There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

/pdf/nitrogen-cycles-past-present-and-future-1zdbw0976r.pdf

Nitrogen cycles: past, present, and future

Single-particle electron cryomicroscopy (cryo-EM) is a powerful method for determining the structures of biological macromolecules. With automated microscopes, cryo-EM data can often be obtained in a few days. However, processing cryo-EM image data to reveal heterogeneity in the protein structure and to refine 3D maps to high resolution frequently becomes a severe bottleneck, requiring expert intervention, prior structural knowledge, and weeks of calculations on expensive computer clusters. Here we show that stochastic gradient descent (SGD) and branch-and-bound maximum likelihood optimization algorithms permit the major steps in cryo-EM structure determination to be performed in hours or minutes on an inexpensive desktop computer. Furthermore, SGD with Bayesian marginalization allows ab initio 3D classification, enabling automated analysis and discovery of unexpected structures without bias from a reference map. These algorithms are combined in a user-friendly computer program named cryoSPARC (http://www.cryosparc.com).

cryoSPARC: algorithms for rapid unsupervised cryo-EM structure determination

Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

A review of electrolyte materials and compositions for electrochemical supercapacitors

Earth-abundant, low-cost electrocatalysts with outstanding catalytic activity in the electrochemical hydrogen evolution reaction (HER) are critical in realizing the hydrogen economy to lift our future welfare and civilization. Here we report that excellent HER activity has been achieved with three-dimensional core/shell Co/Co3O4 nanosheets composed of a metallic cobalt core and an amorphous cobalt oxide shell. A benchmark HER current density of 10 mA cm(-2) has been achieved at an overpotential of ∼90 mV in 1 M KOH. The excellent activity is enabled with the unique metal/oxide core/shell structure, which allows high electrical conductivity in the core and high catalytic activity on the shell. This finding may open a door to the design and fabrication of earth-abundant, low-cost metal oxide electrocatalysts with satisfactory hydrogen evolution reaction activities.

Three-Dimensional Crystalline/Amorphous Co/Co3O4 Core/Shell Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution Reaction

We assessed the drought risk for world crop production under current and future cli- matic conditions by using an integrated approach to analyze the correlation between historical crop yield and meteorological drought Future drought frequencies are estimated based on ensemble results from 20 general circulation model (GCM) climate change patterns and 6 emissions scenarios from SRES (Special Report on Emissions Scenarios) using a revised Palmer Drought Severity Index The drought risk index was established by combining the effects of drought-disaster frequency, drought severity, production (yield) and extent of irrigation Results indicate that, for most regions, the probability density functions (PDF) of the 120 drought disaster frequency projections for 2100 show quasi-normal distributions and consistently project higher drought disaster frequency (DDF) than that of baseline, which indicates an overall enhanced drought risk in the future climate change Globally, the drought disaster-affected area will increase with the rising global temperature, from 154 to 4400% by 2100 The average cropland drought risk index (DRI) doubles from 5245 to 10460 in 2050 projections In 2100, the projection for the DRI increases to 12940 Among the regions, Africa is ranked as the highest, with a baseline DRI value of 9577 which increases to 20546 in 2100 projec- tions Correspondingly, the rates of yield reduction related to drought disaster for major crops will increase significantly with future climate change, by >50% in 2050 and almost 90% in 2100 for the major crops Adaptation measures to avoid aggravated drought-disaster risks are called for

/pdf/climate-change-and-drought-a-risk-assessment-of-crop-yield-123c109shl.pdf

Climate change and drought: a risk assessment of crop-yield impacts.

Crystalline/amorphous Ni/NiO core/shell nanosheets as highly active electrocatalysts for hydrogen evolution reaction

AUTO3DEM--an automated and high throughput program for image reconstruction of icosahedral particles.

Iron phosphide (FeP) has been recently demonstrated as a very attractive electrocatalyst for the hydrogen evolution reaction (HER). However, the understanding of its properties is far from satisfactory. Herein, we report the HER performance of FeP nanoparticles is enhanced after a stability test due to reduced surface-charge-transfer resistance in the HER process. The synthetic temperature and reactant ratio are important for surface-charge-transfer resistance, the electrochemically active surface area, and HER activity. Hydrogenation apparently improves the HER performance of FeP nanoparticles by reducing the surface-charge-transfer resistance, overpotential, and Tafel slope. Enhanced HER performance is observed after a stability test for both bare and hydrogenated FeP nanoparticles in the HER due to reduced surface-charge-transfer resistance. Thus, this study may enrich our knowledge and understanding to advance HER catalysis for electrochemical hydrogen generation.

Xiaodong Yan

Papers

Three-Dimensional Crystalline/Amorphous Co/Co3O4 Core/Shell Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution Reaction

Climate change and drought: a risk assessment of crop-yield impacts.

Crystalline/amorphous Ni/NiO core/shell nanosheets as highly active electrocatalysts for hydrogen evolution reaction

AUTO3DEM--an automated and high throughput program for image reconstruction of icosahedral particles.

Electrochemical Activity of Iron Phosphide Nanoparticles in Hydrogen Evolution Reaction