Association of riparian features and water chemistry with reed litter breakdown in a volcanic lake (Lake Vico,Italy)     

Maria Letizia Costantini  Loreto Rossi  Fabrizio Scialanca  Giuseppe Nascetti  David Rossi  Letizia Sabetta 《Aquatic Sciences - Research Across Boundaries》2007,69(4):503-510

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An incentive mechanism for reducing emissions from conversion of intact and non-intact forests   总被引：1，自引：0，他引：1  

Danilo Mollicone  Frédéric Achard  Sandro Federici  Hugh D. Eva  Giacomo Grassi  Alan Belward  Frank Raes  Günther Seufert  Hans-Jürgen Stibig  Giorgio Matteucci  Ernst-Detlef Schulze 《Climatic change》2007,83(4):477-493

This paper presents a new accounting mechanism in the context of the UNFCCC issue on reducing emissions from deforestation in developing countries, including technical options for determining baselines of forest conversions. This proposal builds on the recent scientific achievements related to the estimation of tropical deforestation rates and to the assessment of ‘intact’ forest areas. The distinction between ‘intact’ and ‘non intact’ forests used here arises from experience with satellite-based deforestation measurements and allows accounting for carbon losses from forest degradation. The proposed accounting system would use forest area conversion rates as input data. An optimal technical solution to set baselines would be to use historical average figures during the time period from 1990 to 2005. The system introduces two different schemes to account for preserved carbon: one for countries with high forest conversion rates where the desired outcome would be a reduction in their rates, and another for countries with low rates. A ‘global’ baseline rate would be used to discriminate between these two country categories (high and low rates). For the hypothetical accounting period 2013–2017 and considering 72% of the total tropical forest domain for which data are available, the scenario of a 10% reduction of the high rates and of the preservation of low rates would result in approximately 1.6 billion tCO₂ of avoided emissions. The resulting benefits of this reduction would be shared between those high-rate countries which reduced deforestation and those low-rate countries which did not increase their deforestation over an agreed threshold (e.g., half of “global” baseline rate).  相似文献   

Decentralization, forests and livelihoods: Theory and narrative   总被引：3，自引：0，他引：3  

Luca Tacconi   《Global Environmental Change》2007,17(3-4):338-348

This paper discusses the theory of decentralized forest management, the associated narrative and the underlying hypotheses. That discussion informs the assessment of whether decentralization can lead to forest conservation. The paper argues that the ideal model of democratic decentralization described in the literature is unlikely to be implemented given the governance constraints present in many tropical forest countries. Even if that model could be implemented, it is shown that decentralization cannot be expected to necessarily lead to forest conservation. The policies required to complement the current decentralization model are discussed, including financial incentives and monitoring and evaluation mechanisms.  相似文献   

Incommensurate–normal phase transition in natural melilite: an in situ high-temperature X-ray single-crystal study     

Luca Bindi  P. Bonazzi 《Physics and Chemistry of Minerals》2005,32(2):89-96

The structure of a natural melilite with chemical composition (Ca_1.87Sr_0.02Na_0.10K_0.02)_2.01(Mg_0.96Al_0.07)_1.03(Si_1.98Al_0.02)_2.00O₇ has been investigated by X-ray single-crystal diffraction methods within the temperature range 298–773 K. The values of the coefficient of the modulation wave vector were determined at 298 K, 323 K, 348 K, and 358 K. These values show a continuous linear decrease from 0.2833(6) at 298 K to 0.2763(9) at 358 K. The incommensurate phase undergoes a phase transition to the normal phase at 359 K. The refinements of the structure, carried out at 298 K, 348 K, 359 K, 373 K, 413 K, 463 K, 513 K, 573 K, 673 K, and 773 K, showed that the normal phase (high-temperature phase) does not significantly differ from the basic structure (the average structure of the incommensurate structure). This study confirms that in natural melilites with chemical composition close to that of åkermanite the wavelength of the incommensurate modulation increases when the temperature rises. The different behaviour of the q-vector as a function of temperature in natural and synthetic åkermanite is discussed.  相似文献   

Thermodynamic behaviour of the high-temperature P\bar 1{\text{-}}I\bar 1 phase transition along the CaAl2Si2O8–SrAl2Si2O8 join     

M. Tribaudino  P. Benna  F. Nestola  C. Meneghini  E. Bruno 《Physics and Chemistry of Minerals》2005,32(4):314-321

In situ high-temperature synchrotron radiation powder diffraction patterns were taken from room temperature to T = 740°C from synthetic feldspars along the join CaAl₂Si₂O₈–SrAl₂Si₂O₈ (An–SrF). Three samples of composition An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ were investigated, and the evolution of cell parameters with T was determined by Rietveld analysis of powder X-ray diffraction patterns. The high-temperature $P\bar 1{\text{-}}I\bar 1$ phase transition, previously observed with T _c = 241°C in anorthite, was found in An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ feldspars at T _c = 233(5)°, 195(2)° and 174(2)°C respectively. The transition was revealed by the disappearance of critical reflections and variations in the rate of change of cell parameters with temperature. A significant, although small (between 0.0025 and 0.0012 at room temperature), spontaneous strain could be measured, allowing the thermodynamic behaviour of the transition to be modelled. A second-order trend for An₉₀SrF₁₀ and An₈₅SrF₁₅ [β = 0.504(7) and 0.505(7) respectively] or nearly second-order for An₉₅SrF₅[β = 0.458(4)] was observed in contrast with tricritical behaviour of end member anorthite. An extrapolation of the T _c versus composition to room temperature indicates that the critical composition for the $P\bar 1$ phase is An₆₀SrF₄₀.  相似文献   

Meridional variations of temperature, C₂H₂ and C₂H₆ abundances in Saturn's stratosphere at southern summer solstice     

Thomas K. Greathouse  John H. Lacy  Bruno Bézard  Caitlin A. Griffith 《Icarus》2005,177(1):18-31

Measurements of the vertical and latitudinal variations of temperature and C₂H₂ and C₂H₆ abundances in the stratosphere of Saturn can be used as stringent constraints on seasonal climate models, photochemical models, and dynamics. The summertime photochemical loss timescale for C₂H₆ in Saturn's middle and lower stratosphere (∼40-10,000 years, depending on altitude and latitude) is much greater than the atmospheric transport timescale; ethane observations may therefore be used to trace stratospheric dynamics. The shorter chemical lifetime for C₂H₂ (∼1-7 years depending on altitude and latitude) makes the acetylene abundance less sensitive to transport effects and more sensitive to insolation and seasonal effects. To obtain information on the temperature and hydrocarbon abundance distributions in Saturn's stratosphere, high-resolution spectral observations were obtained on September 13-14, 2002 UT at NASA's IRTF using the mid-infrared TEXES grating spectrograph. At the time of the observations, Saturn was at a LS≈270°, corresponding to Saturn's southern summer solstice. The observed spectra exhibit a strong increase in the strength of methane emission at 1230 cm⁻¹ with increasing southern latitude. Line-by-line radiative transfer calculations indicate that a temperature increase in the stratosphere of ≈10 K from the equator to the south pole between 10 and 0.01 mbar is implied. Similar observations of acetylene and ethane were also recorded. We find the 1.16 mbar mixing ratio of C₂H₂ at −1° and −83° planetocentric latitude to be and , respectively. The C₂H₂ mixing ratio at 0.12 mbar is found to be at −1° planetocentric latitude and at −83° planetocentric latitude. The 2.3 mbar mixing ratio of C₂H₆ inferred from the data is and at −1° and −83° planetocentric latitude, respectively. Further observations, creating a time baseline, will be required to completely resolve the question of how much the latitudinal variations of C₂H₂ and C₂H₆ are affected by seasonal forcing and/or stratospheric circulation.  相似文献   

Modélisation du courant sagittal induit par les vagues au-dessus des systèmes barre/baïne de la côte aquitaine (France)     

Bruno Castelle  Philippe Bonneton 《Comptes Rendus Geoscience》2006,338(10):711-717

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UV-Vis spectrophotometric and XAFS studies of ferric chloride complexes in hyper-saline LiCl solutions at 25-90 °C     

Weihua Liu  Barbara Etschmann  Leone Spiccia  Brent McInnes 《Chemical Geology》2006,231(4):326-349

The speciation and thermodynamic properties of ferric chloride complexes in hydrothermal solutions and hypersaline brines are still poorly understood, despite the importance of this element as a micronutrient and ore-component. Available experimental data are limited to room temperature and relatively low chloride concentrations. This paper reports results of UV-Vis spectrophotometric and synchrotron XAFS experiments of ferric chloride complexes in chloride concentrations up to 15 m and at temperatures of 25-90 °C. Qualitative interpretation of the UV-Vis spectra shows that FeCl²⁺, FeCl₂⁺, FeCl_3(aq) and FeCl₄⁻ were present in the experimental solutions. As chloride concentrations increase, higher ligand number complexes become important with FeCl₄⁻ predominating in solutions containing more than 10 m at 25 °C. The predominance fields of FeCl_3(aq) and FeCl₄⁻ expand to lower Cl concentrations with increasing T. Both XANES and UV-Vis spectra reveal a major change in the geometry of the complex between FeCl₂⁺ and FeCl_3(aq). EXAFS data confirm that the number of chloride ligands increases with increasing chloride concentration and show that Fe³⁺, FeCl²⁺ and FeCl₂⁺ share an octahedral geometry. FeCl_3(aq) could be either tetrahedral or trigonal dipyramidal, while FeCl₄⁻ is expected to be tetrahedral. EXAFS data support a tetrahedral geometry for FeCl₄⁻, especially at 90 °C, but do not allow to distinguish between a tetrahedral or trigonal dipyramidal geometry for FeCl_3(aq) because of similar Fe-Cl distances. At room temperature, EXAFS data suggest that FeCl_3(aq) may be a mixture of octahedral and tetrahedral or trigonal dipyramidal forms.The room temperature formation constants for three ferric chloride complexes (FeCl₂⁺, FeCl_3(aq) and FeCl₄⁻) determined from the UV data are generally in good agreement with previous studies. Calculations based on the properties extrapolated to 300 °C show that hematite solubility is much higher than previously estimated, and that the high orders complexes FeCl_3(aq) and FeCl₄⁻ are important at high temperatures even in solutions with low chloride concentrations. The accuracy of these properties is limited by a poor understanding of activity-composition relationships in concentrated electrolytes, and by limitations in the available experimental techniques and extrapolation algorithms; however, the inclusion of higher order complexes in numerical models of ore transport and deposition allows for a more accurate qualitative prediction of Fe behaviour in hydrothermal and hypersaline systems.  相似文献   

Geometry of Poincaré's Variables and the Secular Planetary Problem     

Bruno Cordani 《Celestial Mechanics and Dynamical Astronomy》2004,89(2):165-179

A method for the expansion of the perturbative Hamiltonian in the planetary problem is presented, which allows one to immediately detect the terms vanishing under the averaging process. The method bases itself on a geometrical analysis, through the groups SO(3) and SU(2), of the Poincaré canonical variables or of the similar Laplace variables. As an outcome, one obtains a MAPLE program, which calculates the first averaged terms of the perturbative Hamiltonian. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Intermittency of magnetic turbulence in slow solar wind     

Vincenzo Carbone  Roberto Bruno  Fabio Lepreti 《Planetary and Space Science》2004,52(10):953-956

We investigate the properties of intermittency of magnetic turbulence by using magnetic field data collected by the Helios spacecraft in the inner heliosphere. Clear scaling laws for magnetic structure functions are visible in periods where the velocity of the bulk plasma is low. Within these periods we found that intermittency of magnetic turbulence is high with respect to velocity field. A comparison with fluid flows where passive scalars are more intermittent than velocity, yields to consider the magnetic field like a “passive vector”.  相似文献