Angle Parameters Research Articles

ANN-Assisted Beampattern Optimization of Semi-Coprime Array for Beam-Steering Applications

In this paper, an artificial neural network (ANN) has been proposed to estimate the required values of the adjustable parameters of a Semi-Coprime array with staggered steering (SCASS), which was proposed recently. By adjusting the amount of staggering and the sidelobe attenuation (SLA) factor of Chebyshev weights, SCASS can promise a quite small half-power beamwidth (HPBW) and a high peak-to-side-lobe ratio (PLSR), even when the beam is steered away from broadside direction. However, HPBW and PSLR cannot be improved simultaneously. There is always a trade-off between the two performance metrics. Therefore, in this paper, a mechanism has been introduced to minimize HPBW for a desired PSLR. The proposed ANN takes the array of architectural parameters, the required steering angle, and the desired performance metric, i.e., PSLR, as input and suggests the values of the adjustable parameters, which can promise the minimum HPBW for the desired PSLR and steering angle. To train the ANN, we have developed a dataset in Matlab by calculating HPBW and PSLR from the beampattern generated for a large number of combinations of all the variable parameters. It has been shown in this work that the trained ANN can suggest the optimum values of the adjustable parameters that promise the minimum HPBW for the given steering angle, PSLR, and array architectural parameters. The trained ANN can suggest the required adjustable parameters for the desired performance with mean absolute error within just 0.83%.

A Novel Electrocardiographic Marker to Predict the Development of Preeclampsia: Frontal QRS-T Angle—A Prospective Pilot Study

Background and Objectives: Preeclampsia, a pregnancy-induced hypertensive disorder, shares cardiovascular characteristics in etiology, prognosis, and fetomaternal risks. Electrocardiography plays a pivotal role in assessing cardiovascular risks. Beyond conventional predictors, identifying easily obtainable and reproducible electrocardiographic markers may significantly contribute to the early identification of individuals at risk of preeclampsia. In this study, we aimed to investigate the value of the Frontal QRS-T angle and other electrocardiographic parameters in predicting the development of preeclampsia. Materials and Methods: A total of 62 pregnant patients diagnosed with preeclampsia and 50 healthy pregnant patients as the control group were included in this study. The first- and third-trimester electrocardiographic parameters were compared within groups and between groups. Results: The Frontal QRS-T angle was significantly elevated in patients with preeclampsia compared to the controls (55.0 ± 40.8 vs. 19.5 ± 15.1; p = 0.002). The first-trimester Frontal QRS-T angles in the patients with preeclampsia were higher than those of the controls (29.5 ± 25.0 vs. 15.3 ± 11.5; p = 0.015). A high Frontal QRS-T angle independently marked preeclampsia development in antenatal and late pregnancy (p = 0.003 and p = 0.042, respectively). The diagnostic accuracy of the Frontal QRS-T angle in predicting preeclampsia surpassed other electrocardiographic parameters. Conclusions: This study shows that the Frontal QRS-T angle may be a candidate to be an independent predictor for the development of preeclampsia. In this context, the Frontal QRS-T angle, which is an electrocardiographic parameter, seems promising.

Modeling and Measurement of Tool Wear During Angular Positioning of a Round Cutting Insert of a Toroidal Milling Tool for Multi-Axis Milling

The aim of this study was to develop a concept for an angular positioning method for a round cutting insert in a torus cutter body dedicated to the multi-axis milling process under high-speed machining cutting conditions. The method concept is based on a developed wear model using a non-linear estimation method adopting a quasi-linear function. In addition, a tool life model was developed, taking into account the cutting blade work angle parameter, the laser marking method for the round cutting insert, and a wear measurement methodology. The developed tool wear model provides an accuracy of 90% in predicting the flank wear of the cutting blade. The developed procedure for angular positioning of the round cutting insert enables the entire cutting edge to be fully utilized, extending the total tool life. In addition, the measured largest defect values between the worn cutting edge and the nominal outline of the round cutting insert indicate the location of notching-type wear.

Foot Progression Angle in Relation to Spatiotemporal Parameters of Gait in Children with Cerebral Palsy

OBJECTIVE: This study assessed the difference in the foot progression angle and measure spatiotemporal parameters of gait of children with diplegic cerebral palsy and to examine the relation among foot progression angle of right and left lower limb and spatiotemporal parameters of gait. DESIGN: Cross-sectional and Correlation study. SUBJECTS: Sixty children with spastic diplegia, aged 5 to 8 years. The participants were categorized into 3 age groups of equivalent number: group A (5 to 6 years), group B (6 to 7 years), as well as group C (7 to 8 years). METHODS: Foot progression angle and spatiotemporal parameters of the gait for both feet were evaluated utilizing a dynamic footprint. RESULTS: a moderate negative significant correlation was noted among left FPA and right step length, and right stride length. There was moderate positive significant correlation among left FPA and cadence . A weak non-significant correlation was observed among right and left FPA and gait parameters among three groups. CONCLUSION: foot progression angle assessment and spatiotemporal measurements and the correlation among them can give objective and quantitative data that could be utilized in rehabilitation and clinical evaluations to identify functional deficiencies.

Aerodynamic performance evaluation of subsonic compressor cascade blade with leading-edge damage

Abstract Material loss at the leading edge of in-service gas-turbine engine blades is detrimental to the aerodynamic performances of compressors. In this study, computational simulations and experiments using pneumatic probes were conducted to measure the total pressure loss of compressor cascade blades with material loss at their leading edges. The correlations between blade leading-edge damage geometries and cascade blade total pressure losses were analyzed. The geometrical features of blade leading-edge damage that most affect the cascade blade total pressure loss were distinguished, and the influences of leading-edge damage region cross-sectional shapes on the cascade blade total pressure loss were examined. Two methods for evaluating the total pressure loss of damaged cascade blades were developed using experimental and numerical data. In the first method, an attempt is made to correlate the cascade blade total pressure loss with a characteristic parameter that is defined using scale and angle parameters of the leading-edge damage region. The second method is based on the probability distribution function as well as the critical loss boundary of the geometrical parameters of the leading-edge damage region. The results of this study provide a better understanding of the influence of damaged leading edges on compressor cascade blade aerodynamic performance and can help establish low-cost methods for the estimation of compressor performance degradation.

Precise Orientation Estimation for Rotated Object Detection Based on a Unit Vector Coding Approach

Existing rotated object detection methods usually use angular parameters to represent the object orientation. However, due to the symmetry and periodicity of these angular parameters, a well-known boundary discontinuity problem often results. More specifically, when the object orientation angle approaches the periodic boundary, the predicted angle may change rapidly and adversely affect model training. To address this problem, this paper introduces a new method that can effectively solve the boundary discontinuity problem related to angle parameters in rotated object detection. Our approach involves a novel vector-based encoding and decoding technique for angular parameters, and a cosine distance loss function for angular accuracy evaluation. By utilizing the characteristics of unit vectors and cosine similarity functions, our method parameterizes the orientation angle as components of the unit vector during the encoding process and redefines the orientation angle prediction task as a vector prediction problem, effectively avoiding the boundary discontinuity problem. The proposed method achieved a mean average precision (mAP) of 87.48% and an average cosine similarity (CS) of 0.997 on the MVTec test set. It also achieved an mAP score of 90.54% on the HRSC2016 test set, which is better than several existing state-of-the-art methods and proves its accuracy and effectiveness.

Recursive-RARE-based three-dimensional parameter estimation of near-field source considering amplitude attenuation

This paper addresses the issue for near-field (NF) localization considering amplitude attenuation, proposing a recursive rank-reduction (RARE) method for three-dimensional (3-D) parameter estimation of NF sources incident on a symmetrical cross array. The proposed method constructs several one-dimensional (1-D) spectral peak search estimators to obtain two-dimensional angle and range parameters. Initially, using the received data from symmetrical array elements in one axis, a 1-D spectral peak search estimator is constructed. The origins of two types of pseudo peaks within this estimator are analyzed, and then, corresponding pseudo peaks removal methods, namely the initial screening method and the recursive RARE method, are presented to obtain the estimate of the first angle parameter. Subsequently, the estimated results are fed into another 1-D spectral peak search estimator constructed from the original received data to obtain the range parameter. Finally, the same process is applied to the other axis to obtain the second angle and range parameters, followed by a parameter matching operation for 3-D parameters. Compared to existing NF source localization methods, the proposed method more effectively eliminates pseudo peaks, and demonstrates superior parameter estimation performance under conditions of small number of snapshots and low signal-to-noise ratio, as validated by several simulation results.

Comparison and parametric study of characteristics of eleven types of anisotropic woods based on the behaviour of Lamb wave propagation

AbstractKnowledge in advance of the nine orthotropic independent elastic constants (Cij) of the wood medium is essential for evaluating its mechanical properties. The most prominent technique to retrieve Cij is the ultrasonic testing technique. This technique uses guided waves that can propagate through the material under test. Accordingly, it is worth noting that the numerical modelling of the phase and group velocities of guided waves is an unavoidable preliminary step before experimentally producing guided wave modes. Therefore, the main goal of the present work is to numerically calculate the phase velocity, group velocity and the relevant optimal incidence angles of Lamb waves in anisotropic wood that can be used as a numerical parametric study for any future experimental setup. Here, Lamb dispersion curves are calculated for eleven types of woods, where the Legendre polynomial method is employed to solve the wave equations. Moreover, the optimal incidence angle for each Lamb mode is calculated according to the Snell–Descartes law. By calculating out the three parameters of phase velocity, group velocity and optimal incidence angle of Lamb modes in eleven types of anisotropic woods, we hope to fast-track the researchers in considering the present work to facilitate their experimental measurements.

Exploring Kinematic Variations in Clear Hip Circle to Handstand: A Case Study of Performance Styles on Uneven Bars

(1) Background: This case study analyzed the successful performances of female gymnasts in the finals of the 39th and 40th World Cup in Maribor (SLO). The aim was to identify variations in their execution of the Clear Hip Circle to Handstand (CHCH) on uneven bars based on kinematic parameters. (2) Methods: This study involved elite female gymnasts from the 39th (n = 5, age: 17 ± 6 months) and 40th (n = 8, age: 17.5 ± 6 months) World Cups, totaling 13 gymnasts. Kinematic analysis was performed on 15 successful routines using the Ariel Performance Analysis System (Ariel Dynamics Inc., San Diego, CA). The analysis focused on 16 anthropometric reference points and 8 body segments, including the body mass center of gravity (CG). The main reference points analyzed were the hip joint, the shoulder joint, and the CG along the xy-axes. Trajectory, velocity, angle, and angular velocity of the hips and shoulders were calculated. Pearson correlation analysis was employed to assess the relationships between the kinematic variables. (3) Results: High intercorrelations between the reference points along the xy-axes (0.81–0.99) and optimal movement velocity were found. Dispersed results were observed for kinematic parameters of angle (0.10–0.16) and angular velocity of the hip joints (0.60–1.00), with similar dispersions for shoulder joints (0.51–1.00). Three distinct techniques were identified: (1) stretched body with minimal hip joint flexion throughout; (2) extended body with a short, quick hip joint extension during shoulder movement; and (3) hyperextension in the hip joint. (4) Conclusions: The kinematic analysis revealed three different performance styles of the CHCH among finalists. These variations in technique do not affect the success of the performance. This research contributes to a better understanding of the technique but does not prefer one style over another.

Numerical and experimental analysis of Al/GFRP joint for optimization of adhesive bonding strength using response surface method by considering surface patterning of the joints

Nowadays, adhesive bonding of metals and composites is widely used in the aerospace, automotive and military industries. In the present research, the finite element analysis (FEA) and response surface method (RSM) are used to optimize adhesive bonding strength between aluminum (Al) and glass fiber reinforced polymer (GFRP). For this purpose, the influence of the parameters of joint type, groove shape, groove number, and groove angle was investigated on the bonding strength. The joint type includes Al/Al, Al/GFRP and GFRP/GFRP, the groove shape includes V-shape, square and concave, the groove number includes 1, 3 and 5 grooves, and the groove angle includes 0, 45 and 90º. In order to model the crack growth in the simulation of adhesive bonding, the cohesive zone model was applied. Finally, the optimal sample is fabricated to examine its strength in temperature-humidity environmental conditions. The results of simulation and optimization indicated that the bonding strength improved in Al/Al mode with one square groove at 0° groove angle. The stress-strain diagram obtained from the simulation and optimization results was in good agreement with the sample made under optimal conditions. Moreover, the tensile strength of the optimal sample at temperature-humidity conditions was higher than the tensile force of the sample without groove.

Measurements of Sunspot Group Tilt Angles Based on SOHO/MDI and SDO/HMI Magnetograms

The tilt angle of sunspot groups plays a crucial role in solar dynamo models for the generation of the poloidal field, yet the statistical properties of the tilt angle are not fully comprehended. This study employs magnetograms from the Solar and Heliospheric Observatory/Michelson Doppler Imager and Solar Dynamics Observatory/Helioseismic and Magnetic Imager to measure the tilt angles of 11,373 sunspot groups over the period from 2008 to 2023. This comprehensive analysis examines the relationship between the tilt angle and latitude of the sunspot groups, as well as the correlation between the tilt angle and solar cycle strength. The methodology involves calculating tilt angles within the ±45° central meridian distance, comparing mean-based and median-based measurements, and applying specific angular separation criteria. The findings reveal that during solar cycle 24, the tilt angles increase by approximately 4° for every 10° increase in latitude, in line with Joy’s law. A significant anticorrelation is observed between the latitude-normalized tilt angle (γ/∣L∣) and solar cycle strength. The research also uncovers a substantial hemispheric asymmetry in tilt angle parameters, with the southern hemisphere (m Joy: 0.23 ± 0.092 ∼ 0.24 ± 0.074, γ = 8.°14 ± 0.°43 ∼ 9.°04 ± 0.°486) consistently showing larger tilt angles than the northern hemisphere (m Joy: 0.47 ± 0.096 ∼ 0.51 ± 0.062, γ = 6.°14 ± 0.°304 ∼ 6.°64 ± 0.°334).

An analytical study of Euler angle and Rodrigues parameter representations of $\mathbb{SO}(3)$ towards describing subsets of ${\mathbb{SO}}(3)$ geometrically and establishing the relations between these

Abstract Descriptions of various subsets of $\mathbb{SO}(3)$ are encountered frequently in robotics, for example, in the context of specifying the orientation workspaces of manipulators. Often, the Cartesian concept of a cuboid is extended into the domain of Euler angles, notwithstanding the fact that the physical implications of this practice are not documented. Motivated by this lacuna in the existing literature, this article focuses on studying sets of rotations described by such cuboids by mapping them to the space of Rodrigues parameters, where a physically meaningful measure of distance from the origin is available and the spherical geometry is intrinsically pertinent. It is established that the planar faces of the said cuboid transform into hyperboloids of one sheet and hence, the cuboid itself maps into a solid of complicated non-convex shape. To quantify the extents of these solids, the largest spheres contained within them are computed analytically. It is expected that this study would help in the process of design and path planning of spatial robots, especially those of parallel architecture, due to a better and quantitative understanding of their orientation workspaces.

Short-term changes in the trabecular iris angle and anterior chamber during wear of scleral lenses with different diameters

ABSTRACT Clinical relevance Scleral lens (SL) compression on the conjunctiva/episclera during wear may alter adjacent structures related to aqueous humour drainage. Background The aim of this work was to assess short-term changes in the four quadrants of trabecular iris angle (TIA) and anterior chamber parameters during SL wear, using anterior segment optical coherence tomography (AS-OCT). Methods Prospective study was conducted involving 16 healthy subjects with a mean age of 28 ± 5 years. Two SL of diameter 15.80 mm (L1) and 16.80 mm (L2) with the same parameters were used for 2 hours in different days. The central fluid reservoir (FR), the TIA in superior, inferior, nasal, temporal quadrants, and anterior chamber parameters; anterior chamber depth (ACD), anterior chamber width (ACW), anterior chamber area (ACAr) and anterior chamber volume (ACV) were measured with AS-OCT. These measurements were performed immediately after SL application (0 h), one hour (1 h) and two hours (2 h) of SL wear. Results TIA decreases significantly in the superior quadrant at 2 hours of L2 wear (−5.19 ± 7.79º) (p = 0.04). In this sector, differences were also observed between the changes induced by both lenses during the 2 hours of wear (p = 0.04) and between first and second hours of wear (p = 0.04). ACD was significantly lower with L1 (−0.09 ± 0.14 mm) relative to L2 (0.00 ± 0.06 mm) between immediately after the application and 2 hours of wear (p = 0.02). A significant reduction in ACAr at 1 hour (−0.65 ± 0.75 mm2) (p = 0.01) and 2 hours of wear (−0.81 ± 1.15 mm2) (p = 0.04), as well as in ACW at 2 hours (−0.11 ± 0.14 mm) (p = 0.02) compared to immediately after application of L1 was found. Conclusion Small changes in TIA and anterior chamber occur during two hours of SL wear, but these changes are of limited clinical relevance in healthy subjects.

Corrosion effects on flexural behaviour of EPS sandwich concrete panels: a study using acoustic emission technique

The experimental research utilized expanded polystyrene (EPS) panels sized at 1300 × 600 × 130 mm (length × width × thickness) and induced with corrosion via an impressed current method. Varied extents of corrosion were applied for 120, 240, 360, and 480 h, resulting in mass loss percentages of 6.67%, 8.41%, 10.76%, and 18.13% of reinforcement in different panels. The flexural testing along with acoustic emission (AE) monitoring were performed for evaluation of EPS panels. Results obtained defend the correlation of AE energy with the load energy in the EPS panels. The AE parameters of rise angle and average frequency assist in distinguishing between tensile and shear crack types. The energy released during tensile crack formation in EPS panels is minimal compared to that during shear crack formation. These findings are a basis for further AE investigations into EPS panels and developing AE sensor-based methods for identifying corrosion-induced degradation in EPS panels within structures.

A generic detailed multibody model for simulating thoracic spine and ribcage kinematics

AbstractA reliable and comprehensive multibody musculoskeletal model of the thoracic spine and ribcage can offer valuable insight into the biomechanics of healthy and curved spines. In this study, we developed a generic rigid-body thoracic spine and ribcage model, which is kinematically determinate and controlled by spinal posture. A newly devised averaging constraint was implemented to model the kinematics of individual ribs and the sternum. Rib motion validation confirmed that the movement of adjacent ribs matched measured data across different tasks. We simulated 39 adolescent idiopathic scoliosis subjects aged 7–17 years, with an average (SD) Cobb angle of 15.9 (8.2) degrees. The average errors of multiple scoliosis metrics were less than 4 degrees for angle parameters, 5 mm for displacement parameters, and 3 percent for the ratio parameter. The model is straightforward and can simulate various daily activities (e.g., spinal articulation and breathing) while accurately capturing pathological deformities conforming to experimental data. It is available to the public on the open science platform Zenodo and will also be accessible through the AnyBody Managed Model Repository.

Boostering motor imagery processing to improve gait in patients with Parkinson disease and freezing of gait: A pilot study

BackgroundGiven that patients with Parkinson's Disease (PD) and Freezing of Gait (FoG) may lack the cognitive resources necessary to activate the motor imagery (MI) process, investigating how to boost MI vividness and accuracy could be a valuable therapeutic strategy in MI Practice (MIP). ObjectiveWe aim to evaluate the priming effect of visual, or auditory, or attentional stimuli in enhancing MI ability by using quantitative data on gait and turning performance. MethodsNineteen PD participants with FoG underwent four one-week sessions of MIP, with pre and post clinical assessments. Each session included MI alone or one of three booster MI tasks (Attentional, Action observation, or Auditory) before imagining and executing walking straight and performing a 180° turn. Gait and turning performances were evaluated using six inertial sensors before and after each session. ResultsOur findings showed that both MI and boosted MI induced similar improvement in gait (speed and stride length) and 180° (step number and velocity) and 360° turning (velocity, angle) parameters compared to baseline. When differences among “booster” tasks were analyzed, results showed that Auditory and Attentional boosted MI were superior to MI alone in some gait and turning parameters. At the end of the 4 sessions, MI ability measured by means of Kinesthetic and Visual Imagery Questionnaire and Gait Imagery Questionnaire and FoG symptoms were also improved. ConclusionOur preliminary results suggest that boosting MI is a feasible strategy for enhancing MI ability and addressing FoG symptoms. Auditory and Attentional conditions appear to enhance the priming effect of MI on gait and turning performance more effectively.

Main lobe deceptive jamming suppression based on blind source separation and energy detection for monopulse radar

AbstractMain lobe deceptive jamming always causes the serious degradation of signal detection ability and angle measurement precision of monopulse radar. In recent years, the Blind Source Separation (BSS) method has been adopted to suppress the main lobe jamming. However, the separation results of BSS have the problem of amplitude ambiguity, which will cause the radar using monopulse angle measurement fail to measure the angle parameters after jamming suppression. To tackle this problem, a novel main lobe jamming suppression method is proposed based on BSS and energy detection. Firstly, the models of target echoes and jamming in the sum and difference beam receiving channels are derived. Secondly, the target echoes and interferences are separated by the Joint Approximate Diagonalisation of Eigenmatrices (JADE) algorithm, and then the unperturbed signal segments in the mixed signal are extracted by energy detection, thereby obtaining the precise ratio of the sum and difference channels to complete the angle measurement. Performance of the method was verified by numerical simulation. The results show that the proposed method can achieve interference suppression while accurately estimating the angle parameter of the target.

Assessing bonding and debonding properties of Evotherm modified bitumen with natural aggregates using surface free energy approach

ABSTRACT An incongruous pairing of aggregates and bitumen can result in early pavement failures such as stripping, raveling, and fatigue cracking. Surface free energy (SFE) assessments of aggregates and bitumen offer a means to evaluate the compatibility of the aggregate-bitumen system. It is important to emphasise that the SFE of both bitumen and aggregates significantly influences the determination of a compatible aggregate-bitumen combination. In this study, the moisture damage resistance of unmodified bitumen types (VG20, VG40) and modified bitumen types (PMB40, CRMB60) incorporating chemical-based warm mix asphalt (WMA) additives, specifically Evotherm, was investigated. The SFE approach was utilised to gain insights into their performance. In the laboratory, the static contact angle and SFE parameters of both unmodified and modified bitumen, with and without Evotherm, were determined using the Sessile drop method. Five different aggregate types were employed to calculate SFE performance parameters. Subsequently, the SFE performance parameter of forty combinations of aggregates and bitumen was calculated. As part of the assessment of moisture damage resistance, the compatibility ratio (CR) parameter was estimated using the dry adhesion energy, bitumen cohesion energy, wet adhesion energy, and wettability of different combinations of bitumen with aggregates. From the result, Evotherm addition to base bitumen (excluding VG20) significantly improved CR across various aggregates. Notable increases were observed for VG40, PMB40, and CRMB60 after Evotherm addition, with improvements of 66.67%, 48.48%, and 64.54% respectively for basalt aggregate. PMB40+EM with basalt aggregate exhibited the highest CR and Tensile Strength Ratio (TSR), suggesting superior moisture damage resistance compared to other bitumen combinations.

Darcy-Brinkman Flow of a Micropolar Fluid through an Anisotropic Porous Channel

This study investigates the Darcy-Brinkman flow of micropolar fluid through an anisotropic porous channel, a configuration relevant to various industrial and natural processes involving complex fluid flow. The anisotropy of the porous medium is characterized by its permeability aligned along two principal axes, with one axis forming an angle with the horizontal direction. The model applies no-slip and no-spin boundary conditions at the channel’s impermeable walls. Using a combination of analytical techniques and graphical analysis, we explore how key parameters such as the Darcy number, anisotropy angle, permeability ratio, and micropolar material parameters affect the flow behavior. Results reveal that increasing the anisotropy angle and permeability ratio leads to a reduction in both fluid velocity and micro rotational velocity, while the Darcy number promotes an increase in flow velocity. Additionally, the study discusses the impact of these parameters on shear stress and couple stress at the channel walls. The findings contribute to a deeper understanding of micropolar fluid behavior in porous media, with potential applications in filtration, lubrication, and subsurface fluid dynamics.

Observation and analysis of infrasound signals from the 1 January 2024 Japan earthquake

The 1 January 2024 Japan Earthquake occurred off the coast of Noto Peninsula, Japan. Three infrasound arrays s located more than 1400 km away from the epicenter received both local seismic and infrasound signals atmospherically propagating from the epicenter. The back azimuth, elevation angle and other parameters are calculated for the two types of infrasound signals received by the subarray through procedures of Progressive Multi-Channel Correlation (PMCC) and Frequency-Wavenumber (F-K) analysis. Source localization and other processing are also conducted. A recognition feature based on a low-frequency multi-scale entropy algorithm is proposed, and the received seismic signals of this event are correctly identified by using Support Vector Machine (SVM). This paper explores the calculation of earthquake parameters based on local infrasound wave and atmospherically propagated infrasound signals excited by distant earthquake events, and proposes a new method for infrasound signals event identification.