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Metal–Metal Bonding as an Electrode Design Principle in the Low-Strain Cluster Compound LiScMo₃O₈
No full textElectrode materials for Li⁺-ion batteries require optimization along several disparate axes related to cost, performance, and sustainability. One of the important performance axes is the ability to retain structural integrity though cycles of charge/discharge. Metal–metal bonding is a distinct feature of some refractory metal oxides that has been largely underutilized in electrochemical energy storage, but that could potentially impact structural integrity. Here LiScMo₃O₈, a compound containing triangular clusters of metal–metal bonded Mo atoms, is studied as a potential anode material in Li⁺-ion batteries. Electrons inserted though lithiation are localized across rigid Mo₃ triangles (rather than on individual metal ions), resulting in minimal structural change as suggested by operando diffraction. The unusual chemical bonding allows this compound to be cycled with Mo atoms below a formally +4 valence state, resulting in an acceptable voltage regime that is appropriate for an anode material. Several characterization methods including potentiometric entropy measurements indicate two-phase regions, which are attributed through extensive first-principles modeling to Li⁺ ordering. This study of LiScMo₃O₈ provides valuable insights for design principles for structural motifs that stably and reversibly permit Li⁺ (de)insertion
Nonreciprocal infrared absorption via resonant magneto-optical coupling to InAs
No full textNonreciprocal elements are a vital building block of electrical and optical systems. In the infrared regime, there is a particular interest in structures that break reciprocity because their thermal absorptive (and emissive) properties should not obey the Kirchhoff thermal radiation law. In this work, we break time-reversal symmetry and reciprocity in n-type–doped magneto-optic InAs with a static magnetic field where light coupling is mediated by a guided-mode resonator structure, whose resonant frequency coincides with the epsilon-near-zero resonance of the doped indium arsenide. Using this structure, we observe the nonreciprocal absorptive behavior as a function of magnetic field and scattering angle in the infrared. Accounting for resonant and nonresonant optical scattering, we reliably model experimental results that break reciprocal absorption relations in the infrared. The ability to design these nonreciprocal absorbers opens an avenue to explore devices with unequal absorptivity and emissivity in specific channels
Countdown to perovskite space launch: Guidelines to performing relevant radiation-hardness experiments
No full textPerovskite photovoltaics (PVs) are under intensive development for promise in terrestrial energy production. Soon, the community will find out how much of that promise may become reality. Perovskites also open new opportunities for lower cost space power. However, radiation tolerance of space environments requires appropriate analysis of relevant devices irradiated under representative radiation conditions. We present guidelines designed to rigorously test the radiation tolerance of perovskite PVs. We review radiation conditions in common orbits, calculate nonionizing and ionizing energy losses (NIEL and IEL) for perovskites, and prioritize proton radiation for effective nuclear interactions. Low-energy protons (0.05–0.15 MeV) create a representative uniform damage profile, whereas higher energy protons (commonly used in ground-based evaluation) require significantly higher fluence to accumulate the equivalent displacement damage dose due to lower scattering probability. Furthermore, high-energy protons may “heal” devices through increased electronic ionization. These procedural guidelines differ from those used to test conventional semiconductors
In situ recording of Mars soundscape
No full textBefore the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat, (2) the speed of sound varies at the surface with frequency and (3) high-frequency waves are strongly attenuated with distance in CO₂ (refs. 2,3,4). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s⁻¹ apart below and above 240 Hz, a unique characteristic of low-pressure CO₂-dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO₂ vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus
Imaging nitrogen fixation at lithium solid electrolyte interphases via cryo-electron microscopy
No full textElectrifying ammonia synthesis will be vital to the decarbonization of the chemical industry, as the Haber-Bosch process contributes significantly to global carbon emissions. A lithium-mediated pathway is among the most promising ambient-condition electrochemical ammonia synthesis methods. However, the role of metallic lithium and its passivation layer, the solid electrolyte interphase (SEI), remains unresolved. Here, we apply a multiscale approach that leverages the powerful cryogenic transmission electron microscopy (cryo-TEM) technique to reveal new insights that were previously inaccessible with conventional methods. We discover that the proton donor (e.g. ethanol) governs lithium reactivity toward nitrogen fixation. Without ethanol, the SEI passivates lithium metal, rendering it inactive for ammonia production. Ethanol disrupts this passivation layer, enabling continuous reactivity at the lithium surface. As a result, metallic lithium is consumed via reactions with nitrogen, proton donor, and other electrolyte components. This reactivity across the SEI is vital to device-level performance of lithium-mediated ammonia synthesis
Nonlinear Noise Cleaning in Gravitational-Wave Detectors With Convolutional Neural Networks
No full textCurrently, the sub-60 Hz sensitivity of gravitational-wave (GW) detectors like Advanced LIGO (aLIGO) is limited by the control noises from auxiliary degrees of freedom which nonlinearly couple to the main GW readout. One promising way to tackle this challenge is to perform nonlinear noise mitigation using convolutional neural networks (CNNs), which we examine in detail in this study. In many cases, the noise coupling is bilinear and can be viewed as a few fast channels' outputs modulated by some slow channels. We show that we can utilize this knowledge of the physical system and adopt an explicit “slow×fast” structure in the design of the CNN to enhance its performance of noise subtraction. We then examine the requirements in the signal-to-noise ratio (SNR) in both the target channel (i.e., the main GW readout) and in the auxiliary sensors in order to reduce the noise by at least a factor of a few. In the case of limited SNR in the target channel, we further demonstrate that the CNN can still reach a good performance if we use curriculum learning techniques, which in reality can be achieved by combining data from quiet times and those from periods with active noise injections
Möbius Disjointness for C^(1+ε) Skew Products
No full textWe show that for ε > 0, every C^(1+ε) skew product on T² over a rotation of T¹ satisfies Sarnak’s conjecture. This is an improvement of earlier results of Kułaga–Przymus–Lemańczyk, Huang–Wang–Ye, and Kanigowski–Lemańczyk–Radziwiłł
Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO–Virgo Run O3b
No full textWe search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC–2020 March 27 17:00 UTC). We conduct two independent searches: a generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate
Large-scale Analysis of Sleep in Zebrafish
No full textOver the past decade, zebrafish have emerged as a powerful model for the study of vertebrate sleep and wake behaviors. Experimental evidence has demonstrated behavioral, anatomical, genetic, and pharmacological conservation of sleep between zebrafish and mammals, suggesting that discoveries in zebrafish can inform our understanding of mammalian sleep. Here, we describe a protocol for performing sleep behavioral experiments in larval zebrafish, using a high-throughput video tracking system. We explain how to set up a sleep behavioral experiment and provide guidelines on how to analyze the data. Using this protocol, a typical experiment can be completed in less than five days, and this method provides a scalable platform to perform genetic and pharmacological screens in a simple and cost-effective vertebrate model. By combining high-throughput behavioral assays with several advantageous features of zebrafish, this model system provides new opportunities to make discoveries that clarify the genetic and neurological mechanisms that regulate sleep
Utilizing correlation functions to develop a multistate model of P. denitrificans F₁-ATPase and enhance single-molecule imaging resolution
No full textF₁-ATPase enzyme is a biological motor which hydrolyzes ATP. The enzyme has been observed via single-molecule imaging experiments wherein the enzyme is allowed to rotate freely while being recorded using a gold nanoparticle. During hydrolysis, the enzyme causes Brownian noise when rotating to new chemical states because of a size difference between the 4 nm enzyme and 40 nm probe. The unconvoluted rotary movement has been revealed using techniques including rotational correction, correlation functions, and comparison of average rotational jumps which contribute to developing a multistate model. Within P. denitrificans F₁, the timestep used in experimentation is limited to 100 μs. After correction for tilting, a method for evaluating all three subunits uniformly was implemented in further evaluations. Using corrected data, the torsional spring constant of the rotary shaft was found to be near 25 pN nM for most subunits with a few subunits at much higher values. Implementation of the time correlation function which was proven to be stationary yielded a viscoelastic relaxation time around unity. The relaxation time provides a method for calculating a diffusion coefficient to develop a multistate model and elucidate hidden kinetic states of the functioning enzyme