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  • 1
    Electronic Resource
    Electronic Resource
    Computerized analysis of thermal correlations using Peltier ac heating (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 2754-2761 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Estimating uncontrolled thermal gradients between a system thermometer and a sample mounted in some measurement cell is a problem recognized in many experimental situations. To demonstrate a solution we describe a computer based low-frequency ac method for determining the relevant thermal impedances in a high-resolution capacitance dilatometer/oven system. Heat generated sinusoidally in time from a Peltier element allows measurements of complex transfer functions relating the response of thermometers placed at different locations. In particular, letting thermal expansion of a mounted sample represent its temperature has permitted a precise frequency analysis of the thermal separation from the primary system thermometer. The results characterizing the apparatus are compared to simple models for heat transport where the frequency response is described in terms of a relaxation time or an effective thermal diffusivity. The method is adaptable to a wide variety of measurement cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337106
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    Paper (German National Licenses)
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  • 2
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    Collective directional locking of colloidal monolayers on a periodic substrate (2020)
    Details
    Publication Date: 2021-02-01
    Description: We investigate the directional locking effects that arise when a monolayer of paramagnetic colloidal particles is driven across a triangular lattice of magnetic bubbles. We use an external rotating magnetic field to generate a two-dimensional traveling wave ratchet forcing the transport of particles along a direction that intersects two crystallographic axes of the lattice. We find that, while single particles show no preferred direction, collective effects induce transversal current and directional locking at high density via a spontaneous symmetry breaking. The colloidal current may be polarized via an additional bias field that makes one transport direction energetically preferred.
    Language: English
    Type: article , doc-type:article
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  • 3
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    Thermally active nanoparticle clusters enslaved by engineered domain wall traps (2021)
    Details
    Publication Date: 2021-10-05
    Description: The stable assembly of fluctuating nanoparticle clusters on a surface represents a technological challenge of widespread interest for both fundamental and applied research. Here we demonstrate a technique to stably confine in two dimensions clusters of interacting nanoparticles via size-tunable, virtual magnetic traps. We use cylindrical Bloch walls arranged to form a triangular lattice of ferromagnetic domains within an epitaxially grown ferrite garnet film. At each domain, the magnetic stray field generates an effective harmonic potential with a field tunable stifness. The experiments are combined with theory to show that the magnetic confinement is effectively harmonic and pairwise interactions are of dipolar nature, leading to central, strictly repulsive forces. For clusters of magnetic nanoparticles, the stationary collective states arise from the competition between repulsion, confinement and the tendency to fill the central potential well. Using a numerical simulation model as a quantitative map between the experiment and theory we explore the field-induced crystallization process for larger clusters and unveil the existence of three different dynamical regimes. The present method provides a model platform for investigations of the collective phenomena emerging when strongly confined nanoparticle clusters are forced to move in an idealized, harmonic-like potential.
    Language: English
    Type: article , doc-type:article
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    OPUS
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