Loss of strength in Ni3Al at elevated temperatures

Stress decrease above the stress peak temperature (750 K) is studied in h123i single crystals of Ni3(Al, 3 at.% Hf ). Two thermally activated deformation mechanisms are evidenced on the basis of stress relaxation and strain rate change experiments. From 500 to 1070 K, the continuity of the activation volume/temperature curves reveals a single mechanism of activation enthalpy 3.8 eV/atom and volume 90 b3 at 810K with an athermal stress of 330 MPa. Over the very same temperature interval, impurity or solute diffusion towards dislocation cores is evidenced through serrated yielding, peculiar shapes of stress–strain curves while changing the rate of straining and stress relaxation experiments. This complicates the identification of the deformation mechanism, which is likely connected with cube glide. From 1070 to 1270 K, the high-temperature mechanism has an activation enthalpy and volume of 4.8 eV/atom and 20 b3, respectively, at 1250 K

Non-contrast MRI perfusion imaging

Tato bakalářská práce je zaměřena na bezkontrastní techniky magnetické rezonance pro kvantitativní hodnocení prokrvení tkáně. Práce obsahuje popis základních funkčních principů magnetické rezonance a je zaměřena především na techniky Arterial Spin Labeling (ASL). Princip této metody spočívá ve využití protonů molekul vody v tepenné krvi jako nitrotělní kontrastní látky. Pomocí této metody je možné vytvořit mapu prokrvení libovolného orgánu bez použití invazivních technik a kontrastních látek. V této práci byla ke kvantifikaci prokrvení zvolena technika FAIR-RARE, jedna z technik z široké skupiny pulsního ASL.This bachelor paper is focused on the magnetic resonance perfusion imaging technic without the usage of an external contrast media. This paper contains a look at the basic functional principle of the magnetic resonance. The focus is then set set on the Arterial Spin Labeling (ASL) technic. The basic principle of ASL uses protons from the water mocelules in arterial blood as an endogenous contrast agent. This technic can be used for obtaining a perfusion map of any tissue without the usage of invasiont echnics or contrast agents. The quantification of perusion was done applying the FAIR-RARE scheme, which belongs to the large family pulsed ASL.

A comparison of different measurement methods of mechanical properties of Al thin films

The paper compares two different methods for testing of metallic thin films: microcompression test and nanoindentation. Microcompression test is one possibility how to perform mechanical tests on a very small scale. This method requires preparation of a small cylindrical specimen (micropillar) of micrometric size by FIB and execution of a compression test using nanoindenter device equipped with a flat diamond punch. Stressstrain curves of the thin films were obtained from such tests. Nanoindentation tests were then conducted to compare the results on the same films. Two different metal thin films - AlCuW, AlCuSi with thickness 2 mu m and grain size 3.8 mu m in average were prepared by PVD method. In this paper, we announce the results of measurements, a comparison of the results obtained by each method and identify advantages and limitations of the methods

Groupoid sheaves as quantale sheaves

Several notions of sheaf on various types of quantale have been proposed and studied in the last twenty five years. It is fairly standard that for an involutive quantale Q satisfying mild algebraic properties the sheaves on Q can be defined to be the idempotent self-adjoint Q-valued matrices. These can be thought of as Q-valued equivalence relations, and, accordingly, the morphisms of sheaves are the Q-valued functional relations. Few concrete examples of such sheaves are known, however, and in this paper we provide a new one by showing that the category of equivariant sheaves on a localic etale groupoid G (the classifying topos of G) is equivalent to the category of sheaves on its involutive quantale O(G). As a means towards this end we begin by replacing the category of matrix sheaves on Q by an equivalent category of complete Hilbert Q-modules, and we approach the envisaged example where Q is an inverse quantal frame O(G) by placing it in the wider context of stably supported quantales, on one hand, and in the wider context of a module theoretic description of arbitrary actions of \'etale groupoids, both of which may be interesting in their own right.Comment: 62 pages. Structure of preprint has changed. It now contains the contents of former arXiv:0807.3859 (withdrawn), and the definition of Q-sheaf applies only to inverse quantal frames (Hilbert Q-modules with enough sections are given no special name for more general quantales

Biological sequence classification utilizing lossless data compression algorithms

Tato diplomová práce se zabývá možností využití bezeztrátových kompresních algoritmů ke klasifikaci biologických sekvencí. Nejdříve je představena literární rešerše o bezeztrátových kompresních algoritmech, která byla využita k výběru slovníkového algoritmu vytvořeného A. Lempelem a J. Zivem v roce 1976 (LZ77). Tento algoritmus je běžně používán k datové kompresi a v předkládané práci byl modifikován tak, aby umožnil klasifikaci biologických sekvencí. K algoritmu byly navrženy další modifikace, které rozvíjí jeho klasifikační možnosti. V průběhu práce byla sestavena sada datasetů biologických sekvencí, která umožnila podrobné testování algoritmu. Algoritmus byl porovnán s klasickými zarovnávacími metodami: Jukes-Cantor, Tamura a Kimura. Bylo ukázáno, že algoritmus dosahuje srovnatelných výsledků v oblasti klasifikace biologických sekvencí a dokonce je u 20% datasetů překonává. Lepší výsledky dosahuje zejména u sekvencí, jež jsou si vzájemně vzdálené.This master thesis is developing the idea of using lossless compression algorithms as a mean of classification of biological sequences. At first an overview of lossless data compression algorithms is presented, based on which the dictionary algorithm created by A. Lempel and J. Ziv in 1976 (LZ77) has been selected. This algorithm, that commonly serves for data compression, has been modified in order to enable the classification of biological sequences. Further modifications have been introduced to enhance the classification capabilities of the algorithm. Several datasets of biological sequences have been collected enabling a correct assessment of the LZ algorithm capability. The algorithm was compared to the classical alignment based methods: Jukes-Cantor, Tamura and Kimura. It has been proven that the algorithm has comparable results in the field of classification of biological sequences and even surpasses the alignment methods in 20% of the datasets. Best results are especially achieved with distant sequences.

Determination of mechanical properties from microcompression test

This paper describes a microcompression test of thin Al - 1.5 wt. % Cu thin film deposited on Si substrate. Microcompression combines the sample preparation with the use of ion focused beam (FIB) with a compression test carried out using nanoindenter. Cylindrical specimens (pillars) were prepared using FIB. The diameter of pillars was about 1.3 um and their height was about 2 um (equal to the film thickness). Stress-strain curves of the thin film were obtained. The results depend on crystallographic orientation of pillar. The paper is focused to an attempt to determine as precisely as possible Young modulus of the film using experimental data and finite element modelling

MECHANICAL PROPERTIES OF AL THIN FILM MEASURED BY TWO DIFFERENT METHODS

Abstract Mechanical properties of an aluminium thin film were measured by microcompression and indentation tests. The microcompression technique combines preparation of specimens using focused ion beam (FIB) and compression test by a nanoindeter device. Cylindrical specimens were prepared by focused ion beam milling. The height of cylindrical specimens was about 2 µm and their diameter about 1,3 µm. The load and displacement were continuously measured during tests. The stress-strain curves were obtained in two representations. Stresses of the first plastic bursts were determined in both representations. Hardness and Young modulus were measured by indentation test using continuous stiffness method. Representative values of thin film were calculated