Processes of evaporation from vegetation of the uplands of Scotland

1987 ◽  
Vol 78 (4) ◽  
pp. 327-334 ◽  
Author(s):  
R. L. Hall
Keyword(s):  
Diffusion Theory ◽  
Coniferous Forest ◽  
Significant Proportion ◽  
Indigenous Species ◽  
Transport Mechanisms ◽  
Model Predictions ◽  
Process Studies ◽  
Series Of Experiments ◽  
High Altitude Grassland ◽  
Snow Precipitation

ABSTRACTThe results of a series of experiments to study the physical processes governing the evaporation from upland vegetation in Scotland, i.e. coniferous forest, heather and grass, are described. Particular attention is given to the interception process occurring in heather, one of the dominant indigenous species in Scottish upland catchments. Attention is also given to the interception of snow precipitation which in the Scottish uplands is a significant proportion of the total precipitation. A comparison of the parameters describing the efficiency of the transport process of water vapour for coniferous forest and heather indicates that the process is more efficient than predicted by classical diffusion theory: additional transport mechanisms are considered. A simple model, based upon the results of the process studies, was applied to data from the Monachyle catchment (Balquhidder) and the model predictions compared with observations. This study, in conjunction with recent results from the Balquhidder catchment experiment, illustrates the necessity of further investigations to give a fuller understanding of the evaporation from high altitude grassland.

Transport Mechanisms in Electrokinetic Nanoscale Channels

2004 ◽  
Author(s):  
Sumita Pennathur ◽  
Juan G. Santiago
Keyword(s):  
Field Theory ◽  
Parametric Study ◽  
Nanometer Scale ◽  
Transport Mechanisms ◽  
Electrokinetic Transport ◽  
Zeta Potentials ◽  
Numerical Studies ◽  
Debye Layer ◽  
Model Predictions ◽  
Shape And Size

We investigate electrokinetic transport in nanometer-scale fluidic channels. Our study includes numerical studies of nanofluidic transport of both charged and uncharged analytes in conditions of finite Debye layer thickness and high zeta potentials. The models are based on continuum mass transport and field theory. We also perform an experimental parametric study using etched nanoscale channels. Experimental results agree with model predictions and show that bulk electrokinetic transport in nanoscale channels depends strongly on the shape and size of the EDL and on the effects of transverse electrophoretic migration.

Modelling Silver: Evaluation of German Experience

2008 ◽  
Author(s):  
Hanno van der Merwe ◽  
Dirk Olivier
Keyword(s):  
Diffusion Theory ◽  
Operating Conditions ◽  
Test Results ◽  
Transport Mechanisms ◽  
Transport Parameters ◽  
Transport Models ◽  
Dose Rates ◽  
Irradiation Test ◽  
High Temperature Reactor ◽  
Silver Release

For direct cycle gas cooled high temperature reactor designs, operating conditions may be limited as a result of excessive maintenance dose rates caused by the Ag-110m source term on the turbine. It is therefore important to accurately predict silver release from fuel during reactor operation. Traditionally diffusion models were used to derive transport parameters from limited irradiation testing of fuel materials and components. Best estimates for all applicable German fuel irradiation tests with defendable uncertainty ranges were never derived. However, diffusion theory and current parameters cannot account for all irradiation and heat-up test results, and for some tests, it appears unacceptably conservative. Other transport mechanisms have been suggested, and alternative calculation models are being considered. In this paper the applicable German irradiation test results are evaluated with a classic diffusion model as well as an alternative model called the Molecular Vapour transport Release (MVR) model. New transport models and parameters for silver in fuel materials are suggested and compared.

scholarly journals The detection of nocturnal N<sub>2</sub>O<sub>5</sub> as HNO<sub>3</sub> by alkali- and aqueous-denuder techniques

2013 ◽  
Vol 6 (2) ◽  
pp. 231-237 ◽  
Author(s):  
G. J. Phillips ◽  
U. Makkonen ◽  
G. Schuster ◽  
N. Sobanski ◽  
H. Hakola ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Gas Phase ◽  
Significant Proportion ◽  
Sampling Location ◽  
Ambient Conditions ◽  
Phase Component ◽  
Dinitrogen Pentoxide ◽  
Annular Denuder ◽  
Process Studies ◽  
Measurement Campaigns

Abstract. The almost total anthropogenic control of the nitrogen cycle has led to wide ranging trans-national and national efforts to quantify the effects of reactive nitrogen on the environment. A number of monitoring techniques have been developed for the measurement of nitric acid and subsequent estimation of nitrogen deposition within large networks and for process studies on shorter measurement campaigns. We discuss the likelihood that many of these techniques are sensitive to another important gas-phase component of oxidized nitrogen: dinitrogen pentoxide (N2O5). We present measurements using a MARGA wet annular denuder device alongside measurements of N2O5 with a discussion of evidence from the laboratory and the field which suggests that alkali- and aqueous-denuder measurements are sensitive to the sum of HNO3 + 2N2O5. Nocturnal data from these denuder devices should be treated with care before using HNO3 concentrations derived from these data. This is a systematic error which is highly dependent on ambient conditions and is likely to cause systematic misinterpretation of datasets in periods where N2O5 is significant proportion of NOy. It is also likely that deposition estimates of HNO3 via data obtained with these methods is compromised to greater and lesser extents depending on the season and environment of the sampling location.

Peritoneal physicochemical transport mechanisms: Hypotheses, models and controversies

2021 ◽  
pp. 089686082110024
Author(s):  
Matthew B Wolf
Keyword(s):  
Lymph Flow ◽  
Time Varying ◽  
Transport Mechanisms ◽  
Mean Values ◽  
Intraperitoneal Pressure ◽  
Model Predictions ◽  
Time Varying Parameters ◽  
Transport Kinetic ◽  
The Mean ◽  
Parameter Values

This study answers criticisms by Waniewski et al. of the recent paper by Wolf on peritoneal transport kinetic models. Their criticisms centre on the accuracy of the data used for model fits, the hypothesis presented, which involves changes in glucose membrane parameters at high peritoneal glucose concentration and on the necessary techniques required to achieve accurate model parameter estimation. In response, this article shows that (1) the mean values previously captured from graphical depictions of Heimburger et al. are not different than those captured from the recent Waniewski et al. graphs, (2) a much simpler hypothesis is proposed, which centres on intraperitoneal pressure-induced lymph flow during the dialysis dwell and (3) the finding that the new model predictions, with only two constant parameter values, as estimated by the Powell algorithm, give a closer fit than the Waniewski model, which uses many time-varying parameters. The current findings again bring into question of the validity of their vasodilation hypothesis, leading to transient changes in capillary surface area during the dwell.

Estimating forest productivity in the eastern Siskiyou Mountains of southwestern Oregon using a satellite driven process model, 3-PGS

2001 ◽  
Vol 31 (1) ◽  
pp. 143-154 ◽  
Author(s):  
N C Coops ◽  
R H Waring
Keyword(s):  
Process Model ◽  
Drought Index ◽  
Net Primary Production ◽  
Coniferous Forest ◽  
Soil Survey ◽  
Weather Data ◽  
Productive Capacity ◽  
Water Storage Capacity ◽  
Gross Photosynthesis ◽  
Model Predictions

The 3-PGS (physiological principles for predicting growth using satellite data) model generates monthly estimates of transpiration, photosynthesis, and net primary production (NPP), the latter derived as a fixed proportion (0.47) of gross photosynthesis. To assess the reliability of a simplified process model (3-PGS) to predict the productive capacity of coniferous forest across diverse landscapes in southwestern Oregon, we first used a geographic information system to display and manipulate basic data. This involved the following steps: (i) extrapolate monthly mean weather data to reflect topographic variation; (ii) transform monthly temperature extremes to spatial resolution of 4 ha and estimate incoming solar radiation, subfreezing days per month, daytime vapor pressure deficits, and mean temperatures; (iii) convert statewide soil survey maps into topographically adjusted estimates of soil fertility and water storage capacity (θ); and (iv) acquire satellite-derived estimates of the faction of light intercepted by vegetation during midsummer. Model predictions of soil water availability during summer months compared well with those reported from published measurements of predawn water potentials at three contrasting sites and with measurements acquired at the end of seasonal drought at 18 sites (r2 = 0.78 with mean monthly modeled drought index; r2 = 0.57 with seasonal modeled drought index). Similarly, seasonal shifts in the relative importance of various climatic and edaphic variables closely matched those defined in previously published studies. Finally, model predictions of maximum annual aboveground growth were compared with those derived from forestry yield tables based on height-age relationships with a resulting r2 of 0.76, and a standard error of 1.2 m3·ha-1·year-1 (P < 0.01).

scholarly journals Depth- and range-dependent variation in the performance of aquatic telemetry systems: understanding and predicting the susceptibility of acoustic tag–receiver pairs to close proximity detection interference

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4249 ◽  
Author(s):  
Stephen R. Scherrer ◽  
Brendan P. Rideout ◽  
Giacomo Giorli ◽  
Eva-Marie Nosal ◽  
Kevin C. Weng
Keyword(s):  
Average Distance ◽  
Mechanistic Model ◽  
Proximity Detection ◽  
Average Maximum ◽  
Close Proximity ◽  
Model Predictions ◽  
Acoustic Tags ◽  
Series Of Experiments ◽  
Path Lengths ◽  
Passive Acoustic

Background Passive acoustic telemetry using coded transmitter tags and stationary receivers is a popular method for tracking movements of aquatic animals. Understanding the performance of these systems is important in array design and in analysis. Close proximity detection interference (CPDI) is a condition where receivers fail to reliably detect tag transmissions. CPDI generally occurs when the tag and receiver are near one another in acoustically reverberant settings. Here we confirm transmission multipaths reflected off the environment arriving at a receiver with sufficient delay relative to the direct signal cause CPDI. We propose a ray-propagation based model to estimate the arrival of energy via multipaths to predict CPDI occurrence, and we show how deeper deployments are particularly susceptible. Methods A series of experiments were designed to develop and validate our model. Deep (300 m) and shallow (25 m) ranging experiments were conducted using Vemco V13 acoustic tags and VR2-W receivers. Probabilistic modeling of hourly detections was used to estimate the average distance a tag could be detected. A mechanistic model for predicting the arrival time of multipaths was developed using parameters from these experiments to calculate the direct and multipath path lengths. This model was retroactively applied to the previous ranging experiments to validate CPDI observations. Two additional experiments were designed to validate predictions of CPDI with respect to combinations of deployment depth and distance. Playback of recorded tags in a tank environment was used to confirm multipaths arriving after the receiver’s blanking interval cause CPDI effects. Results Analysis of empirical data estimated the average maximum detection radius (AMDR), the farthest distance at which 95% of tag transmissions went undetected by receivers, was between 840 and 846 m for the deep ranging experiment across all factor permutations. From these results, CPDI was estimated within a 276.5 m radius of the receiver. These empirical estimations were consistent with mechanistic model predictions. CPDI affected detection at distances closer than 259–326 m from receivers. AMDR determined from the shallow ranging experiment was between 278 and 290 m with CPDI neither predicted nor observed. Results of validation experiments were consistent with mechanistic model predictions. Finally, we were able to predict detection/nondetection with 95.7% accuracy using the mechanistic model’s criterion when simulating transmissions with and without multipaths. Discussion Close proximity detection interference results from combinations of depth and distance that produce reflected signals arriving after a receiver’s blanking interval has ended. Deployment scenarios resulting in CPDI can be predicted with the proposed mechanistic model. For deeper deployments, sea-surface reflections can produce CPDI conditions, resulting in transmission rejection, regardless of the reflective properties of the seafloor.

Human ecology of sacred space: Church forests in the highlands of northwestern Ethiopia

2017 ◽  
Vol 45 (3) ◽  
pp. 291-300 ◽  
Author(s):  
MORGAN L. RUELLE ◽  
KARIM-ALY KASSAM ◽  
ZEMEDE ASFAW
Keyword(s):  
Significant Proportion ◽  
Woody Species ◽  
Church History ◽  
Agricultural Landscapes ◽  
Indigenous Species ◽  
Orthodox Christian ◽  
Sacred Spaces ◽  
Christian Churches ◽  
Alternative Material ◽  
Trees And Shrubs

SUMMARYIn the highlands of northwestern Ethiopia, Orthodox Christian churches provide habitats for plants that have become rare in the surrounding agricultural landscapes. The objective of this paper is to investigate why and how the local clergy and laypeople protect and promote woody plants within their sacred spaces. Interviews at 11 churches in the Debark District of North Gonder generated a list of 47 woody species, of which most are rare in the rest of the landscape. Three tree species (indigenous cedar, Juniperus procera; indigenous olive, Olea europaea subsp. cuspidata; and exotic Eucalyptus globulus) were identified as most important. While cedar and olive are symbols of tradition and witnesses to church history, eucalyptus is a source of income and alternative material for church construction and repair. A significant proportion of indigenous species within Debark's church forests were said to have been planted, including cedars and olives. Knowledge that these species are cultivated enhances the conservation value of these forests by inspiring local people to continue planting trees and shrubs. In addition to serving as refugia for rare species, Ethiopia's church forests nurture the knowledge necessary to promote plant diversity in the rest of the landscape and serve as archetypes for community-driven conservation.

scholarly journals The detection of nocturnal N<sub>2</sub>O<sub>5</sub> as HNO<sub>3</sub> by alkali- and aqueous-denuder techniques

2012 ◽  
Vol 5 (5) ◽  
pp. 7489-7505
Author(s):  
G. J. Phillips ◽  
U. Makkonen ◽  
G. Schuster ◽  
N. Sobanski ◽  
H. Hakola ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Gas Phase ◽  
Significant Proportion ◽  
Sampling Location ◽  
Ambient Conditions ◽  
Phase Component ◽  
Dinitrogen Pentoxide ◽  
Annular Denuder ◽  
Process Studies ◽  
Measurement Campaigns

Abstract. The almost total anthropogenic control of the nitrogen cycle has led to wide ranging trans-national and national efforts to quantify the effects of reactive nitrogen on the environment. A number of monitoring techniques have been developed for the measurement of nitric acid and subsequent estimation of nitrogen deposition within large networks and for process studies on shorter measurement campaigns. We discuss the likelihood that many of these techniques are sensitive to another important gas-phase component of oxidized nitrogen; dinitrogen pentoxide (N2O5). We present measurements using a MARGA wet annular denuder device alongside measurements of N2O5 with a discussion of evidence from the laboratory and the field which suggests that alkali- and aqueous-denuder measurements are sensitive to the sum of HNO3 + N2O5. Nocturnal data from these denuder devices should be treated with care before using HNO3 concentrations derived from these data. This is a systematic error which is highly dependent on ambient conditions and is likely to cause systematic misinterpretation of datasets in periods where N2O5 is significant proportion of NOy. It is also likely that deposition estimates of HNO3 via data obtained with these methods is compromised to greater or lesser extents depending on the season and environment of the sampling location.

Intracellular transport mechanisms: a critique of diffusion theory

1995 ◽  
Vol 176 (2) ◽  
pp. 261-272 ◽  
Author(s):  
P.S. Agutter ◽  
P.C. Malone ◽  
D.N. Wheatley
Keyword(s):  
Intracellular Transport ◽  
Diffusion Theory ◽  
Transport Mechanisms
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