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In this study, we leverage wavelet-based bispectral analysis of magnetic fluctuation data to identify likely candidates for nonlinear three-wave coupling, which are subsequently investigated with bandpass filtering. The participating waves, two TAEs and a low-frequency magnetohydrodynamic (MHD) mode, are seen to satisfy coupling conditions in both frequency and toroidal wavenumber, consistent with nonlinear generation. We conclude that the detection of quadratic nonlinearities on sub-millisecond time scales is possible with this technique.

The paper is organized as follows: Sec. II provides an overview of the relevant theory of TAE, while Sec. III contextualizes the experiment and describes its data. Section IV provides a primer on bicoherence analysis, in addition to simple examples of its implementation. Section V applies time-resolved bispectral analysis to the experimental data, focusing on the detection of quadratic nonlinearities. Section VI summarizes our work and considers the next steps of the analysis.

With the continual miniaturization of electronic devices, there is an urgent need to understand the electron emission and the mechanism of electrical breakdown at nanoscale. For a nanogap, the complete process of the electrical breakdown includes the nano-protrusion growth, electron emission and thermal runaway of the nano-protrusion, and plasma formation. This review summarizes recent theories, experiments, and advanced atomistic simulation related to this breakdown process. First, the electron emission mechanisms in nanogaps and their transitions between different mechanisms are emphatically discussed, such as the effects of image potential (of different electrode’s configurations), anode screening, electron space-charge potential, and electron exchange-correlation potential. The corresponding experimental results on electron emission and electrical breakdown are discussed for fixed nanogaps on substrate and adjustable nanogaps, including space-charge effects, electrode deformation, and electrical breakdown characteristics. Advanced atomistic simulations about the nano-protrusion growth and the nanoelectrode or nano-protrusion thermal runaway under high electric field are discussed. Finally, we conclude and outline the key challenges for and perspectives on future theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes.

The double-cone ignition scheme is a novel approach with the potential to achieve a high gain fusion with a relatively smaller drive laser energy. To optimize the colliding process of the plasma jets formed by the CHCl/CD shells embedded in the gold cones, an x-ray streak camera was used to capture the spontaneous x-ray emission from the CHCl and CD plasma jets. High-density plasma jets with a velocity of 220 ± 25 km/s are observed to collide and stagnate, forming an isochoric plasma with sharp ends. During the head-on colliding process, the self-emission intensity nonlinearly increases because of the rapid increase in the density and temperature of the plasma jets. The CD colliding plasma exhibited stronger self-emission due to its faster implosion process. These experimental findings effectively agree with the two-dimensional fluid simulations.

This article is part of a series of pieces on advances in sustainable battery technologies that Physics Magazine is publishing to celebrate Earth Week 2024. See also: Q&A: Electrochemists Wanted for Vocational Degrees; Research News: Lithium-Ion “Traffic Jam” Behind Reduced Battery Performance; Q&A: The Path to Making Batteries Green; News Feature: Sodium Batteries as a Greener Lithium Substitute.

Since the first prototype made its debut in 2000, rechargeable magnesium batteries have continued to be both technologically attractive and commercially out of reach. The attraction arises from magnesium’s advantages over lithium: it is 1,000 times more abundant in Earth’s crust and is chemically less hazardous. The unrealized commercialization is largely down to the difficulty in identifying a material to serve as an effective and robust cathode. Tomoya Kawaguchi of Tohoku University in Japan and his collaborators may now have solved that problem through their demonstration of a material that satisfies one of the most important requirements of a good cathode: it can reversibly accept and release ions over repeated charging cycles [1].

The discharge of an electrochemical battery releases electrons that flow through the connected circuit. It also releases ions from the battery’s anode that flow through the battery’s electrolyte, in the opposite direction to the electrons, and then lodge in the cathode. The flows reverse directions during recharging. In a lithium-ion battery, the cathode is made from a lithium oxide and takes the form of either a layered material or a crystalline solid known as a spinel.

For Shirley Meng, the biggest barrier to achieving sustainable batteries is sociological not technological, requiring a change in mindset about how we consume and dispose of batteries.

Real-time in situ x-ray observations of new nickel-rich lithium-ion batteries reveal that reduced performance comes from lithium ions getting trapped in the cathode.

This article is part of a series of pieces on advances in sustainable battery technologies that Physics Magazine is publishing to celebrate Earth Week 2024. See also: Q&A: Electrochemists Wanted for Vocational Degrees; Q&A: The Path to Making Batteries Green; News Feature: Sodium as a Green Substitute for Lithium in Batteries; Research News: A New Cathode for Rechargeable Magnesium Batteries.

Electric vehicles are picking up visibility in the public eye. But their adoption is slowed down by batteries that degrade over time, an issue commercial ventures are especially keen on addressing as they adopt increasingly nickel-rich cathodes—the cathode du jour for high-end electric vehicles. The substitution of nickel for cobalt in earlier versions of these cathodes can improve their performance, but it also accelerates degradation. Earlier this year, Louis Piper, University of Warwick, UK, and his colleagues devised and demonstrated an x-ray technique that can examine industry-grade versions of nickel-rich lithium-ion batteries in real time [1]. Their observations help to narrow down why these batteries degrade and lead to suggestions for how to prolong battery lifespans.

Most models for the overall shape and geometry of the Universe—including some exotic ones—are compatible with the latest cosmic observations.

Is the Universe simply connected like a sphere or does it contain holes like a doughnut or a more complicated structure? The topology of the Universe—that is, its overall geometry—remains far from settled, according to a collaboration of cosmologists. Despite past claims that observations of the cosmic microwave background (CMB) rule out various topologies, the researchers contend that many of these shapes, including some strange ones, have not been contradicted by the evidence [1].

The overall geometry of the Universe is thought to have been determined by quantum processes that unfolded in the initial moment of the big bang. Identifying the topology of the Universe would provide researchers with an important clue as to the nature of those quantum processes and could help them sift through the many proposed theories of the early Universe.

Varying the parameters of weight distribution did not account for the observed amount of HD information conveyed by PoSub-FS cells (Fig. 2a). Rather, we found that the number of inputs received by each output unit was a key factor influencing the amount of HD information (Extended Data Fig. 5e). Varying both weight distribution and the number of input units, we obtained a distribution of HD information in output tuning curves that matched the real data (Extended Data Fig. 5f), revealing that the tuning of PoSub-FS cells can be used to estimate both the distribution of weights and the number of input neurons. Notably, under optimal network conditions, Isomap projection of output tuning curve auto-correlograms has a similar geometry to that of real PoSub-FS cells (Extended Data Fig. 5g), confirming similar distribution of tuning shapes.

To further quantify the relative contributions of ADN and local PoSub inputs to PoSub-FS cell tuning, we expanded the simulation to include the following two inputs: one with tuning curve widths corresponding to ADN-HD cells and one with tuning curve widths corresponding to PoSub-HD cells (Fig. 4h, left). We then trained the model using gradient descent to find the variances and means of input weights that result in the best fit between the simulated output and real data. The combination of parameters that best described the real data resulted in ADN inputs distributed in a near Gaussian-like manner but a heavy-tailed distribution of PoSub-HD inputs (Fig. 4h, middle). Using these distribution parameters, we performed simulations to determine the contribution of ADN-HD and PoSub-HD inputs to the output tuning curves and established that PoSub-FS cell-like outputs are best explained by flat, high firing rate inputs from ADN-HD cells and low firing rate, HD-modulated inputs from PoSub-HD cells (Fig. 4h, right).

Our simulations, complemented by direct analytical derivation (detailed in the Supplementary Methods), not only support the hypothesis that the symmetries observed in PoSub-FS cell tuning curves originate from local cortical circuits but also demonstrate that these symmetries emerge from strongly skewed distributions of synaptic weights.

A study investigates subcellular, single-cell and network-level comunication within the astrocyte network in response to the two major neurotransmitter inputs.