bluuebunny/crossref_metadata_2025 huggingface dataset:
Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts
Authors: Choi Ran , Choi Sang‐Il , Choi Chang Hyuck , Nam Ki Min , Woo Seong Ihl , Park Joon T. , Han Sang Woo
Published: April 2013

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.
Multiresponsive Viscoelastic Vesicle Gels of Nonionic C12EO4 and Anionic AzoNa
Authors: Wang Dong , Wei Guangcheng , Dong Renhao , Hao Jingcheng
Published: April 2013

Viscoelastic vesicle gels were prepared by mixing a nonionic surfactant, tetraethylene glycol monododecyl ether (C12EO4), and an anionic dye, sodium 4‐phenylazobenzoic acid (AzoNa). The gels, which were composed of multilamellar vesicles, were analyzed by cryogenic transmission electron microscopy (cryo‐TEM), freeze–fracture transmission electron microscopy (FF‐TEM), 2H NMR spectroscopy, and small‐angle X‐ray scattering (SAXS). The mechanism of vesicle‐gel formation is explained by the influence of anionic molecules on the bilayer bending modulus. Interestingly, the vesicle gels were observed to be sensitive to temperature, pH, and light. The viscoelastic vesicle gels respond to heat; they thin at lower temperatures and become thicker at higher temperatures. The vesicle gels are only stable from pH 7 to 11, and the gels become thinner outside of this range. UV light can also trigger a structural phase transition from micelles to multilamellar vesicle gels.
Catalytic Asymmetric Synthesis of Spirocyclic Azlactones by a Double Michael‐Addition Approach
Authors: Weber Manuel , Frey Wolfgang , Peters René
Published: April 2013

Spirocyclic azlactones are shown to be useful precursors of cyclic quaternary amino acids, such as the constrained cyclohexane analogues of phenylalanine. These compounds are of interest as building blocks for the synthesis of artificial peptide analogues with controlled folds in the peptide backbone. They were prepared in the present study by a step‐ and atom‐economic catalytic asymmetric tandem approach, requiring two steps starting from N‐benzoyl glycine and divinylketones. The key of this protocol is the enantioselective formation of the azlactone spirocycles, which involves a PdII‐catalyzed double 1,4‐addition of an in situ generated azlactone intermediate to the dienone (a formal [5+1] cycloaddition). As the catalyst, a planar chiral ferrocene bispalladacycle was used. Mechanistic studies suggest a monometallic reaction pathway. Although the diastereoselectivity was found to be moderate, the enantioselectivity is usually high for the formation of the azlactone spirocycles, which contain up to three contiguous stereocenters. Spectroscopic studies have shown that the spirocycles often prefer a twist over a chair conformation of the cyclohexanone moiety.
The EvCA project: A brief history
Authors: Hordijk Wim
Published: April 2013

This article presents a brief history of the Evolving Cellular Automata (EvCA) project. In the EvCA project, a genetic algorithm was used to evolve cellular automata to perform certain (nontrivial) computational tasks, in an effort to gain more insight into the question: “How does evolution produce sophisticated emergent computation in systems composed of simple components limited to local interactions?” Next to providing many interesting results and useful insights, the EvCA project seems to have spawned a whole research area of its own. Here, a brief overview is given of how it all started, developed, and inspired further work. © 2013 Wiley Periodicals, Inc. Complexity 18: 15–19, 2013
Electronically Connected [n]Helicenes: Synthesis and Chiroptical Properties of Enantiomerically Pure (E)‐1,2‐Di([6]helicen‐2‐yl)ethenes
Authors: Roose Jesse , Achermann Stefan , Dumele Oliver , Diederich François
Published: April 2013

We synthesized stilbenoid (E)‐(P,P)‐ and (E)‐(M,M)‐[6]helicene dimers in enantiomerically pure form as part of a program aimed at the exploration of new strategies for the synthesis of large helicenes. The [2+2+2] cyclotrimerization of suitable triynes, reported by Starý and co‐workers, was applied for the preparation of a racemic 2‐hydroxymethylated [6]helicene precursor, which was conveniently resolved by HPLC on a chiral stationary phase. Two optically active helicenes were subsequently connected to the stilbenoid dimer by olefin metathesis. Electronic circular dichroism (ECD) studies of the stilbenoid ethen‐1,2‐diyl‐linked dimer revealed bathochromically shifted ECD bands with exceptionally large Cotton effects relative to those of the monomeric [6]helicenes or to that of a dimeric [6]helicene with a saturated ethan‐1,2‐diyl linker. These comparative studies, complemented by computational investigations, show that the pronounced chiroptical properties of the stilbenoid dimer originate from π‐conjugation between the two [6]helicene moieties and from the rigidity that results from conjugation. All attempts to form (P)‐[13]helicene by photocyclodehydrogenation of the stilbenoid (P,P)‐dimer were unsuccessful.
Actuator dynamics compensation based on upper bound delay for real‐time hybrid simulation
Authors: Wu Bin , Wang Zhen , Bursi Oreste S.
Published: April 2013

Real‐time hybrid simulation represents a powerful technique capable of evaluating the structural dynamic performance by combining the physical simulation of a complex and rate‐dependent portion of a structure with the numerical simulation of the remaining portion of the same structure. Initially, this paper shows how the stability of real‐time hybrid simulation with time delay depends both on compensation techniques and on time integration methods. In particular, even when time delay is exactly known, some combinations of numerical integration and displacement prediction schemes may reduce the response stability with conventional compensation methods and lead to unconditional instability in the worst cases. Therefore, to deal with the inaccuracy of prediction and the uncertainty of delay estimation, a nearly exact compensation scheme is proposed, in which the displacement is compensated by means of an upper bound delay and the desired displacement is picked out by an optimal process. Finally, the advantages of the proposed scheme over conventional delay compensation techniques are shown through numerical simulation and actual tests. Copyright © 2013 John Wiley & Sons, Ltd.
Impact of machine‐type communications on energy and delay performance of random access channel in LTE‐advanced
Authors: Gerasimenko Mikhail , Petrov Vitaly , Galinina Olga , Andreev Sergey , Koucheryavy Yevgeni
Published: April 2013

Machine‐type communications (MTC) are a rapidly growing technology, which is expected to generate significant revenues to mobile network operators. In particular, smart grid is predicted to become one of the key MTC use cases that involves unattended meters autonomously reporting information to a grid infrastructure. With this research, we consider a typical smart metering MTC application scenario in the context of 3GPP LTE‐advanced wireless cellular system featuring a large number of devices connecting to the network near‐simultaneously. The resulting overload of the random access channel requires a novel evaluation methodology based on comprehensive analysis and simulations. In this paper, we target to complement a validated evaluation framework fully compatible with the 3GPP test cases with a thorough analysis of random access channel performance in overloaded MTC scenarios. We also look at the regular MTC operation, when the devices are sending their data after initial network entry has been performed. By including energy consumption into our methodology together with the conventional performance metrics, we aim at providing a complete and unified insight into MTC device operation, including its energy efficiency. Copyright © 2013 John Wiley & Sons, Ltd.
Enhanced Performance and Durability of a High Temperature Steam Electrolysis Stack
Authors: Mougin J. , Mansuy A. , Chatroux A. , Gousseau G. , Petitjean M. , Reytier M. , Mauvy F.
Published: April 2013

High temperature steam electrolysis (HTSE) is one of the most promising ways for hydrogen mass production. If coupled to a CO2‐free electricity and a low cost heat source, this process is liable to a high efficiency. High levels of performance and durability, in association with cost‐effective stack and system components are the key points. To reach such goals, a low‐weight stack has been designed, keeping the advantages of the high performing and robust stack previously validated in terms of performance, durability, and cyclability [1], but aiming at reducing the cost by the use of thin interconnects. This low‐weight stack has demonstrated at the scale of a 3‐cell stack a good performance of –1.0 A cm–2 at 1.3 V at 800 °C. Before performing the durability test, preliminary studies at the cell level have been carried out to highlight the effect of two major operating parameters that are the current density and the steam conversion (SC) ratio, those studies being carried out at one temperature, 800 °C. Based on these results, optimized operating parameters have been defined to perform the durability test on the stack, that is –0.5 A cm–2 and a SC ratio of 25%. Degradation rates around 3–4% 1,000 h–1 have been measured. The thermal cyclability of this stack has also been demonstrated with one thermal cycle. Therefore it can be concluded that these results make HTSE technology getting closer to the objectives of performance, durability, thermal cyclability, and cost.
The Use of Methane‐Containing Syngas in a Solid Oxide Fuel Cell: A Comparison of Kinetic Models and a Performance Evaluation
Authors: Liu M. , Pourquie M. J. B. M. , Fan L. , Halliop W. , Cobas V. R. M. , Verkooijen A. H. M. , Aravind P. V.
Published: April 2013

The nickel‐based anodes of solid oxide fuel cells (SOFCs) can catalytically reform hydrocarbons, which make natural gas, gasification syngas, etc., become potential fuels in addition to hydrogen. SR and water–gas shift (WGS) often occur inside SOFCs when operated on these fuels. Their reaction rates affect the partial pressures of hydrogen and carbon monoxide, the local temperatures and the related Nernst voltages. Consequently, the reaction rates affect the electrochemical reactions in the fuel cell. Three different kinetic models were used to characterize methane SR in a tubular SOFC; the results of each model were evaluated and compared. The polarizations of the fuel cell results of these models were validated against experimental data. The performance of a fuel cell operated with different fuels and based on a selected kinetic model was further studied in terms of the anode oxygen partial pressure, the thermo‐electrochemical distribution, and the system level performance.
Influence of water on rheology and strain localization in the lower continental crust
Authors: Getsinger A. J. , Hirth G. , Stünitz H. , Goergen E. T.
Published: April 2013

We investigated deformation processes within a lower crustal shear zone exposed in gabbros from Arnøya, Norway. Over a distance of ∼1 m, the gabbro progresses from nominally undeformed to highly sheared where it is adjacent to a hydrous pegmatite. With increasing proximity to the pegmatite, there is a significant increase in the abundance of amphibole and zoisite (which form at the expense of pyroxene and calcic plagioclase) and a slight increase in the strength of plagioclase lattice‐preferred orientation, but there is little change in recrystallized plagioclase grain size. Phase diagrams, the presence of hydrous reaction products, and deformation mechanism maps all indicate that the water activity (aH2O) during deformation must have been high (∼1) in the sheared gabbro compared with the nonhydrated, surrounding host gabbro. These observations indicate that fluid intrusion into mafic lower crust initiates syn‐deformational, water‐consuming reactions, creating a rheological contrast between wet and dry lithologies that promote strain localization. Thus, deformation of lower continental crust can be accommodated in highly localized zones of enhanced fluid infiltration. These results provide an example of how fluid weakens lower continental crust lithologies at high pressures and temperatures.
Direct radiative effects of an unseasonal dust storm at a western Indo Gangetic Plain station Delhi in ultraviolet, shortwave, and longwave regions
Authors: Singh Sachchidanand , Naseema Beegum S.
Published: April 2013

The aerosol direct radiative effects (DRE) in the ultraviolet, shortwave, and longwave range due to an unusual dust storm during 21 March 2012 have been quantified from surface measurements of aerosol optical depth (AOD) and radiation fluxes at Delhi, a western Indo Gangetic Plain station. The intrusion of dust over Delhi caused an increase in daily average AOD at 500 nm from 0.6 to 0.8, with a corresponding decrease in Angstrom exponent from 0.4 to subzero value. The dust severely affected the incoming solar radiation flux in the UV, shortwave, and longwave regions. The DRE at surface in the UV and shortwave regions decreased from −4.6 to −5.9 Wm−2 and from −68 to −86 Wm−2, respectively, while the longwave DRE increased from 27 to 45 Wm−2.
Cracking the ENCODE: From transcription to therapeutics
Authors: Mehta Gautam , Jalan Rajiv , Mookerjeee Rajeshwar P
Published: April 2013

The human genome encodes the blueprint of life, but the function of the vast majority of its nearly three billion bases is unknown. The Encyclopedia of DNA Elements (ENCODE) project has systematically mapped regions of transcription, transcription factor association, chromatin structure and histone modification. These data enabled us to assign biochemical functions for 80% of the genome, in particular outside of the well-studied protein-coding regions. Many discovered candidate regulatory elements are physically associated with one another and with expressed genes, providing new insights into the mechanisms of gene regulation. The newly identified elements also show a statistical correspondence to sequence variants linked to human disease, and can thereby guide interpretation of this variation. Overall, the project provides new insights into the organization and regulation of our genes and genome, and is an expansive resource of functional annotations for biomedical research.
Effects of oral 5‐hydroxytryptophan on a standardized planning task: insight into possible dopamine/serotonin interactions in the forebrain
Authors: Gendle Mathew H. , Young Erica L. , Romano Alexandra C.
Published: April 2013

Objective

Several studies have suggested that exogenous administration of the serotonin precursor 5‐hydroxytryptophan (5‐HTP) can result in the ectopic production of serotonin in dopaminergic neurons and a concomitant reduction in dopamine release. This study tested this hypothesis using the Tower of London (TOL), a test of planning and executive control that is sensitive to changes in forebrain dopamine activity, but insensitive to alterations in serotonin.

Methods

A sample of 68 undergraduates participated, and each received either three 50‐mg 5‐HTP capsules or placebos, and completed the TOL following a set absorption period.

Results

5‐HTP significantly lengthened the average time needed to complete each of the 10 trials of the TOL. 5‐HTP did not affect accuracy on this task.

Conclusions

Oral exogenous 5‐HTP disrupts dopaminergic function in the human forebrain. Copyright © 2013 John Wiley & Sons, Ltd.
Developing predictive systems models to address complexity and relevance for ecological risk assessment
Authors: Forbes Valery E , Calow Peter
Published: April 2013

Ecological risk assessments (ERAs) are not used as well as they could be in risk management. Part of the problem is that they often lack ecological relevance; that is, they fail to grasp necessary ecological complexities. Adding realism and complexity can be difficult and costly. We argue that predictive systems models (PSMs) can provide a way of capturing complexity and ecological relevance cost-effectively. However, addressing complexity and ecological relevance is only part of the problem. Ecological risk assessments often fail to meet the needs of risk managers by not providing assessments that relate to protection goals and by expressing risk in ratios that cannot be weighed against the costs of interventions. Once more, PSMs can be designed to provide outputs in terms of value-relevant effects that are modulated against exposure and that can provide a better basis for decision making than arbitrary ratios or threshold values. Recent developments in the modeling and its potential for implementation by risk assessors and risk managers are beginning to demonstrate how PSMs can be practically applied in risk assessment and the advantages that doing so could have. Integr Environ Assess Manag 2013;9:e75–e80. © 2013 SETAC
Mechanisms of the Statins Cytotoxicity in Freshly Isolated Rat Hepatocytes
Authors: Abdoli Narges , Heidari Reza , Azarmi Yadollah , Eghbal Mohammad Ali
Published: April 2013

Statins are potent drugs, used as lipid‐lowering agents in cardiovascular diseases. Hepatotoxicity is one of the serious adverse effects of statins, and the exact mechanism of hepatotoxicity is not yet clear. In this study, the cytotoxic effects of the most commonly used statins, that is, atorvastatin, lovastatin, and simvastatin toward isolated rat hepatocytes, were evaluated. Markers, such as cell death, reactive oxygen species (ROS) formation, lipid peroxidation, mitochondrial membrane potential, and the amount of reduced and oxidized glutathione in the statin‐treated hepatocytes, were investigated. It was found that the statins caused cytotoxicity toward rat hepatocytes dose dependently. An elevation in ROS formation, accompanied by a significant amount of lipid peroxidation and mitochondrial depolarization, was observed. Cellular glutathione reservoirs were decreased, and a significant amount of oxidized glutathione was formed. This study suggests that the adverse effect of statins toward hepatocytes is mediated through oxidative stress and the hepatocytes mitochondria play an important role in the statin‐induced toxicity. © 2013 Wiley Periodicals, Inc. J BiochemMol Toxicol 27:287‐294, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/jbt.21485
Consider a Non‐Spherical Elephant: Computational Fluid Dynamics Simulations of Heat Transfer Coefficients and Drag Verified Using Wind Tunnel Experiments
Authors: Dudley Peter N. , Bonazza Riccardo , Porter Warren P.
Published: April 2013

Animal momentum and heat transfer analysis has historically used direct animal measurements or approximations to calculate drag and heat transfer coefficients. Research can now use modern 3D rendering and computational fluid dynamics software to simulate animal–fluid interactions. Key questions are the level of agreement between simulations and experiments and how superior they are to classical approximations. In this paper we compared experimental and simulated heat transfer and drag calculations on a scale model solid aluminum African elephant casting. We found good agreement between experimental and simulated data and large differences from classical approximations. We used the simulation results to calculate coefficients for heat transfer and drag of the elephant geometry. J. Exp. Zool. 319A:319–327, 2013. © 2013 © 2013 Wiley Periodicals, Inc.
Modeling of the ionospheric Alfvén resonator in dipolar geometry
Authors: Lysak Robert L. , Waters Colin L. , Sciffer Murray D.
Published: April 2013

A new model for the propagation of ultralow‐frequency (ULF) waves in dipolar geometry has been developed. This model features a full height‐resolved ionosphere including finite Pedersen, Hall, and parallel conductivities. By using a nonorthogonal coordinate system, this model is capable of calculating the ground magnetic field produced by ULF waves and comparing these fields to those measured in the ionosphere and magnetosphere. This model has been used to investigate the properties of the ionospheric Alfvén resonator (IAR) in a dipolar magnetosphere. Although the IAR mode frequencies are not strongly affected by the finite magnetic zenith angle, the damping of these waves is enhanced by the presence of the height‐resolved ionosphere. Pedersen conductivity shields higher frequency ULF waves such as Pc1 from penetrating through the ionosphere, limiting the magnitude of the ground magnetic field, whereas Hall conductivity and finite azimuthal wave number enhance the coupling to the ground. Results for runs in which a wave packet is introduced into the model show that the ground magnetic field is enhanced when the central frequency of the wave packet matches a resonant frequency of the IAR. Including a more realistic height‐resolved ionosphere yields a more direct calculation of ionospheric fields, allowing a comparison between ground and ionospheric fields.
Large amplitude nonlinear waves in Venus magnetosheath
Authors: Golbraikh E. , Gedalin M. , Balikhin M. , Zhang T. L.
Published: April 2013

Large‐amplitude variations of the magnetic field in the Venusian magnetosheath are observed when the distance between the bow shock and the magnetic pileup boundary is small, of the order of the ion convective gyroradius. It is proposed that these oscillations are nonlinear standing waves. A theoretical model is developed within one‐dimensional two‐fluid hydrodynamics, which is in good agreement with the observed features of the structure.
Large deviations of the magnetic field from the Parker spiral in CRRs: Validity of the Schwadron model
Authors: Smith Edward J.
Published: April 2013

A difference in solar wind speed inside and outside a Coronal Hole Boundary (CHB) causes the field and solar wind to expand rapidly with distance to form a Corotating Rarefaction Region (CRR). In the Parker model, field lines inside the CRR form spirals determined by the local solar wind speed. Observationally, however, CRR fields often diverge from the Parker spiral by tens of degrees and in a more radial direction. In a model developed by Schwadron (2002), in addition to the velocity gradient, the field lines rotate differentially across the CHB. The solar wind speed then varies along the field lines rather than remaining constant as in the Parker model. The plausibility of the model is supported by calculations using nominal model parameters that reproduce the systematic deviations from the Parker spiral. The present study establishes the validity of the model by comparing observations of nine CRRs between 1 and 4 AU with model predictions. Estimates are obtained for the width, velocity gradient, differential velocity of the CRR, and the transit time of the magnetic field. These parameters are obtained at the surface near 10 solar radii where the pressure of the coronal magnetic field first becomes balanced.
Advancing in situ modeling of ICMEs: New techniques for new observations
Authors: Mulligan T. , Reinard Alysha A. , Lynch Benjamin J.
Published: April 2013

It is generally known that multispacecraft observations of interplanetary coronal mass ejections (ICMEs) are more likely to reveal their three‐dimensional structure than single‐spacecraft observations. The launch of STEREO in October 2006 has greatly increased the number of multipoint ICME studies, but the field is still in its infancy. To date, many studies still use flux rope models that rely on single track observations through a vast, multifaceted structure, which oversimplifies the problem and hinders interpretation of the large‐scale geometry. This oversimplification is especially problematic for multispacecraft ICME observations in which only one spacecraft observes a flux rope structure. To tackle these complex problems, we describe two new techniques and combine them to analyze two ICMEs observed at the twin STEREO spacecraft on 22–23 May 2007, when the spacecraft were separated by ∼ 9∘. We find a combination of non–force‐free flux rope multispacecraft modeling, together with a new non–flux rope ICME plasma flow deflection model, better constrains the large‐scale structure of these ICMEs. We also introduce a new spatial mapping technique that allows us to put multispacecraft observations and the new ICME model results in context with the convecting solar wind. What is distinctly different about this analysis is that it reveals aspects of ICME geometry and dynamics in a far more visually intuitive way than previously accomplished. In the case of the 22–23 May ICMEs, the analysis facilitates a more physical understanding of ICME large‐scale structure, the location and geometry of flux rope substructures within these ICMEs, and their dynamic interaction with the ambient solar wind.
Comparative analysis of low‐altitude ENA emissions in two substorms
Authors: Buzulukova N. , Fok M.‐C. , Roelof E. , Redfern J. , Goldstein J. , Valek P. , McComas D.
Published: April 2013

We report on the dynamics of low‐altitude energetic neutral atom (ENA) emissions during two substorms that occurred during the main phases of two storms: (1) a CIR‐driven storm on 11 October 2008 and (2) a coronal mass ejection (CME)‐driven storm on 5 April 2010. For both of these storms, we have complementary spacecraft and ground‐based observations. The dual‐spacecraft Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission obtained ENA images containing low‐altitude emissions (LAEs). Substorm dynamics is inferred from THEMIS all‐sky imagers. TWINS‐observed LAEs are compared with trapped/loss cone proton fluxes from the low‐altitude NOAA/MetOp spacecraft constellation. We find that the timing and intensity profiles of LAEs are different for the two selected events. For the 11 October 2008 event, the LAEs rise during substorm recovery phase and storm main phase. On 5 April 2010, the LAEs tend to peak near substorm onset. We argue that the different LAE behavior results from different pitch‐angle distributions (PADs) of the ion source population. Ion PADs are isotropic during substorm recovery phase for the 11 October 2008 event and have empty loss cone for the 5 April 2010 event. For both cases, LAE intensification marks the onset of activity in the magnetotail and precedes the large substorm onset. We conclude that the LAE production starts in the transition region between the magnetotail and ring current and may expand/move into the inner magnetosphere together with ring current formation.
The composition of Mars' topside ionosphere: Effects of hydrogen
Authors: Matta Majd , Withers Paul , Mendillo Michael
Published: April 2013

A one‐dimensional model of the Martian ionosphere is used to explore the importance of atomic and molecular hydrogen chemistry in the upper atmosphere and ionosphere. Neutral and ionized H and H2 undergo chemical reactions that lead to the production of the hydrogenated ions: H+, H2+, H3+, OH+, HCO+, ArH+, N2H+, HCO2+, and HOC+. Simulations are conducted for the cases of photochemistry only and photochemistry coupled with transport in order to asses the separate effects of plasma diffusion in the topside ionosphere. For both of these cases, the sensitivity of the ionosphere is tested for (1) molecular hydrogen abundance and (2) reaction rate, k1, for the charge exchange between H+ and H2. Results are reported for midday solar minimum conditions. We find that the ionospheric composition of Mars is sensitive to H2 abundance, but relatively insensitive to the reaction rate, k1. Depending on the conditions simulated, the topside ionosphere can contain appreciable amounts of hydrogenated species such as H3+, OH+, and HCO+. Comparisons are made with Viking ion density measurements as well as with results of other published Mars ionospheric models. Future comparisons with more extensive ion composition will be available when the Mars Atmosphere and Volatile Evolution mission arrives at Mars.
Plasmoid growth and expulsion revealed by two‐point ARTEMIS observations
Authors: Li S‐S. , Angelopoulos V. , Runov A. , Kiehas S.A. , Zhou X‐Z.
Published: April 2013

On 12 October 2011, two ARTEMIS probes, in lunar orbit ~9 RE north of the neutral sheet, sequentially observed a tailward‐moving, expanding plasmoid. Their observations revealed a multilayered plasma sheet composed of tailward‐flowing hot plasma within the plasmoid surrounded by earthward‐flowing, less energetic plasma. Prior observations of similar earthward flows ahead of or behind plasmoids have been interpreted as earthward outflow from a continuously active distant‐tail neutral line opposite an approaching plasmoid. No evidence of active distant neutral line reconnection was observed by the probes, however, as they traversed the plasmoid's leading and trailing edges, penetrating above its core. We suggest an alternate interpretation: compression of ambient plasma by the tailward‐moving plasmoid proper propels the plasma lobeward and earthward, i.e., above and below the plasmoid proper. Using the propagation velocity obtained from timing analysis, we estimate the average plasmoid proper size in its propagation direction to be 9 RE and its expansion rate to be ~7 RE/min at the observation locations. This observation of plasmoid expansion made at the plasmoid boundary is interpreted as plasmoid growth in both the XGSM and the ZGSM directions due to near‐Earth‐neutral‐line reconnection on closed plasma sheet field lines. The velocity inside the plasmoid proper was found to be nonuniform; the core likely moves as fast as 500 km/s, yet the outer layers move more slowly (and in the reverse direction). The absence of lobe reconnection, in particular on the earthward side, suggests that plasmoid formation and expulsion both result from closed plasma sheet field‐line reconnection.
Proton thermal energetics in the solar wind: Helios reloaded
Authors: Hellinger Petr , Trávníček Pavel M. , Štverák Štěpán , Matteini Lorenzo , Velli Marco
Published: April 2013

The proton thermal energetics in the slow solar wind between 0.3 and 1 AU is reinvestigated using the Helios 1 and 2 data, complementing a similar analysis for the fast solar wind [Hellinger et al., 2011]. The results for slow and fast solar winds are compared and discussed in the context of previous results. Protons need to be heated in the perpendicular direction with respect to the ambient magnetic field from 0.3 to 1 AU. In the parallel direction, protons need to be cooled at 0.3 AU, with a cooling rate comparable to the corresponding perpendicular heating rate; between 0.3 and 1 AU, the required cooling rate decreases until a transition to heating occurs: by 1 AU the protons require parallel heating, with a heating rate comparable to that required to sustain the perpendicular temperature. The heating/cooling rates (per unit volume) in the fast and slow solar winds are proportional to the ratio between the proton kinetic energy and the expansion time. On average, the protons need to be heated and the necessary heating rates are comparable to the energy cascade rate of the magnetohydrodynamic turbulence estimated from the stationary Kolmogorov‐Yaglom law at 1 AU; however, in the expanding solar wind, the stationarity assumption for this law is questionable. The turbulent energy cascade may explain the average proton energetics (although the stationarity assumption needs to be justified) but the parallel cooling is likely related to microinstabilities connected with the structure of the proton velocity distribution function. This is supported by linear analysis based on observed data and by results of numerical simulations.
Physical improvements to the solar wind reconnection control function for the Earth's magnetosphere
Authors: Borovsky Joseph E.
Published: April 2013

In a 2008 publication a first principles calculation of the dayside reconnection rate expressed in terms of upstream–solar wind parameters led to a rudimentary solar wind coupling function R1 for the Earth's magnetosphere. Four improvements to that derivation are added in the present paper, resulting in a more correct solar wind control function describing the rate at which solar wind magnetic field lines connect into the Earth's magnetosphere. The first is the inclusion of the effect of β‐dependent plasma compressibility on the reconnection rate. The second is a corrected calculation of the inflow of magnetic field lines into the reconnection X‐line. The third is a more accurate estimate of the orientation of the reconnection X‐line for asymmetric reconnection. The fourth correction accounts for the compression ratio of the Earth's bow shock for arbitrary orientation of the solar wind magnetic field. Two solar wind control functions result: one function, R2CS, is based on the Cassak‐Shay equation and another function, R2CSB, is based on the Cassak‐Shay‐Birn equation. The control functions are tested using solar wind measurements and geomagnetic indices from 1980 to 2012, and some improved correlation coefficients over the rudimentary function R1 are found. Simplified approximations to the new control functions are supplied: one is R2CS‐approx = 1.68 × 10−2 sin2(θ/2)no1/2vo2MA−0.3044exp(−[MA/3.18]1/2), where the subscript “o” denotes the solar wind upstream of the bow shock and MA is the solar wind Alfvén Mach number.
Electron fluxes and pitch‐angle distributions at dipolarization fronts: THEMIS multipoint observations
Authors: Runov A. , Angelopoulos V. , Gabrielse C. , Zhou X.‐Z. , Turner D. , Plaschke F.
Published: April 2013

Taking advantage of multipoint observations from a Cluster‐like Time History of Events and Macroscale Interactions during Substorms (THEMIS) probe configuration repeated in three events, we study pitch‐angle distributions (PAD) of lower energy (0.2–keV) electrons and omnidirectional energy‐time spectrograms of higher energy (30–500 keV) electrons observed at and near dipolarization fronts in the plasma sheet. Recent observations have shown that dipolarization fronts in the plasma sheet provide an impulsive electric field suggested to cause electron energization and dispersionless injections. Increase and decrease in energetic electron flux are equally probable at the fronts, however. Our case studies demonstrate increased energetic electron flux in the front's central region but decreased flux on its dusk side, where diverted plasma flow forms a vortex. An electric field associated with this vortex causes the electron flux decrease. We also find that shorter‐term energetic flux decreases, often observed before injections, coincide with a dip in the northward magnetic field ahead of the front. We attribute these decreases to particle energy loss via the inverse betatron effect. Our case studies reveal that pancake‐type (maximum at 90° pitch angle) and cigar‐type (maxima at 0 and 180°) PADs coexist at the same front. Our data analysis suggests that energetic electron PADs are mainly pancake type near the neutral sheet (|Bx| < 5 nt) and mainly cigar type at |Bx| > 10 nt. These results, to be confirmed in statistical studies, provide important constraints for further modeling of electron energization and transport toward the inner magnetosphere.
MESSENGER observations of magnetopause structure and dynamics at Mercury
Authors: DiBraccio Gina A. , Slavin James A. , Boardsen Scott A. , Anderson Brian J. , Korth Haje , Zurbuchen Thomas H. , Raines Jim M. , Baker Daniel N. , McNutt Ralph L. , Solomon Sean C.
Published: April 2013

On 18 March 2011, MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) became the first spacecraft to orbit Mercury, providing a new opportunity to study the outer boundary of the planet's magnetosphere—the magnetopause. Here we characterize Mercury's magnetopause using measurements collected by MESSENGER's Magnetometer and Fast Imaging Plasma Spectrometer. Analysis of measurements from two of MESSENGER's “hot seasons,” when the orbital periapsis is on Mercury's dayside and the magnetopause crossing takes place in the subsolar region, resulted in 43 events with well‐determined boundary normals. The typical duration of a magnetopause traversal was ~5 s. The average normal magnetic field component was ~20 nT, and the dimensionless reconnection rate, i.e., the ratio of the normal magnetic field component to the total field magnitude just inside the magnetopause, was 0.15 ± 0.02. This rate is a factor of ~3 larger than values found during the most extensive surveys at Earth. The ratio of the reconnection rate at Mercury to that of the Earth is comparable to the ratio of the solar wind Alfvén speeds at their respective orbits. We also find that the magnetopause reconnection rate at Mercury is independent of magnetic field shear angle, but it varies inversely with plasma β, the ratio of total thermal pressure to magnetic pressure, in the magnetosheath. These results suggest that reconnection at Mercury is not only more intense than at Earth but also that it occurs for nearly all orientations of the interplanetary magnetic field due to the low‐β nature of the solar wind in the inner heliosphere.
Particle acceleration in dipolarization events
Authors: Birn J. , Hesse M. , Nakamura R. , Zaharia S.
Published: April 2013

Using the electromagnetic fields of a recent MHD simulation of magnetotail reconnection, flow bursts and dipolarization, we investigate the acceleration of test particles (protons and electrons) to suprathermal energies, confirming and extending earlier results on acceleration mechanisms and sources. (Part of the new results have been reviewed recently in Birn et al., Space Science Reviews, 167, doi:10.1007/ s11214‐012‐9874‐4.) The test particle simulations reproduce major features of energetic particle events (injections) associated with substorms or other dipolarization events, particularly a rapid rise of energetic particle fluxes over limited ranges of energy. The major acceleration mechanisms for electrons are betatron acceleration and Fermi acceleration in the collapsing magnetic field. Ions, although non‐adiabatic, undergo similar acceleration. Two major entry mechanisms into the acceleration site are identified: cross‐tail drift from the inner tail plasma sheet and reconnection entry from field lines extending to the more distant plasma sheet. The former dominates early in an event and at higher energies (hundreds of keV) while the latter constitutes the main source later and at lower energies (tens of keV). Despite the fact that the injection front moves earthward in the tail, the peak of energetic particle fluxes moves to higher latitude when mapped from the near‐Earth boundary to Earth in a static magnetic field model.
Flow bouncing and electron injection observed by Cluster
Authors: Nakamura R. , Baumjohann W. , Panov E. , Volwerk M. , Birn J. , Artemyev A. , Petrukovich A. A. , Amm O. , Juusola L. , Kubyshkina M. V. , Apatenkov S. , Kronberg E. A. , Daly P. W. , Fillingim M. , Weygand J. M. , Fazakerley A. , Khotyaintsev Y.
Published: April 2013

Characteristics of particles and fields in the flow‐bouncing region are studied based on multipoint observations from Cluster located at 13–15RE downtail during a substorm event around 12:50 UT on 7 September 2007. The Cluster spacecraft were separated by a distance of up to 10,000 km and allowed to determine the mesoscale evolution of the current sheet as well as the development of the dipolarization front. We show that the flow bouncing took place associated with a tailward‐directed j × B force in a disturbed current sheet in addition to an enhanced tailward pressure gradient force. Multiple Earthward propagating dipolarization fronts accompanied by enhanced flux of energetic electrons were observed before the flow bouncing. The sequence of events started with a localized dipolarization front and ended with a large scale (>10RE) dipolarization front accompanied by a major increase in energetic electrons at all spacecraft and immediately followed by flow bouncing. Multiple dipolarization fronts result in the formation of compressed magnetic field with a plasma bulge bounded by thin ion‐scale current layers, a favorable condition for flow bouncing. These observations suggest that to understand the flow bouncing and related acceleration of plasma in the near‐Earth tail, both the large‐scale MHD properties and the transient and small‐scale effect of the plasma interaction with the Earth‐dipole field need to be taken into account.
Whistler propagation in the plasmapause
Authors: Woodroffe J.R. , Streltsov A.V.
Published: April 2013

Variations in plasma density and magnetic field have a strong effect on the propagation of very low frequency waves in the whistler mode. Numerous studies have established that field‐aligned density irregularities (sometimes called ducts) symmetrical relative their axis can effectively guide whistlers along the ambient magnetic field. In this paper, we demonstrate that whistlers can be guided by a single transverse gradient in density when there is a gradient in the background magnetic field in the same direction as a density gradient. These gradients in the density and the background magnetic field forms two ducts: one on the inner edge of the density gradient and another on the outer edge. This situation is very relevant to what is observed in the Earth's magnetosphere near the plasmapause. Numerical simulations performed for the typical plasmapause densities and magnetic fields demonstrate trapping and propagation of whistler‐mode waves in these ducts.
Effects of different geomagnetic storm drivers on the ring current: CRCM results
Authors: Cramer W.D. , Turner N.E. , Fok M.‐C. , Buzulukova N.Y.
Published: April 2013

The storm‐time magnetic disturbance at the Earth's equator, as commonly measured by the Dst index, is induced by currents in the near‐Earth magnetosphere. The ring current is generally considered the most important contributor, but other magnetospheric currents have also been found to have significant effects. Of the two main types of solar geomagnetic storm drivers, Coronal Mass Ejections (CMEs) tend to have a much greater impact on Dst than Corotating Interaction Regions (CIRs). Ring current models have been found to underestimate Dst, particularly during storms driven by CIRs. One possible explanation is that the models neglect to handle some aspect of ring current physics that is particularly important for CIRs. This study uses the Comprehensive Ring Current Model (CRCM) to estimate the ring current contribution to Dst for a selection of storms of various strengths and different drivers (CMEs and CIRs) that have solar wind parameters that fit a typical profile. The model boundary is set to 10 RE at the equator, encompassing the entire ring current region. The magnetic field is held fixed, based on average storm parameters, which limits our model results to the effects of convection and plasma sheet density at the model boundary. Our model results generally show good agreement with the size and timing of fluctuations in Dst, which indicates that convection and boundary conditions play an important role in shaping Dst. We also find excellent agreement with the magnitude of Dst for CME‐driven storms. For CIR‐driven storms, however, the magnitude at the peak of the storm frequently deviates from actual Dst. In general, we agree with the results of previous research that CIR‐driven storms are more underpredicted. However, this study includes some weaker CIR‐driven storms for which Dst is actually overpredicted. Overall, when examining the dependence of modeled Dst* on actual Dst* at storm peak, we find that there is a statistically significant difference between CME‐ and CIR‐driven storms. We also find that approximately half of the total ring current energy lies beyond an L‐value of 6.6. However, this figure could be overestimated due to the use of a static magnetic field, which limits radial transport.
Statistical study of global modes outside the plasmasphere
Authors: Hartinger M. D. , Angelopoulos V. , Moldwin M. B. , Takahashi K. , Clausen L. B. N.
Published: April 2013

Global modes, trapped fast mode magnetohydrodynamic (MHD) waves in the Earth's magnetosphere, may exhibit a monochromatic frequency spectrum even in the presence of a driver with a broadband frequency spectrum; they can in turn drive standing Alfvén waves at discrete frequencies via field line resonance (FLR). Direct observations of global modes are limited to a few case studies due to unique challenges associated with detecting them in situ. In this study, we use electric field, magnetic field, and plasma data from multiple THEMIS spacecraft as well as ground‐based observations to identify and characterize global modes outside the nominal plasmapause location. We establish a lower bound of 1.0% for the global mode occurrence rate in the 3–20 mHz frequency range in that region and show that global modes occur more frequently during high‐speed solar wind intervals. We also show that global modes with frequency between 10 and 20 mHz occur preferentially in the noon local time sector and are likely driven by processes in the ion foreshock.
Dayside auroral hiss observed at South Pole Station
Authors: Yan X. , LaBelle J. , Haerendel G. , Spasojevic M. , Bunch N. , Golden D. I. , Frey H. U. , Weatherwax A. T.
Published: April 2013

We performed a statistical study of low frequency (LF) auroral hiss recorded at South Pole Station in 2004, 2005, and 2007, and very low frequency (VLF) hiss recorded in 2000–2008. As expected, most auroral hiss occurs in the pre‐midnight sector. However, there is a secondary peak in occurrence in the pre‐noon sector (1000–1530 UT; ∼ 0630–1200 magnetic local time (MLT)) and somewhat more events occur in the post‐noon sector (1530–2100 UT; ∼ 1200–1730 MLT), with a null in occurrence around noon MLT. Individual dayside events appear similar to nightside hiss, but statistically they do not extend to as high frequencies. Solar wind discontinuities or impulses on the magnetopause are not correlated with these events. All‐sky camera, photometer, magnetometer, riometer, and VLF receiver data show that dayside LF hiss almost always extends to the VLF range and is often associated with active aurora. Examination of interplanetary magnetic field (IMF), substorm conditions, and Kp/AE/QI indices at times of dayside hiss suggests differences between the pre‐noon and post‐noon events: pre‐noon events are associated with IMF By < 0, whereas post‐noon events favor Bz < 0 and show a weaker correlation with By > 0. The correlation between pre‐noon events and By < 0 may arise because under those conditions, the pattern of field‐aligned currents (FACs) shifts to later magnetic local times, causing upward FACs to be dominant during pre‐noon hours at 74°, the invariant latitude of the South Pole. Unlike pre‐noon events, post‐noon events are more often associated with substorm activity on the nightside and favor elevated Kp indices, suggesting a connection of post‐noon events to nightside activity.