Geometric finite-time inner-outer loop trajectory tracking control strategy for quadrotor slung-load transportation

Nonlinear Dynamics - This paper presents a geometric finite-time inner-outer loop control strategy for slung payload transportation using a quadrotor. The underactuated nature of the quadrotor in...     

Mössbauer Studies of Nanosize CuFe2O4 Particles

⁵⁷Fe Mössbauer spectra of pulsed-laser deposited (PLD) films of CoFe₂O₄ of 0.3 µm thickness is investigated using transmission geometry is reported. Mössbauer parameters were determined for the tetrahedral (A) and octahedral (B) sites. The PLD processed films gave measurable spectra with no visible evidence of clustering or multiple phases present. Results on the films agreed with those of the bulk material. The films exhibited magnetic hyperfine and quadruple splittings similar to that of bulk CoFe₂O₄. This work demonstrates that measurable transmission Mössbauer spectra may be obtained for PLD deposited CoFe₂O₄ thick films.     

Mössbauer studies of ɛ-Fe3−x Ni x N and γ′-Fe4−y Ni y N nanoparticles

Nanocrystalline ?-Fe_3?x Ni _x N (0.0?≤?×?≤?0.8) particles are synthesized by precursor technique and nitridation of decomposed products in NH₃ (g) in the temperature range 673 K-823 K. For x?=?0.1–0.4 compositions, single phase ?-Fe_3?x Ni _x N hexagonal structure with space group P6₃/mmc is formed, while for x?=?0.5–0.8, fcc γ′-Fe_4?y Ni _y N phase is also precipitated. The room temperature Mössbauer spectrum for all the compositions shows the presence of superparamagnetic doublet, which is attributed to ?-Fe_3?x Ni _x N phase. For x?=?0.5–0.8 compositions, two additional sextets are observed corresponding to two different iron sites, the corner position (Fe^c) and the fcc position (Fe^f), in γ′-Fe_4?y Ni _y N. The added Ni atoms preferentially substitute the corner Fe^c positions. The isomer shift, quadrupole splitting and hyperfine field values are found to change with the Ni content.     

Mössbauer and magnetic studies on nanocrystalline NiFe2O4 particles prepared by ethylene glycol route

NiFe₂O₄ nanoparticles have been synthesized by co-precipitation method at 145°C in N₂ atmosphere using ethylene glycol as solvent and capping agent. This gives the promising synthesis route for nanoparticles at low temperature. The as-synthesized NiFe₂O₄ is subsequently heated at 400°C, 500°C, 700°C and 800°C. Crystallite size increases with the heat treatment temperature. The heat treatment temperature has direct effect on the electron paramagnetic resonance and intrinsic magnetic properties. The room temperature Mössbauer spectrum of the 800°C heated sample shows the two sextets pattern indicating that the sample is ferrimagnetic and Fe^3?+? ions occupy both tetrahedral and octahedral sites of spinel structure.     

Synthesis of Ultrafine Cobalt Ferrite by Thermal Decomposition of Citrate Precursor

Ultrafine particle of CoFe2O4 has been synthesized using citrate precursor technique. Thermal decomposition of the citrate precursor, Co3Fe6O4(C6H6O7)8·6H2O, was investigated by TG, DTA and DTG techniques, gas and chemical analyses and was found to decompose in one or two major steps depending on the heating rate in static/flowing air atmosphere. In the lower heating rate (5°C min-1), metastable acetonedicarboxylate complex was isolated with the evolution of CO gas and coordinated water molecule in the temperature range of 120-220°C. Complete decomposition of the citrate network occurs between 220-330°C with the simultaneous evolution of CO2 and acetone. However both these steps appeared as simultaneous and/or single step process (between 120-160°C), when the heating rate is high (10°C min-1 and above). The ultrafine CoFe2O4 particles are observed as the aggregates having surface area 133.8 m2 g-1 composed of 4.8 nm crystallites. The citrate precursor and the decomposed products were characterized by IR, NMR, XRD, SEM and surface area measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

A GC-ECD method for estimation of free and bound amino acids, gamma-aminobutyric acid, salicylic acid, and acetyl salicylic acid from Solanum lycopersicum (L.)

A gas chromatograph with electron capture detection method for estimation of selected metabolites--amino acids (free and bound), gamma-aminobutyric acid (GABA), salicylic acid (SA), and acetyl salicylic acid (ASA) from tomato--is reported. The method is based on nitrophenylation of the metabolites by 1-fluoro-2, 4-dinitrobenzene under aqueous alkaline conditions to form dinitophenyl derivatives. The derivatives were stable under the operating conditions of GC. Analysis of bound amino acids comprised perchloric acid precipitation of protein, alkylation (carboxymethylation) with iodoacetic acid, vapor-phase hydrolysis, and derivatization with 1-fluoro-2,4-dinitrobenzene in that order. The metabolites were resolved in 35 min, using a temperature-programmed run. The method is rapid, sensitive, and precise. It easily measured the typical amino acids (aspartate, asparagine, glutamate, glutamine, alanine, leucine, lysine, and phenylalanine) used for identification and quantification of a protein, resolved amino acids of the same mass (leucine and isoleucine), satisfactorily measured sulfur amino acid (methionine, cystine, and cysteine), and quantified GABA, SA, and ASA, as well. The developed method was validated for specificity, linearity, and precision. It has been applied and recommended for estimation of 25 metabolites from Solanum lycopersicum (L.).     

Magnetic and Mössbauer study of ε-Fe<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>N (2 < <Emphasis Type="Italic">y</Emphasis> < 3) nanoparticles

ε-Fe _y N (2 < y < 3) nanoparticles were prepared by the nitridation of spindle type hematite nanoparticles using ammonia at a temperature of 550 °C. Chemical analysis for the elements brings out the composition as y = 2.56. These nanoparticles show ferromagnetic behaviour even though it has higher nitrogen content than the stoichiometric Fe₃N. The quenching of the particles from higher temperature and the higher nitrogen content introduces disorder in the system unlike the ordered ε-Fe₃N. Mössbauer spectroscopy at lower temperature clearly shows the existence of two sextets corresponds to the two types of iron environments. The presence of more than one site excludes perfect ordering. This is consistent with the peak widths which result from variations in the distributions of next nearest interstitial neighbours. Existence of two different Debye temperatures for two iron sites shows that it varies according to the number and type of neighbouring atoms.