Measuring the Wave (Physics)

New method displays accelerating field in plasma accelerator with unparalleled precision.

The technology of plasma-based acceleration promises to deliver a new generation of powerful and compact particle accelerators. Prior to applying this new technology, however, various obstacles must be overcome. In particular precise control of the acceleration process itself must be achieved. Using an innovative technique researchers at DESY have now succeeded in measuring the accelerating plasma wake with previously unattained precision. Their method allows the shape of the effective accelerating field to be determined with a resolution on the order of femtoseconds (trillionths of a millionth of a second) so that the acceleration process can be studied in great detail, thereby paving the way for the controlled and optimised operation of future plasma accelerators, as the team led by DESY’s Jens Osterhoff explains in the journal Nature Communications.

An electron bunch with varying energy (dark blue to orange) drives a plasma wave (white) with strong electric fields (red and blue). Removing thin slices from the tail of the electron bunch in a controlled manner allows the precise measurement of the electric fields. Credit: DESY, Ángel Ferran Pousa

A plasma is a gas but with its molecules stripped of their electrons. A high-energy laser or particle beam can force these freely-moving plasma electrons to oscillate, which results in strong electric fields. These can then be used to accelerate charged particles. To achieve this DESY’s FLASHForward facility fires bunches of electrons into a plasma at close to the speed of light. “A wake of plasma electrons forms behind the electron bunch and another electron bunch can surf along on this wake, whereby it is accelerated in the process: like a wakeboarder riding the wake of a boat,” explains Osterhoff. “This is why the technique is also known as plasma wakefield acceleration.”
The acceleration produced by the plasma wake can be up to a thousand times greater than that of the strongest conventional systems currently in operation. “To achieve optimal acceleration the electron bunches and the wake need to be precisely tuned to each other,” explains Sarah Schröder, the principal author of the paper, who works at DESY and the University of Hamburg. “To do that you have to be able to measure the shape of the wake precisely and this is very challenging due to its small dimensions, being just a few thousandths of a millimetre long.”

So the team developed a method whereby the accelerated electrons themselves are used to reveal the shape of the plasma wake’s accelerating field. To achieve this, the electron bunch is first rotated by a magnetic chicane. Thin slices can then be removed from the bunch tail by transversely inserting a piece of metal. Finally the electron bunch is rotated back again.

View of the FLASHForward accelerator module. The plasma is generated in the narrow channel in the centre by a high voltage. Credit: DESY, Alexander Knetsch

The resulting energy spectrum of the outgoing electron bunch is, therefore, altered due to the missing electrons, allowing the strength of the accelerating field at the location where part of the bunch was removed to be deduced. If the bunch is sliced thinly enough, the profile of the effective accelerating field in the plasma wake can be determined with a temporal resolution of femtoseconds. In the experiment, the team was able to achieve a resolution of 15 femtoseconds – corresponding to a spatial resolution of around 5 thousandths of a millimetre in the wake. The researchers believe that even higher resolutions are possible.
“For the first time we have precisely measured the effective electric field responsible for the acceleration,” Schröder points out. “Using this technique the interaction between the individual experimental components and the process of acceleration can now be studied in detail.”

Other experimental facilities for plasma acceleration also stand to benefit from the new technology. “Our method is an important step on the path to a detailed understanding of the plasma wake and to optimising it,” explains Osterhoff.

“This experiment demonstrates the exquisite precision that can be achieved in measuring the accelerating fields and paves the way for the new era of control and stability that plasma accelerators are entering,” adds Wim Leemans, Director of DESY’s accelerator division.

Reference: High-resolution sampling of beam-driven plasma wakefields; S. Schröder, C.A. Lindstrøm, S. Bohlen, G. Boyle, R. D’Arcy, S. Diederichs, M.J. Garland, P. Gonzalez, A. Knetsch, V. Libov, P. Niknejadi, K. Põder, L. Schaper, B. Schmidt, B. Sheeran, G. Tauscher, S. Wesch, J. Zemella, M. Zeng, and J. Osterhoff; Nature Communications, 2020; DOI: 10.1038/s41467-020-19811-9

Provided by DESY

Research Boost To Find Treatments For ‘Undruggable’ Cancers (Medicine)

Bath researchers collaborate with Sapience Therapeutics to find new treatments for cancer cell targets that don’t respond to other drugs.

A research team at the University of Bath, in collaboration with biotechnology company Sapience Therapeutics, is redoubling its efforts to discover new peptide-based treatments capable of acting upon ‘undruggable’ targets in cancer cells.

Discovering new peptide-based treatments to target ‘undruggable’ cancer cells ©University of Bath

Some cancers are notoriously resistant to treatment – it is these tumours that are the focus of the ongoing collaboration between Sapience and scientists at the Department of Biology & Biochemistry. The drug-discovery project between the two organisations began in 2018 and is now extending for another two to three years.

Professor Jody Mason, who leads the Bath team, said: “In the first phase of our collaboration with Sapience, we generated a number of hits against high mortality cancer targets, with several of these peptides now being progressed towards clinical trials.”

Professor Mason has spent the past two decades developing and refining approaches to screen vast libraries of peptides (short chains of amino acids – the building blocks of proteins), identifying those that show greatest promise at blocking key players within the disease, and learning more about the characteristics of these peptides.

Professor Mason is particularly interested in drug candidates that target specific interactions, known as protein-protein interactions. These interactions can be responsible either for making cells cancerous or for dampening the immune response to tumours. The proteins involved in these interactions are generally hard to treat because they lack the deep binding pockets needed for small molecule drugs to cling to. Also, they are often located inside the cell, making them difficult to treat with larger molecules, such as monoclonal antibodies used in immunotherapy.

The Bath-Sapience project is now geared towards producing new peptides that can both disrupt specific protein-protein interactions and penetrate cancer cells in order to do so.

Professor Mason said: “Protein-protein interactions represent a class of drug target conventionally considered undruggable using small-molecule approaches. We’re incredibly excited by the prospect of targeting previously undruggable oncogenic protein-protein interactions with peptide-based therapeutics.”

He added: “During our initial collaboration with Sapience, we identified six promising peptides, each of which binds to a different protein target implicated in cancers that are difficult to treat. I’m delighted to be continuing with our ambitious discovery program and am looking forward to identifying new and interesting molecules.”

Dr Barry Kappel, founder and chief executive officer of Sapience Therapeutics, said: “The continuation of this drug discovery partnership with Professor Jody Mason and the University of Bath speaks to the success of our initial two-year collaboration. Although separated by distance, our teams have worked seamlessly with one another to produce promising peptide ‘hits’ to several important therapeutic targets within the cancer cell. The next phase of this joint effort will focus on the characterization and development of these hits into lead compounds as well as the discovery of new hits against additional promising cancer targets.”

Under the terms of the agreement, Sapience will have exclusive rights to the development and commercialisation of any novel compounds arising from this research. For molecules developed under the agreement, University of Bath will receive milestone payments associated with clinical development and a royalty on future commercial sales.

Provided by University of Bath

New Analysis Refutes Claim That Dinosaurs Were in Decline Before Asteroid Hit (Paleontology)

A new statistical analysis of dinosaur diversity shows they were not in decline at the time of their extinction by an asteroid hit 66 million years ago.

Researchers from the University of Bath and the Natural History Museum London say that had the impact not happened, dinosaurs might have continued to dominate the Earth.

Titanosaurs were common at the time of the asteroid hit at the end of the Cretaceous 66 million years ago. (Credit: AlienCat)

Dinosaurs were widespread globally at the time of the asteroid impact at the end of the Late Cretaceous period, occupying every continent on the planet and were the dominant form of animal of most terrestrial ecosystems.

However, it is still contentious amongst paleobiologists as to whether dinosaurs were declining in diversity at the time of their extinction.

Statistical modelling

In order to address this question, the research team collected a set of different dinosaur family trees and used statistical modelling to assess if each of the main dinosaur groups was still able to produce new species at this time.

Their study, published in the journal Royal Society Open Science, found that dinosaurs were not in decline before the asteroid hit, contradicting some previous studies. The authors also suggest that had the impact not occurred, dinosaurs might have continued to be the dominant group of land animals on the planet.

Lead author of the study, Joe Bonsor, is undertaking his PhD jointly at the Milner Centre for Evolution at the University of Bath and the Natural History Museum.

He said: “Previous studies done by others have used various methods to draw the conclusion that dinosaurs would have died out anyway, as they were in decline towards the end of the Cretaceous period.

“However, we show that if you expand the dataset to include more recent dinosaur family trees and a broader set of dinosaur types, the results don’t actually all point to this conclusion – in fact only about half of them do.”

Sampling bias

It is difficult to assess the diversity of dinosaurs due to gaps in the fossil record. This can be due to factors such as which bones are preserved as fossils, how accessible the fossils are in the rock to allow them to be found, and the locations where palaeontologists search for them.

The researchers used statistical methods to overcome these sampling biases, looking at the rates of speciation of dinosaur families rather than simply counting the number of species belonging to the family.

Joe Bonsor said: “The main point of our paper is that it isn’t as simple as looking at a few trees and making a decision – The large unavoidable biases in the fossil record and lack of data can often show a decline in species, but this may not be a reflection of the reality at the time.

“We may never know the true rates of evolution of the dinosaurs, since the only way to know for sure is to fill in the gaps in the record to get the best answer, and we simply don’t think we’re there just yet.

“Our data don’t currently show they were in decline, in fact some groups such as hadrosaurs and ceratopsians were thriving and there’s no evidence to suggest they would have died out 66 million years ago had the extinction event not happened.”

Whilst mammal existed at the time of the asteroid hit, it was only due to the extinction of the dinosaurs that led to the niches being vacated, allowing mammals to fill them and later dominate the planet.

The research was funded by the Leverhulme Trust and Natural History Museum.

References: Bonsor J.A, Barrett P.M, Raven T.J, Cooper N. (2020) “Dinosaur diversification rates were not in decline prior to the K-Pg boundary” is published in Royal Society Open Science 7: 201195. DOI: 10.1098/rsos.201195

Provided by University of Bath

Are Gamma-ray Bursts Powered By a Star’s Collapsing Magnetic Fields? (Astronomy)

When a massive star in a distant galaxy collapses, forming a black hole, two giant jets of light-emitting plasma shoot from its core. These extremely bright gamma-ray bursts (GRBs) are the most powerful explosions in the universe, and when a jet points towards Earth, the afterglow can be detected from ground and space-borne telescopes. Material does not simply catapult from an exploding star, it accelerates to ultra-high speeds along the narrow beam of the gamma-ray jet, leaving astrophysics puzzled over the power source driving these extraordinary explosions. Now a new international study led by the University of Bath promises to shed light on this mysterious phenomenon.

An artist’s impression of a star’s gamma-ray bursts in the moment after its collapse. Credit: University of Bath

Many astronomers favour an explanation for GRBs based on the baryonic jet model. This states that repeated violent collisions between material blasted out during the explosion and material surrounding the dying star produce the gamma-ray flash and the subsequent fading afterglow—the dying embers of the expanding fireball.

A second hypothesis, called the magnetic model, posits that a huge, primordial magnetic field in the star collapses within seconds of the initial explosion, releasing energy to power the prodigious blast.

Now, for the first time, an international team of researchers has found evidence backing this magnetic model. Working in collaboration with researchers from the UK, Italy, Slovenia, Russia, South Africa and Spain, Bath astrophysicists examined data from the collapse of a massive star in a galaxy 4.5 billion light-years away. They were alerted to the star’s collapse after its gamma-ray flash (named GRB 190114C) was detected by NASA’s space-borne Neil Gehrels Swift Observatory.

The researchers noted a startlingly low level of polarisation in the gamma-ray burst in the moments straight after the star’s collapse, indicating the star’s magnetic field had been destroyed during the explosion.

Nuria Jordana-Mitjans, lead author of the Astrophysical Journal paper, and holder of the Hiroko and Jim Sherwin Postgraduate Scholarship in Astrophysics, said: “From previous studies, we expected to detect polarisation as high as 30% during the first hundred seconds after the explosion. So we were surprised to measure just 7.7% less than a minute after the burst, followed by a sudden drop to 2% soon after.”

She added: “This tells us that the magnetic fields collapsed catastrophically straight after the explosion, releasing their energy and powering the bright light detected across the electromagnetic spectrum.”

GRBs are detected by dedicated satellites orbiting Earth, however no one can predict where or when a GRB will appear, so scientists rely on autonomous rapid-response robotic telescopes to catch the fast-fading light of the afterglow. Seconds after the NASA observatory identified GRB 190114C, robotic telescopes located in the Canary Islands and South Africa received NASA’s discovery notification and repointed. Within one minute of the GRB discovery, the telescopes were gathering data about the emissions.

Professor Carole Mundell, head of Astrophysics at the University of Bath and co-author on the research, said: “Our innovative telescope systems are entirely autonomous, with no humans in the loop, so they slued very quickly and began taking observations of the GRB almost immediately after its discovery by the Swift satellite.”

Prof Mundell continued: “It is remarkable that from the comfort of our own homes, we were able to discover the importance of primordial magnetic fields in powering a cosmic explosion in a distant galaxy.”

References: N. Jordana-Mitjans et al, Lowly Polarized Light from a Highly Magnetized Jet of GRB 190114C, The Astrophysical Journal, Volume 892, Number 2, 2020. DOI: 10.3847/1538-4357/ab7248 https://iopscience.iop.org/article/10.3847/1538-4357/ab7248

Provided by University of Bath

Are There Radio-loud And Radio-quiet Gamma-Ray Bursts? (Astronomy)

Joshua Osborne and colleagues discussed the significance of the differences between the energetics and temporal properties of the two proposed classes of radio-loud and radio-quiet Long-duration Gamma-Ray Bursts (LGRBs) in their recently published paper.

An artist’s impression of a star’s gamma-ray bursts in the moment after its collapse. Credit: University of Bath

Gamma-ray bursts (GRBs) are extremely energetic explosions, the Long-duration class of which has been long hypothesized to be due to the death super-massive stars, releasing energies on the orders of 10^48 to 10^52 ergs and occur at distances far from us on the cosmological scale. The current afterglow model is that of an expanding fireball where the high energy prompt gamma-ray emission is first observed, followed by afterglow emission at lower-energy frequencies after a few hours or days from the initial gamma-ray prompt emission.

The standard fireball model used today was proposed after the first observation of both X-ray and optical afterglows in February of 1997. Not long after, the first GRB without an optical afterglow counterpart was found. This class of bursts without optical afterglows became known as the dark GRBs. On October 9, 2000, however, the second High Energy Transient Explorer (HETE-2) was launched and in December of 2002 it viewed it’s first dark GRB where the optical afterglow was seen, but disappeared and was no longer visible after 2 hours. This begged the question, is there ever truly such a phenomenon as a dark GRB or is it possible that with better equipment and timing no such phenomena would ever appear?

More recently, studies have raised the possibility of the existence of a new population of Long-duration GRBs (LGRBs) that are intrinsically dark in the radio-bandwidth afterglow. These events, named ‘radio-dark’, ‘radio-quiet’, or ‘radio-faint’ LGRBs, have been hypothesized to have progenitors that are different from the progenitors of the mainstream ‘radio-bright’ or synonymously-named ‘radio-loud’ LGRBs.

The radio-quiet LGRBs have been found to have, on average, lower total isotropic gamma-ray emissions (Eiso) and shorter intrinsic prompt gamma-ray durations (e.g., T90z). In addition, a redshift – T90z anti-correlation has been discovered among the radio-loud LGRBs, which is reportedly missing in the radio-quiet class.

Now, Osborne and colleagues, argued the existence of two classes of radio-loud and radio-quiet LGRBs with potentially different progenitors. Radio-loud LGRBs have been shown to be on average more energetic, longer-duration and exhibit weaker positive Eiso – T90z but stronger negative (z + 1) – T90z correlations than the radio-quiet class of LGRBs (shown in Fig 1.

Figure 1. The bootstrapping simulation results for the some of the population properties of the two classes of radio-loud and radio-quiet LGRBs. Plots (a), (b), (c) display respectively, the bootstrapping distributions of the averages of the distributions of z + 1, Eiso, T90z distributions of the two radio classes. In the same order, plots (d), (e), (f) display the corresponding bootstrapping distributions of the standard deviations of the three LGRB property distributions for the two classes. Plots (g), (h), (i) display the bootstrapping distributions of the Spearman’s correlation strengths between the three LGRB properties. The inset values represent the mean and the 1σ dispersions in the bootstrap distributions in each plot, with π(·) denoting the probability and ρ denoting the Spearman’s correlation strength. © Osborne et al.

In their work, they have shown that much of the evidence in favor of such radio classification of LGRBs and their distinct progenitors can be purely attributed to the complex effects of detection thresholds of gamma-ray detectors and radio telescopes on the observed sample of bright LGRBs. Their arguments are built upon the recent discovery of a significant positive Eiso – T90z correlation (ρ ∼ 0.5 – 0.6) in both populations of LGRBs and SGRBs. They have shown that the intrinsic Eiso – T90z correlation (figure 2) along with a potential positive correlation between the gamma-ray and radio luminosity of LGRBs (Figure 3) are sufficient conditions to generate much of the differing characteristics of radio-loud and radio-quiet LGRBs, without recourse to any radio classification of LGRBs.

Figure 2. An illustration of the predicted underlying intrinsic distribution of LGRBs in the Eiso – T90z plane. Associated with each simulated LGRB is also a probability of it being detectable by the Swift BAT, represented by the cyan-magenta color-map. The overlaid yellow and black points represent the sample of bright radio-loud and radio-quiet LGRBs in L19 collected such that Eiso ∼ 10^52 [ergs]. The effective detection threshold of Swift BAT and the classification limit that separates the two classes of radio-loud and radio-quiet LGRBs are shown by the brown dashed lines. These two limits together potentially shape the narrow distribution of radio-quiet sample (black dots on this plane). © Osborne et al.
Figure 3. (a): An illustration of the observational sample of Chandra & Frail (2012) showing the relationship between Eiso and the peak radio luminosity. The only X-Ray Flash (XRF) event in the sample of Chandra & Frail (2012) is shown by the red point. Exclusion of the XRF from the plots results in a minor decrease in the Spearman’s correlation strength from ρ = 0.45±0.13 to ρ = 0.43±0.13. (b): A schematic illustration of the combined effects of the gamma-ray and radio detection thresholds as well as the potential existence of an underlying correlation between the radio and gamma-ray emissions of LGRBs on the observed LGRBs sample and how these factors can lead to the appearance of two separate classes of radio-loud and radio-quiet LGRBs. The red oval represents the positive underlying correlation between Eiso and the radio emission. However, the gamma-ray detector threshold (and the complex redshift selection effects) impose a severe cut on the y-axis, hiding much of the cosmic population of LGRBs (represented by the pink color) from our view. Simultaneously, the radio detector threshold effects, place another severe cut on the observed sample of LGRBs to create an impression of two separate classes of radio-loud and radio-quiet LGRBs. Because of the positive correlation of Eiso with the radio emission, any LGRB above a certain Eiso threshold (i.e., the radio classification limit) will be automatically always classified as a radio-loud event. This leads to an apparent increase in the average Eiso of the radio-loud sample (represented by the yellow-colored points) relative to the radio-quiet sampled (represented by the black-colored points), similar to what has been reported in the literature as the differing characteristics of radio-quiet and radio-loud LGRBs.

Bootstrapping simulations indicated that some of the proposed spectral and temporal differences between the two proposed radio classes are not statistically significant. Furthermore, Monte Carlo simulations of the gamma-ray properties of the two radio classes reveal that more than 50% of the reported difference between the (z + 1) – T90z correlation strengths of the proposed radio classes can be readily and purely explained in terms of selection effects, sample incompleteness and the strong positive Eiso – T90z correlation in LGRBs.

“In the light of the above arguments, it would seem likely that the presence of the very high energy GeV extended emission in the class of radio-loud LGRBs also results from the overall brighter light-curves of such LGRBs across all energy wavelengths, from radio to GeV.”, said authors in their paper.

They concluded that future radio telescopes with increased sensitivities will be able to detect the radio afterglows of more LGRB events. The future projects such as the Square Kilometer Array (whose operation is expected in 2027) and the recent upgrades to the existing telescopes such as the Giant Metrewave Radio Telescope and many others will provide a definite answer to the problem of radio-classification of LGRBs.

References: Joshua Alexander Osborne, Fatemeh Bagheri, Amir Shahmoradi, “Are there radio-loud and radio-quiet Gamma-Ray Bursts?”, ArXiv, pp. 1-11, 2020. https://arxiv.org/abs/2010.08877v1

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Molecular Switch Controls Ability to Repair Hearing Loss in Mice (Neuroscience)

In a study in mice, Johns Hopkins Medicine researchers have found a molecular switch that turns off the animal’s ability to repair damaged cells in the inner ear. The findings shed light on regenerative abilities that are present in many species of birds and fish, but get turned off in mammals, including humans.

Photomicrograph showing a cross section of the wall of a mouse cochlea, a bony structure within the inner ear. The hair cells on top capture sound waves. In a new study, Johns Hopkins Medicine researchers found that a molecular “switch” within the supporting cells seen at the bottom of the photo may be able to turn on and off the ability to repair damaged hair cells. Credit: Division of Neurology, Johns Hopkins Medicine

The study was published Sept. 8, 2020, in The Proceedings of the National Academy of Sciences.

“We might have for the first time identified something that explains why humans lost the ability to repair cells related to hearing loss,” says Angelika Doetzlhofer, Ph.D., associate professor of neuroscience at the Johns Hopkins University School of Medicine, and co-author of the study.

More than 37 million adults in the United States report hearing loss. In the majority of cases, it results from damage to sound receptor cells deep within the human ear known as hair cells. These cells line the spiral-shaped walls of the cochlea, a bony structure in the inner ear, and capture sound waves reverberating in the area. Then, they convert the vibrations into electrical impulses that are carried to the brain by nerves.

Hair cells are kept healthy by a layer of cells called supporting cells. In birds and fish, supporting cells can function as progenitors to replace lost hair cells. Recent studies of mammals have shown that supporting cells have some regenerative potential early in life, before the animals start hearing. For example, supporting cells in mouse pups are able to create new hair cells at birth. However, the ability to repair or replace them stops within a week. At that point, any damage done to the hair cells is irreversible.

Based on these data from previous mouse studies, Doetzlhofer and study co-author Xiaojun Li, Ph.D., a postdoctoral fellow in her laboratory, looked to the rodents as a way to better understand what controls the decline in regenerative ability in mammals.

The researchers achieved this by following the levels of a protein and micro RNA in mice, called LIN28B and let-7, respectively. LIN28B and let-7 are what scientists call “mutual agonists,”‘ meaning they control each other’s function within the cell.

They found that when let-7 levels ramp up, LIN28B levels drop at the same time, turning off the mouse’s regenerative ability.

The two researchers found that without LIN28B, hair cell regeneration does not occur. They tested this by using cochlear tissue and cells from genetically engineered mice that enabled the protein and its agonistic RNA to be turned on and off as needed.

The researchers say that their findings suggest LIN28B is the deciding factor as to whether or not the hair cells retain their regenerative abilities. LIN28B, they believe, promotes the regenerative process by turning on progenitor-specific genes in supporting cells, which then reprograms supporting cells into hair cell progenitor-like bodies.

“The most exciting part was seeing the dramatic effects of manipulating these factors. We began the experiment hoping to get any type of response, and to see a restoration regeneration capability was really thrilling,” says Doetzlhofer.

The researchers say that a better understanding of the biology behind hair cell regeneration may lead to the development of future treatments for hearing loss.

References: Xiao-Jun Li, Angelika Doetzlhofer, “LIN28B/let-7 control the ability of neonatal murine auditory supporting cells to generate hair cells through mTOR signaling”, Proceedings of the National Academy of Sciences Sep 2020, 117 (36) 22225-22236; DOI: 10.1073/pnas.2000417117 https://www.pnas.org/content/117/36/22225

Provided by Johns Hopkins University

USTCers Find Conformational Disorder Tuning Charge Carrier Mobility in 2D Perovskites (Engineering / Electronics)

The organic-inorganic hybrid perovskites (OIHPs) have a multiple application on solar cells, lighting-emitting diodes (LEDs), field effect transistors (FETs) and photodetectors. Among the parameters valuing the power conversion efficiency (PCE) of devices based on perovskite materials, the mobility of carriers undoubtedly captures a high weight.

Although researchers have made massive progress by introducing new components into the structure to control the mobility of the carriers, the understanding on the atom level about how the component affects the performance is still unknown.

To solve the problem, the research team led by Prof. LUO Yi and Prof. YE Shuji from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) synthesized a series of 2D OHIPs films with large organic spacer cations.

By a sequence of measurements, including sum frequency generation vibrational spectroscopy (SFG-VS), optical-pump terahertz-probe spectroscopy (OPTPS), current voltage (I-V) measurements, temperature-dependent PL spectroscopy and X-ray diffraction (XRD) measurements, the researchers found the correlation among the conformation of the organic cations, the charge-carrier mobility and broadband emission.

The relationship between in-plane mobility reduction, broad emission and the conformation of the organic cations ©USTC

Mobility and broadband emission showed strong dependence on the molecular conformational order of organic cations. The gauche defect and local chain distortion of organic cations are the structural origin of the in-plane mobility reduction and broad emission in 2D OIHP films. The interlayer distance and the conformational order of the organic cations co-regulate the out-of-plane mobility.

The result was published in Nature Communications on Oct. 30.

This work provides a physical understanding of the important role of organic cation conformation in optimizing the optoelectronic properties of 2D OIHPs, revealing the structure-property relationship in the perovskite research at the molecular level.

Paper link:

https://www.nature.com/articles/s41467-020-19330-7 

Provided by USTC

Six Years in 120 Pages: Researches Shed Light on Ricci Flows (Astronomy / Maths)

Differential geometry is the study of space geometry. Multiple natural phenomena, from the universe expansion to thermal expansion and contraction, can come down to spatial evolution. The two core conjectures in this field, Hamilton-Tian conjecture and the Partial C0-conjecture, had remained as puzzles for more than 20 years.

The serval stages of Ricci Flow on a 2D manifold. ©UTSC

Most of the pebbles on the beach are round. They might have had edges and corners at first, but as time goes by and the tide ebbs and flows, their shape will get closer and closer to perfection and standard. But no matter how perfect the evolution is, there might still be some abnormalities, which are called ‘singularities’ in geometry.

The Hamilton-Tian Conjecture is that most of the space is perfect, while the size of the ‘singularity’ can be restricted to a low-dimensional space, introduced by Prof. CHEN Xiuxiong, the founder of the Institute of Geometry and Physics, University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS).

Prof CHEN, alongside with Prof. WANG Bing from USTC, first proved the aforementioned two conjectures.

Their paper was split into two parts, the first of which was published in 2017, and the second part of 123 pages was published this year on Journal of Differential Geometry, one of the leading publications in the field of geometry which also published Hamilton’s fundamental work about Ricci flow, after a long course of 5 years of developing the theory and 6 years of peer-reviewing since its first submission.

This work emphasized on the weak compactness theory for non-collapsed Ricci flows. It introduced many innovative thoughts and methods, which contributed far-reaching implications in the field of geometric analysis, especially for the studies of Ricci flows.

In fact, many other works have been developed based on this article. For example, a new solution for stability of Yau’s conjecture based on the structure theory of Ricci flows was given by Prof. CHEN, Prof. WANG and Dr. SUN Song of USTC with their derivation published in the top journal, Geometry and Topology. Before that, they were rewarded Oswald Veblen Prize in Geometry for their provision of the first solution of stability of Yau’s conjecture.

The theory and methods presented in this article were also applied into a series of works of Prof. WANG and his cooperators in recent years.

The core ideas of this article were generalized to the research of mean curvature flow by Prof. WANG and Prof. LI Haozhao, who solved the extension problem, and the result was published in Inventions Mathematicae.

The cooperated paper by Prof. WANG, Dr. HUANG Shaosai, and Dr. LI Yu, On the Regular-Convexity of Ricci Shrinker Limit Spaces, published on Crelle’s Journal, has proved that the limit of non-collapsed shrinking Ricci solitons must be the cone shape defined by Prof. CHEN and Prof. WANG.

Besides, the work, Heat Kernel on Ricci Shrinkers published on Calculus of Variations and Partial Differential Equations by Prof. WANG and Dr. LI, developed several estimates through the study of the heat kernel on Ricci shrinkers, and provided necessary tools to analyze short time singularities of the Ricci flows of general dimension.

This breakthrough was honored by the reviewer of the journal and the winner of Fields Metal, Prof. Simon Donaldson, who commented, this work is a major breakthrough in geometric analysis, and it no doubt will lead many other related research projects.

Paper link:

https://projecteuclid.org/euclid.jdg/1599271253 

(Written by LI Zikang and JIANG Pengcen, USTC News Center)

Provided by University of Science and Technology China

Testing the Turquoise Waters of Paradise (Amazing Places)

Brazil’s Fernando de Noronha is fabled as an eco-wonderland and a beach-lovers’ Shangri-la, where even the sharks are friendly. Mike Hodgkinson finds out if it lives up to the hype.

Ask about Fernando de Noronha when you’re in Sao Paulo, and your enquiry will invariably meet with a combination of wonderment, national pride, jealousy and misinformation. Fernando de Noronha is an island – named after a 16th-century Portuguese nobleman who may never have actually set foot there – that exists in the Brazilian imagination somewhere not far from Shangri-la, Atlantis and paradise. People glaze over when you mention it: eyeballs tend to roll upwards in that universal gesture of delight.

We were told by friends, acquaintances and strangers – none of whom had actually been to Fernando de Noronha – to expect the most spectacular beaches in all of Brazil. Some were certain that jet aircraft are barred from landing there; others warned that there is only one hotel and absolutely no internet. Naomi Campbell, we were reliably informed, goes there to unwind after Sao Paulo Fashion Week, but – far from being just a bolt-hole for the wealthy – it is also a fiercely protected eco-wonderland, favoured by naturalists and marine biologists. The island’s luxuriously warm and unsullied emerald waters are, it was widely agreed, teeming with dolphins and turtles. What’s more, the consensus assured us that every type of shark common to the area is, in fact, friendly.

Like most people from outside Latin American we had never heard of Fernando de Noronha, and because less than half of what we’d been told seemed even remotely plausible, we turned to Charles Darwin for supporting testimony. He stopped there in 1832, after one of his crew had harpooned a porpoise for supper (Darwin was evidently no Dr Dolittle), but spent only a day “wandering about the woods” before setting off in hopes of finding “greater wonders” elsewhere. His account – except for reports of “a conical hill, about one thousand feet high, the upper part of which is exceedingly steep” – is distinctly underwhelming. Would this living paradise, in reality, turn out to be little more than a product of mass exaggeration? Or would it live up to the hype?

Fernando de Noronha is, strictly speaking, an archipelago made up of one 11-square-mile chunk of volcanic rock and 20 smaller islands, three degrees south of the equator, 220 miles from Brazil’s north-eastern coast. The flight from Sao Paulo – on a modern passenger jet, for the record – pauses briefly in the seafront city of Recife before continuing out into the Atlantic, and touching down on an airstrip that occupies a large portion of the lush, green interior. From above, the promise of an outrageously attractive wonderland – glinting turquoise sea, pristine sand – is instantly made good.

After happily coughing up an Environment Protection Tax at the airport (seven days costs about £65 per person), we were taken by Land Rover to our hotel – the Pousada do Vale – a friendly place on a wooded lane near the island’s first permanent settlement, the Vila dos Remédios. Within half an hour, we fully understood the basic climatic reality of life on Noronha during the rainy season (April to August) – bursts of blistering sunshine punctuated by torrential downpours. As a result, nature goes into overdrive: explosions of greenery; reptilian battalions of frogs and native, yellow-eyed mabuya lizards; and clouds of low-flying, almost invisible borrachudo mosquitoes that have a voracious appetite for human ankle flesh. Self-preservation quickly drove us to the most effective, but least environmentally friendly, of the two insect repellants offered by the pousada: not the ideal start on a Unesco World Heritage Site and designated maritime national park where swimming in sun-screen is, in places, forbidden lest the delicate eco-system be damaged.

As night fell like a cosh, the island’s split-personality began to reveal itself. All the evidence so far had marked out Noronha as a dream destination for tropic-hardened biologists, but the appearance of several smartly dressed couples, picking their way gingerly over rain-slicked cobblestones, confirmed its bread-and-butter identity as a magnet for well-heeled honeymooners. Their shoes were muddied, and their lower legs were – like ours – borrachudo’d, but they had paid good money for romance in paradise and no extremes of nature were going to take that from them. The remoteness of the island – and its perceived value as the perfect holiday destination – keeps prices (food, lodging) perennially high, on a par with pricier quarters of Sao Paulo, enhancing its exclusivity and mystique.

The evening, spent over several cans of lager at a bar called Tom Marrom, surrendered a colourful procession of diverse characters: a local teenager rode past on a horse, followed by a man in a dune buggy who appeared to be modelling himself after Steve McQueen’s Thomas Crown. The dune buggy turns out to be the island’s most common form of transportation: not exactly the environmentalist’s first choice, but practical given a road system structured largely around the pot-hole, the gully and the rut. The bar’s waitresses wore fake pig-tails and painted-on freckles, and danced – between deliveries of food – to the live forró band. Forró is an accordion-based type of folk-dance music particular to the north-east of Brazil, with an intoxicating and swampy feel to it. One band member traditionally plays the triangle, which we assumed was the least-taxing, most Bez-like role, until our trianglist started to sing, very well, and instantly shot up in our estimation.

After a night spent under the watchful eye of several mabuyas, we set about discovering that the best of Noronha is to be found on and under the water. A three-hour round trip by boat from the island’s small harbour is as good an introduction to the island as any, and features a 40-minute snorkelling stop at the astoundingly pretty Baia do Sancho. En route we were shown rock formations that (sort of) resemble a dog, an Egyptian mummy and King Kong, caught passing glimpses of flying fish, a stray turtle and several javelin-shaped barracuda. The big draw, though, was the resident spinner dolphins – so-called because they jump clear of the water in acrobatic spirals – that turn up in their hundreds on a daily basis. You just can’t argue with wild dolphins en masse: some would insist they’re worth the hefty price of admission to Noronha alone.

We could neither confirm nor deny the rumoured friendliness of the local sharks – the lemon shark, nurse shark and Caribbean reef shark are the most common – because we didn’t see any, but we can state that there have been no reported attacks (touch wood). In marked contrast to the mainland coast near Recife, where environmental disruption has provoked a dramatic rise in fatal shark encounters, the protected marine eco-system around Noronha appears to offer the creatures all the sustenance they require.

Other nature-based highlights included the walking route to Baia do Sancho, which involves negotiating two ladders on a sheer cliff-face and feels moderately adventurous, until you realise that it’s regularly tackled by old ladies in flip-flops; and a lunch of freshly caught barracuda at Bar do Meio on the Praia do Meio, frigate birds circling overhead. Away from the beaches, the ruins of a prison offers a hint of life on Noronha before the modern tourist era. Gypsies (in 1739) and capoeira fighters (in 1890) were incarcerated there, unaware that their living hell would one day morph into a high-end eco-destination.

Fish night back at the Pousada do Vale – during which the hand-delivered catch is wrapped in banana leaves and grilled – is free for guests on Thursdays. The hotel’s two-storey “bungalows” have balconies with hammocks, and it was in one of them that we weighed up our thoughts on the island. Had Noronha lived up to the hype? No question about it, the place is gorgeous – whatever nature had taken away by sending deluges of Atlantic rain and vindictive insects, it had given back in spades with stunning marine life, dramatic rock formations and priceless sunsets. But there was still the sneaking suspicion that Fernando de Noronha has something of an identity crisis. By selling itself as both a strictly patrolled eco-paradise and a dream destination for the well-off – where bicycles are out-muscled by petrol-chugging buggies, and much of the food is flown in – the island comes across as confused. The price-tag for a holiday there is likely to deter many, but for honeymooning scuba divers who aren’t short of a bob or two, Fernando de Noronha is a live contender.

Getting there
When to go: Dry/high season (from September up to March) and rainy/low season (from April up to August)

Specialist operator: Tim Best Travel; +44 (0)20 7591 0300; timbesttravel.com; info@timbesttravel.com

Where to stay:

Pousada do Vale, Rua Pescador Sérgio Lino, 18 – Jardim Elizabeth; pousadadovale.com/ingles; +55 (81) 3619 1293. Bungalows from 648 reais; £200 a night

Pousada Maravilha, BR 363 Sueste; pousadamaravilha.com.br/ingles/pousada.htm; +55 (81) 3619 0028. From 1,230 to 2,710 reais per night (£385 to £848)

Pousada Zé Maria, Rua Nice Cordeiro, 01 – Floresta Velha; pousadazemaria.com.br; +55 (81) 3619 1258. Doubles from 558 reais in the low-season (£174)

This article is republished here from Guardian under common creative licenses.