Search results for "tracer"
showing 10 items of 145 documents
Secondary sclerosing cholangitis after long-term treatment in an intensive care unit: clinical presentation, endoscopic findings, treatment, and foll…
2006
Background and study aims We present ten patients who developed secondary sclerosing cholangitis following long-term treatment in an intensive care unit (ICU) between 1999 and 2004. Patients and methods Ten consecutive patients who had no evidence suggestive of pre-existing hepatobiliary disease were admitted to an ICU because of trauma (n = 5), intracerebral hemorrhage (n = 3), or nonabdominal postsurgical complications (n = 2). All the patients had required treatment with long-term ventilation, catecholamines, total parenteral nutrition, and several antimicrobial agents. Results Cholestasis was first noted within 11 days after the initial insult. Endoscopic retrograde cholangiopancreatogr…
Dynamics in the extratropical tropopause region: A case of transition between dynamically active and passive tracer advection?
2005
It is argued that certain aspects of tracer patterns and related stirring by the flow in the extratropical tropopause region can be understood in terms of a transition between dynamically active and passive tracer advection, called ‘active-to-passive tracer transition’. In the framework of surface quasi-geostrophic dynamics, a specific initial-value problem is defined and investigated. It features a gradual transition between the two paradigms of tracer advection and allows a clear interpretation thanks to the idealized nature of the model setup. Physical reasoning and anecdotal evidence from previous studies suggest that, at least in specific cases, this interpretation is relevant for the …
Fish introductions and light modulate food web fluxes in tropical streams : a whole-ecosystem experimental approach
2016
Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen (15N) stable isotope tracer to compare basal resource treatments (thinned canopy vs. con…
Mercury concentration, speciation and budget in volcanic aquifers: Italy and Guadeloupe (Lesser Antilles)
2009
Abstract Quantifying the contribution of volcanism to global mercury (Hg) emissions is important to understand the pathways and the mechanisms of Hg cycling through the Earth's geochemical reservoirs and to assess its environmental impacts. While previous studies have suggested that degassing volcanoes might contribute importantly to the atmospheric budget of mercury, little is known about the amount and behaviour of Hg in volcanic aquifers. Here we report on detailed investigations of both the content and the speciation of mercury in aquifers of active volcanoes in Italy and Guadeloupe Island (Lesser Antilles). In the studied groundwaters, total Hg (THg) concentrations range from 10 to 500…
An evaluation of the estimation of road traffic emission factors from tracer studies
2010
Road traffic emission factors (EFs) are one of the main sources of uncertainties in emission inventories; it is necessary to develop methods to reduce these uncertainties to manage air quality more efficiently. Recently an alternative method has been proposed to estimate the EFs. In that work the emission factors were estimated from a long term tracer study developed in Ho Chi Minh City (HCMC) Vietnam. A passive tracer was continuously emitted from a finite line source placed in one side of an urban street canyon. Simultaneously, the resulting tracer concentrations were monitored at the other side of the street. The results of this experiment were used to calculate the dispersion factors an…
Impulse response tests in completely mixed tanks and reactors. Key assumptions and steps in mathematical developments.
2010
Stimulus-response technique is a method to obtain the Residence Time Distribution (RTD) for the elements of a fluid passing through a vessel. Generally speaking, in reactor science unsteady-state tests may often appear preferable to steady-state since they are made up of a chain of intermediate ones; but without any theoretical necessity holding. In RTD studies, however, non-steady state tests are the only conceivable ones if conservative tracers are employed, because once a transition is over there is no way to reconstruct it and assess the hydraulic behaviour of the tank. Only a series of tests with non-conservative tracers of known disappearance rate would achieve the task, but at the pr…
Development and characterization of a Drop-on-Demand inkjet printing system for nuclear target fabrication
2017
Abstract A novel target preparation method based on Drop-on-Demand (DoD) inkjet printing has been developed. Conventional preparation methods like the electrochemical method “Molecular Plating” or the “Polymer-Assisted Deposition Method” are often limited, e.g., concerning the dimensions and geometries of depositions or by the requirement for electrically conducting substrates. Here, we report on the development of a new technique, which overcomes such limits by using a commercially available DoD dispenser. A variety of solutions with volumes down to 5 nL can be dispensed onto every manageable substrate. The dispensed volumes were determined with a radioactive tracer and the deposits of eva…
Rethinking vineyard ground management to counter soil tillage erosion
2022
Tillage erosion is a relevant process of soil redistribution in sloping arable land, but little research has analysed the effect of shallow tillage on soil erosion in vineyards. The goal of this study was to quantify the soil tillage effect on soil translocation and erosion at the territorial level in a large vineyard area in Sicily. The soil loss and soil erosion tolerance limits were compared to identify the vineyards with a high risk of soil degradation. An alternative management scenario to traditional tillage was proposed to evaluate the effectiveness of the best management practices on soil conservation. The experimental trials were conducted in 14 vineyards with different slopes and …
A numerical study of tropical cross-tropopause transport by convective overshoots
2007
Abstract. Observations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local tropopause. The case was investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation reproduced the measurements along the flight track fairly well. A reasonable agreement with MSG observations was also achieved: the 10.8-μm brightness temperature (BT) minimum of 187 K was reproduced (a value 6 K colder than the environmental cold-point temperature) as was the positive BT difference between the 6.2- and 10…
The Cerebral Thrombin System Is Activated after Intracerebral Hemorrhage and Contributes to Secondary Lesion Growth and Poor Neurological Outcome in …
2020
With increasing evidence for the existence of a cerebral thrombin system, coagulation factor IIa (thrombin) is suspected to influence the pathogenesis of secondary injury progression after intracerebral hemorrhage (ICH). We hypothesized that mechanisms associated with local volume expansion after ICH, rather than blood constituents, activate the cerebral thrombin system and are responsible for detrimental neurological outcome. To test this hypothesis, we examine the local thrombin expression after ICH in a C57BL/6N mouse model in the presence and absence of blood constituents. ICH was established using stereotaxic orthotopic injection of utologous blood (