Search results for "electromagnetic fields"
showing 10 items of 100 documents
Field theoretic study of bilayer membrane fusion: I. Hemifusion mechanism
2003
Self-consistent field theory is used to determine structural and energetic properties of metastable intermediates and unstable transition states involved in the standard stalk mechanism of bilayer membrane fusion. A microscopic model of flexible amphiphilic chains dissolved in hydrophilic solvent is employed to describe these self-assembled structures. We find that the barrier to formation of the initial stalk is much smaller than previously estimated by phenomenological theories. Therefore its creation it is not the rate limiting process. The barrier which is relevant is associated with the rather limited radial expansion of the stalk into a hemifusion diaphragm. It is strongly affected by…
Three-dimensional Hall effect accelerometer for recording head movements of freely moving laboratory animals
1991
A Hall effect device was constructed for a measurement of head movements in three spatial dimensions during classical conditioning experiments in cats. A Hall sensor was used to detect movements of a magnetic fragment floating in a small (15 x 15 mm) cube. The magnetic fragment was kept in the centre of the sealed cube with a thin coil spring which was filled with thin oil for damping excessive afteroscillations. A comparison of this device to a commercial accelerometer showed that the accuracy of the Hall device is sufficient for the movement recordings and that the device is sensitive also to slowly accelerating movements. The construction is compact and can be easily mounted, for example…
Magnetic resonance imaging of (1)H long lived states derived from parahydrogen induced polarization in a clinical system.
2015
Hyperpolarization is a powerful tool to overcome the low sensitivity of nuclear magnetic resonance (NMR). However, applications are limited due to the short lifetime of this non equilibrium spin state caused by relaxation processes. This issue can be addressed by storing hyperpolarization in slowly decaying singlet spin states which was so far mostly demonstrated for non-proton spin pairs, e.g. 13C-13C. Protons hyperpolarized by parahydrogen induced polarization (PHIP) in symmetrical molecules, are very well suited for this strategy because they naturally exhibit a long-lived singlet state. The conversion of the NMR silent singlet spin state to observable magnetization can be achieved by ma…
A Pooled Analysis of Extremely Low-Frequency Magnetic Fields and Childhood Brain Tumors
2010
Pooled analyses may provide etiologic insight about associations between exposure and disease. In contrast to childhood leukemia, no pooled analyses of childhood brain tumors and exposure to extremely low-frequency magnetic fields (ELF-MFs) have been conducted. The authors carried out a pooled analysis based on primary data (1960–2001) from 10 studies of ELF-MF exposure and childhood brain tumors to assess whether the combined results, adjusted for potential confounding, indicated an association. The odds ratios for childhood brain tumors in ELF-MF exposure categories of 0.1–<0.2 μT, 0.2–<0.4 μT, and ≥0.4 μT were 0.95 (95% confidence interval: 0.65, 1.41), 0.70 (95% CI: 0.40, 1.22), and 1.1…
Planar metamaterial analogue of electromagnetically induced transparency for plasmonic sensing.
2009
We experimentally demonstrate a planar metamaterial analogue of electromagnetically induced transparency at optical frequencies. The structure consists of an optically bright dipole antenna and an optically dark quadrupole antenna, which are cut-out structures in a thin gold film. A pronounced coupling-induced reflectance peak is observed within a broad resonance spectrum. A metamaterial sensor based on these coupling effects is experimentally demonstrated and yields a sensitivity of 588 nm/RIU and a figure of merit of 3.8.
Clutch size and egg volume in great tits (Parus major) increase under low intensity electromagnetic fields: a long-term field study.
2012
Exposure to electromagnetic fields (EMFs) can affect a wide range of biological processes, including reproduction, growth and development. Experiments aimed at investigating the biological effects of EMFs, focused on potential harmful effects on humans, have been mostly carried out in vitro or with animal models in laboratory conditions. By contrast, studies performed on wild animals are scarce. The effects of EMFs created by an electric power line on reproductive traits of a wild great tit (Parus major) population were explored by analysing data gathered during nine breeding seasons. EMF exposure significantly increased clutch size (7%) and egg volume (3%), implying a 10% increase in clutc…
On the anomalous Stark effect in a thin disc-shaped quantum dot
2010
The effect of a lateral external electric field F on an exciton ground state in an InAs disc-shaped quantum dot has been studied using a variational method within the effective mass approximation. We consider that the radial dimension of the disc is very large compared to its height. This situation leads to separating the excitonic Hamiltonian into two independent parts: the lateral confinement which corresponds to a two-dimensional harmonic oscillator and an infinite square well in the growth direction. Our calculations show that the complete description of the lateral Stark shift requires both the linear and quadratic terms in F which explains that the exciton possess nonzero lateral dipo…
LocalD=4field theory onκ-deformed Minkowski space
2000
We describe the local $D=4$ field theory on $\ensuremath{\kappa}$-deformed Minkowski space as a nonlocal relativistic field theory on standard Minkowski space-time. For simplicity the case of a $\ensuremath{\kappa}$-deformed scalar field $\ensuremath{\varphi}$ with the interaction $\ensuremath{\lambda}{\ensuremath{\varphi}}^{4}$ is considered, and the $\ensuremath{\kappa}$-deformed interaction vertex is described. It appears that the fundamental mass parameter $\ensuremath{\kappa}$ plays the role of regularizing the imaginary Pauli-Villars mass in the $\ensuremath{\kappa}$-deformed propagator.
Magnetized boxes for housing polarized spins in homogeneous fields
2010
Abstract We present novel types of permanently magnetized as well as current powered boxes built from soft-ferromagnetic materials. They provide shielded magnetic fields which are homogeneous within a large fraction of the enclosed volume, thus minimizing size, weight, and costs. For the permanently magnetized solutions, homogenization is achieved either by an optimized distribution of the permanent field sources or by jacketing the field with a soft-ferromagnetic cylindrical shell which is magnetized in parallel to the enclosed field. The latter principle may be applied up to fields of about 0.1 T. With fields of about 1 mT, such boxes are being used for shipping spin-polarized 3 He worldw…
Parametric excitation of bending deformations of a rod by periodic twist
2013
A model of a semiflexible magnetic filament with magnetization frozen in the direction perpendicular to the tangent of its center line is formulated. It is shown that if the rod is magnetized at its ends in opposite directions, an AC magnetic field causes parametric excitation of bending deformations. Neutral curves of parametric excitation are calculated both analytically and numerically. The shapes arising upon parametric excitation of bending deformations are chiral. Periodic rotation of the chiral filament due to nonhomogeneous twist in a nonhomogeneous AC field causes its unidirectional motion.