Eric Gans

Reduction in required magnetic field to induce twin-boundary motion in ferromagnetic shape memory alloys

Tensile and compressive loading experiments were conducted at room temperature on a thin slab (1 mm) of Ni50Mn33Ga17 single crystal ferromagnetic shape memory alloy while subjected to cyclic magnetic field (up to 550 kA/m). Tensile loads ranged from 0.4 MPa to 0.8 MPa while compressive loads ranged from 0.4 MPa to 2.2 MPa, with increasing compressive loads resulting in a reduced overall strain. Results indicate that magnetic field produces significant strains (over 4%) within the material. Experimental data also show that a tensile load reduces the required magnetic field for actuation by almost 80%.

Cyclic actuation of Ni–Mn–Ga composites

Planar (2-2) and fibular (1-3) composites were fabricated by embedding single crystal Ni49.9Mn29.1Ga21.0 in a polyurethane resin. Magnetic and mechanical testing was performed on all samples. Mechanical testing showed the twin boundary yield stress to be 1.0 and 0.3MPa for the monolithic and composites, respectively. Magnetic testing was performed to determine the magnetic field induced strain as a function of increasing compressive preloads (from 0to2.0MPa). Actuation strains without an external preload are 4.9% for the monolithic and 1.0% for the composite samples. The composite samples show considerable cyclic strain without the application of a compressive loading, unlike the monolithic material. A rule of mixture model is presented to predict the strain output of the composite samples under a magnetic field and explain the reduced twin boundary yield stress.

Damping of Polycrystalline Ni-Mn-Ga, Bulk, PLD, and Sputtered Thin Film

Polycrystalline Ni-Mn-Ga in bulk, pulsed laser deposition (PLD) thin film, and radio frequency (RF) sputtered thin film are studied. A thin film of direct current (DC) magnetron sputter deposited NiTi was also used in the study. A polycrystalline Ni-Mn-Ga bulk sample was measured to have a tan δ = 0.4925 and a maximum elastic modulus E = 7.3 GPa. Material characterization studies were performed on polycrystalline Ni-Mn-Ga thin films deposited by PLD onto single crystal (100) Si and (100) MgO substrates at substrate temperatures ranging from 550°C to 650°C. Damping measurements on RF sputter deposition of 1 μm Ni-Mn-Ga and 10 μm of NiTi both on copper substrates were performed in cantilever beam ring down tests. Results show 1 μm RF sputter deposited Ni-Mn-Ga thin film on a 54 μm copper substrate improves damping properties.

High energy absorption in bulk ferromagnetic shape memory alloys (Ni50Mn29Ga21)

Mechanical testing of a bulk, single-crystal sample of Ni50Mn29Ga21 produced large hysteresis loops indicating the potential for the material to be used as a damper. Damping capacity was measured as a function of energy absorbed by the material relative to the mechanical energy input to the system. Tan delta, the tangent of the phase lag between stress and strain, was calculated and shown to increase as a function of maximum strain level. Five strain levels were evaluated (1%, 2%, 3%, 3.5%, and 3.7%) with tan delta values increasing from 0.6 at 1% strain level to 1.1 at 3.7% strain level. The secant modulus of these curves was also evaluated at each strain level to characterize the sample in terms of both damping and stiffness. The maximum secant modulus of 285 MPa occurred at the 1% strain level and decreased to 56 MPa at 3.7% strain. Examining the stress and strain values in the time domain reveals a varying time lag and thus the reported values for tan d are considered an average measure of the materials damping capacity.

STRESS INDUCED PHASE CHANGING MATERIAL FOR THERMOACOUSTIC REFRIGERATION

ABSTRACT A novel concept to use a stress induced phase transformation in NiMnGa for solid state refrigeration is investigated. The stress needed to induce a phase transformation was measured at temperatures from 24 to 60°C. The stresses were sufficiently low enough such that an acoustic wave can in theory induce the phase transformation. DSC measurements were done on the NiMnGa material to measure the latent heat that can be absorbed and release. Theoretical calculations of the coefficient of performance for a heat pump using this stress induced thermal phenomena showed a possible efficiency of 67%. A solid state heat pump using a piezoelectric or magnetostrictive transducer to generate the acoustic pressure wave and a fluid medium suspended with NiMnGa nanoparticles is suggested as a possible implementation of the concept.

The Name of God

Uppsatsen handlar om hur religion kan användas samt komma till uttryck i hårdrockstexter. Undersökningen har skett genom analys av åtta olika låttexter, som belyser olika aspekter av religionen. Analysen tog fasta på texternas religiösa budskap, användandet av eventuella religiösa metaforer samt hur texterna kan ses som en del av en religiös mångfald. Metoden som har använts är en kvalitativ textanalys med en hermeneutisk utgångspunkt. Som teori valdes Rodney Starks ”fortlevnadsteori” som utgår från den ”rational choice”-teoretiska modellen. Resultatet av undersökningen visade på en stor bredd av budskap. I ett av fallen kunde en vädjan om att börja tro på Gud uttydas, i två andra fanns en underton av varning för destruktiva sekter, två av texterna kritiserade kristendomen utifrån två olika aspekter och slutligen fanns två texter med ett direkt sataniskt och individualistiskt budskap. Direkta religiösa metaforer förekom endast i två texter. Vad gäller den religiösa mångfalden kunde man konstatera att texterna i flera fall kan vara ett uttryck för detta. Detta gäller inte minst i en tid då privatreligiositet sakta utkonkurrerar den organiserade, traditionella religionen och med tanke på de närmast religiösa känslor som musiken kan väcka hos lyssnaren. Detta förklaras genom att tron finner nya sätt att nå ut till människor, vilket även är relaterat till hur samhällsmönstret förändras. Nyckelord: Hårdrock, musik, textanalys, kristendomen, satanism, religionskritik, fundamentalism

Originary democracy and the critique of pure fairness

Thucydides’ account of Pericles’ funeral oration demonstrates that the first democracy was sensitive to what generative anthropology considers the central function of political systems: holding in check the resentment inevitably generated by inequality among beings whose possession of language instills in them a ‘moral model’ of ‘symmetrical reciprocity’. Pericles’ words demonstrate an awareness that the increased fairness of democratic choice only exacerbates the resentment of those not chosen. Democracy emerged in Athens as a liberation from the traditional system of sacrificial tribute. It could not survive in antiquity because the liberation from the economic activity associated with payment of tribute depended, in Rome as in Athens, on slave labour. Modern democracy emerged in tandem with the modern market, and, in contrast to the politics‐centred world of the polis, is auxiliary to civil society. In liberal democracy the political sphere functions to provide a secure basis for economic life and to permit the negotiation of the resentments that emerge within it. This system is maximally stable and fair, but its stability cannot become absolute because its fairness can never eliminate resentment. Whereas the opposition of ethnic and other ascriptive minorities can in principle be reduced by an increase in fairness, this is not true of the opposition of ‘losers’ who blame their failure on betrayal by the system. Such persons are tempted by the self‐justifying extremist refusal to negotiate their resentments within the political system; they consequently represent a permanent danger to liberal democracy.