Protons could be lighter than we thought

24 Aug 2020 Isabelle Dumé

Aside view of the ion trap apparatus used in the experiment. (Courtesy: JCJ Koelemeij)

The most precise measurement to date of the proton-electron mass ratio suggests that the proton may be lighter than previously thought. The result, from researchers in the Netherlands and France, provides a crucial independent cross-check with previous measurements of the ratio, which yielded inconsistent values.

The proton-electron mass ratio is an important quantity in physics and a benchmark for molecular theory. It can be determined by measuring the rotations and vibrations of ordinary molecular hydrogen ions (H2+) and comparing them to similar ro-vibrational measurements in their deuterated cousins (HD+). Both entities are the very simplest bound systems that can be termed “molecules”, and as such they are ideal for probing models of fundamental physics. Indeed, when researchers first performed measurements of ro-vibrational transitions in HD+ 40 years ago, they suggested that the results could be used to test the theory of quantum electrodynamics (QED) in molecules.

Acoustic imaging promises real-time dose measurement for FLASH radiotherapy

18 Aug 2020 Laura Patricia Kaplan

(A) Combined ultrasound and ionizing radiation acoustic image of a rabbit liver phantom. (B) Combined images from real-time dual-modality imaging at different time points when the phantom was translated. (Courtesy: Med. Phys. 10.1002/MP.14358, Wiley, © 2020 American Association of Physicists in Medicine)

Ultrahigh dose rate radiation therapy (FLASH) is currently one of the hottest topics in radiotherapy research. Several animal studies (and recently, a first-in-human case report) have shown that the probability of radiotherapy side effects can be greatly reduced when the radiation dose rate is ramped up from the standard 0.1 Gy/s to 40 Gy/s or more.

In order to use such high dose rate treatments safely, it is imperative to continuously monitor where and how much dose is really being deposited in the patient. This is currently only possible for tumours on or close to the skin surface where dosimeters can be placed easily. Researchers at the University of Michigan have now proposed a new method to measure dose, even deep within a patient, while simultaneously obtaining images of the radiation target and surrounding tissue. They have published the details of their study in Medical Physics.

‘World’s smallest’ imaging device takes a closer look at heart disease

24 Aug 2020 Ben Lewis

Schematic image of an ultrathin 3D-printed endoscope imaging an artery. (Courtesy: Simon Thiele and Jiawen Li)

To successfully diagnose diseases and disorders, doctors need the best possible tools to see inside the human body. Imaging the body’s tightest spaces without causing damage, however, can be tricky and necessitates camera-like devices that are smaller than was previously possible to engineer. An international team of researchers has now overcome these technical challenges to produce a camera that is small enough to see inside even the narrowest blood vessels.

The team, led by researchers from the University of Adelaide and the University of Stuttgart, has manufactured the smallest 3D imaging probe ever reported. They used 3D micro-printing to put a miniature lens onto the end of an optical fibre that is the same thickness as a human hair. Together with a sheath to protect the surrounding tissue and a special coil to help it rotate and create 3D images, the entire probe is less than half a millimetre across – the same thickness as a few sheets of paper.

Did a supernova trigger the late Devonian extinction?

30 Jul 2020

Safe distance: supernova SN 1987A as seen by the ESO Schmidt Telescope. Located 168,000 light-years away, this object posed no danger to Earth. (Courtesy: ESO)

The explosion of a nearby star could have caused a mass extinction that occurred long ago on Earth. That is the conclusion of a study by an international team of scientists, which suggests that this scenario could be confirmed by looking for a plutonium isotope in fossils.

Around 359 million years ago, at the boundary between the Devonian and Carboniferous periods, the Earth suffered an intense loss of species diversity that lasted for at least 300,000 years. Called the Hangenberg Crisis, the event is thought to have been caused by long-lasting ozone depletion, which would have allowed much more of the Sun’s ultraviolet (UV) radiation to reach and harm life on Earth.

How to hack a self-driving car

18 Aug 2020

Taken from the August 2020 issue of Physics World. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

Cars that drive themselves may one day improve road safety by reducing human error – and hopefully deaths by accidents too. However, the hardware and software behind the technology opens up a range of opportunities to hackers, as Stephen Ornes finds out

(Courtesy: iStock/peshkov)

One morning in March 2019, a brand new, cherry-red Tesla Model 3 sat in front of a Sheraton hotel in Vancouver, Canada. Once they were inside the car, Amat Cama and Richard Zhu, both tall and lean twentysomethings, needed only a few minutes. They exploited a weakness in the browser of the “infotainment” system to get inside one of the car’s computers. Then they used the system to run a few lines of their own code, and soon their commands were appearing on the screen.

They’d hacked the Tesla.

Cama and Zhu got the car, but they weren’t thieves. They’re a pair of legendary “white hats” – good-guy hackers who find, exploit and reveal vulnerabilities in devices that connect to the Internet, or other devices. A car packed with self-driving features could be the ultimate prize for hackers who can’t resist a challenge.

Grasshopper jumping on a Bloch sphere, red bricks store electrical energy, dynamics of jail dodgeball

14 Aug 2020 Hamish Johnston

Hop to it: the grasshopper problem has been solved on a sphere. (Courtesy: Tomfriedel/ CC BY 3.0)

A few years ago, the physicists Olga Goulko, Damián Pitalúa-García and Adrian Kent proposed the grasshopper problem. Think of a grasshopper that hops a fixed distance in a random direction. If the grasshopper begins at a random position on a lawn, which shape of lawn has the highest probability of retaining the grasshopper?

It turns out that the answer is not a circle or other simple shape, but rather a rich variety of different shapes at different jump sizes. What is more, the work provides useful insight into Bell-type inequalities relating probabilities of the spin states of two separated quantum-entangled particles.

The future of flying antennas

20 Aug 2020

Taken from the 2020 Physics World Instruments & Vacuum Briefing. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

Designing equipment that meets stringent size and mass restrictions for use on aircraft brings extra challenges for instrument developers, as Tamara Clelford explains

(CC BY-SA Bin im Garten)

Antennas are used for a huge range of applications, from mobile phones and “smart” WiFi-connected appliances to GPS and systems that track aircraft and help pilots land safely. These systems usually have a few things in common: the antenna itself, which manipulates electromagnetic radiation in the radio and microwave parts of the spectrum; a receiver (if the system receives signals); and a transmitter (if the system transmits). Over the years, several distinct types of antennas have come into common use, with designs, frequencies and operating power levels that depend strongly on their purpose. Examples include patch antennas in mobile phones, wire antennas in household radio receivers, and reflector antennas for satellite TV.

Within this antenna “zoo”, the antennas attached to flying structures are unique in several respects. Stringent mass and size restrictions make their design more complicated, and they must be able to cope with several challenges over and above meeting basic radio-frequency (RF) requirements. These problems are most acute for radar systems, which require a highly directional beam that can be scanned in different directions.

Why LHCb is so good at discovering tetraquarks, medical sensors that are drawn on the skin

20 Aug 2020 Hamish Johnston

This summer, physicists working on the LHCb experiment at CERN have announced the discovery of two new tetraquarks. In this week’s podcast, CERN’s Dan Johnson and Tim Gershon of the University of Warwick explain why these exotic hadrons are special and also chat about why LHCb is a champion when it comes to spotting tetraquarks.

Physics World’s Tami Freeman and Hamish Johnston also look at two new technologies that involve drawing or printing electronic circuits onto substrates including skin. It turns out that draw-on-skin medical sensors can be more reliable than contact-style devices such as fitness watches and have the added bonus of being able to speed-up wound healing.

from physicsworld.com 23/8/2020

Second critical point appears in two models of water

18 Aug 2020 Isabelle Dumé

(Courtesy: iStock/borchee)

Researchers in the US and Italy have identified a second critical point in two realistic theoretical models of water. This finding, which draws on state-of-the-art computational methods and supports a hypothesis first put forward more than 25 years ago, suggests that water exists in two distinct liquid phases, one of which is less dense and more structured than the other.

The central role of water in life as we know it makes it easy to forget just how unusual it is. Unlike most other liquids, water is denser at ambient pressure than the ice it forms when it freezes. It also exhibits negative thermal expansion (meaning that it expands on cooling, rather than contracting), becomes less viscous when compressed and boasts no fewer than 17 crystalline phases.

But the list of oddities doesn’t end there. In 1976, Austen Angell and Robin Speedy discovered that water’s behaviour becomes even more atypical when it is cooled below its freezing point while remaining in liquid form – a “supercooled” state that occurs naturally in high-altitude clouds. Then, in 1992, a computational study by Peter Poole and colleagues at Boston University in the US suggested an even more tantalizing possibility. According to their simulations, supercooled water undergoes an additional phase transition between two liquid phases, with a liquid-liquid critical point (LLCP) occurring at pressures 2000 times higher than atmospheric pressure at sea level.

How to avoid coffee rings when printing graphene devices

19 Aug 2020

On the move: particle trajectories in a drying droplet, with red arrows showing the trajectory end. (Courtesy: Tawfique Hasan)

The coffee ring effect can be suppressed in 2D-crystal ink droplets by using a specific mixture of alcohols as a solvent. That is the conclusion of an international research team led by Tawfique Hasan at the University of Cambridge. It has found that Marangoni flow in the drying droplets suppresses the capillary flow that creates rings. The study could lead to better techniques for printing nanoparticles onto substrates for the manufacture of electronic and photonic devices.

Nanoparticles and 2D nanocrystals such as graphene have unique electronic and optical properties that can be very useful for creating new technologies.

Space-based spectrometer enters neutron lifetime debate

20 Jul 2020 Isabelle Dumé

Artist impression of MESSENGER spacecraft in orbit at Mercury. (Courtesy: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

While protons remain stable for at least 1034 years outside the nucleus, a free neutron survives for just under 15 minutes before it decays. The neutron’s precise lifetime is, however, a matter of some debate, as the two techniques commonly used to measure it have produced conflicting results of 880 and 888 seconds.

A team of researchers at the Johns Hopkins University Applied Physics Laboratory in the US led by Jack Wilson has now put forward a third, radically different technique that involves measuring the number of neutrons near a planet. Using data acquired by the neutron spectrometer on NASA’s MESSENGER spacecraft during flybys of Venus and Mercury in 2007 and 2008, they calculated the neutron lifetime to be 780 +/- 90 seconds. While this measurement has a large uncertainty, the researchers note that the MESSENGER instrument was never designed to perform studies of this type – meaning that a dedicated instrument on a future mission could produce a measurement with much higher precision.

ASA launches Mars Perseverance rover

31 Jul 2020

Mars bound: NASA's Perseverance rover will explore the Martian geology and climate and look for signs of past microbial life. (Courtesy: NASA/Joel Kowsky)

The summer of Mars launches continued yesterday as NASA successfully sent its Mars 2020 on a seven-month journey to the red planet. Taking off from the Kennedy Space Center in Florida at 7:50 a.m. local time, the probe is the third mission sent to Mars in just 10 days following China’s Tianwen-1 orbiter and rover as well as the United Arab Emirates’ Hope orbiter. All three craft will reach the red planet in February 2021.

The Mars 2020 mission is set to land in a river delta within Jezero Crater and it will aim to repeat the same thrilling entry, descent and landing that happened for NASA’s Curiosity rover in 2012, which continues to roam the martian surface today. The main aspect of Mars 2020 is the Perseverance rover that will use seven instruments to explore Mars’ geology and climate and look for signs of past microbial life. “The science goal ultimately is to search for signs of life,” says Mars 2020 team member Melissa Rice, “like biosignatures that would be preserved in the rocks and to understand the geologic context in which these rocks formed.”

Microwave anomalies strengthen the case for loop quantum cosmology, say physicists

17 Aug 2020

What Planck saw: does the cosmic microwave background harbour evidence for loop quantum cosmology? (Courtesy: ESA and the Planck Collaboration)

A theory of quantum gravity that describes the universe as beginning in a “Big Bounce” rather than a Big Bang has succeeded in explaining several anomalies in the cosmic microwave background (CMB) radiation.

Loop quantum gravity (LQG) is an alternative to string theory, and describes space itself as being quantized at the smallest scales, known as the Planck length, about 10–35 m. According to LQG, space cannot be crushed down any smaller than this, and the application of LQG to the broader Universe is known as loop quantum cosmology (LQC).

In standard Big Bang cosmology, were we to run the history of the universe backwards so that it collapses rather than expands, the universe would contract into an unknowable singularity. However, in LQC, the collapsing universe would stop collapsing at the Planck length, and then rebound. This suggests that if LQC is correct, there was no Big Bang singularity, but a Big Bounce resulting from the collapse of a previous universe.

Artificial spider web gets an ionic boost

13 Aug 2020 Isabelle Dumé

The artificial ionic spiderweb. Credit: Lee et al., Sci. Robot. 5, eaaz5405 (2020)

An artificial material with the same elastic, adhesive, self-cleaning, sensing and tensile properties as natural spider silk has been created by researchers in South Korea. The synthetic web, which is made from a semi-solid stretchy gel, works using electrostatics and might have applications in artificial muscles, grippers and self-cleaning wall-climbing devices.

Spider silk has a tensile strength five times higher than that of steel, and its stretchable threads boast an adhesive coating that enables spiders to capture and trap prey in their webs. This adhesive coating does have a down side, however, which is that it attracts contaminants from the environment, causing the webs’ capturing efficiency to deteriorate.

Electronics drawn directly on the skin creates robust biosensors

19 Aug 2020 Samuel Vennin

"Drawn-on-skin” electronics penned directly on the patient’s skin can create multifunctional sensors and circuits to collect various physiological signals. (Courtesy: Cunjiang Yu, University of Houston

Researchers from the University of Houston have developed a new form of bioelectronics known as “drawn-on-skin” (DoS) electronics, in which multifunctional sensors and circuits can be drawn directly onto the skin with a specialized ink pen. Their study, published in Nature Communications, shows that information collected using DoS electronics is more reliable and consistent than that obtained with electrodes commonly used in wearable bioelectronics.

“[The circuits are] applied like you would use a pen to write on a piece of paper,” says senior author Cunjiang Yu. “We prepare several electronic materials and then use pens to dispense them. Coming out, it is liquid. But like ink on paper, it dries very quickly.”Senior author Cunjiang Yu.

Yu and colleagues used three different inks to draw the various elements of the bioelectronic platform (conductors, semiconductors and dielectrics) into the outlines of a stencil. Any imperfection can be corrected by simply drawing on top of it. Once dried, the drawn structure can deform with the skin and collect a wealth of physiological signals.

Superhydrophobic surfaces toughen up

15 Jul 2020 Isabelle Dumé

A schematic representation of how the surface looks, and how the structure repels water. (Courtesy: Aalto University)

A micron-scale “armour” that protects highly water-repellent nanostructures from damage has been developed by researchers in China and Finland. The new extra-durable coating could make it possible to employ these “superhydrophobic” surfaces on devices such as solar panels and vehicle windscreens that experience tough environmental conditions.

As their name suggests, superhydrophobic materials repel water extremely well. They owe this impressive ability to a thin layer of air that develops around nanometre-scale structures on their surface. By ensuring that droplets barely touch the solid part of the surface at all, the air layer effectively acts as a lubricant, allowing water droplets to roll off with near-zero friction.

Mediator atoms help graphene self-heal

16 Jul 2020 Isabelle Dumé

Mediator atoms in graphene. (Courtesy: C Ewels)

Graphene and other carbon materials are known to change their structure and even self-heal defects, but the processes involved in these atomic rearrangements often have high energy barriers and so shouldn’t occur under normal conditions. An international team of researchers in Korea, the UK, Japan, the US and France has now cleared up the mystery by showing that fast-moving carbon atoms catalyse many of the restructuring processes.

Graphene – a carbon sheet just one atomic layer thick – is an ideal system for studying defects because of its simple two-dimensional single-element structure. Until now, researchers typically explained the structural evolution of graphene defects via a mechanism known as a Stone-Thrower-Wales type bond rotation. This mechanism involves a change in the connectivity of atoms within the lattice, but it has a relatively large activation energy, making it “forbidden” without some form of assistance.