New mechanism could reduce plasma turbulence in stellarators

14 Aug 2020

Recreating the Sun: the Wendelstein 7-X stellarator (Courtesy: Gwurden/CC BY-SA 4.0)

A new mechanism that could reduce plasma turbulence in stellarators has been identified in computer simulations done by researchers in the US and Germany. A similar effect has already been predicted to occur in tokamaks, which like stellarators, confine hot plasmas using magnetic fields.

A plasma is an extremely hot state of matter in which electrons and ions are no longer bound together. The Sun is a dense plasma where nuclei have enough energy to undergo fusion, unleashing huge amounts of energy.

 

Nanodiamond quantum thermometer measures the temperature of worms

08 Oct 2020 Isabelle Dumé

Researchers measured the temperature of C. elegans nematode worms via tracking of embedded nanodiamonds. (Courtesy: Masazumi Fujiwara, Osaka City University)

How do you take a worm’s temperature? With a quantum thermometer of course. This is exactly what researchers have achieved using devices containing nanodiamonds with nitrogen-vacancy (NV) defect centres, the magnetic resonances of which change with temperature. The new technique could be important for a range of clinical applications.

You may ask, why take the temperature of a worm? One of the reasons is that the temperature within a living organism is a direct measure of the biological activities happening inside.

 

Tiny ingestible capsule helps treat gastrointestinal disorders

08 Oct 2020 Rojin Jafari

The STIMS capsule attaches to stomach lining and electrically stimulates muscle contractions. (Courtesy: Alex Abramson)

Researchers in the US, Denmark and Sweden have designed a novel microstimulation device that can attach to the gastrointestinal (GI) tract and electrically stimulate the stomach muscles to induce contractions. The new device, described in Science Advances, aims to treat disorders such as gastroparesis, which prevents the stomach from properly emptying.

Decades of scientific and medical research has shown that, due to the presence of neural circuits in the GI tract, electrical impulses that stimulate nerves and muscles can improve the health and quality-of-life of patients with GI-related disorders.

 

Tiny ultrasound detector achieves super-resolution imaging

07 Oct 2020

Sound idea: this silicon chip (3×6 mm) has multiple SWED detectors. The fine black engravings on the surface of the chip are the photonics circuits interconnecting the detectors, which are not visible. In the background is a larger scale photonics circuit on a silicon wafer. (Courtesy: Helmholtz Zentrum Muenchen / Roman Shnaiderman)

A device described as the world’s smallest ultrasound detector has been created by Vasilis Ntziachristos and colleagues at the Technical University of Munich and Helmholtz Zentrum München. The extremely sensitive device can image structures smaller than individual living cells and is made using inexpensive and readily available silicon-on-insulator technology. With further optimization, the team says their detector could be mass-produced for use in a broad range of imaging applications.

Traditionally, ultrasound detectors use piezoelectric transducers to both broadcast high-frequency sound and also pick up sound that has reflected from target objects – using the reflected signal to create an image.

 

Physicists pin down deuteron mass

09 Oct 2020 Isabelle Dumé

Assembly of the LIONTRAP Penning-trap system.

© MPIK

Physicists in Germany say they have made the world’s most precise measurement of the deuteron mass by comparing it to the mass of the carbon-12 nucleus. The new work, which was carried out by confining deuterons (which are nuclei of deuterium, or “heavy” hydrogen) and carbon-12 nuclei with strong magnetic and electric fields, provides a crucial independent cross-check with previous measurements that yielded inconsistent values.

Knowing the precise masses of simple atomic nuclei such as hydrogen, its isotopes deuterium and tritium, and the molecular hydrogen ions H2+ and HD+ (a proton and a deuteron, bound by an electron) is crucial for testing fundamental physics theories such as quantum electrodynamics. The mass of the deuteron can also be used to derive the mass of the neutron, which has implications for metrology as well as for atomic, molecular and neutrino physics.

 

Fukushima may have scattered plutonium widely

20 Jul 2020

Explosive event: The upper side of the unit 3 reactor building at Fukushima Daiichi was damaged by a hydrogen explosion. This area housed the spent fuel pool and the fuel handling machines. (Courtesy: TEPCO)

Tiny fragments of plutonium may have been carried more than 200 km by caesium particles released following the meltdown at the Fukushima Daiichi nuclear power plant in Japan in 2011. So says an international group of scientists that has made detailed studies of soil samples at sites close to the damaged reactors. The researchers say the findings shed new light on conditions inside the sealed-off reactors and should aid the plant’s decommissioning.

The disaster at Fukushima occurred after a magnitude-9 earthquake struck off the north-east coast of Japan and sent a 14 m-high tsunami crashing over the plant’s seawalls. With low-lying back-up generators knocked out, the site’s three operating reactors overheated and melted down.

 

First ‘open flavour’ tetraquark is spotted by LHCb at CERN

12 Aug 2020 Hamish Johnston

No pairs: the first ‘open flavour’ tetraquark has been spotted at CERN (Courtesy: Shutterstock/paul_june)

The first tetraquark composed of four quarks of different flavours has been discovered by physicists working on the LHCb experiment at CERN. Dubbed X(2900), the “open flavour” tetraquark has a mass of about 2.9 GeV/c2 and has been spotted in two spin states. The tetraquark was made by smashing protons together at the Large Hardron Collider (LHC) to produce B mesons – and then searching the B meson decay products for signs of new particles.

While LHCb physicists are not completely certain about the nature of the particle – hence the “X” in the name – they believe it contains four quarks: anticharm, antistrange, up and down. Because the tetraquark does not contain a quark–antiquark pair of the same flavour, no quark flavours are hidden and therefore the tetraquark is described as open flavour.

 

Quantum treatment sheds fresh light on triboelectricity

06 Oct 2020 Anna Demming

Ancient observations, modern explanation: Robert Alicki (left) and Alejandro Jenkins (right). Alicki holds a bust of Thales, the pre-Socratic philosopher who described magnetic and “amber” effects as evidence of a material’s soul. Credit: Maria Alicki

Shuffling around on a carpet to give someone an electric shock might seem like the oldest trick in the book, yet scientists know surprisingly little about why it happens. “I believed – like I think most physicists – that these phenomena were understood by the experts,” says Robert Alicki, a mathematical and theoretical physicist at the University of Gdansk, Poland. “But it was not the case. It was still an open question.”

Thanks to Alicki and his colleague Alejandro Jenkins of the Universidad de Costa Rica, the mystery surrounding triboelectricity (as the “charging by rubbing” effect is known) may be clearing up. According to Alicki and Jenkins, a major barrier to understanding triboelectricity is that physicists tend to view the phenomenon in terms of electrostatic potentials, even though “from a potential effect, you are never going to sustain a current that is going around a circuit,” Jenkins says. “It’s like the problem of perpetual motion.”

Alicki and Jenkins formulated their alternative description by incorporating the concept of pumping into a new, quantum model of a system undergoing triboelectric processes. “Pumping can replenish a potential, but it is not describable by a potential,” Jenkins explains. “It can do something that no potential can do, and that is to drive something around on a closed path.”

 

Roger Penrose, Reinhard Genzel and Andrea Ghez bag the Nobel Prize for Physics

06 Oct 2020 Hamish Johnston

New laureates: Roger Penrose, Reinhard Genzel and Andrea Ghez have won the the 2020 Nobel Prize for Physics. (Courtesy: IOP Publishing/Tushna Commissariat; CC-BY-SA H Garching; UCLA/Christopher Dibble)

The 2020 Nobel Prize for Physics has been awarded to Roger Penrose, Reinhard Genzel and Andrea Ghez for their work on black holes.

The prize is worth 10 million Swedish krona (about $1.1 million) and half goes to Penrose, with Genzel and Ghez sharing the other half of the prize.

The Nobel Committee cites Penrose “for the discovery that black hole formation is a robust prediction of the general theory of relativity”, and Genzel and Ghez “for the discovery of a supermassive compact object at the centre of our galaxy”.

After the announcement was made this morning by the Royal Swedish Academy of Sciences, Ghez answered questions remotely from the US.

 

Overlooked for the Nobel: Jocelyn Bell Burnell

30 Sep 2020 Matin Durrani

The 2020 Nobel Prize for Physics will be announced on Tuesday 6 October. In the run-up to the announcement, Physics World editors have picked some of the people who they think have been overlooked for a prize in the past

Astrophysics pioneer: Jocelyn Bell Burnell (centre) thinks she missed out on a Nobel prize for discovering pulsars because she was a student at the time (Courtesy: Institute of Physics)

I’ve met Jocelyn Bell Burnell twice.

The first was when I sat next to her at a dinner in London in 2007. The other occasion was last year when I interviewed her about her incredibly generous donation of $3m to set up the Bell Burnell Graduate Scholarship Fund.

Run by the Institute of Physics, which publishes Physics World, the fund supports PhD students from under-represented groups at universities in the UK and Ireland, with the first recipients having recently been announced.

On both occasions, I resisted the temptation to ask Bell Burnell why she feels she was never awarded a share of the Nobel Prize for Physics for the discovery of pulsars.

 

Overlooked for the Nobel: Chien-Shiung Wu

02 Oct 2020 Hamish Johnston

The 2020 Nobel Prize for Physics will be announced on Tuesday 6 October. In the run-up to the announcement, Physics World editors have picked some of the people who they think have been overlooked for a prize in the past

Overlooked: Chien-Shiung Wu in 1963 at Columbia University. (Courtesy: Smithsonian Institution)

The 1957 Nobel Prize for Physics was shared by Chen Ning Yang and Tsung-Dao Lee “for their penetrating investigation of the so-called parity laws which has led to important discoveries regarding the elementary particles”. However, some physicists argue that the Chinese-American physicist Chien-Shiung Wu should have shared the prize for providing the experimental evidence for Lee and Yang’s theoretical prediction of parity violation. Furthermore, some believe that Wu was denied the prize because she was a woman.

Based at Columbia University in the late 1950s, Wu designed an experiment that tested parity laws by observing beta decay at ultracold temperatures. While Wu was an expert in measuring beta decay, she collaborated with scientists at the National Bureau of Standards (NBS) in Washington DC (now NIST) to meet the cryogenic requirements of what is now known as the “Wu experiment”.

In an 2012 article for Physics World (“Credit where credit’s due?”) the Hungarian chemist and historian of science Magdolna Hargittai dug deep into the claims and counter claims of who, if anybody, should have shared the 1957 prize with Lee and Yang.

Three competing groups

 

Experiments pin down conditions that make hot water freeze before cold

05 Aug 2020 Anna Demming

Optical tweezers: Avinash Kumar, who built the Mpemba effect apparatus and carried out the experiments under the guidance of John Bechhoefer, at work in the lab. (Courtesy: Prithviraj Basak)

In 1963, a Tanzanian schoolboy called Erasto Mpemba was making ice cream when he noticed something strange: hot water sometimes freezes faster than cold water. Though Mpemba was not the first to wonder about this phenomenon, his report nevertheless captured the scientific imagination. The so-called “Mpemba effect” has remained contentious ever since – not least because the complex matrix of interactions at work when freezing a cup of hot water, coupled with water’s many anomalies, make it difficult to reproduce.

Researchers at Simon Fraser University in Canada have now overcome this problem with a simplified experimental model of a hot system relaxing to equilibrium with a colder heat bath. According to team leader John Bechhoefer, the technique he developed with PhD student Avinash Kumar enabled them to replicate the Mpemba effect in a reliable way, making it possible to pin down the precise conditions it requires.

 

Pions form a new kind of helium

11 May 2020

Pionic helium In this experiment, a pion – shown here with one orange and one blue particle representing its quark and anti-quark – replaces one of the two electrons in the helium atom. This new metastable atom is then excited with laser light (shown here in red) to probe its properties. (Courtesy: Max Planck Institute of Quantum Optics/Thorsten Naeser)

The ability to make artificial atoms containing exotic particles in place of electrons is giving physicists a new way of probing fundamental interactions. Now, researchers have created and interrogated a novel kind of helium atom in which one of the electrons is replaced by a sub-atomic particle known as a pion. The work could shed light on the nature of both pions and neutrinos – tiny, neutral particles for which certain attributes, including mass, remain relatively poorly understood.

Among the particles previously used to make these unusual atoms is the muon, which is about 200 times as massive as the electron but otherwise has identical properties. In 2010 Randolf Pohl and colleagues at the Max Planck Institute of Quantum Optics (MPQ) in Garching, Germany, carried out spectroscopic measurements on muonic hydrogen. They used their data to great effect, calculating a value for the proton’s charge radius that was completely at odds with the then-accepted value and forcing other groups to try to resolve the discrepancy.

 

New microwave bolometers could boost quantum computers

05 Oct 2020 Hamish Johnston

Nordic device: Artistic image of the Aalto University graphene bolometer controlled by electric field. (Courtesy: Heikka Valja)

Two graphene-based bolometers that are sensitive to detect single microwave photons have been built by independent teams of physicists. The devices could find a range of applications in quantum technologies, radio astronomy and even in the search for dark matter.

One bolometer was created in Finland by Mikko Möttönen and colleagues at Aalto University and VTT Technical Research Centre of Finland, while the other was created by an international team led by Kin Chung Fong at Raytheon BBN Technologies in the US.

A bolometer measures the energy of incoming radiation by determining how much the radiation heats up a material. Bolometers capable of detecting single microwave photons would be very useful in creating quantum computers and other technologies that use superconducting quantum bits (qubits). This is because superconducting qubits interact via microwaves and single photons provide a very efficient way of transferring quantum information between qubits.

 

Nanoparticles warm-up faster than they cool down

29 Sep 2020

Hot and cold Bouncing off walls slows the cooling of hot nanoparticles. (Courtesy: iStock/Mervana)

On the nanoscale, objects warm-up faster than they cool down. That is the surprising conclusion of Alessio Lapolla and Aljaž Godec at the Max Planck Institute of Biophysical Chemistry in Germany, who have predicted this asymmetry using mathematical models of confined nanoparticles.

One basic assumption in thermodynamics is that an object that is either hotter or colder than its surrounding environment will cool down or heat up, respectively, at the same rate. So, an object that is slightly warmer than room temperature will reach room temperature at the same time as an identical object that started slightly below room temperature.

 

COVID Research and Resources Group brings physicists together

21 Sep 2020 Tami Freeman

The newly formed CRRG will bring together physicists, engineers, and other medical and biological experts to collaborate on COVID-19 research. (Courtesy: iStock/RomoloTavani)

Physics has an important role to play in tackling the COVID-19 pandemic. Many physicists are already contributing to COVID-related research, in areas including computational modelling, medical imaging and development of protective and therapeutic equipment. Many such physicists are working in isolation, however, and only interacting on a local level. The newly formed COVID Research and Resources Group (CRRG) aims to bring these physicists and related researchers together, allowing them to benefit from a more coordinated approach.Robert Jeraj.

Leading the initiative is Robert Jeraj, professor of medical physics at the University of Wisconsin–Madison. He tells Physics World how the CRRG originated: “The American Physical Society [APS] has a Topical Group on Medical Physics, GMED, and we had a discussion about how we can help to bring together physicists that are interested in COVID-related research, those already doing research and those who want to contribute and share resources. Partnering with many other APS units, this turned into the COVID Research and Resources Group.”

 

Machine-learning study of metallic hydrogen provides clues about Jupiter’s interior

22 Sep 2020

Deep within the interiors of gas-giant planets like Jupiter, materials can be subjected to millions of atmospheres of

 Smooth transition: a machine learning study of metallic hydrogen could shed light on the interiors of gas giants like Jupiter. (Courtesy: NASA/ESA/A Simon (Goddard Space Flight Center)/MH Wong (University of California, Berkeley))

pressure. In the most extreme conditions, even hydrogen no longer exists in its usual molecular form. Instead, its covalent bonds break down and the material is believed to become a metallic solid. As astronomers seek to understand the physical structures of gas giants, a detailed knowledge of this metallization process is crucial.

To gain these insights, researchers must look to hydrogen’s phase diagram – which depicts how its physical properties vary with temperature and pressure. Although the phase diagram for hydrogen in less extreme conditions has been precisely mapped out, this is far from the case for extremely dense, metallic hydrogen. This gap in knowledge has prompted numerous investigations into where the boundary lies between molecular liquid hydrogen, and its solid metal form. However, it is proving to be extremely difficult to create the necessary high pressures in the lab.