Evidence for PeVatrons, the Milky Way’s Most Powerful Particle Accelerators (Astronomy)

The Tibet ASγ experiment, a China-Japan joint research project on cosmic-ray observation, has discovered ultra-high-energy diffuse gamma rays from the Milky Way galaxy. The highest energy detected is estimated to be unprecedentedly high, nearly 1 Peta electronvolts (PeV, or one million billion eV).

Surprisingly, these gamma rays do not point back to known high-energy gamma-ray sources, but are spread out across the Milky Way (see Featured image).

Scientists believe these gamma rays are produced by the nuclear interaction between cosmic rays escaping from the most powerful galactic sources (“PeVatrons”) and interstellar gas in the Milky Way galaxy. This observational evidence marks an important milestone in revealing the origin of cosmic rays, which has puzzled mankind for more than a century.

Cosmic rays are high-energy particles from outer space that are mainly composed of protons and nuclei, as well as small numbers of electrons/positrons and gamma rays. Cosmic rays below a few PeV are believed to be produced in our Milky Way galaxy, and a source that can accelerate cosmic rays up to PeV energy is called a PeVatron. Although supernova remnants, star-forming regions and the supermassive black hole at the galactic center are suggested to be candidate PeVatrons, none have been identified observationally yet, mainly because the majority of cosmic rays have an electric charge and will lose their original direction when propagating in the Milky Way as well as be bent by the magnetic field.

However, cosmic rays can interact with the interstellar medium near their acceleration place and produce gamma rays with roughly 10% of the energy of their parent cosmic rays. As the direction of electrically neutral gamma rays cannot be changed by the magnetic field, ultra-high-energy gamma rays (0.1-1 PeV) may tell us where the PeVatrons are in the Milky Way.

The Tibet ASγ experiment was started in 1990. After several expansions, the current air shower array consists of more than 500 radiation detectors distributed across about 65,000 square meters. In order to improve its sensitivity to gamma rays observations, new water Cherenkov-type muon detectors with a total effective area of 3,400 m2 were added under the existing surface cosmic-ray detectors in 2014 (see Fig. 2).

Since gamma-rays events are muon poor and the dominant proton/nucleus events are muon rich, this feature can be used to suppress the background induced by the proton/nucleus events. Using this technique, the Tibet ASγ experiment successfully reduced proton/nucleus background events to one millionth, the most efficient one ever realized in this kind of experiment. We can therefore detect ultra-high-energy gamma rays almost free of cosmic-ray background events.

Scientists from the Tibet ASγ experiment observed gamma rays with energies between about 0.1 and 1 PeV coming from the galactic disk regions. Specifically, they found 23 ultra-high-energy cosmic gamma rays with energies above 398 TeV along the Milky Way. Of these, the highest energy observed was nearly 1 PeV, which is a new world record for gamma ray photons detected anywhere.

Surprisingly, these gamma rays do not point back to the most powerful known high-energy gamma-ray sources, but are spread out along the Milky Way! Scientists soon noticed that these gamma rays probably originated from the interaction of PeV cosmic rays and the interstellar medium after they escaped from the acceleration sources (PeVatrons). This process, known as “hadronic origin,” produces gamma rays with energies roughly one-tenth that of their parent cosmic rays via the production and subsequent decay of neutral pions.

These diffuse gamma rays hint at the ubiquitous existence of powerful cosmic particle accelerators (PeVatrons) within the Milky Way. In other words, if PeVatrons exist, the cosmic rays they emit would permeate the galaxy, producing a diffuse glow of gamma rays of extreme energies. That’ s just what scientists with the Tibet ASγ experiment have found. This is a long-awaited discovery for decades, providing unequivocal evidence for the existence of PeVatrons in the past and/or now in our Milky Way galaxy.

Two years ago, scientists of the Tibet ASγ experiment found extremely energetic gamma rays from the Crab Nebula, a pulsar wind nebula in the Milky Way. Those gamma rays were probably produced in a different manner, such as by high energy electrons/positrons in the nebula, a process called “leptonic origin.”

Fig. 2. The China-Japan collaboration placed new water Cherenkov-type muon detectors under the existing air-shower array in 2014. (Image by IHEP)
Fig. 3. The Tibet air shower array located 4300 m above sea level in Tibet, China. (Image by IHEP)

Featured image: Fig. 1. Distribution of the ultra-high-energy gamma rays (yellow points) detected by the Tibet ASγ experiment in the galactic coordinate system. They are obviously concentrated along the galactic disk. The gray shaded area indicates what is outside of the field of view. The background color shows atomic hydrogen distribution in the galactic coordinates. (Image by https://lambda.gsfc.nasa.gov/product/foreground/fg_hi4pi_get.cfm)

Provided by Chinese Academy of Sciences

May LIGO Events Like GW190521, Have Emerged From The Mirror World Binaries? (Cosmology /Astronomy)


Beradze and Gogberashvili considered the possibility that LIGO events GW190521, GW190425 and GW190814 may have emerged from the mirror world binaries.

According to them, to form binaries similar to GW190521, GW190425 and GW190814, the component masses of which lie in the upper and lower mass gaps, hierarchical mergers of very rare systems are required.

They argued that such scenarios are order of magnitude more probable in mirror world, where star formation begins earlier and matter density can exceed 5 times the ordinary matter density.

Moreover, M-World is dominated by helium stars which evolve faster and create compact objects earlier.

So, in M-World hierarchical mergers are more probable and second-generation compact objects (remnants of first generation mergers) are formed with higher rate.

In May 2019, Advanced LIGO/VIRGO detected the signal GW 190521, which was radiated by the coalescence of two massive progenitor black holes (BHs) (91.4 M and 66.8 M). The most massive final blackhole (at 157.9 M), the very first “Intermediate Mass Black Hole” ever detected. It is located about 15 billion light-years away. Yeah, so, so far. The biggest surprise of GW190521 was that the primary BHs with massed 91 and 67 M lie within the mass gap produced by pair-instability supernova processes. There are also other unexpected GW signals like GW 190425 and GW190814 which astronomers believe that, they were likely radiated by the coalescence of objects with masses 2 & 1.4 M, 23.2 BH and 2.59 NS, respectively. Due to lack of objects discovered with these properties, we don’t have a definite theory for their formation mechanism for now.

Now, Beradze and Gogberashvili considered the possibility that LIGO events GW190521, GW190425 and GW190814 may have emerged from the mirror world binaries. According to them, to form binaries similar to GW190521, GW190425 and GW190814, the component masses of which lie in the upper and lower mass gaps, hierarchical mergers of very rare systems are required. They argued that such scenarios are order of magnitude more probable in mirror world, where star formation begins earlier and matter density can exceed 5 times the ordinary matter density. Their research paper recently appeared on Journal Monthly Notices of the Royal Astronomical Society.

Mirror World (M-World) was introduced to restore left-right symmetry of nature, suggesting that each Standard Model particle has its mirror partner with opposite chirality. The fundamental reason for existence of mirror partners has been first revealed in 1956 by Lee and Yang. Later, based on this idea, theory of M-World was introduced, stating that mirror particles are invisible for ordinary observers and vice versa. Only way for the interaction between these two worlds is gravity. So, gravitational waves (GW) radiated by mirror matter can be sensed by an ordinary observer.

If M-World really exists, it was created by the Big Bang along the ordinary universe. But its temperature, T′, must be lower than the temperature of our world, T. This requirement emerges from the fact that mirror particles, having similar cosmological abundance, also contribute into the Hubble expansion rate and they should not violate the Big Bang Nucleosynthesis (BBN) bound. This could be achieved if mirror and ordinary worlds are reheated asymmetrically after inflationary epoch.

Due to some factors, evolution of mirror stars can be somehow different from ordinary stars. Unlike our universe, in M-World with the lower temperature, T′ < T , all the processes occur earlier at higher redshifts. This means that the star formation rate, depending on the temperature ratio, will peak earlier at z ∼ 10, corresponding to the lookback time in our world. This implies that mirror BHs and NSs have more time to pick up mass and to create binaries in the area covered by the LIGO observations.

As M-World is several times colder, at ordinary BBN epoch the universe expansion rate is completely determined by ordinary world itself. So, M-World contribution into the ordinary light element production is negligible. In contrary, in the M-World nucleosynthesis epoch, the contribution of ordinary matter scales as x¯4 and plays a crucial role. It was shown that, for x ≲ 0.3, the mirror helium mass fraction can reach 75 − 80%. Thus, M-World is dominated by mirror helium and mirror stars are mostly He-stars.

Evolution of He-stars should be similar to ordinary stars, when latter have converted most of hydrogen into helium and formed a helium core. During the process of gravitational collapse of protogalaxy, it fragments into hydrogen clouds, which then cools and collapses until the opacity of the system becomes so high that the gas prefers to fragments into protostars. This is a way how first stars (Pop. III stars) in the Universe are formed. The lack of metals for that time, makes cooling process less efficient within clouds. So, their fragmentation could produce only high mass stars.

In the He-dominated world, the cooling process inside primordial clouds should have also a lower efficiency and mirror stars are formed even more massive. We know that higher is the mass of the ordinary star, the shorter is its life, as it burns out fuel faster. Increasing the initial helium abundance of a star, corresponds to the increase of the mean molecular weight, and correspondingly in both luminosity and effective temperature, that leads to the shorter lifetime. For instance, 10M⊙ star with 70% initial He content has the evolution timescale ∼ 10 times faster than the star with ordinary He abundance (24%).

At first, Beradze & Gogberashvili in their paper, considered possible M-World origin of the black holes (BHs) event GW190521. In principle, BH-BH mergers, which account for the most amount of LIGO events, should not have optical counterparts, so they can be originated from both normal (Pop III) stars and mirror ones. However, BH binaries of mirror origin merely amplifies chance of these BH-BH mergers. As the microphysics of mirror stars is similar to that of ordinary stars, they probably also are subject to pair instability and produce the mass gap for intermediate mass BHs. However, stars in M-World are born with higher initial mass, compared to ordinary stars, they evolve faster and higher quantity of massive BHs are formed in short period of time. Adding the fact that the mirror matter density is ∼ 5 times the ordinary matter density, collisions of BHs formed by mirror stars are more frequent, increasing merger rate naturally. As a consequence, formation of intermediate mass BHs is easier in M-World, that could be a good interpretation for the heavy components of GW190521. Also, BHs formed in the mirror matter environment, can increase in mass by accretion of mirror matter that has higher abundance compared to ordinary matter.

Another consequence of the M-World scenario, can be explanation of lower mass gap compact objects of the events GW190425 and GW190814. NS-NS or BH-NS mergers, in case they contain normal neutron stars (NSs), both should be typically accompanied by GRB and optical afterglows. However, neither GW190425 nor GW190814 had such associations. In their previous paper, Beradze et al. suggested that this could indicate to their mirror origin, i.e. as merger of mirror NSs in which case no optical counterpart should be expected. This can be not completely true in the presence of neutron-mirror neutron transitions, which can be rather fast process. Due to this effect, cores of normal matter can be formed inside the mirror NS, which can make their merger also optically observable though perhaps more faint.

So, the fact that ”heavy” NSs are not detected through electromagnetic spectrum but are observed through gravitational radiation, may be indication that they exist in the mirror world. As discussed in paper, in order to form a GW190425-like binary NS system, ultra-tight binary with NS and massive He-star is required, that is more easily achieved in mirror world, as M-World is inhabited mostly by He-stars. The formation of GW190814-like systems is also challenging for current theories and their abundance is expected to be extremely low. However, in M-World the abundance of matter exceeds ∼ 5 times the abundance of ordinary matter and stars in MWorld evolve a way faster.

This increases the probability of hierarchical mergers may by an order of magnitude, and the formation of GW190814-like systems is more common.

— concluded authors of the study

Reference: Revaz Beradze, Merab Gogberashvili, Unexpected LIGO events and the mirror world, Monthly Notices of the Royal Astronomical Society, Volume 503, Issue 2, May 2021, Pages 2882–2886, https://doi.org/10.1093/mnras/stab685

Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us

Two Plant Immune Branches More Intimately Connected than Previously Believed (Botany)

Plant inducible defense starts with the recognition of microbes, which leads to the activation of a complex set of cellular responses. There are many ways to recognize a microbe, and recognition of microbial features by pattern recognition receptors (PRRs) outside the cell was long thought to activate the first line of defense: Pattern Triggered Immunity, or PTI. To avoid these defense responses, microbes of all kinds evolved the ability to deliver effector molecules to the plant cell, either directly into the cytoplasm or into the area just outside the cell, where they are taken up into the cytoplasm. Response to these effector molecules was thought to be mediated exclusively by intracellular nucleotide-binding domain leucine-rich repeat receptors (NLRs) which induce Effector Triggered Immunity, or ETI. These two signaling pathways are often thought of as two distinct branches of the plant immune response, with each contributing differently to overall immunity. However, the dichotomy between PTI and ETI has become blurred due to recent discoveries, indicating that responses to PRR receptor signaling and NLR signaling extensively overlap.

“The two immune branches were previously considered to be separate but increasing evidence in recent years shows that they are intimately connected,” explained Kenichi Tsuda, a plant biologist at Huazhong Agricultural University in China. “It is time to re-think the current model.”

Over the past year and a half, exciting findings have revealed a much more complex and nuanced picture of plant defense. Tsuda and colleague You Lu, of the University of Minnesota in the United States, collaborated on a review recently published in the MPMI journal. Their goal was to integrate these new ideas with the long-standing model of separate ETI and PTI pathways into a newer, more nuanced model in which the pathways do exist, but with multiple points of interaction between them and in which each pathway is intimately connected.

These ideas are central to our understanding of the interactions between plants and microbes, but also have important implications for agriculture. “These two branches of plant immunity contribute majorly to pathogen resistance,” said Tsuda. “Modes of action of the plant immune system is fundamental to any application of our knowledge into practice such as agriculture.”

Despite the huge effort from the research community to understand plant defense signaling and the many recent advances, there are still many unknowns in this area. For example, Tsuda says the mechanism of “how NLRs use PRRs is completely unknown.” In fact, Lu and Tsuda propose two models that might explain this interaction at a cellular level, one of which involves signaling between cells in a tissue, leading to Tsuda’s recommendation for researchers to examine immune responses at the single cell level.

“As many researchers are tackling this question, we will need to update our model on a yearly basis,” Tsuda concluded.

Read more in “Intimate Association of PRR- and NLR-Mediated Signaling in Plant Immunity.” This study was made available online in December 2020 ahead of final publication in issue in January 2021. This article is part of the Top 10 Unanswered Questions invited review series in MPMI. See the list of the top 10 unanswered questions here. You can also watch Dr. Kenichi Tsuda present on this review article in his free virtual seminar.

Featured image: Dr. Kenichi Tsuda, plant biologist at Huazhong Agricultural University in China © Dr. Kenichi Tsuda

Reference: You Lu and Kenichi Tsuda, “Intimate Association of PRR- and NLR-Mediated Signaling in Plant Immunity”, IS-MPMI, 2021.


Provided by American Phytopathological Society

Potential New Treatment Strategy for Breast Cancer Cells That Have Spread to the Brain (Medicine)

Blocking fat production may starve the cells and shrink tumors

New research reveals that when breast cancer cells spread to the brain, they must boost production of fatty acids, the building blocks of fat, in order to survive there. The work, which is published in Nature Cancer and was led by investigators at Massachusetts General Hospital (MGH) and the Koch Institute of the Massachusetts Institute of Technology (MIT), points to a potential new treatment target for shrinking brain tumors that arise secondary to breast cancer.

Therapies that target the human epidermal growth factor receptor 2 (HER2) have transformed treatment for patients with breast cancer whose tumor cells express HER2, but brain metastases from this disease are typically fatal because they are resistant to anti-cancer therapies that are effective in other locations in the body. This is in part due to the blood-brain barrier that protects the brain against circulating toxins and pathogens, but changes in the cancer cells once they reach the brain may also play a role.

Such changes may occur because cancer cells that metastasize to the brain encounter differences in nutrient availability in brain tissue relative to other tissues in the body. Therefore, the malignant cells may have to alter how and what they metabolize to support tumor survival and growth. To investigate this possibility, researchers designed experiments in mice that assessed how metabolism differs between breast tumors that traveled to the brain and other locations in the body.

The team found that access to fats is limited for breast tumors to grow in the brain. In response, fatty acid synthesis is elevated in these tumor cells, as a result of increased activity of an enzyme called fatty acid synthase. “Consistent with our preclinical findings, clinical specimens of brain metastases from patients over-express fatty acid synthase relative to tumors that have not metastasized,” says co-lead author Gino Ferraro, PhD, a postdoctoral fellow in the E.L. Steele Laboratories for Tumor Biology at MGH.

The findings demonstrate that when a cancer has spread to a particular organ, potential treatment strategies could take advantage of the nutrient availability at that site. Inhibiting the cancer cells’ ability to use that nutrient may lead to their demise.

“To date, targeted therapies mostly focus on genetic vulnerabilities of cancer cells. Our work demonstrates that the environment in which the cancer cells reside can also dictate metabolic vulnerabilities that should be considered during the development of treatment strategies,” says co-corresponding author Rakesh K. Jain, PhD, director of the E.L. Steele Laboratories for Tumor Biology at MGH and the Andrew Werk Cook Professor of Radiation Oncology at Harvard Medical School.

The team notes that an inhibitor of fatty acid synthase, called TVB2166, is currently being evaluated in patients with metastatic breast cancer. “This compound is not brain-permeable, however, and patients with symptomatic brain metastases are excluded from these trials,” says co-corresponding author Matthew Vander Heiden, MD, PhD, an associate director of the Koch Institute at MIT and a member of the Broad Institute of MIT and Harvard. “Therefore, the efficacy and safety of this strategy in patients with brain metastases remains to be explored using brain-penetrable fatty acid synthase inhibitors.”

This work was supported in part by a Koch Institute/DFHCC Bridge project grant, Susan G. Komen for the Cure, HHMI, National Science Foundation, Ludwig Center for Molecular Oncology Fund, Novo Nordisk Foundation, Knut and Alice Wallenberg Foundation, NIH, National Foundation for Cancer Research, the Ludwig Center at Harvard, Jane’s Trust Foundation, Advanced Medical Research Foundation, U.S. Department of Defense Breast Cancer Research Program Innovator Award, Stand Up to Cancer, the MIT Center for Precision Cancer Medicine, the Ludwig Center at MIT and the Emerald Foundation.

Reference: Ferraro, G.B., Ali, A., Luengo, A. et al. Fatty acid synthesis is required for breast cancer brain metastasis. Nat Cancer (2021). https://www.nature.com/articles/s43018-021-00183-y https://doi.org/10.1038/s43018-021-00183-y

Provided by Massachusetts General Hospital

How the Chicxulub Impactor Gave Rise to Modern Rainforests? (Paleontology)

About 66 million years ago, a huge asteroid crashed into what is now the Yucatan, plunging the Earth into darkness. The impact transformed tropical rainforests, giving rise to the reign of flowers.

Tropical rainforests today are biodiversity hotspots and play an important role in the world’s climate systems. A new study published today in Science sheds light on the origins of modern rainforests and may help scientists understand how rainforests will respond to a rapidly changing climate in the future.

The study led by researchers at the Smithsonian Tropical Research Institute (STRI) shows that the asteroid impact that ended the reign of dinosaurs 66 million years ago also caused 45% of plants in what is now Colombia to go extinct, and it made way for the reign of flowering plants in modern tropical rainforests.

“We wondered how tropical rainforests changed after a drastic ecological perturbation such as the Chicxulub impact, so we looked for tropical plant fossils,” said Mónica Carvalho, first author and joint postdoctoral fellow at STRI and at the Universidad del Rosario in Colombia. “Our team examined over 50,000 fossil pollen records and more than 6,000 leaf fossils from before and after the impact.”

125 to 100 million years ago, during the reign of the dinosaurs, much of what is now Colombia was covered in forests dominated by conifers and ferns. Credit: Hace Tiempo. Un viaje paleontologico ilustrado por Colombia. Instituto Alexander von Humboldt e Instituto Smithsonian de Investigaciones Tropicales. Banco de Imágenes (BIA), Instituto Alexander von Humboldt.
Modern Bogotá is an Andean city at almost 3000m (9000 feet) above sea level. But in the Paleocene (the 10-million-year period following the asteroid impact) it was covered by tropical forest. Insect damage on fossil leaves collected near Bogotá tells researchers that after the impact, insects that picky eaters (insects that only ate a certain species) became less common, replaced by insects with more broad taste that could eat many different plants. Credit: Hace Tiempo. Un viaje paleontologico ilustrado por Colombia. Instituto Alexander von Humboldt e Instituto Smithsonian de Investigaciones Tropicales. Banco de Imágenes (BIA), Instituto Alexander von Humboldt.
From 66 to 100 million years ago, flowering plants began to diversify in sea level swamps and lowland forests, where the Andes mountains are today. Credit: Hace Tiempo. Un viaje paleontologico ilustrado por Colombia. Instituto Alexander von Humboldt e Instituto Smithsonian de Investigaciones Tropicales. Banco de Imágenes (BIA), Instituto Alexander von Humboldt.

In Central and South America, geologists hustle to find fossils exposed by road cuts and mines before heavy rains wash them away and the jungle hides them again. Before this study, little was known about the effect of this extinction on the evolution of flowering plants that now dominate the American tropics.

Carlos Jaramillo, staff paleontologist at STRI and his team, mostly STRI fellows—many of them from Colombia—studied pollen grains from 39 sites that include rock outcrops and cores drilled for oil exploration in Colombia, to paint a big, regional picture of forests before and after the impact. Pollen and spores obtained from rocks older than the impact show that rainforests were equally dominated by ferns and flowering plants. Conifers, such as relatives of the of the Kauri pine and Norfolk Island pine, sold in supermarkets at Christmas time (Araucariaceae), were common and cast their shadows over dinosaur trails. After the impact, conifers disappeared almost completely from the New World tropics, and flowering plants took over. Plant diversity did not recover for around 10 million years after the impact.

After the asteroid impact in Mexico, almost half of the plants existing before the impact became extinct. After the impact, flowering plants came to dominate modern tropical forests.. Credit: Hace Tiempo. Un viaje paleontologico ilustrado por Colombia. Instituto Alexander von Humboldt e Instituto Smithsonian de Investigaciones Tropicales. Banco de Imágenes (BIA), Instituto Alexander von Humboldt.
New and improved plant sex: Plants produced attractive flowers containing sugary rewards for insects who carry pollen (basically the male sperm of the plants) to other flowers, helping plants reproduce. This strategy was so successful that flowering plants took over tropical forests, and the world.. Credit: Hace Tiempo. Un viaje paleontologico ilustrado por Colombia. Instituto Alexander von Humboldt e Instituto Smithsonian de Investigaciones Tropicales. Banco de Imágenes (BIA), Instituto Alexander von Humboldt.
Modern tropical forests, like this lowland tropical forest in central Panama, are dominated by flowering plants. Credit: STRI Archives.

Leaf fossils told the team much about the past climate and local environment. Carvalho and Fabiany Herrera, postdoctoral research associate at the Negaunee Institute for Conservation Science and Action at the Chicago Botanic Garden, led the study of over 6,000 specimens. Working with Scott Wing at the Smithsonian’s National Museum of Natural History and others, the team found evidence that pre-impact tropical forest trees were spaced far apart, allowing light to reach the forest floor. Within 10 million years post-impact, some tropical forests were dense, like those of today, where leaves of trees and vines cast deep shade on the smaller trees, bushes and herbaceous plants below. The sparser canopies of the pre-impact forests, with fewer flowering plants, would have moved less soil water into the atmosphere than did those that grew up in the millions of years afterward.

“It was just as rainy back in the Cretaceous, but the forests worked differently.” Carvalho said.

The team found no evidence of legume trees before the extinction event, but afterward there was a great diversity and abundance of legume leaves and pods. Today, legumes are a dominant family in tropical rainforests, and through associations with bacteria, take nitrogen from the air and turn it into fertilizer for the soil. The rise of legumes would have dramatically affected the nitrogen cycle.

Carvalho also worked with Conrad Labandeira at the Smithsonian’s National Museum of Natural History to study insect damage on the leaf fossils.

Carlos Jaramillo, paleobiologist at the Smithsonian Tropical Research Institute in Panama, describes pollen grains based on up to 70 different characteristics. Is it brown or black, bumpy, smooth or pitted?. Credit: Jorge Aleman, STRI.
Mónica Carvalho and Fabiany Herrera collect leaf fossils from 58-60 Myr-old Neotropical rainforests near Bogotá, Colombia. Credit: Monica Carvahlo and Fabiany Herrera.
Carlos Jaramillo’s lab at the Center for Tropical Paleobiology and Archaeology is part of the Smithsonian Tropical Research Institute in Panama. Visiting scientists and students come to learn about the past from fossil leaves (shown here), animal fossils and fossilized plant pollen collected across Central and South America. Credit: Jorge Aleman, STRI.

“Insect damage on plants can reveal in the microcosm of a single leaf or the expanse of a plant community, the base of the trophic structure in a tropical forest,” Labandeira said. “The energy residing in the mass of plant tissues that is transmitted up the food chain—ultimately to the boas, eagles and jaguars—starts with the insects that skeletonize, chew, pierce and suck, mine, gall and bore through plant tissues. The evidence for this consumer food chain begins with all the diverse, intensive and fascinating ways that insects consume plants.”

 “Before the impact, we see that different types of plants have different damage: feeding was host-specific,” Carvalho said. “After the impact, we find the same kinds of damage on almost every plant, meaning that feeding was much more generalistic.”

How did the after effects of the impact transform sparse, conifer-rich tropical forests of the dinosaur age into the rainforests of today—towering trees dotted with yellow, purple and pink blossoms, dripping with orchids? Based on evidence from both pollen and leaves, the team proposes three explanations for the change, all of which may be correct. One idea is that dinosaurs kept pre-impact forests open by feeding and moving through the landscape. A second explanation is that falling ash from the impact enriched soils throughout the tropics, giving an advantage to the faster-growing flowering plants. The third explanation is that preferential extinction of conifer species created an opportunity for flowering plants to take over the tropics.

“Our study follows a simple question: How do tropical rainforests evolve?” Carvalho said. “The lesson learned here is that under rapid disturbances—geologically speaking—tropical ecosystems do not just bounce back; they are replaced, and the process takes a really long time.”

Fossil leaves from the collection used for this study. Heavily insect-fed spurge leaves from the 58-60 Myr-old Neotropical rainforests of the Bogotá Formation in Colombia. Today, the spurge family is one of the most abundant and diverse in lowland tropical rainforests. Credit: from Monica Carvalho.
Legume leaflets showing cylindrically shaped case-bearer (Lepidoptera: Coleophoridae)structures and evidence of adjacent leaf mining.
66-70 Million-year old, undamaged leaf next to a heavily eaten and insect-mined leaf depict host specificity in insect feeding patterns in the Late Cretaceous tropical rainforests of Colombia. Credit: from Monica Carvalho.
A Paleocene bug’s life. 58-60 Million year-old mallow leaf with insect feeding-damage, exemplifies the abundant and generalized herbivory found in Paleocene, modern-like tropical rainforests of Colombia. Credit: from Monica Carvalho.

Reference: Carvalho, M.R., Jaramillo, C., de la Parra, F., et al. 2021. Extinction at the end-Cretaceous and the origin of modern neotropical rainforests. Science. Link to the paper

The authors of this paper are affiliated with STRI in Panama, the Universidad del Rosario Bogota, Colombia; The Université de Montpellier, CNRS, EPHE, IRD, France; Universidad de Salamanca, Spain; the Instituto Colombiano del Petróleo, Bucaramanga, Colombia; the Chicago Botanic Garden; National Museum of Natural History, Washington, D.C.,; University of Florida, U.S.; Universidade Federal de Mato Grosso, Cuiabá, Brazil; ExxonMobil Corporation, Spring, Texas, U.S.; Centro Científico Tecnológico-CONICET, Mendoza, Argentina; Universidad de Chile, Santiago; University of Maryland, College Park, U.S.; Capital Normal University, Beijing, China; Corporación Geológica Ares, Bogota, Colombia; Paleoflora Ltda., Zapatoca, Colombia; University of Houston, Texas, U.S.; Instituto Amazónico de Investigaciones Científicas SINCHI, Leticia, Colombia; Universidad Nacional de Colombia, Medellín, Colombia; Boise State University, Boise, Idaho, U.S.; BP Exploration Co. Ltd., UK; and University of Fribourg, Switzerland.

Provided by Smithsonian Tropical Research Institute

Physicists Observed New State of Light (Physics)

Physicists at the University of Bonn observe new phase in Bose-Einstein condensate of light particles

A single “super photon” made up of many thousands of individual light particles: About ten years ago, researchers at the University of Bonn produced such an extreme aggregate state for the first time and presented a completely new light source. The state is called optical Bose-Einstein condensate and has captivated many physicists ever since, because this exotic world of light particles is home to its very own physical phenomena. Researchers led by Prof. Dr. Martin Weitz, who discovered the super photon, and theoretical physicist Prof. Dr. Johann Kroha have returned from their latest “expedition” into the quantum world with a very special observation. They report of a new, previously unknown phase transition in the optical Bose-Einstein condensate. This is a so-called overdamped phase. The results may in the long term be relevant for encrypted quantum communication. The study has been published in the journal Science.

The Bose-Einstein condensate is an extreme physical state that usually only occurs at very low temperatures. What’s special: The particles in this system are no longer distinguishable and are predominantly in the same quantum mechanical state, in other words they behave like a single giant “superparticle”. The state can therefore be described by a single wave function.

In 2010, researchers led by Martin Weitz succeeded for the first time in creating a Bose-Einstein condensate from light particles (photons). Their special system is still in use today: Physicists trap light particles in a resonator made of two curved mirrors spaced just over a micrometer apart that reflect a rapidly reciprocating beam of light. The space is filled with a liquid dye solution, which serves to cool down the photons. This is done by the dye molecules “swallowing” the photons and then spitting them out again, which brings the light particles to the temperature of the dye solution – equivalent to room temperature. Background: The system makes it possible to cool light particles in the first place, because their natural characteristic is to dissolve when cooled.

Clear separation of two phases

Phase transition is what physicists call the transition between water and ice during freezing. But how does the particular phase transition occur within the system of trapped light particles? The scientists explain it this way: The somewhat translucent mirrors cause photons to be lost and replaced, creating a non-equilibrium that results in the system not assuming a definite temperature and being set into oscillation. This creates a transition between this oscillating phase and a damped phase. Damped means that the amplitude of the vibration decreases.

Prof. Dr. Martin Weitz, Dr. Julian Schmitt, Dr. Frank Vewinger, Prof. Dr. Johann Kroha and Göran Hellmann from the Institute of Applied Physics at the University of Bonn. © Gregor Hübl/Uni Bonn

“The overdamped phase we observed corresponds to a new state of the light field, so to speak,” says lead author Fahri Emre Öztürk, a doctoral student at the Institute for Applied Physics at the University of Bonn. The special characteristic is that the effect of the laser is usually not separated from that of Bose-Einstein condensate by a phase transition, and there is no sharply defined boundary between the two states. This means that physicists can continually move back and forth between effects.

“However, in our experiment, the overdamped state of the optical Bose-Einstein condensate is separated by a phase transition from both the oscillating state and a standard laser,” says study leader Prof. Dr. Martin Weitz. “This shows that there is a Bose-Einstein condensate, which is really a different state than the standard laser. “In other words, we are dealing with two separate phases of the optical Bose-Einstein condensate,” he emphasizes.

The researchers plan to use their findings as a basis for further studies to search for new states of the light field in multiple coupled light condensates, which can also occur in the system. “If suitable quantum mechanically entangled states occur in coupled light condensates, this may be interesting for transmitting quantum-encrypted messages between multiple participants,” says Fahri Emre Öztürk.


The study received funding from the Collaborative Research Center TR 185 “OSCAR – Control of Atomic and Photonic Quantum Matter by Tailored Coupling to Reservoirs” of the Universities of Kaiserslautern and Bonn and the Cluster of Excellence ML4Q of the Universities of Cologne, Aachen, Bonn and the Research Center Jülich, funded by the German Research Foundation. The Cluster of Excellence is embedded in the Transdisciplinary Research Area (TRA) “Building Blocks of Matter and Fundamental Interactions” of the University of Bonn. In addition, the study was funded by the European Union within the project “PhoQuS – Photons for Quantum Simulation” and the German Aerospace Center with funding from the Federal Ministry for Economic Affairs and Energy.

Video:  https://youtu.be/PHSNJIu2IVo

Featured image: On the right is a microscope objective used to observe and analyze the light emerging from the Resonator. © Gregor Hübl/Uni Bonn

Publication: Fahri Emre Öztürk, Tim Lappe, Göran Hellmann, Julian Schmitt, Jan Klaers, Frank Vewinger, Johann Kroha & Martin Weitz: Observation of a Non-Hermitian Phase Transition in an Optical Quantum Gas. Science, DOI: 10.1126/science.abe9869

Provided by University of Bonn

Dynamic Model of SARS-CoV-2 Spike Protein Reveals Potential New Vaccine Targets (Biology)

New model captures glycan molecules whose motions shield much of the spike from immune defenses

A new, detailed model of the surface of the SARS-CoV-2 spike protein reveals previously unknown vulnerabilities that could inform development of vaccines. Mateusz Sikora of the Max Planck Institute of Biophysics in Frankfurt, Germany, and colleagues present these findings in the open-access journal PLOS Computational Biology.

SARS-CoV-2 is the virus responsible for the COVID-19 pandemic. A key feature of SARS-CoV-2 is its spike protein, which extends from its surface and enables it to target and infect human cells. Extensive research has resulted in detailed static models of the spike protein, but these models do not capture the flexibility of the spike protein itself nor the movements of protective glycans–chains of sugar molecules–that coat it.

To support vaccine development, Sikora and colleagues aimed to identify novel potential target sites on the surface of the spike protein. To do so, they developed molecular dynamics simulations that capture the complete structure of the spike protein and its motions in a realistic environment.

These simulations show that glycans on the spike protein act as a dynamic shield that helps the virus evade the human immune system. Similar to car windshield wipers, the glycans cover nearly the entire spike surface by flopping back and forth, even though their coverage is minimal at any given instant.

By combining the dynamic spike protein simulations with bioinformatic analysis, the researchers identified spots on the surface of the spike proteins that are least protected by the glycan shields. Some of the detected sites have been identified in previous research, but some are novel. The vulnerability of many of these novel sites was confirmed by other research groups in subsequent lab experiments.

“We are in a phase of the pandemic driven by the emergence of new variants of SARS-CoV-2, with mutations concentrated in particular in the spike protein,” Sikora says. “Our approach can support the design of vaccines and therapeutic antibodies, especially when established methods struggle.”

The method developed for this study could also be applied to identify potential vulnerabilities of other viral proteins.

In your coverage please use this URL to provide access to the freely available article in PLOS Computational Biologyhttps://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1008790

Funding: This work was supported by the Max Planck Society (https://www.mpg.de) (GH), the Austrian Science Fund FWF Schrödinger Fellowship J4332-B28 (https://www.fwf.ac.at) (MS), the Human Frontier Science Program RGP0026/2017 (https://www.hfsp.org) (GH), the Landes-Offensive zur Entwicklung Wissenschaftlich-Ökonomischer Exzellenz LOEWE of the State of Hesse (https://wissenschaft.hessen.de/wissenschaft/landesprogramm-loewe): DynaMem (GH) and CMMS (RC and GH), the Frankfurt Institute for Advanced Studies (https://fias.institute): (RC), and the Leibniz Supercomputing Centre Munich (https://www.lrz.de): SUPERspike (GH). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Featured image: In this visualization of antibody target sites, the SARS-CoV-2 spike protein is tethered to the viral membrane with a slender stalk. Patches of intense purple color at the surface of spike indicate potential target sites for antibodies that are not protected by the glycans –chains of sugar molecules–shown in green. These binding sites and their accessibility were identified with molecular dynamics simulations that capture the complete structure of the spike protein and its motions in a realistic environment. © Mateusz Sikora, Sören von Bülow, Florian E. C. Blanc, Michael Gecht, Roberto Covino and Gerhard Hummer

Reference: Sikora M, von Bülow S, Blanc FEC, Gecht M, Covino R, Hummer G (2021) Computational epitope map of SARS-CoV-2 spike protein. PLoS Comput Biol 17(4): e1008790. https://doi.org/10.1371/journal.pcbi.1008790

Provided by PLoS

Reverse-order Heart-liver Transplant Helps Prevent Rejection for Highly Sensitized Patients (Medicine)

All too often, patients with high levels of antibodies face major challenges getting a transplant. These highly sensitized patients have a much higher risk of death while waiting for suitable organs they are less likely to reject. But there is new hope for highly sensitized patients in need of a combined heart and liver transplant, thanks to an innovative surgical approach at Mayo Clinic.

Traditionally, surgeons transplant the heart first, followed by the liver. But Mayo Clinic heart transplant team decided to reverse the order for highly sensitized patients in the hopes that the liver would absorb some of the patient’s antibodies, removing them from circulation and lowering the risk of antibody-mediated rejection. The strategy worked, according to a study recently published in the Journal of the American College of Cardiology.

“This unique approach to heart-liver transplant opens the door to more highly sensitized patients getting the transplants they desperately need,” says Sudhir Kushwaha, M.D., a Mayo Clinic cardiologist and the study’s senior author.

More than 107,000 people in the U.S. are on the waitlist for a lifesaving transplant, according to the Organ Procurement and Transplantation Network. An estimated 20% of people waiting for a transplant are highly sensitized, meaning they have high antibody levels that can cause the immune system to reject a transplanted organ. People can become sensitized due to blood transfusions, pregnancies and previous transplants. April is National Donate Life Month, which encourages people to register to be organ, eye and tissue donors, and honor those who have given the gift of life.

The Mayo Clinic team was inspired to try the heart-after-liver transplant procedure after noting that patients who had undergone a traditional heart-liver transplant were much less likely to experience rejection than those who had a heart transplant alone. Previous research has shown a similar phenomenon for patients undergoing a simultaneous kidney-liver transplant.

Mayo Clinic began offering the pioneering heart-after-liver transplant surgery in 2011. The recently published study reviews the outcomes for seven patients who underwent the procedure. The patients were ages 33–51, and six of the seven were women. All experienced a significant drop in antibodies after the procedure was performed, and none of the patients had experienced rejection within four years following surgery. The study’s limitations include its small sample size and younger age of typical transplant patients.

While this new procedure is promising, it comes with major challenges. The heart is usually transplanted first because it is more time-sensitive than other organs. The reverse-order procedure requires a complex choreography between the heart and liver transplant teams to accomplish the procedure.

“Timing is everything. These surgeries require the heart and liver transplant teams to work closely together to limit the time it takes to transplant the donated organs,” says Richard Daly, M.D., a Mayo Clinic cardiothoracic surgeon and the paper’s first author.

Additional research is needed to see whether transplanting a portion of a donor’s liver would offer the same protective benefit for highly sensitized heart transplant patients. A recent editorial in the Journal of the American College of Cardiology concludes that heart-after-liver transplant surgery “could potentially increase the number of highly sensitized patients who undergo successful transplantation, shorten their waiting times, and clarify our understanding of how to improve tolerance and outcomes in all transplant recipients.”

The study’s other co-authors ― all of Mayo Clinic ― are Andrew Rosenbaum, M.D.; Joseph Dearani, M.D.Alfredo Clavell, M.D.; Naveen Pereira, M.D.; Barry Boilson, M.D.; Robert Frantz, M.D.Atta Behfar, M.D., Ph.D.; Shannon Dunlay, M.D.Richard Rodeheffer, M.D.; Timucin Taner, M.D., Ph.D.; Manish Gandhi, M.D.Julie Heimbach, M.D.; Charles Rosen, M.D.; and Brooks Edwards, M.D. The authors report no conflicts of interest.

Reference: Richard C. Daly, Andrew N. Rosenbaum et al., “Heart-After-Liver Transplantation Attenuates Rejection of Cardiac Allografts in Sensitized Patients”, J Am Coll Cardiol. 2021 Mar, 77 (10) 1331–1340. https://www.jacc.org/doi/10.1016/j.jacc.2021.01.013

Provided by Mayo Clinic

Consumers are Searching Online but Not Buying. Why? (Psychology)

Study reveals the keys to more efficient and profitable retargeting campaigns for online marketers.

Key Takeaways: 

  • Discounting or couponing is not the most effective way to tap the power of retargeting in online marketing.
  • Customized seller recommendations may be more powerful than discounting.
  • Seller auctions that allow marketers to self-select in the retargeting process improve cost efficiency.

Online marketers have seen the pattern: 95%-98% of online visitors search for something, but the search never converts into a purchase and they leave the site without buying. For marketers, this results in speculation and assumptions that can lead to wasted time and investments in ineffective marketing programs.

One of the more common ways online marketers attempt to solve this problem is to “retarget,” which tracks those consumers and reconnects with them at a later point by showing display ads when they browse other websites. You’ve probably noticed this when using Google Search to find something, such as a pair of shoes, and then later when you’re reading a separate news site, you’re exposed to a number of display ads centered on that very thing you were searching for earlier. 

Once that marketer gets your attention, what can they do to increase the likelihood that you will make a purchase? That question is at the center of a new study that reveals what the best approach to increase conversion rates may be. 

The research study to be published in the April issue of the INFORMS journal Marketing Science, “Consumer Search and Purchase: An Empirical Investigation of Retargeting Based on Consumer Online Behaviors,” is authored by Zhenling Jiang of The Wharton School at the University of Pennsylvania; Tat Chan of Washington University in St. Louis; Hai Che of the University of California; and Youwei Wang of Fudan University in Shanghai.

To conduct their research, the authors analyzed consumer behaviors in response to two distinct marketing strategies. In one approach, they sent out coupons via those retargeted display ads to be redeemed upon purchasing. In the other approach, the authors used the same display ads to provide seller recommendations that centered on a specific product offering customized to the user, but with no coupon or discount. 

“We found that while both strategies help increase the conversion rate, the seller recommendations were more effective than coupons,” said Jiang. “This told us that providing consumers with the sellers’ information that is most relevant to them may be a more effective way to tap the power of retargeting.”

To conduct their research, the authors tapped empirical data from Taobao.com, which is owned by Alibaba, and is the largest online retail platform in China. Like other major e-commerce platforms, it collects consumer browsing history and can reach consumers through direct messaging on the platform, either through the website or its mobile app. The researchers built a consumer search model to establish the relationship between consumer preference and search behaviors. They studied the behavior of 104,189 consumers who searched for a specific product among 20 sellers. 

“We noticed some predictable patterns,” said Jiang. “Consumers who had a higher search intensity for a specific product were more likely to actually make a purchase. Search intensity was measured in the volume of clicks tied to the same search or search term. What we found was that even where the consumer clicked on multiple possible products, it was the first link they clicked on that had the highest potential of generating a sale. In other words, after a more intense search, the consumer is more likely to go back to that initial seller once a decision to make a purchase is made.”

In addition to the two basic retargeting strategies – discounting or customization – the authors proposed to use auction as a pricing mechanism to implement the policies. The auction pricing mechanism requires the seller to self-select. This means the seller selects certain criteria for its ideal customer for a specific product at a specific price point, and then bids on how much it will pay to reach that consumer.

“Through our research, we were also able to show that a pricing mechanism, such as an auction, also tends to improve the effectiveness of a retargeting program,” said Jiang. “When Taobao used a pricing mechanism such as an auction, the company was able to improve the efficiency of its retargeting campaigns.”

Reference: Zhenling Jiang , Tat Chan, Hai Che , Youwei Wang, “Consumer Search and Purchase: An Empirical Investigation of Retargeting Based on Consumer Online Behaviors”, Informs, 12 Jan 2021. https://doi.org/10.1287/mksc.2020.1255 Link to Study

Provided by INFORMS and Marketing Science

About INFORMS and Marketing Science 

Marketing Science is a premier peer-reviewed scholarly marketing journal focused on research using quantitative approaches to study all aspects of the interface between consumers and firms. It is published by INFORMS, the leading international association for operations research and analytics professionals. More information is available at www.informs.org or @informs.