Materials can behave in unexpected ways after absorbing light. In some cases, light pushes them into photoinduced states with properties that are very different from those they display under ordinary conditions. These states give researchers another way to alter material behavior beyond conventional approaches such as heating or cooling. Learning exactly how they form could be important for developing future photoresponsive materials and advanced optical technologies.

Capturing a Transformation in Femtoseconds

One of the biggest challenges is speed. The first steps in forming a photoinduced state can unfold on the femtosecond (fs) timescale (a millionth of a billionth of a second), making them exceptionally difficult to observe.

To investigate these earliest moments, a team led by Assistant Professor Tadahiko Ishikawa from the Department of Chemistry, School of Science, Institute of Science Tokyo (Science Tokyo), Japan, worked with then doctoral student Samiran Banu (currently a Special Postdoctoral Researcher at RIKEN) and collaborators at Tohoku University and Nagoya Institute of Technology, Japan.

The researchers focused on a metal-organic framework (MOF), a material constructed by connecting metal ions with organic molecules. Their goal was to determine exactly how a photoinduced hidden state develops. The findings were published in the journal Physical Review Letters.

“We found that the photoinduced hidden state forms within 30 fs through a previously unknown intermediate electronic state,” says Ishikawa.

Ultrafast Lasers Reveal a Hidden State

To follow the transformation, the researchers used time-resolved reflectance spectroscopy and ultrashort laser pulses lasting only six fs. The method allowed them to measure how the light reflected by the material changed almost immediately after the MOF absorbed a laser pulse.

With this extremely fine time resolution, the team tracked rapid changes in the material’s electronic behavior. Within 30 fs, its reflectance spectrum shifted dramatically and developed features linked to the appearance of a new optical absorption band. Those changes indicated that the photoinduced hidden state had formed.

Experiments alone, however, could not fully explain what was happening. The researchers therefore combined their measurements with theoretical calculations to reconstruct the sequence of events inside the material.

A Fleeting Electronic State Comes First

The analysis showed that immediately after absorbing light, the material briefly entered an intermediate electronic state. During this moment, electronic bonds between neighboring sites alternated between stronger and weaker in a repeating pattern. This configuration is known as a bond-order wave state.

The state existed only briefly. It was followed by small movements in the positions of atoms within the material, and those structural changes ultimately produced the photoinduced hidden state.

Theoretical calculations also suggested that the newly formed state may be polar. In such a state, positive and negative electrical charges are distributed unevenly across the material. If these photoinduced polar states can be reliably created and controlled, they could provide new ways to manipulate electronic properties using light.

“By revealing intermediate states, our method could help design materials that can be efficiently controlled using light,” explains Ishikawa.

Toward Materials Controlled by Light

Beyond showing how a photoinduced hidden state develops, the research points to a possible strategy for manipulating material properties with extremely short pulses of light. Being able to create and control these temporary states could contribute to new photoresponsive materials designed for high-speed electronics, optoelectronic devices, and other technologies that require precise control over how materials behave.

Future research could extend the same experimental and theoretical approach to other types of materials. By exposing the previously invisible steps that occur during ultrafast transformations, scientists may move closer to designing materials whose properties can be deliberately and efficiently controlled with light.

A new study published in Frontiers in Materials is helping fill that gap. Researchers in France and Croatia analyzed the protective coating on the Roman Republic shipwreck Ilovik-Paržine 1, which sank about 2,200 years ago off the coast of what is now Croatia.

“In archaeology, little attention is paid to organic waterproofing materials. Yet they are essential for navigation at sea or on rivers and are true witnesses of past naval technologies,” said first author Dr. Armelle Charrié, an archaeometrist at the Laboratory of Mass Spectrometry of Interactions and Systems in Strasbourg. “Studying the coatings, we found two different kinds on this vessel: one made of pine tar, also called pitch, and the other of a mixture of pine tar and beeswax. Analysis of pollen in the coating made it possible to identify the plant taxa present in the immediate environment during the construction or repairs of the ship.”

Pine Tar and Beeswax Protected the Hull

The wreck was discovered in 2016, and both the vessel and its cargo have been investigated several times since then. This study is the first to combine molecular and pollen analysis to identify the ship’s coatings and reconstruct the vegetation present when those materials were produced and applied to the hull.

The research was carried out through a collaboration between the Department for Underwater Archaeology of the Croatian Conservation Institute and the ‘ADRIBOATS’ program of the Centre Camille Jullian at Aix-Marseille University in France.

“Some regions throughout the Adriatic have particular characteristics that led local populations to develop a specific shipbuilding style,” said Charrié. “Only studies like ours offer an overview of these traditions which bear witness to genuine know-how and diverse traditions.”

To investigate the coatings, the researchers performed structural, molecular, and pollen analyses. They used methods including mass spectrometry, which can identify and measure unknown substances within complex organic mixtures.

The team analyzed 10 coating samples to determine the biological origins of the natural materials used on the vessel. Molecular fingerprinting revealed compounds associated with pine trees, showing that every sample was dominated by heated coniferous resin or coniferous tar, also called pitch.

One sample, however, contained a different formulation made from beeswax and tar. This mixture – known to Greek shipbuilders as zopissa – improves the adhesive’s flexibility and is easier to apply when hot.

Ancient Pollen Preserved in Sticky Pitch

Because pitch is naturally sticky, it can capture pollen from nearby vegetation and preserve it for long periods. By studying the types of pollen trapped in the coatings and measuring their relative abundance, the researchers were able to narrow down where some of the pitch may have been produced or reapplied during repairs.

The pollen recovered from Ilovik-Paržine 1 pointed to a wide range of environments. Some came from landscapes typical of Mediterranean and Adriatic coasts and valleys, including forests of holly oak and pine as well as matorral – a kind of Mediterranean shrubland – where olive and hazel trees grow.

Alder and ash pollen indicated vegetation associated with riverbanks and seashores, which occur along the coast and in the nearby hinterland. Small amounts of fir and beech were also present. These trees are associated with mountainous terrain and are characteristic of the north-eastern Adriatic coast, where the mountain ranges of Istria and Dalmatia lie relatively close to the sea.

Evidence of Repeated Repairs Across the Adriatic

The analysis also suggests that the vessel received four to five separate batches of coating over time. The stern and central section appear to have been covered with the same material, while researchers identified three distinct coating batches at the bow.

That pattern may indicate that the ship was repaired repeatedly, with materials obtained from different locations around the Mediterranean.

Earlier research on the vessel’s ballast pointed to Brundisium – today Brindisi – on the south-eastern coast of Italy as the place where the ship was built. The new pollen evidence suggests that some of its coatings may also have been applied in that area.

Other layers, however, may have been added along the north-eastern Adriatic coast, close to where the wreck was ultimately found.

“While it seems obvious that ships sailing long distances need repairs, it’s simply not easy to demonstrate this,” concluded Charrié. “Pollen has been very useful in identifying different coatings where the molecular profiles were identical.”

The study, published in Molecular Psychiatry, was led by senior authors Avram Holmes, associate professor of psychiatry at Robert Wood Johnson Medical School and core faculty member of the Center for Advanced Human Brain Imaging Research within the Rutgers Brain Health Institute, and Rajiv Radhakrishnan, associate professor of psychiatry and radiology and biomedical imaging at Yale University. First author Sidhant Chopra, formerly a postdoctoral fellow in the Holmes Lab, is a McKenzie Research Fellow at Orygen, Australia’s Centre of Excellence in Youth Mental Health, and the University of Melbourne in Australia.

Measuring the Brain’s Synaptic Connections

Synapses are tiny junctions that allow brain cells to communicate with one another across neural circuits. Problems involving these connections are believed to play a role in the cognitive and emotional symptoms of schizophrenia. Until now, however, scientists have had a limited understanding of exactly where synaptic loss occurs in the brains of living people because conventional imaging methods such as magnetic resonance imaging cannot specifically measure synapses.

The research involved 122 people, including 29 diagnosed with schizophrenia, making it one of the largest synaptic density PET imaging studies conducted so far. Compared with healthy participants, people with schizophrenia showed a pronounced and widespread reduction in synaptic connections across several parts of the brain. These included frontal and temporal regions as well as areas involved in memory and emotion. The loss was also considerably greater on the left side of the brain than on the right.

Researchers found that this synaptic pattern did not match the changes in brain volume typically seen with standard MRI scans. That distinction suggests synaptic loss and changes in brain volume may reflect separate biological processes rather than two imaging methods capturing the same underlying change.

A Molecular Pattern Behind Synaptic Loss

The team also discovered that the brain regions showing the greatest synaptic losses tended to contain high concentrations of receptors for important neurotransmitters, including serotonin, gamma-aminobutyric acid and glutamate. The finding suggests that the molecular characteristics of individual brain regions may influence how vulnerable they are to changes associated with schizophrenia.

To explore how synaptic loss might move through the brain, the researchers used computer simulations based on the brain’s structural connections. Their modeling identified an area in the left frontal lobe as a likely starting point from which synaptic loss could spread into connected regions.

“These findings suggest that in schizophrenia, synaptic loss is not random,” Chopra said. “Rather, it follows the brain’s molecular and connectivity architecture, which could eventually help identify where and how to intervene.”

“This detailed mapping of synaptic vulnerability could eventually help identify where and how to intervene to preserve or restore brain function, such as emerging therapies to prevent and regrow synapses,” Holmes added.

Toward More Precise Schizophrenia Treatments

The researchers said future work will build on these results by investigating how synaptic loss changes over time and how it responds to clinical treatments. A better understanding of that progression could ultimately help researchers develop more precise and personalized approaches to schizophrenia care.

The research was led by Prof. Shudong Wang of the Aerospace Information Research Institute of the Chinese Academy of Sciences (AIRCAS). The team sought to overcome two major obstacles to understanding groundwater in the region: limited on-the-ground data and the extremely complex mountainous landscape. The findings were recently published in Environmental Research Letters.

AI and Satellites Reveal Two Decades of Change

To build a clearer picture of what is happening underground, the researchers created an artificial intelligence (AI) powered assessment model that combines observations from multiple satellites, Earth system modeling, and explainable AI.

Using this approach, they reconstructed about 20 years of groundwater storage (GWS) changes across High Mountain Asia. The system also helped identify the main forces driving those changes and allowed the researchers to explore how groundwater risks could develop under future scenarios.

The results show that roughly two-thirds of HMA experienced declining groundwater storage between 2003 and 2020. The largest losses occurred in heavily populated downstream basins where irrigation demands are high, including the Ganges-Brahmaputra, Indus and Amu Darya basins. Some inland areas at higher elevations, however, experienced localized increases in groundwater storage.

Climate and Human Water Use Drive the Decline

Climate-related forces explain nearly half of the observed variation in GWS, with changes involving the cryosphere playing an especially important role.

At the same time, human withdrawals of groundwater have become an increasingly significant source of depletion, particularly in downstream agricultural regions that rely heavily on irrigation. The influence of human water use became even more pronounced after 2010.

Researchers also project that groundwater losses will continue if current patterns of water use remain in place. In some locations, increased glacier melt could temporarily reduce the pace of groundwater decline around the 2060s. But this “buffer effect” cannot continue indefinitely and is expected to be followed by faster losses.

If present water use patterns do not change, groundwater depletion could accelerate further, increasing the threat to agricultural areas downstream that depend on these reserves.

A New Way to Track Groundwater in Mountain Regions

For the analysis, the researchers used a framework guided by existing scientific knowledge while also drawing on large amounts of observational data. Information from multiple satellite sensors was used to estimate GWS changes over the past 20 years.

The framework incorporates a lightweight Transformer architecture designed to account for hydrological memory and delayed effects within mountainous catchments. The researchers also used explainable machine learning methods to determine the physical factors associated with the groundwater changes identified by the system.

To test the reliability of the results, the team compared its findings with thousands of measurements from groundwater wells as well as independent datasets. Those comparisons provided additional support for the study’s conclusions.

By combining remote sensing observations, established hydrological knowledge, and interpretable AI methods, the framework helps address long-standing difficulties in studying High Mountain Asia, including rugged terrain and incomplete information about human water use.

The research was funded by the National Key R&D Program of China and the Key Program of the National Natural Science Foundation of China (NSFC).