Evaluation of riverbed magnetic susceptibility for mapping biogeochemical hot spots in groundwater-impacted rivers     

Chen Wang  Martin A. Briggs  Frederick D. Day-Lewis  Lee D. Slater 《水文研究》2021,35(5):e14184

Redox hot spots occurring as metal-rich anoxic groundwater discharges through oxic wetland and river sediments commonly result in the formation of iron (Fe) oxide precipitates. These redox-sensitive precipitates influence the release of nutrients and metals to surface water and can act as ‘contaminant sponges’ by absorbing toxic compounds. We explore the feasibility of a non-invasive, high-resolution magnetic susceptibility (MS) technique to efficiently map the spatial variations of magnetic Fe oxide precipitates in the shallow bed of three rivers impacted by anoxic groundwater discharge. Laboratory analyses on Mashpee River (MA, USA) sediments demonstrate the sensitivity of MS to sediment Fe concentrations. Field surveys in the Mashpee and Quashnet rivers (MA, USA) reveal several discrete high MS zones, which are associated with likely anoxic groundwater discharge as evaluated by riverbed temperature, vertical head gradient, and groundwater chemistry measurements. In the East River (CO, USA), widespread cobbles/rocks exhibit high background MS from geological ferrimagnetic minerals, thereby obscuring the relatively small enhancement of MS from groundwater induced Fe oxide precipitates. Our study suggests that, in settings with low geological sources of magnetic minerals such as lowland rivers and wetlands, MS may serve as a complementary tool to temperature methods for efficiently mapping Fe oxide accumulation zones due to anoxic groundwater discharges that may function as biogeochemical hot spots and water quality control points in gaining systems.  相似文献   

Testing accretion mechanisms of the H chondrite parent body utilizing nucleosynthetic anomalies     

Sren Grube Pedersen  Martin Schiller  James N. Connelly  Martin Bizzarro 《Meteoritics & planetary science》2019,54(6):1215-1227

Planetary bodies a few hundred kilometers in radii are the precursors to larger planets but it is unclear whether these bodies themselves formed very rapidly or accreted slowly over several millions of years. Ordinary H chondrite meteorites provide an opportunity to investigate the accretion time scale of a small planetary body given that variable degrees of thermal metamorphism present in H chondrites provide a proxy for their stratigraphic depth and, therefore, relative accretion times. We exploit this feature to search for nucleosynthetic isotope variability of ⁵⁴Cr, which is a sensitive tracer of spatial and temporal variations in the protoplanetary disk's solids, between 17 H chondrites covering all petrologic types to obtain clues about the parent body accretionary rate. We find no systematic variability in the mass‐biased corrected abundances of ⁵³Cr or ⁵⁴Cr outside of the analytical uncertainties, suggesting very rapid accretion of the H chondrite parent body consistent with turbulent accretion. By utilizing the μ⁵⁴Cr–planetary mass relationship observed between inner solar system planetary bodies, we calculate that the H chondrite accretion occurred at 1.1 ± 0.4 or 1.8 ± 0.2 Myr after the formation of calcium‐aluminum‐rich inclusions (CAIs), assuming either the initial ²⁶Al/²⁷Al abundance of inner solar system solids determined from angrite meteorites or CAIs from CV chondrites, respectively. Notably, these ages are in agreement with age estimates based on the parent bodies’ thermal evolution when correcting these calculations to the same initial ²⁶Al/²⁷Al abundance, reinforcing the idea of a secular evolution in the isotopic composition of inner disk solids.  相似文献   

ALMA observations of the circumstellar envelope around EP Aqr     

Pham Thi Tuyet Nhung  Do Thi Hoai  Pham Tuan-Anh  Thibaut Le Bertre  Pierre Darriulat  Pham Ngoc Diep  Nguyen Thi Phuong  Nguyen Thi Thao  Jan Martin Winters 《天文和天体物理学研究(英文版)》2019,(3)

Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better spatial resolution than previously available. They are analysed with emphasis on the de-projection in space of the effective emissivity and flux of matter using as input a prescribed configuration of the velocity field, assumed to be radial. The data are found to display an intrinsic axisymmetry with respect to an axis making a small angle with respect to the line of sight. A broad range of wind configurations, from prolate(bipolar) to oblate(equatorial) has been studied and found to be accompanied by significant equatorial emission. Qualitatively, the effective emissivity is enhanced near the equator to produce the central narrow component observed in the Doppler velocity spectra and its dependence on star latitude generally follows that of the wind velocity with the exception of an omni-present depression near the poles. In particular, large equatorial expansion velocities produce a flared disc or a ring of effective emissivity and mass loss. The effect on the determination of the orientation of the star axis of radial velocity gradients, and possibly competing rotation and expansion in the equatorial disc, is discussed. In general,the flux of matter is found to reach a broad maximum at distances of the order of 500 AU from the star.Arguments are given that may be used to favour one wind velocity distribution over another. As a result of the improved quality of the data, a deeper understanding of the constraints imposed on morphology and kinematics has been obtained.  相似文献   

The Effects of Ocean Acidification on Feeding and Contest Behaviour by the Beadlet Anemone <Emphasis Type="Italic">Actinia equina</Emphasis>     

Tess Olivia Bamber  Angus Charles Jackson  Robert Philip Mansfield 《Ocean Science Journal》2018,53(2):215-224

Increasing concentrations of atmospheric carbon dioxide are causing oceanic pH to decline worldwide, a phenomenon termed ocean acidification. Mounting experimental evidence indicates that near-future levels of CO₂ will affect calcareous invertebrates such as corals, molluscs and gastropods, by reducing their scope for calcification. Despite extensive research into ocean acidification in recent years, the effects on non-calcifying anthozoans, such as sea anemones, remain little explored. In Western Europe, intertidal anemones such as Actinia equina are abundant, lower trophic-level organisms that function as important ecosystem engineers. Changes to behaviours of these simple predators could have implications for intertidal assemblages. This investigation identified the effects of reduced seawater pH on feeding and contest behaviour by A. equina. Video footage was recorded for A. equina feeding at current-day seawater (pH 8.1), and the least (pH 7.9) and most (pH 7.6) severe end-of-century predictions. Footage was also taken of contests over ownership of space between anemones exposed to reduced pH and those that were not. No statistically significant differences were identified in feeding duration or various aspects of contest behaviour including initiating, winning, inflating acrorhagi, inflicting acrorhagial peels and contest duration. Multivariate analyses showed no effect of pH on a combination of these variables. This provides contrast with other studies where anemones with symbiotic algae thrive in areas of natural increased acidity. Thus, novel experiments using intraspecific contests and resource-holding potential may prove an effective approach to understand sub-lethal consequences of ocean acidification for A. equina, other sea anemones and more broadly for marine ecosystems.  相似文献   

An interacting new holographic dark energy in the framework of fractal cosmology     

Ehsan Sadri  Martiros Khurshudyan 《Astrophysics and Space Science》2018,363(11):230

In this paper, we study an interacting holographic dark energy model in the framework of fractal cosmology. The features of fractal cosmology could pass ultraviolet divergencies and also make a better understanding of the universe in different dimensions. We discuss a fractal FRW universe filled with the dark energy and cold dark matter interacting with each other. It is observed that the Hubble parameter embraces the recent observational range while the deceleration parameter demonstrates an accelerating universe and a behavior similar to \(\Lambda \mbox{CDM}\). Plotting the equation of state shows that it lies in phantom region for interaction mode. We use \(\mathit{Om}\)-diagnostic tool and it shows a phantom behavior of dark energy which is a condition of avoiding the formation of black holes. Finally we execute the StateFinder diagnostic pair and all the trajectories for interacting and non-interacting state of the model meet the fixed point \(\Lambda \mbox{CDM}\) at the start of the evolution. A behavior similar to Chaplygin gas also can be observed in statefinder plane. We find that new holographic dark energy model (NHDE) in fractal cosmology expressed the consistent behavior with recent observational data and can be considered as a model to avoid the formation of black holes in comparison with the main model of NHDE in the simple FRW universe. It has also been observed that for the interaction term varying with matter density, the model generates asymptotic de-Sitter solution. However, if the interaction term varies with energy density, then the model shows Big-Rip singularity. Using our modified CAMB code, we observed that the interacting model suppresses the CMB spectrum at low multipoles \(l<50\) and enhances the acoustic peaks. Based on the observational data sets used in this paper and using Metropolis-Hastings method of MCMC numerical calculation, it seems that the best value with \(1\sigma \) and \(2\sigma \) confidence interval are \(\Omega _{m0}=0.278^{+0.008~+0.010} _{-0.007~-0.009}\), \(H_{0}=69.9^{+0.95~+1.57}_{-0.95~-1.57}\), \(r_{c}=0.08^{+0.02~+0.027}_{-0.002~-0.0027}\), \(\beta =0.496^{+0.005~+0.009} _{-0.005~-0.009}\), \(c= 0.691^{+0.024~+0.039}_{-0.025~-0.037}\) and \(b^{2}=0.035\) according to which we find that the proposed model in the presence of interaction is compatible with the recent observational data.  相似文献   

Sunspot Positions and Areas from Observations by Pierre Gassendi     

Mikhail Vokhmyanin  Nadezhda Zolotova 《Solar physics》2018,293(11):150

Solar activity behaviour on the eve of the Maunder minimum may provide important information on the period of further suppression of sunspot population. We analyse sunspot positions and areas in the 1630s extracted from rare drawings published by Pierre Gassendi in Opera Omnia. This work was published in two different editions, the first in Lyon and the second almost 70 years later in Florence. The drawings published in Lyon are found to be slightly different from those published in Florence, which produces a discrepancy in the position of spots of a few degrees, while sunspot group areas may differ by a factor of two. We reveal that the orientation of the drawings in the book is not always the same as might be seen in the telescope. We conjecture that the time of Gassendi’s observations covers the beginning of a new Schwabe cycle in the southern hemisphere. The differential rotation rate in the 1630s is also assessed and discussed.  相似文献   

Low resolution spectroscopy of selected Algol systems     

Shanti Priya Devarapalli  Rukmini Jagirdar  M. Parthasarathy  D. K. Sahu  Vijay Mohan  B. C. Bhatt  Vineet S. Thomas 《Astrophysics and Space Science》2018,363(4):69

The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand presence of mass transfer, a disk or circumstellar matter and chromospheric emission. We also present first spectroscopic and period study for few Algols and conclude that high resolution spectra within and outside the primary minimum are needed for better understanding of these Algol type close binaries.  相似文献   

Understanding the Role of Mass-Unloading in a Filament Eruption     

J. M. Jenkins  D. M. Long  L. van Driel-Gesztelyi  J. Carlyle 《Solar physics》2018,293(1):7

We describe a partial filament eruption on 11 December 2011 that demonstrates that the inclusion of mass is an important next step for understanding solar eruptions. Observations from the Solar Terrestrial Relations Observatory-Behind (STEREO-B) and the Solar Dynamics Observatory (SDO) spacecraft were used to remove line-of-sight projection effects in filament motion and correlate the effect of plasma dynamics with the evolution of the filament height. Flux cancellation and nearby flux emergence are shown to have played a role in increasing the height of the filament prior to eruption. The two viewpoints allow the quantitative estimation of a large mass-unloading, the subsequent radial expansion, and the eruption of the filament to be investigated. A 1.8 to 4.1 lower-limit ratio between gravitational and magnetic-tension forces was found. We therefore conclude that following the loss-of-equilibrium of the flux-rope, the radial expansion of the flux-rope was restrained by the filamentary material until 70% of the mass had evacuated the structure through mass-unloading.  相似文献   

Comparison of the spatio-temporal dynamics of vegetation between the Changbai Mountains of eastern Eurasia and the Appalachian Mountains of eastern North America     

Xiao-yi Guo  Hong-yan Zhang  Ye-qiao Wang  Hong-shi He  Zheng-fang Wu  Ying-hua Jin  Zheng-xiang Zhang  Jian-jun Zhao 《山地科学学报》2018,15(1):1-12

The Changbai Mountains and the Appalachian Mountains have similar spatial contexts. The elevation, latitude, and moisture gradients of both mountain ranges offer regional insight for investigating the vegetation dynamics in eastern Eurasia and eastern North America. We determined and compared the spatial patterns and temporal trends in the normalized difference vegetation index (NDVI) in the Changbai Mountains and the Appalachian Mountains using time series data from the Global Inventory Modeling and Mapping Studies 3rd generation dataset from 1982 to 2013. The spatial pattern of NDVI in the Changbai Mountains exhibited fragmentation, whereas NDVI in the Appalachian Mountains decreased from south to north. The vegetation dynamics in the Changbai Mountains had an insignificant trend at the regional scale, whereas the dynamics in the Appalachian Mountains had a significant increasing trend. NDVI increased in 55% of the area of the Changbai Mountains and in 95% of the area of the Appalachian Mountains. The peak NDVI occurred one month later in the Changbai Mountains than in the Appalachian Mountains. The results revealed a significant increase in NDVI in autumn in both mountain ranges. The climatic trend in the Changbai Mountains included warming and decreased precipitation, and whereas that in the Appalachian Mountains included significant warming and increased precipitation. Positive and negative correlations existed between NDVI and temperature and precipitation, respectively, in both mountain ranges. Particularly, the spring temperature and NDVI exhibited a significant positive correlation in both mountain ranges. The results of this study suggest that human actives caused the differences in the spatial patterns of NDVI and that various characteristics of climate change and intensity of human actives dominated the differences in the NDVI trends between the Changbai Mountains and the Appalachian Mountains. Additionally, the vegetation dynamics of both mountain ranges were not identical to those in previous broader-scale studies.  相似文献   

The Influence of Two Kinds of El Niño Events on the Strong Tropical Cyclone Generation and Strength in the Pacific Ocean     

Xingchi Wang  Shuzong Han  Xin Wang  Yujie Dong 《中国海洋大学学报(英文版)》2018,17(5):1011-1018

This paper focuses on the effects of two types of El Niño events on tropical cyclone activity. We classified El Niño events from 1961 to 2015 according to their sea surface temperature (SST) anomalies into an eastern type and a central type. Then we selected strong tropical cyclones to statistically analyze the tropical cyclone characteristics during different events and their effects, as well as to study the possible mechanisms related to thermodynamic and dynamic factors. The tropical cyclone generation areas were found to be very similar during the two kinds of events. The average number of tropical cyclone in the eastern event is more than that in central event, and the hurricane in northeastern Pacific (HNP) has more energy than the typhoon in northwestern Pacific (TNP) in all cases. The seasonal distribution of the TNP high-incidence centers during central El Niño events is opposite to that of the HNP. The TNP accumulated cyclone energy (ACE) intensity is similar in the fall and summer, and the HNP ACE intensity in the summer is greater than that in the fall. The SSTs are consistent with the TNP and HNP movement trends. The Walker circulation intensity was strongly affected by the eastern events, but it quickly returned to its normal state, while the intensity was slightly reduced in the central events, and it slowly returned to its normal state. The vertical velocity distributions in the Pacific are different at different stages of both events, and the distributions of vertical velocity anomalies for typhoons and hurricanes are consistent.  相似文献