Intensity Vector Research Articles

Performance of the phase and amplitude gradient estimator intensity method in interference fields

The phase and gradient amplitude estimator (PAGE) method improves the frequency bandwidth of estimated acoustic intensity over the traditional p-p method without altering the spacing between microphones [D. C. Thomas et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)]. For many broadband sources, accurate estimates may be obtained beyond the spatial Nyquist frequency by unwrapping the phase of a transfer function used in obtaining the phase gradient. However, inaccurate phase unwrapping in interference fields, such as those produced by two loudspeakers with equal strengths but opposite phase, has been observed. This results in erroneous intensity vectors. A two-dimensional, multi-microphone intensity probe was employed to investigate this phenomenon. Findings include: (a) the unwrapping error does not occur for all interference nulls, but is more likely to occur for deeper interference nulls where there is reduction in coherence; (b) rotation of the probe in the field alters which pair-wise transfer function unwraps erroneously, but does not significantly alter the direction that contains the inaccurate intensity vectors; (c) removal of the interference nulls by driving the loudspeakers as incoherent sources allows for phase unwrapping to occur multiple times and accurate estimation of intensity vectors beyond 10 kHz. [Work supported by NSF.]

Geoacoustic inversion based on particle velocity

An approach to geoacoustic inversion using a non-dimensional vector quantity, known as circularity, is discussed. This quantity corresponds to the difference in phase and magnitude of the vertical and horizontal components of particle velocity, and is also the normalized curl of the active intensity vector. As such, it is highly dependent on the phase, amplitude, and arrival angle of interfering multipath arrivals, with value as a function of source depth that depends on both frequency and bottom type. We first show results from the Targets and Reverberation Experiment (TREX) which took place off Panama City, where frequencies in the range of 1–4 kHz are used to study sandy sediments [Dall’Osto et al., J. Acoust. Soc. Am. 139, 311–319, 2016]. The approach is next applied hypothetically at lower frequencies for which fewer modes are supported in the waveguide, and to different seabed conditions to demonstrate how a range of sediments from sand to mud are distinguished.

Diffusion flame in an electric field with a variable spatial configuration

The influence of an electric field whose intensity vector rotates around the flame axis on the shape of the diffusion flame of propane is experimentally studied. Application of spectrozonal registration makes it possible to obtain information about the radiation intensity distribution at wavelengths of intermediate reaction products (OH, CH, and C2). Different positions of the peak intensity of the own radiation of the flame at different wavelengths testify to the influence of such an electric field on the mixing processes, namely, mixing is more intense than that in the regime without application of the electric field. This feature may turn out to be useful for increasing the efficiency of combustion of gaseous hydrocarbon fuels.

Coil-to-coil physiological noise correlations and their impact on functional MRI time-series signal-to-noise ratio.

Physiological nuisance fluctuations ("physiological noise") are a major contribution to the time-series signal-to-noise ratio (tSNR) of functional imaging. While thermal noise correlations between array coil elements have a well-characterized effect on the image Signal to Noise Ratio (SNR0 ), the element-to-element covariance matrix of the time-series fluctuations has not yet been analyzed. We examine this effect with a goal of ultimately improving the combination of multichannel array data. We extend the theoretical relationship between tSNR and SNR0 to include a time-series noise covariance matrix Ψt , distinct from the thermal noise covariance matrix Ψ0 , and compare its structure to Ψ0 and the signal coupling matrix SSH formed from the signal intensity vectors S. Inclusion of the measured time-series noise covariance matrix into the model relating tSNR and SNR0 improves the fit of experimental multichannel data and is shown to be distinct from Ψ0 or SSH . Time-series noise covariances in array coils are found to differ from Ψ0 and more surprisingly, from the signal coupling matrix SSH . Correct characterization of the time-series noise has implications for the analysis of time-series data and for improving the coil element combination process. Magn Reson Med 76:1708-1719, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

The influence of technogenic factors on the karst activization of Precarpathian salt sediments and karst natural lows.

Abstract. Understanding the laws development of processes is one from way to make the right decisions at the forecasting stage and developing them. This is especially true salt deposits, which are located in complex geological conditions. Carpathian foredeep has a very difficult geological structure. The development of karst processes in Precarpathians conditions shown that salt karst is a complex multi-system process where all components have a significant impact on the results that are directly related to each other. Purpose of this article within the distribution of Precarpathians salt-bearing Miocene sediments to conduct analysis of technologically and naturally caused factors that influence on the development and intensification of salt karst and harmful exogenic geological process that are related with its. And too at the base of the conducted review the natural laws of karst development to highlight. Results of the completed research confirmed that features spatial development of karst processes in the Carpathian salt deposits is caused by complex geological structure of Miocene sediments. Spatial development of karst processes depends on heterogeneity in plan and section water penetration of salt-bearing sediments. This forms the predominant vector of underground leaching intensity along geological boundaries. Permeability and solubility salt bearing deposits along the bedding are higher relative to the permeability and solubility across of geological structures. Faults which occur across the strike of geological layers act as a containment of karst processes along the geological borders.

Calibration and Compensation of Geomagnetic Vector Measurement System and Improvement of Magnetic Anomaly Detection

The magnetometer error and distortion magnetic field of an inertial navigation system are the major two factors influencing the measurement accuracy of geomagnetic vector information measurement systems. The calibration and compensation methods are proposed in this letter. As a first step, a calibration model for a three-axis magnetometer is established, and a nonlinear least square algorithm is used to estimate thoroughly the error parameters. Then, a distortion compensation model based on relative attitude information is proposed, in which only four groups of attitude information are needed to estimate precisely the distortion parameters. Finally, the whole system is used for magnetic anomaly detection. Experimental results suggest that the magnetometer error can be accurately calibrated, and the magnetic field distortion can be suppressed significantly. After calibration and compensation, the intensity and magnetic anomaly vectors such as west vector, south vector, and vertical vector can be accurately measured by the geomagnetic vector measurement system. It demonstrates that the proposed method can effectively improve the accuracy of the geomagnetic vector measurement system.

Histogram of Oriented Gradient Based Gist Feature for Building Recognition.

We proposed a new method of gist feature extraction for building recognition and named the feature extracted by this method as the histogram of oriented gradient based gist (HOG-gist). The proposed method individually computes the normalized histograms of multiorientation gradients for the same image with four different scales. The traditional approach uses the Gabor filters with four angles and four different scales to extract orientation gist feature vectors from an image. Our method, in contrast, uses the normalized histogram of oriented gradient as orientation gist feature vectors of the same image. These HOG-based orientation gist vectors, combined with intensity and color gist feature vectors, are the proposed HOG-gist vectors. In general, the HOG-gist contains four multiorientation histograms (four orientation gist feature vectors), and its texture description ability is stronger than that of the traditional gist using Gabor filters with four angles. Experimental results using Sheffield Buildings Database verify the feasibility and effectiveness of the proposed HOG-gist.

Linewidth Reconstruction Employing a Radial Basis Function Network in Optical Scatterometry

This paper applied a radial basis function network (RBFN) in coherent Fourier scatterometry (CFS) to reconstruct the linewidth of periodic line/space (L/S) patterns. The fast, nondestructive, and repeatable measurement capability of CFS enables its integration with intelligent lithography systems. Two steps to reconstruct the linewidth of the L/S patterns were performed in this paper. The first step was to use the finite difference time domain numerical electromagnetic tool to rigorously establish the library of modeled diffraction signatures by using the L/S patterns. Each modeled signature was converted to an intensity vector as the training data to construct the RBFN. The trained RBFN has a simple architecture consisting of three layers: input, hidden, and output layers. The second step was to collect the experimental signatures and feed them into the trained RBFN model to predict the linewidth of L/S patterns. This paper used the transverse electric polarized incident beam at the wavelength of 632 nm in the experimental setup of the CFS. Five L/S patterns were used to test the constructed RBFN. The experimental results indicated that the maximal difference was 13 nm between the CFS and the atomic force microscopy (AFM) measurements for the sample D with an L/S of 200 nm. The minimum difference was 2 nm for the sample A with an L/S of 140 nm. The correlation coefficient between the CFS and AFM metrology measurement running through five samples was 0.972. The high correlation between the CFS with the proposed RBFN measurements and the AFM revealed the potential to implement the radial basis learning kernel in optical metrology to achieve intelligent lithography.

Changing the magnetic field intensity during the motion of spacecraft

In this paper the change of the intensity vector of geomagnetic field during the motion of the spacecraft in orbit in direct dipole model was investigated. The dependences of the intersection point coordinates of the vector intensity of the geomagnetic field with the unit radius Earth sphere were found, their graphs were built and their extremes were determined. The relations of the intersection point velocity of the vector intensity of the geomagnetic field to the unit radius Earth sphere were found, their graphs were built and their extremes determined. The graphs of each component of the geomagnetic field along the trajectory of the spacecraft and the combined graphs were built.

Cryptanalysis and security enhancement of optical cryptography based on computational ghost imaging

Optical cryptography based on computational ghost imaging (CGI) has attracted much attention of researchers because it encrypts plaintext into a random intensity vector rather than complexed-valued function. This promising feature of the CGI-based cryptography reduces the amount of data to be transmitted and stored and therefore brings convenience in practice. However, we find that this cryptography is vulnerable to chosen-plaintext attack because of the linear relationship between the input and output of the encryption system, and three feasible strategies are proposed to break it in this paper. Even though a large number of plaintexts need to be chosen in these attack methods, it means that this cryptography still exists security risks. To avoid these attacks, a security enhancement method utilizing an invertible matrix modulation is further discussed and the feasibility is verified by numerical simulations.

Optimized vector sound intensity measurements with a tetrahedral arrangement of microphones in a spherical shell.

Recent times have seen the introduction of small spherical arrays whose usefulness as sound intensity probes is the focus of this paper. The presented probe consists of a spherical shell, 30 mm in diameter, housing four 14 in. microphones arranged in a regular tetrahedral configuration. Classical formulae may be used to estimate the sound intensity vector, as may methods based on spherical harmonics decomposition. Results are shown to be comparable to those obtained from classical sound intensity probes. The existence of an analytical model for a plane wave's diffraction about a sphere provides a means for adopting common optimization techniques for potentially improving the intensity vector estimate, however. This paper examines the validity of non-linear least squares optimization in conjunction with the proposed spherical sound intensity probe when placed in the following sound fields: (1) a simple plane wave; (2) a plane wave corrupted by noise; and (3) multiple incident plane waves. Under certain conditions, the probe is shown to greatly extend the operational frequency range of classical sound intensity probes. The optimization algorithm is found to lack robustness against deviations from plane wave conditions, however.

Source characterization of full-scale jet noise using acoustic intensity

Vector acoustic intensity provides both the direction and magnitude of energy flow at the probe location and is, hence, more informative than acoustic pressure measurements. However, this important quantity has seen little application previously in aeroacoustics. In the present work, an intensity probe, consisting of four microphones, captured the radiated field to the sideline and aft of a tethered, full-scale military jet aircraft as one engine was operated at multiple engine conditions. Data from each probe location provide a frequency-dependent map of the sound flow near the aircraft. The vector acoustic intensity is estimated using a recently developed processing technique that extends the upper frequency limit of the traditional cross-spectrum-based calculations. The dominant intensity vectors are traced back to the jet centerline as a method of approximating the extent and location of the source region as a function of frequency. As expected for jet mixing noise sources, the resulting source region estimates contract and move upstream with increasing frequency. A comparison of estimated source regions and intensity directionalities between military and afterburner engine conditions reveals important distinctions in the sound fields.

Modeling of porous piezoelectric structures by the meshless local Petrov-Galerkin method

ABSTRACTA meshless method based on the local Petrov-Galerkin approach is proposed to solve initial-boundary value problems of porous piezoelectric solids. Constitutive equations for porous piezoelectric materials possess a coupling between mechanical displacements and electric intensity vectors in both solid and fluid phases. Stationary and transient 2-D and 3-D axisymmetric problems are considered in this article. Nodal points are spread on the problem domain, and each node is surrounded by a small circle for simplicity. The spatial variation of displacements and electric potentials for both phases is approximated by the moving least-squares scheme. After performing the spatial integration, one obtains a system of ordinary differential equations for certain nodal unknowns. The resulting system is solved numerically by the Houbolt finite-difference scheme as a time stepping method. The proposed method is applied to bending problems associated with a porous piezoelectric 2-D plate and 3-D axisymmetric cylinder under simply supported and clamped boundary conditions.

Multiple-image encryption based on computational ghost imaging

We propose an optical multiple-image encryption scheme based on computational ghost imaging with the position multiplexing. In the encryption process, each plain image is encrypted into an intensity vector by using the computational ghost imaging with a different diffraction distance. The final ciphertext is generated by superposing all the intensity vectors together. Different from common multiple-image cryptosystems, the ciphertext in the proposed scheme is simply an intensity vector instead of a complex amplitude. Simulation results are presented to demonstrate the validity and security of the proposed multiple-image encryption method. The multiplexing capacity of the proposed method is also investigated. Optical experiment is presented to verify the validity of the proposed scheme in practical application.

The handedness and classification of materials

According to direction relationship among the triplet of vectors of electric field intensity, magnetic field intensity and wave vector of electromagnetic wave, materials have usually been classified as right- and left-handed material. Here, we shall strictly and systematically demonstrate that, in a linear isotropic homogeneous medium, the direction relationship among the triplet of vectors of electric field intensity, magnetic field intensity and wave vector of electromagnetic wave may generally alter between right-handedness and left-handedness with change of time except for the special cases. Thus the further classification of materials according to handedness and corresponding criterion are proposed.

Intensity-vesselness Gaussian mixture model (IVGMM) for 2D + t segmentation of coronary arteries for X-ray angiography image sequences.

This study aimed to propose an intensity-vesselness Gaussian mixture model (IVGMM) tracking for 2D + t segmentation of coronary arteries for X-ray angiography (XA) image sequences. We compose a two dimensional (2D) feature vector of intensity and vesselness to characterize the Gaussian mixture models. In our IVGMM tracking, vessel segmentation is performed for each image frame based on these vessel and background IVGMMs and then the segmentation results of the current image frame is used to update these IVGMMs. The 2D + t segmentation of coronary arteries over the 2D XA image sequence is solved by means of iterating two processes, i.e., segmentation of coronary arteries and update of the IVGMMs. The performance of the proposed IVGMM tracking was evaluated using clinical 2D XA datasets. We evaluated the segmentation accuracy of the IVGMM tracking by comparing with two previous 2D vessel segmentation methods and seven background subtraction (BGS) methods. Of the ten segmentation methods, IVGMM tracking shows the highest similarity to the manual segmentation in terms of precision, recall, Jaccard index (JI), F1 score, and peak signal-to-noise ratio (PSNR). It is concluded that the IVGMM tracking could obtain reasonable segmentation accuracy outperforming conventional vessel enhancement methods and object tracking methods.

Source characterization of full-scale jet noise using vector intensity

Vector acoustic intensity has the benefit over pressure measurements in that both the direction and magnitude of energy flow are represented. However, this important quantity has seen little application previously in aeroacoustics. In the present work, an intensity probe captured the radiated field to the sideline and aft of a tethered, full-scale military jet aircraft as one engine was operated at multiple engine conditions. Intensity data from each probe location provide a frequency-dependent map of the sound flow near the aircraft. The vector acoustic intensity is estimated using a recently developed processing technique that extends the traditional upper-frequency limit on estimation accuracy. The intensity vectors are traced back to the jet centerline as a method of approximating the extent and location of the source region as a function of frequency. This method is validated by numerical simulation. As expected for jet mixing noise sources, the resulting source region estimates contract and move upstream with increasing frequency. In addition, the source region at afterburner compared to full-throttle is located about 1 m farther downstream at frequencies above about 300 Hz, and the intensity tends to point more to the sideline by up to 10°. [Work supported by ONR.]

Using vector sensors to measure the complex acoustic intensity field

The acoustic intensity vector field, defined as the product of pressure particle velocity fields, describes the flow of energy from an acoustic source. Following a brief introduction of acoustic vector sensors, which includes some direct measurements of acoustic intensity, the intensity field is shown to be composed of active and reactive components. Active intensity streamlines depict the time-averaged flow of acoustic energy and reveal characteristics of acoustic propagation including environmental influences. These streamlines do not characterize reactive intensity, which corresponds to the portion of acoustic intensity that time-averages to zero. Reactive intensity is significant in the near-field of a source and in environments where multipath interfere occurs. To examine the interplay between active and reactive acoustic intensity, the acoustic field generated by an airborne source positioned well above a water surface is presented. Acoustic measurements of a passing airplanes, made simultaneously above and below this sea-surface, are used to demonstrate properties of active and reactive intensity, including how reactive intensity can serve as an indicator of source altitude and range.

Analytical intensity calculated from a wavepacket model and comparison to intensity measurements near a high-performance military aircraft

To create an equivalent source description of jet noise, a wavepacket model is used to determine the acoustic vector intensity away from the source. This paper represents an initial investigation into using the measured vector acoustic intensity to define wavepacket parameters. The complex pressure of a line source is defined according to an analytical hyperbolic tangent wavepacket model and Rayleigh integration is used to find the pressure, particle velocity, and time-averaged intensity at observer locations. The parameters that define the shape of the wavepacket are initially based on prior pressure level-based optimization carried out for ground-based microphones. The resulting calculated acoustic intensity vectors are compared to vector intensity measurements previously taken near a tethered high-performance military aircraft at military and afterburner engine conditions. The wavepacket parameters are then varied to provide an optimal fit using the intensity, rather than pressure level, as the cost function, and the differences between the two models are described. [Work supported by the Office of Naval Research.]

Effects of temperature and electric field on the structure of liquid crystals in the presence of carbon nanotube

The results from computer modeling of the behavior of nematic liquid crystals on two-walled carbon nanotubes under the effects of temperature and an electric field are presented. It is found that two-axis states appear when the direction of vectors of electric field intensity and nanotube axis match. The differences between the behavior of polar and nonpolar liquid crystals are demonstrated.