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Thermal expansion and phonon anharmonicity of cuprite studied by inelastic neutron scattering and ab initio calculations
No full textInelastic neutron scattering measurements were performed with a time-of-flight chopper spectrometer to observe phonons in all parts of the Brillouin zone of a single crystal of cuprite Cu₂O. We reduced the experimental data to phonon dispersions in the high-symmetry directions, and changes between 10 and 300 K are reported. In this paper, we show ab initio quasiharmonic (QH) and anharmonic (AH) calculations of phonon dispersions. We performed all AH calculations with a temperature-dependent effective potential method. Both QH and AH calculations account for the small negative thermal expansion of cuprite at low temperatures. However, the measured temperature-dependent phonon behavior was predicted more accurately with the AH calculations than the QH ones. Nevertheless, at 300 K, the cubic AH used in this paper did not entirely account for the experimental phonon dispersions in cuprite
Synergistic HNO₃–H₂SO₄–NH₃ upper tropospheric particle formation
No full textNew particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN). However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO₃–H₂SO₄–NH₃ nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere
An Exploration of Sulfur Redox in Lithium Battery Cathodes
No full textSecondary Li-ion batteries have enabled a world of portable electronics and electrification of personal and commercial transportation. However, the charge storage capacity of conventional intercalation cathodes is reaching the theoretical limit set by the stoichiometry of Li in the fully lithiated structure. Increasing the Li:transition metal ratio and consequently involving structural anions in the charge compensation, a mechanism termed anion redox, is a viable method to improve storage capacities. Although anion redox has recently become the front-runner as a next-generation storage mechanism, the concept has been around for quite some time. In this perspective, we explore the contribution of anions in charge compensation mechanisms ranging from intercalation to conversion and the hybrid mechanisms between. We focus our attention on the redox of S because the voltage required to reach S redox lies within the electrolyte stability window, which removes the convoluting factors caused by the side reactions that plague the oxides. We highlight examples of S redox in cathode materials exhibiting varying degrees of anion involvement with a particular focus on the structural effects. We call attention to those with intermediate anion contribution to redox and the hybrid intercalation- and conversion-type structural mechanism at play that takes advantage of the positives of both mechanistic types to increase storage capacity while maintaining good reversibility. The hybrid mechanisms often invoke the formation of persulfides, and so a survey of binary and ternary materials containing persulfide moieties is presented to provide context for materials that show thermodynamically stable persulfide moieties
Proton coupling and the multiscale kinetic mechanism of a peptide transporter
No full textProton-coupled peptide transporters (POTs) are crucial for the uptake of di- and tripeptides as well as drug and prodrug molecules in prokaryotes and eukaryotic cells. We illustrate from multiscale modeling how transmembrane proton flux couples within a POT protein to drive essential steps of the full functional cycle: 1) protonation of a glutamate on transmembrane helix 7 (TM7) opens the extracellular gate, allowing ligand entry; 2) inward proton flow induces the cytosolic release of ligand by varying the protonation state of a second conserved glutamate on TM10; 3) proton movement between TM7 and TM10 is thermodynamically driven and kinetically permissible via water proton shuttling without the participation of ligand. Our results, for the first time, give direct computational confirmation for the alternating access model of POTs, and point to a quantitative multiscale kinetic picture of the functioning protein mechanism
Film formation mechanisms in mixed-dimensional 2D/3D halide perovskite films revealed by in situ grazing-incidence wide-angle X-ray scattering
No full textMixed-dimensional 2D/3D hybrid halide perovskites retain the stability of 2D perovskites (formula (A′)2(A)₍ₙ₋₁₎PbₙI₍₃ₙ₊₁₎) and long diffusion lengths of the 3D materials (AMX₃), thereby affording devices with extended stability as well as state-of-the art efficiencies approaching those of the 3D materials. These films are made by spin-coating precursor solutions with an arbitrarily large average layer thickness n (⟨n⟩ > 7) to give films with both 2D and 3D phases. Although the 2D and 3D perovskite film formation mechanisms have been studied, little is understood about composite 2D/3D film formation. We used in-situ grazing-incidence wide-angle scattering with synchrotron radiation to characterize the films fabricated from precursor solutions with stoichiometries of (BA)₂(MA)₍ₙ₋₁₎PbₙI₍₃ₙ₊₁₎ (⟨n⟩ = 3, 4, 5, 7, 12, 50, and ∞ (MAPbI₃)). Four different mechanisms are seen depending on the stoichiometry in the precursor solution. Kinetic analysis shows faster and earlier growth of the solvate with increasing ⟨n⟩
Phasic Alertness and Multisensory Integration Contribute to Visual Awareness of Weak Visual Targets in Audio-Visual Stimulation under Continuous Flash Suppression
No full textMultisensory stimulation is associated with behavioural benefits, including faster processing speed, higher detection accuracy, and increased subjective awareness. These effects are most likely explained by multisensory integration, alertness, or a combination of the two. To examine changes in subjective awareness under multisensory stimulation, we conducted three experiments in which we used Continuous Flash Suppression to mask subthreshold visual targets for healthy observers. Using the Perceptual Awareness Scale, participants reported their level of awareness of the visual target on a trial-by-trial basis. The first experiment had an audio-visual Redundant Signal Effect paradigm, in which we found faster reaction times in the audio-visual condition compared to responses to auditory or visual signals alone. In two following experiments, we separated the auditory and visual signals, first spatially (experiment 2) and then temporally (experiment 3), to test whether the behavioural benefits in our multisensory stimulation paradigm could best be explained by multisensory integration or increased phasic alerting. Based on the findings, we conclude that the largest contributing factor to increased awareness of visual stimuli accompanied by auditory tones is a rise in phasic alertness and a reduction in temporal uncertainty with a small but significant contribution of multisensory integration
Thank You to Our 2021 Peer Reviewers
No full textOn behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts for us in 2021. The hours reading and commenting on manuscripts not only improve the manuscripts, but also increase the scientific rigor of future research in the field. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. The COVID pandemic continued to impose additional stresses on the review process, as many reviewers had to juggle increased family commitments, hours of online meetings, remote work and instruction, lack of physical access to library resources, and other hardships, to maintain the quality and timeliness of their reviews. We received 4,832 submissions in 2021 and 5,232 reviewers contributed to their evaluation by providing 8,874 reviews in total. Although we witnessed an increase in the number of submissions, the average number of days to complete a review increased only slightly! That says a lot about the diligence of our reviewers. We deeply appreciate their contributions in these challenging times
Developmental Self-Assembly of a DNA Ring with Stimulus-Responsive Size and Growth Direction
No full textDevelopmental self-assembly of DNA nanostructures provides an ideal platform for studying the power and programmability of kinetically controlled structural growth in engineered molecular systems. Triggered initiation and designated sequencing of assembly and disassembly steps have been demonstrated in structures with branches and loops. Here we introduce a new strategy for selectively activating distinct subroutines in a developmental self-assembly program, allowing structures with distinct properties to be created in response to various molecular signals. We demonstrate this strategy in triggered self-assembly of a DNA ring, the size and growth direction of which are responsive to a key molecule. We articulate that reversible assembly steps with slow kinetics at appropriate locations in a reaction pathway could enable multiple populations of structures with stimulus-responsive properties to be simultaneously created in one developmental program. These results open up a broad design space for the self-assembly of molecules with adaptive behaviors toward advanced control in synthetic materials and molecular motors
Crossmodal Postdiction: Conscious Perception as Revisionist History
No full textPostdiction occurs when later stimuli influence the perception of earlier stimuli. As the multisensory science field has grown in recent decades, the investigation of crossmodal postdictive phenomena has also expanded. Crossmodal postdiction can be considered (in its simplest form) the phenomenon in which later stimuli in one modality influence earlier stimuli in another modality (e.g., Intermodal Apparent Motion). Crossmodal postdiction can also appear in more nuanced forms, such as unimodal postdictive illusions (e.g., Apparent Motion) that are influenced by concurrent crossmodal stimuli (e.g., Crossmodal Influence on Apparent Motion), or crossmodal illusions (e.g., the Double Flash Illusion) that are influenced postdictively by a stimulus in one or the other modality (e.g., a visual stimulus in the Illusory Audiovisual Rabbit Illusion). In this review, these and other varied forms of crossmodal postdiction will be discussed. Three neuropsychological models proposed for unimodal postdiction will be adapted to the unique aspects of processing and integrating multisensory stimuli. Crossmodal postdiction opens a new window into sensory integration, and could potentially be used to identify new mechanisms of crossmodal crosstalk in the brain
Evidence for unconventional superconductivity in twisted trilayer graphene
No full textMagic-angle twisted trilayer graphene (MATTG) has emerged as a moiré material that exhibits strong electronic correlations and unconventional superconductivity. However, local spectroscopic studies of this system are still lacking. Here we perform high-resolution scanning tunnelling microscopy and spectroscopy of MATTG that reveal extensive regions of atomic reconstruction favouring mirror-symmetric stacking. In these regions, we observe symmetry-breaking electronic transitions and doping-dependent band-structure deformations similar to those in magic-angle bilayers, as expected theoretically given the commonality of flat bands. Most notably in a density window spanning two to three holes per moiré unit cell, the spectroscopic signatures of superconductivity are manifest as pronounced dips in the tunnelling conductance at the Fermi level accompanied by coherence peaks that become gradually suppressed at elevated temperatures and magnetic fields. The observed evolution of the conductance with doping is consistent with a gate-tunable transition from a gapped superconductor to a nodal superconductor, which is theoretically compatible with a sharp transition from a Bardeen–Cooper–Schrieffer superconductor to a Bose–Einstein-condensation superconductor with a nodal order parameter. Within this doping window, we also detect peak–dip–hump structures that suggest that superconductivity is driven by strong coupling to bosonic modes of MATTG. Our results will enable further understanding of superconductivity and correlated states in graphene-based moiré structures beyond twisted bilayers