723 research outputs found
High soil carbon efflux rates in several ecosystems in southern Sweden
Soil C effluxes were measured at five forest stands with different vegetation and a meadow in southeastern Sweden (57ÂĄ5«N, 16ÂĄ7«E). Exponential regressions of soil respiration against air and soil temperatures were used to model soil respiration at forests stands. For the meadow, a light response curve with gross primary production (GPP) against PAR and a cubic regression with GPP against air temperature were used to model GPP. Soil water content limited soil respiration in all ecosystems but spruce where the limitation appeared only at high soil water content. In the forest ecosystems, the forest floor vegetation was scarce and its C uptake had no significant effect on soil C effluxes. Annual soil respiration in all sites was between 2.05 and 4.34 kg CO2 mâ2 yrâ1, which is large as compared with that reported in many other studies. Annual GPP of meadow was between 1.81 and 1.99 kg CO2 mâ2 yrâ1, which gives a NEE between 1.39 and 2.41 kg CO2 mâ2 yrâ1, i.e. a significant loss of C
Driver Response to Automatic Braking under Split Friction Conditions
At normal pedal braking on split-Ό a driver can actively steer or adjust brake level to control lateral drift. The same driver response and thus lateral deviation cannot be assumed when brakes are automatically triggered by a collision mitigation system, since the driver can be expected as less attentive. To quantify lateral deviation in this scenario a test was run at 50 km/h with 12 unaware drivers in a heavy truck. Brakes were configured to emulate automatic braking on split-Ό. Results show that the produced maximum lateral deviation from the original direction was 0.25 m on average. Two drivers deviated by 0.5 m. This can be compared to 2.2 m which was reached when steering was held fixed
Applicability of leaf area index products for boreal regions of Sweden
Leaf area index (LAI) of boreal ecosystems were estimated with optical instruments at the Laxemar and the Forsmark investigation areas in Sweden. The aim was to study the relationship between LAI and the normalized difference vegetation index (NDVI) from Landsat-5 and SPOT and evaluate the applicability of the MODIS (Moderate Resolution Imaging Spectroradiometer) LAI product for small boreal regions. Relationships between ground-estimated LAI and NDVI were significant for coniferous, deciduous and mixed forest sites in Laxemar. For Forsmark, effective LAI was correlated to NDVI for all sites. LAI estimated from NDVI was also used for evaluating accuracy of the MODIS LAI product. The comparison showed no correlation between MODIS LAI and NDVI-based LAI in Forsmark whereas there was in Laxemar. MODIS LAI was on average 2.28 higher than NDVI-based LAI and it also showed larger scatter. Scale issues were the main explanation to high MODIS LAI, since the heterogeneous landscapes with open areas (given a value of zero in the NDVI estimates) was seen as forest in the large pixels of the MODIS LAI product. Therefore, we do not recommend using the MODIS LAI product in small boreal regional landscapes, such as the Forsmark and Laxemar investigation areas
Combining Coordination of Motion Actuators with Driver Steering Interaction
Objective: A new method is suggested for coordination of vehicle motion actuators; where driver feedback and capabilities become natural elements in the prioritization.
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Methods: The method is using a weighted least squares control allocation formulation, where driver characteristics can be added as virtual force constraints. The approach is in particular suitable for heavy commercial vehicles that in general are over actuated. The method is applied, in a specific use case, by running a simulation of a truck applying automatic braking on a split friction surface. Here the required driver steering angle, to maintain the intended direction, is limited by a constant threshold. This constant is automatically accounted for when balancing actuator usage in the method.
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Results: Simulation results show that the actual required driver steering angle can be expected to match the set constant well. Furthermore, the stopping distance is very much affected by this set capability of the driver to handle the lateral disturbance, as expected.
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Conclusion: In general the capability of the driver to handle disturbances should be estimated in real-time, considering driver mental state. By using the method it will then be possible to estimate e.g. stopping distance implied from this. The setup has the potential of even shortening the stopping distance, when the driver is estimated as active, this compared to currently available systems. The approach is feasible for real-time applications and requires only measurable vehicle quantities for parameterization. Examples of other suitable applications in scope of the method would be electronic stability control, lateral stability control at launch and optimal cornering arbitration
First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems
The importance of semi-arid ecosystems in the global carbon cycle as sinks
for CO2 emissions has recently been highlighted. Africa is a carbon sink and
nearly half its area comprises arid and semi-arid ecosystems. However, there
are uncertainties regarding CO2 fluxes for semi-arid ecosystems in Africa,
particularly savannas and dry tropical woodlands. In order to improve on
existing remote-sensing based methods for estimating carbon uptake across
semi-arid Africa we applied and tested the recently developed plant phenology
index (PPI). We developed a PPI-based model estimating gross primary
productivity (GPP) that accounts for canopy water stress, and compared it
against three other Earth observation-based GPP models: the temperature and
greenness model, the greenness and radiation model and a light use efficiency
model. The models were evaluated against in situ data from four semi-arid sites
in Africa with varying tree canopy cover (3 to 65 percent). Evaluation results
from the four GPP models showed reasonable agreement with in situ GPP measured
from eddy covariance flux towers (EC GPP) based on coefficient of variation,
root-mean-square error, and Bayesian information criterion. The PPI-based GPP
model was able to capture the magnitude of EC GPP better than the other tested
models. The results of this study show that a PPI-based GPP model is a
promising tool for the estimation of GPP in the semi-arid ecosystems of Africa.Comment: Accepted manuscript; 12 pages, 4 tables, 9 figure
Real-time performance of control allocation for actuator coordination in heavy vehicles
This paper shows how real-time optimisation for actuator coordination, known as control allocation, can be a viable choice for heavy vehicle motion control systems. For this purpose, a basic stability control system implementing the method is presented. The real-time performance of two different control allocation solvers is evaluated and the use of dynamic weighting is analysed. Results show that sufficient vehicle stability can be achieved when using control allocation for actuator coordination in heavy vehicle stability control. Furthermore, real-time simulations indicate that the optimisation can be performed with the computational capacity of today's standard electronic control units. © 2009 IEEE
Evaluation of the Plant Phenology Index (PPI), NDVI and EVI for Start-of-Season Trend Analysis of the Northern Hemisphere Boreal Zone
Utbildning, VĂ€rderingar och Demokrati: Utbildning som konsoliderande kraft
Följande skrivning Àmnar undersöka kopplingen mellan utbildning och demokrati, genom att studera enkÀtresultat vÀrlden över samt stÀlla detta mot andra forskares fynd pÄ omrÄdet. Högre nivÄer av utbildning verkar samvariera med mer positiva instÀllningar gentemot demokrati men Àven hur pass aktiv man Àr som medborgare tycks korrelera positivt med utbildningsnivÄ. BÄde distribution av utbildning i en befolkning samt dess karaktÀr och utformning visade sig vara andra viktiga aspekter. Ungern undersöks som ett fall av demokratisk recession och denna uppsats finner en koppling mellan framför allt utformningen av Ungersk utbildning och bristen pÄ aktivt medborgarskap i landet. Formell utbildning och tycks alltsÄ kunna kopplas till en demokratis vÀlmÄende
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