Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres

The X-ray nebula around the Seyfert 2 galaxy NGC4388

We report on X-ray emission from the Seyfert 2 galaxy NGC4388 observed with the Chandra X-ray Observatory. A hard X-ray peak is found at the position of the active nucleus suggested by optical and radio observations. Extended soft X-ray emission correlates well with the ionization cone found in optical line emission. A large soft X-ray extension is found up to 16 kpc to the north of the galaxy. Photoionized gas with low ionization parameters (xi<3) appears to be the likely explanation of this emission. The same ionized gas clouds could be responsible for the optical [OIII] emission. Fe K line emission from cold material is found to be extended by a few kpc.Comment: 12 pages, one colour figure included, MNRAS in pres

Measuring Black Hole Spin using X-ray Reflection Spectroscopy

I review the current status of X-ray reflection (a.k.a. broad iron line) based black hole spin measurements. This is a powerful technique that allows us to measure robust black hole spins across the mass range, from the stellar-mass black holes in X-ray binaries to the supermassive black holes in active galactic nuclei. After describing the basic assumptions of this approach, I lay out the detailed methodology focusing on "best practices" that have been found necessary to obtain robust results. Reflecting my own biases, this review is slanted towards a discussion of supermassive black hole (SMBH) spin in active galactic nuclei (AGN). Pulling together all of the available XMM-Newton and Suzaku results from the literature that satisfy objective quality control criteria, it is clear that a large fraction of SMBHs are rapidly-spinning, although there are tentative hints of a more slowly spinning population at high (M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of the spins of stellar-mass black holes in X-ray binaries. In general, reflection-based and continuum-fitting based spin measures are in agreement, although there remain two objects (GROJ1655-40 and 4U1543-475) for which that is not true. I end this review by discussing the exciting frontier of relativistic reverberation, particularly the discovery of broad iron line reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk reflection, this detection of reverberation demonstrates that future large-area X-ray observatories such as LOFT will make tremendous progress in studies of strong gravity using relativistic reverberation in AGN.Comment: 19 pages. To appear in proceedings of the ISSI-Bern workshop on "The Physics of Accretion onto Black Holes" (8-12 Oct 2012). Revised version adds a missing source to Table 1 and Fig.6 (IRAS13224-3809) and corrects the referencing of the discovery of soft lags in 1H0707-495 (which were in fact first reported in Fabian et al. 2009

Polymeric Films for the Encapsulation, Storage, and Tunable Release of Therapeutic Microbes

Microbe-based therapeutics (MBTs) are an emerging therapeutic modality for treating gastrointestinal infections and inflammatory bowel diseases. Current formulations for oral delivery of MBTs use capsules to achieve safe gastric transit, but oral formulations that control the spatiotemporal concentration of MBTs are yet to be developed, despite well-established connections between all therapeutics and their location, concentration, and distribution at sites of action. The development of a multi-functional polymer-based encapsulation system to formulate MBTs for enhanced storage and delivery through formulation of a model MBT, Lactobacillus casei ATCC393, is reported here. This approach enables the additive inclusion of excipients and polymers to grant specific functions, toward the development of a modular MBT platform. Through addition of established excipients, the formulation provides long-term storage of the encapsulated MBT. By adding higher molecular weight polymers, the release kinetics of the encapsulated MBTs can be modified. The inclusion of a mucoadhesive polymer significantly increases the adhesion force between the formulation and the intestinal tissue. Together, mucoadhesive and sustained release properties can be used to modulate the spatiotemporal concentration of MBTs. The formulation is compatible with standard oral capsules, thus maintaining existing clinical advantages of oral capsules while providing new functions from film encapsulation

The COVID-19 pandemic and OBGYN residency training: We have a problem and it’s not just masks

Background: The COVID-19 pandemic has left no one untouched. Resident trainees have been driven to reconsider virtually every component of their daily lives. The purpose of this pilot study is to evaluate the impact of the COVID-19 pandemic on Obstetrics and Gynecology (OBGYN) residency training and education. Methods: A cross-sectional pilot study was conducted between 2/2022 and 5/2022. A survey was created and distributed to OBGYN residents. The survey queried the effects of the pandemic on OBGYN residents’ procedure skills training and mental health. Results: A total of 95 OBGYN residents across programs affiliated with each American College of Obstetricians and Gynecologists (ACOG) district participated in the survey. Among them, just over half (n = 52, 55%) self-identified as under-represented minorities. A significant majority, 80% (n = 81), felt their gynecological training was inadequate, with 70% of fourth-year residents expressing a lack of confidence in their ability to independently practice gynecology after graduation. This lack of confidence among fourth-year residents suggests a notable disparity in readiness for independent gynecological practice, linked to meeting ACGME requirements before completing their residency (p = 0.013). Among the residents who reported a negative impact of the pandemic on their mental health (n = 76, 80%), about 40% (n = 31) had contemplated self-harm or knew a colleague who considered or attempted suicide (p < 0.001). This issue was especially pronounced in residents experiencing burnout (n = 44, 46%), as nearly half (n = 19, 43%) reported suicidal thoughts or knew someone in their program who had such thoughts or engaged in self-harm (p = 0.048). Conclusions: Residents expressed concerns about reduced hands-on gynecological training and doubts about their readiness for independent practice post-residency, highlighting the need for enhanced support through mentorship and revised training curriculums. Additionally, despite the availability of mental health resources to address pandemic-induced burnout, their underuse suggests a need for more accessible time for residents to use at their discretion and flexible training schedules that encourage mental health support resource utilization

Numerical convergence of the block-maxima approach to the Generalized Extreme Value distribution

In this paper we perform an analytical and numerical study of Extreme Value distributions in discrete dynamical systems. In this setting, recent works have shown how to get a statistics of extremes in agreement with the classical Extreme Value Theory. We pursue these investigations by giving analytical expressions of Extreme Value distribution parameters for maps that have an absolutely continuous invariant measure. We compare these analytical results with numerical experiments in which we study the convergence to limiting distributions using the so called block-maxima approach, pointing out in which cases we obtain robust estimation of parameters. In regular maps for which mixing properties do not hold, we show that the fitting procedure to the classical Extreme Value Distribution fails, as expected. However, we obtain an empirical distribution that can be explained starting from a different observable function for which Nicolis et al. [2006] have found analytical results.Comment: 34 pages, 7 figures; Journal of Statistical Physics 201

Computational Fluorescence Suppression in Shifted Excitation Raman Spectroscopy

Fiber-based Raman spectroscopy in the context of &lt;italic&gt;in vivo&lt;/italic&gt; biomedical application suffers from the presence of background fluorescence from the surrounding tissue that might mask the crucial but inherently weak Raman signatures. One method that has shown potential for suppressing the background to reveal the Raman spectra is shifted excitation Raman spectroscopy (SER). SER collects multiple emission spectra by shifting the excitation by small amounts and uses these spectra to computationally suppress the fluorescence background based on the principle that Raman spectrum shifts with excitation while fluorescence spectrum does not. We introduce a method that utilizes the spectral characteristics of the Raman and fluorescence spectra to estimate them more effectively, and compare this approach against existing methods on real world datasets.</p

Atenolol versus losartan in children and young adults with Marfan's syndrome

BACKGROUND : Aortic-root dissection is the leading cause of death in Marfan's syndrome. Studies suggest that with regard to slowing aortic-root enlargement, losartan may be more effective than beta-blockers, the current standard therapy in most centers. METHODS : We conducted a randomized trial comparing losartan with atenolol in children and young adults with Marfan's syndrome. The primary outcome was the rate of aortic-root enlargement, expressed as the change in the maximum aortic-root-diameter z score indexed to body-surface area (hereafter, aortic-root z score) over a 3-year period. Secondary outcomes included the rate of change in the absolute diameter of the aortic root; the rate of change in aortic regurgitation; the time to aortic dissection, aortic-root surgery, or death; somatic growth; and the incidence of adverse events. RESULTS : From January 2007 through February 2011, a total of 21 clinical centers enrolled 608 participants, 6 months to 25 years of age (mean [+/- SD] age, 11.5 +/- 6.5 years in the atenolol group and 11.0 +/- 6.2 years in the losartan group), who had an aorticroot z score greater than 3.0. The baseline-adjusted rate of change (+/- SE) in the aortic-root z score did not differ significantly between the atenolol group and the losartan group (-0.139 +/- 0.013 and -0.107 +/- 0.013 standard-deviation units per year, respectively; P = 0.08). Both slopes were significantly less than zero, indicating a decrease in the degree of aortic-root dilatation relative to body-surface area with either treatment. The 3-year rates of aortic-root surgery, aortic dissection, death, and a composite of these events did not differ significantly between the two treatment groups. CONCLUSIONS : Among children and young adults with Marfan's syndrome who were randomly assigned to losartan or atenolol, we found no significant difference in the rate of aorticroot dilatation between the two treatment groups over a 3-year period