A comprehensive approach to broadband characterization of soft ferrites

We present and discuss methods, setups, and results concerning the characterization of Mn-Zn and Ni-Zn ferrites in the frequency range DC-1 GHz, by which we bring to light the physical mechanisms responsible for the observed frequency behavior of magnetic losses W and permeability mu and provide thorough assessment of the broadband response of the material. A comprehensive array of polarization J(p) and frequency f values is investigated. A fluxmetric approach is applied up to a few MHz, which is substituted by a transmission line method at higher frequencies, up to 1 GHz. The fluxmetric measurements are made at defined J(p) value, typically from a few mT to some hundred mT. The waveguide characterization, centered on the use of a network analyzer, is instead made under defined exciting power. But a full experimental W(J(p), f) matrix up to 1 GHz and J(p) values typically belonging to the Rayleigh region is in any case retrieved, thanks to the linear response of the material at high-frequencies. Disaccommodation measurements are the route followed in these experiments to separate the rotations from the domain wall process at all frequencies. Whatever the magnetization mode, the role of eddy currents in Mn-Zn ferrite losses is put in evidence by means of resistivity measurements and ensuing multiscale numerical modeling, the loss experiments being made on progressively thinned ring samples. It is concluded that an eddy current free W(J(p), f) behavior can always be obtained, which can be decomposed into domain wall and rotation related contributions. The latter can be calculated assuming a suitable distribution of the effective internal anisotropy fields and its introduction in the Landau-Lifshitz-Gilbert derivation of the rotational susceptibility

Magnetic losses versus sintering treatment in Mn-Zn ferrites

partially_open5sìpartially_openBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, FaustoBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, Faust

The temperature dependence of magnetic losses in CoO-doped Mn-Zn ferrites

CoO-doping is known to stabilize the temperature dependence of initial permeability and magnetic losses in Mn-Zn ferrites, besides providing, with appropriate dopant contents, good soft magnetic response at and around room temperature. These effects, thought to derive from the mechanism of anisotropy compensation, are, however, poorly assessed from a quantitative viewpoint. In this work, we overcome such limitations by providing, besides extensive experimental investigation vs frequency (DC–1GHz), CoO content (0 ≤ CoO ≤ 6000 ppm), and temperature (−20 °C ≤ T ≤ 130 °C) of permeability and losses of sintered Mn-Zn ferrites, a comprehensive theoretical framework. This relies on the separate identification of domain wall motion and moment rotations and on a generalized approach to magnetic loss decomposition. The average effective anisotropy constant ⟨Keff⟩ is obtained and found to monotonically decrease with temperature, depending on the CoO content. The quasistatic energy loss Wh is then predicted to pass through a deep minimum for CoO = 3000–4000 ppm at and below the room temperature, while becoming weakly dependent on CoO under increas- ing T. The rotational loss Wrot(f) is calculated via the complex permeability, as obtained from the Landau-Lifshitz equation for distributed values of the local effective anisotropy field Hk,eff (i.e., ferromagnetic resonance frequency). Finally, the excess loss Wexc(f) is derived and found to comply with suitable analytical formulation. It is concluded that, by achieving, via the rotational permeability, value and behavior of the magnetic anisotropy constant, we can predict the ensuing properties of hysteresis, excess, and rotational losses

Ubiquitin-dependent endocytosis of NKG2D-DAP10 receptor complexes activates signaling and functions in human NK cells

Cytotoxic lymphocytes share the presence of the activating receptor NK receptor group 2, member D (NKG2D) and the signaling-competent adaptor DNAX-activating protein 10 (DAP10), which together play an important role in antitumor immune surveillance. Ligand stimulation induces the internalization of NKG2D-DAP10 complexes and their delivery to lysosomes for degradation. In experiments with human NK cells and cell lines, we found that the ligand-induced endocytosis of NKG2D-DAP10 depended on the ubiquitylation of DAP10, which was also required for degradation of the internalized complexes. Moreover, through combined biochemical and microscopic analyses, we showed that ubiquitin-dependent receptor endocytosis was required for the activation of extracellular signal-regulated kinase (ERK) and NK cell functions, such as the secretion of cytotoxic granules and the inflammatory cytokine interferon-γ. These results suggest that NKG2D-DAP10 endocytosis represents a means to decrease cell surface receptor abundance, as well as to control signaling outcome in cytotoxic lymphocytes

Magnetic loss, permeability, and anisotropy compensation in CoO-doped Mn-Zn ferrites

Mn-Zn ferrite samples prepared by conventional solid state reaction method and sintering at 1325 °C were Co-enriched by addition of CoO up to 6000 ppm and characterized versus frequency (DC – 1GHz), peak polarization (2 mT – 200 mT), and temperature (23 °C – 120 °C). The magnetic losses at room temperature are observed to pass through a deep minimum value around 4000 ppm CoO at all polarizations values. This trend is smoothed out either by approaching the MHz range or by increasing the temperature. Conversely, the initial permeability attains its maximum value around the same CoO content, while showing moderate monotonical decrease with increasing CoO at the typical working temperatures of 80 – 100 °C. The energy losses, measured by a combination of fluxmetric and transmission line methods, are affected by the eddy currents, on the conventional 5 mm thick ring samples, only beyond a few MHz. Their assessment relies on the separation of rotational and domain wall processes, which can be done by analysis of the complex permeability and its frequency behavior. This permits one, in particular, to calculate the magnetic anisotropy and its dependence on CoO content and temperature and bring to light its decomposition into the host lattice and Co2+ temperature dependent contributions. The temperature and doping dependence of initial permeability and magnetic losses can in this way be qualitatively justified, without invoking the passage through zero value of the effective anisotropy constant upon doping

Carbon Dioxide Removal with Tuff: Experimental Measurement of Adsorption Properties and Breakthrough Modeling Using CFD Approach

Abstract This work presents the study of tuff as an alternative material for CO 2 capturing and removal by pressure swing adsorption techniques. Tuff represents an economic and environmentally sustainable alternative to commonly-used synthetic zeolites. The proposed methodology includes a laboratory characterization of the CO 2 adsorption process under different operative conditions and experimental layouts. Measured data are also used to setup computational fluid dynamics simulations of the fixed-bed adsorption column. Results can be used to define optimal design parameters needed to implement and to improve different applications for biogas upgrading (CO 2 /CH 4 ratio adjustment) or carbon capture and storage