Mastering hysteresis in magnetocaloric materials Gutfleisch, O.; Gottschall, T.; Fries, M. ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
08/2016, Letnik:
374, Številka:
2074
Journal Article
Recenzirano
Odprti dostop
Hysteresis is more than just an interesting oddity that occurs in materials with a first-order transition. It is a real obstacle on the path from existing laboratory-scale prototypes of magnetic ...refrigerators towards commercialization of this potentially disruptive cooling technology. Indeed, the reversibility of the magnetocaloric effect, being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, therefore, it is necessary to understand the mechanisms causing hysteresis and to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, we discuss the fundamental aspects that can contribute to thermal hysteresis and the strategies that we are developing to at least partially overcome the hysteresis problem in some selected classes of magnetocaloric materials with large application potential. In doing so, we refer to the most relevant classes of magnetic refrigerants La-Fe-Si-, Heusler- and Fe2P-type compounds.
This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’.
Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved ...dark matter decay mode, n→X+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.
•Improved and prediction of mass transport limitation during electrodeposition.•Comparison of numerical simulations and experimental results.•Increase of velocity and diffusivity increases coating ...thickness homogeneity.•Decrease of deposition parameters increases coating thickness homogeneity.•Migration has only a negligible influence on the coating thickness homogeneity.
The limited quantity of raw materials leads to application-optimised materials, such as open-cell hybrid foams. A nanocrystalline nickel coating significantly enhances the crash absorber properties of aluminum and PU foams with only a small increase in weight. The coating is applied by an electrodeposition process. Due to mass transport limitations during the process, an inhomogeneous coating thickness is created resulting in inhomogeneous material properties. To avoid different coating thicknesses at different points of the foam, the electrodeposition process in the foam is modelled and simulated. The results of the simulation are compared with experimental data and the influence of different parameters on the coating homogeneity is investigated by means of simulation.
A Reduced Organic Carbon Component in Martian Basalts Steele, A.; McCubbin, F. M.; Fries, M. ...
Science (American Association for the Advancement of Science),
07/2012, Letnik:
337, Številka:
6091
Journal Article
Recenzirano
The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion ...years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.
The magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to 62T. The maximum observed adiabatic temperature change is ΔTad=60.5K, the initial temperature T0 ...being just above 300K. The field dependence of ΔTad is found to follow the usual H2/3 law, with a small correction in H4/3. However, as H is increased, a radical change is observed in the dependence of ΔTad on T0, at H=const. The familiar caret-shaped peak situated at T0=TC becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, μ0H≳140T, calculations predict a complete disappearance of the maximum near TC and an emergence of a new very broad maximum far above TC.
Fluid-rock interactions in hydrothermal systems at or near mid-oceanic ridges (MOR) play a major role in determining the composition of the oceanic crust and seawater. To quantify the processes that ...govern cation exchange in these environments we have experimentally studied the isotopic evolution of δ26/24Mg in the fluid phase during seawater-basalt interaction at 250 and 290 °C. Mass balance constraints indicate that isotopically heavy Mg was preferentially incorporated into non-exchangeable (octahedral) sites in secondary clay minerals such as saponite (Mg-rich smectite), leaving residual fluids enriched in light Mg isotopes. The magnitude of fractionation observed during smectite precipitation in our experiments (εSmectite-Liquid26/24) ranged from 0.35‰ to 0.42‰. This observation, which contrasts with the preferential uptake of light Mg isotopes into biogenic and inorganic marine carbonates, highlights the potential utility of Mg isotopes as tracers of the precipitation dynamics of authigenic Mg-silicate and Mg-carbonate phases. Furthermore, although Mg isotopic fractionation is often masked by the almost complete removal of Mg in high temperature marine hydrothermal systems, our experiments demonstrate that it does become significant at lower temperatures where Mg removal by clay formation is incomplete. Under such conditions, this fractionation will create isotopically light fluids due to smectite precipitation, thus potentially represents an important component of the marine Mg isotope inventory.
Objectives
To examine (1) the association between perceived discrimination, including everyday perceived discrimination and major lifetime perceived discrimination, and cognitive function and (2) the ...mediating role of depression between discrimination and cognitive function among older Puerto Ricans.
Methods
Data came from the Boston Puerto Rican Health Study, collected from 562 Puerto Ricans aged 60+. Structural Equation Modelling was used to examine the association between discrimination and cognitive function and the mediating effect of depression.
Results
Everyday perceived discrimination was negatively associated with cognitive function, which was fully mediated by depression. Major Lifetime perceived discrimination was not associated with cognitive function.
Conclusions
The findings contribute new information regarding the impact of perceived discrimination on cognitive function among older Puerto Ricans and underscore the importance of assessing experiences of discrimination to prevent depression and cognitive decline in this population.
Key points
Everyday perceived discrimination was negatively associated with cognitive function, which was fully mediated by depression
Major Lifetime perceived discrimination was not associated with cognitive function
Abstract
Objectives
Ageism is a prevalent, insidious social justice issue that has harmful effects on the health of older adults. Preliminary literature explores the intersectionality of ageism with ...sexism, ableism, and ageism experienced among LGBTQ+ older adults. Yet, the intersectionality of ageism with racism remains largely absent from the literature. Therefore, this study explores the lived experience of the intersectionality of ageism and racism among older adults.
Methods
This qualitative study applied a phenomenological approach. Twenty participants 60+ years of age (M = 69, standard deviation = 8.84) in the U.S. Mountain West identifying as Black, Latino(a), Asian–American/Pacific Islander, Indigenous, or White engaged in a 1-hr interview between February and July 2021. A 3-cycle coding process applied constant comparison methods. Five coders independently coded interviews, engaging in critical discussion to resolve disagreements. An audit trail, member checking, and peer debriefing enhanced credibility.
Results
This study focuses on individual-level experiences exemplified by 3 umbrella themes and 7 subthemes. The subthemes are (a) compounding oppression, (b) intersection of disparities, (c) White privilege, (d) racism and ageism: being tokenized or ignored, (e) ageism and racism: unspoken bias, (f) racism versus ageism: overt or covert? and (g) racism versus ageism: differentiated or ubiquitous?
Discussion
The findings indicate how ageism may be racialized through stereotypes related to mental (in)capability. Practitioners can apply the findings to enhance support for older adults by designing interventions aimed at reducing racialized ageist stereotypes and increasing collaboration through education across anti-ageism/anti-racism initiatives. Future research should focus on the impacts of the intersectionality of ageism and racism on specific health outcomes in addition to structural-level interventions.
Water-rock interactions are relevant to planetary habitability, influencing mineralogical diversity and the production of organic molecules. We examine carbonates and silicates in the martian ...meteorite Allan Hills 84001 (ALH 84001), using colocated nanoscale analyses, to characterize the nature of water-rock reactions on early Mars. We find complex refractory organic material associated with mineral assemblages that formed by mineral carbonation and serpentinization reactions. The organic molecules are colocated with nanophase magnetite; both formed in situ during water-rock interactions on Mars. Two potentially distinct mechanisms of abiotic organic synthesis operated on early Mars during the late Noachian period (3.9 to 4.1 billion years ago).
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