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1

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Growth, microstructure and electronic properties of amorphous carbon nitride films investigated by plasma diagnostics (1999)

Bhattacharyya, Somnath ; Granier, A. ; Turban, G.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 4668-4676

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Amorphous nitrogenated carbon films are prepared in a dual electron cyclotron resonance-radio frequency plasma from a mixture of methane and nitrogen gas. A marked variation of electronic properties and microstructure of the films as a function of nitrogen concentration is observed from Fourier transform infrared (FTIR) spectra, electron energy loss spectra, optical absorption spectra, x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and electrical conductivity. From the variation of intensity of different positive ions and neutral radicals, using quadrupole mass spectroscopy and optical emission spectroscopy, the growth rate, structure and properties of the films are investigated. The density of methyl (CH3) radicals and the film growth rate are found to decrease with the increase of nitrogen concentration. A correlation between the C/N atomic ratio in the films and CH/CN and also CH/N ratio in the plasma is noticed. Also, the CH radical intensity in the plasma and the amount of CH bonds in the films, observed from FTIR spectra, vary in a similar fashion as a function of nitrogen concentration. A model describing film growth and nitrogen incorporation in the films is proposed. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.371419

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2

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Transpiration of trees and forest stands: short and long-term monitoring using sapflow methods (1996)

GRANIER, A. ; BIRON, P. ; BRÉDA, N. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Global change biology 2 (1996), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement.Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985).Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10–15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35–50%) in a tropical rain forest. It also increases after thinning or during a dry spell.A set of 5–10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend.For modelling purposes, tree canopy conductance (gc) was calculated from Penman-Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of gc for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2486.1996.tb00078.x

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3

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Soil water dynamics in an oak stand (1995)

Bréda, N. ; Granier, A. ; Barataud, F. ; [et al.]

Springer

Plant and soil 172 (1995), S. 17-27

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ISSN: 1573-5036

Keywords: drought ; in situ ; leaf water potential ; Quercus petraea ; Quercus robur ; soil water ; soil water potential ; soil water uptake ; root

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Soil water dynamics under a mixed stand of mature sessile and pedunculate oaks were studied both under natural conditions and during imposed water shortages in a lysimeter. Root densities of each species were described in situ by counting roots in the trench surrounding the dry plot. Soil water contents and potentials, and pre-dawn leaf water potentials (Ψwp) were monitored during three successive years. Soil water retention characteristics were obtained from field measurements of water potential and water content. The decreasing rooting density with depth was strongly related to soil physical properties. The root system was separated into two compartments by a layer with a high clay content. The deepest soil compartment was mainly explored by fine roots. Neutron probe measurements allowed the detection of variations in water content down to a depth of 2.00 m. The distribution of water uptake among the different soil layers changed when drought increased. Water was extracted from the deepest reservoir, and capillary rises even occurred after partial water depletion in the upper part of the soil. Seasonal trends of pre-dawn leaf water potential generally matched those of soil water potential in the wettest rooted zone, which was at − 140 cm. In the upper, dry, horizons, the sharp loss of soil hydraulic conductivity reduced water transport to roots leading to impossible equilibrium between roots and soil at pre-dawn. Finally, Ψwp presented a low sensitivity to variations of total soil water content between 40% and 100% of extractable water. Below this threshold, Ψwp decreased sharply to a minimal value of about − 2.0 MPa.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00020856

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4

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Soil water dynamics in an oak stand (1995)

Barataud, F. ; Moyne, C. ; Bréda, N. ; [et al.]

Springer

Plant and soil 172 (1995), S. 29-43

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ISSN: 1573-5036

Keywords: modelisation ; soil-root interface ; soil water potential ; soil water uptake ; transient state

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract A model describing water uptake by plants with particular attention to the soil-root interface under transient conditions is derived and discussed. Field data on a daily scale enable the unknown parameters of the model to be determined with the help of an identification technique. The model is then used to analyse the experimental results presented in part I of this paper. The loss of total conductivity of the soil-tree system under drought conditions whereas the metabolism of the trees seems to remain unaffected can be explained by the increase of the soil-root resistance. In fact this resistance becomes the limiting factor when the volumetric soil water content decreases (below θ=0.33 for the superficial layer and 0.36 for the deeper one in the studied case). Such values can be frequently encountered at the end of summer.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00020857

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5

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Polymer treatment in the flowing afterglow of an oxygen microwave discharge: Active species profile concentrations and kinetics of the functionalization (1995)

Normand, F. ; Granier, A. ; Leprince, P. ; [et al.]

Springer

Plasma chemistry and plasma processing 15 (1995), S. 173-198

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ISSN: 1572-8986

Keywords: Singlet molecular oxygen ; atomic oxygen ; flowing afterglow ; downstream reactor ; microwave discharge ; PP ; PF ; PC ; hexatriacontane ; octadecyloctadecanoate ; functionalization

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology

Notes: Abstract The surface treatment of different polymers and their corresponding model surfaces in the flowing afterglow of an oxygen microwave plasma is investigated. The concentration profiles of tire long-lived species issued from the plasma are measured and calculated in the downstream area The influence of atomic and singlet molecular oxygen in the behavior of different polymers is investigated. It appears that the evolution of the surface energy can be explained by an initiation of the functionalization by the oxygen atoms impinging upon the surface followed by reaction of the radicals formed with molecular oxygen. The concentration of functions at the sureface is limited due to their destruction by reaction with oxygen atoms. Furthermore, the functionalization level is higher in the /lowing afterglow than in the plasma, without any significant degradation of the polymer surface. Therefore, the treatment in the flowing afterglow is more efficient to increase suface energy in particular, for polymers which undergo high backbone chain scission.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01459695

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6

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The HartX-synthesis: An experimental approach to water and carbon exchange of a Scots pine plantation (1996)

Bernhofer, Ch. ; Gay, L. W. ; Granier, A. ; [et al.]

Springer

Theoretical and applied climatology 53 (1996), S. 173-183

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ISSN: 1434-4483

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Summary In May 1992 during the interdisciplinary measurement campaign HartX (Hartheim eXperiment), several independent estimates of stand water vapor flux were compared at a 12-m high Scots pine (Pinus silvestris) plantation on a flat fluvial terrace of the Rhine close to Freiburg, Germany. Weather during the HartX period was characterized by ten consecutive clear days with exceptionally high input of available energy for this time of year and with a slowly shifting diurnal pattern in atmospheric variables like vapor pressure deficit. Methods utilized to quantify components of stand water flux included porometry measurements on understory graminoid leaves and on pine needles and three different techniques for determining individual tree xylem sap flow. Micrometeorological methods included eddy covariance and eddy covariance energy balance techniques with six independent systems on two towers separated by 40 m. Additionally, Bowen ratio energy balance estimates of water flux were conducted and measurements of the gradients in water vapor, CO2, and trace gases within and above the stand were carried out with an additional, portable 30 m high telescoping mast. Biologically-based estimates of overstory transpiration were obtained by up-scaling tree sap flow rates to stand level via cumulative sapwood area. Tree transpiration contributed between 2.2 and 2.6 mm/day to ET for a tree leaf area index (LAI) of 2.8. The pine stand had an understory dominated by sedge and grass species with overall average LAI of 1.5. Mechanistic canopy gas exchange models that quantify both water vapor and CO2 exchange were applied to both understory and tree needle ecosystem compartments. Thus, the transpiration by graminoid species was estimated at approximately 20% of total stand ET. The modelled estimates for understory contribution to stand water flux compared well with micrometeorologically-based determinations. Maximum carbon gain was estimated from the canopy models at approximately 425 mmol/(m2day) for the tree needles and at 100 mmol/(m2day) for the understory. Carbon gain was suggested by the modelling analysis to remain relatively constant during the HartX period, while water use efficiency in carbon fixation increased with decreasing vapor pressure deficit. Biologically- and micrometeorologically-based estimates of stand water flux showed good general agreement with variation of up to 20% that reflects both errors due to the inherent assumptions associated with different methods as well as natural spatial variability in fluxes. The various methods support a reliable estimate of average ET from this homogeneous canopy during HartX of about 2.6 mm/day (a maximum of about 3.1 mm/day) with an insignificant decreasing trend in correlation with decreasing vapor pressure deficit and possibly soil moisture. Findings during HartX were embedded in local scale heterogeneity with greater roughness over the forest and much higher ET over the surrounding agricultural fields which results in weak but clearly existant circulation patterns. A variety of measurements were continued after the HartX campaign. They allow us to extend our findings for six months with changing environmental conditions, including shortage of soil moisture. Hydrological estimates of soil water extractions and micrometeorological estimates of ET by the one-propeller eddy covariance (OPEC) system were in very good agreement, supporting the use of this robust eddy covariance energy balance technique for long-term monitoring.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00866421

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Comparisons of xylem sap flow and water vapour flux at the stand level and derivation of canopy conductance for Scots pine (1996)

Granier, A. ; Biron, P. ; Köstner, B. ; [et al.]

Springer

Theoretical and applied climatology 53 (1996), S. 115-122

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ISSN: 1434-4483

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Summary Simultaneous measurements of xylem sap flow and water vapour flux over a Scots pine (Pinus sylvestris) forest (Hartheim, Germany), were carried out during the Hartheim Experiment (HartX), an intensive observation campaign of the international programme REKLIP. Sap flow was measured every 30 min using both radial constant heating (Granier, 1985) and two types of Cermak sap flowmeters installed on 24 trees selected to cover a wide range of the diameter classes of the stand (min 8 cm; max 17.5 cm). Available energy was high during the observation period (5.5 to 6.9 mm.day−1), and daily cumulated sap flow on a ground area basis varied between 2.0 and 2.7 mm day−1 depending on climate conditions. Maximum hourly values of sap flow reached 0.33 mm h−1, i.e., 230 W m−2. Comparisons of sap flow with water vapour flux as measured with two OPEC (One Propeller Eddy Correlation, University of Arizona) systems showed a time lag between the two methods, sap flow lagging about 90 min behind vapour flux. After taking into account this time lag in the sap flow data set, a good agreement was found between both methods: sap flow = 0.745* vapour flux,r 2 = 0.86. The difference between the two estimates was due to understory transpiration. Canopy conductance (g c ) was calculated from sap flow measurements using the reverse form of Penman-Monteith equation and climatic data measured 4 m above the canopy. Variations ofg c were well correlated (r 2 = 0.85) with global radiation (R) and vapour pressure deficit (vpd). The quantitative expression forg c =f (R, vpd) was very similar to that previously found with maritime pine (Pinus pinaster) in the forest of Les Landes, South Western France.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00866416

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Estimates of water vapor flux and canopy conductance of Scots pine at the tree level utilizing different xylem sap flow methods (1996)

Köstner, B. ; Biron, P. ; Siegwolf, R. ; [et al.]

Springer

Theoretical and applied climatology 53 (1996), S. 105-113

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ISSN: 1434-4483

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Summary During the Hartheim Experiment (HartX) 1992 conducted in the upper Rhine Valley, Germany, three different methods were used to measure sap flow in Scots pine trees via heating of water transported in the xylem: (1) constant heating applied radially in the sapwood (“Granier-system”-G), (2) constant heating of a stem segment (“Čermák-system”-C), and (3) regulated variable heating of a stem segment that locally maintains a constant temperature gradient in the trunk (“Čermák/Schulze-system”-CS). While the constant heating methods utilize changes in the induced temperature gradient to quantify sap flux, the CS-system estimates water flow from the variable power requirement to maintain a 2 or 3 degree Kelvin temperature gradient over a short distance between inserted electrodes and reference point. The C- and CS-systems assume that all transported water is encompassed and equally heated by the electrodes. In this case, flux rate is determined from temperature difference or energy input and the heat capacity of water. Active sapwood area need not be determined exactly. In contrast, the G-system requires an empirical calibration of the sensors that allows conversion of temperature difference into sap flow density. Estimates of sapwood area are used to calculate the total flux. All three methods assume that the natural fluctuation in temperature of the trunk near the point of insertion of heating and sensing elements is the same as that where reference thermocouples are inserted. Using all three systems, 24 trees were simultaneously monitored during the HartX campaign. Tree size within the stand ranged between 18 and 61 cm circumference at breast height, while sample trees ranged between 24 and 55 cm circumference. The smallest trees could only be measured by utilizing the G-system. Sap flow rates of individual trees measured at breast height increased rapidly in the morning along with increases in irradiance and vapor pressure deficit (D), decreased slowly during the course of the afternoon with continued increase inD, and decreased more slowly during the night. Ignoring potential effects introduced by the different methods, maximum flow rates of individual trees ranged between 0.5 and 2.5 kg H2O h−1 tree−1 or 0.3 and 0.6 mm h−1 related to projected crown area of trees and daily sums of sap flow for individual trees varied between 4.4 and 24 kg H2O tree−1 d−1 or 1.1 and 6.0 mm d−1. Maximum sap flow rates per sapwood area of trees varied least for the G-system (11–17 g cm−2 h−1) and was of similar magnitude as the C- (8–21 g cm−2 h−1) and CS-system (4–14 g cm−2 h−1). Regressions of total tree conductance (g t ) derived from sap flow estimates demonstrated the same linear increase of conductance with increasing irradiance, however decrease of conductance with increasingD under non-limiting light conditions was different for the three systems with strongest reduction ofg t measured with the CS-system followed by the C- and G-system. This led to different estimates of daily sap flow rates especially during the second part of the measurement period. Variation in sap flow rates is explained on the basis of variation in leaf area index of individual trees, heterogeneity in soil conditions, and methodological differences in sap flow measurements. Despite the highly uniform plantation forest at the scale of hectares, the heterogeneity in tree size and soil depth at the scale of square meters still make it difficult to appropriately and efficiently select sample trees and to scale-up water flux from individual trees to the stand level.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00866415

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