It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
PULLMAN, Wash. - A tiny bee imposter, the syrphid fly, may be a big help to some gardens and farms, new research from Washington State University shows.
An observational study in Western Washington found that out of more than 2,400 pollinator visits to flowers at urban and rural farms about 35% of were made by flies--most of which were the black-and-yellow-striped syrphid flies, also called hover flies. For a few plants, including peas, kale and lilies, flies were the only pollinators observed. Overall, bees were still the most common, accounting for about 61% of floral visits, but the rest were made by other insects and spiders.
"We found that there really were a dramatic number of pollinators visiting flowers that were not bees," said Rae Olsson, a WSU post-doctoral fellow and lead author of the study published in Food Webs. "The majority of the non-bee pollinators were flies, and most of those were syrphid flies which is a group that commonly mimics bees."
Syrphid flies' bee-like colors probably help them avoid predators who are afraid of getting stung, but they are true flies with two wings as opposed to bees which have four. The flies might have additional benefits for plants, Olsson added, since as juveniles they eat pests like aphids. As adults, they consume nectar and visit flowers so have the potential to move pollen the same way that bees do, though it is less intentional than bees who collect pollen to feed their young.
For the study, the researchers surveyed plants and pollinating insects and spiders on 19 rural farms and 17 urban farms and gardens along the Interstate 5 corridor in Western Washington. They conducted surveys six separate times over two years. In addition to the visits by bees and syrphid flies, they also catalogued more rare visits by other arthropods including wasps, lacewings, spiders, butterflies, dragonflies, beetles and ants--all with visits of less than 4%.
Olsson first noticed the many different non-bee pollinators while working on a bee-survey project led by Elias Bloom, a recent WSU doctoral graduate. The results of this study underscore the need for researchers as well as gardeners and farmers to pay more attention to alternative pollinators, Olsson said, and hoped that similar studies would be conducted in other regions of the country.
"Bee populations are declining, and we are trying to help them, but there's room at the table for all the pollinators," Olsson said. "There are a lot of conservation and monitoring efforts for bees, but that doesn't extend to some of the other pollinators. I think people will be surprised to find that there are a lot more different types of pollinating insects - all we really need to do is to start paying a little more attention to them."
The study also noted pollinator differences between rural and urban spaces. Observations sites in urban areas showed a greater diversity of pollinators corresponding with the wider range of plants grown in city gardens and smaller-sized farms. Rural farms with their larger fields of plants had a greater abundance.
For every grower, urban or rural, who is interested in increasing the number and diversity of pollinators visiting their fields or gardens, Olsson recommended increasing the variety of flowering plants.
Making sure that something is flowering all throughout the season, even if on the edge of a field, will support the biodiversity of pollinators because their different life stages happen at different times of the year.
"Some pollinators like certain butterflies and moths are only present in a pollinating form for a small period of time," Olsson said. "They may only live for a few days as adults, so when they emerge and are ready to pollinate, it's good to make sure that you have something for them to eat."
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Crustal block tectonics offer clues to Venus' geology, study finds
New study that includes contributions by Baylor planetary geophysicist Peter James, identifies previously unrecognized pattern of tectonic deformation on Venus
IMAGE: BAYLOR UNIVERSITY PLANETARY PHYSICIST PETER JAMES, PH.D., PROVIDED CALCULATIONS OF THE VARIOUS MECHANISMS THAT COULD BE RESPONSIBLE FOR THE FORCE DRIVING THE GEOLOGIC ACTIVITY ON VENUS view more
CREDIT: ROBERT ROGERS, BAYLOR UNIVERSITY
WACO, Texas (June 21, 2021) - A new analysis of Venus' surface shows evidence of tectonic motion in the form of crustal blocks that have jostled against each other like broken chunks of pack ice. Published in the PNAS (Proceedings of the National Academy of Sciences), the study -- which includes contributions by Baylor University planetary physicist Peter James, Ph.D. -- found that the movement of these blocks could indicate that Venus is still geologically active and give scientists insight into both exoplanet tectonics and the earliest tectonic activity on Earth.
"We have identified a previously unrecognized pattern of tectonic deformation on Venus, one that is driven by interior motion just like on Earth," said Paul Byrne, Ph.D., associate professor of planetary science at North Carolina State University and lead and co-corresponding author of the work. "Although different from the tectonics we currently see on Earth, it is still evidence of interior motion being expressed at the planet's surface."
Venus had long been assumed to have an immobile solid outer shell, or lithosphere, just like Mars or Earth's moon. In contrast, Earth's lithosphere is broken into tectonic plates, which slide against, apart from, and underneath each other on top of a hot, weaker mantle layer.
James, an assistant professor of planetary geophysics and founder of Baylor University's Planetary Research Group, was part of the international group of researchers involved with the study. He has taken part in three NASA missions and specializes in using of spacecraft data to study the crusts and mantles of planets and moons.
"Earth is the only planet in the solar system with plate tectonics, so our planet is quite exceptional in that regard," James said. "That is particularly interesting when it comes to Venus: Why does a planet like Venus -- roughly the same size as Earth and made of the same types of rocks -- not behave the same way as Earth geologically?"
To answer that question, the team used radar images from NASA's Magellan mission to map the surface of Venus. In examining the extensive Venusian lowlands that make up most of the planet surface, they saw areas where large blocks of the lithosphere seem to have moved: pulling apart, pushing together, rotating and sliding past each other like broken pack ice over a frozen lake.
James provided calculations of the various mechanisms that could be responsible for the force driving the geologic activity on Venus. NASA's Magellan spacecraft measured the gravity field of Venus -- the subtle changes in the strength of gravity in different places on the planet. James was able to use this gravity field to demonstrate that viscous mantle flow, or slow churning, is strongly coupled to the crust.
"The mantle inside Venus pushes and pulls on the surface of the planet more strongly than Earth's mantle does. These calculations of the driving forces corroborated the discovery of block motion and helped us have a better understanding of how it works," James said.
The interior mantle flow found by the study's calculations is significant because it hasn't been demonstrated on a global scale previously. The movement of these crustal blocks could also indicate that Venus is still geologically active.
"We know that much of Venus has been volcanically resurfaced over time, so some parts of the planet might be really young, geologically speaking," Byrne said. "But several of the jostling blocks have formed in and deformed these young lava plains, which means that the lithosphere fragmented after those plains were laid down. This gives us reason to think that some of these blocks may have moved geologically very recently - perhaps even up to today."
The researchers are optimistic that Venus' newly recognized "pack ice" pattern could offer clues to understanding tectonic deformation on planets outside of our solar system, as well as on a much younger Earth.
"One of the neat things about planet research like this is that it helps us understand why our own planet works the way it does," James said. "The theme of our Planetary Research Group at Baylor is a quote from C.S. Lewis's Mere Christianity: 'Aim at heaven and you will get Earth thrown in.' That quote is intended in a spiritual context -- we should seek the kingdom of God before all else, and then this kingdom-mindset can even bear fruit in a secular sense. We like the double meaning of using space research to understand our own planet better."
Science related to Venus is especially timely -- NASA recently announced that it would be sending two new spacecrafts to Venus, VERITAS and DAVINCI+. These will be the first NASA missions launched to Venus since the 1980s. Additionally, the European Space Agency announced last week that it would be sending its own spacecraft called Envision to Venus.
"Strategically, this research is positioning Baylor to be involved with upcoming spacecraft missions. Venus is becoming a bigger priority for space agencies around the world, and we're plugged in to the exciting science opportunities that are on the horizon," James said.
Baylor will continue to be part of Venus research through James' lab. Rudger Dame, a Ph.D. candidate in James' lab, is focusing on Venus for his dissertation research. He has an internship this summer with the NASA Jet Propulsion Laboratory, under the advisement of Sue Smrekar, the principal investigator for the recently announced VERITAS spacecraft.
In addition, James is collaborating with NASA's Goddard Space Flight Center to study the planet Mercury's crust. He also led a recent study published in the journal Geophysical Research Letters about the discovery of a mysterious huge mass of material on the far side of the Moon -- beneath the largest crater in our solar system. The mass -- at least five times larger than the Big Island of Hawaii -- may contain metal from an asteroid that may have crashed into the Moon and formed the crater.
The South Pole-Aitken basin -- thought to have been created about 4 billion years ago -- is "one of the best natural laboratories for studying catastrophic impact events, an ancient process that shaped all of the rocky planets and moons we see today."
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*Sean Solomon of Columbia University is co-corresponding author. Richard Ghail of the University of London, Surrey; A. M. Celâl ?engör of Istanbul Technical University; and Christian Klimczak of the University of Georgia also contributed to the work.
ABOUT BAYLOR UNIVERSITY Baylor University is a private Christian University and a nationally ranked research institution. The University provides a vibrant campus community for more than 19,000 students by blending interdisciplinary research with an international reputation for educational excellence and a faculty commitment to teaching and scholarship. Chartered in 1845 by the Republic of Texas through the efforts of Baptist pioneers, Baylor is the oldest continually operating University in Texas. Located in Waco, Baylor welcomes students from all 50 states and more than 90 countries to study a broad range of degrees among its 12 nationally recognized academic divisions.
Researchers trace dust grain's journey through newborn solar system
Combining atomic-scale sample analysis and models simulating likely conditions in the nascent solar system, the study revealed clues about the origin of crystals that formed more than 4.5 billion years ago
IMAGE: ARTIST'S ILLUSTRATION OF THE EARLY SOLAR SYSTEM, AT A TIME WHEN NO PLANETS HAD FORMED YET. A SWIRLING CLOUD OF GAS AND DUST SURROUNDED THE YOUNG SUN. THE CUTAWAY THROUGH... view more
CREDIT: HEATHER ROPER
A research team led by the University of Arizona has reconstructed in unprecedented detail the history of a dust grain that formed during the birth of the solar system more than 4.5 billion years ago. The findings provide insights into the fundamental processes underlying the formation of planetary systems, many of which are still shrouded in mystery.
For the study, the team developed a new type of framework, which combines quantum mechanics and thermodynamics, to simulate the conditions to which the grain was exposed during its formation, when the solar system was a swirling disk of gas and dust known as a protoplanetary disk or solar nebula. Comparing the predictions from the model to an extremely detailed analysis of the sample's chemical makeup and crystal structure, along with a model of how matter was transported in the solar nebula, revealed clues about the grain's journey and the environmental conditions that shaped it along the way.
The grain analyzed in the study is one of several inclusions, known as calcium-aluminum rich inclusions, or CAIs, discovered in a sample from the Allende meteorite, which fell over the Mexican state of Chihuahua in 1969. CAIs are of special interest because they are thought to be among the first solids that formed in the solar system more than 4.5 billion years ago.
Similar to how stamps in a passport tell a story about a traveler's journey and stops along the way, the samples' micro- and atomic-scale structures unlock a record of their formation histories, which were controlled by the collective environments to which they were exposed.
"As far as we know, our paper is the first to tell an origin story that offers clues about the likely processes that happened at the scale of astronomical distances with what we see in our sample at the scale of atomic distances," said Tom Zega, a professor in the University of Arizona's Lunar and Planetary Laboratory and the first author of the paper, published in The Planetary Science Journal.
Zega and his team analyzed the composition of the inclusions embedded in the meteorite using cutting-edge atomic-resolution scanning transmission electron microscopes - one at UArizona's Kuiper Materials Imaging and Characterization Facility, and its sister microscope located at the Hitachi factory in Hitachinaka, Japan.
The inclusions were found to consist mainly of types of minerals known as spinel and perovskite, which also occur in rocks on Earth and are being studied as candidate materials for applications such as microelectronics and photovoltaics.
Similar kinds of solids occur in other types of meteorites known as carbonaceous chondrites, which are particularly interesting to planetary scientists as they are known to be leftovers from the formation of the solar system and contain organic molecules, including those that may have provided the raw materials for life.
Precisely analyzing the spatial arrangement of atoms allowed the team to study the makeup of the underlying crystal structures in great detail. To the team's surprise, some of the results were at odds with current theories on the physical processes thought to be active inside protoplanetary disks, prompting them to dig deeper.
"Our challenge is that we don't know what chemical pathways led to the origins of these inclusions," Zega said. "Nature is our lab beaker, and that experiment took place billions of years before we existed, in a completely alien environment."
Zega said the team set out to "reverse-engineer" the makeup of the extraterrestrial samples by designing new models that simulated complex chemical processes, which the samples would be subjected to inside a protoplanetary disk.
"Such models require an intimate convergence of expertise spanning the fields of planetary science, materials science, mineral science and microscopy, which was what we set out to do," added Krishna Muralidharan, a study co-author and an associate professor in the UArizona's Department of Materials Science and Engineering.
Based on the data the authors were able to tease from their samples, they concluded that the particle formed in a region of the protoplanetary disk not far from where Earth is now, then made a journey closer to the sun, where it was progressively hotter, only to later reverse course and wash up in cooler parts farther from the young sun. Eventually, it was incorporated into an asteroid, which later broke apart into pieces. Some of those pieces were captured by Earth's gravity and fell as meteorites.
The samples for this study were taken from the inside of a meteorite and are considered primitive - in other words, unaffected by environmental influences. Such primitive material is believed to not have undergone any significant changes since it first formed more than 4.5 billion years ago, which is rare. Whether similar objects occur in asteroid Bennu, samples of which will be returned to Earth by the UArizona-led OSIRIS-REx mission in 2023, remains to be seen. Until then, scientists rely on samples that fall to Earth via meteorites.
"This material is our only record of what happened 4.567 billion years ago in the solar nebula," said Venkat Manga, a co-author of the paper and an assistant research professor in the UArizona Department of Materials Science and Engineering. "Being able to look at the microstructure of our sample at different scales, down to the length of individual atoms, is like opening a book."
The authors said that studies like this one could bring planetary scientists a step closer to "a grand model of planet formation" - a detailed understanding of the material moving around the disk, what it is composed of, and how it gives rise to the sun and the planets.
Powerful radio telescopes like the Atacama Large Millimeter/submillimeter Array, or ALMA, in Chile now allow astronomers to see stellar systems as they evolve, Zega said.
"Perhaps at some point we can peer into evolving disks, and then we can really compare our data between disciplines and begin answering some of those really big questions," Zega said. "Are these dust particles forming where we think they did in our own solar system? Are they common to all stellar systems? Should we expect the pattern we see in our solar system - rocky planets close to the central star and gas giants farther out - in all systems?
"It's a really interesting time to be a scientist when these fields are evolving so rapidly," he added. "And it's awesome to be at an institution where researchers can form transdisciplinary collaborations among leading astronomy, planetary and materials science departments at the same university."
CAPTION
A slice through an Allende meteorite reveals various spherical particles, known as chondrules. The irregularly shaped "island" left of the center is a calcium-aluminum rich inclusion, or CAI. The grain in this study was isolated from such a CAI.
CREDIT
Shiny Things/Wikimedia Commons
The study was co-authored by Fred Ciesla at the University of Chicago and Keitaro Watanabe and Hiromi Inada, both with the Nano-Technology Solution Business Group at Hitachi High-Technologies Corp. in Japan.
Funding was provided through NASA's Emerging Worlds Program; NASA's Origins Program; and NASA's Nexus for Exoplanet System Science (NExSS) research coordination network, which is sponsored by NASA's Science Mission Directorate. NASA and the National Science Foundation provided the funding for the instrumentation in LPL's Kuiper Materials Imaging and Characterization Facility.
CAPTION
Illustration of the dynamic history that the modeled particle could have experienced during the formation of the solar system. Analyzing the particle's micro- and atomic-scale structures and combining them with new models that simulated complex chemical processes in the disk revealed its possible journey over the course of many orbits around the sun (callout box and diagram on the right). Originating not far from where Earth would form, the grain was transported into the inner, hotter regions, and eventually washed up in cooler regions.
CREDIT
Heather Roper/Tom Zega et al.
Ancient bones provide clues about Kangaroo Island's past and future
A Curtin University-led study of ancient bones on South Australia's Kangaroo Island has provided new information about the Island's past fauna and an insight into how species may live there in the future
IMAGE: STOCK IMAGE OF KANGAROO ISLAND IN SOUTH AUSTRALIA. view more
CREDIT: N/A
A Curtin University-led study of ancient bones on South Australia's Kangaroo Island has provided new information about the Island's past fauna and an insight into how species may live there in the future.
Published in Quaternary Science Reviews, the researchers analysed around 2,000 bone fragments with the aim of eventually being able to establish a more complete picture of past biodiversity on the Island.
Lead researcher Dr Frederik Seersholm from Curtin's School of Molecular and Life Sciences said DNA studies on such a large scale have never been done on the Island before.
"We identified 33 species, 10 of which are extinct on the island today. We also found DNA traces from both the Eastern and the Western grey kangaroos- which is interesting given it was previously thought that only the Western used to roam the Island," Dr Seersholm said.
"Our research also discovered an extinct population of spotted-tailed quoll, different from both the modern mainland and Tasmanian populations, indicating that it once lived on Kangaroo Island and perhaps other parts of South Australia too.
"While Kangaroo Island is a renowned biodiversity hotspot, and natural haven for several threatened and endemic species, it has been continuously losing species richness since European arrival on the Island 200 years ago.
"From excavations of these ancient fossil bones, we now know more about the species that used to roam the Island before this human-caused decimation."
Dr Seersholm said this research was particularly important in the wake of the major bushfires of 2019/2020 which had a devastating impact on Kangaroo Island's pristine ecosystem.
"We hope our work in accurately identifying species can aid conservation and restoration efforts and help to restore the biodiversity on Kangaroo Island," Dr Seersholm said.
"While more research is needed in this area, our study has confirmed that Kangaroo Island could be a potential haven for the reintroduction of some species.
"If a quoll population should be introduced to the island, it is essential to get a detailed picture of the extinct quoll population. The research has also added the eastern grey kangaroo to the list of potential reintroduction candidates
"More data from similar cave sites is needed to generate a complete picture of the genetic diversity before European arrival and further samples of the spotted-tailed quoll from mainland South Australia will help to clarify whether they were unique to the island."
IMAGE: OBJECTS INCLUDING BONE SPOONS, QUERNSTONES AND GAMING PIECES WERE INCORPORATED INTO THE WALLS OF THIS IRON AGE ROUNDHOUSE AT BROXMOUTH IN NE SCOTLAND. view more
CREDIT: BROXMOUTH PROJECT ARCHIVE
Holding onto everyday items as keepsakes when a loved one dies was as commonplace in prehistory as it is today, a new study suggests.
The study from the University of York suggests mundane items like spoons and grinding stones were kept by Iron Age people as an emotional reminder and a 'continuing bond' with the deceased - a practice which is replicated in societies across the globe today.
The research focused on "problematic stuff": everyday items used or owned by a deceased person that relatives might not want to reuse but which they are unable to simply throw away.
At the Scottish hillfort settlement of Broxmouth, dating from 640BC to AD210, everyday items like quernstones, used for grinding grain, and bone spoons found between roundhouse walls could have been placed there by loved ones as a means of maintaining a connection with the person who had died.
The study compared this with contemporary examples of similar behaviour, with the retention of relatives' clothing or worn-out shoes being particularly recurrent themes.
Dr Lindsey Büster from the Department of Archaeology said: "It is important to recognise the raw emotional power that everyday objects can acquire at certain times and places.
"Archaeologists have tended to focus on the high material value or the quantity of objects recovered and have interpreted these as deposited for safe keeping or gifts to the gods.
"My work uses archaeology to open up discussions around death, dying and bereavement in contemporary society, demonstrating that even the most mundane objects can take on special significance if they become tangible reminders of loved ones no longer physically with us."
The paper demonstrates that in many societies, everyday items might well be included in the grave with the dead. Traditional interpretations of grave goods have often seen them as necessary for accompanying the dead to the afterlife, but the easy disposal of "problematic stuff" - that is objects not needed or desired by living relatives but not appropriate for throwing out onto the rubbish heap - is another possible explanation.
Dr Büster added: "Archaeologists tend to caution against the transplanting of modern emotions onto past societies but I suggest that the universality of certain emotions does allow for the extrapolation of modern experiences onto the past, even if the specifics vary.
"I consider the experience of grief and bereavement to be one such emotion, even if the ways in which this was processed and navigated varies between individuals and societies. This research helps bring us a little closer to past individuals whose experience of life (and death), was in some ways, not so different from our own."
The paper, "'Problematic stuff': death, memory and the interpretation of cached objects" is published in Antiquity.
New modeling technique shows greater likelihood, frequency of urban extreme heat events
UNIVERSITY OF ILLINOIS GRAINGER COLLEGE OF ENGINEERING
IMAGE: LEI ZHAO, UNIVERSITY OF ILLINOIS URBANA-CHAMPAIGN. view more
CREDIT: UNIVERSITY OF ILLINOIS URBANA-CHAMPAIGN
Extreme heat waves in urban areas are much more likely than previously thought, according to a new modeling approach designed by researchers including University of Illinois Urbana-Champaign Civil and Environmental Engineering (CEE) assistant professor Lei Zhao and alumnus Zhonghua Zheng (MS 16, PhD 20). Their paper with co-author Keith W. Oleson of the National Center for Atmospheric Research, "Large model structural uncertainty in global projections of urban heat waves," is published in the journal Nature Communications.
Urban heat waves (UHWs) can be devastating; a 1995 heat wave in Chicago caused more than 1,000 deaths. Last year's heat wave on the west coast caused wildfires. Global warming is expected to increase the incidence and severity of UHWs, but if cities fully understand their risk, they can prepare better with forecasts and warnings, safety guidance and improving access to health facilities like cooling centers and hospitals. Longer-term strategies include adaptation practices, which help cities adapt to the warmer temperatures induced by climate change - such as highly reflective roofs and pavements and green infrastructure - and mitigation practices, which help reduce the carbon emission - like renewable energy.
In recent years, though, an increase in record-breaking UHWs has caused concerns that the computer models used to predict them are flawed, leading to a systematic underestimation of their frequency and severity. Without accurate models, cities may dramatically misjudge their risk and fail to prepare accordingly, putting their citizens at greater risk as the world heats up.
Zhao's team has developed a model that closes two major gaps in urban climate modeling. First, most traditional climate models effectively ignore cities entirely. Urban areas make up only 2-3 percent of the earth's land, so their effect on global models is negligible, but more than half of the world's population lives in urban areas, so their impact is significant. The team's new modeling approach addresses that by providing urban-specific climate signals.
Second, because of this lack of urban representation in state-of-the-art climate models, there were no global-scale, multi-model projections for urban climates. The multi-model projections are critical to characterize the robustness and uncertainty of the projections, which is very important for estimating the climate-driven risks, for example, the likelihood of climate extremes. The new model provides global multi-model projections of local urban climates.
The paper also highlights four high-stakes regions - the Great Lakes region, southern Europe, central India and north China - and finds that cities in those areas had dramatically lower probabilities of risk with a single-model approach than with the researchers' multi-model approach. For example, the researchers found that using only traditional models, the Great Lakes region was expected to experience an extreme heat event only once in 10,000 years; with the researchers' new modeling technique, such events could be expected once every four years.
"This work highlights the critical importance of having multi-model projections to accurately estimate the likelihood of extreme events that will occur in the future under climate change," Zhao said.
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Funding for this work was provided by a start-up grant from CEE at Illinois. High-performance computing support was provided by the National Center for Atmospheric Research, funded by the National Science Foundation.
Novel smart cement can be used to build more durable roads and cities
Incorporating nanomaterials into traditional cement improves water and fracture resistance
IMAGE: PROFESSOR ANGE-THERESE AKONO HOLDS A SAMPLE OF HER SMART CEMENT. view more
CREDIT: NORTHWESTERN UNIVERSITY
Forces of nature have been outsmarting the materials we use to build our infrastructure since we started producing them. Ice and snow turn major roads into rubble every year; foundations of houses crack and crumble, in spite of sturdy construction. In addition to the tons of waste produced by broken bits of concrete, each lane-mile of road costs the U.S. approximately $24,000 per year to keep it in good repair.
Engineers tackling this issue with smart materials typically enhance the function of materials by increasing the amount of carbon, but doing so makes materials lose some mechanical performance. By introducing nanoparticles into ordinary cement, Northwestern University researchers have formed a smarter, more durable and highly functional cement.
The research was published today (June 21) in the journal Philosophical Transactions of the Royal Society A.
With cement being the most widely consumed material globally and the cement industry accounting for 8% of human-caused greenhouse gas emissions, civil and environmental engineering professor Ange-Therese Akono turned to nanoreinforced cement to look for a solution. Akono, the lead author on the study and an assistant professor in the McCormick School of Engineering, said nanomaterials reduce the carbon footprint of cement composites, but until now, little was known about its impact on fracture behavior.
"The role of nanoparticles in this application has not been understood before now, so this is a major breakthrough," Akono said. "As a fracture mechanics expert by training, I wanted to understand how to change cement production to enhance the fracture response."
Traditional fracture testing, in which a series of light beams is cast onto a large block of material, involves lots of time and materials and seldom leads to the discovery of new materials.
By using an innovative method called scratch testing, Akono's lab efficiently formed predictions on the material's properties in a fraction of the time. The method tests fracture response by applying a conical probe with increasing vertical force against the surface of microscopic bits of cement. Akono, who developed the novel method during her Ph.D. work, said it requires less material and accelerates the discovery of new ones.
"I was able to look at many different materials at the same time," Akono said. "My method is applied directly at the micrometer and nanometer scales, which saves a considerable amount of time. And then based on this, we can understand how materials behave, how they crack and ultimately predict their resistance to fracture."
Predictions formed through scratch tests also allow engineers to make changes to materials that enhance their performance at the larger scale. In the paper, graphene nanoplatelets, a material rapidly gaining popularity in forming smart materials, were used to improve the resistance to fracture of ordinary cement. Incorporating a small amount of the nanomaterial also was shown to improve water transport properties including pore structure and water penetration resistance, with reported relative decreases of 76% and 78%, respectively.
Implications of the study span many fields, including building construction, road maintenance, sensor and generator optimization and structural health monitoring.
By 2050, the United Nations predicts two-thirds of the world population will be concentrated in cities. Given the trend toward urbanization, cement production is expected to skyrocket.
Introducing green concrete that employs lighter, higher-performing cement will reduce its overall carbon footprint by extending maintenance schedules and reducing waste.
Alternately, smart materials allow cities to meet the needs of growing populations in terms of connectivity, energy and multifunctionality. Carbon-based nanomaterials including graphene nanoplatelets are already being considered in the design of smart cement-based sensors for structural health monitoring.
Akono said she's excited for both follow-ups to the paper in her own lab and the ways her research will influence others. She's already working on proposals that look into using construction waste to form new concrete and is considering "taking the paper further" by increasing the fraction of nanomaterial that cement contains.
"I want to look at other properties like understanding the long-term performance," Akono said. "For instance, if you have a building made of carbon-based nanomaterials, how can you predict the resistance in 10, 20 even 40 years?"
The study, "Fracture toughness of one- and two-dimensional nanoreinforced cement via scratch testing," was supported by the National Science Foundation Division of Civil, Mechanical and Manufacturing Innovation (award number 18929101).
Akono will give a talk on the paper at The Royal Society's October meeting, "A Cracking Approach to Inventing Tough New Materials: Fracture Stranger Than Friction," which will highlight major advances in fracture mechanics from the past century.
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The Science of tsunamis
Mechanical engineer Alban Sauret and colleagues develop a model to better understand the forces that generate these devastating waves
The word "tsunami" brings immediately to mind the havoc that can be wrought by these uniquely powerful waves. The tsunamis we hear about most often are caused by undersea earthquakes, and the waves they generate can travel at speeds of up to 250 miles per hour and reach tens of meters high when they make landfall and break. They can cause massive flooding and rapid widespread devastation in coastal areas, as happened in Southeast Asia in 2004 and in Japan in 2011.
But significant tsunamis can be caused by other events as well. The partial collapse of the volcano Anak Krakatau in Indonesia in 2018 caused a tsunami that killed more than 400 people. Large landslides, which send immense amounts of debris into the sea, also can cause tsunamis. Scientists naturally would like to know how and to what extent they might be able to predict the features of tsunamis under various circumstances.
Most models of tsunamis generated by landslides are based on the idea that the size and power of a tsunami is determined by the thickness, or depth, of the landslide and the speed of the "front" as it meets the water. In a paper titled "Nonlinear regimes of tsunami waves generated by a granular collapse," published online in the Journal of Fluid Mechanics, UC Santa Barbara mechanical engineer Alban Sauret and his colleagues, Wladimir Sarlin, Cyprien Morize and Philippe Gondret at the Fluids, Automation and Thermal Systems (FAST) Laboratory at the University of Paris-Saclay and the French National Centre for Scientific Research (CNRS), shed more light on the subject. (The article also will appear in the journal's July 25 print edition.)
This is the latest in a series of papers the team has published on environmental flows, and on tsunami waves generated by landslides in particular. Earlier this year, they showed that the velocity of a collapse -- i.e., the rate at which the landslide is traveling when it enters the water -- controls the amplitude, or vertical size, of the wave.
In their most recent experiments, the researchers carefully measured the volume of the granular material, which they then released, causing it to collapse as a cliff would, into a long, narrow channel filled with water. They found that while the density and diameter of the grains within a landslide had little effect on the amplitude of the wave, the total volume of the grains and the depth of the liquid played much more crucial roles.
"As the grains enter the water, they act as a piston, the horizontal force of which governs the formation of the wave, including its amplitude relative to the depth of the water," said Sauret. (A remaining challenge is to understand what governs the speed of the piston.) "The experiments also showed that if we know the geometry of the initial column [the material that flows into the water] before it collapses and the depth of the water where it lands, we can predict the amplitude of the wave."
The team can now add this element to the evolving model they have developed to couple the dynamics of the landslide and the generation of the tsunami. A particular challenge is to describe the transition from an initial dry landslide, when the particles are separated by air, to an underwater granular flow, when the water has an important impact on particle motion. As that occurs, the forces acting on the grains change drastically, affecting the velocity at which the front of grains that make up the landslide enters the water.
Currently, there is a large gap in the predictions of tsunamis based on simplified models that consider the field complexity (i.e., the geophysics) but do not capture the physics of the landslide as it enters the water. The researchers are now comparing the data from their model with data collected from real-life case studies to see if they correlate well and if any field elements might influence the results.
