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- ItemRoles of hydrogenation, annealing and field in the structure and magnetic entropy change of Tb-based bulk metallic glasses(New York : American Institute of Physics, 2013) Luo, Qiang; Schwarz, Björn; Mattern, Norbert; Shen, Jun; Eckert, JürgenThe reduction of open-volume regions in Tb-based metallic glass (MG) by annealing and hydrogen charging was found to rearrange the atomic structure and tune the magnetic behaviors. After crystallization, the magnetic structure and magnetic entropy change (MEC) alters due to the structural transformation, and a plateau-like-MEC behavior can be obtained. The hydrogen concentration after charging at 1mA/cm2 for 576 h reaches as high as 3290 w-ppm. The magnetization behavior and the MEC change due to the modification of the exchange interaction and the random magnetic anisotropy (RMA) upon hydrogenation. At low temperatures, irreversible positive MEC was obtained, which is related to the internal entropy production. The RMA-to-exchange ratio acts as a switch to control the irreversible entropy production channel and the reversible entropy transfer channel. The field dependence of the MEC is discussed in term of the competition among Zeeman energy, exchange interaction and RMA.
- ItemMagnetocaloric properties of multicomponent Laves phase compounds and their composites(Bristol : IOP Publ., 2021) Ćwik, J.; Koshkid’ko, Yu; Nenkov, K.; Kolchugina, N.Heat capacity measurements have been performed for multicomponent (Ho0.9Er0.1)1-xGdxCo2 compounds with x = 0.05, 0.1, and 0.15. The isothermal magnetic entropy change, ΔSmag, allowing the estimation of the magnetocaloric effect, was determined based on the heat capacity measurements in magnetic fields up to 2 T. A numerical method, with the magnetic entropy change of individual (Ho0.9Er0.1)1-xGdxCo2 compounds, was used to calculate the optimal molar composition of the constituents and the resulting change of the isothermal magnetic entropy of composite, ΔScomp. The results show that proposed composite can be considered as a refrigerant material in magnetic refrigerators performing an Ericsson cycle in a temperature range of 90-130 K.
- ItemThe complexity of gene expression dynamics revealed by permutation entropy(London : BioMed Central Ltd., 2010) Sun, Xiaoliang; Zou, Yong; Nikiforova, Victoria; Kurths, Jürgen; Walther, DirkBackground: High complexity is considered a hallmark of living systems. Here we investigate the complexity of temporal gene expression patterns using the concept of Permutation Entropy (PE) first introduced in dynamical systems theory. The analysis of gene expression data has so far focused primarily on the identification of differentially expressed genes, or on the elucidation of pathway and regulatory relationships. We aim to study gene expression time series data from the viewpoint of complexity.Results: Applying the PE complexity metric to abiotic stress response time series data in Arabidopsis thaliana, genes involved in stress response and signaling were found to be associated with the highest complexity not only under stress, but surprisingly, also under reference, non-stress conditions. Genes with house-keeping functions exhibited lower PE complexity. Compared to reference conditions, the PE of temporal gene expression patterns generally increased upon stress exposure. High-complexity genes were found to have longer upstream intergenic regions and more cis-regulatory motifs in their promoter regions indicative of a more complex regulatory apparatus needed to orchestrate their expression, and to be associated with higher correlation network connectivity degree. Arabidopsis genes also present in other plant species were observed to exhibit decreased PE complexity compared to Arabidopsis specific genes.Conclusions: We show that Permutation Entropy is a simple yet robust and powerful approach to identify temporal gene expression profiles of varying complexity that is equally applicable to other types of molecular profile data.
- ItemEntropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range(Basel : MDPI, 2018-8-30) Haas, Sebastian; Mosbacher, Mike; Senkov, Oleg N; Feuerbacher, Michael; Freudenberger, Jens; Gezgin, Senol; Völkl, Rainer; Glatzel, UweWe determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy.
- ItemQuantum collapse rules from the maximum relative entropy principle(Bristol : Institute of Physics Publishing, 2016) Hellmann, F.; Kamiński, W.; Kostecki, R.P.
- ItemMagnetoelastic 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.