Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni2+ substitution effect in Co1-xNixFe2O4 (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni2+ concentration. The M-H loops reveals that saturation magnetization(Ms), coercive field(Hc) remanence magnetization(Mr) and magnetron number(ηB) decreases significantly with increasing Ni2+ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(Hc) is found strongly dependent on the concentration of Ni2+ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni2+ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application. 相似文献
Tolerances are basic to the production of every part. This is because perfect parts cannot be produced with existing processes and machines. The determination of tolerances for the individual parts of a functional assembly is critical, but not trivial. Numerous approaches are suggested in past literature for (analytical) tolerance allocation. With the advent of total automation, more attempts are being made to computerize manual design tasks. Tolerance design, assignment and allocation can also be fully automated if the assembly function can be estimated by the computer.
In the present paper, an attempt is made to computerize tolerance assignment. A simple example of a two piece assembly, viz., a fit, is used to demonstrate the developed methodology. A feature extraction is first performed from both detail and assembly drawings. Then, probable assembly interfaces are determined using a rule based procedure. Consequently, tolerances are assigned to the basic dimensions of each feature and to the assembly interfaces using a tolerance database and user interaction. More complex analysis for tolerance allocation is also under study. 相似文献
Several methods have been investigated to determine the deviation of manufactured spherical parts from ideal geometry. One of the most popular is the least squares technique, which is still widely employed in coordinate measuring machines used by industries. The least squares algorithm is optimal under the assumption that the data set is very large and has the inherent disadvantage of overestimating the minimum tolerance zone, resulting sometimes in the rejection of good parts. In addition, it requires that the data be distributed normally. The support vector regression approach alleviates the necessity for these assumptions. While most fitting algorithms in practice today require that the sampled data accurately represent the surface being inspected, support vector regression provides a generalization over the surface. We describe how the concepts of support vector regression can be applied to the determination of tolerance zones of nonlinear surfaces; to demonstrate the unique potential of support vector machine algorithms in the area of coordinate metrology. In specific, we address part quality inspection of spherical geometries. 相似文献
Phosphorus (P) enrichment can lead to imbalance in nutrient availability and pollution of terrestrial and aquatic ecosystems. Hence studies were carried out to investigate fractionation and sorption of P in eleven P-enriched soils collected from different agro-climatic sites in Norway. Different P fractions viz. total, organic, inorganic (easily soluble P, Fe-P, Al-P, Ca-P and occluded P), Pw (water extractable), and NH4-lactate extractable P (PAL) at the beginning and after the completion of the experiments varied widely among the soils studied, indicating a wide variability of P supplying capacity of these soils. Soluble P was positively correlated to Ca-P (r = 0.94; P < 0.001), Pw (r = 0.87; P < 0.001), pH (r = 0.79; P < 0.01) and PAL (r = 0.79; P < 0.01), whereas it was negatively correlated with ammonium oxalate-extractable Al (Alox) (r = ?0.68; P < 0.05). Iron-P was only moderately related to Alox(r = 0.64; P < 0.05) and Pox(r = 0.70; P < 0.05), whereas it was not related to any of the other parameters tested. The α [α = Pox/(Feox + Alox)] was highly correlated with PAL (r = 0.93; P < 0.001), pH (r = 0.87; P < 0.001), inorganic P (r = 0.80; P < 0.01) and Pw(r = 0.77; P < 0.01) but moderately to total P (r = 0.71; P < 0.05). Adsorption data fitted well to the Langmuir equation for most soils. The P affinity constant (k), adsorption maximum (b) and thus maximum buffering capacity (mbc) and adsorption isotherm of P were highest in the sandy clay soil from Øsaker, which also contained high amounts of Fe, Al and clay particles and the lowest in sandy soil from Vestrålen, which contained very high initial PALand the lowest content of Fe, Al, silt and clay among all the soils studied. The P affinity constant (k) was correlated positively and significantly to clay content (r = 0.66; P < 0.05), whereas mbc was correlated positively and significantly to clay content (r = 0.63; P < 0.05) and ammonium oxalate-extractable Fe (Feox) (r = 0.63; P < 0.05). Phosphorus desorption of the soils varied widely depending on the initial P status and texture of the soils. Phosphorus desorbed by NH4-lactate was many fold higher as compared to CaCl2 in most soils. 相似文献
We investigate the ability to move of large objects—referred to as intruders—embedded in a granular material and subjected to cyclic loadings. A discrete element method is used to simulate the dynamics response of intruders subjected to a vertical uplift cyclic force, exploring a wide range of loading magnitudes and frequencies. The analysis of the intruder and grains displacements over many cycles reveals three mobility regimes. In the first two regimes, called confined and failure the intruder either do not significantly move or consistently moves upward after each cycles. We introduce a physically based model considering an inertial drag force to rationalise the existence of these regimes depending on the loading frequency and magnitude. We further evidence a third intermediate regime of creep, where intruder trajectories exhibit long periods of confinement punctuated by shorter periods of sustained uplift motion. Finally, we observe unexpected failures at low loading magnitudes and specific frequencies, which we attribute to a process of elasto-inertial resonance. These results highlight the important differences in the mobility of intruders upon constant and cyclic loadings. 相似文献
This paper presents the influence of cylindricity and surface modification on load bearing ability of interference fitted assemblies. Assemblies were made of EN 8 steel with and without (plain) nubs. The influence of cylindrical profile or waviness of pins, with and without nubs on load bearing ability is analyzed by experimental and harmonic analysis. Results show that pins with nubs can carry higher load and pins with and without nubs having harmonics of smaller amplitude can carry higher load for a given interference. Also, increase in average undulation number increases the load bearing ability. Further, finite element method (FEM) was used to evaluate the Von Mises stresses on the performance of interference fitted assemblies. An appropriate finite element model was developed to analyze the pattern of contact stresses in interference fitted assemblies for with and without nubs with varying interference. The results reveal that pins with nubs can with stand higher stresses. 相似文献
This paper analyzes the influence of electric poling on structure, magnetism, and ferroelectricity by temperature-dependent Raman scattering (180 K–500 K), magnetic susceptibility, and ferroelectric measurements on Pb0.9Bi0.1Fe0.55Nb0.45O3 (PBFNO) multiferroic. X-ray diffraction (XRD) has confirmed the monoclinic structure for PBFNO sample before and after poling. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb–O, and Bi-O modes with small variation in the lattice parameters. The unpoled PBFNO exhibits broad and overlapping 10 active modes at room temperature (100 to 1300 cm?1) at 147, 212, 255, 431, 479, 561, 700, 795, 835, and 1112 cm?1. In case of a poled sample, Pb–O and Nb–O-Nb modes become more active compared to the unpoled sample. Changes observed in the temperature-dependent magnetic measurements, i.e., ZFC/FC and M-H loop, evidence the poling effects on Fe–O and Nb–O active modes. By poling the improvement in ferroelectric domain, ordering occurs, and it is confirmed by P-E loops. The consequences of numerous investigations on electric poling of PBFNO will provide the foundation for future device development and design.