1,627 research outputs found
Energy-efficient traffic engineering
The energy consumption in telecommunication networks is expected to grow considerably, especially in core networks. In this chapter, optimization of energy consumption is approached from two directions. In a first study, multilayer traffic engineering (MLTE) is used to assign energy-efficient paths and logical topology to IP traffic. The relation with traditional capacity optimization is explained, and the MLTE strategy is applied for daily traffic variations. A second study considers the core network below the IP layer, giving a detailed power consumption model. Optical bypass is evaluated as a technique to achieve considerable power savings over per-hop opticalelectronicoptical regeneration.
Document type: Part of book or chapter of boo
Online attention for interpretable conflict estimation in political debates
Conflict arises naturally in dyadic interactions when involved individuals act on incompatible goals, interests, or actions. In this paper, the problem of conflict intensity estimation from audiovisual recordings is addressed. To this end, we propose an online attention-based neural network in order to learn a mapping from a sequence of audiovisual features to time-series describing conflict intensity. The proposed method is evaluated by conducting experiments in conflict intensity estimation by employing the CONFER dataset. Experimental results indicate the superiority of the proposed model compared to the state of the art. Furthermore, we demonstrate that by incorporating sparsity in the model, the origin of conflict can be traced back to specific key frames facilitating the interpretation of conflict escalation
On the information content of incubation studies
The measurement of the production of CO2 from soils in incubation studies has been used for many years to gain information about the influence of different soils types, changing temperatures and water contents, as well as the addition of amendments on the soil respiration. While in the early years the kinetic modelling (or fitting) was restricted to the single or one pool model due to the possibility of solving the problem by log-transforming the observed data an using a linear regression for the estimation of the rate constant (by doing so an analytical solution can be applied), more recent publications chose multi-pool models (2, 3, and even 4-pools), which can will be fitted iteratively using appropriate computer software. In general, there are different methods used in literature to estimate the kinetic parameters resulting in different kinetic parameter values even for the same data set. Additionally, screening of existing literature revealed that the 2-pool model (or even higher pool models) were sometimes obviously wrong fitted or over fitted. In our presentation, we will show how different constrains in the fitting process will influence the results of the kinetic parameter values, how obviously wrong fitting and overfitting can be easily detected, and how the information content of the incubation data can be easily judged prior any fitting. Finally, we will provide recommendations how to extract information from incubation experiments
Utilisation de l'expérience de drainage à pas de pression multiples pour la détermination des fonctions hydrauliques du sol par la méthode inverse : résultats expérimentaux
La méthode de drainage à pas de pression multiples, combinée avec la méthode inverse, permet la détermination des fonctions hydrauliques du sol (têta(h) et K(h)) simultanément. Cependant, le choix des fonctions décrivant têta(h) et K(h) du sol est d'une importance capitale dans cette méthode. Les résultats expérimentaux montrent que le modèle de CAMPBELL (1974) dans sa version améliorée par HUTSON et CASS (1987) permet une description raisonnable du processus du drainage en fonction du temps et correspondant à des pas de pression croissants. Les courbes de rétention d'eau déduites des paramètres optimisés par la méthode inverse ont les mêmes allures que celles déterminées par la méthode standard (bac de sable et cellules à basses et hautes pressions). Ces résultats sont plus représentatifs de la réalité lorsque les paramètres têta(s) et K(s) sont fixes et égaux aux valeurs expérimentales, avec une précision sensiblement la même dans les cas d'optimisation, où têta(s) est fixe et têta(s) et K(s) fixes et égaux aux valeurs expérimentales; le premier cas où seulement le paramètre têta(s) est fixe est suggéré (il y a moins de paramètres à mesurer). (Résumé d'auteur
Atomic Layer Deposition-Based Synthesis of Photoactive TiO2 Nanoparticle Chains by Using Carbon Nanotubes as Sacrificial Templates
Highly ordered and self supported anatase TiO2 nanoparticle chains were
fabricated by calcining conformally TiO2 coated multi-walled carbon nanotubes
(MWCNTs). During annealing, the thin tubular TiO2 coating that was deposited
onto the MWCNTs by atomic layer deposition (ALD) was transformed into chains of
TiO2 nanoparticles (~12 nm diameter) with an ultrahigh surface area (137 cm2
per cm2 of substrate), while at the same time the carbon from the MWCNTs was
removed. Photocatalytic tests on the degradation of acetaldehyde proved that
these forests of TiO2 nanoparticle chains are highly photo active under UV
light because of their well crystallized anatase phase
Deriving soil hydraulic parameters in a high spatial resolution for a heterogeneous agricultural field-site
Providing information about the structure of the subsurface plays an important role for setting up soil hydraulic models, which are in turn an important prerequisite for ecosystem modelling approaches. Because soils often show a high within-field heterogeneity in terms of texture, stone content, and bulk density, they may also exhibit a wide range of hydraulic properties in the field. During water stress periods and especially on agricultural fields, which are characterized by uniform vegetation, the occurrence of a within-field heterogeneity in terms of soil hydraulic properties can be observed as it affects the different water status of the plants. The patterns of visible plant water stress and areas of low apparent electrical conductivities measured by electromagnetic induction measurements (EMI) often coincide, for e.g. within sugar beet cropped fields. Such observations have also been made beforehand at the current study site; an agricultural field (2.7 ha) that is situated in an area developed by fluvial processes. To account for this, the current approach included a sampling campaign on a field with 70 drilling locations for texture and organic carbon analyses. Furthermore, soil water retention functions and saturated hydraulic conductivity were determined at 20 sampling locations. Our approach for ecosystem modelling is based on 4 m² grid cells over the whole study site. To consider within-field heterogeneity in the ecosystem model, soil hydraulic parameters were predicted for each grid cell, whereby different approaches such as spatial interpolation, Miller-Miller scaling, and the use of pedotransfer functions were taken into account to identify the most appropriate approach
Utilisation de l'expérience de drainage à pas de pression multiples pour la détermination des fonctions hydrauliques du sol par la méthode inverse : présentation et évaluation de la méthode
L'optimisation des paramètres des fonctions décrivant les propriétés hydrauliques du sol têta(h) et K(h), basée sur les résultats de l'expérience de drainage interne à pas de pression multiples est une méthode prometteuse. En effet, cette dernière fournit suffisamment d'informations sur les propriétés hydrauliques essentielles d'un sol. Le modèle utilisé pour décrire les relations entre la teneur en eau volumique têta et la pression de l'eau h, d'une part, et entre la conductivité hydraulique K et h, d'autre part, est celui de CAMPBELL (1974) dans sa version améliorée par HUTSON et CASS (1987). Les résultats montrent que ce modèle décrit raisonnablement le processus du drainage en fonction du temps correspondant à des pas de pressions croissantes. La solution de la méthode d'identification des paramètres est unique tant que les valeurs assignées aux paramètres au départ sont proches (plus ou moins 20 %) de celles du sol étudié. L'effet d'une erreur expérimentale allant jusqu'à 10 % n'est pas significatif pour les résultats des paramètres optimisés. (Résumé d'auteur
Synthesis of a 3D network of Pt nanowires by atomic layer deposition on carbonaceous template
The formation of a 3D network composed of free standing and interconnected Pt
nanowires is achieved by a two-step method, consisting of conformal deposition
of Pt by atomic layer deposition (ALD) on a forest of carbon nanotubes and
subsequent removal of the carbonaceous template. Detailed characterization of
this novel 3D nanostructure was carried out by transmission electron microscopy
(TEM) and electrochemical impedance spectroscopy (EIS). These characterizations
showed that this pure 3D nanostructure of platinum is self-supported and offers
an enhancement of the electrochemically active surface area by a factor of 50
The atmospheric impacts of monoterpene ozonolysis on global stabilised Criegee intermediate budgets and SO2 oxidation : experiment, theory and modelling
The gas-phase reaction of alkenes with ozone is known to produce stabilised
Criegee intermediates (SCIs). These biradical/zwitterionic species have the
potential to act as atmospheric oxidants for trace pollutants such as
SO<sub>2</sub>, enhancing the formation of sulfate aerosol with impacts on air
quality and health, radiative transfer and climate. However, the importance
of this chemistry is uncertain as a consequence of limited understanding of
the abundance and atmospheric fate of SCIs. In this work we apply
experimental, theoretical and numerical modelling methods to quantify the
atmospheric impacts, abundance and fate of the structurally diverse SCIs
derived from the ozonolysis of monoterpenes, the second most abundant group
of unsaturated hydrocarbons in the atmosphere. We have investigated the
removal of SO<sub>2</sub> by SCIs formed from the ozonolysis of three
atmospherically important monoterpenes (<i>α</i>-pinene, <i>β</i>-pinene and
limonene) in the presence of varying amounts of water vapour in large-scale
simulation chamber experiments that are representative of boundary layer conditions.
The SO<sub>2</sub> removal displays a clear dependence on water vapour
concentration, but this dependence is not linear across the range of
[H<sub>2</sub>O] explored. At low [H<sub>2</sub>O] a strong dependence of SO<sub>2</sub>
removal on [H<sub>2</sub>O] is observed, while at higher [H<sub>2</sub>O] this dependence
becomes much weaker. This is interpreted as being caused by the production of
a variety of structurally (and hence chemically) different SCIs in each of the
systems studied, which displayed different rates of reaction with water and
of unimolecular rearrangement or decomposition. The determined rate constants,
<i>k</i>(SCI+H<sub>2</sub>O), for those SCIs that react primarily with H<sub>2</sub>O range
from 4 to 310  ×  10<sup>−15</sup> cm<sup>3</sup> s<sup>−1</sup>. For those SCIs that
predominantly react unimolecularly, determined rates range from
130 to 240 s<sup>−1</sup>. These values are in line with previous results for the
(analogous) stereo-specific SCI system of <i>syn</i>-/<i>anti</i>-CH<sub>3</sub>CHOO. The experimental results are
interpreted through theoretical studies of the SCI unimolecular reactions and
bimolecular reactions with H<sub>2</sub>O, characterised for <i>α</i>-pinene and
<i>β</i>-pinene at the M06-2X/aug-cc-pVTZ level of theory. The theoretically
derived rates agree with the experimental results within the uncertainties. A
global modelling study, applying the experimental results within the
GEOS-Chem chemical transport model, suggests that > 97 % of
the total monoterpene-derived global SCI burden is comprised of SCIs with a
structure that determines that they react slowly with water and that their atmospheric
fate is dominated by unimolecular reactions. Seasonally averaged boundary
layer concentrations of monoterpene-derived SCIs reach up to
1.4  ×  10<sup>4</sup> cm<sup>−3</sup> in regions of elevated monoterpene
emissions in the tropics. Reactions of monoterpene-derived SCIs with SO<sub>2</sub>
account for < 1 % globally but may account for up to 60 % of
the gas-phase SO<sub>2</sub> removal over areas of tropical forests, with
significant localised impacts on the formation of sulfate aerosol and hence
the lifetime and distribution of SO<sub>2</sub>
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