Magnetic Equivalence Research Articles

Have null, will fly

This article is concerned exclusively with data tags which are machine readable and which do not require contact between the tag and the reader. Such devices are of considerable commercial interest, either because they speed up a data collection process, or because they provide a new function, or both. The goal of very low cost, vibration-free tagging was finally realised with SGL's 1995 invention of flying null (FN) technology. An FN data tag is the magnetic equivalent of an optical bar code. In the case of FN, however, the bars in the code are made from a very soft (low coercivity), high permeability, magnetic alloy, and the tag is read using a special magnetic reader. Very little material is required and there are no special packaging requirements, so FN tags can be made for a fraction of the cost of other tags. The reader is the key to the technology. It creates a narrow region of zero field (a null) in space, surrounded by regions where the field strength is sufficient to saturate the magnetic material used in the tag. In a typical implementation, it also applies a low-amplitude alternating magnetic field to the interrogation region, so that a soft magnetic element in the null region is driven into and out of saturation, thereby radiating harmonics of the interrogation frequency. These harmonics can be detected, and their time of occurrence related to the position of the element with respect to the null. In typical systems, a spatial resolution of better than 50 μm can be achieved for a reader-to-tag separation of many millimetres.

Discrimination of Speech and of Complex Nonspeech Sounds of Different Temporal Structure in the Left and Right Cerebral Hemispheres

The key question in understanding the nature of speech perception is whether the human brain has unique speech-specific mechanisms or treats all sounds equally. We assessed possible differences between the processing of speech and complex nonspeech sounds in the two cerebral hemispheres by measuring the magnetic equivalent of the mismatch negativity, the brain's automatic change–detection response, which was elicited by speech sounds and by similarly complex nonspeech sounds with either fast or slow acoustic transitions. Our results suggest that the right hemisphere is predominant in the perception of slow acoustic transitions, whereas neither hemisphere clearly dominates the discrimination of nonspeech sounds with fast acoustic transitions. In contrast, the perception of speech stimuli with similarly rapid acoustic transitions was dominated by the left hemisphere, which may be explained by the presence of acoustic templates (long-term memory traces) for speech sounds formed in this hemisphere.

Supplementary Motor Area Activation Preceding Voluntary Movement Is Detectable with a Whole-Scalp Magnetoencephalography System

Despite the fact that the knowledge about the structure and the function of the supplementary motor area (SMA) is steadily increasing, the role of the SMA in the human brain, e.g., the contribution of the SMA to the Bereitschaftspotential, still remains unclear and controversial. The goal of this study was to contribute further to this discussion by taking advantage of the increased spatial information of a whole-scalp magnetoencephalography (MEG) system enabling us to record the magnetic equivalent of the Bereitschaftspotential 1, the Bereitschaftsfeld 1 (BF 1) or readiness field 1. Five subjects performed a complex, and one subject a simple, finger-tapping task. It was possible to record the BF 1 for all subjects. The first appearance of the BF 1 was in the range of −1.9 to −1.7 s prior to movement onset, except for the subject performing the simple task (−1 s). Analysis of the development of the magnetic field distribution and the channel waveforms showed the beginning of the Bereitschaftsfeld 2 (BF 2) or readiness field 2 at about −0.5 s prior to movement onset. In the time range of BF 1, dipole source analysis localized the source in the SMA only, whereas dipole source analysis containing also the time range of BF 2 resulted in dipole models, including dipoles in the primary motor area. In summary, with a whole-head MEG system, it was possible for the first time to detect SMA activity in healthy subjects with MEG.

A Giant Snare for Monopoles

Physicists have spent much time searching fruitlessly for magnetic monopoles, the magnetic equivalent of the fundamental bits of electric charge carried by electrons; now they have used the world9s highest energy accelerator and once again come up empty. This nondiscovery, now in press at Physical Review Letters, puts some new limits on the mass of this aspiring particle and has also sparked a bit of a debate about how to look for it.

The gamma band response may account for poor P50 suppression in schizophrenia.

The relationship between gamma band response (GBR) and P50 suppression was investigated among 10 DSM-IV schizophrenia patients and 10 normal comparison subjects using neuromagnetic and electrical recordings. In a paired-click paradigm, the neuromagnetic GBR and M100 suppression data improved schizophrenia-normal group separations over the typical electrical, vertex-recorded P50 suppression measure. The neuromagnetic GBR was also superior to the magnetic equivalent of P50 (M50) for discriminating schizophrenia and normal subjects. Our data are consistent with the hypothesis that P50 may be a subcomponent of the GBR, and that P50 suppression may be a proxy for GBR suppression. Measurement of the GBR should be given consideration as another, and perhaps better, means for evaluating auditory-evoked response abnormalities among schizophrenia patients.

An Unusual Determinant of Chirality. Unique Solution Chemistry and Novel NMR Spectroscopic Changes in Fluxional Re(V)O Complexes with Rearranging meso N2S2 Ligands

The nature of metal species in aqueous solution is often ambiguous since the two processes, OH- coordination and ligand deprotonation, have the same pH profile. This problem plagues the assessment of the form of some radiopharmaceuticals present at physiological pH. Representative M(V)O(N2S2) (M = 99mTc, Re) radiopharmaceuticals include ReO(ECH3) complexes (ECH3 = thrice deprotonated ethylene di(cysteine), ECH6). We found that syn-ReO(dl-ECH3) (1) (meso-ECH3, formed from dl-cysteine) and the tetramethyl analog, syn-ReO(dl-TMECH3) (2, TMECH6 = ethylene di(penicillamine)), have uniquely informative spectral properties. Two equivalents of OH- convert 1 and 2 to the dianionic form. This form of 2 has only one set of three penicillamine (pen) 1H NMR signals near pH 6. However, these signals underwent major changes from pH 6 to 10 as follows: they broadened and collapsed; two equal sets of three signals emerged; these then broadened and collapsed; and the original set of three signals reemerged. Combined with the Raman data given below, these results require that one form is present from pH 6 to 10 and that this form be chiral and both conformationally and configurationally fluxional; one N is protonated and the other N bears a lone pair (Lp). The determinant of chirality of this NH/NLp form is the site of the NH group. The magnetic equivalence leading to one set of pen signals observed at the low and high ends of the pH range demonstrates the occurrence of fast exchange of the NH site between the two N's. This exchange leads to rapid inversion of complex chirality through symmetric intermediates, an NH/NH monoanion and an NLp/NLp trianion, in the acid- and base-catalyzed processes, respectively. At neutral pH, the H+ and OH- concentrations are low; as a result, the inversion of chirality is slow compared to the NMR time scale, and the two halves of the ligand are magnetically inequivalent. The two ReO bands found in a fixed ratio in the resonance Raman spectra of 2 between pH 6 and 10 indicate that two major NH/NLp conformers are present throughout the range, including physiological pH. Two conformers of a form axially ligated by OH- cannot explain the two equal sets of pen NMR signals. However, two NH/NLp conformers differing only in NLp orientation and in rapid interchange via NLp inversion explain all the spectral results. Thus, the use of fast and slow time scale spectroscopies eliminates the ligation/deprotonation ambiguity in this case.

Magnetic Equivalence between Nuclei of Spin Greater than [formula omitted]in Presence of Relaxation

Both formal reasoning and numerical calculations of spectral lineshape functions confirm that magnetic equivalence between nuclei of spin greater than 12 is generally broken in presence of relaxation. This results in a dependence of the lineshape functions on the values ofJ-couplings between the nuclei that would be equivalent in absence of relaxation. Effects of this sort may be of practical importance for systemsAnX, where theAnuclei are relaxed by quadrupolar interactions which are highly cross-correlated at differentAsites.

Multilayers as spin-wave emitting diodes

Magnon-electron interaction is enhanced in the vicinity of an interface between ferromagnetic and normal layers, in metallic thin films. When a dc current crosses this interface, stimulated emission of spin-waves is predicted to take place. Beyond a certain critical current density ≃107 A/cm2, a spontaneous precession of the magnetization is predicted to arise. This SWASER (Spin Wave Amplification by Stimulated Emission of Radiation) is the magnetic equivalent of the injection laser. In the earlier theories, the thickness of the precessing magnetic layer was assumed to be larger than the electron mean free path. We now treat the case of general value of that thickness L2x. The current-induced amplification rate of spin-waves is proportional to L2x in the limit L2x≃0, and goes through a maximum for L2x≃π/|k↑−k↓|. Here, k↑ and k↓ are the spin-up and spin-down Fermi wave numbers. At larger L2x, the amplification rate of spin-waves decreases towards zero. On that general decrease are superposed damped periodic variations of wavelength ≃2π/|k↑−k↓|.

The Rise of Twisted Magnetic Tubes in a Stratified Medium

First results from a two-dimensional numerical study of the buoyant rise of twisted magnetic flux tubes in the solar convection zone are presented. We show in detail the process by which the transverse component of the field can suppress the splitting of the rising tube into two vortex filaments. For the suppression to be effective, the pitch angle of the twisted field lines has to be above a threshold given by the condition that the magnetic equivalent of the Weber number (see § 2.2) be below 1. The shape obtained for the tube and wake is strongly reminiscent of laboratory experiments with air bubbles rising in liquids. The magnetized region outside an equipartition boundary is peeled away from the tube: two sidelobes are formed, which lag behind the tube and contain only a fraction of the initial magnetic flux. This is similar to the formation of a skirt in the fluid dynamical case. The velocities of rise predicted by the thin flux tube approximation are compared with those obtained here.

96/04322 Characteristics of 90Sr, 137Cs and 239, 240Pu migration in undisturbed soils of Southern Belarus after the Chernobyl accident

Proton magnetic resonance studies show that UO2(DMF)2+5, pentakis(N,N-dimethylformamide)dioxouranium(VI) ion, is the greatly predominant dioxouranium(VI) species in mixed solutions of DMF and d2-methylene chloride. The virtual independence of the rate of intermolecular exchange of DMF of free DMF concentration over a 20.3 fold concentration range is interpreted in terms of a dissociative exchange mechanism. A typical set of kinetic data for this process is kex(220K) = 199 ± 11 s−1, ΔH♯ = 31.9 ± 0.3 kJ mol−1 and ΔS♯ = −53.4 ± 1.5 J K−1 mol−1, where the observed exchange rate = 5 kex[UO2(DMF)2+5], and the concentrations of UO2(DMF)2+5, DMF and d2-methylenechloride are respectively 0.008648, 0.04323 and 15.05 mol dm−3. The observed magnetic equivalence of the methyl groups in bound DMF over the experimental temperature range 170–300 K is shown to arise as a consequence of the cis and trans DMF methyl groups experiencing significantly different magnetic shielding modifications upon coordination to the dioxouranium(VI) ion probably in part as a consequence of the magnetic anisotropy of that ion.

Human middle latency auditory evoked magnetic fields.

The magnetic equivalents of SN10, Po, Na, Pa, Nb and Pb (SN10m, Pom, Nam, Pam, Nbm, and Pbm) in short and middle latency auditory evoked potentials were measured with a 7-channel DC superconducting quantum interference device (SQUID). The sources of Pom, Nam, Pam, Nbm and Pbm responses were estimated to be located in the auditory cortex, while the source of SN10m was considered to be in a deeper part of the brain. In addition, the source of Pam was estimated to be in the vicinity of the moving N100m source. The source of Pbm was considered to be in a separate area, anterior to the source of Pam and N100m, which suggested that source of Pam was located in the primary auditory cortex, while the source of Pbm was located in the secondary auditory cortex. The source of N100m was considered to spread from the primary auditory cortex to the secondary auditory cortex.

Auditory event-related magnetic fields in a tone-duration discrimination task. Source localization for the mismatch field and for a new component M2".

Auditory event related magnetic fields were measured using an odd-ball paradigm in which the rare event was a tone of short duration, D2, and the frequent one a tone of longer duration, D1. The subjects were required to attend to and count the number of rare stimuli. In the average across target stimuli a mismatch field (MMF) occurs and the dependence of the MMF, especially its latency, on the tone duration D2 is examined in detail. The location of an equivalent current dipole for the MMF-source is found and turns out to be at variance with earlier results. In addition to the MMF we propose a new component, here called M2", which in time overlaps the magnetic equivalent of the P200 signal and which has a source location (equivalent current dipole) lying rather close to the MMF-source. The two sources are, however, active at latencies differing by a time equal to D2. We speculate that M2" indicates the onset of the process: "evaluation of tone-duration" while the MMF indicates the end of this process.

Pitch change of a continuous tone activates two distinct processes in human auditory cortex: a study with whole-head magnetometer

Previous studies have shown that a frequency change in a continuous tone elicits an NI type of ERP (event-related potential) component. It remained unclear, however, whether this response is a “genuine” N1 (onset detector response) or the mismatch negativity (MMN), a change-detector type of ERP response, elicited in previous studies by an infrequent change in a sequence of homogeneous stimuli. A further possibility is a nearly perfect overlap of the two types of ERP components. The advent of modern, high-resolution magnetometers has opened a new, powerful way to tackle such component-overlap problems. Subjects were presented with a continuous tone of 988 Hz which was occasionally increased to 1108 Hz for a period of 100 msec. The magnetic responses to this change consisted of two partially overlapping components with peaks separated by 30 msec. The earlier component was probably generated by neuronal populations of the auditory cortex corresponding to the supratemporal N1, whereas the later one, generated anteriorly and inferiorly to the first, probably reflects a mismatch process causing the magnetic equivalent of the electrical MMN.

Contrasting routes to the Kostka coefficients of λ [boxvr] n (l n)-permutational module expansions for 6⩽ n⩽8: Applications to NMR spin clusters under SU( m⩽ n)×L n spin symmetries

Aspects of the higher- n λ( l n ) permutational modules associated with Young subgroups of various highly-branched high- n fold algebras, which are pertinent to identical spin NMR clusters, are presented for λ [boxvr] n (or λ [boxvR] n), aRota p-tuple or number partition; the method of optimal choice for deriving the Λ [λ′] Kostka coefficients, found in {[λ′]} sets derived from λ permutational module expansions, rests on the ordering of the λ-(shape) to the self-associated diagram(s) in the dominance hierarchy. Hence, physical insight into these cage-cluster NMR systems is developed both from these properties and from the inter-related induced symmetries of GL( n, ▪) and l n groups. From these associated combinatorial, mapping or scalar invariant aspects of SU( m⩽ n)× l n symmetry, one may define the [A] n ( l n ) systems of [AX] n NMR problems in a general semi-topological limit. This corresponds to a high- n l n limit in which the individual spin cluster exhibits a lack of any (intracluster) ‘magnetic equivalence’ properties.

Effects of stimulation side on human middle latency auditory evoked magnetic fields

We investigated the effects of the stimulation side on middle latency auditory evoked responses (MLR) with neuromagnetic methods. Middle latency auditory evoked magnetic fields elicited by 1.0 ms clicks presented at ipsilateral and contralateral ear were recorded with a 7-channel DC SQUID. The amplitudes and latencies of the magnetic equivalents of Pa and Pb responses, which are the two main peaks of MLR, were measured. The amplitude of the contralateral Pa response was found to be significantly larger than the ipsilateral Pa response. On the other hand, no significant difference was observed in the latencies of Pa and Pb between the ipsi- and contralateral responses.

Measurement of auditory evoked brain responses elicited by ipsilateral and contralateral ear stimulation with a high-sensitivity SQUID system

The effects of the stimulation side on human middle latency auditory evoked responses (MLR) were investigated with a high-sensitivity 7-channel DC SQUID system. We recorded middle latency auditory evoked magnetic fields elicited by ipsilateral and contralateral ear stimuli, and compared the amplitudes and latencies of the magnetic equivalents of Pa and Pb responses, which are the two main components of MLR. The amplitude of the contralateral Pa response was found to be significantly larger than the ipsilateral Pa response. On the other hand, no significant difference was observed in the latencies of Pa and Pb between the ipsi- and contralateral responses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Inequivalent proton hyperfine couplings of CrO 3−4 in LiNH 4SO 4 and LiKSO 4 crystals: An EPR study

The CrO 3− 4 radicals produced by λ-irradiation in LiNH 4SO 4 and LiKSO 4 crystals exhibit hyperfine splittings due to two magnetically inequivalent protons. This is in contrast to the magnetic equivalence of the proton hyperfine splittings observed for the NH + 3 radicals simultaneously produced in these same host lattices. The proton hyperfine splittings of the CrO 3− 4 radicals also exhibit much more significant anisotropies than those exhibited by the protons of the NH + 3 radicals. These imply a slowing-down of dynamics of the ammonium protons adjacent to the CrO 3− 4 radical.

Tonotopic auditory cortex and the magnetoencephalographic (MEG) equivalent of the mismatch negativity.

Two tone stimuli, one frequent (standard) and the other infrequent (a slightly higher, deviant tone), were presented in random order and at short intervals to subjects reading texts they had selected. In different blocks, standards were either 250, 1,000, or 4,000 Hz, with the deviants always being 10% higher in frequency than the standards of the same blocks. Magnetic responses elicited by the standard and deviant tones included N1m, the magnetoencephalographic equivalent of the electrical N1 (its supratemporal component). In addition, deviant stimuli elicited MMNm, the magnetic equivalent of the electrical mismatch negativity, MMN. The equivalent dipole sources of the two responses were located in supratemporal auditory cortex, with the MMNm source being anterior to that of N1m. The dipole orientations of both sources in teh sagittal plane depended on stimulus frequency, suggesting that the responses are generated by tonotopically organized neuronal populations. The tonotopy reflected by the frequency dependence of the MMNm source might be that of the neural trace system underlying frequency representation of auditory stimuli in sensory memory.

A violation of the magnetic equivalence of nuclei in chemically induced dynamic nuclear polarization spectroscopy

It has been shown that a correlation between the hyperfine coupling constant and the ability of a given nucleus to be abstracted in the radical reaction could cause a violation of the equality in CIDNP signals from protons constituting a group of magnetically equivalent nuclei in the radical undergoing the abstraction. The scale of the effect is analyzed and optimal conditions for its detection are found.

Crystal structure of [Pd(μ 3-2-propenyl)(dps)][Pd(μ 3-2-propenyl)Cl 2]. NMR evidence of binuclear μ 3-allyl palladium(II) species with bridging dps

The reactions of di-2-pyridyl sulfide (dps) with (μ 3-allyl)palladium chloride dimers gave the ionic compounds [Pd(μ 3-allyl)(dps)][Pd(μ 3-allyl)Cl 2] (allyl=2-propenyl ( 1), 2-methyl-2-propenyl ( 2), 2-butenyl ( 3)). The structure of 1 has been determined by X-ray diffraction methods. Crystals are triclinic, space group P 1 , with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) Å, α= 98.82(1), β=90.46(1), γ=95.46(1)°. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 3855 observed relections to R and R w values of 0.0269 and 0.0339, respectively. Compound 1 consists of discrete complex ion pairs, containing allyl groups coordinated to both the cationic and anionic palladium centres. In the cationic portion the dps acts as a chelate ligand and adopts an N,N inside conformation. The six-membered chelate ring shows a boat conformation. The cation and anion are connected by a short Pd2…Cl2 interaction (3.073(1) Å) which determines pseudo-five-coordination for the cation. At low temperature the 1H NMR spectra in CD 3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl 3 they also indicate the presence of a binuclear species with bridging dps. The 1H NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl 3, a lower energy process makes the π-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti π-allyl protons at high temperature.