A mean field dynamo from negative eddy diffusivity

Using direct numerical simulations, we verify that "flow IV" of Roberts (1972) exhibits dynamo action dominated by horizontally averaged large-scale magnetic field. With the test-field method we compute the turbulent magnetic diffusivity and find that it is negative and overcomes the molecular diffusivity, thus explaining quantitatively the large-scale dynamo for magnetic Reynolds numbers above $\approx8$. As expected for a dynamo of this type, but contrary to $\alpha$-effect dynamos, the two horizontal field components grow independently of each other and have arbitrary amplitude ratios and phase differences. Small length scales of the mean magnetic field are shown to be stabilized by the turbulent magnetic diffusivity becoming positive at larger wavenumbers. Oscillatory decaying or growing solutions have also been found in certain wavenumber intervals and sufficiently large values of the magnetic Reynolds number. For magnetic Reynolds numbers below $\approx0.5$ the turbulent magnetic diffusivity is confirmed to be positive, as expected for all incompressible flows. Earlier claims of a dynamo driven by a modified Taylor-Green flow through negative eddy diffusivity could not be confirmed.Comment: 7 pages, 9 figures, accepted to MNRA

A new model for heating of Solar North Polar Coronal Hole

This paper presents a new model of North Polar Coronal Hole (NPCH) to study dissipation/propagation of MHD waves. We investigate the effects of the isotropic viscosity and heat conduction on the propagation characteristics of the MHD waves in NPCH. We first model NPCH by considering the differences in radial as well as in the direction perpendicular to the line of sight (\textit{los}) in temperature, particle number density and non-thermal velocities between plumes and interplume lanes for the specific case of \ion{O}{VI} ions. This model includes parallel and perpendicular (to the magnetic field) heat conduction and viscous dissipation. Next, we derive the dispersion relations for the MHD waves in the case of absence and presence of parallel heat conduction. In the case of absence of parallel heat conduction, we find that MHD wave dissipation strongly depends on the viscosity for modified acoustic and Alfven waves. The energy flux density of acoustic waves varies between $10^{4.7}$ and $10^7 \,erg\,cm^{-2}\,s^{-1}$ while the energy flux density of Alfven waves turned out to be between $10^6-10^{8.6} \,erg\,cm^{-2}\,s^{-1}$. But, solutions of the magnetoacustic waves show that the parallel heat conduction introduce anomalous dispersion to the NPCH plasma wherein the group velocity of waves exceeds the speed of light in vacuum. Our results suggests all these waves may provide significant source for the observed preferential accelerating and heating of \ion{O}{VI} ions, in turn coronal plasma heating and an extra accelerating agent for fast solar wind in NPCH.Comment: 17 pages, 11 figures, Submitted to MNRA

Finite Larmor Radius Effects on Weakly Magnetized, Dilute Plasmas

We investigate the stability properties of a hot, dilute and differentially rotating weakly magnetized plasma which is believed to be found in the interstellar medium of galaxies and protogalaxies and in the low-density accretion flows around some giant black holes like the one in the Galactic center. In the linear MHD regime, we consider the combined effects of gyroviscosity and parallel viscosity on the magnetorotational instability. The helical magnetic field is considered in the investigation. We show that the gyroviscous effect and the pitch angles cause a powerful gyroviscous instability. Furthermore, in most of the cases, plasma with the above mentioned properties is unstable and the growth rates of the unstable modes are larger than that of the magnetorotational instability.Comment: 7 pages, 4 figures. Accepted for publication in MNRA

Magnetorotational Instability in Diamagnetic, Misaligned Protostellar Discs

In the present study, we addressed the question of how the growth rate of the magnetorotational instability is modified when the radial component of the stellar dipole magnetic field is taken into account in addition to the vertical component. Considering a fiducial radius in the disc where diamagnetic currents are pronounced, we carried out a linear stability analysis to obtain the growth rates of the magnetorotational instability for various parameters such as the ratio of the radial-to-vertical component and the gradient of the magnetic field, the Alfvenic Mach number and the diamagnetization parameter. Our results show that the interaction between the diamagnetic current and the radial component of the magnetic field increases the growth rate of the magnetorotational instability and generates a force perpendicular to the disc plane which may induce a torque. It is also shown that considering the radial component of the magnetic field and taking into account a radial gradient in the vertical component of the magnetic field causes an increase in the magnitudes of the growth rates of both the axisymmetric ($m=0$) and the non-axisymmetric ($m=1$) modes.Comment: 9 pages, 5 figures, published in MNRAS, 2020, vol. 491, pages 5481-548

Mouse Dynamics Behavioral Biometrics: A Survey

Utilization of the Internet in our everyday lives has made us vulnerable in terms of privacy and security of our data and systems. Therefore, there is a pressing need to protect our data and systems by improving authentication mechanisms, which are expected to be low cost, unobtrusive, and ideally ubiquitous in nature. Behavioral biometric modalities such as mouse dynamics (mouse behaviors on a graphical user interface (GUI)) and widget interactions (another modality closely related to mouse dynamics that also considers the target (widget) of a GUI interaction, such as links, buttons, and combo-boxes) can bolster the security of existing authentication systems because of their ability to distinguish an individual based on their unique features. As a result, it can be difficult for an imposter to impersonate these behavioral biometrics, making them suitable for authentication. In this paper, we survey the literature on mouse dynamics and widget interactions dated from 1897 to 2023. We begin our survey with an account of the psychological perspectives on behavioral biometrics. We then analyze the literature along the following dimensions: tasks and experimental settings for data collection, taxonomy of raw attributes, feature extractions and mathematical definitions, publicly available datasets, algorithms (statistical, machine learning, and deep learning), data fusion, performance, and limitations. Lastly, we end the paper with presenting challenges and promising research opportunities.Comment: 32 page

On the lack of X-ray pulsation in most neutron star low-mass X-ray binaries

We have investigated whether the lack of X-ray pulsations from most neutron star (NS) low-mass X-ray binaries (LMXBs) could be due to the extension of their inner disc to the NS surface. To estimate the inner disc radii, we have employed the model, recently proposed to account for the torque reversals of LMXBs. In this model, the inner disc radius depends on the spin period as well as the dipole moment and the mass inflow rate of the disc. Our model results indicate that most LMXBs have mass accretion rates above the minimum critical rates required for the inner disc to reach down to the NS surface and thereby quench the pulsed X-ray emission. For most sources X-ray pulsations are allowed when the period decreases below a certain critical value. For the same parameters, the model is also consistent with the observed X-ray luminosity ranges of the individual accreting millisecond X-ray pulsars (AMXPs). The paucity of AMXPs compared to the majority population of non-pulsing LMXBs is explained, as well as the fact that AMXPs are transient sources.Comment: 10 pages, 5 figures, accepted for publication in MNRA

The patient experience with fatigue and content validity of a measure to assess fatigue severity: qualitative research in patients with ankylosing spondylitis (AS)

Abstract Background Ankylosing spondylitis (AS) is an autoimmune disorder characterized by inflammation of the spine and large joints. Fatigue is a common symptom that many AS patients find significantly impacts their health-related quality of life. The Worst Fatigue – Numeric Rating Scale (WF-NRS) assesses the severity of this symptom during the previous 24-hour period. The objective of this study was to perform qualitative research to support the development and content validity of the WF-NRS. Methods Patients with AS were recruited from clinical sites in the U.S. for a qualitative study which first entailed concept elicitation interviews to gain understanding of the patients’ experience with AS and fatigue. Subsequently, cognitive debriefing interviews were undertaken to assess the understandability, clarity, and appropriateness from the patient’s perspective, of the content of a measure of fatigue severity. Results Thirteen patients with AS participated in concept elicitation interviews and cognitive debriefing of the Brief Fatigue Inventory (BFI) fatigue severity subscale. The WF-NRS was developed from the worst fatigue item of the BFI as patients generally reported it to be understandable and covered an important concept, the completion instructions were modified, but the response scale remained as it was familiar and readily completed, and the recall period was appropriate. Conclusions Patient responses resulted in the development of and supported the content validity of the WF-NRS. Further quantitative evaluation of the WF-NRS is warranted in order to assess its psychometric properties and confirm its usefulness as a clinical trial tool. </jats:sec

The Burden of Inflammatory Bowel Disease: A Patient-Reported Qualitative Analysis and Development of a Conceptual Model

Background The aim of this study was to describe the impacts of inflammatory bowel disease (IBD) from the patients’ perspective, and to inform the development of a conceptual model. Methods Focus groups and one-on-one interviews were undertaken in adult patients with IBD. Transcripts from the focus groups and interviews were analyzed to identify themes and links between themes, assisted by qualitative data software MaxQDA. Themes from the qualitative research were supplemented with those reported in the literature and concepts included in IBD-specific patient-reported outcome (PRO) measures. Results Twenty-seven patients participated. Key physical symptoms included pain, bowel-related symptoms such as frequency, urgency, incontinence, diarrhea, passing blood, and systemic symptoms such as weight loss and fatigue. Participants described continuing and variable symptom experiences. IBD symptoms caused immediate disruption of activities but also had ongoing impacts on daily activities, including dietary restrictions, lifestyle changes, and maintaining close proximity to a toilet. More distal impacts included interference with work, school, parenting, social and leisure activities, relationships, and psychological well-being. The inconvenience of rectal medications, refrigerated biologics, and medication refills emerged as novel burdens not identified in existing PRO measures. Conclusions IBD symptoms cause immediate disruption in activities, but patients may continue to experience some symptoms on a chronic basis. The conceptual model presented here may be useful for identifying target concepts for measurement in future studies in IBD