bluuebunny/crossref_metadata_2025 huggingface dataset:
Sex differences in tool use acquisition in bonobos (Pan paniscus)
Authors: Boose Klaree J. , White Frances J. , Meinelt Audra
Published: April 2013

All the great ape species are known tool users in both the wild and captivity, although there is great variation in ability and behavioral repertoire. Differences in tool use acquisition between chimpanzees and gorillas have been attributed to differing levels of social tolerance as a result of differences in social structure. Chimpanzees also show sex differences in acquisition and both chimpanzees and bonobos demonstrate a female bias in tool use behaviors. Studies of acquisition are limited in the wild and between species comparisons are complicated in captivity by contexts that often do not reflect natural conditions. Here we investigated tool use acquisition in a captive group of naïve bonobos by simulating naturalistic conditions. We constructed an artificial termite mound fashioned after those that occur in the wild and tested individuals within a social group context. We found sex differences in latencies to attempt and to succeed where females attempted to fish, were successful more quickly, and fished more frequently than males. We compared our results to those reported for chimpanzees and gorillas. Males across all three species did not differ in latency to attempt or to succeed. In contrast, bonobo and chimpanzee females succeeded more quickly than did female gorillas. Female bonobos and female chimpanzees did not differ in either latency to attempt or to succeed. We tested the social tolerance hypothesis by investigating the relationship between tool behaviors and number of neighbors present. We also compared these results to those reported for chimpanzees and gorillas and found that bonobos had the fewest numbers of neighbors present. The results of this study do not support the association between number of neighbors and tool behavior reported for chimpanzees. However, bonobos demonstrated a similar sex difference in tool use acquisition, supporting the hypothesis of a female bias in tool use inPan. Am. J. Primatol. 75:917–926, 2013. © 2013 Wiley Periodicals, Inc.
A commanding view of the Pacific: highland land use as viewed from Vainu'u, a multi‐component site on Tutuila Island, American Samoa
Authors: Eckert Suzanne L. , Welch Daniel R.
Published: April 2013

We discuss recent findings from Vainu'u (AS‐32‐016), a multi‐component highland site on Tutuila Island, American Samoa. Vainu'u is of interest for at least three reasons. First, as the earliest recorded highland site in the Samoan archipelago, this site changes our understanding of the Samoan cultural chronology. Second, as a ceramic‐bearing site, material culture recovered from Vainu'u complements assemblages recovered from lowland and coastal sites. Third, the post‐ceramic occupation observed at Vainu'u provides interesting insights into residential occupation during the Monument Building Period.
An optimal aircraft fleet management decision model under uncertainty
Authors: Khoo Hooi Ling , Teoh Lay Eng
Published: April 2013

Decision planning for an efficient fleet management is crucial for airlines to ensure a profit while maintaining a good level of service. Fleet management involves acquisition and leasing of aircraft to meet travelers' demand. Accordingly, the methods used in modeling travelers' demand are crucial as they could affect the robustness and accuracy of the solutions. Compared with most of the existing studies that consider deterministic demand, this study proposes a new methodology to find optimal solutions for a fleet management decision model by considering stochastic demand. The proposed methodology comes in threefold. First, a five‐step modeling framework, which is incorporated with a stochastic demand index (SDI), is proposed to capture the occurrence of uncertain events that could affect the travelers' demand. Second, a probabilistic dynamic programming model is developed to optimize the fleet management model. Third, a probable phenomenon indicator is defined to capture the targeted level of service that could be achieved satisfactorily by the airlines under uncertainty. An illustrative case study is presented to evaluate the applicability of the proposed methodology. The results show that it is viable to provide optimal solutions for the aircraft fleet management model. Copyright © 2013 John Wiley & Sons, Ltd.
SAR exposure from UHF RFID reader in adult, child, pregnant woman, and fetus anatomical models
Authors: Fiocchi Serena , Markakis Ioannis A. , Ravazzani Paolo , Samaras Theodoros
Published: April 2013

The spread of radio frequency identification (RFID) devices in ubiquitous applications without their simultaneous exposure assessment could give rise to public concerns about their potential adverse health effects. Among the various RFID system categories, the ultra high frequency (UHF) RFID systems have recently started to be widely used in many applications. This study addresses a computational exposure assessment of the electromagnetic radiation generated by a realistic UHF RFID reader, quantifying the exposure levels in different exposure scenarios and subjects (two adults, four children, and two anatomical models of women 7 and 9 months pregnant). The results of the computations are presented in terms of the whole‐body and peak spatial specific absorption rate (SAR) averaged over 10 g of tissue to allow comparison with the basic restrictions of the exposure guidelines. The SAR levels in the adults and children were below 0.02 and 0.8 W/kg in whole‐body SAR and maximum peak SAR levels, respectively, for all tested positions of the antenna. On the contrary, exposure of pregnant women and fetuses resulted in maximum peak SAR10 g values close to the values suggested by the guidelines (2 W/kg) in some of the exposure scenarios with the antenna positioned in front of the abdomen and with a 100% duty cycle and 1 W radiated power. Bioelectromagnetics. 34:443–452. © 2013 Wiley Periodicals, Inc.
Bayesian analysis of multivariate mixed models for a prospective cohort study using skew‐elliptical distributions
Authors: Kazemi Iraj , Mahdiyeh Zahra , Mansourian Marjan , Park Jongbae J.
Published: April 2013

Classical multivariate mixed models that acknowledge the correlation of patients through the incorporation of normal error terms are widely used in cohort studies. Violation of the normality assumption can make the statistical inference vague. In this paper, we propose aBayesian parametric approach by relaxing this assumption and substituting some flexible distributions in fitting multivariate mixed models. This strategy allows for the skewness and the heavy tails of error‐term distributions and thus makes inferences robust to the violation. This approach uses flexible skew‐elliptical distributions, including skewed, fat, or thin‐tailed distributions, and imposes the normal model as a special case. We use real data obtained from a prospective cohort study on the low back pain to illustrate the usefulness of our proposed approach.
Concise Synthesis and Biological Assessment of (+)‐Neopeltolide and a 16‐Member Stereoisomer Library of 8,9‐Dehydroneopeltolide: Identification of Pharmacophoric Elements
Authors: Fuwa Haruhiko , Kawakami Masato , Noto Kenkichi , Muto Takashi , Suga Yuto , Konoki Keiichi , Yotsu‐Yamashita Mari , Sasaki Makoto
Published: April 2013

We describe herein a concise synthesis of (+)‐neopeltolide, a marine macrolide natural product that elicits a highly potent antiproliferative activity against several human cancer cell lines. Our synthesis exploited the powerful bond‐forming ability and high functional group compatibility of olefin metathesis and esterification reactions to minimize manipulations of oxygen functionalities and to maximize synthetic convergency. Our findings include a chemoselective olefin cross‐metathesis reaction directed by H‐bonding, and a ring‐closing metathesis conducted under non‐high dilution conditions. Moreover, we developed a 16‐member stereoisomer library of 8,9‐dehydroneopeltolide to systematically explore the stereostructure–activity relationships. Assessment of the antiproliferative activity of the stereoisomers against A549 human lung adenocarcinoma, MCF‐7 human breast adenocarcinoma, HT‐1080 human fibrosarcoma, and P388 murine leukemia cell lines has revealed marked differences in potency between the stereoisomers. This study provides comprehensive insights into the structure–activity relationship of this important antiproliferative agent, leading to the identification of the pharmacophoric structural elements and the development of truncated analogues with nanomolar potency.
Abyssal connections of Antarctic Bottom Water in a Southern Ocean State Estimate
Authors: van Sebille Erik , Spence Paul , Mazloff Matthew R. , England Matthew H. , Rintoul Stephen R. , Saenko Oleg A.
Published: April 2013

Antarctic Bottom Water (AABW) is formed in a few locations around the Antarctic continent, each source with distinct temperature and salinity. After formation, the different AABW varieties cross the Southern Ocean and flow into the subtropical abyssal basins. It is shown here, using the analysis of Lagrangian trajectories within the Southern Ocean State Estimate (SOSE) model, that the pathways of the different sources of AABW have to a large extent amalgamated into one pathway by the time it reaches 31°S in the deep subtropical basins. The Antarctic Circumpolar Current appears to play an important role in the amalgamation, as 70% of the AABW completes at least one circumpolar loop before reaching the subtropical basins. This amalgamation of AABW pathways suggests that on decadal to centennial time scales, changes to properties and formation rates in any of the AABW source regions will be conveyed to all three subtropical abyssal basins.
Active blind thrusts beneath the Tokyo metropolitan area: Seismic hazards and inversion tectonics
Authors: Ishiyama Tatsuya , Sato Hiroshi , Kato Naoko , Nakayama Toshio , Abe Susumu
Published: April 2013

The Tokyo metropolitan area, underlain by Neogene and Quaternary sediments more than 5 km thick, is currently deformed by blind thrusts that could generate hazardous earthquakes. However, their little geomorphic expression and dense urbanization make understanding of folds produced above them and recent deformation highly elusive. Here we show subsurface geometries of several active blind thrusts beneath this highly urbanized area, based on tectonic landforms, high‐resolution seismic reflection data, and Quaternary stratigraphy. Deep seismic reflection profiles corroborate the notion that steeply dipping blind thrusts are reactivated normal faults originally formed by middle Miocene extensional tectonics. Despite very slow (less than 0.1 mm/yr) late Quaternary slip rates, our work suggests the presence of previously unrecognized faults that pose seismic hazards to Tokyo and outlying communities, highlighting the need for additional information to define recent slip rates, magnitude, and recurrence of past earthquakes on them.
Hyperpycnal plume‐derived fans in the Santa Barbara Channel, California
Authors: Warrick Jonathan A. , Simms Alexander R. , Ritchie Andy , Steel Elisabeth , Dartnell Pete , Conrad James E. , Finlayson David P.
Published: April 2013

Hyperpycnal gravity currents rapidly transport sediment across shore from rivers to the continental shelf and deep sea. Although these geophysical processes are important sediment dispersal mechanisms, few distinct geomorphic features on the continental shelf can be attributed to hyperpycnal flows. Here we provide evidence of large depositional features derived from hyperpycnal plumes on the continental shelf of the northern Santa Barbara Channel, California, from the combination of new sonar, lidar, and seismic reflection data. These data reveal lobate fans directly offshore of the mouths of several watersheds known to produce hyperpycnal concentrations of suspended sediment. The fans occur on an upwardly concave section of the shelf where slopes decrease from 0.04 to 0.01, and the location of these fans is consistent with wave‐ and auto‐suspending sediment gravity current theories. Thus, we provide the first documentation that the morphology of sediment deposits on the continental shelf can be dictated by river‐generated hyperpycnal flows.
WAITING TIME AND SOCIOECONOMIC STATUS—AN INDIVIDUAL‐LEVEL ANALYSIS
Authors: Monstad Karin , Engesæter Lars Birger , Espehaug Birgitte
Published: April 2013

Waiting time is a rationing mechanism that is used in publicly funded healthcare systems. From an equity viewpoint, it is regarded as preferable to co‐payments. However, long waits are an indication of poor quality of service. To our knowledge, this analysis is the first to benefit from individual‐level data from administrative registers to investigate the relationship between waiting time, income, and education. Furthermore, it makes use of an extensive set of medical information that serves as indicators of patient need. Differences in waiting time by socioeconomic status are detected. For men, there is a statistically highly significant negative association between income and waiting time, driven by men in the highest income group, which constitutes 12% of all men. More educated women, that is, those having an education above compulsory schooling, experience lower waiting time than their fellow sisters with the lowest level of education. Copyright © 2013 John Wiley & Sons, Ltd.
Dietary selenium supplementation modifies breast tumor growth and metastasis
Authors: Chen Yu‐Chi , Prabhu K. Sandeep , Das Arunangshu , Mastro Andrea M.
Published: April 2013

The survival rate for breast cancer drops dramatically once the disease progresses to the metastatic stage. Selenium (Se) is an essential micronutrient credited with having high anticancer and chemopreventive properties. In our study, we investigated if dietary Se supplementation modified breast cancer development in vivo. Three diets supplemented with sodium selenite, methylseleninic acid (MSA) or selenomethionine (SeMet), as well as a Se‐deficient and a Se‐adequate diet were fed to mice before mammary gland inoculation of 4T1.2 cells. The primary tumor growth, the numbers of cancer cells present in lungs, hearts, livers, kidneys and femurs and several proinflammatory cytokines were measured. We found that inorganic selenite supplementation provided only short‐term delay of tumor growth, whereas the two organic SeMet and MSA supplements provided more potent growth inhibition. These diets also affected cancer metastasis differently. Mice fed selenite developed the most extensive metastasis and had an increased incidence of kidney and bone metastasis. On the other hand, mice fed the SeMet diet showed the least amount of cancer growth at metastatic sites. The MSA diet also provided some protection against breast cancer metastasis although the effects were less significant than those of SeMet. The cytokine profiles indicated that serum levels of interlukin‐2, interleukin‐6, interferon γ and vascular endothelial growth factor were elevated in SeMet‐supplemented mice. There was no significant difference in tumor growth and the patterns of metastasis between the Se‐deficient and Se‐adequate groups. Our data suggest that organic Se supplementation may reduce/delay breast cancer metastasis, while selenite may exacerbate it.
Parameters for molecular dynamics simulations of iron‐sulfur proteins
Authors: Carvalho Alexandra T. P. , Teixeira, Ana F. S. , Ramos Maria J.
Published: April 2013

Iron‐sulfur proteins involved in electron transfer reactions have finely tuned redox potentials, which allow them to be highly efficient and specific. Factors such as metal center solvent exposure, interaction with charged residues, or hydrogen bonds between the ligand residues and amide backbone groups have all been pointed out to cause such specific redox potentials. Here, we derived parameters compatible with the AMBER force field for the metal centers of iron‐sulfur proteins and applied them in the molecular dynamics simulations of three iron‐sulfur proteins. We used density‐functional theory (DFT) calculations and Seminario's method for the parameterization. Parameter validation was obtained by matching structures and normal frequencies at the quantum mechanics and molecular mechanics levels of theory. Having guaranteed a correct representation of the protein coordination spheres, the amide H‐bonds and the water exposure to the ligands were analyzed. Our results for the pattern of interactions with the metal centers are consistent to those obtained by nuclear magnetic resonance spectroscopy (NMR) experiments and DFT calculations, allowing the application of molecular dynamics to the study of those proteins. © 2013 Wiley Periodicals, Inc.
Enzymatic hydrolysis of Norway spruce and sugarcane bagasse after treatment with 1‐allyl‐3‐methylimidazolium formate
Authors: Soudham Venkata Prabhakar , Gräsvik John , Alriksson Björn , Mikkola Jyri‐Pekka , Jönsson Leif J.
Published: April 2013

BACKGROUND

Enzymatic hydrolysis of cellulose in lignocellulosic materials suffers from slow reaction rates due to limited access to enzyme adsorption sites and to the high crystallinity of the cellulose. In this study, an attempt was made to facilitate enzymatic hydrolysis by pretreatment of cellulosic materials using the ionic liquid (IL) 1‐allyl‐3‐methylimidazolium formate ([Amim][HCO2]) under mild reaction conditions. The effect of the IL was compared with that of thermochemical pretreatment under acidic conditions.

RESULTS

The lignocellulosic substrates investigated were native and thermochemically pretreated Norway spruce and sugarcane bagasse. Microcrystalline cellulose (Avicel) was included for comparison. The IL treatments were performed in the temperature range 45–120 °C and, after regeneration and washing of the cellulosic substrates, enzymatic saccharification was carried out at 45 °C for 72 h. After 12 h of hydrolysis, the glucose yields from regenerated native spruce and sugarcane bagasse were up to nine times higher than for the corresponding untreated substrates. The results also show positive effects of pretreatment using [Amim][HCO2] on the hydrolysis of xylan and mannan.

Conclusion

The present work demonstrates that both native wood and agricultural residues are readily soluble in [Amim][HCO2] under gentle conditions, and that pretreatment with ionic liquids such as [Amim][HCO2] warrants further attention as a potential alternative to conventional pretreatment techniques. © 2013 Society of Chemical Industry
On the occurrence of equatorial F‐region irregularities during solar minimum using radio occultation measurements
Authors: Carter B. A. , Zhang K. , Norman R. , Kumar V. V. , Kumar Sushil
Published: April 2013

The technique of radio occultation (RO) is demonstrated to be a powerful tool for studying equatorial F‐region irregularities (EFIs) associated with equatorial plasma bubbles. The extensive 4.9 year RO dataset of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites was employed in this study and contains EFI observations under a wide variety of solar and geomagnetic conditions. From an analysis of the EFI occurrence dependence on season/longitude, it is found that the EFI occurrence statistics largely match those reported previously, with the exception of an equinoctial EFI occurrence maximum in the American sector that is absent from previous studies. It is revealed that this maximum is due to enhanced EFI occurrence near the South Atlantic anomaly, where EFIs are expected to be suppressed by particle precipitation. An investigation into the solar activity dependence of the EFI occurrence characteristics revealed significant increases in the range of local times and latitudes with solar activity for most longitude sectors and seasons. Finally, the EFI suppression and enhancement effects of storm‐time electric fields are also investigated using the COSMIC data.
Electrostatic Solitary Waves in the Solar Wind: Evidence for Instability at Solar Wind Current Sheets
Authors: Malaspina David M. , Newman David L. , Willson Lynn B. , Goetz Keith , Kellogg Paul J. , Kerstin Kris
Published: April 2013

A strong spatial association between bipolar electrostatic solitary waves (ESWs) and magnetic current sheets (CSs) in the solar wind is reported here for the first time. This association requires that the plasma instabilities (e.g., Buneman, electron two stream) which generate ESWs are preferentially localized to solar wind CSs. Distributions of CS properties (including shear angle, thickness, solar wind speed, and vector magnetic field change) are examined for differences between CSs associated with ESWs and randomly chosen CSs. Possible mechanisms for producing ESW‐generating instabilities at solar wind CSs are considered, including magnetic reconnection.
Search for Saturn's X‐ray aurorae at the arrival of a solar wind shock
Authors: Branduardi‐Raymont G. , Ford P. G. , Hansen K. C. , Lamy L. , Masters A. , Cecconi B. , Coates A. J. , Dougherty M. K. , Gladstone G. R. , Zarka P.
Published: April 2013

After a decade of observations, evidence for X‐ray auroral emission from Saturn has yet to be found. By analogy with processes known to take place on Jupiter, Saturnian X‐ray aurorae may be expected to be powered by charge exchange (CX) between energetic ions and the planet's atmospheric neutrals; if the ions are of solar origin, the emission should be brightest during episodes of enhanced solar wind (SW). We have explored this possibility by propagating SW parameters measured near the Earth to Saturn, and triggering X‐ray observations at the time SW enhancements were expected to reach the planet. This was done in April–May 2011 with the Chandra X‐ray Observatory, and we report on two observations carried out at the time when a significant SW disturbance reached Saturn, as indicated by Cassini magnetic field, plasma and radio measurements: variability is observed between the two Chandra datasets, but we do not find evidence for X‐ray brightening in the auroral regions. The variability can be explained by scattering of solar X‐rays in Saturn's atmosphere during an episode of solar X‐ray flaring. We conclude that the strength of any CX auroral X‐ray emission on Saturn was below Chandra's detectability threshold. By‐products of this investigation are stringent upper limits on the X‐ray emission of Titan and Enceladus. The Cassini measurements concurrent with the Chandra observations confirm and pinpoint temporally the arrival of the SW enhancement at Saturn. SW propagation predictions are a useful tool for investigating and interpreting the effects of SW interactions with planetary environments.
Fundamental properties of substorm time energetic electrons in the inner magnetosphere
Authors: Ebihara Y. , Tanaka T.
Published: April 2013

We studied fundamental properties of spatial‐temporal evolution of energetic electrons trapped in the inner magnetosphere (L ≤ 7.4) during an isolated substorm by using a four‐dimensional drift kinetic simulation under the time‐dependent electric and magnetic fields provided by a global magnetohydrodynamics (MHD) simulation. When the interplanetary magnetic field turns southward, both the potential and induction electric fields start to increase in the inner magnetosphere, resulting in a gradual injection of low‐energy electrons (≤51.9 keV) and deceleration of high‐energy electrons (≥114 keV). The deceleration of high‐energy electrons results in a decrease in the phase space density of the high‐energy electrons during the growth phase. After a while, an abrupt transition of phase state (a substorm onset) occurs in the magnetosphere, which triggers abrupt changes in the magnetosphere and ionosphere. The AL index decreases rapidly, and magnetic field lines become dipole‐like. The dipolarization does not proceed smoothly in the inner magnetosphere because of significant force imbalance between the J × B force and the grad P force. As a consequence, the electric field oscillates with a period of 2–3 min, resulting in multiple injections of the low‐energy electrons. The low‐ and high‐energy electrons are accelerated under the strong influence of the drift betatron and gyro betatron, so that the acceleration process is essentially nonlinear. Our simulation results suggest that the force‐induced processes play an essential role in the substorm‐associated redistribution of energetic particles in the inner magnetosphere.
Observations of polar cap flow channel and plasma sheet flow bursts during substorm expansion
Authors: Pitkänen T. , Aikio A. T. , Juusola L.
Published: April 2013

We present the first simultaneous observations of an enhanced polar cap flow impinging on the nightside polar cap boundary (PCB), two flow bursts in the plasma sheet and a conjugate ionospheric flow burst within the auroral oval. The ionospheric measurements on 3 September 2006 were made by the European Incoherent Scatter (EISCAT) radars and the magnetospheric measurements by the four Cluster spacecraft. In the end of a substorm growth phase, EISCAT measured a channel of enhanced equatorward plasma flow within the polar cap, which was about 1° wide in latitude and drifted slowly equatorward. During the substorm expansion phase, the PCB started to contract poleward. The interaction between the equatorward drifting polar cap flow channel and the poleward contracting PCB took 2–3 min. During this time, the F‐region electron temperature was elevated at the PCB, which is interpreted as a possible signature of an auroral poleward boundary intensification (PBI). After that, enhanced equatorward flows were measured inside the auroral oval by EISCAT. During this period, the Cluster satellites measured two fast earthward flow bursts in the plasma sheet, which were associated with dipolarizations of the magnetic field, depletions in plasma density, and return flows. We suggest that the second flow burst in the plasma sheet represents the same flow burst that is seen in the ionosphere by EISCAT and propose that the plasma sheet flow bursts were triggered by the enhanced flow structure on open polar cap field lines. The suggestion is in line with Lyons et al. (2011).
Aurora on Ganymede
Authors: McGrath Melissa A. , Jia Xianzhe , Retherford Kurt , Feldman Paul D. , Strobel Darrell F. , Saur Joachim
Published: April 2013

We present four sets of ultraviolet images of Ganymede acquired with the Hubble Space Telescope (HST) from 1998 to 2007, all of which show auroral emission from electron excited atomic oxygen. The three different hemispheres of Ganymede captured in the observations show strikingly different emission morphologies. Ultraviolet emission at 1356 Å is brightest at relatively high latitude on the orbital trailing (upstream plasma) hemisphere and in an auroral oval that extends to as low as ~10°N latitude on the orbital leading (downstream plasma) hemisphere. Two sets of images of the Jupiter‐facing hemisphere acquired at nearly the same sub‐Earth longitude but separated by ~4 years show very similar emission morphology that is consistent with the pattern of emission seen in the upstream and downstream images: the emission is at high latitude in the upstream quadrant and at low latitude in the downstream quadrant. This implies that the large‐scale, nominal “auroral oval” on Ganymede is apparently quite stable with time, despite significant brightness fluctuations within the overall stable pattern during the 10–30 min time scale between individual images. The overall emission morphology appears to be driven primarily by the strong Jovian magnetospheric plasma interaction with Ganymede and does not appear to be strongly influenced by the orientation of the background Jovian magnetic field. The observed auroral oval pattern is reasonably well matched by a magnetohydrodymanic (MHD) model optimized to fit the Galileo magnetic field measurements near Ganymede. The location of the auroral oval from these data provides a reasonable match to the location of the well‐defined visible boundary of the Ganymede polar cap except in the northern, leading hemisphere.
Inner radiation belt particle acceleration and energy structuring by drift resonance with ULF waves during geomagnetic storms
Authors: Sauvaud J.‐A. , Walt M. , Delcourt D. , Benoist C. , Penou E. , Chen Y. , Russell C. T.
Published: April 2013

Geomagnetic storms are frequently associated with the formation of multiple bands of energetic electrons inside the inner radiation belt at L = 1.1–1.9 and with prominent energy structures of protons inside the slot region at L = 2.2–3.5. These structures typically from 100 keV up to the MeV range result from coherent interactions of energetic particles with quasi‐monochromatic ultra‐low frequency (ULF) waves. These waves are induced by magnetospheric changes due to the arrival of dense solar material and related nightside injections of particles from the outer magnetosphere that destabilize field lines in the inner magnetosphere down to L = 1.1. Using low‐altitude data from the polar orbiting Demeter spacecraft, we perform case and statistical studies of these structures. We show that with such a spacecraft, these structures are best seen near the South Atlantic Anomaly because of lowering of the belt particle mirror point. As evidenced from ground measurements, energy bands are associated with quasi‐sinusoidal ULF Pc5 and Pc4 waves with periods in the 1000 s range for L = 1.1–1.9 and in the 60 s range for L = 2.2–3.5. Numerical simulations of the coherent drift resonance of energetic particles with ultra‐low frequency waves show how the particles are accelerated and how the observed structures build up.
Long‐term variations in solar wind velocity and radiation belt electrons
Authors: Reeves Geoff , Morley Steve , Cunningham Greg
Published: April 2013

In this paper we analyze the relationship between yearly variations in MeV radiation belt electron fluxes and solar wind velocity (Vsw). We find that the long‐term trends have properties that are important for physical understanding of solar wind‐magnetosphere coupling processes and, potentially, for improvements of short‐term space weather forecasts. A statistical analysis of solar wind velocity shows that years with high average solar wind velocity are not high simply due to a larger number of days with high Vsw. Rather the entire distribution (median and percentiles) shifts along with the mean Vsw. Similar behavior is seen in the MeV geosynchronous electron fluxes. By subtracting out a 365 day running average baseline, we show that the distribution of log fluxes around the mean is remarkably stable from year to year within a solar cycle and from one solar cycle to another. In contrast, the long‐term trends in the baseline show significant changes from year to year and from one solar cycle to another suggesting that solar wind coupling to radiation belt fluxes is not constant but varies over long, as well as short, time scales. In some epicycles, the mean flux is strongly dependent on Vsw while in others the dependence is weak. Similarly, a given average Vsw may produce high average fluxes in one epicycle and low average fluxes in another. Future study of these epicycles and the relative variations within them may improve both physical understanding of solar wind‐magnetosphere coupling and space weather forecasting.
Ion entry into the wake behind a nonmagnetized obstacle in the solar wind: Two‐dimensional particle‐in‐cell simulations
Authors: Nakagawa Tomoko
Published: April 2013

The ion entry into the wake behind an obstacle in the solar wind is studied using two‐dimensional, electromagnetic full‐particle simulations. A significant difference is found between the number of ions and electrons in the near wake, mainly due to the negative electric charge on the nightside surface of the obstacle. The ion acceleration toward the void is observed far from the position of the rarefaction wave expected in the self‐similar solution. The velocity profile of the ions in the wake approaches the self‐similar solution with finite ion temperature asymptotically until they reach the distance where the ions from both sides of the wake meet. The ions that entered from both sides are accelerated in the opposite directions. They raise the ion temperature and the pressure in the center of the wake, although each component remains cool when treated separately. The electron temperature appears nearly constant, except for the edge of the complete void of electrons. The large‐scale obstacle and a slow solar wind are favorable conditions for a detection of well‐accelerated ions near the nightside surface of the obstacle, because they have enough time to accelerate. The direction of the electric field in the wake seems consistent with the gradient of the electron pressure.
Linear scaling and periodicity on the measures of global and local scale complexities of total electron content dynamics
Authors: Kumar C. V. Anil , Eapen Suja
Published: April 2013

In this paper, we compare the local and global dynamics of total electron content (TEC) by analyzing Lyapunov exponents and correlation dimensions. The internal structure of the underlying system is studied using TEC data from the solar minimum years 2007–2008. The mutual information, false nearest neighbors, and space‐time separation of both local and global snapshots are estimated and analyzed. It indicates that although the internal dynamics changes with season, the pattern of variation over the seasons remains identical for both the years, suggesting that the characteristics of these changes might be predictable. We report the evidence of a linear scaling with slope 0.00187 and a periodicity with period of 1 year on measures of global and local scale complexities of TEC dynamics. This behavior appears to be a universal phenomenon unaffected by change of cycles and amount of information influencing the complexity, since they are almost constant over the 2 years. The global Lyapunov exponent increases linearly over a year, whereas the local Lyapunov exponent increases up to the middle of the year, attains greatest local complexity, and then decreases. This suggests that local prediction is more reliable than the global one. The estimated invariants characterize the complex dynamics as it evolve from local time to global time and also provide information to the system's heterogeneity. The features such as presence of multiple attractors, linear scaling, and nearly regular seasonal periodicity may have practical consequences and could yield insights into the internal dynamics of TEC and the modeling of its variations.
Equatorial ionospheric electrodynamic perturbations during Southern Hemisphere stratospheric warming events
Authors: Olson M. E. , Fejer B. G. , Stolle C. , Lühr H. , Chau J. L.
Published: April 2013

We use ground‐based and satellite measurements to examine, for the first time, the characteristics of equatorial electrodynamic perturbations measured during the 2002 major and 2010 minor Southern Hemisphere sudden stratospheric warming (SSW) events. Our data suggest the occurrence of enhanced quasi 2 day fluctuations during the 2002 early autumnal equinoctial warming. They also show a moderately large multi‐day perturbation pattern, resembling those during arctic SSW events, during 2002 late equinox, as the major SSW was weakening. We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during arctic SSW events.
Simulated energetic particle transport in the interplanetary space: The Palmer consensus revisited
Authors: Tautz R. C. , Shalchi A.
Published: April 2013

Reproducing measurements of the scattering mean free paths for energetic particles propagating through the solar system has been a major problem in space physics. The pioneering work of Bieber et al. (1994) provided a theoretical explanation of such observations, which, however, was based on assumptions such as the questionable hypothesis that quasi‐linear theory is correct for parallel diffusion. By employing a hybrid plasma‐wave/magnetostatic turbulence model, a test‐particle code is used to investigate the scattering of energetic particles. The results show excellent agreement with solar wind observations.
Empirical relationship between electron precipitation and far‐ultraviolet auroral emissions from DMSP observations
Authors: Sotirelis Thomas , Korth Haje , Hsieh Syau‐Yun , Zhang Yongliang , Morrison Daniel , Paxton Larry
Published: April 2013

Auroral emissions observed in the far‐ultraviolet wavelength range are compared with measurements of the coincident precipitating electrons and ions that produce the emissions in a large‐scale correlative study. The auroral emissions and particle precipitation are observed with the Special Sensor Ultraviolet Spectrographic Imager and SSJ5 detectors, respectively, both onboard the DMSP F16 satellite. Coincident observations along the same magnetic field line in the Northern Hemisphere are assembled from two consecutive winters (during 2005–2007). A numerical fit to 27,922 coincident observations provides an empirical relationship between the electron energy flux and the intensity of Lyman‐Birge‐Hopfield long emissions, JEe = 4.90 ⋅108 (eV s–1 sr–1 cm–2)/R ILBHL (valid in the absence of significant ion fluxes: JEe > 10 JEion). A fit to 1308 coincident observations provides the relationship between the average electron energy and the Lyman‐Birge‐Hopfield short to Lyman‐Birge‐Hopfield long emission ratio,  = 19.6 keV exp(–2.34 ILBHS / ILBHL) (valid from 3 to 19.6 keV). These resulting empirical relationships permit the energy flux and average energy of precipitating electrons to be inferred from far‐ultraviolet imagery, in the absence of significant ion precipitation.
Frequency drift of Saturn chorus emission compared to nonlinear theory
Authors: Menietti J. D. , Katoh Y. , Hospodarsky G. B. , Gurnett D. A.
Published: April 2013

The fine structure of nonlinear drifting‐frequency chorus is observed at Saturn by the Cassini Radio and Plasma Wave Investigation. During a high‐inclination orbit in which Cassini is at near‐constant L‐shell within about 10° of the magnetic equator, moderately intense nonlinear chorus is observed. Cassini observed a region of intense chorus and large bandwidth a few degrees on either side of the magnetic equator, with lower intensities and bandwidths observed nearest the magnetic equator. Using the observed plasma wave spectra and electron phase space distribution, we have measured plasma parameters within or near the chorus generation region and evaluated the theoretical value of the frequency sweep rate, ∂f/∂t, based on the nonlinear wave growth theory of Omura et al. and the backward wave oscillator theory of Trakhtengerts. Both theories produce rates that are within a factor of 2 of the observed values, but the nonlinear wave growth theory values are closer to the observations for the cases examined. The work presented is consistent with nonlinear theory in the generation of chorus, but also reveals a distinct region of weaker or linear chorus growth nearest to the magnetic equator at Saturn.
Simultaneous observations of quasi‐periodic ELF/VLF wave emissions and electron precipitation by DEMETER satellite: A case study
Authors: Hayosh M. , Pasmanik D. L. , Demekhov A. G. , Santolik O. , Parrot M. , Titova E. E.
Published: April 2013

We present results of case studies of quasi‐periodic (QP) ELF/VLF hiss emissions detected onboard the DEMETER satellite. Three events with simultaneous periodic modulation in VLF wave intensity and energetic electron precipitation are found. In each event we observe exact coincidence of one or two busts of VLF wave intensity with energetic electron precipitation peaks. To our knowledge, such observations made onboard satellites have not been reported earlier. All events are observed at fairly quiet geomagnetic conditions (Kp <3). The dynamic spectrum of the VLF waves in these QP events was characterized by a regular frequency increase in each burst, and the repetition period was less than or about 20 s. These features allow us to suggest that the observed events belong to the QP2‐class, i.e., events which are not associated with geomagnetic pulsations. We also analyze energetic electron data from NOAA‐17 spacecraft which has helio‐synchronous circular orbit similar to DEMETER spacecraft and measured in the same region of the magnetosphere within 30 min for the analyzed events. NOAA‐17 data confirm that the QP emissions were detected by DEMETER in the region of isotropization of energetic electrons, which is typically associated with the development of the cyclotron instability. Modulation of electron flux with a period close to the QP emission period is observed in two events. Based on the observed correlation between bursts of wave intensity and energetic particle flux, we estimate the location and spatial extent of the source region for QP emissions.
The ionospheric Sq current system obtained by spherical harmonic analysis
Authors: Stening R. J. , Winch D. E.
Published: April 2013

An earlier comprehensive analysis of geomagnetic tides by Winch is revisited to display changes in the current systems with season and longitude. The data used come from the quiet Sun years 1964–1965. We choose to present some total equivalent current systems, being the sum of the external and internal parts derived in the spherical harmonic analysis. The latitudes and local times of the current system foci are generally in agreement with other workers. The amplitudes of the current system vortices follow an annual variation with maximum in summer. The longitude variations of the vortex amplitudes vary as the inverse of the magnetic field strength at both equinoxes but have different variations at the solstices. Other longitude maxima which have been reported in the equatorial electrojet intensity were not found. We examine in detail the “invasions” of the summer current systems across the equator, identifying these as signatures of field‐aligned currents (FACs). The tilting of current contours with respect to the equator is interpreted as being due to midday FACs. As others have found, the identification of afternoon FACs is more difficult. The seasonal swap‐over of FAC directions occurs not in September but in October–November.
GPS phase scintillation associated with optical auroral emissions: First statistical results from the geographic South Pole
Authors: Kinrade Joe , Mitchell Cathryn N. , Smith Nathan D. , Ebihara Yusuke , Weatherwax Allan T. , Bust Gary S.
Published: April 2013

Ionospheric irregularities affect the propagation of Global Navigation Satellite System (GNSS) signals, causing radio scintillation. Particle precipitation from the magnetosphere into the ionosphere, following solar activity, is an important production mechanism for ionospheric irregularities. Particle precipitation also causes the aurorae. However, the correlation of aurorae and GNSS scintillation events is not well established in literature. This study examines optical auroral events during 2010–2011 and reports spatial and temporal correlations with Global Positioning System (GPS) L1 phase fluctuations using instrumentation located at South Pole Station. An all‐sky imager provides a measure of optical emission intensities ([OI] 557.7 nm and 630.0 nm) at auroral latitudes during the winter months. A collocated GPS antenna and scintillation receiver facilitates superimposition of auroral images and GPS signal measurements. Correlation statistics are produced by tracking emission intensities and GPS L1 σφ indices at E and F‐region heights. This is the first time that multi‐wavelength auroral images have been compared with scintillation measurements in this way. Correlation levels of up to 74% are observed during 2–3 hour periods of discrete arc structuring. Analysis revealed that higher values of emission intensity corresponded with elevated levels of σφ. The study has yielded the first statistical evidence supporting the previously assumed relationship between the aurorae and GPS signal propagation. The probability of scintillation‐induced GPS outages is of interest for commercial and safety‐critical operations at high latitudes. Results in this paper indicate that image databases of optical auroral emissions could be used to assess the likelihood of multiple satellite scintillation activity.
Statistical comparison of isolated and non‐isolated auroral substorms
Authors: Liou Kan , Newell Patrick T. , Zhang Yong‐Liang , Paxton Larry J.
Published: April 2013

The present study compares isolated and non‐isolated substorms in terms of their global morphology and energy deposition. The analysis is based on a list of geomagnetic substorm onsets identified with magnetometer data from SuperMAG and published previously by Newell and Gjerlove (2011a). Isolated substorms are defined as those with separation of two consecutive onsets no less than 3 h. The auroral data are obtained from the global ultraviolet imager (GUVI) on board the TIMED satellite and are rebinned into typical magnetic latitude‐magnetic local time maps. The auroral maps are then averaged in 1 min intervals to show the dynamic change of the aurora. The three phases of the substorm are clearly demonstrated in both isolated and non‐isolated substorms. However, there are noticeable differences between the two types of substorms: (1) While the nighttime auroral power for both types of substorms slightly increases in the growth phase, isolated (non‐isolated) substorms are associated with smaller (greater) nighttime auroral power. (2) In the expansion phase, isolated substorms are associated with greater and more explosive energy release than non‐isolated substorms. (3) The time for the recovery phase is ~2 times longer for isolated than for non‐isolated substorms. (4) The winter‐to‐summer auroral power ratio is approximately constant throughout the three substorm phases and the ratio is larger for isolated (~30%) than that for non‐isolated (~10%) substorms. It is also found that the polar cap area increases during the growth phase until ~10 min prior to the magnetic substorm onset and decreases rapidly thereafter. The decrease is found to result from the closure of the nightside polar cap associated with substorm expansion. It is found that the observed differences between the two types of substorms simply reflect the differences in the solar wind and EUV drivers. Thus, we conclude that there is no intrinsic difference between isolated and non‐isolated substorms in terms of auroral energy release and subsequent auroral power decay.