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Subject: Expansion ×

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Now showing 1 - 4 of 4
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    The force of MOFs: The potential of switchable metal-organic frameworks as solvent stimulated actuators
    (Cambridge : RSC, 2020) Freund, Pascal; Senkovska, Irena; Zheng, Bin; Bon, Volodymyr; Krause, Beate; Maurin, Guillaume; Kaskel, Stefan
    We evaluate experimentally the force exerted by flexible metal-organic frameworks through expansion for a representative model system, namely MIL-53(Al). The results obtained are compared with data collected from intrusion experiments while molecular simulations are performed to shed light on the re-opening of the guest-loaded structure. The critical impact of the transition stimulating medium on the magnitude of the expansion force is demonstrated.
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    Kinematics of femtosecond laser-generated plasma expansion: Determination of sub-micron density gradient and collisionality evolution of over-critical laser plasmas
    ([S.l.] : American Institute of Physics, 2021) Scott, G.G.; Indorf, G.F.H.; Ennen, M.A.; Forestier-Colleoni, P.; Hawkes, S.J.; Scaife, L.; Sedov, M.; Symes, D.R.; Thornton, C.; Beg, F.; Ma, T.; McKenna, P.; Andreev, A.A.; Teubner, U.; Neely, D.
    An optical diagnostic based on resonant absorption of laser light in a plasma is introduced and is used for the determination of density scale lengths in the range of 10 nm to >1 μm at the critical surface of an overdense plasma. This diagnostic is also used to extract the plasma collisional frequency, allowing inference of the temporally evolving plasma composition on the tens of femtosecond timescale. This is found to be characterized by two eras: the early time and short scale length expansion (L < 0.1λ), where the interaction is highly collisional and target material dependent, followed by a period of material independent plasma expansion for longer scale lengths (L > 0.1λ); this is consistent with a hydrogen plasma decoupling from the bulk target material. Density gradients and plasma parameters on this scale are of importance to plasma mirror optical performance and comment is made on this theme.
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    The dynamical evolution of planetary nebulae
    (Bristol : IOP Publ., 2016) Schönberner, Detlef
    Based on modern 1D-radiation-hydrodynamics simulations of formation and evolution of planetary nebulae, I discuss in detail the basic dynamical processes responsible for the "grand design" of most planetary nebulae, i.e. their double-shell morphology and their typical expansion properties. Special emphasis is given for a proper definition of a nebula's true expansion rate and its relation to spectroscopically measurable Doppler velocities of the expanding material. It is found that the typical nebular expansion is about twice as fast as hitherto assumed, viz. ≃45 kms-1.
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    Magnetoelastic coupling and ferromagnetic-type in-gap spin excitations in multiferroic α-Cu2V2O7
    (Bristol : Institute of Physics Publishing, 2018) Wang, L.; Werner, J.; Ottmann, A.; Weis, R.; Abdel-Hafiez, M.; Sannigrahi, J.; Majumdar, S.; Koo, C.; Klingeler, R.
    We investigate magnetoelectric coupling and low-energy magnetic excitations in multiferroic α-Cu2V2O7 by detailed thermal expansion, magnetostriction, specific heat and magnetization measurements in magnetic fields up to 15 T and by high-field/high-frequency electron spin resonance studies. Our data show negative thermal expansion in the temperature range ≤200 K under study. Well-developed anomalies associated with the onset of multiferroic order (canted antiferromagnetism with a significant magnetic moment and ferroelectricity) imply pronounced coupling to the structure. We detect anomalous entropy changes in the temperature regime up to ∼80 K which significantly exceed the spin entropy. Failure of Grüneisen scaling further confirms that several dominant ordering phenomena are concomitantly driving the multiferroic order. By applying external magnetic fields, anomalies in the thermal expansion and in the magnetization are separated. Noteworthy, the data clearly imply the development of a canted magnetic moment at temperatures above the structural anomaly. Low-field magnetostriction supports the scenario of exchange-striction driven multiferroicity. We observe low-energy magnetic excitations well below the antiferromagnetic gap, i.e., a ferromagnetic-type resonance branch associated with the canted magnetic moment arising from Dzyaloshinsii-Moriya (DM) interactions. The anisotropy parameter meV indicates a sizeable ratio of DM- and isotropic magnetic exchange.