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

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

Symptom clusters in adults with inflammatory bowel disease

Symptoms (pain, fatigue, sleep disturbance, depression, and anxiety) in inflammatory bowel disease (IBD) are associated with reduced quality of life. Understanding how IBD symptoms cluster and the clinical and demographic factors associated with symptom clusters will enable focused development of symptom management interventions. The study purposes were to (i) identify symptom cluster membership among adults with IBD and (ii) examine associations between demographic (age, gender, race/ethnicity, and education) and clinical factors (smoking status, time since diagnosis, medication type, IBD type, disease activity), and membership in specific symptom cluster groups. We conducted a retrospective study of data from the Crohn's and Colitis Foundation of America's (CCFA) Partners Cohort and used Patient Reported Outcome Measurement Information System (PROMIS) measures to measure pain interference, fatigue, sleep disturbance, anxiety, and depression. The sample included 5,296 participants with IBD (mean age 44, 72% female). In latent class analysis (LCA), four groups of participants were identified based on symptoms: "low symptom burden" (26% of sample), "high symptom burden" (38%), "physical symptoms" (22%), and "psychological symptoms" (14%). In multinomial regression, female gender, smoking, corticosteroids, Crohn's disease, and active disease state were associated with membership in the high symptom burden group. Additional research is needed to test interventions that may be effective at reducing symptom burden for individuals with IBD

Anxiety disorders in headache patients in a specialised clinic: prevalence and symptoms in comparison to patients in a general neurological clinic

Data from several studies indicate an association of headache with anxiety disorders. In this study, we assessed and differentiated anxiety disorders in 100 headache patients by using the PSWQ (Penn State Worry Questionnaire) screening tool for generalised anxiety disorder (GAD) and the ACQ (Agoraphobic Cognitions Questionnaire) and BSQ (Body Sensation Questionnaire) for panic disorder (PD). Control groups were constructed: (1) on the basis of epidemiological studies on PD and GAD in the general population and (2) by including neurological patients. 37.0% of headache patients had a GAD. 27% of headache patients met the score for PD in the BSQ, 4.0% in the ACQ. Significant results were obtained in comparison to the general population (p < 0.001) and with regard to GAD in comparison with a sample of neurological patients (p < 0.005). The BSQ significantly correlated with the number of medication days (p < 0.005). The results confirm the increased prevalence of GAD in headache patients. PD seems to increase the risk of medication overuse