A new class of Cr(V) peroxychromates, those containing waters of hydration (Li3CrO8·10H2O, Na3CrO8·14H2O and Cs3CrO8·3H2O), has been synthesized and characterized by single-crystal X-ray diffraction, magnetic susceptibility, specific heat, and EPR techniques. The Li salt crystallizes into the orthorhombic (Cmcm) group, whereas the Na and Cs salts exhibit the triclinic (P1̄) and monoclinic P2(1)/n space groups, respectively. Crystal structure analysis indicated the availability of low-dimensional spin-exchange pathways. The orientation dependence of the EPR line width exhibited the (3 cos2 θ − 1)4/3 behavior characteristic of linear chain compounds, with θ = 0 coinciding with the chain axis. Correlation of the EPR and X-ray data allowed for the explicit determination of the magnetic chain axes in the crystal and molecular frameworks. Magnetic susceptibility, χ, measurements on oriented single crystals yielded negative values for the Curie−Weiss temperatures, indicating dominant antiferromagnetic interactions. The χ data yielded the Curie constants that appear to be inversely related to the number of waters of hydration in the crystal structure; this observation is not yet understood. Correlation of the EPR line width, nearest neighbor distances, and Curie constants attested to the essential correctness of the linear chain spin exchange and dipolar fields in the Li and Cs salts, and to a lesser extent also for the Na salt. The specific heat data indicated that all these compounds have the potential to be useful for devices requiring strong heat sinks as well as magnetic refrigerants in the 250 mK temperature regime. They appear to be good as model systems for theoretical investigations on low-dimensional magnetic lattices and for understanding aspects of Cr(VI)-based catalysis and carcinogenesis.
2001dielectric properties, magnetic properties dielectric properties, magnetic properties D 9000 -013Hydrated Cr(V) Peroxychromates M 3 CrO 8 ·xH 2 O (M: Li, Na, Cs): Model 3d 1 Systems Exhibiting Linear Chain Behavior and Antiferromagnetic Interactions.-The title compounds, M 3 Cr(O 2 ) 4 ·xH 2 O (M: Li, Na, Cs) are prepared from aqueous solutions of CrO 3 and MOH (M: Li, Na, Cs) by addition of cold H 2 O 2 (5 • C, 3-5 d). As revealed by single crystal XRD the lithium salt crystallizes in the orthorhombic space group Cmcm with Z = 4, the cesium compound in the monoclinic space group P2 1 /n with Z = 4, and the sodium salt in the triclinic space group P1 with Z = 1. Angular-dependent EPR measurements show characteristics of linear chain compounds and magnetic susceptibility measurements indicate antiferromagnetic interactions. Heat capacity data reveal that these compounds may find useful applications as magnetic refrigerants and heat sinks in the 250 mK region. The title compounds appear to be good model systems for theoretical investigations on low-dimensional magnetic lattices and for understanding aspects of Cr(VI)-based catalysis and carcinogenesis.-(CAGE, BRANT; GEYER, WILLIAM; ABBOUD, KHALIL A.; DALAL, BAR S.; Chem. Mater. 13 (2001) 3, 871-879; Dep.
In this work, a statistical time series method that is capable of effective multicopter rotor fault detection, identification, and quantification within a unified stochastic framework is introduced. The proposed framework is based on the functional model based method for fault magnitude estimation tackled within the context of statistical time series approaches. Estimator uncertainties are taken into account, and confidence intervals are provided for the fault magnitude of multicopter rotors. The framework employs functionally pooled (FP) models which are characterized by parameters that depend on the fault magnitude, as well as on proper statistical estimation and decision-making schemes. The validation and assessment is assessed via a proof-of-concept application to a hexacopter flying forward with a constant velocity under turbulence. The fault scenarios considered consist of the front and side rotor degradation ranging from healthy to complete failure with 20% fault increments. The method is shown to achieve fast fault detection, accurate identification, and precise magnitude estimation based on even a single measured signal obtained from aircraft sensors during flight. Furthermore, fault quantification is addressed via the use of both local ( boom acceleration) and global (IMU) sensors, with the signals collected from the boom supporting the identified faulty rotor proven to achieve better performance than the global signals, yet with a shorter signal length.
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