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  • Artikel  (32)
  • Neueste Artikel (Zeitschrifteninhaltsverzeichnisse / in press)  (29)
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  • Neueste Artikel (Zeitschrifteninhaltsverzeichnisse / in press)  (29)
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  • 1
    Publikationsdatum: 2021-10-29
    Beschreibung: Cold (few eV) ions of ionospheric origin are widely observed in the lobe region of Earth’s magnetotail and can enter the ion jet region after magnetic reconnection is triggered in the magnetotail. Here, we investigate a magnetotail crossing with cold ions in one tailward and two earthward ion jets observed by the Magnetospheric Multiscale (MMS) constellation of spacecraft. Cold ions co-existing with hot plasma-sheet ions form types of ion velocity distribution functions (VDFs) in the three jets. In one earthward jet, MMS observe cold-ion beams with large velocities parallel to the magnetic fields, and we perform quantitative analysis on the ion VDFs in this jet. The cold ions, together with the hot ions, are reconnection outflow ions and are a minor population in terms of number density inside this jet. The average bulk speed of the cold-ion beams is approximately 38% larger than that of the hot plasma-sheet ions. The cold-ion beams inside the explored jet are about one order of magnitude colder than the hot plasma-sheet ions. These cold-ion beams could be accelerated by the Hall electric field in the cold ion diffusion region and the shrinking magnetic field lines through the Fermi effect.
    Digitale ISSN: 2296-987X
    Thema: Maschinenbau , Physik
    Publiziert von Frontiers Media
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2021-11-01
    Beschreibung: Autonomy is becoming increasingly important for the robotic exploration of unpredictable environments. One such example is the approach, proximity operation, and surface exploration of small bodies. In this article, we present an overview of an estimation framework to approach and land on small bodies as a key functional capability for an autonomous small-body explorer. We use a multi-phase perception/estimation pipeline with interconnected and overlapping measurements and algorithms to characterize and reach the body, from millions of kilometers down to its surface. We consider a notional spacecraft design that operates across all phases from approach to landing and to maneuvering on the surface of the microgravity body. This SmallSat design makes accommodations to simplify autonomous surface operations. The estimation pipeline combines state-of-the-art techniques with new approaches to estimating the target’s unknown properties across all phases. Centroid and light-curve algorithms estimate the body–spacecraft relative trajectory and rotation, respectively, using a priori knowledge of the initial relative orbit. A new shape-from-silhouette algorithm estimates the pole (i.e., rotation axis) and the initial visual hull that seeds subsequent feature tracking as the body gets more resolved in the narrow field-of-view imager. Feature tracking refines the pole orientation and shape of the body for estimating initial gravity to enable safe close approach. A coarse-shape reconstruction algorithm is used to identify initial landable regions whose hazardous nature would subsequently be assessed by dense 3D reconstruction. Slope stability, thermal, occlusion, and terra-mechanical hazards would be assessed on densely reconstructed regions and continually refined prior to landing. We simulated a mission scenario for approaching a hypothetical small body whose motion and shape were unknown a priori, starting from thousands of kilometers down to 20 km. Results indicate the feasibility of recovering the relative body motion and shape solely relying on onboard measurements and estimates with their associated uncertainties and without human input. Current work continues to mature and characterize the algorithms for the last phases of the estimation framework to land on the surface.
    Digitale ISSN: 2296-9144
    Thema: Informatik
    Publiziert von Frontiers Media
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2021-10-29
    Beschreibung: Nitrapyrin, a nitrification inhibitor, produces liver tumors in B6C3F1 mice. In a 2-year oncogenicity study, increased incidence of mice with hepatocellular tumors was observed following exposure to 125 (females only) or 250 mg/kg/day (males and females) nitrapyrin in the diet. Previous data was generated in male mice to support a mode-of-action (MoA) characterized by constitutive androstane receptor (CAR) nuclear receptor (NR) activation, increased hepatocellular proliferation, and subsequent hepatocellular foci and tumor formation. Uncertainty as to the relevance of this MoA for females remained given the increased sensitivity to tumor formation in female mice. A targeted MoA study was conducted to evaluate CAR activation and hepatic responses in female mice treated with the female carcinogenic dose of nitrapyrin for 4 days. Nitrapyrin induced a treatment-related increase in hepatocellular hypertrophy and hepatocellular proliferation. Nitrapyrin also induced a dose-related increase in the Cyp2b10/CAR-associated transcript and liver weights. Nitrapyrin-induced liver weights and Cyp2b10 gene expression for both males and females were compared to data generated from three other established CAR activators; methyl isobutyl ketone, phenobarbital, and sulfoxaflor. The response observed in female mice following exposure to nitrapyrin was within range of the degree of change observed in mice following exposure to tumorigenic doses of other CAR activators. Consistent with the liver MoA in male mice, these data support a CAR-mediated mode of action for nitrapyrin-induced liver tumors in female mice, with the understanding that a focused approach minimizing animal use can bridge male and female datasets when sex-specific carcinogenic differences are observed.
    Digitale ISSN: 2673-3080
    Thema: Chemie und Pharmazie
    Publiziert von Frontiers Media
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  • 4
    Publikationsdatum: 2021-11-01
    Beschreibung: Maastrichtian–Danian sediments of the Navesink and Hornerstown formations at the Jean and Ric Edelman Fossil Park of Rowan University in Mantua Township, New Jersey, have long intrigued paleontologists. Within the basal Hornerstown Formation occurs the Main Fossiliferous Layer (MFL), a regionally well-known and diverse bonebed. The lithostratigraphic and chronostratigraphic position of this fossil layer have been debated for more than 50 years, fueling debate over its origin. Herein, we present the results of a microstratigraphic analysis of the fossil composition and distribution of the MFL undertaken to rectify these discrepancies. Through methodical top-down excavation, we recorded the three-dimensional position of every fossil encountered. Three-dimensional visualization and analyses of these data in ArcGIS Pro yielded an unprecedented view of this bonebed. Most reported discrepancies about the stratigraphic placement and thickness of the MFL can be explained by the presence of two distinct fossil assemblages within this interval that are occasionally combined into a single bonebed. The stratigraphically-lower assemblage, herein termed an “oyster layer”, is geometrically-tabular and exhibits low taxonomic diversity, high abundance of the oyster Pycnodonte, and moderate taxonomic richness. The stratigraphically-higher assemblage, the MFL, occurs approximately 9 cm higher in section and exhibits high values of taxonomic diversity, fossil abundance, and taxonomic richness. Sedimentological homogeneity throughout this interval suggests that these faunal contrasts arise from the two assemblages having formed via independent taphonomic pathways. Specifically, prevalence of Pycnodonte in the oyster layer implies formation by a selective mortality event, whereas the diversity of the MFL appears to reflect a more universal agent of mortality. Spatial variations in the stratigraphic distribution of fossils within the MFL in our excavation area indicate this assemblage does not form a simple, tabular layer as previously thought and may, in part, record original bathymetry. Importantly, our definition of the MFL and detailed characterization of its stratigraphic placement are essential for future studies on the taphonomic origin and chronostratigraphy of this bonebed. Universal use of this definition would allow researchers to confidently elucidate the exact lithostratigraphic positions of precise chronostratigraphic indicators within the MFL and accurately estimate the degree of time averaging of its fossils.
    Digitale ISSN: 2296-6463
    Thema: Geologie und Paläontologie
    Publiziert von Frontiers Media
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2023-03-11
    Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Conte, M., Pàmies, R., Honda, M., & Herndl, G. Editorial: the oceanic particle flux and its cycling within the deep water column. Frontiers in Earth Science, 10, (2022): 1020065, https://doi.org/10.3389/feart.2022.1020065.
    Beschreibung: The oceanic particle flux transfers energy and material from the surface through the water column to the seafloor. (See review by Conte (2019) and references therein). The particle flux fuels life below the sunlit photic zone, exerts a major control on the global cycling of carbon and particle-associated elements, and also plays a major role in long-term carbon sequestration. In this Research Topic we present a collection of articles that provide a broad overview of current research on the interlinked processes controlling the magnitude and composition of the oceanic particle flux, and its cycling and depth attenuation within the deep water column.
    Schlagwort(e): Particle flux ; Deep ocean ; Marine particles ; Ocean biogeochemistry ; Carbon cycling ; Marine chemistry
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 6
    Publikationsdatum: 2023-03-02
    Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Koguchi, Y., Tokuhiro, K., Ashjian, C., Campbell, R., & Yamaguchi, A. Inter-species comparison of the copepodite stage morphology, vertical distribution, and seasonal population structure of five sympatric mesopelagic aetideid copepods in the western Arctic Ocean. Frontiers in Marine Science, 9, (2022): 943100, https://doi.org/10.3389/fmars.2022.943100.
    Beschreibung: Aetideidae is a calanoid copepod family dominant in the mesopelagic layer of the Arctic Ocean for which little ecological information is available because species identification, especially of early copepodite stages, is difficult. In this study, we developed a species identification flow for the whole copepodite stages of five sympatric aetideid copepods (Chiridius obtusifrons, Gaetanus tenuispinus, G. brevispinus, Aetideopsis multiserrata, and A. rostrata). Vertical distributions and seasonal population structures of these species were evaluated using a year-round sample time-series collected at the drifting ice station (SHEBA) in the western Arctic Ocean. Combinations of morphological characteristics (prosome length, cephalosome, and prosome widths) were used to identify the early copepodite stages to species. Aetideopsis rostrata was distributed in deep waters (1,032–1,065 m) throughout the year. The other species all were found at 600–700 m during the midnight sun. However, during the polar night, the vertical distributions of each species were distinct, resulting from ascent, descent, or depth maintenance, indicating seasonal vertical migration which may function to reduce inter-specific competition during the polar night when food resources are scarce. Reproduction timing varied among four aetideid copepods: C.obtusifrons and G. tenuispinus showed polar night ascent and reproduction at the end of the polar night, whereas G. brevispinus and A. multiserrata showed descent or depth maintenance during the polar night and reproduction at the beginning of the polar night. There was not sufficient data to examine reproduction timing of A. rostrata. Common for all aetideid species, δ15N values of the adult females indicate more carnivorous feeding modes during the polar night than those in the midnight sun. Such vertical distribution and timing of reproduction variation among these five aetideid copepods may function to reduce species competition in the mesopelagic layer of the Arctic Ocean.
    Beschreibung: Collection of the samples was supported in part by grants #OCE9707184 to CA and #OCE9707182 to RC from the US National Science Foundation. This work was partially supported by the Arctic Challenge for Sustainability II (ArCS II), Program Grant Number JPMXD1420318865. This research was also supported by the Environment Research and Technology Development Fund (JPMEERF20214002) of the Environmental Restoration and Conservation Agency of Japan. In addition, this work was partly supported by a Grant-in-Aid for Challenging Research (Pioneering) JP20K20573, and Scientific Research JP20H03054 (B), JP19H03037 (B), JP21H02263 (B), and JP17H01483 (A) from the Japanese Society for the Promotion of Science (JSPS).
    Schlagwort(e): Aetideidae ; Sympatric mesopelagic copepods ; Vertical distribution ; Population structure ; Reproduction ; The Arctic Ocean
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2023-02-21
    Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fairall, C. W. W., Yang, M., Brumer, S. E. E., Blomquist, B. W. W., Edson, J. B. B., Zappa, C. J. J., Bariteau, L., Pezoa, S., Bell, T. G. G., & Saltzman, E. S. S. Air-Sea trace gas fluxes: direct and indirect measurements. Frontiers in Marine Science, 9, (2022): 826606, https://doi.org/10.3389/fmars.2022.826606.
    Beschreibung: The past decade has seen significant technological advance in the observation of trace gas fluxes over the open ocean, most notably CO2, but also an impressive list of other gases. Here we will emphasize flux observations from the air-side of the interface including both turbulent covariance (direct) and surface-layer similarity-based (indirect) bulk transfer velocity methods. Most applications of direct covariance observations have been from ships but recently work has intensified on buoy-based implementation. The principal use of direct methods is to quantify empirical coefficients in bulk estimates of the gas transfer velocity. Advances in direct measurements and some recent field programs that capture a considerable range of conditions with wind speeds exceeding 20 ms-1 are discussed. We use coincident direct flux measurements of CO2 and dimethylsulfide (DMS) to infer the scaling of interfacial viscous and bubble-mediated (whitecap driven) gas transfer mechanisms. This analysis suggests modest chemical enhancement of CO2 flux at low wind speed. We include some updates to the theoretical structure of bulk parameterizations (including chemical enhancement) as framed in the COAREG gas transfer algorithm.
    Beschreibung: This work, and the contributions of MY and TB, is supported by the UK Natural Environment Research Council’s ORCHESTRA (Grant No. NE/N018095/1) and PICCOLO (Grant No. NE/P021409/1) projects, and by the European Space Agency’s AMT4OceanSatFlux project (Grant No. 4000125730/18/NL/FF/gp). CF and BB are funded by the National Oceanic and Atmospheric Administration’s Global Ocean Monitoring and Observing program (http://data.crossref.org/fundingdata/funder/10.13039/100018302). CZ was funded by the National Science Foundation (CJZ: OCE-2049579, Grants OCE-1537890 and OCE-1923935). Funding for HiWinGS was provided by the US National Science Foundation grant AGS-1036062. The Knorr-11 and SOAP campaigns were supported by the NSF Atmospheric Chemistry Program (Grant No. ATM-0426314, AGS-08568, -0851472, -0851407 and -1143709).
    Schlagwort(e): Gas transfer velocity ; Chemical enhancement ; Bubble mediated transfer ; COARE gas flux parameterization ; Dimethylsufide (DMS) ; Cardon dioxide (CO2) ; Bulk algorithm ; Direct observation
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2021-10-29
    Beschreibung: Heat stress affects oocyte developmental competence and is a major cause of reduced fertility in heat stressed cattle. Negative effects of heat stress on the oocyte have been observed at morphological, biochemical and developmental levels. However, the mechanisms by which heat stress affects the oocyte at the transcriptional and epigenetic levels remain to be further elucidated. Here we aimed to investigate the effect of heat stress on oocyte quality, transcriptomic profiles and DNA methylation of oocytes collected through the transition from spring to summer under Louisiana conditions. Summer season resulted in a lower number of high quality oocytes obtained compared to the spring season. There was no difference in in vitro maturation rates of oocytes collected during spring as compared to summer. RNA sequencing analysis showed that a total of 211 and 92 genes were differentially expressed as a result of heat stress in GV and MII oocytes, respectively. Five common genes (E2F8, GATAD2B, BHLHE41, FBXO44, and RAB39B) were significantly affected by heat in both GV and MII oocytes. A number of pathways were also influenced by heat stress including glucocorticoid biosynthesis, apoptosis signaling, and HIPPO signaling in GV oocytes, and Oct4 pluripotency, Wnt/beta-catenin signaling, and melatonin degradation I in MII oocytes. In addition, fluorescent immunocytochemistry analysis showed no difference in global levels of DNA methylation and DNA hydroxymethylation at either the GV or MII stage between spring and summer oocytes. The results of this study contribute to a better understanding of the effect of heat stress on the molecular mechanisms altered in bovine oocytes.
    Digitale ISSN: 1664-8021
    Thema: Biologie , Medizin
    Publiziert von Frontiers Media
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  • 9
    Publikationsdatum: 2021-10-29
    Beschreibung: Characterizing Mycobacterium abscessus complex (MABSC) biofilms under host-relevant conditions is essential to the design of informed therapeutic strategies targeted to this persistent, drug-tolerant, population of extracellular bacilli. Using synthetic cystic fibrosis medium (SCFM) which we previously reported to closely mimic the conditions encountered by MABSC in actual cystic fibrosis (CF) sputum and a new model of biofilm formation, we show that MABSC biofilms formed under these conditions are substantially different from previously reported biofilms grown in standard laboratory media in terms of their composition, gene expression profile and stress response. Extracellular DNA (eDNA), mannose-and glucose-containing glycans and phospholipids, rather than proteins and mycolic acids, were revealed as key extracellular matrix (ECM) constituents holding clusters of bacilli together. None of the environmental cues previously reported to impact biofilm development had any significant effect on SCFM-grown biofilms, most likely reflecting the fact that SCFM is a nutrient-rich environment in which MABSC finds a variety of ways of coping with stresses. Finally, molecular determinants were identified that may represent attractive new targets for the development of adjunct therapeutics targeting MABSC biofilms in persons with CF.
    Digitale ISSN: 1664-302X
    Thema: Biologie
    Publiziert von Frontiers Media
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2021-10-29
    Beschreibung: The survival of coral reefs largely depends among other factors on the recruitment of a new generation of coral individuals that are more adapted to a rapidly changing climate and other anthropogenic stressors (e.g., pollution, sedimentation). Therefore, a better understanding of the coral settlement process, the molecules involved as well as crucial environmental drivers that control settlement success are needed. In this study, we identified a novel settlement inducer for the brooding scleractinian coral Leptastrea purpurea and highlight the importance of light for the settlement process. Crude extract of the red-pigmented bacterium Pseudoalteromonas rubra reliably triggered attachment and metamorphosis in L. purpurea larvae in less than 24 h. Prodigiosin (II) and the two derivatives, cycloprodigiosin (I) and 2-methyl-3-hexyl prodiginine (III) were isolated and structurally elucidated from the crude extract of P. rubra. We demonstrated that the photosensitive pigment cycloprodigiosin (I) was the responsible compound for attachment and metamorphosis in L. purpurea larvae. Under the tested light regimes (i.e., darkness, constant light and a dark-light alternation), cycloprodigiosin (I) triggered approximately 90% settlement at a concentration of 0.2 μg mL–1 under a 12 h alternating dark-light cycle, mimicking the light-flooded coral reef environment. Our findings enable for the first time a mechanistic understanding of the light-dependent larva to polyp transformation by discovering the novel bacterial settlement cue cycloprodigiosin and its photosensitivity as a determining factor for coral settlement.
    Digitale ISSN: 2296-7745
    Thema: Biologie
    Publiziert von Frontiers Media
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