Virtual Trunk Simulation

One of the activities of the ACTS project EXPERT is to perform trials demonstrating the use of advancedResource Management and Routing (RMR) algorithms in ATM networks. The RMR model chosen for those trials is based on the Virtual Trunk (VT) concept. In ATM networks, a VT is a virtual path connectionsetup by the network for reducing connection awareness at the transit nodes. A virtual trunk is considered as a connection by the network supporting it (the VP network), and as a logical trunk by the connections supported.In this context, VTs are considered to be VBR connections. In order to adapt the VT level to the changes in traffic, we use dynamic virtual trunks. In this paper, we compare the VBR-over-VBR approach to a moretraditional VBR-over-CBR approach. The comparison is based on the simulations performed in the EXPERT project by WP3.2. In addition, a dynamic VP bandwidth allocation method is demonstrated by simulations

Modelling spatio-temporal soil moisture dynamics in mountain tundra

Abstract Soil moisture has a fundamental influence on the processes and functions of tundra ecosystems. Yet, the local dynamics of soil moisture are often ignored, due to the lack of fine resolution, spatially extensive data. In this study, we modelled soil moisture with two mechanistic models, SpaFHy (a catchment-scale hydrological model) and JSBACH (a global land surface model), and examined the results in comparison with extensive growing-season field measurements over a mountain tundra area in northwestern Finland. Our results show that soil moisture varies considerably in the study area and this variation creates a mosaic of moisture conditions, ranging from dry ridges (growing season average 12 VWC%, Volumetric Water Content) to water-logged mires (65 VWC%). The models, particularly SpaFHy, simulated temporal soil moisture dynamics reasonably well in parts of the landscape, but both underestimated the range of variation spatially and temporally. Soil properties and topography were important drivers of spatial variation in soil moisture dynamics. By testing the applicability of two mechanistic models to predict fine-scale spatial and temporal variability in soil moisture, this study paves the way towards understanding the functioning of tundra ecosystems under climate change. This article is protected by copyright. All rights reserved.Peer reviewe

M/G/1/MLPS compared to M/G/1/PS

Multilevel Procesor Sharing scheduling disciplines have recently been resurrected in papers that focus on the differentiation between short and long TCP flows in the Internet. We prove that, for M/G/1 queues, such disciplines are better than the Processor Sharing discipline with respect to the mean delay whenever the hazard rate of the service time distribution is decreasing

Diurnal patterns in Scots pine stem oleoresin pressure in a boreal forest

Coniferous tree stems contain large amounts of oleoresin under positive pressure in the resin ducts. Studies in North-American pines indicated that the stem oleoresin exudation pressure (OEP) correlates negatively with transpiration rate and soil water content. However, it is not known how the OEP changes affect the emissions of volatile vapours from the trees. We measured the OEP, xylem diameter changes indicating changes in xylem water potential and monoterpene emissions under field conditions in mature Scots pine (Pinus sylvestris L.) trees in southern Finland. Contrary to earlier reports, the diurnal OEP changes were positively correlated with temperature and transpiration rate. OEP was lowest at the top part of the stem, where water potentials were also more negative, and often closely linked to ambient temperature and stem monoterpene emissions. However, occasionally OEP was affected by sudden changes in vapour pressure deficit (VPD), indicating the importance of xylem water potential on OEP as well. We conclude that the oleoresin storage pools in tree stems are in a dynamic relationship with ambient temperature and xylem water potential, and that the canopy monoterpene emission rates may therefore be also regulated by whole tree processes and not only by the conditions prevailing in the upper canopy.Peer reviewe

Explicitly accounting for needle sugar pool size crucial for predicting intra-seasonal dynamics of needle carbohydrates delta O-18 and delta C-13

We explore needle sugar isotopic compositions (delta O-18 and delta C-13) in boreal Scots pine (Pinus sylvestris) over two growing seasons. A leaf-level dynamic model driven by environmental conditions and based on current understanding of isotope fractionation processes was built to predict delta O-18 and delta C-13 of two hierarchical needle carbohydrate pools, accounting for the needle sugar pool size and the presence of an invariant pinitol pool. Model results agreed well with observed needle water delta O-18, delta O-18 and delta C-13 of needle water-soluble carbohydrates (sugars + pinitol), and needle sugar delta C-13 (R-2 = 0.95, 0.84, 0.60, 0.73, respectively). Relative humidity (RH) and intercellular to ambient CO2 concentration ratio (C-i/C-a) were the dominant drivers of delta O-18 and delta C-13 variability, respectively. However, the variability of needle sugar delta O-18 and delta C-13 was reduced on diel and intra-seasonal timescales, compared to predictions based on instantaneous RH and C-i/C-a, due to the large needle sugar pool, which caused the signal formation period to vary seasonally from 2 d to more than 5 d. Furthermore, accounting for a temperature-sensitive biochemical O-18-fractionation factor and mesophyll resistance in C-13-discrimination were critical. Interpreting leaf-level isotopic signals requires understanding on time integration caused by mixing in the needle sugar pool.Peer reviewe