bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of the relative effect of the Earth's quasi‐DC and AC electric field on gradient drift waves in large‐scale plasma structures in the polar regions
Authors: Burston Robert , Mitchell Cathryn , Astin Ivan 
Published: August 2016

AbstractRadio signals traversing polar cap plasma patches and other large‐scale plasma structures in polar regions are prone to scintillation. This implies that irregularities in electron concentration often form within such structures. The current standard theory of the formation of such irregularities is that the primary gradient drift instability drives a cascade from larger to smaller wavelengths that manifest as variations in electron concentration. The electric field can be described as the sum of a quasi‐DC and an AC component. While the effect of the quasi‐DC component has been extensively investigated in theory and by modeling, the contribution of the AC component has been largely neglected. This paper investigates the relative contributions of both components, using data from the Dynamics Explorer 2 satellite. It concludes that the contribution of the AC electric field to irregularity growth cannot be neglected. This has consequences for our understanding of large‐scale plasma structures in polar regions (and any associated radio scintillation) as the AC electric field component varies in all directions. Hence, its effect is not limited to the trailing edge of such structures, as it is for the quasi‐DC component. This raises the need for new experimental and modeling investigations of these phenomena.
Generation of field‐aligned current (FAC) and convection through the formation of pressure regimes: Correction for the concept of Dungey's convection
Authors: Tanaka T. , Watanabe M. , Den M. , Fujita S. , Ebihara Y. , Kikuchi T. , Hashimoto K. K. , Kataoka R. 
Published: August 2016

AbstractIn this paper, we try to elucidate the generation mechanism of the field‐aligned current (FAC) and coexisting convection. From the comparison between the theoretical prediction and the state of numerical solution from the high‐resolution global simulation, we obtain the following conclusions about the distribution of dynamo, the magnetic field structure along the flow path that diverges Poynting flux, and energy conversion promoting the generation of electromagnetic energy. The dynamo for the region 1 FAC, which is in the high‐latitude‐side cusp‐mantle region, has a structure in which magnetic field is compressed along the convection path by the slow mode motion. The dynamo for the region 2 FAC is in the ring current region at the inner edge of the plasma sheet, and has a structure in which magnetic field is curved outward along the convection path. Under these structures, electromagnetic energy is generated from the work done by pressure gradient force, in both dynamos for the region 1 and region 2 FACs. In these generation processes of the FACs, the excitation of convection and the formation of pressure regimes occur as interdependent processes. This structure leads to a modification in the way of understanding the Dungey's convection. Generation of the FAC through the formation of pressure regimes is essential even for the case of substorm onset.
Formation of the inner electron radiation belt by enhanced large‐scale electric fields
Authors: Su Yi‐Jiun , Selesnick Richard S. , Blake J. B. 
Published: August 2016

AbstractA two‐dimensional bounce‐averaged test particle code was developed to examine trapped electron trajectories during geomagnetic storms with the assumption of conservation of the first and second adiabatic invariants. The March 2013 storm was selected as an example because the geomagnetic activity Kp index sharply increased from 2 + to 7− at 6:00 UT on 17 March. Electron measurements with energies between 37 and 460 keV from the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard Van Allen Probes (VAP) are used as initial conditions prior to the storm onset and served to validate test particle simulations during the storm. Simulation results help to interpret the observed electron injection as nondiffusive radial transport over a short distance in the inner belt and slot region based on various electric field models, although the quantitative comparisons are not precise. We show that electron drift trajectories are sensitive to the selection of electric field models. Moreover, our simulation results suggest that the actual field strength of penetration electric fields during this storm is stronger than any existing electric field model, particularly for L ≤ 2.
On the reduced geoeffectiveness of solar cycle 24: A moderate storm perspective
Authors: Selvakumaran R. , Veenadhari B. , Akiyama S. , Pandya Megha , Gopalswamy N. , Yashiro S. , Kumar Sandeep , Mäkelä P. , Xie H. 
Published: August 2016

AbstractThe moderate and intense geomagnetic storms are identified for the first 77 months of solar cycles 23 and 24. The solar sources responsible for the moderate geomagnetic storms are indentified during the same epoch for both the cycles. Solar cycle 24 has shown nearly 80% reduction in the occurrence of intense storms whereas it is only 40% in case of moderate storms when compared to previous cycle. The solar and interplanetary characteristics of the moderate storms driven by coronal mass ejection (CME) are compared for solar cycles 23 and 24 in order to see reduction in geoeffectiveness has anything to do with the occurrence of moderate storm. Though there is reduction in the occurrence of moderate storms, the Dst distribution does not show much difference. Similarly, the solar source parameters like CME speed, mass, and width did not show any significant variation in the average values as well as the distribution. The correlation between VBz and Dst is determined, and it is found to be moderate with value of 0.68 for cycle 23 and 0.61 for cycle 24. The magnetospheric energy flux parameter epsilon (ε) is estimated during the main phase of all moderate storms during solar cycles 23 and 24. The energy transfer decreased in solar cycle 24 when compared to cycle 23. These results are significantly different when all geomagnetic storms are taken into consideration for both the solar cycles.
Control of the innermost electron radiation belt by large‐scale electric fields
Authors: Selesnick R. S. , Su Y.‐J. , Blake J. B. 
Published: August 2016

AbstractElectron measurements from the Magnetic Electron Ion Spectrometer instruments on Van Allen Probes, for kinetic energies ∼100 to 400 keV, show characteristic dynamical features of the innermost (
) radiation belt: rapid injections, slow decay, and structured energy spectra. There are also periods of steady or slowly increasing intensity and of fast decay following injections. Local time asymmetry, with higher intensity near dawn, is interpreted as evidence for drift shell distortion by a convection electric field of magnitude ∼0.4 mV/m during geomagnetically quiet times. Fast fluctuations in the electric field, on the drift time scale, cause inward diffusion. Assuming that they are proportional to changes in Kp, the resulting diffusion coefficient is sufficient to replenish trapped electrons lost by atmospheric scattering. Major electric field increases cause injections by inward electron transport. An injection associated with the June 2015 magnetic storm is consistent with an enhanced field magnitude ∼5 mV/m. Subsequent drift echoes cause spectral structure.
Apparent triggering function of aftershocks resulting from rate‐dependent incompleteness of earthquake catalogs
Authors: Hainzl Sebastian 
Published: August 2016

AbstractThe onset of the aftershock decay after main shocks is controversial. Physical models predict that the onset time is stress dependent, and catalog analysis shows a clear increase of thecvalue of the Omori‐Utsu law with increasing main shock magnitude. However, earthquake catalogs are known to have variable quality and completeness levels; in particular, they miss events directly after main shocks. Thus, it has been also argued that the delayed onset of recorded aftershock activity triggered by large earthquakes is simply an artifact of the time‐varying completeness. Here I utilize a recent approach describing the detection probability of earthquakes as function of the actual earthquake rate. I derive an analytical relation between apparent and true earthquake rate which only depends on the blind time of detection algorithms after the occurrence of an earthquake. This relation is tested and verified for synthetic simulations of Omori‐type aftershock sequences. For a comparison, I analyze earthquake sequences occurred in Southern California and Taiwan, finding that the derived analytical decay function consistently explains the empirical aftershock activity in the catalogs. This indicates that the observed scaling of the Omoricvalue is mainly related to catalog incompleteness and not to any underlying physical process.
Three‐dimensional simulations of fracture dissolution
Authors: Starchenko Vitaliy , Marra Cameron J. , Ladd Anthony J. C. 
Published: August 2016

AbstractNumerical studies of fracture dissolution are frequently based on two‐dimensional models, where the fracture geometry is represented by an aperture field h(x,y). However, it is known that such models can break down when the spatial variations in aperture are rapid or large in amplitude; for example, in a rough fracture or when instabilities in the dissolution front develop into pronounced channels (or wormholes). Here we report a finite‐volume implementation of a three‐dimensional reactive transport model using the OpenFOAM® toolkit. Extensions to the OpenFOAM source code have been developed which displace and then relax the mesh in response to variations in the surface concentration; up to 100‐fold increases in fracture aperture are possible without remeshing. Our code has simulated field‐scale fractures with physical dimensions of about 10 m. We report simulations of smooth fractures, with small, well‐controlled perturbations in fracture aperture introduced at the inlet. This allows for systematic convergence studies and for detailed comparisons with results from a two‐dimensional model. Initially, the fracture aperture develops similarly in both models, but as local inhomogeneities develop the results start to diverge. We investigate numerically the onset of instabilities in the dissolution of fractures with small random variations in the initial aperture field. Our results show that elliptical cross sections, which are characteristic of karstic conduits, can develop very rapidly, on time scales of 10–20 years in calcite rocks.
Annual cycle and destruction of Eighteen Degree Water
Authors: Billheimer Sam , Talley Lynne D. 
Published: August 2016

AbstractEighteen Degree Water (EDW), the subtropical mode water of the western North Atlantic, is a voluminous, weakly stratified upper ocean water mass that acts as a subsurface reservoir of heat, nutrients, and CO2. This thick layer persists throughout the year, but nearly half of its volume is dispersed or mixed away, diffusing its properties into the thermocline, from the time it outcrops in winter until it is renewed the following year. CTD observations from Argo profiling floats and acoustically tracked, isothermally bound profiling floats are used to quantify EDW destruction rates and investigate the relevant processes responsible for the large annual cycle of EDW. EDW destruction occurs primarily at the top of the EDW layer, with the highest EDW destruction rates occurring during early summer. Slower, steadier EDW destruction is observed in early winter. EDW destruction is dominated by 1‐D vertical diffusion, while mesoscale, along‐isopycnal stirring is also significant, explaining approximately 1/3 of the total annual EDW destruction. Destruction via along‐isopycnal processes is more prevalent near the Gulf Stream than in the southern Sargasso Sea, due to higher potential vorticity gradients and enhanced mesoscale activity.
Subsurface morphology and scaling of lunar impact basins
Authors: Miljković K. , Collins G. S. , Wieczorek M. A. , Johnson B. C. , Soderblom J. M. , Neumann G. A. , Zuber M. T. 
Published: August 2016

AbstractImpact bombardment during the first billion years after the formation of the Moon produced at least several tens of basins. The Gravity Recovery and Interior Laboratory (GRAIL) mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions, allowing for detailed subsurface and morphological analyses to be made across the entire globe. GRAIL‐derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins, which represents a less unambiguous measure of a basin size than those based on topographic features. The formation of lunar impact basins was modeled numerically by using the iSALE‐2D hydrocode, with a large range of impact and target conditions typical for the first billion years of lunar evolution. In the investigated range of impactor and target conditions, the target temperature had the dominant effect on the basin subsurface morphology. Model results were also used to update current impact scaling relationships applicable to the lunar setting (based on assumed target temperature). Our new temperature‐dependent impact‐scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by GRAIL. As the formation of lunar impact basins is associated with the first ~700 Myr of the solar system evolution when the impact flux was considerably larger than the present day, our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the Moon and terrestrial planets in the early solar system.
The latitudinal variation of geoelectromagnetic disturbances during large (Dst≤−100 nT) geomagnetic storms
Authors: Woodroffe J. R. , Morley S. K. , Jordanova V. K. , Henderson M. G. , Cowee M. M. , Gjerloev J. G. 
Published: August 2016

AbstractGeoelectromagnetic disturbances (GMDs) are an important consequence of space weather that can directly impact many types of terrestrial infrastructure. In this paper, we analyze 30 years of SuperMAG magnetometer data from the range of magnetic latitudes 20°≤λ≤75° to derive characteristic latitudinal profiles for median GMD amplitudes. Based on this data, we obtain a parameterization of these latitudinal profiles of different types of GMDs, providing an analytical fit with Dst‐dependent parameters. We also obtain probabilistic estimates for the magnitudes of “100 year” GMDs, finding that
= 6.9 (3.60–12.9) nT/s should be expected at 45°≤λ < 50°, exceeding the 5 nT/s threshold for dangerous inductive heating.
Preparation of biphenyl‐bridged, crosslinked polyalkoxysilanes: Determination of oil/organic solvent absorption features
Authors: Kizil Soner , Bulbul Sonmez Hayal 
Published: August 2016

ABSTRACTA novel type of biphenyl‐bridged alkoxysilane‐based crosslinked polyalkoxysilane was prepared by the condensation of 4,4′‐bis(triethoxysilyl)−1,1′‐biphenyl and different lengths of linear aliphatic diols. Fourier transform infrared spectroscopy, solid‐state 13C and 29Si cross‐polarization magic angle spinning nuclear magnetic resonance, and thermogravimetric analysis were used to characterize the biphenyl‐bridged, crosslinked polyalkoxysilanes. The crosslinked polymers were found to have very quick and high swelling capabilities in organic solvents and oils. The absorption–desorption kinetics and reusability features of the crosslinked polymers were also studied, and we found that the synthesized polymers reached their maximum absorption capacity during a variety of tests without losing capacity. We also tested the absorption performance of the sorbents from water surfaces. All of these results confirm that biphenyl‐bridged, crosslinked polyalkoxysilanes could be good candidates as sorbent materials for the cleaning of water from organic contaminants. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44193.
Effect of an alkalized‐modified halloysite on PLA crystallization, morphology, mechanical, and thermal properties of PLA/halloysite nanocomposites
Authors: Guo Jianhua , Qiao Junxia , Zhang Xin 
Published: August 2016

ABSTRACTPoly(lactic acid) (PLA)/alkalized halloysite nanotube (HNTa) nanocomposites were prepared by melt mixing. The morphology, crystallization behavior, mechanical properties, and thermal stability of the nanocomposites were investigated in comparison with those of the pristine PLA. HNTa can nucleate PLA, leading to a lower recrystallization temperature and higher crystallinity. Infrared spectra revealed that the hydroxyl groups of the PLA interacted with the external hydroxyl groups of HNTa nanofillers via hydrogen bonding. The thermal stability of the nanocomposites was improved with the addition of HNTa. The PLA/HNTa nanocomposites exhibited higher modulus and tensile strength than those of the PLA composites containing unmodified halloysite nanotubes (HNTs). The improvement in properties was probably due to a better dispersion of the HNTa in the PLA matrix compared to that of the unmodified HNTs. Therefore, the facile alkali treatment of HNTs offers a low cost nanofiller for the preparation of PLA based nanocomposites with high tensile modulus and tensile strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44272.
Rheology of polyacrylonitrile‐based precursor polymers produced from controlled (RAFT) and conventional polymerization: Its role in solution spinning
Authors: Kaur J. , Millington K. , Cai J.Y. 
Published: August 2016

ABSTRACTPolymer solutions in dimethyl sulfoxide (DMSO) as a solvent, made from reversible addition fragmentation chain transfer (RAFT)‐mediated polyacrylonitrile (RAFT¥ PAN) terpolymer with molecular weight (MW) of 260,000 g/mol and dispersity (Ð) of 1.29, behave differently under applied shear stress than polymer solutions made from conventional PAN (Control PAN) with similar MW (258,000 g/mol) but Ð of 2.05 in the same solvent. The unique rheology of RAFT PAN is because of the reduced amount of high MW polymer fractions. Specifically, a 25% (w/v) polymer solution of RAFT PAN had a viscosity of 198 Pas while the equivalent control PAN polymer solution had a viscosity of 968 Pas at a shear rate of 1 s−1. Also, RAFT PAN polymer solutions had a longer Newtonian plateau than control PAN polymer solutions. This exhibits more liquid character in RAFT PAN polymer solutions than control PAN polymer solutions at same temperature and concentration. In dynamic tests, RAFT PAN polymer solutions gelled slower than their equivalent control PAN polymer solutions because of their longer polymer chain relaxation times. Slow gelling and higher liquid character in RAFT PAN polymer solutions can result in obtaining stronger and finer precursor fibers during wet spinning. Since RAFT PAN polymer solutions exhibit low viscosity and higher liquid character when compared to its equivalent control PAN at same concentration and temperature, these can allow a wider working window for wet spinning and can also allow higher solid content in the polymer solutions that remain easy to wet spin. This is expected to lead to compact and finer fibers with less voids and higher strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44273.
A High‐Temperature Order–Disorder Phase Transition Coupled With Conformational Change in the Hybrid Material [C6H13NH]2⋅ZnBr4
Authors: Khan Tariq , Asghar Muhammad Adnan , Sun Zhihua , Zeb Aurang , Li Lina , Sijie Liu , Zhao Sangen , Ji Chengmin , Luo Junhua 
Published: August 2016

AbstractA new high‐temperature, hybrid, phase‐transition material, 1‐methylpiperidinium tetrabromozincate (1), that shows a reversible transition at 345 K was synthesized. Differential scanning calorimetry and specific heat capacity measurements confirmed this reversible transformation with a large heat hysteresis of 25 K, which describes a typical first‐order phase transition in 1. The dielectric constant exhibited a steplike anomaly and showed high and low dielectric states in the high‐ and room‐temperature phases, respectively, and therefore, this hybrid might be considered as a potential switchable dielectric material. The variable‐temperature powder X‐ray diffraction patterns displayed remarkable shifts between the experimental patterns at the two different phases. Single‐crystal X‐ray diffraction analyses at various temperatures revealed that the origin of this transformation could be attributed to disordering of the bromine atoms in the anion and the nitrogen atom of the cation. The cation also assumed a conformational change, which was likely induced by the disordered nitrogen atom. The conformational onset of the transformation of the cation from a planar conformer into a relaxed chair also occurred upon decreasing the temperature below transition point; thus, the combined order–disorder and conformational change induced the structural transformation and the change in symmetry.
Heparin's solution structure determined by small‐angle neutron scattering
Authors: Rubinson Kenneth A. , Chen Yin , Cress Brady F. , Zhang Fuming , Linhardt Robert J. 
Published: August 2016

AbstractHeparin is a linear, anionic polysaccharide that is widely used as a clinical anticoagulant. Despite its discovery 100 years ago in 1916, the solution structure of heparin remains unknown. The solution shape of heparin has not previously been examined in water under a range of concentrations, and here is done so in D2O solution using small‐angle neutron scattering (SANS). Solutions of 10 kDa heparin—in the millimolar concentration range—were probed with SANS. Our results show that when sodium concentrations are equivalent to the polyelectrolyte's charge or up to a few hundred millimoles higher, the molecular structure of heparin is compact and the shape could be well modeled by a cylinder with a length three to four times its diameter. In the presence of molar concentrations of sodium, the molecule becomes extended to nearly its full length estimated from reported X‐ray measurements on stretched fibers. This stretched form is not found in the presence of molar concentrations of potassium ions. In this high‐potassium environment, the heparin molecules have the same shape as when its charges were mostly protonated at pD ≈ 0.5, that is, they are compact and approximately half the length of the extended molecules.