bluuebunny/crossref_metadata_2025 huggingface dataset:
Weak‐harmonic regularization for quantitative susceptibility mapping
Authors: Milovic Carlos , Bilgic Berkin , Zhao Bo , Langkammer Christian , Tejos Cristian , Acosta‐Cabronero Julio
Published: September 2018

Purpose

Background‐field removal is a crucial preprocessing step for quantitative susceptibility mapping (QSM). Remnants from this step often contaminate the estimated local field, which in turn leads to erroneous tissue‐susceptibility reconstructions. The present work aimed to mitigate this undesirable behavior with the development of a new approach that simultaneously decouples background contributions and local susceptibility sources on QSM inversion.

Methods

Input phase data for QSM can be seen as a composite scalar field of local effects and residual background components. We developed a new weak‐harmonic regularizer to constrain the latter and to separate the 2 components. The resulting optimization problem was solved with the alternating directions of multipliers method framework to achieve fast convergence. In addition, for convenience, a new alternating directions of multipliers method–based preconditioned nonlinear projection onto dipole fields solver was developed to enable initializations with wrapped‐phase distributions. Weak‐harmonic QSM, with and without nonlinear projection onto dipole fields preconditioning, was compared with the original (alternating directions of multipliers method–based) total variation QSM algorithm in phantom and in vivo experiments.

Results

Weak‐harmonic QSM returned improved reconstructions regardless of the method used for background‐field removal, although the proposed nonlinear projection onto dipole fields method often obtained better results. Streaking and shadowing artifacts were substantially suppressed, and residual background components were effectively removed.

Conclusion

Weak‐harmonic QSM with field preconditioning is a robust dipole inversion technique and has the potential to be extended as a single‐step formulation for initialization with uncombined multi‐echo data.
A Comparison of Recall Error in Recreational Fisheries Surveys with One- and Two-Month Reference Periods
Authors: Andrews William R. , Papacostas Katherine J. , Foster John
Published: September 2018

Many fisheries monitoring programs use self-administered surveys to collect data, which are subject to recall error. Recall error occurs when respondents inaccurately remember past events due to telescoping (remembering events more recently or further back in time than they occurred) or omission error (forgetting events altogether). Previous research on the effects of variable reference periods in fisheries surveys has been inconclusive due to difficulty in disentangling method effects from recall error and in determining whether estimates from shorter recall periods are less biased or more subject to telescoping. The National Marine Fisheries Service has developed a new household mail survey, the Fishing Effort Survey (FES), in which anglers are asked to recall cumulative fishing effort over the past 2 months, from which estimates of saltwater fishing effort are produced. Here, we examined how the length of the reference period may affect the FES in four U.S. states by comparing effort estimates to two feasible alternatives: (1) a survey administered monthly with both a 1- and 2-month reference period (wherein respondents were asked to recall fishing effort for each of the past 2 months individually); and (2) a survey administered monthly with a 1-month reference period. To further explore bias in the designs, we compared total effort, fishing prevalence, and mean trips per household estimates derived from the two experimental surveys. We found no significant differences between the FES and experimental survey estimates. However, we found evidence that multiple reference periods in a single survey may reduce bias for 1-month estimates. Increased understanding of (1) techniques that can reduce recall bias and (2) the trade-offs of shorter or longer reference periods will ultimately help fisheries survey designers more accurately weigh bias against survey costs and improve the quality of data used to inform management decisions.
Study of nanocomposites based on cellulose nanoparticles and natural rubber latex by ATR/FTIR spectroscopy: The impact of reinforcement
Authors: Agrebi Fatma , Ghorbel Nouha , Bresson Serge , Abbas Ouissam , Kallel Ali
Published: September 2018

In materials research, polymer nanocomposites have attracted great attention worldwide from both academic and industrial points of view. The material properties of polymers can be enhanced dramatically by incorporating nanoelements from renewable resources depending on their biological origin (e.g., cellulose, starch, and chitin). We have used as the reinforcing phase, in this work, cellulose nanowhiskers (CNWs) and nanofibrillated cellulose (NFC) to prepare nanocomposite films by casting/evaporation using natural rubber (NR) latex as the matrix. Our interest is focused, in this work, especially on the investigation of the chemical bonds of the NR matrix and the chemical links of nanowhiskers added to the matrix and therefore the physical and chemical interactions which could happen between the reinforcement and the matrix. Many techniques have been used to explore the interface. Among these techniques, attenuated total reflectance/Fourier transform infrared spectroscopy (ATR/FTIR), which is employed in this work. It is exhibited that some differences are observed in FTIR spectra of nanocomposite films when adding cellulose nanoparticles into NR matrix. Overall IR spectroscopy clearly demonstrated that the interfacial adhesion in the case of NR‐NFC nanocomposite is higher than that of NR‐CNW one which was explained by the presence of residual lignin at the NFC surface that play the role of “compatibilizing” agent that enhance the adhesion between the NFC and the NR. POLYM. COMPOS., 2018. © 2018 Society of Plastics Engineers
Impacts of gamma irradiation on the properties of hardwood composite based on rice straw and recycled polystyrene foam wastes
Authors: Eskander Samir B. , Tawfik Magda E.
Published: September 2018

A hardwood composite (HWC) was formulated by adding rice straw (RS), as filler, to the recycled polystyrene (WPS) foam waste, as a matrix, at 170°C and pressing under 40 kPa. The air dried RS fiber reinforced the recycled spent polymer at fiber content of 50% (mass:mass), then the combination was treated with the maleated form of the polystyrene waste (WPS‐g‐MA), as coupling agent, at a predetermine ratio. The final HWC boards were subjected to gamma irradiation, in air and at ambient temperature (≈30 ± 3°C), using radiocobalt source (60Co) at a dose rate 0.96 kGy h−1 in the range of integrated doses from 0.5 to 500 kGy. The impacts of increasing gamma absorbed doses on mechanical properties of final product were evaluated based on flexural strength, tensile strength, elongation at break, and tensile modulus measurements. Water absorption by the HWC boards was, also, elaborated under the increasing irradiation doses. To achieve a complete characterization of the prepared composite, the obtained hard samples were investigated applying the Fourier‐transform infrared (FTIR) and the scanning electron microscope (SEM) tools. Depending on the experimental data, the renewability in the properties of HWC product is its high resistance capability against γ‐irradiation up to 500 kGy and their acceptable attenuation potential, in the range of the applied doses. This provided an additional attractive advantage to the eco‐friendly quality of the acquired HWCs based on recycled thermoplastic spent polystyrene foam reinforced with air dried RS. POLYM. COMPOS., 40:2284–2291, 2019. © 2018 Society of Plastics Engineers
Interlaminar fracture toughness of hybrid carbon fiber‐carbon nanotubes‐reinforced polymer composites
Authors: Boroujeni Ayoub Yari , Al‐Haik Marwan S.
Published: September 2018

In this study, a relatively low temperature synthesis technique; graphitic structure by design (GSD), was employed to grow multi‐walled carbon nanotubes (MWCNTs) over carbon fiber fabrics. The MWCNTs forests were grown into two different morphologies, uniform and patterned. Hybrid carbon fiber‐reinforced polymer composites (CFRPs) were fabricated based on the hybrid reinforcement. Double cantilever beam tests were performed to investigate the effect of the surface grown nano‐reinforcements on the Mode I interlaminar fracture toughness (GIc) of the hybrid CFRPs. Results revealed that the surface grown MWCNTs enhanced the GIc of the CFRPs by 22 and 32%, via uniform and checkerboard‐patterned growth morphologies, respectively. Fractography was also employed to reveal the MWCNTs’ role in interlaminar crack stoppage and deflection resulting in improving GIc of the hybrid CFRPs. POLYM. COMPOS., 40:E1470–E1478, 2019. © 2018 Society of Plastics Engineers
Synthesis and characterisation of fluorescent pyrene‐end‐capped polylactide fibres
Authors: Alwattar Aula , Haddad Athir , Zhou Quan , Nascimento Tatiana , Greenhalgh Ryan , Medeiros Eliton , Blaker Jonny , Parry Adam , Quayle Peter , Yeates Stephen
Published: September 2018

Fluorescent markers are critical for tracking the position and movement of molecules both in vivo and in vitro. Conventionally, synthetic dyes are non‐covalently added to polymers for fluorescent tracking, but often diffuse away. Here we demonstrate, for the first time, a facile method for the synthesis of fluorescent poly(lactic acid) nano‐/microfibres for biomedical applications using solution spin blowing. Pyrene‐end‐capped poly(l‐lactide) (PLLA) derivatives were synthesised using the ring‐opening polymerisation of l‐lactide and they were characterised using spectroscopic and thermal analyses. Submicrometre‐sized fluorescent fibres were produced from these PLLA derivatives using solution blow spinning techniques generating polymer blends and core–shell fibres. Such system could be further exploited to incorporate electrically conductive carbon allotropes via the pyrene aromaticity, producing fluorescent and electrically active fibres for in vitro monitoring and electrical stimulation. © 2018 Society of Chemical Industry
Human Rights by Design: The Responsibilities of Social Media Platforms to Address Gender‐Based Violence Online
Authors: Suzor Nicolas , Dragiewicz Molly , Harris Bridget , Gillett Rosalie , Burgess Jean , Van Geelen Tess
Published: September 2018

Gender‐based violence online is rampant, ranging from harassment of women who are public figures on social media to stalking intimate partners using purpose‐built apps. This is not an issue that can be addressed by individual states alone, nor can it be addressed satisfactorily through legal means. The normalization of misogyny and abuse online both reflects and reinforces systemic inequalities. Addressing gender‐based violence online will require the intervention of the technology companies that govern the commercial Internet to prevent and combat abuse across networks and services. We argue that international human rights instruments provide an opportunity to identify with more precision the responsibilities of telecommunications companies and digital media platforms to mitigate harm perpetrated through their networks, and ensure that the systems they create do not reproduce gendered inequality. Finally, we present initial recommendations for platforms to promote human rights and fulfill their responsibilities under the United Nations Guiding Principles on Business and Human Rights.
Laser welding of polymers using unsymmetrical squaraine dyes
Authors: Bak Helle Østergren , Nielsen Bjarne Enrico , Jeppesen Anne , Brock‐Nannestad Theis , Nielsen Christian Benedikt Orea , Pittelkow Michael
Published: September 2018

Transmission laser welding of plastic is typically achieved by incorporating a laser absorbing dye into one of the two pieces of plastic one wishes to weld together and mediating the welding process using a laser emitting light at a suitable wavelength. Desirable properties of laser absorbing dyes include: (1) the dye is colorless in the visible region but absorbs strongly in the region at the wavelength where the laser emits, (2) the dye has a good conversion of the energy from the laser to heat, (3) the dye is stable enough to be incorporated into the molten plastic, (4) the dye is soluble in the plastic of choice to give an even distribution in the plastic, and (5) the dye is nontoxic. Here, we explore an alternative approach to achieve laser welding of colorless plastics using a laser dye that is colored, but that can be bleached after the welding process. Nonsymmetrical squaraine dyes were prepared by condensation of squaric acid and two equivalents of various 3,5‐dimethoxy‐N,N‐dialkylanilines. After the incorporation into polyethylene and laser welding, the plastic was bleached either by heat treatment or by irradiation with a high pressure Xe‐lamp giving colorless polyethylene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2245–2254
Electrochemically mediated atom transfer radical polymerization with dithiocarbamates as alkyl pseudohalides
Authors: Wang Yi , Fantin Marco , Matyjaszewski Krzysztof
Published: September 2018

Electrochemically mediated atom transfer radical polymerizations (ATRPs) provide well‐defined polymers with designed dispersity as well as under external temporal and spatial control. In this study, 1‐cyano‐1‐methylethyl diethyldithiocarbamate, typically used as chain‐transfer agent (CTA) in reversible addition–fragmentation chain transfer (RAFT) polymerization, was electrochemically activated by the ATRP catalyst CuI/2,2′‐bipyridine (bpy) to control the polymerization of methyl methacrylate. Mechanistic study showed that this polymerization was mainly controlled by the ATRP equilibrium. The effect of applied potential, catalyst counterion, catalyst concentration, and targeted degree of polymerization were investigated. The chain‐end functionality was preserved as demonstrated by chain extension of poly(methyl methacrylate) with n‐butyl methacrylate and styrene. This electrochemical ATRP procedure confirms that RAFT CTAs can be activated by an electrochemical stimulus. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 376–381
Oxidative stress‐induced structural changes in the microtubule‐associated flavoenzyme Irc15p from Saccharomyces cerevisiae
Authors: Koch Karin , Strandback Emilia , Jha Shalinee , Richter Gesa , Bourgeois Benjamin , Madl Tobias , Macheroux Peter
Published: September 2018

The genome of the yeast Saccharomyces cerevisiae encodes a canonical lipoamide dehydrogenase (Lpd1p) as part of the pyruvate dehydrogenase complex and a highly similar protein termed Irc15p (increased recombination centers 15). In contrast to Lpd1p, Irc15p lacks a pair of redox active cysteine residues required for the reduction of lipoamide and thus it is very unlikely that Irc15p performs a similar dithiol‐disulfide exchange reaction as reported for lipoamide dehydrogenases. We expressed IRC15 in Escherichia coli and purified the produced protein to conduct a detailed biochemical characterization. Here, we show that Irc15p is a dimeric protein with one FAD per protomer. Photoreduction of the protein generates the fully reduced hydroquinone without the occurrence of a flavin semiquinone radical. Similarly, reduction with NADH or NADPH yields the flavin hydroquinone without the occurrence of intermediates as observed for lipoamide dehydrogenase. The redox potential of Irc15p was −313 ± 1 mV and is thus similar to lipoamide dehydrogenase. Reduced Irc15p is oxidized by several artificial electron acceptors such as potassium ferricyanide, 2,6‐dichlorophenol‐indophenol, 3‐(4,5‐dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide, and menadione. However, disulfides such as cystine, glutathione, and lipoamide were unable to react with reduced Irc15p. Limited proteolysis and SAXS‐measurements revealed that the NADH‐dependent formation of hydrogen peroxide caused a substantial structural change in the dimeric protein. Therefore, we hypothesize that Irc15p undergoes a conformational change in the presence of elevated levels of hydrogen peroxide, which is a putative biomarker of oxidative stress. This conformational change may in turn modulate the interaction of Irc15p with other key players involved in regulating microtubule dynamics.
Isotonic concentrations of excipients control the dimerization rate of a therapeutic immunoglobulin G1 antibody during refrigerated storage based on their rank order of native‐state interaction
Authors: Banks Douglas D. , Cordia Jon F. , Spasojevic Vladimir , Sun Jeonghoon , Franc Sarah , Cho Younhee
Published: September 2018

Inert co‐solutes, or excipients, are often included in protein biologic formulations to adjust the tonicity of liquid dosage forms intended for subcutaneous delivery. Despite the low concentration of their use, many of these excipients alter protein–protein interactions such as dimerization and aggregation rates of high concentration monoclonal antibody (mAb) therapeutics to varying extents during long‐term refrigerated clinical storage, challenging the formulation scientist to make informed excipient selections at the earliest stages of development when protein supply and time are often limited. The objectives of this study were to better understand how isotonic concentrations of excipients influence the dimerization rates of a model mAb stored at refrigerated and room temperatures and explore protein sparing biophysical methods capable of predicting this dependence. Despite their prevalence of use in the biopharmaceutical industry, methods for assessing conformational stability such differential scanning calorimetry and isothermal equilibrium unfolding showed little predictive power and we highlight some of the assumptions and technical challenges of their use with mAbs. Conversely, measures of colloidal stability of the native‐state such as preferential interaction coefficients measured by vapor pressure osmometry and solubility assessed by polyethylene–glycol induced precipitation correlated reasonably well with the mAb dimerization data and are most consistent with the excipients tested minimizing dimerization by interacting favorably with the residues comprising the protein–protein association interface.
Selective ensemble mean technique for severe European windstorms
Authors: Scher Sebastian , Messori Gabriele
Published: September 2018

We show that ensemble forecasts of extreme European windstorms can be improved up to a lead time of 36–48 hr by sub‐selecting ensemble members based on their performance at very short lead times (up to 12 hr). This applies to both the ensemble mean position of the cyclone centre and the ensemble windstorm footprint over the continent. A number of ensemble forecasts, including those from the ECMWF Ensemble Prediction System, are initialised every 12 hr and disseminated several hours after initialisation; therefore our approach has the potential to provide improved forecasts in an operational context. The analysis is performed on GEFS reforecast data.
Photodissociation of phenol in the adiabatic representation: Tunneling, motions of phenyl ring, and kinetic isotope effects
Authors: He Ying , Zhao Huali , Wang Wenji
Published: September 2018

The photodissociation of phenol is a prototype of the photoinduced hydrogen detachment reaction. The dissociation rates of phenol through the excited S1 state are calculated with the quantum instanton method in full dimensionality. The Arrhenius plot of the rates shows that the quantum tunneling dominates the OH bond dissociation at low temperatures. The degrees of freedom of phenyl ring (C6H5) play extremely important roles in the dissociation of phenol. Fixing the phenyl ring at the equilibrium geometry can only provide reliable rates between 400 K and 800 K. The motions of phenyl ring have an impact on enhancing the dissociation by lowering the free energy barrier. The larger the amplitudes of the phenyl ring motions are, the more the free energy barrier will be reduced. The dissociation rates of C6H5OH are much larger than those of C6H5OD, which is due to the zero‐point energy and entropy effects.
Momentum space calculations of the binding energies of argon dimer
Authors: Sahraeian Taghi , Hadizadeh M. R.
Published: September 2018

The binding energies of argon dimer are calculated by solving the homogeneous Lippmann‐Schwinger integral equation in momentum space. Our numerical analysis using two models of argon‐argon interaction developed by Patkowski et al. not only confirms the eight argon dimer vibrational levels of the ground state of argon dimer (ie, for j = 0) predicted by other groups but also provides a very precise means for determining the binding energy of the ninth state which its value is a matter of discussion. Our calculations have been also extended to states with higher rotational quantum number j and we have calculated the energy of all 174 bound states for both potential models. Our numerical results for vibrational levels of the ground state of argon dimer are in excellent agreement with other theoretical calculations and available experimental data.
Engaging students in computational modeling: The role of an external audience in shaping conceptual learning, model quality, and classroom discourse
Authors: Pierson Ashlyn E. , Clark Douglas B.
Published: September 2018

Research suggests that designing for an external audience may support conceptual understanding by offering students increased opportunities to reframe perspectival thinking in ways that support domain‐specific reasoning. While this argument is theoretically compelling, to our knowledge, it has not been empirically tested in terms of comparing the conceptual growth of students designing computational models for an external audience to the conceptual growth of students designing computational models for a classroom audience of their teacher and peers. In a constructionist agent‐based computational modeling environment, we compare the conceptual understanding, artifact quality, and discourse of 6th grade students designing models of tides primarily for an external audience of younger students (i.e., designing for 5th graders) to the conceptual understanding of 6th grade students designing models for a classroom audience. We found that students who designed for an external audience of younger children displayed greater conceptual growth about the mechanisms that cause tidal bulges as evidenced by students’ pre–post assessments, models, and user guides/reports. Our analysis of classroom discourse suggests that designing for an audience of younger children may have facilitated domain‐specific reasoning in whole‐class discussions by creating opportunities for shifts between students’ own perspectives and the perspectives of their anticipated audience.
Internal Morphological Effects of Growth Hormone Transgenesis in Coho Salmon
Authors: Gaffney L. P. , Watson B. M. , Oakes J. D. , Devlin R. H.
Published: September 2018

Effects of growth hormone (GH) overexpression on internal morphology were examined in homozygous and hemizygous GH transgenic Coho Salmon Oncorhynchus kisutch aided by clearing and staining and magnetic resonance imaging methodologies. Morphological effects of transgenesis were observed in pin bones in fast‐growing hemizygous transgenic salmon, in vertebral column and swim bladder deformities in homozygotes, and as nonproportional modifications to some cranial structures examined among groups. These data provide further examples of the complex pleiotropic effects arising from GH overexpression in transgenic salmon.
Interrogating Depictions of Disability in Children's Picturebooks
Authors: Kleekamp Monica C. , Zapata Angie
Published: September 2018

Diverse classroom libraries offer opportunities for students to not only see themselves represented in books but also encounter lived experiences and perspectives that are different from their own. As classrooms increasingly include learners with cognitively and physically diverse abilities, teachers are faced with the challenge of selecting literature with humanizing depictions of individuals with disability labels. Historically, portrayals of disabilities in children's literature have included themes of pity and exclusion. In this article, the authors introduce a framework that educators can employ when selecting inclusive literature for their classroom libraries. Using this framework, the authors analyzed three sample picture books that teachers might also share with students to help them read with and against these texts. As a whole, this article offers a starting point for teachers beginning the process of creating inclusive spaces that foster the multitude of ways that students come to be, know, and learn.
Emerging evolutionary paradigms in antibiotic discovery
Authors: Chevrette Marc G , Currie Cameron R
Published: September 2018

Antibiotics revolutionized medicine and remain its cornerstone. Despite their global importance and the continuous threat of resistant pathogens, few antibiotics have been discovered in recent years. Natural products, especially the secondary metabolites of Actinobacteria, have been the traditional discovery source of antibiotics. In nature, the chemistry of antibiotic natural products is shaped by the unique evolution and ecology of their producing organisms, yet these influences remain largely unknown. Here, we highlight the ecology of antibiotics employed by microbes in defensive symbioses and review the evolutionary processes underlying the chemical diversity and activity of microbe-derived antibiotics, including the dynamics of vertical and lateral transmission of biosynthetic pathways and the evolution of efficacy, targeting specificity, and toxicity. We argue that a deeper understanding of the ecology and evolution of microbial interactions and the metabolites that mediate them will allow for an alternative, rational approach to discover new antibiotics.
Self-similar gelling solutions for the coagulation equation with diagonal kernel
Authors: Bonacini Marco , Niethammer Barbara , Velázquez Juan J.L.
Published: September 2018

We consider Smoluchowski's coagulation equation in the case of the diagonal kernel with homogeneity

\gamma > 1

. In this case the phenomenon of gelation occurs and solutions lose mass at some finite time. The problem of the existence of self-similar solutions involves a free parameter
b
, and one expects that a physically relevant solution (i.e. nonnegative and with sufficiently fast decay at infinity) exists for a single value of
b
, depending on the homogeneity
γ
. We prove this picture rigorously for large values of
γ
. In the general case, we discuss in detail the behavior of solutions to the self-similar equation as the parameter
b
changes.
Variability of Spatter Morphology in Pyroclastic Deposits in Southern Idaho, as Correlated to Thermal Conditions and Eruptive Environment
Authors: Rader E. , Kobs Nawotniak S. , Heldmann J.
Published: September 2018

To investigate the thermal conditions of spatter eruptions on Earth, other planets, and moons we measured and categorized the physical characteristics of clasts in spatter deposits in Southern Idaho, USA. Physical characteristics of clasts, such as aspect ratio and degree of welding, are influenced by the style of eruption, distance from the vent, and lava properties. The correlation between morphological characteristics and the degree of fusion constrains thermal conditions of unwitnessed spatter‐producing eruptions on Earth and extraterrestrial volcanoes. We categorize spatter deposits into three groups, as defined by their emplacement conditions: primary vent, distal (spatter exposed in noneruptive cracks on the flanks of primary vents), and hornito (secondary spatter from a nonprimary cone); and show the variability of clast morphology within the three categories. Primary vent deposits typically show a wide range of fused perimeters between clasts (18–82%), lower aspect ratios (0.20–0.49), and larger void space, both between clasts (4–21%) and within clasts (referred to as hollow cores, up to 93%). Hornitos typically have less fusion (14–22%) between clasts, higher aspect ratios (0.45–0.49), and lower proportions of void space (6–10%). Distal outcrops are easily distinguished by the lack of void space (<8%) and the very high aspect ratio of clasts (close to 1). When chemical composition and outcrop proximity are accounted for, the accumulation rate appears to be primarily responsible for spatter clast morphology. Our results are based on field measurements of clasts; however, digital imagery could be used to categorize and interpret pyroclastic deposits in planetary systems by robotic spacecraft.
A Modeling Toolbox for Permafrost Landscapes
Authors: Overeem Irina , Jafarov Elchin , Wang Kang , Schaefer Kevin , Stewart Scott , Clow Gary , Piper Mark , Elshorbany Yasin
Published: September 2018

A new resource makes it easier for researchers to explore predictions of how melting permafrost might affect carbon release, wetlands, and river deltas as they evolve and other interacting effects.
UCAR to Keep Managing National Center for Atmospheric Research
Authors: Showstack Randy
Published: September 2018

The head of the University Corporation for Atmospheric Research says he is excited about “taking our science to the next level.”
Deciphering the Role of Water Column Redoxclines on Methylmercury Cycling Using Speciation Modeling and Observations From the Baltic Sea
Authors: Soerensen A. L. , Schartup A. T. , Skrobonja A. , Bouchet S. , Amouroux D. , Liem‐Nguyen V. , Björn E.
Published: September 2018

Oxygen‐depleted areas are spreading in coastal and offshore waters worldwide, but the implication for production and bioaccumulation of neurotoxic methylmercury (MeHg) is uncertain. We combined observations from six cruises in the Baltic Sea with speciation modeling and incubation experiments to gain insights into mercury (Hg) dynamics in oxygen depleted systems. We then developed a conceptual model describing the main drivers of Hg speciation, fluxes, and transformations in water columns with steep redox gradients. MeHg concentrations were 2–6 and 30–55 times higher in hypoxic and anoxic than in normoxic water, respectively, while only 1–3 and 1–2 times higher for total Hg (THg). We systematically detected divalent inorganic Hg (HgII) methylation in anoxic water but rarely in other waters. In anoxic water, high concentrations of dissolved sulfide cause formation of dissolved species of HgII: HgS2H−(aq) and Hg (SH)20(aq). This prolongs the lifetime and increases the reservoir of HgII readily available for methylation, driving the high MeHg concentrations in anoxic zones. In the hypoxic zone and at the hypoxic‐anoxic interface, Hg concentrations, partitioning, and speciation are all highly dynamic due to processes linked to the iron and sulfur cycles. This causes a large variability in bioavailability of Hg, and thereby MeHg concentrations, in these zones. We find that zooplankton in the summertime are exposed to 2–6 times higher MeHg concentrations in hypoxic than in normoxic water. The current spread of hypoxic zones in coastal systems worldwide could thus cause an increase in the MeHg exposure of food webs.
Miocene to Holocene Marine Tephrostratigraphy Offshore Northern Central America and Southern Mexico: Pulsed Activity of Known Volcanic Complexes
Authors: Schindlbeck J. C. , Kutterolf S. , Freundt A. , Eisele S. , Wang K.‐L. , Frische M.
Published: September 2018

We studied the tephra inventory of 14 deep sea drill sites of three Deep Sea Drilling Project and Ocean Drilling Program legs drilled offshore Guatemala and El Salvador (Legs 67, 84, and 138) and one leg offshore Mexico (Leg 66). Marine tephra layers reach back from the Miocene to the Holocene. We identified 223 primary ash beds and correlated these between the drill sites, with regions along the volcanic arcs, and to specific eruptions known from land. In total, 24 correlations were established between marine tephra layers and to well‐known Quaternary eruptions from El Salvador and Guatemala. Additional 25 tephra layers were correlated between marine sites. Another 108 single ash layers have been assigned to source areas on land resulting in a total of 157 single eruptive events. Tephra layer correlations to independently dated terrestrial deposits provide new time markers and help to improve or confirm age models of the respective drill sites. Applying the respective sedimentation rates derived from the age models, we calculated ages for all marine ash beds. Hence, we also obtained new age estimates for eight known but so far undated large terrestrial eruptions. Furthermore, this enables us to study the temporal evolution of explosive eruptions along the arc, and we discovered five pulses of increased activity: (1) a pulse during the Quaternary, (2) a Pliocene pulse between 6 and 3 Ma, (3) a Late Miocene pulse between 10 and 7 Ma, (4) a Middle Miocene pulse between 17 and 11 Ma, and (5) an Early Miocene pulse (ca. >21 Ma).
Tropical Precipitation and Cross‐Equatorial Heat Transport in Response to Localized Heating: Basin and Hemisphere Dependence
Authors: White R. H. , McFarlane A. A. , Frierson D. M. W. , Kang S. M. , Shin Y. , Friedman M.
Published: September 2018

A heat source is applied to different surface locations in a fully coupled climate model to study the cross‐equatorial energy transport and tropical precipitation responses. Remarkably different tropical precipitation responses are seen, varying from a large shift toward, to a small shift away from, the heated hemisphere. These differences are dominated by changes in top‐of‐atmosphere radiation, with some contribution from changes in ocean cross‐equatorial heat flux. The atmospheric fraction of the total cross‐equatorial heat flux is consistently larger for Northern Hemisphere (NH) heating relative to Southern Hemisphere heating. This results in a larger tropical rainfall shift in response to NH heating. Positive shortwave radiative feedbacks, associated with a burn‐off of low clouds in the North Pacific, also amplify the tropical rainfall response to NH heating. The Pacific Ocean dominates the ocean response to Southern Hemisphere heating, while the Atlantic Ocean dominates the ocean response to NH heating.
Greenland Submarine Melt Water Observed in the Labrador and Irminger Sea
Authors: Rhein Monika , Steinfeldt Reiner , Huhn Oliver , Sültenfuß Jürgen , Breckenfelder Tilia
Published: September 2018

Helium and Neon distributions from 1994 to 2015 are used to identify and quantify submarine melt water (SMW) from the Greenland Ice Sheet in the Labrador and Irminger Sea. SMW fractions >0.2% (maximum 0.62 ± 0.075%) are confined in the upper 400 m of the Greenland shelf and slope and account for 12 ± 6% of the total east Greenland freshwater flux. SMW is embedded in water of different mixtures of cold and fresh Polar Water and warm and saline Atlantic Water. The resulting salinity range from that mixture exceeds the effect of SMW addition by one order of magnitude. Up to now, SMW is not detectable in the formation region of the Labrador Sea Water. Episodically, He and Ne excess anomalies are found in the deep ocean, probably introduced by the East Greenland Current spill jets.
Dispersion Aerosol Indirect Effect in Turbulent Clouds: Laboratory Measurements of Effective Radius
Authors: Chandrakar K. K. , Cantrell W. , Kostinski A. B. , Shaw R. A.
Published: September 2018

Cloud optical properties are determined not only by the number density nd and mean radius
of cloud droplets but also by the shape of the droplet size distribution. The change in cloud optical depth with changing nd, due to the change in distribution shape, is known as the dispersion effect. Droplet relative dispersion is defined as
. For the first time, a commonly used effective radius parameterization is tested in a controlled laboratory environment by creating a turbulent cloud. Stochastic condensation growth suggests d independent of nd for a nonprecipitating cloud, hence nearly zero albedo susceptibility due to the dispersion effect. However, for size‐dependent removal, such as in a laboratory cloud or highly clean atmospheric conditions, stochastic condensation produces a weak dispersion effect. The albedo susceptibility due to turbulence broadening has the same sign as the Twomey effect and augments it by order 10%.
Continued Emissions of the Ozone‐Depleting Substance Carbon Tetrachloride From Eastern Asia
Authors: Lunt M. F. , Park S. , Li S. , Henne S. , Manning A. J. , Ganesan A. L. , Simpson I. J. , Blake D. R. , Liang Q. , O'Doherty S. , Harth C. M. , Mühle J. , Salameh P. K. , Weiss R. F. , Krummel P. B. , Fraser P. J. , Prinn R. G. , Reimann S. , Rigby M.
Published: September 2018

Carbon tetrachloride (CCl4) is an ozone‐depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl4 emissions from the eastern part of China did not decline between 2009 and 2016. This finding is in contrast to a recent bottom‐up estimate, which predicted a significant decrease in emissions after the introduction of production controls. We find eastern Asian emissions of CCl4 to be 16 (9–24) Gg/year on average between 2009 and 2016, with the primary source regions being in eastern China. The spatial distribution of emissions that we derive suggests that the source distribution of CCl4 in China changed during the 8‐year study period, indicating a new source or sources of emissions from China's Shandong province after 2012.
Ion Cyclotron Waves Rippling Ballooning/InterChange Instability Heads
Authors: Panov E. V. , Pritchett P. L.
Published: September 2018

A dawnward drifting Ballooning/InterChange Instability (BICI) head is identified and studied using high‐resolution Time History of Events and Macroscale Interactions during Substorms observations at XGSM≈−11RE on 15 February 2008 between 10:18 UT and 10:30 UT and compared with particle‐in‐cell simulation run results for a charged current sheet. A prediction of the earlier particle‐in‐cell simulation for a neutral sheet, that duskward drifting BICI heads are subject to a current‐driven ion cyclotron instability, is found to be true also for dawnward drifting BICI heads in the charged sheet simulations. This specific prediction and the Time History of Events and Macroscale Interactions during Substorms data indicate the presence of electromagnetic ion cyclotron wave activity that ripples the background BICI head shape. The waves propagated azimuthally with δEy/δBz≈4.5VA. The waves are found in a region of the strongest differential drift between the electrons and ions, suggesting that the drift generated the waves.
Roles of Flow Braking, Plasmaspheric Virtual Resonances, and Ionospheric Currents in Producing Ground Pi2 Pulsations
Authors: Takahashi Kazue , Hartinger Michael D. , Vellante Massimo , Heilig Balázs , Lysak Robert L. , Lee Dong‐Hun , Smith Charles W.
Published: September 2018

In one model, Pi2 pulsations are driven pulse by pulse by fast mode pulses that are launched as periodic bursty bulk flows brake when they approach the Earth. We have examined this model by analyzing data from multiple spacecraft and ground magnetometers for a Pi2 pulsation event. During the event, which started at ∼2226 UT on 8 November 2014, Time History of Events and Macroscale Interactions during Substorms (THEMIS)‐D detected an ∼2‐min‐period plasma bulk flow oscillation in the near‐Earth magnetotail, while THEMIS‐E and Van Allen Probes‐B, both located on the nightside just earthward of the electron plasmapause, detected a Pi2 pulsation consisting of a 10‐mHz oscillation in the azimuthal component of the electric field and a 19‐mHz oscillation in the compressional component of the magnetic field. On the ground, magnetic field oscillations containing both frequencies were observed both on the nightside and on the dayside. The nightside observations indicated that the pulsation had a radially standing structure, which is consistent with plasmaspheric virtual resonances (PVRs) excited in a magnetohydrodynamic simulation assuming an impulsive energy source. Cross‐spectral analysis of the magnetotail flow oscillation and the Pi2 pulsation indicated low coherence between them. These results suggest that the flow oscillation contributed to the Pi2 pulsation as a broadband energy source and that only the spectral components matching the PVR frequencies were detected with well‐defined frequencies. Ionospheric currents connected to the PVRs may be responsible for the appearance of the pulsation on the dayside.
The Breakdown of the Fluid Approximation for Electrons in a Plasma Wake
Authors: Wang Joseph , Hu Yuan
Published: September 2018

A comparative study using a fluid‐based analytic solution, hybrid particle‐ion fluid‐electron particle‐in‐cell (PIC), and fully kinetic PIC is carried out to examine a collisionless, mesothermal plasma flow over a large, unbiased plate. We find that the plasma wake may be characterized into two regions based on the electron characteristics: a fluid electron expansion region and a kinetic electron expansion region. In the fluid electron expansion region, the electrons may be considered to be an equilibrium fluid and all the three approaches lead to a similar result. In the kinetic electron expansion region, the local electron velocity distributions are strongly non‐Maxwellian and the commonly used fluid approximation for electrons breaks down. The results also show that the error of the hybrid PIC simulation strongly correlates with a nonequilibrium parameter based on the weighted deviation of the electron velocity distribution from the equilibrium.
Dual‐Isotope Constraints on Seasonally Resolved Source Fingerprinting of Black Carbon Aerosols in Sites of the Four Emission Hot Spot Regions of China
Authors: Fang Wenzheng , Du Ke , Andersson August , Xing Zhenyu , Cho Chaeyoon , Kim Sang‐Woo , Deng Junjun , Gustafsson Örjan
Published: September 2018

Despite much recent efforts, the emission sources of black carbon (BC) aerosols―central input to understanding and predicting environmental and climate impact―remain highly uncertain. Here we present observational δ13C/Δ14C‐based constraints on the sources of BC aerosols over the four seasons in each of the four key hot spot emission regions of China: Beijing‐Tianjin‐Hebei (BTH‐Wuqing; where Wuqing is the sampling location), Yangtze River Delta (YRD‐Haining), Pearl River Delta (PRD‐Zhongshan), and Sichuan Basin (SC‐Deyang). Overall, BC loadings were highest in winter, yet elevated loadings were also observed in other seasons, for example, spring at SC‐Deyang and fall at PRD‐Zhongshan. Annually, the dominant BC sources were coal (50 ± 20%) for BTH‐Wuqing, liquid fossil for YRD‐Haining (46 ± 8%) and PRD‐Zhongshan (48 ± 18%), whereas liquid fossil (42 ± 17%) and biomass burning (41 ± 14%) equally affected SC‐Deyang. There is also different but distinct seasonalities in BC sources for the different sites. As an example, for BTH‐Wuqing coal burning increased from summer to winter, while summer and spring BTH‐Wuqing were more influenced by liquid fossil. In contrast, for YRD‐Haining, the relative importance of emission sources was more constant over the year. These quantitative observational constraints on source‐seasonality of BC aerosols in receptor sites located in China's four key economic zones highlight that regulatory control on BC aerosol emissions from different fuels should consider both seasonal and regional variations. Our results also suggest that models on estimates of BC‐induced climate and air quality should consider variations over both regional and seasonal scales.
Isolating and Reconstructing Key Components of North Atlantic Ocean Variability From a Sclerochronological Spatial Network
Authors: Reynolds D. J. , Hall I. R. , Slater S. M. , Mette M. J. , Wanamaker A. D. , Scourse J. D. , Garry F. K. , Halloran P. R.
Published: September 2018

Our understanding of North Atlantic Ocean variability within the coupled climate system is limited by the brevity of instrumental records and a deficiency of absolutely dated marine proxies. Here we demonstrate that a spatial network of marine stable oxygen isotope series derived from molluscan sclerochronologies (δ18Oshell) can provide skillful annually resolved reconstructions of key components of North Atlantic Ocean variability with absolute dating precision. Analyses of the common δ18Oshell variability, using principal component analysis, highlight strong connections with tropical North Atlantic and subpolar gyre (SPG) sea surface temperatures and sea surface salinity in the North Atlantic Current (NAC) region. These analyses suggest that low‐frequency variability is dominated by the tropical Atlantic signal while decadal variability is dominated by variability in the SPG and salinity transport in the NAC. Split calibration and verification statistics indicate that the composite series produced using the principal component analysis can provide skillful quantitative reconstructions of tropical North Atlantic and SPG sea surface temperatures and NAC sea surface salinities over the industrial period (1864–2000). The application of these techniques with extended individual δ18Oshell series provides powerful baseline records of past North Atlantic variability into the unobserved preindustrial period. Such records are essential for developing our understanding of natural climate variability in the North Atlantic Ocean and the role it plays in the wider climate system, especially on multidecadal to centennial time scales, potentially enabling reduction of uncertainties in future climate predictions.
Direction Finding for Radio Transmitters With Mini Interferometric Network
Authors: Qu X. , Xu X. , Wang S. , Li J. , Zhu W. , Fang G.
Published: September 2018

In this paper, we present the design and deployment of a broadband interferometric mini array. The network with five electromagnetic signal detectors deployed over an area about 1 km2 is applied here to record 20‐ to 70‐kHz vertical electric fields emitted by radio transmitters in very low frequency/low‐frequency band. Furthermore, interferometric imaging algorithm is employed to evaluate the elevation angles and azimuth angles of the electromagnetic radiation source. It is found that the deviation between expected azimuth and the mean value of calculated azimuth is less than 0.2° with standard deviation of 3.55°. The experiment results indicate that the mini array may provide benefits in determining the precise locations of electromagnetic radiation sources.
Copper-catalyzed propargylic [3+3] cycloaddition with 1H-pyrazol-5(4H)-ones: enantioselective access to optically active dihydropyrano[2,3-c]pyrazoles
Authors: Li Ling , Liu Zhen-Ting , Hu Xiang-Ping
Published: September 2018

A copper-catalyzed propargylic [3+3] cycloaddition with 1H-pyrazol-5(4H)-ones as C,O-bisnucleophiles through the desilylation-activated strategy has been developed. With the support of a chiral tridentate P,N,N-ligand, the reaction gave rise to a variety of optically active dihydropyrano[2,3-c]pyrazoles cyclohexadienone derivatives with up to 96% ee.
Photo-induced free radical production in a tetraphenylethylene ligand-based metal–organic framework
Authors: Xu Kui , Yu Bing , Li Yuanyuan , Su Huifang , Wang Bingnan , Sun Kai , Liu Yuanyuan , Peng Qiuchen , Hou Hongwei , Li Kai
Published: September 2018

Photo-induced free radical production was observed in an AIE ligand-based MOF, which exhibited a reversible, fast, obvious, and controllable photo-induced color/emission transformation.
Metabolic profiling of silver nanoparticle toxicity in Microcystis aeruginosa
Authors: Zhang Ji Lai , Zhou Zhi Peng , Pei Ying , Xiang Qian Qian , Chang Xue Xiu , Ling Jian , Shea Damian , Chen Li Qiang
Published: September 2018

The manifestation of differential metabolic profiles combined with the perturbation of physiological indicators in M. aeruginosa upon silver nanoparticle exposure is taken as evidence of damage to photosynthesis and membranes.