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  • 1
    Publication Date: 2024-01-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The páramos are Neotropical alpine tundra‐like ecosystems that play a crucial role as biodiversity hotspots and also act as water sources for the inter‐Andean regions and cities. Improving our understanding of hydrological processes, here evapotranspiration, is crucial, especially in the context of global changes. In páramos, most research have focused on estimating potential evapotranspiration (ETo) using the Penman–Monteith method. Only a few studies have quantified actual evapotranspiration using mostly the Eddy covariance method (EC) or volumetric lysimeters. Importantly, these studies focused only on tussock grass communities, and none have addressed the effect of other plant communities specific to páramos on the actual evapotranspiration of this ecosystem. In this research, portable closed chambers were installed for the first time in a páramo (in 〈italic〉Los Nevados〈/italic〉 National Park, between 3900 and 4100 masl) to quantify actual evapotranspration (ETa) in March and May 2019 in three representative plant communities of the páramo (giant rosettes, shrubs and tussock grasses). The ETa rates measured were then compared with ETo estimated using the Penman–Monteith method. Also, environmental factors of solar radiation, temperature and relative humidity were recorded and their influence on ETa variation was analysed. Our results indicate that ETa daily rates were very low with a high daily variation (0.290 ± 0.266 mm day〈sup〉−1〈/sup〉). The shrubs showed higher ETa rates even though differences among communities were not significant. ETo rates calculated via the Penman–Monteith method were significantly higher (1.017 ± 0.468 mm day〈sup〉−1〈/sup〉) than those measured using the portable chambers. Portable closed chamber is a promising method to assess ETa at small spatial and time scales and under controlled environment; however, they should be improved to enable ETa measurements on longer time periods. This study confirms the highly variable and low evapotranspiration rate of the páramo vegetation, here confirmed across different plant communities and underlines the importance of solar radiation and temperature, which were positively correlated with evapotranspiration rates.〈/p〉
    Keywords: Calamagrostis ; Espeletia ; evapotranspiration ; high altitude ecosystem ; Penman–Monteith ; Pentacalia ; stomatal conductance
    Language: English
    Type: doc-type:article
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  • 2
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    Elsevier Science
    In:  München, Elsevier Science, vol. 34, no. 1, pp. 65-66, (ISBN: 3-528-02574-3)
    Publication Date: 2001
    Keywords: Handbook of geophysics ; Handbook of physics ; Handbook of engineering ; Handbook of informatics ; Seismology ; Earthquake precursor: prediction research ; comets ; Chaotic behaviour ; Source ; Plate tectonics ; Elasticity ; compilers ; earth Core ; earth mantle ; Acoustics ; Earthquake engineering, engineering seismology ; history ; Rock mechanics ; Artificial intelligence (AI) ; mathematics ; Geochemistry ; Fracture ; fatigue ; FractureT ; Geodesy ; Geomagnetics ; Statistical investigations ; Geothermics ; Global Positioning System ; Green's function ; Fluids ; ConvolutionE ; plumes ; Mineralogy ; Modelling ; Tectonics ; SOC ; percolation ; Oceanography ; Planetology ; MOON ; SAR ; InSAR ; Stress ; Tsunami(s) ; Volcanology ; Whitman ; Rikitake ; Stein ; Oreskes ; Loper ; Jeanloz ; Lee ; Mandelbrot ; Vanicek ; Bock ; Olson ; Campbell ; Madariaga ; Staufer ; Dickinson ; van ; Zyl ; Zoback ; Turcotte ; Ward ; Sigurdsson
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  • 3
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    In:  Other Sources
    Publication Date: 2011-08-24
    Description: One of the most important elements in laser velocimetry, yet the most neglected, is the small particle embedded in the flow field that scatters the light necessary to make velocity measurements. The characteristics of this small particle are often ignored in the effort to obtain data. This seems strange since it is the primary cause of measurement error. If the particle is too large, it will not follow the flow resulting in an inaccurate representation of the fluid velocity. If the particle is too small, it will not scatter sufficient light to provide the signal-to-noise necessary to minimize measurement uncertainty in the signal processing electronics. This lecture will attempt to remove the confusion in choosing a seeding method by assessing many of the techniques currently used. It will outline their characteristics and typical limitations imposed by various applications. The lecture will then focus on the ramifications of these methods on measurement accuracy.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: Optical Velocity Measurements; D/1994/0238/425
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  • 4
    Publication Date: 2011-08-24
    Description: A new laser velocimetry technique, Doppler global velocimetry, is described. This technique is capable of simultaneously measuring in real time the three components of velocity of an entire particle field illuminated by a laser light sheet. A prototype one-component velocimeter is described along with the signal processing electronics. The system was tested by measuring the velocity field from a rotating wheel and a small subsonic jet flow in the laboratory. The first wind tunnel test measured the vortical velocity field above a delta wing. The results are presented and compared with fringe-type laser velocimeter and five-hole probe data.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 289-296.
    Format: text
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  • 5
    Publication Date: 2011-08-24
    Description: With high-resolution network transmission required for telemedicine, education, and guided-image acquisition, the impact of errors and transmission rates on image quality needs evaluation. METHODS: We transmitted clinical echocardiograms from 2 National Aeronautics and Space Administration (NASA) research centers with the use of Motion Picture Expert Group-2 (MPEG-2) encoding and asynchronous transmission mode (ATM) network protocol over the NASA Research and Education Network. Data rates and network quality (cell losses [CLR], errors [CER], and delay variability [CVD]) were altered and image quality was judged. RESULTS: At speeds of 3 to 5 megabits per second (Mbps), digital images were superior to those on videotape; at 2 Mbps, images were equivalent. Increasing CLR caused occasional, brief pauses. Extreme CER and CDV increases still yielded high-quality images. CONCLUSIONS: Real-time echocardiographic acquisition, guidance, and transmission is feasible with the use of MPEG-2 and ATM with broadcast quality seen above 3 Mbps, even with severe network quality degradation. These techniques can be applied to telemedicine and used for planned echocardiography aboard the International Space Station.
    Keywords: Life Sciences (General)
    Type: Journal of the American Society of Echocardiography : official publication of the American Society of Echocardiography (ISSN 0894-7317); Volume 13; 8; 764-70
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  • 6
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: The historical development of techniques for measuring three velocity components using laser velocimetry is presented. The techniques are described and their relative merits presented. Many of the approaches currently in use based on the fringe laser velocimeter have yielded inaccurate measurements of turbulence intensity in the on-axis component. A possible explanation for these inaccuracies is presented along with simulation results.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 7
    Publication Date: 2011-08-19
    Description: Studies were conducted to establish the effects of specimen geometry on the thermo-oxidative stability and the mechanical properties retention of unidirectional Celion 12000 graphite fiber reinforced PMR-15 polyimide composites. Weight loss, flexural strength and interlaminar shear strength are measured at isothermal aging times as long as 1639 hr at a temperature of 316 C for three different specimen geometries. It is found that the three different types of specimen surfaces exhibit different values of weight loss/unit area. The mechanical properties retention is also found to be dependent on geometry for these composites. The interlaminar shear strength decreases significantly over the complete range of aging times. The flexural strength retention starts showing geometric dependency after about 1000 hr of aging at 316 C. Weight loss fluxes, associated with the three different types of exposed surfaces, are calculated and used to develop an empirical mathematical model for predicting the weight loss behavior of unidirectional composites of arbitrary geometries. Data are presented comparing experimentally determined weight loss with weight loss values predicted using the empirical model.
    Keywords: COMPOSITE MATERIALS
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  • 8
    Publication Date: 2011-08-19
    Description: An account is given of the findings contained in a concensus document compiled by a group of experts on laser anemometry concerning statistical particle bias and its possible remedies. Emphasis is placed on the systematic character of this bias, rather than its magnitude. Since bias errors are a function of flow velocity and turbulence intensity, the measured results may contain apparent trends due solely to the measurement process. Attention is given to the panel's attempt to clear up terminological confusions in the matter of rates, scales, and magnitudes, as well as to its suggested processing methods for the elimination of velocity bias and the remedy of angle bias.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 109; 89-93
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  • 9
    Publication Date: 2011-08-16
    Description: Superconducting phase transition temperature measurements as function of magnetic field in thin film hollow Al and In cylinders
    Keywords: PHYSICS, SOLID-STATE
    Type: ; IBRATIONAL COMBUSTIO
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  • 10
    Publication Date: 2011-08-19
    Description: A new laser velocimeter signal processor is described which uses advanced digital circuitry to configure itself to maximize measurement accuracy based on the characteristics of the input signals. This processor maintains measurement independence from burst to burst and yields measurement accuracies better than 0.2 percent for signal frequencies up to 100 MHz.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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