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Sample records for air residence time

  1. Air Parcel Residence Times within Tropical Forest Canopies and Implications for Reactive Gases

    NASA Astrophysics Data System (ADS)

    Gerken, T.; Chamecki, M.; Fuentes, J. D.

    2014-12-01

    The Amazon rainforest is the world's largest natural emitter of reactive trace gases. Due to its dense vegetation (leaf area index > 4), turbulence fluctuations are highly attenuated deep inside the canopy. However, strong coherent eddies that penetrate the upper portion of the canopy can be very effective in transporting gases. Sweeps and ejections act in the order of seconds and transport air parcels into or out of the canopy. The effects of coherent structures on the air parcel residence times and associated chemical processing of reactive gases remain largely unquantified in tropical forests. We combine canopy resolving Large-Eddy Simulation (LES) and field observations in the Brazilian Amazon to study residence times of air parcels in the rainforest as a function of canopy structure and height (h). Good agreement is obtained between simulated and observed turbulence statistics within and above the forest. Coherent structure properties obtained from quadrant analysis are also well reproduced. A Lagrangian particle tracking algorithm is used to quantify the distribution of residence times of air parcels "released" at different heights. Canopy residence times were determined from the particle trajectories. The resulting probability density function (PDF) strongly depended on the particle release height (z). For particles released in the upper canopy (at z/h=0.75) the most frequent residence times were in the order of 30s, with 50% of all particles ejected from the canopy after ~2 minutes. The mean residence time was close to 5 minutes, indicating a very skewed PDF. At z/h=0.25 the PDF was more evenly distributed with its median and mean in the order of ~10 minutes. Due to sweeps, both simulations had a non- negligible fraction of particles transported deep into the canopy, thus increasing greatly their residence times. As the reaction timescales of many biogenic volatile organic compounds (BVOC) are in the order of seconds to minutes, significant chemical

  2. Air-vegetation exchange of SOCs as a control of atmospheric concentrations and residence times

    SciTech Connect

    Hornbuckle, K.C.; Eisenreich, S.J.

    1994-12-31

    Semi-volatile organic compounds (SOCs) such as the polychlorinated biphenyls exhibit seasonal maxima in atmospheric concentrations with highest values in the warm summer. This generally believed to result from the effect of temperature on SOC vapor pressure with direct and important implications to global transport. The authors have conducted a series of field experiments whereby air samples were collected above an ombrotrophic, forested bog in northern MN at a frequency of 6 day{sup {minus}1} during the fall, winter, spring and summer. Samples of Sphagnum moss and other vegetation were also collected on each occasion. All samples were analyzed for PCBs, low MW PAHs, gaseous hydrocarbons and selected pesticides. Meteorological and soils data were collected during all experiments (air and soil temperature, wind direction and velocity, RH). Diurnal concentration data, air-plant and air-soil partition coefficients and probable mechanisms and kinetics of SOC-plant interactions will be presented.

  3. Variable residence time vortex combustor

    DOEpatents

    Melconian, Jerry O.

    1987-01-01

    A variable residence time vortex combustor including a primary combustion chamber for containing a combustion vortex, and a plurality of louvres peripherally disposed about the primary combustion chamber and longitudinally distributed along its primary axis. The louvres are inclined to impel air about the primary combustion chamber to cool its interior surfaces and to impel air inwardly to assist in driving the combustion vortex in a first rotational direction and to feed combustion in the primary combustion chamber. The vortex combustor also includes a second combustion chamber having a secondary zone and a narrowed waist region in the primary combustion chamber interconnecting the output of the primary combustion chamber with the secondary zone for passing only lower density particles and trapping higher density particles in the combustion vortex in the primary combustion chamber for substantial combustion.

  4. Residence time determination for adsorbent beds of different configurations

    SciTech Connect

    Otermat, J.E.; Wikoff, W.O.; Kovach, J.L.

    1995-02-01

    The residence time calculations of ASME AG-1 Code, Section FC, currently specify a screen surface area method, that is technically incorrect. Test data has been obtained on Type II adsorber trays of different configurations to establish residence time in the adsorber trays. These data indicate that the air volume/carbon volume ratio or the average screen area are more appropriate for the calculation of the residence time calculation than the currently used, smallest screen area basis.

  5. A revised picture of the atmospheric moisture residence time

    NASA Astrophysics Data System (ADS)

    Läderach, Alexander; Sodemann, Harald

    2016-01-01

    Refined Lagrangian moisture source diagnostics are applied on an air mass transport climatology covering the period 1979-2013 to provide an estimate of the atmospheric moisture residence time. Our diagnostics yield an estimate of about 4-5 days for the global mean residence time, which is about half compared to depletion times that are commonly interpreted as proxies for the residence time. The discrepancies to depletion times are mainly explained by the fact that these are based on simplified representations of precipitation processes. The revised picture given by our results is supported by the overall consistency with the footprints of precipitation producing weather systems in different regions of the Earth.

  6. Residence time statistics for N renewal processes.

    PubMed

    Burov, S; Barkai, E

    2011-10-21

    We present a study of residence time statistics for N renewal processes with a long tailed distribution of the waiting time. Such processes describe many nonequilibrium systems ranging from the intensity of N blinking quantum dots to the residence time of N Brownian particles. With numerical simulations and exact calculations, we show sharp transitions for a critical number of degrees of freedom N. In contrast to the expectation, the fluctuations in the limit of N→∞ are nontrivial. We briefly discuss how our approach can be used to detect nonergodic kinetics from the measurements of many blinking chromophores, without the need to reach the single molecule limit. PMID:22107497

  7. Stochastic resonance: A residence time approach

    SciTech Connect

    Gammaitoni, L. |; Marchesoni, F. |; Menichella Saetta, E.; Santucci, S.

    1996-06-01

    The Stochastic Resonance phenomenon is described as a synchronization process between periodic signals and the random response in bistable systems. The residence time approach as a useful tool in characterizing hidden periodicities is discussed. {copyright} {ital 1996 American Institute of Physics.}

  8. Residence times of branching diffusion processes

    NASA Astrophysics Data System (ADS)

    Dumonteil, E.; Mazzolo, A.

    2016-07-01

    The residence time of a branching Brownian process is the amount of time that the mother particle and all its descendants spend inside a domain. Using the Feynman-Kac formalism, we derive the residence-time equation as well as the equations for its moments for a branching diffusion process with an arbitrary number of descendants. This general approach is illustrated with simple examples in free space and in confined geometries where explicit formulas for the moments are obtained within the long time limit. In particular, we study in detail the influence of the branching mechanism on those moments. The present approach can also be applied to investigate other additive functionals of branching Brownian process.

  9. Residence time of osmium in the oceans

    NASA Astrophysics Data System (ADS)

    Oxburgh, Rachel

    2001-06-01

    Estimates of osmium residence time in the oceans that are based on oceanic mass balance calculations (35-50 kyr) appear irreconcilable with those inferred from the recent evolution of the osmium isotope composition of seawater (3-4 kyr). It is argued that the osmium budget of the oceans is currently close to steady state and thus that the estimates made by the two methods should agree. As the inventory of osmium in the oceans is relatively well constrained, these disparate residence time estimates imply wildly different osmium input fluxes to the oceans. An osmium residence time of 8-10 kyr is proposed by evaluating the uncertainties and limitations of both methods, and it is argued that osmium inputs to the ocean are currently underestimated by a factor of ˜3. This reflects in part the underestimation of the river input of osmium to the oceans owing to a bias within the existing data set and in part the probable existence of sources of osmium to the oceans that have not yet been identified. The very short residence time of 3-4 kyr inferred from the postglacial change in seawater composition (assuming a single step change in input flux) is rejected as it implies unreasonably high osmium input fluxes to the oceans. It is concluded that a postglacial spike in osmium flux, associated with a meltwater event, must have driven part of the change in seawater composition. However, it is also shown that such a spike cannot be the dominant cause of the most recent shift in seawater 187Os/188Os.

  10. Controlled short residence time coal liquefaction process

    DOEpatents

    Anderson, Raymond P.; Schmalzer, David K.; Wright, Charles H.

    1982-05-04

    Normally solid dissolved coal product and a distillate liquid product are produced by continuously passing a feed slurry comprising raw feed coal and a recycle solvent oil and/or slurry together with hydrogen to a preheating-reaction zone (26, alone, or 26 together with 42), the hydrogen pressure in the preheating-reaction zone being at least 1500 psig (105 kg/cm.sup.2), reacting the slurry in the preheating-reaction zone (26, or 26 with 42) at a temperature in the range of between about 455.degree. and about 500.degree. C. to dissolve the coal to form normally liquid coal and normally solid dissolved coal. A total slurry residence time is maintained in the reaction zone ranging from a finite value from about 0 to about 0.2 hour, and reaction effluent is continuously and directly contacted with a quenching fluid (40, 68) to substantially immediately reduce the temperature of the reaction effluent to below 425.degree. C. to substantially inhibit polymerization so that the yield of insoluble organic matter comprises less than 9 weight percent of said feed coal on a moisture-free basis. The reaction is performed under conditions of temperature, hydrogen pressure and residence time such that the quantity of distillate liquid boiling within the range C.sub.5 -455.degree. C. is an amount at least equal to that obtainable by performing the process under the same conditions except for a longer total slurry residence time, e.g., 0.3 hour. Solvent boiling range liquid is separated from the reaction effluent and recycled as process solvent.

  11. Mean residence time in barchan dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Yang, X.; Rozier, O.; Narteau, C.

    2013-12-01

    A barchan dune migrates when the sediment trapped on its lee side is remobilized by the flow. Then, sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady-state barchan dunes by tracking individual cells of a 3D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan dune shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchan dunes. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchan dunes is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan dune morphodynamics. Finally, we initiate a discussion about sediment transport and memory in presence of bed forms using the advantages of the particle tracking technique.

  12. Mean sediment residence time in barchan dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Yang, X.; Rozier, O.; Narteau, C.

    2014-03-01

    When a barchan dune migrates, the sediment trapped on its lee side is later mobilized when exposed on the stoss side. Then sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady state barchans by tracking individual cells of a 3-D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan morphodynamics. Finally, we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique.

  13. A revised picture of the atmospheric moisture residence time

    NASA Astrophysics Data System (ADS)

    Läderach, Alexander; Sodemann, Harald

    2016-04-01

    The atmospheric branch of the hydrological cycle is a key component of variability in the global water and energy budget. We study the transport of moisture by weather systems using a refined Lagrangian moisture source diagnostics on a global air mass transport climatology calculated with the FLEXPART model for the period 1979-2013. The diagnostics determine source-sink relationships for all precipitation events in the ERA-Interim data set, which provides a new estimate of the atmospheric moisture residence time (defined as the time moisture spends in the atmosphere between evaporation and precipitation). The global mean residence time of 4 to 5 days obtained from our diagnostics is about half the value assumed so far. This is mainly because previous estimates neglect moisture transport, and assume that depletion time constants can be considered as a proxy for the time moisture spends in the atmosphere. We show from different arguments that these assumptions are generally not fulfilled. The revised spatial and temporal picture of the atmospheric moisture residence time reveals patterns that are consistent with the footprints of precipitation producing weather systems in different regions of the earth. This will be exemplified with examples from tropical and extratropical regions.

  14. RESIDENCE TIME DISTRIBUTION OF FLUIDS IN STIRRED ANNULAR PHOTOREACTORS

    EPA Science Inventory

    When gases flow through an annular photoreactor at constant rate, some of the gas spends more or less than the average residence time in the reactor. This spread of residence time can have an important effect on the performance of the reactor. this study tested how the residence...

  15. Time- versus Competency-Based Residency Training.

    PubMed

    Nguyen, Vu T; Losee, Joseph E

    2016-08-01

    Graduate medical education is at the brink of a paradigm shift in educating the next generation of physicians. Over 100 years ago, the Flexner report helped usher in the Halstedian residency, based on timed exposure and knowledge assessment as the cornerstones of medical education. The addition of operative case logs and respective board examinations to the current model of surgical education has served to establish practice minimums; however, they do not provide any assessment of actual operative capability or clinical competence. Although these facets have been tempered over time, one could argue that they currently exist only as surrogates for the true goal of all graduate medical education: the development of competent, graduating physicians, capable of independent and ethical practice. There now exists a growing body of evidence that competency-based medical education is this century's Flexnerian revolution. By the objective, subjective, and global assessment of competence, it is thought that we can more effectively and efficiently educate our trainees, provide much needed accountability to our individual patients and to the public as a whole, and establish a lasting model of self-motivated, lifelong learning. PMID:27465174

  16. Timely Completion of Paperwork: Are Some Residents Consistently Late Responders?

    PubMed Central

    Metheny, William P.

    2014-01-01

    Background One element of competence in professionalism entails the timely completion of paperwork. Early identification of residents who are consistently late in completing their assignments might be the first step in helping them change this habit. Objective This study sought to determine if program coordinators' ratings of residents' response habits to completing assignments were associated with existing measures of resident response times tracked by the institution. Methods Program coordinators rated residents as early, mid, or late responders based on their experience with them. We compared coordinators' ratings with the response time of these same residents in returning orientation materials to the institution, completing a patient safety survey and duty hour logs, and providing their required countersignature on telephone and verbal orders. A total of 196 residents enrolled at this institution were eligible for this comparison in the 2012–2013 academic year. Results Program coordinators rated 23% (40 of 177) of the residents as late responders. These ratings were significantly associated with the response time of residents in returning orientation materials and the completed patient safety survey. Residents identified as late responders were 2.45 times (confidence interval, 1.09 ± 5.64) more likely to have delinquent medical records. Conclusions This exploratory study suggests that residents who are late responders can be identified as early as orientation and that they likely maintain this response habit in completing assignments throughout residency. To address this professionalism issue, programs should track and counsel residents on their timeliness in completing paperwork. PMID:24949137

  17. Prolonged and tunable residence time using reversible covalent kinase inhibitors

    PubMed Central

    Bradshaw, J. Michael; McFarland, Jesse M.; Paavilainen, Ville O.; Bisconte, Angelina; Tam, Danny; Phan, Vernon T.; Romanov, Sergei; Finkle, David; Shu, Jin; Patel, Vaishali; Ton, Tony; Li, Xiaoyan; Loughhead, David G.; Nunn, Philip A.; Karr, Dane E.; Gerritsen, Mary E.; Funk, Jens Oliver; Owens, Timothy D.; Verner, Erik; Brameld, Ken A.; Hill, Ronald J.; Goldstein, David M.; Taunton, Jack

    2015-01-01

    Drugs with prolonged, on-target residence time often show superior efficacy, yet general strategies for optimizing drug-target residence time are lacking. Here, we demonstrate progress toward this elusive goal by targeting a noncatalytic cysteine in Bruton's tyrosine kinase (BTK) with reversible covalent inhibitors. Utilizing an inverted orientation of the cysteine-reactive cyanoacrylamide electrophile, we identified potent and selective BTK inhibitors that demonstrate biochemical residence times spanning from minutes to 7 days. An inverted cyanoacrylamide with prolonged residence time in vivo remained bound to BTK more than 18 hours after clearance from the circulation. The inverted cyanoacrylamide strategy was further utilized to discover fibroblast growth factor receptor (FGFR) kinase inhibitors with residence times of several days, demonstrating generalizability of the approach. Targeting noncatalytic cysteines with inverted cyanoacrylamides may serve as a broadly applicable platform that facilitates “residence time by design”, the ability to modulate and improve the duration of target engagement in vivo. PMID:26006010

  18. Long residence times - bad tracer tests?

    NASA Astrophysics Data System (ADS)

    Ghergut, Julia; Behrens, Horst; Sauter, Martin

    2015-04-01

    Tracer tests conducted at geothermal well doublets or triplets in the Upper Rhine Rift Valley [1] all face, with very few exceptions so far, one common issue: lack of conclusive tracer test results, or tracer signals still undetectable for longer than one or two years after tracer injection. While the reasons for this surely differ from site to site (Riehen, Landau, Insheim, Bruchsal, ...), its effects on how the usefulness of tracer tests is perceived by the non-tracer community are pretty much the same. The 'poor-signal' frustration keeps nourishing two major 'alternative' endeavours : (I) design and execute tracer tests in single-well injection-withdrawal (push-pull), 'instead of' inter-well flow-path tracing configurations; (II) use 'novel' tracer substances instead of the 'old' ones which have 'obviously failed'. Frustration experienced with most inter-well tracer tests in the Upper Rhine Rift Valley has also made them be regarded as 'maybe useful for EGS' ('enhanced', or 'engineered' geothermal systems, whose fluid RTD typically include a major share of values below one year), but 'no longer worthwhile a follow-up sampling' in natural, large-scale hydrothermal reservoirs. We illustrate some of these arguments with the ongoing Bruchsal case [2]. The inter-well tracer test conducted at Bruchsal was (and still is!) aimed at assessing inter-well connectivity, fluid residence times, and characterizing the reservoir structure [3]. Fluid samples taken at the geothermal production well after reaching a fluid turnover of about 700,000 m3 showed tracer concentrations in the range of 10-8 Minj per m3, in the liquid phase of each sample (Minj being the total quantity of tracer injected as a short pulse at the geothermal re-injection well). Tracer signals might actually be higher, owing to tracer amounts co-precipitated and/or adsorbed onto the solid phase whose accumulation in the samples was unavoidable (due to pressure relief and degassing during the very sampling

  19. Hazard Assessment of Chemical Air Contaminants Measured in Residences

    SciTech Connect

    Logue, J.M.; McKone, T.E.; Sherman, M. H.; Singer, B.C.

    2010-05-10

    Identifying air pollutants that pose a potential hazard indoors can facilitate exposure mitigation. In this study, we compiled summary results from 77 published studies reporting measurements of chemical pollutants in residences in the United States and in countries with similar lifestyles. These data were used to calculate representative mid-range and upper bound concentrations relevant to chronic exposures for 267 pollutants and representative peak concentrations relevant to acute exposures for 5 activity-associated pollutants. Representative concentrations are compared to available chronic and acute health standards for 97 pollutants. Fifteen pollutants appear to exceed chronic health standards in a large fraction of homes. Nine other pollutants are identified as potential chronic health hazards in a substantial minority of homes and an additional nine are identified as potential hazards in a very small percentage of homes. Nine pollutants are identified as priority hazards based on the robustness of measured concentration data and the fraction of residences that appear to be impacted: acetaldehyde; acrolein; benzene; 1,3-butadiene; 1,4-dichlorobenzene; formaldehyde; naphthalene; nitrogen dioxide; and PM{sub 2.5}. Activity-based emissions are shown to pose potential acute health hazards for PM{sub 2.5}, formaldehyde, CO, chloroform, and NO{sub 2}.

  20. A METHOD TO INCORPORATE ECOLOGY INTO RESIDENCE TIME OF CHEMICALS IN EMBAYMENTS: LOCAL EFFECT TIME

    EPA Science Inventory

    Residence times are classically defined by the physical and chemical aspects of water bodies rather than by their ecological implications. Therefore, a more clear and direct connection between the residence times and ecological effects is necessary to quantitatively relate these ...

  1. Effect of residence time on the efficacy of antidandruff shampoos.

    PubMed

    Piérard-Franchimont, C; Uhoda, E; Loussouarn, G; Saint-Léger, D; Piérard, G E

    2003-12-01

    Dandruff is known to be controlled by fungistatic shampoos active against Malassezia spp. These products also remove the loosely attached scales. This study was performed to assess the effect of a 5-min residence time on the efficacy of antidandruff shampoos. Two commercially available shampoos were used in two groups of 21 panelists with severe dandruff. They contained either 1% ketoconazole or 1% piroctone olamine. In each group, intraindividual comparisons were made by a split-scalp design between the effect of a 5-min residence time versus no residence time. Both shampoos induced significant reductions in scaliness and yeast colonization. The beneficial effects were obvious immediately after one single shampooing and 3 days later as well. The improvement was greater with a 5-min residence time. The piroctone olamine treatment benefited more than the ketoconazole treatment from the extension of shampoo-exposure time. In conclusion, the benefit of a residence time in treating dandruff is documented. The level of improvement in efficacy may vary according to the nature of the shampoo. PMID:18494909

  2. Online residence time distribution measurement of thermochemical biomass pretreatment reactors

    SciTech Connect

    Sievers, David A.; Kuhn, Erik M.; Stickel, Jonathan J.; Tucker, Melvin P.; Wolfrum, Edward J.

    2015-11-03

    Residence time is a critical parameter that strongly affects the product profile and overall yield achieved from thermochemical pretreatment of lignocellulosic biomass during production of liquid transportation fuels. The residence time distribution (RTD) is one important measure of reactor performance and provides a metric to use when evaluating changes in reactor design and operating parameters. An inexpensive and rapid RTD measurement technique was developed to measure the residence time characteristics in biomass pretreatment reactors and similar equipment processing wet-granular slurries. Sodium chloride was pulsed into the feed entering a 600 kg/d pilot-scale reactor operated at various conditions, and aqueous salt concentration was measured in the discharge using specially fabricated electrical conductivity instrumentation. This online conductivity method was superior in both measurement accuracy and resource requirements compared to offline analysis. Experimentally measured mean residence time values were longer than estimated by simple calculation and screw speed and throughput rate were investigated as contributing factors. In conclusion, a semi-empirical model was developed to predict the mean residence time as a function of operating parameters and enabled improved agreement.

  3. Online residence time distribution measurement of thermochemical biomass pretreatment reactors

    DOE PAGESBeta

    Sievers, David A.; Kuhn, Erik M.; Stickel, Jonathan J.; Tucker, Melvin P.; Wolfrum, Edward J.

    2015-11-03

    Residence time is a critical parameter that strongly affects the product profile and overall yield achieved from thermochemical pretreatment of lignocellulosic biomass during production of liquid transportation fuels. The residence time distribution (RTD) is one important measure of reactor performance and provides a metric to use when evaluating changes in reactor design and operating parameters. An inexpensive and rapid RTD measurement technique was developed to measure the residence time characteristics in biomass pretreatment reactors and similar equipment processing wet-granular slurries. Sodium chloride was pulsed into the feed entering a 600 kg/d pilot-scale reactor operated at various conditions, and aqueous saltmore » concentration was measured in the discharge using specially fabricated electrical conductivity instrumentation. This online conductivity method was superior in both measurement accuracy and resource requirements compared to offline analysis. Experimentally measured mean residence time values were longer than estimated by simple calculation and screw speed and throughput rate were investigated as contributing factors. In conclusion, a semi-empirical model was developed to predict the mean residence time as a function of operating parameters and enabled improved agreement.« less

  4. Effects of bioaerosol polluted outdoor air on airways of residents: a cross sectional study

    PubMed Central

    Herr, C; zur Nieden, A; Jankofsky, M; Stilianakis, N; Boedeker, R; Eikmann, T

    2003-01-01

    Background: Bioaerosol pollution of workplace and home environments mainly affects airways and mucous membranes. The effect of environmental outdoor residential bioaerosol pollution, for example, livestock holdings, farming, and waste disposal plants, is unclear. Aims: To investigate the perceived health of residents living in areas with measurable outdoor bioaerosol pollution (for example, spores of Aspergillus fumigatus and actinomycetes), and effects of accompanying odours. Methods: In a cross sectional study, double blinded to ongoing microbial measurements, doctors collected 356 questionnaires from residents near a large scale composting site, and from unexposed controls in 1997. Self reported prevalence of health complaints during the past year, doctors' diagnoses, as well as residential odour annoyance were assessed. Microbiological pollution was measured simultaneously in residential outdoor air. Results: Concentrations of >105 colony forming units of thermophilic actinomycetes, moulds, and total bacteria/m3 air were measured 200 m from the site, dropping to near background concentrations within 300 m. Positive adjusted associations were observed for residency within 150–200 m from the site versus unexposed controls for self reported health complaints: "waking up due to coughing", odds ratio (OR) 6.59 (95% confidence interval (CI) 2.57 to 17.73); "coughing on rising or during the day", OR 3.18 (95% CI 1.24 to 8.36); "bronchitis", OR 3.59 (95% CI 1.40 to 9.4); and "excessive tiredness", OR 4.27 (95% CI 1.56 to 12.15). Reports of irritative airway complaints were associated with residency in the highest bioaerosol exposure, 150–200 m (versus residency >400–500 m) from the site, and period of residency more than five years, but not residential odour annoyance. Lifetime prevalence of self reported diseases did not differ with exposure. Conclusions: Bioaerosol pollution of residential outdoor air can occur in concentrations found in occupational

  5. Nonlinear sensors: an approach to the residence time detection strategy.

    PubMed

    Dari, A; Bosi, L; Gammaitoni, L

    2010-01-01

    The monitoring of the residence time difference in bistable sensors has been recently proposed as a valid scheme for improving the detection capabilities of sensors as diverse as fluxgate magnetometers, ferroelectric sensors and mechanical sensors. In this paper we propose an approach to the residence time based detection strategy based on the measurement of the slope m of the sensor output integral. We demonstrate that such a method, far from degrading the detection performances can provide an easier way to realize fast and reliable sensors without the computationally demanding task related with the computation of the residence time difference. We introduce the receiver operating characteristic curve as a quantitative estimator for the comparison of the two methods and show that the detector performances increase with increasing the periodic bias amplitude A up to a maximum value. This condition has potentially relevant consequences in the future detectors design. PMID:20365331

  6. Estimation of residence time in a shallow lacustrine embayment

    NASA Astrophysics Data System (ADS)

    Razmi, A. M.; Barry, D. A.; Lemmin, U.; Bakhtyar, R.

    2012-12-01

    Near-shore water quality in lacustrine bays subjected to effluent or stream discharges is affected by, amongst other things, the residence time within a given bay. Vidy Bay, located on the northern shore of Lake Geneva, Switzerland, receives discharge from a wastewater treatment plant, the Chamberonne River and a storm-water drain. The residence time of water in the bay largely depends on water exchanges with the main basin (Grand Lac) of Lake Geneva. Field investigations and modeling of the hydrodynamics of Vidy Bay have shown that currents are variable, due mainly to wind variability over the lake. However, in broad terms there are two main current patterns in the bay, (i) currents are linked to large gyres in the Grand Lac, or (ii) currents are partially independent of the Grand Lac and are controlled by small-scale gyres within the bay. Residence times in Vidy Bay were computed using the hydrodynamic model Delft3D. Since the Vidy Bay shoreline follows a shallow arc, the definition of the off-shore extent of the bay is ambiguous. Here, the largest within-bay gyre is used. Particle tracking was conducted for each of the three discharges into the bay. Model results were computed using meteorological data for 2010, and thus include the natural variability in wind patterns and seasonal stratification. An analysis of the results shows that a water parcel from the waste water outfall has a residence time ranging from hours to days. The water residence time is minimum near to the surface and maximum at the near bottom layer. The results confirmed that wind force, thermal stratification, and water depth are the main factors influencing residence time.

  7. Indoor Residence Times of Semivolatile Organic Compounds: Model Estimation and Field Evaluation

    EPA Science Inventory

    Indoor residence times of semivolatile organic compounds (SVOCs) are a major and mostly unavailable input for residential exposure assessment. We calculated residence times for a suite of SVOCs using a fugacity model applied to residential environments. Residence times depend on...

  8. Stable, Ultra-Low Residence Time Partial Oxidation

    DOEpatents

    Schmidt, Lanny D.; Hickman, Daniel A.

    1997-07-15

    A process for the catalytic partial oxidation of methane in gas phase at very short residence time (800,000 to 12,000,000 hr.sup.-1) by contacting a gas stream containing methane and oxygen with a metal supported catalyst, such as platinum deposited on a ceramic monolith.

  9. ON THE RESIDENCE TIME DISTRIBUTION IN IDEALIZED GROUNDWATERSHEDS

    EPA Science Inventory

    The relative cumulative frequency distribution of residence times F(T) is calculated for an entire groundwatershed under steady-state conditions and assuming Dupuit-Forchheimer flow. It appears that F(T) is always the same: , provided that the aquifer recharge rate and are cons...

  10. The residence time of carbon in Amazonian primary forests

    NASA Astrophysics Data System (ADS)

    Trumbore, S.; Vieira, S. A.; Camargo, P.; Chambers, J. Q.; Higuchi, N.; Selhorst, D.; Martinelli, L. A.

    2004-12-01

    The residence time of carbon is a major determiner of the capacity of an ecosystem to function as a source or sink of carbon. The overall residence time of carbon in primary forests is determined by (1) what fraction of photosynthetic products get respired quickly and (2) the residence time of C allocated to living plant tissues, and (3) the time each of these components takes to decay, including what fraction is oxidized to CO2 versus what becomes stabilized in soil organic matter. Using radiocarbon to determine the age of carbon in various pools in forests, we conclude that: (1) carbon use efficiency of these forests is low, with ~70% of photosynthetic products respired within a year, and only 30% allocated to growth of wood, root and leaf tissues; (2) carbon resides on average for 2-3 years in leaves and 3-10 years in fine roots; very rapid or ephemeral root turnover is assigned in our budgets to AƒAøAøâ_sA¬A<Å"autotrophicAƒAøAøâ_sA¬Aøâ_zAø respiration (3) the mean age of carbon in living trees is longer (200-260 years) than the mean residence time of carbon derived from the biomass stock divided by annual wood growth increment (40-100 years) because most of the biomass is in the largest, fastest growing, trees, while most of the individuals are smaller, slower growing, shaded trees; (4) decomposition rates are rapid, but potentially recycling of carbon in the microbial community leads to a significant decadally cycling pool in near-surface organic matter. We will summarize these findings and use them with models of carbon dynamics to estimate carbon storage and loss potential on interannual to decadal timescales. The overall age of heterotrophically respired carbon (carbon derived from microbial decomposition) is 6-10 years, with much of the time lag due to the time spent by C in living leaf and root tissues. Even when combined with 70% autotrophically respired C with residence times of <1 year, this significant time lag can lead to large

  11. Mean Residence Time and Emergency Drinking Water Supply.

    NASA Astrophysics Data System (ADS)

    Kralik, Martin; Humer, Franko

    2013-04-01

    Immediately after securing an endangered population, the first priority of aid workers following a disaster is the distribution of drinking water. Such emergency situations are reported from many parts of the world following regional chemical or nuclear pollution accidents, floods, droughts, rain-induced landslides, tsunami, and other extreme events. It is often difficult to organise a replacement water supply when regular water systems with short residence times are polluted, infiltrated or even flooded by natural or man-made disasters. They are either unusable or their restoration may take months or even years. Groundwater resources, proven safe and protected by the geological environment, with long residence times and the necessary infrastructure for their exploitation, would provide populations with timeous replacement of vulnerable water supply systems and make rescue activities more rapid and effective. Such resources have to be identified and investigated, as a substitute for affected drinking water supplies thereby eliminating or reducing the impact of their failure following catastrophic events. Even in many areas such water resources with long residence times in years or decades are difficult to find it should be known which water supply facilities in the region are matching these requirements to allow in emergency situation the transport of water in tankers to the affected regions to prevent epidemics, importing large quantities of bottled water. One should know the residence time of the water supply to have sufficient time to plan and install new safe water supply facilities. Development of such policy and strategy for human security - both long term and short term - is therefore needed to decrease the vulnerability of populations threatened by extreme events and water supplies with short residence times. Generally: The longer the residence time of groundwater in the aquifer, the lower its vulnerability. The most common and economic methods to estimate

  12. Residence and exposure times : when diffusion does not matter

    NASA Astrophysics Data System (ADS)

    Delhez, Éric J. M.; Deleersnijder, Éric

    2012-12-01

    Under constant hydrodynamic conditions and assuming horizontal homogeneity, negatively buoyant particles released at the surface of the water column have a mean residence time in the surface mixed layer of h/ w, where h is the thickness of the latter and w ( > 0) is the sinking velocity Deleersnijder (Environ Fluid Mech 6(6):541-547, 2006a). The residence time does not depend on the diffusivity and equals the settling timescale. We show that this behavior is a result of the particular boundary conditions of the problem and that it is related to a similar property of the exposure time in a one-dimensional infinite domain. In 1-D advection-diffusion problem with a constant and uniform velocity, the exposure time—which is a generalization of the residence time measuring the total time spent by a particle in a control domain allowing the particle to leave and reenter the control domain—is also equal to the advection timescale at the upstream boundary of the control domain. To explain this result, the concept of point exposure is introduced; the point exposure is the time integral of the concentration at a given location. It measures the integrated influence of a point release at a given location and is related to the concept of number of visits of the theory of random walks. We show that the point exposure takes a constant value downstream the point of release, even when the diffusivity varies in space. The analysis of this result reveals also that the integrated downstream transport of a passive tracer is only effected by advection. While the diffusion flux differs from zero at all times, its integrated value is strictly zero.

  13. Short residence time coal liquefaction process including catalytic hydrogenation

    DOEpatents

    Anderson, Raymond P.; Schmalzer, David K.; Wright, Charles H.

    1982-05-18

    Normally solid dissolved coal product and a distillate liquid product are produced by continuously passing a feed slurry comprising raw feed coal and a recycle solvent oil and/or slurry together with hydrogen to a preheating-reaction zone (26, alone, or 26 together with 42), the hydrogen pressure in the preheating-reaction zone being at least 1500 psig (105 kg/cm.sup.2), reacting the slurry in the preheating-reaction zone (26, or 26 with 42) at a temperature in the range of between about 455.degree. and about 500.degree. C. to dissolve the coal to form normally liquid coal and normally solid dissolved coal. A total slurry residence time is maintained in the reaction zone ranging from a finite value from about 0 to about 0.2 hour, and reaction effluent is continuously and directly contacted with a quenching fluid (40, 68) to substantially immediately reduce the temperature of the reaction effluent to below 425.degree. C. to substantially inhibit polymerization so that the yield of insoluble organic matter comprises less than 9 weight percent of said feed coal on a moisture-free basis. The reaction is performed under conditions of temperature, hydrogen pressure and residence time such that the quantity of distillate liquid boiling within the range C.sub.5 -454.degree. C. is an amount at least equal to that obtainable by performing the process under the same condition except for a longer total slurry residence time, e.g., 0.3 hour. Solvent boiling range liquid is separated from the reaction effluent (83) and recycled as process solvent (16). The amount of solvent boiling range liquid is sufficient to provide at least 80 weight percent of that required to maintain the process in overall solvent balance.

  14. Short residence time coal liquefaction process including catalytic hydrogenation

    DOEpatents

    Anderson, R.P.; Schmalzer, D.K.; Wright, C.H.

    1982-05-18

    Normally solid dissolved coal product and a distillate liquid product are produced by continuously passing a feed slurry comprising raw feed coal and a recycle solvent oil and/or slurry together with hydrogen to a preheating-reaction zone, the hydrogen pressure in the preheating-reaction zone being at least 1,500 psig (105 kg/cm[sup 2]), reacting the slurry in the preheating-reaction zone at a temperature in the range of between about 455 and about 500 C to dissolve the coal to form normally liquid coal and normally solid dissolved coal. A total slurry residence time is maintained in the reaction zone ranging from a finite value from about 0 to about 0.2 hour, and reaction effluent is continuously and directly contacted with a quenching fluid to substantially immediately reduce the temperature of the reaction effluent to below 425 C to substantially inhibit polymerization so that the yield of insoluble organic matter comprises less than 9 weight percent of said feed coal on a moisture-free basis. The reaction is performed under conditions of temperature, hydrogen pressure and residence time such that the quantity of distillate liquid boiling within the range C[sub 5]-454 C is an amount at least equal to that obtainable by performing the process under the same condition except for a longer total slurry residence time, e.g., 0.3 hour. Solvent boiling range liquid is separated from the reaction effluent and recycled as process solvent. The amount of solvent boiling range liquid is sufficient to provide at least 80 weight percent of that required to maintain the process in overall solvent balance. 6 figs.

  15. The residence time of intensively managed agricultural landscapes

    NASA Astrophysics Data System (ADS)

    Bowling, Laura; Cherkauer, Keith; Chiu, Chun-mei; Rahman, Sanoar

    2015-04-01

    Much of the agricultural landscape across the Midwestern United States is intensively managed through numerous surface and subsurface drainage improvements, and the growing extraction of groundwater resources. The relatively recent glaciation of the North Central region means that the landscape is less dissected and hydrologically connected than older till areas. Low topographic gradients and underlying dense till which restricts vertical water movement, as well as kettle depressions, have led to poorly drained soils and extensive wetlands within the landscape. Large areas of this land could only be farmed once the excess water was removed through artificial surface and subsurface drainage. Conventional wisdom in the region maintains that subsurface tile drainage reduces the occurrence of peak flow events by increasing soil water storage capacity. At the watershed scale, this view does not take into account the coincident increase in surface drainage and reduction in residence time in surface depressions. This paper explores to what degree water management and irrigation has changed surface and subsurface water storage and residence time over the last century and how this has impacted flow duration throughout the Wabash River system in Indiana, USA. The effects of subsurface tile drains, wetlands and aquifer storage are explicitly represented within the Variable Infiltration Capacity (VIC) macroscale hydrology model. We maintain a focus on the entire Wabash River, a river system of historic importance that is also representative of many similar areas in the till plain region of the agricultural Midwest, which contribute to water quality and flood dynamics of the Mississippi river system. By lowering the water table, surface and subsurface drainage improvements have increased the subsurface storage capacity at the beginning of rain events, but this is overwhelmed by the decrease in surface storage capacity for intermediate to large events, decreasing the current

  16. UASB reactor hydrodynamics: residence time distribution and proposed modelling tools.

    PubMed

    López, I; Borzacconi, L

    2010-05-01

    The hydrodynamic behaviour of UASB (Up Flow Anaerobic Sludge Blanket) reactors based on residence time distribution curves allows the implementation of global models, including the kinetic aspects of biological reactions. The most relevant hydrodynamic models proposed in the literature are discussed and compared with the extended tanks in series (ETIS) model. Although derived from the tanks in series model, the ETIS model's parameter is not an integer. The ETIS model can be easily solved in the Laplace domain and applied to a two-stage anaerobic digestion linear model. Experimental data from a 250 m3 UASB reactor treating malting wastewater are used to calibrate and validate the proposed model. PMID:20540420

  17. A comment on the use of flushing time, residence time, and age as transport time scales

    USGS Publications Warehouse

    Monsen, N.E.; Cloern, J.E.; Lucas, L.V.; Monismith, Stephen G.

    2002-01-01

    Applications of transport time scales are pervasive in biological, hydrologic, and geochemical studies yet these times scales are not consistently defined and applied with rigor in the literature. We compare three transport time scales (flushing time, age, and residence time) commonly used to measure the retention of water or scalar quantities transported with water. We identify the underlying assumptions associated with each time scale, describe procedures for computing these time scales in idealized cases, and identify pitfalls when real-world systems deviate from these idealizations. We then apply the time scale definitions to a shallow 378 ha tidal lake to illustrate how deviations between real water bodies and the idealized examples can result from: (1) non-steady flow; (2) spatial variability in bathymetry, circulation, and transport time scales; and (3) tides that introduce complexities not accounted for in the idealized cases. These examples illustrate that no single transport time scale is valid for all time periods, locations, and constituents, and no one time scale describes all transport processes. We encourage aquatic scientists to rigorously define the transport time scale when it is applied, identify the underlying assumptions in the application of that concept, and ask if those assumptions are valid in the application of that approach for computing transport time scales in real systems.

  18. The determination of residence times in a pilot plant

    NASA Astrophysics Data System (ADS)

    Ramírez, F. Pablo; Cortés, M. Eugenia

    2004-01-01

    It is well known that residence time distributions (RTD) are very important in many chemical processes such as separation, reforming, hydrocracking, fluid catalytic cracking, hydrodesulfuration, hydrogenation among others [3 Procédés de transformation, Editions Technip, Institute Francais du Petrole, Paris, France, 1998]. In addition, tracers can be used to measure the velocity, distribution and residence time of any stream through any part of an industrial [Guidebook on Radioisotope Tracers in Industry, IAEA, Vienna, 1990] or experimental system. Perhaps the best quality of radiotracers is that they do not interfere with normal unit operations or production scheduling. In this paper are presented the RTDs obtained in a pilot plant for a hydrogenation process [IMP, Technical Report, Determinación del tiempo de residencia promedio en el reactor de la planta piloto de hidroagotamiento de crudo, 2002]. The RTDs show a random phenomenon, which is not typical of this type of chemical processes. Several RTDs were determined in order to confirm this random behavior. The data were obtained using as a tracer a radioactive form of sodium iodide containing iodine-131 [The Condensed Chemical Dictionary, 10th Ed., Van Nostrand Reinhold, USA, 1981]. The process works with two phases in a countercurrent flow, inside a packed column. The liquid phase goes down by gravity. The gas phase goes up due to pressure difference [3 Procédés de transformation, Editions Technip, Institute Francais du Petrole, Paris, France, 1998]. The tracer was selected such that it would follow the liquid phase.

  19. Residence time estimates for asymmetric simple exclusion dynamics on strips

    NASA Astrophysics Data System (ADS)

    Cirillo, Emilio N. M.; Krehel, Oleh; Muntean, Adrian; van Santen, Rutger; Sengar, Aditya

    2016-01-01

    The target of our study is to approximate numerically and, in some particular physically relevant cases, also analytically, the residence time of particles undergoing an asymmetric simple exclusion dynamics on a two-dimensional vertical strip. The sources of asymmetry are twofold: (i) the choice of boundary conditions (different reservoir levels) and (ii) the strong anisotropy from a drift nonlinear in density with prescribed directionality. We focus on the effect of the choice of anisotropy on residence time. We analyze our results by means of two theoretical models, a Mean Field and a one-dimensional Birth and Death one. For positive drift we find a striking agreement between Monte Carlo and theoretical results. In the zero drift case we still find agreement as long as particles can freely escape the strip through the bottom boundary. Otherwise, the two models give different predictions and their ability to reproduce numerical results depends on the horizontal displacement probability. The topic is relevant for situations occurring in pedestrian flows or biological transport in crowded environments, where lateral displacements of the particles occur predominantly affecting therefore in an essentially way the efficiency of the overall transport mechanism.

  20. THE LOCAL EFFECT TIME (LET) AND HOW IT INCORPORATES ECOLOGY INTO RESIDENCE TIME

    EPA Science Inventory

    A clear and direct connection between constituent/water residence times and ecological effects is necessary to quantitatively relate these time scales to ecology. The concept of "local effect time" (LET) is proposed here as a time scale with adequate spatial resolution to relate ...

  1. Sources of indoor air pollution in New York City residences of asthmatic children.

    PubMed

    Habre, Rima; Coull, Brent; Moshier, Erin; Godbold, James; Grunin, Avi; Nath, Amit; Castro, William; Schachter, Neil; Rohr, Annette; Kattan, Meyer; Spengler, John; Koutrakis, Petros

    2014-01-01

    Individuals spend ∼90% of their time indoors in proximity to sources of particulate and gaseous air pollutants. The sulfur tracer method was used to separate indoor concentrations of particulate matter (PM) PM2.5 mass, elements and thermally resolved carbon fractions by origin in New York City residences of asthmatic children. Enrichment factors relative to sulfur concentrations were used to rank species according to the importance of their indoor sources. Mixed effects models were used to identify building characteristics and resident activities that contributed to observed concentrations. Significant indoor sources were detected for OC1, Cl, K and most remaining OC fractions. We attributed 46% of indoor PM2.5 mass to indoor sources related to OC generation indoors. These sources include cooking (NO2, Si, Cl, K, OC4 and OP), cleaning (most OC fractions), candle/incense burning (black carbon, BC) and smoking (K, OC1, OC3 and EC1). Outdoor sources accounted for 28% of indoor PM2.5 mass, mainly photochemical reaction products, metals and combustion products (EC, EC2, Br, Mn, Pb, Ni, Ti, V and S). Other indoor sources accounted for 26% and included re-suspension of crustal elements (Al, Zn, Fe, Si and Ca). Indoor sources accounted for ∼72% of PM2.5 mass and likely contributed to differences in the composition of indoor and outdoor PM2.5 exposures. PMID:24169876

  2. Are we missing the tail (and the tale) of residence time distributions in watersheds?

    NASA Astrophysics Data System (ADS)

    Frisbee, Marty D.; Wilson, John L.; Gomez-Velez, Jesus D.; Phillips, Fred M.; Campbell, Andrew R.

    2013-09-01

    times provide vital information on hydrological, geochemical, and ecological processes in watersheds. The common perception is that mean residence times in watersheds are very short, on the order of days to years. However, there is growing concern that longer residence times of centuries to millennia are not being captured by traditional surface water age-dating methods. We hypothesize that if mean residence times are biased short, then weathering rates calculated from mean residence times will be forced unrealistically high to match observed solute concentrations. We test this hypothesis by calculating weathering rates from springs based upon residence times estimated using three different age-dating methods. Observed solute concentrations require unrealistically large weathering rates if typical short residence times are employed as compared to rates derived from longer residence times. Residence time distributions in watersheds have substantially longer tails than previously thought, with implications for age-dating methods and their interpretation to infer process behavior.

  3. Annoyance due to noise and air pollution to the residents of heavily frequented streets

    NASA Technical Reports Server (NTRS)

    Wanner, H. U.; Wehrli, B.; Nemecek, J.; Turrian, V.

    1980-01-01

    The residents of different streets with varying traffic density and building density were questioned about annoyance due to traffic noise and air pollution. Results show that annoyance felt is dependent not only on the measured noise levels and/or air pollution concentrations, but that there do exist interactions between the residential quarters and annoyance. These interactions should be considered when fixing the limits and standards.

  4. RTDB: A memory resident real-time object database

    SciTech Connect

    Jerzy M. Nogiec; Eugene Desavouret

    2003-06-04

    RTDB is a fast, memory-resident object database with built-in support for distribution. It constitutes an attractive alternative for architecting real-time solutions with multiple, possibly distributed, processes or agents sharing data. RTDB offers both direct and navigational access to stored objects, with local and remote random access by object identifiers, and immediate direct access via object indices. The database supports transparent access to objects stored in multiple collaborating dispersed databases and includes a built-in cache mechanism that allows for keeping local copies of remote objects, with specifiable invalidation deadlines. Additional features of RTDB include a trigger mechanism on objects that allows for issuing events or activating handlers when objects are accessed or modified and a very fast, attribute based search/query mechanism. The overall architecture and application of RTDB in a control and monitoring system is presented.

  5. Residence times and boundary-following behavior in animals

    NASA Astrophysics Data System (ADS)

    Weitz, Sebastian; Blanco, Stéphane; Fournier, Richard; Gautrais, Jacques; Jost, Christian; Theraulaz, Guy

    2014-05-01

    Many animals in heterogeneous environments bias their trajectories displaying a preference for the vicinity of boundaries. Here we propose a criterion, relying on recent invariance properties of residence times for microreversible Boltzmann's walks, that permits detecting and quantifying boundary-following behaviors. On this basis we introduce a boundary-following model that is a nonmicroreversible Boltzmann's walk and that can represent all kinds of boundary-following distributions. This allows us to perform a theoretical analysis of field-resolved boundary following in animals. Two consequences are pointed out and are illustrated: A systematic procedure can now be used for extraction of individual properties from experimental field measurements, and boundary-curvature influence can be recovered as an emerging property without the need for individuals perceiving the curvature via complex physiological mechanisms. The presented results apply to any memoryless correlated random walk, such as the run-and-tumble models that are widely used in cell motility studies.

  6. Teaching Affective Skills to Residents in Decreased Instruction Time.

    ERIC Educational Resources Information Center

    Dedman, Elizabeth B.; And Others

    1987-01-01

    A study to determine whether affective skills could be taught to residents in a family practice center without placing arduous constraints on their schedules is described. Residents at the University of Louisville Department of Family Practice were videotaped during a regular patient visit and then scheduled for review sessions. (MLW)

  7. Ligand Release Pathways Obtained with WExplore: Residence Times and Mechanisms.

    PubMed

    Dickson, Alex; Lotz, Samuel D

    2016-06-23

    The binding of ligands with their molecular receptors is of tremendous importance in biology. Although much emphasis has been placed on characterizing binding sites and bound poses that determine the binding thermodynamics, the pathway by which a ligand binds importantly determines the binding kinetics. The computational study of entire unbiased ligand binding and release pathways is still an emerging field, made possible only recently by advances in computational hardware and sampling methodologies. We have developed one such method (WExplore) that is based on a weighted ensemble of trajectories, which we apply to ligand release for the first time, using a set of three previously characterized interactions between low-affinity ligands and the protein FKBP-12 (FK-506 binding protein). WExplore is found to be more efficient that conventional sampling, even for the nanosecond-scale unbinding events observed here. From a nonequilibrium ensemble of unbinding trajectories, we obtain ligand residence times and release pathways without using biasing forces or a Markovian assumption of transitions between regions. We introduce a set of analysis tools for unbinding transition pathways, including using von Mises-Fisher distributions to model clouds of ligand exit points, which provide a quantitative proxy for ligand surface diffusion. Differences between the transition pathway ensembles of the three ligands are identified and discussed. PMID:27231969

  8. Particle tracking and mean residence time in barchan dunes

    NASA Astrophysics Data System (ADS)

    Zhang, Deguo; Narteau, Clement; Rozier, Olivier

    2013-04-01

    We analyze sediment particles motions in steady-state barchan dunes by tracking individual cells of a 3-D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan dune shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchan dunes. Then, for different flow strength and dune size, we find that the mean residence time of sediment particles in barchan dunes is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan dune morphodynamics. Finally, we initiate a discussion about sediment transport and memory in presence of bedforms using the advantages of the particle tracking technique.

  9. Sediment residence time distributions: Theory and application from bed elevation measurements

    NASA Astrophysics Data System (ADS)

    Voepel, Hal; Schumer, Rina; Hassan, Marwan A.

    2013-12-01

    distance and residence time probability distributions are the key components of stochastic models for coarse sediment transport. Residence time for individual grains is difficult to measure, and residence time distributions appropriate to field and laboratory settings are typically inferred theoretically or from overall transport characteristics. However, bed elevation time series collected using sonar transducers and lidar can be translated into empirical residence time distributions at each elevation in the bed and for the entire bed thickness. Sediment residence time at a given depth can be conceptualized as a stochastic return time process on a finite interval. Overall sediment residence time is an average of residence times at all depths weighted by the likelihood of deposition at each depth. Theory and experiment show that when tracers are seeded on the bed surface, power law residence time will be observed until a timescale set by the bed thickness and bed fluctuation statistics. After this time, the long-time (global) residence time distribution will take exponential form. Crossover time is the time of transition from power law to exponential behavior. The crossover time in flume studies can be on the order of seconds to minutes, while that in rivers can be days to years.

  10. Characterization of air manganese exposure estimates for residents in two Ohio towns.

    PubMed

    Colledge, Michelle A; Julian, Jaime R; Gocheva, Vihra V; Beseler, Cheryl L; Roels, Harry A; Lobdell, Danelle T; Bowler, Rosemarie M

    2015-08-01

    This study was conducted to derive receptor-specific outdoor exposure concentrations of total suspended particulate (TSP) and respirable (dae ≤ 10 µm) air manganese (air-Mn) for East Liverpool and Marietta (Ohio) in the absence of facility emissions data, but where long-term air measurements were available. Our "site-surface area emissions method" used U.S. Environmental Protection Agency's (EPA) AERMOD (AMS/EPA Regulatory Model) dispersion model and air measurement data to estimate concentrations for residential receptor sites in the two communities. Modeled concentrations were used to create ratios between receptor points and calibrated using measured data from local air monitoring stations. Estimated outdoor air-Mn concentrations were derived for individual study subjects in both towns. The mean estimated long-term air-Mn exposure levels for total suspended particulate were 0.35 μg/m³ (geometric mean [GM]) and 0.88 μg/m³ (arithmetic mean [AM]) in East Liverpool (range: 0.014-6.32 μg/m³) and 0.17 μg/m³ (GM) and 0.21 μg/m³ (AM) in Marietta (range: 0.03-1.61 μg/m³). Modeled results compared well with averaged ambient air measurements from local air monitoring stations. Exposure to respirable Mn particulate matter (PM10; PM <10 μm) was higher in Marietta residents. PMID:26211636

  11. Inpatient Performance of Primary Care Residents: Impact of Reduction in Time on the Ward.

    ERIC Educational Resources Information Center

    And Others; Goroll, Allan H.

    1979-01-01

    The inpatient (ward/intensive care unit) performance of primary care medical residents was compared with that of their peers in the standard internal medicine residency program. Nearly identical performances of the two groups suggests that substantial time in the first two years of residency can be devoted successfully to ambulatory training.…

  12. Controls on residence time and exchange in a system of shallow coastal bays

    NASA Astrophysics Data System (ADS)

    Safak, I.; Wiberg, P. L.; Richardson, D. L.; Kurum, M. O.

    2015-04-01

    Patterns of transport and residence time influence the morphology, ecology and biogeochemistry of shallow coastal bay systems in important ways. To better understand the factors controlling residence time and exchange in coastal bays, a three-dimensional finite-volume coastal ocean model was set up and validated with field observations of circulation in a system of 14 shallow coastal bays on the Atlantic coast of the USA (Virginia Coast Reserve). Residence times of neutrally buoyant particles as well as exchange among the bays in the system and between the bays and the ocean were examined with Lagrangian particle tracking. There was orders of magnitude variation in the calculated residence time within most of the bays, ranging from hours in the tidally refreshed (repletion) water near the inlets to days-weeks in the remaining (residual) water away from the inlets. Residence time in the repletion waters was most sensitive to the tidal phase (low vs. high) when particles were released whereas residence time in the residual waters was more sensitive to wind forcing. Wind forcing was found to act as a diffuser that shortens particle residence within the bays; its effect was higher away from the inlets and in relatively confined bays. Median residence time in the bays significantly decreased with an increase in the ratio between open water area and total area (open water plus marsh). Exchange among the bays and capture areas of inlets (i.e., exchange between the bays and the ocean) varied considerably but were insensitive to tidal phase of release, wind, and forcing conditions in different years, in contrast to the sensitivity of residence time to these factors. We defined a new quantity, termed shortest-path residence time, calculated as distance from the closest inlet divided by root-mean-square velocity at each point in model domain. A relationship between shortest-path residence time and particle-tracking residence time provides a means of estimating residence time

  13. Characterization of air manganese exposure estimates for residents in two Ohio towns

    PubMed Central

    Colledge, Michelle A.; Julian, Jaime R.; Gocheva, Vihra V.; Beseler, Cheryl L.; Roels, Harry A.; Lobdell, Danelle T.; Bowler, Rosemarie M.

    2016-01-01

    This study was conducted to derive receptor-specific outdoor exposure concentrations of total suspended particulate (TSP) and respirable (dae ≤ 10 μm) air manganese (air-Mn) for East Liverpool and Marietta (Ohio) in the absence of facility emissions data, but where long-term air measurements were available. Our “site-surface area emissions method” used U.S. Environmental Protection Agency’s (EPA) AERMOD (AMS/EPA Regulatory Model) dispersion model and air measurement data to estimate concentrations for residential receptor sites in the two communities. Modeled concentrations were used to create ratios between receptor points and calibrated using measured data from local air monitoring stations. Estimated outdoor air-Mn concentrations were derived for individual study subjects in both towns. The mean estimated long-term air-Mn exposure levels for total suspended particulate were 0.35 μg/m3 (geometric mean [GM]) and 0.88 μg/m3 (arithmetic mean [AM]) in East Liverpool (range: 0.014–6.32 μg/m3) and 0.17 μg/m3 (GM) and 0.21 μg/m3 (AM) in Marietta (range: 0.03–1.61 μg/m3). Modeled results compared well with averaged ambient air measurements from local air monitoring stations. Exposure to respirable Mn particulate matter (PM10; PM <10 μm) was higher in Marietta residents. Implications Few available studies evaluate long-term health outcomes from inhalational manganese (Mn) exposure in residential populations, due in part to challenges in measuring individual exposures. Local long-term air measurements provide the means to calibrate models used in estimating long-term exposures. Furthermore, this combination of modeling and ambient air sampling can be used to derive receptor-specific exposure estimates even in the absence of source emissions data for use in human health outcome studies. PMID:26211636

  14. Polychlorinated biphenyls (PCBs) in indoor air and in serum among older residents of upper Hudson River communities.

    PubMed

    Fitzgerald, Edward F; Shrestha, Srishti; Palmer, Patrick M; Wilson, Lloyd R; Belanger, Erin E; Gomez, Marta I; Cayo, Michael R; Hwang, Syni-An

    2011-09-01

    A study was conducted to evaluate the association between PCBs in residential indoor air and in the serum of older, long time residents of three upper Hudson River communities. Samples of indoor air and of serum were collected from 170 persons 55 to 74 years of age, and analyzed for PCBs using glass capillary gas chromatography. After adjusting for age, BMI, cigarette smoking, and Hudson River fish consumption with multiple linear regression analysis, the results indicated statistically significant associations between concentrations in indoor air and serum for PCB-28, a lightly chlorinated congener common in air that accumulates in serum, and PCB-105. Duration of exposure was an important factor, since among persons who had lived in their home for 39 years or more, 11 of the 12 most commonly detected congeners were significantly correlated, as was their sum (∑ PCB). Significant associations between indoor air and serum PCB concentrations also were more likely when collected in cooler months and if the two samples were collected within 20 d of each other. The study is among the first to indicate that PCB concentrations characteristic of residential indoor air are associated with a detectable increase in body burden. PMID:21724230

  15. 26 CFR 301.7701(b)-4 - Residency time periods.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... meets the substantial presence test is the first day during the calendar year on which the individual is... resident test (green card test), described in paragraph (b)(1) of § 301.7701(b)-1, is the first day during... test and the green card test will be the earlier of the first day the individual is physically...

  16. Fluid flow pattern and water residence time in waste stabilisation ponds.

    PubMed

    Badrot-Nico, F; Guinot, V; Brissaud, F

    2009-01-01

    As treatment processes are kinetic-dependent, a consistent description of water residence times is essential to the prediction of waste stabilization ponds performance. A physically-based 3D transient CFD model simulating the water velocity, temperature and concentration fields as a function of all influent meteorological factors--wind speed and direction, solar radiation, air temperature and relative humidity--was used to identify the relationships between the meteorological conditions and the hydrodynamic patterns and water residence times distributions in a polishing pond. The required meteorological data were recorded on site and water temperatures recorded at 10 sampling sites for 141 days. Stratification events appear on very calm days for wind speeds lower than 3 m s(-1) and on sunny days for wind speeds lower than 5 m s(-1). De-stratification is related to two mixing processes: nightly convection cells and global mixing patterns. Numerical tracer experiments show that the results of the flow patterns can be evaluated using the dispersed flow regime approximation and, for wind speeds exceeding 6 m s(-1), the completely stirred tank reactor assumption. PMID:19342800

  17. Effects of zebra mussels on food webs: Interactions with juvenile bluegill and water residence time

    USGS Publications Warehouse

    Richardson, W.B.; Bartsch, L.A.

    1997-01-01

    We evaluated how water residence time mediated the impact of zebra mussels Dreissena polymorpha and bluegill sunfish Lepomis macrochirus on experimental food webs established in 1100-1 outdoor mesocosms. Water residence time was manipulated as a surrogate for seston resupply - a critical variable affecting growth and survival of suspension-feeding invertebrates. We used a 2 x 2 x 2 factorial experimental design with eight treatment combinations (3 replicates/treatment) including the presence or absence of Dreissena (2000 per m2), juvenile bluegill (40 per mesocosm), and short (1100 1 per d) or long (220 1 per d) water residence time. Measures of seston concentration (chlorophyll a, turbidity and suspended solids) were greater in the short- compared to long water-residence mesocosms, but intermediate in short water-residence mesocosms containing Dreissena. Abundance of rotifers (Keratella and Polyarthra) was reduced in Dreissena mesocosms and elevated in short residence time mesocosms. Cladocera abundance, in general, was unaffected by the presence of Dreissena; densities were higher in short-residence time mesocosms, and reduced in the presence of Lepomis. The growth of juvenile Lepomis were unaffected by Dreissena because of abundant benthic food. The final total mass of Dreissena was significantly greater in short- than long-residence mesocosms. Impacts of Dreissena on planktonic food webs may not only depend on the density of zebra mussels but also on the residence time of the surrounding water and the resupply of seston. ?? 1997 Kluwer Academic Publishers.

  18. Joint space-time geostatistical model for air quality surveillance

    NASA Astrophysics Data System (ADS)

    Russo, A.; Soares, A.; Pereira, M. J.

    2009-04-01

    Air pollution and peoples' generalized concern about air quality are, nowadays, considered to be a global problem. Although the introduction of rigid air pollution regulations has reduced pollution from industry and power stations, the growing number of cars on the road poses a new pollution problem. Considering the characteristics of the atmospheric circulation and also the residence times of certain pollutants in the atmosphere, a generalized and growing interest on air quality issues led to research intensification and publication of several articles with quite different levels of scientific depth. As most natural phenomena, air quality can be seen as a space-time process, where space-time relationships have usually quite different characteristics and levels of uncertainty. As a result, the simultaneous integration of space and time is not an easy task to perform. This problem is overcome by a variety of methodologies. The use of stochastic models and neural networks to characterize space-time dispersion of air quality is becoming a common practice. The main objective of this work is to produce an air quality model which allows forecasting critical concentration episodes of a certain pollutant by means of a hybrid approach, based on the combined use of neural network models and stochastic simulations. A stochastic simulation of the spatial component with a space-time trend model is proposed to characterize critical situations, taking into account data from the past and a space-time trend from the recent past. To identify near future critical episodes, predicted values from neural networks are used at each monitoring station. In this paper, we describe the design of a hybrid forecasting tool for ambient NO2 concentrations in Lisbon, Portugal.

  19. Seasonal variations of aerosol residence time in the lower atmospheric boundary layer.

    PubMed

    Ahmed, A A; Mohamed, A; Ali, A E; Barakat, A; Abd El-Hady, M; El-Hussein, A

    2004-01-01

    During a one year period, from Jan. 2002 up to Dec. 2002, approximately 130 air samples were analyzed to determine the atmospheric air activity concentrations of short- and long-lived (222Rn) decay products 214Pb and 210Pb. The samples were taken by using a single-filter technique and gamma-spectrometry was applied to determine the activity concentrations. A seasonal fluctuation in the concentration of 214Pb and 210Pb in surface air was observed. The activity concentrations of both radionuclides were observed to be relatively higher during the winter/autumn season than in spring/summer season. The mean activity concentration of 214Pb and 210Pb within the whole year was found to be 1.4+/-0.27 Bq m(-3) and 1.2+/-0.15 mBq m(-3), respectively. Different 210Pb:214Pb activity ratios during the year varied between 1.78 x 10(-4) and 1.6 x 10(-3) with a mean value of 8.9 x 10(-4) +/- 7.6 x 10(-5). From the ratio between the activity concentrations of the radon decay products 214Pb and 210Pb a mean residence time (MRT) of aerosol particles in the atmosphere of about 10.5+/-0.91 d could be estimated. The seasonal variation pattern shows relatively higher values of MRT in spring/summer season than in winter/autumn season. The MRT data together with relative humidity (RH), air temperature (T) and wind speed (WS), were used for a comprehensive regression analysis of its seasonal variation in the atmospheric air. PMID:15381321

  20. Ross ice shelf cavity circulation, residence time, and melting: Results from a model of oceanic chlorofluorocarbons

    NASA Astrophysics Data System (ADS)

    Reddy, Tasha E.; Holland, David M.; Arrigo, Kevin R.

    2010-04-01

    Despite their harmful effects in the upper atmosphere, anthropogenic chlorofluorocarbons dissolved in seawater are extremely useful for studying ocean circulation and ventilation, particularly in remote locations. Because they behave as a passive tracer in seawater, and their atmospheric concentrations are well-mixed, well-known, and have changed over time, they are ideal for gaining insight into the oceanographic characteristics of the isolated cavities found under Antarctic ice shelves, where direct observations are difficult to obtain. Here we present results from a modeling study of air-sea chlorofluorocarbon exchange and ocean circulation in the Ross Sea, Antarctica. We compare our model estimates of oceanic CFC-12 concentrations along an ice shelf edge transect to field data collected during three cruises spanning 16 yr. Our model produces chlorofluorocarbon concentrations that are quite similar to those measured in the field, both in magnitude and distribution, showing high values near the surface, decreasing with depth, and increasing over time. After validating modeled circulation and air-sea gas exchange through comparison of modeled temperature, salinity, and chlorofluorocarbons with field data, we estimate that the residence time of water in the Ross Ice Shelf cavity is approximately 2.2 yr and that basal melt rates for the ice shelf average 10 cm yr -1. The model predicts a seasonal signature to basal melting, with highest melt rates in the spring and also the fall.

  1. Residence time control on hot moments of net nitrate production and uptake in the hyporheic zone

    USGS Publications Warehouse

    Briggs, Martin A.; Lautz, Laura K.; Hare, Danielle K.

    2014-01-01

    moments of net production and uptake, enhancing NO3- production as residence times approach the anaerobic threshold, and changing zones of net NO3- production to uptake as residence times increase past the net sink threshold. The anaerobic and net sink thresholds for beaver-influenced streambed morphology occur at much shorter residence times (1.3 h and 2.3 h, respectively) compared to other documented hyporheic systems, and the net sink threshold compares favorably to the lower boundary of the anaerobic threshold determined for this system with the new oxygen Damkohler number. The consistency of the residence time threshold values of NO3- cycling in this study, despite environmental variability and disparate morphology, indicates that NO3- hot moment dynamics are primarily driven by changes in physical hydrology and associated residence times.

  2. Modelling residence-time response to freshwater input in Apalachicola Bay, Florida, USA

    NASA Astrophysics Data System (ADS)

    Huang, Wenrui; Spaulding, M.

    2002-10-01

    Residence time of an estuary can be used to estimate the rate of removal of freshwater and pollutants from river inflow. In this study, a calibrated three-dimensional hydrodynamic model was used to determine residence time in response to the change of freshwater input in Apalachicola Bay. The bay is about 40 km long and 7 km wide, with an average 3 m water depth. Through hydrodynamic model simulations, the spatial and temporal salinity and the total freshwater volume in the bay were calculated. Then the freshwater fraction method was used to estimate the residence time. Results indicate that the residence time in Apalachicola Bay typically ranges between 3 and 10 days for the daily freshwater input ranging from 177 m3/s to 4561 m3/s. Regression analysis of model results shows that an exponential regression equation can be used to correlate the estuarine residence time to changes of freshwater input.

  3. Training for Efficiency: Work, Time and Systems-based Practice in Medical Residency*

    PubMed Central

    Szymczak, Julia E.; Bosk, Charles L.

    2013-01-01

    Medical residency is a period of intense socialization with a heavy workload. Previous sociological studies have identified efficiency as a practical skill necessary for success. However, many contextual features of the training environment have undergone dramatic change since these studies were conducted. What are the consequences of these changes for the socialization of residents to time management and the development of a professional identity? Based on observations of and interviews with internal medicine residents at 3 training programs, we find that efficiency is both a social norm and strategy that residents employ to manage a workload for which the demand for work exceeds the supply of time available to accomplish it. We found that residents struggle to be efficient in the face of seemingly intractable “systems” problems. Residents work around these problems, and in doing so develop a tolerance for organizational vulnerabilities. PMID:22863601

  4. Mixing and residence times of stormwater runoff in a detection system

    USGS Publications Warehouse

    Martin, Edward H.

    1989-01-01

    Five tracer runs were performed on a detention pond and wetlands system to determine mixing and residence times in the system. The data indicate that at low discharges and with large amounts of storage, the pond is moderately mixed with residence times not much less than the theoretical maximum possible under complete mixing. At higher discharges and with less storage in the pond, short-circuiting occurs, reducing the amount of mixing in the pond and appreciably reducing the residence times. The time between pond outlet peak concentrations and wetlands outlet peak concentrations indicate that in the wetlands, mixing increases with decreasing discharge and increasing storage.

  5. Children's Perspectives on Everyday Experiences of Shared Residence: Time, Emotions and Agency Dilemmas

    ERIC Educational Resources Information Center

    Haugen, Gry Mette D.

    2010-01-01

    Shared residence is often presented as an arrangement that is in the best interests of the child following the divorce of its parents. Based on in-depth interviews with Norwegian children who have experienced shared residence, this article seeks to explore some dilemmas concerning time, agency and the children's emotions. Three characteristics of…

  6. Respiratory effects of secondhand smoke exposure among young adults residing in a "clean" indoor air state.

    PubMed

    Lee, David J; Dietz, Noella A; Arheart, Kristopher L; Wilkinson, James D; Clark, John D; Caban-Martinez, Alberto J

    2008-06-01

    The objective of this study is to estimate the prevalence of self-reported secondhand smoke (SHS) exposures and its association with respiratory symptoms in a sample of young adults residing in a state with a partial clean indoor air law. A cross-sectional telephone survey of Florida households and a single state University was conducted in 2005. Enrolled participants between 18 and 24 years of age completed a 15-20 min interview assessing past and current SHS exposure and current respiratory symptoms (n = 1858). Approximately 60% of the sample were female; nearly 70% were non-Hispanic white, 10% were non-Hispanic Black, and 11% were Hispanic. Over two-thirds reported completing at least some college; 23% reported smoking in the past month. Nearly two-thirds (64%) reported visiting a bar or nightclub which exposed them to SHS in the previous month; nearly half (46%) reported SHS exposure while riding in automobiles; 15% reported occupational SHS exposure; and nearly 9% reported living with at least one smoker. In multivariable models, personal smoking behavior, parental smoking history, and exposure to SHS in automobiles and in bars or nightclubs were significantly associated with increased reports of respiratory symptoms. Despite residing in a "clean" indoor air state, the majority of surveyed young adults continue to report exposure to SHS, especially in automobiles and in bars, and these exposures adversely impact respiratory health. All municipalities should pursue clean indoor air legislation which does not exempt bars and restaurants. Educational campaigns directed at reducing SHS exposure in motor vehicles also are needed. PMID:18246415

  7. Using a composite grid approach in a complex coastal domain to estimate estuarine residence time

    NASA Astrophysics Data System (ADS)

    Warner, John C.; Rockwell Geyer, W.; Arango, Hernan G.

    2010-07-01

    We investigate the processes that influence residence time in a partially mixed estuary using a three-dimensional circulation model. The complex geometry of the study region is not optimal for a structured grid model and so we developed a new method of grid connectivity. This involves a novel approach that allows an unlimited number of individual grids to be combined in an efficient manner to produce a composite grid. We then implemented this new method into the numerical Regional Ocean Modeling System (ROMS) and developed a composite grid of the Hudson River estuary region to investigate the residence time of a passive tracer. Results show that the residence time is a strong function of the time of release (spring vs. neap tide), the along-channel location, and the initial vertical placement. During neap tides there is a maximum in residence time near the bottom of the estuary at the mid-salt intrusion length. During spring tides the residence time is primarily a function of along-channel location and does not exhibit a strong vertical variability. This model study of residence time illustrates the utility of the grid connectivity method for circulation and dispersion studies in regions of complex geometry.

  8. Evaluation of Residence Time on Nitrogen Oxides Removal in Non-Thermal Plasma Reactor.

    PubMed

    Talebizadeh, Pouyan; Rahimzadeh, Hassan; Babaie, Meisam; Javadi Anaghizi, Saeed; Ghomi, Hamidreza; Ahmadi, Goodarz; Brown, Richard

    2015-01-01

    Non-thermal plasma (NTP) has been introduced over the last few years as a promising after- treatment system for nitrogen oxides and particulate matter removal from diesel exhaust. NTP technology has not been commercialised as yet, due to its high rate of energy consumption. Therefore, it is important to seek out new methods to improve NTP performance. Residence time is a crucial parameter in engine exhaust emissions treatment. In this paper, different electrode shapes are analysed and the corresponding residence time and NOx removal efficiency are studied. An axisymmetric laminar model is used for obtaining residence time distribution numerically using FLUENT software. If the mean residence time in a NTP plasma reactor increases, there will be a corresponding increase in the reaction time and consequently the pollutant removal efficiency increases. Three different screw thread electrodes and a rod electrode are examined. The results show the advantage of screw thread electrodes in comparison with the rod electrode. Furthermore, between the screw thread electrodes, the electrode with the thread width of 1 mm has the highest NOx removal due to higher residence time and a greater number of micro-discharges. The results show that the residence time of the screw thread electrode with a thread width of 1 mm is 21% more than for the rod electrode. PMID:26496630

  9. Evaluation of Residence Time on Nitrogen Oxides Removal in Non-Thermal Plasma Reactor

    PubMed Central

    Talebizadeh, Pouyan; Rahimzadeh, Hassan; Babaie, Meisam; Javadi Anaghizi, Saeed; Ghomi, Hamidreza; Ahmadi, Goodarz; Brown, Richard

    2015-01-01

    Non-thermal plasma (NTP) has been introduced over the last few years as a promising after- treatment system for nitrogen oxides and particulate matter removal from diesel exhaust. NTP technology has not been commercialised as yet, due to its high rate of energy consumption. Therefore, it is important to seek out new methods to improve NTP performance. Residence time is a crucial parameter in engine exhaust emissions treatment. In this paper, different electrode shapes are analysed and the corresponding residence time and NOx removal efficiency are studied. An axisymmetric laminar model is used for obtaining residence time distribution numerically using FLUENT software. If the mean residence time in a NTP plasma reactor increases, there will be a corresponding increase in the reaction time and consequently the pollutant removal efficiency increases. Three different screw thread electrodes and a rod electrode are examined. The results show the advantage of screw thread electrodes in comparison with the rod electrode. Furthermore, between the screw thread electrodes, the electrode with the thread width of 1 mm has the highest NOx removal due to higher residence time and a greater number of micro-discharges. The results show that the residence time of the screw thread electrode with a thread width of 1 mm is 21% more than for the rod electrode. PMID:26496630

  10. Multimedia level-III partitioning and residence times of xenobiotics in water-rich and water-poor environments

    SciTech Connect

    Breitkopf, C.; Kuehne, R.; Schueuermann, G.

    2000-05-01

    The environmental fate of 10 compounds covering a wide range of intrinsic persistence and volatility is studied with a multimedia level-III fugacity model at two system temperatures (293 and 282 K) using water-rich and water-poor model environments and standard emission scenarios to air and water, respectively. The resultant level-III partitionings depend significantly on the entry mode and on the relative compartment sizes, and the variation with system temperature is more pronounced for polar compounds and when air is the primary discharge compartment. For example, the steady-state portion in soil of airborne phenol varies from 21 to 89%, whereas waterborne phenol resides in water at a rate of 100% in both water-rich and water-poor environments. For some compounds, the residence time (considering both advection and degradation) is substantially affected by intermedia transport processes such as rainfall. With airborne atrazine, the regional residence time is comparable to that of DDT and significantly greater than the ones of hexachlorobenzene, polychlorinated biphenyl 28, and lindane, although the latter have much longer media-specific half-lives and much greater hydrophobicity. The discussion includes detailed analyses of the compound properties and their impact on the level-III environmental fate.

  11. The effect of tidal exchange on residence time in a coastal embayment

    NASA Astrophysics Data System (ADS)

    Rynne, Patrick; Reniers, Ad; van de Kreeke, Jacobus; MacMahan, Jamie

    2016-04-01

    Numerical simulations of an idealized lagoon that is connected to the ocean via a tidal inlet show that the mean residence time is inversely proportional to tidal exchange. In the Delft3D model the tidal exchange is controlled by varying the inlet length, width and depth. These changes in the inlet geometry affect the tidal prism and the ebb/flood flow structure, which are shown to control the exchange of lagoon water with seawater. To map residence time within the lagoon, a new method that implements dye tracer is developed and shows that the tidally averaged residence time exhibits significant spatial variability. For inlet systems in which, as a first approximation, the lagoon can be described by a uniformly fluctuating water level, a simple transport model is developed to elucidate the specific processes that control tidal exchange and their effect on residence time. In this transport model tidal exchange is decomposed into two fractions, an ocean exchange fraction and a lagoon exchange fraction. It is shown that both fractions need to be included to better describe tidal exchange. Specifically, inclusion of a lagoon exchange fraction improves previous tidal prism models that assume complete mixing in the lagoon. The assumption of complete mixing results in an under-prediction of residence time. Relating the spatially averaged residence time results to the exchange fractions for each inlet geometry show that the residence time is inversely proportional to the product of the tidal exchange fractions. For these single inlet systems, Keulegan's 0-D hydrodynamic model shows good agreement with Delft3D in predicting the tidal prism, maximum flow velocity, and exchange fractions. With these parameters, estimates of the mean residence time can be reached through a relationship derived from the simple transport model.

  12. Modelling and observations of tidal wave propagation, circulation and residence times in Puttalam Lagoon, Sri Lanka

    NASA Astrophysics Data System (ADS)

    Wijeratne, E. M. S.; Rydberg, L.

    2007-09-01

    Tidal measurements and a depth-averaged 2D model are used to examine wave progression and circulation in a long, shallow, micro-tidal lagoon in Sri Lanka. Ranges and phase lags for different tidal constituents are used to calibrate the model. A single drag coefficient, Cd = 0.0032, gives almost perfect agreement with data. Current measurements are used for validation of the model. The lagoon tide consists of a combination of progressive and standing waves, where progressive waves dominate in the outer part and standing waves in the inner. A Lagrangian based particle-tracking method is developed to study tidally and wind induced residence times. If tides were the only factor affecting the residual circulation, the residence time inside the narrowest section would be approximately 100 days. Steady winds (of typical monsoon average) decrease the residence times to 60-90 days. Estuarine forcing due to net freshwater supply is not modelled (due to lack of reliable runoff data), but independent, long-term salinity observations and calculations based on volume and salt conservation during periods of negligible freshwater supply (the lagoon is seasonally hypersaline) indicate residence times ranging from 40 to 80 days. Model derived residence times based on tides alone represent a minimum exchange. Even weak forcing, through winds, excess evaporation or freshwater supply efficiently reduces residence times.

  13. A Method to Estimate the Chronic Health Impact of Air Pollutants in U.S. Residences

    PubMed Central

    Price, Phillip N.; Sherman, Max H.; Singer, Brett C.

    2011-01-01

    Background: Indoor air pollutants (IAPs) cause multiple health impacts. Prioritizing mitigation options that differentially affect individual pollutants and comparing IAPs with other environmental health hazards require a common metric of harm. Objectives: Our objective was to demonstrate a methodology to quantify and compare health impacts from IAPs. The methodology is needed to assess population health impacts of large-scale initiatives—including energy efficiency upgrades and ventilation standards—that affect indoor air quality (IAQ). Methods: Available disease incidence and disease impact models for specific pollutant–disease combinations were synthesized with data on measured concentrations to estimate the chronic heath impact, in disability-adjusted life-years (DALYs) lost, due to inhalation of a subset of IAPs in U.S. residences. Model results were compared with independent estimates of DALYs lost due to disease. Results: Particulate matter ≤ 2.5 μm in aerodynamic diameter (PM2.5), acrolein, and formaldehyde accounted for the vast majority of DALY losses caused by IAPs considered in this analysis, with impacts on par or greater than estimates for secondhand tobacco smoke and radon. Confidence intervals of DALYs lost derived from epidemiology-based response functions are tighter than those derived from toxicology-based, interspecies extrapolations. Statistics on disease incidence in the United States indicate that the upper-bound confidence interval for aggregate IAP harm is implausibly high. Conclusions: The approach demonstrated in this study may be used to assess regional and national initiatives that affect IAQ at the population level. Cumulative health impacts from inhalation in U.S. residences of the IAPs assessed in this study are estimated at 400–1,100 DALYs lost annually per 100,000 persons. PMID:22094717

  14. 26 CFR 301.7701(b)-4 - Residency time periods.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... statement (described in paragraph (c)(3)(v)(C) of this section) to the individual's income tax return (Form... tax return for the election year, the alien individual may request an extension of time for filing the return until a reasonable period after he or she has satisfied such test, provided that the...

  15. Peak Alert Time and Rapport between Residence Hall Roommates.

    ERIC Educational Resources Information Center

    Carey, John C.; And Others

    1988-01-01

    Examined whether peak alert time is related to compatibility for college roommates. Data from 66 male pairs and from 55 female pairs of roommates revealed that pairs who were similar on self-reported peak circadian alertness had higher levels of rapport. (Author/NB)

  16. Activity size distribution and residence time of 7Be aerosols in the Arctic atmosphere

    NASA Astrophysics Data System (ADS)

    Ioannidou, Alexandra; Paatero, Jussi

    2014-05-01

    The activity size distributions of the natural radionuclide tracer 7Be in different size range fractions (<0.39 μm, 0.39-0.69 μm, 0.69-1.3 μm, 1.3-2.1 μm, 2.1-4.2 μm, 4.2-10.2 μm and >10.2 μm) were determined in the boreal atmosphere in the Arctic Research Centre of the Finnish Meteorological Institute (FMI) at Sodankylä, Finland (67°22‧ N, 26°38‧ E, 180 m asl). The activity median aerodynamic diameter (AMAD) ranged from 0.54 μm to 1.05 μm (average 0.83 μm). A residence time of about 8 days applies to aerosols of 0.83 μm diameter, representing the residence of aerosol particles in arctic environment. The observed positive correlation between AMAD values and RH% can be explained by the fact that condensation during high relative humidity conditions becomes more intense, resulting in increased particle sizes of atmospheric aerosols. However, greater aerosol particle sizes means higher wet scavenging rate of aerosols and as a result lower activity concentration of 7Be in the atmosphere, explaining the anti-correlation between the AMAD values and activity concentrations of 7Be. But this associated with possibly higher scavenging rates of aerosols does not necessarily alone explain the anti-correlation between the AMAD and the 7Be activities. The air mass origin associated with synoptic scale weather phenomena may contribute to that too. The Flextra model was used to assess the transport pattern and to explain the deviation in radionuclide activity concentrations and AMAD values observed in the site of investigation.

  17. The imprint of climate and geology on the residence times of groundwater

    NASA Astrophysics Data System (ADS)

    Maxwell, Reed M.; Condon, Laura E.; Kollet, Stefan J.; Maher, Kate; Haggerty, Roy; Forrester, Mary Michael

    2016-01-01

    Surface and subsurface flow dynamics govern residence time or water age until discharge, which is a key metric of storage and water availability for human use and ecosystem function. Although observations in small catchments have shown a fractal distribution of ages, residence times are difficult to directly quantify or measure in large basins. Here we use a simulation of major watersheds across North America to compute distributions of residence times. This simulation results in peak ages from 1.5 to 10.5 years, in agreement with isotopic observations from bomb-derived radioisotopes, and a wide range of residence times—from 0.1 to 10,000 years. This simulation suggests that peak residence times are controlled by the mean hydraulic conductivity, a function of the prevailing geology. The shape of the residence time distribution is dependent on aridity, which in turn determines water table depth and the frequency of shorter flow paths. These model results underscore the need for additional studies to characterize water ages in larger systems.

  18. Residence time and Posidonia oceanica in Cabrera Archipelago National Park, Spain

    NASA Astrophysics Data System (ADS)

    Orfila, A.; Jordi, A.; Basterretxea, G.; Vizoso, G.; Marbà, N.; Duarte, C. M.; Werner, F. E.; Tintoré, J.

    2005-07-01

    Flushing time and residence time are studied in a small inlet in Cabrera National Park, Western Mediterranean Sea. Flushing time is studied using ADCP in situ data. Observed flushing time data are compared with the simulations from a three-dimensional coastal ocean numerical model. Residence time is assessed using virtual lagrangian particles and studying the number remaining within the analyzed domain. Results show a good agreement between observations and modeling estimations of the flushing time (i.e. 6 days from the ADCP data and 5.6 days from the numerical model). Residence time estimations yield a broad range of values, from 1 h in the Bay to over 30 days depending also on the horizontal and vertical position where particles were released. A continuous stirred tank reactor (CSTR) model for the Port yields a value of 8.7 days. Results obtained for the residence time appear to have a determinant impact over the meadows of the seagrass Posidonia oceanica, present inside the Port. Recirculation patterns and complex flows in coastal environments create a non-uniform distribution of the areas of accumulation of non-conservative properties that indicate that residence time concept is the correct approach when studying the impact of water transport over biological communities.

  19. Observations and modeling of exchange and residence time in tidal inlets

    NASA Astrophysics Data System (ADS)

    Rynne, Patrick Forde

    The exchange of water in a coastal embayment with seawater is forced by tidally driven and gravitational flows. Tidal flows oscillate temporally based on planetary motion, while gravitational flows like those found in rivers act in one direction from high to low altitude. These flows determine the residence time, or the time water will remain within an embayment. At the ocean boundary, many coasts contain barrier islands with inlets through which these flows propagate. The effect that inlets have on the exchange of inland water with the sea has been the subject of research for nearly a century. Residence time is a bulk parameter that can be used to indicate the efficiency of an inlet system to rid itself of contaminants and maintain good water quality. Because coastal embayments are often exposed to anthropogenic pollutants, understanding the processes that control residence time improves our ability to protect coastal ecosystems. Inlet systems, including lagoons and estuaries, are subject to processes of a wide range of spatial and temporal scales. As such, past efforts to identify which processes control the motion and transport of water often rely on assumptions that simplify the kinematics. Today, the rapid evolution of personal computing has enabled the creation of numerical models that resolve the Reynolds Averaged Navier Stokes Equations (RANS) for complex flows found in inlet environments. This dissertation focuses on utilizing such a model to examine the flow in tidal inlet systems and to identify the dominant processes that control exchange and residence time. First, modeling experiments of idealized lagoons are conducted with the aim of quantifying how the shape of an inlet affects residence time. Seventeen different inlet configurations are examined. Methods of quantifying residence time based on previous analytical models are applied to a numerical model for the first time. To better understand the mechanism of exchange, a simple transport model is

  20. Respiratory function impairment and cardiopulmonary consequences in long-time residents of the Canadian Arctic.

    PubMed Central

    Schaefer, O; Eaton, R D; Timmermans, F J; Hildes, J A

    1980-01-01

    Spirometry, roentgenography and electrocardiography were performed during community health surveys in 1976-78 in 176 Inuit and other long-time residents of the northeastern (Arctic Bay) and western (Inuvik) Canadian Arctic, and the results were related to age, ethnic origin, occupation and history of climatic exposure, smoking and hospitalization for tuberculosis. In Arctic Bay the young men showed excellent respiratory function, normal-sized pulmonary arteries and normal electrocardiograms, but abnormalities of all three types were increasingly frequent and severe after age 25. The forced mid-expiratory flow (FMF) fell to less than 50% of the norm by age 40, and dilatation of the pulmonary artery, hypertrophy of the right ventricle, right bundle branch block and a pseudoinfarction pattern on the ECG were frequently associated. In contrast, the men in Inuvik, an urbanized centre, maintained above normal respiratory function until age 40, and the FMF and pulmonary artery diameter remained normal in the older men except for Inuit and white trappers over 60 years old who had run fox trap lines along the Arctic coast in the 1920s and 30s. These data suggest that inhalation of extremely cold air at maximum ventilation may be a prime factor in the chronic obstructive lung disease of Inuit hunters, whereas smoking has only a minor role and hospitalization for tuberculosis appears to protect from rather than contribute to this disorder. PMID:7448675

  1. Consistent Estimates for the Residence Time of Micro-tidal Estuaries

    NASA Astrophysics Data System (ADS)

    Rasmussen, B.; Josefson, A. B.

    2002-01-01

    Water exchange and residence time are calculated for 31 small Danish estuaries to assess the spatial variability of estuarine processes and biogeochemical properties. To identify the uncertainty of the residence time estimates, three different model types have been applied to the estuaries. The dynamic models applied comprise hydrodynamic (HD) models, and a well-mixed batch reactor model for the winter-nitrate concentration. Residence times of the dynamic models range from 0·3 to 127 d. The median value of the deviation between the results of these two model types is 30%. Furthermore, a morphological model is formulated. It includes entrance width as the independent variable, and the approximation that the saltwater flow per unit entrance width is equal for investigated Danish estuaries. This model yields a fair representation of water exchange and residence time over three and two orders of magnitude, respectively. The deviation from the dynamic model results is 40%. Hence, in comparison to entrance width, differences in mixing and forcing appear to be of limited importance to the water exchange variability between Danish estuaries. The morphological model may thus be used to give a sound estimate of the water exchange for Danish estuaries, where more detailed modelling is lacking. However, in either model comparison, the deviation between model results is less than the residence time variability between the estuaries. The models may thus supplement one another for making quantitatively acceptable analysis of processes and bio-geochemical properties in Danish estuaries.

  2. Experimental study of residence time distributions of ball-mill circuits grinding coal-water mixtures

    SciTech Connect

    Shoji, K.; Takahashi, Y.; Ohtake, A.; Austin, L.G.

    2008-08-15

    Residence time distributions (RTDs) were estimated by water tracing in a number of wet overflow ball mills (diameters 0.38 to 4.65 m) producing dense, coal-water slurries. In open-circuit mills of 0.38 m diameter and various length-diameter (LID) ratios, the mean residence times of solid were also determined from measured mill holdups. Holdup increased with increased mill feed rate, but the mean residence times of coal and water were still equal to each other. The experimental residence time distributions were fitted to the Mori-Jimbo-Yamazaki semi-infinite, axial mixing model, and the dimensionless mixing coefficient was determined for each of 25 tests in single- and two-compartment mills. This coefficient was found to be independent to the feed rate but linearly proportional to the D/L ratio. The mixing coefficient was smaller for two-compartment mills than for single-compartment mills, showing that there was reduced mixing introduced by the diaphragm separating the compartments. Equations are given to scale residence time distributions for changes in mill diameter and length.

  3. Controlling factors for water residence time and flow patterns in Ekeby treatment wetland, Sweden

    NASA Astrophysics Data System (ADS)

    Kjellin, Johan; Wörman, Anders; Johansson, Håkan; Lindahl, Anna

    2007-04-01

    Treatment wetlands play an important role in reducing nutrient content and heavy metals in wastewater and run-off water. The treatment efficiency strongly depends on flow pattern and residence times of the water. Here, we study the impact of different factors on water flow patterns based on a tracer experiment with tritiated water in a 2.6 ha constructed wetland pond. A 2D flow and inert transport model was used to evaluate the relative importance of bottom topography, vegetation distribution, water exchange with stagnant zones and dispersion. Results from computer simulations and independent measurements of friction losses as well as wetland geometry showed that variations in bottom topography, formed by several deep zones, decreased the variance in water residence times to a minor extent. Heterogeneity in vegetation, on the other hand, significantly contributed to the spread in water residence times and explained the multiple peaks observed in the breakthrough curves. Analyses showed that in the Ekeby treatment wetland, basin shape explained about 10% of the variance in the observed residence times, whereas vegetation explained about 60-80%. To explain all variance secondary factors were needed, such as dispersion and water exchange with stagnant zones. These were shown to contribute to the spread of residence times and primarily to the long tail of the observed breakthrough curves.

  4. Effect of plateout, air motion and dust removal on radon decay product concentration in a simulated residence.

    PubMed

    Rudnick, S N; Hinds, W C; Maher, E F; First, M W

    1983-08-01

    The effectiveness of increased air motion and dust removal in reducing radon decay product concentration in residences subject to radon intrusion was evaluated in a 78-m3 room under steady-state conditions for air infiltration rates between 0.2 and 0.9 air changes per hour. Room-size, portable electrostatic precipitators and high-efficiency fibrous filters were tested as typical residential air cleaning devices; a portable box fan and a ceiling fan were employed as typical residential air movers. Reductions in working levels of 40-90% were found. The fate of radon decay products, with and without mixing fans, was determined by direct measurement. When mixing fans were used, most of the nonairborne potential alpha-energy was plated out on the room surfaces; less than 10% was deposited on the fan blades or housing. Results were compared to a mathematical model based on well-mixed room air, and good agreement was obtained. PMID:6885451

  5. Residency Time as an Indicator of Reproductive Restraint in Male Burying Beetles

    PubMed Central

    Smith, Ashlee N.; Belk, Mark C.; Creighton, J. Curtis

    2014-01-01

    The cost of reproduction theory posits that there are trade-offs between current and future reproduction because resources that are allocated to current offspring cannot be used for future reproductive opportunities. Two adaptive reproductive strategies have been hypothesized to offset the costs of reproduction and maximize lifetime fitness. The terminal investment hypothesis predicts that as individuals age they will allocate more resources to current reproduction as a response to decreasing residual reproductive value. The reproductive restraint hypotheses predicts that as individuals age they will allocate fewer resources to current reproduction to increase the chance of surviving for an additional reproductive opportunity. In this study, we test for adaptive responses to advancing age in male burying beetles, Nicrophorus orbicollis. Burying beetles use facultative biparental care, but the male typically abandons the brood before the female. Previous work in male burying beetles has suggested several factors to explain variation in male residency time, but no study has observed male behavior throughout their entire reproductive lifetimes to determine whether males change residency time in an adaptive way with age. We compared residency time of males that reproduced biparentally, uniparentally, and on different-sized carcasses to determine if they used an adaptive reproductive strategy. Males did not increase residency time as they aged when reproducing biparentally, but decreased residency time with age when reproducing uniparentally. A decrease in parental care with age is consistent with a reproductive restraint strategy. When female age increased over time, males did not increase their residency time to compensate for deteriorating female condition. To our knowledge, this is the first test of adaptive reproductive allocation strategies in male burying beetles. PMID:25295755

  6. Strategic Application of Residence-Time Control in Continuous-Flow Reactors

    PubMed Central

    Mándity, István M; Ötvös, Sándor B; Fülöp, Ferenc

    2015-01-01

    As a sustainable alternative for conventional batch-based synthetic techniques, the concept of continuous-flow processing has emerged in the synthesis of fine chemicals. Systematic tuning of the residence time, a key parameter of continuous-reaction technology, can govern the outcome of a chemical reaction by determining the reaction rate and the conversion and by influencing the product selectivity. This review furnishes a brief insight into flow reactions in which high chemo- and/or stereoselectivity can be attained by strategic residence-time control and illustrates the importance of the residence time as a crucial parameter in sustainable method development. Such a fine reaction control cannot be performed in conventional batch reaction set-ups. PMID:26246983

  7. Computation of residence time in the simulation of pulsatile ventricular assist devices

    NASA Astrophysics Data System (ADS)

    Long, C. C.; Esmaily-Moghadam, M.; Marsden, A. L.; Bazilevs, Y.

    2014-10-01

    A continuum-based model of particle residence time for moving-domain fluid mechanics and fluid-structure interaction (FSI) computations is proposed, analyzed, and applied to the simulation of an adult pulsatile ventricular assist device (PVAD). Residence time is a quantity of clinical interest for blood pumps because it correlates with thrombotic risk. The proposed technique may be easily implemented in any flow or FSI solver. In the context of PVADs the results of the model may be used to assess how efficiently the pump moves the blood through its interior. Three scalar measures of particle residence time are also proposed. These scalar quantities may be used in the PVAD design with the goal of reducing thrombotic risk.

  8. Catchment travel and residence time distributions: a theoretical framework for solute transport modeling

    NASA Astrophysics Data System (ADS)

    Botter, G.; Bertuzzo, E.; Rinaldo, A.

    2011-12-01

    The probability density functions (pdf's) of travel and residence times are key descriptors of the mechanisms through which catchments retain and release old and event water, transporting solutes to receiving water bodies. In this contribution we derive a general stochastic framework applicable to arbitrary catchment control volumes, where time-variable precipitation, evapotranspiration and discharge are assumed to be the major hydrological drivers for water and solutes. A master equation for the residence time pdf is derived and solved analytically, providing expressions for travel and residence time pdf's as a function of input/output fluxes and of the relevant mixing processes occurring along streamflow production and plant upatke. Our solutions suggest intrinsically time variant travel and residence time pdf's through a direct dependence on the underlying hydrological forcings and soil vegetation dynamics. The proposed framework highlights the dependence of water/solute travel times on eco-hydrological processes (especially transpiration and uptake), and integrates age-dating and tracer hydrology techniques by providing a coherent framework for catchment transport models. An application to the release of pesticides from an agricultural watershead is also discussed.

  9. Relating hyporheic fluxes, residence times, and redox-sensitive biogeochemical processes upstream of beaver dams

    USGS Publications Warehouse

    Briggs, Martin A.; Lautz, Laura; Hare, Danielle K.

    2013-01-01

    ¨hler number seemed to overestimate the actual transition as indicated by multiple secondary electron acceptors, illustrating the gradient nature of anaerobic transition. Temporal flux variability in low-flux morphologies generated a much greater range in hyporheic redox conditions compared to high-flux zones, and chemical responses to changing flux rates were consistent with those predicted from the empirical relationship between redox condition and residence time. The Raz tracer revealed that hyporheic flow paths have strong net aerobic respiration, particularly at higher residence time, but this reactive exchange did not affect the net stream signal at the reach scale.

  10. Radiogenic and Radioactive Isotopic Evidence for a Dynamic Residence Time of the Athabasca Glacier Subglacial Water

    NASA Astrophysics Data System (ADS)

    Arendt, C. A.; Aciego, S.; Sims, K. W.; Aarons, S. M.

    2011-12-01

    Little is known about the time it takes precipitation, input of water from reservoirs, surface melt, and basal melt to migrate to the base of a glacier and discharge. Previous work on the residence time of subglacial water has proven to be either inconclusive or inconsistent. Our research will address the primary subglacial water questions; the flux of subglacial water correlates directly to the mass balance of a glacier but what role does subglacial water storage play in that mass balance? Can we determine residence time of subglacial water? And, how variable is residence time seasonally and on longer time scales? The regional focus of our research is the Athabasca Glacier, part of the Columbia Icefield located in Jasper National Park, Alberta, Canada. Uranium-series (U-series) dating methods based on the ingrowth of daughter isotopes from parents (234U, 230Th and 222Rn from the primary parent 238U) have been used to study the residence time of aquifer systems. Here we show the feasibility of applying these techniques to subglacial water. Samples were collected over two 25-day field periods to account for hydrological and chemical fluctuations between the onset of melt and peak melt. Daily physical observations, 222Rn concentrations (from a Durridge RAD7), conductivity, total alkalinity, pH, maximum velocity, and discharge measurements were taken. Fifty daily 10-40L subglacial water and filtered sediment samples were collected and filtered at our collection site in the main channel at the toe of the Athabasca Glacier. The 238U /234U and 87Sr/86Sr isotopic compositions and U, Th, and Sr concentrations of the filtrate and captured sediments is pending. We will extrapolate the residence time of the water based on the accumulation of 234U and 230Th in our samples from alpha decay, which can be coupled to a radiometric timescale. Given that the 238U /234U and 234U/230Th isotopic composition of subglacial water is dependent on recoil and sediment dissolution processes

  11. Effect of channel size on solute residence time distributions in rivers

    NASA Astrophysics Data System (ADS)

    Deng, Zhi-Qiang; Jung, Hoon-Shin; Ghimire, Bhuban

    2010-09-01

    The effect of channel size on residence time distributions (RTDs) of solute in rivers is investigated in this paper using tracer test data and the variable residence time (VART) model. Specifically, the investigation focuses on the influence of shear dispersion and hyporheic exchange on the shape of solute RTD, and how these two transport processes prevail in larger and smaller streams, respectively, leading to distinct tails of RTD. Simulation results show that (1) RTDs are dispersion-dependent and thereby channel-size (scale) dependent. RTDs increasing longitudinal dispersion coefficient. Small streams with negligible dispersion coefficient may display various types of RTD from upward curving patterns to a straight line (power-law distributions) and further to downward curving lognormal distributions when plotted in log-log coordinates. Moderate-sized rivers are transitional in terms of RTDs and commonly exhibit lognormal and power-law RTDs; (2) the incorporation of water and solute losses/gains in the VART model can improve simulation results and make parameter values more reasonable; (3) the ratio of time to peak concentration to the minimum mean residence time is equal to the recovery ratio of tracer. The relation provides a simple method for determining the minimum mean residence time; and (4) the VART model is able to reproduce various RTDs observed in rivers with 3-4 fitting parameters while no user-specified RTD functions are needed.

  12. Factors Associated with Time to Identify Physical Problems of Nursing Home Residents with Dementia

    PubMed Central

    Kovach, Christine R.; Logan, Brent R.; Simpson, Michelle R.; Reynolds, Sheila

    2010-01-01

    This study describes new problems emerging over six weeks for nursing home residents with advanced dementia and factors associated with time to identify the problems. The sample of 65 developed 149 new acute problems or exacerbations of existing conditions over the six weeks of data collection. The majority of these problems involved uncontrolled pain, new infections and severe psychoses. Nurse assessment skill was associated with a shorter time to identify the new problem and more time spent on the problem. A higher ratio of new to existing interventions was also associated with a shorter time to identify the problem. Other patient characteristics associated with time to identify problems included non-specific vocalizations, physical signs, cognitive status and length of stay. While future research is warranted, findings from this study highlight the frequency of problems requiring treatment and suggest that improved assessment of residents may decrease the time to identify new problems. PMID:20237337

  13. Residence times in river basins as determined by analysis of long-term tritium records

    NASA Astrophysics Data System (ADS)

    Michel, Robert L.

    1992-01-01

    The US Geological Survey has maintained a network of stations to collect samples for the measurement of tritium concentrations in precipitation and streamflow since the early 1960s. Tritium data from outflow waters of river basins draining 4500-75000 km 2 are used to determine average residence times of water within the basins. The basins studied are the Colorado River above Cisco, Utah; the Kissimmee River above Lake Okeechobee, Florida; the Mississippi River above Anoka, Minnesota; the Neuse River above Streets Ferry Bridge near Vanceboro, North Carolina; the Potomac River above Point of Rocks, Maryland; the Sacramento River above Sacramento, California; the Susquehanna River above Harrisburg, Pennsylvania. The basins are modeled with the assumption that the outflow in the river comes from two sources—prompt (within-year) runoff from precipitation, and flow from the long-term reservoirs of the basin. Tritium concentration in the outflow water of the basin is dependent on three factors: (1) tritium concentration in runoff from the long-term reservoir, which depends on the residence time for the reservoir and historical tritium concentrations in precipitation; (2) tritium concentrations in precipitation (the within-year runoff component); (3) relative contributions of flow from the long-term and within-year components. Predicted tritium concentrations for the outflow water in the river basins were calculated for different residence times and for different relative contributions from the two reservoirs. A box model was used to calculate tritium concentrations in the long-term reservoir. Calculated values of outflow tritium concentrations for the basin were regressed against the measured data to obtain a slope as close as possible to 1. These regressions assumed an intercept of zero and were carried out for different values of residence time and reservoir contribution to maximize the fit of modeled versus actual data for all the above rivers. The final slopes of

  14. Residence times in river basins as determined by analysis of long-term tritium records

    USGS Publications Warehouse

    Michel, R.L.

    1992-01-01

    The US Geological Survey has maintained a network of stations to collect samples for the measurement of tritium concentrations in precipitation and streamflow since the early 1960s. Tritium data from outflow waters of river basins draining 4500-75000 km2 are used to determine average residence times of water within the basins. The basins studied are the Colorado River above Cisco, Utah; the Kissimmee River above Lake Okeechobee, Florida; the Mississippi River above Anoka, Minnesota; the Neuse River above Streets Ferry Bridge near Vanceboro, North Carolina; the Potomac River above Point of Rocks, Maryland; the Sacramento River above Sacramento, California; the Susquehanna River above Harrisburg, Pennsylvania. The basins are modeled with the assumption that the outflow in the river comes from two sources-prompt (within-year) runoff from precipitation, and flow from the long-term reservoirs of the basin. Tritium concentration in the outflow water of the basin is dependent on three factors: (1) tritium concentration in runoff from the long-term reservoir, which depends on the residence time for the reservoir and historical tritium concentrations in precipitation; (2) tritium concentrations in precipitation (the within-year runoff component); (3) relative contributions of flow from the long-term and within-year components. Predicted tritium concentrations for the outflow water in the river basins were calculated for different residence times and for different relative contributions from the two reservoirs. A box model was used to calculate tritium concentrations in the long-term reservoir. Calculated values of outflow tritium concentrations for the basin were regressed against the measured data to obtain a slope as close as possible to 1. These regressions assumed an intercept of zero and were carried out for different values of residence time and reservoir contribution to maximize the fit of modeled versus actual data for all the above rivers. The final slopes of the

  15. Recruitment, growth and residence time of fishes in a tropical Australian mangrove system

    NASA Astrophysics Data System (ADS)

    Robertson, Alistar I.; Duke, Norman C.

    1990-11-01

    Twenty fish species accounted for > 96% of the catch by numbers in mangrove habitats in Alligator Creek, in tropical Queensland, Australia. The timing of recruitment, residency status, the period of residence and growth of fish during the time they spent in the mangrove habitat was assessed by examining gonad maturity and following changes in size-frequency plots for each species over 13 months. Five species were permanent residents, completing their life-cycles in mangrove swamps; eight were 'long-term' temporary residents, being present for ˜ 1 year as juveniles before moving to other near-shore habitats; and seven were 'short-term' residents or sporadic users of the mangrove habitat. Amongst the latter group, four species lived in the mangrove habitat for between 1 and 4 consecutive months, while three engraulid species appeared to move rapidly, and often, between mangrove and other near-shore habitats. One of the resident species spawned and recruited throughout the year, but recruitment for most species was highly seasonal, being concentrated in the late dry season (October) to mid wet season (February) period. Temporary resident species dominated the fish community in the wet season (December-April), but resident species comprised more than 90% of total fish numbers in the mid dry season (August) after temporary residents left the mangroves in the early dry season. Several species had more than one peak of recruitment during the wet season. The cohort of 0 + aged Leiognathus equulus which recruited in December grew more rapidly and remained in the mangroves for a shorter period than the cohort which recruited later in the wet season (February). Only nine of the 20 species examined are strictly dependent on mangrove-lined estuaries, the remaining 11 are captured in significant numbers in other near-shore habitats. Only four of the 20 species are of direct commercial importance in Australia, but most are major prey for several valuable, commercial species

  16. EFFECTS OF NITROGEN LOADING, FRESHWATER RESIDENCE TIME, AND INTERNAL LOSSES ON NITROGEN CONCENTRATIONS IN ESTUARIES

    EPA Science Inventory

    A simple model is presented that uses the annual loading rate of total nitrogen (TN) and the water residence time to calculate: 1) average annual TN concentration and intemalloss rates (e.g. denitrification and incorporation in sediments) in an estuary, and 2) the rate of nitroge...

  17. Conceptual framework for model-based analysis of residence time distribution in twin-screw granulation.

    PubMed

    Kumar, Ashish; Vercruysse, Jurgen; Vanhoorne, Valérie; Toiviainen, Maunu; Panouillot, Pierre-Emmanuel; Juuti, Mikko; Vervaet, Chris; Remon, Jean Paul; Gernaey, Krist V; De Beer, Thomas; Nopens, Ingmar

    2015-04-25

    Twin-screw granulation is a promising continuous alternative for traditional batchwise wet granulation processes. The twin-screw granulator (TSG) screws consist of transport and kneading element modules. Therefore, the granulation to a large extent is governed by the residence time distribution within each module where different granulation rate processes dominate over others. Currently, experimental data is used to determine the residence time distributions. In this study, a conceptual model based on classical chemical engineering methods is proposed to better understand and simulate the residence time distribution in a TSG. The experimental data were compared with the proposed most suitable conceptual model to estimate the parameters of the model and to analyse and predict the effects of changes in number of kneading discs and their stagger angle, screw speed and powder feed rate on residence time. The study established that the kneading block in the screw configuration acts as a plug-flow zone inside the granulator. Furthermore, it was found that a balance between the throughput force and conveying rate is required to obtain a good axial mixing inside the twin-screw granulator. Although the granulation behaviour is different for other excipients, the experimental data collection and modelling methods applied in this study are generic and can be adapted to other excipients. PMID:25698071

  18. Residence Time Distribution Measurement and Analysis of Pilot-Scale Pretreatment Reactors for Biofuels Production: Preprint

    SciTech Connect

    Sievers, D.; Kuhn, E.; Tucker, M.; Stickel, J.; Wolfrum, E.

    2013-06-01

    Measurement and analysis of residence time distribution (RTD) data is the focus of this study where data collection methods were developed specifically for the pretreatment reactor environment. Augmented physical sampling and automated online detection methods were developed and applied. Both the measurement techniques themselves and the produced RTD data are presented and discussed.

  19. HOW TO MODEL HYDRODYNAMICS AND RESIDENCE TIMES OF 27 ESTUARIES IN 4 MONTHS

    EPA Science Inventory

    The hydrodynamics and residence times of 27 embayments were modeled during the first year of a project whose goal is to define the relation between nitrogen loadings and ecological responses of 44 systems that range from small to the size of Narragansett Bay and Buzzards Bay. The...

  20. Molecular Dynamics Simulations and Kinetic Measurements to Estimate and Predict Protein-Ligand Residence Times.

    PubMed

    Mollica, Luca; Theret, Isabelle; Antoine, Mathias; Perron-Sierra, Françoise; Charton, Yves; Fourquez, Jean-Marie; Wierzbicki, Michel; Boutin, Jean A; Ferry, Gilles; Decherchi, Sergio; Bottegoni, Giovanni; Ducrot, Pierre; Cavalli, Andrea

    2016-08-11

    Ligand-target residence time is emerging as a key drug discovery parameter because it can reliably predict drug efficacy in vivo. Experimental approaches to binding and unbinding kinetics are nowadays available, but we still lack reliable computational tools for predicting kinetics and residence time. Most attempts have been based on brute-force molecular dynamics (MD) simulations, which are CPU-demanding and not yet particularly accurate. We recently reported a new scaled-MD-based protocol, which showed potential for residence time prediction in drug discovery. Here, we further challenged our procedure's predictive ability by applying our methodology to a series of glucokinase activators that could be useful for treating type 2 diabetes mellitus. We combined scaled MD with experimental kinetics measurements and X-ray crystallography, promptly checking the protocol's reliability by directly comparing computational predictions and experimental measures. The good agreement highlights the potential of our scaled-MD-based approach as an innovative method for computationally estimating and predicting drug residence times. PMID:27391254

  1. Untangling hyporheic residence time distributions and whole stream metabolisms using a hydrological process model

    NASA Astrophysics Data System (ADS)

    Altenkirch, Nora; Mutz, Michael; Molkenthin, Frank; Zlatanovic, Sanja; Trauth, Nico

    2016-04-01

    The interaction of the water residence time in hyporheic sediments with the sediment metabolic rates is believed to be a key factor controlling whole stream metabolism. However, due to the methodological difficulties, there is little data that investigates this fundamental theory of aquatic ecology. Here, we report on progress made to combine numerical modeling with a series of manipulation to laboratory flumes overcoming methodological difficulties. In these flumes, hydraulic conditions were assessed using non-reactive tracer and heat pulse sensor. Metabolic activity was measured as the consumption and production of oxygen and the turnover of reactive tracers. Residence time and metabolic processes were modeled using a multicomponent reactive transport code called Min3P and calibrated with regard to the hydraulic conditions using the results obtained from the flume experiments. The metabolic activity was implemented in the model via Monod type expressions e.g. for aerobic respiration rates. A number of sediment structures differing in residence time distributions were introduced in both, the model and the flumes, specifically to model the biogeochemical performance and to validate the model results. Furthermore, the DOC supply and surface water flow velocity were altered to test the whole stream metabolic response. Using the results of the hydrological process model, a sensitivity analysis of the impact of residence time distributions on the metabolic activity could yield supporting proof of an existing link between the two.

  2. Bridging Home: Building Relationships between Immigrant and Long-Time Resident Youth

    ERIC Educational Resources Information Center

    Dryden-Peterson, Sarah

    2010-01-01

    Background: There is rising evidence that relationships that bridge between immigrants and long-time residents are critical to immigrant integration and to the overall heath of communities. The processes by which this bridging social capital is built are not well understood. Schools in new immigrant destinations, as spaces in which diverse youth…

  3. Residence times of 234Th and 7Be in Lake Geneva

    NASA Astrophysics Data System (ADS)

    Dominik, J.; Schuler, Ch.; Santschi, P. H.

    1989-07-01

    The activities of two short-lived natural radionuclides, 234Th and 7Be, were measured in Lake Geneva water, suspended solids and sediments, in order to obtain their removal residence times in the lake. Four independent methods of estimation are presented and compared. The calcuated residence times of 234Th and 7Be vary from 60 to 280 days and from 60 to 1100 days, respectively, depending on season and the method used. In general, 7Be residence times are significantly longer than those of 234Th. For both nuclides the removal residence times are significantly longer than their respective radioactive mean-lives. As a consequence, the estimates based on their water column inventories are not as reliable as the estimates obtained from the measured fluxes of these nuclides into sediment traps. Estimates based on the bottom sediment inventories are similar in magnitude to those obtained from flux into sediment traps, but occasionally are erroneous because of small-scale sediment heterogeneity.

  4. LABORATORY AND NUMERICAL INVESTIGATIONS OF RESIDENCE TIME DISTRIBUTION OF FLUIDS IN LAMINAR FLOW STIRRED ANNULAR PHOTOREACTOR

    EPA Science Inventory

    Laboratory and Numerical Investigations of Residence Time Distribution of Fluids in Laminar Flow Stirred Annular Photoreactor

    E. Sahle-Demessie1, Siefu Bekele2, U. R. Pillai1

    1U.S. EPA, National Risk Management Research Laboratory
    Sustainable Technology Division,...

  5. Cosmogenic, radiogenic, and stable isotopic constraints on groundwater residence time in the nubian aquifer, western desert of egypt

    SciTech Connect

    Patterson, Leslie J.; Sturchio, Neil C.; Kennedy, B.Mack; van Soest, Matthias C.; Sultan, Mohamed; Lu, Zheng-Tian; Lehmann, Bernhard; Purtschert, Roland; El Alfy, Zeinhom; El Kaliouby, Baher; Dawood, Yehia; Abdallah, Ali

    2004-06-01

    Measurements of radiochlorine ({sup 36}Cl), radiogenic noble gases ({sup 4}He and {sup 40}Ar), and stable chlorine isotope ratios were obtained to assess the residence time of groundwater in the Nubian Aquifer of the Western Desert of Egypt. Measured {sup 36}Cl/Cl ratios yield apparent residence times from {approx}0.2 to 1.2 x 10{sup 6} years in the deep (600-1200 m) groundwater (assuming constant Cl) and {le} 0.16 x 10{sup 6} years in the shallow (<600 m) groundwater. Values of {delta}{sup 37}Cl in the groundwater strengthen the application of the {sup 36}Cl dating method by constraining Cl sources and identifying groundwater mixing. Dissolved gases were measured in some of the deep groundwater samples. Measured {sup 4}He concentrations indicate accumulation of radiogenic {sup 4}He that is qualitatively consistent with the age progression indicated by the {sup 36}Cl/Cl ratios, but the flux of external {sup 4}He from the underlying crust has not been quantified and is not constant throughout the aquifer. Concentrations of {sup 40}Ar range from 3.3 to 6.7 x 10{sup -4} ccSTP/g and indicate excess air incorporation at recharge. Measured {sup 40}Ar/{sup 36}Ar ratios do not exceed the atmospheric ratio. A two-dimensional numerical hydrodynamic transect of the aquifer was modeled from the area of the Uweinat Uplift to the northern Bahariya Oasis. Predicted groundwater velocities in the deep portion of the aquifer are 0.5-3.5 m/yr with groundwater residence times up to 9 x 10{sup 5} years; residence times up to 1.3 x 10{sup 6} years are predicted in the confining shale. Aquifer properties are estimated by using the model to fit the measured {sup 36}Cl/Cl ratios. Under these conditions, hydrodynamic residence times are within about 30 percent of those calculated from {sup 36}Cl when mixing of Cl{sup -} is accounted for in the highest-Cl{sup -} deep groundwaters. By mutually calibrating multiple methods (hydrodynamic, {sup 36}Cl, and {sup 4}He), a consistent picture of the

  6. The role of residence times in two-patch dengue transmission dynamics and optimal strategies.

    PubMed

    Lee, Sunmi; Castillo-Chavez, Carlos

    2015-06-01

    The reemergence and geographical dispersal of vector-borne diseases challenge global health experts around the world and in particular, dengue poses increasing difficulties in the Americas, due in part to explosive urban and semi-urban growth, increases of within and between region mobility, the absence of a vaccine, and the limited resources available for public health services. In this work, a simple deterministic two-patch model is introduced to assess the impact of dengue transmission dynamics in heterogeneous environments. The two-patch system models the movement (e.g. urban versus rural areas residence times) of individuals between and within patches/environments using residence-time matrices with entries that budget within and between host patch relative residence times, under the assumption that only the human budgets their residence time across regions. Three scenarios are considered: (i) resident hosts in Patch i visit patch j, where i≠j but not the other way around, a scenario referred to as unidirectional motion; (ii) symmetric bi-directional motion; and (iii) asymmetric bi-directional motion. Optimal control theory is used to identify and evaluate patch-specific control measures aimed at reducing dengue prevalence in humans and vectors at a minimal cost. Optimal policies are computed under different residence-matrix configurations mentioned above as well as transmissibility scenarios characterized by the magnitude of the basic reproduction number. Optimal patch-specific polices can ameliorate the impact of epidemic outbreaks substantially when the basic reproduction number is moderate. The final patch-specific epidemic size variation increases as the residence time matrix moves away from the symmetric case (asymmetry). As expected, the patch where individuals spend most of their time or in the patch where transmissibility is higher tend to support larger patch-specific final epidemic sizes. Hence, focusing on intervention that target areas where

  7. "There's no-fresh air there": narratives of smoke exposure among residents of extended-stay hotels.

    PubMed

    Lewinson, Terri; Bryant, Lawrence Oliver

    2015-05-01

    Hotel environments have been identified as places where hospitality workers and patrons are at an increased risk for smoke exposure and associated health hazards. However, little research has been conducted to understand experiences of long-term hotel residents. This article presents narrative accounts of tobacco smoke exposure from 37 residents at extended-stay hotels in a large metropolitan Atlanta county. Residents' narratives included an awareness of smoking as an unhealthy habit but a shared activity that facilitates social engagement at the hotel. Secondhand smoke narratives included descriptions of exposure from roommates and hotel neighbors. Thirdhand smoke narratives included reports of persistent pollution and smoke residue in the hotel environment. These results suggest a need for further research to understand the extent and impact of tobacco smoke exposure among this understudied population. The implications of this research support the efforts of social workers to engage in clean air advocacy and policy making for a vulnerable population. PMID:26027415

  8. Sustained increase in resident meal time hand hygiene through an interdisciplinary intervention engaging long-term care facility residents and staff.

    PubMed

    O'Donnell, Marguerite; Harris, Tony; Horn, Terancita; Midamba, Blondelle; Primes, Vickie; Sullivan, Nancy; Shuler, Rosalyn; Zabarsky, Trina F; Deshpande, Abhishek; Sunkesula, Venkata C K; Kundrapu, Sirisha; Donskey, Curtis J

    2015-02-01

    Hand hygiene by patients may prevent acquisition and dissemination of health care-associated pathogens, but limited efforts have been made to engage patients in hand hygiene interventions. In a long-term care facility, we found that residents were aware of the importance of hand hygiene, but barriers, such as inaccessible products or difficult to use products, limited compliance. A dramatic and sustained improvement in meal time hand hygiene was achieved through engagement of staff and residents. PMID:25637117

  9. Influence of temperature on patch residence time in parasitoids: physiological and behavioural mechanisms.

    PubMed

    Moiroux, Joffrey; Abram, Paul K; Louâpre, Philippe; Barrette, Maryse; Brodeur, Jacques; Boivin, Guy

    2016-04-01

    Patch time allocation has received much attention in the context of optimal foraging theory, including the effect of environmental variables. We investigated the direct role of temperature on patch time allocation by parasitoids through physiological and behavioural mechanisms and its indirect role via changes in sex allocation and behavioural defences of the hosts. We compared the influence of foraging temperature on patch residence time between an egg parasitoid, Trichogramma euproctidis, and an aphid parasitoid, Aphidius ervi. The latter attacks hosts that are able to actively defend themselves, and may thus indirectly influence patch time allocation of the parasitoid. Patch residence time decreased with an increase in temperature in both species. The increased activity levels with warming, as evidenced by the increase in walking speed, partially explained these variations, but other mechanisms were involved. In T. euproctidis, the ability to externally discriminate parasitised hosts decreased at low temperature, resulting in a longer patch residence time. Changes in sex allocation with temperature did not explain changes in patch time allocation in this species. For A. ervi, we observed that aphids frequently escaped at intermediate temperature and defended themselves aggressively at high temperature, but displayed few defence mechanisms at low temperature. These defensive behaviours resulted in a decreased patch residence time for the parasitoid and partly explained the fact that A. ervi remained for a shorter time at the intermediate and high temperatures than at the lowest temperature. Our results suggest that global warming may affect host-parasitoid interactions through complex mechanisms including both direct and indirect effects on parasitoid patch time allocation. PMID:26961124

  10. Influence of temperature on patch residence time in parasitoids: physiological and behavioural mechanisms

    NASA Astrophysics Data System (ADS)

    Moiroux, Joffrey; Abram, Paul K.; Louâpre, Philippe; Barrette, Maryse; Brodeur, Jacques; Boivin, Guy

    2016-04-01

    Patch time allocation has received much attention in the context of optimal foraging theory, including the effect of environmental variables. We investigated the direct role of temperature on patch time allocation by parasitoids through physiological and behavioural mechanisms and its indirect role via changes in sex allocation and behavioural defences of the hosts. We compared the influence of foraging temperature on patch residence time between an egg parasitoid, Trichogramma euproctidis, and an aphid parasitoid, Aphidius ervi. The latter attacks hosts that are able to actively defend themselves, and may thus indirectly influence patch time allocation of the parasitoid. Patch residence time decreased with an increase in temperature in both species. The increased activity levels with warming, as evidenced by the increase in walking speed, partially explained these variations, but other mechanisms were involved. In T. euproctidis, the ability to externally discriminate parasitised hosts decreased at low temperature, resulting in a longer patch residence time. Changes in sex allocation with temperature did not explain changes in patch time allocation in this species. For A. ervi, we observed that aphids frequently escaped at intermediate temperature and defended themselves aggressively at high temperature, but displayed few defence mechanisms at low temperature. These defensive behaviours resulted in a decreased patch residence time for the parasitoid and partly explained the fact that A. ervi remained for a shorter time at the intermediate and high temperatures than at the lowest temperature. Our results suggest that global warming may affect host-parasitoid interactions through complex mechanisms including both direct and indirect effects on parasitoid patch time allocation.

  11. [Correlation between results of the residency admission test and of pediatric certification test in Buenos Aires, Argentina].

    PubMed

    Ferreira, Juan Pablo; Hamui, Magali; Paganini, Agustina; Torres, Fernando A; Ossorio, María Fabiana; Eiguchi, Kumiko; Ferrero, Fernando

    2016-01-01

    In the city of Buenos Aires (CABA), pediatric residents enter the residency program after taking a unified admission test. After completion of the program and passing a final test, the Universidad de Buenos Aires (UBA) provides a professional certification. The objective of this study is to determine if the results obtained in the residency admission test (RAT) and those of the professional certification test (PCT) correlated. This is a cross-sectional study, that included all subjects who passed the pediatrics RAT in CABA in 2004-2009, and that attended the pediatric PCT of the UBA. The score for each subject in both tests was obtained and the corresponding correlation was calculated. Results were divided in quintiles, and the proportion of subjects who improved their position in the PCT with respect to the RAT was calculated. Data from 303 subjects was obtained. The RAT showed a median of 45.0 (over 60 maximum) (IC-range: 43.0-48.7), and the PCT showed a median of 6 points (over 10 max.)(IC-range: 6-8). A significative correlation between results in RAT and PCT was observed (r = 0.37, p < 0.001). Based on their position in the RAT, 43.8% of subjects improved their position in the PCT, without differences between residents attending pediatric and general hospitals (45.6 vs. 31.5%; p = 0.1). In the case of pediatric residents, results of the residency admission test correlate with those obtained in the professional certification test. PMID:27295703

  12. Flume experiments elucidate relationships between stream morphology, hyporheic residence time, and nitrous oxide production

    NASA Astrophysics Data System (ADS)

    Quick, Annika; Farrell, Tiffany B.; Reeder, William Jeffrey; Feris, Kevin P.; Tonina, Daniele; Benner, Shawn G.

    2015-04-01

    The hyporheic zone is a potentially important producer of nitrous oxide, a powerful greenhouse gas. The location and magnitude of nitrous oxide generation within the hyporheic zone involves complex interactions between multiple nitrogen species, redox conditions, microbial communities, and hydraulics. To better understand nitrous oxide generation and emissions from streams, we conducted large-scale flume experiments in which we monitored pore waters along hyporheic flow paths within stream dune structures. Measurements of dissolved oxygen, ammonia, nitrate, nitrite, and dissolved nitrous oxide showed distinct spatial relationships reflecting redox changes along flow paths. Using residence times along a flow path, clear trends in oxygen conditions and nitrogen species were observed. Three dune sizes were modeled, resulting in a range of residence times, carbon reactivity levels and respiration rates. We found that the magnitude and location of nitrous oxide production in the hyporheic zone is related to nitrate loading, dune morphology, and residence time. Specifically, increasing exogenous nitrate levels in surface water to approximately 3 mg/L resulted in an increase in dissolved N2O concentrations greater than 500% (up to 10 µg/L N-N2O) in distinct zones of specific residence times. We also found, however, that dissolved N2O concentrations decreased to background levels further along the flow path due to either reduction of nitrous oxide to dinitrogen gas or degassing. The decrease in measurable N2O along a flow path strongly suggests an important relationship between dune morphology, residence time, and nitrous oxide emissions from within stream sediments. Relating streambed morphology and loading of nitrogen species allows for prediction of nitrous oxide production in the hyporheic zone of natural systems.

  13. Inverse dependency of particle residence times in ponds to the concentration of phosphate, the limiting nutrient.

    PubMed

    Roberts, Kimberly A; Santschi, Peter H

    2004-01-01

    234Th, a commonly used short-lived particle-reactive tracer in marine systems, was measured in three different holding pond series at the Rocky Flats Environmental Technology Site (RFETS), Colorado, along with its parent nuclide 238U, to determine steady-state residence times of particle-reactive actinides such as Pu, and of particles. Series B ponds, which received industrial effluent that includes ortho-phosphate (PO4) and actinides, differed from series A and C ponds, which did not. This difference was also evident in the calculated particle residence times, which were <1 day for the ponds B4 and B5, where PO4 concentrations were higher (1.4 and 1.8 mg/l), and 3 and 3.4 days for ponds A3 and C2, respectively, where ortho-phosphate concentrations were lower (<0.1 mg/l). Particle residence times thus showed an inverse relationship with the concentration of ortho-phosphate, the limiting nutrient in fresh water systems. The same relationship to the concentration of ortho-phosphate or any of the other nutrient elements was not evident for the residence times of dissolved 234Th, which ranged between 0.1 and 2 days. This can be attributed to higher concentrations of dissolved and particulate ligands with greater binding potential for actinides such as four-valent Th and Pu in ponds with higher ortho-phosphate concentrations. Regardless of actual ortho-phosphate concentration, however, at water residence (holding) times of 1 month in these ponds, particles and associated actinides would be expected to be completely removed from the pond water to sediments. PMID:15261419

  14. Microbial Biogeography along an Estuarine Salinity Gradient: Combined Influences of Bacterial Growth and Residence Time

    PubMed Central

    Crump, Byron C.; Hopkinson, Charles S.; Sogin, Mitchell L.; Hobbie, John E.

    2004-01-01

    Shifts in bacterioplankton community composition along the salinity gradient of the Parker River estuary and Plum Island Sound, in northeastern Massachusetts, were related to residence time and bacterial community doubling time in spring, summer, and fall seasons. Bacterial community composition was characterized with denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S ribosomal DNA. Average community doubling time was calculated from bacterial production ([14C]leucine incorporation) and bacterial abundance (direct counts). Freshwater and marine populations advected into the estuary represented a large fraction of the bacterioplankton community in all seasons. However, a unique estuarine community formed at intermediate salinities in summer and fall, when average doubling time was much shorter than water residence time, but not in spring, when doubling time was similar to residence time. Sequencing of DNA in DGGE bands demonstrated that most bands represented single phylotypes and that matching bands from different samples represented identical phylotypes. Most river and coastal ocean bacterioplankton were members of common freshwater and marine phylogenetic clusters within the phyla Proteobacteria, Bacteroidetes, and Actinobacteria. Estuarine bacterioplankton also belonged to these phyla but were related to clones and isolates from several different environments, including marine water columns, freshwater sediments, and soil. PMID:15006771

  15. Hydrothermal carbonisation of poultry litter: Effects of treatment temperature and residence time on yields and chemical properties of hydrochars.

    PubMed

    Ghanim, Bashir M; Pandey, Daya Shankar; Kwapinski, Witold; Leahy, James J

    2016-09-01

    In this study, hydrochars were prepared by hydrothermal carbonisation (HTC) of poultry litter (PL) at temperatures between 150-300°C with residence times of 30, 120 and 480min. The effects of treatment temperature and residence time on the yield and composition of hydrochar were investigated. Both treatment temperature and residence time effects were observed however, the effect of residence time was lower. The results indicated that the HHV was improved by up to 25.17% and the overall ash in hydrochar was significantly lower compared to PL, however this coincided with a lower hydrochar yield. PMID:27262091

  16. In-line real time air monitor

    DOEpatents

    Wise, M.B.; Thompson, C.V.

    1998-07-14

    An in-line gas monitor capable of accurate gas composition analysis in a continuous real time manner even under strong applied vacuum conditions operates by mixing an air sample with helium forming a sample gas in two complementary sample loops embedded in a manifold which includes two pairs of 3-way solenoid valves. The sample gas is then analyzed in an ion trap mass spectrometer on a continuous basis. Two valve drivers actuate the two pairs of 3-way valves in a reciprocating fashion, so that there is always flow through the in-line gas monitor via one or the other of the sample loops. The duty cycle for the two pairs of 3-way valves is varied by tuning the two valve drivers to a duty cycle typically between 0.2 to 0.7 seconds. 3 figs.

  17. In-line real time air monitor

    DOEpatents

    Wise, Marcus B.; Thompson, Cyril V.

    1998-01-01

    An in-line gas monitor capable of accurate gas composition analysis in a continuous real time manner even under strong applied vacuum conditions operates by mixing an air sample with helium forming a sample gas in two complementary sample loops embedded in a manifold which includes two pairs of 3-way solenoid valves. The sample gas is then analyzed in an ion trap mass spectrometer on a continuous basis. Two valve drivers actuate the two pairs of 3-way valves in a reciprocating fashion, so that there is always flow through the in-line gas monitor via one or the other of the sample loops. The duty cycle for the two pairs of 3-way valves is varied by tuning the two valve drivers to a duty cycle typically between 0.2 to 0.7 seconds.

  18. Residence time distribution (RTD) of particulate foods in a continuous flow pilot-scale ohmic heater.

    PubMed

    Sarang, Sanjay; Heskitt, Brian; Tulsiyan, Priyank; Sastry, Sudhir K

    2009-08-01

    The residence time distribution (RTD) of a model particulate-fluid mixture (potato in starch solution) in the ohmic heater in a continuous sterilization process was measured using a radio frequency identification (RFID) methodology. The effect of solid concentration and the rotational speed of the agitators on the RTD were studied. The velocity of the fastest particle was 1.62 times the mean product velocity. In general, particle velocity was found to be greater than the product bulk average velocity. Mean particle residence time (MPRT) increased with an increase in the rotational speed of the agitators (P < 0.05), and no particular trend was observed between the MPRT and the solid concentration. The distribution curves E (theta) were skewed to the right suggesting slow moving zones in the system. PMID:19723195

  19. Estimating Regional Water Residence Time Changes in the Colonial Northeast United States

    NASA Astrophysics Data System (ADS)

    Green, M. B.; Arrigo, J.; Duncan, J.; Parolari, T.

    2008-12-01

    The Northeast United States experienced a fundamental change following colonization by Europeans. During the period from 1600 to 1800 forests were cleared, agricultural lands were expanded, beavers were hunted to near-extinction, wetlands were drained or filled, and cities were built. Such activities had important implications for the stocks of water on and the fluxes of water through that landscape. We have made an early attempt to quantify the changed water stocks and fluxes in the Northeast during this time period using historical information and simple analyses. Simple calculations and estimates of stock and flux uncertainty were used to compute the distribution of land surface water residence times at the beginning and ending of the Colonial Era. Our estimates show that humans shifted water residence towards shorter times, which would have important implications for geomorphology, biogeochemistry, and how humans responded to their alteration of the hydrologic cycle.

  20. Th-230 - U-238 series disequilibrium of the Olkaria rhyolites Gregory Rift Valley, Kenya: Residence times

    NASA Technical Reports Server (NTRS)

    Black, S.; Macdonald, R.; Kelly, M.

    1993-01-01

    U-series disequilibrium analyses have been conducted on samples from Olkaria rhyolite centers with ages being available for all but one center using both internal and whole rock isochrons. 67 percent of the rhyolites analyzed show U-Th disequilibrium, ranging from 27 percent excess thorium to 36 percent excess uranium. Internal and whole rock isochrons give crystallization/formation ages between 65 ka and 9 ka, in every case these are substantially older than the eruptive dates. The residence times of the rhyolites (U-Th age minus the eruption date) have decreased almost linearly with time, from 45 ka to 7 Ka suggesting a possible increase of activity within the system related to increased basaltic input. The long residence times are mirrored by large Rn-222 fluxes from the centers which cannot be explained by larger U contents.

  1. Spatial Patterns of Carbon Residence Time and Sequestration Capacity in Terrestrial Ecosystems of the Conterminous USA

    NASA Astrophysics Data System (ADS)

    Zhou, T.; Xu, T.; Luo, Y.

    2005-12-01

    To model carbon (C) sequestration and its spatial pattern, three key parameters need to be quantified: (1) canopy carbon influx; (2) carbon residence time in an ecosystem; and (3) initial values of pool sizes. While spatial distributions of canopy carbon influx have been extensively studied, spatial patterns of carbon residence times have not been carefully characterized. In this study, we conducted an inverse analysis to estimate the carbon residence times in ecosystems of the conterminous US from 12 data sets. The 12 data sets are three NPP data sets (i.e., NPP in leaves, stems, and roots), five biomass data sets (i.e., biomass of leaves, stem, and roots in three soil layers), one litter data set (i.e., fine litter mass), and three SOC data sets in the three soil layers. The inverse analysis was based on a process-based Terrestrial ECOsystem Regional (TECOR) model and used the genetic algorithm for optimal parameter estimation. The inverted residence times and increase trends of net primary production (NPP) were then fed into a forward modeling analysis to map spatial patterns of carbon sequestration capacity. Our analysis estimated that the mean residence time for the whole conterminous US is 46 years with a range from 10 to 150 years. The central Great Plains have the lowest residence times (mean = 28 years, std = 13 years) and the west regions have the highest ones (mean = 64 years, std = 34 years) with the east regions in between (mean = 41 years, std = 20 years). When a 0.5 percent increase of NPP per year was uniformly applied to the whole conterminous US, our forward modeling showed that most of the eastern regions and some of the northwest regions have large carbon sequestration capacity. When a satellite-data-derived spatial distribution of NPP was applied in the forward modeling, it was estimated that the cropland has the largest carbon sequestration capacity followed by the deciduous broadleaf forest, grassland, wooded grassland, and mixed forest. The

  2. The Pools, Fluxes and Residence Time of Water Across the Amazon Basin

    NASA Astrophysics Data System (ADS)

    Goldsmith, G. R.; Fisher, J. B.; McDonnell, J.; Malhi, Y.

    2014-12-01

    What can ecology tell us about the hydrology of the Amazon? And what can hydrology tell us about the ecology? From a hydrological perspective, plant water storage and use contributes to determining the rate and time scales at which water is recycled from soil to the atmosphere. From an ecological perspective, plant water storage and use contributes to determining the rate and time scales at which water plants can support function. Conceptualized as residence time, the relationship between plant water storage and use can provide fundamental insights into ecohydrology. We explore the spatial variation in the aboveground storage, use, and residence time of water across the Amazon. To do so, we pair estimates of aboveground woody biomass from 413 1-ha old growth forest census plots situated across the Amazon Basin with high resolution estimates of intra- and inter- annual evapotranspiration derived from remote sensing. Aboveground water storage capacity (17.4 ± 6.3 mm) and evapotranspiration (3.7 ± 0.4 mm day-1) result in a residence time of 4.7 ± 1.5 days, equivalent to the use of ca. 24% of stored water day-1. The results indicate that residence time varies due to a predictable relationship between evapotranspiration and biomass at local, regional and landscape scales. The ecohydrology of the Amazon plays a critical role in water and carbon cycling on a global scale. We discuss how our results can help inform our understanding of both the hydrology and ecology of the Amazon Basin in the context of anthropogenic change.

  3. Radiochemical constraints on the crustal residence time of submarine hydrothermal fluids: Endeavour Ridge

    SciTech Connect

    Kadko, D. ); Moore, W. )

    1988-03-01

    The {sup 210}Pb/Pb and {sup 228}Ra/{sup 226}Ra ratios measured in fluids and particles venting from the Endeavour Ridge are used to constrain the crustal residence time of the convecting hydrothermal fluid from the initiation of basalt alteration where Mg{sup +2} loss from seawater results in rapidly falling pH conditions, to termination at seafloor venting. The {sup 210}Pb/Pb ratios of hot, low Mg fluids are close to that of the basalts, suggesting a residence time of no greater than ten years. Particles associated with these vents have slightly higher ratios which may in part be due to scavenging of seawater {sup 210}Pb. The {sup 228}Ra/{sup 226}Ra ratios of the fluids and an associated Ba-rich particle samples were also close to the basalt ratios, further constraining the residence time to 3 years or less. These estimates indicate that the mass of fluid interacting with newly formed crust at any one time is less than 9 x 10{sup 13}kg, if the axial heat flux is to be no greater than 30% of the total advective heat loss from the oceanic crust.

  4. Towards the reliable calculation of residence time for off-lattice kinetic Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Alexander, Kathleen C.; Schuh, Christopher A.

    2016-08-01

    Kinetic Monte Carlo (KMC) methods have the potential to extend the accessible timescales of off-lattice atomistic simulations beyond the limits of molecular dynamics by making use of transition state theory and parallelization. However, it is a challenge to identify a complete catalog of events accessible to an off-lattice system in order to accurately calculate the residence time for KMC. Here we describe possible approaches to some of the key steps needed to address this problem. These include methods to compare and distinguish individual kinetic events, to deterministically search an energy landscape, and to define local atomic environments. When applied to the ground state  ∑5(2 1 0) grain boundary in copper, these methods achieve a converged residence time, accounting for the full set of kinetically relevant events for this off-lattice system, with calculable uncertainty.

  5. Method for Making Measurements of the Post-Combustion Residence Time in a Gas Turbine Engine

    NASA Technical Reports Server (NTRS)

    Miles, Jeffrey H (Inventor)

    2015-01-01

    A system and method of measuring a residence time in a gas-turbine engine is provided, whereby the method includes placing pressure sensors at a combustor entrance and at a turbine exit of the gas-turbine engine and measuring a combustor pressure at the combustor entrance and a turbine exit pressure at the turbine exit. The method further includes computing cross-spectrum functions between a combustor pressure sensor signal from the measured combustor pressure and a turbine exit pressure sensor signal from the measured turbine exit pressure, applying a linear curve fit to the cross-spectrum functions, and computing a post-combustion residence time from the linear curve fit.

  6. Residence Times of Receptors in Dendritic Spines Analyzed by Stochastic Simulations in Empirical Domains

    PubMed Central

    Hoze, Nathanael; Holcman, David

    2014-01-01

    Analysis of high-density superresolution imaging of receptors reveals the organization of dendrites at nanoscale resolution. We present here an apparently novel method that uses local statistics extracted from short-range trajectories for the simulations of long-range trajectories in empirical live cell images. Based on these empirical simulations, we compute the residence time of a receptor in dendritic spines that accounts for receptors’ local interactions and geometrical membrane organization. We report here that depending on the type of the spine, the residence time varies from 1 to 5 min. Moreover, we show that there exists transient organized structures, previously described as potential wells that can regulate the trafficking of receptors to dendritic spine: the simulation results suggest that receptor trafficking is regulated by transient structures. PMID:25517165

  7. Experimental study and verification of the residence time distribution using fluorescence spectroscopy and color measurement

    NASA Astrophysics Data System (ADS)

    Aigner, Michael; Lepschi, Alexander; Aigner, Jakob; Garmendia, Izaro; Miethlinger, Jürgen

    2015-05-01

    We report on the inline measurement of residence time (RT) and residence time distribution (RTD) by means of fluorescence spectroscopy [1] and optical color measurements [2]. Measurements of thermoplastics in a variety of single-screw extruders were conducted. To assess the influence of screw configurations, screw speeds and mass throughput on the RT and RTD, tracer particles were introduced into the feeding section and the RT was measured inline in the plasticization unit. Using special measurement probes that can be inserted into 1/2″ - 20 UNF (unified fine thread) bore holes, the mixing ability of either the whole plasticization unit or selected screw regions, e.g., mixing parts, can be validated during the extrusion process. The measurement setups complement each other well, and their combined use can provide further insights into the mixing behavior of single-screw plasticization units.

  8. Use of simultaneous radionuclide and other trace constituent measurements to determine fluxes and atmospheric residence times

    NASA Technical Reports Server (NTRS)

    Kritz, Mark

    1985-01-01

    Finding a way to use atmospheric concentrations to determine source strengths and atmospheric residence times pose considerable difficulties. An approach is to use simultaneously measured radionuclide concentrations as a means of deriving fluxes and residence times for certain atmospheric trace constituents of interest. The study and use of such methods in a pilot field experiment were among the original goals of this program. Four such approaches were studied or developed; suitable sampling and analysis systems were built and tested or are in the final stages of construction; and a small scale field experiment. The evolution is reviewed of the program and the field experiment is described along with the possibilities for its eventual extension to include other species of interest. The four radionuclide based approaches studied are: Mean vertical profiles; Trajectory correlation; Boundary layer discontinuity; and Lead deposition.

  9. An overview of oil palm biomass torrefaction: Effects of temperature and residence time

    NASA Astrophysics Data System (ADS)

    Yaacob, N.; Rahman, N. A.; Matali, S.; Idris, S. S.; Alias, A. B.

    2016-06-01

    Biomass is characterized as high moisture content, low bulk and energy density, possesses hygroscopic behaviour and poor grindability material as compared to the superior coal. A thermal treatment called torrefaction is a heating of biomass in a temperature range between 200°C to 300°C under inert atmosphere in order to upgrade biomass properties. Torrefied biomass has many similar characteristics to coal such as low moisture content, high bulk and energy density, hydrophobic and good grindability. This paper reviews the effects of oil palm biomass torrefaction in terms of temperature and residence time. This is because comprehensive studies on torrefaction parameters need to be carried out since different parameters might affect the chemical and physical characteristic of the torrefied product. Hence, this paper aims to discuss the effects of different torrefaction temperature and residence time towards physicochemical characteristic, mass and energy yield as well as calorific value of torrefied oil palm biomass.

  10. Acute air pollution-related symptoms among residents in Chiang Mai, Thailand.

    PubMed

    Wiwatanadate, Phongtape

    2014-01-01

    Open burnings (forest fires, agricultural, and garbage burnings) are the major sources of air pollution in Chiang Mai, Thailand. A time series prospective study was conducted in which 3025 participants were interviewed for 19 acute symptoms with the daily records of ambient air pollutants: particulate matter less than 10 microm in size (PM10), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and ozone (O3). PM10 was positively associated with blurred vision with an adjusted odds ratio (OR) of 1.009. CO was positively associated with lower lung and heart symptoms with adjusted ORs of 1.137 and 1.117. NO2 was positively associated with nosebleed, larynx symptoms, dry cough, lower lung symptoms, heart symptoms, and eye irritation with the range of adjusted ORs (ROAORs) of 1.024 to 1.229. SO2 was positively associated with swelling feet, skin symptoms, eye irritation, red eyes, and blurred vision with ROAORs of 1.205 to 2.948. Conversely, O3 was negatively related to running nose, burning nose, dry cough, body rash, red eyes, and blurred vision with ROAORs of 0.891 to 0.979. PMID:24645417

  11. Indoor air quality, ventilation and respiratory health in elderly residents living in nursing homes in Europe.

    PubMed

    Bentayeb, Malek; Norback, Dan; Bednarek, Micha; Bernard, Alfred; Cai, Guihong; Cerrai, Sonia; Eleftheriou, Konstantinos Kostas; Gratziou, Christina; Holst, Gitte Juel; Lavaud, François; Nasilowski, Jacek; Sestini, Piersante; Sarno, Giuseppe; Sigsgaard, Torben; Wieslander, Gunilla; Zielinski, Jan; Viegi, Giovanni; Annesi-Maesano, Isabella

    2015-05-01

    Few data exist on respiratory effects of indoor air quality and comfort parameters in the elderly. In the context of the GERIE study, we investigated for the first time the relationships of these factors to respiratory morbidity among elderly people permanently living in nursing homes in seven European countries. 600 elderly people from 50 nursing homes underwent a medical examination and completed a standardised questionnaire. Air quality and comfort parameters were objectively assessed in situ in the nursing home. Mean concentrations of air pollutants did not exceed the existing standards. Forced expiratory volume in 1 s/forced vital capacity ratio was highly significantly related to elevated levels of particles with a 50% cut-off aerodynamic diameter of <0.1 µm (PM0.1) (adjusted OR 8.16, 95% CI 2.24-29.3) and nitrogen dioxide (aOR 3.74, 95% CI 1.06-13.1). Excess risks for usual breathlessness and cough were found with elevated PM10 (aOR 1.53 (95% CI 1.15-2.07) and aOR 1.73 (95% CI 1.17-10.3), respectively) and nitrogen dioxide (aOR 1.58 (95% CI 1.15-2.20) and aOR 1.56 (95% CI 1.03-2.41), respectively). Excess risks for wheeze in the past year were found with PM0.1 (aOR 2.82, 95% CI 1.15-7.02) and for chronic obstructive pulmonary disease and exhaled carbon monoxide with formaldehyde (aOR 3.49 (95% CI 1.17-10.3) and aOR 1.25 (95% CI 1.02-1.55), respectively). Breathlessness and cough were associated with higher carbon dioxide. Relative humidity was inversely related to wheeze in the past year and usual cough. Elderly subjects aged ≥80 years were at higher risk. Pollutant effects were more pronounced in the case of poor ventilation. Even at low levels, indoor air quality affected respiratory health in elderly people permanently living in nursing homes, with frailty increasing with age. The effects were modulated by ventilation. PMID:25766977

  12. Eulerian and Lagrangian Measurements of Water Flow and Residence Time in a Fringing Coral Reef Embayment

    NASA Astrophysics Data System (ADS)

    Storlazzi, C. D.; Messina, A. M.; Cheriton, O. M.; Biggs, T. W.

    2014-12-01

    Hydrodynamic processes on coral reefs are important for nutrient cycling, larval dispersal, temperature variability, and understanding the impacts of terrestrial sediment, nutrients, and contaminants from adjacent impaired watersheds on coral reef ecosystems. Our goal was to understand the spatial and temporal variability in flow velocities and the associated residence time of water in the fringing coral reef flat-lined embayment of Faga'alu, on the island of Tutuila in American Samoa. To accomplish this, data from three bottom-mounted acoustic current profilers and 102 individual Lagrangian ocean surface current drifter deployments (5 drifters x 21 deployments) were combined with meteorologic data and numerical wave model results. These data and model results, collected over nine days, made it possible to evaluate the relative contribution of tidal, wind, and wave forcing on the flow patterns. The high number of drifter deployments made it possible for the velocity data to be binned into 100 m x 100 m grid cells and the resulting residence times computed for the different sets of forcing conditions. Cumulative progressive vectors calculated from the acoustic current profilers closely matched the tracks from concurrently deployed surface current drifters, showing the applicability of this hybrid Lagrangian-Eulerian measurement scheme to understand flow patterns in this geomorphically complex embayment. The bay-wide man current speeds (residence times) varied from 1-37 cm/s (2.78-0.08 hr), 1-36 cm/s (2.78-0.08 hr), and 5-64 cm/s (0.56-0.04 hr) under tidal, wind, and wave forcing, respectively; the highest speeds (shortest residence times) were measured on the outer reef flat closest to where waves were breaking on the reef crest and were slowest (longest) over the inner reef flat close to shore and deep in the embayment.

  13. New residence times of the Holocene reworked shells on the west coast of Bohai Bay, China

    NASA Astrophysics Data System (ADS)

    Shang, Zhiwen; Wang, Fu; Li, Jianfen; Marshall, William A.; Chen, Yongsheng; Jiang, Xingyu; Tian, Lizhu; Wang, Hong

    2016-01-01

    Shelly cheniers and shell-rich beds found intercalated in near-shore marine muds and sandy sediments can be used to indicate the location of ancient shorelines, and help to estimate the height of sea level. However, dating the deposition of material within cheniers and shell-rich beds is not straightforward because much of this material is transported and re-worked, creating an unknown temporal off-set, i.e., the residence time, between the death of a shell and its subsequent entombment. To quantify the residence time during the Holocene on a section of the northern Chinese coastline a total 47 shelly subsamples were taken from 17 discrete layers identified on the west coast of Bohai Bay. This material was AMS 14C dated and the calibrated ages were systematically compared. The subsamples were categorized by type as articulated and disarticulated bivalves, gastropod shells, and undifferentiated shell-hash. It was found that within most individual layers the calibrated ages of the subsamples got younger relative to the amount of apparent post-mortem re-working the material had been subject to. For examples, the 14C ages of the bivalve samples trended younger in this order: shell-hash → split shells → articulated shells. We propose that the younger subsample age determined within an individual layer will be the closest to the actual depositional age of the material dated. Using this approach at four Holocene sites we find residence times which range from 100 to 1260 cal yrs, with two average values of 600 cal yrs for the original 14C dates older than 1 ka cal BP and 100 cal yrs for the original 14C dates younger than 1 ka cal BP, respectively. Using this semi-empirical estimation of the shell residence times we have refined the existing chronology of the Holocene chenier ridges on the west coast of Bohai Bay.

  14. Tracing time scales of fluid residence and migration in the crust (Invited)

    NASA Astrophysics Data System (ADS)

    Yokochi, R.; Sturchio, N. C.; Purtschert, R.; Jiang, W.; Lu, Z.; Müller, P.; Yang, G.; Kennedy, B. M.

    2013-12-01

    Crustal fluids (water, gas and oil) mediate chemical reactions, and they may transport, concentrate or disperse elements in the crust; the fluids are often valuable resources in their own right. In this context, determining the time scales of fluid transport and residence time is essential for understanding geochemical cycle of elements, as well as risk and resource management. Crustal fluids contain stable and radioactive noble gases indigenous to the fluid, which may be of magmatic or atmospheric origin of various ages. In addition, radiogenic and nucleogenic noble gases (both stable and radioactive) are continuously produced by the decay of U, Th and K and related nuclear reactions in the crust at known rates and in known relative proportions. They may be released from their production sites and incorporated into the fluid, acting as natural spikes to trace fluid flow. The concentrations of a noble gas isotope in a crustal fluid in a system devoid of phase separation or mixing varies as a function of decay time and supply from the production sites into the fluids. The release rate of noble gases from the production sites in minerals to the fluid phase may be determined uniquely through the studies of noble gas radionuclides (Yokochi et al., 2012), which is fundamental to the behavior of volatile elements in geochemistry. A pilot study of noble gas radionuclides in an active geothermal system was performed at Yellowstone National Park (Yokochi et al., 2013). Prior studies of the Yellowstone system using stable noble gas isotopes show that the thermal fluids contain a mixture of atmospheric, mantle, and crustal components. Noble gas radionuclide measurements provide new chronometric constraints regarding the subsurface residence times of Yellowstone thermal fluids. Upper limits on deep thermal fluid mean residence times, estimated from 39Ar/40Ar* ratios, range from 118 to 137 kyr for features in the Gibbon and Norris Geyser Basin areas, and are about 16 kyr in

  15. Fertilizer residence time affects nitrogen uptake efficiency and growth of sweet corn.

    PubMed

    Zotarelli, L; Scholberg, J M; Dukes, M D; Muñoz-Carpena, R

    2008-01-01

    Understanding plant N uptake dynamics is critical for increasing fertilizer N uptake efficiency (FUE) and minimize the risk of N leaching. The objective of this research was to determine the effect of residence time of N fertilizer on N uptake and FUE of sweet corn. Plants were grown in 25 L columns during the fall and spring to mimic short-term N uptake dynamics. Nitrogen was applied either 1, 3, or 7 d before a weekly leaching event, using KNO3 solution (total of 393 kg N ha(-1)). Residence times (tR) were tR-1, tR-3, and tR-7 d before weekly removal of residual soil N. Plant N uptake was calculated by comparing weekly N recovery from planted with non-planted columns. During the fall, N uptake values at 70 d after emergence were 59, 73, and 126 kg N ha(-1). During the spring, corresponding values were 54, 108, and 159 kg N ha(-1). A linear response of plant growth and yield to the tR was observed under cooler conditions, whereas a quadratic response occurred under warmer conditions. There was correlation between root length density and yield. It is concluded that increasing N fertilizer residence time, which is indicative of better irrigation practices, enhanced overall sweet corn growth, yield, N uptake, and FUE, consequently reduced the risk of N being leached below the root zone before complete N uptake. PMID:18453447

  16. Influence of the gas and particle residence time on fast pyrolysis of lignite

    SciTech Connect

    Cui, L.J.; Song, W.L.; Zhang, J.Y.; Yao, J.Z.; Lin, W.G.

    2007-06-15

    Coal resource is abundant in China, while the reserves of natural gas and petroleum are limited. Due to the rapid increase in the number of automobiles, a competitive way to produce liquid fuels from coal is urgently needed in China. A so-called 'coal topping process' is under development at the Institute of Process Engineering, Chinese Academy of Sciences, from which liquid products can be obtained by flash pyrolysis in an integrated circulating fluidized bed system. In order to achieve a high yield of liquid products from high volatile coal, controlling the residence time of coal particles and produced gas may be of importance for minimizing the degree of the secondary reactions; i.e., polymerization and cracking of the liquid products. Experiments of the flash pyrolysis of coal have been conducted in an entrained bed reactor which is especially designed to study the influence of the coal particle residence time on the product distribution. The results show that the gaseous, liquid, and solid product distribution, the gas compositions as well as the liquid compositions depend strongly on the gas and particle residence time.

  17. Discovery of novel Jak2-Stat pathway inhibitors with extended residence time on target.

    PubMed

    Guan, Huiping; Lamb, Michelle L; Peng, Bo; Huang, Shan; Degrace, Nancy; Read, Jon; Hussain, Syeed; Wu, Jiaquan; Rivard, Caroline; Alimzhanov, Marat; Bebernitz, Geraldine; Bell, Kirsten; Ye, Minwei; Zinda, Michael; Ioannidis, Stephanos

    2013-05-15

    The discovery of the activating mutation V617F in the JH2 domain of Jak2 and the modulation of oncogenic Stat3 by Jak2 inhibitors have spurred a great interest in the inhibition of the Jak2/Stat pathway in oncology. In this Letter, we communicate the discovery of novel inhibitors of the Jak2/Stat5 axis, the N-(1H-pyrazol-3-yl)pyrimidin-2-amino derivatives. The rationale, synthesis and biological evaluation of these derivatives are reported. Two lead analogs from this series, 6 and 9, displayed prolonged residence time on Jak2, at enzymatic level. Although 6 and 9 exhibited moderate selectivity in a selected kinase panel, we chose to test these inhibitors in vivo as a consequence to their long residence time. However, extended inhibition of Jak2 due to the long residence time, in the form of inhibiting phosphorylation of downstream Stat5, was not recapitulated in an in vivo setting. PMID:23562594

  18. SIMPLIFIED MODELING OF AIR FLOW DYNAMICS IN SSD RADON MITIGATION SYSTEMS FOR RESIDENCES WITH GRAVEL BEDS

    EPA Science Inventory

    In an attempt to better understand the dynamics of subslab air flow, the report suggests that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained between two impermeable disks. (NOTE: Many subslab depressurization syste...

  19. Groundwater Residence Times: A Key Parameter for Investigating Effects of River Restoration on Riverbank Filtration

    NASA Astrophysics Data System (ADS)

    Vogt, Tobias; Hoehn, Eduard; Schneider, Philipp; Schirmer, Mario; Cirpka, Olaf A.

    2010-05-01

    Many Swiss municipal pumping wells, located near the banks of a losing river, are designed to capture a mixture of freshly infiltrated river water and old alluvial groundwater. Riverbank filtration is assumed to substantially reduce concentrations of pathogens, pesticides, and organic pollutants relative to the river water. Although the number of river restoration projects increases, the effects of river restoration on riverbank filtration are still not well understood. River restoration includes widening of the riverbed and removal of bank armoring in order to establish a more natural sediment transport regime and give the river more space. These measures improve ecological habitat diversity and contribute to flood protection. However, they may cause conflicts with groundwater abstraction for drinking water, because travel times from rivers to pumping stations may be significantly reduced. In Switzerland the minimum mean travel time required for the protection of a drinking-water well is 10 days. Thus, for detailed investigation on river water infiltration into the aquifer, the distribution of groundwater travel times from rivers to observation and production wells and mixing ratios of freshly infiltrated and older alluvial groundwater are key parameters. Due to the high hydraulic conductivity of most Swiss prealpine gravel aquifers, the residence time of water entering many pumping wells is the range of weeks. Therefore, special methods are needed to assess residence times of young groundwater. We analyze time series of electrical conductivity in the river and adjacent groundwater observation wells to investigate travel times of young hyporheic groundwater in adjoining channelized and restored sections of the River Thur in North-East Switzerland. The test site has been established by the RECORD Project (Assessment and Modeling of Coupled Ecological and Hydrological Dynamics in the Restored Corridor of a River (Restored Corridor Dynamics)). To quantify residence

  20. Probabilistic approach of water residence time and connectivity using Markov chains with application to tidal embayments

    NASA Astrophysics Data System (ADS)

    Bacher, C.; Filgueira, R.; Guyondet, T.

    2016-01-01

    Markov chain analysis was recently proposed to assess the time scales and preferential pathways into biological or physical networks by computing residence time, first passage time, rates of transfer between nodes and number of passages in a node. We propose to adapt an algorithm already published for simple systems to physical systems described with a high resolution hydrodynamic model. The method is applied to bays and estuaries on the Eastern Coast of Canada for their interest in shellfish aquaculture. Current velocities have been computed by using a 2 dimensional grid of elements and circulation patterns were summarized by averaging Eulerian flows between adjacent elements. Flows and volumes allow computing probabilities of transition between elements and to assess the average time needed by virtual particles to move from one element to another, the rate of transfer between two elements, and the average residence time of each system. We also combined transfer rates and times to assess the main pathways of virtual particles released in farmed areas and the potential influence of farmed areas on other areas. We suggest that Markov chain is complementary to other sets of ecological indicators proposed to analyse the interactions between farmed areas - e.g., depletion index, carrying capacity assessment. Markov chain has several advantages with respect to the estimation of connectivity between pair of sites. It makes possible to estimate transfer rates and times at once in a very quick and efficient way, without the need to perform long term simulations of particle or tracer concentration.

  1. An influential factor for external radiation dose estimation for residents after the Fukushima Daiichi Nuclear Power Plant accident-time spent outdoors for residents in Iitate Village.

    PubMed

    Ishikawa, Tetsuo; Yasumura, Seiji; Ohtsuru, Akira; Sakai, Akira; Akahane, Keiichi; Yonai, Shunsuke; Sakata, Ritsu; Ozasa, Kotaro; Hayashi, Masayuki; Ohira, Tetsuya; Kamiya, Kenji; Abe, Masafumi

    2016-06-01

    Many studies have been conducted on radiation doses to residents after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Time spent outdoors is an influential factor for external dose estimation. Since little information was available on actual time spent outdoors for residents, different values of average time spent outdoors per day have been used in dose estimation studies on the FDNPP accident. The most conservative value of 24 h was sometimes used, while 2.4 h was adopted for indoor workers in the UNSCEAR 2013 report. Fukushima Medical University has been estimating individual external doses received by residents as a part of the Fukushima Health Management Survey by collecting information on the records of moves and activities (the Basic Survey) after the accident from each resident. In the present study, these records were analyzed to estimate an average time spent outdoors per day. As an example, in Iitate Village, its arithmetic mean was 2.08 h (95% CI: 1.64-2.51) for a total of 170 persons selected from respondents to the Basic Survey. This is a much smaller value than commonly assumed. When 2.08 h is used for the external dose estimation, the dose is about 25% (23-26% when using the above 95% CI) less compared with the dose estimated for the commonly used value of 8 h. PMID:27034103

  2. Assessment of air quality at neighbor residences in the vicinity of swine production facilities.

    PubMed

    Donham, Kelley J; Lee, Joung Ae; Thu, Kendall; Reynolds, Stephen J

    2006-01-01

    Air sampling was completed on the front lawn of 35 homes neighboring swine farms in three different regions in the Upper Midwest of the United States. One region was dominated by large scale, swine confined animal feeding operations (CAFO's) noted as swine confinement area (SCA). The second area was dominated by smaller scale operations utilizing hoop structure facilities (HA). The third area was basically devoid of livestock, dominated by row-crop production, and served as the control area (CA). The time weighted average concentrations of hydrogen sulfide (8.42 ppb) was higher (p = 0.047) in SCA area than the control (3.48 ppb). However, carbon dioxide (449.6 ppm), ammonia (12.78 ppb) and PM10 (42.25 microg/m3) were higher in the hoop structure area than the other areas. Swine population density, distance between the homes and swine facilities, and wind direction had an interactive effect on the average levels of ammonia (p = 0.04). The contaminant levels at the homes were relatively low compared to typical concentrations inside animal buildings. However, exceedences of federal recommended limits for hydrogen sulfide in outdoor air were observed in the swine CAFO area. Concentration of hydrogen sulfide exceeded the recommended limits of the ATSDR (30 ppb) for chronic exposure at two of the 12 homes in the CAFO area (17%). Average hydrogen sulfide concentration exceeded the EPA recommended community standards (0.7 ppb) in all three areas assessed (SCA, HA, and CA). As chronic exposure to hydrogen sulfide may be present in areas of production agriculture, a potential health risk may be present. Further studies to provide additional information regarding exposures to hydrogen sulfide in rural environments are warranted. PMID:19274894

  3. Air Change Rates and Interzonal Flows in Residences, and the Need for Multi-Zone Models for Exposure and Health Analyses

    PubMed Central

    Du, Liuliu; Batterman, Stuart; Godwin, Christopher; Chin, Jo-Yu; Parker, Edith; Breen, Michael; Brakefield, Wilma; Robins, Thomas; Lewis, Toby

    2012-01-01

    Air change rates (ACRs) and interzonal flows are key determinants of indoor air quality (IAQ) and building energy use. This paper characterizes ACRs and interzonal flows in 126 houses, and evaluates effects of these parameters on IAQ. ACRs measured using weeklong tracer measurements in several seasons averaged 0.73 ± 0.76 h−1 (median = 0.57 h−1, n = 263) in the general living area, and much higher, 1.66 ± 1.50 h−1 (median = 1.23 h−1, n = 253) in bedrooms. Living area ACRs were highest in winter and lowest in spring; bedroom ACRs were highest in summer and lowest in spring. Bedrooms received an average of 55 ± 18% of air from elsewhere in the house; the living area received only 26 ± 20% from the bedroom. Interzonal flows did not depend on season, indoor smoking or the presence of air conditioners. A two-zone IAQ model calibrated for the field study showed large differences in pollutant levels between the living area and bedroom, and the key parameters affecting IAQ were emission rates, emission source locations, air filter use, ACRs, interzonal flows, outdoor concentrations, and PM penetration factors. The single-zone models that are commonly used for residences have substantial limitations and may inadequately represent pollutant concentrations and exposures in bedrooms and potentially other environments other where people spend a substantial fraction of time. PMID:23235286

  4. Mineralogical Controls over Carbon Storage and Residence Times in Grassland Soils

    NASA Astrophysics Data System (ADS)

    Dwivedi, D.; Riley, W. J.; Torn, M. S.; Spycher, N.

    2014-12-01

    Globally, soil organic matter (SOM) contains approximately three times more carbon than the atmosphere and terrestrial vegetation contain combined. However, it is not well understood why some SOM persists for a long time while other SOM decomposes quickly. For future climate predictions, representing soil organic matter (SOM) dynamics accurately in Earth system models is essential. Soil minerals stabilize organic carbon in soil; however, there are gaps in our understanding of how soil mineralogy controls the quantity and turnover of long-residence-time organic carbon. To investigate the impact of soil mineralogy on SOM dynamics, we used a new model (Biotic and Abiotic Model of SOM—BAMS1 [Riley et al., 2014]) integrated with a three-dimensional, multiphase reactive transport solver (TOUGHREACT). The model represents bacterial and fungal activity, archetypal polymer and monomer carbon substrate groups, aqueous chemistry, gaseous diffusion, aqueous advection and diffusion, and adsorption and desorption processes. BAMS1 can predict bulk SOM and radiocarbon signatures without resorting to an arbitrary depth-dependent decline in SOM turnover rates. Results show a reasonable match between observed and simulated depth-resolved SOM and ∆14C in grassland ecosystems (soils formed on terraces south of Eureka, California, and the Central Chernozem Region of Russia) and were consistent with expectations of depth-resolved profiles of lignin content and fungi:aerobic bacteria ratios. Results also suggest that clay-mineral surface area and soil sorption coefficients constitute dominant controls over organic carbon stocks and residence times, respectively. Bibliography: Riley, W.J., F.M. Maggi, M. Kleber, M.S. Torn, J.Y. Tang, D. Dwivedi, and N. Guerry (2014), Long residence times of rapidly decomposable soil organic matter: application of a multi-phase, multi-component, and vertically resolved model (BAMS1) to soil carbon dynamics, Geoscientific Model Development, vol. 7, 1335

  5. The Role of Noble Gases in Defining the Mean Residence Times of Fluids within Precambrian Crustal Systems

    NASA Astrophysics Data System (ADS)

    Warr, O.; Sherwood Lollar, B.; Fellowes, J.; Sutcliffe, C. N.; McDermott, J. M.; Holland, G.; Mabry, J.; Ballentine, C. J.

    2015-12-01

    Brines rich in N2, H2, CH4 and He hosted within Precambrian crustal rocks are known to sustain microbial life [1]. The geological systems containing these brines have the potential to isolate organisms over planetary timescales and so can provide unique insight into the diversity and evolution of terrestrial life [1-3]. Long considered geological outliers, the prevalence of systems containing these ancient, deep fracture waters is only now being revealed. Recent studies demonstrate the Precambrian crust which accounts for ~70% of total crustal surface area has a global hydrogen production comparable to marine systems [2]. In addition to H2-producing reactions (e.g. radiolysis and serpentinization), a diversity of CH4-producing reactions also occur in these systems through both microbial and water-rock interactions [1, 2]. However, the role these Precambrian systems have in global hydrogen and carbon cycles is poorly understood. For this we need good constraints on the origins, residence times and degree of microbial activity of the fluids within these systems as well as the degree of interaction with external systems. Fortunately, noble gases are ideal for this role [1,3]. Previous noble gas analysis of N2, H2, CH4 and He-rich fluid samples collected at 2.4 km depth from a Cu-Zn mine in Timmins, Ontario, identified isolated fracture fluids with the oldest residence times ever observed (>1.1 Ga) [3]. This study has been significantly expanded now to fluids from an even greater depth (3 km) at Timmins, and from two new mines in the Sudbury Basin. Preliminary data from the deeper Timmins level indicate a new closed system with 136Xe/130Xe ratios 93% above modern air values (20% at 2.4 km) and an early atmosphere 124Xe/130Xe signal approaching the age of the host rock (~2.7 Ga) [4]. In comparison, the Sudbury system indicates exchange with an external source, being highly enriched in helium (30% gas volume) but with a low fissiogenic 136Xe/130Xe excess (10-38% above

  6. Burnout and training satisfaction of medical residents in Greece: will the European Work Time Directive make a difference?

    PubMed Central

    2010-01-01

    Background The aim of this study is to determine the prevalence of burnout in Greek medical residents, investigate its relationship with training satisfaction during residency and survey Greek medical residents' opinion towards the European Work Time Directive (EWTD). Methods A Multi-centre, cross-sectional survey of Greek residents was performed. The Maslach Burnout Inventory (MBI) was used to measure burnout, which was defined as high emotional exhaustion, combined with high depersonalization or low personal accomplishment. In addition, seven questions were designed for this study to evaluate self-reported resident training satisfaction and three questions queried residents' opinion on the EWTD and its effects on their personal and social life as well as their medical training. Univariate, bivariate and multivariate statistical models were used for the evaluation of data. Results Out of 311 respondents (77.8% response rate), 154 (49.5%) met burnout criteria and 99 (31.8%) indicated burnout on all three subscale scores. The number of residents that were dissatisfied with the overall quality of their residency training were 113 individuals (36.3%). Only 32 residents (10.3%) believed that the EWTD implementation will not have any beneficial effects for them. Conclusions Both burnout and training dissatisfaction were common among Greek residents. Systemic interventions are thus required within the Greek health system, aimed at reducing resident impairment due to burnout and at improving their educational and professional perspectives. Although residents' opinion on the EWTD was not associated with burnout levels, the EWTD was found to be predominantly supported and anticipated by Greek residents and should be implemented to alleviate their workload and stress. PMID:20594310

  7. Predicting mean residence time and exchange velocity in the hyporheic zone of restored streams

    NASA Astrophysics Data System (ADS)

    Morén, Ida; Wörman, Anders; Riml, Joakim

    2016-04-01

    The hyporheic zones of streams and rivers have been identified as hotspots for biogeochemical reactions in the aquatic environment, making the retention time and exchange velocity of the hyporheic zone essential parameters in the modelling of these processes. However, exact site-specific values of those parameters are often missing in stream restoration projects because there are no well-defined scaling relationships linking them to measurable reach characteristics. In this study we derive semi-analytical solutions for the retention time and exchange velocity in the hyporheic zone. In particular the effect on hyporheic exchange is expressed by the use of physically based models and by superimposing different geomorphologic features of different scales. It is suggested that all exchange phenomena can be modelled as head anomalies expressed with a harmonic distribution along the stream with specific wavelength and head amplitude. The maximum head of an exchange phenomena is either dominated by hydrodynamic or hydrostatic water pressure, depending on the size of the feature causing the exchange. The theory leads to constitutive relationships for exchange velocity and residence time expressed as functions of the distribution of wavelengths, distribution of head amplitude and hydraulic conductivity. In order to validate and evaluate certain empirical coefficients, a number of Rhodamine WT tracer tests were performed in a partly restored agricultural stream in the south of Sweden called the Tullstorps brook. To evaluate the tracer test in sections where remediation actions have been undertaken we used the method of temporal moments. In conjunction with the tracer tests a characterisation of the stream was carried out where hydraulic conductivity of the streambed and stream morphology was measured. The study verifies that the residence time in the hyporheic zone decreases with the maximum hydraulic head of the largest (dominating) geomorphic feature of the reach, and

  8. A contaminant transport model for wetlands accounting for distinct residence time bimodality

    NASA Astrophysics Data System (ADS)

    Musner, T.; Bottacin-Busolin, A.; Zaramella, M.; Marion, A.

    2014-07-01

    Vegetation plays a major role in controlling the fate of contaminants in natural and constructed wetlands. Estimating the efficiency of contaminant removal of a wetland requires separate knowledge of the residence time statistics in the main flow channels, where the flow velocity is relatively higher, and in the more densely vegetated zones, where the velocity is smaller and most of the biochemical transformations occur. A conceptual wetland characterized by a main flow channel (MFC) and lateral vegetated zones (LVZs) is modeled here using a two-dimensional depth-averaged hydrodynamic and advection-dispersion model. The effect of vegetation is described as a flow resistance represented in the hydrodynamic model as a function of the stem density. Simulations are performed for a given flow discharge and for increasing values of the ratio between the vegetation density in the LVZs and in the MFC. Residence time distributions (RTDs) of a nonreactive tracer are derived from numerical simulations of the solute breakthrough curves (BTCs) resulting from a continuous concentration input. Results show that increasing vegetation densities produce an increasingly pronounced bimodality of the RTDs. At longer times, the RTDs decrease exponentially, with different timescales depending on the stem density ratio and other system parameters. The overall residence time distribution can be decomposed into a first component associated with the relatively fast transport in the MFC, and a second component associated with the slower transport in the LVZs. The weight of each temporal component is related to the exchange flux at the MFC-LVZ interface. A one-dimensional transport model is proposed that is capable to reproduce the RTDs predicted by the depth-averaged model, and the relationship between model and system parameters is investigated using a combination of direct and inverse modeling approaches.

  9. Noble gas residence times of saline waters within crystalline bedrock, Outokumpu Deep Drill Hole, Finland

    NASA Astrophysics Data System (ADS)

    Kietäväinen, Riikka; Ahonen, Lasse; Kukkonen, Ilmo T.; Niedermann, Samuel; Wiersberg, Thomas

    2014-11-01

    Noble gas residence times of saline groundwaters from the 2516 m deep Outokumpu Deep Drill Hole, located within the Precambrian crystalline bedrock of the Fennoscandian Shield in Finland, are presented. The accumulation of radiogenic (4He, 40Ar) and nucleogenic (21Ne) noble gas isotopes in situ together with the effects of diffusion are considered. Fluid samples were collected from depths between 180 and 2480 m below surface, allowing us to compare the modelled values with the measured concentrations along a vertical depth profile. The results show that while the concentrations in the upper part are likely affected by diffusion, there is no indication of diffusive loss at or below 500 m depth. Furthermore, no mantle derived gases were found unequivocally. Previous studies have shown that distinct vertical variation occurs both in geochemistry and microbial community structuring along the drill hole, indicating stagnant waters with no significant exchange of fluids between different fracture systems or with surface waters. Therefore in situ accumulation is the most plausible model for the determination of noble gas residence times. The results show that the saline groundwaters in Outokumpu are remarkably old, with most of the samples indicating residence times between ∼20 and 50 Ma. Although being first order approximations, the ages of the fluids clearly indicate that their formation must predate more recent events, such as Quaternary glaciations. Isolation within the crust since the Eocene-Miocene epochs has also direct implications to the deep biosphere found at Outokumpu. These ecosystems must have been isolated for a long time and thus very likely rely on energy and carbon sources such as H2 and CO2 from groundwater and adjacent bedrock rather than from the ground surface.

  10. Geometrical effects on the electron residence time in semiconductor nano-particles

    SciTech Connect

    Koochi, Hakimeh; Ebrahimi, Fatemeh

    2014-09-07

    We have used random walk (RW) numerical simulations to investigate the influence of the geometry on the statistics of the electron residence time τ{sub r} in a trap-limited diffusion process through semiconductor nano-particles. This is an important parameter in coarse-grained modeling of charge carrier transport in nano-structured semiconductor films. The traps have been distributed randomly on the surface (r{sup 2} model) or through the whole particle (r{sup 3} model) with a specified density. The trap energies have been taken from an exponential distribution and the traps release time is assumed to be a stochastic variable. We have carried out (RW) simulations to study the effect of coordination number, the spatial arrangement of the neighbors and the size of nano-particles on the statistics of τ{sub r}. It has been observed that by increasing the coordination number n, the average value of electron residence time, τ{sup ¯}{sub r} rapidly decreases to an asymptotic value. For a fixed coordination number n, the electron's mean residence time does not depend on the neighbors' spatial arrangement. In other words, τ{sup ¯}{sub r} is a porosity-dependence, local parameter which generally varies remarkably from site to site, unless we are dealing with highly ordered structures. We have also examined the effect of nano-particle size d on the statistical behavior of τ{sup ¯}{sub r}. Our simulations indicate that for volume distribution of traps, τ{sup ¯}{sub r} scales as d{sup 2}. For a surface distribution of traps τ{sup ¯}{sub r} increases almost linearly with d. This leads to the prediction of a linear dependence of the diffusion coefficient D on the particle size d in ordered structures or random structures above the critical concentration which is in accordance with experimental observations.

  11. Characterization of Air Manganese Exposure Estimates for Residents in Two Ohio Towns

    EPA Science Inventory

    This study was conducted to derive receptor-specific outdoor exposure concentrations of total suspended particulate (TSP) and respirable (dae ≤1O µm) air manganese (air-Mn) for East Liverpool and Marietta (Ohio) in the absence of facility emissions data, but where long-t...

  12. Air conditioning in a tropical climate: Impacts upon European residents in Darwin, Australia

    NASA Astrophysics Data System (ADS)

    Auliciems, A.; Dedear, R.

    1986-09-01

    The efficacy of current practices in air conditioning is investigated in the two monsoonal seasons in Darwin. Assessment is made of atmospheric parameters, clothing, metabolic rate. Some 1000 questionnaires are applied dealing with adaptations, health perceptions and preferences as related to air cooling and ventilation. The findings are discussed with reference to energy balance calculations and current models of psychological control in thermoregulation. The results indicate that Darwin's population is considerably overcooled, and contrary to assumptions and practice, air conditioning is not desired in office buildings during the “Dry”. In the home, air conditioning is not regarded as essential. The indications are that a rationalization of air cooling to comply with natural variability in warmth would lead to a significant reduction in energy consumption, and an overall enhancement to the health and comfort of the population through the greater ventilation rates that would be economically feasible were design temperatures lifted.

  13. Groundwater residence times in Shenandoah National Park, Blue Ridge Mountains, Virginia, USA: A multi-tracer approach

    USGS Publications Warehouse

    Plummer, L.N.; Busenberg, E.; Böhlke, J.K.; Nelms, D.L.; Michel, R.L.; Schlosser, P.

    2001-01-01

    Chemical and isotopic properties of water discharging from springs and wells in Shenandoah National Park (SNP), near the crest of the Blue Ridge Mountains, VA, USA were monitored to obtain information on groundwater residence times. Investigated time scales included seasonal (wet season, April, 1996; dry season, August-September, 1997), monthly (March through September, 1999) and hourly (30-min interval recording of specific conductance and temperature, March, 1999 through February, 2000). Multiple environmental tracers, including tritium/helium-3 (3H/3He), chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), sulfur-35 (35S), and stable isotopes (??18O and ??2H) of water, were used to estimate the residence times of shallow groundwater discharging from 34 springs and 15 wells. The most reliable ages of water from springs appear to be based on SF6 and 3H/3He, with most ages in the range of 0-3 years. This range is consistent with apparent ages estimated from concentrations of CFCs; however, CFC-based ages have large uncertainties owing to the post-1995 leveling-off of the CFC atmospheric growth curves. Somewhat higher apparent ages are indicated by 35S (> 1.5 years) and seasonal variation of ??18O (mean residence time of 5 years) for spring discharge. The higher ages indicated by the 35S and ??18O data reflect travel times through the unsaturated zone and, in the case of 35S, possible sorption and exchange of S with soils or biomass. In springs sampled in April, 1996, apparent ages derived from the 3H/3He data (median age of 0.2 years) are lower than those obtained from SF6 (median age of 4.3 years), and in contrast to median ages from 3H/3He (0.3 years) and SF6 (0.7 years) obtained during the late summer dry season of 1997. Monthly samples from 1999 at four springs in SNP had SF6 apparent ages of only 1.2 to 2.5 ?? 0.8 years, and were consistent with the 1997 SF6 data. Water from springs has low excess air (0-1 cm3 kg-1) and N2-Ar temperatures that vary

  14. Air Pollution from Industrial Swine Operations and Blood Pressure of Neighboring Residents

    PubMed Central

    Horton, Rachel Avery; Rose, Kathryn M.

    2012-01-01

    Background: Industrial swine operations emit odorant chemicals including ammonia, hydrogen sulfide (H2S), and volatile organic compounds. Malodor and pollutant concentrations have been associated with self-reported stress and altered mood in prior studies. Objectives: We conducted a repeated-measures study of air pollution, stress, and blood pressure in neighbors of swine operations. Methods: For approximately 2 weeks, 101 nonsmoking adult volunteers living near industrial swine operations in 16 neighborhoods in eastern North Carolina sat outdoors for 10 min twice daily at preselected times. Afterward, they reported levels of hog odor on a 9-point scale and measured their blood pressure twice using an automated oscillometric device. During the same 2- to 3-week period, we measured ambient levels of H2S and PM10 at a central location in each neighborhood. Associations between systolic and diastolic blood pressure (SBP and DBP, respectively) and pollutant measures were estimated using fixed-effects (conditional) linear regression with adjustment for time of day. Results: PM10 showed little association with blood pressure. DBP [β (SE)] increased 0.23 (0.08) mmHg per unit of reported hog odor during the 10 min outdoors and 0.12 (0.08) mmHg per 1-ppb increase of H2S concentration in the same hour. SBP increased 0.10 (0.12) mmHg per odor unit and 0.29 (0.12) mmHg per 1-ppb increase of H2S in the same hour. Reported stress was strongly associated with BP; adjustment for stress reduced the odor–DBP association, but the H2S–SBP association changed little. Conclusions: Like noise and other repetitive environmental stressors, malodors may be associated with acute blood pressure increases that could contribute to development of chronic hypertension. PMID:23111006

  15. Residence time and movements of postbreeding shorebirds on the northern coast of Alaska

    USGS Publications Warehouse

    Taylor, Audrey R.; Lanctot, Richard B.; Powell, A.N.; Kendall, S.J.; Nigro, Debora A.

    2011-01-01

    Relatively little is known about shorebird movements across the coast of northern Alaska, yet postbreeding shorebirds use this coastline extensively prior to fall migration. We deployed 346 radio transmitters on 153 breeding and 193 postbreeding shorebirds of five species from 2005 to 2007.We examined two hypotheses regarding postbreeding shorebirds' movements: (1) whether such movements reflect ultimate routes of southbound migration and (2) whether migration strategy (length of flights) or timing of molt in relation to migration (molt occurring in breeding or winter range) are more influential in determining postbreeding shorebirds' behavior. Semipalmated Sandpipers (Calidris pusilla) moved east, consistent with the direction of their ultimate migration, but patterns of other species' movements did not reflect ultimate migration direction. Timing of postnuptial molt appeared to have more influence over residence time and movements than did migration strategy. Postcapture residence time for the Semipalmated Sandpiper was less than for the Western Sandpiper (C. mauri) and significantly less than for Dunlin (C. alpina), and the Semipalmated Sandpiper's movements between were quicker and more frequent than those of the Dunlin. We expected to see the opposite patterns if migration strategy were more influential. Our data shed light on how different shorebird species use the northern Alaska coast after breeding: most species are likely to be stopping over at postbreeding areas, whereas the Dunlin and some Western Sandpipers may be staging. We suggest the coast of northern Alaska be viewed as an interconnected network of postbreeding sites that serve multiple populations of breeding shorebirds. ?? The Cooper Ornithological Society 2011.

  16. Indoor air quality in 24 California residences designed as high-performance homes

    SciTech Connect

    Less, Brennan; Mullen, Nasim; Singer, Brett; Walker, Iain

    2015-01-01

    Today’s high performance green homes are reaching previously unheard of levels of airtightness and are using new materials, technologies and strategies, whose impacts on Indoor Air Quality (IAQ) cannot be fully anticipated from prior studies. This research study used pollutant measurements, home inspections, diagnostic testing and occupant surveys to assess IAQ in 24 new or deeply retrofitted homes designed to be high performance green buildings in California. Although the mechanically vented homes were six times as airtight as non-mechanically ventilated homes (medians of 1.1 and 6.1 ACH50, n=11 and n=8, respectively), their use of mechanical ventilation systems and possibly window operation meant their median air exchange rates were almost the same (0.30 versus 0.32 hr-1, n=8 and n=8, respectively). Pollutant levels were also similar in vented and unvented homes. In addition, these similarities were achieved despite numerous observed faults in complex mechanical ventilation systems. More rigorous commissioning is still recommended. Cooking exhaust systems were used inconsistently and several suffered from design flaws. Failure to follow best practices led to IAQ problems in some cases. Ambient nitrogen dioxide standards were exceeded or nearly so in four homes that either used gas ranges with standing pilots, or in Passive House-style homes that used gas cooking burners without venting range hoods. Homes without active particle filtration had particle count concentrations approximately double those in homes with enhanced filtration. The majority of homes reported using low-emitting materials; consistent with this, formaldehyde levels were approximately half those in conventional, new CA homes built before 2008. Emissions of ultrafine particles (with diameters <100 nm) were dramatically lower on induction electric cooktops, compared with either gas or resistance electric models. These results indicate that high performance homes can achieve

  17. Is stratospheric air getting younger with time?

    NASA Astrophysics Data System (ADS)

    Monge-Sanz, Beatriz; Chipperfield, Martyn; Dee, Dick; Simmons, Adrian; Stiller, Gabriele

    2014-05-01

    Most climate models have predicted that with the increase in greenhouse gases concentrations, the stratospheric circulation will intensify, showing younger age-of-air (AoA) values in this region (e.g. Butchart et al., 2010; WMO, 2011). However, balloon and satellite observations do not agree with the widespread modelled trend towards younger age-of-air (Engel et al., 2009; Stiller et al., 2012). To increase our confidence in climate-chemistry projections, the causes for the apparent age-of-air disagreement between observations and most models need to be identified. Here we have carried out stratospheric simulations with a chemistry transport model (CTM) to evaluate the stratospheric circulation with the ERA-Interim dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim reanalysis provides age-of-air (AoA) distributions in very good agreement with observations in the lower stratosphere. Given this agreement, we have used our simulations to quantify interannual variability and trends in the stratospheric AoA for the whole ERA-Interim period (1979-present). Our model results with ERA-Interim fields disagree with the decreasing tendency in age-of-air widespread in most models, but are in good agreement with the recent age-of-air studies based on observations. To explore potential causes for the AoA trends in our model, Lagrangian calculations are also performed to assess mixing processes for the ERA-Interim period. Potential links between our modelled AoA trends and stratospheric ozone evolution are also shown. References: Butchart, et al., 2010. J. Climate, 23, 5349-5374, doi:10.1175/2010JCLI3404.1. Engel et al., 2009. Nat. Geosci. 2: 28-31, doi:10.1038/ngeo388. Stiller et al., 2012. Atmos. Chem. Phys. 12: 3311-3331, doi:10.5194/acp-12-3311-2012. WMO. 2011. Global Ozone Research and Monitoring Project -Report No. 52.

  18. Geomorphic Control on Mineral and Fluid Residence Times and Implications for the Hydrochemistry of Weathering

    NASA Astrophysics Data System (ADS)

    Torres, M. A.; West, A. J.; Clark, K. E.; Feakins, S. J.; Ponton, C.

    2014-12-01

    Understanding how hydrologic and geochemical processes are coupled, and how this coupling is linked to geomorphic boundary conditions, remains a fundamental problem in the Geosciences, with implications from hydrology and ecosystem science to the geologic carbon cycle. In this study, we present paired measurements of water chemistry and river runoff in four nested catchments spanning the transition from the Andes Mountains to the foreland floodplain in Peru. These data provide insight into the linkages between catchment hydrology and weathering across a dramatic geomorphic gradient. Along the studied gradient, bedrock-derived solute concentrations range from being nearly constant in the Andes to showing significant dilution in response to increasing runoff in the foreland floodplain. Mean catchment slope appears to be a robust predictor of the power law exponent relating solute concentrations and runoff, which implies that erosional processes are an underlying control on concentration-runoff relationships. A number of factors may explain the observed slope-dependency of concentration-runoff relationships, including both mineral and fluid residence times. Seasonal variation in the δD of the Andean rivers is significantly damped relative to variation in the δD of precipitation. Along with consideration of the annual water budget, these data suggest that water is transiently stored within fractured bedrock in the Andean catchments. Across the entire study area, the seasonal variation in the δD of tributaries (i.e. streams that drain only a narrow range of elevations) increases with decreasing mean catchment elevation, which suggests that fluid residence times are shorter in the foreland floodplain relative to the Andes. Together, we interpret these factors to suggest that erosional processes, by modulating both the residence time of water and minerals in the critical zone, control the hydrologic sensitivity of weathering processes along the Andes-to-Amazon gradient.

  19. Time series analyses of gas-bubble residence time in porous media

    NASA Astrophysics Data System (ADS)

    Lazik, Detlef; Krauss, Gunnar; Geistlinger, Helmut; Vogel, Hans-Jörg

    2010-05-01

    Gas injection into coarse, water saturated sediments results in buoyancy driven bubble movement between an incoherent more or less stable trapped gas phase. The quantitative understanding of the coupled processes resulting in entrapment and movement of the incoherent gas phase allows for optimizing the interaction of trapped and moving gas clusters during air sparging. For granular media with particles larger than 4 mm gas flow becomes continuous without entrapment of large gas clusters. For particles smaller than 1 mm channeling flow is observed. For intermediate particle sizes the gas phase moves within buoyancy driven bubbles between entrapped clusters. To analyze this phenomena we designed a 2D flow cell filled with 2 mm glass beads. The total gas saturation could be measured gravimetrically at high temporal resolution. Gas was injected close to the lower boundary where the volume of injected gas bubbles could be controlled between 10 cm³ and 5000 cm³. This was achieved by changing the size of a reservoir attached to the injection point in which the gas pressure was increased until the air-enty point of the porous medium was reached and the gas cluster was relesed. The pressure of the reservoir was monitored to detect the frequncy of injected gas bubbles. Based on these data the mean and variance of traveltimes could be reliabely determined. The measurements are related to the bulk material and are not restricted to optical observations at the container wall. Thus our method can be applied to any type of sample containment. Nevertheless, the results are in agreement with additional optical measurements obtained at the transparent cell wall. We found that the mean traveltimes are the same irrespective the size of injected bubbles however the variance depends on bubble size in a non-liner manner. In conclusion we discuss the possibility to control the interaction between injected and trapped gas through the injected bubble size.

  20. Stable isotope fractionation in response to variable fluid residence time distributions

    NASA Astrophysics Data System (ADS)

    Druhan, J. L.; Maher, K.

    2013-12-01

    Hydrogeochemical processes governing groundwater quantity and quality are often inferred from fluid samples that are the flux-weighted average of a heterogeneous system. This connection has been demonstrated for solutes subject to transport and equilibrium constraints, in which the steady state concentration - discharge relationship is cast in terms of the choice of expression for residence time distribution (Maher, 2011). Here, we examine the extent to which the spatial correlation of the permeability field, which governs the fluid residence time distribution, exerts a principle control on the partitioning of stable isotopes between reactant and product species during heterogeneous reactions in groundwater systems. We demonstrate this relationship using numerical simulations of δ53Cr fractionation due to abiotic CrO42- reduction by Fe2+, implemented in the reactive transport code CrunchFlow. The chemically homogeneous redox reaction generates Cr3+ with an isotope ratio distinct from the reactant pool, and in turn this product species precipitates as a mineral phase Cr(OH)3(s) through a non-fractionating reaction. The corresponding chromate δ53Cr enrichment across a homogeneous domain varies from a maximum value set by the kinetic fractionation factor (αk) at high mean fluid residence times, to a value <αk as fluid velocity increases, demonstrating a transition from reaction-limited to transport-limited regimes. For physically heterogeneous flow fields, the transition in isotopic fractionation from a reaction-limited to a transport-limited regime becomes variable, and falls between the upper and lower bounds set by the homogeneous simulations at slow and fast precipitation rates, respectively. Our results show that while minimal variation occurs in the steady-state isotopic profile of the reactant species (δ53Cr of CrO42-), the combined effects of the precipitation rate and the heterogeneous structure of the porous media lead to a wide range in the steady

  1. On solute residence time in the storage zones of small streams - experimental study and scaling law

    NASA Astrophysics Data System (ADS)

    Schmid, Bernhard

    2013-04-01

    Transient storage has a major influence on solute transport in streams, on biogeochemical cycling, water quality and on the functioning of aquatic ecosystems. The first part of the research reported here focuses on surface transient storage (STS) zones between groins along small streams. Such groins are used to protect banks, but also to increase habitat diversity and are, thus, not restricted to large rivers. Repeated tracer dilution experiments on the Mödlingbach, a small stream in Austria some 30 km south of Vienna, have been analyzed to determine the solute residence time between groins and to characterize the exchange processes between dead zones and main stream. Pairs of related breakthrough curves were measured in main stream and storage zones, resp., and used subsequently to estimate the solute residence time in the surface dead zones under study. Following previous work (Weitbrecht et al., 2008; Jackson et al., 2012) these residence times were, in turn, expressed as T = -W-.hD- k ?u hE (1) with W denoting groin length, u main stream flow velocity, hD mean water depth between the groins and hE depth at the interface dead zone - main stream. Coefficient k, finally, is thought to depend on a type of hydraulic radius, RD = W.L/(W+L), with L denoting the distance between the groins, measured in main flow direction. Using both the Mödlingbach STS zone data and the results of the aforementioned study (Weitbrecht et al., 2008) the following regression equation was derived (hS denotes main stream water depth): k = 0.00282? RD + 0.00802 hS (2) The second part of this research focuses on the dependency of solute residence time on flow rate, which is important for an improved understanding of longitudinal solute transport in streams and for the application of mathematical models. The scaling law proposed here is based on a physics-related theory combined with extensive data sets available form a decade of stream tracer experiments on the Mödlingbach stream

  2. Dispersed fluid flow in fractured reservoirs: An analysis of tracer-determined residence time distributions

    NASA Astrophysics Data System (ADS)

    Robinson, Bruce A.; Tester, Jefferson W.

    1984-11-01

    A methodology for analyzing the internal flow characteristics of a fractured geothermal reservoir using tracer-determined residence time distribution curves is outlined. Emphasis is placed on comparison of the statistical quantities obtained from the tracer curves of different reservoirs or of the same reservoir under different conditions. In this way, model-independent information may be used unambiguously to construct empirical reservoir performance correlations. Downhole measurements of the tracer response exiting from discrete fracture zones permit further characterization of reservoir fluid flow behavior. Tracer experiments conducted in prototype hot dry rock geothermal reservoirs in fractured rock are examined using these statistically based data analysis methods.

  3. A residence-time-based transport approach for the groundwater pathway in performance assessment models

    NASA Astrophysics Data System (ADS)

    Robinson, Bruce A.; Chu, Shaoping

    2013-03-01

    This paper presents the theoretical development and numerical implementation of a new modeling approach for representing the groundwater pathway in risk assessment or performance assessment model of a contaminant transport system. The model developed in the present study, called the Residence Time Distribution (RTD) Mixing Model (RTDMM), allows for an arbitrary distribution of fluid travel times to be represented, to capture the effects on the breakthrough curve of flow processes such as channelized flow and fast pathways and complex three-dimensional dispersion. Mathematical methods for constructing the model for a given RTD are derived directly from the theory of residence time distributions in flowing systems. A simple mixing model is presented, along with the basic equations required to enable an arbitrary RTD to be reproduced using the model. The practical advantages of the RTDMM include easy incorporation into a multi-realization probabilistic simulation; computational burden no more onerous than a one-dimensional model with the same number of grid cells; and straightforward implementation into available flow and transport modeling codes, enabling one to then utilize advanced transport features of that code. For example, in this study we incorporated diffusion into the stagnant fluid in the rock matrix away from the flowing fractures, using a generalized dual porosity model formulation. A suite of example calculations presented herein showed the utility of the RTDMM for the case of a radioactive decay chain, dual porosity transport and sorption.

  4. Sediment residence time and connectivity in non-equilibrium and transient geomorphic systems

    NASA Astrophysics Data System (ADS)

    Hoffmann, Thomas; Hillebrand, Gudrun

    2016-04-01

    Growing empirical evidence shows that sediment delivery in many geomorphic systems is in transient state or out of equilibrium with respect to the external driving forces. The transient state is often related to the (dis)connectivity of the many constituent parts of geomorphic systems as a result of sediment storage along the sediment flow path from its source to the final sink. The response time of geomorphic systems to external changes is thus dependent on the residence time of sediment in various storage compartments. Here, a mathematical concept based on reservoir theory to model residence time of sediment in various depositional environments is presented. The concept allows to reinterpret millennial scale sediment budges, but can be also applied to decal sediment storage in reservoirs and aids sediment management practices in river systems. The framework sheds light on the limitation of the sediment delivery ratio, which is often used as a measure of sediment connectivity in geomorphic systems, and provides analytical information on process type, pace of sediment flux and connectivity of storage compartments along the sediment cascade. Examples will be given using Postglacial sediment budgets from the Canadian Rocky mountains on the one hand and short-term (~15 yrs.) sediment dynamics in the Iffezheim barrage in the Upper Rhine (Germany).

  5. Analysis Of Residence Time Distribution Of Fluid Flow By Axial Dispersion Model

    SciTech Connect

    Sugiharto; Su'ud, Zaki; Kurniadi, Rizal; Waris, Abdul; Abidin, Zainal

    2010-12-23

    Radioactive tracer {sup 82}Br in the form of KBr-82 with activity {+-} 1 mCi has been injected into steel pipeline to qualify the extent dispersion of water flowing inside it. Internal diameter of the pipe is 3 in. The water source was originated from water tank through which the water flow gravitically into the pipeline. Two collimated sodium iodide detectors were used in this experiment each of which was placed on the top of the pipeline at the distance of 8 and 11 m from injection point respectively. Residence time distribution (RTD) curves obtained from injection of tracer are elaborated numerically to find information of the fluid flow properties. The transit time of tracer calculated from the mean residence time (MRT) of each RTD curves is 14.9 s, therefore the flow velocity of the water is 0.2 m/s. The dispersion number, D/uL, for each RTD curve estimated by using axial dispersion model are 0.055 and 0.06 respectively. These calculations are performed after fitting the simulated axial dispersion model on the experiment curves. These results indicated that the extent of dispersion of water flowing in the pipeline is in the category of intermediate.

  6. Bistable sensors based on broken symmetry phenomena: The residence time difference vs. the second harmonic method

    NASA Astrophysics Data System (ADS)

    Nikitin, A.; Stocks, N. G.; Bulsara, A. R.

    2013-10-01

    A periodically driven noisy bistable system can be used as a sensor of a dc target signal. In the presence of the dc signal the symmetry of the potential energy function that underpins the sensor dynamics can be broken, leading to even harmonics of the driving frequency in the power spectrum. Both the power of the second harmonic and the mean residence time difference can be used for an estimation of the dc signal. In this paper we introduce a method for the power spectrum estimation from the experimental time series. This method can be considered to be an alternative to methods based on the Fourier transform. The presented method is faster for computation than the Fast Fourier Transform, and it allow us to estimate the power contained in peaks (or features) without their mixture with the power spectrum background. Using this method we compute the power of the second harmonic in the response power spectrum and compare the accuracy of the second harmonic method and the mean residence time difference (RTD) via the Shannon mutual information. We find that the RTD, generally, yields better performance in bistable noisy sensors.

  7. Analysis Of Residence Time Distribution Of Fluid Flow By Axial Dispersion Model

    NASA Astrophysics Data System (ADS)

    Sugiharto, Su'ud, Zaki; Kurniadi, Rizal; Waris, Abdul; Abidin, Zainal

    2010-12-01

    Radioactive tracer 82Br in the form of KBr-82 with activity ± 1 mCi has been injected into steel pipeline to qualify the extent dispersion of water flowing inside it. Internal diameter of the pipe is 3 in. The water source was originated from water tank through which the water flow gravitically into the pipeline. Two collimated sodium iodide detectors were used in this experiment each of which was placed on the top of the pipeline at the distance of 8 and 11 m from injection point respectively. Residence time distribution (RTD) curves obtained from injection of tracer are elaborated numerically to find information of the fluid flow properties. The transit time of tracer calculated from the mean residence time (MRT) of each RTD curves is 14.9 s, therefore the flow velocity of the water is 0.2 m/s. The dispersion number, D/uL, for each RTD curve estimated by using axial dispersion model are 0.055 and 0.06 respectively. These calculations are performed after fitting the simulated axial dispersion model on the experiment curves. These results indicated that the extent of dispersion of water flowing in the pipeline is in the category of intermediate.

  8. Residence times of stream-groundwater exchanges due to transient stream stage fluctuations

    NASA Astrophysics Data System (ADS)

    McCallum, James L.; Shanafield, Margaret

    2016-03-01

    The biogeochemical functioning of stream ecosystems is heavily dependent on water and water-borne nutrient fluxes between the stream itself and the streambed and banks (i.e., the hyporheic zone). The travel time of water exchanges through the hyporheic zone has been investigated previously; however, these studies have primarily modeled exchanges under steady state conditions assuming spatial pressure variations. This assumes that the hydraulic gradients that drive the exchanges are maintained the whole time the stream water remains in the bed or banks, which is unrealistic. Therefore, in this study we use a transient approach to investigate residence time distributions (RTDs) of bank inflow and bank outflow during both regular, diurnal stream stage variations and storm flow events. We demonstrate that RTDs reflect the timing and magnitude bank inflows, rather than smooth RTDs. We also show that small percentages of water from a given bank inflow event may be present in bank outflows for long periods of time, due to dispersion and diffusion within the bank, and lower rates of bank outflow, relative to bank inflow. This is apparent in the synthetic model of a single storm flow event, where 10% remained in the bank after 50 days. Additionally, residence times for a given bank inflow event are longer when repeated events occur, because the bank outflows from one event are "interrupted" by an increase in stream stage during a successive event. For example, field data capturing events of variable timing and magnitude showed that 70 days after each of three storm flow events occurred, 40, 12 and 30% of the bank inflow event remained in the banks. These cases indicate that bank exchanges are temporally dynamic and the RTDs of return flows can have significant tailing, which will dictate rates of nutrient exchange within the near-stream environment.

  9. A non-discrete method for computation of residence time in fluid mechanics simulations

    NASA Astrophysics Data System (ADS)

    Esmaily-Moghadam, Mahdi; Hsia, Tain-Yen; Marsden, Alison L.

    2013-11-01

    Cardiovascular simulations provide a promising means to predict risk of thrombosis in grafts, devices, and surgical anatomies in adult and pediatric patients. Although the pathways for platelet activation and clot formation are not yet fully understood, recent findings suggest that thrombosis risk is increased in regions of flow recirculation and high residence time (RT). Current approaches for calculating RT are typically based on releasing a finite number of Lagrangian particles into the flow field and calculating RT by tracking their positions. However, special care must be taken to achieve temporal and spatial convergence, often requiring repeated simulations. In this work, we introduce a non-discrete method in which RT is calculated in an Eulerian framework using the advection-diffusion equation. We first present the formulation for calculating residence time in a given region of interest using two alternate definitions. The physical significance and sensitivity of the two measures of RT are discussed and their mathematical relation is established. An extension to a point-wise value is also presented. The methods presented here are then applied in a 2D cavity and two representative clinical scenarios, involving shunt placement for single ventricle heart defects and Kawasaki disease. In the second case study, we explored the relationship between RT and wall shear stress, a parameter of particular importance in cardiovascular disease.

  10. Chemotaxis Increases the Residence Time of Bacteria in Granular Media Containing Distributed Contaminant Sources.

    PubMed

    Adadevoh, Joanna S T; Triolo, Sarah; Ramsburg, C Andrew; Ford, Roseanne M

    2016-01-01

    The use of chemotactic bacteria in bioremediation has the potential to increase access to, and the biotransformation of, contaminant mass within the subsurface. This laboratory-scale study aimed to understand and quantify the influence of chemotaxis on the residence times of pollutant-degrading bacteria within homogeneous treatment zones. Focus was placed on a continuous-flow sand-packed column in which a uniform distribution of naphthalene crystals created distributed sources of dissolved-phase contaminant. A 10 mL pulse of Pseudomonas putida G7, which is chemotactic to naphthalene, and Pseudomonas putida G7 Y1, a nonchemotactic mutant strain, were simultaneously introduced into the sand-packed column at equal concentrations. Breakthrough curves obtained from experiments conducted with and without naphthalene were used to quantify the effect of chemotaxis on transport parameters. In the presence of the chemoattractant, longitudinal dispersion of PpG7 increased by a factor of 3, and percent recovery decreased by 43%. In contrast, PpG7 Y1 transport was not influenced by the presence of naphthalene. The results imply that pore-scale chemotaxis responses are evident at an interstitial velocity of 1.8 m/day, which is within the range of typical groundwater flow. Within the context of bioremediation, chemotaxis may work to enhance bacterial residence times in zones of contamination, thereby improving treatment. PMID:26605857

  11. Thiolated α-Cyclodextrin: The Invisible Choice to Prolong Ocular Drug Residence Time.

    PubMed

    Ijaz, Muhammad; Ahmad, Mahmood; Akhtar, Naveed; Laffleur, Flavia; Bernkop-Schnürch, Andreas

    2016-09-01

    It was the aim of this study to develop cysteamine-conjugated α-cyclodextrin (α-CD) enabled to form disulfide bonds with cysteine-rich substructures of the ocular mucus layer to provide a prolonged residence time of incorporated drugs at the site of action. Cysteamine was covalently attached to oxidized α-CD via reductive amination. The resulting α-CD-cysteamine conjugates (α-CD-Cys) were characterized regarding the amount of free thiol groups attached to the oligomer backbone via Ellman's reagent; resazurin assay was conducted for cytotoxicity, and mucoadhesive properties were evaluated on porcine intestinal and ocular mucosal tissues. Furthermore, albino rabbits were used for assessing the irritation-masking effects of α-CD-Cys. Free thiol groups attached to the backbone were in the range of 558 ± 24-1143 ± 92 μmol/g. None of these α-CD-Cys unduly affected the viability of Caco-2 cells in a concentration of 0.5%. Mucoadhesive properties of α-CD-Cys were up to 32-fold improved compared to unmodified α-CD. Encapsulation of cetirizine into α-CD-Cys resulted in significantly reduced local ocular mucosal irritation of this model drug. According to these results, α-CD-Cys is a promising new tool to prolong drug residence time on the ocular mucosal surface. PMID:27233687

  12. A non-discrete method for computation of residence time in fluid mechanics simulations

    PubMed Central

    Esmaily-Moghadam, Mahdi; Hsia, Tain-Yen; Marsden, Alison L.

    2013-01-01

    Cardiovascular simulations provide a promising means to predict risk of thrombosis in grafts, devices, and surgical anatomies in adult and pediatric patients. Although the pathways for platelet activation and clot formation are not yet fully understood, recent findings suggest that thrombosis risk is increased in regions of flow recirculation and high residence time (RT). Current approaches for calculating RT are typically based on releasing a finite number of Lagrangian particles into the flow field and calculating RT by tracking their positions. However, special care must be taken to achieve temporal and spatial convergence, often requiring repeated simulations. In this work, we introduce a non-discrete method in which RT is calculated in an Eulerian framework using the advection-diffusion equation. We first present the formulation for calculating residence time in a given region of interest using two alternate definitions. The physical significance and sensitivity of the two measures of RT are discussed and their mathematical relation is established. An extension to a point-wise value is also presented. The methods presented here are then applied in a 2D cavity and two representative clinical scenarios, involving shunt placement for single ventricle heart defects and Kawasaki disease. In the second case study, we explored the relationship between RT and wall shear stress, a parameter of particular importance in cardiovascular disease. PMID:24046509

  13. Tritium activity concentrations and residence times of groundwater collected in Rokkasho, Japan.

    PubMed

    Hasegawa, Hidenao; Ueda, Shinji; Akata, Naofumi; Kakiuchi, Hideki; Hisamatsu, Shun'ichi

    2015-11-01

    Tritium ((3)H) concentrations were measured in groundwater samples from four surface wells (4-10 m deep), four shallow wells (24-26.5 m deep) and a 150-m-deep well in the Futamata River catchment area, which is adjacent to the large-scale commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan. The (3)H concentrations in most of the surface- and shallow-well samples (<0.03-0.57 Bq l(-1)) were similar to those in precipitation (annual mean: 0.31-0.79 Bq l(-1)), suggesting that the residence time of the water in those wells was 0-15 y. The (3)H concentrations in the samples from a 26-m-deep well and the 150-m-deep well were lower than those in the other wells, indicating that groundwater with a long residence time exists in deep aquifers and the estuary area of the catchment. It is not clear whether (3)H released during test operation of the plant with actual spent nuclear fuel affected the (3)H concentrations observed in this study. PMID:25944959

  14. Investigation of liquid phase axial dispersion in Taylor bubble flow by radiotracer residence time distribution analysis

    NASA Astrophysics Data System (ADS)

    Chughtai, I. R.; Iqbal, W.; Din, G. U.; Mehdi, S.; Khan, I. H.; Inayat, M. H.; Jin, J. H.

    2013-05-01

    A gas-liquid Taylor bubble flow occurs in small diameter channels in which gas bubbles are separated by slugs of pure liquid. This type of flow regime is well suited for solid catalyzed gas-liquid reactors in which the reaction efficiency is a strong function of axial dispersion in the regions of pure liquid. This paper presents an experimental study of liquid phase axial dispersion in a Taylor bubble flow developed in a horizontal tube using high speed photography and radiotracer residence time distribution (RTD) analysis. A parametric dependence of axial dispersion on average volume fraction of gas phase was also investigated by varying the relative volumetric flow rates of the two phases. 137mBa produced from a 137Cs/137mBa radionuclide generator was used as radiotracer and measurements were made using the NaI(Tl) scintillation detectors. Validation of 137mBa in the form of barium chloride as aqueous phase radiotracer was also carried out. Axial Dispersion Model (ADM) was used to simulate the hydrodynamics of the system and the results of the experiment are presented. It was observed that the system is characterized by very high values of Peclet Number (Pe˜102) which reveals an approaching plug type flow. The experimental and model estimated values of mean residence times were observed in agreement with each other.

  15. Chemotaxis Increases the Residence Time Distribution of Bacteria in Granular Media Containing Distributed Contaminant Sources

    NASA Astrophysics Data System (ADS)

    Adadevoh, J.; Triolo, S.; Ramsburg, C. A.; Ford, R.

    2015-12-01

    The use of chemotactic bacteria in bioremediation has the potential to increase access to, and biotransformation of, contaminant mass within the subsurface environment. This laboratory-scale study aimed to understand and quantify the influence of chemotaxis on residence times of pollutant-degrading bacteria within homogeneous treatment zones. Focus was placed on a continuous flow sand-packed column system in which a uniform distribution of naphthalene crystals created distributed sources of dissolved phase contaminant. A 10 mL pulse of Pseudomonas putida G7, which is chemotactic to naphthalene, and Pseudomonas putida G7 Y1, a non-chemotactic mutant strain, were simultaneously introduced into the sand-packed column at equal concentrations. Breakthrough curves obtained for the bacteria from column experiments conducted with and without naphthalene were used to quantify the effect of chemotaxis on transport parameters. In the presence of the chemoattractant, longitudinal dispersivity of PpG7 increased by a factor of 3 and percent recovery decreased from 21% to 12%. The results imply that pore-scale chemotaxis responses are evident at an interstitial fluid velocity of 1.7 m/d, which is within the range of typical groundwater flow. Within the context of bioremediation, chemotaxis may work to enhance bacterial residence times in zones of contamination thereby improving treatment.

  16. Prevalence and Cost of Full-Time Research Fellowships During General Surgery Residency – A National Survey

    PubMed Central

    Robertson, Charles M.; Klingensmith, Mary E.; Coopersmith, Craig M.

    2009-01-01

    Structured Abstract Objective To quantify the prevalence, outcomes, and cost of surgical resident research. Summary Background Data General surgery is unique among graduate medical education programs because a large percentage of residents interrupt their clinical training to spend 1-3 years performing full-time research. No comprehensive data exists on the scope of this practice. Methods Survey sent to all 239 program directors of general surgery residencies participating in the National Resident Matching Program. Results Response rate was 200/239 (84%). A total of 381 out of 1052 trainees (36%) interrupt residency to pursue full-time research. The mean research fellowship length is 1.7 years, with 72% of trainees performing basic science research. A significant association was found between fellowship length and post-residency activity, with a 14.7% increase in clinical fellowship training and a 15.2% decrease in private practice positions for each year of full-time research (p<0.0001). Program directors at 31% of programs reported increased clinical duties for research fellows as a result of ACGME work hour regulations for clinical residents, while a further 10% of programs are currently considering such changes. It costs $41.5 million to pay the 634 trainees who perform research fellowships each year, the majority of which is paid for by departmental funds (40%) and institutional training grants (24%). Conclusions Interrupting residency to perform a research fellowship is a common and costly practice among general surgery residents. While performing a research fellowship is associated with clinical fellowship training after residency, it is unclear to what extent this practice leads to the development of surgical investigators after post-graduate training. PMID:19106692

  17. Residence Times of Juvenile Salmon and Steelhead in Off-Channel Tidal Freshwater Habitats, Columbia River, USA

    SciTech Connect

    Johnson, Gary E.; Ploskey, Gene R.; Sather, Nichole K.; Teel, D. J.

    2015-05-01

    We estimated seasonal residence times of acoustic-tagged juvenile salmonids in off-channel, tidal freshwater habitats of the Columbia River near the Sandy River delta (rkm 198; 2007, 2008, 2010, and 2011) and Cottonwood Island (rkm 112; 2012).

  18. Distribution and variability of the 24-h average air exchange rates and interzonal flow rates in 26 Japanese residences in 5 seasons

    NASA Astrophysics Data System (ADS)

    Shinohara, Naohide; Kataoka, Toshiyuki; Takamine, Koichi; Gamo, Masashi

    2011-07-01

    In this study, to evaluate the distribution of air exchange rates in Japan, daily, seasonal, and inter-residence variabilities were determined as well as the air exchange rate itself. In addition, airflows among multiple zones were also evaluated. For this purpose, the 24 h average air exchange rates and interzonal air flow rates were measured using a passive perfluorocarbon tracer (PFT) method with three kinds of tracer gases for 1 week in three rooms of 26 Japanese residences over five seasons: summer and autumn of 2005, and winter, spring, and summer of 2006. During these seasons, the weekly average air exchange rates were found to be 1.6 ± 1.7, 0.58 ± 0.94, 0.61 ± 0.93, 1.2 ± 2.5, and 1.7 ± 1.8 h -1, respectively. Two-way repeated measure analysis of variance (ANOVA) revealed that the air exchange rates differed significantly with respect to the seasons, residences, and interaction of seasons and residences ( p < 0.01). In addition, the air exchange rates in both summers and spring were statistically higher than those in autumn and winter (Sheffe test, p < 0.01). According to the ANOVA, the percentage contribution of inter-residence variability, seasonal variability, interaction of seasonal and inter-residence variabilities, and daily variability to the total variability of the 24 h average air exchange rates in the present survey was 51%, 44%, 3.7%, and 1.0%, respectively.

  19. Numerical model of circulation and residence times in the Persian Gulf

    NASA Astrophysics Data System (ADS)

    O'Donncha, Fearghal; Ragnoli, Emanuele

    2014-05-01

    parameters. The resultant time-series comprised tidal harmonic constituents and residuals composed of primarily density-driven and wind-driven (near surface) currents. To further decompose the residual currents time series are further filtered based on the differing scaling times of both wind-driven (days) and density-driven (weeks) flows. The resulting datasets enable a comprehensive classification of the relative influence of tides, wind and density effects across the domain. As a summary measure of circulation within the region, the model was used to compute the residence time for a water parcel in the gulf. Several transport time scales were calculated, including the average residence time and variations across the region. Residence statistics provide several insights into circulation in the gulf, in particular, knowledge of circulation patterns through the Straits of Hormuz, regional variation of residence times from North-South, and the impacts of wind and density-driven circulation on particle renewal within the domain.

  20. Effective denitrification at the groundwater surface-water interface: exposure rather than residence time

    NASA Astrophysics Data System (ADS)

    Peiffer, Stefan; Frei, Sven

    2014-05-01

    Effective processing of material in aquatic systems, e. g. removal of nitrate upon denitrification, requires sufficient reaction time. This statement sounds trivial albeit its implication for biogeochemistry seems to be not fully recognized. The time teff required for effective processing of nitrate is controlled by the underlying biogeochemical rate law. In the simplest case of a 1st order reaction, teff is often calculated as the time when 63% of the initial concentration is consumed setting teff as 1/kreaction. It may, however, be more appropriate to derive teff,90%or teff,99% from the respective rate law. Hence a minimum time t > teff is required that exposes a specific biogeochemical process to conditions favourable for this process, which is anoxia in case of denitrification. This exposure time τexp is not necessarily identical to the residence time τ of water in the particular system or flow path. Rather, the exposure time can be much shorter and may even fluctuate with time. As a consequence, Damköhler numbers (Da = τexp/teff) for denitrification < 1 may be the consequence even though the age of water may be comparatively high. We therefore argue that the key for understanding denitrification efficiency at the groundwater surface-water interface (or in groundwater systems in general) is the quantification of the exposure time. This contribution therefore aims i) to estimate exposure times required for effective denitrification based on an analysis of rate constants for denitrification, ii) to relate these time scales to typical residence time distributions found at the groundwater surface-water interface and iii) to discuss implications for denitrification efficiencies. References: Oldham, C; Farrow, DE; Peiffer, S (2013): A generalized Damköhler number for classifying material processing in hydrological systems, Hydrology and Earth System Sciences, 17, 1133-1148 Frei, S; Knorr, KH; Peiffer, S; Fleckenstein, J (2012): Surface micro-topography causes

  1. Attack of the vog: Natural air pollution has residents of Hawaii all choked up

    SciTech Connect

    Monastersky, R.

    1995-05-06

    In Hawaii, measurements of sulfur dioxide of 600-1000 ppb have been measured, almost as high as the deadly London Fog of 1952. The Kilauea Volcano has produced a slow but steady supply of lava since 1986, emiting as a by product about 1,000 tones of sulfur dioxide gas each day, one of the biggest air pollution sources on the island. This article examines the origins of the `Vog` and discusses its effect on human health, comparing it to National Ambient Air Quality Standards.

  2. Coupling groundwater residence time and 234U/238U isotopic ratios in a granitic catchment (Vosges, Eastern France)

    NASA Astrophysics Data System (ADS)

    Viville, Daniel; Aquilina, Luc; Ackerer, Julien; Chatton, Eliot; Labasque, Thierry; Pierret, Marie-Claire; Granet, Mathieu; Perrone, Thierry; Chabaux, François

    2016-04-01

    Weathering processes are active in surface waters but groundwater also represents no neglectable chemical fluxes. As residence-time in groundwater are high, silicate weathering might take place and control Si, Ca and C fluxes. Weathering processes can be deduced from U isotopic ratios but the kinetics of these processes remain relatively poorly constrained. In order to better characterize these processes, we have coupled residence-times deduced from anthropogenic gases (CFC and SF6) analysis and 234U/238U isotopic ratios determination. Samples were collected in the Strengbach catchment (Hydro-geochemical Observatory OHGE, Vosges, eastern France). Two campaigns were carried out in May and August 2015 during two highly contrasted hydro-climatic periods. Both springs and boreholes down to 80 m depth have been sampled. A very clear geochemical distinction is observed between groundwater from surface springs and deeper groundwater from boreholes. Springs show much lower residence-time (few years) and specific chemical composition. Deeper groundwater have residence-time of several decades and different geochemical composition. A clear SF6 production is observed with increasing SF6 concentrations with residence-time. The campaign of May is characterized by highly groundwater levels and spring fluxes. All groundwater show very low residence time, except in the boreholes at depth greater than 40 m. Conversely, during low groundwater-level period in August, the residence times are much higher and CFC concentrations indicate a large mixing process between surface groundwater and deeper levels. The 234U/238U isotopic ratios confirm this vertical zonation in the boreholes, with much higher activity ratios in the deep ground-waters from borehole than in the surface and spring waters; Such high U activity ratios are indicative of long water-rock interactions, which is consistent with the long residence times deducted from the CFC and SF6 data.

  3. Evaluation of indoor air composition time variation in air-tight occupied spaces during night periods

    NASA Astrophysics Data System (ADS)

    Markov, Detelin

    2012-11-01

    This paper presents an easy-to-understand procedure for prediction of indoor air composition time variation in air-tight occupied spaces during the night periods. The mathematical model is based on the assumptions for homogeneity and perfect mixing of the indoor air, the ideal gas model for non-reacting gas mixtures, mass conservation equations for the entire system and for each species, a model for prediction of basal metabolic rate of humans as well as a model for prediction of O2 consumption rate and both CO2 and H2O generation rates by breathing. Time variation of indoor air composition is predicted at constant indoor air temperature for three scenarios based on the analytical solution of the mathematical model. The results achieved reveal both the most probable scenario for indoor air time variation in air-tight occupied spaces as well as the cause for morning tiredness after having a sleep in a modern energy efficient space.

  4. Signal detection via residence-time asymmetry in noisy bistable devices.

    PubMed

    Bulsara, A R; Seberino, C; Gammaitoni, L; Karlsson, M F; Lundqvist, B; Robinson, J W C

    2003-01-01

    We introduce a dynamical readout description for a wide class of nonlinear dynamic sensors operating in a noisy environment. The presence of weak unknown signals is assessed via the monitoring of the residence time in the metastable attractors of the system, in the presence of a known, usually time-periodic, bias signal. This operational scenario can mitigate the effects of sensor noise, providing a greatly simplified readout scheme, as well as significantly reduced processing procedures. Such devices can also show a wide variety of interesting dynamical features. This scheme for quantifying the response of a nonlinear dynamic device has been implemented in experiments involving a simple laboratory version of a fluxgate magnetometer. We present the results of the experiments and demonstrate that they match the theoretical predictions reasonably well. PMID:12636577

  5. AIR POLLUTION AND HEALTH EFFECTS IN CHILDREN RESIDING IN AKRON, OHIO

    EPA Science Inventory

    The purpose of this study was to determine the effects of ambient air pollutants on respiratory function, incidence, and severity of acute respiratory illness, nature of pulmonary epidemiology, and trace element accumulation, in 4th, 5th, and 6th grade children in Akron, Ohio. Ai...

  6. Sources of groundwater nitrate revealed using residence time and isotope methods

    SciTech Connect

    Moore, K B; Ekwurzel, B; Esser, B K; Hudson, G B; Moran, J E

    2004-10-07

    Nitrate concentrations approaching and greater than the maximum contaminant level (MCL) are impairing the viability of many groundwater basins as drinking water sources. Nitrate isotope data are effective in determining contaminant sources, especially when combined with other isotopic tracers such as stable isotopes of water and tritium-helium ages to give insight into the routes and timing of nitrate inputs to the flow system. This combination of techniques is demonstrated in Livermore, CA, where it is determined that low nitrate reclaimed wastewater predominates in the northwest, while two flowpaths with distinct nitrate sources originate in the southeast. Along the eastern flowpath, {delta}{sup 15}N values greater than 10{per_thousand} indicate that animal waste is the primary source. Diminishing concentrations over time suggest that contamination results from historical land use practices. The other flowpath begins in an area where rapid recharge, primarily of low-nitrate imported water (identified by stable isotopes of water and a tritium-helium residence time of less than 1 year), mobilizes a significant local nitrate source, bringing groundwater concentrations up to 53 mg NO{sub 3} L{sup -1}. In this area, artificial recharge of imported water via local arroyos increases the flux of nitrate to the regional aquifer. The low {delta}{sup 15}N value (3.1{per_thousand}) in this location implicates synthetic fertilizer. In addition to these anthropogenic sources, natural nitrate background levels between 15 and 20 mg NO{sub 3} L{sup -1} are found in deep wells with residence times greater than 50 years.

  7. The Effects of Solute Breakthrough Curve Tail Truncation on Residence Time Estimates and Mass Recovery

    NASA Astrophysics Data System (ADS)

    Drummond, J. D.; Covino, T. P.; Aubeneau, A. F.; Patil, S.; Leong, D. N.; Ran, L.; Packman, A. I.; Schumer, R.

    2010-12-01

    Solute transport and hydrologic retention strongly affect biogeochemical processes that are critical to stream ecosystems. Tracer injections are used to characterize solute transport and storage in stream reaches, but the range of processes accurately resolved using this approach is not clear. The solute residence time distribution (RTD) depends on both in-stream mixing and exchange with the hyporheic zone. For shorter residence times, in-stream breakthrough curves (BTCs) can be modeled well with the classical advection-dispersion equation, whereas longer RTDs produce highly skewed in-stream BTCs for which traditional solute models are inappropriate. Observed BTCs have most commonly been modeled with in-stream advection-dispersion plus an exponential RTD, but process-based models suggest that hyporheic retention extends to much longer times and a power-law RTD is more appropriate. We synthesized results from a variety of tracer-injection studies to investigate how experimental design and tracer sensitivity influence the interpretation of tailing behavior and RTDs. We found that BTC tails are often not well observed in stream tracer experiments. The two main reasons for this are: 1) experimental truncation, which occurs when sampling ends before all tracer mass reaches the sampling location, and 2) sensitivity truncation, when tracer concentrations in the tail are too low to be detected reliably above background levels. Continuous Time Random Walk (CTRW) theory was used to determine the effects of tail truncation on tracer mass recovery and tailing behavior. Tail truncation due to both experimental and sensitivity truncation decreased mass recovery and obscured assessment of BTC tailing. Failure to consider tail truncation leads to underestimation of the retention of solutes in the streambed and subsurface (i.e., transient storage). Based on these findings, we propose criteria for stream tracer experiments to minimize tail truncation and improve inverse modeling of

  8. Estimating renewal timescales with residence time and connectivity in an urban man-made lake in China.

    PubMed

    Gao, Xueping; Xu, Liping; Zhang, Chen

    2016-07-01

    Residence times and connectivity are computed for 12 subregions in an urban man-made lake in China using a high-resolution tracer-transport model. The renewal timescales are explicitly defined and computed for two groups of four freshwater inflow scenarios related to water diversion projects. First, the timescale values are computed and compared using different computational criteria for the upper limit of integration in the residence time equation. The sensitivity analysis suggests that a calculation time of 300 days is necessary to satisfy the relative error (0.001) and 5 % cutoff value criteria. Secondly, the residence times can range from 1.5 to 102 and 1.0 to 66 days under low and high flow conditions, respectively. Water in the inner lake would reside in the lake for less than 66 days prior to exiting the region of interest. The timescale values can be applied to impact studies that investigate the extent of sudden water pollution events that initially affect a subdomain of a lake. Finally, the lacustrine residence times are decomposed into the different subregion residence times, resulting in a connectivity matrix. This matrix can illustrate preferential connections among the individual subregions and reveal hidden patterns relating to local hydrodynamics in the lake. PMID:27040544

  9. First-Passage and Residence Times in a Periodically Driven Integrate-and-Fire Model

    NASA Astrophysics Data System (ADS)

    Talkner, Peter; Schindler, Michael; Hänggi, Peter

    2004-03-01

    The stochastic integrate-and-fire model presents a simple description of the spiking behavior of neurons.In this model a neuron ``fires'' if an Ornstein-Uhlenbeck process crosses a prescribed threshold. After the firing the process is assumed to be in a refractory state, and from there it is put back into its initial, active state.This process can be characterized by the distribution of the first passage times of the threshold and by the residence times in the active states.We determined the distributions of these times for the integrate-and-fire model for short refractory times in the presence of a periodic signal.This is done by numerical solutions both of the respective Langevin equation and the equivalent Fokker-Planck equation. The results are compared with an approximate analytic theory. If the period of the signal is large compared to the relaxation time of the Ornstein-Uhlenbeck process and if the threshold is higher than a few times the noise strength we find theory and numerics to be in excellent agreement.

  10. Trait differences between naturalized and invasive plant species independent of residence time and phylogeny.

    PubMed

    Gallagher, R V; Randall, R P; Leishman, M R

    2015-04-01

    The ability to predict which alien plants will transition from naturalized to invasive prior to their introduction to novel regions is a key goal for conservation and has the potential to increase the efficacy of weed risk assessment (WRA). However, multiple factors contribute to plant invasion success (e.g., functional traits, range characteristics, residence time, phylogeny), and they all must be taken into account simultaneously in order to identify meaningful correlates of invasion success. We compiled 146 pairs of phylogenetically paired (congeneric) naturalized and invasive plant species in Australia with similar minimum residence times (i.e., time since introduction in years). These pairs were used to test for differences in 5 functional traits (flowering duration, leaf size, maximum height, specific leaf area [SLA], seed mass) and 3 characteristics of species' native ranges (biome occupancy, mean annual temperature, and rainfall breadth) between naturalized and invasive species. Invasive species, on average, had larger SLA, longer flowering periods, and were taller than their congeneric naturalized relatives. Invaders also exhibited greater tolerance for different environmental conditions in the native range, where they occupied more biomes and a wider breadth of rainfall and temperature conditions than naturalized congeners. However, neither seed mass nor leaf size differed between pairs of naturalized and invasive species. A key finding was the role of SLA in distinguishing between naturalized and invasive pairs. Species with high SLA values were typically associated with faster growth rates, more rapid turnover of leaf material, and shorter lifespans than those species with low SLA. This suite of characteristics may contribute to the ability of a species to transition from naturalized to invasive across a wide range of environmental contexts and disturbance regimes. Our findings will help in the refinement of WRA protocols, and we advocate the inclusion

  11. Residence time distribution measurements in a pilot-scale poison tank using radiotracer technique.

    PubMed

    Pant, H J; Goswami, Sunil; Samantray, J S; Sharma, V K; Maheshwari, N K

    2015-09-01

    Various types of systems are used to control the reactivity and shutting down of a nuclear reactor during emergency and routine shutdown operations. Injection of boron solution (borated water) into the core of a reactor is one of the commonly used methods during emergency operation. A pilot-scale poison tank was designed and fabricated to simulate injection of boron poison into the core of a reactor along with coolant water. In order to design a full-scale poison tank, it was desired to characterize flow of liquid from the tank. Residence time distribution (RTD) measurement and analysis was adopted to characterize the flow dynamics. Radiotracer technique was applied to measure RTD of aqueous phase in the tank using Bromine-82 as a radiotracer. RTD measurements were carried out with two different modes of operation of the tank and at different flow rates. In Mode-1, the radiotracer was instantaneously injected at the inlet and monitored at the outlet, whereas in Mode-2, the tank was filled with radiotracer and its concentration was measured at the outlet. From the measured RTD curves, mean residence times (MRTs), dead volume and fraction of liquid pumped in with time were determined. The treated RTD curves were modeled using suitable mathematical models. An axial dispersion model with high degree of backmixing was found suitable to describe flow when operated in Mode-1, whereas a tanks-in-series model with backmixing was found suitable to describe flow of the poison in the tank when operated in Mode-2. The results were utilized to scale-up and design a full-scale poison tank for a nuclear reactor. PMID:26057343

  12. Indoor Air Quality in 24 California Residences Designed as High-Performance Homes

    SciTech Connect

    Less, Brennan; Mullen, Nasim; Singer, Brett; Walker, Iain

    2015-07-01

    Today’s high performance green homes are reaching previously unheard of levels of airtightness and are using new materials, technologies and strategies, whose impacts on Indoor Air Quality (IAQ) cannot be fully anticipated from prior studies. This research study used pollutant measurements, home inspections, diagnostic testing and occupant surveys to assess IAQ in 24 new or deeply retrofitted homes designed to be high performance green buildings in California.

  13. Estimation of the effects of ambient air pollution on life expectancy of urban residents in China

    NASA Astrophysics Data System (ADS)

    Wang, Cuicui; Zhou, Xiaodan; Chen, Renjie; Duan, Xiaoli; Kuang, Xingya; Kan, Haidong

    2013-12-01

    The air quality in China's cities has improved in recent years, but its impact on public health has rarely been investigated. This study was aimed at estimating the potential effects of air quality on life expectancy between 2003 and 2010 in China. We collected annual average concentrations of particulate matter less than 10 microns in aerodynamic diameter (PM10) in 113 key cities, covering all provinces in China, along with the national average age-specific mortality from 2003 to 2010. We constructed a cause-eliminated life table after excluding premature deaths attributable to PM10. The annual average PM10 levels in these cities decreased from 125.3 μg m-3 in 2003 to 88.3 μg m-3 in 2010. As the result, life expectancy loss due to PM10 decreased from 2.13 years in 2003 to 1.30 years in 2010. The estimated life expectancy increase due to PM10 mitigation accounted for 34% of the total increase in life expectancy in the same period. Our results suggested that air quality might have contributed substantially to life expectancy in China.

  14. Household Cooking Fuel Use among Residents of a Sub-Urban Community in Nigeria: Implications for Indoor Air Pollution

    PubMed Central

    Isara, Alphonsus Rukevwe; Aigbokhaode, Adesuwa Queen

    2014-01-01

    Objective: The aim of this study is to assess the types of household cooking fuel used by residents of Isiohor community in Edo State, Nigeria. Materials and Methods: This descriptive cross-sectional study was conducted among 133 household heads or their representatives in Isiohor Community in Edo State, Nigeria. Data collection was by means of a structured interviewer administered questionnaire. Results: Half (50.3%) of the households studied were made up of 4-6 persons living in them. Sixty-two (46.6%) respondents had tertiary level of education and a third 44 (33.1%) earned between 21,000 and 30,000 naira (150-200 dollars) monthly. Forty six (34.6%) and 27 (20.3%) respondents live in passage houses and flats respectively. Two thirds (68.4%) of the respondents cook their food indoors. The predominant household cooking fuels used by the respondents were cooking gas (51.1%), Kerosene (45.9%), vegetables (25.6%) and firewood (14.3%). Majority 106 (79.7%) had poor knowledge of the health effects of prolonged exposure to smoke arising from indoor cooking. There was a statistically significant association between the occupation of the respondents and the type of household cooking fuel used (p=0.002). Conclusion: The use of unclean indoor cooking fuel was high among the residents of Isiohor community in Edo State, Nigeria. Also, there was poor knowledge of the health effects of prolonged exposure to smoke from unclean cooking fuel among the respondents and this has serious implications for indoor air pollution. There is an urgent need for health/hygiene education on the health effects of use of unclean indoor cooking fuel among these residents. There is also need for use of clean/green cooking stoves and construction of exhaust ventilation pipes in these households. PMID:25610326

  15. Local dominance of exotic plants declines with residence time: a role for plant–soil feedback?

    PubMed Central

    Speek, Tanja A.A.; Schaminée, Joop H.J.; Stam, Jeltje M.; Lotz, Lambertus A.P.; Ozinga, Wim A.; van der Putten, Wim H.

    2015-01-01

    Recent studies have shown that introduced exotic plant species may be released from their native soil-borne pathogens, but that they become exposed to increased soil pathogen activity in the new range when time since introduction increases. Other studies have shown that introduced exotic plant species become less dominant when time since introduction increases, and that plant abundance may be controlled by soil-borne pathogens; however, no study yet has tested whether these soil effects might explain the decline in dominance of exotic plant species following their initial invasiveness. Here we determine plant–soil feedback of 20 plant species that have been introduced into The Netherlands. We tested the hypotheses that (i) exotic plant species with a longer residence time have a more negative soil feedback and (ii) greater local dominance of the introduced exotic plant species correlates with less negative, or more positive, plant–soil feedback. Although the local dominance of exotic plant species decreased with time since introduction, there was no relationship of local dominance with plant–soil feedback. Plant–soil feedback also did not become more negative with increasing time since introduction. We discuss why our results may deviate from some earlier published studies and why plant–soil feedback may not in all cases, or not in all comparisons, explain patterns of local dominance of introduced exotic plant species. PMID:25770013

  16. Analysis of catchment behavior using residence time distributions with application to the Thuringian Basin

    NASA Astrophysics Data System (ADS)

    Prykhodko, Vladyslav; Heße, Falk; Kumar, Rohini; Samaniego, Luis; Attinger, Sabine

    2014-05-01

    Residence time distribution (RTD), as presented e.g. by Botter et al., are a novel mathematical framework for a quantitative characterization of hydrological systems. These distributions contain information about water storage, flow pathways and water sources and therefore improve the classical hydrograph methods by allowing both nonlinear as well as time-dependent dynamics. In our study we extend this previous works by applying this theoretical framework on real-world heterogeneous catchments. To that end we use a catchment-scale hydrological model (mHM) and apply the approach of Botter et al. to each spatial grid cell of mHM. To facilitate the coupling we amended Botter's approach by introducing additional fluxes (like runoff from unsaturated zone) and specifying the structure of the groundwater zone. By virtue of this coupling we could then make use of the realistic hydrological fluxes and state variables as provided by mHM. This allowed us to use both observed (precipitation, temperature, soil type etc.) and modeled data sets and asses their impact on the behavior of the resulting RTD's. We extended the aforementioned framework to analyze large catchments by including geomorphic effect due to the actual arrangement of subcatchments around the channel network using the flood routing algorithm of mHM. Additionally we study dependencies of the stochastic characteristics of RTD's on the meteorological and hydrological processes as well as on the morphological structure of the catchment. As a result we gained mean residence times (MRT) of base flow and groundwater flow on the mesoscale (4km x 4km). We compare the spatial distribution of MRT's with land cover and soil moisture maps as well as driving forces like precipitation and temperature. Results showed that land cover is a major predictor for MRT's whereas its impact on the mean evapotranspiration time was much lower. Additionally we determined the temporal evolution of mean travel times by using time series of

  17. Optimal beam pattern to maximize inclusion residence time in an electron beam melting hearth

    SciTech Connect

    Powell, A.; Pal, U.; Avyle, J. van den

    1997-02-01

    Approximate probabilities of inclusion survival through an electron beam melting hearth are computed from nitride dissolution rates, flotation velocities, and residence times. Dissolution rates were determined by measuring shrinkage rates of pure TiN and nitrided sponge in small pools of molten titanium in an electron beam melting hearth. Flotation velocities were calculated using correlations for fluid flow around spheres, and show that particles sink or float unless their densities are extremely close to that of molten titanium. Flow field characteristics which lead to effective inclusion removal are discussed in terms of heat flux pattern required to produce them, based on the electron beam`s unique ability to impart a nearly arbitrary heat flux pattern to the melt surface.

  18. Target engagement and drug residence time can be observed in living cells with BRET.

    PubMed

    Robers, Matthew B; Dart, Melanie L; Woodroofe, Carolyn C; Zimprich, Chad A; Kirkland, Thomas A; Machleidt, Thomas; Kupcho, Kevin R; Levin, Sergiy; Hartnett, James R; Zimmerman, Kristopher; Niles, Andrew L; Ohana, Rachel Friedman; Daniels, Danette L; Slater, Michael; Wood, Monika G; Cong, Mei; Cheng, Yi-Qiang; Wood, Keith V

    2015-01-01

    The therapeutic action of drugs is predicated on their physical engagement with cellular targets. Here we describe a broadly applicable method using bioluminescence resonance energy transfer (BRET) to reveal the binding characteristics of a drug with selected targets within intact cells. Cell-permeable fluorescent tracers are used in a competitive binding format to quantify drug engagement with the target proteins fused to Nanoluc luciferase. The approach enabled us to profile isozyme-specific engagement and binding kinetics for a panel of histone deacetylase (HDAC) inhibitors. Our analysis was directed particularly to the clinically approved prodrug FK228 (Istodax/Romidepsin) because of its unique and largely unexplained mechanism of sustained intracellular action. Analysis of the binding kinetics by BRET revealed remarkably long intracellular residence times for FK228 at HDAC1, explaining the protracted intracellular behaviour of this prodrug. Our results demonstrate a novel application of BRET for assessing target engagement within the complex milieu of the intracellular environment. PMID:26631872

  19. Target engagement and drug residence time can be observed in living cells with BRET

    PubMed Central

    Robers, Matthew B.; Dart, Melanie L.; Woodroofe, Carolyn C.; Zimprich, Chad A.; Kirkland, Thomas A.; Machleidt, Thomas; Kupcho, Kevin R.; Levin, Sergiy; Hartnett, James R.; Zimmerman, Kristopher; Niles, Andrew L.; Ohana, Rachel Friedman; Daniels, Danette L.; Slater, Michael; Wood, Monika G.; Cong, Mei; Cheng, Yi-Qiang; Wood, Keith V.

    2015-01-01

    The therapeutic action of drugs is predicated on their physical engagement with cellular targets. Here we describe a broadly applicable method using bioluminescence resonance energy transfer (BRET) to reveal the binding characteristics of a drug with selected targets within intact cells. Cell-permeable fluorescent tracers are used in a competitive binding format to quantify drug engagement with the target proteins fused to Nanoluc luciferase. The approach enabled us to profile isozyme-specific engagement and binding kinetics for a panel of histone deacetylase (HDAC) inhibitors. Our analysis was directed particularly to the clinically approved prodrug FK228 (Istodax/Romidepsin) because of its unique and largely unexplained mechanism of sustained intracellular action. Analysis of the binding kinetics by BRET revealed remarkably long intracellular residence times for FK228 at HDAC1, explaining the protracted intracellular behaviour of this prodrug. Our results demonstrate a novel application of BRET for assessing target engagement within the complex milieu of the intracellular environment. PMID:26631872

  20. A new approach to the analysis of vessel residence time distribution curves

    NASA Astrophysics Data System (ADS)

    Ferro, Sergio P.; Principe, R. Javier; Goldschmit, Marcela B.

    2001-12-01

    Mathematical models for the evaluation of residence time distribution (RTD) curves on a large variety of vessels are presented. These models have been constructed by combination of different tanks or volumes. In order to obtain a good representation of RTD curves, a new volume (called convection diffusion volume) is introduced. The convection-diffusion volume allows the approximation of different experimental or numerical RTD curves with very simple models. An algorithm has been developed to calculate the parameters of the models for any given set of RTD curve experimental points. Validation of the models is carried out by comparison with experimental RTD curves taken from the literature and with a numerical RTD curve obtained by three-dimensional simulation of the flow inside a tundish.

  1. A nanoparticle formulation of disulfiram prolongs corneal residence time of the drug and reduces intraocular pressure.

    PubMed

    Nagai, Noriaki; Yoshioka, Chiaki; Mano, Yu; Tnabe, Wataru; Ito, Yoshimasa; Okamoto, Norio; Shimomura, Yoshikazu

    2015-03-01

    The goal in the search for successful therapies for glaucoma is the reduction of intraocular pressure (IOP), and the search for effective eye drops that reduce IOP is a high priority. We previously reported the potential of a 2-hydroxypropyl-β-cyclodextrin (HPβCD) solution containing 0.5% DSF (DSF solution) to provide effective anti-glaucoma treatment in eye drop form. In this study, we designed new ophthalmic formulations containing 0.5% DSF nanoparticles prepared by a bead mill method (DSFnano dispersion; particle size 183 ± 92 nm, mean ± S.D.), and compared the IOP-reducing effects of a DSFnano dispersion with those of a DSF solution. The high stability of the DSFnano dispersion was observed until 7 days after preparation, and the DSFnano dispersion showed high antimicrobial activity against Escherichia coli (ATCC 8739). In transcorneal penetration experiments using rabbit corneas, only diethyldithiocarbamate (DDC) was detected in the aqueous humor, while no DSF was detected. The DDC penetration level (area under the curve, AUC) and corneal residence time (mean residence time, MRT) of the DSFnano dispersion were approximately 1.45- and 1.44-fold higher than those of the DSF, respectively. Moreover, the IOP-reducing effects of the DSFnano dispersion were significantly greater than those of the DSF solution in rabbits (the IOP was enhanced by placing the rabbits in a dark room for 5 h). In addition, DSFnano dispersion are tolerated better by a corneal epithelial cell than DSF solution and commercially available timolol maleate eye drops. It is possible that dispersions containing DSF nanoparticles will provide new possibilities for the effective treatment of glaucoma, and that an ocular drug delivery system using drug nanoparticles may expand their usage as therapy in the ophthalmologic field. These findings provide significant information that can be used to design further studies aimed at developing anti-glaucoma drugs. PMID:25633346

  2. CISOCUR - Residence time modelling in the Curonian Lagoon and validation through stable isotope measurements

    NASA Astrophysics Data System (ADS)

    Umgiesser, Georg; Razinkovas-Baziukas, Arturas; Zemlys, Petras; Ertürk, Ali; Mėžinė, Jovita

    2015-04-01

    The spatial pattern of the hydrodynamic circulation of the Curonian lagoon, the largest European coastal lagoon, is still little understood. In absence of automatic current registration data all the existing models relied mostly on such data as water levels leaving high level of uncertainty. Here we present CISOCUR, a new project financed by European Social Fund under the Global Grant measure. The project applies a new methodology that uses the carbon stable isotope (SI) ratio of C12 and C13 that characterize different water sources entering the lagoon and may be altered by internal kinetic processes. Through the tracing of these isotope ratios different water masses can be identified. This gives the possibility to validate several hypotheses of water circulation and validate hydrodynamic models. In particular it will be possible to 1) trace water masses entering the lagoon through the Nemunas and the Klaipeda strait; 2) test the hypothesis of sediment transport mechanisms inside the lagoon; 3) evaluate the importance of physical forcing on the lagoon circulation. The use of a hydrodynamic finite element model, coupled with the SI method, will allow for a realistic description of the transport processes inside the Curonian lagoon. So the main research goal is to apply the stable isotope tracers and a finite element model to determine the circulation patterns in the Curonian lagoon. Here we show how the SI analysis was used to validate the hydrodynamic model on the basis of residence time. The average residence time of the Nemunas waters is estimated through SI data and is then compared with the model data computed through standard algorithms. Seasonal changes of carbon content are taken care of through a preliminary application of a carbon kinetic model. The results are compared to literature data.

  3. Residence time of water discharging from the Hanging Gardens of Zion Park

    USGS Publications Warehouse

    Kimball, B.A.; Christensen, P.K.

    1996-01-01

    The Hanging Gardens are a unique feature of Zion National Park. Knowledge of the source and residence time of water discharging from the Hanging Gardens is necessary to help preserve these features. Ground-water chemical and isotopic data distinguish the discharge from seeps and springs into two groups, one of low and one of high conductivity. Water with low conductivity likely originates as recharge near the steps and springs, and it only interacts with the Navajo Sandstone. High conductivity water, on the other hand, originates as recharge on the tops of plateaus to the east, where it interacts with marine rocks of the Carmel Formation. Carbon dating of these ground waters indicates that the low conductivity water is essentially modern recharge, while the high conductivity water was recharged 1,000 to 4,000 years ago.The Hanging Gardens are a unique feature of Zion National Park. Knowledge of the source and residence time of water discharging from the Hanging Gardens is necessary to help preserve these features. Ground-water chemical and isotopic data distinguish the discharge from seeps and springs into two groups, one of low and one of high conductivity. Water with low conductivity likely originates as recharge near the seeps and springs, and it only interacts with the Navajo Sandstone. High conductivity water, on the other hand, originates as recharge on the tops of plateaus to the cast, where it interacts with marine rocks of the Carmel Formation. Carbon dating of these ground waters indicates that the low conductivity water is essentially modern recharge, while the high conductivity water was recharged 1,000 to 4,000 years ago.

  4. Flowpaths, source water contributions and water residence times in a Mexican tropical dry forest catchment

    NASA Astrophysics Data System (ADS)

    Farrick, Kegan K.; Branfireun, Brian A.

    2015-10-01

    Runoff in forested tropical catchments has been frequently described in the literature as dominated by the rapid translation of rainfall to runoff through surface and shallow subsurface pathways. However, studies examining runoff generation in tropical catchments with highly permeable soils have received little attention, particularly in tropical dry forests. We present a study focused on identifying the dominant flowpaths, water sources and stream water residence times in a tropical dry forest catchment near the Pacific coast of central Mexico. During the wet season, pre-event water contributions to stormflow ranged from 72% to 97%, with the concentrations of calcium, magnesium, sodium and potassium closely coupling the geochemistry of baseflow and groundwater from the narrow riparian/near-stream zone. Baseflow from the intermittent stream showed a strongly damped isotopic signature and a mean baseflow residence time of 52-110 days was estimated. These findings all suggest that instead of the surface and near-surface subsurface lateral pathways observed over many tropical catchments, runoff is generated through vertical flow processes and the displacement and discharge of stored water from the saturated zone. As the wet season progressed, contributions from the saturated zone persisted; however, the stormflow and baseflow geochemistry suggests that the contributing area of the catchment increased. Our results show that during the early part of the wet season, runoff originated primarily from the headwater portion of the catchment. As the wet season progressed and catchment wetness increased, connectivity among sub-basin was improved, resulting in runoff contributions from across the entire catchment.

  5. Residence times of neutrally-buoyant matter such as larvae, sewage or nutrients on coral reefs

    NASA Astrophysics Data System (ADS)

    Black, Kerry P.; Gay, Stephen L.; Andrews, John C.

    1990-12-01

    Coral reef flushing times at an individual reef scale are specified and a general formula to determine these times is developed. The formula is confirmed by comparison with residence times predicted by numerical small-scale reef models, including those from a 4 month unsteady current simulation of John Brewer Reef on Australia's Great Barrier Reef. The method proves to be a satisfactory alternative to the numerical modelling. When neutrally-buoyant material around a reef is removed by the currents, the concentrations decay exponentially. The decay rate depends primarily on free stream current and reef dimensions. Secondary factors are the tidal excursion, shelf depth, lagoon size and residual current in the lee of the reef. These factors, when combined into a decay coefficient, specify the rate of loss of neutrally-buoyant material (e.g. some larvae, pollutants and sewage) from a coral reef and its surrounds. The analytical formula can be used to predict the flushing rates or the percentage of material still remaining on a reef after a selected time interval. We demonstrate that material can remain on or near typical reefs in common weather conditions for several weeks.

  6. PEGylation of antibody fragments greatly increases their local residence time following delivery to the respiratory tract.

    PubMed

    Koussoroplis, Salome Juliette; Paulissen, Geneviève; Tyteca, Donatienne; Goldansaz, Hadi; Todoroff, Julie; Barilly, Céline; Uyttenhove, Catherine; Van Snick, Jacques; Cataldo, Didier; Vanbever, Rita

    2014-08-10

    Inhalation aerosols offer a targeted therapy for respiratory diseases. However, the therapeutic efficacy of inhaled biopharmaceuticals is limited by the rapid clearance of macromolecules in the lungs. The aim of this research was to study the effects of the PEGylation of antibody fragments on their local residence time after administration to the respiratory tract. We demonstrate that the conjugation of a two-armed 40-kDa polyethylene glycol (PEG) chain to anti-interleukin-17A (IL-17A) F(ab')2 and anti-IL-13 Fab' greatly prolonged the presence of these fragments within the lungs of mice. The content of PEGylated antibody fragments within the lungs plateaued up to 4h post-delivery, whereas the clearance of unconjugated proteins started immediately after administration. Forty-eight hours post-delivery, F(ab')2 and Fab' contents in the lungs had decreased to 10 and 14% of the dose initially deposited, respectively. However, this value was 40% for both PEG40-F(ab')2 and PEG40-Fab'. The prolonged pulmonary residency of the anti-IL-17A PEG40-F(ab')2 translated into an improved efficacy in reducing lung inflammation in a murine model of house dust mite-induced lung inflammation. We demonstrate that PEGylated proteins were principally retained within the lung lumen rather than the nasal cavities or lung parenchyma. In addition, we report that PEG increased pulmonary retention of antibody fragments through mucoadhesion and escape from alveolar macrophages rather than increased hydrodynamic size or improved enzymatic stability. The PEGylation of proteins might find broad application in the local delivery of therapeutic proteins to diseased airways. PMID:24845126

  7. A Randomized Cross-over Air Filtration Intervention Trial for Reducing Cardiovascular Health Risks in Residents of Public Housing near a Highway

    PubMed Central

    Padró-Martínez, Luz T.; Owusu, Emmanuel; Reisner, Ellen; Zamore, Wig; Simon, Matthew C.; Mwamburi, Mkaya; Brown, Carrie A.; Chung, Mei; Brugge, Doug; Durant, John L.

    2015-01-01

    Exposure to traffic-generated ultrafine particles (UFP; particles <100 nm) is likely a risk factor for cardiovascular disease. We conducted a trial of high-efficiency particulate arrestance (HEPA) filtration in public housing near a highway. Twenty residents in 19 apartments living <200 m from the highway participated in a randomized, double-blind crossover trial. A HEPA filter unit and a particle counter (measuring particle number concentration (PNC), a proxy for UFP) were installed in living rooms. Participants were exposed to filtered air for 21 days and unfiltered air for 21 days. Blood samples were collected and blood pressure measured at days 0, 21 and 42 after a 12-hour fasting period. Plasma was analyzed for high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), tumor necrosis factor alpha-receptor II (TNF-RII) and fibrinogen. PNC reductions ranging from 21% to 68% were recorded in 15 of the apartments. We observed no significant differences in blood pressure or three of the four biomarkers (hsCRP, fibrinogen, and TNF-RII) measured in participants after 21-day exposure to HEPA-filtered air compared to measurements after 21-day exposure to sham-filtered air. In contrast, IL-6 concentrations were significantly higher following HEPA filtration (0.668 pg/mL; CI = 0.465–0.959) compared to sham filtration. Likewise, PNC adjusted for time activity were associated with increasing IL-6 in 14- and 21-day moving averages, and PNC was associated with decreasing blood pressure in Lags 0, 1 and 2, and in a 3-day moving average. These negative associations were unexpected and could be due to a combination of factors including exposure misclassification, unsuccessful randomization (i.e., IL-6 and use of anti-inflammatory medicines), or uncontrolled confounding. Studies with greater reduction in UFP levels and larger sample sizes are needed. There also needs to be more complete assessment of resident time activity and of outdoor vs. indoor source contributions

  8. A Randomized Cross-over Air Filtration Intervention Trial for Reducing Cardiovascular Health Risks in Residents of Public Housing near a Highway.

    PubMed

    Padró-Martínez, Luz T; Owusu, Emmanuel; Reisner, Ellen; Zamore, Wig; Simon, Matthew C; Mwamburi, Mkaya; Brown, Carrie A; Chung, Mei; Brugge, Doug; Durant, John L

    2015-07-01

    Exposure to traffic-generated ultrafine particles (UFP; particles <100 nm) is likely a risk factor for cardiovascular disease. We conducted a trial of high-efficiency particulate arrestance (HEPA) filtration in public housing near a highway. Twenty residents in 19 apartments living <200 m from the highway participated in a randomized, double-blind crossover trial. A HEPA filter unit and a particle counter (measuring particle number concentration (PNC), a proxy for UFP) were installed in living rooms. Participants were exposed to filtered air for 21 days and unfiltered air for 21 days. Blood samples were collected and blood pressure measured at days 0, 21 and 42 after a 12-hour fasting period. Plasma was analyzed for high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), tumor necrosis factor alpha-receptor II (TNF-RII) and fibrinogen. PNC reductions ranging from 21% to 68% were recorded in 15 of the apartments. We observed no significant differences in blood pressure or three of the four biomarkers (hsCRP, fibrinogen, and TNF-RII) measured in participants after 21-day exposure to HEPA-filtered air compared to measurements after 21-day exposure to sham-filtered air. In contrast, IL-6 concentrations were significantly higher following HEPA filtration (0.668 pg/mL; CI = 0.465-0.959) compared to sham filtration. Likewise, PNC adjusted for time activity were associated with increasing IL-6 in 14- and 21-day moving averages, and PNC was associated with decreasing blood pressure in Lags 0, 1 and 2, and in a 3-day moving average. These negative associations were unexpected and could be due to a combination of factors including exposure misclassification, unsuccessful randomization (i.e., IL-6 and use of anti-inflammatory medicines), or uncontrolled confounding. Studies with greater reduction in UFP levels and larger sample sizes are needed. There also needs to be more complete assessment of resident time activity and of outdoor vs. indoor source contributions

  9. Evaluation of hydraulic efficiency of disinfection systems based on residence time distribution curves.

    PubMed

    Wilson, Jordan M; Venayagamoorthy, Subhas K

    2010-12-15

    Hydraulic efficiency is a vital component in evaluating the disinfection capability of a contact system. Current practice evaluates these systems based upon the theoretical detention time (TDT) and the rising limb of the residence time distribution (RTD) curve. This evaluation methodology is expected because most systems are built based on TDT under a "black-box" approach to disinfection system design. Within recent years, the proliferation of computational fluid dynamics (CFD) has allowed a more insightful approach to disinfection system design and analysis. Research presented in this study using CFD models and physical tracer studies shows that evaluation methods based upon TDT tend to overestimate, severely in some instances, the actual hydraulic efficiency as obtained from the system's flow and scalar transport dynamics and subsequent RTD curve. The main objective of this study was to analyze an alternative measure of hydraulic efficiency, the ratio t(10)/t(90), where t(10) and t(90) are the time taken for 10 and 90% of the input concentration to be observed at the outlet of a system, respectively, for various disinfection systems, primarily a pipe loop system, pressurized tank system, and baffled tank system, from their respective RTD curves and compare the results to the current evaluation method. PMID:21090605

  10. Determination of the Residence Time of Food Particles During Aseptic Sterilization

    NASA Technical Reports Server (NTRS)

    Carl, J. R.; Arndt, G. D.; Nguyen, T. X.

    1994-01-01

    The paper describes a non-invasive method to measure the time an individual particle takes to move through a length of stainless steel pipe. The food product is in two phase flow (liquids and solids) and passes through a pipe with pressures of approximately 60 psig and temperatures of 270-285 F. The proposed problem solution is based on the detection of transitory amplitude and/or phase changes in a microwave transmission path caused by the passage of the particles of interest. The particles are enhanced in some way, as will be discussed later, such that they will provide transitory changes that are distinctive enough not to be mistaken for normal variations in the received signal (caused by the non-homogeneous nature of the medium). Two detectors (transmission paths across the pipe) will be required and place at a known separation. A minimum transit time calculation is made from which the maximum velocity can be determined. This provides the minimum residence time. Also average velocity and statistical variations can be computed so that the amount of 'over-cooking' can be determined.

  11. U Isotope Systematics on Groundwaters from Southwestern France : Mixing Processes and Residence Times

    NASA Astrophysics Data System (ADS)

    Innocent, C.; Malcuit, E.; Négrel, P.

    2011-12-01

    The Eocene Sands Aquifer of the Aquitanian Basin (Southwestern France) has been extensively studied for its hydrology, hydrogeochemistry and also for stable isotopes (André, 2002; André et al., 2005). 14C dates were also obtained in the southern part of the aquifer (André, 2002). Recently, in the framework of the CARISMEAU research project (Négrel et al., 2007), groundwaters have been analyzed for their U activity ratio in order to put some constraints on their residence time in the aquifer. A excellent correlation has been found between 234U/238U ratios (which can be as high as 13.5) and 14C dates, which allowed to propose residence times for the analyzed groundwaters at the scale of the whole aquifer (including the city of Bordeaux and its suburb) (Innocent and Négrel, 2008; submitted). The second step of the CARISMEAU research project (CARISMEAU 2) now focusses on the restricted "Entre-Deux-Mers" area. New groundwaters have been recovered and analyzed for their U isotopic composition. As for previous data, U activity ratios are typically very high, ranging from 2.9 to 8.6. Owing to additional 14C ages from the northern part of the aquifer, it is shown that most of the measured uranium activity ratios correlate with these 14C dates and fall on or close to the straight line defined previously (see above). As a consequence, residence times derived from U isotopic compositions fairly agree with 14C data, with only one exception from a groundwater which plots apart from the correlation line. Pumping tests have been done at a selected site (EMZM 7), involving pumping times of 1 hour, 8 hours and 16 hours. For each pumping time, waters have been recovered at different, increasing pumping rates of 80 m3 per hour, 120 m3 per hour, 160 m3 per hour, and 120 m3 per hour. The chemical composition of these twelve waters has not been found to vary significantly. Uranium activities are constant for ten of the twelve groundwaters (around 6.5, with a U concentration around

  12. Organizational and Individual Conditions Associated with Depressive Symptoms among Nursing Home Residents over Time

    ERIC Educational Resources Information Center

    Cassie, Kimberly M.; Cassie, William E.

    2012-01-01

    Purpose: To examine the effect of organizational culture and climate on depressive symptoms among nursing home residents. Design and Methods: Using a pooled cross-sectional design, this study examines a sample of 23 nursing homes, 1,114 employees, and 5,497 residents. Depressive symptoms were measured using the Minimum Data Set, Depression Rating…

  13. Effect of storm events and sustained winds on residence time in a shallow, back-barrier estuary

    NASA Astrophysics Data System (ADS)

    Defne, Z.; Ganju, N. K.

    2012-12-01

    The Barnegat Bay-Little Egg Harbor estuary is a back-barrier lagoon that stretches 70 km along New Jersey's Atlantic coast. With an average depth of 1.5 meters and three restricted inlets, it is relatively shallow and poorly flushed. Ongoing urbanization in the watershed and other stressors have been implicated in deteriorating water quality; the relatively long residence time (i.e. the time it takes for a sample water parcel to leave the estuary) may be a hindrance to improvements. Prior studies based on a depth-averaged two-dimensional numerical circulation model indicate an average residence time of 7 weeks (up to 10 weeks in a less dynamic period during summer season) for Barnegat Bay. We developed and calibrated a three-dimensional hydrodynamic model of the Barnegat Bay-Little Egg Harbor system to investigate scenarios of residence time. Preliminary results show that the historical change of the bathymetry and morphology of Barnegat Inlet has a substantial impact on the hydrodynamics within the bay. Therefore, the model was run with updated bathymetry from recent multibeam surveys to estimate residence times under several forcing scenarios. The model was forced with tides, atmospheric forcing, and riverine inflow and was calibrated with the observed water levels over a two-month period. Particles were seeded randomly throughout the estuary (horizontally and vertically) and released after the model spin-up time. The relative influences of the forcing mechanisms were investigated by selectively eliminating them from the model. Storm events can be identified with the relative increase in flushing due to remote forcing and wind setup, whereas sustained winds may reduce or increase the residence time depending on their direction. Future changes in storm strength and frequency may alter residence times in a nonlinear fashion.

  14. Determining the True Residence Time Distribution Curve of Phase I System

    SciTech Connect

    Robinson, Bruce A.

    1982-08-24

    Previous engineering analysis of the Br82 tracer experiments failed to account for the fact that the fluid was being recirculated during these tests. Thus, the concentration vs. volume curves shown in the Run Segments 4 and 5 reports and elsewhere are not really the response of the system to a pulse of tracer. These data are complicated by the fact that at later times most of the tracer being measured was not the original pulse, but the tracer on its second or third pass through the reservoir. When this recirculation effect is subtracted out of the original concentration vs. volume curves, the true residence time distribution (RTD) for the Phase I system indicates that the "long tail" on these curves is not caused by dispersion but results almost entirely from recirculation. The RTD curve for this system cannot be modeled precisely using a one parameter model, but can probably be described by a combination of hydrodynamic and turbulent dispersion in a single fracture. Alternatively, flow through multiple fractures could easily result in the RTD curves determined during Run Segments 4 and 5.

  15. TSPO ligand residence time: a new parameter to predict compound neurosteroidogenic efficacy

    PubMed Central

    Costa, Barbara; Da Pozzo, Eleonora; Giacomelli, Chiara; Barresi, Elisabetta; Taliani, Sabrina; Da Settimo, Federico; Martini, Claudia

    2016-01-01

    The pharmacological activation of the cholesterol-binding Translocator Protein (TSPO) leads to an increase of endogenous steroids and neurosteroids determining benefic pleiotropic effects in several pathological conditions, including anxiety disorders. The relatively poor relationship between TSPO ligand binding affinities and steroidogenic efficacies prompted us to investigate the time (Residence Time, RT) that a number of compounds with phenylindolylglyoxylamide structure (PIGAs) spends in contact with the target. Here, given the poor availability of TSPO ligand kinetic parameters, a kinetic radioligand binding assay was set up and validated for RT determination using a theoretical mathematical model successfully applied to other ligand-target systems. TSPO ligand RT was quantified and the obtained results showed a positive correlation between the period for which a drug interacts with TSPO and the compound ability to stimulate steroidogenesis. Specifically, the TSPO ligand RT significantly fitted both with steroidogenic efficacy (Emax) and with area under the dose-response curve, a parameter combining drug potency and efficacy. A positive relation between RT and anxiolytic activity of three compounds was evidenced. In conclusion, RT could be a relevant parameter to predict the steroidogenic efficacy and the in vivo anxiolytic action of new TSPO ligands. PMID:26750656

  16. Computerized evaluation of mean residence times in multicompartmental linear system and pharmacokinetics.

    PubMed

    Villalba, J M; Barbero, A J; Diaz-Sierra, R; Arribas, E; Garcia-Meseguer, M J; Garcia-Sevilla, F; Garcia-Moreno, M; De Labra, J A Vidal; Varon, R

    2011-04-15

    Deriving mean residence times (MRTs) is an important task both in pharmacokinetics and in multicompartmental linear systems. Taking as starting point the analysis of MRTs in open or closed (Garcia-Meseguer et al., Bull Math Biol 2003, 65, 279) multicompartmental linear systems, we implement a versatile software, using the Visual Basic 6.0 language for MS-Windows, that is easy to use and with a user-friendly format for the input of data and the output of results. For any multicompartmental linear system of up to 512 compartments, whether closed or open, with traps or without traps and with zero input in one or more of the compartments, this software allows the user to obtain the symbolic expressions, in the most simplified form, and/or the numerical values of the MRTs in any of its compartments, in the entire system or in a part of the system. As far as we known from the literature, such a software has not been implemented before. The advantage of the present software is that it reduces on the work time needed and minimizes the human errors that are frequent in compartmental systems even those that are relatively staightforward. The software bioCelTer, along with instructions, can be downloaded from http://oretano.iele-ab.uclm.es/~fgarcia/bioCelTer/. PMID:20960438

  17. Seasonal variation of residence time in spring and groundwater evaluated by CFCs and numerical simulation in mountainous headwater catchment

    NASA Astrophysics Data System (ADS)

    Tsujimura, Maki; Watanabe, Yasuto; Ikeda, Koichi; Yano, Shinjiro; Abe, Yutaka

    2016-04-01

    Headwater catchments in mountainous region are the most important recharge area for surface and subsurface waters, additionally time information of the water is principal to understand hydrological processes in the catchments. However, there have been few researches to evaluate variation of residence time of subsurface water in time and space at the mountainous headwaters especially with steep slope. We investigated the temporal variation of the residence time of the spring and groundwater with tracing of hydrological flow processes in mountainous catchments underlain by granite, Yamanashi Prefecture, central Japan. We conducted intensive hydrological monitoring and water sampling of spring, stream and ground waters in high-flow and low-flow seasons from 2008 through 2013 in River Jingu Watershed underlain by granite, with an area of approximately 15 km2 and elevation ranging from 950 m to 2000 m. The CFCs, stable isotopic ratios of oxygen-18 and deuterium, inorganic solute constituent concentrations were determined on all water samples. Also, a numerical simulation was conducted to reproduce of the average residence times of the spring and groundwater. The residence time of the spring water estimated by the CFCs concentration ranged from 10 years to 60 years in space within the watershed, and it was higher (older) during the low flow season and lower (younger) during the high flow season. We tried to reproduce the seasonal change of the residence time in the spring water by numerical simulation, and the calculated residence time of the spring water and discharge of the stream agreed well with the observed values. The groundwater level was higher during the high flow season and the groundwater dominantly flowed through the weathered granite with higher permeability, whereas that was lower during the low flow season and that flowed dominantly through the fresh granite with lower permeability. This caused the seasonal variation of the residence time of the spring

  18. Naturalization of central European plants in North America: species traits, habitats, propagule pressure, residence time.

    PubMed

    Pyšek, Petr; Manceur, Ameur M; Alba, Christina; McGregor, Kirsty F; Pergl, Jan; Stajerová, Katerina; Chytrý, Milan; Danihelka, Jiří; Kartesz, John; Klimesova, Jitka; Lucanova, Magdalena; Moravcová, Lenka; Nishino, Misako; Sadlo, Jiri; Suda, Jan; Tichy, Lubomir; Kühn, Ingolf

    2015-03-01

    The factors that promote invasive behavior in introduced plant species occur across many scales of biological and ecological organization. Factors that act at relatively small scales, for example, the evolution of biological traits associated with invasiveness, scale up to shape species distributions among different climates and habitats, as well as other characteristics linked to invasion, such as attractiveness for cultivation (and by extension propagule pressure). To identify drivers of invasion it is therefore necessary to disentangle the contribution of multiple factors that are interdependent. To this end, we formulated a conceptual model describing the process of invasion of central European species into North America based on a sequence of "drivers." We then used confirmatory path analysis to test whether the conceptual model is supported by a statistical model inferred from a comprehensive database containing 466 species. The path analysis revealed that naturalization of central European plants in North America, in terms of the number of North American regions invaded, most strongly depends on residence time in the invaded range and the number of habitats occupied by species in their native range. In addition to the confirmatory path analysis, we identified the effects of various biological traits on several important drivers of the conceptualized invasion process. The data supported a model that included indirect effects of biological traits on invasion via their effect on the number of native range habitats occupied and cultivation in the native range. For example, persistent seed banks and longer flowering periods are positively correlated with number of native habitats, while a stress-tolerant life strategy is negatively correlated with native range cultivation. However, the importance of the biological traits is nearly an order of magnitude less than that of the larger scale drivers and highly dependent on the invasion stage (traits were associated

  19. Watershed Influences on Residence Time and Oxygen Reduction Rates in an Agricultural Landscape

    NASA Astrophysics Data System (ADS)

    Shope, C. L.; Tesoriero, A. J.

    2015-12-01

    Agricultural use of synthetic fertilizers and animal manure has led to increased crop production, but also elevated nitrogen concentrations in groundwater, resulting in impaired water quality. Groundwater oxygen concentrations are a key indicator of potential biogeochemical processes, which control water/aquifer interactions and contaminant transport. The U.S. Geological Survey's National Water-Quality Assessment Program has a long-history of studying nutrient transport and processing across the United States and the Glacial Aquifer system in particular. A series of groundwater well networks in Eastern Wisconsin is being used to evaluate the distribution of redox reaction rates over a range of scales with a focus on dissolved O2 reduction rates. An analysis of these multi-scale networks elucidates the influence of explanatory variables (i.e.: soil type, land use classification) on reduction rates and redox reactions throughout the Fox-Wolf-Peshtigo watersheds. Multiple tracers including dissolved gasses, tritium, helium, chlorofluorocarbons, sulfur hexafluoride, and carbon-14 were used to estimate groundwater ages (0.8 to 61.2 yr) at over 300 locations. Our results indicate O2 reduction rates along a flowpath study area (1.2 km2) of 0.15 mg O2 L-1 yr-1 (0.12 to 0.18 mg O2 L-1 yr-1) up to 0.41 mg O2 L-1 yr-1 (0.23 to 0.89 mg O2 L-1 yr-1) for a larger scale land use study area (3,300 km2). Preliminary explanatory variables that can be used to describe the variability in reduction rates include soil type (hydrologic group, bulk density) and chemical concentrations (nitrite plus nitrate, silica). The median residence time expected to reach suboxic conditions (≤ 0.4 mg O2 L-1) for the flowpath and the land use study areas was 66 and 25 yr, respectively. These results can be used to elucidate and differentiate the impact of residence time on groundwater quality vulnerability and sustainability in agricultural regions without complex flow models.

  20. Residence time, mineralization processes and groundwater origin within a carbonate coastal aquifer with a thick unsaturated zone

    NASA Astrophysics Data System (ADS)

    Santoni, S.; Huneau, F.; Garel, E.; Vergnaud-Ayraud, V.; Labasque, T.; Aquilina, L.; Jaunat, J.; Celle-Jeanton, H.

    2016-09-01

    This study aims at establishing groundwater residence times, identifying mineralization processes and determining groundwater origins within a carbonate coastal aquifer with thick unsaturated zone and lying on a granitic depression. A multi-tracer approach (major ions, SiO2, Br-, Ba+, Sr2+, 18O, 2H, 13C, 3H, Ne, Ar) combined with a groundwater residence time determination using CFCs and SF6 allows defining the global setting of the study site. A typical mineralization conditioned by the sea sprays and the carbonate matrix helped to validate the groundwater weighted residence times from using a binary mixing model. Terrigenic SF6 excesses have been detected and quantified, which permits to identify a groundwater flow from the surrounding fractured granites towards the lower aquifer principally. The use of CFCs and SF6 as a first hydrogeological investigation tool is possible and very relevant despite the thick unsaturated zone and the hydraulic connexion with a granitic environment.

  1. Variability of Residence Time tracer Concentrations at the Southern Sierra Critical Zone Observatory during the California Drought

    NASA Astrophysics Data System (ADS)

    Visser, A.; Thaw, M.; Stacy, E.; Hunsaker, C. T.; Bibby, R. K.; Deinhart, A.; Schorzman, K.; Egnatuk, C. M.; Conklin, M. H.; Esser, B.

    2015-12-01

    California water supply from high elevation snow melt is vulnerable to climate change and prolonged drought conditions. Reduced snow pack and earlier snow melt will result in a greater reliance on man-made reservoirs and subsurface catchment storage. To gain insight into the subsurface storage volume of high elevation catchments, we studied the residence time distribution of surface water leaving the Southern Sierra Critical Zone Observatory. Since October 2014, we have collected monthly samples of two residence time tracers with contrasting half-lives: sulfur-35 (87.5 days) and tritium (12.32 years). Upstream catchment area at the three nested sampling locations is 1 km2 (P301 sub-catchment), 4 km2 (Providence Creek) and ~50 km2 (Big Creek). Samples were analyzed at LLNL by low level liquid scintillation counting and noble gas mass spectrometry after helium accumulation. Variations in tracer concentrations in precipitation, both for tritium (11-24 pCi/L) and sulfur-35 (24-100 mBq/L), complicate straightforward interpretation of residence times. Sulfur-35 concentrations show that last year precipitation contributes 1% - 10% of total stream flow, even during peak snowmelt. Tritium concentrations in stream flow vary between 40% and 60% of the initial concentration in precipitation (15.5 pCi/L), indicating that water leaving the catchment has a residence time on the order of years to decades. Additional analyses of sodium-22 (2.6 year half-life) will aid in deconvoluting the residence time distribution. These low tracer concentrations can be attributed to current severe drought conditions, resulting in low discharge rates and longer residence times. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-675107

  2. RELIANCE ON GEOCODED MATERNAL RESIDENCE: IMPACT ON A POPULATION-BASED CASE-CONTROL STUDY OF AIR QUALITY AND BIRTH DEFECTS

    EPA Science Inventory

    Introduction: Unbiased geocoding of maternal residence is critical to the success of an ongoing population-based case-control study of exposure to five criteria air pollutants and the risk of selected birth defects in seven Texas counties between 1997 and 2000. The geocoded res...

  3. Effects of temperature, moisture and residence time in the properties of full fat soybean flour produced in a twin extruder.

    PubMed

    Serna-Saldivar, S O; Cabral, L C

    1997-03-01

    Soybeans were dehulled, roll-milled into grits, conditioned to 18 or 21% moisture and continuously cooked in a twin extruder at three temperature programs and two residence times. The resulting extrudates were further dried and roll-milled into flour and characterized for their physical, chemical and functional properties. The urease activity and nitrogen solubility index (NSI) decreased with increased extrusion temperature, residence time and soybean grits moisture content. The best pre-cooked full fat flours had a urease activity lower than 0.2 and a NSI higher than 15%. PMID:9429645

  4. Groundwater residence time : tell me who you are and I will tell which information you may provide

    NASA Astrophysics Data System (ADS)

    Aquilina, Luc; Labasque, Thierry; Kolbe, Tamara; Marçais, Jean; Leray, Sarah; Abbott, Ben; de Dreuzy, Jean-Raynald

    2016-04-01

    Groundwater residence-time or ages have been widely used in hydrogeology during the last decades. Following tritium measurements, anthropogenic gases (CFC, SF6, 35Kr) have been developed. They provide information at the aquifer scale on long residence times. They complement the more localized data obtained from sparse boreholes with hydraulic and geophysical methods. Anthropogenic tracer concentrations are most generally considered as "Groundwater ages" using a piston flow model providing an order of magnitude for the residence time. More advanced information can however be derived from the combined analysis of the tracer concentrations. For example, the residence time distribution over the last 50 years can be well approached by the concentration of two sufficient different anthropogenic tracers in the group (CFC, SF6, 35Kr), i.e. tracers whose anthropogenic chronicles are sufficiently different. And, with additional constrains on geological and hydraulic properties, groundwater ages contribute to characterize the aquifer structures and the groundwater resources. Complex geological environments also include old groundwater bodies in extremely confined aquifer sections. In such cases, various tracers are related to highly different processes. CFCs can be taken as a marker of modern contamination to track exchanges between shallower and deeper aquifers, leakage processes, and modification of circulations linked to recent anthropogenic changes. 14C or 36Cl can be used to evidence much older processes but have to be related to the history of the chemical element itself. Numerous field studies in fact demonstrate the broad-range extent of the residence time distribution spanning in some cases several orders of magnitude. Flow and transport models in heterogeneous structures confirm such wide residence times and help to characterize their distribution. Residence times also serve as a privileged interface to the fate of some contaminants in aquifers or to trace

  5. Estimation of sediment residence times in subtropical highland catchments of central Mexico combining river gauging and fallout radionuclides

    NASA Astrophysics Data System (ADS)

    Evrard, Olivier; Némery, Julien; Gratiot, Nicolas; Duvert, Clément; Lefèvre, Irène; Ayrault, Sophie; Esteves, Michel; Bonté, Philippe

    2010-05-01

    Subtropical regions of the world are affected by intense soil erosion associated with deforestation, overgrazing and cropping intensification. This land degradation leads to important on-site (e.g. decrease in soil fertility) and off-site impacts (e.g. reservoir sedimentation, water pollution). This study determined the mean sediment residence times in soils and rivers of three catchments (3 - 12 km²) with contrasted land uses (i.e. cropland, forests, rangelands, extended gully networks) located in highlands of the transvolcanic belt of central Mexico. Calculations were based on rainfall and river gauging as well as on fallout radionuclide measurements (Be-7, Cs-137, Pb-210). Atmospheric deposition of Be-7 and Pb-210 was estimated based on the analysis of rainfall precipitated samples. Rainfall samples were collected all throughout the rainy season in order to take account of the temporal variations of the radionuclide fluxes. Furthermore, sampling of suspended sediment was conducted at the outlet of each catchment during most of the storms that occurred throughout the 2009 rainy season. Be-7, Cs-137 and Pb-210 concentrations of this sediment were determined by gamma-spectrometry. A two-box balance model was then used to estimate the sediment residence time and the inventory of radionuclides in the three selected catchments. This model subdivided each catchment into two boxes: (i) a "soil-box" characterised by low transport velocities and hence long radionuclide residence times and (ii) a "river-box" covering the river surface and its surroundings characterised by quicker exchanges and shorter radionuclide residence times. Input and output fluxes of sediment and radionuclides were taken into account in each box. Radioactive decay during the residence time of sediment was also considered. The mean residence time of sediment in soils ranged between 13,300 - 28,500 years. In contrast, sediment residence time in rivers was much shorter, fluctuating between 28 and 393

  6. Greenland meltwater impacts on the 234U/238U composition of seawater, the role of subglacial residence time.

    NASA Astrophysics Data System (ADS)

    Arendt, C. A.; Aciego, S.; Sims, K. W. W.; Stevenson, E. I.

    2014-12-01

    The chemical composition of seawater depends on the sources and sinks of the constituent elements, including those derived from continental weathering and transported by rivers. Glacial melt rivers compose a significant percentage of contributing water in the high latitudes, and potentially impact the overall composition of seawater. The magnitude of the chemical changes glacial melt can have on adjacent seawater depends on the composition of glacial melt, which is directly influenced by the subglacial residence time of meltwater. Long residence times correlate to subglacial water with both high cation concentrations and 234U/238U isotopic compositions. Thus, the residence time of subglacial water and corresponding subglacial geochemistry impacts the 234U/238U composition of proximal seawater and potentially global seawater. To test the influence of subglacial water residence times on seawater chemistry we examined the U-series composition of four outlet glaciers directly connected to the Southern Greenland Ice Sheet located near Narsarsuaq, Ilulissat, Nuuk and Kulusuk, and adjacent seawater at each site. All outlet glaciers in this study are located within three of the five primary drainage basins beneath the Greenland Ice Sheet, each in varying stages of subglacial hydrologic evolution, resulting in unique chemical compositions of meltwater draining from each location. At these four locations we found subglacial water residence time values of 10-1000 years. In regions where the U concentration, 234U/238U isotopic composition and residence times were high (1.01 ppb, 1.263 and ~1,000 years in Narsarsuaq) the adjacent seawater 234U/238U composition was elevated (1.152) compared to regions where the U concentration, 234U/238U isotopic composition and residence times were low (0.05 ppb, 1.008 and ~10 years in Illulisat) the adjacent seawater 234U/238U composition remained around the assumed seawater average (1.145). Through this study we observed a direct impact of

  7. Effects of residence time on summer nitrate uptake in Mississippi River flow-regulated backwaters

    USGS Publications Warehouse

    James, W.F.; Richardson, W.B.; Soballe, D.M.

    2008-01-01

    Nitrate uptake may be improved in regulated floodplain rivers by increasing hydrological connectivity to backwaters. We examined summer nitrate uptake in a series of morphologically similar backwaters on the Upper Mississippi River receiving flow-regulated nitrate loads via gated culverts. Flows into individual backwaters were held constant over a summer period but varied in the summers of 2003 and 2004 to provide a range of hydraulic loads and residence times (??). The objectives were to determine optimum loading and ?? for maximum summer uptake. Higher flow adjustment led to increased loading but lower ?? and contact time for uptake. For highest flows, ?? was less than 1 day resulting in lower uptake rates (Unet, 4000 m). For low flows, ?? was greater than 5 days and U% approached 100%, but Unet was 200 mg m-2 day-1. Snet was < half the length of the backwaters under these conditions indicating that most of the load was assimilated in the upper reaches, leading to limited delivery to lower portions. Unet was maximal (384-629 mg m-2 day-1) for intermediate flows and ?? ranging between 1 and 1.5 days. Longer Snet (2000-4000 m) and lower U% (20-40%) reflected limitation of uptake in upper reaches by contact time, leading to transport to lower reaches for additional uptake. Uptake by ???10 000 ha of reconnected backwaters along the Upper Mississippi River (13% of the total backwater surface area) at a Unet of ???630 mg m-2 day-1 would be the equivalent of ???40% of the summer nitrate load (155 mg day-1) discharged from Lock and Dam 4. These results indicate that backwater nitrate uptake can play an important role in reducing nitrate loading to the Gulf of Mexico. Copyright ?? 2008 John Wiley & Sons, Ltd.

  8. Mean residence time of leaf number, area, mass, and nitrogen in canopy photosynthesis.

    PubMed

    Hirose, Tadaki; Oikawa, Shimpei

    2012-08-01

    Mean residence time (MRT) of plant nitrogen (N), which is an indicator of the expected length of time N newly taken up is retained before being lost, is an important component in plant nitrogen use. Here we extend the concept MRT to cover such variables as leaf number, leaf area, leaf dry mass, and nitrogen in the canopy. MRT was calculated from leaf duration (i.e., time integral of standing amount) divided by the total production of leaf variables. We determined MRT in a Xanthium canadense stand established with high or low N availability. The MRT of leaf number may imply longevity of leaves in the canopy. We found that the MRT of leaf area and dry mass were shorter than that of leaf number, while the MRT of leaf N was longer. The relatively longer MRT of leaf N was due to N resorption before leaf shedding. The MRT of all variables was longer at low N availability. Leaf productivity is the rate of canopy photosynthesis per unit amount of leaf variables, and multiplication of leaf productivity by MRT gives the leaf photosynthetic efficiency (canopy photosynthesis per unit production of leaf variables). The photosynthetic efficiency of leaf number implies the lifetime carbon gain of a leaf in the canopy. The analysis of plant-level N use efficiency by evaluating the N productivity and MRT is a well-established approach. Extension of these concepts to leaf number, area, mass, and N in the canopy will clarify the underlying logic in the study of leaf life span, leaf area development, and dry mass and N use in canopy photosynthesis. PMID:22349752

  9. Rn as a geochemical tool for estimating residence times in the hyporheic zone and its application to biogeochemical processes

    NASA Astrophysics Data System (ADS)

    Gilfedder, Benjamin; Dörner, Sebastian; Ebertshäuser, Marlene Esther; Glaser, Barbara; Klug, Maria; Pittroff, Marco; Pieruschka, Ines; Waldemer, Carolin

    2014-05-01

    The hyporheic zone is at the interface between groundwater and surface water systems. It is also often a geochemical and redox boundary between typically reduced groundwater and oxic surface water. It experiences dynamic physical and chemical conditions as both groundwater fluxes and surface water levels vary in time and space. This can be particularly important for processes such as biogeochemical processing of nutrients and carbon. There has recently been an increasing focus on coupling residence times of surface water in the hyporheic zone with biogeochemical reactions. While geochemical profiles can be readily measured using established geochemical sampling techniques (e.g. peepers), quantifying surface water residence times and flow paths within the hyporheic zone is more elusive. The nobel gas radon offers a method for quantification of surface water residence times in the hyporheic zone. Radon activities are typically low in surface waters due to degassing to the atmosphere and decay. However once the surface water flows into the hyporheic zone radon accumulates along the flow path due to emanation from the sediments. Using simple analytical equations the water residence time can be calculated based on the difference between measured 222Rn activities and 222Rn activities at secular equilibrium, with a maximum limit of about 20 days (depending on measurement precision). Rn is particularly suited to residence time measurements in the hyporheic zone since it does not require addition of tracers to the stream nor does it require complex simulations and assumptions (such as 1D vertical flow) as for temperature measurements. As part of the biogeochemistry course at the University of Bayreuth, we have investigated the coupling of redox processes and water residence times in the hyporheic zone using 222Rn as a tracer for residence time. Of particular interest were nitrate and sulfate reduction and methane and CO2 production. Measurements were made in a sandy section

  10. Subunit Stabilization and Polyethylene Glycolation of Cocaine Esterase Improves In Vivo Residence Time

    SciTech Connect

    Narasimhan, Diwahar; Collins, Gregory T.; Nance, Mark R.; Nichols, Joseph; Edwald, Elin; Chan, Jimmy; Ko, Mei-Chuan; Woods, James H.; Tesmer, John J.G.; Sunahara, Roger K.

    2012-03-15

    No small-molecule therapeutic is available to treat cocaine addiction, but enzyme-based therapy to accelerate cocaine hydrolysis in serum has gained momentum. Bacterial cocaine esterase (CocE) is the fastest known native enzyme that hydrolyzes cocaine. However, its lability at 37 C has limited its therapeutic potential. Cross-linking subunits through disulfide bridging is commonly used to stabilize multimeric enzymes. Herein we use structural methods to guide the introduction of two cysteine residues within dimer interface of CocE to facilitate intermolecular disulfide bond formation. The disulfide-crosslinked enzyme displays improved thermostability, particularly when combined with previously described mutations that enhance stability (T172R-G173Q). The newly modified enzyme yielded an extremely stable form of CocE (CCRQ-CocE) that retained greater than 90% of its activity after 41 days at 37 C, representing an improvement of more than 4700-fold over the wild-type enzyme. CCRQ-CocE could also be modified by polyethylene glycol (PEG) polymers, which improved its in vivo residence time from 24 to 72 h, as measured by a cocaine lethality assay, by self-administration in rodents, and by measurement of inhibition of cocaine-induced cardiovascular effects in rhesus monkeys. PEG-CCRQ elicited negligible immune response in rodents. Subunit stabilization and PEGylation has thus produced a potential protein therapeutic with markedly higher stability both in vitro and in vivo.

  11. Structure-guided residence time optimization of a dabigatran reversal agent.

    PubMed

    Schiele, Felix; van Ryn, Joanne; Litzenburger, Tobias; Ritter, Michael; Seeliger, Daniel; Nar, Herbert

    2015-01-01

    Novel oral anticoagulants are effective and safe alternatives to vitamin-K antagonists for anticoagulation therapy. However, anticoagulation therapy in general is associated with an elevated risk of bleeding. Idarucizumab is a reversal agent for the direct thrombin inhibitor, dabigatran etexilate (Pradaxa®) and is currently in Phase 3 studies. Here, we report data on the antibody fragment aDabi-Fab2, a putative backup molecule for idarucizumab. Although aDabi-Fab2 completely reversed effects of dabigatran in a rat model in vivo, we observed significantly reduced duration of action compared to idarucizumab. Rational protein engineering, based on the X-ray structure of aDabi-Fab2, led to the identification of mutant Y103W. The mutant had optimized shape complementarity to dabigatran while maintaining an energetically favored hydrogen bond. It displayed increased affinity for dabigatran, mainly driven by a slower off-rate. Interestingly, the increased residence time translated into longer duration of action in vivo. It was thus possible to further enhance the efficacy of aDabi-Fab2 based on rational design, giving it the potential to serve as a back-up candidate for idarucizumab. PMID:26047352

  12. Structure-guided residence time optimization of a dabigatran reversal agent

    PubMed Central

    Schiele, Felix; van Ryn, Joanne; Litzenburger, Tobias; Ritter, Michael; Seeliger, Daniel; Nar, Herbert

    2015-01-01

    Novel oral anticoagulants are effective and safe alternatives to vitamin-K antagonists for anticoagulation therapy. However, anticoagulation therapy in general is associated with an elevated risk of bleeding. Idarucizumab is a reversal agent for the direct thrombin inhibitor, dabigatran etexilate (Pradaxa®) and is currently in Phase 3 studies. Here, we report data on the antibody fragment aDabi-Fab2, a putative backup molecule for idarucizumab. Although aDabi-Fab2 completely reversed effects of dabigatran in a rat model in vivo, we observed significantly reduced duration of action compared to idarucizumab. Rational protein engineering, based on the X-ray structure of aDabi-Fab2, led to the identification of mutant Y103W. The mutant had optimized shape complementarity to dabigatran while maintaining an energetically favored hydrogen bond. It displayed increased affinity for dabigatran, mainly driven by a slower off-rate. Interestingly, the increased residence time translated into longer duration of action in vivo. It was thus possible to further enhance the efficacy of aDabi-Fab2 based on rational design, giving it the potential to serve as a back-up candidate for idarucizumab. PMID:26047352

  13. Treating Stormwater with Green Infrastructure: Plants, Residence Time Distributions, and the Removal of Fecal Indicator Bacteria

    NASA Astrophysics Data System (ADS)

    Parker, E.; Grant, S. B.; Rippy, M.; Winfrey, B.; Mehring, A.

    2015-12-01

    In many cities, green infrastructure is increasingly used to capture and treat stormwater runoff, due to the many opportunities these systems afford for protecting receiving water quality and ecology while mitigating water scarcity. Here, we focus on how plants affect the removal of fecal indicator bacteria (FIB) in newly-constructed stormwater biofilters, a type of green infrastructure consisting of unconsolidated granular media containing one or more plant species. Input-response experiments were carried out using both non-reactive (salt) and reactive (sewage) tracers on six laboratory-scale (~1m long by 24 cm diameter) biofilters, half of which were planted with the sedge Carex appressa (treatment replicates) and half of which were unplanted (control replicates). C. appressa modifies the residence time distribution (RTD) in a biofilter by creating preferential flow paths along which water and mass can move quickly, but does not appear to alter the intrinsic rate at which FIB are removed. Thus, the "green" component of green infrastructure can alter pollutant removal by changing the RTD, with or without a concomitant change in pollutant reactivity.

  14. Subunit Stabilization and Polyethylene Glycolation of Cocaine Esterase Improves In Vivo Residence TimeS⃞

    PubMed Central

    Narasimhan, Diwahar; Collins, Gregory T.; Nance, Mark R.; Nichols, Joseph; Edwald, Elin; Chan, Jimmy; Ko, Mei-Chuan; Woods, James H.; Tesmer, John J. G.

    2011-01-01

    No small-molecule therapeutic is available to treat cocaine addiction, but enzyme-based therapy to accelerate cocaine hydrolysis in serum has gained momentum. Bacterial cocaine esterase (CocE) is the fastest known native enzyme that hydrolyzes cocaine. However, its lability at 37°C has limited its therapeutic potential. Cross-linking subunits through disulfide bridging is commonly used to stabilize multimeric enzymes. Herein we use structural methods to guide the introduction of two cysteine residues within dimer interface of CocE to facilitate intermolecular disulfide bond formation. The disulfide-crosslinked enzyme displays improved thermostability, particularly when combined with previously described mutations that enhance stability (T172R-G173Q). The newly modified enzyme yielded an extremely stable form of CocE (CCRQ-CocE) that retained greater than 90% of its activity after 41 days at 37°C, representing an improvement of more than 4700-fold over the wild-type enzyme. CCRQ-CocE could also be modified by polyethylene glycol (PEG) polymers, which improved its in vivo residence time from 24 to 72 h, as measured by a cocaine lethality assay, by self-administration in rodents, and by measurement of inhibition of cocaine-induced cardiovascular effects in rhesus monkeys. PEG-CCRQ elicited negligible immune response in rodents. Subunit stabilization and PEGylation has thus produced a potential protein therapeutic with markedly higher stability both in vitro and in vivo. PMID:21890748

  15. Control of selectivity in heterogeneous catalysis by tuning nanoparticle properties and reactor residence time.

    PubMed

    Gross, Elad; Liu, Jack Hung-Chang; Toste, F Dean; Somorjai, Gabor A

    2012-11-01

    A combination of the advantages of homogeneous and heterogeneous catalysis could enable the development of sustainable catalysts with novel reactivity and selectivity. Although heterogeneous catalysts are often recycled more easily than their homogeneous counterparts, they can be difficult to apply in traditional organic reactions and modification of their properties towards a desired reactivity is, at best, complex. In contrast, tuning the properties of homogeneous catalysts by, for example, modifying the ligands that coordinate a metal centre is better understood. Here, using olefin cyclopropanation reactions catalysed by dendrimer-encapsulated Au nanoclusters as examples, we demonstrate that changing the dendrimer properties allows the catalytic reactivity to be tuned in a similar fashion to ligand modification in a homogeneous catalyst. Furthermore, we show that these heterogeneous catalysts employed in a fixed-bed flow reactor allow fine control over the residence time of the reactants and thus enables the control over product distribution in a way that is not easily available for homogeneous catalysts. PMID:23089871

  16. Subunit stabilization and polyethylene glycolation of cocaine esterase improves in vivo residence time.

    PubMed

    Narasimhan, Diwahar; Collins, Gregory T; Nance, Mark R; Nichols, Joseph; Edwald, Elin; Chan, Jimmy; Ko, Mei-Chuan; Woods, James H; Tesmer, John J G; Sunahara, Roger K

    2011-12-01

    No small-molecule therapeutic is available to treat cocaine addiction, but enzyme-based therapy to accelerate cocaine hydrolysis in serum has gained momentum. Bacterial cocaine esterase (CocE) is the fastest known native enzyme that hydrolyzes cocaine. However, its lability at 37°C has limited its therapeutic potential. Cross-linking subunits through disulfide bridging is commonly used to stabilize multimeric enzymes. Herein we use structural methods to guide the introduction of two cysteine residues within dimer interface of CocE to facilitate intermolecular disulfide bond formation. The disulfide-crosslinked enzyme displays improved thermostability, particularly when combined with previously described mutations that enhance stability (T172R-G173Q). The newly modified enzyme yielded an extremely stable form of CocE (CCRQ-CocE) that retained greater than 90% of its activity after 41 days at 37°C, representing an improvement of more than 4700-fold over the wild-type enzyme. CCRQ-CocE could also be modified by polyethylene glycol (PEG) polymers, which improved its in vivo residence time from 24 to 72 h, as measured by a cocaine lethality assay, by self-administration in rodents, and by measurement of inhibition of cocaine-induced cardiovascular effects in rhesus monkeys. PEG-CCRQ elicited negligible immune response in rodents. Subunit stabilization and PEGylation has thus produced a potential protein therapeutic with markedly higher stability both in vitro and in vivo. PMID:21890748

  17. Sand residence times of one million years in the Namib Sand Sea from cosmogenic nuclides

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.; Fenton, C. R.; Kober, F.; Wiggs, G. F. S.; Bristow, C. S.; Xu, S.

    2010-12-01

    The Namib Sand Sea is one of the world's oldest and largest sand deserts, yet little is known about the source of the sand in this, or other large deserts. In particular, it is unclear whether the sand is derived from local sediment or comes from remote sources. The relatively uniform appearance of dune sands and low compositional variability within dune fields make it difficult to address this question. Here we combine cosmogenic-nuclide measurements and geochronological techniques to assess the provenance and migration history of sand grains in the Namib Sand Sea. We use U-Pb geochronology of detrital zircons to show that the primary source of sand is the Orange River at the southern edge of the Namib desert. Our burial ages obtained from measurements of the cosmogenic nuclides 10Be, 26Al and 21Ne suggest that the residence time of sand within the sand sea is at least one million years. We therefore conclude that, despite large climatic changes in the Namib region associated with Quaternary glacial-interglacial cycles, the area currently occupied by the Namib Sand Sea has never been entirely devoid of sand during the past million years.

  18. Aerosol residence times and changes in radioiodine-131I and radiocaesium-137 Cs activity over Central Poland after the Fukushima-Daiichi Nuclear reactor accident.

    PubMed

    Długosz-Lisiecka, Magdalena; Bem, Henryk

    2012-05-01

    The first detectable activities of radioiodine (131)I, and radiocaesium (134)Cs and (137)Cs in the air over Central Poland were measured in dust samples collected by the ASS-500 station in the period of 21(st) to 24(th) of March, 2011. However, the highest activity of both fission products, (131)I and (137)Cs: 8.3 mBq m(-3) and 0.75 mBq m(-3), respectively, were obtained in the samples collected on 30(th) March, i.e.∼18 days after the beginning of the fission products' discharge from the damaged units of the Fukushima Daiichi Nuclear Power Plant. The simultaneously determined corrected aerosol residence time for the same samples by (210)Pb/(210)Bi and (210)Pb/(210)Po methods was equal to 10 days. Additionally, on the basis of the activity ratio of two other natural cosmogenic radionuclides, (7)Be and (22)Na in these aerosol samples, it was possible to estimate the aerosol residence time at ∼150 days for the solid particles coming from the stratospheric fallout. These data, as well as the differences in the activity size distribution of (7)Be and (131)I in the air particulate matter, show, in contrast to the Chernobyl discharge, a negligible input of stratospheric transport of Fukushima-released fission products. PMID:22481111

  19. Effect of timed secondary-air injection on automotive emissions

    NASA Technical Reports Server (NTRS)

    Coffin, K. P.

    1973-01-01

    A single cylinder of an automotive V-8 engine was fitted with an electronically timed system for the pulsed injection of secondary air. A straight-tube exhaust minimized any mixing other than that produced by secondary-air pulsing. The device was operated over a range of engine loads and speeds. Effects attributable to secondary-air pulsing were found, but emission levels were generally no better than using the engine's own injection system. Under nontypical fast-idle, no-load conditions, emission levels were reduced by roughly a factor of 2.

  20. Impact of model geometry and recharge rates on catchment's residence time distributions - numerical experiments

    NASA Astrophysics Data System (ADS)

    Neubauer, M.; Musolff, A.; Fleckenstein, J. H.

    2013-12-01

    Residence time distributions (RTD) of water in catchments are promising tools to characterize and model solute transport on a larger scale. In the last decade, much research has been conducted on the estimation and the application of RTD's. However, there are still some major issues to be addressed to complex derivation, parameterization and transient behavior. Through improved remote sensing data, the surface elevation can mostly be resolved in detail, while subsurface volumes and boundaries remain highly undetermined. Our objectives are to systematically evaluate the impact of different depths and geometries of the domain bottom and groundwater recharge rates on RTD's. The study site is a small (1.6 km2) headwater catchment located within the Harz Mountains, Germany. For this catchment long time series of climate, discharge and hydrochemistry are available while groundwater flow field and subsurface structure are less known. The site is intensively influenced by agricultural land use and exhibits strong seasonal dynamics of water flow and hydrochemistry due to the snowmelt. The modeling was performed using HydroGeoSphere, a coupled surface and subsurface model, which solves the Richards Equation for variable saturated soils. The Open Source software Paraview and R was chosen as postprocessors to perform and analyze forward particle tracking algorithms under steady state conditions. Ten depth and geometry scenarios of the domain bottom were created (5 horizontal bottom geometries - constant base and 5 variable bottom geometries - parallel to surface topography; both minimum depths ranging from 2 m to 50 m). The model's internal structure was discretized by two homogenous layers (averaged catchment representation) parallel to the input digital elevation model (2x2 m). The geometry scenarios were combined with fifteen steady state simulations for different groundwater recharge rate scenarios (0.1 mm up to 15 mm per day). Model results indicate a strong influence of

  1. Time-resolved air monitoring using Fourier absorption spectroscopy

    SciTech Connect

    Biermann, H.W.

    1995-12-31

    Two categories where spectroscopic techniques excel are the capabilities to perform air analyses in situ and to obtain data at very high time resolutions. Because of these features, the Department of Pesticide Regulation augmented its extensive air monitoring capabilities with a Fourier transform infrared (FTIR) spectrometer using open-path optical systems for time resolved ambient air monitoring. A description of the instrumentation and the data analysis procedures will be presented based on two data sets obtained with this FTIR system. In one case, a 100 m folded optical path was used to measure methyl bromide concentrations after fumigation in a warehouse with a time resolution of 15 min and a detection limit of 0.2 ppm. And trying to assess the capability of this FTIR spectrometer to determine flux, water vapor concentrations were measured with a four-meter path length at a time resolution of 0.6 seconds.

  2. Flow residence time and regions of intraluminal thrombus deposition in intracranial aneurysms.

    PubMed

    Rayz, V L; Boussel, L; Ge, L; Leach, J R; Martin, A J; Lawton, M T; McCulloch, C; Saloner, D

    2010-10-01

    Thrombus formation in intracranial aneurysms, while sometimes stabilizing lesion growth, can present additional risk of thrombo-embolism. The role of hemodynamics in the progression of aneurysmal disease can be elucidated by patient-specific computational modeling. In our previous work, patient-specific computational fluid dynamics (CFD) models were constructed from MRI data for three patients who had fusiform basilar aneurysms that were thrombus-free and then proceeded to develop intraluminal thrombus. In this study, we investigated the effect of increased flow residence time (RT) by modeling passive scalar advection in the same aneurysmal geometries. Non-Newtonian pulsatile flow simulations were carried out in base-line geometries and a new postprocessing technique, referred to as "virtual ink" and based on the passive scalar distribution maps, was used to visualize the flow and estimate the flow RT. The virtual ink technique clearly depicted regions of flow separation. The flow RT at different locations adjacent to aneurysmal walls was calculated as the time the virtual ink scalar remained above a threshold value. The RT values obtained in different areas were then correlated with the location of intra-aneurysmal thrombus observed at a follow-up MR study. For each patient, the wall shear stress (WSS) distribution was also obtained from CFD simulations and correlated with thrombus location. The correlation analysis determined a significant relationship between regions where CFD predicted either an increased RT or low WSS and the regions where thrombus deposition was observed to occur in vivo. A model including both low WSS and increased RT predicted thrombus-prone regions significantly better than the models with RT or WSS alone. PMID:20499185

  3. Phosphorus as indicator of magmatic olivine residence time, morphology and growth rate

    NASA Astrophysics Data System (ADS)

    Sobolev, Alexander; Batanova, Valentina

    2015-04-01

    Phosphorus is among of slowest elements by diffusion rate in silicate melts and crystals (e.g. Spandler et al, 2007). In the same time it is moderately incompatible to compatible with olivine (Brunet & Chazot, 2001; Grant & Kohn, 2013). This makes phosphorus valuable tracer of olivine crystallization in natural conditions. Indeed, it is shown that natural magmatic olivine crystals commonly posses strong and complicated zoning in phosphorus (Milman-Barris et al, 2008; Welsch et al, 2014). In this paper we intend to review phosphorus behavior in olivine in published experimental and natural olivine studies and present large set of new EPMA data on phosphorus zoning in olivine phenocrysts from MORBs, OIBs, komatiites and kimberlites. We will show that sharp olivine zones enriched in phosphorus by a factor of 10-20 over prediction by equilibrium partition may be due to formation of P-rich boundary layer on the interface of fast growing olivine. This is proved by finding of small-size (normally 10 mkm or less) exceptionally P-rich melt inclusions in olivine, which are otherwise similar in composition to typical melt. These observations could provide potential olivine growth speedometer. We will also demonstrate, that sharp zoning in phosphorus may provide valuable information on the residence time of olivine crystals in different environments: magma chambers and conduits as well as mantle sources. This study has been founded by Russian Science Foundation grant 14-17-00491. References: Spandler, et al, 2007, Nature, v. 447, p. 303-306; Brunet & Chazot, 2001, Chemical Geology, v. 176, p. 51-72; Grant & Kohn, 2013, American Mineralogist, v. 98, p. 1860-1869; Milman-Barris et al, 2008, Contr. Min. Petrol. v. 155, p.739-765; Welsch et al, 2014, Geology, v. 42, p.867-870.

  4. Reflections in a time of transition: orthopaedic faculty and resident understanding of accreditation schemes and opinions on surgical skills feedback

    PubMed Central

    Gundle, Kenneth R.; Mickelson, Dayne T.; Hanel, Doug P.

    2016-01-01

    Introduction Orthopaedic surgery is one of the first seven specialties that began collecting Milestone data as part of the Accreditation Council for Graduate Medical Education's Next Accreditation System (NAS) rollout. This transition from process-based advancement to outcome-based education is an opportunity to assess resident and faculty understanding of changing paradigms, and opinions about technical skill evaluation. Methods In a large academic orthopaedic surgery residency program, residents and faculty were anonymously surveyed. A total of 31/32 (97%) residents and 29/53 (55%) faculty responded to Likert scale assessments and provided open-ended responses. An internal end-of-rotation audit was conducted to assess timeliness of evaluations. A mixed-method analysis was utilized, with nonparametric statistical testing and a constant-comparative qualitative method. Results There was greater familiarity with the six core competencies than with Milestones or the NAS (p<0.05). A majority of faculty and residents felt that end-of-rotation evaluations were not adequate for surgical skills feedback. Fifty-eight per cent of residents reported that end-of-rotation evaluations were rarely or never filled out in a timely fashion. An internal audit demonstrated that more than 30% of evaluations were completed over a month after rotation end. Qualitative analysis included themes of resident desire for more face-to-face feedback on technical skills after operative cases, and several barriers to more frequent feedback. Discussion The NAS and outcome-based education have arrived. Residents and faculty need to be educated on this changing paradigm. This transition period is also a window of opportunity to address methods of evaluation and feedback. In our orthopaedic residency, trainees were significantly less satisfied than faculty with the amount of technical and surgical skills feedback being provided to trainees. The quantitative and qualitative analyses converge on one

  5. Ligand Residence Time at G-protein-Coupled Receptors-Why We Should Take Our Time To Study It.

    PubMed

    Hoffmann, C; Castro, M; Rinken, A; Leurs, R; Hill, S J; Vischer, H F

    2015-09-01

    Over the past decade the kinetics of ligand binding to a receptor have received increasing interest. The concept of drug-target residence time is becoming an invaluable parameter for drug optimization. It holds great promise for drug development, and its optimization is thought to reduce off-target effects. The success of long-acting drugs like tiotropium support this hypothesis. Nonetheless, we know surprisingly little about the dynamics and the molecular detail of the drug binding process. Because protein dynamics and adaptation during the binding event will change the conformation of the protein, ligand binding will not be the static process that is often described. This can cause problems because simple mathematical models often fail to adequately describe the dynamics of the binding process. In this minireview we will discuss the current situation with an emphasis on G-protein-coupled receptors. These are important membrane protein drug targets that undergo conformational changes upon agonist binding to communicate signaling information across the plasma membrane of cells. PMID:26152198

  6. Atmospheric residence times from transpiration and evaporation to precipitation: An age-weighted regional evaporation tagging approach

    NASA Astrophysics Data System (ADS)

    Wei, Jianhui; Knoche, Hans Richard; Kunstmann, Harald

    2016-06-01

    The atmospheric water residence time is a fundamental descriptor that provides information on the timescales of evaporation and precipitation. In this study, a regional climate model-based evaporation tagging algorithm is extended with an age tracer approach to calculate moisture residence times, defined as time between the original evaporation and the returning of water masses to the land surface as precipitation. Our case study addresses how long this time is for the transpired and for the direct evaporated moisture. Our study region is the Poyang Lake region in Southeast China, the largest freshwater lake in the country. We perform simulations covering the period from October 2004 to December 2005. In 2005, 11% of direct evaporated water (10% of transpired water) precipitates locally. Direct evaporated water accounts for 64% and transpired water for 36% of the total tagged moisture with a mean age of around 36 h for both. Considering precipitation, a large proportion (69%) originates from direct evaporated water with a mean atmospheric residence time of 6.6 h and a smaller amount from transpired water with a longer residence time of 10.7 h. Modulated by the East Asian monsoon, the variation of the meteorological conditions, the magnitude of the partitioned moisture, and the corresponding residence time patterns change seasonally and spatially and reveal the different fate of transpired and direct evaporated water in the atmospheric hydrological cycle. We conclude that our methodological approach has the potential to be used for addressing how timescales of the hydrological cycle changes regionally under global warming.

  7. Time in U.S. Residency and the Social, Behavioral, and Emotional Adjustment of Latino Immigrant Families

    ERIC Educational Resources Information Center

    Martinez, Charles R., Jr.; McClure, Heather H.; Eddy, J. Mark; Wilson, D. Molloy

    2011-01-01

    Little is known about contributors to positive social, behavioral, and emotional adjustment among foreign-born youth at different stages of adapting to life in the United States. Using baseline data from the Adolescent Latino Acculturation Study (N = 217), this article examines the effects of time in residency on parent adjustment, family stress,…

  8. Study of residence-time distribution of non-Newtonian fluids in scraped-surface heat exchangers

    SciTech Connect

    Benezech, T.; Maingonnat, J.F. )

    1993-04-01

    The change of residence-time distribution in scraped-surface heat exchangers handling shear thinning fluids has been studied as a function of the speed of rotation of the shaft, the axial flow rate, the number of blades (2 or 4), the length of the heat exchanger, and the rheological parameters of the fluids. Spreading of the residence-time distribution is caused by rotational flow of the fluid. A particular value of the generalized Taylor number has been identified, which corresponds to the appearance of Taylor vortices and a change in the shape of the residence-time distribution curves. The mean rate of flow and the number of blades did not have any effect under the operating conditions used in this work. In contrast, a decrease in the ratio of the length of heat exchanger to the inside diameter of the heat-exchange surface has resulted in a spreading of the residence-time distribution in the presence of Taylor vortices. Finally, the axial dispersion coefficient determined in this work correlates, quantitatively, with the axial thermal diffusivity.

  9. Examination of residence time and its relevance to water quality within a coastal mega-structure: The Palm Jumeirah Lagoon

    NASA Astrophysics Data System (ADS)

    Cavalcante, Geórgenes H.; Kjerfve, Björn; Feary, David A.

    2012-10-01

    SummaryA numerical modeling study was carried out to compute average residence time in the semi-enclosed lagoon formed by the man-made island Palm Jumeirah (Dubai, United Arab Emirates), termed Palm Jumeirah Lagoon (PJL). The PJL encompasses a main island axis with 17 'fronds' radiating from this axis, all encapsulated within a semi-circular breakwater system. A coupled hydrodynamic and solute transport model was developed for the waters of the PJL, based on depth-integrated conservation equations. Numerical model predictions were then verified against a set of field-measured hydrodynamic data. Model-predicted water elevations and velocities were in good agreement with field measurements. Residence times for this tidal dominated system were investigated through numerical experiments using a conservative tracer as a surrogate. The results indicated that average residence time varied spatially throughout the PJL depending on tidal flushing. Average residence time was unequally distributed throughout the PJL, with the eastern side showing higher flushing times than the western side. In addition, there were also differences between sections of the PJL in average residence time of a tracer: between frond tips and the surrounding breakwater the tracer was reduced to 30-40% of its original value after approximately 1 week, while a tracer placed between the fronds was reduced to 30-40% of its value after 20 days. The findings of this research provide vital information for understanding the water transport process in this man-made lagoon, and will be important in assessing the potential impact on coastal water quality conditions in coastal developments within the Middle East.

  10. Hydraulic residence time and iron removal in a wetland receiving ferruginous mine water over a 4 year period from commissioning.

    PubMed

    Kusin, F M; Jarvis, A P; Gandy, C J

    2010-01-01

    Analysis of residence time distribution (RTD) has been conducted for the UK Coal Authority's mine water treatment wetland at Lambley, Northumberland, to determine the hydraulic performance of the wetland over a period of approximately 4 years since site commissioning. The wetland RTD was evaluated in accordance with moment analysis and modelled based on a tanks-in-series (TIS) model to yield the hydraulic characteristics of system performance. Greater hydraulic performance was seen during the second site monitoring after 21 months of site operation i.e. longer hydraulic residence time to reflect overall system hydraulic efficiency, compared to wetland performance during its early operation. Further monitoring of residence time during the third year of wetland operation indicated a slight reduction in hydraulic residence time, thus a lower system hydraulic efficiency. In contrast, performance during the fourth year of wetland operation exhibited an improved overall system hydraulic efficiency, suggesting the influence of reed growth over the lifetime of such systems on hydraulic performance. Interestingly, the same pattern was found for iron (which is the primary pollutant of concern in ferruginous mine waters) removal efficiency of the wetland system from the second to fourth year of wetland operation. This may therefore, reflect the maturity of reeds for maintaining efficient flow distribution across the wetland to retain a longer residence time and significant fractions of water involved to enhance the extent of treatment received for iron attenuation. Further monitoring will be conducted to establish whether such performance is maintained, or whether efficiency decreases over time due to accumulation of dead plant material within the wetland cells. PMID:20962411

  11. Combining direct residence time measurements and biogeochemistry to calculate in-situ reaction rates in the hyporheic zone

    NASA Astrophysics Data System (ADS)

    Pittroff, Marco; Gilfedder, Benjamin

    2015-04-01

    The hyporheic zone is an active interface between groundwater, riparian and surface water systems. Exchange and reaction of water, nutrients, and organic matter occur due to variations in surface and groundwater flow regimes, bed topography and active biogeochemistry fuelled by bioavailable carbon. There has been an increasing focus on coupling the residence time of surface water in the hyporheic zone with biogeochemical reactions. However, there are very few tracers that can be used to measure residence times in-situ, especially in complex groundwater-surface water settings. In this work we have used the natural radioisotope Radon (222Rn) as an in-situ tracer for river water residence time in a riffle-pool sequence (Rote Main River), and combined this information with biogeochemical parameters (DOC and C quality, O3, NO3, CO2). We can clearly observe a dependence of reaction progress on the water residence times, with oxygen and nitrate reduction following inverse logarithmic trends as a function of time. By comparing with initial concentrations (the river end member) with riverbed levels we have estimated first-order in-situ reduction rates for nitrate and oxygen. Nitrate reduction rates are at the higher end of published values, which is likely due to the continual supply of bioavailable carbon from the river system. This work helps to better understand the function and efficiency of the hyporheic zone as a natural filter for redox sensitive species such as nitrate at the groundwater - steam interface. It also provides a useful method for estimating residence times in complex, higher order river systems.

  12. Flow rates, residence times and origin of fluids in the Hikurangi forearc, New Zealand

    NASA Astrophysics Data System (ADS)

    Reyes, A. G.

    2013-12-01

    meteoric water and more intense interaction with the rock. Initial estimates of saline water residence time in Te Puia, based on present-day rates of subduction and uplift is <100ka. Possible residence times of other aqueous solutions, based on the intensity of water-rock interaction relative to Te Puia, are youngest in the central block and >100ka in several springs in the southern block. Fluids in the northern and southern blocks become increasingly enriched in Cl, I and Br contents and exhibit decreased water-rock interaction towards the central block. The central block is deemed most open, due to fracture permeability enhanced by localised tears in the overlying plate from the subduction of seamounts, to the most recent influx of subducted waters. The unusual occurrence of hot and cold springs in the central and northern blocks with high concentrations of isotopic He is attributed to anomalously deep and highly permeable faults that channel mantle gases and also allow aqueous solutions to rise very rapidly from as deep as the fracture zone between the overriding and down going plates.

  13. Estimation of ground water residence times in the Critical zone: insight from U activity ratios

    NASA Astrophysics Data System (ADS)

    Chabaux, Francois; Ackerer, Julien; Lucas, Yann; viville, Daniel

    2016-04-01

    The use of radioactive disequilibria as tracers and chronometers of weathering processes and related mass transfers has been recognized since the 60'. The development, over the last two decades, of analytical methods for measuring very precisely U-series nuclides (especially, 234U, 230Th and 226Ra) in environmental samples has opened up new scientific applications in Earth Surface Sciences. Here, we propose to present the potential of U activity ratios in surface waters as chronometer of water transfers at a watershed scale. This will be illustrated from studies performed at different scales, with the analysis of U activity ratios in surface waters from small watersheds (Strengbach and Ringelbach watersheds in the Vosges Mountain, France) but also from watersheds of much more regional extension (e.g., the Upper Rhine basin or the Ganges basin). These various studies show that variations of U activity ratios in surface waters are mainly associated with 234U-238U fractionations occurring during the water transfer within the bedrock, which intensity depends on two main parameters: the petro-physical characteristics of the aquifer, principally the geometry of water-rock interfaces and the duration of the water-rock interactions. This readily explains why different U activity ratios (UAR) can be observed in the different aquifers of a continental hydrosystem and hence why UAR can be used to trace the source of river waters. For a hydrological system developed on a substratum marked by fairly homogeneous petro-physical characteristics, the main parameter controlling the UAR in waters draining such a system would be the duration of the water-rock interactions. Variations of UAR in stream or spring waters of such a system can therefore be modeled using simple reactive transport model, which allows the estimation of both the dissolution rate of the bedrock and the residence time of the waters within the aquifer.

  14. Isotopic metrics for structure, connectivity, and residence time in urban water supply systems

    NASA Astrophysics Data System (ADS)

    Bowen, Gabriel; Kennedy, Casey; Good, Stephen; Ehleringer, James

    2014-05-01

    Public water supply systems are the life-blood of urban areas, accessing, managing, and distributing water from an often complex array of sources to provide on-demand access to safe, potable water at the point-of-use. Water managers are faced with a wide range of potential threats, ranging from climate change to infrastructure failure to supply contamination. Information on the structure of supply and conveyance systems, connectivity within these systems, and links between the point-of-use and environmental water sources are thus critical to assessing the stability of water supplies and responding efficiently and effectively to water supply threats. We report datasets documenting stable hydrogen and oxygen isotope ratios of public supply water in cities of the United States across a range of scales. The data show a wide range of spatial and temporal variability that can be attributed to a combination of regional hydroclimate and water supply characteristics. Comparisons of public supply waters with model-based estimates of the isotopic composition of regional water sources suggests that major factors reflected in the tap water data include the degree of fragmentation of natural and man-made storage and conveyance systems, inter-basinal transfer of water, evaporative losses, and the total residence time of the natural and artificial systems being exploited. Because each of these factors contributes to determining the sustainability of water supply systems and their sensitivity to environmental disturbance, we propose a set of isotope-based metrics that can be used to efficiently assess and monitor the characteristics of public-supply systems in water security assessments and in support of management, planning, and outreach activities.

  15. Emulator based identification of model differences in describing the residence time of vegetation carbon.

    NASA Astrophysics Data System (ADS)

    Garcia Cantu Ros, Anselmo; Frieler, Katja

    2015-04-01

    The past three decades have witnessed the development of so-called global vegetation models (GVMs), encompassing accurate representations of a wide range of cross-scale biophysical processes, at the core of the carbon dynamics of terrestrial ecosystems. When forced with climate projections derived from Global Circulation Models (GCMs), GVMs enable one to quantify global-scale, multi-decadal impacts in terms of changes in plant type composition and ecosystem-atmosphere fluxes, at different levels of global warming and CO2 atmospheric concentrations. However, impacts estimated along individual emission pathways appear to be specific of the combination GCM--GVM that is used in the quantification of impacts. In order to gain insights into the sources of multi-model uncertainties of impacts in biomes, it is convenient to resort to simplified representations -so called emulators, of dominant processes explaining the response of biomes, in terms of aggregate variables. This work presents novel results, that illustrate the use of emulators in the analysis of inter-model differences. In particular, we build on ISI-MIP model output data to identify sources of uncertainty in the residence time of carbon in natural vegetation, resulting from 4 representative GVMs under the forcing of 4 RCP scenarios. Our results provide a reliable basis for future model improvement, as well as the possibility to efficiently reproduce the response of vegetation along arbitrary trajectories of CO2 and global warming. This is of special interest in the context of integrated impact assessment, where the application of GVMs becomes computationally unaffordable.

  16. Residence times of groundwater and nitrate transport in coastal aquifer systems: Daweijia area, northeastern China.

    PubMed

    Han, Dongmei; Cao, Guoliang; McCallum, James; Song, Xianfang

    2015-12-15

    Groundwater within the coastal aquifer systems of the Daweijia area in northeastern China is characterized by a large of variations (33-521mg/L) in NO3(-) concentrations. Elevated nitrate concentrations, in addition to seawater intrusion in the Daweijia well field, both attributable to anthropogenic activities, may impact future water-management practices. Chemical and stable isotopic (δ(18)O, δ(2)H) analysis, (3)H and CFCs methods were applied to provide a better understanding of the relationship between the distribution of groundwater mean residence time (MRT) and nitrate transport, and to identify sources of nitrate concentrations in the complex coastal aquifer systems. There is a relatively narrow range of isotopic composition (ranging from -8.5 to -7.0‰) in most groundwater. Generally higher tritium contents observed in the wet season relative to the dry season may result from rapid groundwater circulation in response to the rainfall through the preferential flow paths. In the well field, the relatively increased nitrate concentrations of groundwater, accompanied by the higher tritium contents in the wet season, indicate the nitrate pollution can be attributed to domestic wastes. The binary exponential and piston-flow mixing model (BEP) yielded feasible age distributions based on the conceptual model. The good inverse relationship between groundwater MRTs (92-467years) and the NO3(-) concentrations in the shallow Quaternary aquifers indicates that elevated nitrate concentrations are attributable to more recent recharge for shallow groundwater. However, there is no significant relationship between the MRTs (8-411years) and the NO3(-) concentrations existing in the carbonate aquifer system, due to the complex hydrogeological conditions, groundwater age distributions and the range of contaminant source areas. Nitrate in the groundwater system without denitrification effects could accumulate and be transported for tens of years, through the complex carbonate

  17. Carbon residence time dominates uncertainty in terrestrial vegetation responses to future climate and atmospheric CO2

    PubMed Central

    Friend, Andrew D.; Lucht, Wolfgang; Rademacher, Tim T.; Keribin, Rozenn; Betts, Richard; Cadule, Patricia; Ciais, Philippe; Clark, Douglas B.; Dankers, Rutger; Falloon, Pete D.; Ito, Akihiko; Kahana, Ron; Kleidon, Axel; Lomas, Mark R.; Nishina, Kazuya; Ostberg, Sebastian; Pavlick, Ryan; Peylin, Philippe; Schaphoff, Sibyll; Vuichard, Nicolas; Warszawski, Lila; Wiltshire, Andy; Woodward, F. Ian

    2014-01-01

    Future climate change and increasing atmospheric CO2 are expected to cause major changes in vegetation structure and function over large fractions of the global land surface. Seven global vegetation models are used to analyze possible responses to future climate simulated by a range of general circulation models run under all four representative concentration pathway scenarios of changing concentrations of greenhouse gases. All 110 simulations predict an increase in global vegetation carbon to 2100, but with substantial variation between vegetation models. For example, at 4 °C of global land surface warming (510–758 ppm of CO2), vegetation carbon increases by 52–477 Pg C (224 Pg C mean), mainly due to CO2 fertilization of photosynthesis. Simulations agree on large regional increases across much of the boreal forest, western Amazonia, central Africa, western China, and southeast Asia, with reductions across southwestern North America, central South America, southern Mediterranean areas, southwestern Africa, and southwestern Australia. Four vegetation models display discontinuities across 4 °C of warming, indicating global thresholds in the balance of positive and negative influences on productivity and biomass. In contrast to previous global vegetation model studies, we emphasize the importance of uncertainties in projected changes in carbon residence times. We find, when all seven models are considered for one representative concentration pathway × general circulation model combination, such uncertainties explain 30% more variation in modeled vegetation carbon change than responses of net primary productivity alone, increasing to 151% for non-HYBRID4 models. A change in research priorities away from production and toward structural dynamics and demographic processes is recommended. PMID:24344265

  18. Carbon residence time dominates uncertainty in terrestrial vegetation responses to future climate and atmospheric CO2.

    PubMed

    Friend, Andrew D; Lucht, Wolfgang; Rademacher, Tim T; Keribin, Rozenn; Betts, Richard; Cadule, Patricia; Ciais, Philippe; Clark, Douglas B; Dankers, Rutger; Falloon, Pete D; Ito, Akihiko; Kahana, Ron; Kleidon, Axel; Lomas, Mark R; Nishina, Kazuya; Ostberg, Sebastian; Pavlick, Ryan; Peylin, Philippe; Schaphoff, Sibyll; Vuichard, Nicolas; Warszawski, Lila; Wiltshire, Andy; Woodward, F Ian

    2014-03-01

    Future climate change and increasing atmospheric CO2 are expected to cause major changes in vegetation structure and function over large fractions of the global land surface. Seven global vegetation models are used to analyze possible responses to future climate simulated by a range of general circulation models run under all four representative concentration pathway scenarios of changing concentrations of greenhouse gases. All 110 simulations predict an increase in global vegetation carbon to 2100, but with substantial variation between vegetation models. For example, at 4 °C of global land surface warming (510-758 ppm of CO2), vegetation carbon increases by 52-477 Pg C (224 Pg C mean), mainly due to CO2 fertilization of photosynthesis. Simulations agree on large regional increases across much of the boreal forest, western Amazonia, central Africa, western China, and southeast Asia, with reductions across southwestern North America, central South America, southern Mediterranean areas, southwestern Africa, and southwestern Australia. Four vegetation models display discontinuities across 4 °C of warming, indicating global thresholds in the balance of positive and negative influences on productivity and biomass. In contrast to previous global vegetation model studies, we emphasize the importance of uncertainties in projected changes in carbon residence times. We find, when all seven models are considered for one representative concentration pathway × general circulation model combination, such uncertainties explain 30% more variation in modeled vegetation carbon change than responses of net primary productivity alone, increasing to 151% for non-HYBRID4 models. A change in research priorities away from production and toward structural dynamics and demographic processes is recommended. PMID:24344265

  19. Time series analysis of air pollutants in Beirut, Lebanon.

    PubMed

    Farah, Wehbeh; Nakhlé, Myriam Mrad; Abboud, Maher; Annesi-Maesano, Isabella; Zaarour, Rita; Saliba, Nada; Germanos, Georges; Gerard, Jocelyne

    2014-12-01

    This study reports for the first time a time series analysis of daily urban air pollutant levels (CO, NO, NO2, O3, PM10, and SO2) in Beirut, Lebanon. The study examines data obtained between September 2005 and July 2006, and their descriptive analysis shows long-term variations of daily levels of air pollution concentrations. Strong persistence of these daily levels is identified in the time series using an autocorrelation function, except for SO2. Time series of standardized residual values (SRVs) are also calculated to compare fluctuations of the time series with different levels. Time series plots of the SRVs indicate that NO and NO2 had similar temporal fluctuations. However, NO2 and O3 had opposite temporal fluctuations, attributable to weather conditions and the accumulation of vehicular emissions. The effects of both desert dust storms and airborne particulate matter resulting from the Lebanon War in July 2006 are also discernible in the SRV plots. PMID:25150052

  20. Comparison of Residence Time Estimation Methods for Radioimmunotherapy Dosimetry and Treatment Planning—Monte Carlo Simulation Studies

    PubMed Central

    He, Bin; Wahl, Richard L.; Du, Yong; Sgouros, George; Jacene, Heather; Flinn, Ian; Frey, Eric C.

    2008-01-01

    Estimating the residence times in tumor and normal organs is an essential part of treatment planning for radioimmunotherapy (RIT). This estimation is usually done using a conjugate view whole body scan time series and planar processing. This method has logistical and cost advantages compared to 3-D imaging methods such as Single photon emission computed tomography (SPECT), but, because it does not provide information about the 3-D distribution of activity, it is difficult to fully compensate for effects such as attenuation and background and overlapping activity. Incomplete compensation for these effects reduces the accuracy of the residence time estimates. In this work we compare residence times estimates obtained using planar methods to those from methods based on quantitative SPECT (QSPECT) reconstructions. We have previously developed QSPECT methods that provide compensation for attenuation, scatter, collimator-detector response, and partial volume effects. In this study we compared the use of residence time estimation methods using QSPECT to planar methods. The evaluation was done using the realistic NCAT phantom with organ time activities that model 111In ibritumomab tiuxetan. Projection data were obtained using Monte Carlo simulations (MCS) that realistically model the image formation process including penetration and scatter in the collimator-detector system. These projection data were used to evaluate the accuracy of residence time estimation using a time series of QSPECT studies, a single QSPECT study combined with planar scans and the planar scans alone. The errors in the residence time estimates were <3.8%, <15%, and 2%–107% for the QSPECT, hybrid planar/QSPECT, and planar methods, respectively. The quantitative accuracy was worst for pure planar processing and best for pure QSPECT processing. Hybrid planar/QSPECT methods, where a single QSPECT study was combined with a series of planar scans, provided a large and statistically significant improvement

  1. Linking granulation performance with residence time and granulation liquid distributions in twin-screw granulation: An experimental investigation.

    PubMed

    Kumar, Ashish; Alakarjula, Maija; Vanhoorne, Valérie; Toiviainen, Maunu; De Leersnyder, Fien; Vercruysse, Jurgen; Juuti, Mikko; Ketolainen, Jarkko; Vervaet, Chris; Remon, Jean Paul; Gernaey, Krist V; De Beer, Thomas; Nopens, Ingmar

    2016-07-30

    Twin-screw granulation is a promising wet granulation technique for the continuous manufacturing of pharmaceutical solid dosage forms. A twin screw granulator displays a short residence time. Thus, the solid-liquid mixing must be achieved quickly by appropriate arrangement of transport and kneading elements in the granulator screw allowing the production of granules with a size distribution appropriate for tableting. The distribution of residence time and granulation liquid is governed by the field conditions (such as location and length of mixing zones) in the twin-screw granulator, thus contain interesting information on granulation time, mixing and resulting sub-processes such as wetting, aggregation and breakage. In this study, the impact of process (feed rate, screw speed and liquid-to-solid ratio) and equipment parameters (number of kneading discs and stagger angle) on the residence time (distribution), the granulation liquid-powder mixing and the resulting granule size distributions during twin-screw granulation were investigated. Residence time and axial mixing data was extracted from tracer maps and the solid-liquid mixing was quantified from moisture maps, obtained by monitoring the granules at the granulator outlet using near infra-red chemical imaging (NIR-CI). The granule size distribution was measured using the sieving method. An increasing screw speed dominantly reduced the mean residence time. Interaction of material throughput with the screw speed and with the number of kneading discs led to most variation in the studied responses including residence time and mixing capacity. At a high screw speed, granulation yield improved due to high axial mixing. However, increasing material throughput quickly lowers the yield due to insufficient mixing of liquid and powder. Moreover, increasing liquid-to-solid ratio resulted in more oversized granules, and the fraction of oversized granules further increased at higher throughput. Although an increasing number

  2. Impact of solids residence time on biological nutrient removal performance of membrane bioreactor.

    PubMed

    Ersu, Cagatayhan Bekir; Ong, Say Kee; Arslankaya, Ertan; Lee, Yong-Woo

    2010-05-01

    Impact of long solids residence times (SRTs) on nutrient removal was investigated using a submerged plate-frame membrane bioreactor with anaerobic and anoxic tanks. The system was operated at 10, 25, 50 and 75 days SRTs with hydraulic retention times (HRTs) of 2 h each for the anaerobic and anoxic tanks and 8 h for the oxic tank. Recirculation of oxic tank mixed liquor into the anaerobic tank and permeate into the anoxic tank were fixed at 100% each of the influent flow. For all SRTs, percent removals of soluble chemical oxygen demand were more than 93% and nitrification was more than 98.5% but total nitrogen percent removal seemed to peak at 81% at 50 days SRT while total phosphorus (TP) percent removal showed a deterioration from approximately 80% at 50 days SRT to 60% at 75 days SRT. Before calibrating the Biowin((R)) model to the experimental data, a sensitivity analysis of the model was conducted which indicated that heterotrophic anoxic yield, anaerobic hydrolysis factors of heterotrophs, heterotrophic hydrolysis, oxic endogenous decay rate for heterotrophs and oxic endogenous decay rate of PAOs had the most impact on predicted effluent TP concentration. The final values of kinetic parameters obtained in the calibration seemed to imply that nitrogen and phosphorus removal increased with SRT due to an increase in anoxic and anaerobic hydrolysis factors up to 50 days SRT but beyond that removal of phosphorus deteriorated due to high oxic endogenous decay rates. This indirectly imply that the decrease in phosphorus removal at 75 days SRT may be due to an increase in lysis of microbial cells at high SRTs along with the low food/microorganisms ratio as a result of high suspended solids in the oxic tank. Several polynomial correlations relating the various calibrated kinetic parameters with SRTs were derived. The Biowin((R)) model and the kinetic parameters predicted by the polynomial correlations were verified and found to predict well the effluent water quality

  3. Estimation of gastric residence time of the Heidelberg capsule in humans: effect of varying food composition

    SciTech Connect

    Mojaverian, P.; Ferguson, R.K.; Vlasses, P.H.; Rocci, M.L. Jr.; Oren, A.; Fix, J.A.; Caldwell, L.J.; Gardner, C.

    1985-08-01

    In animal and human studies, the gastric emptying of large (greater than 1 mm) indigestible solids is due to the activity of the interdigestive migrating myoelectric complex. The gastric residence time (GRT) of an orally administered, nondigestible, pH-sensitive, radiotelemetric device (Heidelberg capsule) was evaluated in three studies in healthy volunteers. In 6 subjects, the GRT of the Heidelberg capsule was compared with the half-emptying time (t1/2) of diethylenetriaminepentaacetic acid labeled with technetium 99m after a 4-ml/kg liquid fatty meal. The mean (+/-SD) GRT (4.3 +/- 1.4 h) was significantly (p less than 0.001) longer than the mean t1/2 (1.1 +/- 0.3 h); the GRT was prolonged compared with the t1/2 in each subject. In a randomized, crossover trial in 10 subjects, frequent feeding caused a dramatic prolongation in mean GRT of the capsule compared with the fasting state (greater than 14.5 vs. 0.5 h, p less than 0.005). In another crossover study in 6 subjects, the GRT of the capsule was evaluated after an overnight fast, a standard breakfast including solid food, and a liquid meal (i.e., 200 ml of diluted light cream). The mean GRT was 2.6 +/- 0.9 h after the liquid meal vs. 1.2 +/- 0.8 h after fasting (p less than 0.025). The mean GRT after the breakfast was 4.8 +/- 1.5 h, which was significantly greater than that after fasting (p less than 0.001) and after the liquid meal (p less than 0.01). These data suggest that the GRT of the Heidelberg capsule is a marker of the interdigestive migrating myoelectric complex in humans, the interdigestive migrating myoelectric complex can be markedly delayed by frequent feedings with solids, and the interdigestive migrating myoelectric complex is delayed by both liquid and solid meals.

  4. Training for Efficiency: Work, Time, and Systems-Based Practice in Medical Residency

    ERIC Educational Resources Information Center

    Szymczak, Julia E.; Bosk, Charles L.

    2012-01-01

    Medical residency is a period of intense socialization with a heavy workload. Previous sociological studies have identified efficiency as a practical skill necessary for success. However, many contextual features of the training environment have undergone dramatic change since these studies were conducted. What are the consequences of these…

  5. Chemical composition profiles during alkaline flooding at different temperatures and extended residence times

    SciTech Connect

    Aflaki, R.; Handy, L.L.

    1992-12-01

    The objective of this work was to investigate whether or not caustic sweeps the major portion of the reservoir efficiently during an alkaline flood process. It was also the objective of this work to study the state of final equilibrium during a caustic flood through determination of the pH and chemical composition profiles along the porous medium. For this purpose, a long porous medium which provided extended residence times was required. It was necessary to set up the porous medium such that the changes in the pH and chemical composition of the solution could be monitored. Four Berea sandstone cores (8 in. length and1 in. diameter) placed in series provided the desired length and the opportunity for sampling in-between cores. This enabled establishment of pH and chemical composition profiles. The experiments were run at, temperatures up.to 180{degrees}C, and the flow rates varied from 4.8 to 0.2 ft/day. The samples were analyzed for pH and for Si and Al concentrations.The results show that caustic consumption is insignificant for temperatures up to 100{degrees}C. Above 100{degrees}C consumption increases and is accompanied by a significant decrease in pH. The sharp decline in pH also coincides with a sharp decline in concentration of silica in solution. The results also show that alumina is removed from the solution and solubility of alumina ultimately reaches zero. Sharp silica and pH declines take place even in the absence of any alumina in solution. As a result, removal of silica from solution is attributed to the irreversible caustic/rock interaction. This interaction is in the form of chemisorption reactions in which silica is adsorbed onto the rock surface consuming hydroxyl ion. Once these reactions were satisfied, caustic breakthrough occurs at a high pH. However, significant pore volumes of caustic must be injected for completion of the chemisorption.

  6. Chemical composition profiles during alkaline flooding at different temperatures and extended residence times

    SciTech Connect

    Aflaki, R.; Handy, L.L.

    1992-12-01

    The objective of this work was to investigate whether or not caustic sweeps the major portion of the reservoir efficiently during an alkaline flood process. It was also the objective of this work to study the state of final equilibrium during a caustic flood through determination of the pH and chemical composition profiles along the porous medium. For this purpose, a long porous medium which provided extended residence times was required. It was necessary to set up the porous medium such that the changes in the pH and chemical composition of the solution could be monitored. Four Berea sandstone cores (8 in. length and1 in. diameter) placed in series provided the desired length and the opportunity for sampling in-between cores. This enabled establishment of pH and chemical composition profiles. The experiments were run at, temperatures up.to 180[degrees]C, and the flow rates varied from 4.8 to 0.2 ft/day. The samples were analyzed for pH and for Si and Al concentrations.The results show that caustic consumption is insignificant for temperatures up to 100[degrees]C. Above 100[degrees]C consumption increases and is accompanied by a significant decrease in pH. The sharp decline in pH also coincides with a sharp decline in concentration of silica in solution. The results also show that alumina is removed from the solution and solubility of alumina ultimately reaches zero. Sharp silica and pH declines take place even in the absence of any alumina in solution. As a result, removal of silica from solution is attributed to the irreversible caustic/rock interaction. This interaction is in the form of chemisorption reactions in which silica is adsorbed onto the rock surface consuming hydroxyl ion. Once these reactions were satisfied, caustic breakthrough occurs at a high pH. However, significant pore volumes of caustic must be injected for completion of the chemisorption.

  7. Lagrangian simulation of transport pathways and residence times along the western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Piñones, Andrea; Hofmann, Eileen E.; Dinniman, Michael S.; Klinck, John M.

    2011-07-01

    The relative contribution of ocean circulation in producing areas where marine mammals and other predators concentrate to produce biological hot spots along the continental shelf of the western Antarctic Peninsula (wAP) was investigated with numerical Lagrangian particle tracking simulations. Circulation distributions used in the Lagrangian simulations were obtained from the Regional Ocean Modeling System (ROMS) configured for the wAP region, with a horizontal resolution of 4 km and a vertical resolution of 24 sigma-layers. To determine release points for the floats, the simulated circulation fields were first analyzed to estimate scales of temporal variability. The temporal decorrelation scales of the simulated surface flow over most of the wAP shelf were 2-3 days. However, decorrelation scales of about 40 days were found for the surface flow in the southern part of Marguerite Bay. Temporal decorrelation scales for the flow below the permanent pycnocline at the depth of Circumpolar Deep Water (CDW) intrusions (below 250 m) were between 40 and 70 days along the northern flank of Marguerite Trough and extending into Marguerite Bay. Near Adelaide Island, Anvers Island and the offshore side of Alexander Island, the velocity decorrelation scales varied between 40 and 60 days. Floats were released in the wAP simulated circulation fields along the outer and mid-shelf at a range of depths in different seasons. The simulated particle trajectories showed preferred sites for across-shelf transport, with Marguerite Trough being a primary pathway for movement of floats into Marguerite Bay, Crystal Sound and the inner shelf region. The three primary biological hot spots, Crystal Sound, Laubeuf Fjord, and off Alexander Island, were sites with the longest particle residence times, being 18-27 days for Alexander Island and Crystal Sound to almost 35 days for Laubeuf Fjord. However, the source regions and circulation processes that provided the input of particles differed for each

  8. Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

    NASA Astrophysics Data System (ADS)

    Handley, Heather K.; Turner, Simon; Afonso, Juan C.; Dosseto, Anthony; Cohen, Tim

    2013-02-01

    Quantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geometric and surface area measurement with an incorporated fractal correction) and typical assumed input parameter values found in the literature. The calculated recoil loss factors and comminution ages are highly dependent on the method of recoil loss factor determination used and the chosen assumptions. To appraise the ramifications of the assumptions inherent in the comminution age approach and determine individual and combined comminution age uncertainties associated to each variable, Monte Carlo simulations were conducted for a synthetic sediment sample. Using a reasonable associated uncertainty for each input factor and including variations in the source rock and measured (234U/238U) ratios, the total combined uncertainty on comminution age in our simulation (for both methods of recoil loss factor estimation) can amount to ±220-280 ka. The modelling shows that small changes in assumed input values translate into large effects on absolute comminution age. To improve the accuracy of the technique and provide meaningful absolute comminution ages, much tighter constraints are required on the assumptions for input factors such as the fraction of α-recoil lost 234Th and the initial (234U/238U) ratio of the source material. In order to be able to directly compare calculated comminution ages produced by different research groups, the standardisation of pre-treatment procedures, recoil loss factor estimation and assumed input parameter values

  9. A model to predict CWD residence times in tropical forests along an altitudinal gradient in Australia

    NASA Astrophysics Data System (ADS)

    Torello-Raventos, Mireia; Ford, Andrew; Saiz, Gus; Bloomfield, Keith; Lloyd, Jon; Bird, Michael

    2014-05-01

    More reliable knowledge on the complex responses of vegetation to climate change is one of the most urgent needs for tropical forest preservation and recent data models indicate an increase of tree mortality in tropical forests as a consequence of climate change1. Coarse woody debris dynamics in tropical forests remain poorly understood2. Tropical forests are known for possessing a wide range of wood densities- with different wood traits and secondary wood chemical components-, adding complexity to the accurate estimations of coarse woody debris residence times (τ). Quantifying τ in these ecosystems along an altitudinal gradient provides a way to improve our understanding of carbon dynamics in the face of climate change. This study examines τ from different tree tropical forest species -ranging from soft to hardwoods- and under different decay status, to understand the effects of climate on the chemical and physical decay of CWD on an elevation gradient from 102 m above sea level (MAT = 23.7° C) to 1500 m above sea level (MAT = 16.7° C) in Australia. Wood density together with Carbon:Nitrogen ratio enabled prediction of the variation in τ between decay classes within tree species, between tree species and along the elevation gradient. τ increased with decreasing the decay status, increasing wood density and temperature also played an important role as τ increased with increasing site elevation. The study also highlighted the importance of including seasonal variation of climate in short term field studies, as a single wet season reduced the τ of the CWD compared to τ after a year of exposure. Intraspecific variation of plant traits and secondary wood chemicals explained the observed range in τ for species with similar wood densities, decreasing with increasing decayed status of the samples. This study will aid in the development of predictive relationships between wood density and environmental variables to infer carbon dynamics at local and global scale

  10. Trait differences between naturalized and invasive plant species independent of residence time and phylogeny

    PubMed Central

    Gallagher, R V; Randall, R P; Leishman, M R

    2015-01-01

    The ability to predict which alien plants will transition from naturalized to invasive prior to their introduction to novel regions is a key goal for conservation and has the potential to increase the efficacy of weed risk assessment (WRA). However, multiple factors contribute to plant invasion success (e.g., functional traits, range characteristics, residence time, phylogeny), and they all must be taken into account simultaneously in order to identify meaningful correlates of invasion success. We compiled 146 pairs of phylogenetically paired (congeneric) naturalized and invasive plant species in Australia with similar minimum residence times (i.e., time since introduction in years). These pairs were used to test for differences in 5 functional traits (flowering duration, leaf size, maximum height, specific leaf area [SLA], seed mass) and 3 characteristics of species’ native ranges (biome occupancy, mean annual temperature, and rainfall breadth) between naturalized and invasive species. Invasive species, on average, had larger SLA, longer flowering periods, and were taller than their congeneric naturalized relatives. Invaders also exhibited greater tolerance for different environmental conditions in the native range, where they occupied more biomes and a wider breadth of rainfall and temperature conditions than naturalized congeners. However, neither seed mass nor leaf size differed between pairs of naturalized and invasive species. A key finding was the role of SLA in distinguishing between naturalized and invasive pairs. Species with high SLA values were typically associated with faster growth rates, more rapid turnover of leaf material, and shorter lifespans than those species with low SLA. This suite of characteristics may contribute to the ability of a species to transition from naturalized to invasive across a wide range of environmental contexts and disturbance regimes. Our findings will help in the refinement of WRA protocols, and we advocate the

  11. Time-based collision risk modeling for air traffic management

    NASA Astrophysics Data System (ADS)

    Bell, Alan E.

    Since the emergence of commercial aviation in the early part of last century, economic forces have driven a steadily increasing demand for air transportation. Increasing density of aircraft operating in a finite volume of airspace is accompanied by a corresponding increase in the risk of collision, and in response to a growing number of incidents and accidents involving collisions between aircraft, governments worldwide have developed air traffic control systems and procedures to mitigate this risk. The objective of any collision risk management system is to project conflicts and provide operators with sufficient opportunity to recognize potential collisions and take necessary actions to avoid them. It is therefore the assertion of this research that the currency of collision risk management is time. Future Air Traffic Management Systems are being designed around the foundational principle of four dimensional trajectory based operations, a method that replaces legacy first-come, first-served sequencing priorities with time-based reservations throughout the airspace system. This research will demonstrate that if aircraft are to be sequenced in four dimensions, they must also be separated in four dimensions. In order to separate aircraft in four dimensions, time must emerge as the primary tool by which air traffic is managed. A functional relationship exists between the time-based performance of aircraft, the interval between aircraft scheduled to cross some three dimensional point in space, and the risk of collision. This research models that relationship and presents two key findings. First, a method is developed by which the ability of an aircraft to meet a required time of arrival may be expressed as a robust standard for both industry and operations. Second, a method by which airspace system capacity may be increased while maintaining an acceptable level of collision risk is presented and demonstrated for the purpose of formulating recommendations for procedures

  12. Fast Pyrolysis Behavior of Banagrass as a Function of Temperature and Volatiles Residence Time in a Fluidized Bed Reactor

    PubMed Central

    Morgan, Trevor James; Turn, Scott Q.; George, Anthe

    2015-01-01

    A reactor was designed and commissioned to study the fast pyrolysis behavior of banagrass as a function of temperature and volatiles residence time. Four temperatures between 400 and 600°C were examined as well as four residence times between ~1.0 and 10 seconds. Pyrolysis product distributions of bio-oil, char and permanent gases were determined at each reaction condition. The elemental composition of the bio-oils and chars was also assessed. The greatest bio-oil yield was recorded when working at 450°C with a volatiles residence time of 1.4 s, ~37 wt% relative to the dry ash free feedstock (excluding pyrolysis water). The amounts of char (organic fraction) and permanent gases under these conditions are ~4 wt% and 8 wt% respectively. The bio-oil yield stated above is for 'dry' bio-oil after rotary evaporation to remove solvent, which results in volatiles and pyrolysis water being removed from the bio-oil. The material removed during drying accounts for the remainder of the pyrolysis products. The 'dry' bio-oil produced under these conditions contains ~56 wt% carbon which is ~40 wt% of the carbon present in the feedstock. The oxygen content of the 450°C, 1.4 s 'dry' bio-oil is ~38 wt%, which accounts for ~33 wt% of the oxygen in the feedstock. At higher temperature or longer residence time less bio-oil and char is recovered and more gas and light volatiles are produced. Increasing the temperature has a more significant effect on product yields and composition than increasing the volatiles residence time. At 600°C and a volatiles residence time of 1.2 seconds the bio-oil yield is ~21 wt% of the daf feedstock, with a carbon content of 64 wt% of the bio-oil. The bio-oil yield from banagrass is significantly lower than from woody biomass or grasses such as switchgrass or miscanthus, but is similar to barley straw. The reason for the low bio-oil yield from banagrass is thought to be related to its high ash content (8.5 wt% dry basis) and high concentration of alkali

  13. Fast Pyrolysis Behavior of Banagrass as a Function of Temperature and Volatiles Residence Time in a Fluidized Bed Reactor

    DOE PAGESBeta

    Morgan, Trevor James; Turn, Scott Q.; George, Anthe

    2015-08-26

    A reactor was designed and commissioned to study the fast pyrolysis behavior of banagrass as a function of temperature and volatiles residence time. Four temperatures between 400 and 600°C were examined as well as four residence times between ~1.0 and 10 seconds. Pyrolysis product distributions of bio-oil, char and permanent gases were determined at each reaction condition. The elemental composition of the bio-oils and chars was also assessed. The greatest bio-oil yield was recorded when working at 450°C with a volatiles residence time of 1.4 s, ~37 wt% relative to the dry ash free feedstock (excluding pyrolysis water). The amountsmore » of char (organic fraction) and permanent gases under these conditions are ~4 wt% and 8 wt% respectively. The bio-oil yield stated above is for 'dry' bio-oil after rotary evaporation to remove solvent, which results in volatiles and pyrolysis water being removed from the bio-oil. The material removed during drying accounts for the remainder of the pyrolysis products. The 'dry' bio-oil produced under these conditions contains ~56 wt% carbon which is ~40 wt% of the carbon present in the feedstock. The oxygen content of the 450°C, 1.4 s 'dry' bio-oil is ~38 wt%, which accounts for ~33 wt% of the oxygen in the feedstock. At higher temperature or longer residence time less bio-oil and char is recovered and more gas and light volatiles are produced. Increasing the temperature has a more significant effect on product yields and composition than increasing the volatiles residence time. At 600°C and a volatiles residence time of 1.2 seconds the bio-oil yield is ~21 wt% of the daf feedstock, with a carbon content of 64 wt% of the bio-oil. The bio-oil yield from banagrass is significantly lower than from woody biomass or grasses such as switchgrass or miscanthus, but is similar to barley straw. In conclusion, the reason for the low bio-oil yield from banagrass is thought to be related to its high ash content (8.5 wt% dry basis) and high

  14. Patterns and processes of fluvial discontinuity and sediment residence times on the lower Macquarie River, Murray-Darling Basin, Australia

    NASA Astrophysics Data System (ADS)

    Larkin, Zacchary; Ralph, Timothy; Hesse, Paul

    2014-05-01

    The supply, transport and deposition of fine-grained sediment are important factors determining the morphology of lowland rivers that experience channel breakdown and have wetlands on their lower reaches. Sediment supply and residence time determine whether reaches accumulate sediment (wetland areas) or erode sediment (channelised areas). This research investigated how processes of sedimentation and erosion drive channel breakdown and reformation in the Macquarie Marshes, a large anastomosing wetland system in the Murray-Darling Basin, Australia. Channel breakdown is attributed to a dominance of in-stream sedimentation that leads to a point where single-thread river channels cannot be maintained and so avulsion and floodout processes create smaller distributary channels and wetlands. Avulsions may reconnect channels, changing the sediment supply regime in those particular channels. Channel reformation occurs on the trunk stream where the floodplain gradient steepens enough to allow convergence of small tributaries, locally increasing stream power (and erosive energy in channels). As each river reach reforms following channel breakdown, the channel is smaller, shallower and straighter than the previous reach. One reach in this system recently (in the 1970s) became connected with a parallel channel through avulsion and has morphological characteristics that indicate a significant change in flow and sediment supply. In a pilot study using uranium-series disequilibrium methods and OSL dating, a sediment residence time of 58 +/- 2 ka was determined for sediment in the base of the active channel and a sediment residence time of 153 +/- 5 ka was determined for sediment buried in an adjacent meander that was cut off from the main channel 1,000 years ago. The apparent dramatic decrease in sediment residence time to this active channel poses an interesting question about the role of relatively new channels in transporting and depositing sediment more rapidly than the

  15. Fast Pyrolysis Behavior of Banagrass as a Function of Temperature and Volatiles Residence Time in a Fluidized Bed Reactor.

    PubMed

    Morgan, Trevor James; Turn, Scott Q; George, Anthe

    2015-01-01

    A reactor was designed and commissioned to study the fast pyrolysis behavior of banagrass as a function of temperature and volatiles residence time. Four temperatures between 400 and 600°C were examined as well as four residence times between ~1.0 and 10 seconds. Pyrolysis product distributions of bio-oil, char and permanent gases were determined at each reaction condition. The elemental composition of the bio-oils and chars was also assessed. The greatest bio-oil yield was recorded when working at 450°C with a volatiles residence time of 1.4 s, ~37 wt% relative to the dry ash free feedstock (excluding pyrolysis water). The amounts of char (organic fraction) and permanent gases under these conditions are ~4 wt% and 8 wt% respectively. The bio-oil yield stated above is for 'dry' bio-oil after rotary evaporation to remove solvent, which results in volatiles and pyrolysis water being removed from the bio-oil. The material removed during drying accounts for the remainder of the pyrolysis products. The 'dry' bio-oil produced under these conditions contains ~56 wt% carbon which is ~40 wt% of the carbon present in the feedstock. The oxygen content of the 450°C, 1.4 s 'dry' bio-oil is ~38 wt%, which accounts for ~33 wt% of the oxygen in the feedstock. At higher temperature or longer residence time less bio-oil and char is recovered and more gas and light volatiles are produced. Increasing the temperature has a more significant effect on product yields and composition than increasing the volatiles residence time. At 600°C and a volatiles residence time of 1.2 seconds the bio-oil yield is ~21 wt% of the daf feedstock, with a carbon content of 64 wt% of the bio-oil. The bio-oil yield from banagrass is significantly lower than from woody biomass or grasses such as switchgrass or miscanthus, but is similar to barley straw. The reason for the low bio-oil yield from banagrass is thought to be related to its high ash content (8.5 wt% dry basis) and high concentration of alkali

  16. Fast Pyrolysis Behavior of Banagrass as a Function of Temperature and Volatiles Residence Time in a Fluidized Bed Reactor

    SciTech Connect

    Morgan, Trevor James; Turn, Scott Q.; George, Anthe

    2015-08-26

    A reactor was designed and commissioned to study the fast pyrolysis behavior of banagrass as a function of temperature and volatiles residence time. Four temperatures between 400 and 600°C were examined as well as four residence times between ~1.0 and 10 seconds. Pyrolysis product distributions of bio-oil, char and permanent gases were determined at each reaction condition. The elemental composition of the bio-oils and chars was also assessed. The greatest bio-oil yield was recorded when working at 450°C with a volatiles residence time of 1.4 s, ~37 wt% relative to the dry ash free feedstock (excluding pyrolysis water). The amounts of char (organic fraction) and permanent gases under these conditions are ~4 wt% and 8 wt% respectively. The bio-oil yield stated above is for 'dry' bio-oil after rotary evaporation to remove solvent, which results in volatiles and pyrolysis water being removed from the bio-oil. The material removed during drying accounts for the remainder of the pyrolysis products. The 'dry' bio-oil produced under these conditions contains ~56 wt% carbon which is ~40 wt% of the carbon present in the feedstock. The oxygen content of the 450°C, 1.4 s 'dry' bio-oil is ~38 wt%, which accounts for ~33 wt% of the oxygen in the feedstock. At higher temperature or longer residence time less bio-oil and char is recovered and more gas and light volatiles are produced. Increasing the temperature has a more significant effect on product yields and composition than increasing the volatiles residence time. At 600°C and a volatiles residence time of 1.2 seconds the bio-oil yield is ~21 wt% of the daf feedstock, with a carbon content of 64 wt% of the bio-oil. The bio-oil yield from banagrass is significantly lower than from woody biomass or grasses such as switchgrass or miscanthus, but is similar to barley straw. In conclusion, the reason for the low bio-oil yield from banagrass is thought to be related to its high ash content (8.5 wt% dry basis) and high

  17. RESIDENCE TIME OF CONTAMINANTS RELEASED IN SURFACE COAL MINES: A WIND TUNNEL STUDY

    EPA Science Inventory

    The 1990 Clean Air Act Amendments direct the U.S. Environmental Protection Agency to evaluate and modify, as required, existing dispersion models for the prediction of dispersion of dust from surface coal mines. he application of mathematical air pollution dispersion models to th...

  18. Vanadium in ambient air: concentrations in lung tissue from autopsies of Mexico City residents in the 1960s and 1990s.

    PubMed

    Fortoul, Teresa Imelda; Quan-Torres, Alma; Sánchez, Ivonne; López, Irma Elena; Bizarro, Patricia; Mendoza, Maria Luisa; Osorio, Liliana Saldivar; Espejel-Maya, Guadalupe; Avila-Casado, Maria del Carmen; Avila-Costa, Maria Rosa; Colin-Barenque, Laura; Villanueva, Daniel Navarro; Olaiz-Fernandez, Gustavo

    2002-01-01

    Vanadium concentrations in lung tissue were determined by atomic absorption spectrometry from autopsy specimens taken from residents of Mexico City during the 1960s and 1990s (20 males and 19 females, and 30 males and 18 females, respectively). Samples from the 1990s had significantly increased mean vanadium concentrations (mean +/- standard deviation: 1.36 +/- 0.08), compared with those from the 1960s (1.04 +/- 0.05). Concentrations were not correlated with gender, smoking habit, age, cause of death, or occupation. These findings suggest that vanadium in ambient air is increasing and it represents a potential health hazard for Mexico City residents. Air pollution monitoring efforts should include vanadium concentrations in suspended particles to follow-up the findings reported herein. Researchers need to acquire a better knowledge of the levels of airborne vanadium exposure at which risk to human health occurs. PMID:12641188

  19. Residence times of fine tropospheric aerosols as determined by {sup 210}Pb progeny.

    SciTech Connect

    Marley, N. A.; Gaffney, J. S.; Drayton, P. J.; Cunningham, M. M.; Mielcarek, C.; Ravelo, R.; Wagner, C.

    1999-10-05

    Fine tropospheric aerosols can play important roles in the radiative balance of the atmosphere. The fine aerosols can act directly to cool the atmosphere by scattering incoming solar radiation, as well as indirectly by serving as cloud condensation nuclei. Fine aerosols, particularly carbonaceous soots, can also warm the atmosphere by absorbing incoming solar radiation. In addition, aerosols smaller than 2.5 {micro}m have recently been implicated in the health effects of air pollution. Aerosol-active radioisotopes are ideal tracers for the study of atmospheric transport processes. The source terms of these radioisotopes are relatively well known, and they are removed from the atmosphere only by radioactive decay or by wet or dry deposition of the host aerosol. The progeny of the primordial radionuclide {sup 238}U are of particular importance to atmospheric studies. Uranium-238 is common throughout Earth's crust and decays to the inert gas {sup 222}Rn, which escapes into the atmosphere. Radon-222 decays by the series of alpha and beta emissions shown in Figure 1 to the long-lived {sup 210}Pb. Once formed, {sup 210}Pb becomes attached to aerosol particles with average attachment times of 40 s to 3 min.

  20. Estimation of baseflow residence times in watersheds from the runoff hydrograph recession: method and application in the Neversink watershed, Catskill Mountains, New York

    NASA Astrophysics Data System (ADS)

    Vitvar, Tomas; Burns, Douglas A.; Lawrence, Gregory B.; McDonnell, Jeffrey J.; Wolock, David M.

    2002-06-01

    A method for estimation of mean baseflow residence time in watersheds from hydrograph runoff recession characteristics was developed. Runoff recession characteristics were computed for the period 1993-96 in the 2 km2 Winnisook watershed, Catskill Mountains, southeastern New York, and were used to derive mean values of subsurface hydraulic conductivity and the storage coefficient. These values were then used to estimate the mean baseflow residence time from an expression of the soil contact time, based on watershed soil and topographic characteristics. For comparison, mean baseflow residence times were calculated for the same period of time through the traditional convolution integral approach, which relates rainfall 18O to 18O values in streamflow. Our computed mean baseflow residence time was 9 months by both methods. These results indicate that baseflow residence time can be calculated accurately using recession analysis, and the method is less expensive than using environmental and/or artificial tracers. Published in 2002 by John Wiley & Sons, Ltd.

  1. Population-mixing at the place of residence at the time of birth and incidence of childhood leukaemia in France.

    PubMed

    Rudant, J; Baccaïni, B; Ripert, M; Goubin, A; Bellec, S; Hémon, D; Clavel, J

    2006-05-01

    The association between the risk of childhood leukaemia before age 7 years and population-mixing at the place of residence at birth was investigated by retrospectively considering all the children born in mainland French communes between 1st January 1990 and 31st December 1998. An increased risk of acute lymphoblastic leukaemia was found with higher levels of migration for children residing at birth in isolated communes with a population density > or =50 people per km2 (SIRR = 2.59, 95% CI: 1.48-4.49). No association was observed with lower population densities. For children residing in non-isolated communes at birth, the results were similar but less marked. The risk tended to increase only for population densities > or =5000 people per km2 (SIRR = 1.57, 95% CI: 0.99-2.52). The findings are consistent with epidemic models and support the hypothesis of an infectious aetiology relating to population-mixing. Population density may be seen as an indicator of the opportunity of contacts between inhabitants and should therefore be taken into account when investigating an infectious hypothesis. This is the first systematic study of population-mixing at the place of residence at the time of birth to be conducted on a national scale. PMID:16530405

  2. Caregiver Person-Centeredness and Behavioral Symptoms in Nursing Home Residents With Dementia: A Timed-Event Sequential Analysis

    PubMed Central

    Gilmore-Bykovskyi, Andrea L.; Roberts, Tonya J.; Bowers, Barbara J.; Brown, Roger L.

    2015-01-01

    Purpose: Evidence suggests that person-centered caregiving approaches may reduce dementia-related behavioral symptoms; however, little is known about the sequential and temporal associations between specific caregiver actions and behavioral symptoms. The aim of this study was to identify sequential associations between caregiver person-centered actions, task-centered actions, and resident behavioral symptoms and the temporal variation within these associations. Design and Methods: Videorecorded observations of naturally occurring interactions (N = 33; 724min) between 12 nursing home (NH) residents with dementia and eight certified nursing assistants were coded for caregiver person-centered actions, task-centered actions, and resident behavioral symptoms and analyzed using timed-event sequential analysis. Results: Although caregiver actions were predominantly person-centered, we found that resident behavioral symptoms were significantly more likely to occur following task-centered caregiver actions than person-centered actions. Implications: Findings suggest that the person-centeredness of caregivers is sequentially and temporally related to behavioral symptoms in individuals with dementia. Additional research examining the temporal structure of these relationships may offer valuable insights into the utility of caregiver person-centeredness as a low-cost strategy for improving behavioral symptom management in the NH setting. PMID:26055782

  3. Calculation of surface diffusivity and residence time by molecular dynamics with application to nanoscale selective-area growth

    NASA Astrophysics Data System (ADS)

    Almeida, S.; Ochoa, E.; Chavez, J. J.; Zhou, X. W.; Zubia, D.

    2015-08-01

    The surface diffusivity and residence time were calculated by molecular dynamics simulations in order to solve the surface diffusion equations for selective-area growth. The calculations for CdTe/CdS material system were performed in substrates with Cd termination and S termination. The surface diffusivity and residence time were obtained at different temperatures (600 K, 800 K, 1000 K, 1200 K, and 1400 K). The thermal activation energies were extracted from Arrhenius equation for each substrate termination. Thereafter, values obtained by molecular dynamics were used in a surface diffusion model to calculate the surface concentration profile of adatoms. Alternating the surface termination has the potential to achieve nanoscale selective-area growth without the need of a dielectric film as a mask.

  4. Measurement of residence time distribution of liquid phase in an industrial-scale continuous pulp digester using radiotracer technique.

    PubMed

    Sheoran, Meenakshi; Goswami, Sunil; Pant, Harish J; Biswal, Jayashree; Sharma, Vijay K; Chandra, Avinash; Bhunia, Haripada; Bajpai, Pramod K; Rao, S Madhukar; Dash, A

    2016-05-01

    A series of radiotracer experiments was carried out to measure residence time distribution (RTD) of liquid phase (alkali) in an industrial-scale continuous pulp digester in a paper industry in India. Bromine-82 as ammonium bromide was used as a radiotracer. Experiments were carried out at different biomass and white liquor flow rates. The measured RTD data were treated and mean residence times in individual digester tubes as well in the whole digester were determined. The RTD was also analyzed to identify flow abnormalities and investigate flow dynamics of the liquid phase in the pulp digester. Flow channeling was observed in the first section (tube 1) of the digester. Both axial dispersion and tanks-in-series with backmixing models preceded with a plug flow component were used to simulate the measured RTD and quantify the degree of axial mixing. Based on the study, optimum conditions for operating the digester were proposed. PMID:26896681

  5. Atmospheric residence time of (210)Pb determined from the activity ratios with its daughter radionuclides (210)Bi and (210)Po.

    PubMed

    Semertzidou, P; Piliposian, G T; Appleby, P G

    2016-08-01

    The residence time of (210)Pb created in the atmosphere by the decay of gaseous (222)Rn is a key parameter controlling its distribution and fallout onto the landscape. These in turn are key parameters governing the use of this natural radionuclide for dating and interpreting environmental records stored in natural archives such as lake sediments. One of the principal methods for estimating the atmospheric residence time is through measurements of the activities of the daughter radionuclides (210)Bi and (210)Po, and in particular the (210)Bi/(210)Pb and (210)Po/(210)Pb activity ratios. Calculations used in early empirical studies assumed that these were governed by a simple series of equilibrium equations. This approach does however have two failings; it takes no account of the effect of global circulation on spatial variations in the activity ratios, and no allowance is made for the impact of transport processes across the tropopause. This paper presents a simple model for calculating the distributions of (210)Pb, (210)Bi and (210)Po at northern mid-latitudes (30°-65°N), a region containing almost all the available empirical data. By comparing modelled (210)Bi/(210)Pb activity ratios with empirical data a best estimate for the tropospheric residence time of around 10 days is obtained. This is significantly longer than earlier estimates of between 4 and 7 days. The process whereby (210)Pb is transported into the stratosphere when tropospheric concentrations are high and returned from it when they are low, significantly increases the effective residence time in the atmosphere as a whole. The effect of this is to significantly enhance the long range transport of (210)Pb from its source locations. The impact is illustrated by calculations showing the distribution of (210)Pb fallout versus longitude at northern mid-latitudes. PMID:27132252

  6. Regional oxygen reduction and denitrification rates in groundwater from multi-model residence time distributions, San Joaquin Valley, USA

    USGS Publications Warehouse

    Green, Christopher T.; Jurgens, Bryant; Zhang, Yong; Starn, Jeffrey; Singleton, Michael J.; Esser, Bradley K.

    2016-01-01

    Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary and covary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight into the characteristics of residence times and rates of O2 reduction and denitrification (NO3− reduction) by comparing reaction rates using multi-model analytical residence time distributions (RTDs) applied to a data set of atmospheric tracers of groundwater age and geochemical data from 141 well samples in the Central Eastern San Joaquin Valley, CA. The RTD approach accounts for mixtures of residence times in a single sample to provide estimates of in-situ rates. Tracers included SF6, CFCs, 3H, He from 3H (tritiogenic He),14C, and terrigenic He. Parameter estimation and multi-model averaging were used to establish RTDs with lower error variances than those produced by individual RTD models. The set of multi-model RTDs was used in combination with NO3− and dissolved gas data to estimate zero order and first order rates of O2 reduction and denitrification. Results indicated that O2 reduction and denitrification rates followed approximately log-normal distributions. Rates of O2 and NO3− reduction were correlated and, on an electron milliequivalent basis, denitrification rates tended to exceed O2 reduction rates. Estimated historical NO3− trends were similar to historical measurements. Results show that the multi-model approach can improve estimation of age distributions, and that relatively easily measured O2 rates can provide information about trends in denitrification rates, which are more difficult to estimate.

  7. Hydrodynamics, temperature/salinity variability and residence time in the Chilika lagoon during dry and wet period: Measurement and modeling

    NASA Astrophysics Data System (ADS)

    Mahanty, M. M.; Mohanty, P. K.; Pattnaik, A. K.; Panda, U. S.; Pradhan, S.; Samal, R. N.

    2016-08-01

    This paper investigated the hydrodynamics, spatio-temporal variability of temperature/salinity and the residence time of tracer concentrations in a largest brackish water coastal lagoon in Asia, namely the Chilika lagoon, India. An integrated approach combined the measurement and 2D hydrodynamic-advection/dispersion model is used to simulate circulation and temperature/salinity, and estimated the water residence time in lagoon under different forcing mechanisms, such as tide, wind and freshwater discharge during the dry and wet periods. Water circulation inside the lagoon is simulated when wind is included with the tide only forcing during dry period, and freshwater influx is included with the tide and wind forcing during wet period. Under the realistic forcing conditions, the computed temporal variability of water temperature and salinity are well correlated with the measurements in both the periods. The spatial variations of water temperature within the lagoon is influenced by the meteorological conditions, tide and freshwater influx as well as the shallowness of the lagoon, whereas the salinity is spatially controlled by the freshwater influx from the riverine system and seawater intrusion through the tidal inlets. The numerical model results show that in the Chilika lagoon tidal and river influx affect significantly the residence time spatially, and is site specific. The residence time varies from values of 4-5 days in the outer channel (OC) and 132 days at the northern sector (NS) in the main body of lagoon. The current study represents a first attempt to use a combined model approach, which is therefore, a useful tool to support the ecological implication of the lagoon ecosystem.

  8. Effects of solute breakthrough curve tail truncation on residence time estimates: A synthesis of solute tracer injection studies

    NASA Astrophysics Data System (ADS)

    Drummond, J. D.; Covino, T. P.; Aubeneau, A. F.; Leong, D.; Patil, S.; Schumer, R.; Packman, A. I.

    2012-09-01

    Hydrologic transport and retention strongly affect biogeochemical processes that are critical to stream ecosystems. Tracer injection studies are often used to characterize solute transport and retention in stream reaches, but the range of processes accurately resolved with this approach is not clear. Solute residence time distributions depend on both in-stream mixing and exchange with the hyporheic zone and the larger groundwater system. Observed in-stream breakthrough curves have most commonly been modeled with in-stream advection-dispersion plus an exponential residence time distribution, but process-based models suggest that hyporheic exchange is a fractal process, and that hyporheic residence time distributions are more appropriately characterized by power law tailing. We synthesized results from a variety of tracer-injection studies to investigate the information content of tracer breakthrough curves. We found that breakthrough curve tails are often not well characterized in stream tracer experiments. The two main reasons for this are: 1) experimental truncation of breakthrough curves, which occurs when sampling ends before all tracer mass reaches the sampling location, and 2) sensitivity truncation of breakthrough curves, when tracer concentrations in the tail are too low to be detected reliably above background levels. Tail truncation reduces observed mass recovery and obscures assessment of breakthrough curve tailing and solute residence time. Failure to consider tail truncation leads to underestimation of hyporheic exchange and solute retention and to corresponding overestimation of hyporheic biogeochemical transformation rates. Based on these findings, we propose criteria for improved design of in-stream tracer injection experiments to improve assessment of solute tailing behavior.

  9. Influence of substrate heterogeneity on the hydraulic residence time and removal efficiency of horizontal subsurface flow constructed wetlands

    NASA Astrophysics Data System (ADS)

    Carranza-Diaz, O.; Brovelli, A.; Rossi, L.; Barry, D. A.

    2009-04-01

    Horizontal, subsurface flow constructed wetlands are wastewater treatment devices. The influent polluted water flows through a porous substrate where the contaminants are removed, for example by microbial oxidation, surface adsorption and mineral precipitation. These systems are widely used with varying degrees of success to treat municipal and agricultural contaminated waters and remove the organic carbon and nutrient load. Constructed wetlands are an appealing and promising technology, because they (i) are potentially very efficient in removing the pollutants, (ii) require only a small external energy input and (iii) require low maintenance. However, practical experience has shown that the observed purification rate is highly variable and is often much smaller than expected. One of the numerous reasons proposed to explain the variable efficiency of constructed wetlands is the existence of highly conductive zones within the porous substrate, which produce a dramatic reduction of the hydraulic residence time and therefore directly decreases the overall water purification rate. This work aims to understand quantitatively the relationship between the spatial variability in the hydraulic properties of the substrate and the effective residence time in constructed wetlands. We conducted two suites of stochastic numerical simulations, modelling the transport of a conservative tracer in a three-dimensional simulated constructed wetland in one case, and the microbial oxidation of a carbon source in the other. Within each group of simulations, different hydraulic conductivity fields were tested. These were based on a log-normal, spatially correlated random field (with exponential spatial correlation). The amount of heterogeneity was varied by changing the variance correlation length in the three directions. For each set of parameters, different realizations are considered to deduce both the expected residence time for a certain amount of heterogeneity, and its range of

  10. Receptor residence time trumps drug-likeness and oral bioavailability in determining efficacy of complement C5a antagonists.

    PubMed

    Seow, Vernon; Lim, Junxian; Cotterell, Adam J; Yau, Mei-Kwan; Xu, Weijun; Lohman, Rink-Jan; Kok, W Mei; Stoermer, Martin J; Sweet, Matthew J; Reid, Robert C; Suen, Jacky Y; Fairlie, David P

    2016-01-01

    Drug discovery and translation are normally based on optimizing efficacy by increasing receptor affinity, functional potency, drug-likeness (rule-of-five compliance) and oral bioavailability. Here we demonstrate that residence time of a compound on its receptor has an overriding influence on efficacy, exemplified for antagonists of inflammatory protein complement C5a that activates immune cells and promotes disease. Three equipotent antagonists (3D53, W54011, JJ47) of inflammatory responses to C5a (3nM) were compared for drug-likeness, receptor affinity and antagonist potency in human macrophages, and anti-inflammatory efficacy in rats. Only the least drug-like antagonist (3D53) maintained potency in cells against higher C5a concentrations and had a much longer duration of action (t1/2 ~ 20 h) than W54011 or JJ47 (t1/2 ~ 1-3 h) in inhibiting macrophage responses. The unusually long residence time of 3D53 on its receptor was mechanistically probed by molecular dynamics simulations, which revealed long-lasting interactions that trap the antagonist within the receptor. Despite negligible oral bioavailability, 3D53 was much more orally efficacious than W54011 or JJ47 in preventing repeated agonist insults to induce rat paw oedema over 24 h. Thus, residence time on a receptor can trump drug-likeness in determining efficacy, even oral efficacy, of pharmacological agents. PMID:27094554

  11. Receptor residence time trumps drug-likeness and oral bioavailability in determining efficacy of complement C5a antagonists

    PubMed Central

    Seow, Vernon; Lim, Junxian; Cotterell, Adam J.; Yau, Mei-Kwan; Xu, Weijun; Lohman, Rink-Jan; Kok, W. Mei; Stoermer, Martin J.; Sweet, Matthew J.; Reid, Robert C.; Suen, Jacky Y.; Fairlie, David P.

    2016-01-01

    Drug discovery and translation are normally based on optimizing efficacy by increasing receptor affinity, functional potency, drug-likeness (rule-of-five compliance) and oral bioavailability. Here we demonstrate that residence time of a compound on its receptor has an overriding influence on efficacy, exemplified for antagonists of inflammatory protein complement C5a that activates immune cells and promotes disease. Three equipotent antagonists (3D53, W54011, JJ47) of inflammatory responses to C5a (3nM) were compared for drug-likeness, receptor affinity and antagonist potency in human macrophages, and anti-inflammatory efficacy in rats. Only the least drug-like antagonist (3D53) maintained potency in cells against higher C5a concentrations and had a much longer duration of action (t1/2 ~ 20 h) than W54011 or JJ47 (t1/2 ~ 1–3 h) in inhibiting macrophage responses. The unusually long residence time of 3D53 on its receptor was mechanistically probed by molecular dynamics simulations, which revealed long-lasting interactions that trap the antagonist within the receptor. Despite negligible oral bioavailability, 3D53 was much more orally efficacious than W54011 or JJ47 in preventing repeated agonist insults to induce rat paw oedema over 24 h. Thus, residence time on a receptor can trump drug-likeness in determining efficacy, even oral efficacy, of pharmacological agents. PMID:27094554

  12. Receptor residence time trumps drug-likeness and oral bioavailability in determining efficacy of complement C5a antagonists

    NASA Astrophysics Data System (ADS)

    Seow, Vernon; Lim, Junxian; Cotterell, Adam J.; Yau, Mei-Kwan; Xu, Weijun; Lohman, Rink-Jan; Kok, W. Mei; Stoermer, Martin J.; Sweet, Matthew J.; Reid, Robert C.; Suen, Jacky Y.; Fairlie, David P.

    2016-04-01

    Drug discovery and translation are normally based on optimizing efficacy by increasing receptor affinity, functional potency, drug-likeness (rule-of-five compliance) and oral bioavailability. Here we demonstrate that residence time of a compound on its receptor has an overriding influence on efficacy, exemplified for antagonists of inflammatory protein complement C5a that activates immune cells and promotes disease. Three equipotent antagonists (3D53, W54011, JJ47) of inflammatory responses to C5a (3nM) were compared for drug-likeness, receptor affinity and antagonist potency in human macrophages, and anti-inflammatory efficacy in rats. Only the least drug-like antagonist (3D53) maintained potency in cells against higher C5a concentrations and had a much longer duration of action (t1/2 ~ 20 h) than W54011 or JJ47 (t1/2 ~ 1–3 h) in inhibiting macrophage responses. The unusually long residence time of 3D53 on its receptor was mechanistically probed by molecular dynamics simulations, which revealed long-lasting interactions that trap the antagonist within the receptor. Despite negligible oral bioavailability, 3D53 was much more orally efficacious than W54011 or JJ47 in preventing repeated agonist insults to induce rat paw oedema over 24 h. Thus, residence time on a receptor can trump drug-likeness in determining efficacy, even oral efficacy, of pharmacological agents.

  13. Natural radionuclides (210)Po and (210)Pb in the Delaware and Chesapeake Estuaries: modeling scavenging rates and residence times.

    PubMed

    Marsan, D; Rigaud, S; Church, T

    2014-12-01

    During the spring and summer months of 2012, (210)Po and (210)Pb activity were measured in the dissolved and particulate phases from the Delaware and upper Chesapeake estuaries. The upper Delaware estuary, near the freshwater end member, was characterized by high-suspended matter concentrations that scavenged dissolved (210)Po and (210)Pb. Box models were applied using mass balance calculations to assess the nuclides residence times in each estuary. Only 60% of the dissolved (210)Po and 55% of the dissolved (210)Pb from the Delaware estuary were exported to coastal waters. A large fraction of soluble (210)Po and (210)Pb within the estuary was either reversibly adsorbed onto suspended particles, trapped in sediment accumulation zones (such as intertidal marshes), bioaccumulated into phytoplankton and discharged to the coastal ocean. The upper Chesapeake estuary was largely characterized by sub-oxic bottom waters that contained higher concentrations of dissolved (210)Po and (210)Pb, hypothesized to be subjected to redox cycling of manganese. The Delaware and Chesapeake estuary mean residence times for (210)Po differed significantly at 86 ± 7 and 126 ± 10 days respectively, while they were similar for (210)Pb (67 ± 6-55 ± 5 days). The difference in residence times corresponds to the greater extent of biogeochemical scavenging and regeneration processes within the upper Chesapeake. PMID:25239647

  14. SUBSURFACE RESIDENCE TIMES AS AN ALGORITHM FOR AQUIFER SENSITIVITY MAPPING: TESTING THE CONCEPT WITH ANALYTIC ELEMENT GROUND WATER MODELS IN THE CONTENTNEA CREEK BASIN, NORTH CAROLINA, USA

    EPA Science Inventory

    The objective of this research is to test the utility of simple functions of spatially integrated and temporally averaged ground water residence times in shallow "groundwatersheds" with field observations and more detailed computer simulations. The residence time of water in the...

  15. INDOOR, OUTDOOR, AND PERSONAL AIR EXPOSURES TO PARTICLES, ELEMENTS, AND NICOTINE FOR 178 RESIDENTS OF RIVERSIDE, CALIFORNIA

    EPA Science Inventory

    Personal, indoor, and outdoor concentrations of inhalable particles and 15 elements were measured for a probability sample of 178 persons representing 139,000 nonsmoking residents of Riverside, California. ewly designed personal monitors were employed. ersonal exposures often exc...

  16. The response of streambed nitrogen cycling to spatial and temporal hyporheic vertical flux patterns and associated residence times

    NASA Astrophysics Data System (ADS)

    Briggs, M. A.; Lautz, L. K.; Hare, D. K.

    2011-12-01

    Small beaver dams enhance the development of patchy micro-environments along the stream corridor by trapping sediment and creating complex streambed morphologies. This generates intricate hyporheic flux patterns that govern the exchange of oxygen and redox sensitive solutes between the water column and the streambed, and exert control on the biogeochemical cycling of nitrogen. Specifically, flowpaths from the stream into the subsurface with low residence times create oxic conditions that favor nitrification, while flowpaths with longer residence times become anoxic and favor denitrification. To investigate these processes we collected vertical profiles of pore water upstream of two beaver dams in Wyoming, USA at nine locations with varied morphology. We sampled pore water to the 0.55 m depth every week for five weeks as stream discharge dropped by 45% and subsequently measured concentrations of dissolved oxygen and several redox sensitive solutes, including nitrate. Additionally, estimates of hyporheic flux along these nine vertical profiles through time were made using high-resolution heat data combined with 1-D heat transport modeling. The data show that areas of rapid, deep hyporheic flux at the glides immediately upstream of the dams were oxygen rich, and were generally sites of moderate net nitrification to at least the 0.35 m depth. These conditions were relatively steady over the study period. Hyporheic zones at sediment bars closest to the dams were hotspots of nitrate production to a depth of 0.35 m, with nitrate concentrations increasing by as much as 400% as vertical flux fell sharply and residence times increased over the study period. In contrast, shallow bars farther upstream from the dams showed increasing fluxes and decreased residence times, which caused a shift from net denitrification to net nitrification over the period at shallow depths. These results support previous work indicating threshold behavior of nitrogen cycling in response to

  17. Impact of Timing of Birth and Resident Duty-Hour Restrictions on Outcome of Small Preterm Infants

    PubMed Central

    Bell, Edward F.; Hansen, Nellie I.; Morriss, Frank H.; Stoll, Barbara J.; Ambalavanan, Namasivayam; Gould, Jeffrey B.; Laptook, Abbot R.; Walsh, Michele C.; Carlo, Waldemar A.; Shankaran, Seetha; Das, Abhik; Higgins, Rosemary D.

    2010-01-01

    OBJECTIVE To examine the impact of birth at night, on the weekend, and during July or August – the first months of the academic year – and the impact of resident duty-hour restrictions on mortality and morbidity of VLBW infants. METHODS Outcomes were analyzed for 11,137 infants with birth weight 501–1250 grams enrolled in the NICHD Neonatal Research Network registry 2001–2005. Approximately half were born before the introduction of resident duty-hour restrictions in 2003. Follow-up assessment at 18–22 months was completed for 4,508 infants. Mortality (7-day and 28-day), short-term morbidities, and neurodevelopmental outcome were examined with respect to the timing of birth: night vs day, weekend vs weekday, and July or August vs other months, and after vs before implementation of resident duty-hour restrictions. RESULTS There was no effect of hour, day, or month of birth on mortality and no impact on the risks of short-term morbidities except the risk of ROP requiring operative treatment was lower for infants born during the late night hours than during the day. There was no impact of timing of birth on neurodevelopmental outcome except the risk of hearing impairment or death was slightly lower among infants born in July or August compared with other months. The introduction of resident and fellow duty-hour restrictions had no impact on mortality or neurodevelopmental outcome. The only change in short-term morbidity after duty-hour restrictions were introduced was an increase in the risk of ROP (stage 2 or higher). CONCLUSION In this network of academic centers, the timing of birth and the introduction of duty-hour restrictions had little effect on the risks of mortality and morbidity of VLBW infants, suggesting that staffing patterns were adequate to provide consistent care. PMID:20643715

  18. Mapping real-time air pollution health risk for environmental management: Combining mobile and stationary air pollution monitoring with neural network models.

    PubMed

    Adams, Matthew D; Kanaroglou, Pavlos S

    2016-03-01

    Air pollution poses health concerns at the global scale. The challenge of managing air pollution is significant because of the many air pollutants, insufficient funds for monitoring and abatement programs, and political and social challenges in defining policy to limit emissions. Some governments provide citizens with air pollution health risk information to allow them to limit their exposure. However, many regions still have insufficient air pollution monitoring networks to provide real-time mapping. Where available, these risk mapping systems either provide absolute concentration data or the concentrations are used to derive an Air Quality Index, which provides the air pollution risk for a mix of air pollutants with a single value. When risk information is presented as a single value for an entire region it does not inform on the spatial variation within the region. Without an understanding of the local variation residents can only make a partially informed decision when choosing daily activities. The single value is typically provided because of a limited number of active monitoring units in the area. In our work, we overcome this issue by leveraging mobile air pollution monitoring techniques, meteorological information and land use information to map real-time air pollution health risks. We propose an approach that can provide improved health risk information to the public by applying neural network models within a framework that is inspired by land use regression. Mobile air pollution monitoring campaigns were conducted across Hamilton from 2005 to 2013. These mobile air pollution data were modelled with a number of predictor variables that included information on the surrounding land use characteristics, the meteorological conditions, air pollution concentrations from fixed location monitors, and traffic information during the time of collection. Fine particulate matter and nitrogen dioxide were both modelled. During the model fitting process we reserved

  19. Residence times and nitrate transport in ground water discharging to streams in the Chesapeake Bay Watershed

    USGS Publications Warehouse

    Lindsey, Bruce D.; Phillips, Scott; Donnelly, Colleen A.; Speiran, Gary K.; Plummer, L. Niel; Bohlke, John-Karl; Focazio, Michael J.; Burton, William C.; Busenberg, Eurybiades

    2003-01-01

    One of the major water-quality problems in the Chesapeake Bay is an overabundance of nutrients from the streams and rivers that discharge to the Bay. Some of these nutrients are from nonpoint sources such as atmospheric deposition, agricultural manure and fertilizer, and septic systems. The effects of efforts to control nonpoint sources, however, can be difficult to quantify because of the lag time between changes at the land surface and the response in the base-flow (ground water) component of streams. To help resource managers understand the lag time between implementation of management practices and subsequent response in the nutrient concentrations in the base-flow component of streamflow, a study of ground-water discharge, residence time, and nitrate transport in springs throughout the Chesapeake Bay Watershed and in four smaller watersheds in selected hydrogeomorphic regions (HGMRs) was conducted. The four watersheds were in the Coastal Plain Uplands, Piedmont crystalline, Valley and Ridge carbonate, and Valley and Ridge siliciclastic HGMRs. A study of springs to estimate an apparent age of the ground water was based on analyses for concentrations of chlorofluorocarbons in water samples collected from 48 springs in the Chesapeake Bay Watershed. Results of the analysis indicate that median age for all the samples was 10 years, with the 25th percentile having an age of 7 years and the 75th percentile having an age of 13 years. Although the number of samples collected in each HGMR was limited, there did not appear to be distinct differences in the ages between the HGMRs. The ranges were similar between the major HGMRs above the Fall Line (modern to about 50 years), with only two HGMRs of small geographic extent (Piedmont carbonate and Mesozoic Lowland) having ranges of modern to about 10 years. The median values of all the HGMRs ranged from 7 to 11 years. Not enough samples were collected in the Coastal Plain for comparison. Spring samples showed slightly

  20. Greenhouse Gas Growth Rates from AIRS Hyperspectral Radiance Time Series

    NASA Astrophysics Data System (ADS)

    Strow, L. L.; Desouza-Machado, S. G.; Hannon, S.; Imbiriba, B.; Schou, P.

    2009-12-01

    The AIRS seven year hyperspectral radiance record provides an ideal platform for measurings growth rates of infrared active minor gases, especially carbon dioxide and methane. The largest changes in CLARREO radiances will likely be due to increasing carbon dioxide and other greenhouse gases. We have produced a 5+ year record of almost cloud-free AIRS radiances, from which we have derived the radiance anomaly and linear time rate of change. The source of these radiances are the L1b radiances corrected for small frequency drifts. Growth rates of carbon dioxide, nitrous oxide, methane, ozone, and CFC11 are simultaneously derived from zonal averages of these radiance rates for tropics, and mid-latitude northern and southern hemispheres. The effective linear rate of change of ~5 layers of water vapor and temperature, plus the surface temperature are also simultaneously derived with the minor gas rates. No model data or prior is needed and more than 1000 channels are used in the fit. Sampling issues may preclude the use of the mid-latitude temperature and water vapor rates for climate analysis, but possibly not for the tropics. The resulting greenhouse gas growth rates agree very well with in-situ measurements, which suggests high radiometric stability for AIRS. Radiance intercomparisons for climate analysis between IASI and AIRS will also be presented.

  1. Macro and nano scale modelling of water-water interactions at ambient and low temperature: relaxation and residence times.

    PubMed

    Morón, María Carmen; Prada-Gracia, Diego; Falo, Fernando

    2016-04-14

    The decay dynamics of ambient and low temperature liquid water has been investigated through all-atom molecular dynamics simulations, residence times calculations and time correlation functions from 300 K down to 243 K. Those simulations replicate the experimental value of the self-diffusion constant as a function of temperature by tuning the damping factor of the Langevin equation of motion. A stretched exponential function exp[-(t/τ)(β)] has been found to properly describe the relaxation of residence times calculated at different temperatures for solvent molecules in a nanodrop of free water modelled as a sphere of nanometric dimensions. As the temperature goes down the decay time τ increases showing a divergence at Ts = 227 ± 3 K. The temperature independence of the dimensionless stretched exponent β = 0.59 ± 0.01 suggests the presence of, not a characteristic relaxation time (since β≠ 1), but a distribution of decay times that also holds at low temperature. An explanation for such heterogeneity can be found at the nanoscopic level. Moreover it can be concluded that the distribution of times already reported for the dynamics of water surrounding proteins (β≤ 0.5) can not be exclusively due to the presence of the biomolecule itself since isolated water also exhibits such behaviour. The above reported Ts and β values quantitatively reproduce experimental data. PMID:26782269

  2. Daily variation of radon gas and its short-lived progeny concentration near ground level and estimation of aerosol residence time

    NASA Astrophysics Data System (ADS)

    M, Mohery; A, M. Abdallah; A, Ali; S, S. Baz

    2016-05-01

    Atmospheric concentrations of radon (222Rn) gas and its short-lived progenies 218Po, 214Pb, and 214Po were continuously monitored every four hours at the ground level in Jeddah city, Kingdom of Saudi Arabia. The measurements were performed three times every week, starting from November 2014 to October 2015. A method of electrostatic precipitation of positively charged 218Po and 214Po by a positive voltage was applied for determining 222Rn gas concentration. The short-lived 222Rn progeny concentration was determined by using a filter holder connected with the alpha-spectrometric technique. The meteorological parameters (relative air humidity, air temperature, and wind speed) were determined during the measurements of 222Rn and its progeny concentrations. 222Rn gas as well as its short-lived progeny concentration display a daily and seasonal variation with high values in the night and early morning hours as compared to low values at noon and in the afternoon. The observed monthly atmospheric concentrations showed a seasonal trend with the highest values in the autumn/winter season and the lowest values in the spring/summer season. Moreover, and in parallel with alpha-spectrometric measurements, a single filter-holder was used to collect air samples. The deposited activities of 214Pb and the long-lived 222Rn daughter 210Pb on the filter were measured with the gamma spectrometric technique. The measured activity concentrations of 214Pb by both techniques were found to be relatively equal largely. The highest mean seasonally activity concentrations of 210Pb were observed in the autumn/winter season while the lowest mean were observed in the spring/summer season. The mean residence time (MRT) of aerosol particles in the atmospheric air could be estimated from the activity ratios of 210Pb/214Pb. Project supported by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah (Grant No. 291/965/1434).

  3. Maintaining social cohesion is a more important determinant of patch residence time than maximizing food intake rate in a group-living primate, Japanese macaque (Macaca fuscata).

    PubMed

    Kazahari, Nobuko

    2014-04-01

    Animals have been assumed to employ an optimal foraging strategy (e.g., rate-maximizing strategy). In patchy food environments, intake rate within patches is positively correlated with patch quality, and declines as patches are depleted through consumption. This causes patch-leaving and determines patch residence time. In group-foraging situations, patch residence times are also affected by patch sharing. Optimal patch models for groups predict that patch residence times decrease as the number of co-feeding animals increases because of accelerated patch depletion. However, group members often depart patches without patch depletion, and their patch residence time deviates from patch models. It has been pointed out that patch residence time is also influenced by maintaining social proximity with others among group-living animals. In this study, the effects of maintaining social cohesion and that of rate-maximizing strategy on patch residence time were examined in Japanese macaques (Macaca fuscata). I hypothesized that foragers give up patches to remain in the proximity of their troop members. On the other hand, foragers may stay for a relatively long period when they do not have to abandon patches to follow the troop. In this study, intake rate and foraging effort (i.e., movement) did not change during patch residency. Macaques maintained their intake rate with only a little foraging effort. Therefore, the patches were assumed to be undepleted during patch residency. Further, patch residence time was affected by patch-leaving to maintain social proximity, but not by the intake rate. Macaques tended to stay in patches for short periods when they needed to give up patches for social proximity, and remained for long periods when they did not need to leave to keep social proximity. Patch-leaving and patch residence time that prioritize the maintenance of social cohesion may be a behavioral pattern in group-living primates. PMID:24515524

  4. Shortening the Defrost Time on a Heat Pump Air Conditioner

    NASA Astrophysics Data System (ADS)

    Kuwahara, Eiji; Yamazaki, Masaya; Kawamura, Toshiaki

    Methods to shorten the defrost time have been studied on a heat pump air conditioner. The experiment has been carried out using a 0.75kW heat pump and the energy balance during defrosting has been analyzed. We have found that the following methods are effective to shorten the defrost time; (1) Increase in power inqut to the compressor during defrosting, (2) Utilization of the compressor for thermal energy storage, (3) Reduction of the water left on the outdoor heat exchanger fins. The heat pump with the new defrosting system has been made on an experimental basis. lts defrost time is 1 minute and 55 seconds under the defrost condition of the Japanese Industrial Standard. The defrost time of a conventional heat pump is about 4 or 5 minutes.

  5. Modeling sediment transport processes and residence times in the shallow coastal bay complex of the Virginia Coast Reserve

    NASA Astrophysics Data System (ADS)

    Safak, I.; Wiberg, P. L.

    2011-12-01

    Patterns of sediment transport and particle residence times influence the morphology and ecology of shallow coastal bays in important ways. The Virginia Coast Reserve (VCR), a barrier island-lagoon-marsh system on the Eastern Shore of Virginia, is typical of many shallow coastal bay complexes that lack a significant fluvial source of freshwater and sediment. Sediment redistribution within the bays in response to storms and sea-level rise, together with the dynamics of marsh and lagoon-bottom plants, largely governs the morphological evolution of this system. There are also important feedbacks between sediment and ecosystem dynamics. This is particularly true in the VCR, which is relatively unaffected by human activities. As a step towards evaluating the impact of hydrodynamics on sediment and ecological processes in the VCR, a single unified model that accounts for circulation, surface waves, wave-current interaction, and sediment processes is employed. This three-dimensional unstructured grid finite-volume coastal ocean model (FVCOM) is validated with field observations of wind- and tide-induced water flow (water level and current velocities) in Hog Island Bay, centrally located within the VCR. Here, the resulting patterns of sediment transport and particle residence times over event and seasonal time scales are presented. Water and particle exchange within the VCR and between the VCR and the ocean is examined with the Lagrangian particle-tracking module in FVCOM. We focus on three bays with strongly varying bathymetry and coastline geometry, which are also located along a gradient of nitrogen input to the system. The results indicate that residence time of particles within the system vary greatly depending on the location of particle release, bay morphology, and wind conditions. The implications for morphologic evolution and ecosystem response to climate and land-use changes are evaluated.

  6. Slow-Onset Inhibition of Mycobacterium tuberculosis InhA: Revealing Molecular Determinants of Residence Time by MD Simulations

    PubMed Central

    Merget, Benjamin; Sotriffer, Christoph A.

    2015-01-01

    An important kinetic parameter for drug efficacy is the residence time of a compound at a drug target, which is related to the dissociation rate constant koff. For the essential antimycobacterial target InhA, this parameter is most likely governed by the ordering of the flexible substrate binding loop (SBL). Whereas the diphenyl ether inhibitors 6PP and triclosan (TCL) do not show loop ordering and thus, no slow-binding inhibition and high koff values, the slightly modified PT70 leads to an ordered loop and a residence time of 24 minutes. To assess the structural differences of the complexes from a dynamic point of view, molecular dynamics (MD) simulations with a total sampling time of 3.0 µs were performed for three ligand-bound and two ligand-free (perturbed) InhA systems. The individual simulations show comparable conformational features with respect to both the binding pocket and the SBL, allowing to define five recurring conformational families. Based on their different occurrence frequencies in the simulated systems, the conformational preferences could be linked to structural differences of the respective ligands to reveal important determinants of residence time. The most abundant conformation besides the stable EI* state is characterized by a shift of Ile202 and Val203 toward the hydrophobic pocket of InhA. The analyses revealed potential directions for avoiding this conformational change and, thus, hindering rapid dissociation: (1) an anchor group in 2'-position of the B-ring for scaffold stabilization, (2) proper occupation of the hydrophobic pocket, and (3) the introduction of a barricade substituent in 5'-position of the diphenyl ether B-ring. PMID:25996598

  7. Air pollutants degrade floral scents and increase insect foraging times

    NASA Astrophysics Data System (ADS)

    Fuentes, Jose D.; Chamecki, Marcelo; Roulston, T.'ai; Chen, Bicheng; Pratt, Kenneth R.

    2016-09-01

    Flowers emit mixtures of scents that mediate plant-insect interactions such as attracting insect pollinators. Because of their volatile nature, however, floral scents readily react with ozone, nitrate radical, and hydroxyl radical. The result of such reactions is the degradation and the chemical modification of scent plumes downwind of floral sources. Large Eddy Simulations (LES) are developed to investigate dispersion and chemical degradation and modification of floral scents due to reactions with ozone, hydroxyl radical, and nitrate radical within the atmospheric surface layer. Impacts on foraging insects are investigated by utilizing a random walk model to simulate insect search behavior. Results indicate that even moderate air pollutant levels (e.g., ozone mixing ratios greater than 60 parts per billion on a per volume basis, ppbv) substantially degrade floral volatiles and alter the chemical composition of released floral scents. As a result, insect success rates of locating plumes of floral scents were reduced and foraging times increased in polluted air masses due to considerable degradation and changes in the composition of floral scents. Results also indicate that plant-pollinator interactions could be sensitive to changes in floral scent composition, especially if insects are unable to adapt to the modified scentscape. The increase in foraging time could have severe cascading and pernicious impacts on the fitness of foraging insects by reducing the time devoted to other necessary tasks.

  8. Time-based air traffic management using expert systems

    NASA Technical Reports Server (NTRS)

    Tobias, L.; Scoggins, J. L.

    1986-01-01

    A prototype expert system has been developed for the time scheduling of aircraft into the terminal area. The three functions of the air-traffic-control schedule advisor are as follows: (1) for each new arrival, it develops an admisible flight plan for that aircraft; (2) as the aircraft progresses through the terminal area, it monitors deviations from the aircraft's flight plan and provides advisories to return the aircraft to its assigned schedule; and (3) if major disruptions such as missed approaches occur, it develops a revised plan. The advisor is operational on a Symbolics 3600, and is programmed in MRS (a logic programming language), Lisp, and Fortran.

  9. Time-based air traffic management using expert systems

    NASA Technical Reports Server (NTRS)

    Tobias, L.; Scoggins, J. L.

    1986-01-01

    A prototype expert system was developed for the time scheduling of aircraft into the terminal area. The three functions of the air traffic control schedule advisor are as follows: first, for each new arrival, it develops an admissible flight plan for that aircraft. Second, as the aircraft progresses through the terminal area, it monitors deviations from the flight plan and provides advisories to return the aircraft to its assigned schedule. Third, if major disruptions such as missed approaches occur, it develops a revised plan. The advisor is operational on a Symbolics 3600, and is programed in MRS (a logic programming language), Lisp, and FORTRAN.

  10. Dissolved organic carbon lability increases with water residence time in the alluvial aquifer of a river floodplain ecosystem

    NASA Astrophysics Data System (ADS)

    Helton, Ashley M.; Wright, Meredith S.; Bernhardt, Emily S.; Poole, Geoffrey C.; Cory, Rose M.; Stanford, Jack A.

    2015-04-01

    We assessed spatial and temporal patterns of dissolved organic carbon (DOC) lability and composition throughout the alluvial aquifer of the 16 km2 Nyack Floodplain in northwest Montana, USA. Water influx to the aquifer derives almost exclusively from the Middle Fork of the Flathead River, and water residence times within the aquifer range from days to months. Across seasons and channel discharge conditions, we measured DOC concentration, lability, and optical properties of aquifer water sampled from 12 wells, both near and ~3 m below the water table. Concentrations of DOC were typically low (542 ± 22.7 µg L-1; mean ± se), and the percentage of labile DOC averaged 18 ± 12% during 3 day laboratory assays. Parallel factor analysis of fluorescence excitation-emission matrices revealed two humic-like and two amino acid-like fluorescence groups. Total DOC, humic-like components, and specific UV absorbance decreased with water residence time, consistent with sorption to aquifer sediments. However, labile DOC (both concentration and fraction) increased with water residence time, suggesting a concurrent influx or production of labile DOC. Thus, although the carbon-poor, oxygen-rich aquifer is a net sink for DOC, recalcitrant DOC appears to be replaced with more labile DOC along aquifer flow paths. Our observation of DOC production in long flow paths contrasts with studies of hyporheic DOC consumption along short (centimeters to meters) flow paths and highlights the importance of understanding the role of labile organic matter production and/or influx in alluvial aquifer carbon cycling.

  11. Redeposition in plasma-assisted atomic layer deposition: Silicon nitride film quality ruled by the gas residence time

    SciTech Connect

    Knoops, Harm C. M. E-mail: w.m.m.kessels@tue.nl; Peuter, K. de; Kessels, W. M. M. E-mail: w.m.m.kessels@tue.nl

    2015-07-06

    The requirements on the material properties and growth control of silicon nitride (SiN{sub x}) spacer films in transistors are becoming ever more stringent as scaling of transistor structures continues. One method to deposit high-quality films with excellent control is atomic layer deposition (ALD). However, depositing SiN{sub x} by ALD has turned out to be very challenging. In this work, it is shown that the plasma gas residence time τ is a key parameter for the deposition of SiN{sub x} by plasma-assisted ALD and that this parameter can be linked to a so-called “redeposition effect”. This previously ignored effect, which takes place during the plasma step, is the dissociation of reaction products in the plasma and the subsequent redeposition of reaction-product fragments on the surface. For SiN{sub x} ALD using SiH{sub 2}(NH{sup t}Bu){sub 2} as precursor and N{sub 2} plasma as reactant, the gas residence time τ was found to determine both SiN{sub x} film quality and the resulting growth per cycle. It is shown that redeposition can be minimized by using a short residence time resulting in high-quality films with a high wet-etch resistance (i.e., a wet-etch rate of 0.5 nm/min in buffered HF solution). Due to the fundamental nature of the redeposition effect, it is expected to play a role in many more plasma-assisted ALD processes.

  12. Prolongation of residence time of liposome by surface-modification with mixture of hydrophilic polymers.

    PubMed

    Shehata, Tamer; Ogawara, Ken-Ichi; Higaki, Kazutaka; Kimura, Toshikiro

    2008-07-01

    The objective of this study is to evaluate the biodistribution characteristics of liposomes surface-modified with the mixture of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as a drug carrier for passive targeting of drugs. The liposomes (egg phosphatidylcholine:cholesterol=55:40, molar ratio) modified with both PEG and PVA (4:1 molar ratio) (PEG4%/PVA1% liposome) provided the largest AUC, which could be attributed to the smallest hepatic clearance of the liposomes. The liver perfusion studies clearly indicated that lower hepatic disposition of PEG4%/PVA1% liposome was ascribed to the decrease in its hepatic uptake via receptor-mediated endocytosis. Furthermore, the amounts of whole serum proteins and of opsonins such as complement C3 and immunoglobulin G adsorbed on PEG4%/PVA1% liposome were significantly smaller than those on the liposome solely modified with PEG (PEG5% liposome). On the other hand, several proteins were adsorbed at larger amount on PEG4%/PVA1% liposome than PEG5% liposome, and the protein identification by LC-MS/MS suggested that some of those proteins including albumin might function as dysopsonins. The decrease in the adsorbed amount of several opsonins and the increase in the adsorbed dysopsonins would be responsible for its lower affinity to the liver and long residence in the systemic circulation of PEG4%/PVA1% liposome. PMID:18486370

  13. [Pregnancy during residency].

    PubMed

    Maas, S M; van 't Hoff, B W; Rings, E H; van der Waals, F W; Büller, H A

    1992-12-19

    The number of female residents in the Netherlands has steadily increased in recent years. Due to the increased time on waiting lists to enter residency programmes and to the increased duration of training, female residents will be older during their residencies. This will probably result in an increased number of pregnancies during residencies. A questionnaire regarding pregnancy during residency was sent to 191 residents in two university hospitals in the Netherlands. The response rate was 74.3%. Fifty percent of the male and only 19% of the female residents had children. No negative effects of a pregnancy on their training were experienced or anticipated by the residents. However, a negative effect on the functioning of the department was expected. No formal provisions, like replacements were available and many solutions to replace pregnant colleagues depended on the flexibility of the colleagues. The wish to have children was high and equally distributed among male and female residents, 92% and 96%, resp. Given the difficulty to seek a permanent position and to have children after residency, the choice of many female residents will be to have their children during residency. This increase in number of pregnancies requires anticipation of the residency programme directors. They should take the lead in proposing adequate regulations. PMID:1470257

  14. Treatment of zinc-rich acid mine water in low residence time bioreactors incorporating waste shells and methanol dosing.

    PubMed

    Mayes, W M; Davis, J; Silva, V; Jarvis, A P

    2011-10-15

    Bioreactors utilising bacterially mediated sulphate reduction (BSR) have been widely tested for treating metal-rich waters, but sustained treatment of mobile metals (e.g. Zn) can be difficult to achieve in short residence time systems. Data are presented providing an assessment of alkalinity generating media (shells or limestone) and modes of metal removal in bioreactors receiving a synthetic acidic metal mine discharge (pH 2.7, Zn 15 mg/L, SO(4)(2-) 200mg/L, net acidity 103 mg/L as CaCO(3)) subject to methanol dosing. In addition to alkalinity generating media (50%, v.v.), the columns comprised an organic matrix of softwood chippings (30%), manure (10%) and anaerobic digested sludge (10%). The column tests showed sustained alkalinity generation, which was significantly better in shell treatments. The first column in each treatment was effective throughout the 422 days in removing >99% of the dissolved Pb and Cu, and effective for four months in removing 99% of the dissolved Zn (residence time: 12-14 h). Methanol was added to the feedstock after Zn breakthrough and prompted almost complete removal of dissolved Zn alongside improved alkalinity generation and sulphate attenuation. While there was geochemical evidence for BSR, sequential extraction of substrates suggests that the bulk (67-80%) of removed Zn was associated with Fe-Mn oxide fractions. PMID:21864976

  15. Measurements of liquid phase residence time distributions in a pilot-scale continuous leaching reactor using radiotracer technique.

    PubMed

    Pant, H J; Sharma, V K; Shenoy, K T; Sreenivas, T

    2015-03-01

    An alkaline based continuous leaching process is commonly used for extraction of uranium from uranium ore. The reactor in which the leaching process is carried out is called a continuous leaching reactor (CLR) and is expected to behave as a continuously stirred tank reactor (CSTR) for the liquid phase. A pilot-scale CLR used in a Technology Demonstration Pilot Plant (TDPP) was designed, installed and operated; and thus needed to be tested for its hydrodynamic behavior. A radiotracer investigation was carried out in the CLR for measurement of residence time distribution (RTD) of liquid phase with specific objectives to characterize the flow behavior of the reactor and validate its design. Bromine-82 as ammonium bromide was used as a radiotracer and about 40-60MBq activity was used in each run. The measured RTD curves were treated and mean residence times were determined and simulated using a tanks-in-series model. The result of simulation indicated no flow abnormality and the reactor behaved as an ideal CSTR for the range of the operating conditions used in the investigation. PMID:25528019

  16. The role of residence time in diagnostic models of global carbon storage capacity: model decomposition based on a traceable scheme

    PubMed Central

    Yizhao, Chen; Jianyang, Xia; Zhengguo, Sun; Jianlong, Li; Yiqi, Luo; Chengcheng, Gang; Zhaoqi, Wang

    2015-01-01

    As a key factor that determines carbon storage capacity, residence time (τE) is not well constrained in terrestrial biosphere models. This factor is recognized as an important source of model uncertainty. In this study, to understand how τE influences terrestrial carbon storage prediction in diagnostic models, we introduced a model decomposition scheme in the Boreal Ecosystem Productivity Simulator (BEPS) and then compared it with a prognostic model. The result showed that τE ranged from 32.7 to 158.2 years. The baseline residence time (τ′E) was stable for each biome, ranging from 12 to 53.7 years for forest biomes and 4.2 to 5.3 years for non-forest biomes. The spatiotemporal variations in τE were mainly determined by the environmental scalar (ξ). By comparing models, we found that the BEPS uses a more detailed pool construction but rougher parameterization for carbon allocation and decomposition. With respect to ξ comparison, the global difference in the temperature scalar (ξt) averaged 0.045, whereas the moisture scalar (ξw) had a much larger variation, with an average of 0.312. We propose that further evaluations and improvements in τ′E and ξw predictions are essential to reduce the uncertainties in predicting carbon storage by the BEPS and similar diagnostic models. PMID:26541245

  17. A new methodology for measurement of sludge residence time distribution in a paddle dryer using X-ray fluorescence analysis.

    PubMed

    Charlou, Christophe; Milhé, Mathieu; Sauceau, Martial; Arlabosse, Patricia

    2015-02-01

    Drying is a necessary step before sewage sludge energetic valorization. Paddle dryers allow working with such a complex material. However, little is known about sludge flow in this kind of processes. This study intends to set up an original methodology for sludge residence time distribution (RTD) measurement in a continuous paddle dryer, based on the detection of mineral tracers by X-ray fluorescence. This accurate analytical technique offers a linear response to tracer concentration in dry sludge; the protocol leads to a good repeatability of RTD measurements. Its equivalence to RTD measurement by NaCl conductivity in sludge leachates is assessed. Moreover, it is shown that tracer solubility has no influence on RTD: liquid and solid phases have the same flow pattern. The application of this technique on sludge with different storage duration at 4 °C emphasizes the influence of this parameter on sludge RTD, and thus on paddle dryer performances: the mean residence time in a paddle dryer is almost doubled between 24 and 48 h of storage for identical operating conditions. PMID:25463926

  18. Increasing functional modularity with residence time in the co-distribution of native and introduced vascular plants.

    PubMed

    Hui, Cang; Richardson, David M; Pyšek, Petr; Le Roux, Johannes J; Kučera, Tomáš; Jarošík, Vojtěch

    2013-01-01

    Species gain membership of regional assemblages by passing through multiple ecological and environmental filters. To capture the potential trajectory of structural changes in regional meta-communities driven by biological invasions, one can categorize species pools into assemblages of different residence times. Older assemblages, having passed through more environmental filters, should become more functionally ordered and structured. Here we calculate the level of compartmentalization (modularity) for three different-aged assemblages (neophytes, introduced after 1500 AD; archaeophytes, introduced before 1500 AD, and natives), including 2,054 species of vascular plants in 302 reserves in central Europe. Older assemblages are more compartmentalized than younger ones, with species composition, phylogenetic structure and habitat characteristics of the modules becoming increasingly distinctive. This sheds light on two mechanisms of how alien species are functionally incorporated into regional species pools: the settling-down hypothesis of diminishing stochasticity with residence time, and the niche-mosaic hypothesis of inlaid neutral modules in regional meta-communities. PMID:24045305

  19. Sewage sludge ash to phosphate fertilizer by chlorination and thermal treatment: residence time requirements for heavy metal removal.

    PubMed

    Nowak, Benedikt; Wegerer, Harald; Aschenbrenner, Philipp; Rechberger, Helmut; Winter, Franz

    2012-01-01

    Heavy metal removal from sewage sludge ash can be performed by mixing the ash with environmentally compatible chlorides (e.g. CaCl2 or MgCl2) and water, pelletizing the mixture and treating the pellets in a rotary reactor at about 1000 degrees C. Thermogravimetry-mass spectroscopy, muffle oven tests (500-1150 degrees C) and investigations in a laboratory-scale rotary reactor (950-1050 degrees C, residence time 1-25 min) were carried out. In the rotary reactor, up to 97% of Cu, 95% Pb and 95% Zn can be removed at 1050 degrees C. As Cl release starts from 400 degrees C (obtained from thermogravimetry-mass spectrometry experiments), heavy metals are already removed partially within the heating period. This heavy metal removal can be described as being similar to a first-order rate law. To meet the limit values specified in the Austrian and German fertilizer ordinances, residence times of the order of minutes are sufficient at 950 degrees C. PMID:23393980

  20. The role of residence time in diagnostic models of global carbon storage capacity: model decomposition based on a traceable scheme.

    PubMed

    Yizhao, Chen; Jianyang, Xia; Zhengguo, Sun; Jianlong, Li; Yiqi, Luo; Chengcheng, Gang; Zhaoqi, Wang

    2015-01-01

    As a key factor that determines carbon storage capacity, residence time (τE) is not well constrained in terrestrial biosphere models. This factor is recognized as an important source of model uncertainty. In this study, to understand how τE influences terrestrial carbon storage prediction in diagnostic models, we introduced a model decomposition scheme in the Boreal Ecosystem Productivity Simulator (BEPS) and then compared it with a prognostic model. The result showed that τE ranged from 32.7 to 158.2 years. The baseline residence time (τ'E) was stable for each biome, ranging from 12 to 53.7 years for forest biomes and 4.2 to 5.3 years for non-forest biomes. The spatiotemporal variations in τE were mainly determined by the environmental scalar (ξ). By comparing models, we found that the BEPS uses a more detailed pool construction but rougher parameterization for carbon allocation and decomposition. With respect to ξ comparison, the global difference in the temperature scalar (ξt) averaged 0.045, whereas the moisture scalar (ξw) had a much larger variation, with an average of 0.312. We propose that further evaluations and improvements in τ'E and ξw predictions are essential to reduce the uncertainties in predicting carbon storage by the BEPS and similar diagnostic models. PMID:26541245

  1. Increasing functional modularity with residence time in the co-distribution of native and introduced vascular plants

    PubMed Central

    Hui, Cang; Richardson, David M.; Pyšek, Petr; Le Roux, Johannes J.; Kučera, Tomáš; Jarošík, Vojtěch

    2013-01-01

    Species gain membership of regional assemblages by passing through multiple ecological and environmental filters. To capture the potential trajectory of structural changes in regional meta-communities driven by biological invasions, one can categorize species pools into assemblages of different residence times. Older assemblages, having passed through more environmental filters, should become more functionally ordered and structured. Here we calculate the level of compartmentalization (modularity) for three different-aged assemblages (neophytes, introduced after 1500 AD; archaeophytes, introduced before 1500 AD, and natives), including 2,054 species of vascular plants in 302 reserves in central Europe. Older assemblages are more compartmentalized than younger ones, with species composition, phylogenetic structure and habitat characteristics of the modules becoming increasingly distinctive. This sheds light on two mechanisms of how alien species are functionally incorporated into regional species pools: the settling-down hypothesis of diminishing stochasticity with residence time, and the niche-mosaic hypothesis of inlaid neutral modules in regional meta-communities. PMID:24045305

  2. A [32P]-NAD+-based method to identify and quantitate long residence time enoyl-ACP reductase inhibitors

    PubMed Central

    Yu, Weixuan; Neckles, Carla; Chang, Andrew; Bommineni, Gopal Reddy; Spagnuolo, Lauren; Zhang, Zhuo; Liu, Nina; Lai, Christina; Truglio, James; Tonge, Peter J.

    2015-01-01

    The classical methods for quantifying drug-target residence time (tR) use loss or regain of enzyme activity in progress curve kinetic assays. However, such methods become imprecise at very long residence times, mitigating the use of alternative strategies. Using the NAD(P)H-dependent FabI enoyl-ACP reductase as a model system, we developed a Penefsky column-based method for direct measurement of tR, where the off-rate of the drug was determined with radiolabeled [adenylate-32P] NAD(P+) cofactor. Twenty-three FabI inhibitors were analyzed and a mathematical model was used to estimate limits to the tR values of each inhibitor based on percent drug-target complex recovery following gel filtration. In general, this method showed good agreement with the classical steady state kinetic methods for compounds with tR values of 10-100 min. In addition, we were able to identify seven long tR inhibitors (100-1500 min) and to accurately determine their tR values. The method was then used to measure tR as a function of temperature, an analysis not previously possible using the standard kinetic approach due to decreased NAD(P)H stability at elevated temperatures. In general, a 4-fold difference in tR was observed when the temperature was increased from 25 °C to 37 °C . PMID:25684450

  3. Residence times and mixing of water in river banks: implications for recharge and groundwater - surface water exchange

    NASA Astrophysics Data System (ADS)

    Unland, N. P.; Cartwright, I.; Cendón, D. I.; Chisari, R.

    2014-02-01

    The residence time of groundwater within 50 m of the Tambo River, South East Australia, has been estimated through the combined use of 3H and 14C. Groundwater residence times increase towards the Tambo River which implies a gaining river system and not increasing bank storage with proximity to the Tambo River. Major ion concentrations and δ2H and δ18O values of bank water also indicate that bank infiltration does not significantly impact groundwater chemistry under baseflow and post-flood conditions, suggesting that the gaining nature of the river may be driving the return of bank storage water back into the Tambo River within days of peak flood conditions. The covariance between 3H and 14C indicates the leakage and mixing between old (~17 200 yr) groundwater from a semi-confined aquifer and younger groundwater (<100 yr) near the river where confining layers are less prevalent. The presence of this semi-confined aquifer has also been used to help explain the absence of bank storage, as rapid pressure propagation into the semi-confined aquifer during flooding will minimise bank infiltration. This study illustrates the complex nature of river groundwater interactions and the potential downfall in assuming simple or idealised conditions when conducting hydrogeological studies.

  4. Improving AirNow Air Quality Products with NASA Near-Real-Time Remote Sensing Data (Invited)

    NASA Astrophysics Data System (ADS)

    Dye, T.; Pasch, A. N.; DeWinter, J. L.; Haderman, M.; Szykman, J.; White, J. E.; van Donkelaar, A.; Martin, R.

    2013-12-01

    The U.S. Environmental Protection Agency's (EPA) AirNow program provides the public with real-time and forecasted air quality conditions. Millions of people each day use it to protect their health. The AirNow program (http://www.airnow.gov), reports ground-level ozone (O3) and fine particulate matter (PM2.5) in a standardized index called the Air Quality Index (AQI). AirNow aggregates information from over 130 state, local, and federal air quality agencies and provides tools for over 2,000 agency staff responsible for monitoring, forecasting, and communicating local air quality. Each hour, AirNow systems generate thousands of maps and products. This presentation will describe how AirNow is benefiting from NASA's remote sensing data. We will describe two applications of NASA near-real-time remote sensing data within AirNow through case studies, focusing specifically on days when large spatial gradients in AQI and wildfire smoke impacts were observed. The first case study will show how AirNow is merging satellite-estimated PM2.5 concentrations into the AQI maps via the AirNow Satellite Data Processor (ASDP). AirNow derives these satellite estimates using NASA/NOAA satellite aerosol optical depth (AOD) retrievals and GEOS-Chem modeled ratios of surface PM2.5 concentrations to AOD. The second case study will show how NASA's Global Image Browse Services (GIBS) provides a near-real-time satellite product in AirNow-Tech for agency users to quickly identify smoke plumes and access air quality conditions in data-sparse areas during wildland fires.

  5. Lateral and Time Distributions of Extensive Air Showers for CHICOS

    NASA Astrophysics Data System (ADS)

    Jillings, C. J.; Wells, D.; Chan, K. C.; Hill, J.; Falkowski, B.; Sepikas, J.

    2005-04-01

    We report results of a series of detailed Monte-Carlo calculations to determine the density and arrival-time distribution of charged particles in extensive air showers. We have parameterized both distributions as a function of distance from the shower axis, energy of the primary cosmic-ray proton, and incident zenith angle. Muons and electrons are parameterized separately. These parameterizations can be easily used in maximum-likelihood reconstruction of air showers. Calculations were performed for primary energies between 10^18 and 10^21eV and zenith angles out to approximately 50^o. The calculations are appropriate for the California High School Cosmic Ray Observatory: a 400 km^2 array of scintillation detectors in Los Angeles county. The average elevation of the array is approximately 250 meters above sea level. Currently 64 of 90 sites are operational. The array will be completed this year. We thank the NSF, the CURE program at the Jet Propulsion Laboratory, the SURF program at Caltech, and the Chinese University of Hong Kong.

  6. Transport and residence times of tropospheric aerosols inferred from a global three-dimensional simulation of Pb-210

    NASA Technical Reports Server (NTRS)

    Balkanski, Yves J.; Jacob, Daniel J.; Gardner, Geraldine M.; Graustein, William C.; Turekian, Karl K.

    1993-01-01

    A global three-dimensional model is used to investigate the transport and tropospheric residence time of Pb-210, an aerosol tracer produced in the atmosphere by radioactive decay of Rn-222 emitted from soils. The model uses meteorological input with 4 deg x 5 deg horizontal resolution and 4-hour temporal resolution from the Goddard Institute for Space Studies general circulation model (GCM). It computes aerosol scavenging by convective precipitation as part of the wet convective mass transport operator in order to capture the coupling between vertical transport and rainout. Scavenging in convective precipitation accounts for 74% of the global Pb-210 sink in the model; scavenging in large-scale precipitation accounts for 12%, and scavenging in dry deposition accounts for 14%. The model captures 63% of the variance of yearly mean Pb-210 concentrations measured at 85 sites around the world with negligible mean bias, lending support to the computation of aerosol scavenging. There are, however, a number of regional and seasonal discrepancies that reflect in part anomalies in GCM precipitation. Computed residence times with respect to deposition for Pb-210 aerosol in the tropospheric column are about 5 days at southern midlatitudes and 10-15 days in the tropics; values at northern midlatitudes vary from about 5 days in winter to 10 days in summer. The residence time of Pb-210 produced in the lowest 0.5 km of atmosphere is on average four times shorter than that of Pb-210 produced in the upper atmosphere. Both model and observations indicate a weaker decrease of Pb-210 concentrations between the continental mixed layer and the free troposphere than is observed for total aerosol concentrations; an explanation is that Rn-222 is transported to high altitudes in wet convective updrafts, while aerosols and soluble precursors of aerosols are scavenged by precipitation in the updrafts. Thus Pb-210 is not simply a tracer of aerosols produced in the continental boundary layer, but

  7. Quantification of Particle Residence Time in Abdominal Aortic Aneurysms Using Magnetic Resonance Imaging and Computational Fluid Dynamics

    PubMed Central

    Suh, Ga-Young; Les, Andrea S.; Tenforde, Adam S.; Shadden, Shawn C.; Spilker, Ryan L.; Yeung, Janice J.; Cheng, Christopher P.; Herfkens, Robert J.; Dalman, Ronald L.; Taylor, Charles A.

    2011-01-01

    Hemodynamic conditions are hypothesized to affect the initiation, growth, and rupture of abdominal aortic aneurysms (AAAs), a vascular disease characterized by progressive wall degradation and enlargement of the abdominal aorta. This study aims to use magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) to quantify flow stagnation and recirculation in eight AAAs by computing particle residence time (PRT). Specifically, we used gadolinium-enhanced MR angiography to obtain images of the vessel lumens, which were used to generate subject-specific models. We also used phase-contrast MRI to measure blood flow at supraceliac and infrarenal locations to prescribe physiologic boundary conditions. CFD was used to simulate pulsatile flow, and PRT, particle residence index, and particle half-life of PRT in the aneurysms were computed. We observed significant regional differences of PRT in the aneurysms with localized patterns that differed depending on aneurysm geometry and infrarenal flow. A bulbous aneurysm with the lowest mean infrarenal flow demonstrated the slowest particle clearance. In addition, improvements in particle clearance were observed with increase of mean infrarenal flow. We postulate that augmentation of mean infrarenal flow during exercise may reduce chronic flow stasis that may influence mural thrombus burden, degradation of the vessel wall, and aneurysm growth. PMID:21103933

  8. A Comparison of Part-Time and Full-Time Degree Students: The One-Year Residence Program Advisors' Study.

    ERIC Educational Resources Information Center

    Starr, Rose; Walker, Joel

    1982-01-01

    A study described and compared masters-level social work students in a traditional full-time program and part-time degree program. Differences in performance (classroom, fieldwork, student recordings, advisor discussions) and fieldwork (supervision, assignments, additional learning experiences, agency attitudes) are noted and implications drawn…

  9. Structure, provenance and residence time of terrestrial organic carbon: insights from Programmed temperature Pyrolysis-Combustion of river sediments

    NASA Astrophysics Data System (ADS)

    Feng, X.; Galy, V.; Rosenheim, B. E.; Roe, K. M.; Williams, E. K.

    2010-12-01

    The terrestrial organic carbon (OC) represents one of the largest reservoirs of C on earth and thus plays a crucial role in the global C cycle, participating to the regulation of atmospheric chemistry. While degradation of sedimentary OC (petrogenic C) is a source of CO2 for the atmosphere, burial of biospheric C (e.g. plant debris and soil OC) is a long-term sequestration of atmospheric CO2. Over short timescales, the atmospheric CO2 level is also sensitive to variations of the residence time of carbon in continental reservoirs. Fluvial transport plays a crucial role in the organic carbon cycle, constituting the connection between the different reservoirs and promoting the transfer of C from one reservoir to the other. Moreover, thanks to the integrating effect of erosion, studying river sediments allows the spatial and temporal integration of organic carbon exchanges occurring in a given basin. OC transported by rivers (riverine OC) is known to be extremely heterogeneous in nature and reactivity, however; ranging from extremely refractory petrogenic C (e.g. graphite) to soil complex OC to labile vegetation debris. Here we use a recently developed method, a programmed-temperature pyrolysis-combustion system (PTP-CS) coupled to multiisotopic analysis, to determine the reactivity, age and nature of OC in river sediments. The method takes advantage of the wide range of reactivity and radiocarbon content of different components of riverine OC. We submitted to PTP-CS a set of river sediments from 1) the Ganges-Brahmputra river system and, 2) the lower Mississippi river. Preliminary results highlight the heterogeneous nature of riverine OC. Different components of the riverine OC pool decompose at different temperature and are characterized by extremely variable isotopic compositions. The decomposition of radiocarbon dead petrogenic C at very high temperature allows estimating the respective contribution of biospheric and petrogenic C. Moreover, biospheric OC appears to

  10. Can we differentiate alpine groundwater storages regarding volume and residence time by recession observations, ion composition and tracer balance?

    NASA Astrophysics Data System (ADS)

    Floriancic, Marius; Smoorenburg, Maarten; Margreth, Michael; Naef, Felix

    2015-04-01

    Research on how catchments store and release water is essential to improve flood and low flow prediction in (un)gauged watersheds. Despite their importance for catchment scale assessments on runoff generation, knowledge on storage properties and residence times is still limited. Here we present some approaches to separate different storage types regarding their residence time and a quantification of the volumes of these storages based on a dataset of winter recession observation in the alpine Poschiavino headwater area. This spatially highly resolved dataset of discharge, electric conductivity and ion composition from a watershed with strongly contrasting storage properties, allowed separating three main contributing sources: continuous discharge from bedrock cracks, strongly delayed discharge from thick sediment deposits and fractured rock and rapid discharge from shallow layers. The gradients of the recession curves, the variation of electric conductivity in the river network and calculated tracer balance were used to separate contribution from different sources. Additionally contribution from sedimentary rocks and crystalline layers could be separated based on the variation of ion composition in the water samples. We derived recession curves for a period of four months for the separated storages in different parts of the catchment allowing estimation of the contributed volumes in this time period. Finally the spatial distribution of the storage types could be mapped throughout the catchment based on information like geo(morpho)logical maps, aerial photographs, DEM and field observations. We found significant variation comparing the discharged volume and specific discharge throughout the winter season in the different subcatchments. Constant discharge from bedrock cracks is similar in all catchment parts. Storage in the shallow deposits depleted quickly. High winter discharge could be attributed to thick quaternary deposits contributing during the whole

  11. Foraging strategy of a neotropical primate: how intrinsic and extrinsic factors influence destination and residence time.

    PubMed

    Plante, Sabrina; Colchero, Fernando; Calmé, Sophie

    2014-01-01

    Most animals need to actively search for food to meet energetic requirements and live in heterogeneous environments where food resources have complex spatio-temporal patterns of availability. Consequently, foraging animals need to find a balance between effort and resource allocation while accounting for intrinsic and extrinsic factors, which are often overlooked when modelling foraging behaviour. We identified the decision rules for foraging in black howler monkeys (Alouatta pigra), according to food preferences, locations of high-quality patches and previously eaten trees, phenology of food resources and hunger state. We depicted foraging in two stages: (i) the choice of the immediate next tree and (ii) the time spent on this tree. We used a recently developed model for inference of movement processes, incorporating resource selection functions into a Markov chain framework. We found that monkeys tend to move to preferred tree species at each step. However, we did not find conclusively that, at each step, monkeys direct their movements to reach high-quality patches. In fact, they were using these patches intensively, thus limiting the possibility to move towards other high-quality patches. Time spent on a tree was positively and strongly affected by the presence of preferred food items, but not by its species. We also showed that time spent on trees increased as a function of satiation state. We suggest that the strategy adopted by black howlers tends to be efficient because choosing preferred trees at each step and spending spend more time where preferred resources are available should favour energy intake and restrain movement costs. This study showcases a modelling framework that can be widely used in ecology to describe movements as a combination of multiple attraction and repulsion sources, such as mates and competitors. PMID:23957316

  12. Association between Ambient Air Pollution and Asthma Prevalence in Different Population Groups Residing in Eastern Texas, USA.

    PubMed

    Gorai, Amit Kr; Tchounwou, Paul B; Tuluri, Francis

    2016-04-01

    Air pollution has been an on-going research focus due to its detrimental impact on human health. However, its specific effects on asthma prevalence in different age groups, genders and races are not well understood. Thus, the present study was designed to examine the association between selected air pollutants and asthma prevalence in different population groups during 2010 in the eastern part of Texas, USA.The pollutants considered were particulate matter (PM2.5 with an aerodynamic diameter less than 2.5 micrometers) and surface ozone. The population groups were categorized based on age, gender, and race. County-wise asthma hospital discharge data for different age, gender, and racial groups were obtained from Texas Asthma Control Program, Office of Surveillance, Evaluation and Research, Texas Department of State Health Services. The annual means of the air pollutants were obtained from the United States Environmental Protection Agency (U.S. EPA)'s air quality system data mart program. Pearson correlation analyzes were conducted to examine the relationship between the annual mean concentrations of pollutants and asthma discharge rates (ADR) for different age groups, genders, and races. The results reveal that there is no significant association or relationship between ADR and exposure of air pollutants (PM2.5, and O₃). The study results showed a positive correlation between PM2.5 and ADR and a negative correlation between ADR and ozone in most of the cases. These correlations were not statistically significant, and can be better explained by considering the local weather conditions. The research findings facilitate identification of hotspots for controlling the most affected populations from further environmental exposure to air pollution, and for preventing or reducing the health impacts. PMID:27043587

  13. Association between Ambient Air Pollution and Asthma Prevalence in Different Population Groups Residing in Eastern Texas, USA

    PubMed Central

    Gorai, Amit Kr.; Tchounwou, Paul B.; Tuluri, Francis

    2016-01-01

    Air pollution has been an on-going research focus due to its detrimental impact on human health. However, its specific effects on asthma prevalence in different age groups, genders and races are not well understood. Thus, the present study was designed to examine the association between selected air pollutants and asthma prevalence in different population groups during 2010 in the eastern part of Texas, USA.The pollutants considered were particulate matter (PM2.5 with an aerodynamic diameter less than 2.5 micrometers) and surface ozone. The population groups were categorized based on age, gender, and race. County-wise asthma hospital discharge data for different age, gender, and racial groups were obtained from Texas Asthma Control Program, Office of Surveillance, Evaluation and Research, Texas Department of State Health Services. The annual means of the air pollutants were obtained from the United States Environmental Protection Agency (U.S. EPA)’s air quality system data mart program. Pearson correlation analyzes were conducted to examine the relationship between the annual mean concentrations of pollutants and asthma discharge rates (ADR) for different age groups, genders, and races. The results reveal that there is no significant association or relationship between ADR and exposure of air pollutants (PM2.5, and O3). The study results showed a positive correlation between PM2.5 and ADR and a negative correlation between ADR and ozone in most of the cases. These correlations were not statistically significant, and can be better explained by considering the local weather conditions. The research findings facilitate identification of hotspots for controlling the most affected populations from further environmental exposure to air pollution, and for preventing or reducing the health impacts. PMID:27043587

  14. Supra-canonical 26Al/27Al and the residence time of CAIs in the solar protoplanetary disk.

    PubMed

    Young, Edward D; Simon, Justin I; Galy, Albert; Russell, Sara S; Tonui, Eric; Lovera, Oscar

    2005-04-01

    The canonical initial 26Al/27Al ratio of 4.5 x 10(-5) has been a fiducial marker for the beginning of the solar system. Laser ablation and whole-rock multiple-collector inductively coupled plasma-source mass spectrometry magnesium isotope analyses of calcium- and aluminum-rich inclusions (CAIs) from CV3 meteorites demonstrate that some CAIs had initial 26Al/27Al values at least 25% greater than canonical and that the canonical initial 26Al/27Al cannot mark the beginning of solar system formation. Using rates of Mg diffusion in minerals, we find that the canonical initial 26Al/27Al is instead the culmination of thousands of brief high-temperature events incurred by CAIs during a 10(5)-year residence time in the solar protoplanetary disk. PMID:15746387

  15. LUMPED: a Visual Basic code of lumped-parameter models for mean residence time analyses of groundwater systems

    NASA Astrophysics Data System (ADS)

    Ozyurt, N. N.; Bayari, C. S.

    2003-02-01

    A Microsoft ® Visual Basic 6.0 (Microsoft Corporation, 1987-1998) code of 15 lumped-parameter models is presented for the analysis of mean residence time in aquifers. Groundwater flow systems obeying plug and exponential flow models and their combinations of parallel or serial connection can be simulated by these steady-state models which may include complications such as bypass flow and dead volume. Each model accepts tritium, krypton-85, chlorofluorocarbons (CFC-11, CFC-12 and CFC-113) and sulfur hexafluoride (SF 6) as environmental tracer. Retardation of gas tracers in the unsaturated zone and their degradation in the flow system may also be accounted for. The executable code has been tested to run under Windows 95 or higher operating systems. The results of comparisons between other comparable codes are discussed and the limitations are indicated.

  16. Estimating estuarine flushing and residence times in Charlotte Harbor, Florida, via salt balance and a box model

    USGS Publications Warehouse

    Miller, R.L.; McPherson, B.F.

    1991-01-01

    The new concept is that, over many tidal cycles, the tidally averaged "flow' (Qg) of water from the Gulf of Mexico, with a salinity of 35???, can be treated as a constant at any point in the estuary. This flow is used in a simple mixing equation to predict salinity in the estuary at different river inflows, and the predicted salinities are used to compute residence times for water in the estuary. The techniques developed to achieve optimal precision in the relation between river inflow and salinity include a newly derived equation to fit Qg by a least-squares method and a procedure to determine the optimal averaging period for river inflow. Results from Charlotte Harbor indicate that, under average (70 m3s-1) river inflow, 95% of the original water present in the harbor flushes into the gulf in 130 d. -from Authors

  17. The decadal state of the terrestrial carbon cycle: Global retrievals of terrestrial carbon allocation, pools, and residence times.

    PubMed

    Bloom, A Anthony; Exbrayat, Jean-François; van der Velde, Ivar R; Feng, Liang; Williams, Mathew

    2016-02-01

    The terrestrial carbon cycle is currently the least constrained component of the global carbon budget. Large uncertainties stem from a poor understanding of plant carbon allocation, stocks, residence times, and carbon use efficiency. Imposing observational constraints on the terrestrial carbon cycle and its processes is, therefore, necessary to better understand its current state and predict its future state. We combine a diagnostic ecosystem carbon model with satellite observations of leaf area and biomass (where and when available) and soil carbon data to retrieve the first global estimates, to our knowledge, of carbon cycle state and process variables at a 1° × 1° resolution; retrieved variables are independent from the plant functional type and steady-state paradigms. Our results reveal global emergent relationships in the spatial distribution of key carbon cycle states and processes. Live biomass and dead organic carbon residence times exhibit contrasting spatial features (r = 0.3). Allocation to structural carbon is highest in the wet tropics (85-88%) in contrast to higher latitudes (73-82%), where allocation shifts toward photosynthetic carbon. Carbon use efficiency is lowest (0.42-0.44) in the wet tropics. We find an emergent global correlation between retrievals of leaf mass per leaf area and leaf lifespan (r = 0.64-0.80) that matches independent trait studies. We show that conventional land cover types cannot adequately describe the spatial variability of key carbon states and processes (multiple correlation median = 0.41). This mismatch has strong implications for the prediction of terrestrial carbon dynamics, which are currently based on globally applied parameters linked to land cover or plant functional types. PMID:26787856

  18. The decadal state of the terrestrial carbon cycle: Global retrievals of terrestrial carbon allocation, pools, and residence times

    PubMed Central

    Bloom, A. Anthony; Exbrayat, Jean-François; van der Velde, Ivar R.; Feng, Liang; Williams, Mathew

    2016-01-01

    The terrestrial carbon cycle is currently the least constrained component of the global carbon budget. Large uncertainties stem from a poor understanding of plant carbon allocation, stocks, residence times, and carbon use efficiency. Imposing observational constraints on the terrestrial carbon cycle and its processes is, therefore, necessary to better understand its current state and predict its future state. We combine a diagnostic ecosystem carbon model with satellite observations of leaf area and biomass (where and when available) and soil carbon data to retrieve the first global estimates, to our knowledge, of carbon cycle state and process variables at a 1° × 1° resolution; retrieved variables are independent from the plant functional type and steady-state paradigms. Our results reveal global emergent relationships in the spatial distribution of key carbon cycle states and processes. Live biomass and dead organic carbon residence times exhibit contrasting spatial features (r = 0.3). Allocation to structural carbon is highest in the wet tropics (85–88%) in contrast to higher latitudes (73–82%), where allocation shifts toward photosynthetic carbon. Carbon use efficiency is lowest (0.42–0.44) in the wet tropics. We find an emergent global correlation between retrievals of leaf mass per leaf area and leaf lifespan (r = 0.64–0.80) that matches independent trait studies. We show that conventional land cover types cannot adequately describe the spatial variability of key carbon states and processes (multiple correlation median = 0.41). This mismatch has strong implications for the prediction of terrestrial carbon dynamics, which are currently based on globally applied parameters linked to land cover or plant functional types. PMID:26787856

  19. Prolonged Residence Time of a Noncovalent Molecular Adapter, β-Cyclodextrin, within the Lumen of Mutant α-Hemolysin Pores

    PubMed Central

    Gu, Li-Qun; Cheley, Stephen; Bayley, Hagan

    2001-01-01

    Noncovalent molecular adapters, such as cyclodextrins, act as binding sites for channel blockers when lodged in the lumen of the α-hemolysin (αHL) pore, thereby offering a basis for the detection of a variety of organic molecules with αHL as a sensor element. β-Cyclodextrin (βCD) resides in the wild-type αHL pore for several hundred microseconds. The residence time can be extended to several milliseconds by the manipulation of pH and transmembrane potential. Here, we describe mutant homoheptameric αHL pores that are capable of accommodating βCD for tens of seconds. The mutants were obtained by site-directed mutagenesis at position 113, which is a residue that lies near a constriction in the lumen of the transmembrane β barrel, and fall into two classes. Members of the tight-binding class, M113D, M113N, M113V, M113H, M113F and M113Y, bind βCD ∼104-fold more avidly than the remaining αHL pores, including WT-αHL. The lower Kd values of these mutants are dominated by reduced values of koff. The major effect of the mutations is most likely a remodeling of the binding site for βCD in the vicinity of position 113. In addition, there is a smaller voltage-sensitive component of the binding, which is also affected by the residue at 113 and may result from transport of the neutral βCD molecule by electroosmotic flow. The mutant pores for which the dwell time of βCD is prolonged can serve as improved components for stochastic sensors. PMID:11696607

  20. Changing restoration rules: exotic bivalves interact with residence time and depth to control phytoplankton productivity

    USGS Publications Warehouse

    Lucas, Lisa V.; Thompson, Janet K.

    2012-01-01

    Non-native species are a prevalent ecosystem stressor that can interact with other stressors to confound resource management and restoration. We examine how interactions between physical habitat attributes and a particular category of non-native species (invasive bivalves) influence primary production in aquatic ecosystems. Using mathematical models, we show how intuitive relationships between phytoplankton productivity and controllable physical factors (water depth, hydraulic transport time) that hold in the absence of bivalves can be complicated—and even reversed—by rapid bivalve grazing. In light-limited environments without bivalves, shallow, hydrodynamically “slow” habitats should generally have greater phytoplankton biomass and productivity than deeper, “faster” habitats. But shallower, slower environments can be less productive than deeper, faster ones if benthic grazing is strong. Moreover, shallower and slower waters exhibit a particularly broad range of possible productivity outcomes that can depend on whether bivalves are present. Since it is difficult to predict the response of non-native bivalves to habitat restoration, outcomes for new shallow, slow environments can be highly uncertain. Habitat depth and transport time should therefore not be used as indicators of phytoplankton biomass and production where bivalve colonization is possible. This study provides for ecosystem management a particular example of a broad lesson: abiotic ecosystem stressors should be managed with explicit consideration of interactions with other major (including biotic) stressors. We discuss the applicability and management implications of our models and results for a range of aquatic system types, with a case study focused on the Sacramento-San Joaquin Delta (California, USA). Simple mathematical models like those used here can illuminate interactions between ecosystem stressors and provide process-based guidance for resource managers as they develop strategies

  1. Health effects of particulate air pollution: time for reassessment?

    PubMed Central

    Pope, C A; Bates, D V; Raizenne, M E

    1995-01-01

    Numerous studies have observed health effects of particulate air pollution. Compared to early studies that focused on severe air pollution episodes, recent studies are more relevant to understanding health effects of pollution at levels common to contemporary cities in the developed world. We review recent epidemiologic studies that evaluated health effects of particulate air pollution and conclude that respirable particulate air pollution is likely an important contributing factor to respiratory disease. Observed health effects include increased respiratory symptoms, decreased lung function, increased hospitalizations and other health care visits for respiratory and cardiovascular disease, increased respiratory morbidity as measured by absenteeism from work or school or other restrictions in activity, and increased cardiopulmonary disease mortality. These health effects are observed at levels common to many U.S. cities including levels below current U.S. National Ambient Air Quality Standards for particulate air pollution. Images Figure 1. PMID:7656877

  2. Clearing the Air: Smoke-Free Housing Policies, Smoking, and Secondhand Smoke Exposure Among Affordable Housing Residents in Minnesota, 2014–2015

    PubMed Central

    Reckinger, Dawn

    2016-01-01

    Introduction During the past 30 years, local and state tobacco use control laws in the United States have helped reduce smoking prevalence and exposure to secondhand smoke, but progress among low socioeconomic populations has been slow. Implementing smoke-free housing policies in affordable housing may help address this issue. The purpose of our study was to assess how such policies affect smoking rates and exposure to secondhand smoke among residents of affordable housing. Methods We conducted a pretest–posttest longitudinal study of 180 residents from 8 affordable housing properties in Minnesota. Participating properties agreed to adopt a smoke-free housing policy covering indoor grounds, and 3 of these properties also prohibited smoking on all outdoor grounds. Policies were implemented with assistance from local public health departments and the Statewide Health Improvement Program. Participants completed surveys one month before policy implementation and 6 months postimplementation. Surveys assessed smoking, quit attempts, and indoor and outdoor secondhand smoke exposure. Results Results indicated a significant reduction in nonsmokers’ indoor exposure to secondhand smoke (F 1,144 = 22.69, P < .001) and no change in outdoor exposure to secondhand smoke from Time 1 (pretest) to Time 2 (posttest) (F 1,140 = 2.17, P = .14). However, when examining sites that only prohibited smoking indoors, we observed an increase in outdoor secondhand smoke exposure that approached significance (F 1,118 = 3.76, P = .055). Results showed no change in quit attempts over time, but 77% of residents who smoked at pretest reported reducing the amount that they smoked at posttest, and an additional 5% reported that they had quit. Conclusions Smoke-free housing policies may be an effective strategy to reduce exposure to indoor secondhand exposure and promote decreased cigarette smoking among residents of affordable housing. PMID:27536903

  3. Air

    MedlinePlus

    ... do to protect yourself from dirty air . Indoor air pollution and outdoor air pollution Air can be polluted indoors and it can ... this chart to see what things cause indoor air pollution and what things cause outdoor air pollution! Indoor ...

  4. Infectious Diseases in Immigrant Population Related to the Time of Residence in Spain.

    PubMed

    Cobo, Fernando; Salas-Coronas, Joaquín; Cabezas-Fernández, M Teresa; Vázquez-Villegas, José; Cabeza-Barrera, M Isabel; Soriano-Pérez, Manuel J

    2016-02-01

    The aim of this study was to evaluate the data on the main imported infectious diseases and public health issues arising from the risk of transmission of tropical and common diseases in the immigrant population. During the period of study, 2,426 immigrants were attended in the Tropical Medicine Unit of the Hospital of Poniente. For each patient, a complete screening for common and tropical diseases was performed. The prevalence and main features of intestinal and urinary parasites, microfilarias, Chagas disease, malaria, hepatitis B (HBV) and C (HCV) viruses, extrapulmonary tuberculosis and syphilis was investigated taking into account the length of stay in Spain. Sub-Saharan Africa patients who had lived for <3 years in Spain had a high significantly number of infections produced by hookworms, Ascaris lumbricoides, Trichuris trichiura, Schistosoma mansoni, Giardia lamblia, Entamoeba histolytica/dispar and Plasmodium spp. In patients who had lived for more than 3 years, there were significantly high rates of HBV infections, although HBV rates in sub-Saharan African patients are high even if the patients have been in Spain for <3 years. However, patients with large stays in Spain had also an important number of parasitological diseases. The main objective of the diagnosis is to avoid important public health problems and further complications in patients. It is advisable to carry out a screening of the main transmissible infections in all immigrant population regardless of the time outside their country. This screening should be individualized according to the geographical area of origin. PMID:25466580

  5. A Multiphase Assessment of Melt Segregation, Residence Time and Compositional Evolution in Crustal Magmatic Systems

    NASA Astrophysics Data System (ADS)

    Dufek, J.; Ghiorso, M. S.

    2012-12-01

    Compositional diversity in evolving magmatic systems is driven in large part by the multiphase dynamics of melt-crystal separation. Key to quantitative description of these systems is to accurately calculate the rate and timing of crystal-melt separation. This calculation involves three separate, but closely linked, problems: heat transfer, phase equilibria, and multiphase dynamics. To examine these problems we have developed a coupled fluid dynamics and thermodynamics approach. With this approach we can determine the spatial and temporal variability in composition, melt fraction, phase equilibrium, and velocities of different crystal phases and melt. We use a multiphase (Eulerian-Eulerian-Lagrangian, EEL) approach to compute extraction in magmatic systems. Each phase (melt or crystal phase) is represented by conservation equations for the mass, momentum and enthalpy. Enthalpy closure is determined from a version of rhyolite-MELTS with callable library functions that provide phase equilibrium results to the fluid dynamics code. This method accounts for the partitioning of latent and sensible heat in complex geochemical systems. Further, phase properties (for example density and heat capacity) are determined using MELTS, and as such are internally consistent with extensive thermodynamic and experimental data. Chemical species for each phase (major oxides) have separate transport equations permitting the exploration of fractionation behaviour as well as providing detailed geochemical information that can be used to compare to field observations (e.g. solid solution in phases, major oxide composition of melts). A typical simulation involves millions of phase equilibrium calculations and transport of several crystalline phases. We have parallelized this approach to work on large cluster computers for extensive calculations, and are working toward a publically available version. We use this new model to demonstrate dynamics on several different scales: 1. Melt

  6. Breast Cancer Risk in Relation to Ambient Air Pollution Exposure at Residences in the Sister Study Cohort

    PubMed Central

    Reding, Kerryn W.; Young, Michael T.; Szpiro, Adam A.; Han, Claire J.; DeRoo, Lisa A.; Weinberg, Clarice; Kaufman, Joel D.; Sandler, Dale P.

    2015-01-01

    Background Some but not all past studies reported associations between components of air pollution and breast cancer, namely fine particulate matter ≤ 2.5 μm (PM2.5) and nitrogen dioxide (NO2). It is yet unclear whether risks differ according to estrogen receptor (ER) and progesterone receptor (PR) status. Methods This analysis includes 47,591 women from the Sister Study cohort enrolled from August 2003-July 2009, in whom 1,749 invasive breast cancer cases arose from enrollment to January 2013. Using Cox proportional hazards and polytomous logistic regression, we estimated breast cancer risk associated with residential exposure to NO2, PM2.5, and PM10. Results While breast cancer risk overall was not associated with PM2.5 (Hazards ratio [HR] = 1.03; 95% CI: 0.96–1.11), PM10 (HR = 0.99; 95% CI: 0.98–1.00), or NO2 (HR = 1.02; 95% CI: 0.97–1.07), the association with NO2 differed according to ER/PR subtype (p = 0.04). For an interquartile range (IQR) difference of 5.8 parts per billion (ppb) in NO2, the relative risk (RR) of ER+/PR+ breast cancer was 1.10 (95% CI: 1.02–1.19), while there was no evidence of association with ER−/PR− (RR=0.92; 95% CI: 0.77–1.09; pinteraction=0.04). Conclusions Within the Sister Study cohort, we found no significant associations between air pollution and breast cancer risk overall. But we observed an increased risk of ER+/PR+ breast cancer associated with NO2. Impact Though these results suggest there is no substantial increased risk for breast cancer overall in relation to air pollution, NO2, a marker of traffic related air pollution, may differentially affect ER+/PR+ breast cancer. PMID:26464427

  7. Household air pollution and personal exposure risk of polycyclic aromatic hydrocarbons among rural residents in Shanxi, China.

    PubMed

    Chen, Y; Shen, G; Huang, Y; Zhang, Y; Han, Y; Wang, R; Shen, H; Su, S; Lin, N; Zhu, D; Pei, L; Zheng, X; Wu, J; Wang, X; Liu, W; Wong, M; Tao, S

    2016-04-01

    Polycyclic aromatic hydrocarbons (PAHs) are a group of pollutants of widespread concerns. Gaseous and size-segregated particulate-phase PAHs were collected in indoor and outdoor air in rural households. Personal exposure was measured and compared to the ingestion exposure. The average concentrations of 28 parent PAHs and benzo(a)pyrene (BaP) were 9000 ± 8390 and 131 ± 236 ng/m(3) for kitchen, 2590 ± 2270 and 43 ± 95 ng/m(3) for living room, and 2800 ± 3890 and 1.6 ± 0.7 ng/m(3) for outdoor air, respectively. The mass percent of high molecular weight (HMW) compounds with 5-6 rings contributed 1.3% to total 28 parent PAHs. Relatively higher fractions of HMW PAHs were found in indoor air compared to outdoor air. Majorities of particle-bound PAHs were found in the finest PM0.25 , and the highest levels of fine PM0.25 -bound PAHs were in the kitchen using peat and wood as energy sources. The 24-h personal PAH exposure concentration was 2100 ± 1300 ng/m(3) . Considering energies, exposures to those using wood were the highest. The PAH inhalation exposure comprised up to about 30% in total PAH exposure through food ingestion and inhalation, and the population attributable fraction (PAF) for lung cancer in the region was 0.85%. The risks for inhaled and ingested intakes of PAHs were 1.0 × 10(-5) and 1.1 × 10(-5) , respectively. PMID:25808453

  8. Relationship between pulmonary function and indoor air pollution from coal combustion among adult residents in an inner-city area of southwest China

    PubMed Central

    Jie, Y.; Houjin, H.; Xun, M.; Kebin, L.; Xuesong, Y.; Jie, X.

    2014-01-01

    Few studies evaluate the amount of particulate matter less than 2.5 mm in diameter (PM2.5) in relation to a change in lung function among adults in a population. The aim of this study was to assess the association of coal as a domestic energy source to pulmonary function in an adult population in inner-city areas of Zunyi city in China where coal use is common. In a cross-sectional study of 104 households, pulmonary function measurements were assessed and compared in 110 coal users and 121 non-coal users (≥18 years old) who were all nonsmokers. Several sociodemographic factors were assessed by questionnaire, and ventilatory function measurements including forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), the FEV1/FVC ratio, and peak expiratory flow rate (PEFR) were compared between the 2 groups. The amount of PM2.5 was also measured in all residences. There was a significant increase in the relative concentration of PM2.5 in the indoor kitchens and living rooms of the coal-exposed group compared to the non-coal-exposed group. In multivariate analysis, current exposure to coal smoke was associated with a 31.7% decrease in FVC, a 42.0% decrease in FEV1, a 7.46% decrease in the FEV1/FVC ratio, and a 23.1% decrease in PEFR in adult residents. The slope of lung function decrease for Chinese adults is approximately a 2-L decrease in FVC, a 3-L decrease in FEV1, and an 8 L/s decrease in PEFR per count per minute of PM2.5 exposure. These results demonstrate the harmful effects of indoor air pollution from coal smoke on the lung function of adult residents and emphasize the need for public health efforts to decrease exposure to coal smoke. PMID:25296361

  9. Relationship between pulmonary function and indoor air pollution from coal combustion among adult residents in an inner-city area of southwest China.

    PubMed

    Jie, Y; Houjin, H; Xun, M; Kebin, L; Xuesong, Y; Jie, X

    2014-11-01

    Few studies evaluate the amount of particulate matter less than 2.5 mm in diameter (PM₂.₅) in relation to a change in lung function among adults in a population. The aim of this study was to assess the association of coal as a domestic energy source to pulmonary function in an adult population in inner-city areas of Zunyi city in China where coal use is common. In a cross-sectional study of 104 households, pulmonary function measurements were assessed and compared in 110 coal users and 121 non-coal users (≥18 years old) who were all nonsmokers. Several sociodemographic factors were assessed by questionnaire, and ventilatory function measurements including forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), the FEV₁/FVC ratio, and peak expiratory flow rate (PEFR) were compared between the 2 groups. The amount of PM₂.₅ was also measured in all residences. There was a significant increase in the relative concentration of PM₂.₅ in the indoor kitchens and living rooms of the coal-exposed group compared to the non-coal-exposed group. In multivariate analysis, current exposure to coal smoke was associated with a 31.7% decrease in FVC, a 42.0% decrease in FEV₁, a 7.46% decrease in the FEV₁/FVC ratio, and a 23.1% decrease in PEFR in adult residents. The slope of lung function decrease for Chinese adults is approximately a 2-L decrease in FVC, a 3-L decrease in FEV₁, and an 8 L/s decrease in PEFR per count per minute of PM₂.₅ exposure. These results demonstrate the harmful effects of indoor air pollution from coal smoke on the lung function of adult residents and emphasize the need for public health efforts to decrease exposure to coal smoke. PMID:25296361

  10. Time variant cross correlation to assess residence time of water and implication for hydraulics of a sink-rise karst system

    NASA Astrophysics Data System (ADS)

    Bailly-Comte, V.; Martin, Jonathan B.; Screaton, E. J.

    2011-05-01

    Transport rates and residence time in the subsurface are critical parameters for understanding water-rock interactions for efficient contaminant remediation. This paper presents a methodology for assessing flow and transit time of water through hydrological systems, with specific applications to karst systems and implication for hydraulics of a conduit system surrounded by a porous and permeable intergranular matrix. A time variant cross-correlation function analysis is applied to bivariate time series that characterize mass transfer, assuming a stationary system using sliding windows of various sizes. We apply the method to 1 year long temperature records in the Santa Fe River (north central Florida) measured at (1) the River Sink, where all the incoming surface water drains into a sinkhole, (2) Sweetwater Lake, where the river resurges into a 500 m long karst window, and (3) the River Rise, where the water discharges from a first-magnitude karst spring. Results are compared with those obtained using specific conductivity. Estimated residence time ranges from less than 1 day during floods to more than 15 days during base flow within the 8000 m flow path between the River Sink and the River Rise. Results are used to characterize geometric, hydraulic, and hydrodynamic properties of this sink-rise system with strong matrix-conduit interactions. These properties are critical to the chemical and physical behavior of surface water-groundwater mixing. Our results also have direct implications for sampling strategies and hydrograph separation of many karst systems with different degrees and types of matrix porosity and permeability.

  11. Imputation of missing data in time series for air pollutants

    NASA Astrophysics Data System (ADS)

    Junger, W. L.; Ponce de Leon, A.

    2015-02-01

    Missing data are major concerns in epidemiological studies of the health effects of environmental air pollutants. This article presents an imputation-based method that is suitable for multivariate time series data, which uses the EM algorithm under the assumption of normal distribution. Different approaches are considered for filtering the temporal component. A simulation study was performed to assess validity and performance of proposed method in comparison with some frequently used methods. Simulations showed that when the amount of missing data was as low as 5%, the complete data analysis yielded satisfactory results regardless of the generating mechanism of the missing data, whereas the validity began to degenerate when the proportion of missing values exceeded 10%. The proposed imputation method exhibited good accuracy and precision in different settings with respect to the patterns of missing observations. Most of the imputations obtained valid results, even under missing not at random. The methods proposed in this study are implemented as a package called mtsdi for the statistical software system R.

  12. Belowground carbon allocation in a temperate beech forest: new insight into carbon residence time using whole tree 13C labelling

    NASA Astrophysics Data System (ADS)

    Epron, D.; Ngao, J.; Plain, C.; Longdoz, B.; Granier, A.

    2011-12-01

    Belowground carbon allocation is an important component of forest carbon budget, affecting tree growth (competition between aboveground and belowground carbon sinks), acquisition of belowground resources (nutrients and water) that are often limiting forest ecosystems and soil carbon sequestration. Total belowground carbon flow can be estimated using a mass-balance approach as cumulative soil CO2 efflux minus the carbon input from aboveground litter plus the changes in the C stored in roots, in the forest floor, and in the soil, and further compared to gross annual production. While this approach is useful for understanding the whole ecosystem carbon budget, uncertainties remain about the contribution of the different belowground pools of carbon to ecosystem respiration and carbon sequestration. New insights into transfer rate and residence time of carbon in belowground compartments can be gained from in situ whole-crown 13C labelling experiments. We combined both approaches in a young temperate beech forest in north-eastern France where ecosystem carbon fluxes are recorded since a decade. Carbon allocated belowground represented less than 40% of gross primary production in this young beech forest. Autotrophic respiration assessed by comparing soil CO2 efflux measured on normal and on root exclusion plots, accounted for 60% of the total belowground carbon flow. This indicated a rather short mean residence time of carbon allocated belowground in the soil compartments. The recovery of 13C in soil CO2 efflux after pulse-labelling entire crowns of tree with 13CO2 at several occasions during the growing season was observed a few couple of hours after the labelling. That indicates a rapid transfer of 13C belowground with a maximum occurring within 2 to 4 days after labelling. Label was recovered at the same time in the respiration and in the biomass of both fine roots and soil microbes. Allocation of recently assimilated carbon to soil microbial respiration was greater in

  13. Continuous, high-resolution spatial mapping of water isotopes: improving tools for quantifying local evaporation and residence times

    NASA Astrophysics Data System (ADS)

    Dennis, Kate J.; Carter, Jeffrey A.; Winkler, Renato; Downing, Brian; Kendall, Carol; Bergamaschi, Brian

    2015-04-01

    Stable isotopes of water (d2H, d18O) are unique tracers of many hydrological processes including evaporation, precipitation, reservoir mixing and residence time. Historically, discrete water samples have been collected and analyzed via either Isotope Ratio Mass Spectrometry, or more recently laser-based spectroscopic methods, such as Cavity Ring-Down Spectroscopy (CRDS). However, the analysis of discrete samples precludes the ability to construct high resolution water isotope data sets through time and space. By coupling a recently developed front-end peripheral device (Continuous Water Sampler or CWS) to a CRDS analyzer (Picarro L2130-i), we continuously measured and spatially mapped water isotopes on a transect of the Sacramento River Delta following an extended period of drought. More than two-thousand five-second average d18O and d2H measurements were made aboard the R/V King (USGS) over a six-hour period. In addition to water isotopes, nitrate, chlorophyll, dissolved organic matter (DOM) fluorescence, and other water quality parameters were also measured continuously. As you travel northeast up the delta, surface waters become progressively more enriched in 18O and 2H, while nitrate decreased in concentration and chlorophyll and DOM increased. We utilize the spatially-mapped isotope data within a single transect to understand local evaporation and residence time by (i) utilizing the secondary parameter, d-excess, and (ii) using a simple mass balance model of water moving through the system (inflow, outflow and evaporation). Additional transects, to be conducted during the rainy season, should highlight how the Delta system evolves seasonally. In concert with other data previously collected from the Sacramento River Delta, we suggest the lower region represents a mixture of river waters derived from the Sierra Nevada Mountains and the more marine waters from the mouth of the San Francisco Bay. Moving NE up the Delta into shallow sloughs through flooded wetlands

  14. RESIDENCE TIMES OF PARTICLES IN DIFFUSIVE PROTOPLANETARY DISK ENVIRONMENTS. II. RADIAL MOTIONS AND APPLICATIONS TO DUST ANNEALING

    SciTech Connect

    Ciesla, F. J.

    2011-10-10

    The origin of crystalline grains in comets and the outer regions of protoplanetary disks remains a mystery. It has been suggested that such grains form via annealing of amorphous precursors in the hot, inner region of a protoplanetary disk, where the temperatures needed for such transformations were found, and were then transported outward by some dynamical means. Here we develop a means of tracking the paths that dust grains would have taken through a diffusive protoplanetary disk and examine the types and ranges of environments that particles would have seen over a 10{sup 6} yr time period in the dynamic disk. We then combine this model with three annealing laws to examine how the dynamic evolution of amorphous grains would have led to their physical restructuring and their delivery to various regions of the disk. It is found that 'sibling particles' - those particles that reside at the same location at a given period of time-take a wide range of unique and independent paths through the disk to arrive there. While high temperatures can persist in the disk for very long time periods, we find that those grains that are delivered to the cold outer regions of the disk are largely annealed in the first few x10{sup 5} yr of disk history. This suggests that the crystallinity of grains in the outer disk would be determined early and remain unchanged for much of disk history, in agreement with recent astronomical observations.

  15. Characterization of surface and ground water δ18O seasonal variation and its use for estimating groundwater residence times

    USGS Publications Warehouse

    Reddy, Michael M.; Schuster, Paul F.; Kendall, Carol; Reddy, Micaela B.

    2006-01-01

    18O is an ideal tracer for characterizing hydrological processes because it can be reliably measured in several watershed hydrological compartments. Here, we present multiyear isotopic data, i.e. 18O variations (δ18O), for precipitation inputs, surface water and groundwater in the Shingobee River Headwaters Area (SRHA), a well-instrumented research catchment in north-central Minnesota. SRHA surface waters exhibit δ18O seasonal variations similar to those of groundwaters, and seasonal δ18O variations plotted versus time fit seasonal sine functions. These seasonal δ18O variations were interpreted to estimate surface water and groundwater mean residence times (MRTs) at sampling locations near topographically closed-basin lakes. MRT variations of about 1 to 16 years have been estimated over an area covering about 9 km2 from the basin boundary to the most downgradient well. Estimated MRT error (±0·3 to ±0·7 years) is small for short MRTs and is much larger (±10 years) for a well with an MRT (16 years) near the limit of the method. Groundwater transit time estimates based on Darcy's law, tritium content, and the seasonal δ18O amplitude approach appear to be consistent within the limits of each method. The results from this study suggest that use of the δ18O seasonal variation method to determine MRTs can help assess groundwater recharge areas in small headwaters catchments.

  16. Polybrominated diphenyl ethers in the air and comparison of the daily intake and uptake through inhalation by Shanghai residents with those through other matrices and routes.

    PubMed

    Li, Chunlei; Zhao, Zhishen; Lei, Bingli; An, Jing; Zhang, Xinyu; Yu, Yingxin

    2015-02-01

    To obtain a comprehensive understanding of the main source and route of human exposure to polybrominated diphenyl ethers (PBDEs), the daily intake and uptakes through inhalation, ingestion, and dermal contact for Shanghai residents were estimated on the basis of the PBDE concentrations in the air obtained in the present study and previous data reported in the literature. The PBDE concentrations in the gas and particle phases collected in Shanghai were 0.99-57.5 and 0.1-234 pg/m(3), respectively. The contamination levels of PBDEs in the air in Shanghai were similar to or slightly lower than the data from other regions. The estimated total daily intakes of PBDEs through the three routes were 607 and 1,636 ng/day for children and adults, respectively, while they decreased to 63.0 and 93.1 ng/day when the uptake efficiency (which is the fraction of contaminants that reaches the systemic circulation) of PBDEs was added to calculation. The results showed that dust is the main source of human exposure to PBDEs when PBDE uptake efficiency was not considered. It accounted for 66.2-79.2 % of the total PBDE intake. However, food is the main source, which accounted for 66.6-75.1 %, when the uptake efficiency was added to calculation. Among the three routes, dermal contact (53.1-76.6 %) is the main pathway, whereas ingestion (84.7-92.9 %) is the main one when the uptake efficiency was considered. Furthermore, risk assessment showed that the PBDE exposure amount would not cause obvious non-cancer and cancer risks to local residents. PMID:25009095

  17. Time Relevance of Convective Weather Forecast for Air Traffic Automation

    NASA Technical Reports Server (NTRS)

    Chan, William N.

    2006-01-01

    The Federal Aviation Administration (FAA) is handling nearly 120,000 flights a day through its Air Traffic Management (ATM) system and air traffic congestion is expected to increse substantially over the next 20 years. Weather-induced impacts to throughput and efficiency are the leading cause of flight delays accounting for 70% of all delays with convective weather accounting for 60% of all weather related delays. To support the Next Generation Air Traffic System goal of operating at 3X current capacity in the NAS, ATC decision support tools are being developed to create advisories to assist controllers in all weather constraints. Initial development of these decision support tools did not integrate information regarding weather constraints such as thunderstorms and relied on an additional system to provide that information. Future Decision Support Tools should move towards an integrated system where weather constraints are factored into the advisory of a Decision Support Tool (DST). Several groups such at NASA-Ames, Lincoln Laboratories, and MITRE are integrating convective weather data with DSTs. A survey of current convective weather forecast and observation data show they span a wide range of temporal and spatial resolutions. Short range convective observations can be obtained every 5 mins with longer range forecasts out to several days updated every 6 hrs. Today, the short range forecasts of less than 2 hours have a temporal resolution of 5 mins. Beyond 2 hours, forecasts have much lower temporal. resolution of typically 1 hour. Spatial resolutions vary from 1km for short range to 40km for longer range forecasts. Improving the accuracy of long range convective forecasts is a major challenge. A report published by the National Research Council states improvements for convective forecasts for the 2 to 6 hour time frame will only be achieved for a limited set of convective phenomena in the next 5 to 10 years. Improved longer range forecasts will be probabilistic

  18. Carotid Intima-Media Thickness and Long-Term Exposure to Traffic-Related Air Pollution in Middle-Aged Residents of Taiwan: A Cross-Sectional Study

    PubMed Central

    Su, Ta-Chen; Hwang, Juey-Jen; Shen, Yu-Cheng

    2015-01-01

    Background Associations between long-term exposure to air pollution and carotid intima-media thickness (CIMT) have inconsistent findings. Objectives In this study we aimed to evaluate association between 1-year average exposure to traffic-related air pollution and CIMT in middle-aged adults in Asia. Methods CIMT was measured in Taipei, Taiwan, between 2009 and 2011 in 689 volunteers 35–65 years of age who were recruited as the control subjects of an acute coronary heart disease cohort study. We applied land-use regression models developed by the European Study of Cohorts for Air Pollution Effects (ESCAPE) to estimate each subject’s 1-year average exposure to traffic-related air pollutants with particulate matter diameters ≤ 10 μm (PM10) and ≤ 2.5 μm (PM2.5) and the absorbance levels of PM2.5 (PM2.5abs), nitrogen dioxide (NO2), and nitrogen oxides (NOx) in the urban environment. Results One-year average air pollution exposures were 44.21 ± 4.19 μg/m3 for PM10, 27.34 ± 5.12 μg/m3 for PM2.5, and (1.97 ± 0.36) × 10–5/m for PM2.5abs. Multivariate regression analyses showed average percentage increases in maximum left CIMT of 4.23% (95% CI: 0.32, 8.13) per 1.0 × 10–5/m increase in PM2.5abs; 3.72% (95% CI: 0.32, 7.11) per 10-μg/m3 increase in PM10; 2.81% (95% CI: 0.32, 5.31) per 20-μg/m3 increase in NO2; and 0.74% (95% CI: 0.08, 1.41) per 10-μg/m3 increase in NOx. The associations were not evident for right CIMT, and PM2.5 mass concentration was not associated with the outcomes. Conclusions Long-term exposures to traffic-related air pollution of PM2.5abs, PM10, NO2, and NOx were positively associated with subclinical atherosclerosis in middle-aged adults. Citation Su TC, Hwang JJ, Shen YC, Chan CC. 2015. Carotid intima–media thickness and long-term exposure to traffic-related air pollution in middle-aged residents of Taiwan: a cross-sectional study. Environ Health Perspect 123:773–778; http://dx.doi.org/10.1289/ehp.1408553 PMID:25793433

  19. A Study of the Combined Effects of Physical Activity and Air Pollution on Mortality in Elderly Urban Residents: The Danish Diet, Cancer, and Health Cohort

    PubMed Central

    de Nazelle, Audrey; Mendez, Michelle Ann; Garcia-Aymerich, Judith; Hertel, Ole; Tjønneland, Anne; Overvad, Kim; Raaschou-Nielsen, Ole; Nieuwenhuijsen, Mark J.

    2015-01-01

    K, Raaschou-Nielsen O, Nieuwenhuijsen MJ. 2015. A study of the combined effects of physical activity and air pollution on mortality in elderly urban residents: the Danish Diet, Cancer, and Health cohort. Environ Health Perspect 123:557–563; http://dx.doi.org/10.1289/ehp.1408698 PMID:25625237

  20. The Evolution and Increasing Complexity of the Resident Assistant Role in the United States from Colonial to Modern Times

    ERIC Educational Resources Information Center

    Boone, Katherine B.; Davidson, Denise L.; Bauman, Mark

    2016-01-01

    The evolution of the resident assistant position and its history are important to understanding its increasing complexities. In this article we examine how court cases and federal legislation, along with changes in popular culture, have altered and shaped the role of the resident assistant. Our premise is that this role, originally relatively…

  1. Real-time simulation of helicopter air-to-air combat

    NASA Technical Reports Server (NTRS)

    Austin, Fred; George, Dino; Bivens, Court

    1991-01-01

    The AUTOMAN computer program develops automated maneuvering decisions for helicopters during air-to-air combat over hilly terrain. Recently, the capabilities of this program have been extended and enhanced significantly. The revised program was installed at the NASA Ames manned flight-simulation facility to drive a computer-generated image of an enemy helicopter, thereby providing an adversary for the human pilot. Maneuvers are selected by employing game theory. Enhancements include a guidance law for target acquisition when a firing opportunity arises; fire-control sequence logic; improved low-flying capabilities; line-of-sight computations for the cockpit field-of-view, terrain obstructions, and visual range limits; use of terrain for masking; air-to-air collision-avoidance maneuvers; decision on dispensing flares and chaff; and adjustable levels of pilot experience. The program was found to be extremely useful for both rotorcraft handling-quality evaluations and air-to-air combat training.

  2. Seasonal recharge and mean residence times of soil and epikarst water in a small karst catchment of southwest China

    NASA Astrophysics Data System (ADS)

    Hu, Ke; Chen, Hongsong; Nie, Yunpeng; Wang, Kelin

    2015-05-01

    Soil and epikarst play an important role in the hydrological cycle in karst regions. This paper focuses on investigating the seasonal recharge and mean residence time (MRT) of soil water and epikarst water in a small karst catchment of southwest China. The deuterium contents in precipitation, creek, soil baseflow (direct recharge of the saturated soil water to the stream), epikarst spring, and soil waters were monitored weekly for two years, and MRT was calculated by an exponential model (EM) and a dispersion model (DM). The obvious seasonal variation of deuterium in rainfall was buffered in epikarst water, indicating sufficient water mixing. Soil baseflow contained less rainy-season rainwater than epikarst spring discharge, reflecting the retarded effect of soil thickness on rainwater recharge. MRTs of all water bodies were 41-71 weeks, and soils in the depression extended those of shallow groundwater. This demonstrated that the deep soil layer played an important role in karst hydrological processes in the study catchment. The creek was recharged mostly by rainfall through epikarst, indicating its crucial role in water circulation. These results showed epikarst had a strong water-holding capacity and also delayed water contact time with dolomite.

  3. Seasonal recharge and mean residence times of soil and epikarst water in a small karst catchment of southwest China.

    PubMed

    Hu, Ke; Chen, Hongsong; Nie, Yunpeng; Wang, Kelin

    2015-01-01

    Soil and epikarst play an important role in the hydrological cycle in karst regions. This paper focuses on investigating the seasonal recharge and mean residence time (MRT) of soil water and epikarst water in a small karst catchment of southwest China. The deuterium contents in precipitation, creek, soil baseflow (direct recharge of the saturated soil water to the stream), epikarst spring, and soil waters were monitored weekly for two years, and MRT was calculated by an exponential model (EM) and a dispersion model (DM). The obvious seasonal variation of deuterium in rainfall was buffered in epikarst water, indicating sufficient water mixing. Soil baseflow contained less rainy-season rainwater than epikarst spring discharge, reflecting the retarded effect of soil thickness on rainwater recharge. MRTs of all water bodies were 41-71 weeks, and soils in the depression extended those of shallow groundwater. This demonstrated that the deep soil layer played an important role in karst hydrological processes in the study catchment. The creek was recharged mostly by rainfall through epikarst, indicating its crucial role in water circulation. These results showed epikarst had a strong water-holding capacity and also delayed water contact time with dolomite. PMID:25959092

  4. Seasonal recharge and mean residence times of soil and epikarst water in a small karst catchment of southwest China

    PubMed Central

    Hu, Ke; Chen, Hongsong; Nie, Yunpeng; Wang, Kelin

    2015-01-01

    Soil and epikarst play an important role in the hydrological cycle in karst regions. This paper focuses on investigating the seasonal recharge and mean residence time (MRT) of soil water and epikarst water in a small karst catchment of southwest China. The deuterium contents in precipitation, creek, soil baseflow (direct recharge of the saturated soil water to the stream), epikarst spring, and soil waters were monitored weekly for two years, and MRT was calculated by an exponential model (EM) and a dispersion model (DM). The obvious seasonal variation of deuterium in rainfall was buffered in epikarst water, indicating sufficient water mixing. Soil baseflow contained less rainy-season rainwater than epikarst spring discharge, reflecting the retarded effect of soil thickness on rainwater recharge. MRTs of all water bodies were 41-71 weeks, and soils in the depression extended those of shallow groundwater. This demonstrated that the deep soil layer played an important role in karst hydrological processes in the study catchment. The creek was recharged mostly by rainfall through epikarst, indicating its crucial role in water circulation. These results showed epikarst had a strong water-holding capacity and also delayed water contact time with dolomite. PMID:25959092

  5. Mixing controls on nitrogen and oxygen concentrations and the relationship to mean residence time in a hyporheic zone of a riffle-pool sequence.

    NASA Astrophysics Data System (ADS)

    Naranjo, R. C.; Niswonger, R. G.; Davis, C. J.

    2014-12-01

    Flow paths and residence times in the hyporheic zone are known to control biogeochemical processes such as nitrification and denitrification. The exchange across the sediment-water interface involves mixing of surface water and groundwater through complex hyporheic flow paths that contribute highly variable biogeochemical active zones. The objectives of this study were to determine the fate of nitrate (NO3) and dissolved oxygen (DO) during temporally varying flow conditions and compare concentrations to residence times simulated along a longitudinal cross-section accounting for mixing behavior of vertical and horizontal flow paths. In this study, the spatial and temporal distribution of nutrients was monitored in the hyporheic zone beneath a riffle-pool sequence on the Truckee River, NV using in-stream piezometers and riparian monitoring wells. Time-varying river discharge, spatially-varying hyporheic flow, and the distribution and mixing of flow paths appear to control the nitrification and denitrification process, and result in biogeochemical hot spots and hot moments. Results indicate that dissolved organic nitrogen concentrations in the hyporheic zone are generally greater than surface water concentrations, especially in down-welling zones. Concentrations of NO3 and DO were greater beneath the riffle areas as compared to pool areas, as a result of mineralization and nitrification of down-welling surface water. Replenishment of DO appears to support nitrification over long flow paths (101 of meters) and residence times (days). Denitrification along longer horizontal flow paths is limited by the influx of DO into the riverbed and the reductions in mean residence times. It is important to consider the occurrence of rapid inflows of surface water into the hyporheic zones resulting from variability in stage and riverbed topography, that replenishes DO and controls reaction rates and solute residence times. Flow-tube conceptual models for simulating residence times

  6. Journey-time exposure to particulate air pollution

    NASA Astrophysics Data System (ADS)

    Gulliver, John; Briggs, David J.

    Journey-time exposures to particulate air pollution were investigated in Leicester, UK, between January and March 2005. Samples of TSP, PM 10, PM 2.5, and PM 1 were simultaneously collected using light scattering devices whilst journeys were made by walking an in-car. Over a period of two months, 33 pairs of walking and in-car measurements were collected along two circular routes. Average exposures while walking were seen to be higher than those found in-car for each of the particle fractions: average walking to in-car ratios were 1.2 (± 0.6), 1.5 (± 0.6), 1.3 (± 0.6), and 1.4 (± 0.6) μg m -3 for coarse (TSP-PM 10), intermediate (PM 10-PM 2.5), fine (PM 2.5-PM 1), and very fine particles (PM 1), respectively. Correlations between walking and in-car exposures were seen to be weak for coarse particles ( r=0.10, p=0.58), moderate for the intermediate particles ( r=0.49, p<0.01) but strong for fine ( r=0.89, p<0.01) and very fine ( r=0.90, P<0.01) particles. PM 10 exposures while walking were on average 70% higher than a nearby roadside fixed-site monitor whilst in-car exposures were 25% higher than the same fixed-site monitor. Particles with an aerodynamic diameter of less than 2.5 μm were seen to be highly correlated between walking and in-car particle exposures and a rural fixed-site monitor about 30 km south of Leicester.

  7. Resident recruitment.

    PubMed

    Longmaid, H Esterbrook

    2003-02-01

    This article has introduced the reader to the critical components of successful recruitment of radiology residents. With particular attention to the ACGME institutional and program requirements regarding resident recruitment, and an explanation of the support systems (ERAS and NRMP) currently available to those involved in applicant review and selection, the article has sought to delineate a sensible approach to recruitment. Successful recruiters have mastered the essentials of these programs and have learned to adapt the programs to their needs. As new program directors work with their departments' resident selection committees, they will identify the factors that faculty and current residents cite as most important in the successful selection of new residents. By structuring the application review process, exploiting the power of the ERAS, and crafting a purposeful and friendly interview process, radiology residency directors can find and recruit the residents who best match their programs. PMID:12585436

  8. Traffic-related air pollution and respiratory symptoms among asthmatic children, resident in Mexico City: the EVA cohort study

    PubMed Central

    Escamilla-Nuñez, Maria-Consuelo; Barraza-Villarreal, Albino; Hernandez-Cadena, Leticia; Moreno-Macias, Hortensia; Ramirez-Aguilar, Matiana; Sienra-Monge, Juan-Jose; Cortez-Lugo, Marlene; Texcalac, Jose-Luis; del Rio-Navarro, Blanca; Romieu, Isabelle

    2008-01-01

    Background Taffic-related air pollution has been related to adverse respiratory outcomes; however, there is still uncertainty concerning the type of vehicle emission causing most deleterious effects. Methods A panel study was conducted among 147 asthmatic and 50 healthy children, who were followed up for an average of 22 weeks. Incidence density of coughing, wheezing and breathing difficulty was assessed by referring to daily records of symptoms and child's medication. The association between exposure to pollutants and occurrence of symptoms was evaluated using mixed-effect models with binary response and poisson regression. Results Wheezing was found to relate significantly to air pollutants: an increase of 17.4 μg/m3 (IQR) of PM2.5 (24-h average) was associated with an 8.8% increase (95% CI: 2.4% to 15.5%); an increase of 34 ppb (IQR) of NO2 (1-h maximum) was associated with an 9.1% increase (95% CI: 2.3% to16.4%) and an increase of 48 ppb (IQR) in O3 levels (1 hr maximum) to an increase of 10% (95% CI: 3.2% to 17.3%). Diesel-fueled motor vehicles were significantly associated with wheezing and bronchodilator use (IRR = 1.29; 95% CI: 1.03 to 1.62, and IRR = 1.32; 95% CI: 0.99 to 1.77, respectively, for an increase of 130 vehicles hourly, above the 24-hour average). Conclusion Respiratory symptoms in asthmatic children were significantly associated with exposure to traffic exhaust, especially from natural gas and diesel-fueled vehicles. PMID:19014608

  9. Estimation of groundwater residence times in watersheds using the runoff recession hydrograph: Application and comparison with the isotopic approach in two headwater watersheds

    NASA Astrophysics Data System (ADS)

    Vitvar, T.; Burns, D. A.; McDonnell, J. J.

    2001-05-01

    A need exists for a method to estimate groundwater residence time in watersheds that uses readily available data. Current methods require intensive and expensive collection of isotope or other tracer data. We have developed a method for estimation of mean baseflow residence time in watersheds based on runoff recession characteristics in the Winnisook watershed, Catskill Mts, New York, USA, and in the Maimai watershed, New Zealand. We first derived mean transmissivity and storativity of the dynamic subsurface water storage based on calculated runoff recession characteristics, and then we used these to estimate mean baseflow residence time. The two selected watersheds represent two different geomorphic, climatic and hydrological regimes: the Winnisook is an upland forested catchment with 20\\deg mean slope angles, thin soils (<1.0 m) developed in glacial till, 1570 mm annual rainfall and is underlain by permeable layered sedimentary bedrock. The Maimai watershed is a steep humid catchment with 35\\deg mean slope angles, thin soils (<0.5 m), 2700 mm annual rainfall and is underlain by impermeable bedrock. To test the new approach, mean baseflow residence times were calculated using the convolution integral approach relating rainfall to sampled streamflow 18O values. Mean baseflow residence time for the 2 km&^{2}$ Winnisook watershed was about 9 months using both the convolution integral approach and the recession hydrograph approach. The mean baseflow residence time for the 0.3 ha Maimai watershed was 3 months based on the convolution integral approach. The recession hydrograph method yields a slightly different result dependent on the variable shape of the recession hydrograph in this wet climatic regime. This new baseflow recession method may be an alternative to the convolution integral approach, and can delineate dynamic and static reservoirs for solving mixing problems at the watershed scale.

  10. TEMPORAL SIGNATURES OF AIR QUALITY OBSERVATIONS AND MODEL OUTPUTS: DO TIME SERIES DECOMPOSITION METHODS CAPTURE RELEVANT TIME SCALES?

    EPA Science Inventory

    Time series decomposition methods were applied to meteorological and air quality data and their numerical model estimates. Decomposition techniques express a time series as the sum of a small number of independent modes which hypothetically represent identifiable forcings, thereb...

  11. Residence times and diel passage distributions of radio-tagged juvenile spring chinook salmon and steelhead in a gatewell and fish collection channel of a Columbia River Dam

    USGS Publications Warehouse

    Beeman, J.W.; Maule, A.G.

    2001-01-01

    The amount of time radio-tagged juvenile spring chinook salmon Oncorhynchus tshawytscha and juvenile steelhead O. mykiss spent within a gatewell and the juvenile collection channel at McNary Dam, Columbia River, USA, was measured to determine the diel passage behavior and residence times within these portions of the juvenile bypass system. The median gatewell residence times were 8.9 h for juvenile chinook salmon and 3.2 h for steelhead. Juvenile spring chinook salmon spent 83% of their time in the 18-m-deep gatewell at depths of 9 m or less, and juvenile steelhead spent 96% of their time in the upper 11 m. Fish released during midday and those released in the evening generally exited the gatewell in the evening, indicating that fish entering the gatewell during daylight will have prolonged residence times. Median collection-channel residence times of juvenile chinook salmon were much shorter (2.3 min) than those of steelhead (28.0 min), most likely because of the greater size of the steelhead and the high water velocities within the channel (2.1 m/s). This and other studies indicate most juvenile salmonids enter gatewells of several Columbia and Snake river dams in the evening and pass into the collection channels quickly. However, this is not consistent with the natural in-river migration patterns of these species and represents a delay in dam passage.

  12. Performance linked to residence time distribution by a novel wool-based bioreactor for tertiary sewage treatment.

    PubMed

    Hu, Bibo; Wheatley, Andrew; Ishtchenko, Vera; Huddersman, Katherine

    2012-05-01

    Laboratory-scale experiments were carried out using up-flow 7 L Submerged Aerated Filter reactors packed with wool fibre or commercial plastic pall rings, Kaldnes, (70% by volume) support media for the tertiary treatment of sewage. The performance of the wool bioreactor was more consistent than that with Kaldnes medium, for both TOC removal (93%) and SS removal (90%). Both plastic and wool-packed bioreactors achieved complete nitrification at the load of about 0.4 kgCOD/m(3)/day. The sludge yield of the wool bioreactor was almost half that of the bioreactor with Kaldnes suggesting that wool could retain residual organics and particulates. The wool however was degraded and it was concluded that wool would have to be considered as additional sacrificial adsorption capacity rather than an alternative medium. The performance was linked to the residence time distribution studies and these changes in the wool structure. Biomass growth increased the retention of the tracer in the wool reactor by, it was suggested, exposing a greater surface area. Results from the plastic media on the other hand showed increased mixing possibly by increasing the mobility of the plastic. Aeration increased the mixing in both reactors, and patterns were in all cases predominantly well-mixed. PMID:22080341

  13. Estimation of the residence time of permafrost groundwater in the middle of the Lena River basin, eastern Siberia

    NASA Astrophysics Data System (ADS)

    Hiyama, Tetsuya; Asai, Kazuyoshi; Kolesnikov, Alexander B.; Gagarin, Leonid A.; Shepelev, Victor V.

    2013-09-01

    Detection of changes in the hydrological cycles of permafrost regions is a critical issue in hydrology. Better understanding of groundwater dynamics in permafrost regions is needed to assess the vulnerability of the cryolithic water environment to changing climate. However, little is known about the age of groundwater in the Siberian Arctic region. In order to determine the residence time of permafrost groundwater in eastern Siberia, transient tracers including tritium (3H), chlorofluorocarbons (CFCs), and sulfur hexafluoride (SF6) were used to analyze a mixture of supra-permafrost and intra-permafrost groundwater in the middle of the Lena River basin. Tritium analyses showed that the concentration ranges from 1.0 to 16.8 TU, and the apparent age of groundwater ranged from around 1 to 55 years. One of the spring waters appeared to contain more than 90% water recharged by precipitation before the 1960s nuclear testing era, and the water could be partly sourced from thawing permafrost. Comparisons of apparent groundwater ages estimated from different tracers imply that 3H and CFC-12 are the most applicable to groundwater vulnerability assessments in this region. Because the apparent age is a mixture of those from supra-permafrost and intra-permafrost groundwater, further analysis would be required to assess the contribution ratio of the two types of groundwater.

  14. Refined assessment of associations between drinking water residence time and emergency department visits for gastrointestinal illness in Metro Atlanta, Georgia.

    PubMed

    Levy, Karen; Klein, Mitchel; Sarnat, Stefanie Ebelt; Panwhar, Samina; Huttinger, Alexandra; Tolbert, Paige; Moe, Christine

    2016-08-01

    Recent outbreak investigations suggest that a substantial proportion of waterborne disease outbreaks are attributable to water distribution system issues. In this analysis, we examine the relationship between modeled water residence time (WRT), a proxy for probability of microorganism intrusion into the distribution system, and emergency department visits for gastrointestinal (GI) illness for two water utilities in Metro Atlanta, USA during 1993-2004. We also examine the association between proximity to the nearest distribution system node, based on patients' residential address, and GI illness using logistic regression models. Comparing long (≥90th percentile) with intermediate WRTs (11th to 89th percentile), we observed a modestly increased risk for GI illness for Utility 1 (OR = 1.07, 95% CI: 1.02-1.13), which had substantially higher average WRT than Utility 2, for which we found no increased risk (OR = 0.98, 95% CI: 0.94-1.02). Examining finer, 12-hour increments of WRT, we found that exposures >48 h were associated with increased risk of GI illness, and exposures of >96 h had the strongest associations, although none of these associations was statistically significant. Our results suggest that utilities might consider reducing WRTs to <2-3 days or adding booster disinfection in areas with longer WRT, to minimize risk of GI illness from water consumption. PMID:27441862

  15. Charge and energy dependence of the residence time of cosmic ray nuclei below 15 GeV/nucleon

    NASA Technical Reports Server (NTRS)

    Soutoul, A.; Ferrando, P.; Koch-Miramond, L.; Masse, P.; Webber, W. R.; Engelmann, J. J.

    1985-01-01

    The relative abundance of nuclear species measured in cosmic rays at Earth has often been interpreted with the simple leaky box model. For this model to be consistent an essential requirement is that the escape length does not depend on the nuclear species. The discrepancy between escape length values derived from iron secondaries and from the B/C ratio was identified by Garcia-Munoz and his co-workers using a large amount of experimental data. Ormes and Protheroe found a similar trend in the HEAO data although they questioned its significance against uncertainties. They also showed that the change in the B/C ratio values implies a decrease of the residence time of cosmic rays at low energies in conflict with the diffusive convective picture. These conclusions crucially depend on the partial cross section values and their uncertainties. Recently new accurate cross sections of key importance for propagation calculations have been measured. Their statistical uncertainties are often better than 4% and their values significantly different from those previously accepted. Here, these new cross sections are used to compare the observed B/C+O and (Sc to Cr)/Fe ratio to those predicted with the simple leaky box model.

  16. The α-Arrestin ARRDC3 Regulates the Endosomal Residence Time and Intracellular Signaling of the β2-Adrenergic Receptor.

    PubMed

    Tian, Xufan; Irannejad, Roshanak; Bowman, Shanna L; Du, Yang; Puthenveedu, Manojkumar A; von Zastrow, Mark; Benovic, Jeffrey L

    2016-07-01

    Arrestin domain-containing protein 3 (ARRDC3) is a member of the mammalian α-arrestin family, which is predicted to share similar tertiary structure with visual-/β-arrestins and also contains C-terminal PPXY motifs that mediate interaction with E3 ubiquitin ligases. Recently, ARRDC3 has been proposed to play a role in regulating the trafficking of G protein-coupled receptors, although mechanistic insight into this process is lacking. Here, we focused on characterizing the role of ARRDC3 in regulating the trafficking of the β2-adrenergic receptor (β2AR). We find that ARRDC3 primarily localizes to EEA1-positive early endosomes and directly interacts with the β2AR in a ligand-independent manner. Although ARRDC3 has no effect on β2AR endocytosis or degradation, it negatively regulates β2AR entry into SNX27-occupied endosomal tubules. This results in delayed recycling of the receptor and a concomitant increase in β2AR-dependent endosomal signaling. Thus, ARRDC3 functions as a switch to modulate the endosomal residence time and subsequent intracellular signaling of the β2AR. PMID:27226565

  17. A non-discrete method for residence time calculation as an indicator of thrombus formation in cardiovascular applications

    NASA Astrophysics Data System (ADS)

    Esmaily Moghadam, Mahdi; Marsden, Alison

    2012-11-01

    Cardiovascular simulations provide a promising means to predict risk of thrombosis in grafts, devices, and surgical anatomies in adult and pediatric patients. Although the pathways for platelet activation and clot formation are not fully understood, recent findings suggest that thrombosis risk correlates with the presence of recirculation regions with high residence time (RT). Current approaches for calculating RT are often based on releasing a finite number of Lagrangian particles in the flow and calculating RT by tracking their pathways. However, this method requires several simulations for a single case study, each of which requires releasing a significant number of particles, to obtain temporal and spatial convergence. In this work, we introduce a new non-discrete method, in which RT is calculated in an Eulerian non-discrete framework, using the advection-diffusion equation. Starting with an existing and a newly developed intuitive definition for the RT, the formulation for calculating RT in a region of interest is presented. The physical significance and sensitivity of each measure of RT is discussed and an extension of these definitions to a point-wise value is presented. Application to simulations of shunt insertion for single ventricle heart patients is demonstrated.

  18. Slow-Onset Inhibition of the FabI Enoyl Reductase from Francisella tularensis: Residence Time and in Vivo Activity

    SciTech Connect

    Lu, H.; England, K; Ende, C; Truglio, J; Luckner, S; Reddy, B; Marlenee, N; Knudson, S; Knudson, D; et. al.

    2009-01-01

    Francisella tularensis is a highly virulent and contagious Gram-negative intracellular bacterium that causes the disease tularemia in mammals. The high infectivity and the ability of the bacterium to survive for weeks in a cool, moist environment have raised the possibility that this organism could be exploited deliberately as a potential biological weapon. Fatty acid biosynthesis (FAS-II) is essential for bacterial viability and has been validated as a target for the discovery of novel antibacterials. The FAS-II enoyl reductase ftuFabI has been cloned and expressed, and a series of diphenyl ethers have been identified that are subnanomolar inhibitors of the enzyme with MIC90 values as low as 0.00018 ?g mL-1. The existence of a linear correlation between the Ki and MIC values strongly suggests that the antibacterial activity of the diphenyl ethers results from direct inhibition of ftuFabI within the cell. The compounds are slow-onset inhibitors of ftuFabI, and the residence time of the inhibitors on the enzyme correlates with their in vivo activity in a mouse model of tularemia infection. Significantly, the rate of breakdown of the enzyme-inhibitor complex is a better predictor of in vivo activity than the overall thermodynamic stability of the complex, a concept that has important implications for the discovery of novel chemotherapeutics that normally rely on equilibrium measurements of potency.

  19. Size of spawning population, residence time, and territory shifts of individuals in the spawning aggregation of a riverine catostomid

    USGS Publications Warehouse

    Grabowski, T.B.; Isely, J.J.

    2008-01-01

    Little is known about the behavior of individual fish in a spawning aggregation, specifically how long an individual remains in an aggregation. We monitored Moxostoma robustum (Cope) (Robust Redhorse) in a Savannah River spawning aggregation during spring 2004 and 2005 to provide an estimate of the total number of adults and the number of males comprising the aggregation and to determine male residence time and movements within a spawning aggregation. Robust Redhorse were captured using prepostioned grid electrofishers, identified to sex, weighed, measured, and implanted with a passive integrated transponder. Spawning aggregation size was estimated using a multiple census mark-and-recapture procedure. The spawning aggregation seemed to consist of approximately the same number of individuals (82-85) and males (50-56) during both years of this study. Individual males were present for a mean of 3.6 ?? 0.24 days (?? SE) during the 12-day spawning period. The mean distance between successive recaptures of individual males was 15.9 ?? 1.29 m (?? SE). We conclude that males establish spawning territories on a daily basis and are present within the spawning aggregation for at least 3-4 days. The relatively short duration of the aggregation may be the result of an extremely small population of adults. However, the behavior of individuals has the potential to influence population estimates made while fish are aggregated for spawning.

  20. Contrasting residence times and fluxes of water and sulfate in two small forested watersheds in Virginia, USA

    USGS Publications Warehouse

    Böhlke, J.K.; Michel, R.L.

    2009-01-01

    Watershed mass balances for solutes of atmospheric origin may be complicated by the residence times of water and solutes at various time scales. In two small forested headwater catchments in the Appalachian Mountains of Virginia, USA, mean annual export rates of SO4= differ by a factor of 2, and seasonal variations in SO4= concentrations in atmospheric deposition and stream water are out of phase. These features were investigated by comparing 3H, 35S, ??34S, ??2H, ??18O, ??3He, CFC-12, SF6, and chemical analyses of open deposition, throughfall, stream water, and spring water. The concentrations of SO4= and radioactive 35S were about twice as high in throughfall as in open deposition, but the weighted composite values of 35S/S (11.1 and 12.1 ?? 10- 15) and ??34S (+ 3.8 and + 4.1???) were similar. In both streams (Shelter Run, Mill Run), 3H concentrations and ??34S values during high flow were similar to those of modern deposition, ??2H and ??18O values exhibited damped seasonal variations, and 35S/S ratios (0-3 ?? 10- 15) were low throughout the year, indicating inter-seasonal to inter-annual storage and release of atmospheric SO4= in both watersheds. In the Mill Run watershed, 3H concentrations in stream base flow (10-13??TU) were consistent with relatively young groundwater discharge, most ??34S values were approximately the same as the modern atmospheric deposition values, and the annual export rate of SO4= was equal to or slightly greater than the modern deposition rate. In the Shelter Run watershed, 3H concentrations in stream base flow (1-3??TU) indicate that much of the discharging ground water had been deposited prior to the onset of atmospheric nuclear bomb testing in the 1950s, base flow ??34S values (+ 1.6???) were significantly lower than the modern deposition values, and the annual export rate of SO4= was less than the modern deposition rate. Concentrations of 3H and 35S in Shelter Run base flow, and of 3H, 3He, CFC-12, SF6, and 35S in a spring

  1. Emissions of CO2 and criteria air pollutants from mobile sources: Insights from integrating real-time traffic data into local air quality models

    NASA Astrophysics Data System (ADS)

    Gately, Conor; Hutyra, Lucy

    2016-04-01

    In 2013, on-road mobile sources were responsible for over 26% of U.S. fossil fuel carbon dioxide (ffCO2) emissions, and over 34% of both CO and NOx emissions. However, accurate representations of these emissions at the scale of urban areas remains a difficult challenge. Quantifying emissions at the scale of local streets and highways is critical to provide policymakers with the information needed to develop appropriate mitigation strategies and to guide research into the underlying process that drive mobile emissions. Quantification of vehicle ffCO2 emissions at high spatial and temporal resolutions requires a detailed synthesis of data on traffic activity, roadway attributes, fleet characteristics and vehicle speeds. To accurately characterize criteria air pollutant emissions, information on local meteorology is also critical, as the temperature and relative humidity can affect emissions rates of these pollutants by as much as 400%. As the health impacts of air pollutants are more severe for residents living in close proximity (<500m) to road sources, it is critical that inventories of these emissions rely on highly resolved source data to locate potential hot-spots of exposure. In this study we utilize real-time GPS estimates of vehicle speeds to estimate ffCO2 and criteria air pollutant emissions at multiple spatial and temporal scales across a large metropolitan area. We observe large variations in emissions associated with diurnal activity patterns, congestion, sporting and civic events, and weather anomalies. We discuss the advantages and challenges of using highly-resolved source data to quantify emissions at a roadway scale, and the potential of this methodology for forecasting the air quality impacts of changes in infrastructure, urban planning policies, and regional climate.

  2. Whale Shark (Rhincodon typus) Seasonal Presence, Residence Time and Habitat Use at Darwin Island, Galapagos Marine Reserve

    PubMed Central

    Acuña-Marrero, David; Jiménez, Jesús; Smith, Franz; Doherty, Paul F.; Hearn, Alex; Green, Jonathan R.; Paredes-Jarrín, Jules; Salinas-de-León, Pelayo

    2014-01-01

    The life history of the whale shark (Rhincodon typus), including its reproductive ecology, still remains largely unknown. Here, we present results from the first whale shark population study around Darwin Island, Galapagos Marine Reserve. Following a diversified approach we characterized seasonal occurrence, population structure and size, and described habitat use of whale sharks based on fine scale movements around the island. Whale shark presence at Darwin Island was negatively correlated with Sea Surface Temperature (SST), with highest abundance corresponding to a cool season between July and December over six years of monitoring. From 2011 to 2013 we photo-identified 82 whale sharks ranging from 4 to 13.1 m Total Length (TL). Size distribution was bimodal, with a great majority (91.5%) of adult female individuals averaging 11.35 m±0.12 m (TL±SE), all but one showing signs of a potential pregnancy. Population dynamics models for apparently pregnant sharks estimated the presence of 3.76±0.90 (mean ± SE) sharks in the study area per day with an individual residence time of 2.09±0.51 (mean ± SE) days. Movement patterns analysis of four apparently pregnant individuals tracked with acoustic tags at Darwin Island revealed an intense use of Darwin's Arch, where no feeding or specific behavior has been recorded, together with periodic excursions around the island's vicinity. Sharks showed a preference for intermediate depths (20–30 m) with occasional dives mostly to mid-water, remaining the majority of their time at water temperatures between 24–25°C. All of our results point to Darwin Island as an important stopover in a migration, possibly with reproductive purposes, rather than an aggregation site. Current studies carried out in this area to investigate regional scale movement patterns may provide essential information about possible pupping grounds for this enigmatic species. PMID:25551553

  3. Estimation of groundwater residence time using environmental radioisotopes (14C,T) in carbonate aquifers, southern Poland.

    PubMed

    Samborska, Katarzyna; Różkowski, Andrzej; Małoszewski, Piotr

    2013-01-01

    Triassic carbonate aquifers in the Upper Silesia region, affected by intense withdrawal, have been investigated by means of isotopic analyses of (14)C, δ(13)C, δ(2)H, δ(18)O and (3)H. The isotopic examinations were carried out in the 1970s and in the early 1980s, and it was the first application of tracers to estimate age and vulnerability for the contamination of groundwater in this region. Similar isotopic analyses were conducted in 2007 and 2008 with the same Triassic carbonate formation. The isotopic examinations were performed within the confined part of the carbonate formation, wherein aquifers are covered by semi-permeable deposits. The direct recharge of the aquifer occurs in the outcrop areas, but it mainly takes place due to percolation of the water through aquitards and erosional windows. The Triassic aquifer has been intensively drained by wells and by lead-zinc mines. Nowadays, the declining water demand and closure of some mines have induced a significant increase in the water table level. The detailed analysis of the results, including the radiocarbon age corrections and the comparison of radioisotope activities, has made it possible to estimate the range of residence time within the carbonate Triassic aquifer. This range from several tens to several tens of thousands indicates that the recharge of aquifers might have occurred between modern times and the Pleistocene. The apparent age of the water estimated on the basis of (14)C activity was corrected considering the carbon isotope exchange and the diffusion between mobile water in fractures and stagnant water in micropores. The obtained corrected period of recharge corresponds to the result of investigations of noble gases, which were carried out in the 1990s. In almost half of the cases, groundwater is a mixture of young and old water. The mixing processes occur mainly in areas of heavy exploitation of the aquifer. PMID:22607326

  4. Using stable isotopes to estimate and compare mean residence times in contrasting geologic catchments (Attert River, NW Luxembourg)

    NASA Astrophysics Data System (ADS)

    Martínez-Carreras, N.; Fenicia, F.; Frentress, J.; Wrede, S.; Pfister, L.

    2012-04-01

    In recent years, stable isotopes have been increasingly used to characterize important aspects of catchment hydrological functioning, such as water storage dynamics, flow pathways and water sources. These characteristics are often synthesized by the Mean Residence Time (MRT), which is a simple catchment descriptor that employ the relation of distinct stable isotopic signatures in the rainfall input and streamflow output of a catchment that are significantly dampened through sub-surface propagation. In this preliminary study, MRT was estimated in the Attert River catchment (NW Luxembourg), where previous studies have shown that lithology exerts a major control on runoff generation. The Attert catchment lies at the transition zone of contrasting bedrock lithology: the Northern part is characterized by Devonian schist of the Ardennes massif, while sedimentary deposits of sandstone and marls dominate in the south of the catchment. As a consequence of differing lithologic characteristics, hydrological processes change across scales. The schistose catchments exhibit a delayed shallow groundwater component, sandstone catchments have slow-responding year-round groundwater component, whereas flashy runoff regimes prevails in the marly catchments. Under these circumstances, the MRTs are expected to vary significantly according to lithology, and provide additional understanding in internal catchment processes and their scale dependencies. In order to test this, bi-weekly monitoring of rainfall and discharge stable water isotope composition (oxygen-18 and deuterium) has been carried out since 2007 in 10 nested sub-catchments ranging in size from 0.4 to 247 km2 in the Attert catchment. MRT was estimated using different lumped convolution integral models and sine wave functions with varying transit times distributions (TTDs). TTDs were evaluated through calibration. Further research efforts will deal with the application of conceptual models to simulate and compare TTD, using

  5. Whale shark (Rhincodon typus) seasonal presence, residence time and habitat use at darwin island, galapagos marine reserve.

    PubMed

    Acuña-Marrero, David; Jiménez, Jesús; Smith, Franz; Doherty, Paul F; Hearn, Alex; Green, Jonathan R; Paredes-Jarrín, Jules; Salinas-de-León, Pelayo

    2014-01-01

    The life history of the whale shark (Rhincodon typus), including its reproductive ecology, still remains largely unknown. Here, we present results from the first whale shark population study around Darwin Island, Galapagos Marine Reserve. Following a diversified approach we characterized seasonal occurrence, population structure and size, and described habitat use of whale sharks based on fine scale movements around the island. Whale shark presence at Darwin Island was negatively correlated with Sea Surface Temperature (SST), with highest abundance corresponding to a cool season between July and December over six years of monitoring. From 2011 to 2013 we photo-identified 82 whale sharks ranging from 4 to 13.1 m Total Length (TL). Size distribution was bimodal, with a great majority (91.5%) of adult female individuals averaging 11.35 m±0.12 m (TL±SE), all but one showing signs of a potential pregnancy. Population dynamics models for apparently pregnant sharks estimated the presence of 3.76±0.90 (mean ± SE) sharks in the study area per day with an individual residence time of 2.09±0.51 (mean ± SE) days. Movement patterns analysis of four apparently pregnant individuals tracked with acoustic tags at Darwin Island revealed an intense use of Darwin's Arch, where no feeding or specific behavior has been recorded, together with periodic excursions around the island's vicinity. Sharks showed a preference for intermediate depths (20-30 m) with occasional dives mostly to mid-water, remaining the majority of their time at water temperatures between 24-25°C. All of our results point to Darwin Island as an important stopover in a migration, possibly with reproductive purposes, rather than an aggregation site. Current studies carried out in this area to investigate regional scale movement patterns may provide essential information about possible pupping grounds for this enigmatic species. PMID:25551553

  6. Effects of the particle residence time and the spray droplet size on the particle removal efficiencies in a wet scrubber

    NASA Astrophysics Data System (ADS)

    Koo, J.; Hong, J.; Lee, H.; Shin, S.

    2010-06-01

    A new type of scrubbing system equipped with air-atomized spray nozzles, full cone type spray nozzles and the maze shape channels has been developed and the mass transfer mechanism to remove sub-micron particles is analyzed. There is a minimal time duration for the mixture of air and sprayed water droplets should remain in the scrubbing zone for the sub-micron particles and hydrogen fluoride (HF) gas to diffuse and be captured by water droplets. The grown water droplets enter the maze shape channels which have sharp corners and bends to eliminate the water droplets by collision with the walls. As a result of applying the developed design methodology, the sub-micron particle removal efficiencies of the scrubber are found to be above 99% for the particles of 0.5-1 μm, 96% for those of 0.3-0.5 μm, and 86% for those smaller than 0.3 μm in diameter under the optimum operating condition.

  7. On the possibility of real time air quality and toxicology assessment using multi-wavelength photoacoustic spectroscopy

    NASA Astrophysics Data System (ADS)

    Ajtai, Tibor; Pinter, Mate; Utry, Noemi; Kiss-Albert, Gergely; Palagyi, Andrea; Manczinger, Laszlo; Vagvölgyi, Csaba; Szabo, Gabor; Bozoki, Zoltan

    2016-04-01

    In this study we present results of field measurement campaigns focusing on the in-situ characterization of absorption spectra and the health relevance of light absorbing carbonaceous (LAC) in the ambient. The absorption spectra is measured @ 266, 355, 532 and 1064 nm by our state-of-the-art four-wavelength photoacoustic instrument, while for health relevance the eco- cito and genotoxicity parameters were measured using standardized methodologies. We experimentally demonstrated a correlation between the toxicities and the measured absorption spectra quantified by its wavelength dependency. Based on this correlation, we present novel possibilities on real-time air quality monitoring. LAC is extensively studied not only because of its considerable climate effects but as a serious air pollutant too. Gradually increasing number of studies demonstrated experimentally that the health effect of LAC is more serious than it is expected based on its share in total atmospheric aerosol mass. Furthermore during many local pollution events LAC not only has dominancy but it is close to exclusivity. Altogether due to its climate and health effects many studies and proposed regulations focus on the physical, chemical and toxicological properties of LAC as well as on its source apportionment. Despites of its importance, there is not yet a widely accepted standard methodology for the real-time and selective identification of LAC. There are many different reasons of that: starting from its complex inherent physicochemical features including many unknown constituents, via masking effect of ambient on the inherent physicochemical properties taking place even in case of a short residence, ending with the lack of reliable instrumentation for its health or source relevant parameters. Therefore, the methodology and instrument development for selective and reliable identification of LAC is timely and important issues in climate and air quality researches. Recently, many studies demonstrated

  8. A SIMPLE MODEL OF THE EFFECTS OF NITROGEN LOADING, FRESHWATER RESIDENCE TIME, AND INTERNAL LOSSES ON THE NITROGEN CONCENTRATIONS AND EXPORT IN ESTUARIES

    EPA Science Inventory

    This simple model uses the annual loading rate of total nitrogen (TN) and the water residence time to calculate average annual TN concentration and internal loss rates (e.g. denitrification and incorporation in sediments) in an estuary, and rate of nitrogen export across the seaw...

  9. SUBSURFACE RESIDENCE TIMES AS AN ALGORITHM FOR AQUIFER SENSITIVITY MAPPING: TESTING THE CONCEPT WITH GROUND WATER MODELS IN THE CONTENTNEA CREEK BASIN, NORTH CAROLINA, USA

    EPA Science Inventory

    This poster will present a modeling and mapping assessment of landscape sensitivity to non-point source pollution as applied to a hierarchy of catchment drainages in the Coastal Plain of the state of North Carolina. Analysis of the subsurface residence time of water in shallow a...

  10. FURTHER EVALUATION OF TRICKLE BED BIOFILTER PERFORMANCE AS A FUNCTION OF LADING, RESIDENCE TIME, AND BIOMASS CONTROL

    EPA Science Inventory

    The 1990 Amendments to the Clean Air Act have stimulated strong interest in the use of biofiltration for the economical engineered control of VOCs in effluent air streams. rickle bed air biofilters (TBABS) are especially applicable for treating VOCs at high loadings. or long term...

  11. Relating stable isotope and geochemical data to conclude on water residence times in four small alpine headwater catchments with differing vegetation cover

    NASA Astrophysics Data System (ADS)

    Mueller, M. H.; Weingartner, R.; Alewell, C.

    2012-09-01

    The mean water residence time (MRT) in a catchment gives information about storage, flow pathways, sources of water and thus also about retention and release of solutes in a catchment. To our knowledge there are no catchment studies on the influence of vegetation cover change on base flow mean water residence times. The main changes in vegetation cover in the Swiss Alps are massive shrub encroachment and forest expansion into formerly open habitats. Four small and relatively steep catchments in the Swiss Alps (Ursern valley) were investigated to relate different vegetation cover to water residence times and geochemical behaviour of runoff. Time series of water stable isotopes were used to calculate mean water residence times. The high temporal variation of the stable isotope signals in precipitation was strongly dampened in stream base flow samples. Mean water residence times of the four catchments were 64-98 weeks. The strong dampening of our input signal might point to deeper flow paths and mixing of waters of different ages at the catchments outlets. Parent geological materials are mainly gneisses and schists but they can contain dolomite, carbonate or gypsum rich zones. The major part of the quickly infiltrating precipitation likely percolates through these deeper zones. Relatively high stream water pH, Ca and SO42- concentrations in micro catchment outlets support this conclusion. We conclude that in mountainous headwater catchments with relatively thin soil layers the geological and topographical situation and snow dynamics influence storage, mixing and release of meteoric waters and its geochemistry in a stronger way than vegetation cover or catchment size do.

  12. Time trends of persistent organic pollutants in spanish air.

    PubMed

    Torre, Adrián de la; Sanz, Paloma; Navarro, Irene; Martínez, María Ángeles

    2016-10-01

    Passive air samplers consisting of polyurethane foam (PUF) disks were deployed in seven remote points and four urban locations to assess levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and some organochlorine pesticides including: 1,1'-(2,2,2-trichloroethane-1,1-diyl)bis(4-chlorobenzene) (DDT) and their metabolites (1,1-bis-(4-chlorophenyl)-2,2-dichloroethene (DDE) and 1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethyl]benzene (DDD)), hexaclorobenzene (HCB) and hexachlorocyclohexanes (HCHs), in the Spanish ambient air. Results revealed HCB (49 pg m(-3); median) as the major pollutant, followed in decreasing order by HCHs (21 pg m(-3)), ∑DDT/E/Ds (20 pg m(-3)), PCBs (20 pg m(-3)), PBDEs (3.3 pg m(-3)) and PCDD/Fs (0.04 pg m(-3)), when urban and remote locations are evaluated together. Urban areas presented statistically significant (p < 0.05, Mann-Whitney U test) higher levels for all families studied, except for HCB, compared to remote locations revealing anthropogenic activities as potential sources for these chemicals. On the contrary, HCB concentrations seem to reflect background levels. Interestingly, results reveal a decreasing trend for PCBs, PBDEs and DDTs levels in remote areas, while this behaviour is only statistically significant in the case of the former chemicals in urban locations. The present study is framed in the Spanish air monitoring plan and represents the first complete analysis related to POP presence in Spanish air coming from inner sites. PMID:26843029

  13. Nitrogen transport and transformations in a coastal plain watershed: Influence of geomorphology on flow paths and residence times

    USGS Publications Warehouse

    Tesoriero, A.J.; Spruill, T.B.; Mew, H.E., Jr.; Farrell, K.M.; Harden, S.L.

    2005-01-01

    Nitrogen transport and groundwater-surface water interactions were examined in a coastal plain watershed in the southeastern United States. Groundwater age dates, calculated using chlorofluorocarbon and tritium concentrations, along with concentrations of nitrogen species and other redox-active constituents, were used to evaluate the fate and transport of nitrate. Nitrate is stable only in recently recharged (<10 years) water found in the upper few meters of saturated thickness in the upland portion of a surficial aquifer. Groundwater with a residence time between 10 and 30 years typically has low nitrate and elevated excess N2 concentrations, indications that denitrification has reduced nitrate concentrations. Groundwater older than 30 years also has low nitrate concentrations but contains little or no excess N2, suggesting that this water did not contain elevated concentrations of nitrate along its flow path. Nitrate transport to streams varies between first- and third-order streams. Hydrologic, lithologic, and chemical data suggest that the surficial aquifer is the dominant source of flow and nitrate to a first-order stream. Iron-reducing conditions occur in groundwater samples from the bed and banks of the first-order stream, suggesting that direct groundwater discharge is denitrified prior to entering the stream. However, nitrogen from the surficial aquifer is transported directly to the stream via a tile drain that bypasses these reduced zones. In the alluvial valley of a third-order stream the erosion of a confining layer creates a much thicker unconfined alluvial aquifer with larger zones of nitrate stability. Age dating and chemical information (SiO 2, Na/K ratios) suggest that water in the alluvial aquifer is derived from short flow paths through the riparian zone and/or from adjacent streams during high-discharge periods. Copyright 2005 by the American Geophysical Union.

  14. Using water isotopes for assessing catchment water mean residence time. An analysis of the impact of mixing assumptions.

    NASA Astrophysics Data System (ADS)

    Fenicia, Fabrizio; Wrede, Sebastian; Kavetski, Dmitri; Pfister, Laurent; Savenije, Hubert H. G.; McDonnell, Jeff

    2010-05-01

    One of the main applications of stable water isotopes (Oxygen-18 and Deuterium) is the estimation of catchment water mean residence time (Tmr). This estimation is often performed through lumped parameter models based on convolution and sinewave functions. 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 paper, 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 model, where rainfall water is assumed to mix completely and instantaneously with the total catchment storage, with a partial-mixing 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 complete-mixing model returns estimates of Tmr that are well-identifiable and in general agreement with previous studies of the Maimai catchment. On the other hand, the partial mixing 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 analyzed 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.

  15. Systematic Analysis of the Effect of Small Scale Permeability Heterogeneity on Hyporheic Exchange Flux and Residence Times

    NASA Astrophysics Data System (ADS)

    Laube, G.; Schmidt, C.; Fleckenstein, J. H.

    2014-12-01

    The hyporheic zone (HZ) contributes significantly to whole stream biogeochemical cycling. Biogeochemical reactions within the HZ are often transport limited, thus, understanding these reactions requires knowledge about the magnitude of hyporheic fluxes (HF) and the residence time (RT) of these fluxes within the HZ. While the hydraulics of HF are relatively well understood, studies addressing the influence of permeability heterogeneity lack systematic analysis and have even produced contradictory results (e.g. [1] vs. [2]). In order to close this gap, this study uses a statistical numerical approach to elucidate the influence of permeability heterogeneity on HF and RT. We simulated and evaluated 3750 2D-scenarios of sediment heterogeneity by means of Gaussian random fields with focus on total HF and RT distribution. The scenarios were based on ten realizations of each of all possible combinations of 15 different correlation lengths, 5 dipping angles and 5 permeability variances. Roughly 500 hyporheic stream traces were analyzed per simulation, for a total of almost two million stream traces analyzed for correlations between permeability heterogeneity, HF, and RT. Total HF and the RT variance positively correlated with permeability variance while the mean RT negatively correlated with permeability variance. In contrast, changes in correlation lengths and dipping angles had little effect on the examined properties RT and HF. These results provide a possible explanation of the seemingly contradictory conclusions of recent studies, given that the permeability variances in these studies differ by several orders of magnitude. [1] Bardini, L., Boano, F., Cardenas, M.B, Sawyer, A.H, Revelli, R. and Ridolfi, L. "Small-Scale Permeability Heterogeneity Has Negligible Effects on Nutrient Cycling in Streambeds." Geophysical Research Letters, 2013. doi:10.1002/grl.50224. [2] Zhou, Y., Ritzi, R. W., Soltanian, M. R. and Dominic, D. F. "The Influence of Streambed Heterogeneity on

  16. Laundry greywater treatment using a fluidized bed reactor: a proposed model based on greywater biodegradation and residence time distribution approach.

    PubMed

    David, Pierre-luc; Bulteau, Gaëlle; Humeau, Philippe; Gérente, Claire; Andrès, Yves

    2013-01-01

    The increasing demand for water and the decrease in global water resources require research into alternative solutions to preserve them. The present study deals with the optimization of a treatment process, i.e. an aerobic fluidized bed reactor and the modelling of the degradation that takes place within it. The methodology employed is based on the hydrodynamics of the treatment process linked to the biodegradation kinetics of greywater coming from a washing machine. The residence time distribution (RTD) approach is selected for the hydrodynamic study. Biodegradation kinetics are quantified by respirometry and dissolved organic carbon (DOC) analysis on several mass quantities of colonized particles. RTD determinations show that there are no dysfunctions in the fluidized bed. Its hydrodynamic behaviour is similar to the one of a continuous stirred-tank reactor. A first-order reaction is obtained from the DOC biodegradation study. A model describing the degradation that takes place into the reactor is proposed, and from a sensitive study, the influence of the operating conditions on DOC biodegradation is defined. The theoretical results calculated from the first-order equation C(t) = 0.593 x C(0) x e(-kt) are compared with the experimental results and validated by a Student test. The value of the kinetic constant k is 0.011 h(-1) in the presence of a biomass carrier. The results highlight that it is possible to design a reactor in order to obtain a carbon content lower than 15 mg C L(-1) when the characteristics of raw greywater are known. PMID:24617067

  17. Effect of temperature, hydraulic residence time and elevated PCO2 on acid neutralization within a pulsed limestone bed reactor

    USGS Publications Warehouse

    Watten, B.J.; Lee, P.C.; Sibrell, P.L.; Timmons, M.B.

    2007-01-01

    Limestone has potential for reducing reagent costs and sludge volume associated with treatment of acid mine drainage, but its use is restricted by slow dissolution rates and the deposition of Fe, Al and Mn-based hydrolysis products on reactive surfaces. We evaluated a pulsed limestone bed (PLB) reactor (15 L/min capacity) that uses a CO2 pretreatment step to accelerate dissolution and hydraulic shearing forces provided by intermittent fluidization to abrade and carry away surface scales. We established the effects of hydraulic residence time (HRT, 5.1-15.9 min), temperature (T, 12-22 ??C) and CO2 tension (PCO2, 34.5-206.8 kPa) on effluent quality when inlet acidity (Acy) was fixed at 440 mg/L (pH=2.48) with H2SO4. The PLB reactor neutralized all H+ acidity (N=80) while concurrently providing unusually high levels of effluent alkalinity (247-1028 mg/L as CaCO3) that allow for side-stream treatment with blending. Alkalinity (Alk) yields rose with increases in PCO2, HRT and settled bed height (BH, cm) and decreased with T following the relationship (R2=0.926; p<0.001): (Alk)non-filtered=-548.726+33.571??(PCO2)0.5+33.671??(HRT)+7.734??(BH)-5.197??(T). Numerical modeling showed CO2 feed requirements for a target Alk yield decrease with increases in HRT, T and the efficiency of off-gas (CO2) recycling. ?? 2007 Elsevier Ltd. All rights reserved.

  18. Residence time of carbon substrate for autotrophic respiration of a grassland ecosystem correlates with the carbohydrate status of its vegetation

    NASA Astrophysics Data System (ADS)

    Ostler, Ulrike; Lehmeier, Christoph A.; Schleip, Inga; Schnyder, Hans

    2016-04-01

    Ecosystem respiration is composed of two component fluxes: (1) autotrophic respiration, which comprises respiratory activity of plants and plant-associated microbes that feed on products of recent photosynthetic activity and (2) heterotrophic respiration of microbes that decompose organic matter. The mechanistic link between the availability of carbon (C) substrate for ecosystem respiration and its respiratory activity is not well understood, particularly in grasslands. Here, we explore, how the kinetic features of the supply system feeding autotrophic ecosystem respiration in a temperate humid pasture are related to the content of water-soluble carbohydrates and remobilizable protein (as potential respiratory substrates) in vegetation biomass. During each September 2006, May 2007 and September 2007, we continuously labeled 0.8 m2 pasture plots with 13CO2/12CO2 and observed ecosystem respiration and its tracer content every night during the 14-16 day long labeling periods. We analyzed the tracer kinetics with a pool model, which allowed us to precisely partition ecosystem respiration into its autotrophic and heterotrophic flux components. At the end of a labeling campaign, we harvested aboveground and belowground plant biomass and analyzed its non-structural C contents. Approximately half of ecosystem respiration did not release any significant amount of tracer during the labeling period and was hence characterized as heterotrophic. The other half of ecosystem respiration was autotrophic, with a mean residence time of C in the respiratory substrate pool between 2 and 6 d. Both the rate of autotrophic respiration and the turnover of its substrate supply pool were correlated with plant carbohydrate content, but not with plant protein content. These findings are in agreement with studies in controlled environments that revealed water-soluble carbohydrates as the main substrate and proteins as a marginal substrate for plant respiration under favorable growth conditions

  19. Estimates of residence time and related variations in quality of ground water beneath Submarine Base Bangor and vicinity, Kitsap County, Washington

    USGS Publications Warehouse

    Cox, S.E.

    2003-01-01

    Estimates of residence time of ground water beneath Submarine Base Bangor and vicinity ranged from less than 50 to 4,550 years before present, based on analysis of the environmental tracers tritium, chlorofluorocarbons (CFCs), and carbon-14 (14C), in 33 ground-water samples collected from wells tapping the ground-water system. The concentrations of multiple environmental tracers tritium, CFCs, and 14C were used to classify ground water as modern (recharged after 1953), pre-modern (recharged prior to 1953), or indeterminate. Estimates of the residence time of pre-modern ground water were based on evaluation of 14C of dissolved inorganic carbon present in ground water using geochemical mass-transfer modeling to account for the interactions of the carbon in ground water with carbon of the aquifer sediments. Ground-water samples were obtained from two extensive aquifers and from permeable interbeds within the thick confining unit separating the sampled aquifers. Estimates of ground-water residence time for all ground-water samples from the shallow aquifer were less than 45 years and were classified as modern. Estimates of the residence time of ground water in the permeable interbeds within the confining unit ranged from modern to 4,200 years and varied spatially. Near the recharge area, residence times in the permeable interbeds typically were less than 800 years, whereas near the discharge area residence times were in excess of several thousand years. In the deeper aquifers, estimates of ground-water residence times typically were several thousand years but ranged from modern to 4,550 years. These estimates of ground-water residence time based on 14C were often larger than estimates of ground-water residence time developed by particle-tracking analysis using a ground-water flow model. There were large uncertainties?on the order of 1,000-2,000 years?in the estimates based on 14C. Modern ground-water tracers found in some samples from large-capacity production wells

  20. A computational model of wall shear and residence time of particles conveyed by steady flow in a curved tube

    NASA Astrophysics Data System (ADS)

    Thiriet, M.; Graham, J. M. R.; Issa, R. I.

    1993-01-01

    A finite-volume model of steady flow of an incompressible viscous fluid has been carried out in a smooth rigid 90° bend of circular cross-section. The inlet boundary conditions for laminar flow are either an entry Poiseuille regime or a constant injection velocity for a range of Dean number 140 leq De leq 430. A numerical test of turbulent flow was performed for De sim 22 100 with a flat velocity profile at the model entry. The lower the role played by the viscous forces, the larger the distance necessary to set an outer shift of the peak axial velocity. The axial velocity of laminar flow depends not only on the value of the Dean number, but also on separate effects of the Reynolds number and of the tube curvature. The larger the laminar boundary layer at the bend inlet, the nearer from the entry the bend segment where the strongest secondary motion is located. With increasing Reynolds number, the secondary flow develops over a longer bend region and the wall shear rises. Upstream and downstream effect of the bend on the shear stress, as well as flow disturbances induced by very small curvature, were observed. The residence time of conveyed particles is enhanced by the presence of a curved section in the conduit with respect to a straight pipe only at the inner edge of the straight section located downstream from the bend. When the Reynolds number rises, the flow regime remaining laminar, the residence time is smaller in the whole pipe. However for turbulent flow, the residence time, which has much smaller values, takes its highest values in the exit straight section. Les équations de conservation de la masse et de la quantité de mouvement ont été résolues pour un écoulement stationnaire d'un fluide incompressible visqueux dans un coude (angle de 90°), de parois lisses et rigides et de section droite uniforme et circulaire, par la méthode des volumes finis. Les conditions limites en entrée pour l'écoulement laminaire sont soit un profil parabolique, soit

  1. Effect of air on energy and rise-time spectra measured by proportional gas counter

    SciTech Connect

    Kawano, T.; Tanaka, M.; Isozumi, S.; Isozumi, Y.; Tosaki, M.; Sugiyama, T.

    2015-03-15

    Air exerts a negative effect on radiation detection using a gas counter because oxygen contained in air has a high electron attachment coefficient and can trap electrons from electron-ion pairs created by ionization from incident radiation in counting gas. This reduces radiation counts. The present study examined the influence of air on energy and rise-time spectra measurements using a proportional gas counter. In addition, a decompression procedure method was proposed to reduce the influence of air and its effectiveness was investigated. For the decompression procedure, the counting gas inside the gas counter was decompressed below atmospheric pressure before radiation detection. For the spectrum measurement, methane as well as various methane and air mixtures were used as the counting gas to determine the effect of air on energy and rise-time spectra. Results showed that the decompression procedure was effective for reducing or eliminating the influence of air on spectra measurement using a proportional gas counter. (authors)

  2. Characterization of the Gacka River basin karst aquifer (Croatia): hydrochemistry, stable isotopes and tritium-based mean residence times.

    PubMed

    Ozyurt, Nur N; Lutz, Hans O; Hunjak, Tamara; Mance, Diana; Roller-Lutz, Zvjezdana

    2014-07-15

    The Gacka River basin aquifer is a highly-developed karst system, located in the Croatian Dinarides. It is mostly composed of permeable Jurassic and Cretaceous carbonate rocks, and clastic sedimentary rocks of Paleogene age. Gacka River provides high quality water for the town of Otočac and several villages; together with the neighboring Lika River, the water is used for the Hydroelectric Power Plant at Senj on the coast. About 10 perennial and over 20 seasonal springs are located at 450 to 460 ma.s.l. (above sea level). Three major springs (Pećina, Majerovo and Tonkovića) provide 57% of the mean annual river flow. Similarities between the average groundwater temperatures as well as between the average specific electrical conductivity values (9.0°C-328 μS/cm, 9.6°C-350 μS/cm and 8.9°C-312 μS/cm) of the springs imply that they are fed from aquifers with similar mean residence times (MRTs). The mean δ(18)O contents of Majerovo, Tonkovića, and Pećina are around -10.1‰, -9.2‰ and -8.9‰, respectively, revealing differences in the mean recharge area elevations. Compared to the temporal amplitude of the(18)O signal of precipitation, the (18)O signal variations of the springs are substantially attenuated because the recharges occurring at different times are well mixed within the aquifers. This indicates MRTs of more than just a few years. The average tritium contents of Pećina, Majerovo and Tonkovića are 5.48 TU, 6.13 TU and 6.17 TU, respectively. Serially connected exponential-plug type unsteady lumped-parameter models run on an annual time scale resulted in rather satisfactory matches between the observed and calculated tritium contents for all studied springs. The models revealed similar MRTs (and corresponding reservoir volumes) for Pećina, Tonkovića and Majerovo of 12 years (470 Mm(3)), 12 years (1,190 Mm(3)), and 12.2 years (1,210 Mm(3)), respectively. Plug flow conditions dominate in about 90% of the total aquifer volumes. PMID:24784749

  3. 40 CFR 23.3 - Timing of Administrator's action under Clean Air Act.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 1 2012-07-01 2012-07-01 false Timing of Administrator's action under Clean Air Act. 23.3 Section 23.3 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GENERAL JUDICIAL REVIEW UNDER EPA-ADMINISTERED STATUTES § 23.3 Timing of Administrator's action under Clean Air...

  4. 40 CFR 23.3 - Timing of Administrator's action under Clean Air Act.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 1 2010-07-01 2010-07-01 false Timing of Administrator's action under Clean Air Act. 23.3 Section 23.3 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GENERAL JUDICIAL REVIEW UNDER EPA-ADMINISTERED STATUTES § 23.3 Timing of Administrator's action under Clean Air...

  5. 40 CFR 23.3 - Timing of Administrator's action under Clean Air Act.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 1 2011-07-01 2011-07-01 false Timing of Administrator's action under Clean Air Act. 23.3 Section 23.3 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GENERAL JUDICIAL REVIEW UNDER EPA-ADMINISTERED STATUTES § 23.3 Timing of Administrator's action under Clean Air...

  6. 40 CFR 23.3 - Timing of Administrator's action under Clean Air Act.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 1 2014-07-01 2014-07-01 false Timing of Administrator's action under Clean Air Act. 23.3 Section 23.3 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GENERAL JUDICIAL REVIEW UNDER EPA-ADMINISTERED STATUTES § 23.3 Timing of Administrator's action under Clean Air...

  7. 40 CFR 23.3 - Timing of Administrator's action under Clean Air Act.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 1 2013-07-01 2013-07-01 false Timing of Administrator's action under Clean Air Act. 23.3 Section 23.3 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GENERAL JUDICIAL REVIEW UNDER EPA-ADMINISTERED STATUTES § 23.3 Timing of Administrator's action under Clean Air...

  8. SU-E-T-45: Antibody Mean Residence Time in Blood and Its Correlation with Protein Molecular Weight

    SciTech Connect

    Kwok, C; Williams, L

    2014-06-01

    Purpose: Animal biodistribution data are required prior to introducing a new radiopharmaceutical into clinical trials. Protein engineering, using recombinant DNA techniques can produce a large number of related (cognate) antibodies to a given molecular target. Thus, it is important that these constructs be numerically related to one another via a single criterion. In the following, we use the mean residence time (MRT) in murine blood as this criterion. Methods: Five cognate anti-CEA (Carcinoembryonic Antigen) antibodies were compared with regard to their MRT in whole blood of CEA-positive tumor-bearing (LS174T) mice. MRT was defined by blood AUC (area under the curve) divided by the initial blood uptake value; all in units of percent injected dose per gram (%ID/g). Cognates included single chain scFv (25 kDa), diabody (50 kDa), minibody (80 kDa), F(ab')2 (120 kDa), and intact (155 kDa) forms of the murine cT84.66 antibody against CEA. All were labeled with radioactive iodine. Results: The agents, in the sequence listed, exhibited MRT values of 1.16 +/- 0.01 h, 0.99 h, 5.06 +/- 0.70 h, 6.61 +/- 0.36 h, and 59.3 +/- 2.4 h respectively. Because of the monotonic nature of the sequence, a linear correlation analysis was performed between molecular weight (MW) and MRT or ln(MRT) of the 5 proteins. Probability of random correlation was 0.10 for MRT and 0.01 for ln(MRT). Conclusion: MRT values of cognate anti-CEA antibodies were found to be a monotonically increasing sequence with respect to MW. Cognate MW values correlated best to ln(MRT) of the protein species. Thus MRT was proportional to an exponential function of molecular weight. The extended intact antibody circulation time presumably reflected its relatively maximal MW. Presence of an intact FC segment on this native antibody may also have influenced these results.

  9. Engaging nursing home residents with dementia in activities: The effects of modeling, presentation order, time of day, and setting characteristics

    PubMed Central

    Cohen-Mansfield, Jiska; Thein, Khin; Dakheel-Ali, Maha; Marx, Marcia S.

    2011-01-01

    We examined the impact of setting characteristics and presentation effects on engagement with stimuli in a group of 193 nursing home residents with dementia (recruited from a total of seven nursing homes). Engagement was assessed through systematic observations using the Observational Measurement of Engagement (OME), and data pertaining to setting characteristics (background noise, light, and number of persons in proximity) were recorded via the environmental portion of the Agitation Behavior Mapping Inventory (ABMI; Cohen-Mansfield, Werner, & Marx, (1989). An observational study of agitation in agitated nursing home residents. International Psychogeriatrics, 1, 153–165). Results revealed that study participants were engaged more often with moderate levels of sound and in the presence of a small group of people (from four to nine people). As to the presentation effects, multiple presentations of the same stimulus were found to be appropriate for the severely impaired as well as the moderately cognitively impaired. Moreover, modeling of the appropriate behavior significantly increased engagement, with the severely cognitively impaired residents receiving the greatest benefit from modeling. These findings have direct implications for the way in which caregivers could structure the environment in the nursing home and how they could present stimuli to residents in order to optimize engagement in persons with dementia. PMID:20455123

  10. Preliminary estimates of residence times and apparent ages of ground water in the Chesapeake Bay watershed, and water-quality data from a survey of springs

    USGS Publications Warehouse

    Focazio, Michael J.; Plummer, L. Neil; Bohlke, John K.; Busenberg, Eurybiades; Bachman, L. Joseph; Powars, David S.

    1998-01-01

    Knowledge of the residence times of the ground-water systems in Chesapeake Bay watershed helps resource managers anticipate potential delays between implementation of land-management practices and any improve-ments in river and estuary water quality. This report presents preliminary estimates of ground-water residence times and apparent ages of water in the shallow aquifers of the Chesapeake Bay watershed. A simple reservoir model, published data, and analyses of spring water were used to estimate residence times and apparent ages of ground-water discharge. Ranges of aquifer hydraulic characteristics throughout the Bay watershed were derived from published literature and were used to estimate ground-water residence times on the basis of a simple reservoir model. Simple combinations of rock type and physiographic province were used to delineate hydrogeomorphic regions (HGMR?s) for the study area. The HGMR?s are used to facilitate organization and display of the data and analyses. Illustrations depicting the relation of aquifer characteristics and associated residence times as a continuum for each HGMR were developed. In this way, the natural variation of aquifer characteristics can be seen graphically by use of data from selected representative studies. Water samples collected in September and November 1996, from 46 springs throughout the watershed were analyzed for chlorofluorocarbons (CFC?s) to estimate the apparent age of ground water. For comparison purposes, apparent ages of water from springs were calculated assuming piston flow. Additi-onal data are given to estimate apparent ages assuming an exponential distribution of ages in spring discharge. Additionally, results from previous studies of CFC-dating of ground water from other springs and wells in the watershed were compiled. The CFC data, and the data on major ions, nutrients, and nitrogen isotopes in the water collected from the 46 springs are included in this report. The apparent ages of water

  11. Distribution of 2,4-D in air and on surfaces inside residences after lawn applications: comparing exposure estimates from various media for young children.

    PubMed Central

    Nishioka, M G; Lewis, R G; Brinkman, M C; Burkholder, H M; Hines, C E; Menkedick, J R

    2001-01-01

    We collected indoor air, surface wipes (floors, table tops, and window sills), and floor dust samples at multiple locations within 11 occupied and two unoccupied homes both before and after lawn application of the herbicide 2,4-D. We measured residues 1 week before and after application. We used collected samples to determine transport routes of 2,4-D from the lawn into the homes, its subsequent distribution between the indoor surfaces, and air concentration as a function of airborne particle size. We used residue measurements to estimate potential exposures within these homes. After lawn application, 2,4-D was detected in indoor air and on all surfaces throughout all homes. Track-in by an active dog and by the homeowner applicator were the most significant factors for intrusion. Resuspension of floor dust was the major source of 2,4-D in indoor air, with highest levels of 2,4-D found in the particle size range of 2.5-10 microm. Resuspended floor dust was also a major source of 2,4-D on tables and window sills. Estimated postapplication indoor exposure levels for young children from nondietary ingestion may be 1-10 microg/day from contact with floors, and 0.2-30 microg/day from contact with table tops. These are estimated to be about 10 times higher than the preapplication exposures. By comparison, dietary ingestion of 2,4-D is approximately 1.3 microg/day. PMID:11713005

  12. Is Eruption Style Linked to Magma Residence Time at Kilauea Volcano? Results from Chemical Zoning in Olivine

    NASA Astrophysics Data System (ADS)

    Lynn, K. J.; Costa Rodriguez, F.; Shea, T.; Garcia, M. O.

    2015-12-01

    Kilauea is generally characterized by its modern effusive activity, but the past 2500 years were dominated by cycles of explosive and effusive eruptions lasting 100's of years (Swanson et al. 2012). These different eruption styles may reflect variable volatile contents in the source that control magma ascent rate and storage durations (e.g., Sides et al. 2014). A detailed petrological study of the dominantly explosive Keanakako'i tephras (1500-1820 CE) was undertaken to better understand the storage and transport conditions preceding high-energy eruptions. Here, we focus on preliminary results for olivine from the 1500 CE Basal Reticulite (>600 m fountain; May et al. 2015). Olivine major (Fe, Mg), minor (Mn, Ca, Ni) and trace (Li, Na, Al, P, Sc, Ti, V, Cr, Co, Zn) element traverses and 2D maps were collected for 10 crystals and reveal two major populations. The dominant population has homogeneous Fo89 and Fo87 cores with thin (3-12 μm) rims of intermediate composition (Fo87.5-88.5). Normal, reverse, and complex trace element zoning (Al, P, Ti, Cr) is prominent in these otherwise homogenous (Fo, Ni, Ca, Mn) crystals. 2D maps reveal early skeletal growth and the progressive decrease of Cr from core to rim suggests olivine and Cr-spinel crystallization, which should produce significant Fo zoning. Absence of Fo zoning could imply significant storage time in a reservoir allowing homogenization. The majority of rim compositions are out of equilibrium with adhering glass, and Fe-Mg modeling indicates that their residence within the carrier melt was of a few days. A second population consists of strongly zoned (normal and reverse) crystals with a wide range of core Fo (78 to 89) and Fo82-84 rims. Timescales from Fe-Mg zoning are up to 1 year, and may record storage histories before interaction with the carrier melt. The diversity in olivine zoning suggests at least two stages of magma mixing, and a more complex evolution for the magmas that fed the reticulite eruptions

  13. Emissions of VPOC from residences in the metropolitan Toronto area

    SciTech Connect

    Fellin, P.; Otson, R.

    1997-12-31

    Airborne vapor phase organic compound (VPOC) concentrations were determined indoors and outdoors concurrently over 24 h periods for 44 randomly selected residences in the Greater Toronto Area (GTA). Indoor to outdoor air exchange rates, measured by means of a perfluorocarbon tracer technique, averaged 0.45 and ranged from 0.04 to 2.2 air changes per hour (ach). For compounds occurring above the method detection limits (MDL), indoor sources contributed significantly to the occurrence of 7 of the 30 target VPOC since indoor to outdoor concentration ratios were greater than 1 for more than 50% of the homes for these compounds. Emissions from residences to the ambient air were calculated, and ranged up to 725 g/yr/residence for the sum of the target compounds for the residence with the largest emissions and averaged 96 g/yr/residence for all residences. The four compounds with the largest emissions averaged 53 (maximum, 500), 41 (maximum, 220), 22 (maximum, 110) and 20 (maximum, 240) g/yr/residence, respectively, for 1,4-dichlorobenzene, d-limonene, naphthalene and toluene. In a previous study, 1,4-dichlorobenzene and toluene were among the three VPOC with the greatest emissions from residences. However, the emissions were calculated from measured indoor concentrations, outdoor values were obtained at different times or by different methods, and average rather than individually measured air exchange rates were used. The emissions estimated in this study were compared to those from the previous study, and their impact on ambient air quality was estimated.

  14. Climate impacts on groundwater storage, hydrochemistry and residence time in geologically variable, snowmelt-dominated mountain catchments, Front Range, Colorado

    NASA Astrophysics Data System (ADS)

    Zeliff, M. M.; Williams, M. W.

    2012-12-01

    Groundwater storage, hydrochemistry and residence time are all known to vary widely depending on hydrogeologic conditions. In mountainous terrain hydrogeology can vary greatly over short distances, from bedrock aquifers on ridge tops to colluvial and fluvial aquifers in valleys. Determining how climate alters groundwater in the context of variable hydrogeologic conditions is needed to understand in-stream flows and biogeochemical cycles in these climactically sensitive alpine settings. In 2005 at the Niwot LTER six piezometers were installed in surficial diamicton and colluvium at the base of a semi-permanent snowfield at the Martinelli site (3440 m). Eight piezometers were also installed at the Saddle on a ridge-top in the alpine tundra (3528 m). In 2010 12 piezometers were installed at the C1 site (3025 m) in the subalpine atop moraine deposits. Groundwater monitoring for all sites is year-round and is comprised of depth-to-water measurements by hand and pressure transducers for select wells, as well as chemistry samples for major solutes including dissolved organic matter and stable isotopes of water, δ18O and δD. Across the Niwot LTER precipitation falls predominately as snow creating a strongly snowmelt-dominated hydrograph. Groundwater response to this seasonality is reflected in both physical and hydrochemical groundwater measurements. Snowmelt leads to sharp increases in water level in all piezometers including up to 7 m of water table change at the Saddle, up to 3 m of change at Martinelli and up to 5 m of water table change at C1. Minimum water table levels are not always measureable as the water table can drop below the extent of the piezometers, however, at the Saddle there are decreasing trends in annual minimum groundwater level in 3 of the 4 deep piezometers, possibly reflecting a decrease in total aquifer storage. Hydrochemical groundwater response to snowmelt is evident in distinct harmonic trends in major solute and isotope chemistry. Time

  15. Precise time technology for selected Air Force systems: Present status and future requirements

    NASA Technical Reports Server (NTRS)

    Yannoni, N. F.

    1981-01-01

    Precise time and time interval (PTTI) technology is becoming increasingly significant to Air Force operations as digital techniques find expanded utility in military missions. Timing has a key role in the function as well as in navigation. A survey of the PTTI needs of several Air Force systems is presented. Current technology supporting these needs was reviewed and new requirements are emphasized for systems as they transfer from initial development to final operational deployment.

  16. Using heat as a tracer to estimate spatially distributed mean residence times in the hyporheic zone of a riffle-pool sequence

    USGS Publications Warehouse

    Naranjo, Ramon C.

    2013-01-01

    Biochemical reactions that occur in the hyporheic zone are highly dependent on the time solutes that are in contact with sediments of the riverbed. In this investigation, we developed a 2-D longitudinal flow and solute-transport model to estimate the spatial distribution of mean residence time in the hyporheic zone. The flow model was calibrated using observations of temperature and pressure, and the mean residence times were simulated using the age-mass approach for steady-state flow conditions. The approach used in this investigation includes the mixing of different ages and flow paths of water through advection and dispersion. Uncertainty of flow and transport parameters was evaluated using standard Monte Carlo and the generalized likelihood uncertainty estimation method. Results of parameter estimation support the presence of a low-permeable zone in the riffle area that induced horizontal flow at a shallow depth within the riffle area. This establishes shallow and localized flow paths and limits deep vertical exchange. For the optimal model, mean residence times were found to be relatively long (9–40.0 days). The uncertainty of hydraulic conductivity resulted in a mean interquartile range (IQR) of 13 days across all piezometers and was reduced by 24% with the inclusion of temperature and pressure observations. To a lesser extent, uncertainty in streambed porosity and dispersivity resulted in a mean IQR of 2.2 and 4.7 days, respectively. Alternative conceptual models demonstrate the importance of accounting for the spatial distribution of hydraulic conductivity in simulating mean residence times in a riffle-pool sequence.

  17. Performance Evaluation of a Low-Cost, Real-Time Community Air Monitoring Station

    EPA Science Inventory

    The US EPA’s Village Green Project (VGP) is an example of using innovative technology to enable community-level low-cost real-time air pollution measurements. The VGP is an air monitoring system configured as a park bench located outside of a public library in Durham, NC. ...

  18. Determining the residence time distribution of various screw elements in a co-rotating twin-screw extruder by means of fluorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Lepschi, Alexander; Gerstorfer, Gregor; Miethlinger, Jürgen

    2015-05-01

    The Residence Time Distribution (RTD) is key to optimizing the mixing ability of an extruder. For both sensitive and reactive materials, it is important to know how long particles remain in the barrel and how long the polymer remains, for instance, in a kneading element. To assess the influence of different screw configurations on the RTD, a low-concentration tracer particle was injected into the feeding section and measured inline by fluorescence spectroscopy1 both inside the barrel and at the extruder exit. The measurements were conducted using polypropylene with different amounts of organic peroxide. Measuring the residence time at various positions along the screw allows the RTD to be determined for just one screw element. Furthermore, we show the influence of different screw configurations on the polydispersity of polypropylene.

  19. Effect of gas residence time on near-edge X-ray absorption fine structures of hydrogenated amorphous carbon films grown by plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jia, Lingyun; Sugiura, Hirotsugu; Kondo, Hiroki; Takeda, Keigo; Ishikawa, Kenji; Oda, Osamu; Sekine, Makoto; Hiramatsu, Mineo; Hori, Masaru

    2016-04-01

    In hydrogenated amorphous carbon films, deposited using a radical-injection plasma-enhanced chemical vapor deposition system, the chemical bonding structure was analyzed by near-edge X-ray absorption fine-structure spectroscopy. With a change in the residence times of source gases in a reactor, whereby total gas flow rates of H2/CH4 increased from 50 to 400 sccm, sp2-C fractions showed the minimum value at 150 sccm, while H concentration negligibly changed according to the results of secondary ion mass spectroscopy. On the other hand, widths of σ* C-C peaks increased with decreasing gas residence time, which indicates an increase in the fluctuation of bonding structures.

  20. Urban air pollution by odor sources: Short time prediction

    NASA Astrophysics Data System (ADS)

    Pettarin, Nicola; Campolo, Marina; Soldati, Alfredo

    2015-12-01

    A numerical approach is proposed to predict the short time dispersion of odors in the urban environment. The model is based on (i) a three dimensional computational domain describing the urban topography at fine spatial scale (1 m) and on (ii) highly time resolved (1 min frequency) meteorological data used as inflow conditions. The time dependent, three dimensional wind velocity field is reconstructed in the Eulerian framework using a fast response finite volume solver of Navier-Stokes equations. Odor dispersion is calculated using a Lagrangian approach. An application of the model to the historic city of Verona (Italy) is presented. Results confirm that this type of odor dispersion simulations can be used (i) to assess the impact of odor emissions in urban areas and (ii) to evaluate the potential mitigation produced by odor abatement systems.

  1. Real-Time Aerodynamic Parameter Estimation without Air Flow Angle Measurements

    NASA Technical Reports Server (NTRS)

    Morelli, Eugene A.

    2010-01-01

    A technique for estimating aerodynamic parameters in real time from flight data without air flow angle measurements is described and demonstrated. The method is applied to simulated F-16 data, and to flight data from a subscale jet transport aircraft. Modeling results obtained with the new approach using flight data without air flow angle measurements were compared to modeling results computed conventionally using flight data that included air flow angle measurements. Comparisons demonstrated that the new technique can provide accurate aerodynamic modeling results without air flow angle measurements, which are often difficult and expensive to obtain. Implications for efficient flight testing and flight safety are discussed.

  2. Coagulation effect on the activity size distributions of long lived radon progeny aerosols and its application to atmospheric residence time estimation techniques.

    PubMed

    Anand, S; Mayya, Y S

    2015-03-01

    The long lived naturally occurring radon progeny species in the atmosphere, namely (210)Pb, (210)Bi and (210)Po, have been used as important tracers for understanding the atmospheric mixing processes and estimating aerosol residence times. Several observations in the past have shown that the activity size distribution of these species peaks at larger particle sizes as compared to the short lived radon progeny species - an effect that has been attributed to the process of coagulation of the background aerosols to which they are attached. To address this issue, a mathematical equation is derived for the activity-size distribution of tracer species by formulating a generalized distribution function for the number of tracer atoms present in coagulating background particles in the presence of radioactive decay and removal. A set of these equations is numerically solved for the progeny chain using Fuchs coagulation kernel combined with a realistic steady-state aerosol size spectrum that includes nucleation, accumulation and coarse mode components. The important findings are: (i) larger shifts in the modal sizes of (210)Pb and (210)Po at higher aerosol concentrations such as that found in certain Asian urban regions (ii) enrichment of tracer specific activity on particles as compared to that predicted by pure attachment laws (iii) sharp decline of daughter-to-parent activity ratios for decreasing particle sizes. The implication of the results to size-fractionated residence time estimation techniques is highlighted. A coagulation corrected graphical approach is presented for estimating the residence times from the size-segregated activity ratios of (210)Bi and (210)Po with respect to (210)Pb. The discrepancy between the residence times predicted by conventional formula and the coagulation corrected approach for specified activity ratios increases at higher atmospheric aerosol number concentrations (>10(10) #/m(3)) for smaller sizes (<1 μm). The results are further

  3. Hillslope lowering rates and mobile-regolith residence times from in situ and meteoric 10Be analysis: Boulder Creek Critical Zone Observatory, Colorado

    NASA Astrophysics Data System (ADS)

    Foster, M. A.; Anderson, R. S.; Wyshnytzky, C.; Ouimet, W. B.; Dethier, D. P.

    2014-12-01

    Mobile regolith is produced as weathered saprolite is entrained into the mobile layer. The rate of mobile-regolith production and its residence time on hillslopes shapes the topography and evolution of hillslopes. We calculate the production rate of mobile regolith and the mobile-regolith residence times on active hillslopes in Gordon Gulch, within the Boulder Creek Critical Zone Observatory (CZO), Colorado. We find mobile-regolith production rates (average 3.1 cm/ka) and residence times (average 10-20 ka) derived from both in situand meteoric methods agree. Lowering-rates derived from our study are also comparable to basin-averaged denudation rates for small basins in the Colorado Front Range (Dethier and Lazarus, 2006). In this study, we have measured both in situ and meteoric 10Be in saprolite and mobile regolith separately. We find that, on average, two-thirds of in situ 10Be is produced within saprolite, and that at least one-tenth of the meteoric 10Be inventories are stored in saprolite. In the case of in situ 10Be, this simply reflects the exponential fall-off in production rates through a thin mobile-regolith cover. In the case of meteoric 10Be, our calculations suggest that >40% of the meteoric 10Be deposition occurs within the saprolite. Most studies that utilize 10Be report residence times and soil-production rates based on concentrations in either the mobile regolith or saprolite; therefore, our 10Be data highlight the importance of clearly identifying mobile and immobile portions of the regolith, constraining its 10Be inventory, and use of consistent terminology for the mobile-layer.

  4. Landing-Time-Controlled Management Of Air Traffic

    NASA Technical Reports Server (NTRS)

    Erzberger, Heinz; Tobias, Leonard

    1988-01-01

    Conceptual system controls aircraft with old and new guidance equipment. Report begins with overview of concept, then reviews controller-interactive simulations. Describes fuel-conservative-trajectory algorithm, based on equations of motion for controlling landing time. Finally, presents results of piloted simulations.

  5. Permanent resident

    PubMed Central

    Fisher, John F.

    2016-01-01

    The training of physicians in the past century was based primarily on responsibility and the chain-of-command. Those with the bulk of that responsibility in the fields of pediatrics and internal medicine were residents. Residents trained the medical students and supervised them carefully in caring for patients. Most attending physicians supervised their teams at arm's length, primarily serving as teachers of the finer points of diagnosis and treatment during set periods of the day or week with a perfunctory signature on write-ups or progress notes. Residents endeavored to protect the attending physician from being heavily involved unless they were unsure about a clinical problem. Before contacting the attending physician, a more senior resident would be called. Responsibility was the ultimate teacher. The introduction of diagnosis-related groups by the federal government dramatically changed the health care delivery system, placing greater emphasis on attending physician visibility in the medical record, ultimately resulting in more attending physician involvement in day-to-day care of patients in academic institutions. Without specified content in attending notes, hospital revenues would decline. Although always in charge technically, attending physicians increasingly have assumed the role once dominated by the resident. Using biographical experiences of more than 40 years, the author acknowledges and praises the educational role of responsibility in his own training and laments its declining role in today's students and house staff. PMID:27193992

  6. Mixing interfaces, fluxes, residence times and redox conditions of the hyporheic zones induced by dune-like bedforms and ambient groundwater flow

    NASA Astrophysics Data System (ADS)

    Marzadri, Alessandra; Tonina, Daniele; Bellin, Alberto; Valli, Alberto

    2016-02-01

    Recent studies highlighted the importance of the interface between streams and their surrounding sediment, known as the hyporheic zone, where stream waters flow through the alluvium. These pore water fluxes stem from the interaction among streambed morphology, stream hydraulics and surrounding groundwater flow. We analytically model the hyporheic hydraulics induced by a spatially uniform ambient groundwater flow made of a horizontal, underflow, and a vertical, basal, component, which mimics gaining and losing stream conditions. The proposed analytical solution allows to investigate the control of simple hydromorphological quantities on the extent, residence time and redox conditions of the hyporheic zone, and the thickness of the mixing interface between hyporheic and groundwater cells. Our analysis shows that the location of the mixing zone shallows or deepens in the sediment as a function of bedform geometry, surface hydraulic and groundwater flow. The point of stagnation, where hyporheic flow velocities vanish and where the separation surface passes through, is shallower than or coincides with the deepest point of the hyporheic zone only due to underflow. An increase of the ambient flow causes a reduction of the hyporheic zone volume similarly in both losing and gaining conditions. The hyporheic residence time is lognormally distributed under neutral, losing and gaining conditions, with the residence time moments depending on the same set of parameters describing dune morphology and stream flow.

  7. Characterizing the trophic niches of stocked and resident cyprinid fishes: consistency in partitioning over time, space and body sizes.

    PubMed

    Bašić, Tea; Britton, J Robert

    2016-07-01

    Hatchery-reared fish are commonly stocked into freshwaters to enhance recreational angling. As these fishes are often of high trophic position and attain relatively large sizes, they potentially interact with functionally similar resident fishes and modify food-web structure. Hatchery-reared barbel Barbus barbus are frequently stocked to enhance riverine cyprinid fish communities in Europe; these fish can survive for over 20 years and exceed 8 kg. Here, their trophic consequences for resident fish communities were tested using cohabitation studies, mainly involving chub Squalius cephalus, a similarly large-bodied, omnivorous and long-lived species. These studies were completed over three spatial scales: pond mesocosms, two streams and three lowland rivers, and used stable isotope analysis. Experiments in mesocosms over 100 days revealed rapid formation of dietary specializations and discrete trophic niches in juvenile B. barbus and S. cephalus. This niche partitioning between the species was also apparent in the streams over 2 years. In the lowland rivers, where fish were mature individuals within established populations, this pattern was also generally apparent in fishes of much larger body sizes. Thus, the stocking of these hatchery-reared fish only incurred minor consequences for the trophic ecology of resident fish, with strong patterns of trophic niche partitioning and diet specialization. Application of these results to decision-making frameworks should enable managers to make objective decisions on whether cyprinid fish should be stocked into lowland rivers according to ecological risk. PMID:27547336

  8. Time-space modeling of journey-time exposure to traffic-related air pollution using GIS.

    PubMed

    Gulliver, John; Briggs, David J

    2005-01-01

    Journey-time exposures represent an important, though as yet little-studied, component of human exposure to traffic-related air pollution, potentially with important health effects. Methods for assessing journey-time exposures, either as part of epidemiological studies or for policy assessment, are, however, poorly developed. This paper describes the development and testing of a GIS-based system for modeling human journey-time exposures to traffic-related air pollution: STEMS (Space-Time Exposure Modeling System). The model integrates data on source activity, pollutant dispersion, and travel behavior to derive individual- or group-level exposure measures to atmospheric pollution. The model, which is designed to simulate exposures of people as they move through a changing air pollution field, was developed, validated, and trialed in Northampton, UK. The system currently uses ArcInfo to couple four separate submodels: a source activity/emission model (SATURN), a proprietary atmospheric dispersion model (ADMS-Urban), an empirically derived background air pollution model, and a purposely designed time-activity-based exposure model (TOTEM). This paper describes the structure of the modeling system; presents results of field calibration, validation, and sensitivity analysis; and illustrates the use of the model to analyze journey-time exposures of schoolchildren. PMID:15476729

  9. Time-resolved interference imaging of the air disc under an impacting drop

    NASA Astrophysics Data System (ADS)

    Li, E. Q.; Thoroddsen, S. T.

    2015-11-01

    Water drop impacting on dry, solid surface, is rapidly decelerated by an air cushion. This thin air layer is formed by lubrication pressure in the gas, which is strong enough to stop the inertia of the drop liquid and deform its bottom tip. The contact of the drop with the solid therefore occurs along a ring, entrapping a central bubble. For very large impact velocities the lubrication pressure becomes large enough to compress the gas. We use the Kirana ultra-high-speed video camera and 50 ns pulsed laser-diodes for interferometric imaging, at time-resolution of 200 ns. We capture the evolution of the air-layer thickness profile over the entire bubble entrapment process. The maximum diameter of the air disc is in perfect agreement with earlier theoretical models, if one uses the bottom radius of curvature of the drop. The air-layer thickness is also in agreement with available theoretical models, if one assumes adiabatic compression of the gas. For the largest impact velocities the air is compressed by more than a factor of 10. Immediately after first contact, the air disc expands rapidly in the vertical. The outer edge of the air-disk forms a kink in the free surface. This kink can move radially outwards just before contact, at speed as large as 50 times the impact velocity.

  10. The Effect of Beaver Activity on the Ammonium Uptake and Water Residence Time Characteristics of a Third-Order Stream Reach

    NASA Astrophysics Data System (ADS)

    Briggs, M.; Gooseff, M. N.; Wollheim, W. M.; Peterson, B. J.; Morkeski, K.

    2009-12-01

    Increasing beaver populations within low gradient basins in the northeastern United States are fundamentally changing the way water and dissolved nutrients are exported through these stream networks to the coast. Beaver dams can increase water residence time and contact with organic material, promote anoxic conditions and enhance both surface and hyporheic transient storage; all of these may have an impact on biogeochemical reactivity and nutrient retention. To quantitatively assess some of these effects we co-injected NaCl and NH4+ into the same 3rd-order stream reach in Massachusetts, USA under pre- and post-dam conditions. These experiments were done at similar discharge rates to isolate the impacts of a large natural beaver dam (7 m X 1.3 m) on the low-gradient (0.002) system where variable discharge also imparts a strong control on residence time. During the post-dam experiment there was an estimated 2300 m3 of water impounded behind the structure, which influenced more than 300 m of the 650 m stream reach. Our results showed that median transport time through the reach increased by 160% after dam construction. Additionally the tracer tailing time normalized to the corresponding median transport time increased from 1.08 to 1.51, indicating a pronounced tailing of the tracer signal in the post-dam condition. Data collected within the beaver pond just upstream of the dam indicated poor mixing and the presence of preferential flow paths through the generally stagnant zone. The uptake length (Sw) for NH4+ was 1250 m under the pre-dam condition, and may have changed for the post-dam reach in part because of the observed changes in residence time. As beaver population growth continues within these basins the consequences may be a smoothing of the outlet hydrograph and increased nutrient and organic matter removal and storage along the stream network.

  11. Identifying residence times and streamflow generation processes using δ18O and δ2H in meso-scale catchments in the Abay/Upper Blue Nile, Ethiopia

    NASA Astrophysics Data System (ADS)

    Tekleab, S.; Wenninger, J.; Uhlenbrook, S.

    2013-08-01

    Measurements of the stable isotopes oxygen-18 (18O) and deuterium (2H) were carried out in two meso-scale catchments, Chemoga (358 km2) and Jedeb (296 km2) south of Lake Tana, Abay/Upper Blue Nile basin, Ethiopia. The region is of paramount importance for the water resources in the Nile basin. Stable isotope composition in precipitation, spring water and streamflow were analyzed (i) to characterize the spatial and temporal variations of water fluxes; (ii) to estimate the mean residence time of water using a sine wave regression approach; and (iii) to identify runoff components using classical two component hydrograph separations at a seasonal time scale. The results show that the isotopic composition of precipitation exhibit marked seasonal variations, which suggests different sources of moisture generation for the rainfall in the study area. The Atlantic-Indian ocean, Congo basin, and the Sud swamps are the likely the potential moisture source areas during the main rainy (summer) season. While, the Indian-Arabian, and Mediterranean Sea moisture source areas during little rain (spring), and dry (winter) seasons. The spatial variation of the isotopic composition is affected by the amount effect and to less extent by altitude and temperature effects. A mean altitude effect of -0.12‰ (100 m)-1 for 18O and -0.58‰ (100 m)-1 for 2H were discernable in precipitation isotope composition. The seasonal variations of the isotopic signature of the spring water exhibit a damped response as compared to the river waters, which shows that the spring water has longer residence times than the river water. Results from the hydrograph separation at a seasonal time scale indicate the dominance of event water with an average of 71% and 64% of the total runoff during the wet season in the Chemoga and Jedeb catchment, respectively. The stable isotope compositions of streamflow samples were damped compared to the input function of precipitation for both catchments and this damping was

  12. Crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at Mt. Etna during the last 400 years

    NASA Astrophysics Data System (ADS)

    Viccaro, Marco; Barca, Donatella; Bohrson, Wendy A.; D'Oriano, Claudia; Giuffrida, Marisa; Nicotra, Eugenio; Pitcher, Bradley W.

    2016-04-01

    Trace element zoning in plagioclase of selected alkaline lavas from the historic (1607-1892 AD) and recent (1983-2013 AD) activity of Mt. Etna volcano has been used to explore the possible role that volcano-tectonics exert on magma transfer dynamics. The observed textural characteristics of crystals include near-equilibrium textures (i.e., oscillatory zoning) and textures with variable extent of disequilibrium (patchy zoning, coarse sieve textures and dissolved cores). Historic crystals exhibit lower K concentrations at lower anorthite contents, a feature in agreement with the general more potassic character of the recent lavas if compared to the historic products. Historic plagioclases have statistically higher Ba and lower Sr concentrations than the recent crystals, which result in different Sr/Ba ratios for the two suites of plagioclase. Variations in the anorthite content along core-to-rim profiles obtained on crystals with different types of textures for both the historic and recent eruptive periods were evaluated particularly versus Sr/Ba. At comparable average An contents, crystals characterized by oscillatory zoning, which are representative of near-equilibrium crystallization from the magma, display distinct Sr/Ba ratios. We suggest that these features are primarily related to recharge of a new, geochemically-distinct magma into the storage and transport system of the volcano. In addition to distinct trace element and textural characteristics of plagioclase, Sr diffusion modeling for plagioclase suggests that residence times are generally shorter for crystals found in recently erupted lavas (25-77 years, average 43 years) compared to those of the historic products (43-163 years, average 99 years). Shorter residences times correlate with gradual increases in eruption volume and eruption frequency rates through time. We attribute these features to an increasing influence, since the 17th century, of extensional tectonic structures within the upper 10 km of

  13. Using Open and Interoperable Ways to Publish and Access LANCE AIRS Near-Real Time Data

    NASA Astrophysics Data System (ADS)

    Zhao, P.; Lynnes, C.; Vollmer, B.; Savtchenko, A. K.; Yang, W.

    2011-12-01

    Atmospheric Infrared Sounder (AIRS) Near-Real Time (NRT) data from the Land Atmosphere Near real time Capability for EOS (LANCE) provide the information on the global and regional atmospheric state with very low latency. An open and interoperable platform is useful to facilitate access to and integration of LANCE AIRS NRT data. This paper discusses the use of open-source software components to build Web services for publishing and accessing AIRS NRT data in the context of Service Oriented Architecture (SOA). The AIRS NRT data have also been made available through an OPeNDAP server. OPeNDAP allows several open-source netCDF-based tools such as Integrated Data Viewer, Ferret and Panoply to directly display the Level 2 data over the network. To enable users to locate swath data files in the OPeNDAP server that lie within a certain geographical area, graphical "granule maps" are being added to show the outline of each file on a map of the Earth. The metadata of AIRS NRT data and services is then explored to implement information advertisement and discovery in catalogue systems. Datacasting, an RSS-based technology for accessing Earth Science data and information to facilitate the subscriptions to AIRS NRT data availability, filtering, downloading and viewing data, is also discussed. To provide an easy entry point to AIRS NRT data and services, a Web portal designed for customized data downloading and visualization is introduced.

  14. Near real-time AIRS processing and distribution system: from design to operations

    NASA Astrophysics Data System (ADS)

    Wolf, Walter; King, Thomas; Goldberg, Mitchell D.; Zhou, Lihang; Barnet, Chris D.

    2004-10-01

    A near real-time AIRS processing and distribution system is fully operational at NOAA/NESDIS/ORA. The AIRS system went though three separate production phases: design and development, implementation, and operations. The design and development phase consisted of two years of preparation for the near real-time AIRS data. The approach was to fully emulate the AIRS measurement stream. This was accomplished by using a forecast model to represent the geophysical state and computation of simulated AIRS measurements using the characteristics of the AIRS channels. The preparation included file format development and the creation of a program to subset the radiance and product data. The implementation phase lasted over a year and involved utilizing AIRS/AMSU/HSB simulated data quasi-operationally. This simulated data was placed into deliverable files and distributed to the customers for their pre-launch preparations. The operational phase consisted of switching the simulation system to real data and is the current system status. Details of what went right and wrong at each production phase will be presented. This methodology eased the transition to operations and will be applied to other advanced sounders such as IASI and CrIS.

  15. Aquifer residence times for recycled water estimated using chemical tracers and the propagation of temperature signals at a managed aquifer recharge site in Australia

    NASA Astrophysics Data System (ADS)

    Bekele, Elise; Patterson, Bradley; Toze, Simon; Furness, Andrew; Higginson, Simon; Shackleton, Mark

    2014-09-01

    A prerequisite for minimizing contamination risk whilst conducting managed aquifer recharge (MAR) with recycled water is estimating the residence time in the zone where pathogen inactivation and biodegradation processes occur. MAR in Western Australia's coastal aquifers is a potential major water source. As MAR with recycled water becomes increasingly considered in this region, better knowledge of applied and incidental tracer-based options from case studies is needed. Tracer data were collected at a MAR site in Floreat, Western Australia, under a controlled pumping regime over a distance of 50 m. Travel times for bromide-spiked groundwater were compared with two incidental tracers in recycled water: chloride and water temperature. The average travel time using bromide was 87 ± 6 days, whereas the estimates were longer based on water temperature (102 ± 17 days) and chloride (98 ± 60 days). The estimate of average flow velocity based on water temperature data was identical to the estimate based on bromide within a 25-m section of the aquifer (0.57 ± 0.04 m day-1). This case study offers insights into the advantages, challenges and limitations of using incidental tracers in recycled water as a supplement to a controlled tracer test for estimating aquifer residence times.

  16. Residence times and age distributions of spring waters at the Semmering catchment area, Eastern Austria, as inferred from tritium, CFCs and stable isotopes.

    PubMed

    Han, Liangfeng; Hacker, Peter; Gröning, Manfred

    2007-03-01

    The groundwater system in the mountainous area of Semmering, Austria, was studied by environmental tracers in several karst springs. The tracers used included stable isotopes ((18)O, (2)H), tritium ((3)H) and chlorofluorocarbons (CFCs). The tracers provided valuable information in regard to (1) the mean altitude of the spring catchment areas; (2) the residence time and age distribution of the spring waters; and (3) the interconnection of the springs to a sinkhole. The combination of the stable isotopic data and the topography/geology provided the estimates of the mean altitudes of the catchment areas. Based on the stable isotopic data the recharge temperature of the spring waters was estimated. The smoothing of precipitation's isotopic signal in spring discharge provided information on the minimum transit time of the spring waters. Due to short observation time, (3)H data alone cannot be used for describing the mean residence time of the karst waters. CFCs, though useful in recognizing the co-existence of young (post-1993) water with old (CFC-free) water, could not be used to resolve age distribution models. It is shown in this article, however, that the combined use of tritium and CFCs can provide a better assessment of models to account for different groundwater age distributions. In Appendix A, a simplified method for collecting groundwater samples for the analysis of CFCs is described. The method provides a real facilitation for fieldwork. Test data are given for this sampling method in regard to potential contamination by atmospheric CFCs. PMID:17454271

  17. Measurements of electron avalanche formation time in W-band microwave air breakdown

    SciTech Connect

    Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.

    2011-08-15

    We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are {approx}0.1-2 {mu}s over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

  18. Measurements of electron avalanche formation time in W-band microwave air breakdown

    NASA Astrophysics Data System (ADS)

    Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.

    2011-08-01

    We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are ˜0.1-2 μs over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

  19. Time-series analysis for determining vertical air permeability in unsaturated zones

    SciTech Connect

    Lu, N.

    1999-01-01

    The air pressure in the unsaturated subsurface changes dynamically as the barometric pressure varies with time. Depending on the material properties and boundary conditions, the intensity of the correlation between the atmospheric and subsurface pressures may be evidenced in two persistent patterns: (1) the amplitude attenuation; and (2) the phase lag for the principal modes, such as the diurnal, semidiurnal, and 8-h tides. The amplitude attenuation and the phase lag generally depend on properties that can be classified into two categories: (1) The barometric pressure parameters, such as the apparent pressure amplitudes and frequencies controlled by the atmospheric tides and others; and (2) the material properties of porous media, such as the air viscosity, air-filled porosity, and permeability. Based on the principle of superposition and a Fourier time-series analysis, an analytical solution for predicting the subsurface air pressure variation caused by the atmospheric pressure fluctuation is presented. The air permeability (or pneumatic diffusivity) can be quantitatively determined by using the calculated amplitude attenuations (or phase lags) and the appropriate analytical relations among the parameters of the atmosphere and the porous medium. An analysis using the field data shows that the Fourier time-series analysis may provide a potentially reliable and simple method for predicting the subsurface barometric pressure variation and for determining the air permeability of unsaturated zones.

  20. Modeling duration of time lived in a residence, a community and mobility in rural areas of Merced and Ventura, California to assess potential health risks to airborne contaminants.

    PubMed

    Driver, Jeffrey; Price, Paul; vanWesenbeeck, Ian; Kaplan, William; Holden, Larry; Ross, John; Landenberger, Bryce

    2016-11-01

    A de novo population mobility survey of 800 households (random digit dialing-based phone interviews) was conducted in high demand areas of the agricultural fumigant, 1,3-dichloropropene (1,3-D) in Merced and Ventura counties of California. The survey included approximately 20 questions relating to the length of time individuals had lived in the high demand areas in each county, and also relating to weekly and annual mobility patterns. Lifetime inhalation exposures to 1,3-D are determined, in part, by the number of years individuals spend in an area where the fumigant is used. The purpose of the survey was to provide location-specific data for probabilistic modeling of long-term inhalation exposures to 1,3-D. The survey found that the majority of residents do not live in a high demand area or in the same house (99.99%) for 70years (a default assumption used by some regulatory agencies). It was also observed that residents move frequently and are mobile day-to-day and week-to-week, within the use area. Finally, estimates of total residency duration, derived from the survey results indicate that median times spent within a high demand area (which could include more than one residential location) were 18 and 26years for Ventura and Merced high demand areas, respectively. The average time spent in the high demand areas was 22 and 27years for the Ventura and Merced community, respectively. Less than 0.01% of the populations in either of the high demand areas spend 70years in the same house. PMID:27436777

  1. Numerical model of hyporheic exchange and reactive transport dynamics from the perspective of residence time on upwelling and downwelling zones at River Bure, UK

    NASA Astrophysics Data System (ADS)

    Gokdemir, C.; Heppell, K.; Tonina, D.; Harvey, G.; Bellin, A.

    2013-12-01

    The hyporheic zone is often defined as where mixing of surface water and groundwater occurs in shallow sediments beneath and adjacent to rivers. This mixing is credited with creating unique biogeochemical conditions that can attenuate contaminants from either upstream surface water or groundwater under gaining and losing conditions. Hyporheic exchange often results from differences in the channel near-bed total pressures as they vary in response to interactions between the surface flow and bed topography and the nearby water table. Reactions of contaminants in groundwater also dependent on mixing from surface water. Therefore, representation of the profile of upwelling and downwelling exchange between surface water and groundwater have important consequences for contaminant transport. Here we are studying nitrogen fate within a restored reach of the River Bure, Norfolk, United Kingdom. We combine field measurements of surface flow properties, nearby groundwater table and nitrogen compound concentration with numerical simulation of the hyporheic flow path. We numerically model mixing between hyporheic flow paths induced by sediment, bedform, meanders on riverbed, and flow paths of adjacent upwelling of deeper groundwater. Preliminary results indicate that with the coarse topographical data and with limited surface water hydraulic data it is possible to define the spatial extent of hyporheic exchange and potential mixing zones for contaminants as a function of residence time. The proposed work has the potential to depict high residence time zones and biogeochemical reactivity in homogeneous and heterogeneous sediments. Furthermore, our results aim to clarify hyporheic zone definitions from the perspective of residence time and of upwelling and downwelling contaminants in order to understand real case biogeochemical dynamics.

  2. Estimation of mean residence times of subsurface waters using seasonal variation in deuterium excess in a small headwater catchment in Japan

    NASA Astrophysics Data System (ADS)

    Kabeya, Naoki; Katsuyama, Masanori; Kawasaki, Masatoshi; Ohte, Nobuhito; Sugimoto, Atsuko

    2007-01-01

    We measured deuterium excess (d = D - 818O) in throughfall, groundwater, soil water, spring water, and stream water for 3 years in a small headwater catchment (Matsuzawa, 0.68 ha) in the Kiryu Experimental Watershed in Japan. The d value represents a kinetic effect produced when water evaporates. The d value of the throughfall showed a sinusoidal change (amplitude: 6.9 relative to Vienna standard mean ocean water (V-SMOW)) derived from seasonal changes in the source of water vapour. The amplitude of this sinusoidal change was attenuated to 1.3-6.9 V-SMOW in soil water, groundwater, spring water, and stream water. It is thought that these attenuations derive from hydrodynamic transport processes in the subsurface and mixing processes at an outflow point (stream or spring) or a well. The mean residence time (MRT) of water was estimated from d value variations using an exponential-piston flow model and a dispersion model. MRTs for soil water were 0-5 months and were not necessarily proportional to the depth. This may imply the existence of bypass flow in the soil. Groundwater in the hillslope zone had short residence times, similar to those of the soil water. For groundwater in the saturated zone near the spring outflow point, the MRTs differed between shallow and deeper groundwater; shallow groundwater had a shorter residence time (5-8 months) than deeper groundwater (more than 9 months). The MRT of stream water (8-9 months) was between that of shallow groundwater near the spring and deeper groundwater near the spring. The seasonal variation in the d value of precipitation arises from changes in isotopic water vapour composition associated with seasonal activity of the Asian monsoon mechanism. The d value is probably an effective tracer for estimating the MRT of subsurface water not only in Japan, but also in other East Asian countries influenced by the Asian monsoon. Copyright

  3. Extracellular amylases of starch-fermenting yeast: pH effect on export and residence time in the periplasm

    SciTech Connect

    Calleja, G.B.; Levy-Rick, S.R.; Nasim, A.; Lusena, C.V.

    1987-01-01

    Aerobic cultures of S. alluvius in Wickerham's yeast-nitrogen-base medium with starch as sole carbon source become strongly acidic and contain no detectable extra-cellular amylolytic activity during stationary phase, when the activity in buffered cultures is maximal. The extracellular amylases are irreversibly inactivated at the low pH value (less than 3.5) attained by the cultures. When adequately buffered, the medium yields maximal extracellular amylolytic activity. About 0.2 M phosphate buffer is adequate for substrate concentrations of up to 0.5% starch; higher starch concentrations require more buffer. Unbuffered cultures that are adjusted once with alkali to pH 5.5 also allow maximal extracellular amylolytic activity, provided the adjustment is made prior to the end of exponential growth. Automatic pH control allows use of high starch concentrations of up to 4%. Export is optimal at pH values higher than the optima for enzyme activity and stability and for population growth. The need for pH adjustment prior to the appearance of amylolytic activity in the medium suggests pH dependence of the export process itself and/or acid inactivation of enzymes transiently resident in the periplasm. (Refs. 23).

  4. LUMPED Unsteady: a Visual Basic ® code of unsteady-state lumped-parameter models for mean residence time analyses of groundwater systems

    NASA Astrophysics Data System (ADS)

    Ozyurt, N. Nur; Bayari, C. Serdar

    2005-04-01

    A Microsoft ® Visual Basic 6.0 (Microsoft Corporation, 1987-1998) code of 9 lumped-parameter models of unsteady flow is presented for the analysis of mean residence time in aquifers. Groundwater flow systems obeying plug and well-mixed flow models and their combinations in parallel or serial connection can be simulated by the code. Models can use tritium, tritiugenic He-3, oxygen-18, deuterium, krypton-85, chlorofluorocarbons (CFC-11, CFC-12 and CFC-113) and sulfur hexafluoride (SF 6) as the environmental tracers. The executable code runs under all 32-bit Windows operating systems. Details of the code are explained and its limitations are indicated.

  5. Long-term observations of bedrock groundwater dynamics and contributions to stream in a Granite catchment - Approach with mean residence time and hydrochemistry

    NASA Astrophysics Data System (ADS)

    Katsuyama, M.; Kosugi, K.; Tani, M.

    2013-12-01

    Exploration of bedrock groundwater dynamics is one of the latest frontier of hillslope- and catchment hydrology. We have been keeping on monitoring of the chemical and isotopic compositions of bedrock groundwater in Kiryu Experimental Watershed (KEW), Japan since 2003. We set up a hillslope plot in a subcatchment of KEW, and monthly sampled the streamwater of the subcatchment, the outflow from the plot, which occurs as saturated throughflow on the soil-bedrock interface during rainstorms, and groundwater in the soil sediment. Moreover, we excavated the bedrock and installed some tension lysimeters at 0.1, 0.2, 0.4, and 0.8 m deep and boreholes at 12, 15, and 20 m deep below bedrock surface, and sampled them. The streamflow from this subcatchment was perennial. The SiO2 concentration, which is mainly supplied by chemical weathering, increased along with the infiltration process. On the other hand, the NO3- concentration was highest at the surface soil water, and removed along with the infiltration process. The concentrations of both solutes in the streamwater were intermediate between the concentrations in the surface soil water and bedrock groundwater. The mean residence times calculated by delta 18O variations were about 4 or 5 months in the groundwater in the soil sediment and in the shallow (<0.8m) bedrock groundwaters, about 50 months in 12- and 15 m deep, and about 120 months in 20 m deep, respectively. Some studies have pointed out that the mean residence time over 4 years cannot be estimated by the stable isotope methods, because the variations of isotope signals will become flat. However, the isotope signals in 20 m deep borehole showed long-tern variation, and we could successfully estimate the residence time combined with long-term isotope signal of rainfall. That in the streamwater was estimated as about 30 months. These results suggest that a part of the bedrock groundwater can contribute to the stream from the shallower layers. The fact that the

  6. Evaluation of quantitative imaging methods for organ activity and residence time estimation using a population of phantoms having realistic variations in anatomy and uptake

    PubMed Central

    He, Bin; Du, Yong; Segars, W. Paul; Wahl, Richard L.; Sgouros, George; Jacene, Heather; Frey, Eric C.

    2009-01-01

    Estimating organ residence times is an essential part of patient-specific dosimetry for radioimmunotherapy (RIT). Quantitative imaging methods for RIT are often evaluated using a single physical or simulated phantom but are intended to be applied clinically where there is variability in patient anatomy, biodistribution, and biokinetics. To provide a more relevant evaluation, the authors have thus developed a population of phantoms with realistic variations in these factors and applied it to the evaluation of quantitative imaging methods both to find the best method and to demonstrate the effects of these variations. Using whole body scans and SPECT∕CT images, organ shapes and time-activity curves of 111In ibritumomab tiuxetan were measured in dosimetrically important organs in seven patients undergoing a high dose therapy regimen. Based on these measurements, we created a 3D NURBS-based cardiac-torso (NCAT)-based phantom population. SPECT and planar data at realistic count levels were then simulated using previously validated Monte Carlo simulation tools. The projections from the population were used to evaluate the accuracy and variation in accuracy of residence time estimation methods that used a time series of SPECT and planar scans. Quantitative SPECT (QSPECT) reconstruction methods were used that compensated for attenuation, scatter, and the collimator-detector response. Planar images were processed with a conventional (CPlanar) method that used geometric mean attenuation and triple-energy window scatter compensation and a quantitative planar (QPlanar) processing method that used model-based compensation for image degrading effects. Residence times were estimated from activity estimates made at each of five time points. The authors also evaluated hybrid methods that used CPlanar or QPlanar time-activity curves rescaled to the activity estimated from a single QSPECT image. The methods were evaluated in terms of mean relative error and standard deviation of

  7. Evaluation of quantitative imaging methods for organ activity and residence time estimation using a population of phantoms having realistic variations in anatomy and uptake

    SciTech Connect

    He Bin; Du Yong; Segars, W. Paul; Wahl, Richard L.; Sgouros, George; Jacene, Heather; Frey, Eric C.

    2009-02-15

    Estimating organ residence times is an essential part of patient-specific dosimetry for radioimmunotherapy (RIT). Quantitative imaging methods for RIT are often evaluated using a single physical or simulated phantom but are intended to be applied clinically where there is variability in patient anatomy, biodistribution, and biokinetics. To provide a more relevant evaluation, the authors have thus developed a population of phantoms with realistic variations in these factors and applied it to the evaluation of quantitative imaging methods both to find the best method and to demonstrate the effects of these variations. Using whole body scans and SPECT/CT images, organ shapes and time-activity curves of 111In ibritumomab tiuxetan were measured in dosimetrically important organs in seven patients undergoing a high dose therapy regimen. Based on these measurements, we created a 3D NURBS-based cardiac-torso (NCAT)-based phantom population. SPECT and planar data at realistic count levels were then simulated using previously validated Monte Carlo simulation tools. The projections from the population were used to evaluate the accuracy and variation in accuracy of residence time estimation methods that used a time series of SPECT and planar scans. Quantitative SPECT (QSPECT) reconstruction methods were used that compensated for attenuation, scatter, and the collimator-detector response. Planar images were processed with a conventional (CPlanar) method that used geometric mean attenuation and triple-energy window scatter compensation and a quantitative planar (QPlanar) processing method that used model-based compensation for image degrading effects. Residence times were estimated from activity estimates made at each of five time points. The authors also evaluated hybrid methods that used CPlanar or QPlanar time-activity curves rescaled to the activity estimated from a single QSPECT image. The methods were evaluated in terms of mean relative error and standard deviation of the

  8. Evaluation of quantitative imaging methods for organ activity and residence time estimation using a population of phantoms having realistic variations in anatomy and uptake.

    PubMed

    He, Bin; Du, Yong; Segars, W Paul; Wahl, Richard L; Sgouros, George; Jacene, Heather; Frey, Eric C

    2009-02-01

    Estimating organ residence times is an essential part of patient-specific dosimetry for radioimmunotherapy (RIT). Quantitative imaging methods for RIT are often evaluated using a single physical or simulated phantom but are intended to be applied clinically where there is variability in patient anatomy, biodistribution, and biokinetics. To provide a more relevant evaluation, the authors have thus developed a population of phantoms with realistic variations in these factors and applied it to the evaluation of quantitative imaging methods both to find the best method and to demonstrate the effects of these variations. Using whole body scans and SPECT/CT images, organ shapes and time-activity curves of 111In ibritumomab tiuxetan were measured in dosimetrically important organs in seven patients undergoing a high dose therapy regimen. Based on these measurements, we created a 3D NURBS-based cardiac-torso (NCAT)-based phantom population. SPECT and planar data at realistic count levels were then simulated using previously validated Monte Carlo simulation tools. The projections from the population were used to evaluate the accuracy and variation in accuracy of residence time estimation methods that used a time series of SPECT and planar scans, Quantitative SPECT (QSPECT) reconstruction methods were used that compensated for attenuation, scatter, and the collimator-detector response. Planar images were processed with a conventional (CPlanar) method that used geometric mean attenuation and triple-energy window scatter compensation and a quantitative planar (QPlanar) processing method that used model-based compensation for image degrading effects. Residence times were estimated from activity estimates made at each of five time points. The authors also evaluated hybrid methods that used CPlanar or QPlanar time-activity curves rescaled to the activity estimated from a single QSPECT image. The methods were evaluated in terms of mean relative error and standard deviation of the

  9. Derivation of a Multiparameter Gamma Model for Analyzing the Residence-Time Distribution Function for Nonideal Flow Systems as an Alternative to the Advection-Dispersion Equation

    DOE PAGESBeta

    Embry, Irucka; Roland, Victor; Agbaje, Oluropo; Watson, Valetta; Martin, Marquan; Painter, Roger; Byl, Tom; Sharpe, Lonnie

    2013-01-01

    A new residence-time distribution (RTD) function has been developed and applied to quantitative dye studies as an alternative to the traditional advection-dispersion equation (AdDE). The new method is based on a jointly combined four-parameter gamma probability density function (PDF). The gamma residence-time distribution (RTD) function and its first and second moments are derived from the individual two-parameter gamma distributions of randomly distributed variables, tracer travel distance, and linear velocity, which are based on their relationship with time. The gamma RTD function was used on a steady-state, nonideal system modeled as a plug-flow reactor (PFR) in the laboratory to validate themore » effectiveness of the model. The normalized forms of the gamma RTD and the advection-dispersion equation RTD were compared with the normalized tracer RTD. The normalized gamma RTD had a lower mean-absolute deviation (MAD) (0.16) than the normalized form of the advection-dispersion equation (0.26) when compared to the normalized tracer RTD. The gamma RTD function is tied back to the actual physical site due to its randomly distributed variables. The results validate using the gamma RTD as a suitable alternative to the advection-dispersion equation for quantitative tracer studies of non-ideal flow systems.« less

  10. Emissions of an AVCO Lycoming 0-320-DIAD air cooled light aircraft engine as a function of fuel-air ratio, timing, and air temperature and humidity

    NASA Technical Reports Server (NTRS)

    Meng, P. R.; Skorobatckyi, M.; Cosgrove, D. V.; Kempke, E. E., Jr.

    1976-01-01

    A carbureted aircraft engine was operated over a range of test conditions to establish the exhaust levels over the EPA seven-mode emissions cycle. Baseline (full rich production limit) exhaust emissions at an induction air temperature of 59 F and near zero relative humidity were 90 percent of the EPA standard for HC, 35 percent for NOx, and 161 percent for CO. Changes in ignition timing around the standard 25 deg BTDC from 30 deg BTDC to 20 deg BTDC had little effect on the exhaust emissions. Retarding the timing to 15 deg BTDC increased both the HC and CO emissions and decreased NOx emissions. HC and CO emissions decreased as the carburetor was leaned out, while NOx emissions increased. The EPA emission standards were marginally achieved at two leanout conditions. Variations in the quantity of cooling air flow over the engine had no effect on exhaust emissions. Temperature-humidity effects at the higher values of air temperature and relative humidity tested indicated that the HC and CO emissions increased significantly, while the NOx emissions decreased.

  11. Carbon transfer, partitioning and residence time in the plant-soil system: a comparison of two 13CO2 labelling techniques

    NASA Astrophysics Data System (ADS)

    Studer, M. S.; Siegwolf, R. T. W.; Abiven, S.

    2014-03-01

    Various 13CO2 labelling approaches exist to trace carbon (C) dynamics in plant-soil systems. However, it is not clear if the different approaches yield the same results. Moreover, there is no consistent way of data analysis to date. In this study we compare with the same experimental setup the two main techniques: pulse and continuous labelling. We evaluate how these techniques perform to estimate the C transfer time, the C partitioning along time and the C residence time in different plant-soil compartments. We used identical plant-soil systems (Populus deltoides × nigra, Cambisol soil) to compare the pulse labelling approach (exposure to 99 atom % 13CO2 for three hours, traced for eight days) with a continuous labelling (exposure to 10 atom % 13CO2, traced for 14 days). The experiments were conducted in climate chambers under controlled environmental conditions. Before label addition and at four successive sampling dates, the plant-soil systems were destructively harvested, separated into leaves, petioles, stems, cuttings, roots and soil and soil microbial biomass was extracted. The soil CO2 efflux was sampled throughout the experiment. To model the C dynamics we used an exponential function to describe the 13C signal decline after pulse labelling. For the evaluation of the 13C distribution during the continuous labelling we applied a logistic function. Pulse labelling is best suited to assess the minimum C transfer time from the leaves to other compartments, while continuous labelling can be used to estimate the mean transfer time through a compartment, including short-term storage pools. The C partitioning between the plant-soil compartments obtained was similar for both techniques, but the time of sampling had a large effect: shortly after labelling the allocation into leaves was overestimated and the soil 13CO2 efflux underestimated. The results of belowground C partitioning were consistent for the two techniques only after eight days of labelling, when the

  12. Parametric time-series analysis of daily air pollutants of city of Shumen, Bulgaria

    NASA Astrophysics Data System (ADS)

    Ivanov, A.; Voynikova, D.; Gocheva-Ilieva, S.; Boyadzhiev, D.

    2012-10-01

    The urban air pollution is one of the main factors determining the ambient air quality, which affects on the human health and the environment. In this paper parametric time series models are obtained for studying the distribution over time of primary pollutants as sulphur and nitrogen oxides, particulate matter and a secondary pollutant ground level ozon in the town of Shumen, Bulgaria. The methods of factor analysis and ARIMA are used to carry out the time series analysis based on hourly average data in 2011 and first quarter of 2012. The constructed models are applied for a short-term air pollution forecasting. The results are estimated on the basis of national and European regulation indices. The sources of pollutants in the region and their harmful effects on human health are also discussed.

  13. Exploiting crowdsourced observations: High-resolution mapping of real-time urban air quality throughout Europe

    NASA Astrophysics Data System (ADS)