219 research outputs found
On the reflectance spectroscopy of snow
We propose a system of analytical equations to retrieve snow grain
size and absorption coefficient of pollutants from snow reflectance or snow
albedo measurements in the visible and near-infrared regions of the
electromagnetic spectrum, where snow single-scattering albedo is close to
1.0. It is assumed that ice grains and impurities (e.g., dust, black and
brown carbon) are externally mixed, and that the snow layer is semi-infinite and
vertically and horizontally homogeneous. The influence of close-packing
effects on reflected light intensity are assumed to be small and ignored. The
system of nonlinear equations is solved analytically under the assumption that
impurities have the spectral absorption coefficient, which obey the
Ångström power law, and the impurities influence the registered spectra
only in the visible and not in the near infrared (and vice versa for ice grains).
The theory is validated using spectral reflectance measurements and albedo of
clean and polluted snow at various locations (Antarctica Dome C, European
Alps). A technique to derive the snow albedo (plane and spherical) from
reflectance measurements at a fixed observation geometry is proposed. The
technique also enables the simulation of hyperspectral snow reflectance
measurements in the broad spectral range from ultraviolet to the
near infrared for a given snow surface if the actual
measurements are performed at a restricted number of wavelengths (two to four,
depending on the type of snow and the measurement system).</p
Revisiting the contribution of transpiration to global terrestrial evapotranspiration
Even though knowing the contributions of transpiration (T), soil and open water evaporation (E), and interception (I) to terrestrial evapotranspiration (ET=T+E+I) is crucial for understanding the hydrological cycle and its connection to ecological processes, the fraction of T is unattainable by traditional measurement techniques over large scales. Previously reported global mean T/(E+T+I) from multiple independent sources, including satellite-based estimations, reanalysis, land surface models, and isotopic measurements, varies substantially from 24% to 90%. Here we develop a new ET partitioning algorithm, which combines global evapotranspiration estimates and relationships between leaf area index (LAI) and T/(E+T) for different vegetation types, to upscale a wide range of published site-scale measurements. We show that transpiration accounts for about 57.2% (with standard deviation6.8%) of global terrestrial ET. Our approach bridges the scale gap between site measurements and global model simulations,and can be simply implemented into current global climate models to improve biological CO2 flux simulations
Saharan dust events in the European Alps: role in snowmelt and geochemical characterization
The input of mineral dust from arid regions impacts snow
optical properties. The induced albedo reduction generally alters the
melting dynamics of the snowpack, resulting in earlier snowmelt. In this
paper, we evaluate the impact of dust depositions on the melting dynamics of
snowpack at a high-elevation site (2160 m) in the European Alps (Torgnon,
Aosta Valley, Italy) during three hydrological years (2013–2016). These
years were characterized by several Saharan dust events that deposited
significant amounts of mineral dust in the European Alps. We quantify the
shortening of the snow season due to dust deposition by comparing observed snow
depths and those simulated with the Crocus model accounting, or not, for the
impact of impurities. The model was run and tested using meteorological data
from an automated weather station. We propose the use of repeated digital
images for tracking dust deposition and resurfacing in the snowpack. The
good agreement between model prediction and digital images allowed us to
propose the use of an RGB index (i.e. snow darkening index – SDI) for
monitoring dust on snow using images from a digital camera. We also present
a geochemical characterization of dust reaching the Alpine chain during
spring in 2014. Elements found in dust were classified as a function of
their origin and compared with Saharan sources. A strong enrichment in Fe
was observed in snow containing Saharan dust. In our case study, the
comparison between modelling results and observations showed that impurities
deposited in snow anticipated the disappearance of snow up to 38 d a out of
a total 7 months of typical snow duration. This happened for the season
2015–2016 that was characterized by a strong dust deposition event. During
the other seasons considered here (2013–2014 and 2014–2015), the snow
melt-out date was 18 and 11 d earlier, respectively. We conclude that the
effect of the Saharan dust is expected to reduce snow cover duration through
the snow-albedo feedback. This process is known to have a series of further
hydrological and phenological feedback effects that should be characterized
in future research.</p
Unlocking legal validity. Some remarks on the artificial ontology of law
Following Kelsen’s influential theory of law, the concept of validity has been used in the literature to refer to different properties of law (such as existence, membership, bindingness, and more) and so it is inherently ambiguous. More importantly, Kelsen’s equivalence between the existence and the validity of law prevents us from accounting satisfactorily for relevant aspects of our current legal practices, such as the phenomenon of ‘unlawful law’. This chapter addresses this ambiguity to argue that the most important function of the concept of validity is constituting the complex ontological paradigm of modern law as an institutional-normative practice. In this sense validity is an artificial ontological status that supervenes on that of existence of legal norms, thus allowing law to regulate its own creation and creating the logical space for the occurrence of ‘unlawful law’. This function, I argue in the last part, is crucial to understanding the relationship between the ontological and epistemic dimensions of the objectivity of law. For given the necessary practice-independence of legal norms, it is the epistemic accessibility of their creation that enables the law to fulfill its general action-guiding (and thus coordinating) function
Leaf photosynthesis and respiration of three bioenergy crops in relation to temperature and leaf nitrogen: how conserved are biochemical model parameters among crop species?
Given the need for parallel increases in food and energy production from crops in the context of global change, crop simulation models and data sets to feed these models with photosynthesis and respiration parameters are increasingly important. This study provides information on photosynthesis and respiration for three energy crops (sunflower, kenaf, and cynara), reviews relevant information for five other crops (wheat, barley, cotton, tobacco, and grape), and assesses how conserved photosynthesis parameters are among crops. Using large data sets and optimization techniques, the C3 leaf photosynthesis model of Farquhar, von Caemmerer, and Berry (FvCB) and an empirical night respiration model for tested energy crops accounting for effects of temperature and leaf nitrogen were parameterized. Instead of the common approach of using information on net photosynthesis response to CO2 at the stomatal cavity (An–Ci), the model was parameterized by analysing the photosynthesis response to incident light intensity (An–Iinc). Convincing evidence is provided that the maximum Rubisco carboxylation rate or the maximum electron transport rate was very similar whether derived from An–Ci or from An–Iinc data sets. Parameters characterizing Rubisco limitation, electron transport limitation, the degree to which light inhibits leaf respiration, night respiration, and the minimum leaf nitrogen required for photosynthesis were then determined. Model predictions were validated against independent sets. Only a few FvCB parameters were conserved among crop species, thus species-specific FvCB model parameters are needed for crop modelling. Therefore, information from readily available but underexplored An–Iinc data should be re-analysed, thereby expanding the potential of combining classical photosynthetic data and the biochemical model
Gregarine Cephaloidophora communis mawrodiadi, 1908 in the barnacle Euraphia rhyzophorae, Oliveira, 1940 from Brazil
A unique approach to demonstrating that apical bud temperature specifically determines leaf initiation rate in the dicot Cucumis sativus
Finzioni giuridiche e letterarie: è possibile una teoria unificata?
Il saggio presenta una teoria coerentista delle finzioni, concentrandosi sulle finzioni giuridiche e letterarie e mostrando come, nonostante le loro differenze, questi due tipi di finzioni rispondano a dei requisiti di credibilità come coerenza
Pragmática de lo indeterminado
Viene trattato in termini pragmatici il problema dell'indeterminatezza del linguaggio giuridico, proponendo alcuni criteri pragmatici per la sua riduzione
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