Friday, August 09, 2024

NON-PYTHGORIAN

Hidden Harmonies

Team discovers Magnon-phonon Fermi resonance in an antiferromagnet

Helmholtz-Zentrum Dresden-Rossendorf

image:
Artistic illustration of Magnon-phonon Fermi resonance in an antiferromagnet.
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Credit: B. Schröder / HZDR

A bottleneck of nowadays data processing technology is the slow and energy-consuming data storage. Soon, data storage centers are expected to consume almost 10 percent of the world’s energy generation. This increase is, among other things, due to intrinsic limitations of the materials used – ferromagnets. Consequently, this problem has ignited a quest for faster and more energy efficient materials. One of the most encouraging pathways are antiferromagnets – materials that not only promise more robust and 1.000 times faster read and write operations but also are more abundant than their ferromagnetic counterparts. Understanding and control of these quantum materials is key to advancing future technologies. An international research team now reports on a major step forward in this endeavor, as the scientists report in the journal Nature Communications (DOI: 10.1038/s41467-024-49716-w).

Interaction between spins and the crystal lattice of a material is essential in spintronic applications, as they use spin – the electron´s magnetic moment – to write information in magnetic bits. In ferromagnetic materials, these spins interact strongly, creating a ripple effect known as a spin wave, which can travel through the material. Spin waves are exciting because they can carry information without moving electrons, unlike the electric currents in today’s computer chips, which means less heat is produced. And just as light can be thought of as quantized particles called photons, spin waves have their own quasiparticles called magnons. On the other hand, when atoms in a material´s lattice vibrate uniformly, this motion is described by quasiparticles called phonons.

The team’s research focused on the antiferromagnetic material cobalt difluoride (CoF2) where magnons and phonons coexist. In this material, neighboring spins are aligned antiparallel, allowing for spin dynamics a thousand times faster than in conventional ferromagnetic materials. This advancement could lead to faster and more energy efficient data bit writing. Scientists excite these spin dynamics by coupling with light pulses at terahertz frequencies.

In addition, the so-called Fermi resonance, first described almost a century ago in carbon dioxide, occurs at the atomic and molecular level when two vibrational modes caused by the absorption of thermal energy interact and one is twice the frequency of the other. The principle of Fermi resonance has so far been extended to magnonic or phononic systems. In this work however, scientists achieve for the first time a strong coupling between the spin and the crystal lattice which constitutes a mutual energy transfer between these subsystems of an antiferromagnetically ordered material.

Magnons and phonon in sync

In this project, experimental and theoretical condensed matter scientists from the Institute for Molecules and Materials (IMM) of Radboud University, the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), University of Cologne, and the Ioffe Institute, revealed a novel energy transfer channel between magnons and phonons in an antiferromagnet under the condition of Fermi resonance. This may enable future control of such antiferromagnetic systems for faster and more energy-efficient data storage. Using the intense and spectrally bright accelerator-based superradiant THz source at HZDR’s ELBE Center for High-Power Radiation Sources, the researchers selectively excited the antiferromagnetic spin resonance and tuned its center frequency by high external magnetic field up to several Tesla. This configuration allowed them to tune the spin resonance frequencies to half the lattice vibration frequency fulfilling the Fermi resonance condition.

The researchers found a new regime of coupled magnon-phonon dynamics that allows energy exchange between these two subsystems at the Fermi resonance. By tuning the frequencies of the magnons, the researchers can control this process and in particular enhance the magnon-phonon coupling. This new regime was observed as a broadening of the phonon spectra and an asymmetric redistribution of the phonon spectral weight. Ultimately, their results suggest a hybridized two-magnon-one-phonon state. Their work could prove important in the fields of magnonics and phononics where coherent energy control plays a central role.

Innovative functionalities in future data storage

The research results offer a pathway to manipulate spin-lattice coupling on demand. Firstly, this allows for a considerable increase in operational frequency from the conventional GHz rate offered by ferromagnetic materials up to the THz scale in antiferromagnetic materials. Secondly, this might significantly enhance the efficiency of magnetic writing, which, in turn, will reduce the minimal amount of energy required for bit writing operations, thereby considerably lowering total energy consumption. Therefore, the results propose an innovative way to control the dynamics of antiferromagnets, leading to conceptually new data storage technologies based on such materials. In future studies, the research team aims to explore if the condition of Fermi resonance can be expanded to control other novel quantum materials, potentially leading to advancing material science and technology.

Publication:
T. W. J. Metzger, K. A. Grishunin, C. Reinhoffer, R. M. Dubrovin, A. Arshad, I. Ilyakov, T. V.A.G. de Oliveira, A. Ponomaryov, J.- C. Deinert, S. Kovalev, R. V. Pisarev, M. I. Katsnelson, B. A. Ivanov, P. H. M. van Loosdrecht, A. V. Kimel, E. A. Mashkovich, Magnon-phonon Fermi resonance in antiferromagnetic CoF2, in Nature Communications, 2024 (DOI: 10.1038/s41467-024-49716-w )

More information:
Jan-Christoph Deinert
Institute of Radiation Physics at HZDR
Phone: +49 351 260 3626 | Email: j.deinert@hzdr.de

Thomas Metzger
Institute for Molecules and Materials (IMM) | Radboud University
Email: thomas.metzger@.ru.nl

Evgeny A. Mashkovich
University of Cologne, Institute of Physics II
Phone: +49 221 470 1710 | Email: mashkovich@ph2.uni-koeln.de

Media contact:
Simon Schmitt | Head
Communications and Media Relations at HZDR
Phone: +49 351 260 3400 | Mobile: +49 175 874 2865 | Email: s.schmitt@hzdr.de

The Helmholtz-Zentrum Dresden-Rossendorf (HZDR) performs – as an independent German research center – research in the fields of energy, health, and matter. We focus on answering the following questions:

How can energy and resources be utilized in an efficient, safe, and sustainable way?
How can malignant tumors be more precisely visualized, characterized, and more effectively treated?
How do matter and materials behave under the influence of strong fields and in smallest dimensions?

To help answer these research questions, HZDR operates large-scale facilities, which are also used by visiting researchers: the Ion Beam Center, the Dresden High Magnetic Field Laboratory and the ELBE Center for High-Power Radiation Sources.
HZDR is a member of the Helmholtz Association and has six sites (Dresden, Freiberg, Görlitz, Grenoble, Leipzig, Schenefeld near Hamburg) with almost 1,500 members of staff, of whom about 670 are scientists, including 220 Ph.D. candidates.

Journal

Nature Communications

DOI

10.1038/s41467-024-49716-w

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Magnon-phonon Fermi resonance in antiferromagnetic CoF2

Researchers show pesticide contamination is more than apple skin deep

American Chemical Society

Pesticides and herbicides are critical to ensuring food security worldwide, but these substances can present a safety risk to people who unwittingly ingest them. Protecting human health, therefore, demands sensitive analytical methods to identify even trace levels of potentially harmful substances. Now, researchers reporting in ACS’ Nano Letters have developed a high-tech imaging method to detect pesticide contamination at low levels, and its application on fruits reveals that current food safety practices may be insufficient.

The analytical method called surface-enhanced Raman spectroscopy (SERS) is gaining popularity as a nondestructive method for detecting chemicals from modern farming on produce. With SERS, metal nanoparticles or nanosheets are used to amplify the signals created by molecules when they are exposed to a Raman laser beam. The patterns created by the metal-enhanced scattered light serve as molecular signatures and can be used to identify small amounts of specific compounds. Looking to improve SERS sensitivity for pesticide detection, Dongdong Ye, Ke Zheng, Shaobo Han and colleagues designed a metal-coated membrane they could lay atop farm-grown produce. They also wanted to develop the material to be versatile enough to accommodate an array of other applications.

The researchers started with a cellulose hydrogel film, which they stretched to form aligned nanoscale wrinkles along its surface. They then immersed the film in a solution of silver nitrate to coat the grooves with SERS-enhancing silver nanoparticles. The resulting membrane was highly flexible and practically transparent in visible light, essential features for SERS signal detection.

In tests of the silver-embedded membrane for food safety applications, the researchers sprayed the pesticides thiram and carbendazim, alone or together, onto apples, air-dried the fruits and then washed them to mimic everyday practices. When they laid their membrane over the apples, SERS detected pesticides on the apples, even though the chemicals were present at low concentrations. The team was also able to clearly resolve scattered-light signatures for each pesticide on apples sprayed with both thiram and carbendazim, as well as detect pesticide contamination through the fruit’s peel and into the outermost layer of pulp.

These results suggest that washing alone could be insufficient to prevent pesticide ingestion and that peeling would be required to remove potential contamination in the skin and outer pulp, the researchers say. Beyond apples, they also used the SERS membrane system to detect pesticides on cucumbers, shrimp, chili powder and rice.

The authors acknowledge funding from the National Natural Science Foundation of China.

The paper’s abstract will be available on Aug. 7 at 8 a.m. Eastern time here: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.4c01513

For more of the latest research news, register for our upcoming meeting, ACS Fall 2024. Journalists and public information officers are encouraged to apply for complimentary press registration by completing this form.

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The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS’ mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and all its people. The Society is a global leader in promoting excellence in science education and providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, eBooks and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a leader in scientific information solutions, its CAS division partners with global innovators to accelerate breakthroughs by curating, connecting and analyzing the world’s scientific knowledge. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.

Registered journalists can subscribe to the ACS journalist news portal on EurekAlert! to access embargoed and public science press releases. For media inquiries, contact newsroom@acs.org.

Note: ACS does not conduct research, but publishes and publicizes peer-reviewed scientific studies.

Journal

Nano Letters

DOI

10.1021/acs.nanolett.4c01513

Article Title

Cellulose Surface Nanoengineering for Visualizing Food Safety

Article Publication Date

7-Aug-2024

Pesticide exposure linked to stillbirth risk in new study

Increased rates of stillborn births were seen among people who lived near areas where pesticides were used during their first trimester of pregnancy or pre-conception.

Peer-Reviewed Publication

University of Arizona Health Sciences

image:
Melissa Furlong, PhD, is an assistant professor and environmental epidemiologist at the Zuckerman College of Public Health and a member of the Southwest Environmental Health Sciences Center at the R. Ken Coit College of Pharmacy.

view more
Credit: Photo by Kris Hanning, University of Arizona Health Sciences

Living less than about one-third of a mile from pesticide use prior to conception and during early pregnancy could increase the risk of stillbirths, according to new research led by researchers at the Mel and Enid Zuckerman College of Public Health and Southwest Environmental Health Sciences Center.

Researchers found that during a 90-day pre-conception window and the first trimester of pregnancy, select pesticides, including organophosphates as a class, were associated with stillbirth.

The paper, “Pre-Conception And First Trimester Exposure To Pesticides And Associations With Stillbirth,” was published in the American Journal of Epidemiology.

“In this study, some specific ingredients stood out due to their significant associations with stillbirth risk,” said first author Melissa Furlong, PhD, who studies the chronic health effects of environmental contaminants as an assistant professor and environmental epidemiologist at the Zuckerman College of Public Health and a member of the Southwest Environmental Health Sciences Center at the R. Ken Coit College of Pharmacy. “These findings underscore the importance of considering individual pesticides rather than just the overall pesticide class, as specific chemical compounds may pose unique risks. It also highlights the potential for pre-pregnancy exposures to affect reproductive outcomes.”

To conduct the study, researchers linked Arizona pesticide use records for 27 different pesticides with state birth certificate data that included 1,237,750 births and 2,290 stillbirths from 2006 to 2020.

They found that living within .31 miles (500 meters) of specific pyrethroid, organophosphate or carbamate pesticide applications during a 90-day pre-conception window or the first trimester was associated with an increased risk of stillbirth.

Specifically, the pesticides cyfluthrin, zeta-cypermethrin, organophosphates as a class, malathion, carbaryl and propamocarb hydrochloride were linked to increased stillborn births pre-conception. During the first trimester, fenpropathrin, permethrin, organophosphates as a class, acephate and formetanate hydrochloride were associated with stillbirths.

“Among organophosphates, acephate showed the strongest effect estimates on stillbirth, so that exposure to acephate in the first trimester was associated with a doubling of risk,” said co-author Paloma Beamer, PhD, a professor and interim associate dean at the Zuckerman College of Public Health and a member of the Southwest Environmental Health Sciences Center, U of A Health Sciences Asthma and Airway Disease Research Center and BIO5 Institute. “Within the pyrethroid class, cyfluthrin exposure during the 90 days prior to conception almost doubled the risk of stillbirth.”

Pesticides are chemical substances used to control pests in various settings. They are commonly categorized into different classes, such as organophosphates, pyrethroids and carbamates. The primary route of exposure for most people is through diet, but household use, agricultural drift and occupational exposure are also significant pathways.

Researchers say while some pesticides may not have been directly implicated in this study, they could still pose risks to maternal and fetal health.

Pregnant women may be particularly vulnerable to the adverse effects of pesticide exposure due to physiological changes during pregnancy, such as increased metabolic rate, altered hormone levels and changes in the immune system. The developing fetus may be more susceptible to the toxic effects of pesticides during this period of rapid growth and development.

“Further research is essential to fully understand the safety profiles of various pesticides and to understand the underlying mechanisms of pesticide-induced stillbirth,” Furlong said. “This study underscores the need to develop strategies for mitigating exposure to protect maternal and fetal health.”

Co-authors from the University of Arizona include Alfred Fournier, PhD, an associate specialist in entomology in the College of Agriculture, Life and Environmental Sciences; Peter Ellsworth, PhD, professor in the Department of Entomology at the College of Agriculture, Life and Environmental Sciences; Avelino Arrelano, PhD, an associate professor of data assimilation and atmospheric chemistry at the College of Science Department of Hydrology and Atmospheric Sciences; and Edward Bedrick, PhD, a professor in the Department of Epidemiology and Biostatistics at the Zuckerman College of Public Health. Other co-authors include Kimberly Parra, PhD, who was a doctoral candidate at the Zuckerman College of Public Health when the research was conducted and is now a research fellow at Harvard University’s T.H. Chan School of Public Health; Beate Ritz, MD, PhD, and Kimberly Paul, PhD, from the University of California, Los Angeles; and Myles Cockburn, PhD, from University of Southern California.

This research was supported in part by the National Institute of Environmental Health Sciences, a division of the National Institutes of Health, under Award Nos. R00ES028743 and P30ES006694.Living less than about one-third of a mile from pesticide use prior to conception and during early pregnancy could increase the risk of stillbirths, according to new research led by researchers at the Mel and Enid Zuckerman College of Public Health and Southwest Environmental Health Sciences Center.

Researchers found that during a 90-day pre-conception window and the first trimester of pregnancy, select pesticides, including organophosphates as a class, were associated with stillbirth.

The paper, “Pre-Conception And First Trimester Exposure To Pesticides And Associations With Stillbirth,” was published in the American Journal of Epidemiology.

“In this study, some specific ingredients stood out due to their significant associations with stillbirth risk,” said first author Melissa Furlong, PhD, who studies the chronic health effects of environmental contaminants as an assistant professor and environmental epidemiologist at the Zuckerman College of Public Health and a member of the Southwest Environmental Health Sciences Center at the R. Ken Coit College of Pharmacy. “These findings underscore the importance of considering individual pesticides rather than just the overall pesticide class, as specific chemical compounds may pose unique risks. It also highlights the potential for pre-pregnancy exposures to affect reproductive outcomes.”

To conduct the study, researchers linked Arizona pesticide use records for 27 different pesticides with state birth certificate data that included 1,237,750 births and 2,290 stillbirths from 2006 to 2020.

They found that living within .31 miles (500 meters) of specific pyrethroid, organophosphate or carbamate pesticide applications during a 90-day pre-conception window or the first trimester was associated with an increased risk of stillbirth.

Specifically, the pesticides cyfluthrin, zeta-cypermethrin, organophosphates as a class, malathion, carbaryl and propamocarb hydrochloride were linked to increased stillborn births pre-conception. During the first trimester, fenpropathrin, permethrin, organophosphates as a class, acephate and formetanate hydrochloride were associated with stillbirths.

“Among organophosphates, acephate showed the strongest effect estimates on stillbirth, so that exposure to acephate in the first trimester was associated with a doubling of risk,” said co-author Paloma Beamer, PhD, a professor and interim associate dean at the Zuckerman College of Public Health and a member of the Southwest Environmental Health Sciences Center, U of A Health Sciences Asthma and Airway Disease Research Center and BIO5 Institute. “Within the pyrethroid class, cyfluthrin exposure during the 90 days prior to conception almost doubled the risk of stillbirth.”

Pesticides are chemical substances used to control pests in various settings. They are commonly categorized into different classes, such as organophosphates, pyrethroids and carbamates. The primary route of exposure for most people is through diet, but household use, agricultural drift and occupational exposure are also significant pathways.

Researchers say while some pesticides may not have been directly implicated in this study, they could still pose risks to maternal and fetal health.

Pregnant women may be particularly vulnerable to the adverse effects of pesticide exposure due to physiological changes during pregnancy, such as increased metabolic rate, altered hormone levels and changes in the immune system. The developing fetus may be more susceptible to the toxic effects of pesticides during this period of rapid growth and development.

“Further research is essential to fully understand the safety profiles of various pesticides and to understand the underlying mechanisms of pesticide-induced stillbirth,” Furlong said. “This study underscores the need to develop strategies for mitigating exposure to protect maternal and fetal health.”

Co-authors from the University of Arizona include Alfred Fournier, PhD, an associate specialist in entomology in the College of Agriculture, Life and Environmental Sciences; Peter Ellsworth, PhD, professor in the Department of Entomology at the College of Agriculture, Life and Environmental Sciences; Avelino Arrelano, PhD, an associate professor of data assimilation and atmospheric chemistry at the College of Science Department of Hydrology and Atmospheric Sciences; and Edward Bedrick, PhD, a professor in the Department of Epidemiology and Biostatistics at the Zuckerman College of Public Health. Other co-authors include Kimberly Parra, PhD, who was a doctoral candidate at the Zuckerman College of Public Health when the research was conducted and is now a research fellow at Harvard University’s T.H. Chan School of Public Health; Beate Ritz, MD, PhD, and Kimberly Paul, PhD, from the University of California, Los Angeles; and Myles Cockburn, PhD, from University of Southern California.

This research was supported in part by the National Institute of Environmental Health Sciences, a division of the National Institutes of Health, under Award Nos. R00ES028743 and P30ES006694.

Journal

American Journal of Epidemiology

DOI

10.1093/aje/kwae198

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

Pre-Conception And First Trimester Exposure To Pesticides And Associations With Stillbirth

COI Statement

PCE has received research grants and contracts from pesticide registrants unrelated to the research reported here.

Researchers create new device for on-the-spot water testing

University of Galway

Researchers at University of Galway have developed a new, portable technology for on-the-spot testing of water quality to detect one of the most dangerous types of bacteria.

Ireland regularly reports the highest crude incidence rates of the pathogen Shiga toxigenic Escherichia coli - STEC for short - in Europe over the recent years.

The bacteria produces the harmful Shiga toxin, which, if ingested by humans, can cause severe stomach illnesses and, in some cases, life-threatening complications especially in children under 5 years, older people and immunocompromised individuals.

A work led by Dr Zina Alfahl, lecturer in bacteriology in the University’s College of Medicine, Nursing and Health Sciences, and Dr Louise O’Connor, senior research fellow with the University’s College of Science and Engineering, developed a technology for rapid, sensitive and accurate testing of STEC in water sources, including rivers, lakes and wells.

The results have been published in the journal, Microbiology.

Dr Alfahl said: “Our technology is a significant advancement in on-site water testing. It is portable, straightforward and safe to use. It is accurate, highly sensitive and the results are delivered quickly, on-site.

“We are hoping that Environmental Health Officers and groundwater schemes in Ireland could use the technology on-site allowing for more frequent testing especially in or after extreme weather, periods of intense rainfall, because it is those conditions which lead to water supplies being contaminated.”

Dr O’Connor said: “This technology could be a crucial intervention in helping to prevent outbreaks of infection in families and communities using wells, private water supplies and groundwater schemes.

“Immediate results can help public health officers and water management authorities make informed decisions to protect public health. This rapid response capability is crucial for preventing the spread of waterborne diseases and ensuring the safety of drinking water."

STEC is normally found in the intestines of healthy animals like cows and sheep, which carry it without getting sick. The bacteria spreads to people through contact with animal waste, or by eating or drinking contaminated food or water.

A small sample of water can be tested on-site using isothermal amplification technology which can identify the genetic markers of STEC bacteria, and related E. coli. The results are delivered in about 40minutes through a reading on screen. Traditional lab testing of samples can take days for results to be returned.

The research, funded by Environment Protection Agency through the DERIVE project, tested samples from various water sources, including groundwater wells, rivers, a turlough and a farm drain on the Corrib catchment in Galway. Of the samples tested 61% were positive for the presence of this dangerous pathogen.

Dr Alfahl said: “Our testing is sensitive enough to identify as low as two cells of the STEC bacteria. The gold standard for testing is culture in a lab, but this can take days and often weeks, and on occasion can return a false negative result – just because the culture does not grow in the lab does not always mean the bacteria has not been present in the water. Our test removes the necessity for samples to go to a lab. It offers on-the-spot results and is of huge benefit to the people using the water as a first-step in identifying a contamination and a potential health risk.”

Dr O’Connor said: “This new testing method is particularly important for areas that rely on private groundwater wells, which can be more prone to contamination. In Ireland, a significant portion of the population depends on these for their drinking water - about 720,000 people, or one in every 5 households, but quality has been an issue as regulation is less stringent on these sources and testing is less frequent.”

Ends

Journal

Microbiology

DOI

10.1099/mic.0.001485

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

A rapid on-site loop-mediated isothermal amplification technology as an early warning system for the detection of Shiga toxin-producing Escherichia coli in water

Article Publication Date

7-Aug-2024

Using historical radar data to map changes in urban environments

Journal of Remote Sensing

Three-dimensional urbanization — image:
Scientists from China Agricultural University reconstructed long-term backscatter coefficient to investigate three-dimensional urbanization.
view more
Credit: Xuecao Li, China Agricultural University

Synthetic aperture radar (SAR) is a type of remote sensing from satellites that uses the reflection of radio waves to relay information about the surface of the earth. This reflection, or backscatter, is responsive to physical properties, such as roughness, vertical structure, and moisture. SAR is widely used for different types of mapping and monitoring, but signal interference in urban environments can cause distortions that make SAR data difficult to interpret.

By combining optical signals with historical SAR backscatter coefficient data, SAR data can be refined and used to monitor changes to an urban environment over time. This reconstruction technique was described in a paper published in Journal of Remote Sensing on 23 July.

“We set out to fill the knowledge gaps in the reconstruction of long-term backscatter coefficient data. This study developed a method that would reconstruct the data over the past three decades (1990 through 2022) based on Sentinel-1 Ground Range Detected data and long-term Landsat data in the Jing-Jin-Ji region. This could significantly support three-dimensional dynamics in urban domains,” said Xuecao Li, a professor at the College of Land Science and Technology at the China Agricultural University in Beijing, China.

Researchers chose the Jing-Jin-Ji region of China, which includes Beijing and Tianjin and 11 major cities, to test their reconstruction technique because this part of China has changed drastically over the past 40 years due to rapid urbanization. They developed a building height model based on reference building heights in seven cities. To understand the relationship between the backscatter coefficient of Sentinel-1 and optical Landsat images, researchers used a regression model and then expanded it to cover the entire region.

The trained model was able to successfully map the optical data over the long-time backscatter coefficient. The success of this technique was clear when it was used to estimate changing building height. When the historical backscatter coefficient data was used to estimate building heights, the data was able to accurately capture nuances in the changing urban landscape of Beijing. It was able to accurately depict areas of rapid construction in the urban core of Beijing and in the Haidian and Chaoyang neighborhoods where average building height increased between 1990 and 2000. It also accurately mapped the increased building height in the outer areas of Beijing in the following decades.

“Overall, our results suggest that the estimated backscatter coefficient has a promising potential for exploring urban expansion in the vertical dimension,” said Li. “In addition to estimating building height, the long-term and high-resolution backscatter coefficient also has promising potential for urban studies regarding impervious surface classification, change detection, and flood extent mapping. The proposed approach in this study allows researchers to estimate the backscatter with finer resolutions for decades regarding seasonal or monthly changes.”

Looking ahead, researchers hope to apply what they learned through this study on a global scale. “The estimated building height in the Jing-Jin-Ji region can be further used for investigating the urban environmental issues regarding the 3D perspective, such as the urban heat island, dynamic building height, and carbon emissions, which are expected to provide useful information for achieving sustainable development goals,” said Li.

Other contributors include Bo Yuan at Tarim University; Guojiang Yu at China Agricultural University; Linze Li at China Three Gorges Corporation; Donglie Liu at the Natural Resources Satellite Remote Sensing Application Center; Jincheng Guo at the Guizhou First Surveying and Mapping Institute; and Yangchun Li at the Guizhou Geological Environment Monitoring Institute.

The National Natural Science Foundation of China, the National Natural Science Foundation of China/RGC Joint Research Scheme, the NSFC Excellent Young Scientists Fund, and the Chinese University Scientific Fund supported this research.

Journal

Journal of Remote Sensing

DOI

10.34133/remotesensing.0172

Method of Research

Imaging analysis

Subject of Research

Not applicable

Article Title

Reconstructing Long-Term Synthetic Aperture Radar Backscatter in Urban Domains Using Landsat Time Series Data: A Case Study of Jing–Jin–Ji Region

Most existing heat wave indices fail to capture heat wave severity

Cell Press

Even though climate change is bringing more frequent and severe heat waves, there is no standard, global way to measure heat-wave severity, and existing indices have different thresholds for defining dangerous heat-stress conditions. Researchers report August 7 in the journal Nexus that five out of six existing heat-wave indices were unable to capture the severity and spatial distribution of recent lethal heat waves in India, Spain, and the USA. The sixth index—the lethal heat-stress index—was better able to identify dangerous heat-stress conditions, particularly in low-humidity regions.

“We found that some existing indices may not be appropriate to all geographical regions and climate conditions,” says senior author and geospatial expert Qihao Weng (@Qihao_Weng) of the Hong Kong Polytechnic University. “It’s important that scientific communities, public health circles, and policy makers come together and reconsider the existing indices.”

Currently, countries around the world have different ways of measuring and defining heat waves, but it’s not clear which of these methods is most effective or how their performance is impacted by background climatic conditions. Some of these metrics are based purely on the maximum air temperature while others include factors such as radiation, wind, and, crucially, humidity.

“Even in relatively low-temperature conditions, if the humidity is high, it can still be dangerous for people with health problems,” says Weng. “In humid conditions, even 28°C, wet-bulb conditions can lead to severe strain and heat stroke.”

To compare the effectiveness of existing heat-wave indices under different conditions, the researchers applied six existing indices to climate data from heat waves that occurred in Spain and the United States in 2022 and in India in 2023. In all cases, they found that one method—the lethal heat-stress index—outperformed the others. Compared to the other indices, the lethal heat-stress index could differentiate between areas that were or were not impacted by extreme heat stress and could pinpoint on which days these dangerous heat conditions occurred.

The lethal heat-stress index is a temperature- and humidity-based metric for identifying conditions that are likely to lead to human death (in contrast to other indices that use endpoints such as “extreme danger” and “heat stroke imminent”). Though most of the other indices also include humidity in their calculations in some way, the way that they do this differs.

“The lethal heat stress index applies a correction factor to relative humidity, which means that it is better at predicting dangerous heat conditions in regions which have very low humid conditions compared to the other indices,” says first author Pir Mohammad, an earth scientist at Hong Kong Polytechnic University.

The researchers emphasize that heat waves are experienced differently by different people, even within the same region, because of factors including age, pre-existing health conditions, and socioeconomic status, which is associated with access to adequate cooling and the privilege of not working outdoors during hot conditions.

Though they identified the lethal heat-stress index as the best current option, the researchers say that this index could still be improved with more research. They also note that while their study focuses on outdoor air temperatures, more heat-related mortalities occur indoors than outdoors, and future research should also address indoor conditions during heat waves and examine how they are impacted by things such as building age and materials.

Ultimately, they hope their findings will help scientists develop a universal definition of the threshold for dangerous heat conditions.

“We need to deploy a global framework that considers temperature, humidity, and other factors like socioeconomic status and age so that we can mitigate dangerous heat-wave conditions,” says Mohammad. “The UK government recently redefined their limiting criteria for heat waves, and it might be a good time for other countries to also think about how we can define heat waves more effectively.”

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This research was supported by the Hong Kong SAR Government, the Research Talent Hub of the Innovation and Technology Fund of Hong Kong, and the Hong Kong Polytechnic University.

Nexus, Mohammad and Weng, “Comparing Existing Heat Wave Indices in Identifying Dangerous Heat Wave Outdoor Conditions” https://www.cell.com/nexus/fulltext/S2950-1601(24)00025-1

Nexus, (@Nexus_CellPress) a partnership between The Hong Kong Polytechnic University and Cell Press, is a gold open access journal that publishes cutting-edge research in applied sciences, engineering, technology, and inter- and multi-disciplinary fields that tackle the world’s grand challenges. Visit https://www.cell.com/nexus. To receive Cell Press media alerts, contact press@cell.com.

Journal

Nexus

DOI

10.1016/j.ynexs.2024.100027

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

Comparing Existing Heat Wave Indices in Identifying Dangerous Heat Wave Outdoor Conditions

Article Publication Date

7-Aug-2024