Effect of electric and magnetic stresses on ferroelectric single crystals and ceramics

La présence de charges libres a des conséquences considérables sur les propriétés diélectriques des matériaux. Pour mettre en évidence ces contributions, nous avons étudié l influence de contraintes électriques et magnétiques sur des monocristaux de BaTiO3 dopé Fer et de KTiOPO4 (KTP). Dans BaTiO3, l application d un champ magnétique perturbe le mécanisme de pertes diélectriques résultant de mécanismes polaroniques. Dans le KTP c est la localisation des ions K+ qui est perturbée par un champ électrique comme nous l avons démontré en étudiant la séparation des raies de résonances piézoélectriques. Dans une deuxième partie, nous avons synthétisé et étudié la polarisation de phosphates de composition BaFeTi(PO4)3 and BiFe2(PO4)3. Cependant, l ion Bi3+ n est jamais positionné sur son site d inversion, ce qui est prometteur. Enfin, nous avons étudié la spinelle Co3O4 par spectroscopie diélectrique et RPE et nous avons montré l induction d un état polaire sous l effet d un champ magnétique.The mobility of free charges and its localization mechanism has considerable effect on the dielectric properties of the materials. Therefore single crystal of Fe doped BaTiO3 and KTiOPO4 (KTP) which have predominantly electronic and ionic conductivity respectively were studied under external stresses like electric and magnetic field. The application of external magnetic field affects the hopping of electrons which lead to tuning of polaron losses in BaTiO3 whereas in case of KTP localization of K+ ions give rise to splitting of piezoelectric resonance and it can be tuned by external electric field. In the second part new phosphates of formula BaFeTi(PO4)3 and BiFe2(PO4)3 were synthesized to look for polarization property. However Bi3+ ions are not localized on their inversion symmetry site which is promising. Finally spinel Co3O4 was investigated under dielectric and Electron Paramagnetic Resonance spectroscopy which reveal an induction of polar state under external magnetic field.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

The benefits of an additional practice in descriptive geomerty course: non obligatory workshop at the Faculty of Civil Engineering in Belgrade

At the Faculty of Civil Engineering in Belgrade, in the Descriptive geometry (DG) course, non-obligatory workshops named “facultative task” are held for the three generations of freshman students with the aim to give students the opportunity to get higher final grade on the exam. The content of this workshop was a creative task, performed by a group of three students, offering free choice of a topic, i.e. the geometric structure associated with some real or imagery architectural/art-work object. After the workshops a questionnaire (composed by the professors at the course) is given to the students, in order to get their response on teaching/learning materials for the DG course and the workshop. During the workshop students performed one of the common tests for testing spatial abilities, named “paper folding". Based on the results of the questionnairethe investigation of the linkages between:students’ final achievements and spatial abilities, as well as students’ expectations of their performance on the exam, and how the students’ capacity to correctly estimate their grades were associated with expected and final grades, is provided. The goal was to give an evidence that a creative work, performed by a small group of students and self-assessment of their performances are a good way of helping students to maintain motivation and to accomplish their achievement. The final conclusion is addressed to the benefits of additional workshops employment in the course, which confirmhigherfinal scores-grades, achievement of creative results (facultative tasks) and confirmation of DG knowledge adaption

The contemporary visualization and modelling technologies and the techniques for the design of the green roofs

The contemporary design solutions are merging the boundaries between real and virtual world. The Landscape architecture like the other interdisciplinary field stepped in a contemporary technologies area focused on that, beside the good execution of works, designer solutions has to be more realistic and “touchable”. The opportunities provided by Virtual Reality are certainly not negligible, it is common knowledge that the designs in the world are already presented in this way so the Virtual Reality increasingly used. Following the example of the application of virtual reality in landscape architecture, this paper deals with proposals for the use of virtual reality in landscape architecture so that designers, clients and users would have a virtual sense of scope e.g. rooftop garden, urban areas, parks, roads, etc. It is a programming language that creates a series of images creating a whole, so certain parts can be controlled or even modified in VR. Virtual reality today requires a specific gadget, such as Occulus, HTC Vive, Samsung Gear VR and similar. The aim of this paper is to acquire new theoretical and practical knowledge in the interdisciplinary field of virtual reality, the ability to display using virtual reality methods, and to present through a brief overview the plant species used in the design and construction of an intensive roof garden in a Mediterranean climate, the basic characteristics of roofing gardens as well as the benefits they carry. Virtual and augmented reality as technology is a very powerful tool for landscape architects, when modeling roof gardens, parks, and urban areas. One of the most popular technologies used by landscape architects is Google Tilt Brush, which enables fast modeling. The Google Tilt Brush VR app allows modeling in three-dimensional virtual space using a palette to work with the use of a three dimensional brush. The terms of two "programmed" realities - virtual reality and augmented reality - are often confused. One thing they have in common, though, is VRML - Virtual Reality Modeling Language. In this paper are shown the ways on which this issue can be solved and by the way, get closer the term of Virtual Reality (VR), also all the opportunities which the Virtual reality offered us. As well, in this paper are shown the conditions of Mediterranean climate, the conceptual solution and the plant species which will be used by execution of intensive green roof on the motel “Marković”

Large bichromatic point sets admit empty monochromatic 4-gons

We consider a variation of a problem stated by Erd˝os and Szekeres in 1935 about the existence of a number fES(k) such that any set S of at least fES(k) points in general position in the plane has a subset of k points that are the vertices of a convex k-gon. In our setting the points of S are colored, and we say that a (not necessarily convex) spanned polygon is monochromatic if all its vertices have the same color. Moreover, a polygon is called empty if it does not contain any points of S in its interior. We show that any bichromatic set of n ≥ 5044 points in R2 in general position determines at least one empty, monochromatic quadrilateral (and thus linearly many).Postprint (published version

Distance based heterogeneous volume modelling.

Natural objects, such as bones and watermelons, often have a heterogeneous composition and complex internal structures. Material properties inside the object can change abruptly or gradually, and representing such changes digitally can be problematic. Attribute functions represent physical properties distribution in the volumetric object. Modelling complex attributes within a volume is a complex task. There are several approaches to modelling attributes, but distance functions have gained popularity for heterogeneous object modelling because, in addition to their usefulness, they lead to predictability and intuitiveness. In this thesis, we consider a unified framework for heterogeneous volume modelling, specifically using distance fields. In particular, we tackle various issues associated with them such as the interpolation of volumetric attributes through time for shape transformation and intuitive and predictable interpolation of attributes inside a shape. To achieve these results, we rely on smooth approximate distance fields and interior distances. This thesis deals with outstanding issues in heterogeneous object modelling, and more specifically in modelling functionally graded materials and structures using different types of distances and approximation thereof. We demonstrate the benefits of heterogeneous volume modelling using smooth approximate distance fields with various applications, such as adaptive microstructures, morphological shape generation, shape driven interpolation of material properties through time and shape conforming interpolation of properties. Distance based modelling of attributes allows us to have a better parametrization of the object volume and design gradient properties across an object. This becomes more important nowadays with the growing interest in rapid prototyping and digital fabrication of heterogeneous objects and can find practical applications in different industries

Interpreting parametric-biomimicry design from cad тo bim software: digital modelling based on a sketch of nandi flame

This research represents an application of two digital modelling softwares, first digital modelling software, chosen as representative of Computer-Aided Design – CAD modelling tool was Fusion 360. The representative of Building Information Modelling (BIM) as second digital modelling software was ArchiCAD. The aim of the research was to translate the same parametric-biomimicry design methodology used in CAD process modelling into BIM environment. African species Spathodea campanulata P. Beauv, whose common name in Kenya is Nandi flame, has been selected for the purpose of this digital modelling processes. As one of the most spectacular flowering plants, Nandi flame is indigenous to the tropical dry forests in Kenya. The decorative flower of this species was the basic model, more precisely the botanical sketches of the flower. This sketches were implemented into digital modelling softwares and used for parametric modelling. The results of this processes were represented as urban models or installations (landscape-architectural elements) in open space. This approach of digitally generating conceptual solutions from nature elements has capability to boost the formulation of new creative inventions in the different fields. The unique geometric patterns found in the flower of Spathodea campanulata P. Beauv served as a good example of how we may transform these ideas into actual design installations– using CAD or BIM software tools. This research has been carried out with the aim to find the position of BIM tools in parametric biomimicry design

Active Materials

What is an active material? This book aims to redefine perceptions of the materials that respond to their environment. Through the theory of the structure and functionality of materials found in nature a scientific approach to active materials is first identified. Further interviews with experts from the natural sciences and humanities then seeks to question and redefine this view of materials to create a new definition of active materials

Redistribution dynamics of ultrathin vanadium oxide layers under catalytic conditions and activation of diffusion by surface acoustic waves

The reaction-induced redistribution of vanadium oxide supported on noble metal single crystal surfaces (inverse model catalysts), and the influence of surface acoustic waves (SAW) on the composition of a bimetallic Rh/Pt surface are studied. Previously, the movement and coalescence of macroscopic, two-dimensional vanadium oxide islands on Rh(111) during catalytic methanol oxidation was explained with a polymerization / depolymerization mechanism. To investigate how general this mechanism is, the reaction dynamics of vanadium oxide on Rh(111), Rh(110) and Pt(111) are investigated in a number of catalytic reactions. Island formation and coalescence are observed in ammonia, CO, and methanol oxidation on VOx/Rh(111) in the 0.0001 mbar range. Exchanging oxygen by NO as oxidizing agent results in an inverse pattern, i. e. holes in a dense vanadium oxide film instead of vanadium oxide islands surrounded by bare Rh surface. Spectroscopic LEEM reveals, that NO influences the width of the interface vanadium oxide island / bare Rh(111), thus indicating a change in the line tension. The line tension possibly explains the complementary types of pattern formation. Indications for a Rh surface oxide under reaction conditions are found. In the 0.0001 mbar range on Rh(111), oscillating vanadium oxide islands occur. A tentative mechanism is proposed, based on phase transitions inside the vanadium oxide islands, which result from gradients in the oxygen coverage. With near ambient pressure LEEM, turbulent redistribution dynamics are observed during methanol oxidation at 0.02mbar. On VOx/Rh(110) island formation occurs, but no island coalescence is seen. Instead, a wealth of chemical wave pattern is found: traveling interface modulations (TIMs), traveling wave fragments and target pattern, as well as chemical waves propagating over both, the bare Rh(110) substrate and macroscopic vanadium oxide islands. TIMs are explained by a mechanism based on the reversible creation of surface defects at the interface. The system VOx/Pt(111) is characterized by the reversible diffusion of V into the Pt bulk under reaction conditions. As a consequence, no pattern formation occurs. A strong effect of the metallic support on the behavior of VOx catalysts is demonstrated by the different types of pattern formation in VOx/Rh(111), VOx/Rh(110), and VOx/Pt(111). In addition to different types of pattern formation, also the selectivity and catalytic activity is strongly influenced by the support. Whereas formaldehyde is the main product in catalytic methanol oxidation on VOx/Rh(111), no formaldehyde production is detected on VOx/Rh(110) and VOx/Pt(111). The influence of SAWs on the diffusive intermixing of a Rh/Pt surface is investigated by laterally resolved X-ray spectroscopy. The results are compared to Auger spectroscopy measurements on the thermal diffusion of Rh into the Pt bulk on a Pt(100) single crystal and on polycrystalline Pt. At 445 K, a SAW-induced intermixing of Pt and Rh is detected. In thermal diffusion experiments, the onset of Rh diffusion into the Pt bulk is found to occur around 500 to 550 K. The experiments are a first step towards verifying the working hypothesis, that structural defects caused by SAWs are the main reason for a SAW-induced increase in catalytic activity reported in literature

Active Materials

What is an active material? This book aims to redefine perceptions of the materials that respond to their environment. Through the theory of the structure and functionality of materials found in nature a scientific approach to active materials is first identified. Further interviews with experts from the natural sciences and humanities then seeks to question and redefine this view of materials to create a new definition of active materials