Zeeman shift--a tool for assignment of 14N NQR lines of nonequivalent 14N atoms in powder samples.

The use of Zeeman perturbed 14N nuclear quadrupole resonance (NQR) to determine the ν+ and ν-14N lines in polycrystalline samples with several nonequivalent nitrogen atoms was investigated. The 14N NQR line shift due to a weak external Zeeman magnetic field was calculated, assuming isotropic distribution of EFG tensor directions. We calculated the broad line distribution of the ν+ and ν- line shifts and experimentally confirmed the calculated Zeeman field dependence of singularities (NQR peaks) in cyclotrimethylenetrinitramine (RDX) and aminotetrazole monohydrate (ATMH). The calculated and measured frequency shifts agreed well. The proposed measurement method enabled determination of which 14N NQR lines in ATMH belong to ν+ and which to ν- transitions.

Intracellular axial current in Chara corallina reflects the altered kinetics of ions in cytoplasm under the influence of light.

Recent experiments demonstrate that the concentration of Ca2+ in cytoplasm of Chara corallina internodal cells plays important role in electrical excitation of the plasma membrane. The concentration of free Ca2+ in the cytoplasm -[Ca2+]c is also sensitive to visible light. Both phenomena were simultaneously studied by noninvasive measuring action potential (AP) and magnetic field with a superconducting quantum interference device magnetometer in very close vicinity of electrically excited internodal C. corallina cells. A temporal shift in the depolarization maximum, which progressively occurred after transferring cells from the dark into the light, can be explained by the extended Othmer model. Assuming that the change in membrane voltage during the depolarization part of AP is the direct consequence of an activation of [Ca2+]c sensitive Cl- channels, the model simulations compare well with the experimental data. We can say that we have an example of electrically elicited AP that is of biochemical nature. Electric and magnetic measurements are in good agreement.

Value and limitations of an inverse solution for two equivalent dipoles in localising dual accessory pathways.

Investigations were carried out into whether an equivalent generator consisting of two dipoles could be used to detect dual sites of ventricular activity. A computer model of the human ventricular myocardium was used to simulate activation sequences initiated at eight different pairs of sites positioned on the epicardial surface of the atrio-ventricular ring. From these sequences, 117-lead body surface potentials (covering the anterior and posterior torso), 64-lead magnetic field maps (above the anterior chest) and 128-lead magnetic field maps (above the anterior and posterior chest) were simulated and were then used to localise dual accessory pathways employing pairs of equivalent dipoles. Average localisation errors were 12 mm, 12 mm and 9 mm, respectively, when body surface potentials, 64-lead and 128-lead magnetic fields were used. The results of the study suggest that solving the inverse problem for two dipoles could provide additional information on dual accessory pathways prior to electrophysiological study.

Magnetic detection of injury-induced ionic currents in bean plants.

A superconducting quantum interference device (SQUID) multichannel magnetometer was used to measure the temporal and spatial evolution of the magnetic field accompanying stimulation by burning and/or cutting of Vicia faba plants. These magnetic fields are caused by ionic currents that appear after injury in different parts of the plant. All measured V. faba plants responded to the burning stimulation with detectable quasi-d.c. magnetic signals. In order to measure these signals, a suitable modulation had to be used. The covariance method was applied to analyse the measured data. The results demonstrate a dipolar-like magnetic signal, exponentially decreasing in time, above the cutting type of injury. After the burning stimulation, the magnetically detected activity was concentrated predominantly above the leaves/petioles and less above the stem. Possible mechanisms for this behaviour are suggested. A comparison with previously known electrical measurements of plant injury is given.

Magnetic detection of a single action potential in Chara corallina internodal cells.

The electrical activity that occurs in plants has not yet been detected magnetically. Magnetic detection of electrical activity in some animal as well as in human cells and organs, on the other hand, is an established research method. Our experiments demonstrate the propagation of a single action potential in the internodal cell of the green algae Chara corallina, measured magnetically. The propagation velocity and the intracellular current were determined.

Multipole expansions in the representation of current sources.

After obtaining the measured magnetic field or its components in the form of an isofield map one has to decide which approximation to use in solving the inverse problem. A single current dipole as an equivalent current source is often used. It will be shown when this approximation fails and one possible way to improve the equivalent source description. The expansion of current multipoles is discussed up to the second order. The localization of an equivalent current source in this case is considered. The application of this type of expansion is analysed and discussed.