Variability in active galactic nuclei: confrontation of models with observations

The variability of active galactic nuclei (AGN) has long held the promise of shedding light on their detailed structure, and possibly other astrophysical phenonema. Different emission mechanisms lead to different patterns of variability in flux which are in principle easily distinguishable. Recent predictions for the expected spectrum of variations for various models are now in such a form that they can be compared with the observed statistical properties of AGN light curves from large scale monitoring programmes. In this paper, we use the results of a long term monitoring programme of a large sample of quasars and Seyfert galaxies, as well as individual light curves from the literature, to distinguish between the various model predictions. The results favour a model based on accretion disc instability over the starburst model where the variation comes from a succession of supernova bursts, but it also appears that much of the observed variation in quasars is due to gravitational microlensing.Comment: 12 pages including 10 figures. Accepted for publication in MNRA

Production of cartilage oligomeric matrix protein (COMP) by cultured human dermal and synovial fibroblasts

AbstractObjective: Cartilage oligomeric matrix protein (COMP) is a large disulfide-linked pentameric protein. Each of its five subunits is approximately 100,000 Da in molecular weight. COMP was originally identified and characterized in cartilage and it has been considered a marker of cartilage metabolism because it is currently thought not to be present in other joint tissues, except for tendon. To confirm the tissue specificity of COMP expression we examined cultured human dermal fibroblasts, human foreskin fibroblasts, and normal human synovial cells for the synthesis of COMP in culture.Method: Normal synovial cells and normal human dermal foreskin fibroblasts were isolated from the corresponding tissues by sequential enzymatic digestions and cultured in media containing 10% fetal bovine serum until confluent. During the final 24 h of culture, the cells were labeled with35S-methionine and35S-cysteine in serum- and cysteine/methionine-free medium. The newly synthesized COMP molecules were immunoprecipitated from the culture media with a COMP-specific polyclonal antiserum, or with monoclonal antibodies or affinity-purified COMP antibodies. The immunoprecipitated COMP was analyzed by electrophoresis in 5.5% polyacrylamide gels. For other experiments, synovial cells cultured from the synovium of patients with rheumatoid arthritis (RA) and osteoarthritis (OA) were similarly examined.Results: A comparison of the amounts of COMP produced by each cell type (corrected for the DNA content) revealed that synovial cells produced ≥9 times more COMP than chondrocytes or dermal fibroblasts. COMP could be easily detected by immunoprecipitation in all cell types. Electrophoretic analysis revealed a distinct band with an apparent MW of 115–120 kDa in samples from each of the three cell types, regardless of the antibody used. COMP expression in cultures of synoviocytes derived from OA and RA patients showed that OA and RA synovial cells produced similar amounts of monomeric COMP of identical size to those COMP monomers produced by normal synovial cells. The addition of TGF-β to these cultures resulted in an increase in COMP production in normal, OA and RA synovial cells (45, 116 and 115% respectively).Conclusion: These studies demonstrate that substantial amounts of COMP are produced by several mesenchymal cells including synoviocytes and dermal fibroblasts. These findings raise important concerns regarding the utility of measurements of COMP levels in serum or in synovial fluid as markers of articular cartilage degradation because of the likelihood that a substantial proportion of COMP or COMP fragments in serum or synovial fluid may be produced by cells other than articular chondrocytes

Reflections from Research in Gender and Ethics: Building Stronger Health Systems (RinGs)

Gender analysis is an important component of health systems research (HSR) as it reveals how power relations create inequalities in health system needs, experiences, and outcomes among women, men, and people of other genders. Various challenges must be overcome to successfully mainstream gender into health systems practice and research

The importance of gender analysis in research for health systems strengthening

This editorial discusses a collection of papers examining gender across a range of health policy and systems contexts, from access to services, governance, health financing, and human resources for health. The papers interrogate differing health issues and core health systems functions using a gender lens. Together they produce new knowledge on the multiple impacts of gender on health experiences and demonstrate the importance of gender analyses and gender sensitive interventions for promoting well-being and health systems strengthening. The findings from these papers collectively show how gender intersects with other axes of inequity within specific contexts to shape experiences of health and health seeking within households, communities and health systems; illustrate how gender power relations affect access to important resources; and demonstrate that gender norms, poverty and patriarchy interplay to limit women’s choices and chances both within household interactions and within the health sector. Health systems researchers have a responsibility to promote the incorporation of gender analyses into their studies in order to inform more strategic, effective and equitable health systems interventions, programmes, and policies. Responding to gender inequitable systems, institutions, and services in this sector requires an ‘all hands-on deck’ approach. We cannot claimto take a ‘people-centred approach’ to health systems if the status quo continues

Microfluidic devices for terahertz spectroscopy of biomolecules

We demonstrate microfluidic devices for terahertz spectroscopy of biomolecules in aqueous solutions. The devices are fabricated out of a plastic material that is both mechanically rigid and optically transparent with near-zero dispersion in the terahertz frequency range. Using a low-power terahertz time-domain spectrometer, we experimentally measure the absorption spectra of the vibrational modes of bovine serum albumin from 0.5–2.5 THz and find good agreement with previously reported data obtained using large-volume solutions and a high-power free-electron laser. Our results demonstrate the feasibility of performing high sensitivity terahertz spectroscopy of biomolecules in aqueous solutions with detectable molecular quantities as small as 10 picomoles using microfluidic devices

A Discovery of Rapid Optical Flares from Low-Luminosity Active Nuclei in Massive Galaxies

We report a serendipitous discovery of six very low-luminosity active galactic nuclei (AGNs) only by optical variability in one-month baseline. The detected flux variability is ~ 1-5% of the total luminosity of host galaxies. Careful subtraction of host galaxy components in nuclear regions indicates that the fractional variability (Delta F / F) of the nuclei is of order unity. At least one of them is showing a compelling flaring activity within just a few days, which appears to be quite different from previously known AGN variability. We obtained spectroscopic data for the one showing the largest flare and confirmed that it is in fact an AGN at z = 0.33 with an estimated black hole mass of ~10^8 M_sun. As a possible interpretation, we suggest that these activities are coming from the region around the black hole event horizon, which is physically similar to the recently discovered near-infrared flares of our Galactic nucleus. It is indicated that our Galaxy is not special, and that surprisingly rapid flaring activity in optical/near-infrared bands may be commonly hidden in nuclei of apparently normal galaxies with low Eddington ratios, in contrast to the variability of well-studied luminous AGNs or quasars.Comment: Accepted to ApJ Letter