Publications

Abstract Ab initio computations in the DFT framework for mixtures of different transition metal oxides capable of acting as electrode material for lithium batteries are presented.

Abstract Dryland carbon fluxes, particularly those driven by ecosystem respiration, are highly sensitive to water availability and rain pulses. However, the magnitude of rain-induced carbon emissions remains unclear globally. Here we quantify the impact of rain-pulse events on the carbon balance of global drylands and characterize their spatiotemporal controls. Using eddy-covariance observations of carbon, water and energy fluxes from 34 dryland sites worldwide, we produce an inventory of over 1,800 manually identified rain-induced CO 2 pulse events. Based on this inventory, a machine learning algorithm is developed to automatically detect rain-induced CO 2 pulse events. Our findings show that existing partitioning methods underestimate ecosystem respiration and photosynthesis by up to 30% during rain-pulse events, which annually contribute 16.9 ± 2.8% of ecosystem respiration and 9.6 ± 2.2% of net ecosystem productivity. We show that the carbon loss intensity correlates most strongly with annual productivity, aridity and soil pH. Finally, we identify a universal decay rate of rain-induced CO 2 pulses and use it to bias-correct respiration estimates. Our research highlights the importance of rain-induced carbon emissions for the carbon balance of global drylands and suggests that ecosystem models may largely underrepresent the influence of rain pulses on the carbon cycle of drylands.

Short-range ordering in was investigated with NMR and first principles structure computations. NMR indicates that the tendency for to replace in the layers decreases with decreasing nickel content. Li in the Ni/Mn layers preferentially occupies sites near and avoids the ions, leading to nonrandom configurations. Calculations indicate that the ground state of contains zigzag rows of and ions. Although a disordering temperature of approximately 1000 K is calculated, ordered fragments persist above the phase transition and these materials contain significant short-range order, even when quenched from high temperature. © 2004 The Electrochemical Society. All rights reserved.

The Earth’s surface is shaped by the interaction of tectonics, water, sediment, solutes, and biota over a wide range of spatial and temporal scales and across diverse environments. Development of a predictive science of Earth-surface dynamics would integrate many disciplines and approaches, including hydrology, geomorphology, atmospheric science, biology, sedimentary and structural geology, and ecology. This paper discusses challenges, opportunities, and a few example problems that can serve as pathways towards this integration.

Policies for climate mitigation on land rarely acknowledge biophysical factors, such as reflectivity, evaporation, and surface roughness. Yet such factors can alter temperatures much more than carbon sequestration does, and often in a conflicting way. We outline a framework for examining biophysical factors in mitigation policies and provide some best-practice recommendations based on that framework. Tropical projects—avoided deforestation, forest restoration, and afforestation—provide the greatest climate value, because carbon storage and biophysics align to cool the Earth. In contrast, the climate benefits of carbon storage are often counteracted in boreal and other snow-covered regions, where darker trees trap more heat than snow does. Managers can increase the climate benefit of some forest projects by using more reflective and deciduous species and through urban forestry projects that reduce energy use. Ignoring biophysical interactions could result in millions of dollars being invested in some mitigation projects that provide little climate benefit or, worse, are counter-productive.

The hole story? A super-supertetrahedral anionic cluster of 214 atoms and 80 tetrahedral units is prepared. The crystal structure has finite tetrahedral units of [Cd16In64S134]44− ions composed of four T4 supertetrahedra (see picture). Each cluster is nearly a regular tetrahedron with edge lengths of 31.06 and 31.07 Å, and has large octahedral cavity (yellow sphere).

The stoichiometry and ubiquitous observation of p-type conductivity of synthetic pyrite FeS[subscript 2] thin films are investigated via first-principles computations of native (vacancies, interstitials, antisites) and extrinsic (O[subscript S], O[subscript i]) point defects. Native defects have high formation energies and are predicted to occur in low concentrations within the Fe- and S-rich limits, showing that pyrite should be intrinsically stoichiometric. Under sufficiently oxidizing conditions, O[subscript S] becomes the most dominant defect type and induces p-type conductivity. At the experimental oxygen impurity concentration, the hole concentration is predicted to be O(10[superscript 19]) cm[superscript −3], in agreement with Hall measurements reported in the literature. Therefore, we attribute the unintentional p-type conductivity of pyrite to oxygen impurities and propose that improvements in device performance may be achieved under more reducing conditions.

Abstract Controlled modifications of amino acids are an indispensable tool for advancing fundamental and translational research based on peptides and proteins. Yet, we still lack methods to chemically modify each naturally occurring amino acid sidechain. To help address this gap, we show that N , α ‐diaryl oxaziridines expand the scope of bioconjugation methods to chemically modify cysteine, methionine, and tryptophan residues with evidence for additional tyrosine labelling in a proteomic context. Conjugation primarily at tryptophan sites can be accessed by selective cleavage of modifications at other sidechains. The N , α ‐diaryl oxaziridine reagents are accessed through photoisomerization of nitrones, which serve as photocaged reagents, thus providing an additional level of control over reactivity. Initial guiding principles for the design of nitrone reagents are developed by exploring the impact of structure on UV/Vis absorption, photoisomerization, and reactivity. We identify a nitrone structure that maximizes photoisomerization efficiency, the aqueous stability of the oxaziridine, the extent of amino acid modification, and the stability of the resulting amino acid conjugates. We then translate nitrone reagents to modify proteins in aqueous conditions. Finally, we use nitrones to profile reactive residues across the proteome of a mammalian cell line and find that they expand the proteome coverage.

Enzymatic ligation of discrete nanoparticle-DNA conjugates creates nanoparticle dimer and trimer structures in which the nanoparticles are linked by single-stranded DNA, rather than by double-stranded DNA as in previous experiments. Ligation was verified by agarose gel and small-angle X-ray scattering. This capability was utilized in two ways: first, to create a new class of multiparticle building blocks for nanoscale self-assembly and, second, to develop a system that can amplify a population of discrete nanoparticle assemblies.

The measurement of pH of aqueous systems at high temperature is becoming increasingly important because of the need to monitor the chemistry of nuclear power plant cooling water systems and the cycle chemistry of fossil‐fueled power reactors. We have previously shown that the yttria‐stabilized zirconia pH sensor can be used for accurate pH measurements of aqueous systems up to 320°C. This paper describes the viability of pH measurement of aqueous systems up to and above the critical temperature of water.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Using CoOx thin films supported on Au(111) single crystal surfaces as model catalysts for the CO oxidation reaction we show that three reaction regimes exist in response to chemical and topographic restructuring of the CoOx catalyst as a function of reactant gas phase CO/O2 stoichiometry a finding that highlights the versatility of catalysts and their evolution in response to reaction conditions. Under oxygen-lean conditions and moderate temperatures (below 150C degrees) partially oxidized films containing CoO were found to be efficient catalysts. In contrast, stoichiometric CoO films containing only Co2+ form carbonates in the presence of CO that poison the reaction below 300 C degrees. Under oxygen-rich conditions a more oxidized catalyst phase forms containing Co3+ species that is effective in a wide temperature range. Resonant photoemission spectroscopy (ResPES) revealed the unique role of Co3+ sites in catalyzing the CO oxidation. DFT calculations provided deeper insights into the pathway and free energy barriers for the reactions on these oxide phases.

Summary form only given.Optical single sideband modulation has received great interest as a way to reduce the dispersion penalty of analog fiber-optic systems. We propose and demonstrate a tandem single sideband fiber-optic link, which uses a dual-electrode Mach-Zehnder modulator to place different information in each of the two sidebands, thus doubling the bandwidth efficiency.