Tag Archives: #air

Box Fan Air Cleaner Greatly Reduces Virus Transmission (Engineering)

Decades-old public classrooms with inadequate ventilation can be made safer with the use of a cardboard frame, air filter, and a low-cost box fan

Improved ventilation can lower the risk of transmission of the COVID-19 virus, but large numbers of decades-old public school classrooms lack adequate ventilation systems. A systematic modeling study of simple air cleaners using a box fan reported in Physics of Fluids, by AIP Publishing, shows these inexpensive units can greatly decrease the amount of airborne virus in these spaces, if used appropriately.

A low-cost air cleaner can be easily constructed from a cardboard frame topped by an air filter and a box fan. The air filter is placed between the fan and the cardboard base. The fan is oriented so that air is drawn in from the top and forced through the filter, discharging cleaned air downward.

The investigators measured the clean air delivery rate of the air cleaning system in experiments conducted at two independent laboratories. Tobacco smoke was used to simulate the airborne virus, since the virus is known to travel through the air after exhalation in droplets about the same size as smoke particulates.

The experimental measurements were incorporated into a detailed computational model of a classroom. In addition to the box fan air cleaner, a ventilation unit known as an HUV, or a horizontal unit ventilator, was included in the simulation. This type of ventilation system is very common in public schools and is usually placed along an outside wall, drawing in air near the floor and exhausting it at the top to circulate fresh air around a classroom.

A cloud of virus particles was assumed to enter the simulation from an infected individual. The investigators assumed this individual was the instructor and experimented with different placements of the box fan air cleaner.

“Placing the air cleaner near the potential infector is the most effective way to reduce the aerosol spread,” said author Jiarong Hong.

The simulations showed the best results were obtained by shifting both the box fan air cleaner and the infected instructor to a location near the HUV.

“At this location, owing to its proximity to both the infector and the HUV, the air cleaner extracts the majority of aerosols, leaving only a small percentage suspended in the air,” Hong said.

Although placing the air cleaner near an infected individual is best, it is not always possible to know who is infected. In this situation, the investigators recommend placing the air cleaner near the HUV, with the air cleaner outflow pointing toward the inlet of the HUV.

“In addition, we find that in large classrooms, distributing multiple air cleaners in the space is more effective in controlling aerosol spread than simply enhancing the flow rate of the HUV or air cleaners alone,” Hong said.

The article “Airborne transmission of COVID-19 and mitigation using box fan air cleaners in a poorly ventilated classroom” is authored by Ruichen He, Wanjiao Liu, John Elson, Rainer Vogt, Clay Maranville, and Jiarong Hong. The article will appear in Physics of Fluids on May 11, 2021 (DOI: 10.1063/5.0050058). After that date, it can be accessed at https://aip.scitation.org/doi/10.1063/5.0050058.

Featured image: Low-cost portable air cleaner for reducing virus spread in public school classrooms. © Ruichen He, Jiarong Hong


Provided by American Institute of Physics

Grabbing Viruses Out of Thin Air (Material Science)

The future could hold portable and wearable sensors for detecting viruses and bacteria in the surrounding environment. But we’re not there yet. Scientists at Tohoku University have been studying materials that can change mechanical into electrical or magnetic energy, and vice versa, for decades. Together with colleagues, they published a review in the journal Advanced Materials about the most recent endeavours into using these materials to fabricate functional biosensors.

A proposed future society. ©Tohoku University

“Research on improving the performance of virus sensors has not progressed much in recent years,” says Tohoku University materials engineer Fumio Narita. “Our review aims to help young researchers and graduate students understand the latest progress to guide their future work for improving virus sensor sensitivity.”

Piezoelectric materials convert mechanical into electrical energy. Antibodies that interact with a specific virus can be placed on an electrode incorporated onto a piezoelectric material. When the target virus interacts with the antibodies, it causes an increase in mass that decreases the frequency of the electric current moving through the material, signalling its presence. This type of sensor is being investigated for detecting several viruses, including the cervical-cancer-causing human papilloma virus, HIV, influenza A, Ebola and hepatitis B.

Magnetostrictive materials convert mechanical into magnetic energy and vice versa. These have been investigated for sensing bacterial infections, such as typhoid and swine fever, and for detecting anthrax spores. Probing antibodies are fixed onto a biosensor chip placed on the magnetostrictive material and then a magnetic field is applied. If the targeted antigen interacts with the antibodies, it adds mass to the material, leading to a magnetic flux change that can be detected using a sensing ‘pick-up coil’.

Narita says that developments in artificial intelligence and simulation studies can help find even more sensitive piezoelectric and magnetostrictive materials for detecting viruses and other pathogens. Future materials could be coilless, wireless, and soft, making it possible to incorporate them into fabrics and buildings.

Scientists are even investigating how to use these and similar materials to detect SARS-CoV-2, the virus that causes COVID-19, in the air. This sort of sensor could be incorporated into underground transportation ventilation systems, for example, in order to monitor virus spread in real time. Wearable sensors could also direct people away from a virus-containing environment.

“Scientists still need to develop more effective and reliable sensors for virus detection, with higher sensitivity and accuracy, smaller size and weight, and better affordability, before they can be used in home applications or smart clothing,” says Narita. “This sort of virus sensor will become a reality with further developments in materials science and technological progress in artificial intelligence, machine learning, and data analytics.”

References: Narita, F., Wang, Z., Kurita, H., Li, Z., Shi, Y., Jia, Y., Soutis, C., A Review of Piezoelectric and Magnetostrictive Biosensor Materials for Detection of COVID‐19 and Other Viruses. Adv. Mater. 2020, 2005448. https://onlinelibrary.wiley.com/doi/10.1002/adma.202005448 https://doi.org/10.1002/adma.202005448

Provided by Tohoku University

Membrane-Winged Dinosaurs Yi and Ambopteryx were Poor Gliders (Paleontology)

Yi qi and Ambopteryx longibrachium are two bizarre scansoriopterygid theropods that lived in what is now China about 160 million years ago (Late Jurassic epoch). They had skin stretched between elongate fingers that form a potential membranous wing. Most theropods were ground-loving carnivores, but Yi qi and Ambopteryx longibrachium were at home in the trees and lived on a diet of insects, seeds, and other plants. According to a new study published in the journal iScience, Yi qi and Ambopteryx longibrachium struggled to fly, only managing to glide clumsily between the trees where they lived; unable to compete with other tree-dwelling dinosaurs and early birds, they went extinct after just a few million years.

Ambopteryx longibrachium. Image credit: Chung-Tat Cheung & Min Wang / Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.

“Once birds got into the air, these two species were so poorly capable of being in the air that they just got squeezed out,” said first author Dr. Thomas Dececchi, a researcher in the Department of Biology at Mount Marty University.

“Maybe you can survive a few million years underperforming, but you have predators from the top, competition from the bottom, and even some small mammals adding into that, squeezing them out until they disappeared.”

Curious about how Yi qi and Ambopteryx longibrachium fly, Dr. Dececchi and colleagues scanned fossils using laser-stimulated fluorescence, a technique that uses laser light to pick up soft-tissue details that can’t be seen with standard white light.

They then used mathematical models to predict how these dinosaurs might have flown, testing many different variables like weight, wingspan, and muscle placement.

“They really can’t do powered flight. You have to give them extremely generous assumptions in how they can flap their wings,” Dr. Dececchi said.

‘You basically have to model them as the biggest bat, make them the lightest weight, make them flap as fast as a really fast bird, and give them muscles higher than they were likely to have had to cross that threshold.”

“They could glide, but even their gliding wasn’t great,” he noted.

Yi qi. Image credit: Highlightskids.

While gliding is not an efficient form of flight, since it can only be done if the animal has already climbed to a high point, it did help Yi qi and Ambopteryx longibrachium stay out of danger while they were still alive.

“If an animal needs to travel long distances for whatever reason, gliding costs a bit more energy at the start, but it’s faster. It can also be used as an escape hatch,” Dr. Dececchi said.

“It’s not a great thing to do, but sometimes it’s a choice between losing a bit of energy and being eaten.”

“Once they were put under pressure, they just lost their space. They couldn’t win on the ground. They couldn’t win in the air. They were done.”

The authors are now looking at the muscles that powered Yi qi and Ambopteryx longibrachium to construct an accurate image of these bizarre little creatures.

“I’m used to working with the earliest birds, and we sort of have an idea of what they looked like already,” Dr. Dececchi said.

“To work where we’re just trying to figure out the possibilities for a weird creature is kind of fun.”

References: T. Alexander Dececchi et al. Aerodynamics Show Membrane-Winged Theropods Were a Poor Gliding Dead-end. iScience, published online October 22, 2020; doi: 10.1016/j.isci.2020.101574

This article is republished here from sci news under common creative licenses.

Scientists Find Upper Limit For The Speed Of Sound (Physics)

A research collaboration between Queen Mary University of London, the University of Cambridge and the Institute for High Pressure Physics in Troitsk has discovered the fastest possible speed of sound.

The result- about 36 km per second—is around twice as fast as the speed of sound in diamond, the hardest known material in the world.

Waves, such as sound or light waves, are disturbances that move energy from one place to another. Sound waves can travel through different mediums, such as air or water, and move at different speeds depending on what they’re travelling through. For example, they move through solids much faster than they would through liquids or gases, which is why you’re able to hear an approaching train much faster if you listen to the sound propagating in the rail track rather than through the air.

Einstein’s theory of special relativity sets the absolute speed limit at which a wave can travel which is the speed of light, and is equal to about 300,000 km per second. However until now it was not known whether sound waves also have an upper speed limit when travelling through solids or liquids.

The study, published in the journal Science Advances, shows that predicting the upper limit of the speed of sound is dependent on two dimensionless fundamental constants: the fine structure constant and the proton-to-electron mass ratio.

These two numbers are already known to play an important role in understanding our Universe. Their finely-tuned values govern nuclear reactions such as proton decay and nuclear synthesis in stars and the balance between the two numbers provides a narrow ‘habitable zone’ where stars and planets can form and life-supporting molecular structures can emerge. However, the new findings suggest that these two fundamental constants can also influence other scientific fields, such as materials science and condensed matter physics, by setting limits to specific material properties such as the speed of sound.

The scientists tested their theoretical prediction on a wide range of materials and addressed one specific prediction of their theory that the speed of sound should decrease with the mass of the atom. This prediction implies that the sound is the fastest in solid atomic hydrogen. However, hydrogen is an atomic solid at very high pressure above 1 million atmospheres only, pressure comparable to those in the core of gas giants like Jupiter. At those pressures, hydrogen becomes a fascinating metallic solid conducting electricity just like copper and is predicted to be a room temperature superconductor. Therefore, researchers performed state-of-the-art quantum mechanical calculations to test this prediction and found that the speed of sound in solid atomic hydrogen is close to the theoretical fundamental limit.

Professor Chris Pickard, Professor of Materials Science at the University of Cambridge, said: “Soundwaves in solids are already hugely important across many scientific fields. For example, seismologists use sound waves initiated by earthquakes deep in the Earth interior to understand the nature of seismic events and the properties of Earth composition. They’re also of interest to materials scientists because sound waves are related to important elastic properties including the ability to resist stress.”

References: K. Trachenko, B. Monserrat, “Speed of sound from fundamental physical constants”, Science Advances 09 Oct 2020, Vol. 6, no. 41, eabc8662 DOI: 10.1126/sciadv.abc8662 link: https://advances.sciencemag.org/content/6/41/eabc8662

Provided by Queen Mary, University of London

Carboniferous-Period Sea Scorpion, “Eurypterid” Was Capable of Breathing Air (Paleontology)

Paleontologists have examined the fossilized remains of a previously unknown species of eurypterid (sea scorpion) and found direct evidence that these marine creatures were able to breathe in subaerial environments through their main respiratory organs.

Lamsdell et al present details of the respiratory organs of Adelophthalmus pyrrhae from the Carboniferous of Montagne Noire, France, revealed through micro computed tomography (μ-CT) imaging. Image credit: Lamsdell et al, doi: 10.1016/j.cub.2020.08.034

The new species, named Adelophthalmus pyrrhae, lived about 350 million years ago during the Carboniferous period.

It belongs to Eurypterida, a large group of extinct arthropods that thrived from the Ordovician through the Permian period.

Their closest living relatives are horseshoe crabs, which lay eggs on land but are unable to breathe above water.

The three-dimensionally preserved specimen of Adelophthalmus pyrrhae was found 25 years ago in the Lydiennes Formation in Montagne Noire region, France.

Using micro computed tomography (μ-CT) imaging technique, Dr. Lamsdell and colleagues studied the respiratory organs of Adelophthalmus pyrrhae.

First, they noticed that each gill on the sea scorpion was composed of a series of plates. But the back contained fewer plates than the front, prompting them to question how it could even breathe.

Then they zeroed in on trabeculae — pillars connecting the different plates of the gill, which are seen in modern scorpions and spiders.

The discovery of air-breathing structures in Adelophthalmus pyrrhae indicates that terrestrial characteristics occurred in the arachnid stem lineage, suggesting that the ancestor of arachnids were semi-terrestrial.

References: James C. Lamsdell et al. Air Breathing in an Exceptionally Preserved 340-Million-Year-Old Sea Scorpion. Current Biology, published online September 10, 2020; doi: 10.1016/j.cub.2020.08.034