The ferromagnetic shape memory alloy, Fe7Pd3, not only offers promising applications, but also reveals a number of unresolved scientific questions, including coupling between a series of martensite and order–disorder transitions, which are in the focus of the present study. To address and understand these aspects, which are of particular importance for controlling phase stability in Fe7Pd3, an ab initio based Monte Carlo simulation code is developed, whose results demonstrate that equilibrated ordered or disordered phases show distinct dependencies coupled to temperature and lattice structure. Moreover, in equiatomic domains emerging from initially randomized disorder, an intermediate, entropy stabilized phase is identified with significantly higher magnetic anisotropy energy, being advantageous for miniaturized applications. This phase, among other observed configurations, is comprehensively characterized by free energy landscapes and magneto-structural coupling derived from vibrational analysis of molecular dynamics trajectories and full relativistic spin polarized density functional theory ground state calculations, respectively.

Nowadays vehicle design paradigm influences not only the effectiveness of the different means of transport, but also the environment and economy in a critical way. The assessment of the consequences that design choices have on society at large are necessary to understand the limits of the methods and techniques currently employed. One of the mechanisms set in motion is the planned obsolescence of products and services. This has affected vehicle design paradigm in such a way that the variety in the market has shadowed the primary function of vehicle systems: the transport of persons and goods. Amongst the consequences of the expansion of such market is the exponential rise on combustion emissions to the atmosphere, which has become a great hindrance for humans health and survival of ecosystems. The development of evaluation tools for such consequences and their piloting mechanisms is needed so as to implement an ECO2  (Ecological and Economical) vehicle design paradigm. Moreover, the multifunctional design paradigm that drives aeronautical and vehicle engineering is an ever-growing demand of smart materials and structures, able to fulfil multiple requirements in an effective way. The understanding of certain phenomena intrinsic to the introduction of novel materials has found certain limits due to the complexity of the models needed. This work presents as a first step an assessment of the causes and consequences of the vehicle exponential market growth based on the analysis of the planned obsolescence within. Furthermore, a method for the acoustic response analysis of multilayered structures including anisotropic poroelastic materials is introduced. The methodology consists in a plane wave approach as a base for introducing the complex mechanic and acoustic equations governing anisotropic homogeneous media, e.g. open-celled foams, into an alternative mathematical tool manipulating physical wave amplitudes propagation within the studied media. In addition, this method is coupled to a power partitioning and energetic assessment tool so as to understand the phenomena present in complex multilayered designs. / <p>QC 20150323</p>

<p>Similar to thermodynamic phase transitions in matter, readily apparent changes in optical response arise in the transition from isotropic to anisotropic optical phases. Treating the anisotropy of the dielectric permittivity as a control parameter, which changes continuously from zero to a nonzero finite value at the transition, in this work we describe the resulting effect on light propagation. </p> <p><br></p> <p>We begin by investigating a simple case of the manifestations of such optical transition in lossy media. In the presence of loss, isotropic materials do not support Brewster phenomenon, however, if one changes the anisotropy continuously, the exact zero in the reflection at the Brewster incidence angle is recovered. Next, in the case of uniaxial anisotropy, we uncover dramatic changes in far-field thermal radiation induced by the transitions between metal, dielectric, and hyperbolic optical regimes that can be observed in the same material. We demonstrate that continuous evolution between different ''phases'' in the electromagnetic response imprints a characteristic signature in the far-field thermal emission. Finally, we show that the evolution of the optical anisotropy from uniaxial to biaxial symmetry brings qualitatively new optical modes which are different from the conventional propagating and evanescent fields. These emergent ''ghost'' waves offer a unique way to control mode interactions in optical systems. Our work uncovers the connection between the macroscopic properties of the optical materials and the transitions between different regimes of the electromagnetic response in these media. At last, we propose a range of potential applications of the resulting phenomena, from perfect absorption in lossy media to thermal radiation and optical sensing.</p>

Выполнено систематическое исследование магнитных свойств аморфных плёнок (РЗМ)xCo100-x, содержащих редкоземельные металлы РЗМ различного типа: La не имеет магнитного момента; Gd обладает сферической электронной оболочкой; Tb характеризуется анизотропией электронной структуры. На основе анализа спонтанной намагниченности плёнок определены концентрационные зависимости средних атомных магнитных моментов кобальта (mCo), гадолиния (mGd) и тербия (mTb). Показано, что в интервале 0 < x < 50 % mCo уменьшается от 1,7 µB до нуля, mGd не меняется и практически совпадает с магнитным моментом свободного атома (7 µB), а mTb монотонно снижается, причем скорость уменьшения зависит от способа получения образцов. Найденные закономерности связываются с концентрационным изменением электронной структуры Со и спецификой магнитной структуры плёнок, которая имеет ферромагнитный, ферримагнитный или сперимагнитный характер для образцов, содержащих La, Gd или Tb соответственно. Установлено, что в пленках систем Gd-Co и Tb-Co может присутствовать одноосная магнитная анизотропия, сильно различающаяся по своей величине. Механизм её формирования может быть связан с упорядочением пар атомов в GdxCo100-x и магнитострикционной деформацией или проявлением локальной анизотропии атомами тербия в TbxCo100-x. / A systematic study of magnetic properties of (RE)xCo100-x amorphous films, containing rare earth metals of various types, was conducted: La has no magnetic moment; Gd has a spherical electron shell; Tb is characterized by anisotropy of the electron structure. Concentration dependences of average atomic magnetic moments of cobalt (mCo), gadolinium (mGd), and terbium (mTb) were determined based on the films spontaneous magnetization analysis. It was shown that mCo decreases in the range of 0 < x < 50 % from 1.7 μB to zero, mGd does not change and it is almost identical to the magnetic moment of a free atom (7 μB), and mTb decreases monotonically, and the reduction rate depends on the method of samples preparation. The observed behavior is associated with the change in the electron shell of Co and specificity of the films magnetic structure, which is ferromagnetic, ferrimagnetic or sperimagnetic for the samples, containing La, Gd, and Tb, respectively. It was found that Gd-Co and Tb-Co systems films can demonstrate uniaxial anisotropy of considerably different magnitude. The mechanism of its formation may be associated with the atoms pairs ordering in GdxCo100-x and magnetostrictive deformation or manifestation of the local anisotropy of terbium atoms in TbxCo100-x.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24926号 / エネ博第468号 / 新制||エネ||88(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)准教授 南 貴司, 教授 稲垣 滋, 教授 田中 仁 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Cold spray has seen rapid advancement since its inception and has shown significant potential as a method of additive manufacturing. However, the large plastic deformation and repeated heating/cooling cycles that the material undergoes during the cold spray process can result in gradients in material structure and large residual stresses. The purpose of this study is to extend the existing EMMI material model to include anisotropic material response through the use of orientation distribution functions to predict residual stresses and anisotropy resulting from cold spray and similar additive manufacturing processes. Through the use of a finite element simulation, yield surfaces for a two-step tension problem were generated and analyzed to capture the effects of the four coaxiality parameters that govern the model.

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Coordinated electrical activation of the heart is essential for the maintenance of a regular cardiac rhythm and effective contractions. Action potentials spread from one cell to the next via gap junction channels. Because of the elongated shape of cardiomyocytes, longitudinal resistivity is lower than transverse resistivity causing electrical anisotropy. Moreover, non-uniformity is created by clustering of gap junction channels at cell poles and by non-excitable structures such as collagenous strands, vessels or fibroblasts. Structural changes in cardiac disease often affect passive electrical properties by increasing non-uniformity and altering anisotropy. This disturbs normal electrical impulse propagation and is, consequently, a substrate for arrhythmia. However, to investigate how these structural changes lead to arrhythmias remains a challenge. One important mechanism, which may both cause and prevent arrhythmia, is the mismatch between current sources and sinks. Propagation of the electrical impulse requires a sufficient source of depolarizing current. In the case of a mismatch, the activated tissue (source) is not able to deliver enough depolarizing current to trigger an action potential in the non-activated tissue (sink). This eventually leads to conduction block. It has been suggested that in this situation a balanced geometrical distribution of gap junctions and reduced gap junction conductance may allow successful propagation. In contrast, source-sink mismatch can prevent spontaneous arrhythmogenic activity in a small number of cells from spreading over the ventricle, especially if gap junction conductance is enhanced. Beside gap junctions, cell geometry and non-cellular structures strongly modulate arrhythmogenic mechanisms. The present review elucidates these and other implications of passive electrical properties for cardiac rhythm and arrhythmogenesis.