Search results for "low frequency"

Sampling methods for low-frequency electromagnetic imaging

2007

For the detection of hidden objects by low-frequency electromagnetic imaging the linear sampling method works remarkably well despite the fact that the rigorous mathematical justification is still incomplete. In this work, we give an explanation for this good performance by showing that in the low-frequency limit the measurement operator fulfils the assumptions for the fully justified variant of the linear sampling method, the so-called factorization method. We also show how the method has to be modified in the physically relevant case of electromagnetic imaging with divergence-free currents. We present numerical results to illustrate our findings, and to show that similar performance can b…

Dielectric Behavior of Aqueous Solutions of α,β-Poly(aspartyl hydrazide) and α,β-Poly(N-hydroxyethyl aspartamide): An Investigation of the Structural…

1994

The dielectric properties of aqueous solutions of α,β-poly(aspartyl hydrazide) (PAHy) and of α,β-poly( N-hydroxyethyl aspartamide) (PHEA) were measured at 25 ° C in the frequency range of 100 MHz to 15 GHz using a time domain reflection method (TDR). Single time relaxation processes were found at 2 GHz and 15 GHz, respectively. The low frequency dispersion was inter preted in terms of the dynamics of polymeric segments based on the dielectric relaxation strength and the relaxation time. The high frequency process which is attributed to the rotational relaxation of water, indicated that water mole cules surrounding the polymeric backbone and in the pure state have a similar rotational behav…

Radio emissions from double RHESSI TGFs

2016

Abstract A detailed analysis of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flashes (TGFs) is performed in association with World Wide Lightning Location Network (WWLLN) sources and very low frequency (VLF) sferics recorded at Duke University. RHESSI clock offset is evaluated and found to experience changes on the 5 August 2005 and 21 October 2013, based on the analysis of TGF‐WWLLN matches. The clock offsets were found for all three periods of observations with standard deviations less than 100 μs. This result opens the possibility for the precise comparative analyses of RHESSI TGFs with the other types of data (WWLLN, radio measurements, etc.) In ca…

84 Enhanced Characterization of the Thickness and Bone Mineral Density of the Radius and Tibia by Low-Frequency Guided-Wave Ultrasound

2009

Coherence between brain activation and speech envelope at word and sentence levels showed age-related differences in low frequency bands

2021

Abstract Speech perception is dynamic and shows changes across development. In parallel, functional differences in brain development over time have been well documented and these differences may interact with changes in speech perception during infancy and childhood. Further, there is evidence that the two hemispheres contribute unequally to speech segmentation at the sentence and phonemic levels. To disentangle those contributions, we studied the cortical tracking of various sized units of speech that are crucial for spoken language processing in children (4.7–9.3 years old, N = 34) and adults (N = 19). We measured participants’ magnetoencephalogram (MEG) responses to syllables, words, and…

The association between extremely low-frequency electromagnetic fields and childhood leukaemia in epidemiology: enough is enough?

2010

Background: Previous pooled analyses have reported an association between magnetic fields and childhood leukaemia. We present a pooled analysis based on primary data from studies on residential magnetic fields and childhood leukaemia published after 2000. Methods: Seven studies with a total of 10 865 cases and 12 853 controls were included. The main analysis focused on 24-h magnetic field measurements or calculated fields in residences. Results: In the combined results, risk increased with increase in exposure, but the estimates were imprecise. The odds ratios for exposure categories of 0.1–0.2 μT, 0.2–0.3 μT and ⩾0.3 μT, compared with <0.1 μT, were 1.07 (95% CI 0.81–1.41), 1.16 (0.69–1.93)…

High precision numerical estimates of acoustic phonon frequencies of nonspherical nanoparticles

2006

We introduce an adapted method for calculating the acoustic vibrational frequencies of arbitrarily shaped nanoparticles to high precision. Molecular dynamics simulation results are tested against exact solutions for a free sphere, a hollow sphere and a spheroid. This permits theoretical predictions of the frequencies of peaks in low frequency Raman spectra. Our results demonstrate that vibrational frequencies can be calculated for a wide range of low frequency modes with accuracies on the order of a tenth of a percent.

Synthesis and low-frequency vibrational spectra of some halo- and pseudohalo-diphenylantimonates(V)

1976

Abstract The syntheses of diphenylantimonates(V) of the type M(I) [PH 2 XbX 4 ] (M(I) = PH 4 As; X = F, Cl, Br, N 3 , NCS; X 4 = Cl 3 Br, Cl 3 N 3 ) are described. Far-Ir spectra of these compounds and of previously synthesized M(I) [Ph 2 SbCl 3 X] species (M(I) = Me 4 N; X = Cl, Br, N 3 ; M(I) = Ph 4 As; X = NCS) are reported. Raman spectra of tetrafluoro and tetrachloro salts are also given. Vibrational data are interpreted in terms of the presence of solid of trans -Ph 2 SbX 4 - species and assignments of skeletal modes are suggested.

Selection of blood pressure signal for baroreflex analysis

2020

This study aims to evaluate the strength of the causal coupling among systolic, mean and diastolic blood pressure (SBP, MBP and DBP) with heart period (RR interval) (evaluating cardiac chronotropic baroreflex arm) and peripheral vascular resistance (PVR) (evaluating vascular resistance baroreflex arm) in frequency domain using partial spectral decomposition method. We recorded beat-to-beat RR, SBP, MBP and DBP and PVR values in 39 volunteers during supine rest and head-up tilt. Our results showed that during supine rest the most dominant causal coupling was from DBP to RR in both low and high frequency bands and significantly decreased during orthostasis. The strength of spectral couplings …

Evaluation of the Strength of Coupling Between a Vibrational Exciton and a Specific Low Frequency Mode

1993

In Davydov’s theory, one dimensional sub-systems within molecular crystals may exhibit self-trapping of some high frequency phonons as these travel by dipole resonance interaction, due to coupling to some specific soft oscillation mode1