101 research outputs found
Non destructive dose determination and depth profiling of arsenic ultrashallow junctions with total reflection X-ray fluorescence analysis compared to dynamic secondary ion mass spectrometry
No full textSecondary ion mass spectrometry (SIMS) has been the most widely used technique for the measurement of dopant distribution in Si
because of its ability of determining profile shape, junction depth, and dose with adequate depth resolution and detection limits. In the case of
ultrashallow implants though, SIMS is going towards its intrinsic limits; in fact, initial transient width and native oxide-induced matrix effects
affect the measurement in the first nanometres where a relevant part of the dopant is confined. Therefore, complementary techniques able to
give information on the dose and on the distribution in the first nanometres are required. In this work, total reflection X-ray fluorescence
analysis (TXRF) resolved in angle has been evaluated as a candidate, given its high sensitivity in the near surface region, its ability of a
quantitative analysis, its multielement capability, and its nondestructiveness. Three arsenic implanted Si samples have been analysed by
SIMS and TXRF. The SIMS measurements have been carried out by a magnetic sector instrument of new generation with a Cs+ primary
beam and by monitoring negative secondary ions. The TXRF measurements were performed at beamline 6-2 of the Stanford Synchrotron
Radiation Laboratory. For the fluorescence measurements, an absolute quantification by fundamental parameters and comparison with the Si
fluorescence signal has been adopted. The TXRF dose determination showed good agreement with other techniques. TXRF could also
evaluate the accuracy of the SIMS profile in the first nanometres
Positieve veiligheid: Safety I en Safety II combineren
No full textNiet zo heel lang geleden stormde een veiligheidsprofessional na afloop van een praatje op mij af om mij te bezweren dat het vasthouden van de leuning eenvoortreffelijke maatregel is. In mijn ogen is het eerder betuttelend. Negatieve veiligheid, we moeten er nu écht vanaf.Safety and Security Scienc
Measurement of horizontal and vertical advection of CO2 within a forest canopy
No full textEddy covariance measurements often underestimate the net exchange of CO2 between forest canopies and the atmosphere under stable atmospheric conditions, when horizontal and vertical advection are significant. A novel experimental design was used to measure all terms in the mass balance of CO2 in a 50 m × 50 m wide, 6 m tall control volume (CV) located on the floor of a 40 m tall Eucalyptus forest to examine the contributions of the eddy flux, the change in storage and the horizontal and vertical advection terms. Horizontal flux divergences between the four vertical walls of the CV were determined using perforated tubing arranged parallel to the ground to measure CO2 mixing ratios. The change in storage was calculated using CO2 concentration profiles measured in the centre of the CV. Vertical advection was calculated using these profiles, combined with vertical velocities, wc, calculated using the mass continuity equation and horizontal velocities measured at the mid-point of each wall of the CV. Vertical and horizontal advection and the eddy flux terms all contributed significantly to the mass balance of the CV at night, while the eddy flux term was dominant and negative for a short period around noon when photosynthesis exceeded respiration. Large vertical gradients of CO2 at night cause estimates of vertical advection to be extremely sensitive to small errors in wc with standard errors of the mean flux exceeding 3 μmol CO2 m-2 s-1. Vertical velocities need be measured to an accuracy better than 1 mm s-1 to minimize errors in vertical advection when vertical gradients of CO2 ratios are very large at night. Calculated horizontal advection is sensitive to errors in the wind vectors through the faces of the CV when horizontal concentrations gradients are large. Errors in eddy fluxes and change in storage are smaller than for the advection terms and errors for all components are smaller during the day than at night. Crow
Measurement of horizontal and vertical advection of CO2 within a forest canopy
No full textEddy covariance measurements often underestimate the net exchange of CO2 between forest canopies and the atmosphere under stable atmospheric conditions, when horizontal and vertical advection are significant. A novel experimental design was used to measure all terms in the mass balance of CO2 in a 50 m × 50 m wide, 6 m tall control volume (CV) located on the floor of a 40 m tall Eucalyptus forest to examine the contributions of the eddy flux, the change in storage and the horizontal and vertical advection terms. Horizontal flux divergences between the four vertical walls of the CV were determined using perforated tubing arranged parallel to the ground to measure CO2 mixing ratios. The change in storage was calculated using CO2 concentration profiles measured in the centre of the CV. Vertical advection was calculated using these profiles, combined with vertical velocities,No Full Tex
Stabiliteit van een dragende-leuning brug uitgevoerd in beton. Stability of a concrete pedestrain bridge with load bearing railings
No full textUsually, concrete bridges contain a ‘thick’ bridge deck. For various reasons, bridges are constructed with railings. This thesis discusses the stability problem of concrete bridges, which are designed with integrated railings into the carrying construction. The most important advantage, using load bearing railings, is a thinner bridge deck. This was also one of the requests of Public Works Rotterdam. The load bearing railings have to endure buckling. This phenomena is not very common in massive concrete bridges. Since the request for to alternative bridges with a thinner bridge deck, like this one, is becoming larger and larger, there is need for a simple rule of thumb. This indication is necessary for estimating the dimensions of this kind of bridge without a complicated calculation. For this thesis, the stability of a concrete pedestrian bridge with load bearing railings, has been checked in three ways. There has been focussed at the compression zone of the bridge, the handrails. 1. First the buckling force is calculated. Using the buckling force and the actual normal force in the handrails, it is possible to calculate the second order effects. 2. The total resisting moment in the handrails must be large enough to withstand the external first and second order moments. The resisting moment is based on uncracked concrete, therefore no tension stresses in the handrails are aloud. 3. If stability isn’t the problem, strength is. Hence the external normal force in the handrails most be lower than the normal force resisted. The problem has been analysed. The three checking’s are visualized in graphs over various dimensions. These graphs were used as a starting point of a parameter study to get a rule of thumb, which can be used for concrete pedestrian bridges with load bearing railings. There is also concluded that bridges with load bearing railings are more sensitive to local forces (on bridge deck and railings), than plate bridges are. The rule of thumb is applicable for bridges larger than 14 meter and smaller than 23 meter, depending on the applied concrete strength. Using this indications gives a correct estimation of the dimensions of a concrete pedestrian bridge with load bearing railings.Design and ConstructionCivil Engineering and Geoscience
Precipitation as driver of carbon fluxes in 11 African ecosystems
No full textThis study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320 mm (Sudan) to 1150 mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments.
Values for maximum net carbon assimilation rates (photosynthesis) ranged from −12.5 μmol CO2 m−2 s−1 in a dry, open Millet cropland (C4-plants) up to −48 μmol CO2 m−2 s−1 for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r2=0.74). Maximum photosynthetic uptake rates (Fpmax) were positively related to satellite-derived fAPAR. Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All included ecosystems dominated by C3-plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa
Interrelation of mechanical properties and magneto-mechanical coupling of non-oriented electrical steel
No full textModeling daily gas exchange of a Douglas-fir forest : comparison of three stomatal conductance models with and without a soil water stress function
No full textModeling stomatal conductance is a key element in predicting tree growth and water use at the stand scale. We compared three commonly used models of stomatal conductance, the Jarvis-Loustau, Ball-Berry and Leuning models, for their suitability for incorporating soil water stress into their formulation, and for their performance in modeling forest ecosystem fluxes. We optimized the parameters of each of the three models with sap flow and soil water content data. The optimized Ball-Berry model showed clear relationships with air temperature and soil water content, whereas the optimized Leuning and Jarvis-Loustau models only showed a relationship with soil water content. We conclude that use of relative humidity instead of vapor pressure deficit, as in the Ball-Berry model, is not suitable for modeling daily gas exchange in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in the Speulderbos forest near the village of Garderen, The Netherlands. Based on the calculated responses to soil water content, we linked a model of forest growth, FORGRO, with a model of soil water, SWIF, to obtain a forest water-balance model that satisfactorily simulated carbon and water (transpiration) fluxes and soil water contents in the Douglas-fir forest for 1995
δ13C of organic matter transported from the leaves to the roots in Eucalyptus delegatensis: short-term variations and relation to respired CO2
No full textPost-photosynthetic carbon isotope fractionation might alter the isotopic signal imprinted on organic matter (OM) during primary carbon fixation by Rubisco. To characterise the influence of post-photosynthetic processes, we investigated the effect of starch storage and remobilisation on the stable carbon isotope signature (delta C-13) of different carbon pools in the Eucalyptus delegatensis R. T. Baker leaf and the potential carbon isotope fractionation associated with phloem transport and respiration. Twig phloem exudate and leaf water-soluble OM showed diel variations in delta C-13 of up to 2.5 and 2 parts per thousand, respectively, with C-13 enrichment during the night and depletion during the day. Damped diel variation was also evident in bulk lipids of the leaf and in the leaf wax fraction. delta C-13 of nocturnal phloem exudate OM corresponded with the delta C-13 of carbon released from starch. There was no change in delta C-13 of phloem carbon along the trunk. CO2 emitted from trunks and roots was C-13 enriched compared with the potential organic substrate, and depleted compared with soil-emitted CO2. The results are consistent with transitory starch accumulation and remobilisation governing the diel rhythm of delta C-13 in phloem-transported OM and fragmentation fractionation occurring during respiration. When using delta C-13 of OMor CO2 for assessing ecosystem processes or plant reactions towards environmental constraints, post- photosynthetic discrimination should be considered
Supplement 1. Data used in the present analysis, including new stomatal slope data for five species and previously published Switchgrass observations of Vc,max, SLA, leaf width, and fine-root : leaf ratio.
No full textFile List
stomatal_slope.csv (MD5: e7be44c77a35e03b1f4b8d3666f7ebb1)
pavi_data.csv (MD5: 614c310d746cb8f31a58db3a8c7a23e9) – Previously published Switchgrass data used in the present analysis.
Description
Stomatal slope was estimated using measurements of four leaves from each of five field-grown energy crop species during the 2010 growing season. The five species included two C4 grasses: Miscanthus (Miscanthus x giganteus) and Switchgrass (Panicum virgatum) planted in 2008 and three deciduous tree species: Red Maple (Acer rubrum), Eastern Cottonwood (Populus deltoides) and Sherburne Willow (Salix x Sherburne) planted in 2010 as 2 year old saplings. All plants were grown at the Energy Biosciences Institute Energy Farm (40°10'N, 88°03'W). Photosynthesis (A), stomatal conductance (gs), intercellular [CO2] (ci), and humidity deficit at the leaf surface (Ds) were obtained via open gas exchange systems with 2 cm² leaf chambers housing infrared gas analyzers to measure fluxes of both CO2 and water (LI-6400; LI-COR Inc., Lincoln, NE, USA). Data were collected following a simplified version of the protocol described by Leakey et al. (2006) in which photosynthetic photon flux density was maintained at 1500 μmol·m-2·s-1, leaf temperature was 25±3°C and the vapor pressure deficit from leaf to air was 2] entering the chamber was varied stepwise (400, 250, 350, 450, 650, 850, 1200, 1500 ppm). A minimum of 20 minutes was allowed for A and gs to completely stabilize before data were collected at each [CO2]. For each individual leaf, linear least squares regression was used to estimate the stomatal slope based on the Ball et al. (1987) model of stomatal conductance (not used in present study but provided as data in [appendix]), and then separately for the Leuning (1995) model of stomatal conductance. A common value of Γ = 40μP/Pa, and D0 = 1500 Pa was used in accordance with Leuning (1995).
The stomatal_slope.csv file contains the following columns:
number: order of measurement
species: latin name of plant species measured
m_bb: slope from the Ball et al. (1985) model
se_bb: standard error for estimate of m_bb
m_leuning: slope from Leuning (1995) model
m_se_leuning: standard error for estimate of m_leuning
go_leuning
go_se_leuning: standard error for estimate of go_leuning
trait_id: primary key for identification in BETYdb (www.betydb.org), additional metadata available for trait available at www.betydb.org/traits/
The pavi_data.csv file contains the following columns:
trait: name of trait, with units
mean: mean of observations
n: number of observations
se: standard error (or conservative estimate of standard error, derived using calculations in [Supplement 2]).
citation: Author and year citation where first published (see below)
trait_id: primary key for identification in BETYdb (www.betydb.org), additional metadata available for trait available at www.betydb.org/traits/>
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