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Magnetic Flux Density (magnetic + flux_density)

Distribution by Scientific Domains
Medical Sciences11%

Selected Abstracts

Polarimetry in Solar and Stellar Physics , Techniques, Observations and Diagnostics

ASTRONOMISCHE NACHRICHTEN, Issue S3 2003
Horst BalthasarArticle first published online: 18 JUL 200
D01 Split Pupil Imaging Polarimeters for Optical Night Time Astronomy D02 The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) for the LBT D03 Velocity and Magnetic Fields in Sunspot Penumbrae at Hight Spatial and Spectral Resolution D04 Infrared Polarimetry at the MPAe: The Solar Atmosphere from the Photosphere to the Upper Chromosphere D05 Properties of a Simple Sunspot Observed in the Near Infrared D06 Hausdorff-Dimension of Magnetic Structures D07 Distribution of the Magnetic Flux Density at the Solar Surface [source]

ELF-magnetic flux densities measured in a city environment in summer and winter

BIOELECTROMAGNETICS, Issue 1 2008
Aksel Straume
Abstract Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4,µT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4,µT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13,µT (summer), 0.85,µT (winter, cold), and 0.90,µT (winter, snow), with the highest recorded value of 37,µT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate. Bioelectromagnetics 29:20,28, 2008. © 2007 Wiley-Liss, Inc. [source]

Some remarks concerning the measurement of the ferromagnetic losses under non-sinusoidal conditions

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2002
Andrei, ugulea
The present standards concerning the measurement of the losses in ferromagnetic media, namely the IEC publications 404-2 (1978), 404-;3 (1982) and 404,10 (1988), refer only to the magnetic flux densities between 1 T and 1.85 T, if the magnetic sheets are grain oriented, and 1 T and 1.5 T if the magnetic sheets are nonoriented. The time variation of the magnetic fluxes must be almost sinusoidal at industrial frequencies of 50 Hz or 60 Hz and medium frequencies between 400 Hz and 10,000 Hz. In the above-mentioned standards there are no references concerning the measurement of losses under non-sinusoidal conditions. The paper deals with some theoretical aspects concerning the power-flows under non-sinusoidal time variation of the electromagnetic fields. The theoretical conclusions are applied to the study of the losses in ferromagnetic media. It is shown that new norms or standards are necessary. Some practical suggestions are given at the end. [source]

Static Magnetic Fields Affect Capillary Flow of Red Blood Cells in Striated Skin Muscle

MICROCIRCULATION, Issue 1 2008
Gunnar Brix
ABSTRACT Blood flowing in microvessels is one possible site of action of static magnetic fields (SMFs). We evaluated SMF effects on capillary flow of red blood cells (RBCs) in unanesthetized hamsters, using a skinfold chamber technique for intravital fluorescence microscopy. By this approach, capillary RBC velocities (vRBC), capillary diameters (D), arteriolar diameters (Dart), and functional vessel densities (FVD) were measured in striated skin muscle at different magnetic flux densities. Exposure above a threshold level of about 500 mT resulted in a significant (P < 0.001) reduction of vRBC in capillaries as compared to the baseline value. At the maximum field strength of 587 mT, vRBC was reduced by more than 40%. Flow reduction was reversible when the field strength was decreased below the threshold level. In contrast, mean values determined at different exposure levels for the parameters D, Dart, and FVD did not vary by more than 5%. Blood flow through capillary networks is affected by strong SMFs directed perpendicular to the vessels. Since the influence of SMFs on blood flow in microvessels directed parallel to the field as well as on collateral blood supply could not be studied, our findings should be carefully interpreted with respect to the setting of safety guidelines. [source]

ELF-magnetic flux densities measured in a city environment in summer and winter

BIOELECTROMAGNETICS, Issue 1 2008
Aksel Straume
Abstract Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4,µT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4,µT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13,µT (summer), 0.85,µT (winter, cold), and 0.90,µT (winter, snow), with the highest recorded value of 37,µT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate. Bioelectromagnetics 29:20,28, 2008. © 2007 Wiley-Liss, Inc. [source]

Metabolic effects of static magnetic fields on streptococcus pyogenes

BIOELECTROMAGNETICS, Issue 6 2007
A.C. Morrow
Abstract This study aimed to develop a simple experimental system utilising bacterial cells to investigate the dose responses resulting from exposures to static magnetic flux densities ranging from 0.05 to 0.5 T on viability, bacterial metabolism and levels of DNA damage in Streptococcus pyogenes. Exposure of S. pyogenes to a field of 0.3 T at 24 °C under anaerobic conditions resulted in a significant (P,<,0.05) decrease in growth rate, with an increased mean generation time of 199,±,6 min compared to the control cells at 165,±,6 min (P,<,0.05). Conversely, exposure to magnetic fields of 0.5 T significantly accelerated the growth rate at 24 °C compared to control cells, with a decreased mean generation time of 147,±,4 min (P,<,0.05). The patterns of metabolite release from cells incubated in phosphate buffered saline (PBS) at 24 °C and exposed to different magnetic flux densities (0.05,0.5 T) were significantly (P,<,0.05) altered, compared to non-exposed controls. Concentrations of metabolites, with the exception of aspartic acid (r,=,0.44), were not linearly correlated with magnetic flux density, with all other r,<,0.20. Instead, "window" effects were observed, with 0.25,0.3 T eliciting the maximal release of the majority of metabolites, suggesting that magnetic fields of these strengths had significant impacts on metabolic homeostasis in S. pyogenes. The exposure of cells to 0.3 T was also found to significantly reduce the yield of 8-hydroxyguanine in extracted DNA compared to controls, suggesting some possible anti-oxidant protection to S. pyogenes at this field strength. Bioelectromagnetics 28:439,445, 2007. © 2007 Wiley-Liss, Inc. [source]

Numerical computation of distortions in magnetic fields and induced currents in physiological solutions produced by microscope objectives

BIOELECTROMAGNETICS, Issue 7 2001
Indira Chatterjee
Abstract Identifying distortions produced by commonly employed microscope objectives and their components in uniform DC and 60 Hz AC magnetic fields is important in imaging studies involving exposure of cells to spatially uniform or nonuniform magnetic fields. In this study, DC and 60 Hz AC magnetic flux densities were numerically computed in the presence of finite element models of various components of commonly utilized microscope objectives, as well as a model of a complete objective. Also computed were the distortions in the current density induced by an applied time-varying magnetic field in a physiological buffer contained within a Petri dish. We show that the magnetic flux density could be increased up to 65% in the presence of the nickel,chrome plating of an objective housing and that the presence of ferromagnetic components like a screw or spring could produce peaks that are 7% higher than the undistorted value of magnetic flux density. In addition, a slight tilt of 1% in the objective with respect to the magnetic field could cause a 93% deviation in magnetic flux density from the unperturbed value. These results correlate well with previously published experimental measurements that showed the presence of significant and sometimes asymmetric distortions in both DC and 60 Hz magnetic fields. Moreover, this study further reports that induced current density changed up to 37% compared to values in the absence of the objective. The existence of distortions in applied magnetic fields and induced currents could affect the interpretation of results of cell function studies if it is assumed that the cells are exposed to uniform magnetic flux densities in the presence of a microscope objective. Such assumptions of uniform magnetic flux density could also account for the lack of reproducibility in several studies that examined changes in intracellular calcium by imaging techniques. Bioelectromagnetics 22:463,469, 2001. © 2001 Wiley-Liss, Inc. [source]

Cytological effects of 60,Hz magnetic fields on human lymphocytes in vitro: sister-chromatid exchanges, cell kinetics and mitotic rate

BIOELECTROMAGNETICS, Issue 3 2001
J. Antonio Heredia, Rojas
Abstract Incubation for 72,h of human peripheral blood cultures in the presence of 60,Hz sinusoidal magnetic fields (MF) at magnetic flux densities of 1.0, 1.5, and 2.0,mT led to stimulation of lymphocyte proliferation but had no influence on the frequency of sister-chromatid exchanges (SCE). The cytotoxic potential of MF combined with the mutagen Mitomycin-C also was analyzed. An opposite effect between MF exposure and Mitomycin-C treatment in terms of cell kinetics and mitotic rate was found, whereas no variation in SCE frequency was observed for this coexposure condition. Bioelectromagnetics 22:145,149, 2001. © 2001 Wiley-Liss, Inc. [source]

A new contact design based on a quadrupolar axial magnetic field and its characteristics

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2000
H. Fink
Axial magnetic field (AMF) contacts are applied within vacuum interrupters especially in case of high short-circuit current. In this paper a new AMF contact design based on a quadrupolar field arrangement and its characteristics are presented. In the first part the basic principle of the new contact design is introduced. This is followed by three-dimensional field simulations performed with the aid of a Finite-Element-program. The magnitude of the axial magnetic flux density, the phase-shift between current and magnetic flux density, and the current flow within the contact plate are investigated during arcing. The impact of quadrupolar AMF on the arc behaviour during the high current phase is analysed by high-speed films and pictures of the contact surface after arcing. The interruption performance of the principle has been validated by short-circuit tests up to 12 kV/63 kA. [source]

Magneto-motive detection of tissue-based macrophages by differential phase optical coherence tomography

LASERS IN SURGERY AND MEDICINE, Issue 3 2007
Junghwan Oh PhD
Abstract Background and Objectives A novel method to detect tissue-based macrophages using a combination of superparamagnetic iron oxide (SPIO) nanoparticles and differential phase optical coherence tomography (DP-OCT) with an external oscillating magnetic field is reported. Study Design/Material and Methods Magnetic force acting on iron-laden tissue-based macrophages was varied by applying a sinusoidal current to a solenoid containing a conical iron core that substantially focused and increased magnetic flux density. Results Nanoparticle motion was detected with DP-OCT, which can detect tissue movement with nanometer resolution. Frequency response of iron-laden tissue movement was twice the modulation frequency since the magnetic force is proportional to the product of magnetic flux density and gradient. Conclusions Results of our experiments indicate that DP-OCT can be used to identify tissue-based macrophage when excited by an external focused oscillating magnetic field. Lasers Surg. Med. 39:266,272, 2007. © 2007 Wiley-Liss, Inc. [source]

Effects of strong static magnetic fields used in magnetic resonance imaging on insulin-secreting cells

BIOELECTROMAGNETICS, Issue 1 2009
Tomonori Sakurai
Abstract The magnetic flux density of MRI for clinical diagnosis has been steadily increasing. However, there remains very little biological data regarding the effect of strong static magnetic fields (SMFs) on human health. To evaluate the effects of strong SMFs on biological systems, we cultured insulin-secreting cells under exposure to sham and SMF conditions (3,10 T of magnetic flux density, and 0,41.7 T/m of magnetic field gradient) for 0.5 or 1 h, and analyzed insulin secretion, mRNA expression, glucose-stimulated insulin secretion, insulin content, cell proliferation and cell number. Exposure to SMF with a high magnetic field gradient for 1 h significantly increased insulin secretion and insulin 1 mRNA expression. Exposure to SMF with a high magnetic flux density for 0.5 h significantly enhanced responsiveness to glucose stimulation. Exposure to SMF did not affect the insulin content, cell proliferation or cell number. Our results suggested that MRI systems with a higher magnetic flux density might not cause cell proliferative or functional damages on insulin-secreting cells, and that SMF with a high magnetic field gradient might be used clinically after thorough in vivo investigations are conducted. Bioelectromagnetics 30:1,8, 2009. © 2008 Wiley-Liss, Inc. [source]

ELF-magnetic flux densities measured in a city environment in summer and winter

BIOELECTROMAGNETICS, Issue 1 2008
Aksel Straume
Abstract Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4,µT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4,µT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13,µT (summer), 0.85,µT (winter, cold), and 0.90,µT (winter, snow), with the highest recorded value of 37,µT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate. Bioelectromagnetics 29:20,28, 2008. © 2007 Wiley-Liss, Inc. [source]

Metabolic effects of static magnetic fields on streptococcus pyogenes

BIOELECTROMAGNETICS, Issue 6 2007
A.C. Morrow
Abstract This study aimed to develop a simple experimental system utilising bacterial cells to investigate the dose responses resulting from exposures to static magnetic flux densities ranging from 0.05 to 0.5 T on viability, bacterial metabolism and levels of DNA damage in Streptococcus pyogenes. Exposure of S. pyogenes to a field of 0.3 T at 24 °C under anaerobic conditions resulted in a significant (P,<,0.05) decrease in growth rate, with an increased mean generation time of 199,±,6 min compared to the control cells at 165,±,6 min (P,<,0.05). Conversely, exposure to magnetic fields of 0.5 T significantly accelerated the growth rate at 24 °C compared to control cells, with a decreased mean generation time of 147,±,4 min (P,<,0.05). The patterns of metabolite release from cells incubated in phosphate buffered saline (PBS) at 24 °C and exposed to different magnetic flux densities (0.05,0.5 T) were significantly (P,<,0.05) altered, compared to non-exposed controls. Concentrations of metabolites, with the exception of aspartic acid (r,=,0.44), were not linearly correlated with magnetic flux density, with all other r,<,0.20. Instead, "window" effects were observed, with 0.25,0.3 T eliciting the maximal release of the majority of metabolites, suggesting that magnetic fields of these strengths had significant impacts on metabolic homeostasis in S. pyogenes. The exposure of cells to 0.3 T was also found to significantly reduce the yield of 8-hydroxyguanine in extracted DNA compared to controls, suggesting some possible anti-oxidant protection to S. pyogenes at this field strength. Bioelectromagnetics 28:439,445, 2007. © 2007 Wiley-Liss, Inc. [source]

Effects of a 50 Hz sinusoidal magnetic field on cell adhesion molecule expression in two human osteosarcoma cell lines (MG-63 and Saos-2)

BIOELECTROMAGNETICS, Issue 5 2003
Maria Teresa Santini
Abstract The possibility that a sinusoidal 50 Hz magnetic field with a magnetic flux density of 0.5 mT can induce variations in the expression of cell adhesion molecules (CAMs) in two human osteosarcoma cell lines (MG-63 and Saos-2) was investigated. In particular, the expression of two important integrins, VLA-2, the receptor for collagen, and VLA-5, the receptor for fibronectin, as well as CD44, were examined in both cell lines after these had been exposed for 7 and 14 days to a 50 Hz, 0.5 mT field. Cell surface morphology (scanning electron microscopy), cell growth characteristics (growth curves and cell cycle phase distribution), and cell death (necrosis and apoptosis) were also examined. The results demonstrate that no variations in surface morphology and cell death occurred between control and exposed cells in both MG-63 and Saos-2 cells, while significant changes were noted in cell growth and fibronectin and CD44 expression in MG-63 cells. The results are discussed in view of the important role that CAMs play in controlling various cancer cell functions, particularly proliferation and metastasis. Bioelectromagnetics 24:327-338, 2003. © 2003 Wiley-Liss, Inc. [source]

Numerical computation of distortions in magnetic fields and induced currents in physiological solutions produced by microscope objectives

BIOELECTROMAGNETICS, Issue 7 2001
Indira Chatterjee
Abstract Identifying distortions produced by commonly employed microscope objectives and their components in uniform DC and 60 Hz AC magnetic fields is important in imaging studies involving exposure of cells to spatially uniform or nonuniform magnetic fields. In this study, DC and 60 Hz AC magnetic flux densities were numerically computed in the presence of finite element models of various components of commonly utilized microscope objectives, as well as a model of a complete objective. Also computed were the distortions in the current density induced by an applied time-varying magnetic field in a physiological buffer contained within a Petri dish. We show that the magnetic flux density could be increased up to 65% in the presence of the nickel,chrome plating of an objective housing and that the presence of ferromagnetic components like a screw or spring could produce peaks that are 7% higher than the undistorted value of magnetic flux density. In addition, a slight tilt of 1% in the objective with respect to the magnetic field could cause a 93% deviation in magnetic flux density from the unperturbed value. These results correlate well with previously published experimental measurements that showed the presence of significant and sometimes asymmetric distortions in both DC and 60 Hz magnetic fields. Moreover, this study further reports that induced current density changed up to 37% compared to values in the absence of the objective. The existence of distortions in applied magnetic fields and induced currents could affect the interpretation of results of cell function studies if it is assumed that the cells are exposed to uniform magnetic flux densities in the presence of a microscope objective. Such assumptions of uniform magnetic flux density could also account for the lack of reproducibility in several studies that examined changes in intracellular calcium by imaging techniques. Bioelectromagnetics 22:463,469, 2001. © 2001 Wiley-Liss, Inc. [source]