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Significant earthquakes, from gentle shaking to devastating tremors, are hazards caused by a sudden release of stress that has built up in geological faults. More subtle events called slow slips are attracting increasing attention as nonshaky versions of the dramatic seismic fractures of the largest earthquakes.

A database of information on previous slow slips to develop a model of the mechanisms of these geological events has now been compiled by KAUST and University of Geneva researchers, in collaboration with colleagues at ETH Zürich in Switzerland, GFZ in Germany and the University of Bologna in Italy.

Slow slips, also known as silent earthquakes, are fractures of the Earth's crust that propagate very slowly without producing seismic waves. They typically proceed over a few weeks or months, and their duration can range from less than a day to more than a year.

"Slow slips alone pose no threat since they don't generate shaking and therefore cause no damage or disruption to properties, but they cause disturbances that can trigger regular earthquakes nearby," says Luigi Passarelli, formerly of KAUST and now in ETH Zürich.

The potential of triggering regular earthquakes is one reason why researchers are keen to learn more about slow slip events. Another reason is that they come with smaller tremors or sometimes a flurry of small earthquakes, a so-called seismic swarm, in a process not yet fully understood.

Slow slip events occur in many regions where tectonic plates collide and slide but especially in subduction zones around Japan, New Zealand and North and Central America. They also occur near volcanoes such as Mt. Etna in Italy and Kilauea in Hawaii.

 "We have compiled the first systematic catalogue of the aseismic and seismic characteristics of slow slip events to better understand the physical mechanisms that generate both," says Passarelli. He adds that this was a big challenge as the data are not all consistently archived or readily available.

The results have allowed the team to assess the correlation between the characteristics of each slow event and the triggered tremor activity, as size and duration, and the likely immediate and possible long-term consequences. This information can now be used to improve a model to predict the changes and hazards associated with specific types of event.

"We have made a step toward an improved understanding of the processes that control slow slips and seismic tremors, although there is more to investigate," says Passarelli. The researchers hope that their database and modeling can be developed further to build a better understanding of those complex processes.

- KAUST Discovery

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​Super-thin carbon molecular sieve (CMS) membranes may not be best for separating industrially important chemical mixtures. However, ensuring the CMS film thickness is just right could enable more energy-efficient purification of chemical products, KAUST researchers have shown.

CMS membranes, as their name suggests, can purify mixtures of liquids or gases by permitting only certain molecules to pass through their subnanometer-sized pores. Currently, the chemical industry mainly uses heat-based processes such as distillation to separate product mixtures, but these processes consume about 10 percent of global energy output. "This situation is highly unsustainable," says Wojciech Ogieglo, a research scientist at KAUST. "We believe that a good portion of these energy-intensive separations could be replaced by much more environmentally friendly membrane separations."

 CMS membranes are created by depositing a layer of carbon-rich polymers on to a suitable support, then applying heat to convert the polymer into a microporous CMS film. "CMS materials display by far the best performance for a wide variety of highly energy-intensive membrane-based gas separation applications," says group leader Ingo Pinnau.

"These materials are also particularly chemically robust," notes Ogieglo. "They are promising for situations such as plastics production or greenhouse gas capture because they perform reliably even in very harsh chemical environments and at high temperatures," he says.

One aspect of CMS membrane research is to optimize the CMS film thickness to minimize the energy required to separate a chemical mixture. "Intuitively, one could think that the thinner the membrane, the better," Ogieglo says. A thinner CMS layer would be expected to pose the least transport resistance to molecules passing through its pores. However, the team found that when they created sub-50 nanometer CMS films, the CMS layer was very compact with low microporosity. "Such extremely thin films turn out to pose much more transport resistance than expected," Ogieglo says. Thicker 300 nanometer CMS films had significantly higher microporosity, the team showed.

"We believe that there must be a sweet spot in the thickness range — not too thin, not too thick — where the membrane performance is optimal," Ogieglo says. "We are currently trying to find out where this sweet spot lies for different types of membrane materials."

"The results will feed into the team's wider efforts to create scalable, industry-ready CMS separation membranes," Pinnau says. "We are currently scaling up the production of CMS composite membranes to test their performance and long-term stability in membrane modules," he adds.

- KAUST Discovery

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A new organic (carbon-based) semiconducting material has been developed that outperforms existing options for building the next generation of biosensors. An international research team led by KAUST is the first to overcome some critical challenges in developing this polymer.

Much research effort is currently expended into novel types of biosensors that interact directly with the body to detect key biochemicals and serve as indicators of health and disease.

"For a sensor to be compatible with the body, we need to use soft organic materials with mechanical properties that match those of biological tissues," says Rawad Hallani, a former research scientist in the KAUST team, who developed the polymer along with researchers at several universities in the U.S. and the U.K.

Hallani explains that the polymer is designed for use in devices called organic electrochemical transistors (OECTs). For these types of devices, the polymer should allow specific ions and biochemical compounds to permeate into the polymer and dope it, which in turn can modulate its electrochemical semiconducting properties. "The fluctuation in the electrochemical properties is what we are actually measuring as an output signal of the OECT," he says.

The team had to confront several chemical challenges because even minor changes in the polymer's structure can have a significant impact on performance. Many other research groups have tried to make this particular polymer, but the KAUST team is the first to succeed.

Their innovation is based on polymers called polythiophenes with chemical groups called glycols attached in precisely controlled positions. Learning how to control the locations of the glycol groups in ways not previously achieved was a key aspect of the breakthrough.

"Identifying the right polymer design to fit all the criteria that you are looking for is the tough part," says Hallani. "Sometimes what can optimize the performance of the material can negatively affect its stability, so we need to keep in mind the energetic as well as the electronic properties of the polymer."

Sophisticated computational chemistry modeling was used to help achieve the right design. The team was also aided by specialized x-ray scattering analysis and scanning tunneling electron microscopy to monitor the structure of their polymers. These techniques revealed how the location of the glycol groups affected the material's microstructure and electronic properties.

"We are excited by the progress Rawad made on the polymer synthesis, and we are now looking forward to testing our new polymer in specific biosensor devices." says Iain McCulloch of the KAUST team, who is also attached to the University of Oxford in the U.K.

McCulloch says that the research group is now trying to improve the stability of their polymers and the sensors built from them, as they move from laboratory demonstrations toward real world applications. 

- KAUST Discovery

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As our society and transportation systems become increasingly electrified, scientists worldwide are seeking more efficient and higher capacity storage systems. Researchers at KAUST have made an important contribution by modifying lithium-sulfur (Li-S) batteries to suppress a problem known as polysulfide shuttling.

"The bottleneck in the utilization of renewable energy, especially in transportation, is the need for high-density batteries," says Eman Alhajji, Ph.D. student and first author of the research paper.

Li-S batteries have several potential advantages over the most commonly used types of batteries. They have a higher theoretical energy storage capacity and sulfur is a nontoxic element readily available in nature. Sulfur is also a waste product of the petrochemical industry, so it could be obtained relatively cheaply while increasing the sustainability of another industry.

Polysulfide shuttling involves the movement of sulfur-containing intermediates between the cathode and anode during the battery's chemical processes. This seriously degrades the capacity and recharging ability of the Li-S battery technologies that have been explored to date.

 The KAUST team's solution is based on a layer of graphene. They make this by subjecting a polyimide polymer to laser energy in a process called laser scribing, creating a suitably structured porous material. A key feature is that the material is hierarchically porous in three dimensions, meaning it has an array of pores of different sizes. Nano-sized carbon particles are then added and taken up by the pores to form the final product.

Alhajji and her colleagues found that placing a thin layer of this material between the cathode and anode of a Li-S battery significantly suppresses the polysulfide shuttling.

"Making this freestanding interlayer just a few micrometers thick was a challenge," says Alhajji, adding, "It was fun to roll it like playdough, but then I had to handle it in a very gentle manner, especially during battery assembly."

 Until now, most options proposed to solve the polysulfide shuttling problem have suffered from limitations that make them unsuitable for large-scale commercial application. In contrast, the laser-scribed graphene developed at KAUST is produced by a method that the researchers describe as "scalable and straightforward."

Alhajji won a 2021 Materials Research Society Best Poster Award based on her idea for suppressing the shuttling. "This is a really challenging competition," says Alhajji's supervisor Husam Alshareef, adding, "Only a handful of students from the Materials Science & Engineering program at KAUST have won this award."

- KAUST Discovery

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KAUST Professor of Earth Science and Engineering, Martin Mai, has been named Editor-in-Chief of Bulletin of the Seismological Society of America (BSSA).

First published in 1911, BSSA is the premier journal of advanced research in earthquake seismology and related disciplines. BSSA publishes original papers advancing our understanding of seismology and seismic hazard analyses, as well as review articles summarizing important research topics. The journal's format allows papers to fully explore research topics in detail.

For further information, please visit

https://www.seismosoc.org/news/p-martin-mai-named-bssa-editor-in-chief/

https://www.seismosoc.org/publications/bssa/

Research

Professor Mai's research addresses the physics of earthquakes and the complexity of earthquake phenomena, with focus on earthquake-source imaging, dynamic rupture modeling, and earthquake mechanics. His work extends to strong ground-motion properties and high-performance computing-enabled physics-based seismic (including scattering in heterogeneous media) and tsunami simulations, and thereby spans from fundamental earthquake physics to earthquake-engineering applications.

Another major part of Professor Mai's research involves seismic data to image the structure of the Earth's crust and upper mantle beneath the Arabian plate, with the goal to help unravel the geodynamics of the Arabian plate and the Red Sea.

He has published more than 100 peer-reviewed papers, and since 2003 has supervised more than 35 graduate students (Ph.D. and M.Sc.) and over 15 postdoctoral researchers. He served as president of the Seismology Division of the European Geosciences Union from 2015 to 2019.

Read more about Professor Mai's full profile.

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The inclusion of biological uncertainty and the latest case data can significantly improve the prediction accuracy of standard epidemiological models of virus transmission, new research led by KAUST and the Kuwait College of Science and Technology (KCST) has shown.

Modern mathematical epidemic models have been tested like never before during the COVID-19 pandemic. These models use mathematics to describe the various biological and transmission processes involved in an epidemic. However, when such factors are highly uncertain, such as during the emergence of a new virus like COVID-19, the predictions can be unreliable.

"The susceptible-exposed-infected-recovered model, SEIR, is a standard mathematical approach for forecasting the spread of an epidemic in a population," says Rabih Ghostine, formerly of KAUST and now at KCST. "This model is based on several assumptions, such as homogeneous mixing of the population and the omission of migration, births or deaths from causes other than the epidemic. The parameters in the traditional SEIR model also do not allow for quantification of uncertainty, being single values reflecting the modeler's best guess."

"We wanted to develop a robust mathematical model that takes into account such uncertainties and incorporates epidemic data in order to enhance forecasting accuracy," explained Ghostine.

Ghostine, along with KAUST's Ibrahim Hoteit and fellow researchers, developed an extended SEIR model compromising seven compartments: susceptible, exposed, infectious, quarantined, recovered, deaths and vaccinated. They then added uncertainty definitions and a data assimilation process to drive progressive improvement of the model.

"Our data assimilation approach exploits new incoming observations to calibrate the model with recent information in order to continuously provide improved predictions, and also to estimate uncertainties," says Ghostine. "This is a popular framework in the atmospheric and ocean research communities and is at the basis of all operational weather and ocean modeling."

The model uses an "ensemble" approach, in which a set of predictions is generated across different parameter uncertainties. This ensemble is then integrated forward in time to forecast the future state. A correction step is performed to update the forecast with the latest data. Validation using real data for Saudi Arabia showed the model to provide reliable forecasts for up to 14 days in advance.

"Mathematical models can play an important role in understanding and predicting COVID-19 transmission as well as provide crucial information to policymakers to implement appropriate measures and efficient strategies to control the pandemic spread and mitigate its impact," says Hoteit. "Our method, which we developed to simulate the COVID-19 spread in Saudi Arabia, can also be applied to forecast the spread of any pandemic in a population."

- KAUST Discovery

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KAUST Professor of Chemical Science, Niveen M. Khashab, has been named a Fellow of the Royal Society of Chemistry (FRSC).

The Royal Society of Chemistry (RSC) is the United Kingdom's professional body for chemists and the largest organization in Europe for advancing the chemical sciences. The designation Fellow of the Royal Society of Chemistry (FRSC) is given to elected Fellows who have made an outstanding contribution to the advancement of chemical sciences, or to the advancement of the chemical sciences as a profession. 

At KAUST, Professor Khashab is affiliated with the Advanced Membranes & Porous Materials Research Center.

Research

"Professor Khashab's research interests focus on the synthesis, and applications of "smart" programmable assemblies that mimic natural designs. These nanomaterials are assembled using supramolecular tools with emphasis on the controlled release and delivery aspects for biomedical applications and molecular recognition with pore and surface engineering for industrial separations. Read Professor Khashab's full profile.

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An electrode coating just one molecule thick can significantly enhance the performance of an organic photovoltaic cell, KAUST researchers have found. The coating outperforms the leading material currently used for this task and may pave the way for improvements in other devices that rely on organic molecules, such as light-emitting diodes and photodetectors.

Unlike the most common photovoltaic cells that use crystalline silicon to harvest light, organic photovoltaic cells (OPVs) rely on a light-absorbing layer of carbon-based molecules. Although OPVs cannot yet rival the performance of silicon cells, they could be easier and cheaper to manufacture at a very large scale using printing techniques.

When light enters a photovoltaic cell, its energy frees a negative electron and leaves behind a positive gap, known as a hole. Different materials then gather the electrons and holes and guide them to different electrodes to generate an electrical current. In OPVs, a material called PEDOT:PSS is widely used to ease the transfer of generated holes into an electrode; however, PEDOT:PSS is expensive, acidic and can degrade the cell's performance over time.

The KAUST team has now developed a better alternative to PEDOT:PSS. They use a much thinner coating of a hole-transporting molecule called Br-2PACz, which binds to an indium tin oxide (ITO) electrode to form a single-molecule layer. The organic cell using Br-2PACz achieved a power conversion efficiency of 18.4 percent, whereas an equivalent cell using PEDOT:PSS reached only 17.5 percent.

"We were very surprised indeed by the performance enhancement," says Yuanbao Lin, Ph.D. student and member of the team. "We believe Br-2PACz has the potential to replace PEDOT:PSS due to its low cost and high performance."

Br-2PACz increased the cell's efficiency in several ways. Compared with its rival, it caused less electrical resistance, improved hole transport and allowed more light to shine through to the absorbing layer. Br-2PACz also improved the structure of the light-absorbing layer itself, an effect that may be related to the coating process.

The coating could even improve the recyclability of the solar cell. The researchers found that the ITO electrode could be removed from the cell, stripped of its coating and then reused as if it was new. In contrast, PEDOT:PSS roughens the surface of the ITO so that it performs poorly if reused in another cell. "We anticipate this will have a dramatic impact on both the economics of OPVs and the environment," says Thomas Anthopoulos, who led the research.

- KAUST Discovery

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Rising temperatures are increasingly affecting the quality of life in many regions, setting new challenges for architects, urban planners and healthcare systems. Researchers at KAUST have analyzed discomfort due to outdoor heat across Saudi Arabia and neighboring regions to help understand and combat the problem.

"Living conditions in the Kingdom have been particularly affected by the changing climate," says Hari Dasari, first author of the paper. He also emphasizes the unique challenges facing the Hajj pilgrimage visits by several million people each year. Between 2014 and 2018, the Hajj occurred in summer months when the average temperature often exceeded 40 degrees Celsius with 80 percent humidity.

The team examined the variability and trends in a measure called the thermal discomfort index (DI), computed from temperature and humidity records collected from 1980 to 2018. The DI evaluates how these two factors combine to cause heat stress and discomfort. 

Surprisingly, most cities in Saudi Arabia recorded an improvement in DI levels during the past 20 years, but significant exceptions were Yanbu, Makkah, Medina and Taif. The danger of increasing DI values in the Makkah region was confirmed by examining clinical records, which suggest a correlation with heat-related deaths during the Hajj pilgrimage.

"Many of us expected that the rising temperatures due to global warming and rapid growth in urbanization during recent decades should have reduced human comfort levels over KSA," says Dasari. A valuable insight from the research is the discovery that the situation is more complicated, with many regional variations worthy of further exploration.

Increased heat discomfort levels were concentrated mainly in neighboring regions of the Arabian Gulf, including the United Arab Emirates, Oman and Qatar.

Ibrahim Hoteit, leader of the research group, says the findings will help regional authorities, engineers and architects to plan the most effective developments in infrastructure, building design and healthcare interventions to improve safety and comfort across the region.

"We now plan to develop an atlas of DI values with risk maps indicating the trends through an online interactive visualization and analysis interface that provides real-time access for nonexpert users, and also a forecasting system to support the management of various outdoor activities and minimize health-related chronic symptoms." says Hoteit.

The team expect the further development of this research will also be critically important for supporting several large-scale projects currently being developed in Saudi Arabia, including the city of NEOM and the Red Sea Project and AMAALA tourism initiatives.

- KAUST Discovery