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See detailMechanical characterisation of alkali activated clay - based geopolymer binder made out of gravel wash mud
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

in Iacobescu, Remus Ion; Malfliet, Annelies (Eds.) Proceedings of the 5th International Slag Valorisation Symposium (2017, April)

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits1 and classifies all forms of inorganic polymeric material ... [more ▼]

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits1 and classifies all forms of inorganic polymeric material synthesised by chemical reaction of aluminosilicates and an alkaline activating solution. The production of geopolymer binder comprises in two main procedures: calcination and geopolymerisation. The synthesised geopolymer shows interesting characteristics like good mechanical properties, high strength and good durability. [less ▲]

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See detailMechanical characterisation of alkali activated clay - based geopolymer binder made out of gravel wash mud
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

Poster (2017, April 03)

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits and classifies all forms of inorganic polymeric material ... [more ▼]

One of the most promising cement alternatives are geopolymer cements. The term “geopolymer” was mentioned for the first time by Davidovits and classifies all forms of inorganic polymeric material synthesised by chemical reaction of aluminosilicates and an alkaline activating solution. The production of geopolymer binder comprises in two main procedures: calcination and geopolymerisation. The synthesised geopolymer shows interesting characteristics like good mechanical properties, high strength and good durability. [less ▲]

Detailed reference viewed: 219 (40 UL)
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See detailMechanical Characteristics of Laser Braze-Welded Aluminium-Copper Connections
Solchenbach, Tobias UL; Plapper, Peter UL

in Optics & Laser Technology (2013)

Abstract The mechanical characteristics of dissimilar Al-Cu connections, joined by a novel, robust laser braze-welding process are reported. A ber laser is used in combination with a 2D galvoscanner to ... [more ▼]

Abstract The mechanical characteristics of dissimilar Al-Cu connections, joined by a novel, robust laser braze-welding process are reported. A ber laser is used in combination with a 2D galvoscanner to provide spatial power modulation by superposed circular beam oscillation. With the help of statistical experimental design, a broad range of processing parameters has been inves- tigated in order to understand their e ects on the joint characteristics. A maximum shear strength of 121 MPa has been detected within the scope of the experiments. [less ▲]

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See detailA mechanical design model for steel and concrete composite members with web openings
Claßen, Martin; Kurz, Wolfgang; Schäfer, Markus UL et al

in Engineering Structures (2019), Engineering Structures 197:109417(109417),

In web opening regions, a significant share of the global shear force is redistributed from the perforated web of the steel beam to the reinforced concrete (RC) slab. This redistribution leads to vertical ... [more ▼]

In web opening regions, a significant share of the global shear force is redistributed from the perforated web of the steel beam to the reinforced concrete (RC) slab. This redistribution leads to vertical forces in the shear connectors close to both edges of the opening and influences the internal forces in the steel beam and the RC slab over a length of approximately three times the opening length a0. The global shear failure in the web opening region is affected by the rather brittle behavior of the concrete and is either characterized by a diagonal shear cracking failure of the RC slab, or a local bending failure at the opening edges, or vertical connector failure (concrete break-out) at the ends of the opening. This paper is intended to clarify the structural behavior of web opening regions and proposes easy-to-use models that make it possible to analyze the local internal forces of each partial beam in a mechanically consistent manner. Based on these models, a novel design procedure is presented, that allows efficient design and dimensioning of web openings as well as prediction of shear resistance and failure mode. [less ▲]

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See detailMechanical failure in microstructural heterogeneous materials
Bordas, Stéphane UL; Hoppe, R. H. W.; Petrova, S. I.

in Lecture Notes in Computer Science (2007), 4310 LNCS

Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and ... [more ▼]

Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and propagation of cracks in places of high pore density in the microstructures. A multi-scale method based on the asymptotic homogenization theory together with the mesh superposition method (s-version of FEM) is presented for modeling of cracks. The homogenization approach is used on the global domain excluding the vicinity of the crack where the periodicity of the microstructures is lost and this approach fails. The multiple scale method relies on efficient combination of both macroscopic and microscopic models. The mesh superposition method uses two independent (global and local) finite element meshes and the concept of superposing the local mesh onto the global continuous mesh in such a way that both meshes not necessarily coincide. The homogenized material model is considered on the global mesh while the crack is analyzed in the local domain (patch) which allows to have an arbitrary geometry with respect to the underlying global finite elements. Numerical experiments for biomorphic cellular ceramics with porous microstructures produced from natural wood are presented. [less ▲]

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See detailMechanical Interphases in Epoxies as seen by Nondestructive High-Performance Brillouin Microscopy
Krüger, Jan-Kristian UL; Müller, Ulrich UL; Bactavatchalou, Ravindrakumar et al

in Adhesion - Current Research and Application (2005)

Detailed reference viewed: 57 (5 UL)
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See detailMechanical material properties of polymethylmethacrylate (PMMA) für medical applications
Thielen, Thomas UL; Maas, Stefan UL; Zürbes, Arno UL et al

in Materials Testing = Materialprüfung (2009), 51(4), 203-209

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See detailMechanical Model to Predict the Resistance of the Shear Connection in Composite Beams with Deep Steel Decking
Odenbreit, Christoph UL; Nellinger, Sebastian UL

in Eurosteel 2017 (2017, September 13)

The resistance of a typical shear connection with headed shear studs in a composite beam is analysed in the normal case in accordance with EN 1994-1-1. The reducing effect of a trapezoidal metal decking ... [more ▼]

The resistance of a typical shear connection with headed shear studs in a composite beam is analysed in the normal case in accordance with EN 1994-1-1. The reducing effect of a trapezoidal metal decking onto the ultimate load bearing capacity is considered with empirically derived reduction factors and equations, which have been developed in the last century between the late 70th and the early 80th. The RFCS research project “DISCCO” investigated the shear stud resistance with novel types of steel decking. In many cases, the shear resistance, which was predicted by EN 1994-1-1 was not reached in tests. In the respective experiments with composite beams and deep decking, a concrete cone failure mode was identified and not a pure shear failure of the stud. This failure mode acted in combination with the load bearing capacity of the shear stud, which formed one or two plastic hinges in the shaft - depending on the available geometry. Based on these observations, new equations have been developed to predict the shear connection’s resistance with more accurcy. The yield hinge mechanism of the shear stud, which was developed by Lungershausen, was extended by the above mentioned load bearing component ‘concrete cone’. The formulae consider the geometry of the stud and the steel decking, the material strength of the stud and of the concrete material. The statistical evaluation of the developed equations shows a good accordance with test results. [less ▲]

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See detailMechanical model to predict the resistance of the shear connection in composite beams with deep steel decking
Odenbreit, Christoph UL; Nellinger, Sebastian UL

in Steel Construction (2017), 10(3), 248-253

The resistance of a typical shear connection with headed shear studs in a composite beam is analysed for the normal case in accordance with EN 1994-1-1. The reducing effect of a trapezoidal metal decking ... [more ▼]

The resistance of a typical shear connection with headed shear studs in a composite beam is analysed for the normal case in accordance with EN 1994-1-1. The reducing effect of a trapezoidal metal decking to the ultimate loadbearing capacity is considered with empirically derived reduction factors and equations that were developed between the late 1970s and early 1980s. The RFCS research project ”DISCCO“ investigated the shear stud resistance with novel types of steel decking. In many cases, the shear resistance predicted by EN 1994-1-1 was not reached in tests. In the respective experiments with composite beams and deep decking, a concrete cone failure mode was identified and not a pure shear failure of the stud. This failure mode acted in combination with the loadbearing capacity of the shear stud, which formed one or two plastic hinges in the shaft depending on the actual geometry. Based on these observations, new equations have been developed to predict the shear connection's resistance with more accuracy. The yield hinge mechanism of the shear stud, which was developed by Lungershausen, was extended by the aforementioned loadbearing component ”concrete cone“. The formulae consider the geometry of the stud and the steel decking and the material strength of the stud and the concrete. The statistical evaluation of the equations developed demonstrates good agreement with test results. [less ▲]

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See detailMechanical parameters identification of keloid and surrounding healthy skin using Digital Image Correlation measurements in vivo
Elouneg, Aflah; Sutula, Danas; Sensale, Marco UL et al

Scientific Conference (2019, December 09)

The human skin behaves as an elastic membrane initially prestressed but not uniformly. The presence of anatomical sites favorable to the appearance of some tumors, a keloid in our case, while other sites ... [more ▼]

The human skin behaves as an elastic membrane initially prestressed but not uniformly. The presence of anatomical sites favorable to the appearance of some tumors, a keloid in our case, while other sites never develop them attests to the importance of the mechanical environment of the tissue. Thus, a mechanical characterization of the tumored skin is necessary to understand the keloid expansion from a mechanical point of view. Our case study consists in modeling a bi-material structure composed of a keloid skin surrounded by healthy skin located on upper left arm of a young female. From the experimental measurements in vivo, by combining force sensor, displacement sensor and Digital Image Correlation techniques, we perform a mechanical analysis to characterize the mechanical stress fields over the entire area and on the interface ‘healthy skin/keloid skin’. Since the mechanical behavior of the tumorous skin is unknown, many physical models can be implemented and assessed very easily inside the specific digital software to fit with the real data. Once a set of mechanical parameters for both the healthy skin and the keloid skin are identified, the stress fields around the keloid are calculated. Next steps consist in determining matching preferential directions in order to define as precisely as possible the specifications of a device for preventing the growth of keloids. [less ▲]

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See detailMechanical Properties of Laser Braze-Welded Al-Cu connections
Solchenbach, Tobias UL; Plapper, Peter UL

in Mechanical Properties of Laser Braze-Welded Al-Cu connections (2012, November)

The paper describes an innovative, laser based joining method for dissimilar Al-Cu connections. The main objective is the improvement of the mechanical and electrical properties of the joints.

Detailed reference viewed: 108 (12 UL)
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See detailThe mechanical reliability of an electronic textile investigated using the virtual-power-based quasicontinuum method
Beex, Lars UL; Peerlings, Ron; Van Os, Koen et al

in Mechanics of Materials (2015), 80

The quasicontinuum (QC) method is a multiscale method for the solution of lattice models that combines coarse-grained regions and fully resolved regions with individual lattice events. QC methodologies ... [more ▼]

The quasicontinuum (QC) method is a multiscale method for the solution of lattice models that combines coarse-grained regions and fully resolved regions with individual lattice events. QC methodologies are mainly used to reduce the computational costs of conservative atomistic lattice computations. Recently, a virtual-power-based variant has been proposed that enables its use for non-conservative lattice computations. In this contribution the virtual-power-based QC approach is adopted in combination with a recently proposed mesostructural lattice model for electronic textile in order to investigate its mechanical behaviour. The interactions of the lattice model for electronic textile are modelled elastoplastically and hence, regular conservative QC approaches are not adequate. This article incorporates a modification of a previously defined exact summation rule for QC methods –by sampling the lattice interactions directly instead of via the lattice nodes. This leads to a significant reduction of the computational cost, whereas the accuracy of the summation rule remains unaffected. The presented methodology is used to efficiently investigate the failure envelope of an electronic textile – a woven fabric with embedded electronic components and conductive wires. The dependence of the failure envelope on the locations of the conductive wires and the stiffness of the weft yarns is investigated as well. [less ▲]

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See detailMechanical Resonances of Mobile Impurities in a One-Dimensional Quantum Fluid
Schmidt, Thomas UL; Dolcetto, Giacomo; Pedder, Christopher et al

in Physical Review Letters (2019), 123

We study a one-dimensional interacting quantum liquid hosting a pair of mobile impurities causing backscattering. We determine the effective retarded interaction between the two impurities mediated by the ... [more ▼]

We study a one-dimensional interacting quantum liquid hosting a pair of mobile impurities causing backscattering. We determine the effective retarded interaction between the two impurities mediated by the liquid. We show that for strong backscattering this interaction gives rise to resonances and antiresonances in the finite-frequency mobility of the impurity pair. At the antiresonances, the two impurities remain at rest even when driven by a (small) external force. At the resonances, their synchronous motion follows the external drive in phase and reaches maximum amplitude. Using a perturbative renormalization group analysis in quantum tunneling across the impurities, we study the range of validity of our model. We predict that these mechanical antiresonances are observable in experiments on ultracold atom gases confined to one dimension. [less ▲]

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See detailMechanical strength assessment of a drilled hole in the contralateral cortex at the end of the open wedge for high tibial osteotomy.
Diffo Kaze, Arnaud UL; Maas, Stefan UL; Hoffmann, Alexander et al

in Journal of Experimental Orthopaedics (2017), 4(1),

BACKGROUND: This study aimed to investigate, by means of finite element analysis, the effect of a drill hole at the end of a horizontal osteotomy to reduce the risk of lateral cortex fracture while ... [more ▼]

BACKGROUND: This study aimed to investigate, by means of finite element analysis, the effect of a drill hole at the end of a horizontal osteotomy to reduce the risk of lateral cortex fracture while performing an opening wedge high tibial osteotomy (OWHTO). The question was whether drilling a hole relieves stress and increases the maximum correction angle without fracture of the lateral cortex depending on the ductility of the cortical bone. METHODS: Two different types of osteotomy cuts were considered; one with a drill hole (diameter 5 mm) and the other without the hole. The drill holes were located about 20 mm distally to the tibial plateau and 6 mm medially to the lateral cortex, such that the minimal thickness of the contralateral cortical bone was 5 mm. Based on finite element calculations, two approaches were used to compare the two types of osteotomy cuts considered: (1) Assessing the static strength using local stresses following the idea of the FKM-guideline, subsequently referred to as the "FKM approach" and (2) limiting the total strain during the opening of the osteotomy wedge, subsequently referred to as "strain approach". A critical opening angle leading to crack initiation in the opposite lateral cortex was determined for each approach and was defined as comparative parameter. The relation to bone aging was investigated by considering the material parameters of cortical bones from young and old subjects. RESULTS: The maximum equivalent (von-Mises) stress was smaller for the cases with a drill hole at the end of the osteotomy cut. The critical angle was approximately 1.5 times higher for the specimens with a drill hole compared to those without. This corresponds to an average increase of 50%. The calculated critical angle for all approaches is below 5°. The critical angle depends on the used approach, on patient's age and assumed ductility of the cortical bone. CONCLUSIONS: Drilling a hole at the end of the osteotomy reduces the stresses in the lateral cortex and increases the critical opening angle prior to cracking of the opposite cortex in specimen with small correction angles. But the difference from having a drill hole or not is not so significant, especially for older patients. The ductility of the cortical bone is the decisive parameter for the critical opening angle. [less ▲]

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See detailMechanical strength of a new plate compared to six previously tested opening wedge high tibial osteotomy implants
Diffo Kaze, Arnaud; Maas, Stefan UL; Belsey, James et al

in Journal of Experimental Orthopaedics (2019)

Background This study aimed to assess the mechanical static and fatigue strength provided by the FlexitSystem plate in medial opening wedge high tibial osteotomies (MOWHTO), and to compare it to six ... [more ▼]

Background This study aimed to assess the mechanical static and fatigue strength provided by the FlexitSystem plate in medial opening wedge high tibial osteotomies (MOWHTO), and to compare it to six previously tested implants: the TomoFix small stature, the TomoFix standard, the ContourLock, the iBalance, the second generation PEEKPower and the size 2 Activmotion. Thus, this will provide surgeons with data that will help in the choice of the most appropriate implant for MOWHTO. Methods Six fourth-generation tibial bone composites underwent a MOWHTO and each was fixed using six FlexitSystem plates, according to standard techniques. The same testing procedure that has already been previously defined, used and published, was used to investigate the static and dynamic strength of the prepared bone-implant constructs. The test consisted of static loading and cyclical loading for fatigue testing. Results During static testing, the group constituted by the FlexitSystem showed a fracture load higher than the physiological loading of slow walking (3.7 kN > 2.4 kN). Although this fracture load was relatively small compared to the average values for the other Implants from our previous studies, except for the TomoFix small stature and the Contour Lock. During fatigue testing, FlexitSystem group showed the smallest stiffness and higher lifespan than the TomoFix and the PEEKPower groups. Conclusions The FlexitSystem plate showed sufficient strength for static loading, and average fatigue strength compared to the previously tested implants. Full body dynamic loading of the tibia after MOWHTO with the investigated implants should be avoided for at least three weeks. Implants with a wider T-shaped proximal end, positioned onto the anteromedial side of the tibia head, or inserted in the osteotomy opening in a closed-wedge construction, provided higher mechanical strength than implants with small a T-shaped proximal end, centred onto the medial side of the tibia head. [less ▲]

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See detailMechanische und thermische Untersuchungen zur Entwicklung eines Wärmedämmsteines aus Leichtbeton
Leufgens, Nadine UL

Doctoral thesis (2010)

The current discussion about the necessity of sustainable reduction of primary energy for heating of housing structures and of CO2 – emissions led the University of Luxembourg to issue a project to ... [more ▼]

The current discussion about the necessity of sustainable reduction of primary energy for heating of housing structures and of CO2 – emissions led the University of Luxembourg to issue a project to develop hybrid light-weight concrete blocks with high heat-insulating properties. Therefore, the demand for wall constructions limiting the heat flow through the outer wall was steadily growing. Because of the progressing standard of national and European Energy Saving Regulations for housing structures and office buildings in the past years, most of the producers of bricks and concrete masonry blocks were forced to develop new, innovative wall materials and constructions. For assessing the real actual state of the art of masonry blocks, 15 different bricks and blocks were taken from European free market as samples. It was shown, that especially for highly-heat insulating masonry lightweight concrete blocks (e.g. Vbl SW 2) with dry densities below 800 kg/m3 an optimization potential still exists. A relevant aspect for a critical estimation of a wall construction is the knowledge of mechanical and thermal lightweight aggregate concrete (LAC) parameters. The present work describes investigations for determining design limit values of the thermal and mechanical properties of LAC. Based on this, a mathematical approach to describe the strength, the thermal conductivity and for e.g. the stress-strain-relationship linked to the dry density in a range between 500 and 2000 kg/m3 was derived. For studying the material behavior of LAC, specimens were produced in laboratory tests as well as in the production line by fabricating solid lightweight concrete blocks without inner air holes. Due to the unsatisfying results of the market study, further investigations had to be done to determine the influence of size and slenderness effects on the strength of solid specimen and masonry blocks with inner air holes made of LAC. Additionally, combined influencing factors were studied on block sections cut out of hollow and solid masonry blocks. In the following, the experimental results were verified by simulations with the Finite-Element-Method using the commercial software ANSYS© for modeling different LAC-specimen geometries and the influence of the kind of load applications by a contact zone between steel plates and specimen. Subsequently, the results of these investigations and the achieved knowledge of the influencing factors on the load carrying capacity of the block structures lead to an analytical model approach for design purpose of masonry blocks based on the elasticity theory. This model allows quantitative predictions of the load bearing strength of hollow and solid masonry blocks with inner air holes arranged in a grid system. The analytical model is verified by comparison of experimental results of different block geometries. Finally, the knowledge of the load carrying behavior of different LAC specimen geometries achieved by various experimental and numerical results contribute to the construction of new prototypes of heat insulating masonry blocks made of LAC. Based on the results of the market study and numerical parameter studies, it is revealed that it is suggestive to separate the load bearing from the thermal function of the block by developing 3-layered Sandwich and composite blocks made of an insulating and load bearing part. [less ▲]

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See detail[Mechanism of action of calcium antagonists].
Stimpel, M.; Neyses, Ludwig UL

in Schweizerische Rundschau fur Medizin Praxis = Revue suisse de medecine Praxis (1985), 74(19), 483-90

Detailed reference viewed: 41 (0 UL)
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See detailMechanism of fast peptide recognition by SH3 domains
Ahmad, Mazen; Gu, Wei UL; Helms, Volkhard

in Angewandte Chemie International Edition (2008), 47(40), 7626-7630

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See detailMechanism of PP2A-mediated IKK beta dephosphorylation: a systems biological approach.
Witt, Johannes; Barisic, Sandra; Schumann, Eva et al

in BMC Systems Biology (2009), 3

BACKGROUND: Biological effects of nuclear factor-kappaB (NF kappaB) can differ tremendously depending on the cellular context. For example, NF kappaB induced by interleukin-1 (IL-1) is converted from an ... [more ▼]

BACKGROUND: Biological effects of nuclear factor-kappaB (NF kappaB) can differ tremendously depending on the cellular context. For example, NF kappaB induced by interleukin-1 (IL-1) is converted from an inhibitor of death receptor induced apoptosis into a promoter of ultraviolet-B radiation (UVB)-induced apoptosis. This conversion requires prolonged NF kappaB activation and is facilitated by IL-1 + UVB-induced abrogation of the negative feedback loop for NF kappaB, involving a lack of inhibitor of kappaB (I kappaB alpha) protein reappearance. Permanent activation of the upstream kinase IKK beta results from UVB-induced inhibition of the catalytic subunit of Ser-Thr phosphatase PP2A (PP2Ac), leading to immediate phosphorylation and degradation of newly synthesized I kappaB alpha. RESULTS: To investigate the mechanism underlying the general PP2A-mediated tuning of IKK beta phosphorylation upon IL-1 stimulation, we have developed a strictly reduced mathematical model based on ordinary differential equations which includes the essential processes concerning the IL-1 receptor, IKK beta and PP2A. Combining experimental and modelling approaches we demonstrate that constitutively active, but not post-stimulation activated PP2A, tunes out IKK beta phosphorylation thus allowing for I kappaB alpha resynthesis in response to IL-1. Identifiability analysis and determination of confidence intervals reveal that the model allows reliable predictions regarding the dynamics of PP2A deactivation and IKK beta phosphorylation. Additionally, scenario analysis is used to scrutinize several hypotheses regarding the mode of UVB-induced PP2Ac inhibition. The model suggests that down regulation of PP2Ac activity, which results in prevention of I kappaB alpha reappearance, is not a direct UVB action but requires instrumentality. CONCLUSION: The model developed here can be used as a reliable building block of larger NF kappa B models and offers comprehensive simplification potential for future modeling of NF kappa B signaling. It gives more insight into the newly discovered mechanisms for IKK deactivation and allows for substantiated predictions and investigation of different hypotheses. The evidence of constitutive activity of PP2Ac at the IKK complex provides new insights into the feedback regulation of NF kappa B, which is crucial for the development of new anti-cancer strategies. [less ▲]

Detailed reference viewed: 50 (0 UL)