PubMed Health⌕ Search

Biomedical subjects

S Krupa

Publications and source records attributed to S Krupa.

16 recordsLinked to original sources
PubMed2006

Quantifying submarine groundwater discharge in the coastal zone via multiple methods.

Submarine groundwater discharge (SGD) is now recognized as an important pathway between land and sea. As such, this flow may contribute to the biogeochemical and other marine budgets of near-shore waters. These discharges typically display significant spatial and temporal variability making assessments difficult. Groundwater seepage is patchy, diffuse, temporally variable, and may involve multiple aquifers. Thus, the measurement of its magnitude and associated chemical fluxes is a challenging enterprise. A joint project of UNESCO and the International Atomic Energy Agency (IAEA) has examined several methods of SGD assessment and carried out a series of five intercomparison experiments in different hydrogeologic environments (coastal plain, karst, glacial till, fractured crystalline rock, and volcanic terrains). This report reviews the scientific and management significance of SGD, measurement approaches, and the results of the intercomparison experiments. We conclude that while the process is essentially ubiquitous in coastal areas, the assessment of its magnitude at any one location is subject to enough variability that measurements should be made by a variety of techniques and over large enough spatial and temporal scales to capture the majority of these changing conditions. We feel that all the measurement techniques described here are valid although they each have their own advantages and disadvantages. It is recommended that multiple approaches be applied whenever possible. In addition, a continuing effort is required in order to capture long-period tidal fluctuations, storm effects, and seasonal variations.

Brazil↗
PubMed2003

A multi-variate statistical model integrating passive sampler and meteorology data to predict the frequency distributions of hourly ambient ozone (O3) concentrations.

A multi-variate, non-linear statistical model is described to simulate passive O3 sampler data to mimic the hourly frequency distributions of continuous measurements using climatologic O3 indicators and passive sampler measurements. The main meteorological parameters identified by the model were, air temperature, relative humidity, solar radiation and wind speed, although other parameters were also considered. Together, air temperature, relative humidity and passive sampler data by themselves could explain 62.5-67.5% (R(2)) of the corresponding variability of the continuously measured O3 data. The final correlation coefficients (r) between the predicted hourly O3 concentrations from the passive sampler data and the true, continuous measurements were 0.819-0.854, with an accuracy of 92-94% for the predictive capability. With the addition of soil moisture data, the model can lead to the first order approximation of atmospheric O3 flux and plant stomatal uptake. Additionally, if such data are coupled to multi-point plant response measurements, meaningful cause-effect relationships can be derived in the future.

Air Pollutants↗
PubMed2001

Relationships between passive sampler and continuous ozone (O3 ) measurement data in ecological effects research.

In ecological effects research, there is a rapid increase in the application of passive sampling techniques for measuring ambient ozone (O3) concentrations. Passive samplers provide data on cumulative exposures of a plant to a pollutant. However, O3 is not an accumulative contaminant within the plant tissue, and use of prolonged passive sampling durations cannot account for the dynamics of the occurrences of O3 that have a significant influence on the plant response. Therefore, a stochastic Weibull probability model was previously developed and applied to a site in Washington State (1650 m MSL) to simulate the cumulative exposure data from a passive sampler, to mimic the corresponding frequency distributions of hourly O3 concentrations that would otherwise have been obtained by continuous monitoring. At that site the correlation between the actual passive sampler and the continuous monitor data was R2 = 0.74. The simulation of the hourly O3 data was based on and compared with the results obtained from a colocated continuous monitor. In this paper we report the results of the model application to data from an unrelated monitoring site (New Hampshire, 476 m MSL) with poor correlation between the passive sampling and continuous monitoring (R2 = 0.24). In addition, as opposed to the previous work, we provide comparisons of the frequency distributions of the hourly O3 concentrations obtained by the simulation and the actual continuous monitoring. In spite of the major difference in the R2 values, at both sites the simulation provided very satisfactory results within the 95% confidence interval, suggesting its broad applicability. The final objective of this overall approach is to develop a generic model that can simulate reasonably well the occurrences of ambient O3 concentrations that are dependent upon the elevation of the measurement site and the synoptic and local meteorology. Such an effort would extend the relative utility of the passive sampling data in explaining stochastic plant responses.

Computer Simulation↗
PubMed2001

Use of passive ambient ozone (O3) samplers in vegetation effects assessment.

A stochastistic, Weibull probability model was developed and verified to simulate the underlying frequency distributions of hourly ozone (O3) concentrations (exposure dynamics) using the single, weekly mean values obtained from a passive (sodium nitrite absorbent) sampler. The simulation was based on the data derived from a co-located continuous monitor. Although at the moment the model output may be considered as being specific to the elevation and location of the study site, the results were extremely good. This effort for the approximation of the O3 exposure dynamics can be extended to other sites with similar data sets and in developing a generalized understanding of the stochastic O3 exposure-plant response relationships, conferring measurable benefits to the future use of passive O3 samplers, in the absence of continuous monitoring.

Air Pollutants↗
PubMed1999

Photochemical oxidants: state of the science.

Atmospheric photochemical processes resulting in the production of tropospheric ozone (O(3)) and other oxidants are described. The spatial and temporal variabilities in the occurrence of surface level oxidants and their relationships to air pollution meteorology are discussed. Models of photooxidant formation are reviewed in the context of control strategies and comparisons are provided of the air concentrations of O(3) at select geographic locations around the world. This overall oxidant (O(3)) climatology is coupled to human health and ecological effects. The discussion of the effects includes both acute and chronic responses, mechanisms of action, human epidemiological and plant population studies and briefly, efforts to establish cause-effect relationships through numerical modeling. A short synopsis is provided of the interactive effects of O(3) with other abiotic and biotic factors. The overall emphasis of the paper is on identifying the current uncertainties and gaps in our understanding of the state of the science and some suggestions as to how they may be addressed.

Journal Article↗
PubMed1998

Impaired circadian waking arousal in narcolepsy-cataplexy.

The 24-hour sleep/wake distributions of untreated patients with narcolepsy-cataplexy and matched normal habitual nappers were compared using home ambulatory monitoring. Subjects followed their usual sleep patterns including, for the habitual nappers, a self-selected daytime nap. There were no differences in 24-hour totals of sleep between groups other than a small increase in SWS in narcolepsy. Narcolepsy showed greater amounts of day sleep (stages 2, SWS, REM and total sleep) and less night sleep (stage 2, total sleep). Data were collapsed into 5 min epochs and entered into a matrix. The data in the two groups were then "wrapped" (re-aligned) around the 24 hours with phase 0 as each of the times of: evening sleep onset, onset of SWS, mid-point of night sleep and moment of morning awakening. In habitual nappers alignment beginning at morning wake-up produced the highest amplitude, least temporal dispersion and greatest kurtosis of daytime sleep (naps). The 24-hour sleep/wake distribution curves of both subject groups (data aligned at morning wake-up) based on collapsed data into 5 min bins then underwent curve fitting using 15th order polynomial regression. As with visual analyses of the raw data, the curve fits confirmed that the peak in daytime sleep propensity in narcoleptics was earlier by about 40 (2.66 hours). It was concluded that decreased daytime amplitude of a circadian arousal system was the most parsimonious explanation for the increased amount, broader temporal distribution and relative phase advance of day sleep in narcolepsy and that, as well, such a mechanism could explain a number of other features of the disease.

Chronobiology Disorders↗
PubMed1997

PLATIN (plant-atmosphere interaction) II: Co-occurrence of high ambient ozone concentrations and factors limiting plant absorbed dose.

There is an ongoing debate as to which components of the ambient ozone (O3) exposure dynamics best explain adverse crop yield responses. A key issue is regarding the importance of peak versus mid-range hourly ambient O3 concentrations. While in this paper the importance of peak atmospheric O3 concentrations is not discounted, if they occur at a time when plants are conducive for uptake, the corresponding importance of more frequently occurring mid-range O3 concentrations is described. The probability of co-occurrence of high O3 concentrations and O3 uptake limiting factors is provided using coherent data sets of O3 concentration, air temperature, air humidity, mean horizontal wind velocity and global radiation measured at representative US and German air quality monitoring sites. Using the PLant-ATmosphere INteraction (PLATIN) model, the significance of the aforementioned meteorological parameters on ozone uptake is examined. In addition, the limitations of describing the O3 exposure for plants under ambient, chamberless conditions by SUM06, AOT40 or W126 exposure indices are discussed.

Journal Article↗
PubMed1991

Future research directions and data requirements for developing ambient ozone guidelines or standards for agroecosystems.

The ambient air quality in Central Europe appears to have the potential to adversely affect the productivity of the agroecosystems in that geographic area. Therefore, there is a need to develop, validate, and apply air pollutant exposure-plant response models to explain the relationships between the stochastic chemical climate and ecosystem responses. Such models will have to include numerical terms for the effective air pollutant exposure regime to account for the fluxes of matter, energy and information within the ecosystem and its components. The structure and function of the ecosystem which are influenced by the air pollutant flux can be described by a combination of empirical and mechanistic models. A discussion of such an approach is presented in this paper.

Journal Article↗
PubMed1987

An analysis of numerical models of air pollutant exposure and vegetation response.

A number of empirical (statistical, regression oriented) and mechanistic (process oriented) models are presently available to examine the relationship between air pollution stress and plant response. These models have their strengths and weaknesses. In all these models, a major concern is the numerical definition of the pollutant exposure kinetics (dose). At present there are no numerical definitions of dose which make satisfactory biological sense. A key issue is the existence of a biological time clock where plants respond differently to the pollutant stress at different stages of their growth. On the other hand, policy makers and regulatory personnel prefer a simple approach which would facilitate implementation and administration of ambient air quality standards. Long-term air pollutant averaging techniques create artifacts due to the non-normal distribution of ambient concentrations. A more appropriate approach may be the use of 'median' and 'percentiles' computed from short duration pollutant concentrations. Such an approach would be free of the influence of the non-normal distribution, but would require the development of appropriate exposure-response models. Any transfer of results from unit level models to regional level leads to 'scaling error'. There is no general agreement among researchers on how to deal with the scale problem. While this situation persists, any policy formulated on regional impact assessment must acknowledge the uncertainty.

Journal Article↗
PubMed1984

The cytotoxic action in vitro of catalytically sulphurated unsaturated fatty acids on Ehrlich's ascites cancer and normal peritoneal exudate (leucocytes).

Diethanolamine salts of the catalytically sulphurated oleic acid (X-303/1) and of the catalytically sulphurated fatty acids isolated from linseed oil (X-303/2) were found to exhibit a strong cytotoxic in vitro activity against Ehrlich ascites cancer cells with minimal cytotoxic effect on normal cells (leukocytes) of the peritoneal exudate in rabbits.

Animals↗
PubMed1977

Cytotoxic effect of fatty acids in vitro on Ehrlich exudative carcinoma cells and normal exudative cells (leukocytes).

A mixture of pure fatty acids isolated hydrolytically from linseed oil in the form of water-soluble salts with ethanolamine were examined for cytotoxicity for Ehrlich carcinoma and normal exudative cells. Cytotoxicity of the mixture was similar to that of salts of oleic and linolenic acids. On the other hand, the mixture of fatty acids and oleic acids was more toxic for normal exudative cells than linolenic acid.

Animals↗