Stimulating resonance with two very different forces (Vol. 51, No. 3)

Fine-tuning frequencies to achieve resonance

In some specialised oscillators, two driving forces with significantly different frequencies can work together to make the whole system resonate.

“Nonlinear’ systems can display dramatic responses when the forces which cause them to vibrate are changed. Some of these systems are sensitive to changes in the parameters which define their driving forces, and can be well described using mathematical equations. In this work, it is shown in detail for the first time that some ‘parametric’ oscillators can be made to resonate when tuned by a high driving frequency to match a separate, far lower frequency.

S Roy, D Das, D Banerjee, Nonlinear Response of a Parametric Bistable Oscillator with Multiple Excitations, Eur. Phys. J. B 93, 12 (2020)

Frozen-planet states in exotic helium atoms (Vol. 51, No. 3)

Low energy anti-proton accelerator. © Wikipedia, Tom Purves from Toronto, Canada

Mapping the energy levels and estimated the stability of a ‘frozen planet’ configuration of anti-protonic helium.

Exotic subatomic particles that are like ‘normal’ particles apart from one, opposite, property - such as the positron, which is like an electron but positively rather than negatively charged - are collectively known as antimatter. Direct studies of collisions between particles of matter and those of antimatter using giant facilities such as those at CERN can advance our understanding of the nature of matter. In this work, the energy levels of an exotic form of helium produced in this way are mapped. The work has been described by one commentator as ‘... a new jewel in the treasure of scientific achievements in atomic physics theory”.

T.P. Grozdanov, E.A. Solov'ev , Hidden-crossing explanation of frozen-planet resonances in antiprotonic helium; their positions and widths, Eur. Phys. J. D 74, 50 (2020)

Distortion isn’t a drag on fluid-straddling particles (Vol. 51, No. 3)

Straddling particles deform fluid interfaces

The drag forces experienced by particles which straddle and distort the interfaces between un-mixable fluids are less influenced by the shape of the distortion than previously thought.

Some intriguing physics can be found at the interfaces between fluids, particularly if they are straddled by particles like proteins or dust grains. When placed between un-mixable fluids such as oil and water, a variety of processes, including inter-molecular interactions, will cause the particles to move around. These motions are characterised by the drag force experienced by the particles, which is itself thought to depend on the extent to which they distort fluid interfaces. In this work it is shown that the drag force experienced by fluid-straddling particles is less affected by interface distortion than previously believed.

J-C Loudet, M. Qiu, J Hemauer, J J Feng, Drag force on a particle straddling a fluid interface: influence of interfacial deformations, Eur. Phys. J. E 43, 13 (2020)

Models explain changes in cooking meat (Vol. 51, No. 3)

Moisture flows in cooking meat. Temperature at 10 min. (blue), 30 min. (red) and 50 min. (yellow).

By treating meat as a network of flexible polymers surrounded by flowing moisture, computer models can accurately predict how much it will shrink when cooked.

Made up of complex networks of moisture-saturated proteins, meat displays some intriguing physical properties when it is cooked. In this work, mathematicians show that by modelling meat as a fluid-saturated matrix of elastic proteins, which are deformed as the fluid moves, cooking behaviours can be simulated precisely.

S Deyo, S Granzier-Nakajima, H Nelson, P Puente, K Tully, J Webb, A mathematical model for meat cooking, Eur. Phys. J. Plus 135, 322 (2020)

HIAS 2019 (Vol. 51, No. 3)

HIAS 2019 group photo

In September 2019, the Department of Nuclear Physics of the Australian National University welcomed delegates from around the world to Canberra for the 7th Heavy Ion Accelerator Symposium (HIAS 2019).

The Symposium series takes place at Australia’s Heavy Ion Accelerator Facility and provide a forum to build cross-institutional and interdisciplinary links in research areas exploiting the capabilities of heavy-ion accelerators and their associated state-of-the-art instrumentation.

HIAS 2019 had a particular focus on Nuclear structure and nuclear data, Accelerator Mass Spectrometry Applications, Nuclear Astrophysics, Nuclear Reactions, and New Instrumentation for Nuclear Science and Applications.

A.J. Mitchell, S. Pavetich and D. Koll (Eds.), Heavy Ion Accelerator Symposium (HIAS 2019), Canberra, Australia, September 9-13, 2019, EPJ Web of Conferences 232 (2020)

Many-body localisation in generalized Kondo lattice with disorder (Vol. 51, No. 3)

Schematic demonstrations of the decoherent state (left panel) and the localised state (right panel).

Many-body localisation (MBL) has gained widespread attentions in theoretical and experimental physics, the scenario of which is essentially different with that of the Anderson’s localization (AL).

In this work, we study the MBL transition in a generalised Kondo lattice, where a one-dimensional Hubbard chain with disordered spin-orbit coupling couples to a fixed impurity of spin 1/2. Based on exact diagonalisation, we calculate various quantities that can distinguish an MBL state from either an AL state or a thermal state. The model can be implemented in ultra-cold Fermi gases of alkaline-earth-like atoms in one-dimensional optical lattices and Raman-assisted spin-orbit coupling.


Ye Cao and Wei Zhang, Many-body localisation in generalized Kondo lattice with disorder, EPL 129 2000 (2020)

Precursors to Rare Events in Stochastic Resonance (Vol. 51, No. 3)

(a)-(c) Trajectories of the system x(t) during a transition with noise realisations p(t) (crosses) and analytical predictions (solid lines) for three different simulations characterised by a Lyapunov exponent of the stable orbit, λ_s. (d) The mean standard error (MSE) of noise realisations with respect to their predicted behaviour using the same data of the box in (c) displayed over a larger time window. The solid line is the average MSE, the dashed line corresponds to the p(t) in the inset of (c) and the dotted line is the minimum value reached by the MSE if these values of p(t) are removed.

Niels Bohr has often been attributed with saying "Prediction is difficult, especially about the future."

Indeed, predicting the states of real world noisy dynamical systems continues to be a fundamental scientific challenge. In stochastic resonance a periodically forced Brownian particle jumps at rare intervals between two states. We have found precursors—predictors—to these stochastic transitions by revealing how the noise fluctuations become deterministic as the system approaches the rare event. Our path-integral method agrees with numerical simulations in extracting precursor fluctuations from data in the vast range of systems that exhibit stochastic resonance.


L. T. Giorgini et al, Precursors to rare events in stochastic resonance, EPL 129 40003 (2020)