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PubMed2002

An open magnet utilizing ferro-refraction current magnification.

Ferro-refraction is the field magnification that is obtained when a current segment is near a high magnetic permeable boundary. It is shown that ferro-refraction may be used in the design of magnets for NMR or MRI to increase the efficiency of these magnets. The field may be modeled analytically with the Biot--Savart law and the inclusion of mirror image currents. Ferro-refraction is particularly useful in the design of monohedral magnets, magnets producing a remote homogeneous region which have the magnetic sources arranged to one side. These magnets have also been called planar magnets. Two designs for a monohedral magnet which produce good agreement between experimental and analytic results are presented.

Journal Article↗
PubMed1996

Discrepancy between brain magnetic fields elicited by pattern and luminance stimulations in the fovea: adequate stimulus positions and a measure of discrepancy.

A conventional equivalent current dipole estimation provides one of the quantitative measures to evaluate the discrepancy between two single-dipole-like magnetic field patterns, though there is one problem; all stimulus positions in the visual field do not necessarily contribute to the generation of a single-dipole-like magnetic field. Another important problem occurs when the field pattern is complex and cannot be approximated by a dipole. This makes it difficult to evaluate the discrepancy between two magnetic field patterns by the dipole parameters. In this paper, we determined the stimulus positions adequate for generating single-dipole-like magnetic field patterns by evaluating the magnetic field's goodness-of-fit to the field generated by a single dipole. We propose to use a similarity (SIM) as a quantitative measure of the discrepancy between two complex magnetic field patterns. The SIM is defined as an angle between two magnetic field vectors. We evaluated the discrepancy between the 100 ms post-stimulus responses to pattern-reversal (Rv) stimulus, pattern-onset (Pat) stimulus, and luminance-onset (Lumi) stimulus. The following results were obtained: (1) Stimulation of some of the octants in the fovea, far from the vertical meridian, elicited a single-dipole-like magnetic field pattern at a latency of 100 ms, though stimulation of the central part of the fovea, and stimulation of the octants along the vertical meridian, did not elicit a single-dipole-like magnetic field pattern; (2) The discrepancy between responses was quantitatively evaluated by the SIM even if the field patterns were complex; (3) The SIM analysis showed that the discrepancy between the responses to the Rv and the Lumi stimuli, as well as that between the responses to the Pat and the Lumi stimuli, were greater than that between the responses to the Rv and the Pat stimuli.

Adult↗
PubMed2006

Low-frequency magnetic field effect on cytoskeleton and chromatin.

The effect of magnetic fields on the living systems is studied in vivo or in vitro in very broad spectrum of organisms, cells and tissues. The mechanism of their acting is not known until now. We studied low-frequency magnetic field effect on cytoskeleton and on the structure of chromatin in human cells. We used cell line of small lung carcinoma (A549) and the effects of magnetic field on cytoskeleton and higher-order chromatin structure were analyzed 96 h of magnetic field exposure. Magnetic field generated by the cylindrical soil was homogenous and the cells were cultivated at 37 degrees C in humidified atmosphere containing 5% CO(2). Magnetic field induction was B(m)=2 mT and the net frequency f=50 Hz. In such affected and control cells the F-actin was estimated using FITC-conjugated Phalloidin and mitochondria were studied using MitoTracker (Molecular Probes). Images of cytoskeleton and genetic loci were acquired using confocal microscopy and analysis was performed by FISH 2.0 software. Slight morphological changes of F-actin filaments and mitochondria were observed in affected cells and nuclear condensation was found. These effects could be related to the process of cell death apoptosis probably induced by magnetic field. The studies aimed at centromeric heterochromatin (9cen) did not show statistically significant changes. Therefore, we suggest that magnetic field has no influence on higher order chromatin structure but certain changes could be observed on the level of cytoskeleton. However, these statements need a thorough verification. Our preliminary experiments will be extended and the effect of magnetic field on another structures of cytoskeleton and cell nuclei will be further studied.

Cell Line, Tumor↗
PubMed2005

Transport coefficients and orientational distributions of rodlike particles with magnetic moment normal to the particle axis under circumstances of a simple shear flow.

We have investigated the influences of the magnetic field strength, shear rate, and random forces on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of rodlike particles of a dilute colloidal dispersion. This dispersion is composed of ferromagnetic spheroidal particles with a magnetic moment normal to the particle axis. In the present analysis, these spheroidal particles are assumed to conduct the rotational Brownian motion in a simple shear flow as well as an external magnetic field. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved numerically. The results obtained here are summarized as follows. For a very strong magnetic field, the rodlike particle is significantly restricted in the field direction, so that the particle points to a direction normal to the flow direction (and also to the magnetic field direction). However, the present particle does not exhibit a strong directional characteristic, which is one of the typical properties for the previous particle with a magnetic moment parallel to the particle axis. That is, the particle can rotate around the axis of the magnetic moment, although the magnetic moment nearly points to the field direction. The viscosity significantly increases with the field strength, as in the previous particle model. The particle of a larger aspect ratio leads to the larger increase in the viscosity, since such elongated particles induce larger resistance in a flow field. The diffusion coefficient under circumstances of an applied magnetic field is in reasonable agreement between theoretical and experimental results.

Journal Article↗
PubMed2002

Transcranial magnetic stimulation (TMS) effects on testosterone, prolactin, and corticosterone in adult male rats.

BACKGROUND: Transcranial magnetic stimulation is a relatively new technique for inducing small, localized, and reversible changes in living brain tissue. Although transcranial magnetic stimulation generally results in no immediate changes in plasma corticosterone, prolactin, and testosterone, it normalizes the dexamethasone suppression test in some depressed subjects and has been shown to attenuate stress-induced increases in adrenocorticotropic hormone in rats. METHODS: In this study, serum corticosterone and testosterone concentrations were assayed in male rats immediately and 3, 6, 9, 12, 24, and 48 hours following a single transcranial magnetic stimulation or sham application. Serum prolactin concentrations were determined immediately and 2 hours following a one-time application of either transcranial magnetic stimulation or sham. RESULTS: Transcranial magnetic stimulation animals displayed significantly lower corticosterone concentrations at 6 and 24 hours following a single application compared with sham-control values. Transcranial magnetic stimulation also resulted in lower corticosterone concentrations numerically but not statistically in transcranial magnetic stimulation animals immediately after application (p =.089). No significant differences were found between groups for serum prolactin or testosterone levels at any given collection time point. CONCLUSIONS: These findings 1) suggest that transcranial magnetic stimulation alters the hypothalamic-pituitary-adrenal stress axis and 2) provide time-course data for the implications of the hormonal mechanism that may be involved in the actions of transcranial magnetic stimulation.

Animals↗
PubMed2000

Effects of static magnetic field on dissolved oxygen levels in aqueous solutions containing copper(II), iron(II), and heme iron(III) complexes.

Trace metal ions like copper and iron play important roles such as binding, transport, and storage of molecular dioxygen in a wide variety of living systems. The effects of static magnetic fields on the dissolved oxygen (DO) levels in aqueous solutions containing copper(II), iron(II), and their bioligand complexes were investigated. The DO levels in aqueous solutions containing the stable copper(II) complexes such as Cu(II)-Arg, His, GGH and BSA systems increased when the applied magnetic field increased. However, the magnetic field-dependent changes of DO levels were not observed by the unstable Cu(II) complexes such as Cu(II)-Lys, Gly, Gly-His and Hb systems. Especially, DO levels in aqueous solutions containing Cu(II)-His or BSA complexes increased 1.1-fold to those of the control levels at 200 mT of the applied magnetic field. In contrast, DO levels in aqueous solutions containing iron(II) decreased significantly when the magnetic field increased, which in turn promoted the Fe(II)-induced lipidperoxidation in liposomes. DO levels in aqueous solutions containing Fe(II)-His complex decreased 0.9-fold to those of the control levels at 200 mT of the magnetic field for 30 min. While, the magnetic field-dependent changes of DO levels increased significantly in aqueous solutions containing heme iron(III)-complexes, suggesting that heme iron(III) is reduced to heme iron(II) under exposure of the magnetic field and thus the incorporation of molecular dioxygen in aqueous solutions is enhanced. These results indicate that the effect of the magnetic fields on DO levels in aqueous solutions must be discussed in terms of a concept: formation of intermediate complexes consisting of molecular dioxygen-copper or iron and bioligands under physiological conditions and the following enhancement of incorporation of molecular dioxygen by the complexes, that in turn activate the molecular dioxygen.

Journal Article↗
PubMed2002

Change in broth culture is associated with significant suppression of Escherichia coli death under high magnetic field.

When Escherichia coli B was cultivated under an inhomogeneous magnetic field of 5.2-6.1 T, a significant 100,000-fold suppression of cell death was observed [Bioelectrochemistry 53 (2001) 149]. The limited magnetic field exposure for 12 h after logarithmic growth phase was sufficient to observe similar suppressive effects on cell death [Bioelectrochemistry 54 (2001) 101]. These results suggest some possible changes in either the medium or the cells during the magnetic field exposure. When the cell-free filtrate of the broth cultured under the magnetic field for 10 h and the cells of E. coli cultivated under the geomagnetic field for 30 h were mixed, and the mixture was subsequently cultivated under the geomagnetic field, the number of cells observed in the filtrate exposed to the high magnetic field was 20,000 times higher than that in the filtrate exposed to the geomagnetic field. When the cells cultivated under the magnetic field for 10 h and the cell-free filtrate of the broth culture exposed to the geomagnetic field were mixed, only a 50-fold difference in the number of cell between under the magnetic field and under the geomagnetic field was observed. This suggests that the filtrate of the broth culture exposed to the magnetic field is primarily responsible for the cell death suppression. It was also revealed that the small difference in pH of the filtrates of the broth culture between under the magnetic field and under the geomagnetic field was critical for the cell death suppression.

Cell Cycle↗
PubMed2000

A method for determination of particle magnetic susceptibility with analytical magnetapheresis

We recently developed a new method for simple determination of particle magnetic susceptibility using analytical magnetapheresis. This new method does not require laborious calibration plots and trial susceptibility values as do previous analytical magnetapheresis methods. The new method is based on balancing channel flow rates and magnetically induced flow rates for particle deposition in analytical magnetapheresis. The maximal flow rate for complete particle deposition was determined experimentally and set to equal the magnetically induced flow rate for determining particle magnetic susceptibility. This magnetic susceptibility determination generally takes less than 20 min. Several magnetically susceptible and ion-labeled particles were tested using this new method. The carrier magnetic susceptibilities were varied, and erbium ion-labeled particles were studied experimentally, resulting in successful susceptibility determinations of erbium ion-labeled particles and yeasts. The precision of each measurement was generally approximately 10%. Experimental determination of particle magnetic susceptibilities differed by less than 10% from reference measurements taken using a superconducting quantum interference device magnetometer. This method can determine minimal susceptibilities on the order of 10(-9) cgs. The minimum number of erbium labeling ions per particle required for complete deposition of silicas and yeasts was found to be 6.7 x 10(9). Analytical magnetapheresis shows good potential for use in simple determination of particle magnetic susceptibilities and should become a useful technique.

Journal Article↗
PubMed2002

High-spin molecules: synthesis, X-ray characterization, and magnetic behavior of two new cyano-bridged Ni(II)(9)Mo(V)(6) and Ni(II)(9)W(V)(6) clusters with a S = 12 ground state.

The preparations, X-ray structures, and magnetic characterizations are presented for two new pentadecanuclear cluster compounds: [Ni(II)(Ni(II)(MeOH)(3))(8)(mu-CN)(30)(M(V)(CN)(3))(6)].xMeOH.yH(2)O (M(V) = Mo(V) (1) with x = 17, y = 1; M(V) = W(V) (2) with x = 15, y = 0). Both compounds crystallize in the monoclinic space group C2/c, with cell dimensions of a = 28.4957(18) A, b = 19.2583(10) A, c = 32.4279(17) A, beta = 113.155(6) degrees, and Z = 4 for 1 and a = 28.5278(16) A, b = 19.2008(18) A, c = 32.4072(17) A, beta = 113.727(6) degrees, and Z = 4 for 2. The structures of 1 and 2 consist of neutral cluster complexes comprising 15 metal ions, 9 Ni(II) and 6 M(V), all linked by mu-cyano ligands. Magnetic susceptibilities and magnetization measurements of compounds 1 and 2 in the crystalline and dissolved state indicate that these clusters have a S = 12 ground state, originating from intracluster ferromagnetic exchange interactions between the mu-cyano-bridged metal ions of the type Ni(II)-NC-M(V). Indeed, these data show clearly that the cluster molecules stay intact in solution. Ac magnetic susceptibility measurements reveal that the cluster compounds exhibit magnetic susceptibility relaxation phenomena at low temperatures since, with nonzero dc fields, chi"(M) has a nonzero value that is frequency dependent. However, there appears no out-of-phase (chi"(M)) signal in zero dc field down to 1.8 K, which excludes the expected signature for a single molecule magnet. This finding is confirmed with the small uniaxial magnetic anisotropy value for D of 0.015 cm(-1), deduced from the high-field, high-frequency EPR measurement, which distinctly reveals a positive sign in D. Obviously, the overall magnetic anisotropy of the compounds is too low, and this may be a consequence of a small single ion magnetic anisotropy combined with the highly symmetric arrangement of the metal ions in the cluster molecule.

Journal Article↗
PubMed2004

Coordination complexes of 2-(4-quinolyl)nitronyl nitroxide with M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)]: syntheses, crystal structures, and magnetic characterization.

Three new complexes of the formula M(2)L(2) derived from 2-(4-quinolyl)nitronyl nitroxide (4-QNNN) and M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)], (4-QNNN)(2).[Mn(hfac)(2)](2) (1), (4-QNNN)(2).[Co(hfac)(2)](2).2H(2)O (2), and (4-QNNN)(2).Cu(hfac)(2).Cu'(hfac)(2) (3), were synthesized and characterized structurally as well as magnetically. Complexes 1 and 2 are four-spin complexes with quadrangle geometry, in which both the nitrogen atoms of quinoline rings and oxygen atoms of nitronyl nitroxides are involved in the formation of coordination bonds. For complex 3, however, the nitrogen atoms of quinoline rings are coordinated with Cu(II) ion to afford a three-spin complex, which is further linked to another molecule of Cu(hfac)(2) (referred to as Cu'(hfac)(2)) to form a 1D alternating chain. The magnetic behaviors of the three complexes were investigated. For complex 1, as the nitronyl nitroxides and Mn(II) ions are strongly antiferromagnetically coupled, consequently its temperature dependence of magnetic susceptibility was fitted to the model of spin-dimer with S = 2, yielding the intradimer magnetic exchange constant of J = -0.82 cm(-1). For complex 2, the temperature dependence of the magnetic susceptibility in the T > 50 K region was simulated with the model of two-spin unit with S(1) = 3/2 and S(2) = 1/2, leading to J = -321.9 cm(-1) for the magnetic interaction due to Co(II).O coordination bonding, D = -16.3 cm(-1) (the zero-field splitting parameter), g = 2.26, and zJ = -3.8 cm(-1) for the magnetic interactions between Co(II) ions and nitronyl nitroxides through quinoline rings and those between nitronyl nitroxides due to the short O.O short contacts. The temperature dependence of magnetic susceptibility of 3 was approximately fitted to a model described previously affording J(1) = -6.52 cm(-1) and J(2) = 3.64 cm(-1) for the magnetic interaction between nitronyl nitroxides and Cu(II) ions through the quinoline unit via spin polarization mechanism and the weak O.Cu coordination bonding, respectively.

Journal Article↗
PubMed1998

Observation of Spontaneous Magnetization in the Layered Perovskite Ferromagnet, (p-Chloroanilinium)(2)CuBr(4).

The crystal structure and magnetic properties of the layered perovskite, (p-chloroanilinium)(2)CuBr(4) (1) have been investigated. The crystal of 1 belongs to the orthorhombic Pbca space group [a = 7.551(2) Å, b = 32.082(10) Å, c = 7.879(2) Å, and Z = 4], which is typical of the material family. The temperature dependence of the ac susceptibility (chi(ac) = ( partial differentialM/ partial differentialH)) of a polycrystalline sample shows magnetic ordering at 15 K with an abrupt increase of the value. In the ordered state, the field dependence of chi(ac), namely the differential susceptibility, and the dc magnetization indicate a hysteresis loop of the magnetization, which can be ascribed to the presence of spontaneous magnetization. Furthermore, single-crystal magnetic measurements indicate that the magnetic properties of 1 are quite anisotropic. When the field is along the b axis (perpendicular to the inorganic layer), the field dependence of chi(ac) shows the hysteresis behavior, as observed for the polycrystals, but when it is parallel to the a axis (parallel to the layer), chi(ac) shows metamagnetic transitions. The observed anisotropy can be understood in terms of a magnetic easy axis parallel to the a axis, an antiferromagnetic interlayer interaction, and a spin canting which produces spontaneous magnetization along the b axis.

Journal Article↗
PubMed2002

Nickel(II)-molybdenum(III)-cyanide clusters: synthesis and magnetic behavior of species incorporating [(Me(3)tacn)Mo(CN)(3)].

The substitution of Mo(III) for Cr(III) in metal-cyanide clusters is demonstrated as an effective means of increasing the strength of the magnetic exchange coupling and introducing magnetic anisotropy. Synthesis of the octahedral complex [(Me(3)tacn)Mo(CN)(3)] (Me(3)tacn = N,N',N"-trimethyl-1,4,7-triazacyclononane) is accomplished with the addition of precisely 3 equiv of LiCN to a solution of [(Me(3)tacn)Mo(CF(3)SO(3))(3)] in DMF. An excess of LiCN prompts formation of a seven-coordinate complex, [(Me(3)tacn)Mo(CN)(4)](1)(-), whereas less LiCN produces multinuclear species such as [(Me(3)tacn)(2)Mo(2)(CN)(5)](1+). In close parallel to reactions previously performed with [(Me(3)tacn)Cr(CN)(3)], assembly reactions between [(Me(3)tacn)Mo(CN)(3)] and [Ni(H(2)O)(6)](2+) or [(cyclam)Ni(H(2)O)(2)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) afford face-centered cubic [(Me(3)tacn)(8)Mo(8)Ni(6)(CN)(24)](12+) and linear [(Me(3)tacn)(2)(cyclam)NiMo(2)(CN)(6)](2+) clusters, respectively. Generation of the former involves a thermally induced cyanide linkage isomerization, which rapidly leads to a low-spin form of the cluster containing diamagnetic Ni(II) centers. The cyclic voltammagram of this species in DMF reveals a sequence of six successive reduction waves spaced approximately 130 mV apart, suggesting class II mixed-valence behavior upon reduction. The magnetic properties of the aforementioned linear cluster are consistent with the expected ferromagnetic coupling and an S = 4 ground state, but otherwise vary slightly with the specific conformation adopted (as influenced by the packing of associated counteranions and solvate molecules in the crystal). Magnetization data indicate an axial zero-field splitting parameter with a magnitude falling in the range [D] = 0.44-0.72 cm(-1), and fits to the magnetic susceptibility data yield exchange coupling constants in the range J = 17.0-17.6 cm(-1). These values represent significant increases over those displayed by the analogous Cr(III)-containing cluster. When perchlorate is used as a counteranion, [(Me(3)tacn)(2)(cyclam)NiMo(2)(CN)(6)](2+) crystallizes from water in a dimeric form with pairs of the linear clusters directly linked via hydrogen bonding. In this case, fitting the magnetic susceptibility data requires use of two coupling constants: one intramolecular with J = 14.9 cm(-1) and another intermolecular with J' = -1.9 cm(-1). Reacting [(Me(3)tacn)Mo(CN)(3)] with a large excess of [(cyclam)Ni(H(2)O)(2)](2+) produces a [(Me(3)tacn)(2)(cyclam)(3)(H(2)O)(2)Ni(3)Mo(2)(CN)(6)](6+) cluster possessing a zigzag structure that is a simple extension of the linear cluster geometry. Its magnetic behavior is consistent with weaker ferromagnetic coupling and an S = 6 ground state. Similar reactions employing an equimolar ratio of reactants afford related one-dimensional chains of formula [(Me(3)tacn)(cyclam)NiMo(CN)(3)](2+). Once again, the ensuing structure depends on the associated counteranions, and the magnetic behavior indicates ferromagnetic coupling. It is hoped that substitutions of the type exemplified here will be of utility in the design of new single-molecule magnets.

Journal Article↗
PubMed2002

Transition-metal-based magnetic refrigerants for room-temperature applications.

Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.

Journal Article↗
PubMed2003

Three-dimensional magnetic field topology in a region of solar coronal heating.

Flares and X-ray jets on the Sun arise in active regions where magnetic flux emerges from the solar interior amd interacts with the ambient magnetic field. The interactions are believed to occur in electric current sheets separating regions of opposite magnetic polarity. The current sheets located in the corona or upper chromosphere have long been thought to act as an important source of coronal heating, requiring their location in the corona or upper chromosphere. The dynamics and energetics of these sheets are governed by a complex magnetic field structure that, until now, has been difficult to measure. Here we report the determination of the full magnetic vector in an interaction region near the base of the solar corona. The observations reveal two magnetic features that characterize young active regions on the Sun: a set of rising magnetic loops and a tangential discontinuity of the magnetic field direction, the latter being the observational signature of an electric current sheet. This provides strong support for coronal heating models based on the dissipation of magnetic energy at current sheets.

Journal Article↗
PubMed2004

Magnetic phase control by an electric field.

The quest for higher data density in information storage is motivating investigations into approaches for manipulating magnetization by means other than magnetic fields. This is evidenced by the recent boom in magnetoelectronics and 'spintronics', where phenomena such as carrier effects in magnetic semiconductors and high-correlation effects in colossal magnetoresistive compounds are studied for their device potential. The linear magnetoelectric effect-the induction of polarization by a magnetic field and of magnetization by an electric field-provides another route for linking magnetic and electric properties. It was recently discovered that composite materials and magnetic ferroelectrics exhibit magnetoelectric effects that exceed previously known effects by orders of magnitude, with the potential to trigger magnetic or electric phase transitions. Here we report a system whose magnetic phase can be controlled by an external electric field: ferromagnetic ordering in hexagonal HoMnO3 is reversibly switched on and off by the applied field via magnetoelectric interactions. We monitor this process using magneto-optical techniques and reveal its microscopic origin by neutron and X-ray diffraction. From our results, we identify basic requirements for other candidate materials to exhibit magnetoelectric phase control.

Journal Article↗
PubMedDate not supplied

Comparison of extremely low frequency (ELF) magnetic field personal exposure monitors.

The MultiWave System III (MW III), a recently developed personal monitor for extremely low frequency (ELF) magnetic fields, was compared with the standard EMDEX Lite (Electric and Magnetic Field Digital Exposure System), the type of monitor widely used in epidemiology and other exposure assessments. The MW III captures three-axis magnetic field waveforms for the calculation of many exposure metrics, while the EMDEX monitors measure only the root-mean-squared (RMS) vector magnitude (or resultant). Thirty-eight partial period personal samples were monitored in six different job classifications. The sampling time for each personal sample ranged from 90 to 133 min, with a mean sample time of 110 min. The EMDEX Lite and MW III were evaluated by comparing the maximum and partial period time-weighted average (TWA) of the ELF magnitude. TWA exposures measured for the 38 partial period samples by the EMDEX Lite ranged from 1.2 to 65.3 mG, with a mean of 18.1 mG, while corresponding values for the MW III ranged from 1.1 to 65.8 mG, with a mean of 17.7 mG. The maximum magnetic field exposures measured for the 38 partial period personal samples by the EMDEX Lite ranged from 27.0 to 420.2 mG, with a mean of 216.3 mG, while corresponding values for the MW III ranged from 40.2 to 1311.8 mG, with a mean of 368.4 mG. The maximum and TWA ELF magnetic field exposures measured by the EMDEX Lite and MW III were compared using a two-tailed, paired t-test. Analyses indicate that there was no significant difference in the TWA magnetic field magnitude measured by the EMDEX Lite and MW III. On the other hand, the EMDEX Lite reported significantly lower (P=0.002) maximum magnetic field measurements compared to the MW III. From a detailed analysis of the time traces, the EMDEX Lite appears to measure the ELF magnitude inaccurately when the field changes rapidly over a 4-s sampling interval. The results of this comparison suggest that the standard EMDEX Lite and MW III provide similar measure of the TWA magnetic field in a variety of occupational settings and ELF magnetic field magnitudes. However, the EMDEX Lite underestimates maximum exposures when compared to the MW III.

Electromagnetic Fields↗
PubMed2003

Structural and magnetic properties of vanadyl dichloride solvates: from molecular units to extended hydrogen-bonded solids.

The preparation, structural characterization and magnetic properties of three solvent adducts of VOCl(2), trans-VOCl(2)(THF)(2)(H(2)O) (1), trans-VOCl(2)(H(2)O)(2).2Et(2)O (2) and cis-VOCl(2)(MeOH)(3) (3) are described. In these solids, hydrogen bonding among the inorganic complexes is the critical determinant of the formation of extended magnetic networks. Compound forms one-dimensional double chains where alternating monomers from the two branches of the chain are hydrogen bonded via the V-Cl ... H-O-V network (with an axial water molecule and equatorial chloride ions). Magnetic studies indicate no interaction among the vanadyl centers. The paramagnetism of 1 is consistent with the extension of the network from the hydrogen donor site of the axial water, which is orthogonal to the d(xy) magnetic orbital. Compound 2 forms one-dimensional chains with water molecules of adjacent monomers held together by hydrogen bonds to ether molecules (V-O-H ... O(ether) ... H -O-V). The chain network radiates only through the equatorial plane of the complex where the water molecules are located. The presence of the intervening solvent molecule between hydrogen bonds of the primary coordination sphere magnetically insulates metal centers and compound is also a simple paramagnet. Removal of the solvent turns on the magnetic interaction and neighboring spin centers couple antiferromagnetically. Compound 3 forms a layered structure via V-Cl ... H-O-V hydrogen bonding, where all the hydrogen donor sites participate in the formation of the network. The vanadyl spin centers, at distances of 5.5 and 6.5 A from each other, couple antiferromagnetically (J/k=-0.7 K). Thus, magnetic coupling among metal centers is achieved when the hydrogen bond network directly radiates from the coordination plane containing the magnetic orbital. These results further support the utility of hydrogen bond as a viable design element in the construction of low dimensional, magnetic solids.

Journal Article↗
PubMed2004

Low-temperature susceptibility of concentrated magnetic fluids.

The initial susceptibility of concentrated magnetic fluids (ferrocolloids) has been experimentally investigated at low temperatures. The results obtained indicate that the interparticle dipole-dipole interactions can increase the susceptibility by several times as compared to the Langevin value. It is shown that good agreement between recent theoretical models and experimental observations can be achieved by introducing a correction for coefficients in the series expansion of susceptibility in powers of density and aggregation parameter. A modified equation for equilibrium susceptibility is offered to sum over corrections made by Kalikmanov (Statistical Physics of Fluids, Springer-Verlag, Berlin, 2001) and by B. Huke and M. Lucke (Phys. Rev. E 67, 051403, 2003). The equation gives good quantitative agreement with the experimental data in the wide range of temperature and magnetic particles concentration. It has been found that in some cases the magnetic fluid solidification occurs at temperature several tens of kelvins higher than the crystallization temperature of the carrier liquid. The solidification temperature of magnetic fluids is independent of particle concentration (i.e., magneto-dipole interparticle interactions) and dependent on the surfactant type and carrier liquid. This finding allows us to suggest that molecular interactions and generation of some large-scale structure from colloidal particles in magnetic fluids are responsible for magnetic fluid solidification. If the magnetic fluid contains the particles with the Brownian relaxation mechanism of the magnetic moment, the solidification manifests itself as the peak on the "susceptibility-temperature" curve. This fact proves the dynamic nature of the observed peak: it arises from blocking the Brownian mechanism of the magnetization relaxation.

Journal Article↗