226 research outputs found
Numerical Analysis of the Dynamics in Gas-Solid Fluidized Beds and Experimental Validation Using Ultra-Fast X-ray Tomography
Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda
Quasar bolometric corrections: theoretical considerations
Bolometric corrections based on the optical-to-ultraviolet continuum spectrum
of quasars are widely used to quantify their radiative output, although such
estimates are affected by a myriad of uncertainties, such as the generally
unknown line-of-sight angle to the central engine. In order to shed light on
these issues, we investigate the state-of-the-art models of Hubeny et al. that
describe the continuum spectrum of thin accretion discs and include
relativistic effects. We explore the bolometric corrections as a function of
mass accretion rates, black hole masses and viewing angles, restricted to the
parameter space expected for type-1 quasars. We find that a nonlinear
relationship log L_bol=A + B log(lambda L_lambda) with B<=0.9 is favoured by
the models and becomes tighter as the wavelength decreases. We calculate from
the model the bolometric corrections corresponding to the wavelengths lambda =
1450A, 3000A and 5100A. In particular, for lambda=3000A we find A=9.24 +- 0.77
and B=0.81 +- 0.02. We demonstrate that the often-made assumption that quasars
emit isotropically may lead to severe systematic errors in the determination of
L_bol, when using the method of integrating the "big blue bump" spectrum. For a
typical viewing angle of ~30 degrees to the quasar central engine, we obtain
that the value of L_bol resulting from the isotropy assumption has a systematic
error of ~30% high compared to the value of L_bol which incorporates the
anisotropic emission of the accretion disc. These results are of direct
relevance to observational determinations of the bolometric luminosities of
quasars, and may be used to improve such estimates.Comment: 9 pages, 11 figures, accepted for publication in MNRA
The interaction of images and text during comprehension of garden-path sentences: is integration better than good enough?
One of the main goals of reading is to construct a discourse representation. However, when information in the discourse is confusing or ambiguous, readers are often not able to create a fluid, accurate understanding of the text. Decades of research on temporarily ambiguous garden-path sentences have given the field of psycholinguistics a comprehensive understanding of how readers process, and often misinterpret, garden-path sentences. Both online and offline data demonstrate that when reading garden-path sentences (e.g., As the guard and officer wrestled the thief that was fleeing fell down the stairs), readers may not arrive at the correct, syntactically-licensed interpretation (i.e., that the guard and officer are wrestling each other) despite apparent reanalysis. The garden-path sentence processing model claims that readers often parse sentences by developing only shallow representations of the structure, and thus never return from "down the garden path" to arrive at the correct, syntactically licensed interpretation (Ferreira, Ferraro, & Bailey, 2002; Ferreira & Patson, 2007).
In this dissertation, I seek to test the bounds of the garden-path model of sentence processing by investigating contextual influences on language processing. Specifically, how are reading processes are affected by the presence of extralinguistic information (e.g., imagery) with garden-path sentences. If readers are able to properly make use of linguistic (words) and nonlinguistic (pictorial) information, does it help them avoid inaccurate interpretation? For means of comparison, a related question is the role of imagery on linguistic disambiguation for less proficient readers who might rely more on the nonlinguistic code (e.g., nonnative speakers). I approach the issue of visual and linguistic (multimedia) processing by investigating specifically whether or not nonnative speakers of English, compared to native speakers, rely differently on non-linguistic information to parse and understand ambiguous, garden-path sentences
RNA interference in Lepidoptera: an overview of successful and unsuccessful studies and implications for experimental design
A
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Marine organic matter in the remote environment of the Cape Verde islands-an introduction and overview to the MarParCloud campaign
The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September-October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation-and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean-atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecularweight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited. © Author(s) 2020
Marine organic matter in the remote environment of the Cape Verde islands – an introduction and overview to the MarParCloud campaign
The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September–October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place.
Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis.
During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation- and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean–atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources.
In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited
The Intestinal Microbiota Plays a Role in Salmonella-Induced Colitis Independent of Pathogen Colonization
The intestinal microbiota is composed of hundreds of species of bacteria, fungi
and protozoa and is critical for numerous biological processes, such as nutrient
acquisition, vitamin production, and colonization resistance against bacterial
pathogens. We studied the role of the intestinal microbiota on host resistance
to Salmonella enterica serovar Typhimurium-induced colitis.
Using multiple antibiotic treatments in 129S1/SvImJ mice, we showed that
disruption of the intestinal microbiota alters host susceptibility to infection.
Although all antibiotic treatments caused similar increases in pathogen
colonization, the development of enterocolitis was seen only when streptomycin
or vancomycin was used; no significant pathology was observed with the use of
metronidazole. Interestingly, metronidazole-treated and infected C57BL/6 mice
developed severe pathology. We hypothesized that the intestinal microbiota
confers resistance to infectious colitis without affecting the ability of
S. Typhimurium to colonize the intestine. Indeed, different
antibiotic treatments caused distinct shifts in the intestinal microbiota prior
to infection. Through fluorescence in situ hybridization,
terminal restriction fragment length polymorphism, and real-time PCR, we showed
that there is a strong correlation between the intestinal microbiota composition
before infection and susceptibility to Salmonella-induced
colitis. Members of the Bacteroidetes phylum were present at significantly
higher levels in mice resistant to colitis. Further analysis revealed that
Porphyromonadaceae levels were also increased in these mice. Conversely, there
was a positive correlation between the abundance of
Lactobacillus sp. and predisposition to colitis. Our data
suggests that different members of the microbiota might be associated with
S. Typhimurium colonization and colitis. Dissecting the
mechanisms involved in resistance to infection and inflammation will be critical
for the development of therapeutic and preventative measures against enteric
pathogens
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Future Sea Level Change Under Coupled Model Intercomparison Project Phase 5 and Phase 6 Scenarios From the Greenland and Antarctic Ice Sheets
Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming
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