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The movement of plants, animals, and microorganisms by humans, consciously or unconsciously, has changed both ecosystems and societies throughout history. This article focuses on one such transformative species, lodgepole pine, and its relocation from northwestern America to northern Sweden in the mid-twentieth century. A cultural biography of the lodgepole pine's existence in Sweden examines how this tree has been linked to different value regimes, which creates a historical pattern. Through so-called 'thinning processes', powerful actors, in both production forestry and the environmental movement, have tried to reduce the importance of the species to a limited meaning and context. At the same time, more arguments, knowledge and changed contexts have made the lodgepole pine a 'thick thing', with superimposed values and meanings. Although the tree has moved far geographically, from one continent to another, its importance has continued to be framed by interacting international, national and local perspectives. The lodgepole pine, however, is not just an inert thing that is determined by cultural discourses. It is a living tree, with its own ability to act and whose life in a foreign land has created a dynamic that crosses the border between nature and culture. [ABSTRACT FROM AUTHOR]

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The disc brake works in an open environment in contact with the outside world. The particles will cause fluctuations in the friction coefficient of the brake. A friction model is established to reflect the morphology characteristics of the surface and the particles, as well as the relationship between the mechanical properties of the brake pair and friction-velocity. The influence of surface morphology parameters and particle parameters on the friction model is analyzed. Based on the model, the stability of the braking system was analyzed, and the influence of friction parameters on the stick-slip vibration characteristics of the system was studied numerically. The results show that the variation of particle parameters has a great influence on the motion stability of the braking system. [ABSTRACT FROM AUTHOR]

The large-scale introduction of lodgepole pine (Pinus contorta ssp. latifolia, LP) into Swedish forests was initiated around 1970, and currently 520,000 hectares of the forest land are dominated by the species. Even though the tree has mostly serotine cones, adapted to open after forest fires, it has proved able to self-regenerate in Sweden. This study is the first to present, scientifically, the extent of self-regeneration covering the whole current range of LP-forests in Sweden. LP-saplings were recorded for three years, 2015–2017, in 8194 subplots distributed over 214 randomly selected LP-stands from latitude 59.6–66.9°N and altitude 88–710 m asl. Of all subplots, 3% contained LP-saplings, and regeneration was found in 53% of all stands. The probability of finding LP-saplings was significantly dependent on the plots' distance from the edge of the LP-stand, and 78% of all saplings were found within and up to 15 m beyond the stand edge. Most, 63%, of the plots with LP were found on disturbed ground such as wheel tracks, roadsides and where there had been site preparation. The results show that LP can naturally spread under a range of conditions in the studied region. The regeneration is, however, concentrated in particular stands and should be possible to control with monitoring programmes and measures to eradicate self-dispersed trees in unwanted areas. [ABSTRACT FROM AUTHOR]

Nitrogen fertilization can increase above- and belowground forest growth and carbon storage in low nitrogen (N) environments. However, it may also induce changes in other parts of the ecosystem, such as altered composition and diversity of the ground vegetation. These changes may occur, for example, because of increased availability of nitrogen and light depletion due to a denser tree canopy. We studied vegetation changes at 11 experimental sites in Pinus sylvestris stands with low N-deposition, along a south–north gradient in Sweden. We estimated the relative cover of individual species and the data were analysed with a linear model, using total amount of fertilizer-N added, years since last fertilization, site and site index as independent variables. The relative cover of the dominant dwarf shrubs (Vaccinium myrtillus and Vaccinium vitis-idaea) increased following fertilization. In the bottom layer, N significantly increased the total cover of two of the three dominant species (Pleurozium schreberi and Dicranum spp.). For the third species (Hylocomium splendens) no detectable effect was found. For lichens as a group, the cover decreased following N fertilization. No effect of N fertilization on species diversity was detected at any of the sites, and the forest vegetation types remained unchanged. [ABSTRACT FROM AUTHOR]

Copyright of Metal Forming / Obróbka Plastyczna Metali is the property of Instytut Obrobki Plastycznej and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Current information on the root sucker ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is in most cases based on clone mixtures. In this study, we could separate the performance among clones by using two experimental sites with monoclonal plots of the crossing. The natural regeneration was followed for 2 years after harvest of the formerly planted stands, clear-cut at 22 and 25 years of age, respectively. We found that clonal differences were present in the number of root suckers produced per area unit and their biomass production. However, all included clones produced sufficiently many root suckers for a successful regeneration. To receive a more complete evaluation of the root sucker dynamics for future selection on the clonal level, further studies are needed where vitality, self-thinning and effects of thinning measures are coupled to the goal of the aspen forestry. [ABSTRACT FROM AUTHOR]

Abstract: Elevated nitrogen (N) deposition may increase net primary productivity in N‐limited terrestrial ecosystems and thus enhance the terrestrial carbon (C) sink. To assess the magnitude of this N‐induced C sink, we performed a meta‐analysis on data from forest fertilization experiments to estimate N‐induced C sequestration in aboveground tree woody biomass, a stable C pool with long turnover times. Our results show that boreal and temperate forests responded strongly to N addition and sequestered on average an additional 14 and 13 kg C per kg N in aboveground woody biomass, respectively. Tropical forests, however, did not respond significantly to N addition. The common hypothesis that tropical forests do not respond to N because they are phosphorus‐limited could not be confirmed, as we found no significant response to phosphorus addition in tropical forests. Across climate zones, we found that young forests responded more strongly to N addition, which is important as many previous meta‐analyses of N addition experiments rely heavily on data from experiments on seedlings and young trees. Furthermore, the C–N response (defined as additional mass unit of C sequestered per additional mass unit of N addition) was affected by forest productivity, experimental N addition rate, and rate of ambient N deposition. The estimated C–N responses from our meta‐analysis were generally lower that those derived with stoichiometric scaling, dynamic global vegetation models, and forest growth inventories along N deposition gradients. We estimated N‐induced global C sequestration in tree aboveground woody biomass by multiplying the C–N responses obtained from the meta‐analysis with N deposition estimates per biome. We thus derived an N‐induced global C sink of about 177 (112–243) Tg C/year in aboveground and belowground woody biomass, which would account for about 12% of the forest biomass C sink (1,400 Tg C/year). [ABSTRACT FROM AUTHOR]

In a combustion engine, the valve system controls the flow of gases in to and out of the combustion chamber. The contacting surfaces experience a harsh tribological situation with high temperatures, high speed impacts, corrosive environment and high closing forces causing micro sliding in the interface. The components have to endure in the range of hundreds of millions to a billion operational cycles, resulting in extreme demands on low wear rate. Such low wear rates can be accomplished by the protective action from tribofilms forming from oil residues, avoiding a pure metal-tometal contact. Such tribofilms are found on well-functioning engine valves from a variety of engines, but some stationary gas engines experience problems with wear occurring seemingly randomly at normal running conditions. For some reason, the tribofilm has not protected the surfaces sufficiently, causing wear. One way to combat the random behaviour could be to promote robust function of the protective tribofilms by texturing the valve sealing surfaces to improve the capture and storage of oil residues. By stabilising the supply in this way, the damage from periods with low access to tribofilm forming material could be reduced. The present work demonstrates that turning of the valve seat inserts, creating valleys perpendicular to the sliding motion, can be developed into a useful solution. The amount and localisation of tribofilms became more predictable and stable than without the texture, leading to reduced component wear. The valleys should not be too wide, since this increased the amount of exposed metal if the tribofilm flaked off. When having the same width, the deeper valleys showed less flaking off of the tribofilm. [ABSTRACT FROM AUTHOR]

Surface texturing in materials is one of the current process that satisfying the industrial needs and providing ample support to the production managers in machining. During machining for producing various products the major task is the reduction of materials waste, assessment of tool wear and its happening. Tool wear affects the production cost severely also incurring the material waste. One of the effective methods to reduce this problem and improving the tool life considerably is the surface texturing process. This can be carried out in work piece material neither the tool also. Surface texturing done on the surface of the tool or the work piece material to give aesthetic look alsomainly enhances the performance in various aspects. Many industrialists and researchers carried out the surface texturing process for various machining applications such as lathe, milling with various surface texturing techniques. This article present a detail review about the need for surface texturing in materials, its importance and its role in tool life enhancement had been discussed and reported. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In Fennoscandia, logging residues (LR) are increasingly being harvested to provide fuel for renewable energy. However, the removal of LR is thought to lead to decreased growth in the next generation of trees. The effect on tree growth has generally been obtained by comparing the total removal of residues with retained residues spread evenly on the ground. With current clear-cutting practices, residues can be left with different spatial distributions, confounding the effects of residue removal. Field experiments were, therefore, established at two Norway spruce sites, comprising six treatments with varying distributions and volumes of residues. Before planting seedlings, the sites were disc-trenched. At one of the sites, seedling survival was significantly lower when all residues were removed immediately. At both sites, after 10 years there were statistically significant growth losses after removal of residues. There were no differences in plant growth if the residues were concentrated in small heaps and strings, simulating the normal distribution of LR following stem-only harvesting, compared with residues left evenly spread on the ground. To determine the duration of the observed growth effects, these study sites must be monitored more long term. [ABSTRACT FROM PUBLISHER]

It has been shown many times that cosputtering low-friction coatings of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) with other elements can improve the structural, mechanical, and tribological properties. To achieve the lowest friction, MoS2or WS2should be doped with element(s) improving the hardness and density of the coatings. On the other hand, such elements, or their compounds, should not be present in the outermost molecular layers at the sliding interface. This article suggests that there are important differences between how MoS2and WS2coatings respond to or react with doping elements, despite the almost identical structure and behavior of the undoped materials. Two systems have been investigated by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) electron energy loss spectroscopy (EELS), W-S-C-Cr and W-S-C-Ti, and showed significant amounts of oxides, which typically formed a layer just underneath the crystalline WS2top layer. Further, carbon was almost completely absent in the tribofilms, despite the fact that the as-deposited coatings contained as much as 40–50 at% C. An interesting observation here is that WS2basal planes surround or embed Fe wear particles, suggesting a relatively strong adhesion or a Fe-S chemical bonding between iron/steel and WS2. The result of this is that the wear particles become pacified and remain in the contact as low-friction material. [ABSTRACT FROM AUTHOR]

Tribochemically active Ti -C -S coatings are nanocomposite coatings containing a S-doped titanium carbide, from which S can be released in a tribological contact. This work studies tribochemical reactions between a Ti -C -S coating and various counter surface materials, and their effect on the tribological performance. Tribological tests were performed in a ball-on-disc set-up, using balls of five different materials as sliding partners for the coating: 100Cr6 steel, pure W, WC, 316-L steel and AlO. For W balls, a WS tribofilm was formed, leading to low friction (down to µ = 0.06). Furthermore, increasing normal load on the W balls was found to lead to a strong decrease in µ and earlier formation of the low-friction WS tribofilm. Similar WS and MoS tribofilms were, however, not formed from WC- and Mo-containing 316-L balls. The performance when using WC and AlO balls was significantly worse than for the two steel balls. It is suggested that this is due to sulphide formation from Fe, analogous to formation of anti-seizure tribofilms from S-containing extreme pressure additives and steel surfaces. The tribochemical activity of Ti -C -S coatings, with the possibility of S release, is thus beneficial not only for pure W counter surfaces, but also for Fe-based sliding partners. [ABSTRACT FROM AUTHOR]

Increasing use of forest fuels for energy production is generating greater quantities of wood ash. In Sweden, it is recommended that this ash should be returned to the forest to counter soil acidification and avoid potential future nutrient deficiencies, but the effects on tree growth require clarification. Thus, 10 field experiments were established in Sweden in 1990–2006 to study the effects of adding wood ash of various origins, doses and combinations of both ash and nitrogen on stem growth in Scots pine (Pinus sylvestrisL.) and Norway spruce (Picea abiesL. Karst.) stands on mineral soil. Observations after 5–15 years show that growth responses were strongest when N was added, either alone or with wood ash. Growth responses to additions of wood ash without N were small and variable and statistically insignificant at all study sites. However, there were indications that adding wood ash may increase stem-wood growth at fertile sites and decrease it at less fertile sites. Hence, at fertile sites, it may compensate for the growth reductions that normally follow whole-tree harvests, at least temporarily, presumably due to its effects on soil N turnover. At less fertile sites, adding N is probably essential to counteract these growth reductions. [ABSTRACT FROM AUTHOR]

Taguchi method has been a successful technique in improving the product quality and process performance for the past couple of decades. The present study optimizes the wearing rate of AISI 202. Since the price of nickel is so high, low nickel or non-nickel grade stainless steel is recommended to design the product. Dry sliding wear test was conducted to understand the wear and friction characteristics of samples. The tests were carried out in a purpose built-in vacuum pin-on-disc tribometer capable of testing the material up to a temperature 1000°C and in vacuum. Relationships between the weight loss and applied load, time in seconds and friction coefficient were established. It was observed that reduction in the applied load reduces the friction factor and reduction in load reduces the weight loss. Also, the friction coefficient reduces when temperature increases, for all the parameters considered. The design of experiment approach was employed to determine the optimal combination of the testing parameters in a controlled way using Taguchi method for minimum wear rate. An orthogonal array and signal-to-noise ratio were employed to investigate the wear behaviour of AISI 202. The confirmation test was conducted to verify the experimental results. SEM images have been taken for certain wear specimens and the observations have been reported in this paper. The morphology of the worn surface was examined using scanning electron microscope and the micro-structure of the sub surface is also studied. It is observed that at temperatures above 400°C, this material exhibits adhesive wear and the evidence of self-welding of mating parts has been observed in microstructures. It is also observed that the SS202 undergoes shear deformation during sliding wear. [ABSTRACT FROM AUTHOR]

In the sport of curling, stones are slid across an ice sheet, aimed towards a target area. A sliding stone does not move in a straight line, but follows a curled trajectory, deviating in a direction determined by its rotation. As yet, no satisfactory explanation for this motion has been presented, although many attempts have been made. In many of them, the curling motion has been attributed to an asymmetrical distribution of the friction force acting on the sliding stone, typically such that the friction on the rear of the stone (as seen in the direction of motion) is higher than that on the front. In this paper, the motion of a rotating curling stone sliding over ice is calculated, for different assumed distributions of the coefficient of friction in the contact between stone and ice, using a numerical method. It is shown that no redistribution of the friction, no matter how extreme, can explain the observed motion of a real curling stone. [ABSTRACT FROM AUTHOR]

High friction and transfer of work material to tool surfaces constitute important industrial problems in forming of many metals and alloys. However, it is very hard to gain a deeper understanding of these phenomena by studying real forming operations. In this paper, we have tried to gain fundamental understanding by avoiding as much as possible of the complexity of real forming. This has been realised by studying the friction and material transfer between well-defined tool material surfaces; uncoated and DLC-coated tool steel, and a needle shaped austenitic stainless steel tip, in situ in the SEM. The tool materials were tested in two conditions; well polished and well polished with local intentional scratches. It was found that work material was immediately transferred to the tool steel surface. When passing an intentional scratch, the local transfer was on a much larger scale, and the friction was higher, but the effect was mostly local. For the polished DLC-coated surface, almost no work material was transferred and the friction was low. An intentional scratch in the polished DLC surface barely influenced the galling behaviour. The present results are discussed in the light of previously published results from an analogous study with aluminium as work material. [ABSTRACT FROM AUTHOR]

Many of the failures of total joint replacements are related to tribology, i.e., wear of the cup, head and liner. Accumulation of wear particles at the implants can be linked to osteolysis which leads to bone loss and in the end aseptic implant loosening. Therefore it is highly desirable to reduce the generation of wear particles from the implant surfaces. Silicon nitride (Si3N4) has shown to be biocompatible and have a low wear rate when sliding against itself and is therefore a good candidate as a hip joint material. Furthermore, wear particles of Si3N4 are predicted to slowly dissolve in polar liquids and they therefore have the potential to be resorbed in vivo, potentially reducing the risk for aseptic loosening. In this study, it was shown that α-Si3N4-powder dissolves in PBS. Adsorption of blood plasma indicated a good acceptance of Si3N4 in the body with relatively low immune response. Si3N4 sliding against Si3N4 showed low wear rates both in bovine serum and PBS compared with the other tested wear couples. Tribofilms were built up on the Si3N4 surfaces both in PBS and in bovine serum, controlling the friction and wear characteristics. [ABSTRACT FROM AUTHOR]

Adding nitrogen to coniferous forests on mineral soils will increase stem-wood growth in most boreal forests. The addition of nitrogen affects soils and waters as well. This investigation was conducted to evaluate the long-term effects of nitrogen fertilization at different intensities on soil chemistry in nitrogen-limited ecosystems. The study was performed at three experimental sites that were originally established around 1980 in Scots pine (Pinus sylvestris L.) stands. Fertilization regimes with applications ranging from conceivable commercial rates to very intensive rates (3× 150 kg N·ha-1 up to 12× 150 kg N·ha-1) had been applied. Samples were collected from the FH horizon at all sites and 0-20 cm in the mineral soil at two sites and analyzed for pH and major nutrients. The carbon to nitrogen ratio in the FH horizon decreased with increasing total nitrogen application, while the concentrations and contents of nitrogen and exchangeable magnesium and phosphorus increased. The concentration and contents of exchangeable potassium decreased in both the FH horizon and the mineral soil. In general, larger effects on soil chemistry were observed with increasing fertilization intensity. L'ajout d'azote dans les forêts de conifères établies sur des sols minéraux augmentera la croissance du tronc des arbres dans la plupart des peuplements boréaux. L'ajout d'azote affecte aussi le sol et l'eau. Cette étude visait à évaluer les effets à long terme de différentes intensités de fertilisation azotée sur les caractéristiques chimiques du sol dans les écosystèmes pauvres en azote. L'étude a été effectuée dans trois stations expérimentales où les traitements initiaux ont été appliqués vers 1980 dans des peuplements de pin sylvestre (Pinus sylvestris L.). Des régimes de fertilisation avec des taux d'application variant d'un taux correspondant à une application commerciale à un taux très élevé (de 3 à 12× 150 kg N·ha-1) avaient été utilisés. Des échantillons ont été prélevés dans l'horizon FH de toutes les stations et à une profondeur de 0 à 20 cm dans le sol minéral de deux stations. Ces échantillons ont ensuite été analysés pour déterminer le pH et la concentration des principaux nutriments. Le rapport entre le carbone et l'azote de l'horizon FH diminuait avec la quantité totale d'azote qui avait été appliquée alors que la concentration et le contenu en azote, en magnésium échangeable et en phosphore échangeable augmentaient. La concentration et le contenu en potassium échangeable avaient diminué dans l'horizon FH et dans le sol minéral. D'une façon générale, l'ampleur des effets sur les caractéristiques chimiques du sol augmentait avec l'intensité de la fertilisation. [ABSTRACT FROM AUTHOR]

Influence from surface roughness of a forming tool surface on its ability to pick up work material was investigated by laboratory testing. One powder metallurgical tool steel was given different surface roughnesses and tested in sliding contact against one austenitic stainless steel (SS) and one aluminium alloy (Al). Generally, the risk of work material adhesion and transfer increased with the roughness of the tool material. However, SS gave a low friction and very little metal transfer for a tool roughness of the order of the relatively soft SS oxide thickness. The Al alloy, on the other hand, which oxide is much harder than the parent metal, has no critical surface roughness below which adhesive transfer will not occur. The oxide fractures and oxide fragments indent the tool surface increasing the risk of adhesion. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Studies growth responses to refertilization, Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands used in long-term nitrogen (N) fertilization experiments that were refertilized with N, either alone or with various combinations and doses of phosphorus (P), potassium (K), and magnesium (Mg). Experimental plots that had previously been subjected to heavy N fertilization regimes; N addition that resulted in a significant growth increase; Differences in growth response between fertilization with N alone or in combination with P?K?Mg that were in most cases insignificant for both tree species; Joint addition of P?K?Mg that resulted in a nonsignificant additional growth increase; Repeated additions of N alone that had no effect on the P, K, and Mg concentrations in current-year needles; Conclusion that the repeated N fertilizations did not cause any serious nutrient deficiencies.

Deposition of air pollutants, together with intensified harvesting practices, has led to concern about the declining base cation status and the acidifying effects in the soil, with possible implications for silviculture. The aim of this study was to analyse the effects of a previous high N addition on the nutritional status in the above-ground part of a tree stand. We sampled various biomass fractions in a highly productive Norway spruce (Picea abies (L.) Karst.) stand in the province of Värmland, western Sweden. The experimental plots had been fertilized with urea four times at intervals of 5 yrs, the last time being 13 yrs before our study. The total amount of N added was in the range 480-2400 kg ha[sup -1]. Despite the high N addition and an insignificant growth increase following N input, there were no obvious residual changes of nutrient concentrations in the above-ground parts of trees. [ABSTRACT FROM AUTHOR]

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

In the absence of a lubricant, the friction we measure in sliding contact between metals is typically high and quite erratic, with rapid fluctuations. If we filter out these rapid fluctuations, we can typically also notice slower trends, which can lead to quite dramatic friction changes. Unless careful studies are performed, the cause to this behaviour cannot be understood. How come a material couple cannot be characterised with a specific coefficient of friction? The present paper sets out to add understanding to this area, by conduction and analysing an experimental series involving sliding between a needle-like aluminium tip against tool steel flats. The load is high enough to cause substantial plastic deformation of the aluminium needle; its tip becomes formed by the contact against the tool steel. These small-scale, low sliding distance tests facilitate detailed studies of the initial stages of various friction trends, and the effects of initial surface roughness and shifts of this roughness caused by material transfer between the sliding surfaces. Specifically, the effects on the transfer and friction behaviour from presence or absence of a boundary lubricant film and atmospheric oxygen were studied. It was found that very smooth sliding surfaces can offer low-friction conditions for these metal types. However, the smooth sliding interface is very fragile. In all unlubricated cases tested, it very rapidly (in less than a few mm sliding) became ruined due to transfer, and the friction level correspondingly increased. The boundary lubricant could only offer low friction in cases where the flat steel surface was very smooth. The lubricant also facilitated smoothening of transferred aluminium. As long has been well known, boundary lubrication films typically do not totally hinder direct metallic contact in solid to solid contact. The present results strengthen this view and further suggests that in these direct contacts one of the major friction reducing effects of the lubricant is to efficiently limit transfer, which otherwise acts to make the sliding surface rough. [ABSTRACT FROM AUTHOR]

THE FOREST INDUSTRY IS A VERY IMPORTANT SECTOR IN SWEDEN, a country with only 9 million inhabitants. Sweden is the world's fourth largest export of pulp and paper, and the […]