Vibrational–Translational Energy Transfer in the Near-Adiabatic Approximation

Vibrational–translational energy transfer is examined in the near-adiabatic (or perturbed stationary states) approximation. The results are classical, and the method used is related to that of Marcus [J. Chem. Phys. 49, 2617 (1968)]. The results are compared with those of the more usual ("static") approximation and with the exact results. The PSS results were good at low energies at all mass ratios studied, unlike the static results. For certain mass ratios the static approximation fails badly, even at very low transition probabilities. For other mass ratios, the results are of comparable accuracy except at high energies where the static one is somewhat better. Reasons for the above behavior are discussed, and implications regarding existing infinite-order distorted wave and semiclassical calculations are noted. The relation to a recent correction of the Jackson–Mott calculation is described

DEVELOPMENT OF AN INSTRUMENT TO MEASURE THE „QUASI-STATIC“ SENCE OF BALANCE

INTRODUCTION: A measuring instrument was developed to record oscillations with regard to the projection of the center of gravity of the body (on an axis to the position where the subject stands). The measuring instrument works like a seesaw. The axis runs along the standing position. Variations are recorded by two linear positional sensors placed under the construction. The standing surface can be rotated up to 5.6°, and additionally, swaying is dampened by springs. METHODS: In the study the above-mentioned construction was compared with the Kistler force platform, with which the body’s center of gravity is projected onto the base ground. Nineteen subjects took part in the study, which required them to stand on one foot for 40 seconds with closed eyes; each subject repeated this five times, each time trying to maintain his balance. The test was repeated one week later. Different features of both measuring instruments were compared. These were among other things the mean variation of measurements, the average of the mean, the length of the curve of the projection and the greatest divergence from the mean. RESULTS: As a result it can be stated that each feature states a different aspect of the motor quality ‘quasi-static balance’. The degree of definiteness among features of one measuring instrument differed between 2% and 95%. A significant correlation between the features of both measuring instruments was detectable in a significant way for two features. Retest reliability could be detected for almost all features with high significance (p < .01). Quality criteria were fulfilled, in the sense of classical test theory, i.e., reliability, validity and objectivity. Furthermore, the measuring system weighs only 5 kg and is thus easy to transport. CONCLUSIONS: This study shows that the developed measuring instrument is suitable as an alternative measuring system to the Kistler force platform in the measuring of quasi-static balance on one axis. REFERENCES: Bös, K. (1987). Handbuch sportmotorischer Tests. Göttingen: Dr. C. J. Hogrefe. Fetz, F. (1994). Sensomotorisches Gleichgewicht im Sport. Vienna: Österreichischer Bundesverlag

BIOMECHANICAL ANALYSIS OF SPRINTING TO IMPROVE THE INDIVIDUAL TECHNIQUE

INTRODUCTION: The aim of this study is to record dynamic and cinematic parameters during sprinting with maximum velocity. The sprint start is also examined. The motion analysis aims for an improvement of the individual technique METHODS: 21 male and 3 female runners took part in this study. Cinematic and dynamic parameters were recorded during start and fast running. In the sagitall plane the following parameters were analysed: joint-angles, velocities and acceleration of joints, centres of joints, joint forces and joint moments. These parameters were recorded with two high-speed cameras (250 Hz) and a 3- dimensional force platform (measuring area 240x80 cm). The experimental set-up allowed the recording of two successive steps on the force platform while the dynamical- and kinematical-data was synchronously obtained. Additionally the reaction time was measured. The reaction time is the time from the start signal to the moment the rear leg leaves the block,. The high-speed video data were interpreted with the software package winanalyze from Mikromak. RESULTS: Very different rotary actions of the shoulders to balance the hip action were observed. The main differences between the single athletes became evident in the velocities and the accelerations of the hip and the knee-angles. Particularly variable forces in the direction of movement (retarding stroke) came forward between the different athletes. The observed tendencies will be verfied in another study in June. OUTLOOK: After the inquiry of the general fitness of the sprinters the development of a special training-program for each athlete is intended in the next step. It will be based on the Multi-Joint-Concept form R. P. Narcessian. REFERENCES: Hay, J. G. (1993). The Biomechanics of Sports Techniques. Englewood Cliffs, N.J.: Prentice-Hall

A feedback loop links brownification to anoxia in a temperate, shallow lake

This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of adjacent degraded peatlands. Leaching from the flooded soils provided an initial increase in DOC concentrations (from a 2010 mean of 12 ± 1 mg L−1 to a maximum concentration of 53 mg L−1 by June 2012). Increasing water levels, DOC, and phytoplankton concentrations reduced light reaching the sediment surface, eliminating most benthic primary production and promoting anoxia in the hypolimnion. From January to June 2012 there was a sudden increase in total phosphorus (from 57 µg L−1 to 216 µg L−1), DOC (from 24.6 mg L−1 to 53 mg L−1), and iron (from 0.12 mg L−1 to 1.07 mg L−1) concentrations, without any further large fluxes in water levels. We suggest that anoxic conditions at the sediment surface and flooded soils produced a dramatic release of these chemicals that exacerbated brownification and eutrophication, creating anoxic conditions that persisted roughly 6 months below a water depth of 1 m and extended periodically to the water surface. This brownification-anoxia feedback loop resulted in a near-complete loss of macroinvertebrate and fish populations, and increased surface carbon dioxide (CO2) emissions by an order of magnitude relative to previous years

Empirical Correspondence Between Trophic Transfer Efficiency in Freshwater Food Webs and the Slope of Their Size Spectra

The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density-size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi-trophic communities is exactly 1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator-prey mass ratio (PPMR) is fixed at 104 . Here we provide evidence from four multi-trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than 1.0 (range 1.14 to 1.19, with 95% CIs excluding 1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass-size data pairs from the four systems (1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (1.18) assuming a constant PPMR of 104 . Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass-size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat-specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE-estimates

Testing woodchips for their efficiency in stimulating aquatic nutrient uptake at different experimental and spatial scales

IntroductionWoodchips as a source of particulate organic carbon (POC) are proposed as a nature-based solution to enhance nutrient uptake and retention in agricultural streams. However, the effective implementation of woodchips for nutrient removal in streams requires an advanced understanding of their potential and limits, considering their performance under various environmental conditions. This study tested the efficiency of woodchips on the uptake of soluble reactive phosphorus (SRP) and ammonium (N-NH4) across different experimental scales and complexity. We investigated whether the presence of woodchips can increase SRP and N-NH4 uptake in laboratory flumes under controlled conditions, outdoor flumes under semi-controlled conditions, and agricultural streams. Additionally, we examined how the effects of woodchips will change over time via a 6-week incubation in the outdoor flumes.MethodsThe woodchips were pre-colonized for four weeks to allow the growth of biofilms. We performed short-term nutrient additions without (control) and with (treatment) woodchips in all three experimental setups. Uptake parameters were determined via concentration changes over time in the laboratory flumes and concentration changes over travel distance in the outdoor flumes and the stream channels. The effects of woodchips on SRP and N-NH4 uptake rates were analyzed using an effect size model.ResultsWe found positive effects of woodchips on nutrient uptake only in the laboratory flumes but no or even negative effects in the outdoor flumes and the agricultural streams. Over the 6-week incubation in the outdoor flumes, we did not observe significant changes in the effects of woodchips on nutrient uptake.DiscussionThese findings highlight that considering experimental scales and influencing environmental conditions is crucial when testing the application of woodchips as nature-based solutions to mitigate nutrient loads in agricultural streams

A regime shift from macrophyte to phytoplankton dominance enhances carbon burial in a shallow, eutrophic lake

Ecological regime shifts and carbon cycling in aquatic systems have both been subject to increasing attention in recent years, yet the direct connection between these topics has remained poorly understood. A four-fold increase in sedimentation rates was observed within the past 50 years in a shallow eutrophic lake with no surface in- or outflows. This change coincided with an ecological regime shift involving the complete loss of submerged macrophytes, leading to a more turbid, phytoplankton- dominated state. To determine whether the increase in carbon (C) burial resulted from a comprehensive transformation of C cycling pathways in parallel to this regime shift, we compared the annual C balances (mass balance and ecosystem budget) of this turbid lake to a similar nearby lake with submerged macrophytes, a higher transparency, and similar nutrient concentrations. C balances indicated that roughly 80% of the C input was permanently buried in the turbid lake sediments, compared to 40% in the clearer macrophyte-dominated lake. This was due to a higher measured C burial efficiency in the turbid lake, which could be explained by lower benthic C mineralization rates. These lower mineralization rates were associated with a decrease in benthic oxygen availability coinciding with the loss of submerged macrophytes. In contrast to previous assumptions that a regime shift to phytoplankton dominance decreases lake heterotrophy by boosting whole-lake primary production, our results suggest that an equivalent net metabolic shift may also result from lower C mineralization rates in a shallow, turbid lake. The widespread occurrence of such shifts may thus fundamentally alter the role of shallow lakes in the global C cycle, away from channeling terrestrial C to the atmosphere and towards burying an increasing amount of C

Invasive floating macrophytes reduce greenhouse gas emissions from a small tropical lake

Floating macrophytes, including water hyacinth (Eichhornia crassipes), are dominant invasive organisms in tropical aquatic systems, and they may play an important role in modifying the gas exchange between water and the atmosphere. However, these systems are underrepresented in global datasets of greenhouse gas (GHG) emissions. This study investigated the carbon (C) turnover and GHG emissions from a small (0.6 km2) water-harvesting lake in South India and analysed the effect of floating macrophytes on these emissions. We measured carbon dioxide (CO2) and methane (CH4) emissions with gas chambers in the field as well as water C mineralization rates and physicochemical variables in both the open water and in water within stands of water hyacinths. The CO2 and CH4 emissions from areas covered by water hyacinths were reduced by 57% compared with that of open water. However, the C mineralization rates were not significantly different in the water between the two areas. We conclude that the increased invasion of water hyacinths and other floating macrophytes has the potential to change GHG emissions, a process that might be relevant in regional C budgets

Comprehensive analysis of chemical and biological problems associated with browning agents used in aquatic studies

Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amounts of dissolved organic matter with optical and chemical properties resembling indigenous organic matter. Here, we compared the impacts of two leonardite products (HuminFeed and SuperHume) and a freshly derived reverse osmosis concentrate of organic matter in a set of comprehensive mesocosm- and laboratory-scale experiments and analyses. The chemical properties of the reverse osmosis concentrate and the leonardite products were very different, with leonardite products being low and the reverse osmosis concentrate being high in carboxylic functional groups. Light had a strong impact on the properties of leonardite products, including loss of color and increased particle formation. HuminFeed presented a substantial impact on microbial communities under light conditions, where bacterial production was stimulated and community composition modified, while in dark potential inhibition of bacterial processes was detected. While none of the browning agents inhibited the growth of the tested phytoplankton Gonyostomum semen, HuminFeed had detrimental effects on zooplankton abundance and Daphnia reproduction. We conclude that the effects of browning agents extracted from leonardite, particularly HuminFeed, are in sharp contrast to those originating from terrestrially derived dissolved organic matter. Hence, they should be used with great caution in experimental studies on the consequences of terrestrial carbon for aquatic systems

Character and environmental lability of cyanobacteria-derived dissolved organic matter

Autotrophic dissolved organic matter (DOM) is central to the carbon biogeochemistry of aquatic systems, and the full complexity of autotrophic DOM has not been extensively studied, particularly by high-resolution mass spectrometry (HRMS). Terrestrial DOM tends to dominate HRMS studies in freshwaters due to the propensity of such compounds to ionize by negative mode electrospray, and possibly also because ionizable DOM produced by autotrophy is decreased to low steady-state concentrations by heterotrophic bacteria. In this study, we investigated the character of DOM produced by the widespread cyanobacteriaMicrocystis aeruginosausing high-pressure liquid chromatography-electrospray ionization-high-resolution mass spectrometry.M. aeruginosaproduced thousands of detectable compounds in axenic culture. These compounds were chromatographically resolved and the majority were assigned to aliphatic formulas with a broad polarity range. We found that the DOM produced byM. aeruginosawas highly susceptible to removal by heterotrophic freshwater bacteria, supporting the hypothesis that this autotroph-derived organic material is highly labile and accordingly only seen at low concentrations in natural settings