Can A Traversable Wormhole Exist Only At The Planck Scale? (Quantum / Cosmology)

Hideki Maeda presented a simple traversable wormhole solution which violate energy conditions only at the planck scale

Wormhole is a configuration of spacetimes containing distinct non-timelike infinities. In particular, a wormhole that contains a casual curve connecting such infinities are referred to as a traversable wormhole. Several examples of traversable wormholes have been already discussed by us in our articles. Now, Hideki Maeda presented a simple static spacetime which describes a spherically symmetric traversable worm-hole characterized by a length parameter, l and reduces to Minkowski in the limit l → 0. His findings recently appeared in Arxiv.

He showed that, this wormhole connects two distinct asymptotically flat regions with vanishing ADM mass and the areal radius of its throat is exactly l. Additionally, all the standard energy conditions i.e. null-energy condition, weak energy condition, dominant energy condition and standard energy condition are violated outside the proper radial distance approximately 1.60 l from the wormhole throat.

Finally, he computed the total amount of negative energy required to support this wormhole and found that, if l is identified as the Planck length lp (≃ 1.616 × 10¯35 m), the total amount of the negative energy supporting this wormhole is only E ≃ −2.65 mpc², which is the rest mass energy of about – 5.77 × 10¯5 g. For a “humanly traversable” wormhole with l = 1m, he obtained mass of −3.57 × 1027 kg, which is about –1.88 times as large as Jupiter’s mass.

“Ofcourse, an important task is to identify a theory of gravity which admits the static spacetime as a solution. Once such theory is identified, a subsequent task is to study the stability. Since the region of the NEC violation is tiny, our wormhole could be a dynamically stable configuration in the semiclassical regime. These important tasks are left for future investigations.”

— he concluded.

Reference: Hideki Maeda, “A simple traversable wormhole violating energy conditions only at the Planck scale”, Arxiv, pp. 1-4, 2021.

Note for editors of other websites: To reuse this article fully or partially kindly give credit either to our author/editor S. Aman or provide a link of our article

New Findings On The Function of Mitofusin 2 in The Cellular Energy Metabolism (Biology)

Mitofusin 2 is a key protein in the regulation of the physiology of mitochondria—cellular organelles that produce energy—involved in several neurodegenerative and cardiovascular diseases, as well as in cancer. Now, a study published in the journal EMBO Reports reveals that the regulation of the bioenergetic activity in the mitochondria requires mitofusin 2 to be found in the endoplasmic reticulum, a system built by a complex network of membranes in the cell cytoplasm.

The study is led by the lecturer Francesc Soriano, from the Faculty of Biology and the Institute of Neurosciences (UBNeuro) of the UB. Other co-authors of the paper are the experts Ofelia M. Martínez and Francesc Villarroya, from the Faculty of Biology and the Institute of Biomedicine (IBUB) of the UB, and Manuel Reina, from the same faculty, among others.

Mitofusin 2: A bridge between cell organelles

Mitofusin 2 (Mfn2) is a protein in the external membrane of the mitochondria with a distinguished role in several physiological processes: mitochondrial dynamics, energy metabolism, embryo development, cell death, etc. This essential protein in the morphology and function of mitochondria is involved in several pathologies related to dysfunctions in the production of mitochondrial energy. Therefore, understanding how Mfn2 regulates the mitochondrial bioenergy could serve to design new therapeutic strategies to work on neurodegenerative diseases in which the functionality of this protein is altered.

“Cells have a series of small specialized structures—cell organelles—that are not independent entities, but they interact, and this helps to regulate their function”, notes Professor Francesc Soriano, from the Department of Cell Biology, Physiology and Immunology. “Specifically, the Mfn2 has a mainly mitochondrial localization, but a small portion of the protein is also in the endoplasmic reticulum. In this location, Mfn2 interacts with the mitochondrial Mfn2 and Mfn1 proteins and establishes a bridge between both cell organelles”.

In the study, the team confirmed that the problems in the mitochondrial bioenergy in cells with Mfn2 deficiency can be solved with the expression of an artificial Mfn2 protein exclusively localized in the endoplasmic reticulum. “The bioenergetic physiology is restored in the cell, since it allows the establishing of the contacts between those two organelles, so it favors the journey of the calcium from the endoplasmic reticulum to the mitochondria that activates several enzymes involved in the generation of mitochondrial energy”.

Specifically, the team could reverse the defects in the neurite growth in neurons with Mfn2 deficiency thanks to the expression of an artificial Mfn2 protein that joins the endoplasmic reticulum and mitochondria. The study is a first proof of concept of new therapeutic strategies based on the restoration of cellular contacts between the endoplasmic reticulum and the mitochondria in the physiopathology of diseases associated with the Mfn2 protein.

Featured image: The Mfn2 has a mainly mitochondrial localization, but a small portion of the protein is also in the endoplasmic reticulum. Credit: University of Barcelona

More information: Sergi Casellas‐Díaz et al, Mfn2 localization in the ER is necessary for its bioenergetic function and neuritic development, EMBO reports (2021). DOI: 10.15252/embr.202051954

Provided by University of Barcelona

Water As A Metal (Physics)

Under normal conditions, pure water is an almost perfect insulator. Water only develops metallic properties under extreme pressure, such as exists deep inside of large planets. Now, an international collaboration has used a completely different approach to produce metallic water and documented the phase transition at BESSY II. The study is published now in Nature.

Every child knows that water conducts electricity—but this refers to “normal” everyday water that contains salts. Pure, distilled water, on the other hand, is an almost perfect insulator. It consists of H2O molecules that are loosely linked to one another via hydrogen bonds. The valence electrons remain bound and are not mobile. To create a conduction band with freely moving electrons, water would have to be pressurized to such an extent that the orbitals of the outer electrons overlap. However, a calculation shows that this pressure is only present in the core of large planets such as Jupiter.

Providing electrons

An international collaboration of 15 scientists from eleven research institutions has now used a completely different approach to produce a aqueous solution with metallic properties for the first time and documented this phase transition at BESSY II. To do this, they experimented with alkali metals, which release their outer electron very easily.

Avoiding explosion

However, the chemistry between alkali metals and water is known to be explosive. Sodium or other alkali metals immediately start to burn in water. But the team found a way to keep this violent chemistry in check: They did not throw a piece of alkali metal into water, but they did it the other way round: they put a tiny bit of water on a drop of alkali metal, a sodium-potassium (Na-K) alloy, which is liquid at room temperature.

Metallic water prepared for first time under terrestrial conditions
The first image shows a pure drop of sodium-potassium alloy; in the next images, we see the drop exposed to the action of the water vapor at 10-4 mbar. A layer of water forms on the drop, in which electrons liberated from the metal dissolve, giving it a golden metallic sheen. Credit: Phil Mason / IOCB Prague

Experiment at BESSY II

At BESSY II, they set up the experiment in the SOL3PES high vacuum sample chamber at the U49/2 beamline. The sample chamber contains a fine nozzle from which the liquid Na-K alloy drips. The silver droplet grows for about 10 seconds until it detaches from the nozzle. As the droplet grows, some water vapor flows into the sample chamber and forms an extremely thin skin on the surface of the droplet, only a few layers of water molecules. This almost immediately causes the electrons as well as the metal cations to dissolve from the alkali alloy into the water. The released electrons in the water behave like free electrons in a conduction band.

Golden water skin

“You can see the phase transition to metallic water with the naked eye! The silvery sodium-potassium droplet covers itself with a golden glow, which is very impressive,” reports Dr. Robert Seidel, who supervised the experiments at BESSY II. The thin layer of gold-colored metallic water remains visible for a few seconds. This enabled the team led by Prof. Pavel Jungwirth, Czech Academy of Sciences, Prague, to prove with spectroscopic analyses at BESSY II and at the IOCB in Prague that it is indeed water in a metallic state.

Fingerprints of the metallic phase

The two decisive fingerprints of a metallic phase are the plasmon frequency and the conduction band. The groups were able to determine these two quantities using optical reflection spectroscopy and synchrotron X-ray photoelectron spectroscopy: While the plasmon frequency of the gold-colored, metallic ‘water skin’ is about 2.7 eV (i.e. in the blue range of visible light), the conduction band has a width of about 1.1 eV with a sharp Fermi edge. “Our study not only shows that metallic water can indeed be produced on Earth, but also characterizes the spectroscopic properties associated with its beautiful golden metallic luster,” says Seidel.

Featured image: In the sample chamber, the NaK alloy drips from a nozzle. As the droplet grows, water vapor flows into the sample chamber and forms a thin skin on the drop’s surface. Credit: HZB

Reference: Philip E. Mason et al, Spectroscopic evidence for a gold-coloured metallic water solution, Nature (2021). DOI: 10.1038/s41586-021-03646-5

Provided by Helmholtz Association of German Research Centres

Hot And Dry: SPIRou Reveals the Atmosphere Of Hot Jupiter Tau Boötis b (Planetary Science)

Measuring the composition of the atmosphere of the hot Jupiter Tau Boötis b more precisely than ever, an iREx-led team of astronomers provides a better understanding of giant exoplanets.

Using the SPIRou spectropolarimeter on the Canada-France-Hawaii Telescope in Hawaii, a team led by Stefan Pelletier, a PhD student at Université de Montréal’s Institute for Research on Exoplanets (iREx), studied the atmosphere of the gas giant exoplanet Tau Boötis b, a scorching hot world that takes a mere three days to orbit its host star. 

Their detailed analysis, presented in a paper published today in the Astronomical Journal, shows that the atmosphere of the gaseous planet contains carbon monoxide, as expected, but surprisingly no water, a molecule that was thought to be prevalent and should have been easily detectable with SPIRou. 

Tau Boötis b is a planet that is 6.24 times more massive than Jupiter and eight times closer to its parent star than Mercury is to the Sun. Located only 51 light-years from Earth and 40 per cent more massive than the Sun, its star, Tau Boötis, is one of the brightest known planet-bearing stars, and is visible to the naked eye in the Boötes constellation.

Tau Boötis b was one of the first exoplanets ever discovered, in 1996, thanks to the radial velocity method, which detects the slight back-and-forth motion of a star generated by the gravitational tug of its planet. Its atmosphere had been studied a handful of times before, but never with an instrument as powerful as SPIRou to reveal  its molecular content. 

Searching for water 

Assuming Tau Boötis b formed in a protoplanetary disk with a composition similar to that of our Solar System, models show that water vapour should be present in large quantities in its atmosphere. It should thus have been easy to detect with an instrument such as SPIRou.

“We expected a strong detection of water, with maybe a little carbon monoxide,” explained Pelletier. “We were, however, surprised to find the opposite: carbon monoxide, but no water.”

The team worked hard to make sure the results could not be attributed to problems with the instrument or the analysis of the data.

“Once we convinced ourselves the content of water was indeed much lower than expected on Tau Boötis b, we were able to start searching for formation mechanisms that could explain this,” said Pelletier.

Studying hot Jupiters to better understand Jupiter and Saturn

“Hot Jupiters like Tau Boötis b offer an unprecedented opportunity to probe giant planet formation”, said co-author Björn Benneke, an astrophysics professor and  Pelletier’s PhD supervisor at UdeM. “The composition of the planet gives clues as to where and how this giant planet formed.”

The key to revealing the formation location and mechanism of giant planets is imprinted in their molecular atmospheric composition. The extreme temperature of hot Jupiters allows most molecules in their atmospheres to be in gaseous form, and therefore detectable with current instruments. Astronomers can thus precisely measure the content of their atmospheres.

“In our Solar System, Jupiter and Saturn are really cold,” said Benneke. “Some molecules such as water are frozen and hidden deep in their atmospheres; thus, we have a very poor knowledge of their abundance. Studying hot Jupiters provides a way to better understand our own giant planets. The low amount of water on Tau Boötis b could mean that our own Jupiter is also drier than we had previously thought.” 

The Canada-France-Hawaii Telescope, that hosts the SPIRou instrument that allowed Pelletier and his team to analyse exoplanet Tau Boötis b. Credits: Canada-France-Hawaii Telescope/Cuillandre.

SPIRou: a unique instrument

Tau Boötis b is one of the first planets studied with the new SPIRou instrument since it was recently put into service at the Canada-France-Hawaii Telescope. This instrument was developed by researchers from several scientific institutions including UdeM.

“This spectropolarimeter can analyze the planet’s thermal light — the light emitted by the planet itself — in an unprecedentedly large range of colours, and with a resolution that allows for the identification of many molecules at once: water, carbon monoxide, methane, etc.” said co-author and iREx researcher Neil Cook, an expert on the SPIRou instrument. 

The team spent 20 hours observing the exoplanet with SPIRou between April 2019 and June 2020.

“We measured the abundance of all major molecules that contain either carbon or oxygen,” said Pelletier. “Since they are the two most abundant elements in the universe, after hydrogen and helium, that gives us a very complete picture of the content of the atmosphere.” 

Like most planets, Tau Boötis b does not pass in front of its star as it orbits around it, from Earth’s point of view. However, the study of exoplanet atmospheres has mostly been limited to “transiting” planets – those that cause periodic dips in the light of their star when they obscure part of their light.

“It is the first time that we get such precise measurements on the atmospheric composition of a non-transiting exoplanet,” said PhD student Caroline Piaulet, a co-author of the study.

“This work opens the door to studying in detail the atmospheres of a large number of exoplanets, even those that do not transit their star.” 

A composition similar to Jupiter

Through their analysis, Pelletier and his colleagues were able to conclude that Tau Boötis b’s atmospheric composition has roughly five times as much carbon as that found in the Sun, quantities similar to that measured for Jupiter. 

This may be a suggest that hot Jupiters could form much further from their host star, at distances that are similar to the giant planets in our Solar System, and have simply experienced a different evolution, which included a migration towards the star. 

“According to what we found for Tau Boötis b, it would seem that, at least composition-wise, hot Jupiters may not be so different from our own Solar System giant planets after all,” concluded Pelletier.

About this study 

Where is the water? Jupiter-like C/H ratio but strong H2O depletion found on Tau Boötis b using SPIRou,” by Stefan Pelletier et al., was published July 28th, 2021 in the Astronomical Journal. 

In addition to Stefan PelletierBjörn BennekeNeil Cook and Caroline Piaulet, the team includes Institute for research on exoplanets (iREx) members Antoine Darveau-BernierAnne BoucherLouis-Philippe CoulombeÉtienne ArtigauDavid LafrenièreSimon DelisleRomain AllartRené DoyonCharles Cadieux and Thomas Vandal, all based at Université de Montréal, and seven other co-authors from France, the United States, Portugal and Brazil. 

Funding was provided by the the Technologies for Exo-Planetary Science (TEPS) CREATE program, the Fonds de recherche du Québec – Nature et technologies (FRQNT), the Natural Sciences and Engineering Research Council of Canada (NSERC), the Trottier Family Foundation and the French National Research Agency (ANR).

Featured image: Artistic rendition of the exoplanet Tau Boötis b and its host star, Tau Boötis. Credit : ESO/L. Calçada.

Reference: Stefan Pelletier et al, Where Is the Water? Jupiter-like C/H Ratio but Strong H2O Depletion Found on τ Boötis b Using SPIRou, The Astronomical Journal (2021). DOI: 10.3847/1538-3881/ac0428

Provided by University of Montreal

Molecular Atlas Reveals How Brain Cells Develop (Neuroscience)

As the fertilized egg divides, initially undifferentiated cells take on specific functions, becoming more distinct as different tissues and organs emerge. Understanding how hundreds of disparate cell types arise has proven difficult, largely because scientists have lacked the technologies to capture cellular decision making over time.

Recent advances have allowed researchers to measure changes in gene activity of individual cells, so several groups started to study in detail how specialized cell types are formed in specific brain regions. However, nobody had thus far traced the patterns of gene expression across the entire developing brain.

Now, for the first time, EPFL researchers and their collaborators at Karolinska Institute in Sweden mapped the genetic and developmental trajectories that embryonic cells follow toward their fate in the maturing brain. This molecular atlas could not only help better understand the healthy and diseased brain, but also improve therapeutic approaches such as cell replacement therapy for neurodegenerative diseases, says study lead author Gioele La Manno, head of the Laboratory of Neurodevelopmental Systems Biology at EPFL. The findings were published in Nature.

To monitor decision making in individual cells over time, La Manno and his colleagues analyzed brain samples from mouse embryos every day from day 7 after fertilization until birth. Using a combination of powerful sequencing techniques and mathematical methods, the researchers obtained about 290,000 gene expression profiles of individual cells from all brain regions, as well as nearly 800 cellular ‘states’ that included the developmental programs for different cells, including neurons and neuronal support cells.

As neuronal progenitors mature, they stop proliferating and differentiate into scores of different neurons. The researchers tracked the emergence of this diversity and described the timing of appearance of primitive nerve cells, called neuroblasts, across different brain regions. In mice, the first neuroblasts appear early, before day 9 of embryonic development—which roughly corresponds to the beginning of the first pregnancy trimester in humans. These pioneer neurons are involved in sensory and motor functions, the researchers found. “One of the first things to do is to set up the motor and sensory functions, because if you don’t set these up early, later on it will become more difficult to build ‘highways’ towards the periphery,” La Manno says.

The researchers also found specific types of neuronal progenitors, called organizer radial glial cells, whose role is to guide the development of neighboring cells by producing molecular messengers that help establish the position of various specialized cell types within the brain. “If the brain were an orchestra, organizer radial glial cells would be the director,” La Manno says. These radial glial cells produce a greater variety of molecular messengers than scientists thought, the team found.

The analysis also allowed the researchers to identify cell populations of different sizes, with some populations made of 100 times more cells than others. One of the biggest populations appears to be that of excitatory neurons in the forebrain, an area that comprises most regions involved in higher-order cognition. One of the smallest populations identified was that of a type of neuronal support cell called ependymal cells, which produce the fluid that surrounds the brain and spinal cord.

La Manno hopes that the wealth of information contained in this brain atlas could help identify genes involved in neurodevelopmental conditions and determine the origin of malignant cells in brain cancer. The atlas, he says, could also serve as a reference to evaluate brain tissues generated from stem cells in a laboratory dish. To help others study cells and tissues of medical interest, the researchers made the atlas publicly available as a browsable web resource.

Next, La Manno plans to uncover where in the developing brain the different cell populations are located. “The current atlas is a molecular chart that tells you which kind of cells are similar and which ones are different,” La Manno says. “Now, we want to see where these cells sit within the brain.”

Reference: Gioele La Manno et al, Molecular architecture of the developing mouse brain, Nature (2021). DOI: 10.1038/s41586-021-03775-x

Provided by Ecole Polytechnique Federale de Lausanne

Superconductivity in Cuprates: ‘From Maximal To Minimal Dissipation’ – A New Model? (Physics)

Researchers from the University of Bristol’s School of Physics used some of Europe’s strongest continuous magnetic fields to uncover evidence of exotic charge carriers in the metallic state of copper-oxide high-temperature superconductors.

Their results have been published this week in Nature. In a related publication in SciPost Physics last week, the team postulated that it is these exotic charge carriers that form the superconducting pairs, in marked contrast with expectations from conventional theory.

Conventional superconductivity

Superconductivity is a fascinating phenomenon in which, below a so-called critical temperature, a material loses all its resistance to electrical currents. In certain materials, at low temperatures, all electrons are entangled in a single, macroscopic quantum state, meaning that they no longer behave as individual particles but as a collective – resulting in superconductivity. The general theory for this collective electron behaviour has been known for a long time, but one family of materials, the cuprates, refuses to conform to the paradigm. They also possess the highest ambient-pressure superconducting transition temperatures known to exist. It was long thought that for these materials the mechanism that ‘glues together’ the electrons must be special, but recently the attention has shifted and now physicists investigate the non-superconducting states of cuprates, hoping to find clues to the origin of high-temperature superconductivity and its distinction from normal superconductors.

High-temperature superconductivity

Most superconductors, when heated to exceed their critical temperature, change into ‘ordinary’ metals. The quantum entanglement that causes the collective behaviour of the electrons fades away, and the electrons start to behave like an ordinary ‘gas’ of charged particles.

Cuprates are special, however. Firstly, as mentioned above, because their critical temperature is considerably higher than that of other superconductors. Secondly, they have very special measurable properties even in their ‘metallic phase’. In 2009, physicist Prof Nigel Hussey and collaborators observed experimentally that the electrons in these materials form a new type of structure, different from that in ordinary metals, thereby establishing a new paradigm that scientists now call the ‘strange metal’. Specifically, the resistivity at low temperatures was found to be proportional to temperature, not at a singular point in the temperature versus doping phase diagram (as expected for a metal close to a magnetic quantum critical point) but over an extended range of doping. This extended criticality became a defining feature of the ‘strange metal’ phase from which superconductivity emerges in the cuprates.

Magnetoresistance in a strange metal

In the first of these new reports, EPSRC Doctoral Prize Fellow Jakes Ayres and PhD student Maarten Berben (based at HFML-FELIX in Nijmegen, the Netherlands) studied the magnetoresistance – the change in resistivity in a magnetic field – and discovered something unexpected. In contrast to the response of usual metals, the magnetoresistance was found to follow a peculiar response in which magnetic field and temperature appear in quadrature. Such behaviour had only been observed previously at a singular quantum critical point, but here, as with the zero-field resistivity, the quadrature form of the magnetoresistance was observed over an extended range of doping. Moreover, the strength of the magnetoresistance was found to be two orders of magnitude larger than expected from conventional orbital motion and insensitive to the level of disorder in the material as well as to the direction of the magnetic field relative to the electrical current. These features in the data, coupled with the quadrature scaling, implied that the origin of this unusual magnetoresistance was not the coherent orbital motion of conventional metallic carriers, but rather a non-orbital, incoherent motion from a different type of carrier whose energy was being dissipated at the maximal rate allowed by quantum mechanics.

From maximal to minimal dissipation

Prof Hussey said: “Taking into account earlier Hall effect measurements, we had compelling evidence for two distinct carrier types in cuprates – one conventional, the other ‘strange’. The key question then was which type was responsible for high-temperature superconductivity? Our team led by Matija Čulo and Caitlin Duffy then compared the evolution of the density of conventional carriers in the normal state and the pair density in the superconducting state and came to a fascinating conclusion; that the superconducting state in cuprates is in fact composed of those exotic carriers that undergo such maximal dissipation in the metallic state. This is a far cry from the original theory of superconductivity and suggests that an entirely new paradigm is needed, one in which the strange metal takes centre stage.” 

Reference Paper: Ayres, J., Berben, M., Čulo, M. et al. Incoherent transport across the strange-metal regime of overdoped cuprates. Nature 595, 661–666 (2021).

Provided by University of Bristol

Chaotic Electrons Heed ‘Limit’ in Strange Metals (Physics)

Electrons in metals try to behave like obedient motorists, but they end up more like bumper cars. They may be reckless drivers, but a new Cornell-led study confirms this chaos has a limit established by the laws of quantum mechanics.

The team’s paper, “Linear-in Temperature Resistivity From an Isotropic Planckian Scattering Rate,” written in collaboration with researchers led by Louis Taillefer from the University of Sherbrooke in Canada, published July 28 in Nature. The paper’s lead author is Gael Grissonnanche, a postdoctoral fellow with the Kavli Institute at Cornell for Nanoscale Science.

Metals carry electric current when electrons all move together in tandem. In most metals, such as the copper and gold used for electrical wiring, the electrons try to avoid each other and flow in unison. However, in the case of certain “strange” metals, this harmony is broken and electrons dissipate energy by bouncing off each other at the fastest rate possible. The laws of quantum mechanics essentially play the role of an electron traffic cop, dictating an upper limit on how often these collisions can occur. Scientists previously observed this limit on the collision rate, also known as the “Planckian limit,” but there is no concrete theory that explains why the limit should exist, nor was it known how electrons reach this limit in strange metals. So the researchers set out to carefully measure it.

“Empirically, we’ve known that electrons can only bounce into each other so fast. But we have no idea why,” said Brad Ramshaw, the Dick & Dale Reis Johnson Assistant Professor in the College of Arts and Sciences, and the paper’s senior author. “Before, the ‘Planckian limit’ was just kind of inferred from data using very simple models. We did a very careful measurement and calculation and showed that it really is obeyed right down to the fine details. And we found that it’s isotropic, so it’s the same for electrons traveling in any direction. And that was a big surprise.”

The researchers focused their study on a copper oxide-based high-temperature superconductor known as a cuprate. Working with collaborators at the National High Magnetic Field Laboratory in Tallahassee, Florida, they introduced a sample of cuprate metal into a 45-tesla hybrid magnet – which holds the world record for creating the highest continuous magnetic field – and recorded the change in the sample’s electrical resistance while shifting the magnetic field’s angle. Ramshaw’s team then spent the better part of two years creating numerical data analysis software to extract the pertinent information.

Surprisingly, they were able to analyze their data with the same relatively simple equations used for conventional metals, and they found the cuprate metal’s electrons obeyed the Planckian limit.

“This approach that we used was supposed to be too naïve,” Grissonnanche said. “For scientists in the field, it is not obvious a priori that this should work, but it does. So with this new discovery, we have killed two birds with one stone: we have extended the validity of this simple approach to strange metals and we have accurately measured the Planckian limit. We are finally unlocking the enigma behind the intense motions of electrons in strange metals.”

“It doesn’t seem to depend on the details of the material in particular,” Taillefer said. “So it has to be something that’s almost like an overriding principle, insensitive to detail.”

Ramshaw believes that other researchers may now use this calculation framework to analyze a wide class of experimental problems and phenomena. After all, if it works in strange metals, it should work in many other areas.

And perhaps those strange metals are a little more orderly than previously thought.

“You’ve got these wildly complicated microscopic ingredients and quantum mechanics and then, out the other side, you get a very simple law, which is the scattering rate depends only on the temperature and nothing else, with a slope that’s equal to the fundamental constants of nature that we know,” he said. “And that emergence of something simple from such complicated ingredients is really beautiful and compelling.”

Such discoveries may also enable deeper understanding of the connections between quantum systems and similar phenonmena in gravitation, such as the physics of black holes – in effect, bridging the dizzyingly small world of quantum mechanics and their “dual” theories in general relativity, two branches of physics that scientists have been trying to reconcile for nearly a century.

Co-authors include doctoral student Yawen Fang and researchers from Université de Sherbrooke in Canada, University of Texas at Austin, the National High Magnetic Field Laboratory and University of Warwick in the United Kingdom.

The research was supported in part by the National Science Foundation, the European Research Council, the Canadian Institute for Advanced Research, the Natural Sciences and Engineering Research Council of Canada, the Canada First Research Excellence Fund and the Gordon and Betty Moore Foundation’s EPiQS Initiative.

Featured image: An artist’s impression of electrons orbiting the nucleus. © Roman Sigaev/

Reference: Grissonnanche, G., Fang, Y., Legros, A. et al. Linear-in temperature resistivity from an isotropic Planckian scattering rate. Nature 595, 667–672 (2021).

Provided by Cornell University

Bacteria From Nematodes Could Be Used To Kill Fire Ants (Biology)

Bacteria-infected nematodes may provide biological control of invasive European fire ants found in Maine, according to a University of Maine-led study.

UMaine scientists found that dead fire ants, Myrmica rubra, in colonies on Mount Desert Island and Orono were infected by nematodes, or roundworms, harboring bacteria, particularly in their digestive tracts. Their findings led them to investigate whether the nematodes killed the ants by transporting bacteria from the soil to the ants, where they may have contributed to ant mortality. They also explored what bacteria communities might be involved. 

The researchers found that bacteria species in the Serratia and Pseudomonas genuses were able to be transported by nematodes into ants or other insects they infect, and may be  the cause of the fire ant mortality. Many different species of Serratia and Pseudomonas are found in the environment and under the right conditions, they can cause harm to insects, animals or humans, researchers say.  They also argue that the life stages and morphology of nematodes may play a role in the attachment and retention of environmental bacteria. 

Their findings are published in the journal iScience

“There is a lot of research left before nematode transmission of bacteria could be used as biological control against ants, but it remains an intriguing possibility,” says lead author Sue Ishaq, an assistant professor of animal and veterinary sciences.

Ishaq and her colleagues say that bacteria found in the digestive tracts of nematodes or on their exterior cuticle could be carried into the bodies of the ants when the nematodes infect their hosts. To test this, they conducted a lab experiment in which they fed fluorescent bacteria to nematodes and then examined the nematodes for signs that fluorescent bacteria could be carried on or in their bodies and into exposed waxworms. 

Adult nematodes from the study had high concentrations of bacteria in their digestive tracts, but none on their cuticles, according to researchers. Juvenile nematodes had more on their cuticle than in the digestive tract. In a preliminary assay, the researchers didn’t find that labeled bacteria had transferred into the waxworm larvae, which they say leaves the effectiveness of nematode as a consistent vector for lethal bacteria transmission in fire ants in question. Further study, they say, is necessary to confirm this.

Alice Hotopp
Alice Hotopp © Photo courtesy of Alice Hotopp

Where nematodes come from, which determines which bacteria communities they access, might also affect their ability to cause fire ant mortality. Local conditions contribute to how bacteria in the environment “grow up,” and some conditions might favor the development of bacteria that are more infectious, Ishaq says. Only nematodes from Breakneck Road in Acadia National Park and Orono, and not the Visitor Center in Hulls Cove, caused ants to die off, presumably because the nematodes harbored bacteria that killed insects, according to researchers.  

“The problem with using bacteria as a mode of biological control is that they don’t always act the way you want them to — sometimes they are uncooperative team members,” Ishaq says.    

The new study builds on more than a decade of research into possible methods for controlling the invasive ants, which have infested areas across Maine, particularly along the coast, for about 50 years. Their competitive and aggressive nature have made fire ants, named for their painful sting, almost impossible to eradicate, prompting scientists to turn to biological methods.

Eleanor Groden, a recently retired UMaine professor of entomology and a co-author of the latest study, has been at the forefront of UMaine’s investigation of the problem since the mid-2000s, leading multiple studies exploring possible ways to eradicate them. In 2015, she and her colleagues released a study detailing their discovery of a new species of fungi that had killed fire ants in Maine. At the time, however, Groden said “it may be too difficult to reproduce, which would hamper its development as a biological control mechanism.” Additional investigations turned Groden and University of Arizona professor Patricia Stock, who also contributed to the latest study, toward nematodes.

The latest study served as the culmination of research from various scientists, Ishaq says, including Jean MacRae, an associate professor of civil and environmental engineering, and UMaine Honors College alumni Amy Michaud, now a researcher from the University of California, Davis, Jonathan Dumont, now an instructor with Husson University, and others. 

Ishaq says she conducted DNA sequencing data analysis from earlier bacterial experiments with UMaine graduate students Alice Hotopp and Samanatha Silverbrand as part of their graduate-level data analysis course. Their work rounded out the investigations so far conducted by the research team, and it was collectively published this year in the iScience report. Typically, Ishaq says she works on the bacteria that associate with mammals.

“I am delighted to have participated in this research, as it gave me a new research perspective on the way that bacteria might interact with insect or animal hosts,” Ishaq says.

Reference: Suzanne L. Ishaq et al, Bacterial transfer from Pristionchus entomophagus nematodes to the invasive ant Myrmica rubra and the potential for colony mortality in coastal Maine, iScience (2021). DOI: 10.1016/j.isci.2021.102663

Provided by University of Maine

Novel Method For Fast 3D Microscopy (Physics)

In the past, many discoveries have been made because better, more accurate measurement methods have become available, making it possible to obtain data from previously unexplored phenomena. For example, high-resolution microscopy has begun to dramatically change our perspectives of cell function and dynamics. Researchers at the ImmunoSensation2 Cluster of Excellence at the University of Bonn, the University Hospital and the research center caesar have now develop a method that allows using multi-focal images to reconstruct the movement of fast biological processes in 3D. The study has been recently published in the journal Nature Communications.

Many biological processes happen on a nano- to millimeter scale and within milliseconds. Established methods such as confocal microscopy are suitable for precise 3D recordings but lack the temporal or spatial resolution to resolve fast 3D processes and require labeled samples. For many investigations in biology, image acquisition at high frame rates is essential to record and understand the principles that govern cellular functions or fast animal behaviors. The challenge facing the scientists can be compared to following a thrilling tennis match: Sometimes it is not possible to follow the fast-moving ball with precision, or the ball is not discovered before it is already out of bounds.

With previous methods, the researchers were unable to track the shot because the image was blurred or the object of interest was simply no longer in the field-of-view after the picture was taken. Standard multifocal imaging methods allow high-speed 3D imaging but are limited by the compromise between high resolution and large field-of-view, and they often require bright fluorescent labels.

For the first time, the hereby described method allows multifocal imaging with both a large field of view and a high spatio-temporal resolution to be used. In this study, the scientists track the movement of non-labeled spherical and filamentous structures quickly and accurately.

As very strikingly described in the study, the new method now provides novel insight into the dynamics of flagellar beating and its connection to the swimming behavior of sperm. This connection has been possible because the researchers were able to precisely record the flagellar beat of free-swimming sperm in 3D over a long period of time and simultaneously follow sperm trajectories of individual sperm. In addition, the scientists determined the 3D fluid flow around the beating sperm. Such findings not only open the door to understand causes of infertility, but could also be used in so-called “bionics,” i.e., the transfer of principles found in nature to technical applications.

Researchers at the ImmunoSensation2 Cluster of Excellence can already use the new method—and not just to observe sperm. This method could also be used to determine the 3D flow maps that result from the beating of motile cilia. Motile cilia beat in a similar way to the sperm tail and transport fluid. Cilia-driven flow plays an important role in the ventricle of the brain or in the airways where it serves to transport mucus out of the lungs and into the throat- this is also how pathogens are transported out and warded off.

The multi-focal imaging concept reported in this study is cost-effective, can be easily implemented, and does not rely on object labeling. The researchers assert that their new method can find its way into other fields as well, and they see many other potential applications.

Featured image: A new method – provides novel insight into the dynamics of flagellar beating and its connection to the swimming behavior of sperm. Credit: René Pascal

Reference: Jan N. Hansen et al, Multifocal imaging for precise, label-free tracking of fast biological processes in 3D, Nature Communications (2021). DOI: 10.1038/s41467-021-24768-4

Provided by University of Bonn