| 45071. |
- Jarlemark, Per O. J., 1962, et al.
(författare)
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Ground-Based GPS for Validation of Climate Models: The Impact of Satellite Antenna Phase Center Variations
- 2010
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 48:10, s. 3847-3854
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Tidskriftsartikel (refereegranskat)abstract
- The amount of water vapor in the atmosphere is an important indicator for climate change. Using the Global Positioning System (GPS), it is possible to estimate the integrated water vapor (IWV) above the ground-based GPS receiver. In order to optimally determine the IWV, a correct model of the received signal phase is essential. We have studied the effect of the satellite antenna phase center variations (PCVs) on the IWV estimates by simulating the effect and by studying the estimates of the IWV based on the observed GPS signals. During a period of five years, from 2003 to 2008, a new satellite type was introduced, and it steadily grew in numbers. The antenna PCVs for these satellites deviate from the earlier satellite types and contribute to excess IWV estimates. We find that ignoring satellite antenna phase variations for this time period can lead to an additional IWV trend of about 0.15 kg/m2/year for regular GPS processing.
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| 45072. |
- Jarochowska, Emilia, et al.
(författare)
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Conodonts in Silurian hypersaline environments : specialized an dunexpectedly diverse
- 2017
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 45:1, s. 3-6
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Tidskriftsartikel (refereegranskat)abstract
- Hypersaline environments are commonly assumed to be barren of metazoans and therefore are avoided by paleontologists, yet a number of early Paleozoic jawless vertebrate groups specialized to live in such settings. Sampling bias against restricted settings resulted in substantial underestimation of their diversity. Rare studies venturing into such environments yielded multiple new species of conodonts, suggesting that the diversity and habitat range of these hyperdiverse predators of the early oceans are equally underestimated. We describe here autochthonous conodont fauna from evaporite-bearing horizons from the middle Silurian of Estonia that provide evidence for efficient osmoregulation in this group. Based on a global compilation of coeval conodont assemblages, we show that marginal-marine, periodically emergent environments were characterized by higher conodont diversity than open-marine shallow settings. This diversity is due to a high number of species occurring in these environments only. The high degree of specialization is also reflected by the highest within-habitat variability (β diversity) in marginal settings. Most conodont species had narrow environmental niches and, unlike in marine invertebrates, extreme environments were inhabited by the most specialized taxa. Such environments represent a large proportion of early Paleozoic tropical epicratonic basins. Our analysis allows quantification of the degree to which mid-Silurian conodont diversity is underestimated as a result of sampling bias against marginal-marine settings.
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| 45073. |
- Javanroodi, K., et al.
(författare)
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Quantifying the impacts of urban morphology on modifying microclimate conditions in extreme weather conditions
- 2021. - 1
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Ingår i: Journal of Physics: Conference Series : CISBAT 2021 Carbon-neutral cities - energy efficiency and renewables in the digital era 8-10 September 2021, EPFL Lausanne, Switzerland - CISBAT 2021 Carbon-neutral cities - energy efficiency and renewables in the digital era 8-10 September 2021, EPFL Lausanne, Switzerland. - : IOP Publishing. - 1742-6588. ; 2042
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Konferensbidrag (refereegranskat)abstract
- It is well-known that the morphology of urban areas modifies the variations of climate variables at microscale; known as microclimate conditions. The complexity of urban morphology can lead to undesired wind conditions or excessive air temperature; particularly in extreme weather conditions. This study attempts to quantify the impacts of urban morphology on the evolution of wind speed and air temperature at the urban canopy layer using Computational Fluid Dynamic (CFD) simulations. In this regard, three urban neighbourhoods are generated based on a novel urban morphology parameterization method and assessed in two extreme low and high wind conditions. Results showed that wind speed (up to 75%) and air temperature (up to 28%) at the microscale can get amplified or dampened in extreme conditions. A negative correlation was observed between wind speed and air temperature variations indicating a great potential to reduce outdoor air temperature through heat removal in urban canyons. The findings of the study are categorized based on the morphological parameters to present a series of design-based strategies for the newly-built urban neighbourhoods.
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| 45074. |
- Javanshir, Sepideh, et al.
(författare)
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Leaching behavior of Cu, Zn, Fe and Pb from polymetallic tailings
- 2024
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Ingår i: Separation science and technology (Print). - : Taylor & Francis. - 0149-6395 .- 1520-5754.
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Tidskriftsartikel (refereegranskat)abstract
- Copper tailings are a common byproduct of copper production, containing high levels of heavy metals which are released into the environment. Conventional methods have historically prioritized copper recovery, and often overlooking the leaching of other valuable elements. However, the rising demand for nonferrous metals necessitates understanding their leaching behavior from copper tailings. This study examined the atmospheric leaching of Cu, Fe, Pb, Zn, and CuO from a polymetallic tailing ore. Leaching recoveries of 63.5% for Cu, 97.5% for CuO, 1% for Fe, and 100% for Zn were achieved under the optimum conditions of 0.5 M sulfuric acid concentration, 25% solids percentage, 65°C, stirring speed of 100rpm, particle size of 75 µm within 30 minutes. Results indicated that the dissolution of oxide minerals such as CuO and ZnO was significant; however, copper sulfides need oxidant to be dissolved. In this condition, iron oxides and silicates were partially reacted by sulfuric acid, and Pb-bearing minerals formed lead sulfate. The presence of iron and lead-bearing minerals in the leaching residue was confirmed by XRF, XRD, and SEM analyses, and was in agreement with the information displayed in the Eh-pH diagrams.
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| 45075. |
- Javeline, Debra, 1977-, et al.
(författare)
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Russia in a changing climate
- 2024
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Ingår i: Wiley Interdisciplinary Reviews. - : John Wiley & Sons. - 1757-7780 .- 1757-7799. ; 15:2
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Forskningsöversikt (refereegranskat)abstract
- Climate change will shape the future of Russia, and vice versa, regardless of who rules in the Kremlin. The world's largest country is warming faster than Earth as a whole, occupies more than half the Arctic Ocean coastline, and is waging a carbon-intensive war while increasingly isolated from the international community and its efforts to reduce greenhouse gas emissions. Officially, the Russian government argues that, as a major exporter of hydrocarbons, Russia benefits from maintaining global reliance on fossil fuels and from climate change itself, because warming may increase the extent and quality of its arable land, open a new year-round Arctic sea route, and make its harsh climate more livable. Drawing on the collective expertise of a large group of Russia-focused social scientists and a comprehensive literature review, we challenge this narrative. We find that Russia suffers from a variety of impacts due to climate change and is poorly prepared to adapt to these impacts. The literature review reveals that the fates of Russia's hydrocarbon-dependent economy, centralized political system, and climate-impacted population are intertwined and that research is needed on this evolving interrelationship, as global temperatures rise and the international economy decarbonizes in response.
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| 45076. |
- Javier Alvaro, J., et al.
(författare)
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Guzhangian (mid Cambrian) trilobites from siliceous concretions of the Valtorres Formation, Iberian Chains, NE Spain
- 2013
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Ingår i: Geological Magazine. - 0016-7568. ; 150:1, s. 123-142
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Tidskriftsartikel (refereegranskat)abstract
- In the carbonate-siliciclastic strata of West Gondwana (e. g. in the Montagne Noire, France), the aftermath of the mid Languedocian (mid Cambrian) regression is characterized by a late Languedocian major turnover of trilobite families and a Furongian-early Tremadocian radiation related to the stepwise immigration of trilobite invaders from East Gondwana under persistent transgressive conditions. The scarcity of upper Languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the Iberian Chains (Spain), where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions. These have yielded the trilobites Peronopsis cf. insignis, Oidalagnostus trispinifer, Proampyx difformis (= Proampyx aculeatus), Bailiaspis? glabrata (= Holocephalina agrauloides, by ontogeny), Holasaphus cf. centropyge and a paradoxidid gen. et sp. indet. Despite preservation and sampling biases, the identification of this taphonomic window in offshore clayey substrates of West Gondwana allows the recognition of a strong biogeographical link with Baltica, and the correlation of the global Guzhangian Stage and the Solenopleura? brachymetopa Zone of Scandinavia with part of the Mediterranean upper Languedocian Substage.
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| 45077. |
- Javier Alvaro, J., et al.
(författare)
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Skeletal carbonate productivity and phosphogenesis at the lower-middle Cambrian transition of Scania, southern Sweden
- 2010
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Ingår i: Geological Magazine. - 0016-7568. ; 147:1, s. 59-76
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Tidskriftsartikel (refereegranskat)abstract
- The lower-middle Cambrian transitional interval of Scania is largely represented by condensed limestone beds, lithostratigraphically grouped in the Gislov Formation (1-5.7 m thick), and the Forsemolla and Exsulans Limestone beds (lower part of the Alum Shale Formation, up to 4 in thick). The strata display a combination of skeletal carbonate productivity, episodic nucleation of phosphate hardground nodules, and polyphase reworking recorded on a platform bordering the NW corner of Baltica. The shell accumulations can be subdivided into three deepening-upward parasequences, separated by distinct erosive unconformities. The parasequences correspond biostratigraphically to the Holmia kjerulfi, Ornamentaspis? linnarssoni and Ptlychagnostus gibbus zones, the latter two generally being separated by a stratigraphic gap that includes the middle Cambrian Acadoparadoxides oelandicus Superzone. Except for the Exsulans Limestone, the carbonates reflect development of a prolific epibenthic biota, dominated by filter-feeding nonreefal chancelloriid-echinoderm-sponge meadows, rich in trilobites and brachiopods, and which were subjected to high-energy conditions. The absence of microbial mats or veneers encrusting the erosive surfaces of these event-concentration low-relief shoal complexes may be related to long hiatal episodes resulting in microboring proliferation. High levels of nutrient supply resulted in high primary productivity, eutrophic conditions, glauconite precipitation, phosphogenesis (in some case microbially mediated) and rnicroendolithic infestation. An early-diagenetic mildly reducing environment is suggested by the presence of authigenic (subsequently reworked) pyrite, which contrasts with the syndepositional normal oxygenated conditions reflected by macroburrowing and the abundance of benthic fossils.
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| 45078. |
- Jayaweera, Avon P., et al.
(författare)
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On the Mechanism and Quantum Tunneling of the CO2 + OH Anion Reaction in Ice: A Computational Study
- 2024
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Ingår i: ACS EARTH AND SPACE CHEMISTRY. - 2472-3452. ; 8:7, s. 1451-1459
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the reaction between CO2 and OH- (anion) in ice cluster models was determined using density functional theory (DFT), employing the omega B97X-D functional and def2-TZVP basis sets for all atoms. A range of reaction barriers, 0.08-0.43 eV, were found, and the lowest energy path has a barrier of 0.08 eV, giving rise to the bicarbonate ion (HCO3-). Computed rate constants, accounting for quantum tunneling by employing the Eckart potential, suggest that the CO2 + OH- -> HCO3- reaction can operate in ice at low temperatures (e.g., 10 K). In contrast, relatively high reaction barriers (0.52-0.74 eV) were found for the CO2 + OH center dot (radical) -> HCO3 center dot (radical) reaction, and the computed rate constants at low temperatures (e.g., 10 K) are extremely small. Based on the computed data, we argue that OH- can react with CO2 trapped in interstellar ice at 10 K, and the product of the reaction, HCO3-, is stable in ice. On the other hand, the OH radical does not react with CO2 in ice. Therefore, we propose that OH anions in interstellar ice play a role in the formation of precursors of complex organic molecules (COMs) in the interstellar medium. The present findings will open a new dimension to explore the chemical evolution in the interstellar medium through the chemistry of anions in interstellar ices.
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| 45079. |
- Jeddi, Zeinab, et al.
(författare)
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Ambient-noise tomography of Katla volcano, south Iceland
- 2017
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 347, s. 264-277
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Tidskriftsartikel (refereegranskat)abstract
- A shear-wave velocity model of subglacial Katla volcano, southern Iceland, has been developed using ambient seismic noise tomography based on data from a temporary network operating between May 2011 and August 2013 and permanent stations around the volcano. Phase-velocity dispersion curves were obtained using cross correlations of vertical components of 136 station pairs and non-linearly inverted for phase-velocity maps between 1.7 and 7.5 s. Local dispersion curves were inverted for shear-velocity variation with depth using a grid search imposing a fixed ice layer at the top. The resulting one-dimensional (1-D) velocity models were combined to obtain a pseudo three-dimensional (3-D) model with estimated lateral resolution of 8 km and depth resolution varying from close to 1 km near the surface to about 8 km at 10 km depth. Shear wave velocities are generally higher within the Katla central volcano than in its surroundings. The most striking feature of the model is a high-velocity anomaly beneath the caldera at >6 km depth interpreted to be due to cumulates resulting from differentiation of shallower magma intrusions and remelting of subsiding upper crust. No shallow low-velocity anomaly is resolved beneath the central caldera, but a low-velocity region is found at 2-4 km depth beneath the western half of the caldera. V-p/V-s ratios, estimated from average velocity-depth profiles from surface-wave data and higher frequency P-wave data, are anomalously high (>1.9) compared to average Icelandic crust, particularly in the top 2-3 km. This is argued not to be an artifact due to lateral refraction or topography. Instead, this anomaly could be explained as an artifact caused by velocity dispersion due to attenuation and a difference in frequency content, and possibly to a degree by the compositional difference between the transalkalic Fe-Ti basalts of Katla and average tholeiitic Icelandic crust.
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| 45080. |
- Jelbring, Hans, 1945-
(författare)
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Wind controlled climate
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)
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