Measuring magnetic fields

Magnetism often has a slight overtone of being mysterious. This is probably caused by the surprisingly strong forces between magnets which everybody can experience with magnetic toys, magnet boards, or similar objects. A strange effect is the unique ability of magnetic fields to penetrate many substances without any attenuation. Though the physical basis of magnetism is well explored, the outsider usually does not know very much about the details and sometimes tends to overestimate the real possibilities provided by magnetism.

656p chuyenphimbuon 21-07-2012 46 9   Download

In this paper, we consider the mean-field Heisenberg model with deterministic external magnetic field. We prove a large deviation principle for Sn/n with respect to the associated Gibbs measure, where Sn/n is the scaled partial sum of spins. In particular, we obtain an explicit expression for the rate function.

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Photon - axion conversions in static electromagnetic fields of the size a × b × c are considered in detail by the Feynman diagram methods. The differential cross sections are presented and the numerical evaluations of the total cross section are given. Our result shows that the conversion cross-sections in the electric field are quite small, while in the strong magnetic field, the cross-sections are much enhanced, which can be measurable in current experiments.

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This paper presents the study results on the fabrication of a structural integrity assessment apparatus by determining stress concentration zones in pressure pipeline and equipment. The apparatus uses a triaxial magnetic field sensor to measure magnetic field components in three axes Ox, Oy, and Oz, in the working range of the magnetic field from -300 µT to 300 µT.

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The result of magnetization measurements showed that the magnetization at a magnetic field as high as 1 T abnormally depends on x, increases with increasing x to a maximum at x=0.1 then decreases monotonously afterward. There are possibilities to account for this anomalous magnetic behavior such as the Fe3+-to-Fe4+ and/or Ti4+-to-Ti3+ change(s) induced by oxygen vacancies. The substitution of Fe into Ti sites also changes the conductivity of the material and impurity (acceptor) levels in the band gap.

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The Potts model on a Cayley tree in the presence of competing two binary interactions and magnetic field is considered. We exactly solve a problem of phase transitions for the model, namely we calculate critical surface such that there is a phase transition above it and a single Gibbs state found elsewhere.

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It has been observed that some geophysical parameters could be changed during a solar eclipse. We have therefore measured gravity and magnetic fields during solar eclipses. We also measured the gravity field during the previous eclipse on the 11th of August, 1999.

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A concept of a planar vector magnetic sensor comprising in-plane tunnel magnetoresistive (TMR) sensors and an active flux-guide (AFG) was introduced in this work. The AFG redirected the magnetic flux at high-frequency benefiting a vertical detection capability and suppressing the field noise of the TMR at low-frequency measurement. The vertical sensitivity of 19.5 V/T was close to the in-plane sensitivity of 19.2 V/T.

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Influence of substitution of 3d metals for Mn on properties of La0.67Ca0.33Mn0.9 TM0.1O3 (TM = Fe, Co, Ni) compounds was studied. Ferromagnetic – paramagnetic and metals – insulator transitions were significantly affected by Mn-site substitution. However, no observable difference was found in their crystal structure from X-ray diffraction analysis. At room temperature the structure characterization of these compounds gave the single phase and structure is the distortion orthorhombic cell with space group symmetry Pnma.

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The study of microstructure shows no obvious change of grain size and shape. The magnetic properties of the as-prepared samples show the linear magnetic field dependence of magnetization, suggesting the antiferromagnetic feature of polycrystalline ceramics. The field dependence of magnetization measured after two-years synthesis and after applying an electric field reveal a decrease of maximum magnetization but the hysteresis loops retain the antiferromagnetic behavior.

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The field of medical imaging is advancing at a rapid pace. Imaging modalities like x-ray radiography, x-ray computed tomography (CT), ultrasound, nuclear imaging, magnetic resonance imaging (MRI), and optical imaging have been used in biology and medicine to visualize anatomical structures as large as the lung and liver and as small as molecules. Ultrasound is considered the most cost-effective among them. It is used routinely in hospitals and clinics for diagnosing a variety of diseases.

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The West Pearl Queen reservoir project also used soil gas surveys to detect PFC tracers that were injected into the reservoir with the CO2. Soil gas sampling was conducted before and after the CO2 injection by using capillary tubes and adsorbent packets for the tracers. Brookhaven National Laboratory (BNL) supplied the tracers and performed the tracer concentration analysis (Wells et al., 2007). Near-Surface Geophysics – The use of magnetometers is another possible near-surface geophysical technique.

140p bin_pham 06-02-2013 45 3   Download

Today, research and technology play a decisive role for the European food sector for the development of new products as well as for improved safety measures. In July 2000, DG RTD requested a study on potential future European research priorities in food technology and food safety from the Institute for Prospective Technological Studies (IPTS), Joint Research Centre. The study design comprised the involvement of external expertise from industry as well as from academia: The results of the study were derived from two experts workshops held in Sevilla at the IPTS in December 2000 and May 2001.

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The Gaussian spin fluctuation theory is applied to study magnetic properties (Curie temperature, magnetization) of EuO ultra-thin films within nearest neighbor and next nearest neighbor exchange approximation. The dependence of Curie temperature on the thickness of the free EuO ultrathin film is calculated and compared with the results of the other mean field methodconstant coupling approximation. The effect of nearly independence of saturation magnetization on the EuO films thickness measured in [8] can be explained by controlling the next nearest neighbor exchange in presence of substrates.

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In this work, a highly sensitive low-field magnetometer has been implemented for navigation, electronic compass, and monitoring security. The sensor structure consists of the soft-magnetic core cobalt base, the excitation coil, and the sensing coil. A current passing through the excitation coil at high frequency modulates the permeability of the soft magnetic core.

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Magnetization and Curie temperature of the samples were measured with the SQUID and VSM equipments. The non-magnetic indium ions were found to reside at the octahedral sites, leading to an increase of the total magnetization and a decrease in the Curie temperature. Molecular field coefficients Naa, Ndd and Nad were determined by fitting the experimental thermomagnetization curves in the framework of a two-sublattice ferrimagnetic model.

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The intrinsic muscles of the foot are key contributors to foot function and are important to evaluate in lower limb disorders. Magnetic resonance imaging (MRI), provides a non-invasive option to measure muscle morphology and composition, which are primary determinants of muscle function. Ultra-high-field (7-T) magnetic resonance imaging provides sufficient signal to evaluate the morphology of the intrinsic foot muscles, and, when combined with chemical-shift sequences, measures of muscle composition can be obtained.

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Summary. In this introductory chapter, the definition and history of tribology and their industrial significance and origins and significance of an emerging field of micro/nanotribology are described. Next, various measurement techniques used in micro/nanotribological and micro/nanomechanical studies are described. The interest in micro/nanotribology field grew from magnetic storage devices and latter the applicability to emerging field micro/nanoelectromechanical systems (MEMS/NEMS) became clear.

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The first edition of the Handbook of Micro/Nanotribology was published in the Spring of 1995. Soon after its publication, the first-of-a-kind monograph became a reference book for the novice, as well as experts, in the emerging field of micro/nanotribology. Since the field is evolving very rapidly, we felt that the monograph needed a second edition. The second edition is totally revised. The scope of the first edition has been expanded. In the first part, Basic Studies, two new chapters on AFM Instrumentation and Tips and Surface Forces and Adhesion have been added.

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