Showing papers by "Colorado State University published in 1992"
TL;DR: The POM fraction was isolated by dispersing the soil in 5 g L-1 hexametaphosphate and passing the dispersed soil samples through a 53-micrometer sieve as mentioned in this paper.
Abstract: Many models have been constructed in an attempt to describe the dynamics of soil organic-matter (SOM) turnover, most of which include 2 to 3 kinetically defined organic-matter pools. Physical and chemical definition of these conceptualized SOM pools has been difficult. We describe a simple method for dispersion of soil to isolate a particulate organic-matter (POM) fraction that may represent an important SOM pool in grassland soils. The POM fraction was isolated by dispersing the soil in 5 g L-1 hexametaphosphate and passing the dispersed soil samples through a 53-micrometer sieve. We compared POM and mineral-associated C among three tillage treatments (20 yr under cultivation) and an undisturbed grassland at Sidney, NE. The POM C in the native sod represented 39% of the total soil organic C. Twenty years of bare-fallow, stubble-mulch, and no-till management reduced the C content in this fraction to 18, 19, and 25%, respectively, of the total organic C. The mineral-associated organic-matter fraction showed no reduction in C content in the bare-fallow treatment compared with the grassland soil but increased in the no-till and stubble-mulch treatments. Nitrogen dynamics generally mirrored those observed for C. Analysis of the POM fraction for lignin and cellulose content indicated that this fraction was 47% lignin and had a lignocellulose index of 0.7. The stable C-isotope composition of the POM fraction suggests that wheat-derived POM turns over faster than grass-derived POM. We suggest the POM fraction closely matches the characteristics of a SOM pool variously described as slow, decomposable, or stabilized organic matter
2,259 citations
TL;DR: In this paper, a range of applications of the Regional Atmospheric Modeling System (RAMS), a comprehensive mesoscale meterological modeling system, are discussed, including large eddy simulations (LES) and simulations of thunderstorms, cumulus fields, mesoscales, convective systems, mid-latitude cirrus clouds, winter storms, mechanically and thermally-forced meso-scale systems, and mesoscopic atmospheric disperision.
Abstract: This paper presents a range of applications of the Regional Atmospheric Modeling System (RAMS), a comprehensive mesoscale meterological modeling system. Applications discussed in this paper include large eddy simulations (LES) and simulations of thunderstorms, cumulus fields, mesoscale convective systems, mid-latitude cirrus clouds, winter storms, mechanically- and thermally-forced mesoscale systems, and mesoscale atmospheric disperision. A summary of current RAMS options is also presented. Improvements to RAMS currently underway include refinements to the cloud radiation, cloud microphysics, cumulus, and surface soil/vegetative parameterization schemes, the parallelization of the code, development of a more versatile visualization capability, and research into meso-α-scale cumulus parameterization.
1,685 citations
TL;DR: In this paper, a model combining the effects of deposition and condensation-freezing nucleation is formulated based on data obtained from continuous-flow diffusion chambers, which indicate an exponential variation of ice-nuclei concentrations with ice supersaturation reasonably independent of temperatures between −7° and −20°C.
Abstract: Two new primary ice-nucleation parameterizations are examined in the Regional Atmospheric Modeling System (RAMS) cloud model via sensitivity tests on a wintertime precipitation event in the Sierra Nevada region. A model combining the effects of deposition and condensation-freezing nucleation is formulated based on data obtained from continuous-flow diffusion chambers. The data indicate an exponential variation of ice-nuclei concentrations with ice supersaturation reasonably independent of temperatures between −7° and −20°C. Predicted ice concentrations from these measurements exceed values predicted by the widely used temperatures dependent Fletcher approximation by as much as one order of magnitude at temperatures warmer than −20°C. A contact-freezing nucleation model is also formulated based on laboratory data gathered by various authors using techniques that isolated this nucleation mode. Predicted contact nuclei concentrations based on the newer measurements are as much as three orders of mag...
842 citations
TL;DR: The reliability and validity data on an extensive study of the Suinn-Lew Asian Self-Identity Acculturation Scale (SL-ASIA) involving a sample of 324 adults were provided by as mentioned in this paper.
Abstract: The current report covers the reliability and validity data on an extensive study of the Suinn-Lew Asian Self-Identity Acculturation Scale (SL-ASIA) involving a sample of 324 adults. Concurrent validity results showed that the SL-ASIA scores were significantly correlated with demographic information hypothesized to reflect levels of Asian-American identity. For example, high SL-ASIA scores were found associated with having attended school in the U.S. over a longer period of time, during which time the subject's Asian identity would have been reduced. Factorial validity was determined by comparing factors obtained for the SL-ASIA with factors reported for a similar scale measuring ethnic identity of Hispanics, the ARSMA. Of the four interpretable factors reported for the ARSMA, three were identified for the SL-ASIA.
646 citations
TL;DR: Constraint caused by vegetation structure is the reason why regional ANPP-precipitation models have a steeper slope than long-term models and point out a weakness of exchanging space for time in predicting production patterns.
Abstract: We evaluated the relationship between annual forage production and annual and seasonal precipitation and temperature at a shortgrass steppe site in north-central Colorado using a long-term data set (52 yr). We also constructed a relationship between forage production and aboveground net primary production (ANPP). Precipitation fluctuated randomly, but temperature had clear warming and cooling trends including a 17-yr warming trend from 1974 to 1990. Forage production was significantly related to both annual and seasonal precipitation but not temperature. Precipitation events between 15 and 30 mm accounted for most of the variability in production because they accounted for most of the variability in precipitation and because they wetted the soil layers that have the largest effect on production. Forage production amplified variability in annual precipitation. Production showed time lags of several years in responding to increases in precipitation. Change in vegetation structure has a characteristic response time, which contrains production responses in wet years. Constraint caused by vegetation structure is the reason why regional ANPP-precipitation models have a steeper slope than long-term models and point out a weakness of exchanging space for time in predicting production patterns.
644 citations
06 Jun 1992
TL;DR: An overview of this body of literature drawing out common themes and providing, where possible, the emerging wisdom about what seems to work and what does not is provided.
Abstract: Various schemes for combining genetic algorithms and neural networks have been proposed and tested in recent years, but the literature is scattered among a variety of journals, proceedings and technical reports. Activity in this area is clearly increasing. The authors provide an overview of this body of literature drawing out common themes and providing, where possible, the emerging wisdom about what seems to work and what does not. >
592 citations
TL;DR: In this paper, the effects of organic matter and fertilizer additions on soil organic-matter dynamics were analyzed using the CENTURY model, using results from a 30yr-old Swedish field experiment, using the Century model.
Abstract: To study the effects of organic matter and fertilizer additions on soil organic-matter (SOM) dynamics, we analyzed results from a 30yr-old Swedish field experiment, using the CENTURY model. Field treatments on a sandy clay loam included biannual addition (up to 4000 kg C ha ) of straw, sawdust, and no organic additions, with and without N fertilizer (80 kg N ha), and green manure, farmyard manure, and bare fallow. Soil C and N, crop production (small-grain and root crops), N uptake, and mineralization and immobilization of N were modeled and compared with field measurements. Changes in soil C and N, as much as 30% after 30 yr, were generally well represented by the model. Most of the treatment differences in SOM could be explained by the rate of organic-matter input, its lignin content, and C/N ratio, plus the effect of N fertilizer on belowground C inputs. However, there appeared to be additional positive effects of N supply on SOM accumulation that were not fully explained by the model. The quality of organic amendments strongly influenced N uptake and crop productivity, through controls on N mineralization and immobilization. Mean annual N uptake ranged from a low of 3.1 g m 2 in sawdust-amended soil to a high of 9.2 g m 2 in fertilized, strawamended soil. Simulated N losses accounted for 7 to 20% of total N inputs. Nitrogen-balance estimates by the model were consistent with the observed data for four of the treatments, but treatments with low N availability appeared to have additional, unexplained N inputs. View complete article To view this complete article, insert Disc 5 then click button8
574 citations
TL;DR: A methodology for representing mental models as maps, extracting these maps from texts, and analyzing and comparing the extracted maps is described, supporting both qualitative and quantitative comparisons of the resulting representations.
Abstract: When making decisions or talking to others, people use mental models of the world to evaluate choices and frame discussions. This paper describes a methodology for representing mental models as maps, extracting these maps from texts, and analyzing and comparing the extracted maps. The methodology employs a set of computer-based tools to analyze written and spoken texts. These tools support textual comparison both in terms of what concepts are present and in terms of what structures of information are present. The methodology supports both qualitative and quantitative comparisons of the resulting representations. This approach is illustrated using data drawn from a larger study of students learning to write where it is possible to compare the students' mental models with that of instructor. EXTRACTING, REPRESENTING AND ANALYZING MENTAL MODELS
565 citations
TL;DR: This paper examined the relationship between board composition and stock ownership and the passage of "poison pill" takeover defense provisions by U.S. industrial manufacturing firms and found that board composition was correlated with stock ownership.
Abstract: This research examined the relationships between board composition and stock ownership and the passage of “poison pill” takeover defense provisions by U.S. industrial manufacturing firms. Results i...
510 citations
Book•
27 Nov 1992TL;DR: Schmitt and Borman as discussed by the authors reviewed the book "Personnel Selection in Organizations, edited by Neal Schmitt and Walter C. Borman" and presented a review of the book's contents.
Abstract: The article presents a review of the book “Personnel Selection in Organizations,” edited by Neal Schmitt and Walter C. Borman.
485 citations
TL;DR: In this paper, the complexity of the sperm plasma membrane and the many steps in a cryopreservation procedure where membrane perturbations can occur are described, and an attempt has been made to describe the complexities of the SPM and its interaction with its components.
TL;DR: In this paper, the authors describe several theoretical approaches for modeling the diffusion, foraging behavior, and population dynamics of animals in heterogeneous landscapes, including: (1) scaling relationships derived from percolation theory and fractal geometry, (2) extensions of traditional patch-based metapopulation models, and (3) individual-based, spatially explicit models governed by local rules.
Abstract: Organisms respond to environmental heterogeneity at different scales and in different ways. These differences are consequences of how the movement characteristics of animals—their movement rates, directionality, turning frequencies, and turning angles—interact with patch and boundary features in landscape mosaics. The interactions of movement patterns with landscape features in turn produce spatial patterns in individual space-use, population dynamics and dispersion, gene flow, and the redistribution of nutrients and other materials. We describe several theoretical approaches for modeling the diffusion, foraging behavior, and population dynamics of animals in heterogeneous landscapes, including: (1) scaling relationships derived from percolation theory and fractal geometry, (2) extensions of traditional patch-based metapopulation models, and (3) individual-based, spatially explicit models governed by local rules. We conclude by emphasizing the need to couple theoretical models with empirical studies and the usefulness of ‘microlandscape’ investigations.
TL;DR: In this paper, a scale for assessing emotional attachment of individuals to their pets, the Lexington Attachment to Pets Scale (LAPS), was developed, having excellent psychometric properties.
Abstract: This paper reports on the development and psychometric evaluation of a scale for assessing emotional attachment of individuals to their pets. Previous attachment scales have suffered variously from low internal consistency and reliance on small or nonrepresentative samples for their development. Telephone interviews of a random, representative sample of 412 pet owners in Fayette County, Kentucky, were completed in September 1990; a 69.5 percent response rate was achieved. From a preliminary set of 42 questions, a final 23-question instrument, the Lexington Attachment to Pets Scale (LAPS), was developed, having excellent psychometric properties. The scale is suitable for use with dog and cat owners. Data on internal consistency, factor structure, and item response theory (IRT) modeling are presented, along with correlations between the LAPS and several domains of variables known to relate to pet attachment.
TL;DR: The theory of risk communication was tested with data on public perception of risk and response to aftershock warnings during the post-impact Loma Prieta earthquake emergency as discussed by the authors, and it was concluded that the social psychological process which explains postimpact public warning response is not identical to the one which explains public response to pre-impact warnings.
Abstract: The theory of risk communication was tested with data on public perception of risk and response to aftershock warnings during the post-impact Loma Prieta earthquake emergency. Findings from samples of households in Santa Cruz and San Francisco Counties were consistent, confirm established propositions, and suggest theoretical refinement. It was concluded that the social psychological process which explains post-impact public warning response is not identical to the one which explains public response to pre-impact warnings. The lack of mainshock damage created a “normalization bias” for non-victims. This bias constrained perception of risk to damaging aftershocks and protective response to warnings.
01 Jan 1992
TL;DR: A proper model is fully supported by the data, and has enough parameters to avoid bias, but not too many that precision is lost (the Principle of Parsimony).
Abstract: Selection of an appropriate model as the basis for data analysis is critical for valid inference. Fundamental to this issue is the concept that the datawill only “support” limited inference. A model should have enough structure and parameters to account adequately for the significant variability in the data, otherwise bias in the estimators is likely. However, if the model has too much structure or too many parameters, then precision is unnecessarily lost and “effects” may be inferred that are not justified by the data. A proper model is fully supported by the data, and has enough parameters to avoid bias, but not too many that precision is lost (the Principle of Parsimony) .Thus, for given data, there is a need to choose objectively from among alternative models, each based on biological considerations.
TL;DR: In this article, person-and context-oriented definitions of age were used to predict three sets of work outcomes: work attitudes, performance ratings, and reports of developmental practices, including subjective age, self-perceptions of age, and social age.
Abstract: Person- and context-oriented definitions of age were used to predict three sets of work outcomes: work attitudes, performance ratings, and reports of developmental practices. The five age measures included employee chronological age, employee subjective age (i.e., self-perceptions of age), and social age (i.e., others' perceptions of age), as well as self- and supervisors' perceptions of the employee's relative age (i.e., compared with the employee's work group). The study assessed (a) the relationships among the age measures, (b) the additive relationships among the age measures that predicted work outcomes, and (c) the interactive relationships among the age measures that predicted work outcomes. Each prediction received some support except for (b). Furthermore, many of the age--work-outcome relationships were replicated in the managerial sample. Implications for the use of alternative age measures are discussed.
TL;DR: Results with actual testing and debugging data suggest that neural-network models are better at endpoint predictions than analytic models, and can be more accurate than some commonly used analytic models.
Abstract: It is shown that neural network reliability growth models have a significant advantage over analytic models in that they require only failure history as input and not assumptions about either the development environment or external parameters. Using the failure history, the neural-network model automatically develops its own internal model of the failure process and predicts future failures. Because it adjusts model complexity to match the complexity of the failure history, it can be more accurate than some commonly used analytic models. Results with actual testing and debugging data which suggest that neural-network models are better at endpoint predictions than analytic models are presented. >
Book•
03 Dec 1992TL;DR: Wilson and the Age of Socialist Inquiry as mentioned in this paper and Searching for a New Diplomacy, searching for a new international order, is a political Autobiography of a political leader and an account of the origins of Progressive and Conservative Internationalism.
Abstract: Preface1A Political Autobiography32Wilson and the Age of Socialist Inquiry153Searching for a New Diplomacy314The Political Origins of Progressive and Conservative Internationalism485The Turning Point706Raising a New Flag: The League and the Coalition of 1916857"All the Texts of the Rights of Man": Manifestoes for Peace and War1058"If the War Is Too Strong": The Travail of Progressive Internationalism and the Fourteen Points1239Waiting for Wilson: The Wages of Delay and Repression14810"The War Thus Comes to an End"16711The Stern Covenanter19412"A Practical Document and a Humane Document"21013"The Thing Reaches the Depths of Tragedy"22714Wilson's Fate246Epilogue, Echoes from Pueblo271Abbreviations277Notes279Bibliography341Index359
Journal Article•
TL;DR: The hypothesis that proteins secreted or otherwise leaked from the dividing mycobacterium are pinocytosed from the phagosome and used by the infected macrophage as the key protective Ag leading to T cell sensitization explains why protective immunity is generated even while the organism is still multiplying in an apparently unrestrained manner.
Abstract: Recent evidence suggests the existence of at least two pathways of acquired specific resistance to Mycobacterium tuberculosis infection; the first consisting of cytokine-mediated activation of parasitized host cells by protective T cells, and the second involving the lysis of these cells by cytolytic T cells. Evidence presented in this report shows that both of the above mechanisms are operative in experimentally infected mice, but that they differ markedly in terms of their kinetics of emergence and loss. It was found that protective T cell activity was acquired very early during the course of the infection, and was temporally associated with the onset of bacterial elimination; however, cytolytic activity did not peak until 10 to 20 days later. This report shows further that the target Ag of these effector T cell populations were apparently numerous with no evidence for preferential recognition of a few immunodominant Ag. In view of the preponderance of target proteins in the bacterial filtrate, we present the hypothesis that such proteins secreted or otherwise leaked from the dividing mycobacterium are pinocytosed from the phagosome and used by the infected macrophage as the key protective Ag leading to T cell sensitization. This hypothesis thus explains the preferential requirement for the viable bacterium in the generation of specific resistance, and further explains why protective immunity is generated even while the organism is still multiplying in an apparently unrestrained manner.
TL;DR: In this paper, seasonal variability of Atlantic basin tropical cyclones with respect to the monsoon rainfall over West Africa was examined with a detrended analysis, showing that a strong association still exists, though reduced somewhat in variance explained.
Abstract: Seasonal variability of Atlantic basin tropical cyclones is examined with respect to the monsoon rainfall over West Africa. Variations of intense hurricanes are of the most interest, as they are responsible for over three-quarters of United States tropical cyclone spawned destruction, though they account for only one-fifth of all landfalling cyclones. Intense hurricanes have also shown a strong downward trend during the last few decades. It is these storms that show the largest concurrent association with Africa's western Sahelian June-September rainfall for the years 1949–90. Though the Sahel is currently experiencing a multidecadal drought, the relationship between Atlantic tropical cyclones and western Sahelian rainfall is not dependent on the similar downward trends in both datasets. A detrended analysis confirms that a strong association still exists, though reduced somewhat in variance explained. Additionally, independent data from the years 1899 to 1948 substantiate the existence of the tr...
TL;DR: In this article, the authors study the problem of estimating autoregressive parameters when the observations are from an AR process with innovations in the domain of attraction of a stable law and show that non-degenerate limit laws exist for M-estimates if the loss function is sufficiently smooth; these results remain valid if location and scale are also estimated.
TL;DR: It is reported that the termini of LAM from the virulent, Erdman, strain of Mycobacterium tuberculosis, unlike those from the attenuated H37Ra strain, are extensively capped with mannosyl (Manp) residues, either a single alpha-D-Manp, a dimannoside, or a trimannuside.
TL;DR: Based on the recent experiment results, a formula is proposed to be used in numerical weather-climate models to estimate the soil surface humidity as discussed by the authors, which has a very simple form and shows a smooth transition in soil surface specific humidity between wet and dry soil states.
Abstract: Based on the recent experiment results, a formula is proposed to be used in numerical weather-climate models to estimate the soil surface humidity. The formula has a very simple form and shows a smooth transition in the soil surface specific humidity between wet and dry soil states. The formula is recommended as a replacement to the Philip formula.
TL;DR: It was found that L AM from the avirulent H37Ra strain was 100-fold more potent at inducing tumor necrosis factor secretion than LAM from the virulent Erdman strain, thus leading to the hypothesize that the structure of LAMFrom a given mycobacterial isolate may directly influence its ability to elicit, or avoid, cytokine-mediated mechanisms of host resistance.
Abstract: The results of this study show that lipoarabinomannans (LAM) isolated from a virulent strain and from an avirulent strain of Mycobacterium tuberculosis, which have recently been shown to differ markedly in terms of the structures of their nonreducing termini, also differ markedly in the capacity to induce the secretion of tumor necrosis factor from murine macrophages. It was found that LAM from the avirulent H37Ra strain was 100-fold more potent at inducing tumor necrosis factor secretion than LAM from the virulent Erdman strain, thus leading us to hypothesize that the structure of LAM from a given mycobacterial isolate may directly influence its ability to elicit, or avoid, cytokine-mediated mechanisms of host resistance.
TL;DR: There are increasing anecdotal reports of the clinical value of the squeeze machine, including suggestions that it can be used to reduce required doses of psychostimulant medications, and a review of the animal literature reveals that animals have similar calming reactions, and also suggests possible additional physiological effects of deep touch pressure.
Abstract: Many people with autistic disorder have problems with oversensitivity to both touch and sound. The author (an autistic person) developed a device that delivers deep touch pressure to help her learn to tolerate touching and to reduce anxiety and nervousness. The "squeeze machine" applies lateral, inwardly directed pressure to both lateral aspects of a person's entire body, by compressing the user between two foam-padded panels. Clinical observations and several studies suggest that deep touch pressure is therapeutically beneficial for both children with autistic disorder and probably children with attention-deficit hyperactivity disorder. Only minor and occasional adverse effects have been noted. Data are reported that show a similar calming effect in nonreferred college students. A review of the animal literature reveals that animals have similar calming reactions, and also suggests possible additional physiological effects of deep touch pressure. At present, there are increasing anecdotal reports of the clinical value of the squeeze machine, including suggestions that it can be used to reduce required doses of psychostimulant medications. More clinical studies are needed to evaluate the potential role of this seemingly beneficial form of "physiological" stimulation.
TL;DR: One hundred and fifteen dogs with neoplasms of the lower urinary tract (bladder and/or urethra) were retrospectively evaluated at five referral institutions participating in ongoing studies by the Veterinary Cooperative Oncology Group.
Abstract: One hundred and fifteen dogs with neoplasms of the lower urinary tract (bladder and/or urethra) were retrospectively evaluated at five referral institutions participating in ongoing studies by the Veterinary Cooperative Oncology Group. Most tumors were malignant (97%) and of epithelial origin (97%). Lower urinary tract tumors were more common in older dogs weighing greater than 10 kg. The following significant (P less than 0.05) statistical associations were found using the University of Guelph hospital population as control; there was no sex predisposition although the female:male ratio was 1.95:1. Neutered dogs were predisposed as were Airedale Terriers, Beagles, and Scottish Terriers, whereas German Shepherds were significantly under-represented among dogs with lower urinary tract tumors. These statistical associations should be interpreted cautiously because of possible demographic differences in hospital populations among the University of Guelph and other cooperating institutions. There were no significant correlations between age, gender, weight, breed, response to therapy, and survival time. Clinical signs were indicative of lower urinary tract disease and included hematuria, stranguria, and pollakiuria. The laboratory data were nonspecific except for urinalysis test results. Hematuria and inflammatory urinary sediments were most commonly reported; neoplastic cells were identified in the urine sediment of 30% of dogs with lower urinary tract tumors. Contrast cystography was a useful noninvasive diagnostic method since 96% of the dogs had a mass or filling defect in the lower urinary tract demonstrated by this technique.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The analysis shows that the connectionist approach is capable of developing models of varying complexity and may adapt well across different data sets and exhibit better predictive accuracy.
Abstract: The usefulness of connectionist models for software reliability growth prediction is illustrated. The applicability of the connectionist approach is explored using various network models, training regimes, and data representation methods. An empirical comparison is made between this approach and five well-known software reliability growth models using actual data sets from several different software projects. The results presented suggest that connectionist models may adapt well across different data sets and exhibit a better predictive accuracy. The analysis shows that the connectionist approach is capable of developing models of varying complexity. >
Book•
01 Jan 1992TL;DR: The 2007 edition of Human Impacts on Weather and Climate examines the scientific and political debates surrounding anthropogenic impacts on the Earth's climate and presents the most recent theories, data and modeling studies as mentioned in this paper.
Abstract: This 2007 edition of Human Impacts on Weather and Climate examines the scientific and political debates surrounding anthropogenic impacts on the Earth's climate and presents the most recent theories, data and modeling studies. The book discusses the concepts behind deliberate human attempts to modify the weather through cloud seeding, as well as inadvertent modification of weather and climate on the regional scale. The natural variability of weather and climate greatly complicates our ability to determine a clear cause-and-effect relationship to human activity. The authors describe the basic theories and critique them in simple and accessible terms. This fully revised edition will be a valuable resource for undergraduate and graduate courses in atmospheric and environmental science, and will also appeal to policy makers and general readers interested in how humans are affecting the global climate.
TL;DR: In this article, the dependence of the oxygen reduction kinetics on oxygen pressure was investigated in Proton Exchange Membrane (PEM) fuel cells, and the authors showed that the diffusion coefficient of oxygen is invariant with pressure, however, the diffusion coefficients for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration.
Abstract: The investigation of oxygen reduction kinetics at the platinum/Nafion interface is of great importance in the advancement of proton-exchange-membrane (PEM) fuel-cell technology. This study focuses on the dependence of the oxygen reduction kinetics on oxygen pressure. Conventional Tafel analysis of the data shows that the reaction order with respect to oxygen is unity at both high and low current densities. Chronoamperometric measurements of the transport parameters for oxygen in Nafion show that oxygen dissolution follows Henry's isotherm. The diffusion coefficient of oxygen is invariant with pressure; however, the diffusion coefficient for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration. These results are of value in understanding the influence of O2 partial pressure on the performance of PEM fuel cells and also in elucidating the mechanism of oxygen reduction at the platinum/Nafion interface.