Convective magneto-rotational instabilities in accretion disks

We present a study of instabilities occuring in thick magnetized accretion disks. We calculate the growth rates of these instabilities and characterise precisely the contribution of the magneto-rotational and the convective mechanism. All our calculations are performed in radially stratified disks in the cylindrical limit. The numerical calculations are performed using the appropriate local dispersion equation solver discussed in Blokland et al. (2005). A comparison with recent results by Narayan et al. (2002) shows excellent agreement with their approximate growth rates only if the disks are weakly magnetized. However, for disks close to equipartition, the dispersion equation from Narayan et al. (2002) loses its validity. Our calculations allow for a quantitative determination of the increase of the growth rate due to the magneto-rotational mechanism. We find that the increase of the growth rate for long wavelength convective modes caused by this mechanism is almost neglible. On the other hand, the growth rate of short wavelength instabilities can be significantly increased by this mechanism, reaching values up to 60%.Comment: 10 pages, 9 figures, Accepted for publication in Astronomy & Astrophysic

Magneto-rotational overstability in accretion disks

We present analytical and numerical studies of magnetorotational instabilities occuring in magnetized accretion disks. In these studies we make use of the linearised compressible MHD equations. These calculations are performed for general radially stratified disks in the cylindrical limit. In particular, we investigate the influence of nonvanishing toroidal magnetic field component on the growth rate and oscillation frequency of magnetorotational instabilities in Keplerian disks. We find the persistence of these instabilities in accretion disks close to equipartition. Our calculations show that these eigenmodes become overstable (complex eigenvalue), due to the presence of a toroidal magnetic field component, while their growth rate reduces slightly. Furthermore, we demonstrate the presence of magneto-rotational overstabilities in weakly magnetized sub-Keplerian rotating disks. We show that the growth rate scales with the rotation frequency of the disk. These eigenmodes also have a nonzero oscillation frequency, due to the presence of the dominant toroidal magnetic field component. The overstable character of the MRI increases as the rotation frequency of the disk decreases.Comment: 11 pager, 18 Postscript figures, accepted for publication in Astronomy & Astrophysic

Exploring the nature of calls to South African mental health helplines

Introduction: In South Africa, 30.3% of the population experience mental illness during their lifetime, at least 1 in 10 non-natural deaths are due to suicide, and poverty, crime, and HIV are common local psychosocial stressors. Despite this, it’s estimated only 5% of the national health expenditure is allocated to mental health, and nearly 75% of those with a mental health condition are untreated. Within this context exists an NPO offering free national mental health helplines, yet little is known about the population accessing these lines, the nature of difficulties reported, and the kind of assistance provided. It is this knowledge gap the present study addresses. Methods: During this exploratory mixed method archival research, the NPO’s existing telephone counselling records from February and March 2017 were sampled (N = 300) to determine caller demographics, timing of calls, object of concern, nature of difficulty expressed, and form of assistance. Descriptive, inferential, and content analyses were applied to evaluate the data. Results: Results show that helpline callers were mostly female (76.3%), aged 20 to 29 (41.7%), of Black race (61.3%), and from Gauteng (56%). The highest volume of calls was received on Thursdays (23%), and the busiest time was the 12:00 to 16:00 shift (47.3%). The majority of people called for self-related concerns (85%), most frequently mental illness (227 references) and interpersonal problems (105 references). The NPO predominantly assisted callers with referrals to other resources (86%), mainly support structures (144 references) and counselling services (127 references) run by other NPOs. The discovery of significant associations between age & race; gender & race; province & race; age & week day; province & shift; week day & shift, suggests the caller profile may vary depending on race and temporal factors. Conclusion: Callers who most readily reached out to the helplines were women, and those aged 20 to 40. Mental health support and counselling services appeared to be most needed, with a heavy reliance on NPOs – at least double that on government services, and nearly triple that on the private sector. This suggests informal resources are central to South Africa’s mental healthcare system, substantiating greater investment in informal community care

Non-locality and Medium Effects in the Exclusive Photoproduction of Eta Mesons on Nuclei

A relativistic model for the quasifree exclusive photoproduction of $\eta$ mesons on nuclei is extended to include both non-local and medium effects. The reaction is assumed to proceed via the dominant contribution of the S$_{11}$(1535) resonance. The complicated integrals resulting from the non-locality are simplified using a modified version of a method given by Cooper and Maxwell. The non-locality effects are found to affect the magnitude of the cross section. Some possibilities reflecting the effects of the medium on the propagation and properties of the intermediate S$_{11}$ resonance are studied. The effects of allowing the S$_{11}$ to interact with the medium via mean field scalar and vector potentials are considered. Both broadening of width and reduction in mass of the resonance lead to a suppression of the calculated cross sections.Comment: 19 pages, 7 figure

Sex differences in leukocyte profile in ST-elevation myocardial infarction patients

BACKGROUND: Whether sex differences exist in the inflammatory response after ST-elevation myocardial infarction (STEMI) remains to be elucidated. We studied leukocyte profiles and their prognostic value in men and women presenting with STEMI. METHODS: From a total of 552 consecutive STEMI patients, blood samples were collected at hospital admission. Linear regression was used to assess the relationship between leukocyte profiles and enzymatic infarct size. Cox regression was used to assess the association between leukocyte profiles and one-year mortality. RESULTS: Women presented with higher lymphocyte counts (2.3·109 cells/L (IQR 1.6-3.1) vs. 1.8·109 cells/L (IQR 1.4-2.5), p = 3.00 ∙ 10-4) and percentages (21.1% (IQR 14.4-28.1) vs. 17.1% (IQR 12.3-24.3), p = 0.004). Lymphocyte to monocyte ratio (LMR) was also higher in women (3.25 (IQR 2.56-4.5) vs. 2.68 (IQR 2.08-3.59), p = 7.28 ∙ 10-7). Higher LMR was associated with lower peak CK-MB (β = -0.27 (95% CI: -0.50, -0.03), p = 0.026), lower peak troponin T (β = -0.45 (95% CI: -0.77, -0.13), p = 0.006) and lower one-year mortality risk (HR 0.35 (95% CI: 0.13, 0.96), p = 0.042). CONCLUSION: At admission for STEMI, women present with higher lymphocyte count and LMR. Higher LMR is associated with smaller infarct size and decreased one-year mortality risk and could be used as a biomarker to predict outcome

Regulation of cellular senescence by extracellular matrix during chronic fibrotic diseases

The extracellular matrix (ECM) is a complex network of macromolecules surrounding cells providing structural support and stability to tissues. The understanding of the ECM and the diverse roles it plays in development, homoeostasis and injury have greatly advanced in the last three decades. The ECM is crucial for maintaining tissue homoeostasis but also many pathological conditions arise from aberrant matrix remodelling during ageing. Ageing is characterised as functional decline of tissue over time ultimately leading to tissue dysfunction, and is a risk factor in many diseases including cardiovascular disease, diabetes, cancer, dementia, glaucoma, chronic obstructive pulmonary disease (COPD) and fibrosis. ECM changes are recognised as a major driver of aberrant cell responses. Mesenchymal cells in aged tissue show signs of growth arrest and resistance to apoptosis, which are indicative of cellular senescence. It was recently postulated that cellular senescence contributes to the pathogenesis of chronic fibrotic diseases in the heart, kidney, liver and lung. Senescent cells negatively impact tissue regeneration while creating a pro-inflammatory environment as part of the senescence-associated secretory phenotype (SASP) favouring disease progression. In this review, we explore and summarise the current knowledge around how aberrant ECM potentially influences the senescent phenotype in chronic fibrotic diseases. Lastly, we will explore the possibility for interventions in the ECM-senescence regulatory pathways for therapeutic potential in chronic fibrotic diseases.</p

Contributions of semi-hadronic states Pγ;Sγ,π+π−γP\gamma;S\gamma, \pi^+\pi^-\gamma to amm of muon, in frames of Nambu-Jona-Lasinio model

We calculate the contribution of semi-hadronic states with pseudoscalar $P=\pi^0, \eta$ and scalar ($\sigma$(550))meson accompanied with real photon as an intermediate state of a heavy photon to the anomalous magnetic moment of muon. We consider the intermediate states with $\pi_0$ and $\sigma$ as a hadrons in frames of Nambu-Jona-Lasinio model. The contribution of $\pi_0\gamma$ state is in agreement with results obtained in previous theoretical considerations as well as with experimental data $a_\mu^{\pi_0\gamma}\approx 4.5 \times 10^{-10}$, besides we estimate $a_{\mu}^{\eta\gamma}=0.7 \times 10^{-10}, a_{\mu}^{\sigma\gamma} \sim 1.5 \times 10^{-11}, a_{\mu}^{\pi^+\pi^-\gamma} \sim 3.2 \times 10^{-10}.$ We discass as well the LbL mechanism with $a_{\mu}^{lbl}=10.5 \cdot 10^{-10}.$Comment: 6 pages, 2 figure