scholarly journals Limitations of Hall MHD as a model for turbulence in weakly collisional plasmas

2009 ◽  
Vol 16 (2) ◽  
pp. 219-232 ◽  
Author(s):  
G. G. Howes
Keyword(s):  
Solar Wind ◽  
Ion Temperature ◽  
Wide Range ◽  
Spurious Wave ◽  
Hall Mhd ◽  
Shed Light ◽  
Dissipation Range ◽  
Linear Kinetic ◽  
Kinetic Alfvén Waves ◽  
Wave Modes

Abstract. The limitations of Hall MHD as a model for turbulence in weakly collisional plasmas are explored using quantitative comparisons to Vlasov-Maxwell kinetic theory over a wide range of parameter space. The validity of Hall MHD in the cold ion limit is shown, but spurious undamped wave modes exist in Hall MHD when the ion temperature is finite. It is argued that turbulence in the dissipation range of the solar wind must be one, or a mixture, of three electromagnetic wave modes: the parallel whistler, oblique whistler, or kinetic Alfvén waves. These modes are generally well described by Hall MHD. Determining the applicability of linear kinetic damping rates in turbulent plasmas requires a suite of fluid and kinetic nonlinear numerical simulations. Contrasting fluid and kinetic simulations will also shed light on whether the presence of spurious wave modes alters the nonlinear couplings inherent in turbulence and will illuminate the turbulent dynamics and energy transfer in the regime of the characteristic ion kinetic scales.

Non-adiabatic interaction of ions with solar wind discontinuities

2020 ◽  
Author(s):  
Alexander Vinogradov ◽  
Anton Artemyev ◽  
Ivan Vasko ◽  
Alexei Vasiliev ◽  
Anatoly Petrukovich
Keyword(s):  
Solar Wind ◽  
Observational Data ◽  
Solar Wind Plasma ◽  
Theoretical Models ◽  
High Amplitude ◽  
Small Scale ◽  
Ion Scattering ◽  
Ion Temperature ◽  
Wide Range ◽  
Radial Evolution

<p>According to Helios, Ulysses, New Horizons measurements at a wide range of distances from the Sun, radial evolution of solar wind ion temperature significantly deviates from the adiabatic expansion model:  additional heating of the solar wind plasma is required to describe observational data. Solution of the solar wind heating problem is extremely important both for understanding the structure of the heliosphere and for adequately describing the atmospheres of distant stars. Solar wind magnetic field is turbulent and this turbulence is dominated by numerous small-scale high-amplitude coherent structures – such as quasi-1D discontinuities. Modern theoretical models predict that quasi-1D discontinuities can play important role in solar wind heating. We collected the statistics of MMS observations of thin quasi-1D discontinuities in the solar wind to reveal their characteristics. Analyzing observational data, we construct the discontinuity model and use it to consider non-adiabatic interaction of ions with solar wind discontinuities. We mainly focus on discontinuity roles in solar wind ion scattering and thermalization. This presentation shows how discontinuity configuration affects the scattering rates.</p>

scholarly journals Observational tests of the properties of turbulence in the Very Local Interstellar Medium

2010 ◽  
Vol 17 (6) ◽  
pp. 785-793 ◽  
Author(s):  
S. R. Spangler ◽  
A. H. Savage ◽  
S. Redfield
Keyword(s):  
Solar Wind ◽  
Interstellar Medium ◽  
Large Scale ◽  
Larmor Radius ◽  
Published Data ◽  
Local Interstellar Medium ◽  
Ion Temperature ◽  
Velocity Fluctuations ◽  
Single Temperature ◽  
Wide Range

Abstract. The Very Local Interstellar Medium (VLISM) contains clouds which consist of partially-ionized plasma. These clouds can be effectively diagnosed via high resolution optical and ultraviolet spectroscopy of the absorption lines they form in the spectra of nearby stars. Information provided by these spectroscopic measurements includes values for ξ, the root-mean-square velocity fluctuation due to turbulence in these clouds, and T, the ion temperature, which may be partially determined by dissipation of turbulence. We consider whether this turbulence resembles the extensively studied and well-diagnosed turbulence in the solar wind and solar corona. Published observations are used to determine if the velocity fluctuations are primarily transverse to a large-scale magnetic field, whether the temperature perpendicular to the large scale field is larger than that parallel to the field, and whether ions with larger Larmor radii have higher temperatures than smaller gyroradius ions. We ask if the spectroscopically-deduced parameters such as ξ and T depend on the direction on the sky. We also consider the degree to which a single temperature T and turbulence parameter ξ account for the spectral line widths of ions with a wide range of masses. A preliminary examination of the published data shows no evidence for anisotropy of the velocity fluctuations or temperature, nor Larmor radius-dependent heating. These results indicate differences between solar wind and Local Cloud turbulence. Possible physical reasons for these differences are discussed.

scholarly journals THEMIS satellite observations of hot flow anomalies at Earth's bow shock

2017 ◽  
Vol 35 (3) ◽  
pp. 443-451 ◽  
Author(s):  
Christina Chu ◽  
Hui Zhang ◽  
David Sibeck ◽  
Antonius Otto ◽  
QiuGang Zong ◽  
...  
Keyword(s):  
Solar Wind ◽  
Energy Density ◽  
Temperature Increase ◽  
Time History ◽  
Bow Shock ◽  
Local Times ◽  
Kinetic Energy Density ◽  
Ion Temperature ◽  
Wide Range ◽  
Earth’S Bow Shock

Abstract. Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and also as regular or spontaneous hot flow anomalies (SHFAs). The dataset has 17 young SHFAs, 49 mature SHFAs, 15 young HFAs, and 55 mature HFAs. They span a wide range of magnetic local times (MLTs) from approximately 7 to 16.5 MLT. The largest ratio of solar wind to HFA core density occurred near dusk and at larger distances from the bow shock. In this study, HFAs and SHFAs were observed up to 6.3 RE and 6.1 RE (Earth radii), respectively, upstream from the model bow shock. HFA–SHFA occurrence decreases with distance upstream from the bow shock. HFAs of the highest event core ion temperatures were not seen at the flanks. The ratio of HFA ion temperature increase to HFA electron temperature increase is highest around 12 MLT and slightly duskward. For SHFAs, (Tihfa∕Tisw)/(Tehfa∕Tesw) generally increased with distance from the bow shock. Both mature and young HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. HFAs occur most preferentially for solar wind speeds from 550 to 600 km s−1. The correlation coefficient between the HFA increase in thermal energy density from solar wind values and the decrease in kinetic energy density from solar wind values is 0.62. SHFAs and HFAs do not show major differences in this study.

Sentence-Based Experience Logging in New Hearing Aid Users

2020 ◽  
Vol 29 (3S) ◽  
pp. 631-637
Author(s):  
Katja Lund ◽  
Rodrigo Ordoñez ◽  
Jens Bo Nielsen ◽  
Dorte Hammershøi
Keyword(s):  
Hearing Aid ◽  
Patient Experiences ◽  
Online Tool ◽  
Rehabilitation Process ◽  
Hearing Rehabilitation ◽  
Clinical Observations ◽  
Hearing Aid Use ◽  
Wide Range ◽  
Insight Into ◽  
Shed Light

Purpose The aim of this study was to develop a tool to gain insight into the daily experiences of new hearing aid users and to shed light on aspects of aided performance that may not be unveiled through standard questionnaires. Method The tool is developed based on clinical observations, patient experiences, expert involvement, and existing validated hearing rehabilitation questionnaires. Results An online tool for collecting data related to hearing aid use was developed. The tool is based on 453 prefabricated sentences representing experiences within 13 categories related to hearing aid use. Conclusions The tool has the potential to reflect a wide range of individual experiences with hearing aid use, including auditory and nonauditory aspects. These experiences may hold important knowledge for both the patient and the professional in the hearing rehabilitation process.

scholarly journals The Location of Magnetic Reconnection at Earth’s Magnetopause

2021 ◽  
Vol 217 (3) ◽  
Author(s):  
K. J. Trattner ◽  
S. M. Petrinec ◽  
S. A. Fuselier
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Ion Beams ◽  
Review Article ◽  
Observational Evidence ◽  
Magnetic Shear ◽  
General Direction ◽  
Shear Model ◽  
Wide Range

AbstractOne of the major questions about magnetic reconnection is how specific solar wind and interplanetary magnetic field conditions influence where reconnection occurs at the Earth’s magnetopause. There are two reconnection scenarios discussed in the literature: a) anti-parallel reconnection and b) component reconnection. Early spacecraft observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection X-line location with respect to the spacecraft. An improved view of the reconnection location at the magnetopause evolved from ionospheric emissions observed by polar-orbiting imagers. These observations and the observations of accelerated ion beams revealed that both scenarios occur at the magnetopause. Improved methodology using the time-of-flight effect of precipitating ions in the cusp regions and the cutoff velocity of the precipitating and mirroring ion populations was used to pinpoint magnetopause reconnection locations for a wide range of solar wind conditions. The results from these methodologies have been used to construct an empirical reconnection X-line model known as the Maximum Magnetic Shear model. Since this model’s inception, several tests have confirmed its validity and have resulted in modifications to the model for certain solar wind conditions. This review article summarizes the observational evidence for the location of magnetic reconnection at the Earth’s magnetopause, emphasizing the properties and efficacy of the Maximum Magnetic Shear Model.

scholarly journals Beyond cultural and geographical proximity: delving into the factors that influence the dynamics of academic relationships between students in higher education

2021 ◽  
Author(s):  
José-Vicente Tomás-Miquel ◽  
Jordi Capó-Vicedo
Keyword(s):  
University Students ◽  
Academic Research ◽  
Past Research ◽  
Academic Networks ◽  
Level Data ◽  
Wide Range ◽  
Specific Stage ◽  
The University ◽  
Proximity Dimensions ◽  
Shed Light

AbstractScholars have widely recognised the importance of academic relationships between students at the university. While much of the past research has focused on studying their influence on different aspects such as the students’ academic performance or their emotional stability, less is known about their dynamics and the factors that influence the formation and dissolution of linkages between university students in academic networks. In this paper, we try to shed light on this issue by exploring through stochastic actor-oriented models and student-level data the influence that a set of proximity factors may have on formation of these relationships over the entire period in which students are enrolled at the university. Our findings confirm that the establishment of academic relationships is derived, in part, from a wide range of proximity dimensions of a social, personal, geographical, cultural and academic nature. Furthermore, and unlike previous studies, this research also empirically confirms that the specific stage in which the student is at the university determines the influence of these proximity factors on the dynamics of academic relationships. In this regard, beyond cultural and geographic proximities that only influence the first years at the university, students shape their relationships as they progress in their studies from similarities in more strategic aspects such as academic and personal closeness. These results may have significant implications for both academic research and university policies.

scholarly journals Messianism, rationalism and inter-Asian connections: The Majalis-i Jahangiri (1608–11) and the socio-intellectual history of the Mughal ‘ulama

2017 ◽  
Vol 54 (3) ◽  
pp. 317-338 ◽  
Author(s):  
Corinne Lefèvre
Keyword(s):  
Central Asia ◽  
Intellectual History ◽  
State Building ◽  
Specific Role ◽  
Wide Range ◽  
History Of ◽  
Muslim Intellectuals ◽  
Shed Light

Relying on the Majalis-i Jahangiri (1608–11) by ʿAbd al-Sattar b. Qasim Lahauri, this essay explores some of the discussions the Mughal Emperor Jahangir (r. 1605–27) conducted with a wide range of scholars, from Brahmans and ʿulama to Jesuit padres and Jewish savants. By far the most numerous, the debates bearing on Islam and involving Muslim intellectuals are especially significant on several accounts. First, because they illuminate how, following in the steps of his father Akbar (r. 1556–605), Jahangir was able to conciliate his messianic claims with a strong engagement with reason and to turn this combination into a formidable instrument for confession and state building. These conversations also provide promising avenues to think afresh the socio-intellectual history of the Mughal ʿulama inasmuch as they capture the challenges and adjustments attendant on imperial patronage, depict the jockeying for influence and positions among intellectuals (particularly between Indo-Muslim and Iranian lettrés), and shed light on relatively little known figures or on unexplored facets of more prominent individuals. In addition, the specific role played by scholars hailing from Iran—and, to a lesser extent, from Central Asia—in the juridical-religious disputes of the Indian court shows how crucial inter-Asian connections and networks were in the fashioning of Mughal ideology but also the ways in which the ongoing flow of émigré ʿulama was disciplined before being incorporated into the empire.

scholarly journals Book Review: Islam: A Worldwide Encyclopedia

2017 ◽  
Vol 57 (2) ◽  
pp. 151
Author(s):  
Paul Fehrmann
Keyword(s):  
International Law ◽  
Common Ground ◽  
Controversial Issues ◽  
Islamic Studies ◽  
Law And Politics ◽  
Wide Range ◽  
Senior Researcher ◽  
Shed Light ◽  
Academic Debate

It is clear that the world of Islam is profoundly important, and also that there are wide and conflicting views on Islam today. Similarly, it seems clear that we should pursue efforts to promote the understanding of Islam. In response, a goal of the four volume Islam: A Worldwide Encyclopedia (IAWE) is to give “basic information on Islam” and to “shed light” on “controversial issues” (xxvii). In his opening comments, the editor, a Professor of International Law and Politics at Eskişehir Osmangazi University and Senior Researcher at the Wise Men Center for Strategic Research in Turkey, notes that there have been “a wide range of different interpretations and variations of Islam throughout history” (xxvii). He suggests that Muslims need to revive the “strong tradition of academic debate” that was integral to Islamic studies “in early decades of Islam,” and affirms support for the “diverse and plural nature of contemporary Islamic scholarship” (xxviii). At the same time, he is concerned that “disputed issues” may lead to “biases and stereotypes in the minds of Western people,” and hopes that this new resource can both “contribute to the pursuit of a common ground” between those of different faiths, and help a Western audience become more familiar with what Islam has to offer (xxviii).

scholarly journals Ceramics as the conveyance of art

2017 ◽  
Vol 6 (4) ◽  
pp. 133-139
Author(s):  
Olcay Boratav
Keyword(s):  
Time Perspective ◽  
Background Knowledge ◽  
Original Structure ◽  
The Arts ◽  
Art Form ◽  
Wide Range ◽  
Different Shapes ◽  
Different Cultures ◽  
Greek Pottery ◽  
Shed Light

AbstractThe concept of art has varied according to space and time perspective in each and every period and it has emerged in different forms in every culture. Artists or designers produce a wide range of forms with different materials representing the period and culture while creating their ceramics. Ceramics symbolizes a thousand-year-old endeavor as well as being considered as one of the arts. It has shed light on the history in different shapes and cultures in addition to undertaking the task of conveyance of art with original structure and formal style in the works of art. Ceramics makes identity differences thanks to background knowledge, form and decorative techniques and originality. Art is not for society’s sake; it aims to relieve the tension, to satisfy pleasure, to enable people to see and hear, to use and to evaluate. Different cultures have generated new styles in their ceramics by integrating creativity into their own traditions and techniques as well as interacting with Mayan vases and pots, Greek pottery, Anatolian ceramics and tiles. Some of these impacts have been so profound in ceramics that they have been passed on from generation to generation.This paper seeks to address to the following questions: How was ceramics used in different cultures and periods with composition features such as form, decoration, motif and figure; and how has it undertaken the task of conveyance of art by investigating what features they have. Keywords: ceramics, art, conveyance of art, form, figure.

scholarly journals Seeking Practical CDCL Insights from Theoretical SAT Benchmarks

2018 ◽  
Author(s):  
Jan Elffers ◽  
Jesús Giráldez-Cru ◽  
Stephan Gocht ◽  
Jakob Nordström ◽  
Laurent Simon
Keyword(s):  
Systematic Study ◽  
Boolean Satisfiability ◽  
Proof System ◽  
Sat Solvers ◽  
Proof Search ◽  
Wide Range ◽  
Clause Learning ◽  
Resolution Proof ◽  
Shed Light

Over the last decades Boolean satisfiability (SAT) solvers based on conflict-driven clause learning (CDCL) have developed to the point where they can handle formulas with millions of variables. Yet a deeper understanding of how these solvers can be so successful has remained elusive. In this work we shed light on CDCL performance by using theoretical benchmarks, which have the attractive features of being a) scalable, b) extremal with respect to different proof search parameters, and c) theoretically easy in the sense of having short proofs in the resolution proof system underlying CDCL. This allows for a systematic study of solver heuristics and how efficiently they search for proofs. We report results from extensive experiments on a wide range of benchmarks. Our findings include several examples where theory predicts and explains CDCL behaviour, but also raise a number of intriguing questions for further study.

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