In-situ studies of bulk deformation structures: Static properties under load and Dynamics during deformation

(Abridged, full abstract available in the text) The main goal of the study presented in this thesis was to perform in-situ investigations on deformation structures in plastically deformed polycrystalline copper at low degrees (<5%) of tensile deformation. Copper is taken as a model system for pure fcc metals. A novel synchrotron-radiation based technique has been developed. The technique allows for in-situ 3D reciprocal space mapping of reflections from deeply-embedded individual grains in polycrystalline samples during tensile deformation. We have shown that the resulting 3D maps from copper, consists of bright sharp peaks superimposed on a cloud of enhanced intensity. It is concluded that the individual peaks arise from the individual dislocation-free regions (the subgrains) in the dislocation structure. Based on data taken under static load, the strain distribution in and between the individual subgrains is analyzed and compared to composite type models. The consequences of stress relaxation and unloading is moreover discussed. The dynamics of the dislocation structure are investigated by continuous and stepwise deformation experiments. On the basis of such data the unset of subgrain formation and the subgrain refinement process is analyzed.Comment: Ph.D. thesis, 120 pages, 45 figure

KÆRLIGHEDSLIVETS PSYKOLOGI I EKSISTENTIEL BELYSNING

I artiklen beskrives fænomenet kærlighed med særligt henblik på dets rolle i den voksnes liv og udvikling. Med udgangspunkt i den eksistentielle og humanistiske psykologi beskrives kærligheden som en afgørende form for menneskelig livsudfoldelse. Kærlighedens centrale kerne indkredses og dens mere perifere repræsentationer omtales ligesom dens opblanding med andre livsudtryk. Også kærligheden som kulturfænomen beskrives, og spørgsmålet om, hvorvidt vort nuværende samfund er tilstrækkeligt kærlighedsrigt, rejses. Til sidst føres artiklens analyse over i en udpegning af, hvilke muligheder det voksne individ har for at fremme sin egen kærlighed gennem sin voksenudvikling, og hvilke muligheder vi som psykologer har for at hjælpe i denne proces

Communication: High pressure specific heat spectroscopy reveals simple relaxation behavior of glass forming molecular liquid

The frequency dependent specific heat has been measured under pressure for the molecular glass forming liquid 5-polyphenyl-4-ether in the viscous regime close to the glass transition. The temperature and pressure dependence of the characteristic timescale associated with the specific heat is compared to the equivalent timescale from dielectric spectroscopy performed under identical conditions. It is shown that the ratio between the two timescales is independent of both temperature and pressure. This observation is non-trivial and demonstrates the existence of specially simple molecular liquids in which different physical relaxation processes are both as function of temperature and pressure/density governed by the same underlying "inner clock". Furthermore, the results are discussed in terms of the recent conjecture that van der Waals liquids, like the measured liquid, comply to the isomorph theory.Comment: 6 pages, 3 figure

Investigation of the shear-mechanical and dielectric relaxation processes in two mono-alcohols close to the glass transition

Shear-mechanical and dielectric measurements on the two monohydroxy (mono-alcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to the glass transition temperature are presented. The shear-mechanical data are obtained using the piezoelectric shear-modulus gauge method covering frequencies from 1mHz to 10kHz. The shear-mechanical relaxation spectra show two processes, which follow the typical scenario of a structural (alpha) relaxation and an additional (Johari-Goldstein) beta relaxation. The dielectric relaxation spectra are dominated by a Debye-type peak with an additional non-Debye peak visible. This Debye-type relaxation is a common feature peculiar to mono-alcohols. The time scale of the non-Debye dielectric relaxation process is shown to correspond to the mechanical structural (alpha) relaxation. Glass-transition temperatures and fragilities are reported based on the mechanical alpha relaxation and the dielectric Debye-type process, showing that the two glass-transition temperatures differ by approximately 10K and that the fragility based on the Debye-type process is a factor of two smaller than the structural fragility. If a mechanical signature of the Debye-type relaxation exists in these liquids, its relaxation strength is at most 1% and 3% of the full relaxation strength of 2-butanol and 2-ethyl-1-hexanol respectively. These findings support the notion that it is the non-Debye dielectric relaxation process that corresponds to the structural alpha relaxation in the liquid.Comment: 8 pages, 6 figures. Minor corrections, updated figures, more dielectric data show

Frequency Dependent Specific Heat from Thermal Effusion in Spherical Geometry

We present a novel method of measuring the frequency dependent specific heat at the glass transition applied to 5-polyphenyl-4-ether. The method employs thermal waves effusing radially out from the surface of a spherical thermistor that acts as both a heat generator and thermometer. It is a merit of the method compared to planar effusion methods that the influence of the mechanical boundary conditions are analytically known. This implies that it is the longitudinal rather than the isobaric specific heat that is measured. As another merit the thermal conductivity and specific heat can be found independently. The method has highest sensitivity at a frequency where the thermal diffusion length is comparable to the radius of the heat generator. This limits in practise the frequency range to 2-3 decades. An account of the 3omega-technique used including higher order terms in the temperature dependency of the thermistor and in the power generated is furthermore given.Comment: 17 pages, 15 figures, Substantially revised versio