Lars Eliasson

Ion energization mechanisms at 1700 km in the auroral region

Observations obtained by the Freja satellite at altitudes around 1700 km in the high-latitude magnetosphere are used to study ion energization perpendicular to the geomagnetic field. Investigations ...

Ion cyclotron heating in the dayside magnetosphere

Observations of waves and particles obtained by the Freja satellite at altitudes around 1700 km in the dayside high-latitude magnetosphere are used to study ion energization. We find that ions, inc ...

The COST model for calculation of forest operations costs

Since the late nineteenth century when high-cost equipment was introduced into forestry there has been a need to calculate the cost of this equipment in more detail with respect to, for example, cost of ownership, cost per hour of production, and cost per production unit. Machine cost calculations have been made using various standard economic methods, where costs have been subdivided into capital costs and operational costs. Because of differences between methods and between national regulations, mainly regarding tax rules and subsidies, international comparisons of machine costs are difficult. To address this, one of the goals of the European Cooperation in Science and Technology (COST) Action FP0902 was to establish a simple format for transparent cost calculations for machines in the forest biomass procurement chain. A working group constructed a Microsoft Excel–based spreadsheet model which is easy to understand and use. Input parameters are easy to obtain or possible to estimate by provided rules of thumb. The model gives users a simultaneous view of the input parameters and the resulting cost outputs. This technical note presents the model, explains how the calculations are made, and provides future users with a guide on how to use the model. Prospective users can view the model in the Supplementary Material linked to this article online.

Productivity and Costs in Shelterwood Harvesting

Harvesting costs have a significant influence on the application and potential use of the shelterwood system. These costs are strongly related to the time needed for the logging operations. In this study, which was carried out in Norway spruce [Picea abies (L.) Karst.] stands in northern Sweden, the effective time (E 0) of a single-grip harvester in shelterwood cutting, thinning of shelterwoods and clearcutting was measured. Based on these data the costs of shelterwood harvestings and clearcutting were calculated and compared. It was found that (1) the time per tree in shelterwood cutting and thinning of shelterwoods was greater than in clearcutting, (2) the time per cubic metre was higher in sparse shelterwoods than in dense shelterwoods, (3) most of this increase was due to longer driving time because fewer trees were harvested, and (4) the longer time and higher logging costs in the shelterwood system (compared with the clearcutting system) were mostly related to the establishment of the shelterwood. It was concluded that the shelterwood alternative is especially competitive when it is desirable to maximize the share of saw logs at the expense of pulpwood.

Simulation Study of a Single-grip Harvester in Thinning from Below and Thinning from Above

Abstract The time consumption and productivity of a single-grip harvester were studied, using a simulation model, when thinning from below and above in eight randomly selected stands. The model estimated the time required for each work element, given machine and tree positions, and tree size. A 2×5 factorial design was used with factors thinning type [from below (Tb) and above (Ta)] and tree size. Trees were subjectively selected for harvest according to thinning type. Total basal area removal was 30% plot−1. Approximately 50% more trees were harvested in Tb than in Ta Time consumption tree−1 was higher for Ta than Tb. Time consumption for machine and boom movements decreased with increasing number of harvested trees, and time for felling and processing of trees increased with harvested mean stem volume. Harvester productivity was 36% higher for Ta, since the increase in harvested mean stem volume was higher than the increase in time consumption tree−1.

Comparison of Single-Grip Harvester Productivity in Clear- and Shelterwood Cutting

Abstract An increased interest in the use of shelterwood stands to promote regeneration has led to an interest in how single-grip harvester productivity is affected by shelterwood cutting compared to clearcutting. A comparative time study of a large single-grip harvester was made in a spruce stand in northern Sweden. Three treatments were used. Shelterwood cutting leaving: 1) a sparse stand, 2) a dense residual stand, and 3) clearcut†ing. Each treatment was replicated three times. Results show that productivity decreases from 64 m3 per effective hour in clearcutting to 54 and 41 m3 per effective hour when shelterwoods with 259 and 381 stems ha−1, respectively, were retained.

Observations of mesoscale auroral plasma cavity crossings with the Freja satellite

We have used data from the Freja satellite, with an apogee of 1700 km over the auroral oval, to make a statistical analysis of mesoscale auroral plasma density cavities. Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted-V events in which the plasma density abruptly drops to less than 50% of the ambient plasma density. We present occurrence distributions by magnetic activity, local time, and magnetic latitude. It is found that cavity occurrence does not depend on magnetic activity. In contrast to earlier studies, we find cavities at all local times; however, a dawn-dusk asymmetry is found in the distribution. There is likewise a weak dawn-dusk asymmetry in the latitudinal distribution. Since our data cover a full year, seasonal dependence of cavity occurrence can also be investigated. We find a small seasonal trend, with cavities found more commonly during the dark season, but the trend is not quite statistically significant. We also study several plasma depletion processes that could be responsible for cavities at this altitude. The results suggest that more than one process is compatible with the distributions we find.

Observations of electron conies by the Viking satellite

Electron angular distributions peaked at oblique angles to the magnetic field, electron conies, are frequently found in the Viking data at all magnetic local times, but with a maximum in the dusk sector. Several types of electron conies have been observed by Viking as well as by other satellites. One type is frequently seen below the acceleration region. It is caused by adiabatic motion of electrons with a field-aligned distribution that has a broader angular width than the loss cone. The atmospheric loss of particles will result in a distribution peaked at pitch angles close to the loss cone. Another type is due to heating or acceleration processes at low altitudes and is seen above the acceleration region. Particle and wave characteristics and possible generation mechanisms for this type of electron conic are discussed. The ion arid electron angular distributions observed by Viking indicate that a parallel electric field is present below Viking during this type of event. Ion observations give important information on the processes that produce the electron conies. Almost 200 electron conic events have been detected in the Viking data, that is, in about every third orbit that was studied. Their frequency of occurrence in altitude maximizes in the upper part of the acceleration region, between 10,000 and 11,000 km. The number of events are found to decrease at higher altitudes. This might indicate that diffusion processes, associated with wave generation, remove the anisotropy in the electron distribution function in and above the acceleration region. Wave observations show the presence of both low-frequency waves and waves close to the electron gyro frequency. Acceleration in a fluctuating (approximately 1 Hz) parallel electric field is suggested as a likely mechanism to create the electron conies observed by Viking. The period of the fluctuations is comparable to the travel time, below the acceleration region, of the electrons forming the conic distribution.

Simulation-based evaluation of supply chains for stump fuel

Current concerns about climate change and fossil-fuel dependency have intensified interest in renewable energy and increased demand for suitable substrates. Softwood tree stumps could be a very interesting renewable fuel assortment, since large volumes of unutilized stump biomass are available. The stump-root system constitutes about 25% of stem volume. However, optimization of logistics issues within the supply chain of stump fuel is crucial in ensuring low procurement costs, particularly for transport and comminution operations. Bulky stumps can be transported and comminuted in different ways, and if the system is planned properly it can reduce the supply costs and help deliver a fuel at a competitive price. This study evaluated various systems for stump transport and comminution in terms of cutting unnecessary costs and making the systems more resource-efficient. A discrete-event simulation approach was applied, using the ExtendSim simulation software. Simulation results obtained using the model developed show large variations in system performance and system costs. The costs of the best and worst alternatives differed by around a factor of 2, irrespective of transport distance. The most cost-effective option proved to be crushing stumps into the ground and using a self-loading truck for wood fuel transport.

Periodontal evaluation of teeth in bone grafted regions in patients with unilateral cleft lip and cleft palate

In 28 patients with unilateral cleft lip and cleft palate who were provided treatment that included bone grafting at an age of 8 to 13 years, periodontal conditions of teeth in the cleft region were monitored from a time point before bone grafting until the canine was fully erupted through the grafted region. Widths of keratinized and attached gingiva tended to increase between preoperative and postoperative examinations. Gingival recession was observed preoperatively for the tooth mesial to the cleft in 14 of the 28 patients. Postoperatively, only three of these patients showed recession. Improvements of the marginal bone level were observed both for teeth mesial and distal to the cleft. Canines having erupted through the grafted defect showed periodontal conditions similar to those of the contralateral canine. The findings demonstrate that treatment, which included osseous grafting before the eruption of the canine, resulted in satisfactory periodontal conditions for teeth in the cleft region.