Publications

The micrometeorological flux measurement technique known as relaxed eddy accumulation (REA) holds promise as a powerful new tool for ecologists. The more popular eddy covariance (eddy correlation) tech- nique requires the use of sensors that can respond at fast rates (10 Hz), and these are unavailable for many eco- logically relevant compounds. In contrast, the use of REA allows flux measurement with sensors that have much slower response time, such as gas chromatography and mass spectrometry. In this review, relevant micro- meteorological details underlying REA are presented, and critical analytical and system design details are discussed, with the goal of introducing the technique and its potential applications to ecologists. The validity of REA for measuring fluxes of isoprene, a photochemi- cally reactive hydrocarbon emitted by several plant species, was tested with measurements over an oak- hickory forest in the Walker Branch Watershed in eastern Tennessee. Concurrent eddy covariance mea- surements of isoprene flux were made using a newly available chemiluminesence instrument. Excellent agreement was obtained between the two techniques (r 2 a 0.974, n a 62), providing the first direct com- parison between REA and eddy covariance for mea- suring the flux rate of a reactive compound. The influ- ence of a bias in vertical wind velocity on the accuracy of REA was examined. This bias has been thought to be a source of significant error in the past. Measurements of normalized bias (w=rw) alone would lead us to think that a large potential error exists at this site. However, with our isoprene data and through simulations of REA with fast-response H2O and CO2 data, we conclude that accurate REA flux measurements can be made even in the presence of a bias in w.

Summary Large numbers of supernovae (SNe) have been discovered in recent years, and many more will be found in the near future. Once discovered, further study of a SN and its possible use as an astronomical tool (e.g., as a distance estimator) require knowledge of the SN type. Current classification methods rely almost solely on the analysis of SN spectra to determine their type. However, spectroscopy may not be possible or practical. We present a classification method for SNe based on the comparison of their observed colors with synthetic ones, calculated from a large database of multi-epoch optical spectra of nearby events. Broadband photometry at optical wavelengths allows classification of SNe up to z = 0.75, and the use of infrared bands extends it further to z = 2.5. We demonstrate the applicability of this method, outline the observational data required to further improve the usefulness of the method, and discuss prospects for its use on future SN samples. Community access to the tools developed is provided by a dedicated website.

We experimentally demonstrate 204x spontaneous emission rate enhancement from an electrically-injected nanoLED coupled to a cavity-backed optical slot antenna. This places the spontaneous emission rate on par with the stimulated emission rate.

Hydrogen is regarded as an attractive alternative energy carrier due to its high gravimetric energy density and only water production upon combustion. However, due to its low volumetric energy density, there are still some challenges in practical hydrogen storage and transportation. In the past decade, using chemical bonds of liquid organic molecules as hydrogen carriers to generate hydrogen in situ provided a feasible method to potentially solve this problem. Research efforts on liquid organic hydrogen carriers (LOHCs) seek practical carrier systems and advanced catalytic materials that have the potential to reduce costs, increase reaction rate, and provide a more efficient catalytic hydrogen generation/storage process. In this work, we used methanol as a hydrogen carrier to release hydrogen in situ with the single-site Pt₁/CeO₂ catalyst. Moreover, in this reaction, compared with traditional nanoparticle catalysts, the single site catalyst displays excellent hydrogen generation efficiency, 40 times higher than 2.5 nm Pt/CeO₂ sample, and 800 times higher compared to 7.0 nm Pt/CeO₂ sample. This in-depth study highlights the benefits of single-site catalysts and paves the way for further rational design of highly efficient catalysts for sustainable energy storage applications.

The Late Cretaceous-Quaternary Cameroon Volcanic Line (CVL) is a 1600km long chain of volcanoes that straddles the continent-ocean boundary and extends from the Gulf of Guinea to the interior of the African continent. The magmatic activity started at 70Ma and has continued until the present. The products of this magmatic activity are distinctive in terms of petrology and isotope geochemistry, the variety of volcanic rocks ranging from ultrabasic, alkaline to sub-alkaline lavas to highly evolved alkaline lavas with isotopic compositions indicating complex combinations of both sub-lithospheric (HIMU, EM, DMM) and lithospheric components (sub-continental lithospheric mantle and crust). We conducted a petrological and geochemical study of a set of volcanic rocks, sampled from the rim and interior of the Miocene Mt Bambouto caldera, one of the 12 main volcanic centres of the CVL. The rocks were analysed for their whole-rock major and trace element contents, 40Ar/39Ar ages and whole-rock Sr-Nd-Pb-Os isotopic compositions. Phonolites and quartz-trachytes of the Mt Bambouto caldera are derived by fractional crystallization of highly alkaline and moderately alkaline parental basic magmas, respectively. Assimilation of the shallow crust has affected both alkaline and subalkaline magmas, suggesting that the petrogenesis of the differentiated rocks cannot be explained by crustal contamination alone. Only minor amounts (usually less than 5%) of assimilation of upper crustal silicic rocks from the local Pan-African basement are required to produce the most differentiated compositions. The rocks with the highest crustal contribution are Q-normative trachytes from peripheral cones, as well as one Ne-trachyte. Mt Bambouto basic-ultrabasic rocks, including basanites and alkali-basalts with high 187Os/188Osi, might have experienced some crustal contamination, but it must have been a limited process. Some Mt Bambouto ultrabasic to basic rocks show large ion lithophile element enrichment, notably of Sr, Ba and P compared with Zr. These samples also have relatively radiogenic Sr and unradiogenic Pb isotopic compositions. Such compositions are similar to those of the high-Sr group identified by previous studies. Most of the basic rocks do not show such characteristics and are identified as a low-Sr group. We interpret the geochemical characteristics of the high-Sr group as resulting from the partial melting of a depleted mantle (DMM-like) peridotite source containing pyroxenite veins that had interacted with carbonatitic fluids. To test this hypothesis, we used a new modelling approach based on Monte Carlo simulation; this method has the advantage of deciphering how different mantle components interacted through time. Our modelling confirms the plausibility of a three-component source. In addition, it suggests that the carbonatitic fluid first mixed with the pyroxenititic component and the resulting melt interacted with a DMM-like mantle. Both high-Sr and low-Sr groups can be produced by such a mixing scenario but with a stronger contribution of the carbonatitic fluid for the high-Sr group. At the time of melting, these source components could have been located in a metasomatized region of the sublithospheric mantle (uppermost section of the asthenosphere) or in the sub-continental lithospheric mantle.

Linear algebra operations are widely used in scientific computing and machine learning applications. However, it is challenging for scientists and data analysts to run linear algebra at scales beyond a single machine. Traditional approaches either require access to supercomputing clusters, or impose configuration and cluster management challenges. In this paper we show how the disaggregation of storage and compute resources in so-called "serverless" environments, combined with compute-intensive workload characteristics, can be exploited to achieve elastic scalability and ease of management. We present numpywren, a system for linear algebra built on a serverless architecture. We also introduce LAmbdaPACK, a domain-specific language designed to implement highly parallel linear algebra algorithms in a serverless setting. We show that, for certain linear algebra algorithms such as matrix multiply, singular value decomposition, and Cholesky decomposition, numpywren's performance (completion time) is within 33% of ScaLAPACK, and its compute efficiency (total CPU-hours) is up to 240% better due to elasticity, while providing an easier to use interface and better fault tolerance. At the same time, we show that the inability of serverless runtimes to exploit locality across the cores in a machine fundamentally limits their network efficiency, which limits performance on other algorithms such as QR factorization. This highlights how cloud providers could better support these types of computations through small changes in their infrastructure.

Adolescence is a developmental period characterized by a greater tendency to take risks. While the adult literature has shown that sex steroids influence reward-related brain functioning and risk taking, research on the role of these hormones during puberty is limited. In this study, we examined the relation between pubertal hormones and adolescent risk taking using a probabilistic decision-making task. In this task, participants could choose on each trial to play or pass based on explicit information about the risk level and stakes involved in their decision. We administered this task to 58 11-to-13-year-old girls while functional MRI images were obtained to examine reward-related brain processes associated with their risky choices. Results showed that higher testosterone levels were associated with increased risk taking, which was mediated by increased medial orbitofrontal cortex activation. Furthermore, higher estradiol levels were associated with increased nucleus accumbens activation, which in turn related to decreased risk taking. These findings offer potential neuroendocrine mechanisms that can explain why some adolescent girls might engage in more risk taking compared to others.

The utility of the method is demonstrated by the formal synthesis of (-)-isocynometrine (XVI) via pyrrolidine (XIVa).

An aqueous electrochemically controlled host-guest encapsulation system demonstrates a large and synthetically tunable redox entropy change. Electrochemical entropy is the basis for thermally regenerative electrochemical cycles (TRECs), which utilize reversible electrochemical processes with large molar entropy changes for thermogalvanic waste-heat harvesting and electrochemical cooling, among other potential applications. A supramolecular host-guest system demonstrates a molar entropy change of 4 times that of the state-of-the-art aqueous TREC electrolyte potassium ferricyanide. Upon encapsulation of a guest, water molecules that structurally resemble amorphous ice are displaced from the host cavity, leveraging a change in the degrees of freedom and ordering of the solvent rather than the solvation of the redox-active species to increase entropy. The synthetic tunability of the host allows rational optimization of the system's Δ<i>S</i>, showing a range of -51 to -101 cal mol^-1 K^-1 (-2.2 to -4.4 mV K^-1) depending on ligand and metal vertex modifications, demonstrating the potential for rational design of high-entropy electrolytes and a new strategy to overcome theoretical limits on ion solvation reorganization entropy.