm discharge — we don’t commonly find that combination of metals in other conditions. That realization was a big help to forensic scientists in firearms-related investigations.”

But over the years, ammunition has changed. More primers are manufactured without metals harmful to the environment and human health. That’s a challenge for GSR analysis and the reason forensic science — a field that uses scientific methods to help solve crimes and examine trial evidence — is looking beyond inorganic compounds like metals to organic compounds like nitroglycerine that are also released when a gun fires.

“If we combine information about organic and inorganic compounds in GSR, we can have more confidence in our results,” Luis Arroyo, an analytical chemist and associate professor, said. “For over a decade, scientific groups have said we need to know more about organic gunshot residue. We’re missing opportunities to confirm the presence of GSR, and this research funded by the National Institute of Justice is helping to narrow that gap.”

The research establishes how organic and inorganic compounds in GSR differ in the ways they each persist on surfaces and transfer to other surfaces during activities like running, hand shaking or washing.

Trejos and Arroyo published the results of the studies in a Forensic Chemistry paper co-authored with WVU graduate students Courtney Vander Pyl, Kourtney Dalzell, Korina Menking-Hoggatt and Thomas Ledergerber.

To gather data, the team created new and improved organic and inorganic GSR “reference standards” or methodologies for creating standardized mixes of particles that accurately mirror real-world gunshot residue, allowing different labs to meaningfully compare results.

They applied those particles to fabrics, to the skin and hair of real human volunteers and to an artificial skin product called Strat-M. Then they subjected those surfaces to real and simulated activities like running, struggling, washing and rubbing, before measuring the remaining particles.

Trejos said the experiments established Strat-M as a viable substitute for human skin.

“Artificial skin has been used by fields like pharmaceuticals, cosmetics, health sciences. Now we have proved it can provide a consistent forensic standard while allowing us to test conditions that wouldn’t be feasible or safe for a person’s skin.”

The researchers found inorganic GSR particles persist longer on a surface — a palm, a sweatshirt — than organic compounds, but they’re more susceptible to being lost or transferred by common activities. A shooter who washes their hands with soap and water, then dries them with a paper towel, will likely prevent crime scene investigators from identifying GSR based on analysis of lead, barium and antimony particles on their hands.

The fact that inorganic particles persist over time and are significantly lost only due to outside forces can be critical to questions about whether someone is the victim of a suicide or homicide, Trejos said.

Organic compounds, conversely, may be lost from clothing if a suspect struggles during arrest, but they are less likely to transfer to someone else, like the arresting officer.

Up to 100 characteristic inorganic particles could transfer from one person to another during a handshake, compared to no transfer at all for organic compounds. But unlike inorganic particles, organic particles are lost over time due to factors like evaporation from the skin.

Trejos said the next step is to put the findings to use in combination with another methodology the group recently developed, which allows field CSIs to immediately analyze possible GSR at a crime scene.

As enthusiastic as Trejos is about the research, she emphasizes that real-life CSIs don’t have as many answers as the ones on television.

“Right now, we can do a pretty good job answering the question, ‘Is GSR present or not?’ But the next and more interesting question is, ‘Did this person fire the gun?’ Forensics is not always able to answer that with high certainty. This research opens new avenues to answer questions relevant to a judge or jury.

“By providing faster and more informative investigative tools, we’re helping to apprehend offenders with more solid evidence, and we’re minimizing the potential for false incarcerations.”

But when electrons pair up, they can rise above the fray and glide through a material without friction. This “superconducting” behavior occurs in a range of materials, though at ultracold temperatures. If these materials can be made to superconduct closer to room temperature, they could pave the way for zero-loss devices, such as heat-free laptops and phones, and ultraefficient power lines. But first, scientists will have to understand how electrons pair up in the first place.

Now, new snapshots of particles pairing up in a cloud of atoms can provide clues to how electrons pair up in a superconducting material. The snapshots were taken by MIT physicists and are the first images that directly capture the pairing of fermions — a major class of particles that includes electrons, as well as protons, neutrons, and certain types of atoms.

In this case, the MIT team worked with fermions in the form of potassium-40 atoms, and under conditions that simulate the behavior of electrons in certain superconducting materials. They developed a technique to image a supercooled cloud of potassium-40 atoms, which allowed them to observe the particles pairing up, even when separated by a small distance. They could also pick out interesting patterns and behaviors, such as a the way pairs formed checkerboards, which were disturbed by lonely singles passing by.

The observations, reported today in Science, can serve as a visual blueprint for how electrons may pair up in superconducting materials. The results may also help to describe how neutrons pair up to form an intensely dense and churning superfluid within neutron stars.

“Fermion pairing is at the basis of superconductivity and many phenomena in nuclear physics,” says study author Martin Zwierlein, the Thomas A. Frank Professor of Physics at MIT. “But no one had seen this pairing in situ. So it was just breathtaking to then finally see these images onscreen, faithfully.”

The study’s co-authors include Thomas Hartke, Botond Oreg, Carter Turnbaugh, and Ningyuan Jia, all members of MIT’s Department of Physics, the MIT-Harvard Center for Ultracold Atoms, and the Research Laboratory of Electronics.

A decent view

To directly observe electrons pair up is an impossible task. They are simply too small and too fast to capture with existing imaging techniques. To understand their behavior, physicists like Zwierlein have looked to analogous systems of atoms. Both electrons and certain atoms, despite their difference in size, are similar in that they are fermions — particles that exhibit a property known as “half-integer spin.” When fermions of opposite spin interact, they can pair up, as electrons do in superconductors, and as certain atoms do in a cloud of gas.

Zwierlein’s group has been studying the behavior of potassium-40 atoms, which are known fermions, that can be prepared in one of two spin states. When a potassium atom of one spin interacts with an atom of another spin, they can form a pair, similar to superconducting electrons. But under normal, room-temperature conditions, the atoms interact in a blur that is difficult to capture.

To get a decent view of their behavior, Zwierlein and his colleagues study the particles as a very dilute gas of about 1,000 atoms, that they place under ultracold, nanokelvin conditions that slow the atoms to a crawl. The researchers also contain the gas within an optical lattice, or a grid of laser light that the atoms can hop within, and that the researchers can use as a map to pinpoint the atoms’ precise locations.

In their new study, the team made enhancements to their existing technique for imaging fermions that enabled them to momentarily freeze the atoms in place, then take snapshots separately of potassium-40 atoms with one particular spin or the other. The researchers could then overlay an image of one atom type over the other, and look to see where the two types paired up, and how.

“It was bloody difficult to get to a point where we could actually take these images,” Zwierlein says. “You can imagine at first getting big fat holes in your imaging, your atoms running away, nothing is working. We’ve had terribly complicated problems to solve in the lab through the years, and the students had great stamina, and finally, to be able to see these images was absolutely elating.”

Pair dance

What the team saw was pairing behavior among the atoms that was predicted by the Hubbard model — a widely held theory believed to hold they key to the behavior of electrons in high-temperature superconductors, materials that exhibit superconductivity at relatively high (though still very cold) temperatures. Predictions of how electrons pair up in these materials have been tested through this model, but never directly observed until now.

The team created and imaged different clouds of atoms thousands of times and translated each image into a digitized version resembling a grid. Each grid showed the location of atoms of both types (depicted as red versus blue in their paper). From these maps, they were able to see squares in the grid with either a lone red or blue atom, and squares where both a red and blue atom paired up locally (depicted as white), as well as empty squares that contained neither a red or blue atom (black).

Already individual images show many local pairs, and red and blue atoms in close proximity. By analyzing sets of hundred of images, the team could show that atoms indeed show up in pairs, at times linking up in a tight pair within one square, and at other times forming looser pairs, separated by one or several grid spacings. This physical separation, or “nonlocal pairing,” was predicted by the Hubbard model but never directly observed.

The researchers also observed that collections of pairs seemed to form a broader, checkerboard pattern, and that this pattern wobbled in and out of formation as one partner of a pair ventured outside its square and momentarily distorted the checkerboard of other pairings. This phenomenon, known as a “polaron,” was also predicted but never seen directly.

“In this dynamic soup, the particles are constantly hopping on top of each other, moving away, but never dancing too far from each other,” Zwierlein notes.

The pairing behavior between these atoms must also occur in superconducting electrons, and Zwierlein says the team’s new snapshots will help to inform scientists’ understanding of high-temperature superconductors, and perhaps provide insight into how these materials might be tuned to higher, more practical temperatures.

“If you normalize our gas of atoms to the density of electrons in a metal, we think this pairing behavior should occur far above room temperature,” Zwierlein offers. “That gives a lot of hope and confidence that such pairing phenomena can in principle occur at elevated temperatures, and there’s no a priori limit to why there shouldn’t be a room-temperature superconductor one day.”

This research was supported, in part, by the U.S. National Science Foundation, the U.S. Air Force Office of Scientific Research, and the Vannevar Bush Faculty Fellowship.

Operative word: Envisioned.

Scientists at Michigan State University (MSU), University of Waterloo, and University of Alaska Fairbanks report in Climatic Change where vessels are traveling in the ice-covered waters of the Arctic between Alaska and Russia, and what those reports may mean for important wildlife and communities in the region.

“Even with climate change, sea ice is still a substantial barrier to Arctic vessel traffic,” said Kelly Kapsar, a research associate at MSU’s Center for Systems Integration and Sustainability (CSIS). “Sea ice also provides critical habitat for many endemic Arctic species and a hunting platform for Indigenous subsistence hunters. Understanding when and where ships are entering areas of sea ice can help us to better understand potential impacts of vessel traffic in the region.”

Whether its fishing vessels seeking better catches over a longer season, or Russian shipping companies eager for better ways to deliver oil and gas to Chinese customers, increased marine traffic is a given. Whether this traffic occurs only in the open water season, or also in times of ice cover is not.

But the researchers point out the difference between what ships could do as ice changes, and what they will do can be vastly different.

“Up until now projections have been about theoretical ships, such as noting certain vessel types can travel through up to 2 meters of ice,” Kapsar said. “But that’s like saying a car can drive up to 200 mph — just because it can doesn’t mean it will.”

Combining satellite pictures of ice cover with GPS vessel tracking data the team was able to analyze how the ships have been behaving as the shipping passages change. What they’ve found is that many ships are following the ice, fishing close to the edge of ice packs. The researchers also found marked overlap between areas with vessels traveling in sea ice and the overwintering areas for bowhead whales.

Previous research by another group has demonstrated that between 1990 and 2012, some 12% of bowhead whales harvested by Alaska Native subsistence hunters showed signs they had been tangled in fishing gear, and 2% had scars from being struck by vessels. The new analysis points to a growing threat to wildlife which also are using the receding ice as they travel and breed.

Noise from large boats also can disrupt marine mammals. Ships equipped to break ice potentially could strand both animals and people traveling across the frozen expanses. Increased traffic also raises fear of accidents and oil spills. The new pathways are far away from rescue or clean-up crews.

So far, Kapsar said, their work indicates ship travel reflects a certain caution, offering indications that capability is balanced by practical and economic realities. For now.

Kapsar and co-author Jianguo “Jack” Liu are members of MSU’s Ecology, Evolution, and Behavior Program. “Mapping vessel traffic patterns in the ice-covered waters of the Pacific Arctic” also was written by Lawson Brigham and Grant Gunn. The work is funded by the National Science Foundation.

“Prevention strategies for Alzheimer’s and related dementias are urgently needed,” said study author Suzette J. Bielinski, PhD, of the Mayo Clinic in Rochester, Minnesota. “Routine screenings for cholesterol and triglyceride levels are commonly done as part of standard medical care. Fluctuations in these results over time could potentially help us identify who is at greater risk for dementia, help us understand mechanisms for the development of dementia and ultimately determine whether leveling out these fluctuations could play a role in reducing dementia risk.”

Researchers used health care data to identify 11,571 people age 60 or older who did not have a prior diagnosis of Alzheimer’s disease or dementia. Researchers looked at participants’ measurements of total cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL) and high-density lipoprotein cholesterol (HDL) on at least three different days in the five years before the start of the study.

Then researchers divided participants into five equal groups based on how much the measurements fluctuated. The lowest group had the least variation over time and the highest group had the most variation.

Participants were followed for an average of 13 years. During that time, 2,473 people developed Alzheimer’s disease or another form of dementia.

After adjusting for variables that could affect risk of dementia including sex, race, education and lipid-lowering treatments, researchers found for total cholesterol, participants in the highest group had a 19% increased risk of dementia compared to those in the lowest group. Of the 2,311 people in the highest group, 515 developed dementia compared to 483 of the 2,311 people in the lowest group. For triglycerides, those in highest group had a 23% increased risk.

Researchers did not find a link between variations in LDL and HDL and an increased risk of dementia.

“It remains unclear why and how fluctuating levels of cholesterol and triglycerides are related to the risk of Alzheimer’s disease,” said Bielinski. “Further studies looking at the changes over time for this relationship are needed in order to confirm our results and potentially consider preventative strategies.”

A limitation of the study was researchers looked at Alzheimer’s disease and related dementias as a whole and did not differentiate between the types of dementia.

The study was supported by the National Heart, Lung and Blood Institute.