Low-Temperature Magnetothermodynamics Performance of Tb1-xErxNi2 Laves-Phases Compounds for Designing Composite Refrigerants

In this paper, the results of heat capacity measurements performed on the polycrystalline Tb1-xErxNi2 intermetallic compounds with x = 0.25, 0.5 and 0.75 are presented. The Debye temperatures and lattice contributions as well as the magnetic part of the heat capacity were determined and analyzed. The heat capacity measurements reveal that the substitution of Tb atoms for Er atoms leads to a linear reduction of the Curie temperatures in the investigated compounds. The ordering temperatures decrease from 28.3 K for Tb0.25Er0.75Ni2 to 12.9 K for Tb0.75Er0.25Ni2. Heat capacity measurements enabled us to calculate with good approximation the isothermal magnetic entropy ΔSmag and adiabatic temperature changes ΔTad for Tb1-xErxNi2, for the magnetic field value equal to 1 T and 2 T. The optimal molar ratios of individual Tb0.75Er0.25Ni2, Tb0.5Er0.5Ni2 and Tb0.25Er0.75Ni2 components in the final composite were theoretically determined. According to the obtained results, the investigated composites make promising candidates that can find their application as an active body in a magnetic refrigerator performing an Ericsson cycle at low temperatures. Moreover, for the Tb0.5Er0.5Ni2 compound, direct measurements of adiabatic temperature change in the vicinity of the Curie temperature in the magnetic field up to 14 T were performed. The obtained high-field results are compared to the data for the parent TbNi2 and ErNi2 compounds, and their magnetocaloric properties near the Curie temperature are analyzed in the framework of the Landau theory for the second-order phase transitions

Structure and Giant Inverse Magnetocaloric Effect of Epitaxial Ni-Co-Mn-Al Films

The structural, magnetic, and magnetocaloric properties of epitaxial Ni-Co-Mn-Al thin films with different compositions have been studied. The films were deposited on MgO(001) substrates by co-sputtering on heated substrates. All films show a martensitic transformation, where the transformation temperatures are strongly dependent on the composition. The structure of the martensite phase is shown to be 14M. The metamagnetic martensitic transformation occurs from strongly ferromagnetic austenite to weakly magnetic martensite. The structural properties of the films were investigated by atomic force microscopy and temperature dependent X-ray diffraction. Magnetic and magnetocaloric properties were analyzed using temperature dependent and isothermal magnetization measurements. We find that Ni$_{41}$Co$_{10.4}$Mn$_{34.8}$Al$_{13.8}$ films show giant inverse magnetocaloric effects with magnetic entropy change of 17.5\,J\,kg$^{-1}$K$^{-1}$ for $\mu_0 \Delta H=5\,\text{T}$.Comment: 8 pages, 8 figure

Magnetocaloric performance of the three-component Ho1-xErxNi2 (x = 0.25, 0.5, 0.75) Laves phases as composite refrigerants

To date, significant efforts have been put into searching for materials with advanced magnetocaloric properties which show promise as refrigerants and permit realization of efficient cooling. The present study, by an example of Ho1−xErxNi2, develops the concept of magnetocaloric efficiency in the rare-earth Laves-phase compounds. Based on the magneto-thermodynamic properties, their potentiality as components of magnetocaloric composites is illustrated. The determined regularities in the behaviour of the heat capacity, magnetic entropy change, and adiabatic temperature change of the system substantiate reaching high magnetocaloric potentials in a desired temperature range. For the Ho1−xErxNi2 solid solutions, we simulate optimal molar ratios and construct the composites used in magnetic refrigerators performing an Ericsson cycle at low temperatures. The tailored magnetocaloric characteristics are designed and efficient procedures for their manufacturing are developed. Our calculations based on the real empirical data are very promising and open avenue to further experimental studies. Systems showing large magnetocaloric effect (MCE) at low temperatures are of importance due to their potential utilization in refrigeration for gas liquefaction

Coupling Phenomena in Magnetocaloric Materials

Strong coupling effects in magnetocaloric materials are the key factor to achieve a large magnetic entropy change. Combining insights from experiments and ab initio calculations, we review relevant coupling phenomena, including atomic coupling, stress coupling, and magnetostatic coupling. For the investigations on atomic coupling, we have used Heusler compounds as a flexible model system. Stress coupling occurs in first-order magnetocaloric materials, which exhibit a structural transformation or volume change together with the magnetic transition. Magnetostatic coupling has been experimentally demonstrated in magnetocaloric particles and fragment ensembles. Based on the achieved insights, we have demonstrated that the materials properties can be tailored to achieve optimized magnetocaloric performance for cooling applications

Community description

petersanders2015aThis document constitutes the 3rd revision of Ready4SmartCities’ Community Description onthe plan on how to build a community for the Ready4SmartCities roadmap, vision andoutcome, also in the light of the targeted data interoperability proposals work packages 2, 3and 4 dealt with. It intends to depict the project’s community of communities at the end ofthe project’s lifetime, the different means the project used to get in touch with it and the viewof building a “data community” via semantic web technologies. It recapitulates and criticallyassesses the problems encountered during the execution of the project concerninginteractions and a channel used, and discusses issues arising in the work to fully reach thetargeted audience(s)

Demagnetizing field-induced magnetocaloric effect in Gd

We have studied the impact of demagnetizing fields on the magnetocaloric effect of commercial-grade gadolinium plates. Adiabatic temperature changes (⁠ ⁠) were measured for magnetic fields applied along the parallel and perpendicular directions of the plates. The differences in the obtained values were accounted for by differences in the internal field due to demagnetizing effects. A combination of calorimetric measurements under a magnetic field and thermometric measurements has enabled us to obtain Brayton cycles for the two different magnetic field orientations. It has been found that the refrigerant capacity for a Brayton cycle working at 1.6 T around room temperature reduces from to  J kg when the demagnetizing factor changes from  = 0.035 to for the parallel and perpendicular configurations, respectively. It has been shown that it is possible to obtain significant demagnetizing field-induced magnetocaloric effects by rotating the sample in a region of a constant applied magnetic field. The refrigerant capacity of a Brayton cycle around room temperature for a T constant applied magnetic field is  J kg ⁠. The feasibility of these demagnetizing field-induced effects has been confirmed by direct thermometric measurements, which reveal adiabatic temperature changes of 1 K when the sample is rotated between the perpendicular and parallel configurations

The BKB_K Parameter in the 1/Nc1/N_c Expansion

We calculate the $B_K$ parameter within the framework of the $1/N_c$ expansion. We essentially use the technique presented by Bardeen, Buras and G\'erard but calculate an off-shell Green function in order to disentangle different contributions. We study this Green function in pure Chiral Perturbation Theory (CHPT) first and afterwards in the $1/N_c$ expansion in the presence of an explicit cut-off to determine $B_K$ and the counterterms appearing in CHPT. The high energy part is done using the renormalization group. For the low-energy contributions we use both CHPT and an Extended Nambu--Jona-Lasinio model. This model has the right properties to match with the high energy QCD behaviour. We then study explicit chiral symmetry breaking effects by calculating with both massless and degenerate quarks together with the real case. A detailed analysis and comparison with the results found within other approaches is done. Consequences for present lattice calculations of this parameter are then obtained. As final result we get $0.60 < \hat B_K < 0.80$. If $m_s=m_d=0$ we get $0.25 < \hat B^\chi_K < 0.55$.Comment: 44 pages, uses epsf.sty, 9 figures included (8 postscript, 1 LaTeX

Constraining hydrological model parameters using water isotopic compositions in a glacierized basin, Central Asia

Water stable isotope signatures can provide valuable insights into the catchment internal runoff processes. However, the ability of the water isotope data to constrain the internal apportionments of runoff components in hydrological models for glacierized basins is not well understood. This study developed an approach to simultaneously model the water stable isotopic compositions and runoff processes in a glacierized basin in Central Asia. The fractionation and mixing processes of water stable isotopes in and from the various water sources were integrated into a glacio- hydrological model. The model parameters were calibrated on discharge, snow cover and glacier mass balance data, and additionally isotopic composition of streamflow. We investigated the value of water isotopic compositions for the calibration of model parameters, in comparison to calibration methods without using such measurements. Results indicate that: (1) The proposed isotope-hydrological integrated modeling approach was able to reproduce the isotopic composition of streamflow, and improved the model performance in the evaluation period; (2) Involving water isotopic composition for model calibration reduced the model parameter uncertainty, and helped to reduce the uncertainty in the quantification of runoff components; (3) The isotope-hydrological integrated modeling approach quantified the contributions of runoff components comparably to a three-component tracer-based end-member mixing analysis method for summer peak flows, and required less water tracer data. Our findings demonstrate the value of water isotopic compositions to improve the quantification of runoff components using hydrological models in glacierized basins

Ontologies and datasets for energy management system interoperability

weise2015aInternational audienceThis document presents a final report of the work carried out as part of work package 2 of the READY4SmartCitiesproject (R4SC), whose goal it is to identify the knowledge and data resources that support interoperability for energymanagement systems. The document is divided into two parts

Mismatches in Scale Between Highly Mobile Marine Megafauna and Marine Protected Areas

Marine protected areas (MPAs), particularly large MPAs, are increasing in number and size around the globe in part to facilitate the conservation of marine megafauna under the assumption that large-scale MPAs better align with vagile life histories; however, this alignment is not well established. Using a global tracking dataset from 36 species across five taxa, chosen to reflect the span of home range size in highly mobile marine megafauna, we show most MPAs are too small to encompass complete home ranges of most species. Based on size alone, 40% of existing MPAs could encompass the home ranges of the smallest ranged species, while only \u3c 1% of existing MPAs could encompass those of the largest ranged species. Further, where home ranges and MPAs overlapped in real geographic space, MPAs encompassed \u3c 5% of core areas used by all species. Despite most home ranges of mobile marine megafauna being much larger than existing MPAs, we demonstrate how benefits from MPAs are still likely to accrue by targeting seasonal aggregations and critical life history stages and through other management techniques