PCB Concentration Trends in Lake Michigan Coho (Oncorhynchus kisutch) and Chinook Salmon (O. tshawytscha)

1994 ◽  
Vol 51 (6) ◽  
pp. 1384-1390 ◽  
Author(s):  
Craig A. Stow ◽  
Stephen R. Carpenter ◽  
James F. Amrhein
Keyword(s):  
Exponential Decay ◽  
Chinook Salmon ◽  
Management Practices ◽  
Lake Michigan ◽  
Oncorhynchus Kisutch ◽  
Parameter Estimates ◽  
Concentration Data ◽  
Decay Model ◽  
Double Exponential ◽  
Exponential Decay Model

Lake Michigan coho (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) PCB concentration data from 1974 to 1990 were examined. The mean and variance of the concentrations exhibited a generally decreasing pattern in each species. Three alternative models, an exponential decay model, a double exponential decay model, and an exponential decay model with a nonzero asymptote, were fit to the data. The double exponential model provided the best fit for both species. Estimated rate coefficients for this model indicated that an early rapid decrease in PCBs has slowed and that PCBs may currently be increasing in coho and chinook salmon. These PCB increases may be the indirect result of a decline in the alewife (Alosa pseudoharengus) forage base that occurred during the 1980s. Parameter estimates from the nonzero asymptote model suggested that PCB levels may not decrease substantially below the current 2 mg/kg FDA action level. Significant decreases of PCB concentrations in coho and chinook salmon may depend on fisheries management practices that promote higher fish growth rates.

Tree windthrow and forest soil turnover

1989 ◽  
Vol 19 (3) ◽  
pp. 386-389 ◽  
Author(s):  
D. A. Norton
Keyword(s):  
Forest Soil ◽  
Exponential Decay ◽  
Half Life ◽  
Soil Development ◽  
Turnover Time ◽  
Important Influence ◽  
Plant Distribution ◽  
Canopy Trees ◽  
Decay Model ◽  
Exponential Decay Model

Soil turnover as a result of tree windthrow has an important influence on soil development and plant distribution in forests. Estimates of the time needed for soil turnover in a given area are often made, but unless these take into account the potential for reestablishment of canopy trees onto sites previously affected by windthrow, they are likely to substantially underestimate turnover time. Soil turnover is not a regular, uniform process, but rather results in a mosaic of soils with different turnover histories. Because soil turnover follows an exponential decay model, some area of soil will never be turned over. As it is therefore not possible to define the time when all the soil in an area has been turned over, it is proposed that soil turnover half-life (the time at which half the soil has been turned over) be used as a measure of soil turnover.

scholarly journals Exponential Decay Model of TVOC Emission from Indoor Building Materials

2020 ◽  
Vol 435 ◽  
pp. 012035
Author(s):  
Y Zhang ◽  
Y R Niu ◽  
Y Liu ◽  
Y F Wu ◽  
J X Jiang ◽  
...  
Keyword(s):  
Exponential Decay ◽  
Building Materials ◽  
Decay Model ◽  
Exponential Decay Model

Flow Properties and Passive Scalar Transport in a Model Room With Relevance to Ventilation Efficiency

1996 ◽  
Vol 210 (4) ◽  
pp. 297-307 ◽  
Author(s):  
İ B Özdemir ◽  
J H Whitelaw ◽  
A F Biçen
Keyword(s):  
Time Scales ◽  
Exponential Decay ◽  
Passive Scalar ◽  
Scalar Transport ◽  
Mixing Efficiency ◽  
Decay Model ◽  
Passive Scalar Transport ◽  
Exponential Decay Model ◽  
Statistical Time ◽  
Model Room

This paper describes an experimental investigation of air flow patterns and related passive scalar transport inside a model room with emphasis on the statistical time-scales of the dispersion process and the local ventilation effectiveness. Time-averaged and instantaneous structures of the turbulent flow were examined by local measurements inside a negatively pressurized cubic enclosure of 2 m side dimension and ventilated through single-supply and exhaust registers at an extract flowrate of 1.81 m3/min with a corresponding air change of 13.6 per hour. Sulphur hexafluoride was introduced at the centre of the enclosure and used to mark the flow. The distributions of its time-averaged concentration inside the room were used to deduce the degree of mixing and passive scalar transport. The measurements of the time-averaged flow field showed that the arrangement with no sources of forced internal mixing resulted in the ventilating flow occurring in a channel connecting the supply and exhaust. Outside this jet-like main stream and particularly in corners, the flow stagnated with high concentrations of the tracer gas in these regions. Time variations of the instantaneous local concentration values at different locations inside the room for a process of purging following steady injection were used to estimate the probability density function of the local residence age whose shape provided further experimental evidence of the prolonged dilution due to pollutant fluid which entered stagnation zones. The results also showed that the statistical time-scales of the dispersion and the mixing efficiency are independent of the level of the steady pollutant generation. The ratio of the mean age to its standard deviation is recommended as a local mixedness factor and comparison with the mixing efficiency defined on the basis of integral time-scales and the exponential decay model revealed that it represents better the local variations, which is essential to assessing local indoor air quality. The extent of validity of the exponential decay model was also evaluated by comparing the time constant of this model with model-independent integral time-scales and it is shown that the underlying assumptions of the exponential decay model precludes the representation of spatial gradients.

Inverse method to estimate mineralisation rate constants for nitrogen simulation models: interaction between sampling strategy and quality of parameter estimates

Soil Research ◽  
1998 ◽  
Vol 36 (1) ◽  
pp. 1 ◽  
Author(s):  
V. O. Snow ◽  
W. J. Bond
Keyword(s):  
Management Practices ◽  
Agricultural Practices ◽  
Sampling Strategy ◽  
Simulation Models ◽  
Simulation Modelling ◽  
Land Application ◽  
Parameter Estimates ◽  
Concentration Data ◽  
Data Set ◽  
Sustainable Agricultural Practices

Sustainable agricultural practices and land application of wastes require that the accession of nitrate to groundwater be within acceptable limits. Simulation modelling is a valuable aid to the development and testing of management practices that achieve this goal, but requires unbiased and precise parameter estimates. Here we consider the role of simple lysimeter-based techniques, which may yield only a single integral observation in the form of total solute leached or total drainage, in supplementing infrequent concentration data for the purposes of parameter optimisation. The utility of such techniques was evaluated using a simulation model to create a ‘no-error data set’ of nitrate concentration values and summary observations of the total mass of nitrate leached and total drainage over a 182-day period. From that no-error data set a more realistic data set incorporating random error was created. By using those concentrations, the value of the mass of nitrate leached or total drainage was evaluated by their effect on the unbias and precision of optimised mineralisation or evaporation parameters. The effects of observation weight, error in the observations, and 2 other experimental strategies involving a higher intensity of solute sampling were also tested. It was found that the summary observations, such as those obtainable from simple lysimeter-based techniques, had the potential to reduce bias and improve the precision of the optimised parameters. The consequence of this effectiveness was that error in the summary observations led to considerable error in the optimised parameters.

scholarly journals A Novel Curve Database for Moisture Evaluation of Transformer Oil-Immersed Cellulose Insulation Using FDS and Exponential Decay Model

IEEE Access ◽  
2020 ◽  
Vol 8 ◽  
pp. 180728-180737
Author(s):  
Jiefeng Liu ◽  
Zixiao Wang ◽  
Xianhao Fan ◽  
Yiyi Zhang ◽  
Jiaqi Wang
Keyword(s):  
Exponential Decay ◽  
Transformer Oil ◽  
Decay Model ◽  
Exponential Decay Model ◽  
Cellulose Insulation

scholarly journals A volumetric prediction model for postoperative cyst shrinkage

2021 ◽  
Author(s):  
Balazs Feher ◽  
Florian Frommlet ◽  
Stefan Lettner ◽  
Reinhard Gruber ◽  
Letizia Elisabeth Nemeth ◽  
...  
Keyword(s):  
Decay Rate ◽  
Exponential Decay ◽  
Clinical Success ◽  
Volumetric Shrinkage ◽  
Ct Scans ◽  
Patient Specific ◽  
Cyst Volume ◽  
Decay Model ◽  
Jaw Cyst ◽  
Exponential Decay Model

Abstract Objectives With only limited information available on dimensional changes after jaw cyst surgery, postoperative cyst shrinkage remains largely unpredictable. We aimed to propose a model for volumetric shrinkage based on time elapsed since cyst surgery. Material and methods We used data from patients that underwent cyst enucleation or decompression between 2007 and 2017 and had at least three computed tomography (CT) scans per patient. We fitted one simple exponential decay model [V(t) = V0 · e−ɑt] and one model with a patient-specific decay rate [Vk(t) = V0 · e−βt + γkt]. Results Based on 108 CT scans from 36 patients (median age at surgery: 45.5 years, IQR: 32.3–55.3, 44% female), our simple exponential decay model is V(t) = V0· e−0.0035t where V(t) is the residual cyst volume after time t elapsed since surgery, V0 is the initial cyst volume, and e is the base of the natural logarithm. Considering a patient-specific decay rate, the model is Vk(t) = V0· e−0.0049t + γkt where γk is normally distributed, with expectation 0 and standard deviation 0.0041. Conclusions Using an exponential regression model, we were able to reliably estimate volumetric shrinkage after jaw cyst surgery. The patient-specific decay rate substantially improved the fit of the model, whereas adding specific covariates as interaction effects to model the decay rate did not provide any significant improvement. Clinical relevance Estimating postoperative cyst shrinkage is relevant for both treatment planning of jaw cyst surgery as well as evaluating the clinical success of the surgical approach.

scholarly journals Study of epidemiological behaviour of malaria and its control in the Purulia district of West Bengal, India (2016–2020)

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Sayantan Pradhan ◽  
Samrat Hore ◽  
Suman Kumar Maji ◽  
Simi Manna ◽  
Abhijit Maity ◽  
...  
Keyword(s):  
High Risk ◽  
Exponential Decay ◽  
West Bengal ◽  
Sharp Decrease ◽  
Age Group ◽  
Decay Model ◽  
Exponential Decay Model ◽  
The Government ◽  
Purulia District ◽  
Free Status

AbstractPurulia is a malaria-prone district in West Bengal, India, with approximately half of the blocks defined as malaria endemic. We analyzed the malaria case in each block of the Purulia district from January 1, 2016, to December 31, 2020. As per the API, 20 blocks of Purulia were assigned to four different categories (0–3) and mapped using ArcGIS software. An exponential decay model was fitted to forecast the trend of malaria cases for each block of Purulia (2021–2025). There was a sharp decrease in total malaria cases and API from 2016 to 2020 due to the mass distribution of LLINs. The majority of cases (72.63%) were found in ≥ 15-year age group. Males were more prone to malaria (60.09%). Malaria was highly prevalent among Scheduled Tribes (48.44%). Six blocks were reported in Category 3 (high risk) and none in Category 0 (no risk) in 2016, while no blocks were determined to be in Category 3, and three blocks were in Category 0 in 2020. The exponential decay model prediction is oriented towards gaining malaria-free status in thirteen blocks of Purulia by 2025. This study will incite the government to uphold and strengthen the current efforts to meet the malaria elimination goals.

An exponential decay model

2017 ◽  
pp. 95-106
Author(s):  
Minh Tuan Phung ◽  
Ly Thi Minh Pham
Keyword(s):  
Exponential Decay ◽  
Decay Model ◽  
Exponential Decay Model
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