An Electrochemical Ethylamine/Acetonitrile Redox Method for Ambient Hydrogen Storage

Hydrogen storage presents a major difficulty in the development of hydrogen economy. Herein, we report a new electrochemical ethylamine/acetonitrile redox method for hydrogen storage with an 8.9 wt.% theoretical storage capacity under ambient conditions. This method exhibits low onset overpotentials of 0.19 V in CH3CH2NH2 dehydrogenation to CH3CN and 0.09 V in CH3CN hydrogenation to CH3CH2NH2 using commercial Pt black catalyst. By assembling a full cell that couples CH3CH2NH2/CH3CN redox reactions with hydrogen evolution and oxidation reactions, we demonstrate a complete hydrogen storage cycle at fast rates, with only 52.5 kJ/mol energy consumption for H2 uptake and release at a rate of 1 L/m2·h. This method provides a viable hydrogen storage strategy that meets the 2025 Department of Energy onboard hydrogen storage target.

Understanding the critical rate of environmental change for ecosystems, cyanobacteria as an example

Recently it has been show that in some ecosystems fast rates of change of environmental drivers may trigger a critical transition, whereas change of the same magnitude but at slower rates would not. So far, few studies describe this phenomenon of rate-induced tipping, while it is important to understand this phenomenon in the light of the ongoing rapid environmental change. Here, we demonstrate rate-induced tipping in a simple model of cyanobacteria with realistic parameter settings. We explain graphically that there is a range of initial conditions at which a gradual increase in environmental conditions can cause a collapse of the population, but only if the change is fast enough. In addition, we show that a pulse in the environmental conditions can cause a temporary collapse, but that is dependent on both the rate and the duration of the pulse. Furthermore, we study whether the autocorrelation of stochastic environmental conditions can influence the probability of inducing rate-tipping. As both the rate of environmental change, and autocorrelation of the environmental variability are increasing in parts of the climate, the probability for rate-induced tipping to occur is likely to increase. Our results imply that, even though the identification of rate sensitive ecosystems in the real world will be challenging, we should incorporate critical rates of change in our ecosystem assessments and management.

Cyclic oxygen exchange capacity of Ce-doped V2O5 materials for syngas production via high-temperature thermochemical-looping reforming of methane

Cerium doping into the V2O5 lattice forms a reversible V2O3/VO redox pair after sequential methane partial oxidation and CO2/H2O splitting reactions and produces syngas (H2, CO) with fast rates and high oxygen exchange capacity.

The role of cochlear place coding in the perception of frequency modulation

Natural sounds convey information via frequency and amplitude modulations (FM and AM). Humans are acutely sensitive to the slow rates of FM that are crucial for speech and music. This sensitivity has long been thought to rely on precise stimulus-driven auditory-nerve spike timing (time code), whereas a coarser code, based on variations in the cochlear place of stimulation (place code), represents faster FM rates. We tested this theory in listeners with normal and impaired hearing, spanning a wide range of place-coding fidelity. Contrary to predictions, sensitivity to both slow and fast FM correlated with place-coding fidelity. We also used incoherent AM on two carriers to simulate place coding of FM and observed poorer sensitivity at high carrier frequencies and fast rates, two properties of FM detection previously ascribed to the limits of time coding. The results suggest a unitary place-based neural code for FM across all rates and carrier frequencies.

Evolution in the Courtroom: Using Phylogenetics to Investigate Legal Claims of HIV Transmission

DNA sequences have become ubiquitous across the biological sciences and are even embedded in the public psyche, perhaps most famously in the context of forensic science. A human being’s DNA changes very little over his or her lifetime, and this inherent stability lends itself well to positively identifying individuals using DNA samples. However, not all genomes are so stable, even over short timespans. One particularly dramatic example is human immunodeficiency virus (HIV-1). Unlike the human genome, the HIV-1 genome has an extraordinarily high mutation rate. This, in combination with recombination, rapid proliferation, and strong selection exerted by host immune systems, leads to exceptionally fast rates of evolution. The result of these interacting processes is a population of diverse and dynamically evolving HIV-1 genomes in the host, which is one reason why the virus is so difficult to eradicate. HIV-1’s rapid rate of evolution also prevents the use of standard DNA fingerprinting techniques that rely on stable, unchanging genomes to connect the infections in different individuals, but such rapid evolution does lend itself particularly well to phylogenetic analysis.

Adaptive Trust Region Policy Optimization: Global Convergence and Faster Rates for Regularized MDPs

Trust region policy optimization (TRPO) is a popular and empirically successful policy search algorithm in Reinforcement Learning (RL) in which a surrogate problem, that restricts consecutive policies to be ‘close’ to one another, is iteratively solved. Nevertheless, TRPO has been considered a heuristic algorithm inspired by Conservative Policy Iteration (CPI). We show that the adaptive scaling mechanism used in TRPO is in fact the natural “RL version” of traditional trust-region methods from convex analysis. We first analyze TRPO in the planning setting, in which we have access to the model and the entire state space. Then, we consider sample-based TRPO and establish Õ(1/√N) convergence rate to the global optimum. Importantly, the adaptive scaling mechanism allows us to analyze TRPO in regularized MDPs for which we prove fast rates of Õ(1/N), much like results in convex optimization. This is the first result in RL of better rates when regularizing the instantaneous cost or reward.

The time course of updating in running span

Running span can be performed by either passively listening to to-be-remembered items or actively updating the target set during presentation. This choice of strategy is influenced by the rate of presentation in the task. Previous research suggests that the active updating process is demanding and time-consuming. It is favored at relatively slow rates of presentation, while the passive strategy is more successful when applied at fast rates. In two experiments the time course of resource demand during task performance and its sensitivity to presentation rate was examined. We hypothesized that running span imposes a high cognitive load only when active updating is employed. Participants performed running span simultaneously with a spatial reaction time (RT) task, and RTs on the concurrent task were used to index the resource demands of the memory task. A slow-paced running span exhibited a large overall resource demand in comparison with the serial recall tasks (Experiment 1) and fast-paced running span (Experiment 2). This demand was observed from the position in the list from which participants are presumed to start updating, suggesting a cognitive shift to a demanding mode of updating. In addition, a demand burst was found approximately 1000ms following item onset at these later positions. These data establish that the process of active updating in running span task is slow and cognitively demanding and indicate that this limits its application during fast presentation rates.

Perception of frequency modulation is mediated by cochlear place coding

Natural sounds convey information via frequency and amplitude modulations (FM and AM). Humans are acutely sensitive to the slow rates of FM that are crucial for speech and music. This sensitivity has been thought to rely on precise stimulus-driven auditory-nerve spike timing (time code), whereas a coarser code, based on variations in the cochlear place of stimulation (place code), represents faster FM. Here we test this longstanding theory in listeners with normal and impaired hearing, resulting in widely varying place-coding fidelity. Contrary to predictions, FM detection thresholds at slow and fast rates are highly correlated and closely related to the fidelity of cochlear place coding. We support this conclusion with additional data showing that place-based coding degrades at high modulation rates and in high spectral regions in ways that were previously interpreted as reflecting the limits of fine neural timing. The results suggest a unitary place-based neural code for FM.

Homology and Specificity of Natural Sound-Encoding in Human and Monkey Auditory Cortex

Understanding homologies and differences in auditory cortical processing in human and nonhuman primates is an essential step in elucidating the neurobiology of speech and language. Using fMRI responses to natural sounds, we investigated the representation of multiple acoustic features in auditory cortex of awake macaques and humans. Comparative analyses revealed homologous large-scale topographies not only for frequency but also for temporal and spectral modulations. In both species, posterior regions preferably encoded relatively fast temporal and coarse spectral information, whereas anterior regions encoded slow temporal and fine spectral modulations. Conversely, we observed a striking interspecies difference in cortical sensitivity to temporal modulations: While decoding from macaque auditory cortex was most accurate at fast rates (> 30 Hz), humans had highest sensitivity to ~3 Hz, a relevant rate for speech analysis. These findings suggest that characteristic tuning of human auditory cortex to slow temporal modulations is unique and may have emerged as a critical step in the evolution of speech and language.

Trends and Patterns of Concealed Handgun License Applications: A Multistate Analysis

Recent waves of legislation have made it much easier for gun owners to obtain a Concealed Handgun License (CHL) and thereby carry their guns in public except when explicitly prohibited. Because data are difficult to access, our understanding of who seeks and obtains such licenses remains limited. Using data obtained through Freedom of Information Act requests, this article fills this empirical gap by describing demographic trends and characteristics of applicants for CHLs in five states: Florida, Indiana, Massachusetts, Texas, and Utah. The results establish that (1) applications for CHLs are growing at fast rates; (2) there are significant gender and racial disparities in terms of who applies for CHLs, with men 2.9 to 5.5 times more likely to apply than women, and whites 1.3 to 2.0 times more likely to apply than blacks; (3) in Florida and Utah, these demographic gaps have widened over time; and (4) there are significant racial disparities in terms of application outcomes, with black applicants being 3.3 to 5.5 times more likely to be denied a license than white applicants. Moreover, we do not find the patterns in Massachusetts, a may-issue state, to be significantly different from the shall-issue states in our sample.