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1

High-frequency harmonic imaging of the eye  

Microsoft Academic Search

Purpose: Harmonic imaging has become a well-established technique for ultrasonic imaging at fundamental frequencies of 10 MHz or less. Ophthalmology has benefited from the use of fundamentals of 20 MHz to 50 MHz. Our aim was to explore the ability to generate harmonics for this frequency range, and to generate harmonic images of the eye. Methods: The presence of harmonics

Ronald H. Silverman; D. Jackson Coleman; Jeffrey A. Ketterling; Frederic L. Lizzi

2005-01-01

2

High frequency harmonic imaging in presence of intravascular stents  

Microsoft Academic Search

High frequency second harmonic imaging was compared with fundamental imaging when highly reflective stents were present in the near field of a spherically focused PVDF transducer. Hydrophone measurements of the harmonic beam at 40 MHz showed a relative lower signal strength in the near field compared to the fundamental modes at 20 and 40 MHz. The beam width (-3dB) of

M. E. Frijlink; D. E. Goertz; F. S. Foster

2003-01-01

3

Harmonic intravascular ultrasound imaging with a dual-frequency catheter  

Microsoft Academic Search

Recent studies have shown the feasibility of tissue and contrast harmonic imaging with a prototype nonlinear intravascular ultrasound (IVUS) system using a conventional single-element rotating IVUS catheter. In this study, a dual-frequency transducer element was mounted in an IVUS catheter and its second harmonic imaging performance was investigated and compared with that of a conventional IVUS catheter. Hydrophone measurements showed

Martijn E. Frijlink; David E. Goertz; Hendrik J. Vos; Erik Tesselaar; Gerrit Blacquière; Andries Gisolf; Rob Krams; Antonius F. W. van der Steen

2006-01-01

4

Harmonic intravascular ultrasound imaging with a dual-frequency catheter.  

PubMed

Recent studies have shown the feasibility of tissue and contrast harmonic imaging with a prototype nonlinear intravascular ultrasound (IVUS) system using a conventional single-element rotating IVUS catheter. In this study, a dual-frequency transducer element was mounted in an IVUS catheter and its second harmonic imaging performance was investigated and compared with that of a conventional IVUS catheter. Hydrophone measurements showed a transmit efficiency improvement of >6 dB for the dual-frequency catheter at 20 MHz. In vitro phantom experiments showed a signal-to noise ratio improvement of >5 dB in second harmonic mode at 40 MHz (H40) with the dual-frequency catheter, when using equal transmit voltage for both catheters. Finally, in vivo experiments were conducted and showed image improvement in H40 acquisitions with respect to the conventional IVUS catheter. PMID:17112951

Frijlink, Martijn E; Goertz, David E; Vos, Hendrik J; Tesselaar, Erik; Blacquière, Gerrit; Gisolf, Andries; Krams, Rob; van der Steen, Antonius F W

2006-11-01

5

Chirp-encoded excitation for dual-frequency ultrasound tissue harmonic imaging.  

PubMed

Dual-frequency (DF) transmit waveforms comprise signals at two different frequencies. With a DF transmit waveform operating at both fundamental frequency (f(0)) and second-harmonic frequency (2f(0)), tissue harmonic imaging can be simultaneously performed using not only the conventional 2f(0) second-harmonic signal but also using the f(0 )frequency-difference harmonic signal. Nonetheless, when chirp excitation is incorporated into the DF transmit waveform for harmonic SNR improvement, a particular waveform design is required to maintain the bandwidth of the f(0) harmonic signal. In this study, two different DF chirp waveforms are proposed to produce equal harmonic bandwidth at both the f(0) and 2f(0) frequencies to achieve speckle reduction by harmonic spectral compounding and to increase harmonic SNR for enhanced penetration and sensitivity. The UU13 waveform comprises an up-sweeping f(0) chirp and an up-sweeping 2f(0) chirp with triple bandwidth, whereas the UD11 waveform includes an up-sweeping f(0) chirp and a down-sweeping 2f(0) chirp with equal bandwidth. Experimental results indicate that the UU13 tends to suffer from a high range side lobe level resulting from 3f(0) interference. Consequently, the 2f(0) harmonic envelopes of the UD11 and the UU13 waveforms have compression qualities of 87% and 77%, respectively, when the signal bandwidth is 30%. When the bandwidth increases to 50%, the compression quality of the 2f(0) harmonic envelope degrades to 78% and 54%, respectively, for the UD11 and the UU13 waveforms. The compression quality value of the f0 harmonic envelope remains similar between the two DF transmit waveforms for all signal bandwidths. B-mode harmonic images also show that the UD11 is less contaminated by range side lobe artifacts than is the UU13. Compared with a short pulse with equal bandwidth, the UD11 waveform not only preserves the same spatial resolution after compression but also improves the image SNR by about 10 dB. Moreover, the image contrast-to-noise ratio (CNR), defined as the ratio of the mean to the standard deviation of image intensity in the speckle region, can be increased from 1.0 to about 1.2 when DF spectral compounding is performed. Therefore, it is concluded that the UD11 waveform is a potential solution for chirp-encoded DF harmonic imaging. PMID:23192805

Shen, Che-Chou; Lin, Chin-Hsiang

2012-11-01

6

Development of Ultrasound Transducer with Double-Peak-Type Frequency Characteristics for Harmonic Imaging and Subharmonic Imaging  

NASA Astrophysics Data System (ADS)

Development of ultrasound transducers with double-peak-type frequency characteristics for harmonic imaging and subharmonic imaging is reported in this paper. The peak on the low-frequency side in the frequency characteristics is used to transmit ultrasound into tissues or microbubble ultrasound contrast agents, and another peak on the high-frequency side is used to receive the second harmonic component in the ultrasound transducer with double-peak-type frequency characteristics for harmonic imaging. On the other hand, the peak on the high-frequency side in the frequency characteristics is used to transmit ultrasound and another peak on the low-frequency side is used to receive the 1/2 subharmonic component in the ultrasound transducer with double-peak-type frequency characteristics for subharmonic imaging. The results of the transducer design based on numerical calculation are reported in this paper.

Takeuchi, Shinichi; Zaabi, Mohamed Rashed Ali Al; Sato, Toshio; Kawashima, Norimichi

2002-05-01

7

20 MHz/40 MHz Dual Element Transducers for High Frequency Harmonic Imaging  

PubMed Central

Concentric annular type dual element transducers for second harmonic imaging at 20 MHz / 40 MHz were designed and fabricated to improve spatial resolution and depth of penetration for ophthalmic imaging applications. The outer ring element was designed to transmit the 20 MHz signal and the inner circular element was designed to receive the 40 MHz second harmonic signal. Lithium niobate (LiNbO3), with its low dielectric constant, was used as the piezoelectric material to achieve good electrical impedance matching. Double matching layers and conductive backing were used and optimized by KLM modeling to achieve high sensitivity and wide bandwidth for harmonic imaging and superior time-domain characteristics. Prototype transducers were fabricated and evaluated quantitatively and clinically. The average measured center frequency for the transmit ring element was 21 MHz and the one-way –3 dB bandwidth was greater than 50%. The 40 MHz receive element functioned at 31 MHz center frequency with acceptable bandwidth to receive attenuated and frequency downshifted harmonic signal. The lateral beam profile for the 20 MHz ring elements at the focus matched the Field II simulated results well, and the effect of outer ring diameter was also examined. Images of a posterior segment of an excised pig eye and a choroidal nevus of human eye were obtained both for single element and dual element transducers and compared to demonstrate the advantages of dual element harmonic imaging.

Kim, Hyung Ham; Cannata, Jonathan M.; Liu, Ruibin; Chang, Jin Ho; Silverman, Ronald H.; Shung, K. Kirk

2009-01-01

8

20 MHz/40 MHz dual element transducers for high frequency harmonic imaging.  

PubMed

Concentric annular type dual element transducers for second harmonic imaging at 20 MHz / 40 MHz were designed and fabricated to improve spatial resolution and depth of penetration for ophthalmic imaging applications. The outer ring element was designed to transmit the 20 MHz signal and the inner circular element was designed to receive the 40 MHz second harmonic signal. Lithium niobate (LiNbO(3)), with its low dielectric constant, was used as the piezoelectric material to achieve good electrical impedance matching. Double matching layers and conductive backing were used and optimized by KLM modeling to achieve high sensitivity and wide bandwidth for harmonic imaging and superior time-domain characteristics. Prototype transducers were fabricated and evaluated quantitatively and clinically. The average measured center frequency for the transmit ring element was 21 MHz and the one-way --3 dB bandwidth was greater than 50%. The 40 MHz receive element functioned at 31 MHz center frequency with acceptable bandwidth to receive attenuated and frequency downshifted harmonic signal. The lateral beam profile for the 20 MHz ring elements at the focus matched the Field II simulated results well, and the effect of outer ring diameter was also examined. Images of a posterior segment of an excised pig eye and a choroidal nevus of human eye were obtained both for single element and dual element transducers and compared to demonstrate the advantages of dual element harmonic imaging. PMID:19126492

Kim, Hyung Ham; Cannata, Jonathan M; Liu, Ruibin; Chang, Jin Ho; Silverman, Ronald H; Shung, K Kirk

2008-12-01

9

Frequency domain 3D simplified spherical harmonics approximation: development, validation, and implication in bioluminescence imaging  

NASA Astrophysics Data System (ADS)

A three dimensional (3D) photon transport model has been developed based on the frequency domain simplified spherical harmonics approximation (SPN) to the Radiative Transport Equation. Based on preliminary Monte Carlo studies, it is shown that for problems exhibiting strong absorption, the solutions using the 7th order SPN model (N = 7) are significantly more accurate than those from a standard Diffusion (SP1) based solver. This advance is of particular interest in the field of bioluminescent imaging where the peak emission of light emitting molecular markers are closer to the visible range (500 - 650 nm) corresponding to strong absorption due to hemoglobin.

Chu, M.; Klose, A. D.; Styles, I. B.; Vishwanath, K.; Dehghani, H.

2009-02-01

10

A parallel adaptive finite element simplified spherical harmonics approximation solver for frequency domain fluorescence molecular imaging.  

PubMed

Fluorescence molecular imaging/tomography may play an important future role in preclinical research and clinical diagnostics. Time- and frequency-domain fluorescence imaging can acquire more measurement information than the continuous wave (CW) counterpart, improving the image quality of fluorescence molecular tomography. Although diffusion approximation (DA) theory has been extensively applied in optical molecular imaging, high-order photon migration models need to be further investigated to match quantitation provided by nuclear imaging. In this paper, a frequency-domain parallel adaptive finite element solver is developed with simplified spherical harmonics (SP(N)) approximations. To fully evaluate the performance of the SP(N) approximations, a fast time-resolved tetrahedron-based Monte Carlo fluorescence simulator suitable for complex heterogeneous geometries is developed using a convolution strategy to realize the simulation of the fluorescence excitation and emission. The validation results show that high-order SP(N) can effectively correct the modeling errors of the diffusion equation, especially when the tissues have high absorption characteristics or when high modulation frequency measurements are used. Furthermore, the parallel adaptive mesh evolution strategy improves the modeling precision and the simulation speed significantly on a realistic digital mouse phantom. This solver is a promising platform for fluorescence molecular tomography using high-order approximations to the radiative transfer equation. PMID:20671350

Lu, Yujie; Zhu, Banghe; Shen, Haiou; Rasmussen, John C; Wang, Ge; Sevick-Muraca, Eva M

2010-07-30

11

P3P-2 Dual Element Transducers for High Frequency Harmonic Imaging  

Microsoft Academic Search

Concentric annular type dual element transducers for second harmonic imaging at 20 MHz \\/ 40 MHz were designed and fabricated to improve spatial resolution with sufficient penetration for ophthalmic imaging applications. The outer ring element was designed to transmit the 20 MHz signal and the inner element was designed to receive the 40 MHz second harmonic signal. Lithium niobate (LiNbO3)

H. H. Kim; J. M. Cannata; R. Liu; L. Sun; K. K. Shung; R. H. Silverman; S. Babar

2006-01-01

12

20 MHz\\/40 MHz dual element transducers for high frequency harmonic imaging  

Microsoft Academic Search

Concentric annular type dual element transducers for second harmonic imaging at 20 MHz \\/ 40 MHz were designed and fabricated to improve spatial resolution and depth of penetration for ophthalmic imaging applications. The outer ring element was designed to transmit the 20 MHz signal and the inner circular element was designed to receive the 40 MHz second harmonic signal. Lithium

Hyung Kim; J. Cannata; R. Liu; Jin Chang; R. Silverman; K. Shung

2008-01-01

13

Color harmonization for images  

NASA Astrophysics Data System (ADS)

Color harmonization is an artistic technique to adjust a set of colors in order to enhance their visual harmony so that they are aesthetically pleasing in terms of human visual perception. We present a new color harmonization method that treats the harmonization as a function optimization. For a given image, we derive a cost function based on the observation that pixels in a small window that have similar unharmonic hues should be harmonized with similar harmonic hues. By minimizing the cost function, we get a harmonized image in which the spatial coherence is preserved. A new matching function is proposed to select the best matching harmonic schemes, and a new component-based preharmonization strategy is proposed to preserve the hue distribution of the harmonized images. Our approach overcomes several shortcomings of the existing color harmonization methods. We test our algorithm with a variety of images to demonstrate the effectiveness of our approach.

Tang, Zhen; Miao, Zhenjiang; Wan, Yanli; Wang, Zhifei

2011-04-01

14

Optimization of a phased-array transducer for multiple harmonic imaging in medical applications: frequency and topology.  

PubMed

Second-harmonic imaging is currently one of the standards in commercial echographic systems for diagnosis, because of its high spatial resolution and low sensitivity to clutter and near-field artifacts. The use of nonlinear phenomena mirrors is a great set of solutions to improve echographic image resolution. To further enhance the resolution and image quality, the combination of the 3rd to 5th harmonics--dubbed the superharmonics--could be used. However, this requires a bandwidth exceeding that of conventional transducers. A promising solution features a phased-array design with interleaved low- and high-frequency elements for transmission and reception, respectively. Because the amplitude of the backscattered higher harmonics at the transducer surface is relatively low, it is highly desirable to increase the sensitivity in reception. Therefore, we investigated the optimization of the number of elements in the receiving aperture as well as their arrangement (topology). A variety of configurations was considered, including one transmit element for each receive element (1/2) up to one transmit for 7 receive elements (1/8). The topologies are assessed based on the ratio of the harmonic peak pressures in the main and grating lobes. Further, the higher harmonic level is maximized by optimization of the center frequency of the transmitted pulse. The achievable SNR for a specific application is a compromise between the frequency-dependent attenuation and nonlinearity at a required penetration depth. To calculate the SNR of the complete imaging chain, we use an approach analogous to the sonar equation used in underwater acoustics. The generated harmonic pressure fields caused by nonlinear wave propagation were modeled with the iterative nonlinear contrast source (INCS) method, the KZK, or the Burger's equation. The optimal topology for superharmonic imaging was an interleaved design with 1 transmit element per 6 receive elements. It improves the SNR by ~5 dB compared with the interleaved (1/2) design reported in literature. The optimal transmit frequency for superharmonic echocardiography was found to be 1.0 to 1.2 MHz. For superharmonic abdominal imaging this frequency was found to be 1.7 to 1.9 MHz. For 2nd-harmonic echocardiography, the optimal transmit frequency of 1.8 MHz reported in the literature was corroborated with our simulation results. PMID:21429845

Matte, Guillaume M; Van Neer, Paul L M J; Danilouchkine, Mike G; Huijssen, Jacob; Verweij, Martin D; de Jong, Nico

2011-03-01

15

Imaging elastic properties of biological tissues by low-frequency harmonic vibration  

Microsoft Academic Search

The elastic properties of soft tissues are closely related to their structure, biological conditions, and pathology. For years, physicians have used palpation as a crude elasticity measurement tool to diagnose diseases in the human body. Based on this simple concept, but using modern technology, several elasticity imaging schemes have been developed during the past two decades. In this paper, we

Mostafa Fatemi; Armando Manduca; James F. Greenleaf

2003-01-01

16

Development of high frequency, cyclotron harmonic gyrotron oscillator  

Microsoft Academic Search

The oscillation results of a high frequency gyrotron which operates at the fundamental cyctron frequency and its higher harmonics (s=1, 2, 3) are described. The fairly high frequency of 220 GHz (corresponding wave length 1.35 mm) has been achieved at the fundamental and second harmonic of the cyclotron frequency. The scaling law of output power to harmonic number s is

Toshitaka Idehara; Toshiaki Tatsukawa; Satoru Matsumoto; Kohji Kunieda; Kazuhisa Hemmi; Tomohiro Kanemaki

1988-01-01

17

Fully parallel adaptive finite element simulation using the simplified spherical harmonics approximations for frequency-domain fluorescence-enhanced optical imaging  

NASA Astrophysics Data System (ADS)

Fluorescence-enhanced optical imaging/tomography may play an important role in preclinical research and clinical diagnostics as a type of optical molecular. Time- and frequency-domain measurement can acquire more measurement information, reducing the ill-posedness and improving the reconstruction quality of fluorescence-enhanced optical tomography. Although the diffusion approximation (DA) theory has been extensively in optical imaging, high-order photon migration models must be further investigated for application to complex and small tissue volumes. In this paper, a frequency-domain fully parallel adaptive finite element solver is developed with the simplified spherical harmonics (SPN) approximations. To fully evaluate the performance of the SPN approximations, a fast tetrahedron-based Monte Carlo simulator suitable for complex heterogeneous geometries is developed using the convolution strategy to realize the simulation of the fluorescence excitation and emission. With simple and real digital mouse phantoms, the results show that the significant precision and speed improvements are obtained from the parallel adaptive mesh evolution strategy.

Lu, Yujie; Zhu, Banghe; Shen, Haiou; Rasmussen, John C.; Wang, Ge; Sevick-Muraca, Eva M.

2011-02-01

18

Relations between harmonic frequencies of diatomic molecules.  

PubMed

The relations between the harmonic frequencies of different molecules are revealed with the aid of the spring constants of atoms in molecules. Using the atomic spring constants in the related molecules, the force constants for a new molecule can be estimated. The simplest scheme to obtain the force constant of a given molecule is similar to a simple chemical reaction formula, such as A(2) + B(2) ? AB, and the corresponding relation between the molecular force constants is k(AB)(-1) = (2k(A(2)))(-1) + (2k(B(2)))(-1). For a given molecule, one can design numerous schemes to obtain its force constant from the atomic spring constants in other molecules. A high degree of periodical regularity appears in the application of different kinds of schemes to the ground states. The reliable schemes for the ground electronic states can be adopted for the excited states. Over two hundred molecules with experimental data available for comparison have been tested. The discrepancies between the calculated and the experimental harmonic frequencies can reach 1% and better; the results show that the present approach is simple in theory and handy to use. The harmonic frequencies for dozens of hetero-nuclear molecules of the transition-metal elements are also predicted. PMID:23223638

Hou, Shilin

2013-01-28

19

Harmonic Image Reconstruction Assisted by a Nonlinear Metmaterial Surface  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate a microwave far-field image reconstruction modality with the transverse resolution exceeding the diffraction limit by using a single layer of highly nonlinear metamaterial. The harmonic fields of the nonlinear metamaterial surface allow the far-field propagation of wave fronts with spatial frequencies several times higher than that of the fundamental field. Near-field images can thus be mathematically recovered from the far-field patterns of the harmonic fields.

Wang, Zhiyu; Luo, Yu; Jiang, Tao; Wang, Zheng; Huangfu, Jiangtao; Ran, Lixin

2011-01-01

20

Analysis of high frequency partials in Bayesian harmonic model  

Microsoft Academic Search

Bayesian harmonic modeling and parameters estimation is a new approach in audio signal synthesizing. However current Bayesian harmonic modeling canpsilat effectively extract high frequency partials. In this paper we propose an improved model with parameters of high frequency partials for audio signal with harmonic modeling. We estimate partials in a Bayesian framework with the prior knowledge and likelihood function of

Jinghua Yan; Hui Wang; Chuanzhen Li; Qin Zhang

2008-01-01

21

THERMAL WAVE IMAGING USING HARMONIC DETECTION OF THE PHOTOACOUSTIC SIGNAL  

Microsoft Academic Search

We describe a thermal wave imaging system based on gas-microphone detection of the harmonic component of the photoacoustic (PA) signal. In this system the sample is excited by a laser beam modulated at a frequency ƒ and the detection of the associated thermal wave field is carried out at a frequency 2ƒ. The technique demonstrates lateral resolution comparable to conventional

S. B. PERALTA; H. H. AL-KHAFAJI; A. W. WILLIAMS

1991-01-01

22

Narrow size distribution of microbubbles for enhancement of harmonic imaging.  

PubMed

An ultrasound microbubble contrast agent is a promising technique in clinical diagnosis because ultrasound in combination with microbubbles enhances the ultrasound backscatter to produce an increased contrast images. In this study, we developed phospholipid-based microbubbles showing a relatively narrow size distribution of 0.8-1.3 microm. The optimal resonance frequency of developed microbubbles was determined to be 2.5-3.0 MHz by measuring echo signals at various frequencies. Ultrasound harmonic imaging was performed in a vessel phantom at the optimal resonance frequencies. Microbubble contrast-enhanced ultrasound images visualized a vessel tube clearly and demonstrated much improved image quality, compared to the control. In conclusion, the ultrasonography in the harmonic mode is capable of maximally resonating micrbubbles with a narrow size distribution at a specific frequency for enhanced ultrasound imaging. PMID:23802414

Moon, Hyungwon; Yu, Jaesok; Park, Sunyoung; Chang, Jin Ho; Song, Tai-Kyong; Kim, Hyuncheol

2013-05-01

23

Reduced Switching Frequency Active Harmonic Elimination for Multilevel Converters  

SciTech Connect

This paper presents a reduced switching-frequency active-harmonic-elimination method (RAHEM) to eliminate any number of specific order harmonics of multilevel converters. First, resultant theory is applied to transcendental equations to eliminate low-order harmonics and to determine switching angles for a fundamental frequency-switching scheme. Next, based on the number of harmonics to be eliminated, Newton climbing method is applied to transcendental equations to eliminate high-order harmonics and to determine switching angles for the fundamental frequency-switching scheme. Third, the magnitudes and phases of the residual lower order harmonics are computed, generated, and subtracted from the original voltage waveform to eliminate these low-order harmonics. Compared to the active-harmonic-elimination method (AHEM), which generates square waves to cancel high-order harmonics, RAHEM has lower switching frequency. The simulation results show that the method can effectively eliminate all the specific harmonics, and a low total harmonic distortion (THD) near sine wave is produced. An experimental 11-level H-bridge multilevel converter with a field-programmable gate-array controller is employed to experimentally validate the method. The experimental results show that RAHEM does effectively eliminate any number of specific harmonics, and the output voltage waveform has low switching frequency and low THD.

Du, Zhong [ORNL; Tolbert, Leon M [ORNL; Chiasson, John N [ORNL; Ozpineci, Burak [ORNL

2008-01-01

24

Design of chirp excitation waveform for dual-frequency harmonic contrast detection.  

PubMed

Tissue background suppression is essential for harmonic detection of ultrasonic contrast microbubbles. To reduce the tissue harmonic amplitude for improvement of contrast-to-tissue ratio (CTR), the method of third harmonic (3f(0)) transmit phasing uses an additional 3f(0) transmit signal to provide mutual cancellation between the frequency-sum component and the frequency-difference component of tissue harmonic signal. Chirp excitation can further improve the SNR in harmonic imaging without requiring an excessive transmit pressure and thus reduce potential bubble destruction. However, for effective suppression of tissue harmonic background in 3f(0) transmit phasing, the 3f(0) chirp waveform has to be carefully designed for the generation of spectrally matched cancellation pairs over the entire second harmonic band. In this study, we proposed a chirp waveform suitable for the method of 3f(0) transmit phasing, the different-bandwidth chirp signal (DBCS). With the DBCS waveform, the frequency-difference component of tissue harmonic signal becomes a chirp signal similar to its frequency-sum counterpart. Thus, the combination of the DBCS waveform with the 3f(0) transmit phasing can markedly suppress the tissue harmonic amplitude for CTR improvement together with effective SNR increase of contrast harmonic signal. Our results indicate that, as compared with the conventional Gaussian pulse, the DBCS waveform can provide 6-dB improvement of SNR in 3f(0) transmit phasing with a CTR increase of 3 dB. Nevertheless, the limitation of available transmit bandwidth and the frequency-dependent attenuation can degrade the performance of the DBCS waveform in tissue suppression. The design of the DBCS waveform is also applicable to other dual-frequency imaging techniques that rely on the harmonic generation at the difference frequency. PMID:19942507

Shen, Che-Chou; Chiu, Yi-Yuan

2009-10-01

25

A 20-40 MHz ultrasound transducer for intravascular harmonic imaging  

Microsoft Academic Search

Recent studies have suggested the feasibility of tissue harmonic imaging (THI) with intravascular ultrasound (IVUS). This paper describes the design, fabrication and characterization of a piezoelectric transducer optimized for tissue harmonic IVUS. Ideally, such a transducer should efficiently transmit a short acoustic pulse at the fundamental transmission frequency and should be sensitive to its second harmonic echo, for which we

H. J. Vos; M. E. Frijlink; E. Droog; D. E. Goertz; G. Blacquiere; A. Gisolf; N. De Jong

2004-01-01

26

Dark-field third-harmonic imaging  

NASA Astrophysics Data System (ADS)

Coherent cancellation of third-harmonic generation (THG) in a tightly focused laser beam is shown to enable a label-free imaging of individual neurons in representative brain tissues. The intrinsic coherence of third-harmonic buildup and cancellation combined with the nonlinear nature of the process enhances the locality of the dark signal in THG, translating into a remarkable sharpness of dark-field THG images. Unique advantages of this technique for high-contrast subcellular-resolution neuroimaging are demonstrated by comparing THG images of hippocampus and somatosensory cortex in a mouse brain with images visualizing fluorescent protein biomarkers.

Doronina-Amitonova, L. V.; Lanin, A. A.; Fedotov, I. V.; Ivashkina, O. I.; Zots, M. A.; Fedotov, A. B.; Anokhin, K. V.; Zheltikov, A. M.

2013-08-01

27

Perfusion harmonic imaging of the human brain  

NASA Astrophysics Data System (ADS)

The fast visualisation of cerebral microcirculation supports diagnosis of acute cerebrovascular diseases. However, the commonly used CT/MRI-based methods are time consuming and, moreover, costly. Therefore we propose an alternative approach to brain perfusion imaging by means of ultrasonography. In spite of the low signal/noise-ratio of transcranial ultrasound and the high impedance of the skull, flow images of cerebral blood flow can be derived by capturing the kinetics of appropriate contrast agents by harmonic ultrasound image sequences. In this paper we propose three different methods for human brain perfusion imaging, each of which yielding flow images indicating the status of the patient's cerebral microcirculation by visualising local flow parameters. Bolus harmonic imaging (BHI) displays the flow kinetics of bolus injections, while replenishment (RHI) and diminution harmonic imaging (DHI) compute flow characteristics from contrast agent continuous infusions. RHI measures the contrast agents kinetics in the influx phase and DHI displays the diminution kinetics of the contrast agent acquired from the decay phase. In clinical studies, BHI- and RHI-parameter images were found to represent comprehensive and reproducible distributions of physiological cerebral blood flow. For DHI it is shown, that bubble destruction and hence perfusion phenomena principally can be displayed. Generally, perfusion harmonic imaging enables reliable and fast bedside imaging of human brain perfusion. Due to its cost efficiency it complements cerebrovascular diagnostics by established CT/MRI-based methods.

Metzler, Volker H.; Seidel, Guenter; Wiesmann, Martin; Meyer, Karsten; Aach, Til

2003-05-01

28

Harmonic holography for three-dimensional cellular imaging  

NASA Astrophysics Data System (ADS)

Luminescent markers play a key role in imaging techniques for life sciences since they provide a contrast mechanism between signal and background. We describe a new type of marker using second harmonic generation (SHG) from noncentrosymmetric BaTiO3 nanocrystals. These nanoparticles are attractive due to their stable, non-saturating and coherent signal with a femtosecond-scale response time and a broad flexibility in the choice of excitation wavelength. We use the coherent SHG signal from BaTiO3 nanoparticles for three-dimensional (3D) imaging without scanning. We built a harmonic holographic (H2) microscope which records digital holograms at the second harmonic frequency. Highresolution 3D distributions of these SHG markers in mammalian cells are successfully captured and interpreted by the H2 microscope.

Hsieh, Chia-Lung; Grange, Rachel; Pu, Ye; Psaltis, Demetri

2009-05-01

29

Frequency-resolved optical grating using third-harmonic generation  

SciTech Connect

We demonstrate the first frequency-resolved optical gating measurement of an laser oscillator without the time ambiguity using third-harmonic generation. The experiment agrees well with the phase-retrieved spectrograms.

Tsang, T. [Brookhaven National Laboratory, Upton, NY (United States); Krumbuegel, M.A.; Delong, K.W. [Sandia National Laboratories, Livermore, CA (United States)] [and others

1995-12-01

30

Harmonic emission from high-power high-frequency gyrotrons  

Microsoft Academic Search

The results of a study of second-harmonic emission from a gyrotron designed for high-power high-frequency operation at the fundamental of the cyclotron frequency are presented. Stable, very narrow bandwidth second-harmonic cavity emission from 209 GHz to 302 GHz has been observed. An output power of 25 kW and efficiency of 6·5% in the TE11, 2, 1, mode at 241 GHz

J. L. BYERLY; B. G. DANLY; K. E. KREISCHER; R. J. TEMKIN; W. J. MULLIGAN; P. WOSKOBOINIKOW

1984-01-01

31

Transducer for harmonic intravascular ultrasound imaging  

Microsoft Academic Search

A recent study has shown the feasibility of tissue harmonic imaging (THI) using an intravascular ultrasound (IVUS) transducer. This correspondence describes the design, fabrication, and characterization of a THI-optimized piezoelectric transducer with oval aperture of 0.75 mm by 1 mm. The transducer operated at 20 MHz and 40 MHz, and was comprised of a single piezoelectric layer with additional passive

Hendrik J. Vos; Martijn E. Frijlink; Erik Droog; David E. Goertz; Gerrit Blacquiere; Anton Gisolf; Jong de Nico; A. F. W. van der Steern

2005-01-01

32

Frequency division multiplexed imaging  

NASA Astrophysics Data System (ADS)

In this paper, we describe frequency division multiplexed imaging (FDMI), where multiple images are captured simultaneously in a single shot and can later be extracted from the multiplexed image. This is achieved by spatially modulating the images so that they are placed at different locations in the Fourier domain. The technique assumes that the images are band-limited and they are placed at non-overlapping frequency regions through the modulation process. The FDMI technique can be used for extracting sub-exposure information and in applications where multiple cameras or captures are needed, such as high-dynamic-range and stereo imaging. We present experimental results to illustrate the FDMI idea.

Gunturk, Bahadir K.; Feldman, Martin

2013-01-01

33

Qualitative and quantitative effects of harmonic echocardiographic imaging on endocardial edge definition and side-lobe artifacts  

Microsoft Academic Search

Harmonic imaging is a new ultrasonographic technique that is designed to improve image quality by exploiting the spontaneous generation of higher frequencies as ultrasound propagates through tissue. We studied 51 difficult-to-image patients with blinded side-by-side cineloop evaluation of endocardial border definition by harmonic versus fundamental imaging. In addition, quantitative intensities from cavity versus wall were compared for harmonic versus fundamental

David N. Rubin; Naji Yazbek; Mario J. Garcia; William J. Stewart; James D. Thomas

2000-01-01

34

A split-frequency harmonic balance method for nonlinear oscillators with multi-harmonic forcing  

NASA Astrophysics Data System (ADS)

A new harmonic balance method (HBM) is presented for accurately computing the periodic responses of a nonlinear sdof oscillator with multi-harmonic forcing and non-expansible nonlinearities. The presence of multi-harmonic forcing requires a large number of solution harmonics with a substantial increase in computational demand for either the conventional or the incremental HBM. In this method, the oscillator equation-error is first defined in terms of two functions (originally proposed for obtaining free-vibration periods in: R.E. Mickens, Iteration procedure for determining approximate solutions to nonlinear oscillator equations, Journal of Sound and Vibration 116 (1987) 185 187; and more recently: R.E. Mickens, A Generalised iteration procedure for calculating approximations to periodic solutions of “truly nonlinear oscillations”, Journal of Sound and Vibration 287 (2005) 1045 1051). A Fourier series solution is assumed, in which the total number of harmonics is fixed by the chosen discrete-time interval—this series is split into two partial sums nominally associated with either low-frequency or high-frequency harmonics. By exploiting a convergence property of the equation-error functions, the total solution is obtained in a new iterative scheme in which the low-frequency components are computed via a conventional HBM using a small number of algebraic equations, whereas the high frequency components are obtained in a separate step by updating. By gradually increasing the number of harmonics in the low-frequency group, the equation-error can be progressively reduced. Efficient use is made of FFT-based algebraic equation generation which allows an important class of non-expansible nonlinearities to be handled. The proposed method is tested on a Duffing-type oscillator, and an oscillator with a non-expansible 7th power stiffness term, where in both cases up to 24 component multi-harmonic forcing is applied. As a comparison, a conventional HBM is also used on the Duffing model in which the algebraic equations are generated in symbolic form to totally avoid errors from entering the formulation through complicated expansion of the cubic stiffness term (as in: I. Senjanovi?, Harmonic analysis of nonlinear oscillations of cubic dynamical systems, Journal of Ship Research 38 (3) (1994) 225 238; and in: A. Raghothama, S. Narayanan, Periodic response and chaos in nonlinear systems with parametric excitation and time delay, Nonlinear dynamics 27 (2002) 341 365). The paper shows that in obtaining period-1 solutions, the computational accuracy and efficiency of the proposed method is very good.

Dunne, J. F.; Hayward, P.

2006-08-01

35

Lens-less surface second harmonic imaging  

PubMed Central

Lens-less surface second harmonic generation imaging (SSHGI) is used to image an SHG active molecule, (S)-( + )-1,1’-bi-2-naphthol (SBN), incorporated into a lipid bilayer patterned with the 1951 United States Air Force resolution test target. Data show the coherent plane-wave nature of SHG allows direct imaging without the aid of a lens system. Lens-less SSHGI readily resolves line-widths as small as 223 ?m at an object-image distance of 7.6 cm and line-widths of 397 ?m at distances as far as 30 cm. Lens-less SSHGI simplifies the detection method, raises photon collection efficiency, and expands the field-of-view. These advantages allow greater throughput and make lens-less SSHGI a potentially valuable detection method for biosensors and medical diagnostics.

Sly, Krystal L.; Nguyen, Trang T.; Conboy, John C.

2012-01-01

36

Lens-less surface second harmonic imaging.  

PubMed

Lens-less surface second harmonic generation imaging (SSHGI) is used to image an SHG active molecule, (S)-(+)-1,1'-bi-2-naphthol (SBN), incorporated into a lipid bilayer patterned with the 1951 United States Air Force resolution test target. Data show the coherent plane-wave nature of SHG allows direct imaging without the aid of a lens system. Lens-less SSHGI readily resolves line-widths as small as 223 ?m at an object-image distance of 7.6 cm and line-widths of 397 ?m at distances as far as 30 cm. Lens-less SSHGI simplifies the detection method, raises photon collection efficiency, and expands the field-of-view. These advantages allow greater throughput and make lens-less SSHGI a potentially valuable detection method for biosensors and medical diagnostics. PMID:23037346

Sly, Krystal L; Nguyen, Trang T; Conboy, John C

2012-09-24

37

Effect of leakage inductance on high frequency transformer harmonics  

Microsoft Academic Search

Nowadays, switching power supplies are used in almost all electronic devices to regulate the voltage amplitude. The only obstacle on using these devices is the production of high frequency harmonics that violates different standards such as (FCC, VDE, 461). In this paper the sources of various noises in switching power supplies will be introduced. Then, using appropriate model for high

Babak Abdi; Mohammad Hadi Joukar; Amir Hossein Ranjbar

2009-01-01

38

Multi-Frequency Harmonics Technique for HIFU Tissue Treatment  

NASA Astrophysics Data System (ADS)

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.

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

2010-03-01

39

Harmonic models of shape transformations in digital images and patterns  

Microsoft Academic Search

A harmonic model of shape transformations is presented. In this model, harmonic functions are governed by the Laplace equation. This model can convert all image or a pattern to another with arbitrary shapes. The transformation process is harmonic, without abruptness and discontinuity. This model can be used to generate and recognize handwritten Roman letters and Chinese characters, fingerprints, and other

Z. C. Li; C. Y. Suen; T. D. Bui; Q. L. Gu

1990-01-01

40

GENERAL: Stability Analysis of an Inverted Pendulum Subjected to Combined High Frequency Harmonics and Stochastic Excitations  

Microsoft Academic Search

Stability of vertical upright position of an inverted pendulum with its suspension point subjected to high frequency harmonics and stochastic excitations is investigated. Two classes of excitations, i.e., combined high frequency harmonic excitation and Gaussian white noise excitation, and high frequency bounded noise excitation, respectively, are considered. Firstly, the terms of high frequency harmonic excitations in the equation of motion

Zhi-Long Huang; Xiao-Ling Jin; Zi-Qi Zhu

2008-01-01

41

Perceptual learning of fundamental frequency discrimination: effects of fundamental frequency, harmonic number, and component phase.  

PubMed

Thresholds (F0DLs) were measured for discrimination of the fundamental frequency (F0) of a group of harmonics (group B) embedded in harmonics with a fixed F0. Miyazono and Moore [(2009). Acoust. Sci. & Tech. 30, 383386] found a large training effect for tones with high harmonics in group B, when the harmonics were added in cosine phase. It is shown here that this effect was due to use of a cue related to pitch pulse asynchrony (PPA). When PPA cues were disrupted by introducing a temporal offset between the envelope peaks of the harmonics in group B and the remaining harmonics, F0DLs increased markedly. Perceptual learning was examined using a training stimulus with cosine-phase harmonics, F0 = 50 Hz, and high harmonics in group B, under conditions where PPA was not useful. Learning occurred, and it transferred to other cosine-phase tones, but not to random-phase tones. A similar experiment with F0 = 100 Hz showed a learning effect which transferred to a cosine-phase tone with mainly high unresolved harmonics, but not to cosine-phase tones with low harmonics, and not to random-phase tones. The learning found here appears to be specific to tones for which F0 discrimination is based on distinct peaks in the temporal envelope. PMID:21218897

Miyazono, Hiromitsu; Glasberg, Brian R; Moore, Brian C J

2010-12-01

42

Second Harmonic Generation Imaging Microscopy: Applications to Diseases Diagnostics  

PubMed Central

Second Harmonic Generation microscopy has emerged as a powerful new optical imaging modality. This Feature describes its chemical and physical principles and highlights current applications in disease diagnostics.

Campagnola, Paul

2011-01-01

43

On the feasibility of real-time, in vivo harmonic imaging with proteinaceous microspheres.  

PubMed

Harmonic imaging is a new contrast-specific imaging modality, which utilizes the nonlinear properties of microbubble-based sonographic contrast agents by transmitting at the fundamental frequency but receiving at the second harmonic frequency. The feasibility of improving the detection of slow, small-volume blood flow using real-time harmonic imaging has been investigated in vivo. Proteinaceous microspheres (FS069) were administrated to four dogs, two woodchucks (with multiple hepatomas), and one rabbit. Three different scanners were used to obtain real-time images of kidneys and liver (including vessels) in harmonic and conventional gray scale and color flow modes. The duration of contrast enhancement lasted significantly longer in harmonic than in conventional modes (on average 87 s; P = 0.008). Harmonic images were less susceptible to artifacts, such as acoustic shadowing, and a clear increase in the (flow) signal-to-noise ratio was observed. These preliminary in vivo results demonstrate the feasibility of performing real-time, contrast-enhanced harmonic imaging, but further studies are required to establish clinical efficacy. PMID:8947861

Forsberg, F; Goldberg, B B; Liu, J B; Merton, D A; Rawool, N M

1996-12-01

44

Investigation of transmit and receive performance at the fundamental and third harmonic resonance frequency of a medical ultrasound transducer.  

PubMed

In this study, the phenomenon of higher harmonic thickness resonance of a piezoelectric transducer was used to investigate potentially additional sensitivity at the third harmonic frequency for conventional medical transducers. The motivation for this research is that some applications in medical ultrasound (e.g. third harmonic transmit phasing and contrast imaging) need probes which are sensitive around both the fundamental and third harmonic frequencies, and that these higher harmonic thickness modes, although often considered as undesired, might be used beneficially. The novelty aspect in this study is the presented transmit and receive potential at both the fundamental and third harmonic of a conventional cardiac probe with modified electrical tuning. Elements of an experimental PZT-based phased-array probe (f(c)=3 MHz, 64 elements, element width=0.3mm, elevation aperture=13 mm) were electrically retuned with series inductors around the third harmonic resonance frequency at 10 MHz. Hydrophone measurements with 10-MHz-tuned elements showed that, as compared to a conventionally tuned element, the transmit transfer function at the third harmonic increased more than 23 dB, while the sensitivity at the fundamental frequency was only 6 dB lower. Pulse-echo measurements showed that the two-way transfer function of a 10-MHz-tuned element resulted in 20 dB increased sensitivity around the third harmonic as compared to an untuned element. Simulated transfer functions, from both a 1D KLM and 2D finite element model of an element of the experimental array transducer, confirmed the measured sensitivity peaks at the fundamental and third harmonic. In conclusion, this study demonstrated the effect of changing the electrical tuning on a conventional array transducer which increased the sensitivity around the third harmonic resonance frequency, while maintaining good sensitivity at the fundamental frequency. PMID:19403153

Frijlink, Martijn E; Løvstakken, Lasse; Torp, Hans

2009-04-07

45

A high frequency harmonic VCO with an artificial varactor  

Microsoft Academic Search

A tunable LC-oscillator utilising an artificial varactor is presented in this paper. The proposed variable capacitor is based on the well-known Miller effect. A theoretical model is developed to study the capacitance tuning range and the corresponding Q-value. Most radio frequency harmonic voltage-controlled oscillators are tuned by changing the capacitance of a pn-junction diode. The inadequate capacitance tuning range of

Kari Stadius; Risto Kaunisto; Veikko Porra

1998-01-01

46

Status of a high-frequency harmonic amplifier's development  

Microsoft Academic Search

The harmonic amplifier (HARA) is a very compact, high efficiency amplifier that has been under development at Microwave Technologies in the past few years. The HARA uses a two-cavity system in conjunction with a spiraling beam to produce high-frequency radiation. In this paper we will review C-band, Ka-band and W-band HARA experiments currently underway at Microwave Technologies. We will also

J. E. Velazco; P. H. Ceperley

2002-01-01

47

Transducer for harmonic intravascular ultrasound imaging.  

PubMed

A recent study has shown the feasibility of tissue harmonic imaging (THI) using an intravascular ultrasound (IVUS) transducer. This correspondence describes the design, fabrication, and characterization of a THI-optimized piezoelectric transducer with oval aperture of 0.75 mm by 1 mm. The transducer operated at 20 MHz and 40 MHz, and was comprised of a single piezoelectric layer with additional passive layers. The Krimholtz-Leedom-Matthaei (KLM) model was used to iteratively find optimal material properties of the different layers. The transducer characterization showed -6 dB fractional bandwidths of 30% and 25%, and two-way insertion losses of -20 dB and -36 dB, respectively. PMID:16463509

Vos, Hendrik J; Frijlink, Martijn E; Droog, Erik; Goertz, David E; Blacquière, Gerrit; Gisolf, Anton; de Jong, Nico; van der Steen, Antonius F W

2005-12-01

48

Harmonic nanoparticles for nonlinar bio-imaging and detection  

NASA Astrophysics Data System (ADS)

In this contribution we present the motivations underlying the introduction of harmonic nanoparticles, i.e. second harmonic contrast agents for nonlinear microscopy. Their properties will be discussed in the light of various biological applications including imaging of stem cells and rare event detection in physiological media.

Bonacina, Luigi; Magouroux, Thibaud; Rogov, Andrii; Staedler, Davide; Joulaud, Cécile; Schwung, Sebastian; Passemard, Solène; Le dantec, Ronan; Mugnier, Yannick; Rytz, Daniel; Gerber-Lemaire, Sandrine; Wolf, Jean-Pierre

2013-03-01

49

Efficient broadband third harmonic frequency conversion via angular dispersion  

SciTech Connect

In this paper we present experimental measurements and theoretical modeling of third harmonic (3{omega}) conversion efficiency with optical bandwidth. Third harmonic conversion efficiency drops precipitously as the input bandwidth significantly exceeds the phase matching limitations of the conversion crystals. For Type I/Type II frequency tripling, conversion efficiency be-gins to decrease for bandwidths greater than {approximately}60 GHz. However, conversion efficiency corresponding to monochromatic phase-matched beams can be recovered provided that the instantaneous Propagation vectors are phase matched at all times. This is achieved by imposing angular spectral dispersion (ASD) on the input beam via a diffraction grating, with a dispersion such that the phase mismatch for each frequency is zero. Experiments were performed on the Optical Sciences Laser (OSL), a 1--100 J class laser at LLNL. These experiments used a 200 GHz bandwidth source produced by a multipassed electro-optic phase modulator. The spectrum produced was composed of discrete frequency components spaced at 3 GHz intervals. Angular dispersion was incorporated by the addition of a 1200 gr/mm diffraction grating oriented at the Littrow angle, and capable of rotation about the beam direction. Experiments were performed with a pulse length of 1-ns and a 1{omega} input intensity of {approximately} 4 GW/cm{sup 2} for near optimal dispersion for phase matching, 5.2 {mu}rad/GHz, with 0.1, 60, and 155 GHz bandwidth, as well as for partial dispersion compensation, 1.66 {mu}rad/GHz, with 155 GHz and 0.1 GHz bandwidth. The direction of dispersion was varied incrementally 360{degrees} about the beam diameter. The addition of the grating to the beamline reduced the narrowband conversion efficiency by approximately 10%.

Pennington, D.M.; Henesian, M.A.; Milam, D.; Eimerl, D.

1995-07-18

50

Development of a high-frequency, second-harmonic gyrotron tunable up to 636 GHz  

Microsoft Academic Search

A high-frequency, second-harmonic gyrotron using a 12 T superconducting magnet is described. It has achieved a maximum frequency of 636 GHz (corresponding to a wavelength of 472 microns). Operating at both the fundamental and the second harmonic of the electron cyclotron frequency enables the gyrotron to act as a high power (several 100 W), step tunable, millimeter to submillimeter wave

T. Idehara; T. Tatsukawa; I. Ogawa; Y. Shimizu; S. Makino; T. Kanemaki

1993-01-01

51

Harmonic analysis and simulation of high frequency inverter system in Fuel Cell Engine  

Microsoft Academic Search

For the Fuel Cell Engine, the air compressor driving motor is controlled by high frequency inverter system. Because of the period interruption caused by commutation and limitation of the switch frequency, there are more harmonic components in inverter during high frequency region. In this paper, harmonic analysis and simulation are presented in different voltage modulation techinques. The simulation results indicated

Baiqing Sun; Qiancheng Zhao; Jinhu Shen; Qiuhao Zhang

2011-01-01

52

Clarification and measurements of high frequency harmonic resonance by a voltage sourced converter  

Microsoft Academic Search

This work presents the clarification and measurements of a high-order harmonic resonance phenomenon for voltage sourced converters. When a voltage sourced converter is connected to a power system through a cable, there is a possibility that small, high frequency, harmonic voltages due to the converter are magnified by series and parallel resonances. The cause of the high-order harmonic resonance is

Koji Temma; Fujio Ishiguro; Naohiro Toki; Isao Iyoda; John J. Paserba

2005-01-01

53

High-frequency even harmonics generation in a plasma with electron heat flux  

Microsoft Academic Search

It is shown that in a weakly nonuniform plasma with electron heat flux the generation of odd and even harmonics of high frequency radiation is possible. The even harmonics properties qualitatively differ as compared to those of odd harmonics and depend in an essential way on the heat flux value and orientation with respect to the fundamental wave polarization and

G. Ferrante; M. Zarcone; S. A Uryupin

2004-01-01

54

Fourier analysis of harmonic frequency transmission dielectric structures  

NASA Astrophysics Data System (ADS)

We use an analytical calculation based on the Fourier-transform method to study the transmission spectra of multilayer dielectric optical structures as a function of the relative widths of the layers that constitute the unit cell. We can select which harmonics of the fundamental design frequency are transmitted. The results of this Fourier-transform approach are compared with the exact transmission calculated by means of the transfer matrix method and provide a more intuitive understanding of the transmission spectrum. A simple phasor diagram is derived from this Fourier-transform analysis for this purpose. Inasmuch as it is difficult for us to perform experiments in the optical region, we fabricate rf analogs of these structures, using coaxial cables that have different impedances. Experimental results agree with theory.

del Mar Sánchez-López, María; Cos, Joaquín; Davis, Jeffrey A.; Miller, Darren A.; Moreno, Ignacio

2005-06-01

55

Imaging with second-harmonic radiation probes in living tissue  

PubMed Central

We demonstrate that second-harmonic radiation imaging probes are efficient biomarkers for imaging in living tissue. We show that 100 nm and 300 nm BaTiO3 nanoparticles used as contrast markers could be detected through 50 ?m and 120 ?m of mouse tail tissue in vitro or in vivo. Experimental results and Monte-Carlo simulations are in good agreement.

Grange, Rachel; Lanvin, Thomas; Hsieh, Chia-Lung; Pu, Ye; Psaltis, Demetri

2011-01-01

56

Stimulated scattering of relativistically strong radiation from an underdense plasma at high-frequency harmonics  

Microsoft Academic Search

The theory of stimulated scattering of relativistically strong, arbitrarily polarized laser radiation from an underdense plasma is developed. It is shown that, in addition to the scattering at the near-carrier frequency, the scattering at the odd and even high-frequency harmonics can occur in a wide range of angles. The growth rates of the instability associated with the harmonic generation are

A. S. Sakharov; V. I. Kirsanov

1997-01-01

57

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

NASA Astrophysics Data System (ADS)

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.

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

2005-04-01

58

Imaging leukocytes in vivo with third harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Without a labeling, we demonstrated that lipid granules in leukocytes have distinctive third harmonic generation (THG) contrast. Excited by a 1230nm femtosecond laser, THG signals were generated at a significantly higher level in neutrophils than other mononuclear cells, whereas signals in agranular lymphocytes were one order smaller. These characteristic THG features can also be observed in vivo to trace the newly recruited leukocytes following lipopolysaccharide (LPS) challenge. Furthermore, using video-rate THG microscopy, we also captured images of blood cells in human capillaries. Quite different from red-blood-cells, every now and then, round and granule rich blood cells with strong THG contrast appeared in circulation. The corresponding volume densities in blood, evaluated from their frequencies of appearance and the velocity of circulation, fall within the physiological range of human white blood cell counts. These results suggested that labeling-free THG imaging may provide timely tracing of leukocyte movement and hematology inspection without disturbing the normal cellular or physiological status.

Tsai, Cheng-Kun; Chen, Chien-Kuo; Chen, Yu-Shing; Wu, Pei-Chun; Hsieh, Tsung-Yuan; Liu, Han-Wen; Yeh, Chiou-Yueh; Lin, Win-Li; Chia, Jean-San; Liu, Tzu-Ming

2013-02-01

59

Confocal imaging of biological tissues using second harmonic generation  

NASA Astrophysics Data System (ADS)

A confocal microscopy imaging system was devised to selectively detect second harmonic signals generated by biological tissues. Several types of biological tissues were examined using this imaging system, including human teeth, bovine blood vessels, and chicken skin. All these tissues generated strong second harmonic signals. There is considerable evidence that the source of these signals in tissue is collagen. Collagen, the predominant component of most tissues, is known to have second order nonlinear susceptibility. This technique may have diagnostic usefulness in pathophysiological conditions characterized by changes in collagen structure including malignant transformation of nevi, progression of diabetic complications, and abnormalities in wound healing.

Kim, Beop-Min; Stoller, Patrick C.; Reiser, Karen M.; Eichler, Juergen P.; Yan, Ming; Rubenchik, Alexander M.; Da Silva, Luiz B.

2000-06-01

60

Confocal imaging of biological tissues using second harmonic generation  

NASA Astrophysics Data System (ADS)

A confocal microscopy imaging system was devised to selectively detect second harmonic signals generated by biological tissues. Several types of biological tissues were examined using this imaging system, including human teeth, bovine blood vessels, and chicken skin. All these tissues generated strong second harmonic signals. There is considerable evidence that the source of these signals in tissue is collagen. Collagen, the predominant component of most tissues, is known to have second order nonlinear susceptibility. This technique may have diagnostic usefulness in pathophysiological conditions characterized by changes in collagen structure including malignant transformation of nevi, progression of diabetic complications, and abnormalities in wound healing.

Kim, Beop-Min; Stoller, Patrick C.; Reiser, Karen M.; Eichler, Juergen P.; Yan, Ming; Rubenchik, Alexander M.; Da Silva, Luiz B.

2000-04-01

61

Confocal Imaging of Biological Tissues Using Second Harmonic Generation  

SciTech Connect

A confocal microscopy imaging system was devised to selectively detect Second harmonic signals generated by biological tissues. Several types of biological tissues were examined using this imaging system, including human teeth, bovine blood vessels, and chicken skin. All these tissues generated strong second harmonic signals. There is considerable evidence that the source of these signals in tissue is collagen. Collagen, the predominant component of most tissues, is known to have second order nonlinear susceptibility. This technique may have diagnostic usefulness in pathophysiological conditions characterized by changes in collagen structure including malignant transformation of nevi, progression of diabetic complications, and abnormalities in wound healing.

Kim, B-M.; Stoller, P.; Reiser, K.; Eichler, J.; Yan, M.; Rubenchik, A.; Da Silva, L.

2000-03-06

62

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

NASA Astrophysics Data System (ADS)

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.

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

2006-05-01

63

Nonlinear Chemical Imaging Microscopy:  Near-Field Third Harmonic Generation Imaging of Human Red Blood Cells  

Microsoft Academic Search

Third harmonic generation (THG) imaging using a near- field scanning optical microscope (NSOM) is demon- strated for the first time. A femtosecond, tunable near- infrared laser was used to generate both nonresonant and resonantly enhanced third harmonic radiation in human red blood cells. We show that resonantly enhanced THG is a chemically specific bulk probe in NSOM imaging by tuning

Richard D. Schaller; Justin C. Johnson; Richard J. Saykally

2000-01-01

64

Second Harmonic and Sum Frequency Generation on Dye-Coated Surfaces Using Collinear and Non-Collinear Excitation Geometries.  

National Technical Information Service (NTIS)

Doubly resonantly enhanced sum frequency generation from rhodamine 6G monolayers adsorbed on glass substates is compared with resonantly enhanced second harmonic generation using a collinear excitation geometry. Second harmonic and sum frequency generatio...

R. E. Muenchausen D. C. Nguyen R. A. Keller N. S. Nogar

1986-01-01

65

Second harmonic generation imaging of skeletal muscle tissue and myofibrils  

Microsoft Academic Search

Second Harmonic Generation (SHG) imaging microscopy is used to examine the morphology and structural properties of intact muscle tissue. Using biochemical and optical analysis, we characterize the molecular structure underlying SHG from the complex muscle sarcomere. We find that SHG from isolated myofibrils is abolished by extraction of myosin, but is unaffected by removal or addition of actin filaments. We

Paul J. Campagnola; William H. Mohler; Sergey Plotnikov; Andrew C. Millard

2006-01-01

66

Improving AFM images with harmonic interference by spectral analysis.  

PubMed

Atomic force microscopy (AFM) is one of the most sensitive tools for nanoscale imaging. As such, it is very sensitive to external noise sources that can affect the quality of collected data. The intensity of the disturbance depends on the noise source and the mode of operation. In some cases, the internal noise from commercial AFM controllers can be significant and difficult to remove. Thus, a new method based on spectrum analysis of the scanned images is proposed to reduce harmonic disturbances. The proposal is a post-processing method and can be applied at any time after measurements. This article includes a few methods of harmonic cancellation (e.g., median filtering, wavelet denoising, Savitzky-Golay smoothing) and compares their effectiveness. The proposed method, based on Fourier transform of the scanned images, was more productive than the other methods mentioned before. The presented data were achieved for images of conductive layers taken in a contact AFM mode. PMID:22214544

Kiwilszo, Marek; Zieli?ski, Artur; Smulko, Janusz; Darowicki, Kazimierz

2012-01-04

67

Monte Carlo harmonic-balance and drift-diffusion harmonic-balance analyses of 100-600 GHz Schottky barrier varactor frequency multipliers  

Microsoft Academic Search

To date, high frequency multipliers have been designed and analyzed using harmonic-balance codes incorporating equivalent circuit models for the diodes. These codes, however, are unable to accurately predict circuit performance at frequencies above 100 GHz and do not allow a means for studying the physics of electron transport. In order to analyze these high frequency Schottky doublers, a novel harmonic-balance

R. E. Lipsey; S. H. Jones; J. R. Jones; T. W. Crowe; L. F. Horvath; U. V. Bhapkar; R. J. Mattauch

1997-01-01

68

High Frequency Even Harmonics Generation in the Plasmas with Electron Fluxes  

Microsoft Academic Search

The flux density time evolution of radiation at the even harmonics frequencies of a test wave is found and its link with the evolution of the current density produced by a constant electric field is established. Even harmonics generation is studied in two regimes: that of free accelerated motion which takes place for small time intervals and that of current

S. A. Uryupin; G. Ferrante

2006-01-01

69

An experimental and theoretical comparison for the insertion loss of paired IDTs for high frequency harmonics  

Microsoft Academic Search

Several theoretical models are known to describe the harmonic response of surface acoustic wave (SAW) interdigital transducers (IDTs) of different topologies. The experimental results for insertion loss for IDTs, obtained for several tens of frequency harmonics, are compared with theoretical predictions of the well-known model, based on the \\

V. I. Fedosov; Fred S. Hickernell

2003-01-01

70

Comparison of adaptive and fixed-band hysteresis current control considering high frequency harmonics  

Microsoft Academic Search

Shunt active power filters (APF) are widely used in power systems to eliminate the current harmonics and to compensate reactive power due to their accurate and fast operation. In this paper the instantaneous power theory is used to extract the harmonic components of system current. Then fixed- band hysteresis current control is explained. Because of fixed- band variable frequency disadvantages,

Hani Vahedi; Yasser Rahmati Kukandeh; Mahsa Ghapandar Kashani; Aliakbar Dankoob; Abdolreza Sheikholeslami

2011-01-01

71

Clarification and Measurements of High Frequency Harmonic Resonance by a Voltage Sourced Converter  

Microsoft Academic Search

Summary form only given. This paper presents the clarification and measurements of a high-order harmonic resonance phenomenon for voltage sourced converters. When a voltage sourced converter is connected to a power system through a cable, there is a possibility that small, high frequency, harmonic voltages due to the converter are magnified by series and parallel resonances. The cause of the

K. Temma; F. Ishiguro; N. Toki; I. Iyoda; J. Paserba

2006-01-01

72

Imaging Collagen Orientation Using Polarization-Modulated Second Harmonic Generation  

SciTech Connect

We use polarization-modulated second harmonic generation to image fiber orientation in collagen tissues, with an axial resolution of about 10 {micro}m and a transverse resolution of up to 1 {micro}m. A linearly polarized ultra-short pulse (200 fs) Ti:Sapphire laser beam is modulated using an electro-optic modulator and quarter-wave plate combination and focused onto a translation stage mounted sample using a microscope objective. The generated second harmonic light is collected using a photomultiplier tube and demodulated using phase sensitive detection to obtain signal intensity and fiber orientation information. In order to obtain second harmonic generation images of different types of collagen organization, we analyze several different tissues, including rat-tail tendon, mouse aorta, mouse fibrotic liver, and porcine skin. We can use our technique to image fibrotic tissue in histological sections of damaged liver and to identify burned tissue in porcine skin to a depth of a few hundred microns. Polarization-modulated second harmonic generation potentially could be a useful clinical technique for diagnosing collagen related disease or damage, especially in the skin.

Stoller, P; Celliers, P M; Reiser, K M; Rubenchik, A M

2002-01-10

73

New mode of domain imaging: Second harmonic generation microscopy (abstract)  

SciTech Connect

Magnetization induced second harmonic generation (MSHG) is a novel magneto-optical technique that has an enhanced surface/interface sensitivity and demonstrates very large magneto-optical effects. It is described by a generalized nonlinear optical tensor {chi}{sup (2)} which has different transformation properties as compared to the linear tensor {chi}{sup (1)}. As a consequence, in the same geometry MSHG may be sensitive to other magnetization components than linear magneto-optics. Therefore linear and nonlinear magneto-optics should work best in a combination. Here we report the development of a magneto-optical microscope that is sensitive simultaneously to the linear (Faraday or Kerr) and nonlinear (MSHG) magneto-optical effects. MSHG, on the one hand, is able to visualize some exotic domain structures, e.g., 180{degree} domains in antiferromagnetics and ferroelectrics. On the other hand, because of its interface sensitivity it might help to visualize the magnetic structure at the interface between two different magnetic materials (including metals). Last but not least, the microscope evidently has an enhanced resolution due to the frequency doubling of detected light. First, we apply the microscope to the study of domains in magnetic garnet films, where a considerable difference between Faraday and MSHG images in the {ital same} configuration is demonstrated. A complicated noncollinear domain structure is straightforwardly derived from the MSHG images. Next, we consider the application of our technique to the magnetic metal surfaces and thin films (in reflection). The utilization of the microscope to correlate the surface/interface morphology with its magnetic properties is discussed. {copyright} {ital 1997 American Institute of Physics.}

Kirilyuk, V.; Kirilyuk, A.; Rasing, T. [Research Institute for Materials, University of Nijmegen, 6525 ED Nijmegen (The Netherlands)

1997-04-01

74

Storage ring free electron laser dynamics in presence of an auxiliary harmonic radio frequency cavity  

NASA Astrophysics Data System (ADS)

In a Storage Ring Free Electron Laser (SRFEL) there is a strong interdependence between the laser beam and the electron beam from which the laser is generated. The Super ACO storage ring has a second Radio Frequency (RF) cavity at the 5th harmonic of the main RF cavity. It is used to shorten the bunch length, thereby enhancing the laser gain. Employing this RF harmonic cavity instabilities are observed with a strong effect on both the laser radiation properties and the electron beam behaviour. In this paper, we first present beam characteristics of Super-ACO as influenced by the harmonic cavity, and the instabilities of the beam due to this RF cavity. Then we discuss the FEL properties in presence of the harmonic RF cavity. In general the harmonic cavity functions as intended, and it is observed that the laser suppresses the instabilities caused by the harmonic cavity in the absence of the FEL.

Thomas, C. A.; Botman, J. I. M.; Bruni, C.; Orlandi, G.; de Ninno, G.; Garzella, D.; Couprie, M. E.

2005-01-01

75

Frequency-resolved optical grating using surface third-harmonic generation  

SciTech Connect

We demonstrate the frequency-resolved optical grating technique using third-harmonic generation on the surface of a cover glass with ultra-short optical pulses and compare that with the phase-retrieved spectrogram.

Tsang, T. [Brookhaven National Lab., Upton, NY (United States); Krumbuegel, M.A.; Delong, K.W.; Fittinghoff, D.N.; Trebino, R. [Sandia National Labs., Livermore, CA (United States)

1995-11-01

76

Spatial Harmonic Imaging of X-ray Scattering--Initial Results  

PubMed Central

Coherent X-ray scattering is related to the electron density distribution by a Fourier transform, and therefore a window into the microscopic structures of biological samples. Current techniques of scattering rely on small-angle measurements from highly collimated X-ray beams produced from synchrotron light sources. Imaging of the distribution of scattering provides a new contrast mechanism which is different from absorption radiography, but is a lengthy process of raster or flue scans of the beam over the object. Here, we describe an imaging technique in the spatial frequency domain capable of acquiring both the scattering and absorption distributions in a single exposure. We present first results obtained with conventional X-ray equipment. This method interposes a grid between the X-ray source and the imaged object, so that the grid-modulated image contains a primary image and a grid harmonic image. The ratio between the harmonic and primary images is shown to be a pure scattering image. It is the auto-correlation of the electron density distribution at a specific distance. We tested a number of samples at 60–200 nm autocorrelation distance, and found the scattering images to be distinct from the absorption images and reveal new features. This technique is simple to implement, and should help broaden the imaging applications of X-ray scattering.

Bennett, Eric E.; Hegedus, Monica M.; Carroll, Stefanie C.

2010-01-01

77

Second-harmonic generation frequency-resolved optical gating in the single-cycle regime  

Microsoft Academic Search

The problem of measuring broad-band femtosecond pulses by the technique of second-harmonic generation frequency-resolved optical gating (SHG FROG) is addressed. We derive the full equation for the FROG signal, which is valid even for single-optical-cycle pulses. The effect of the phase mismatch in the second-harmonic crystal, the implications of the beam geometry, and the frequency-dependent variation of the nonlinearity are

A. Baltuska; Maxim S. Pshenichnikov; Douwe A. Wiersma

1999-01-01

78

Second-harmonic imaging from a modulated domain structure.  

PubMed

We present a new second-harmonic (SH) imaging technique to study the domains in a hexagonally poled LiTaO(3) nonlinear photonic crystal by using a femtosecond laser. By detecting the SH images at different planes, the distribution of the 180 degrees -inverted ferroelectric domains can be characterized, and the contributions of different nonlinear tensor components, modulated differently in the domain structure, can be selectively determined. Fundamental understanding and potential applications of such SH imaging techniques for the inverted nonlinear domain structures are presented and discussed. PMID:20081960

Zhang, Yong; Wang, Fuming; Geren, Katrina; Zhu, S N; Xiao, Min

2010-01-15

79

High-frequency section of harmonics of undulatory radiation  

Microsoft Academic Search

In this paper, the spectral'distribution is computed of the radiation of an undulator containing a large number of periods in the case of arbitrary transverse velocity. An analytic expression is found for the function cutting off the radiation spectrum on the boundaries of each harmonic.

V. Yu. Muravyatkin; M. M. Nikitin; V. Ya. Épp

1991-01-01

80

Second harmonic generation imaging of endogenous structural proteins  

Microsoft Academic Search

We find that several key endogenous structural proteins including collagen, acto-myosin, and tubulin give rise to intense second harmonic generation (SHG) and that these structures can be imaged in intact tissues on a laser-scanning microscope. Because SHG is a non-resonant process, this modality suffers little inherent photobleaching or toxicity. In this study we demonstrate the clarity of SHG optical sectioning

Paul J. Campagnola; William H. Mohler; Sergey Plotnikov; Andrew C. Millard

2003-01-01

81

Second harmonic generation imaging of endogenous structural proteins  

Microsoft Academic Search

We show that structural protein arrays consisting largely of collagen, myosin, and tubulin, and their associated proteins can be imaged in three dimensions with high contrast and resolution by laser-scanning second harmonic generation (SHG) microscopy. SHG is a nonlinear optical scheme and this form of microscopy shares several common advantages with multiphoton excited fluorescence, namely, intrinsic three-dimensionality and reduced out-of-plane

William Mohler; Andrew C. Millard; Paul J. Campagnola

2003-01-01

82

A Method for Harmonic Measurement of Real Power Grid Signals with Frequency Drift using Instruments with Internally Generated Reference Frequency  

NASA Astrophysics Data System (ADS)

The authors have recently developed a number of instruments for measuring harmonic composition of power grid signals. These instruments have a simple, predominantly digital architecture and they are based on an assumption that the frequency of the measured signals equals its nominal value (50 Hz, 60 Hz or 400 Hz). This approach has enabled the measurement of a high number of harmonics within a single period. However, the internal oscillator in the instrument generates the nominal frequency and cannot adapt to frequency changes in the input signal. This paper presents a method for the improvement of the operation of the developed instruments in cases when the fundamental frequency drifts from its nominal value as is the case with real power grid signals. Based on this method, modified versions of the harmonic measurement instruments have been developed. A comparison of the measurement error with and without the application of the proposed method is presented in the paper.

Anti?, B. M.; Mitrovi?, Z. L.; Vuji?i?, V. V.

2012-12-01

83

Frequency modulated thermal wave imaging  

NASA Astrophysics Data System (ADS)

Pulsed thermography (PT), being simple and fast, remains one of the most popular thermographic NDE techniques, though it has intrinsic limitations. An alternative method is suggested and named frequency modulated thermal wave imaging (FMTWI), where the heating waveform phase relations are adjusted over a bandwidth (B) in such a way, that a chirp (frequency modulated) signal of duration T, with much reduced peak power is produced. FMTWI, while retaining all characteristics of lock-in thermography, has the added advantage of overcoming the blind frequency problem. It can be processed by matched filtering (pulse compression) to improve sensitivity.

Tuli, S.; Chatterjee, K.

2012-05-01

84

The influence of winding capacitance on high frequency time harmonic losses in induction motors  

Microsoft Academic Search

An experimental study of motor current and power for time harmonic frequencies up to 100-200 kHz has been carried out. It is shown that motor losses can be significantly increased at frequencies above the first resonance by the very nonuniform voltage distribution along the winding turns. Tests on small motors (up to ten horsepower) indicate that the first resonance can

D. Maly; D. W. Novotny; C. Thompson

1992-01-01

85

High-frequency harmonic distortion in feedback amplifiers: analysis and applications  

Microsoft Academic Search

An approach for the evaluation of high-frequency harmonic-distortion factors in feedback systems is proposed and the results obtained are applied to feedback amplifiers. Under the assumption that transistors are not driven out of their linear operating regions, small-signal analysis and conventional algebra are exploited to derive understandable and compact expressions highly improving the comprehension of harmonic-distortion generation. The impact of

Gaetano Palumbo; Salvatore Pennisi

2003-01-01

86

Second harmonic imaging improves sensitivity of dobutamine stress echocardiography for the diagnosis of coronary artery disease  

Microsoft Academic Search

Objective Our purpose was to assess the value of second harmonic imaging compared with fundamental imaging for the diagnosis of coronary artery disease during dobutamine stress echocardiography. Patients and Methods Sixty-four patients underwent dobutamine stress echocardiography with both fundamental imaging and second harmonic imaging. Coronary angiography was performed within 3 months. Ischemia was defined as new or worsening wall motion

Fabiola B. Sozzi; Don Poldermans; Jeroen J. Bax; Eric Boersma; Wim B. Vletter; Abdou Elhendy; Alberico Borghetti; Jos R. T. C. Roelandt

2001-01-01

87

Towards adaptivity of image watermarking in polar harmonic transforms domain  

NASA Astrophysics Data System (ADS)

A successful image watermarking method is identified by the high performance in a number of basic requirements such as robustness, imperceptibility, capacity and complexity. Enhancement could be achieved through an adaptive process that handles individually the embedded information to each coefficient. The specific need for adaptivity is justified through this work by a set of experiments applied to the traditional moment families (Zernike, Pseudo-Zernike, Tchebichef), where more optimum results are produced. The extensive study of Polar Harmonic Transforms' (PHTs) significance parameters (order, magnitude) along with the use of a generalized embedding strength calculation process, easily applied to circularly orthogonal transformations, leads to a promising solution of the adaptivity issue. Experimental results justify that the proposed image watermarking scheme clearly outperforms the compared methods in terms of robustness, capacity and complexity and promotes the traditional schemes to a next generation of moment-based image watermarking.

Tsougenis, E. D.; Papakostas, G. A.; Koulouriotis, D. E.; Tourassis, V. D.

2013-12-01

88

P2-8: The influence of the high-frequency parameter on harmonic of traveling-wave tube  

Microsoft Academic Search

High-frequency parameter determines the output power and gain characteristics of a traveling wave tube. The relationship between the harmonics and the fundamental parameters determines the harmonic and fundamental proportion of the output power. Within a relatively broad range of parameter variation, the impacts on second harmonic from the distribution of phase velocity and coupling impedance are compared. We conclude that

Guoxing Miao; Xiaobao Su; Na Wei

2010-01-01

89

Comparison study of harmonic imaging (HI) and fundamental imaging (FI) in fetal echocardiography  

Microsoft Academic Search

Objectives: To directly compare the quality of harmonic imaging (HI) and fundamental imaging (FI) in fetal echocardiography\\u000a and to determine any difference in image quality between the two modalities. Methods: Fetal echocardiograms were performed\\u000a with the use of FI and HI in 58 fetuses, image quality and visualization of left and right atria, left and right ventricles,\\u000a mitral and tricuspid

Bo-wen Zhao; Fu-gang Tang; Jin-duo Shou; Hai-shan Xu; Jiang-hong Lu; Miao-ying Fan; Xiao-min Fan; Mei Pan

2003-01-01

90

Electron cyclotron harmonic resonances in high-frequency heating of the ionosphere  

NASA Astrophysics Data System (ADS)

Electron acceleration by upper hybrid waves under cyclotron harmonic resonance interaction is studied. Theory is formulated; the analytical solutions in the second and fourth harmonic cyclotron resonance cases are obtained, and in the third harmonic case, a first order differential equation governing the evolution of the electron energy is derived. The theory is applied for explaining the generation of artificial ionization layers observed in high-frequency (HF) ionospheric heating experiments. The upper hybrid waves are assumed to be excited parametrically by the O-mode HF heating wave. As the decay mode is the lower hybrid wave, the excited upper hybrid waves have wavelengths ranging from 0.25 to 0.5 m, which are short enough to effectively incorporate the finite Larmour radius effect for the harmonic cyclotron resonance interactions as well as have a frequency bandwidth of about 20 kHz, which provides an altitude region of about 10 km for continuous harmonic cyclotron resonance interaction between electrons and descending waves in the slightly inhomogeneous geomagnetic field. The numerical results on electron acceleration show that electron fluxes with energies larger than 14 eV are generated in the three harmonic cases. These energetic electrons cause impact ionizations, which are descending to form artificial ionization layers at the bottom of the ionospheric F region.

Kuo, Spencer P.

2013-09-01

91

Comparisons between harmonic balance and nonlinear output frequency response function in nonlinear system analysis  

NASA Astrophysics Data System (ADS)

By using the Duffing oscillator as a case study, this paper shows that the harmonic components in the nonlinear system response to a sinusoidal input calculated using the nonlinear output frequency response functions (NOFRFs) are one of the solutions obtained using the harmonic balance method (HBM). A comparison of the performances of the two methods shows that the HBM can capture the well-known jump phenomenon, but is restricted by computational limits for some strongly nonlinear systems and can fail to provide accurate predictions for some harmonic components. Although the NOFRFs cannot capture the jump phenomenon, the method has few computational restrictions. For the nonlinear damping systems, the NOFRFs can give better predictions for all the harmonic components in the system response than the HBM even when the damping system is strongly nonlinear.

Peng, Z. K.; Lang, Z. Q.; Billings, S. A.; Tomlinson, G. R.

2008-03-01

92

The value of ultrasound harmonic imaging in the diagnostics of gall bladder cholesterol polyps.  

PubMed

The aim of the study was to assess the value of harmonic imaging in US evaluation of gall bladder cholesterol polyps. Material comprises 40 patients with pathology of gall bladder diagnosed in US examination. 10 patients from this group with gall bladder cholesterol polyps diagnosed in US were included into the study. In each patient supplementary US examination in the harmonic mode was performed. The quality of images in the harmonic mode was better. The walls of the gall bladder were more distinct. The polyps were more evident on harmonic images. THI enable more precise measurements of the polyps. In three cases in the standard mode the inspissated bile was found in gall bladder, and in those patients polyps were difficult to assess. Examination of those patients in the harmonic mode excluded the presence of the bile sludge, and facilitates the assessment of the polyps. In four patients on harmonic images more polyps were found than in the standard mode. In the harmonic mode the level of artifacts generated by the body wall is reduced and contrast resolution is increased due to reduction in noise level. The visualization of gallbladder is improved in the harmonic mode. The assessment of gallbladder polyps in the harmonic mode is easier. The polyps are easily seen, assessment of their margins and size is facilitated by harmonic imaging. The number of polyps revealed in US examination is larger in the harmonic mode. PMID:16146095

Pas?awski, Marek; Krupski, Witold; Z?omaniec, Janusz

2004-01-01

93

Localized Harmonic Motion Imaging for Focused Ultrasound Surgery Targeting  

PubMed Central

Recently, an in vivo real-time ultrasound-based monitoring technique that uses localized harmonic motion (LHM) to detect changes in tissues during focused ultrasound surgery (FUS) has been proposed to control the exposure. This technique can potentially be used as well for targeting imaging. In the present study we evaluated the potential of using LHM to detect changes in stiffness and the feasibility of using it for imaging purposes in phantoms and in vivo tumor detection. A single-element FUS transducer (80 mm focal length, 100 mm diameter, 1.485 MHz) was used for inducing a localized harmonic motion and a separate ultrasound diagnostic transducer excited by a pulser/receiver (5 kHz PRF, 5 MHz) was used to track motion. The motion was estimated using cross-correlation techniques on the acquired RF signal. Silicon phantom studies were performed in order to determine the size of inclusion that was possible to detect using this technique. Inclusions were discerned from the surroundings as a reduction on LHM amplitude and it was possible to depict inclusions as small as 4 mm. The amplitude of the induced LHM was always lower at the inclusions as compared with the one obtained at the surroundings. Ten New Zealand rabbits had VX2 tumors implanted on their thighs and LHM was induced and measured at the tumor region. Tumors (as small as 10 mm in length and 4 mm in width) were discerned from the surroundings as a reduction on LHM amplitude.

Curiel, Laura; Hynynen, Kullervo

2011-01-01

94

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

NASA Astrophysics Data System (ADS)

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.

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

2010-02-01

95

HIGH FREQUENCY ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION  

Microsoft Academic Search

High frequency ultrasonic imaging is considered by many to be the next frontier in ultrasonic imaging. It has many clinical applications ranging from imaging the eye and skin to small animal imaging. Small animal imaging has recently generated intense interest for the purpose of evaluating the efficacy of drugs and gene therapy. Commercial high frequency scanners often termed \\

K. K. Shung

96

Harmonic-suppressed quadrature-input frequency divider for OFDM systems  

NASA Astrophysics Data System (ADS)

A fully balanced harmonic-suppressed quadrature-input frequency divider is proposed. The frequency divider improves the quadrature phase accuracy at the output by using both input I/Q signals. Compared with conventional dividers, the circuit achieves an output I/Q phase sequence that is independent of the input I/Q phase sequence. Moreover, the third harmonic is effectively suppressed by employing a double degeneration technique. The design is fabricated in TSMC 0.13-?m CMOS and operated at 1.2 V. While locked at 8.5 GHz, the proposed divider measures a maximum third harmonic rejection of 45 dB and a phase noise of -124 dBc/Hz at a 10 MHz offset. The circuit achieves a locking range of 15% while consuming a total current of 4.5 mA.

Haipeng, Fu; Junyan, Ren; Wei, Li; Ning, Li

2011-12-01

97

Statistical phase-screen model for second-harmonic beam distortion by body wall tissue in tissue harmonic imaging  

NASA Astrophysics Data System (ADS)

In certain clinical situations, tissue harmonic imaging reduces distortion due to phase aberrations introduced by the body wall layer. A statistical model was developed to describe the effects of random inhomogeneity in the body wall on the second-harmonic beam structure. This inhomogeneity is represented by a thin random phase screen located close to the source. Phase variations across the screen are characterized statistically. An analytical solution was derived for the expected value of the intensity of the second-harmonic field for a source that radiates a focused Gaussian beam. The focal beam pattern for the second-harmonic field is compared with that of the fundamental field as a function of correlation length and variance of the phase screen, for values based on measured human abdominal wall statistics.

Yan, X.; Hamilton, M. F.

2006-05-01

98

Representation theorems for the solutions of high-frequency harmonic oscillations in elastic plates  

Microsoft Academic Search

Somigliana-type representation formulae are established for regular solutions in the theory of high-frequency harmonic oscillations of elastic plates with transverse shear deformation. In the exterior domain case, a special far-field pattern is introduced, which makes it easier to verify the radiation conditions.

G. R. Thomson; C. Constanda

1998-01-01

99

Electromagnetic fields from high frequency currents harmonically distributed on infinitely long circular cylinders  

Microsoft Academic Search

High frequency currents harmonically distributed around the surface of infinitely long circular cylinders, in the directions of the generatrices and of the circles, are identified, and their associated electromagnetic fields are constructed. The latter are obtained as exact traveling wave solutions of Maxwell equations in differential and boundary condition forms. The study of these systems is appropriate for Electromagnetic Theory

E. Ley Koo; M. A. Rosales

2004-01-01

100

Propagation of high-frequency harmonic elastic waves from an axially symmetric cavity  

Microsoft Academic Search

An asymptotic ray method is developed for studying propagation of high-frequency harmonic elastic waves from a smooth, convex, axially symmetric cavity. The dynamic stresses near a prolate spheroidal cavity, to whose surface is applied a normal, angle-independent load, are investigated as a specific numerical example. It is shown that account of three terms of the ray series makes it possible

Yu. K. Rubtsov; P. N. Soroka

1991-01-01

101

Cochlear Implant Melody Recognition as a Function of Melody Frequency Range, Harmonicity, and Number of Electrodes  

Microsoft Academic Search

Objective: The primary goal of the present study was to determine how cochlear implant melody recognition was affected by the frequency range of the melodies, the harmonicity of these melodies, and the number of activated electrodes. The secondary goal was to investigate whether melody recognition and speech recognition were differentially affected by the limitations imposed by cochlear implant processing. Design:

Sonya Singh; Ying-Yee Kong; Fan-Gang Zeng

2009-01-01

102

Adaptive harmonic time-frequency decomposition of audio using shift-invariant PLCA  

Microsoft Academic Search

Numerous methods have been developed for the time-frequency analysis and smart decomposition of audio signals. However, these techniques are not consistently suitable for real music signals where each note presents continuous variations of both pitch and spectral envelope. This paper presents a new model for analyzing the harmonic structures of an audio signal that can jointly handle those two types

Benoit Fuentes; Roland Badeau; Gael Richard

2011-01-01

103

Thermal problems caused by harmonic frequency leakage fluxes in three-phase, three-winding converter transformers  

Microsoft Academic Search

Harmonic frequency leakage flux can be a limiting factor in three-phase, three-winding HVDC converter transformers. Investigation of a three-phase, three-winding 240-MVA converter transformer failure indicated the failure was caused by harmonic fluxes. Calculations indicated that the magnitudes of these harmonic fluxes to be approximately 45% of the power frequency leakage flux for the transformer, and are little affected by the

J. A. C. Forrest; B. Allard

2004-01-01

104

Moving two-axle high frequency harmonic loads on axially loaded pavement systems  

Microsoft Academic Search

The dynamic displacement response of axially loaded pavement models was investigated comprehensively when the system was subjected\\u000a to two-axle moving harmonic loads whose frequencies were higher than the natural frequency of the system. The axially loaded\\u000a beam on an elastic foundation was employed as a simplified pavement model under axial compression. The foundation was assumed\\u000a to have damping of a

Seong-Min Kim; Sungchul Yang

2010-01-01

105

Preliminary analysis of MV cable line models for high frequency harmonic penetration studies  

Microsoft Academic Search

The large penetration of distributed generation requires accurate line and cable models in a frequency range much wider than the classical interval, 0-2.5 kHz, used for traditional harmonic and interharmonic penetration studies. In the paper, the behavior of MV cable lines is considered in the frequency range from 0 to 100 kHz, with reference to a casestudy. Models base on

R. Langella; L. Nunges; F. Pilo; G. Petretto; S. Scalari; A. Testa

2011-01-01

106

First-passage time of an inverted pendulum subject to high frequency harmonic and Gaussian white noise excitations  

Microsoft Academic Search

The first-passage time of an inverted pendulum subject to a combination of high frequency harmonic excitation and Gaussian white noise excitation is investigated. The high frequency harmonic excitation term is simplified to an equivalent autonomous nonlinear stiffness term by using the method of direct partition of motions. Then, the equations of motion of the equivalent system are reduced to an

Z. L. Huang; Z. Q. Zhu; X. L. Jin

2009-01-01

107

Imaging articular cartilage using second harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Sub cellular resolution images of equine articular cartilage have been obtained using both second harmonic generation microscopy (SHGM) and two-photon fluorescence microscopy (TPFM). The SHGM images clearly map the distribution of the collagen II fibers within the extracellular matrix while the TPFM images show the distribution of endogenous two-photon fluorophores in both the cells and the extracellular matrix, highlighting especially the pericellular matrix and bright 2-3?m diameter features within the cells. To investigate the source of TPF in the extracellular matrix experiments have been carried out to see if it may originate from the proteoglycans. Pure solutions of the following proteoglycans hyaluronan, chondroitin sulfate and aggrecan have been imaged, only the aggrecan produced any TPF and here the intensity was not great enough to account for the TPF in the extracellular matrix. Also cartilage samples were subjected to a process to remove proteoglycans and cellular components. After this process the TPF from the samples had decreased by a factor of two, with respect to the SHG intensity.

Mansfield, Jessica C.; Winlove, C. Peter; Knapp, Karen; Matcher, Stephen J.

2006-03-01

108

Simultaneous Multichannel Nonlinear Imaging: Combined Two-Photon Excited Fluorescence and Second-Harmonic Generation Microscopy.  

National Technical Information Service (NTIS)

Simultaneous two-photon excited fluorescence (TPF) and second- harmonic generation (SHG) imaging is demonstrated using a single femtosecond laser and a scanning microscope. This composite nonlinear microscopic technique was applied to imaging DNA and chro...

C. J. Sheppard P. B. Lukins R. Gauderon

2000-01-01

109

Generation of harmonic frequencies and their effects in present day ICRF systems  

SciTech Connect

The whole TEXTOR-94 ICRF system circuit has been analyzed, partially modelled and studied at the fundamental operating frequency and, more important, at harmonic frequencies thereof. It has been found that without appropriate measures, present day systems and especially the TEXTOR ICRF system are prone to spurious generation of power at the second harmonic frequency. This leads either to erroneous activation of the reflected power safety protection or to highly increased (in some cases doubled) voltages in the transmission lines and antennas. As the voltage standing waves at the second harmonic displace the total voltage maxima in the transmission lines and antennas, this also explains why arcs are not always found at the expected voltage maxima for the fundamental frequency. The model is also able to give additional explanations why the ASDEX-Upgrade ICRF system has dramatically improved its power handling capabilities after the introduction of the '3dB coupler reflection compensation scheme'. The output of one of the TEXTOR transmitters has been fitted with a quarter wave length shorted stub which has no effect on the operation at the fundamental frequency but which effectively shorts out the second harmonic. It has to be noted that eg. the Tore Supra RDL antennas are fitted with such a stub in the feeding transmission line whose function is to enter cooling water into the transmission line system. Hence, this could be the explanation of the apparent higher than average power handling capabilities of the TS antenna system. Experimental results clearly indicate a much improved operational power handling capability on plasma and an increased voltage stand-off when conditioning this antenna pair on vacuum. Limits have yet to be explored but already remarkable is the fact that since the installation of the quarter wavelength stub the reflected power safety system has been activated only once and furthermore so in poorly matched conditions.

Durodie, F.; Vervier, M. [Laboratorium voor Plasma Fysica-Laboratoire de Physique des Plasmas Associatie 'EURATOM-Belgische Staat'-Association -EURATOM-Etat Belge - Koninklijke Militaire School-Ecole Royale Militaire Renaissancelaan 30-B-1000 Brussels-30, Av. de la Renaissance (Belgium)

1999-09-20

110

Cardiac motion tracking using CINE harmonic phase (HARP) magnetic resonance imaging  

Microsoft Academic Search

This article introduces a new image processing technique for rapid analysis of tagged cardiac magnetic resonance image sequences. The method uses isolated spectral peaks in SPAMM- tagged magnetic resonance images, which contain information about cardiac motion. The inverse Fourier transform of a spectral peak is a complex image whose calculated angle is called a harmonic phase (HARP) image. It is

Nael F. Osman; William S. Kerwin; Elliot R. McVeigh; Jerry L. Prince

1999-01-01

111

The value of ultrasound harmonic imaging in the diagnostics of the abdomen.  

PubMed

The tissue harmonic imaging (THI) is a new modality of ultrasonograph examination. The harmonic mode is characterized by a lower level of artifacts, due to reduction of side lobes energy and narrowed beam. The penetration in harmonic mode is also improved, so the visualization of deeper structures is often better. The assessment of liquid structures such as gallbladder, urinary bladder or large vessels and their pathologies is usually improved in the harmonic mode. The evaluation of cystic lesions, and differentiation cystic lesions and the hipoechogenic pathologies is easier in THI. Gallbladder stones localized in the gallbladder cervix are better evaluated in the harmonic mode. So the tissue harmonic imaging should be a part of standard ultrasonographic examination. PMID:15323169

Krupski, Witold; Pas?awski, Marek; Z?omaniec, Janusz

2003-01-01

112

Storage ring free electron laser dynamicsin presence of an auxiliary harmonic radio frequency cavity  

Microsoft Academic Search

.  In a Storage Ring Free Electron Laser (SRFEL) there is a\\u000astrong interdependence between the laser beam and the electron\\u000abeam from which the laser is generated. The Super ACO storage ring\\u000ahas a second Radio Frequency (RF) cavity at the 5th harmonic of\\u000athe main RF cavity. It is used to shorten the bunch length,\\u000athereby enhancing the laser

C. A. Thomas; J. I. M. Botman; C. Bruni; G. Orlandi; G. de Ninno; D. Garzella; M. E. Couprie

2005-01-01

113

A spectral finite element approach to modeling soft solids excited with high-frequency harmonic loads  

Microsoft Academic Search

An approach for efficient and accurate finite element analysis of harmonically excited soft solids using high-order spectral finite elements is presented and evaluated. The Helmholtz-type equations used to model such systems suffer from additional numerical error known as pollution when excitation frequency becomes high relative to stiffness (i.e. high wave number), which is the case, for example, for soft tissues

John C. Brigham; Wilkins Aquino; Miguel A. Aguilo; Peter J. Diamessis

2011-01-01

114

Lowand high frequency harmonic reduction in a PWM inverter using dithered sigma-delta modulation  

Microsoft Academic Search

This paper presents the use of dithered sigma-delta modulation (??M) to mitigate low and high frequency harmonics of pulse-width modulated (PWM) inverters without increasing switching losses. A PWM bit stream generated by a 1 bit- 1st-order discrete ??M is converted into a continuous pulse train which controls the inverter operation. The minimum pulse width of the pulse train is strictly

Wonjin Cho; Edward J. Powers; Surya Santoso

2010-01-01

115

Molecular Mie model for second harmonic generation and sum frequency generation  

NASA Astrophysics Data System (ADS)

A theoretical model to simulate second harmonic and sum frequency generation from stratified spherical particles of arbitrary material is presented and compared with the widely used Rayleigh-Gans-Debye approximation and to experimental results from polystyrene particles with adsorbed malachite green molecules. In this model, the nonlinear polarization is caused by individual dipoles placed in the vicinity of the sphere and is simulated on a molecular basis. This offers greater flexibility to model more sophisticated systems.

Wunderlich, Sarina; Schürer, Benedikt; Sauerbeck, Christian; Peukert, Wolfgang; Peschel, Ulf

2011-12-01

116

The hp-local discontinuous Galerkin method for low-frequency time-harmonic Maxwell equations  

Microsoft Academic Search

The local discontinuous Galerkin method for the numerical ap- proximation of the time-harmonic Maxwell equations in a low-frequency regime is introduced and analyzed. Topologically nontrivial domains and heteroge- neous media are considered, containing both conducting and insulating mate- rials. The presented method involves discontinuous Galerkin discretizations of the curl-curl and grad-div operators, derived by introducing suitable auxiliary variables and so-called

Ilaria Perugia; Dominik Schötzau

2003-01-01

117

Symposium on low frequency harmonic acceleration, the rotatory chair. Responses to low-frequency harmonic acceleration in patients with acoustic neuromas.  

PubMed

There has been increased interest in harmonic acceleration (HA) for the evaluation of vestibular pathology in recent years. The purpose of this study was to determine the value of harmonic acceleration testing in 24 patients with surgically proven acoustic neuromas. All patients were tested preoperatively and postoperatively, and none were lost to follow-up. Thirteen were tested one year or more after surgery. For rotational evaluation, each patient was seated in an enclosed chair driven by a D.C. torque motor turntable system and rotated utilizing five low frequency sinusoids (.01 - .16 Hz). Slow eye movements in response to acceleration were analyzed by analog and digital computer techniques. Output measures were the phase relationships between the input stimulus velocity and the slow phase eye movement velocity and labyrinthine preponderance (LP) or asymmetry. Preoperative results showed that caloric examination identified 79% of patients with tumors and HA 67% (2 standard deviation criteria). When both tests were evaluated together they identified 91% of all patients with tumors. Of the 4 small tumors (less than 2 cm), HA identified 4 and caloric examination 2. All patients were tested approximately 7 days postoperatively and had statistically significant shifts in their phase and LP measures. The shifts in phase were stable up to 3 years after surgery; however, the LP returned toward normal values. These findings indicate that the vestibular system can compensate but not repair itself after the loss of one labyrinth. In those patients who continued to be symptomatic 1 year or more after surgery, the LP did not return to normal values. Harmonic acceleration testing complemented caloric testing in the identification of patients with tumors and objectively demonstrated patients with continued symptomatology after surgery. PMID:6973678

Olson, J E; Wolfe, J W; Engelken, E J

1981-08-01

118

Automatic recognition of harmonic bird sounds using a frequency track extraction algorithm.  

PubMed

This paper demonstrates automatic recognition of vocalizations of four common bird species (herring gull [Larus argentatus], blue jay [Cyanocitta cristata], Canada goose [Branta canadensis], and American crow [Corvus brachyrhynchos]) using an algorithm that extracts frequency track sets using track properties of importance and harmonic correlation. The main result is that a complex harmonic vocalization is rendered into a set of related tracks that is easily applied to statistical models of the actual bird vocalizations. For each vocalization type, a statistical model of the vocalization was created by transforming the training set frequency tracks into feature vectors. The extraction algorithm extracts sets of frequency tracks from test recordings that closely approximate harmonic sounds in the file being processed. Each extracted set in its final form is then compared with the statistical models generated during the training phase using Mahalanobis distance functions. If it matches one of the models closely, the recognizer declares the set an occurrence of the corresponding vocalization. The method was evaluated against a test set containing vocalizations of both the 4 target species and 16 additional species as well as background noise containing planes, cars, and various natural sounds. PMID:19045673

Heller, Jason R; Pinezich, John D

2008-09-01

119

The value of ultrasound harmonic imaging in the diagnostics of gall bladder concrements.  

PubMed

The aim of the study was to assess the value of harmonic imaging in US evaluation of gall bladder concrements. The material comprised 40 patients with pathology of gall bladder diagnosed in US examination. 21 patients from this group with gall bladder concrements diagnosed in US was included into the study. In each patient supplementary US examination in the harmonic mode was performed. In three patients the deposits were localized in the cervix of the gallbladder. In two of them the acoustic shadow was seen only on THI images. In one patient the fibrotic gall bladder was found. In seven cases the concrements were sharper and more distinctly visible on harmonic images and acoustic shadow was more evident in eight. In five cases in the standard mode the presence of inspissated bile was found in gall bladder, but examination in the harmonic mode excluded the diagnosis in four of them. In the harmonic mode the level of artifacts generated by the body wall is reduced and contrast resolution is increased due to reduction in the noise level. The visualization of gallbladder is improved in the harmonic mode. The assessment of gallbladder stones in the harmonic mode is easier because: 1) images of the gall bladder lumen are clearer due to the reduced level of artifacts; 2) the resolution and contrast between the concrements and the bile are increased; 3) the acoustic shadow is more evident on harmonic images. Diagnosis of concrements localized in the gall bladder cervix is especially improved in the harmonic mode. Differentiation of solitary and multiple concernments is also facilitated by harmonic imaging. PMID:16146105

Pas?awski, Marek; Krupski, Witold; Z?omaniec, Janusz

2004-01-01

120

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations demonstrated that the angle between the main and grating lobe amounted to 90°. The difference in the fundamental pressure level between those lobes was equal to -26.8 dB. Those results suggest that the superharmonic content in the grating lobe was acceptably low. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the 3rd harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited an absence of the multiple reflection artifacts in the focal and post-focal regions. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual pulse technique, while the full frame rate is maintained.

Danilouchkine, Mikhail G.; van Neer, Paul L. M. J.; Matte, Guillaume M.; Verweij, Martin D.; de Jong, Nico

2011-03-01

121

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

PubMed Central

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%.

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

122

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

PubMed Central

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%.

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

123

Measurement of nonthermal oscillations at the plasma frequency and its harmonics in a magnetized arc plasma, using the high-frequency stark effect  

Microsoft Academic Search

High frequency oscillations of the electric field have been observed in a magnetized arc plasma using the high-frequency Stark effect. These oscillations seem to appear around the plasma frequency and its harmonics, one order of magnitude above thermal level. The position of the satellites shifts with electron density.

H. Ringler

1972-01-01

124

Harmonic optical microscopy and fluorescence lifetime imaging platform for multimodal imaging.  

PubMed

In this work, we proposed and built a multimodal optical setup that extends a commercially available confocal microscope (Olympus VF300) to include nonlinear second harmonic generation (SHG) and third harmonic generation (THG) optical (NLO) microscopy and fluorescence lifetime imaging microscopy (FLIM). We explored all the flexibility offered by this commercial confocal microscope to include the nonlinear microscopy capabilities. The setup allows image acquisition with confocal, brightfield, NLO/multiphoton and FLIM imaging. Simultaneously, two-photon excited fluorescence (TPEF) and SHG are well established in the biomedical imaging area, because one can use the same ultrafast laser and detectors set to acquire both signals simultaneously. Because the integration with FLIM requires a separated modulus, there are fewer reports of TPEF+SHG+FLIM in the literature. The lack of reports of a TPEF+SHG+THG+FLIM system is mainly due to difficulties with THG because the present NLO laser sources generate THG in an UV wavelength range incompatible with microscope optics. In this article, we report the development of an easy-to-operate platform capable to perform two-photon fluorescence (TPFE), SHG, THG, and FLIM using a single 80 MHz femtosecond Ti:sapphire laser source. We described the modifications over the confocal system necessary to implement this integration and verified the presence of SHG and THG signals by several physical evidences. Finally, we demonstrated the use of this integrated system by acquiring images of vegetables and epithelial cancer biological samples. PMID:22648907

Pelegati, Vitor B; Adur, Javier; De Thomaz, André A; Almeida, Diogo B; Baratti, Mariana O; Andrade, Liliana A L A; Bottcher-Luiz, Fátima; Cesar, Carlos L

2012-05-31

125

Harmonic power mode Doppler using microbubble contrast agents: an improved method for small vessel flow imaging  

Microsoft Academic Search

By virtue of their ability to enhance the weak echoes received from flow in small blood vessels, ultrasound contrast agents render flow in a lower level of the circulation detectable to colour Doppler imaging. We combine contrast imaging with power Doppler, which is a more appropriate colour mode for contrast enhanced Doppler imaging. We demonstrate that the combination of harmonic

P. N. Burns; J. E. Powers; D. H. Simpson; A. Brezina; A. Kolin; C. T. Chin; V. Uhlendorf; T. Fritzsch

1994-01-01

126

Design and performance of the Beamlet laser third harmonic frequency converter  

SciTech Connect

The Beamlet laser is a full-scale, single-aperture scientific prototype of the frequency-tripled Nd:glass laser for the proposed National Ignition Facility. At aperture sizes of 30 cm x 30 cm and 34 cm x 34 cm using potassium dihydrogen phosphate crystals of 32 cm x 32 cm and 37 cm x 37 cm, respectively, the authors have obtained up to 8.3 kJ of third harmonic energy at 70%--80% whole beam conversion efficiency.

Barker, C.E.; Wonterghem, B.M. Van; Auerbach, J.M.; Foley, R.J.; Murray, J.R.; Campbell, J.H.; Caird, J.A.; Speck, D.R.; Woods, B.

1995-09-12

127

3D quantitative Fourier analysis of second harmonic generation microscopy images of collagen structure in cartilage  

NASA Astrophysics Data System (ADS)

One of the main advantages of nonlinear microscopy is that it provides 3D imaging capability. Second harmonic generation is widely used to image the 3D structure of collagen fibers, and several works have highlighted the modification of the collagen fiber fabric in important diseases. By using an ellipsoidal specific fitting technique on the Fourier transformed image, we show, using both synthetic images and SHG images from cartilage, that the 3D direction of the collagen fibers can be robustly determined.

Romijn, Elisabeth I.; Lilledahl, Magnus B.

2013-02-01

128

Estimating the frequency interval of a regularly spaced multicomponent harmonic line signal in colored noise  

NASA Astrophysics Data System (ADS)

The radar returns from some classes of time-varying point targets can be represented by the discrete-time signal plus noise model: xt equals st plus [vt plus (eta) t] equals (summation)i equals o P minus 1 Aiej2(pi f(i)/f(s)t) plus vt plus (eta) t, t (epsilon) 0, . . ., N minus 1, fi equals kfI plus fo where the received signal xt corresponds to the radar return from the target of interest from one azimuth-range cell. The signal has an unknown number of components, P, unknown complex amplitudes Ai and frequencies fi. The frequency parameters fo and fI are unknown, although constrained such that fo less than fI/2 and parameter k (epsilon) {minus u, . . ., minus 2, minus 1, 0, 1, 2, . . ., v} is constrained such that the component frequencies fi are bound by (minus fs/2, fs/2). The noise term vt, is typically colored, and represents clutter, interference and various noise sources. It is unknown, except that (summation)tvt2 less than infinity; in general, vt is not well modelled as an auto-regressive process of known order. The additional noise term (eta) t represents time-invariant point targets in the same azimuth-range cell. An important characteristic of the target is the unknown parameter, fI, representing the frequency interval between harmonic lines. It is desired to determine an estimate of fI from N samples of xt. We propose an algorithm to estimate fI based on Thomson's harmonic line F-Test, which is part of the multi-window spectrum estimation method and demonstrate the proposed estimator applied to target echo time series collected using an experimental HF skywave radar.

Frazer, Gordon J.; Anderson, Stewart J.

1997-10-01

129

Fast frequency-resolved terahertz imaging  

NASA Astrophysics Data System (ADS)

We propose a fast, frequency-resolved, real-time, terahertz imaging method. With our method, images at two specific terahertz frequencies can be acquired in 1 min. Three kinds of drugs (L-histidine, maltose, and CBZ3), which have absorption peaks in the terahertz region, were distinguished in 3 min by using our method. This technique can be used in industrial applications, such as nondestructive testing.

Yasuda, Takashi; Kawada, Yoichi; Toyoda, Haruyoshi; Nakanishi, Atsushi; Akiyama, Koichiro; Takahashi, Hironori

2011-03-01

130

Fast frequency-resolved terahertz imaging.  

PubMed

We propose a fast, frequency-resolved, real-time, terahertz imaging method. With our method, images at two specific terahertz frequencies can be acquired in 1 min. Three kinds of drugs (L-histidine, maltose, and CBZ3), which have absorption peaks in the terahertz region, were distinguished in 3 min by using our method. This technique can be used in industrial applications, such as nondestructive testing. PMID:21456777

Yasuda, Takashi; Kawada, Yoichi; Toyoda, Haruyoshi; Nakanishi, Atsushi; Akiyama, Koichiro; Takahashi, Hironori

2011-03-01

131

Low Frequency Electromagnetic Cross-Borehole Imaging.  

National Technical Information Service (NTIS)

Most of the research in cross-borehole electromagnetic (EM) imaging has been done at high frequencies (17 to 200 Mhz). At these frequencies, the propagation distance through-the-earth is limited to less than 8 meters and the attenuation of the signal depe...

M. Pihlman P. E. Harben

1988-01-01

132

Spatial Kernel K-Harmonic Means Clustering for Multispectral Image Segmentation  

Microsoft Academic Search

The problem of image segmentation using intensity clustering approaches has been addressed in the literature. Grouping pixels of similar intensity to form clusters in an image has been tackled using a number of methods, such as the K-Means (KM) algorithm. The K-Harmonic Means (KHM) was proposed to overcome the sensitivity of KM to centre initialisation. In this paper, we investigate

Qi Li; Nikolaos Mitianoudis; Tania Stathaki

2006-01-01

133

Optical Clearing for Improved Contrast in Second Harmonic Generation Imaging of Skeletal Muscle  

Microsoft Academic Search

Using second harmonic generation (SHG) imaging microscopy, we have examined the effect of optical clearing with glycerol to achieve greater penetration into specimens of skeletal muscle tissue. We find that treatment with 50% glycerol results in a 2.5-fold increase in achievable SHG imaging depth. Signal processing analyses using fast Fourier transform and continuous wavelet transforms show quantitatively that the periodicity

Sergey Plotnikov; Vaibhav Juneja; Ariel B. Isaacson; William A. Mohler; Paul J. Campagnola

2006-01-01

134

High-resolution imaging of a corneal incision by second- and third-harmonic generation microscopy  

Microsoft Academic Search

We demonstrate high spatial resolution imaging of a stromal cut in the ex-vivo pig cornea, using second- and third-harmonic generation microscopy. From these images, we see in detail how the cut affects the corneal layers. In the beginning of the cut, the anterior layers, in which the blade is passing through, are disorganized, which could explain the shadows observed on

L. Jay; C. Dion; A. Brocas; K. Singh; J.-C. Kieffer; I. Brunette; T. Ozaki

2010-01-01

135

Face Recognition from a Single Training Image under Arbitrary Unknown Lighting Using Spherical Harmonics  

Microsoft Academic Search

In this paper, we propose two novel methods for face recognition under arbitrary unknown lighting by using spherical harmonics illumination representation, which require only one training image per subject and no 3D shape information. Our methods are based on the recent result which demonstrated that the set of images of a convex Lambertian object obtained under a wide variety of

Lei Zhang; Dimitris Samaras

2006-01-01

136

Simultaneous acquisition of spatial harmonics (SMASH): Fast imaging with radiofrequency coil arrays  

Microsoft Academic Search

This report presents a fast-imaging technique that al- lows some fraction of signal data points to be acquired in parallel, rather than sequentially in time. Previously, several fast imaging schemes have been proposed using simultaneous data acquisition in multiple RF coils (8- 13). The technique described here, dubbed simultaneous acquisition of spatial harmonics (SMASH), reduces im- age acquisition times by

Daniel K. Sodickson; Warren J. Manning

1997-01-01

137

Multiscale image features analysis with circular harmonic wavelets  

NASA Astrophysics Data System (ADS)

In this contribution we introduce a new family of wavelets named Circular Harmonic Wavelets (CHW), suited for multiscale feature-based representations, that constitute a basis for general steerable wavelets. The family is based on Circular Harmonic Functions (CHF) derived by the Fourier expansion of local Radial Tomographic Projections. A multiscale general feature analysis can be performed by linearly combining the outputs of CHW operators of different order. After a survey on the general properties of the CHFs, we investigate the relationship between CHF and the wavelet expansion, stating the basic admissibility and stability conditions with reference to the Hankel transform of the radial profiles and describing some fundamental mathematical properties. Finally some applications are illustrated through examples.

Jacovitti, Giovanni; Neri, Alessandro

1995-09-01

138

The Frequency Dependence of Harmonic Fluid Flow Through Networks of Cracks and Pores  

NASA Astrophysics Data System (ADS)

The "dynamic" permeability k(?) of heterogeneous networks of cracks, tubes and spheres, was determined by numerically simulating the harmonic flow of an interstitial fluid for a wide range of frequencies. For comparison with previous works, this procedure was applied to the 100 network realizations used in Bernabé (1995). In most cases, the calculated frequency dependence of the real and imaginary parts of k(?) was consistent with the JKD model (Johnsonet al., 1987), showing a transition from "viscous", macroscopic flow at low frequencies to "inertial" flow at high frequencies. The viscous skin depth ?c at the transition was found to be proportional to the critical capillary radius rc from a capillary invasion (Katz and Thompson, 1986). A simple explanation is that these two length scales arise from the same percolation problem. On the other hand, ?c was not well correlated with the JKD parameter ?. The conclusion is that ? and ?c (or rc ) are two independent parameters, derived from two unrelated approaches (i.e., weighted averaging and percolation theory). Finally, an attempt was made to relax the initial assumptions of a rigid solid matrix and an incompressible fluid. It was observed that the effect of the fluid compressibility could occasionally be very large, especially when networks with large amounts of storage pore space were considered.

Bernabé, Y.

139

Harmonic oscillator model of early visual image processing  

NASA Astrophysics Data System (ADS)

To characterize how the human visual system responds to spatial patterns, a 'black box' method was adopted, in which visual evoked potentials (VEPs) were taken as outputs and visual patterned stimuli were taken as inputs. The stimuli were gratings whose function profiles were weighted Hermite polynomials (WHPs). A model, mathematically analogous to harmonic oscillators in quantum mechanics, was developed to describe the black box and the quantitative relationships between the VEPs and the WHPs.

Yang, Jian; Reeves, Adam J.

1991-11-01

140

A high order purely frequency-based harmonic balance formulation for continuation of periodic solutions  

NASA Astrophysics Data System (ADS)

Combining the harmonic balance method (HBM) and a continuation method is a well-known technique to follow the periodic solutions of dynamical systems when a control parameter is varied. However, since deriving the algebraic system containing the Fourier coefficients can be a highly cumbersome procedure, the classical HBM is often limited to polynomial (quadratic and cubic) nonlinearities and/or a few harmonics. Several variations on the classical HBM, such as the incremental HBM or the alternating frequency/time-domain HBM, have been presented in the literature to overcome this shortcoming. Here, we present an alternative approach that can be applied to a very large class of dynamical systems (autonomous or forced) with smooth equations. The main idea is to systematically recast the dynamical system in quadratic polynomial form before applying the HBM. Once the equations have been rendered quadratic, it becomes obvious to derive the algebraic system and solve it by the so-called asymptotic numerical method (ANM) continuation technique. Several classical examples are presented to illustrate the use of this numerical approach.

Cochelin, Bruno; Vergez, Christophe

2009-07-01

141

Squeezing induced in a harmonic oscillator by a sudden change in mass or frequency  

NASA Astrophysics Data System (ADS)

The Kanai-Caldirola (Bateman) Hamiltonian is used to derive the dynamics of a simple harmonic oscillator, initially in a minimum uncertainty state, under the influence of an external agency which causes the mass parameter to change from M0 to M1 in a short time ?. Then the frequency changes from ?0 to ?1=(M0/M1)?0+O(?2). In the limit ?-->0, no squeezing or loss of coherence occurs. If M1/M0=1+/-? (0

Abdalla, M. Sebawe; Colegrave, R. K.

1993-08-01

142

Imaging the bipolarity of myosin filaments with Interferometric Second Harmonic Generation microscopy  

PubMed Central

We report that combining interferometry with Second Harmonic Generation (SHG) microscopy provides valuable information about the relative orientation of noncentrosymmetric structures composing tissues. This is confirmed through the imaging of rat medial gastrocnemius muscle. The inteferometric Second Harmonic Generation (ISHG) images reveal that each side of the myosin filaments composing the A band of the sarcomere generates ? phase shifted SHG signal which implies that the myosin proteins at each end of the filaments are oriented in opposite directions. This highlights the bipolar structural organization of the myosin filaments and shows that muscles can be considered as a periodically poled biological structure.

Rivard, Maxime; Couture, Charles-Andre; Miri, Amir K.; Laliberte, Mathieu; Bertrand-Grenier, Antony; Mongeau, Luc; Legare, Francois

2013-01-01

143

Ab Initio Theoretical Investigation of the Frequency Comb Structure in the XUV Regime via High Harmonic Generation  

NASA Astrophysics Data System (ADS)

We present an ab initio quantum investigation of the frequency comb structure formed within each high harmonic generation (HHG) power spectrum driven by a train of equal- spacing short laser pulses. The HHG power spectrum of atomic hydrogen is calculated by solving the time-dependent Schr"o dinger equation accurately and efficiently by means of the time- dependent generalized pseudospectral method. We found that the frequency comb structure is preserved within each harmonic. In addition, the repetition frequency of the comb laser depends upon the pulse separation ? and the spectral width of each individual comb fringe is inversely proportional to the number of pulses (n) used. However, the global HHG power spectrum pattern depends only upon the laser frequency and intensity used and is not sensitive to the ? and n parameters. Finally, the frequency comb structure persists even in the presence of appreciable ionization.

Carrera, Juan J.; Son, Sang-Kil; Chu, Shih-I.

2007-06-01

144

Asymmetric Molecular Imaging through Decoding Odd-Even High-Order Harmonics  

NASA Astrophysics Data System (ADS)

The exquisite procedure for imaging a molecular orbital with high-order harmonics proposed by Itatani et al. [Nature (London) 432, 867 (2004)] encounters difficulty when extended to an asymmetric molecule because the wave function there usually does not have a definite parity. With the observation that the wave function can be decomposed into a sum of odd and even functions and that the ionization process in harmonic generation is usually not sensitive to the asymmetry of the molecular potential, we predict that asymmetric molecular orbital imaging can be implemented through decoding odd-even high-order harmonics. A generalized tomography procedure is proposed, which has been certified by analytic deduction and numerical simulation. The above finding greatly extends the molecular tomography procedure and will further stimulate related experiments.

Chen, Y. J.; Fu, L. B.; Liu, J.

2013-08-01

145

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

PubMed

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%. PMID:10829639

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

2000-03-01

146

Resonance Properties and Frequencies of AN Electro-Rheological Clutch at Harmonic Load  

NASA Astrophysics Data System (ADS)

In this paper, a concentric electro-rheological clutch (ERC) is considered, embedded into a broader system: electro-hydro-aggregate (EHA) consisting of an induction motor as an electrodrive (ED) and a brake (B) as a loading machine. For ED, its dynamic moment characteristics and for B, a harmonic loading moment are taken into account. One starts from the corresponding nonlinear nondimensional dynamic model of EHA which is of the 5th order with 14 nondimensional parameters. The steady solution of the model can exhibit resonance which, due to complexity and extensiveness of the model, is very difficult to detect and analyze. Therefore, an analytical solution in the frame of the first approximation is sought, based on the method of small parameter. For this, a few simplifying assumptions are adopted (undamped system, small amplitude and frequency of load and narrow gap in ERC). Then, undamped resonance frequencies are derived and analyzed. Results are compared with resonance curves of the original and unsimplified system and further solution of the problem in question is proposed.

Oravský, Vladimír

147

Efficient procedure for the numerical calculation of harmonic vibrational frequencies based on internal coordinates.  

PubMed

We propose a general procedure for the numerical calculation of the harmonic vibrational frequencies that is based on internal coordinates and Wilson's GF methodology via double differentiation of the energy. The internal coordinates are defined as the geometrical parameters of a Z-matrix structure, thus avoiding issues related to their redundancy. Linear arrangements of atoms are described using a dummy atom of infinite mass. The procedure has been automated in FORTRAN90 and its main advantage lies in the nontrivial reduction of the number of single-point energy calculations needed for the construction of the Hessian matrix when compared to the corresponding number using double differentiation in Cartesian coordinates. For molecules of C1 symmetry the computational savings in the energy calculations amount to 36N - 30, where N is the number of atoms, with additional savings when symmetry is present. Typical applications for small and medium size molecules in their minimum and transition state geometries as well as hydrogen bonded clusters (water dimer and trimer) are presented. In all cases the frequencies based on internal coordinates differ on average by <1 cm(-1) from those obtained from Cartesian coordinates. PMID:23406376

Miliordos, Evangelos; Xantheas, Sotiris S

2013-03-05

148

Temporal Coherence Effects on Coherent Diffractive Imaging of a Binary Sample by a High Harmonic Source  

NASA Astrophysics Data System (ADS)

Coherent Diffractive Imaging (CDI) is performed with single and multiple harmonics from an ultrafast HHG source. The effect of HHG source bandwidth on the effectiveness of the reconstruction algorithms is compared. A low quality reconstruction from broadband data is achieved assuming full coherence in the algorithm.

Parsons, A. D.; Chapman, R. T.; Mills, B.; Bajt, S.; Frey, J. G.; Brocklesby, W. S.

2013-03-01

149

Direct imaging through scattering media by use of efficient third-harmonic generation in organic materials  

NASA Astrophysics Data System (ADS)

We report on real-time, time-gated, direct imaging through scattering media with an attenuation of 14 mean-free paths by use of third-harmonic generation in the eye-safe and telecommunication-compatible near-IR spectral region (1550 nm).

Ramos-Ortiz, Gabriel; Cha, Myoungsik; Kippelen, Bernard; Walker, Gregory A.; Barlow, Stephen; Marder, Seth R.

2004-11-01

150

Fast Determination of Regional Myocardial Strain Fields From Tagged Cardiac Images Using Harmonic Phase MRI  

Microsoft Academic Search

Background—Tagged MRI of the heart is difficult to implement clinically because of the lack of fast analytical techniques. We investigated the accuracy of harmonic phase (HARP) imaging for rapid quantification of myocardial strains and for detailed analysis of left ventricular (LV) function during dobutamine stimulation. Methods and Results—Tagged MRI was performed in 10 volunteers at rest and during 5 to

Jerome Garot; David A. Bluemke; Nael F. Osman; Carlos E. Rochitte; Elliot R. McVeigh; Elias A. Zerhouni; Jerry L. Prince; Joao A. C. Lima

2010-01-01

151

Quantitative Second Harmonic Generation Imaging of the Diseased State Osteogenesis Imperfecta: Experiment and Simulation  

Microsoft Academic Search

We report the integrated use of 3D second harmonic generation (SHG) imaging microscopy and Monte Carlo simulation as a combined metric to quantifiably differentiate normal and diseased tissues based on the physical properties of the respective extracellular matrix. To achieve this, we have identified a set of parameters comprised of the SHG creation attributes and the bulk optical parameters, which

Ronald LaComb; Oleg Nadiarnykh; Paul J. Campagnola

2008-01-01

152

Real-time Focused Ultrasound Surgery (FUS) Monitoring Using Harmonic Motion Imaging (HMI)  

Microsoft Academic Search

Monitoring changes in tissue mechanical properties to optimally control thermal exposure is important in thermal therapies. The amplitude-modulated (AM) harmonic motion imaging (HMI) for focused ultrasound (HMIFU) technique is a radiation force technique, which has the capability of tracking tissue stiffness during application of an oscillatory force. The feasibility of HMIFU for assessing mechanical tissue properties has been previously demonstrated.

Caroline Maleke; Elisa E. Konofagou

2009-01-01

153

High-resolution imaging of a corneal incision by second- and third-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

We demonstrate high spatial resolution imaging of a stromal cut in the ex-vivo pig cornea, using second- and third-harmonic generation microscopy. From these images, we see in detail how the cut affects the corneal layers. In the beginning of the cut, the anterior layers, in which the blade is passing through, are disorganized, which could explain the shadows observed on the images. In the stroma, the cut can be imaged by third harmonic microscopy, probably due to the ?3 contrast. Although the current results were obtained from the healthy ex-vivo cornea, it already allows one to understand the effects of the cut on the tissue characteristics (such as scattering).

Jay, L.; Dion, C.; Brocas, A.; Singh, K.; Kieffer, J.-C.; Brunette, I.; Ozaki, T.

2010-02-01

154

Face Recognition Under Variable Lighting using Harmonic Image Exemplars  

Microsoft Academic Search

We propose a new approach for face recognition under arbitrary illumination conditions, which requires only one training image per subject (if there is no pose variation) and no 3D shape information. Our method is based on the recent result (1) which demostrated that the set of images of a convex Lambertian object obtained under a wide vari- ety of lighting

Lei Zhang; Dimitris Samaras

2003-01-01

155

In vivo polarization dependant Second and Third harmonic generation imaging of Caenorhabditis elegans pharyngeal muscles  

NASA Astrophysics Data System (ADS)

In this study Second and Third harmonic generation (SHG-THG) imaging measurements were performed to the pharyngeal muscles of the nematode Caenorhabditis elegans, in vivo with linearly polarized laser beam. Complementary information about the anatomy of the pharynx and the morphology of the anterior part of the worm were extracted. THG signals proved to have no dependence on incident light polarization, while SHG images are highly sensitive to the changes of the incident linearly polarized light.

Filippidis, G.; Troulinaki, K.; Fotakis, C.; Tavernarakis, N.

2009-07-01

156

Long-term imaging of mouse embryos using adaptive harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

We present a detailed description of an adaptive harmonic generation (HG) microscope and culture techniques that permit long-term, three-dimensional imaging of mouse embryos. HG signal from both pre- and postimplantation stage (0.5-5.5 day-old) mouse embryos are fully characterized. The second HG images reveal central spindles during cytokinesis whereas third HG images show several features, such as lipid droplets, nucleoli, and plasma membranes. The embryos are found to develop normally during one-day-long discontinuous HG imaging, permitting the observation of several dynamic events, such as morula compaction and blastocyst formation.

Thayil, Anisha; Watanabe, Tomoko; Jesacher, Alexander; Wilson, Tony; Srinivas, Shankar; Booth, Martin

2011-04-01

157

A Spectral Finite Element Approach to Modeling Soft Solids Excited with High-Frequency Harmonic Loads  

PubMed Central

An approach for efficient and accurate finite element analysis of harmonically excited soft solids using high-order spectral finite elements is presented and evaluated. The Helmholtz-type equations used to model such systems suffer from additional numerical error known as pollution when excitation frequency becomes high relative to stiffness (i.e. high wave number), which is the case, for example, for soft tissues subject to ultrasound excitations. The use of high-order polynomial elements allows for a reduction in this pollution error, but requires additional consideration to counteract Runge's phenomenon and/or poor linear system conditioning, which has led to the use of spectral element approaches. This work examines in detail the computational benefits and practical applicability of high-order spectral elements for such problems. The spectral elements examined are tensor product elements (i.e. quad or brick elements) of high-order Lagrangian polynomials with non-uniformly distributed Gauss-Lobatto-Legendre nodal points. A shear plane wave example is presented to show the dependence of the accuracy and computational expense of high-order elements on wave number. Then, a convergence study for a viscoelastic acoustic-structure interaction finite element model of an actual ultrasound driven vibroacoustic experiment is shown. The number of degrees of freedom required for a given accuracy level was found to consistently decrease with increasing element order. However, the computationally optimal element order was found to strongly depend on the wave number.

Brigham, John C.; Aquino, Wilkins; Aguilo, Miguel A.; Diamessis, Peter J.

2010-01-01

158

Structures, electron affinities, and harmonic vibrational frequencies of the simplest alkyl peroxyl radicals and their anions.  

PubMed

The molecular structures and electron affinities of the R-OO/R-OO(-) (R = CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, i-C3H7, t-C4H9) species have been determined using seven different density functional or hybrid Hartree-Fock density functional methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s-type and p-type functions, denoted DZP++. The geometries are fully optimized with each density functional theory method. Harmonic vibrational frequencies were found to be within 3.1% of available experimental values for most functionals. Two different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity and the vertical detachment energy. The most reliable adiabatic electron affinities obtained at the DZP++ BP86 level of theory are 1.150 (CH3OO), 1.124 (C2H5OO), 1.146 (n-C3H7OO), 1.173 (n-C4H9OO), 1.184 (n-C5H11OO), 1.145 (i-C3H7OO), and 1.114 eV (t-C4H9OO). Compared with the experimental values, the average absolute error of the BPW91 method is 0.05 eV. PMID:18597444

Xu, Wenguo; Lu, Gaoyu

2008-07-03

159

The energy level spacing for two harmonic oscillators with golden mean ratio of frequencies  

Microsoft Academic Search

Berry and Tabor discussed, among other things, a beautiful problem about the energy level spacing distribution for a system of two harmonic oscillators. They gave some interesting theoretical arguments which show that there is no level clustering for generic harmonic oscillators, and various numerical experiments were exposed and discussed. But the main question they posed about the existence of the

P. M. Bleher

1990-01-01

160

High frequency harmonic components of leakage current for monitoring insulator performance in cold fog  

Microsoft Academic Search

High harmonic components of leakage current are often ignored from the analysis of insulator performance, whether they are effective for monitoring insulator performance or not needs better investigation. In this paper, experiments have been carried out on SIR insulators in cold fog and harmonic components of leakage current are extracted for monitoring the surface performance. The leakage current is separated

B. X. Du; Yong Liu

2008-01-01

161

High-Speed Camera for Frequency Domain Imaging  

Microsoft Academic Search

We describe a high-speed camera system for performing frequency domain imaging with applications to photon migration imaging or fluorescence lifetime imaging. Field programmable gate arrays allow processing images up to 2 gigapixels per second.

Abneesh Srivastava; David Watt; Gregory W. Faris

2007-01-01

162

Modelling of global boundary effects on harmonic motion imaging of soft tissues.  

PubMed

Biomechanical imaging techniques have been developed for soft tissue characterisation and detection of breast tumours. Harmonic motion imaging (HMI) uses a focused ultrasound technology to generate a harmonic radiation force in a localised region inside a soft tissue. The resulting dynamic response is used to map the local distribution of the mechanical properties of the tissue. In this study, a finite element (FE) model is developed to investigate the effect of global boundary conditions on the dynamic response of a soft tissue during HMI. The direct-solution steady-state dynamic analysis procedure is used to compute the harmonic displacement amplitude in FE simulations. The model is parameterised in terms of boundary conditions and viscoelastic properties, and the corresponding raster-scan displacement amplitudes are captured to examine its response. The effect of the model's global dimensions on the harmonic response is also investigated. It is observed that the dynamic response of soft tissue with high viscosity is independent of the global boundary conditions for regions remote to the boundary; thus, it can be subjected to local analysis to estimate the underlying mechanical properties. However, the dynamic response is sensitive to global boundary conditions for tissue with low viscosity or regions located near to the boundary. PMID:23167660

Zhao, Xiaodong; Pelegri, Assimina A

2012-11-21

163

A Multivariate, Multitaper Approach to Detecting and Estimating Harmonic Response in Cortical Optical Imaging Data  

PubMed Central

The efficiency and accuracy of cortical maps from optical imaging experiments have been improved using periodic stimulation protocols. The resulting data analysis requires the detection and estimation of periodic information in a multivariate dataset. To date, these analyses have relied on discrete Fourier transform (DFT) sinusoid estimates. Multitaper methods have become common statistical tools in the analysis of univariate time series that can give improved estimates. Here, we extend univariate multitaper harmonic analysis methods to the multivariate, imaging context. Given the hypothesis that a coherent oscillation across many pixels exists within a specified bandwidth, we investigate the problem of its detection and estimation in noisy data by constructing Hotelling’s generalized T2-test. We then extend the investigation of this problem in two contexts, that of standard Canonical Variate Analysis (CVA) and that of Generalized Indicator Function Analysis (GIFA) which is often more robust in extracting a signal in spatially correlated noise. We provide detailed information on the fidelities of the mean estimates found with our methods and comparison with DFT estimates. Our results indicate that GIFA provides particularly good estimates of harmonic signals in spatially correlated noise and is useful for detecting small amplitude harmonic signals in applications such as biological imaging measurements where spatially correlated noise is common. We demonstrate the power of our methods with an optical imaging dataset of the periodic response to a periodically rotating oriented drifting grating stimulus experiment in cat visual cortex.

Sornborger, A.T.; Yokoo, T.

2011-01-01

164

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

PubMed

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 -60dB 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 20-60MHz phantom and ex vivo results. A simulation study shows that the range side lobe level of CPI-CTHI is 16dB lower than PI-CTHI, assuming that the transducer translates incident positions by 50?m 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 12dB lower range side lobe level and a 7dB higher echo signal to noise ratio than PI-CTHI, while the lateral resolution and side lobe level are 50?m finer and -3dB 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?m in diameter with 6dB 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

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

2012-07-21

165

Harmonic Response of Cellular Membrane Pumps to Low Frequency Electric Fields  

NASA Astrophysics Data System (ADS)

We report on harmonic generation by budding yeast cells in response to a sinusoidal electric field, 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 reportedly responsible for nonlinear response in yeast, reduces the threshold field amplitude, increasing harmonic generation at low amplitudes while reducing it at large amplitudes, whereas the addition of glucose dramatically increases the production of even harmonics. Finally, a simple model is proposed to interpret the observed behavior.

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

2005-10-01

166

Gray scale second harmonic imaging of the liver: a preliminary animal study.  

PubMed

Gray scale second harmonic imaging (2.5 MHz/5.0 MHz) was evaluated in preliminary animal studies with a new ultrasound contrast agent (FS069). FS069 was administered intravenously in 10 rabbits (6 with normal liver, and 4 with implanted VX-2 tumors) and two woodchucks with hepatocellular carcinomas. The vasculature (including tumor vessels) and liver parenchyma were clearly enhanced at a low dosage (optimal dose was from 0.1 to 0.2 mL/kg) in all cases. Enhancement was reproducible and generally dose-dependent. Tumors were enhanced well during the early phase and tumor enhancement disappeared earlier than that of surrounding normal liver. Arterial phase and portal phase were easily distinguished and patterns of enhancement were diagnostic of the tumors. Gray scale second harmonic imaging is useful in the detection of hepatic tumors and in diagnosis of their hemodynamics. PMID:9253819

Kono, Y; Moriyasu, F; Nada, T; Suginoshita, Y; Matsumura, T; Kobayashi, K; Nakamura, T; Chiba, T

1997-01-01

167

Harmonic Motion Imaging for Focused Ultrasound (HMIFU): Initial in vivo results  

Microsoft Academic Search

The capability of Harmonic Motion Imaging for Focused Ultrasound (HMIFU) for real-time monitoring of tissue stiffness changes during thermal therapy was previously demonstrated ex vivo. In this paper, initial feasibility of the HMIFU for thermal ablation generation and monitoring is shown in a transgenic mouse model of breast cancer in vivo. The HMIFU system consists of a 4.5-MHz focused ultrasound

Caroline Maleke; Elisa E. Konofagou

2009-01-01

168

Frequency-resolved optical gating with the use of second-harmonic generation  

SciTech Connect

We discuss the use of second-harmonic generation (SHG) as the nonlinearity in the technique of frequency-resolved optical gating (FROG) for measuring the full intensity and phase evolution of an arbitrary ultrashort pulse. FROG that uses a third-order nonlinearity in the polarization-gate geometry has proved extremely successful, and the algorithm required for extraction of the intensity and the phase from the experimental data is quite robust. However, for pulse intensities less than [similar to] 1 MW, third-order nonlinearities generate insufficient signal strength, and therefore SHG FROG appears necessary. We discuss the theoretical, algorithmic, and experimental considerations of SHG FROG in detail. SHG FROG has an ambiguity in the direction of time, and its traces are somewhat unintuitive. Also, previously published algorithms are generally ineffective at extracting the intensity and the phase of an arbitrary laser pulse from the SHG FROG trace. We present an improved pulse-retrieval algorithm, based on the method of generalized projections, that is far superior to the previously published algorithms, although it is still not so robust as the polarization-gate algorithm. We discuss experimental sources of error such as pump depletion and group-velocity mismatch. We also present several experimental examples of pulses measured with SHG FROG and show that the derived intensities and phases are in agreement with more conventional diagnostic techniques, and we demonstrate the high-dynamic-range capability of SHG FROG. We conclude that, despite the above drawbacks, SHG FROG should be useful in measuring low-energy pulses.

DeLong, K.W.; Trebino, R. (Combustion Research Facility, MS-9057, Sandia National Laboratories, Livermore, California 94551-0969 (United States)); Hunter, J.; White, W.E. (Lawrence Livermore National Laboratory, Livermore, California 94550 (United States))

1994-11-01

169

Imaging 2-D Structures With Receiver Functions Using Harmonic Stripping  

NASA Astrophysics Data System (ADS)

I present a novel technique to image dipping and anisotropic structures using receiver functions. Receiver functions isolate phase conversions from interfaces close to the seismic station. Standard analysis assumes a quasi-flat layered structure and dampens arrivals from dipping interfaces and anisotropic layers, with attempts to extract information on such structures relying on cumbersome and nonunique forward modeling. I use a simple relationship between the radial and transverse component receiver function to detect dipping and anisotropic layers and map their depth and orientation. For dipping interfaces, layers with horizontal or plunging axis anisotropy, and point scatterers, the following relationships hold: After subtracting the azimuthally invariant portion of the radial receiver functions, the remaining signal is an azimuthally shifted version of the transverse receiver functions. The strike of the dipping interface or anisotropy is given by the azimuth of polarity reversals, and the type of structure can be inferred from the amount of phase shift between the components. For a known structure type, the phase shift between the two components provides pseudoevents from back-azimuths with little seismicity. The technique allows structural mapping at depth akin to geological mapping of rock fabric and dipping layers at the surface. It reduces complex wavefield effects to two simple and geologically meaningful parameters, similar to shear wave splitting. I demonstrate the method on the Wind River Thrust as well as other structures within the Transportable Array footprint.

Schulte-Pelkum, V.

2010-12-01

170

Quantitative extraction of the emission times of high-order harmonics via the determination of instantaneous frequencies  

NASA Astrophysics Data System (ADS)

We introduce a method using the concept of instantaneous frequency, as determined with the help of a Hilbert transform, to achieve an accurate time-frequency analysis of the dipole issued from the numerical resolution of the time-dependent Schrödinger equation for any model system driven by an intense laser field. It permits the quantitative extraction of the emission times of the harmonics that coincide with the recollision times of the laser-driven electronic wave packet with the ionic core, for the first and the second return.

Risoud, François; Caillat, Jérémie; Maquet, Alfred; Taïeb, Richard; Lévêque, Camille

2013-10-01

171

Second-harmonic generation imaging of collagen fibers in myocardium for atrial fibrillation diagnosis  

NASA Astrophysics Data System (ADS)

Atrial fibrillation (AF) is the most common irregular heart rhythm and the mortality rate for patients with AF is approximately twice the mortality rate for patients with normal sinus rhythm (NSR). Some research has indicated that myocardial fibrosis plays an important role in predisposing patients to AF. Therefore, realizing the relationship between myocardial collagen fibrosis and AF is significant. Second-harmonic generation (SHG) is an optically nonlinear coherent process to image the collagen network. We perform SHG microscopic imaging of the collagen fibers in the human atrial myocardium. Utilizing the SHG images, we can identify the differences in morphology and the arrangement of collagen fibers between NSR and AF tissues. We also quantify the arrangement of the collagen fibers using Fourier transform images and calculating the values of angle entropy. We indicate that SHG imaging, a nondestructive and reproducible method to analyze the arrangement of collagen fibers, can provide explicit information about the relationship between myocardial fibrosis and AF.

Tsai, Ming-Rung; Chiu, Yu-Wei; Lo, Men Tzung; Sun, Chi-Kuang

2010-03-01

172

A multi-output high frequency cycloinverter operation for induction-heating cooking appliances - Harmonic study  

Microsoft Academic Search

In this paper, low frequency AC (LFAC) to high frequency AC (HFAC) power conversion system conditioning and processing circuit without DC smoothing. Capacitor filter link from the voltage grid of utility frequency AC power supply source is proposed and introduced. The operating principle of utility frequency AC-high frequency AC power frequency conversion circuit defined as high frequency cycloinverter is described.

S. M. W. Ahmed; M. M. Eissa; M. Edress; T. S. Abdel-Hameed

2009-01-01

173

Lensless Diffractive Imaging Using Tabletop Coherent High-Harmonic Soft-X-Ray Beams  

SciTech Connect

We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.

Sandberg, Richard L.; Paul, Ariel; Raymondson, Daisy A.; Haedrich, Steffen; Gaudiosi, David M.; Holtsnider, Jim; Tobey, Ra'anan I.; Cohen, Oren; Murnane, Margaret M.; Kapteyn, Henry C.; Song, Changyong; Miao Jianwei; Liu Yanwei; Salmassi, Farhad [JILA and Department of Physics, University of Colorado and NSF Engineering Research Center in Extreme Ultraviolet Science and Technology, Boulder, Colorado 80309 (United States); Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Center for X-Ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2007-08-31

174

Quantified characterization of dermal collagen structure in human cutaneous scars from second harmonic generation imaging  

NASA Astrophysics Data System (ADS)

In this paper, high resolution images of collagens based on second harmonic generation (SHG) were obtained in the dermis of different scar tissues and surrounding considered uninjured skins, demonstrating differences in their microstructures. In order to quantitatively analyze their structural features, Fourier analysis was applied for the SHG images to compare the alteration in collagen orientation of different scars. Moreover, depth dependant decay of SHG signals was also analyzed to provide more credible information. Our results show that the different types of scar tissues can be successfully distinguished with the two combined methods, which will help to determine the most appropriate clinical treatment strategy.

Zhu, Xiaoqin; Chen, Youting; Zhuo, Shuangmu; Yu, Biying; Zheng, Liqin; Lu, Kecheng; Chen, Jianxin

2009-08-01

175

Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy  

PubMed Central

Microtubule (MT) ensemble polarity is a diagnostic determinant of the structure and function of neuronal processes. Here, polarized MT structures are selectively imaged with second-harmonic generation (SHG) microscopy in native brain tissue. This SHG is found to colocalize with axons in both brain slices and cultured neurons. Because SHG arises only from noninversion symmetric structures, the uniform polarity of axonal MTs leads to the observed signal, whereas the mixed polarity in dendrites leads to destructive interference. SHG imaging provides a tool to investigate the kinetics and function of MT ensemble polarity in dynamic native brain tissue structures and other subcellular motility structures based on polarized MTs.

Dombeck, Daniel A.; Kasischke, Karl A.; Vishwasrao, Harshad D.; Ingelsson, Martin; Hyman, Bradley T.; Webb, Watt W.

2003-01-01

176

Modeling of large aperture third harmonic frequency conversion of high power Nd:glass laser systems  

SciTech Connect

To provide high-energy, high-power beams at short wavelengths for inertial-confinement-fusion experiments, we routinely convert the 1.053-{mu}m output of the Nova, Nd:phosphate-glass, laser system to its third-harmonic wavelength. We describe performance and conversion efficiency modeling of the 3 {times} 3 arrays potassium-dihydrogen-phosphate crystal plates used for type II/type II phase-matched harmonic conversion of Nova 0.74-m diameter beams, and an alternate type I/type II phase-matching configuration that improves the third-harmonic conversion efficiency. These arrays provide energy conversion of up to 65% and intensity conversion to 70%. 19 refs., 11 figs.

Henesian, M.A.; Wegner, P.J.; Speck, D.R.; Bibeau, C.; Ehrlich, R.B.; Laumann, C.W.; Lawson, J.K.; Weiland, T.L.

1991-03-13

177

Ultrahigh 22 nm resolution coherent diffractive imaging using a desktop 13 nm high harmonic source.  

PubMed

New diffractive imaging techniques using coherent x-ray beams have made possible nanometer-scale resolution imaging by replacing the optics in a microscope with an iterative phase retrieval algorithm. However, to date very high resolution imaging (< 40 nm) was limited to large-scale synchrotron facilities. Here, we present a significant advance in image resolution and capabilities for desktop soft x-ray microscopes that will enable widespread applications in nanoscience and nanotechnology. Using 13 nm high harmonic beams, we demonstrate a record 22 nm spatial resolution for any tabletop x-ray microscope. Finally, we show that unique information about the sample can be obtained by extracting 3-D information at very high numerical apertures. PMID:22109124

Seaberg, Matthew D; Adams, Daniel E; Townsend, Ethan L; Raymondson, Daisy A; Schlotter, William F; Liu, Yanwei; Menoni, Carmen S; Rong, Lu; Chen, Chien-Chun; Miao, Jianwei; Kapteyn, Henry C; Murnane, Margaret M

2011-11-01

178

In Vivo Imaging of Myelin in the Vertebrate Central Nervous System Using Third Harmonic Generation Microscopy  

PubMed Central

Loss of myelin in the central nervous system (CNS) leads to debilitating neurological deficits. High-resolution optical imaging of myelin in the CNS of animal models is limited by a lack of in vivo myelin labeling strategies. We demonstrated that third harmonic generation (THG) microscopy—a coherent, nonlinear, dye-free imaging modality—provides micrometer resolution imaging of myelin in the mouse CNS. In fixed tissue, we found that THG signals arose from white matter tracts and were colocalized with two-photon excited fluorescence (2PEF) from a myelin-specific dye. In vivo, we used simultaneous THG and 2PEF imaging of the mouse spinal cord to resolve myelin sheaths surrounding individual fluorescently-labeled axons, and followed myelin disruption after spinal cord injury. Finally, we suggest optical mechanisms that underlie the myelin specificity of THG. These results establish THG microscopy as an ideal tool for the study of myelin loss and recovery.

Farrar, Matthew J.; Wise, Frank W.; Fetcho, Joseph R.; Schaffer, Chris B.

2011-01-01

179

High-frequency harmonic generation in a toroidal magnetized laboratory plasma and detection of plasma turbulence  

Microsoft Academic Search

We show for the first time experimentally that plasma turbulence can be detected easily when an electromagnetic extraordinary wave launched from the inner side of a toroidal magnetized plasma reaches a turbulent resonance layer. The second-harmonic wave generated inside the resonance layer is detected from outside the magnetized plasma and its power spectrum is analyzed. This new technique could be

A. Ajendouz; Th. Pierre; M. Boussouis; K. Quotb

2008-01-01

180

Extra Low-Frequency Terrestrial Radio-Wave Field Calculations with the Zonal Harmonics Series.  

National Technical Information Service (NTIS)

Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is ...

J. R. Johler R. L. Lewis

1968-01-01

181

Extra Low-Frequency Terrestrial Radio-Wave Field Calculations with the Zonal Harmonics Series  

Microsoft Academic Search

Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is analyzed into a direct wave and a wave that has traveled the circumference of the earth. The location of

J. Ralph Johler; Richard L. Lewis

1969-01-01

182

Optical frequency standard based on a Nd:YAG laser stabilised by saturated absorption resonances in molecular iodine using second-harmonic radiation  

Microsoft Academic Search

The results of studies devoted to the development of the optical frequency standard based on a diode-pumped 1064-nm single-frequency ring Nd:YAG laser with intracavity frequency doubling are presented. The laser frequency was stabilised by saturated absorption resonances in molecular iodine at the second-harmonic frequency of the laser (at 532 nm). The saturated absorption resonances were observed in an external luminescent

Mikhail N Skvortsov; M V Okhapkin; A Yu Nevsky; Sergei N Bagaev

2004-01-01

183

Dielectric spectroscopy of proteins as a quantitative experimental test of computational models of their low-frequency harmonic motions.  

PubMed

Decades of molecular dynamics and normal mode calculations suggest that the largest-scale collective vibrational modes of proteins span the picosecond to nanosecond time scale. Experimental investigation of these harmonic, low-amplitude motions, however, has proven challenging. In response, we have developed a vector network analyzer-based spectrometer that supports the accurate measurement of both the absorbance and refractive index of solvated biomolecules over the corresponding gigahertz to terahertz frequency regime, thus providing experimental information regarding their largest-scale, lowest frequency harmonic motions. We have used this spectrometer to measure the complex dielectric response of lysozyme solutions over the range 65 to 700 GHz and an effective medium model to separate the dielectric response of the solvated protein from that of its buffer. In doing so, we find that each lysozyme is surrounded by a tightly bound layer of 165 ± 15 water molecules that, in terms of their picosecond dynamics, behave as if they are an integral part of the protein. We also find that existing computational descriptions of the protein's dynamics compare poorly with the results of our experiment. Specifically, published normal mode and molecular dynamics simulations do not explain the measured dielectric response unless we introduce a cutoff frequency of 250 GHz below which the density of vibrational modes drops to zero. This cutoff is physically plausible, given the known size of the protein and the known speed of sound in proteins, raising questions as to why it is not apparent in computational models of the protein's motions. PMID:21542634

Vinh, N Q; Allen, S James; Plaxco, Kevin W

2011-05-20

184

Second harmonic generation imaging of the collagen in myocardium for atrial fibrillation diagnosis  

NASA Astrophysics Data System (ADS)

Myocardial fibrosis, a common sequela of cardiac hypertrophy, has been shown to be associated with arrhythmias in experimental models. Some research has indicated that myocardial fibrosis plays an important role in predisposing patients to atrial fibrillation. Second harmonic generation (SHG) is an optically nonlinear coherent process to image the collagen network. In this presentation, we observe the SHG images of the collagen matrix in atrial myocardium and we analyzed of collagen fibers arrangement by using Fourier-transform analysis. Moreover, comparing the SHG images of the collagen fibers in atrial myocardium between normal sinus rhythm (NSR) and atrial fibrillation (AF), our result indicated that it is possible to realize the relation between myocardial fibrosis and AF.

Tsai, Ming-Rung; Chiou, Yu-We; Sun, Chi-Kuang

2009-02-01

185

The utilization of the bubble pressure dependent harmonic resonance frequency for enhanced heating during high intensity focused ultrasound treatments  

NASA Astrophysics Data System (ADS)

The use of bubbles in High Intensity Focused Ultrasound (HIFU) enhances tissue heating; however, localization of the treatment is difficult due to harmful effects at non-focal regions. In this study the bubble dynamics were studied through the utilization of resonance curves and bifurcation diagrams of the normalized bubble oscillation amplitude (NBOA) (time varying radius/initial radius) by solving the Hoff model. This method allowed us to study the bubble dynamics in wide ranges of control parameters. Results indicate that, by sonicating the bubbles with their pressure dependent harmonic resonance frequency (e.g. 3.1 MHz for a 5 micron bubble with shell shear modulus of 50 MPa and 100nm thickness), the (NBOA) is negligible below a threshold pressure (PT) (~1.5 MPa). For pressures above the PT, the NBOA increases and remains constant for a large pressure range concomitant with a significant increase in higher harmonic emissions. Because of the steep spatial pressure gradient of the HIFU transducer, the non-focal bubbles will be non-resonant as the non-focal pressure is below the PT. Therefore, the undesirable effects of non-focal bubbles will be minimized. The resonant bubbles at the focal region are stable (NBOA<1.4) and radiate significant harmonics thus providing a long lasting controllable enhanced heating.

Sojahrood, Amin Jafari; Kolios, Michael C.

2012-10-01

186

Echelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal  

SciTech Connect

Details for constructing an astronomical frequency comb suitable as a wavelength reference for echelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 {mu}m. The means of producing a repetition rate greater than 7 GHz and a peak optical power of {approx}8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested.

McFerran, J. J.

2009-05-10

187

Optical second-harmonic susceptibilities: Frequency-dependent formulation with results for GaP and GaAs  

NASA Astrophysics Data System (ADS)

A formula for frequency-dependent optical second-harmonic susceptibilities for insulating crystals, including local-field corrections, is presented. In analogy to a formula given previously for the static limit, the formula is analyzed in terms of ``virtual electron'' (ccv) and ``virtual hole'' (vvc) terms to obtain a numerically stable form. Numerical results for GaP and GaAs agree with most of the experimental values suggested in a recent review article by Roberts. Miller's ?M is predicted to vary by 13% from the laser lines at 10.6 to 1.32 ?m for GaP.

Levine, Zachary H.

1994-02-01

188

Optical second-harmonic susceptibilities: Frequency-dependent formulation with results for GaP and GaAs  

SciTech Connect

A formula for frequency-dependent optical second-harmonic susceptibilities for insulating crystals, including local-field corrections, is presented. In analogy to a formula given previously for the static limit, the formula is analyzed in terms of virtual electron'' ([ital ccv]) and virtual hole'' ([ital vvc]) terms to obtain a numerically stable form. Numerical results for GaP and GaAs agree with most of the experimental values suggested in a recent review article by Roberts. Miller's [Delta][sub [ital M

Levine, Z.H. (Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106 (United States))

1994-02-15

189

Myocardial contrast echocardiography with 1.5-harmonic imaging in the diagnosis of cardiac malignant lymphoma.  

PubMed

We applied myocardial contrast echocardiography with 1.5-harmonic imaging to an atrioventricular groove tumor in a patient with malignant lymphoma. Contrast echocardiography initially showed one centric legion and some patchy echogenic foci within the tumor, all of which were indicative of arterial components. Subsequently, the tumor was enhanced homogenously, reflecting parenchymal hyperperfusion. These findings were consistent with previous observations of malignant lymphoma using color Doppler. We believe that myocardial contrast echocardiography could afford an important clue to the histologic diagnosis of cardiac tumors. PMID:16084343

Shimizu, Masatoshi; Takahashi, Hanayo; Tatsumi, Kazuhiro

2005-08-01

190

Imaging molecular structure with Stokes-polarimeter based second harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

We analyzed the polarization states of second harmonic generation (SHG) signals from starch granules and type I collagen through a four-channel photon counting based Stokes-polarimeter. The 2D SHG images of samples are reconstructed using various polarization parameters, such as the degree of polarization (DOP), the degree of linear polarization (DOLP), the degree of circular polarization (DOCP), as well as the anisotropy from the acquired Stokes parameters. Furthermore, we have demonstrated that the polarization parameters are changes at different input polarizations and focusing depths.

Mazumder, Nirmal; Qiu, Jianjun; Hu, Chih-Wei; Kao, Fu-Jen

2013-02-01

191

Second harmonic generating (SHG) nanoprobes: a new tool for biomedical imaging  

NASA Astrophysics Data System (ADS)

Fluorescence microscopy has profoundly changed how cell and molecular biology is studied in almost every aspect. However, the need of characterizing biological targets is largely unmet due to deficiencies associated with the use of fluorescent agents. Dye bleaching, dye signal saturation, blinking, and tissue autofluorescence can severely limit the signal-to-noise ratio (SNR). Given the photophysical properties are fundamentally different to the fluorescent agents currently used in biomedical research, second harmonic generating (SHG) nanoprobes can be suitable for biomedical imaging and can eliminate most of the drawbacks encountered in classical fluorescence systems.

Pantazis, Periklis; Pu, Ye; Psaltis, Demetri; Fraser, Scott

2009-02-01

192

Optical frequency standard based on a Nd:YAG laser stabilised by saturated absorption resonances in molecular iodine using second-harmonic radiation  

SciTech Connect

The results of studies devoted to the development of the optical frequency standard based on a diode-pumped 1064-nm single-frequency ring Nd:YAG laser with intracavity frequency doubling are presented. The laser frequency was stabilised by saturated absorption resonances in molecular iodine at the second-harmonic frequency of the laser (at 532 nm). The saturated absorption resonances were observed in an external luminescent cell. The relative long-term frequency stability achieved in experiments was {approx}6x10{sup -15}. The physical and technical factors affecting the long-term frequency stability and reproducibility are investigated. (optical metrology and quantum frequency standards)

Skvortsov, Mikhail N; Okhapkin, M V; Nevsky, A Yu; Bagaev, Sergei N [Institute of Laser Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation)

2004-12-31

193

Frequency hopping patterns for simultaneous multiple-beam sonar imaging  

Microsoft Academic Search

This paper describes the design of frequency-hopped signals for a multi-beam imaging system. A frequency hopping pattern is a frequency-coded uniform pulse train. The signal is divided into M time intervals, with each interval assigned a different frequency chosen from a set of N frequencies. A set of N patterns composed of N-1 frequencies can be generated using first-order Reed-Solomon

Philippe M. Cassereau; Jules S. Jaffe

1987-01-01

194

Real-time imaging of two-dimensional cardiac strain using a harmonic phase magnetic resonance imaging (HARP-MRI) pulse sequence  

Microsoft Academic Search

The harmonic phase (HARP) method provides automatic and rapid analysis of tagged magnetic resonance (MR) images for quantification and visualization of myocardial strain. In this article, the development and implementation of a pulse se- quence that acquires HARP images in real time are described. In this pulse sequence, a CINE sequence of images with 1-1 spatial modulation of magnetization (SPAMM)

Smita Sampath; J. Andrew Derbyshire; Ergin Atalar; Nael F. Osman; Jerry L. Prince

2003-01-01

195

Inter- and Intra-Observer Variability in Prostate Definition With Tissue Harmonic and Brightness Mode Imaging  

SciTech Connect

Purpose: The objective of this study was to compare the relative utility of tissue harmonic (H) and brightness (B) transrectal ultrasound (TRUS) images of the prostate by studying interobserver and intraobserver variation in prostate delineation. Methods and Materials: Ten patients with early-stage disease were randomly selected. TRUS images of prostates were acquired using B and H modes. The prostates on all images were contoured by an experienced radiation oncologist (RO) and five equally trained observers. The observers were blinded to information regarding patient and imaging mode. The volumes of prostate glands and areas of midgland slices were calculated. Volumes contoured were compared among the observers and between observer group and RO. Contours on one patient were repeated five times by four observers to evaluate the intraobserver variability. Results: A one-sample Student t-test showed the volumes outlined by five observers are in agreement (p > 0.05) with the RO. Paired Student t-test showed prostate volumes (p = 0.008) and midgland areas (p = 0.006) with H mode were significantly smaller than that with B mode. Two-factor analysis of variances showed significant interobserver variability (p < 0.001) in prostate volumes and areas. Inter- and intraobserver consistency was quantified as the standard deviation of mean volumes and areas, and concordance indices. It was found that for small glands ({<=}35 cc) H mode provided greater interobserver consistency; however, for large glands ({>=}35 cc), B mode provided more consistent estimates. Conclusions: H mode provided superior inter- and intraobserver agreement in prostate volume definition for small to medium prostates. In large glands, H mode does not exhibit any additional advantage. Although harmonic imaging has not proven advantageous for all cases, its utilization seems to be judicious for small prostates.

Sandhu, Gurpreet Kaur, E-mail: Gurpreet.Sandhu2@albertahealthservices.ca [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Dunscombe, Peter [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada); Meyer, Tyler [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Pavamani, Simon [Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada); Department of Radiation Oncology, Christian Medical College, Vellore (India); Khan, Rao [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada)

2012-01-01

196

Quantitative second-harmonic generation imaging to detect osteogenesis imperfecta in human skin samples  

NASA Astrophysics Data System (ADS)

Osteogenesis Imperfecta (OI) is a genetic disorder that leads to bone fractures due to mutations in the Col1A1 or Col1A2 genes that affect the primary structure of the collagen I chain with the ultimate outcome in collagen I fibrils that are either reduced in quantity or abnormally organized in the whole body. A quick test screening of the patients would largely reduce the sample number to be studied by the time consuming molecular genetics techniques. For this reason an assessment of the human skin collagen structure by Second Harmonic Generation (SHG) can be used as a screening technique to speed up the correlation of genetics/phenotype/OI types understanding. In the present work we have used quantitative second harmonic generation (SHG) imaging microscopy to investigate the collagen matrix organization of the OI human skin samples comparing with normal control patients. By comparing fibril collagen distribution and spatial organization, we calculated the anisotropy and texture patterns of this structural protein. The analysis of the anisotropy was performed by means of the two-dimensional Discrete Fourier Transform and image pattern analysis with Gray-Level Co-occurrence Matrix (GLCM). From these results, we show that statistically different results are obtained for the normal and disease states of OI.

Adur, J.; Ferreira, A. E.; D'Souza-Li, L.; Pelegati, V. B.; de Thomaz, A. A.; Almeida, D. B.; Baratti, M. O.; Carvalho, H. F.; Cesar, C. L.

2012-02-01

197

In vivo multiphoton imaging of the cornea: polarization-resolved second harmonic generation from stromal collagen  

NASA Astrophysics Data System (ADS)

Multiphoton microscopy provides specific and contrasted images of unstained collagenous tissues such as tendons or corneas. Polarization-resolved second harmonic generation (SHG) measurements have been implemented in a laserscanning multiphoton microscope. Distortion of the polarimetric response due to birefringence and diattenuation during propagation of the laser excitation has been shown in rat-tail tendons. A model has been developed to account for these effects and correct polarization-resolved SHG images in thick tissues. This new modality is then used in unstained human corneas to access two quantitative parameters: the fibrils orientation within the collagen lamellae and the ratio of the main second-order nonlinear tensorial components. Orientation maps obtained from polarization resolution of the trans-detected SHG images are in good agreement with the striated features observed in the raw images. Most importantly, polarization analysis of the epi-detected SHG images also enables to map the fibrils orientation within the collagen lamellae while epi-detected SHG images of corneal stroma are spatially homogenous and do not enable direct visualization of the fibrils orientation. Depth profiles of the polarimetric SHG response are also measured and compared to models accounting for orientation changes of the collagen lamellae within the focal volume. Finally, in vivo polarization-resolved SHG is performed in rat corneas and structural organization of corneal stroma is determined using epi-detected signals.

Latour, G.; Gusachenko, I.; Kowalczuk, L.; Lamarre, I.; Schanne-Klein, M.-C.

2012-02-01

198

Analysis of spatial lamellar distribution from adaptive-optics second harmonic generation corneal images  

PubMed Central

The spatial organization of stromal collagen of ex-vivo corneas has been quantified in adaptive-optics second harmonic generation (SHG) images by means of an optimized Fourier transform (FT) based analysis. At a particular depth location, adjacent lamellae often present similar orientations and run parallel to the corneal surface. However this pattern might be combined with interweaved collagen bundles leading to crosshatched structures with different orientations. The procedure here reported provides us with both principal and crosshatched angles. This is also able to automatically distinguish a random distribution from a cross-shaped one, since it uses the ratio of the axes lengths of the best-fitted ellipse of the FT data as an auxiliary parameter. The technique has successfully been applied to SHG images of healthy corneas (both stroma and Bowman’s layer) of different species and to corneas undergoing cross-linking treatment.

Bueno, Juan M.; Palacios, Raquel; Chessey, Mary K.; Ginis, Harilaos

2013-01-01

199

Analysis of spatial lamellar distribution from adaptive-optics second harmonic generation corneal images.  

PubMed

The spatial organization of stromal collagen of ex-vivo corneas has been quantified in adaptive-optics second harmonic generation (SHG) images by means of an optimized Fourier transform (FT) based analysis. At a particular depth location, adjacent lamellae often present similar orientations and run parallel to the corneal surface. However this pattern might be combined with interweaved collagen bundles leading to crosshatched structures with different orientations. The procedure here reported provides us with both principal and crosshatched angles. This is also able to automatically distinguish a random distribution from a cross-shaped one, since it uses the ratio of the axes lengths of the best-fitted ellipse of the FT data as an auxiliary parameter. The technique has successfully been applied to SHG images of healthy corneas (both stroma and Bowman's layer) of different species and to corneas undergoing cross-linking treatment. PMID:23847727

Bueno, Juan M; Palacios, Raquel; Chessey, Mary K; Ginis, Harilaos

2013-06-04

200

Application of Fourier transform-second-harmonic generation imaging to the rat cervix.  

PubMed

We present the application of Fourier transform-second-harmonic generation (FT-SHG) imaging to evaluate the arrangement of collagen fibers in five nonpregnant rat cervices. Tissue slices from the mid-cervix and near the external orifice of the cervix were analyzed in both two-dimensions (2D) and three-dimensions (3D). We validate that the cervical microstructure can be quantitatively assessed in three dimensions using FT-SHG imaging and observe collagen fibers oriented both in and out-of-plane in the outermost and the innermost layers, which cannot be observed using 2D FT-SHG analysis alone. This approach has the potential to be a clinically applicable method for measuring progressive changes in collagen organization during cervical remodeling in humans. PMID:23600456

Lau, T Y; Sangha, H K; Chien, E K; McFarlin, B L; Wagoner Johnson, A J; Toussaint, K C

2013-04-19

201

First EISCAT observations of the modification of F-region electron temperatures during RF heating at harmonics of the electron gyro frequency  

Microsoft Academic Search

Results are presented from recent ionospheric F-region modification experiments in which the heater induced anomalous absorption and electron temperature changes were measured for a variety of heater frequencies which included the third and fourth harmonics of the electron gyro frequencies. The results indicate that there are strong minima in the responses of both anomalous absorption and electron heating in the

T. R. Robinson; F. Honary; A. J. Stocker; T. B. Jones; P. Stubbe

1996-01-01

202

ON THE USE OF SCHROEDER PHASED HARMONIC SEQUENCES IN MULTI-FREQUENCY VIBRATION CONTROL OF FLEXIBLE ROTOR\\/MAGNETIC BEARING SYSTEMS  

Microsoft Academic Search

Control strategies based on synchronous vibration cancellation have been successfully applied to rotor- bearing systems incorporating magnetic bearings. In this paper, such a control strategy is extended to provide attenuation of sub and super-harmonic vibration components resulting from multi-frequency excitation of the system. System identification is achieved using test signals applied through the magnetic bearings that consist of multiple frequency

Mehmet N. Sahinkaya; Matthew O. T. Cole; Clifford R. Burrows

203

Harmonic motion imaging for focused ultrasound (HMIFU): a fully integrated technique for sonication and monitoring of thermal ablation in tissues.  

PubMed

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. PMID:18367802

Maleke, C; Konofagou, E E

2008-03-07

204

Harmonic quadrature demodulation for extracting the envelope of the second harmonic component  

NASA Astrophysics Data System (ADS)

An efficient method for separating the harmonic component (2f0) from the fundamental component (f0) using harmonic quadrature demodulation is presented. In the proposed method, the focused ultrasound signal is mixed with cosine and sine signal waveforms of harmonic frequency 2f0 to produce the inphase and quadrature components, respectively. The quadrature component is Hilbert-transformed and then added to the inphase component. This process cancels out both the high and low frequency components of the mixed fundamental signal and the high frequency component of the mixed harmonic signal, leaving only the envelope of the harmonic signal at the base band. This signal is then fed to a low-pass filter to remove out of band noise. In summary, this method can extract the harmonic signal after a single transmit-receive event even when there exists frequency overlap between the f0 and 2f0 components. Hence, the proposed method is superior to the pulse inversion method which requires twice as many transmit-receive cycles as well as the conventional filtering method which has a bandwidth limitation. Therefore, one can find the proposed method useful not only for tissue harmonic imaging but also for contrast agent imaging in applications where high frame rate or low motion artifact is important. The proposed method is verified by both the analytic and computer simulation studies. For a stationary target, the difference between the estimated harmonic signals by the proposed and the pulse inversion methods is within 0.1%.

Kim, Sang-Min; Song, Jae-Hee; Song, Tai-Kyong

2008-04-01

205

Optical Clearing for Improved Contrast in Second Harmonic Generation Imaging of Skeletal Muscle  

PubMed Central

Using second harmonic generation (SHG) imaging microscopy, we have examined the effect of optical clearing with glycerol to achieve greater penetration into specimens of skeletal muscle tissue. We find that treatment with 50% glycerol results in a 2.5-fold increase in achievable SHG imaging depth. Signal processing analyses using fast Fourier transform and continuous wavelet transforms show quantitatively that the periodicity of the sarcomere structure is unaltered by the clearing process and that image quality deep in the tissue is improved with clearing. Comparison of the SHG angular polarization dependence also shows no change in the supramolecular organization of acto-myosin complexes. By contrast, identical treatment of mouse tendon (collagen based) resulted in a strong decrease in SHG response. We suggest that the primary mechanism of optical clearing in muscle with glycerol treatment results from the reduction of cytoplasmic protein concentration and concomitant decrease in the secondary inner filter effect on the SHG signal. The lack of glycerol concentration dependence on the imaging depth indicates that refractive index matching plays only a minor role in the optical clearing of muscle. SHG and optical clearing may provide an ideal mechanism to study physiology in highly scattering skeletal or cardiac muscle tissue with significantly improved depth of penetration and achievable imaging depth.

Plotnikov, Sergey; Juneja, Vaibhav; Isaacson, Ariel B.; Mohler, William A.; Campagnola, Paul J.

2006-01-01

206

Ex vivo imaging and quantification of liver fibrosis using second-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Conventionally, liver fibrosis is diagnosed using histopathological techniques. The traditional method is time-consuming in that the specimen preparation procedure requires sample fixation, slicing, and labeling. Our goal is to apply multiphoton microscopy to efficiently image and quantitatively analyze liver fibrosis specimens bypassing steps required in histological preparation. In this work, the combined imaging modality of multiphoton autofluorescence (MAF) and second-harmonic generation (SHG) was used for the qualitative imaging of liver fibrosis of different METAVIR grades under label-free, ex vivo conditions. We found that while MAF is effective in identifying cellular architecture in the liver specimens, it is the spectrally distinct SHG signal that allows the characterization of the extent of fibrosis. We found that qualitative SHG imaging can be used for the effective identification of the associated features of liver fibrosis specimens graded METAVIR 0 to 4. In addition, we attempted to associate quantitative SHG signal to the different METAVIR grades and found that an objective determination of the extent of disease progression can be made. Our approach demonstrates the potential of using multiphoton imaging in rapid classification of ex vivo liver fibrosis in the clinical setting and investigation of liver fibrosis-associated physiopathology in animal models in vivo.

Sun, Tzu-Lin; Liu, Yuan; Sung, Ming-Chin; Chen, Hsiao-Ching; Yang, Chun-Hui; Hovhannisyan, Vladimir; Lin, Wei-Chou; Jeng, Yung-Ming; Chen, Wei-Liang; Chiou, Ling-Ling; Huang, Guan-Tarn; Kim, Ki-Hean; So, Peter T. C.; Chen, Yang-Fang; Lee, Hsuan-Shu; Dong, Chen-Yuan

2010-05-01

207

Low-Power Analog Processing for Sensing Applications: Low-Frequency Harmonic Signal Classification  

PubMed Central

A low-power analog sensor front-end is described that reduces the energy required to extract environmental sensing spectral features without using Fast Fouriér Transform (FFT) or wavelet transforms. An Analog Harmonic Transform (AHT) allows selection of only the features needed by the back-end, in contrast to the FFT, where all coefficients must be calculated simultaneously. We also show that the FFT coefficients can be easily calculated from the AHT results by a simple back-substitution. The scheme is tailored for low-power, parallel analog implementation in an integrated circuit (IC). Two different applications are tested with an ideal front-end model and compared to existing studies with the same data sets. Results from the military vehicle classification and identification of machine-bearing fault applications shows that the front-end suits a wide range of harmonic signal sources. Analog-related errors are modeled to evaluate the feasibility of and to set design parameters for an IC implementation to maintain good system-level performance. Design of a preliminary transistor-level integrator circuit in a 0.13 ?m complementary metal-oxide-silicon (CMOS) integrated circuit process showed the ability to use online self-calibration to reduce fabrication errors to a sufficiently low level. Estimated power dissipation is about three orders of magnitude less than similar vehicle classification systems that use commercially available FFT spectral extraction.

White, Daniel J.; William, Peter E.; Hoffman, Michael W.; Balkir, Sina

2013-01-01

208

In Vivo Feasibility of Real-Time Monitoring of Focused Ultrasound Surgery (FUS) Using Harmonic Motion Imaging (HMI)  

Microsoft Academic Search

In this study, the Harmonic Motion Imaging for Focused Ultrasound (HMIFU) technique is applied to monitor changes in mechanical properties of tissues during thermal therapy in a transgenic breast cancer mouse model in vivo. An HMIFU system, composed of a 4.5-MHz focused ultrasound (FUS) and a 3.3-MHz phased-array imaging transducer, was mechanically moved to image and ablate the entire tumor.

Caroline Maleke

2010-01-01

209

Neural Network Based High Accuracy Frequency Harmonic Analysis in Power System  

Microsoft Academic Search

A back-propagation neural network method is proposed for accurate frequencies, amplitudes and phases estimation from periodic\\u000a signals in power systems, and the convergence theorem shows that the proposed algorithm can be convergent asymptotically to\\u000a its global minimum. The method is aimed at the system in which the sampling frequency cannot be locked on the actual fundamental\\u000a frequency. Some simulating examples

Xiaohua Wang; Yigang He; Ying Long

2007-01-01

210

Stepped frequency imaging for flaw monitoring: Final report  

Microsoft Academic Search

This report summarizes the results of research into the usefulness of stepped frequency imaging (SFI) to nuclear power plant inspection. SFI is a method for producing ultrasonic holographic images without the need to sweep a two-dimensional aperture with the transducer. Instead, the transducer may be translated along a line. At each position of the transducer the frequency is stepped over

Hildebrand

1988-01-01

211

Harmonic tracking of acoustic radiation force-induced displacements.  

PubMed

Ultrasound-based elasticity imaging methods rely upon accurate estimates of tissue deformation to characterize the mechanical properties of soft tissues. These methods are corrupted by clutter, which can bias and/or increase variance in displacement estimates. Harmonic imaging methods are routinely used for clutter suppression and improved image quality in conventional B-mode ultrasound, but have not been utilized in ultrasound-based elasticity imaging methods. We introduce a novel, fully-sampled pulse-inversion harmonic method for tracking tissue displacements that corrects the loss in temporal sampling frequency associated with conventional pulse-inversion techniques. The method is implemented with acoustic radiation force impulse (ARFI) imaging to monitor the displacements induced by an impulsive acoustic radiation force excitation. Custom pulse sequences were implemented on a diagnostic ultrasound scanner to collect spatially-matched fundamental and harmonic information within a single acquisition. B-mode and ARFI images created from fundamental data collected at 4 MHz and 8 MHz are compared with 8-MHz harmonic images created using a band-pass filter approach and the fully sampled pulse-inversion method. In homogeneous, tissue-mimicking phantoms, where no visible clutter was observed, there was little difference in the axial displacements, estimated jitter, and normalized cross-correlation among the fundamental and harmonic tracking methods. The similarity of the lower- and higher-frequency methods suggests that any improvement resulting from the increased frequency of the harmonic components is negligible. The harmonic tracking methods demonstrated a marked improvement in B-mode and ARFI image quality of in vivo carotid arteries. Improved feature detection and decreased variance in estimated displacements were observed in the arterial walls of harmonic ARFI images, especially in the pulse-inversion harmonic ARFI images. Within the lumen, the harmonic tracking m. PMID:24158290

2013-11-01

212

Effect of bandwidth on beam smoothing and frequency conversion at the third harmonic of the Nova laser  

NASA Astrophysics Data System (ADS)

We present the results of experiments performed on the Nova laser system to determine the effect of bandwidth on third harmonic (3(omega) ) frequency conversion and beam smoothing by spectral dispersion (SSD). Our experiments utilized a wide bandwidth fiber optic cross- phase modulated (XPM) source and a narrower bandwidth microwave modulated (FM) source, each centered at 1053 nm (1 (omega) ). A significant fraction (> 50%) of the 1(omega) XPM bandwidth was transferred to the 3(omega) beam (22 cm-1 yields 36 cm-1), yielding 0.13% bandwidth at 3(omega) . The maximum intrinsic narrowband 3(omega) frequency conversion obtained using a type-II/type-II KDP crystal array was 62%. The intrinsic efficiency obtained at the Nova 10-beam chamber is typically > 65%. Frequency conversion was essentially unaffected by the 2 cm-1 bandwidth obtained from FM source. However, the 5 - 16 cm-1 of bandwidth from the XPM source reduced the conversion efficiency to approximately 24%. We have developed broadband frequency conversion codes and broadband pulse simulations to model our results, and have obtained good agreement with experiment.

Pennington, Deanna M.; Henesian, Mark A.; Dixit, Sham N.; Powell, Howard T.; Thompson, Calvin E.; Weiland, Timothy L.

1993-05-01

213

Theoretical analysis of dynamic chemical imaging with lasers using high-order harmonic generation  

SciTech Connect

We report theoretical investigations of the tomographic procedure suggested by Itatani et al. [Nature (London) 432, 867 (2004)] for reconstructing highest occupied molecular orbitals (HOMOs) using high-order harmonic generation (HHG). Due to the limited range of harmonics from the plateau region, we found that even under the most favorable assumptions, it is still very difficult to obtain accurate HOMO wave functions using the tomographic procedure, but the symmetry of the HOMOs and the internuclear separation between the atoms can be accurately extracted, especially when lasers of longer wavelengths are used to generate the HHG. Since the tomographic procedure relies on approximating the continuum wave functions in the recombination process by plane waves, the method can no longer be applied upon the improvement of the theory. For future chemical imaging with lasers, we suggest that one may want to focus on how to extract the positions of atoms in molecules instead, by developing an iterative method such that the theoretically calculated macroscopic HHG spectra can best fit the experimental HHG data.

Van-Hoang Le [J. R. Macdonald Laboratory, Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506 (United States); Department of Physics, University of Pedagogy, 280 An Duong Vuong, Ward 5, Ho Chi Minh City (Viet Nam); Anh-Thu Le; Xie Ruihua; Lin, C. D. [J. R. Macdonald Laboratory, Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506 (United States)

2007-07-15

214

Observations of high-frequency harmonic tremor in Fogo, Cape Verde Islands  

Microsoft Academic Search

We report observations of high-frequency (HF) volcanic tremor, with spectral peaks in the band 5 20 Hz, recorded in Fogo Island, Cape Verde archipelago. Several occurrences are characterized by regularly spaced spectral peaks, but the fundamental frequency is missing. The signal is strong enough to be weakly detected on the southern islands of the archipelago, at distances of 20, 80

Sandra I. N. Heleno; Bruno V. E. Faria; Zuleyka Bandomo; João F. B. D. Fonseca

2006-01-01

215

Second-harmonic and sum-frequency generation for surface studies  

SciTech Connect

Second harmonic generation (SHG) has now been well established as a versatile surface-sensitive probe. It has been used to study electrochemical processes at electrode surfaces, molecular adsorption and desorption at metal and semiconductor surfaces, orientational phase transition of molecular monolayers on water, surface reconstruction and epitaxial growth, and so on. More recently, it has been employed as a tool to monitor monolayer polymerization and other surface reactions, to probe polar order of molecules at interfaces, and to measure molecular nonlinearity. While most surface techniques are restricted to the solid/vacuum environment, SHG is applicable to nearly all interfaces as long as the interfaces are accessible by light. In addition, SHG has the advantages of being capable of in-situ measurements with high temporal, spatial, and spectral resolutions.

Hunt, J.H.; Guyot-Sionnest, P.; Shen, Y.R.

1987-07-01

216

Multiple harmonic plasma emission  

SciTech Connect

A generalized weak turbulence theory for electromagnetic emission at multiple harmonics of the plasma frequency is developed. In the literature, the electromagnetic emission at the plasma frequency and/or its second harmonic has been intensively studied. However, the emission at harmonics higher than the second harmonic is scarcely discussed. In the present paper, the higher harmonic plasma emission is explained by taking the interactions between the transverse mode and electrostatic nonlinear eigenmodes into consideration. The present analysis incorporates electrostatic nonlinear harmonic Langmuir waves into the fully electromagnetic weak turbulence formalism recently reformulated on the basis of the statistical mechanical Klimontovich approach. The wave kinetic equations for the transverse electromagnetic and Langmuir waves interacting with the harmonic Langmuir waves are derived, on the basis of which the emission of electromagnetic waves near multiple harmonics of the plasma frequency is qualitatively discussed.

Yi, Sumin; Yoon, Peter H.; Ryu, Chang-Mo [Department of Physics, Pohang University of Science and Technology, Pohang (Korea, Republic of); Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); Department of Physics, Pohang University of Science and Technology, Pohang (Korea, Republic of)

2007-01-15

217

Thin and Slow Smoke Detection by Using Frequency Image  

NASA Astrophysics Data System (ADS)

In this paper, a new method to detect thin and slow smoke for early fire alarm by using frequency image has been proposed. The correlation coefficient of the frequency image between the current stage and the initial stage are calculated, so are the gray image correlation coefficient of the color image. When the thin smoke close to transparent enters into the camera view, the correlation coefficient of the frequency image becomes small, while the gray image correlation coefficient of the color image hardly change and keep large. When something which is not transparent, like human beings, etc., enters into the camera view, the correlation coefficient of the frequency image becomes small, as well as that of color image. Based on the difference of correlation coefficient between frequency image and color image in different situations, the thin smoke can be detected. Also, considering the movement of the thin smoke, miss detection caused by the illustration change or noise can be avoided. Several experiments in different situations are carried out, and the experimental results show the effect of the proposed method.

Zheng, Guang; Oe, Shunitiro

218

Observations of high-frequency harmonic tremor in Fogo, Cape Verde Islands  

Microsoft Academic Search

We report observations of high-frequency (HF) volcanic tremor, with spectral peaks in the band 5–20 Hz, recorded in Fogo Island, Cape Verde archipelago. Several occurrences are characterized by regularly spaced spectral peaks, but the fundamental frequency is missing. The signal is strong enough to be weakly detected on the southern islands of the archipelago, at distances of 20, 80 and 120 km

Sandra I. N. Heleno; Bruno V. E. Faria; Zuleyka Bandomo; João F. B. D. Fonseca

2006-01-01

219

OPTICAL METROLOGY AND QUANTUM FREQUENCY STANDARDS: Optical frequency standard based on a Nd:YAG laser stabilised by saturated absorption resonances in molecular iodine using second-harmonic radiation  

NASA Astrophysics Data System (ADS)

The results of studies devoted to the development of the optical frequency standard based on a diode-pumped 1064-nm single-frequency ring Nd:YAG laser with intracavity frequency doubling are presented. The laser frequency was stabilised by saturated absorption resonances in molecular iodine at the second-harmonic frequency of the laser (at 532 nm). The saturated absorption resonances were observed in an external luminescent cell. The relative long-term frequency stability achieved in experiments was ~6×10-15. The physical and technical factors affecting the long-term frequency stability and reproducibility are investigated.

Skvortsov, Mikhail N.; Okhapkin, M. V.; Nevsky, A. Yu; Bagaev, Sergei N.

2004-12-01

220

Three-dimensional echocardiography with tissue harmonic imaging shows excellent reproducibility in assessment of left ventricular volumes  

Microsoft Academic Search

We studied the reproducibility of repeated measurements of left ventricular (LV) volumes by 2-dimensional (biplane method of disks) and 3-dimensional echocardiography (coaxial scanning) with tissue harmonic imaging. Ten healthy subjects underwent estimation of LV volumes by transthoracic echocardiography twice within 1 week by 2 different operators to investigate interexamination and operator variance. In addition, the analysis of LV volume was

W. Yong Kim; Peter Søgaard; Henrik Egeblad; Niels Trolle Andersen; Bent Ø Kristensen

2001-01-01

221

Detection of Myocardial Perfusion in Multiple Echocardiographic Windows With One Intravenous Injection of Microbubbles Using Transient Response Second Harmonic Imaging  

Microsoft Academic Search

Objectives. The purpose of this study was to prove that transient response harmonic imaging could detect normal and abnormal myocardial perfusion in multiple echocardiographic windows with one intravenous injection of microbubbles in humans.Background. Myocardial ultrasound contrast can be produced from intravenous perfluorocarbon-exposed sonicated dextrose albumin, and ultrasound can be significantly improved by briefly suspending the interval between frame rates. Whether

Thomas R. Porter; Shouping Li; David Kricsfeld; Robert W. Armbruster

1997-01-01

222

Face Synthesis and Recognition from a Single Image under Arbitrary Unknown Lighting Using a Spherical Harmonic Basis Morphable Model  

Microsoft Academic Search

Understanding and modifying the effects of arbitrary il- lumination on human faces in a realistic manner is a chal- lenging problem both for face synthesis and recognition. Recent research demonstrates that the set of images of a convex Lambertian object obtained under a wide variety of lighting conditions can be approximated accurately by a low-dimensional linear subspace using spherical harmon-

Lei Zhang; Sen Wang; Dimitris Samaras

2005-01-01

223

Towards nanoscopic imaging using third harmonic generation in nanospheres based on optical trapping  

NASA Astrophysics Data System (ADS)

Imaging cellular structures in vivo with molecular level resolution is Holy Grail of Biological Science. However, the resolution of optical microscopy is limited by the diffraction of light to approximately lambda/2 (250 nm for visible light). While electron microscopy, STM and AFM provide much higher resolution, in vivo imaging is hardly possible. That's why it is important to significantly improve the resolution for optical microscopy, which also provides molecular specific information about the structures of interest. We proposed, designed and built a prototype of a novel type of microscope, which is called Trapped Particle Optical Microscope (TPOM) and uses nanoparticle as a probe. Trapped particle is detected by Dark Field (DF) illumination built upon conical lens and combined with polarization imaging. We believe that for the first we are able observe the motion of colloidal particles as small as 10nm and protein molecules in solution. We were able to trap and steer 10nm to 3 micron particles in 3 dimensions and detect the Third Harmonic (TH) signal generated in particle by trapping continuous wave Near InfraRed (NIR) laser. Based on our ability to trap and steer gold nano sphere and detect TH signal, generated by it, we propose to use TH as near-field detection signal for TPOM. The other great advantage of this microscope is that illumination and detection signals are significantly spectrally separated.

Faustov, Alexei R.

224

Theoretical predictions of harmonic generation from submicron ultrasound contrast agents for nonlinear biomedical ultrasound imaging.  

PubMed

Submicron ultrasound contrast agents have aroused attention for their significant promise in ultrasonic contrast/molecular imaging, targeted therapy and echo particle imaging velocimetry. However, nonlinear acoustic properties of submicron encapsulated gas bubbles for ultrasonic applications are still not clearly understood. In this paper, nonlinear acoustic emission characteristics from submicron bubbles were examined using a numerical study. The modified RP equation incorporating viscosity, acoustic radiation, thermal effects and encapsulated shell was used to study single bubble dynamics. Further, a size integration method, shown previously to be useful in prediction of backscatter spectra from groups of bubbles, was applied to analyse response from a bubble population. We show that bubbles with radii (200-500 nm) produce significant subharmonic and ultraharmonic components of the backscatter spectrum, while smaller bubbles (<200 nm) provide substantial second harmonic components. Additionally, nanoscale bubbles (<100 nm) produce very low backscatter amplitudes and thus may not be useful with the use of current ultrasound technology. Analysing optimal ultrasound driving pressures and bubbles size ranges for maximal subharmonic and ultraharmonic signals showed that sub and ultraharmonic mode nonlinear imaging methods may be potentially competitive for larger size bubbles (>200 nm) in providing proper contrast-to-tissue signal ratios. PMID:16424581

Zheng, Hairong; Mukdadi, Osama; Shandas, Robin

2006-01-11

225

Contrast enhancement in combined two-photon second harmonic imaging of skin by using hyperosmotic agents  

NASA Astrophysics Data System (ADS)

We used combined simultaneous two-photon excitation fluorescence microscopy (TPE) and second harmonic generation microscopy (SHG) on human skin tissue slices. We studied the effect caused by topical application of optical clearing agents (OCAs). We demonstrated that hyperosmotic agents as glycerol, propylene glycol and glucose in aqueous solution, are all effective in improving excitation light penetration depth and in enhancing image contrast. The effect caused on acquired images by sample immersion in OCAs or in their aqueous dilution, was studied. We observed a similar clearing effect with TPE and SHG acquisitions, with different effectiveness and rising time for each agent. The TPE acquired data are in good agreement with a simple diffusion model developed. From the SHG acquisition some different behaviour was observed. All three agents are potentially bio-compatible and effective in reducing scattering, improving light penetration depth and image contrast. Use of OCA can be suitable for in vivo application in two-photon microscopy, as well as in other techniques performing optical biopsy of human skin tissue.

Cicchi, R.; Massi, D.; Stambouli, D.; Sampson, D. D.; Pavone, F. S.

2006-03-01

226

New harmonic materials: index engineering. Thin-thick quadrature frequency conversion  

SciTech Connect

The quadrature conversion scheme is a method of generating the second harmonic. The scheme, which uses two crystals in series, has several advantages over single-crystal or other two crystal schemes. The most important is that it is capable of high conversion efficiency over a large dynamic range of drive intensity and detuning angle. Consider a pair of KDP crystals cut for type-II phase matching. In the quadrature scheme, the optic axes of the crystals are arranged so that the plans containing the direction of the laser beam and their optic axes (the kz planes) are mutually perpendicular. This arrangement has two important properties. First, in type-II phase matching, the incident wave is polarized at 45 deg to the kz plane of the crystal. This, in the quadrature scheme, if the incident wave is correctly polarized for efficient conversion in the first crystal, it is also correctly polarized for efficient conversion in the second crystal. Both crystals can therefore convert efficiently.

Eimerl, D.

1985-02-07

227

Synergy in Two-Frequency Fast Wave Cyclotron Harmonic Absorption in DIII-D  

SciTech Connect

Fast waves (FWs) at 60 MHz and at 90 MHz are coupled to DIII-D discharges for central heating and current drive at net FW power up to 3.5 MW. The primary absorption mechanism is intended to be direct electron damping in the plasma core. In discharges at B = 2 T with fast deuteron populations from neutral beam injection, 4th and 6th deuterium cyclotron harmonic absorption on the fast ions competes with direct electron damping. Previous experiments have shown that the 6{omega}{sub D} absorption of the 90 MHz FWs is weaker than the 4{omega}{sub D} absorption of 60 MHz FWs, in agreement with a model that includes unspecified edge losses. Recent experiments have shown that if the fast deuterons are accelerated by absorption of 60 MHz (4{omega}{sub D}) FWs, adding 90 MHz power (6{omega}{sub D}) can increase the fusion neutron rate by a larger increment than is obtained with 90 MHz power alone. Details of this synergy between 4{omega}{sub D} and 6{omega}{sub D} absorption are presented.

Pinsker, R. I.; Choi, M. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Heidbrink, W. W.; Zhu, Y. [University of California-Irvine, Irvine, California (United States); Porkolab, M. [Massachusetts Institute of Technology, Cambridge, Massachusetts (United States); Baity, F. W. [Oak Ridge National Laboratory, Oak Ridge, Tennessee (United States); Hosea, J. C. [Princeton Plasma Physics Laboratory, Princeton, New Jersey (United States)

2009-11-26

228

Observation of 200th harmonic with fractional linewidth of 10-10 in a microwave frequency comb generated in a tunneling junction  

NASA Astrophysics Data System (ADS)

A microwave frequency comb with up to 200th harmonic of a laser repetition rate is generated by nonlinear intermodal mixing of 15 fs laser pulses in the junction of a scanning tunneling microscope. The highest harmonic has an output power of -146 dBm at 14.85 GHz with a signal/noise ratio of 20 dB and a measured linewidth of 1.2 Hz, which is still larger than the actual linewidth due to phase noise of the spectrum analyzer. Theory suggests that the harmonics have comparable magnitude up to terahertz frequencies, while the observed roll-off is caused by a shunting capacitance in detection circuitry.

Hagmann, Mark J.; Taylor, Antoinette J.; Yarotski, Dmitry A.

2012-12-01

229

Analytical approach of the stator current frequency harmonics computation for detection of induction machine rotor faults  

Microsoft Academic Search

The aim of this paper is to analyze theoretically and experimentally the stator current of a three-phase squirrel cage induction machine in order to show how it is influenced by rotor faults. The approach used for this study analyzes the modification introduced by n broken rotor bars in the rotor cage magnetomotive force (MMF) and then, estimates the resulting frequency

H. Henao; G. A. Capolino; H. Razik

2003-01-01

230

Near Field Imaging at Microwave and Millemeter Wave Frequencies  

SciTech Connect

Near field imaging at microwave and millimeter wave frequencies is useful for a wide variety of applications including concealed weapon detection, through-wall and inner-wall imaging, ground penetrating radar imaging, radar cross section analysis, and non-destructive evaluation of materials. A variety of novel imaging techniques have been developed for many of these applications at the Pacific Northwest National Laboratory (PNNL) . These techniques make use of wideband holographic wavefront reconstruction methods, and have been developed to optimize the image quality and resolution. This paper will summarize several of these techniques and show imaging results for several interesting application areas.

Sheen, David M.; McMakin, Douglas L.; Hall, Thomas E.

2007-06-03

231

Generation of High-Frequency Harmonics in the Case of Large-Amplitude Vibrations of a Gas in a Closed Tube  

Microsoft Academic Search

Based on the model of a viscous compressible heat-conducting gas, the author investigates numerically the vibrations of a gas column in a closed tube in excitation by a flat piston that moves according to a harmonic law with an amplitude comparable to the resonator length. Consideration is given to the process of transformation of the mode and frequency of vibrations

A. L. Tukmakov

2001-01-01

232

Forward and backward second harmonic generation imaging of corneal and scleral collagen  

NASA Astrophysics Data System (ADS)

Collagen is the most abundant protein in mammalian and forms various types of tissues. On ocular surface, sclera, limbus and cornea are composed with fibril form collagen. However, unlike other connective tissues with high opacity, cornea has extraordinary high transparency which originates from the regular arrangement of collagen fibers within cornea. Cornea is responsible for 80% of focusing power of our vision and any corneal damage can cause severe vision loss. The high transparency of cornea makes it difficult to probe it without invasive processes, especially stromal structure alternations. Collagen, however, is an effective second harmonic generator due to its non-centrosymmetric molecule structure and can be visualized with nonlinear optical process without labeling. In addition, the deeper penetration and point like effective volume of SHG can also provide 3-dimensional information with minimum invasion. Backward SHG imaging has been approved effectively demonstrating structure alternation in infective keratitis, thermal damage in cornea, corneal scar, post refractive surgery wound healing and keratoconus which is also a main complication after refractive surgery[1-6]. In practical, backward SHG has the potentiality to be developed as clinical examination modality. However, Han et al also demonstrated that backward SHG (BSHG) imaging provides collagen bundle information while forward SHG (FSHG) provides more detailed, submicron fibril structure visualization within corneal stroma[7]. In sclera, which also has type I collagen as its main composition, BSHG and FSHG imaging reveal similar morphology. Comparing with what Legare et al demonstrated that BSHG in bulk tissue mainly originate from backscattered FSHG[8], the huge difference between corneal BSHG and FSHG imaging originate from the high transparency of cornea. However, only BSHG could be applied in practical. Therefore, if the correlation of BSHG and FSHG, which reveals more architecture details, can be established, BSHG may be used in clinical examination in the future.

Lo, Wen; Tan, Hsin-Yuan; Lin, Ming-Guo; Hsueh, Chu-Mei; Chen, Wei-Liang; Lin, Sung-Jan; Jee, Shiou-Hwa; Dong, Chen-Yuan

2008-03-01

233

Combined two-photon excited fluorescence and second harmonic generation imaging microscopy of collagen structures  

NASA Astrophysics Data System (ADS)

Collagen is known to be a very efficient producer of both second harmonic generation (SHG) and two-photon excited fluorescence and the combined use of those nonlinear signals is emerging as a new imaging probe to be used as a diagnostic tool. By recording structural information of collagen between different samples, the technique shows promising for the study of the distribution of collagen in tissue and for identifying pathologic conditions. Unique information about the molecular organization of collagen can be extracted from SHG and TPEF imaging data in several ways and we have initiated a systematic study of these issues. The main objectives of this work are to combine TPEF and SHG methodologies, in order to elucidate and quantify cross-linking and to describe a model of fibrils orientation within different samples. In this early approach we discuss fundamental principles governing SHG and TPEF and present the first results of applying these rules to collagen type I images analysis. By comparing signals between lyophilized and soluble collagen we validate that the SHG signal arises from dipolar interactions that are enhanced by the quaternary structure of collagen fibrils, while TPEF arises from fluorophores which are suggested to be products of cross-linking. Using a homogenization protocol of acid treated collagen gels we manage to produce SHG and TPEF active thin films, which characterized by means of their contrast capability. A home-built scanning microscope employing SHG and TPEF was used for the high-resolution imaging of endogenous SHG and TPEF signals, without exogenous dyes.

Psilodimitrakopoulos, Sotiris; Filippidis, George; Kouloumentas, Christos; Alexandratou, Eleni; Yova, Dido

2006-03-01

234

Efficient conversion of picosecond laser pulses into second-harmonic frequency using group-velocity dispersion  

Microsoft Academic Search

A computer model has been used to investigate frequency doubling of 1-psec duration high-power pulses in potassium dihydrogen phosphate (KDP) for type-II phase matching. It has been found that group-velocity dispersion can be used to advantage by predelaying the ordinary and extraordinary polarizations appropriately in a thin KDP crystal with its axes aligned at 90° to the main conversion crystal.

Yanjie Wang; R. Dragila

1990-01-01

235

PHASE SPACE ANALYSIS FOR A HIGH FREQUENCY TIME-HARMONIC ACOUSTIC FIELD IN A PLANAR WAVEGUIDE  

Microsoft Academic Search

The aim of this paper is to present a new description of a two-dimensional high frequency acoustic field by means of a conjoint « space-wave number » representation . To a signal with spatial coordinate (x,y), is associated a function defined in the phase space domain (x,y,kx,ky). At each point (x,y) of the field, is asociated a two-dimensional wave number

Benoît Teyssandier; Claude Depollier; Vincent Pagneux; Laurent Simon

236

In vivo wound healing diagnosis with second harmonic and fluorescence lifetime imaging.  

PubMed

Skin wounds heal when a series of cell lineages are triggered, followed by collagen deposition, to reconstruct damaged tissues. This study evaluates the regeneration of collagen and change in cellular metabolic rate in vivo during wound healing in rats, with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy respectively. The metabolic rate of cells is reflected through the lifetime of the autofluorescence from the co-enzyme protein, reduced nicotinamide adenine dinucleotide, due to its change in the relative concentration of bound and free forms. A higher than normal cellular metabolic rate is observed during the first week of healing, which decreases gradually after eight days of wound formation. SHG signal intensity change indicates the net degradation of collagen during the inflammatory phase, and net regeneration begins on day five. Eventually, the quantity of collagen increases gradually to form a scar tissue as the final product. Importantly, this work demonstrates the feasibility of an in vivo imaging approach for a normal wound on rat skin, which has the potential to supplement the noninvasive clinical diagnosis of wounds. PMID:23748703

Deka, Gitanjal; Wu, Wei-Wen; Kao, Fu-Jen

2013-06-01

237

In vivo wound healing diagnosis with second harmonic and fluorescence lifetime imaging.  

PubMed

Skin wounds heal when a series of cell lineages are triggered, followed by collagen deposition, to reconstruct damaged tissues. This study evaluates the regeneration of collagen and change in cellular metabolic rate in vivo during wound healing in rats, with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy respectively. The metabolic rate of cells is reflected through the lifetime of the autofluorescence from the co-enzyme protein, reduced nicotinamide adenine dinucleotide, due to its change in the relative concentration of bound and free forms. A higher than normal cellular metabolic rate is observed during the first week of healing, which decreases gradually after eight days of wound formation. SHG signal intensity change indicates the net degradation of collagen during the inflammatory phase, and net regeneration begins on day five. Eventually, the quantity of collagen increases gradually to form a scar tissue as the final product. Importantly, this work demonstrates the feasibility of an in vivo imaging approach for a normal wound on rat skin, which has the potential to supplement the noninvasive clinical diagnosis of wounds. PMID:23264966

Deka, Gitanjal; Wu, Wei-Wen; Kao, Fu-Jen

2013-06-01

238

Quantification of lamellar orientation in corneal collagen using second harmonic generation images  

PubMed Central

Second harmonic generation (SHG) is a well-established optical modality widely used in biomedical optics to image collagen based tissues. The coherent signal of the forward direction SHG produces a high resolution image that can resolve individual fibers (groups of fibrils). In highly ordered collagen lamellae, such as in the corneal stroma, it is important to determine the orientation of the fibers as they contribute significantly to the biomechanics of the tissue. However, due to the crimped structure of the fibers, it is challenging to robustly determine their orientation using an independent computational method, compared to the straight fibers problem. Previous work in the field used the polarization of the fundamental or other techniques involving a more manual selection of the orientation, in order to differentiate between various directions in corneal structures. Yet those lack accuracy and independency. We present a robust independent technique to determine the orientation of the fibers in the corneal structure. The experimental results presented here, taken from different lamellae, demonstrate strongly the correct orientation.

Mega, Yair; Robitaille, Mike; Zareian, Ramin; McLean, James; Ruberti, Jeffrey; DiMarzio, Charles

2013-01-01

239

Nonlinear optical microscopy in biology: Combining second-harmonic generation and two-photon fluorescence imaging  

NASA Astrophysics Data System (ADS)

Optical microscopy has been since long a truly enabling visualization technique in the biological and biomedical sciences. Linear optical microscopy relies on simple linear optical effects. Nonlinear optical microscopy relies on the nonlinear optical properties of endogenous or exogenous chromophores to produce a better image. Two-photon fluorescence (TPF), a third-order nonlinear optical effect and observed at the focal spot only due to the quadratic intensity dependence, results in inherently higher resolution than possible for one-photon fluorescence, observed over the complete Rayleigh range. Second-harmonic generation (SHG) is a second-order nonlinear optical effect only observed for non-centrosymmetric arrangements of non-centrosymmetric chromophores. While this does put a restriction on the chromophores that can be used, it also results in structural information about symmetry when used in combination with TPF. TPF, being a third-order nonlinear process, is not restricted by any symmetry consideration. We will review the molecular design criteria for exogenous probes for combined SHG and TPF nonlinear microscopy, provide examples of optimized chromophores and show microscopy images demonstrating the use of such chromophores in nonlinear microscopy.

Clays, Koen

2011-03-01

240

Holographic Radar Imaging Privacy Techniques Utilizing Dual-Frequency Implementation  

SciTech Connect

Over the last 15 years, the Pacific Northwest National Laboratory has performed significant research and development activities to enhance the state of the art of holographic radar imaging systems to be used at security checkpoints for screening people for concealed threats hidden under their garments. These enhancement activities included improvements to privacy techniques to remove human features and providing automatic detection of body-worn concealed threats. The enhanced privacy and detection methods used both physical and software imaging techniques. The physical imaging techniques included polarization-diversity illumination and reception, dual-frequency implementation, and high-frequency imaging at 60 GHz. Software imaging techniques to enhance the privacy of the person under surveillance included extracting concealed threat artifacts from the imagery to automatically detect the threat. This paper will focus on physical privacy techniques using dual-frequency implementation.

McMakin, Douglas L.; Hall, Thomas E.; Sheen, David M.

2008-04-18

241

Effects of frequency- and direction-dependent elastic materials on linearly elastic MRE image reconstructions  

NASA Astrophysics Data System (ADS)

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.

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

242

Frequency Compounding of the Ultrasound Images Using Wavelet Packets Decomposition  

Microsoft Academic Search

In a standard ultrasound imaging, the radio-frequency (RF) backscattered signals are decimated to get a medical image. The RF signal carries information about the scattering structure. Analysis of the RF signals may get useful clinical information for the tissue characterization. In this paper, the approach that is wavelet packets (WP) decomposition of I\\/Q ultrasound signals was proposed to gain the

Xiaoming Zhou; D. C. Liu

2010-01-01

243

Frequency-modulated steady-state free precession imaging.  

PubMed

Exploration of the possibilities of steady-state free precession (SSFP) excitation has led to the discovery that it is tolerant of slow variations in spectral offset frequency. The effect has been used to eliminate banding artifacts from images obtained with the fully balanced SSFP imaging sequence. PMID:12210915

Foxall, D L

2002-09-01

244

Methods for estimating selected low-flow frequency statistics and harmonic mean flows for streams in Iowa  

USGS Publications Warehouse

A statewide study was conducted to develop regression equations for estimating six selected low-flow frequency statistics and harmonic mean flows for ungaged stream sites in Iowa. The estimation equations developed for the six low-flow frequency statistics include: the annual 1-, 7-, and 30-day mean low flows for a recurrence interval of 10 years, the annual 30-day mean low flow for a recurrence interval of 5 years, and the seasonal (October 1 through December 31) 1- and 7-day mean low flows for a recurrence interval of 10 years. Estimation equations also were developed for the harmonic-mean-flow statistic. Estimates of these seven selected statistics are provided for 208 U.S. Geological Survey continuous-record streamgages using data through September 30, 2006. The study area comprises streamgages located within Iowa and 50 miles beyond the State's borders. Because trend analyses indicated statistically significant positive trends when considering the entire period of record for the majority of the streamgages, the longest, most recent period of record without a significant trend was determined for each streamgage for use in the study. The median number of years of record used to compute each of these seven selected statistics was 35. Geographic information system software was used to measure 54 selected basin characteristics for each streamgage. Following the removal of two streamgages from the initial data set, data collected for 206 streamgages were compiled to investigate three approaches for regionalization of the seven selected statistics. Regionalization, a process using statistical regression analysis, provides a relation for efficiently transferring information from a group of streamgages in a region to ungaged sites in the region. The three regionalization approaches tested included statewide, regional, and region-of-influence regressions. For the regional regression, the study area was divided into three low-flow regions on the basis of hydrologic characteristics, landform regions, and soil regions. A comparison of root mean square errors and average standard errors of prediction for the statewide, regional, and region-of-influence regressions determined that the regional regression provided the best estimates of the seven selected statistics at ungaged sites in Iowa. Because a significant number of streams in Iowa reach zero flow as their minimum flow during low-flow years, four different types of regression analyses were used: left-censored, logistic, generalized-least-squares, and weighted-least-squares regression. A total of 192 streamgages were included in the development of 27 regression equations for the three low-flow regions. For the northeast and northwest regions, a censoring threshold was used to develop 12 left-censored regression equations to estimate the 6 low-flow frequency statistics for each region. For the southern region a total of 12 regression equations were developed; 6 logistic regression equations were developed to estimate the probability of zero flow for the 6 low-flow frequency statistics and 6 generalized least-squares regression equations were developed to estimate the 6 low-flow frequency statistics, if nonzero flow is estimated first by use of the logistic equations. A weighted-least-squares regression equation was developed for each region to estimate the harmonic-mean-flow statistic. Average standard errors of estimate for the left-censored equations for the northeast region range from 64.7 to 88.1 percent and for the northwest region range from 85.8 to 111.8 percent. Misclassification percentages for the logistic equations for the southern region range from 5.6 to 14.0 percent. Average standard errors of prediction for generalized least-squares equations for the southern region range from 71.7 to 98.9 percent and pseudo coefficients of determination for the generalized-least-squares equations range from 87.7 to 91.8 percent. Average standard errors of prediction for weighted-least-squares equations developed for estimating the harmonic-mean-flow statistic for each of the thr

Eash, David A.; Barnes, Kimberlee K.

2012-01-01

245

A 200 GHz active heterodyne receiver MMIC with low sub-harmonic LO power requirements for imaging frontends  

Microsoft Academic Search

This paper presents the design and performance of a 200 GHz, sub-harmonically-pumped, heterodyne receiver MMIC realized in 100 nm metamorphic HEMT technology. The lownoise amplifier stage sets the receiver noise figure to 7 dB and, in combination with the resistive down-conversion mixer, allows for an overall conversion gain of 7 dB at 200 GHz RF frequency. The mixer LO port

I. Kallfass; A. Tessmann; H. Massler; A. Leuther; M. Schlechtweg; O. Ambacher

2009-01-01

246

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)

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.

Quinlan, F.; Ozharar, S.; Gee, S.; Delfyett, P. J.

2009-10-01

247

Magnetospheric Banded Emissions: Their Distribution, Amplitude and Frequency Shifts, and Ambient Plasma and Cyclotron Frequencies as Determined by IMAGE/RPI  

NASA Astrophysics Data System (ADS)

Magnetospheric banded emissions were investigated using both a statistical analysis and by performing detailed case studies with an emphasis on the dynamics near the magnetic equator. An algorithm to automatically search radio-wave dynamic spectra was used to determine the number of bands detected, their spatial distribution and the ambient plasma conditions in the emission generation regions. The algorithm was applied to Jan 2001 - August 2004 data from the Radio Plasma Imager (RPI) on the IMAGE satellite. The statistical results indicated that when the electron plasma frequency could be determined the banded emissions were most common when (1) the electron plasma to cyclotron frequency ratio was between 7 and 8, (2) the L value was between 5 and 8, (3) the magnetic local time was between 15 and 16 hours, (4) the radial distance was between 5.5 and 7 Earth radii, and (4) IMAGE was located near the magnetic equator but there was a tendency for banded emissions to be observed more often at positive than at negative magnetic latitudes. The case studies indicated that (1) the sudden onset of banded emissions corresponds to a rapid drop in the electron plasma to cyclotron frequency ratio, (2) large positive frequency deviations in the banded emissions from values near the midpoints between the electron cyclotron harmonics occur near the magnetic equator, (3) these frequency increases correlate with large amplitude increases suggesting nonlinear processes.

Benson, R. F.; Webb, P. A.; Osherovich, V. A.; Medeiros, M. P.; Sandberg, J.

2006-12-01

248

Second-Harmonic Generation Imaging of Membrane Potential with Retinal Analogues  

PubMed Central

Second-harmonic generation (SHG) by membrane-incorporated probes is a nonlinear optical signal that is voltage-sensitive and the basis of a sensitive method for imaging membrane potential. The voltage dependence of SHG by four different probes, three retinoids (all-trans retinal), and two new retinal analogs, 3-methyl-7-(4?-dimethylamino-phenyl)-2,4,6-heptatrienal (AR-3) and 3,7-dimethyl-9-(4?-dimethylamino-phenyl)-2,4,6,8-nonatetraenal (AR-4), and a styryl dye (FM4-64), were compared in HEK-293 cells. Results were analyzed by fitting data with an expression based on an electrooptic mechanism for SHG, which depends on the complex-valued first- and second-order nonlinear electric susceptibilities (?2 and ?3) of the probe. This gave values for the voltage sensitivity at the cell's resting potential, the voltage where the SHG is minimal, and the amplitude of the signal at that voltage for each of the four compounds. These measures show that ?2 and ?3 are complex numbers for all compounds except all-trans retinal, consistent with the proximities of excitation and/or emission wavelengths to molecular resonances. Estimates of probe orientation and location in the membrane electric field show that, for the far-from-resonance case, the shot noise-limited signal/noise ratio depends on the location of the probe in the membrane, and on ?3 but not on ?2.

Theer, Patrick; Denk, Winfried; Sheves, Mordechai; Lewis, Aaron; Detwiler, Peter B.

2011-01-01

249

Imaging skeletal muscle using second harmonic generation and coherent anti-Stokes Raman scattering microscopy  

PubMed Central

We describe experimental results on label free imaging of striated skeletal muscle using second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy. The complementarity of the SHG and CARS data makes it possible to clearly identify the main sarcomere sub-structures such as actin, myosin, acto-myosin, and the intact T-tubular system as it emanates from the sarcolemma. Owing to sub-micron spatial resolution and the high sensitivity of the CARS microscopy technique we were able to resolve individual myofibrils. In addition, key organelles such as mitochondria, cell nuclei and their structural constituents were observed revealing the entire structure of the muscle functional units. There is a noticeable difference in the CARS response of the muscle structure within actin, myosin and t-tubule areas with respect to laser polarization. We attribute this to a preferential alignment of the probed molecular bonds along certain directions. The combined CARS and SHG microscopy approach yields more extensive and complementary information and has a potential to become an indispensable method for live skeletal muscle characterization.

Pfeffer, Christian P.; Olsen, Bjorn R.; Ganikhanov, Feruz; Legare, Francois

2011-01-01

250

Low frequency radio synthesis imaging of the galactic center region  

NASA Astrophysics Data System (ADS)

The Very Large Array radio interferometer has been equipped with new receivers to allow observations at 330 and 74 MHz, frequencies much lower than were previously possible with this instrument. Though the VLA dishes are not optimal for working at these frequencies, the system is successful and regular observations are now taken at these frequencies. However, new data analysis techniques are required to work at these frequencies. The technique of self- calibration, used to remove small atmospheric effects at higher frequencies, has been adapted to compensate for ionospheric turbulence in much the same way that adaptive optics is used in the optical regime. Faceted imaging techniques are required to compensate for the noncoplanar image distortion that affects the system due to the wide fields of view at these frequencies (~2.3° at 330 MHz and ~11° at 74 MHz). Furthermore, radio frequency interference is a much larger problem at these frequencies than in higher frequencies and novel approaches to its mitigation are required. These new techniques and new system are allowing for imaging of the radio sky at sensitivities and resolutions orders of magnitude higher than were possible with the low frequency systems of decades past. In this work I discuss the advancements in low frequency data techniques required to make high resolution, high sensitivity, large field of view measurements with the new Very Large Array low frequency system and then detail the results of turning this new system and techniques on the center of our Milky Way Galaxy. At 330 MHz I image the Galactic center region with roughly 10 inches resolution and 1.6 mJy beam -1 sensitivity. New Galactic center nonthermal filaments, new pulsar candidates, and the lowest frequency detection to date of the radio source associated with our Galaxy's central massive black hole result. At 74 MHz I image a region of the sky roughly 40° x 6° with, ~10 feet resolution. I use the high opacity of H II regions at 74 MHz to extract three-dimensional data on the distribution of Galactic cosmic ray emissivity, a measurement possible only at low radio frequencies.

Nord, Michael Evans

2005-11-01

251

High-frequency harmonics generation by Bi2Sr2Ca2Cu3Oy ceramic carrying alternating transport current  

Microsoft Academic Search

We have detected the nonlinear magnetic flux generated by a superconducting slab in the presence of an alternating transport current alone, and with no external fields around during the detection. The temperature dependence of induced flux is found to be analogous in its main features to the nonlinear susceptibility: (1) only odd harmonics exist, (2) the third-harmonic signal is bell

A. M. Grishin; V. N. Korenivski; K. V. Rao; A. N. Ulyanov

1994-01-01

252

Study about the current oscillating and harmonic analysis of high frequency chopped wave cascade speed control system  

Microsoft Academic Search

The chopped wave cascade speed control system is a promising lower energy consumption and reduce pollutants discharging technology. Because the electronics and electric devices are adopted to be its kernel component, it is one of the main harmonic sources for the power grid, and consuming lots of reactive power. The analysis and calculation about its harmonics could be used to

Zhang JunWei; Wang Bingshu

2010-01-01

253

Harmonic reduction in thyristor converters by harmonic current injection  

Microsoft Academic Search

The paper describes analytical and experimental results for a new method of current harmonic reduction in thyristor converters. The principle of the method is to modify the current waveforms on the d.c. windings of the converter transformer by injecting harmonic currents at a particular frequency. In practice, third harmonic currents of the power frequency is most efficient. Experimental results carried

A. Ametani

1976-01-01

254

Harmonic frequency scaling factors for Hartree-Fock, S-VWN, B-LYP, B3-LYP, B3PW91 and MP2 with the Sadlej pVTZ electric property basis set  

Microsoft Academic Search

.   Scaling factors for obtaining fundamental vibrational frequencies from harmonic frequencies calculated at six of the most\\u000a commonly used levels of theory have been determined from regression analysis for the polarized-valence triple-zeta (pVTZ)\\u000a Sadlej electric property basis set. The Sadlej harmonic frequency scaling factors for first- and second-row molecules were\\u000a derived from a comparison of a total of 900 individual

Mathew D. Halls; Julia Velkovski; H. Bernhard Schlegel

2001-01-01

255

Effect of bandwidth on beam smoothing and frequency conversion at the third harmonic of the Nova laser  

SciTech Connect

We present the results of experiments performed on the Nova laser system to determine the effect of bandwidth on third harmonic (3{omega}) frequency conversion and beam smoothing by spectral dispersion (SSD). Our experiments utilized a wide bandwidth fiber optic cross-phase modulated (XPM) source and a narrower bandwidth microwave modulated (FM) source, each centered at 1053 nm (1{omega}). The FM source produced {approximately}2 cm{sup {minus}1} of bandwidth, modulated at 3 GHz; the XPM bandwidth was varied from 5 to 15 cm{sup {minus}1}, modulated by the temporally noisy output of a multimode Nd:glass laser ({le} 500 GHz). The FM beam showed no evidence of self-phase modulation in the laser chain produced by intensity fluctuations, and 1{omega} bandwidth was tripled upon conversion to 3{omega} (2--6 cm{sup {minus}1}). The 1{omega} XPM bandwidth increased by {ge} 25% due to self-phase modulation in the laser chain (16--22 cm{sup {minus}1}) due to it`s relative noisy temporal structure. Over 50% of the 1{omega} XPM bandwidth was transferred to the 3{omega} beam (22--36 cm{sup {minus}1}), yielding 0.13% bandwidth at 3{omega}. The maximum intrinsic narrowband 3{omega} frequency conversion obtained using a type-II/type-II KDP crystal array was 62%. The intrinsic efficiency obtained at the Nova 10-beam chamber is typically > 65%. We have developed broadband frequency conversion codes and broadband pulse simulations to model our results, and have obtained good agreement with experiment. Using a random phase plate without bandwidth, we obtained a smoothing level, {sigma}/I {approximately} 0.79, defined by the rms variance normalized with respect to the average intensity. This is less than the theoretically expected value of 1 for an ideal speckle pattern, and could be evidence of polarization smoothing as a result of focus lens birefringence. With spectral dispersion and RPP we demonstrated an excellent level of smoothing with the XPM source.

Pennington, D.M.; Henesian, M.A.; Dixit, S.N.; Powell, H.T.; Thompson, C.E.; Weiland, T.L.

1993-05-01

256

Photoswitchable Nanoprobes Offer Unlimited Brightness in Frequency-Domain Imaging  

SciTech Connect

A single probe has limited brightness in time-domain imaging and such limitation frequently renders individual molecules undetectable in the presence of interference or complex cellular structures. However, a single photoswitchable probe produces a frequency-locked signal, which can be separated from none frequencydependent interference or noise using photoswitchingenabled Fourier transformation (PFT). As a result, the light-modulated probes can be made super bright in the frequency domain simply by acquiring more cycles in the time-domain.

Li, Alexander D.; Zhan, Chuanlang; Hu, Dehong; Wan, Wei; Yao, Jiannian

2011-05-25

257

Pulse-modulated second harmonic imaging microscope quantitatively demonstrates marked increase of collagen in tumor after chemotherapy  

NASA Astrophysics Data System (ADS)

Pulse-modulated second harmonic imaging microscopes (PM-SHIMs) exhibit improved signal-to-noise ratio (SNR) over conventional SHIMs on sensitive imaging and quantification of weak collagen signals inside tissues. We quantify the spatial distribution of sparse collagen inside a xenograft model of human acute myeloid leukemia (AML) tumor specimens treated with a new drug against receptor tyrosine kinase (ABT-869), and observe a significant increase in collagen area percentage, collagen fiber length, fiber width, and fiber number after chemotherapy. This finding reveals new insights into tumor responses to chemotherapy and suggests caution in developing new drugs and therapeutic regimens against cancers.

Raja, Anju M.; Xu, Shuoyu; Sun, Wanxin; Zhou, Jianbiao; Tai, Dean C. S.; Chen, Chien-Shing; Rajapakse, Jagath C.; So, Peter T. C.; Yu, Hanry

2010-09-01

258

Exchange and polarization effect in high-order harmonic imaging of molecular structures  

SciTech Connect

We analyze the importance of exchange, polarization, and electron-electron correlation in high-order harmonic generation in molecules interacting with intense laser fields. We find that electron exchange can become particularly important for harmonic emission associated with intermediate excitations in the molecular ion. In particular, for orbitals associated with two-hole one-particle excitations, exchange effects can eliminate structure-related minima and maxima in the harmonic spectra. Laser-induced polarization of the neutral molecule may also have major effects on orbital structure-related minima and maxima in the harmonic spectra. Finally, we show how exchange terms in recombination can be viewed as a shakedownlike process induced by sudden electronic excitation in the ion.

Sukiasyan, Suren; Ivanov, Misha Yu. [Department of Physics, Imperial College London, South Kensington Campus, SW7 2AZ London (United Kingdom); Patchkovskii, Serguei [National Research Council, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada); Smirnova, Olga [Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2A, D-12489 Berlin (Germany); Brabec, Thomas [Physics Department and Center for Research in Photonics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5 (Canada)

2010-10-15

259

A cost-efficient frequency-domain photoacoustic imaging system  

NASA Astrophysics Data System (ADS)

Photoacoustic (PA) imaging techniques have recently attracted much attention and can be used for noninvasive imaging of biological tissues. Most PA imaging systems in research laboratories use the time domain method with expensive nanosecond pulsed lasers that are not affordable for most educational laboratories. Using an intensity modulated light source to excite PA signals is an alternative technique, known as the frequency domain method, with a much lower cost. In this paper, we describe a simple frequency domain PA system and demonstrate its imaging capability. The system provides opportunities not only to observe PA signals in tissue phantoms but also to acquire hands-on skills in PA signal detection. It also provides opportunities to explore the underlying mechanisms of the PA effect.

LeBoulluec, Peter; Liu, Hanli; Yuan, Baohong

2013-09-01

260

Fundamental and low frequency harmonic components of leakage current as a diagnostic tool to study aging of RTV and HTV silicone rubber in salt-fog  

Microsoft Academic Search

The paper presents the results of using the fundamental and the low frequency harmonic components of leakage current to study aging of silicone rubber in salt-fog. Experiments have been conducted on RTV and HTV coated rods at different fields (0.25-0.6 kV\\/cm) and conductivities (1000 to 2500 ?S\\/cm). The onset of dry-band arcing on samples could be determined by measuring the

Ayman H. El-Hag; Shesha H. Jayaram; Edward A. Cherney

2003-01-01

261

LASERS: Neodymium-doped yttrium aluminate laser with a pulse repetition frequency of 12.5 Hz and efficient second and third harmonic generation  

Microsoft Academic Search

A pulse-periodic yttrium aluminate (YAlO3:Nd3+) laser consisting of an oscillator and two amplifiers is described. At a fixed pulse repetition frequency of 12.5 Hz, the first harmonic was converted to the second with a 30% efficiency and to the third with a 6% conversion efficiency using KDP crystals. This efficiency was achieved by selecting an unstable resonator configuration in the

T. V. Plakhotnik; A. M. Pyndyk

1987-01-01

262

High-frequency ultrasonic imaging of thickly sliced specimens  

NASA Astrophysics Data System (ADS)

It has been reported that a mechanical scanning reflection acoustic microscope (hereinafter called simply "SAM"), using high frequency ultrasonic tone-burst waves, can form a horizontal cross-sectional image (i.e., c-scan image) showing a highly resolved cellular structure of biological tissue. However, the tissue prepared for the SAM has been mostly a thinly sectioned specimen. In this study, the SAM images of specimens thickly sectioned from the tissue were analyzed. Optical and scanning acoustic microscopies were used to evaluate tissues of human small intestine and esophagus. For preparing thin specimens, the tissue was embedded in paraffin, and substantially sectioned at 5-10?m by the microtome. For optical microscopy, the tissue was stained with hematoxylin and eosin, and affixed onto glass substrates. For scanning acoustic microscopy, two types of specimens were prepared: thinly sectioned specimens affixed on the glass substrate, wherein the specimens were deparaffinized in xylene, but not stained, and thickely sectioned specimens. Images of the thick specimens obtained with frequency at 200 MHz revealed cellular structures. The morphology was very similar to that seen in the thinly sectioned specimens with optical and scanning acoustic microscopy. In addition, scanning electron microscopy was used to compare the images of biological tissue. An acoustic lens with frequency at 200 MHz permitted the imaging of surface and/or subsurface of microstructures in the thick sections of small intestine and esophagus.

Miyasaka, Chiaki; Tittmann, Bernhard R.; Chandraratna, Premindra A. N.

2003-07-01

263

Tomographic imaging via spectral encoding of spatial frequency.  

PubMed

Three-dimensional optical tomographic imaging plays an important role in biomedical research and clinical applications. We introduce spectral tomographic imaging (STI) via spectral encoding of spatial frequency principle that not only has the capability for visualizing the three-dimensional object at sub-micron resolution but also providing spatially-resolved quantitative characterization of its structure with nanoscale accuracy for any volume of interest within the object. The theoretical basis and the proof-of-concept numerical simulations are presented to demonstrate the feasibility of spectral tomographic imaging. PMID:23546131

Uttam, Shikhar; Alexandrov, Sergey A; Bista, Rajan K; Liu, Yang

2013-03-25

264

Harmonic engine  

DOEpatents

A high efficiency harmonic engine based on a resonantly reciprocating piston expander that extracts work from heat and pressurizes working fluid in a reciprocating piston compressor. The engine preferably includes harmonic oscillator valves capable of oscillating at a resonant frequency for controlling the flow of working fluid into and out of the expander, and also preferably includes a shunt line connecting an expansion chamber of the expander to a buffer chamber of the expander for minimizing pressure variations in the fluidic circuit of the engine. The engine is especially designed to operate with very high temperature input to the expander and very low temperature input to the compressor, to produce very high thermal conversion efficiency.

Bennett, Charles L. (Livermore, CA)

2009-10-20

265

An ab initio study of the in-plane harmonic force fields and fundamental vibration frequencies of cis- and trans-1,3-butadiene  

NASA Astrophysics Data System (ADS)

The structure, in-plane force field, and fundamental vibration frequencies of trans- and cis-1,3-butadiene are calculated ab initio using the 4-31G basis set. Using a scaling procedure based on computational results from smaller molecules, the vibration frequencies for the trans-conformer calculated from the ab initio force constant matrix are found on average to be within 2.2% of the experimental values ``harmonized'' according to Dennison's rule. The values predicted for the cis-conformer, for which experimental spectroscopic data are only now becoming available, should facilitate the complete in-plane assignment of fundamentals in the near future.

Bock, Charles W.; Trachtman, Mendel; George, Philip

1980-11-01

266

Employing phase modulation and second harmonic nulling to eliminate the interference fringes from the spectrum of a portable coherent frequency-domain THz spectrometer  

NASA Astrophysics Data System (ADS)

Interpreting the spectrum from a continuous wave frequency domain terahertz spectrometer that employs coherent detection can be challenging due to the presence of an interference pattern. We report on the continued progress of a portable, battery-operated frequency domain terahertz spectrometer with an integrated, fiber-coupled, lithium-niobate optical phase-modulator and how we achieve interference fringe elimination using phase modulation and second harmonic nulling. The implications for both transmission and reflection measurements are discussed and data on the explosive compound RDX will be presented.

Demers, Joseph R.; Kasper, Bryon L.

2013-05-01

267

SIMULATING LOW FREQUENCY RADIO IMAGES OF THE SUN  

NASA Astrophysics Data System (ADS)

At low radio frequencies, the strong density gradients in the large scale solar corona lead to significant refraction. This implies that interpretation of solar radio images must account for these refractive effects, and as the ray paths at different frequencies travel through different parts of the corona, multi-frequency observations can help unravel the density and temperature distributions in a range of coronal heights. While the refractive properties of the medium are determined by the electron number density (Ne), the brightness temperature (Tb) distribution in the resulting image is determined by the electron temperature (Te) and the absorption coefficient (?) distributions. In the solar chromosphere and corona the Ne and Te change by 2, and the ? changes by 7 orders of magnitude, leading to significant changes in the morphology and observed Tb of the solar images. We are developing a flexible and precise tool to simulate brightness temperature, Tb, images of the sun resulting from arbitrary electron density, Ne, and electron temperature, Te, distributions. Although this ray-tracing algorithm is being developed in context of the MWA, a radio interferometer which will operate in the 80-300 MHz band (Oberoi et al., 2009, Rightley et al., 2009), it is of much wider applicability. At high radio frequencies, some rays penetrate into the chromosphere, which has significantly different Ne distribution. This tool implements a mathematical method for smoothly "stitching" the chromospheric and coronal Ne distributions, which are very different functions. As an application of this tool, we present and contrast the brightness temperature images from two well regarded coronal models by Baumbach and Allen (1947) and Saito (1970), and the model for chromosphere by Cillie and Menzel (1935). We also investigate the impact of coronal features like streamers on brightness temperature images.

Benkevitch, L. V.; Oberoi, D.; Sokolov, I.

2009-12-01

268

Instabilities driven by higher-order modes in a radio frequency system with a passive higher-harmonic cavity  

NASA Astrophysics Data System (ADS)

The effect of a higher-order mode upon longitudinal beam stability in an electron storage ring is modeled analytically and with simulations. Narrow band parasitic modes and broadband impedance are considered for the Aladdin and MAX-II electron storage rings. The simulations confirm that a passive harmonic cavity strongly suppresses parasitic coupled-bunch instabilities, in agreement with the analytic model. In the long-bunch regime where the bunch length exceeds the vacuum pipe radius, analytic modeling and simulations indicate that a harmonic cavity also suppresses the microwave instability. In the short-bunch regime where the bunch length is smaller than the vacuum pipe radius, analytic modeling and simulations indicate that tuning in a harmonic cavity may worsen the microwave instability.

Bosch, R. A.

2005-08-01

269

Combined Apertureless Near-Field Optical Seconde-Harmonic Generation/Atomic Force Microscopy Imaging and Nanoscale Limit of Detection  

SciTech Connect

A dual atomic force/near-field scanning optical microscope (AFM/NSOM) with an 800-nm ultrafast laser excitation source was used to investigate apertureless, tip-enhanced second harmonic generation (SHG) of ZnO nanowires. Data from far-field single-particle SHG microscopy images and spectra show little to no contributions from band-gap or other emission. The SHG microscope image and the simultaneous tapping mode AFM and apertureless SHG NSOM images indicate that ZnO nanowires exhibit a strong SHG signal consistent with uniform crystallinity, whereas other ZnO particles found with the wires had a variable, weaker SHG signal. Polarization data established values for Chi(33)/Chi(31) close to previous estimates. Our AFM/SHG NSOM data suggest a particle degradation mechanism under atmospheric conditions starting at the endpoints of the nanowire.

Meyer, Kent A [ORNL; Shuford, Kevin L [ORNL; Gu, Dr Zhanjun [University of Georgia, Athens, GA; Pan, Zhengwei [University of Georgia, Athens, GA; Shaw, Robert W [ORNL

2010-01-01

270

Simulation of low radio frequency solar images using HART  

NASA Astrophysics Data System (ADS)

The diagnostic potential of low radio frequency (< 300 MHz) solar observations has long been recognized. The radio waves are refracted by the smoothly and slowly varying large scale coronal structure and scattered by the small scale inhomogeneities. In addition, the presence of coronal magnetic fields make the coronal plasma dichroic in nature implying that even the unpolarized thermal radiation picks up some degree of polarization depending upon the details of the magnetic field geometry. The very same effects which impart the low radio frequencies its rich diagnostic power, also complicate the interpretation of these observations to extract coronal physics. A detailed analysis of coronal brightness temperature images necessarily requires a sophisticated understanding of coronal propagation and a robust and flexible numerical implementation to serve as a simulation tool. In anticipation of the solar images from the new generation of capable low radio frequency interferometers like the Murchison Widefield Array (MWA), we have been working on the design and development of a coronal propagation simulation tool. Christened Haystack and AOSS Ray Tracer (HART), this tool traces rays through a corona with specified electron density and temperature distributions. HART computes the appropriate radiative transfer to obtain the brightness temperature for each of the rays. This results in a simulated image corresponding to a specified observing frequency in each of the Stokes parameters. In view of the large number of pixels expected in the eventual images from the MWA and other instruments, and the large number of spectral slices for which these images would need to be simulated, considerable attention was paid to developing and implementing a robust and numerically efficient multi-threaded ray tracing algorithm. Here we describe the salient features of the flexible HART framework, presenting the current status of its implementation and the plans for near term development.

Benkevitch, L. V.; Oberoi, D.; Benjamin, M. D.; Sokolov, I.

2011-12-01

271

Hepatocellular carcinoma treated with radio-frequency ablation: spectrum of imaging findings.  

PubMed

Contrast material-enhanced Doppler or gray-scale harmonic ultrasonography (US) may help determine the completeness or long-term therapeutic efficacy of radio-frequency (RF) ablation of hepatocellular carcinoma (HCC). Successfully treated HCC is devoid of vascularity at color or power Doppler US. When the tumor is not completely treated, residual viable tumor can be detected. These contrast-enhanced US techniques may also help identify residual tumor when performed during repeat RF ablation, when accurate localization of viable tumor is needed. To date, contrast-enhanced computed tomography (CT) has been the most widely used imaging modality in the evaluation of therapeutic response after RF ablation of HCC. At follow-up CT, successfully ablated lesions appear as low-attenuation areas with no foci of contrast enhancement either within or at the periphery of the treated lesion, whereas any foci of enhancement indicate residual or recurrent tumor. Reactive hyperemia in tissue surrounding the ablated lesion, iatrogenic arterioportal shunting, and small intralesional air pockets are frequently seen at immediate follow-up CT. Gadolinium-enhanced dynamic magnetic resonance imaging is also useful in assessing therapeutic response following RF ablation of HCC, particularly when CT findings are inconclusive. Familiarity with these imaging findings is helpful in this setting. PMID:12533646

Kim, Seung Kwon; Lim, Hyo Keun; Kim, Young Han; Lee, Won Jae; Lee, Soon Jin; Kim, Seung Hoon; Lim, Jae Hoon; Kim, Soo Ah

272

In vivo imaging of dermal collagen in skin burn by collagen-sensitive second-harmonic-generation microscopy  

NASA Astrophysics Data System (ADS)

Optical assessment of skin burns is possible with second-harmonic-generation (SHG) microscopy due to its high sensitivity to thermal denaturation of collagen molecules. In contrast to previous studies that were performed using excised tissue specimens ex vivo, in this study, we demonstrated in vivo observation of dermal collagen fibers in living rat burn models with SHG microscopy. We confirmed that changes in SHG vanishing patterns in the SHG images depended on the burn degree. The results imply that SHG microscopy can be used as a low-invasiveness, highly quantitative tool for skin burn assessment.

Yasui, Takeshi; Tanaka, Ryosuke; Hase, Eiji; Fukushima, Shu-ichiro; Araki, Tsutomu

2013-02-01

273

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

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. PMID:22036637

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

2011-10-27

274

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)

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.

Peng, Shi-Guo; Liu, Xia-Ji; Hu, Hui; Jiang, Kaijun

2012-12-01

275

A systematic study on the basis set dependence of the Hartree-Fock, MP2 and CIS harmonic force fields and vibrational frequencies of formaldehyde in comparison with the experimental results  

Microsoft Academic Search

The aim of this work was to find the limits of the vibrational frequency calculations by ab initio methods, in the framework of the harmonic frequency model and so find the possibility of eliminating the scaling of force constants.Therefore the efficiency of the different ab initio methods and basis sets were investigated from the point of view of vibrational frequency

Ferenc Billes

1995-01-01

276

Propagation of high-frequency harmonic elastic waves excited by surface perturbation of a noncircular cylindrical cavity  

Microsoft Academic Search

A ray method based on geometrical optics is applied to solve the problem of propagation of harmonic elastic waves excited by the perturbation of the surface of a noncircular cylindrical cavity. Stresses are computed under plane strain conditions for a cavity in the form of a parabolic cylinder and for a cylindrical cavity with a Munger oval section subjected to

P. N. Soroka

1993-01-01

277

Concealed weapons detection using low-frequency magnetic imaging  

Microsoft Academic Search

Military personnel, law-enforcement officers, and civilians face ever-increasing dangers from persons carrying concealed handguns and other weapons. In direct correspondence with this danger is a need for more sophisticated means of detecting concealed weapons. We have developed a novel concealed-weapons detector based on the principle of low- frequency magnetic imaging. The detector is configured as a portal, and constructs an

Byron G. Zollars; Bradley Sallee; Michael Durrett; Clay Cruce; William Hallidy

1997-01-01

278

Pulse inversion chirp coded tissue harmonic imaging (PI-CTHI) of Zebrafish heart using high frame rate ultrasound biomicroscopy.  

PubMed

This paper reports a pulse inversion chirp coded tissue harmonic imaging (PI-CTHI) method for visualizing small animal hearts that provides fine spatial resolution at a high frame rate without sacrificing the echo signal to noise ratio (eSNR). A 40 MHz lithium niobate (LiNbO(3)) single element transducer is employed to evaluate the performance of PI-CTHI by scanning tungsten wire targets, spherical anechoic voids, and zebrafish hearts. The wire phantom results show that PI-CTHI improves the eSNR by 4 dB from that of conventional pulse inversion tissue harmonic imaging (PI-THI), while still maintaining a spatial resolution of 88 and 110 ?m in the axial and lateral directions, respectively. The range side lobe level of PI-CTHI is 11 dB lower than that of band-pass filtered CTHI (or F-CTHI). In the anechoic sphere phantom study, the contrast-to-noise ratio of PI-CTHI is found to be 2.7, indicating a 34% enhancement over conventional PI-THI. Due to such improved eSNR and contrast resolution, blood clots in zebrafish hearts can be readily visualized throughout heart regeneration after 20% of the ventricle is removed. Disappearance of the clots in the early stages of the regeneration has been observed for 7 days without sacrificing the fish. PMID:22930467

Park, Jinhyoung; Huang, Ying; Chen, Ruimin; Lee, Jungwoo; Cummins, Thomas M; Zhou, Qifa; Lien, Ching-Ling; Shung, K K

2012-08-29

279

Concealed weapons detection using low-frequency magnetic imaging  

NASA Astrophysics Data System (ADS)

Military personnel, law-enforcement officers, and civilians face ever-increasing dangers from persons carrying concealed handguns and other weapons. In direct correspondence with this danger is a need for more sophisticated means of detecting concealed weapons. We have developed a novel concealed-weapons detector based on the principle of low- frequency magnetic imaging. The detector is configured as a portal, and constructs an image of electrically conductive objects transported through it with a potential spatial resolution of approximately 1 inch. Measurements on a breadboard version of the weapons detector have, to date, yielded a resolution of 2 inches. In operation, magnetic dipole radiation, emitted by transmitting antennas in the perimeter of the portal, is scattered from conductive objects and is picked up by receive antennas, also positioned around the portal. With sufficient measurements, each with a different geometry, a solution to the inverse scattering problem can be found. The result is an image of conductive objects in the detector. The detector is sensitive to all metals, semiconductors, and conductive composites. The measured conductivity image formed by the detector is combined with the video signal from a visible CCD camera to form a composite image of persons transiting the detector portal and the conductive objects they are carrying. Accompanying image recognition software could be used to determine the threat level of objects based upon shape, conductivity, and placement on the person of the carrier, and provide cueing, logging, or alarm functions to the operator if suspect weapons are identified. The low- power, low-frequency emissions from the detector are at levels considered safe to humans and medical implants..

Zollars, Byron G.; Sallee, Bradley; Durrett, Michael; Cruce, Clay; Hallidy, William

1997-02-01

280

Frequency identification of vibration signals using video camera image data.  

PubMed

This study showed that an image data acquisition system connecting a high-speed camera or webcam to a notebook or personal computer (PC) can precisely capture most dominant modes of vibration signal, but may involve the non-physical modes induced by the insufficient frame rates. Using a simple model, frequencies of these modes are properly predicted and excluded. Two experimental designs, which involve using an LED light source and a vibration exciter, are proposed to demonstrate the performance. First, the original gray-level resolution of a video camera from, for instance, 0 to 256 levels, was enhanced by summing gray-level data of all pixels in a small region around the point of interest. The image signal was further enhanced by attaching a white paper sheet marked with a black line on the surface of the vibration system in operation to increase the gray-level resolution. Experimental results showed that the Prosilica CV640C CMOS high-speed camera has the critical frequency of inducing the false mode at 60 Hz, whereas that of the webcam is 7.8 Hz. Several factors were proven to have the effect of partially suppressing the non-physical modes, but they cannot eliminate them completely. Two examples, the prominent vibration modes of which are less than the associated critical frequencies, are examined to demonstrate the performances of the proposed systems. In general, the experimental data show that the non-contact type image data acquisition systems are potential tools for collecting the low-frequency vibration signal of a system. PMID:23202026

Jeng, Yih-Nen; Wu, Chia-Hung

2012-10-16

281

Harmonic flux penetration of superconductors in low-frequency, high-amplitude, alternating-current magnetic fields  

Microsoft Academic Search

A critical-state model has been used to calculate the magnetic response of a superconducting sample to an applied a.c. magnetic field. The analysis has been performed for both a cylindrical and a slab geometry and evaluated up to the tenth harmonic. It is shown that standard expressions derived using the critical-state model which relate the critical current density to the

H D Ramsbottom; D P Hampshire

282

Harmonic flux penetration of superconductors in low-frequency, high-amplitude, alternating-current magnetic fields  

Microsoft Academic Search

A critical-state model has been used to calculate the magnetic response of a superconducting sample to an applied a.c. magnetic field. The analysis has been performed for both a cylindrical and a slab geometry and evaluated up to the tenth harmonic. It is shown that standard expressions derived using the critical-state model which relate the critical current density to the

H. D. Ramsbottom; D. P. Hampshire

1997-01-01

283

DCT-Based Amplitude and Frequency Modulated Harmonic-Plus-Noise Modelling for Text-to-Speech Synthesis  

Microsoft Academic Search

We present a harmonic-plus-noise modelling (HNM) strategy in the context of corpus-based text-to-speech (TTS) synthesis, in which whole speech phonemes are modelled in their integrity, contrary to the traditional frame-based approach. The pitch and amplitude trajectories of each phoneme are modelled with a low-order DCT expansion. The parameter analysis algorithm is to a large extent aided and guided by the

K. Hermus; H. Van Hamme; W. Verhelst; S. Irhimeh; J. De Moortel

2007-01-01

284

Optimum frequency for subsurface-imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, most conventional synthetic-aperture radars operate at higher microwave frequencies which do not significantly penetrate below the soil surface. This study attempts to provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. Since the radar return from a buried object must compete with the return from surface clutter, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell`s equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Initial results indicate that the HF spectrum (3--30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper vhf through uhf spectrum ({approximately}100 MHz--1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-05-01

285

Optimum frequency for subsurface-imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, most conventional synthetic-aperture radars operate at higher microwave frequencies which do not significantly penetrate below the soil surface. This study attempts to provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. Since the radar return from a buried object must compete with the return from surface clutter, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell's equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Initial results indicate that the HF spectrum (3--30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper vhf through uhf spectrum ([approximately]100 MHz--1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-05-01

286

Coherent Raman spectro-imaging with laser frequency combs.  

PubMed

Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques. PMID:24132293

Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W

2013-10-17

287

Coherent Raman spectro-imaging with laser frequency combs  

NASA Astrophysics Data System (ADS)

Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W.

2013-10-01

288

In vivo feasibility of real-time monitoring of focused ultrasound surgery (FUS) using harmonic motion imaging (HMI).  

PubMed

In this study, the Harmonic Motion Imaging for Focused Ultrasound (HMIFU) technique is applied to monitor changes in mechanical properties of tissues during thermal therapy in a transgenic breast cancer mouse model in vivo. An HMIFU system, composed of a 4.5-MHz focused ultrasound (FUS) and a 3.3-MHz phased-array imaging transducer, was mechanically moved to image and ablate the entire tumor. The FUS transducer was driven by an amplitude-modulated (AM) signal at 15 Hz. The acoustic intensity ( I(spta)) was equal to 1050 W/cm(2) at the focus. A digital low-pass filter was used to filter out the spectrum of the FUS beam and its harmonics prior to displacement estimation. The resulting axial displacement was estimated using 1-D cross-correlation on the acquired RF signals. Results from two mice with eight lesions formed in each mouse (16 lesions total) showed that the average peak-to-peak displacement amplitude before and after lesion formation was respectively equal to 17.34 +/- 1.34 microm and 10.98 +/- 1.82 microm ( p < 0.001). Cell death was also confirmed by hematoxylin and eosin histology. HMI displacement can be used to monitor the relative tissue stiffness changes in real time during heating so that the treatment procedure can be performed in a time-efficient manner. The HMIFU system may, therefore, constitute a cost-efficient and reliable alternative for real-time monitoring of thermal ablation. PMID:19643703

Maleke, Caroline; Konofagou, Elisa E

2009-07-28

289

Drive frequency dependent phase imaging in piezoresponse force microscopy  

SciTech Connect

The drive frequency dependent piezoresponse (PR) phase signal in near-stoichiometric lithium niobate crystals is studied by piezoresponse force microscopy. It is clearly shown that the local and nonlocal electrostatic forces have a great contribution to the PR phase signal. The significant PR phase difference of the antiparallel domains are observed at the contact resonances, which is related to the electrostatic dominated electromechanical interactions of the cantilever and tip-sample system. Moreover, the modulation voltage induced frequency shift at higher eigenmodes could be attributed to the change of indention force depending on the modulation amplitude with a piezoelectric origin. The PR phase of the silicon wafer is also measured for comparison. It is certificated that the electrostatic interactions are universal in voltage modulated scanning probe microscopy and could be extended to other phase imaging techniques.

Bo Huifeng; Kan Yi; Lu Xiaomei; Liu Yunfei; Peng Song; Wang Xiaofei; Cai Wei; Xue Ruoshi; Zhu Jinsong [Department of Physics, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China)

2010-08-15

290

Detecting vocal fatigue in student singers using acoustic measures of mean fundamental frequency, jitter, shimmer, and harmonics-to-noise ratio  

NASA Astrophysics Data System (ADS)

The purpose of this study is to explore the ability of four acoustic parameters, mean fundamental frequency, jitter, shimmer, and harmonics-to-noise ratio, to detect vocal fatigue in student singers. The participants are 15 voice students, who perform two distinct tasks, data collection task and vocal fatiguing task. The data collection task includes the sustained vowel /a/, reading a standard passage, and self-rate on a vocal fatigue form. The vocal fatiguing task is the vocal practice of musical scores for a total of 45 minutes. The four acoustic parameters are extracted using the software EZVoicePlus. The data analyses are performed to answer eight research questions. The first four questions relate to correlations of the self-rating scale and each of the four parameters. The next four research questions relate to differences in the parameters over time using one-factor repeated measures analysis of variance (ANOVA). The result yields a proposed acoustic profile of vocal fatigue in student singers. This profile is characterized by increased fundamental frequency; slightly decreased jitter; slightly decreased shimmer; and slightly increased harmonics-to-noise ratio. The proposed profile requires further investigation.

Sisakun, Siphan

291

Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin  

NASA Astrophysics Data System (ADS)

In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the ?* and ?* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis.

Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T.

2013-01-01

292

Focused high frequency needle transducer for ultrasonic imaging and trapping  

NASA Astrophysics Data System (ADS)

A miniature focused needle transducer (<1 mm) was fabricated using the press-focusing technique. The measured pulse-echo waveform showed the transducer had center frequency of 57.5 MHz with 54% bandwidth and 14 dB insertion loss. To evaluate the performance of this type of transducer, invitro ultrasonic biomicroscopy imaging on the rabbit eye was obtained. Moreover, a single beam acoustic trapping experiment was performed using this transducer. Trapping of targeted particle size smaller than the ultrasonic wavelength was observed. Potential applications of these devices include minimally invasive measurements of retinal blood flow and single beam acoustic trapping of microparticles.

Hsu, Hsiu-Sheng; Zheng, Fan; Li, Ying; Lee, Changyang; Zhou, Qifa; Kirk Shung, K.

2012-07-01

293

Method for imaging with low frequency electromagnetic fields  

DOEpatents

A method is described for imaging with low frequency electromagnetic fields, and for interpreting the electromagnetic data using ray tomography, in order to determine the earth conductivity with high accuracy and resolution. The imaging method includes the steps of placing one or more transmitters, at various positions in a plurality of transmitter holes, and placing a plurality of receivers in a plurality of receiver holes. The transmitters generate electromagnetic signals which diffuse through a medium, such as earth, toward the receivers. The measured diffusion field data H is then transformed into wavefield data U. The travel times corresponding to the wavefield data U, are then obtained, by charting the wavefield data U, using a different regularization parameter [alpha] for each transform. The desired property of the medium, such as conductivity, is then derived from the velocity, which in turn is constructed from the wavefield data U using ray tomography. 13 figures.

Lee, K.H.; Xie, G.Q.

1994-12-13

294

Imaging interplanetary CMEs at radio frequency from solar polar orbit  

NASA Astrophysics Data System (ADS)

Coronal mass ejections (CMEs) represent a great concentration of mass and energy input into the lower corona. They have come to be recognized as the major driver of physical conditions change in the Sun-Earth system. Consequently, observations of CMEs are important for understanding and ultimately predicting space weather conditions. This paper discusses a proposed mission, the Solar Polar Orbit Radio Telescope (SPORT) mission, which will observe the propagation of interplanetary CMEs to distances of near 0.35 AU from the Sun. The orbit of SPORT is an elliptical solar polar orbit. The inclination angle between the orbit and ecliptic plane should be about 90°. The main payload on board SPORT will be an imaging radiometer working at the meter wavelength band (radio telescope), which can follow the propagation of interplanetary CMEs. The images that are obtained by the radio telescope embody the brightness temperature of the objectives. Due to the very large size required for the antenna aperture of the radio telescope, we adopt interferometric imaging technology to reduce it. Interferometric imaging technology is based on indirect spatial frequency domain measurements plus Fourier transformation. The SPORT spacecraft will also be equipped with a set of optical and in situ measurement instruments such as a EUV solar telescope, a solar wind ion instrument, an energetic particle detector, a magnetometer, a wave detector and a solar radio burst spectrometer.

Wu, Ji; Sun, Weiying; Zheng, Jianhua; Zhang, Cheng; Liu, Hao; Yan, Jingye; Wang, Chi; Wang, Chuanbing; Wang, Shui

2011-09-01

295

Harmonic analysis of electrical distribution systems  

SciTech Connect

This report presents data pertaining to research on harmonics of electric power distribution systems. Harmonic data is presented on RMS and average measurements for determination of harmonics in buildings; fluorescent ballast; variable frequency drive; georator geosine harmonic data; uninterruptible power supply; delta-wye transformer; westinghouse suresine; liebert datawave; and active injection mode filter data.

NONE

1996-03-01

296

Microscopic imaging of glyceraldehyde-induced tissue glycation with intrinsic second harmonic generation and two-photon fluorescence contrasts  

NASA Astrophysics Data System (ADS)

The bioinspired approaches to tissue strengthening and preservation rely on non-toxic cross-linking agents one of which is glyceraldehyde. In this study we used multiphoton microscopy that employs second harmonic generation (SHG) contrast to evaluate collagen microstructures and two-photon fluorescence (TPF) contrast to monitor progression of cross-linking upon treatment of tissues with glyceraldehyde. We examined collagen hydrogels assembled at 37 °C and 27 °C, bovine scleral and corneal tissues, skin as well as rat tail tendons. The results show a different effect of glyceraldehyde on collagen microstructures within the above tissues. This effect depends on the original microstructural assembly of collagen within a specific tissue. Our data suggests that epidermis (in skin and cornea) will protect collagen from cross-linking with glyceraldehyde. The work highlights benefits of monitoring progression of collagen cross-linking and effects of cross-linking on fiber microstructures as imaged with SHG and TPF signals.

Hwang, Yu Jer; Granelli, Joseph; Tirumalasetty, Manasa; Lyubovitsky, Julia

2013-02-01

297

Theory of high-order harmonic generation and attosecond pulse emission by a low-frequency elliptically polarized laser field  

SciTech Connect

We present a quantum-mechanical theory of xuv generation by an elliptically polarized intense laser field. Our approach is valid when the Keldysh parameter {gamma} is about unity or less, and the driving ellipticity is less than {radical}(2){gamma}. After the photoionization the motion of the electronic wave packet along the major axis of the driving field polarization ellipse is described quasiclassically, whereas the motion in the transverse direction is considered fully quantum mechanically; we also find the condition that allows the reduction of the motion description to a quantum orbit in the polarization plane of the laser field. We use the ionization rate calculated via numerical solution of the three-dimensional Schroedinger equation (TDSE), and take into account the Coulomb modification of the free electronic wave packet. The predictions of our theory for xuv emission agree well with numerical and experimental results. We study the high harmonic intensities and phases as functions of the driving intensity and ellipticity, and also the ellipticity and the rotation angle of the harmonic field polarization ellipse as functions of the driving ellipticity. The atomic response is decomposed into the contributions of different quantum paths. This allows finding a straightforward explanation for the observed dependencies.

Strelkov, V. V. [General Physics Institute of the Russian Academy of Sciences, Moscow (Russian Federation) and Centre Lasers Intenses et Applications, Universite Bordeaux I, Talence (France)

2006-07-15

298

Image sequence coding using spatial/spatial-frequency representations  

NASA Astrophysics Data System (ADS)

Spatial/spatial-frequency representations have proven to be an interesting and powerful framework for the simulation of a number of visual effects. Results consistent with observations of the human visual system have been obtained at levels ranging from the shape of receptive field profiles to perceptual grouping and texture segmentation. A number of representations are under study, in a number of different fields. A key issue in comparing these representations is the resolution that can be attained (simultaneously) in the joint domain. The uncertainty principle dictates that arbitrarily high resolution cannot be achieved in both space and spatial-frequency. Joint resolution can range from singular functions in space (with infinite extent in spatial-frequency), to the reverse (e.g., the pixel representation at one extreme, and the Fourier transform at the other). In this paper, we discuss some of the available representations in the context of image sequence coding, and establish some of the characteristics desired in a representation for this application. We show that the joint resolution of a representation, in particular, can affect the performance of coding methods based on that representation. Examples which illustrate this point using industry standard DCT-based methods are given.

Reed, Todd R.

1992-08-01

299

Controlled Data Hiding Technique for Color Image Authentication in Frequency Domain (CDHTCIAFD)  

Microsoft Academic Search

This paper presents a new steganographic technique which demonstrates the colour image authentication process in frequency domain based on the Discrete Fourier Transformation (DFT). Image authentication is done by hiding secrete message\\/image into the transformed frequency component of source image. The DFT is applied on sub-image block called mask of size 2 x 2 in row major order. Secrete message\\/image

Nabin Ghoshal; J. K. Mandal

2011-01-01

300

Second Harmonic Generation Spectroscopy and Domain Imaging of the High-Temperature Multiferroic CuO  

NASA Astrophysics Data System (ADS)

An analysis of the magnetically induced ferroelectric phase in the high-temperature multiferroic CuO by optical second harmonic generation (SHG) reveals a rich variety of contributions coupling to the multiferroic order. Observation of a ``giant'' SHG efficiency points to the presence of electronic contributions to the spontaneous polarization. The SHG spectra are dominated by transitions within the Cu2+ band and by SHG resonance enhancement. An investigation of the multiferroic domain structure by SHG shows an isotropic distribution of domains with a lateral extension of about 10 ?m. This value is 1--2 orders of magnitude smaller than in other multiferroics and emphasizes the outstanding position CuO takes in the family of magnetically induced ferroelectrics.

Hoffmann, Tim; Kimura, Kenta; Kimura, Tsuyoshi; Fiebig, Manfred

2012-12-01

301

A Frequency Synthesizer With Optimally Coupled QVCO and Harmonic-Rejection SSBmixer for Multi-Standard Wireless Receiver  

Microsoft Academic Search

This paper presents a wide-band fractional-N fre- quency synthesizer for multi-standard cellular and short-range wireless communication receivers. The synthesizer covers the frequency band from 1.8 to 6 GHz and supports the standards of DCS1800, WCDMA, TD-SCDMA, WLAN802.11 a\\/b\\/g and Bluetooth. Architecture design and frequency planning are care- fully performed to tradeoff wide frequency rang ea nd power efficiency. A quadrature

Deping Huang; Wei Li; Jin Zhou; Ning Li; Jinghong Chen

2011-01-01

302

Nonlinear-optical brain anatomy by harmonic-generation and coherent Raman microscopy on a compact femtosecond laser platform  

NASA Astrophysics Data System (ADS)

An extended-cavity Cr:forsterite laser is integrated with a photonic-crystal fiber soliton frequency shifter and a periodically poled lithium niobate spectrum compressor for simultaneous harmonic-generation and coherent Raman brain imaging. Adapting the laser beam focusing geometry to the tissue morphology is shown to enable complementarity enhancement in tissue imaging by second- and third-harmonic generation, as well as coherent Raman scattering, facilitating quantitative image analysis.

Doronina-Amitonova, Lyubov V.; Lanin, Aleksandr A.; Ivashkina, Olga I.; Zots, Marina A.; Fedotov, Andrei B.; Anokhin, Konstantin V.; Zheltikov, Aleksei M.

2011-12-01

303

Orbital-optimized coupled-electron pair theory and its analytic gradients: accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions.  

PubMed

Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N(6)) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the ?2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (?R is 0.0003 A? on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm(-1)) is fortuitously even better than that of CCSD(T) (50 cm(-1)), while the MAEs of CEPA(0) (184 cm(-1)) and CCSD (84 cm(-1)) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol(-1), which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol(-1)), and comparing to MP2 (7.7 kcal mol(-1)) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is only 0.1 kcal mol(-1) lower than that of OCEPA(0). Overall, the present application results indicate that the OCEPA(0) method is very promising not only for challenging open-shell systems but also for closed-shell molecules. PMID:23927240

Bozkaya, U?ur; Sherrill, C David

2013-08-01

304

Time selection for ISAR imaging based on time-frequency analysis  

NASA Astrophysics Data System (ADS)

Because of target's complicated movement, conventional ISAR imaging algorithm can not meet the demands of maneuvering target imaging. On the basis of analyzing the phase model of target scatterer, a new time selection method for maneuvering target imaging is proposed. Based on adaptive optimal kernel (AOK) time-frequency representation, instantaneous Doppler frequencies of echoes in range bins are estimated. According to the estimated Doppler frequencies, imaging time can be selected. Raw radar data verify the effectiveness of the proposed method.

Li, Rui; Tao, Jiang; Shi, Wang D.

2013-03-01

305

A high-order, purely frequency based harmonic balance formulation for continuation of periodic solutions: The case of non-polynomial nonlinearities  

NASA Astrophysics Data System (ADS)

In this paper, we extend the method proposed by Cochelin and Vergez [A high order purely frequency-based harmonic balance formulation for continuation of periodic solutions, Journal of Sound and Vibration, 324 (2009) 243-262] to the case of non-polynomial nonlinearities. This extension allows for the computation of branches of periodic solutions of a broader class of nonlinear dynamical systems.The principle remains to transform the original ODE system into an extended polynomial quadratic system for an easy application of the harmonic balance method (HBM). The transformation of non-polynomial terms is based on the differentiation of state variables with respect to the time variable, shifting the nonlinear non-polynomial nonlinearity to a time-independent initial condition equation, not concerned with the HBM. The continuation of the resulting algebraic system is here performed by the asymptotic numerical method (high order Taylor series representation of the solution branch) using a further differentiation of the non-polynomial algebraic equation with respect to the path parameter.A one dof vibro-impact system is used to illustrate how an exponential nonlinearity is handled, showing that the method works at very high order, 1000 in that case. Various kinds of nonlinear functions are also treated, and finally the nonlinear free pendulum is addressed, showing that very accurate periodic solutions can be computed with the proposed method.

Karkar, Sami; Cochelin, Bruno; Vergez, Christophe

2013-02-01

306

Lasing on higher harmonics  

SciTech Connect

Lasing at short wavelengths with an accelerator of modest energy can only be achieved with a wiggler of short period and high field operating, perhaps, at a high harmonic of the fundamental frequency. We discuss the characteristics of wigglers of this kind, designed to lase with harmonic numbers as large as fifty or so, emphasizing their gain, efficiency, and sensitivity to emittance and energy spread. 5 refs., 3 figs.

Warren, R.W.

1990-01-01

307

Four-frequency polarizing microscope for recording plasma images in the wavelength range 0.4-1.1 {mu}m  

SciTech Connect

The optical scheme and design of a four-frequency polarizing microscope intended for simultaneous recording of plasma images in the wavelength range 0.4-1.1 {mu}m with the spatial resolution 12 {mu}m in the entire spectral range are described. The effectiveness of such a microscope in studies of plasmas produced on interaction of laser radiation with a target is demonstrated. The plasma images are obtained at the frequencies {omega}{sub 0}, (3/2){omega}{sub 0}, 2{omega}{sub 0}, and (5/2){omega}{sub 0}, where {omega}{sub 0} corresponds to the frequency of heating radiation. The transformation coefficient that characterizes the efficiency of conversion of heating radiation into the 2{omega}{sub 0}, (3/2){omega}{sub 0}, and (5/2){omega}{sub 0} harmonics generated in the plasma is determined.

Vasin, B. L.; Mal'kova, S. V.; Osipov, M. V.; Puzyrev, V. N.; Saakyan, A. T.; Starodub, A. N.; Fedotov, S. I.; Fronya, A. A.; Shutyak, V. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2010-12-15

308

Imageability, age of acquisition, and frequency factors in acronym comprehension.  

PubMed

In spite of their unusual orthographic and phonological form, acronyms (e.g., BBC, HIV, NATO) can become familiar to the reader, and their meaning can be accessed well enough that they are understood. The factors in semantic access for acronym stimuli were assessed using a word association task. Two analyses examined the time taken to generate a word association response to acronym cues. Responses were recorded more quickly to cues that elicited a large proportion of semantic responses, and those that were high in associative strength. Participants were shown to be faster to respond to cues which were imageable or early acquired. Frequency was not a significant predictor of word association responses. Implications for theories of lexical organisation are discussed. PMID:23153389

Playfoot, David; Izura, Cristina

2012-11-16

309

Simple 1D Fokker-Planck modelling of ion cyclotron resonance frequency heating at arbitrary cyclotron harmonics accounting for Coulomb relaxation on non-Maxwellian populations  

NASA Astrophysics Data System (ADS)

A simple method intended to quickly assess the net acceleration of particle populations due to wave heating is proposed. It adopts the philosophy proposed by Stix (1975 Nucl. Fusion 15 737; 1992 Waves in Plasmas (New York: AIP) pp 510-3) to compute the 1D distribution function of ion cyclotron resonance frequency heated species, but extends it on various fronts to allow describing tail formation of both minority and majority populations at any cyclotron harmonic. All plasma constituents are evolved by solving a set of coupled Fokker-Planck equations iteratively. As electrons easily reach high velocities, the relativistic collision operator for electron self-collisions has been implemented. Including a constant finite energy confinement time allows us to incorporate local losses qualitatively.

Van Eester, Dirk; Lerche, Ernesto

2011-09-01

310

Near-field imaging of light propagation in photonic crystal waveguides: Explicit role of Bloch harmonics  

Microsoft Academic Search

We employ a collection scanning near-field optical microscope (SNOM) to image the propagation of light at telecommunication wavelengths along straight and bent regions of silicon-on-insulator photonic crystal waveguides (PCWs) formed by removing a single row of holes in the triangular 410-nm-period lattice along the GammaM direction of the irreducible Brillouin zone. We obtain high quality SNOM images of PCWs excited

Sergey I. Bozhevolnyi; Valentyn S. Volkov; Thomas Søndergaard; Alexandra Boltasseva; Peter I. Borel; Martin Kristensen

2002-01-01

311

Visible spatial frequency domain imaging with a digital light microprojector.  

PubMed

ABSTRACT. There is a need for cost effective, quantitative tissue spectroscopy and imaging systems in clinical diagnostics and pre-clinical biomedical research. A platform that utilizes a commercially available light-emitting diode (LED) based projector, cameras, and scaled Monte Carlo model for calculating tissue optical properties is presented. These components are put together to perform spatial frequency domain imaging (SFDI), a model-based reflectance technique that measures and maps absorption coefficients (?a) and reduced scattering coefficients (?s') in thick tissue such as skin or brain. We validate the performance of the flexible LED and modulation element (FLaME) system at 460, 530, and 632 nm across a range of physiologically relevant ?a values (0.07 to 1.5??mm-1) in tissue-simulating intralipid phantoms, showing an overall accuracy within 11% of spectrophotometer values for ?a and 3% for ?s'. Comparison of oxy- and total hemoglobin fits between the FLaME system and a spectrophotometer (450 to 1000 nm) is differed by 3%. Finally, we acquire optical property maps of a mouse brain in vivo with and without an overlying saline well. These results demonstrate the potential of FLaME to perform tissue optical property mapping in visible spectral regions and highlight how the optical clearing effect of saline is correlated to a decrease in ?s' of the skull. PMID:24005154

Lin, Alexander J; Ponticorvo, Adrien; Konecky, Soren D; Cui, Haotian; Rice, Tyler B; Choi, Bernard; Durkin, Anthony J; Tromberg, Bruce J

2013-09-01

312

All-in-Focus Image Generation by Merging Multiple Differently Focused Images in Three-Dimensional Frequency Domain  

Microsoft Academic Search

\\u000a This paper describes a method of image generation based on transformation integrating multiple differently focused images.\\u000a First, we assume that objects are defocused by a geometrical blurring model. And we combine acquired images on certain imaging\\u000a planes and spatial frequencies of objects by using a convolution of a three-dimensional blur. Then, we reconstruct an all-in-focus\\u000a image from the acquired images

Kazuya Kodama; Hiroshi Mo; Akira Kubota

2005-01-01

313

Ab initio time-dependent density-functional-theory study of the frequency comb structure, coherence, and dephasing of multielectron systems in the vuv-xuv regimes via high-order harmonic generation  

NASA Astrophysics Data System (ADS)

We present an ab initio nonperturbative investigation of the frequency comb structure and coherence within each order of the high-order harmonic generation (HHG) of rare-gas atoms by means of the time-dependent density-functional theory (TDDFT) with optimized effective potential (OEP) and self-interaction correction (SIC). The TDDFT+OEP-SIC equations are solved accurately and efficiently by means of the time-dependent generalized pseudospectral technique. We found that a nested comb structure appears within each order of the harmonics, ranging from the first harmonic all the way to the cutoff region. We explore in detail the temporal coherence and robustness of the comb structure by varying the laser-pulse separation ? , the number of pulses N , the phase difference between pulses ?? , and the laser intensity. The frequency comb structure and coherence are preserved in each harmonic regardless of the values of ? and N used for the case of weak and medium strong incident laser-pulse trains. The time-frequency characteristics of the HHG coherence structure are analyzed in details by means of the wavelet transform of the time-dependent induced dipoles. The interference modulation can be attributed to the constant phase relationship of harmonics among successive pulses. However, under superstrong fields, nonuniform and substantial ionization takes place during each pulse, jeopardizing the temporal coherence of the emitted frequency comb modes. Finally, we found that the dynamical electron correlation, which is included in the present TDDFT+OEP-SIC treatment but not in the single-active-electron model, is significant for the quantitative exploration of the frequency comb structure and coherence of higher harmonics.

Carrera, Juan J.; Chu, Shih-I.

2009-06-01

314

Imaging Interplanetary CMEs at Radio Frequency From Solar Polar Orbit  

NASA Astrophysics Data System (ADS)

Coronal mass ejections (CMEs) are violent discharges of plasma and magnetic fields from the Sun's corona. They have come to be recognized as the major driver of physical conditions in the Sun-Earth system. Consequently, the detection of CMEs is important for un-derstanding and ultimately predicting space weather conditions. The Solar Polar Orbit Radio Telescope (SPORT) is a proposed mission to observe the propagation of interplanetary CMEs from solar polar orbit. The main payload (radio telescope) on board SPORT will be an in-terferometric imaging radiometer working at the meter wavelength band, which will follow the propagation of interplanetary CMEs from a distance of a few solar radii to near 1 AU from solar polar orbit. The SPORT spacecraft will also be equipped with a set of optical and in situ measurement instruments such as a EUV solar telescope, a solar wind plasma experiment, a solar wind ion composition instrument, an energetic particle detector, a wave detector, a mag-netometer and an interplanetary radio burst tracker. In this paper, we first describe the current shortage of interplanetary CME observations. Next, the scientific motivation and objectives of SPORT are introduced. We discuss the basic specifications of the main radio telescope of SPORT with reference to the radio emission mechanisms and the radio frequency band to be observed. Finally, we discuss the key technologies of the SPORT mission, including the con-ceptual design of the main telescope, the image retrieval algorithm and the solar polar orbit injection. Other payloads and their respective observation objectives are also briefly discussed. Key words: Interplanetary CMEs; Interferometric imaging; Solar polar orbit; Radiometer.

Wu, Ji; Sun, Weiying; Zheng, Jianhua; Zhang, Cheng; Wang, Chi; Wang, C. B.; Wang, S.

315

Fluorescence Image of a Single Molecule in a Microsphere: Model.  

National Technical Information Service (NTIS)

We model fluorescence images of single molecules in spherical dielectric microcavities. Molecules are treated as time-harmonic dipoles. Images are integrated over emission frequencies. Because of the strong refractive properties of the enclosing sphere, t...

S. C. Hill P. Nachman S. Arnold J. M. Ramsey M. D. Barnes

1999-01-01

316

Stabilized atomic force microscopy imaging in liquids using second harmonic of cantilever motion for setpoint control  

NASA Astrophysics Data System (ADS)

We present an automated stabilization of the imaging process in tapping mode atomic force microscopy. For biological applications, the requirement of stable imaging conditions to achieve reliable high resolution is contradicted by the necessity to work in solution to ensure biological functionality: thermal and saline variations of the viscosity, in particular when exchanging the solution the sample is surrounded with, strongly affect the cantilever motion rendering the imaging process instable. Using anharmonic contributions in the deflection signal, the amplitude setpoint is controlled to compensate for unavoidable drift in the free oscillation. By this additional feedback, the tip-sample interaction is maintained stable at a low value, making the instrument robust against drift and tolerant to environmental changes. As a delicate test sample, the ``single ring''-mutant of the bacterial chaperonin GroEL from E. coli was imaged. To prove the efficiency of our setup, we show highly stabilized, continuous imaging with minimized user interaction while strong perturbations by exchange of the buffer solution were imposed during the scanning.

Schiener, Jens; Witt, Susanne; Stark, Martin; Guckenberger, Reinhard

2004-08-01

317

Combined nonlinear laser imaging (two-photon excitation fluorescence, second and third-harmonic generation, and fluorescence lifetime imaging microscopies) in ovarian tumors  

NASA Astrophysics Data System (ADS)

We applied Two-photon Excited Fluorescence (TPEF), Second/Third Harmonic Generation (SHG and THG) and Fluorescence Lifetime Imaging (FLIM) Non Linear Optics (NLO) Laser-Scanning Microscopy within the same imaging platform to evaluate their use as a diagnostic tool in ovarian tumors. We assess of applicability of this multimodal approach to perform a pathological evaluation of serous and mucinous tumors in human samples. The combination of TPEF-SHG-THG imaging provided complementary information about the interface epithelium/stromal, such as the transformation of epithelium surface (THG) and the overall fibrillar tissue architecture (SHG). The fact that H&E staining is the standard method used in clinical pathology and that the stored samples are usually fixed makes it important a re-evaluation of these samples with NLO microscopy to compare new results with a library of already existing samples. FLIM, however, depends on the chemical environment around the fluorophors that was completely changed after fixation; therefore it only makes sense in unstained samples. Our FLIM results in unstained samples demonstrate that it is possible to discriminate healthy epithelia from serous or mucinous epithelia. Qualitative and quantitative analysis of the different imaging modalities used showed that multimodal nonlinear microscopy has the potential to differentiate between cancerous and healthy ovarian tissue.

Adur, J.; Pelegati, V. B.; de Thomaz, A. A.; Bottcher-Luiz, F.; Andrade, L. A. L. A.; Almeida, D. B.; Carvalho, H. F.; Cesar, C. L.

2012-02-01

318

Improved linearity using harmonic error rejection in a full-field range imaging system  

Microsoft Academic Search

Full field range imaging cameras are used to simultaneously measure the distance for every pixel in a given scene using an intensity modulated illumination source and a gain modulated receiver array. The light is reflected from an object in the scene, and the modulation envelope experiences a phase shift proportional to the target distance. Ideally the waveforms are sinusoidal, allowing

Andrew D. Payne; Adrian A. Dorrington; Michael J. Cree; Dale A. Carnegie

2008-01-01

319

Image of nonlinear structures of heterogeneous media using the second harmonic in scanning acoustical microscope  

Microsoft Academic Search

Scanning acoustic microscopy (SAM) images are created on the basis of sound reflection from sharp overfall of acoustical impedance. For that reason any internal structural components and inclusions with similar impedance values will be resolved with certain difficulties. In such particular cases, acoustical nonlinear phenomena could provide very important additional information. Interface between two media at certain conditions can be

Fedar M. Severin; Brian O'Neill; Roman Gr. Maev

2000-01-01

320

Multi-scale harmonic model for solar and climate cyclical variation throughout the Holocene based on Jupiter-Saturn tidal frequencies plus the 11-year solar dynamo cycle  

NASA Astrophysics Data System (ADS)

The Schwabe frequency band of the Zurich sunspot record since 1749 is found to be made of three major cycles with periods of about 9.98, 10.9 and 11.86 years. The side frequencies appear to be closely related to the spring tidal period of Jupiter and Saturn (range between 9.5 and 10.5 years, and median 9.93 years) and to the tidal sidereal period of Jupiter (about 11.86 years). The central cycle may be associated to a quasi-11-year solar dynamo cycle that appears to be approximately synchronized to the average of the two planetary frequencies. A simplified harmonic constituent model based on the above two planetary tidal frequencies and on the exact dates of Jupiter and Saturn planetary tidal phases, plus a theoretically deduced 10.87-year central cycle reveals complex quasi-periodic interference/beat patterns. The major beat periods occur at about 115, 61 and 130 years, plus a quasi-millennial large beat cycle around 983 years. We show that equivalent synchronized cycles are found in cosmogenic records used to reconstruct solar activity and in proxy climate records throughout the Holocene (last 12,000 years) up to now. The quasi-secular beat oscillations hindcast reasonably well the known prolonged periods of low solar activity during the last millennium such as the Oort, Wolf, Spörer, Maunder and Dalton minima, as well as the 17 115-year long oscillations found in a detailed temperature reconstruction of the Northern Hemisphere covering the last 2000 years. The millennial three-frequency beat cycle hindcasts equivalent solar and climate cycles for 12,000 years. Finally, the harmonic model herein proposed reconstructs the prolonged solar minima that occurred during 1900-1920 and 1960-1980 and the secular solar maxima around 1870-1890, 1940-1950 and 1995-2005 and a secular upward trending during the 20th century: this modulated trending agrees well with some solar proxy model, with the ACRIM TSI satellite composite and with the global surface temperature modulation since 1850. The model forecasts a new prolonged solar minimum during 2020-2045, which would be produced by the minima of both the 61 and 115-year reconstructed cycles. Finally, the model predicts that during low solar activity periods, the solar cycle length tends to be longer, as some researchers have claimed. These results clearly indicate that both solar and climate oscillations are linked to planetary motion and, furthermore, their timing can be reasonably hindcast and forecast for decades, centuries and millennia. The demonstrated geometrical synchronicity between solar and climate data patterns with the proposed solar/planetary harmonic model rebuts a major critique (by Smythe and Eddy, 1977) of the theory of planetary tidal influence on the Sun. Other qualitative discussions are added about the plausibility of a planetary influence on solar activity.

Scafetta, Nicola

2012-05-01

321

Suppression of Unwanted Harmonics Using Integrated Complementary Split-Ring Resonators in Nonlinear Transmission Line Frequency Multipliers  

Microsoft Academic Search

Inspired by the distributed nature of nonlinear transmission lines (NLTLs), a novel filtering method that integrates the filter stages within the NLTL periodic structure is introduced to suppress unwanted signals. To implement the filter, compact complementary split-ring resonators are designed and included in a coplanar waveguide-based NLTL frequency doubler. Analytical derivations for the filter design and prediction of the dispersion

Kasra Payandehjoo; Ramesh Abhari

2008-01-01

322

Role of clinical judgment and tissue harmonic imaging ultrasonography in diagnosis of paediatric acute appendicitis  

PubMed Central

Background Appendicitis is the most common surgical emergency in children; yet, diagnosis of equivocal presentations continues to challenge clinicians. Aim The objective of this study was to investigate the hypothesis that the use of a modified clinical practice and harmonic ultrasonographic grading scores (MCPGS) may improve the accuracy in diagnosing acute appendicitis in the pediatric population. Patients & Methods Main outcome measures Sensitivity, specificity, and accuracy of the modified scoring system. Five hundred and thirty patients presented with suspected diagnosis of acute appendicitis during the period from December 2000 to December 2009 were enrolled in this study. Children's data that have already been published of those who presented with suspected diagnosis of acute appendicitis- to whom a special clinical practice grading scores (CPGS) incorporating clinical judgment and results of gray scale ultrasonography (US) was applied- were reviewed and compared to the data of 265 pediatric patients with equivocal diagnosis of acute appendicitis (AA), to whom a modified clinical practice grading scores (MCPGS) was applied. Statistical analyses were carried out using Z test for comparing 2 sample proportions and student's t-test to compare the quantitative data in both groups. Sensitivity and specificity for the 2 scoring systems were calculated using Epi-Info software. Results The Number of appendectomies declined from 200 (75.5%) in our previous CPGS to 187 (70.6%) in the MCPGS (P > 0.05). Specificity was significantly higher when applying MCPGS (90.7%) in this study compared to 70.47% in our previous work when CPGS was applied (P < 0.01). Furthermore, the positive predictive value (PPV) was significantly higher (95.72%) than in our previous study (82.88%), (P < 0.01). Overall agreement (accuracy) of MCPGS was 96.98%. Kappa = 0.929 (P < 0.001). Negative predictive power was 100%. And the Overall agreement (accuracy) was 96.98%. Conclusions MCPGS tends to help in reduce the numbers of avoidable and unnecessary appendectomies in suspected cases of pediatric acute appendicitis that may help in saving hospital resources.

2011-01-01

323

A novel technique of image quality objective measurement by wavelet analysis throughout the spatial frequency range  

NASA Astrophysics Data System (ADS)

An essential determinant of the value of surrogate digital images is their quality. Image quality measurement has become crucial for most image processing applications. Over the past years , there have been many attempts to develop models or metrics for image quality that incorporate elements of human visual sensitivity. However, there is no current standard and objective definition of spectral image quality. This paper proposes a reliable automatic method for objective image quality measurement by wavelet analysis throughout the spatial frequency range. This is done by a detailed analysis of an image for a wide range of spatial frequency content, using a combination of modulation transfer function (MTF), brightness, contrast, saturation, sharpness and noise, as a more revealing metric for quality evaluation. A fast lifting wavelet algorithm is developed for computationally efficient spatial frequency analysis, where fine image detail corresponding to high spatial frequencies and image sharpness in regard to lower and mid -range spatial frequencies can be examined and compared accordingly. The wavelet frequency deconstruction is actually to extract the feature of edges in sub-band images. The technique provides a means to relate the quality of an image to the interpretation and quantification throughout the frequency range, in which the noise level is estimated in assisting with quality analysis. The experimental results of using this method for image quality measurement exhibit good correlation to subjective visual quality assessments.

Luo, Gaoyong

2004-10-01

324

Effects of large vibration amplitudes on the mode shapes and natural frequencies of thin elastic structures, Part 3: Fully clamped rectangular isotropic plates - measurements of the mode shape amplitude dependence and the spatial distribution of harmonic distortion  

Microsoft Academic Search

In this work, the amplitude dependence of the resonance frequency and the spatial distribution of the first and second harmonic components of the dynamic response of a fully clamped rectangular homogeneous plate have been investigated experimentally. By using electrodynamic point excitation at the center of the plate and a non-contacting optical vibration transducer for response measurement, the spatial distribution of

R. Benamar; M. M. K. Bennouna; R. G. White

1994-01-01

325

Can recent innovations in harmonic analysis 'explain' key findings in natural image statistics?  

PubMed

Recently, applied mathematicians have been pursuing the goal of sparse coding of certain mathematical models of images with edges. They have found by mathematical analysis that, instead of wavelets and Fourier methods, sparse coding leads towards new systems: ridgelets and curvelets. These new systems have elements distributed across a range of scales and locations, but also orientations. In fact they have highly direction-specific elements and exhibit increasing numbers of distinct directions as we go to successively finer scales. Meanwhile, researchers in natural scene statistics (NSS) have been attempting to find sparse codes for natural images. The new systems they have found by computational optimization have elements distributed across a range of scales and locations, but also orientations. The new systems are certainly unlike wavelet and Gabor systems, on the one hand because of the multi-orientation and on the other hand because of the multi-scale nature. There is a certain degree of visual resemblance between the findings in the two fields, which suggests the hypothesis that certain important findings in the NSS literature might possibly be explained by the slogan: edges are the dominant features in images, and curvelets are the right tool for representing edges. We consider here certain empirical consequences of this hypothesis, looking at key findings of the NSS literature and conducting studies of curvelet and ridgelet transforms on synthetic and real images, to see if the results are consistent with predictions from this slogan. Our first experiment measures the nonGaussianity of Fourier, wavelet, ridgelet and curvelet coefficients over a database of synthetic and photographic images. Empirically the curvelet coefficients exhibit noticeably higher kurtosis than wavelet, ridgelet, or Fourier coefficients. This is consistent with the hypothesis. Our second experiment studies the inter-scale correlation of wavelet coefficient energies at the same location. We describe a simple experiment showing that presence of edges explains these correlations. We also develop a crude nonlinear 'partial correlation' by considering the correlation between wavelet parents and children after a few curvelet coefficients are removed. When we kill the few biggest coefficients of the curvelet transform, much of the correlation between wavelet subbands disappears--consistent with the hypothesis. We suggest implications for future discussions about NSS. PMID:11563535

Donoho, D L; Flesia, A G

2001-08-01

326

Ultralow-power second-harmonic generation frequency-resolved optical gating using aperiodically poled lithium niobate waveguides [Invited  

Microsoft Academic Search

mW 2 in a collinear SHG FROG geometry, approximately 5 orders of magnitude better than previously reported for any FROG measurement modality. We also discuss asymmetric Y-junction A-PPLN waveguides that permit background-free SHG FROG and a polarization-insensitive SHG FROG tech- nique that eliminates the impairment that frequency-independent random polarization fluctuations induce in the FROG measurement. Finally, we applied these SHG

Houxun Miao; Shang-Da Yang; Carsten Langrock; Rostislav V. Roussev; M. M. Fejer; Andrew M. Weiner

2008-01-01

327

Regulatory Harmonization  

Center for Biologics Evaluation and Research (CBER)

. The Agency engages in a range of explicit harmonization initiatives, a subset of which includes the participation of CBER. ... More results from www.fda.gov/biologicsbloodvaccines/internationalactivities

328

Second harmonic generation imaging of collagen matrix remodeling in a stimulated 3D cellular environment: forward versus backward detection  

NASA Astrophysics Data System (ADS)

The structural remodeling of collagen is important in several biological processes such as wound healing, tendon repair, fibrosis and developmental morphogenesis. Multiphoton microscopy, which uses ultra-short femto-second laser pulses as an excitation source, is efficient in the multiphoton excitation fluorescence (MPEF) of exogenous fluorescent labels tagged to various cellular macromolecular objects, as well as in the induction of a highly specific second harmonic generation (SHG) signal from non-centrosymmetric macromolecules such as fibrillar collagens. Although the non-descanned detectors in the reflection geometry have normally been employed for capturing the backward scattered SHG as well as the MPEF signals, considering the wide range of engineered thick tissue imaging applications, there are still un-answered questions about the generated 3D collagen structures because of the directional pattern of SHG signals. The present study dealt with an in vitro collagen-fibroblast raft model in which the stimulation of fibroblast cells induced the lateral orientation of collagen molecules. The SHG signals originating from the 3D collagen matrix were captured simultaneously in both forward and backward scattering directions to understand the collagen structural differences and to generate a comprehensive understanding of collagen matrix remodeling.

Abraham, Thomas; Scott, Alex; Carthy, Jon; McManus, Bruce

2011-02-01

329

Dual aperture dipole magnet with second harmonic component  

DOEpatents

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.

Praeg, W.F.

1983-08-31

330

Dual aperture dipole magnet with second harmonic component  

DOEpatents

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.

Praeg, Walter F. (Palos Park, IL)

1985-01-01

331

Spatial frequency domain image processing for biometric recognition  

Microsoft Academic Search

Biometric recognition refers to the process of matching an input biometric to stored biometric information. In particular, biometric verification refers to matching the live biometric input from an individual to the stored biometric template about that individual. Examples of biometrics include face images, fingerprint images, iris images, retinal scans, etc. Thus, image processing techniques prove useful in the biometric recognition.

B. V. K. Vijaya Kumar; Chunyan Xie; Marios Savvides; Krithika Venkataramani

2002-01-01

332

Non-linear absorption and second harmonic imaging of Zn–BaTiO 3 thin films prepared by laser ablation  

Microsoft Academic Search

Zinc-doped barium titanate samples have been prepared on Corning glass as well as on silicon wafer by laser ablation. Samples on glass having different deposition time and varying zinc oxide content have been studied by Z-scan technique at a wavelength of 540 nm and laser intensity of 20 GW while samples on silicon have been characterized by second harmonic (SH) imaging as

A. Y. Fasasi; M. Maaza; Ch. Theron; P. Neethling; U. Buttner; A. Leitch; A. K. Chaudhary

2008-01-01

333

The first harmonic as a known source for wavefront correction  

NASA Astrophysics Data System (ADS)

It is demonstrated that distortion of a non-linearly generated first harmonic transmit beam due to a near-field aberrator is reduced as transmit pressure is increased. The first harmonic transmit beam is then used as a source for correction of aberration. In the first experiment, pieces of Lucite 11 mm and 24 mm thick were used as near-field aberrators. Beam plots of the fundamental and first harmonic were measured in a water tank with and without the aberrators present at multiple transmit voltages. The Lucite aberrator was then removed and an electronic aberrator with RMS delay error of 138 ns was applied to the transmit and receive apertures. The first harmonic reflected from the tip of a hydrophone was measured, and correcting delays were determined using a multi-lag least-means-squares cross-correlation method. Corrections were applied to an imaging beam transmitted at twice the frequency of the fundamental beam, the same frequency as the generated first-harmonic. Results from the Lucite experiments showed a -6 dB beam width improvement of 1.8 degrees when transmit voltage was increased from 20 volts to 80 volts. Results from first harmonic based correction of the electronic aberrator resulted in significant improvement in beam width and showed an average improvement of 16.8 dB in transmit beam signal level and 31.9 dB improvement in transmit-receive beam signal level.

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

2009-02-01

334

A real-time algorithm for the harmonic estimation and frequency tracking of dominant components in fusion plasma magnetic diagnostics  

NASA Astrophysics Data System (ADS)

The real-time tracking of instantaneous quantities such as frequency, amplitude, and phase of components immerse in noisy signals has been a common problem in many scientific and engineering fields such as power systems and delivery, telecommunications, and acoustics for the past decades. In magnetically confined fusion research, extracting this sort of information from magnetic signals can be of valuable assistance in, for instance, feedback control of detrimental magnetohydrodynamic modes and disruption avoidance mechanisms by monitoring instability growth or anticipating mode-locking events. This work is focused on nonlinear Kalman filter based methods for tackling this problem. Similar methods have already proven their merits and have been successfully employed in this scientific domain in applications such as amplitude demodulation for the motional Stark effect diagnostic. In the course of this work, three approaches are described, compared, and discussed using magnetic signals from the Joint European Torus tokamak plasma discharges for benchmarking purposes.

Alves, D.; Coelho, R.; JET-EFDA Contributors

2013-08-01

335

A real-time algorithm for the harmonic estimation and frequency tracking of dominant components in fusion plasma magnetic diagnostics.  

PubMed

The real-time tracking of instantaneous quantities such as frequency, amplitude, and phase of components immerse in noisy signals has been a common problem in many scientific and engineering fields such as power systems and delivery, telecommunications, and acoustics for the past decades. In magnetically confined fusion research, extracting this sort of information from magnetic signals can be of valuable assistance in, for instance, feedback control of detrimental magnetohydrodynamic modes and disruption avoidance mechanisms by monitoring instability growth or anticipating mode-locking events. This work is focused on nonlinear Kalman filter based methods for tackling this problem. Similar methods have already proven their merits and have been successfully employed in this scientific domain in applications such as amplitude demodulation for the motional Stark effect diagnostic. In the course of this work, three approaches are described, compared, and discussed using magnetic signals from the Joint European Torus tokamak plasma discharges for benchmarking purposes. PMID:24011401

Alves, D; Coelho, R

2013-08-01

336

Defect detection by pulse compression in frequency modulated thermal wave imaging  

Microsoft Academic Search

A new, quantitative, whole field, non-contact and non-destructive technique for sub-surface defect detection is presented based on frequency modulated thermal wave imaging (FMTWI). Electro-thermal modeling and MATLAB-SIMULINK simulation has been carried out for the proposed technique. Experimental results of frequency modulated thermal wave imaging are reported, and defect detection by a correlation approach demonstrated.

Suneet Tuli; Ravibabu Mulaveesala

2005-01-01

337

A compact frequency-domain photon migration system for integration into commercial hybrid small animal imaging scanners for fluorescence tomography.  

PubMed

The work presented herein describes the system design and performance evaluation of a miniaturized near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system with non-contact excitation and homodyne detection capability for small animal fluorescence tomography. The FDPM system was developed specifically for incorporation into a Siemens micro positron emission tomography/computed tomography (microPET/CT) commercial scanner for hybrid small animal imaging, but could be adapted to other systems. Operating at 100 MHz, the system noise was minimized and the associated amplitude and phase errors were characterized to be ±0.7% and ±0.3°, respectively. To demonstrate the tomographic ability, a commercial mouse-shaped phantom with 50 µM IRDye800CW and ??Ga containing inclusion was used to associate PET and NIRF tomography. Three-dimensional mesh generation and anatomical referencing was accomplished through CT. A third-order simplified spherical harmonics approximation (SP?) algorithm, for efficient prediction of light propagation in small animals, was tailored to incorporate the FDPM approach. Finally, the PET-NIRF target co-localization accuracy was analyzed in vivo with a dual-labeled imaging agent targeting orthotopic growth of human prostate cancer. The obtained results validate the integration of time-dependent fluorescence tomography system within a commercial microPET/CT scanner for multimodality small animal imaging. PMID:23171509

Darne, Chinmay D; Lu, Yujie; Tan, I-Chih; Zhu, Banghe; Rasmussen, John C; Smith, Anne M; Yan, Shikui; Sevick-Muraca, Eva M

2012-11-22

338

A compact frequency-domain photon migration system for integration into commercial hybrid small animal imaging scanners for fluorescence tomography  

NASA Astrophysics Data System (ADS)

The work presented herein describes the system design and performance evaluation of a miniaturized near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system with non-contact excitation and homodyne detection capability for small animal fluorescence tomography. The FDPM system was developed specifically for incorporation into a Siemens micro positron emission tomography/computed tomography (microPET/CT) commercial scanner for hybrid small animal imaging, but could be adapted to other systems. Operating at 100 MHz, the system noise was minimized and the associated amplitude and phase errors were characterized to be ±0.7% and ±0.3°, respectively. To demonstrate the tomographic ability, a commercial mouse-shaped phantom with 50 µM IRDye800CW and 68Ga containing inclusion was used to associate PET and NIRF tomography. Three-dimensional mesh generation and anatomical referencing was accomplished through CT. A third-order simplified spherical harmonics approximation (SP3) algorithm, for efficient prediction of light propagation in small animals, was tailored to incorporate the FDPM approach. Finally, the PET-NIRF target co-localization accuracy was analyzed in vivo with a dual-labeled imaging agent targeting orthotopic growth of human prostate cancer. The obtained results validate the integration of time-dependent fluorescence tomography system within a commercial microPET/CT scanner for multimodality small animal imaging.

Darne, Chinmay D.; Lu, Yujie; Tan, I.-Chih; Zhu, Banghe; Rasmussen, John C.; Smith, Anne M.; Yan, Shikui; Sevick-Muraca, Eva M.

2012-12-01

339

Frequency-dependent DQE in dual-screen CR imaging  

Microsoft Academic Search

It has been shown that dual-screen image acquisition technique can be used to improve the image signal-to-noise ratio (SNR) in computed radiography (CR) imaging. In chest imaging situations, acquisition with a high resolution (HR) screen and a standard resolution (ST) screen can also be used to improve the modulation transfer function. Unlike in conventional radiography using two screens, the front

Chris C. Shaw; Xingming Liu; Sophie Chardon; John M. Herron

1998-01-01

340

High frequency nonlinear B-scan imaging of microbubble contrast agents  

Microsoft Academic Search

It was previously shown that it is possible to produce nonlinear scattering from microbubble contrast agents using transmit frequencies in the 14-32 MHz range, suggesting the possibility of performing high-frequency, nonlinear microbubble imaging. In this study, we describe the development of nonlinear microbubble B-scan imaging instrumentation capable of operating at transmit center frequencies between 10 and 50 MHz. The system

David E. Goertz; Emmanuel Cherin; Andrew Needles; Raffi Karshafian; Allison S. Brown; Peter N. Burns; F. Stuart Foster

2005-01-01

341

Simulator for optimization of radio-frequency pulses in magnetic resonance imaging  

Microsoft Academic Search

The surface coils being driven by radio-frequency pulses are often a primary choice in magnetic resonance imaging for both radio-frequency excitation and reception of weak magnetic resonance imaging signals from the volume of interest. The advantages of the surface coils compared to the volume coils are the minimized radio-frequency power deposition in tissue and the improved detection sensitivity due to

Johanna Öberg

342

Harmonic Radar Literature Harmonisk Radar - en Litteraturstudie.  

National Technical Information Service (NTIS)

A harmonic radar sends on a given frequency f sub o and receives on another frequency usually 3 f sub o. The overtone is generated on joints between the metal parts of the radar target. The generated high harmonic frequency is very weak, which is why this...

B. Jansson

1980-01-01

343

Time-frequency analysis of polarimetric SAR images  

Microsoft Academic Search

This article demonstrates the usefulness of time-frequency tools in SAR imagery through two applications. A new method is proposed to analyse moving targets. It uses a two dimensional matching-pursuit algorithm, over a time-frequency dictionary. Point targets speed and scattering characteristics (frequency comportment, angular and polarimetric behaviour) can be retrieved, thus permitting a better knowledge of the target. Urban areas analysis

Paul Leducq; Laurent Ferro-Famil; Eric Pottier

2005-01-01

344

A Simplified Sum-Frequency Vibrational Imaging Setup Used for Imaging Lipid Bilayer Arrays  

PubMed Central

Given the complexity of cell membranes, there is a need for an analytical technique which can explore the physical properties of lipid membranes in a high-throughput and noninvasive manner. A simplified sum-frequency vibrational imaging (SFVI) setup has been developed and characterized using asymmetrically prepared 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC):1,2-distearoyl(d70)-sn-glycero-3-phosphocholine (DSPC-d70) lipid bilayer arrays. Exploiting the vibrational selectivity and inherent symmetry constraints of sum-frequency generation, SFVI was successfully used to probe the transition temperature of a patterned DSPC:DSPC-d70 lipid bilayer array. SFVI was also used to study the phase behavior in a multi-component micropatterned lipid bilayer array (MLBA) prepared using three different binary lipid mixtures (1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC):DSPC, DOPC:1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC:DSPC). This paper demonstrates that a simplified SFVI setup provides the necessary chemical imaging capabilities with the spatial resolution, sensitivity and field of view required for exploring lipid membrane properties in a high-throughput array based assay.

Smith, Kathryn A.; Conboy, John C.

2012-01-01

345

Method to restore images from chaotic frequency-down-converted light using phase matching  

SciTech Connect

We present an optical frequency-down-conversion process of the image of an object illuminated with chaotic light in which also the low-frequency field entering the second-order nonlinear crystal is chaotic. We show that the fulfillment of the phase-matching conditions by the chaotic interacting fields provides the rules to retrieve the object image by calculating suitable correlations of the local intensity fluctuations even if a single record of down-converted chaotic image is available.

Andreoni, Alessandra; Puddu, Emiliano; Bondani, Maria [Dipartimento di Fisica e Matematica and Consiglio Nazionale delle Ricerche-Istituto Nazionale per la Fisica della Materia, CNR-INFM, Via Valleggio 11, 22100 Como (Italy); National Laboratory for Ultrafast and Ultraintense Optical Science, CNR-INFM, Via Valleggio 11, 22100 Como (Italy)

2006-11-15

346

Imaging of rock fractures with low-frequency ultrasonic reflection\\/diffraction  

Microsoft Academic Search

This paper documents the development of a method for imaging millimeter-scale fractures in rock with low-frequency ultrasound and seismic algorithms developed originally for kilometer-scale geologic structures. Low-frequency ultrasonic reflection\\/diffraction imaging provides detailed images of an impedance contrast in terms of two-way travel time from the surface to the fracture, which produces a geometrically distorted representation. Several seismic methods were used

S. D. Glaser; M. K. Hand

1998-01-01

347

Transmit beamforming for optimal second-harmonic generation.  

PubMed

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. PMID:21859575

Hoilund-Kaupang, Halvard; Masoy, Svein-Erik

2011-08-01

348

Amplified, frequency swept lasers for frequency domain reflectometry and OCT imaging: design and scaling principles  

Microsoft Academic Search

We demonstrate a high-speed, frequency swept, 1300 nm laser source for frequency domain reflectometry and OCT with Fourier domain\\/swept-source detection. The laser uses a fiber coupled, semiconductor amplifier and a tunable fiber Fabry-Perot filter. We present scaling principles which predict the maximum frequency sweep speed and trade offs in output power, noise and instantaneous linewidth performance. The use of an

R. Huber; M. Wojtkowski; K. Taira; J. G. Fujimoto; K. Hsu

2005-01-01

349

Region Segmentation in the Frequency Domain Applied to Upper Airway Real-Time Magnetic Resonance Images  

Microsoft Academic Search

We describe a method for unsupervised region seg- mentation of an image using its spatial frequency domain repre- sentation. The algorithm was designed to process large sequences of real-time magnetic resonance (MR) images containing the 2-D midsagittal view of a human vocal tract airway. The segmentation algorithm uses an anatomically informed object model, whose fit to the observed image data

Erik Bresch; Shrikanth Narayanan

2009-01-01

350

Imaging of collagen matrix remodeling in three-dimensional space using second harmonic generation and two photon excitation fluorescence  

NASA Astrophysics Data System (ADS)

Second harmonic generation (SHG), a nonlinear optical phenomenon, exhibits several in-common characteristics of twophoton excited fluorescence (TPEF) microscopy. These characteristics include identical equipment requirements from experiment to experiment and the intrinsic capability of generating 3-dimensional (D) high resolution images. Structural protein arrays that are highly ordered, such as collagen, produce strong SHG signals without the need for any exogenous label (stain). SHG and TPEF can be used together to provide information on structural rearrangements in 3D space of the collagen matrix associated with various physiological processes. In this study, we used SHG and TPEF to detect cellmediated structural reorganization of the extracellular collagen matrix in 3D space triggered by dimensional changes of embedded fibroblasts. These fibroblasts were cultured in native type I collagen gels and were stimulated to contract for a period of 24 hours. The gels were stained for cell nuclei with Hoechst and for actin with phalloidin conjugated to Alexa Fluor 488. We used non-de-scanned detectors and spectral scanning mode both in the reflection geometry for generating the 3D images and for SHG spectra, respectively. We used a tunable infrared laser with 100-fs pulses at a repetition rate of 80-MHz tuned to 800-nm for Hoechst and Alexa 488 excitations. We employed a broad range of excitation wavelengths (800 to 880-nm) with a scan interval of 10 nm to detect the SHG signal. We found that spectrally clean SHG signal peaked at 414-nm with excitation wavelength of 830-nm. The SHG spectrum has a full width half maximum (FWHM) bandwidth of 6.60-nm, which is consistent with its scaling relation to FWHM bandwidth 100-fs excitation pulses. When stimulated to contract, we found the fibroblasts to be highly elongated as well as interconnected in 2D space, and the collagen matrix, in the form of a visibly clear fibril structure, accumulated around the cells. In the absence of contraction, on the other hand, the cells were predominantly round in shape and no sign of collagen accumulation around the cell was evident despite the presence of SHG signal as well as the fibrillar collagen morphology in the collagen matrix. We here conclude that SHG in conjunction with TPEF can serve as a noninvasive method to provide spatially resolved 3D structural reorganization of collagen matrices triggered by various physiological processes.

Abraham, Thomas; Carthy, Jon; McManus, Bruce

2009-02-01

351

Waveguide harmonic damper for klystron amplifier.  

SciTech Connect

A waveguide harmonic damper was designed for removing the harmonic frequency power from the klystron amplifiers of the APS linac. Straight coaxial probe antennas are used in a rectangular waveguide to form a damper. A linear array of the probe antennas is used on a narrow wall of the rectangular waveguide for damping klystron harmonics while decoupling the fundamental frequency in dominent TE{sub 01} mode. The klystron harmonics can exist in the waveguide as waveguide higher-order modes above cutoff. Computer simulations are made to investigate the waveguide harmonic damping characteristics of the damper.

Kang, Y.

1998-10-27

352

Novel Methods for Flame Pulsation Frequency Measurement with Image Analysis  

Microsoft Academic Search

To characterize the periodic pulsation of flame from the flame image sequence, several novel methods for flame pulsation measurement\\u000a were introduced and demonstrated based on flame image analysis. Results show that moment function of flame image, such as\\u000a weighted Euclidean distance and cross correlation coefficient, could represent the geometric and periodic flame pulsation;\\u000a and that both the vertical and horizontal

Ying-chun Wu; Xue-cheng Wu; Shou-xiang Lu; Jia-qing Zhang; Ke-fa Cen

353

Frequency response and distortion properties of nonlinear image processing algorithms and the importance of imaging context.  

PubMed

Purpose: The most common metrics for resolution analysis in medical imaging are valid only for (approximately) linear systems. While analogues to these metrics have been used in attempts to describe resolution performance in nonlinear systems, the analysis is incomplete since distortion effects are often ignored. The authors have developed a methodology to analyze the amplitude modulation and waveform distortion properties of nonlinear systems with specific application to medical image processing algorithms.Methods: Using sinusoidal basis functions, two metrics were derived which distinguish amplitude modulation from nonlinear waveform distortion: principle frequency response and distortion power spectrum, respectively. Additionally, two figures of merit were developed to describe the relative impact of nonlinear distortion as a result of image processing: distortion index (DI) and ?DI. Three nonlinear denoising algorithms, the median, bilateral, and wavelet denoising filters, were selected as example functions to demonstrate the utility of the metrics derived in this study.Results: Each filter showed very different resolution and waveform distortion properties. In particular, the amplitude and extent of nonlinear distortion depended strongly on image context and the type of nonlinear mechanism employed. Nonlinear waveform distortion constituted up to 30% of the median filter output signal power in high contrast-to-noise ratio (CNR) scenarios. Conversely, nonlinear distortion never exceeded 1% of the bilateral filter output signal power. The wavelet denoising response contained between 1% and 9% distortion which varied weakly as a function of CNR.Conclusions: The analytical metrics described in the paper demonstrate the importance of considering both resolution- and distortion-related effects in characterizing the performance of nonlinear imaging systems with specific application to image processing algorithms. Findings with three common nonlinear algorithms demonstrate a range of CNR values over which it is important to consider the impact of the nonlinear nature of each algorithm. Background context is also shown to influence the degree to which the nonlinear nature of the algorithm influences resolution and distortion. While no single metric can yet anticipate observer performance in nonlinear systems, the approach described can demonstrate the range of imaging contexts over which such nonlinear effects are important to consider. PMID:24007157

Wells, Jered R; Dobbins, James T

2013-09-01

354

The response of phospholipid-encapsulated microbubbles to chirp-coded excitation: implications for high-frequency nonlinear imaging.  

PubMed

The current excitation strategy for harmonic and subharmonic imaging (HI and SHI) uses short sine-bursts. However, alternate pulsing strategies may be useful for enhancing nonlinear emissions from ultrasound contrast agents. The goal of this study was to corroborate the hypothesis that chirp-coded excitation can improve the performance of high-frequency HI and SHI. A secondary goal was to understand the mechanisms that govern the response of ultrasound contrast agents to chirp-coded and sine-burst excitation schemes. Numerical simulations and acoustic measurements were conducted to evaluate the response of a commercial contrast agent (Targestar-P(®)) to chirp-coded and sine-burst excitation (10?MHz frequency, peak pressures 290 kPa). The results of the acoustic measurements revealed an improvement in signal-to-noise ratio by 4 to 14?dB, and a two- to threefold reduction in the subharmonic threshold with chirp-coded excitation. Simulations conducted with the Marmottant model suggest that an increase in expansion-dominated radial excursion of microbubbles was the mechanism responsible for the stronger nonlinear response. Additionally, chirp-coded excitation detected the nonlinear response for a wider range of agent concentrations than sine-bursts. Therefore, chirp-coded excitation could be a viable approach for enhancing the performance of HI and SHI. PMID:23654417

Shekhar, Himanshu; Doyley, Marvin M

2013-05-01

355

Attenuation corrected fluorescence extraction using spatial frequency domain imaging system  

NASA Astrophysics Data System (ADS)

In this paper, we present a novel approach to retrieve attenuation corrected fluorescence (ACF) in the image field. This approach can be applied to improve tumor identification for both diagnosis and treatment purpose. Furthermore, this approach will facilitate the development of fluorescence image-guided surgery.

Yang, Bin; Sharma, Manu; Wang, Youmin; Tunnell, James W.

2013-03-01

356

Low Frequency Magnetic Imaging Detector for Concealed Weapons Detection.  

National Technical Information Service (NTIS)

Military personnel, law-enforcement officers, and civilians face every-increasing dangers from persons carrying concealed handguns and other weapons. We have developed a novel concealed-weapons detector based on the principle of low-frequency magnetic ima...

B. Zollars M. Durrett W. Hallidy

1999-01-01

357

Near-field discrete-frequency microwave holographic imaging of buried ordnance  

NASA Astrophysics Data System (ADS)

Images of buried ordnance can accelerate remediation through identification. This paper presents images of a buried, inert projectile. The images are plan views, at fixed but variable depths. The images were formed by processing measured reflectance through Fourier transformation, backward propagation, and inverse transformation. Data were measured in two tests. Both tests utilized a towed array of seven antennas. One test, in 1995, used frequencies between 187.5 and 487.5 MHz; the best images were from the 387.5 MHz data. An earlier test, in 1994, used frequencies 200, 350, and 500 MHz; the best images were formed from the 500 MHz data. The procedures for the two sets of data differed in relative orientation of the sensor antennas and projectile; in addition, soil dielectric constant values differed. Image displays also differed in image data interpolation.

Nilles, James T.; Tricoles, Gus P.; Vance, Gary L.

1996-05-01

358

Performance comparison of ISAR imaging method based on time frequency transforms  

NASA Astrophysics Data System (ADS)

Inverse synthetic aperture radar (ISAR) can image the moving target, especially the target in the air, so it is important in the air defence and missile defence system. Time-frequency Transform was applied to ISAR imaging process widely. Several time frequency transforms were introduced. Noise jamming methods were analysed, and when these noise jamming were added to the echo of the ISAR receiver, the image can become blur even can't to be identify. But the effect is different to the different time frequency analysis. The results of simulation experiment show the Performance Comparison of the method.

Xie, Chunjian; Guo, Chenjiang; Xu, Jiadong

2013-03-01

359

Spatial pattern separation of chemicals and frequency-independent components by terahertz spectroscopic imaging  

NASA Astrophysics Data System (ADS)

We separated the component spatial patterns of frequency-dependent absorption in chemicals and frequency-independent components such as plastic, paper, and measurement noise in terahertz (THz) spectroscopic images, using known spectral curves. Our measurement system, which uses a widely tunable coherent THz-wave parametric oscillator source, can image at a specific frequency in the range 1-2 THz. The component patterns of chemicals can easily be extracted by use of the frequency-independent components. This method could be successfully used for nondestructive inspection for the detection of illegal drugs and devices of bioterrorism concealed, e.g., inside mail and packages.

Watanabe, Yuuki; Kawase, Kodo; Ikari, Tomofumi; Ito, Hiromasa; Ishikawa, Youichi; Minamide, Hiroaki

2003-10-01

360

Theory of frequency modulated thermal wave imaging for nondestructive subsurface defect detection  

NASA Astrophysics Data System (ADS)

This letter provides the theory and mathematical analysis in support of a recently proposed frequency modulated thermal wave imaging for nondestructive subsurface defect detection in solids. The authors illustrate how the technique simultaneously combines the advantages of both conventional pulse based thermography as well as modulated lock-in thermography. A specimen is heated for launching thermal waves into the sample, not at a single frequency (lock-in) or at all frequencies (pulse), but in a desired range of frequencies. While peak power requirement is reduced, phase images obtained retain known advantages. Experimental results from a carbon fiber reinforced plastic sample are presented in support.

Mulaveesala, Ravibabu; Tuli, Suneet

2006-11-01

361

Applications of Frequency Modulated Thermal Wave Imaging For Non-destructive Characterization  

NASA Astrophysics Data System (ADS)

A novel technique, frequency modulated thermal wave imaging (FMTWI) has recently been Proposed and demonstrated for non-destructive subsurface defect detection in solids. Its theory and mathematical analysis is provided in this paper illustrating. how the technique simultaneously combines advantages of conventional pulse based thermography as well as lock-in thermography (LT). The specimen is heated for launching thermal waves into the sample, not at a single frequency (Lock-in) or at all frequencies (pulse). but in a desired range of frequencies. While peak power requirement is reduced, phase images obtained retain known advantages. Experimental results are also presented in support.

Mulaveesala, Ravibabu; Tuli, Suneet

2008-04-01

362

Multi-frequency imaging of perfectly conducting cracks via boundary measurements  

NASA Astrophysics Data System (ADS)

Imaging of perfectly conducting crack(s) in a 2-D homogeneous medium using boundary data is studied. Based on the singular structure of the Multi-Static Response (MSR) matrix whose elements are normalized by an adequate test function at several frequencies, an imaging functional is introduced and analyzed. A non-iterative imaging procedure is proposed. Numerical experiments from noisy synthetic data show that acceptable images of single and multiple cracks are obtained.

Park, Won-Kwang; Lesselier, Dominique

2013-02-01

363

Ab initio time-dependent density-functional-theory study of the frequency comb structure, coherence, and dephasing of multielectron systems in the vuv-xuv regimes via high-order harmonic generation  

Microsoft Academic Search

We present an ab initio nonperturbative investigation of the frequency comb structure and coherence within each order of the high-order harmonic generation (HHG) of rare-gas atoms by means of the time-dependent density-functional theory (TDDFT) with optimized effective potential (OEP) and self-interaction correction (SIC). The TDDFT+OEP-SIC equations are solved accurately and efficiently by means of the time-dependent generalized pseudospectral technique. We

Juan J. Carrera; Shih-I. Chu

2009-01-01

364

Effects of Bias Frequency on 2D Image of Net Production Rate in Two Frequency CCP  

NASA Astrophysics Data System (ADS)

Two frequency capacitively-coupled plasma(2f-CCP) is a major processing tool for SiO2 etching. It is important to optimize the bias frequency for both a control of the ion energy on the wafer and a radial uniformity of 2f-CCP. Effect of bias frequency on 2D(r,z) profiles of axisymmetric 2f-CCP in CF_4/Ar at 25mTorr is investigated by time-resolved OES. Bias frequency in a range of 339kHz ~2.71MHz is applied to the 2f-CCP excited at 13.56MHz. For bias frequencies of 339kHz and 678kHz, the radial uniformity of the net excitation rate of probed-Ar(2p_1) is strongly affected by the bias voltage amplitude due to the excess excitation caused by high energy electrons at the central axis. Radial uniformity is improved for the bias frequency higher than 1.35MHz. The effect of bias frequency is also shown for the temporal variation of the net excitation rate during one bias period. The net rate changes by 50% at 1.35MHz, while it changes by 200% at 678kHz. The effect of secondary electrons from the bias electrode is suppressed in case of 1.35MHz by a temporal trapping. Optimization of the bias frequency above 1MHz becomes a key to enable the bimodal energy distribution of ion on the wafer surface and the radial uniformity of 2f-CCP. Results of VHF(100MHz) excitation and the detail of the sustaining mechanism of 2f-CCP during one RF period are also discussed.

Kitajima, T.; Fujita, T.; Mano, T.; Makabe, T.

1999-10-01

365

Discovery of deep and shallow trap states from step structures of rutile TiO{sub 2} vicinal surfaces by second harmonic and sum frequency generation spectroscopy  

SciTech Connect

In this report, local electronic structures of steps and terraces on rutile TiO{sub 2} single crystal faces were studied by second harmonic and sum frequency generation (SHG/SFG) spectroscopy. We attained selective measurement of the local electronic states of the step bunches formed on the vicinal (17 18 1) and (15 13 0) surfaces using a recently developed step-selective probing technique. The electronic structures of the flat (110)-(1x1) (the terrace face of the vicinal surfaces) and (011)-(2x1) surfaces were also discussed. The SHG/SFG spectra showed that step structures are mainly responsible for the formation of trap states, since significant resonances from the trap states were observed only from the vicinal surfaces. We detected deep hole trap (DHT) states and shallow electron trap (SET) states selectively from the step bunches on the vicinal surfaces. Detailed analysis of the SHG/SFG spectra showed that the DHT and SET states are more likely to be induced at the top edges of the step bunches than on their hillsides. Unlike the SET states, the DHT states were observed only at the step bunches parallel to [1 1 1][equivalent to the step bunches formed on the (17 18 1) surface]. Photocatalytic activity for each TiO{sub 2} sample was also measured through methylene blue photodegradation reactions and was found to follow the sequence: (110) < (17 18 1) < (15 13 0) < (011), indicating that steps along [0 0 1] are more reactive than steps along [1 1 1]. This result implies that the presence of the DHT states observed from the step bunches parallel to [1 1 1] did not effectively contribute to the methylene blue photodegradation reactions.

Takahashi, Hiroaki; Watanabe, Ryosuke; Miyauchi, Yoshihiro; Mizutani, Goro [School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai, Nomi, Ishikawa 923-1292 (Japan)

2011-04-21

366

Frequency Domain Analysis and Synthesis of Image Pyramid Generating Kernels  

Microsoft Academic Search

Construction of image pyramids is described as a two-di-mensional decimation process. Frequently employed generating kernels are compared to the optimal kernel that assures minimal information loss after the resolution reduction, i.e., the one corresponding to an ideal low pass filter. Physically realizable, optimal generating kernels are presented. The amount of computation required for generation of the image pyramid can be

Peter Meer; Ernest S. Baugher; Azriel Rosenfeld

1987-01-01

367

Millimeter-wave imaging with frequency scanning antenna and optical arrayed waveguide gratings  

NASA Astrophysics Data System (ADS)

The principle of a novel passive millimeter-wave (MMW) imaging method using frequency scanning antenna (FSA) and arrayed waveguide grating (AWG) is analyzed theoretically. The imaging processes are divided to three stages and discussed respectively. Then the FSA with 33~ 43GHz frequency scanning range is designed carefully with a field of view of +/-25°for the MMW imaging system. An AWG of 1×24 is then simply designed with a channel spacing of 0.5GHz. The designing and simulating demonstrated the feasibility to build such an imaging system which is progressing.

He, Yuntao; Yu, Guoxin; Fu, Xinyu; Jiang, Yuesong

2012-12-01

368

Optical image and laser slope meter intercomparisons of high-frequency waves  

NASA Astrophysics Data System (ADS)

Spectral analyses of optical images of the ocean surface, obtained by the Riverside Research Institute digital video system, are presented and compared with wave data measured simultaneously by the Jet Propulsion Laboratory (JPL) Waverider-mounted laser slope meter. The image analyses, which incorporate several new ideas, provide two-dimensional wave number spectra of slope, covering wavelengths from 10 cm to 10 m. These slope spectra are converted to wave height spectra by a new technique which includes the effects of sky radiance gradients. Space-time spectra are also presented for waves whose frequencies are less than 2 Hz. The JPL slope frequency spectra are compared with image wave number spectra which have been converted to frequency spectra by use of the gravity wave dispersion relation. Results of comparisons between the frequency spectra obtained from the two different measurements show reasonable agreement for frequencies less than 3 Hz.

Lubard, S. C.; Krimmel, J. E.; Thebaud, L. R.; Evans, D. D.; Shemdin, O. H.

1980-09-01

369

Optical image and laser slope meter intercomparisons of high-frequency waves  

SciTech Connect

Spectral analyses of optical images of the ocean surface, obtained by the Riverside Research Institute digital video system, are presented and compared with wave data measured simultaneously by the Jet Propulsion Laboratory (JPL) Waverider-mounted laser slope meter. The image analyses, which incorporate several new ideas, provide two-dimensional wave number spectra of slope, covering wavelengths from 10 cm to 10 m. These slope spectra are converted to wave height spectra by a new technique which includes the effects of sky radiance gradients. Space-time spectra are also presented for waves whose frequencies are less than 2 Hz. The JPL slope frequency spectra are compared with image wave number spectra which have been converted to frequency spectra by use of the gravity wave dispersion relation. Results of comparisons between the frequency spectra obtained from the two different measurements show reasonable agreement for frequencies less than 3 Hz.

Lubard, S.C.; Krimmel, J.E.; Thebaud, L.R.; Evans, D.D.; Shemdin, O.H.

1980-09-20

370

Harmonized strategy for breaking the striations in the fluorescent lamp  

Microsoft Academic Search

A harmonized strategy for breaking the striations in the fluorescent lamp is proposed. The harmonized circuit (HC) presented is a dependent current source and is used to modulate the lamp current by making the amplitudes of the even harmonics nearly the same as the neighboring odd harmonics. The time and frequency responses of the lamp current without and with HC

Guan-Chyun Hsieh; Chang-Hua Lin

2001-01-01

371

Final Scientific/Technical Report for DE-FG03-02NA00063 Coherent imaging of laser-plasma interactions using XUV high harmonic radiation  

SciTech Connect

The objective of this project was to develop experimental techniques for using coherent extreme-ultraviolet (EUV) radiation generated using the high-order harmonic generation technique, as an illumination source for studies of high-density plasmas relevant to the stockpile stewardship mission. In this project, we made considerable progress, including the first demonstration of imaging of dynamic processes using this coherent ultrashort pulse light. This work also stimulated considerable progress in the development of the required ultrashort EUV pulses, and in the development of new laser technologies that have been commercialized. We also demonstrated the first EUV sources that exhibit full intrinsic optical coherence. This work resulted in 12 publications.

Henry Kapteyn

2006-06-06

372

47 CFR 2.1057 - Frequency spectrum to be investigated.  

Code of Federal Regulations, 2010 CFR

...to the tenth harmonic of the highest fundamental frequency or to 40 GHz...to the fifth harmonic of the highest fundamental frequency or to 100 GHz...to the fifth harmonic of the highest fundamental frequency or to 200...

2010-10-01

373

47 CFR 2.1057 - Frequency spectrum to be investigated.  

Code of Federal Regulations, 2010 CFR

...to the tenth harmonic of the highest fundamental frequency or to 40 GHz...to the fifth harmonic of the highest fundamental frequency or to 100 GHz...to the fifth harmonic of the highest fundamental frequency or to 200...

2009-10-01

374

Digital parallel frequency-domain spectroscopy for tissue imaging  

PubMed Central

Abstract. Near-infrared (NIR) (650 to 1000 nm) optical properties of turbid media can be quantified accurately and noninvasively using methods based on diffuse reflectance or transmittance, such as frequency-domain photon migration (FDPM). Conventional FDPM techniques based on white-light steady-state (SS) spectral measurements in conjunction with the acquisition of frequency-domain (FD) data at selected wavelengths using laser diodes are used to measure broadband NIR scattering-corrected absorption spectra of turbid media. These techniques are limited by the number of wavelength points used to obtain FD data and by the sweeping technique used to collect FD data over a relatively large range. We have developed a method that introduces several improvements in the acquisition of optical parameters, based on the digital parallel acquisition of a comb of frequencies and on the use of a white laser as a single light source for both FD and SS measurements. The source, due to the high brightness, allows a higher penetration depth with an extremely low power on the sample. The parallel acquisition decreases the time required by standard serial systems that scan through a range of modulation frequencies. Furthermore, all-digital acquisition removes analog noise, avoids the analog mixer, and does not create radiofrequency interference or emission.

Arnesano, Cosimo; Santoro, Ylenia; Gratton, Enrico

2012-01-01

375

Simultaneous sum-frequency and vibro-acoustography imaging for nondestructive evaluation and testing applications  

SciTech Connect

High-resolution ultrasound imaging systems for inspection of defects and flaws in materials are of great demand in many industries. Among these systems, Vibro-acoustography (VA) has shown excellent capabilities as a noncontact method for nondestructive high-resolution imaging applications. This method consists of mixing two confocal ultrasound beams, slightly shifted in frequency, to produce a dynamic (oscillatory) radiation force in the region of their intersection. This force vibrates the object placed at the focus of the confocal transducer. As a result of the applied force, an acoustic emission field at the difference frequency of the primary incident ultrasound beams is produced. In addition to the difference frequency acoustic emission signal, there exists another signal at the sum frequency, formed in the intersection region of the two primary beams. The goal of this study is to investigate the formation of high-resolution images using the sum frequency of ultrasound waves in VA while concurrently forming the conventional difference-frequency VA image, thereby increasing the amount of information acquired during a single scan. A theoretical model describing the sum-frequency wave propagation, including beam forming and image formation in the confocal configuration, is developed and verified experimentally. Moreover, sample experiments are performed on a flawed fiber-reinforced ceramic composite plate. Images at both the difference and sum frequencies are compared and discussed. Results show that the sum-frequency image produces a high-resolution C scan of the plate by which the flaws and structural details of the plate can be detected.

Mitri, F. G.; Silva, G. T.; Greenleaf, J. F.; Fatemi, M. [Department of Physiology and Biomedical Engineering, Ultrasound Research Laboratory, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905 (United States); Instituto Nacional de Matematica Pura e Aplicada-IMPA, Rio de Janeiro, RJ 22460-320 (Brazil); Department of Physiology and Biomedical Engineering, Ultrasound Research Laboratory, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905 (United States)

2007-12-01

376

Observation of backward effective third-harmonic generation by cascading completely quasi-phase-matched backward second-harmonic and sum-frequency generation in periodically-poled potassium titanyl phosphate waveguide  

Microsoft Academic Search

Summary form only given. Recently, we achieved backward second-harmonic generation (SHG) in periodically-poled bulk LiNbO3 (PPLN). We have improved the conversion efficiency by about an order of magnitude by using long laser pulses. Here, we report our new results of backward SHG by using periodically-poled potassium titanyl phosphate (PPKTP) waveguide. More importantly, we report our results on first observation of

Xinhua Gu; M. Makarov; Y. J. Ding; J. B. Khurgin; W. P. Risk

1999-01-01

377

High Fidelity Magnetic Resonance Imaging by Frequency Sweep Encoding and Fourier Decoding  

PubMed Central

Using a RF pulse with linear frequency sweep and a simultaneous encoding gradient, magnetization is sequentially excited accompanied by a quadratic phase profile. This quadratic dependence of magnetization phase on position dephases magnetization away from its vertices, allowing direct spatial encoding and image formation in the time domain. In this work we extend this spatial encoding scheme to include nonlinear frequency sweep and show that Fourier decoding or least square fitting in combination with frequency sweep spatial encoding schemes can generate high fidelity images. Application to in vivo multiscan susceptibility-weighted imaging is demonstrated. Our results show that Fourier-decoded, spatially encoded images compare favorably with conventional high resolution images while preserving the unique features of sequential excitation.

Shen, Jun; Xiang, Yun

2010-01-01

378

Ex vivo and in vivo second-harmonic-generation imaging of dermal collagen fiber in skin: comparison of imaging characteristics between mode-locked Cr:forsterite and Ti:sapphire lasers  

Microsoft Academic Search

Second-harmonic-generation (SHG) microscopy is an interesting new tool for observing dermal collagen fiber in skin. However, conventional SHG microscopy using a mode-locked Ti:sapphire laser suffers from low penetration depth and a slow image acquisition rate caused by scattering and absorption in tissue, making it difficult to use for in vivoapplications on human skin. We develop an SHG microscope equipped with

Takeshi Yasui; Yu Takahashi; Masahiro Ito; Shuichiro Fukushima; Tsutomu Araki

2009-01-01

379

Multi-frequency static imaging in electrical impedance tomography: Part 1 instrumentation requirements  

Microsoft Academic Search

Static images of the human body using electrical impedance tomography techniques can be obtained by measuring at two or more\\u000a different frequencies. The frequencies used depend on the application, and their selection depends on the frequency behaviour\\u000a of the impedance for the target tissue. An analysis using available data and theoretical models for tissue impedance yields\\u000a the expected impedance and

P. J. Riu; J. Rosell; A. Lozano; R. Pallà-Areny

1995-01-01

380

Analysis of Errors in ToF Range Imaging With Dual-Frequency Modulation  

Microsoft Academic Search

Range imaging is a technology that utilizes an amplitude-modulated light source and gain-modulated image sen- sor to simultaneously produce distance and intensity data for all pixels of the sensor. The precision of such a system is, in part, dependent on the modulation frequency. There is typically a tradeoff between precision and maximum unambiguous range. Research has shown that, by taking

Adrian P. P. Jongenelen; Donald G. Bailey; Andrew D. Payne; Adrian A. Dorrington; Dale A. Carnegie

2011-01-01

381

Feature extraction of frictional vibration based on CWT time-frequency image  

Microsoft Academic Search

A method to extract features of frictional vibration signals was developed, using continuous wavelet transform (CWT) time-frequency image (TFI) and image processing to analyze the vibration signals, since the frictional vibration signals contain a wealth of information about the interface's fault state and friction wear state. TFIs were generated by CWT theory from the vibration signals produced by cylinder and

Chaoming Huang; Hongliang Yu; Delin Guan; Guobin Li; Qili Wu

2010-01-01

382

Achieving EMC in high frequency and high power switching environment on Radar Imaging Satellite  

Microsoft Academic Search

Satellite deck provides a challenging electro magnetic (EM) environment as the overall volume available is limited and a number of DC-DC converters and clocks are present. Add to this high frequency and high power switching the electro magnetic interference (EMI) scenario couldn't be worse. Radar imaging satellite (RISAT) India's first satellite with day night imaging capability, slated for launch by

G. V. C. Rajan; V. B. Pramod

2008-01-01

383

Attenuation-corrected fluorescence extraction for image-guided surgery in spatial frequency domain  

NASA Astrophysics Data System (ADS)

A new approach to retrieve the attenuation-corrected fluorescence using spatial frequency-domain imaging is demonstrated. Both in vitro and ex vivo experiments showed the technique can compensate for the fluorescence attenuation from tissue absorption and scattering. This approach has potential in molecular image-guided surgery.

Yang, Bin; Sharma, Manu; Tunnell, James W.

2013-08-01

384

Body Image and Marital Satisfaction: Evidence for the Mediating Role of Sexual Frequency and Sexual Satisfaction  

Microsoft Academic Search

How does women's body image shape their interpersonal relationships? Based on recent theories of risk regulation and empirical evidence that sex is an emotionally risky behavior, we predicted that women's body image would predict increased sexual frequency and thus increased sexual and marital satisfaction for both members of established relationships. The current study of 53 recently married couples provided results

Andrea L. Meltzer; James K. McNulty

2010-01-01

385

Application of spatial frequency response as a criterion for evaluating thermal imaging camera performance  

Microsoft Academic Search

Police, firefighters, and emergency medical personnel are examples of first responders that are utilizing thermal imaging cameras in a very practical way every day. However, few performance metrics have been developed to assist first responders in evaluating the performance of thermal imaging technology. This paper describes one possible metric for evaluating spatial resolution using an application of Spatial Frequency Response

Andrew Lock; Francine Amon

2008-01-01

386

Harmonic generation at high intensities  

SciTech Connect

Atomic electrons subject to intense laser fields can absorb many photons, leading either to multiphoton ionization or the emission of a single, energetic photon which can be a high multiple of the laser frequency. The latter process, high-order harmonic generation, has been observed experimentally using a range of laser wavelengths and intensities over the past several years. Harmonic generation spectra have a generic form: a steep decline for the low order harmonics, followed by a plateau extending to high harmonic order, and finally an abrupt cutoff beyond which no harmonics are discernible. During the plateau the harmonic production is a very weak function of the process order. Harmonic generation is a promising source of coherent, tunable radiation in the XUV to soft X-ray range which could have a variety of scientific and possibly technological applications. Its conversion from an interesting multiphoton phenomenon to a useful laboratory radiation source requires a complete understanding of both its microscopic and macroscopic aspects. We present some recent results on the response of single atoms at intensities relevant to the short pulse experiments. The calculations employ time-dependent methods, which we briefly review in the next section. Following that we discuss the behavior of the harmonics as a function of laser intensity. Two features are notable: the slow scaling of the harmonic intensities with laser intensity, and the rapid variation in the phase of the individual harmonics with respect to harmonic order. We then give a simple empirical formula that predicts the extent of the plateau for a given ionization potential, wavelength and intensity.

Schafer, K.J.; Krause, J.L.; Kulander, K.C.

1993-06-01

387

Microwave frequency ferroelectric domain imaging of deuterated triglycine sulfate crystals  

NASA Astrophysics Data System (ADS)

We have used a near-field scanning microwave microscope to image domain structure and quantitatively measure dielectric permittivity and nonlinearity in ferroelectric crystals at 8.1 GHz with a spatial resolution of 1 ?m. We imaged ferroelectric domains in periodically poled LiNbO3, BaTiO3, and deuterated triglycine sulfate (DTGS) with a signal-to-noise ratio of 7. Measurement of the permittivity and nonlinearity of DTGS in the temperature range 300-400 K shows a peak at the Curie temperature, TC~340 K, as well as reasonable agreement with thermodynamic theory. In addition, the domain growth relaxation time shows a minimum near TC. We observe coarsening of ferroelectric domains in DTGS after a temperature quench from 360 to 330 K and evaluate the structure factor.

Steinhauer, D. E.; Anlage, Steven M.

2001-02-01

388

Fabrication and characterization of high frequency phased arrays for NDE imaging  

NASA Astrophysics Data System (ADS)

PMN-PT single crystal 1-3 composite high frequency phased arrays with center frequency of 35 MHz were fabricated and characterized for silicon carbide (SiC) NDE imaging applications. The 35 MHz 64-element array was successfully prototyped using PMN-PT single crystal and PC-MUT technology. The broad bandwidth > 90% and high sensitivity (echo amplitude > 500 mV from the impulse response with 0 gain) was observed with reasonably high uniformity. These high frequency phased arrays are promising for ceramic NDE imaging.

Jiang, Xiaoning; Snook, Kevin; Liu, Ruibin; Geng, Xuecang; Hackenberger, Wesley S.

2010-03-01

389

Microwave Frequency Ferroelectric Domain Imaging of Deuterated Triglycine Sulfate Crystals  

NASA Astrophysics Data System (ADS)

We have used a near-field scanning microwave microscope(D. E. Steinhauer, C. P. Vlahacos, F. C. Wellstood, Steven M. Anlage, C. Canedy, R. Ramesh, A. Stanishevsky, and J. Melngailis, "Quantitative Imaging of Dielectric Permittivity and Tunability with a Near-Field Scanning Microwave Microscope," Rev. Sci. Instrum. 71), 2751-2758 (2000). to image domain structure and quantitatively measure dielectric permittivity and nonlinearity in ferroelectric crystals at 8.1 GHz with a spatial resolution of 1 ?m. We imaged ferroelectric domains in periodically-poled LiNbO_3, BaTiO_3, and deuterated triglycine sulfate (DTGS) with a signal-to-noise ratio of 7. Measurement of the permittivity and nonlinearity of DTGS in the temperature range 300--400 K shows a peak at the Curie temperature, TC ? 340 K, as well as reasonable agreement with thermodynamic theory. In addition, the domain growth relaxation time shows a minimum near T_C. We observe coarsening of ferroelectric domains in DTGS after a temperature quench from 360 K to 330 K, and evaluate the structure factor.

Steinhauer, David E.; Anlage, Steven M.

2001-03-01

390

Imaging Fall Chinook Salmon Redds in the Columbia River with a Dual-Frequency Identification Sonar  

Microsoft Academic Search

We tested the efficacy of a dual-frequency identification sonar (DIDSON) for imaging and enumeration of fall Chinook salmon Oncorhynchus tshawytscha redds in a spawning area below Bonneville Dam on the Columbia River. The DIDSON uses sound to form near-video-quality images and has the advantages of imaging in zero-visibility water and possessing a greater detection range and field of view than

Kenneth F. Tiffan; Dennis W. Rondorf; Joseph J. Skalicky

2004-01-01

391

LETTER TO THE EDITOR: Sub-wavelength imaging at radio frequency  

NASA Astrophysics Data System (ADS)

A slab of material with a negative permeability can act as a super-lens for magnetic fields and generate images with a sub-wavelength resolution. We have constructed an effective medium using a metamaterial with negative permeability in the region of 24 MHz, and used this to form images in free space of radio frequency magnetic sources. Measurements of these images show that a resolution of approximately ?/64 has been achieved, consistent with both analytical and numerical predictions.

Wiltshire, M. C. K.; Pendry, J. B.; Hajnal, J. V.

2006-06-01

392

Frequency domain photoacoustic correlation (radar) imaging: a novel methodology for non-invasive imaging of biological tissues  

NASA Astrophysics Data System (ADS)

We report the development of a novel frequency-domain biomedical photoacoustic (PA) system that utilizes a continuous-wave laser source with a custom intensity modulation pattern for spatially-resolved imaging of biological tissues. The feasibility of using relatively long duration and low optical power laser sources for spatially-resolved PA imaging is presented. We demonstrate that B-mode PA imaging can be performed using an ultrasonic phased array coupled with multi-channel correlation processing and a frequency-domain beamforming algorithm. Application of the frequency-domain PA correlation methodology is shown using tissue-like phantoms with embedded optical contrast, tissue ex-vivo samples and a small animal model in-vivo.

Telenkov, Sergey A.; Alwi, Rudolf; Mandelis, Andreas; Shi, Willa; Chen, Emily; Vitkin, Alex I.

2012-02-01

393

Directional blood flow imaging in volumetric optical microangiography achieved by digital frequency modulation  

PubMed Central

An effective digital frequency modulation approach to achieve directional blood flow imaging within microcirculations in tissue beds in vivo for optical microangiography is presented. The method only requires the system to capture one three-dimensional data set within which the interferograms are modulated by a constant frequency modulation that gives one directional flow information. The result is that the imaging speed is doubled and the computational load is halved. The method is experimentally validated by a flow phantom and is tested for imaging of cerebral vascular blood perfusion in a live mouse with the cranium left intact.

Wang, Ruikang K.

2009-01-01

394

Preliminary investigation of the frequency response and distortion properties of nonlinear image processing algorithms  

NASA Astrophysics Data System (ADS)

Assessment of the resolution properties of nonlinear imaging systems is a useful but challenging task. While the modulation transfer function (MTF) fully describes contrast resolution as a function of spatial frequency for linear systems, an equivalent metric does not exist for systems with significant nonlinearity. Therefore, this preliminary investigation attempts to classify and quantify the amount of scaling and distortion imposed on a given image signal as the result of a nonlinear process (nonlinear image processing algorithm). As a proof-of-concept, a median filter is assessed in terms of its principle frequency response (PFR) and distortion response (DR) functions. These metrics are derived in frequency space using a sinusoidal basis function, and it is shown that, for a narrow-band sinusoidal input signal, the scaling and distortion properties of the nonlinear filter are described exactly by PFR and DR, respectively. The use of matched sinusoidal basis and input functions accurately reveals the frequency response to long linear structures of different scale. However, when more complex (multi-band) input signals are considered, PFR and DR fail to adequately characterize the frequency response due to nonlinear interaction effects between different frequency components during processing. Overall, the results reveal the context-dependent nature of nonlinear image processing algorithm performance, and they emphasize the importance of the basis function choice in algorithm assessment. In the future, more complex forms of nonlinear systems analysis may be necessary to fully characterize the frequency response properties of nonlinear algorithms in a context-dependent manner.

Wells, Jered R.; Dobbins, James T.

2013-03-01

395

A phase-imaging technique for cyclotron-frequency measurements  

NASA Astrophysics Data System (ADS)

A novel approach to mass measurements at the 10-9 level for short-lived nuclides with half-lives well below one second is presented. It is based on the projection of the radial ion motion in a Penning trap onto a position-sensitive detector. Compared with the presently employed time-of-flight ion-cyclotron-resonance technique, the novel approach is 25-times faster and provides a 40-fold gain in resolving power. Moreover, it offers a substantially higher sensitivity since just two ions are sufficient to determine the ion's cyclotron frequency. Systematic effects specific to the technique that can change the measured cyclotron frequency are considered in detail. It is shown that the main factors that limit the maximal accuracy and resolving power of the technique are collisions of the stored ions with residual gas in the trap, the temporal instability of the trapping voltage, the anharmonicities of the trapping potential and the uncertainty introduced by the conversion of the cyclotron to magnetron motion.

Eliseev, S.; Blaum, K.; Block, M.; Dörr, A.; Droese, C.; Eronen, T.; Goncharov, M.; Höcker, M.; Ketter, J.; Ramirez, E. Minaya; Nesterenko, D. A.; Novikov, Yu. N.; Schweikhard, L.

2013-09-01

396

Bistatic frequency-swept microwave imaging: Principle, methodology and experimental results  

SciTech Connect

The basic principle, methodology and experimental results of frequency-swept microwave imaging of continuous shape conducting and discrete line objects in a bistatic scattering arrangement are presented. Theoretical analysis is developed under the assumptions of plane wave illumination and physical optics approximation. The measurement system and calibration procedures are implemented based on the plane wave spectrum analysis. Images of three different types of scattering objects reconstructed from the experimental data measured in the frequency range 7.5-12.5 GHz are shown in good agreement with the scattering object geometries. The results demonstrate that the developed bistatic frequency-swept microwave imaging system has potential as a cost-effective tool for the application of remote sensing, imaging radar, and nondestructive evaluation.

Dingbing Lin; Tahhsiung Chu (National Taiwan Univ., Taipei, (Taiwan, Province of China). Electrical Engineering Dept.)

1993-05-01

397

Fault diagnosis for diesel valve trains based on time frequency images  

NASA Astrophysics Data System (ADS)

In this paper, the Wigner Ville distributions (WVD) of vibration acceleration signals which were acquired from the cylinder head in eight different states of valve train were calculated and displayed in grey images; and the probabilistic neural networks (PNN) were directly used to classify the time frequency images after the images were normalized. By this way, the fault diagnosis of valve train was transferred to the classification of time frequency images. As there is no need to extract further fault features (such as eigenvalues or symptom parameters) from time frequency distributions before classification, the fault diagnosis process is highly simplified. The experimental results show that the faults of diesel valve trains can be classified accurately by the proposed methods.

Wang, Chengdong; Zhang, Youyun; Zhong, Zhenyuan

2008-11-01

398

Hypercomplete circular harmonic pyramids  

NASA Astrophysics Data System (ADS)

In this contribution we present a steerable pyramid based on a particular set of complex wavelets named circular harmonic wavelets (CHW). The proposed CHWs set constitutes a generalization of the smoothed edge wavelets introduced by Mallat, consisting of extending the local differential representation of a signal image from the first order to a generic n-th order. The key feature of the proposed representation is the use of complex operators leading to an expansion in series of polar separable complex functions, which are shown to possess the space-scale representability of the wavelets. The resulting tool is highly redundant, and for this reason is called hypercomplete circular harmonic pyramid (HCHP), but presents some interesting aspects in terms of flexibility, being suited for many image processing applications. In the present contribution the main theoretical aspects of the HCHPs are discussed along with some introductory applications.

Jacovitti, Giovanni; Manca, A.; Neri, Alessandro

1996-10-01

399

Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2-6, and several hexamer local minima at the CCSD(T) level of theory  

NASA Astrophysics Data System (ADS)

We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 A?, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ~15 and ~25 cm-1 are observed for the bending and ``free'' OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (??) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (?R) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation -?? = s . ?R, with a rate of s = 20.2 cm-1/0.001 A? for hydrogen bonded frequencies with IR intensities >400 km/mol. The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory, produce anharmonic CCSD(T) estimates that are within <60 cm-1 from the measured infrared (IR) active bands of the n = 2-6 clusters. Furthermore, the CCSD(T) harmonic redshifts (with respect to the monomer) trace the measured ones quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers.

Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S.

2013-09-01

400

A multifunctional, reconfigurable pulse generator for high-frequency ultrasound imaging.  

PubMed

High-frequency (>20 MHz) ultrasound (HFUS) imaging systems have made it possible to image small structures with fine spatial resolution. They find a variety of biomedical applications in dermatology, ophthalmology, intravascular imaging, and small-animal imaging. One critical technical challenge of HFUS is to generate high-voltage, high-frequency pulsed signals to effectively excite the transducer for a high SNR. This paper presents the development of a multifunctional, reconfigurable pulse generator for HFUS imaging. The pulse generator can produce a high-voltage unipolar pulse, a bipolar pulse, or arbitrary pulses for B-mode imaging, Doppler measurement, and modulated excitation imaging. The characteristics of the pulses, such as timing, waveform, and frequency are reconfigurable by a high-speed field-programmable gate array (FPGA). Customized software was developed to interface with the FPGA through a USB connector for pulse selection, and easy, flexible, real-time pulse management. The hardware was implemented in a compact, printed circuit board (PCB)-based scheme using state-of-the-art electronics for costeffectiveness and fully digital control. Testing results show that the unipolar pulse can reach over 165 Vpp with a 6-dB bandwidth of 70 MHz, and the bipolar pulse and arbitrary pulses can reach 150 and 60 Vpp with central frequencies of 60 and 120 MHz, respectively. PMID:22828850

Qiu, Weibao; Yu, Yanyan; Tsang, Fu; Sun, Lei

2012-07-01

401

Focusing of second-harmonic signals with nonlinear metamaterial lenses: a biphotonic microscopy approach.  

PubMed

Recent research on second-harmonic generation in left-handed materials has shown a light localization mechanism that originates from an all-angle phase-matching condition between counterpropagating electromagnetic modes at fundamental and double frequencies. By combining these properties with negative refraction, we propose in this Letter an original approach to the design of a second-harmonic lens. Numerical simulations demonstrate that feasible metamaterials can be tailored to operate in the visible range of frequency. These nonlinear lenses open an attractive solution for the biphotonic microscopy technique by imaging passive biological structures. PMID:19792566

Ciracì, Cristian; Centeno, Emmanuel

2009-08-04

402

Harmonically excited orbital variations  

SciTech Connect

Rephrasing the equations of motion for orbital maneuvers in terms of Lagrangian generalized coordinates instead of Newtonian rectangular cartesian coordinates can make certain harmonic terms in the orbital angular momentum vector more readily apparent. In this formulation the equations of motion adopt the form of a damped harmonic oscillator when torques are applied to the orbit in a variationally prescribed manner. The frequencies of the oscillator equation are in some ways unexpected but can nonetheless be exploited through resonant forcing functions to achieve large secular variations in the orbital elements. Two cases are discussed using a circular orbit as the control case: (1) large changes in orbital inclination achieved by harmonic excitation rather than one impulsive velocity change, and (2) periodic and secular changes to the longitude of the ascending node using both stable and unstable excitation strategies. The implications of these equations are also discussed for both artificial satellites and natural satellites. For the former, two utilitarian orbits are suggested, each exploiting a form of harmonic excitation. 5 refs.

Morgan, T.

1985-08-06

403

A harmonic signal generator based on DDS and SOPC  

Microsoft Academic Search

A harmonic signal generator with adjustable frequency, phase and harmonic proportion is designed in this paper. The design of this harmonic signal generator is based on direct digital frequency synthesis (DDS) technology and the idea of System on a Programmable Chip (SOPC). The classic structure of DDS is introduced and a kind of compression ROM is designed. Then, the DDS

Zhiqiang Zhang; Feng Dong

2010-01-01

404

Unitary relations in time-dependent harmonic oscillators  

Microsoft Academic Search

For a harmonic oscillator with time-dependent (positive) mass and frequency, a unitary operator is shown to transform the quantum states of the system to those of a harmonic oscillator system of unit mass and time-dependent frequency, as well as operators. For a driven harmonic oscillator, a unitary transformation which relates the driven system and a system of the same mass

Dae-Yup Song

1999-01-01

405

Stand-off real-time synthetic imaging at mm-wave frequencies  

NASA Astrophysics Data System (ADS)

We report on the development of an active stand-off imaging system operating in the 80 GHz - 110 GHz frequency range. 3D real-time imaging is enabled by a combination of a mechanically scanned one-dimensional conventional imaging projection with a rotating metallic reflector and a two-dimensional synthetic imaging reconstruction with a linear array of transmitter (Tx) and receiver (Rx) elements. The system is conceived, in order to allow a resolution better than 1cm both in lateral, as well as in range directions by using a multi-view imaging geometry with an aperture larger than 2 m x 2 m. The operation distance is 8.5 - 9 m. The 2D synthetically reconstructed imaging planes are derived from the correlation of 20 sources and 24 coherent detectors. Range information is obtained by operating in a frequency modulated continuous wave (FMCW) mode. Real-time imaging is enabled by implementing the synthetic image reconstruction algorithms on a general purpose graphics processing unit (GPGPU) system. A multi-view imaging geometry is implemented, in order to enhance the imaging resolution and to reduce the influence of specular reflections.

Kahl, Matthias; Keil, Andreas; Peuser, Joern; Loeffler, Torsten; Paetzold, Martin; Kolb, Andreas; Sprenger, Thorsten; Hils, Bernd; Haring Bolívar, Peter

2012-05-01

406

Multipixel system for gigahertz frequency-domain optical imaging of finger joints  

NASA Astrophysics Data System (ADS)

Frequency-domain optical imaging systems have shown great promise for characterizing blood oxygenation, hemodynamics, and other physiological parameters in human and animal tissues. However, most of the frequency domain systems presented so far operate with source modulation frequencies below 150 MHz. At these low frequencies, their ability to provide accurate data for small tissue geometries such as encountered in imaging of finger joints or rodents is limited. Here, we present a new system that can provide data up to 1 GHz using an intensity modulated charged coupled device camera. After data processing, the images show the two-dimensional distribution of amplitude and phase of the light modulation on the finger surface. The system performance was investigated and test measurements on optical tissue phantoms were taken to investigate whether higher frequencies yield better signal-to-noise ratios (SNRs). It could be shown that local changes in optical tissue properties, as they appear in the initial stages of rheumatoid arthritis in a finger joint, are detectable by simple image evaluation, with the range of modulation frequency around 500 MHz proving to yield the highest SNR.

Netz, Uwe J.; Beuthan, Jürgen; Hielscher, Andreas H.

2008-03-01

407

Higher-order harmonic transmission-line RF coil design for MR applications.  

PubMed

A novel concept based on the use of higher-order harmonic resonances in a transmission-line resonator is introduced for the design of high-frequency RF coils at high and ultrahigh fields, where conventional RF coil designs present difficulties and limitations. To demonstrate this concept, we successfully designed and fabricated a 400-MHz RF coil for rat imaging using a second-harmonic resonant microstrip transmission line. This coil has a high Q-factor, reduces coil-cable interactions without the use of a matching balun, and has a broad range for tuning the coil's resonant frequency at the loaded condition. This work demonstrates that the use of higher-order harmonics in a transmission-line resonator provides an alternative, efficient approach to the design of large and high-frequency RF coils. PMID:15844152

Zhang, Xiaoliang; Zhu, Xiao-Hong; Chen, Wei

2005-05-01

408

Noise evaluation standard of image sensor using visual spatio-temporal frequency characteristics  

NASA Astrophysics Data System (ADS)

Regarding the noise evaluation of image sensor, it is important to establish the objective evaluation method which has high correlation with appearance. It is well known that visual noise standard is a noise evaluation metric using human visual characteristics. The visual noise level can vary depending on the viewing distance, spatial frequency, color and viewing conditions. A method of measuring the visual noise level is provided in ISO 15739.[1][2] Furthermore it was discovered that visual characteristics depend on contrast and frame rate; however, the ISO method doesn't consider that. For example, since ISO15739 focus the absolute threshold of human visual system for still image, in some case, the correlation between subjective evaluation and objective evaluation was not so high. And in moving image sequences case, the faster frame rate becomes, the lower perception of noise becomes. We propose solutions to solve those problems using visual spatio-temporal frequency characteristics. Firstly, we investigated visual spatial frequency characteristics that depend on contrast and propose a new evaluation method. It shows that the image sensor with large pixel count is effective in noise reduction. Secondly, we investigated visual temporal frequency characteristics and propose a new evaluation method for the moving image sequences. It shows that the image sensor with high frame rate is effective in noise reduction. Finally, by combining two proposed methods, we show the method in which a noise evaluation is possible in both a still image and in moving image sequences. We applied the proposal method to moving image sequences acquired by the image sensor and investigated the validity of the method.

Fujii, Takeyuki; Suzuki, Shoichi; Saito, Shinichiro

2013-03-01

409

Optimal modulation frequencies for small-tissue imaging based on the equation of radiative transfer  

NASA Astrophysics Data System (ADS)

The frequency-domain experimental data is typically corrupted by noise and the measurement accuracy is compromised. Assuming the widely used shot-noise model, it is well-known that the signal-to-noise ratio (SNR) of the amplitude signal decreases with increasing frequency, whereas the SNR of phase measurement reaches a peak value in the range between 400 MHz and 800 MHz in tissue volumes typical for small animal imaging studies. As a consequence, it can be assumed that there exists an optimal frequency for which the reconstruction accuracy would be best. To determine optimal frequencies for FDOT, we investigate here the frequency dependence of optical tomographic reconstruction results using the frequency-domain equation of radiative transfer. We present numerical and experimental studies with a focus on small tissue geometries as encountered in small animal imaging and imaging of human finger joints affected by arthritis. Best results were achieved in the 400-800 MHz frequency range, depending on the particular optical properties.

Kim, Hyun Keol; Netz, Uwe J.; Beuthan, J.; Hielscher, Andreas H.

2009-02-01

410

The representation of complex images in spatial frequency domains of primary visual cortex.  

PubMed

The organization of cat primary visual cortex has been well mapped using simple stimuli such as sinusoidal gratings, revealing superimposed maps of orientation and spatial frequency preferences. However, it is not yet understood how complex images are represented across these maps. In this study, we ask whether a linear filter model can explain how cortical spatial frequency domains are activated by complex images. The model assumes that the response to a stimulus at any point on the cortical surface can be predicted by its individual orientation, spatial frequency, and temporal frequency tuning curves. To test this model, we imaged the pattern of activity within cat area 17 in response to stimuli composed of multiple spatial frequencies. Consistent with the predictions of the model, the stimuli activated low and high spatial frequency domains differently: at low stimulus drift speeds, both domains were strongly activated, but activity fell off in high spatial frequency domains as drift speed increased. To determine whether the filter model quantitatively predicted the activity patterns, we measured the spatiotemporal tuning properties of the functional domains in vivo and calculated expected response amplitudes from the model. The model accurately predicted cortical response patterns for two types of complex stimuli drifting at a variety of speeds. These results suggest that the distributed activity of primary visual cortex can be predicted from cortical maps like those of orientation and SF preference generated using simple, sinusoidal stimuli, and that dynamic visual acuity is degraded at or before the level of area 17. PMID:17728445

Zhang, Jing X; Rosenberg, Ari; Mallik, Atul K; Husson, T Robert; Issa, Naoum P

2007-08-29

411

Generating an image of dispersive energy by frequency decomposition and slant stacking  

USGS Publications Warehouse

We present a new algorithm for calculating an image of dispersive energy in the frequency-velocity (f-v) domain. The frequency decomposition is first applied to a shot gather in the offset-time domain to stretch impulsive data into pseudo-vibroseis data or frequency-swept data. Because there is a deterministic relationship between frequency and time in a sweep used in the frequency decomposition, the first step theoretically completes the transform from time to frequency. The slant stacking is then performed on the frequency-swept data to complete the transform from offset to velocity. This simple two-step algorithm generates an image of dispersive energy in the f-v domain. The straightforward transform only uses offset information of data so that this algorithm can be applied to data acquired with arbitrary geophone-acquisition geometry. Examples of synthetic and real-world data demonstrate that this algorithm generates accurate images of dispersive energy of the fundamental as well as higher modes. ?? Birkha??user Verlag, Basel, 2007.

Xia, J.; Xu, Y.; Miller, R. D.

2007-01-01

412

Optimization of contrast-to-tissue ratio by frequency adaptation in pulse inversion imaging.  

PubMed

Contrast imaging has significantly improved clinical diagnosis by increasing the contrast-to-tissue ratio after microbubble injection. Pulse inversion imaging is the most commonly used contrast imaging technique because it greatly increases the contrast-to-tissue ratio by extracting microbubble nonlinearities. The main purpose of our study was to propose an automatic technique providing the best contrast- to-tissue ratio throughout the experiment. For reasons of simplicity, we proposed maximizing the contrast-to-tissue ratio with an appropriate choice of the transmit frequency. The contrast-to-tissue ratio was maximized by a closed-loop system including the pulse inversion technique. An algorithm based on gradient descent provided iterative determination of the optimal transmit frequency. The optimization method converged quickly after six iterations. This optimal control method is easy to implement and it optimizes the contrast-to-tissue ratio by adaptively selecting the transmit frequency. PMID:23192806

Ménigot, Sébastien; Girault, Jean-Marc; Voicu, Iulian; Novell, Anthony

2012-11-01

413

Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances.  

PubMed

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells. PMID:24162458

Tuniz, Alessandro; Kaltenecker, Korbinian J; Fischer, Bernd M; Walther, Markus; Fleming, Simon C; Argyros, Alexander; Kuhlmey, Boris T

2013-10-28

414

An image reconstruction method from Fourier data with uncertainties on the spatial frequencies  

NASA Astrophysics Data System (ADS)

In this paper the reconstruction of a two-dimensional image from a nonuniform sampling of its Fourier transform is considered, in the presence of uncertainties on the frequencies corresponding to the measured data. The problem therefore becomes a blind deconvolution, in which the unknowns are both the image to be reconstructed and the exact frequencies. The availability of information on the image and the frequencies allows to reformulate the problem as a constrained minimization of the least squares functional. A regularized solution of this optimization problem is achieved by early stopping an alternating minimization scheme. In particular, a gradient projection method is employed at each step to compute an inexact solution of the minimization subproblems. The resulting algorithm is applied on some numerical examples arising in a real-world astronomical application.

Cornelio, Anastasia; Bonettini, Silvia; Prato, Marco

2013-10-01

415

A frequency domain radar interferometric imaging (FII) technique based on high-resolution methods  

NASA Astrophysics Data System (ADS)

In the present work, we propose a frequency-domain interferometric imaging (FII) technique for a better knowledge of the vertical distribution of the atmospheric scatterers detected by MST radars. This is an extension of the dual frequency-domain interferometry (FDI) technique to multiple frequencies. Its objective is to reduce the ambiguity (resulting from the use of only two adjacent frequencies), inherent with the FDI technique. Different methods, commonly used in antenna array processing, are first described within the context of application to the FII technique. These methods are the Fourier-based imaging, the Capon's and the singular value decomposition method used with the MUSIC algorithm. Some preliminary simulations and tests performed on data collected with the middle and upper atmosphere (MU) radar (Shigaraki, Japan) are also presented. This work is a first step in the developments of the FII technique which seems to be very promising.

Luce, H.; Yamamoto, M.; Fukao, S.; Helal, D.; Crochet, M.

2001-01-01

416

Automatic classification of sleep stages based on the time-frequency image of EEG signals.  

PubMed

In this paper, a new method for automatic sleep stage classification based on time-frequency image (TFI) of electroencephalogram (EEG) signals is proposed. Automatic classification of sleep stages is an important part for diagnosis and treatment of sleep disorders. The smoothed pseudo Wigner-Ville distribution (SPWVD) based time-frequency representation (TFR) of EEG signal has been used to obtain the time-frequency image (TFI). The segmentation of TFI has been performed based on the frequency-bands of the rhythms of EEG signals. The features derived from the histogram of segmented TFI have been used as an input feature set to multiclass least squares support vector machines (MC-LS-SVM) together with the radial basis function (RBF), Mexican hat wavelet, and Morlet wavelet kernel functions for automatic classification of sleep stages from EEG signals. The experimental results are presented to show the effectiveness of the proposed method for classification of sleep stages from EEG signals. PMID:24008250

Bajaj, Varun; Pachori, Ram Bilas

2013-09-02

417

Frequency-domain pump-probe microscopic imaging using intensity-modulated laser diodes  

NASA Astrophysics Data System (ADS)

We report the implementation of intensity modulated diode lasers in frequency-domain pump-probe studies, diode lasers are compact, stable, and economical units that require little maintenance. In our study, a 365 nm diode laser is used as the excitation source and the output of a 680 nm unit induces stimulated emission from excited state fluorophores. By modulating the intensities of the two diode lasers at slightly different frequencies, and detecting the fluorescence signal at the cross-correlation frequency, both time-resolved and high spatial resolution imaging can be achieved. The laser diodes are modulated in the 100 MHz cross-correlation signal has been used for time-resolved imaging of fluorescent microspheres and mouse fibroblasts labeled with nucleic acid stains TOTO-3. These results demonstrate and feasibility of using intensity modulated diode lasers for frequency-domain, pump-probe studies.

Buehler, Christof; Dong, Chen-Yuan; So, Peter T.; French, Todd E.; Gratton, Enrico

1999-04-01

418

A High-Frequency High Frame Rate Duplex Ultrasound Linear Array Imaging System for Small Animal Imaging  

PubMed Central

High-frequency (HF) ultrasound imaging has been shown to be useful for non-invasively imaging anatomical structures of the eye and small animals in biological and pharmaceutical research, achieving superior spatial resolution. Cardiovascular research utilizing mice requires not only real-time B-scan imaging, but also ultrasound Doppler to evaluate both anatomy and blood flow of the mouse heart. This paper reports the development of a high frequency ultrasound duplex imaging system capable of both B-mode imaging and Doppler flow measurements, using a 64-element linear array. The system included a HF pulsed-wave Doppler module, a 32-channel HF B-mode imaging module, a PC with a 200 MS/s 14-bit A/D card, and real-time LabView software. A 50dB signal-to-noise ratio (SNR) and a depth of penetration of larger than 12 mm were achieved using a 35 MHz linear array with 50 ?m pitch. The two-way beam widths were determined to be 165 ?m to 260 ?m and the clutter energy to total energy ratio (CTR) were 9.1 dB to 12 dB, when the array was electronically focused at different focal points at depths from 4.8 mm to 9.6 mm. The system is capable of acquiring real-time B-mode images at a rate greater than 400 frames per second (fps) for a 4.8 × 13 mm field of view, using a 30 MHz 64-element linear array with 100 ?m pitch. Sample in vivo cardiac high frame rate images and duplex images of mouse hearts are shown to assess its current imaging capability and performance for small animals.

Zhang, Lequan; Xu, Xiaochen; Hu, Changhong; Sun, Lei; Yen, Jesse T.; Cannata, Jonathan M.; Shung, K. Kirk

2010-01-01

419

High Frequency Methods for Simulation of High Resolution Imaging in Terahertz Regime  

Microsoft Academic Search

High resolution imaging in the terahertz (THz) frequency range is investigated theoretically in this paper through the use\\u000a of the high frequency methods in computational electromagnetics (CEM). Physical optics (PO), shooting and bouncing ray (SBR)\\u000a and truncated-wedge incremental length diffraction coefficients (TW-ILDCs) methods are combined together to compute the scattered\\u000a fields, which are then used to construct the inverse synthetic

Zhuo Li; Tie Jun Cui

2010-01-01

420

Molecular Resolution Imaging of Protein Molecules in Liquid Using Frequency Modulation Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

We demonstrated molecular resolution imaging of biological samples such as bacteriorhodopsin protein molecules in purple membrane and isolated chaperonin (GroEL) protein molecules, both adsorbed on mica using frequency modulation atomic force microscope (FM-AFM) in liquid. We also showed that the frequency noise of FM-AFM in liquid can be greatly reduced by the reduction of the noise-equivalent deflection of an optical beam deflection sensor.

Yamada, Hirofumi; Kobayashi, Kei; Fukuma, Takeshi; Hirata, Yoshiki; Kajita, Teruyuki; Matsushige, Kazumi

2009-09-01

421

Long-term in vivo harmonics imaging of zebrafish embryonic development based on a femtosecond Cr:forsterite laser  

NASA Astrophysics Data System (ADS)

Based on a femtosecond Cr:forsterite laser, harmonics optical microscopy (HOM) provides a truly "noninvasive" tool for in vivo and long-term study of vertebrate embryonic development. Based on optical nonlinearity, HOM provides sub-micrometer 3D spatial resolution and high 3D optical-sectioning power without using invasive and toxic fluorophores. Since only virtual-level-transition is involved, HOM is known to leave no energy deposition and no photodamage. Combined with second harmonic generation, which is sensitive to specific structure such as nerve and muscle fibers, HOM can perform functional studies of early developmental dynamics of many vertebrate physiological systems. Recently, zebrafish has become a standard model for many biological and medical studies of vertebrates, due to the similarity between embryonic development of zebrafish and human being. Here we demonstrate in vivo HOM studies of developmental dynamics of several important embryonic physiological systems in live zebrafish embryos, with focuses on the developments of brains, eyes, ears, and hearts. Based on a femtosecond Cr:forsterite laser, which provides the deepest penetration (~1.5mm) and least photodamage in the zebrafish embryo, complete developing processes of different physiological systems within a period of time longer than 20 hours can be non-invasively observed inside the same embryo.

Chen, S.-Y.; Tsai, T.-H.; Hsieh, C.-S.; Tai, S.-P.; Lin, C.-Y.; Ko, C.-Y.; Chen, Y.-C.; Tsai, H.-J.; Hu, C.-H.; Sun, C.-K.

2005-03-01

422

High range resolution medical acoustic vascular imaging with frequency domain interferometry.  

PubMed

For high range resolution acoustic vascular imaging we apply frequency domain interferometry and Capon method to a few frames of in-phase and quadrature (IQ) data acquired by a commercial ultrasonographic device. To suit the adaptive beamforming algorithm to medical acoustic imaging we employ three techniques; frequency averaging, whitening, and pseudo-double RF data conversion. The proposed method detected two couples of boundaries 0.26 and 0.19 mm apart using a single frame and two frames of IQ data, respectively, where each couple of boundaries is indistinguishable from a single boundary utilizing B-mode images. Further this algorithm could depict a swine femoral artery with higher range resolution than conventional B-mode imaging. These results indicate the potential of the proposed method for the range resolution improvement in ultrasonography, originating the progress in detection of vessel stenosis. PMID:21096063

Taki, Hirofumi; Taki, Kousuke; Sakamoto, Takuya; Yamakawa, Makoto; Shiina, Tsuyoshi; Sato, Toru

2010-01-01

423

Frequency-domain analysis of photoacoustic imaging data from prostate adenocarcinoma tumors in a murine model  

PubMed Central

Photoacoustic imaging is an emerging technique for anatomical and functional sub-surface imaging, but previous studies have predominantly focused on time-domain analysis. In this study, frequency-domain analysis of the radio-frequency signals from photoacoustic imaging was performed to generate quantitative parameters for tissue characterization. To account for the response of the imaging system, the photoacoustic spectra were calibrated by dividing the photoacoustic spectra (radio-frequency ultrasound spectra resulting from laser excitation) from tissue by the photoacoustic spectrum of a point absorber excited under the same conditions. The resulting quasi-linear photoacoustic spectra were fit by linear regression, and midband fit, slope, and intercept were computed from the best-fit line. These photoacoustic spectral parameters were compared between the region-of-interests (ROIs) representing prostate adenocarcinoma tumors and adjacent normal flank tissue in a murine model. The mean midband fit and intercept in the ROIs showed significant differences between cancerous and non-cancerous regions. These initial results suggest that such frequency-domain analysis can provide a quantitative method for tumor tissue characterization using photoacoustic imaging in vivo.

Kumon, Ronald E.; Deng, Cheri X.; Wang, Xueding

2011-01-01

424

Three-dimensional ground penetrating radar imaging using multi-frequency diffraction tomography  

SciTech Connect

In this paper we present results from a three-dimensional image reconstruction algorithm for impulse radar operating in monostatic pulse-echo mode. The application of interest to us is the nondestructive evaluation of civil structures such as bridge decks. We use a multi-frequency diffraction tomography imaging technique in which coherent backward propagations of the received reflected wavefield form a spatial image of the scattering interfaces within the region of interest. This imaging technique provides high-resolution range and azimuthal visualization of the subsurface region. We incorporate the ability to image in planarly layered conductive media and apply the algorithm to experimental data from an offset radar system in which the radar antenna is not directly coupled to the surface of the region. We present a rendering in three-dimensions of the resulting image data which provides high-detail visualization.

Mast, J.E.; Johansson, E.M.

1994-07-01

425

Imaging Fall Chinook Salmon Redds in the Columbia River with a Dual-Frequency Identification Sonar  

Microsoft Academic Search

We tested the efficacy of a dual-frequency identification sonar (DIDSON) for imaging and enu- meration of fall Chinook salmon Oncorhynchus tshaw- ytscha redds in a spawning area below Bonneville Dam on the Columbia River. The DIDSON uses sound to form near-video-quality images and has the advantages of im- aging in zero-visibility water and possessing a greater detection range and field

KENNETH F. T IFFAN; DENNIS W. R ONDORF; JOSEPH J. SKALICKY

426

DeStripe: frequency-based algorithm for removing stripe noises from AFM images  

PubMed Central

Background Atomic force microscopy (AFM) is a relatively recently developed technique that shows a promising impact in the field of structural biology and biophysics. It has been used to image the molecular surface of membrane proteins at a lateral resolution of one nanometer or less. An immediate obstacle of characterizing surface features in AFM images is stripe noise. To better interpret structures at a sub-domain level, pre-processing of AFM images for removing stripe noises is necessary. Noise removal can be performed in either spatial or frequency domain. However, denoising processing in the frequency domain is a better solution for preserving edge sharpness. Results We have developed a denoising protocol, called DeStripe, for AFM bio-molecular images that are contaminated with heavy and fine stripes. This program adopts a divide-and-conquer approach by dividing the Fourier spectrum of the image into central and off-center regions for noisy pixels detection and intensity restoration; it is also applicable to other images interfered with high-density stripes such as those acquired by the scanning electron microscope. The denoising effect brought by DeStripe provides better visualization for image objects without introducing additional artifacts into the restored image. Conclusions The DeStripe denoising effect on AFM images is illustrated in the present work. It allows extracting extended information from the topographic measurements and implicitly enhances the molecular features in the image. All the presented images were processed by DeStripe with the raw image as the only input without any requirement for other prior information. A web service, http://biodev.cea.fr/destripe, is available for running DeStripe.

2011-01-01

427

A high frequency amplitude-steered array for real-time volumetric imaging.  

PubMed

Real-time three-dimensional acoustic imaging is difficult in water or tissue because of the slow speed of sound in these media. Conventional pulse-echo data collection, which uses at least one transmit pulse per line in the image, does not allow for the real-time update of a volume of data at practical ranges. Recently, a linear amplitude-steered array was presented that allows the collection of a plane of data with a single transmit pulse by spatially separating frequencies in the lateral direction. Later, by using a linear array with frequency separation in the vertical direction and rotating the array in the horizontal direction, volumetric data were collected with a small number of transmit pulses. By expanding the linear array to a two-dimensional array, data can now be collected for volumetric imaging in real time. In this study, the amplitude-steered array at the heart of a real-time volumetric sonar imaging system is described, giving the design of the array and describing how data are collected and processed to form images. An analysis of lateral resolution in the vertical and horizontal directions shows that resolution is improved in the direction of frequency separation over systems that use a broad transmit beam. Images from simulated data are presented. PMID:12508994

Frazier, Catherine H; Hughes, W Jack; O'Brien, William D

2002-12-01

428

An approach for images with low-frequency noise denoising via pre-emphasis and high-pass filter  

NASA Astrophysics Data System (ADS)

Wavelet-based denoising methods have been successfully applied in processing images with high-frequency noise, such as salt noise, Gausian noise, Poisson noise, etc. However, it is less effective when processing images with low-frequency noise. Seemingly, we can consider using high-pass filter directly to remove the low-frequency noise, but it turns out that when the noise is removed, the useful low-frequency information is also weakened during the process. In this paper, we proposed a new approach to denoise the images with low-frequency noise via pre-emphasis and high-pass filtration. Thereby we removed the low-frequency noise effectively without losing useful low-frequency information. The approach can be well applied in decreasing the interference of low-frequency noise in image transmission.

Zhang, Qi; Ma, Shaobo; Cao, Li

2013-03-01

429

Nonlinear spectral imaging of human normal skin, basal cell carcinoma and squamous cell carcinoma based on two-photon excited fluorescence and second-harmonic generation  

NASA Astrophysics Data System (ADS)

In this work, we use nonlinear spectral imaging based on two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) for analyzing the morphology of collagen and elastin and their biochemical variations in basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and normal skin tissue. It was found in this work that there existed apparent differences among BCC, SCC and normal skin in terms of their thickness of the keratin and epithelial layers, their size of elastic fibers, as well as their distribution and spectral characteristics of collagen. These differences can potentially be used to distinguish BCC and SCC from normal skin, and to discriminate between BCC and SCC, as well as to evaluate treatment responses.

Xiong, S. Y.; Yang, J. G.; Zhuang, J.

2011-10-01

430