bluuebunny/crossref_metadata_2025 huggingface dataset:
In‐Situ Synthesis of Tetraphenylporphyrin/Tungsten (VI) Oxide/Reduced Graphene Oxide (TPP/WO3/RGO) Nanocomposite for Visible Light Photocatalytic Degradation of Acid Blue 25
Authors: Malefane Mope E. , Ntsendwana Bulelwa , Mafa Potlako J. , Mabuba Nonhlangabezo , Feleni Usisipho , Kuvarega Alex T.
Published: August 2019

Environmental pollution is regarded as a major concern and photocatalysis has been used successfully to combat discharges of recalcitrant pollutants. In this study, meso tetraphenylporphyrin (TPP), tungsten (VI) oxide and reduced graphene oxide nanocomposite materials were prepared by in situ method and calcined at different temperatures. The catalysts impact was evaluated for the degradation of acid blue 25 (AB25) under visible light irradiation. The as‐prepared composite materials were characterised for morphological and crystalline structural properties using SEM, Raman, FTIR, TGA, BET and XRD techniques. UV‐Vis and PL absorption studies obtained a band gap energy of 2.14 eV which showed its ability to absorb light in the visible region. The nanocomposite exhibited spherically shaped particles of monoclinic WO3 when using 20 mg TPP and calcination temperature of 350 °C for 4 hours. The highest degradation efficiency of 85% on 20 ppm AB25 as per UV/Vis and TOC results, was obtained for the photocatalyst calcined at 350 °C for 4 hours. The high degradation efficiency can be ascribed to the visible light absorbing nature of the composite and high separation rate of photogenerated charge carriers. This nanocomposite can be a suitable candidate for treatment of other dyestuff in textile effluents.
New Electrochemical Approach for the Synthesis of Pd‐PdO/C Electrocatalyst and Application to Formic Acid Electrooxidation
Authors: Kuriganova Alexandra B. , Faddeev Nikita A. , Leontyev Igor N. , Allix Mathieu , Rakhmatullin Aydar , Smirnova Nina V.
Published: August 2019

Pd‐PdO/C catalyst for formic acid electrooxidation has been synthesized via electrochemical dispersion of Pd foil electrodes under pulse alternating current conditions in NaCl aqueous electrolyte. About 35 wt% of the as‐prepared Pd‐PdO/C specimen is PdO as revealed by X‐ray diffraction. The microstructural characteristics and catalytic activity of the synthesized Pd/C catalyst have been compared with those of a Pt/C catalyst prepared under the same conditions. Pd nanoparticles of Pd‐PdO/C catalyst exhibit smaller average dimensions and narrower particle size distribution – 7.4±0.5 nm and 1.9±0.5 respectively for Pd and PdO particles. The process of ethanol electrooxidation on the catalyst was characterized by high overvoltage (up to 800 mV). The overvoltage of the formic acid electrochemical oxidation on Pd/C is 590 mV less than on Pt/C.
Annelated Aminoimidazoles in Synthesis of Imidazo[4,5‐b]pyridines
Authors: Shvydenko Tetiana , Nazarenko Kostiantyn , Shvydenko Kostiantyn , Rusanov Eduard , Tolmachev Andrei , Kostyuk Aleksandr
Published: August 2019

A convenient method for the synthesis of annelated imidazo[4,5‐b]pyridines was developed. The method is based on condensation of previously unavailable aminoimidazoles with 1,3‐dicarbonyl compounds. Aminoimidazoles 3 were prepared and some their properties were studied. The method gives the target imidazopyridines in good yields and allow varying substituents. A set of imidazopyridines was prepared. As an example, the imidazopyridines featuring carboxylic acids and esters were synthesized. Their structure was unambiguously determined by multinuclear NMR spectroscopy and the molecular structure of imidazopyridine 15 a was determined by single‐crystal X‐Ray diffraction.
Synthesis of Magnetically Separable Nanocatalyst CoFe2O4@SiO2@MIL‐53(Fe) for Highly Efficient and Selective Oxidation of Alcohols and Benzylic Compounds with Hydrogen Peroxide
Authors: Tan Jin , Liu Xiao Bing , Chen Wei Feng , Hu Yu Lin
Published: August 2019

A new methodology for the highly efficient and atom‐economic oxidation of alcohols and benzylic compounds to the corresponding aldehydes and ketones with environmental‐friendly hydrogen peroxide using a magnetic MOF nanocatalyst has been developed. We demonstrated that the resulting magnetic nanocomposite CoFe2O4@SiO2@MIL‐53(Fe) can show excellent catalytic performances in the highly selective oxidation at room temperature, based on a synergetic effect between iron sites and CoFe2O4@SiO2. The nanocatalyst offers simple operation for recovery and the recycling test showed that it could be reused for successive runs without significant degradation in catalytic activity.
1,4‐Conjugate Addition of Aryl boronic Acids on Cyclohexenone as Catalyzed by Rhodium(I) Complexes of C2‐Symmetric Bioxazoline Fused N‐heterocyclic Carbenes
Authors: Ramasamy Balasubramaniyam , Prakasham A. P. , Gangwar Manoj Kumar , Ghosh Prasenjit
Published: August 2019

Rhodium(I) complexes (1‐3) of chiral C2‐symmetric tricyclic bioxazoline fused imidazole derived N‐heterocyclic carbene ligands were efficient precatalysts for the 1,4‐conjugate addition of aryl boronic acids to cyclohexenone yielding 3‐aryl cyclohexanones in moderate to excellent yields but without any chirality transfer. Quite significantly, the intermediates of the proposed catalytic cycle namely, a rhodium hydroxo species (A), a phenyl bound rhodium species (B) and a 3‐phenyl cyclohexenolate bound rhodium species (D) have been detected by mass spectrometry. Lastly, the rhodium(I) precatalysts of the type, {(3R,7R)‐3,7‐di‐R‐2,3,7,8‐tetrahydrodioxazolo[3,2‐c:3′,2′‐e]imidazol‐5‐ylidene}Rh(COD)Cl, [R=s‐butyl (1), i‐butyl (2), i‐propyl (3), COD=1, 5‐cyclooctadiene] were prepared by the direct metalation of tricyclic oxazoline fused imidazole derived N‐heterocyclic carbene precursors namely, (3R,7R)‐3,7‐di‐R‐2,3,7,8‐tetrahydrodioxazolo[3,2‐c:3′,2′‐e]imidazol‐4‐ium trifluoromethanesulfonate, [R=s‐butyl, i‐butyl, i‐propyl] with {(COD)RhCl}2 in presence of t‐BuOK at room temperature.
An automation framework design for secure software development
Authors: Mythily M. , Valarmathi M.L. , Anand Deva Durai C. , Rexie J.A.M.
Published: August 2019

Business process modeling (BPM) is procedural‐oriented advanced activity for representing process models with domain knowledge. It consists of all the functional requirements given by the users to build the software. However, nonfunctional requirements such as cost, time, performance, and security are used to evaluate the performance of a system. Among these requirements, security is the vital attribute to be taken care at the early stage of any software development. For example, even governing bodies are heavily dependents on the data system due to security exposures. So automation on model transformation from non‐secured metamodel to secured metamodels improves the overall execution of the software evolution process. In this paper, the authors propose an Auto Secure Business Process (AutoSBP) system to automate security to the existing software models. The activity model of existing system is dismantled into attributes and actions to extract its business need. Based on the interpretation from business data, security implications are applied to the existing software models. To fine tune the security implications, ID3 decision learning algorithm is applied. The effect of the system‐generated model assures the quality by its complexity metrics.
Structural Optimization of the Production Process in Steel Plants Based on Flexsim Simulation
Authors: Wu Shuangping , Xu Anjun , Song Wei , Li Xiuping
Published: August 2019

The method of structural optimization of the steel manufacturing process is described, and the development logic of layer‐by‐layer progression from the analysis‐optimization of the set of procedures’ functions, the analysis‐optimization of the set of procedures’ relations, to the reconstruction‐optimization of the set of processes’ procedures is explained. Four different simulation models from Kambara Reactor (KR) to continuous casting (CC) are established using Flexsim simulation software. The theory of structural optimization and simulation models complements each other, which promotes the understanding of structural optimization methods and the application of simulation models. The logistics operation of the simulation model under different production conditions is investigated, especially considering the influence of time factors. Finally, the effectiveness of the structural optimization method and the simulation model is verified by comparing the simulation results with the actual production of a steel plant.
Embedding built heritage values in architectural design education
Authors: Clarke Nicholas , Kuipers Marieke , Stroux Sara
Published: August 2019

Continuity and change have become crucial themes for the built environment and heritage buildings; also in the education and practice of architects. Embedding built heritage values into studio-based design education is a daunting new challenge that demands new didactic perspectives and tools. To address the dilemmas that come with design assignments for adaptive reuse, an experiment with new didactic analytical tools has been conducted in the Heritage & Architecture (H&A) architectural design studios at the Delft University of Technology. The analysis attempts to connect matter—physical structures—and meaning in a structured graphical process through predefined mapping exercises. Our aim is to introduce a step-by-step method for exploration that can form the foundation of values-based design from built heritage. Central to our multifaceted approach is a specially developed matrix that is meant to support design-oriented analysis of heritage buildings. This paper situates the H&A perspective on the adaptive reuse of valorised buildings within the heritage discourse and architectural design education in general and further gives insight into the didactics, the tools, their uses and initial results. After a critical reflection on our points of departure, based in an evaluation of results, peer discussion and student evaluation, we conclude that the applied methodology is instructive to the educational goals but also merits further development. One of the lessons learnt for future teaching includes allowing students freedom to discover values themselves. An important conclusion is that an earlier and broader foundation that engages the continuation of tangible and intangible heritage values in the ever-changing built environment is required in architectural educational practice.
Measuring Diversity in Multilingual Communication
Authors: Gazzola Michele , Templin Torsten , McEntee-Atalianis Lisa J.
Published: August 2019

This article develops new indices to measure linguistic diversity. It is new in two respects: firstly, existing indices to measure the probability that in a given multilingual context communication among people speaking different languages can successfully occur are based on the assumption that communication is possible only if at least one single language is shared. This study develops new indices that describe the probability that people with different linguistic repertoires can effectively communicate not only through one common language, but also by relying on their receptive competence in multiple languages, or a mix between the two communication strategies. Secondly, it develops indices to measure the degree of diversity of language policies aimed at providing multilingual communication (through translation and interpretation). The focus, therefore, is on the organisation as collective actors rather than individuals. The indices may be relevant to the study of the political and economic implications of linguistic diversity in multilingual countries, and in the management of diversity in multilingual organisations.
Vascular risk factors are associated with longitudinal changes in cerebrospinal fluid tau markers and cognition in preclinical Alzheimer's disease
Authors: Bos Isabelle , Vos Stephanie J.B. , Schindler Suzanne E. , Hassenstab Jason , Xiong Chengjie , Grant Elizabeth , Verhey Frans , Morris John C. , Visser Pieter Jelle , Fagan Anne M.
Published: August 2019

Introduction

Vascular factors increase the risk of Alzheimer's disease (AD). We investigated the associations between such factors, longitudinal AD cerebrospinal fluid biomarkers, and cognition.

Methods

433 cognitively normal participants were classified into four biomarker groups using their baseline amyloid (A+/−) and tau status (T+/−). 184 participants had undergone serial cerebrospinal fluid collection. Frequencies of risk factors and the Framingham Risk Score (FRS) were compared, and we tested the influence of risk factors on change in biomarker concentrations and cognition.

Results

The absence of obesity, presence of hypertension, and a high FRS were associated with an increase in tau levels, particularly in A+T+ individuals. Risk factors were not associated with amyloid. Depression was associated with higher cognitive scores, whereas high FRS was associated with lower scores and a faster decline.

Discussion

Our results demonstrate that vascular risk factors may enhance neurodegeneration but not amyloid accumulation in preclinical AD.
Scientific Knowledge and the Deep Past
Authors: Currie Adrian
Published: August 2019

Historical sciences like paleontology and archaeology have uncovered unimagined, remarkable and mysterious worlds in the deep past. How should we understand the success of these sciences? What is the relationship between knowledge and history? In Scientific Knowledge and the Deep Past: History Matters, Adrian Currie examines recent paleontological work on the great changes that occurred during the Cretaceous period - the emergence of flowering plants, the splitting of the mega-continent Gondwana, and the eventual fall of the dinosaurs - to analyse the knowledge of historical scientists, and to reflect upon the nature of history. He argues that distinctively historical processes are 'peculiar': they have the capacity to generate their own highly specific dynamics and rules. This peculiarity, Currie argues, also explains the historian's interest in narratives and stories: the contingency, complexity and peculiarity of the past demands a narrative treatment. Overall, Currie argues that history matters for knowledge.
Traumatic Spinal Cord Injuries with Fractures in a Québec Level I Trauma Center
Authors: Wagnac Eric , Mac-Thiong Jean-Marc , Arnoux Pierre-Jean , Desrosiers Jean-Michel , Ménard Anne-Laure , Petit Yvan
Published: August 2019

Background:

Traumatic spinal cord injuries (TSCI) have devastating consequences on patients’ quality of life. More specifically, TSCI with spinal fractures (TSCIF) have the most severe neurological impairment, although limited data are available. This study aimed at providing data and analyzing TSCIF in a level I trauma center in the province of Québec, Canada.

Methods:

Two hundred eighty-two TSCIF were reviewed. Spinal injuries and neurological impairment were assessed with AO classification and AIS, respectively. Variables included age, sex, cause, location, mechanism of injury (MOI), and severity of TSCIF. Chi-squared Pearson determined significant associations (p < 0.05).

Results:

Male-to-female ratio was 3.21:1. Patients were 42.5 ± 18.7 years. The leading causes of TSCIF were high-energy falls (28.4%), cars (26.2%) and vehicle without restraint system (motorcycle, all-terrain vehicle, snowmobile, and bicycle) (21.3%). Vehicle collisions, pooling cars and unrestrained vehicles, mostly affected the 20–49-year population (62.2%). The main MOI was distraction in males (47.9%), and axial compression in females (44.8%). There were significant associations between causes and injured spinal level, as well as between MOI and injured spinal level, sex, and TSCIF severity. Most patients involved in unrestrained vehicle accidents sustained a thoracolumbar spine distraction with complete motor deficit. A severe neurologic deficit affected most patients following car accidents that caused cervical spine distraction or axial torsion.

Conclusions:

In Québec, most TSCIF caused by vehicle collisions affect a young population and have severe neurological impairments. Future efforts should focus on better understanding accidents involving the unrestrained vehicle category to further improve preventive measures.
Small-scale kinematics of two-phase flows: identifying relaxation processes in separated- and disperse-phase flow models
Authors: Drui Florence , Larat Adam , Kokh Samuel , Massot Marc
Published: August 2019

We propose here to investigate the impact of small-scale effects on the bulk evolution of a two-phase flow system. More precisely, we choose to examine the sole influence of a small-scale (with respect to the bulk velocity) off-equilibrium velocity on the system. In order to narrow our analysis and avoid complex well-posedness issues, we choose to examine a simple barotropic 5-equation two-phase flow model that accounts for an equilibrium common bulk velocity and a small-scale off-equilibrium velocity. A full derivation of the model is presented: it is based on a variational principle which allows us to insert the two-scale kinematics into the model by considering two different kinetic energies. Additional entropy dissipation requirements allow us to add dissipative structures to the model. This system is neutral with respect to the topology of the flow structure and is equipped with parameters that can be connected to relaxation processes. When considering instantaneous relaxations, we obtain two limit systems of the literature that are used for the simulation of separated-phase flows. In this sense we obtain a hierarchy of models. We show that the parent 5-equation model is also compatible with the description of a bubbly fluid that allows small-scale vibrations for the disperse phase. This identification is verified and discussed through comparisons with experimental measurements of sound dispersion (Silberman, J. Acoust. Soc. Am., vol. 29, 1957, pp. 925–933; Leroyet al., J. Acoust. Soc. Am., vol. 123, 2008, pp. 1931–1940) and with the dispersion relations of a reference model for bubbly flows by Chenget al.(Trans. ASME J. Heat Transfer, vol. 107, 1985, pp. 402–408). The present work is a first contribution to a larger effort that aims at unifying models that can describe both separated and disperse two-phase flows, coupling small-scale modelling with large-scale resolution.
The minimum flow rate of electrosprays in the cone-jet mode
Authors: Gamero-Castaño Manuel , Magnani M.
Published: August 2019

Stable electrospraying in the cone-jet mode is restricted to flow rates above a minimum, and understanding the physics of this constraint is important to improve this atomization technique. We study this problem by measuring the minimum flow rate of electrosprays of tributyl phosphate and propylene carbonate at varying electrical conductivity $K$ (all other physical properties such as the density $\unicode[STIX]{x1D70C}$, surface tension $\unicode[STIX]{x1D6FE}$ and viscosity $\unicode[STIX]{x1D707}$ are kept constant and equal to those of the pure liquids), and through the analysis of numerical solutions. The experiments show that the dimensionless minimum flow rate is a function of both the dielectric constant $\unicode[STIX]{x1D700}$ of the liquid and its Reynolds number, $Re=(\unicode[STIX]{x1D70C}\unicode[STIX]{x1D700}_{o}\unicode[STIX]{x1D6FE}^{2}/\unicode[STIX]{x1D707}^{3}K)^{1/3}$. This result is unexpected in the light of existing theories which, for the conditions investigated, predict a minimum flow rate that depends only on $\unicode[STIX]{x1D700}$ and/or is marginally affected by $Re$. The experimental dependency on the Reynolds number requires the viscous stress to be a factor in the determination of the minimum flow rate. However, the numerical solutions suggest that a balance of opposing forces including the fixing viscous stress, which at decreasing flow rates may lower the acceleration of the flow to the point of making it unstable, is unlikely to be the cause. An alternative mechanism is the significant viscous dissipation taking place in the transition from cone to jet, and which at low flow rates cannot be supplied by the work done by the tangential electric stress in the same area. Instead, mechanical energy injected into the system farther downstream must be transferred upstream where dissipation predominantly takes place. This mechanism is supported by the balance between the energy dissipated and the work done by the electric stress in the transition from cone to jet, which yields a relationship between the minimum flow rate, the Reynolds number and the dielectric constant that compares well with experiments.
Flight-crash events in superfluid turbulence
Authors: Švančara P. , La Mantia M.
Published: August 2019

We show experimentally that the mechanisms of energy transport in turbulent flows of superfluid $^{4}\text{He}$ are strikingly different from those occurring in turbulent flows of viscous fluids. We argue that the result can be related to the role played by quantized vortices in this unique type of turbulence. The flow-induced motions of relatively small particles suspended in the liquid reveal that, for scales of the order of the mean distance between the vortices, the particles do not tend on average to decelerate faster than they accelerate, whereas, at larger scales, a classical-like asymmetry is recovered. It follows that, in the range of investigated parameters, flight-crash events are less apparent than in classical turbulence. We specifically link the outcome to the time symmetry of quantized vortex reconnections observed at scales comparable to the typical particle size.
A millennium of Icelandic archaeological fish data examined against marine climate records
Authors: Hambrecht George , Feeley Frank , Smiarowski Konrad , Hicks Megan , Harrison Ramona , Brewington Seth , Cesario Grace , Gibbons Kevin
Published: August 2019

This article combines new marine fish faunal data from medieval and early modern Icelandic archaeological sites with previously published data that focused primarily on the Settlement and Commonwealth periods. This synthesis places these new data into the larger scale of Icelandic history and marine conditions (sea-surface temperature and sea ice) to identify patterns and trends across the last 1000 years of the relationship between humans and Icelandic cod populations. We find no direct correlation between zooarchaeological patterns and sea ice or storminess in the medieval period and a possible correlation in the early modern period. We argue that this suggests a nuanced relationship between changing climates and fishing patterns in Icelandic history. While changes in sea temperature and periods of increased storminess might have made fishing productivity more variable and at times more dangerous, it is only in the early modern period that we see change in the marine zooarchaeological record that might indicate a correlation. Instead, we contend that the impacts of the changing climate relative to marine resources were mediated by social, political, economic, and even technological variables.
St Edith of Polesworth and her Cult
Authors: TRINGHAM NIGEL
Published: August 2019

Venerated at Polesworth (Warws.) in the late Anglo-Saxon period, the identity of St Edith remains uncertain, with medieval chroniclers suggesting various candidates, but she is likely to have been a seventh-century Mercian princess, perhaps also connected with a church near Louth (Lincs.). Buried at Polesworth, where miracles were still being recorded in the thirteenth century, and perhaps with relics in the collegiate church at nearby Tamworth, her cult was very localised, with only a few outliers elsewhere in the Midlands, probably linked to the Marmion family, lords of Tamworth castle and the founders in the mid twelfth-century of a female religious house at Polesworth.
Power, Patronage, and the Candidate-nomination Process: Observations from Bangladesh
Authors: KHAN ADEEBA AZIZ
Published: August 2019

In this article, by studying the candidate-nomination process of the two major political parties, I show how power is distributed within the political party in Bangladesh. I show that the general acceptance by scholars that political power lies in the hands of the innermost circle of the political-party leadership in Bangladesh is too simplistic. A more nuanced observation of power and influence within the party structure shows that, in the context of Bangladesh's clientelistic political system, which is based on reciprocity between patrons and clients and relies on the ability of middlemen to organize and mobilize (in order to disrupt through hartals and strikes), power is often in the hands of those mid-level leaders who are in charge of mobilizing because their demands cannot be ignored by the topmost leadership. Through studying the candidate-nomination process of the major political parties and using the Narayanganj mayoral election of 2011 as a case study, I answer questions such as whose interests political parties are representing, what channels of influence are being used, and why these channels exist.
Using linguistically defined specific details to detect deception across domains
Authors: Vogler Nikolai , Pearl Lisa
Published: August 2019

Current automatic deception detection approaches tend to rely on cues that are based either on specific lexical items or on linguistically abstract features that are not necessarily motivated by the psychology of deception. Notably, while approaches relying on such features can do well when the content domain is similar for training and testing, they suffer when content changes occur. We investigate new linguistically defined features that aim to capture specific details, a psychologically motivated aspect of truthful versus deceptive language that may be diagnostic across content domains. To ascertain the potential utility of these features, we evaluate them on data sets representing a broad sample of deceptive language, including hotel reviews, opinions about emotionally charged topics, and answers to job interview questions. We additionally evaluate these features as part of a deception detection classifier. We find that these linguistically defined specific detail features are most useful for cross-domain deception detection when the training data differ significantly in content from the test data, and particularly benefit classification accuracy on deceptive documents. We discuss implications of our results for general-purpose approaches to deception detection.
Game-Framing to Improve Applicant Perceptions of Cognitive Assessments
Authors: Collmus Andrew B. , Landers Richard N.
Published: August 2019

Abstract. General cognitive ability is one of the best predictors of job performance, but applicant reactions are often poor. In two samples, we experimentally tested game-framing, the labeling of an ability test as a “game” without changing its content, as a way to improve applicant reactions. Results were analyzed through the lens of applicant reactions theory. Game-framing was associated with decreases in perceived length, perceived length was positively related to test motivation, and in one sample perceived length mediated the relationship between game-framing and test motivation. The direction of the relationship between motivation and perceived length was observed in both samples and opposite that proposed by reactions theory.
A Person-Centered Representation of Basic Need Satisfaction Balance at Work
Authors: Gillet Nicolas , Morin Alexandre J. S. , Choisay Frédéric , Fouquereau Evelyne
Published: August 2019

Abstract. This study examines how a global overarching need satisfaction construct, together with three specific dimensions (autonomy, competence, and relatedness needs satisfaction) combine within different profiles of workers among two independent samples ( n = 1,419 and n = 677). In addition, this research investigates the role of job demands and resources in the prediction of profile membership, and documents the relation between these profiles and maladaptive outcomes (anxiety and physical fatigue). The results revealed four distinct profiles. Job resources (e.g., participation, organizational support, and work scheduling autonomy) predicted an increased likelihood of membership in the normative profile in both samples. The globally dissatisfied yet moderately autonomous profile was also associated with the highest anxiety levels relative to all other profiles.
Fit and Congruency
Authors: Hogue Mary , Fox-Cardamone Lee , Knapp Deborah Erdos
Published: August 2019

Abstract. Applicant job pursuit intentions impact the composition of an organization’s applicant pool, thereby influencing selection outcomes. An example is the self-selection of women and men into gender-congruent jobs. Such self-selection contributes to a lack of gender diversity across a variety of occupations. We use person-job fit and the role congruity perspective of social role theory to explore job pursuit intentions. We present research from two cross-sectional survey studies (520 students, 174 working adults) indicating that at different points in their careers women and men choose to pursue gender-congruent jobs. For students, the choice was mediated by value placed on the job’s associated gender-congruent outcomes, but for working adults it was not. We offer suggestions for practitioners and researchers.
Changes in Geothermal Activity at Bárdarbunga, Iceland, Following the 2014–2015 Caldera Collapse, Investigated Using Geothermal System Modeling
Authors: Reynolds Hannah I. , Gudmundsson Magnús T. , Högnadóttir Thórdís , Axelsson Gudni
Published: August 2019

The gradual collapse of the subglacial Bárdarbunga caldera in 2014–2015 provided an opportunity to explore the geothermal signals produced by large‐scale volcanic events. In August 2014, four ice cauldrons (shallow depressions on the ice surface) formed on the caldera flank. These cauldrons reached their maximum volume rapidly and then shrank, indicating that they were created during minor subglacial eruptions. Several weeks after the start of the collapse, three cauldrons on the caldera rim grew in volume, with four smaller cauldrons forming in 2015–2017. The cauldrons reached volumes in the range of 1.0 ± 0.2 to 27 ± 3 million m3. HYDROTHERM numerical simulations of fluid flow and heat transport in the uppermost 1 km of the crust were performed to explore possible causes for these thermal signals and in particular assess the role of shallow magmatic intrusions. The heat transfer required to create the more rapidly formed caldera‐rim cauldrons can be reproduced with shallow intrusions into high‐permeability pathways, which greatly enhance the surface thermal signal. The preintrusion temperature of the surrounding bedrock has a major effect on heat transfer to the surface, with cold bedrock causing a buffering effect, whereas temperature conditions close to the boiling point of water produce far more efficient heat transfer due to the formation of steam plumes. Not all observed behavior is reproduced by our models, suggesting that geothermal reservoirs below 1‐km depth may play a significant role in the observed thermal anomalies.
Seasonal Evolution of the Surface Layer Heat Balance in the Eastern Subtropical Indian Ocean
Authors: Cyriac A. , McPhaden M. J. , Phillips H. E. , Bindoff N. L. , Feng M.
Published: August 2019

The South Indian Ocean (SIO) is a region of strong air‐sea heat loss due to the unique ocean circulation pattern influenced by the Indonesian Throughflow. In this study, the seasonal variation of the surface layer heat budget in the eastern SIO is investigated using 2 years of measurements from a mooring at 25°S, 100°E, the only colocated upper ocean and surface meteorology time series in the subtropical Indian Ocean. The mooring data are combined with other in situ and satellite data to examine the role of air‐sea fluxes and ocean heat transport on the evolution of mixed layer temperature using heat budget diagnostic models. Results show that on seasonal time scales, mixed layer heat storage in the eastern SIO is mostly balanced by a combination of surface fluxes and turbulent entrainment with a contribution from horizontal advection at times. Solar radiation dominates the seasonal cycle of net surface heat flux, which warms the mixed layer during austral summer (67 W/m2) and cools it during austral winter (−44 W/m2). Entrainment is in good agreement with the heat budget residual for most of the year. Horizontal advection is spatially variable and appears to be dominated by the presence of mesoscale eddies and possibly annual and semiannual Rossby waves propagating from the eastern boundary. Results from the 2‐year mooring‐based data analysis are in reasonably good agreement with a 12‐year regional heat budget analysis around the mooring location using ocean reanalysis products.
Internal Tides Drive Nutrient Fluxes Into the Deep Chlorophyll Maximum Over Mid‐ocean Ridges
Authors: Tuerena Robyn E. , Williams Richard G. , Mahaffey Claire , Vic Clément , Green J. A. Mattias , Naveira‐Garabato Alberto , Forryan Alexander , Sharples Jonathan
Published: August 2019

Diapycnal mixing of nutrients from the thermocline to the surface sunlit ocean is thought to be relatively weak in the world's subtropical gyres as energy inputs from winds are generally low. The interaction of internal tides with rough topography enhances diapycnal mixing, yet the role of tidally induced diapycnal mixing in sustaining nutrient supply to the surface subtropical ocean remains relatively unexplored. During a field campaign in the North Atlantic subtropical gyre, we tested whether tidal interactions with topography enhance diapycnal nitrate fluxes in the upper ocean. We measured an order of magnitude increase in diapycnal nitrate fluxes to the deep chlorophyll maximum (DCM) over the Mid‐Atlantic Ridge compared to the adjacent deep ocean. Internal tides drive this enhancement, with diapycnal nitrate supply to the DCM increasing by a factor of 8 between neap and spring tides. Using a global tidal dissipation database, we find that this spring‐neap enhancement in diapycnal nitrate fluxes is widespread over ridges and seamounts. Mid‐ocean ridges therefore play an important role in sustaining the nutrient supply to the DCM, and these findings may have important implications in a warming global ocean.
Nitrogen Fixation Changes Regulated by Upper Water Structure in the South China Sea During the Last Two Glacial Cycles
Authors: Li Chen , Jian Zhimin , Jia Guodong , Dang Haowen , Wang Jianxin
Published: August 2019

Marine nitrogen fixation contributes to the budget of biologically available N and thus fuels phytoplankton productivity and carbon cycle through biological pump. Modern N fixation rates are proved to be constrained by oceanographic condition and nutrient supply to the surface waters. However, the paleoceanographic reconstruction of N fixation and its regulation mechanism remain highly uncertain in many regions. Here we present records of N fixation changes in the South China Sea over the past 250,000 years reconstructed by compound‐specific nitrogen isotopes of individual amino acids. The δ15N of source amino acids (δ15NSrc), reflecting the δ15N of the substrate nitrate originating from the subsurface water, is distinctly lower during interglacial periods, indicating intensified N fixation during interglacials. The δ15NSrc of the South China Sea covaries with the thermal gradient between surface and subsurface waters, implying a tight link between the upper water structure and N fixation. It could be hypothesized that stronger mixing during interglacials enhances the supply of excess phosphorous from the subsurface waters and thus encourages the growth of diazotrophs. Furthermore, records of bulk sediment δ15N with relatively high time resolution show dominant precession cycle, probably related to the nutrient supply from subsurface water driven by summer monsoon and associated upper water structure changes. Similar mechanism controlling N fixation is also effective in regions with enough iron supply and low concentrations of nitrogen and phosphorous, like the North Atlantic, supporting that upper water structure can dominate N fixation rates by regulating nutrient stoichiometry supplied to the surface waters.
The Polar Stratosphere as an Arbiter of the Projected Tropical Versus Polar Tug of War
Authors: Peings Yannick , Cattiaux Julien , Magnusdottir Gudrun
Published: August 2019

This study explores the “tug of war” between the effects of Arctic amplification (“AA”) and upper‐troposphere tropical warming (“UTW”) on the response of the future North Atlantic atmospheric circulation. The late 21st century AA and UTW temperature anomalies are imposed in a high‐top atmospheric model by nudging the temperature. Two sets of experiments are performed, with and without feedback of the polar stratosphere to highlight its role in the response to UTW, AA, and both combined. With interactive polar stratosphere, UTW forces an equatorward shift of the eddy‐driven jet that reinforces the response to AA. However, when the polar stratosphere feedback is suppressed, the response to UTW is opposite and reflects the previously identified tug of war between the effects of UTW and AA in midlatitudes. This study highlights that the polar stratosphere is a key component for future changes in the North Atlantic atmospheric circulation and that it must be accurately represented in climate change scenarios.
Cross‐Scale Interactions Dictate Regional Lake Carbon Flux and Productivity Response to Future Climate
Authors: Zwart J. A. , Hanson Z. J. , Read J. S. , Fienen M. N. , Hamlet A. F. , Bolster D. , Jones S. E.
Published: August 2019

Lakes support globally important food webs through algal productivity and contribute significantly to the global carbon cycle. However, predictions of how broad‐scale lake carbon flux and productivity may respond to future climate are extremely limited. Here, we used an integrated modeling framework to project changes in lake‐specific and regional primary productivity and carbon fluxes under 21st century climate for thousands of lakes. We observed high uncertainty in whether lakes collectively were to increase or decrease lake CO2 emissions and carbon burial in our modeled region owing to divergence in projected regional water balance among climate models. Variation in projected air temperature influenced projected changes in lake primary productivity (but not CO2 emissions or carbon burial) as warmer air temperatures decreased productivity through reduced lake water volume. Cross‐scale interactions between regional drivers and local characteristics dictated the magnitude and direction of lake‐specific carbon flux and productivity responses to future climate.
The Geometry of an Electron Scale Magnetic Cavity in the Plasma Sheet
Authors: Liu H. , Zong Q.‐G. , Zhang H. , Sun W. J. , Zhou X.‐Z. , Gershman Daniel J. , Shi C. , Zhang K. , Le Guan , Pollock C.
Published: August 2019

Electron scale magnetic cavities are electron vortex structures formed in turbulent plasma, while the evolution and electron dynamics of these structures have not been fully understood. Recently, high‐energy, angular, and temporal electron measurements from Magnetospheric Multiscale have enabled the application of an energetic particle sounding technique to these structures. This study analyzes an electron scale magnetic cavity observed by Magnetospheric Multiscale on 7 May 2015 in the plasma sheet. A comprehensive sounding technique is applied to obtain the geometry and propagation velocities of the boundaries. The result shows that the scale size of the structure is ∼90 km, and the leading and trailing boundaries are moving in the same direction but with different speeds (∼11.5 ± 2.2 and ∼18.1 ± 3.4 km/s, respectively). The speed difference suggests a shrinking of the structure that may play a significant role in magnetic energy dissipation and electron energization of electron scale magnetic cavities.
Multimodel Analysis of the Atmospheric Response to Antarctic Sea Ice Loss at Quadrupled CO2
Authors: Ayres H.C. , Screen J.A.
Published: August 2019

Antarctic sea ice cover is projected to significantly decrease by the end of the twenty‐first century if greenhouse gas concentrations continue to rise, with potential consequences for Southern Hemisphere weather and climate. Here we examine the atmospheric response to projected Antarctic sea ice loss at quadrupled CO2, inferred from 11 Coupled Model Intercomparison Project phase 5 models. Our study is the first multimodel analysis of the atmospheric response to Antarctic sea ice loss. Projected sea ice loss enhances the negative phase of the Southern Annular Mode, which slightly damps the positive Southern Annular Mode response to increased CO2, particularly in spring. The negative Southern Annular Mode response largely reflects a weakening of the eddy‐driven jet, and to a lesser extent, an equatorward shift of the jet. Sea ice loss induces near‐surface warming over the high‐latitude Southern Ocean, but warming does not penetrate over the Antarctic continent. In spring, we find multimodel evidence for a weakened polar stratospheric vortex in response to sea ice loss.
The Distinction Between the Gulf Stream and Its North Wall
Authors: Chi Lequan , Wolfe Christopher L. P. , Hameed Sultan
Published: August 2019

Downstream of Cape Hatteras, the Gulf Stream (GS) is bounded to the north by a sharp temperature front known as the North Wall (NW). Previous studies have generally assumed that variations of the NW and GS are equivalent. Using satellite sea surface height to identify the GS and the 15 °C isotherm at 200‐m depth to represent the NW, this paper examines their similarities and differences during 1993–2016. The NW and GS are geographically close and vary similarly only to the west of 71°W. Downstream of that, they rapidly diverge—and the variances of their latitudes increase by more than a factor of 2—as the GS flows past the New England Seamounts. Evidence is presented to show that the difference in properties of the NW and the GS is related to the presence of mesoscale eddies in the region separating them.
ULF Waves Modulating and Acting as Mass Spectrometer for Dayside Ionospheric Outflow Ions
Authors: Liu Z.‐Y. , Zong Q.‐G. , Zhou X.‐Z. , Hao Y. X. , Yau A. W. , Zhang H. , Chen X.‐R. , Fu S. Y. , Pollock C. J. , Le G. , Ergun R. E. , Lindqvist P.‐A.
Published: August 2019

Ionospheric outflow has been shown to be a dominant ion source of Earth's magnetosphere. However, most studies in the literature are about ionospheric outflow injected into the nightside magnetosphere. We still know little about ionospheric outflow injected into the dayside magnetosphere and its further energization after it enters the magnetosphere. Here, with data from Magnetospheric Multiscale mission, we report direct observations of the modulation of dayside ionospheric outflow ions by ultralow frequency (ULF) waves. The observations indicate that the modulation is mass dependent, which demonstrates the possibility of using ULF waves as a mass spectrometer to identify ion species. Moreover, the measurement suggests that polarization drift may play a role in O+ modulation, which may lead to a true acceleration and even nonadiabatic behavior of O+. This interaction scenario can work throughout the whole magnetosphere and impact upon the plasma environment and dynamics.
Ross Ice Shelf Icequakes Associated With Ocean Gravity Wave Activity
Authors: Chen Z. , Bromirski P. D. , Gerstoft P. , Stephen R. A. , Lee W. S. , Yun S. , Olinger S. D. , Aster R. C. , Wiens D. A. , Nyblade A. A.
Published: August 2019

Gravity waves impacting ice shelves illicit a suite of responses that can affect ice shelf integrity. Broadband seismometers deployed on the Ross Ice Shelf, complemented by a near‐icefront seafloor hydrophone, establish the association of strong icequake activity with ocean gravity wave amplitudes (AG) below 0.04 Hz. The Ross Ice Shelf‐front seismic vertical displacement amplitudes (ASV) are well correlated with AG, allowing estimating the frequency‐dependent transfer function from gravity wave amplitude to icefront vertical displacement amplitude (TGSV(f)). TGSV(f) is 0.6–0.7 at 0.001–0.01 Hz but decreases rapidly at higher frequencies. Seismicity of strong icequakes exhibits spatial and seasonal associations with different gravity wave frequency bands, with the strongest icequakes observed at the icefront primarily during the austral summer when sea ice is minimal and swell impacts are strongest.
Interhemispheric Asymmetry in Response of Low‐Latitude Ionosphere to Perturbation Electric Fields in the Main Phase of Geomagnetic Storms
Authors: Dashora N. , Suresh Sunanda , Niranjan K.
Published: August 2019

Structures of sudden enhancements/depressions and associated interhemispheric asymmetry in low‐latitude total electron content (TEC) during the main phase (MP) of geomagnetic storms have remained unpredictable majorly due to oscillating equatorial vertical E×B drifts and resultant redistribution of plasma in low latitudes in a given seasonal background. Robust analysis of 7 major and 30 moderate ionospheric storms during the years 2000–2018 is performed with comprehensive literature review encompassing various sources of asymmetry in magnetosphere‐ionosphere coupling. Taking advantage of simultaneous long‐term observations of E×B drift from Jicamarca, H component from magnetometers, and global ionospheric map vertical TEC (VTEC) and TEC observations across the dip equator from the South American sector, simultaneous formation of peaks and valleys in VTEC and associated asymmetry are studied. Additionally, a three‐layer neural network‐based E×B drift model is developed using delta‐H observations that provide drift estimates in the absence of Jicamarca drifts. The main results establish simultaneous high‐magnitude short‐lived (1–2 hr) enhancements and depression in VTEC during the MP in daytime in both hemispheres with varying differences of −30 to 100 TECU with respect to quiet time mean and along with prominent existence of interhemispheric asymmetry in TEC during the MP regardless of seasons. Maximum VTEC in the northern and southern low latitudes is found to occur at different times during storms. Large difference of VTEC is found ranging between 10 and 30 TECU between the near conjugate locations of the hemispheres. Coincident global episodic peaks marked by steep VTEC falls show dominance of episodic eastward and westward penetration electric fields in the low‐latitude daytime ionosphere.
Stochastic Differential Equations for the Variability of Atmospheric Convection Fluctuating Around the Equilibrium
Authors: Machulskaya E. , Seifert A.
Published: August 2019

Most convection parameterization schemes used within current atmospheric models make a convective equilibrium assumption, which breaks at the resolutions currently used by many numerical weather prediction models. To account for fluctuations of the cloud base mass flux about its equilibrium value, stochastic convection schemes have been developed for both deep (Plant & Craig, 2008, https://doi.org/10.1175/2007JAS2263.1) and shallow (Sakradzija et al., 2015, https://doi.org/10.5194/npg-22-65-2015) convection. Due to the need to explicitly track individual clouds in each grid box, these schemes can be computationally expensive. Motivated by the above considerations, the present study demonstrates how the machinery of the above schemes can be reduced to the solution of two ordinary stochastic differential equations for the cloud number and the total cloud base mass flux. The properties of the resulting stochastic processes for the cloud number and the total mass flux are not exactly equivalent to those of the original schemes but recover them to a very good approximation.