Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO2 uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to ...greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun‐induced fluorescence signal on the ground and on a coarse spatial scale using space‐borne imaging spectrometers. Intermediate‐scale observations using airborne‐based imaging spectroscopy, which are critical to bridge the existing gap between small‐scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun‐induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun‐induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun‐induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun‐induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.
Context. The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is at only 0.14 au and is associated with the Geminid meteor stream. Aims. We aim to use all available ...disk-integrated optical data to derive a reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. Methods. We applied the convex inversion method to the new optical data obtained by six instruments and to previous observations. The convex shape model was then used as input for the thermophysical modeling. We also studied the long-term stability of Phaethon’s orbit and spin axis with a numerical orbital and rotation-state integrator. Results. We present a new convex shape model and rotational state of Phaethon: a sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319°, −39°) with a 5° uncertainty. Moreover, we derive its size (D = 5.1 ± 0.2 km), thermal inertia (Γ = 600 ± 200 J m–2 s–1/2 K–1), geometric visible albedo (pV = 0.122 ± 0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during the past several thousand years is not connected to a specific area on the surface, which implies non-preferential heating.
Remote estimation of Sun‐induced chlorophyll fluorescence emitted by terrestrial vegetation can provide an unparalleled opportunity to track spatiotemporal variations of photosynthetic efficiency. ...Here we provide the first direct experimental evidence that the two peaks of the chlorophyll fluorescence spectrum can be accurately mapped from high‐resolution radiance spectra and that the signal is linked to variations in actual photosynthetic efficiency. Red and far red fluorescence measured using a novel airborne imaging spectrometer over a grass carpet treated with an herbicide known to inhibit photosynthesis was significantly higher than the corresponding signal from an equivalent untreated grass carpet. The reflectance signal of the two grass carpets was indistinguishable, confirming that the fast dynamic changes in fluorescence emission were related to variations in the functional status of actual photosynthesis induced by herbicide application. Our results from a controlled experiment at the local scale illustrate the potential for the global mapping of terrestrial photosynthesis through space‐borne measurements of chlorophyll fluorescence.
Key Points
A novel high‐resolution airborne sensor is flown
Both red and far red Sun‐induced fluorescence signals are accurately quantified
Red and far red fluorescence tracks variations in photosynthetic efficiency
•We analyze the WISE thermal infrared data of nine asteroids by means of a thermophysical model (TPM).•We present a novel thermophysical approach – varied shape TPM (VS-TPM).•We consider the ...uncertainties of the shape model and the pole orientation in the TPM.•We show that the uncertainties of the shape model and the pole orientation can be very important.
In the analysis of thermal infrared data of asteroids by means of thermophysical models (TPMs) it is a common practice to neglect the uncertainty of the shape model and the rotational state, which are taken as an input for the model. Here, we present a novel method of investigating the importance of the shape model and the pole orientation uncertainties in the thermophysical modeling – the varied shape TPM (VS-TPM). Our method uses optical photometric data to generate various shape models that map the uncertainty in the shape and the rotational state. The TPM procedure is then run for all these shape models. We apply the implementation of the classical TPM as well as our VS-TPM to the convex shape models of several asteroids together with their thermal infrared data acquired by the NASA’s Wide-field Infrared Survey Explorer (WISE) and compare the results. These show that the uncertainties of the shape model and the pole orientation can be very important (e.g., for the determination of the thermal inertia) and should be considered in the thermophysical analyses. We present thermophysical properties for six asteroids – (624) Hektor, (771) Libera, (1036) Ganymed, (1472) Muonio, (1627) Ivar, and (2606) Odessa.
Age-related macular degeneration (AMD) is a degenerative disease of the retina and the leading cause of blindness in the elderly. Retinal pigment epithelial (RPE) cell death and the resultant ...photoreceptor apoptosis are characteristic of late-stage dry AMD, especially geographic atrophy (GA). Although oxidative stress and inflammation have been associated with GA, the nature and underlying mechanism for RPE cell death remains controversial, which hinders the development of targeted therapy for dry AMD. The purpose of this study is to systematically dissect the mechanism of RPE cell death induced by oxidative stress. Our results show that characteristic features of apoptosis, including DNA fragmentation, caspase 3 activation, chromatin condensation and apoptotic body formation, were not observed during RPE cell death induced by either hydrogen peroxide or tert-Butyl hydroperoxide. Instead, this kind of cell death can be prevented by RIP kinase inhibitors necrostatins but not caspase inhibitor z-VAD, suggesting necrotic feature of RPE cell death. Moreover, ATP depletion, receptor interacting protein kinase 3 (RIPK3) aggregation, nuclear and plasma membrane leakage and breakdown, which are the cardinal features of necrosis, were observed in RPE cells upon oxidative stress. Silencing of RIPK3, a key protein in necrosis, largely prevented oxidative stress-induced RPE death. The necrotic nature of RPE death is consistent with the release of nuclear protein high mobility group protein B1 into the cytoplasm and cell medium, which induces the expression of inflammatory gene TNFα in healthy RPE and THP-1 cells. Interestingly, features of pyroptosis or autophagy were not observed in oxidative stress-treated RPE cells. Our results unequivocally show that necrosis, but not apoptosis, is a major type of cell death in RPE cells in response to oxidative stress. This suggests that preventing oxidative stress-induced necrotic RPE death may be a viable approach for late-stage dry AMD.
We present shape models and volume estimates of twenty asteroids based on relative photometry and adaptive optics images. We discuss error estimation and the effects of myopic deconvolution on shape ...solutions. For further analysis of the information capacities of data sources, we also present and discuss ambiguity and uniqueness results for the reconstruction of nonconvex shapes from photometry.
In this paper, we analyze the increase in the dynamic flexural strength of concrete according to strain rate. A simple beam with center-point loading and a classical electro-mechanical testing ...machine are used to determine the static flexural strength. The dynamic measurements are conducted using a split Hopkinson pressure bar (SHPB) device in the same three-point bending configuration. The outer faces of the beams are instrumented with strain gauges to record the extreme tensile strains. Moreover, full-field displacement measurements are obtained using digital image correlation (DIC) on images recorded by a very high-speed camera. The strain gauge and DIC measurements are compared and used to determine the onset of failure and to evaluate the rate-related tensile strength. Several tests are performed at strain rates in the range from 1/s to 15/s. As expected, a significant increase in the flexural tensile strength with strain-rate is observed, which is consistent with results from the literature.
Context. The recent close approach of the near-Earth asteroid (3200) Phaethon offered a rare opportunity to obtain high-quality observational data of various types. Aims. We used the newly obtained ...optical light curves to improve the spin and shape model of Phaethon and to determine its surface physical properties derived by thermophysical modeling. We also used the available astrometric observations of Phaethon, including those obtained by the Arecibo radar and the Gaia spacecraft, to constrain the secular drift of the orbital semimajor axis. This constraint allowed us to estimate the bulk density by assuming that the drift is dominated by the Yarkovsky effect. Methods. We used the convex inversion model to derive the spin orientation and 3D shape model of Phaethon, and a detailed numerical approach for an accurate analysis of the Yarkovsky effect. Results. We obtained a unique solution for Phaethon’s pole orientation at (318 ° , − 47 ° ) ecliptic longitude and latitude (both with an uncertainty of 5°), and confirm the previously reported thermophysical properties (D = 5.1 ± 0.2 km, Γ = 600 ± 200J m−2 s−0.5 K−1). Phaethon has a top-like shape with possible north-south asymmetry. The characteristic size of the regolith grains is 1 − 2 cm. The orbit analysis reveals a secular drift of the semimajor axis of −(6.9 ± 1.9)×10−4 au Myr−1. With the derived volume-equivalent size of 5.1 km, the bulk density is 1.67 ± 0.47 g cm−3. If the size is slightly larger ∼5.7 − 5.8 km, as suggested by radar data, the bulk density would decrease to 1.48 ± 0.42 g cm−3. We further investigated the suggestion that Phaethon may be in a cluster with asteroids (155140) 2005 UD and (225416) 1999 YC that was formed by rotational fission of a critically spinning parent body. Conclusions. Phaethon’s bulk density is consistent with typical values for large (> 100 km) C-complex asteroids and supports its association with asteroid (2) Pallas, as first suggested by dynamical modeling. These findings render a cometary origin unlikely for Phaethon.
Age-related macular degeneration (AMD) is a degenerative disease of the retina and the leading cause of blindness in the elderly in developed countries. The late stage of dry AMD, or geographic ...atrophy (GA), is characterized by extensive retinal pigment epithelium (RPE) degeneration. The underlying molecular mechanism for RPE cell death in GA remains unclear. Our previous study has established that RPE cells die predominantly from necroptosis in response to oxidative stress in vitro. Here, we extend our study and aim to characterize the nature of RPE cell death in response to sodium iodate (NaIO3) in vitro and in a NaIO3-induced retina degeneration mouse model. We found that NaIO3 induces RPE necroptosis in vitro by using a combination of molecular hallmarks. By using TUNEL assays, active caspase-3 and HMGB1 immunostaining, we confirmed that photoreceptor cells die mainly from apoptosis and RPE cells die mainly from necroptosis in response to NaIO3 in vivo. RPE necroptosis in this model is also supported by use of the RIPK1 inhibitor, Necrostatin-1. Furthermore, using novel RIPK3-GFP transgenic mouse lines, we detected RIPK3 aggregation, a hallmark of necroptosis, in the RPE cells in vivo after NaIO3 injection. Our findings suggest the necessity of re-evaluating RPE cell death mechanism in AMD models and have the potential to influence therapeutic development for dry AMD, especially GA.
•We analyze the thermal infrared data acquired by the NASAs Wide-field Infrared Survey Explorer of about 300 asteroids by means of a thermophysical model.•We report thermophysical properties such as ...size, thermal inertia, surface roughness or visible geometric albedo for more than one hundred asteroids.•The thermal inertia increases with decreasing size, but a large range of thermal inertia values is observed within the similar size ranges between D ∼ 10, 100 km.•The thermal inertia values seem to be consistent within several collisional families.
By means of a varied-shape thermophysical model of Hanuš et al. (2015) that takes into account asteroid shape and pole uncertainties, we analyze the thermal infrared data acquired by the NASA’s Wide-field Infrared Survey Explorer of about 300 asteroids with derived convex shape models. We utilize publicly available convex shape models and rotation states as input for the thermophysical modeling. For more than one hundred asteroids, the thermophysical modeling gives us an acceptable fit to the thermal infrared data allowing us to report their thermophysical properties such as size, thermal inertia, surface roughness or visible geometric albedo. This work more than doubles the number of asteroids with determined thermophysical properties, especially the thermal inertia. In the remaining cases, the shape model and pole orientation uncertainties, specific rotation or thermophysical properties, poor thermal infrared data or their coverage prevent the determination of reliable thermophysical properties. Finally, we present the main results of the statistical study of derived thermophysical parameters within the whole population of main-belt asteroids and within few asteroid families. Our sizes based on TPM are, in average, consistent with the radiometric sizes reported by Mainzer et al. (2016). The thermal inertia increases with decreasing size, but a large range of thermal inertia values is observed within the similar size ranges between D ∼ 10–100 km. We derived unexpectedly low thermal inertias ( < 20 J m−2 s−1/2 K−1) for several asteroids with sizes 10 < D < 50 km, indicating a very fine and mature regolith on these small bodies. The thermal inertia values seem to be consistent within several collisional families, however, the statistical sample is in all cases rather small. The fast rotators with rotation period P ≲ 4 h tend to have slightly larger thermal inertia values, so probably do not have a fine regolith on the surface. This could be explained, for example, by the loss of the fine regolith due to the centrifugal force, or by the ineffectiveness of the regolith production(e.g., by the thermal cracking mechanism of Delbo’ et al. 2014).
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