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Mixing Models (mixing + models)
Selected AbstractsGeochemistry of Darwin glass and target rocks from Darwin crater, Tasmania, AustraliaMETEORITICS & PLANETARY SCIENCE, Issue 3 2008Kieren T. Howard Target rocks at Darwin crater are quartzites and slates (Siluro-Devonian, Eldon Group). Analyses show 2 groups of glass, Average group 1 is composed of: SiO2 (85%), Al2O3 (7.3%), TiO2 (0.05%), FeO (2.2%), MgO (0.9%), and K2O (1.8%). Group 2 has lower average SiO2 (81.1%) and higher average Al2O3 (8.2%). Group 2 is enriched in FeO (+1.5%), MgO (+1.3%) and Ni, Co, and Cr. Average Ni (416 ppm), Co (31 ppm), and Cr (162 ppm) in group 2 are beyond the range of sedimentary rocks. Glass and target rocks have concordant REE patterns (La/Lu = 5.9,10; Eu/Eu* = 0.55,0.65) and overlapping trace element abundances. 87Sr/86Sr ratios for the glasses (0.80778,0.81605) fall in the range (0.76481,1.1212) defined by the rock samples. ,-Nd results range from ,13.57 to ,15.86. Nd model ages range from 1.2,1.9 Ga (CHUR) and the glasses (1.2,1.5 Ga) fall within the range defined by the target samples. The 87Sr/86Sr versus 87Rb/86Sr regression age (411 ± 42 Ma) and initial ratio (0.725 ± 0.016), and the initial 43Nd/144Nd ratio (0.51153 ± 000011) and regression age (451 ± 140 Ma) indicate that the glasses have an inherited isotopic signal from the target rocks at Darwin crater. Mixing models using target rock compositions successfully model the glass for all elementsexcept FeO, MgO, Ni, Co, and Cr in group 2. Mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile. [source] On-line cell lysis and DNA extraction on a microfluidic biochip fabricated by microelectromechanical system technologyELECTROPHORESIS, Issue 9 2008Xing Chen Dr. Abstract Integrating cell lysis and DNA purification process into a micrototal analytical system (,TAS) is one critical step for the analysis of nucleic acids. On-chip cell lysis based on a chemical method is realized by sufficient blend of blood sample and the lyzing reagent. In this paper two mixing models, T-type mixing model and sandwich-type mixing model, are proposed and simulation of those models is conducted. Result of simulation shows that the sandwich-type mixing model with coiled channel performs best and this model is further used to construct the microfluidic biochip for on-line cell lysis and DNA extraction. The result of simulation is further verified by experiments. It asserts that more than 80% mixing of blood sample and lyzing reagent which guarantees that completed cell lysis can be achieved near the inlet location when the cell/buffer velocity ratio is less than 1:5. After cell lysis, DNA extraction by means of a solid-phase method is implemented by using porous silicon matrix which is integrated in the biochip. During continuous flow process in the microchip, rapid cell lysis and PCR-amplifiable genomic DNA purification can be achieved within 20,min. The potential of this microfluidic biochip is illustrated by pretreating a whole blood sample, which shows the possibility of integration of sample preparation, PCR, and separation on a single device to work as portable point-of-care medical diagnostic system. [source] Assessing the impact of mixing assumptions on the estimation of streamwater mean residence timeHYDROLOGICAL PROCESSES, Issue 12 2010Fabrizio Fenicia Abstract Catchment streamwater mean residence time (Tmr) is an important descriptor of hydrological systems, reflecting their storage and flow pathway properties. Tmr is typically inferred from the composition of stable water isotopes (oxygen-18 and deuterium) in observed rainfall and discharge. Currently, lumped parameter models based on convolution and sinewave functions are usually used for tracer simulation. These traditional models are based on simplistic assumptions that are often known to be unrealistic, in particular, steady flow conditions, linearity, complete mixing and others. However, the effect of these assumptions on Tmr estimation is seldom evaluated. In this article, we build a conceptual model that overcomes several assumptions made in traditional mixing models. Using data from the experimental Maimai catchment (New Zealand), we compare a complete-mixing (CM) model, where rainfall water is assumed to mix completely and instantaneously with the total catchment storage, with a partial-mixing (PM) model, where the tracer input is divided between an ,active' and a ,dead' storage compartment. We show that the inferred distribution of Tmr is strongly dependent on the treatment of mixing processes and flow pathways. The CM model returns estimates of Tmr that are well identifiable and are in general agreement with previous studies of the Maimai catchment. On the other hand, the PM model,motivated by a priori catchment insights,provides Tmr estimates that appear exceedingly large and highly uncertain. This suggests that water isotope composition measurements in rainfall and discharge alone may be insufficient for inferring Tmr. Given our model hypothesis, we also analysed the effect of different controls on Tmr. It was found that Tmr is controlled primarily by the storage properties of the catchment, rather than by the speed of streamflow response. This provides guidance on the type of information necessary to improve Tmr estimation. Copyright © 2010 John Wiley & Sons, Ltd. [source] Dynamics of stream nitrate sources and flow pathways during stormflows on urban, forest and agricultural watersheds in central Pennsylvania, USAHYDROLOGICAL PROCESSES, Issue 23 2009Anthony R. Buda Abstract Understanding the influence of storm events on nitrate (NO3,) dynamics is important for efficiently managing NO3, pollution. In this study, five sites representing a downstream progression of forested uplands underlain by resistant sandstone to karst lowlands with agricultural, urban and mixed land-use were established in Spring Creek, a 201 km2 mixed land-use watershed in central Pennsylvania, USA. At each site, stream water was monitored during six storm events in 2005 to assess changes in stable isotopes of NO3, (,15N-NO3, and ,18O-NO3,) and water (,18O-H2O) from baseflow to peakflow. Peakflow fractions of event NO3, and event water were then computed using two-component mixing models to elucidate NO3, flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect NO3, sources and flow pathways. During small storms (<35 mm rainfall), greater event NO3, fractions than event water fractions indicated the prevalence of atmospheric NO3, source contributions at peakflow. During larger storms (>35 mm rainfall), event NO3, fractions were less than event water fractions at peakflow suggesting that NO3, was flushed from stored sources via shallow subsurface flow pathways. For the urbanized site, wash-off of atmospheric NO3, was an important NO3, source at peakflow, especially during short-duration storms where event water contributions indicated the prevalence of overland flow. In the karst lowlands, very low fractions of event water and even lower fractions of event NO3, at peakflow suggested the dominance of ground water flow pathways during storms. These ground water flow pathways likely flushed stored NO3, sources into the stream, while deep soils in the karst lowlands also may have promoted NO3, assimilation. The results of this study illustrated how NO3, isotopes and ,18O-H2O could be combined to show key differences in water and NO3, delivery between forested uplands, karst valleys and fully urbanized watersheds. Copyright © 2009 John Wiley & Sons, Ltd. [source] Individual responses of seabirds to commercial fisheries revealed using GPS tracking, stable isotopes and vessel monitoring systemsJOURNAL OF APPLIED ECOLOGY, Issue 2 2010Stephen C. Votier Summary 1.,The large amount of discards produced by commercial fisheries can have major impacts on marine predator populations: this abundant food may increase populations of some scavengers or decrease others via accidental bycatch. Yet, despite the conservation implications of discard practices, the ecology of individual scavengers is poorly understood. 2.,Here, we assess the influence of commercial fisheries' activity on the foraging behaviour of individual breeding northern gannets Morus bassanus. Using recent developments in stable isotope mixing models (Stable Isotope Analysis in R or SIAR) we estimate individual discard consumption. Using GPS tracking and the Vessel Monitoring System (VMS), we investigate behavioural responses to trawlers. 3.,Analysis of conventional diet samples, as well as stable isotope ratios of carbon and nitrogen in blood (plasma and cells), highlight marked individual differences in the proportion of fishery discards in the diet. Individual differences in foraging behaviour revealed by stable isotopes show evidence of both short-term consistency and behavioural flexibility. 4.,At-sea path tortuosity of 25 gannets (tracked using GPS loggers) revealed scale-dependent adjustments in response to VMS-derived fishing vessel locations, as well as to sea surface temperature, chlorophyll a concentration and copepod abundance. The results also indicate individual variability in behavioural response to trawlers. 5.,Individual differences in the amount of discards estimated from SIAR were negatively correlated with differences in foraging trip length and body condition, indicating potential fitness consequences. 6.,Synthesis and applications. The management of commercial fisheries and apex predators is a daunting task. Ultimately, reducing bycatch and removing dependency on discards remain key conservation priorities, but managers should also ensure that scavenging species have sufficient alternative food to meet their energetic needs, to ameliorate potential unforeseen knock-on consequences. The results of Stable Isotope Analysis (SIAR) reveal intra-population differences in discard consumption by gannets; differences that have impacts on foraging effort and body condition. The use of GPS tracking and Vessel Monitoring Systems (VMS) reveal that gannet at-sea behaviour is influenced by fishing vessels, although this also varies among individuals. A combination of SIAR, GPS tracking and VMS can be used to study fishery/scavenger interactions in detail at the individual level, to answer fundamental questions about scavenging behaviour. [source] Water Sources of Dominant Species in Three Alpine Ecosystems on the Tibetan Plateau, ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2008De-Yu Duan Abstract Plant water sources were estimated by two or three compartment linear mixing models using hydrogen and oxygen isotope (,D and ,18O) values of different components such as plant xylem water, precipitation and river water as well as soil water on the Tibetan Plateau in the summer of 2005. Four dominant species (Quercus aquifolioides, Pinus tabulaeformis, Salix rehderiana and Nitraria tangutorum) in three typical ecosystems (forest, shrub and desert) were investigated in this study. Stable isotope ratios of the summer precipitations and the soil water presented variations in spatial and temporal scales. ,18O values of N. tangutorum xylem water were constant in the whole growth season and very similar to those of deep soil water. Water sources for all of the plants came from both precipitations and soil water. Plants switched rapidly among different water sources when environmental water conditions changed. Rainwater had different contributions to the plants, which was influenced by amounts of precipitation. The percentage of plant xylem water derived from rainwater rose with an increase in precipitation. Water sources for broad-leaved and coniferous species were different although they grew in the same environmental conditions. For example, the broad-leaved species Q. aquifolioides used mainly the water from deep soil, while 92.5% of xylem water of the coniferous species P. tabulaeformis was derived from rainwater during the growth season. The study will be helpful for us to fully understand responses of species on the Tibetan Plateau to changes in precipitation patterns, and to assess accurately changes of vegetation distribution in the future. [source] A trophic pathway from biogenic methane supports fish biomass in a temperate lake ecosystemOIKOS, Issue 2 2010Mark Ravinet Although some primary consumers such as chironomid larvae are known to exploit methane-derived carbon via microbial consortia within aquatic food webs, few studies have traced the onward transfer of such carbon to their predators. The ruffe Gymnocephalus cernuus is a widespread benthivorous fish which feeds predominantly on chironomid larvae and is well adapted for foraging at lower depths than other percids. Therefore, any transfer of methanogenic carbon to higher trophic levels might be particularly evident in ruffe. We sampled ruffe and chironomid larvae from the littoral, sub-littoral and profundal areas of Jyväsjärvi, Finland, a lake which has previously been shown to contain chironomid larvae exhibiting the very low stable carbon isotope ratios indicative of methane exploitation. A combination of fish gut content examination and stable isotope analysis was used to determine trophic linkages between fish and their putative prey. Irrespective of the depth from which the ruffe were caught, their diet was dominated by chironomids and pupae although the proportions of taxa changed. Zooplankton made a negligible contribution to ruffe diet. A progressive decrease in ,13C and ,15N values with increasing water column depth was observed for both chironomid larvae and ruffe, but not for other species of benthivorous fish. Furthermore, ruffe feeding at greater depths were significantly larger than those feeding in the littoral, suggesting an ontogenetic shift in habitat use, rather than diet, as chironomids remained the predominant prey item. The outputs from isotope mixing models suggested that the incorporation of methane-derived carbon to larval chironomid biomass through feeding on methanotrophic bacteria increased at greater depth, varying from 0% in the littoral to 28% in the profundal. Using these outputs and the proportions of littoral, sub-littoral or profundal chironomids contributing to ruffe biomass, we estimated that 17% of ruffe biomass in this lake was ultimately derived from chemoautotrophic sources. Methanogenic carbon thus supports considerable production of higher trophic levels in lakes. [source] Determination of 13C/12C ratios of endogenous urinary steroids: method validation, reference population and application to doping control purposesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2008Thomas Piper The application of a comprehensive gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS)-based method for stable carbon isotopes of endogenous urinary steroids is presented. The key element in sample preparation is the consecutive cleanup with high-performance liquid chromatography (HPLC) of underivatized and acetylated steroids, which allows the isolation of ten analytes (11, -hydroxyandrosterone, 5, -androst-16-en-3, -ol, pregnanediol, androsterone, etiocholanolone, testosterone, epitestosterone, 5, -androstane-3,,17, -diol, 5, -androstane-3,,17, -diol and dehydroepiandrosterone) from a single urine specimen. These steroids are of particular importance to doping controls as they enable the sensitive and retrospective detection of steroid abuse by athletes. Depending on the biological background, the determination limit for all steroids ranges from 5 to 10,ng/mL for a 10,mL specimen. The method is validated by means of linear mixing models for each steroid, which covers repeatability and reproducibility. Specificity was further demonstrated by gas chromatography/mass spectrometry (GC/MS) for each analyte, and no influence of the sample preparation or the quantity of analyte on carbon isotope ratios was observed. In order to determine naturally occurring 13C/12C ratios of all implemented steroids, a reference population of n,=,61 subjects was measured to enable the calculation of reference limits for all relevant steroidal , values. Copyright © 2008 John Wiley & Sons, Ltd. [source] Isotopic ecology ten years after a call for more laboratory experimentsBIOLOGICAL REVIEWS, Issue 1 2009Carlos Martínez del Rio Abstract About 10 years ago, reviews of the use of stable isotopes in animal ecology predicted explosive growth in this field and called for laboratory experiments to provide a mechanistic foundation to this growth. They identified four major areas of inquiry: (1) the dynamics of isotopic incorporation, (2) mixing models, (3) the problem of routing, and (4) trophic discrimination factors. Because these areas remain central to isotopic ecology, we use them as organising foci to review the experimental results that isotopic ecologists have collected in the intervening 10 years since the call for laboratory experiments. We also review the models that have been built to explain and organise experimental results in these areas. [source] | ||||||||||