Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-factor Lateral Mode Transmitters for Intravascular and Intracavity Applications

PubMed Central

Wang, Zhuochen; Martin, K. Heath; Huang, Wenbin; Dayton, Paul A.; Jiang, Xiaoning

2016-01-01

Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique which utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast to tissue ratio (CTR) than second harmonic imaging methods. In this work, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency IVUS transducer was developed for concept validation, which achieved larger signal amplitude, better contrast to noise ratio (CNR) and pulse length compared to the previous work. A dual-frequency PMN-PT array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral size of the microbubbles in a 200 μm tube were measured to be 269 μm and 200 μm, respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when final transducer size requirements dictate design choices. PMID:27775903

The Effects of the Menstrual Cycle on Vibratory Characteristics of the Vocal Folds Investigated With High-Speed Digital Imaging.

PubMed

Kunduk, Melda; Vansant, Mathew B; Ikuma, Takeshi; McWhorter, Andrew

2017-03-01

This study investigated the effect of menstrual cycle on vocal fold vibratory characteristics in young women using high-speed digital imaging. This study examined the menstrual phase effect on five objective high-speed imaging parameters and two self-rated perceptual parameters. The effects of oral birth control use were also investigated. Thirteen subjects with no prior voice complaints were included in this study. All data were collected at three different time periods (premenses, postmenses, ovulation) over the course of one menstrual cycle. For five of the 13 subjects, data were collected for two consecutive cycles. Six of 13 subjects were oral birth control users. From high-speed imaging data, five objective parameters were computed: fundamental frequency, fundamental frequency deviation, harmonics-to-noise ratio, harmonic richness factor, and ratio of first and second harmonics. They were supplemented by two self-rated parameters: Reflux Severity Index and perceptual voice quality rating. Analysis included mixed model linear analysis with repeated measures. Results indicated no significant main effects for menstrual phase, between-cycle, or birth control use in the analysis for mean fundamental frequency, fundamental frequency deviation, harmonics-to-noise ratio, harmonic richness factor, first and second harmonics, Reflux Severity Index, and perceptual voice quality rating. Additionally, there were no interaction effects. Hormone fluctuations observed across the menstrual cycle do not appear to have direct effect on vocal fold vibratory characteristics in young women with no voice concerns. Birth control use, on the other hand, may have influence on spectral richness of vocal fold vibration. Copyright © 2017 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

Development of ultrasound transducer diffractive field theory for nonlinear propagation-based imaging

NASA Astrophysics Data System (ADS)

Kharin, Nikolay A.

2000-04-01

In nonlinear ultrasound imaging the images are formed using the second harmonic energy generated due to the nonlinear nature of finite amplitude propagation. This propagation can be modeled using the KZK wave equation. This paper presents further development of nonlinear diffractive field theory based on the KZK equation and its solution by means of the slowly changing profile method for moderate nonlinearity. The analytical expression for amplitudes and phases of sum frequency wave are obtained in addition to the second harmonic wave. Also, the analytical expression for the relative curvature of the wave fronts of fundamental and second harmonic signals are derived. The media with different nonlinear properties and absorption coefficients were investigated to characterize the diffractive field of the transducer at medical frequencies. All expressions demonstrate good agreement with experimental results. The expressions are novel and provide an easy way for prediction of amplitude and phase structure of nonlinearly distorted field of a transducer. The sum frequency signal technique could be implemented as well as second harmonic technique to improve the quality of biomedical images. The results obtained are of importance for medical diagnostic ultrasound equipment design.

High-resolution frequency domain second harmonic optical coherence tomography

NASA Astrophysics Data System (ADS)

Su, Jianping; Tomov, I. V.; Jiang, Yi; Chen, Zhongping

2007-02-01

We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain SH-OCT to 12μm. The acquisition time was shortened by more than two orders of magnitude compared to time domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on second harmonic has been used to obtain polarization resolved images.

Delay-Encoded Harmonic Imaging (DE-HI) in Multiplane-Wave Compounding.

PubMed

Gong, Ping; Song, Pengfei; Chen, Shigao

2017-04-01

The development of ultrafast ultrasound imaging brings great opportunities to improve imaging technologies such as shear wave elastography and ultrafast Doppler imaging. In ultrafast imaging, several tilted plane or diverging wave images are coherently combined to form a compounded image, leading to trade-offs among image signal-to-noise ratio (SNR), resolution, and post-compounded frame rate. Multiplane wave (MW) imaging is proposed to solve this trade-off by encoding multiple plane waves with Hadamard matrix during one transmission event (i.e. pulse-echo event), to improve image SNR without sacrificing the resolution or frame rate. However, it suffers from stronger reverberation artifacts in B-mode images compared to standard plane wave compounding due to longer transmitted pulses. If harmonic imaging can be combined with MW imaging, the reverberation artifacts and other clutter noises such as sidelobes and multipath scattering clutters should be suppressed. The challenge, however, is that the Hadamard codes used in MW imaging cannot encode the 2 nd harmonic component by inversing the pulse polarity. In this paper, we propose a delay-encoded harmonic imaging (DE-HI) technique to encode the 2 nd harmonic with a one quarter period delay calculated at the transmit center frequency, rather than reversing the pulse polarity during multiplane wave emissions. Received DE-HI signals can then be decoded in the frequency domain to recover the signals as in single plane wave emissions, but mainly with improved SNR at the 2 nd harmonic component instead of the fundamental component. DE-HI was tested experimentally with a point target, a B-mode imaging phantom, and in-vivo human liver imaging. Improvements in image contrast-to-noise ratio (CNR), spatial resolution, and lesion-signal-to-noise ratio ( l SNR) have been achieved compared to standard plane wave compounding, MW imaging, and standard harmonic imaging (maximal improvement of 116% on CNR and 115% on l SNR as compared to standard HI around 55 mm depth in the B-mode imaging phantom study). The potential high frame rate and the stability of encoding and decoding processes of DE-HI were also demonstrated, which made DE-HI promising for a wide spectrum of imaging applications.

Contrast and harmonic imaging improves accuracy and efficiency of novice readers for dobutamine stress echocardiography

NASA Technical Reports Server (NTRS)

Vlassak, Irmien; Rubin, David N.; Odabashian, Jill A.; Garcia, Mario J.; King, Lisa M.; Lin, Steve S.; Drinko, Jeanne K.; Morehead, Annitta J.; Prior, David L.; Asher, Craig R.;

Parallel transmit beamforming using orthogonal frequency division multiplexing applied to harmonic imaging--a feasibility study.

PubMed

Demi, Libertario; Verweij, Martin D; Van Dongen, Koen W A

2012-11-01

Real-time 2-D or 3-D ultrasound imaging systems are currently used for medical diagnosis. To achieve the required data acquisition rate, these systems rely on parallel beamforming, i.e., a single wide-angled beam is used for transmission and several narrow parallel beams are used for reception. When applied to harmonic imaging, the demand for high-amplitude pressure wave fields, necessary to generate the harmonic components, conflicts with the use of a wide-angled beam in transmission because this results in a large spatial decay of the acoustic pressure. To enhance the amplitude of the harmonics, it is preferable to do the reverse: transmit several narrow parallel beams and use a wide-angled beam in reception. Here, this concept is investigated to determine whether it can be used for harmonic imaging. The method proposed in this paper relies on orthogonal frequency division multiplexing (OFDM), which is used to create distinctive parallel beams in transmission. To test the proposed method, a numerical study has been performed, in which the transmit, receive, and combined beam profiles generated by a linear array have been simulated for the second-harmonic component. Compared with standard parallel beamforming, application of the proposed technique results in a gain of 12 dB for the main beam and in a reduction of the side lobes. Experimental verification in water has also been performed. Measurements obtained with a single-element emitting transducer and a hydrophone receiver confirm the possibility of exciting a practical ultrasound transducer with multiple Gaussian modulated pulses, each having a different center frequency, and the capability to generate distinguishable second-harmonic components.

Analysis and measurement of the modulation transfer function of harmonic shear wave induced phase encoding imaging.

PubMed

McAleavey, Stephen A

2014-05-01

Shear wave induced phase encoding (SWIPE) imaging generates ultrasound backscatter images of tissue-like elastic materials by using traveling shear waves to encode the lateral position of the scatters in the phase of the received echo. In contrast to conventional ultrasound B-scan imaging, SWIPE offers the potential advantages of image formation without beam focusing or steering from a single transducer element, lateral resolution independent of aperture size, and the potential to achieve relatively high lateral resolution with low frequency ultrasound. Here a Fourier series description of the phase modulated echo signal is developed, demonstrating that echo harmonics at multiples of the shear wave frequency reveal target k-space data at identical multiples of the shear wavenumber. Modulation transfer functions of SWIPE imaging systems are calculated for maximum shear wave acceleration and maximum shear constraints, and compared with a conventionally focused aperture. The relative signal-to-noise ratio of the SWIPE method versus a conventionally focused aperture is found through these calculations. Reconstructions of wire targets in a gelatin phantom using 1 and 3.5 MHz ultrasound and a cylindrical shear wave source are presented, generated from the fundamental and second harmonic of the shear wave modulation frequency, demonstrating weak dependence of lateral resolution with ultrasound frequency.

Design, Fabrication and Characterization of A Bi-Frequency Co-Linear Array

PubMed Central

Wang, Zhuochen; Li, Sibo; Czernuszewicz, Tomasz J; Gallippi, Caterina M.; Liu, Ruibin; Geng, Xuecang

2016-01-01

Ultrasound imaging with high resolution and large penetration depth has been increasingly adopted in medical diagnosis, surgery guidance, and treatment assessment. Conventional ultrasound works at a particular frequency, with a −6 dB fractional bandwidth of ~70 %, limiting the imaging resolution or depth of field. In this paper, a bi-frequency co-linear array with resonant frequencies of 8 MHz and 20 MHz was investigated to meet the requirements of resolution and penetration depth for a broad range of ultrasound imaging applications. Specifically, a 32-element bi-frequency co-linear array was designed and fabricated, followed by element characterization and real-time sectorial scan (S-scan) phantom imaging using a Verasonics system. The bi-frequency co-linear array was tested in four different modes by switching between low and high frequencies on transmit and receive. The four modes included the following: (1) transmit low, receive low, (2) transmit low, receive high, (3) transmit high, receive low, (4) transmit high, receive high. After testing, the axial and lateral resolutions of all modes were calculated and compared. The results of this study suggest that bi-frequency co-linear arrays are potential aids for wideband fundamental imaging and harmonic/sub-harmonic imaging. PMID:26661069

Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-Factor Lateral Mode Transmitters for Intravascular and Intracavity Applications.

PubMed

Wang, Zhuochen; Heath Martin, K; Huang, Wenbin; Dayton, Paul A; Jiang, Xiaoning

2017-02-01

Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique that utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast-to-tissue ratio than second harmonic imaging methods. In this paper, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency intravascular ultrasound transducer was developed for concept validation, which achieved larger signal amplitude, better contrast-to-noise ratio (CNR), and pulselength compared to the previous work. A dual-frequency [Pb(Mg 1/3 Nb 2/3 )O 3 ]-x[PbTiO 3 ] array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral sizes of the microbubbles in a 200- [Formula: see text] tube were measured to be 269 and [Formula: see text], respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when the final transducer size requirements dictate design choices.

A theory of frequency domain invariants: spherical harmonic identities for BRDF/lighting transfer and image consistency.

PubMed

Mahajan, Dhruv; Ramamoorthi, Ravi; Curless, Brian

2008-02-01

This paper develops a theory of frequency domain invariants in computer vision. We derive novel identities using spherical harmonics, which are the angular frequency domain analog to common spatial domain invariants such as reflectance ratios. These invariants are derived from the spherical harmonic convolution framework for reflection from a curved surface. Our identities apply in a number of canonical cases, including single and multiple images of objects under the same and different lighting conditions. One important case we consider is two different glossy objects in two different lighting environments. For this case, we derive a novel identity, independent of the specific lighting configurations or BRDFs, that allows us to directly estimate the fourth image if the other three are available. The identity can also be used as an invariant to detecttampering in the images. While this paper is primarily theoretical, it has the potential to lay the mathematical foundations for two important practical applications. First, we can develop more general algorithms for inverse rendering problems, which can directly relight and change material properties by transferring the BRDF or lighting from another object or illumination. Second, we can check the consistency of an image, to detect tampering or image splicing.

Dual-Frequency Piezoelectric Transducers for Contrast Enhanced Ultrasound Imaging

PubMed Central

Martin, K. Heath; Lindsey, Brooks D.; Ma, Jianguo; Lee, Mike; Li, Sibo; Foster, F. Stuart; Jiang, Xiaoning; Dayton, Paul A.

2014-01-01

For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. Current clinical practices using microbubble contrast agents rely heavily on user training to evaluate degree of localized perfusion. Advances in separating the signals produced from contrast agents versus surrounding tissue backscatter provide unique opportunities for specialized sensors designed to image microbubbles with higher signal to noise and resolution than previously possible. In this review article, we describe the background principles and recent developments of ultrasound transducer technology for receiving signals produced by contrast agents while rejecting signals arising from soft tissue. This approach relies on transmitting at a low-frequency and receiving microbubble harmonic signals at frequencies many times higher than the transmitted frequency. Design and fabrication of dual-frequency transducers and the extension of recent developments in transducer technology for dual-frequency harmonic imaging are discussed. PMID:25375755

Dual-frequency piezoelectric transducers for contrast enhanced ultrasound imaging.

PubMed

Martin, K Heath; Lindsey, Brooks D; Ma, Jianguo; Lee, Mike; Li, Sibo; Foster, F Stuart; Jiang, Xiaoning; Dayton, Paul A

2014-11-04

For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. Current clinical practices using microbubble contrast agents rely heavily on user training to evaluate degree of localized perfusion. Advances in separating the signals produced from contrast agents versus surrounding tissue backscatter provide unique opportunities for specialized sensors designed to image microbubbles with higher signal to noise and resolution than previously possible. In this review article, we describe the background principles and recent developments of ultrasound transducer technology for receiving signals produced by contrast agents while rejecting signals arising from soft tissue. This approach relies on transmitting at a low-frequency and receiving microbubble harmonic signals at frequencies many times higher than the transmitted frequency. Design and fabrication of dual-frequency transducers and the extension of recent developments in transducer technology for dual-frequency harmonic imaging are discussed.

High-resolution frequency-domain second-harmonic optical coherence tomography

NASA Astrophysics Data System (ADS)

Su, Jianping; Tomov, Ivan V.; Jiang, Yi; Chen, Zhongping

2007-04-01

We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain second-harmonic optical coherence tomography (SH-OCT) to 12 μm. The acquisition time was shortened by more than 2 orders of magnitude compared to the time-domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon, and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on the SH has been used to obtain polarization resolved images.

Target Identification Using Harmonic Wavelet Based ISAR Imaging

NASA Astrophysics Data System (ADS)

Shreyamsha Kumar, B. K.; Prabhakar, B.; Suryanarayana, K.; Thilagavathi, V.; Rajagopal, R.

2006-12-01

A new approach has been proposed to reduce the computations involved in the ISAR imaging, which uses harmonic wavelet-(HW) based time-frequency representation (TFR). Since the HW-based TFR falls into a category of nonparametric time-frequency (T-F) analysis tool, it is computationally efficient compared to parametric T-F analysis tools such as adaptive joint time-frequency transform (AJTFT), adaptive wavelet transform (AWT), and evolutionary AWT (EAWT). Further, the performance of the proposed method of ISAR imaging is compared with the ISAR imaging by other nonparametric T-F analysis tools such as short-time Fourier transform (STFT) and Choi-Williams distribution (CWD). In the ISAR imaging, the use of HW-based TFR provides similar/better results with significant (92%) computational advantage compared to that obtained by CWD. The ISAR images thus obtained are identified using a neural network-based classification scheme with feature set invariant to translation, rotation, and scaling.

Corrosion process monitoring by AFM higher harmonic imaging

NASA Astrophysics Data System (ADS)

Babicz, S.; Zieliński, A.; Smulko, J.; Darowicki, K.

2017-11-01

The atomic force microscope (AFM) was invented in 1986 as an alternative to the scanning tunnelling microscope, which cannot be used in studies of non-conductive materials. Today the AFM is a powerful, versatile and fundamental tool for visualizing and studying the morphology of material surfaces. Moreover, additional information for some materials can be recovered by analysing the AFM’s higher cantilever modes when the cantilever motion is inharmonic and generates frequency components above the excitation frequency, usually close to the resonance frequency of the lowest oscillation mode. This method has been applied and developed to monitor corrosion processes. The higher-harmonic imaging is especially helpful for sharpening boundaries between objects in heterogeneous samples, which can be used to identify variations in steel structures (e.g. corrosion products, steel heterogeneity). The corrosion products have different chemical structures because they are composed of chemicals other than the original metal base (mainly iron oxides). Thus, their physicochemical properties are different from the primary basis. These structures have edges at which higher harmonics should be more intense because of stronger interference between the tip and the specimen structure there. This means that the AFM’s higher-harmonic imaging is an excellent tool for monitoring surficial effects of the corrosion process.

Experimental and numerical investigation of tissue harmonic imaging (THI)

NASA Astrophysics Data System (ADS)

Jing, Yuan; Yang, Xinmai; Cleveland, Robin O.

2003-04-01

In THI the probing ultrasonic pulse has enough amplitude that it undergoes nonlinear distortion and energy shifts from the fundamental frequency of the pulse into its higher harmonics. Images generated from the second harmonic (SH) have superior quality to the images formed from the fundamental frequency. Experiments with a single element focused ultrasound transducer were used to compare a line target embedded in a tissue phantom using either fundamental or SH imaging. SH imaging showed an improvement in both the axial resolution (0.70 mm vs 0.92 mm) and the lateral resolution (1.02 mm vs 2.70 mm) of the target. In addition, the contrast-to-tissue ratio of the target was 2 dB higher with SH imaging. A three-dimensional model of the forward propagation has been developed to simulate the experimental system. The model is based on a time-domain code for solving the KZK equation and accounts for arbitrary spatial variations in all tissue properties. The code was used to determine the impact of a nearfield layer of fat on the fundamental and second harmonic signals. For a 15 mm thick layer the SH side-lobes remained the same but the fundamental side-lobes increased by 2 dB. [Work supported by the NSF through the Center for Subsurface Sensing and Imaging Systems.

Implementation of parallel transmit beamforming using orthogonal frequency division multiplexing--achievable resolution and interbeam interference.

PubMed

Demi, Libertario; Viti, Jacopo; Kusters, Lieneke; Guidi, Francesco; Tortoli, Piero; Mischi, Massimo

2013-11-01

The speed of sound in the human body limits the achievable data acquisition rate of pulsed ultrasound scanners. To overcome this limitation, parallel beamforming techniques are used in ultrasound 2-D and 3-D imaging systems. Different parallel beamforming approaches have been proposed. They may be grouped into two major categories: parallel beamforming in reception and parallel beamforming in transmission. The first category is not optimal for harmonic imaging; the second category may be more easily applied to harmonic imaging. However, inter-beam interference represents an issue. To overcome these shortcomings and exploit the benefit of combining harmonic imaging and high data acquisition rate, a new approach has been recently presented which relies on orthogonal frequency division multiplexing (OFDM) to perform parallel beamforming in transmission. In this paper, parallel transmit beamforming using OFDM is implemented for the first time on an ultrasound scanner. An advanced open platform for ultrasound research is used to investigate the axial resolution and interbeam interference achievable with parallel transmit beamforming using OFDM. Both fundamental and second-harmonic imaging modalities have been considered. Results show that, for fundamental imaging, axial resolution in the order of 2 mm can be achieved in combination with interbeam interference in the order of -30 dB. For second-harmonic imaging, axial resolution in the order of 1 mm can be achieved in combination with interbeam interference in the order of -35 dB.

Ultrafast Harmonic Coherent Compound (UHCC) imaging for high frame rate echocardiography and Shear Wave Elastography

PubMed Central

Correia, Mafalda; Provost, Jean; Chatelin, Simon; Villemain, Olivier; Tanter, Mickael; Pernot, Mathieu

2016-01-01

Transthoracic shear wave elastography of the myocardium remains very challenging due to the poor quality of transthoracic ultrafast imaging and the presence of clutter noise, jitter, phase aberration, and ultrasound reverberation. Several approaches, such as, e.g., diverging-wave coherent compounding or focused harmonic imaging have been proposed to improve the imaging quality. In this study, we introduce ultrafast harmonic coherent compounding (UHCC), in which pulse-inverted diverging-waves are emitted and coherently compounded, and show that such an approach can be used to enhance both Shear Wave Elastography (SWE) and high frame rate B-mode Imaging. UHCC SWE was first tested in phantoms containing an aberrating layer and was compared against pulse-inversion harmonic imaging and against ultrafast coherent compounding (UCC) imaging at the fundamental frequency. In-vivo feasibility of the technique was then evaluated in six healthy volunteers by measuring myocardial stiffness during diastole in transthoracic imaging. We also demonstrated that improvements in imaging quality could be achieved using UHCC B-mode imaging in healthy volunteers. The quality of transthoracic images of the heart was found to be improved with the number of pulse-inverted diverging waves with reduction of the imaging mean clutter level up to 13.8-dB when compared against UCC at the fundamental frequency. These results demonstrated that UHCC B-mode imaging is promising for imaging deep tissues exposed to aberration sources with a high frame-rate. PMID:26890730

Numerical modeling of Harmonic Imaging and Pulse Inversion fields

NASA Astrophysics Data System (ADS)

Humphrey, Victor F.; Duncan, Tracy M.; Duck, Francis

2003-10-01

Tissue Harmonic Imaging (THI) and Pulse Inversion (PI) Harmonic Imaging exploit the harmonics generated as a result of nonlinear propagation through tissue to improve the performance of imaging systems. A 3D finite difference model, that solves the KZK equation in the frequency domain, is used to investigate the finite amplitude fields produced by rectangular transducers driven with short pulses and their inverses, in water and homogeneous tissue. This enables the characteristic of the fields and the effective PI field to be calculated. The suppression of the fundamental field in PI is monitored, and the suppression of side lobes and a reduction in the effective beamwidth for each field are calculated. In addition, the differences between the pulse and inverse pulse spectra resulting from the use of very short pulses are noted, and the differences in the location of the fundamental and second harmonic spectral peaks observed.

Time domain simulation of nonlinear acoustic beams generated by rectangular pistons with application to harmonic imaging

NASA Astrophysics Data System (ADS)

Yang, Xinmai; Cleveland, Robin O.

2005-01-01

A time-domain numerical code (the so-called Texas code) that solves the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation has been extended from an axis-symmetric coordinate system to a three-dimensional (3D) Cartesian coordinate system. The code accounts for diffraction (in the parabolic approximation), nonlinearity and absorption and dispersion associated with thermoviscous and relaxation processes. The 3D time domain code was shown to be in agreement with benchmark solutions for circular and rectangular sources, focused and unfocused beams, and linear and nonlinear propagation. The 3D code was used to model the nonlinear propagation of diagnostic ultrasound pulses through tissue. The prediction of the second-harmonic field was sensitive to the choice of frequency-dependent absorption: a frequency squared f2 dependence produced a second-harmonic field which peaked closer to the transducer and had a lower amplitude than that computed for an f1.1 dependence. In comparing spatial maps of the harmonics we found that the second harmonic had dramatically reduced amplitude in the near field and also lower amplitude side lobes in the focal region than the fundamental. These findings were consistent for both uniform and apodized sources and could be contributing factors in the improved imaging reported with clinical scanners using tissue harmonic imaging. .

Time domain simulation of nonlinear acoustic beams generated by rectangular pistons with application to harmonic imaging.

PubMed

Yang, Xinmai; Cleveland, Robin O

2005-01-01

A time-domain numerical code (the so-called Texas code) that solves the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation has been extended from an axis-symmetric coordinate system to a three-dimensional (3D) Cartesian coordinate system. The code accounts for diffraction (in the parabolic approximation), nonlinearity and absorption and dispersion associated with thermoviscous and relaxation processes. The 3D time domain code was shown to be in agreement with benchmark solutions for circular and rectangular sources, focused and unfocused beams, and linear and nonlinear propagation. The 3D code was used to model the nonlinear propagation of diagnostic ultrasound pulses through tissue. The prediction of the second-harmonic field was sensitive to the choice of frequency-dependent absorption: a frequency squared f2 dependence produced a second-harmonic field which peaked closer to the transducer and had a lower amplitude than that computed for an f1.1 dependence. In comparing spatial maps of the harmonics we found that the second harmonic had dramatically reduced amplitude in the near field and also lower amplitude side lobes in the focal region than the fundamental. These findings were consistent for both uniform and apodized sources and could be contributing factors in the improved imaging reported with clinical scanners using tissue harmonic imaging.

Transmit beamforming for optimal second-harmonic generation.

PubMed

Hoilund-Kaupang, Halvard; Masoy, Svein-Erik

2011-08-01

A simulation study of transmit ultrasound beams from several transducer configurations is conducted to compare second-harmonic imaging at 3.5 MHz and 11 MHz. Second- harmonic generation and the ability to suppress near field echoes are compared. Each transducer configuration is defined by a chosen f-number and focal depth, and the transmit pressure is estimated to not exceed a mechanical index of 1.2. The medium resembles homogeneous muscle tissue with nonlinear elasticity and power-law attenuation. To improve computational efficiency, the KZK equation is utilized, and all transducers are circular-symmetric. Previous literature shows that second-harmonic generation is proportional to the square of the transmit pressure, and that transducer configurations with different transmit frequencies, but equal aperture and focal depth in terms of wavelengths, generate identical second-harmonic fields in terms of shape. Results verify this for a medium with attenuation f1. For attenuation f1.1, deviations are found, and the high frequency subsequently performs worse than the low frequency. The results suggest that high frequencies are less able to suppress near-field echoes in the presence of a heterogeneous body wall than low frequencies.

Physics of tissue harmonic imaging by ultrasound

NASA Astrophysics Data System (ADS)

Jing, Yuan

Tissue Harmonic Imaging (THI) is an imaging modality that is currently deployed on diagnostic ultrasound scanners. In THI the amplitude of the ultrasonic pulse that is used to probe the tissue is large enough that the pulse undergoes nonlinear distortion as it propagates into the tissue. One result of the distortion is that as the pulse propagates energy is shifted from the fundamental frequency of the source pulse into its higher harmonics. These harmonics will scatter off objects in the tissue and images formed from the scattered higher harmonics are considered to have superior quality to the images formed from the fundamental frequency. Processes that have been suggested as possibly responsible for the improved imaging in THI include: (1) reduced sensitivity to reverberation, (2) reduced sensitivity to aberration, and (3) reduction in side lobes. By using a combination of controlled experiments and numerical simulations, these three reasons have been investigated. A single element transducer and a clinical ultrasound scanner with a phased array transducer were used to image a commercial tissue-mimicking phantom with calibrated targets. The higher image quality achieved with THI was quantified in terms of spatial resolution and "clutter" signals. A three-dimensional model of the forward propagation of nonlinear sound beams in media with arbitrary spatial properties (a generalized KZK equation) was developed. A time-domain code for solving the KZK equation was validated with measurements of the acoustic field generated by the single element transducer and the phased array transducer. The code was used to investigate the impact of aberration using tissue-like media with three-dimensional variations in all acoustic properties. The three-dimensional maps of tissue properties were derived from the datasets available through the Visible Female project. The experiments and simulations demonstrated that second harmonic imaging (1) suffers less clutter associated with reverberation; (2) is not immune to aberration effects and (3) suffers less clutter due to reduced side-lobe levels. The results indicate that side lobe suppression is the most significant reason for the improvement of second harmonic imaging.

Two-dimensional multi-frequency imaging of a tumor inclusion in a homogeneous breast phantom using the harmonic motion Doppler imaging method.

PubMed

Tafreshi, Azadeh Kamali; Top, Can Barış; Gençer, Nevzat Güneri

2017-06-21

Harmonic motion microwave Doppler imaging (HMMDI) is a novel imaging modality for imaging the coupled electrical and mechanical properties of body tissues. In this paper, we used two experimental systems with different receiver configurations to obtain HMMDI images from tissue-mimicking phantoms at multiple vibration frequencies between 15 Hz and 35 Hz. In the first system, we used a spectrum analyzer to obtain the Doppler data in the frequency domain, while in the second one, we used a homodyne receiver that was designed to acquire time-domain data. The developed phantoms mimicked the elastic and dielectric properties of breast fat tissue, and included a [Formula: see text] mm cylindrical inclusion representing the tumor. A focused ultrasound probe was mechanically scanned in two lateral dimensions to obtain two-dimensional HMMDI images of the phantoms. The inclusions were resolved inside the fat phantom using both experimental setups. The image resolution increased with increasing vibration frequency. The designed receiver showed higher sensitivity than the spectrum analyzer measurements. The results also showed that time-domain data acquisition should be used to fully exploit the potential of the HMMDI method.

Two-dimensional multi-frequency imaging of a tumor inclusion in a homogeneous breast phantom using the harmonic motion Doppler imaging method

NASA Astrophysics Data System (ADS)

Kamali Tafreshi, Azadeh; Barış Top, Can; Güneri Gençer, Nevzat

2017-06-01

Harmonic motion microwave Doppler imaging (HMMDI) is a novel imaging modality for imaging the coupled electrical and mechanical properties of body tissues. In this paper, we used two experimental systems with different receiver configurations to obtain HMMDI images from tissue-mimicking phantoms at multiple vibration frequencies between 15 Hz and 35 Hz. In the first system, we used a spectrum analyzer to obtain the Doppler data in the frequency domain, while in the second one, we used a homodyne receiver that was designed to acquire time-domain data. The developed phantoms mimicked the elastic and dielectric properties of breast fat tissue, and included a 14~\\text{mm}× 9 mm cylindrical inclusion representing the tumor. A focused ultrasound probe was mechanically scanned in two lateral dimensions to obtain two-dimensional HMMDI images of the phantoms. The inclusions were resolved inside the fat phantom using both experimental setups. The image resolution increased with increasing vibration frequency. The designed receiver showed higher sensitivity than the spectrum analyzer measurements. The results also showed that time-domain data acquisition should be used to fully exploit the potential of the HMMDI method.

Symmetry in circularly polarized molecular high-order harmonic generation with intense bicircular laser pulses

NASA Astrophysics Data System (ADS)

Yuan, Kai-Jun; Bandrauk, André D.

2018-02-01

We present symmetry effects of laser fields and molecular geometries in circularly polarized high-order harmonic generation by bichromatic counter-rotating circularly polarized laser pulses. Simulations are performed on oriented molecules by numerically solving time-dependent Schrödinger equations. We discuss how electron recollision trajectories by the orthogonal laser field polarizations influence the harmonic polarization by using a time-frequency analysis of harmonics. It is found that orientation-dependent asymmetric ionization in linear molecules due to Coulomb potentials gives rise to a dependence of the polarization on the harmonic frequency. Effects of Coriolis forces are also presented on harmonic generation. Electron recollision trajectories illustrate the effects of the relative symmetry of the field and the molecule, thus paving a method for circularly polarized attosecond pulse generation and molecular orbital imaging in more complex systems.

Three-dimensional image formation in fiber-optical second-harmonic-generation microscopy.

PubMed

Gu, Min; Fu, Ling

2006-02-06

Three-dimensional (3-D) image formation in fiber-optical second-harmonic-generation microscopy is revealed to be purely coherent and therefore can be described by a 3-D coherent transfer function (CTF) that exhibits the same spatial frequency passband as that of fiber-optical reflection-mode non-fluorescence microscopy. When the numerical aperture of the fiber is much larger than the angle of convergence of the illumination on the fiber aperture, the performance of fiber-optical second-harmonic-generation microscopy behaves as confocal second-harmonic-generation microscopy. The dependence of axial resolution on fiber coupling parameters shows an improvement of approximately 7%, compared with that in fiber-optical two-photon fluorescence microscopy.

Three dimensional full-wave nonlinear acoustic simulations: Applications to ultrasound imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinton, Gianmarco

Characterization of acoustic waves that propagate nonlinearly in an inhomogeneous medium has significant applications to diagnostic and therapeutic ultrasound. The generation of an ultrasound image of human tissue is based on the complex physics of acoustic wave propagation: diffraction, reflection, scattering, frequency dependent attenuation, and nonlinearity. The nonlinearity of wave propagation is used to the advantage of diagnostic scanners that use the harmonic components of the ultrasonic signal to improve the resolution and penetration of clinical scanners. One approach to simulating ultrasound images is to make approximations that can reduce the physics to systems that have a low computational cost.more » Here a maximalist approach is taken and the full three dimensional wave physics is simulated with finite differences. This paper demonstrates how finite difference simulations for the nonlinear acoustic wave equation can be used to generate physically realistic two and three dimensional ultrasound images anywhere in the body. A specific intercostal liver imaging scenario for two cases: with the ribs in place, and with the ribs removed. This configuration provides an imaging scenario that cannot be performed in vivo but that can test the influence of the ribs on image quality. Several imaging properties are studied, in particular the beamplots, the spatial coherence at the transducer surface, the distributed phase aberration, and the lesion detectability for imaging at the fundamental and harmonic frequencies. The results indicate, counterintuitively, that at the fundamental frequency the beamplot improves due to the apodization effect of the ribs but at the same time there is more degradation from reverberation clutter. At the harmonic frequency there is significantly less improvement in the beamplot and also significantly less degradation from reverberation. It is shown that even though simulating the full propagation physics is computationally challenging it is necessary to quantify ultrasound image quality and its sources of degradation.« less

The Influence of Second Harmonic Phase and Amplitude Variation in Cyclically Pitching Wings

NASA Astrophysics Data System (ADS)

Culler, Ethan; Farnsworth, John

2017-11-01

From wind tunnel testing of a cyber-physical wing model, it has been found that the pitch trajectory for stall flutter is described by an array of higher harmonic frequencies with decaying energy content. These frequencies distort the stall flutter motion from that of a pure sinusoidal oscillation in pitch and can have a significant effect on the resulting force production. In order to understand how these higher harmonic frequencies contribute to the overall pitching moment characteristics of a wing in stall flutter, a rigid finite span wing model, with aspect ratio four, was pitched in the wind tunnel. The prescribed motion of the pitch cycle was varied by changing the amplitude ratio and phase of the second harmonic of the oscillation frequency. The second harmonic represents the second highest energy mode in the pitching cycle spectra. Pitching moment and planar particle image velocimetry data was collected. From these pitching trajectories, a significant dependence of pitching moment on both the phase and amplitude of the prescribed waveforms was found. Specifically, for the same amplitude ratio, variations in the phase produced changes of approximately 30 percent in the phase averaged pitching moment.

Human sperm steer with second harmonics of the flagellar beat.

PubMed

Saggiorato, Guglielmo; Alvarez, Luis; Jikeli, Jan F; Kaupp, U Benjamin; Gompper, Gerhard; Elgeti, Jens

2017-11-10

Sperm are propelled by bending waves traveling along their flagellum. For steering in gradients of sensory cues, sperm adjust the flagellar waveform. Symmetric and asymmetric waveforms result in straight and curved swimming paths, respectively. Two mechanisms causing spatially asymmetric waveforms have been proposed: an average flagellar curvature and buckling. We image flagella of human sperm tethered with the head to a surface. The waveform is characterized by a fundamental beat frequency and its second harmonic. The superposition of harmonics breaks the beat symmetry temporally rather than spatially. As a result, sperm rotate around the tethering point. The rotation velocity is determined by the second-harmonic amplitude and phase. Stimulation with the female sex hormone progesterone enhances the second-harmonic contribution and, thereby, modulates sperm rotation. Higher beat frequency components exist in other flagellated cells; therefore, this steering mechanism might be widespread and could inspire the design of synthetic microswimmers.

In-phased second harmonic wave array generation with intra-Talbot-cavity frequency-doubling.

PubMed

Hirosawa, Kenichi; Shohda, Fumio; Yanagisawa, Takayuki; Kannari, Fumihiko

2015-03-23

The Talbot cavity is one promising method to synchronize the phase of a laser array. However, it does not achieve the lowest array mode with the same phase but the highest array mode with the anti-phase between every two adjacent lasers, which is called out-phase locking. Consequently, their far-field images exhibit 2-peak profiles. We propose intra-Talbot-cavity frequency-doubling. By placing a nonlinear crystal in a Talbot cavity, the Talbot cavity generates an out-phased fundamental wave array, which is converted into an in-phase-locked second harmonic wave array at the nonlinear crystal. We demonstrate numerical calculations and experiments on intra-Talbot-cavity frequency-doubling and obtain an in-phase-locked second harmonic wave array for a Nd:YVO₄ array laser.

All-optical and broadband microwave fundamental/sub-harmonic I/Q down-converters.

PubMed

Gao, Yongsheng; Wen, Aijun; Jiang, Wei; Fan, Yangyu; He, You

2018-03-19

Microwave I/Q down-converters are frequently used in image-reject super heterodyne receivers, zero intermediate frequency (zero-IF) receivers, and phase/frequency discriminators. However, due to the electronic bottleneck, conventional microwave I/Q mixers face a serious bandwidth limitation, I/Q imbalance, and even-order distortion. In this paper, photonic microwave fundamental and sub-harmonic I/Q down-converters are presented using a polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM). Thanks to all-optical manipulation, the proposed system features an ultra-wide operating band (7-40 GHz in the fundamental I/Q down-converter, and 10-40 GHz in the sub-harmonic I/Q down-converter) and an excellent I/Q balance (maximum 0.7 dB power imbalance and 1 degree phase imbalance). The conversion gain, noise figure (NF), even-order distortion, and spurious free dynamic range (SFDR) are also improved by LO power optimization and balanced detection. Using the proposed system, a high image rejection ratio is demonstrated for a super heterodyne receiver, and good EVMs over a wide RF power range is demonstrated for a zero-IF receiver. The proposed broadband photonic microwave fundamental and sub-harmonic I/Q down-converters may find potential applications in multi-band satellite, ultra-wideband radar and frequency-agile electronic warfare systems.

Quantitative analysis of biological tissues using Fourier transform-second-harmonic generation imaging

NASA Astrophysics Data System (ADS)

Ambekar Ramachandra Rao, Raghu; Mehta, Monal R.; Toussaint, Kimani C., Jr.

2010-02-01

We demonstrate the use of Fourier transform-second-harmonic generation (FT-SHG) imaging of collagen fibers as a means of performing quantitative analysis of obtained images of selected spatial regions in porcine trachea, ear, and cornea. Two quantitative markers, preferred orientation and maximum spatial frequency are proposed for differentiating structural information between various spatial regions of interest in the specimens. The ear shows consistent maximum spatial frequency and orientation as also observed in its real-space image. However, there are observable changes in the orientation and minimum feature size of fibers in the trachea indicating a more random organization. Finally, the analysis is applied to a 3D image stack of the cornea. It is shown that the standard deviation of the orientation is sensitive to the randomness in fiber orientation. Regions with variations in the maximum spatial frequency, but with relatively constant orientation, suggest that maximum spatial frequency is useful as an independent quantitative marker. We emphasize that FT-SHG is a simple, yet powerful, tool for extracting information from images that is not obvious in real space. This technique can be used as a quantitative biomarker to assess the structure of collagen fibers that may change due to damage from disease or physical injury.

High resolution subsurface imaging using resonance-enhanced detection in 2nd-harmonic KPFM.

PubMed

Cadena, Maria Jose; Reifenberger, Ronald G; Raman, Arvind

2018-06-28

Second harmonic Kelvin probe force microscopy is a robust mechanism for subsurface imaging at the nanoscale. Here we exploit resonance-enhanced detection as a way to boost the subsurface contrast with higher force sensitivity using lower bias voltages, in comparison to the traditional off-resonance case. In this mode, the second harmonic signal of the electrostatic force is acquired at one of the eigenmode frequencies of the microcantilever. As a result, high-resolution subsurface images are obtained in a variety of nanocomposites. To further understand the subsurface imaging detection upon electrostatic forces, we use a finite element model that approximates the geometry of the probe and sample. This allows the investigation of the contrast mechanism, the depth sensitivity and lateral resolution depending on tip-sample properties. © 2018 IOP Publishing Ltd.

Magneto-thermal-acoustic differential-frequency imaging of magnetic nanoparticle with magnetic spatial localization: a theoretical prediction

NASA Astrophysics Data System (ADS)

Piao, Daqing

2017-02-01

The magneto-thermo-acoustic effect that we predicted in 2013 refers to the generation of acoustic-pressure wave from magnetic nanoparticle (MNP) when thermally mediated under an alternating magnetic field (AMF) at a pulsed or frequency-chirped application. Several independent experimental studies have since validated magneto-thermoacoustic effect, and a latest report has discovered acoustic-wave generation from MNP at the second-harmonic frequency of the AMF when operating continuously. We propose that applying two AMFs with differing frequencies to MNP will produce acoustic-pressure wave at the summation and difference of the two frequencies, in addition to the two second-harmonic frequencies. Analysis of the specific absorption dynamics of the MNP when exposed to two AMFs of differing frequencies has shown some interesting patterns of acoustic-intensity at the multiple frequency components. The ratio of the acoustic-intensity at the summation-frequency over that of the difference-frequency is determined by the frequency-ratio of the two AMFs, but remains independent of the AMF strengths. The ratio of the acoustic-intensity at the summation- or difference-frequency over that at each of the two second-harmonic frequencies is determined by both the frequency-ratio and the field-strength-ratio of the two AMFs. The results indicate a potential strategy for localization of the source of a continuous-wave magneto-thermalacoustic signal by examining the frequency spectrum of full-field non-differentiating acoustic detection, with the field-strength ratio changed continuously at a fixed frequency-ratio. The practicalities and challenges of this magnetic spatial localization approach for magneto-thermo-acoustic imaging using a simple envisioned set of two AMFs arranged in parallel to each other are discussed.

Ultrasound imaging based on nonlinear pressure field properties

NASA Astrophysics Data System (ADS)

Bouakaz, Ayache; Frinking, Peter J. A.; de Jong, Nico

2000-07-01

Ultrasound image quality has experienced a significant improvement over the past years with the utilization of harmonic frequencies. This brings the need to understand the physical processes involved in the propagation of finite amplitude sound beams, and the issues for redesigning and optimizing the phased array transducers. New arrays with higher imaging performances are essential for tissue imaging and contrast imaging as well. This study presents measurements and simulations on a 4.6 MHz square transducer. The numerical scheme used solves the KZK equation in the time domain. Comparison of measured and computed data showed good agreement for low and high excitation levels. In a similar way, a numerical simulation was performed on a linear array with five elements. The simulation showed that the second harmonic beam is narrower than the fundamental with less energy in the near field. In addition, the grating lobes are significantly lower. Accordingly, selective harmonic imaging shows less near field artifacts and will lower the clutter, resulting in much cleaner images.

Analytic solutions to modelling exponential and harmonic functions using Chebyshev polynomials: fitting frequency-domain lifetime images with photobleaching.

PubMed

Malachowski, George C; Clegg, Robert M; Redford, Glen I

2007-12-01

A novel approach is introduced for modelling linear dynamic systems composed of exponentials and harmonics. The method improves the speed of current numerical techniques up to 1000-fold for problems that have solutions of multiple exponentials plus harmonics and decaying components. Such signals are common in fluorescence microscopy experiments. Selective constraints of the parameters being fitted are allowed. This method, using discrete Chebyshev transforms, will correctly fit large volumes of data using a noniterative, single-pass routine that is fast enough to analyse images in real time. The method is applied to fluorescence lifetime imaging data in the frequency domain with varying degrees of photobleaching over the time of total data acquisition. The accuracy of the Chebyshev method is compared to a simple rapid discrete Fourier transform (equivalent to least-squares fitting) that does not take the photobleaching into account. The method can be extended to other linear systems composed of different functions. Simulations are performed and applications are described showing the utility of the method, in particular in the area of fluorescence microscopy.

Dual-frequency super harmonic imaging piezoelectric transducers for transrectal ultrasound

NASA Astrophysics Data System (ADS)

Kim, Jinwook; Li, Sibo; Kasoji, Sandeep; Dayton, Paul A.; Jiang, Xiaoning

2015-03-01

In this paper, a 2/14 MHz dual-frequency single-element transducer and a 2/22 MHz sub-array (16/48-elements linear array) transducer were developed for contrast enhanced super-harmonic ultrasound imaging of prostate cancer with the low frequency ultrasound transducer as a transmitter for contrast agent (microbubble) excitation and the high frequency transducer as a receiver for detection of nonlinear responses from microbubbles. The 1-3 piezoelectric composite was used as active materials of the single-element transducers due to its low acoustic impedance and high coupling factor. A high dielectric constant PZT ceramic was used for the sub-array transducer due to its high dielectric property induced relatively low electrical impedance. The possible resonance modes of the active elements were estimated using finite element analysis (FEA). The pulse-echo response, peak-negative pressure and bubble response were tested, followed by in vitro contrast imaging tests using a graphite-gelatin tissue-mimicking phantom. The single-element dual frequency transducer (8 × 4 × 2 mm3) showed a -6 dB fractional bandwidth of 56.5% for the transmitter, and 41.8% for the receiver. A 2 MHz-transmitter (730 μm pitch and 6.5 mm elevation aperture) and a 22 MHz-receiver (240 μm pitch and 1.5 mm aperture) of the sub-array transducer exhibited -6 dB fractional bandwidth of 51.0% and 40.2%, respectively. The peak negative pressure at the far field was about -1.3 MPa with 200 Vpp, 1-cycle 2 MHz burst, which is high enough to excite microbubbles for nonlinear responses. The 7th harmonic responses from micro bubbles were successfully detected in the phantom imaging test showing a contrast-to-tissue ratio (CTR) of 16 dB.

Nonlinear propagation in ultrasonic fields: measurements, modelling and harmonic imaging.

PubMed

Humphrey, V F

2000-03-01

In high amplitude ultrasonic fields, such as those used in medical ultrasound, nonlinear propagation can result in waveform distortion and the generation of harmonics of the initial frequency. In the nearfield of a transducer this process is complicated by diffraction effects associated with the source. The results of a programme to study the nonlinear propagation in the fields of circular, focused and rectangular transducers are described, and comparisons made with numerical predictions obtained using a finite difference solution to the Khokhlov-Zabolotskaya-Kuznetsov (or KZK) equation. These results are extended to consider nonlinear propagation in tissue-like media and the implications for ultrasonic measurements and ultrasonic heating are discussed. The narrower beamwidths and reduced side-lobe levels of the harmonic beams are illustrated and the use of harmonics to form diagnostic images with improved resolution is described.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging.

PubMed

Nadeau, Kyle P; Rice, Tyler B; Durkin, Anthony J; Tromberg, Bruce J

2015-11-01

We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging

PubMed Central

Nadeau, Kyle P.; Rice, Tyler B.; Durkin, Anthony J.; Tromberg, Bruce J.

2015-01-01

Abstract. We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI. PMID:26524682

Development of 3D microwave imaging reflectometry in LHD (invited).

PubMed

Nagayama, Y; Kuwahara, D; Yoshinaga, T; Hamada, Y; Kogi, Y; Mase, A; Tsuchiya, H; Tsuji-Iio, S; Yamaguchi, S

2012-10-01

Three-dimensional (3D) microwave imaging reflectometry has been developed in the large helical device to visualize fluctuating reflection surface which is caused by the density fluctuations. The plasma is illuminated by the probe wave with four frequencies, which correspond to four radial positions. The imaging optics makes the image of cut-off surface onto the 2D (7 × 7 channels) horn antenna mixer arrays. Multi-channel receivers have been also developed using micro-strip-line technology to handle many channels at reasonable cost. This system is first applied to observe the edge harmonic oscillation (EHO), which is an MHD mode with many harmonics that appears in the edge plasma. A narrow structure along field lines is observed during EHO.

Development of 3D microwave imaging reflectometry in LHD (invited)a)

NASA Astrophysics Data System (ADS)

Nagayama, Y.; Kuwahara, D.; Yoshinaga, T.; Hamada, Y.; Kogi, Y.; Mase, A.; Tsuchiya, H.; Tsuji-Iio, S.; Yamaguchi, S.

2012-10-01

Three-dimensional (3D) microwave imaging reflectometry has been developed in the large helical device to visualize fluctuating reflection surface which is caused by the density fluctuations. The plasma is illuminated by the probe wave with four frequencies, which correspond to four radial positions. The imaging optics makes the image of cut-off surface onto the 2D (7 × 7 channels) horn antenna mixer arrays. Multi-channel receivers have been also developed using micro-strip-line technology to handle many channels at reasonable cost. This system is first applied to observe the edge harmonic oscillation (EHO), which is an MHD mode with many harmonics that appears in the edge plasma. A narrow structure along field lines is observed during EHO.

Analysis of Particle Image Velocimetry (PIV) Data for Acoustic Velocity Measurements

NASA Technical Reports Server (NTRS)

Blackshire, James L.

1997-01-01

Acoustic velocity measurements were taken using Particle Image Velocimetry (PIV) in a Normal Incidence Tube configuration at various frequency, phase, and amplitude levels. This report presents the results of the PIV analysis and data reduction portions of the test and details the processing that was done. Estimates of lower measurement sensitivity levels were determined based on PIV image quality, correlation, and noise level parameters used in the test. Comparison of measurements with linear acoustic theory are presented. The onset of nonlinear, harmonic frequency acoustic levels were also studied for various decibel and frequency levels ranging from 90 to 132 dB and 500 to 3000 Hz, respectively.

Ultrasound contrast agent imaging: Real-time imaging of the superharmonics

NASA Astrophysics Data System (ADS)

Peruzzini, D.; Viti, J.; Tortoli, P.; Verweij, M. D.; de Jong, N.; Vos, H. J.

2015-10-01

Currently, in medical ultrasound contrast agent (UCA) imaging the second harmonic scattering of the microbubbles is regularly used. This scattering is in competition with the signal that is caused by nonlinear wave propagation in tissue. It was reported that UCA imaging based on the third or higher harmonics, i.e. "superharmonic" imaging, shows better contrast. However, the superharmonic scattering has a lower signal level compared to e.g. second harmonic signals. This study investigates the contrast-to-tissue ratio (CTR) and signal to noise ratio (SNR) of superharmonic UCA scattering in a tissue/vessel mimicking phantom using a real-time clinical scanner. Numerical simulations were performed to estimate the level of harmonics generated by the microbubbles. Data were acquired with a custom built dual-frequency cardiac phased array probe. Fundamental real-time images were produced while beam formed radiofrequency (RF) data was stored for further offline processing. The phantom consisted of a cavity filled with UCA surrounded by tissue mimicking material. The acoustic pressure in the cavity of the phantom was 110 kPa (MI = 0.11) ensuring non-destructivity of UCA. After processing of the acquired data from the phantom, the UCA-filled cavity could be clearly observed in the images, while tissue signals were suppressed at or below the noise floor. The measured CTR values were 36 dB, >38 dB, and >32 dB, for the second, third, and fourth harmonic respectively, which were in agreement with those reported earlier for preliminary contrast superharmonic imaging. The single frame SNR values (in which `signal' denotes the signal level from the UCA area) were 23 dB, 18 dB, and 11 dB, respectively. This indicates that noise, and not the tissue signal, is the limiting factor for the UCA detection when using the superharmonics in nondestructive mode.

Contrast-enhanced transcranial two-dimensional ultrasound imaging using shear-mode conversion at low frequency.

PubMed

Lucht, Benjamin; Hubbell, Austin; Hynynen, Kullervo

2013-02-01

The distortion and attenuation of transcranial ultrasound (US) signals are significant problems in US imaging of the brain. Of the variety of proposed solutions, shear-mode transmission through the skull is one of the more recent options and has been shown to reduce distortion of the US beam. This study examined the effects of transcranial shear-mode transmission on the images of a contrast-agent-filled polytetrafluoroethylene tube produced by a 32-element 750 kHz linear phased array transducer through an ex vivo human skull section. Although the tube was successfully imaged using shear-mode transmission with subharmonic imaging in 6 of 9 cases, the tube was visible in only 1 of 9 cases for both the fundamental and the second harmonic frequencies. Some improvement in the location of the axial image was seen at the fundamental frequency using shear mode. No improvement was seen at the other two frequencies, but this may be due to low transducer sensitivity. As well, neither the presence of the skull nor the incident angle changed the distance at which signals from the two tubes could be resolved. With this transducer, these distances were found to be 5 mm laterally and 3 mm axially for the fundamental and second harmonic images, and 10 mm and 5 mm for the subharmonic images. The results show that the subharmonic signal was the most successful of the three examined in penetrating a thick skull but that the success comes at the cost of image resolution. Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Using Passive Cavitation Images to Classify High-Intensity Focused Ultrasound Lesions

PubMed Central

Haworth, Kevin J.; Salgaonkar, Vasant A.; Corregan, Nicholas M.; Holland, Christy K.; Mast, T. Douglas

2015-01-01

Passive cavitation imaging provides spatially resolved monitoring of cavitation emissions. However the diffraction limit of a linear imaging array results in relatively poor range resolution. Poor range resolution has limited prior analyses of the spatial specificity and sensitivity of passive cavitation imaging for predicting thermal lesion formation. In this study, this limitation is overcome by orienting a linear array orthogonal to the HIFU propagation direction and performing passive imaging. Fourteen lesions were formed in ex vivo bovine liver samples as a result of 1.1 MHz continuous-wave ultrasound exposure. The lesions were classified as focal, “tadpole”, or pre-focal based on their shape and location. Passive cavitation images were beam-formed from emissions at the fundamental, harmonic, ultraharmonic, and inharmonic frequencies with an established algorithm. Using the area under a receiver operator characteristic curve (AUROC), fundamental, harmonic, and ultraharmonic emissions were shown to be significant predictors of lesion formation for all lesion types. For both harmonic and ultraharmonic emissions, pre-focal lesions were classified most successfully (AUROC values of 0.87 and 0.88, respectively), followed by tadpole lesions (AUROC values of 0.77 and 0.64, respectively), and focal lesions (AUROC values of 0.65 and 0.60, respectively). PMID:26051309

The design of a multi-harmonic step-tunable gyrotron

NASA Astrophysics Data System (ADS)

Qi, Xiang-Bo; Du, Chao-Hai; Zhu, Juan-Feng; Pan, Shi; Liu, Pu-Kun

2017-03-01

The theoretical study of a step-tunable gyrotron controlled by successive excitation of multi-harmonic modes is presented in this paper. An axis-encircling electron beam is employed to eliminate the harmonic mode competition. Physics images are depicted to elaborate the multi-harmonic interaction mechanism in determining the operating parameters at which arbitrary harmonic tuning can be realized by magnetic field sweeping to achieve controlled multiband frequencies' radiation. An important principle is revealed that a weak coupling coefficient under a high-harmonic interaction can be compensated by a high Q-factor. To some extent, the complementation between the high Q-factor and weak coupling coefficient makes the high-harmonic mode potential to achieve high efficiency. Based on a previous optimized magnetic cusp gun, the multi-harmonic step-tunable gyrotron is feasible by using harmonic tuning of first-to-fourth harmonic modes. Multimode simulation shows that the multi-harmonic gyrotron can operate on the 34 GHz first-harmonic TE11 mode, 54 GHz second-harmonic TE21 mode, 74 GHz third-harmonic TE31 mode, and 94 GHz fourth-harmonic TE41 mode, corresponding to peak efficiencies of 28.6%, 35.7%, 17.1%, and 11.4%, respectively. The multi-harmonic step-tunable gyrotron provides new possibilities in millimeter-terahertz source development especially for advanced terahertz applications.

3D second harmonic generation imaging tomography by multi-view excitation

PubMed Central

Campbell, Kirby R.; Wen, Bruce; Shelton, Emily M.; Swader, Robert; Cox, Benjamin L.; Eliceiri, Kevin; Campagnola, Paul J.

2018-01-01

Biological tissues have complex 3D collagen fiber architecture that cannot be fully visualized by conventional second harmonic generation (SHG) microscopy due to electric dipole considerations. We have developed a multi-view SHG imaging platform that successfully visualizes all orientations of collagen fibers. This is achieved by rotating tissues relative to the excitation laser plane of incidence, where the complete fibrillar structure is then visualized following registration and reconstruction. We evaluated high frequency and Gaussian weighted fusion reconstruction algorithms, and found the former approach performs better in terms of the resulting resolution. The new approach is a first step toward SHG tomography. PMID:29541654

A theoretical investigation of chirp insonification of ultrasound contrast agents.

PubMed

Barlow, Euan; Mulholland, Anthony J; Gachagan, Anthony; Nordon, Alison

2011-08-01

A theoretical investigation of second harmonic imaging of an Ultrasound Contrast Agent (UCA) under chirp insonification is considered. By solving the UCA's dynamical equation analytically, the effect that the chirp signal parameters and the UCA shell parameters have on the amplitude of the second harmonic frequency are examined. This allows optimal parameter values to be identified which maximise the UCA's second harmonic response. A relationship is found for the chirp parameters which ensures that a signal can be designed to resonate a UCA for a given set of shell parameters. It is also shown that the shell thickness, shell viscosity and shell elasticity parameter should be as small as realistically possible in order to maximise the second harmonic amplitude. Keller-Herring, Second Harmonic, Chirp, Ultrasound Contrast Agent. Copyright © 2011 Elsevier B.V. All rights reserved.

Balancing Vibrations at Harmonic Frequencies by Injecting Harmonic Balancing Signals into the Armature of a Linear Motor/Alternator Coupled to a Stirling Machine

NASA Technical Reports Server (NTRS)

Holliday, Ezekiel S. (Inventor)

2014-01-01

Vibrations at harmonic frequencies are reduced by injecting harmonic balancing signals into the armature of a linear motor/alternator coupled to a Stirling machine. The vibrations are sensed to provide a signal representing the mechanical vibrations. A harmonic balancing signal is generated for selected harmonics of the operating frequency by processing the sensed vibration signal with adaptive filter algorithms of adaptive filters for each harmonic. Reference inputs for each harmonic are applied to the adaptive filter algorithms at the frequency of the selected harmonic. The harmonic balancing signals for all of the harmonics are summed with a principal control signal. The harmonic balancing signals modify the principal electrical drive voltage and drive the motor/alternator with a drive voltage component in opposition to the vibration at each harmonic.

Reference-Free Removal of EEG-fMRI Ballistocardiogram Artifacts with Harmonic Regression

PubMed Central

Krishnaswamy, Pavitra; Bonmassar, Giorgio; Poulsen, Catherine; Pierce, Eric T; Purdon, Patrick L.; Brown, Emery N.

2016-01-01

Combining electroencephalogram (EEG) recording and functional magnetic resonance imaging (fMRI) offers the potential for imaging brain activity with high spatial and temporal resolution. This potential remains limited by the significant ballistocardiogram (BCG) artifacts induced in the EEG by cardiac pulsation-related head movement within the magnetic field. We model the BCG artifact using a harmonic basis, pose the artifact removal problem as a local harmonic regression analysis, and develop an efficient maximum likelihood algorithm to estimate and remove BCG artifacts. Our analysis paradigm accounts for time-frequency overlap between the BCG artifacts and neurophysiologic EEG signals, and tracks the spatiotemporal variations in both the artifact and the signal. We evaluate performance on: simulated oscillatory and evoked responses constructed with realistic artifacts; actual anesthesia-induced oscillatory recordings; and actual visual evoked potential recordings. In each case, the local harmonic regression analysis effectively removes the BCG artifacts, and recovers the neurophysiologic EEG signals. We further show that our algorithm outperforms commonly used reference-based and component analysis techniques, particularly in low SNR conditions, the presence of significant time-frequency overlap between the artifact and the signal, and/or large spatiotemporal variations in the BCG. Because our algorithm does not require reference signals and has low computational complexity, it offers a practical tool for removing BCG artifacts from EEG data recorded in combination with fMRI. PMID:26151100

Linking high harmonics from gases and solids.

PubMed

Vampa, G; Hammond, T J; Thiré, N; Schmidt, B E; Légaré, F; McDonald, C R; Brabec, T; Corkum, P B

2015-06-25

When intense light interacts with an atomic gas, recollision between an ionizing electron and its parent ion creates high-order harmonics of the fundamental laser frequency. This sub-cycle effect generates coherent soft X-rays and attosecond pulses, and provides a means to image molecular orbitals. Recently, high harmonics have been generated from bulk crystals, but what mechanism dominates the emission remains uncertain. To resolve this issue, we adapt measurement methods from gas-phase research to solid zinc oxide driven by mid-infrared laser fields of 0.25 volts per ångström. We find that when we alter the generation process with a second-harmonic beam, the modified harmonic spectrum bears the signature of a generalized recollision between an electron and its associated hole. In addition, we find that solid-state high harmonics are perturbed by fields so weak that they are present in conventional electronic circuits, thus opening a route to integrate electronics with attosecond and high-harmonic technology. Future experiments will permit the band structure of a solid to be tomographically reconstructed.

Cerebral perfusion imaging with bolus harmonic imaging (Honorable Mention Poster Award)

NASA Astrophysics Data System (ADS)

Kier, Christian; Toth, Daniel; Meyer-Wiethe, Karsten; Schindler, Angela; Cangur, Hakan; Seidel, Gunter; Aach, Til

2005-04-01

Fast visualisation of cerebral microcirculation supports diagnosis of acute stroke. However, the commonly used CT/MRI-based methods are time consuming, costly and not applicable to every patient. The bolus perfusion harmonic imaging (BHI) method is an ultrasound imaging technique which makes use of the fact, that ultrasound contrast agents unlike biological tissues resonate at harmonic frequencies. Exploiting this effect, the contrast between perfused and non-perfused areas can be improved. Thus, BHI overcomes the low signal-to-noise ratio of transcranial ultrasound and the high impedance of the skull. By analysing image sequences, visualising the qualitative characteristics of an US contrast agent bolus injection becomes possible. The analysis consists of calculating four perfusion-related parameters, Local Peak Intensity, Time To Peak, Area Under Curve, and Average Rising, from the time/intensity curve and providing them as colour-coded images. For calculating these parameters the fundamental assumption is that image intensity corresponds to contrast agent concentration which in turn shows the perfusion of the corresponding brain region. In a clinical study on patients suffering from acute ischemic stroke it is shown that some of the parameters correlate significantly to the infarction area. Thus, BHI becomes a less time-consuming and inexpensive bedside method for diagnosis of cerebral perfusion deficits.

Combined chirp coded tissue harmonic and fundamental ultrasound imaging for intravascular ultrasound: 20–60 MHz phantom and ex vivo results

PubMed Central

Park, Jinhyoung; Li, Xiang; Zhou, Qifa; Shung, K. Kirk

2013-01-01

The application of chirp coded excitation to pulse inversion tissue harmonic imaging can increase signal to noise ratio. On the other hand, the elevation of range side lobe level, caused by leakages of the fundamental signal, has been problematic in mechanical scanners which are still the most prevalent in high frequency intravascular ultrasound imaging. Fundamental chirp coded excitation imaging can achieve range side lobe levels lower than –60 dB with Hanning window, but it yields higher side lobes level than pulse inversion chirp coded tissue harmonic imaging (PI-CTHI). Therefore, in this paper a combined pulse inversion chirp coded tissue harmonic and fundamental imaging mode (CPI-CTHI) is proposed to retain the advantages of both chirp coded harmonic and fundamental imaging modes by demonstrating 20–60 MHz phantom and ex vivo results. A simulation study shows that the range side lobe level of CPI-CTHI is 16 dB lower than PI-CTHI, assuming that the transducer translates incident positions by 50 μm when two beamlines of pulse inversion pair are acquired. CPI-CTHI is implemented for a proto-typed intravascular ultrasound scanner capable of combined data acquisition in real-time. A wire phantom study shows that CPI-CTHI has a 12 dB lower range side lobe level and a 7 dB higher echo signal to noise ratio than PI-CTHI, while the lateral resolution and side lobe level are 50 μm finer and –3 dB less than fundamental chirp coded excitation imaging respectively. Ex vivo scanning of a rabbit trachea demonstrates that CPI-CTHI is capable of visualizing blood vessels as small as 200 μm in diameter with 6 dB better tissue contrast than either PI-CTHI or fundamental chirp coded excitation imaging. These results clearly indicate that CPI-CTHI may enhance tissue contrast with less range side lobe level than PI-CTHI. PMID:22871273

The electromagnetic environment of Magnetic Resonance Imaging systems. Occupational exposure assessment reveals RF harmonics

NASA Astrophysics Data System (ADS)

Gourzoulidis, G.; Karabetsos, E.; Skamnakis, N.; Kappas, C.; Theodorou, K.; Tsougos, I.; Maris, T. G.

2015-09-01

Magnetic Resonance Imaging (MRI) systems played a crucial role in the postponement of the former occupational electromagnetic fields (EMF) European Directive (2004/40/EC) and in the formation of the latest exposure limits adopted in the new one (2013/35/EU). Moreover, the complex MRI environment will be finally excluded from the implementation of the new occupational limits, leading to an increased demand for Occupational Health and Safety (OHS) surveillance. The gradient function of MRI systems and the application of the RF excitation frequency result in low and high frequency exposures, respectively. This electromagnetic field exposure, in combination with the increased static magnetic field exposure, makes the MRI environment a unique case of combined EMF exposure. The electromagnetic field levels in close proximity of different MRI systems have been assessed at various frequencies. Quality Assurance (QA) & safety issues were also faced. Preliminary results show initial compliance with the forthcoming limits in each different frequency band, but also revealed peculiar RF harmonic components, of no safety concern, to the whole range detected (20-1000MHz). Further work is needed in order to clarify their origin and characteristics.

Physics-based analysis and control of human snoring

NASA Astrophysics Data System (ADS)

Sanchez, Yaselly; Wang, Junshi; Han, Pan; Xi, Jinxiang; Dong, Haibo

2017-11-01

In order to advance the understanding of biological fluid dynamics and its effects on the acoustics of human snoring, the study pursued a physics-based computational approach. From human magnetic resonance image (MRI) scans, the researchers were able to develop both anatomically and dynamically accurate airway-uvula models. With airways defined as rigid, and the uvula defined as flexible, computational models were created with various pharynx thickness and geometries. In order to determine vortex shedding with prescribed uvula movement, the uvula fluctuation was categorized by its specific parameters: magnitude, frequency, and phase lag. Uvula vibration modes were based on one oscillation, or one harmonic frequency, and pressure probes were located in seven different positions throughout the airway-uvula model. By taking fast Fourier transforms (FFT) from the pressure probe data, it was seen that four harmonics were created throughout the simulation within one oscillation of uvula movement. Of the four harmonics, there were two pressure probes which maintained high amplitudes and led the researcher to believe that different vortices formed with different snoring frequencies. This work is supported by the NSF Grant CBET-1605434.

Ultrasound contrast agent imaging: Real-time imaging of the superharmonics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peruzzini, D.; Viti, J.; Erasmus MC, ’s-Gravendijkwal 230, Faculty Building, Ee 2302, 3015 CE Rotterdam

2015-10-28

Currently, in medical ultrasound contrast agent (UCA) imaging the second harmonic scattering of the microbubbles is regularly used. This scattering is in competition with the signal that is caused by nonlinear wave propagation in tissue. It was reported that UCA imaging based on the third or higher harmonics, i.e. “superharmonic” imaging, shows better contrast. However, the superharmonic scattering has a lower signal level compared to e.g. second harmonic signals. This study investigates the contrast-to-tissue ratio (CTR) and signal to noise ratio (SNR) of superharmonic UCA scattering in a tissue/vessel mimicking phantom using a real-time clinical scanner. Numerical simulations were performedmore » to estimate the level of harmonics generated by the microbubbles. Data were acquired with a custom built dual-frequency cardiac phased array probe. Fundamental real-time images were produced while beam formed radiofrequency (RF) data was stored for further offline processing. The phantom consisted of a cavity filled with UCA surrounded by tissue mimicking material. The acoustic pressure in the cavity of the phantom was 110 kPa (MI = 0.11) ensuring non-destructivity of UCA. After processing of the acquired data from the phantom, the UCA-filled cavity could be clearly observed in the images, while tissue signals were suppressed at or below the noise floor. The measured CTR values were 36 dB, >38 dB, and >32 dB, for the second, third, and fourth harmonic respectively, which were in agreement with those reported earlier for preliminary contrast superharmonic imaging. The single frame SNR values (in which ‘signal’ denotes the signal level from the UCA area) were 23 dB, 18 dB, and 11 dB, respectively. This indicates that noise, and not the tissue signal, is the limiting factor for the UCA detection when using the superharmonics in nondestructive mode.« less

Optical coherence tomography imaging based on non-harmonic analysis

NASA Astrophysics Data System (ADS)

Cao, Xu; Hirobayashi, Shigeki; Chong, Changho; Morosawa, Atsushi; Totsuka, Koki; Suzuki, Takuya

2009-11-01

A new processing technique called Non-Harmonic Analysis (NHA) is proposed for OCT imaging. Conventional Fourier-Domain OCT relies on the FFT calculation which depends on the window function and length. Axial resolution is counter proportional to the frame length of FFT that is limited by the swept range of the swept source in SS-OCT, or the pixel counts of CCD in SD-OCT degraded in FD-OCT. However, NHA process is intrinsically free from this trade-offs; NHA can resolve high frequency without being influenced by window function or frame length of sampled data. In this study, NHA process is explained and applied to OCT imaging and compared with OCT images based on FFT. In order to validate the benefit of NHA in OCT, we carried out OCT imaging based on NHA with the three different sample of onion-skin,human-skin and pig-eye. The results show that NHA process can realize practical image resolution that is equivalent to 100nm swept range only with less than half-reduced wavelength range.

Driving an Active Vibration Balancer to Minimize Vibrations at the Fundamental and Harmonic Frequencies

NASA Technical Reports Server (NTRS)

Holliday, Ezekiel S. (Inventor)

2014-01-01

Vibrations of a principal machine are reduced at the fundamental and harmonic frequencies by driving the drive motor of an active balancer with balancing signals at the fundamental and selected harmonics. Vibrations are sensed to provide a signal representing the mechanical vibrations. A balancing signal generator for the fundamental and for each selected harmonic processes the sensed vibration signal with adaptive filter algorithms of adaptive filters for each frequency to generate a balancing signal for each frequency. Reference inputs for each frequency are applied to the adaptive filter algorithms of each balancing signal generator at the frequency assigned to the generator. The harmonic balancing signals for all of the frequencies are summed and applied to drive the drive motor. The harmonic balancing signals drive the drive motor with a drive voltage component in opposition to the vibration at each frequency.

Frequency-chirp rates of harmonics driven by a few-cycle pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murakami, M.; Mauritsson, J.; Gaarde, M.B.

2005-08-15

We present numerical calculations of the time-frequency characteristics of cutoff harmonics generated by few-cycle laser pulses. We find that for driving pulses as short as three optical cycles, the adiabatic prediction for the harmonic chirp rate is very accurate. This negative chirp is so large that the resulting bandwidth causes substantial overlap between neighboring harmonics, and the harmonic phase therefore appears to not vary in time or frequency. By adding a compensating positive chirp to the driving pulse, which reduces the harmonic bandwidth and allows for the appearance of the negative chirp, we can measure the harmonic chirp rates. Wemore » also find that the positive chirp on the driving pulse causes the harmonics to shift down in frequency. We show that this counterintuitive result is caused by the change in the strong field continuum dynamics introduced by the variation of the driving frequency with time.« less

A Computationally Efficient Method for Polyphonic Pitch Estimation

NASA Astrophysics Data System (ADS)

Zhou, Ruohua; Reiss, Joshua D.; Mattavelli, Marco; Zoia, Giorgio

2009-12-01

This paper presents a computationally efficient method for polyphonic pitch estimation. The method employs the Fast Resonator Time-Frequency Image (RTFI) as the basic time-frequency analysis tool. The approach is composed of two main stages. First, a preliminary pitch estimation is obtained by means of a simple peak-picking procedure in the pitch energy spectrum. Such spectrum is calculated from the original RTFI energy spectrum according to harmonic grouping principles. Then the incorrect estimations are removed according to spectral irregularity and knowledge of the harmonic structures of the music notes played on commonly used music instruments. The new approach is compared with a variety of other frame-based polyphonic pitch estimation methods, and results demonstrate the high performance and computational efficiency of the approach.

Sub-nano tesla magnetic imaging based on room-temperature magnetic flux sensors with vibrating sample magnetometry

NASA Astrophysics Data System (ADS)

Adachi, Yoshiaki; Oyama, Daisuke

2017-05-01

We developed a two-dimensional imaging method for weak magnetic charge distribution using a commercially available magnetic impedance sensor whose magnetic field resolution is 10 pT/Hz1/2 at 10 Hz. When we applied the vibrating sample magnetometry, giving a minute mechanical vibration to the sample and detecting magnetic signals modulated by the vibration frequency, the effects of 1/f noise and the environmental low-frequency band noise were suppressed, and a weak magnetic charge distribution was obtained without magnetic shielding. Furthermore, improvement in the spatial resolution was also expected when the signals were demodulated at the second harmonic frequency of the vibration. In this paper, a preliminary magnetic charge imaging using the vibrating sample magnetometry and its results are demonstrated.

Measuring full-field displacement spectral components using photographs taken with a DSLR camera via an analogue Fourier integral

NASA Astrophysics Data System (ADS)

Javh, Jaka; Slavič, Janko; Boltežar, Miha

2018-02-01

Instantaneous full-field displacement fields can be measured using cameras. In fact, using high-speed cameras full-field spectral information up to a couple of kHz can be measured. The trouble is that high-speed cameras capable of measuring high-resolution fields-of-view at high frame rates prove to be very expensive (from tens to hundreds of thousands of euro per camera). This paper introduces a measurement set-up capable of measuring high-frequency vibrations using slow cameras such as DSLR, mirrorless and others. The high-frequency displacements are measured by harmonically blinking the lights at specified frequencies. This harmonic blinking of the lights modulates the intensity changes of the filmed scene and the camera-image acquisition makes the integration over time, thereby producing full-field Fourier coefficients of the filmed structure's displacements.

Methods for reverberation suppression utilizing dual frequency band imaging.

PubMed

Rau, Jochen M; Måsøy, Svein-Erik; Hansen, Rune; Angelsen, Bjørn; Tangen, Thor Andreas

2013-09-01

Reverberations impair the contrast resolution of diagnostic ultrasound images. Tissue harmonic imaging is a common method to reduce these artifacts, but does not remove all reverberations. Dual frequency band imaging (DBI), utilizing a low frequency pulse which manipulates propagation of the high frequency imaging pulse, has been proposed earlier for reverberation suppression. This article adds two different methods for reverberation suppression with DBI: the delay corrected subtraction (DCS) and the first order content weighting (FOCW) method. Both methods utilize the propagation delay of the imaging pulse of two transmissions with alternating manipulation pressure to extract information about its depth of first scattering. FOCW further utilizes this information to estimate the content of first order scattering in the received signal. Initial evaluation is presented where both methods are applied to simulated and in vivo data. Both methods yield visual and measurable substantial improvement in image contrast. Comparing DCS with FOCW, DCS produces sharper images and retains more details while FOCW achieves best suppression levels and, thus, highest image contrast. The measured improvement in contrast ranges from 8 to 27 dB for DCS and from 4 dB up to the dynamic range for FOCW.

Investigation of optimal method for inducing harmonic motion in tissue using a linear ultrasound phased array--a simulation study.

PubMed

Heikkilä, Janne; Hynynen, Kullervo

2006-04-01

Many noninvasive ultrasound techniques have been developed to explore mechanical properties of soft tissues. One of these methods, Localized Harmonic Motion Imaging (LHMI), has been proposed to be used for ultrasound surgery monitoring. In LHMI, dynamic ultrasound radiation-force stimulation induces displacements in a target that can be measured using pulse-echo imaging and used to estimate the elastic properties of the target. In this initial, simulation study, the use of a one-dimensional phased array is explored for the induction of the tissue motion. The study compares three different dual-frequency and amplitude-modulated single-frequency methods for the inducing tissue motion. Simulations were computed in a homogeneous soft-tissue volume. The Rayleigh integral was used in the simulations of the ultrasound fields and the tissue displacements were computed using a finite-element method (FEM). The simulations showed that amplitude-modulated sonication using a single frequency produced the largest vibration amplitude of the target tissue. These simulations demonstrate that the properties of the tissue motion are highly dependent on the sonication method and that it is important to consider the full three-dimensional distribution of the ultrasound field for controlling the induction of tissue motion.

Using passive cavitation images to classify high-intensity focused ultrasound lesions.

PubMed

Haworth, Kevin J; Salgaonkar, Vasant A; Corregan, Nicholas M; Holland, Christy K; Mast, T Douglas

2015-09-01

Passive cavitation imaging provides spatially resolved monitoring of cavitation emissions. However, the diffraction limit of a linear imaging array results in relatively poor range resolution. Poor range resolution has limited prior analyses of the spatial specificity and sensitivity of passive cavitation imaging in predicting thermal lesion formation. In this study, this limitation is overcome by orienting a linear array orthogonal to the high-intensity focused ultrasound propagation direction and performing passive imaging. Fourteen lesions were formed in ex vivo bovine liver samples as a result of 1.1-MHz continuous-wave ultrasound exposure. The lesions were classified as focal, "tadpole" or pre-focal based on their shape and location. Passive cavitation images were beamformed from emissions at the fundamental, harmonic, ultraharmonic and inharmonic frequencies with an established algorithm. Using the area under a receiver operating characteristic curve (AUROC), fundamental, harmonic and ultraharmonic emissions were found to be significant predictors of lesion formation for all lesion types. For both harmonic and ultraharmonic emissions, pre-focal lesions were classified most successfully (AUROC values of 0.87 and 0.88, respectively), followed by tadpole lesions (AUROC values of 0.77 and 0.64, respectively) and focal lesions (AUROC values of 0.65 and 0.60, respectively). Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Effect of Context on the Contribution of Individual Harmonics to Residue Pitch.

PubMed

Gockel, Hedwig E; Alsindi, Sami; Hardy, Charles; Carlyon, Robert P

2017-12-01

There is evidence that the contribution of a given harmonic in a complex tone to residue pitch is influenced by the accuracy with which the frequency of that harmonic is encoded. The present study investigated whether listeners adjust the weights assigned to individual harmonics based on acquired knowledge of the reliability of the frequency estimates of those harmonics. In a two-interval forced-choice task, seven listeners indicated which of two 12-harmonic complex tones had the higher overall pitch. In context trials (60 % of all trials), the fundamental frequency (F0) was 200 Hz in one interval and 200 + ΔF0 Hz in the other. In different (blocked) conditions, either the 3rd or the 4th harmonic (plus the 7th, 9th, and 12th harmonics), were replaced by narrowband noises that were identical in the two intervals. Feedback was provided. In randomly interspersed test trials (40 % of all trials), the fundamental frequency was 200 + ΔF0/2 Hz in both intervals; in the second interval, either the third or the fourth harmonic was shifted slightly up or down in frequency with equal probability. There were no narrowband noises. Feedback was not provided. The results showed that substitution of a harmonic by noise in context trials reduced the contribution of that harmonic to pitch judgements in the test trials by a small but significant amount. This is consistent with the notion that listeners give smaller weight to a harmonic or frequency region when they have learned that this frequency region does not provide reliable information for a given task.

Contribution of low-frequency harmonics to Mandarin Chinese tone identification in quiet and six-talker babble background.

PubMed

Liu, Chang; Azimi, Behnam; Bhandary, Moulesh; Hu, Yi

2014-01-01

The goal of this study was to investigate Mandarin Chinese tone identification in quiet and multi-talker babble conditions for normal-hearing listeners. Tone identification was measured with speech stimuli and stimuli with low and/or high harmonics that were embedded in three Mandarin vowels with two fundamental frequencies. There were six types of stimuli: all harmonics (All), low harmonics (Low), high harmonics (High), and the first (H1), second (H2), and third (H3) harmonic. Results showed that, for quiet conditions, individual harmonics carried frequency contour information well enough for tone identification with high accuracy; however, in noisy conditions, tone identification with individual low harmonics (e.g., H1, H2, and H3) was significantly lower than that with the Low, High, and All harmonics. Moreover, tone identification with individual harmonics in noise was lower for a low F0 than for a high F0, and was also dependent on vowel category. Tone identification with individual low-frequency harmonics was accounted for by local signal-to-noise ratios, indicating that audibility of harmonics in noise may play a primary role in tone identification.

Electrostatic waves in the warm magnetoplasma at the cyclotron harmonic frequencies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gwal, A.K.; Misra, K.D.

1977-09-01

Mode conversion and collisionless absorption of electromagnetic wave at the cyclotron harmonic frequencies in an inhomogeneous non-Maxwellian magnetoplasma have been studied. Under suitable energy transfer condition the converted electrostatic wave (plasma wave) either grows or damps. The expressions for the growth/damping rates of this wave have been derived and studied at the cyclotron harmonic frequencies. The effect of the temperature anisotropy on the growth/damping rate of the electrostatic wave at the second cyclotron harmonic frequency has been shown. Growth of such electrostatic waves at ionospheric heights may explain the observed upper hybrid resonance (UHR) echoes and noise bands at themore » second cyclotron harmonic frequency.« less

Realization of a new concept for visible frequency division: phase locking of harmonic and sum frequencies.

PubMed

Telle, H R; Meschede, D; Hänsch, T W

1990-05-15

We explore and demonstrate the feasibility of an optical-frequency-to-radio-frequency division method that is based on visible or near-infrared laser oscillators only. Comparing harmonic and sum frequencies, we generate the arithmetic average of two visible frequencies. Cascading n stages provides difference-frequency division by 2(n). For a demonstration we have phase locked the second harmonic and the sum frequency of two independent diode lasers.

2.32 THz quantum cascade laser frequency-locked to the harmonic of a microwave synthesizer source.

PubMed

Danylov, Andriy A; Light, Alexander R; Waldman, Jerry; Erickson, Neal R; Qian, Xifeng; Goodhue, William D

2012-12-03

Frequency stabilization of a THz quantum cascade laser (QCL) to the harmonic of a microwave source has been accomplished using a Schottky diode waveguide mixer designed for harmonic mixing. The 2.32 THz, 1.0 milliwatt CW QCL is coupled into the signal port of the mixer and a 110 GHz signal, derived from a harmonic of a microwave synthesizer, is coupled into the IF port. The difference frequency between the 21st harmonic of 110 GHz and the QCL is used in a discriminator to adjust the QCL bias current to stabilize the frequency. The short-term frequency jitter is reduced from 550 kHz to 4.5 kHz (FWHM) and the long-term frequency drift is eliminated. This performance is compared to that of several other THz QCL frequency stabilization techniques.

Spatially resolved observation of the fundamental and second harmonic standing kink modes using SDO/AIA

NASA Astrophysics Data System (ADS)

Pascoe, D. J.; Goddard, C. R.; Nakariakov, V. M.

2016-09-01

Aims: We consider a coronal loop kink oscillation observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) which demonstrates two strong spectral components. The period of the lower frequency component being approximately twice that of the shorter frequency component suggests the presence of harmonics. Methods: We examine the presence of two longitudinal harmonics by investigating the spatial dependence of the loop oscillation. The time-dependent displacement of the loop is measured at 15 locations along the loop axis. For each position the displacement is fitted as the sum of two damped sinusoids, having periods P1 and P2, and a damping time τ. The shorter period component exhibits anti-phase oscillations in the loop legs. Results: We interpret the observation in terms of the first (global or fundamental) and second longitudinal harmonics of the standing kink mode. The strong excitation of the second harmonic appears connected to the preceding coronal mass ejection (CME) which displaced one of the loop legs. The oscillation parameters found are P1 = 5.00±0.62 min, P2 = 2.20±0.23 min, P1/ 2P2 = 1.15±0.22, and τ/P = 3.35 ± 1.45. A movie associated to Fig. 5 is available in electronic form at http://www.aanda.org

High-order harmonic generation of CO and N2 molecules under linearly- and bi circularly-polarized laser pulses by TD-DFT

NASA Astrophysics Data System (ADS)

Koushki, A. M.; Sadighi-Bonabi, R.; Mohsen-Nia, M.; Irani, E.

2018-07-01

We present a method for high-order harmonics generation of N2 and CO molecules under two-color circularly polarized counter-rotating laser pulses at frequencies of and 2. Pulse envelope in this investigation is sin-squared and the intensity of each laser beam is with ten-optical cycle (o.c.). We show that an isolated pulse with a pulse duration shorter than 20 attosecond from the superposition of several harmonics can be generated. Both two-color linearly- and bicircularly-polarized laser pulses are considered. Our results have also been compared with the outcomes of the previous theoretical works as well as experiment observations. It is found that for CO molecule, the bicircularly-polarized laser pulses are superior and more efficient, and it can generate narrower attosecond pulses than the linearly-polarized pulses. While for N2 molecule, the two-color linearly-polarized pulses are more efficient, and it can generate narrower attosecond pulses than the bicircularly-polarized pulses. Furthermore, in order to demonstrate the origin of red- and blue-shifts in high-harmonic spectra, the effect of pulse duration on the high-order harmonics spectra is investigated. In addition, to obtain imaging on the temporal dependence of the electron densities, the time dependent electron localization function is used. Moreover, in order to study of the quantum trajectory of electrons, time-frequency analysis is utilized.

Bernstein wave aided laser third harmonic generation in a plasma

NASA Astrophysics Data System (ADS)

Tyagi, Yachna; Tripathi, Deepak; Kumar, Ashok

2016-09-01

The process of Bernstein wave aided resonant third harmonic generation of laser in a magnetized plasma is investigated. The extra-ordinary mode (X-mode) laser of frequency ω 0 and wave number k → 0 , travelling across the magnetic field in a plasma, exerts a second harmonic ponderomotive force on the electrons imparting them an oscillatory velocity v → 2 ω0 , 2 k → 0 . This velocity beats with the density perturbation due to the Bernstein wave to produce a density perturbation at cyclotron frequency shifted second harmonic. The density perturbation couples with the oscillatory velocity v → ω0 , k → 0 of X-mode of the laser to produce the cyclotron frequency shifted third harmonic current density leading to harmonic radiation. The phase matching condition for the up shifted frequency is satisfied when the Bernstein wave is nearly counter-propagating to the laser. As the transverse wave number of the Bernstein wave is large, it is effective in the phase matched third harmonic generation, when the laser frequency is not too far from the upper hybrid frequency.

Cumulative phase delay between second harmonic and fundamental components--a marker for ultrasound contrast agents.

PubMed

Demi, Libertario; Wijkstra, Hessel; Mischi, Massimo

2014-12-01

Several imaging techniques aimed at detecting ultrasound contrast agents (UCAs) echo signals, while suppressing signals coming from the surrounding tissue, have been developed. These techniques are especially relevant for blood flow, perfusion, or contrast dispersion quantification. However, despite several approaches being presented, improving the understanding of the ultrasound/UCAs interaction may support further development of imaging techniques. In this paper, the physical phenomena behind the formation of harmonic components in tissue and UCAs, respectively, are addressed as a possible way to recognize the origin of the echo signals. Simulations based on a modified Rayleigh, Plesset, Noltingk, Neppiras, and Poritsky equation and transmission and backscattering measurements of ultrasound propagating through UCAs performed with a single element transducer and a submergible hydrophone, are presented. Both numerical and in vitro results show the occurrence of a cumulative time delay between the second harmonic and fundamental component which increases with UCA concentration and propagation path length through UCAs, and that was clearly observable at frequencies ( f0 = 2.5 MHz) and pressure regimes (mechanical index = 0.1) of interest for imaging. Most importantly, this delay is not observed in the absence of UCAs. In conclusion, the reported phenomenon represents a marker for UCAs with potential application for imaging.

Third order harmonic imaging for biological tissues using three phase-coded pulses.

PubMed

Ma, Qingyu; Gong, Xiufen; Zhang, Dong

2006-12-22

Compared to the fundamental and the second harmonic imaging, the third harmonic imaging shows significant improvements in image quality due to the better resolution, but it is degraded by the lower sound pressure and signal-to-noise ratio (SNR). In this study, a phase-coded pulse technique is proposed to selectively enhance the sound pressure of the third harmonic by 9.5 dB whereas the fundamental and the second harmonic components are efficiently suppressed and SNR is also increased by 4.7 dB. Based on the solution of the KZK nonlinear equation, the axial and lateral beam profiles of harmonics radiated from a planar piston transducer were theoretically simulated and experimentally examined. Finally, the third harmonic images using this technique were performed for several biological tissues and compared with the images obtained by the fundamental and the second harmonic imaging. Results demonstrate that the phase-coded pulse technique yields a dramatically cleaner and sharper contrast image.

Dual aperture dipole magnet with second harmonic component

DOEpatents

Praeg, Walter F.

1985-01-01

An improved dual aperture dipole electromagnet includes a second-harmonic frequency magnetic guide field winding which surrounds first harmonic frequency magnetic guide field windings associated with each aperture. The second harmonic winding and the first harmonic windings cooperate to produce resultant magnetic waveforms in the apertures which have extended acceleration and shortened reset portions of electromagnet operation.

Dual aperture dipole magnet with second harmonic component

DOEpatents

Praeg, W.F.

1983-08-31

An improved dual aperture dipole electromagnet includes a second-harmonic frequency magnetic guide field winding which surrounds first harmonic frequency magnetic guide field windings associated with each aperture. The second harmonic winding and the first harmonic windings cooperate to produce resultant magnetic waveforms in the apertures which have extended acceleration and shortened reset portions of electromagnet operation.

Harmonic generation by yeast cells in response to low-frequency electric fields

NASA Astrophysics Data System (ADS)

Nawarathna, D.; Claycomb, J. R.; Cardenas, G.; Gardner, J.; Warmflash, D.; Miller, J. H., Jr.; Widger, W. R.

2006-05-01

We report on harmonic generation by budding yeast cells (Saccharomyces cerevisiae, 108cells/ml ) in response to sinusoidal electric fields with amplitudes ranging from zero to 5V/cm in the frequency range 10-300Hz . The cell-generated harmonics are found to exhibit strong amplitude and frequency dependence. Sodium metavanadate, an inhibitor of the proton pump known as H+ -ATPase, and glucose, a substrate of H+ -ATPase, are found to increase harmonic production at low amplitudes while reducing it at large amplitudes. This P-type proton pump can be driven by an oscillatory transmembrane potential, and its nonlinear response is believed to be largely responsible for harmonic production at low frequencies in yeast cells. We find that the observed harmonics show dramatic changes with time and in their field and frequency dependence after perturbing the system by adding an inhibitor, substrate, or membrane depolarizer to the cell suspension.

Measurement of optical-beat frequency in a photoconductive terahertz-wave generator using microwave higher harmonics.

PubMed

Murasawa, Kengo; Sato, Koki; Hidaka, Takehiko

2011-05-01

A new method for measuring optical-beat frequencies in the terahertz (THz) region using microwave higher harmonics is presented. A microwave signal was applied to the antenna gap of a photoconductive (PC) device emitting a continuous electromagnetic wave at about 1 THz by the photomixing technique. The microwave higher harmonics with THz frequencies are generated in the PC device owing to the nonlinearity of the biased photoconductance, which is briefly described in this article. Thirteen nearly periodic peaks in the photocurrent were observed when the microwave was swept from 16 to 20 GHz at a power of -48 dBm. The nearly periodic peaks are generated by the homodyne detection of the optical beat with the microwave higher harmonics when the frequency of the harmonics coincides with the optical-beat frequency. Each peak frequency and its peak width were determined by fitting a Gaussian function, and the order of microwave harmonics was determined using a coarse (i.e., lower resolution) measurement of the optical-beat frequency. By applying the Kalman algorithm to the peak frequencies of the higher harmonics and their standard deviations, the optical-beat frequency near 1 THz was estimated to be 1029.81 GHz with the standard deviation of 0.82 GHz. The proposed method is applicable to a conventional THz-wave generator with a photomixer.

Frequency modulation of high-order harmonic generation in an orthogonally polarized two-color laser field.

PubMed

Li, Guicun; Zheng, Yinghui; Ge, Xiaochun; Zeng, Zhinan; Li, Ruxin

2016-08-08

We have experimentally investigated the frequency modulation of high-order harmonics in an orthogonally polarized two-color laser field consisting of a mid-infrared 1800nm fundamental pulse and its second harmonic pulse. It is demonstrated that the high harmonic spectra can be fine-tuned as we slightly change the relative delay of the two-color laser pulses. By analyzing the relative frequency shift of each harmonic at different two-color delays, the nonadiabatic spectral shift induced by the rapid variation of the intensity-dependent intrinsic dipole phase can be distinguished from the blueshift induced by the change of the refractive index during self-phase modulation (SPM). Our comprehensive analysis shows that the frequency modulation pattern is a reflection of the average emission time of high-order harmonic generation (HHG), thus offering a simple method to fine-tune the spectra of the harmonics on a sub-cycle time scale.

High harmonic emission from a superposition of multiple unrelated frequency fields.

PubMed

Siegel, T; Torres, R; Hoffmann, D J; Brugnera, L; Procino, I; Zaïr, A; Underwood, Jonathan G; Springate, E; Turcu, I C E; Chipperfield, L E; Marangos, J P

2010-03-29

We report observations and analysis of high harmonic generation driven by a superposition of fields at 1290 nm and 780 nm. These fields are not commensurate in frequency and the superposition leads to an increase in the yield of the mid-plateau harmonics of more than two orders of magnitude compared to using the 1290 nm field alone. Significant extension of the cut-off photon energy is seen even by adding only a small amount of the 780 nm field. These observations are explained by calculations performed in the strong field approximation. Most importantly we find that enhancement is found to arise as a consequence of both increased ionization in the sum-field and modification of the electron trajectories leading to an earlier return time. The enhanced yield even when using modest intensity fields of 5 x 10(13) Wcm(-2) is extended to the 80 eV range and is a promising route to provide a greater photon number for applications in XUV imaging and time-resolved experiments at a high repetition rate.

Nonlinear Effects in Three-minute Oscillations of the Solar Chromosphere. I. An Analytical Nonlinear Solution and Detection of the Second Harmonic

NASA Astrophysics Data System (ADS)

Chae, Jongchul; Litvinenko, Yuri E.

2017-08-01

The vertical propagation of nonlinear acoustic waves in an isothermal atmosphere is considered. A new analytical solution that describes a finite-amplitude wave of an arbitrary wavelength is obtained. Although the short- and long-wavelength limits were previously considered separately, the new solution describes both limiting cases within a common framework and provides a straightforward way of interpolating between the two limits. Physical features of the nonlinear waves in the chromosphere are described, including the dispersive nature of low-frequency waves, the steepening of the wave profile, and the influence of the gravitational field on wavefront breaking and shock formation. The analytical results suggest that observations of three-minute oscillations in the solar chromosphere may reveal the basic nonlinear effect of oscillations with combination frequencies, superposed on the normal oscillations of the system. Explicit expressions for a second-harmonic signal and the ratio of its amplitude to the fundamental harmonic amplitude are derived. Observational evidence of the second harmonic, obtained with the Fast Imaging Solar Spectrograph, installed at the 1.6 m New Solar Telescope of the Big Bear Observatory, is presented. The presented data are based on the time variations of velocity determined from the Na I D2 and Hα lines.

Harmonics generation near ion-cyclotron frequency of ECR plasma

NASA Astrophysics Data System (ADS)

Chowdhury, Satyajit; Biswas, Subir; Chakrabarti, Nikhil; Pal, Rabindranath

2017-10-01

Wave excitation at different frequency regime is employed in the MaPLE device ECR plasma for varied excitation amplitude. At very low amplitude excitation, mainly fundamental frequency mode of the exciter signal frequency comes into play. With the increase in amplitude of applied perturbation, harmonics are generated and dominant over the fundamental frequency mode. There is a fixed critical amplitude of exciter to yield the harmonics and is independent of applied frequency. Observed harmonics and the main frequency mode has propagation characteristics and are discussed here. Exact mode number and propagation nature are also tried to measure in the experiment. Detailed experimental results will be presented. Department of Science and Technology of Government of India (Project No. SB/S2/HEP-005/2014).

Harmonic source wavefront aberration correction for ultrasound imaging

PubMed Central

Dianis, Scott W.; von Ramm, Olaf T.

2011-01-01

A method is proposed which uses a lower-frequency transmit to create a known harmonic acoustical source in tissue suitable for wavefront correction without a priori assumptions of the target or requiring a transponder. The measurement and imaging steps of this method were implemented on the Duke phased array system with a two-dimensional (2-D) array. The method was tested with multiple electronic aberrators [0.39π to 1.16π radians root-mean-square (rms) at 4.17 MHz] and with a physical aberrator 0.17π radians rms at 4.17 MHz) in a variety of imaging situations. Corrections were quantified in terms of peak beam amplitude compared to the unaberrated case, with restoration between 0.6 and 36.6 dB of peak amplitude with a single correction. Standard phantom images before and after correction were obtained and showed both visible improvement and 14 dB contrast improvement after correction. This method, when combined with previous phase correction methods, may be an important step that leads to improved clinical images. PMID:21303031

Comparison of Fine Structures of Electron Cyclotron Harmonic Emissions in Aurora

NASA Astrophysics Data System (ADS)

Labelle, J. W.; Dundek, M.

2015-12-01

Recent discoveries of emissions at four and five times the electron cyclotron frequency in aurora occuring under daylit conditions motivated the modification of radio receivers at South Pole Station, Antarctica, to measure fine structure of such emissions during two consecutive austral summers, 2013-4 and 2014-5. The experiment recorded 347 emission events over 376 days of observation. The seasonal distribution of these events revealed that successively higher harmonics require higher solar zenith angles for occurrence, as expected if they are generated at locations where the upper hybrid frequency matches the cyclotron harmonic, which for higher harmonics requires higher electron densities which are associated with higher solar zenith angles. Detailed examination of 21 cases in which two harmonics occur simultaneously showed that only rarely, about ten percent of the time, are the frequencies of the fine structures of the emissions in exact integer ratio (e.g., 3:2, 4:3, or 5:4 depending on which combination of harmonics is observed). In the remaining approximately ninety percent of the cases, the higher harmonic occurred at a lower ratio than the appropriate integer ratio, as expected if the harmonics are generated independently at their separate matching conditions in the bottomside ionosphere, where the upper hybrid frequency increases with altitude while the gyroharmonics decrease with altitude. (The bottomside is the most likely source of the emissions, since from there the mode converted Z-modes have access to ground-level.) Taken together, these results suggest that the dominant mechanism for the higher harmonics is independent generation at locations where the upper hybrid frequency matches each harmonic, i.e., at a separate source altitude for each harmonic. Generation of higher harmonics through coalescence of lower harmonic waves explains at most a small minority of events.

Fundamental analysis and ex vivo validation of thermal lesion mapping using harmonic motion imaging for focused ultrasound (HMIFU)

NASA Astrophysics Data System (ADS)

Hou, Gary Y.; Luo, Jianwen; Maleke, Caroline; Vappou, Jonathan; Marquet, Fabrice; Konofagou, Elisa E.

2012-10-01

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a novel high-intensity focused ultrasound (HIFU) therapy monitoring method with feasibilities demonstrated in vitro, ex vivo and in vivo. Its principle is based on Amplitude-modulated (AM) - Harmonic Motion Imaging (HMI), an oscillatory radiation force used for imaging the tissue mechanical response during thermal ablation. In this study, a theoretical framework of HMIFU is presented, comprising a customized nonlinear wave propagation model, a finite-element (FE) analysis module, and an image-formation model. The objective of this study is to develop such a framework in order to 1) assess the fundamental performance of HMIFU in detecting HIFU lesions based on the change in tissue apparent elasticity, i.e., the increasing Young's modulus, and the HIFU lesion size with respect to the HIFU exposure time and 2) validate the simulation findings ex vivo. The same HMI and HMIFU parameters as in the experimental studies were used, i.e., 4.5-MHz HIFU frequency and 25-Hz AM frequency. For a lesion-to-background Young's modulus ratio of 3, 6, and 9, the estimated HMI displacement ratios were equal to 1.65, 3.19, 4.59, respectively. In experiments, the HMI displacement followed a similar increasing trend of 1.19, 1.28, 1.78 at 10-s, 20-s, and 30-s HIFU exposure, respectively. In addition, moderate agreement in lesion size growth was also found in both simulations (16.2, 73.1 and 334.7 mm2) and experiments (26.2, 94.2 and 206.2 mm2). Therefore, the feasibility of HMIFU for HIFU lesion detection based on the underlying tissue elasticity changes was verified through the developed theoretical framework, i.e., validation of the fundamental performance of the HMIFU system for lesion detection, localization and quantification, was demonstrated both theoretically and ex vivo.

Performance assessment of HIFU lesion detection by Harmonic Motion Imaging for Focused Ultrasound (HMIFU): A 3D finite-element-based framework with experimental validation

PubMed Central

Hou, Gary Y.; Luo, Jianwen; Marquet, Fabrice; Maleke, Caroline; Vappou, Jonathan; Konofagou, Elisa E.

2014-01-01

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a novel high-intensity focused ultrasound (HIFU) therapy monitoring method with feasibilities demonstrated in vitro, ex vivo and in vivo. Its principle is based on Amplitude-modulated (AM) - Harmonic Motion Imaging (HMI), an oscillatory radiation force used for imaging the tissue mechanical response during thermal ablation. In this study, a theoretical framework of HMIFU is presented, comprising a customized nonlinear wave propagation model, a finite-element (FE) analysis module, and an image-formation model. The objective of this study is to develop such a framework in order to 1) assess the fundamental performance of HMIFU in detecting HIFU lesions based on the change in tissue apparent elasticity, i.e., the increasing Young's modulus, and the HIFU lesion size with respect to the HIFU exposure time and 2) validate the simulation findings ex vivo. The same HMI and HMIFU parameters as in the experimental studies were used, i.e., 4.5-MHz HIFU frequency and 25 Hz AM frequency. For a lesion-to-background Young's modulus ratio of 3, 6, and 9, the FE and estimated HMI displacement ratios were equal to 1.83, 3.69, 5.39 and 1.65, 3.19, 4.59, respectively. In experiments, the HMI displacement followed a similar increasing trend of 1.19, 1.28, and 1.78 at 10-s, 20-s, and 30-s HIFU exposure, respectively. In addition, moderate agreement in lesion size growth was also found in both simulations (16.2, 73.1 and 334.7 mm2) and experiments (26.2, 94.2 and 206.2 mm2). Therefore, the feasibility of HMIFU for HIFU lesion detection based on the underlying tissue elasticity changes was verified through the developed theoretical framework, i.e., validation of the fundamental performance of the HMIFU system for lesion detection, localization and quantification, was demonstrated both theoretically and ex vivo. PMID:22036637

Arrhythmia Mechanism and Scaling Effect on the Spectral Properties of Electroanatomical Maps With Manifold Harmonics.

PubMed

Sanroman-Junquera, Margarita; Mora-Jimenez, Inmaculada; Garcia-Alberola, Arcadio; Caamano, Antonio J; Trenor, Beatriz; Rojo-Alvarez, Jose L

2018-04-01

Spatial and temporal processing of intracardiac electrograms provides relevant information to support the arrhythmia ablation during electrophysiological studies. Current cardiac navigation systems (CNS) and electrocardiographic imaging (ECGI) build detailed 3-D electroanatomical maps (EAM), which represent the spatial anatomical distribution of bioelectrical features, such as activation time or voltage. We present a principled methodology for spectral analysis of both EAM geometry and bioelectrical feature in CNS or ECGI, including their spectral representation, cutoff frequency, or spatial sampling rate (SSR). Existing manifold harmonic techniques for spectral mesh analysis are adapted to account for a fourth dimension, corresponding to the EAM bioelectrical feature. Appropriate scaling is required to address different magnitudes and units. With our approach, simulated and real EAM showed strong SSR dependence on both the arrhythmia mechanism and the cardiac anatomical shape. For instance, high frequencies increased significantly the SSR because of the "early-meets-late" in flutter EAM, compared with the sinus rhythm. Besides, higher frequency components were obtained for the left atrium (more complex anatomy) than for the right atrium in sinus rhythm. The proposed manifold harmonics methodology opens the field toward new signal processing tools for principled EAM spatiofeature analysis in CNS and ECGI, and to an improved knowledge on arrhythmia mechanisms.

Harmonic Frequency Lowering

PubMed Central

Kirchberger, Martin

2016-01-01

A novel algorithm for frequency lowering in music was developed and experimentally tested in hearing-impaired listeners. Harmonic frequency lowering (HFL) combines frequency transposition and frequency compression to preserve the harmonic content of music stimuli. Listeners were asked to make judgments regarding detail and sound quality in music stimuli. Stimuli were presented under different signal processing conditions: original, low-pass filtered, HFL, and nonlinear frequency compressed. Results showed that participants reported perceiving the most detail in the HFL condition. In addition, there was no difference in sound quality across conditions. PMID:26834122

Acoustic fingerprints of photoacoustic contrast agents for molecular imaging

NASA Astrophysics Data System (ADS)

McDonald, Michael A.; Jankovic, Ladislav; Shahzad, Khalid; Burcher, Michael; Li, King C. P.

2007-02-01

Protein nanospheres capable of frequency controlled oscillation in response to laser stimulation are presented as contrast agents for photoacoustic imaging. Incident laser energy absorbed by dye-labeled protein nanospheres causes thermoelastically generated sound production. Plotted A-line graphs reveal a distinctive morphology and greater than 2 orders of magnitude increase in signal amplitude subsequent to converting labeled proteins into nanospheres. Evidence of nonlinearity and enhancement of ultrasound backscatter indicate a potential use in contrast-enhanced harmonic imaging. Photoacoustic and ultrasound imaging of protein nanospheres in phantom vessels show enhanced contrast at low concentration and clear delineation of the phantom vessel wall.

Effects of low harmonics on tone identification in natural and vocoded speech.

PubMed

Liu, Chang; Azimi, Behnam; Tahmina, Qudsia; Hu, Yi

2012-11-01

This study investigated the contribution of low-frequency harmonics to identifying Mandarin tones in natural and vocoded speech in quiet and noisy conditions. Results showed that low-frequency harmonics of natural speech led to highly accurate tone identification; however, for vocoded speech, low-frequency harmonics yielded lower tone identification than stimuli with full harmonics, except for tone 4. Analysis of the correlation between tone accuracy and the amplitude-F0 correlation index suggested that "more" speech contents (i.e., more harmonics) did not necessarily yield better tone recognition for vocoded speech, especially when the amplitude contour of the signals did not co-vary with the F0 contour.

Human haemodynamic frequency harmonics regulate the inflammatory phenotype of vascular endothelial cells.

PubMed

Feaver, Ryan E; Gelfand, Bradley D; Blackman, Brett R

2013-01-01

Haemodynamic variations are inherent to blood vessel geometries (such as bifurcations) and correlate with regional development of inflammation and atherosclerosis. However, the complex frequency spectrum characteristics from these haemodynamics have never been exploited to test whether frequency variations are critical determinants of endothelial inflammatory phenotype. Here we utilize an experimental Fourier transform analysis to systematically manipulate individual frequency harmonics from human carotid shear stress waveforms applied in vitro to human endothelial cells. The frequency spectrum, specifically the 0 th and 1st harmonics, is a significant regulator of inflammation, including NF-κB activity and downstream inflammatory phenotype. Further, a harmonic-based regression-model predicts eccentric NF-κB activity observed in the human internal carotid artery. Finally, short interfering RNA-knockdown of the mechanosensor PECAM-1 reverses frequency-dependent regulation of NF-κB activity. Thus, PECAM-1 may have a critical role in the endothelium's exquisite sensitivity to complex shear stress frequency harmonics and provide a mechanism for the focal development of vascular inflammation.

Frequency-doubled microwave waveforms generation using a dual-polarization quadrature phase shift keying modulator driven by a single frequency radio frequency signal

NASA Astrophysics Data System (ADS)

Zhu, Zihang; Zhao, Shanghong; Li, Xuan; Qu, Kun; Lin, Tao

2018-01-01

A photonic approach to generate frequency-doubled microwave waveforms using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator driven by a sinusoidal radio frequency (RF) signal is proposed. By adjusting the dc bias points of the DP-QPSK modulator, the obtained second-order and six-order harmonics are in phase while the fourth-order harmonics are complementary when the orthogonal polarized outputs of the modulator are photodetected. After properly setting the modulation indices of the modulator, the amplitude of the second-order harmonic is 9 times of that of the six-order harmonic, indicating a frequency-doubled triangular waveform is generated. If a broadband 90° microwave phase shifter is attached after the photodetector (PD) to introduce a 90° phase shift, a frequency-doubled square waveform can be obtained after adjusting the amplitude of the second-order harmonic 3 times of that of the six-order harmonic. The proposal is first theoretically analyzed and then validated by simulation. Simulation results show that a 10 GHz triangular and square waveform sequences are successfully generated from a 5 GHz sinusoidal RF drive signal.

Influence of mode-beating pulse on laser-induced plasma

NASA Astrophysics Data System (ADS)

Nishihara, M.; Freund, J. B.; Glumac, N. G.; Elliott, G. S.

2018-04-01

This paper addresses the influence of mode-beating pulse on laser-induced plasma. The second harmonic of a Nd:YAG laser, operated either with the single mode or multimode, was used for non-resonant optical breakdown, and subsequent plasma development was visualized using a streak imaging system. The single mode lasing leads to a stable breakdown location and smooth envelopment of the plasma boundary, while the multimode lasing, with the dominant mode-beating frequency of 500-800 MHz, leads to fluctuations in the breakdown location, a globally modulated plasma surface, and growth of local microstructures at the plasma boundary. The distribution of the local inhomogeneity was measured from the elastic scattering signals on the streak image. The distance between the local structures agreed with the expected wavelength of hydrodynamic instability development due to the interference between the surface excited wave and transmitted wave. A numerical simulation, however, indicates that the local microstructure could also be directly generated at the peaks of the higher harmonic components if the multimode pulse contains up to the eighth harmonic of the fundamental cavity mode.

Experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum tube

NASA Astrophysics Data System (ADS)

Toufexis, Filippos; Tantawi, Sami G.; Jensen, Aaron; Dolgashev, Valery A.; Haase, Andrew; Fazio, Michael V.; Borchard, Philipp

2017-06-01

We report the experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum electronic device, which uses an over-moded spherical sector output cavity. In this device, a pencil electron beam is helically deflected in a transverse deflecting cavity before entering the output cavity. No magnetic field is required to focus or guide the beam. We built and tested a proof-of-principle device with an output frequency of 57.12 GHz. The measured peak power was 52.67 W at the 5th harmonic of the drive frequency. Power at the 4th, 6th, and 7th harmonics was 33.28 dB lower than that at the 5th harmonic.

Experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum tube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toufexis, Filippos; Tantawi, Sami G.; Jensen, Aaron

Here, we report the experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum electronic device, which uses an over-moded spherical sector output cavity. In this device, a pencil electron beam is helically deflected in a transverse deflecting cavity before entering the output cavity. No magnetic field is required to focus or guide the beam. We built and tested a proof-of-principle device with an output frequency of 57.12 GHz. The measured peak power was 52.67 W at the 5th harmonic of the drive frequency. Power at the 4th, 6th, and 7th harmonics was 33.28 dB lower than that at themore » 5th harmonic.« less

Experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum tube

DOE PAGES

Toufexis, Filippos; Tantawi, Sami G.; Jensen, Aaron; ...

2017-06-26

Here, we report the experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum electronic device, which uses an over-moded spherical sector output cavity. In this device, a pencil electron beam is helically deflected in a transverse deflecting cavity before entering the output cavity. No magnetic field is required to focus or guide the beam. We built and tested a proof-of-principle device with an output frequency of 57.12 GHz. The measured peak power was 52.67 W at the 5th harmonic of the drive frequency. Power at the 4th, 6th, and 7th harmonics was 33.28 dB lower than that at themore » 5th harmonic.« less

Imaging with Second-Harmonic Generation Nanoparticles

NASA Astrophysics Data System (ADS)

Hsieh, Chia-Lung

Second-harmonic generation nanoparticles show promise as imaging probes due to their coherent and stable signal with a broad flexibility in the choice of excitation wavelength. In this thesis, we developed and demonstrated barium titanate nanoparticles as second-harmonic radiation imaging probes. We studied the absolute second-harmonic generation efficiency of the nanoparticles on single-particle level. The polarization dependent second-harmonic signal of single nanoparticles was studied in detail. From the measured polar response, we were able to find the orientation of the nanoparticle. We developed a biochemical interface for using the second-harmonic nanoprobes as biomarkers, including in vitro cellular imaging and in vivo live animal imaging. The nanoparticles were surface functionalized with primary amine groups for stable colloidal dispersion. We achieved specific labeling of the second-harmonic nanoprobes via immunostaining where the antibodies were covalently conjugated onto the nanoparticles. We observed no toxicity of the functionalized nanoparticles to biological cells. The coherent second-harmonic signal radiated from the nanoparticles offers opportunities for new imaging techniques. Using interferometric detection, namely harmonic holography, both amplitude and phase of the second-harmonic field can be captured. Through digital beam propagation, three-dimensional field distribution, reflecting three-dimensional distribution of the nanoparticles, can be reconstructed. We achieved a scan-free three-dimensional imaging of nanoparticles in biological cells with sub-micron spatial resolution by using the harmonic holographic microscope. We further exploited the coherent second-harmonic signal for imaging through scattering media by performing optical phase conjugation of the second-harmonic signal. We demonstrated an all-digital optical phase conjugation of the second-harmonic signal originated from a nanoparticle by combining harmonic holography and dynamic computer generated holography using a spatial light modulator. The phase-conjugated second-harmonic scattered field retraced the scattering trajectory and formed a clean focus on the nanoparticle placed inside a scattering medium. The nanoparticle acted as a beacon of light; it helped us find the tailored wavefront for concentrating light at the nanoparticle inside the scattering medium. We also demonstrated imaging through a thin scattering medium by raster-scanning the phase-conjugated focus in the vicinity of the beacon nanoparticle, in which a clear image of a target placed behind a ground glass diffuser was obtained.

Raman Microscopy: A Noninvasive Method to Visualize the Localizations of Biomolecules in the Cornea.

PubMed

Kaji, Yuichi; Akiyama, Toshihiro; Segawa, Hiroki; Oshika, Tetsuro; Kano, Hideaki

2017-11-01

In vivo and in situ visualization of biomolecules without pretreatment will be important for diagnosis and treatment of ocular disorders in the future. Recently, multiphoton microscopy, based on the nonlinear interactions between molecules and photons, has been applied to reveal the localizations of various molecules in tissues. We aimed to use multimodal multiphoton microscopy to visualize the localizations of specific biomolecules in rat corneas. Multiphoton images of the corneas were obtained from nonlinear signals of coherent anti-Stokes Raman scattering, third-order sum frequency generation, and second-harmonic generation. The localizations of the adhesion complex-containing basement membrane and Bowman layer were clearly visible in the third-order sum frequency generation images. The fine structure of type I collagen was observed in the corneal stroma in the second-harmonic generation images. The localizations of lipids, proteins, and nucleic acids (DNA/RNA) was obtained in the coherent anti-Stokes Raman scattering images. Imaging technologies have progressed significantly and been applied in medical fields. Optical coherence tomography and confocal microscopy are widely used but do not provide information on the molecular structure of the cornea. By contrast, multiphoton microscopy provides information on the molecular structure of living tissues. Using this technique, we successfully visualized the localizations of various biomolecules including lipids, proteins, and nucleic acids in the cornea. We speculate that multiphoton microscopy will provide essential information on the physiological and pathological conditions of the cornea, as well as molecular localizations in tissues without pretreatment.

Electromagnetic probes of molecular motors in the electron transport chains of mitochondria and chloroplasts

NASA Astrophysics Data System (ADS)

Miller, J. H., Jr.; Nawarathna, D.; Vajrala, V.; Gardner, J.; Widger, W. R.

2005-12-01

We report on measurements of harmonics generated by whole cells, mitochondria, and chloroplasts in response to applied sinusoidal electric fields. The frequency- and amplitude-dependence of the induced harmonics exhibit features that correlate with physiological processes. Budding yeast (S. cerevisiae) cells produce numerous harmonics, the amplitudes of which depend strongly on frequency. When the second or third harmonic amplitude is plotted vs. applied frequency, we observe two peaks, around 3 kHz and 12 kHz, which are suppressed by respiratory inhibitors. We observe similar peaks when measuring the harmonic response of B. indicas, a relative of the mitochondrial ancestor. In uncoupled mitochondria, in which most of the electron transport chain is active but the ATP-synthase molecular turbine is inactive, only one (lower frequency) of the two peaks is present. Finally, we find that harmonics generated by chloroplasts depend dramatically on incident light, and vanish in the absence of light.

Physiological and harmonic components in neural and muscular coherence in Parkinsonian tremor.

PubMed

Wang, Shouyan; Aziz, Tipu Z; Stein, John F; Bain, Peter G; Liu, Xuguang

2006-07-01

To differentiate physiological from harmonic components in coherence analysis of the tremor-related neural and muscular signals by comparing power, cross-power and coherence spectra. Influences of waveform, burst-width and additional noise on generating harmonic peaks in the power, cross-power and coherence spectra were studied using simulated signals. The local field potentials (LFPs) of the subthalamic nucleus (STN) and the EMGs of the contralateral forearm muscles in PD patients with rest tremor were analysed. (1) Waveform had significant effect on generating harmonics; (2) noise significantly decreased the coherence values in a frequency-dependent fashion; and (3) cross-spectrum showed high resistance to harmonics. Among six examples of paired LFP-EMG signals, significant coherence appeared at the tremor frequency only, both the tremor and double tremor frequencies and the double-tremor frequency only. In coherence analysis of neural and muscular signals, distortion in waveform generates significant harmonic peaks in the coherence spectra and the coherence values of both physiological and harmonic components are modulated by extra noise or non-tremor related activity. The physiological or harmonic nature of a coherence peak at the double tremor frequency may be differentiated when the coherence spectra are compared with the power and in particular the cross-power spectra.

Effect of self-demodulation on the subharmonic response of contrast agent microbubbles

NASA Astrophysics Data System (ADS)

Daeichin, V.; Faez, T.; Renaud, G.; Bosch, J. G.; van der Steen, A. F. W.; de Jong, N.

2012-06-01

Subharmonic (SH) emission from the ultrasound contrast agent (UCA) is of interest since it is produced only by the UCA and not by tissue, opposite to harmonic imaging modes where both tissue and microbubble show harmonics. In this work, the use of the self-demodulation (S-D) signal as a means of microbubble excitation at the SH frequency to enhance the SH emission of UCA is studied. The S-D wave is a low-frequency signal produced by the weak nonlinear propagation of an ultrasound wave. It is proportional to the second time derivative of the squared envelope of the transmitted signal. A diluted population of BR14 UCA (Bracco Research SA, Geneva, Switzerland) was insonified by a 10 MHz transducer focused at 76 mm firing bursts with different envelopes, durations and peak pressure amplitudes. The center frequency of the S-D signal changes from low frequencies (around 0.5 MHz) toward the transmitted frequency (10 MHz) by modifying the envelope function from Gaussian to rectangular. For 6 and 20 transmitted cycles, the SH response is enhanced up to 25 and 22 dB, respectively, when using a rectangular envelope instead of a Gaussian one. The experimental results are confirmed by the numerical simulation. The effects of the excitation duration and pressure amplitude are also studied. This study shows that a suitable design of the envelope of the transmit excitation to generate a S-D signal at the SH frequency can enhance the SH emission of UCA, and the SH imaging is feasible at high frequencies with a shorter transmit burst (six-cycle) and low acoustic pressure (∼100 KPa).

Nonlinear response of a harmonic diatomic molecule: Algebraic nonperturbative calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Recamier, Jose; Mochan, W. Luis; Maytorena, Jesus A.

2005-08-15

Even harmonic molecules display a nonlinear behavior when driven by an inhomogeneous field. We calculate the response of single harmonic molecules to a monochromatic time and space dependent electric field E(r,t) of frequency {omega} employing exact algebraic methods. We evaluate the responses at the fundamental frequency {omega} and at successive harmonics 2{omega}, 3{omega}, etc., as a function of the intensity and of the frequency of the field and compare the results with those of first and second order perturbation theory.

Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging with a Phased Array Transducer

PubMed Central

Song, Pengfei; Zhao, Heng; Urban, Matthew W.; Manduca, Armando; Pislaru, Sorin V.; Kinnick, Randall R.; Pislaru, Cristina; Greenleaf, James F.; Chen, Shigao

2013-01-01

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE. PMID:24021638

Infrasonic and low-frequency insert earphone hearing threshold.

PubMed

Kuehler, Robert; Fedtke, Thomas; Hensel, Johannes

2015-04-01

Low-frequency and infrasonic pure-tone monaural hearing threshold data down to 2.5 Hz are presented. These measurements were made by means of a newly developed insert-earphone source. The source is able to generate pure-tone sound pressure levels up to 130 dB between 2 and 250 Hz with very low harmonic distortions. Behavioral hearing thresholds were determined in the frequency range from 2.5 to 125 Hz for 18 otologically normal test persons. The median hearing thresholds are comparable to values given in the literature. They are intended for stimulus calibration in subsequent brain imaging investigations.

Magneto-Radar Hidden Metal Detector

DOEpatents

McEwan, Thomas E.

2005-07-05

A varying magnetic field excites slight vibrations in an object and a radar sensor detects the vibrations at a harmonic of the excitation frequency. The synergy of the magnetic excitation and radar detection provides increased detection range compared to conventional magnetic metal detectors. The radar rejects background clutter by responding only to reflecting objects that are vibrating at a harmonic excitation field, thereby significantly improving detection reliability. As an exemplary arrangement, an ultra-wideband micropower impulse radar (MIR) is capable of being employed to provide superior materials penetration while providing range information. The magneto-radar may be applied to pre-screening magnetic resonance imaging (MRI) patients, landmine detection and finding hidden treasures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yalong; Jones, Edward A.; Wang, Fred

Arm inductor in a modular multilevel converter (MMC) is used to limit the circulating current and dc short circuit fault current. The circulating current in MMC is dominated by second-order harmonic, which can be largely reduced with circulating current suppressing control. By analyzing the mechanism of the circulating current suppressing control, it is found that the circulating current at switching frequency becomes the main harmonic when suppression control is implemented. Unlike the second-order harmonic that circulates only within the three phases, switching frequency harmonic also flows through the dc side and may further cause high-frequency dc voltage harmonic. This articlemore » develops the theoretical relationship between the arm inductance and switching frequency circulating current, which can be used to guide the arm inductance selection. The experimental results with a downscaled MMC prototype verify the existence of the switching frequency circulating current and its relationship with arm inductance.« less

Quantifying cortical surface harmonic deformation with stereovision during open cranial neurosurgery

NASA Astrophysics Data System (ADS)

Ji, Songbai; Fan, Xiaoyao; Roberts, David W.; Paulsen, Keith D.

2012-02-01

Cortical surface harmonic motion during open cranial neurosurgery is well observed in image-guided neurosurgery. Recently, we quantified cortical surface deformation noninvasively with synchronized blood pressure pulsation (BPP) from a sequence of stereo image pairs using optical flow motion tracking. With three subjects, we found the average cortical surface displacement can reach more than 1 mm and in-plane principal strains of up to 7% relative to the first image pair. In addition, the temporal changes in deformation and strain were in concert with BPP and patient respiration [1]. However, because deformation was essentially computed relative to an arbitrary reference, comparing cortical surface deformation at different times was not possible. In this study, we extend the technique developed earlier by establishing a more reliable reference profile of the cortical surface for each sequence of stereo image acquisitions. Specifically, fast Fourier transform (FFT) was applied to the dynamic cortical surface deformation, and the fundamental frequencies corresponding to patient respiration and BPP were identified, which were used to determine the number of image acquisitions for use in averaging cortical surface images. This technique is important because it potentially allows in vivo characterization of soft tissue biomechanical properties using intraoperative stereovision and motion tracking.

Enhancing resolution and contrast in second-harmonic generation microscopy using an advanced maximum likelihood estimation restoration method

NASA Astrophysics Data System (ADS)

Sivaguru, Mayandi; Kabir, Mohammad M.; Gartia, Manas Ranjan; Biggs, David S. C.; Sivaguru, Barghav S.; Sivaguru, Vignesh A.; Berent, Zachary T.; Wagoner Johnson, Amy J.; Fried, Glenn A.; Liu, Gang Logan; Sadayappan, Sakthivel; Toussaint, Kimani C.

2017-02-01

Second-harmonic generation (SHG) microscopy is a label-free imaging technique to study collagenous materials in extracellular matrix environment with high resolution and contrast. However, like many other microscopy techniques, the actual spatial resolution achievable by SHG microscopy is reduced by out-of-focus blur and optical aberrations that degrade particularly the amplitude of the detectable higher spatial frequencies. Being a two-photon scattering process, it is challenging to define a point spread function (PSF) for the SHG imaging modality. As a result, in comparison with other two-photon imaging systems like two-photon fluorescence, it is difficult to apply any PSF-engineering techniques to enhance the experimental spatial resolution closer to the diffraction limit. Here, we present a method to improve the spatial resolution in SHG microscopy using an advanced maximum likelihood estimation (AdvMLE) algorithm to recover the otherwise degraded higher spatial frequencies in an SHG image. Through adaptation and iteration, the AdvMLE algorithm calculates an improved PSF for an SHG image and enhances the spatial resolution by decreasing the full-width-at-halfmaximum (FWHM) by 20%. Similar results are consistently observed for biological tissues with varying SHG sources, such as gold nanoparticles and collagen in porcine feet tendons. By obtaining an experimental transverse spatial resolution of 400 nm, we show that the AdvMLE algorithm brings the practical spatial resolution closer to the theoretical diffraction limit. Our approach is suitable for adaptation in micro-nano CT and MRI imaging, which has the potential to impact diagnosis and treatment of human diseases.

Characterization of Harmonic Signal Acquisition with Parallel Dipole and Multipole Detectors

NASA Astrophysics Data System (ADS)

Park, Sung-Gun; Anderson, Gordon A.; Bruce, James E.

2018-04-01

Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is a powerful instrument for the study of complex biological samples due to its high resolution and mass measurement accuracy. However, the relatively long signal acquisition periods needed to achieve high resolution can serve to limit applications of FTICR-MS. The use of multiple pairs of detector electrodes enables detection of harmonic frequencies present at integer multiples of the fundamental cyclotron frequency, and the obtained resolving power for a given acquisition period increases linearly with the order of harmonic signal. However, harmonic signal detection also increases spectral complexity and presents challenges for interpretation. In the present work, ICR cells with independent dipole and harmonic detection electrodes and preamplifiers are demonstrated. A benefit of this approach is the ability to independently acquire fundamental and multiple harmonic signals in parallel using the same ions under identical conditions, enabling direct comparison of achieved performance as parameters are varied. Spectra from harmonic signals showed generally higher resolving power than spectra acquired with fundamental signals and equal signal duration. In addition, the maximum observed signal to noise (S/N) ratio from harmonic signals exceeded that of fundamental signals by 50 to 100%. Finally, parallel detection of fundamental and harmonic signals enables deconvolution of overlapping harmonic signals since observed fundamental frequencies can be used to unambiguously calculate all possible harmonic frequencies. Thus, the present application of parallel fundamental and harmonic signal acquisition offers a general approach to improve utilization of harmonic signals to yield high-resolution spectra with decreased acquisition time. [Figure not available: see fulltext.

Continuous-Wave Operation of a Frequency-Tunable 460-GHz Second-Harmonic Gyrotron for Enhanced Nuclear Magnetic Resonance

PubMed Central

Torrezan, Antonio C.; Han, Seong-Tae; Mastovsky, Ivan; Shapiro, Michael A.; Sirigiri, Jagadishwar R.; Temkin, Richard J.; Griffin, Robert G.; Barnes, Alexander B.

2012-01-01

The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. The gyrotron is intended to be used as a submillimeter-wave source for 700-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization. The gyrotron operates in the whispering-gallery mode TE11,2 and has generated 16 W of output power with a 13-kV 100-mA electron beam. The start oscillation current measured over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE11,2,q. The minimum start current is 27 mA. Power and frequency tuning measurements as a function of the electron cyclotron frequency have also been carried out. A smooth frequency tuning range of 1 GHz was obtained for the operating second-harmonic mode either by magnetic field tuning or beam voltage tuning. Long-term CW operation was evaluated during an uninterrupted period of 48 h, where the gyrotron output power and frequency were kept stable to within ±0.7% and ±6 ppm, respectively, by a computerized control system. Proper operation of an internal quasi-optical mode converter implemented to transform the operating whispering-gallery mode to a Gaussian-like beam was also verified. Based on the images of the gyrotron output beam taken with a pyroelectric camera, the Gaussian-like mode content of the output beam was computed to be 92% with an ellipticity of 12%. PMID:23761938

Continuous-Wave Operation of a Frequency-Tunable 460-GHz Second-Harmonic Gyrotron for Enhanced Nuclear Magnetic Resonance

PubMed Central

Torrezan, Antonio C.; Han, Seong-Tae; Mastovsky, Ivan; Shapiro, Michael A.; Sirigiri, Jagadishwar R.; Temkin, Richard J.; Barnes, Alexander B.; Griffin, Robert G.

2011-01-01

The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. The gyrotron is intended to be used as a submillimeter-wave source for 700-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization. The gyrotron operates in the whispering-gallery mode TE11,2 and has generated 16 W of output power with a 13-kV 100-mA electron beam. The start oscillation current measured over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE11,2,q. The minimum start current is 27 mA. Power and frequency tuning measurements as a function of the electron cyclotron frequency have also been carried out. A smooth frequency tuning range of 1 GHz was obtained for the operating second-harmonic mode either by magnetic field tuning or beam voltage tuning. Long-term CW operation was evaluated during an uninterrupted period of 48 h, where the gyrotron output power and frequency were kept stable to within ±0.7% and ±6 ppm, respectively, by a computerized control system. Proper operation of an internal quasi-optical mode converter implemented to transform the operating whispering-gallery mode to a Gaussian-like beam was also verified. Based on the images of the gyrotron output beam taken with a pyroelectric camera, the Gaussian-like mode content of the output beam was computed to be 92% with an ellipticity of 12%. PMID:21243088

Simultaneous negative refraction and focusing of fundamental frequency and second-harmonic fields by two-dimensional photonic crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jun; College of Physics and Electronic Engineering, Henan Normal University, 453007 Xinxiang, Henan; Zhang, Xiangdong, E-mail: zhangxd@bit.edu.cn

2015-09-28

Simultaneous negative refraction for both the fundamental frequency (FF) and second-harmonic (SH) fields in two-dimensional nonlinear photonic crystals have been found through both the physical analysis and exact numerical simulation. By combining such a property with the phase-matching condition and strong second-order susceptibility, we have designed a SH lens to realize focusing for both the FF and SH fields at the same time. Good-quality non-near field images for both FF and SH fields have been observed. The physical mechanism for such SH focusing phenomena has been disclosed, which is different from the backward SH generation as has been pointed outmore » in the previous investigations. In addition, the effect of absorption losses on the phenomena has also been discussed. Thus, potential applications of these phenomena to biphotonic microscopy technique are anticipated.« less

Temperature dependence of acoustic harmonics generated by nonlinear ultrasound beam propagation in ex vivo tissue and tissue-mimicking phantoms.

PubMed

Maraghechi, Borna; Kolios, Michael C; Tavakkoli, Jahan

2015-01-01

Hyperthermia is a cancer treatment technique that could be delivered as a stand-alone modality or in conjunction with chemotherapy or radiation therapy. Noninvasive and real-time temperature monitoring of the heated tissue improves the efficacy and safety of the treatment. A temperature-sensitive acoustic parameter is required for ultrasound-based thermometry. In this paper the amplitude and the energy of the acoustic harmonics of the ultrasound backscattered signal are proposed as suitable parameters for noninvasive ultrasound thermometry. A commercial high frequency ultrasound imaging system was used to generate and detect acoustic harmonics in tissue-mimicking gel phantoms and ex vivo bovine muscle tissues. The pressure amplitude and the energy content of the backscattered fundamental frequency (p1 and E1), the second (p2 and E2) and the third (p3 and E3) harmonics were detected in pulse-echo mode. Temperature was increased from 26° to 46 °C uniformly through both samples. The amplitude and the energy content of the harmonics and their ratio were measured and analysed as a function of temperature. The average p1, p2 and p3 increased by 69%, 100% and 283%, respectively as the temperature was elevated from 26° to 46 °C in tissue samples. In the same experiment the average E1, E2 and E3 increased by 163%, 281% and 2257%, respectively. A similar trend was observed in tissue-mimicking gel phantoms. The findings suggest that the harmonics generated due to nonlinear ultrasound beam propagation are highly sensitive to temperature and could potentially be used for noninvasive ultrasound tissue thermometry.

Vibro-acoustography and multifrequency image compounding.

PubMed

Urban, Matthew W; Alizad, Azra; Fatemi, Mostafa

2011-08-01

Vibro-acoustography is an ultrasound based imaging modality that can visualize normal and abnormal soft tissue through mapping the acoustic response of the object to a harmonic radiation force at frequency Δf induced by focused ultrasound. In this method, the ultrasound energy is converted from high ultrasound frequencies to a low acoustic frequency (acoustic emission) that is often two orders of magnitude smaller than the ultrasound frequency. The acoustic emission is normally detected by a hydrophone. Depending on the setup, this low frequency sound may reverberate by object boundaries or other structures present in the acoustic paths before it reaches the hydrophone. This effect produces an artifact in the image in the form of gradual variations in image intensity that may compromise image quality. The use of tonebursts with finite length yields acoustic emission at Δf and at sidebands centered about Δf. Multiple images are formed by selectively applying bandpass filters on the acoustic emission at Δf and the associated sidebands. The data at these multiple frequencies are compounded through both coherent and incoherent processes to reduce the acoustic emission reverberation artifacts. Experimental results from a urethane breast phantom are described. The coherent and incoherent compounding of multifrequency data show, both qualitatively and quantitatively, the efficacy of this reverberation reduction method. This paper presents theory describing the physical origin of this artifact and use of image data created using multifrequency vibro-acoustography for reducing reverberation artifacts. Copyright © 2011 Elsevier B.V. All rights reserved.

Vibro-acoustography and Multifrequency Image Compounding

PubMed Central

Urban, Matthew W.; Alizad, Azra; Fatemi, Mostafa

2011-01-01

Vibro-acoustography is an ultrasound based imaging modality that can visualize normal and abnormal soft tissue through mapping the acoustic response of the object to a harmonic radiation force at frequency Δf induced by focused ultrasound. In this method, the ultrasound energy is converted from high ultrasound frequencies to a low acoustic frequency (acoustic emission) that is often two orders of magnitude smaller than the ultrasound frequency. The acoustic emission is normally detected by a hydrophone. Depending on the setup, this low frequency sound may reverberate by object boundaries or other structures present in the acoustic paths before it reaches the hydrophone. This effect produces an artifact in the image in the form of gradual variations in image intensity that may compromise image quality. The use of tonebursts with finite length yields acoustic emission at Δf and at sidebands centered about Δf. Multiple images are formed by selectively applying bandpass filters on the acoustic emission at Δf and the associated sidebands. The data at these multiple frequencies are compounded through both coherent and incoherent processes to reduce the acoustic emission reverberation artifacts. Experimental results from a urethane breast phantom are described. The coherent and incoherent compounding of multifrequency data show, both qualitatively and quantitatively, the efficacy of this reverberation reduction method. This paper presents theory describing the physical origin of this artifact and use of image data created using multifrequency vibro-acoustography for reducing reverberation artifacts. PMID:21377181

Generation of five phase-locked harmonics by implementing a divide-by-three optical frequency divider.

PubMed

Suhaimi, Nurul Sheeda; Ohae, Chiaki; Gavara, Trivikramarao; Nakagawa, Ken'ichi; Hong, Feng-Lei; Katsuragawa, Masayuki

2015-12-15

We report the generation of five phase-locked harmonics, f₁:2403  nm, f₂:1201  nm, f₃:801  nm, f₄:600  nm, and f₅:480  nm with an exact frequency ratio of 1:2:3:4:5 by implementing a divide-by-three optical frequency divider in the high harmonic generation process. All five harmonics are generated coaxially with high phase coherence in time and space, which are applicable for various practical uses.

Harmonic Frequency Lowering: Effects on the Perception of Music Detail and Sound Quality.

PubMed

Kirchberger, Martin; Russo, Frank A

2016-02-01

A novel algorithm for frequency lowering in music was developed and experimentally tested in hearing-impaired listeners. Harmonic frequency lowering (HFL) combines frequency transposition and frequency compression to preserve the harmonic content of music stimuli. Listeners were asked to make judgments regarding detail and sound quality in music stimuli. Stimuli were presented under different signal processing conditions: original, low-pass filtered, HFL, and nonlinear frequency compressed. Results showed that participants reported perceiving the most detail in the HFL condition. In addition, there was no difference in sound quality across conditions. © The Author(s) 2016.

Measurement of high-degree solar oscillation frequencies

NASA Technical Reports Server (NTRS)

Bachmann, K. T.; Duvall, T. L., Jr.; Harvey, J. W.; Hill, F.

1995-01-01

We present m-averaged solar p- and f-mode oscillation frequencies over the frequency range nu greater than 1.8 and less than 5.0 mHz and the spherical harmonic degree range l greater than or equal to 100 and less than or equal to 1200 from full-disk, 1000 x 1024 pixel, Ca II intensity images collected 1993 June 22-25 with a temporal cadence of 60 s. We itemize the sources and magnitudes of statistical and systematic uncertainties and of small frequency corrections, and we show that our frequencies represent an improvement in accuracy and coverage over previous measurements. Our frequencies agree at the 2 micro Hz level with Mount Wilson frequencies determined for l less than or equal to 600 from full-disk images, and we find systematic offsets of 10-20 micro Hz with respect to frequencies measured from Big Bear and La Palma observations. We give evidence that these latter offsets are indicative of spatial scaling uncertainties associated with the analysis of partial-disk images. In comparison with theory, our p-mode frequencies agree within 10 micro Hz of frequencies predicted by the Los Alamos model but are as much as 100 micro Hz smaller than frequencies predicted by the Denmark and Yale models at degrees near 1000. We also find systematic differences between our n = 0 frequencies and the frequencies closely agreed upon by all three models.

Modeling of Soft Poroelastic Tissue in Time-Harmonic MR Elastography

PubMed Central

Perriñez, Phillip R.; Kennedy, Francis E.; Van Houten, Elijah E. W.; Weaver, John B.; Paulsen, Keith D.

2010-01-01

Elastography is an emerging imaging technique that focuses on assessing the resistance to deformation of soft biological tissues in vivo. Magnetic resonance elastography (MRE) uses measured displacement fields resulting from low-amplitude, low-frequency (10 Hz–1 kHz) time-harmonic vibration to recover images of the elastic property distribution of tissues including breast, liver, muscle, prostate, and brain. While many soft tissues display complex time-dependent behavior not described by linear elasticity, the models most commonly employed in MRE parameter reconstructions are based on elastic assumptions. Further, elasticity models fail to include the interstitial fluid phase present in vivo. Alternative continuum models, such as consolidation theory, are able to represent tissue and other materials comprising two distinct phases, generally consisting of a porous elastic solid and penetrating fluid. MRE reconstructions of simulated elastic and poroelastic phantoms were performed to investigate the limitations of current-elasticity-based methods in producing accurate elastic parameter estimates in poroelastic media. The results indicate that linearly elastic reconstructions of fluid-saturated porous media at amplitudes and frequencies relevant to steady-state MRE can yield misleading effective property distributions resulting from the complex interaction between their solid and fluid phases. PMID:19272864

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chae, Jongchul; Litvinenko, Yuri E.

The vertical propagation of nonlinear acoustic waves in an isothermal atmosphere is considered. A new analytical solution that describes a finite-amplitude wave of an arbitrary wavelength is obtained. Although the short- and long-wavelength limits were previously considered separately, the new solution describes both limiting cases within a common framework and provides a straightforward way of interpolating between the two limits. Physical features of the nonlinear waves in the chromosphere are described, including the dispersive nature of low-frequency waves, the steepening of the wave profile, and the influence of the gravitational field on wavefront breaking and shock formation. The analytical resultsmore » suggest that observations of three-minute oscillations in the solar chromosphere may reveal the basic nonlinear effect of oscillations with combination frequencies, superposed on the normal oscillations of the system. Explicit expressions for a second-harmonic signal and the ratio of its amplitude to the fundamental harmonic amplitude are derived. Observational evidence of the second harmonic, obtained with the Fast Imaging Solar Spectrograph, installed at the 1.6 m New Solar Telescope of the Big Bear Observatory, is presented. The presented data are based on the time variations of velocity determined from the Na i D{sub 2} and H α lines.« less

A Novel Multimode Waveguide Coupler for Accurate Power Measurement of Traveling Wave Tube Harmonic Frequencies

NASA Technical Reports Server (NTRS)

Wintucky, Edwin G.; Simons, Rainee N.

2014-01-01

This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler fabricated from two dissimilar waveguides is capable of isolating the power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT). In addition to accurate power measurements at harmonic frequencies, a potential application of the MDC is in the design of a beacon source for atmospheric propagation studies at millimeter-wave frequencies.

A masking level difference due to harmonicity.

PubMed

Treurniet, W C; Boucher, D R

2001-01-01

The role of harmonicity in masking was studied by comparing the effect of harmonic and inharmonic maskers on the masked thresholds of noise probes using a three-alternative, forced-choice method. Harmonic maskers were created by selecting sets of partials from a harmonic series with an 88-Hz fundamental and 45 consecutive partials. Inharmonic maskers differed in that the partial frequencies were perturbed to nearby values that were not integer multiples of the fundamental frequency. Average simultaneous-masked thresholds were as much as 10 dB lower with the harmonic masker than with the inharmonic masker, and this difference was unaffected by masker level. It was reduced or eliminated when the harmonic partials were separated by more than 176 Hz, suggesting that the effect is related to the extent to which the harmonics are resolved by auditory filters. The threshold difference was not observed in a forward-masking experiment. Finally, an across-channel mechanism was implicated when the threshold difference was found between a harmonic masker flanked by harmonic bands and a harmonic masker flanked by inharmonic bands. A model developed to explain the observed difference recognizes that an auditory filter output envelope is modulated when the filter passes two or more sinusoids, and that the modulation rate depends on the differences among the input frequencies. For a harmonic masker, the frequency differences of adjacent partials are identical, and all auditory filters have the same dominant modulation rate. For an inharmonic masker, however, the frequency differences are not constant and the envelope modulation rate varies across filters. The model proposes that a lower variability facilitates detection of a probe-induced change in the variability, thus accounting for the masked threshold difference. The model was supported by significantly improved predictions of observed thresholds when the predictor variables included envelope modulation rate variance measured using simulated auditory filters.

Power system frequency estimation based on an orthogonal decomposition method

NASA Astrophysics Data System (ADS)

Lee, Chih-Hung; Tsai, Men-Shen

2018-06-01

In recent years, several frequency estimation techniques have been proposed by which to estimate the frequency variations in power systems. In order to properly identify power quality issues under asynchronously-sampled signals that are contaminated with noise, flicker, and harmonic and inter-harmonic components, a good frequency estimator that is able to estimate the frequency as well as the rate of frequency changes precisely is needed. However, accurately estimating the fundamental frequency becomes a very difficult task without a priori information about the sampling frequency. In this paper, a better frequency evaluation scheme for power systems is proposed. This method employs a reconstruction technique in combination with orthogonal filters, which may maintain the required frequency characteristics of the orthogonal filters and improve the overall efficiency of power system monitoring through two-stage sliding discrete Fourier transforms. The results showed that this method can accurately estimate the power system frequency under different conditions, including asynchronously sampled signals contaminated by noise, flicker, and harmonic and inter-harmonic components. The proposed approach also provides high computational efficiency.

Centroid stabilization in alignment of FOA corner cube: designing of a matched filter

NASA Astrophysics Data System (ADS)

Awwal, Abdul; Wilhelmsen, Karl; Roberts, Randy; Leach, Richard; Miller Kamm, Victoria; Ngo, Tony; Lowe-Webb, Roger

2015-02-01

The current automation of image-based alignment of NIF high energy laser beams is providing the capability of executing multiple target shots per day. An important aspect of performing multiple shots in a day is to reduce additional time spent aligning specific beams due to perturbations in those beam images. One such alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retro-reflecting corner cubes to represent the beam center. The FOA houses the frequency conversion crystals for third harmonic generation as the beams enters the target chamber. Beam-to-beam variations and systematic beam changes over time in the FOA corner-cube images can lead to a reduction in accuracy as well as increased convergence durations for the template based centroid detector. This work presents a systematic approach of maintaining FOA corner cube centroid templates so that stable position estimation is applied thereby leading to fast convergence of alignment control loops. In the matched filtering approach, a template is designed based on most recent images taken in the last 60 days. The results show that new filter reduces the divergence of the position estimation of FOA images.

Optimization of contrast resolution by genetic algorithm in ultrasound tissue harmonic imaging.

PubMed

Ménigot, Sébastien; Girault, Jean-Marc

2016-09-01

The development of ultrasound imaging techniques such as pulse inversion has improved tissue harmonic imaging. Nevertheless, no recommendation has been made to date for the design of the waveform transmitted through the medium being explored. Our aim was therefore to find automatically the optimal "imaging" wave which maximized the contrast resolution without a priori information. To overcome assumption regarding the waveform, a genetic algorithm investigated the medium thanks to the transmission of stochastic "explorer" waves. Moreover, these stochastic signals could be constrained by the type of generator available (bipolar or arbitrary). To implement it, we changed the current pulse inversion imaging system by including feedback. Thus the method optimized the contrast resolution by adaptively selecting the samples of the excitation. In simulation, we benchmarked the contrast effectiveness of the best found transmitted stochastic commands and the usual fixed-frequency command. The optimization method converged quickly after around 300 iterations in the same optimal area. These results were confirmed experimentally. In the experimental case, the contrast resolution measured on a radiofrequency line could be improved by 6% with a bipolar generator and it could still increase by 15% with an arbitrary waveform generator. Copyright © 2016 Elsevier B.V. All rights reserved.

Circulating Current Suppressing Control’s Impact on Arm Inductance Selection for Modular Multilevel Converter

DOE PAGES

Li, Yalong; Jones, Edward A.; Wang, Fred

2016-10-13

Arm inductor in a modular multilevel converter (MMC) is used to limit the circulating current and dc short circuit fault current. The circulating current in MMC is dominated by second-order harmonic, which can be largely reduced with circulating current suppressing control. By analyzing the mechanism of the circulating current suppressing control, it is found that the circulating current at switching frequency becomes the main harmonic when suppression control is implemented. Unlike the second-order harmonic that circulates only within the three phases, switching frequency harmonic also flows through the dc side and may further cause high-frequency dc voltage harmonic. This articlemore » develops the theoretical relationship between the arm inductance and switching frequency circulating current, which can be used to guide the arm inductance selection. The experimental results with a downscaled MMC prototype verify the existence of the switching frequency circulating current and its relationship with arm inductance.« less

Quasi-Static Magnetic Field Shielding Using Longitudinal Mu-Near-Zero Metamaterials.

PubMed

Lipworth, Guy; Ensworth, Joshua; Seetharam, Kushal; Lee, Jae Seung; Schmalenberg, Paul; Nomura, Tsuyoshi; Reynolds, Matthew S; Smith, David R; Urzhumov, Yaroslav

2015-08-03

The control of quasi-static magnetic fields is of considerable interest in applications including the reduction of electromagnetic interference (EMI), wireless power transfer (WPT), and magnetic resonance imaging (MRI). The shielding of static or quasi-static magnetic fields is typically accomplished through the use of inherently magnetic materials with large magnetic permeability, such as ferrites, used sometimes in combination with metallic sheets and/or active field cancellation. Ferrite materials, however, can be expensive, heavy and brittle. Inspired by recent demonstrations of epsilon-, mu- and index-near-zero metamaterials, here we show how a longitudinal mu-near-zero (LMNZ) layer can serve as a strong frequency-selective reflector of magnetic fields when operating in the near-field region of dipole-like sources. Experimental measurements with a fabricated LMNZ sheet constructed from an artificial magnetic conductor - formed from non-magnetic, conducting, metamaterial elements - confirm that the artificial structure provides significantly improved shielding as compared with a commercially available ferrite of the same size. Furthermore, we design a structure to shield simultaneously at the fundamental and first harmonic frequencies. Such frequency-selective behavior can be potentially useful for shielding electromagnetic sources that may also generate higher order harmonics, while leaving the transmission of other frequencies unaffected.

Hadamard-Encoded Multipulses for Contrast-Enhanced Ultrasound Imaging.

PubMed

Gong, Ping; Song, Pengfei; Chen, Shigao

2017-11-01

The development of contrast-enhanced ultrasound (CEUS) imaging offers great opportunities for new ultrasound clinical applications such as myocardial perfusion imaging and abdominal lesion characterization. In CEUS imaging, the contrast agents (i.e., microbubbles) are utilized to improve the contrast between blood and tissue based on their high nonlinearity under low ultrasound pressure. In this paper, we propose a new CEUS pulse sequence by combining Hadamard-encoded multipulses (HEM) with fundamental frequency bandpass filter (i.e., filter centered on transmit frequency). HEM consecutively emits multipulses encoded by a second-order Hadamard matrix in each of the two transmission events (i.e., pulse-echo events), as opposed to conventional CEUS methods which emit individual pulses in two separate transmission events (i.e., pulse inversion (PI), amplitude modulation (AM), and PIAM). In HEM imaging, the microbubble responses can be improved by the longer transmit pulse, and the tissue harmonics can be suppressed by the fundamental frequency filter, leading to significantly improved contrast-to-tissue ratio (CTR) and signal-to-noise ratio (SNR). In addition, the fast polarity change between consecutive coded pulse emissions excites strong nonlinear microbubble echoes, further enhancing the CEUS image quality. The spatial resolution of HEM image is compromised as compared to other microbubble imaging methods due to the longer transmit pulses and the lower imaging frequency (i.e., fundamental frequency). However, the resolution loss was shown to be negligible and could be offset by the significantly enhanced CTR, SNR, and penetration depth. These properties of HEM can potentially facilitate robust CEUS imaging for many clinical applications, especially for deep abdominal organs and heart.

Perception of echo delay is disrupted by small temporal misalignment of echo harmonics in bat sonar

PubMed Central

Bates, Mary E.; Simmons, James A.

2011-01-01

Echolocating big brown bats emit ultrasonic frequency-modulated (FM) biosonar sounds containing two prominent downward-sweeping harmonics (FM1 and FM2) and perceive target distance from echo delay. In naturally occurring echoes, FM1 and FM2 are delayed by the same amount. Even though echoes from targets located off-axis or far away are lowpass filtered, which weakens FM2 relative to FM1, their delays remain the same. We show here that misalignment of FM2 with FM1 by only 2.6 μs is sufficient to significantly disrupt acuity, which then persists for larger misalignments up to 300 μs. However, when FM2 is eliminated entirely rather than just misaligned, acuity is effectively restored. For naturally occurring, lowpass-filtered echoes, neuronal responses to weakened FM2 are retarded relative to FM1 because of amplitude-latency trading, which misaligns the harmonics in the bat's internal auditory representations. Electronically delaying FM2 relative to FM1 mimics the retarded neuronal responses for FM2 relative to FM1 caused by amplitude-latency trading. Echoes with either electronically or physiologically misaligned harmonics are not perceived as having a clearly defined delay. This virtual collapse of delay acuity may suppress interference from off-axis or distant clutter through degradation of delay images for clutter in contrast to sharp images for nearer, frontal targets. PMID:21228198

Three-dimensional high-resolution second-harmonic generation imaging of endogenous structural proteins in biological tissues.

PubMed Central

Campagnola, Paul J; Millard, Andrew C; Terasaki, Mark; Hoppe, Pamela E; Malone, Christian J; Mohler, William A

2002-01-01

We find that several key endogenous protein structures give rise to intense second-harmonic generation (SHG)-nonabsorptive frequency doubling of an excitation laser line. Second-harmonic imaging microscopy (SHIM) on a laser-scanning system proves, therefore, to be a powerful and unique tool for high-resolution, high-contrast, three-dimensional studies of live cell and tissue architecture. Unlike fluorescence, SHG suffers no inherent photobleaching or toxicity and does not require exogenous labels. Unlike polarization microscopy, SHIM provides intrinsic confocality and deep sectioning in complex tissues. In this study, we demonstrate the clarity of SHIM optical sectioning within unfixed, unstained thick specimens. SHIM and two-photon excited fluorescence (TPEF) were combined in a dual-mode nonlinear microscopy to elucidate the molecular sources of SHG in live cells and tissues. SHG arose not only from coiled-coil complexes within connective tissues and muscle thick filaments, but also from microtubule arrays within interphase and mitotic cells. Both polarization dependence and a local symmetry cancellation effect of SHG allowed the signal from species generating the second harmonic to be decoded, by ratiometric correlation with TPEF, to yield information on local structure below optical resolution. The physical origin of SHG within these tissues is addressed and is attributed to the laser interaction with dipolar protein structures that is enhanced by the intrinsic chirality of the protein helices. PMID:11751336

Perception of echo delay is disrupted by small temporal misalignment of echo harmonics in bat sonar.

PubMed

Bates, Mary E; Simmons, James A

2011-02-01

Echolocating big brown bats emit ultrasonic frequency-modulated (FM) biosonar sounds containing two prominent downward-sweeping harmonics (FM1 and FM2) and perceive target distance from echo delay. In naturally occurring echoes, FM1 and FM2 are delayed by the same amount. Even though echoes from targets located off-axis or far away are lowpass filtered, which weakens FM2 relative to FM1, their delays remain the same. We show here that misalignment of FM2 with FM1 by only 2.6 μs is sufficient to significantly disrupt acuity, which then persists for larger misalignments up to 300 μs. However, when FM2 is eliminated entirely rather than just misaligned, acuity is effectively restored. For naturally occurring, lowpass-filtered echoes, neuronal responses to weakened FM2 are retarded relative to FM1 because of amplitude-latency trading, which misaligns the harmonics in the bat's internal auditory representations. Electronically delaying FM2 relative to FM1 mimics the retarded neuronal responses for FM2 relative to FM1 caused by amplitude-latency trading. Echoes with either electronically or physiologically misaligned harmonics are not perceived as having a clearly defined delay. This virtual collapse of delay acuity may suppress interference from off-axis or distant clutter through degradation of delay images for clutter in contrast to sharp images for nearer, frontal targets.

Extraction of small boat harmonic signatures from passive sonar.

PubMed

Ogden, George L; Zurk, Lisa M; Jones, Mark E; Peterson, Mary E

2011-06-01

This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. Noise radiated from a small boats consists of broadband noise and harmonically related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the harmonic structure of noise radiated from small boats is developed. The Harmonic Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the harmonic tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the harmonic tonals to generate a harmonic signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures. © 2011 Acoustical Society of America

A generalized strategy for designing (19)F/(1)H dual-frequency MRI coil for small animal imaging at 4.7 Tesla.

PubMed

Hu, Lingzhi; Hockett, Frank D; Chen, Junjie; Zhang, Lei; Caruthers, Shelton D; Lanza, Gregory M; Wickline, Samuel A

2011-07-01

To propose and test a universal strategy for building (19) F/(1) H dual-frequency RF coil that permits multiple coil geometries. The feasibility to design (19) F/(1) H dual-frequency RF coil based on coupled resonator model was investigated. A series capacitive matching network enables robust impedance matching for both harmonic oscillating modes of the coupled resonator. Two typical designs of (19) F/(1) H volume coils (birdcage and saddle) at 4.7T were implemented and evaluated with electrical bench test and in vivo (19) F/(1) H dual-nuclei imaging. For various combinations of internal resistances of the sample coil and secondary resonator, numerical solutions for the tunable capacitors to optimize impedance matching were obtained using a root-seeking program. Identical and homogeneous B1 field distribution at (19) F and (1) H frequencies were observed in bench test and phantom image. Finally, in vivo mouse imaging confirmed the sensitivity and homogeneity of the (19) F/(1) H dual-frequency coil design. A generalized strategy for designing (19) F/(1) H dual-frequency coils based on the coupled resonator approach was developed and validated. A unique feature of this design is that it preserves the B1 field homogeneity of the RF coil at both resonant frequencies. Thus it minimizes the susceptibility effect on image co-registration. Copyright © 2011 Wiley-Liss, Inc.

The harmonic frequencies of benzene

NASA Astrophysics Data System (ADS)

Handy, Nicholas C.; Maslen, Paul E.; Amos, Roger D.; Andrews, Jamie S.; Murray, Christopher W.; Laming, Gregory J.

1992-09-01

We report calculations for the harmonic frequencies of C 6H 6 and C 6D 6. Our most sophisticated quantum chemistry values are obtained with the MP2 method and a TZ2P+f basis set (288 basis functions), which are the largest such calculations reported on benzene to date. Using the SCF density, we also calculate the frequencies using the exchange and correlation expressions of density functional theory. We compare our calculated harmonic frequencies with those deduced from experiment by Goodman, Ozkabak and Thakur. The density functional frequencies appear to be more reliable predictions than the MP2 frequencies and they are obtained at significantly less cost.

Statistical Properties of Real-Time Amplitude Estimate of Harmonics Affected by Frequency Instability

NASA Astrophysics Data System (ADS)

Bellan, Diego; Pignari, Sergio A.

2016-07-01

This work deals with the statistical characterization of real-time digital measurement of the amplitude of harmonics affected by frequency instability. In fact, in modern power systems both the presence of harmonics and frequency instability are well-known and widespread phenomena mainly due to nonlinear loads and distributed generation, respectively. As a result, real-time monitoring of voltage/current frequency spectra is of paramount importance as far as power quality issues are addressed. Within this framework, a key point is that in many cases real-time continuous monitoring prevents the application of sophisticated algorithms to extract all the information from the digitized waveforms because of the required computational burden. In those cases only simple evaluations such as peak search of discrete Fourier transform are implemented. It is well known, however, that a slight change in waveform frequency results in lack of sampling synchronism and uncertainty in amplitude estimate. Of course the impact of this phenomenon increases with the order of the harmonic to be measured. In this paper an approximate analytical approach is proposed in order to describe the statistical properties of the measured magnitude of harmonics affected by frequency instability. By providing a simplified description of the frequency behavior of the windows used against spectral leakage, analytical expressions for mean value, variance, cumulative distribution function, and probability density function of the measured harmonics magnitude are derived in closed form as functions of waveform frequency treated as a random variable.

Nonlinear oscillation and interfacial stability of an encapsulated microbubble under dual-frequency ultrasound

NASA Astrophysics Data System (ADS)

Calvisi, Michael; Liu, Yunqiao; Wang, Qianxi

2016-11-01

Encapsulated microbubbles (EMBs) are widely used in medical ultrasound imaging as contrast-enhanced agents. However, the potential damaging effects of violent, collapsing EMBs to cells and tissues in clinical practice have remained a concern. Dual-frequency ultrasound is a promising technique for improving the efficacy and safety of sonography. The EMB system modeled consists of the external liquid, membrane, and internal gases. The microbubble dynamics are simulated using a simple nonlinear interactive theory, considering the compressibility of the internal gas, viscosity of the liquid flow, and elasticity of the membrane. The radial oscillation and interfacial stability of an EMB under single and dual-frequency excitations are compared. The simulation results show that the dual-frequency technique produces larger backscatter pressure at higher harmonics of the primary driving frequency. This enriched acoustic spectrum can enhance blood-tissue contrast and improve sonographic image quality. The results further show that the acoustic pressure threshold associated with the onset of shape instability is greater for dual-frequency driving. This suggests that the dual-frequency technique stabilizes the EMB, thereby improving the efficacy and safety of contrast-enhanced agents.

Artificial Ionization and UHF Radar Response Associated with HF Frequencies near Electron Gyro-Harmonics (Invited)

NASA Astrophysics Data System (ADS)

Watkins, B. J.; Fallen, C. T.; Secan, J. A.

2013-12-01

We present new results from O-mode ionospheric heating experiments at the HAARP facility in Alaska to demonstrate that the magnitude of artificial ionization production is critically dependent on the choice of HF frequency near gyro-harmonics. For O-mode heating in the lower F-region ionosphere, typically about 200 km altitude, artificial ionization enhancements are observed in the lower ionosphere (about 150 - 220 km) and also in the topside ionosphere above about 500 km. Lower ionosphere density enhancements are inferred from HF-enhanced ion and plasma-line signals observed with UHF radar. Upper ionospheric density enhancements have been observed with TEC (total electron content) experiments by monitoring satellite radio beacons where signal paths traverse the HF-modified ionosphere. Both density enhancements and corresponding upward plasma fluxes have also been observed in the upper ionosphere via in-situ satellite observations. The data presented focus mainly on observations near the third and fourth gyro-harmonics. The specific values of the height-dependent gyro-harmonics have been computed from a magnetic model of the field line through the HF heated volume. Experiments with several closely spaced HF frequencies around the gyro-harmonic frequency region show that the magnitude of the lower-ionosphere artificial ionization production maximizes for HF frequencies about 1.0 - 1.5 MHz above the gyro-harmonic frequency. The response is progressively larger as the HF frequency is increased in the frequency region near the gyro-harmonics. For HF frequencies that are initially greater than the gyro-harmonic value the UHF radar scattering cross-section is relatively small, and non-existent or very weak signals are observed; as the signal returns drop in altitude due to density enhancements the HF interaction region passes through lower altitudes where the HF frequency is less than the gyro-harmonic value, for these conditions the radar scattering cross-section is significantly increased and strong signals persist while the high-power HF is present . Simultaneous observations of topside TEC measurements and lower-ionosphere UHF radar observations suggest there is an optimum altitude region to heat the lower F-region in order to produce topside ionosphere density enhancements. The observations are dependent on HF power levels and we show several examples where heating results are only observed for the high-power levels attainable with the HAARP facility.

Parametric detection and measurement of perfusion defects in attenuated contrast echocardiographic images.

PubMed

Yoshifuku, Shiro; Chen, Shigao; McMahon, Eileen; Korinek, Josef; Yoshikawa, Akiko; Ochiai, Izuru; Sengupta, Partho P; Belohlavek, Marek

2007-06-01

Attenuation of radio frequency (RF) signals limits the use of contrast echocardiography. The harmonic-to-fundamental ratio (HFR) of the RF signals compensates for attenuation. We tested whether HFR analysis measures the left ventricular nonperfused area under simulated experimental attenuation. Radio frequency image data from short axis systolic projections were obtained from 11 open-chest dogs with left anterior descending or left circumflex coronary artery occlusion followed by left atrial bolus injection of a perflutren microbubble contrast agent. Clinical attenuation was simulated by calibrated silicone pads interposed between the epicardial surface and the transducer to induce mild (7-dB) and severe (14-dB) reduction of the backscattered RF signals. Harmonic-to-fundamental ratio values were calculated for each image pixel for 0-, 7-, and 14-dB attenuation conditions and reproducibly showed a "perfused area" and a "nonperfused area." A reference nonperfused area was obtained by manual delineation in high-quality contrast scans. Correlations of the HFR-detected and manually outlined perfusion defect areas were R = 0.92 for 0 dB, R = 0.94 for 7 dB, and R = 0.90 for 14 dB; the mean difference was less than 0.36 cm(2) (negligible) in all 3 attenuation settings. Conclusions. Attenuation compensation by our HFR method allows precise measurement of myocardial perfusion defect areas in contrast scans with simulated high level of attenuation.

Effect of absorption on nonlinear propagation of short ultrasound pulses generated by rectangular transducers

NASA Astrophysics Data System (ADS)

Khokhlova, Vera A.; Ponomaryov, Anatoly E.; Averkiou, Michalakis A.; Crum, Lawrence A.

2002-11-01

A numerical solution of the KZK-type parabolic nonlinear evolution equation is presented for finite-amplitude sound beams radiated by rectangular sources. The initial acoustic waveform is a short tone burst, similar to those used in diagnostic ultrasound. The generation of higher harmonic components and their spatial structure are investigated for media similar to tissue with various frequency dependent absorption properties. Nonlinear propagation in a thermoviscous fluid with a quadratic frequency law of absorption is compared to that in tissue with a nearly linear frequency law of absorption. The algorithm is based on that originally developed by Lee and Hamilton [J. Acoust. Soc. Am. 97, 906-917 (1995)] to model circular sources. The algorithm is generalized for two-dimensional sources without axial symmetry. The diffraction integral is adapted in the time-domain for two dimensions with the implicit backward finite difference (IBFD) scheme in the nearfield and with the alternate direction implicit (ADI) method at longer distances. Arbitrary frequency dependence of absorption is included in this model and solved in the frequency-domain using the FFT technique. The results of simulation may be used to better understand the nonlinear beam structure for tissue harmonic imaging in modern medical diagnostic scanners. [Work supported by CRDF and RFBR.

Unlocking higher harmonics in atomic force microscopy with gentle interactions.

PubMed

Santos, Sergio; Barcons, Victor; Font, Josep; Verdaguer, Albert

2014-01-01

In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.

Living in a digital world: features and applications of FPGA in photon detection

NASA Astrophysics Data System (ADS)

Arnesano, Cosimo

Optical spectroscopy and imaging outcomes rely upon many factors; one of the most critical is the photon acquisition and processing method employed. For some types of measurements it may be crucial to acquire every single photon quickly with temporal resolution, but in other cases it is important to acquire as many photons as possible, regardless of the time information about each of them. Fluorescence Lifetime Imaging Microscopy belongs to the first case, where the information of the time of arrival of every single photon in every single pixel is fundamental in obtaining the desired information. Spectral tissue imaging belongs to the second case, where high photon density is needed in order to calculate the optical parameters necessary to build the spectral image. In both cases, the current instrumentation suffers from limitations in terms of acquisition time, duty cycle, cost, and radio-frequency interference and emission. We developed the Digital Frequency-Domain approach for photon acquisition and processing purpose using new digital technology. This approach is based on the use of photon detectors in photon counting mode, and the digital heterodyning method to acquire data which is analyzed in the frequency domain to provide the information of the time of arrival of the photons . In conjunction with the use of pulsed laser sources, this method allows the determination of the time of arrival of the photons using the harmonic content of the frequency domain analysis. The parallel digital FD design is a powerful approach that others the possibility to implement a variety of different applications in fluorescence spectroscopy and microscopy. It can be applied to fluorometry, Fluorescence Lifetime Imaging (FLIM), and Fluorescence Correlation Spectroscopy (FCS), as well as multi frequency and multi wavelength tissue imaging in compact portable medical devices. It dramatically reduces the acquisition time from the several minutes scale to the seconds scale, performs signal processing in a digital fashion avoiding RF emission and it is extremely inexpensive. This development is the result of a systematic study carried on a previous design known as the FLIMBox developed as part of a thesis of another graduate student. The extensive work done in maximizing the performance of the original FLIMBox led us to develop a new hardware solution with exciting and promising results and potential that were not possible in the previous hardware realization, where the signal harmonic content was limited by the FPGA technology. The new design permits acquisition of a much larger harmonic content of the sample response when it is excited with a pulsed light source in one single measurement using the digital mixing principle that was developed in the original design. Furthermore, we used the parallel digital FD principle to perform tissue imaging through Diffuse Optical Spectroscopy (DOS) measurements. We integrated the FLIMBox in a new system that uses a supercontinuum white laser with high brightness as a single light source and photomultipliers with large detection area, both allowing a high penetration depth with extremely low power at the sample. The parallel acquisition, achieved by using the FlimBox, decreases the time required for standard serial systems that scan through all modulation frequencies. Furthermore, the all-digital acquisition avoids analog noise, removes the analog mixer of the conventional frequency domain approach, and it does not generate radio-frequencies, normally present in current analog systems. We are able to obtain a very sensitive acquisition due to the high signal to noise ratio (S/N). The successful results obtained by utilizing digital technology in photon acquisition and processing, prompted us to extend the use of FPGA to other applications, such as phosphorescence detection. Using the FPGA concept we proposed possible solutions to outstanding problems with the current technology. In this thesis I discuss new possible scenarios where new FPGA chips are applied to spectral tissue imaging.

Performance assessment of HIFU lesion detection by harmonic motion imaging for focused ultrasound (HMIFU): a 3-D finite-element-based framework with experimental validation.

PubMed

Hou, Gary Y; Luo, Jianwen; Marquet, Fabrice; Maleke, Caroline; Vappou, Jonathan; Konofagou, Elisa E

2011-12-01

Harmonic motion imaging for focused ultrasound (HMIFU) is a novel high-intensity focused ultrasound (HIFU) therapy monitoring method with feasibilities demonstrated in vitro, ex vivo and in vivo. Its principle is based on amplitude-modulated (AM) - harmonic motion imaging (HMI), an oscillatory radiation force used for imaging the tissue mechanical response during thermal ablation. In this study, a theoretical framework of HMIFU is presented, comprising a customized nonlinear wave propagation model, a finite-element (FE) analysis module and an image-formation model. The objective of this study is to develop such a framework to (1) assess the fundamental performance of HMIFU in detecting HIFU lesions based on the change in tissue apparent elasticity, i.e., the increasing Young's modulus, and the HIFU lesion size with respect to the HIFU exposure time and (2) validate the simulation findings ex vivo. The same HMI and HMIFU parameters as in the experimental studies were used, i.e., 4.5-MHz HIFU frequency and 25 Hz AM frequency. For a lesion-to-background Young's modulus ratio of 3, 6 and 9, the FE and estimated HMI displacement ratios were equal to 1.83, 3.69 and 5.39 and 1.65, 3.19 and 4.59, respectively. In experiments, the HMI displacement followed a similar increasing trend of 1.19, 1.28 and 1.78 at 10-s, 20-s and 30-s HIFU exposure, respectively. In addition, moderate agreement in lesion size growth was found in both simulations (16.2, 73.1 and 334.7 mm(2)) and experiments (26.2, 94.2 and 206.2 mm(2)). Therefore, the feasibility of HMIFU for HIFU lesion detection based on the underlying tissue elasticity changes was verified through the developed theoretical framework, i.e., validation of the fundamental performance of the HMIFU system for lesion detection, localization and quantification, was demonstrated both theoretically and ex vivo. Copyright © 2011 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Real-time Monitoring of High Intensity Focused Ultrasound (HIFU) Ablation of In Vitro Canine Livers Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU).

PubMed

Grondin, Julien; Payen, Thomas; Wang, Shutao; Konofagou, Elisa E

2015-11-03

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a technique that can perform and monitor high-intensity focused ultrasound (HIFU) ablation. An oscillatory motion is generated at the focus of a 93-element and 4.5 MHz center frequency HIFU transducer by applying a 25 Hz amplitude-modulated signal using a function generator. A 64-element and 2.5 MHz imaging transducer with 68kPa peak pressure is confocally placed at the center of the HIFU transducer to acquire the radio-frequency (RF) channel data. In this protocol, real-time monitoring of thermal ablation using HIFU with an acoustic power of 7 W on canine livers in vitro is described. HIFU treatment is applied on the tissue during 2 min and the ablated region is imaged in real-time using diverging or plane wave imaging up to 1,000 frames/second. The matrix of RF channel data is multiplied by a sparse matrix for image reconstruction. The reconstructed field of view is of 90° for diverging wave and 20 mm for plane wave imaging and the data are sampled at 80 MHz. The reconstruction is performed on a Graphical Processing Unit (GPU) in order to image in real-time at a 4.5 display frame rate. 1-D normalized cross-correlation of the reconstructed RF data is used to estimate axial displacements in the focal region. The magnitude of the peak-to-peak displacement at the focal depth decreases during the thermal ablation which denotes stiffening of the tissue due to the formation of a lesion. The displacement signal-to-noise ratio (SNRd) at the focal area for plane wave was 1.4 times higher than for diverging wave showing that plane wave imaging appears to produce better displacement maps quality for HMIFU than diverging wave imaging.

Real-time Monitoring of High Intensity Focused Ultrasound (HIFU) Ablation of In Vitro Canine Livers Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)

PubMed Central

Grondin, Julien; Payen, Thomas; Wang, Shutao; Konofagou, Elisa E.

2015-01-01

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a technique that can perform and monitor high-intensity focused ultrasound (HIFU) ablation. An oscillatory motion is generated at the focus of a 93-element and 4.5 MHz center frequency HIFU transducer by applying a 25 Hz amplitude-modulated signal using a function generator. A 64-element and 2.5 MHz imaging transducer with 68kPa peak pressure is confocally placed at the center of the HIFU transducer to acquire the radio-frequency (RF) channel data. In this protocol, real-time monitoring of thermal ablation using HIFU with an acoustic power of 7 W on canine livers in vitro is described. HIFU treatment is applied on the tissue during 2 min and the ablated region is imaged in real-time using diverging or plane wave imaging up to 1,000 frames/second. The matrix of RF channel data is multiplied by a sparse matrix for image reconstruction. The reconstructed field of view is of 90° for diverging wave and 20 mm for plane wave imaging and the data are sampled at 80 MHz. The reconstruction is performed on a Graphical Processing Unit (GPU) in order to image in real-time at a 4.5 display frame rate. 1-D normalized cross-correlation of the reconstructed RF data is used to estimate axial displacements in the focal region. The magnitude of the peak-to-peak displacement at the focal depth decreases during the thermal ablation which denotes stiffening of the tissue due to the formation of a lesion. The displacement signal-to-noise ratio (SNRd) at the focal area for plane wave was 1.4 times higher than for diverging wave showing that plane wave imaging appears to produce better displacement maps quality for HMIFU than diverging wave imaging. PMID:26556647

High order harmonics anomaly of jet screech

NASA Astrophysics Data System (ADS)

Chen, Zhe; Wu, Jiu Hui; Ren, A.-Dan; Chen, Xin

2018-05-01

Imperfectly expanded supersonic jets under strong screech could generate both fundamental screech tones and multiple tones at the harmonics of the fundamental frequency. The paper compares the fundamental frequency of jets from both AR = 3 (Aspect Ratio) and AR = 4 rectangular nozzles, and conducts analysis of harmonics on Sound Pressure Level (SPL) spectrums of jet noise. The research suggests that the fundamental frequency of the first two- or three-order harmonics increases when the Nozzle Pressure Ratio (NPR) decreases, whereas the highest order harmonic decreases when the NPR decreases. Besides, the paper also observes the differences between the highest order harmonics and other harmonics that have never been reported before. Further analysis on flow field schlieren of AR = 3 nozzle indicates that the highest order harmonic is the outcome of interaction between second shock-cell and nonlinear instable wave. The revolution of these high order harmonics can provide guidance for the prevention of small-scale structure fatigue damage. Moreover, the distribution test of the noises is also carried out to verify the high order harmonics anomaly, and indicate that the jet noise spreads mainly towards downstream while screech towards upstream. In addition, the broadband shock-associated noise spreads vertical to the jet flow and exhibits the feature of directivity.

Strongly gliding harmonic tremor during the 2009 eruption of Redoubt Volcano

USGS Publications Warehouse

Hotovec, Alicia J.; Prejean, Stephanie G.; Vidale, John E.; Gomberg, Joan S.

2013-01-01

During the 2009 eruption of Redoubt Volcano, Alaska, gliding harmonic tremor occurred prominently before six nearly consecutive explosions during the second half of the eruptive sequence. The fundamental frequency repeatedly glided upward from < 1 Hz to as high as 30 Hz in less than 10 min, followed by a relative seismic quiescence of 10 to 60 s immediately prior to explosion. High frequency (5 to 20 Hz) gliding returned during the extrusive phase, and lasted for 20 min to 3 h at a time. Although harmonic tremor is not uncommon at volcanoes, tremor at such high frequencies is a rare observation. These frequencies approach or exceed the plausible upper limits of many models that have been suggested for volcanic tremor. We also analyzed the behavior of a swarm of repeating earthquakes that immediately preceded the first instance of pre-explosion gliding harmonic tremor. We find that these earthquakes share several traits with upward gliding harmonic tremor, and favor the explanation that the gliding harmonic tremor at Redoubt Volcano is created by the superposition of increasingly frequent and regular, repeating stick–slip earthquakes through the Dirac comb effect.

The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field.

PubMed

Koushki, A M; Sadighi-Bonabi, R; Mohsen-Nia, M; Irani, E

2018-04-14

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N 2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a result, the spectral modulation is significantly decreased and an intense ultrashort pulse can be generated from the supercontinuum region of high harmonics. With such a scheme, the isolated ultrashort attosecond pulses can be generated in length, velocity, and acceleration gauges. Furthermore, these results are explained by using the classical and quantum time-frequency analyses.

The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field

NASA Astrophysics Data System (ADS)

Koushki, A. M.; Sadighi-Bonabi, R.; Mohsen-Nia, M.; Irani, E.

2018-04-01

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a result, the spectral modulation is significantly decreased and an intense ultrashort pulse can be generated from the supercontinuum region of high harmonics. With such a scheme, the isolated ultrashort attosecond pulses can be generated in length, velocity, and acceleration gauges. Furthermore, these results are explained by using the classical and quantum time-frequency analyses.

The perception of complex tones by a false killer whale (Pseudorca crassidens).

PubMed

Yuen, Michelle M L; Nachtigall, Paul E; Breese, Marlee; Vlachos, Stephanie A

2007-03-01

Complex tonal whistles are frequently produced by some odontocete species. However, no experimental evidence exists regarding the detection of complex tones or the discrimination of harmonic frequencies by a marine mammal. The objectives of this investigation were to examine the ability of a false killer whale to discriminate pure tones from complex tones and to determine the minimum intensity level of a harmonic tone required for the whale to make the discrimination. The study was conducted with a go/no-go modified staircase procedure. The different stimuli were complex tones with a fundamental frequency of 5 kHz with one to five harmonic frequencies. The results from this complex tone discrimination task demonstrated: (1) that the false killer whale was able to discriminate a 5 kHz pure tone from a complex tone with up to five harmonics, and (2) that discrimination thresholds or minimum intensity levels exist for each harmonic combination measured. These results indicate that both frequency level and harmonic content may have contributed to the false killer whale's discrimination of complex tones.

Fully integrated reflection-mode photoacoustic, two-photon, and second harmonic generation microscopy in vivo

NASA Astrophysics Data System (ADS)

Song, Wei; Xu, Qiang; Zhang, Yang; Zhan, Yang; Zheng, Wei; Song, Liang

2016-08-01

The ability to obtain comprehensive structural and functional information from intact biological tissue in vivo is highly desirable for many important biomedical applications, including cancer and brain studies. Here, we developed a fully integrated multimodal microscopy that can provide photoacoustic (optical absorption), two-photon (fluorescence), and second harmonic generation (SHG) information from tissue in vivo, with intrinsically co-registered images. Moreover, using a delicately designed optical-acoustic coupling configuration, a high-frequency miniature ultrasonic transducer was integrated into a water-immersion optical objective, thus allowing all three imaging modalities to provide a high lateral resolution of ~290 nm with reflection-mode imaging capability, which is essential for studying intricate anatomy, such as that of the brain. Taking advantage of the complementary and comprehensive contrasts of the system, we demonstrated high-resolution imaging of various tissues in living mice, including microvasculature (by photoacoustics), epidermis cells, cortical neurons (by two-photon fluorescence), and extracellular collagen fibers (by SHG). The intrinsic image co-registration of the three modalities conveniently provided improved visualization and understanding of the tissue microarchitecture. The reported results suggest that, by revealing complementary tissue microstructures in vivo, this multimodal microscopy can potentially facilitate a broad range of biomedical studies, such as imaging of the tumor microenvironment and neurovascular coupling.

Bounce-harmonic Landau Damping of Plasma Waves

NASA Astrophysics Data System (ADS)

Anderegg, Francois

2015-11-01

We present measurement of plasma wave damping, spanning the temperature regimes of direct Landau damping, bounce-harmonic Landau damping, inter-species drag damping, and viscous damping. Direct Landau damping is dominant at high temperatures, but becomes negligible as v

Theoretical Study on the 1.185-THz Third Harmonic Gyrotron

NASA Astrophysics Data System (ADS)

Dumbrajs, O.; Idehara, T.

2018-02-01

We discuss how the existing University of Fukui (FIR UF) second harmonic double-beam gyrotron with the operating frequency 0.79 THz can be adopted for operation at the third harmonic. The new gyrotron will operate at the frequency 1.185 THz and will significantly increase the frequency of the dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR) spectrometer. This will allow one to study new bio-molecules.A special attention is payed to the mode competition between the operating {TE}_{3,11}+ mode at the third harmonic and the parasitic modes at the second and fundamental harmonics. The operating parameters of the modified gyrotron are U = 20 kV, α = 1.3, I = 0.35 A, and B = 14.60 T and the expected output power about 100W.

PWM Switching Frequency Effects on Eddy Current Sensors for Magnetically Suspended Flywheel Systems

NASA Technical Reports Server (NTRS)

Jansen, Ralph; Lebron, Ramon; Dever, Timothy P.; Birchenough, Arthur G.

2003-01-01

A flywheel magnetic bearing (MB) pulse width modulated power amplifier (PWM) configuration is selected to minimize noise generated by the PWMs in the flywheel position sensor system. Two types of noise are addressed: beat frequency noise caused by variations in PWM switching frequencies, and demodulation noise caused by demodulation of high order harmonics of the switching voltage into the MB control band. Beat frequency noise is eliminated by synchronizing the PWM switch frequencies, and demodulation noise is minimized by selection of a switching frequency which does not have harmonics at the carrier frequency of the sensor. The recommended MB PWM system has five synchronized PWMs switching at a non-integer harmonic of the sensor carrier.

Positional stability and radial dynamics of sonoluminescent bubbles under bi-harmonic driving: Effect of the high-frequency component and its relative phase.

PubMed

Rosselló, J M; Dellavale, D; Bonetto, F J

2016-07-01

The use of bi-frequency driving in sonoluminescence has proved to be an effective way to avoid the spatial instability (pseudo-orbits) developed by bubbles in systems with high viscous liquids like sulfuric or phosphoric acids. In this work, we present extensive experimental and numerical evidence in order to assess the effect of the high frequency component (PAc(HF)) of a bi-harmonic acoustic pressure field on the dynamic of sonoluminescent bubbles in an aqueous solution of sulfuric acid. The present study is mainly focused on the role of the harmonic frequency (Nf0) and the relative phase between the two frequency components (φb) of the acoustic field on the spatial, positional and diffusive stability of the bubbles. The results presented in this work were analyzed by means of three different approaches. First, we discussed some qualitative considerations about the changes observed in the radial dynamics, and the stability of similar bubbles under distinct bi-harmonic drivings. Later, we have investigated, through a series of numerical simulations, how the use of high frequency harmonic components of different order N, affects the positional stability of the SL bubbles. Furthermore, the influence of φb in their radius temporal evolution is systematically explored for harmonics ranging from the second to the fifteenth harmonic (N=2-15). Finally, a multivariate analysis based on the covariance method is performed to study the dependences among the parameters characterizing the SL bubble. Both experimental and numerical results indicate that the impact of PAc(HF) on the positional instability and the radial dynamics turns to be progressively negligible as the order of the high frequency harmonic component grows (i.e. N ≫ 1), however its effectiveness on the reduction of the spatial instability remains unaltered or even improved. Copyright © 2016 Elsevier B.V. All rights reserved.

SPECIAL ISSUE DEVOTED TO THE 80TH BIRTHDAY OF S.A. AKHMANOV: Selective generation of a higher harmonic in plasma

NASA Astrophysics Data System (ADS)

Kulagin, I. A.; Usmanov, T.

2009-07-01

It is shown for the first time that the use of autoionisation states for phase matching leads to the efficient selection of a single harmonic generated in a plateau region in plasma. The selected harmonic frequency can be tuned by changing the relative concentration of plasma components and tuning the fundamental radiation frequency. It is shown that the contrast of the selected harmonic can exceed 104.

Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope.

PubMed

Hagmann, Mark J; Yarotski, Dmitry A; Mousa, Marwan S

2017-04-01

Quasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200 μm of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.

Nonlinear magnetoelectric effects in a composite ferromagnetic-piezoelectric structure under harmonic and noise magnetic pumping

NASA Astrophysics Data System (ADS)

Burdin, D. A.; Chashin, D. V.; Ekonomov, N. A.; Fetisov, Y. K.; Stashkevich, A.

2018-03-01

Low-frequency nonlinear magnetoelectric effects in a composite structure comprised of a piezoelectric langatate slab sandwiched between two Metglas amorphous alloy magnetostrictive layers under simultaneous harmonic and noise magnetic pumping have been investigated. It is shown that the frequency fp of harmonic pumping is linearly reproduced in the piezoelectric voltage spectrum accompanied by its higher harmonics. Similarly, narrow-band magnetic noise with a central frequency fN is present in the output piezoelectric voltage along with two noise peaks in the vicinity of a double 2fN and zero frequency. Simultaneous application of harmonic and noise magnetic fields produces a noticeably more complex output voltage spectrum containing additional noise satellite lines at frequencies fp ±fN , 2fp ±fN etc. as well as a noise "pedestal". Amplitudes of voltage spectral components depend on the applied constant bias magnetic field, scaling as magnetostriction derivatives with respect to this field. The effects observed are well described by the theory of magnetic field mixing in magnetoelectric composites with nonlinear dependence of magnetostriction on applied fields.

Laser Imaging of Airborne Acoustic Emission by Nonlinear Defects

NASA Astrophysics Data System (ADS)

Solodov, Igor; Döring, Daniel; Busse, Gerd

2008-06-01

Strongly nonlinear vibrations of near-surface fractured defects driven by an elastic wave radiate acoustic energy into adjacent air in a wide frequency range. The variations of pressure in the emitted airborne waves change the refractive index of air thus providing an acoustooptic interaction with a collimated laser beam. Such an air-coupled vibrometry (ACV) is proposed for detecting and imaging of acoustic radiation of nonlinear spectral components by cracked defects. The photoelastic relation in air is used to derive induced phase modulation of laser light in the heterodyne interferometer setup. The sensitivity of the scanning ACV to different spatial components of the acoustic radiation is analyzed. The animated airborne emission patterns are visualized for the higher harmonic and frequency mixing fields radiated by planar defects. The results confirm a high localization of the nonlinear acoustic emission around the defects and complicated directivity patterns appreciably different from those observed for fundamental frequencies.

In Situ Observations of Harmonic Alfvén Waves and Associated Heavy Ion Heating

NASA Astrophysics Data System (ADS)

Chen, Huayue; Gao, Xinliang; Lu, Quanming; Wang, Shui

2018-06-01

Resonant ion heating by high-frequency Alfvén waves has long been believed to be the primary dissipation mechanism for solar coronal heating, and these high-frequency Alfvén waves are considered to be generated via cascade from low-frequency Alfvén waves. In this study, we report an unusual harmonic Alfvén event from in situ observations by the Van Allen Probes in the magnetosphere, having an environment similar to that in the solar corona. The harmonic Alfvén waves, which propagate almost along the wave vector of the fundamental waves, are considered to be generated due to the interaction between quasi-parallel Alfvén waves and plasma density fluctuations with almost identical frequency. These high-frequency harmonic Alfvén waves can then cyclotron resonantly heat the heavy ions. Our observations provide an important insight into solar corona heating by Alfvén waves.

Real-Time Monitoring Of Regional Tissue Elasticity During FUS Focused Ultrasound Therapy Using Harmonic Motion Imaging

NASA Astrophysics Data System (ADS)

Maleke, Caroline; Pernot, Mathieu; Konofagou, Elisa

2006-05-01

The feasibility of the Harmonic Motion Imaging (HMI) technique for simultaneous monitoring and generation of focused ultrasound therapy using two separate focused ultrasound transducer elements has previously been shown. In this study, a new HMI technique is described that images tissue displacement induced by a harmonic radiation force induced using a single focused ultrasound element. First, wave propagation simulation models were used to compare the use of a single Amplitude-Modulated (AM) focused beam versus two overlapping focused beams as previously implemented for HMI. Simulation results indicated that, unlike in the two-beam configuration, the AM beam produced a consistent, stable focus for the applied harmonic radiation force. The AM beam thus offered the unique advantage of sustaining the application of the spatially-invariant radiation force. Experiments were then performed on gelatin gel phantoms and tissue in vitro bovine liver. The radiation force was generated by a 4.68 MHz focused transducer using a low-frequency Amplitude-Modulated (AM) RF-signal. RF data were acquired at 7.5 MHz with a PRF of 6.5 kHz and displacements were estimated using a 1D cross-correlation algorithm on successive RF signals. Furthermore, taking advantage of the real-time capability of our method, the change in the elastic properties was monitored during focused ultrasound (FUS) ablation of tissue in vitro bovine liver. Based on the harmonic displacements, their temperature-dependence, and the calculated acoustic radiation force, the change in the relative, regional stiffness could be monitored during heating and ablation, both using the displacement amplitude and the resulting phase shift change of the displacement relative to the radiation force temporal profile. In conclusion, the feasibility of using an AM radiation force for HMI for simultaneous monitoring and treatment during ultrasound therapy was demonstrated in phantoms and tissues in vitro. Further study of this method will include, ex vivo and in vivo, stiffness and temperature.

Frequency locking of a field-widened Michelson interferometer based on optimal multi-harmonics heterodyning.

PubMed

Cheng, Zhongtao; Liu, Dong; Zhou, Yudi; Yang, Yongying; Luo, Jing; Zhang, Yupeng; Shen, Yibing; Liu, Chong; Bai, Jian; Wang, Kaiwei; Su, Lin; Yang, Liming

2016-09-01

A general resonant frequency locking scheme for a field-widened Michelson interferometer (FWMI), which is intended as a spectral discriminator in a high-spectral-resolution lidar, is proposed based on optimal multi-harmonics heterodyning. By transferring the energy of a reference laser to multi-harmonics of different orders generated by optimal electro-optic phase modulation, the heterodyne signal of these multi-harmonics through the FWMI can reveal the resonant frequency drift of the interferometer very sensitively within a large frequency range. This approach can overcome the locking difficulty induced by the low finesse of the FWMI, thus contributing to excellent locking accuracy and lock acquisition range without any constraint on the interferometer itself. The theoretical and experimental results are presented to verify the performance of this scheme.

The N/Rev phenomenon in simulating a blade-element rotor system

NASA Technical Reports Server (NTRS)

Mcfarland, R. E.

1983-01-01

When a simulation model produces frequencies that are beyond the bandwidth of a discrete implementation, anomalous frequencies appear within the bandwidth. Such is the case with blade element models of rotor systems, which are used in the real time, man in the loop simulation environment. Steady state, high frequency harmonics generated by these models, whether aliased or not, obscure piloted helicopter simulation responses. Since these harmonics are attenuated in actual rotorcraft (e.g., because of structural damping), a faithful environment representation for handling qualities purposes may be created from the original model by using certain filtering techniques, as outlined here. These include harmonic consideration, conventional filtering, and decontamination. The process of decontamination is of special interest because frequencies of importance to simulation operation are not attenuated, whereas superimposed aliased harmonics are.

Complex metabolic oscillations in plants forced by harmonic irradiance.

PubMed Central

Nedbal, Ladislav; Brezina, Vítezslav

2002-01-01

Plants exposed to harmonically modulated irradiance, approximately 1 + cos(omegat), exhibit a complex periodic pattern of chlorophyll fluorescence emission that can be deconvoluted into a steady-state component, a component that is modulated with the frequency of the irradiance (omega), and into at least two upper harmonic components (2omega and 3omega). A model is proposed that accounts for the upper harmonics in fluorescence emission by nonlinear negative feedback regulation of photosynthesis. In contrast to simpler linear models, the model predicts that the steady-state fluorescence component will depend on the frequency of light modulation, and that amplitudes of all fluorescence components will exhibit resonance peak(s) when the irradiance frequency is tuned to an internal frequency of a regulatory component. The experiments confirmed that the upper harmonic components appear and exhibit distinct resonant peaks. The frequency of autonomous oscillations observed earlier upon an abrupt increase in CO(2) concentration corresponds to the sharpest of the resonant peaks of the forced oscillations. We propose that the underlying principles are general for a wide spectrum of negative-feedback regulatory mechanisms. The analysis by forced harmonic oscillations will enable us to examine internal dynamics of regulatory processes that have not been accessible to noninvasive fluorescence monitoring to date. PMID:12324435

Wideband tunable 140 GHz second-harmonic InP-TED oscillator

NASA Astrophysics Data System (ADS)

Rydberg, A.; Kollberg, E.

1986-07-01

A second-harmonic InP-TED oscillator, with an output power of more than 3 dBm at 144 GHz and tunable over a 10 percent frequency range, has been developed. The design incorporates two waveguide resonators. One resonator determines the fundamental frequency of oscillation and the other optimizes the second-harmonic output power.

MUSIC-type imaging of a thin penetrable inclusion from its multi-static response matrix

NASA Astrophysics Data System (ADS)

Park, Won-Kwang; Lesselier, Dominique

2009-07-01

The imaging of a thin inclusion, with dielectric and/or magnetic contrasts with respect to the embedding homogeneous medium, is investigated. A MUSIC-type algorithm operating at a single time-harmonic frequency is developed in order to map the inclusion (that is, to retrieve its supporting curve) from scattered field data collected within the multi-static response matrix. Numerical experiments carried out for several types of inclusions (dielectric and/or magnetic ones, straight or curved ones), mostly single inclusions and also two of them close by as a straightforward extension, illustrate the pros and cons of the proposed imaging method.

Time-Frequency Analysis Reveals Pairwise Interactions in Insect Swarms

NASA Astrophysics Data System (ADS)

Puckett, James G.; Ni, Rui; Ouellette, Nicholas T.

2015-06-01

The macroscopic emergent behavior of social animal groups is a classic example of dynamical self-organization, and is thought to arise from the local interactions between individuals. Determining these interactions from empirical data sets of real animal groups, however, is challenging. Using multicamera imaging and tracking, we studied the motion of individual flying midges in laboratory mating swarms. By performing a time-frequency analysis of the midge trajectories, we show that the midge behavior can be segmented into two distinct modes: one that is independent and composed of low-frequency maneuvers, and one that consists of higher-frequency nearly harmonic oscillations conducted in synchrony with another midge. We characterize these pairwise interactions, and make a hypothesis as to their biological function.

The perception of concurrent sound objects through the use of harmonic enhancement: a study of auditory attention.

PubMed

Koulaguina, Elena; Drisdelle, Brandi Lee; Alain, Claude; Grimault, Stephan; Eck, Douglas; Vachon, François; Jolicoeur, Pierre

2015-04-01

When the frequency of one harmonic, in a sound composed of many harmonics, is briefly mistuned and then returned to the 'in-tune' frequency and phase, observers report hearing this harmonic as a separate tone long after the brief period of mistuning - a phenomenon called harmonic enhancement. Here, we examined the consequence of harmonic enhancement on listeners' ability to detect a brief amplitude notch embedded in one of the harmonics after the period of mistuning. When present, the notch was either on the enhanced harmonic or on a different harmonic. Detection was better on the enhanced harmonic than on a non-enhanced harmonic. This finding suggests that attention was drawn to the enhanced harmonic (which constituted a new sound object) thereby easing the processing of sound features (i.e., a notch) within that object. This is the first evidence of a functional consequence of the after-effect of transient mistuning on auditory perception. Moreover, the findings provide support for an attention-based explanation of the enhancement phenomenon.

Self-starting harmonic frequency comb generation in a quantum cascade laser

NASA Astrophysics Data System (ADS)

Kazakov, Dmitry; Piccardo, Marco; Wang, Yongrui; Chevalier, Paul; Mansuripur, Tobias S.; Xie, Feng; Zah, Chung-en; Lascola, Kevin; Belyanin, Alexey; Capasso, Federico

2017-12-01

Optical frequency combs1,2 establish a rigid phase-coherent link between microwave and optical domains and are emerging as high-precision tools in an increasing number of applications3. Frequency combs with large intermodal spacing are employed in the field of microwave photonics for radiofrequency arbitrary waveform synthesis4,5 and for the generation of terahertz tones of high spectral purity in future wireless communication networks6,7. Here, we demonstrate self-starting harmonic frequency comb generation with a terahertz repetition rate in a quantum cascade laser. The large intermodal spacing caused by the suppression of tens of adjacent cavity modes originates from a parametric contribution to the gain due to temporal modulations of population inversion in the laser8,9. Using multiheterodyne self-detection, the mode spacing of the harmonic comb is shown to be uniform to within 5 × 10-12 parts of the central frequency. This new harmonic comb state extends the range of applications of quantum cascade laser frequency combs10-13.

Presence of strong harmonics during visual entrainment: a magnetoencephalography study.

PubMed

Heinrichs-Graham, Elizabeth; Wilson, Tony W

2012-09-01

Visual neurons are known to synchronize their firing with stimuli that flicker at a constant rate (e.g. 12Hz). These so-called visual steady-state responses (VSSR) are a well-studied phenomenon, yet the underlying mechanisms are widely disagreed upon. Furthermore, there is limited evidence that visual neurons may simultaneously synchronize at harmonics of the stimulation frequency. We utilized magnetoencephalography (MEG) to examine synchronization at harmonics of the visual stimulation frequency (18Hz). MEG data were analyzed for event-related-synchronization (ERS) at the fundamental frequency, 36, 54, and 72Hz. We found strong ERS in all bands. Only 31% of participants showed maximum entrainment at the fundamental; others showed stronger entrainment at either 36 or 54Hz. The cortical foci of these responses indicated that the harmonics involved cortices that were partially distinct from the fundamental. These findings suggest that spatially-overlapping subpopulations of neurons are simultaneously entrained at different harmonics of the stimulus frequency. Copyright © 2012 Elsevier B.V. All rights reserved.

Nonlinear electromagnetic responses of active molecular motors in live cells and organelles

NASA Astrophysics Data System (ADS)

Nawarathna, Dharmakirthi; Gardner, Jeffrey; Cardenas, Gustavo; Warmflash, David; Miller, John; Widger, William; Claycomb, James

2006-03-01

The response of biological cells to an oscillatory electric field contains both linear and nonlinear (eg. induced harmonic) components. At low frequencies (about 10Hz), harmonic generation by budding yeast cells is observed. These induced harmonics are sensitive to sodium metavanadate, an inhibitor, and glucose, a substrate, respectively, of P-type ATPase membrane pumps. At higher frequencies, two peaks, around 3kHz and 12kHz, are observed in the frequency-dependent harmonic responses. These are sensitive to potassium cyanide, a respiratory inhibitor that blocks cytochrome c oxidase, an enzyme of the mitochondrial respiratory chain. We have also measured the response of uncoupled mitochondria extracted from bovine heart cells, for which a second harmonic sensitive to pericidin A and carboxin is detected at applied frequencies of 3-4kHz. Finally, in coupled mouse mitochondria, an ADP sensitive peak (12-15kHz) is observed, likely due to the F0 domain of ATP synthase, which acts as a molecular turbine.

Ionospheric modification at twice the electron cyclotron frequency.

PubMed

Djuth, F T; Pedersen, T R; Gerken, E A; Bernhardt, P A; Selcher, C A; Bristow, W A; Kosch, M J

2005-04-01

In 2004, a new transmission band was added to the HAARP high-frequency ionospheric modification facility that encompasses the second electron cyclotron harmonic at altitudes between approximately 220 and 330 km. Initial observations indicate that greatly enhanced airglow occurs whenever the transmission frequency approximately matches the second electron cyclotron harmonic at the height of the upper hybrid resonance. This is the reverse of what happens at higher electron cyclotron harmonics. The measured optical emissions confirm the presence of accelerated electrons in the plasma.

A High Power Frequency Doubled Fiber Laser

NASA Technical Reports Server (NTRS)

Thompson, Robert J.; Tu, Meirong; Aveline, Dave; Lundblad, Nathan; Maleki, Lute

2003-01-01

This viewgraph presentation reports on the development of a high power 780 nm laser suitable for space applications of laser cooling. A possible solution is to use frequency doubling of high power 1560 nm telecom lasers. The presentation shows a diagram of the frequency conversion, and a graph of the second harmonic generation in one crystal, and the use of the cascading crystals. Graphs show the second harmonic power as a function of distance between crystals, second harmonic power vs. pump power, tunability of laser systems.

Nonlinear electromagnetic responses of active membrane protein complexes in live cells and organelles

NASA Astrophysics Data System (ADS)

Nawarathna, Dharmakirthi

The response of biological cells to an applied oscillating electric field contains both linear and nonlinear components (eg. induced harmonics). Such noninvasive measurements can be used to study active processes taking place inside the cells. The measurement of induced harmonics is the tool used for the study described here. A highly sensitive superconducting quantum interference device (SQUID) is used to detect the response at low frequencies, which greatly reduces electrode polarization effects. At high frequencies, a four- probe method is used. At low frequencies, harmonic generation by budding yeast cells in response to a sinusoidal electric field is reported, which is seen to be minimal when the field amplitude is less than a threshold value. Surprisingly, sodium metavanadate, an inhibitor of P-type ATPases and glucose, a substrate of P-type ATPase responsible for nonlinear response in yeast, reduces the threshold field amplitude, increasing harmonic generation at low amplitudes while reducing it at large amplitudes. We have thus proposed a model that explicitly introduces a threshold field, similar to those observed in density waves, where fields above threshold drive charge transport through an energy landscape with multiple wells, and in Coulomb blockade tunnel junctions, recently exploited to define the current standard. At high frequencies, the induced harmonics exhibit pronounced features that depend on the specific organism. Budding yeast (S. cerevisiae ) cells produce numerous harmonics. When the second or third harmonic amplitude is plotted vs. applied frequency, we observe two peaks, around 3 kHz and 12 kHz, which are suppressed by the respiratory inhibitor potassium cyanide. We then measured the response to oscillatory electric fields of intact bovine heart mitochondria, a reproducible second harmonic (at ˜3-4 kHz applied frequency) was detected. Further, with coupled mouse mitochondria, an ADP sensitive peak (˜ 12-15 kHz applied frequency) was observed, possibly due to the F0 domain of ATP synthase. Finally, harmonics generated by chloroplasts, the plant organelles responsible for photosynthesis, were measured, which are similar in structure and function to mitochondria, depend dramatically on incident light, and vanish in the absence of light. Using spinach chloroplasts, light sensitive peaks were detected in the range of 0--12 kHz, again suggesting that these harmonics are indicative of electron processes in the light harvesting complexes, reaction center, and/or photosynthetic electron transport chain.

High-harmonic generation by two-color mixing of circularly polarized laser fields

NASA Astrophysics Data System (ADS)

Milošević, D. B.; Becker, W.; Kopold, R.

2000-06-01

Dipole selection rules prevent harmonic generation by an atom in a circularly polarized laser field. However, this is not the case for a superposition of several circularly polarized fields, such as two circularly polarized fields with frequencies ω and 2ω that corotate or counter-rotate in the same plane. Harmonic generation in this environment has been observed and, in fact, found to be very intense in the counter-rotating case [1]. In a certain frequency region, the harmonics may be stronger than those radiated in a linearly polarized field of either frequency. The selection rules dictate that the harmonics are circularly polarized with a helicity that alternates from one harmonic to the next. Besides their practical interest, these harmonics are also intriguing from a fundamental point of view: the standard simple-man picture does not apply since orbits that start with zero velocity in this field almost never return to their point of departure. In terms of quantum trajectories, we discuss the mechanism that generates these harmonics. In several interesting ways, it is complementary to the case of linear polarization. [1] H. Eichmann et al., Phys. Rev. A 51, R3414 (1995)

High efficiency and output power from second- and third-harmonic millimeter-wave InP-TED oscillators at frequencies above 170 GHz

NASA Astrophysics Data System (ADS)

Rydberg, Anders

1990-10-01

InP TED (transferred electron device) oscillators have been experimentally investigated for frequencies between 170 and 279 GHz. It has been found that output powers of more than 7 and 0.2 mW are possible at 180 and 272 GHz using second- and third-harmonic mode operation, respectively. Conversion efficiencies of more than 13 percent and 0.3 percent between fundamental and second harmonic and fundamental and third harmonic, respectively, have been found. The conversion efficiencies are comparable to GaAs TEDs. The output powers, conversion efficiencies, and tuning ranges (more than 22 percent) are the largest reported for InP TEDs at these frequencies. The output power at third harmonic was sufficient for supplying a superconducting mixer with local oscillator power.

47 CFR 15.33 - Frequency range of radiated measurements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... radiator operates at or above 30 GHz: to the fifth harmonic of the highest fundamental frequency or to 200... kHz, up to at least the frequency shown in this paragraph: (1) If the intentional radiator operates below 10 GHz: to the tenth harmonic of the highest fundamental frequency or to 40 GHz, whichever is...

Frequency lock-in and phase synchronization of vortex shedding behind circular cylinder due to surface waves

NASA Astrophysics Data System (ADS)

Gunnoo, Hans; Abcha, Nizar; Ezersky, Alexander

2016-02-01

The influence of harmonic surface wave on non-regular Karman Vortex Street is investigated. In our experiments, Karman Street arises behind a vertical circular cylinder in a water flow and harmonic surface waves propagating upstream. It is found that surface waves can modify regimes of shedding in Karman Street: frequency lock-in and synchronization of vortex shedding can arise. Intensive surface waves can excite symmetric vortex street instead of chess-like street, and completely suppress shedding behind the cylinder. It is shown experimentally that such effects occur if frequency of harmonic surface wave is approximately twice higher than the frequency of vortex shedding. Region of frequency lock-in is found on the plane amplitude-frequency of surface wave.

Efficient second-harmonic conversion of CW single-frequency Nd:YAG laser light by frequency locking to a monolithic ring frequency doubler

NASA Technical Reports Server (NTRS)

Gerstenberger, D. C.; Tye, G. E.; Wallace, R. W.

1991-01-01

Efficient second-harmonic conversion of the 1064-nm output of a diode-pumped CW single-frequency Nd:YAG laser to 532 nm was obtained by frequency locking the laser to a monolithic ring resonator constructed of magnesium-oxide-doped lithium niobate. The conversion efficiency from the fundamental to the second harmonic was 65 percent. Two hundred milliwatts of CW single-frequency 532-nm light were produced from 310 mW of power of 1064-nm light. This represents a conversion efficiency of 20 percent from the 1-W diode laser used to pump the Nd:YAG laser to single-frequency 532-nm output. No signs of degradation were observed for over 500 h of operation.

Measurement of attenuation coefficients of the fundamental and second harmonic waves in water

NASA Astrophysics Data System (ADS)

Zhang, Shuzeng; Jeong, Hyunjo; Cho, Sungjong; Li, Xiongbing

2016-02-01

Attenuation corrections in nonlinear acoustics play an important role in the study of nonlinear fluids, biomedical imaging, or solid material characterization. The measurement of attenuation coefficients in a nonlinear regime is not easy because they depend on the source pressure and requires accurate diffraction corrections. In this work, the attenuation coefficients of the fundamental and second harmonic waves which come from the absorption of water are measured in nonlinear ultrasonic experiments. Based on the quasilinear theory of the KZK equation, the nonlinear sound field equations are derived and the diffraction correction terms are extracted. The measured sound pressure amplitudes are adjusted first for diffraction corrections in order to reduce the impact on the measurement of attenuation coefficients from diffractions. The attenuation coefficients of the fundamental and second harmonics are calculated precisely from a nonlinear least squares curve-fitting process of the experiment data. The results show that attenuation coefficients in a nonlinear condition depend on both frequency and source pressure, which are much different from a linear regime. In a relatively lower drive pressure, the attenuation coefficients increase linearly with frequency. However, they present the characteristic of nonlinear growth in a high drive pressure. As the diffraction corrections are obtained based on the quasilinear theory, it is important to use an appropriate source pressure for accurate attenuation measurements.

Determination of nonlinear resistance voltage-current relationships by measuring harmonics

NASA Technical Reports Server (NTRS)

Stafford, J. M.

1971-01-01

Test configuration measures harmonic signal amplitudes generated in nonlinear resistance. Vacuum-type voltmeter measures low frequency sinusoidal input signal amplitude and wave-analyzer measures amplitude of harmonic signals generated in junction. Input signal harmonics amplitude must not exceed that of harmonics generated in nonlinear resistance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toufexis, Filippos; Tantawi, Sami G.; Jensen, Aaron

Here, we report the experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum electronic device, which uses an over-moded spherical sector output cavity. In this device, a pencil electron beam is helically deflected in a transverse deflecting cavity before entering the output cavity. No magnetic field is required to focus or guide the beam. We built and tested a proof-of-principle device with an output frequency of 57.12 GHz. The measured peak power was 52.67 W at the 5th harmonic of the drive frequency. Power at the 4th, 6th, and 7th harmonics was 33.28 dB lower than that at themore » 5th harmonic.« less

Observations of volcanic tremor during January-February 2005 eruption of Mt. Veniaminof, Alaska

USGS Publications Warehouse

De Angelis, Slivio; McNutt, Stephen R.

2007-01-01

Mt. Veniaminof, Alaska Peninsula, is a stratovolcano with a summit ice-filled caldera containing a small intracaldera cone and active vent. From January 2 to February 21, 2005, Mt. Veniaminof erupted. The eruption was characterized by numerous small ash emissions (VEI 0 to 1) and accompanied by low-frequency earthquake activity and volcanic tremor. We have performed spectral analyses of the seismic signals in order to characterize them and to constrain their source. Continuous tremor has durations of minutes to hours with dominant energy in the band 0.5– 4.0 Hz, and spectra characterized by narrow peaks either irregularly (non-harmonic tremor) or regularly spaced (harmonic tremor). The spectra of non-harmonic tremor resemble those of low-frequency events recorded simultaneously with surface ash explosions, suggesting that the source mechanisms might be similar or related. We propose that non-harmonic tremor at Mt. Veniaminof results from the coalescence of gas bubbles while low-frequency events are related to the disruption of large gas pockets within the conduit. Harmonic tremor, characterized by regular and quasisinusoidal waveforms, has duration of hours. Spectra containing up to five harmonics suggest the presence of a resonating source volume that vibrates in a longitudinal acoustic mode. An interesting feature of harmonic tremor is that frequency is observed to change over time; spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained. Factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and variations of the effective size of the resonator.

Controlling the high frequency response of H2 by ultra-short tailored laser pulses: A time-dependent configuration interaction study

NASA Astrophysics Data System (ADS)

Schönborn, Jan Boyke; Saalfrank, Peter; Klamroth, Tillmann

2016-01-01

We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H2 treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a "non-harmonic" response of H2 to a laser pulse. Specifically, we will show how adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization.

Advances in generation of high-repetition-rate burst mode laser output.

PubMed

Jiang, Naibo; Webster, Matthew C; Lempert, Walter R

2009-02-01

It is demonstrated that the incorporation of variable pulse duration flashlamp power supplies into an Nd:YAG burst mode laser system results in very substantial increases in the realizable energy per pulse, the total pulse train length, and uniformity of the intensity envelope. As an example, trains of 20 pulses at burst frequencies of 50 and 20 kHz are demonstrated with individual pulse energy at 1064 nm of 220 and 400 mJ, respectively. Conversion efficiency to the second- (532 nm) and third- (355 nm) harmonic wavelengths of approximately 50% and 35-40%, respectively, is also achieved. Use of the third-harmonic output of the burst mode laser as a pump source for a simple, home built optical parametric oscillator (OPO) produces pulse trains of broadly wavelength tunable output. Sum-frequency mixing of OPO signal output at 622 nm with residual output from the 355 nm pump beam is shown to produce uniform bursts of tunable output at approximately 226 nm, with individual pulse energy of approximately 0.5 mJ. Time-correlated NO planar laser induced fluorescence (PLIF) image sequences are obtained in a Mach 3 wind tunnel at 500 kHz, representing, to our knowledge, the first demonstration of NO PLIF imaging at repetition rates exceeding tens of hertz.

Analysis of second-harmonic-generation microscopy in a mouse model of ovarian carcinoma

NASA Astrophysics Data System (ADS)

Watson, Jennifer M.; Rice, Photini F.; Marion, Samuel L.; Brewer, Molly A.; Davis, John R.; Rodriguez, Jeffrey J.; Utzinger, Urs; Hoyer, Patricia B.; Barton, Jennifer K.

2012-07-01

Second-harmonic-generation (SHG) imaging of mouse ovaries ex vivo was used to detect collagen structure changes accompanying ovarian cancer development. Dosing with 4-vinylcyclohexene diepoxide and 7,12-dimethylbenz[a]anthracene resulted in histologically confirmed cases of normal, benign abnormality, dysplasia, and carcinoma. Parameters for each SHG image were calculated using the Fourier transform matrix and gray-level co-occurrence matrix (GLCM). Cancer versus normal and cancer versus all other diagnoses showed the greatest separation using the parameters derived from power in the highest-frequency region and GLCM energy. Mixed effects models showed that these parameters were significantly different between cancer and normal (P<0.008). Images were classified with a support vector machine, using 25% of the data for training and 75% for testing. Utilizing all images with signal greater than the noise level, cancer versus not-cancer specimens were classified with 81.2% sensitivity and 80.0% specificity, and cancer versus normal specimens were classified with 77.8% sensitivity and 79.3% specificity. Utilizing only images with greater than of 75% of the field of view containing signal improved sensitivity and specificity for cancer versus normal to 81.5% and 81.1%. These results suggest that using SHG to visualize collagen structure in ovaries could help with early cancer detection.

Multi-Frequency Harmonics Technique for HIFU Tissue Treatment

NASA Astrophysics Data System (ADS)

Rybyanets, Andrey N.; Lugovaya, Maria A.; Rybyanets, Anastasia A.

2010-03-01

New technique for enhancing of tissue lysis and enlarging treatment volume during one HIFU sonification is proposed. The technique consists in simultaneous or alternative (at optimal repetition frequency) excitation of single element HIFU transducer on a frequencies corresponding to odd natural harmonics of piezoceramic element at ultrasound energy levels sufficient for producing cavitational, thermal or mechanical damage of fat cells at each of aforementioned frequencies. Calculation and FEM modeling of transducer vibrations and acoustic field patterns for different frequencies sets were performed. Acoustic pressure in focal plane was measured in water using calibrated hydrophone and 3D acoustic scanning system. In vitro experiments on different tissues and phantoms confirming the advantages of multifrequency harmonic method were performed.

Harmonic mode-locking using the double interval technique in quantum dot lasers.

PubMed

Li, Yan; Chiragh, Furqan L; Xin, Yong-Chun; Lin, Chang-Yi; Kim, Junghoon; Christodoulou, Christos G; Lester, Luke F

2010-07-05

Passive harmonic mode-locking in a quantum dot laser is realized using the double interval technique, which uses two separate absorbers to stimulate a specific higher-order repetition rate compared to the fundamental. Operating alone these absorbers would otherwise reinforce lower harmonic frequencies, but by operating together they produce the harmonic corresponding to their least common multiple. Mode-locking at a nominal 60 GHz repetition rate, which is the 10(th) harmonic of the fundamental frequency of the device, is achieved unambiguously despite the constraint of a uniformly-segmented, multi-section device layout. The diversity of repetition rates available with this method is also discussed.

Steady-state visual evoked potential (SSVEP)-based communication: impact of harmonic frequency components

NASA Astrophysics Data System (ADS)

Müller-Putz, Gernot R.; Scherer, Reinhold; Brauneis, Christian; Pfurtscheller, Gert

2005-12-01

Brain-computer interfaces (BCIs) can be realized on the basis of steady-state evoked potentials (SSEPs). These types of brain signals resulting from repetitive stimulation have the same fundamental frequency as the stimulation but also include higher harmonics. This study investigated how the classification accuracy of a 4-class BCI system can be improved by incorporating visually evoked harmonic oscillations. The current study revealed that the use of three SSVEP harmonics yielded a significantly higher classification accuracy than was the case for one or two harmonics. During feedback experiments, the five subjects investigated reached a classification accuracy between 42.5% and 94.4%.

Steady-state visual evoked potential (SSVEP)-based communication: impact of harmonic frequency components.

PubMed

Müller-Putz, Gernot R; Scherer, Reinhold; Brauneis, Christian; Pfurtscheller, Gert

2005-12-01

Brain-computer interfaces (BCIs) can be realized on the basis of steady-state evoked potentials (SSEPs). These types of brain signals resulting from repetitive stimulation have the same fundamental frequency as the stimulation but also include higher harmonics. This study investigated how the classification accuracy of a 4-class BCI system can be improved by incorporating visually evoked harmonic oscillations. The current study revealed that the use of three SSVEP harmonics yielded a significantly higher classification accuracy than was the case for one or two harmonics. During feedback experiments, the five subjects investigated reached a classification accuracy between 42.5% and 94.4%.

Modulated CMOS camera for fluorescence lifetime microscopy.

PubMed

Chen, Hongtao; Holst, Gerhard; Gratton, Enrico

2015-12-01

Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime of entire images. However, the complexity and high costs involved in construction of such a system limit the extensive use of this technique. PCO AG recently released the first luminescence lifetime imaging camera based on a high frequency modulated CMOS image sensor, QMFLIM2. Here we tested and provide operational procedures to calibrate the camera and to improve the accuracy using corrections necessary for image analysis. With its flexible input/output options, we are able to use a modulated laser diode or a 20 MHz pulsed white supercontinuum laser as the light source. The output of the camera consists of a stack of modulated images that can be analyzed by the SimFCS software using the phasor approach. The nonuniform system response across the image sensor must be calibrated at the pixel level. This pixel calibration is crucial and needed for every camera settings, e.g. modulation frequency and exposure time. A significant dependency of the modulation signal on the intensity was also observed and hence an additional calibration is needed for each pixel depending on the pixel intensity level. These corrections are important not only for the fundamental frequency, but also for the higher harmonics when using the pulsed supercontinuum laser. With these post data acquisition corrections, the PCO CMOS-FLIM camera can be used for various biomedical applications requiring a large frame and high speed acquisition. © 2015 Wiley Periodicals, Inc.

Fluorescence diffuse tomography of small animals with DsRed2 fluorescent protein

NASA Astrophysics Data System (ADS)

Turchin, I. V.; Plehanov, V. I.; Orlova, A. G.; Kamenskiy, V. A.; Kleshnin, M. S.; Shirmanova, M. V.; Shakhova, N. M.; Balalaeva, I. V.; Savitskiy, A. P.

2006-05-01

Fluorescent compounds are used as markers to diagnose oncological diseases, to study molecular processes typical for carcinogenesis, and to investigate metastasis formation and tumor regress under the influence of therapeutics. Different types of tomography, such as continuous wave (CW), frequency-domain (FD), and time-domain (TD) tomography, allow fluorescence imaging of tumors located deep in human or animal tissue. In this work, preliminary results of the frequency domain fluorescent diffuse tomography (FDT) method in application to DsRed2 protein as a fluorescent agent are presented. For the first step of our experiments, we utilized low-frequency amplitude modulation (1 kHz) of second harmonic of Nd: YAG (532 nm). The transilluminative configuration was used in the setup. The results of post mortem experiments with capsules containing DsRed2 inserted inside the esophagus of a 3-day-old hairless rat to simulate tumor are shown. An algorithm of processing fluorescent images based on calculating the zero of maximum curvature has been applied to detect fluorescent inclusion boundaries in the image. This work demonstrates the potential capability of the FDT method for imaging deep fluorescent tumors in human tissue or animal models of human cancer. Improvement of the setup can be accomplished by using high-frequency modulation (using a 110-MHz acoustooptical modulator).

Relativistic frequency upshift to the extreme ultraviolet regime using self-induced oscillatory flying mirrors

PubMed Central

Kim, I Jong; Pae, Ki Hong; Kim, Chul Min; Kim, Hyung Taek; Yun, Hyeok; Yun, Sang Jae; Sung, Jae Hee; Lee, Seong Ku; Yoon, Jin Woo; Yu, Tae Jun; Jeong, Tae Moon; Nam, Chang Hee; Lee, Jongmin

2012-01-01

Coherent short-wavelength radiation from laser–plasma interactions is of increasing interest in disciplines including ultrafast biomolecular imaging and attosecond physics. Using solid targets instead of atomic gases could enable the generation of coherent extreme ultraviolet radiation with higher energy and more energetic photons. Here we present the generation of extreme ultraviolet radiation through coherent high-harmonic generation from self-induced oscillatory flying mirrors—a new-generation mechanism established in a long underdense plasma on a solid target. Using a 30-fs, 100-TW Ti:sapphire laser, we obtain wavelengths as short as 4.9 nm for an optimized level of amplified spontaneous emission. Particle-in-cell simulations show that oscillatory flying electron nanosheets form in a long underdense plasma, and suggest that the high-harmonic generation is caused by reflection of the laser pulse from electron nanosheets. We expect this extreme ultraviolet radiation to be valuable in realizing a compact X-ray instrument for research in biomolecular imaging and attosecond physics. PMID:23187631

Pattern masking: the importance of remote spatial frequencies and their phase alignment.

PubMed

Huang, Pi-Chun; Maehara, Goro; May, Keith A; Hess, Robert F

2012-02-16

To assess the effects of spatial frequency and phase alignment of mask components in pattern masking, target threshold vs. mask contrast (TvC) functions for a sine-wave grating (S) target were measured for five types of mask: a sine-wave grating (S), a square-wave grating (Q), a missing fundamental square-wave grating (M), harmonic complexes consisting of phase-scrambled harmonics of a square wave (Qp), and harmonic complexes consisting of phase-scrambled harmonics of a missing fundamental square wave (Mp). Target and masks had the same fundamental frequency (0.46 cpd) and the target was added in phase with the fundamental frequency component of the mask. Under monocular viewing conditions, the strength of masking depends on phase relationships among mask spatial frequencies far removed from that of the target, at least 3 times the target frequency, only when there are common target and mask spatial frequencies. Under dichoptic viewing conditions, S and Q masks produced similar masking to each other and the phase-scrambled masks (Qp and Mp) produced less masking. The results suggest that pattern masking is spatial frequency broadband in nature and sensitive to the phase alignments of spatial components.

225-255-GHz InP DHBT Frequency Tripler MMIC Using Complementary Split-Ring Resonator

NASA Astrophysics Data System (ADS)

Li, Xiao; Zhang, Yong; Li, Oupeng; Sun, Yan; Lu, Haiyan; Cheng, Wei; Xu, Ruimin

2017-02-01

In this paper, a novel design of frequency tripler monolithic microwave integrated circuit (MMIC) using complementary split-ring resonator (CSRR) is proposed based on 0.5-μm InP DHBT process. The CSRR-loaded microstrip structure is integrated in the tripler as a part of impedance matching network to suppress the fundamental harmonic, and another frequency tripler based on conventional band-pass filter is presented for comparison. The frequency tripler based on CSRR-loaded microstrip generates an output power between -8 and -4 dBm from 228 to 255 GHz when the input power is 6 dBm. The suppression of fundamental harmonic is better than 20 dBc at 77-82 GHz input frequency within only 0.15 × 0.15 mm2 chip area of the CSRR structure on the ground layer. Compared with the frequency tripler based on band-pass filter, the tripler using CSRR-loaded microstrip obtains a similar suppression level of unwanted harmonics and higher conversion gain within a much smaller chip area. To our best knowledge, it is the first time that CSRR is used for harmonic suppression of frequency multiplier at such high frequency band.

Characterization of Deficiencies in the Frequency Domain Forced Response Analysis Technique for Turbine Bladed Disks

NASA Technical Reports Server (NTRS)

Brown, Andrew M.; Schmauch, Preston

2012-01-01

Turbine blades in rocket and jet engine turbomachinery experience enormous harmonic loading conditions. These loads result from the integer number of upstream and downstream stator vanes as well as the other turbine stages. The standard technique for forced response analysis to assess structural integrity is to decompose a CFD generated flow field into its harmonic components, and to then perform a frequency response analysis at the problematic natural frequencies. Recent CFD analysis and water-flow testing at NASA/MSFC, though, indicates that this technique may miss substantial harmonic and non-harmonic excitation sources that become present in complex flows. These complications suggest the question of whether frequency domain analysis is capable of capturing the excitation content sufficiently. Two studies comparing frequency response analysis with transient response analysis, therefore, have been performed. The first is of a bladed disk with each blade modeled by simple beam elements. It was hypothesized that the randomness and other variation from the standard harmonic excitation would reduce the blade structural response, but the results showed little reduction. The second study was of a realistic model of a bladed-disk excited by the same CFD used in the J2X engine program. The results showed that the transient analysis results were up to 10% higher for "clean" nodal diameter excitations and six times larger for "messy" excitations, where substantial Fourier content around the main harmonic exists.

Methods for Creation and Detection of Ultra-Strong Artificial Ionization in the Upper Atmosphere (Invited)

NASA Astrophysics Data System (ADS)

Bernhardt, P. A.; Siefring, C. L.; Briczinski, S. J.; Kendall, E. A.; Watkins, B. J.; Bristow, W. A.; Michell, R.

2013-12-01

The High Frequency Active Auroral Research Program (HAARP) transmitter in Alaska has been used to produce localized regions of artificial ionization at altitudes between 150 and 250 km. High power radio waves tuned near harmonics of the electron gyro frequency were discovered by Todd Pederson of the Air Force Research Laboratory to produce ionosonde traces that looked like artificial ionization layers below the natural F-region. The initial regions of artificial ionization (AI) were not stable but had moved down in altitude over a period of 15 minutes. Recently, artificial ionization has been produced by the 2nd, 3rd, 4th and 6th harmonics transmissions by the HAARP. In march 2013, the artificial ionization clouds were sustained for more the 5 hours using HAARP tuned to the 4 fce at the full power of 3.6 Mega-Watts with a twisted-beam antenna pattern. Frequency selection with narrow-band sweeps and antenna pattern shaping has been employed for optimal generation of AI. Recent research at HAARP has produced the longest lived and denser artificial ionization clouds using HF transmissions at the harmonics of the electron cyclotron frequency and ring-shaped radio beams tailored to prevent the descent of the clouds. Detection of artificial ionization employs (1) ionosonde echoes, (2) coherent backscatter from the Kodiak SuperDARN radar, (3) enhanced ion and plasma line echoes from the HAARP MUIR radar at 400 MHz, (4) high resolution optical image from ground sites, and (5) unique stimulated electromagnetic emissions, and (6) strong UHF and L-Band scintillation induced into trans-ionospheric signals from satellite radio beacons. Future HAARP experiments will determine the uses of long-sustained AI for enhanced HF communications.

Spin current and second harmonic generation in non-collinear magnetic systems: the hydrodynamic model

NASA Astrophysics Data System (ADS)

Karashtin, E. A.; Fraerman, A. A.

2018-04-01

We report a theoretical study of the second harmonic generation in a noncollinearly magnetized conductive medium with equilibrium spin current. The hydrodynamic model is used to unravel the mechanism of a novel effect of the double frequency signal generation that is attributed to the spin current. According to our calculations, this second harmonic response appears due to the ‘non-adiabatic’ spin polarization of the conduction electrons induced by the oscillations in the non-uniform magnetization forced by the electric field of the electromagnetic wave. Together with the linear velocity response this leads to the generation of the double frequency spin current. This spin current is converted to the electric current via the inverse spin Hall effect, and the double-frequency electric current emits the second harmonic radiation. Possible experiment for detection of the new second harmonic effect is proposed.

Split-Waveguide Mounts For Submillimeter-Wave Multipliers And Harmonic Mixers

NASA Technical Reports Server (NTRS)

Raisanen, Antti; Choudhury, Debabani; Dengler, Robert J.; Oswald, John E.; Siegel, Peter H.

1996-01-01

Novel variation of split-waveguide mount for millimeter-and submillimeter-wavelength frequency multipliers and harmonic mixers developed. Designed to offer wide range of available matching impedances, while maintaining relatively simple fabrication sequence. Wide tuning range achieved with separate series and parallel elements, consisting of two pairs of noncontacting sliding backshorts, at fundamental and harmonic frequencies. Advantages include ease of fabrication, reliability, and tunability.

Theoretical and experimental investigation of millimeter-wave TED's in cross-waveguide oscillators

NASA Astrophysics Data System (ADS)

Rydberg, A.

1985-07-01

Theoretical and experimental investigations of millimeterwave GaAs second harmonic transferred electron device (TED) oscillators using separate circuits for frequency and power optimization, are described. The theory predicts the oscillation frequency with less than 2 percent error for the second harmonic. Apart from the 2d and 3d, a 4th harmonic from the TED was observed up to 130 GHz.

Method of detecting system function by measuring frequency response

NASA Technical Reports Server (NTRS)

Morrison, John L. (Inventor); Morrison, William H. (Inventor); Christophersen, Jon P. (Inventor)

2012-01-01

Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.

Method of detecting system function by measuring frequency response

DOEpatents

Morrison, John L [Butte, MT; Morrison, William H [Manchester, CT; Christophersen, Jon P [Idaho Falls, ID

2012-04-03

Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.

Frequency, pressure and strain dependence of nonlinear elasticity in Berea Sandstone

DOE PAGES

Riviere, Jacques; Johnson, Paul Allan; Marone, Chris; ...

2016-04-14

Acoustoelasticity measurements in a sample of room dry Berea sandstone are conducted at various loading frequencies to explore the transition between the quasi-static ( f → 0) and dynamic (few kilohertz) nonlinear elastic response. We carry out these measurements at multiple confining pressures and perform a multivariate regression analysis to quantify the dependence of the harmonic content on strain amplitude, frequency, and pressure. The modulus softening (equivalent to the harmonic at 0f) increases by a factor 2–3 over 3 orders of magnitude increase in frequency. Harmonics at 2f, 4f, and 6f exhibit similar behaviors. In contrast, the harmonic at 1fmore » appears frequency independent. This result corroborates previous studies showing that the nonlinear elasticity of rocks can be described with a minimum of two physical mechanisms. This study provides quantitative data that describes the rate dependency of nonlinear elasticity. Furthermore, these findings can be used to improve theories relating the macroscopic elastic response to microstructural features.« less

Low-frequency approximation for high-order harmonic generation by a bicircular laser field

NASA Astrophysics Data System (ADS)

Milošević, D. B.

2018-01-01

We present low-frequency approximation (LFA) for high-order harmonic generation (HHG) process. LFA represents the lowest-order term of an expansion of the final-state interaction matrix element in powers of the laser-field frequency ω . In this approximation the plane-wave recombination matrix element which appears in the strong-field approximation is replaced by the exact laser-free recombination matrix element calculated for the laser-field dressed electron momenta. First, we have shown that the HHG spectra obtained using the LFA agree with those obtained solving the time-dependent Schrödinger equation. Next, we have applied this LFA to calculate the HHG rate for inert gases exposed to a bicircular field. The bicircular field, which consists of two coplanar counter-rotating fields having different frequencies (usually ω and 2 ω ), is presently an important subject of scientific research since it enables efficient generation of circularly polarized high-order harmonics (coherent soft x rays). Analyzing the photorecombination matrix element we have found that the HHG rate can efficiently be calculated using the angular momentum basis with the states oriented in the direction of the bicircular field components. Our numerical results show that the HHG rate for atoms having p ground state, for higher high-order harmonic energies, is larger for circularly polarized harmonics having the helicity -1 . For lower energies the harmonics having helicity +1 prevails. The transition between these two harmonic energy regions can appear near the Cooper minimum, which, in the case of Ar atoms, makes the selection of high-order harmonics having the same helicity much easier. This is important for applications (for example, for generation of attosecond pulse trains of circularly polarized harmonics).

Examining the impact of harmonic correlation on vibrational frequencies calculated in localized coordinates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson-Heine, Magnus W. D., E-mail: magnus.hansonheine@nottingham.ac.uk

Carefully choosing a set of optimized coordinates for performing vibrational frequency calculations can significantly reduce the anharmonic correlation energy from the self-consistent field treatment of molecular vibrations. However, moving away from normal coordinates also introduces an additional source of correlation energy arising from mode-coupling at the harmonic level. The impact of this new component of the vibrational energy is examined for a range of molecules, and a method is proposed for correcting the resulting self-consistent field frequencies by adding the full coupling energy from connected pairs of harmonic and pseudoharmonic modes, termed vibrational self-consistent field (harmonic correlation). This approach ismore » found to lift the vibrational degeneracies arising from coordinate optimization and provides better agreement with experimental and benchmark frequencies than uncorrected vibrational self-consistent field theory without relying on traditional correlated methods.« less

Comparison of filtering methods for extracellular gastric slow wave recordings.

PubMed

Paskaranandavadivel, Niranchan; O'Grady, Gregory; Du, Peng; Cheng, Leo K

2013-01-01

Extracellular recordings are used to define gastric slow wave propagation. Signal filtering is a key step in the analysis and interpretation of extracellular slow wave data; however, there is controversy and uncertainty regarding the appropriate filtering settings. This study investigated the effect of various standard filters on the morphology and measurement of extracellular gastric slow waves. Experimental extracellular gastric slow waves were recorded from the serosal surface of the stomach from pigs and humans. Four digital filters: finite impulse response filter (0.05-1 Hz); Savitzky-Golay filter (0-1.98 Hz); Bessel filter (2-100 Hz); and Butterworth filter (5-100 Hz); were applied on extracellular gastric slow wave signals to compare the changes temporally (morphology of the signal) and spectrally (signals in the frequency domain). The extracellular slow wave activity is represented in the frequency domain by a dominant frequency and its associated harmonics in diminishing power. Optimal filters apply cutoff frequencies consistent with the dominant slow wave frequency (3-5 cpm) and main harmonics (up to ≈ 2 Hz). Applying filters with cutoff frequencies above or below the dominant and harmonic frequencies was found to distort or eliminate slow wave signal content. Investigators must be cognizant of these optimal filtering practices when detecting, analyzing, and interpreting extracellular slow wave recordings. The use of frequency domain analysis is important for identifying the dominant and harmonics of the signal of interest. Capturing the dominant frequency and major harmonics of slow wave is crucial for accurate representation of slow wave activity in the time domain. Standardized filter settings should be determined. © 2012 Blackwell Publishing Ltd.

Coherence-domain imaging with harmonic holography

NASA Astrophysics Data System (ADS)

Pu, Ye; Psaltis, Demetri

2017-08-01

Observing the fast dynamics of specific molecules or targets in three-dimensional (3D) space and time inside a crowded and complex environment, such as living cells or tissues, remain one of the grand open challenges in modern science. Harmonic holography tackle this challenge by combining the 3D imaging capability of holography with the ultrafast, coherent optical contrast offered by second-harmonic radiating imaging probes (SHRIMPs). Similar to fluorescence, the second-harmonic signal emitted from SHRIMPs provides a color contrast against the uninterested background scattering, which can be efficiently suppressed by an optical filter. We review the latest developments in SHRIMPs and harmonic holography and discuss their further applications in fluidics and biofluidics.

Multimode Directional Coupler for Utilization of Harmonic Frequencies from TWTAs

NASA Technical Reports Server (NTRS)

Simmons, Rainee N.; Wintucky, Edwin G.

2013-01-01

A novel waveguide multimode directional coupler (MDC) intended for the measurement and potential utilization of the second and higher order harmonic frequencies from high-power traveling wave tube amplifiers (TWTAs) has been successfully designed, fabricated, and tested. The design is based on the characteristic multiple propagation modes of the electrical and magnetic field components of electromagnetic waves in a rectangular waveguide. The purpose was to create a rugged, easily constructed, more efficient waveguide- based MDC for extraction and exploitation of the second harmonic signal from the RF output of high-power TWTs used for space communications. The application would be a satellitebased beacon source needed for Qband and V/W-band atmospheric propagation studies. The MDC could function as a CW narrow-band source or as a wideband source for study of atmospheric group delay effects on highdata- rate links. The MDC is fabricated from two sections of waveguide - a primary one for the fundamental frequency and a secondary waveguide for the second harmonic - that are joined together such that the second harmonic higher order modes are selectively coupled via precision- machined slots for propagation in the secondary waveguide. In the TWTA output waveguide port, both the fundamental and the second harmonic signals are present. These signals propagate in the output waveguide as the dominant and higher order modes, respectively. By including an appropriate mode selective waveguide directional coupler, such as the MDC presented here at the output of the TWTA, the power at the second harmonic can be sampled and amplified to the power level needed for atmospheric propagation studies. The important conclusions from the preliminary test results for the multimode directional coupler are: (1) the second harmonic (Ka-band) can be measured and effectively separated from the fundamental (Ku-band) with no coupling of the latter, (2) power losses in the fundamental frequency are negligible, and (3) the power level of the extracted second harmonic is sufficient for further amplification to power levels needed for practical applications. It was also demonstrated that third order and potentially higher order harmonics are measurable with this device. The design is frequency agnostic, and with the appropriate choice of waveguides, is easily scaled to higher frequency TWTs. The MDC has the same function but with a number of important advantages over the conventional diplexer.

Ultrafast nanoscale imaging using high order harmonic generation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Merdji, Hamed

2017-05-01

Ultrafast coherent diffraction using soft and hard X-rays is actually revolutionizing imaging science thanks to new sources recently available. This powerful technique extends standard X-ray diffraction towards imaging of non-crystalline objects and leads actually to a strong impact in physics, chemistry and biology. New ultrashort pulses recently available hold the promise of watching matter evolving with unprecedented space and time resolution. Femtosecond coherent and intense radiation in the soft X-ray (λ = 10-40 nm) is currently produced in our laboratory, from highly non linear frequency conversion (high harmonic generation). A high intensity UV-X coherent beam is obtained using a loose focusing geometry, which allows coupling a very high amount of Ti:Sapphire laser system energy in the HHG process. Using a long gas cell and a long focal length lens, the emitting volume can be increased by orders of magnitude compared to standard HHG set-ups. This approach, allows reaching up to 1x1011 photons per shot for the 25th harmonic (λ=32nm). We have already demonstrated nanoscale imaging in a single shot mode reaching 70 nm spatial resolution and 20 femtoseconds snapshot [1]. We then implemented a recently proposed holographic technique using extended references. This technique, easy to implement, allows a direct non iterative image reconstruction. In the single shot regime, we demonstrated a spatial resolution of 110nm [2].This opens fascinating perspectives in imaging dynamical phenomena to be spread over a large scientific community. I will present recent results in the investigation of femtosecond phase spin-reversals of magnetic nano-domains [3]. Finally, I will report on recent development on noise sensitivity of the technique and perspectives in attosecond coherent imaging [4]. [1] A. Ravasio et al., Physical Review Letters 103, 028104 (2009). [2] D. Gauthier et al., Physical Review Letters 105, 093901 (2010). [3] Vodungbo et al., Nature Communications 3, 999 (2012) [4] Williams et al., Optics Letters 40 (13), 3205 (2015)

Actuation of atomic force microscopy microcantilevers using contact acoustic nonlinearities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Torello, D.; Degertekin, F. Levent, E-mail: levent.degertekin@me.gatech.edu

2013-11-15

A new method of actuating atomic force microscopy (AFM) cantilevers is proposed in which a high frequency (>5 MHz) wave modulated by a lower frequency (∼300 kHz) wave passes through a contact acoustic nonlinearity at the contact interface between the actuator and the cantilever chip. The nonlinearity converts the high frequency, modulated signal to a low frequency drive signal suitable for actuation of tapping-mode AFM probes. The higher harmonic content of this signal is filtered out mechanically by the cantilever transfer function, providing for clean output. A custom probe holder was designed and constructed using rapid prototyping technologies and off-the-shelfmore » components and was interfaced with an Asylum Research MFP-3D AFM, which was then used to evaluate the performance characteristics with respect to standard hardware and linear actuation techniques. Using a carrier frequency of 14.19 MHz, it was observed that the cantilever output was cleaner with this actuation technique and added no significant noise to the system. This setup, without any optimization, was determined to have an actuation bandwidth on the order of 10 MHz, suitable for high speed imaging applications. Using this method, an image was taken that demonstrates the viability of the technique and is compared favorably to images taken with a standard AFM setup.« less

Multi-Frequency Recirculating Planar Magnetrons

NASA Astrophysics Data System (ADS)

Greening, Geoffrey Bruce

The cavity magnetron is generally accepted as the standard for compactness and high microwave power with applications in industry, science, and defense, with the latter including counter-electronics. In this application, magnetrons are limited because they are narrowband devices. To expand the range of frequencies that can be produced using a single magnetron, a novel multi-frequency variant of the Recirculating Planar Magnetron (RPM) was designed, fabricated, and experimentally demonstrated. This multi-frequency RPM (MFRPM) was the first high-power magnetron capable of generating multiple microwave frequencies simultaneously and demonstrated the first known instance of harmonic frequency-locking in a magnetron. The MFRPM design consisted of two planar cavity arrays coupled by cylindrical electron recirculation bends. The two arrays formed a 1 GHz L-Band Oscillator (LBO) and a 2 GHz S-Band Oscillator (SBO). Experiments were conducted using a 0.1-0.3 T axial magnetic field produced using a pulsed pair of Helmholtz coils and a -300 kV, 200-400 ns, 1-5 kA pulse applied to a Mode-Control Cathode (MCC) using the MELBA-C Marx generator. Six experimental configurations were tested using three anodes (the isolated LBO, the isolated SBO, and the MFRPM), two microwave loads (a standard, matched load, and a waveguide taper load used to characterize the LBO frequency harmonics), and two axial magnetic fields (uniform and nonuniform). Using these configurations, an in-depth characterization of MFRPM operation determined 1) the identity of the observed electromagnetic modes, and the degree of mode competition, 2) the frequencies, powers, and other electrical characteristics associated with those modes and the LBO frequency harmonics, 3) the magnetic fields corresponding to optimal operation, 4) the operational impact of a nonuniform axial magnetic field, and 5) the origin and performance characteristics of a novel harmonic frequency-locked state observed in the MFRPM. The uniform magnetic field consistently yielded better performance relative to the nonuniform magnetic field. In the harmonic frequency-locked state at 0.17 T with the uniform magnetic field, the MFRPM LBO produced 32 +/- 3 MW at 0.984 +/- 0.001 GHz, and the SBO produced 13 +/- 2 MW at 1.970 +/- 0.002 GHz. Relative to the other operating states, the locked state was remarkably consistent. In B = 0.16-0.17 T, the phase drift during a typical locked shot was 8 +/- 4°, and the lock duration was 14 +/- 3 ns. The average phase difference between the oscillators was 93+/-17°. The locking appeared to be Adler-like, where the LBO was the driving oscillator and the SBO was the driven oscillator. Changes in the relative phase difference between the oscillators correlated with changes in the magnetic field, suggesting the coupling occurred through the second harmonic content of the LBO-modulated electron beam as it propagated from the LBO to the SBO. A comparison of the experimental results for this locked state with a new theory for harmonic locking was inconclusive. Using the uniform magnetic field at 0.17 T, the LBO second harmonic power was 178 +/- 60 kW at 1.962 +/- 0.013 GHz. The LBO fourth harmonic power was 5 +/- 1 kW at 3.916 +/- 0.018 GHz. In general, LBO harmonic powers increased when the fundamental circuit modes were operating at reduced power with considerable mode competition. Harmonic powers were also as much as 150% higher using the nonuniform magnetic field relative to the uniform magnetic field.

Directional enhancement of selected high-order-harmonics from intense laser irradiated blazed grating targets.

PubMed

Zhang, Guobo; Chen, Min; Liu, Feng; Yuan, Xiaohui; Weng, Suming; Zheng, Jun; Ma, Yanyun; Shao, Fuqiu; Sheng, Zhengming; Zhang, Jie

2017-10-02

Relativistically intense laser solid target interaction has been proved to be a promising way to generate high-order harmonics, which can be used to diagnose ultrafast phenomena. However, their emission direction and spectra still lack tunability. Based upon two-dimensional particle-in-cell simulations, we show that directional enhancement of selected high-order-harmonics can be realized using blazed grating targets. Such targets can select harmonics with frequencies being integer times of the grating frequency. Meanwhile, the radiation intensity and emission area of the harmonics are increased. The emission direction is controlled by tailoring the local blazed structure. Theoretical and electron dynamics analysis for harmonics generation, selection and directional enhancement from the interaction between multi-cycle laser and grating target are carried out. These studies will benefit the generation and application of laser plasma-based high order harmonics.

A novel speech processing algorithm based on harmonicity cues in cochlear implant

NASA Astrophysics Data System (ADS)

Wang, Jian; Chen, Yousheng; Zhang, Zongping; Chen, Yan; Zhang, Weifeng

2017-08-01

This paper proposed a novel speech processing algorithm in cochlear implant, which used harmonicity cues to enhance tonal information in Mandarin Chinese speech recognition. The input speech was filtered by a 4-channel band-pass filter bank. The frequency ranges for the four bands were: 300-621, 621-1285, 1285-2657, and 2657-5499 Hz. In each pass band, temporal envelope and periodicity cues (TEPCs) below 400 Hz were extracted by full wave rectification and low-pass filtering. The TEPCs were modulated by a sinusoidal carrier, the frequency of which was fundamental frequency (F0) and its harmonics most close to the center frequency of each band. Signals from each band were combined together to obtain an output speech. Mandarin tone, word, and sentence recognition in quiet listening conditions were tested for the extensively used continuous interleaved sampling (CIS) strategy and the novel F0-harmonic algorithm. Results found that the F0-harmonic algorithm performed consistently better than CIS strategy in Mandarin tone, word, and sentence recognition. In addition, sentence recognition rate was higher than word recognition rate, as a result of contextual information in the sentence. Moreover, tone 3 and 4 performed better than tone 1 and tone 2, due to the easily identified features of the former. In conclusion, the F0-harmonic algorithm could enhance tonal information in cochlear implant speech processing due to the use of harmonicity cues, thereby improving Mandarin tone, word, and sentence recognition. Further study will focus on the test of the F0-harmonic algorithm in noisy listening conditions.

Speech recognition against harmonic and inharmonic complexes: Spectral dips and periodicity

PubMed Central

Deroche, Mickael L. D.; Culling, John F.; Chatterjee, Monita; Limb, Charles J.

2014-01-01

Speech recognition in a complex masker usually benefits from masker harmonicity, but there are several factors at work. The present study focused on two of them, glimpsing spectrally in between masker partials and periodicity within individual frequency channels. Using both a theoretical and an experimental approach, it is demonstrated that when inharmonic complexes are generated by jittering partials from their harmonic positions, there are better opportunities for spectral glimpsing in inharmonic than in harmonic maskers, and this difference is enhanced as fundamental frequency (F0) increases. As a result, measurements of masking level difference between the two maskers can be reduced, particularly at higher F0s. Using inharmonic maskers that offer similar glimpsing opportunity to harmonic maskers, it was found that the masking level difference between the two maskers varied little with F0, was influenced by periodicity of the first four partials, and could occur in low-, mid-, or high-frequency regions. Overall, the present results suggested that both spectral glimpsing and periodicity contribute to speech recognition under masking by harmonic complexes, and these effects seem independent from one another. PMID:24815268

Comparison of fundamental and wideband harmonic contrast imaging of liver tumors.

PubMed

Forsberg, F; Liu, J B; Chiou, H J; Rawool, N M; Parker, L; Goldberg, B B

2000-03-01

Wideband harmonic imaging (with phase inversion for improved tissue suppression) was compared to fundamental imaging in vivo. Four woodchucks with naturally occurring liver tumors were injected with Imagent (Alliance Pharmaceutical Corp., San Diego, CA). Randomized combinations of dose (0.05, 0.2 and 0.4 ml/kg) and acoustic output power (AO; 5, 25 and 63% or MI < or = 0.9) were imaged in gray scale using a Sonoline Elegra scanner (Siemens Medical Systems, Issaquah, WA). Tumor vascularity, conspicuity and contrast enhancement were rated by three independent observers. Imagent produced marked tumor enhancement and improved depiction of neovascularity at all dosages and AO settings in both modes. Tumor vascularity and enhancement correlated with mode, dose and AO (P < 0.002). Fundamental imaging produced more enhancement (P < 0.05), but tumor vascularity and conspicuity were best appreciated in harmonic mode (P < 0.05). Under the conditions studied here, the best approach was wideband harmonic imaging with 0.2 ml/kg of Imagent at an AO of 25%.

Nonlinear oscillation and interfacial stability of an encapsulated microbubble under dual-frequency ultrasound

NASA Astrophysics Data System (ADS)

Liu, Yunqiao; Calvisi, Michael L.; Wang, Qianxi

2017-04-01

Encapsulated microbubbles (EMBs) are widely used in medical ultrasound imaging as contrast-enhanced agents. However, the potential damaging effects of violent collapsing EMBs to cells and tissues in clinical settings have remained a concern. Dual-frequency ultrasound is a promising technique for improving the efficacy and safety of sonography. The system modeled consists of the external liquid, membrane and internal gases of an EMB. The microbubble dynamics are simulated using a simple nonlinear interactive theory, considering the compressibility of the internal gas, viscosity of the liquid flow and viscoelasticity of the membrane. The radial oscillation and interfacial stability of an EMB under single- and dual-frequency excitations are compared. The simulation results show that the dual-frequency technique produces larger backscatter pressure at higher harmonics of the primary driving frequency—this enriched acoustic spectrum can enhance blood-tissue contrast and improve the quality of sonographic images. The results further show that the acoustic pressure threshold associated with the onset of shape instability is greater for dual-frequency driving. This suggests that the dual-frequency technique stabilizes the encapsulated bubble, thereby improving the efficacy and safety of contrast-enhanced agents.

Hyperspectral imaging with laser-scanning sum-frequency generation microscopy

PubMed Central

Hanninen, Adam; Shu, Ming Wai; Potma, Eric O.

2017-01-01

Vibrationally sensitive sum-frequency generation (SFG) microscopy is a chemically selective imaging technique sensitive to non-centrosymmetric molecular arrangements in biological samples. The routine use of SFG microscopy has been hampered by the difficulty of integrating the required mid-infrared excitation light into a conventional, laser-scanning nonlinear optical (NLO) microscope. In this work, we describe minor modifications to a regular laser-scanning microscope to accommodate SFG microscopy as an imaging modality. We achieve vibrationally sensitive SFG imaging of biological samples with sub-μm resolution at image acquisition rates of 1 frame/s, almost two orders of magnitude faster than attained with previous point-scanning SFG microscopes. Using the fast scanning capability, we demonstrate hyperspectral SFG imaging in the CH-stretching vibrational range and point out its use in the study of molecular orientation and arrangement in biologically relevant samples. We also show multimodal imaging by combining SFG microscopy with second-harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) on the same imaging platfrom. This development underlines that SFG microscopy is a unique modality with a spatial resolution and image acquisition time comparable to that of other NLO imaging techniques, making point-scanning SFG microscopy a valuable member of the NLO imaging family. PMID:28966861

Multiple layer optical memory system using second-harmonic-generation readout

DOEpatents

Boyd, Gary T.; Shen, Yuen-Ron

1989-01-01

A novel optical read and write information storage system is described which comprises a radiation source such as a laser for writing and illumination, the radiation source being capable of radiating a preselected first frequency; a storage medium including at least one layer of material for receiving radiation from the radiation source and capable of being surface modified in response to said radiation source when operated in a writing mode and capable of generating a pattern of radiation of the second harmonic of the preselected frequency when illuminated by the radiation source at the preselected frequency corresponding to the surface modifications on the storage medium; and a detector to receive the pattern of second harmonic frequency generated.

Tracking Helicopters with a Seismic Array

NASA Astrophysics Data System (ADS)

Eibl, Eva P. S.; Lokmer, Ivan; Bean, Christopher J.; Akerlie, Eggert

2015-04-01

We observed that the pressure or acoustic wave created by the rotor blades of a helicopter can couple to the ground even at 30 km distance where it creates a signal strong enough to be detected by a seismometer. The signal is harmonic tremor with a fundamental frequency downgliding with the inflection point at e.g. 14 Hz and two equally spaced overtones up to the Nyquist frequency of 50 Hz. No difference in the amplitudes between the fundamental frequency and higher harmonics was observed. Such a signature is a consequence of the regularly repeating pressure pulses generated by the helicopter's rotor blades. The signal was recorded by a seven station broadband array with an aperture of 1.6 km. Our spacing is close enough to record the signal at all stations and far enough to observe traveltime differences. The separation of the spectral lines corresponds to the time interval between the repeating sources. The highlighted harmonics contain information about the spectral content of the single source as our signal corresponds to the convolution of an infinite comb function and a single pulse. As we see all harmonics and they have the same amplitude up to the Nyquist frequency we can deduce that the frequency content of the single pulse is flat i.e. it is effectively a delta function up to the Nyquist frequency. We perform a detailed spectral and location analysis of the signal, and compare our results with the known information on the helicopter's speed, location, the frequency of the blades rotation and the amount of blades. This analysis is based on the characteristic shape of the curve i.e. speed of the gliding, minimum and maximum fundamental frequency, amplitudes at the inflection points at different stations and traveltimes deduced from the inflection points at different stations. This observation has an educative value, because the same principle could be used for the analysis of the volcanic harmonic tremor. Harmonic volcanic tremor usually has fundamental frequencies below 10 Hz but frequency downgliding and upgliding up to 30 Hz was observed e.g. on Redoubt volcano. Due to the characteristic shape of the helicopter signal it is nevertheless rather unlikely that this signal is mistaken for volcanic tremor. The helicopter gives us a robust way of testing the method and possible application of the method to volcanic harmonic tremor.

A parametric study of face recognition when image degradations are combined.

PubMed

Uttal, W R; Baruch, T; Allen, L

1997-01-01

This article expands and quantifies one of the classic reports of modern visual perception research--Harmon and Julesz' (1973) demonstration of an enhancement in recognition performance when area averaging (blocking) and spatial frequency filtering are sequentially applied. Our goals were twofold: first, to determine if the existence of the phenomena could be confirmed and replicated in a parametric study; second, to determine if the new results supported the critical band masking theory originally proposed by Harmon and Julesz. We confirmed the presence of the phenomenon for stimuli subtending approximately six deg of visual angle vertically, but observed a surprisingly different pattern of results for smaller stimuli subtending approximately one deg. These and other recent findings from other laboratories raise questions about their masking theory as a complete explanation of the phenomena.

Towards a Compact Fiber Laser for Multimodal Imaging

NASA Astrophysics Data System (ADS)

Nie, Bai; Saytashev, Ilyas; Dantus, Marcos

We report on multimodal depth-resolved imaging of unstained living Drosophila Melanogaster larva using sub-50 fs pulses centered at 1060 nm wavelength. Both second harmonic and third harmonic generation imaging modalities are demonstrated.

Towards a compact fiber laser for multimodal imaging

NASA Astrophysics Data System (ADS)

Nie, Bai; Saytashev, Ilyas; Dantus, Marcos

2014-03-01

We report on multimodal depth-resolved imaging of unstained living Drosophila Melanogaster larva using sub-50 fs pulses centered at 1060 nm wavelength. Both second harmonic and third harmonic generation imaging modalities are demonstrated.

Real time analysis of voiced sounds

NASA Technical Reports Server (NTRS)

Hong, J. P. (Inventor)

1976-01-01

A power spectrum analysis of the harmonic content of a voiced sound signal is conducted in real time by phase-lock-loop tracking of the fundamental frequency, (f sub 0) of the signal and successive harmonics (h sub 1 through h sub n) of the fundamental frequency. The analysis also includes measuring the quadrature power and phase of each frequency tracked, differentiating the power measurements of the harmonics in adjacent pairs, and analyzing successive differentials to determine peak power points in the power spectrum for display or use in analysis of voiced sound, such as for voice recognition.

Power supply and impedance matching to drive technological radio-frequency plasmas with customized voltage waveforms.

PubMed

Franek, James; Brandt, Steven; Berger, Birk; Liese, Martin; Barthel, Matthias; Schüngel, Edmund; Schulze, Julian

2015-05-01

We present a novel radio-frequency (RF) power supply and impedance matching to drive technological plasmas with customized voltage waveforms. It is based on a system of phase-locked RF generators that output single frequency voltage waveforms corresponding to multiple consecutive harmonics of a fundamental frequency. These signals are matched individually and combined to drive a RF plasma. Electrical filters are used to prevent parasitic interactions between the matching branches. By adjusting the harmonics' phases and voltage amplitudes individually, any voltage waveform can be approximated as a customized finite Fourier series. This RF supply system is easily adaptable to any technological plasma for industrial applications and allows the commercial utilization of process optimization based on voltage waveform tailoring for the first time. Here, this system is tested on a capacitive discharge based on three consecutive harmonics of 13.56 MHz. According to the Electrical Asymmetry Effect, tuning the phases between the applied harmonics results in an electrical control of the DC self-bias and the mean ion energy at almost constant ion flux. A comparison with the reference case of an electrically asymmetric dual-frequency discharge reveals that the control range of the mean ion energy can be significantly enlarged by using more than two consecutive harmonics.

Harmonic Phase Response of Nonlinear Radar Targets

DTIC Science & Technology

2015-10-01

while allowing its harmonics to pass through. The weak harmonic responses are then amplified to allow for easier detection and measurement . 4...where the phase of the 2nd and 3rd harmonic of the received electromagnetic wave from nonlinear targets was measured and plotted against the frequency

Generalized Wideband Harmonic Imaging of Nonlinearly Loaded Scatterers: Theory, Analysis, and Application for Forward-Looking Radar Target Detection

DTIC Science & Technology

2014-09-01

signal) operations; it is general enough so that it can accommodate high - power (large-signal) sensing as well—which may be needed to detect targets... Generalized Wideband Harmonic Imaging of Nonlinearly Loaded Scatterers: Theory, Analysis, and Application for Forward-Looking Radar Target...Research Laboratory Adelphi, MD 20783-1138 ARL-TR-7121 September 2014 Generalized Wideband Harmonic Imaging of Nonlinearly Loaded

Divergent oral cavity motor strategies between healthy elite and dystonic horn players.

PubMed

Iltis, Peter W; Frahm, Jens; Voit, Dirk; Joseph, Arun; Schoonderwaldt, Erwin; Altenmüller, Eckart

2015-01-01

This paper describes the use of real-time magnetic resonance imaging in visualizing and quantifying oral cavity motor strategies employed by 6 healthy, elite horn players and 5 horn players with embouchure dystonia. Serial images with an acquisition time of 33.3 ms were obtained from each performer during execution of an 11-note harmonic series encompassing 2.5 octaves on a magnetic resonance imaging-compatible horn. A customized MATLAB toolkit was employed for the extraction of line profiles from magnetic resonance imaging films allowing comparative analyses between elite and dystonic horn players. The data demonstrate differing motor strategies, particularly in moving from the 6th through 9th harmonics. The elite horn player strategy features elevation and anterior displacement of the tongue during ascending sequences, whereas dystonic players showed significantly less movement. The elite horn players thus narrowed the air channel on higher notes, presumably affording faster airflow for vibration of the lips at higher frequencies. We postulate that failure to employ this strategy by dystonic horn players may require greater tension in the embouchure muscles to compensate for slower air speed. Though this may simply be an expression of or adaptation for dystonia, the possibility that it may be a contributing factor in the development of embouchure dystonia is suggested.

Frequency-doubled vertical-external-cavity surface-emitting laser

DOEpatents

Raymond, Thomas D.; Alford, William J.; Crawford, Mary H.; Allerman, Andrew A.

2002-01-01

A frequency-doubled semiconductor vertical-external-cavity surface-emitting laser (VECSEL) is disclosed for generating light at a wavelength in the range of 300-550 nanometers. The VECSEL includes a semiconductor multi-quantum-well active region that is electrically or optically pumped to generate lasing at a fundamental wavelength in the range of 600-1100 nanometers. An intracavity nonlinear frequency-doubling crystal then converts the fundamental lasing into a second-harmonic output beam. With optical pumping with 330 milliWatts from a semiconductor diode pump laser, about 5 milliWatts or more of blue light can be generated at 490 nm. The device has applications for high-density optical data storage and retrieval, laser printing, optical image projection, chemical-sensing, materials processing and optical metrology.

A Novel Ku-Band/Ka-Band and Ka-Band/E-Band Multimode Waveguide Couplers for Power Measurement of Traveling-Wave Tube Amplifier Harmonic Frequencies

NASA Technical Reports Server (NTRS)

Wintucky, Edwin G.; Simons, Rainee N.

2015-01-01

This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler, fabricated from two dissimilar frequency band waveguides, is capable of isolating power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT) amplifier. Test results from proof-of-concept demonstrations are presented for a Ku-band/Ka-band MDC and a Ka-band/E-band MDC. In addition to power measurements at harmonic frequencies, a potential application of the MDC is in the design of a satellite borne beacon source for atmospheric propagation studies at millimeter-wave (mm-wave) frequencies (Ka-band and E-band).

Mechanisms of high-frequency song generation in brachypterous crickets and the role of ghost frequencies.

PubMed

Robillard, Tony; Montealegre-Z, Fernando; Desutter-Grandcolas, Laure; Grandcolas, Philippe; Robert, Daniel

2013-06-01

Sound production in crickets relies on stridulation, the well-understood rubbing together of a pair of specialised wings. As the file of one wing slides over the scraper of the other, a series of rhythmic impacts causes harmonic oscillations, usually resulting in the radiation of pure tones delivered at low frequencies (2-8 kHz). In the short-winged crickets of the Lebinthini tribe, acoustic communication relies on signals with remarkably high frequencies (>8 kHz) and rich harmonic content. Using several species of the subfamily Eneopterinae, we characterised the morphological and mechanical specialisations supporting the production of high frequencies, and demonstrated that higher harmonics are exploited as dominant frequencies. These specialisations affect the structure of the stridulatory file, the motor control of stridulation and the resonance of the sound radiator. We placed these specialisations in a phylogenetic framework and show that they serve to exploit high-frequency vibrational modes pre-existing in the phylogenetic ancestor. In Eneopterinae, the lower frequency components are harmonically related to the dominant peak, suggesting they are relicts of ancestral carrier frequencies. Yet, such ghost frequencies still occur in the wings' free resonances, highlighting the fundamental mechanical constraints of sound radiation. These results support the hypothesis that such high-frequency songs evolved stepwise, by a form of punctuated evolution that could be related to functional constraints, rather than by only the progressive increase of the ancestral fundamental frequency.

Range side lobe inversion for chirp-encoded dual-band tissue harmonic imaging.

PubMed

Shen, Che-Chou; Peng, Jun-Kai; Wu, Chi

2014-02-01

Dual-band (DB) harmonic imaging is performed by transmitting and receiving at both fundamental band (f0) and second-harmonic band (2f0). In our previous work, particular chirp excitation has been developed to increase the signal- to-noise ratio in DB harmonic imaging. However, spectral overlap between the second-order DB harmonic signals results in range side lobes in the pulse compression. In this study, a novel range side lobe inversion (RSI) method is developed to alleviate the level of range side lobes from spectral overlap. The method is implemented by firing an auxiliary chirp to change the polarity of the range side lobes so that the range side lobes can be suppressed in the combination of the original chirp and the auxiliary chirp. Hydrophone measurements show that the RSI method reduces the range side lobe level (RSLL) and thus increases the quality of pulse compression in DB harmonic imaging. With the signal bandwidth of 60%, the RSLL decreases from -23 dB to -36 dB and the corresponding compression quality improves from 78% to 94%. B-mode images also indicate that the magnitude of range side lobe is suppressed by 7 dB when the RSI method is applied.

Characterization of Deficiencies in the Frequency Domain Forced Response Analysis Technique for Supersonic Turbine Bladed Disks

NASA Technical Reports Server (NTRS)

Brown, Andrew M.; Schmauch, Preston

2011-01-01

Turbine blades in rocket and jet engine turbomachinery experience enormous harmonic loading conditions. These loads result from the integer number of upstream and downstream stator vanes as well as the other turbine stages. Assessing the blade structural integrity is a complex task requiring an initial characterization of whether resonance is possible and then performing a forced response analysis if that condition is met. The standard technique for forced response analysis in rocket engines is to decompose a CFD-generated flow field into its harmonic components, and to then perform a frequency response analysis at the problematic natural frequencies. Recent CFD analysis and water-flow testing at NASA/MSFC, though, indicates that this technique may miss substantial harmonic and non-harmonic excitation sources that become present in complex flows. A substantial effort has been made to account for this denser spatial Fourier content in frequency response analysis (described in another paper by the author), but the question still remains whether the frequency response analysis itself is capable of capturing the excitation content sufficiently. Two studies comparing frequency response analysis with transient response analysis, therefore, of bladed-disks undergoing this complex flow environment have been performed. The first is of a bladed disk with each blade modeled by simple beam elements. Six loading cases were generated by varying a baseline harmonic excitation in different ways based upon cold-flow testing from Heritage Fuel Air Turbine Test. It was hypothesized that the randomness and other variation from the standard harmonic excitation would reduce the blade structural response, but the results showed little reduction. The second study was of a realistic model of a bladed-disk excited by the same CFD used in the J2X engine program. It was hypothesized that enforcing periodicity in the CFD (inherent in the frequency response technique) would overestimate the response. The results instead showed that the transient analysis results were up to 10% higher for "clean" nodal diameter excitations and six times larger for "messy" excitations, where substantial Fourier content around the main harmonic exists. Because the bulk of resonance problems are due to the "clean" excitations, a 10% underprediction is not necessarily a problem, especially since the average response in the transient is similar to the frequency response result, and so in a realistic finite life calculation, the life would be same. However, in the rare cases when the "messy" excitations harmonics are identified as the source of potential resonance concerns, this research does indicate that frequency response analysis is inadequate for accurate characterization of blade structural capability.

Improvement of Shear Wave Motion Detection Using Harmonic Imaging in Healthy Human Liver.

PubMed

Amador, Carolina; Song, Pengfei; Meixner, Duane D; Chen, Shigao; Urban, Matthew W

2016-05-01

Quantification of liver elasticity is a major application of shear wave elasticity imaging (SWEI) to non-invasive assessment of liver fibrosis stages. SWEI measurements can be highly affected by ultrasound image quality. Ultrasound harmonic imaging has exhibited a significant improvement in ultrasound image quality as well as for SWEI measurements. This was previously illustrated in cardiac SWEI. The purpose of this study was to evaluate liver shear wave particle displacement detection and shear wave velocity (SWV) measurements with fundamental and filter-based harmonic ultrasound imaging. In a cohort of 17 patients with no history of liver disease, a 2.9-fold increase in maximum shear wave displacement, a 0.11 m/s decrease in the overall interquartile range and median SWV and a 17.6% increase in the success rate of SWV measurements were obtained when filter-based harmonic imaging was used instead of fundamental imaging. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Magnetic-Field-Response Measurement-Acquisition System

NASA Technical Reports Server (NTRS)

Woodward, Stanley E.; Shams, Qamar A.; Fox, Robert L.; Taylor, Bryant D.

2006-01-01

A measurement-acquisition system uses magnetic fields to power sensors and to acquire measurements from sensors. The system alleviates many shortcomings of traditional measurement-acquisition systems, which include a finite number of measurement channels, weight penalty associated with wires, use limited to a single type of measurement, wire degradation due to wear or chemical decay, and the logistics needed to add new sensors. Eliminating wiring for acquiring measurements can alleviate potential hazards associated with wires, such as damaged wires becoming ignition sources due to arcing. The sensors are designed as electrically passive inductive-capacitive or passive inductive-capacitive-resistive circuits that produce magnetic-field-responses. One or more electrical parameters (inductance, capacitance, and resistance) of each sensor can be variable and corresponds to a measured physical state of interest. The magnetic-field- response attributes (frequency, amplitude, and bandwidth) of the inductor correspond to the states of physical properties for which each sensor measures. For each sensor, the measurement-acquisition system produces a series of increasing magnetic-field harmonics within a frequency range dedicated to that sensor. For each harmonic, an antenna electrically coupled to an oscillating current (the frequency of which is that of the harmonic) produces an oscillating magnetic field. Faraday induction via the harmonic magnetic fields produces an electromotive force and therefore a current in the sensor. Once electrically active, the sensor produces its own harmonic magnetic field as the inductor stores and releases magnetic energy. The antenna of the measurement- acquisition system is switched from a transmitting to a receiving mode to acquire the magnetic-field response of the sensor. The rectified amplitude of the received response is compared to previous responses to prior transmitted harmonics, to ascertain if the measurement system has detected a response inflection. The "transmit-receive-compare" of sequential harmonics is repeated until the inflection is identified. The harmonic producing the amplitude inflection is the sensor resonant frequency. Resonant frequency and response amplitude are stored and then correlated to calibration data.

Comparison of mechanisms involved in image enhancement of Tissue Harmonic Imaging

NASA Astrophysics Data System (ADS)

Cleveland, Robin O.; Jing, Yuan

2006-05-01

Processes that have been suggested as responsible for the improved imaging in Tissue Harmonic Imaging (THI) include: 1) reduced sensitivity to reverberation, 2) reduced sensitivity to aberration, and 3) reduction in the amplitude of diffraction side lobes. A three-dimensional model of the forward propagation of nonlinear sound beams in media with arbitrary spatial properties (a generalized KZK equation) was developed and solved using a time-domain code. The numerical simulations were validated through experiments with tissue mimicking phantoms. The impact of aberration from tissue-like media was determined through simulations using three-dimensional maps of tissue properties derived from datasets available through the Visible Female Project. The experiments and simulations demonstrated that second harmonic imaging suffers less clutter from reverberation and side-lobes but is not immune to aberration effects. The results indicate that side lobe suppression is the most significant reason for the improvement of second harmonic imaging.

Two-harmonic complex spectral-domain optical coherence tomography using achromatic sinusoidal phase modulation

NASA Astrophysics Data System (ADS)

Lu, Sheng-Hua; Huang, Siang-Ru; Chou, Che-Chung

2018-03-01

We resolve the complex conjugate ambiguity in spectral-domain optical coherence tomography (SD-OCT) by using achromatic two-harmonic method. Unlike previous researches, the optical phase of the fiber interferometer is modulated by an achromatic phase shifter based on an optical delay line. The achromatic phase modulation leads to a wavelength-independent scaling coefficient for the two harmonics. Dividing the mean absolute value of the first harmonic by that of the second harmonic in a B-scan interferogram directly gives the scaling coefficient. It greatly simplifies the determination of the magnitude ratio between the two harmonics without the need of third harmonic and cumbersome iterative calculations. The inverse fast Fourier transform of the complex-valued interferogram constructed with the scaling coefficient, first and second harmonics yields a full-range OCT image. Experimental results confirm the effectiveness of the proposed achromatic two-harmonic technique for suppressing the mirror artifacts in SD-OCT images.

Second Harmonic Imaging improves Echocardiograph Quality on board the International Space Station

NASA Technical Reports Server (NTRS)

Garcia, Kathleen; Sargsyan, Ashot; Hamilton, Douglas; Martin, David; Ebert, Douglas; Melton, Shannon; Dulchavsky, Scott

2008-01-01

Ultrasound (US) capabilities have been part of the Human Research Facility (HRF) on board the International Space Station (ISS) since 2001. The US equipment on board the ISS includes a first-generation Tissue Harmonic Imaging (THI) option. Harmonic imaging (HI) is the second harmonic response of the tissue to the ultrasound beam and produces robust tissue detail and signal. Since this is a first-generation THI, there are inherent limitations in tissue penetration. As a breakthrough technology, HI extensively advanced the field of ultrasound. In cardiac applications, it drastically improves endocardial border detection and has become a common imaging modality. U.S. images were captured and stored as JPEG stills from the ISS video downlink. US images with and without harmonic imaging option were randomized and provided to volunteers without medical education or US skills for identification of endocardial border. The results were processed and analyzed using applicable statistical calculations. The measurements in US images using HI improved measurement consistency and reproducibility among observers when compared to fundamental imaging. HI has been embraced by the imaging community at large as it improves the quality and data validity of US studies, especially in difficult-to-image cases. Even with the limitations of the first generation THI, HI improved the quality and measurability of many of the downlinked images from the ISS and should be an option utilized with cardiac imaging on board the ISS in all future space missions.

Polydyne displacement interferometer using frequency-modulated light

NASA Astrophysics Data System (ADS)

Arablu, Masoud; Smith, Stuart T.

2018-05-01

A radio-frequency Frequency-Modulated (FM) signal is used to diffract a He-Ne laser beam through an Acousto-Optic Modulator (AOM). Due to the modulation of the FM signal, the measured spectra of the diffracted beams comprise a series of phase-synchronized harmonics that have exact integer frequency separation. The first diffraction side-beam emerging from the AOM is selected by a slit to be used in a polydyne displacement interferometer in a Michelson interferometer topology. The displacement measurement is derived from the phase measurement of selected modulation harmonic pairs. Individual harmonic frequency amplitudes are measured using discrete Fourier transform applied to the signal from a single photodetector. Phase signals are derived from the changes in the amplitudes of different harmonic pairs (typically odd-even pairs) with the phase being extracted using a standard quadrature method. In this study, two different modulation frequencies of 5 and 10 kHz are used at different modulation depths. The measured displacements by different harmonic pairs are compared with a commercial heterodyne interferometer being used as a reference for these studies. Measurements obtained from five different harmonic pairs when the moving mirror of the interferometer is scanned over ranges up to 10 μm all show differences of less than 50 nm from the reference interferometer measurements. A drift test was also used to evaluate the differences between the polydyne interferometer and reference measurements that had different optical path lengths of approximately 25 mm and 50 mm, respectively. The drift test results indicate that about half of the differences can be attributed to temperature, pressure, and humidity variations. Other influences include Abbe and thermal expansion effects. Rough magnitude estimates using simple models for these two effects can account for remaining observed deviations.

Double and triple-harmonic RF buckets and their use for bunch squeezing in AGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gardner, C. J.

2016-08-24

For the past several years we have merged bunches in AGS in order to achieve the desired intensity per bunch prior to injection into RHIC. The merging is done on a flat porch at or above AGS injection energy. Because the merges involve the reduction of the RF harmonic number by a factor of 2 (for a 2 to 1 merge) and then a factor of 3 (for a 3 to 1 merge), one requires RF frequencies 6hf s, 3hf s, 2hf s and hf s, where f s is the revolution frequency on the porch and h = 4more » is the fundamental harmonic number. The standard AGS RF cavities cannot operate at the lowest frequencies 2hf s and hf s; these are provided by two modified cavities. Upon completion of the merges, the bunches are sitting in harmonic h buckets. In order to be accelerated they need to be squeezed into harmonic 3h buckets. This is accomplished by producing a double-harmonic bucket in which harmonics h and 2h act in concert, and then a triple-harmonic bucket in which harmonics h, 2h, and 3h act in concert. Simulations have shown that the squeeze presents an acceptance bottleneck which limits the longitudinal emittance that can be put into the harmonic 3h bucket. In this note the areas of the double and triple-harmonic buckets are calculated explicitly, and it is shown that these go through a minimum as the RF voltages are raised to the desired values. Several RF voltage ranges are examined, and the acceptance bottleneck is determined for each of these. Finally, the acceptance bottleneck for Au77+ bunches in AGS is calculated for several RF voltage ranges. The main result is that the RF voltages for the low-frequency harmonic h and 2h cavities both must be at least 22 kV in order to achieve an acceptance of 0:6 eV s per nucleon. If the harmonic h and 2h voltages are 15 and 22 kV, respectively, then the acceptance is reduced to 0:548 eV s per nucleon.« less

Doppler-based motion compensation algorithm for focusing the signature of a rotorcraft.

PubMed

Goldman, Geoffrey H

2013-02-01

A computationally efficient algorithm was developed and tested to compensate for the effects of motion on the acoustic signature of a rotorcraft. For target signatures with large spectral peaks that vary slowly in amplitude and have near constant frequency, the time-varying Doppler shift can be tracked and then removed from the data. The algorithm can be used to preprocess data for classification, tracking, and nulling algorithms. The algorithm was tested on rotorcraft data. The average instantaneous frequency of the first harmonic of a rotorcraft was tracked with a fixed-lag smoother. Then, state space estimates of the frequency were used to calculate a time warping that removed the effect of a time-varying Doppler shift from the data. The algorithm was evaluated by analyzing the increase in the amplitude of the harmonics in the spectrum of a rotorcraft. The results depended upon the frequency of the harmonics and the processing interval duration. Under good conditions, the results for the fundamental frequency of the target (~11 Hz) almost achieved an estimated upper bound. The results for higher frequency harmonics had larger increases in the amplitude of the peaks, but significantly lower than the estimated upper bounds.

Instruments for Optical Spectroscopy and Imaging of Correlated Spin-Orbit Phases

DTIC Science & Technology

2014-10-20

2014. "A Spatially Resolved Optical Second Harmonic Generation (SHG) Study of the Perovskite Iridate Sr2IrO4 with Bulk Sensitivity". (oral) 6...The scattering plane ( light blue) is defined by the incident (red arrow) and radiated (dark blue arrow) beams. S(P)-polarization denotes an...5d transition metal oxides, with particular emphasis on the iridate family. In a conventional SHG-RA experiment, light of frequency  is impinged

Variability in the relationships among voice quality, harmonic amplitudes, open quotient, and glottal area waveform shape in sustained phonationa

PubMed Central

Kreiman, Jody; Shue, Yen-Liang; Chen, Gang; Iseli, Markus; Gerratt, Bruce R.; Neubauer, Juergen; Alwan, Abeer

2012-01-01

Increases in open quotient are widely assumed to cause changes in the amplitude of the first harmonic relative to the second (H1*–H2*), which in turn correspond to increases in perceived vocal breathiness. Empirical support for these assumptions is rather limited, and reported relationships among these three descriptive levels have been variable. This study examined the empirical relationship among H1*–H2*, the glottal open quotient (OQ), and glottal area waveform skewness, measured synchronously from audio recordings and high-speed video images of the larynges of six phonetically knowledgeable, vocally healthy speakers who varied fundamental frequency and voice qualities quasi-orthogonally. Across speakers and voice qualities, OQ, the asymmetry coefficient, and fundamental frequency accounted for an average of 74% of the variance in H1*–H2*. However, analyses of individual speakers showed large differences in the strategies used to produce the same intended voice qualities. Thus, H1*–H2* can be predicted with good overall accuracy, but its relationship to phonatory characteristics appears to be speaker dependent. PMID:23039455

STREAK CAMERA MEASUREMENTS OF THE APS PC GUN DRIVE LASER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dooling, J. C.; Lumpkin, A. H.

We report recent pulse-duration measurements of the APS PC Gun drive laser at both second harmonic and fourth harmonic wavelengths. The drive laser is a Nd:Glass-based chirped pulsed amplifier (CPA) operating at an IR wavelength of 1053 nm, twice frequency-doubled to obtain UV output for the gun. A Hamamatsu C5680 streak camera and an M5675 synchroscan unit are used for these measurements; the synchroscan unit is tuned to 119 MHz, the 24th subharmonic of the linac s-band operating frequency. Calibration is accomplished both electronically and optically. Electronic calibration utilizes a programmable delay line in the 119 MHz rf path. Themore » optical delay uses an etalon with known spacing between reflecting surfaces and is coated for the visible, SH wavelength. IR pulse duration is monitored with an autocorrelator. Fitting the streak camera image projected profiles with Gaussians, UV rms pulse durations are found to vary from 2.1 ps to 3.5 ps as the IR varies from 2.2 ps to 5.2 ps.« less

Adaptive suppression of power line interference in ultra-low field magnetic resonance imaging in an unshielded environment

NASA Astrophysics Data System (ADS)

Huang, Xiaolei; Dong, Hui; Qiu, Yang; Li, Bo; Tao, Quan; Zhang, Yi; Krause, Hans-Joachim; Offenhäusser, Andreas; Xie, Xiaoming

2018-01-01

Power-line harmonic interference and fixed-frequency noise peaks may cause stripe-artifacts in ultra-low field (ULF) magnetic resonance imaging (MRI) in an unshielded environment and in a conductively shielded room. In this paper we describe an adaptive suppression method to eliminate these artifacts in MRI images. This technique utilizes spatial correlation of the interference from different positions, and is realized by subtracting the outputs of the reference channel(s) from those of the signal channel(s) using wavelet analysis and the least squares method. The adaptive suppression method is first implemented to remove the image artifacts in simulation. We then experimentally demonstrate the feasibility of this technique by adding three orthogonal superconducting quantum interference device (SQUID) magnetometers as reference channels to compensate the output of one 2nd-order gradiometer. The experimental results show great improvement in the imaging quality in both 1D and 2D MRI images at two common imaging frequencies, 1.3 kHz and 4.8 kHz. At both frequencies, the effective compensation bandwidth is as high as 2 kHz. Furthermore, we examine the longitudinal relaxation times of the same sample before and after compensation, and show that the MRI properties of the sample did not change after applying adaptive suppression. This technique can effectively increase the imaging bandwidth and be applied to ULF MRI detected by either SQUIDs or Faraday coil in both an unshielded environment and a conductively shielded room.

Symmetry based frequency domain processing to remove harmonic noise from surface nuclear magnetic resonance measurements

NASA Astrophysics Data System (ADS)

Hein, Annette; Larsen, Jakob Juul; Parsekian, Andrew D.

2017-02-01

Surface nuclear magnetic resonance (NMR) is a unique geophysical method due to its direct sensitivity to water. A key limitation to overcome is the difficulty of making surface NMR measurements in environments with anthropogenic electromagnetic noise, particularly constant frequency sources such as powerlines. Here we present a method of removing harmonic noise by utilizing frequency domain symmetry of surface NMR signals to reconstruct portions of the spectrum corrupted by frequency-domain noise peaks. This method supplements the existing NMR processing workflow and is applicable after despiking, coherent noise cancellation, and stacking. The symmetry based correction is simple, grounded in mathematical theory describing NMR signals, does not introduce errors into the data set, and requires no prior knowledge about the harmonics. Modelling and field examples show that symmetry based noise removal reduces the effects of harmonics. In one modelling example, symmetry based noise removal improved signal-to-noise ratio in the data by 10 per cent. This improvement had noticeable effects on inversion parameters including water content and the decay constant T2*. Within water content profiles, aquifer boundaries and water content are more accurate after harmonics are removed. Fewer spurious water content spikes appear within aquifers, which is especially useful for resolving multilayered structures. Within T2* profiles, estimates are more accurate after harmonics are removed, especially in the lower half of profiles.

Development of high repetition rate nitric oxide planar laser induced fluorescence imaging

NASA Astrophysics Data System (ADS)

Jiang, Naibo

This thesis has documented the development of a MHz repitition rate pulse burst laser system. Second harmonic and third harmonic efficiencies are improved by adding a Phase Conjugate Mirror to the system. Some high energy fundamental, second harmonic, and third harmonic burst sequences consisting of 1--12 pulses separated in time by between 4 and 12 microseconds are now routinely obtained. The reported burst envelopes are quite uniform. We have also demonstrated the ability to generate ultra-high frequency sequences of broadly wavelength tunable, high intensity laser pulses using a home built injection seeded Optical Parametric Oscillator (OPO), pumped by the second and third harmonic output of the pulse burst laser. Typical OPO output burst sequences consist of 6--10 pulses, separated in time by between 6 and 10 microseconds. With third harmonic pumping of the OPO system, we studied four conditions, two-crystal Singly Resonant OPO (SRO) cavity, three-crystal OPO cavity, single pass two-crystal Doubly Resonant OPO (DRO) cavity and double pass two-crystal OPO cavity. The double pass two-crystal OPO cavity gives the best operation in burst mode. For single pass OPO, the average total OPO conversion efficiency is approximately 25%. For double pass OPO, the average total OPO conversion efficiency is approximately 35%. As a preliminary work, we studied 532nm pumping of a single crystal OPO cavity. With single pulse pumping, the conversion efficiency can reach 30%. For both 355nm and 532nm pumping OPO, we have demonstrated injection seeding. The OPO output light linewidth is significantly narrowed. Some preliminary etalon traces are also reported. By mixing the OPO signal output at 622nm with residual third harmonic at 355nm, we obtained 226nm burst sequences with average pulse energy of ˜0.2 mJ. Injection seeding of the OPO increases the energy achieved by a factor of ˜2. 226nm burst sequences with reasonably uniform burst envelopes are reported. Using the system we have obtained, for the first time by any known optical method, Planar Laser Induced Fluorescence (PLIF) image sequences at ultrahigh (≥100kHz) frame rates, in particular NO PLIF image sequences, have been obtained in a Mach 2 jet. We also studied the possibility of utilizing a 250 kHz pulsed Nd:YVO 4 laser as the master oscillator. 10-pulse-10-mus spacing burst sequences with reasonably uniform burst envelope have been obtained. The total energy of the burst sequence is ˜2.5J.

Control Systems with Pulse Width Modulation in Matrix Converters

NASA Astrophysics Data System (ADS)

Bondarev, A. V.; Fedorov, S. V.; Muravyova, E. A.

2018-03-01

In this article, the matrix frequency converter for the system of the frequency control of the electric drive is considered. Algorithms of formation of an output signal on the basis of pulse width modulation were developed for the quantitative analysis of quality of an output signal on the basis of mathematical models. On the basis of simulation models of an output signal, assessment of quality of this signal was carried out. The analysis of harmonic composition of the voltage output received on the basis of pulse width modulation was made for the purpose of determination of opportunities of the control system for improving harmonic composition. The result of such analysis led to the fact that the device formation of switching functions of the control system on the basis of PWM does not lead to a distortion reduction of a harmonic of the control signal, and leads to offset of harmonic in the field of frequencies, the multiple relatively carrier frequency.

A mechanism for plasma waves at the harmonics of the plasma frequency foreshock boundary

NASA Technical Reports Server (NTRS)

Klimas, A. J.

1982-01-01

A bump-on-tail unstable reduced velocity distribution, constructed from data obtained at the upstream boundary of the electron foreshock by the GSFC electron spectrometer experiment on the ISEE-1 satellite, is used as the initial plasma state for a numerical integration of the 1D-Vlasov-Maxwell system of equations. The integration is carried through the growth of the instability, beyond its saturation, and well into the stabilized plasma regime. A power spectrum computed for the electric field of the stabilized plasma is dominated by a narrow peak at the Bohm-Gross frequency of the unstable field mode but also contains significant power at the harmonics of the Bohm-Gross frequency. The harmonic power is in sharp peaks which are split into closely spaced doublets. The fundamental peak at the Bohm-Gross frequency is split into a closely spaced triplet. The mechanism for excitation of the second harmonic is shown to be second order wave-wave coupling.

Spectrum-averaged Harmonic Path (SHAPA) algorithm for non-contact vital sign monitoring with ultra-wideband (UWB) radar.

PubMed

Van Nguyen; Javaid, Abdul Q; Weitnauer, Mary Ann

2014-01-01

We introduce the Spectrum-averaged Harmonic Path (SHAPA) algorithm for estimation of heart rate (HR) and respiration rate (RR) with Impulse Radio Ultrawideband (IR-UWB) radar. Periodic movement of human torso caused by respiration and heart beat induces fundamental frequencies and their harmonics at the respiration and heart rates. IR-UWB enables capture of these spectral components and frequency domain processing enables a low cost implementation. Most existing methods of identifying the fundamental component either in frequency or time domain to estimate the HR and/or RR lead to significant error if the fundamental is distorted or cancelled by interference. The SHAPA algorithm (1) takes advantage of the HR harmonics, where there is less interference, and (2) exploits the information in previous spectra to achieve more reliable and robust estimation of the fundamental frequency in the spectrum under consideration. Example experimental results for HR estimation demonstrate how our algorithm eliminates errors caused by interference and produces 16% to 60% more valid estimates.

Interpretations of Frequency Domain Analyses of Neural Entrainment: Periodicity, Fundamental Frequency, and Harmonics.

PubMed

Zhou, Hong; Melloni, Lucia; Poeppel, David; Ding, Nai

2016-01-01

Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid.

Monitoring and localization of buried plastic natural gas pipes using passive RF tags

NASA Astrophysics Data System (ADS)

Mondal, Saikat; Kumar, Deepak; Ghazali, Mohd. Ifwat; Chahal, Prem; Udpa, Lalita; Deng, Yiming

2018-04-01

A passive harmonic radio frequency (RF) tag on the pipe with added sensing capabilities is proposed in this paper. Radio frequency identification (RFID) based tagging has already emerged as a potential solution for chemical sensing, location detection, animal tagging, etc. Harmonic transponders are already quite popular compared to conventional RFIDs due to their improved signal to noise ratio (SNR). However, the operating frequency, transmitted power and tag efficiency become critical issues for underground RFIDs. In this paper, a comprehensive on-tag sensing, power budget and frequency analyses is performed for buried harmonic tag design. Accurate tracking of infrastructure burial depth is proposed to reduce the probability of failure of underground pipelines. Burial depth is estimated using phase information of received signals at different frequencies calculated using genetic algorithm (GA) based optimization for post processing. Suitable frequency range is determined for a variety of soil with different moisture content for small tag-antenna size. Different types of harmonic tags such as 1) Schottky diode, 2) Non-linear Transmission Line (NLTL) were compared for underground applications. In this study, the power, frequency and tag design have been optimized to achieve small antenna size, minimum signal loss and simple reader circuit for underground detection at up to 5 feet depth in different soil medium and moisture contents.

Dynamical origin of near- and below-threshold harmonic generation of Cs in an intense mid-infrared laser field.

PubMed

Li, Peng-Cheng; Sheu, Yae-Lin; Laughlin, Cecil; Chu, Shih-I

2015-05-20

Near- and below-threshold harmonic generation provides a potential approach to generate vacuum-ultraviolet frequency comb. However, the dynamical origin of in these lower harmonics is less understood and largely unexplored. Here we perform an ab initio quantum study of the near- and below-threshold harmonic generation of caesium (Cs) atoms in an intense 3,600-nm mid-infrared laser field. Combining with a synchrosqueezing transform of the quantum time-frequency spectrum and an extended semiclassical analysis, the roles of multiphoton and multiple rescattering trajectories on the near- and below-threshold harmonic generation processes are clarified. We find that the multiphoton-dominated trajectories only involve the electrons scattered off the higher part of the combined atom-field potential followed by the absorption of many photons in near- and below-threshold regime. Furthermore, only the near-resonant below-threshold harmonic is exclusive to exhibit phase locked features. Our results shed light on the dynamic origin of the near- and below-threshold harmonic generation.

Role of antenna modes and field enhancement in second harmonic generation from dipole nanoantennas.

PubMed

de Ceglia, Domenico; Vincenti, Maria Antonietta; De Angelis, Costantino; Locatelli, Andrea; Haus, Joseph W; Scalora, Michael

2015-01-26

We study optical second harmonic generation from metallic dipole antennas with narrow gaps. Enhancement of the fundamental-frequency field in the gap region plays a marginal role on conversion efficiency. In the symmetric configuration, i.e., with the gap located at the center of the antenna axis, reducing gap size induces a significant red-shift of the maximum conversion efficiency peak. Either enhancement or inhibition of second-harmonic emission may be observed as gap size is decreased, depending on the antenna mode excited at the harmonic frequency. The second-harmonic signal is extremely sensitive to the asymmetry introduced by gap's displacements with respect to the antenna center. In this situation, second-harmonic light can couple to all the available antenna modes. We perform a multipolar analysis that allows engineering the far-field SH emission and find that the interaction with quasi-odd-symmetry modes generates radiation patterns with a strong dipolar component.

Understanding fifth-harmonic generation in CLBO

NASA Astrophysics Data System (ADS)

Patankar, S.; Yang, S. T.; Moody, J. D.; Bayramian, A. J.; Swadling, G. F.; Barker, D.; Datte, P.; Mennerat, G.; Norton, M.; Carr, C. W.; Begishev, I. A.; Bromage, J.; Ross, J. S.

2018-02-01

We report on results of fifth harmonic generation in Cesium Lithium Borate (CLBO) using a three-crystal cascaded frequency conversion scheme designed to study the energy balance of the final sum frequency generation stage. The experimental setup independently combines the first and fourth harmonic of a Nd:Glass laser in a 5mm thick CLBO crystal. Energy balance between the incoming and output energy is close to unity when the CLBO is out of phase matching and approximately 80% when the crystal is in phase matching. A detailed analysis of the residual fundamental and fourth harmonic energy indicates 5th harmonic light is being generated but only 26% is unaccounted for. We attribute the missing light to linear transmission loss in the CLBO oven. The ratio of the output to input energy is unity when the missing 5th harmonic is incorporated into the calculations. Two-dimensional plane wave mixing simulations show agreement with the results at lower intensities.

Method and apparatus for wavefront sensing

DOEpatents

Bahk, Seung-Whan

2016-08-23

A method of measuring characteristics of a wavefront of an incident beam includes obtaining an interferogram associated with the incident beam passing through a transmission mask and Fourier transforming the interferogram to provide a frequency domain interferogram. The method also includes selecting a subset of harmonics from the frequency domain interferogram, individually inverse Fourier transforming each of the subset of harmonics to provide a set of spatial domain harmonics, and extracting a phase profile from each of the set of spatial domain harmonics. The method further includes removing phase discontinuities in the phase profile, rotating the phase profile, and reconstructing a phase front of the wavefront of the incident beam.

KvN mechanics approach to the time-dependent frequency harmonic oscillator.

PubMed

Ramos-Prieto, Irán; Urzúa-Pineda, Alejandro R; Soto-Eguibar, Francisco; Moya-Cessa, Héctor M

2018-05-30

Using the Ermakov-Lewis invariants appearing in KvN mechanics, the time-dependent frequency harmonic oscillator is studied. The analysis builds upon the operational dynamical model, from which it is possible to infer quantum or classical dynamics; thus, the mathematical structure governing the evolution will be the same in both cases. The Liouville operator associated with the time-dependent frequency harmonic oscillator can be transformed using an Ermakov-Lewis invariant, which is also time dependent and commutes with itself at any time. Finally, because the solution of the Ermakov equation is involved in the evolution of the classical state vector, we explore some analytical and numerical solutions.

Preliminary study of synthetic aperture tissue harmonic imaging on in-vivo data

NASA Astrophysics Data System (ADS)

Rasmussen, Joachim H.; Hemmsen, Martin C.; Madsen, Signe S.; Hansen, Peter M.; Nielsen, Michael B.; Jensen, Jørgen A.

2013-03-01

A method for synthetic aperture tissue harmonic imaging is investigated. It combines synthetic aperture sequen- tial beamforming (SASB) with tissue harmonic imaging (THI) to produce an increased and more uniform spatial resolution and improved side lobe reduction compared to conventional B-mode imaging. Synthetic aperture sequential beamforming tissue harmonic imaging (SASB-THI) was implemented on a commercially available BK 2202 Pro Focus UltraView ultrasound system and compared to dynamic receive focused tissue harmonic imag- ing (DRF-THI) in clinical scans. The scan sequence that was implemented on the UltraView system acquires both SASB-THI and DRF-THI simultaneously. Twenty-four simultaneously acquired video sequences of in-vivo abdominal SASB-THI and DRF-THI scans on 3 volunteers of 4 different sections of liver and kidney tissues were created. Videos of the in-vivo scans were presented in double blinded studies to two radiologists for image quality performance scoring. Limitations to the systems transmit stage prevented user defined transmit apodization to be applied. Field II simulations showed that side lobes in SASB could be improved by using Hanning transmit apodization. Results from the image quality study show, that in the current configuration on the UltraView system, where no transmit apodization was applied, SASB-THI and DRF-THI produced equally good images. It is expected that given the use of transmit apodization, SASB-THI could be further improved.

A simple method for correcting spatially resolved solar intensity oscillation observations for variations in scattered light

NASA Technical Reports Server (NTRS)

Jefferies, S. M.; Duvall, T. L., Jr.

1991-01-01

A measurement of the intensity distribution in an image of the solar disk will be corrupted by a spatial redistribution of the light that is caused by the earth's atmosphere and the observing instrument. A simple correction method is introduced here that is applicable for solar p-mode intensity observations obtained over a period of time in which there is a significant change in the scattering component of the point spread function. The method circumvents the problems incurred with an accurate determination of the spatial point spread function and its subsequent deconvolution from the observations. The method only corrects the spherical harmonic coefficients that represent the spatial frequencies present in the image and does not correct the image itself.

Transonic streamline of symmetric wing under the influence unilateral oscillations characterized by the spectrum of two frequencies

NASA Astrophysics Data System (ADS)

Zamuraev, V. P.; Kalinina, A. P.

2017-10-01

Forced high-frequency vibrations of the airfoil surface part with the amplitude almost equal to the sound velocity can change significantly the lift force of the symmetric profile streamlined at zero angle of attack. The oscillation consists of two harmonics. The ratio of harmonics frequencies values is equal to 2. The present work shows that the aerodynamic properties depend significantly on the specific energy contribution of each frequency.

Determination of rotor harmonic blade loads from acoustic measurements

NASA Technical Reports Server (NTRS)

Kasper, P. K.

1975-01-01

The magnitude of discrete frequency sound radiated by a rotating blade is strongly influenced by the presence of a nonuniform distribution of aerodynamic forces over the rotor disk. An analytical development and experimental results are provided for a technique by which harmonic blade loads are derived from acoustic measurements. The technique relates, on a one-to-one basis, the discrete frequency sound harmonic amplitudes measured at a point on the axis of rotation to the blade-load harmonic amplitudes. This technique was applied to acoustic data from two helicopter types and from a series of test results using the NASA-Langley Research Center rotor test facility. The inferred blade-load harmonics for the cases considered tended to follow an inverse power law relationship with harmonic blade-load number. Empirical curve fits to the data showed the harmonic fall-off rate to be in the range of 6 to 9 db per octave of harmonic order. These empirical relationships were subsequently used as input data in a compatible far field rotational noise prediction model. A comparison between predicted and measured off-axis sound harmonic levels is provided for the experimental cases considered.

Ultrathin Nonlinear Metasurface for Optical Image Encoding.

PubMed

Walter, Felicitas; Li, Guixin; Meier, Cedrik; Zhang, Shuang; Zentgraf, Thomas

2017-05-10

Security of optical information is of great importance in modern society. Many cryptography techniques based on classical and quantum optics have been widely explored in the linear optical regime. Nonlinear optical encryption in which encoding and decoding involve nonlinear frequency conversions represents a new strategy for securing optical information. Here, we demonstrate that an ultrathin nonlinear photonic metasurface, consisting of meta-atoms with 3-fold rotational symmetry, can be used to hide optical images under illumination with a fundamental wave. However, the hidden image can be read out from second harmonic generation (SHG) waves. This is achieved by controlling the destructive and constructive interferences of SHG waves from two neighboring meta-atoms. In addition, we apply this concept to obtain gray scale SHG imaging. Nonlinear metasurfaces based on space variant optical interference open new avenues for multilevel image encryption, anticounterfeiting, and background free image reconstruction.

Method, system and computer-readable media for measuring impedance of an energy storage device

DOEpatents

Morrison, John L.; Morrison, William H.; Christophersen, Jon P.; Motloch, Chester G.

2016-01-26

Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. A time profile of this sampled signal has a duration that is a few periods of the lowest frequency. A voltage response of the battery, average deleted, is an impedance of the battery in a time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time profile by rectifying relative to sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.

Intermittent impact dynamics of a cantilever scanning a surface at high speed

NASA Astrophysics Data System (ADS)

Dey, S.; Kartik, V.

2018-03-01

In contact-mode scanning probe microscopy (SPM), the cantilever's dynamics are conventionally investigated by assuming the tip to be always in contact with the sample's surface. At high scanning speeds, however, the cantilever's inertia becomes dominant and the tip can therefore completely detach from the surface and start impacting upon it. Experiments at the macro-scale cannot emulate the complex micro-scale dynamics, as the system exhibits negligible effects due to meniscus forces and the surrounding medium's squeeze film damping; however, they can provide qualitative insight into the cantilever's dynamics at high frequencies, corresponding to those likely to be excited during video-rate SPM imaging. This paper investigates such intermittent impact dynamics for an upscaled cantilever, analytically, numerically, and experimentally. In contact-mode scanning, a critical scan speed exists beyond which the cantilever's tip loses contact with the sample's surface; a closed-form expression for this contact loss frequency is derived. At high scan speeds, impacts cause the cantilever to switch between different contact regimes: in-, off-, and grazing-contact; within each regime, the system's modal configuration is different. Experimentally-obtained Poincare maps indicate quasi-periodic behaviour at frequencies for which the response is repetitive, as is also predicted by the model. Intermittent impacts excite the sub- and super-harmonics of the excitation frequency, which are related to the natural frequencies of different system configurations based on the "effective" tip-end boundary conditions. The cantilever's response exhibits several phenomena, such as modal transition, beating, grazing, and possible chaotic behaviour, depending upon the relation between the excitation harmonics and the natural frequencies.

Pulse compression of harmonic chirp signals using the fractional fourier transform.

PubMed

Arif, M; Cowell, D M J; Freear, S

2010-06-01

In ultrasound harmonic imaging with chirp-coded excitation, a harmonic matched filter (HMF) is typically used on the received signal to perform pulse compression of the second harmonic component (SHC) to recover signal axial resolution. Designing the HMF for the compression of the SHC is a problematic issue because it requires optimal window selection. In the compressed second harmonic signal, the sidelobe level may increase and the mainlobe width (MLW) widen under a mismatched condition, resulting in loss of axial resolution. We propose the use of the fractional Fourier transform (FrFT) as an alternative tool to perform compression of the chirp-coded SHC generated as a result of the nonlinear propagation of an ultrasound signal. Two methods are used to experimentally assess the performance benefits of the FrFT technique over the HMF techniques. The first method uses chirp excitation with central frequency of 2.25 MHz and bandwidth of 1 MHz. The second method uses chirp excitation with pulse inversion to increase the bandwidth to 2 MHz. In this study, experiments were performed in a water tank with a single-element transducer mounted coaxially with a hydrophone in a pitch-catch configuration. Results are presented that indicate that the FrFT can perform pulse compression of the second harmonic chirp component, with a 14% reduction in the MLW of the compressed signal when compared with the HMF. Also, the FrFT provides at least 23% reduction in the MLW of the compressed signal when compared with the harmonic mismatched filter (HMMF). The FrFT maintains comparable peak and integrated sidelobe levels when compared with the HMF and HMMF techniques. Copyright 2010 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Remote listening and passive acoustic detection in a 3-D environment

NASA Astrophysics Data System (ADS)

Barnhill, Colin

Teleconferencing environments are a necessity in business, education and personal communication. They allow for the communication of information to remote locations without the need for travel and the necessary time and expense required for that travel. Visual information can be communicated using cameras and monitors. The advantage of visual communication is that an image can capture multiple objects and convey them, using a monitor, to a large group of people regardless of the receiver's location. This is not the case for audio. Currently, most experimental teleconferencing systems' audio is based on stereo recording and reproduction techniques. The problem with this solution is that it is only effective for one or two receivers. To accurately capture a sound environment consisting of multiple sources and to recreate that for a group of people is an unsolved problem. This work will focus on new methods of multiple source 3-D environment sound capture and applications using these captured environments. Using spherical microphone arrays, it is now possible to capture a true 3-D environment A spherical harmonic transform on the array's surface allows us to determine the basis functions (spherical harmonics) for all spherical wave solutions (up to a fixed order). This spherical harmonic decomposition (SHD) allows us to not only look at the time and frequency characteristics of an audio signal but also the spatial characteristics of an audio signal. In this way, a spherical harmonic transform is analogous to a Fourier transform in that a Fourier transform transforms a signal into the frequency domain and a spherical harmonic transform transforms a signal into the spatial domain. The SHD also decouples the input signals from the microphone locations. Using the SHD of a soundfield, new algorithms are available for remote listening, acoustic detection, and signal enhancement The new algorithms presented in this paper show distinct advantages over previous detection and listening algorithms especially for multiple speech sources and room environments. The algorithms use high order (spherical harmonic) beamforming and power signal characteristics for source localization and signal enhancement These methods are applied to remote listening, surveillance, and teleconferencing.

Enabling the detection of UV signal in multimodal nonlinear microscopy with catalogue lens components.

PubMed

Vogel, Martin; Wingert, Axel; Fink, Rainer H A; Hagl, Christian; Ganikhanov, Feruz; Pfeffer, Christian P

2015-10-01

Using an optical system made from fused silica catalogue optical components, third-order nonlinear microscopy has been enabled on conventional Ti:sapphire laser-based multiphoton microscopy setups. The optical system is designed using two lens groups with straightforward adaptation to other microscope stands when one of the lens groups is exchanged. Within the theoretical design, the optical system collects and transmits light with wavelengths between the near ultraviolet and the near infrared from an object field of at least 1 mm in diameter within a resulting numerical aperture of up to 0.56. The numerical aperture can be controlled with a variable aperture stop between the two lens groups of the condenser. We demonstrate this new detection capability in third harmonic generation imaging experiments at the harmonic wavelength of ∼300 nm and in multimodal nonlinear optical imaging experiments using third-order sum frequency generation and coherent anti-Stokes Raman scattering microscopy so that the wavelengths of the detected signals range from ∼300 nm to ∼660 nm. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Anderson localization of shear waves observed by magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Papazoglou, S.; Klatt, D.; Braun, J.; Sack, I.

2010-07-01

In this letter we present for the first time an experimental investigation of shear wave localization using motion-sensitive magnetic resonance imaging (MRI). Shear wave localization was studied in gel phantoms containing arrays of randomly positioned parallel glass rods. The phantoms were exposed to continuous harmonic vibrations in a frequency range from 25 to 175 Hz, yielding wavelengths on the order of the elastic mean free path, i.e. the Ioffe-Regel criterion of Anderson localization was satisfied. The experimental setup was further chosen such that purely shear horizontal waves were induced to avoid effects due to mode conversion and pressure waves. Analysis of the distribution of shear wave intensity in experiments and simulations revealed a significant deviation from Rayleigh statistics indicating that shear wave energy is localized. This observation is further supported by experiments on weakly scattering samples exhibiting Rayleigh statistics and an analysis of the multifractality of wave functions. Our results suggest that motion-sensitive MRI is a promising tool for studying Anderson localization of time-harmonic shear waves, which are increasingly used in dynamic elastography.

Possible role of cochlear nonlinearity in the detection of mistuning of a harmonic component in a harmonic complex

NASA Astrophysics Data System (ADS)

Stoelinga, Christophe; Heo, Inseok; Long, Glenis; Lee, Jungmee; Lutfi, Robert; Chang, An-Chieh

2015-12-01

The human auditory system has a remarkable ability to "hear out" a wanted sound (target) in the background of unwanted sounds. One important property of sound which helps us hear-out the target is inharmonicity. When a single harmonic component of a harmonic complex is slightly mistuned, that component is heard to separate from the rest. At high harmonic numbers, where components are unresolved, the harmonic segregation effect is thought to result from detection of modulation of the time envelope (roughness cue) resulting from the mistuning. Neurophysiological research provides evidence that such envelope modulations are represented early in the auditory system, at the level of the auditory nerve. When the mistuned harmonic is a low harmonic, where components are resolved, the harmonic segregation is attributed to more centrally-located auditory processes, leading harmonic components to form a perceptual group heard separately from the mistuned component. Here we consider an alternative explanation that attributes the harmonic segregation to detection of modulation when both high and low harmonic numbers are mistuned. Specifically, we evaluate the possibility that distortion products in the cochlea generated by the mistuned component introduce detectable beating patterns for both high and low harmonic numbers. Distortion product otoacoustic emissions (DPOAEs) were measured using 3, 7, or 12-tone harmonic complexes with a fundamental frequency (F0) of 200 or 400 Hz. One of two harmonic components was mistuned at each F0: one when harmonics are expected to be resulted and the other from unresolved harmonics. Many non-harmonic DPOAEs are present whenever a harmonic component is mistuned. These non-harmonic DPOAEs are often separated by the amount of the mistuning (ΔF). This small frequency difference will generate a slow beating pattern at ΔF, because this beating is only present when a harmonic component is mistuned, it could provide a cue for behavioral detection of harmonic complex mistuning and may also be associated with the modulation of auditory nerve responses.

Electromagnetic MUSIC-type imaging of perfectly conducting, arc-like cracks at single frequency

NASA Astrophysics Data System (ADS)

Park, Won-Kwang; Lesselier, Dominique

2009-11-01

We propose a non-iterative MUSIC (MUltiple SIgnal Classification)-type algorithm for the time-harmonic electromagnetic imaging of one or more perfectly conducting, arc-like cracks found within a homogeneous space R2. The algorithm is based on a factorization of the Multi-Static Response (MSR) matrix collected in the far-field at a single, nonzero frequency in either Transverse Magnetic (TM) mode (Dirichlet boundary condition) or Transverse Electric (TE) mode (Neumann boundary condition), followed by the calculation of a MUSIC cost functional expected to exhibit peaks along the crack curves each half a wavelength. Numerical experimentation from exact, noiseless and noisy data shows that this is indeed the case and that the proposed algorithm behaves in robust manner, with better results in the TM mode than in the TE mode for which one would have to estimate the normal to the crack to get the most optimal results.

Second-harmonic generation of a dual-frequency laser in a MgO:PPLN crystal.

PubMed

Kang, Ying; Yang, Suhui; Brunel, Marc; Cheng, Lijun; Zhao, Changming; Zhang, Haiyang

2017-04-10

A dual-frequency CW laser at a wavelength of 1.064 μm is frequency doubled in a MgO:PPLN nonlinear crystal. The fundamental dual-frequency laser has a tunable beat note from 125 MHz to 175 MHz. A laser-diode pumped fiber amplifier is used to amplify the dual-frequency fundamental output to a maximum power of 50 W before frequency doubling. The maximum output power of the green light is 1.75 W when the input fundamental power is 12 W, corresponding to a frequency doubling efficiency of 14.6%. After frequency doubling, green light with modulation frequencies in two bands from 125 MHz to 175 MHz and from 250 MHz to 350 MHz is achieved simultaneously. The relative intensities of the beat notes at the two bands can be adjusted by changing the relative intensities at different frequencies of the fundamental light. The spectral width and frequency stabilities of the beat notes in fundamental wave and green light are also measured, respectively. The modulated green light has potential applications in underwater ranging, communication, and imaging.

Nonlinear Lamb waves for fatigue damage identification in FRP-reinforced steel plates.

PubMed

Wang, Yikuan; Guan, Ruiqi; Lu, Ye

2017-09-01

A nonlinear Lamb-wave-based method for fatigue crack detection in steel plates with and without carbon fibre reinforcement polymer (CFRP) reinforcement is presented in this study. Both numerical simulation and experimental evaluation were performed for Lamb wave propagation and its interaction with a fatigue crack on these two steel plate types. With the generation of the second harmonic, the damage-induced wave nonlinearities were identified by surface-bonded piezoelectric sensors. Numerical simulation revealed that the damage-induced wave component at the second harmonic was slightly affected by the existence of CFRP laminate, although the total wave energy was decreased because of wave leakage into the CFRP laminate. Due to unavoidable nonlinearity from the experimental environments, it was impractical to directly extract the time-of-flight of the second harmonic for locating the crack. To this end, the correlation coefficient of benchmark and signal with damage at double frequency in the time domain was calculated, based on which an imaging method was introduced to locate the fatigue crack in steel plates with and without CFRP laminates. Copyright © 2017 Elsevier B.V. All rights reserved.

Frequency organization and responses to complex sounds in the medial geniculate body of the mustached bat.

PubMed

Wenstrup, J J

1999-11-01

The auditory cortex of the mustached bat (Pteronotus parnellii) displays some of the most highly developed physiological and organizational features described in mammalian auditory cortex. This study examines response properties and organization in the medial geniculate body (MGB) that may contribute to these features of auditory cortex. About 25% of 427 auditory responses had simple frequency tuning with single excitatory tuning curves. The remainder displayed more complex frequency tuning using two-tone or noise stimuli. Most of these were combination-sensitive, responsive to combinations of different frequency bands within sonar or social vocalizations. They included FM-FM neurons, responsive to different harmonic elements of the frequency modulated (FM) sweep in the sonar signal, and H1-CF neurons, responsive to combinations of the bat's first sonar harmonic (H1) and a higher harmonic of the constant frequency (CF) sonar signal. Most combination-sensitive neurons (86%) showed facilitatory interactions. Neurons tuned to frequencies outside the biosonar range also displayed combination-sensitive responses, perhaps related to analyses of social vocalizations. Complex spectral responses were distributed throughout dorsal and ventral divisions of the MGB, forming a major feature of this bat's analysis of complex sounds. The auditory sector of the thalamic reticular nucleus also was dominated by complex spectral responses to sounds. The ventral division was organized tonotopically, based on best frequencies of singly tuned neurons and higher best frequencies of combination-sensitive neurons. Best frequencies were lowest ventrolaterally, increasing dorsally and then ventromedially. However, representations of frequencies associated with higher harmonics of the FM sonar signal were reduced greatly. Frequency organization in the dorsal division was not tonotopic; within the middle one-third of MGB, combination-sensitive responses to second and third harmonic CF sonar signals (60-63 and 90-94 kHz) occurred in adjacent regions. In the rostral one-third, combination-sensitive responses to second, third, and fourth harmonic FM frequency bands predominated. These FM-FM neurons, thought to be selective for delay between an emitted pulse and echo, showed some organization of delay selectivity. The organization of frequency sensitivity in the MGB suggests a major rewiring of the output of the central nucleus of the inferior colliculus, by which collicular neurons tuned to the bat's FM sonar signals mostly project to the dorsal, not the ventral, division. Because physiological differences between collicular and MGB neurons are minor, a major role of the tecto-thalamic projection in the mustached bat may be the reorganization of responses to provide for cortical representations of sonar target features.

Low-amplitude non-linear volume vibrations of single microbubbles measured with an "acoustical camera".

PubMed

Renaud, Guillaume; Bosch, Johan G; Van Der Steen, Antonius F W; De Jong, Nico

2014-06-01

Contrast-enhanced ultrasound imaging is based on the detection of non-linear vibrational responses of a contrast agent after its intravenous administration. Improving contrast-enhanced images requires an accurate understanding of the vibrational response to ultrasound of the lipid-coated gas microbubbles that constitute most ultrasound contrast agents. Variations in the volume of microbubbles provide the most efficient radiation of ultrasound and, therefore, are the most important bubble vibrations for medical diagnostic ultrasound imaging. We developed an "acoustical camera" that measures the dynamic volume change of individual microbubbles when excited by a pressure wave. In the work described here, the technique was applied to the characterization of low-amplitude non-linear behaviors of BR14 microbubbles (Bracco Research, Geneva, Switzerland). The amplitude dependence of the resonance frequency and the damping, the prevalence of efficient subharmonic and ultraharmonic vibrations and the amplitude dependence of the response at the fundamental frequency and at the second harmonic frequency were investigated. Because of the large number of measurements, we provide a statistical characterization of the low-amplitude non-linear properties of the contrast agent. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Non-contact defect diagnostics in Cz-Si wafers using resonance ultrasonic vibrations

NASA Astrophysics Data System (ADS)

Belyaev, A.; Kochelap, V. A.; Tarasov, I.; Ostapenko, S.

2001-01-01

A new resonance effect of generation of sub-harmonic acoustic vibrations was applied to characterize defects in as-grown and processed Cz-Si wafers. Ultrasonic vibrations were generated into standard 8″ wafers using an external ultrasonic transducer and their amplitude recorded in a non-contact mode using a scanning acoustic probe. By tuning the frequency, f, of the transducer we observed generation of intense sub-harmonic acoustic mode ("whistle" or w-mode) with f/2 frequency. The characteristics of the w-mode-amplitude dependence, frequency scans, spatial distribution allow a clear distinction versus harmonic vibrations of the same wafer. The origin of sub-harmonic vibrations observed on 8″ Cz-Si wafers is attributed to a parametric resonance of flexural vibrations in thin silicon circular plates. We present evidence that "whistle" effect shows a strong dependence on the wafer's growth and processing history and can be used for quality assurance purposes.

Twenty-Four Tuba Harmonics Using a Single Pipe Length

ERIC Educational Resources Information Center

Holmes, Bud; Ruiz, Michael J.

2017-01-01

Harmonics arise naturally from the resonances in strings and pipes. A video demonstration (Ruiz 2016 "YouTube: Tuba Harmonics" (https://youtu.be/souhEzOP9c4)) is provided where a tubist (coauthor Holmes) produces a phenomenal 24 harmonics using a single tuba pipe length by controlling the buzz of his lips. The frequencies of the…

Quasi-supercontinuum source in the extreme ultraviolet using multiple frequency combs from high-harmonic generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wünsche, Martin; Fuchs, Silvio; Aull, Stefan

A quasi-supercontinuum source in the extreme ultraviolet (XUV) is demonstrated using a table-top femtosecond laser and a tunable optical parametric amplifier (OPA) as a driver for high-harmonic generation (HHG). The harmonic radiation, which is usually a comb of odd multiples of the fundamental frequency, is generated by near-infrared (NIR) laser pulses from the OPA. A quasi-continuous XUV spectrum in the range of 30 to 100 eV is realized by averaging over multiple harmonic comb spectra with slightly different fundamental frequencies and thus different spectral spacing between the individual harmonics. The driving laser wavelength is swept automatically during an averaging timemore » period. With a total photon flux of 4×10 9 photons/s in the range of 30 eV to 100 eV and 1×10 7 photons/s in the range of 100 eV to 200 eV, the resulting quasi-supercontinuum XUV source is suited for applications such as XUV coherence tomography (XCT) or near-edge absorption fine structure spectroscopy (NEXAFS).« less

Quasi-supercontinuum source in the extreme ultraviolet using multiple frequency combs from high-harmonic generation

DOE PAGES

Wünsche, Martin; Fuchs, Silvio; Aull, Stefan; ...

2017-03-16

A quasi-supercontinuum source in the extreme ultraviolet (XUV) is demonstrated using a table-top femtosecond laser and a tunable optical parametric amplifier (OPA) as a driver for high-harmonic generation (HHG). The harmonic radiation, which is usually a comb of odd multiples of the fundamental frequency, is generated by near-infrared (NIR) laser pulses from the OPA. A quasi-continuous XUV spectrum in the range of 30 to 100 eV is realized by averaging over multiple harmonic comb spectra with slightly different fundamental frequencies and thus different spectral spacing between the individual harmonics. The driving laser wavelength is swept automatically during an averaging timemore » period. With a total photon flux of 4×10 9 photons/s in the range of 30 eV to 100 eV and 1×10 7 photons/s in the range of 100 eV to 200 eV, the resulting quasi-supercontinuum XUV source is suited for applications such as XUV coherence tomography (XCT) or near-edge absorption fine structure spectroscopy (NEXAFS).« less

A Novel Method to Reconstruct the Force Curve by Higher Harmonics of the First Two Flexural Modes in Frequency Modulation Atomic Force Microscope (FM-AFM).

PubMed

Zhang, Suoxin; Qian, Jianqiang; Li, Yingzi; Zhang, Yingxu; Wang, Zhenyu

2018-06-04

Atomic force microscope (AFM) is an idealized tool to measure the physical and chemical properties of the sample surfaces by reconstructing the force curve, which is of great significance to materials science, biology, and medicine science. Frequency modulation atomic force microscope (FM-AFM) collects the frequency shift as feedback thus having high force sensitivity and it accomplishes a true noncontact mode, which means great potential in biological sample detection field. However, it is a challenge to establish the relationship between the cantilever properties observed in practice and the tip-sample interaction theoretically. Moreover, there is no existing method to reconstruct the force curve in FM-AFM combining the higher harmonics and the higher flexural modes. This paper proposes a novel method that a full force curve can be reconstructed by any order higher harmonics of the first two flexural modes under any vibration amplitude in FM-AFM. Moreover, in the small amplitude regime, short range forces are reconstructed more accurately by higher harmonics analysis compared with fundamental harmonics using the Sader-Jarvis formula.

A comparison of spectral magnitude and phase-locking value analyses of the frequency-following response to complex tones

PubMed Central

Zhu, Li; Bharadwaj, Hari; Xia, Jing; Shinn-Cunningham, Barbara

2013-01-01

Two experiments, both presenting diotic, harmonic tone complexes (100 Hz fundamental), were conducted to explore the envelope-related component of the frequency-following response (FFRENV), a measure of synchronous, subcortical neural activity evoked by a periodic acoustic input. Experiment 1 directly compared two common analysis methods, computing the magnitude spectrum and the phase-locking value (PLV). Bootstrapping identified which FFRENV frequency components were statistically above the noise floor for each metric and quantified the statistical power of the approaches. Across listeners and conditions, the two methods produced highly correlated results. However, PLV analysis required fewer processing stages to produce readily interpretable results. Moreover, at the fundamental frequency of the input, PLVs were farther above the metric's noise floor than spectral magnitudes. Having established the advantages of PLV analysis, the efficacy of the approach was further demonstrated by investigating how different acoustic frequencies contribute to FFRENV, analyzing responses to complex tones composed of different acoustic harmonics of 100 Hz (Experiment 2). Results show that the FFRENV response is dominated by peripheral auditory channels responding to unresolved harmonics, although low-frequency channels driven by resolved harmonics also contribute. These results demonstrate the utility of the PLV for quantifying the strength of FFRENV across conditions. PMID:23862815

Assessment of foetal exposure to the homogeneous magnetic field harmonic spectrum generated by electricity transmission and distribution networks.

PubMed

Fiocchi, Serena; Liorni, Ilaria; Parazzini, Marta; Ravazzani, Paolo

2015-04-01

During the last decades studies addressing the effects of exposure to Extremely Low Frequency Electromagnetic Fields (ELF-EMF) have pointed out a possible link between those fields emitted by power lines and childhood leukaemia. They have also stressed the importance of also including in the assessment the contribution of frequency components, namely harmonics, other than the fundamental one. Based on the spectrum of supply voltage networks allowed by the European standard for electricity quality assessment, in this study the exposure of high-resolution three-dimensional models of foetuses to the whole harmonic content of a uniform magnetic field with a fundamental frequency of 50 Hz, was assessed. The results show that the main contribution in terms of induced electric fields to the foetal exposure is given by the fundamental frequency component. The harmonic components add some contributions to the overall level of electric fields, however, due to the extremely low permitted amplitude of the harmonic components with respect to the fundamental, their amplitudes are low. The level of the induced electric field is also much lower than the limits suggested by the guidelines for general public exposure, when the amplitude of the incident magnetic field is set at the maximum permitted level.

Assessment of Foetal Exposure to the Homogeneous Magnetic Field Harmonic Spectrum Generated by Electricity Transmission and Distribution Networks

PubMed Central

Fiocchi, Serena; Liorni, Ilaria; Parazzini, Marta; Ravazzani, Paolo

2015-01-01

During the last decades studies addressing the effects of exposure to Extremely Low Frequency Electromagnetic Fields (ELF-EMF) have pointed out a possible link between those fields emitted by power lines and childhood leukaemia. They have also stressed the importance of also including in the assessment the contribution of frequency components, namely harmonics, other than the fundamental one. Based on the spectrum of supply voltage networks allowed by the European standard for electricity quality assessment, in this study the exposure of high-resolution three-dimensional models of foetuses to the whole harmonic content of a uniform magnetic field with a fundamental frequency of 50 Hz, was assessed. The results show that the main contribution in terms of induced electric fields to the foetal exposure is given by the fundamental frequency component. The harmonic components add some contributions to the overall level of electric fields, however, due to the extremely low permitted amplitude of the harmonic components with respect to the fundamental, their amplitudes are low. The level of the induced electric field is also much lower than the limits suggested by the guidelines for general public exposure, when the amplitude of the incident magnetic field is set at the maximum permitted level. PMID:25837346

Filter bank canonical correlation analysis for implementing a high-speed SSVEP-based brain-computer interface

NASA Astrophysics Data System (ADS)

Chen, Xiaogang; Wang, Yijun; Gao, Shangkai; Jung, Tzyy-Ping; Gao, Xiaorong

2015-08-01

Objective. Recently, canonical correlation analysis (CCA) has been widely used in steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) due to its high efficiency, robustness, and simple implementation. However, a method with which to make use of harmonic SSVEP components to enhance the CCA-based frequency detection has not been well established. Approach. This study proposed a filter bank canonical correlation analysis (FBCCA) method to incorporate fundamental and harmonic frequency components to improve the detection of SSVEPs. A 40-target BCI speller based on frequency coding (frequency range: 8-15.8 Hz, frequency interval: 0.2 Hz) was used for performance evaluation. To optimize the filter bank design, three methods (M1: sub-bands with equally spaced bandwidths; M2: sub-bands corresponding to individual harmonic frequency bands; M3: sub-bands covering multiple harmonic frequency bands) were proposed for comparison. Classification accuracy and information transfer rate (ITR) of the three FBCCA methods and the standard CCA method were estimated using an offline dataset from 12 subjects. Furthermore, an online BCI speller adopting the optimal FBCCA method was tested with a group of 10 subjects. Main results. The FBCCA methods significantly outperformed the standard CCA method. The method M3 achieved the highest classification performance. At a spelling rate of ˜33.3 characters/min, the online BCI speller obtained an average ITR of 151.18 ± 20.34 bits min-1. Significance. By incorporating the fundamental and harmonic SSVEP components in target identification, the proposed FBCCA method significantly improves the performance of the SSVEP-based BCI, and thereby facilitates its practical applications such as high-speed spelling.

Direct measurement of density oscillation induced by a radio-frequency wave.

PubMed

Yamada, T; Ejiri, A; Shimada, Y; Oosako, T; Tsujimura, J; Takase, Y; Kasahara, H

2007-08-01

An O-mode reflectometer at a frequency of 25.85 GHz was applied to plasmas heated by the high harmonic fast wave (21 MHz) in the TST-2 spherical tokamak. An oscillation in the phase of the reflected microwave in the rf range was observed directly for the first time. In TST-2, the rf (250 kW) induced density oscillation depends mainly on the poloidal rf electric field, which is estimated to be about 0.2 kV/m rms by the reflectometer measurement. Sideband peaks separated in frequency by ion cyclotron harmonics from 21 MHz, and peaks at ion cyclotron harmonics which are suggested to be quasimodes generated by parametric decay, were detected.

A mean-based filter to remove power line harmonic noise from seismic reflection data

NASA Astrophysics Data System (ADS)

Karslı, Hakan; Dondurur, Derman

2018-06-01

Power line harmonic noise generated by power lines during the seismic data acquisition in land and marine seismic surveys generally appears as a single frequency with 50/60 Hz (or multiples of these frequencies) and contaminates seismic data leading to complicate the identification of fine details in the data. Commonly applied method during seismic data processing to remove the harmonic noise is classical notch filter (or very narrow band-stop filter), however, it also attenuates all recorded data around the notch frequencies and results in a complete loss of available information which corresponds to fine details in the seismic data. In this study, we introduce an application of the algorithm of iterative trimmed and truncated mean filter method (ITTM) to remove the harmonic noise from seismic data, and here, we name the method as local ITTM (LITTM) since we applied it to the seismic data locally in spectral domain. In this method, an optimal value is iteratively searched depending on a threshold value by trimming and truncating process for the spectral amplitude samples within the specified spectral window. Therefore, the LITTM filter converges to the median, but, there is no need to sort the data as in the case of conventional median filters. On the other hand, the LITTM filtering process doesn't require any reference signal or a precise estimate of the fundamental frequency of the harmonic noise, and only approximate frequency band of the noise within the amplitude spectra is considered. The only required parameter of the method is the width of this frequency band in the spectral domain. The LITTM filter is first applied to synthetic data and then we analyze a real marine dataset to compare the quality of the output after removing the power line noise by classical notch, median and proposed LITTM filters. We observe that the power line harmonic noise is completely filtered out by LITTM filter, and unlike the conventional notch filter, without any damage on the available frequencies around the notch frequency band. It also provides a more balanced amplitude spectrum since it does not produce amplitude notches in the spectrum.

Effect of Frequency and Spatial-Harmonics on Rotary and Linear Induction Motor Characteristics

DOT National Transportation Integrated Search

1972-03-01

A computer analysis is made of the effect of current and MMF airgap harmonics on the output characteristics of rotary and linear induction motors. The current harmonics accompanying thyristor-control operation are evaluated by Fourier analyzing the p...

First-harmonic nonlinearities can predict unseen third-harmonics in medium-amplitude oscillatory shear (MAOS)

NASA Astrophysics Data System (ADS)

Carey-De La Torre, Olivia; Ewoldt, Randy H.

2018-02-01

We use first-harmonic MAOS nonlinearities from G 1' and G 1″ to test a predictive structure-rheology model for a transient polymer network. Using experiments with PVA-Borax (polyvinyl alcohol cross-linked by sodium tetraborate (borax)) at 11 different compositions, the model is calibrated to first-harmonic MAOS data on a torque-controlled rheometer at a fixed frequency, and used to predict third-harmonic MAOS on a displacement controlled rheometer at a different frequency three times larger. The prediction matches experiments for decomposed MAOS measures [ e 3] and [ v 3] with median disagreement of 13% and 25%, respectively, across all 11 compositions tested. This supports the validity of this model, and demonstrates the value of using all four MAOS signatures to understand and test structure-rheology relations for complex fluids.

Research on Harmonic Characteristic of Electronic Current Transformer Based on the Rogowski Coil

NASA Astrophysics Data System (ADS)

Shen, Diqiu; Hu, Bei; Wang, Xufeng; Zhu, Mingdong; Wang, Liang; Lu, Wenxing

2017-05-01

The nonlinear load present in the power system will cause the distortion of AC sine wave and generate the harmonic, which havea severe impact on the accuracy of energy metering and reliability of relay protection. Tosatisfy the requirements of energy metering and relay protection for the new generation of intelligent substation, based on the working principle of Rogowski coil current transformer, mathematical model and transfer characteristics of Rogowski coil sensors were studied in this paper, and frequency response characteristics of Rogowski coil current transformer system were analysed. Finally, the frequency response characteristics of the Rogowski coil current transformer at 2 to 13 harmonics was simulated and experimented. Simulation and experiments show that Rogowski coil current transformer couldmeet 0.2 accuracy requirements of harmonic power measurement of power system, and measure the harmonic components of the grid reliably.

Higher-order power harmonics of pulsed electrical stimulation modulates corticospinal contribution of peripheral nerve stimulation.

PubMed

Chen, Chiun-Fan; Bikson, Marom; Chou, Li-Wei; Shan, Chunlei; Khadka, Niranjan; Chen, Wen-Shiang; Fregni, Felipe

2017-03-03

It is well established that electrical-stimulation frequency is crucial to determining the scale of induced neuromodulation, particularly when attempting to modulate corticospinal excitability. However, the modulatory effects of stimulation frequency are not only determined by its absolute value but also by other parameters such as power at harmonics. The stimulus pulse shape further influences parameters such as excitation threshold and fiber selectivity. The explicit role of the power in these harmonics in determining the outcome of stimulation has not previously been analyzed. In this study, we adopted an animal model of peripheral electrical stimulation that includes an amplitude-adapted pulse train which induces force enhancements with a corticospinal contribution. We report that the electrical-stimulation-induced force enhancements were correlated with the amplitude of stimulation power harmonics during the amplitude-adapted pulse train. In an exploratory analysis, different levels of correlation were observed between force enhancement and power harmonics of 20-80 Hz (r = 0.4247, p = 0.0243), 100-180 Hz (r = 0.5894, p = 0.0001), 200-280 Hz (r = 0.7002, p < 0.0001), 300-380 Hz (r = 0.7449, p < 0.0001), 400-480 Hz (r = 0.7906, p < 0.0001), 500-600 Hz (r = 0.7717, p < 0.0001), indicating a trend of increasing correlation, specifically at higher order frequency power harmonics. This is a pilot, but important first demonstration that power at high order harmonics in the frequency spectrum of electrical stimulation pulses may contribute to neuromodulation, thus warrant explicit attention in therapy design and analysis.

Pulse shape measurements using single shot-frequency resolved optical gating for high energy (80 J) short pulse (600 fs) laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palaniyappan, S.; Johnson, R.; Shimada, T.

2010-10-15

Relevant to laser based electron/ion accelerations, a single shot second harmonic generation frequency resolved optical gating (FROG) system has been developed to characterize laser pulses (80 J, {approx}600 fs) incident on and transmitted through nanofoil targets, employing relay imaging, spatial filter, and partially coated glass substrates to reduce spatial nonuniformity and B-integral. The device can be completely aligned without using a pulsed laser source. Variations of incident pulse shape were measured from durations of 613 fs (nearly symmetric shape) to 571 fs (asymmetric shape with pre- or postpulse). The FROG measurements are consistent with independent spectral and autocorrelation measurements.

A discrepancy within primate spatial vision and its bearing on the definition of edge detection processes in machine vision

NASA Technical Reports Server (NTRS)

Jobson, Daniel J.

1990-01-01

The visual perception of form information is considered to be based on the functioning of simple and complex neurons in the primate striate cortex. However, a review of the physiological data on these brain cells cannot be harmonized with either the perceptual spatial frequency performance of primates or the performance which is necessary for form perception in humans. This discrepancy together with recent interest in cortical-like and perceptual-like processing in image coding and machine vision prompted a series of image processing experiments intended to provide some definition of the selection of image operators. The experiments were aimed at determining operators which could be used to detect edges in a computational manner consistent with the visual perception of structure in images. Fundamental issues were the selection of size (peak spatial frequency) and circular versus oriented operators (or some combination). In a previous study, circular difference-of-Gaussian (DOG) operators, with peak spatial frequency responses at about 11 and 33 cyc/deg were found to capture the primary structural information in images. Here larger scale circular DOG operators were explored and led to severe loss of image structure and introduced spatial dislocations (due to blur) in structure which is not consistent with visual perception. Orientation sensitive operators (akin to one class of simple cortical neurons) introduced ambiguities of edge extent regardless of the scale of the operator. For machine vision schemes which are functionally similar to natural vision form perception, two circularly symmetric very high spatial frequency channels appear to be necessary and sufficient for a wide range of natural images. Such a machine vision scheme is most similar to the physiological performance of the primate lateral geniculate nucleus rather than the striate cortex.

Influence of two-stream relativistic electron beam parameters on the space-charge wave with broad frequency spectrum formation

NASA Astrophysics Data System (ADS)

Alexander, LYSENKO; Iurii, VOLK

2018-03-01

We developed a cubic non-linear theory describing the dynamics of the multiharmonic space-charge wave (SCW), with harmonics frequencies smaller than the two-stream instability critical frequency, with different relativistic electron beam (REB) parameters. The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation. This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect. Different REB parameters such as the input angle with respect to focusing magnetic field, the average relativistic factor value, difference of partial relativistic factors, and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels. We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers, with the main purpose of forming a powerful multiharmonic electromagnetic wave.

A high repetition rate multiwavelength polarized solid state laser source for long range lidar applications

NASA Astrophysics Data System (ADS)

Sudheer, S. K.; Pillai, V. P. Mahadevan; Nayar, V. U.

2006-12-01

Advances in Laser Technology and nonlinear Optical techniques can be effectively utilized for LIDAR applications in space and atmospheric sciences to achieve better flexibility and control of the available optical power. Using such devices, one can achieve highly accurate and resolved, measurement of the distribution for atmospheric scattering layers. In the present investigation a diode double end pumped high repetition rate, multi wavelength Nd:YAG laser is designed, fabricated and various laser beam parameters have been characterized for LIDAR applications. Nonlinear optical techniques have been employed to generate higher harmonics like 532nm, 355nm and 266nm for various spectral studies. The experimental setup mainly consists of two Fiber coupled pump laser diodes (Model FAP- 81-30C-800B, Coherent Inc, USA) with a maximum output power of 30Watt at a wavelength of 807-810nm at 30°C set temperature. A second harmonic LBO crystal cut for critical phase matching placed within the laser resonator is provided for converting a fraction of the fundamental beam to a second harmonic beam. A type II frequency tripling LBO nonlinear crystal (cut for critical phase matching) is also located inside the laser resonator. The third harmonic beam and the unconverted fundamental beam are then directed across a type I fourth harmonic LBO crystal cut for critical phase matching where a portion of the fundamental beam and a portion of the third harmonic beam are converted to a fourth harmonic frequency when both fundamental and third harmonic beams propagate through the frequency quadrupling crystal. The resulting beams which are the fundamental (1064nm), second harmonic (532nm), third harmonic (355nm) and fourth harmonic (266nm) are then directed to a fourth harmonic separator in which the fourth harmonic beam is separated from the fundamental beam. A maximum average power of 12W at 1064nm, 8W at 532nm, 5W at 355nm and 3W at 266nm have been measured at a repetition rate of 10KHz. A minimum pulse width of 25ns have been observed.

Theoretical Analysis About Quantum Noise Squeezing of Optical Fields From an Intracavity Frequency-Doubled Laser

NASA Technical Reports Server (NTRS)

Zhang, Kuanshou; Xie, Changde; Peng, Kunchi

1996-01-01

The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.

Approximating high angular resolution apparent diffusion coefficient profiles using spherical harmonics under BiGaussian assumption

NASA Astrophysics Data System (ADS)

Cao, Ning; Liang, Xuwei; Zhuang, Qi; Zhang, Jun

2009-02-01

Magnetic Resonance Imaging (MRI) techniques have achieved much importance in providing visual and quantitative information of human body. Diffusion MRI is the only non-invasive tool to obtain information of the neural fiber networks of the human brain. The traditional Diffusion Tensor Imaging (DTI) is only capable of characterizing Gaussian diffusion. High Angular Resolution Diffusion Imaging (HARDI) extends its ability to model more complex diffusion processes. Spherical harmonic series truncated to a certain degree is used in recent studies to describe the measured non-Gaussian Apparent Diffusion Coefficient (ADC) profile. In this study, we use the sampling theorem on band-limited spherical harmonics to choose a suitable degree to truncate the spherical harmonic series in the sense of Signal-to-Noise Ratio (SNR), and use Monte Carlo integration to compute the spherical harmonic transform of human brain data obtained from icosahedral schema.

A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation.

PubMed

Hu, Yi

2010-05-01

Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions.

Frequency-domain optical tomographic image reconstruction algorithm with the simplified spherical harmonics (SP3) light propagation model.

PubMed

Kim, Hyun Keol; Montejo, Ludguier D; Jia, Jingfei; Hielscher, Andreas H

2017-06-01

We introduce here the finite volume formulation of the frequency-domain simplified spherical harmonics model with n -th order absorption coefficients (FD-SP N ) that approximates the frequency-domain equation of radiative transfer (FD-ERT). We then present the FD-SP N based reconstruction algorithm that recovers absorption and scattering coefficients in biological tissue. The FD-SP N model with 3 rd order absorption coefficient (i.e., FD-SP 3 ) is used as a forward model to solve the inverse problem. The FD-SP 3 is discretized with a node-centered finite volume scheme and solved with a restarted generalized minimum residual (GMRES) algorithm. The absorption and scattering coefficients are retrieved using a limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm. Finally, the forward and inverse algorithms are evaluated using numerical phantoms with optical properties and size that mimic small-volume tissue such as finger joints and small animals. The forward results show that the FD-SP 3 model approximates the FD-ERT (S 12 ) solution within relatively high accuracy; the average error in the phase (<3.7%) and the amplitude (<7.1%) of the partial current at the boundary are reported. From the inverse results we find that the absorption and scattering coefficient maps are more accurately reconstructed with the SP 3 model than those with the SP 1 model. Therefore, this work shows that the FD-SP 3 is an efficient model for optical tomographic imaging of small-volume media with non-diffuse properties both in terms of computational time and accuracy as it requires significantly lower CPU time than the FD-ERT (S 12 ) and also it is more accurate than the FD-SP 1 .

Utility of Higher Harmonics in Electrospray Ionization Fourier Transform Electrostatic Linear Ion Trap Mass Spectrometry.

PubMed

Dziekonski, Eric T; Johnson, Joshua T; McLuckey, Scott A

2017-04-18

Mass resolution (M/ΔM fwhm) is observed to linearly increase with harmonic order in a Fourier transform electrostatic linear ion trap (ELIT) mass spectrometer. This behavior was predicted by Grosshans and Marshall for frequency-multiple detection in a Fourier transform ion cyclotron resonance mass spectrometer only for situations when the prominent mechanism for signal decay is ion ejection from the trap. As the analyzer pressure in our ELIT chamber is relatively high, such that collisional scattering and collision-induced dissociation are expected to underlie much of the ion loss, we sought to explore the relationship between harmonic order and mass resolution. Mass resolutions of 36 900 (fundamental), 75 850 (2nd harmonic), and 108 200 (3rd harmonic) were obtained for GdO + (avg. m/z 173.919) with a transient length of 300 ms. To demonstrate that the mass resolution was truly increasing with harmonic order, the unresolved isotopes at the fundamental distribution of cytochrome c +8 (m/z ∼ 1549) were nearly baseline, resolved at the third harmonic (mass resolution ≈ 23 000) with a transient length of only 200 ms. This experiment demonstrates that, when the ion density is sufficiently low, ions with frequency differences of less than 4 Hz remain uncoalesced. Higher harmonics can be used to increase the effective mass resolution for a fixed transient length and thereby may enable the resolution of closely spaced masses, determination of a protein ion's charge state, and study of the onset of peak coalescence when the resolution at the fundamental frequency is insufficient.

Simulation of 100-300 GHz solid-state harmonic sources

NASA Technical Reports Server (NTRS)

Zybura, Michael F.; Jones, J. Robert; Jones, Stephen H.; Tait, Gregory B.

1995-01-01

Accurate and efficient simulations of the large-signal time-dependent characteristics of second-harmonic Transferred Electron Oscillators (TEO's) and Heterostructure Barrier Varactor (HBV) frequency triplers have been obtained. This is accomplished by using a novel and efficient harmonic-balance circuit analysis technique which facilitates the integration of physics-based hydrodynamic device simulators. The integrated hydrodynamic device/harmonic-balance circuit simulators allow TEO and HBV circuits to be co-designed from both a device and a circuit point of view. Comparisons have been made with published experimental data for both TEO's and HBV's. For TEO's, excellent correlation has been obtained at 140 GHz and 188 GHz in second-harmonic operation. Excellent correlation has also been obtained for HBV frequency triplers operating near 200 GHz. For HBV's, both a lumped quasi-static equivalent circuit model and the hydrodynamic device simulator have been linked to the harmonic-balance circuit simulator. This comparison illustrates the importance of representing active devices with physics-based numerical device models rather than analytical device models.

Individual differences reveal the basis of consonance.

PubMed

McDermott, Josh H; Lehr, Andriana J; Oxenham, Andrew J

2010-06-08

Some combinations of musical notes are consonant (pleasant), whereas others are dissonant (unpleasant), a distinction central to music. Explanations of consonance in terms of acoustics, auditory neuroscience, and enculturation have been debated for centuries. We utilized individual differences to distinguish the candidate theories. We measured preferences for musical chords as well as nonmusical sounds that isolated particular acoustic factors--specifically, the beating and the harmonic relationships between frequency components, two factors that have long been thought to potentially underlie consonance. Listeners preferred stimuli without beats and with harmonic spectra, but across more than 250 subjects, only the preference for harmonic spectra was consistently correlated with preferences for consonant over dissonant chords. Harmonicity preferences were also correlated with the number of years subjects had spent playing a musical instrument, suggesting that exposure to music amplifies preferences for harmonic frequencies because of their musical importance. Harmonic spectra are prominent features of natural sounds, and our results indicate that they also underlie the perception of consonance. 2010 Elsevier Ltd. All rights reserved.

Multicascade X-Ray Free-Electron Laser with Harmonic Multiplier and Two-Frequency Undulator

NASA Astrophysics Data System (ADS)

Zhukovsky, K. V.

2018-06-01

The feasibility of generation of powerful x-ray radiation by a cascade free-electron laser (FEL) with amplification of higher harmonics using a two-frequency undulator is studied. To analyze the FEL operation, a complex phenomenological single-pass FEL model is developed and used. It describes linear and nonlinear generation of harmonics in the FEL with seed laser that takes into account initial electron beam noise and describes all main losses of each harmonic in each FEL cascade. The model is also calibrated against and approved by the experimental FEL data and available results of three-dimensional numerical simulation. The electron beam in the undulator is assumed to be matched and focused, and the dynamics of power in the singlepass FEL with cascade harmonic multipliers is investigated to obtain x-ray laser radiation in the FEL having the shortest length, beam energy, and frequency of the seed laser as low as possible. In this context, the advantages of the two-frequency undulator used for generation of harmonics are demonstrated. The evolution of harmonics in a multicascade FEL with multiplication of harmonics is investigated. The operation of the cascade FEL at the wavelength λ = 1.14 nm, generating 30 MW already on 38 m with the seed laser operating at a wavelength of 11.43 nm corresponding to the maximal reflectivity of the multilayered mirror MoRu/Be coating is investigated. In addition, the operation of the multicascade FEL with accessible seed UVlaser operating at a wavelength of 157 nm (F2 excimer UV-laser) and electron beam with energy of 0.5 GeV is investigated. X-ray radiation simulated in it at the wavelength λ 3.9 nm reaches power of 50 MW already at 27 m, which is by two orders of magnitude shorter than 3.4 km of the x-ray FEL recently put into operation in Europe.

On the Harmonic Coupling of Components in Pairs of IIIb-III Bursts at Decameter Wavelengths

NASA Astrophysics Data System (ADS)

Brazhenko, A. I.; Melnik, V. N.; Frantsuzenko, A. V.; Dorovskyy, V. V.; Rucker, H. O.; Panchenko, M.

2015-06-01

The properties of IIIb-III pairs observed by the URAN-2 radioThe properties of IIIb-III pairs observed by the URAN-2 radiotelescope at frequencies 16-32 MHz are analyzed. Observations of these bursts were hold in April, June and September 2011. Durations, frequency drift rates, simultaneous frequency ratio of pairs components and their polarizations are analyzed. Pro and contra of IIIb-III harmonic connection are discussed.

In situ quantitative evaluation of osteoblastic collagen synthesis under cyclic strain by using second-harmonic-generation microscope

NASA Astrophysics Data System (ADS)

Matsubara, Oki; Hase, Eiji; Minamikawa, Takeo; Yasui, Takeshi; Sato, Katsuya

2016-03-01

Osteoblast-produced collagen matrix in bone is influenced by the mechanical stimulus from their surroundings. However, it has been still unclear how mechanical stimulus affects collagen production by osteoblasts. Therefore, it is strongly required to investigate the characteristics of osteoblastic bone regenerative tissue engineering. Recently, second-harmonic-generation (SHG) microscope has attracted attention for in situ visualization of collagen fiber because of less invasiveness, unstaining and no fixation, as well as high spatial resolution and 3D imaging. Using SHG microscopy, one can track the temporal dynamics of collagen fiber during the cultured period of the sample. We applied cyclic stretch strain to osteoblasts (MC3T3-E1) by using originally developed cell stretching device. The stimulation time was set to 5min or 3hours with same strain 5% and same frequency 0.5Hz. Cells were seeded onto the PDMS (polydimethylsiloxane) rubber chamber at a density of 50,000 cells/cm2 and cultured in α-MEM with 10% FBS, 1% P/S, 1% Ascorbic acid, 0.2% hydrocortisone and 2% β-Glycerophosphate. SHG imaging was carried out every 7 days. As a result, we confirmed from SHG image that the collagen production was enhanced by the cyclic stretch strain, stretch stimulation time and stretch application term.

Temporal Tuning of Word- and Face-selective Cortex.

PubMed

Yeatman, Jason D; Norcia, Anthony M

2016-11-01

Sensitivity to temporal change places fundamental limits on object processing in the visual system. An emerging consensus from the behavioral and neuroimaging literature suggests that temporal resolution differs substantially for stimuli of different complexity and for brain areas at different levels of the cortical hierarchy. Here, we used steady-state visually evoked potentials to directly measure three fundamental parameters that characterize the underlying neural response to text and face images: temporal resolution, peak temporal frequency, and response latency. We presented full-screen images of text or a human face, alternated with a scrambled image, at temporal frequencies between 1 and 12 Hz. These images elicited a robust response at the first harmonic that showed differential tuning, scalp topography, and delay for the text and face images. Face-selective responses were maximal at 4 Hz, but text-selective responses, by contrast, were maximal at 1 Hz. The topography of the text image response was strongly left-lateralized at higher stimulation rates, whereas the response to the face image was slightly right-lateralized but nearly bilateral at all frequencies. Both text and face images elicited steady-state activity at more than one apparent latency; we observed early (141-160 msec) and late (>250 msec) text- and face-selective responses. These differences in temporal tuning profiles are likely to reflect differences in the nature of the computations performed by word- and face-selective cortex. Despite the close proximity of word- and face-selective regions on the cortical surface, our measurements demonstrate substantial differences in the temporal dynamics of word- versus face-selective responses.

Cumulative phase delay imaging - A new contrast enhanced ultrasound modality

NASA Astrophysics Data System (ADS)

Demi, Libertario; van Sloun, Ruud J. G.; Wijkstra, Hessel; Mischi, Massimo

2015-10-01

Recently, a new acoustic marker for ultrasound contrast agents (UCAs) has been introduced. A cumulative phase delay (CPD) between the second harmonic and fundamental pressure wave field components is in fact observable for ultrasound propagating through UCAs. This phenomenon is absent in the case of tissue nonlinearity and is dependent on insonating pressure and frequency, UCA concentration, and propagation path length through UCAs. In this paper, ultrasound images based on this marker are presented. The ULA-OP research platform, in combination with a LA332 linear array probe (Esaote, Firenze Italy), were used to image a gelatin phantom containing a PVC plate (used as a reflector) and a cylindrical cavity measuring 7 mm in diameter (placed in between the observation point and the PVC plate). The cavity contained a 240 µL/L SonoVueO® UCA concentration. Two insonating frequencies (3 MHz and 2.5 MHz) were used to scan the gelatine phantom. A mechanical index MI = 0.07, measured in water at the cavity location with a HGL-0400 hydrophone (Onda, Sunnyvale, CA), was utilized. Processing the ultrasound signals backscattered from the plate, ultrasound images were generated in a tomographic fashion using the filtered back-projection method. As already observed in previous studies, significantly higher CPD values are measured when imaging at a frequency of 2.5 MHz, as compared to imaging at 3 MHz. In conclusion, these results confirm the applicability of the discussed CPD as a marker for contrast imaging. Comparison with standard contrast-enhanced ultrasound imaging modalities will be the focus of future work.

Adaptive suppression of power line interference in ultra-low field magnetic resonance imaging in an unshielded environment.

PubMed

Huang, Xiaolei; Dong, Hui; Qiu, Yang; Li, Bo; Tao, Quan; Zhang, Yi; Krause, Hans-Joachim; Offenhäusser, Andreas; Xie, Xiaoming

2018-01-01

Power-line harmonic interference and fixed-frequency noise peaks may cause stripe-artifacts in ultra-low field (ULF) magnetic resonance imaging (MRI) in an unshielded environment and in a conductively shielded room. In this paper we describe an adaptive suppression method to eliminate these artifacts in MRI images. This technique utilizes spatial correlation of the interference from different positions, and is realized by subtracting the outputs of the reference channel(s) from those of the signal channel(s) using wavelet analysis and the least squares method. The adaptive suppression method is first implemented to remove the image artifacts in simulation. We then experimentally demonstrate the feasibility of this technique by adding three orthogonal superconducting quantum interference device (SQUID) magnetometers as reference channels to compensate the output of one 2nd-order gradiometer. The experimental results show great improvement in the imaging quality in both 1D and 2D MRI images at two common imaging frequencies, 1.3 kHz and 4.8 kHz. At both frequencies, the effective compensation bandwidth is as high as 2 kHz. Furthermore, we examine the longitudinal relaxation times of the same sample before and after compensation, and show that the MRI properties of the sample did not change after applying adaptive suppression. This technique can effectively increase the imaging bandwidth and be applied to ULF MRI detected by either SQUIDs or Faraday coil in both an unshielded environment and a conductively shielded room. Copyright © 2017 Elsevier Inc. All rights reserved.

Fully automated muscle quality assessment by Gabor filtering of second harmonic generation images

NASA Astrophysics Data System (ADS)

Paesen, Rik; Smolders, Sophie; Vega, José Manolo de Hoyos; Eijnde, Bert O.; Hansen, Dominique; Ameloot, Marcel

2016-02-01

Although structural changes on the sarcomere level of skeletal muscle are known to occur due to various pathologies, rigorous studies of the reduced sarcomere quality remain scarce. This can possibly be explained by the lack of an objective tool for analyzing and comparing sarcomere images across biological conditions. Recent developments in second harmonic generation (SHG) microscopy and increasing insight into the interpretation of sarcomere SHG intensity profiles have made SHG microscopy a valuable tool to study microstructural properties of sarcomeres. Typically, sarcomere integrity is analyzed by fitting a set of manually selected, one-dimensional SHG intensity profiles with a supramolecular SHG model. To circumvent this tedious manual selection step, we developed a fully automated image analysis procedure to map the sarcomere disorder for the entire image at once. The algorithm relies on a single-frequency wavelet-based Gabor approach and includes a newly developed normalization procedure allowing for unambiguous data interpretation. The method was validated by showing the correlation between the sarcomere disorder, quantified by the M-band size obtained from manually selected profiles, and the normalized Gabor value ranging from 0 to 1 for decreasing disorder. Finally, to elucidate the applicability of our newly developed protocol, Gabor analysis was used to study the effect of experimental autoimmune encephalomyelitis on the sarcomere regularity. We believe that the technique developed in this work holds great promise for high-throughput, unbiased, and automated image analysis to study sarcomere integrity by SHG microscopy.

UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects

NASA Astrophysics Data System (ADS)

Watkins, Brenton; Fallen, Christopher; Secan, James

Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF frequency increasing near the gyro-harmonic value were conducted. The FM scan rate was sufficiently slow that the electron density was approximately in an equilibrium state. For these experiments the altitude of the HF interaction follows a near straight line downward parallel to the altitude-dependent gyro-harmonic level.

A new method for gravity field recovery based on frequency analysis of spherical harmonics

NASA Astrophysics Data System (ADS)

Cai, Lin; Zhou, Zebing

2017-04-01

All existing methods for gravity field recovery are mostly based on the space-wise and time-wise approach, whose core processes are constructing the observation equations and solving them by the least square method. It's should be pointed that the least square method means the approximation. On the other hand, we can directly and precisely obtain the coefficients of harmonics by computing the Fast Fourier Transform (FFT) when we do 1-D data (time series) analysis. So the question whether we directly and precisely obtain the coefficients of spherical harmonic by computing 2-D FFT of measurements of satellite gravity mission is of great significance, since this may guide us to a new understanding of the signal components of gravity field and make us determine it quickly by taking advantage of FFT. Like the 1-D data analysis, the 2-D FFT of measurements of satellite can be computed rapidly. If we can determine the relationship between spherical harmonics and 2-D Fourier frequencies and the transfer function from measurements to spherical coefficients, the question mentioned above can be solved. So the objective of this research project is to establish a new method based on frequency analysis of spherical harmonic, which directly compute the confidents of spherical harmonic of gravity field, which is differ from recovery by least squares. There is a one to one correspondence between frequency spectrum and the time series in 1-D FFT. The 2-D FFT has a similar relationship to 1-D FFT. Owing to the fact that any degree or order (higher than one) of spherical function has multi frequencies and these frequencies may be aliased. Fortunately, the elements and ratio of these frequencies of spherical function can be determined, and we can compute the coefficients of spherical function from 2-D FFT. This relationship can be written as equations and equivalent to a matrix, which is solid and can be derived in advance. Until now the relationship has be determined. Some preliminary results, which only compute lower degree spherical harmonics, indicates that the difference between the input (EGM2008) and output (coefficients from recovery) is smaller than 5E-17, while the minimal precision of computer software (Matlab) is 2.2204E-16.

Truncation of Spherical Harmonic Series and its Influence on Gravity Field Modelling

NASA Astrophysics Data System (ADS)

Fecher, T.; Gruber, T.; Rummel, R.

2009-04-01

Least-squares adjustment is a very common and effective tool for the calculation of global gravity field models in terms of spherical harmonic series. However, since the gravity field is a continuous field function its optimal representation by a finite series of spherical harmonics is connected with a set of fundamental problems. Particularly worth mentioning here are cut off errors and aliasing effects. These problems stem from the truncation of the spherical harmonic series and from the fact that the spherical harmonic coefficients cannot be determined independently of each other within the adjustment process in case of discrete observations. The latter is shown by the non-diagonal variance-covariance matrices of gravity field solutions. Sneeuw described in 1994 that the off-diagonal matrix elements - at least if data are equally weighted - are the result of a loss of orthogonality of Legendre polynomials on regular grids. The poster addresses questions arising from the truncation of spherical harmonic series in spherical harmonic analysis and synthesis. Such questions are: (1) How does the high frequency data content (outside the parameter space) affect the estimated spherical harmonic coefficients; (2) Where to truncate the spherical harmonic series in the adjustment process in order to avoid high frequency leakage?; (3) Given a set of spherical harmonic coefficients resulting from an adjustment, what is the effect of using only a truncated version of it?

Twenty-four tuba harmonics using a single pipe length

NASA Astrophysics Data System (ADS)

Holmes, Bud; Ruiz, Michael J.

2017-03-01

Harmonics arise naturally from the resonances in strings and pipes. A video demonstration (Ruiz 2016 YouTube: Tuba Harmonics (https://youtu.be/souhEzOP9c4)) is provided where a tubist (coauthor Holmes) produces a phenomenal 24 harmonics using a single tuba pipe length by controlling the buzz of his lips. The frequencies of the harmonics, measured with the free software program Audacity, fall excellently on a linear fit using a spreadsheet. The skillful musical production of so many harmonics with a fixed pipe length is an extraordinary illustration of physics.

Harmonic magneto-electric response in GaFeO3

NASA Astrophysics Data System (ADS)

Naiya, Amit Kumar; Awasthi, A. M.

2018-04-01

GaFeO3 is a well-known multiferroic material. Like optical second harmonic generation, it also generates radio frequency (RF) second harmonic due to its non-centrosymmetric orthorhombic structure. The harmonic RF response also features a magneto-electric character comparable in prominence to that of the fundamental response. We measured complex parts of the fundamental and the second harmonic over 80 K to 300 K. The second harmonic permittivity and its phase angle change sign at the spin glass transition temperature Tg = 200 K and becomes dispersive above ˜280 K.

Third harmonic generation microscopy

NASA Astrophysics Data System (ADS)

Squier, Jeffrey A.; Muller, Michiel; Brakenhoff, G. J.; Wilson, Kent R.

1998-10-01

Third harmonic generation microscopy is used to make dynamical images of living systems for the first time. A 100 fs excitation pulse at 1.2 æm results in a 400 nm signal which is generated directly within the specimen. Chara plant rhizoids have been imaged, showing dynamic plant activity, and non-fading image characteristics even with continuous viewing, indicating prolonged viability under these THG-imaging conditions.

Controlling the high frequency response of H{sub 2} by ultra-short tailored laser pulses: A time-dependent configuration interaction study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schönborn, Jan Boyke; Saalfrank, Peter; Klamroth, Tillmann, E-mail: klamroth@uni-potsdam.de

2016-01-28

We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H{sub 2} treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a “non-harmonic” response of H{sub 2} to a laser pulse. Specifically, we will show howmore » adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization.« less

Contrast-enhanced harmonic ultrasound imaging in ablation therapy for primary hepatocellular carcinoma.

PubMed

Minami, Yasunori; Kudo, Masatoshi

2009-12-31

The success rate of percutaneous radiofrequency (RF) ablation for hepatocellular carcinoma (HCC) depends on correct targeting via an imaging technique. However, RF electrode insertion is not completely accurate for residual HCC nodules because B-mode ultrasound (US), color Doppler, and power Doppler US findings cannot adequately differentiate between treated and viable residual tumor tissue. Electrode insertion is also difficult when we must identify the true HCC nodule among many large regenerated nodules in cirrhotic liver. Two breakthroughs in the field of US technology, harmonic imaging and the development of second-generation contrast agents, have recently been described and have demonstrated the potential to dramatically broaden the scope of US diagnosis of hepatic lesions. Contrast-enhanced harmonic US imaging with an intravenous contrast agent can evaluate small hypervascular HCC even when B-mode US cannot adequately characterize tumor. Therefore, contrast-enhanced harmonic US can facilitate RF ablation electrode placement in hypervascular HCC, which is poorly depicted by B-mode US. The use of contrast-enhanced harmonic US in ablation therapy for liver cancer is an efficient approach.

Compact single-pass X-ray FEL with harmonic multiplication cascades

NASA Astrophysics Data System (ADS)

Zhukovsky, K.

2018-07-01

The generation of X-ray radiation in cascaded single-pass free electron laser (FEL), which amplifies high harmonics of a two-frequency undulator, is studied. Power dynamics of FEL harmonics is explored with the help of the phenomenological model of a single pass FEL. The model describes both linear and non-linear harmonic generation, starting from a coherent seed laser and initial shot noise with account for main loss factors for each harmonic in each cascade individually: the energy spread and beam divergence, the coupling losses between FEL cascades, the diffraction etc. The model was validated with the experiment and with relevant 3-D simulations. It is employed for modeling the cascaded FELs with harmonic multiplication and analyzing the evolution of FEL harmonic power with the aim to obtain the maximum high harmonic power in the X-ray band at the shortest possible FEL length with the lowest possible seed frequency. The advantages of two-frequency undulators in HGHG FELs are elucidated. The requirements for the electron beam are studied; the need for low energy spread is evidenced: our evaluations yield σe < 2 × 10-4. Several cascaded HGHG FELs with two-frequency undulators are modeled. Generation of soft X-ray radiation at λ = 2 . 71 nm, reaching ∼50 MW power with I0 ∼ 100 A in a cascaded FEL at just 40 m with 13.51 nm seed, matching peak reflectivity of Mo/Si, is demonstrated. The generation of 40 MW radiation power at λ = 2 . 27 nm with the beam current I0 ∼ 100 A, energy E = 950 MeV and the energy spread σe = 2 × 10-4 is studied, using second and third harmonics in three-stage 45 m long FEL. The multistage FEL is modeled for generating radiation in nanometer band: ∼40 MW power at λ ∼ 2 . 6 nm with I0 ∼ 175 A current in just ∼40 m long FEL with commercially available F2 excimer UV laser seed at 157 nm. The peak radiation power rises to ∼0.5 GW for ∼1 kA beam current.

Human brain networks function in connectome-specific harmonic waves.

PubMed

Atasoy, Selen; Donnelly, Isaac; Pearson, Joel

2016-01-21

A key characteristic of human brain activity is coherent, spatially distributed oscillations forming behaviour-dependent brain networks. However, a fundamental principle underlying these networks remains unknown. Here we report that functional networks of the human brain are predicted by harmonic patterns, ubiquitous throughout nature, steered by the anatomy of the human cerebral cortex, the human connectome. We introduce a new technique extending the Fourier basis to the human connectome. In this new frequency-specific representation of cortical activity, that we call 'connectome harmonics', oscillatory networks of the human brain at rest match harmonic wave patterns of certain frequencies. We demonstrate a neural mechanism behind the self-organization of connectome harmonics with a continuous neural field model of excitatory-inhibitory interactions on the connectome. Remarkably, the critical relation between the neural field patterns and the delicate excitation-inhibition balance fits the neurophysiological changes observed during the loss and recovery of consciousness.

Detection of cyclic-fold bifurcation in electrostatic MEMS transducers by motion-induced current

NASA Astrophysics Data System (ADS)

Park, Sangtak; Khater, Mahmoud; Effa, David; Abdel-Rahman, Eihab; Yavuz, Mustafa

2017-08-01

This paper presents a new detection method of cyclic-fold bifurcations in electrostatic MEMS transducers based on a variant of the harmonic detection of resonance method. The electrostatic transducer is driven by an unbiased harmonic signal at half its natural frequency, ω a   =  1/2 ω o . The response of the transducer consists of static displacement and a series of harmonics at 2 ω a , 4 ω a , and so on. Its motion-induced current is shifted by the excitation frequency, ω a , to appear at 3 ω a , 5 ω a , and higher odd harmonics, providing higher sensitivity to the measurement of harmonic motions. With this method, we successfully detected the variation in the location of the cyclic-fold bifurcation of an encapsulated electrostatic MEMS transducer. We also detected a regime of tapping mode motions subsequent to the bifurcation.

The harmonic state of quantum cascade lasers: origin, control, and prospective applications [Invited].

PubMed

Piccardo, Marco; Chevalier, Paul; Mansuripur, Tobias S; Kazakov, Dmitry; Wang, Yongrui; Rubin, Noah A; Meadowcroft, Lauren; Belyanin, Alexey; Capasso, Federico

2018-04-16

The recently discovered ability of the quantum cascade laser to produce a harmonic frequency comb has attracted new interest in these devices for both applications and fundamental laser physics. In this review we present an extensive experimental phenomenology of the harmonic state, including its appearance in mid-infrared and terahertz quantum cascade lasers, studies of its destabilization induced by delayed optical feedback, and the assessment of its frequency comb nature. A theoretical model explaining its origin as due to the mutual interaction of population gratings and population pulsations inside the laser cavity will be described. We explore different approaches to control the spacing of the harmonic state, such as optical injection seeding and variation of the device temperature. Prospective applications of the harmonic state include microwave and terahertz generation, picosecond pulse generation in the mid-infrared, and broadband spectroscopy.

Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

NASA Technical Reports Server (NTRS)

Sim, Ben W.; Potsdam, Mark; Kitaplioglu, Cahit; LeMasurier, Philip; Lorber, Peter; Andrews, Joseph

2012-01-01

A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

Probability of Intercept in Electronic Countermeasures Receivers

DTIC Science & Technology

1975-12-01

modulating signals A and B are input to the 𔃻WT helix caus.ing a single frequency on the helix of TWT #1 to produce phase modu- lation of frequency A...and harmonics of A in TWT #1. A single frequency on the helix of TVT 42 produces phase modulation of frequency B and harmonics of B in TWT #2. The high...with YIG Pres’Žlector 34 9 Superheterodyne Receiver YIG z iter TWT 36 10 Wideband crystal video receiver 38 11 Tangential Sensitivity 40 12 Sensitivity

Cellular internalization of LiNbO3 nanocrystals for second harmonic imaging and the effects on stem cell differentiation

NASA Astrophysics Data System (ADS)

Li, Jianhua; Qiu, Jichuan; Guo, Weibo; Wang, Shu; Ma, Baojin; Mou, Xiaoning; Tanes, Michael; Jiang, Huaidong; Liu, Hong

2016-03-01

Second harmonic generation (SHG) nanocrystals have recently been reported to label cancer cells and other functional cell lines due to their unique double-frequency property. In this paper, we report for the first time the use of lithium niobate (LiNbO3, LN) nanocrystals as SHG labels for imaging stem cells. Rat mesenchymal stem cells (rMSCs) were labeled with LN nanocrystals in order to study the cellular internalization of the nanocrystals and the influence on stem cell differentiation. The results showed that LN nanocrystals were endocytosed by the rMSCs and the distribution of the internalized nanoparticles demonstrated a high consistency with the orientation of the actin filaments. Besides, LN-labeled rMSCs showed a concentration-dependent viability. Most importantly, rMSCs labeled with 50 μg per mL of LN nanocrystals retained their ability to differentiate into both osteogenic and adipogenic lineages. The results prove that LN nanocrystals can be used as a cytocompatible, near-infrared (NIR) light driven cell label for long-term imaging, without hindering stem cell differentiation. This work will promote the use of LN nanocrystals to broader applications like deep-tissue tracking, remote drug delivery and stem cell therapy.Second harmonic generation (SHG) nanocrystals have recently been reported to label cancer cells and other functional cell lines due to their unique double-frequency property. In this paper, we report for the first time the use of lithium niobate (LiNbO3, LN) nanocrystals as SHG labels for imaging stem cells. Rat mesenchymal stem cells (rMSCs) were labeled with LN nanocrystals in order to study the cellular internalization of the nanocrystals and the influence on stem cell differentiation. The results showed that LN nanocrystals were endocytosed by the rMSCs and the distribution of the internalized nanoparticles demonstrated a high consistency with the orientation of the actin filaments. Besides, LN-labeled rMSCs showed a concentration-dependent viability. Most importantly, rMSCs labeled with 50 μg per mL of LN nanocrystals retained their ability to differentiate into both osteogenic and adipogenic lineages. The results prove that LN nanocrystals can be used as a cytocompatible, near-infrared (NIR) light driven cell label for long-term imaging, without hindering stem cell differentiation. This work will promote the use of LN nanocrystals to broader applications like deep-tissue tracking, remote drug delivery and stem cell therapy. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00785f

The control of the magnetosphere by power line radiation

NASA Technical Reports Server (NTRS)

Luette, J. P.; Park, C. G.; Helliwell, R. A.

1979-01-01

Evidence is presented that radiated power line harmonics leak into high-altitude regions of the magnetosphere with sufficient intensity to control the starting frequencies of chorus emissions. OGO-3 data from three passes show that the starting frequencies of all measurable chorus emissions were within a few hertz of power line harmonics. It is also found that emissions detected over Western Europe were controlled by harmonics of 50 Hz; over the eastern United States and Canada by 60 Hz; and along the Alaska-New Zealand meridian by harmonics of both 50 and 60 Hz. These results indicate that man-made VLF noise plays an important role in the generation of chorus, one of the commonly observed forms of wave activity in the outer magnetosphere.

Introduction to Fourier Optics

ERIC Educational Resources Information Center

Huggins, Elisha

2007-01-01

Much like a physical prism, which displays the frequency components of a light wave, Fourier analysis can be thought of as a mathematical prism that can tell us what harmonics or frequency components are contained in a recording of a sound wave. We wrote the MacScope II program so that the user could not only see a plot of the harmonic amplitudes…

Embedding impedance approximations in the analysis of SIS mixers

NASA Technical Reports Server (NTRS)

Kerr, A. R.; Pan, S.-K.; Withington, S.

1992-01-01

Future millimeter-wave radio astronomy instruments will use arrays of many SIS receivers, either as focal plane arrays on individual radio telescopes, or as individual receivers on the many antennas of radio interferometers. Such applications will require broadband integrated mixers without mechanical tuners. To produce such mixers, it will be necessary to improve present mixer design techniques, most of which use the three-frequency approximation to Tucker's quantum mixer theory. This paper examines the adequacy of three approximations to Tucker's theory: (1) the usual three-frequency approximation which assumes a sinusoidal LO voltage at the junction, and a short-circuit at all frequencies above the upper sideband; (2) a five-frequency approximation which allows two LO voltage harmonics and five small-signal sidebands; and (3) a quasi five-frequency approximation in which five small-signal sidebands are allowed, but the LO voltage is assumed sinusoidal. These are compared with a full harmonic-Newton solution of Tucker's equations, including eight LO harmonics and their corresponding sidebands, for realistic SIS mixer circuits. It is shown that the accuracy of the three approximations depends strongly on the value of omega R(sub N)C for the SIS junctions used. For large omega R(sub N)C, all three approximations approach the eight-harmonic solution. For omega R(sub N)C values in the range 0.5 to 10, the range of most practical interest, the quasi five-frequency approximation is a considerable improvement over the three-frequency approximation, and should be suitable for much design work. For the realistic SIS mixers considered here, the five-frequency approximation gives results very close to those of the eight-harmonic solution. Use of these approximations, where appropriate, considerably reduces the computational effort needed to analyze an SIS mixer, and allows the design and optimization of mixers using a personal computer.

Nanoscale imaging with table-top coherent extreme ultraviolet source based on high harmonic generation

NASA Astrophysics Data System (ADS)

Ba Dinh, Khuong; Le, Hoang Vu; Hannaford, Peter; Van Dao, Lap

2017-08-01

A table-top coherent diffractive imaging experiment on a sample with biological-like characteristics using a focused narrow-bandwidth high harmonic source around 30 nm is performed. An approach involving a beam stop and a new reconstruction algorithm to enhance the quality of reconstructed the image is described.

Properties of Decameter IIIb-III Pairs

NASA Astrophysics Data System (ADS)

Melnik, V. N.; Brazhenko, A. I.; Frantsuzenko, A. V.; Dorovskyy, V. V.; Rucker, H. O.

2018-02-01

A large number of Type IIIb-III pairs, in which the first component is a Type IIIb burst and the second one is a Type III burst, are often recorded during decameter Type III burst storms. From the beginning of their observation, the question of whether the components of these pairs are the first and the second harmonics of radio emission or not has remained open. We discuss properties of decameter IIIb-III pairs in detail to answer this question. The components of these pairs, Type IIIb bursts and Type III bursts, have essentially different durations and polarizations. At the same time their frequency drift rates are rather close, provided that the drift rates of Type IIIb bursts are a little larger those of Type III bursts at the same frequency. Frequency ratios of the bursts at the same moment are close to two. This points at a harmonic connection of the components in IIIb-III pairs. At the same time there was a serious difficulty, namely why the first harmonic had fine frequency structure in the form of striae and the second harmonic did not have it. Recently Loi, Cairns, and Li ( Astrophys. J. 790, 67, 2014) succeeded in solving this problem. The physical aspects of observational properties of decameter IIIb-III pairs are discussed and pros and cons of harmonic character of Type IIIb bursts and Type III bursts in IIIb-III pairs are presented. We conclude that practically all properties of the IIIb-III pair components can be understood in the framework of the harmonic relation of the components of the IIIb-III pairs.

The norms and variances of the Gabor, Morlet and general harmonic wavelet functions

NASA Astrophysics Data System (ADS)

Simonovski, I.; Boltežar, M.

2003-07-01

This paper deals with certain properties of the continuous wavelet transform and wavelet functions. The norms and the spreads in time and frequency of the common Gabor and Morlet wavelet functions are presented. It is shown that the norm of the Morlet wavelet function does not satisfy the normalization condition and that the normalized Morlet wavelet function is identical to the Gabor wavelet function with the parameter σ=1. The general harmonic wavelet function is developed using frequency modulation of the Hanning and Hamming window functions. Several properties of the general harmonic wavelet function are also presented and compared to the Gabor wavelet function. The time and frequency spreads of the general harmonic wavelet function are only slightly higher than the time and frequency spreads of the Gabor wavelet function. However, the general harmonic wavelet function is simpler to use than the Gabor wavelet function. In addition, the general harmonic wavelet function can be constructed in such a way that the zero average condition is truly satisfied. The average value of the Gabor wavelet function can approach a value of zero but it cannot reach it. When calculating the continuous wavelet transform, errors occur at the start- and the end-time indexes. This is called the edge effect and is caused by the fact that the wavelet transform is calculated from a signal of finite length. In this paper, we propose a method that uses signal mirroring to reduce the errors caused by the edge effect. The success of the proposed method is demonstrated by using a simulated signal.

In vivo time-harmonic multifrequency elastography of the human liver

NASA Astrophysics Data System (ADS)

Tzschätzsch, Heiko; Ipek-Ugay, Selcan; Guo, Jing; Streitberger, Kaspar-Josche; Gentz, Enno; Fischer, Thomas; Klaua, Robert; Schultz, Michael; Braun, Jürgen; Sack, Ingolf

2014-04-01

Elastography is capable of noninvasively detecting hepatic fibrosis by imposing mechanical stress and measuring the viscoelastic response in the liver. Magnetic resonance elastography (MRE) relies on time-harmonic vibrations, while most dynamic ultrasound elastography methods employ transient stimulation methods. This study attempts to benefit from the advantages of time-harmonic tissue stimulation, i.e. relative insensitivity to obesity and ascites and mechanical approachability of the entire liver, and the advantages of ultrasound, i.e. time efficiency, low costs, and wide availability, by introducing in vivo time-harmonic elastography (THE) of the human liver using ultrasound and a broad range of harmonic stimulation frequencies. THE employs continuous harmonic shear vibrations at 7 frequencies from 30 to 60 Hz in a single examination and determines the elasticity and the viscosity of the liver from the dispersion of the shear wave speed within the applied frequency range. The feasibility of the method is demonstrated in the livers of eight healthy volunteers and a patient with cirrhosis. Multifrequency MRE at the same drive frequencies was used as elastographic reference method. Similar values of shear modulus and shear viscosity according the Kelvin-Voigt model were obtained by MRE and THE, indicating that the new method is suitable for in vivo quantification of the shear viscoelastic properties of the liver, however, in real-time and at a fraction of the costs of MRE. In conclusion, THE may provide a useful tool for fast assessment of the viscoelastic properties of the liver at low costs and without limitations in obesity, ascites or hemochromatosis.

Characteristics of a Strongly-Pulsed Non-Premixed Jet Flame in Cross-flow

NASA Astrophysics Data System (ADS)

Gamba, Mirko; Clemens, Noel T.; Ezekoye, Ofodike A.

2006-11-01

The effects of large-amplitude, high-frequency harmonic forcing of turbulent nonpremixed hydrogen/methane jet flames in cross-flow (JFICF) are investigated experimentally. Flame lengths, penetration lengths, and mixing characteristics are studied using flame luminosity imaging, planar laser Mie scattering visualization and particle image velocimetry. Mean jet Reynolds numbers of 1,600 and 3,250 (peak Re ˜2,500--6,500) with corresponding mean momentum flux ratios, r, of 1.9 and 3.7 (peak r ˜2.6--8.3) are considered. Forcing frequencies of 100 Hz and 300 Hz with amplitudes of ˜60%--300% are investigated. Consistent with previous work, a drastic decrease in flame length and soot emission, an increase in flame penetration and an improved jet fuel/cross-flow air mixing are observed for the larger forcing amplitude cases. Partial pre-mixing induced by near-field reverse flow, near-field vortex/vortex interaction and large-scale stirring, rendered stronger by large forcing amplitudes and frequencies, are thought to play a key role on the observed effects.

Harmonic multiplication using resonant tunneling

NASA Technical Reports Server (NTRS)

Sollner, T. C. L. G.; Brown, E. R.; Goodhue, W. D.; Correa, C. A.

1988-01-01

This paper demonstrates the use of resonant-tunneling diodes as varistors for harmonic multiplication. It is shown that efficient odd-harmonic conversion is possible and that even harmonics do not appear because of the antisymmetry of the current-voltage (I-V) curve. It is also shown that, with the proper choice of resonant-tunneling structure and pump amplitude, most of the harmonic output power can be confined to a single odd-harmonic frequency. Fifth-harmonic multiplication was demonstrated with an output at 21.75 GHz and a power conversion efficiency of 0.5 percent, and a fifth-harmonic efficiency of 2.7 percent was achieved in a circuit simulation using an improved I-V curve.

Third-harmonic entanglement and Einstein-Podolsky-Rosen steering over a frequency range of more than an octave

NASA Astrophysics Data System (ADS)

Olsen, M. K.

2018-03-01

The development of quantum technologies which use quantum states of the light field interacting with other systems creates a demand for such states over wide frequency ranges. In this work we compare the bipartite entanglement and Einstein-Podolsky-Rosen (EPR) -steering properties of the two different parametric schemes which produce third-harmonic optical fields from an input field at the fundamental frequency. The first scheme uses second harmonic cascaded with sum-frequency generation, while the second uses triply degenerate four- wave mixing, also known as direct third-harmonic generation. We find that both schemes produce continuous-variable bipartite entanglement and EPR steering over a frequency range which has previously been unobtainable. The direct scheme produces a greater degree of EPR steering, while the cascaded scheme allows for greater flexibility in having three available bipartitions, thus allowing for greater flexibility in the tailoring of light matter interfaces. There are also parameter regimes in both for which classical mean-field analyses fail to predict the mean-field solutions. Both schemes may be very useful for applications in quantum communication and computation networks, as well as providing for quantum interfaces between a wider range of light and atomic ensembles than is presently practicable.

Instability of surface electron cyclotron TM-modes influenced by non-monochromatic alternating electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Girka, I. O., E-mail: igorgirka@karazin.ua; Girka, V. O.; Sydora, R. D.

2016-06-15

The influence of non-monochromaticity of an external alternating electric field on excitation of TM eigenmodes at harmonics of the electron cyclotron frequency is considered here. These TM-modes propagate along the plasma interface in a metal waveguide. An external static constant magnetic field is oriented perpendicularly to the plasma interface. The problem is solved theoretically using the kinetic Vlasov-Boltzmann equation for description of plasma particles motion and the Maxwell equations for description of the electromagnetic mode fields. The external alternating electric field is supposed to be a superposition of two waves, whose amplitudes are different and their frequencies correlate as 2:1.more » An infinite set of equations for electric field harmonics of these modes is derived with the aid of nonlinear boundary conditions. This set is solved using the wave packet approach consisting of the main harmonic frequency and two nearest satellite temporal harmonics. Analytical studies of the obtained set of equations allow one to find two different regimes of parametric instability, namely, enhancement and suppression of the instability. Numerical analysis of the instability is carried out for the three first electron cyclotron harmonics.« less

Time-Dependent Parabolic Finite Difference Formulation for Harmonic Sound Propagation in a Two-Dimensional Duct with Flow

NASA Technical Reports Server (NTRS)

Kreider, Kevin L.; Baumeister, Kenneth J.

1996-01-01

An explicit finite difference real time iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for future large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable for a harmonic monochromatic sound field, a parabolic (in time) approximation is introduced to reduce the order of the governing equation. The analysis begins with a harmonic sound source radiating into a quiescent duct. This fully explicit iteration method then calculates stepwise in time to obtain the 'steady state' harmonic solutions of the acoustic field. For stability, applications of conventional impedance boundary conditions requires coupling to explicit hyperbolic difference equations at the boundary. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.

Evidence for Harmonic Content and Frequency Evolution of Oscillations During the Rising Phase of X-ray Bursts From 4U 1636-536

NASA Technical Reports Server (NTRS)

Bgattacharyya, Sudip; Strohmayer, E.

2005-01-01

We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst oscillation pulses during the early rising phases of bursts. This is the first such detection in burst rise oscillations, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of oscillation frequency increase during the burst rise. The timing behavior of harmonic content, amplitude, and frequency of burst rise oscillations may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.

Phononic Crystal Waveguide Transducers for Nonlinear Elastic Wave Sensing.

PubMed

Ciampa, Francesco; Mankar, Akash; Marini, Andrea

2017-11-07

Second harmonic generation is one of the most sensitive and reliable nonlinear elastic signatures for micro-damage assessment. However, its detection requires powerful amplification systems generating fictitious harmonics that are difficult to discern from pure nonlinear elastic effects. Current state-of-the-art nonlinear ultrasonic methods still involve impractical solutions such as cumbersome signal calibration processes and substantial modifications of the test component in order to create material-based tunable harmonic filters. Here we propose and demonstrate a valid and sensible alternative strategy involving the development of an ultrasonic phononic crystal waveguide transducer that exhibits both single and multiple frequency stop-bands filtering out fictitious second harmonic frequencies. Remarkably, such a sensing device can be easily fabricated and integrated on the surface of the test structure without altering its mechanical and geometrical properties. The design of the phononic crystal structure is supported by a perturbative theoretical model predicting the frequency band-gaps of periodic plates with sinusoidal corrugation. We find our theoretical findings in excellent agreement with experimental testing revealing that the proposed phononic crystal waveguide transducer successfully attenuates second harmonics caused by the ultrasonic equipment, thus demonstrating its wide range of potential applications for acousto/ultrasonic material damage inspection.

Investigation about relationships between the symmetries of ferroelectric crystal Ca0.28Ba0.72Nb2O6 and second-harmonic patterns

NASA Astrophysics Data System (ADS)

Xu, Tianxiang; Yu, Haohai; Zhang, Huaijin; Wang, Jiyang

2015-08-01

The broadband quasi-phase matching (QPM) process in a uniaxial ferroelectric crystal Ca0.28Ba0.72Nb2O6 (CBN-28) was demonstrated with the second-harmonic wavelength range from 450 nm to 650 nm, and the relationship between the symmetries of CBN-28 and the second-harmonic patterns was experimentally and theoretically investigated based on the random anti-parallel domains in the crystal and QPM conditions. The dependences of frequency-doubled patterns on the wavelength and anisotropy of the nonlinear crystal were also studied, and the frequency-doubled photons were found to be trapped on circles. By analyzing the light-matter interacting Hamiltonians, the trapping force for second-harmonic photons was found to be centripetal and tunable by the fundamental lasers, and the variation tendencies of the rotational velocity of second-harmonic generation photons could also be predicated. The results indicate that the CBN-28 ferroelectric crystal is a promising nonlinear optical material for the generation of broadband frequency-doubled waves, and the analysis on centripetal force based on the interaction Hamiltonians may provide a novel recognition for the investigation of QPM process to be further studied.

Modeling complex tone perception: grouping harmonics with combination-sensitive neurons.

PubMed

Medvedev, Andrei V; Chiao, Faye; Kanwal, Jagmeet S

2002-06-01

Perception of complex communication sounds is a major function of the auditory system. To create a coherent precept of these sounds the auditory system may instantaneously group or bind multiple harmonics within complex sounds. This perception strategy simplifies further processing of complex sounds and facilitates their meaningful integration with other sensory inputs. Based on experimental data and a realistic model, we propose that associative learning of combinations of harmonic frequencies and nonlinear facilitation of responses to those combinations, also referred to as "combination-sensitivity," are important for spectral grouping. For our model, we simulated combination sensitivity using Hebbian and associative types of synaptic plasticity in auditory neurons. We also provided a parallel tonotopic input that converges and diverges within the network. Neurons in higher-order layers of the network exhibited an emergent property of multifrequency tuning that is consistent with experimental findings. Furthermore, this network had the capacity to "recognize" the pitch or fundamental frequency of a harmonic tone complex even when the fundamental frequency itself was missing.

Neural Networks for Segregation of Multiple Objects: Visual Figure-Ground Separation and Auditory Pitch Perception.

NASA Astrophysics Data System (ADS)

Wyse, Lonce

An important component of perceptual object recognition is the segmentation into coherent perceptual units of the "blooming buzzing confusion" that bombards the senses. The work presented herein develops neural network models of some key processes of pre-attentive vision and audition that serve this goal. A neural network model, called an FBF (Feature -Boundary-Feature) network, is proposed for automatic parallel separation of multiple figures from each other and their backgrounds in noisy images. Figure-ground separation is accomplished by iterating operations of a Boundary Contour System (BCS) that generates a boundary segmentation of a scene, and a Feature Contour System (FCS) that compensates for variable illumination and fills-in surface properties using boundary signals. A key new feature is the use of the FBF filling-in process for the figure-ground separation of connected regions, which are subsequently more easily recognized. The new CORT-X 2 model is a feed-forward version of the BCS that is designed to detect, regularize, and complete boundaries in up to 50 percent noise. It also exploits the complementary properties of on-cells and off -cells to generate boundary segmentations and to compensate for boundary gaps during filling-in. In the realm of audition, many sounds are dominated by energy at integer multiples, or "harmonics", of a fundamental frequency. For such sounds (e.g., vowels in speech), the individual frequency components fuse, so that they are perceived as one sound source with a pitch at the fundamental frequency. Pitch is integral to separating auditory sources, as well as to speaker identification and speech understanding. A neural network model of pitch perception called SPINET (SPatial PItch NETwork) is developed and used to simulate a broader range of perceptual data than previous spectral models. The model employs a bank of narrowband filters as a simple model of basilar membrane mechanics, spectral on-center off-surround competitive interactions, and a "harmonic sieve" mechanism whereby the strength of a pitch depends only on spectral regions near harmonics. The model is evaluated using data involving mistuned components, shifted harmonics, complex tones with varying phase relationships, and continuous spectra such as rippled noise and narrow noise bands.

A novel approach for quantitative harmonization in PET.

PubMed

Namías, M; Bradshaw, T; Menezes, V O; Machado, M A D; Jeraj, R

2018-05-04

Positron emission tomography (PET) imaging allows for measurement of activity concentrations of a given radiotracer in vivo. The quantitative capabilities of PET imaging are particularly important in the context of monitoring response to treatment, where quantitative changes in tracer uptake could be used as a biomarker of treatment response. Reconstruction algorithms and settings have a significant impact on PET quantification. In this work we introduce a novel harmonization methodology requiring only a simple cylindrical phantom and show that it can match the performance of more complex harmonization approaches based on phantoms with spherical inserts. Resolution and noise measurements from cylindrical phantoms are used to simulate the spherical inserts from NEMA image quality phantoms. An optimization algorithm was used to find the optimal smoothing filters for the simulated NEMA phantom images to identify those that best harmonized the PET scanners. Our methodology was tested on seven different PET models from two manufacturers installed at five institutions. Our methodology is able to predict contrast recovery coefficients (CRCs) from NEMA phantoms with errors within  ±5.2% for CRCmax and  ±3.7% for CRCmean (limits of agreement  =  95%). After applying the proposed harmonization protocol, all the CRC values were within the tolerances from EANM. Quantitative harmonization in compliance with the EARL FDG-PET/CT accreditation program is achieved in a simpler way, without the need of NEMA phantoms. This may lead to simplified scanner harmonization workflows more accessible to smaller institutions.

Near-field Development of a Turbulent Mixing Layer Periodically Forced by a Bimorph PVDF Film Actuator

NASA Astrophysics Data System (ADS)

Naka, Yoshitsugu; Tsuboi, Ken-Ichiro; Kametani, Yukinori; Fukagata, Koji; Obi, Shinnosuke

We have performed experiments in a turbulent mixing layer with periodic forcing introduced by a Piezo Film Actuator (PFA). Three different lengths of PFAs have been used, and the effects of various combinations of forcing amplitudes and frequencies are investigated. The forcing at the first and second sub-harmonic frequencies against the natural frequency enhances the development of the thickness of the mixing layer: the mixing layer spreads due to the forcing. On the other hand, the forcing near the natural frequency suppresses the development: the mean velocity gradient becomes steeper than the no control case. The vector pattern of the periodic velocity components indicated the formation of the vortical structure. By forcing at the natural and its first sub-harmonic frequencies, two counter-rotating vortices are clearly observed in one period of forcing. By forcing at second sub-harmonic frequency, the vortical structure is found only in the downstream region. The distribution of the periodic Reynolds shear stress significantly varies with the forcing frequency and it takes a positive value when forcing occurs near the natural frequency. However, the total value of the Reynolds shear stress remains negative due to the contribution of the turbulent components.

MMS Observations of Harmonic Electromagnetic Cyclotron Waves

NASA Astrophysics Data System (ADS)

Usanova, M.; Ahmadi, N.; Ergun, R.; Trattner, K. J.; Fuselier, S. A.; Torbert, R. B.; Mauk, B.; Le Contel, O.; Giles, B. L.; Russell, C. T.; Burch, J.; Strangeway, R. J.

2017-12-01

Harmonically related electromagnetic ion cyclotron waves with the fundamental frequency near the O+ cyclotron frequency were observed by the four MMS spacecraft on May 20, 2016. The wave activity was detected by the spacecraft on their inbound passage through the Earth's morning magnetosphere during generally quiet geomagnetic conditions but enhanced solar wind dynamic pressure. It was also associated with an enhancement of energetic H+ and O+ ions. The waves are seen in both magnetic and electric fields, formed by over ten higher order harmonics, most pronounced in the electric field. The wave activity lasted for about an hour with some wave packets giving rise to short-lived structures extending from Hz to kHz range. These observations are particularly interesting since they suggest cross-frequency coupling between the lower and higher frequency modes. Further work will focus on examining the nature and role of these waves in the energetic particle dynamics from a theoretical perspective.

An analytical SMASH procedure (ASP) for sensitivity-encoded MRI.

PubMed

Lee, R F; Westgate, C R; Weiss, R G; Bottomley, P A

2000-05-01

The simultaneous acquisition of spatial harmonics (SMASH) method of imaging with detector arrays can reduce the number of phase-encoding steps, and MRI scan time several-fold. The original approach utilized numerical gradient-descent fitting with the coil sensitivity profiles to create a set of composite spatial harmonics to replace the phase-encoding steps. Here, an analytical approach for generating the harmonics is presented. A transform is derived to project the harmonics onto a set of sensitivity profiles. A sequence of Fourier, Hilbert, and inverse Fourier transform is then applied to analytically eliminate spatially dependent phase errors from the different coils while fully preserving the spatial-encoding. By combining the transform and phase correction, the original numerical image reconstruction method can be replaced by an analytical SMASH procedure (ASP). The approach also allows simulation of SMASH imaging, revealing a criterion for the ratio of the detector sensitivity profile width to the detector spacing that produces optimal harmonic generation. When detector geometry is suboptimal, a group of quasi-harmonics arises, which can be corrected and restored to pure harmonics. The simulation also reveals high-order harmonic modulation effects, and a demodulation procedure is presented that enables application of ASP to a large numbers of detectors. The method is demonstrated on a phantom and humans using a standard 4-channel phased-array MRI system. Copyright 2000 Wiley-Liss, Inc.

On the modulation of low-frequency quasi-periodic oscillations in black hole transients

NASA Astrophysics Data System (ADS)

Pawar, Devraj D.; Motta, Sara; Shanthi, K.; Bhattacharya, Dipankar; Belloni, Tomaso

2015-04-01

We studied the properties of the low-frequency quasi-periodic oscillations detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322, XTE J1859+226, 4U 1630-47, GX 339-4, XTE J1650-500) observed by the Rossi XTE satellite. We analysed the relation between the full width at half-maximum and the frequency of all the narrow peaks detected in power density spectra where a type-C QPO is observed. Our goal was to understand the nature of the modulation of the signal by comparing the properties of different harmonic peaks in the power density spectrum. We find that for the sources in our sample the width of the fundamental and of the first harmonic are compatible with a frequency modulation, while that of the sub-harmonic is independent of frequency, possibly indicating the presence of an additional modulation in amplitude. We compare our results with those obtained earlier from GRS 1915+105 and XTE J1550-564.

Square or sine: finding a waveform with high success rate of eliciting SSVEP.

PubMed

Teng, Fei; Chen, Yixin; Choong, Aik Min; Gustafson, Scott; Reichley, Christopher; Lawhead, Pamela; Waddell, Dwight

2011-01-01

Steady state visual evoked potential (SSVEP) is the brain's natural electrical potential response for visual stimuli at specific frequencies. Using a visual stimulus flashing at some given frequency will entrain the SSVEP at the same frequency, thereby allowing determination of the subject's visual focus. The faster an SSVEP is identified, the higher information transmission rate the system achieves. Thus, an effective stimulus, defined as one with high success rate of eliciting SSVEP and high signal-noise ratio, is desired. Also, researchers observed that harmonic frequencies often appear in the SSVEP at a reduced magnitude. Are the harmonics in the SSVEP elicited by the fundamental stimulating frequency or by the artifacts of the stimuli? In this paper, we compare the SSVEP responses of three periodic stimuli: square wave (with different duty cycles), triangle wave, and sine wave to find an effective stimulus. We also demonstrate the connection between the strength of the harmonics in SSVEP and the type of stimulus.

Optimization of contrast-to-tissue ratio by adaptation of transmitted ternary signal in ultrasound pulse inversion imaging.

PubMed

Ménigot, Sébastien; Girault, Jean-Marc

2013-01-01

Ultrasound contrast imaging has provided more accurate medical diagnoses thanks to the development of innovating modalities like the pulse inversion imaging. However, this latter modality that improves the contrast-to-tissue ratio (CTR) is not optimal, since the frequency is manually chosen jointly with the probe. However, an optimal choice of this command is possible, but it requires precise information about the transducer and the medium which can be experimentally difficult to obtain, even inaccessible. It turns out that the optimization can become more complex by taking into account the kind of generators, since the generators of electrical signals in a conventional ultrasound scanner can be unipolar, bipolar, or tripolar. Our aim was to seek the ternary command which maximized the CTR. By combining a genetic algorithm and a closed loop, the system automatically proposed the optimal ternary command. In simulation, the gain compared with the usual ternary signal could reach about 3.9 dB. Another interesting finding was that, in contrast to what is generally accepted, the optimal command was not a fixed-frequency signal but had harmonic components.

Maximum imaging depth comparison in porcine vocal folds using 776-nm vs. 1552-nm excitation wavelengths

NASA Astrophysics Data System (ADS)

Yildirim, Murat; Ferhanoglu, Onur; Kobler, James B.; Zeitels, Steven M.; Ben-Yakar, Adela

2013-02-01

Vocal fold scarring is one of the major causes of voice disorders and may arise from overuse or post-surgical wound healing. One promising treatment utilizes the injection of soft biomaterials aimed at restoring viscoelasticity of the outermost vibratory layer of the vocal fold, superficial lamina propria (SLP). However, the density of the tissue and the required injection pressure impair proper localization of the injected biomaterial in SLP. To enhance treatment effectiveness, we are investigating a technique to image and ablate sub-epithelial planar voids in vocal folds using ultrafast laser pulses to better localize the injected biomaterial. It is challenging to optimize the excitation wavelength to perform imaging and ablation at depths suitable for clinical use. Here, we compare maximum imaging depth using two photon autofluorescence and second harmonic generation with third-harmonic generation imaging modalities for healthy porcine vocal folds. We used a home-built inverted nonlinear scanning microscope together with a high repetition rate (2 MHz) ultrafast fiber laser (Raydiance Inc.). We acquired both two-photon autofluorescence and second harmonic generation signals using 776 nm wavelength and third harmonic generation signals using 1552 nm excitation wavelength. We observed that maximum imaging depth with 776 nm wavelength is significantly improved from 114 μm to 205 μm when third harmonic generation is employed using 1552 nm wavelength, without any observable damage in the tissue.

Can temporal fine structure represent the fundamental frequency of unresolved harmonics?

PubMed

Oxenham, Andrew J; Micheyl, Christophe; Keebler, Michael V

2009-04-01

At least two modes of pitch perception exist: in one, the fundamental frequency (F0) of harmonic complex tones is estimated using the temporal fine structure (TFS) of individual low-order resolved harmonics; in the other, F0 is derived from the temporal envelope of high-order unresolved harmonics that interact in the auditory periphery. Pitch is typically more accurate in the former than in the latter mode. Another possibility is that pitch can sometimes be coded via the TFS from unresolved harmonics. A recent study supporting this third possibility [Moore et al. (2006a). J. Acoust. Soc. Am. 119, 480-490] based its conclusion on a condition where phase interaction effects (implying unresolved harmonics) accompanied accurate F0 discrimination (implying TFS processing). The present study tests whether these results were influenced by audible distortion products. Experiment 1 replicated the original results, obtained using a low-level background noise. However, experiments 2-4 found no evidence for the use of TFS cues with unresolved harmonics when the background noise level was raised, or the stimulus level was lowered, to render distortion inaudible. Experiment 5 measured the presence and phase dependence of audible distortion products. The results provide no evidence that TFS cues are used to code the F0 of unresolved harmonics.

Parametric phase conjugation for the second harmonic of a nonlinear ultrasonic beam

NASA Astrophysics Data System (ADS)

Brysev, A. P.; Bunkin, F. V.; Hamilton, M. F.; Klopotov, R. V.; Krutyanskii, L. M.; Yan, K.

2003-01-01

The effect of phase conjugation for the second harmonic of a focused ultrasonic beam was investigated experimentally and by numerical simulation. An ultrasonic pulse with the carrier frequency f=3 MHz was emitted into water and focused at a point between the source and the phase conjugating system. The phase conjugation for the second harmonic of the incident wave (2 f=6 MHz) was performed in a magnetostrictive ceramic as a result of the parametric interaction of the incident wave with the pumping magnetic field (the pumping frequency was f p=4 f=12 MHz). The axial and focal distributions of sound pressure in the incident and conjugated beams were measured using a broadband PVDF membrane hydrophone. The corresponding calculations were performed by solving numerically the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation allowing for the nonlinearity, diffraction, and thermoviscous absorption. The results of measurements agreed well with the calculations and showed that the field of a conjugate wave adequately reproduces the field of the second harmonic of the incident wave. A certain advantage of focusing with the phase conjugation for the second harmonic was demonstrated in comparison with the operation at the doubled frequency of the incident wave. The results of this study can serve as a basis for the utilization of the phase conjugation of harmonics in ultrasonic tomography and nondestructive testing.

Waveguide Multimode Directional Coupler for Harvesting Harmonic Power from the Output of Traveling-Wave Tube Amplifiers

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Wintucky, Edwin G.

2017-01-01

This paper presents the design, fabrication, and test results for a novel waveguide multimode directional coupler (MDC). The coupler fabricated from dissimilar frequency band waveguides, is capable of isolating power at the 2nd harmonic frequency from the fundamental power at the output port of traveling-wave tube amplifiers. Test results from proof-of-concept demonstrations are presented for Ku/Ka-band and Ka/E-band MDCs, which demonstrate sufficient power in the 2nd harmonic for a space borne beacon source for mm-wave atmospheric propagation studies.

Investigation of superharmonic sound propagation and imaging in biological tissues in vitro.

PubMed

Ma, Qingyu; Zhang, Dong; Gong, Xiufen; Ma, Yong

2006-04-01

This article presents both theoretical and experimental studies on the superharmonic generation and its imaging in biological tissues. A superharmonic component is defined as a summation of the third-, fourth-, and fifth-order harmonics. A superharmonic signal is produced using an 8-mm-diam, 2.5-MHz planar piston source that is excited by eight-cycle, 2.5-MHz tone bursts. Axial and lateral field distributions of the superharmonic component and the second harmonic are first calculated based on the nonlinear KZK model and then compared with those experimentally determined at two different source pressures of 0.5 and 1 MPa. Results indicate that the amplitude of the superharmonic component can exceed that of the second harmonic, depending on the axial distance and the fundamental pressure amplitude. Also, the 3-dB beamwidth of the superharmonic component is about 23% narrower than that of the second harmonic. Additional experiments are performed in vitro using liver and fatty tissues in transmission mode and produced two-dimensional images using the fundamental, the second harmonic, and the superharmonic signals. Although the clinical applicability of this work still needs to be assessed, these results indicate that the superharmonic image quality is better than that of the other two images.

The radio-frequency fluctuation effect on the floating harmonic method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Jaewon; Kim, Kyung-Hyun; Kim, Dong-Hwan

2016-08-15

The radio-frequency (RF) plasma diagnostics with an electrical probe facing a challenge, because the RF fluctuation oscillates the plasma potential and distorts the current-voltage (I-V) curve. As Langmuir probe is widely used in plasma diagnostics, many researchers have been studying the effect of RF fluctuation on probe and compensation methods. On the other hand, there have not been enough studies on the fluctuation effect on the floating harmonic method. Therefore, we investigated the impact of RF fluctuation on the floating harmonic method theoretically and experimentally. When the electrons are in ideal Maxwellian distribution, the floating potential is negatively shifted bymore » the RF fluctuation, but the fluctuation does not distort I-V curve around the floating potential. However, in practical plasmas, the I-V curve and their harmonic components are distorted. This RF fluctuation effect becomes more significant in a low density plasma with a high impedance sheath. The second harmonic current decreases with the RF fluctuation while the first harmonic current is merely affected. Therefore, the electron temperatures measured with the floating harmonic method under low density plasma with uncompensated probe are overestimated than the results obtained with the compensated probe.« less

Two-Diffraction-Order, Beam-Splitting, Imaging Spectrometer

NASA Technical Reports Server (NTRS)

Labaw, Clayton C.; Burns, Ronald N.

1995-01-01

Two-octave imaging spectrometer utilizes light of two harmonically related wavelengths diffracted to harmonically related orders at same angles, followed by separation via dichroic beam splitter before final imaging. Conceptual design of spectrometer calls for minimum number of optical elements to achieve coverage of required visible and near-infrared wavelengths in instrument of reduced size, weight, and cost.

Electric-field control of a hydrogenic donor's spin in a semiconductor

NASA Astrophysics Data System (ADS)

de, Amrit; Pryor, Craig E.; Flatté, Michael E.

2009-03-01

The orbital wave function of an electron bound to a single donor in a semiconductor can be modulated by an applied AC electric field, which affects the electron spin dynamics via the spin-orbit interaction. Numerical calculations of the spin dynamics of a single hydrogenic donor (Si) using a real-space multi-band k.p formalism show that in addition to breaking the high symmetry of the hydrogenic donor state, the g-tensor has a strong nonlinear dependence on the applied fields. By explicitly integrating the time dependent Schr"odinger equation it is seen that Rabi oscillations can be obtained for electric fields modulated at sub-harmonics of the Larmor frequency. The Rabi frequencies obtained from sub-harmonic modulation depend on the magnitudes of the AC and DC components of the electric field. For a purely AC field, the highest Rabi frequency is obtained when E is driven at the 2nd sub-harmonic of the Larmor frequency. Apart from suggesting ways to measure g-tensor anisotropies and nonlinearities, these results also suggest the possibility of direct frequency domain measurements of Rabi frequencies.

Stimulated Brillouin scattering during electron gyro-harmonic heating at EISCAT

NASA Astrophysics Data System (ADS)

Fu, H. Y.; Scales, W. A.; Bernhardt, P. A.; Briczinski, S. J.; Kosch, M. J.; Senior, A.; Rietveld, M. T.; Yeoman, T. K.; Ruohoniemi, J. M.

2015-08-01

Observations of secondary radiation, stimulated electromagnetic emission (SEE), produced during ionospheric modification experiments using ground-based, high-power, high-frequency (HF) radio waves are considered. The High Frequency Active Auroral Research Program (HAARP) facility is capable of generating narrowband SEE in the form of stimulated Brillouin scatter (SBS) and stimulated ion Bernstein scatter (SIBS) in the SEE spectrum. Such narrowband SEE spectral lines have not been reported using the European Incoherent Scatter (EISCAT) heater facility before. This work reports the first EISCAT results of narrowband SEE spectra and compares them to SEE previously observed at HAARP during electron gyro-harmonic heating. An analysis of experimental SEE data shows observations of emission lines within 100 Hz of the pump frequency, interpreted as SBS, during the 2012 July EISCAT campaign. Experimental results indicate that SBS strengthens as the pump frequency approaches the third electron gyro-harmonic. Also, for different heater antenna beam angles, the CUTLASS radar backscatter induced by HF radio pumping is suppressed near electron gyro-harmonics, whereas electron temperature enhancement weakens as measured by EISCAT/UHF radar. The main features of these new narrowband EISCAT observations are generally consistent with previous SBS measurements at HAARP.

Erratum: Sources of Image Degradation in Fundamental and Harmonic Ultrasound Imaging: A Nonlinear, Full-Wave, Simulation Study

PubMed Central

Pinton, Gianmarco F.; Trahey, Gregg E.; Dahl, Jeremy J.

2015-01-01

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain. This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSFs) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared with fundamental imaging, reverberation clutter in harmonic imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for harmonic imaging, the primary source of degradation is phase aberration. PMID:21693410

Spectral Analysis of Vibrational Harmonic Motion by use of a Continuous-Wave CO2 Doppler Lidar

NASA Technical Reports Server (NTRS)

Jarzembski, Maurice A.; Srivastava, Vandana

1999-01-01

Vibrational motion of a harmonic oscillator was investigated using a focused continuous wave CO2 Doppler lidar at 9.1 microns wavelength. A continuum of frequencies along with many discrete, equally spaced, resonant frequency modes was observed. The frequency modes are similar in structure to the oscillatory longitudinal modes of a laser cavity and arise because of interference of the natural resonant frequency of the oscillator with specific frequencies within the continuum. The spectra revealed departures from linear motion for vigorous vibrations of the oscillator. Each consecutive resonant frequency mode occurred for a movement of the oscillator much less than the wavelength of incident lidar radiation.

Evaluation of Material Nonlinearities Using Rectangular Pulse Trains for Excitation

NASA Astrophysics Data System (ADS)

Chaziachmetovas, Andrius; Svilainis, Linas; Kybartas, Darius; Aleksandrovas, Arturas; Liaukonis, Dobilas

Aim of the presented investigation was to evaluate the suitability of the rectangular pulse trains for nonlinear material parameters study. It was assumed that if duty cycle of the excitation is 50% then second harmonic is significantly reduced. Excitation signal frequency was fixed to the A/D sampling frequency and signal carefully gated to reduce the signal leak into neighbouring frequency bins. Sine wave correlation was used to extract the harmonics content. Results of nonlinear parameters measurement for several materials are given as performance comparison.

Harmonic decomposition of magneto-optical signal from suspensions of superparamagnetic nanoparticles

NASA Astrophysics Data System (ADS)

Patterson, Cody; Syed, Maarij; Takemura, Yasushi

2018-04-01

Magnetic nanoparticles (MNPs) are widely used in biomedical applications. Characterizing dilute suspensions of superparamagnetic iron oxide nanoparticles (SPIONs) in bio-relevant media is particularly valuable for magnetic particle imaging, hyperthermia, drug delivery, etc. Here, we study dilute aqueous suspensions of single-domain magnetite nanoparticles using an AC Faraday rotation (FR) setup. The setup uses an oscillating magnetic field (800 Hz) which generates a multi-harmonic response. Each harmonic is collected and analyzed using the Fourier components of the theoretical signal determined by a Langevin-like magnetization. With this procedure, we determine the average magnetic moment per particle μ , particle number density n, and Verdet constant of the sample. The fitted values of μ and n are shown to be consistent across each harmonic. Additionally, we present the results of these parameters as n is varied. The large values of μ reveal the possibility of clustering as reported in other literature. This suggests that μ is representative of the average magnetic moment per cluster of nanoparticles. Multiple factors, including the external magnetic field, surfactant degradation, and laser absorption, can contribute to dynamic and long-term aggregation leading to FR signals that represent space- and time-averaged sample parameters. Using this powerful analysis procedure, future studies are aimed at determining the clustering mechanisms in this AC system and characterizing SPION suspensions at different frequencies and viscosities.

Passive wide spectrum harmonic filter for adjustable speed drives in oil and gas industry

NASA Astrophysics Data System (ADS)

Al Jaafari, Khaled Ali

Non-linear loads such as variable speed drives constitute the bulky load of oil and gas industry power systems. They are widely used in driving induction and permanent magnet motors for variable speed applications. That is because variable speed drives provide high static and dynamic performance. Moreover, they are known of their high energy efficiency and high motion quality, and high starting torque. However, these non-linear loads are main sources of current and voltage harmonics and lower the quality of electric power system. In fact, it is the six-pulse and twelve-pulse diode and thyristor rectifiers that spoil the AC power line with the dominant harmonics (5th, 7th, 11th). They provide DC voltage to the inverter of the variable speed drives. Typical problems that arise from these harmonics are Harmonic resonances', harmonic losses, interference with electronic equipment, and line voltage distortion at the Point of Common Coupling (PCC). Thus, it is necessary to find efficient, reliable, and economical harmonic filters. The passive filters have definite advantage over active filters in terms of components count, cost and reliability. Reliability and maintenance is a serious issue in drilling rigs which are located in offshore and onshore with extreme operating conditions. Passive filters are tuned to eliminate a certain frequency and therefore there is a need to equip the system with more than one passive filter to eliminate all unwanted frequencies. An alternative solution is Wide Spectrum Harmonic passive filter. The wide spectrum harmonic filters are becoming increasingly popular in these applications and found to overcome some of the limitations of conventional tuned passive filter. The most important feature of wide spectrum harmonic passive filters is that only one capacitor is required to filter a wide range of harmonics. Wide spectrum filter is essentially a low-pass filter for the harmonic at fundamental frequency. It can also be considered as a single-stage passive filter plus input and output inductors. The work proposed gives a complete analysis of wide spectrum harmonic passive filters, the methodology to choose its parameters according to the operational condition, effect of load and source inductance on its characteristics. Also, comparison of the performance of the wide band passive filter with tuned filter is given. The analyses are supported with the simulation results and were verified experimentally. The analysis given in this thesis will be useful for the selection of proper wide spectrum harmonic filters for harmonic mitigation applications in oil and gas industry.

Corneal imaging by second and third harmonic generation microscopy

NASA Astrophysics Data System (ADS)

Brocas, Arnaud; Jay, Louis; Mottay, Eric; Brunette, Isabelle; Ozaki, Tsuneyuki

2008-02-01

Advanced imaging methods are essential tools for improved outcome of refractive surgery. Second harmonic generation (SHG) and third harmonic generation (THG) microscopy are noninvasive high-resolution imaging methods, which can discriminate the different layers of the cornea, thus having strong impact on the outcome of laser surgery. In this work, we use an Ytterbium femtosecond laser as the laser source, the longer wavelength of which reduces scattering, and allows simultaneous SHG and THG imaging. We present SHG and THG images and profiles of pig corneas that clearly show the anterior surface of the cornea, the entry in the stroma and its end, and the posterior surface of the cornea. These observations allow localizing the epithelium, the stroma and the endothelium. Other experiments give information about the structure and cytology of the corneal layers.

Exact solution of a quantum forced time-dependent harmonic oscillator

NASA Technical Reports Server (NTRS)

Yeon, Kyu Hwang; George, Thomas F.; Um, Chung IN

1992-01-01

The Schrodinger equation is used to exactly evaluate the propagator, wave function, energy expectation values, uncertainty values, and coherent state for a harmonic oscillator with a time dependent frequency and an external driving time dependent force. These quantities represent the solution of the classical equation of motion for the time dependent harmonic oscillator.

Harmonic Scalpel Versus Electrocautery in Axillary Dissection in Carcinoma Breast.

PubMed

Nawaz, Allah; Waqar, Sadaf; Khan, Ahsan; Mansoor, Rashid; Butt, Usman Ismat; Ayyaz, Mahmood

2015-12-01

To compare the results between harmonics scalpel and electrocautery use in axillary dissection for carcinoma breast. Randomized controlled trial. Department of Surgery, Services Hospital, Lahore, from December 2013 to June 2014. Eighty patients fulfilling the inclusion criteria were selected and equally divided in two groups. Axillary dissection for carcinoma breast was performed by using the harmonic scalpel in one group and by using electrocautery in the other group. Total mean axillary drain output and frequency of axillary numbness were noted in both groups and compared. All the patients were females with mean age of 53.52 ± 9.8. Mean axillary drain output in harmonic scalpel group was 167.75 ± 43.90 as compared to 310.00 ± 60.09 in electrocautery group while only 12.5% of patients were positive for axillary numbness in harmonic scalpel group as compared to 100% of patients who were positive for electrocautery group. Use of harmonic scalpel in axillary dissection resulted in decreased total mean axillary drain output and lowered frequency of axillary numbness when compared to utilizing electrocautery.

Complex pitch perception mechanisms are shared by humans and a New World monkey.

PubMed

Song, Xindong; Osmanski, Michael S; Guo, Yueqi; Wang, Xiaoqin

2016-01-19

The perception of the pitch of harmonic complex sounds is a crucial function of human audition, especially in music and speech processing. Whether the underlying mechanisms of pitch perception are unique to humans, however, is unknown. Based on estimates of frequency resolution at the level of the auditory periphery, psychoacoustic studies in humans have revealed several primary features of central pitch mechanisms. It has been shown that (i) pitch strength of a harmonic tone is dominated by resolved harmonics; (ii) pitch of resolved harmonics is sensitive to the quality of spectral harmonicity; and (iii) pitch of unresolved harmonics is sensitive to the salience of temporal envelope cues. Here we show, for a standard musical tuning fundamental frequency of 440 Hz, that the common marmoset (Callithrix jacchus), a New World monkey with a hearing range similar to that of humans, exhibits all of the primary features of central pitch mechanisms demonstrated in humans. Thus, marmosets and humans may share similar pitch perception mechanisms, suggesting that these mechanisms may have emerged early in primate evolution.

Highly coherent vacuum ultraviolet radiation at the 15th harmonic with echo-enabled harmonic generation technique

NASA Astrophysics Data System (ADS)

Hemsing, E.; Dunning, M.; Hast, C.; Raubenheimer, T. O.; Weathersby, S.; Xiang, D.

2014-07-01

X-ray free-electron lasers are enabling access to new science by producing ultrafast and intense x rays that give researchers unparalleled power and precision in examining the fundamental nature of matter. In the quest for fully coherent x rays, the echo-enabled harmonic generation technique is one of the most promising methods. In this technique, coherent radiation at the high harmonic frequencies of two seed lasers is generated from the recoherence of electron beam phase space memory. Here we report on the generation of highly coherent and stable vacuum ultraviolet radiation at the 15th harmonic of an infrared seed laser with this technique. The experiment demonstrates two distinct advantages that are intrinsic to the highly nonlinear phase space gymnastics of echo-enabled harmonic generation in a new regime, i.e., high frequency up-conversion efficiency and insensitivity to electron beam phase space imperfections. Our results allow comparison and confirmation of predictive models and scaling laws, and mark a significant step towards fully coherent x-ray free-electron lasers that will open new scientific research.

Harmonic Optimization in Voltage Source Inverter for PV Application using Heuristic Algorithms

NASA Astrophysics Data System (ADS)

Kandil, Shaimaa A.; Ali, A. A.; El Samahy, Adel; Wasfi, Sherif M.; Malik, O. P.

2016-12-01

Selective Harmonic Elimination (SHE) technique is the fundamental switching frequency scheme that is used to eliminate specific order harmonics. Its application to minimize low order harmonics in a three level inverter is proposed in this paper. The modulation strategy used here is SHEPWM and the nonlinear equations, that characterize the low order harmonics, are solved using Harmony Search Algorithm (HSA) to obtain the optimal switching angles that minimize the required harmonics and maintain the fundamental at the desired value. Total Harmonic Distortion (THD) of the output voltage is minimized maintaining selected harmonics within allowable limits. A comparison has been drawn between HSA, Genetic Algorithm (GA) and Newton Raphson (NR) technique using MATLAB software to determine the effectiveness of getting optimized switching angles.

A novel power harmonic analysis method based on Nuttall-Kaiser combination window double spectrum interpolated FFT algorithm

NASA Astrophysics Data System (ADS)

Jin, Tao; Chen, Yiyang; Flesch, Rodolfo C. C.

2017-11-01

Harmonics pose a great threat to safe and economical operation of power grids. Therefore, it is critical to detect harmonic parameters accurately to design harmonic compensation equipment. The fast Fourier transform (FFT) is widely used for electrical popular power harmonics analysis. However, the barrier effect produced by the algorithm itself and spectrum leakage caused by asynchronous sampling often affects the harmonic analysis accuracy. This paper examines a new approach for harmonic analysis based on deducing the modifier formulas of frequency, phase angle, and amplitude, utilizing the Nuttall-Kaiser window double spectrum line interpolation method, which overcomes the shortcomings in traditional FFT harmonic calculations. The proposed approach is verified numerically and experimentally to be accurate and reliable.

Multi-Coil Shimming of the Mouse Brain

PubMed Central

Juchem, Christoph; Brown, Peter B.; Nixon, Terence W.; McIntyre, Scott; Rothman, Douglas L.; de Graaf, Robin A.

2011-01-01

MR imaging and spectroscopy allow the non-invasive measurement of brain function and physiology, but excellent magnetic field homogeneity is required for meaningful results. The homogenization of the magnetic field distribution in the mouse brain (i.e. shimming) is a difficult task due to complex susceptibility-induced field distortions combined with the small size of the object. To date, the achievement of satisfactory whole brain shimming in the mouse remains a major challenge. The magnetic fields generated by a set of 48 circular coils (diameter 13 mm) that were arranged in a cylinder-shaped pattern of 32 mm diameter and driven with individual dynamic current ranges of ±1 A are shown to be capable of substantially reducing the field distortions encountered in the mouse brain at 9.4 Tesla. Static multi-coil shim fields allowed the reduction of the standard deviation of Larmor frequencies by 31% compared to second order spherical harmonics shimming and a 66% narrowing was achieved with the slice-specific application of the multi-coil shimming with a dynamic approach. For gradient echo imaging, multi-coil shimming minimized shim-related signal voids in the brain periphery and allowed overall signal gains of up to 51% compared to spherical harmonics shimming. PMID:21442653

Simulations of magnetic nanoparticle Brownian motion

PubMed Central

Reeves, Daniel B.; Weaver, John B.

2012-01-01

Magnetic nanoparticles are useful in many medical applications because they interact with biology on a cellular level thus allowing microenvironmental investigation. An enhanced understanding of the dynamics of magnetic particles may lead to advances in imaging directly in magnetic particle imaging or through enhanced MRI contrast and is essential for nanoparticle sensing as in magnetic spectroscopy of Brownian motion. Moreover, therapeutic techniques like hyperthermia require information about particle dynamics for effective, safe, and reliable use in the clinic. To that end, we have developed and validated a stochastic dynamical model of rotating Brownian nanoparticles from a Langevin equation approach. With no field, the relaxation time toward equilibrium matches Einstein's model of Brownian motion. In a static field, the equilibrium magnetization agrees with the Langevin function. For high frequency or low amplitude driving fields, behavior characteristic of the linearized Debye approximation is reproduced. In a higher field regime where magnetic saturation occurs, the magnetization and its harmonics compare well with the effective field model. On another level, the model has been benchmarked against experimental results, successfully demonstrating that harmonics of the magnetization carry enough information to infer environmental parameters like viscosity and temperature. PMID:23319830

Effects of sensorineural hearing loss on temporal coding of harmonic and inharmonic tone complexes in the auditory nerve

PubMed Central

Kale, Sushrut; Micheyl, Christophe; Heinz, Michael G.

2013-01-01

Listeners with sensorineural hearing loss (SNHL) often show poorer thresholds for fundamental-frequency (F0) discrimination, and poorer discrimination between harmonic and frequency-shifted (inharmonic) complex tones, than normal-hearing (NH) listeners—especially when these tones contain resolved or partially resolved components. It has been suggested that these perceptual deficits reflect reduced access to temporal-fine-structure (TFS) information, and could be due to degraded phase-locking in the auditory nerve (AN) with SNHL. In the present study, TFS and temporal-envelope (ENV) cues in single AN-fiber responses to bandpass-filtered harmonic and inharmonic complex tones were measured in chinchillas with either normal hearing or noise-induced SNHL. The stimuli were comparable to those used in recent psychophysical studies of F0 and harmonic/inharmonic discrimination. As in those studies, the rank of the center component was manipulated to produce different resolvability conditions, different phase relationships (cosine and random phase) were tested, and background noise was present. Neural TFS and ENV cues were quantified using cross-correlation coefficients computed using shuffled cross-correlograms between neural responses to REF (harmonic) and TEST (F0- or frequency-shifted) stimuli. In animals with SNHL, AN-fiber tuning curves showed elevated thresholds, broadened tuning, best-frequency shifts, and downward shifts in the dominant TFS response component; however, no significant degradation in the ability of AN fibers to encode TFS or ENV cues was found. Consistent with optimal-observer analyses, the results indicate that TFS and ENV cues depended only on the relevant frequency shift in Hz and thus were not degraded because phase-locking remained intact. These results suggest that perceptual “TFS-processing” deficits do not simply reflect degraded phase-locking at the level of the AN. To the extent that performance in F0 and harmonic/inharmonic discrimination tasks depend on TFS cues, it is likely through a more complicated (sub-optimal) decoding mechanism, which may involve “spatiotemporal” (place-time) neural representations. PMID:23716215

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Higher spatial harmonics of photorefractive gratings written by phase-locked detection

NASA Astrophysics Data System (ADS)

Dugin, A. V.; Zel'dovich, Boris Ya; Il'inykh, P. N.; Liberman, V. S.; Nesterkin, O. P.

1992-11-01

The higher spatial harmonics of the photorefractive response have been studied theoretically and experimentally for gratings written by phase-locked detection in an alternating external field. The conditions for writing higher spatial harmonics are derived analytically. The amplitude of the second spatial harmonic has been found experimentally as a function of the spatial frequency in two Bi12TiO20 crystals.

Stochastic and superharmonic stochastic resonances of a confined overdamped harmonic oscillator

NASA Astrophysics Data System (ADS)

Zhang, Lu; Lai, Li; Peng, Hao; Tu, Zhe; Zhong, Suchuan

2018-01-01

The dynamics of many soft condensed matter and biological systems is affected by space limitations, which produce some peculiar effects on the systems' stochastic resonance (SR) behavior. In this study, we propose a model where SR can be observed: a confined overdamped harmonic oscillator that is subjected to a sinusoidal driving force and is under the influence of a multiplicative white noise. The output response of the system is a periodic signal with harmonic frequencies that are odd multiples of the driving frequency. We verify the amplitude resonances at the driving frequencies and superharmonic frequencies that are equal to three, five, and seven times the driving frequency, using a numerical method based on the stochastic Taylor expansion. The synergistic effect of the multiplicative white noise, constant boundaries, and periodic driving force that can induce a SR in the output amplitude at the driving and superharmonic frequencies is found. The SR phenomenon found in this paper is sensitive to the driving amplitude and frequency, inherent potential parameter, and boundary width, thus leading to various resonance conditions. Therefore, the mechanism found could be beneficial for the characterization of these confined systems and could constitute an important tool for controlling their basic properties.

Increased first and second pulse harmonics in Tai Chi Chuan practitioners.

PubMed

Lu, Wan-An; Chen, Yung-Sheng; Kuo, Cheng-Deng

2016-02-29

Tai Chi Chuan (TCC) is known to be a good calisthenics for people. This study examined the relationship between pulse harmonics and autonomic nervous modulation in TCC practitioners. Power spectral measures of right pulse wave and heart rate variability (HRV) measures were compared between TCC practitioners and control subjects. Correlation analyses between pulse harmonics and HRV measures were performed using linear regression analysis. At baseline, the total power of pulse (TPp), powers of all individual pulse harmonics, normalized power of the 1(st) harmonics (nPh1) of TCC practitioners were greater, while the normalized power of the 4(th) pulse harmonics (nPh4) of TCC practitioners was smaller, than those of the controls. Similarly, the baseline standard deviation (SD(RR)), coefficient of variation (CV(RR)), and normalized high-frequency power (nHFP) of RR intervals were smaller, while the normalized very low-frequency power (nVLFP) and low-/high- frequency power ratio (LHR) were larger in the TCC practitioners. The TCC age correlated significantly and negatively with nPh1, and nearly significantly and negatively with nPh2 in the TCC practitioners. Thirty min after TCC exercise, the percentage changes in mRRI, SDRR, TP, VLFP were decreased, while the percentage changes in HR, ULFP, nLFP, and Ph2 were increased, relative to the controls. Correlation analysis shows that the %Ph2 correlates significantly and negatively with %mRRI and significantly and positively with %HR. The TCC practitioners had increased baseline total power of pulse and the 1(st) and 2(nd) pulse harmonics, and decreased power of the 4(th) pulse harmonics, along with decreased vagal modulation and increased sympathetic modulation. After TCC exercise, the power of the 2(nd) harmonics of TCC practitioners was increased which might be related to the increase in HR due to decreased vascular resistance after TCC exercise.

Experimental and simulation studies on the behavior of signal harmonics in magnetic particle imaging.

PubMed

Murase, Kenya; Konishi, Takashi; Takeuchi, Yuki; Takata, Hiroshige; Saito, Shigeyoshi

2013-07-01

Our purpose in this study was to investigate the behavior of signal harmonics in magnetic particle imaging (MPI) by experimental and simulation studies. In the experimental studies, we made an apparatus for MPI in which both a drive magnetic field (DMF) and a selection magnetic field (SMF) were generated with a Maxwell coil pair. The MPI signals from magnetic nanoparticles (MNPs) were detected with a solenoid coil. The odd- and even-numbered harmonics were calculated by Fourier transformation with or without background subtraction. The particle size of the MNPs was measured by transmission electron microscopy (TEM), dynamic light-scattering, and X-ray diffraction methods. In the simulation studies, the magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively. The odd- and even-numbered harmonics were calculated by Fourier transformation under various conditions of DMF and SMF and for three different particle sizes. The behavior of the harmonics largely depended on the size of the MNPs. When we used the particle size obtained from the TEM image, the simulation results were most similar to the experimental results. The similarity between the experimental and simulation results for the even-numbered harmonics was better than that for the odd-numbered harmonics. This was considered to be due to the fact that the odd-numbered harmonics were more sensitive to background subtraction than were the even-numbered harmonics. This study will be useful for a better understanding, optimization, and development of MPI and for designing MNPs appropriate for MPI.

Harmonic generation and parametric decay in the ion cyclotron frequency range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skiff, F.N.; Wong, K.L.; Ono, M.

1984-06-01

Harmonic generation and parametric decay are examined in a toroidal ACT-I plasma using electrostatic plate antennas. The harmonic generation, which is consistent with sheath rectification, is sufficiently strong that the nonlinearly generated harmonic modes themselves decay parametrically. Resonant and nonresonant parametric decay of the second harmonic are observed and compared with uniform pump theory. Resonant decay of lower hybrid waves into lower hybrid waves and slow ion cyclotron waves is seen for the first time. Surprisingly, the decay processes are nonlinearly saturated, indicating absolute instability.

Cumulative phase delay imaging - A new contrast enhanced ultrasound modality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demi, Libertario, E-mail: l.demi@tue.nl; Sloun, Ruud J. G. van; Mischi, Massimo

Recently, a new acoustic marker for ultrasound contrast agents (UCAs) has been introduced. A cumulative phase delay (CPD) between the second harmonic and fundamental pressure wave field components is in fact observable for ultrasound propagating through UCAs. This phenomenon is absent in the case of tissue nonlinearity and is dependent on insonating pressure and frequency, UCA concentration, and propagation path length through UCAs. In this paper, ultrasound images based on this marker are presented. The ULA-OP research platform, in combination with a LA332 linear array probe (Esaote, Firenze Italy), were used to image a gelatin phantom containing a PVC platemore » (used as a reflector) and a cylindrical cavity measuring 7 mm in diameter (placed in between the observation point and the PVC plate). The cavity contained a 240 µL/L SonoVueO{sup ®} UCA concentration. Two insonating frequencies (3 MHz and 2.5 MHz) were used to scan the gelatine phantom. A mechanical index MI = 0.07, measured in water at the cavity location with a HGL-0400 hydrophone (Onda, Sunnyvale, CA), was utilized. Processing the ultrasound signals backscattered from the plate, ultrasound images were generated in a tomographic fashion using the filtered back-projection method. As already observed in previous studies, significantly higher CPD values are measured when imaging at a frequency of 2.5 MHz, as compared to imaging at 3 MHz. In conclusion, these results confirm the applicability of the discussed CPD as a marker for contrast imaging. Comparison with standard contrast-enhanced ultrasound imaging modalities will be the focus of future work.« less

Harmonic motion imaging for focused ultrasound (HMIFU): a fully integrated technique for sonication and monitoring of thermal ablation in tissues.

PubMed

Maleke, C; Konofagou, E E

2008-03-21

FUS (focused ultrasound), or HIFU (high-intensity-focused ultrasound) therapy, a minimally or non-invasive procedure that uses ultrasound to generate thermal necrosis, has been proven successful in several clinical applications. This paper discusses a method for monitoring thermal treatment at different sonication durations (10 s, 20 s and 30 s) using the amplitude-modulated (AM) harmonic motion imaging for focused ultrasound (HMIFU) technique in bovine liver samples in vitro. The feasibility of HMI for characterizing mechanical tissue properties has previously been demonstrated. Here, a confocal transducer, combining a 4.68 MHz therapy (FUS) and a 7.5 MHz diagnostic (pulse-echo) transducer, was used. The therapy transducer was driven by a low-frequency AM continuous signal at 25 Hz, producing a stable harmonic radiation force oscillating at the modulation frequency. A pulser/receiver was used to drive the pulse-echo transducer at a pulse repetition frequency (PRF) of 5.4 kHz. Radio-frequency (RF) signals were acquired using a standard pulse-echo technique. The temperature near the ablation region was simultaneously monitored. Both RF signals and temperature measurements were obtained before, during and after sonication. The resulting axial tissue displacement was estimated using one-dimensional cross correlation. When temperature at the focal zone was above 48 degrees C during heating, the coagulation necrosis occurred and tissue damage was irreversible. The HMI displacement profiles in relation to the temperature and sonication durations were analyzed. At the beginning of heating, the temperature at the focus increased sharply, while the tissue stiffness decreased resulting in higher HMI displacements. This was confirmed by an increase of 0.8 microm degrees C(-1)(r=0.93, p<.005). After sustained heating, the tissue became irreversibly stiffer, followed by an associated decrease in the HMI displacement (-0.79 microm degrees C(-1), r=-0.92, p<0.001). Repeated experiments showed a reproducible pattern of the HMI displacement changes with a temperature at a slope equal to 0.8+/-0.11 and -0.79+/-0.14 microm degrees C(-1), prior to and after lesion formation in seven bovine liver samples, respectively. This technique was thus capable of following the protein-denatured lesion formation based on the variation of the HMI displacements. This method could, therefore, be applied for real-time monitoring of temperature-related stiffness changes of tissues during FUS, HIFU or other thermal therapies.

Cortical pitch regions in humans respond primarily to resolved harmonics and are located in specific tonotopic regions of anterior auditory cortex.

PubMed

Norman-Haignere, Sam; Kanwisher, Nancy; McDermott, Josh H

2013-12-11

Pitch is a defining perceptual property of many real-world sounds, including music and speech. Classically, theories of pitch perception have differentiated between temporal and spectral cues. These cues are rendered distinct by the frequency resolution of the ear, such that some frequencies produce "resolved" peaks of excitation in the cochlea, whereas others are "unresolved," providing a pitch cue only via their temporal fluctuations. Despite longstanding interest, the neural structures that process pitch, and their relationship to these cues, have remained controversial. Here, using fMRI in humans, we report the following: (1) consistent with previous reports, all subjects exhibited pitch-sensitive cortical regions that responded substantially more to harmonic tones than frequency-matched noise; (2) the response of these regions was mainly driven by spectrally resolved harmonics, although they also exhibited a weak but consistent response to unresolved harmonics relative to noise; (3) the response of pitch-sensitive regions to a parametric manipulation of resolvability tracked psychophysical discrimination thresholds for the same stimuli; and (4) pitch-sensitive regions were localized to specific tonotopic regions of anterior auditory cortex, extending from a low-frequency region of primary auditory cortex into a more anterior and less frequency-selective region of nonprimary auditory cortex. These results demonstrate that cortical pitch responses are located in a stereotyped region of anterior auditory cortex and are predominantly driven by resolved frequency components in a way that mirrors behavior.

Multi-photon transitions and Rabi resonance in continuous wave EPR.

PubMed

Saiko, Alexander P; Fedaruk, Ryhor; Markevich, Siarhei A

2015-10-01

The study of microwave-radiofrequency multi-photon transitions in continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance condition, when the radio frequency of the magnetic-field modulation matches the Rabi frequency of a spin system in the microwave field. Using the non-secular perturbation theory based on the Bogoliubov averaging method, the analytical description of the response of the spin system is derived for all modulation frequency harmonics. When the modulation frequency exceeds the EPR linewidth, multi-photon transitions result in sidebands in absorption EPR spectra measured with phase-sensitive detection at any harmonic. The saturation of different-order multi-photon transitions is shown to be significantly different and to be sensitive to the Rabi resonance. The noticeable frequency shifts of sidebands are found to be the signatures of this resonance. The inversion of two-photon lines in some spectral intervals of the out-of-phase first-harmonic signal is predicted under passage through the Rabi resonance. The inversion indicates the transition from absorption to stimulated emission or vice versa, depending on the sideband. The manifestation of the primary and secondary Rabi resonance is also demonstrated in the time evolution of steady-state EPR signals formed by all harmonics of the modulation frequency. Our results provide a theoretical framework for future developments in multi-photon CW EPR spectroscopy, which can be useful for samples with long spin relaxation times and extremely narrow EPR lines. Copyright © 2015 Elsevier Inc. All rights reserved.

Cortical Pitch Regions in Humans Respond Primarily to Resolved Harmonics and Are Located in Specific Tonotopic Regions of Anterior Auditory Cortex

PubMed Central

Kanwisher, Nancy; McDermott, Josh H.

2013-01-01

Pitch is a defining perceptual property of many real-world sounds, including music and speech. Classically, theories of pitch perception have differentiated between temporal and spectral cues. These cues are rendered distinct by the frequency resolution of the ear, such that some frequencies produce “resolved” peaks of excitation in the cochlea, whereas others are “unresolved,” providing a pitch cue only via their temporal fluctuations. Despite longstanding interest, the neural structures that process pitch, and their relationship to these cues, have remained controversial. Here, using fMRI in humans, we report the following: (1) consistent with previous reports, all subjects exhibited pitch-sensitive cortical regions that responded substantially more to harmonic tones than frequency-matched noise; (2) the response of these regions was mainly driven by spectrally resolved harmonics, although they also exhibited a weak but consistent response to unresolved harmonics relative to noise; (3) the response of pitch-sensitive regions to a parametric manipulation of resolvability tracked psychophysical discrimination thresholds for the same stimuli; and (4) pitch-sensitive regions were localized to specific tonotopic regions of anterior auditory cortex, extending from a low-frequency region of primary auditory cortex into a more anterior and less frequency-selective region of nonprimary auditory cortex. These results demonstrate that cortical pitch responses are located in a stereotyped region of anterior auditory cortex and are predominantly driven by resolved frequency components in a way that mirrors behavior. PMID:24336712

Harmonic Motion Imaging (HMI) for Tumor Imaging and Treatment Monitoring.

PubMed

Konofagou, Elisa E; Maleke, Caroline; Vappou, Jonathan

2012-01-01

Palpation is an established screening procedure for the detection of several superficial cancers including breast, thyroid, prostate, and liver tumors through both self and clinical examinations. This is because solid masses typically have distinct stiffnesses compared to the surrounding normal tissue. In this paper, the application of Harmonic Motion Imaging (HMI) for tumor detection based on its stiffness as well as its relevance in thermal treatment is reviewed. HMI uses a focused ultrasound (FUS) beam to generate an oscillatory acoustic radiation force for an internal, non-contact palpation to internally estimate relative tissue hardness. HMI studies have dealt with the measurement of the tissue dynamic motion in response to an oscillatory acoustic force at the same frequency, and have been shown feasible in simulations, phantoms, ex vivo human and bovine tissues as well as animals in vivo. Using an FUS beam, HMI can also be used in an ideal integration setting with thermal ablation using high-intensity focused ultrasound (HIFU), which also leads to an alteration in the tumor stiffness. In this paper, a short review of HMI is provided that encompasses the findings in all the aforementioned areas. The findings presented herein demonstrate that the HMI displacement can accurately depict the underlying tissue stiffness, and the HMI image of the relative stiffness could accurately detect and characterize the tumor or thermal lesion based on its distinct properties. HMI may thus constitute a non-ionizing, cost-efficient and reliable complementary method for noninvasive tumor detection, localization, diagnosis and treatment monitoring.

Harmonic Motion Imaging (HMI) for Tumor Imaging and Treatment Monitoring

PubMed Central

Maleke, Caroline; Vappou, Jonathan

2014-01-01

Palpation is an established screening procedure for the detection of several superficial cancers including breast, thyroid, prostate, and liver tumors through both self and clinical examinations. This is because solid masses typically have distinct stiffnesses compared to the surrounding normal tissue. In this paper, the application of Harmonic Motion Imaging (HMI) for tumor detection based on its stiffness as well as its relevance in thermal treatment is reviewed. HMI uses a focused ultrasound (FUS) beam to generate an oscillatory acoustic radiation force for an internal, non-contact palpation to internally estimate relative tissue hardness. HMI studies have dealt with the measurement of the tissue dynamic motion in response to an oscillatory acoustic force at the same frequency, and have been shown feasible in simulations, phantoms, ex vivo human and bovine tissues as well as animals in vivo. Using an FUS beam, HMI can also be used in an ideal integration setting with thermal ablation using high-intensity focused ultrasound (HIFU), which also leads to an alteration in the tumor stiffness. In this paper, a short review of HMI is provided that encompasses the findings in all the aforementioned areas. The findings presented herein demonstrate that the HMI displacement can accurately depict the underlying tissue stiffness, and the HMI image of the relative stiffness could accurately detect and characterize the tumor or thermal lesion based on its distinct properties. HMI may thus constitute a non-ionizing, cost-efficient and reliable complementary method for noninvasive tumor detection, localization, diagnosis and treatment monitoring. PMID:25364321

Health State Monitoring of Bladed Machinery with Crack Growth Detection in BFG Power Plant Using an Active Frequency Shift Spectral Correction Method.

PubMed

Sun, Weifang; Yao, Bin; He, Yuchao; Chen, Binqiang; Zeng, Nianyin; He, Wangpeng

2017-08-09

Power generation using waste-gas is an effective and green way to reduce the emission of the harmful blast furnace gas (BFG) in pig-iron producing industry. Condition monitoring of mechanical structures in the BFG power plant is of vital importance to guarantee their safety and efficient operations. In this paper, we describe the detection of crack growth of bladed machinery in the BFG power plant via vibration measurement combined with an enhanced spectral correction technique. This technique enables high-precision identification of amplitude, frequency, and phase information (the harmonic information) belonging to deterministic harmonic components within the vibration signals. Rather than deriving all harmonic information using neighboring spectral bins in the fast Fourier transform spectrum, this proposed active frequency shift spectral correction method makes use of some interpolated Fourier spectral bins and has a better noise-resisting capacity. We demonstrate that the identified harmonic information via the proposed method is of suppressed numerical error when the same level of noises is presented in the vibration signal, even in comparison with a Hanning-window-based correction method. With the proposed method, we investigated vibration signals collected from a centrifugal compressor. Spectral information of harmonic tones, related to the fundamental working frequency of the centrifugal compressor, is corrected. The extracted spectral information indicates the ongoing development of an impeller blade crack that occurred in the centrifugal compressor. This method proves to be a promising alternative to identify blade cracks at early stages.

The electrical asymmetry effect in a multi frequency geometrically asymmetric capacitively coupled plasma: A study by a nonlinear global model

NASA Astrophysics Data System (ADS)

Saikia, P.; Bhuyan, H.; Escalona, M.; Favre, M.; Bora, B.; Kakati, M.; Wyndham, E.; Rawat, R. S.; Schulze, J.

2018-05-01

We investigate the electrical asymmetry effect (EAE) and the current dynamics in a geometrically asymmetric capacitively coupled radio frequency plasma driven by multiple consecutive harmonics based on a nonlinear global model. The discharge symmetry is controlled via the EAE, i.e., by varying the total number of harmonics and tuning the phase shifts ( θ k ) between them. Here, we systematically study the EAE in a low pressure (4 Pa) argon discharge with different geometrical asymmetries driven by a multifrequency rf source consisting of 13.56 MHz and its harmonics. We find that the geometrical asymmetry strongly affects the absolute value of the DC self-bias voltage, but its functional dependence on θ k is similar at different values of the geometrical asymmetry. Also, the values of the DC self-bias are enhanced by adding more consecutive harmonics. The voltage drop across the sheath at the powered and grounded electrode is found to increase/decrease, respectively, with the increase in the number of harmonics of the fundamental frequency. For the purpose of validating the model, its outputs are compared with the results obtained in a geometrically and electrically asymmetric 2f capacitively coupled plasmas experiment conducted by Schuengel et al. [J. Appl. Phys. 112, 053302 (2012)]. Finally, we study the self-excitation of nonlinear plasma series resonance oscillations and its dependence on the geometrical asymmetry as well as the phase angles between the driving frequencies.

Phase locking of 2.324 and 2.959 terahertz quantum cascade lasers using a Schottky diode harmonic mixer.

PubMed

Danylov, Andriy; Erickson, Neal; Light, Alexander; Waldman, Jerry

2015-11-01

The 23rd and 31st harmonics of a microwave signal generated in a novel THz balanced Schottky diode mixer were used as a frequency stable reference source to phase lock solid-nitrogen-cooled 2.324 and 2.959 THz quantum cascade lasers. Hertz-level frequency stability was achieved, which was maintained for several hours.

Harmonic analysis of electrified railway based on improved HHT

NASA Astrophysics Data System (ADS)

Wang, Feng

2018-04-01

In this paper, the causes and harms of the current electric locomotive electrical system harmonics are firstly studied and analyzed. Based on the characteristics of the harmonics in the electrical system, the Hilbert-Huang transform method is introduced. Based on the in-depth analysis of the empirical mode decomposition method and the Hilbert transform method, the reasons and solutions to the endpoint effect and modal aliasing problem in the HHT method are explored. For the endpoint effect of HHT, this paper uses point-symmetric extension method to extend the collected data; In allusion to the modal aliasing problem, this paper uses the high frequency harmonic assistant method to preprocess the signal and gives the empirical formula of high frequency auxiliary harmonic. Finally, combining the suppression of HHT endpoint effect and modal aliasing problem, an improved HHT method is proposed and simulated by matlab. The simulation results show that the improved HHT is effective for the electric locomotive power supply system.

Re-examining the upper limit of temporal pitch

PubMed Central

Macherey, Olivier; Carlyon, Robert P.

2015-01-01

Five normally-hearing listeners pitch-ranked harmonic complexes of different fundamental frequencies (F0s) filtered in three different frequency regions. Harmonics were summed either in sine, alternating sine-cosine (ALT), or pulse-spreading (PSHC) phase. The envelopes of ALT and PSHC complexes repeated at rates of 2F0 and 4F0. Pitch corresponded to those rates at low F0s, but, as F0 increased, there was a range of F0s over which pitch remained constant or dropped. Gammatone-filterbank simulations showed that, as F0 increased and the number of harmonics interacting in a filter dropped, the output of that filter switched from repeating at 2F0 or 4F0 to repeating at F0. A model incorporating this phenomenon accounted well for the data, except for complexes filtered into the highest frequency region (7800-10800 Hz). To account for the data in that region it was necessary to assume either that auditory filters at very high frequencies are sharper than traditionally believed, and/or that the auditory system applies smaller weights to filters whose outputs repeat at high rates. The results also provide new evidence on the highest pitch that can be derived from purely temporal cues, and corroborate recent reports that a complex pitch can be derived from very-high-frequency resolved harmonics. PMID:25480066

Molecular imaging of melanin distribution in vivo and quantitative differential diagnosis of human pigmented lesions using label-free harmonic generation biopsy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Sun, Chi-Kuang; Wei, Ming-Liang; Su, Yu-Hsiang; Weng, Wei-Hung; Liao, Yi-Hua

2017-02-01

Harmonic generation microscopy is a noninvasive repetitive imaging technique that provides real-time 3D microscopic images of human skin with a sub-femtoliter resolution and high penetration down to the reticular dermis. In this talk, we show that with a strong resonance effect, the third-harmonic-generation (THG) modality provides enhanced contrast on melanin and allows not only differential diagnosis of various pigmented skin lesions but also quantitative imaging for longterm tracking. This unique capability makes THG microscopy the only label-free technique capable of identifying the active melanocytes in human skin and to image their different dendriticity patterns. In this talk, we will review our recent efforts to in vivo image melanin distribution and quantitatively diagnose pigmented skin lesions using label-free harmonic generation biopsy. This talk will first cover the spectroscopic study on the melanin enhanced THG effect in human cells and the calibration strategy inside human skin for quantitative imaging. We will then review our recent clinical trials including: differential diagnosis capability study on pigmented skin tumors; as well as quantitative virtual biopsy study on pre- and post- treatment evaluation on melasma and solar lentigo. Our study indicates the unmatched capability of harmonic generation microscopy to perform virtual biopsy for noninvasive histopathological diagnosis of various pigmented skin tumors, as well as its unsurpassed capability to noninvasively reveal the pathological origin of different hyperpigmentary diseases on human face as well as to monitor the efficacy of laser depigmentation treatments. This work is sponsored by National Health Research Institutes.

A new approach to harmonic elimination based on a real-time comparison method

NASA Astrophysics Data System (ADS)

Gourisetti, Sri Nikhil Gupta

Undesired harmonics are responsible for noise in a transmission channel, power loss in power electronics and in motor control. Selective Harmonic Elimination (SHE) is a well-known method used to eliminate or suppress the unwanted harmonics between the fundamental and the carrier frequency harmonic/component. But SHE bears the disadvantage of its incapability to use in real-time applications. A novel reference-carrier comparative method has been developed which can be used to generate an SPWM signal to apply in real-time systems. A modified carrier signal is designed and tested for different carrier frequencies based on the generated SPWM FFT. The carrier signal may change for different fundamental to carrier ratio that leads to solving the equations each time. An analysis to find all possible solutions for a particular carrier frequency and fundamental amplitude is performed and found. This proves that there is no one global maxima instead several local maximas exists for a particular condition set that makes this method less sensitive. Additionally, an attempt to find a universal solution that is valid for any carrier signal with predefined fundamental amplitude is performed. A uniform distribution Monte-Carlo sensitivity analysis is performed to measure the window i.e., best and worst possible solutions. The simulations are performed using MATLAB and are justified with experimental results.

Biosonar signals impinging on the target during interception by big brown bats, Eptesicus fuscus.

PubMed

Saillant, Prestor A; Simmons, James A; Bouffard, Frederick H; Lee, David N; Dear, Steven P

2007-05-01

Big brown bats (Eptesicus fuscus) were videotaped in the dark with a night-vision lens and infrared illumination while flying repeatedly along the same straight course to seize a tethered mealworm or a small electret microphone used to record biosonar signals impinging on the target. Bats emitted frequency-modulated sounds with first to third harmonics covering frequencies from 23 to 105 kHz. As the bats neared the target, the first harmonic shifted lower in frequency while the third harmonic strengthened and the fourth harmonic, and sometimes the fifth harmonic, appeared. Incident-sound bandwidth remained broad throughout the maneuver, a feature not seen in field recordings of rapidly moving bats due to propagation losses and uncontrolled directional effects. Sound pressures at the microphone increased by about 20 dB during approach from 2.5 m down to 50 cm and then leveled off, indicating that emitted amplitudes were approximately constant until the terminal stage, when they progressively decreased for the remainder of the maneuver. Interpulse intervals decreased from 80-100 ms down to about 6-7 ms and then stabilized throughout the terminal stage, while durations decreased smoothly from 3-4 ms (limited by adjacent wall) down to 0.5 ms during the terminal stage, which ended with capture.

Data-adaptive harmonic analysis and prediction of sea level change in North Atlantic region

NASA Astrophysics Data System (ADS)

Kondrashov, D. A.; Chekroun, M.

2017-12-01

This study aims to characterize North Atlantic sea level variability across the temporal and spatial scales. We apply recently developed data-adaptive Harmonic Decomposition (DAH) and Multilayer Stuart-Landau Models (MSLM) stochastic modeling techniques [Chekroun and Kondrashov, 2017] to monthly 1993-2017 dataset of Combined TOPEX/Poseidon, Jason-1 and Jason-2/OSTM altimetry fields over North Atlantic region. The key numerical feature of the DAH relies on the eigendecomposition of a matrix constructed from time-lagged spatial cross-correlations. In particular, eigenmodes form an orthogonal set of oscillating data-adaptive harmonic modes (DAHMs) that come in pairs and in exact phase quadrature for a given temporal frequency. Furthermore, the pairs of data-adaptive harmonic coefficients (DAHCs), obtained by projecting the dataset onto associated DAHMs, can be very efficiently modeled by a universal parametric family of simple nonlinear stochastic models - coupled Stuart-Landau oscillators stacked per frequency, and synchronized across different frequencies by the stochastic forcing. Despite the short record of altimetry dataset, developed DAH-MSLM model provides for skillful prediction of key dynamical and statistical features of sea level variability. References M. D. Chekroun and D. Kondrashov, Data-adaptive harmonic spectra and multilayer Stuart-Landau models. HAL preprint, 2017, https://hal.archives-ouvertes.fr/hal-01537797

Investigation about relationships between the symmetries of ferroelectric crystal Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} and second-harmonic patterns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Tianxiang; Yu, Haohai, E-mail: haohaiyu@sdu.edu.cn; Zhang, Huaijin, E-mail: huaijinzhang@sdu.edu.cn

2015-08-07

The broadband quasi-phase matching (QPM) process in a uniaxial ferroelectric crystal Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN-28) was demonstrated with the second-harmonic wavelength range from 450 nm to 650 nm, and the relationship between the symmetries of CBN-28 and the second-harmonic patterns was experimentally and theoretically investigated based on the random anti-parallel domains in the crystal and QPM conditions. The dependences of frequency-doubled patterns on the wavelength and anisotropy of the nonlinear crystal were also studied, and the frequency-doubled photons were found to be trapped on circles. By analyzing the light-matter interacting Hamiltonians, the trapping force for second-harmonic photons was found tomore » be centripetal and tunable by the fundamental lasers, and the variation tendencies of the rotational velocity of second-harmonic generation photons could also be predicated. The results indicate that the CBN-28 ferroelectric crystal is a promising nonlinear optical material for the generation of broadband frequency-doubled waves, and the analysis on centripetal force based on the interaction Hamiltonians may provide a novel recognition for the investigation of QPM process to be further studied.« less

Easily extensible unix software for spectral analysis, display, modification, and synthesis of musical sounds

NASA Astrophysics Data System (ADS)

Beauchamp, James W.

2002-11-01

Software has been developed which enables users to perform time-varying spectral analysis of individual musical tones or successions of them and to perform further processing of the data. The package, called sndan, is freely available in source code, uses EPS graphics for display, and is written in ansi c for ease of code modification and extension. Two analyzers, a fixed-filter-bank phase vocoder (''pvan'') and a frequency-tracking analyzer (''mqan'') constitute the analysis front end of the package. While pvan's output consists of continuous amplitudes and frequencies of harmonics, mqan produces disjoint ''tracks.'' However, another program extracts a fundamental frequency and separates harmonics from the tracks, resulting in a continuous harmonic output. ''monan'' is a program used to display harmonic data in a variety of formats, perform various spectral modifications, and perform additive resynthesis of the harmonic partials, including possible pitch-shifting and time-scaling. Sounds can also be synthesized according to a musical score using a companion synthesis language, Music 4C. Several other programs in the sndan suite can be used for specialized tasks, such as signal display and editing. Applications of the software include producing specialized sounds for music compositions or psychoacoustic experiments or as a basis for developing new synthesis algorithms.

Harmonization of multi-site diffusion tensor imaging data.

PubMed

Fortin, Jean-Philippe; Parker, Drew; Tunç, Birkan; Watanabe, Takanori; Elliott, Mark A; Ruparel, Kosha; Roalf, David R; Satterthwaite, Theodore D; Gur, Ruben C; Gur, Raquel E; Schultz, Robert T; Verma, Ragini; Shinohara, Russell T

2017-11-01

Diffusion tensor imaging (DTI) is a well-established magnetic resonance imaging (MRI) technique used for studying microstructural changes in the white matter. As with many other imaging modalities, DTI images suffer from technical between-scanner variation that hinders comparisons of images across imaging sites, scanners and over time. Using fractional anisotropy (FA) and mean diffusivity (MD) maps of 205 healthy participants acquired on two different scanners, we show that the DTI measurements are highly site-specific, highlighting the need of correcting for site effects before performing downstream statistical analyses. We first show evidence that combining DTI data from multiple sites, without harmonization, may be counter-productive and negatively impacts the inference. Then, we propose and compare several harmonization approaches for DTI data, and show that ComBat, a popular batch-effect correction tool used in genomics, performs best at modeling and removing the unwanted inter-site variability in FA and MD maps. Using age as a biological phenotype of interest, we show that ComBat both preserves biological variability and removes the unwanted variation introduced by site. Finally, we assess the different harmonization methods in the presence of different levels of confounding between site and age, in addition to test robustness to small sample size studies. Copyright © 2017 Elsevier Inc. All rights reserved.

On mapping subangstrom electron clouds with force microscopy.

PubMed

Wright, C Alan; Solares, Santiago D

2011-11-09

In 2004 Hembacher et al. (Science 2004, 305, 380-383) reported simultaneous higher-harmonics atomic force mocroscopy (AFM)/scanning tunneling microscopy (STM) images acquired while scanning a graphite surface with a tungsten tip. They interpreted the observed subatomic features in the AFM images as the signature of lobes of increased electron density at the tungsten tip apex. Although these intriguing images have stirred controversy, an in-depth theoretical feasibility study has not yet been produced. Here we report on the development of a method for simulating higher harmonics AFM images and its application to the same system. Our calculations suggest that four lobes of increased electron density are expected to be present at a W(001) tip apex atom and that the corresponding higher harmonics AFM images of graphite can exhibit 4-fold symmetry features. Despite these promising results, open questions remain since the calculated amplitudes of the higher harmonics generated by the short-range forces are on the order of hundredths of picometers, leading to very small corrugations in the theoretical images. Additionally, the complex, intermittent nature of the tip-sample interaction, which causes constant readjustment of the tip and sample orbitals as the tip approaches and retracts from the surface, prevents a direct quantitative connection between the electron density and the AFM image features.

Neural dynamics during repetitive visual stimulation

NASA Astrophysics Data System (ADS)

Tsoneva, Tsvetomira; Garcia-Molina, Gary; Desain, Peter

2015-12-01

Objective. Steady-state visual evoked potentials (SSVEPs), the brain responses to repetitive visual stimulation (RVS), are widely utilized in neuroscience. Their high signal-to-noise ratio and ability to entrain oscillatory brain activity are beneficial for their applications in brain-computer interfaces, investigation of neural processes underlying brain rhythmic activity (steady-state topography) and probing the causal role of brain rhythms in cognition and emotion. This paper aims at analyzing the space and time EEG dynamics in response to RVS at the frequency of stimulation and ongoing rhythms in the delta, theta, alpha, beta, and gamma bands. Approach.We used electroencephalography (EEG) to study the oscillatory brain dynamics during RVS at 10 frequencies in the gamma band (40-60 Hz). We collected an extensive EEG data set from 32 participants and analyzed the RVS evoked and induced responses in the time-frequency domain. Main results. Stable SSVEP over parieto-occipital sites was observed at each of the fundamental frequencies and their harmonics and sub-harmonics. Both the strength and the spatial propagation of the SSVEP response seem sensitive to stimulus frequency. The SSVEP was more localized around the parieto-occipital sites for higher frequencies (>54 Hz) and spread to fronto-central locations for lower frequencies. We observed a strong negative correlation between stimulation frequency and relative power change at that frequency, the first harmonic and the sub-harmonic components over occipital sites. Interestingly, over parietal sites for sub-harmonics a positive correlation of relative power change and stimulation frequency was found. A number of distinct patterns in delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz) and beta (15-30 Hz) bands were also observed. The transient response, from 0 to about 300 ms after stimulation onset, was accompanied by increase in delta and theta power over fronto-central and occipital sites, which returned to baseline after approx. 500 ms. During the steady-state response, we observed alpha band desynchronization over occipital sites and after 500 ms also over frontal sites, while neighboring areas synchronized. The power in beta band over occipital sites increased during the stimulation period, possibly caused by increase in power at sub-harmonic frequencies of stimulation. Gamma power was also enhanced by the stimulation. Significance. These findings have direct implications on the use of RVS and SSVEPs for neural process investigation through steady-state topography, controlled entrainment of brain oscillations and BCIs. A deep understanding of SSVEP propagation in time and space and the link with ongoing brain rhythms is crucial for optimizing the typical SSVEP applications for studying, assisting, or augmenting human cognitive and sensorimotor function.

Effects of frequency- and direction-dependent elastic materials on linearly elastic MRE image reconstructions

NASA Astrophysics Data System (ADS)

Perreard, I. M.; Pattison, A. J.; Doyley, M.; McGarry, M. D. J.; Barani, Z.; Van Houten, E. E.; Weaver, J. B.; Paulsen, K. D.

2010-11-01

The mechanical model commonly used in magnetic resonance elastography (MRE) is linear elasticity. However, soft tissue may exhibit frequency- and direction-dependent (FDD) shear moduli in response to an induced excitation causing a purely linear elastic model to provide an inaccurate image reconstruction of its mechanical properties. The goal of this study was to characterize the effects of reconstructing FDD data using a linear elastic inversion (LEI) algorithm. Linear and FDD phantoms were manufactured and LEI images were obtained from time-harmonic MRE acquisitions with variations in frequency and driving signal amplitude. LEI responses to artificially imposed uniform phase shifts in the displacement data from both purely linear elastic and FDD phantoms were also evaluated. Of the variety of FDD phantoms considered, LEI appeared to tolerate viscoelastic data-model mismatch better than deviations caused by poroelastic and anisotropic mechanical properties in terms of visual image contrast. However, the estimated shear modulus values were substantially incorrect relative to independent mechanical measurements even in the successful viscoelastic cases and the variations in mean values with changes in experimental conditions associated with uniform phase shifts, driving signal frequency and amplitude were unpredictable. Overall, use of LEI to reconstruct data acquired in phantoms with FDD material properties provided biased results under the best conditions and significant artifacts in the worst cases. These findings suggest that the success with which LEI is applied to MRE data in tissue will depend on the underlying mechanical characteristics of the tissues and/or organs systems of clinical interest.

Effects of frequency- and direction-dependent elastic materials on linearly elastic MRE image reconstructions.

PubMed

Perreard, I M; Pattison, A J; Doyley, M; McGarry, M D J; Barani, Z; Van Houten, E E; Weaver, J B; Paulsen, K D

2010-11-21

The mechanical model commonly used in magnetic resonance elastography (MRE) is linear elasticity. However, soft tissue may exhibit frequency- and direction-dependent (FDD) shear moduli in response to an induced excitation causing a purely linear elastic model to provide an inaccurate image reconstruction of its mechanical properties. The goal of this study was to characterize the effects of reconstructing FDD data using a linear elastic inversion (LEI) algorithm. Linear and FDD phantoms were manufactured and LEI images were obtained from time-harmonic MRE acquisitions with variations in frequency and driving signal amplitude. LEI responses to artificially imposed uniform phase shifts in the displacement data from both purely linear elastic and FDD phantoms were also evaluated. Of the variety of FDD phantoms considered, LEI appeared to tolerate viscoelastic data-model mismatch better than deviations caused by poroelastic and anisotropic mechanical properties in terms of visual image contrast. However, the estimated shear modulus values were substantially incorrect relative to independent mechanical measurements even in the successful viscoelastic cases and the variations in mean values with changes in experimental conditions associated with uniform phase shifts, driving signal frequency and amplitude were unpredictable. Overall, use of LEI to reconstruct data acquired in phantoms with FDD material properties provided biased results under the best conditions and significant artifacts in the worst cases. These findings suggest that the success with which LEI is applied to MRE data in tissue will depend on the underlying mechanical characteristics of the tissues and/or organs systems of clinical interest.

High-power continuous-wave tunable 544- and 272-nm beams based on a diode-oscillator fiber-amplifier for calcium spectroscopy

NASA Astrophysics Data System (ADS)

Ko, Kwang-Hoon; Kim, Yonghee; Park, Hyunmin; Cha, Yong-Ho; Kim, Taek-Soo; Lee, Lim; Lim, Gwon; Han, Jaemin; Ko, Kwang-Hee; Jeong, Do-Young

2015-08-01

Continuous-wave single-frequency tunable 544- and 272-nm beams have been demonstrated by the second- and fourth-harmonic conversions of a 1088-nm fundamental beam from a diode-oscillator fiber-amplifier. The single-pass second-harmonic generation with a MgO-doped periodically poled stoichiometric LiTaO3 crystal and the external-cavity frequency-doubling technique with a bulk BBO crystal were employed to achieve an approximately 6-W 544-nm beam and a 1.5-W 272-nm beam, respectively. We characterized the second- and fourth-harmonic generations and discussed their applications to calcium spectroscopy.

Detection the nonlinear ultrasonic signals based on modified Duffing equations

NASA Astrophysics Data System (ADS)

Zhang, Yuhua; Mao, Hanling; Mao, Hanying; Huang, Zhenfeng

The nonlinear ultrasonic signals, like second harmonic generation (SHG) signals, could reflect the nonlinearity of material induced by fatigue damage in nonlinear ultrasonic technique which are weak nonlinear signals and usually submerged by strong background noise. In this paper the modified Duffing equations are applied to detect the SHG signals relating to the fatigue damage of material. Due to the Duffing equation could only detect the signal with specific frequency and initial phase, firstly the frequency transformation is carried on the Duffing equation which could detect the signal with any frequency. Then the influence of initial phases of to-be-detected signal and reference signal on the detection result is studied in detail, four modified Duffing equations are proposed to detect actual engineering signals with any initial phase. The relationship between the response amplitude and the total driving force is applied to estimate the amplitude of weak periodic signal. The detection results show the modified Duffing equations could effectively detect the second harmonic in SHG signals. When the SHG signals include strong background noise, the noise doesn't change the motion state of Duffing equation and the second harmonic signal could be detected until the SNR of noisy SHG signals are -26.3, yet the frequency spectrum method could only identify when the SNR is greater than 0.5. When estimation the amplitude of second harmonic signal, the estimation error of Duffing equation is obviously less than the frequency spectrum analysis method under the same noise level, which illustrates the Duffing equation has the noise immune capacity. The presence of the second harmonic signal in nonlinear ultrasonic experiments could provide an insight about the early fatigue damage of engineering components.

Second harmonic generation at fatigue cracks by low-frequency Lamb waves: Experimental and numerical studies

NASA Astrophysics Data System (ADS)

Yang, Yi; Ng, Ching-Tai; Kotousov, Andrei; Sohn, Hoon; Lim, Hyung Jin

2018-01-01

This paper presents experimental and theoretical analyses of the second harmonic generation due to non-linear interaction of Lamb waves with a fatigue crack. Three-dimensional (3D) finite element (FE) simulations and experimental studies are carried out to provide physical insight into the mechanism of second harmonic generation. The results demonstrate that the 3D FE simulations can provide a reasonable prediction on the second harmonic generated due to the contact nonlinearity at the fatigue crack. The effect of the wave modes on the second harmonic generation is also investigated in detail. It is found that the magnitude of the second harmonic induced by the interaction of the fundamental symmetric mode (S0) of Lamb wave with the fatigue crack is much higher than that by the fundamental anti-symmetric mode (A0) of Lamb wave. In addition, a series of parametric studies using 3D FE simulations are conducted to investigate the effect of the fatigue crack length to incident wave wavelength ratio, and the influence of the excitation frequency on the second harmonic generation. The outcomes show that the magnitude and directivity pattern of the generated second harmonic depend on the fatigue crack length to incident wave wavelength ratio as well as the ratio of S0 to A0 incident Lamb wave amplitude. In summary, the findings of this study can further advance the use of second harmonic generation in damage detection.

Harmonic generation in magnetized quantum plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Punit; Singh, Abhisek Kumar; Singh, Shiv

2016-05-06

A study of second harmonic generation by propagation of a linearly polarized electromagnetic wave through homogeneous high density quantum plasma in the presence of transverse magnetic field. The nonlinear current density and dispersion relations for the fundamental and second harmonic frequencies have been obtained using the recently developed quantum hydrodynamic (QHD) model. The effect of quantum Bohm potential, Fermi pressure and the electron spin have been taken into account. The second harmonic is found to be less dispersed than the first.

A framework to analyze the stochastic harmonics and resonance of wind energy grid interconnection

DOE PAGES

Cho, Youngho; Lee, Choongman; Hur, Kyeon; ...

2016-08-31

This study addresses a modeling and analysis methodology for investigating the stochastic harmonics and resonance concerns of wind power plants (WPPs). Wideband harmonics from modern wind turbines are observed to be stochastic, associated with real power production, and they may adversely interact with the grid impedance and cause unexpected harmonic resonance if not comprehensively addressed in the planning and commissioning of the WPPs. These issues should become more critical as wind penetration levels increase. We thus propose a planning study framework comprising the following functional steps: First, the best-fitted probability density functions (PDFs) of the harmonic components of interest inmore » the frequency domain are determined. In operations planning, maximum likelihood estimations followed by a chi-square test are used once field measurements or manufacturers' data are available. Second, harmonic currents from the WPP are represented by randomly-generating harmonic components based on their PDFs (frequency spectrum) and then synthesized for time-domain simulations via inverse Fourier transform. Finally, we conduct a comprehensive assessment by including the impacts of feeder configurations, harmonic filters, and the variability of parameters. We demonstrate the efficacy of the proposed study approach for a 100-MW offshore WPP consisting of 20 units of 5-MW full-converter turbines, a realistic benchmark system adapted from a WPP under development in Korea, and discuss lessons learned through this research.« less

New Evidence That Nonlinear Source-Filter Coupling Affects Harmonic Intensity and fo Stability During Instances of Harmonics Crossing Formants.

PubMed

Maxfield, Lynn; Palaparthi, Anil; Titze, Ingo

2017-03-01

The traditional source-filter theory of voice production describes a linear relationship between the source (glottal flow pulse) and the filter (vocal tract). Such a linear relationship does not allow for nor explain how changes in the filter may impact the stability and regularity of the source. The objective of this experiment was to examine what effect unpredictable changes to vocal tract dimensions could have on fo stability and individual harmonic intensities in situations in which low frequency harmonics cross formants in a fundamental frequency glide. To determine these effects, eight human subjects (five male, three female) were recorded producing fo glides while their vocal tracts were artificially lengthened by a section of vinyl tubing inserted into the mouth. It was hypothesized that if the source and filter operated as a purely linear system, harmonic intensities would increase and decrease at nearly the same rates as they passed through a formant bandwidth, resulting in a relatively symmetric peak on an intensity-time contour. Additionally, fo stability should not be predictably perturbed by formant/harmonic crossings in a linear system. Acoustic analysis of these recordings, however, revealed that harmonic intensity peaks were asymmetric in 76% of cases, and that 85% of fo instabilities aligned with a crossing of one of the first four harmonics with the first three formants. These results provide further evidence that nonlinear dynamics in the source-filter relationship can impact fo stability as well as harmonic intensities as harmonics cross through formant bandwidths. Copyright © 2017 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

REVIEWS OF TOPICAL PROBLEMS: Periodic weather and climate variations

NASA Astrophysics Data System (ADS)

Ivanov, Vladimir V.

2002-07-01

Variations in meteorological parameters are largely due to periodic processes and can be forecast for several years. Many such processes are related to astronomical factors such as the gravitational influences of the Moon and the Sun, and the modulation of solar irradiance by lunar and planetary motion. The Moon, Jupiter, and Venus have the strongest effect. These influences produce lines in the spectra of meteorological variations, which are combinations of the harmonics of the frequencies of revolution of the planets, the Earth, and the Moon around the Sun with the harmonics of the lunar revolution around the Earth. Due to frequency differences between the orbital and radial motions, fine spectral features of three types appear: line splitting, line-profile complications due to radial oscillations, and additional lines due to the combination of radial-oscillation frequencies with perturbation harmonics.

Harmonic responses and cavitation activity of encapsulated microbubbles coupled with magnetic nanoparticles.

PubMed

Gu, Yuyang; Chen, Chuyi; Tu, Juan; Guo, Xiasheng; Wu, Hongyi; Zhang, Dong

2016-03-01

Encapsulated microbubbles coupled with magnetic nanoparticles, one kind of hybrid agents that can integrate both ultrasound and magnetic resonance imaging/therapy functions, have attracted increasing interests in both research and clinic communities. However, there is a lack of comprehensive understanding of their dynamic behaviors generated in diagnostic and therapeutic applications. In the present work, a hybrid agent was synthesized by integrating superparamagnetic iron oxide nanoparticles (SPIOs) into albumin-shelled microbubbles (named as SPIO-albumin microbubbles). Then, both the stable and inertial cavitation thresholds of this hybrid agent were measured at varied SPIO concentrations and ultrasound parameters (e.g., frequency, pressure amplitude, and pulse length). The results show that, at a fixed acoustic driving frequency, both the stable and inertial cavitation thresholds of SPIO-albumin microbubble should decrease with the increasing SPIO concentration and acoustic driving pulse length. The inertial cavitation threshold of SPIO-albumin microbubbles also decreases with the raised driving frequency, while the minimum sub- and ultra-harmonic thresholds appear at twice and two thirds resonance frequency, respectively. It is also noticed that both the stable and inertial cavitation thresholds of SonoVue microbubbles are similar to those measured for hybrid microbubbles with a SPIO concentration of 114.7 μg/ml. The current work could provide better understanding on the impact of the integrated SPIOs on the dynamic responses (especially the cavitation activities) of hybrid microbubbles, and suggest the shell composition of hybrid agents should be appropriately designed to improve their clinical diagnostic and therapeutic performances of hybrid microbubble agents. Copyright © 2015 Elsevier B.V. All rights reserved.

On the possibility of a place code for the low pitch of high-frequency complex tonesa

PubMed Central

Santurette, Sébastien; Dau, Torsten; Oxenham, Andrew J.

2012-01-01

Harmonics are considered unresolved when they interact with neighboring harmonics and cannot be heard out separately. Several studies have suggested that the pitch derived from unresolved harmonics is coded via temporal fine-structure cues emerging from their peripheral interactions. Such conclusions rely on the assumption that the components of complex tones with harmonic ranks down to at least 9 were indeed unresolved. The present study tested this assumption via three different measures: (1) the effects of relative component phase on pitch matches, (2) the effects of dichotic presentation on pitch matches, and (3) listeners' ability to hear out the individual components. No effects of relative component phase or dichotic presentation on pitch matches were found in the tested conditions. Large individual differences were found in listeners' ability to hear out individual components. Overall, the results are consistent with the coding of individual harmonic frequencies, based on the tonotopic activity pattern or phase locking to individual harmonics, rather than with temporal coding of single-channel interactions. However, they are also consistent with more general temporal theories of pitch involving the across-channel summation of information from resolved and/or unresolved harmonics. Simulations of auditory-nerve responses to the stimuli suggest potential benefits to a spatiotemporal mechanism. PMID:23231119

Momentum-resolved radio-frequency spectroscopy of a spin-orbit-coupled atomic Fermi gas near a Feshbach resonance in harmonic traps

NASA Astrophysics Data System (ADS)

Peng, Shi-Guo; Liu, Xia-Ji; Hu, Hui; Jiang, Kaijun

2012-12-01

We theoretically investigate the momentum-resolved radio-frequency spectroscopy of a harmonically trapped atomic Fermi gas near a Feshbach resonance in the presence of equal Rashba and Dresselhaus spin-orbit coupling. The system is qualitatively modeled as an ideal gas mixture of atoms and molecules, in which the properties of molecules, such as the wave function, binding energy, and effective mass, are determined from the two-particle solution of two interacting atoms. We calculate separately the radio-frequency response from atoms and molecules at finite temperatures by using the standard Fermi golden rule and take into account the effect of harmonic traps within local density approximation. The total radio-frequency spectroscopy is discussed as functions of temperature and spin-orbit coupling strength. Our results give a qualitative picture of radio-frequency spectroscopy of a resonantly interacting spin-orbit-coupled Fermi gas and can be directly tested in atomic Fermi gases of 40K atoms at Shanxi University and 6Li atoms at the Massachusetts Institute of Technology.

Polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical gating.

PubMed

Miao, Houxun; Weiner, Andrew M; Langrock, Carsten; Roussev, Rostislav V; Fejer, Martin M

2007-04-01

We demonstrate polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical gating (FROG) measurements with a fiber-pigtailed, aperiodically poled lithium niobate waveguide. By scrambling the polarization much faster than the measurement integration time, we eliminate the impairment that frequency-independent random polarization fluctuations induce in FROG measurements. As a result we are able to retrieve intensity and phase profiles of few hundred femtosecond optical pulses with 50 MHz repetition rates at 5.2 nW coupled average power without control of the input polarization.

Multi-frequency klystron designed for high efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jensen, Aaron

A multi-frequency klystron has an electron gun which generates a beam, a circuit of bunch-align-collect (BAC) tuned cavities that bunch the beam and amplify an RF signal, a collector where the beam is collected and dumped, and a standard output cavity and waveguide coupled to a window to output RF power at a fundamental mode to an external load. In addition, the klystron has additional bunch-align-collect (BAC) cavities tuned to a higher harmonic frequency, and a harmonic output cavity and waveguide coupled via a window to an additional external load.

Harmonic motion imaging for abdominal tumor detection and high-intensity focused ultrasound ablation monitoring: an in vivo feasibility study in a transgenic mouse model of pancreatic cancer.

PubMed

Chen, Hong; Hou, Gary Y; Han, Yang; Payen, Thomas; Palermo, Carmine F; Olive, Kenneth P; Konofagou, Elisa E

2015-09-01

Harmonic motion imaging (HMI) is a radiationforce- based elasticity imaging technique that tracks oscillatory tissue displacements induced by sinusoidal ultrasonic radiation force to assess the resulting oscillatory displacement denoting the underlying tissue stiffness. The objective of this study was to evaluate the feasibility of HMI in pancreatic tumor detection and high-intensity focused ultrasound (HIFU) treatment monitoring. The HMI system consisted of a focused ultrasound transducer, which generated sinusoidal radiation force to induce oscillatory tissue motion at 50 Hz, and a diagnostic ultrasound transducer, which detected the axial tissue displacements based on acquired radio-frequency signals using a 1-D cross-correlation algorithm. For pancreatic tumor detection, HMI images were generated for pancreatic tumors in transgenic mice and normal pancreases in wild-type mice. The obtained HMI images showed a high contrast between normal and malignant pancreases with an average peak-to-peak HMI displacement ratio of 3.2. Histological analysis showed that no tissue damage was associated with HMI when it was used for the sole purpose of elasticity imaging. For pancreatic tumor ablation monitoring, the focused ultrasound transducer was operated at a higher acoustic power and longer pulse length than that used in tumor detection to simultaneously induce HIFU thermal ablation and oscillatory tissue displacements, allowing HMI monitoring without interrupting tumor ablation. HMI monitoring of HIFU ablation found significant decreases in the peak-to-peak HMI displacements before and after HIFU ablation with a reduction rate ranging from 15.8% to 57.0%. The formation of thermal lesions after HIFU exposure was confirmed by histological analysis. This study demonstrated the feasibility of HMI in abdominal tumor detection and HIFU ablation monitoring.

Interactive remote data processing using Pixelize Wavelet Filtration (PWF-method) and PeriodMap analysis

NASA Astrophysics Data System (ADS)

Sych, Robert; Nakariakov, Valery; Anfinogentov, Sergey

Wavelet analysis is suitable for investigating waves and oscillating in solar atmosphere, which are limited in both time and frequency. We have developed an algorithms to detect this waves by use the Pixelize Wavelet Filtration (PWF-method). This method allows to obtain information about the presence of propagating and non-propagating waves in the data observation (cube images), and localize them precisely in time as well in space. We tested the algorithm and found that the results of coronal waves detection are consistent with those obtained by visual inspection. For fast exploration of the data cube, in addition, we applied early-developed Period- Map analysis. This method based on the Fast Fourier Transform and allows on initial stage quickly to look for "hot" regions with the peak harmonic oscillations and determine spatial distribution at the significant harmonics. We propose the detection procedure of coronal waves separate on two parts: at the first part, we apply the PeriodMap analysis (fast preparation) and than, at the second part, use information about spatial distribution of oscillation sources to apply the PWF-method (slow preparation). There are two possible algorithms working with the data: in automatic and hands-on operation mode. Firstly we use multiply PWF analysis as a preparation narrowband maps at frequency subbands multiply two and/or harmonic PWF analysis for separate harmonics in a spectrum. Secondly we manually select necessary spectral subband and temporal interval and than construct narrowband maps. For practical implementation of the proposed methods, we have developed the remote data processing system at Institute of Solar-Terrestrial Physics, Irkutsk. The system based on the data processing server - http://pwf.iszf.irk.ru. The main aim of this resource is calculation in remote access through the local and/or global network (Internet) narrowband maps of wave's sources both in whole spectral band and at significant harmonics. In addition, we can obtain temporal dynamics (mpeg- files) of the main oscillation characteristics: amplitude, power and phase as a spatial-temporal coordinates. For periodogram mapping of data cubes as a method for the pre-analysis, we developed preparation of the color maps where the pixel's colour corresponds to the frequency of the power spectrum maximum. The computer system based on applications ION-scripts, algorithmic languages IDL and PHP, and Apache WEB server. The IDL ION-scripts use for preparation and configuration of network requests at the central data server with subsequent connection to IDL run-unit software and graphic output on FTP-server and screen. Web page is constructed using PHP language.

Linear and nonlinear Biot waves in a noncohesive granular medium slab: transfer function, self-action, second harmonic generation.

PubMed

Legland, J-B; Tournat, V; Dazel, O; Novak, A; Gusev, V

2012-06-01

Experimental results are reported on second harmonic generation and self-action in a noncohesive granular medium supporting wave energy propagation both in the solid frame and in the saturating fluid. The acoustic transfer function of the probed granular slab can be separated into two main frequency regions: a low frequency region where the wave propagation is controlled by the solid skeleton elastic properties, and a higher frequency region where the behavior is dominantly due to the air saturating the beads. Experimental results agree well with a recently developed nonlinear Biot wave model applied to granular media. The linear transfer function, second harmonic generation, and self-action effect are studied as a function of bead diameter, compaction step, excitation amplitude, and frequency. This parametric study allows one to isolate different propagation regimes involving a range of described and interpreted linear and nonlinear processes that are encountered in granular media experiments. In particular, a theoretical interpretation is proposed for the observed strong self-action effect.

Shear wave speed recovery in sonoelastography using crawling wave data.

PubMed

Lin, Kui; McLaughlin, Joyce; Renzi, Daniel; Thomas, Ashley

2010-07-01

The crawling wave experiment, in which two harmonic sources oscillate at different but nearby frequencies, is a development in sonoelastography that allows real-time imaging of propagating shear wave interference patterns. Previously the crawling wave speed was recovered and used as an indicator of shear stiffness; however, it is shown in this paper that the crawling wave speed image can have artifacts that do not represent a change in stiffness. In this paper, the locations and shapes of some of the artifacts are exhibited. In addition, a differential equation is established that enables imaging of the shear wave speed, which is a quantity strongly correlated with shear stiffness change. The full algorithm is as follows: (1) extract the crawling wave phase from the spectral variance data; (2) calculate the crawling wave phase wave speed; (3) solve a first-order PDE for the phase of the wave emanating from one of the sources; and (4) compute and image the shear wave speed on a grid in the image plane.

Shear wave speed recovery in sonoelastography using crawling wave data

PubMed Central

Lin, Kui; McLaughlin, Joyce; Renzi, Daniel; Thomas, Ashley

2010-01-01

The crawling wave experiment, in which two harmonic sources oscillate at different but nearby frequencies, is a development in sonoelastography that allows real-time imaging of propagating shear wave interference patterns. Previously the crawling wave speed was recovered and used as an indicator of shear stiffness; however, it is shown in this paper that the crawling wave speed image can have artifacts that do not represent a change in stiffness. In this paper, the locations and shapes of some of the artifacts are exhibited. In addition, a differential equation is established that enables imaging of the shear wave speed, which is a quantity strongly correlated with shear stiffness change. The full algorithm is as follows: (1) extract the crawling wave phase from the spectral variance data; (2) calculate the crawling wave phase wave speed; (3) solve a first-order PDE for the phase of the wave emanating from one of the sources; and (4) compute and image the shear wave speed on a grid in the image plane. PMID:20649204

Driven damped harmonic oscillator resonance with an Arduino

NASA Astrophysics Data System (ADS)

Goncalves, A. M. B.; Cena, C. R.; Bozano, D. F.

2017-07-01

In this paper we propose a simple experimental apparatus that can be used to show quantitative and qualitative results of resonance in a driven damped harmonic oscillator. The driven oscillation is made by a servo motor, and the oscillation amplitude is measured by an ultrasonic position sensor. Both are controlled by an Arduino board. The frequency of free oscillation measured was campatible with the resonance frequency that was measured.

Frequency Dependent Harmonic Powers in a Modified Uni-Traveling Carrier (MUTC) Photodetector

DTIC Science & Technology

2017-01-27

Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/5651--17-9712 Frequency Dependent Harmonic Powers in a Modified Uni- Traveling Carrier...burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing...Modified Uni- Traveling Carrier (MUTC) Photodetector Yue Hu,* Meredith N. Hutchinson, and Curtis R. Menyuk* Naval Research Laboratory 4555 Overlook

Relativistic Corrections to the Properties of the Alkali Fluorides

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Partridge, Harry

1993-01-01

Relativistic corrections to the bond lengths, dissociation energies and harmonic frequencies of KF, RbF and CsF have been obtained at the self-consistent field level by dissociating to ions. The relativistic corrections to the bond lengths, harmonic frequencies and dissociation energies to the ions are very small, due to the ionic nature of these molecules and the similarity of the relativistic and nonrelativistic ionic radii.

Enhanced dynamical stability with harmonic slip stacking

DOE PAGES

Eldred, Jeffrey; Zwaska, Robert

2016-10-26

We develop a configuration of radio-frequency (rf) cavities to dramatically improve the performance of slip-stacking. Slip-stacking is an accumulation technique used at Fermilab to nearly double proton intensity by maintaining two beams of different momenta in the same storage ring. The two particle beams are longitudinally focused in the Recycler by two 53 MHz 100 kV rf cavities with a small frequency difference between them. We propose an additional 106 MHz 20 kV rf cavity with a frequency at the double the average of the upper and lower main rf frequencies. We show the harmonic rf cavity cancels out themore » resonances generated between the two main rf cavities and we derive the relationship between the harmonic rf voltage and the main rf voltage. We find the area factors that can be used to calculate the available phase space area for any set of beam parameters without individual simulation. We establish Booster beam quality requirements to achieve 99\\% slip-stacking efficiency. We measure the longitudinal distribution of the Booster beam and use it to generate a realistic beam model for slip-stacking simulation. In conclusion, we demonstrate that the harmonic rf cavity can not only reduce particle loss during slip-stacking, but also reduce the final longitudinal emittance.« less

Enhanced dynamical stability with harmonic slip stacking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldred, Jeffrey; Zwaska, Robert

We develop a configuration of radio-frequency (rf) cavities to dramatically improve the performance of slip-stacking. Slip-stacking is an accumulation technique used at Fermilab to nearly double proton intensity by maintaining two beams of different momenta in the same storage ring. The two particle beams are longitudinally focused in the Recycler by two 53 MHz 100 kV rf cavities with a small frequency difference between them. We propose an additional 106 MHz 20 kV rf cavity with a frequency at the double the average of the upper and lower main rf frequencies. We show the harmonic rf cavity cancels out themore » resonances generated between the two main rf cavities and we derive the relationship between the harmonic rf voltage and the main rf voltage. We find the area factors that can be used to calculate the available phase space area for any set of beam parameters without individual simulation. We establish Booster beam quality requirements to achieve 99\\% slip-stacking efficiency. We measure the longitudinal distribution of the Booster beam and use it to generate a realistic beam model for slip-stacking simulation. In conclusion, we demonstrate that the harmonic rf cavity can not only reduce particle loss during slip-stacking, but also reduce the final longitudinal emittance.« less

MREIT experiments with 200 µA injected currents: a feasibility study using two reconstruction algorithms, SMM and harmonic B(Z).

PubMed

Arpinar, V E; Hamamura, M J; Degirmenci, E; Muftuler, L T

2012-07-07

Magnetic resonance electrical impedance tomography (MREIT) is a technique that produces images of conductivity in tissues and phantoms. In this technique, electrical currents are applied to an object and the resulting magnetic flux density is measured using magnetic resonance imaging (MRI) and the conductivity distribution is reconstructed using these MRI data. Currently, the technique is used in research environments, primarily studying phantoms and animals. In order to translate MREIT to clinical applications, strict safety standards need to be established, especially for safe current limits. However, there are currently no standards for safe current limits specific to MREIT. Until such standards are established, human MREIT applications need to conform to existing electrical safety standards in medical instrumentation, such as IEC601. This protocol limits patient auxiliary currents to 100 µA for low frequencies. However, published MREIT studies have utilized currents 10-400 times larger than this limit, bringing into question whether the clinical applications of MREIT are attainable under current standards. In this study, we investigated the feasibility of MREIT to accurately reconstruct the relative conductivity of a simple agarose phantom using 200 µA total injected current and tested the performance of two MREIT reconstruction algorithms. These reconstruction algorithms used are the iterative sensitivity matrix method (SMM) by Ider and Birgul (1998 Elektrik 6 215-25) with Tikhonov regularization and the harmonic B(Z) proposed by Oh et al (2003 Magn. Reason. Med. 50 875-8). The reconstruction techniques were tested at both 200 µA and 5 mA injected currents to investigate their noise sensitivity at low and high current conditions. It should be noted that 200 µA total injected current into a cylindrical phantom generates only 14.7 µA current in imaging slice. Similarly, 5 mA total injected current results in 367 µA in imaging slice. Total acquisition time for 200 µA and 5 mA experiments was about 1 h and 8.5 min, respectively. The results demonstrate that conductivity imaging is possible at low currents using the suggested imaging parameters and reconstructing the images using iterative SMM with Tikhonov regularization, which appears to be more tolerant to noisy data than harmonic B(Z).

Bipolar-power-transistor-based limiter for high frequency ultrasound imaging systems.

PubMed

Choi, Hojong; Yang, Hao-Chung; Shung, K Kirk

2014-03-01

High performance limiters are described in this paper for applications in high frequency ultrasound imaging systems. Limiters protect the ultrasound receiver from the high voltage (HV) spikes produced by the transmitter. We present a new bipolar power transistor (BPT) configuration and compare its design and performance to a diode limiter used in traditional ultrasound research and one commercially available limiter. Limiter performance depends greatly on the insertion loss (IL), total harmonic distortion (THD) and response time (RT), each of which will be evaluated in all the limiters. The results indicated that, compared with commercial limiter, BPT-based limiter had less IL (-7.7 dB), THD (-74.6 dB) and lower RT (43 ns) at 100 MHz. To evaluate the capability of these limiters, they were connected to a 100 MHz single element transducer and a two-way pulse-echo test was performed. It was found that the -6 dB bandwidth and sensitivity of the transducer using BPT-based limiter were better than those of the commercial limiter by 22% and 140%, respectively. Compared to the commercial limiter, BPT-based limiter is shown to be capable of minimizing signal attenuation, RT and THD at high frequencies and is thus suited for high frequency ultrasound applications. Copyright © 2013 Elsevier B.V. All rights reserved.

One central oscillatory drive is compatible with experimental motor unit behaviour in essential and Parkinsonian tremor

NASA Astrophysics Data System (ADS)

Dideriksen, Jakob L.; Gallego, Juan A.; Holobar, Ales; Rocon, Eduardo; Pons, Jose L.; Farina, Dario

2015-08-01

Objective. Pathological tremors are symptomatic to several neurological disorders that are difficult to differentiate and the way by which central oscillatory networks entrain tremorogenic contractions is unknown. We considered the alternative hypotheses that tremor arises from one oscillator (at the tremor frequency) or, as suggested by recent findings from the superimposition of two separate inputs (at the tremor frequency and twice that frequency). Approach. Assuming one central oscillatory network we estimated analytically the relative amplitude of the harmonics of the tremor frequency in the motor neuron output for different temporal behaviors of the oscillator. Next, we analyzed the bias in the relative harmonics amplitude introduced by superimposing oscillations at twice the tremor frequency. These findings were validated using experimental measurements of wrist angular velocity and surface electromyography (EMG) from 22 patients (11 essential tremor, 11 Parkinson’s disease). The ensemble motor unit action potential trains identified from the EMG represented the neural drive to the muscles. Main results. The analytical results showed that the relative power of the tremor harmonics in the analytical models of the neural drive was determined by the variability and duration of the tremor bursts and the presence of the second oscillator biased this power towards higher values. The experimental findings accurately matched the analytical model assuming one oscillator, indicating a negligible functional role of secondary oscillatory inputs. Furthermore, a significant difference in the relative power of harmonics in the neural drive was found across the patient groups, suggesting a diagnostic value of this measure (classification accuracy: 86%). This diagnostic power decreased substantially when estimated from limb acceleration or the EMG. Signficance. The results indicate that the neural drive in pathological tremor is compatible with one central network providing neural oscillations at the tremor frequency. Moreover, the regularity of this neural oscillation varies across tremor pathologies, making the relative amplitude of tremor harmonics a potential biomarker for diagnostic use.

One central oscillatory drive is compatible with experimental motor unit behaviour in essential and Parkinsonian tremor.

PubMed

Dideriksen, Jakob L; Gallego, Juan A; Holobar, Ales; Rocon, Eduardo; Pons, Jose L; Farina, Dario

2015-08-01

Pathological tremors are symptomatic to several neurological disorders that are difficult to differentiate and the way by which central oscillatory networks entrain tremorogenic contractions is unknown. We considered the alternative hypotheses that tremor arises from one oscillator (at the tremor frequency) or, as suggested by recent findings from the superimposition of two separate inputs (at the tremor frequency and twice that frequency). Assuming one central oscillatory network we estimated analytically the relative amplitude of the harmonics of the tremor frequency in the motor neuron output for different temporal behaviors of the oscillator. Next, we analyzed the bias in the relative harmonics amplitude introduced by superimposing oscillations at twice the tremor frequency. These findings were validated using experimental measurements of wrist angular velocity and surface electromyography (EMG) from 22 patients (11 essential tremor, 11 Parkinson's disease). The ensemble motor unit action potential trains identified from the EMG represented the neural drive to the muscles. The analytical results showed that the relative power of the tremor harmonics in the analytical models of the neural drive was determined by the variability and duration of the tremor bursts and the presence of the second oscillator biased this power towards higher values. The experimental findings accurately matched the analytical model assuming one oscillator, indicating a negligible functional role of secondary oscillatory inputs. Furthermore, a significant difference in the relative power of harmonics in the neural drive was found across the patient groups, suggesting a diagnostic value of this measure (classification accuracy: 86%). This diagnostic power decreased substantially when estimated from limb acceleration or the EMG. SIGNFICANCE: The results indicate that the neural drive in pathological tremor is compatible with one central network providing neural oscillations at the tremor frequency. Moreover, the regularity of this neural oscillation varies across tremor pathologies, making the relative amplitude of tremor harmonics a potential biomarker for diagnostic use.

Simultaneous stimulated Raman scattering and higher harmonic generation imaging for liver disease diagnosis without labeling

NASA Astrophysics Data System (ADS)

Lin, Jian; Wang, Zi; Zheng, Wei; Huang, Zhiwei

2014-02-01

Nonlinear optical microscopy (e.g., higher harmonic (second-/third- harmonic) generation (HHG), simulated Raman scattering (SRS)) has high diagnostic sensitivity and chemical specificity, making it a promising tool for label-free tissue and cell imaging. In this work, we report a development of a simultaneous SRS and HHG imaging technique for characterization of liver disease in a bile-duct-ligation rat-modal. HHG visualizes collagens formation and reveals the cell morphologic changes associated with liver fibrosis; whereas SRS identifies the distributions of hepatic fat cells formed in steatosis liver tissue. This work shows that the co-registration of SRS and HHG images can be an effective means for label-free diagnosis and characterization of liver steatosis/fibrosis at the cellular and molecular levels.

Enhancement and inhibition of second-harmonic generation and absorption in a negative index cavity.

PubMed

de Ceglia, Domenico; D'Orazio, Antonella; De Sario, Marco; Petruzzelli, Vincenzo; Prudenzano, Francesco; Centini, Marco; Cappeddu, Mirko G; Bloemer, Mark J; Scalora, Michael

2007-02-01

We study second-harmonic generation in a negative-index material cavity. The transmission spectrum shows a bandgap between the electric and magnetic plasma frequencies. The nonlinear process is made efficient by local phase-matching conditions between a forward-propagating pump and a backward-propagating second-harmonic signal. By simultaneously exciting the cavity with counterpropagating pulses, and by varying their relative phase difference, one is able to enhance or inhibit linear absorption and the second-harmonic conversion efficiency.

SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: Operating the SDUV-FEL with the echo-enabled harmonic generation scheme

NASA Astrophysics Data System (ADS)

Chen, Jian-Hui; Deng, Hai-Xiao; Gu, Qiang; Li, Dong-Guo; Wang, Dong; Zhang, Meng; Zhao, Zhen-Tang

2009-08-01

Using the recently proposed echo-enabled harmonic generation (EEHG) free-electron laser (FEL) scheme, it is shown that operating the Shanghai deep ultraviolet FEL (SDUV-FEL) with single-stage to higher harmonics is very promising, with higher frequency up-conversion efficiency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.

Method and apparatus for reducing spacecraft instrument induced jitter via multifrequency cancellation

NASA Technical Reports Server (NTRS)

Liu, Ketao (Inventor); Uetrecht, David S. (Inventor)

2002-01-01

A method, apparatus, article of manufacture, and a memory structure for compensating for instrument induced spacecraft jitter is disclosed. The apparatus comprises a spacecraft control processor for producing an actuator command signal, a signal generator, for producing a cancellation signal having at least one harmonic having a frequency and an amplitude substantially equal to that of a disturbance harmonic interacting with a spacecraft structural resonance and a phase substantially out of phase with the disturbance harmonic interacting with the spacecraft structural resonance, and at least one spacecraft control actuator, communicatively coupled to the spacecraft control processor and the signal generator for inducing satellite motion according to the actuator command signal and the cancellation signal. The method comprises the steps of generating a cancellation signal having at least one harmonic having a frequency and an amplitude substantially equal to that of a disturbance harmonic interacting with a spacecraft structural resonance and a phase substantially out of phase with the disturbance harmonic interacting with the spacecraft structural resonance, and providing the cancellation signal to a spacecraft control actuator. The apparatus comprises a storage device tangibly embodying the method steps described above.

Wiggler magnetic field assisted third harmonic generation in expanding clusters

NASA Astrophysics Data System (ADS)

Vij, Shivani

2018-04-01

A simple theoretical model is constructed to study the wiggler magnetic field assisted third harmonic generation of intense short pulse laser in a cluster in its expanding phase. The ponderomotive force of laser causes density perturbations in cluster electron density which couples with wiggler magnetic field to produce a nonlinear current that generates transverse third harmonic. An intense short pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls via tunnel ionization. Initially, the electron plasma frequency inside the clusters ω pe > \\sqrt{3}{ω }1 (with ω 1 being the frequency of the laser). As the cluster expands under Coulomb force and hydrodynamic pressure, ω pe decreases to \\sqrt{3}{ω }1. At this time, there is resonant enhancement in the efficiency of the third harmonic generation. The efficiency of third harmonic generation is enhanced due to cluster plasmon resonance and by phase matching due to wiggler magnetic field. The effect of cluster size on the expansion rate is studied to observe that the clusters of different radii would expand differently. The impact of laser intensity and wiggler magnetic field on the efficiency of third harmonic generation is also explored.

Investigation of an Ultrafast Harmonic Resonant RF Kicker

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yulu

An Energy Recovery Linac (ERL) based multi-turn electron Circulator Cooler Ring (CCR) is envisaged in the proposed Jefferson Lab Electron Ion Collider (JLEIC) to cool the ion bunches with high energy (55 MeV), high current (1.5 A), high repetition frequency (476.3 MHz), high quality magnetized electron bunches. A critical component in this scheme is a pair of ultrafast kickers for the exchange of electron bunches between the ERL and the CCR. The ultrafast kicker should operate with the rise and fall time in less than 2.1 ns, at the repetition rate of ~10s MHz, and should be able to runmore » continuously during the whole period of cooling. These -and-fall time being combined together, are well beyond the state-of-art of traditional pulsed power supplies and magnet kickers. To solve this technical challenge, an alternative method is to generate this high repetition rate, fast rise-and-fall time short pulse continuous waveform by summing several finite number of (co)sine waves at harmonic frequencies of the kicking repetition frequency, and these harmonic modes can be generated by the Quarter Wave Resonater (QWR) based multifrequency cavities. Assuming the recirculator factor is 10, 10 harmonic modes (from 47.63 MHz to 476.3 MHz) with proper amplitudes and phases, plus a DC offset are combined together, a continuous short pulse waveform with the rise-and-fall time in less than 2.1 ns, repetition rate of 47.63 MHz waveform can be generated. With the compact and matured technology of QWR cavities, the total cost of both hardware development and operation can be reduced to a modest level. Focuse on the technical scheme, three main topics will be discussed in this thesis: the synthetization of the kicking pulse, the design and optimization of the deflecting QWR multi-integer harmonic frequency resonator and the fabrication and bench measurements of a half scale copper prototype. In the kicking pulse synthetization part, we begin with the Fourier Series expansion of an ideal square pulse, and get a Flat-Top waveform which will give a uniform kick over the bunch length of the kicked electron bunches, thus the transverse emittance of these kicked electron bunches can be maintained. By using two identical kickers with the betatron phase advance of 180 degree or its odd multiples, the residual kick voltage wave slopes at the unkicked bunch position will be totally cancelled out. Flat-Top waveform combined with two kicker scheme, the transverse emittance of the cooling electron bunches will be conserved during the whole injection, recirculation, and ejection processes. In the cavity design part, firstly, the cavity geometry is optimized to get high transverse shunt impedance thus less than 100 W of RF losses on the cavity wall can be achieved for all these 10 harmonic modes. To support all these 10 harmonic modes, group of four QWRs are adopted with the mode distribution of 5:3:1:1. In the multi-frequency cavities such as the five-mode-cavity and the three-mode-cavity, tunings are required to achieve the design frequencies for each mode. Slight segments of taper design on the inner conductor help to get the frequencies to be exactly on the odd harmonic modes. Stub tuners equal to the number of resonant modes are inserted to the outer conductor wall to compensate the frequency shifts due manufacturing errors and other perturbations during the operation such as the change of the cavity temperature. Single loop couple is designed for all harmonic modes in each cavity. By adjusting its loop size, position and rotation, it is possible to get the fundamental mode critical coupled and other higher harmonic modes slightly over coupled. A broadband circulator will be considered for absorbing the reflected power. Finally in this part, multipole field components due to the asymmetric cylindrical structure around the beam axis of the cavity as well as the beam-induced higher order mode (HOM) issues will be analyzed and discussed in this thesis. A half-scale copper prototype cavity (resonant frequencies from 95.26 MHz to 857.34 MHz) was fabricated to validate the electromagnetic characteristics. With this half scale prototype, the tuning processes of multiple harmonic frequencies, unloaded quality factor measurements of each mode, and bead-pull measurements are performed. The bench measurement results matched well with the simulation results, which have validated our cavity design and construction methods. Finally, a simple mode combining experiment with five separate signal generators was performed on this prototype cavity and the desired fast rise/fall time (1.2 ns), high repetition rate (95.26 MHz) waveform was captured, which finally proved our design of this ultrafast harmonic kicker.« less

Self-demodulation effect on subharmonic response of ultrasound contrast agent

NASA Astrophysics Data System (ADS)

Daeichin, V.; Faez, T.; Needles, A.; Renaud, G.; Bosch, J. G.; van der Steen, A. F. W.; de Jong, N.

2012-03-01

In this work the use of the self-demodulation (S-D) signal as a mean of microbubble excitation at the subharmonic (SH) frequency to enhance the SH emission of ultrasound contrast agent (UCA) is studied. SH emission from the UCA is of interest since it is produced only by the UCA and is free of the artifacts produced in harmonic imaging modes. The S-D wave is a low-frequency signal produced by nonlinear propagation of an ultrasound wave in the medium. Single element transducer experiments and numerical simulations were conducted at 10 MHz to study the effect of the S-D signal on the SH response of the UCA by modifying the envelope of the excitation bursts. For 6 and 20 transmitted cycles, the SH response is increased up to 25 dB and 22 dB because of the S-D stimulation for a burst with a rectangular envelope compared with a Gaussian envelope burst. Such optimized excitations were used in an array-based micro-ultrasound system (Vevo 2100, VisualSonics Inc., Toronto, ON, Canada) at 18 MHz for in vitro validation of SH imaging. This study suggests that a suitable design of the envelope of the transmit excitation to generate a S-D signal at the SH frequency can enhance the SH emission of UCA and real-time SH imaging is feasible with shorter transmit burst (6- cycle) and low acoustic pressure (~150 KPa) at high frequencies (>15 MHz).

Approaches to creating and controlling motion in MRI.

PubMed

Fischer, Gregory S; Cole, Gregory; Su, Hao

2011-01-01

Magnetic Resonance Imaging (MRI) can provide three dimensional (3D) imaging with excellent resolution and sensitivity making it ideal for guiding and monitoring interventions. The development of MRI-compatible interventional devices is complicated by factors including: the high magnetic field strength, the requirement that such devices should not degrade image quality, and the confined physical space of the scanner bore. Numerous MRI guided actuated devices have been developed or are currently being developed utilizing piezoelectric actuators as their primary means of mechanical energy generation to enable better interventional procedure performance. While piezoelectric actuators are highly desirable for MRI guided actuation for their precision, high holding force, and non-magnetic operation they are often found to cause image degradation on a large enough to scale to render live imaging unusable. This paper describes a newly developed piezoelectric actuator driver and control system designed to drive a variety of both harmonic and non-harmonic motors that has been demonstrated to be capable of operating both harmonic and non-harmonic piezoelectric actuators with less than 5% SNR loss under closed loop control. The proposed system device allows for a single controller to control any supported actuator and feedback sensor without any physical hardware changes.

Hydrophone area-averaging correction factors in nonlinearly generated ultrasonic beams

NASA Astrophysics Data System (ADS)

Cooling, M. P.; Humphrey, V. F.; Wilkens, V.

2011-02-01

The nonlinear propagation of an ultrasonic wave can be used to produce a wavefield rich in higher frequency components that is ideally suited to the calibration, or inter-calibration, of hydrophones. These techniques usually use a tone-burst signal, limiting the measurements to harmonics of the fundamental calibration frequency. Alternatively, using a short pulse enables calibration at a continuous spectrum of frequencies. Such a technique is used at PTB in conjunction with an optical measurement technique to calibrate devices. Experimental findings indicate that the area-averaging correction factor for a hydrophone in such a field demonstrates a complex behaviour, most notably varying periodically between frequencies that are harmonics of the centre frequency of the original pulse and frequencies that lie midway between these harmonics. The beam characteristics of such nonlinearly generated fields have been investigated using a finite difference solution to the nonlinear Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation for a focused field. The simulation results are used to calculate the hydrophone area-averaging correction factors for 0.2 mm and 0.5 mm devices. The results clearly demonstrate a number of significant features observed in the experimental investigations, including the variation with frequency, drive level and hydrophone element size. An explanation for these effects is also proposed.

Caller sex and orientation influence spectral characteristics of "two-voice" stereotyped calls produced by free-ranging killer whales.

PubMed

Miller, Patrick J O; Samarra, Filipa I P; Perthuison, Aurélie D

2007-06-01

This study investigates how particular received spectral characteristics of stereotyped calls of sexually dimorphic adult killer whales may be influenced by caller sex, orientation, and range. Calls were ascribed to individuals during natural behavior using a towed beamforming array. The fundamental frequency of both high-frequency and low-frequency components did not differ consistently by sex. The ratio of peak energy within the fundamental of the high-frequency component relative to summed peak energy in the first two low-frequency component harmonics, and the number of modulation bands off the high-frequency component, were significantly greater when whales were oriented towards the array, while range and adult sex had little effect. In contrast, the ratio of peak energy in the first versus second harmonics of the low-frequency component was greater in calls produced by adult females than adult males, while orientation and range had little effect. The dispersion of energy across harmonics has been shown to relate to body size or sex in terrestrial species, but pressure effects during diving are thought to make such a signal unreliable in diving animals. The observed spectral differences by signaler sex and orientation suggest that these types of information may be transmitted acoustically by freely diving killer whales.

Quantitative analysis of harmonic convergence in mosquito auditory interactions

PubMed Central

Aldersley, Andrew; Champneys, Alan; Robert, Daniel

2016-01-01

This article analyses the hearing and behaviour of mosquitoes in the context of inter-individual acoustic interactions. The acoustic interactions of tethered live pairs of Aedes aegypti mosquitoes, from same and opposite sex mosquitoes of the species, are recorded on independent and unique audio channels, together with the response of tethered individual mosquitoes to playbacks of pre-recorded flight tones of lone or paired individuals. A time-dependent representation of each mosquito's non-stationary wing beat frequency signature is constructed, based on Hilbert spectral analysis. A range of algorithmic tools is developed to automatically analyse these data, and used to perform a robust quantitative identification of the ‘harmonic convergence’ phenomenon. The results suggest that harmonic convergence is an active phenomenon, which does not occur by chance. It occurs for live pairs, as well as for lone individuals responding to playback recordings, whether from the same or opposite sex. Male–female behaviour is dominated by frequency convergence at a wider range of harmonic combinations than previously reported, and requires participation from both partners in the duet. New evidence is found to show that male–male interactions are more varied than strict frequency avoidance. Rather, they can be divided into two groups: convergent pairs, typified by tightly bound wing beat frequencies, and divergent pairs, that remain widely spaced in the frequency domain. Overall, the results reveal that mosquito acoustic interaction is a delicate and intricate time-dependent active process that involves both individuals, takes place at many different frequencies, and which merits further enquiry. PMID:27053654

Health State Monitoring of Bladed Machinery with Crack Growth Detection in BFG Power Plant Using an Active Frequency Shift Spectral Correction Method

PubMed Central

Sun, Weifang; Yao, Bin; He, Yuchao; Zeng, Nianyin; He, Wangpeng

2017-01-01

Power generation using waste-gas is an effective and green way to reduce the emission of the harmful blast furnace gas (BFG) in pig-iron producing industry. Condition monitoring of mechanical structures in the BFG power plant is of vital importance to guarantee their safety and efficient operations. In this paper, we describe the detection of crack growth of bladed machinery in the BFG power plant via vibration measurement combined with an enhanced spectral correction technique. This technique enables high-precision identification of amplitude, frequency, and phase information (the harmonic information) belonging to deterministic harmonic components within the vibration signals. Rather than deriving all harmonic information using neighboring spectral bins in the fast Fourier transform spectrum, this proposed active frequency shift spectral correction method makes use of some interpolated Fourier spectral bins and has a better noise-resisting capacity. We demonstrate that the identified harmonic information via the proposed method is of suppressed numerical error when the same level of noises is presented in the vibration signal, even in comparison with a Hanning-window-based correction method. With the proposed method, we investigated vibration signals collected from a centrifugal compressor. Spectral information of harmonic tones, related to the fundamental working frequency of the centrifugal compressor, is corrected. The extracted spectral information indicates the ongoing development of an impeller blade crack that occurred in the centrifugal compressor. This method proves to be a promising alternative to identify blade cracks at early stages. PMID:28792453

REVIEW ARTICLE: Harmonically mode-locked semiconductor-based lasers as high repetition rate ultralow noise pulse train and optical frequency comb sources

NASA Astrophysics Data System (ADS)

Quinlan, F.; Ozharar, S.; Gee, S.; Delfyett, P. J.

2009-10-01

Recent experimental work on semiconductor-based harmonically mode-locked lasers geared toward low noise applications is reviewed. Active, harmonic mode-locking of semiconductor-based lasers has proven to be an excellent way to generate 10 GHz repetition rate pulse trains with pulse-to-pulse timing jitter of only a few femtoseconds without requiring active feedback stabilization. This level of timing jitter is achieved in long fiberized ring cavities and relies upon such factors as low noise rf sources as mode-lockers, high optical power, intracavity dispersion management and intracavity phase modulation. When a high finesse etalon is placed within the optical cavity, semiconductor-based harmonically mode-locked lasers can be used as optical frequency comb sources with 10 GHz mode spacing. When active mode-locking is replaced with regenerative mode-locking, a completely self-contained comb source is created, referenced to the intracavity etalon.

Third harmonic frequency generation by type-I critically phase-matched LiB3O5 crystal by means of optically active quartz crystal.

PubMed

Gapontsev, Valentin P; Tyrtyshnyy, Valentin A; Vershinin, Oleg I; Davydov, Boris L; Oulianov, Dmitri A

2013-02-11

We present a method of third harmonic generation at 355 nm by frequency mixing of fundamental and second harmonic radiation of an ytterbium nanosecond pulsed all-fiber laser in a type-I phase-matched LiB(3)O(5) (LBO) crystal where originally orthogonal polarization planes of the fundamental and second harmonic beams are aligned by an optically active quartz crystal. 8 W of ultraviolet light at 355 nm were achieved with 40% conversion efficiency from 1064 nm radiation. The conversion efficiency obtained in a type-I phase-matched LBO THG crystal was 1.6 times higher than the one achieved in a type-II LBO crystal at similar experimental conditions. In comparison to half-wave plates traditionally used for polarization alignment the optically active quartz crystal has much lower temperature dependence and requires simpler optical alignment.

Beamed microwave power transmitting and receiving subsystems radiation characteristics

NASA Technical Reports Server (NTRS)

Dickinson, R. M.

1980-01-01

Measured characteristics of the spectrum of typical converters and the distribution of radiated Radio Frequency (RF) energy from the terminals (transmitting antenna and rectenna) of a beamed microwave power subsystem are presented for small transmitting and receiving S-band (2.45 GHz) subarrays. Noise and harmonic levels of tube and solid-state RF power amplifiers are shown. The RF patterns and envelope of a 64 element slotted waveguide antenna are given for the fundamental frequency and harmonics through the fifth. Reflected fundamental and harmonic patterns through the fourth for a 42 element rectenna subarray are presented for various dc load and illumination conditions. Bandwidth measurements for the waveguide antenna and rectenna are shown.

Quaternion-valued single-phase model for three-phase power system

NASA Astrophysics Data System (ADS)

Gou, Xiaoming; Liu, Zhiwen; Liu, Wei; Xu, Yougen; Wang, Jiabin

2018-03-01

In this work, a quaternion-valued model is proposed in lieu of the Clarke's α, β transformation to convert three-phase quantities to a hypercomplex single-phase signal. The concatenated signal can be used for harmonic distortion detection in three-phase power systems. In particular, the proposed model maps all the harmonic frequencies into frequencies in the quaternion domain, while the Clarke's transformation-based methods will fail to detect the zero sequence voltages. Based on the quaternion-valued model, the Fourier transform, the minimum variance distortionless response (MVDR) algorithm and the multiple signal classification (MUSIC) algorithm are presented as examples to detect harmonic distortion. Simulations are provided to demonstrate the potentials of this new modeling method.

Quasi-phase-matching of the dual-band nonlinear left-handed metamaterial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yahong, E-mail: yhliu@nwpu.edu.cn; Song, Kun; Gu, Shuai

2014-11-17

We demonstrate a type of nonlinear meta-atom creating a dual-band nonlinear left-handed metamaterial (DNLHM). The DNLHM operates at two distinct left-handed frequency bands where there is an interval of one octave between the two center frequencies. Under the illumination of a high-power signal at the first left-handed frequency band corresponding to fundamental frequency (FF), second-harmonic generation (SHG) is observed at the second left-handed band. This means that our DNLHM supports backward-propagating waves both at FF and second-harmonic (SH) frequency. We also experimentally demonstrate quasi-phase-matching configurations for the backward SHG. This fancy parametric process can significantly transmits the SH generated bymore » an incident FF wave.« less

Exploiting bistable oscillator subharmonics for magnified broadband vibration energy harvesting

NASA Astrophysics Data System (ADS)

Huguet, Thomas; Badel, Adrien; Lallart, Mickaël

2017-10-01

Recent research on primary battery alternatives for supplying autonomous wireless devices has recently highlighted the advantages of nonlinear oscillators' dynamics and more particularly bistable oscillators' behavior for ambient vibration harvesting. The key property of bistable oscillators compared to linear ones is their enhanced operational frequency bandwidth under harmonic excitation, potentially leading to a better adaptation to the environment. However, the classical frequency response characterization of such devices does not reveal all the possible dynamic behaviors offered by bistable oscillators. Thus, subharmonic motions are experimentally investigated in this letter, and their energy harvesting potential as well as their ability to enhance the bistable generator bandwidth is evaluated. The results obtained with a generator integrating buckled beams for the bistability feature show that, in addition to the commonly considered harmonic behavior, subharmonics allow widening of the useful operating frequency band of the bistable microgenerator by 180% compared to the sole exploitation of the first harmonic motion.

Connectome-harmonic decomposition of human brain activity reveals dynamical repertoire re-organization under LSD.

PubMed

Atasoy, Selen; Roseman, Leor; Kaelen, Mendel; Kringelbach, Morten L; Deco, Gustavo; Carhart-Harris, Robin L

2017-12-15

Recent studies have started to elucidate the effects of lysergic acid diethylamide (LSD) on the human brain but the underlying dynamics are not yet fully understood. Here we used 'connectome-harmonic decomposition', a novel method to investigate the dynamical changes in brain states. We found that LSD alters the energy and the power of individual harmonic brain states in a frequency-selective manner. Remarkably, this leads to an expansion of the repertoire of active brain states, suggestive of a general re-organization of brain dynamics given the non-random increase in co-activation across frequencies. Interestingly, the frequency distribution of the active repertoire of brain states under LSD closely follows power-laws indicating a re-organization of the dynamics at the edge of criticality. Beyond the present findings, these methods open up for a better understanding of the complex brain dynamics in health and disease.

Generation of a tunable environment for electrical oscillator systems.

PubMed

León-Montiel, R de J; Svozilík, J; Torres, Juan P

2014-07-01

Many physical, chemical, and biological systems can be modeled by means of random-frequency harmonic oscillator systems. Even though the noise-free evolution of harmonic oscillator systems can be easily implemented, the way to experimentally introduce, and control, noise effects due to a surrounding environment remains a subject of lively interest. Here, we experimentally demonstrate a setup that provides a unique tool to generate a fully tunable environment for classical electrical oscillator systems. We illustrate the operation of the setup by implementing the case of a damped random-frequency harmonic oscillator. The high degree of tunability and control of our scheme is demonstrated by gradually modifying the statistics of the oscillator's frequency fluctuations. This tunable system can readily be used to experimentally study interesting noise effects, such as noise-induced transitions in systems driven by multiplicative noise, and noise-induced transport, a phenomenon that takes place in quantum and classical coupled oscillator networks.

High-frequency AC/DC converter with unity power factor and minimum harmonic distortion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wernekinch, E.R.

1987-01-01

The power factor is controlled by adjusting the relative position of the fundamental component of an optimized PWM-type voltage with respect to the supply voltage. Current harmonic distortion is minimized by the use of optimized firing angles for the converter at a frequency where GTO's can be used. This feature makes this approach very attractive at power levels of 100 to 600 kW. To obtain the optimized PWM pattern, a steepest descent digital computer algorithm is used. Digital-computer simulations are performed and a low-power model is constructed and tested to verify the concepts and the behavior of the model. Experimentalmore » results show that unity power factor is achieved and that the distortion in the phase currents is 10.4% at 90% of full load. This is less than achievable with sinusoidal PWM, harmonic elimination, hysteresis control, and deadbeat control for the same switching frequency.« less

Power Amplifier Linearizer for High Frequency Medical Ultrasound Applications

PubMed Central

Choi, Hojong; Jung, Hayong; Shung, K. Kirk

2015-01-01

Power amplifiers (PAs) are used to produce high-voltage excitation signals to drive ultrasonic transducers. A larger dynamic range of linear PAs allows higher contrast resolution, a highly desirable characteristic in ultrasonic imaging. The linearity of PAs can be improved by reducing the nonlinear harmonic distortion components of high-voltage output signals. In this paper, a linearizer circuit is proposed to reduce output signal harmonics when working in conjunction with a PA. The PA performance with and without the linearizer was measured by comparing the output power 1-dB compression point (OP1dB), and the second- and third-order harmonic distortions (HD2 and HD3, respectively). The results show that the PA with the linearizer circuit had higher OP1dB (31.7 dB) and lower HD2 (−61.0 dB) and HD3 (−42.7 dB) compared to those of the PA alone (OP1dB (27.1 dB), HD2 (−38.2 dB), and HD3 (−36.8 dB)) at 140 MHz. A pulse-echo measurement was also performed to further evaluate the capability of the linearizer circuit. The HD2 of the echo signal received by the transducer using a PA with the linearizer (−24.8 dB) was lower than that obtained for the PA alone (−16.6 dB). The linearizer circuit is capable of improving the linearity performance of PA by lowering harmonic distortions. PMID:26622209

Nonlinear ultrasonic imaging with X wave

NASA Astrophysics Data System (ADS)

Du, Hongwei; Lu, Wei; Feng, Huanqing

2009-10-01

X wave has a large depth of field and may have important application in ultrasonic imaging to provide high frame rate (HFR). However, the HFR system suffers from lower spatial resolution. In this paper, a study of nonlinear imaging with X wave is presented to improve the resolution. A theoretical description of realizable nonlinear X wave is reported. The nonlinear field is simulated by solving the KZK nonlinear wave equation with a time-domain difference method. The results show that the second harmonic field of X wave has narrower mainlobe and lower sidelobes than the fundamental field. In order to evaluate the imaging effect with X wave, an imaging model involving numerical calculation of the KZK equation, Rayleigh-Sommerfeld integral, band-pass filtering and envelope detection is constructed to obtain 2D fundamental and second harmonic images of scatters in tissue-like medium. The results indicate that if X wave is used, the harmonic image has higher spatial resolution throughout the entire imaging region than the fundamental image, but higher sidelobes occur as compared to conventional focus imaging. A HFR imaging method with higher spatial resolution is thus feasible provided an apodization method is used to suppress sidelobes.

Specialization of the auditory system for the processing of bio-sonar information in the frequency domain: Mustached bats.

PubMed

Suga, Nobuo

2018-04-01

For echolocation, mustached bats emit velocity-sensitive orientation sounds (pulses) containing a constant-frequency component consisting of four harmonics (CF 1-4 ). They show unique behavior called Doppler-shift compensation for Doppler-shifted echoes and hunting behavior for frequency and amplitude modulated echoes from fluttering insects. Their peripheral auditory system is highly specialized for fine frequency analysis of CF 2 (∼61.0 kHz) and detecting echo CF 2 from fluttering insects. In their central auditory system, lateral inhibition occurring at multiple levels sharpens V-shaped frequency-tuning curves at the periphery and creates sharp spindle-shaped tuning curves and amplitude tuning. The large CF 2 -tuned area of the auditory cortex systematically represents the frequency and amplitude of CF 2 in a frequency-versus-amplitude map. "CF/CF" neurons are tuned to a specific combination of pulse CF 1 and Doppler-shifted echo CF 2 or 3 . They are tuned to specific velocities. CF/CF neurons cluster in the CC ("C" stands for CF) and DIF (dorsal intrafossa) areas of the auditory cortex. The CC area has the velocity map for Doppler imaging. The DIF area is particularly for Dopper imaging of other bats approaching in cruising flight. To optimize the processing of behaviorally relevant sounds, cortico-cortical interactions and corticofugal feedback modulate the frequency tuning of cortical and sub-cortical auditory neurons and cochlear hair cells through a neural net consisting of positive feedback associated with lateral inhibition. Copyright © 2018 Elsevier B.V. All rights reserved.

Microwave Imaging Reflectometry for the study of Edge Harmonic Oscillations on DIII-D [Microwave Imaging Reflectometry (MIR) for the study of Edge Harmonic Oscillations (EHOs) on DIII-D

DOE PAGES

Ren, X.; Chen, M.; Chen, X.; ...

2015-10-23

Quiescent H-mode (QH) is an ELM free mode of operation in which edge-localized harmonic oscillations (EHOs) are believed to enhance particle transport, thereby stabilizing ELMs and preventing damage to the divertor and plasma facing components. Microwave Imaging Reflectometer (MIR) enabling direct comparison between the measured and simulated 2D images of density fluctuations near the edge can determine the 2D structure of density oscillation which can help to explain the physics behind EHO modes. MIR data sometimes indicates a counter-propagation between higher (n>1) and dominant (n=1) harmonics of coherent EHOs in the steep gradient regions of the pedestal. To preclude diagnosticmore » artifacts, we have performed forward modeling that includes possible optical misalignments to show that offsets between transmitting and receiving antennas do not account for this feature. We have also simulated the non-uniform rotation of the EHO structure, which induces multiple harmonics that are properly characterized in the synthetic diagnostic. Excluding these possible explanations for the data, the counter-propagation observed in MIR data, which is not corroborated by external Mirnov coil array measurements, may be due to subtleties of the eigenmode structure, such as an inversion radius consistent with a magnetic island. Similar effects are observed in analysis of internal ECE-Imaging and BES data. Furthermore, the identification of a non-ideal structure motivates further exploration of nonlinear models of this instability.« less

Harmonic Brain Modes: A Unifying Framework for Linking Space and Time in Brain Dynamics.

PubMed

Atasoy, Selen; Deco, Gustavo; Kringelbach, Morten L; Pearson, Joel

2018-06-01

A fundamental characteristic of spontaneous brain activity is coherent oscillations covering a wide range of frequencies. Interestingly, these temporal oscillations are highly correlated among spatially distributed cortical areas forming structured correlation patterns known as the resting state networks, although the brain is never truly at "rest." Here, we introduce the concept of harmonic brain modes-fundamental building blocks of complex spatiotemporal patterns of neural activity. We define these elementary harmonic brain modes as harmonic modes of structural connectivity; that is, connectome harmonics, yielding fully synchronous neural activity patterns with different frequency oscillations emerging on and constrained by the particular structure of the brain. Hence, this particular definition implicitly links the hitherto poorly understood dimensions of space and time in brain dynamics and its underlying anatomy. Further we show how harmonic brain modes can explain the relationship between neurophysiological, temporal, and network-level changes in the brain across different mental states ( wakefulness, sleep, anesthesia, psychedelic). Notably, when decoded as activation of connectome harmonics, spatial and temporal characteristics of neural activity naturally emerge from the interplay between excitation and inhibition and this critical relation fits the spatial, temporal, and neurophysiological changes associated with different mental states. Thus, the introduced framework of harmonic brain modes not only establishes a relation between the spatial structure of correlation patterns and temporal oscillations (linking space and time in brain dynamics), but also enables a new dimension of tools for understanding fundamental principles underlying brain dynamics in different states of consciousness.

Mathematics of Computed Tomography

NASA Astrophysics Data System (ADS)

Hawkins, William Grant

A review of the applications of the Radon transform is presented, with emphasis on emission computed tomography and transmission computed tomography. The theory of the 2D and 3D Radon transforms, and the effects of attenuation for emission computed tomography are presented. The algebraic iterative methods, their importance and limitations are reviewed. Analytic solutions of the 2D problem the convolution and frequency filtering methods based on linear shift invariant theory, and the solution of the circular harmonic decomposition by integral transform theory--are reviewed. The relation between the invisible kernels, the inverse circular harmonic transform, and the consistency conditions are demonstrated. The discussion and review are extended to the 3D problem-convolution, frequency filtering, spherical harmonic transform solutions, and consistency conditions. The Cormack algorithm based on reconstruction with Zernike polynomials is reviewed. An analogous algorithm and set of reconstruction polynomials is developed for the spherical harmonic transform. The relations between the consistency conditions, boundary conditions and orthogonal basis functions for the 2D projection harmonics are delineated and extended to the 3D case. The equivalence of the inverse circular harmonic transform, the inverse Radon transform, and the inverse Cormack transform is presented. The use of the number of nodes of a projection harmonic as a filter is discussed. Numerical methods for the efficient implementation of angular harmonic algorithms based on orthogonal functions and stable recursion are presented. The derivation of a lower bound for the signal-to-noise ratio of the Cormack algorithm is derived.

Electromagnetic radiation and nonlinear energy flow in an electron beam-plasma system

NASA Technical Reports Server (NTRS)

Whelan, D. A.; Stenzel, R. L.

1985-01-01

It is shown that the unstable electron-plasma waves of a beam-plasma system can generate electromagnetic radiation in a uniform plasma. The generation mechanism is a scattering of the unstable electron plasma waves off ion-acoustic waves, producing electromagnetic waves whose frequency is near the local plasma frequency. The wave vector and frequency matching conditions of the three-wave mode coupling are experimentally verified. The electromagnetic radiation is observed to be polarized with the electric field parallel to the beam direction, and its source region is shown to be localized to the unstable plasma wave region. The frequency spectrum shows negligible intensity near the second harmonic of the plasma frequency. These results suggest that the observed electromagnetic radiation of type III solar bursts may be generated near the local plasma frequency and observed downstream where the wave frequency is near the harmonic of the plasma frequency.

Microwave Imaging in Large Helical Device

NASA Astrophysics Data System (ADS)

Yoshinaga, T.; Nagayama, Y.; Tsuchiya, H.; Kuwahara, D.; Tsuji-Iio, S.; Akaki, K.; Mase, A.; Kogi, Y.; Yamaguchi, S.; Shi, Z. B.; Hojo, H.

2011-02-01

Microwave imaging reflectometry (MIR) system and electron cyclotron emission imaging (ECEI) system are under development for the simultaneous reconstruction of the electron density and temperature fluctuation structures in the Large Helical Device (LHD). The MIR observes three-dimensional structure of disturbed cutoff surfaces by using the two-dimensionally distributed horn-antenna mixer array (HMA) of 5 × 7 channels in combination with the simultaneous projection of microwaves with four different frequency components (60.410, 61.808, 63.008 and 64.610 GHz). The ECEI is designed to observe two-dimensional structure of electron temperature by detecting second-harmonic ECE at 97-107 GHz with the one-dimensional HMA (7 channels) in the common optics with MIR system. Both the MIR and the ECEI are realized by the HMA and the band-pass filter (BPF) arrays, which are fabricated by micro-strip-line technique at low-cost.

Multiple harmonic frequencies resonant cavity design and half-scale prototype measurements for a fast kicker

DOE PAGES

Huang, Yulu; Wang, Haipeng; Wang, Shaoheng; ...

2016-12-09

Quarter wavelength resonator (QWR) based deflecting cavities with the capability of supporting multiple odd-harmonic modes have been developed for an ultrafast periodic kicker system in the proposed Jefferson Lab Electron Ion Collider (JLEIC, formerly MEIC). Previous work on the kicking pulse synthesis and the transverse beam dynamics tracking simulations show that a flat-top kicking pulse can be generated with minimal emittance growth during injection and circulation of the cooling electron bunches. This flat-top kicking pulse can be obtained when a DC component and 10 harmonic modes with appropriate amplitude and phase are combined together. To support 10 such harmonic modes,more » four QWR cavities are used with 5, 3, 1, and 1 modes, respectively. In the multiple-mode cavities, several slightly tapered segments of the inner conductor are introduced to tune the higher order deflecting modes to be harmonic, and stub tuners are used to fine tune each frequency to compensate for potential errors. In this paper, we summarize the electromagnetic design of the five-mode cavity, including the geometry optimization to get high transverse shunt impedance, the frequency tuning and sensitivity analysis, and the single loop coupler design for coupling to all of the harmonic modes. In particular we report on the design and fabrication of a half-scale copper prototype of this proof-of-principle five-odd-mode cavity, as well as the rf bench measurements. Lastly, we demonstrate mode superposition in this cavity experimentally, which illustrates the kicking pulse generation concept.« less

Low-Power Low-Noise Amplifier Using Attenuation-Adaptive Noise Control for Ultrasound Imaging Systems.

PubMed

Jung, Sung-Jin; Hong, Seong-Kwan; Kwon, Oh-Kyong

2017-02-01

This paper presents a low-noise amplifier (LNA) using attenuation-adaptive noise control (AANC) for ultrasound imaging systems. The proposed AANC reduces unnecessary power consumption of the LNA, which arises from useless noise floor, by controlling the noise floor of the LNA with respect to the attenuation of the ultrasound. In addition, a current feedback amplifier with a source-degenerated input stage reduces variations of the bandwidth and the closed loop gain, which are caused by the AANC. The proposed LNA was fabricated using a 0.18-[Formula: see text] CMOS process. The input-referred voltage noise density of the fabricated LNA is 1.01 [Formula: see text] at the frequency of 5 MHz. The second harmonic distortion is -53.5 dB when the input signal frequency is 5 MHz and the output voltage swing is 2 [Formula: see text]. The power consumption of the LNA using the AANC is 16.2 mW at the supply voltage of 1.8 V, which is reduced to 64% of that without using the AANC. The noise efficiency factor (NEF) of the proposed LNA is 3.69, to our knowledge, which is the lowest NEF compared with previous LNAs for ultrasound imaging.

Online tracking of instantaneous frequency and amplitude of dynamical system response

NASA Astrophysics Data System (ADS)

Frank Pai, P.

2010-05-01

This paper presents a sliding-window tracking (SWT) method for accurate tracking of the instantaneous frequency and amplitude of arbitrary dynamic response by processing only three (or more) most recent data points. Teager-Kaiser algorithm (TKA) is a well-known four-point method for online tracking of frequency and amplitude. Because finite difference is used in TKA, its accuracy is easily destroyed by measurement and/or signal-processing noise. Moreover, because TKA assumes the processed signal to be a pure harmonic, any moving average in the signal can destroy the accuracy of TKA. On the other hand, because SWT uses a constant and a pair of windowed regular harmonics to fit the data and estimate the instantaneous frequency and amplitude, the influence of any moving average is eliminated. Moreover, noise filtering is an implicit capability of SWT when more than three data points are used, and this capability increases with the number of processed data points. To compare the accuracy of SWT and TKA, Hilbert-Huang transform is used to extract accurate time-varying frequencies and amplitudes by processing the whole data set without assuming the signal to be harmonic. Frequency and amplitude trackings of different amplitude- and frequency-modulated signals, vibrato in music, and nonlinear stationary and non-stationary dynamic signals are studied. Results show that SWT is more accurate, robust, and versatile than TKA for online tracking of frequency and amplitude.

Harmonic distortion in microwave photonic filters.

PubMed

Rius, Manuel; Mora, José; Bolea, Mario; Capmany, José

2012-04-09

We present a theoretical and experimental analysis of nonlinear microwave photonic filters. Far from the conventional condition of low modulation index commonly used to neglect high-order terms, we have analyzed the harmonic distortion involved in microwave photonic structures with periodic and non-periodic frequency responses. We show that it is possible to design microwave photonic filters with reduced harmonic distortion and high linearity even under large signal operation.

Doppler-shift compensation in the Taiwanese leaf-nosed bat (Hipposideros terasensis) recorded with a telemetry microphone system during flight

NASA Astrophysics Data System (ADS)

Hiryu, Shizuko; Katsura, Koji; Lin, Liang-Kong; Riquimaroux, Hiroshi; Watanabe, Yoshiaki

2005-12-01

Biosonar behavior was examined in Taiwanese leaf-nosed bats (Hipposideros terasensis; CF-FM bats) during flight. Echolocation sounds were recorded using a telemetry microphone mounted on the bat's head. Flight speed and three-dimensional trajectory of the bat were reconstructed from images taken with a dual high-speed video camera system. Bats were observed to change the intensity and emission rate of pulses depending on the distance from the landing site. Frequencies of the dominant second harmonic constant frequency component (CF2) of calls estimated from the bats' flight speed agreed strongly with observed values. Taiwanese leaf-nosed bats changed CF2 frequencies depending on flight speed, which caused the CF2 frequencies of the Doppler-shifted echoes to remain constant. Pulse frequencies were also estimated using echoes returning directly ahead of the bat and from its sides for two different flight conditions: landing and U-turn. Bats in flight may periodically alter their attended angles from the front to the side when emitting echolocation pulses.

Fiber-based polarization-sensitive Mueller matrix optical coherence tomography with continuous source polarization modulation.

PubMed

Jiao, Shuliang; Todorović, Milos; Stoica, George; Wang, Lihong V

2005-09-10

We report on a new configuration of fiber-based polarization-sensitive Mueller matrix optical coherence tomography that permits the acquisition of the round-trip Jones matrix of a biological sample using only one light source and a single depth scan. In this new configuration, a polarization modulator is used in the source arm to continuously modulate the incident polarization state for both the reference and the sample arms. The Jones matrix of the sample can be calculated from the two frequency terms in the two detection channels. The first term is modulated by the carrier frequency, which is determined by the longitudinal scanning mechanism, whereas the other term is modulated by the beat frequency between the carrier frequency and the second harmonic of the modulation frequency of the polarization modulator. One important feature of this system is that, for the first time to our knowledge, the Jones matrix of the sample can be calculated with a single detection channel and a single measurement when diattenuation is negligible. The system was successfully tested by imaging both standard polarization elements and biological samples.

Efficient 2(nd) and 4(th) harmonic generation of a single-frequency, continuous-wave fiber amplifier.

PubMed

Sudmeyer, Thomas; Imai, Yutaka; Masuda, Hisashi; Eguchi, Naoya; Saito, Masaki; Kubota, Shigeo

2008-02-04

We demonstrate efficient cavity-enhanced second and fourth harmonic generation of an air-cooled, continuous-wave (cw), single-frequency 1064 nm fiber-amplifier system. The second harmonic generator achieves up to 88% total external conversion efficiency, generating more than 20-W power at 532 nm wavelength in a diffraction-limited beam (M(2) < 1.05). The nonlinear medium is a critically phase-matched, 20-mm long, anti-reflection (AR) coated LBO crystal operated at 25 degrees C. The fourth harmonic generator is based on an AR-coated, Czochralski-grown beta-BaB(2)O(4) (BBO) crystal optimized for low loss and high damage threshold. Up to 12.2 W of 266-nm deep-UV (DUV) output is obtained using a 6-mm long critically phase-matched BBO operated at 40 degrees C. This power level is more than two times higher than previously reported for cw 266-nm generation. The total external conversion efficiency from the fundamental at 1064 nm to the fourth harmonic at 266 nm is >50%.

Effects of strong laser fields on hadronic helium atoms

NASA Astrophysics Data System (ADS)

Lee, Han-Chieh; Jiang, Tsin-Fu

2015-12-01

The metastable hadronic helium atoms in microseconds lifetime are available in laboratory, and two-photon spectroscopy was reported recently. This exotic helium atom has an electron in the ground state and a negative hadron rotating around the helium nucleus. We theoretically study the excitation on hadronic helium by femtosecond pulse and elucidate the influence of moleculelike structure and rotation behavior on the photoelectron spectra and high-order harmonic generation. Because of the moleculelike structure, the electronic ground state consists of several angular orbitals. These angular orbitals can enhance photoelectron spectra at high energies, and also influence the harmonic generation spectra considerably. In particular, the harmonic spectra can occur at even harmonic orders because of the transition between these angular orbitals and continuum states. On the other side, the rotation behavior of hadron can induce a frequency shift in the harmonic spectra. The magnitude of the frequency shift depends on the orbiting speed of the hadron, which is considerable because the rotation period is in a few femtoseconds, a time scale that is comparable to that of infrared laser and is feasible in current laser experiments.

Theory of Gyrotron Traveling Wave Amplifiers at Harmonics of the Gyration Frequency

NASA Astrophysics Data System (ADS)

Li, Qiangfa

In developing gyrotrons at millimeter and submillimeter wavelengths, a means of operation at lower applied magnetic fields is desirable because of the size and weight of convetional magnets, and the expense and complexity of cryogenic magnets. This requirement can be met by operating the devices at higher harmonics of the electron gyration frequency. In the present work, a unified theory is developed for the gyrotron traveling wave amplifers (gyro-TWA) at harmonics of the gyration frequency, both in the nonlinear regime and in the linear regime. This theory can be applied to a wide class of waveguide cross sections, arbitrary harmonic number, any waveguide mode, and generalized electron beam model. The fields in the beam-field interaction region in the waveguide are expressed in the form of an infinite series of multipoles expanded around the guiding center of the electrons. A set of equations governing the nonlinear behavior of the gyro-TWA is derived. A general dispersion equation is derived both from that set of nonlinear equations by an iteration method and from plasma kinetic theory. The latter is employed to analyze gyro-TWA devices in a systematic and generalized manner. The Laplace transformation is introduced to allow inclusion of the initial values at the input end of the waveguide. From the linear theory it is found that for a gyrotron working at s-th gyration harmonic the electrons can interact only with the 2s-th order multipole field component. It is also found that a higher order waveguide mode is not always better than a lower order mode for the gyro-TWA working at higher harmonics. A novel out-ridged waveguide is proposed and analyzed for the use in gyrotrons. The prominent features of this new waveguide include simplicity of manufacture, freedom from local modes, good separation of lower order modes, high power handling ability, and high gain per unit length at higher gyration harmonics. A comparison of the gyro-TWAs with several different waveguide structures, such as the out-ridged, magnetron-type, rectangular and circular waveguides, is made through numerical examples of the gain-frequency curves computed from the linear kinetic theory.

Invited Review Article: Imaging techniques for harmonic and multiphoton absorption fluorescence microscopy

PubMed Central

Carriles, Ramón; Schafer, Dawn N.; Sheetz, Kraig E.; Field, Jeffrey J.; Cisek, Richard; Barzda, Virginijus; Sylvester, Anne W.; Squier, Jeffrey A.

2009-01-01

We review the current state of multiphoton microscopy. In particular, the requirements and limitations associated with high-speed multiphoton imaging are considered. A description of the different scanning technologies such as line scan, multifoci approaches, multidepth microscopy, and novel detection techniques is given. The main nonlinear optical contrast mechanisms employed in microscopy are reviewed, namely, multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation. Techniques for optimizing these nonlinear mechanisms through a careful measurement of the spatial and temporal characteristics of the focal volume are discussed, and a brief summary of photobleaching effects is provided. Finally, we consider three new applications of multiphoton microscopy: nonlinear imaging in microfluidics as applied to chemical analysis and the use of two-photon absorption and self-phase modulation as contrast mechanisms applied to imaging problems in the medical sciences. PMID:19725639

Understanding Collagen Organization in Breast Tumors to Predict and Prevent Metastasis

DTIC Science & Technology

2014-09-01

Harmonic Generation to Image the Extracellular Matrix During Tumor Progression. Invited Perspective Intravital Manuscript Submitted. Sullivan K...harmonic generation (the SHG “F/B ratio”) in thick intact tissue, with a single image scan. This will be necessary for us to pursue our goal of...quantifying matrix changes dynamically, in intact tumor models. The first method determines F/B by generating a series of backscattered images using a series

Analysing harmonic motions with an iPhone’s magnetometer

NASA Astrophysics Data System (ADS)

Yavuz, Ahmet; Kağan Temiz, Burak

2016-05-01

In this paper, we propose an experiment for analysing harmonic motion using an iPhone’s (or iPad’s) magnetometer. This experiment consists of the detection of magnetic field variations obtained from an iPhone’s magnetometer sensor. A graph of harmonic motion is directly displayed on the iPhone’s screen using the Sensor Kinetics application. Data from this application was analysed with Eureqa software to establish the equation of the harmonic motion. Analyses show that the use of an iPhone’s magnetometer to analyse harmonic motion is a practical and effective method for small oscillations and frequencies less than 15-20 Hz.

Dynamic characteristics of the blisk with synchronized switch damping based on negative capacitor

NASA Astrophysics Data System (ADS)

Liu, J.; Li, L.; Huang, X.; Jezequel, L.

2017-10-01

In this paper, we propose a method to suppress the vibration of the integral bladed disk ('blisk' for short) in aero-engines using synchronized switch damping based on negative capacitor (SSDNC). Different from the classical piezoelectric shunt damping, SSDNC is a type of nonlinear piezoelectric damping. A multi-harmonic balance method combined with the alternating frequency/time method (MHBM-AFT) is used to predict and further analyze the dynamic characteristics of the electromechanical system, and an arc-length continuation technique is used to improve the convergence of the method. In order to validate the algorithm as well as to recognize the characteristics of the system with SSDNC, a two degree-of-freedom (2-DOF) system with SSDNC is studied at first. The nonlinear complex modal information is calculated and compared with those of the corresponding system with a linear RL shunt circuit. The results indicate that the natural frequencies and modal damping ratio do not change with the modal amplitude, which means that SSDNC has the same modal damping corresponding to different system energy levels. In addition, SSDNC can improve the damping level of all the modes nearly without affecting the natural frequencies of the system. Then, the forced response of the blisk with SSDNC in the frequency domain is calculated and analyzed, including a tuned blisk, which is excited by the traveling wave excitation with a single harmonic and multi-harmonic, and a mistuned blisk, which is excited by traveling wave excitation with a single harmonic and multi-harmonic. We present two advantages of the SSDNC technique when compared with piezoelectric shunt damping. First, SSDNC can suppress the vibration of the blisk under a multi-harmonic wideband the traveling wave, and second, the vibration suppression performance of SSDNC is insensitive to the mistuning of mechanical parameters of the blisk. The results will be of great significance in overcoming the problem of the amplitude magnification induced by the inevitable mistuning of the blisk in aero-engines.

Automated detection and characterization of harmonic tremor in continuous seismic data

NASA Astrophysics Data System (ADS)

Roman, Diana C.

2017-06-01

Harmonic tremor is a common feature of volcanic, hydrothermal, and ice sheet seismicity and is thus an important proxy for monitoring changes in these systems. However, no automated methods for detecting harmonic tremor currently exist. Because harmonic tremor shares characteristics with speech and music, digital signal processing techniques for analyzing these signals can be adapted. I develop a novel pitch-detection-based algorithm to automatically identify occurrences of harmonic tremor and characterize their frequency content. The algorithm is applied to seismic data from Popocatepetl Volcano, Mexico, and benchmarked against a monthlong manually detected catalog of harmonic tremor events. During a period of heightened eruptive activity from December 2014 to May 2015, the algorithm detects 1465 min of harmonic tremor, which generally precede periods of heightened explosive activity. These results demonstrate the algorithm's ability to accurately characterize harmonic tremor while highlighting the need for additional work to understand its causes and implications at restless volcanoes.

Improved Contrast-Enhanced Ultrasound Imaging With Multiplane-Wave Imaging.

PubMed

Gong, Ping; Song, Pengfei; Chen, Shigao

2018-02-01

Contrast-enhanced ultrasound (CEUS) imaging has great potential for use in new ultrasound clinical applications such as myocardial perfusion imaging and abdominal lesion characterization. In CEUS imaging, contrast agents (i.e., microbubbles) are used to improve contrast between blood and tissue because of their high nonlinearity under low ultrasound pressure. However, the quality of CEUS imaging sometimes suffers from a low signal-to-noise ratio (SNR) in deeper imaging regions when a low mechanical index (MI) is used to avoid microbubble disruption, especially for imaging at off-resonance transmit frequencies. In this paper, we propose a new strategy of combining CEUS sequences with the recently proposed multiplane-wave (MW) compounding method to improve the SNR of CEUS in deeper imaging regions without increasing MI or sacrificing frame rate. The MW-CEUS method emits multiple Hadamard-coded CEUS pulses in each transmission event (i.e., pulse-echo event). The received echo signals first undergo fundamental bandpass filtering (i.e., the filter is centered on the transmit frequency) to eliminate the microbubble's second-harmonic signals because they cannot be encoded by pulse inversion. The filtered signals are then Hadamard decoded and realigned in fast time to recover the signals as they would have been obtained using classic CEUS pulses, followed by designed recombination to cancel the linear tissue responses. The MW-CEUS method significantly improved contrast-to-tissue ratio and SNR of CEUS imaging by transmitting longer coded pulses. The image resolution was also preserved. The microbubble disruption ratio and motion artifacts in MW-CEUS were similar to those of classic CEUS imaging. In addition, the MW-CEUS sequence can be adapted to other transmission coding formats. These properties of MW-CEUS can potentially facilitate CEUS imaging for many clinical applications, especially assessing deep abdominal organs or the heart.

Adaptive Piezoelectric Circuitry Sensor Network with High-Frequency Harmonics Interrogation for Structural Damage Detection

DTIC Science & Technology

2014-09-17

AFRL-OSR-VA-TR-2014-0255 ADAPTIVE PIEZOELECTRIC CIRCUITRY SENSOR NETWORK KON -WELL WANG MICHIGAN UNIV ANN ARBOR Final Report 09/17/2014 DISTRIBUTION A...Harmonics Interrogation for Structural Damage Detection FA9550-11-1-0072 Kon -Well Wang and Jiong Tang The Regents of the University of Michigan, 3003...mechanism. These efforts have yielded a complete methodology of adaptive high-frequency piezoelectric self-sensing interrogation. None None None SAR Kon

High-resolution harmonic motion imaging (HR-HMI) for tissue biomechanical property characterization

PubMed Central

Ma, Teng; Qian, Xuejun; Chiu, Chi Tat; Yu, Mingyue; Jung, Hayong; Tung, Yao-Sheng; Shung, K. Kirk

2015-01-01

Background Elastography, capable of mapping the biomechanical properties of biological tissues, serves as a useful technique for clinicians to perform disease diagnosis and determine stages of many diseases. Many acoustic radiation force (ARF) based elastography, including acoustic radiation force impulse (ARFI) imaging and harmonic motion imaging (HMI), have been developed to remotely assess the elastic properties of tissues. However, due to the lower operating frequencies of these approaches, their spatial resolutions are insufficient for revealing stiffness distribution on small scale applications, such as cancerous tumor margin detection, atherosclerotic plaque composition analysis and ophthalmologic tissue characterization. Though recently developed ARF-based optical coherence elastography (OCE) methods open a new window for the high resolution elastography, shallow imaging depths significantly limit their usefulness in clinics. Methods The aim of this study is to develop a high-resolution HMI method to assess the tissue biomechanical properties with acceptable field of view (FOV) using a 4 MHz ring transducer for efficient excitation and a 40 MHz needle transducer for accurate detection. Under precise alignment of two confocal transducers, the high-resolution HMI system has a lateral resolution of 314 µm and an axial resolution of 
147 µm with an effective FOV of 2 mm in depth. Results The performance of this high resolution imaging system was validated on the agar-based tissue mimicking phantoms with different stiffness distributions. These data demonstrated the imaging system’s improved resolution and sensitivity on differentiating materials with varying stiffness. In addition, ex vivo imaging of a human atherosclerosis coronary artery demonstrated the capability of high resolution HMI in identifying layer-specific structures and characterizing atherosclerotic plaques based on their stiffness differences. Conclusions All together high resolution HMI appears to be a promising ultrasound-only technology for characterizing tissue biomechanical properties at the microstructural level to improve the image-based diseases diagnosis in multiple clinical applications. PMID:25694960

High-resolution harmonic motion imaging (HR-HMI) for tissue biomechanical property characterization.

PubMed

Ma, Teng; Qian, Xuejun; Chiu, Chi Tat; Yu, Mingyue; Jung, Hayong; Tung, Yao-Sheng; Shung, K Kirk; Zhou, Qifa

2015-02-01

Elastography, capable of mapping the biomechanical properties of biological tissues, serves as a useful technique for clinicians to perform disease diagnosis and determine stages of many diseases. Many acoustic radiation force (ARF) based elastography, including acoustic radiation force impulse (ARFI) imaging and harmonic motion imaging (HMI), have been developed to remotely assess the elastic properties of tissues. However, due to the lower operating frequencies of these approaches, their spatial resolutions are insufficient for revealing stiffness distribution on small scale applications, such as cancerous tumor margin detection, atherosclerotic plaque composition analysis and ophthalmologic tissue characterization. Though recently developed ARF-based optical coherence elastography (OCE) methods open a new window for the high resolution elastography, shallow imaging depths significantly limit their usefulness in clinics. The aim of this study is to develop a high-resolution HMI method to assess the tissue biomechanical properties with acceptable field of view (FOV) using a 4 MHz ring transducer for efficient excitation and a 40 MHz needle transducer for accurate detection. Under precise alignment of two confocal transducers, the high-resolution HMI system has a lateral resolution of 314 µm and an axial resolution of 
147 µm with an effective FOV of 2 mm in depth. The performance of this high resolution imaging system was validated on the agar-based tissue mimicking phantoms with different stiffness distributions. These data demonstrated the imaging system's improved resolution and sensitivity on differentiating materials with varying stiffness. In addition, ex vivo imaging of a human atherosclerosis coronary artery demonstrated the capability of high resolution HMI in identifying layer-specific structures and characterizing atherosclerotic plaques based on their stiffness differences. All together high resolution HMI appears to be a promising ultrasound-only technology for characterizing tissue biomechanical properties at the microstructural level to improve the image-based diseases diagnosis in multiple clinical applications.

Mixing of two co-directional Rayleigh surface waves in a nonlinear elastic material.

PubMed

Morlock, Merlin B; Kim, Jin-Yeon; Jacobs, Laurence J; Qu, Jianmin

2015-01-01

The mixing of two co-directional, initially monochromatic Rayleigh surface waves in an isotropic, homogeneous, and nonlinear elastic solid is investigated using analytical, finite element method, and experimental approaches. The analytical investigations show that while the horizontal velocity component can form a shock wave, the vertical velocity component can form a pulse independent of the specific ratios of the fundamental frequencies and amplitudes that are mixed. This analytical model is then used to simulate the development of the fundamentals, second harmonics, and the sum and difference frequency components over the propagation distance. The analytical model is further extended to include diffraction effects in the parabolic approximation. Finally, the frequency and amplitude ratios of the fundamentals are identified which provide maximum amplitudes of the second harmonics as well as of the sum and difference frequency components, to help guide effective material characterization; this approach should make it possible to measure the acoustic nonlinearity of a solid not only with the second harmonics, but also with the sum and difference frequency components. Results of the analytical investigations are then confirmed using the finite element method and the experimental feasibility of the proposed technique is validated for an aluminum specimen.

A comparison of field-line resonances observed at the Goose Bay and Wick radars

NASA Astrophysics Data System (ADS)

Provan, G.; Yeoman, T. K.

1997-02-01

Previous observations with the Goose Bay HF coherent-scatter radar have revealed structured spectral peaks at ultra-low frequencies. The frequencies of these spectral peaks have been demonstrated to be extremely consistent from day to day. The stability of these spectral peaks can be seen as evidence for the existence of global magnetospheric cavity modes whose resonant frequencies are independent of latitude. Field-line resonances occur when successive harmonics of the eigenfrequency of the magnetospheric cavity or waveguide match either the first harmonic eigenfrequency of the geomagnetic field lines or higher harmonics of this frequency. Power spectra observed at the SABRE VHF coherent-scatter radar at Wick, Scotland, during night and early morning are revealed to show similarly clearly structured spectral peaks. These spectral peaks are the result of local field-line resonances due to Alfvén waves standing on magnetospheric field lines. A comparison of the spectra observed by the Goose Bay and Wick radars demonstrate that the frequencies of the field-line resonances are, on average, almost identical, despite the different latitudinal ranges covered by the two radars. Possible explanations for the similarity of the signatures on the two radar systems are discussed.

Microwave bio-sensor based on symmetrical split ring resonator with spurline filters for therapeutic goods detection.

PubMed

Alahnomi, Rammah A; Zakaria, Z; Ruslan, E; Ab Rashid, S R; Mohd Bahar, Amyrul Azuan; Shaaban, Azizah

2017-01-01

A novel symmetrical split ring resonator (SSRR) based microwave sensor with spurline filters for detecting and characterizing the properties of solid materials has been developed. Due to the weak perturbation in the interaction of material under test (MUT) and planar microwave sensor, spurline filters were embedded to the SSRR microwave sensor which effectively enhanced Q-factor with suppressing the undesired harmonic frequency. The spurline filter structures force the presented sensor to resonate at a fundamental frequency of 2.2 GHz with the capabilities of suppressing rejected harmonic frequency and miniaturization in circuit size. A wide bandwidth rejection is achieved by using double spurlines filters with high Q-factor achievement (up to 652.94) compared to single spurline filter. The new SSRR sensor with spurline filters displayed desired properties such as high sensitivity, accuracy, and performance with a 1.3% typical percentage error in the measurement results. Furthermore, the sensor has been successfully applied for detecting and characterizing solid materials (such as Roger 5880, Roger 4350, and FR4) and evidently demonstrated that it can suppress the harmonic frequency effectively. This novel design with harmonic suppression is useful for various applications such as food industry (meat, fruit, vegetables), biological medicine (derived from proteins and other substances produced by the body), and Therapeutic goods (antiseptics, vitamins, anti-psychotics, and other medicines).

A method for measuring the nonlinear response in dielectric spectroscopy through third harmonics detection.

PubMed

Thibierge, C; L'Hôte, D; Ladieu, F; Tourbot, R

2008-10-01

We present a high sensitivity method allowing the measurement of the nonlinear dielectric susceptibility of an insulating material at finite frequency. It has been developed for the study of dynamic heterogeneities in supercooled liquids using dielectric spectroscopy at frequencies 0.05 Hz < or = f < or = 3x10(4) Hz. It relies on the measurement of the third harmonics component of the current flowing out of a capacitor. We first show that standard laboratory electronics (amplifiers and voltage sources) nonlinearities lead to limits on the third harmonics measurements that preclude reaching the level needed by our physical goal, a ratio of the third harmonics to the fundamental signal about 10(-7). We show that reaching such a sensitivity needs a method able to get rid of the nonlinear contributions both of the measuring device (lock-in amplifier) and of the excitation voltage source. A bridge using two sources fulfills only the first of these two requirements, but allows to measure the nonlinearities of the sources. Our final method is based on a bridge with two plane capacitors characterized by different dielectric layer thicknesses. It gets rid of the source and amplifier nonlinearities because in spite of a strong frequency dependence of the capacitor impedance, it is equilibrated at any frequency. We present the first measurements of the physical nonlinear response using our method. Two extensions of the method are suggested.

Microwave bio-sensor based on symmetrical split ring resonator with spurline filters for therapeutic goods detection

PubMed Central

Ruslan, E.; Ab Rashid, S. R.; Mohd Bahar, Amyrul Azuan; Shaaban, Azizah

2017-01-01

A novel symmetrical split ring resonator (SSRR) based microwave sensor with spurline filters for detecting and characterizing the properties of solid materials has been developed. Due to the weak perturbation in the interaction of material under test (MUT) and planar microwave sensor, spurline filters were embedded to the SSRR microwave sensor which effectively enhanced Q-factor with suppressing the undesired harmonic frequency. The spurline filter structures force the presented sensor to resonate at a fundamental frequency of 2.2 GHz with the capabilities of suppressing rejected harmonic frequency and miniaturization in circuit size. A wide bandwidth rejection is achieved by using double spurlines filters with high Q-factor achievement (up to 652.94) compared to single spurline filter. The new SSRR sensor with spurline filters displayed desired properties such as high sensitivity, accuracy, and performance with a 1.3% typical percentage error in the measurement results. Furthermore, the sensor has been successfully applied for detecting and characterizing solid materials (such as Roger 5880, Roger 4350, and FR4) and evidently demonstrated that it can suppress the harmonic frequency effectively. This novel design with harmonic suppression is useful for various applications such as food industry (meat, fruit, vegetables), biological medicine (derived from proteins and other substances produced by the body), and Therapeutic goods (antiseptics, vitamins, anti-psychotics, and other medicines). PMID:28934301

Inhibition of linear absorption in opaque materials using phase-locked harmonic generation.

PubMed

Centini, Marco; Roppo, Vito; Fazio, Eugenio; Pettazzi, Federico; Sibilia, Concita; Haus, Joseph W; Foreman, John V; Akozbek, Neset; Bloemer, Mark J; Scalora, Michael

2008-09-12

We theoretically predict and experimentally demonstrate inhibition of linear absorption for phase and group velocity mismatched second- and third-harmonic generation in strongly absorbing materials, GaAs, in particular, at frequencies above the absorption edge. A 100-fs pump pulse tuned to 1300 nm generates 650 and 435 nm second- and third-harmonic pulses that propagate across a 450-microm-thick GaAs substrate without being absorbed. We attribute this to a phase-locking mechanism that causes the pump to trap the harmonics and to impress on them its dispersive properties.

Adaptive Signal Recovery on Graphs via Harmonic Analysis for Experimental Design in Neuroimaging.

PubMed

Kim, Won Hwa; Hwang, Seong Jae; Adluru, Nagesh; Johnson, Sterling C; Singh, Vikas

2016-10-01

Consider an experimental design of a neuroimaging study, where we need to obtain p measurements for each participant in a setting where p ' (< p ) are cheaper and easier to acquire while the remaining ( p - p ') are expensive. For example, the p ' measurements may include demographics, cognitive scores or routinely offered imaging scans while the ( p - p ') measurements may correspond to more expensive types of brain image scans with a higher participant burden. In this scenario, it seems reasonable to seek an "adaptive" design for data acquisition so as to minimize the cost of the study without compromising statistical power. We show how this problem can be solved via harmonic analysis of a band-limited graph whose vertices correspond to participants and our goal is to fully recover a multi-variate signal on the nodes, given the full set of cheaper features and a partial set of more expensive measurements. This is accomplished using an adaptive query strategy derived from probing the properties of the graph in the frequency space. To demonstrate the benefits that this framework can provide, we present experimental evaluations on two independent neuroimaging studies and show that our proposed method can reliably recover the true signal with only partial observations directly yielding substantial financial savings.