The research team from SLAC, Stanford and other institutions started with what is now a fairly standard technique: They zapped a mixture of ferricyanide and water with an ultraviolet laser and bright X-rays generated by the Linac Coherent Light Source (LCLS) X-ray free-electron laser. The ultraviolet light kicked the molecule into an excited state while the X-rays probed the sample’s atoms, revealing features of ferricyanide’s atomic and electronic structure and motion.

What was different this time is how the researchers extracted information from the X-ray data. Instead of studying only one spectroscopic region, known as the Kβ main emission line, the team captured and analyzed a second emission region, called valence-to-core, which has been significantly more challenging to measure on ultrafast timescales. Combining information from both regions enabled the team to obtain a detailed picture of the ferricyanide molecule as it evolved into a key transitional state.

The team showed that ferricyanide enters an intermediate, excited state for about 0.3 picoseconds — or less than a trillionth of a second — after being hit with a UV laser. The valence-to-core readings then revealed that following this short-lived, excited period, ferricyanide loses one of its molecular cyanide “arms,” called a ligand. Ferricyanide then either fills this missing joint with the same carbon-based ligand or, less likely, a water molecule.

“This ligand exchange is a basic chemical reaction that was thought to occur in ferricyanide, but there was no direct experimental evidence of the individual steps in this process,” SLAC scientist and first author Marco Reinhard said. “With only a Kβ main emission line analysis approach, we wouldn’t really be able to see what the molecule looks like when it is changing from one state to the next; we’d only obtain a clear picture of the beginning of the process.”

“You want to be able to replicate what nature does to improve technology and increase our foundational scientific knowledge,” SLAC senior scientist Dimosthenis Sokaras said. “And in order to better replicate natural processes, you have to know all of the steps, from the most obvious to those that happen in the dark, so to speak.”

In the future, the research team wants to study more complex molecules, such as hemeproteins, which transport and store oxygen in red blood cells — but which can be tricky to study because scientists do not understand all the intermediate steps of their reactions, Sokaras said.

The research team refined their X-ray spectroscopy technique at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) and the LCLS over many years, and then combined all this expertise at the LCLS’s X-ray Correlation Spectroscopy (XCS) instrument to capture the molecular structural changes of ferricyanide. The team published their results today in Nature Communications.

“We leveraged both SSRL and LCLS to complete the experiment. We couldn’t have finished developing our method without access to both facilities and our longstanding collaboration together,” said Roberto Alonso-Mori, SLAC lead scientist. “For years, we have been developing these methods at these two X-ray sources, and now we plan to use them to uncover previously inaccessible secrets of chemical reactions.”

240 study participants viewed an interactive Monet Water Lily art exhibition from Google Arts and Culture. By filling out a questionnaire, they provided information about their state of mind, how much pleasure they felt when looking at the pictures, and how meaningful they considered the experience to be. The results showed significant improvements in mood and anxiety after just a few minutes of viewing.

“Online art viewing is an untapped source of support for well-being that can be consumed as bite-sized bits of meaning-making and pleasure,” says MacKenzie Trupp, first author from the University of Vienna.

The study also found that some participants were more receptive to art than others and were able to benefit more. This advantage could be predicted using a metric called “aesthetic responsiveness.”

“Aesthetic responsiveness describes how people react to diverse aesthetic stimuli, like art and nature. The results showed that individuals with high levels of art and aesthetic responsiveness benefit more from online art viewing due to having more pleasurable and meaningful art experiences,” explains Edward A. Vessel of MPIEA, developer of the Aesthetic Responsiveness Assessment (AReA).

The findings of this study are particularly interesting for people who are unable to visit museums in person, such as those with health problems. Furthermore, the results suggest that interactive art exhibitions and similar online experiences should be designed with an awareness of individual differences in aesthetic responsiveness. The study thus expands insight into the benefits and limitations of art in digital media and points the way for increasing the wellness potential of online art.

“This technology could be useful for a wide range of applications,” said research team member Aurora Maccarone, a Royal Academy of Engineering research fellow from Heriot-Watt University in the United Kingdom. “For example, it could be used to inspect underwater installations, such as underwater wind farm cables and the submerged structure of the turbines. Underwater lidar can also be used for monitoring or surveying submerged archaeology sites and for security and defense applications.”

Obtaining 3D images through ocean water can be challenging because it is light-limited, and any particles in the water will scatter light and distort the image. However, single-photon detection, which is a quantum-based technique, allows very high penetration and works even in low-light conditions.

In the Optica Publishing Group journal Optics Express, researchers from Heriot-Watt University and the University of Edinburgh describe experiments in which an entire single-photon lidar system was submerged in a large water tank. The new demonstrations bring the technology closer to practical applications compared to the research team’s earlier experiments with underwater single-photon detection, which were performed in carefully controlled laboratory conditions with the optical setup placed outside the water tank and data analysis performed offline. They also implemented new hardware and software developments that allow the 3D images acquired by the system to be reconstructed in real time.

“This work aims to make quantum detection technologies available for underwater applications, which means that we will be able to image the scene of interest in very low light conditions,” said Maccarone. “This will impact the use of offshore cable and energy installations, which are used by everyone. This technology could also allow monitoring without the presence of humans, which would mean less pollution and a less invasive presence in the marine environment.”

Faster low-light detection

Lidar systems create images by measuring how long it takes laser light to be reflected from objects in the scene and travel back to the system’s receiver, known as the “time of flight.” In the new work, the researchers sought to develop a way to acquire 3D images of targets that are obscured by turbid water and thus not visible to conventional lidar imaging systems.

They designed a lidar system that uses a green pulsed laser source to illuminate the scene of interest. The reflected pulsed illumination is detected by an array of single-photon detectors, which allows ultrafast low light detection and greatly reduces measurement time in photon-starved environments such as highly attenuating water.

“By taking time-of-flight measurements with picosecond timing resolution, we can routinely resolve millimeter details of the targets in the scene,” said Maccarone. “Our approach also allows us to distinguish the photons reflected by the target from those reflected by particles in the water, making it particularly suitable to performing 3D imaging in highly turbid waters where optical scattering can ruin image contrast and resolution.”

The fact that this approach requires thousands of single-photon detectors, all producing many hundreds of events per second, makes it extremely challenging to retrieve and process the data necessary to reconstruct the 3D image in a short time, especially for real-time applications. To solve this problem, the researchers developed algorithms specifically for imaging in highly scattering conditions and applied them in conjunction with widely available graphics processing unit (GPU) hardware.

The new technique builds on some important technological advances. “Heriot-Watt University has a long track record in single-photon detection techniques and image processing of single-photon data, which allowed us to demonstrate advanced single?photon imaging in extremely challenging conditions,” said Maccarone. “The University of Edinburgh has achieved fundamental advances in the design and fabrication of single-photon avalanche diode detector arrays, which allowed us to build compact and robust imaging systems based on quantum detection technologies.”

Underwater testing

After optimizing the optical setup on a laboratory optical bench, the researchers connected the lidar system to a GPU to achieve real-time processing of the data while also implementing a number of image processing approaches for three-dimensional imaging. Once the system was working properly, they moved it to a tank that was 4 meters long, 3 meters wide, and 2 meters deep.

With the system submerged in the water, the researchers added a scattering agent in a controlled manner to make the water more turbid. Experiments at three different turbidity levels demonstrated successful imaging in controlled highly scattering scenarios at distances of 3 meters.

“Single-photon technologies are rapidly developing, and we have demonstrated very promising results in underwater environments,” said Maccarone. “The approach and image processing algorithms could also be used in a wider range of scenarios for improved vision in free space such as in fog, smoke or other obscurants.”

The researchers are now working to reduce the size of the system so that it could be integrated into an underwater vehicle.Through the UK Quantum Technology Hub Network and InnovateUK, the researchers are partnering with industry to make the technology accessible for a range of underwater applications.

Five of the 60 beverages tested contained levels of a toxic metal above federal drinking water standards, according to the study from Tulane University. Two mixed juices had levels of arsenic above the 10 microgram/liter standard. A cranberry juice, a mixed carrot and fruit juice and an oat milk each had levels of cadmium exceeding the 3 parts per billion standard.

The sampled beverages, which included those commonly found in grocery stores — single and mixed fruit juices, plant-based milks, sodas, and teas — were measured for 25 different toxic metals and trace elements. Mixed-fruit juices and plant-based milks (such as oat and almond) contained elevated concentrations of toxic metals more often than other drinks, according to the findings published in the Journal of Food Composition and Analysis.

All told, seven of the 25 elements exceeded drinking water standards in some of the drinks, including nickel, manganese, boron, cadmium, strontium, arsenic, and selenium. While lead was detected in more than 93% of the 60 samples, most contained very low levels, below 1 part per billion. The highest level (6.3 micrograms/kg ) was found in a lime sports drink, though that’s below both EPA and WHO standards for drinking water.

Tewodros Godebo, lead author and assistant professor of environmental health sciences at Tulane University School of Public Health and Tropical Medicine, said the study was important because there are few peer-reviewed studies examining the contents of American beverages.

“It was surprising that there aren’t a lot of studies out there concerning toxic and essential elements in soft drinks in the United States,” Godebo said. “This creates awareness that there needs to be more study.”

These soft drinks are often consumed in smaller quantities than water, meaning the health risks for adults are most likely low. But Godebo said parents should be cautious about what drinks they offer their children.

“People should avoid giving infants and young children mixed-fruit juices or plant-based milks at high volume,” Godebo said. “Arsenic, lead, and cadmium are known carcinogens and well established to cause internal organ damage and cognitive harm in children especially during early brain development.”

Godebo said most of these elements found in beverages presumably come from contaminated soil.

“These metals are naturally occurring so it’s hard to get rid of completely,” Godebo said.

Hannah Stoner and Julia Ashmead, Tulane University students who participated in the study, said they hope the findings encourage people to think more about what they consume.

“I don’t think there needs to be fear,” Stoner said. “In toxicity, it’s the dosage that often makes the difference so everything in moderation. But this creates awareness that there needs to be more study.”

Godebo said the next step is to conduct a risk assessment based on the data collected to see the impacts of consuming toxic metals in children and adults.

“We are curious to keep exploring what’s in our drinks and foods commercially sold to the consumers,” Godebo said.