bluuebunny/crossref_metadata_2025 huggingface dataset:
2D Crystals in Three Dimensions: Electronic Decoupling of Single‐Layered Platelets in Colloidal Nanoparticles
Authors: Kempt Roman , Kuc Agnieszka , Han Jae Hyo , Cheon Jinwoo , Heine Thomas
Published: November 2018

2D crystals, single sheets of layered materials, often show distinct properties desired for optoelectronic applications, such as larger and direct band gaps, valley‐ and spin‐orbit effects. Being atomically thin, the low amount of material is a bottleneck in photophysical and photochemical applications. Here, the formation of stacks of 2D crystals intercalated with small surfactant molecules is proposed. It is shown, using first principles calculations, that the very short surfactant methyl amine electronically decouples the layers. The indirect–direct band gap transition characteristic for Group 6 transition metal dichalcogenides is demonstrated experimentally by observing the emergence of a strong photoluminescence signal for ethoxide‐intercalated WSe2 and MoSe2 multilayered nanoparticles with lateral size of about 10 nm and beyond. The proposed hybrid materials offer the highest possible density of the 2D crystals with electronic properties typical of monolayers. Variation of the surfactant's chemical potential allows fine‐tuning of electronic properties and potentially elimination of trap states caused by defects.
An ensemble CPU load prediction algorithm using a Bayesian information criterion and smooth filters in a cloud computing environment
Authors: Tofighy Sajjad , Rahmanian Ali A. , Ghobaei‐Arani Mostafa
Published: November 2018

Cloud resource management requires complex policies and decisions to ensure the suitable use of computing resources due to fluctuations in the demanding workload. Deciding the right amount of resource usage for performing user requests in cloud environments is not trivial. Therefore, an efficient resource prediction model can play important roles in cloud resource management to estimate the needed resources properly. In this paper, we propose an ensemble CPU load prediction model using a Bayesian information criterion to choose the best constituent model in each time slot based on the cloud resource usage history. Further, we apply a couple of smooth filters in order to decrease the negative impacts of outliers in the observed data points. We also present a framework for cloud resource management including a prediction module to estimate the resource usage more accurately. The experimental results on the data set of the CoMon project indicate that the proposed approach achieves higher accuracy compared with the other ensemble prediction algorithms.
A new positive finite volume scheme for two‐dimensional convection‐diffusion equation
Authors: Lan Bin , Sheng Zhiqiang , Yuan Guangwei
Published: November 2018

A new positive finite volume scheme for the two‐dimensional convection‐diffusion equation on deformed meshes is proposed. The approximation of the convective flux is based on some available information of the diffusive flux. The scheme can keep local conservation of normal flux on the cell‐edge and can be used to deal with the case that the diffusive coefficients are discontinuous and anisotropic. In addition, no limiter is introduced. For the unsteady problem, the existence of a solution for the nonlinear discrete system is proved. Numerical results show that the new scheme has second order accuracy and can preserve the positivity.
Seifert fibering operators in 3d $$ \mathcal{N}=2 $$ theories
Authors: Closset Cyril , Kim Heeyeon , Willett Brian
Published: November 2018

Abstract

We study 3d

$$ \mathcal{N}=2 $$

N
=
2

supersymmetric gauge theories on closed oriented Seifert manifolds — circle bundles over an orbifold Riemann surface —, with a gauge group G given by a product of simply-connected and/or unitary Lie groups. Our main result is an exact formula for the supersymmetric partition function on any Seifert manifold, generalizing previous results on lens spaces. We explain how the result for an arbitrary Seifert geometry can be obtained by combining simple building blocks, the “fibering operators.” These operators are half-BPS line defects, whose insertion along the S
1 fiber has the effect of changing the topology of the Seifert fibration. We also point out that most supersymmetric partition functions on Seifert manifolds admit a discrete refinement, corresponding to the freedom in choosing a three-dimensional spin structure. As a strong consistency check on our result, we show that the Seifert partition functions match exactly across infrared dualities. The duality relations are given by intricate (and seemingly new) mathematical identities, which we tested numerically. Finally, we discuss in detail the supersymmetric partition function on the lens space L(p, q)
b
with rational squashing parameter b
2 ∈ ℚ, comparing our formalism to previous results, and explaining the relationship between the fibering operators and the three-dimensional holomorphic blocks.
Higher-point positivity
Authors: Chandrasekaran Venkatesa , Remmen Grant N. , Shahbazi-Moghaddam Arvin
Published: November 2018

Abstract

We consider the extension of techniques for bounding higher-dimension operators in quantum effective field theories to higher-point operators. Working in the context of theories polynomial in X = (∂ϕ)2, we examine how the techniques of bounding such operators based on causality, analyticity of scattering amplitudes, and unitarity of the spectral representation are all modified for operators beyond (∂ϕ)4. Under weak-coupling assumptions that we clarify, we show using all three methods that in theories in which the coefficient λ

n
of the X

n
term for some n is larger than the other terms in units of the cutoff, λ

n
must be positive (respectively, negative) for n even (odd), in mostly-plus metric signature. Along the way, we present a first-principles derivation of the propagator numerator for all massive higher-spin bosons in arbitrary dimension. We remark on subtleties and challenges of bounding P(X) theories in greater generality. Finally, we examine the connections among energy conditions, causality, stability, and the involution condition on the Legendre transform relating the Lagrangian and Hamiltonian.
Quantization of the particle with a linear massless solution
Authors: Jusinskas Renann Lipinski
Published: November 2018

Abstract

In this work, a solution linear in the momentum for the massless constraint P

m

P

m
= 0 is investigated. It is presented in terms of a SO(2n, ℂ) to U(n) decomposition and interpreted in terms of projective pure spinors, which are known to parametrize the

$$ \frac{\mathrm{SO}(2n)}{\mathrm{U}(n)} $$

SO

2
n

U

n

coset. The worldline action is quantized using the BRST formalism and, using the results of Berkovits and Cherkis, the ghost number zero wave function is shown to generate massless solutions for field equations of arbitrary spin. The model can be covariantly expressed by the action recently proposed in D = 10 by Berkovits, in terms of a twistor-like constraint. However, a thorough account of its gauge symmetries does not lead to a spacetime supersymmetric theory. In order to derive from first principles the superparticle in the pure spinor formalism, a new model is proposed with partial worldline supersymmetry. The gauge algebra is then analyzed within the Batalin-Vilkovisky formalism and the gauge fixed action is finally shown to describe the pure spinor superparticle times a U(1) decoupled sector.
Conference report: 17th EDF–Pprime workshop
Authors: Atkinson Simon
Published: November 2018

The 17th EDF–Pprime workshop was held in Paris, France, on 4 October 2018. Here, we provide a review of the event based on a brief report submitted to Sealing Technology by Institut Pprime's Noël Brunetière.
Editorial
Authors: Barrett Steve
Published: November 2018

20 years have passed since the Fuel Cells Bulletin was launched, so it seems an appropriate time to look back at the front pages and see how the sector has changed…
Becoming a Correspondent: The Foundations of New Merchant Relationships in Early Modern French Trade (1730–1820)
Authors: BARTOLOMEI ARNAUD , LEMERCIER CLAIRE , REBOLLEDO-DHUIN VIERA , SOUGY NADÈGE
Published: November 2018

This article discusses the relational and rhetorical foundations of more than 300 first letters sent in the eighteenth and early nineteenth centuries by merchant or banking houses based in Europe, the Mediterranean, and the Americas to two prominent French firms: Roux Brothers and Greffulhe Montz & Cie. We used a quantitative analysis of qualitative aspects of first letters to go beyond the standard opposition between premodern personal exchanges and modern impersonal transactions. The expansion of commercial networks during the period under analysis is often believed to have relied on families and ethnic networks and on explicit recommendations worded in the formulas prescribed in merchant manuals. However, most first letters did not use such resources. In many cases, commercial operations began thanks to a mutual acquaintance but without a formal recommendation. This was in fact the norm in the eighteenth century—and an underestimated foundation of the expansion of European commercial networks. In the early nineteenth century, this norm became less prevalent: it was replaced by diverse relational and rhetorical strategies, from recommendations to prospective letters dispensing with any mention of relationships. Whether before or after 1800, the relational and rhetorical resources displayed in letters did not systematically influence the sender’s chances of becoming a correspondent; instead, they depended on the receiving firm’s commercial strategy.
Perturbative expansions of the conformation tensor in viscoelastic flows
Authors: Hameduddin Ismail , Gayme Dennice F. , Zaki Tamer A.
Published: November 2018

We consider the problem of formulating perturbative expansions of the conformation tensor, which is a positive definite tensor representing polymer deformation in viscoelastic flows. The classical approach does not explicitly take into account that the perturbed tensor must remain positive definite – a fact that has important physical implications, e.g. extensions and compressions are represented similarly to within a negative sign, when physically the former are unbounded and the latter are bounded from below. Mathematically, the classical approach assumes that the underlying geometry is Euclidean, and this assumption is not satisfied by the manifold of positive definite tensors. We provide an alternative formulation that retains the conveniences of classical perturbation methods used for generating linear and weakly nonlinear expansions, but also provides a clear physical interpretation and a mathematical basis for analysis. The approach is based on treating a perturbation as a sequence of successively smaller deformations of the polymer. Each deformation is modelled explicitly using geodesics on the manifold of positive definite tensors. Using geodesics, and associated geodesic distances, is the natural way to model perturbations to positive definite tensors because it is consistent with the manifold geometry. Approximations of the geodesics can then be used to reduce the total deformation to a series expansion in the small perturbation limit. We illustrate our approach using direct numerical simulations of the nonlinear evolution of Tollmien–Schlichting waves.
Lock-in regions of laminar flows over a streamwise oscillating circular cylinder
Authors: Kim Ki-Ha , Choi Jung-Il
Published: November 2018

In this paper, flow over a streamwise oscillating circular cylinder is numerically simulated to examine the effects of the driving amplitude and frequency on the distribution of the lock-in regions in laminar flows. At $Re=100$, lock-in is categorized according to the spectral features of the lift coefficient as two different lock-in phenomena: harmonic and subharmonic lock-in. These lock-in phenomena are represented as maps on the driving amplitude–frequency plane, which have subharmonic lock-in regions and two harmonic lock-in regions. The frequency range of the subharmonic region is shifted to lower frequencies with increasing amplitude, and the lower boundary of this subharmonic region is successfully predicted. A symmetric harmonic region with a symmetric vortex pattern is observed in a certain velocity range for a moving cylinder. Aerodynamic features induced by different flow patterns in each region are presented on the driving amplitude–frequency plane. The lock-in region and aerodynamic features at $Re=200$ and $40$ are compared with the results for $Re=100$. A subharmonic region and two harmonic regions are observed at $Re=200$, and these show the same features as for $Re=100$ at a low driving amplitude. Lock-in at $Re=40$ also shows one subharmonic region and two harmonic regions. However, compared with the $Re=100$ case, the symmetric harmonic lock-in is dominant. The features of aerodynamic force at $Re=200$ and $40$ are represented on a force map, which shows similar characteristics in corresponding regions for the $Re=100$ case.
Initiation of diffusive layering by time-dependent shear
Authors: Brown Justin M. , Radko Timour
Published: November 2018

The Arctic halocline is generally stable to the development of double-diffusive and dynamic instabilities – the two major sources of small-scale mixing in the mid-latitude oceans. Despite this, observations show the abundance of double-diffusive staircases in the Arctic Ocean, which suggests the presence of some destabilizing process facilitating the transition from smooth-gradient to layered stratification. Recent studies have shown that an instability can develop in such circumstances if weak static shear is present even when the flow is dynamically and diffusively stable. However, the impact of oscillating shear, associated with the presence of internal gravity waves, has not yet been addressed for the diffusive case. Through two-dimensional simulations of diffusive convection, we have investigated the impact of the magnitude and frequency of externally forced oscillatory shear on the thermohaline-shear instability. Simulations with stochastic shear – characterized by a continuous spectrum of frequencies from inertial to buoyancy – indicate that thermohaline layering does occur due to the presence of destabilizing modes (oscillations of near the buoyancy frequency). These simulations show that such layers appear as well-defined steps in the temperature and salinity profiles. Thus, the thermohaline-shear instability is a plausible mechanism for staircase formation in the Arctic and merits substantial future study.
Reconsidering the seizure threshold? A retrospective study about seizure quality among patients with maintenance ECT
Authors: Taib Simon , Levy Anna , Arbus Christophe , Schmitt Laurent , Yrondi Antoine
Published: November 2018

Objectives

Electroconvulsive therapy (ECT) is a safe and validated technique used to treat various psychiatric conditions. It triggers an artificially-induced seizure. This seizure is defined using several parameters such as the amount of energy, duration, frequency, pulse width and intensity. Efficacy and adverse events depend on the amount of energy delivered. Due to technical control, the amount of energy delivered by our unit’s ECT device was limited to 614 mC, 60% of the maximum possible output of the device. We wondered if lowering the dose would lead to better seizure quality among maintenance ECT patients.

Methods

We assessed seizure quality based on the EEG, using a validated tool created by MacPherson. Two evaluators independently rated the seizures. Pre- and post-control scores were compared using Student’s t-test for paired samples.

Results

We analysed data from 15 patients. Mean age was 65 years old. Twelve had depressive disorder, two had schizophrenia and one had schizo-affective disorder. Mean duration of seizure before control was 41.1 s [95% confidence interval (95CI)=26.1, 51.1]. The mean MacPherson’s score was 20.3 (95CI=16.2, 24.4). After control, the mean MacPherson’s score was 28.2 (23.1, 33.3), showing a significant difference with the pre-control dataset (p=0.032; t=−2.4; df=14). Specifically, peak mid-ictal amplitude increased from 6.9 (95CI=5.1, 8.7) to 10.0 (95CI=7.2, 12.8). Other sub-scores remained unchanged.

Conclusion

Lowering the energy delivered led to an overall increase of seizure quality among our sample. This highlights the necessity and utility of retitration during ECT maintenance, possibly leading to better management of our patients.
Modeling Asymmetric Relationships from Symmetric Networks
Authors: Rozenas Arturas , Minhas Shahryar , Ahlquist John
Published: November 2018

Many bilateral relationships requiring mutual agreement produce observable networks that are symmetric (undirected). However, the unobserved, asymmetric (directed) network is frequently the object of scientific interest. We propose a method that probabilistically reconstructs the latent, asymmetric network from the observed, symmetric graph in a regression-based framework. We apply this model to the bilateral investment treaty network. Our approach successfully recovers the true data generating process in simulation studies, extracts new, politically relevant information about the network structure inaccessible to alternative approaches, and has superior predictive performance.
ROS regulate differentiation of visceralizingLeishmaniaspecies into the virulent amastigote form
Authors: Khan Yousuf A. , Andrews Norma W. , Mittra Bidyottam
Published: November 2018

Leishmaniavirulence and disease development critically depends on the ability ofLeishmaniapromastigotes to infect, differentiate into amastigote forms and replicate inside mammalian host macrophages. Understanding changes associated with amastigote differentiation in axenic culture conditions is a key to identifying virulence factors. Here we compared efficiency of the conventional pH–temperature-dependent shift method to induce amastigote differentiation with the recently identified trigger for differentiation mediated by mitochondrial reactive oxygen species (ROS). Using two different visceral leishmaniasis species,L. infantumand.L. donovani, we show that ROS-generating methods such as iron deprivation or exposure to sub-lethal concentrations of hydrogen peroxide (H2O2) or menadione are significantly more effective in promoting promastigote–amastigote differentiation than the low pH–high temperature shift, leading to higher survival rates, morphological changes and gene expression patterns characteristic of the amastigote stage. Notably, both H2O2and menadione-mediated differentiation did not require upregulation of the mitochondrial electron transport chain-associated protein p27, suggesting that treatment with oxidants bypasses the necessity to upregulate mitochondrial activity, a precondition for mROS generation. Our findings confirm that ROS-induced differentiation occurs in multipleLeishmaniaspecies, including the medically important visceralizing species, and provide mechanistic rationale for earlier reports demonstrating markedly increased virulence ofL. infantumpromastigotes pre-treated with oxidative reagents.
Are long-term trends in Bewick’s Swan Cygnus columbianus bewickii numbers driven by changes in winter food resources?
Authors: WOOD KEVIN A. , NEWTH JULIA L. , BRIDES KANE , BURDEKIN MIKE , HARRISON ANNE L. , HEAVEN STEVE , KITCHIN CHARLIE , MARSHALL LEIGH , MITCHELL CARL , PONTING JESSICA , SCOTT DAFILA K. , SMITH JON , TIJSEN WIM , HILTON GEOFF M. , REES EILEEN C.
Published: November 2018

The north-west European population of Bewick’s SwanCygnus columbianus bewickiideclined by 38% between 1995 and 2010 and is listed as ‘Endangered’ on the European Red List of birds. Here, we combined information on food resources within the landscape with long-term data on swan numbers, habitat use, behaviour and two complementary measures of body condition, to examine whether changes in food type and availability have influenced the Bewick’s Swan’s use of their main wintering site in the UK, the Ouse Washes and surrounding fens. Maximum number of Bewick’s Swans rose from 620 in winter 1958/59 to a high of 7,491 in winter 2004/05, before falling to 1,073 birds in winter 2013/14. Between winters 1958/59 and 2014/15 the Ouse Washes supported between 0.5 and 37.9 % of the total population wintering in north-west Europe (mean ± 95 % CI = 18.1 ± 2.4 %). Swans fed on agricultural crops, shifting from post-harvest remains of root crops (e.g. sugar beet and potatoes) in November and December to winter-sown cereals (e.g. wheat) in January and February. Inter-annual variation in the area cultivated for these crops did not result in changes in the peak numbers of swans occurring on the Ouse Washes. Behavioural and body condition data indicated that food supplies on the Ouse Washes and surrounding fens remain adequate to allow the birds to gain and maintain good body condition throughout winter with no increase in foraging effort. Our findings suggest that the recent decline in numbers of Bewick’s Swans at this internationally important site was not linked to inadequate food resources.
Assemblage urbanism. Becoming urban in late medieval Southampton
Authors: Jervis Ben
Published: November 2018

It is proposed that assemblage theory offers the possibility of exploring archaeological evidence in innovative ways, in order to write alternative narratives of urban development. By combining historical and archaeological scholarship with work in contemporary urban geography, it is proposed that the concept of urban decline in the later Middle Ages is problematic and a more fruitful alternative approach would be to focus on the transformation of urban assemblages. These ideas are explored by drawing upon archaeological evidence from Southampton, UK.
Lyrics for a duskier Enlightenment. In response to Alexandra Ion
Authors: Pétursdóttir Þóra
Published: November 2018

In her article ‘A taphonomy of a dark Anthropocene’, Alexandra Ion responds to and criticizes my discussion around the topic of archaeology and the Anthropocene recently published in this journal. She takes issue with most of my central arguments and especially with my leaning towards object-oriented ontology, speculative realism and the like, describing my perspective as one that is literally dark and depressing and which may lead nowhere but to a dead end. While I make it clear that I will neither answer for nor shield myself behind other peoples’ articulations of OOO, I will in what follows react to Ion's rather harsh critique and use the opportunity to sharpen my arguments further by focusing on three central themes: first, OOO and the archaeological object; second, darkness, dead ends and knowledge of things; and third, ethics, politics and responsibility.
THE PERIPATETIC PROGRAM IN CATEGORICAL LOGIC: LEIBNIZ ON PROPOSITIONAL TERMS
Authors: MALINK MARKO , VASUDEVAN ANUBAV
Published: November 2018

Greek antiquity saw the development of two distinct systems of logic: Aristotle’s theory of the categorical syllogism and the Stoic theory of the hypothetical syllogism. Some ancient logicians argued that hypothetical syllogistic is more fundamental than categorical syllogistic on the grounds that the latter relies on modes of propositional reasoning such asreductio ad absurdum. Peripatetic logicians, by contrast, sought to establish the priority of categorical over hypothetical syllogistic by reducing various modes of propositional reasoning to categorical form. In the 17th century, this Peripatetic program of reducing hypothetical to categorical logic was championed by Gottfried Wilhelm Leibniz. In an essay titledSpecimina calculi rationalis, Leibniz develops a theory of propositional terms that allows him to derive the rule ofreductio ad absurdumin a purely categorical calculus in which every proposition is of the formA is B. We reconstruct Leibniz’s categorical calculus and show that it is strong enough to establish not only the rule ofreductio ad absurdum, but all the laws of classical propositional logic. Moreover, we show that the propositional logic generated by the nonmonotonic variant of Leibniz’s categorical calculus is a natural system of relevance logic known as RMI$_{{}_ \to ^\neg }$.
Deep Floats Reveal Complex Ocean Circulation Patterns
Authors: Ramsey Andr�e , Furey Heather , Bower Amy
Published: November 2018

Acoustically tracked floats drift far below the ocean’s surface, providing fresh discoveries about deep-sea currents. A new archive gathers decades’ worth of float data into a central repository.
Brucker Receives 2018 Cryosphere Early Career Award
Authors:   AGU
Published: November 2018

Ludovic Brucker will receive the 2018 Cryosphere Early Career Award at AGU’s Fall Meeting 2018, to be held 10–14 December in Washington, D. C. The award is for “significant early career contributions to cryospheric science and technology.”
Simulation of Focusing Effect of Traveling Ionospheric Disturbances on Meter‐Decameter Solar Dynamic Spectra
Authors: Koval Artem , Chen Yao , Stanislavsky Aleksander , Kashcheyev Anton , Zhang Qing‐He
Published: November 2018

For the first time we present simulation results of the focusing effect of the ionospheric plasma density irregularities, namely, medium‐scale traveling ionospheric disturbances (MSTIDs), on solar radio emission by applying a ray tracing method to the Earth's ionosphere with MSTIDs. With this technique we investigate the focusing effect that manifests itself in the form of peculiar spectral disturbances in intensity with specific morphology, so‐called Spectral Caustics (SCs), occasionally appearing in dynamic spectra of different solar radio instruments operating in the meter‐decameter wavelength range. We show that the simulated spectral shapes of SCs are in good agreement with the ones detected in real solar radio spectrograms. In particular, SCs that are classified as inverted V‐like, V‐like, X‐like, and fiber‐like types have been reproduced. It is also found that the seasonal dependence in the occurrence of SCs, which has been discovered recently, can be understood through a strong relation between the focusing frequency—the most important characteristic point in most SC patterns—and the elevation angle of the Sun. We find that under typical parameters of MSTIDs with spatial and temporal periods set to be 300 km and 40 min, respectively, the focusing frequency decreases with the growth of the elevation angle. Physical interpretations of the results and implications on the analysis of solar radio data with SCs are discussed.
North‐South Asymmetric Kelvin‐Helmholtz Instability and Induced Reconnection at the Earth's Magnetospheric Flanks
Authors: Fadanelli S. , Faganello M. , Califano F. , Cerri S. S. , Pegoraro F. , Lavraud B.
Published: November 2018

We present a three‐dimensional study of the plasma dynamics at the flank magnetopause of the Earth's magnetosphere during mainly northward interplanetary magnetic field periods. Two‐fluid simulations show that the initial magnetic shear at the magnetopause and the field line bending caused by the dynamics itself (in a configuration taken as representative of the properties of the flank magnetopause) influence both the location where the Kelvin‐Helmholtz (KH) instability and the induced magnetic reconnection take place and their nonlinear development. The KH vortices develop asymmetrically with respect to the Earth's equatorial plane where the local KH linear growth rate is maximal. Vortex‐driven reconnection processes take place at different latitudes, ranging from the equatorial plane to midlatitude regions but only in the hemisphere that turns out to be the less KH unstable. These results suggest that KH‐induced reconnection is not limited to specific regions around the vortices (inside, below, or above) but may be triggered over a broad and continuous range of locations in the vicinity of the vortices.
MMS Observations of Electrostatic Waves in an Oblique Shock Crossing
Authors: Goodrich Katherine A. , Ergun Robert , Schwartz Steven J. , Wilson Lynn B. , Newman David , Wilder Frederick D. , Holmes Justin , Johlander Andreas , Burch James , Torbert Roy , Khotyaintsev Yuri , Lindqvist Per‐Arne , Strangeway Robert , Russell Christopher , Gershman Daniel , Giles Barbara , Andersson Laila
Published: November 2018

High‐resolution particle and wave measurements taken during an oblique bow shock crossing by the Magnetospheric Multiscale (MMS) mission are analyzed. Two regions of differing magnetic behavior are identified within the shock, one with active magnetic fluctuations and one with laminar interplanetary magnetic field topology. A prominent reflected ion population is observed in both regions. The active magnetic region is characterized by large‐amplitude (>100 mV/m) electrostatic solitary waves, electron Bernstein waves, and ion acoustic waves, along with intermittent current activity and localized electron heating. In the region of laminar magnetic field, ion acoustic waves are prominently observed. Solar wind ion deceleration is observed in both regions of active and laminar magnetic field. All observations suggest that solar wind deceleration can occur as a result of multiple independent processes, in this case current and ion‐ion instabilities.
Planetary Period Modulation of Reconnection Bursts in Saturn's Magnetotail
Authors: Bradley T. J. , Cowley S. W. H. , Bunce E. J. , Smith A. W. , Jackman C. M. , Provan G.
Published: November 2018

We conduct a statistical analysis of 2,094 reconnection events in Saturn's near‐equatorial magnetotail previously identified in Cassini magnetometer data from intervals during 2006 and 2009/2010. These consist of tailward propagating plasmoids and planetward propagating dipolarizations, with approximately twice as many plasmoids as dipolarizations. We organize these by three related planetary period oscillation (PPO) phase systems, the northern and southern PPO phases relative to noon, the same phases retarded by a radial propagation delay, and the local retarded phases that take account of the azimuth (local time) of the observation. Clear PPO modulation is found for both plasmoid and dipolarization events, with local retarded phases best organizing the event data with the modulation in event frequency propagating across the tail as the PPO systems rotate. This indicates that the events are localized in azimuth, rather than simultaneously affecting much of the tail width. Overall, events occur preferentially by factors of ~3 at northern and southern phases where the tail current sheet is expected locally to be thinnest in the PPO cycle, with field lines contracting back from their maximum radial displacement, compared with the antiphase conditions. Separating the events into those representing the start of independent reconnection episodes, occurring at least 3 hr after the last, and events in subsequent clusters, shows that the above phases are predominantly characteristic of the majority cluster events. The phases at the start of independent reconnection episodes are typically ~60° earlier.
Double Plasma Resonance at Ion Cyclotron Harmonics in the Jovian Magnetosphere
Authors: Shaposhnikov V. E. , Zaitsev V. V. , Litvinenko G. V.
Published: November 2018

The ion cyclotron waves instability near the frequencies of ionic cyclotron harmonics is studied under conditions typical for the Jovian kilometer radio emission source. This instability is caused by the presence of the ions with a nonequilibrium loss cone‐type distribution function in the source. Expressions for the growth rate of the ion cyclotron wave's instability are obtained, and it is shown that the amplification of these waves significantly increases when the frequency of the lower‐hybrid resonance coincides with one of the ion cyclotron harmonics. Possible mechanisms for conversion of the ion cyclotron waves excited in the Jovian kilometer radio emission source into electromagnetic radiation are discussed. It is shown that the conversion of ion cyclotron waves, due to their coalescence with high‐frequency plasma waves, is possible only into ordinary electromagnetic waves, while the process capable of providing conversion of ion cyclotron waves into fast extraordinary electromagnetic waves is scattering by suprathermal electron fluxes. In the latter, despite the thermal spread of electron velocities, the radiation that leaves the source region is concentrated in a narrow frequency range Δω ≪ ω near the local gyrofrequency ω≃ωBe, and the polarization of this radiation corresponds to the extraordinary wave. The estimates of the electron energy, which is necessary for such conversion, have shown the possibility of the process realizing under conditions characteristic for the Jovian kilometer radio emission source.
Improved Interpretation of Deep Seismic Reflection Data in Areas of Complex Geology Through Integration With Passive Seismic Data Sets
Authors: Dentith Michael , Yuan Huaiyu , Murdie Ruth Elaine , Pina‐Varas Perla , Johnson Simon P. , Gessner Klaus , Korhonen Fawna J.
Published: November 2018

The Capricorn Orogen records the Paleoproterozoic amalgamation of the West Australian Craton. 2‐D deep‐seismic reflection data across the Orogen are difficult to interpret due to the complex geology, and fundamental questions remain about the nature of the basement in the northern part of the Orogen. Passive seismic data have been collected along a 250‐km‐long transect across the central part of the Capricorn Orogen. The passive seismic recordings utilized teleseismic arrivals to construct a velocity section using the receiver function common conversion point method and to estimate crustal thickness and Vp/Vs using the H‐k method. A shear velocity cross section was created using ambient noise‐based methods. An integrated interpretation of all the seismic data sets shows that basement in the central Capricorn Orogen comprises a series of distinct terranes. These are recognized based on changes in crustal reflectivity, velocity and Vp/Vs. We interpret these terranes as originating from an island arc caught in the collision between the Glenburgh Terrane and the Pilbara Craton as part of the 2215–2145 Ma Ophthalmia Orogeny. Although passive seismic data do not have the resolution of reflection data, the information gained from the passive data places important constraints on the reflection interpretation and provides complementary information about changes in crustal composition. We propose that passive seismic data represent a cost‐effective complementary geophysical data set that can greatly assist with the interpretation of deep reflection sections in areas of complex geology.
Roles of Wind‐Driven Currents and Surface Waves in Sediment Resuspension and Transport During a Tropical Storm
Authors: Xie Xiaohui , Li Ming , Ni Wenfei
Published: November 2018

Satellite remote sensing shows two hot spots of high suspended sediment concentration during the passage of Hurricane Irene (2011) over Chesapeake Bay: the shallow shoals in the mid Bay and the area around the mouth of the estuary. A coupled ocean wave sediment transport model is used to investigate mechanisms driving sediment resuspension and transport during the storm. The model reproduces the observed spatial variations of suspended sediment concentration and surface wave heights in the estuary and shows that both wave‐ and current‐induced shear stresses are important in stirring bottom sediment. In the mid‐Bay region, large wave‐induced shear stress causes sediment resuspension on the shallow shoals, while wind‐driven currents advect the suspended sediment downstream. Around the mouth of the estuary, the combined action of large waves and strong outflows produces high suspended sediment concentration, resulting in the export of ~0.8 Mt of estuarine sediments to the shelf. The storm‐induced sediment resuspension and export could be an important term in the sedimentary budget of an estuary.
The Aftermath of Petermann Glacier Calving Events (2008–2012): Ice Island Size Distributions and Meltwater Dispersal
Authors: Crawford Anna J. , Mueller Derek , Desjardins Luc , Myers Paul G.
Published: November 2018

Three large calving events occurred at Petermann Glacier in northwest Greenland between 2008 and 2012 that generated ice islands (large tabular icebergs) that ranged from ~30 to 300 km2in areal extent. Ice islands are known to deteriorate, via fracture and melt, during their drift through regional water bodies where they pose a potential risk to offshore resource extraction operations and disperse freshwater from the Greenland Ice Sheet. This study presents the first analysis of the deterioration occurring across the flux of ice islands that travel between Nares Strait and the North Atlantic after Petermann Glacier calving events. The evolution of Petermann ice island size distributions was evaluated, and the spatial dispersal of meltwater was quantified, through analyses that utilized the newly developed Canadian Ice Island Drift, Deterioration and Detection Database. Size‐frequency distributions remained relatively consistent, both spatially and temporally, and were well fit by power law models with slopes of approximately −1.7. This suggested that fracture was an important process by which the Petermann ice islands deteriorated, regardless of elapsed time or distance from the glacier. Ice island meltwater fluxes into the Baffin Island and Labrador currents were not large enough to slow down the Atlantic Meridional Overturning Circulation by weakening deep‐water convection in the Labrador Sea. However, augmented meltwater input was calculated within Petermann Fjord (2.0 mSv) and in the vicinity of grounding locations (0.4 mSv). Further research is necessary to better understand how this freshwater alters fjord circulation and influences the composition of local ocean waters.
Ecogeomorphic Feedbacks that Grow Deltas
Authors: Ma Hongxu , Larsen Laurel G. , Wagner R. Wayne
Published: November 2018

Coastal river deltas are complex and dynamic ecosystems where vegetation plays an essential role in influencing, as well as being influenced by, physical processes, creating ecogeomorphic feedbacks between vegetation canopy characteristics and topography. However, this feedback is poorly understood. This knowledge gap is due to difficulties in detecting and quantifying the interactions that define the feedback. Emerging technology and data analysis techniques like transfer entropy have made it possible to overcome former difficulties associated with sampling constraints and delineate bidirectional feedback within many vegetation classes at the delta scale. Here the transfer entropy analysis was consistent with widespread understanding of marsh zonation, yet produced additional insight into which vegetation classes specifically had a dominant impact on topographic change. Ecogeomorphic feedback was resolvable only within native vegetation classes (Nelumbo and Polygonum) that occur over low to moderate elevations within the Wax Lake Delta Louisiana. In contrast, nonnative vegetation classes (Colocasia and Eichhornia) were not as effective at accreting sediment as native classes. The transfer entropy analysis suggests that different vegetation communities play functionally different roles in landscape evolution that should be differentiated in ecogeomorphic models. Within such models, it would be most imperative to resolve detailed flow characteristics at lower to low‐middle island elevations. Furthermore, within elevation zones, it is likely important to differentiate between the roles of multiple vegetation communities rather than treating the entire elevation zone as a single ecogeomorphic entity.
Productivity Evolution in the South Brazilian Bight During the Last 40,000 Years
Authors: Pereira Lígia S. , Arz Helge W. , Pätzold Jürgen , Portilho‐Ramos Rodrigo C.
Published: November 2018

Marine productivity largely controls the oceanic uptake of atmospheric carbon dioxide and contributed to the global climate changes that led to the termination of the last glacial cycle. Past changes in marine productivity were presumably associated with disturbances in the Atlantic meridional overturning circulation (AMOC). In the South Atlantic, however, the evolution of marine productivity throughout the last glacial–interglacial cycle is still poorly constrained mainly due to the scarcity of records with high temporal resolution. Here we present high‐resolution records of paleoproductivity and upper‐water‐column properties from the western subtropical South Atlantic covering the last 40,000 years. Our records are based on faunal and stable oxygen isotopic analyses of planktonic foraminifera from a marine sediment core collected from an upwelling region off southeastern South America (27°S). We used the relative abundance of eutrophic planktonic foraminifera (i.e., Globigerinita glutinata and Globigerina bulloides) as proxies of primary productivity. Our findings reveal, for the first time, enhanced primary productivity during Heinrich Stadials along the last glacial, when the AMOC showed reduced strength. Additionally, our results reveal decreased primary productivity over the Last Glacial Maximum, a period of markedly lower sea level; and the Younger Dryas, when the AMOC showed only moderate reductions. The most outstanding productivity decline, however, is depicted at the onset of the Holocene, when the AMOC recovers its strength. We hypothesize that the observed changes were triggered by the dynamics of the Brazil Current primarily driven by disturbances in the AMOC.
Simulating Flood‐Induced Riverbed Transience Using Unmanned Aerial Vehicles, Physically Based Hydrological Modeling, and the Ensemble Kalman Filter
Authors: Tang Qi , Schilling Oliver S. , Kurtz Wolfgang , Brunner Philip , Vereecken Harry , Hendricks Franssen Harrie‐Jan
Published: November 2018

Flood events can change the riverbed topography as well as the riverbed texture and structure, which in turn can influence the riverbed hydraulic conductivity (Krb) and river‐aquifer exchange fluxes. A major flood event occurred in the Emme River in Switzerland in 2014, with major implications for the riverbed structure. The event was simulated with the fully integrated hydrological model HydroGeoSphere. The aim was to investigate the effect of the spatial and temporal variability of riverbed topography and Krb on predictions of hydraulic states and fluxes and to test whether data assimilation (DA) based on the ensemble Kalman filter (EnKF) can better reproduce flood‐induced changes to hydraulic states and parameters with the help of riverbed topography changes recorded with an unmanned aerial vehicle (UAV) and through‐water photogrammetry. The performance of DA was assessed by evaluating the reproduction of the hydraulic states for the year 2015. While the prediction of surface water discharge was not affected much by the changes in riverbed topography and in Krb, using the UAV‐derived postflood instead of the preflood riverbed topography reduced the root‐mean‐square error of predicted heads (RMSE [h]) by 24%. If, in addition to using the postflood riverbed topography, also Krb and aquifer hydraulic conductivity (Kaq) were updated through DA after the flood, the RMSE (h) was reduced by 55%. We demonstrate how updating of Krb and Kaq based on EnKF and UAV‐based observations of riverbed topography transience after a major flood event strongly improve predictions of postflood hydraulic states.
Application of the Generalized Clapeyron Equation to Freezing Point Depression and Unfrozen Water Content
Authors: Zhou Jiazuo , Wei Changfu , Lai Yuanming , Wei Houzhen , Tian Huihui
Published: November 2018

Freezing point and unfrozen water content are key parameters in modeling the heat and mass transfer under the cyclic change of atmosphere temperature. It is theoretically revealed the relation between the measured pore pressure and true pore pressure with physicochemical interactions. A new generalized Clapeyron equation is derived, which addresses the relationship among the measured pore water, ice‐liquid capillary pressure, and pore solution concentration for the frozen soil. The generalized Clapeyron equation is applied to derive the expressions for the freezing point and unfrozen water content in frozen soils at various thermodynamical conditions. The freezing point of soil is calculated and compared with the experimental results, showing that the freezing point depression becomes more pronounced as water content decreases and solution concentration increases. It is also shown that the NaCl solution with relatively high concentration in soil pore approximates the ideal dilute solution while Na2CO3 and some other solutions in soil are significantly different than the ideal dilute solution. Upon assuming the unfrozen water content is only determined by the capillary pressure, the Clapeyron equation links the soil water characteristic curve into the soil freezing characteristic curve. The unfrozen water content in the saline frozen soil and the frozen soil under overburden pressure is also calculated according to the expression derived from the generalized Clapeyron equation.
Time Compression Approximation Relationship for Infiltration in the Presence of a Shallow Water Table: Evaluating the Role of Péclet Number
Authors: Yao Lili , Wang Dingbao , Hooshyar Milad , Singh Arvind , Sivapalan Murugesu
Published: November 2018

The time compression (or time condensation) approximation (TCA) is commonly used in conjunction with an infiltration capacity equation for predicting the postponding infiltration rate, or, more generally, infiltration under time‐varying precipitation. In this paper a power function relationship for TCA between infiltration capacity and its time derivative is proposed for infiltration in the presence of a shallow water table. The results show that the exponent (β) in the power function relationship is not a constant but decreases as infiltration proceeds. The change of β indicates that the TCA relationship changes during infiltration and further suggests the necessity of using different TCA relationships for predicting infiltration rate during different stages after ponding. We argue that the change of β is due to the gradual dynamic change of the relative role of gravity and capillarity during infiltration. A Péclet number (Pe) is proposed for measuring the relative effect of gravity and capillarity. In the early times of infiltration when Pe < 1, with the increase of Pe, β decreases roughly from 3.5 to 2 for clay, silty clay loam, and silty loam, and from 3 to 2 for sandy loam and sand; during the longer times when Pe > 1, β has a linear relationship with Pe. The relationship between Pe and β provides an objective approach to select the suitable TCA function during different infiltration stages after ponding.