bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Role of Breccia Lenses in Regolith Generation From the Formation of Small, Simple Craters: Application to the Apollo 15 Landing Site
Authors: Hirabayashi M. , Howl B. A. , Fassett C. I. , Soderblom J. M. , Minton D. A. , Melosh H. J. 
Published: February 2018

AbstractImpact cratering is likely a primary agent of regolith generation on airless bodies. Regolith production via impact cratering has long been a key topic of study since the Apollo era. The evolution of regolith due to impact cratering, however, is not well understood. A better formulation is needed to help quantify the formation mechanism and timescale of regolith evolution. Here we propose an analytically derived stochastic model that describes the evolution of regolith generated by small, simple craters. We account for ejecta blanketing as well as regolith infilling of the transient crater cavity. Our results show that the regolith infilling plays a key role in producing regolith. Our model demonstrates that because of the stochastic nature of impact cratering, the regolith thickness varies laterally, which is consistent with earlier work. We apply this analytical model to the regolith evolution at the Apollo 15 site. The regolith thickness is computed considering the observed crater size‐frequency distribution of small, simple lunar craters (< 381 m in radius for ejecta blanketing and <100 m in radius for the regolith infilling). Allowing for some amount of regolith coming from the outside of the area, our result is consistent with an empirical result from the Apollo 15 seismic experiment. Finally, we find that the timescale of regolith growth is longer than that of crater equilibrium, implying that even if crater equilibrium is observed on a cratered surface, it is likely that the regolith thickness is still evolving due to additional impact craters.
Effects of Polar Indirect Circulation on Superrotation and Multiple Equilibrium in Long‐Term AGCM Experiments With an Idealized Venus‐Like Forcing: Sensitivity to Horizontal Resolution and Initial Condition
Authors: Yamamoto Masaru , Takahashi Masaaki 
Published: February 2018

AbstractA simplified model setup has been used in atmospheric general circulation models (AGCMs), to clarify the fluid dynamical process of terrestrial planets. In the present work, the research aim is to ascertain the dynamical effects of polar indirect circulation on superrotation and multiple equilibrium states in Venus‐like planets. The model setup previously used for Venus AGCM intercomparison is applied to the Model for Interdisciplinary Research On Climate AGCM, and the horizontal resolution and initial conditions are altered in the long‐term experiments. The structures of general circulation and planetary‐scale waves in the T42 (Truncation wave number 42) experiment are similar to those in the T63 experiment. In the presence of the polar indirect circulation, the superrotational flow weakens in the cloud layer and its momentum is transported toward the lower atmosphere at high latitudes. In contrast, in the T21 experiment, because the polar indirect circulation is not fully resolved, the vertical momentum transport due to the indirect circulation is ineffective in the lower atmosphere, and thus, the cloud top superrotational flow becomes greater than those in the higher‐resolution experiments. The multiple equilibrium states caused by different initial zonal flows appear in the T21 experiments, although they are not seen in the experiments of T42 and higher. Thus, the polar indirect circulation in the Gierasch‐Rossow‐Williams mechanism weakens the superrotational flow in the cloud layer and breaks the steady state multiplicity of the general circulation.
Direct Numerical Simulation of Transverse Ripples: 1. Pattern Initiation and Bedform Interactions
Authors: Zgheib N. , Fedele J. J. , Hoyal D. C. J. D. , Perillo M. M. , Balachandar S. 
Published: February 2018

AbstractWe present results of coupled direct numerical simulations between flow and a deformable bed in a horizontally periodic, turbulent open channel at a shear Reynolds number of Reτ = 180. The feedback between the temporally and spatially evolving bed and the flow is enforced via the immersed boundary method. Using the near‐bed flow field, we provide evidence on the role of locally intense near‐bed vortical structures during the early stages of bed formation, from the emergence of quasi‐streamwise streaks to the formation of incipient bedform crestlines. Additionally, we take a new look at a number of defect‐related bedform interactions, including lateral linking, defect and bedform repulsion, merging, and defect creation, and show that the underlying mechanisms, in these flow‐aligned interactions, are very similar to each other. Consequently, the interactions are labeled differently depending on the geometry of interacting structures and the outcome of the interaction. In the companion paper, we compare our results to published experimental data and provide an extensive quantitative analysis of the bed, where we demonstrate the importance of neighboring structures, especially upstream neighbors, on bedform dynamics (growth/decay and speed) and wave coarsening. Video files of bed evolution are available in the supporting information.
Variance and Rate‐of‐Change as Early Warning Signals for a Critical Transition in an Aquatic Ecosystem State: A Test Case From Tasmania, Australia
Authors: Beck Kristen K. , Fletcher Michael‐Shawn , Gadd Patricia S. , Heijnis Henk , Saunders Krystyna M. , Simpson Gavin L. , Zawadzki Atun 
Published: February 2018

AbstractCritical transitions in ecosystem states are often sudden and unpredictable. Consequently, there is a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquatic ecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapid response times. Using palaeoecological techniques, we can measure properties of time series data to determine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS. Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, and charcoal influx), we assess whether a critical transition in diatom community structure was preceded by measurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatom community dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yr BP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as a transition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, and Fragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, and Gomphonema multiforme). We observe a marked increase in compositional variance and rate‐of‐change prior to this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetation remains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invade and the vegetation system experiences an increase in both compositional variance and rate‐of‐change. These trends imply an approaching critical transition in the vegetation and the probable collapse of the local rain forest system.
Productivity Contribution of Paleozoic Woodlands to the Formation of Shale‐Hosted Massive Sulfide Deposits in the Iberian Pyrite Belt (Tharsis, Spain)
Authors: Fernández‐Remolar David C. , Harir Mourad , Carrizo Daniel , Schmitt‐Kopplin Philippe , Amils Ricardo 
Published: February 2018

AbstractThe geological materials produced during catastrophic and destructive events are an essential source of paleobiological knowledge. The paleobiological information recorded by such events can be rich in information on the size, diversity, and structure of paleocommunities. In this regard, the geobiological study of late Devonian organic matter sampled in Tharsis (Iberian Pyrite Belt) provided some new insights into a Paleozoic woodland community, which was recorded as massive sulfides and black shale deposits affected by a catastrophic event. Sample analysis using TOF‐SIMS (Time of Flight Secondary Ion Mass Spectrometer), and complemented by GC/MS (Gas Chromatrograph/Mass Spectrometer) identified organic compounds showing a very distinct distribution in the rock. While phytochemical compounds occur homogeneously in the sample matrix that is composed of black shale, the microbial‐derived organics are more abundant in the sulfide nodules. The cooccurrence of sulfur bacteria compounds and the overwhelming presence of phytochemicals provide support for the hypothesis that the formation of the massive sulfides resulted from a high rate of vegetal debris production and its oxidation through sulfate reduction under suboxic to anoxic conditions. A continuous supply of iron from hydrothermal activity coupled with microbial activity was strictly necessary to produce this massive orebody. A rough estimate of the woodland biomass was made possible by accounting for the microbial sulfur production activity recorded in the metallic sulfide. As a result, the biomass size of the late Devonian woodland community was comparable to modern woodlands like the Amazon or Congo rainforests.
Source Partitioning of Methane Emissions and its Seasonality in the U.S. Midwest
Authors: Chen Zichong , Griffis Timothy J. , Baker John M. , Millet Dylan B. , Wood Jeffrey D. , Dlugokencky Edward J. , Andrews Arlyn E. , Sweeney Colm , Hu Cheng , Kolka Randall K. 
Published: February 2018

AbstractThe methane (CH4) budget and its source partitioning are poorly constrained in the Midwestern United States. We used tall tower (185 m) aerodynamic flux measurements and atmospheric scale factor Bayesian inversions to constrain the monthly budget and to partition the total budget into natural (e.g., wetlands) and anthropogenic (e.g., livestock, waste, and natural gas) sources for the period June 2016 to September 2017. Aerodynamic flux observations indicated that the landscape was a CH4 source with a mean annual CH4 flux of +13.7 ± 0.34 nmol m−2 s−1 and was rarely a net sink. The scale factor Bayesian inversion analyses revealed a mean annual source of +12.3 ± 2.1 nmol m−2 s−1. Flux partitioning revealed that the anthropogenic source (7.8 ± 1.6 Tg CH4 yr−1) was 1.5 times greater than the bottom‐up gridded United States Environmental Protection Agency inventory, in which livestock and oil/gas sources were underestimated by 1.8‐fold and 1.3‐fold, respectively. Wetland emissions (4.0 ± 1.2 Tg CH4 yr−1) were the second largest source, accounting for 34% of the total budget. The temporal variability of total CH4 emissions was dominated by wetlands with peak emissions occurring in August. In contrast, emissions from oil/gas and other anthropogenic sources showed relatively weak seasonality.
Optimized Application of Biome‐BGC for Modeling the Daily GPP of Natural Vegetation Over Peninsular Spain
Authors: Sanchez‐Ruiz Sergio , Chiesi Marta , Fibbi Luca , Carrara Arnaud , Maselli Fabio , Gilabert María Amparo 
Published: February 2018

AbstractA methodology for improving the application of Biome‐BGC in peninsular Spain was developed focusing on the optimization of the rooting depth (zroot), which is not available for the study area on a spatially distributed basis. The optimal zroot was identified by comparing daily gross primary production (GPP) simulations with varying zroot to GPP estimations from a production efficiency model previously optimized for and validated in the study area. The methodology was first tested in four eddy covariance (EC) sites representative of Mediterranean ecosystems and next applied at a regional scale to the whole study area. As a result, daily GPP simulated maps for the 2005–2012 period and an optimal zroot map were obtained. Optimal zroot in the four EC sites was shallower than the default one (100 cm) and led to better simulation results. Realistic, spatially distributed GPP estimates were obtained at regional scale. Withal, some discrepancies appeared both at local and regional scale emphasizing the difficulty to adequately simulate the site's water budget and the need for proper setting of inputs, including zroot for the correct functioning of Biome‐BGC. The performed optimization opens the door for using Biome‐BGC to simulate other main vegetation processes, such as net carbon fluxes, in the study area.
Particulate Organic Carbon Composition in Temperature Fronts of the Northeastern Arabian Sea during Winter
Authors: Krishna M. S. , Mukherjee J. , Dalabehera H. B. , Sarma V. V. S. S. 
Published: February 2018

AbstractIn order to understand the major sources of particulate organic carbon (POC) in the frontal zones and to examine their variability with space and time, a total of five temperature fronts of different ages was sampled in the northeastern Arabian Sea during winter. Compared to the nonfrontal regions, POC and chlorophyll‐a were higher within the coastal fronts, whereas chlorophyll‐a was lower within the open ocean front (T1). The variation of POC between coastal and open ocean fronts is attributed to the combined influence of variable vertical mixing, heterotrophic transformation and age of the front. Relatively depleted δ13CPOC and δ15NPN were observed within the fronts, suggesting that POC pool is contributed by in situ production supported by upwelling of nutrient‐rich water and zooplankton biomass. Elemental C:N ratios, POC:Chl‐a, δ13CPOC, and δ15NPN suggest that POC is mainly contributed from primary producers and heterotrophs in the study region. However, relative contributions from these two sources vary spatially from coastal to open ocean and with the age of the front. Stable Isotope Analysis in R (SIAR) model revealed that zooplankton biomass largely contributed to POC in the open ocean (60–80%) than phytoplankton (20–40%) and nearly equal contribution was observed in the coastal fronts (50–60% and 40–50%, respectively). This study, thus, demonstrates that dominant heterotrophy and autotrophy in the open ocean and coastal fronts and it is consistent with their biomasses. Predominant heterotrophy in the open ocean is attributed to deeper mixed layer resulting in upwelling of bacteria‐rich and phytoplankton‐poor water to surface leading to existence of microbial loop.
Composition and Impedance Heterogeneity in Oxide Electrode Cross‐Sections Detected by Raman Spectroscopy
Authors: Gilbert James A. , Maroni Victor A. , Cui Yanjie , Gosztola David J. , Miller Dean J. , Abraham Daniel P. 
Published: February 2018

AbstractLithium‐bearing layered transition metal oxides are the materials of choice for positive electrodes in high energy lithium‐ion cells being developed for electric vehicle applications. During electrochemical cycling, the loss of mobile lithium‐ions due to undesirable side reactions and an increase in cell resistance leads to a decline in the energy and power performance of the cells. This performance loss is often nonuniform across multiple cells, especially for those cycled at high voltages or high C‐rates. This nonuniformity results from inhomogeneous behavior in the battery electrodes, which can lead to localized areas that deteriorate faster than the neighboring regions. Raman spectroscopy is among the many techniques that are used to probe inhomogeneity in electrode behavior. Typically, Raman spectroscopy measurements on lithium‐ion cell electrodes are conducted in the top‐down mode, and at‐best produce an incomplete, surface biased account of electrode behavior. In contrast, micro‐Raman measurements conducted on ion‐milled electrode cross‐sections provide information from regions that span the full thickness of the electrode. Here, Raman spectroscopy data from pristine, aged, and relithiated/aged positive electrodes are reported. The spectral differences between oxide particles near the top‐surface and particles deeper into the aged electrodes clearly indicate compositional heterogeneities that arise during cell aging.
Crystal clear: Vibrational spectroscopy reveals intrabone, intraskeleton, and interskeleton variation in human bones
Authors: Gonçalves D. , Vassalo A. R. , Mamede A. P. , Makhoul C. , Piga G. , Cunha E. , Marques M. P. M. , Batista de Carvalho L. A. E. 
Published: February 2018

AbstractObjectivesVibrational spectroscopy is a valuable tool for the study of burned skeletal remains. Nonetheless, most investigations have been focused on a limited number of samples as well as on faunal bones rather than human bones. Conclusions based on those investigations may lack representativeness, namely about the intrabone, intra‐ and interskeleton variability of several chemometric indices. We aimed to investigate this issue on a large sample of human bones.Material and MethodsPowder samples were collected from 168 bones from four human skeletons. The sampling targeted 47 long bones, 72 short bones, and 49 tarsal bones as well as different bone regions in a total of 638 powder samples. Bones were experimentally burned in an electric muffle furnace for two hours to maximum temperatures ranging from 400°C to 1000°C. Another 623 burned samples were then collected totaling 1261 samples subjected to FTIR‐ATR analysis. The CI, BPI, C/C, and OH/P indices were calculated.ResultsAn important intrabone, intra‐ and interskeleton variation was observed, especially for the BPI. The CI, C/C, and OH/P indices revealed much less variation so site‐specific sampling may not be as critical in these cases. Clear differences between our results and those from previous investigations were observed, namely on the temperature increment evolution of the CI and C/C indices.DiscussionThe relatively large heterogeneity, especially at the intrabone level, is possibly the consequence of microstructural bone differences. The dissimilarities observed between our investigation and other published studies are probably due to the fact that the samples used here came from human rather than faunal bones. Also, our samples were buried previously to the experimental burning so this may also partly explain our contrasting results, since previous research was mostly performed on fresh bone. Future inferences based on vibrational spectroscopy analyses should take into account the possible effect of all these sources.
Nocturnal behavior by a diurnal ape, the West African chimpanzee (Pan troglodytes verus), in a savanna environment at Fongoli, Senegal
Authors: Pruetz Jill D. 
Published: February 2018

AbstractObjectivesI report on the nocturnal behavior of Fongoli chimpanzees in a savanna mosaic during different seasons and lunar phases and test the hypothesis that hot daytime temperatures influence activity at night. I predicted that apes would be more active at night during periods of greater lunar illuminosity given diurnal primates’ lack of visual specializations for low‐light conditions and in dry season months when water scarcity exacerbated heat stress.Materials and MethodsI observed chimpanzees for 403 hrs on 40 nights between 2007 and 2013 and categorized their activity as social, movement, or vocalization. I scored their activity as occurring after moonrise or before moonset and considered the influence of moon phase (fuller versus darker phases) as well as season on chimpanzee nocturnal behavior in the analyses.ResultsResults indicate that apes were more active after moonrise or before moonset during fuller moon phases in the dry season but not the wet season. Most night‐time activity involved movement (travel or forage), followed by social behavior, and long‐distance vocal communication.DiscussionAnimals in highly seasonal habitats often exhibit thermoregulatory adaptations but, like other primates, chimpanzees lack physiological mechanisms to combat thermal stress. This study provides evidence that they may exhibit behaviors that allow them to avoid high temperatures in a savanna environment, such as feeding and socializing at night during the hottest time of year and in the brightest moon phases. The results support theories invoking thermal stress as a selective pressure for hominins in open environments where heat would constrain temporal foraging niches, and suggest an adaptability of sleeping patterns in response to external factors.
Amygdala‐stimulation‐induced apnea is attention and nasal‐breathing dependent
Authors: Nobis William P. , Schuele Stephan , Templer Jessica W. , Zhou Guangyu , Lane Gregory , Rosenow Joshua M. , Zelano Christina 
Published: February 2018

ObjectiveEvidence suggests that disordered breathing is critically involved in Sudden Unexpected Death in Epilepsy (SUDEP). To that end, evaluating structures that are activated by seizures and can activate brain regions that produce cardiorespiratory changes can further our understanding of the pathophysiology of SUDEP. Past preclinical studies have shown that electrical stimulation of the human amygdala induces apnea, suggesting a role for the amygdala in controlling respiration. In this study, we aimed to both confirm these findings in a larger group of patients with intractable temporal lobe epilepsy (TLE) and also further explore the anatomical and cognitive properties of this effect.MethodsSeven surgical TLE patients had depth electrodes implanted in the amygdala that were used to deliver electrical stimulation during functional mapping preceding resection. Real‐time respiratory monitoring was performed in each patient to confirm apnea.ResultsOur data confirm that amygdala stimulation reliably induces apnea (occurring in all 7 patients) and further suggest that apnea can be overcome by instructing the patient to inhale, and can be prevented entirely by breathing through the mouth before electrical stimulation. Finally, stimulation‐induced apnea occurred only when stimulating the medial‐most amygdalar contacts located in the central nucleus.InterpretationThese findings confirm a functional connection between the amygdala and respiratory control in humans. Moreover, they suggest specific amygdalar nuclei may be critical in mediating this effect and that attentional state is critical to apnea mediated by amygdala activation—perhaps alluding to future development of strategies for the prevention of SUDEP. Ann Neurol 2018;83:460–471
Crystalline‐Sponge‐Based Structural Analysis of Crude Natural Product Extracts
Authors: Wada Naoki , Kersten Roland D. , Iwai Takahiro , Lee Shoukou , Sakurai Fumie , Kikuchi Takashi , Fujita Daishi , Fujita Makoto , Weng Jing‐Ke 
Published: February 2018

AbstractCharacterization of complex natural product mixtures to the absolute structural level of their components often requires significant amounts of starting materials and lengthy purification process, followed by arduous structure elucidation efforts. The crystalline sponge (CS) method has demonstrated utility in the absolute structure elucidation of isolated organic compounds at miniscule quantities compared to conventional methods. In this work, we developed a new CS‐based workflow that greatly expedites the in‐depth structural analysis of crude natural product extracts. Using a crude extract of the red alga Laurencia pacifica, we showed that CS affinity screening prior to compound isolation enables prioritization of analytes present in the extract, and we subsequently resolved the molecular structures of six sesquiterpenes with stereochemical clarity from around 10 mg crude extract. This study demonstrates a new chemotyping workflow that can greatly accelerate natural product discovery from complex samples.