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  • 64201.
    Zhu, Z.
    et al.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, China.
    Cao, P.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, China.
    Guo, X.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, China.
    Qiu, X.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, China.
    Xie, S.
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, China.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cutting performance of cemented carbide cutting tool in turning high‐density fiberboard2018In: Materialwissenschaft und Werkstofftechnik, ISSN 0933-5137, E-ISSN 1521-4052, Vol. 49, no 12, p. 1476-1484Article in journal (Refereed)
    Abstract [en]

    In order to provide a scientific and reliable guidance for wood processing industry, the effects of cutting parameters on cutting forces, cutting temperature and tool wear were studied when turning high‐density fiberboard by use of cemented‐carbide cutting tools. The results showed that cutting forces (normal force and radial force) and cutting temperature are not affected by the cutting parameters in the same way: cutting forces decrease with increasing spindle speed, whereas cutting temperature increase with an increase of the spindle speed. However, there is a positive relation for cutting forces and temperature, to the feed per turn when cutting. The wear of the cemented‐carbide cutting tool is shown by two mechanisms: Mainly adhesive wear but also abrasive wear, showed by loss of carbide‐grains and by cracking and chipping, respectively. This study also indicated that higher‐speed cutting is beneficial for wood‐processing; evident by reduced energy for cutting and higher efficiency in production.

  • 64202.
    Zhu, Zhaolong
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Nanjing Forestry University, Coll Mat Sci & Engn, Nanjing, Jiangsu, China.
    Buck, Dietrich
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Guo, Xiaolei
    Nanjing Forestry University, Coll Mat Sci & Engn, Nanjing, Jiangsu, China.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cao, Pingxiang
    Nanjing Forestry University, Coll Mat Sci & Engn, Nanjing, Jiangsu, China.
    Effect of Cutting Speed on Machinability of Stone–Plastic Composite Material2019In: Science of Advanced Materials, ISSN 1947-2935, E-ISSN 1947-2943, Vol. 11, no 6, p. 884-892Article in journal (Refereed)
    Abstract [en]

    This research examined the orthogonal cutting of stone–plastic composite with diamond cutting tools. The objective was to quantify features relating to machinability, including cutting forces, cutting heat, chip formation, and machining quality with respect to cutting speed. The conclusions are as follows. An increased cutting speed promotes a decrease in the resulting force, causes cutting temperature to increase, makes the cutting processes more stable, and reduces the surface roughness. Chip-breaking length increases with an increase in cutting speed, and chip morphology changes from particle, to curve, to helical, and finally, to flow chips. Overall, a higher cutting speed is more suitable for machining stone–plastic composite materials: it not only increases the stability of cutting process, but also improves the final product of stone–plastic composite by promoting production of a smoother surface.

  • 64203.
    Zhu, Zhaolong
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Buck, Dietrich
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Guo, Xiaolei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cao, Pingxiang
    College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Performance of stone-plastic composites with different mix ratios during orthogonal cutting2019In: Materials Express, ISSN 2158-5849, Vol. 9, no 7, p. 749-756Article in journal (Refereed)
    Abstract [en]

    The present study aimed to increase understanding of the machinability of stone-plastic materials with different mix ratios subjected to diamond planing. To that end, orthogonal cutting was carried out. Different stone-plastic materials were machined by diamond cutting tools to produce chips. Based on the results, four conclusions are drawn: (1) Among stone-plastic materials with decreasing polyvinyl chloride content ratio, the maximum cutting forces and fluctuation of dynamic forces show decreasing trends, and cutting stability increases. (2) The temperature of chips is slightly higher than that of tool edges; the cutting heat generated during machining is mainly absorbed by the chips of removed material and, to a lesser extent, stored in the tool edge. The type of stone-plastic material has a great effect on the changes in the temperatures of chip and tool edge. (3) With a decrease in polyvinyl chloride content, the chip shapes evolve from crack, to arc, and eventually to elemental chips. (4) The cutting quality of the machined surface improves with a decrease in the polyvinyl chloride content ratio of the stone-plastic materials.

  • 64204.
    Zhu, Zhaolong
    et al.
    College of Material Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Buck, Dietrich
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Guo, Xiaolei
    College of Material Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pingxiang, Cao
    College of Material Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China.
    Wu, Zhenzeng
    Department of Material Engineering, Fujian Agriculture and Forestry University, Fujian, China.
    Machinability investigation in turning of high density fiberboard2018In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 13, no 9, p. 1-13, article id e0203838Article in journal (Refereed)
    Abstract [en]

    A series of experiments were conducted to assess the machinability of high density fiberboardusing cemented carbide cutting tools. The objective of this work was to investigate theinfluence of two cutting parameters, spindle speed and feed per turn, on cutting forces, chipformation and cutting quality. The results are as follows: cutting forces and chip-breakinglength decrease with increasing spindle speed and decreasing feed per turn. In contrast,surface roughness increases with decrease of spindle speed and increase in feed perturn. Chips were divided into four categories based on their shape: dust, particle, splinter,and semicontinuous chips. Chip-breaking length had a similar tendency to the varianceof cutting forces with respect to average roughness and mean peak-to-valley height: anincrease in the variance of cutting forces resulted in increased average roughness andmean peak-to-valley height. Thus, high cutting speed and low feed rate are parameters suitablefor high-quality HDF processing and will improve not only machining quality, but productionefficiency.

  • 64205.
    Zhu, Zhaolong
    et al.
    Nanjing Forestry University.
    Guo, Xiaolei
    Nanjing Forestry University.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cao, Pingxiang
    Nanjing Forestry University.
    Na, Bin
    Nanjing Forestry University.
    Zhu, Nanfeng
    Nanjing Forestry University.
    The Effects of Cutting Parameters and Tool Geometry on Cutting Forces and Tool Wear in Milling High-density Fiberboard with Ceramic Tools2017In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 91, no 9-12, p. 4033-4041Article in journal (Refereed)
    Abstract [en]

    In this paper, the effects of cutting parametersand tool geometry on cutting forces and tool wear whenup-milling high-density fiberboard with alumina ceramiccutting tools were investigated. Under the condition ofthe same feed per tooth, average chip thickness, andclearance angle, the results shown are as follows: first,the tangential forces Ft and normal forces Fr at lowspeedcutting were higher than those at high-speed cutting,but increased slowly with the increase of cuttinglength and rake angle decrease. Second, increased cuttingspeed and decreased rake angle had a great effecton rake face wear. Third, the wear patterns of tool wearwere rake wear and flank wear, which included pull-outof grain, flaking, and chipping. The wear mechanismswere adhesive wear and abrasive wear. Finally, at lowspeedcutting, the cutting tools with bigger rake anglecan be selected to reduce the energy consumption ofmachine tools. The tools with smaller rake angle canbe used for high-speed cutting to improve tool lifeand productivity of processing.

  • 64206.
    Zhu, Zhaolong
    et al.
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Guo, Xiaolei
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Na, Bin
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Liang, Xingyu
    Nanjing Forestry University, Faculty of Material Science and Engineering.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ji, Futang
    Shanghai Vohringer Wood Product Co., Ltd.
    Research on cutting performance of ceramic cutting tools in milling high density fiberboard2017In: Wood research, ISSN 1336-4561, Vol. 62, no 1, p. 125-138Article in journal (Refereed)
    Abstract [en]

    The effect of cutting parameters and tool parameters on cutting forces and tool wear wereinvestigated in high density fiberboard (HDF) peripheral up-milling using toughened ceramiccutting tools. The results showed that whether at low speed cutting or high speed cutting, thetangential forces Ft and normal forces Fr increased slowly with the increase of cutting length. Thetangential forces Ft and normal forces Fr at low speed cutting were higher than that at high speedcutting. The tangential forces Ft and normal forces Fr decreased with the decrease of wedge anglein the same rake angle. Then, the effect of high cutting speed on the flank wear was greater thanthat at low cutting speed. The bigger wedge angle tools led to the serious flank wear. The mainwear pattern in milling HDF consisted of pull-out of the grain, flaking, chipping and cracking,the main wear mechanism were adhesive and abrasive wear

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  • 64207.
    Zhuang, Hui
    et al.
    Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services, University of Science and Technology.
    Li, Jintao
    Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services, University of Science and Technology.
    Geng, Weibiao
    Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services, University of Science and Technology.
    Dai, Xiaoming
    Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services, University of Science and Technology.
    Zhang, Zhogshan
    Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services, University of Science and Technology.
    Vasilakos, Athanasios
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Duplexer design and implementation for self-interference cancellation in full-duplex communications2016In: European Signal Processing Conference, EUSIPCO 2016, Piscataway, NJ: IEEE Computer Society Digital Library, 2016, p. 125-129, article id 7760223Conference paper (Refereed)
    Abstract [en]

    The full-duplex (FD) based devices are capable of concurrently transmitting and receiving signals with a single frequency band. However, a severe self-interference (SI) due to the large difference between the power of the devices' own transmission and that of the signal of interest may be imposed on the FD based devices, thus significantly eroding the received signal-to-interference-plus-noise ratio (SINR). To implement the FD devices, the SI power must be sufficiently suppressed to provide a high-enough received SINR for satisfying the decoding requirement. In this paper, the design and implementation of the duplexer for facilitating SI cancellation in FD based devices are investigated, with a new type of duplexer (i.e. an improved directional coupler) designed and verified. It is shown that the SI suppression capability may be up to 36 dB by using the proposed design, which is much higher than that attainable in the commonly designed ferrite circulator

  • 64208.
    Zhuang, Linqi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effects of Non-uniform Fiber Distribution on Fiber/matrix Interface Crack Propagation in Polymeric Composites2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fiber/matrix interface cracking plays an important role in determining the final failureof unidirectional (UD) composites. When subjected to longitudinally tensile loading,fiber/matrix interface debonds originate from fiber breaks or initial defects propagatealong loading direction. Depending on the quality of fiber/matrix interface, debondscould keep growing longitudinally which leads to the degradation of compositestiffness or kink out of interface and connect with neighboring debonds or fiberbreaks that forms a so called critical fracture plane which leads to the final failure ofUD composite. For UD composite subjected to transversely tensile loading, theinitiation, growth and coalesce of arc-shape fiber/matrix interface debonds result inthe formation of macro-size transverse cracks, the propagation and multiplication ofthese transverse cracks, although would not directly lead to the final failure ofcomposite, could cause significant stiffness degradation of composite structures.In the presence thesis, the growth of a fiber/matrix interface debond of a UDcomposite with hexagonal fiber packing under longitudinal and transverse tensileloading was investigated numerically, with the special focus on the influence ofneighboring fibers. In the current study, energy release rate (ERR) is considered as thedriving force for the debond growth and was calculated based on J Integral andVirtual Crack Closure Technique (VCCT) using finite element software ANSSY.Papers A – C in the present thesis deal with the influence of neighboring fibers on theERR of a debond emanating from a fiber break under longitudinal loading condition.In longitudinal loading case, debond growth is mode II dominated. In paper A, anaxisymmetric model consisting 5 concentric cylinders that represent broken fiber withdebond, surrounding matrix, neighboring fibers, surrounding matrix and effectivecomposite was generated. It’s found that there are two stages of debond growth, thefirst stage is when debond length is short, the ERR decreases with increasing debondlength, and the presence of neighboring fibers significantly increase the ERR ofdebond. For relatively long debond, the debond growth is steady when ERR is almostconstant regardless of debond length. In steady state of debond growth, the presenceof neighboring fibers have little effect on the ERR. In papers B and C, a 3-D modelwas generated with broken fiber and its 6 nearest fibers in a hexagonal packed UDcomposite were modelled explicitly, surrounded by the homogenized composite.

    Based on the obtained results, it’s shown that ERR is varying along debond front, andhas its maximum at the circumferential location where the distance between two fibercenter is the smallest. This indicates that the debond front is not a circle. For steadystate debond, the presence of neighboring fibers have little effect on averaged ERR(averages of ERR along debond front). For short debond, the presences ofneighboring fibers increases the averaged ERR, and that increase is more significantwhen inter-fiber distance is the smallest. Paper D investigates the growth of afiber/matrix debond along fiber circumference under transverse loading. It’s foundthat debond growth in this case is mixed-mode, and both mode I and mode II ERRcomponents increase with increasing debond angle and then decreases. Debondgrowth is mode I dominated for small debond angle and then switch to mode IIdominated. The presence of neighboring fibers have an enhancement effect on debondgrowth up to certain small debond angle and then changes to a protective effect. InPaper E, the interaction between two arc-size debond under transverse loading isinvestigated. It’s found that when two debonds are close to each other, the interactionbetween two debond becomes much stronger, and that interaction leads to the increaseof ERR of each debond significantly, which facilitates further growth for bothdebond.

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  • 64209.
    Zhuang, Linqi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fiber/matrix interface crack propagation in polymeric unidirectional composite2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fiber/matrix interface cracking plays an important role in determining the final failure of unidirectional composites. In the present study, energy release rate (ERR) for fiber/matrix interface debond growth originated from fiber break in unidirectional composite is calculated using 5-cylinders axisymmetric and 3-D FEM models with hexagonal fiber arrangement. In the model the debonded fiber is central in the hexagonal unit which is surrounded by effective composite. The effect of neighboring fibers focusing on local fiber clustering on the ERR is analyzed by varying the distance between fibers in the unit. Two different scenarios are considered, one is the steady-state debond where debond are long and thus there is no interaction between debond tip and fiber break; the other case is when debond are relatively short when debond tip interacts with fiber break. The steady-state ERR is calculated from potential energy difference between a unit in the bonded region far away from the debond front and a unit in the debonded region far behind the debond front. The ERR for different modes of crack propagation is obtained from a FEM model containing a long debond by analyzing the stress at the debond front. For very short debonds, the ERR was calculated by both the J integral and the Virtual crack closure technique (VCCT).For steady-state debond growth, results show that in mechanical axial tensile loading fracture Mode II is dominating, it has strong angular dependence (effect of closest fibers) but the average ERR is not sensitive to the local fiber clustering. In thermal loading the Mode III is dominating and the average ERR is highly dependent on the distance to neighboring fibers. For short debod growth, results show that the debond growth is Mode II dominated and that the ERR strongly depends on the angular coordinate. The local fiber clustering has larger effect on the angular variation for shorter debonds and the effect increases with larger local fiber volume fraction. Finally, the ERR values from 5-cylinder axisymmetric model could be considered as upper bound for the 3-D hexagonal model.

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  • 64210.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Aerospace Engineering, Texas A&M University.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of neighboring fibers on energy release rate during fiber/matrix debond growth2014In: 16th European Conference on Composite Materials, ECCM 2014, European Conference on Composite Materials, ECCM , 2014Conference paper (Refereed)
    Abstract [en]

    In this paper fiber/matrix interface debond growth in unidirectional composites subjected to mechanical tensile loading is analyzed using fracture mechanics principles of energy release rate (ERR). The objective of the present study is to analyze the effect of neighboring fibers on the ERR. 5-cylinder axisymmetric FEM models with adjustable inter-fiber distance were used for ERR calculations. The results show that the ERR slightly increases with the inter-fiber distance in the case of long debonds. For short debonds, however, because the stress-state is more complex, it was found that the debond propagates in a mixed Mode I and Mode II and contribution of each mode to the ERR depends on the actual debond length. It was found that for very small debond lengths ERR significantly increases with the inter-fiber distance.

  • 64211.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, Nancy Universite, Science et Ingénierie des Matériaux et Métallurgie (SI2M), Institut Jean Lamour, Nancy, Laboratoire de Science et Génie des Surfaces, EEIGM, Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Effect of fiber clustering on debond growth energy release rate in UD composites with hexagonal packing2016In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 161, p. 76-88Article in journal (Refereed)
    Abstract [en]

    Steady-state energy release rate (ERR) for fiber/matrix interface debond growth originated from fiber break in unidirectional composite is calculated using 3-D FEM models with hexagonal fiber arrangement. In the model the debonded fiber is central in the hexagonal unit which is surrounded by effective composite. The effect of neighboring fibers focusing on local fiber clustering on the ERR is analyzed by varying the distance between fibers in the unit. The steady-state ERR is calculated from potential energy difference between a unit in the bonded region far away from the debond front and a unit in the debonded region far behind the debond front. The ERR for different modes of crack propagation is obtained from a FEM model containing a long debond by analyzing the stress at the debond front.Results show that in mechanical axial tensile loading fracture Mode II is dominating, it has strong angular dependence (effect of closest fibers) but the average ERR is not sensitive to the local fiber clustering. In thermal loading the Mode III is dominating and the average ERR is highly dependent on the distance to neighboring fibers. However, for realistic loads the thermal ERR is much smaller than the mechanical.

  • 64212.
    Zhuang, Linqi
    et al.
    Department of Aerospace Engineering, Texas A&M University, Texas A&M University, College Station.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, Nancy Universite, Science et Ingénierie des Matériaux et Métallurgie (SI2M), Institut Jean Lamour, Nancy, Laboratoire de Science et Génie des Surfaces, EEIGM, Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, University of Lorraine, F-54010, Nancy.
    Fiber/matrix debond growth from fiber break in unidirectional composite with local hexagonal fiber clustering2016In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 101, p. 124-131Article in journal (Refereed)
    Abstract [en]

    Energy release rate (ERR) for fiber/matrix debonding in composite with local fiber clustering, subjected to axial tension, has been investigated numerically by a 3-D finite element (FE) model. In the model, broken fiber is central in a hexagonal unit which is embedded in an effective composite. Fiber/matrix debond with circular front is assumed to be originated from the fiber break. The effect of the local fiber clustering on ERR is studied by varying distance between the broken fiber and the neighboring fibers. For very short debonds as well as for long debonds (almost steady-state growth) the ERR was calculated by both the J integral and the Virtual crack closure technique (VCCT). Results show that the debond growth is Mode II dominated and that the ERR strongly depends on the angular coordinate. The local fiber clustering has larger effect on the angular variation for shorter debonds and the effect increases with larger local fiber volume fraction. The results obtained from the 3-D hexagonal model are compared with those obtained previously using 5-cylinder axisymmetric model developed by the same authors. The ERR values from 5-cylinder axisymmetric model could be considered as upper bound for the 3-D hexagonal model.

  • 64213.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Texas A&M, College Station; University of Lorraine, France.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. SICOMP Swerea.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Talreja, Ramesh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Texas A&M University, College Station, TX .
    Ayadi, Zoubir
    University of Lorraine.
    Effects of Inter-Fiber Spacing on Fiber-matrix Debond Crack Growth in Unidirectional Composites under Transverse Loading2018In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 109, p. 463-471Article in journal (Refereed)
    Abstract [en]

    The energy release rate (ERR) of a fiber-matrix debond crack in a unidirectional composite subjected to transverse tension is studied numerically. The focus of the study is the effect of the proximity of the neighboring fibers on the ERR. For this, a hexagonal pattern of fibers in the composite cross-section is considered. Assuming one fiber to be debonded at certain initial debond arc-length, the effect of the closeness of the surrounding six fibers on the ERR of the crack is studied with the inter-fiber distance as a parameter. Using an embedded cell consisting of discrete fibers in a matrix surrounded by the homogenized composite, a finite element model and the virtual crack closure technique are used to calculate the ERR. Results show that the presence of the local fiber cluster accelerates the crack growth up to a certain initial crack angle, beyond which the opposite effect occurs. It is also found that the residual stress due to thermal cooldown reduces the ERR. However, the thermal cooldown is found to enhance the debond growth in plies within a cross-ply laminate.

  • 64214.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Talreja, Ramesh
    Analysis of Formation of the Critical State in Tensile Failure of Unidirectional Composites2016In: ASME 2015 International Mechanical Engineering Congress and Exposition, New York: American Society of Mechanical Engineers , 2016, Vol. 9 : Mechanics of Solids, Structures and Fluids, article id UNSP V009T12A031Conference paper (Refereed)
    Abstract [en]

    Unidirectional (UD) composites are building blocks in most load bearing structural components for lightweight applications in aerospace, automotive and wind energy industries. The loss of the structural load bearing capacity is governed by the instability of the fiber breakage process in the UD composites. When subjected to increasing or repeated tensile loading along fiber direction, the first failure event within these composites occurs as discrete fibers break at weak points followed by fiber/matrix debonding due to high stress concentration caused by fiber breaks. Upon further loading, or on repeated loading, more fiber breaks occur along with other accumulated damage events such as debond growth and matrix cracking. Final failure of a UD composite occurs when a critical fracture plane is formed by interconnecting individual broken fibers and associated debonding through matrix cracking. This failure process has emerged from numerous experimental studies, which also suggest that the critical fracture plane contains only a small number of broken fibers for commonly used composites such as glass/epoxy and carbon/epoxy. However, the mechanisms underlying the critical fracture plane formation are not clear. As the first step to clarify the creation of a critical fracture plane, the conditions for connectivity of a broken fiber end with neighboring broken fibers is studied in this work. In order to investigate the local stress field surrounding the broken fiber, a finite element (FE) model is constructed in which six neighboring fibers are placed as a ring of concentric axisymmetric cylinder embedded in the matrix. The discrete fiber region is surrounded by a concentric outer cylinder ring of homogenized composite. The entire FE model is subjected to axial tensile loading. To account for the consequence of the stress enhancement at the broken fiber end, a debond crack at the fiber/matrix interface extending a short distance from the fiber end is included in the analysis. Realizing that the debond crack by itself would not connect with other fiber failures, focus of the stress and failure analysis is placed on deviation of the debond crack laterally into the matrix. For this purpose, matrix cracking in two possible modes ductile and brittle is considered, Energy based criteria are used to study the competition between the cracking modes and the crack path into the matrix from the end of debond to the neighboring fibers is determined. Next the failure of the neighboring fibers caused by the intense stress field accompanying the matrix cracks is studied. The conditions for generating a plane connecting the initially broken fiber end to subsequent fiber failures are finally determined. Further ongoing studies are aimed at clarifying the limiting conditions for avoiding the fiber failure criticality, and thereby improving the load bearing capacity of UD composites. The statistical considerations regarding fiber failure will also be incorporated in these studies.

  • 64215.
    Zhuang, Linqi
    et al.
    Department of Aerospace Engineering, Texas A&M University.
    Talreja, Ramesh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effects of Voids on Postbuckling Delamination Growth in Unidirectional Composites2014In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, no 5, p. 936-944Article in journal (Refereed)
    Abstract [en]

    This work examines the effects of manufacturing induced voids on the postbuckling behavior of delaminated unidirectional composites. In the finite element model developed, a through-width delamination is introduced close to one surface of a flat panel, and a void is placed in the delamination plane ahead of each delamination front. The panel is subjected to compression in the fiber direction. The postbuckling delamination growth is studied by calculating the strain energy release rate (SERR) using the virtual crack closure technique. Local stress analyses of the region near the delamination front are also performed to further investigate the void effects. It is found that although the presence of void does not significantly alter the postbuckling transverse displacement of the delaminated panel, the induced stress perturbation by the void affects the SERR. The Mode II SERR as well as the total SERR increase depending on the size of the void and its distance from the delamination front. Since the Mode I SERR shows non-monotonic behavior with the applied load, the effects of voids are studied on its maximum value.

  • 64216.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Texas A and M University, College Station, TX, United States; University of Lorraine, SI2M, Nance, France.
    Talreja, Ramesh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Texas A and M University, College Station, TX, United States.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of cooldown induced fiber/matrix interfacial2017In: 32nd Technical Conference of the American Society for Composites 2017 / [ed] Yu W.,Pipes R.B.,Goodsell J., DEStech Publications Inc , 2017, Vol. 2, p. 1095-1102Conference paper (Refereed)
    Abstract [en]

    Despite efforts to improve the overall quality of composite materials, the presence of fiber/matrix interfacial defects seems inevitable. In composites with high fiber volume fraction, the small inter-fiber spacing can lead to development of high tensile radial stress at the fiber/matrix interfaces on cooldown from a high cure temperature. This stress can cause failure from defects at the interfaces earlier before any mechanical loads are applied. In the present paper, we study further progression of cracking from a preexisting disbond (debonding crack) that has been formed by thermal cooldown on remotely applying transverse tension to the composite. In the finite element model, a local region of hexagonally packed fibers embedded in a homogenized composite is analyzed. The cooldown induced disbond is assumed to initiate at the location where tensile radial stress resulting from cooldown is the highest. Energy release rate of the debonding crack is calculated by the Virtual Crack Closure Technique (VCCT). Upon loading, it is found that the debonding crack tends to grow towards the symmetry plane normal to the loading direction. Furthermore, this crack is found not to kink out of the interface until it has fully propagated past the symmetry plane. As a result, further growth of the cooldown induced disbond as well as the potential kinking process are found to be the same as when the disbond initiates due to applied transverse tension. 

  • 64217.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Talreja, Ramesh
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of manufacturing induced fiber break on local tensile failure in composites2016In: Proceedings of the American Society for Composites: 31st Technical Conference, ASC 2016 / [ed] Davidson B.D.,Czabaj M.W.,Ratcliffe J.G, DEStech Publications Inc , 2016Conference paper (Refereed)
    Abstract [en]

    Fiber breakages are commonly found during composites manufacturing process. In the current study, the effect of manufacturing induced fiber break on local tensile failure in unidirectional (UD) composites is investigated numerically. In the finite element (FE) model, a broken fiber is placed centrally in a hexagonally packed UD composite and is assumed to be perfectly bonded to the matrix. Since the stress perturbation caused by a single fiber breakage is local, only the six most affected nearest-neighbor fibers are modeled and are placed as a ring of concentric axisymmetric cylinder embedded in the matrix. The discrete fiber region is surrounded by a concentric outer cylinder ring of homogenized composite. The entire FE model is subjected to axial tensile loading. Upon loading, it is found that matrix crack would most likely initiate perpendicular to fiber axis by cavitation due to tri-axial stress state near fiber break, and the thermal residual stress is found to promote the cavitation process. Once the matrix crack initiates from fiber break, fracture mechanics methodology is adopted by using extended finite element method (XFEM) to simulate the matrix crack propagation. The stress concentration factors (SCF) along the neighboring fibers are calculated during matrix crack propagation and obtained results show that the maximum SCF is the highest when matrix crack reaches a neighboring fiber. Finally, the statistical consideration regarding neighboring fiber failure is incorporated and it is found that the initial fiber breakage, together with the matrix cracking that follows, greatly enhance the probability of neighboring fiber failing at the local region close to the original fiber-break plane, which indicates that a planar fracture plane is expected if final tensile failure of UD composite starts from a manufacturing induced fiber break.

  • 64218.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Talreja, Ramesh
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tensile failure of unidirectional composites from a local fracture plane2016In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 133, p. 119-127Article in journal (Refereed)
    Abstract [en]

    Final failure in composite structures often occurs from fiber failures in a local region. This paper aims to study the formation of a critical fracture plane that simulates the local failure region in a unidirectional composite. The nucleation site for the critical plane is assumed to be a broken fiber. An axisymmetric finite element model is constructed to study the progression of failure from the broken fiber placed at the center and surrounded by intact fibers. Two scenarios are considered: one, where the broken fiber results from a manufacturing process, and two, where a fiber fails at a weak point under loading. In the first case, a matrix crack is found to initiate from the broken fiber end and grow normal to the fiber axis, while in the second case, a matrix crack kinks out of an (assumed) short fiber/matrix debond crack and grows out towards the neighboring fibers. The consequent stress enhancement in the neighboring fibers is analyzed to determine their probability of failure. The influence of the initial debond length on the formation of the critical fracture plane is also studied.

  • 64219.
    Zhuang, Linqi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Texas A&M University, College Station, TX, USA.
    Talreja, Ramesh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science and Engineering, Texas A&M University, College Station, TX, USA. Department of Aerospace Engineering, Texas A&M University, College Station, TX, USA.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Transverse crack formation in unidirectional composites by linking of fibre/matrix debond cracks2018In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 107, p. 294-303Article in journal (Refereed)
    Abstract [en]

    Plausible mechanisms of transverse crack formation in unidirectional (UD) composites under applied tension normal to fibres are investigated numerically using a finite element model. Two initial scenarios are considered: Scenario 1 where a pre-existing single fibre/matrix debond crack kinks out into the matrix and induces fibre/matrix debonding at neighbouring fibres, and Scenario 2 where multiple pre-existing debond cracks link up by the debond growth and crack kink-out process. The 2-D finite element model consists of a circular region of matrix with a central fibre surrounded by six fibres in a hexagonal pattern. The region is embedded in a homogenized UD composite of rectangular outer boundary. Energy release rates (ERRs) of interface cracks and kinked-out cracks are calculated under applied tension normal to fibres. Results show that Scenario 2 is more likely to lead to formation of a transverse crack than Scenario 1. These results provide understanding of the roles of fibre clustering and fibre volume fraction on transverse crack formation in composites

  • 64220. Ziaie, Sousan
    Hur arbete eller sysselsättning i Sverige har influerat de vardagliga aktiviteterna efter invandring2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
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  • 64221.
    Ziegler, Ildiko Mohammedne
    Luleå tekniska universitet.
    Adsorption of pinosylvin onto the structure of wood: mechanism and adsorption parameters2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pinosylvin and polyhydroxybenzene derivatives are natural components of wood, known for their fungicidal/fungistatic properties. These components were used as adsorbates in the present investigation. Lignin and a-cellulose powder were used as model substrates in order to aquire information about the attachment of the adsorbates to the structure of wood. The adsorbate-substrate interaction was investigateded by the diffuse reflectance technique, commonly known as DRIFT. Furthermore, the adsorption of pinosylvin onto twelve different types of wood was studied, by means of the Raman microprobe technique. The effects of the solvents used, B.E.T. specific surface area, heat treatment and lignin content (as measured by the k-value), have been quantified by means of the Raman intensity ratios of characteristic peaks. The amount of solvent residue in each sample has been measured by the DRIFT technique. The morphology of the samples was investigated with the aid of scanning electron microscopy. In this licentiate work it was found that the adsorption is mainly due to the formation of hydrogen bonds. The lignin content and the composition of wood have significant effects on the surface concentration of pinosylvin adsorbed. The specific surface area of wood, as measured by the B.E.T. method, is rather low and does not diretly correlate with the amount adsorbed. The chemical changes after prolonged wood storage cause an increase in the hydrophobicity of wood, resulting in reduced adsorption efficiency.

  • 64222.
    Ziese, M.
    et al.
    Leipzig University, Abteilung Supraleitung & Magnetismus.
    Vrejoiu, I.
    Max-Planck-Institut für Mikrostrukturphysik.
    Pippel, E.
    Max-Planck-Institut für Mikrostrukturphysik.
    Esquinazi, P.
    Leipzig University, Abteilung Supraleitung & Magnetismus.
    Hesse, D.
    Max-Planck-Institut für Mikrostrukturphysik.
    Etz, Corina
    Max-Planck-Institut für Mikrostrukturphysik.
    Henk, J.
    Martin Luther Universität.
    Ernst, A.
    Max-Planck-Institut für Mikrostrukturphysik.
    Maznichenko, Igor
    Institut für Physik, Martin-Luther-Universität Halle-Wittenberg.
    Hergert, W.
    Institut für Physik, Martin-Luther-Universität Halle-Wittenberg.
    Mertig, Ingrid
    Institut für Physik, Martin-Luther-Universität Halle-Wittenberg.
    Tailoring Magnetic Interlayer Coupling in La0.7Sr0.3MnO3/SrRuO3 Superlattices2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 16, article id 167203Article in journal (Refereed)
    Abstract [en]

    The magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices was investigated. High quality superlattices with ultrathin La0.7Sr0.3MnO3 and SrRuO3 layers were fabricated by pulsed laser deposition. The superlattices grew coherently with Mn/Ru intermixing restricted to about one interfacial monolayer. Strong antiferromagnetic interlayer coupling depended delicately on magnetocrystalline anisotropy and intermixing at interfaces. Ab initio calculations elucidated that the antiferromagnetic coupling is mediated by the Mn-O-Ru bond. The theoretical calculations allowed for a quantitative correlation between the total magnetic moment of the superlattice and the degree of Mn/Ru intermixing.

  • 64223. Ziethén, Maria
    et al.
    Åberg, Mi
    Vad tycker kunden?: en fallstudie av ett företags mätmetod1999Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
  • 64224.
    Zimmerman, Claus
    Luleå tekniska universitet.
    Product liability and software engineering: a case study of poor ATM design, and the potential liability for a lack of ergonomics in public computer interface design1999In: Proceedings of the 10th year anniversary of M. Sc. ergonomics: International conference, Luleå, Sweden, 29-30 October 1999 / [ed] John Abeysekera; Emma-Christin Lönnroth; D. Paul T. Piamonte; Houshang Shahnavaz, Luleå: Luleå University of Technology. Department of Human Work Sciences. Division of Industrial Ergonomics , 1999, p. 191-197Conference paper (Refereed)
  • 64225.
    Zimmerman, Tanja
    et al.
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Bordeanu, Nico
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Eyholzer, Christian
    Richter, Klaus
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Characteristics and technical applications of cellulose nanofibrils2008In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235, no 25Article in journal (Other academic)
  • 64226.
    Zimmerman, Tanja
    et al.
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Bordeanu, Nico
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Eyholzer, Christian
    Richter, Klaus
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Nanofibrillated cellulose for technical applications2008Conference paper (Other academic)
  • 64227.
    Zimmerman, Tanja
    et al.
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Bordeau, Nico
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Eyholzer, Christian
    Richter, Klaus
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    High potential of cellulose nanofibrils for technical applications2008In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235, no 24Article in journal (Other academic)
    Abstract [en]

    Cellulose nanofibrils could be very useful for an application in waterborne coatings or adhesives to improve hardness, cohesive and adhesive strength, stiffness, exploitation or thermal creep. Application developments in electronics (LCD panels) where the transparency of cellulose nanocomposites could be used or in nanopapers for filters and membranes are also conceivable. A challenge is the combination of cellulose fibrils with natural polymers. Extensive applications in medicine, food, packaging or transportation are conceivable. Possible raw materials are polymers like poly lactic acid (PLA). To expand the use of bio-based nanocomposites for high-value applications, it is necessary to avoid the reagglomeration and internal entanglement of cellulose fibrils and to improve their homogeneous dispersion in hydrophobic polymers. Special research emphasis is therefore given to the appropriate chemical modification of cellulose nanofibrils. An overview of the high application potential of cellulose nanofibrils with respect to own product development activities will be presented.

  • 64228. Zimmermann, Julien
    Study of the reactions between iron ore slag and refractories2007Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For the fabrication of iron ore pellets at LKAB (Luossavaara-Kiirunavaara AB), one of the methods used is to sinter the pellets in a rotary kiln. This Kiln has a drift temperature of 1250°C in average. During this process a coating, causing the wear of the refractories materials, is formed, inducing expensive maintenance periods. The aim of this work is to find the reaction that takes place between the Slag and the bricks, in order to find the parameters that have to be changed to improve the bricks lifetime in the kiln. The use of bricks with higher alumina content is one of the solutions, but it is expensive. The influence of Alkalis and especially Na2O has been studied before in inert atmosphere. In this work it will be studied in air as well as the influence of the alumina content of the brick. Experiments were performed in air atmosphere, using powder samples that have been compressed into pellets. The devices used to characterize the reaction and the product of the reaction were: Kanthal furnace, X-ray diffraction (XRD), dilatometer, differential scanning calorimetry and thermogravimetry (DSC/TG) in-situ mass spectrometer, Scanning electron microscope (SEM) and Energy dispersive spectrometry (EDS). The XRD experiments permitted to show the presence of a glassy phase after a heat treatment of the samples containing alkalis at 1350°C. Dilatometer experiments gave more information about the influence of alkalis: it catalyzed the sintering reaction. The DSC/TG/spectrometer permitted to show three main reactions. One at 1175°C for the samples containing a low content of alkalis and a low content of Alumina. For the samples with addition of 10wt% of Na2CO3, and 20wt% and more of alumina to the brick, a reaction is observed at 1235°C and one with a maximum at 1300°C. The SEM pictures and EDS show the formation of different phases. Unfortunately it was only possible to identify with certitude the Hematite, the Corundum and a glassy phase. The reliability off the EDS measurements is low, due to the oxides used and a special correction of the data had to be done. The conclusions of the study are: - For the samples with a small amount of alkalis, hematite dissolves mullite at 1175°C and forms Fe2O3Al2O3 and a phase with a nepheline composition (Na2O.Al2O3.2SiO2) that melts at 1235°C. - For the samples with high content of alkalis, all the mullite is dissolved. Silica coming form the decomposition of mullite enters completely the melt and needles crystallize in the melt around 1300°C. - Brick with high alumina content start to react with the slag at 1235°C to form needles around 1300°C. In a future work, WDS or TEM will give a higher reliability than EDS, according detection of the phases.

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  • 64229.
    Zimmermann, Tanja
    et al.
    Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Tingaut, P.
    Eyholzer, Christian
    Richter, Klaus
    Applications of nanofibrillated cellulose in polymer composites2012Conference paper (Refereed)
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  • 64230.
    Zinger, Yaron
    et al.
    Centre for Water Sensitive Cities, Department of Civil Engineering, Monash University.
    Blecken, Godecke-Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Deletic, Ana
    Monash University, Melbourne, VIC.
    Fletcher, Tim
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Retrofitting a Saturated Zone (RSAZ) in stormwater biofilters: impact on pollutants removal2012In: WSUD 2012: Water Sensitve Urban Design - 21 - 23 February 2012, Melbourne Cricket Ground : building the water sensitve community, Barton: Institution of Engineers, Australia , 2012Conference paper (Refereed)
    Abstract [en]

    Stormwater biofilters are good nitrogen control measures. However there are lots of cases in practice, where they failed to meet nitrogen removal targets mainly due to their poor design. Retrofitting a Saturated Zone (SAZ) into a poorly performing biofilters, could be a solution since SAZ will both enhance nitrate removal and assure that plants are well water. The aim of this study was to evaluate the influence of a retrofitted SAZ on nitrogen removal in biofilters. Fifteen mature biofilter columns planted with Dianella revoluta and Microleana stipoides were used since they showed the poorest nitrogen removal of a range of plant species (leaching up to -250% of TN), as well as Carex appressa biofilter columns that achieved removal of TN of over 50%. These columns where sampled over a year before retrofitting the 450mm deep SAZ, and 3 months after the retrofitting. The samples analysed for TSS, total nitrogen (TN) and the nitrogen species NH4 and NOx (nitrite and nitrate), total phosphorus (TP) and filterable reactive phosphorus (FRP), and Cu, Pb and Zn. RSAZ columns showed up to 450% increase in NOx removal capacity for Dianella and 360% for Microlaena, while the control Carex columns enhanced their NOx removal by 35%. Unsurprisingly, TP removal (FRP driven) reduced in all treatments due to presence of organic matter in filter media within the RSAZ. This study showed that potentially we can start retrofitting SAZ into poorly performing biofilters in practice, to make them more effective in stormwater pollution control practice.

  • 64231.
    Zinger, Yaron
    et al.
    Centre for Water Sensitive Cities, Department of Civil Engineering, Monash University.
    Blecken, Godecke-Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Fletscher, Tim D.
    Department of Geography & Resource management, Melbourne University.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Deletic, Ana
    Centre for Water Sensitive Cities, Department of Civil Engineering, Monash University.
    Optimising nitrogen removal in existing stormwater biofilters: Benefits and tradeoffs of a retrofitted saturated zone2013In: Ecological Engineering: The Journal of Ecotechnology, ISSN 0925-8574, E-ISSN 1872-6992, Vol. 51, p. 75-82Article in journal (Refereed)
    Abstract [en]

    Nitrogen excess is a key trigger for eutrophication of water bodies. Stormwater can be an important N source in urban environments and thus requires effective treatment. Stormwater biofilters can remove a wide range of pollutants. However, removal of N is often insufficient due to a lack of denitrification in freely drained biofilters. We tested whether existing stormwater biofilters with poor N removal could be enhanced if a saturated zone is retrofitted to create anaerobic conditions for effective denitrification. We evaluated this by measuring removal of nitrogen, phosphorus and metals in retrofitted biofilters using laboratory mesocosms. For over 18 months five replicates of typical biofiltration configurations, that include freely draining 690 mm deep loamy sand media above a 140 mm deep transition layer and a 70 mm gravel layer planted with popular plant species (Dianella revoluta, Microlaena stipoides and Carex appressa), were tested for typical operational conditions. The biofilter columns planted with D. revoluta and M. stipoides showed poor N removal, while biofilters planted with C. appressa were performing well. All columns were then retrofitted with a 450 mm deep saturated zone, and testing continued using the same operational conditions. After retrofitting the saturated zone, NOx removal was significantly increased (mean increase: 370% for Dianella and 180% for Microlaena) which enhanced overall N removal. TP removal was less efficient after retrofitting the saturated zone due to presence of organic matter in the filter media within the saturated zone. The removal of metals was not affected in practical terms, despite some statistically significant effects. The results of this study suggest that retrofitting a saturated zone in existing standard biofilters should be recommended if the existing filter has inadequate N removal and if N discharges pose a potential threat to the receiving environment.

  • 64232.
    Zinger, Yaron
    et al.
    Monash University, Melbourne, VIC.
    Fletcher, Tim
    Monash University, Melbourne, VIC.
    Deletic, Ana
    Monash University, Melbourne, VIC.
    Blecken, Godecke-Tobias
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Optimisation of the nitrogen retention capacity of stormwater biofiltration systems2007In: Techniques et stratégies durables pour la gestion des eaux urbaines par temps de pluie: 6e Conférence internationale, [25-27] juin 2007, Lyon, France, Villeurbanne: Graie , 2007Conference paper (Refereed)
    Abstract [en]

    Excess nitrogen in stormwater is a principal cause for eutrophication of many water bodies in the world. Biofilters, which used a vegetated soil media, have been shown to reduce nitrogen concentrations in stormwater, although there is substantial scope to improve their current nitrogen removal performance. This paper explores the nitrogen transformations in biofilters and optimised theirs design to maximise removal. To achieve this, 20 columns were constructed to test a range of submerged anoxic zone (SAZ) depths, to maximise denitrification. The effect of adding a carbon source to act as an electron donor supplement in the filter media was also tested. Nitrate removal of up to 99% was achieved, with removal by columns with added carbon significantly greater, with a mean removal of greater than 90%, whilst the non-carbon columns showed an average 50% nitrate removal. Depth profiles revealed that mineralization is the limiting step of nitrogen removal in the biofilter columns. The results will contribute to guidelines for optimal biofilter design.

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  • 64233. Zingerman, Simon
    Hur lyckas jag själv genom att hylla andra som lyckats?2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
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  • 64234.
    Zingmark, Karin
    Umeå University, Department of Nursing.
    Experiences related to home in people with Alzheimer's disease2000Doctoral thesis, comprehensive summary (Other academic)
  • 64235.
    Zingmark, Karin
    University of Umeå, Department of Advanced Nursing.
    Promoting an experience of at-homeness in people with Alzheimer's disease1994Licentiate thesis, comprehensive summary (Other academic)
  • 64236.
    Zingmark, Karin
    Fou-enheten i Piteå älvdal.
    Ökat stöd i hemmet till äldre med demenssjukdom och deras anhöriga2002Report (Other academic)
  • 64237.
    Zingmark, Karin
    et al.
    University of Umeå, Department of Advanced Nursing.
    Norberg, A.
    University of Umeå, Department of Advanced Nursing.
    Sandman, P. O.
    University of Umeå, Department of Advanced Nursing.
    The experience of being at home throughout the life span. Investigation of persons aged from 2 to 1021995In: The International Journal of Aging & Human Development, ISSN 0091-4150, E-ISSN 1541-3535, Vol. 41, no 1, p. 47-62Article in journal (Refereed)
    Abstract [en]

    One hundred and fifty persons aged two to 102 narrated their experiences related to the phenomenon 'being at home.' Several common interdependent and interrelated aspects of the experience of being at home were identified throughout the life span. These aspects are believed to entail cognitive, emotional, and conative dimensions of the experience: safety, rootedness, harmony, joy, privacy, togetherness, recognition, order, control, possession, nourishment, initiative, power, freedom. The sense of being related was found to be a common condition of the experience of being at home, i.e., related to significant others, significant things, significant places, significant activities, oneself, and transcendence. In the process of maintaining the experience of being at home throughout life the phenomena 'being given a home,' 'creating a home,' 'sharing a home,' and 'offering a home' were integral parts. A progression in the experience of being at home throughout the life span was identified.

  • 64238.
    Zingmark, Karin
    et al.
    Department of Advanced Nursing, University of Umeå.
    Norberg, Astrid
    Department of Advanced Nursing, University of Umeå.
    Sandman, Per-Olof
    Nursing Science, Department of Advanced Nursing, University of Umeå.
    Experience of at-homeness and homesickness in patients with Alzheimer’s disease1993In: American Journal of Alzheimer's Disease and Other Dementias, ISSN 1533-3175, Vol. 8, no 3, p. 10-16Article in journal (Refereed)
    Abstract [en]

    In order to gain deeper understanding of the patient’s everyday life participant and non-participant observations were performed at a group-dwelling for Alzheimer patients, during one year and eight months. The patients’ talking and acting in various situations were noted, and the contexts were described. The phenomena, “longing for home,” “on their way home “ and “being at home “ were identified and regarded as expressions of the experience of homesickness and at homeness in the patients

  • 64239.
    Zingmark, Karin
    et al.
    Umeå University, Department of Nursing.
    Sandman, P. O.
    Umeå University, Department of Nursing.
    Norberg, A.
    Umeå University, Department of Nursing.
    Promoting a good life among people with Alzheimer's disease2002In: Journal of Advanced Nursing, ISSN 0309-2402, E-ISSN 1365-2648, Vol. 38, no 1, p. 50-58Article in journal (Refereed)
    Abstract [en]

    Aim. To illuminate the meaning of offering care and a place to live to people with Alzheimer's disease in a special care unit. Rationale. There is a need to gain a deeper understanding about so called 'homelike' care settings, and about how to promote experiences of being at home in residents with Alzheimer's disease. The study is part of a long-term study in a special care unit. Methods. The study comprises phenomenological hermeneutic interpretation of interviews with 10 care providers. Results. The analyses revealed a number of caring aspects such as, for example, 'viewing dignity and striving to preserve a sense of self in the resident', 'encouraging a sense of belonging', 'offering relief and 'promoting a sense of power and control in the resident', although integrated and reflected in each other. The caring aspects constituted the themes confirmation, familiarity, communion and agency considered as dimensions of the good life. Conclusion. To avoid simplification in which, for example, the furniture from a certain decade become the standard for good care, it seems important to focus upon the meaning of the good life. Care that promotes a good life of people with Alzheimer's disease seemed relationship centred.

  • 64240.
    Ziouvelou, Xenia
    et al.
    University of Southampton.
    Alexandrou, Panagiotis
    Computer Technology Institute & Press Diophantus, Patras.
    Angelopoulos, Marios
    University of Geneva.
    Evangelatos, Orestis
    University of Geneva.
    Fernandes, Joao
    Aleksandra Institute Aarhus.
    Loumis, Nicolaus
    University of Surrey.
    McGroarty, Frank
    University of Southampton.
    Nikoletseas, Sotiris
    Computer Technology Institute & Press Diophantus, Patras.
    Rankov, Aleksandra
    DunavNET, Novi Sad.
    Raptis, Theophanis
    Computer Technology Institute & Press Diophantus, Patras.
    Ståhlbröst, Anna
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Ziegler, Sebastien
    Mandat International, Geneva.
    Crowd-driven IoT/IoE ecosystems: a multidimensional approach2017In: Beyond the Internet of Things: Everything Interconnected / [ed] Jordi Mongay Batalla, George Mastorakis, Constandinos X. Mavromoustakis, Evangelos Pallis, Springer International Publishing , 2017, p. 341-375Chapter in book (Refereed)
    Abstract [en]

    During the past few years an astonishing paradigm shift has occurred; user-driven, open and collaborative innovation practices have emerged and an increasing number of users mutually collaborate by openly communicating their ideas, sharing best practices, and creating new knowledge across various sectors. These online, distributed crowd-driven networks leverage the network effects so as to harness the collective power and intelligence. Recently, there is an increasing interest in mobile crowd sensing (MCS) in the context of IoT/IoE which leverages both the power and the wisdom of the crowd in order to observe, measure and make sense of particular phenomena, such as environmental ones, using user-owned mobile and wearable devices. However, in order to ensure the success of such ecosystems, a number of diverse criteria need to be considered. As such this paper provides a framework, which supports the use of multiple perspectives (holistic approach) for the design of crowd-driven ecosystems. The proposed framework utilises three key perspectives: technical, business and end-user (people), in order to describe, analyse and finally design crowd-driven IoT/IoE ecosystems. In addition, this chapter examines the proposed model, in the context of IoT Lab, as a best practice crowd-driven IoT ecosystem, in order to explain how these perspectives can be used to promote ecosystem success.

  • 64241.
    Zipser, L.
    et al.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Franke, H.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ultrasound object fields in air reconstructed using digital phase conjugation2002In: Proceedings: 2002 IEEE Ultrasonics Symposium : October 8 - 11, 2002, Forum Hotel, Munich, Germany / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2002, p. 765-768Conference paper (Refereed)
    Abstract [en]

    A scanning laser Doppler vibrometer is used to record 2D ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction using phase conjugation (time reversal) of the object sound field is then performed and the original object field intensity and phase is reconstructed.

  • 64242.
    Zipser, Lothar
    et al.
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Franke, Heinz
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Reconstructing two-dimensional acoustic object fields by use of digital phase conjugation of scanning laser vibrometry recordings2003In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 29, p. 5831-5838Article in journal (Refereed)
    Abstract [en]

    scanning laser Doppler vibrometer is used to record two-dimensional ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction by use of phase conjugation (time reversal) of the object sound field is then performed, and the original object field intensity and phase is reconstructed

  • 64243.
    Zirgulis, Giedrius
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Svec, Oldrih
    Risø, DTU, Division of Building and Construction, Danish Technological Institute (DTI), Taastrup.
    Geiger, Mette
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cwirzen, Andrzej
    Aalto University School of Engineering, Department of Civil and Structural Engineering, Finland.
    Kanstadt, Terje
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Variation in fiber volume and orientation in walls: experimental and numerical investigations2016In: Structural Concrete, ISSN 1464-4177, E-ISSN 1751-7648, Vol. 17, no 4, p. 576-587Article in journal (Refereed)
    Abstract [en]

    Previous research with fibre-reinforced slab elements has shown that the surface roughness of formwork and the presence of rebars affect fibre orientation and fibre volume distribution. This paper discusses the orientation and volume distribution of steel fibres in wall elements cast from a single point. In particular, the effect of formwork tie bars on fibre orientation and distribution was studied. To quantify the fibre orientation and distribution, numerical simulations and X-ray computed tomography were applied, and the mechanical performance was determined using three-point bending tests on sawn beams. The Thorenfeldt model (applied in the Norwegian proposal of the new fibre-reinforced concrete guideline) was used to estimate the residual flexural tensile strength based on fibre orientation and distribution. The simulation results show that the fibre orientation can be related to the flow pattern. The results indicate a large variation in fibre orientation, which was experimentally confirmed. The fibre volume distribution was mostly uniform, except for an area with fewer fibres at the casting point. The large variation in fibre orientation was reflected by a large variation in residual flexural tensile strengths. Weak zones due to anisotropic fibre orientation caused by formwork tie bars were observed.

  • 64244.
    Zischg, Jonatan
    et al.
    Unit of Environmental Engineering, University of Innsbruck,Innsbruck, Austria.
    Goncalves, M. L. R.
    Unit of Environmental Engineering, University of Innsbruck,Innsbruck, Austria.
    Leonhardt, Günther
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water. Unit of Environmental Engineering, University of Innsbruck.
    Kleidorfer, Manfred
    Unit of Environmental Engineering, University of Innsbruck,Innsbruck, Austria.
    Rauch, Wolfgang
    Unit of Environmental Engineering, University of Innsbruck,Innsbruck, Austria.
    Sitzenfrei, Robert
    Unit of Environmental Engineering, University of Innsbruck,Innsbruck, Austria.
    Von grauer zu grüner Wasserinfrastruktur am Fallbeispiel Kiruna2016In: Tagungsband Aqua Urbanica 2016: "Miss es oder vergiss es" - Daten, Wissen und Konzepte für denGewässerschutz bei Regenwetter, Rigi-Kaltbad, Switzerland, 2016, p. 113-118Conference paper (Other academic)
    Abstract [de]

    In dieser Arbeit wird ein möglicher Übergang von grauer (traditioneller) zu grünerInfrastruktur anhand der Stadt Kiruna (Schweden) untersucht, in der in den nächsten Jahrzehnten einegroße Stadtumwandlung bevorsteht und die Implementierung von dezentralen (grünen)Entwässerungsanlagen angestrebt wird. Dabei wird die hydraulische Leistungsfähigkeit desstädtischen Entwässerungssystems über die Zeit anhand von drei unterschiedlichenImplementierungsmaßstäben grüner Infrastruktur, sowie unter Berücksichtigung von zukünftigenUnsicherheiten (zufolge Klimawandel und Urbanisierung) untersucht. Im Zuge der Umwandlungwerden die Systeme mit den verfolgten Strategien über die Zeit bewertet und ermöglichen dem Planereinen Vergleich der Systemvarianten und die Identifizierung von kritischen Zuständen. Zudem solleine robuste Systemvariante ermittelt werden, welche unter einer großen Bandbreite möglicherzukünftiger Entwicklungen seine Funktionsfähigkeit beibehält. Der entwickelte generische Ansatzstellt eine Methodik zur Beurteilung jeglicher Stadttransformationsprozesse und deren Auswirkungenauf die Wasserinfrastruktur dar (bspw. Stadtwachstum, Absiedlung, Umsiedlung, etc.).

  • 64245.
    Zischg, Jonatan
    et al.
    Unit of Environmental Engineering, University of Innsbruck, Austria.
    Goncalves, Mariana L. R.
    Unit of Environmental Engineering, University of Innsbruck, Austria.
    Bacchin, Taneha K.
    Environmental Technology & Design, Department of Urbanism, Faculty of Architecture and the Built Environment, Delft University of Technology, The Netherlands.
    Leonhardt, Günther
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    van Timmeren, Arjan
    Environmental Technology & Design, Department of Urbanism, Faculty of Architecture and the Built Environment, Delft University of Technology, The Netherlands.
    Rauch, Wolfgang
    Unit of Environmental Engineering, University of Innsbruck, Austria.
    Sitzenfrei, Robert
    Unit of Environmental Engineering, University of Innsbruck, Austria.
    Info-Gap robustness pathway method for transitioning of urban drainage systems under deep uncertainties2017In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 76, no 5, p. 1272-1281Article in journal (Refereed)
    Abstract [en]

    In the urban water cycle, there are different ways of handling stormwater runoff. Traditional systems mainly rely on underground piped, sometimes named ‘gray’ infrastructure. New and so-called ‘green/blue’ ambitions aim for treating and conveying the runoff at the surface. Such concepts are mainly based on ground infiltration and temporal storage. In this work a methodology to create and compare different planning alternatives for stormwater handling on their pathways to a desired system state is presented. Investigations are made to assess the system performance and robustness when facing the deeply uncertain spatial and temporal developments in the future urban fabric, including impacts caused by climate change, urbanization and other disruptive events, like shifts in the network layout and interactions of ‘gray’ and ‘green/blue’ structures. With the Info-Gap robustness pathway method, three planning alternatives are evaluated to identify critical performance levels at different stages over time. This novel methodology is applied to a real case study problem where a city relocation process takes place during the upcoming decades. In this case study it is shown that hybrid systems including green infrastructures are more robust with respect to future uncertainties, compared to traditional network design.

  • 64246.
    Zischg, Jonatan
    et al.
    Unit of Environmental Engineering, Univeristy of Innsbruck, Innsbruck, Austria.
    Goncalves, Mariana
    Unit of Environmental Engineering, Univeristy of Innsbruck, Innsbruck, Austria.
    Leonhardt, Günther
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Kleidorfer, Manfred
    Unit of Environmental Engineering, Univeristy of Innsbruck, Innsbruck, Austria.
    Rauch, Wolfgang
    Unit of Environmental Engineering, Univeristy of Innsbruck, Innsbruck, Austria.
    Sitzenfrei, Robert
    Unit of Environmental Engineering, Univeristy of Innsbruck, Innsbruck, Austria.
    Transformation der Stadtentwässerung unter Berücksichtigung von „grüner“ und „blauer“ Infrastruktur2017In: Österreichische Wasser- und Abfallwirtschaft, ISSN 0945-358X, Vol. 69, no 3, p. 180-185Article in journal (Refereed)
    Abstract [de]

    Neue Bestrebungen in der Siedlungswasserwirtschaft zielen darauf ab, leitungsgebundene („graue“) Wasserinfrastruktur und die damit verbundene rasche Ableitung von Niederschlagswasser zu vermeiden. Neben einer Annäherung an den natürlichen Wasserkreislauf besteht die Erwartung, dass „grün-blaue“ Konzepte flexibler und robuster hinsichtlich zukünftiger Veränderungen, wie Klimawandel oder Urbanisierung, sind. In dieser Arbeit wird ein möglicher Übergang von grauer (traditioneller) zu grün-blauer Infrastruktur anhand der Stadt Kiruna (Schweden) untersucht, in der in den nächsten Jahrzehnten eine große Stadtumwandlung bevorsteht und die Implementierung von dezentralen (grün-blauen) Entwässerungsanlagen angestrebt wird. Dabei wird die hydraulische Leistungsfähigkeit des städtischen Entwässerungssystems über die Zeit anhand von unterschiedlichen Implementierungsmaßstäben grün-blauer Infrastruktur sowie unter Berücksichtigung von zukünftigen Unsicherheiten (zufolge Klimawandel und Urbanisierung) untersucht. Im Zuge der Umwandlung werden die Systeme mit den verfolgten Strategien über die Zeit bewertet und ermöglichen dem Planer einen Vergleich der Systemvarianten und die Identifizierung von kritischen Zuständen. Zudem soll eine robuste Systemvariante ermittelt werden, welche unter einer großen Bandbreite möglicher zukünftiger Entwicklungen ihre Funktionsfähigkeit beibehält. Der entwickelte generische Ansatz stellt eine Methodik zur Beurteilung jeglicher Stadttransformationsprozesse und deren Auswirkungen auf die Wasserinfrastruktur dar (bspw. Stadtwachstum, Absiedlung, Umsiedlung etc.).

  • 64247. Zitron, Sanna
    Upplevelsebegreppets värde inom marknadskommunikation2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The word experience is described by the Swedish Nationalencyklopedin as something hard to describe or a non-analyzed feeling. All though the word is hard to describe it has been written about all since the 1970s when the futurist wrote how the human needs would go from material to meaningful experiences. Today the word experience is well used, especially in the marketing business where several communication agencies say that they are working with experience marketing. The purpose of this paper is to study what value communications agencies provides the word experience. The paper has been prepared with a hermeneutic and inductive approach and a qualitative approach theory. The empirical material was generated through two interviews with informants at two different agencies. The study shows that the word experience does not have a clear definition that is consistently in the branch of communication. It also shows that it is difficult to say what value the word has, whether you're talking financially or emotionally. As the definition and value is not the same for all agencies in the industry this study also discusses what difference a given definition could make.

    Download full text (pdf)
    FULLTEXT02
  • 64248. Znoeva, Anna Vladimirovna
    The improvement of anodic stripping voltammetric (ASV) method of cadmium and mercury determination2006Student paper otherStudent thesis
    Abstract [en]

    Among the various environmental pollutants, heavy metals such as cadmium and mercury are considered the most important. Due to high stability and ability for bioaccumulation they are extremely dangerous for all biological organisms and especially for humans. That’s why a matter of great importance is to analyze and quantify these toxic agents in the environment. In this regard, methods of analysis play not the last role. Methods are different: atomic absorption spectrometry, atomic emission spectrometry etc. Often these techniques require complex sample preparation and expensive instrumentations. In contrast, voltammetric methods particularly anodic stripping voltammetric (ASV) have some advantages such as little or no sample pretreatment and low cost instrumentation. In addition the analytical set is very compact. The aim of this work was to improve anodic striping voltammetric (ASV) methods of analysis for mercury and cadmium detection. The improved method was applied for natural water quality monitoring: some water samples from the delta of Northern Dvina River were analyzed by the method.

    Download full text (pdf)
    FULLTEXT01
  • 64249.
    Zobel, Thomas
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    A critical review of industrial management approaches for climate change mitigation2015Conference paper (Other academic)
    Download full text (pdf)
    FULLTEXT01
  • 64250.
    Zobel, Thomas
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Characterisation of environmental policy implementation in an EMS context: a multiple-case study in Sweden2008In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 16, no 1, p. 37-50Article in journal (Refereed)
    Abstract [en]

    The heart of an environmental management system is the implementation of environmental policy in an organisation by the use of environmental aspects, goals and management programmes. The aim of this paper is to characterise this implementation and discuss how it could be improved. In order to achieve the objective of the paper a multiple-case study was performed in ISO 14001-certified or EMAS-registered organisations in Sweden. It is concluded that the implementation of environmental policy is strictly controlled by specifications in ISO 14001 or EMAS. Some organisations, mostly smaller, are forced to form their environmental policy implementation in a way that is not suited for their type of organisation. Many organisations find it hard to measure their environmental goals and to set long-term or medium-long-term time periods for their goals. In addition, the organisations do not involve their employees to a very great extent in the implementation of the environmental policy. If they do let middle managers and line personnel to participate, it is usually early in the process, as early as in the identification of environmental aspects.

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