ABSTRACT
We report on the Imaging X-ray Polarimetry Explorer (IXPE) observation of the closest and X-ray brightest Compton-thick active galactic nucleus (AGN), the Circinus galaxy. We find the source ...to be significantly polarized in the 2–6 keV band. From previous studies, the X-ray spectrum is known to be dominated by reflection components, both neutral (torus) and ionized (ionization cones). Our analysis indicates that the polarization degree is 28 ± 7 per cent (at 68 per cent confidence level) for the neutral reflector, with a polarization angle of 18° ± 5°, roughly perpendicular to the radio jet. The polarization of the ionized reflection is unconstrained. A comparison with Monte Carlo simulations of the polarization expected from the torus shows that the neutral reflector is consistent with being an equatorial torus with a half-opening angle of 45°–55°. This is the first X-ray polarization detection in a Seyfert galaxy, demonstrating the power of X-ray polarimetry in probing the geometry of the circumnuclear regions of AGNs, and confirming the basic predictions of standard Unification Models.
The water storage capacity of the root zone can determine whether plants survive dry periods and control the partitioning of precipitation into streamflow and evapotranspiration. It is currently ...thought that top‐down, climatic factors are the primary control on this capacity via their interaction with plant rooting adaptations. However, it remains unclear to what extent bottom‐up, geologic factors can provide an additional constraint on storage capacity. Here we use a machine learning approach to identify regions with lower than climatically expected apparent storage capacity. We find that in seasonally dry California these regions overlap with particular geologic substrates. We hypothesize that these patterns reflect diverse mechanisms by which substrate can limit storage capacity, and highlight case studies consistent with limited weathered bedrock extent (melange in the Northern Coast Range), toxicity (ultramafic substrates in the Klamath‐Siskiyou region), nutrient limitation (phosphorus‐poor plutons in the southern Sierra Nevada), and low porosity capable of retaining water (volcanic formations in the southern Cascades). The observation that at regional scales climate alone does not “size” the root zone has implications for the parameterization of storage capacity in models of plant dynamics (and the interrelated carbon and water cycles), and also underscores the importance of geology in considerations of climate‐change induced biome migration and habitat suitability.
Plain Language Summary
What determines how much water plants can store in their root zone? One school of thought posits that plants “size” the root‐zone capacity to survive a drought of a particular return period. In this scenario, plants extend their roots into the subsurface in response to climate drivers (e.g., precipitation magnitude‐frequency and atmospheric water demand). This worldview neglects the potential for geology to restrict root access to water. “Bottom‐up” limitations on storage capacity have been described at individual field sites, but it has been unclear how to identify geologic limitations at large scales. Here, we introduce an approach that quantifies differences between the climatically expected and locally observed apparent storage capacity, and relate these spatial patterns to geologic substrate. Importantly, we quantify apparent storage capacity via a method that includes water below the upper 1.5 m, within weathered bedrock, which is an important water source in seasonally dry climates and is typically excluded from traditional soil texture databases. We find that geology limits storage capacity at regional scales, and synthesize existing field evidence to hypothesize mechanisms of bottom‐up control. Our findings have important implications for water‐carbon cycle modeling efforts and the prediction of plant biome migration in response to climate change.
Key Points
Regionally extensive areas of low apparent root‐zone storage capacity for a particular climate coincide with particular geologic substrates
Hypothesized geologic controls include water storage capacity limitation, nutrient limitation, and toxicity
Video observations of lunar impact flashes have been made by a number of researchers since the late 1990's and the problem of determination of the impact energies has been approached in different ...ways Bellot Rubio et al. (2000a, b), Yanagisawa et al. (2008), Bouley et al. (2012), Suggs et al. (2014), Rembold and Ryan (2015), Ortiz et al. (2015), Madiedo et al. (2015). The wide spectral response of the unfiltered video cameras in use for all published measurements necessitates color correction for the standard filter magnitudes available for the comparison stars but this is not typically considered. In our approach, the published color of the comparison star and an estimate of the color of the impact flash is used to correct it to the chosen filter bandpass. Magnitudes corrected to standard filters are then used to determine the luminous energy in the filter bandpass according to the stellar atmosphere calibrations of Bessell et al. (1998). In this paper we compare the various photometric calibration techniques and calculation of luminous energy (radiometry) of impact flashes. This issue has significant implications for determination of luminous efficiency, predictions of impact crater sizes for observed flashes, and the determination of the flux of meteoroids in the 10s of grams to kilograms mass range.
•Radiometric calibration of video recordings of lunar impact flashes has been accomplished by a variety of techniques.•The use of unfiltered video cameras adds complexity to calibration and determination of luminous energy.•Color corrections for the comparison stars and the impact flashes are necessary.•Comparison of luminous energies from various researchers demonstrates differences due to calibration techniques.
We investigate the role of M(2)-muscarinic receptors in maintaining neurogenic bladder contraction during hyperglycemia. Mice were injected with a single dose of streptozotocin (125 mg/kg), and ...neurogenic contraction of urinary bladder from wild type and M(2)-muscarinic receptor knockout (M(2) KO) mice was measured at 8 to 24 weeks after treatment. In wild-type bladder lacking urothelium, the summation of the cholinergic (64%) and purinergic (56%) components of the electrical-field-stimulated response exceeded 100%, indicating a reserve capacity. Although the cholinergic component was slightly less in the M(2) KO mouse, the total electrical-field-stimulated contraction was the same as wild type. The cholinergic and purinergic components of contraction in wild-type bladder were minimally affected by streptozotocin treatment. In M(2) KO bladder, streptozotocin treatment reduced both the cholinergic (after 8-9 and 20-24 weeks) and purinergic (after 20-24 weeks only) components. The loss of function was approximately 50 to 70%. Similar results were observed in bladder with intact urothelium. M(2) KO bladder was more sensitive to the relaxant effect of isoproterenol compared with wild type, and this difference significantly increased at the early and late time points after streptozotocin treatment. In the presence of urothelium, however, this difference in isoproterenol sensitivity was smaller with streptozotocin treatment, but this trend reversed over time. Our results show that M(2) receptors oppose urinary bladder distension in wild-type bladder and inhibit streptozotocin-induced neuropathy.
We investigated the contractile roles of M
2
and M
3
muscarinic receptors in urinary bladder from streptozotocin-treated mice. Wild-type and M
2
muscarinic receptor knockout (M
2
KO) mice were given ...a single injection of vehicle or streptozotocin (125 mg kg
−1
) 2–24 weeks prior to bladder assays. The effect of forskolin on contractions elicited to the muscarinic agonist, oxotremorine-M, was measured in isolated urinary bladder (intact or denuded of urothelium). Denuded urinary bladder from vehicle-treated wild-type and M
2
KO mice exhibited similar contractile responses to oxotremorine-M, when contraction was normalized relative to that elicited by KCl (50 mM). Eight to 9 weeks after streptozotocin treatment, the EC
50
value of oxotremorine-M increased 3.1-fold in urinary bladder from the M
2
KO mouse (
N
= 5) compared to wild type (
N
= 6;
P
< 0.001). Analogous changes were observed in intact bladder. In denuded urinary bladder from vehicle-treated mice, forskolin (5 µM) caused a much greater inhibition of contraction in M
2
KO bladder compared to wild type. Following streptozotocin treatment, this forskolin effect increased 1.6-fold (
P
= 0.032). At the 20- to 24-week time point, the forskolin effect increased 1.7-fold for denuded as well as intact bladders (
P
= 0.036, 0.01, respectively). Although streptozotocin treatment inhibits M
3
receptor-mediated contraction in denuded urinary bladder, muscarinic contractile function is maintained in wild-type bladder by enhanced M
2
contractile function. M
2
receptor activation opposes forskolin-induced relaxation of the urinary bladder, and this M
2
function is enhanced following streptozotocin treatment.
Muscarinic receptors are expressed in smooth muscle throughout the body. In most instances, the muscarinic receptor population in smooth muscle is composed of mainly the M
2 and M
3 subtypes in an ...80% to 20% mixture. The M
3 subtype mediates phosphoinositide hydrolysis and calcium mobilization, whereas the M
2 subtype mediates an inhibition of cAMP accumulation. In addition, a variety of ionic conductances are elicited by muscarinic receptors. Muscarinic agonists stimulate a nonselective cation conductance that is pertussis toxin-sensitive and dependent on calcium. The pertussis toxin-sensitivity of this response suggests that it is mediated by M
2 receptors. Following agonist induced depolarization of smooth muscle, voltage dependent calcium channels are activated to enable an influx of calcium. In some instances, muscarinic agonists enhance this conductance through a mechanism involving protein kinase C, whereas in other instances, muscarinic agonists suppress this calcium conductance. Smooth muscle often contains calcium activated potassium channels that tend to repolarize the membrane following calcium influx. Activation of muscarinic receptors suppresses this potassium conductance in some smooth muscles. Under standard conditions, muscarinic agonists elicit pertussis toxin-insensitive contractions through activation of the M
3 receptor. When most of the M
3 receptors are inactivated, it is possible to measure a pertussis toxin-sensitive contractile response to muscarinic agonists that is most likely mediated through M
2 receptors. M
2 receptors also cause an indirect contraction by inhibiting the relaxant effects of agents that increase cAMP (e.g., forskolin and isoproterenol).
ixpeobssim is a simulation and analysis framework, based on the Python programming language and the associated scientific ecosystem, specifically developed for the Imaging X-ray Polarimetry Explorer ...(IXPE). Given a source model and the response functions of the telescopes, it is designed to produce realistic simulated observations, in the form of event lists in FITS format, containing a strict super-set of the information provided by standard IXPE level-2 files. The core ixpeobssim simulation capabilities are complemented by a full suite of post-processing applications, allowing for the implementation of complex, polarization-aware analysis pipelines, and facilitating the inter-operation with the standard visualization and analysis tools traditionally in use by the X-ray community. We emphasize that, although a significant part of the framework is specific to IXPE, the modular nature of the underlying implementation makes it potentially straightforward to adapt it to different missions with polarization capabilities.
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