We search for a spin-dependent P- and T-violating nucleon-nucleon interaction mediated by light pseudoscalar bosons such as axions or axionlike particles. We employ an ultrasensitive low-field ...magnetometer based on the detection of free precession of colocated 3He and 129Xe nuclear spins using SQUIDs as low-noise magnetic flux detectors. The precession frequency shift in the presence of an unpolarized mass was measured to determine the coupling of pseudoscalar particles to the spin of the bound neutron. For boson masses between 2 and 500 μeV (force ranges between 3×1(-4) m and 10(-1) m) we improved the laboratory upper bounds by up to 4 orders of magnitude.
Non-invasive EEG detection of very high frequency somatosensory evoked potentials featuring frequencies up to and above 1 kHz has been recently reported. Here, we establish the detectability of such ...components by combined low-noise EEG/MEG. We recorded SEP/SEF simultaneously using median nerve stimulation in five healthy human subjects inside an electromagnetically shielded room, combining a low-noise EEG custom-made amplifier (4.7 nV/√Hz) and a custom-made single-channel low-noise MEG (0.5 fT/√Hz @ 1 kHz). Both, low-noise EEG and MEG revealed three spectrally distinct and temporally overlapping evoked components: N20 (<100 Hz), sigma-burst (450-750 Hz), and kappa-burst (850-1200 Hz). The two recording modalities showed similar relative scaling of signal amplitude in all three frequencies domains (EEG 10 nV ≅ MEG 1 fT). Pronounced waveform (peak-by-peak) overlap of EEG and MEG signals is observed in the sigma band, whereas in the kappa band overlap was only partial. A decreasing signal-to-noise ratio (SNR; calculated for n = 12.000 averages) from sigma to kappa components characterizes both, electric and magnetic field recordings: Sigma-band SNR was 12.9 ± 5.5/19.8 ± 12.6 for EEG/MEG, and kappa-band SNR at 3.77 ± 0.8/4.5 ± 2.9. High-frequency performance of a tailor-made MEG matches closely with simultaneously recorded low-noise EEG for the non-invasive detection of somatosensory evoked activity at and above 1 kHz. Thus, future multi-channel dual-mode low-noise technology could offer complementary views for source reconstruction of the neural generators underlying such high-frequency responses, and render neural high-frequency processes related to multi-unit spike discharges accessible in non-invasive recordings.
We report a new limit on a possible short range spin-dependent interaction from the precise measurement of the ratio of Larmor precession frequencies of stored ultracold neutrons and Hg199 atoms ...confined in the same volume. The measurement was performed in a ∼1μT vertical magnetic holding field with the apparatus searching for a permanent electric dipole moment of the neutron at the Paul Scherrer Institute. A possible coupling between freely precessing polarized neutron spins and unpolarized nucleons of the wall material can be investigated by searching for a tiny change of the precession frequencies of neutron and mercury spins. Such a frequency change can be interpreted as a consequence of a short range spin-dependent interaction that could possibly be mediated by axions or axion-like particles. The interaction strength is proportional to the CP violating product of scalar and pseudoscalar coupling constants gSgP. Our result confirms limits from complementary experiments with spin-polarized nuclei in a model-independent way. Limits from other neutron experiments are improved by up to two orders of magnitude in the interaction range of 10−6<λ<10−4m.
Magnetic shielding made from permalloy is frequently used to provide a time-stable magnetic field environment. A low magnetic field and low field gradients inside the shield can be obtained by using ...demagnetization coils through the walls, encircling edges of the shield. We first introduce and test the computational models to calculate magnetic properties of large size shields with thin shielding walls. We then vary the size, location and shape of the openings for the demagnetization coils at the corners of a cubic shield. It turns out that the effect on the shielding factor and the expected influence on the residual magnetic field homogeneity in the vicinity of the center of the shield is negligible. Thus, a low-cost version for the openings can be chosen and their size could be enlarged to allow for additional cables and easier handling. A construction of a shield with beveled edges and open corners turned out to substantially improve the shielding factor.
Introduction Human high-frequency EEG responses evoked by median nerve stimulation are non-invasive markers of cortical population spikes. For long, their reliable detection required averaging ...thousands of trials. Recently, low-noise EEG amplifiers combined with extensive electro-magnetic shielding allowed for a sensitive single-trial non-invasive detection of human high-frequency SEP. Here, using as few as 8 standard surface electrodes we demonstrate how specialized neurotechnology and offline analysis can achieve single-trial hf-SEP recordings without elaborate shielding. Methods In 6 healthy male subjects, 8 sintered Ag/AgCl surface EEG electrodes (reference at nose) were distributed above the left somatosensory cortex with impedances at about 1 kOhm. EEG was recorded upon right median nerve stimulation using a custom-built CE-certified low-noise EEG amplifier, specifically engineered to insulate the EEG from electromagnetic interferences. The signal was filtered spectrally and spatially (canonical correlation analysis variant) and transformed to the time–frequency domain (S transform). Results Bursting activity at about 600 Hz (‘ σ -burst’) in response to median nerve stimulation was detectable in all six subjects, both in the average SEP and in the average time–frequency-transform of single-trial responses. Moreover, this approach allowed to analyze the intrinsic single-trial variability of the hf-SEP. Significance Using tailor-made neurotechnology, evoked human cortical population spikes can be measured non-invasively in single-trial EEG without elaborate shielding and using a small number of standard surface electrodes, thus enabling clinical applicability.
We report results of a new technique to measure the electric dipole moment of Xe129 with He3 comagnetometry. Both species are polarized using spin-exchange optical pumping, transferred to a ...measurement cell, and transported into a magnetically shielded room, where SQUID magnetometers detect free precession in applied electric and magnetic fields. The result from a one week measurement campaign in 2017 and a 2.5 week campaign in 2018, combined with detailed study of systematic effects, is dA(Xe129)=(1.4±6.6stat±2.0syst)×10-28 e cm. This corresponds to an upper limit of |dA(Xe129)|<1.4×10-27 e cm (95% C.L.), a factor of 5 more sensitive than the limit set in 2001.
Magnetically shielded rooms for specific high resolution physiological measurements exploiting the magnetic field, e.g., of the brain (dc-magnetoencephalography), low-field NMR, or magnetic marker ...monitoring, need to be reproducibly demagnetized to achieve reliable measurement conditions. We propose a theoretical, experimental, and instrumental base whereupon the parameters which affect the quality of the demagnetization process are described and how they have to be handled. It is demonstrated how conventional demagnetization equipment could be improved to achieve reproducible conditions. The interrelations between the residual field and the variability at the end of the demagnetization process are explained on the basis of the physics of ferromagnetism and our theoretical predictions are evaluated experimentally.
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