Phase stability and magnetic properties of SrFe18O27 W-type hexagonal ferrite

W-type ferrite is a member of the hexagonal ferrite family and a potential permanent magnet material. However, its synthesis conditions are not fully understood yet. Samples were sintered either at 1400°C in air and quenched, or at 1300°C at reduced oxygen partial pressure. The precise stability conditions of this W-type ferrite were investigated in the temperature range of 1200°C-1400°C using thermogravimetry, XRD, and electron microscopy. At 1300°C, the ferrite is stable at oxygen partial pressures of . At more oxidizing conditions, the ferrite decomposes into M-type ferrite and hematite, while at more reducing atmospheres Sr₄Fe₆O₁₃ and magnetite are formed. The nonstoichiometry δ of SrFe_18−δO₂₇ was derived from thermal analysis data at 1300°C as function of oxygen partial pressure and was found to be mainly due to cation vacancies. Magnetization measurements show that this W-type ferrite exhibits M_s = 103 emu/g at T = 4 K, which agrees well with a ferrimagnetic spin arrangement according to Gorter's model. As alternative, Zn-substituted W-ferrite was found to be stable in air at 1200°C with a large M_s = 123 emu/g at 4 K.     

The Malta cistern mapping project: Underwater robot mapping and localization within ancient tunnel systems

This paper documents the development of an underwater robot system enabled with several mapping and localization techniques applied to a particular archaeological expedition. The goal of the expedition was to explore and map ancient cisterns located on the islands of Malta and Gozo. The cisterns of interest acted as water storage systems for fortresses, private homes, and churches. Such cisterns often consisted of several connected chambers, still containing water. A sonar‐equipped remotely operated vehicle (ROV) was deployed into these cisterns to obtain both video footage and sonar range measurements. Six different mapping and localization techniques were employed, including (1) sonar image mosaics using stationary sonar scans, (2) sonar image mosaics using stationary sonar scans with Smart Tether position data, (3) simultaneous localization and mapping (SLAM) while the vehicle was in motion, (4) SLAM using stationary sonar scans, (5) localization using previously created maps, and (6) SLAM while the vehicle was in motion with Smart Tether position data. Top‐down‐view maps of 22 different cisterns were successfully constructed. It is estimated that the cisterns were built as far back as 300 B.C., and few records of their size, shape, and connectivity existed before the expedition. © 2010 Wiley Periodicals, Inc.     

Sintering,microwave properties,and circulator applications of textured Sc-substituted M-type ferrite thick films

Sc³⁺ substituted M-type ferrites are effective microwave magnetic materials with a ferromagnetic resonance frequency in the range of 20 GHz–50 GHz. We report on the fabrication of oriented ferrite thick films as microwave components for application in the K_a-band at 30 GHz. Films of BaFe_11.5.Sc_0.5O₁₉ were prepared by screen-printing on alumina substrates, drying in an external magnetic field, and sintering at 900 °C. Low-temperature sintering is achieved through use of a mixed BBSZ/CuO sintering aid. A strong anisotropy of the sintered ferrite films is revealed by XRD analysis. Microwave properties of the films were determined in a coplanar waveguide setup. The ferromagnetic resonance frequency of the films is at 30 GHz and the textured films possess good nonreciprocal properties which scale with film thickness. The films were tested in a Y-junction circulator, and represent promising materials for self-biased microwave components fabricated in thick film technology.     

Facilitation of consumer loyalty toward branded applications: The dual-route perspective

Although many brands develop mobile applications (apps) to build relationships with consumers, most branded apps fail to retain consumers’ loyalty. This study examines the facilitation of consumer loyalty toward branded apps (continuance intention, in-app purchase intention, and word-of-mouth intention) from the dual-route perspective. One route is the affective (relationship) route, where brand benefits (functional benefits, experiential benefits, symbolic benefits, and monetary benefits) drive parasocial interactions between consumers and the brand, which, in turn, influences branded app loyalty. The other route is the utility route, where system characteristics (system quality and information quality) affect perceived usefulness, which, in turn, facilitates branded app loyalty. An online survey was conducted, and the research model was empirically tested using partial least squares structural equation modeling. The findings support the dual-route perspective according to which both affective and utilitarian paths facilitate branded app loyalty. The key theoretical contribution of this study is that it moves beyond the utilitarian path and finds the affective (relationship) path to give a more complete picture of the facilitation of consumer loyalty in the branded app context. A strategy is provided to suggest to practitioners how to design branded apps to facilitate consumer loyalty.     

Sintering behavior,microstructure and thermoelectric properties of calcium cobaltite thick films for transversal thermoelectric multilayer generators

The sintering behavior and the thermoelectric performance of Ca₃Co₄O₉ multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca₃Co₄O₉ green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT = 200 K in the temperature interval of 25 °C to 300 °C.     

Influence of pressure and dwell time on pressure-assisted sintering of calcium cobaltite

Calcium cobaltite Ca₃Co₄O₉, abbreviated Co349, is a promising thermoelectric material for high-temperature applications in air. Its anisotropic properties can be assigned to polycrystalline parts by texturing. Tape casting and pressure-assisted sintering (PAS) are a possible future way for a cost-effective mass-production of thermoelectric generators. This study examines the influence of pressure and dwell time during PAS at 900°C of tape-cast Co349 on texture and thermoelectric properties. Tape casting aligns lentoid Co349. PAS results in a textured Co349 microstructure with the thermoelectrically favorable ab-direction perpendicular to the pressing direction. By pressure variation during sintering, the microstructure of Co349 can be tailored either toward a maximum figure of merit as required for energy harvesting or toward a maximum power factor as required for energy harvesting. Moderate pressure of 2.5 MPa results in 25% porosity and a textured microstructure with a figure of merit of 0.13 at 700°C, two times higher than the dry-pressed, pressureless-sintered reference. A pressure of 7.5 MPa leads to 94% density and a high power factor of 326 µW/mK² at 800°C, which is 11 times higher than the dry-pressed reference (30 MPa) from the same powder.     

Determinants of emoticon usage in mobile instant messaging: a construal level theory perspective

Mobile instant messaging is experiencing immense growth, and using emoticons has become a prevalent and highly popular means of communication. The small digital images are ubiquitous, from smartphone applications to social media, and people delight in sending them. Drawing from construal level theory, the aim of this research is to examine the underlying mechanism that drives the usage of emoticons and its usage enjoyment. People with experience using mobile instant messaging were recruited to participate in an online survey, resulting in 202 usable questionnaires. The research model was tested empirically. Covariance-based structural equation modelling was used to analyze the data. The findings highlight that the determinants of individual’s emoticon usage are driven by a dual-route path. One is the self-concept route, where self-image congruity between emoticons and individuals drives psychological ownership, which in turn influences word of mouth (WOM) intention and perceived enjoyment of emoticon use. The other is the utility route, driven by emoticons’ familiarity and perceived synchronicity. The findings reveal the importance of emoticon usage through a contextual lens that shows that a dual-route path has a prominent impact upon these digital-based communication behaviours, which provides important managerial implications.     

Probing Binding and Cellular Activity of Pyrrolidinone and Piperidinone Small Molecules Targeting the Urokinase Receptor

The urokinase receptor (uPAR) is a cell‐surface protein that is part of an intricate web of transient and tight protein interactions that promote cancer cell invasion and metastasis. Here, we evaluate the binding and biological activity of a new class of pyrrolidinone and piperidinone compounds, along with derivatives of previously‐identified pyrazole and propylamine compounds. Competition assays revealed that the compounds displace a fluorescently labeled peptide (AE147‐FAM) with inhibition constant (K_i) values ranging from 6 to 63 μM . Structure‐based computational pharmacophore analysis followed by extensive explicit‐solvent molecular dynamics (MD) simulations and free energy calculations suggested the pyrazole‐based and piperidinone‐based compounds adopt different binding modes, despite their similar two‐dimensional structures. In cells, pyrazole‐based compounds showed significant inhibition of breast adenocarcinoma (MDA‐MB‐231) and pancreatic ductal adenocarcinoma (PDAC) cell proliferation, but piperidinone‐containing compounds exhibited no cytotoxicity even at concentrations of 100 μM . One pyrazole‐based compound impaired MDA‐MB‐231 invasion, adhesion, and migration in a concentration‐dependent manner, while the piperidinone inhibited only invasion. The pyrazole derivative inhibited matrix metalloprotease‐9 (gelatinase) activity in a concentration‐dependent manner, while the piperidinone showed no effect suggesting different mechanisms for inhibition of cell invasion. Signaling studies further highlighted these differences, showing that pyrazole compounds completely inhibited ERK phosphorylation and impaired HIF1α and NF‐κB signaling, while pyrrolidinones and piperidinones had no effect. Annexin V staining suggested that the effect of the pyrazole‐based compound on proliferation was due to cell killing through an apoptotic mechanism. The compounds identified represent valuable leads in the design of further derivatives with higher affinities and potential probes to unravel the protein–protein interactions of uPAR.     

Integration of High‐Frequency M‐Type Hexagonal Ferrite Inductors in LTCC Multilayer Modules

Monolithic hexagonal BaCo_1,3Ti_1,3Fe_9,4O₁₉ ferrite multilayers sintered at 900°C exhibit a fine‐grained microstructure with permeability of μ′ = 16 and a resonance frequency f_r ≥ 1GHz. Co‐firing of hetero‐laminates of ferrite with CT700 glass–ceramic LTCC tapes and with polycrystalline zinc titanate (ZT) LTCC tapes was studied. Co‐firing at 900°C of ferrite/CT700 leads to multilayers with cracks caused by substantial thermal expansion mismatch. Co‐fired ferrite/ZT multilayer laminates exhibit a permeability of μ′ = 16 and do not show any defects. Hexagonal ferrite multilayer inductor elements were integrated into ZT‐based multilayer LTCC modules and co‐fired at 900°C with Ag metallization.