bluuebunny/crossref_metadata_2025_split huggingface dataset:
Significant wave heights from Sentinel‐1 SAR: Validation and applications
Authors: Stopa J. E. , Mouche A. 
Published: December 2016

AbstractTwo empirical algorithms are developed for wave mode images measured from the synthetic aperture radar aboard Sentinel‐1 A. The first method, called CWAVE_S1A, is an extension of previous efforts developed for ERS2 and the second method, called Fnn, uses the azimuth cutoff among other parameters to estimate significant wave heights (Hs) and average wave periods without using a modulation transfer function. Neural networks are trained using colocated data generated from WAVEWATCH III and independently verified with data from altimeters and in situ buoys. We use neural networks to relate the nonlinear relationships between the input SAR image parameters and output geophysical wave parameters. CWAVE_S1A performs well and has reduced precision compared to Fnn with Hs root mean square errors within 0.5 and 0.6 m, respectively. The developed neural networks extend the SAR's ability to retrieve useful wave information under a large range of environmental conditions including extratropical and tropical cyclones in which Hs estimation is traditionally challenging.
Methane and nitrous oxide distributions across the North American Arctic Ocean during summer, 2015
Authors: Fenwick Lindsay , Capelle David , Damm Ellen , Zimmermann Sarah , Williams William J. , Vagle Svein , Tortell Philippe D. 
Published: December 2016

AbstractWe collected Arctic Ocean water column samples for methane (CH4) and nitrous oxide (N2O) analysis on three separate cruises in the summer and fall of 2015, covering a ∼10,000 km transect from the Bering Sea to Baffin Bay. This provided a three‐dimensional view of CH4 and N2O distributions across contrasting hydrographic environments, from the oligotrophic waters of the deep Canada Basin and Baffin Bay, to the productive shelves of the Bering and Chukchi Seas. Percent saturation relative to atmospheric equilibrium ranged from 30 to 800% for CH4 and 75 to 145% for N2O, with the highest concentrations of both gases occurring in the northern Chukchi Sea. Nitrogen cycling in the shelf sediments of the Bering and Chukchi Seas likely constituted the major source of N2O to the water column, and the resulting high N2O concentrations were transported across the Arctic Ocean in eastward‐flowing water masses. Methane concentrations were more spatially heterogeneous, reflecting a variety of localized inputs, including likely sources from sedimentary methanogenesis and sea ice processes. Unlike N2O, CH4 was rapidly consumed through microbial oxidation in the water column, as shown by the 13C enrichment of CH4 with decreasing concentrations. For both CH4 and N2O, sea‐air fluxes were close to neutral, indicating that our sampling region was neither a major source nor sink of these gases. Our results provide insight into the factors controlling the distribution of CH4 and N2O in the North American Arctic Ocean, and an important baseline data set against which future changes can be assessed.
A simple hypothesis of how leaf and canopy‐level transpiration and assimilation respond to elevated CO2 reveals distinct response patterns between disturbed and undisturbed vegetation
Authors: Donohue Randall J. , Roderick Michael L. , McVicar Tim R. , Yang Yuting 
Published: December 2016

AbstractElevated CO2 increases leaf‐level water‐use efficiency (ω) almost universally. How canopy‐level transpiration and assimilation fluxes respond to increased ω is currently unclear. We present a simple, resource‐availability‐based hypothesis of how equilibrium (or mature) leaf and canopy transpiration and assimilation rates, along with leaf area index (L), respond to elevated CO2. We quantify this hypothesis in the form of a model and test it against observations from eight Free Air CO2 Enrichment sites that span a wide range of resource availabilities. Sites were grouped according to vegetation disturbance status. We find the model adequately accounts for the responses of undisturbed vegetation (R2 = 0.73, 11% error) but cannot account for the responses of disturbed vegetation (R2 = 0.47, 17% error). At undisturbed sites, the responses of L and of leaf and canopy transpiration vary predictably (7% error) with resource availability, whereas the leaf assimilation response is less predictable. In contrast, the L and transpiration flux responses at the disturbed (mostly forested) sites are highly variable and are not strongly related to resource availability. Initial analyses suggest that they are more strongly related to regrowth age than to resource availability. We conclude that (i) our CO2 response hypothesis is valid for capturing the responses of undisturbed vegetation only, (ii) that the responses of disturbed vegetation are distinctly different from undisturbed vegetation, and (iii) that these differences need to be accounted for when predicting the effects of elevated CO2 on land surface processes generally, and on leaf area and water fluxes in particular.
Biodegradation kinetics of dissolved organic matter chromatographic fractions in an intermittent river
Authors: Catalán N. , Casas‐Ruiz J. P. , von Schiller D. , Proia L. , Obrador B. , Zwirnmann E. , Marcé R. 
Published: December 2016

AbstractControls on the degradation of dissolved organic matter (DOM) are complex but key to understand the role of freshwaters in the carbon cycle. Both the origin and previous degradation history have been suggested to determine DOM reactivity, but it is still a major challenge to understand the links between DOM composition and biodegradation kinetics. An appropriate context to study these links are intermittent rivers, as summer drought naturally diversifies DOM sources and sinks. Here we investigated the biodegradation kinetics of DOM in the main aquatic environments present in a temporary river. During dark incubations we traced the dynamics of bulk DOM and its main chromatographic fractions defined using LC‐OCD: high molecular weight substances (HMWS), low molecular weight substances (LMWS), and humic substances and building blocks. Bulk DOM decay patterns were successfully fitted to the reactivity continuum (RC) biodegradation model. The RC parameters depicted running waters as the sites presenting a more reactive DOM, and temporary pools, enriched in leaf litter, as the ones with slowest DOM decay. The decay patterns of each DOM fraction were consistent throughout sites. LMWS and HMWS decayed in all cases and could be modeled using the RC model. Notably, the dynamics of LMWS controlled the bulk DOM kinetics. We discuss the mechanistic basis for the chromatographic fractions' kinetics during biodegradation and the implications that preconditioning and summer drought can have for DOM biodegradation in intermittent rivers.
Evaluation of oxygen isotope and Mg/Ca ratios in high‐magnesium calcite from benthic foraminifera as a proxy for water temperature
Authors: Maeda Ayumi , Fujita Kazuhiko , Horikawa Keiji , Suzuki Atsushi , Yoshimura Toshihiro , Tamenori Yusuke , Kawahata Hodaka 
Published: December 2016

AbstractOxygen isotope ratios (δ18O) and Mg/Ca ratios in organically produced calcium carbonate (calcite and aragonite) by marine species have been used as proxies for paleotemperature. The relationship between the components of large benthic foraminiferal tests (high‐magnesium calcite) and seawater temperature has been little investigated yet. We conducted culture experiments using two species of reef‐dwelling large benthic foraminifera under six temperature conditions (21–30°C). We selected the perforate species Calcarina gaudichaudii, and the imperforate species Amphisorus kudakajimensis, both of which are host to algal symbionts, for the experiments. The results indicated the significant correlation of Mg/Ca ratios (C. gaudichaudii and A. kudakajimensis) and δ18O (C. gaudichaudii) with temperature. The test weight of both species showed temperature dependency, with maxima at 27°C or 29°C and subsequent decline at 30°C. After correction for the contribution of the initial tests, which can be calculated from the weight ratios of the initial and cultured tests, the relationships of the Mg/Ca ratios and δ18O to temperature were obtained with the least squares best fit method as follows: C. gaudichaudii: T = 18.5–4.52 (δ18Oc–δ18Osw), A. kudakajimensis: T = 25.0–4.96 (δ18Oc–δ18Osw), and C. gaudichaudii and A. kudakajimensis: Mg/Ca = 2.85 T + 81.20. We concluded that species‐specific calibration is unnecessary for Mg/Ca‐temperature relationship, although it is necessary for δ18O related to the different calcification mechanisms of imperforate (A. kudakajimensis) and perforate (C. gaudichaudii) species.
Low photolability of yedoma permafrost dissolved organic carbon
Authors: Stubbins Aron , Mann Paul J. , Powers Leanne , Bittar Thais B. , Dittmar Thorsten , McIntyre Cameron P. , Eglinton Timothy I. , Zimov Nikita , Spencer Robert G. M. 
Published: December 2016

AbstractVast stores of arctic permafrost carbon that have remained frozen for millennia are thawing, releasing ancient dissolved organic carbon (DOC) to arctic inland waters. Once in arctic waters, DOC can be converted to CO2 and emitted to the atmosphere, accelerating climate change. Sunlight‐driven photoreactions oxidize DOC, converting a portion to CO2 and leaving behind a photomodified pool of dissolved organic matter (DOM). Samples from the Kolyma River, its tributaries, and streams draining thawing yedoma permafrost were collected. Irradiation experiments and radiocarbon dating were employed to assess the photolability of ancient permafrost‐DOC in natural and laboratory generated samples containing a mix of modern and ancient DOC. Photolabile DOC was always modern, with no measurable photochemical loss of ancient permafrost‐DOC. However, optical and ultrahigh resolution mass spectrometric measurements revealed that both modern river DOM and ancient permafrost‐DOM were photomodified during the irradiations, converting aromatic compounds to less conjugated compounds. These findings suggest that although sunlight‐driven photoreactions do not directly mineralize permafrost‐DOC, photomodification of permafrost‐DOM chemistry may influence its fate and ecological functions in aquatic systems.
The dynamic response of the water retention curve in unsaturated soils during drainage to acoustic excitations
Authors: Lo Wei‐Cheng , Yang Chi‐Chin , Hsu Shao‐Yiu , Chen Chu‐Hui , Yeh Chao‐Lung , Hilpert Markus 
Published: December 2016

AbstractWe examined the effects of acoustic excitations on the water retention curve, i.e., the relationship between capillary pressure
and water saturation
in unsaturated porous media, during drainage. The water retention curves were measured under static and dynamic conditions, where water was withdrawn from a sandbox with three different pumping rates, 12.6, 19.7, and 25.2 mL/s. Excitations with frequencies of 75, 100, 125, and 150 Hz were applied. The acoustic excitations had no effect on the static water retention curve but altered the dynamic water retention curve. The acoustic excitations lowered the dynamic
, especially under the dynamic condition where the pumping rate was 25.2 mL/s and when
varied between 0.6 and 0.95. The differences between the capillary pressures measured under static and dynamic conditions decreased when acoustic excitations were applied. We link this finding to the change in contact angle induced by the acoustic excitation. The dynamic coefficients,
, for the dynamic water retention curves that we fitted to the experimental data were smaller with than without acoustic excitations. We attribute the decrease of the dynamic coefficient to the combination of the increase in the permeability and the decline in the air‐entry pressure caused by adding acoustic excitations.
A coupled three‐dimensional hydrodynamic model for predicting hypolimnetic oxygenation and epilimnetic mixing in a shallow eutrophic reservoir
Authors: Chen Shengyang , Lei Chengwang , Carey Cayelan C. , Gantzer Paul A. , Little John C. 
Published: December 2016

AbstractArtificial mixing and hypolimnetic oxygenation are two common methods for improving water quality in reservoirs. To examine the effects of their operation on the thermal structure of the water column, we used a three‐dimensional hydrodynamic model coupled with a newly developed water‐jet model and an existing linear bubble‐plume model in conjunction with whole‐reservoir in situ mixing experiments in a drinking‐water reservoir. This reservoir has a side‐stream supersaturation (SSS) hypolimnetic oxygenation system and a bubble‐plume epilimnetic mixing (EM) system installed to reduce hypolimnetic hypoxia and algal blooms. The results show that the SSS successfully adds dissolved oxygen to the hypolimnion without destratifying the reservoir, whereas the EM, located at the lower metalimnetic boundary, deepens this boundary and partially mixes the metalimnion and epilimnion. The newly developed water‐jet model coupled with the hydrodynamic model can successfully predict the variation of the thermal structure in the reservoir. The extent to which the SSS and EM systems affect the thermal structure of the reservoir is also quantified by further application of the coupled hydrodynamic model.
What is the “active layer”?
Authors: Church M. , Haschenburger J. K. 
Published: December 2016

AbstractWe note the presence in the literature of two different concepts of the term “active layer” in relation to fluvial sediment transport. It has been used to represent the current dynamically active streambed surface, or to represent the depth of event‐scale scour and fill. These concepts involve distinct length and time scales. We propose that, when the distinction is important, the concepts be distinguished as either a “dynamical active layer” or an “event active layer.”
Constraining the annual groundwater contribution to the water balance of an agricultural floodplain using radon: The importance of floods
Authors: Webb Jackie R. , Santos Isaac R. , Robson Barbara , Macdonald Ben , Jeffrey Luke , Maher Damien T. 
Published: December 2016

AbstractThe water balance of drained floodplains is highly dynamic with complex groundwater–surface water interactions operating over varying spatial and temporal scales. Here we hypothesize that the majority of groundwater discharge will follow flood events in a modified wetland. To test this hypothesis, we developed a detailed water balance that quantifies the contribution of groundwater discharge to the annual water budget of an extensively drained agricultural floodplain. A clear relationship between surface water radon measurements and groundwater level indicated alternating connection–disconnection dynamics between the drains and shallow groundwater. This relationship was used to develop a radon mass balance to quantitatively model groundwater discharge continuously throughout the year. Groundwater discharge varied by four orders of magnitude over the study period, with daily average rates ranging from 0 to 27,200 m3 d−1, peaking just a few hours after floods receded. Flood events occurred only 12% of the time yet contributed 72–76% of the total groundwater discharge. During flood recession periods, aerial groundwater discharge rates reached up to 325 cm d−1 which were some of the highest rates ever estimated. We proposed that the high drainage density of this site (12.4 km constructed drains km−2 catchment area) enhanced groundwater discharge during wet periods due to increased connectivity with the soil. Overall, groundwater discharge contributed 30–80% to the total surface water discharge. This study offers insight into the dynamic behavior of groundwater within an extensively drained floodplain, and the importance of capturing flood events to quantify total groundwater contribution to floodplain water balances.
Imaging and quantification of spreading and trapping of carbon dioxide in saline aquifers using meter‐scale laboratory experiments
Authors: Trevisan Luca , Pini Ronny , Cihan Abdullah , Birkholzer Jens T. , Zhou Quanlin , González‐Nicolás Ana , Illangasekare Tissa H. 
Published: December 2016

AbstractThe role of capillary forces during buoyant migration of CO2 is critical toward plume immobilization within the postinjection phase of a geological carbon sequestration operation. However, the inherent heterogeneity of the subsurface makes it very challenging to evaluate the effects of capillary forces on the storage capacity of these formations and to assess in situ plume evolution. To overcome the lack of accurate and continuous observations at the field scale and to mimic vertical migration and entrapment of realistic CO2 plumes in the presence of a background hydraulic gradient, we conducted two unique long‐term experiments in a 2.44 m × 0.5 m tank. X‐ray attenuation allowed measuring the evolution of a CO2‐surrogate fluid saturation, thus providing direct insight into capillarity‐dominated and buoyancy‐dominated flow processes occurring under successive drainage and imbibition conditions. The comparison of saturation distributions between two experimental campaigns suggests that layered‐type heterogeneity plays an important role on nonwetting phase (NWP) migration and trapping, because it leads to (i) longer displacement times (3.6 months versus 24 days) to reach stable trapping conditions, (ii) limited vertical migration of the plume (with center of mass at 39% versus 55% of aquifer thickness), and (iii) immobilization of a larger fraction of injected NWP mass (67.2% versus 51.5% of injected volume) as compared to the homogenous scenario. While these observations confirm once more the role of geological heterogeneity in controlling buoyant flows in the subsurface, they also highlight the importance of characterizing it at scales that are below seismic resolution (1–10 m).
Numerical study on CO2 leakage detection using electrical streaming potential data
Authors: Büsing Henrik , Vogt Christian , Ebigbo Anozie , Klitzsch Norbert 
Published: December 2016

AbstractWe study the feasibility of detecting carbon dioxide (CO2) movement in the overburden of a storage reservoir due to CO2 leakage through an abandoned well by self‐potential (SP) measurements at the surface. This is achieved with three‐dimensional numerical (SP) modeling of two‐phase fluid flow and electrokinetic coupling between flow and streaming potential. We find that, in typical leakage scenarios, for leaky and/or injection wells with conductive metal casing, self‐potential signals originating from injection can be identified at the surface. As the injection signal is also observed at the leaky well with metal casing, SP monitoring can be applied for detecting abandoned wells. However, leakage signals are much smaller than the injection signal and thus masked by the latter. We present three alternatives to overcome this problem: (i) simulate the streaming potential of the nonleaky scenario and subtract the result from the measured streaming potential data; (ii) exploit the symmetry of the injection signal by analyzing the potential difference of dipoles with the dipole center at the injection well; or (iii) measure SP during periods where the injection is interrupted. In our judgement, the most promising approach for detecting a real‐world CO2 leakage is by combining methods (i) and (ii), because this would give the highest signal from the leakage and omit signals originating from the injection well. Consequently, we recommend SP as monitoring method for subsurface CO2 storage, especially because a leakage can be detected shortly after the injection started even before CO2 arrives at the leaky well.
Extended and direct evaluation of RT‐QuIC assays for Creutzfeldt‐Jakob disease diagnosis
Authors: Groveman Bradley R. , Orrú Christina D. , Hughson Andrew G. , Bongianni Matilde , Fiorini Michele , Imperiale Daniele , Ladogana Anna , Pocchiari Maurizio , Zanusso Gianluigi , Caughey Byron 
Published: December 2016

AbstractReal‐Time Quaking‐Induced Conversion (RT‐QuIC) testing of human cerebrospinal fluid (CSF) is highly sensitive and specific in discriminating sporadic CJD patients from those without prion disease. Here, using CSF samples from 113 CJD and 64 non‐prion disease patients, we provide the first direct and concurrent comparison of our improved RT‐QuIC assay to our previous assay, which is similar to those commonly used internationally for CJD diagnosis. This extended comparison demonstrated a ~21% increase in diagnostic sensitivity, a 2‐day reduction in average detection time, and 100% specificity.
Electron‐Transfer Reactions Triggered by Uncharged or Cationic Photosensitizer: Methodology for Generation of o‐Quinodimethane and Analysis of Back Electron‐Transfer Process
Authors: Matsui Yasunori , Ikeda Teruyo , Takahashi Yasutake , Kamata Masaki , Akagi Megumi , Ohya Yukako , Fujino Ryota , Namai Hayato , Ohta Eisuke , Ogaki Takuya , Miyashi Tsutomu , Tero‐Kubota Shozo , Mizuno Kazuhiko , Ikeda Hiroshi 
Published: December 2016

AbstractPhotoinduced electron transfer (PET) followed by back electron transfer (BET) reactions of 1,2‐bis(α‐styryl)benzenes 1, generates o‐quinodimethane derivative 2 via the corresponding radical cation 2⋅+. This process serves as a facile method to form o‐quinodimethane intermediates. The intermediacy of 2⋅+ and 2 were confirmed by using various spectroscopic methods and trapping reactions with 3O2 and dienophiles. Kinetic analysis using nanosecond time‐resolved absorption showed that 2⋅+ was transformed to 2 via a BET process, in which the decay of 2⋅+ and rise of 2 have almost the same rate constants of kDECAY=5.6×105 s−1 and kRISE=5.9×105 s−1, respectively. The net BET rate constant evaluated by using Marcus theory is much faster than these experimental values, owing to the reduction based on diffusion.
Out‐of‐time‐order correlations in many‐body localized and thermal phases
Authors: Chen Xiao , Zhou Tianci , Huse David A. , Fradkin Eduardo 
Published: December 2016

We use the out‐of‐time‐order (OTO) correlators to study the slow dynamics in the many‐body localized (MBL) phase. We investigate OTO correlators in the effective (“l‐bit”) model of the MBL phase, and show that their amplitudes after disorder averaging approach their long‐time limits as power‐laws of time. This power‐law dynamics is due to dephasing caused by interactions between the localized operators that fall off exponentially with distance. The long‐time limits of the OTO correlators are determined by the overlaps of the local operators with the conserved l‐bits. We demonstrate numerically our results in the effective model and three other more “realistic” spin chain models. Furthermore, we extend our calculations to the thermal phase and find that for a time‐independent Hamiltonian, the OTO correlators also appear to vanish as a power law at long time, perhaps due to coupling to conserved densities. In contrast, we find that in the thermal phase of a Floquet spin model with no conserved densities the OTO correlator decays exponentially at long times.
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Elucidation of the Dexter‐Type Energy Transfer in DNA by Thymine–Thymine Dimer Formation Using Photosensitizers as Artificial Nucleosides
Authors: Antusch Linda , Gaß Nadine , Wagenknecht Hans‐Achim 
Published: December 2016

AbstractC‐nucleosides of 4‐methylbenzophenone, 4‐methoxybenzophenone, and 2′‐methoxyacetophenone were synthetically incorporated as internal photosensitizers into DNA double strands. This structurally new approach makes it possible to study the distance dependence of thymidine dimer formation because the site of photoinduced triplet energy transfer injection is clearly defined. The counterstrands to these modified strands lacked the phosphodiester bond between the two adjacent thymidines that are supposed to react with each other. Their dimerization could be evidenced by gel electrophoresis because the covalent connection by cyclobutane formation between the two thymidines changes the mobility. A shallow exponential distance dependence for the formation of thymidine dimers over up to 10 A‐T base pairs was observed that agrees with a Dexter‐type triplet–triplet energy transfer mechanism. Concomitantly, a significant amount of photoinduced DNA crosslinking was observed.