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Online Knowledge Repositories (OKRs) like Wikipedia offer communities a way\nto share and preserve information about themselves and their ways of living.\nHowever, for communities with low-resourced languages -- including most African\ncommunities -- the quality and volume of content available are often\ninadequate. One reason for this lack of adequate content could be that many\nOKRs embody Western ways of knowledge preservation and sharing, requiring many\nlow-resourced language communities to adapt to new interactions. To understand\nthe challenges faced by low-resourced language contributors on the popular OKR\nWikipedia, we conducted (1) a thematic analysis of Wikipedia forum discussions\nand (2) a contextual inquiry study with 14 novice contributors. We focused on\nthree Ethiopian languages: Afan Oromo, Amharic, and Tigrinya. Our analysis\nrevealed several recurring themes; for example, contributors struggle to find\nresources to corroborate their articles in low-resourced languages, and\nlanguage technology support, like translation systems and spellcheck, result in\nseveral errors that waste contributors' time. We hope our study will support\ndesigners in making online knowledge repositories accessible to low-resourced\nlanguage speakers.\n
The dicationic Pt complex [(tBu2bpy)Pt](NTf2)2·1/2C6H6 (tBu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, NTf2– = N(SO2CF3)2–) has been isolated and characterized. The new complex is supported by a simple bidentate bipyridine ligand and weakly coordinating, easily displaced triflimidate counterions. The Pt salt is competent for allylic C–H activation in aprotic, nonpolar media.
Summary: Stimulation of natural killer (NK) cells is regulated by a complex balance of inhibitory and stimulatory receptors expressed by NK cells. However, the interaction of stimulatory receptors and their ligands is poorly understood. One stimulatory receptor, NKG2D, is expressed by all NK cells, stimulated CD8 + T cells, γδ T cells and macrophages. Recently, progress has been made in defining cellular ligands for NKG2D. Four different families of ligands have been identified in mice and humans, all of which are distantly related to MHC class I molecules. Some of the ligands are upregulated in transformed and infected cells, provoking an attack by the innate and adaptive immune systems. It appears that these “induced‐self” ligands recognized by the NKG2D receptor may be a precedent for a new strategy of target cell recognition by the immune system. The authors wish to thank Dennis Wolan for preprints and discussions on the manuscript. AD is a Physician Postdoctoral Fellow of the Howard Hughes Medical Institute.
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Some reports of supernova (SN) discoveries turn out not to be true\ncore-collapse explosions. One such case was SN 2009ip, which was recognized to\nbe a luminous blue variable (LBV) eruption. This source had a massive hot\nprogenitor star identified in pre-explosion data, it had documented evidence of\npre-outburst variability, and it was subsequently discovered to have a 2nd\noutburst in 2010. This same source rebrightened again in 2012, and early\nspectra showed the same narrow-line profiles as before, suggesting another\nLBV-like eruption. We present new photometry and spectroscopy of SN 2009ip,\nindicating that it has transitioned into a true SN. The most striking discovery\nin these data is that unlike previous reports, the spectrum exhibited Balmer\nlines with very broad P-Cygni profiles characteristic of normal Type II\nsupernovae (SNe II), in addition to narrow emission lines seen in SNe IIn and\nLBVs. Emission components have FWHM 8000 km/s, while the P-Cygni absorption\ncomponent has blue wings extending to -13,000 km/s. These velocities are\ntypical of SNe II, but have never been associated with emission lines from a\nnonterminal LBV-like eruption. Initially, the peak absolute magnitude seemed\nfainter than that of normal SNe. However, after a brief period of fading, the\nsource quickly brightened again to M_R=-17.5 mag over a couple days. The broad\nlines mostly disappeared, and the spectrum began to resemble the early\noptically thick phases of SNe IIn. Two weeks later the source leveled off near\n-18 mag, after which broad emission lines again developed in the spectrum as\nthe source faded. We conclude that the 2012 outburst of SN 2009ip was the\nresult of a true core-collapse SN IIn that occured when the progenitor star was\nin an LBV-like outburst phase, and where the SN was initially faint and then\nrapidly brightened due to interaction with circumstellar material (abridged).\n
The primary objectives of the proposed research was the development of deterministic, physico-electrochemical models for predicting the accumulation of localized corrosion damage (pitting corrosion, stress corrosion cracking and corrosion fatigue) in the primary coolant circuits of the currently operating fleet of Light Water Reactors (LWRs) and the embedment of the models into the Grizzly code currently being developed at the Idaho National Laboratory as part of their program on nuclear power plant component aging. Localized corrosion in LWR (BWR and PWR) primary coolant circuits (PCC) is primarily an electrochemical phenomenon, augmented by mechanics and microstructure, the rate of which is determined by certain electrochemical properties, such as the electrochemical corrosion potential (ECP), solution conductivity, temperature, pH, flow rate, and the kinetics of the reduction of redox depolarizers (e.g. O<sub>2</sub>, H<sub>2</sub>O<sub>2</sub>, and H<sub>2</sub>) on the surfaces external to the crack, in addition to mechanical loading (stress intensity factor on the crack) and micro-structural/micro-chemical factors (grain size, precipitates, etc). Because the efficient control of environmentally-assisted cracking (EAC) damage accumulation requires the accurate control of these parameters, it is necessary to develop codes that can accurately predict ECP and crack growth rate (CGR) at any point in the primary coolant circuit (PCC) over wide ranges of temperature (25 <sup>o</sup>C to 320 <sup>o</sup>C), pH (6 – 8), ECP (-0.9 V<sub>she</sub> to 0.2 V<sub>she</sub>), solution conductivity, flow rate (1 – 6 m/s), and stress intensity factor (5 MPa.m<sup>1/2</sup> – 50 MPa.m<sup>1/2</sup>). Knowledge of these parameters, along with suitable damage prediction codes, would allow an operator to predict the accumulated damage in PCC as a function of the future operating history of the reactor (the “corrosion evolutionary path,” CEP). In performing this study, we have further developed our previous prediction codes in the form of BWR_MASTER and PWR_MASTER by upgrading all sub-models for calculating radiolytic species concentration, ECP, and crack growth rate (CGR) as a function of reactor operating variables (power, radiation density, temperature, location in the PCC, flow velocity, coolant pH and conductivity, and operating history). The codes have been used to predict the accumulation of IGSCC damage in Type 304 SS in the core shroud of a BWR over a fuel cycle and to estimate the damage at the same location during start-up, considering transients in reactor power, temperature, and conductivity (due to hide-out/hide-out return). The predicted damage is in good agreement with plant observation. Regarding PWRs, we have developed two new models for calculating CGR in mill-annealed, Alloy 600, by considerably upgrading the MPM (mixed potential model for estimating the ECP), the Coupled 2 Environment Fracture Model (CEFM) that were originally developed to predict ECP and CGR in sensitized stainless steels, to predict CGR in nickel-base alloys, as well as developing a micro- void pressurization model for also estimating CGR in MA Alloy 600. Both CGR models yield CGRs that are in excellent agreement with the experiment. We have also successfully developed crack initiation models for both stainless steels and mill-annealed, Alloy 600. That for stainless steels is based on a pit being the initiation site, whereas in that for mill-annealed, Alloy 600 postulates that initiation occurs at emergent grain boundaries that have been wedged open by internal oxidation. Experiments show that the crack initiation time (CIT) is highly distributed and is a seemingly, random quantity that exhibits trends with various system properties, such as surface stress, hardness, yield strength, etc. Although not identified in the SoW, we have developed a theoretical framework for describing the distributions in the CIT by assuming a normal distribution in the number of initiation sites concerning surface stress. It is well-known from experiments that CGRs are highly distributed quantities also, with almost all systems exhibiting log-normal distributions. In work outside of that proposed, we used the ANN and CEFM to confirm that a log-normal distribution in CGR is expected theoretically if the independent variables are normally distributed. This work essentially defines the accuracy that one might expect in the calculated CGR due to randomness in the independent variables. To provide fundamental, input data for the various models, we have made extensive measurement of the kinetic parameters (exchange current density and Tafel constants) for the oxygen electrode reaction (OER) and the hydrogen electrode reaction (OER) on stainless steels (Types 304 and 316) and nickel-base alloys (Alloys 600 and 690) in reactor coolant at temperatures to 300<sup> o</sup>C and as a function of pH, [O<sub>2</sub>], and [H<sub>2</sub>]. We have also optimized the Point Defect Model for passivity and passivity breakdown on measured electrochemical impedance spectroscopic (EIS) data for all alloys studied in
Abstract The conditions under which it is possible to neglect the change of the saturation of the liquid in SG crevices were obtained. It has been shown that in the entry region of the SG crevices the liquid velocity can be described by a linear function. The calculations show that the species concentrations and the potential reach quasi - asymptotic limits throughout the cavity; the limits are determined by the available superheat. After the attainment of these limits, a constant crevice corrosion rate is predicted. The condition was determined whereby the transport processes in the external environment determine the corrosion current density in the crevice. Due to the low value of conductivity and a relatively large crevice width assumed in the calculations, this condition can actually be fulfilled, if the cathodic processes in the crevice do not essentially reduce the current, which flows out of the crevice.
The photophysical properties of a series of laser−dye-labeled poly(aryl ether) dendrimers, generations 1−4, have been determined. The dendrimers act as extremely efficient light-harvesting antennae capable of transferring light energy through space from their periphery to their core. The light-harvesting ability of these molecules increases with generation due to an increase in the number of peripheral chromophores. The energy-transfer efficiency was found to be quantitative for generations 1−3, with only a slight decrease observed for the fourth generation (∼93%). Due to the high extinction coefficients and fluorescence quantum yields of the chromophores and the efficient intramolecular energy transfer of the dendritic assemblies, these macromolecules have the potential to become integral components of molecular photonic devices.
Electrochemical and mechanical experiments were conducted to analyze the environmentally influenced cracking behavior of a bulk amorphous metal, Zr41.2Ti13.8Cu12.5Ni10Be22.5. This study was motivated by a scientific interest in mechanisms of fatigue–crack propagation in an amorphous metal, and by a practical interest in the use of this amorphous metal in applications that take advantage of its unique properties, including high specific strength, large elastic strains, and low damping. The objective of the work was to determine the rate and mechanisms of subcritical crack growth in this metallic glass in an aggressive environment. Specifically, fatigue–crack propagation behavior was investigated at a range of stress intensities in air and aqueous salt solutions by examining the effects of loading cycle, stress-intensity range, solution concentration, anion identity, solution deaeration, and bulk electrochemical potential. Results indicate that crack growth in aqueous solution in this alloy is driven by a stress-assisted anodic reaction at the crack tip. Rate-determining steps for such behavior are reasoned to be an electrochemical, stress-dependent reaction at near-threshold levels, and mass transport at higher (steady-state) growth rates.
Linking molecular building units by covalent bonds to make crystalline extended structures has given rise to metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), thus bringing the precision and versatility of covalent chemistry beyond discrete molecules to extended structures. The key advance in this regard has been the development of strategies to overcome the "crystallization problem", which is usually encountered when attempting to link molecular building units into covalent solids. Currently, numerous MOFs and COFs are made as crystalline materials in which the large size of the constituent units provides for open frameworks. The molecular units thus reticulated become part of a new environment where they have (a) lower degrees of freedom because they are fixed into position within the framework; (b) well-defined spatial arrangements where their properties are influenced by the intricacies of the pores; and (c) ordered patterns onto which functional groups can be covalently attached to produce chemical complexity. The notion of covalent chemistry beyond molecules is further strengthened by the fact that covalent reactions can be carried out on such frameworks, with full retention of their crystallinity and porosity. MOFs are exemplars of how this chemistry has led to porosity with designed metrics and functionality, chemically-rich sequences of information within their frameworks, and well-defined mesoscopic constructs in which nanoMOFs enclose inorganic nanocrystals and give them new levels of spatial definition, stability, and functionality.
Significance Neural oscillations have been shown to support a range of cognitive abilities. Here we demonstrate that delta activity (2–4 Hz) in the prefrontal cortex tracked the current task context and modulated sensory processing in a top-down manner. We show that frontal delta and parietooccipital alpha (8–12 Hz) oscillations are functionally coupled and jointly guide visual perception to integrate sensory evidence with current task demands. We observed strong moment-to-moment behavioral fluctuations, which cycled at the rate of the endogenous prefrontal oscillatory brain activity. Our findings suggest that neuronal oscillations provide the functional basis for context-dependent visual perception.
Several fundamental problems and conjectures in nonlinear circuit theory posed in the sixtiés have been satisfactorily resolved only recently. Virtually every circuit-and system-theoretic technique have been tried during the intervening years with little success. The breakthrough came only after modern tools from differential topology and algebraic geometry have become available and applied in a non-trivial way. The purpose of this lecture is to sample some of these results from several recent papers [1-6], with special emphasis on the roles played by several differential-geometric concepts and tools, such as differentiable manifolds, transversality, degree theory, Hodge decomposition, etc.
