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Copyright of Boletín Latinoamericano y del Caribe de Plantas Medicinales y Aromáticas is the property of Universidad de Santiago de Chile and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The purpose of this article is to describe the development and validation of a Kerr effect magnetometer, built in order to promote the research on the magnetic properties of magnetic thin films. A conventional Kerr effect magnetometer uses a lock-in amplifier to detect changes in the Kerr signal. The construction of a Kerr effect magnetometer using instrumentation and transimpedance amplifiers is presented, avoiding the use of a lock-in amplifier which has a high economic cost. [ABSTRACT FROM AUTHOR]

Cyclic testing of four 1:4 scale buckling restrained braces (BRB), built with local materials and labor are realized. The braces consist of a configuration of steel plate core, an insulating surface, filling mortar as confining material and hollow steel structural as a confinement sleeve. The force-displacement curves, the characteristic curve of the braces and the adjustment strength factors are determined and studied. It is concluded that the tests satisfy the ac-ceptance criteria for qualifying cyclic testing. There is no stiffness degradation of hysteresis loops. The cumulative inelastic axial deformation of the specimen is higher than recommended normative. [ABSTRACT FROM AUTHOR]

Cobalt ferrite (CoFe2O4) nanoparticles were synthesized using polyethyleneglycol as surfactant in a simple reflux system and subsequently heat treated from 200°C to 800°C in N2 atmosphere. The samples were characterized using: X-ray diffraction, Infrared spectroscopy, Scanning electron microscopy, Transmission electron microscopy, Thermogravimetry, Differential scanning calorimetry, surface area and Vibrating sample magnetometry. Nanoparticles obtained crystallize with a spinel type cubic structure and an average size between 9 and 102 nm and a surface area between 77.6 and 14.9 m²/g. Magnetization measurements versus applied field verified the strong influence of synthesis conditions on the particle size and therefore on the magnetic properties. The maximum field magnetization M(H) shows hysteresis loops that not saturate at the maximum field applied, reaching a maximum magnetization of 44.62 emu/g. [ABSTRACT FROM AUTHOR]

Copyright of Revista Científica Guillermo de Ockham is the property of Revista Cientifica Guillermo de Ockham, Universidad de San Buenaventura and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The main characteristic of a material with ferroelectric properties is the hysteresis loop of its polarization. On the other hand, the information about the switching time is necessary in the application of the ferroelectric materials prepared as thin films in random access non volatile memories (NvFeRAM). On the other hand flexible systems to do ferroelectrics measurements can be implemented combining specific equipments controlled by a computer. In this work is described the upgrading of an installation to measure the hysteresis loops and the switching current transitory in thin films. The installation has been developed using the virtual instrumentation techniques, using conventional equipment of measurements coupled to a personal computer through a standard interface IEE488 and LabVIEW. [ABSTRACT FROM AUTHOR]

In this work, we analysed the behaviour of a buck-boost electronic converter. The objective of the zero hysteresis controller is to track user defined sinusoidal signals, usually featuring high power level and variable frequency, amplitude and wave form. The controller was implemented in the laboratory, where load and reference signal disturbances were introduced. The controller achieved a fast and adequate behaviour. The converter was implemented using a half bridge monophasic inverter, and a rapid control prototyping (RCP) DS1104 in real time for the control task. [ABSTRACT FROM AUTHOR]

Thin films were deposited by RF sputtering in oxygen atmosphere of the ferrite dopped with Mn and Zn in the Mn0.5Zn0.5Fe2O4 composition. We investigated their magnetic properties and its dependence with the thickness. Magnetic hysteresis loops were measured by a MOKE system (Magneto-Optical Kerr Effect) at room temperature. A critical grain size was observed, in which the pinning reaches its maximum value, suggesting the change from a monodomain to a multidomain regime. The hysteresis curves were evaluated by a phenomenological model that allows to evaluate the κ pinning parameter, which governs such behaviour. A correlation between the size of the superficial structures of the film and the strength of the pinning is suggested. [ABSTRACT FROM AUTHOR]

In this work we study the behavior of the hysteresis loops at low temperatures for ferrimagnetic nanoparticles of maghemite γ-Fe2O3 as the single ion Néel surface anisotropy increases in magnitude several decades respect to the core anisotropy. Our model employs a classical Heisenberg Hamiltonian which takes into account a coupling term involving Fe3+-Fe3+ magnetic nearest neighbors superexchange interactions in tetrahedral and octahedral sites, magnetocrystalline core and surface anisotropies as well as a Zeeman term. The Monte Carlo method implemented with a Metropolis dynamics was used as energy minimization tool. Results reveal remarkable changes in the magnetic structure contrasting with the single domain state as the surface anisotropy increases. Such changes are characterized by certain degree of surface disorder in the angular distribution of spins which propagates through the core via superexchange coupling. Finally, the influence of these changes in the magnetic structure upon the symmetry of the hysteresis loops and the onset of exchange bias, by analyzing the magnetization versus magnetic field curves, is presented and discussed. [ABSTRACT FROM AUTHOR]

This paper deals with calculations of hysteresis loops in soft magnetic materials. We obtain the hysteresis loops by means of the Jiles-Atherton model. The influence of domain walls pinning on the form of the loops and coercivity has been discussed. The theoretical hysteresis loops are compared with experimental hysteresis loops for NiZn ferrites thin films. The loops have been calculated by the expression: Mi = M[Mi-1(Hi-1),Hi] + C. [ABSTRACT FROM AUTHOR]

This experiment studies the hysteresis loop dependence of an elastic band to its length. From the hysteresis loop area which evidences the presence of a non-conservative force, we calculated the work conducted during the stretching and retracting process of the elastic band. The mechanical work loss during hysteresis loop increased as the length of the band is increases, following a lineal tendency. This result can be explained given that when the elastic band length is increased, the number of molecular bonds available for breakage also increases. Finally, we highlight the fact that this experiment can be carried out in a simple manner and at very low costs. [ABSTRACT FROM AUTHOR]

This paper describes the development of an installation to acquire the ferroelectric hysteresis loop of ceramic materials and to measure its characteristic parameters. The installation has been developed using the virtual instrumentation methods and is used in the characterization of ferroelectric materials developed by the Cuban groups of investigation in new materials and in laboratory practice of the matter Experimental Methods of the Physics. [ABSTRACT FROM AUTHOR]