Self-localization of monaural microphone using dipole sound sources.

This paper introduces a method for indoor self-localization of a monaural microphone, which is required for various location-based services. By generating two pairs of dipole sound fields, localization is performed on each device, irrespective of the number of devices, based on orthogonal detection of observed signals and some simple operations that are feasible with limited computational resources. A method using multiple source frequencies for enhancing robustness against the effects of reflection and scattering is also proposed. The effectiveness of this method was evaluated by numerical simulations and experiments in an anechoic chamber and indoor environment, and the average errors for the azimuth and zenith angles were 4.8 and 1.9 deg, respectively, in the anechoic chamber and 21 and 11 deg, respectively, in the indoor environment.

Sequential structured volumetric ultrasound holography for self-positioning using monaural recording.

In this article, a structured acoustic holography technique in the self-positioning method of a single microphone from the monaurally recorded signals is proposed. A series of three-dimensional ultrasonic holograms, designed for positioning in a workspace, are sequentially projected. As a result, the microphone receives a position-dependent sequence of amplitude signals encoded with information on the observation position. Subsequently, the microphone position is determined by obtaining the peak position of the cross-correlation function between the received signal and the reference signal. Experiments were conducted using a custom-made phased array of 40-kHz ultrasound transducers to evaluate the positioning accuracy. It is demonstrated that when applied to a 100×100×50 mm3 workspace, the measurement error was less than 1 mm at all observation points in the numerical experiment, which was maintained for more than 96% of the points in the real-environment experiments. The proposed method is advantageous in that it does not use the phase information of the recorded signals, thus requiring no multiple synchronized recordings as the microphone-array-based methods. In addition, this scheme does not directly use the absolute value of the received amplitude as a positioning clue, which means that no amplitude-to-voltage calibration is required.

Magnetic resonance imaging of blood perfusion rate based on Helmholtz decomposition of heat flux.

Objective.Thermal property (TP) maps of human tissues are useful for tumor treatment and diagnosis. In particular, the blood perfusion rate is significantly different for tumors and healthy tissues. Noninvasive techniques that reconstruct TPs from the temperature measured via magnetic resonance imaging (MRI) by solving an inverse bioheat transfer problem have been developed. A few conventional methods can reconstruct spatially varying TP distributions, but they have several limitations. First, most methods require the numerical Laplacian computation of the temperature, and hence they are sensitive to noise. In addition, some methods require the division of a region of interest (ROI) into sub-regions with homogeneous TPs using prior anatomical information, and they assume an unmeasurable initial temperature distribution. We propose a novel robust reconstruction method without the division of an ROI or the assumption of an initial temperature distribution.Approach.The proposed method estimates blood perfusion rate maps from relative temperature changes. This method avoids the computation of the Laplacian by using integral representations of the Helmholtz decomposition of the heat flux.Main Result.We compare the reconstruction results of the conventional and proposed methods using numerical simulations. The results indicate the robustness of the proposed method.Significance.This study suggests the feasibility of thermal property mapping with MRI using the robust proposed method.

Limiting parameter range for cortical-spherical mapping improves activated domain estimation for attention modulated auditory response.

BACKGROUND: Attention is one of the factors involved in selecting input information for the brain. We applied a method for estimating domains with clear boundaries using magnetoencephalography (the domain estimation method) for auditory-evoked responses (N100m) to evaluate the effects of attention in milliseconds. However, because the surface around the auditory cortex is folded in a complicated manner, it is unknown whether the activity in the auditory cortex can be estimated. NEW METHOD: The parameter range to express current sources was set to include the auditory cortex. Their search region was expressed as a direct product of the parameter ranges used in the adaptive diagonal curves. RESULTS: Without a limitation of the range, activity was estimated in regions other than the auditory cortex in all cases. However, with the limitation of the range, the activity was estimated in the primary or higher auditory cortex. Further analysis of the limitation of the range showed that the domains activated during attention included the regions activated during no attention for the participants whose amplitudes of N100m were higher during attention. COMPARISON WITH EXISTING METHOD: We proposed a method for effectively limiting the search region to evaluate the extent of the activated domain in regions with complex folded structures. CONCLUSION: To evaluate the extent of activated domains in regions with complex folded structures, it is necessary to limit the parameter search range. The area of the activated domains in the auditory cortex may increase by attention on the millisecond timescale.

Partial differential equation-based localization of a monopole source from a circular array.

Wave source localization from a sensor array has long been the most active research topics in both theory and application. In this paper, an explicit and time-domain inversion method for the direction and distance of a monopole source from a circular array is proposed. The approach is based on a mathematical technique, the weighted integral method, for signal/source parameter estimation. It begins with an exact form of the source-constraint partial differential equation that describes the unilateral propagation of wide-band waves from a single source, and leads to exact algebraic equations that include circular Fourier coefficients (phase mode measurements) as their coefficients. From them, nearly closed-form, single-shot and multishot algorithms are obtained that is suitable for use with band-pass/differential filter banks. Numerical evaluation and several experimental results obtained using a 16-element circular microphone array are presented to verify the validity of the proposed method.

Explicit calculation method for cell alignment in non-circular geometries.

The alignment of spindle-shaped cells in two-dimensional geometries induces singular points called topological defects, at which the alignment angle of the cell cannot be defined. To control defects related to biological roles such as cell apoptosis, calculation methods for predicting the defect positions are required. This study proposes an explicit calculation method for predicting cell alignment and defect positions in non-circular geometries. First, a complex potential is introduced to describe the alignment angles of cells, which is used to derive an explicit formula for cell alignment in a unit disc. Then, the derived formula for the unit disc is extended to the case for non-circular geometries using a numerical conformal mapping. Finally, the complex potential allows a calculation of the Frank elastic energy, which can be minimized with respect to the defect positions to predict their equilibrium state in the geometry. The proposed calculation method is used to demonstrate a numerical prediction of multiple defects in circular and non-circular geometries, which are consistent with previous experimental results.

A Method for Electrical Property Tomography Based on a Three-Dimensional Integral Representation of the Electric Field.

Magnetic resonance electrical properties tomography (MREPT) noninvasively reconstructs high-resolution electrical property (EP) maps using MRI scanners and is useful for diagnosing cancerous tissues. However, conventional MREPT methods have limitations: sensitivity to noise in the numerical Laplacian operation, difficulty in reconstructing three-dimensional (3D) EPs and convergence not guaranteed in the iterative process. We propose a novel, iterative 3D reconstruction MREPT method without a numerical Laplacian operation. We derive an integral representation of the electric field using its Helmholtz decomposition with Maxwell's equations, under the assumption that the EPs are known on the boundary of the region of interest with the approximation that the unmeasurable magnetic field components are zero. Then, we solve the simultaneous equations composed of the integral representation and Ampere's law using a convex projection algorithm whose convergence is theoretically guaranteed. The efficacy of the proposed method was validated through numerical simulations and a phantom experiment. The results showed that this method is effective in reconstructing 3D EPs and is robust to noise. It was also shown that our proposed method with the unmeasurable component H- enhances the accuracy of the EPs in a background and that with all the components of the magnetic field reduces the artifacts at the center of the slices except when all the components of the electric field are close to zero.

Effect of novel recovery garments utilising nanodiamond- and nanoplatinum-coated materials (DPV576-C) on physical and psychological stress in baseball players: A randomised, placebo-controlled trial.

Based on research suggesting that nanomaterial containing nanodiamond- and nanoplatinum-coated fibres (DPV576-C) may reduce the stress response, garments to enhance athletes' recovery from training-induced stress have been manufactured. This study examined the effects of wearing recovery garments on the physical and psychological stress of Japanese male baseball players. Thirty-eight players aged 18-21 (19.6 ± 0.2 years) who participated in a two-week intensified training programme were randomly assigned to two groups: 19 wore recovery (DPV576-C) garments (RG group) and 19 wore non-recovery garments (placebo group). Both groups wore the garments overnight. Mood states, using the Profile of Mood States questionnaire, and salivary cortisol levels were measured before (day 0) and after (day 14) the training period. Saliva samples were collected from 07:00-07:30 am. Both groups' fatigue scores significantly increased after the training period (RG: 8.4 ± 0.8-10.1 ± 0.8 score; placebo: 9.8 ± 1.0-11.7 ± 1.0 score). The total mood disturbance (TMD) score increased significantly in the placebo group (21.0 ± 2.3-27.2 ± 3.0 score) but not in the RG group (17.4 ± 2.7-20.2 ± 2.2 score). Salivary cortisol concentrations decreased significantly in the RG group (0.71 ± 0.08-0.49 ± 0.05 µg/dL) but not in the placebo group (0.61 ± 0.06-0.58 ± 0.10 µg/dL). Therefore, wearing the DPV576-C garments overnight attenuated increases in TMD levels and decreased salivary cortisol levels following intensified training. DPV576-C garments may have beneficial effects on training-induced physical and psychological stress among athletes.

Direct reconstruction algorithm of current dipoles for vector magnetoencephalography and electroencephalography.

This paper presents a novel algorithm to reconstruct parameters of a sufficient number of current dipoles that describe data (equivalent current dipoles, ECDs, hereafter) from radial/vector magnetoencephalography (MEG) with and without electroencephalography (EEG). We assume a three-compartment head model and arbitrary surfaces on which the MEG sensors and EEG electrodes are placed. Via the multipole expansion of the magnetic field, we obtain algebraic equations relating the dipole parameters to the vector MEG/EEG data. By solving them directly, without providing initial parameter guesses and computing forward solutions iteratively, the dipole positions and moments projected onto the xy-plane (equatorial plane) are reconstructed from a single time shot of the data. In addition, when the head layers and the sensor surfaces are spherically symmetric, we show that the required data reduce to radial MEG only. This clarifies the advantage of vector MEG/EEG measurements and algorithms for a generally-shaped head and sensor surfaces. In the numerical simulations, the centroids of the patch sources are well localized using vector/radial MEG measured on the upper hemisphere. By assuming the model order to be larger than the actual dipole number, the resultant spurious dipole is shown to have a much smaller strength magnetic moment (about 0.05 times smaller when the SNR = 16 dB), so that the number of ECDs is reasonably estimated. We consider that our direct method with greatly reduced computational cost can also be used to provide a good initial guess for conventional dipolar/multipolar fitting algorithms.