2,160 research outputs found

    Cosmic ray isotope measurements with a new Cerenkov X total energy telescope

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    Measurements of the isotopic composition of cosmic nuclei with Z = 7-20 are reported. These measurements were made with a new version of a Cerenkov x total E telescope. Path length and uniformity corrections are made to all counters to a RMS level 1%. Since the Cerenkov counter is crucial to mass measurements using the C x E technique - special care was taken to optimize the resolution of the 2.4 cm thick Pilot 425 Cerenkov counter. This counter exhibited a beta = 1 muon equivalent LED resolution of 24%, corresponding to a total of 90 p.e. collected at the 1st dynodes of the photomultiplier tubes

    Cosmic ray charge and energy spectrum measurements using a new large area Cerenkov x dE/dx telescope

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    In September, 1981, a new 0.5 square meter ster cosmic ray telescope was flown to study the charge composition and energy spectrum of cosmic ray nuclei between 0.3 and 4 GeV/nuc. A high resolution Cerenkov counter, and three dE/dx measuring scintillation counters, including two position scintillators were contained in the telescope used for the charge and energy spectrum measurements. The analysis procedures did not require any large charge or energy dependent corrections, and absolute fluxes could be obtained to an accuracy approximately 5%. The spectral measurements made in 1981, at a time of extreme solar modulation, could be compared with measurements with a similar telescope made by our group in 1977, at a time of minimum modulation and can be used to derive absolute intensity values for the HEAO measurements made in 1979 to 80. Using both data sets precise energy spectra and abundance ratios can be derived over the entire energy range from 0.3 to greater than 15 GeV/nuc

    Spatial and temporal variation of methane emissions in drained eutrophic peat agro-ecosystems: drainage ditches as emission hotspots

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    International audienceOur research investigates the spatial and temporal variability of methane (CH4) emissions in two drained eutrophic peat areas (one intensively managed and the other less intensively managed) and the correlation between CH4 emissions and soil temperature, air temperature, soil moisture content and water table. We stratified the landscape into landscape elements that represent different conditions in terms of topography and therefore differ in moisture conditions. There was great spatial variability in the fluxes in both areas; the ditches and ditch edges (together 27% of the landscape) were methane hotspots whereas the dry fields had the smallest fluxes. In the intensively managed site the fluxes were significantly higher by comparison with the less intensively managed site. In all the landscape element elements the best explanatory variable for CH4 emission was temperature. Neither soil moisture content nor water table correlated significantly with CH4 emissions, except in April, where soil moisture was the best explanatory variable

    Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

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    Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past. <br><br> Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging) are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode

    Verapamil protects against progression of experimental chronic renal failure

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    Verapamil protects against progression of experimental chronic renal failure. Chronic administration of verapamil (Ver) decreases nephrocalcinosis and tubular ultrastructural abnormalities in the remnant model of chronic renal disease. In the present study, the effect of chronic Ver administration on renal function, renal histology and mortality after subtotal nephrectomy was examined. Fourteen days after staged subtotal nephrectomy rats were paired according to renal functional impairment, mean arterial pressure (MAP), and body weight. Rats were pair fed and received either Ver (0.1 µg/g sc bid, N = 10) or saline (0.1ml sc bid, N = 10) for up to 23 weeks. Both members of each pair were sacrificed shortly before the uremic death of controls. At sacrifice, rats treated with Ver had a lower serum creatinine (2.29 vs. 2.99 mg/dl, P < 0.05) and a higher creatinine clearance (318 vs. 164 µl/min, P < 0.05) than controls. In a second experiment, survival was superior in rats treated with Ver than in controls from week seven (P < 0.0025 by week 14). Serum creatinine was higher at week 10 in control rats (1.68 vs. 1.10 mg/dl, P < 0.05). MAP was no different between the two groups, irrespective of the time between Ver administration and the measurement of MAP. Histological damage and nephrocalcinosis were worse, and renal and myocardial calcium content was higher in controls. In conclusion, independent of any effect on systematic MAP, chronic administration of Ver protects against renal dysfunction, histological damage, nephrocalcinosis and myocardictl calcification, and improves survival in the remnant model of chronic renal disease

    Evaluation of the EndoPAT as a Tool to Assess Endothelial Function

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    Endothelial dysfunction is a potential target for (pharmaceutical) intervention of several systemic pathological conditions. We investigated the feasibility of the EndoPAT to evaluate acute changes in endothelial function with repeated noninvasive measurements and assessed its discriminating power in different populations. Endothelial function was stable over a longer period of time in renally impaired patients (coefficient of variation 13%). Endothelial function in renally impaired and type 2 diabetic patients was not decreased compared to healthy volunteers (2.9 ± 1.4 and 1.8 ± 0.3, resp., versus 1.8 ± 0.5, P > 0.05). The EndoPAT did not detect an effect of robust interventions on endothelial function in healthy volunteers (glucose load: change from baseline 0.08 ± 0.50, 95% confidence interval −0.44 to 0.60; smoking: change from baseline 0.49 ± 0.92, 95% confidence interval −0.47 to 1.46). This suggests that at present the EndoPAT might not be suitable to assess (changes in) endothelial function in early-phase clinical pharmacology studies. Endothelial function as measured by the EndoPAT could be physiologically different from endothelial function as measured by conventional techniques. This should be investigated carefully before the EndoPAT can be considered a useful tool in drug development or clinical practice

    CO2 exchange and carbon balance in two grassland sites on eutrophic drained peat soils.

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    In this study we investigated the role of intensive and extensive dairy farm practices on CO<sub>2</sub> exchange and the carbon balance of peatlands by means of eddy covariance (EC) measurements. Year long EC measurements were made in two adjacent farm sites on peat soil in the western part of the Netherlands. One site (Stein) is a new meadow bird reserve and is managed predominantly by mowing in June and August. The second site (Oukoop) is an intensive dairy farm. Maximum photosynthetic uptake of the grass sward (range 2 to 34 mu mol CO<sub>2</sub> m(-2) s(-1)) showed a close and similar linear relationship with Leaf Area Index (LAI; range 1 to 5) except in maturing hay meadows, where maximum photosynthetic uptake did not increase further. Apparent quantum yield varied between 0.02 and 0.08 (mean 0.045) mu mol CO<sub>2</sub> mu mol(-1) photons at both sites and was significantly correlated with LAI during the growth season. Ecosystem Respiration at 10 degrees C (R-10) calculated from the year round data set was 3.35 mu mol CO<sub>2</sub> m(-2) s(-1) at Stein and 3.69 mu mol CO<sub>2</sub> m(-2) s(-1) at Oukoop. Both sites were a source of carbon in winter and a sink during summer with net ecosystem exchange varying between 50 to 100 mmol CO<sub>2</sub> m(-2) d(-1) in winter to below -400 mmol CO<sub>2</sub> m(-2) d(-1) in summer. Periodically, both sites became a source after mowing. Net annual ecosystem exchange (NEE) for Stein was -5.7 g C m(-2) a(-1) and for Oukoop 133.9 g C m(-2) a(-1). When biomass removal, manure applications and estimates of methane emissions ware taken into account, both eutrophic peat meadows are a strong source for C around 420 g C m(-2) a(-1)

    Role of chemokines and cytokines in a reactivation model of arthritis in rats induced by injection with streptococcal cell walls

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    Intraarticular injection of streptococcal cell wall (SCW) antigen followed by intravenous challenge results in a T cellâ mediated monoarticular arthritis in female Lewis rats. Initial studies showed that this reactivation response to intravenous SCW antigen is dependent on the presence of interleukinâ 1 (ILâ 1) and tumor necrosis factor α (TNFâ α) and that the early phase of swelling is neutrophilâ dependent. Neutrophil depletion or passive immunization with antibodies to Pâ selectin or macrophage inflammatory proteinâ 2 reduced the intensity of ankle edema and the influx of neutrophils. After the first few days, however, the arthritic response is mediated primarily by mononuclear cells. Joint tissues showed upâ regulation of mRNA for monocyte chemotactic proteinâ 1 (MCPâ 1), which could be inhibited in part by antiâ ILâ 4; treatment of rats with antibodies to ILâ 4 or MCPâ 1 significantly suppressed development of ankle edema and histopathological evidence of inflammation. Antibodies to interferonâ γ or ILâ 10 had no effect. Treatment with antiâ MCPâ 1 also suppressed influx of 111Inâ labeled T cells into the ankle joint. These data suggest that the late, mononuclearâ dependent phase of SCWâ induced arthritis in female Lewis rats requires cytokines that upâ regulate MCPâ 1, which in turn may facilitate recruitment and extravasation of mononuclear cells into the joint. J. Leukoc. Biol. 63: 359â 363; 1998.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142294/1/jlb0359.pd