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See detailExperimental observation of third-order effect in magnetic small-angle neutron scattering
Metlov, Konstantin L.; Suzuki, Kiyonori; Honecker, Dirk UL et al

in Physical Review. B, Condensed Matter and Materials Physics (2020), 101

Detailed reference viewed: 61 (1 UL)
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See detailAn experimental scrutiny of visual design modelling: VCL up against UML+OCL
Amalio, Nuno UL; Briand, Lionel UL; Kelsen, Pierre UL

in Empirical Software Engineering (2019)

The graphical nature of prominent modelling notations, such as the standards UML and SysML, enables them to tap into the cognitive benefits of diagrams. However, these notations hardly exploit the ... [more ▼]

The graphical nature of prominent modelling notations, such as the standards UML and SysML, enables them to tap into the cognitive benefits of diagrams. However, these notations hardly exploit the cognitive potential of diagrams and are only partially graphical with invariants and operations being expressed textually. The Visual Contract Language (VCL) aims at improving visual modelling; it tries to (a) maximise diagrammatic cognitive effectiveness, (b) increase visual expressivity, and (c) level of rigour and formality. It is an alternative to UML that does largely pictorially what is traditionally done textually. The paper presents the results of a controlled experiment carried out four times in different academic settings and involving 43 participants, which compares VCL against UML and OCL and whose goal is to provide insight on benefits and limitations of visual modelling. The paper’s hypotheses are evaluated using a crossover design with the following tasks: (i) modelling of state space, invariants and operations, (ii) comprehension of modelled problem, (iii) detection of model defects and (iv) comprehension of a given model. Although visual approaches have been used and advocated for decades, this is the first empirical investigation looking into the effects of graphical expression of invariants and operations on modelling and model usage tasks. Results suggest VCL benefits in defect detection, model comprehension, and modelling of operations, providing some empirical evidence on the benefits of graphical software design. [less ▲]

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See detailExperimental Stock Market Dynamics: Excess bids, directional learning, and adaptive style-investing in a call-auction with multiple multi-period lived assets
Neugebauer, Tibor UL; Reinhard, Selten

in Journal of Economic Behavior and Organization (2019), (157), 209-224

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See detailExperimental studies of the technical feasibility of a lamination process for PVT-direct modules
Hilger, Lukas; Roßbach, Nils; Wirth, Florian et al

Poster (2016)

The PVT-direct module covers the technical connection of solar PV technology and solarthermal systems. The structure is similar to conventional PV modules apart from the backsheet which is replaced by an ... [more ▼]

The PVT-direct module covers the technical connection of solar PV technology and solarthermal systems. The structure is similar to conventional PV modules apart from the backsheet which is replaced by an aluminum backside plate. Along with compressor, gas cooler for heat rejection and expansion valve the PVT-direct module acts as an evaporator in a heat-pump cycle. The module is characterized by a direct CO2 evaporation in small microchannels which are brazed on the aluminum backside plate. The combination of both photovoltaic and thermal components in one module leads to high demands in terms of the choice of materials and the production process itself. In this context, further investigations on the technical feasibility of a lamination process for solar PVT-direct modules are necessary in order to guarantee an intended market maturity. The development of a suitable lamination process and its parameters form the major part of this work. The lamination schedule depends on the performance and structure of the used encapsulating material as well as the laminator itself. The lamination process is adjusted through experimental studies until satisfactory results are achieved. It can be characterized by the maximum lamination temperature and the total process time along with the heating/cooling ramp. The additional aluminum backside plate including headers and microchannels can have a significant impact on the PVT-direct module during lamination process. Therefore, measurement methods which indicate the state of the module after the lamination are required. On the one hand, the quality of the adhesion between the different parts of the module is an important factor for long-term resistance of the system. The cross linking of the encapsulating material and of the adhesion layer is verified by DSC-Measuring. On the other hand - due to a changed design of the PVT direct module and mechanical stress distribution during the lamination process - the mechanical condition of the cells inside of the laminate is checked. This can be evaluated by Electroluminescence-Measuring in order to ensure the absence of cracks and fraction of the PV-cells. Current tasks involve the distortion of the laminated modules due to different thermal expansion coefficients of glass and aluminum as well as the occurrence of blisters in the laminate. These issues and the lamination of a module in standard measures will be addressed in the ongoing process of the project. [less ▲]

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See detailExperimental Studies on Subjective Views of Aging: Overview, Challenges, and Future Directions
Wahl, Hans-Werner; Kornadt, Anna Elena UL

in Diehl, Manfred; Palgi, Yuval; Shrira, Amit (Eds.) Subjective Views of Aging: Theory, Research, and Practice (in press)

A major body of evidence points to the significant associations between views on aging (VoA) and key developmental outcomes, such as health and well-being. While much of this evidence comes from ... [more ▼]

A major body of evidence points to the significant associations between views on aging (VoA) and key developmental outcomes, such as health and well-being. While much of this evidence comes from longitudinal studies, research on VoA has also been strongly experimental since its inception. Our chapter aims to provide an overview about the major lines of prior experimental research on VoA and by this means derive its role for present and future VoA research overall. We first offer an organizing scheme for the existing body of experimental work on VoA. We arrive at the conclusion that previous experimental research on VoA with older adults has been conducted in a broad range of studies with different dependent variables and experimental manipulations, showing the importance of VoA and their impact on a wide range on phenomena. We then go into more detail of VoA research that has been done in the past decade. Here, our conclusion is that recent experimental research on VoA is taking up societal challenges, such as the aging workforce, older people in the health care system, and stereotype threat elicited by digital technologies. At the same time, current VoA research is adding to the differentiation of established effects in the prior literature as well as helped to identify moderating and contextual conditions not considered previously. We end with a set of recommendations for future experimental VoA research including strengthening the needed liaison with other research formats. [less ▲]

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See detailExperimental studies on the development of a solar hybrid module with an aluminum microchannel evaporator
Rullof, Johannes UL; Lambers, Klaus Jürgen; Dick, Christian et al

in Proceedings of 2016 International Energy and Sustainability Conference (IESC 2016) (2016)

In recent years, the possibility to combine photovoltaics (PV) and solar thermal collectors into one hybrid module (PVT-module) has been increasingly investigated. PVT-modules produce thermal and ... [more ▼]

In recent years, the possibility to combine photovoltaics (PV) and solar thermal collectors into one hybrid module (PVT-module) has been increasingly investigated. PVT-modules produce thermal and electrical energy at the same time. As the efficiency of a photovoltaic module decreases with temperature, the temperature of the heat transfer media is often limited to about 30 °C and the PVT-module is combined with a heat pump, which increases the temperature on the “warm side”. This paper deals with a PVT-module, which combines a microchannel based evaporator of a CO2 (R744) heat pump with a PV panel (PVT-direct). The PVT-direct overall system is reduced to the refrigerant circuit due to the direct refrigerant expansion in the PVT-module. A conventional PVT heat pump system has an additional glycol-water circuit. Since a pump and an additional heat exchanger for the secondary cycle were omitted, the system has increased efficiency. Due to lower module temperatures, the increase of the photovoltaic efficiency is a further advantage of the PVT-direct-module. To prove the feasibility of the PVT-direct heat pump system, the Cologne Institute for Renewable Energy (CIRE) is developing and modeling a test facility for this purpose within the research project “PVT-direkt”. Furthermore, a functional PVT-direct-module with a microchannel based evaporator was designed and built. Much importance has been given to experimental studies under laboratory conditions in order to investigate (1) the adjustment of the functionality and layout of the PVT-direct-module for characterizing the joining of brazed joints in aluminum microchannel evaporators and (2) the influence of the backside aluminum plate of the PVT-direct-module regarding leakage currents and parasitic capacitances. The overall results obtained in these experimental studies are analyzed in this paper. [less ▲]

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See detailExperimental Study of an Underlay Cognitive Radio System: Model Validation and Demonstration
Becker, Hanna; Kaushik, Ankit; Sharma, Shree Krishna UL et al

in Proceedings of CROWNCOM 2016 (2016, May)

Cognitive radio is one of the potential contenders that address the problem of spectrum scarcity by making e efficient use of the currently allocated spectrum below 6 GHz. A secondary access to the ... [more ▼]

Cognitive radio is one of the potential contenders that address the problem of spectrum scarcity by making e efficient use of the currently allocated spectrum below 6 GHz. A secondary access to the licensed spectrum is only possible, if the cognitive radio systems restrict the interference to the primary systems. However, the performance analysis of such a cognitive radio system is a challenging task. Currently, performance evaluation of underlay systems is limited to theoretical analysis. Most of the existing theoretical investigations make certain assumptions in order to sustain analytical tractability, which could be unrealistic from the deployment perspective. Motivated by this fact, in this work, we validate the performance of an underlay system by means of laboratory measurements, and consequently propose a hardware demonstrator of such a system. Moreover, we present a graphical user interface to provide insights to the working of the proposed demonstrator and highlight the main issues faced during this experimental study. [less ▲]

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See detailExperimental validation of a newly designed 6 degrees of freedom scanning laser head: Application to three-dimensional beam structure
Copertaro, Edoardo UL; Di Maio, Dario

in Review of Scientific Instruments (2013), 84

A new scanning laser head is designed to use single Laser Doppler Vibrometer (LDV) for performing measurements up to 6 degrees of freedom (DOF) at a target. The scanning head is supported by a rotating ... [more ▼]

A new scanning laser head is designed to use single Laser Doppler Vibrometer (LDV) for performing measurements up to 6 degrees of freedom (DOF) at a target. The scanning head is supported by a rotating hollow shaft, which allows the laser beam to travel up to the scanning head from an opposite direction where an LDV is set up. The scanning head is made of a set of two mirrors, which deflects the laser beam with an angle so that the rotation of the scanning head produces a conical scan. When measurements are performed at the focal point of the conical scan then three translational vibration components can be measured, otherwise the very small circle scan, before and after the focal point, can measure up to 6 degrees of freedom, including three translations and three rotations. This paper presents the 6DOF scanning head and the measurements of 3D operational deflection shapes of a test structure. [less ▲]

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See detailExperimental validation of adaptive control for a Shape Memory Alloy actuated lightweight robotic arm
Quintanar Guzman, Serket UL; Kannan, Somasundar UL; Voos, Holger UL et al

in ASME 2018 Conferences on Smart Materials, Adaptive Structures and Intelligent Systems, San Antonio 10-12 September 2018 (2018, September)

This article presents the experimental validation of a Direct Adaptive Control for angular position regulation of a lightweight robotic arm. The robotic arm is single degree-of-freedom (DOF) system ... [more ▼]

This article presents the experimental validation of a Direct Adaptive Control for angular position regulation of a lightweight robotic arm. The robotic arm is single degree-of-freedom (DOF) system, actuated by two Shape Memory Alloy (SMA) wires. The proposed adaptive control is capable of adapting itself to the hysteretic behavior of SMA wires and update its behavior to deal with the changing parameters of the material over time. The closed-loop approach is tested experimentally showing its effectiveness to deal with the highly nonlinear dynamics of the SMA wires. These results are discussed and compared with a classical control approach. The updated design and hardware development and modeling of the robotic arm are shown. [less ▲]

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See detailAn experimental/numerical investigation into the main driving force for crack propagation in uni-directional fibre-reinforced composite laminae
Cahill, L. M. A.; Natarajan, S.; Bordas, Stéphane UL et al

in Composite Structures (2014), 107

This paper presents an enriched finite element method to simulate the growth of cracks in linear elastic, aerospace composite materials. The model and its discretisation are also validated through a ... [more ▼]

This paper presents an enriched finite element method to simulate the growth of cracks in linear elastic, aerospace composite materials. The model and its discretisation are also validated through a complete experimental test series. Stress intensity factors are calculated by means of an interaction integral. To enable this, we propose application of (1) a modified approach to the standard interaction integral for heterogeneous orthotropic materials where material interfaces are present; (2) a modified maximum hoop stress criterion is proposed for obtaining the crack propagation direction at each step, and we show that the “standard” maximum hoop stress criterion which had been frequently used to date in literature, is unable to reproduce experimental results. The influence of crack description, material orientation along with the presence of holes and multi-material structures are investigated. It is found, for aerospace composite materials with View the MathML source ratios of approximately 10, that the material orientation is the driving factor in crack propagation. This is found even for specimens with a material orientation of 90°, which were previously found to cause difficulty in both damage mechanics and discrete crack models e.g. by the extended finite element method (XFEM). The results also show the crack will predominantly propagate along the fibre direction, regardless of the specimen geometry, loading conditions or presence of voids. [less ▲]

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See detailExperimentation of Proactive Computing in Context Aware Systems: Case Study of Human-Computer Interactions in e-Learning Environment
Shirnin, Denis UL; Reis, Sandro UL; Zampunieris, Denis UL

in Cognitive Methods in Situation Awareness and Decision Support (CogSIMA), 2013 IEEE International Multi-Disciplinary Conference on (2013)

In this paper we show the implementation of the concept of Proactivity applied as the core mechanism in our Proactive Context Aware System (PCAS), which is capable to detect and extract the related events ... [more ▼]

In this paper we show the implementation of the concept of Proactivity applied as the core mechanism in our Proactive Context Aware System (PCAS), which is capable to detect and extract the related events of interest from the user's contextual situation and to provide the appropriate goal-oriented actions to this event with the objective to help or assist the user or the group of users. We have chosen the academic environment as the ongoing contextual setting for our system. From this perspective, we designed Proactive Scenarios for an automatic and enhanced management of the online learning and teaching activities on Moodle™ for both student and teacher users. Due to the diversity of the potential contexts and situations arising from the user's activity, we developed two kinds of Proactive Scenarios. The first type or Meta Scenarios are responsible for capturing the changes in the outward context. The second type or Target Scenarios are triggered off by Meta Scenarios and aim to undertake the appropriate actions in response to the conditions of the user's contextual situation. In order to test and validate the capability of our software as well as to analyse its context related outcomes we have performed empirical studies. The experiments consisted in creating two groups of students, on the one hand the study group, which used the Moodle™ platform enhanced by PCAS, and on the other hand the control group, which used the standard version of Moodle™. The subsequent data analysis showed significant differences in specific related results such as notable advantage of the study group outcomes in the category of passing the final exam, where the study group has performed by 11 percentage points better than the control group. [less ▲]

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See detailExperimente und Modellierung zur heterogenen und homogenen Verbrennung.
Peters, Bernhard UL; Krebs, L.

in FZKA-Bericht (1998), 6084

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See detailExperimente unerwünscht!?! Sonntagsfilme der Konsumgesellschaft im lokalen Wettbewerb mit ambitioniertem Autorenfilm 
Wack, Julia UL

Presentation (2019, May)

Aufgrund einer großen Anzahl unterschiedlicher Definitionen des Avantgarde-Begriffes in verschiedenen Feldern durch die Jahrzehnte ist es von Vorteil sich zunächst auf einige grundlegende Parameter zu ... [more ▼]

Aufgrund einer großen Anzahl unterschiedlicher Definitionen des Avantgarde-Begriffes in verschiedenen Feldern durch die Jahrzehnte ist es von Vorteil sich zunächst auf einige grundlegende Parameter zu einigen, die den Begriff ein- und abgrenzen, bevor er Eingang in die Debatte findet. Mit dem Mainstream verhält es sich etwas einfacher, denn obschon seine Begrifflichkeit sehr weitläufig ist, ist er in sich homogener und Teil des Alltagsdiskurses geworden. Sind eine Vorreiterrolle, oder auch ein Bestreben nach sozialer Neuerung und politischem Umschwung, Abkehr von Traditionen, Elemente die man in der Praxis der Amateurfilmclubs der Großregion in den 60er Jahren findet? Das Amateurfilmen erfreute sich in Folge neuester Entwicklungen in der Schmalfilmtechnologie in den langen 60er Jahren großer Beleibtheit, in- und außerhalb des Vereinskontexts Es war unter anderem dieser technische Fortschritt, der, neben neuerlich erschwinglichem Material, vereinfachter Handhabung und verbesserter Qualität, einlud, inhaltliche, technische und künstlerische Experimente zu unternehmen. Während der Großteil der Clubmitglieder sich auf ähnliche Motive wie seine Kollegen außerhalb der Vereine beschränkte, bspw. Familienfeiern, -ausflüge oder Reisen, fühlten sich einige Mitglieder zur Filmautorenschaft berufen und kreierten als Drehbuchautor, Regisseur und Kameramann in Personalunion anspruchsvollere Filmwerke; hauptsächlich zur Vorführung in vereinsinternen, regionalen, nationalen und internationalen Wettbewerben. Doch auch innerhalb dieses aufwendiger produzierten Werkkorpus’, der v.a. der Übersetzung der zeitgenössischen Alltagskultur auf Zelluloid Raum gab, wurde nur eine geringe Anzahl von Filmen, die avantgardistische Merkmale aufweist, produziert. Die wenigsten waren visuell, inhaltlich oder technisch radikal oder innovativ jenseits bekannter Lesweisen. Im Gegenteil gab es Ausnahmefälle kommerzieller Auftragsarbeiten, oder Amateurproduktionen, die im Nachhinein vom Fernsehen aufgekauft wurden. Die Filmarbeiten verschiedener Genres waren oft nur innerhalb der Vereinsarbeit möglich, da ambitionierte Produktionen nach Arbeitsteilung und Kooperation ähnlich dem professionellen Sektor verlangten. Zum einen tauschten die Amateure sich über Schnitt-, Licht- oder Montagetechniken aus, zum anderen wurden Aufgaben wie Beleuchtung und Ton oder Kulissenbau aufgeteilt, viele Filme so zu Gemeinschafts-produktionen. Neben dieser mehr industrialisierte, organisierte Form des Amateurfilms, die oft auf die Rezeption des Publikums und die Bewertung durch eine Jury Gleichgesinnter abzielte, und so die dem Amateur eigene Autonomie vom Filmbetrieb aufgab; gab es wenige Versuche, Filme, die nicht dem üblichen Narrativkonstrukt der ‘Standard-Version’ des kommerziellen Produktionswesens entsprachen, zu drehen. In Hochzentren kultureller Produktion wie New York, London, Paris oder Los Angeles kam es zu gelegentlichem Austausch zwischen Amateur- und kommerzieller sowie nicht-kommerzieller Filmproduktion, welche sich jeweils beeinflußten. Da die Großregion dieser Jahre bezüglich kultureller Produktion und Amateurpartizipation getrost als Peripherie bezeichnet werden kann, mag einer der Gründe für die geringe Repräsentation innovativer oder experimenteller Filmarbeiten die geringe Abdeckung durch Kunst-und Filmakademien sein, die einen Austausch, wie er der Avantgarde eigen ist, hätten anregen können. Doch auch international und in größeren Städten existierte kaum eine lebendige Avantgarde-Szene innerhalb von Amateurfilmklubnetzwerken. Weitere Gründe, die sich überregional anwenden lassen, könnten daher die Institutionalisierung (gegen die die Avantgarde generell anging) durch die Club- und Verbandsstruktur und das Wettbewerbsverhalten, das mit ‘Mainstreaming’ einher geht; sowie die Demografie der Clubs sein. Letztere war in der Großregion - wie international - stark homogen (was wiederum in Kontrast mit der Avantgarde steht) und von technisch interessierten, arbeitenden Männern mittleren und fortgeschrittenen Alters - d.h. kulturell während und kurz nach dem Zweiten Weltkrieg sozialisiert - bestimmt. Neben den eigentlichen Filmquellen ist auch das Vereinsleben Teil der Recherchen: Unterscheidet sich das Sozialleben der Mitglieder eines Filmclubs von dem eines Sportvereins und findet die populärkulturelle Sozialisation der Mitglieder und ihrer Angehörigen Eingang in Vereinsleben und Filmproduktionen? [less ▲]

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See detailExperimentelle Medienarchäologie: das Beispiel Kunstkopf-Stereophonie
Krebs, Stefan UL

Scientific Conference (2017)

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See detailExperimentelle Überprüfung eines antagonistisches Erklärungsmodells zum selbstgesteuerten Bewegungslernen
Bund, Andreas UL; Ferwagner, Dirk

Scientific Conference (2005, May)

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See detailExperimentelle Untersuchungen und analytischen Modellierung von adiabaten Siedevorgängen in Naturumlaufsystemen
Haag, Michel UL

Doctoral thesis (2020)

Modern nuclear reactors increasingly use passive safety systems to ensure the integrity of the containment in the event of an accident. Natural circulation systems allow passive heat removal from the ... [more ▼]

Modern nuclear reactors increasingly use passive safety systems to ensure the integrity of the containment in the event of an accident. Natural circulation systems allow passive heat removal from the containment to the environment. One of their disadvantages is that instabilities develop as soon as evaporation occurs in the system. This thesis investigates instabilities in two-phase natural circulation systems. After comprehensive literature review on existing test facilities, the first part of this work presents experimental investigations on the stability behaviour of natural circulation systems. To conduct these investigations, the INTRAVIT test facility was designed and constructed at the University of Luxembourg. INTRAVIT offers both a high degree of flexibility in the design of the pipelines and the advantage of a direct, electrically controllable heat supply. Two measurement campaigns were carried out. During the first campaign, the influence of the heating tube inclination angle on the instabilities was investigated at constant riser pipe length. During the second measurement campaign, the influence of the riser pipe length and the influence of the flow resistance in the downcomer pipe were investigated at a constant inclination angle of the heating tube. For these investigations, temperatures, mass flow and the distribution of void in the riser pipe were analysed. In addition, pressure response during the instabilities was measured to investigate the pressure shocks caused by water hammering. The second part of this work develops an analytical model to decribe evaporation processes in adiabatic pipes. The model consists of several sub models that calculate the interfacial surface density and the evaporation rate as a function of the flow pattern. An integrated nucleation model calculates the onset of the evaporation. The derived model was implemented in the system code ATHLET. Experiments from the INTRAVIT measurement campaigns were then modelled using the new evaporation model as well as the standard evaporation model. Both were compared with the measurement data. The design and construction of the INTRAVIT test facility is a foundation for future research on instabilities in natural circulation systems. Moreover, a new evaporation model is presented, which can easily be adapted and refined by modifying individual sub models. [less ▲]

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See detailExperimenter Effects in Children Using the Smileyometer Scale
Lehnert, Florence Kristin UL; Lallemand, Carine UL; Fischbach, Antoine UL et al

Scientific Conference (2020, November 19)

Researchers in the social sciences like human-computer interaction face novel challenges concerning the development of methods and tools for evaluating interactive technology with children. One of these ... [more ▼]

Researchers in the social sciences like human-computer interaction face novel challenges concerning the development of methods and tools for evaluating interactive technology with children. One of these challenges is related to the validity and reliability of user experience measurement tools. Scale designs, like the Smileyometer, have been proven to contain biases such as the tendency for children to rate almost every technology as great. This explorative paper discusses a possible effect of two experimenter styles on the distribution of 6-8 years old pupils' ratings (N= 73) to the Smileyometer. We administered the scale before and after a tablet-based assessment in two schools. Experimenter 1 employed a child-directed speech compared to a monotone speech of Experimenter 2. While brilliant (5 out of 5) was the most frequent answer option in all conditions, the mean scores were higher and associated with a lower variability across both conditions for Experimenter 2. We discuss a possible experimenter effect in the Smileyometer and implications for evaluating children’s user experiences. [less ▲]

Detailed reference viewed: 113 (5 UL)