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1

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

2

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

PubMed

Real-time 2-D or 3-D ultrasound imaging systems are currently used for medical diagnosis. To achieve the required data acquisition rate, these systems rely on parallel beamforming, i.e., a single wide-angled beam is used for transmission and several narrow parallel beams are used for reception. When applied to harmonic imaging, the demand for high-amplitude pressure wave fields, necessary to generate the harmonic components, conflicts with the use of a wide-angled beam in transmission because this results in a large spatial decay of the acoustic pressure. To enhance the amplitude of the harmonics, it is preferable to do the reverse: transmit several narrow parallel beams and use a wide-angled beam in reception. Here, this concept is investigated to determine whether it can be used for harmonic imaging. The method proposed in this paper relies on orthogonal frequency division multiplexing (OFDM), which is used to create distinctive parallel beams in transmission. To test the proposed method, a numerical study has been performed, in which the transmit, receive, and combined beam profiles generated by a linear array have been simulated for the second-harmonic component. Compared with standard parallel beamforming, application of the proposed technique results in a gain of 12 dB for the main beam and in a reduction of the side lobes. Experimental verification in water has also been performed. Measurements obtained with a single-element emitting transducer and a hydrophone receiver confirm the possibility of exciting a practical ultrasound transducer with multiple Gaussian modulated pulses, each having a different center frequency, and the capability to generate distinguishable second-harmonic components. PMID:23192807

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

2012-11-01

3

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

PubMed Central

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 (SPN) approximations. To fully evaluate the performance of the SPN 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 SPN 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.

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

2010-01-01

4

Multi-frequency harmonic arrays: initial experience with a novel transducer concept for nonlinear contrast imaging.  

PubMed

Nonlinear contrast imaging modes such as second harmonic imaging (HI) and subharmonic imaging (SHI) are increasingly important for clinical applications. However, the performance of currently available transducers for HI and SHI is significantly constrained by their limited bandwidth. To bypass this constraint, a novel transducer concept termed multi-frequency harmonic transducer arrays (MFHA's) has been designed and a preliminary evaluation has been conducted. The MFHA may ultimately be used for broadband contrast enhanced HI and SHI with high dynamic range and consists of three multi-element piezo-composite sub-arrays (A-C) constructed so the center frequencies are 4f(A) = 2f(B) = f(C) (specifically 2.5/5.0/10.0 MHz and 1.75/3.5/7.0 MHz). In principle this enables SHI by transmitting on sub-array C receiving on B and, similarly, from B to A as well as HI by transmitting on A receiving on B and, likewise, from B to C. Initially transmit and receive pressure levels of the arrays were measured with the elements of each sub-array wired in parallel. Following contrast administration, preliminary in vitro HI and SHI signal-to-noise ratios of up to 40 dB were obtained. In conclusion, initial design and in vitro characterization of two MFHA's have been performed. They have an overall broad frequency bandwidth of at least two octaves. Due to the special design of the array assembly, the SNR for HI and SHI was comparable to that of regular B-mode and better than commercially available HI systems. However, further research on multi-element MFHA's is required before their potential for in vivo nonlinear contrast imaging can be assessed. PMID:15530981

Forsberg, Flemming; Shi, William T; Jadidian, Bahram; Winder, Alan A

2004-12-01

5

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

6

Harmonic generation with a dual frequency pulse.  

PubMed

Nonlinear imaging was implemented in commercial ultrasound systems over the last 15 years offering major advantages in many clinical applications. In this work, pulsing schemes coupled with a dual frequency pulse are presented. The pulsing schemes considered were pulse inversion, power modulation, and power modulated pulse inversion. The pulse contains a fundamental frequency f and a specified amount of its second harmonic 2f. The advantages and limitations of this method were evaluated with both acoustic measurements of harmonic generation and theoretical simulations based on the KZK equation. The use of two frequencies in a pulse results in the generation of the sum and difference frequency components in addition to the other harmonic components. While with single frequency pulses, only power modulation and power modulated pulse inversion contained odd harmonic components, with the dual frequency pulse, pulse inversion now also contains odd harmonic components. PMID:24815238

Keravnou, Christina P; Averkiou, Michalakis A

2014-05-01

7

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

Microsoft Academic Search

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

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

2010-01-01

8

Chromatic second harmonic imaging.  

PubMed

We report a non-axial-scanning second harmonic imaging technique, in which the chromatic aberration of a Fresnel lens is exploited to focus different wavelengths of a fundamental beam into different axial positions to effectively realize axial scanning. Since the second harmonic signals at different axial positions are generated by different fundamental wavelengths and hence accordingly have different center wavelengths, they can be resolved and detected in parallel by using a spectrometer without axial mechanical scanning. We have demonstrated a system capable of achieving about 8 ?m effective axial scanning range. Proof-of-concept imaging results are also presented. PMID:21164728

Yang, Chuan; Shi, Kebin; Li, Haifeng; Xu, Qian; Gopalan, Venkatraman; Liu, Zhiwen

2010-11-01

9

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

10

Simulation and analysis of magnetic resonance elastography wave images using coupled harmonic oscillators and Gaussian local frequency estimation  

Microsoft Academic Search

New methods for simulating and analyzing Magnetic Resonance Elastography (MRE) images are introduced. To simulate a two-dimensional shear wave pattern, the wave equation is solved for a field of coupled harmonic oscillators with spatially varying coupling and damping coefficients in the presence of an external force. The spatial distribution of the coupling and the damping constants are derived from an

Jürgen Braun; Gerd Buntkowsky; Johannes Bernarding; Thomas Tolxdorff; Ingolf Sack

2001-01-01

11

Simulation and analysis of magnetic resonance elastography wave images using coupled harmonic oscillators and Gaussian local frequency estimation  

Microsoft Academic Search

Abstract New methods,for simulating and analyzing Magnetic Resonance Elastography (MRE) images,are introduced. To simulate a two- dimensional shear wave pattern, the wave equation is solved for a field of coupled harmonic oscillators with spatially varying coupling and damping,coefficients in the presence of an external force. The spatial distribution of the coupling and the damping,constants are derived from an MR image,of

Ju Rgen Braun; Gerd Buntkowsky; Johannes Bernarding; Thomas Tolxdorff; Ingolf Sack

12

Low frequency multiple harmonic oscillations in NSTX  

NASA Astrophysics Data System (ADS)

Low frequency (100kHz) MHD activities are very common in NSTX. They can appear in many plasma conditions with neutral beam and/or high harmonic fast wave heating. Their presence is usually associated with a rotating magnetic island identified by a flat region in the toroidal plasma rotation profile, and their frequencies equal to the multiple harmonics of the island toroidal rotation frequency. They can produce stochastic magnetic field and enhance plasma transport. The island location may vary from the plasma core to the plasma edge. These oscillations are usually detected by Mirnov coils. Oscillations at the same frequencies can also appear in the high-k scattering signal if the scattering volume is at the right location. Data from various plasmas will be presented, and their effects on plasma transport will be discussed.

Wong, King-Lap

2011-11-01

13

High-resolution frequency domain second harmonic optical coherence tomography  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

14

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

15

Interface imaging by second-harmonic microscopy  

Microsoft Academic Search

Second-harmonic microscopy (SHM) is a fast noncontact surface specific imaging technique for the quantitative {ital in situ} characterization of a large variety of real interfaces including liquid surfaces, surfaces in vacuum, and buried interfaces. The conventional surface second-harmonic generation experiment reveals the surface order and symmetry averaged over the area illuminated with an intense laser beam. In contrast, the SHM

M. Floersheimer; M. Boesch; Ch. Brillert; M. Wierschem; H. Fuchs

1997-01-01

16

Elastography using harmonic ultrasonic imaging: a feasibility study.  

PubMed

Tissue Harmonic Imaging (THI) is a relatively new modality that has had a significant impact in the ultrasound field. In the recent past, imaging the mechanical properties of tissues using elastography has also gained great interest. In this paper, we investigate the feasibility of combining these two state-of-the-art ultrasound-imaging modalities. The performance of elastograms obtained using harmonic ultrasonic signals is studied with simulations and compared to the performance of conventional elastograms using standard statistical methods. Experiments are used as a proof of the technical feasibility of generating tissue-harmonic elastograms using experimental harmonic signals. The results of our simulation study indicate that all image quality factors considered in this study (elastographic signal-to-noise ratio, elastographic contrast-to-noise ratio and spatial resolution) may be improved when using harmonic ultrasonic signals, provided that the ultrasound system is characterized by high bandwidth, high sampling frequency and large lateral sampling. Preliminary experimental results suggest that it is technically feasible to generate experimental elastograms using harmonic signals, provided that the sonographic signal-to-noise ratio of the pre- and postcompression harmonic frames is sufficiently high to guarantee reliable values of correlation. PMID:20687278

Desai, Raghavendra Reddy; Krouskop, Thomas A; Righetti, Raffaella

2010-04-01

17

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

18

He's frequency-amplitude formulation for the Duffing harmonic oscillator  

Microsoft Academic Search

He’s frequency–amplitude formulation is used to solve the Duffing harmonic oscillator problem. The solution procedure is simple, and the result obtained is valid for the whole solution domain with high accuracy.

Jie Fan

2009-01-01

19

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

20

Biological applications of second harmonic imaging  

Microsoft Academic Search

Second Harmonic Generation (SHG) microscopy dates back to 1974, but effective biological use of the technique has a history\\u000a of barely 10 years. It is now widely used to image collagen in many different applications, and is becoming useful for imaging\\u000a myosin and some polysaccharides. A separate line on research has focussed on SHG dyes, which can provide high-speed indication\\u000a of

Guy Cox

21

Harmonics  

NSDL National Science Digital Library

This simulation illustrates the behavior of standing waves in situation where one end fixed, both ends are fixed, and both ends are free. The simulation allows the user to examine the standing wave behavior at the fundamental frequency and when the first three harmonics are added. The user can control the amplitude of each of the harmonics and observe the resulting pattern.

Renault, Pascal

2009-01-22

22

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

PubMed

In high amplitude ultrasonic fields, such as those used in medical ultrasound, nonlinear propagation can result in waveform distortion and the generation of harmonics of the initial frequency. In the nearfield of a transducer this process is complicated by diffraction effects associated with the source. The results of a programme to study the nonlinear propagation in the fields of circular, focused and rectangular transducers are described, and comparisons made with numerical predictions obtained using a finite difference solution to the Khokhlov-Zabolotskaya-Kuznetsov (or KZK) equation. These results are extended to consider nonlinear propagation in tissue-like media and the implications for ultrasonic measurements and ultrasonic heating are discussed. The narrower beamwidths and reduced side-lobe levels of the harmonic beams are illustrated and the use of harmonics to form diagnostic images with improved resolution is described. PMID:10829672

Humphrey, V F

2000-03-01

23

Detecting the harmonics of oscillations with time-variable frequencies  

Microsoft Academic Search

A method is introduced for the spectral analysis of complex noisy signals containing several frequency components. It enables components that are independent to be distinguished from the harmonics of nonsinusoidal oscillatory processes of lower frequency. The method is based on mutual information and surrogate testing combined with the wavelet transform, and it is applicable to relatively short time series containing

L. W. Sheppard; A. Stefanovska; P. V. E. McClintock

2011-01-01

24

Ultrasonography of the pancreas. 2. Harmonic imaging.  

PubMed

Tissue harmonic imaging (THI) is a relatively new ultrasonographic imaging modality which has been implemented in many modern scanners. As several previous studies have pointed out, THI can help to overcome some shortcomings of conventional B-mode ultrasonography (US). The aim of this article is to give a compact summary of the potentials of THI, focused on pancreatic imaging. Beginning with a recapitulation of the technical background of THI, the particularities and suitable applications of THI in US of the pancreas are discussed. Examination protocols and typical indications are presented together with example images. Finally, new trends and developments in B-mode sonography of the pancreas such as panorama US, compound imaging, and photopic US are mentioned. PMID:16850350

Hohl, C; Schmidt, T; Honnef, D; Günther, R W; Haage, P

2007-01-01

25

A Novel Split-Waveguide Mount Design For MM and SubMM wave frequency multipliers and Harmonic Mixers  

NASA Technical Reports Server (NTRS)

A novel split-waveguide mount for millimeter and submillimeter wave frequency multipliers and harmonic mixers is presented. It consists of only two pieces, block halves, which are mirror images of each other.

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

1993-01-01

26

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

NASA Technical Reports Server (NTRS)

BACKGROUND: Newer contrast agents as well as tissue harmonic imaging enhance left ventricular (LV) endocardial border delineation, and therefore, improve LV wall-motion analysis. Interpretation of dobutamine stress echocardiography is observer-dependent and requires experience. This study was performed to evaluate whether these new imaging modalities would improve endocardial visualization and enhance accuracy and efficiency of the inexperienced reader interpreting dobutamine stress echocardiography. METHODS AND RESULTS: Twenty-nine consecutive patients with known or suspected coronary artery disease underwent dobutamine stress echocardiography. Both fundamental (2.5 MHZ) and harmonic (1.7 and 3.5 MHZ) mode images were obtained in four standard views at rest and at peak stress during a standard dobutamine infusion stress protocol. Following the noncontrast images, Optison was administered intravenously in bolus (0.5-3.0 ml), and fundamental and harmonic images were obtained. The dobutamine echocardiography studies were reviewed by one experienced and one inexperienced echocardiographer. LV segments were graded for image quality and function. Time for interpretation also was recorded. Contrast with harmonic imaging improved the diagnostic concordance of the novice reader to the expert reader by 7.1%, 7.5%, and 12.6% (P < 0.001) as compared with harmonic imaging, fundamental imaging, and fundamental imaging with contrast, respectively. For the novice reader, reading time was reduced by 47%, 55%, and 58% (P < 0.005) as compared with the time needed for fundamental, fundamental contrast, and harmonic modes, respectively. With harmonic imaging, the image quality score was 4.6% higher (P < 0.001) than for fundamental imaging. Image quality scores were not significantly different for noncontrast and contrast images. CONCLUSION: Harmonic imaging with contrast significantly improves the accuracy and efficiency of the novice dobutamine stress echocardiography reader. The use of harmonic imaging reduces the frequency of nondiagnostic wall segments.

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

2002-01-01

27

Multimode Directional Coupler for Utilization of Harmonic Frequencies from TWTAs  

NASA Technical Reports Server (NTRS)

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

Simmons, Rainee N.; Wintucky, Edwin G.

2013-01-01

28

Speckle Noise Reduction by Superposing Many Higher Harmonic Images  

Microsoft Academic Search

A novel ultrasonic imaging method offering high resolution and high-quality images for clinical diagnosis has been developed. This method produces an image using many higher harmonic components contained in the echoes from the inside of a human body, generated due to ultrasonic nonlinear propagation through biological tissues. A new ultrasonic probe has been designed to detect higher harmonic components efficiently

Iwaki Akiyama; Akihisa Ohya; Shigemi Saito

2005-01-01

29

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

30

Detection and Imaging of Nonmetallic Inclusions in Continuously Cast Steel Plates by Higher Harmonics  

Microsoft Academic Search

Nonmetallic inclusions within coarse columnar dendrites in continuously cast steel plates were detected and imaged by a nonlinear ultrasonic imaging technique. The nonlinear response of the inclusion\\/steel interface to tensile and compressive stress results in waveform distortion of the incident tone-burst wave, namely, higher harmonics in the frequency domain. By extracting the second harmonic with a band-pass filter and mapping

Koichiro Kawashima; Toshihiro Ito; Yasuaki Nagata

2010-01-01

31

An effective scaling frequency factor method for harmonic vibrational frequencies: The factors’ transferability problem  

Microsoft Academic Search

Performance of the so-called effective scaling frequency factor method, ESFF, for scaling of harmonic theoretical frequencies is analyzed and compared with the well-known SQM method. A training set of 30 molecules (660 experimental frequencies) has been used to optimize a set of 11 scaling factors. Results point towards somewhat lower RMS deviation with respect to the experimental values obtained with

Piotr Borowski; Aleksandra Drzewiecka; Manuel Fernández-Gómez; Maria Paz Fernández-Liencres; Tomás Peña Ruiz

2008-01-01

32

Detecting the harmonics of oscillations with time-variable frequencies.  

PubMed

A method is introduced for the spectral analysis of complex noisy signals containing several frequency components. It enables components that are independent to be distinguished from the harmonics of nonsinusoidal oscillatory processes of lower frequency. The method is based on mutual information and surrogate testing combined with the wavelet transform, and it is applicable to relatively short time series containing frequencies that are time variable. Where the fundamental frequency and harmonics of a process can be identified, the characteristic shape of the corresponding oscillation can be determined, enabling adaptive filtering to remove other components and nonoscillatory noise from the signal. Thus the total bandwidth of the signal can be correctly partitioned and the power associated with each component then can be quantified more accurately. The method is first demonstrated on numerical examples. It is then used to identify the higher harmonics of oscillations in human skin blood flow, both spontaneous and associated with periodic iontophoresis of a vasodilatory agent. The method should be equally relevant to all situations where signals of comparable complexity are encountered, including applications in astrophysics, engineering, and electrical circuits, as well as in other areas of physiology and biology. PMID:21405759

Sheppard, L W; Stefanovska, A; McClintock, P V E

2011-01-01

33

Detecting the harmonics of oscillations with time-variable frequencies  

NASA Astrophysics Data System (ADS)

A method is introduced for the spectral analysis of complex noisy signals containing several frequency components. It enables components that are independent to be distinguished from the harmonics of nonsinusoidal oscillatory processes of lower frequency. The method is based on mutual information and surrogate testing combined with the wavelet transform, and it is applicable to relatively short time series containing frequencies that are time variable. Where the fundamental frequency and harmonics of a process can be identified, the characteristic shape of the corresponding oscillation can be determined, enabling adaptive filtering to remove other components and nonoscillatory noise from the signal. Thus the total bandwidth of the signal can be correctly partitioned and the power associated with each component then can be quantified more accurately. The method is first demonstrated on numerical examples. It is then used to identify the higher harmonics of oscillations in human skin blood flow, both spontaneous and associated with periodic iontophoresis of a vasodilatory agent. The method should be equally relevant to all situations where signals of comparable complexity are encountered, including applications in astrophysics, engineering, and electrical circuits, as well as in other areas of physiology and biology.

Sheppard, L. W.; Stefanovska, A.; McClintock, P. V. E.

2011-01-01

34

A prototype imaging second harmonic interferometer  

SciTech Connect

We have built a prototype imaging second harmonic interferometer, which is intended to test critical elements of a design for a tangential array interferometer on C-Mod{sup 6}. The prototype uses a pulsed, 35 mJ, 10 Hz multimode, Nd:YAG laser, LiB{sub 3}O{sub 5} doublers, a fan beam created by a cylindrical lens, four retroreflector elements, and a CCD camera as a detector. The prototype also uses a polarization scheme in which the interference information is eventually carried by two second harmonic beams with crossed polarization. These are vector summed and differenced, and separated, by a Wollaston prism, to give two spots on the CCD. There is a pair of these spots for each retroreflector used. The phase information is directly available as the ratio of the difference to sum the intensities of the two spots. We have tested a single channel configuration of this prototype, varying the phase by changing the pressure in an air cell, and we have obtained a 5:1 light to dark ratio, and a clear sinusoidal variation of the ratio as a function of pressure change. {copyright} {ital 1997 American Institute of Physics.}

Jobes, F.C.; Bretz, N.L. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

1997-01-01

35

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

36

Indoor imaging of targets enduring simple harmonic motion using Doppler radars  

Microsoft Academic Search

In this paper, we demonstrate the micro-Doppler signatures of rotational\\/vibrational targets enduring simple harmonic motions (SHM). The SHM, whether it represents vibrations or rotations, induces frequency modulations on radar returns. The returns capture certain extrinsic motion characteristics of the target which have a sinusoidal instantaneous frequency. Indoor imaging data collection experiments have been performed. The experiments have been designed, keeping

Pawan Setlur; Moeness Amin; Fauzia Ahmad; Thayananthan Thayaparan

2005-01-01

37

Critical frequency control in harmonic quantum Brownian motion  

NASA Astrophysics Data System (ADS)

The dissipative effects of a quantum harmonic oscillator, initially set in a coherent state and linearly coupled to a continuous distribution of frequency modes, are analyzed over long time scales in relation to the behavior of the spectral density near an arbitrary band gap, arbitrarily shaped at the higher frequencies. The reservoir is initially set either in the vacuum state or in continuous distributions of coherent states. These distributions are arbitrarily shaped at high frequencies and structured in sub- or super-ohmic configurations near an arbitrary band gap frequency. Similarly to certain decoherence processes of a qubit, critical conditions emerge, such that arbitrarily slow inverse power law relaxations of the expectation values of the observables, are obtained by approaching the boundary between the sub- and the super-ohmic regimes. Also, in such critical conditions, a trapping of the number of excitations appears in the super-ohmic regime. The technique of critical frequency control, emerging in the scenario of the environment-induced decoherence of a qubit via the reservoir engineering approach, is extended to the harmonic quantum Brownian motion.

Giraldi, Filippo; Petruccione, Francesco

2013-01-01

38

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

NASA Astrophysics Data System (ADS)

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

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

2007-04-01

39

Nonlinear wave-particle interactions at cyclotron harmonic frequencies  

SciTech Connect

Waves with frequencies near multiples of the gyrofrequency are commonly employed to heat plasmas to high temperatures in magnetically confined fusion experiments. When particle orbits are trapped very near a cyclotron harmonic resonance, the quasilinear concept of weakly perturbed, uncorrelated passages through resonance breaks down, and nonlinear effects become important. Numerical as well as analytic studies demonstrate that relativistic detuning of the resonance can be important for electrons even at low initial energies (approx. 20 eV). Also, coupling to perturbed parallel motion can lead to strong interactions for turning points where the wave frequency differs from a harmonic multiple of the bounce averaged gyrofrequency by an integral multiple, m, of the bounce frequency. The resultant motion is described by large periodic energy excursions for which small angle Coulomb collisions or other randomization processes, are required to realize net heating. Analytic formulae are derived that describe the energy excursion behavior in a parabolic magnetic well in terms of an effective potential and two constants of motion: the Hamiltonian and a parallel action. A Fokker-Planck heating model is developed for diffusive decorrelation of the energy excursions, and Fokker-Planck coefficients are generated. This model demonstrates that the nonlinear heating is a function of the decorrelation mechanism.

Carter, M.D.

1985-01-01

40

Frequency tracking in power networks in the presence of harmonics  

SciTech Connect

Three new techniques for frequency measurement are proposed in the paper. The first is a modified zero crossing method using curve fitting of voltage samples. The second method is based on polynomial fitting of the DFT quasi-stationary phasor data for calculation of the rate of change of the positive sequence phase angle. The third method operates on a complex signal obtained by the standard technique of quadrature demodulation. All three methods are characterized by immunity to reasonable amounts of noise and harmonics in power systems. The performance of the proposed techniques is illustrated on several scenarios by computer simulation.

Begovic, M.M.; Dunlap, S. (Georgia Inst. of Technology, Atlanta, GA (United States). School of Electrical Engineering); Djuric, P.M. (State Univ. of New York, Stony Brook, NY (United States). Dept. of Electrical Engineering); Phadke, A.G. (Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Electrical Engineering)

1993-04-01

41

Optical generation of a precise microwave frequency comb by harmonic frequency locking  

NASA Astrophysics Data System (ADS)

A semiconductor laser under negative optoelectronic feedback is applied to the generation of a microwave frequency comb through the nonlinear dynamics. The laser system is operated in a harmonic frequency-locked pulsing state, where its power spectrum is a microwave frequency comb that consists of multiples of a locking frequency. Every frequency component of the comb can be simultaneously stabilized by simply injecting an external microwave modulation at any component of the comb. This phenomenon can be viewed as a kind of microwave injection locking of the laser dynamics.

Chan, Sze-Chun; Xia, Guang-Qiong; Liu, Jia-Ming

2007-07-01

42

Differential Roles of Frequency-following and Frequency-doubling Visual Responses Revealed by Evoked Neural Harmonics  

PubMed Central

Frequency-following and frequency-doubling neurons are ubiquitous in both striate and extrastriate visual areas. However, responses from these two types of neural populations have not been effectively compared in humans because previous EEG studies have not successfully dissociated responses from these populations. We devised a light–dark flicker stimulus that unambiguously distinguished these responses as reflected in the first and second harmonics in the steady-state visual evoked potentials. These harmonics revealed the spatial and functional segregation of frequency-following (the first harmonic) and frequency-doubling (the second harmonic) neural populations. Spatially, the first and second harmonics in steady-state visual evoked potentials exhibited divergent posterior scalp topographies for a broad range of EEG frequencies. The scalp maximum was medial for the first harmonic and contralateral for the second harmonic, a divergence not attributable to absolute response frequency. Functionally, voluntary visual–spatial attention strongly modulated the second harmonic but had negligible effects on the simultaneously elicited first harmonic. These dissociations suggest an intriguing possibility that frequency-following and frequency-doubling neural populations may contribute complementary functions to resolve the conflicting demands of attentional enhancement and signal fidelity—the frequency-doubling population may mediate substantial top–down signal modulation for attentional selection, whereas the frequency-following population may simultaneously preserve relatively undistorted sensory qualities regardless of the observer’s cognitive state.

Kim, Yee-Joon; Grabowecky, Marcia; Paller, Ken A.; Suzuki, Satoru

2012-01-01

43

Bond length, dipole moment, and harmonic frequency of CO  

NASA Technical Reports Server (NTRS)

A detailed comparison of some properties of CO is given, at the modified coupled-pair functional, single and double excitation coupled-cluster (CCSD), and CCSD(T) levels of theory (including a perturbational estimate for connected triple excitations), using a variety of basis sets. With very large one-particle basis sets, the CCSD(T) method gives excellent results for the bond distance, dipole moment, and harmonic frequency of CO. In a (6s 5p 4d 3f 2g 1h) + (1s 1p 1d) basis set, the bond distance is about 0.005a0 too large, the dipole moment about 0.005 a.u. too small, and the frequency about 6/cm too small, when compared with experimental results.

Barnes, Leslie A.; Liu, Bowen; Lindh, Roland

1993-01-01

44

Comparison of conventional B-scan, tissue harmonic imaging, compound imaging and tissue harmonic compound imaging in neck lesion characterisation.  

PubMed

In recent years, further technical developments of ultrasound scanning techniques, such as tissue harmonic imaging (THI) and compound imaging (CI), have become available and promise considerable improvement in image quality. No comparative assessments have yet been made of their systematic use in the head and neck. We studied 313 lesions of the head and neck detected on ultrasound scanning. Ultrasound images were obtained using a state-of-the-art scanning system. Two experts evaluated the images obtained for each lesion with conventional B-scan mode (BSCAN), THI, CI, and tissue harmonic compound imaging (THICI) with respect to four different aspects of image quality. Largely concordant results were found for each of the parameters studied: overall image quality, tissue contrast, lesion conspicuity, and internal structure. Evaluations of CI and THICI were frequently ranked higher (p < 0.001) than BSCAN and THI (p < 0.001). Images obtained in BSCAN mode often had better scores than images in THI mode alone (p < 0.001). Comparison of CI and THICI showed no statistically significant differences for any of the parameters studied. After a learning period, compound imaging methods improve image quality of the soft tissues of neck and may be included in the routine settings of ultrasound systems. PMID:20422202

Bozzato, Alessandro; Loika, Anne; Hornung, Joachim; Koch, Michael; Zenk, Johannes; Uter, Wolfgang; Iro, Heinrich

2010-10-01

45

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

NASA Technical Reports Server (NTRS)

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 imaging. Harmonic imaging improved left ventricular endocardial border delineation over fundamental imaging (superior: harmonic = 71.1%, fundamental = 18.7%; similar: 10.2%; P <.001). Quantitative analysis of 100 wall/cavity combinations demonstrated brighter wall segments and more strikingly darker cavities during harmonic imaging (cavity intensity on a 0 to 255 scale: fundamental = 15.6 +/- 8.6; harmonic = 6.0 +/- 5.3; P <.0001), which led to enhanced contrast between the wall and cavity (1.89 versus 1.19, P <.0001). Harmonic imaging reduces side-lobe artifacts, resulting in a darker cavity and brighter walls, thereby improving image contrast and endocardial delineation.

Rubin, D. N.; Yazbek, N.; Garcia, M. J.; Stewart, W. J.; Thomas, J. D.

2000-01-01

46

Imaging diffusion in a microfluidic device by third harmonic microscopy  

NASA Astrophysics Data System (ADS)

We monitor and characterize near-surface diffusion of miscible, transparent liquids in a microfluidic device by third harmonic microscopy. The technique enables observations even of transparent or index-matched media without perturbation of the sample. In particular, we image concentrations of ethanol diffusing in water and estimate the diffusion coefficient from the third harmonic images. We obtain a diffusion coefficient D = (460 ± 30) ?m2/s, which is consistent with theoretical predictions. The investigations clearly demonstrate the potential of harmonic microscopy also under the challenging conditions of transparent fluids.

Petzold, Uwe; Büchel, Andreas; Hardt, Steffen; Halfmann, Thomas

2012-09-01

47

One atomic beam as a detector of classical harmonic vibrations with micro amplitudes and low frequencies  

NASA Astrophysics Data System (ADS)

We propose a simplest detector of harmonic vibrations with micro amplitudes and low frequencies, i.e. a detector consisting of one atomic beam. Here, the atomic beam is induced by a plane harmonic wave and has classical collective harmonic vibrations, whose vibrant directions are perpendicular to the wave vectors of the atomic beam. Compared with a detector consisting of an atomic Mach-Zehnder interferometer, the new detector has two advantages: (1) it is suitable for the detection of harmonic vibrations induced either by a longitudinal plane harmonic wave or by using a transverse plane harmonic wave: (2) the quantum noise fluctuation of the atomic beam is exactly zero. We present the principle for detecting classical harmonic vibrations with micro amplitudes and low frequencies by using the new detector. The frequency of a classical harmonic vibration with a micro amplitude can be evaluated by measuring the variations in the mean numbers of atoms arriving at the atomic detector.

Huang, Yong-Yi

2014-03-01

48

Statistical model of clutter suppression in tissue harmonic imaging  

PubMed Central

A statistical model is developed for the suppression of clutter in tissue harmonic imaging (THI). Tissue heterogeneity is modeled as a random phase screen that is characterized by its correlation length and variance. With the autocorrelation function taken to be Gaussian and for small variance, statistical solutions are derived for the mean intensities at the fundamental and second-harmonic frequencies in the field of a focused sound beam that propagates through the phase screen. The statistical solutions are verified by comparison with ensemble averaging of direct numerical simulations. The model demonstrates that THI reduces the aberration clutter appearing in the focal region regardless of the depth of the aberrating layer, with suppression of the clutter most effective when the layer is close to the source. The model is also applied to the reverberation clutter that is transmitted forward along the axis of the beam. As with aberration clutter, suppression of such reverberation clutter by THI is most pronounced when the tissue heterogeneity is located close to the source.

Yan, Xiang; Hamilton, Mark F.

2011-01-01

49

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

SciTech Connect

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

Murakami, M.; Mauritsson, J.; Gaarde, M.B. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States)

2005-08-15

50

Special frequencies and Lifshitz singularities in binary random harmonic chains  

SciTech Connect

The authors consider a one-dimensional chain of coupled harmonic oscillators; the mass of each atom is a random variable taking only two values (M or 1). They investigate the integrated density of states H(omega/sup 2/) near special frequencies: a given frequency omega/sub s/ with rational wavelength becomes special if the mass ratio M exceeds a certain critical value M/sub c/. They show that H has essential singularities of the types H/sub sg/approx. exp(-C/sub 1/ absolute value of omega/sup 2/-omega/sub s//sup 2//sup 1/2/) or exp(-C/sub 2/absolute value of omega/sup 2/-omega/sub s//sup 2/ /sup -1/), according to the value of M and the sign of (omega/sup 2/-omega/sub s//sup 2/). The Lifshitz singularity at the band edge is analyzed in the same way. In each case, the constant C/sub 1/ or C/sub 2/ is evaluated explicitly and compared with a vast amount of numerical work. All these exponential singularities are modulated by periodic amplitudes. The properties of the eigenfunctions with frequencies close to the special values are also discussed, and are illustrated by numerical data.

Nieuwenhuizen, T.M.; Luck, J.M.; Canisius, J.; van Hemmen, J.L.; Ventevogel, W.J.

1986-11-01

51

Quantitative viscoelastic parameters measured by harmonic motion imaging  

Microsoft Academic Search

Quantifying the mechanical properties of soft tissues remains a challenging objective in the field of elasticity imaging. In this work, we propose an ultrasound-based method for quantitatively estimating viscoelastic properties, using the amplitude-modulated harmonic motion imaging (HMI) technique. In HMI, an oscillating acoustic radiation force is generated inside the medium by using focused ultrasound and the resulting displacements are measured

Jonathan Vappou; Caroline Maleke; Elisa E. Konofagou

2009-01-01

52

Imaging intracellular Ca2+ dynamic with third harmonic generation microscope  

Microsoft Academic Search

Summary form only given. The validity of the third harmonic generation (THG) microscopy for imaging has been shown and its potential use in material science and more precisely in biology. All these studies have demonstrated that THG microscopy is a method which has the advantage that no labeling is necessary. In order to develop further imaging instruments, biological dynamic events

L. Canioni; S. Rivet; L. Sarger; R. Barille; P. Vacher; P. Voisin

2001-01-01

53

Fast image interpolation using Circular Harmonic Functions  

Microsoft Academic Search

In this paper we introduce a novel edge directed image interpolation algorithm so as to obtain an high-resolution image, given a low-resolution image. The interpolation is based on the local image directionality features estimated on the low-resolution image. The in depth analysis of the local edge features is accomplished at a low computational cost by filtering the low-resolution image by

Stefania Colonnese; Roberto Randi; Stefano Rinauro; Gaetano Scarano

2010-01-01

54

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

55

Tromsoe heating experiments: Stimulated emission at HF pump harmonic and subharmonic frequencies  

Microsoft Academic Search

Observations of electromagnetic emissions on the HF heater subharmonic and several harmonic frequencies are presented. Often the second harmonic emissions show characteristic amplitude variation, frequency shift, and spectral broadening that clearly have their origin in ionospheric plasma processes. The strongest candidate is a combined parametric decay and Raman up-conversion processes. The subharmonic emission is believed to be evidence of absolute

H. Derblom; B. Thide; T. B. Leyser; J. A. Nordling; A. Hedberg; P. Stubbe; H. Kopka; M. Rietveld

1989-01-01

56

Nonlinear optical generation of radiation near the frequency of the third harmonic of an iodine laser  

Microsoft Academic Search

Nonlinear optical generation of the third harmonic in the vapour of a metal at a frequency close to the tripled frequency of an iodine laser was achieved for the first time. Phase-matching conditions in the presence of a buffer gas and the nonlinear susceptibility were close to the calculated predictions. A change in the energy of the third harmonic pulses

A S Aleksandrovskii; V P Gerasimov; A K Popov; V V Slabko

1996-01-01

57

Type II radio bursts with triple harmonic structure at frequencies 10-30 MHz.  

NASA Astrophysics Data System (ADS)

In this presentation we report about the first observations of Type II bursts with three harmonics in frequency range 10 - 30 MHz. The most representative of them was registered on June 4, 2004 with the UTR-2 radio telescope and consisted of three lanes. Wide frequency band of the analysis allowed to observe all three harmonics of the burst at one moment of time (7h53m50s UT). The observational properties, which confirm the harmonic structure of the burst, are discussed. The frequency ratios of the harmonics at fixed moment of time were f2-f1=2 and f3-f1=2.8, where f1, f2 and f3 are the harmonic frequencies. All three harmonics of the observed Type II burst had fine structure in the form of fast drifting sub-bursts. The durations of sub-bursts of different harmonics were also different (in average 7 s for fundamental, 3 s for second and 1-2 s for third harmonic). The frequency drift rates at fixed moment of time appeared to be -10 kHz/s for fundamental (f=10 MHz), -30 kHz/s for second harmonic (f=20 MHz) and -50 kHz/s for third harmonic (f=30 MHz). The consistency of the three harmonics hypothesis was tested in the frames of four different corona models. For each model corresponding source velocities were calculated. The connection between the observed Type-II burst and CMEs was analyzed. The extension of this Type II burst at lower frequencies (WIND data at frequencies 1-11 MHz) was also found. Some other examples of Type II bursts possibly having the triple harmonic structure are shown.

Dorovskyy, Vladimir; Melnik, Valentin; Konovalenko, Alexander; Rucker, Helmut; Abranin, Eduard

2010-05-01

58

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

59

Quantitative viscoelastic parameters measured by harmonic motion imaging.  

PubMed

Quantifying the mechanical properties of soft tissues remains a challenging objective in the field of elasticity imaging. In this work, we propose an ultrasound-based method for quantitatively estimating viscoelastic properties, using the amplitude-modulated harmonic motion imaging (HMI) technique. In HMI, an oscillating acoustic radiation force is generated inside the medium by using focused ultrasound and the resulting displacements are measured using an imaging transducer. The proposed approach is a two-step method that uses both the properties of the propagating shear wave and the phase shift between the applied stress and the measured strain in order to infer to the shear storage (G') and shear loss modulus (G''), which refer to the underlying tissue elasticity and viscosity, respectively. The proposed method was first evaluated on numerical phantoms generated by finite-element simulations, where a very good agreement was found between the input and the measured values of G' and G''. Experiments were then performed on three soft tissue-mimicking gel phantoms. HMI measurements were compared to rotational rheometry (dynamic mechanical analysis), and very good agreement was found at the only overlapping frequency (10 Hz) in the estimate of the shear storage modulus G' (14% relative error, averaged p-value of 0.34), whereas poorer agreement was found in G'' (55% relative error, averaged p-value of 0.0007), most likely due to the significantly lower values of G'' of the gel phantoms, posing thus a greater challenge in the sensitivity of the method. Nevertheless, this work proposes an original model-independent ultrasound-based elasticity imaging method that allows for direct, quantitative estimation of tissue viscoelastic properties, together with a validation against mechanical testing. PMID:19454785

Vappou, Jonathan; Maleke, Caroline; Konofagou, Elisa E

2009-06-01

60

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

NASA Astrophysics Data System (ADS)

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

Yang, Xinmai; Cleveland, Robin O.

2005-01-01

61

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

PubMed

A time-domain numerical code (the so-called Texas code) that solves the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation has been extended from an axis-symmetric coordinate system to a three-dimensional (3D) Cartesian coordinate system. The code accounts for diffraction (in the parabolic approximation), nonlinearity and absorption and dispersion associated with thermoviscous and relaxation processes. The 3D time domain code was shown to be in agreement with benchmark solutions for circular and rectangular sources, focused and unfocused beams, and linear and nonlinear propagation. The 3D code was used to model the nonlinear propagation of diagnostic ultrasound pulses through tissue. The prediction of the second-harmonic field was sensitive to the choice of frequency-dependent absorption: a frequency squared f2 dependence produced a second-harmonic field which peaked closer to the transducer and had a lower amplitude than that computed for an f1.1 dependence. In comparing spatial maps of the harmonics we found that the second harmonic had dramatically reduced amplitude in the near field and also lower amplitude side lobes in the focal region than the fundamental. These findings were consistent for both uniform and apodized sources and could be contributing factors in the improved imaging reported with clinical scanners using tissue harmonic imaging. PMID:15704404

Yang, Xinmai; Cleveland, Robin O

2005-01-01

62

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

63

Corneal imaging by second and third harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Advanced imaging methods are essential tools for improved outcome of refractive surgery. Second harmonic generation (SHG) and third harmonic generation (THG) microscopy are noninvasive high-resolution imaging methods, which can discriminate the different layers of the cornea, thus having strong impact on the outcome of laser surgery. In this work, we use an Ytterbium femtosecond laser as the laser source, the longer wavelength of which reduces scattering, and allows simultaneous SHG and THG imaging. We present SHG and THG images and profiles of pig corneas that clearly show the anterior surface of the cornea, the entry in the stroma and its end, and the posterior surface of the cornea. These observations allow localizing the epithelium, the stroma and the endothelium. Other experiments give information about the structure and cytology of the corneal layers.

Brocas, Arnaud; Jay, Louis; Mottay, Eric; Brunette, Isabelle; Ozaki, Tsuneyuki

2008-03-01

64

Harmonic frequency locking in a semiconductor laser with delayed negative optoelectronic feedback  

NASA Astrophysics Data System (ADS)

The locking states of a delayed negative optoelectronic feedback system are studied experimentally. Harmonic locking is observed in this system. Instead of locking to the frequency of the delay loop, the pulsing frequency of the system locks to a harmonic of the loop frequency. Moreover, a period-adding route of the locking states is found and locking states of Farey fractions up to order 17 are reported. The plot of the rotation number of the locking states shows a Devil's staircase structure.

Lin, F. Y.; Liu, J. M.

2002-10-01

65

Third-harmonic frequency multiplication of a two-stage tapered gyrotron TWT amplifier  

Microsoft Academic Search

The frequency multiplication of a two-stage tapered gyrotron traveling wave tube amplifier is experimentally verified in low-voltage and low-current operation. By modulating an axis-encircling electron beam at the fundamental harmonic cyclotron frequency in the input stage, a frequency-tripled signal induced by the third-harmonic component of the modulated beam current is chosen to be extracted from the output stage. Both interaction

Chan-Wook Baik; Seok-Gy Jeon; Dae-Ho Kim; Nobuyuki Sato; Kuniyoshi Yokoo; Gun-Sik Park

2005-01-01

66

Harmonic imaging improves estimation of left ventricular mass  

Microsoft Academic Search

Objectives: To assess the effect of tissue harmonic imaging (THI) on assessment of left ventricular mass index (LVMI) measurements by M-mode trans-thoracic echocardiography, when compared with magnetic resonance imaging (MRI). Methods: 20 hypertensive male subjects were studied. LVMI was measured in all subjects by both gradient-echo MRI (Lscelsint Prestige 1.9 T) and by transthoracic echocardiography (ATL HDI 5000). M-mode echocardiography

James C. S. Spratt; Stephen J. Leslie; Audrey White; Lynn Fenn; Colin Turnbull; David B. Northridge

2004-01-01

67

High Harmonic Imaging of Conical Intersections  

NASA Astrophysics Data System (ADS)

Conical intersections (CI) are crucially involved in light harvesting, primary visual processes, DNA UV stabilization and atmospheric chemistry. A wave packet typically moves through the intersection on a femtosecond time scale, demonstrating the need for ultrafast tools that are sensitive to the electronic state change occurring in passing the CI. We propose a novel femtosecond pump-probe scheme based on high harmonic generation (HHG). A first pulse (pump) creates a molecular wave packet on excited electronic surfaces, and the time delayed, high intensity probe pulse produces HHG on the excited molecule as it moves through the CI region. We use the symmetry of the electronic wave functions [1] to detect the electronic state change in the CI via HHG. Furthermore, we use two center interference effects in the HHG [1] to determine the nuclear dynamics that is accompanied by the CI passage. To demonstrate our scheme, we perform simple model calculations on the triatomic molecule SO2, which will be ideally suited for experiments because of its high UV excitation cross sections for pumping the wave packet to the CI region. [1] J. Itatani et al, Phys. Rev. Lett., 94, 123902 (2005) [2] T. Kanai et al, Nature, 435, 470 (2005)

Guehr, Markus; McFarland, Brian K.; Farrell, Joe P.; Bucksbaum, Philip H.

2007-06-01

68

Investigating Mechanisms of Image Quality Enhancement Associated with Tissue Harmonic Imaging  

NASA Astrophysics Data System (ADS)

Enhancements to the compactness of the nonlinearly generated second harmonic (2f) field component (narrower main-lobe and reduced side-lobe levels) and reduced impact of phase and amplitude aberration, with respect to the fundamental (1f) field component, are among the proposed factors contributing to the observed image quality improvements with harmonic imaging in diagnostic ultrasound. Despite the wide clinical use of harmonic imaging, however, the details of the mechanisms responsible for the associated image quality improvements are still not fully understood. The concept of an ``effective apodization'' is defined as a potentially useful tool for providing a linear approximation to the nonlinearly generated field components.

Wallace, Kirk D.; Holland, Mark R.; Miller, James G.

2006-05-01

69

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

70

Stepped Frequency Imaging Radar Simulation.  

National Technical Information Service (NTIS)

In this thesis, a technique involving Stepped Frequency and Inverse Synthetic Aperture Radar (ISAR) processing have been employed to develop two- dimensional radar images of an aircraft target. Radar returns from prominent scatterers of various parts of t...

K. L. Mun

2000-01-01

71

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

72

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

73

Comparison of multistage gyroamplifiers operating in the frequency-multiplication regime with gyroamplifiers operating at a given Cyclotron harmonic  

Microsoft Academic Search

The operation of gyrodevices at cyclotron harmonics is very attractive because of the possibility to reduce the magnetic field requirement by s times, where s is the cyclotron harmonic number. In recent years, two methods of harmonic operation in multistage gyroamplifiers have been actively studied: operation at a given harmonic in all stages and operation in the frequency-multiplying regime when

Gregory S. Nusinovich; Oleksandr V. Sinitsyn; J. Rodgers; Thomas M. Antonsen; Victor L. Granatstein

2004-01-01

74

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

75

Coherent states and uncertainty relations for the damped harmonic oscillator with time-dependent frequency  

NASA Technical Reports Server (NTRS)

Starting with evaluations of propagator and wave function for the damped harmonic oscillator with time-dependent frequency, exact coherent states are constructed. These coherent states satisfy the properties which coherent states should generally have.

Yeon, Kyu-Hwang; Um, Chung-In; George, Thomas F.; Pandey, Lakshmi N.

1993-01-01

76

Position estimation in induction machines utilizing rotor bar slot harmonics and carrier frequency signal injection  

Microsoft Academic Search

This paper presents a simple and robust way of utilizing harmonic saliencies for the estimation of rotor position. A carrier frequency voltage excitation is used to produce a carrier frequency current, which contains the desired spatial information. A closed-loop, tracking observer is then used to estimate the rotor position. Due to its reliance on a spatial saliency and carrier frequency

M. W. Degnert; R. D. Lorenzt

1997-01-01

77

Ka Band Broadband Fourth Harmonic Image Rejection Mixer  

Microsoft Academic Search

This paper presents the design and implementation of Ka band broadband hybrid integrated image rejection mixer with a fourth\\u000a harmonic mixer as unit mixer. Detailed design and analysis have been carried out. The mixer was fabricated by hybrid microwave\\u000a integrated circuit (HMIC) process based on the thin film ceramic substrate which can reduce the cost compared to monolithic\\u000a microwave integrated

Fang Fang Fan; Ze Hong Yan

2008-01-01

78

Sensitive Detection of Malaria Infection by Third Harmonic Generation Imaging  

Microsoft Academic Search

Malaria remains a major health concern worldwide, with 350–500million cases reported annually in endemic countries. In this study, we report a novel and highly sensitive optical-based detection of malaria-infected blood cells by third harmonic generation (THG) imaging of hemozoin pigment that is naturally deposited by the parasite during its lifecycle. The THG signal from the hemozoin was greater than we

Jonathan M. Bélisle; Santiago Costantino; Mara L. Leimanis; Marie-Josée Bellemare; D. Scott Bohle; Elias Georges; Paul W. Wiseman

2008-01-01

79

Second harmonic generation imaging microscopy of cellular structure and function  

Microsoft Academic Search

Second harmonic generation (SHG) imaging microscopy is an important emerging technique for biological research, with many advantages over existing one- or two-photon fluorescence techniques. A non-linear phenomenon employing mode-locked Ti:sapphire or fiber-based lasers, SHG results in intrinsic optical sectioning without the need for a confocal aperture. Furthermore, as a second-order process SHG is confined to loci lacking a center of

Andrew C. Millard; Lei Jin; Leslie M. Loew

2005-01-01

80

Second harmonic imaging and scoring of collagen in fibrotic tissues  

NASA Astrophysics Data System (ADS)

We compare second harmonic generation (SHG) to histological and immunohistochemical techniques for the visualization and scoring of collagen in biological tissues. We show that SHG microscopy is highly specific for fibrillar collagens and that combined SHG and two-photon excited fluorescence (2PEF) imaging can provide simultaneous three-dimensional visualization of collagen synthesis and assembly sites in transgenic animal models expressing GFP constructs. Finally, we propose several scores for characterizing collagen accumulation based on SHG images and appropriate for different types of collagen distributions. We illustrate the sensitivity of these scores in a murine model of renal fibrosis using a morphological segmentation of the tissue based on endogenous 2PEF signals.

Strupler, M.; Pena, A.-M.; Hernest, M.; Tharaux, P.-L.; Martin, J.-L.; Beaurepaire, E.; Schanne-Klein, M.-C.

2007-04-01

81

Coupling CARS with multiphoton fluorescence and high harmonic generation imaging modalities using a femtosecond laser source  

NASA Astrophysics Data System (ADS)

Multimodal nonlinear optical imaging has opened new opportunities and becomes a powerful tool for imaging complex tissue samples with inherent 3D spatial resolution.. We present a robust and easy-to-operate approach to add the coherent anti-stokes Raman scattering (CARS) imaging modality to a widely used multiphoton microscope. The laser source composed of a Mai Tai femtosecond laser and an optical parametric oscillator (OPO) offers one-beam, two-beam and three-beam modalities. The Mai Tai output at 790 nm is split into two beams, with 80% of the power being used to pump the OPO. The idler output at 2036 nm from OPO is doubled using a periodically poled lithium niobate (PPLN) crystal. This frequency-doubled idler beam at 1018 nm is sent through a delay line and collinearly combined with the other Mai Tai beam for CARS imaging on a laser-scanning microscope. This Mai Tai beam is also used for multiphoton fluorescence and second harmonic generation (SHG) imaging. The signal output at 1290 nm from OPO is used for SHG and third-harmonic generation (THG) imaging. External detectors are installed for both forward and backward detection, whereas two internal lamda-scan detectors are employed for microspectroscopy analysis. This new system allows vibrationally resonant CARS imaging of lipid bodies, SHG imaging of collagen fibers, and multiphoton fluorescence analysis in fresh tissues. As a preliminary application, the effect of diacylglycerol acyltransferase 1 (DGAT1) deficiency on liver lipid metabolism in mice was investigated.

Chen, Hongtao; Slipchenko, Mikhail N.; Zhu, Jiabin; Buhman, Kimberly K.; Cheng, Ji-Xin

2009-02-01

82

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the 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 (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. 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 a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third 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 the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. 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, M. G.; van Neer, P. L. M. J.; Verweij, M. D.; Matte, G. M.; Vletter, W. B.; van der Steen, A. F. W.; de Jong, N.

2013-07-01

83

Single pulse frequency compounding protocol for superharmonic imaging.  

PubMed

Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the 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 (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. 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 a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third 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 the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. 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. PMID:23787259

Danilouchkine, M G; van Neer, P L M J; Verweij, M D; Matte, G M; Vletter, W B; van der Steen, A F W; de Jong, N

2013-07-21

84

Non-uniform time sampling for multiple-frequency harmonic balance computations  

NASA Astrophysics Data System (ADS)

A time-domain harmonic balance method for the analysis of almost-periodic (multi-harmonics) flows is presented. This method relies on Fourier analysis to derive an efficient alternative to classical time marching schemes for such flows. It has recently received significant attention, especially in the turbomachinery field where the flow spectrum is essentially a combination of the blade passing frequencies. Up to now, harmonic balance methods have used a uniform time sampling of the period of interest, but in the case of several frequencies, non-necessarily multiple of each other, harmonic balance methods can face stability issues due to a bad condition number of the Fourier operator. Two algorithms are derived to find a non-uniform time sampling in order to minimize this condition number. Their behavior is studied on a wide range of frequencies, and a model problem of a 1D flow with pulsating outlet pressure, which enables to prove their efficiency. Finally, the flow in a multi-stage axial compressor is analyzed with different frequency sets. It demonstrates the stability and robustness of the present non-uniform harmonic balance method regardless of the frequency set.

Guédeney, Thomas; Gomar, Adrien; Gallard, François; Sicot, Frédéric; Dufour, Guillaume; Puigt, Guillaume

2013-03-01

85

Effects of introducing low-frequency harmonics in the perception of vocoded telephone speech1  

PubMed Central

Several studies have demonstrated that telephone use presents a challenge for most cochlear implant (CI) users, and this is attributed mainly to the narrow bandwidth (300–3400 Hz) introduced by the telephone network. The present study focuses on answering the question whether telephone speech recognition in noise can be improved by introducing, prior to vocoder processing, low-frequency harmonic information encompassing the missing (due to the telephone network) information residing in the 0–300 Hz band. Experiment 1 regenerates the main harmonics and adjacent partials within the 0–600 Hz range in corrupted (by steady noise) telephone speech which has been vocoded to simulate electric-acoustic stimulation (EAS). Results indicated that introducing the main harmonics alone did not produce any benefits in intelligibility. Substantial benefit (20%) was observed, however, when both main harmonics and adjacent partials were regenerated in the acoustic portion of EAS-vocoded telephone speech. A similar benefit was noted in Experiment 2 when low-frequency harmonic information was introduced prior to processing noise-corrupted telephone speech using an eight-channel vocoder. The gain in telephone speech intelligibility in noise obtained when low-frequency harmonic information was introduced can be attributed to the listeners having more reliable access to a combination of F0, glimpsing and lexical segmentation cues.

Hu, Yi; Loizou, Philipos C.

2010-01-01

86

Imaging granularity of leukocytes with third harmonic generation microscopy  

PubMed Central

Using third harmonic generation (THG) microscopy, we demonstrate that granularity differences of leukocytes can be revealed without a label. Excited by a 1230 nm 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 of magnitude smaller. Interestingly, the characteristic THG features can also be observed in vivo to track the newly recruited leukocytes following lipopolysaccharide (LPS) challenge. These results suggest that label-free THG imaging may provide timely tracking of leukocyte movement without disturbing the normal cellular or physiological status.

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

2012-01-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

88

Evading surface and detector frequency noise in harmonic oscillator measurements of force gradients  

PubMed Central

We introduce and demonstrate a method of measuring small force gradients acting on a harmonic oscillator in which the force-gradient signal of interest is used to parametrically up-convert a forced oscillation below resonance into an amplitude signal at the oscillator’s resonance frequency. The approach, which we demonstrate in a mechanically detected electron spin resonance experiment, allows the force-gradient signal to evade detector frequency noise by converting a slowly modulated frequency signal into an amplitude signal.

Moore, Eric W.; Lee, SangGap; Hickman, Steven A.; Harrell, Lee E.; Marohn, John A.

2010-01-01

89

Self-referenced, trimmed and compensated RF CMOS harmonic oscillators as monolithic frequency generators  

Microsoft Academic Search

Self-referenced, trimmed and temperature-compensated radio frequency (RF) CMOS LC, or harmonic oscillators (CHOs) are presented as high-accuracy and low-jitter monolithic frequency generators. CHOs are discussed within the context of recent efforts toward replacement of piezoelectric frequency references with silicon MEMS technology. In contrast, CHOs are self-referenced solid-state oscillators which can be fabricated in a standard microelectronic process technology. The CHO

Michael S. McCorquodale

2008-01-01

90

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

PubMed Central

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

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

2014-01-01

91

Modeling of electric railway vehicle for harmonic analysis of traction power-supply system using spline interpolation in frequency domain  

Microsoft Academic Search

It is essential to model nonlinear traction power converter loads for the harmonic analysis of traction systems. A behavioral model in the frequency domain to represent electric railway vehicles based on testing and measurements is proposed for harmonic analysis. The harmonic current characteristics are represented by a set of polynomials generated from cubic smoothing spline interpolation. The purpose of this

K. H. Yuen; M. H. Pong; W. C. Lo; Z. M. Ye

1999-01-01

92

Value of tissue harmonic imaging (THI) and contrast harmonic imaging (CHI) in detection and characterisation of breast tumours  

PubMed Central

The purpose of this study was to investigate the extent to which tissue harmonic imaging (THI), speckle reduction imaging (SRI), spatial compounding (SC) and contrast can improve detection and differentiation of breast tumours. We examined 38 patients (14 benign, 24 malignant tumours) with different combinations of THI, SRI and SC. The effect on delineation, margin, tissue differentiation and posttumoral phenomena was evaluated with a three-point score. Additionally, 1oo not palpable tumours (diameters: 4–15 mm) were examined by contrast harmonic imaging (CHI) with power Doppler. After bolus injection (0.5 ml Optison), vascularisation and enhancement were observed for 20 min. The best combination for detection of margin, infiltration, echo pattern and posterior lesion boundary was the combination of SRI level 2 with SC low. THI was helpful for lesions OF more than 1 cm depth. In native Power Doppler, vessels were found in 54 of 100 lesions. Within 5 min after contrast medium (CM) injection, marginal and penetrating vessels increased in benign and malignant tumours and central vessels mostly in carcinomas (p<0.05). A diffuse CM accumulation was observed up to 20 min after injection in malignant tumours only (p<0.05). THI, SRI and SC improved delineation and tissue differentiation. Second-generation contrast agent allowed detection of tumour vascularisation with prolonged enhancement.

Jung, E. M.; Jungius, K.-P.; Ertan, K.

2006-01-01

93

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

SciTech Connect

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. [Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, New York 11201 (United States)] [Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, New York 11201 (United States)

2013-09-15

94

Diffeomorphic image registration of diffusion MRI using spherical harmonics.  

PubMed

Nonrigid registration of diffusion magnetic resonance imaging (MRI) is crucial for group analyses and building white matter and fiber tract atlases. Most current diffusion MRI registration techniques are limited to the alignment of diffusion tensor imaging (DTI) data. We propose a novel diffeomorphic registration method for high angular resolution diffusion images by mapping their orientation distribution functions (ODFs). ODFs can be reconstructed using q-ball imaging (QBI) techniques and represented by spherical harmonics (SHs) to resolve intra-voxel fiber crossings. The registration is based on optimizing a diffeomorphic demons cost function. Unlike scalar images, deforming ODF maps requires ODF reorientation to maintain its consistency with the local fiber orientations. Our method simultaneously reorients the ODFs by computing a Wigner rotation matrix at each voxel, and applies it to the SH coefficients during registration. Rotation of the coefficients avoids the estimation of principal directions, which has no analytical solution and is time consuming. The proposed method was validated on both simulated and real data sets with various metrics, which include the distance between the estimated and simulated transformation fields, the standard deviation of the general fractional anisotropy and the directional consistency of the deformed and reference images. The registration performance using SHs with different maximum orders were compared using these metrics. Results show that the diffeomorphic registration improved the affine alignment, and registration using SHs with higher order SHs further improved the registration accuracy by reducing the shape difference and improving the directional consistency of the registered and reference ODF maps. PMID:21134814

Geng, Xiujuan; Ross, Thomas J; Gu, Hong; Shin, Wanyong; Zhan, Wang; Chao, Yi-Ping; Lin, Ching-Po; Schuff, Norbert; Yang, Yihong

2011-03-01

95

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

96

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

97

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: Application to 1,2,4-triazole derivatives  

Microsoft Academic Search

Scaling of harmonic frequencies of a molecule is one of the methods of improving the agreement between the calculated from a quadratic force field and experimental vibrational spectrum. An application of the recently proposed effective scaling frequency factor (ESFF) method to the complicated 1,2,4-triazole derivatives is presented. The calculations are based on the DFT\\/B3LYP\\/6-311G** quadratic force fields. It is shown

Piotr Borowski; Karol Pilorz; Monika Pitucha

2010-01-01

98

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: theory and preliminary application to toluene  

Microsoft Academic Search

In this Letter, we propose a new method for scaling of harmonic vibrational frequencies named effective scaling frequency factor (ESFF) method. It uses effective scaling factors obtained through diagonal coefficients of the potential energy distribution matrix, PED, on the basis of a non-redundant natural coordinates set. The preliminary application of ESFF method at B3LYP\\/6-311G?? level to toluene in the region

Piotr Borowski; Manuel Fernández-Gómez; Maria-Paz Fernández-Liencres; Tomás Peña Ruiz

2007-01-01

99

Imaging morphodynamics of human blood cells in vivo with video-rate third harmonic generation microscopy  

PubMed Central

With a video-rate third harmonic generation (THG) microscopy system, we imaged the micro-circulation beneath the human skin without labeling. Not only the speed of circulation but also the morpho-hydrodynamics of blood cells can be analyzed. Lacking of nuclei, red blood cells (RBCs) shows typical parachute-like and hollow-core morphology under THG microscopy. Quite different from RBCs, every now and then, round and granule rich blood cells with strong THG contrast appear 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.

Chen, Chien-Kuo; Liu, Tzu-Ming

2012-01-01

100

Theory of high-harmonic generation by low-frequency laser fields  

Microsoft Academic Search

We present a simple, analytic, and fully quantum theory of high-harmonic generation by low-frequency laser fields. The theory recovers the classical interpretation of Kulander {ital et} {ital al}. in {ital Proceedings} {ital of} {ital the} {ital SILAP} {ital III} {ital Works} {ital hop}, edited by B. Piraux (Plenum, New York, 1993) and Corkum [Phys. Rev. Lett. 71, 1994 (1993)] and

M. Yu M. Lewenstein; Ph. Balcou; M. Y. Ivanov; P. B. Corkum

1994-01-01

101

NONLINEAR OPTICAL PHENOMENA: Nonlinear optical generation of radiation near the frequency of the third harmonic of an iodine laser  

Microsoft Academic Search

Nonlinear optical generation of the third harmonic in the vapour of a metal at a frequency close to the tripled frequency of an iodine laser was achieved for the first time. Phase-matching conditions in the presence of a buffer gas and the nonlinear susceptibility were close to the calculated predictions. A change in the energy of the third harmonic pulses

A. S. Aleksandrovskii; V. P. Gerasimov; A. K. Popov; V. V. Slabko

1996-01-01

102

High-Resolution Nonlinear Optical Imaging of Live Cells by Second Harmonic Generation  

Microsoft Academic Search

By adapting a laser scanning microscope with a titanium sapphire femtosecond pulsed laser and transmission optics, we are able to produce live cell images based on the nonlinear optical phenomenon of second harmonic generation (SHG). Second harmonic imaging (SHIM) is an ideal method for probing membranes of living cells because it offers the high resolution of nonlinear optical microscopy with

Paul J. Campagnola; Mei-de Wei; Aaron Lewis; Leslie M. Loew

1999-01-01

103

Depth-resolved structural imaging by third-harmonic generation microscopy  

Microsoft Academic Search

Third harmonic generation microscopy is shown to be a robust method for obtaining structural information on a variety of biological specimens. Its nature allows depth-resolved imaging of inhomogeneities with virtually no background from surrounding homogeneous media. With an appropriate illumination geometry, third harmonic generation microscopy is shown to be particularly suitable for imaging of biogenic crystals, enabling extraction of the

Dan Oron; Dvir Yelin; Eran Tal; Sefi Raz; Rachel Fachima; Yaron Silberberga

2003-01-01

104

Second harmonic generating (SHG) nanoprobes for in vivo imaging  

PubMed Central

Fluorescence microscopy has profoundly changed cell and molecular biology studies by permitting tagged gene products to be followed as they function and interact. The ability of a fluorescent dye to absorb and emit light of different wavelengths allows it to generate startling contrast that, in the best cases, can permit single molecule detection and tracking. However, in many experimental settings, fluorescent probes fall short of their potential due to dye bleaching, dye signal saturation, and tissue autofluorescence. Here, we demonstrate that second harmonic generating (SHG) nanoprobes can be used for in vivo imaging, circumventing many of the limitations of classical fluorescence probes. Under intense illumination, such as at the focus of a laser-scanning microscope, these SHG nanocrystals convert two photons into one photon of half the wavelength; thus, when imaged by conventional two-photon microscopy, SHG nanoprobes appear to generate a signal with an inverse Stokes shift like a fluorescent dye, but with a narrower emission. Unlike commonly used fluorescent probes, SHG nanoprobes neither bleach nor blink, and the signal they generate does not saturate with increasing illumination intensity. The resulting contrast and detectability of SHG nanoprobes provide unique advantages for molecular imaging of living cells and tissues.

Pantazis, Periklis; Maloney, James; Wu, David; Fraser, Scott E.

2010-01-01

105

Functional imaging of muscle cells by second harmonic generation  

NASA Astrophysics Data System (ADS)

The intrinsically ordered arrays of proteins (mainly actin and myosin) constituting the myofibrils within muscle cells are at the basis of a strong Second Harmonic Generation (SHG) from muscle fibers and isolated myofibrils. We have characterized the SHG signal with regard to its polarization and potential source within the muscle cell. The lateral resolution that can be achieved through SHG imaging of muscle strongly depends on sample depth. In fact, a comparison between intact muscle fibers and single myofibrils demonstrates that, whereas in both cases the alternation of dark I bands and bright A bands is visible, the contours of these bands are much better resolved in myofibrils than in fibers. Further, imaging of myofibrils revealed the presence of a darker zone in the centre of the A band. These effects of scattering by tissue on the image resolution were also studied with regard to the polarization of the SHG signal. The polarization-dependence of SHG intensity represents a powerful tool for the investigation of the structural dynamics occurring in the emitting proteins during the active cycle of muscle contraction. The prospective to perform functional studies requires a complete characterization of the effects of scattering and possibly multiple emitting populations on the measured SHG signal. Also, SHG is extremely sensitive to the degree of order present in the filament array, offering an interesting potential in the development of non-invasive tools for the diagnosis of degenerative diseases affecting skeletal muscles.

Nucciotti, Valentina; Sacconi, Leonardo; Linari, Marco; Lombardi, Vincenzo; Piazzesi, Gabriella; Piroddi, Nicoletta; Poggesi, Corrado; Tesi, Chiara; Vanzi, Francesco; Pavone, Francesco S.

2006-03-01

106

Methods for reverberation suppression utilizing dual frequency band imaging.  

PubMed

Reverberations impair the contrast resolution of diagnostic ultrasound images. Tissue harmonic imaging is a common method to reduce these artifacts, but does not remove all reverberations. Dual frequency band imaging (DBI), utilizing a low frequency pulse which manipulates propagation of the high frequency imaging pulse, has been proposed earlier for reverberation suppression. This article adds two different methods for reverberation suppression with DBI: the delay corrected subtraction (DCS) and the first order content weighting (FOCW) method. Both methods utilize the propagation delay of the imaging pulse of two transmissions with alternating manipulation pressure to extract information about its depth of first scattering. FOCW further utilizes this information to estimate the content of first order scattering in the received signal. Initial evaluation is presented where both methods are applied to simulated and in vivo data. Both methods yield visual and measurable substantial improvement in image contrast. Comparing DCS with FOCW, DCS produces sharper images and retains more details while FOCW achieves best suppression levels and, thus, highest image contrast. The measured improvement in contrast ranges from 8 to 27 dB for DCS and from 4 dB up to the dynamic range for FOCW. PMID:23967962

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

2013-09-01

107

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

108

Frequency-resolved optical-gating measurements of ultrashort pulses using surface third-harmonic generation  

Microsoft Academic Search

We demonstrate what is to our knowledge the first frequency-resolved optical gating (FROG) technique to measure ultrashort pulses from an unamplified Ti:sapphire laser oscillator without direction-of-time ambiguity. This technique utilizes surface third-harmonic generation as the nonlinear-optical effect and, surprisingly, is the most sensitive third-order FROG geometry yet. {copyright} {ital 1996 Optical Society of America.}

Thomas Tsang; M. A. Krumbuegel; Kenneth W. DeLong; David N. Fittinghoff; Rick Trebino

1996-01-01

109

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

110

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

Microsoft Academic Search

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

K. W. DeLong; Rick Trebino; J. Hunter; W. E. White

1994-01-01

111

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

NASA Technical Reports Server (NTRS)

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

Klimas, A. J.

1982-01-01

112

Speckle reduction of echographic images using higher order harmonic components  

Microsoft Academic Search

This paper proposes a novel speckle reduction technique using higher order harmonic components in echoes due to nonlinear propagation of finite amplitude ultrasonic waves. The probe of separation of transmission and reception transducer is used. Especially, the reception transducer is made of PVDF film of broadband characteristics. As a result of experiments with the probe, tenth orders of harmonic components

I. Akiyama; H. Yamamoto; G. Ohashi; A. Ohya

2003-01-01

113

Second harmonic generation imaging of endogenous structural proteins  

NASA Astrophysics Data System (ADS)

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 within unfixed, unstained thick specimens, including fish scales, C. elegans, and mouse muscle, where penetration into tissue upwards of 600 microns was achieved. The simultaneous use of SHG and two-photon excited GFP fluorescence allows for the inference of the molecular isoform that gives rise to SHG from the myofilament lattice in C. elegans. The physical origin of SHG within these tissues is addressed and is attributed to the laser interaction with dipolar protein structures. SHG polarization anisotropy is also used to determine the extent of dipolar order and radial symmetry in the helical structures. Comparisons are drawn between SHG and other forms of microscopy including polarization and fluorescence microscopy, highlighting the advantages and disadvantages.

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

2003-07-01

114

A Practical Guide to Harmonic Frequency Interference Affecting High-Voltage Power-Line Carrier Coupling Systems  

Microsoft Academic Search

Power-line carrier (PLC) systems have proven to be susceptible to interference caused by harmonics produced by loads, such as HVDC converters, DC electric arc furnaces, static var compensators, and motor speed controllers. Previous work in this area has provided information regarding the nature and origin of harmonic frequency interference affecting PLC systems as well as discussion of problem mitigation. However,

Gregory A. Franklin

2009-01-01

115

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

PubMed

A new method for measuring optical-beat frequencies in the terahertz (THz) region using microwave higher harmonics is presented. A microwave signal was applied to the antenna gap of a photoconductive (PC) device emitting a continuous electromagnetic wave at about 1 THz by the photomixing technique. The microwave higher harmonics with THz frequencies are generated in the PC device owing to the nonlinearity of the biased photoconductance, which is briefly described in this article. Thirteen nearly periodic peaks in the photocurrent were observed when the microwave was swept from 16 to 20 GHz at a power of -48 dBm. The nearly periodic peaks are generated by the homodyne detection of the optical beat with the microwave higher harmonics when the frequency of the harmonics coincides with the optical-beat frequency. Each peak frequency and its peak width were determined by fitting a Gaussian function, and the order of microwave harmonics was determined using a coarse (i.e., lower resolution) measurement of the optical-beat frequency. By applying the Kalman algorithm to the peak frequencies of the higher harmonics and their standard deviations, the optical-beat frequency near 1 THz was estimated to be 1029.81 GHz with the standard deviation of 0.82 GHz. The proposed method is applicable to a conventional THz-wave generator with a photomixer. PMID:21639489

Murasawa, Kengo; Sato, Koki; Hidaka, Takehiko

2011-05-01

116

Information-theoretic and Wigner function approaches to the nonclassical states dynamics for the variable frequency harmonic oscillator.  

National Technical Information Service (NTIS)

Coherent and squeezed states for the time-dependent frequency harmonic oscillator are analysed using Maximum Entropy Principle techniques. The information-theoretic procedure leads to results equivalent to that of the Wigner function formalism, although t...

J. Aliaga G. Crespo A. N. Proto

1992-01-01

117

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

118

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

2012-10-01

119

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

PubMed

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

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

2010-06-01

120

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

PubMed

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 TE(11,2) 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 TE(11,2,q). The minimum start current is 27 mA. Power and frequency tuning measurements as a function of the electron cyclotron frequency have also been carried out. A smooth frequency tuning range of 1 GHz was obtained for the operating second-harmonic mode either by magnetic field tuning or beam voltage tuning. Long-term CW operation was evaluated during an uninterrupted period of 48 h, where the gyrotron output power and frequency were kept stable to within ±0.7% and ±6 ppm, respectively, by a computerized control system. Proper operation of an internal quasi-optical mode converter implemented to transform the operating whispering-gallery mode to a Gaussian-like beam was also verified. Based on the images of the gyrotron output beam taken with a pyroelectric camera, the Gaussian-like mode content of the output beam was computed to be 92% with an ellipticity of 12%. PMID:21243088

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

2010-06-01

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.; Barnes, Alexander B.; Griffin, Robert G.

2011-01-01

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.; Griffin, Robert G.; Barnes, Alexander B.

2012-01-01

123

An autocorrelation model with place dependence to account for the effect of harmonic number on fundamental frequency discrimination  

PubMed Central

Fundamental frequency (f0) difference limens (DLs) were measured as a function of f0 for sine-and random-phase harmonic complexes, bandpass filtered with 3-dB cutoff frequencies of 2.5 and 3.5 kHz (low region) or 5 and 7 kHz (high region), and presented at an average 15 dB sensation level (approximately 48 dB SPL) per component in a wideband background noise. Fundamental frequencies ranged from 50 to 300 Hz and 100 to 600 Hz in the low and high spectral regions, respectively. In each spectral region, f0 DLs improved dramatically with increasing f0 as approximately the tenth harmonic appeared in the passband. Generally, f0 DLs for complexes with similar harmonic numbers were similar in the two spectral regions. The dependence of f0 discrimination on harmonic number presents a significant challenge to autocorrelation (AC) models of pitch, in which predictions generally depend more on spectral region than harmonic number. A modification involving a “lag window” is proposed and tested, restricting the AC representation to a limited range of lags relative to each channel's characteristic frequency. This modified unitary pitch model was able to account for the dependence of f0 DLs on harmonic number, although this correct behavior was not based on peripheral harmonic resolvability.

Bernstein, Joshua G. W.; Oxenham, Andrew J.

2005-01-01

124

A Method for Improving Signal-to-Noise Ratio of Tissue Harmonic Imaging Based on Bayesian Inference Using Information of Fundamental Echoes  

NASA Astrophysics Data System (ADS)

A medical ultrasound imaging technique with a high spatial resolution and a high signal-to-noise ratio (SNR) is strongly required for precise diagnosis. To obtain high-resolution images, tissue harmonic imaging (THI) can be effectively adopted because of its wide bandwidth characteristics compared with fundamental imaging. However, the amplitude of harmonic components is much smaller than that of a fundamental component. Additionally, frequency dependent attenuation is severe, especially for harmonic components. These phenomena mean that THI is susceptible to noise. From these considerations, in this study, we propose a method for improving the SNR of THI by reducing noise using a signal processing technique. The proposed method is constructed based on the Bayesian inference using fundamental components of echoes, and it can hold the high-resolution nature of THI. We show the effectiveness of the proposed method through simulations.

Yamamura, Takuya; Tanabe, Masayuki; Okubo, Kan; Tagawa, Norio

2012-07-01

125

Infrared-pumped third-harmonic and sum-frequency generation in diatomic molecules  

NASA Technical Reports Server (NTRS)

Using molecular hydrogen as a model system, we present a calculation which demonstrates the feasibility of efficient third-harmonic and sum-frequency generation of IR laser radiation by diatomic molecular gases. A conversion efficiency of 10% without phase matching is achievable with a modest laser intensity of about 20 MW/sq cm. In addition to a two-photon resonance, the efficient conversion depends on a mechanism which makes use of virtual vibronic transitions exclusively. Possible methods for phase matching are also suggested.

She, C. Y.; Billman, K. W.

1975-01-01

126

A piezoelectric pulse generator for low frequency non-harmonic vibration  

NASA Astrophysics Data System (ADS)

This paper reports a new piezoelectric prototype for pulse generation by energy harvesting from low frequency non-harmonic vibration. The pulse generator presented here consists of two parts: the electromechanical part and the load circuit. A metal rolling rod is used as the proof mass, moving along the substrate to achieve both actuating of the piezoelectric cantilever by magnetic coupling and self-synchronous switching of the circuit. By using this new approach, the energy from the piezoelectric transduction mechanism is regulated simultaneously when it is extracted. This allows a series of tuneable pulses to be generated, which can be applied to self-powered RF wireless sensor network (WSN) nodes.

Jiang, Hao; Yeatman, Eric M.

2013-12-01

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

Molecular Expressions: Digital Image Sampling Frequency  

NSDL National Science Digital Library

This item is an interactive Java simulation relating to digital imaging with optical microscopes. The "sampling interval" is the spatial resolution of a digital image, as determined by the distance between pixels. Analog signals must be digitized at an appropriate sampling frequency to produce acceptable image resolution. This simulation allows users to explore how variations in the sampling frequency affect the final image. This item is part of a larger collection of materials on optics and microscopy developed by the National High Magnetic Field Laboratory and Florida State University.

Davidson, Michael; Spring, Kenneth R.; Parry-Hill, Matthew J.; Russ, John C.

2008-08-16

129

Sources of image degradation in fundamental and harmonic ultrasound imaging using nonlinear, full-wave simulations.  

PubMed

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-andsum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is reverberation from near-field structures. Reverberation clutter in the harmonic PSF is 26 dB higher than the fundamental PSF. An artificial medium with uniform velocity but unchanged impedance characteristics indicates that for the fundamental PSF, the primary source of degradation is phase aberration. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beamforming algorithm to generate images. These beamformed images are compared with images obtained from convolution of the PSF with a scatterer field to demonstrate that a very large portion of the PSF must be used to accurately represent the clutter observed in conventional imaging. PMID:21507753

Pinton, Gianmarco F; Trahey, Gregg E; Dahl, Jeremy J

2011-04-01

130

HF pump-induced E-region irregularities: is there a gyro-harmonic frequency dependence ?  

NASA Astrophysics Data System (ADS)

E-region irregularities of 1-m scale length can be produced by high power O-mode HF transmissions, as shown by observations using the STARE (Scandinavian Twin Auroral Radar Experiment) 140 MHz coherent radars. The current understanding of the generation of these density irregularities by HF-heating lies within the frame-work of excitation of the thermal resonance instability at the upper hybrid level, like the irregularities generated in F region. In the F region the production of such decameter-scale irregularities shows a minimum when the HF pump frequency is close to a harmonic of the electron gyro-frequency. The natural question arises whether this is also true for the meter-scale irregularities in the E region. To answer this, HF-pumping experiments have been performed while monitoring the backscatter intensity from the Malvik (Norway) radar in near real-time. Results from these experiments will be presented.

Rietveld, M. T.; Nielsen, E.; Bruns, M.; Schmidt, W.

131

Lifshitz singularities in random harmonic chains: periodic amplitudes near the band edge and near special frequencies  

SciTech Connect

The authors give a complete description of the scaling behavior of the integrated density of states of random harmonic chains with random masses near the band edge omega/sub max/ and near special frequencies omega/sub s/. There are four different situations: omega upward arrow omega/sub max/, omega upward arrow omega/sub s/, omega upward arrow omega/sub s/ (critical case), omega upward arrow omega/sub s/ (general case). Their analytic results have the form of infinite sums involving Fourier coefficients of the scaling behavior of the Dyson-Schmidt function at the special frequency or the band edge. Binary mass distributions are considered in detail in the limit of a small fraction rho of light masses. Their predictions are compared with extensive numerical data.

Nieuwenhuizen, T.M.; Luck, J.M.

1987-08-01

132

Complex-conjugate-resolved imaging using two-harmonic FD-OCT  

NASA Astrophysics Data System (ADS)

The two-harmonic FD-OCT method, where the quadrature components of the spectral interferogram are obtained by simultaneous acquisition of the first and second harmonics of the phase-modulated interferogram, is used for complex-conjugate- resolved imaging of biological samples. The method is implemented using sampling of the phase modulated interferogram with an integrating detector array followed by digital demodulation at the first and second harmonics. A complex conjugate rejection ratio as high as 70 dB is achieved.

Vakhtin, Andrei B.; Peterson, Kristen A.; Kane, Daniel J.

2007-03-01

133

Higher harmonic atomic force microscopy: imaging of biological membranes in liquid.  

PubMed

The contribution of higher harmonics to the movement of a dynamic force microscope cantilever interacting with a sample in liquid was investigated. The amplitude of the second harmonic has been found to be an order of magnitude higher in liquid than in air, reflecting an increased sensitivity to local variations in elasticity and interaction geometries. A theoretical model of the tip-sample interactions in liquid was introduced and shown to be consistent with experimental findings. Second harmonic amplitude images were recorded on soft biological samples yielding a lateral resolution of approximately 0.5 nm. PMID:17678377

Preiner, Johannes; Tang, Jilin; Pastushenko, Vasilli; Hinterdorfer, Peter

2007-07-27

134

ISAR Imaging via Sparse Probing Frequencies  

Microsoft Academic Search

Based on compressive sampling theory, a novel method for high-resolution inverse synthetic aperture radar (ISAR) imaging is presented in this letter by transmitting sparse probing frequencies. In this method, only a few measurements in the range frequency and cross-range time domains are needed to reconstruct the target scene by solving an inverse problem through either a linear program or a

Hongxian Wang; Yinghui Quan; Mengdao Xing; Shouhong Zhang

2011-01-01

135

MREIT conductivity imaging based on the local harmonic Bz algorithm: Animal experiments  

NASA Astrophysics Data System (ADS)

From numerous numerical and phantom experiments, MREIT conductivity imaging based on harmonic Bz algorithm shows that it could be yet another useful medical imaging modality. However, in animal experiments, the conventional harmonic Bz algorithm gives poor results near boundaries of problematic regions such as bones, lungs, and gas-filled stomach, and the subject boundary where electrodes are not attached. Since the amount of injected current is low enough for the safety for in vivo animal, the measured Bz data is defected by severe noise. In order to handle such problems, we use the recently developed local harmonic Bz algorithm to obtain conductivity images in our ROI(region of interest) without concerning the defected regions. Furthermore we adopt a denoising algorithm that preserves the ramp structure of Bz data, which informs of the location and size of anomaly. Incorporating these efficient techniques, we provide the conductivity imaging of post-mortem and in vivo animal experiments with high spatial resolution.

Jeon, Kiwan; Lee, Chang-Ock; Woo, Eung Je; Kim, Hyung Joong; Seo, Jin Keun

2010-04-01

136

Optical frequency comb generation based on electro-optical modulation with high-order harmonic of a sine RF signal  

NASA Astrophysics Data System (ADS)

By using cascaded intensity and phase modulators, optical frequency comb (OFC) is generated. In the OFC generation scheme, high-order harmonic of a RF signal is used for driving intensity modulator (IM) or phase modulator (PM). Experimental and theoretical results indicate when IM is driven by high-order harmonic, lower RF driving power for PM is required to generate an OFC with the best flatness.

Wei, Renjie; Yan, JuanJuan; Peng, Yichao; Yao, Xiayuan; Bai, Ming; Zheng, Zheng

2013-03-01

137

Measurement of the Intensity-Dependent Atomic Dipole Phase of a High Harmonic by Frequency-Resolved Optical Gating  

Microsoft Academic Search

The temporal profile and phase of the fifth harmonic of a Ti:sapphire laser were fully characterized by two-photon ionization frequency-resolved optical gating technique for the first time. The fifth harmonic was found to have negative chirp and the pulse compression was demonstrated. The negative chirp is well explained by using a zero-range potential model. This technique is scalable to extreme

Taro Sekikawa; Tomotaka Katsura; Satoshi Miura; Shuntaro Watanabe

2002-01-01

138

Improved Harmonic Phase (HARP) Method for Motion Tracking a Tagged Cardiac MR images  

Microsoft Academic Search

The diagnosis of cardiovascular disease requires precise assessment of both morphology and function of the heart. Currently, magnetic resonance imaging (MRI) provides a useful tool for accurate and reproducible assessment of regional function of the left ventricle noninvasively. MR tagging produces images of the heart that can be analyzed using harmonic phase (HARP) method to describe the regional function of

Ayman M. Khalifa; A. B. M. Youssef; Nael F. Osman

2005-01-01

139

Cell tracking in live Caenorhabditis elegans embryos via third harmonic generation imaging microscopy measurements  

Microsoft Academic Search

In this study, we demonstrate the potential of employing third harmonic generation (THG) imaging microscopy measurements for cell tracking studies in live Caenorhabditis elegans (C. elegans) embryos. A 1028-nm femtosecond laser was used for the excitation of unstained C. elegans samples. Different C. elegans embryonic stages (from two-cell to threefold) were imaged. Live biological specimens were irradiated for prolonged periods

George J. Tserevelakis; George Filippidis; Evgenia V. Megalou; Costas Fotakis; Nektarios Tavernarakis

2011-01-01

140

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

141

A preliminary engineering design of intravascular dual-frequency transducers for contrast-enhanced acoustic angiography and molecular imaging.  

PubMed

Current intravascular ultrasound (IVUS) probes are not optimized for contrast detection because of their design for high-frequency fundamental-mode imaging. However, data from transcutaneous contrast imaging suggests the possibility of utilizing contrast ultrasound for molecular imaging or vasa vasorum assessment to further elucidate atherosclerotic plaque deposition. This paper presents the design, fabrication, and characterization of a small-aperture (0.6 × 3 mm) IVUS probe optimized for high-frequency contrast imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz) transducer arrangement for exciting microbubbles at low frequencies (near their resonance) and detecting their broadband harmonics at high frequencies, minimizing detected tissue backscatter. The prototype probe is able to generate nonlinear microbubble response with more than 1.2 MPa of rarefractional pressure (mechanical index: 0.48) at 6.5 MHz, and is also able to detect microbubble response with a broadband receiving element (center frequency: 30 MHz, ¿6-dB fractional bandwidth: 58.6%). Nonlinear super-harmonics from microbubbles flowing through a 200-¿m-diameter micro-tube were clearly detected with a signal-to-noise ratio higher than 12 dB. Preliminary phantom imaging at the fundamental frequency (30 MHz) and dual-frequency super-harmonic imaging results suggest the promise of small aperture, dual-frequency IVUS transducers for contrast-enhanced IVUS imaging. PMID:24801226

Ma, Jianguo; Martin, K; Dayton, Paul; Jiang, Xiaoning

2014-05-01

142

A Preliminary Engineering Design of Intravascular Dual-Frequency Transducers for Contrast-Enhanced Acoustic Angiography and Molecular Imaging  

PubMed Central

Current intravascular ultrasound (IVUS) probes are not optimized for contrast detection because of their design for high-frequency fundamental-mode imaging. However, data from transcutaneous contrast imaging suggests the possibility of utilizing contrast ultrasound for molecular imaging or vasa vasorum assessment to further elucidate atherosclerotic plaque deposition. This paper presents the design, fabrication, and characterization of a small-aperture (0.6 × 3 mm) IVUS probe optimized for high-frequency contrast imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz) transducer arrangement for exciting microbubbles at low frequencies (near their resonance) and detecting their broadband harmonics at high frequencies, minimizing detected tissue backscatter. The prototype probe is able to generate nonlinear microbubble response with more than 1.2 MPa of rarefractional pressure (mechanical index: 0.48) at 6.5 MHz, and is also able to detect microbubble response with a broadband receiving element (center frequency: 30 MHz, ?6-dB fractional bandwidth: 58.6%). Nonlinear super-harmonics from microbubbles flowing through a 200-?m-diameter micro-tube were clearly detected with a signal-to-noise ratio higher than 12 dB. Preliminary phantom imaging at the fundamental frequency (30 MHz) and dual-frequency super-harmonic imaging results suggest the promise of small aperture, dual-frequency IVUS transducers for contrast-enhanced IVUS imaging.

Ma, Jianguo; Martin, K. Heath; Dayton, Paul A.; Jiang, Xiaoning

2014-01-01

143

Two-Dimensional Polar Harmonic Transforms for Invariant Image Representation  

Microsoft Academic Search

This paper introduces a set of 2D transforms, based on a set of orthogonal projection bases, to generate a set of features which are invariant to rotation. We call these transforms Polar Harmonic Transforms (PHTs). Unlike the well-known Zernike and pseudo-Zernike moments, the kernel computation of PHTs is extremely simple and has no numerical stability issue whatsoever. This implies that

Pew-Thian Yap; Xudong Jiang; Alex ChiChung Kot

2010-01-01

144

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

PubMed

Dual-band (DB) harmonic imaging is performed by transmitting and receiving at both fundamental band (f0) and second-harmonic band (2f0). In our previous work, particular chirp excitation has been developed to increase the signal- to-noise ratio in DB harmonic imaging. However, spectral overlap between the second-order DB harmonic signals results in range side lobes in the pulse compression. In this study, a novel range side lobe inversion (RSI) method is developed to alleviate the level of range side lobes from spectral overlap. The method is implemented by firing an auxiliary chirp to change the polarity of the range side lobes so that the range side lobes can be suppressed in the combination of the original chirp and the auxiliary chirp. Hydrophone measurements show that the RSI method reduces the range side lobe level (RSLL) and thus increases the quality of pulse compression in DB harmonic imaging. With the signal bandwidth of 60%, the RSLL decreases from -23 dB to -36 dB and the corresponding compression quality improves from 78% to 94%. B-mode images also indicate that the magnitude of range side lobe is suppressed by 7 dB when the RSI method is applied. PMID:24474143

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

2014-02-01

145

Enhanced Higher Harmonic Imaging of Heterogeneities and Local Plastic Deformation in Steel Plates  

NASA Astrophysics Data System (ADS)

Conventional ultrasonic imaging based on the difference in acoustic impedance fails to detect and visualize small heterogeneities and local plastic deformation in metals. Nonlinear ultrasonic imaging technique visualizes higher harmonic amplitudes which are generated at the heterogeneities by finite amplitude sinusoidal burst waves, therefore, it can be applied for detecting small non-metallic inclusions, local plastic deformation and micro cracks. By transmitting 35 MHz sine burst waves and receiving harmonics of 105 MHz in the maximum, non-metallic inclusions in stainless steel of some ten in size and crack tip plastic zone of 2 mm in diameter are visualized.

Kawashima, K.; Imanishi, R.; Aida, T.; Zhou, Y.

2014-06-01

146

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

PubMed

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. PMID:24156065

Rivard, Maxime; Couture, Charles-André; Miri, Amir K; Laliberté, Mathieu; Bertrand-Grenier, Antony; Mongeau, Luc; Légaré, François

2013-01-01

147

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

148

Performance comparison of five frequency domain system identification techniques for helicopter higher harmonic control  

NASA Technical Reports Server (NTRS)

This paper presents the results of a computer simulation comparing the performance of five system identification techniques currently proposed for use with helicopter, frequency domain, higher harmonic vibration control algorithms. The system identification techniques studied were: (1) the weighted least squares method in moving block format, (2) the classical Kalman filter, (3) a generalized Kalman filter, (4) the classical least mean square (LMS) filter, and (5) a generalized LMS filter. The generalized Kalman and LMS filters were derived by allowing for multistep operation, rather than the single-step update approach used by their classical versions. Both open-loop and closed-loop (vibration control mode) identification results are presented in the paper. The algorithms are evaluated in terms of their accuracy, stability, convergence properties, computation speeds, and the relative ease with which these techniques may be directly applied to the helicopter vibration control problem.

Jacklin, Stephen A.

1988-01-01

149

Diffeomorphic Image Registration of Diffusion MRI Using Spherical Harmonics  

Microsoft Academic Search

Nonrigid registration of diffusion magnetic resonance imaging (MRI) is crucial for group analyses and building white matter and fiber tract atlases. Most current diffusion MRI regis- tration techniques are limited to the alignment of diffusion tensor imaging(DTI)data.Weproposeanoveldiffeomorphicregistration method for high angular resolution diffusion images by mapping their orientation distribution functions (ODFs). ODFs can be reconstructed using q-ball imaging (QBI) techniques

Xiujuan Geng; Thomas J. Ross; Hong Gu; Wanyong Shin; Wang Zhan; Yi-Ping Chao; Ching-Po Lin; Norbert Schuff; Yihong Yang

2011-01-01

150

Integration of the denoising, inpainting and local harmonic Bz algorithm for MREIT imaging of intact animals  

NASA Astrophysics Data System (ADS)

Conductivity imaging based on the current-injection MRI technique has been developed in magnetic resonance electrical impedance tomography. Current injected through a pair of surface electrodes induces a magnetic flux density distribution inside an imaging object, which results in additional magnetic field inhomogeneity. We can extract phase changes related to the current injection and obtain an image of the induced magnetic flux density. Without rotating the object inside the bore, we can measure only one component Bz of the magnetic flux density B = (Bx, By, Bz). Based on a relation between the internal conductivity distribution and Bz data subject to multiple current injections, one may reconstruct cross-sectional conductivity images. As the image reconstruction algorithm, we have been using the harmonic Bz algorithm in numerous experimental studies. Performing conductivity imaging of intact animal and human subjects, we found technical difficulties that originated from the MR signal void phenomena in the local regions of bones, lungs and gas-filled tubular organs. Measured Bz data inside such a problematic region contain an excessive amount of noise that deteriorates the conductivity image quality. In order to alleviate this technical problem, we applied hybrid methods incorporating ramp-preserving denoising, harmonic inpainting with isotropic diffusion and ROI imaging using the local harmonic Bz algorithm. These methods allow us to produce conductivity images of intact animals with best achievable quality. We suggest guidelines to choose a hybrid method depending on the overall noise level and existence of distinct problematic regions of MR signal void.

Jeon, Kiwan; Kim, Hyung Joong; Lee, Chang-Ock; Seo, Jin Keun; Woo, Eung Je

2010-12-01

151

Effects of Dual Apodization With Cross-Correlation on Tissue Harmonic and Pulse Inversion Harmonic Imaging in the Presence of Phase Aberration  

PubMed Central

Dual apodization with cross-correlation (DAX) is a relatively new beamforming technique which can suppress side lobes and clutter to enhance ultrasound image contrast. However, previous studies have shown that with increasing aberrator strength, contrast enhancements with DAX diminish and DAX becomes more prone to image artifacts. In this paper, we propose integrating DAX with tissue harmonic imaging (THI) or pulse inversion harmonic imaging (PIHI) to overcome their shortcomings and achieve higher image contrast. Compared with conventional imaging, our experimental results showed that DAX with THI allows for synergistic enhancements of image contrast with improvements of more than 231% for a 5-mm pork aberrator and 703% for a 12-mm pork aberrator. With PIHI, improvements of 238% and 890% were observed for the two pork tissue samples. Our results suggest that the complementary contrast enhancement mechanism employed by the proposed method may be useful in improving imaging of technically difficult patients in clinics.

Shin, Junseob; Yen, Jesse T.

2013-01-01

152

Effects of dual apodization with cross-correlation on tissue harmonic and pulse inversion harmonic imaging in the presence of phase aberration.  

PubMed

Dual apodization with cross-correlation (DAX) is a relatively new beamforming technique which can suppress side lobes and clutter to enhance ultrasound image contrast. However, previous studies have shown that with increasing aberrator strength, contrast enhancements with DAX diminish and DAX becomes more prone to image artifacts. In this paper, we propose integrating DAX with tissue harmonic imaging (THI) or pulse inversion harmonic imaging (PIHI) to overcome their shortcomings and achieve higher image contrast. Compared with conventional imaging, our experimental results showed that DAX with THI allows for synergistic enhancements of image contrast with improvements of more than 231% for a 5-mm pork aberrator and 703% for a 12-mm pork aberrator. With PIHI, improvements of 238% and 890% were observed for the two pork tissue samples. Our results suggest that the complementary contrast enhancement mechanism employed by the proposed method may be useful in improving imaging of technically difficult patients in clinics. PMID:23475931

Shin, Junseob; Yen, Jesse T

2013-03-01

153

Two-dimensional polar harmonic transforms for invariant image representation.  

PubMed

This paper introduces a set of 2D transforms, based on a set of orthogonal projection bases, to generate a set of features which are invariant to rotation. We call these transforms Polar Harmonic Transforms (PHTs). Unlike the well-known Zernike and pseudo-Zernike moments, the kernel computation of PHTs is extremely simple and has no numerical stability issue whatsoever. This implies that PHTs encompass the orthogonality and invariance advantages of Zernike and pseudo-Zernike moments, but are free from their inherent limitations. This also means that PHTs are well suited for application where maximal discriminant information is needed. Furthermore, PHTs make available a large set of features for further feature selection in the process of seeking for the best discriminative or representative features for a particular application. PMID:20489228

Yap, Pew-Thian; Jiang, Xudong; Kot, Alex Chichung

2010-07-01

154

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

Microsoft Academic Search

The feasibility of the Harmonic Motion Imaging (HMI) technique for simultaneous monitoring and generation of focused ultrasound therapy using two separate focused ultrasound transducer elements has previously been shown. In this study, a new HMI technique is described that images tissue displacement induced by a harmonic radiation force induced using a single focused ultrasound element. First, wave propagation simulation models

Caroline Maleke; Mathieu Pernot; Elisa Konofagou

2006-01-01

155

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

NASA Astrophysics Data System (ADS)

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

Maleke, Caroline; Pernot, Mathieu; Konofagou, Elisa

2006-05-01

156

Frequency up-conversion of quantum images.  

PubMed

We develop the theory of frequency up-conversion of an arbitrary spatially-broadband quantum state (quantum image), deriving the analytical solutions for the cases of plane-wave pump and short crystal with arbitrary pump. By using an example of the quantum image imposed by the orbital angular momentum of the pump beam in spontaneous parametric down-conversion, we show that 99%-fidelity up-conversion of quantum images from an infrared wavelength to the visible wavelength can be obtained in periodically-poled lithium-niobate crystals at reasonable pump intensities well below the crystal damage threshold. PMID:22418548

Vasilyev, Michael; Kumar, Prem

2012-03-12

157

Second harmonic generation imaging of fascia within thick tissue block  

NASA Astrophysics Data System (ADS)

Comparing the SHG image formation for thin sections of tail tendon fascia and skeletal muscle fascia, we demonstrate that the forward (F) and backward (B) SHG images are vastly different. In addition, despite the different arrangement of the collagen Type I fibrillar architecture forming these two fascias, their ratios of forward over backward signal (F/B) are nearly equal. SHG images of thick tissue blocks of the fascia-muscle unit show only backward features, as opposed to SHG images of tissue blocks of the fascia-tendon unit. These images are an amalgamation of forward and backward features due to the backscattering of forward components within tendon. These forward features disappear when this tissue block is immersed in glycerol as backscattering is hereby suppressed.

Pfeffer, Christian P.; Olsen, Bjorn R.; Légaré, François

2007-06-01

158

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

159

A dual frequencies MMW holographic imaging system  

Microsoft Academic Search

A new MMW holographic system using dual frequencies for not only imaging hologram but also measuring distance automatically between a certain object and the system aperture is presented. Concretely, the scheme for the transmitter and receiver about it and the relative simulation are made, which show that for an object at an arbitrary distance to some extent the system presented

Zhenxin Caoa; Wenbin Doua; Hongyan Su

2009-01-01

160

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

2013-08-15

161

Harmonic analysis of irradiation asymmetry for cylindrical implosions driven by high-frequency rotating ion beams.  

PubMed

Cylindrical implosions driven by intense heavy ion beams should be instrumental in the near future for study of high-energy-density matter. By rotating the beam by means of a high-frequency wobbler, it should be possible to deposit energy in the outer layers of a cylinder, compressing the material deposited in its core. The beam's temporal profile should, however, generate an inevitable irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI) during the implosion phase. In this paper, we compute the Fourier components of the target irradiation in order to make the connection with previous works on the RTI performed in this setting. Implementing one- and two-dimensional beam models, we find that these components can be expressed exactly in terms of the Fourier transform of the temporal beam profile. If T is the beam duration and ? its rotation frequency, "magic products" ?T can be identified which cancel the first harmonic of the deposited density, resulting in an improved irradiation symmetry. PMID:22587191

Bret, A; Piriz, A R; Tahir, N

2012-03-01

162

Harmonic analysis of irradiation asymmetry for cylindrical implosions driven by high-frequency rotating ion beams  

NASA Astrophysics Data System (ADS)

Cylindrical implosions driven by intense heavy ion beams should be instrumental in the near future for study of high-energy-density matter. By rotating the beam by means of a high-frequency wobbler, it should be possible to deposit energy in the outer layers of a cylinder, compressing the material deposited in its core. The beam's temporal profile should, however, generate an inevitable irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI) during the implosion phase. In this paper, we compute the Fourier components of the target irradiation in order to make the connection with previous works on the RTI performed in this setting. Implementing one- and two-dimensional beam models, we find that these components can be expressed exactly in terms of the Fourier transform of the temporal beam profile. If T is the beam duration and ? its rotation frequency, “magic products” ?T can be identified which cancel the first harmonic of the deposited density, resulting in an improved irradiation symmetry.

Bret, A.; Piriz, A. R.; Tahir, N.

2012-03-01

163

Sources of image degradation in fundamental and harmonic ultrasound imaging: a nonlinear, full-wave, simulation study.  

PubMed

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain. This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSFs) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared with fundamental imaging, reverberation clutter in harmonic imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for harmonic imaging, the primary source of degradation is phase aberration. PMID:21693410

Pinton, Gianmarco F; Trahey, Gregg E; Dahl, Jeremy J

2011-06-01

164

Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330GHz Gyrotron for Dynamic Nuclear Polarization  

Microsoft Academic Search

The design and the operation of a frequency-tunable continuous-wave (CW) 330-GHz gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency are reported. The gyrotron has generated 18 W of power from a 10.1-kV 190-mA electron beam working in a TE?4,3 cylindrical mode, corresponding to an efficiency of 0.9%. The measured start oscillation current over a range of

Antonio C. Torrezan; Michael A. Shapiro; Jagadishwar R. Sirigiri; Richard J. Temkin; Robert G. Griffin

2011-01-01

165

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

PubMed Central

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

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

2002-01-01

166

Second-harmonic generation and fluorescence lifetime imaging microscopy through a rodent mammary imaging window  

NASA Astrophysics Data System (ADS)

Tumor-Associated Collagen Signatures (TACS) have been identified that manifest in specific ways during breast tumor progression and that correspond to patient outcome. There are also compelling metabolic changes associated with carcinoma invasion and progression. We have characterized the difference in the autofluorescent properties of metabolic co-factors, NADH and FAD, between normal and carcinoma breast cell lines. Also, we have shown in vitro that increased collagen density alters metabolic genes which are associated with glycolysis and leads to a more invasive phenotype. Establishing the relationship between collagen density, cellular metabolism, and metastasis in physiologically relevant cancer models is crucial for developing cancer therapies. To study cellular metabolism with respect to collagen density in vivo, we use multiphoton fluorescence excitation microscopy (MPM) in conjunction with a rodent mammary imaging window implanted in defined mouse cancer models. These models are ideal for the study of collagen changes in vivo, allowing determination of corresponding metabolic changes in breast cancer invasion and progression. To measure cellular metabolism, we collect fluorescence lifetime (FLIM) signatures of NADH and FAD, which are known to change based on the microenvironment of the cells. Additionally, MPM systems are capable of collecting second harmonic generation (SHG) signals which are a nonlinear optical property of collagen. Therefore, MPM, SHG, and FLIM are powerful tools with great potential for characterizing key features of breast carcinoma in vivo. Below we present the current efforts of our collaborative group to develop intravital approaches based on these imaging techniques to look at defined mouse mammary models.

Young, Pamela A.; Nazir, Muhammad; Szulczewski, Michael J.; Keely, Patricia J.; Eliceiri, Kevin W.

2012-02-01

167

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

PubMed Central

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

2012-01-01

168

Determination of the Expanded Optical Transfer Function in Saturated Excitation Imaging and High Harmonic Demodulation  

NASA Astrophysics Data System (ADS)

Most limits of a microscope can be understood in terms of its spatial frequency mapping ability, known as the optical transfer function (OTF). Here, we demonstrate the expansion of the confocal fluorescence microscopy OTF under conditions where the population of excitation states of the sample is saturated. We show how the OTF of saturated excitation can be determined by estimating fluorescence signals using a five-level molecular electronic state model. We then show how modulating excitation and demodulating fluorescence signals can extract high frequency components. We provide experimental validation by demonstrating that harmonic demodulation can extract high frequency OTF components.

Kawano, Shogo; Smith, Nicholas I.; Yamanaka, Masahito; Kawata, Satoshi; Fujita, Katsumasa

2011-04-01

169

A Theoretical Analysis of the Harmonic Content of PWM Waveforms for Multiple-Frequency Modulators  

Microsoft Academic Search

This paper theoretically identifies the harmonic components of a carrier-based pulsewidth-modulated (PWM) voltage-source converter (VSC) output voltage when the modulating wave includes fundamental and baseband harmonic components. This occurs, for example, when a VSC is used as an active power filter. The general analytical solution provided can be applied with a minimum additional mathematical effort to any harmonic combination in

Milijana Odavic; Mark Sumner; Pericle Zanchetta; Jon C. Clare

2010-01-01

170

Harmonic generation and parametric decay in the ion cyclotron frequency range  

SciTech Connect

Harmonic generation and parametric decay are examined in a toroidal ACT-I plasma using electrostatic plate antennas. The harmonic generation, which is consistent with sheath rectification, is sufficiently strong that the nonlinearly generated harmonic modes themselves decay parametrically. Resonant and nonresonant parametric decay of the second harmonic are observed and compared with uniform pump theory. Resonant decay of lower hybrid waves into lower hybrid waves and slow ion cyclotron waves is seen for the first time. Surprisingly, the decay processes are nonlinearly saturated, indicating absolute instability.

Skiff, F.N.; Wong, K.L.; Ono, M.

1984-06-01

171

Generation of higher-order harmonics upon the addition of high-frequency XUV radiation to IR radiation: Generalization of the three-step model  

NASA Astrophysics Data System (ADS)

The irradiation of atoms by a strong, quasicontinuous IR laser field of frequency ? results in the emission of odd harmonics of ? (“IR harmonics”), by high-harmonic generation. It has been recently shown [A. Fleischer and N. Moiseyev, Phys. Rev. A 77, 010102(R) (2008)] that the addition of a weak XUV field of harmonic frequency q? to the IR driver field leads to the appearance of a new set of higher-order harmonics (“XUV harmonics”) q±2K ( q,K integers) which were absent in the spectra in the presence of the IR field alone. Here we generalize these results by studying the generation of XUV harmonics upon the addition of an arbitrary high-frequency XUV field qtilde ? , with frequency not necessarily a harmonic of ? , and amplitude ? qtilde in , which might be large. We have found that as the intensity of the XUV field increases, higher sets of XUV harmonics qtilde ±2K,2 qtilde ±(2K-1),3 qtilde ±2K,… . gradually appear, where each XUV harmonics set n qtilde qtilde ±[2K-1+mod(n qtilde ,2)] (n qtilde =1,2,3,…) is ((? qtilde in)/( qtilde 2?2))2n qtilde times weaker than the set of IR harmonics. The mechanism responsible for the appearance of the XUV harmonics is analyzed analytically using a generalization of the semiclassical recollision (three-step) model of high-harmonic generation (HHG). It is shown that the emitted HHG radiation field can be written as a series of terms, with the zeroth-order term representing the three-step recollision mechanism in its most familiar context [P. B. Corkum, Phys. Rev. Lett. 71, 1994 (1993)] and giving rise to IR harmonics in the spectra. The higher-order terms, which are responsible for the appearance of the new sets of XUV harmonics in the spectra, are shown to originate from the polarization (ac-Stark oscillations) which is induced by the XUV field on the returning electronic wave packet in the recollision process. The XUV harmonics are formed by the same electron trajectories which form the IR harmonics and have the same emission times as the IR harmonics. Due to the small quiver amplitude of the ac-Stark oscillation, they are, however, much weaker than the IR harmonics. Nevertheless, this mechanism allows an extension of the cutoff in the harmonic generation spectra without the necessity of increasing the IR field intensity, as is verified numerically by a quantum-mechanical simulation of a Xe atom irradiated by a combination of IR and XUV classical fields.

Fleischer, Avner

2008-11-01

172

Simultaneous stimulated Raman scattering and higher harmonic generation imaging for liver disease diagnosis without labeling  

NASA Astrophysics Data System (ADS)

Nonlinear optical microscopy (e.g., higher harmonic (second-/third- harmonic) generation (HHG), simulated Raman scattering (SRS)) has high diagnostic sensitivity and chemical specificity, making it a promising tool for label-free tissue and cell imaging. In this work, we report a development of a simultaneous SRS and HHG imaging technique for characterization of liver disease in a bile-duct-ligation rat-modal. HHG visualizes collagens formation and reveals the cell morphologic changes associated with liver fibrosis; whereas SRS identifies the distributions of hepatic fat cells formed in steatosis liver tissue. This work shows that the co-registration of SRS and HHG images can be an effective means for label-free diagnosis and characterization of liver steatosis/fibrosis at the cellular and molecular levels.

Lin, Jian; Wang, Zi; Zheng, Wei; Huang, Zhiwei

2014-02-01

173

Submillisecond second harmonic holographic imaging of biological specimens in three dimensions  

PubMed Central

Optical microscopy has played a critical role for discovery in biomedical sciences since Hooke’s introduction of the compound microscope. Recent years have witnessed explosive growth in optical microscopy tools and techniques. Information in microscopy is garnered through contrast mechanisms, usually absorption, scattering, or phase shifts introduced by spatial structure in the sample. The emergence of nonlinear optical contrast mechanisms reveals new information from biological specimens. However, the intensity dependence of nonlinear interactions leads to weak signals, preventing the observation of high-speed dynamics in the 3D context of biological samples. Here, we show that for second harmonic generation imaging, we can increase the 3D volume imaging speed from sub-Hertz speeds to rates in excess of 1,500 volumes imaged per second. This transformational capability is possible by exploiting coherent scattering of second harmonic light from an entire specimen volume, enabling new observational capabilities in biological systems.

Smith, David R.; Winters, David G.; Bartels, Randy A.

2013-01-01

174

Invited Review Article: Imaging techniques for harmonic and multiphoton absorption fluorescence microscopy  

PubMed Central

We review the current state of multiphoton microscopy. In particular, the requirements and limitations associated with high-speed multiphoton imaging are considered. A description of the different scanning technologies such as line scan, multifoci approaches, multidepth microscopy, and novel detection techniques is given. The main nonlinear optical contrast mechanisms employed in microscopy are reviewed, namely, multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation. Techniques for optimizing these nonlinear mechanisms through a careful measurement of the spatial and temporal characteristics of the focal volume are discussed, and a brief summary of photobleaching effects is provided. Finally, we consider three new applications of multiphoton microscopy: nonlinear imaging in microfluidics as applied to chemical analysis and the use of two-photon absorption and self-phase modulation as contrast mechanisms applied to imaging problems in the medical sciences.

Carriles, Ramon; Schafer, Dawn N.; Sheetz, Kraig E.; Field, Jeffrey J.; Cisek, Richard; Barzda, Virginijus; Sylvester, Anne W.; Squier, Jeffrey A.

2009-01-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

176

Infrared and infrared-visible sum frequency generation spectroscopic response of harmonic monolayer vibrons: Homogeneous profile  

NASA Astrophysics Data System (ADS)

We determine the profile of the vibrational band of an ordered monolayer adsorbed on a clean surface corresponding to the infrared spectrum and to the resonant infrared-visible sum frequency generation spectrum. The theoretical model is based on the renormalization of the monolayer and substrate Hamiltonians. The harmonic dynamics of the effective vibrons characterizing the collective internal vibrations of the admolecules is written in terms of a complex dynamical matrix whose elements can be expressed as correlation functions of the external libron and phonon modes. The dephasing broadening is obtained by solving a master equation for the time evolution of the vibron modes while the external dynamics of the layer is described by using molecular dynamics simulation. An application to the calculation of the profile of the vibrational band of the low temperature (2×1) CO monolayer adsorbed on NaCl(100) is performed without any adjustable parameter by considering a well established semiempirical potential to describe the molecule-surface and molecule-molecule interactions. The comparison with experimental spectra shows that the homogeneous phase relaxation due to the coupling between the vibrons and the monolayer phonons-librons accounts for the most part of the peak width and interprets the temperature dependence of this width. Extension of the calculations to the interpretation of the orientationally disordered phase obtained for CO at higher temperature is done which corroborates very well the temperature behavior of the monolayer structure and profile.

Pouthier, V.; Hoang, P. N. M.; Girardet, C.

1999-04-01

177

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

PubMed

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. PMID:21461402

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

2011-01-15

178

A Daily Oscillation in the Fundamental Frequency and Amplitude of Harmonic Syllables of Zebra Finch Song  

PubMed Central

Complex motor skills are more difficult to perform at certain points in the day (for example, shortly after waking), but the daily trajectory of motor-skill error is more difficult to predict. By undertaking a quantitative analysis of the fundamental frequency (FF) and amplitude of hundreds of zebra finch syllables per animal per day, we find that zebra finch song follows a previously undescribed daily oscillation. The FF and amplitude of harmonic syllables rises across the morning, reaching a peak near mid-day, and then falls again in the late afternoon until sleep. This oscillation, although somewhat variable, is consistent across days and across animals and does not require serotonin, as animals with serotonergic lesions maintained daily oscillations. We hypothesize that this oscillation is driven by underlying physiological factors which could be shared with other taxa. Song production in zebra finches is a model system for studying complex learned behavior because of the ease of gathering comprehensive behavioral data and the tractability of the underlying neural circuitry. The daily oscillation that we describe promises to reveal new insights into how time of day affects the ability to accomplish a variety of complex learned motor skills.

Wood, William E.; Osseward, Peter J.; Roseberry, Thomas K.; Perkel, David J.

2013-01-01

179

A daily oscillation in the fundamental frequency and amplitude of harmonic syllables of zebra finch song.  

PubMed

Complex motor skills are more difficult to perform at certain points in the day (for example, shortly after waking), but the daily trajectory of motor-skill error is more difficult to predict. By undertaking a quantitative analysis of the fundamental frequency (FF) and amplitude of hundreds of zebra finch syllables per animal per day, we find that zebra finch song follows a previously undescribed daily oscillation. The FF and amplitude of harmonic syllables rises across the morning, reaching a peak near mid-day, and then falls again in the late afternoon until sleep. This oscillation, although somewhat variable, is consistent across days and across animals and does not require serotonin, as animals with serotonergic lesions maintained daily oscillations. We hypothesize that this oscillation is driven by underlying physiological factors which could be shared with other taxa. Song production in zebra finches is a model system for studying complex learned behavior because of the ease of gathering comprehensive behavioral data and the tractability of the underlying neural circuitry. The daily oscillation that we describe promises to reveal new insights into how time of day affects the ability to accomplish a variety of complex learned motor skills. PMID:24312654

Wood, William E; Osseward, Peter J; Roseberry, Thomas K; Perkel, David J

2013-01-01

180

Assessment of harmonic source correction for ultrasound medical imaging  

NASA Astrophysics Data System (ADS)

Tissue velocity and attenuation inhomogeneities reduce ultrasound image quality in many patients. Over the years a number of methods have been developed to estimate the corrective delays necessary for phase aberration correction. Past methods were based on assumptions of the target or required a separate transducer acting as a transponder point source. A method is proposed which creates a known acoustical source in the tissue suitable for wavefront correction without a priori assumptions of the target or requiring a point source transponder. This method was tested with multiple electronically produced aberrations with RMS focusing errors of 0.25? radians, 0.44? radians, and 0.87? radians at 4.17 MHz. These aberrators were corrected using excised pork kidneys and on the left kidney of human volunteers as targets. Waveform correction on pork kidney led to an improvement in imaging beam amplitude and side-lobe level. Waveform correction on human subjects for a 0.87? radians RMS error aberrator led to a 15.4 dB improvement in imaging beam amplitude and an 11.8 dB improvement in side-lobe level. This method shows promise of overcoming the limitations of previous phase correction methods.

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

2010-03-01

181

Multi-line transmission in medical imaging using the second-harmonic signal.  

PubMed

The emergence of three-dimensional imaging in the field of medical ultrasound imaging has greatly increased the number of transmissions needed to insonify a whole volume. With a large number of transmissions comes a low image frame rate. When using classical transmission techniques, as in two-dimensional imaging, the frame rate becomes unacceptably low, prompting the use of alternative transmission patterns that require less time. One alternative is to use a multi-line transmission (MLT) technique which consists of transmitting several pulses simultaneously in different directions. Perturbations appear when acquiring and beamforming the signal in the direction of one pulse because of the pulses sent in other directions. The edge waves from the pulses transmitted in a different direction add to the signal transmitted in the direction of interest, resulting in artifacts in the final image. Taking advantage of the nonlinear propagation of sound in tissue, the second-harmonic signal can be used with the MLT technique. The image obtained using the second-harmonic signal, compared with an image obtained using the fundamental signal, should have reduced artifacts coming from other pulses transmitted simultaneously. Simulations, backed up by experiments imaging a wire target and an in vivo left ventricle, confirm that the hypothesis is valid. In the studied case, the perturbations appear as an increase in the signal level around the main echo of a point scatterer. When using the fundamental signal, the measured amplitude level of the perturbations was approximately -40 dB compared with the maximum signal amplitude (-27 dB in vivo), whereas it was around -60 dB (-45 dB in vivo) for the second-harmonic signal. The MLT technique encounters limitations in the very near field where the pulses overlap and the perturbation level also increases for images with strong speckle and low contrast. PMID:24297034

Prieur, Fabrice; Dénarié, Bastien; Austeng, Andreas; Torp, Hans

2013-12-01

182

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

183

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

2014-07-01

184

Time-gated imaging for multifocus second-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

We developed a scanning second-harmonic generation (SHG) microscope with a time-gated image intensifier. The combination of a microlens array scanner and the gated image intensifier allows us to perform simultaneous time-resolved detection of SHG at multiple positions in a sample. By tuning the time delay of the gated detection from pulsed laser illumination by a mode-locked Ti:sapphire laser, background noise originating from the image intensifier dark current, fluorescence from the sample, and stray light are effectively reduced.

Kobayashi, Minoru; Fujita, Katsumasa; Nakamura, Osamu; Kawata, Satoshi

2005-07-01

185

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

2013-02-01

186

Second-harmonic near-field imaging of ferroelectric domain structure of YMnO3  

Microsoft Academic Search

Near-field tip-enhanced and symmetry-selective nonlinear light scattering is demonstrated for imaging nanoscopic ferroelectric order. The surface topology of antiparallel ferroelectric domains in multiferroic YMnO3 is spatially resolved by second-harmonic generation (SHG). Optical phase contrast is obtained by interference between the local near-field SHG and a self-homodyne far-field reference SHG field. Ferroelectric domains anisotropically elongated along the hexagonal crystallographic axis were

Catalin C. Neacsu; Bas B. van Aken; Manfred Fiebig; Markus B. Raschke

2009-01-01

187

Sparsity-Promoting Tomographic Fluorescence Imaging With Simplified Spherical Harmonics Approximation  

Microsoft Academic Search

Fluorescence molecular tomography has become a promising technique for in vivo small animal imaging and has many potential applications. Due to the ill-posed and the ill-conditioned nature of the problem, Tikhonov regularization is generally adopted to stabilize the solution. However, the result is usually over-smoothed. In this letter, the third-order simplified spherical harmonics approximation to radiative transfer equation is utilized

Dong Han; Jie Tian; Kai Liu; Jinchao Feng; Bo Zhang; Xibo Ma; Chenghu Qin

2010-01-01

188

Diffractive imaging using a polychromatic high-harmonic generation soft-x-ray source  

SciTech Connect

A new approach to diffractive imaging using polychromatic diffraction data is described. The method is tested using simulated and experimental data and is shown to yield high-quality reconstructions. Diffraction data produced using a high-harmonic generation source are considered explicitly here. The formalism can be readily adapted, however, to any short-wavelength source producing a discrete spectrum and possessing sufficient spatial coherence.

Dilanian, Ruben A.; Chen Bo; Williams, Garth J.; Quiney, Harry M.; Nugent, Keith A. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, University of Melbourne, Victoria 3010 (Australia); Teichmann, Sven; Hannaford, Peter; Dao, Lap V. [ARC Centre of Excellence for Coherent X-ray Science and Centre for Atom Optics and Ultrafast Spectroscopy, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Victoria 3122 (Australia); Peele, Andrew G. [Department of Physics, ARC Centre of Excellence for Coherent X-ray Science, La Trobe University, Bundoora, Victoria 3086 (Australia)

2009-07-15

189

Imaging lipid bodies in cells and tissues using third-harmonic generation microscopy  

Microsoft Academic Search

Lipid bodies have an important role in energy storage and lipid regulation. Here we show that lipid bodies are a major source of contrast in third-harmonic generation (THG) microscopy of cells and tissues. In hepatocytes, micrometer-sized lipid bodies produce a THG signal 1–2 orders of magnitude larger than other structures, which allows one to image them with high specificity. THG

Delphine Débarre; Willy Supatto; Ana-Maria Pena; Aurélie Fabre; Thierry Tordjmann; Laurent Combettes; Marie-Claire Schanne-Klein; Emmanuel Beaurepaire

2005-01-01

190

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

191

Measurement and control of the frequency chirp rate of high-order harmonic pulses  

SciTech Connect

We measure the chirp rate of harmonics 13 to 23 in argon by cross correlation with a 12 femtosecond probe pulse. Under low ionization conditions, we directly measure the negative chirp due to the atomic dipole phase, and show that an additional chirp on the pump pulse is transferred to the qth harmonic as q times the fundamental chirp. Our results are in accord with simulations using the experimentally measured 815 nm pump and probe pulses. The ability to measure and manipulate the harmonic chirp rate is essential for the characterization and optimization of attosecond pulse trains.

Mauritsson, J.; Johnsson, P.; Lopez-Martens, R.; Varju, K.; L'Huillier, A. [Department of Physics, Lund Institute of Technology, P. O. Box 118, SE-221 00 Lund (Sweden); Kornelis, W.; Biegert, J.; Keller, U. [Physics Department, Swiss Federal Institute of Technology (ETH Zuerich), CH-8093 Zurich (Switzerland); Gaarde, M.B.; Schafer, K.J. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States)

2004-08-01

192

High frequency coded imaging system with RF.  

PubMed

Coded transmission is an approach to solve the inherent compromise between penetration and resolution required in ultrasound imaging. Our goal was to examine the applicability of the coded excitation to HF (20-35 MHz) ultrasound imaging. A novel real-time imaging system for research and evaluation of the coded transmission was developed. The digital programmable coder- digitizer module based on the field programmable gate array (FPGA) chip supports arbitrary waveform coded transmission and RF echo sampling up to 200 megasamples per second, as well as real-time streaming of digitized RF data via a high-speed USB interface to the PC. All RF and image data processing were implemented in the software. A novel balanced software architecture supports real-time processing and display at rates up to 30 frames/sec. The system was used to acquire quantitative data for sine burst and 16-bit Golay code excitation at 20 MHz fundamental frequency. SNR gain close to 14 dB was obtained. The example of the skin scan clearly shows the extended penetration and improved contrast when a 35-MHz Golay code is used. The system presented is a practical and low-cost implementation of a coded excitation technique in HF ultrasound imaging that can be used as a research tool as well as to be introduced into production. PMID:18986930

Lewandowski, Marcin; Nowicki, Andrzej

2008-08-01

193

Effect of fast harmonic excitation on frequency-locking in a van der Pol–Mathieu–Duffing oscillator  

Microsoft Academic Search

We study the effect of high-frequency harmonic excitation on the entrainment area of the main resonance in a van der Pol–Mathieu–Duffing oscillator. An averaging technique is used to derive a self- and parametrically driven equation governing the slow dynamic of the oscillator. The multiple scales method is then performed on the slow dynamic near the main resonance to obtain a

Abdelhak Fahsi; Mohamed Belhaq

2009-01-01

194

An ab initio study of the harmonic force field and vibrational frequencies of thionylimide: Basis set and electron correlation effects  

Microsoft Academic Search

Basis set and electron correlation effects on the geometry and harmonic force field of thionylimide (HNSO) are investigated in detail. d functions on S are essential in describing the bonding in this compound. The calculated Hartree–Fock vibrational frequencies are about 15% too high. Inclusion of electron correlation at the second and third order Moller–Plesset perturbation levels (MP2 and MP3) gives

Krishnan Raghavachari

1982-01-01

195

Collinear type II second-harmonic-generation frequency-resolved optical gating for use with high-numerical-aperture objectives  

Microsoft Academic Search

Ultrashort-pulse lasers are now commonly used for multiphoton microscopy, and optimizing the performance of such systems requires careful characterization of the pulses at the tight focus of the microscope objective. We solve this problem by use of a collinear geometry in frequency-resolved optical gating that uses type II second-harmonic generation and that allows the full N.A. of the microscope objective

David N. Fittinghoff; Jeff A. Squier; C. P. J. Barty; John N. Sweetser; Rick Trebino; M. Mueller

1998-01-01

196

Chiral imaging of collagen by second-harmonic generation circular dichroism  

PubMed Central

We provide evidence that the chirality of collagen can give rise to strong second-harmonic generation circular dichroism (SHG-CD) responses in nonlinear microscopy. Although chirality is an intrinsic structural property of collagen, most of the previous studies ignore that property. We demonstrate chiral imaging of individual collagen fibers by using a laser scanning microscope and type-I collagen from pig ligaments. 100% contrast level of SHG-CD is achieved with sub-micrometer spatial resolution. As a new contrast mechanism for imaging chiral structures in bio-tissues, this technique provides information about collagen morphology and three-dimensional orientation of collagen molecules.

Lee, H.; Huttunen, M. J.; Hsu, K.-J.; Partanen, M.; Zhuo, G.-Y.; Kauranen, M.; Chu, S.-W.

2013-01-01

197

Contour mapping of Europa using frequency diverse spatial heterodyne imaging  

Microsoft Academic Search

Three dimensional imaging of planetary and lunar surfaces has traditionally been the purview of Synthetic Aperture Radar payloads. We propose an active imaging technique that utilizes laser frequency diversity coupled with spatial heterodyne imaging. Spatial heterodyne imaging makes use of a local oscillator which encodes pupil plane object information on a carrier frequency. The object information is extracted via Fourier

R. L. Kendrick; Thomas Höft; J. C. Marron; Joe Pitman; Nathan Seldomridge

2006-01-01

198

Highly efficient quasi-phase-matched second-harmonic generation by frequency doubling of a high-frequency superimposed laser diode.  

PubMed

We report highly efficient blue-light generation by frequency doubling of a high-frequency superimposed laser diode, stabilized by a grating feedback technique, in a periodically domain-inverted LiTaO(3) waveguide. To increase second-harmonic generation conversion efficiency, we enhanced the peak power of the laser diode by using a gain-switching method. Locking the oscillation wavelength of the laser diode by the grating feedback technique, we obtained 4.5 mW of average blue-light power with 13% conversion efficiency. PMID:19859158

Yamamoto, K; Mizuuchi, K; Kitaoka, Y; Kato, M

1995-02-01

199

Homodyne High-Harmonic Spectroscopy: Coherent Imaging of a Unimolecular Chemical Reaction  

NASA Astrophysics Data System (ADS)

At the heart of high harmonic generation lies a combination of optical and collision physics entwined by a strong laser field. An electron, initially tunnel-ionized by the field, driven away then back in the continuum, finally recombines back to rest in its initial ground state via a radiative transition. The emitted attosecond (atto=10-18) XUV light pulse carries all the information (polarization, amplitude and phase) about the photorecombination continuum-to-ground transition dipolar field. Photorecombination is related to the time-reversed photoionization process. In this perspective, high-harmonic spectroscopy extends well-established photoelectron spectroscopy, based on charged particle detection, to a fully coherent one, based on light characterization. The main achievement presented in this thesis is to use high harmonic generation to probe femtosecond (femto=10-15) chemical dynamics for the first time. Thanks to the coherence imposed by the strong driving laser field, homodyne detection of attosecond pulses from excited molecules undergoing dynamics is achieved, the signal from unexcited molecules acting as the reference local oscillator. First, applying time-resolved high-harmonic spectroscopy to the photodissociation of a diatomic molecule, Br2 ? Br + Br, allows us to follow the break of a chemical bond occurring in a few hundreds of femtoseconds. Second, extending it to a triatomic (NO2) lets us observe both the previously unseen (but predicted) early femtosecond conical intersection dynamics followed by the late picosecond statistical photodissociation taking place in the reaction NO2 ? NO + O. Another important realization of this thesis is the development of a complementary technique to time-resolved high-harmonic spectroscopy called LAPIN, for Linked Attosecond Phase INterferometry. When combined together, time-resolved high-harmonic spectroscopy and LAPIN give access to the complex photorecombination dipole of aligned excited molecules. These achievements lay the basis for electron recollision tomographic imaging of a chemical reaction with unprecedented angstrom (1 angstrom= 0.1 nanometer) spatial resolution. Other contributions dedicated to the development of attosecond science and the generalization of high-harmonic spectroscopy as a novel, fully coherent molecular spectroscopy will also be presented in this thesis.

Beaudoin Bertrand, Julien

200

Sources of Image Degradation in Fundamental and Harmonic Ultrasound Imaging: A Nonlinear, Full-Wave, Simulation Study  

PubMed Central

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared to fundamental imaging, reverberation clutter in harmonic imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for fundamental imaging, the primary source of degradation is phase aberration.

Pinton, Gianmarco F.; Trahey, Gregg E.; Dahl, Jeremy J.

2011-01-01

201

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

202

Image enhancement by non-linear extrapolation in frequency space  

NASA Technical Reports Server (NTRS)

An input image is enhanced to include spatial frequency components having frequencies higher than those in an input image. To this end, an edge map is generated from the input image using a high band pass filtering technique. An enhancing map is subsequently generated from the edge map, with the enhanced map having spatial frequencies exceeding an initial maximum spatial frequency of the input image. The enhanced map is generated by applying a non-linear operator to the edge map in a manner which preserves the phase transitions of the edges of the input image. The enhanced map is added to the input image to achieve a resulting image having spatial frequencies greater than those in the input image. Simplicity of computations and ease of implementation allow for image sharpening after enlargement and for real-time applications such as videophones, advanced definition television, zooming, and restoration of old motion pictures.

Anderson, Charles H. (Inventor); Greenspan, Hayit K. (Inventor)

1998-01-01

203

Steady-State Characteristics of a Torque and Speed Control System of an Induction Motor Utilizing Rotor Slot Harmonics for Slip Frequency Sensing  

Microsoft Academic Search

A method is proposed to detect the slip frequency of a three phase squirrel-cage induction motor from rotor slot harmonics. A method of torque and speed control of the induction motor using the proposed slip frequency detector is presented. The torque and speed control system is realized considering characteristics of the slip frequency detector. Experimental results show that the proposed

Muneaki Ishida; Koji Iwata

1987-01-01

204

Modulation Technique for Low Frequency Harmonic Cancellation in Auxiliary Railway Power Supplies  

Microsoft Academic Search

The auxiliary railway power supply (ARPS) is needed in order to provide low and medium voltages to the onboard systems from the catenary high voltage. The outputs of the ARPS can be dc (24 Vdc ÷ 100 Vdc) or ac (400 Vac) .I n the case of ac voltage generation, the ac output voltage is under very restrictive total harmonic

Isabel Quesada; Antonio Lazaro; Carlos Martinez; Andrés Barrado; Marina Sanz; Cristina Fernandez; Ramón Vazquez; Ignacio Gonzalez

2011-01-01

205

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

206

Optical delineation of human malignant melanoma using second harmonic imaging of collagen  

PubMed Central

Skin cancer incidence has increased exponentially over the last three decades. In 2008 skin cancer caused 2280 deaths in the UK, with 2067 due to malignant melanoma. Early diagnosis can prevent mortality, however, conventional treatment requires multiple procedures and increasing treatment times. Second harmonic generation (SHG) imaging could offer diagnosis and demarcation of melanoma borders non-invasively at presentation thereby short-cutting the excision biopsy stage. To test the efficacy and accuracy of SHG imaging of collagen in skin and to delineate the borders of skin cancers, unstained human melanoma biopsy sections were imaged using SHG microscopy. Comparisons with sister sections, stained with H&E or Melan-A were made for correlation of invasion borders. Fresh ex vivo normal human and rat skin was imaged through its whole thickness using SHG to demonstrate this technique is transferable to in vivo tissues. SHG imaging demonstrated detailed collagen distribution in normal skin, with total absence of SHG signal (fibrillar collagen) within the melanoma-invaded tissue. The presence or absence of signal changes dramatically at the borders of the melanoma, accurately demarcating the edges that strongly correlated with H&E and Melan-A defined borders (p<0.002). SHG imaging of ex vivo human and rat skin demonstrated collagen architecture could be imaged through the full thickness of the skin. We propose that SHG imaging could be used for diagnosis and accurate demarcation of melanoma borders on presentation and therefore potentially reduce mortality rates.

Thrasivoulou, C.; Virich, G.; Krenacs, T.; Korom, I.; Becker, D. L.

2011-01-01

207

Membrane potential dynamics of axons in cultured hippocampal neurons probed by second-harmonic-generation imaging  

NASA Astrophysics Data System (ADS)

The electrical properties of axons critically influence the nature of communication between neurons. However, due to their small size, direct measurement of membrane potential dynamics in intact and complex mammalian axons has been a challenge. Furthermore, quantitative optical measurements of axonal membrane potential dynamics have not been available. To characterize the basic principles of somatic voltage signal propagation in intact axonal arbors, second-harmonic-generation (SHG) imaging is applied to cultured mouse hippocampal neurons. When FM4-64 is applied extracellularly to dissociated neurons, whole axonal arbors are visualized by SHG imaging. Upon action potential generation by somatic current injection, nonattenuating action potentials are recorded in intact axonal arbors. Interestingly, however, both current- and voltage-clamp recordings suggest that nonregenerative subthreshold somatic voltage changes at the soma are poorly conveyed to these axonal sites. These results reveal the nature of membrane potential dynamics of cultured hippocampal neurons, and further show the possibility of SHG imaging in physiological investigations of axons.

Nuriya, Mutsuo; Yasui, Masato

2010-03-01

208

Epi-third and second harmonic generation microscopic imaging of abnormal enamel.  

PubMed

Enamel covers the tooth crown and is responsible for protecting the inner tissues of the teeth. It is thus clinically important to diagnose the anomalies in tooth enamel structures in the early stage for prevention and treatment. In this article, we report the epi-harmonic-generation-microscopic study of various abnormal enamel from the nature surface of human teeth. With a 1230 nm light source and with an epi-collection scheme, an imaging depth greater than 300 microm can be achieved. The contrast sources of THG and SHG in the abnormal enamel have been identified and verified by comparing the images from the sound enamel with those from white spot lesions, cracks, and the irradiated enamel. Besides the previously reported interprismatic space, THG is found to be contributed from cracks or the material inhomogeneities inside the enamel prisms; while SHG is attributed to the strain-induced breakage of the 6/m point group symmetry. Combined with the high 3D spatial resolution and no energy release during imaging, our study shows that the infrared-laser-based epi-harmonic generation microscopy can provide different contrasts to differentiate the abnormal enamel from sound enamel and could provide a valuable tool for in vivo monitoring of both morphological changes and strain status of hydroxyapatite crystals in the enamel without sectioning and staining. PMID:18648488

Chen, Szu-Yu; Hsu, Chin-Ying S; Sun, Chi-Kuang

2008-07-21

209

Digital pathology and image analysis augment biospecimen annotation and biobank quality assurance harmonization.  

PubMed

Standardization of biorepository best practices will enhance the quality of translational biomedical research utilizing patient-derived biobank specimens. Harmonization of pathology quality assurance procedures for biobank accessions has lagged behind other avenues of biospecimen research and biobank development. Comprehension of the cellular content of biorepository specimens is important for discovery of tissue-specific clinically relevant biomarkers for diagnosis and treatment. While rapidly emerging technologies in molecular analyses and data mining create focus on appropriate measures for minimizing pre-analytic artifact-inducing variables, less attention gets paid to annotating the constituent makeup of biospecimens for more effective specimen selection by biobank clients. Both pre-analytic tissue processing and specimen composition influence acquisition of relevant macromolecules for downstream assays. Pathologist review of biorepository submissions, particularly tissues as part of quality assurance procedures, helps to ensure that the intended target cells are present and in sufficient quantity in accessioned specimens. This manual procedure can be tedious and subjective. Incorporating digital pathology into biobank quality assurance procedures, using automated pattern recognition morphometric image analysis to quantify tissue feature areas in digital whole slide images of tissue sections, can minimize variability and subjectivity associated with routine pathologic evaluations in biorepositories. Whole-slide images and pathologist-reviewed morphometric analyses can be provided to researchers to guide specimen selection. Harmonization of pathology quality assurance methods that minimize subjectivity and improve reproducibility among collections would facilitate research-relevant specimen selection by investigators and could facilitate information sharing in an integrated network approach to biobanking. PMID:24362266

Wei, Bih-Rong; Simpson, R Mark

2014-03-01

210

Polarization-resolved second-harmonic-generation imaging of photoaged dermal collagen fiber  

NASA Astrophysics Data System (ADS)

Polarization-resolved second-harmonic-generation (SHG) microscopy is useful for assessment of collagen fiber orientation in tissues. In this paper, we investigated the relation between wrinkle direction and collagen orientation in ultraviolet-B-exposed (UVB-exposed) skin using polarization-resolved SHG microscopy. A polarization anisotropic image of the SHG light indicated that wrinkle direction in UVB-exposed skin is predominantly parallel to the orientation of dermal collagen fibers whereas no-UVB-exposed skin was dominated by collagen orientation parallel to the meridian line of body. The method proposed has the potential to become a powerful non-invasive tool for assessment of cutaneous photoaging.

Yasui, Takeshi; Takahashi, Yu; Araki, Tsutomu

2009-02-01

211

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

212

Interferometric Backward Third Harmonic Generation Microscopy for Axial Imaging with Accuracy Beyond the Diffraction Limit  

PubMed Central

A new nonlinear microscopy technique based on interference of backward-reflected third harmonic generation (I-THG) from multiple interfaces is presented. The technique is used to measure height variations or changes of a layer thickness with an accuracy of up to 5 nm. Height variations of a patterned glass surface and thickness variations of fibroblasts are visualized with the interferometric epi-THG microscope with an accuracy at least two orders of magnitude better than diffraction limit. The microscopy technique can be broadly applied for measuring distance variations between membranes or multilayer structures inside biological tissue and for surface height variation imaging.

Coelho, Nuno M.; McCulloch, Christopher; Barzda, Virginijus

2014-01-01

213

Contrast harmonic power Doppler imaging of congenital ventricular diverticulum--a case report.  

PubMed

A case of an 81-year-old woman with a left ventricular diverticulum who underwent myocardial contrast echocardiography is reported. After administration of the contrast agent, a pulsed Doppler flow measurement clearly revealed the biphasic waveform of the ejection flow in the pre-systolic and systolic phase at the ostium of the diverticular cavity. A harmonic power Doppler image showed that part of the diverticulum wall had similar acoustic properties to the ventricular septal wall. Intracardiac blood flow and myocardial perfusion could be clearly evaluated and a ventricular diverticulum was correctly diagnosed using contrast echocardiography. PMID:11386388

Ueda, T; Mizushige, K; Yukiiri, K; Aoyama, T; Kondo, I; Kohno, M; Matsuo, H

2001-05-01

214

Demonstration of a Frequency-Demodulation CMOS Image Sensor  

Microsoft Academic Search

A frequency-demodulation CMOS image sensor for capturing images only by the modulated light is proposed and demonstrated. The pixel circuit has two FD (floating diffusion) for accumulating signal charges and one photo-gate for detecting the modulated light and the background light. By operating the image sensor synchronously with a frequency and a phase of the modulated light, signal charges generated

Koji Yamamoto; Keiichiro Kagawa; Jun Ohta; Masahiro Nunoshita

215

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

PubMed

Details for constructing an astronomical frequency comb suitable as a wavelength reference for échelle 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 microm. The means of producing a repetition rate greater than 7 GHz and a peak optical power of approximately 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. PMID:19424399

McFerran, J J

2009-05-10

216

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

217

Removing the depth-degeneracy in optical frequency domain imaging with frequency shifting  

PubMed Central

A novel technique using an acousto-optic frequency shifter in optical frequency domain imaging (OFDI) is presented. The frequency shift eliminates the ambiguity between positive and negative differential delays, effectively doubling the interferometric ranging depth while avoiding image cross-talk. A signal processing algorithm is demonstrated to accommodate nonlinearity in the tuning slope of the wavelength-swept OFDI laser source.

Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Bouma, B. E.

2009-01-01

218

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

219

In vivo structural imaging of the cornea by polarization-resolved second harmonic microscopy  

PubMed Central

The transparency and mechanical strength of the cornea are related to the highly organized three-dimensional distribution of collagen fibrils. It is of great interest to develop specific and contrasted in vivo imaging tools to probe these collagenous structures, which is not available yet. Second Harmonic Generation (SHG) microscopy is a unique tool to reveal fibrillar collagen within unstained tissues, but backward SHG images of cornea fail to reveal any spatial features due to the nanometric diameter of stromal collagen fibrils. To overcome this limitation, we performed polarization-resolved SHG imaging, which is highly sensitive to the sub-micrometer distribution of anisotropic structures. Using advanced data processing, we successfully retrieved the orientation of the collagenous fibrils at each depth of human corneas, even in backward SHG homogenous images. Quantitative information was also obtained about the submicrometer heterogeneities of the fibrillar collagen distribution by measuring the SHG anisotropy. All these results were consistent with numerical simulation of the polarization-resolved SHG response of cornea. Finally, we performed in vivo SHG imaging of rat corneas and achieved structural imaging of corneal stroma without any labeling. Epi-detected polarization-resolved SHG imaging should extend to other organs and become a new diagnosis tool for collagen remodeling.

Latour, Gael; Gusachenko, Ivan; Kowalczuk, Laura; Lamarre, Isabelle; Schanne-Klein, Marie-Claire

2011-01-01

220

Collinear type II second-harmonic-generation frequency-resolved optical gating for use with high-numerical-aperture objectives.  

PubMed

Ultrashort-pulse lasers are now commonly used for multiphoton microscopy, and optimizing the performance of such systems requires careful characterization of the pulses at the tight focus of the microscope objective. We solve this problem by use of a collinear geometry in frequency-resolved optical gating that uses type II second-harmonic generation and that allows the full N.A. of the microscope objective to be used. We then demonstrate the technique by measuring the intensity and the phase of a 22-fs pulse focused by a 20x, 0.4-N.A. air objective. PMID:18087424

Fittinghoff, D N; Squier, J A; Barty, C P; Sweetser, J N; Trebino, R; Müller, M

1998-07-01

221

Fast Arbitrary BRDF Shading for Low-Frequency Lighting Using Spherical Harmonics  

Microsoft Academic Search

Real-time shading using general (e.g., anisotropic) BRDFs has so far been limited to a few point or directional light sources. We extend such shading to smooth, area lighting using a low-order spherical harmonic basis for the lighting environment. We represent the 4D product function of BRDF times the cosine factor (dot product of the incident lighting and surface normal vectors)

Jan Kautz; John Snyder; Peter-Pike J. Sloan

2002-01-01

222

Position estimation in induction machines utilizing rotor bar slot harmonics and carrier-frequency signal injection  

Microsoft Academic Search

This paper presents a simple and robust way of utilizing harmonic saliencies created by rotor and stator slotting, present in some induction machine designs, for the estimation of rotor position. The injection of a carrier-signal voltage, in addition to the fundamental excitation, produces a carrier-signal current that contains the desired spatial information. A closed-loop tracking observer is then used to

Michael W. Degner; Robert D. Lorenz

2000-01-01

223

Design of Active Integrated Antenna for Dual Frequency Image Rejection  

Microsoft Academic Search

This paper is discusses a new configuration of integrated antenna for dual frequency operations and image frequency rejection. Microstrip patch antenna is design in such away to operate in dual frequencies band. The RF 90° hybrid, LNA's, mixers, LO and IF coupler are integrated to a dual frequency microstrip patch antenna to produce a single module of integrated antenna system

Sohiful Anuar Zainol Murad; Widad Ismail

2006-01-01

224

Biomechanical assessment and monitoring of thermal ablation using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)  

NASA Astrophysics Data System (ADS)

Cancer remains, one of the major public health problems in the United States as well as many other countries worldwide. According to According to the World Health Organization, cancer is currently the leading cause of death worldwide, accounting for 7.6 million deaths annually, and 25% of the annual death was due to Cancer during the year of 2011. In the long history of the cancer treatment field, many treatment options have been established up to date. Traditional procedures include surgical procedures as well as systemic therapies such as biologic therapy, chemotherapy, hormone therapy, and radiation therapy. Nevertheless, side-effects are often associated with such procedures due to the systemic delivery across the entire body. Recently technologies have been focused on localized therapy under minimally or noninvasive procedure with imaging-guidance, such as cryoablation, laser ablation, radio-frequency (RF) ablation, and High Intensity F-ocused Ultrasound (HIFU). HIFU is a non-invasive procedure aims to coagulate tissue thermally at a localized focal zone created with noninvasively emitting a set of focused ultrasound beams while the surrounding healthy tissues remain relatively untreated. Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a dynamic, radiation-force-based imaging technique, which utilizes a single HIFU transducer by emitting an Amplitude-modulated (AM) beam to both thermally ablate the tumor while inducing a stable oscillatory tissue displacement at its focal zone. The oscillatory response is then estimated by a cross-correlation based motion tracking technique on the signal collected by a confocally-aligned diagnostic transducer. HMIFU addresses the most critical aspect and one of the major unmet needs of HIFU treatment, which is the ability to perform real-time monitoring and mapping of tissue property change during the HIFU treatment. In this dissertation, both the assessment and monitoring aspects of HMIFU have been investigated fundamentally and experimentally through development of both a 1-D and 2-D based system. The performance assessment of HMIFU technique in depicting the lesion size increase as well as the lesion-to-background displacement contrast was first demonstrated using a 3D, FE-based interdisciplinary simulation framework. Through the development of 1-D HMIFU system, a multi-parametric monitoring approach was presented where presented where the focal HMI displacement, phase shift (Delta?), and correlation coefficients were monitored along with thermocouple and PCD under the HIFU treatment sequence with boiling and slow denaturation. For HIFU treatments with slow denaturation, consistent displacement increase-then-decrease trend was observed, indicating tissue softening-then-stiffening and phase shift increased with treatment time in agreement with mechanical testing outcomes. The correlation coefficient remained high throughout the entire treatment time under a minimized broadband energy and boiling mechanism. Contrarily, both displacement and phase shift changes lacked consistency under HIFU treatment sequences with boiling due to the presence of strong boiling mechanism confirmed by both PCD and thermocouple monitoring. In order to facilitate its clinical translation, a fully-integrated, clinically 2D real-time HMIFU system was also developed, which is capable of providing 2D real-time streaming during HIFU treatment up to 15 Hz without interruption. Reproducibility studies of the system showed consistent displacement estimation on tissue-mimicking phantoms as well as monitoring of tissue-softening-then-stiffening phase change across 16 out of 19 liver specimens (Increasing rate in phase shift (Delta?): 0.73+/-0.69 %/s, Decreasing rate in phase shift (Delta?): 0.60+/-0.19 %/s) along with thermocouple monitoring (Increasing: 0.84+/-1.15 %/ °C, Decreasing: 2.03+/- 0.93%/ °C) and validation of tissue stiffening using mechanical testing. In addition, the 2-D HMIFU system feasibility on preclinical pancreatic tumor mice model was also demonstrated in vivo, where HMI displa

Hou, Gary Yi

225

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

226

Spherical harmonics-based parametric deconvolution of 3D surface images using bending energy minimization.  

PubMed

Numerical deconvolution of 3D fluorescence microscopy data yields sharper images by reversing the known optical aberrations introduced during the acquisition process. When additional prior information such as the topology and smoothness of the imaged object surface is available, the deconvolution can be performed by fitting a parametric surface directly to the image data. In this work, we incorporate such additional information into the deconvolution process and focus on a parametric shape description suitable for the study of organelles, cells and tissues. Such membrane-bound closed biological surfaces are often topologically equivalent to the sphere and can be parameterized as series expansions in spherical harmonic functions (SH). Because image data are noisy and the SH-parameterization is prone to the formation of high curvatures even at low expansion orders, the parametric deconvolution problem is ill-posed and must be regularized. We use the shape bending energy as a regularizing (smoothing) function, and determine the regularization parameter graphically with the help of the L-curve method. We demonstrate the complete deconvolution scheme, including the initial image segmentation, the calculation of a good starting surface and the construction of the L-curve, using real and synthetic image data. PMID:18055248

Khairy, Khaled; Howard, Jonathon

2008-04-01

227

Computational segmentation of collagen fibers from second-harmonic generation images of breast cancer.  

PubMed

Second-harmonic generation (SHG) imaging can help reveal interactions between collagen fibers and cancer cells. Quantitative analysis of SHG images of collagen fibers is challenged by the heterogeneity of collagen structures and low signal-to-noise ratio often found while imaging collagen in tissue. The role of collagen in breast cancer progression can be assessed post acquisition via enhanced computation. To facilitate this, we have implemented and evaluated four algorithms for extracting fiber information, such as number, length, and curvature, from a variety of SHG images of collagen in breast tissue. The image-processing algorithms included a Gaussian filter, SPIRAL-TV filter, Tubeness filter, and curvelet-denoising filter. Fibers are then extracted using an automated tracking algorithm called fiber extraction (FIRE). We evaluated the algorithm performance by comparing length, angle and position of the automatically extracted fibers with those of manually extracted fibers in twenty-five SHG images of breast cancer. We found that the curvelet-denoising filter followed by FIRE, a process we call CT-FIRE, outperforms the other algorithms under investigation. CT-FIRE was then successfully applied to track collagen fiber shape changes over time in an in vivo mouse model for breast cancer. PMID:24407500

Bredfeldt, Jeremy S; Liu, Yuming; Pehlke, Carolyn A; Conklin, Matthew W; Szulczewski, Joseph M; Inman, David R; Keely, Patricia J; Nowak, Robert D; Mackie, Thomas R; Eliceiri, Kevin W

2014-01-01

228

Computational segmentation of collagen fibers from second-harmonic generation images of breast cancer  

NASA Astrophysics Data System (ADS)

Second-harmonic generation (SHG) imaging can help reveal interactions between collagen fibers and cancer cells. Quantitative analysis of SHG images of collagen fibers is challenged by the heterogeneity of collagen structures and low signal-to-noise ratio often found while imaging collagen in tissue. The role of collagen in breast cancer progression can be assessed post acquisition via enhanced computation. To facilitate this, we have implemented and evaluated four algorithms for extracting fiber information, such as number, length, and curvature, from a variety of SHG images of collagen in breast tissue. The image-processing algorithms included a Gaussian filter, SPIRAL-TV filter, Tubeness filter, and curvelet-denoising filter. Fibers are then extracted using an automated tracking algorithm called fiber extraction (FIRE). We evaluated the algorithm performance by comparing length, angle and position of the automatically extracted fibers with those of manually extracted fibers in twenty-five SHG images of breast cancer. We found that the curvelet-denoising filter followed by FIRE, a process we call CT-FIRE, outperforms the other algorithms under investigation. CT-FIRE was then successfully applied to track collagen fiber shape changes over time in an in vivo mouse model for breast cancer.

Bredfeldt, Jeremy S.; Liu, Yuming; Pehlke, Carolyn A.; Conklin, Matthew W.; Szulczewski, Joseph M.; Inman, David R.; Keely, Patricia J.; Nowak, Robert D.; Mackie, Thomas R.; Eliceiri, Kevin W.

2014-01-01

229

Quantitative analysis of diseased horse tendons using Fourier-transform-second-harmonic generation imaging  

NASA Astrophysics Data System (ADS)

Fourier transform-second-harmonic generation (FT-SHG) imaging is used to quantitatively assess the structural organization of collagen fibers in tendonitis-induced horse tendons. Fiber orientation, isotropy, and the ratio of forward to backward SHG signal (F/B ratio) are used to differentiate the fiber organization between the normal and diseased horse tendons. Each second-harmonic generation (SHG) image is divided into several smaller regions of interest (ROI) and the aforementioned quantitative metrics are calculated across the whole grid. ROIs are further labeled as dark (no or minimal presence of fibers), isotropic (random fiber organization), or anisotropic (regular fiber organization) regions. Results show that the normal tendon possesses minimal isotropic regions and small standard deviations in the histograms of orientation and F/B ratio, indicating an intact and highly regular fiber organization. However, the tendonitis-induced horse tendons possess higher number of dark and isotropic regions, and larger standard deviations of the measured parameters, suggesting significantly disoriented and disorganized collagen fibers. This type of quantification would be highly beneficial in diagnosing and determining the stage of tendonitis in clinical settings. Not limited to tendonitis, the technique could also be applied to other diseases that structurally affect collagen fibers. The advantage of FT-SHG over the conventional polarization microscopy is also discussed.

Sivaguru, Mayandi; Durgam, Sushmitha; Ambekar, Raghu; Luedtke, David; Fried, Glenn; Stewart, Allison; Toussaint, Kimani C., Jr.

2011-02-01

230

Second harmonic generation microscopy as a powerful diagnostic imaging modality for human ovarian cancer.  

PubMed

In this study we showed that second-harmonic generation (SHG) microscopy combined with precise methods for images evaluation can be used to detect structural changes in the human ovarian stroma. Using a set of scoring methods (alignment of collagen fibers, anisotropy, and correlation), we found significant differences in the distribution and organization of collagen fibers in the stroma component of serous, mucinous, endometrioid and mixed ovarian tumors as compared with normal ovary tissue. This methodology was capable to differentiate between cancerous and healthy tissue, with clear cut distinction between normal, benign, borderline, and malignant tumors of serous type. Our results indicated that the combination of different image-analysis approaches presented here represent a powerful tool to investigate collagen organization and extracellular matrix remodeling in ovarian tumors. PMID:23024013

Adur, Javier; Pelegati, Vitor B; de Thomaz, Andre A; Baratti, Mariana O; Andrade, Liliana A L A; Carvalho, Hernandes F; Bottcher-Luiz, Fátima; Cesar, Carlos Lenz

2014-01-01

231

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

232

Molecular probes for two-photon excited fluorescence and second harmonic generation imaging of biological membranes  

NASA Astrophysics Data System (ADS)

Novel microscopies based on nonlinear optical (NLO) phenomena are attracting increasing interest in the biology community owing to their potentialities in the area of real-time, non-damaging imaging of biological systems. In particular, second-harmonic generation (SHG) and two-photon excited fluorescence (TPEF) are NLO phenomena that scale with excitation intensity squared, and thus give rise to an intrinsic 3-dimensional resolution when used in microscopic imaging. In this perspective, we have implemented a molecular engineering approach toward NLO-probes specifically designed for SHG and/or TPEF imaging of cellular membranes. We have designed nanoscale rod-like fluorophores showing very large TPEF cross-sections in the visible red, outperforming standard fluorophores such as fluorescein by up to two orders of magnitude. Bolaamphiphilic derivatives combining high TPEF cross-sections and affinity for cellular membranes were prepared. Their incorporation into model or cell membranes can be monitored by TPEF microscopy. Amphiphilic push-pull chromophores showing both high TPA and SHG cross-sections in the near-IR region were designed as NLO-probes for imaging of biological membranes by simultaneous SHG and TPEF microscopy. These NLO-phores offer intriguing potentialities for imaging of fundamental biological processes such as adhesion, fusion or for reporting of membrane electrical potentials.

Porres, Laurent; Mongin, Olivier; Bhatthula, Bharath K. G.; Blanchard-Desce, Mireille H.; Ventelon, Lionel; Moreaux, Laurent; Pons, T.; Mertz, Jerome

2002-09-01

233

Optical clearing for improved contrast in second harmonic generation imaging of skeletal muscle.  

PubMed

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. PMID:16214853

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

2006-01-01

234

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

235

Low-power analog processing for sensing applications: low-frequency harmonic signal classification.  

PubMed

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 µm 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. PMID:23892765

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

2013-01-01

236

Sparsity enhanced fast subsurface imaging for stepped frequency GPRs  

Microsoft Academic Search

A sparsity enhanced and fast data acquisition and imaging method is presented for stepped-frequency continuous-wave ground penetrating radars (SFCW GPRs). In previous work it is shown that if the target space is sparse like the point like targets, an image of the target space can be constructed with making measurements at only a small number of random frequencies by solving

M. A. C. Tuncer; A. C. Gu?rbuz

2010-01-01

237

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

238

Coherent diffractive imaging microscope with a tabletop high harmonic EUV source  

NASA Astrophysics Data System (ADS)

Coherent diffractive imaging (CDI) using EUV/X-rays has proven to be a powerful microscopy method for imaging nanoscale objects. In traditional CDI, the oversampling condition limits its applicability to small, isolated objects. A new technique called keyhole CDI was demonstrated on a synchrotron X-ray source to circumvent this limitation. Here we demonstrate the first keyhole CDI result with a tabletop extreme ultraviolet (EUV) source. The EUV source is based on high harmonic generation (HHG), and our modified form of keyhole CDI uses a highly reflective curved EUV mirror instead of a lossy Fresnel zone plate, offering a ~10x increase in photon throughput of the imaging system, and a more uniform illumination on the sample. In addition, we have demonstrated a record 22 nm resolution using our tabletop CDI setup, and also the successful extension to reflection mode for a periodic sample. Combining these results with keyhole CDI will open the path to the realization of a compact EUV microscope for imaging general non-isolated and non-periodic samples, in both transmission and reflection mode.

Zhang, Bosheng; Seaberg, Matthew D.; Adams, Daniel E.; Gardner, Dennis F.; Murnane, Margaret M.; Kapteyn, Henry C.

2013-03-01

239

Polarization second harmonic generation by image correlation spectroscopy on collagen type I hydrogels.  

PubMed

Successful engineering of biomimetic tissue relies on an accurate quantification of the mechanical properties of the selected scaffold. To improve this quantification, typical bulk rheological measurements are often complemented with microscopic techniques, including label-free second harmonic generation (SHG) imaging. Image correlation spectroscopy (ICS) has been applied to obtain quantitative information from SHG images of fibrous scaffolds. However, the typical polarization SHG (P-SHG) effect, which partly defines the shape of the autocorrelation function (ACF), has never been taken into account. Here we propose a new and flexible model to reliably apply ICS to P-SHG images of fibrous structures. By starting from a limited number of straightforward assumptions and by taking into account the P-SHG effect, we were able to cope with the typically observed ACF particularities. Using simulated datasets, the resulting model was thoroughly evaluated and compared with models previously described in the literature. We showed that our new model has no restrictions concerning the fibre length for the density retrieval. For certain length ranges, the model can additionally be used to obtain the average fibre length and the P-SHG related non-zero susceptibility tensor element ratios. From experimental data on collagen type I hydrogels, values of SHG tensor element ratios and fibre thickness were determined which match values reported in the literature, thereby underpinning the validity and applicability of our new model. PMID:24444774

Paesen, Rik; Sanen, Kathleen; Smisdom, Nick; Michiels, Luc; Ameloot, Marcel

2014-05-01

240

An Anti-Harmonic Locking, DLL Frequency Multiplier with Low Phase Noise and Reduced Spur  

Microsoft Academic Search

This paper presents a new programmable delay-locked loop based frequency multiplier with a period error compensation loop (PECL) designed to reduce the output spurious power level. The low bandwidth auxiliary PECL compensates the output period error caused by the in-lock errors from various noise sources. By employing a novel switching control scheme, the circuit is capable of locking to frequencies

Q. J. Du; J. C. Zhuang; T. Kwasniewski

2006-01-01

241

Spatial frequency bandwidth used in the recognition of facial images  

Microsoft Academic Search

The purpose of the study was to find out what spatial frequency information human observers use in the recognition of face images. Signal-to-noise ratio thresholds for the recognition of facial images were measured as a function of the centre spatial frequency of narrow-band additive spatial noise. The relative sensitivity of recognition to different spatial frequencies was derived from these results.

Risto Näsänen

1999-01-01

242

Molecular geometries and harmonic frequencies from the parametric two-electron reduced density matrix method with application to the HCN < = > HNC isomerization.  

PubMed

Energies, geometries, and harmonic frequencies of the chemical species in the HCN < = > HNC isomerization including the transition state are computed with the parametric variational two-electron reduced density matrix (2-RDM) method. The parametric 2-RDM method parametrizes the 2-RDM with single- and double-excitation coefficients to be both size-consistent and nearly N-representable [DePrince, A. E., III; Mazziotti, D. A. Phys. Rev. A 2007, 73, 042501.]. With the inclusion of the zero-point energies of both species, the energy of HNC relative to HCN in a polarized valence triple-zeta basis set is 14.2 kcal/mol, which agrees with the experimental value of 14.8 +/- 2 kcal/mol. The present calculations provide the first assessment of the method for computing harmonic frequencies from a molecular geometry optimization. Bond lengths, angles, and harmonic frequencies are also computed for HF, CO, and H2O. PMID:19367796

DePrince, A Eugene; Mazziotti, David A

2008-12-18

243

Harmonic radar literature  

NASA Astrophysics Data System (ADS)

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 radar has an extremely low range of detection. Natural objects in the target area do not disturb the high frequency harmonics. The radar becomes clutter free. The principals of generating high frequency harmonics cover tunneling, semiconductor and microwave effects. Signal generation is most powerful when f sub o is between 100 and 1000 MHz.

Jansson, B.

1980-07-01

244

Instantaneous parameter estimation in cardiovascular time series by harmonic and time-frequency analysis.  

PubMed

Time-frequency distributions, such as smoothed pseudo Wigner-Ville distribution (SPWVD), complex demodulation (CDM), and provide useful time-varying spectral parameter estimators. However, each of these methods has limitations that a joint utilization could largely reduce, due to their interesting complementary features. The aim of this paper is to validate the joint SPWVD-CDM method on synthetic and real cardiovascular time series with normal and reduced variability such as in autonomic blockade or autonomic deficiency. We propose two indexes related to the noise present in the signal and to the dispersion of the power spectrum in order to validate instantaneous parameter estimation. In the low-frequency band, the interpretation of the instantaneous frequency and phase of cardiovascular time-series should be discarded in many real-life situations. Conversely, in the high frequency band, under paced breathing, the reliability of the instantaneous parameters is demonstrated even in conditions of reduced cardiovascular variability. PMID:12549736

Monti, Alessandro; Médigue, Claire; Mangin, Laurence

2002-12-01

245

Low-frequency atmospheric correction of space images  

NASA Astrophysics Data System (ADS)

An adaptive procedure for low-frequency space image correction is proposed. The formulas obtained for reduction and dispersion coefficients are used at the preliminary stage of the procedure. The practical realization of the procedure lies in the pixel-by-pixel inverse transformation to obtain a corrected image. To test the adaptive procedure, atmospheric correction of LANDSAT 7 image was successfully carried out.

Smirnov, S. A.; Terletsky, R. P.; Gontarenko, I. S.

246

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: The use of redundant primitive coordinates  

Microsoft Academic Search

A modified effective scaling frequency factor (ESFF) method that takes advantage of the potential energy distribution (PED) coefficients calculated in the basis of redundant primitive internal coordinates is presented. This approach is simpler and more flexible than that based on the natural internal coordinates. The sets of optimal scaling factors for routine 9- and 11-parameter ESFF calculations based on B3LYP\\/6-311G??

Piotr Borowski

2010-01-01

247

Music Onset Detection Based on Resonator Time Frequency Image  

Microsoft Academic Search

This paper describes a new method for music onset detection. The novelty of the approach consists mainly of two elements: the time-frequency processing and the detection stages. The resonator time frequency image (RTFI) is the basic time-frequency analysis tool. The time-frequency processing part is in charge of transforming the RTFI energy spectrum into more natural energy- change and pitch-change cues

Ruohua Zhou; Marco Mattavelli; Giorgio Zoia

2008-01-01

248

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

NASA Astrophysics Data System (ADS)

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. In this paper, a confocal transducer, combining a 4.5 MHz FUS transducer and a 3.3 MHz phased array imaging transducer, was used. The FUS transducer was driven by AM wave at 15 Hz with an acoustic intensity (Ispta) was equal to 1050 W/cm2. A lowpass digital filter was used to remove the spectrum of the higher power beam prior to displacement estimation. The resulting axial tissue displacement was estimated using 1D cross-correlation with a correlation window of 2 mm and a 92.5% overlap. A thermocouple was also used to measure the temperature near the ablated region. 2D HMI-images from six-bovine-liver specimens indicated the onset of coagulation necrosis through changes in amplitude displacement after coagulation due to its simultaneous probing and heating capability. The HMI technique can thus be used to monitor temperature-related stiffness changes of tissues during thermal therapies in real-time, i.e., without interrupting or modifying the treatment protocol.

Maleke, Caroline; Konofagou, Elisa E.

2009-04-01

249

Quantitative evaluation of skeletal muscle defects in second harmonic generation images  

PubMed Central

Abstract. Skeletal muscle pathologies cause irregularities in the normally periodic organization of the myofibrils. Objective grading of muscle morphology is necessary to assess muscle health, compare biopsies, and evaluate treatments and the evolution of disease. To facilitate such quantitation, we have developed a fast, sensitive, automatic imaging analysis software. It detects major and minor morphological changes by combining texture features and Fourier transform (FT) techniques. We apply this tool to second harmonic generation (SHG) images of muscle fibers which visualize the repeating myosin bands. Texture features are then calculated by using a Haralick gray-level cooccurrence matrix in MATLAB. Two scores are retrieved from the texture correlation plot by using FT and curve-fitting methods. The sensitivity of the technique was tested on SHG images of human adult and infant muscle biopsies and of mouse muscle samples. The scores are strongly correlated to muscle fiber condition. We named the software MARS (muscle assessment and rating scores). It is executed automatically and is highly sensitive even to subtle defects. We propose MARS as a powerful and unbiased tool to assess muscle health.

Liu, Wenhua; Raben, Nina; Ralston, Evelyn

2013-01-01

250

Quantitative evaluation of skeletal muscle defects in second harmonic generation images  

NASA Astrophysics Data System (ADS)

Skeletal muscle pathologies cause irregularities in the normally periodic organization of the myofibrils. Objective grading of muscle morphology is necessary to assess muscle health, compare biopsies, and evaluate treatments and the evolution of disease. To facilitate such quantitation, we have developed a fast, sensitive, automatic imaging analysis software. It detects major and minor morphological changes by combining texture features and Fourier transform (FT) techniques. We apply this tool to second harmonic generation (SHG) images of muscle fibers which visualize the repeating myosin bands. Texture features are then calculated by using a Haralick gray-level cooccurrence matrix in MATLAB. Two scores are retrieved from the texture correlation plot by using FT and curve-fitting methods. The sensitivity of the technique was tested on SHG images of human adult and infant muscle biopsies and of mouse muscle samples. The scores are strongly correlated to muscle fiber condition. We named the software MARS (muscle assessment and rating scores). It is executed automatically and is highly sensitive even to subtle defects. We propose MARS as a powerful and unbiased tool to assess muscle health.

Liu, Wenhua; Raben, Nina; Ralston, Evelyn

2013-02-01

251

Structural Characterization of Edematous Corneas by Forward and Backward Second Harmonic Generation Imaging  

PubMed Central

Abstract The purpose of this study was to image and quantify the structural changes of corneal edema by second harmonic generation (SHG) microscopy. Bovine cornea was used as an experimental model to characterize structural alterations in edematous corneas. Forward SHG and backward SHG signals were simultaneously collected from normal and edematous bovine corneas to reveal the morphological differences between them. In edematous cornea, both an uneven expansion in the lamellar interspacing and an increased lamellar thickness in the posterior stroma (depth > 200 ?m) were identified, whereas the anterior stroma, composed of interwoven collagen architecture, remained unaffected. Our findings of heterogeneous structural alteration at the microscopic scale in edematous corneas suggest that the strength of collagen cross-linking is heterogeneous in the corneal stroma. In addition, we found that qualitative backward SHG collagen fiber imaging and depth-dependent signal decay can be used to detect and diagnose corneal edema. Our work demonstrates that SHG imaging can provide morphological information for the investigation of corneal edema biophysics, and may be applied in the evaluation of advancing corneal edema in vivo.

Hsueh, Chiu-Mei; Lo, Wen; Chen, Wei-Liang; Hovhannisyan, Vladimir A.; Liu, Guang-Yu; Wang, Sheng-Shun; Tan, Hsin-Yuan; Dong, Chen-Yuan

2009-01-01

252

Quantitative evaluation of skeletal muscle defects in second harmonic generation images.  

PubMed

Skeletal muscle pathologies cause irregularities in the normally periodic organization of the myofibrils. Objective grading of muscle morphology is necessary to assess muscle health, compare biopsies, and evaluate treatments and the evolution of disease. To facilitate such quantitation, we have developed a fast, sensitive, automatic imaging analysis software. It detects major and minor morphological changes by combining texture features and Fourier transform (FT) techniques. We apply this tool to second harmonic generation (SHG) images of muscle fibers which visualize the repeating myosin bands. Texture features are then calculated by using a Haralick gray-level cooccurrence matrix in MATLAB. Two scores are retrieved from the texture correlation plot by using FT and curve-fitting methods. The sensitivity of the technique was tested on SHG images of human adult and infant muscle biopsies and of mouse muscle samples. The scores are strongly correlated to muscle fiber condition. We named the software MARS (muscle assessment and rating scores). It is executed automatically and is highly sensitive even to subtle defects. We propose MARS as a powerful and unbiased tool to assess muscle health. PMID:23377006

Liu, Wenhua; Raben, Nina; Ralston, Evelyn

2013-02-01

253

Tip-Enhanced Near-Field Second-Harmonic Imaging of Ferroelectric Domain Structure of YMnO3  

Microsoft Academic Search

The spatially resolved imaging of ferroelectric domain structure of unpoled YMnO3 was achieved combining second-harmonic generation with tip-enhanced near-field optical microscopy. Domains elongated along the hexagonal axis with dimensions of several 100 nm were observed.

C. C. Neacsu; B. B. Van Aken; M. Fiebig; M. B. Raschke

2007-01-01

254

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

255

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

256

Spatial frequency, phase, and the contrast of natural images  

Microsoft Academic Search

We examined contrast sensitivity and suprathreshold apparent contrast with natural images. The spatial-frequency components within single octaves of the images were removed (notch filtered), their phases were randomized, or the polarity of the images was inverted. Of Michelson contrast, root-mean-square (RMS) contrast, and band-limited contrast, RMS contrast was the best index of detectability. Negative images had lower apparent contrast than

Peter J. Bex; Walter Makous

2002-01-01

257

Harmonic radar literature  

Microsoft Academic Search

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 radar has an extremely low range of detection. Natural objects in the target

B. Jansson

1980-01-01

258

Harmonic nanoparticles for regenerative research.  

PubMed

In this visualized experiment, protocol details are provided for in vitro labeling of human embryonic stem cells (hESC) with second harmonic generation nanoparticles (HNPs). The latter are a new family of probes recently introduced for labeling biological samples for multi-photon imaging. HNPs are capable of doubling the frequency of excitation light by the nonlinear optical process of second harmonic generation with no restriction on the excitation wavelength. Multi-photon based methodologies for hESC differentiation into cardiac clusters (maintained as long term air-liquid cultures) are presented in detail. In particular, evidence on how to maximize the intense second harmonic (SH) emission of isolated HNPs during 3D monitoring of beating cardiac tissue in 3D is shown. The analysis of the resulting images to retrieve 3D displacement patterns is also detailed. PMID:24836220

Ronzoni, Flavio; Magouroux, Thibaud; Vernet, Remi; Extermann, Jérôme; Crotty, Darragh; Prina-Mello, Adriele; Ciepielewski, Daniel; Volkov, Yuri; Bonacina, Luigi; Wolf, Jean-Pierre; Jaconi, Marisa

2014-01-01

259

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

260

Second harmonic generation imaging of skin wound healing and scarring in a rabbit ear model  

NASA Astrophysics Data System (ADS)

Skin wound healing and scarring in rabbit ears was examined by second harmonic generation (SHG) microscopy. Rabbit ear wound model was created by punching from the ventral surface with removal of epidermis, dermis and perichondrium. The samples were collected weekly, and cut into 100 ?m thickness sections for SHG imaging. SHG imaging system was operated at 810 nm, producing SHG signals at half the excitation wavelength 405 nm. A Plan-Neofluar objective (x40 and NA=0.75) was employed for focusing the excitation beam into tissue samples and was also used to collect the backscattered intrinsic SHG signals. Our results showed apparent difference in collagen content and microstructure at various wound healing and scarring time points. It suggested that SHG signals from collagen can serve as a good indicator for characterization of wound status. With the advancement on miniaturization, microscopy based on SHG will become a valuable tool for monitoring the wound healing and scarring in vivo, and help to guide the improvement of scar appearance with appropriate and subtle modulation during wound healing based on better understanding of scarring response mechanism.

Tang, Yiyan; Zhu, Xiaoqin; Xiong, Shuyuan; Chen, Jianxin

2012-12-01

261

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

262

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

263

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

264

Functional imaging of skeletal muscle fiber in different physiological states by second harmonic generation  

NASA Astrophysics Data System (ADS)

The intrinsically ordered arrays of proteins in skeletal muscle allows imaging of this tissue by Second Harmonic Generation (SHG). Biochemical and colocalization studies have gathered an increasing wealth of clues for the attribution of the molecular origin of the muscle SHG signal to the motor protein myosin. Thus, SHG represents a potentially very powerful tool in the investigation of structural dynamics occurring in muscle during active production of force. A full characterization of the polarization-dependence of the SHG signal represents a very selective information on the orientation of the emitting proteins and their dynamics during contraction, provided that different physiological states of muscle (relaxed, rigor and active) exhibit distinct patterns of SHG polarization dependence. Here polarization data are obtained from single frog muscle fibers at rest and during isometric contraction and interpreted, by means of a model, in terms of an average orientation of the SHG emitters which are structured with a cylindrical symmetry about the fiber axis. Optimizing the setup for accurate polarization measurements with SHG, we developed a line scan imaging method allowing measurement of SHG polarization curves in different physiological states. We demonstrate that muscle fiber displays a measurable variation of the orientation of SHG emitters with the transition from rest to isometric contraction.

Nucciotti, V.; Stringari, C.; Sacconi, L.; Vanzi, F.; Tesi, C.; Piroddi, N.; Poggesi, C.; Castiglioni, C.; Milani, A.; Linari, M.; Piazzesi, G.; Lombardi, V.; Pavone, F. S.

2007-07-01

265

Second harmonic generation imaging as a potential tool for staging pregnancy and predicting preterm birth  

NASA Astrophysics Data System (ADS)

We use second harmonic generation (SHG) microscopy to assess changes in collagen structure of murine cervix during cervical remodeling of normal pregnancy and in a preterm birth model. Visual inspection of SHG images revealed substantial changes in collagen morphology throughout normal gestation. SHG images collected in both the forward and backward directions were analyzed quantitatively for changes in overall mean intensity, forward to backward intensity ratio, collagen fiber size, and porosity. Changes in mean SHG intensity and intensity ratio take place in early pregnancy, suggesting that submicroscopic changes in collagen fibril size and arrangement occur before macroscopic changes become evident. Fiber size progressively increased from early to late pregnancy, while pores between collagen fibers became larger and farther apart. Analysis of collagen features in premature cervical remodeling show that changes in collagen structure are dissimilar from normal remodeling. The ability to quantify multiple morphological features of collagen that characterize normal cervical remodeling and distinguish abnormal remodeling in preterm birth models supports future studies aimed at development of SHG endoscopic devices for clinical assessment of collagen changes during pregnancy in women and for predicting risk of preterm labor which occurs in 12.5% of all pregnancies.

Akins, Meredith L.; Luby-Phelps, Katherine; Mahendroo, Mala

2010-03-01

266

Moving targets imaging for stepped frequency radar  

Microsoft Academic Search

During the coherent processing in a stepped frequency radar, the velocity error usually affects the obtained range profile greatly. Two methods have been given to extract the target from overlapped high resolution range profiles and analyzed to show how spurious peaks appear. To surmount the influence of spurious peaks caused by velocity error, a reverse count algorithm is provided. Another

Wen Lei; Teng Long; YeQiu Han

2000-01-01

267

Harmonic Tracking of Acoustic Radiation Force Induced Displacements  

PubMed Central

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 bandpass 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 due to 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 methods improved the discrimination of the blood–vessel interface, making it easier to visualize plaque boundaries. Improvements in harmonic ARFI images in vivo were consistent with suppressed clutter supported by improved contrast and CNR in the matched harmonic B-mode images compared to the fundamental B-mode images. These results suggest that harmonic tracking methods can improve the clinical utility and diagnostic accuracy of ultrasound-based elasticity imaging methods.

Doherty, Joshua R.; Dahl, Jeremy J.; Trahey, Gregg E.

2014-01-01

268

Frequency-domain lifetime imaging methods at unilever research  

Microsoft Academic Search

Fluorescence lifetime imaging methodology has been successfully implemented at Unilever Research in a frequency-domain manner.\\u000a The experimental rig constructed comprises a wide-bandwidth electrooptic modulator operating on a CW argon-ion laser. The\\u000a modulated excitation with a typical upper modulation frequency limit of 200 MHz falls on macroscopic samples and the resultant\\u000a scattered light or fluorescence emission is then imaged onto a

John J. Birmingham

1997-01-01

269

Quantum teleportation of optical images with frequency conversion  

Microsoft Academic Search

A new version of quantum teleportation of optical images in continuous variables is considered. The new scheme is based on\\u000a quantum entanglement in continuous variables between light fields of different frequencies and allows wavelength conversion\\u000a between input and teleported images. The protocol of quantum teleportation with frequency conversion can be used as a combined\\u000a part of light\\/matter interface in quantum

Liubov V. Magdenko; Ivan V. Sokolov; Mikhail I. Kolobov

2007-01-01

270

DC Link Voltage and Supply-Side Current HarmonicsMinimization of Three Phase PWM BoostRectifiers Using Frequency Domain BasedRepetitive Current Controllers  

Microsoft Academic Search

This paper presents a digital plug-in frequency domain based repetitive control scheme for minimizing the odd order harmonics in the supply line side currents of the three phase pulsewidth modulation (PWM) boost rectifier under the distorted and unbalanced supply voltage conditions. Based on the mathematical model of the three-phase PWM boost rectifier under the generalized supply voltage conditions, the control

X. H. Wu; S. K. Panda; J. X. Xu

2008-01-01

271

Second harmonic generation and sum frequency mixing of dual wavelength Nd:YALO3 laser in flux grown KTiOPO4 crystal  

Microsoft Academic Search

On the basis of accurately measured refractive indexes, the authors have obtained the Sellmeier's equations for flux grown KTiOPO4 (KTP) crystal and used them to calculate the phase matched angles (theta sub m, phi sub m) and effective nonlinear coefficients (d sub eff) for type I and III second harmonic generation (SHG) and sum frequency mixing (SFM) of radiations at

H. Y. Shen; Y. P. Zhou; W. X. Lin; Z. D. Zeng; R. R. Zeng; G. F. Yu; C. H. Huang; A. D. Jiang; S. Q. Jia; D. Z. Shen

1992-01-01

272

Generating high-frequency, rotating magnetic fields with low harmonic content  

SciTech Connect

The future electron-ion collider (eRHIC) at Brookhaven National Laboratory demands a high-current, polarized, bunched electron beam [http://www.bnl.gov/cad/eRhic]. One of the challenges here is to combine the bunched beams generated by multiple cathodes so to address the issue of designing and prototyping a combiner with high-frequency (700 kHz) rotational magnetic fields. This article presents its design, and simulation, and details some of the test results from this unprecedented device.

Ben-Zvi, I.; Chang, X.; Litvinenko, V.; Meng, W.; Pikin, A.; Skaritka, J.

2011-09-13

273

Frequency-difference electrical impedance tomography: Phantom imaging experiments  

Microsoft Academic Search

Frequency-difference electrical impedance tomography (fdEIT) using a weighted voltage difference has been proposed as a means to provide images of admittivity changes at different frequencies. This weighted difference method is an effective way to extract anomaly information while eliminating background effects by unknown boundary geometry, uncertainty in electrode positions and other systematic measurement artefacts. It also properly handles the interplay

Sujin Ahn; Sung Chan Jun; Jin Keun Seo; Jeehyun Lee; Eung Je Woo; David Holder

2010-01-01

274

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods  

Microsoft Academic Search

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra

Usha Rani; Halil Oturak; S. Sudha; N. Sundaraganesan

2011-01-01

275

The Calculation of Accurate Harmonic Frequencies of Large Molecules: The Polycyclic Aromatic Hydrocarbons, a Case Study  

NASA Technical Reports Server (NTRS)

The vibrational frequencies and infrared intensities of naphthalene neutral and cation are studied at the self-consistent-field (SCF), second-order Moller-Plesset (MP2), and density functional theory (DFT) levels using a variety of one-particle basis sets. Very accurate frequencies can be obtained at the DFT level in conjunction with large basis sets if they are scaled with two factors, one for the C-H stretches and a second for all other modes. We also find remarkably good agreement at the B3LYP/4-31G level using only one scale factor. Unlike the neutral PAHs where all methods do reasonably well for the intensities, only the DFT results are accurate for the PAH cations. The failure of the SCF and MP2 methods is caused by symmetry breaking and an inability to describe charge delocalization. We present several interesting cases of symmetry breaking in this study. An assessment is made as to whether an ensemble of PAH neutrals or cations could account for the unidentified infrared bands observed in many astronomical sources.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)

1996-01-01

276

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

PubMed

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. PMID:21030746

Perreard, I M; Pattison, A J; Doyley, M; McGarry, M D J; Barani, Z; Van Houten, E E; Weaver, J B; Paulsen, K D

2010-11-21

277

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

278

Analytical Bistatic k Space Images Compared to Experimental Swept Frequency EAR Images  

NASA Technical Reports Server (NTRS)

A case study of flat plate scattering images obtained by the analytical bistatic k space and experimental swept frequency ISAR methods is presented. The key advantage of the bistatic k space image is that a single excitation is required, i.e., one frequency I one angle. This means that prediction approaches such as MOM only need to compute one solution at a single frequency. Bistatic image Fourier transform data are obtained by computing the scattered field at various bistatic positions about the body in k space. Experimental image Fourier transform data are obtained from the measured response to a bandwidth of frequencies over a target rotation range.

Shaeffer, John; Cooper, Brett; Hom, Kam

2004-01-01

279

Integration of the denoising, inpainting and local harmonic B(z) algorithm for MREIT imaging of intact animals.  

PubMed

Conductivity imaging based on the current-injection MRI technique has been developed in magnetic resonance electrical impedance tomography. Current injected through a pair of surface electrodes induces a magnetic flux density distribution inside an imaging object, which results in additional magnetic field inhomogeneity. We can extract phase changes related to the current injection and obtain an image of the induced magnetic flux density. Without rotating the object inside the bore, we can measure only one component B(z) of the magnetic flux density B = (B(x), B(y), B(z)). Based on a relation between the internal conductivity distribution and B(z) data subject to multiple current injections, one may reconstruct cross-sectional conductivity images. As the image reconstruction algorithm, we have been using the harmonic B(z) algorithm in numerous experimental studies. Performing conductivity imaging of intact animal and human subjects, we found technical difficulties that originated from the MR signal void phenomena in the local regions of bones, lungs and gas-filled tubular organs. Measured B(z) data inside such a problematic region contain an excessive amount of noise that deteriorates the conductivity image quality. In order to alleviate this technical problem, we applied hybrid methods incorporating ramp-preserving denoising, harmonic inpainting with isotropic diffusion and ROI imaging using the local harmonic B(z) algorithm. These methods allow us to produce conductivity images of intact animals with best achievable quality. We suggest guidelines to choose a hybrid method depending on the overall noise level and existence of distinct problematic regions of MR signal void. PMID:21098914

Jeon, Kiwan; Kim, Hyung Joong; Lee, Chang-Ock; Seo, Jin Keun; Woo, Eung Je

2010-12-21

280

A Proposal of Co-occurrence Frequency Image  

NASA Astrophysics Data System (ADS)

Image processing is generally constructed based on the gray information such as statistical gray histogram, gradient, texture, etc. However, a concrete technique that used this co-occurrence procession had been chiefly limited to the texture identification. Since the gray histogram is the most influential for extracting the global image properties, it has been always expected to be improved or extended. From this view point, it was notable that Dr. Kashiwagi proposed a new paradigm of feature extraction called Frequency Image (FI). As well as histogram, co-occurrence histogram or co-occurrence matrix is also such influential basic image feature especially for the texture feature analysis. In this paper, we introduce a new paradigm of texture feature image called “Co-occurrence Frequency Image (CFI)” as a complete extension of FI.

Yamaashi, Kazuhiko; Fujiwara, Takayuki; Koshimizu, Hiroyasu

281

Magnetic particle imaging with a planar frequency mixing magnetic detection scanner  

NASA Astrophysics Data System (ADS)

We present the first experimental results of our planar-Frequency Mixing Magnetic Detection (p-FMMD) technique to obtain Magnetic Particles Imaging (MPI). The p-FMMD scanner consists of two magnetic measurement heads with intermediate space for the analysis of the sample. The magnetic signal originates from the nonlinear magnetization characteristics of superparamagnetic particles as in case of the usual MPI scanner. However, the detection principle is different. Standard MPI records the higher order harmonic response of particles at a field-free point or line. By contrast, FMMD records a sum-frequency component generated from both a high and a low frequency magnetic field incident on the magnetically nonlinear particles. As compared to conventional MPI scanner, there is no limit on the lateral dimensions of the sample; just the sample height is limited to 2 mm. In addition, the technique does not require a strong magnetic field or gradient because of the mixing of the two different frequencies. In this study, we acquired an 18 mm × 18 mm image of a string sample decorated with 100 nm diameter magnetic particles, using the p-FMMD technique. The results showed that it is feasible to use this novel MPI scanner for biological analysis and medical diagnostic purposes.

Hong, Hyobong; Lim, Jaeho; Choi, Chel-Jong; Shin, Sung-Woong; Krause, Hans-Joachim

2014-01-01

282

Far-field imaging with a multi-frequency metalens  

NASA Astrophysics Data System (ADS)

A metalens, i.e., a dense array of identical resonators, allows to image an object pattern at subwavelength scale from far field radiation field. Here, we show that the efficiency can be improved when the resonant frequencies of the cell are distributed over a given frequency range. Because in such systems each eigen mode is localized, the subwavelength image is built from a spectral analysis of the radiated field. A simple model based on coupled resonant dipoles is used to find the best frequency distribution. This multifrequency metalens approach is validated using a flat array of split ring resonators. We experimentally demonstrate the subwavelength resolution of such a device at microwave range.

Jouvaud, C.; Ourir, A.; de Rosny, J.

2014-06-01

283

Imaging interferometric microscopy: Resolution to the limit of frequency space  

NASA Astrophysics Data System (ADS)

We demonstrate an increase of resolution over conventional microscopy configuration optical system using imaging interferometric microscopy (IIM), which is related to holography, synthetic aperture imaging and off-axis/dark-field illumination techniques. This involves both off-axis coherent illumination and re-injection of appropriate zero-order reference beams onto the image plane for image formation. First, in this dissertation, a simple case of IIM is presented where only one offset exposure in each direction was used. This allows 0.5 mum (0.8 lambda) feature resolution using 0.4 NA (numerical aperture) objective and 633 nm illumination source in contrast with conventional microscope resolution limited by 0.6lambda/NA=1.5lambda˜950 nm. After that, we show the extension of frequency space coverage to 1+ NA using two offset sub-images in each direction. Position and intensity of the sub-images are determined by comparison of the reference object with corresponding simulations by MSE (mean-square-error) calculation. We describe image distortions due to the subimages overlapping in Fourier space and show the necessity of filtering images. Then, we approach the lambda/4 theoretical linear systems limits of optical resolution by tilting the object plane. We describe the frequency space distortions due to the nonlinear frequency transformation, associated with a non unaxial optical system and propose the method of the frequencies recalculation. After fast Fourier transform (FFT) of the experimental (distorted) real space high-frequency sub-image is taken to provide a frequency space, the experimental frequencies are corrected. Fractional frequencies are used for the inverse transform or interpolation (both amplitude and phase) to assign values to the nearest frequencies on the appropriate grid. Images are reconstructed after converting back to real space. In the present experiments, the frequency space coverage extends to 1.87/lambda, or to a pitch of 170 nm using a 633-nm wavelength source. These results are achieved using a modest 0.4-NA optical system and retain the working distance, field-of-view and depth-of-field advantages of low NA systems while approaching ultimate linear-systems resolution limits. Extension of this approach to 193-nm immersion provides a route to < 40-nm resolution optical microscopy. This technique may be useful for solving defocusing problems, mask inspection, biological research and other applications.

Kuznetsova, Yuliya

284

Detecting subtle plasma membrane perturbation in living cells using second harmonic generation imaging.  

PubMed

The requirement of center asymmetry for the creation of second harmonic generation (SHG) signals makes it an attractive technique for visualizing changes in interfacial layers such as the plasma membrane of biological cells. In this article, we explore the use of lipophilic SHG probes to detect minute perturbations in the plasma membrane. Three candidate probes, Di-4-ANEPPDHQ (Di-4), FM4-64, and all-trans-retinol, were evaluated for SHG effectiveness in Jurkat cells. Di-4 proved superior with both strong SHG signal and limited bleaching artifacts. To test whether rapid changes in membrane symmetry could be detected using SHG, we exposed cells to nanosecond-pulsed electric fields, which are believed to cause formation of nanopores in the plasma membrane. Upon nanosecond-pulsed electric fields exposure, we observed an instantaneous drop of ~50% in SHG signal from the anodic pole of the cell. When compared to the simultaneously acquired fluorescence signals, it appears that the signal change was not due to the probe diffusing out of the membrane or changes in membrane potential or fluidity. We hypothesize that this loss in SHG signal is due to disruption in the interfacial nature of the membrane. The results show that SHG imaging has great potential as a tool for measuring rapid and subtle plasma membrane disturbance in living cells. PMID:24853757

Moen, Erick K; Ibey, Bennett L; Beier, Hope T

2014-05-20

285

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

286

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

PubMed Central

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 are used collectively via comparative analysis. Monte Carlo simulations of the SHG axial directional and attenuation responses allow their decomposition into the underlying factors that are not readily obtainable through experimental techniques. Specifically, this approach allows for estimation of the SHG creation attributes (directionality and relative conversion efficiency) and separation of primary and secondary filter effects, collectively that form the observed SHG contrast. The quantitative metric is shown for the connective tissue disorder Osteogenesis Imperfecta (characterized by abnormal assembly of type I collagen) using a murine model that expresses the disease in the dermis layer of skin. Structural dissimilarities between the osteogenesis imperfecta mouse and wild-type tissues lead to significant differences in the SHG depth-dependent directionality and signal attenuation. The Monte Carlo simulations of these responses using measured bulk optical parameters reproduce the experimental data trends, and the extracted emission directionality and conversion efficiencies are consistent with independent determinations. The simulations also illustrate the dominance of primary filter affects on overall SHG generation and attenuation. Thus, the combined method of 3D SHG imaging and modeling forms an essential foundation for parametric description of the matrix properties that are not distinguishable by sole consideration of either bulk optical parameters or SHG alone. Moreover, due to the quasi-coherence of the SHG process in tissues, we submit that this approach contains unique information not possible by purely scattering based methods and that these methods will be applicable in the general case where the complex fibrillar structure is difficult to fully quantify via morphological analysis.

LaComb, Ronald; Nadiarnykh, Oleg; Campagnola, Paul J.

2008-01-01

287

Quantitative second harmonic generation imaging of the diseased state osteogenesis imperfecta: experiment and simulation.  

PubMed

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 are used collectively via comparative analysis. Monte Carlo simulations of the SHG axial directional and attenuation responses allow their decomposition into the underlying factors that are not readily obtainable through experimental techniques. Specifically, this approach allows for estimation of the SHG creation attributes (directionality and relative conversion efficiency) and separation of primary and secondary filter effects, collectively that form the observed SHG contrast. The quantitative metric is shown for the connective tissue disorder Osteogenesis Imperfecta (characterized by abnormal assembly of type I collagen) using a murine model that expresses the disease in the dermis layer of skin. Structural dissimilarities between the osteogenesis imperfecta mouse and wild-type tissues lead to significant differences in the SHG depth-dependent directionality and signal attenuation. The Monte Carlo simulations of these responses using measured bulk optical parameters reproduce the experimental data trends, and the extracted emission directionality and conversion efficiencies are consistent with independent determinations. The simulations also illustrate the dominance of primary filter affects on overall SHG generation and attenuation. Thus, the combined method of 3D SHG imaging and modeling forms an essential foundation for parametric description of the matrix properties that are not distinguishable by sole consideration of either bulk optical parameters or SHG alone. Moreover, due to the quasi-coherence of the SHG process in tissues, we submit that this approach contains unique information not possible by purely scattering based methods and that these methods will be applicable in the general case where the complex fibrillar structure is difficult to fully quantify via morphological analysis. PMID:18281387

Lacomb, Ronald; Nadiarnykh, Oleg; Campagnola, Paul J

2008-06-01

288

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

289

Frequency division multiplexed imaging: a Texas Instruments DMD implementation  

NASA Astrophysics Data System (ADS)

Recently we proposed frequency division multiplexed imaging (FDMI), which allows capturing multiple images in a single shot through spatial modulation and frequency domain filtering. This is achieved by spatially modulating the images so that different images or sub-exposures are placed at different locations in the Fourier domain. As long as there is no overlap of the individual bands, we can recover different components by band-pass filtering the multiplexed image. In this paper, we present a Texas Instruments DMD based implementation of FDMI. An image is formed on the DMD chip; pixels are modulated by the micro-mirrors; and the modulated image is captured by a camera. By applying modulation during a sub-exposure period, the corresponding sub-exposure image is at the end recovered from the fullexposure image. Such a system could be used in a variety of applications, such as motion analysis and image deblurring. We will provide experimental results with the setup, and discuss possible applications as well as limitations.

Habibkhani, Houman; Gunturk, Bahadir K.; Feldman, Martin; Batur, Aziz U.

2014-03-01

290

Evaluation of high-frequency sinusoidal waveform superposed with 3rd harmonic for stable operation of metal halide lamps  

Microsoft Academic Search

In this paper a novel topology to supply MH lamps using sinusoidal waveform with superposed third harmonic is proposed. By employing this technique, the lamp is supplied with an approximated square waveform, but reducing the harmonic content and therefore EMI and RFI. The proposed topology is analyzed and designed for a 35 W MH lamp with ceramic discharge tube. Experimental

J. M. Alonso; J. Ribas; M. Rico-Secades; J. Garcia; J. Cardesin

2002-01-01

291

Evidence for Harmonic Content and Frequency Evolution of Oscillations During the Rising Phase of X-ray Bursts From 4U 1636-536  

NASA Technical Reports Server (NTRS)

We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst oscillation pulses during the early rising phases of bursts. This is the first such detection in burst rise oscillations, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of oscillation frequency increase during the burst rise. The timing behavior of harmonic content, amplitude, and frequency of burst rise oscillations may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.

Bgattacharyya, Sudip; Strohmayer, E.

2005-01-01

292

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

293

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

294

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

NASA Astrophysics Data System (ADS)

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

Park, Won-Kwang; Lesselier, Dominique

2009-11-01

295

Time-Frequency Analysis in Terahertz-Pulsed Imaging  

Microsoft Academic Search

Recent advances in laser and electro-optical technologies have made the previously underutilized terahertz frequency band\\u000a of the electromagnetic spectrum accessible for practical imaging. Applications are emerging, notably in the biomedical domain.\\u000a In this chapter the technique of terahertz-pulsed imaging is introduced in some detail. The need for special computer vision\\u000a methods, which arises from the use of pulses of radiation

Elizabeth Berry; Roger D Boyle; Anthony J Fitzgerald; James Handley

296

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

297

Fast Polar Harmonic Transforms  

Microsoft Academic Search

Polar Harmonic Transform (PHT) is termed to represent a set of transforms those kernels are basic waves and harmonic in nature. PHTs consist of Polar Complex Exponential Transform (PCET), Polar Cosine Transform (PCT) and Polar Sine Transform (PST). They are proposed to represent invariant image patterns for two dimensional image retrieval and pattern recognition tasks. They are demonstrated to show

Zhuo Yang; Sei-ichiro Kamata

2010-01-01

298

High Frequency Electromagnetic Fields in Magnetic Resonance Imaging.  

NASA Astrophysics Data System (ADS)

Radiofrequency (RF) electromagnetic fields are widely used in Nuclear Magnetic Resonance Imaging. The signal-to-noise of the image increases as the frequency of the RF does and, for that reason, high frequency systems (~64MHz) are currently being used, and still higher frequencies (170MHz) are being considered for the future. However, this could be both inconvenient and dangerous. As the frequency of the field increases, there is less field penetration into matter, due to conductivity effects. Information from a given spatial point in the object under imaging strongly depends on the value that the RF magnetic field takes at that location and sometimes it is required that the field takes prescribed values at all points in a given region of the sample. This is in contradiction with the boundary conditions of the problem (the problem is inconsistently overconstrained), unless sufficiently low frequencies are used. When high frequencies are used, a correction scheme or, at least, a knowledge of the image non-uniformity due to penetration effects is needed. On the other hand, the heat deposited inside the object also increases with frequency. The knowledge of the heat absorbed by the object is important in that it sets upper bounds on the frequency to be used or the duty cycle if irreversible changes in the sample are to be avoided. In this work we study such problem analytically, numerically, and experimentally for a variety of body shapes and field distributions. We find that 170 MHz is an approximate upper bound for the Magnetic Resonance Imaging frequency in order for it to be safely used in medical applications; different sequences were simulated in the leg and the brain in order to obtain the power deposition under them, spin echo and FLASH sequences show that the power deposited up to 170 MHz does not exceed international safety regulations of 2 W/Kg locally and 0.4 W/Kg on the average. This will not be the case any longer if 3D fast imaging is implemented at 170 MHz. We evaluate the numerical approaches and find that the one based on the use of the vector potential rather than fields and/or currents is optimal. (Abstract shortened with permission of author.).

Zypman Niechonski, Fredy Ruben

299

A New High Frequency Ultrasound Skin Imaging System: Imaging Properties and Clinical in Vivo Results  

NASA Astrophysics Data System (ADS)

In this paper, a new high frequency ultrasound (HFUS) system for high-resolution skin imaging is presented. For imaging, mechanical scans are performed with spherically focused single element transducers. Two separate applicators with different transducers are utilized to fulfill the different requirements for imaging the skin with 20MHz ultrasound and for lower range high resolution imaging of the uppermost skin layers with HFUS in the 100MHz range. Clinical images were acquired in the imaging lab of the Dermatological University Hospital. Imaging results of wound healing process and skin lesion nevus investigations are presented

Vogt, M.; Scharenberg, R.; Moussa, G.; Sand, M.; Hoffmann, K.; Altmeyer, P.; Ermert, H.

300

In vivo and ex vivo imaging of intra-tissue elastic fibers using third-harmonic-generation microscopy.  

PubMed

Elastin is an essential and widespread structural protein in charge of the integrity on tissues and organs. In this study, we demonstrate that elastin is a major origin of the third-harmonic-generation (THG) contrast under Cr:forsterite laser excitation operating at 1230nm, with selective visualization inside many tissues such as lung tissues and arteries. In vivo imaging of the nude mouse elastic cartilage beneath the hypodermis by epi- THG microscopy keeps the high resolution and contrast in all three dimensions. Combined with second-harmonic-generation microscopy, THG microscopy exhibits the ability to show the extraordinary proliferation of elastic fibers for the ophthalmic disease of pterygium and the capability of distinguishable visualization from collagen. PMID:19547471

Sun, Chi-Kuang; Yu, Che-Hang; Tai, Shih-Peng; Kung, Chun-Ta; Wang, I-Jong; Yu, Han-Chieh; Huang, Hsiang-Ju; Lee, Wen-Jeng; Chan, Yi-Fan

2007-09-01

301

Diagnosis of colon cancer using frequency domain fluorescence imaging technique  

NASA Astrophysics Data System (ADS)

Early detection and treatment of colon cancer has been associated with better disease prognosis. Conventional and reported optical techniques have limitations in detecting early stages of colon cancer growth. In this paper, a homodyne signal processing assisted frequency domain (FD) fluorescence imaging methodology is proposed for the early diagnosis of colon cancer. Simulated phantom tissues representing the biopsy samples at different stages of colon cancer growth are prepared and used for the imaging study. Selective imaging of healthy and diseased sites simulated in the samples was achieved even for fluorescence emissions having close lifetimes and wavelength values. Possible extension of the methodology for in vivo investigations is also discussed.

Dinish, U. S.; Gulati, P.; Murukeshan, V. M.; Seah, L. K.

2007-03-01

302

Experimental investigation of the ionospheric hysteresis effect on the threshold excitation level of the Stimulated Electromagnetic Emission (SEE) during heating at the second electron gyro-harmonic frequency  

NASA Astrophysics Data System (ADS)

Recent experimental observations of the stimulated electromagnetic emission (SEE) spectrum during heating at the second electron gyro-harmonic show structures ordered by ion gyro-frequency. The proposed generation mechanism considers parametric decay of a pump upper hybrid/electron Bernstein (UH/EB) wave into another UH/EB and a group of neutralized ion Bernstein waves. The presumption of the proposed mechanism is that the pump electromagnetic wave is converted into the UH/EB wave. This conversion process generates field aligned irregularity which exhibits hysteresis effect. The predicted ionospheric hysteresis effect is studied during the PARS 2012 at HAARP. The preliminary results are presented for the first time. Also, experimental study of the effects of 1) the transmitter beam angle and 2) the transmitter frequency offset relative to the second electron gyro-harmonic frequency on the ion gyro-harmonic structures in the SEE spectrum are provided. The aforementioned observations are compared to the predictions of the analytical model. Possible connection of the SEE spectral features and artificially generated ionospheric descending layer is also discussed

Samimi, A.; Scales, W.; Cruz, M.; Isham, B.; Bernhardt, P. A.

2012-12-01

303

Coronal loops diagnostics using the parameters of U-burst harmonic pair at frequencies 10-70 MHz  

NASA Astrophysics Data System (ADS)

The results of the first observations of solar sporadic radio emission using one section of the new being currently created Giant Ukrainian Radio Telescope (GURT) are presented. The parameters of inverted U-burst with harmonic structure observed with GURT are considered. The main attention is paid to the time delay between the fundamental and harmonic components. The analytical model explaining the observed time delay is proposed.

Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.; Bubnov, I. N.; Gridin, A. A.; Shevchuk, N. V.; Rucker, H. O.; Panchenko, M.

2013-09-01

304

Imaging of point scatterers from step-frequency ISAR data  

Microsoft Academic Search

A high-resolution method for imaging of point scatterers from step-frequency inverse synthetic-aperture radar (ISAR) data is presented. An analysis of the noise sensitivity of the method is provided to show the high performance of the method. Simulation results are given to show the robustness of the method against model errors

Y. Hua; F. A. Baqai; Y. Zhu; D. J. Heilbronn

1993-01-01

305

Photoacoustic imaging using a frequency domain synthetic aperture focusing technique  

NASA Astrophysics Data System (ADS)

This paper describes the application of a frequency domain synthetic aperture focusing technique to photoacoustic imaging. The photoacoustic probe consisted of a laser delivery fiber-optic (diameter of 600 ?m, plastic coated silica) combined with a polymer (PVDF) transducer for ultrasonic detection. This system had a broadband frequency response in the MHz region. Such an integral probe was designed to optically transmit and receive near on-axis ultrasonic transients simultaneously, in under water applications. A frequency domain synthetic aperture method was successfully applied using phantom samples to produce 2D images from A-scan signals received from the probe. A range of samples were examined, including black nylon with 1 mm circular holes at a depth of 5.9 mm from the surface. A comparison was made with conventional B-scan images and with time domain synthetic aperture images. Results showed that synthetic focusing apertures, in time or frequency domains, offer better signal-to-noise ratios with improved capabilities in lateral resolution.

Boonsang, S.; Zainal, J.; Dewhurst, Richard J.

2004-07-01

306

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

307

Space-frequency quantization for wavelet image coding  

NASA Astrophysics Data System (ADS)

A novel wavelet packet image coder is introduced in this paper. It is based on our previous work on wavelet image coding using space-frequency quantization (SFQ), in which zerotree quantization and scalar quantization are jointly optimized in a rate-distortion sense. In this paper, we extend the powerful SFQ coding paradigm from the wavelet transform to the more general wavelet packet transformation. The resulting wavelet packet coder offers a universal transform coding framework within the constraints of filter bank structures by allowing joint transform and quantizer design without assuming a priori statistics of the input image. In other words, the new coder adaptively chooses the representation to suit the image and the quantization to suit the representation. Experimental results show that, for some image classes, our new coder is capable of achieving the best coding performances among those in the published literature.

Xiong, Zixiang; Ramchandran, Kannan; Orchard, Michael T.

1996-11-01

308

Detection of deformable objects in 3D images using Markov-Chain Monte Carlo and spherical harmonics.  

PubMed

We address the problem of segmenting 3D microscopic volumetric intensity images of a collection of spatially correlated objects (such as fluorescently labeled nuclei in a tissue). This problem arises in the study of tissue morphogenesis where cells and cellular components are organized in accord with biological role and fate. We formulate the image model as stochastically generated based on biological priors and physics of image formation. We express the segmentation problem in terms of Bayesian inference and use data-driven Markov Chain Monte Carlo to fit the image model to data. We perform an initial step in which the intensity volume is approximated as an expansion in 4D spherical harmonics, the coefficients of which capture the general organization of objects. Since cell nuclei are membrane-bound their shapes are subject to membrane lipid bilayer bending energy, which we use to constrain individual contours. Moreover, we parameterize the nuclear contours using spherical harmonic functions, which provide a shape description with no restriction to particular symmetries. We demonstrate the utility of our approach using synthetic and real fluorescence microscopy data. PMID:18982711

Khairy, Khaled; Reynaud, Emmanuel; Stelzer, Ernst

2008-01-01

309

An experimental investigation of refraction-induced distortions in harmonic-light images of laser-produced plasmas  

SciTech Connect

In this paper the results of a simple experiment designed to study refraction-induced distortion of images of narrow-band-light-emitting regions in a laser-produced plasma are described. Source regions were formed by relaying the image of a backlit pinhole array into the plasma (25 {mu}m-diam. pinhole; 30-ps, 0.25-{mu}m backlighter beam). Images of these source regions were recorded on film and compared with and without plasma present. Refraction effects, evidenced by translation of the apparent pinhole locations and blurring of the pinhole spots, are compared for different plasma sizes and for different delays of the backlighter pulse with respect to the plasma-production laser pulse. These results were then compared with expectations based on numerical raytraces through a plasma-density profile derived from a hydrodynamic simulation of our exploding-foil plasma. The significance of these results in the imaging of harmonic and half-harmonic light as a plasma-density diagnostic is discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

Darrow, C.; Montgomery, D.S.; Estabrook, K.; Drake, R.P. (Lawrence Livermore National Laboratory, Box 808, Livermore, California 94550 (USA)); Busch, G.E.; Gabl, E.F. (KMS Fusion Inc., 3621 South State Road, Ann Arbor, Michigan 48106 (USA))

1990-04-15

310

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

311

Frequency-selected enhancement of high-order-harmonic generation by interference of degenerate Rydberg states in a few-cycle laser pulse  

NASA Astrophysics Data System (ADS)

We demonstrate that the frequency-selected enhancement of high-order-harmonic generation (HHG) can be achieved by a few-cycle laser pulse interacting with a coherent superposition state, which is prepared by the ground state and two degenerate Rydberg states. The degenerate states have the same orbital radius and hence have a large overlap in the electronic density distribution. By controlling the relative phase between the two degenerate states, the constructive or destructive interference of them can markedly change the initial density distribution of the Rydberg electron, thereby we can manipulate the characteristics and the conversion efficiency of HHG. Specifically, a significant enhancement in the continuous harmonics near HHG cutoff can be obtained, hence an intense isolated pulse with a duration less than 100 attoseconds is straightforwardly generated. On the other hand, since there exists a specific dependence of the harmonic efficiency on the relative phase of the two degenerate states, one can expect that the relative phase may be probed by examining the corresponding harmonic intensity. In practice, we may apply a weak static electric field in the whole dynamic process to obtain an asymmetry electron density distribution at a large radius; hence similar HHG results can be obtained.

Chen, Jigen; Wang, Ruquang; Zhai, Zhen; Chen, Jing; Fu, Panming; Wang, Bingbing; Liu, Wu-Ming

2012-09-01

312

Imaging of low-frequency fluctuations in dipole confined plasma  

NASA Astrophysics Data System (ADS)

Two 16-channel photodiodes arrays have been constructed to image the structure of low frequency (0.5-10 kHz) fluctuations observed in the LDX plasmas. Fluctuations in the 1-10 kHz range have previously been observed in LDX plasmas created with the internal coil supported [2]. We now report on observations of plasmas with the internal coil fully levitated. Fluctuations in this frequency range are still observed during multi-frequency heating and in addition fluctuations on the order of a few hundred Hz are also observed during 2.45 GHz only heating. Data from the 4-channel interferometer suggests these modes have some broad radial structure and electrostatic probes and Mirnov coils indicate an m=1 toroidal mode structure. The photodiode arrays will provide better radial resolution while simultaneously providing a measure of the toroidal mode number. A Phantom fast camera also images the plasma and we will compare results from the photodiode array to images from the fast camera. 2. Garnier et al, ``Stabilization of low frequency instability in a dipole plasma,'' to be published in Journal of Plasma Physics (2008).

Ellsworth, Jennifer; Bergmann, R. M.; Boxer, A. C.; Kesner, J.; Garnier, D. T.; Mauel, M. E.

2008-11-01

313

Do High Frequency Ultrasound Images Support Clinical Skin Assessment?  

PubMed Central

High frequency ultrasound imaging has been reported as a potential method of identifying the suspected tissue damage in patients “at risk” of pressure ulceration. The aim of this study was to explore whether ultrasound images supported the clinical skin assessment in an inpatient population through identification of subcutaneous tissue damage. Skin on the heels and/or sacral coccygeal area of fifty vascular surgery inpatients was assessed clinically by tissue viability nurses and with ultrasound pre operatively and at least every other day until discharge. Images were compared to routine clinical skin assessment outcomes. Qualitative classification of ultrasound images did not match outcomes yielded through the clinical skin assessment. Images corresponding to 16 participants were classified as subgroup 3 damage at the heels (equivalent to grade 2 pressure ulceration); clinical skin assessment rated no heels as greater than grade 1a (blanching erythema). Conversely, all images captured of the sacral coccygeal area were classified as normal; the clinical skin assessment rated two participants as grade 1b (non-blanching erythema). Ultrasound imaging is a potentially useful adjunct to the clinical skin assessment in providing information about the underlying tissue. However, further longitudinal clinical assessment is required to characterise images against actual and “staged” pressure ulceration.

Porter-Armstrong, Alison P.; Adams, Catherine; Moorhead, Anne S.; Donnelly, Jeannie; Nixon, Jane; Bader, Daniel L.; Lyder, Courtney; Stinson, May D.

2013-01-01

314

Robust nonrigid multimodal image registration using local frequency maps.  

PubMed

Automatic multi-modal image registration is central to numerous tasks in medical imaging today and has a vast range of applications e.g., image guidance, atlas construction, etc. In this paper, we present a novel multi-modal 3D non-rigid registration algorithm where in 3D images to be registered are represented by their corresponding local frequency maps efficiently computed using the Riesz transform as opposed to the popularly used Gabor filters. The non-rigid registration between these local frequency maps is formulated in a statistically robust framework involving the minimization of the integral squared error a.k.a. L2E (L2 error). This error is expressed as the squared difference between the true density of the residual (which is the squared difference between the non-rigidly transformed reference and the target local frequency representations) and a Gaussian or mixture of Gaussians density approximation of the same. The non-rigid transformation is expressed in a B-spline basis to achieve the desired smoothness in the transformation as well as computational efficiency. The key contributions of this work are (i) the use of Riesz transform to achieve better efficiency in computing the local frequency representation in comparison to Gabor filter-based approaches, (ii) new mathematical model for local-frequency based non-rigid registration, (iii) analytic computation of the gradient of the robust non-rigid registration cost function to achieve efficient and accurate registration. The proposed non-rigid L2E-based registration is a significant extension of research reported in literature to date. We present experimental results for registering several real data sets with synthetic and real non-rigid misalignments. PMID:17354721

Jian, Bing; Vemuri, Baba C; Marroquin, José L

2005-01-01

315

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

316

Phase-inversion tissue harmonic imaging compared with conventional B-mode ultrasound in the evaluation of pancreatic lesions.  

PubMed

The aim of this study was to compare the diagnostic sensitivity, specificity, and image quality of conventional B-mode US (BM) and phase-inversion tissue harmonic imaging (PTHI) regarding pancreatic pathology. In a prospective study, 107 patients, aged between 28 and 85 years, underwent US examinations of the pancreas with both BM and PTHI in a randomly chosen order. As diagnostic reference, either contrast-enhanced CT or MRI examinations of the upper abdomen were obtained in all patients. Sensitivity and specificity were evaluated using the Student's t test. Differences in overall image quality, lesion conspicuity, fluid-solid differentiation, and delineation of the pancreatic tail were analyzed using Wilcoxon's signed ranks test and Bowker's symmetry test. Sixteen of 107 examined patients (15%) were non-diagnostic and excluded due to technical limitations such as abdominal gas. A total of 60 pancreatic lesions (cysts, acute pancreatitis, dilatation of the pancreatic duct, calcifications, and solid tumors) were diagnosed by CT or MRI. Phase-inversion tissue harmonic imaging had a higher sensitivity of 70% (14 of 20) than BM (60%; 24 of 40) for the detection of pancreatic lesions; however, the difference was not statistically significant ( p=0.46). In the assessment of lesions <1 cm of size, PTHI had a sensitivity of 70% and BM 46.7%, whereby the difference again was not statistically significant. Phase-inversion tissue harmonic imaging proved to be superior to BM regarding overall image quality ( p<0.0001), lesion conspicuity ( p=0.0045), and fluid-solid differentiation ( p=0.0002), as well as the delineation of the pancreatic tail ( p<0.0001). These differences were statistically significant. The statistically significant improvement of image quality with regards to lesion conspicuity, fluid-solid differentiation, and delineation of the pancreatic tail favors the use of PTHI when evaluating the pancreas with US. Sensitivity for pancreatic lesions is increased with PTHI in comparison with conventional sonography (BM), especially in lesions <1 cm in diameter, although the difference was not statistically significant. PMID:14714139

Hohl, Christian; Schmidt, Thorsten; Haage, Patrick; Honnef, Dagmar; Blaum, Marcus; Staatz, Gundula; Guenther, Rolf W

2004-06-01

317

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

PubMed Central

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

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

2014-01-01

318

High-frequency ultrasonic arrays for ocular imaging  

NASA Astrophysics Data System (ADS)

High-resolution ultrasound imaging of the anterior portion of the eye has been shown to provide important information for sizing of intraocular lens implants, diagnosis of pathological conditions, and creation of detailed maps of corneal topography to guide refractive surgery. Current ultrasound imaging systems rely on mechanical scanning of a single acoustic element over the surface of the eye to create the three-dimensional information needed by clinicians. This mechanical scanning process is time-consuming and subject to errors caused by eye movement during the scanning period. This paper describes development of linear ultrasound imaging arrays intended to increase the speed of image acquisition and reduce problems associated with ocular motion. The arrays consist of a linear arrangement of high-frequency transducer elements designed to operate in the 50 - 75 MHz frequency range. The arrays are produced using single-crystal lithium niobate piezoelectric material, thin film electrodes, and epoxy-based acoustic layers. The array elements have been used to image steel test structures and bovine cornea.

Jaeger, M. D.; Kline-Schoder, R. J.; Douville, G. M.; Gagne, J. R.; Morrison, K. T.; Audette, W. E.; Kynor, D. B.

2007-03-01

319

Broadband Frequency Mixing and Second-Harmonic Generation in 2-METHYL-4-NITROANILINE Thin Crystal from 250 FS Pulses  

NASA Astrophysics Data System (ADS)

In this paper, we present the experimental proof that even for highly nonlinear (NL), such as 2-methyl-4-nitroaniline (MNA), wave mixing has negligible effect on the second-harmonic generation (SHG) using 250 fs fundamental pulses. We explain our experimental results with a simple formalism based on monochromatic plane wave (MPW).

Ben-Messaoud, T.; Desforges, J.; Gauvin, S.

320

A neuro-genetic and time-frequency approach to macromodeling dynamic hysteresis in the harmonic regime  

Microsoft Academic Search

A numerical approach for the evaluation of hysteresis loops in the harmonic regime is presented. Genetic algorithms (GAs) are used to train neural networks (NNs) with the aim of generalizing the Jiles-Atherton (JA) static hysteresis model for dynamic loops. The NN training is based on symmetrical and asymmetrical, major and minor loops under sinusoidal excitation with or without offset. Subsequently,

Alessandro Salvini; Francesco Riganti Fulginei; Christian Coltelli

2003-01-01

321

ACCURATE SHORT-TERM ANALYSIS OF THE FUNDAMENTAL FREQUENCY AND THE HARMONICS-TO-NOISE RATIO OF A SAMPLED SOUND  

Microsoft Academic Search

We present a straightforward and robust algorithm for periodicity detection, working in the lag (autocorrelation) domain. When it is tested for periodic signals and for signals with additive noise or jitter, it proves to be several orders of magnitude more accurate than the methods commonly used for speech analysis. This makes our method capable of measuring harmonics-to-noise ratios in the

Paul Boersma

1993-01-01

322

Multispectral mid-infrared imaging using frequency upconversion  

NASA Astrophysics Data System (ADS)

It has recently been shown that it is possible to upconvert infrared images to the near infrared region with high quantum efficiency and low noise by three-wave mixing with a laser field [1]. If the mixing laser is single-frequency, the upconverted image is simply a band-pass filtered version of the infrared object field, with a bandwidth corresponding given by the acceptance parameter of the conversion process, and a center frequency given by the phase-match condition. Tuning of the phase-matched wavelengths has previously been demonstrated by changing the temperature [2] or angle [3 Keywords: Infrared imaging, nonlinear frequency conversion, diode lasers, upconversion ] of the nonlinear material. Unfortunately, temperature tuning is slow, and angle tuning typically results in alignment issues. Here we present a novel approach where the wavelength of the mixing field is used as a tuning parameter, allowing for fast tuning and hence potentially fast image acquisition, paving the way for upconversion based real time multispectral imaging. In the present realization the upconversion module consists of an external cavity tapered diode laser in a Littrow configuration with a computer controlled feedback grating. The output from a tunable laser is used as seed for a fiber amplifier system, boosting the power to approx. 3 W over the tuning range from 1025 to 1085 nm. Using a periodically poled lithium niobate crystal, the infrared wavelength that can be phase-matched is tunable over more than 200 nm. Using a crystal with multiple poling periods allows for upconversion within the entire transparency range of the nonlinear material.

Sanders, Nicolai; Dam, Jeppe Seidelin; Jensen, Ole Bjarlin; Tidemand-Lichtenberg, Peter; Pedersen, Christian

2013-03-01

323

Quantification of collagen fiber organization in biological tissues at cellular and molecular scales using second-harmonic generation imaging  

NASA Astrophysics Data System (ADS)

Collagen is the most abundant structural protein found in the human body, and is responsible for providing structure and function to tissues. Collagen molecules organize naturally into structures called fibers on the scale of the wavelength of light and lack inversion symmetry, thus allowing for the process of second harmonic generation (SHG) when exposed to intense incident light. We have developed two quantitative techniques: Fourier transform-second-harmonic generation (FT-SHG) imaging and generalized chi2 second-harmonic generation (chi2-SHG) imaging. In order to show that FT-SHG imaging can be used as a valuable diagnostic tool for real-world biological problems, we first investigate collagenase-induced injury in horse tendons. Clear differences in collagen fiber organization between normal and injured tendon are quantified. In particular, we observe that the regularly oriented organization of collagen fibers in normal tendons is disrupted in injured tendons leading to a more random organization. We also observe that FT-SHG microscopy is more sensitive in assessing tendon injury compared to the conventional polarized light microscopy. The second study includes quantifying collagen fibers in cortical bone using FT-SHG imaging and comparing it with scanning electron microscopy (SEM). Further, as an example study, we show how FT-SHG imaging could be used to quantify changes in bone structure as a function of age. Some initial work and future directions for extending FT-SHG to 3D are also discussed. The second technique, chi2-SHG imaging, takes advantage of the coherent nature of SHG and utilizes polarization to extract the second-order susceptibility (d elements) which provides information on molecular organization, i.e., it provides access to sub-diffractional changes "optically". We use chi2-SHG in combination with FT-SHG imaging to investigate a couple of biological problems. First, we quantify differences in collagen fiber organization between cornea and sclera of the eye in order to investigate their properties of transparency and opacity, respectively. We find from chi2-SHG imaging that there is no statistical difference in the values of d elements between cornea and sclera, indicating that the underlying collagen structure generating SHG from the two is similar at the level of detection of SHG microscopy. However, the difference lies in the spatial organization of these collagen fibers as observed from FT-SHG imaging. We find that cornea contains lamellae with patches of ordered and uniform diameter collagen fibers with axial order, which could be the reason for its transparent behavior. Conversely, there are no lamellae in sclera (i.e., no axial order), and fibers are thicker, denser, have inconsistent diameters, and possess relatively inhomogeneous orientations, leading to its opaque nature. We also utilized the two techniques to assess differences in stromal collagen fibers for several human breast tissue conditions: normal, hyperplasia, dysplasia, and malignant. Using FT-SHG imaging, we note differences between malignant and other pathological conditions through the metric A.I. ratio. Using generalized chi2-SHG imaging, we observe structural changes in collagen at the molecular scale, and a particular d element showed a more sensitive differentiation between breast tissue conditions, except between hyperplasia and normal/dysplasia. We also find that the trigonal symmetry (3m) is a more appropriate model to describe collagen fibers in malignant tissues as opposed to the conventionally used hexagonal symmetry (C6). Furthermore, the percentage of abnormal collagen fibers could potentially be used as a metric for differentiating breast tissue conditions. We also introduce a technique for extending chi2-SHG to fibers with curvature which is useful for generating chi2-image maps (in terms of d elements) instead of the conventional SHG intensity images. The spatial variations in d elements will provide additional information. For example, in breast cancer tissues, it may help in observing how fibers chang

Ambekar Ramachandra Rao, Raghu

324

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

2013-01-01

325

Quantitative analysis of collagen fiber organization in injured tendons using Fourier transform-second harmonic generation imaging.  

PubMed

Fourier transform-second harmonic generation (FT-SHG) imaging is used as a technique for evaluating collagenase-induced injury in horse tendons. The differences in collagen fiber organization between normal and injured tendon are quantified. Results indicate that the organization of collagen fibers is regularly oriented in normal tendons and randomly organized in injured tendons. This is further supported through the use of additional metrics, in particular, the number of dark (no/minimal signal) and isotropic (no preferred fiber orientation) regions in the images, and the ratio of forward-to-backward second-harmonic intensity. FT-SHG microscopy is also compared with the conventional polarized light microscopy and is shown to be more sensitive to assessing injured tendons than the latter. Moreover, sample preparation artifacts that affect the quantitative evaluation of collagen fiber organization can be circumvented by using FT-SHG microscopy. The technique has potential as an assessment tool for evaluating the impact of various injuries that affect collagen fiber organization. PMID:21164843

Sivaguru, Mayandi; Durgam, Sushmitha; Ambekar, Raghu; Luedtke, David; Fried, Glenn; Stewart, Allison; Toussaint, Kimani C

2010-11-22

326

Pulse Inversion Chirp Coded Tissue Harmonic Imaging (PI-CTHI) of Zebrafish Heart Using High Frame Rate Ultrasound Biomicroscopy  

PubMed Central

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 (LiNbO3) 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.

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

2012-01-01

327

Multitone harmonic radar  

NASA Astrophysics Data System (ADS)

Nonlinear radar exploits the electronic response from a target whose reflected frequencies are different from those transmitted. Reception of frequencies that are not part of the transmitted probe distinguishes the received signal from a linear return produced by clutter and indicates the presence of electronics. Presented in this paper is a type of nonlinear radar that transmits multiple frequencies and listens for a harmonic of these frequencies as well as other frequencies near that harmonic. A laboratory test-bed has been constructed to demonstrate the multitone radar concept. Measurements of nonlinear responses from RF devices probed by multiple tones are reported.

Mazzaro, Gregory J.; Martone, Anthony F.

2013-05-01

328

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods.  

PubMed

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule. PMID:21334254

Rani, Usha; Oturak, Halil; Sudha, S; Sundaraganesan, N

2011-05-01

329

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule.

Rani, Usha; Oturak, Halil; Sudha, S.; Sundaraganesan, N.

2011-05-01

330

Applying Echoes Mean Frequency Shift for Attenuation Imaging in Tissue  

NASA Astrophysics Data System (ADS)

The purpose of this study was to develop the attenuation parametric imaging technique and to apply it for in vivo characterization of tissue. Local attenuation coefficient was determined by evaluating the frequency downshift that encounters the amplitude spectrum of the interrogating ultrasonic pulse during propagation in the absorbing tissue. Operation and accuracy of the processing methods were verified by assessing the size-independent region of interest (ROI) for attenuation determination and calculating the attenuation coefficient distribution for experimentally recorded tissue-phantom scattered waveforms. The Siemens Antares scanner equipped with Ultrasound Research Interface unit allowing for direct radiofrequency (RF) signals recording was used for B-scan imaging of the tissue- mimicking phantom in vitro and liver in vivo. RF data were processed to determine attenuation coefficient along the B-scan lines. Also, the preliminary studies of backscattered signals from skin recorded using a skin scanner were performed to calculate parametric-attenuation images.

Litniewski, J.; Klimonda, Z.; Nowicki, A.

331

Single-Shot Diffractive Imaging with a Table-Top Femtosecond Soft X-Ray Laser-Harmonics Source  

SciTech Connect

Coherent x-ray diffractive imaging is a powerful method for studies on nonperiodic structures on the nanoscale. Access to femtosecond dynamics in major physical, chemical, and biological processes requires single-shot diffraction data. Up to now, this has been limited to intense coherent pulses from a free electron laser. Here we show that laser-driven ultrashort x-ray sources offer a comparatively inexpensive alternative. We present measurements of single-shot diffraction patterns from isolated nano-objects with a single 20 fs pulse from a table-top high-harmonic x-ray laser. Images were reconstructed with a resolution of 119 nm from the single shot and 62 nm from multiple shots.

Ravasio, A.; Gauthier, D.; Billon, M.; Caumes, J-P.; Garzella, D.; Geleoc, M.; Gobert, O.; Hergott, J-F.; Pena, A-M.; Perez, H.; Carre, B. [Commissariat a l'Energie Atomique, Service des Photons, Atomes et Molecules, Batiment 522, Centre d'Etude de Saclay, 91191 Gif-sur-Yvette (France); Maia, F. R. N. C. [Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3 (Box 596), SE-751 24 Uppsala (Sweden); Bourhis, E.; Gierak, J.; Madouri, A.; Mailly, D.; Schiedt, B. [Laboratoire de Photonique et Nanostructures, CNRS-UPR20, Route de Nozay, F-91460 Marcoussis (France); Fajardo, M. [Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Avenue Rovisco Pais, 1049-001 Lisboa (Portugal); Gautier, J.; Zeitoun, P. [Laboratoire d'Optique Appliquee, Ecole Nationale Superieure de Technique Avancees, Ecole Polytechnique, CNRS UMR7639, Chemin de la Huniere, 91761 Palaiseau Cedex (France)

2009-07-10

332

Extended finite element method with simplified spherical harmonics approximation for the forward model of optical molecular imaging.  

PubMed

An extended finite element method (XFEM) for the forward model of 3D optical molecular imaging is developed with simplified spherical harmonics approximation (SP(N)). In XFEM scheme of SP(N) equations, the signed distance function is employed to accurately represent the internal tissue boundary, and then it is used to construct the enriched basis function of the finite element scheme. Therefore, the finite element calculation can be carried out without the time-consuming internal boundary mesh generation. Moreover, the required overly fine mesh conforming to the complex tissue boundary which leads to excess time cost can be avoided. XFEM conveniences its application to tissues with complex internal structure and improves the computational efficiency. Phantom and digital mouse experiments were carried out to validate the efficiency of the proposed method. Compared with standard finite element method and classical Monte Carlo (MC) method, the validation results show the merits and potential of the XFEM for optical imaging. PMID:23227108

Li, Wei; Yi, Huangjian; Zhang, Qitan; Chen, Duofang; Liang, Jimin

2012-01-01

333

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 G.; Cruce, Clay; Hallidy, William

1997-02-01

334

Characteristics of the mode converter of Gyrotron FU CW GII radiating Gaussian beams in both the fundamental and second harmonic frequency bands  

NASA Astrophysics Data System (ADS)

Gyrotron FU CW GII, the second gyrotron of the Gyrotron FU CW G-series with an internal quasi-optical mode converter, was recently developed at the Research Center for Development of Far-Infrared Region, University of Fukui (FIR FU) [Y. Tatematsu et al., J. Infrared, Millimeter, Terahertz Waves 35, 169 (2014)]. The design oscillation mode of this gyrotron is TE8,3 with a corresponding frequency of 393.4 GHz in the second harmonic cyclotron resonance. We observed oscillations of different modes including fundamental harmonic modes in the 200-GHz band upon varying the strength of the magnetic field in the cavity. Radiation patterns corresponding to these modes emitted from the window were Gaussian although the internal mode converter was designed for the TE8,3 mode. The directions of the radiated Gaussian beams were found to depend on the oscillation modes with a relation similar to that obtained for another gyrotron that was also equipped with a mode converter. This relation is explained based on geometrical optics. Moreover, numerical calculation with the electromagnetic wave code developed in FIR FU confirmed the same relation. The observed features of the Gyrotron FU CW GII show that it can serve as a unique power source with two frequency bands at 200 and 400 GHz. This result provides a way of developing multiple-frequency gyrotrons.

Tatematsu, Yoshinori; Yamaguchi, Yuusuke; Idehara, Toshitaka; Kawase, Tatsuru; Ogawa, Isamu; Saito, Teruo; Fujiwara, Toshimichi

2014-04-01

335

Characteristics of the mode converter of Gyrotron FU CW GII radiating Gaussian beams in both the fundamental and second harmonic frequency bands  

NASA Astrophysics Data System (ADS)

Gyrotron FU CW GII, the second gyrotron of the Gyrotron FU CW G-series with an internal quasi-optical mode converter, was recently developed at the Research Center for Development of Far-Infrared Region, University of Fukui (FIR FU) [Y. Tatematsu et al., J. Infrared, Millimeter, Terahertz Waves 35, 169 (2014)]. The design oscillation mode of this gyrotron is TE8,3 with a corresponding frequency of 393.4 GHz in the second harmonic cyclotron resonance. We observed oscillations of different modes including fundamental harmonic modes in the 200-GHz band upon varying the strength of the magnetic field in the cavity. Radiation patterns corresponding to these modes emitted from the window were Gaussian although the internal mode converter was designed for the TE8,3 mode. The directions of the radiated Gaussian beams were found to depend on the oscillation modes with a relation similar to that obtained for another gyrotron that was also equipped with a mode converter. This relation is explained based on geometrical optics. Moreover, numerical calculation with the electromagnetic wave code developed in FIR FU confirmed the same relation. The observed features of the Gyrotron FU CW GII show that it can serve as a unique power source with two frequency bands at 200 and 400 GHz. This result provides a way of developing multiple-frequency gyrotrons.

Tatematsu, Yoshinori; Yamaguchi, Yuusuke; Idehara, Toshitaka; Kawase, Tatsuru; Ogawa, Isamu; Saito, Teruo; Fujiwara, Toshimichi

2014-07-01

336

Linewidth of the harmonics in a microwave frequency comb generated by focusing a mode-locked ultrafast laser on a tunneling junction  

NASA Astrophysics Data System (ADS)

Previous analyses suggest that microwave frequency combs (MFCs) with harmonics having extremely narrow linewidths could be produced by photodetection with a mode-locked ultrafast laser. In the MFC generated by focusing a passively mode-locked ultrafast laser on a tunneling junction, 200 harmonics from 74.254 MHz to 14.85 GHz have reproducible measured linewidths approximating the 1 Hz resolution bandwidth (RBW) of the spectrum analyzer. However, in new measurements at a RBW of 0.1 Hz, the linewidths are distributed from 0.12 to 1.17 Hz. Measurements and analysis suggest that, because the laser is not stabilized, the stochastic drift in the pulse repetition rate is the cause for the distribution in measured linewidths. It appears that there are three cases in which the RBW is (1) greater than, (2) less than, or (3) comparable with the intrinsic linewidth. The measured spectra in the third class are stochastic and may show two or more peaks at a single harmonic.

Hagmann, Mark J.; Stenger, Frank S.; Yarotski, Dmitry A.

2013-12-01

337

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

338

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

339

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

Microsoft Academic Search

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

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

2010-01-01

340

Frequency-radial duality based photoacoustic image reconstruction.  

PubMed

Photoacoustic image reconstruction algorithms are usually slow due to the large sizes of data that are processed. This paper proposes a method for exact photoacoustic reconstruction for the spherical geometry in the limiting case of a continuous aperture and infinite measurement bandwidth that is faster than existing methods namely (1) backprojection method and (2) the Norton-Linzer method [S. J. Norton and M. Linzer, "Ultrasonic reflectivity imaging in three dimensions: Exact inverse scattering solution for plane, cylindrical and spherical apertures," Biomedical Engineering, IEEE Trans. BME 28, 202-220 (1981)]. The initial pressure distribution is expanded using a spherical Fourier Bessel series. The proposed method estimates the Fourier Bessel coefficients and subsequently recovers the pressure distribution. A concept of frequency-radial duality is introduced that separates the information from the different radial basis functions by using frequencies corresponding to the Bessel zeros. This approach provides a means to analyze the information obtained given a measurement bandwidth. Using order analysis and numerical experiments, the proposed method is shown to be faster than both the backprojection and the Norton-Linzer methods. Further, the reconstructed images using the proposed methodology were of similar quality to the Norton-Linzer method and were better than the approximate backprojection method. PMID:22779464

Akramus Salehin, S M; Abhayapala, Thushara D

2012-07-01

341

Drive frequency dependent phase imaging in piezoresponse force microscopy  

NASA Astrophysics Data System (ADS)

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

2010-08-01

342

Strain-encoded (SENC) harmonic phase imaging for fast magnetic resonance elastography  

NASA Astrophysics Data System (ADS)

A new method is proposed for imaging the elasticity of tissue using magnetic resonance (MR). Using an external actuator to deform the tissue, local strains way according to local elasticity. The method produces images shows the distribution of strains with different grades of intensity; thus, revealing the underlying elasticity distribution. The advantages of the method are that imaging is much faster than other magnetic resonance elastography (MRE) techniques, there is no need for complicated computations, and it produces high-resolution images.

Osman, Nael F.

2001-05-01

343

High Frequency Quantitative Ultrasound Imaging of Solid Tumors in Mice  

NASA Astrophysics Data System (ADS)

A mammary carcinoma and a sarcoma were grown in mice and imaged with ultrasound transducers operating with a center frequency of 20 MHz. Quantitative ultrasound (QUS) analysis was used to characterize the tumors using the bandwidth of 10 to 25 MHz. Initial QUS estimates of the scatterer properties (average scatterer diameter and acoustic concentration) did not reveal differences between the two kinds of tumors. Examination of the tumors using light microscopy indicated definite structural differences between the two kinds of tumors. In order to draw out the structural differences with ultrasound, a higher frequency probe (center frequency measured at 70 MHz) was used to interrogate the two kinds of tumors and new models were applied to the QUS analysis. QUS scatterer diameter images of the tumors were constructed using the high frequency probe. Several models for scattering were implemented to obtain estimates of scatterer properties in order to relate estimated scatterer properties to real tissue microstructure. The Anderson model for scattering from a fluid-filled sphere differentiated the two kinds of tumors but did not yield scatterer property estimates that resembled underlying structure. Using the Anderson model, the average estimated scatterer diameters were 25.5 ± 0.14 ?m for the carcinoma and 57.5 ± 2.90 for the sarcoma. A new cell model was developed, which was based on scattering from a cell by incorporating the effects of the cytoskeleton and nucleus. The new cell model yielded estimates that appeared to reflect underlying structure more accurately but did not separate the two kinds of tumors. Using the new cell model, the average estimated scatterer diameters were 15.6 ± 2.2 ?m for the carcinoma and 16.8 ± 3.82 ?m for the sarcoma. The new cell model yielded estimates close to the actual nuclear diameter of the cell (13 ?m)

Oelze, M. L.; O'Brien, W. D.; Zachary, J. F.

344

Simulation study of amplitude-modulated (AM) harmonic motion imaging (HMI) for stiffness contrast quantification with experimental validation.  

PubMed

The objective of this study is to show that Harmonic Motion Imaging (HMI) can be used as a reliable tumor-mapping technique based on the tumor's distinct stiffness at the early onset of disease. HMI is a radiation-force-based imaging method that generates a localized vibration deep inside the tissue to estimate the relative tissue stiffness based on the resulting displacement amplitude. In this paper, a finite-element model (FEM) study is presented, followed by an experimental validation in tissue-mimicking polyacrylamide gels and excised human breast tumors ex vivo. This study compares the resulting tissue motion in simulations and experiments at four different gel stiffnesses and three distinct spherical inclusion diameters. The elastic moduli of the gels were separately measured using mechanical testing. Identical transducer parameters were used in both the FEM and experimental studies, i.e., a 4.5-MHz single-element focused ultrasound (FUS) and a 7.5-MHz diagnostic (pulse-echo) transducer. In the simulation, an acoustic pressure field was used as the input stimulus to generate a localized vibration inside the target. Radiofrequency (rf) signals were then simulated using a 2D convolution model. A one-dimensional cross-correlation technique was performed on the simulated and experimental rf signals to estimate the axial displacement resulting from the harmonic radiation force. In order to measure the reliability of the displacement profiles in estimating the tissue stiffness distribution, the contrast-transfer efficiency (CTE) was calculated. For tumor mapping ex vivo, a harmonic radiation force was applied using a 2D raster-scan technique. The 2D HMI images of the breast tumor ex vivo could detect a malignant tumor (20 x 10 mm2) surrounded by glandular and fat tissues. The FEM and experimental results from both gels and breast tumors ex vivo demonstrated that HMI was capable of detecting and mapping the tumor or stiff inclusion with various diameters or stiffnesses. HMI may thus constitute a promising technique in tumor detection (>3 mm in diameter) and mapping based on its distinct stiffness. PMID:20718245

Maleke, Caroline; Luo, Jianwen; Gamarnik, Viktor; Lu, Xin L; Konofagou, Elisa E

2010-07-01

345

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

346

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

347

Method for imaging with low frequency electromagnetic fields  

DOEpatents

A method 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 traveltimes 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.

Lee, Ki H. (Lafayette, CA); Xie, Gan Q. (Berkeley, CA)

1994-01-01

348

High-Throughput Screening of Drug-Lipid Membrane Interactions via Counter-Propagating Second Harmonic Generation Imaging  

PubMed Central

Here we report the use of counter-propagating second harmonic generation (SHG) to image the interactions between the local anesthetic tetracaine and a multi-component planar supported lipid bilayer array in a label-free manner. The lipid bilayer arrays, prepared using a 3D continuous flow microspotter, allow the effects of lipid phase and cholesterol content on tetracaine binding to be examined simultaneously. SHG images show that tetracaine has a higher binding affinity to liquid-crystalline phase lipids than to solid-gel phase lipids. The presence of 28 mol % cholesterol decreased the binding affinity of tetracaine to bilayers composed of the mixed chain lipid, 1-steroyl-2-oleoyl-sn-glycero-3-phophocholine (SOPC) and the saturated lipids 1,2-dimyristoyl-sn-glycero-3-phophocholine (DMPC) and 1,2-dipamitoyl-sn-glycero-3-phophocholine (DPPC) while having no effect on di-unsaturated 1,2-dioleoyl-sn-glycero-3-phophocholine (DOPC). The maximum surface excess of tetracaine increases with the degree of unsaturation of the phospholipids and decreases with cholesterol in the lipid bilayers. The paper demonstrates that SHG imaging is a sensitive technique that can directly image and quantitatively measure the association of a drug to a multi-component lipid bilayer array, providing a high-throughput means to assess drug-membrane interactions.

Nguyen, Trang T.; Conboy, John C.

2011-01-01

349

Automated multiscale morphometry of muscle disease from second harmonic generation microscopy using tensor-based image processing.  

PubMed

Practically, all chronic diseases are characterized by tissue remodeling that alters organ and cellular function through changes to normal organ architecture. Some morphometric alterations become irreversible and account for disease progression even on cellular levels. Early diagnostics to categorize tissue alterations, as well as monitoring progression or remission of disturbed cytoarchitecture upon treatment in the same individual, are a new emerging field. They strongly challenge spatial resolution and require advanced imaging techniques and strategies for detecting morphological changes. We use a combined second harmonic generation (SHG) microscopy and automated image processing approach to quantify morphology in an animal model of inherited Duchenne muscular dystrophy (mdx mouse) with age. Multiphoton XYZ image stacks from tissue slices reveal vast morphological deviation in muscles from old mdx mice at different scales of cytoskeleton architecture: cell calibers are irregular, myofibrils within cells are twisted, and sarcomere lattice disruptions (detected as "verniers") are larger in number compared to samples from healthy mice. In young mdx mice, such alterations are only minor. The boundary-tensor approach, adapted and optimized for SHG data, is a suitable approach to allow quick quantitative morphometry in whole tissue slices. The overall detection performance of the automated algorithm compares very well with manual "by eye" detection, the latter being time consuming and prone to subjective errors. Our algorithm outperfoms manual detection by time with similar reliability. This approach will be an important prerequisite for the implementation of a clinical image databases to diagnose and monitor specific morphological alterations in chronic (muscle) diseases. PMID:21908249

Garbe, Christoph S; Buttgereit, Andreas; Schürmann, Sebastian; Friedrich, Oliver

2012-01-01

350

Harmonic Golay coded excitation based on harmonic quadrature demodulation method.  

PubMed

Harmonic coded excitation techniques have been used to increase SNR of harmonic imaging with limited peak voltage. Harmonic Golay coded excitation, in particular, generates each scan line using four transmit-receive cycles, unlike conventional Golay coded excitation method, thus resulting in low frame rates. In this paper we propose a method of increasing the frame rate of said method without impacting the image quality. The proposed method performs two transmit-receive cycles using QPSK code to ensure that the harmonic components of incoming signals are Golay coded and uses harmonic quadrature demodulation to extract compressed second harmonic component only. The proposed method has been validated through mathematical analysis and MATLAB simulation, and has been verified to yield a limited error of -52.08dB compared to the ideal case. Therefore, the proposed method doubles the frame rate compared to the existing harmonic Golay coded excitation method without significantly deteriorating the image quality. PMID:19164018

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

2008-01-01

351

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

352

Even harmonic lasing  

SciTech Connect

Operation of a free-electron laser at harmonics of the fundamental frequency is explored with the numerical simulation code HELEX. This code includes coupling to the harmonics caused by misalignment of the electrons with the optical beam and coupling due to transverse gradients. Albeit weak, the transverse gradients produce the dominant coupling of the electrons to the even-harmonic light. Even-harmonic lasing occurs in a TEM{sub 0,2m+1}-like mode where the field on axis is zero. As bunching of the electron beam progresses, radiation at the higher odd harmonics is suppressed owing to the absence of higher-order odd-harmonic Fourier components in the bunch. Growth of the even-harmonic power from small signal requires suppression of competing harmonics (including the fundamental) that have higher gain. Lasing at an even harmonic has yet to be experimentally demonstrated in an open resonator (i.e. optical cavity). Strategies to make such an experiment possible are discussed. 9 refs., 5 figs., 1 tab.

Schmitt, M.J.

1991-01-01

353

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

354

Finite-Frequency Imaging of Transition Zone Discontinuities  

NASA Astrophysics Data System (ADS)

Lateral variations in the 410-km and 660-km discontinuity depths are important for understanding thermal structure in the transition zone. Teleseismic P-wave coda have been widely used in imaging seismic discontinuities as the relative timing between the direct P wave and P-to-S converted waves provides important constraints on discontinuity depths. P-wave coda can be contaminated by strong scattering and stacking are often used in back-projection methods to reduce structural noise. In this study, we explore an alternative approach in imaging mantle discontinuity using long-period P-wave coda. We calculate the sensitivity of P-wave coda to transition zone discontinuity depth variations in the framework of surface-wave mode summation. We show that the sensitivities do not show a simple doughnut structure due to multiples of shallow discontinuities as well as other seismic phases such as pP and PcP waves. Furthermore, a discontinuity depth deflection farther away from a receiver or an opposite deflection of the same discontinuity closer to the receiver may produce same time shift in receiver functions, therefore, back-projection CCP stacking images can be strongly biased. The finite-frequency sensitivities are calculated based on a single-scattering approximation. We will discuss the validity of the approximation in discontinuity imaging using P-wave coda recorded at USArray TA stations.

Zhou, Y.

2013-12-01

355

Time domain simulation of harmonic ultrasound images and beam patterns in 3D using the k-space pseudospectral method.  

PubMed

A k-space pseudospectral model is developed for the fast full-wave simulation of nonlinear ultrasound propagation through heterogeneous media. The model uses a novel equation of state to account for nonlinearity in addition to power law absorption. The spectral calculation of the spatial gradients enables a significant reduction in the number of required grid nodes compared to finite difference methods. The model is parallelized using a graphical processing unit (GPU) which allows the simulation of individual ultrasound scan lines using a 256 x 256 x 128 voxel grid in less than five minutes. Several numerical examples are given, including the simulation of harmonic ultrasound images and beam patterns using a linear phased array transducer. PMID:22003638

Treeby, Bradley E; Tumen, Mustafa; Cox, B T

2011-01-01

356

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

357

Iridoschisis: high frequency ultrasound imaging. Evidence for a genetic defect?  

PubMed Central

AIMS: To elucidate changes in the anatomy of the anterior chamber associated with iridoschisis, a rare form of iris atrophy, and their potential contribution to angle closure glaucoma. METHODS: Both eyes of a 71-year-old woman with bilateral iridoschisis and fibrous dysplasia and her asymptomatic 50-year-old daughter were scanned with a very high frequency (50 MHz) ultrasound system. RESULTS: The symptomatic patient exhibited diffuse changes in the iris stoma with an intact posterior iris pigmented layer in both eyes. These changes were clinically compatible with the lack of iris transillumination defects. Additionally, iris bowing with a resultant narrowing of the angle occurred. The asymptomatic daughter showed discrete, but less severe iris stromal changes. CONCLUSION: This is the first detailed study of high frequency ultrasonic imaging of the iris in iridoschisis. The observed structural changes suggest angle narrowing by forward bowing of the anterior iris stroma may be a mechanism of IOP elevation in this condition. The ultrasonic detection of iris changes in the asymptomatic daughter of the symptomatic patient and the association of iridoschisis with fibrous dysplasia suggest a possible genetic component in the pathogenesis of this condition. Images

Danias, J; Aslanides, I M; Eichenbaum, J W; Silverman, R H; Reinstein, D Z; Coleman, D J

1996-01-01

358

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

Microsoft Academic Search

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

Hairong Zheng; Osama Mukdadi; Robin Shandas

2006-01-01

359

Active harmonic elimination for multilevel converters  

Microsoft Academic Search

This paper presents an active harmonic elimination method to eliminate any number of specific higher order harmonics of multilevel converters with equal or unequal dc voltages. First, resultant theory is applied to transcendental equations characterizing the harmonic content to eliminate low order harmonics and to determine switching angles for the fundamental frequency switching scheme and a unipolar switching scheme. Next,

Zhong Du; L. M. Tolbert; J. N. Chiasson

2006-01-01

360

Multi-parametric monitoring of high intensity focused ultrasound (HIFU) treatment using harmonic motion imaging for focused ultrasound (HMIFU)  

NASA Astrophysics Data System (ADS)

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and relative phase-shift during high energy HIFU where tissue boiling occurs. Forty three (n=18) thermal lesions were formed in ex vivo canine liver specimens. Two dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10-, 20-and 30-s HIFU durations at three different acoustic powers of 8, 10, and 11W. For the 10-, 20-, and 30-s treatment cases, a steady decrease in the displacement (-8.67+/-4.80, -14.44+/-7.77, 24.03+/-12.11?m), compressive strain -0.16+/-0.06, -0.71+/-0.30, -0.68+/-0.36 %, and phase shift +1.80+/-6.80, -15.80+/-9.44, -18.62+/-13.14 ° were obtained, respectively, indicating overall increase of relative stiffness and decrease of the viscosity-to-stiffness ratio during heating. After treatment, 2D HMI displacement images of the thermal lesions showed an increased lesion-to-background contrast of 1.34+/-0.19, 1.98+/-0.30, 2.26+/-0.80 and lesion size of 40.95+/-8.06, 47.6+/-4.87, and 52.23+/-2.19 mm2, respectively, which was validated again with pathology 25.17+/-6.99, 42.17+/-1.77, 47.17+/-3.10 mm2. Additionally, studies also investigated the performance of mutli-parametric monitoring under the influence of boiling and attenuation change due to tissue boiling, where discrepancies were found such as deteriorated displacement SNR and reversed lesion-to-background displacement contrast with indication on possible increase in attenuation and tissue gelatification or pulverization. Despite the challenge of the boiling mechanism, the relative phase shift served as consist biomechanical tissue response independent of changes in acoustic properties throughout the HIFU treatment. In addition, the 2D HMI displacement images were able to confirm and quantify the change in dimensions of the thermal lesion site. Therefore, the multi-parametric HMIFU was shown capable of monitoring and mapping tissue viscoelastic response changes during and after HIFU treatment.

Hou, Gary Y.; Marquet, Fabrice; Wang, Shutao; Konofagou, Elisa

2012-11-01

361

Harmonic Drive.  

National Technical Information Service (NTIS)

The harmonic drive has utility in optical tracking telescopes, radar antenna drives, aircraft control surface actuators, and high precision X-Y plotting equipment. Two harmonic drive units, each having its own input motor, are coupled together. One of the...

R. H. Lapp

1965-01-01

362

Transmit Aperture Processing for Nonlinear Contrast Agent Imaging  

Microsoft Academic Search

Nonlinear contrast agents, such as bubbles, are used in ultrasound to enhance backscatter from blood. To increase contrast between these agents and tissue, nonlinear imaging methods, such as harmonic imaging or difference frequency imaging, can be used. For these, power is transmitted at one frequency and received at a different frequency. Nonlinear imaging methods, however, suffer from reduced contrast because

S. Krishnan; M. O'Donnell

1996-01-01

363

Feasibility of High Frequency Acoustic Imaging for Inspection of Containments  

SciTech Connect

The Nuclear Regulatory Commission has a program at the Oak Ridge National Laboratory to provide assistance in their assessment of the effects of potential degradation on the structural integrity and Ieaktightness of metal containment vessels and steel liners of concrete containment in nuclear power plants. One of the program objectives is to identify a technique(s) for inspection of inaccessible portions of the containment pressure boundary. Acoustic imaging has been identified as one of these potential techniques. A numerical feasibility study investigated the use of high-frequency bistatic acoustic imaging techniques for inspection of inaccessible portions of the metallic pressure boundary of nuclear power plant containment. The range-dependent version of the OASES Code developed at the Massachusetts Institute of Technology was utilized to perform a series of numerical simulations. OASES is a well developed and extensively tested code for evaluation of the acoustic field in a system of stratified fluid and/or elastic layers. Using the code, an arbitrary number of fluid or solid elastic layers are interleaved, with the outer layers modeled as halfspaces. High frequency vibrational sources were modeled to simulate elastic waves in the steel. The received field due to an arbitrary source array can be calculated at arbitrary depth and range positions. In this numerical study, waves that reflect and scatter from surface roughness caused by modeled degradations (e.g., corrosion) are detected and used to identify and map the steel degradation. Variables in the numerical study included frequency, flaw size, interrogation distance, and sensor incident angle.Based on these analytical simulations, it is considered unlikely that acoustic imaging technology can be used to investigate embedded steel liners of reinforced concrete containment. The thin steel liner and high signal losses to the concrete make this application difficult. Results for portions of steel containment embedded in concrete are more encouraging in that they indicate that the intrinsic backscatter from degradations representing thickness reductions from 10 to 80% the shell thickness are sufficient to permit detection. It is recommended that a controlled experimental program be conducted in which sensor levels are calibrated against degradations to determine if current sensor technology can input sufficient power into the system to provide return levels within the dynamic range of the receivers.

C.N. Corrado; J.E. Bondaryk; V. Godino

1998-08-01

364

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

NASA Astrophysics Data System (ADS)

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(N6) 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.

Bozkaya, U?ur; Sherrill, C. David

2013-08-01

365

Assessment of Multiple Sclerosis Lesions with Spherical Harmonics: Comparison of MR Imaging and Pathologic Findings1  

PubMed Central

Spherical harmonics (SH) were used to approximate the volume and three-dimensional geometry of multiple sclerosis (MS) lesions in deceased patients. The institutional ethical committee does not require its approval for studies involving pathologic specimens. Pathologic findings were used as the reference standard. In addition, lesion volume was measured with cylindrical approximation (CA). Volumetric comparisons of biases were based on summary statistics, Spearman correlation, Wilcoxon test, and two-way analysis of variance. Shape comparison metrics included mean distance and Dice similarity coefficient (DSC). Eight of 11 lesions had smaller biases with SH method (P < .001). Median biases with SH and CA did not differ significantly, as compared with pathologic findings (r = 1.00 vs 0.99, respectively). Variances of the biases were significantly smaller for SH (P =.04). Ranges of normalized distance and DSC were 0.1%–2.5% and 75%–96%, respectively. Mean DSC was significantly higher than 70% (P < .001). SH method provided unbiased lesion volume and added geometric information that may enable a better understanding of the pathogenesis and lesion evolution over time.

Goldberg-Zimring, Daniel; Shalmon, Bruria; Zou, Kelly H.; Azhari, Haim; Nass, Dvora; Achiron, Anat

2005-01-01

366

Harmonic frequency analysis of SAW resonator chemical sensors: application to the detection of carbon dioxide and humidity 1 Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corporation for the US Department of Energy under Contract No. DE-AC05-96OR22464. 1  

Microsoft Academic Search

We have investigated the possibility of increasing surface acoustic wave (SAW) gas sensor sensitivity and detection limit by operating a SAW device at its fundamental frequency (250 MHz for the devices used in this paper), while monitoring frequency changes at a higher harmonic. In particular we have compared frequency changes at the third harmonic with that of the fundamental mode,

Kofi Korsah; C. L. Ma; Bill Dress

1998-01-01

367

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

368

Nonlinear intravascular ultrasound contrast imaging  

Microsoft Academic Search

Nonlinear contrast agent imaging with intravascular ultrasound (IVUS) is investigated using a prototype IVUS system and an experimental small bubble contrast agent. The IVUS system employed a mechanically scanned single element transducer and was operated at a 20 MHz transmit frequency (F20) for second harmonic imaging (H40), and at a 40 MHz transmit frequency (F40) for subharmonic imaging (SH20). Characterization

David E. Goertz; Martijn E. Frijlink; Nico de Jong; Antonius F. W. van der Steen

2006-01-01

369

Automated camera-phone experience with the frequency of imaging necessary to capture diet.  

PubMed

Camera-enabled cell phones provide an opportunity to strengthen dietary recall through automated imaging of foods eaten during a specified period. To explore the frequency of imaging needed to capture all foods eaten, we examined the number of images of individual foods consumed in a pilot study of automated imaging using camera phones set to an image-capture frequency of one snapshot every 10 seconds. Food images were tallied from 10 young adult subjects who wore the phone continuously during the work day and consented to share their images. Based on the number of images received for each eating experience, the pilot data suggest that automated capturing of images at a frequency of once every 10 seconds is adequate for recording foods consumed during regular meals, whereas a greater frequency of imaging is necessary to capture snacks and beverages eaten quickly. PMID:20656101

Arab, Lenore; Winter, Ashley

2010-08-01

370

Cassini/RPWS: A low frequency radio imager at Saturn  

NASA Astrophysics Data System (ADS)

The High Frequency Receiver (HFR) of the Radio and Plasma Waves Science experiment (RPWS) onboard Cassini is a sensitive, and versatile radio instrument. Although the radio antenna connected to this instrument have no intrinsic directivity, the HFR measurements can provide instantaneous direction of arrival, flux density and polarization degree of the observed radio waves. Hence, the HFR can be described as an full-sky radio imager. As the instrument provides direction of arrival, radio sources can be located with some assumption on the propagation between the source and the observer. Hence, it is possible to produce radio source maps and correlate them with observations at other wavelengths, such as UV or IR observations of the auroral regions of Saturn. The flux and polarization measurements together with the time-frequency shape of the radio emissions can also be used to identify the radio emission processes. We present a review of the results of the Cassini/RPWS/HFR observations since its arrival at Saturn in 2004: interpretation of the radio arc shapes and equatorial shadow zones; in-situ observations in the radio source region; comparison with other wavelengths and particle measurements; confirmation of the Cyclotron Maser Instability (CMI) as the main emission mechanism for auroral radio emissions; monitoring of the radio emission variability in time and location, etc.

Cecconi, Baptiste; Lamy, Laurent; Zarka, Philippe

2014-05-01

371

A low power Pulse Frequency Modulated UWB radar transmitter concept based on switched injection locked harmonic sampling  

Microsoft Academic Search

Pulse Frequency Modulated ultra-wideband (PFM-UWB) radar signals have been introduced as a very capable option for UWB ranging and wireless local positioning. PFM-UWB signals allow for simple correlating receivers and for a very efficient use of the UWB spectral mask. The generation of pulse frequency modulated (PFM) ultra-wideband (UWB) signals usually requires a fast tunable RF-VCO and good linear RF

Christian Carlowitz; Alexander Esswein; Robert Weigel; Martin Vossiek

2012-01-01

372

Soliton self-frequency shift and third-harmonic generation in a four-hole As?S? microstructured optical fiber.  

PubMed

Soliton self-frequency shift (SSFS) and third-harmonic generation (THG) are observed in a four-hole As2S5 chalcogenide microstructured optical fiber (MOF). The As2S5 MOF is tapered to offer an ideal environment for SSFS. After tapering, the zero-dispersion wavelength (ZDW) shifts from 2.02 to 1.61 ?m, and the rate of SSFS can be enhanced by increasing the energy density of the pulse. By varying the average input power from 220 to 340 mW, SSFS of a soliton central wavelength from 2.206 to 2.600 ?m in the mid-infrared is observed in the tapered segment, and THG at 632 nm is observed in the untapered segment. PMID:24663691

Cheng, Tonglei; Usaki, Ryo; Duan, Zhongchao; Gao, Weiqing; Deng, Dinghuan; Liao, Meisong; Kanou, Yasuhire; Matsumoto, Morio; Misumi, Takashi; Suzuki, Takenobu; Ohishi, Yasutake

2014-02-24

373

ATOMIC AND MOLECULAR PHYSICS: Investigation of analytical potential energy function, harmonic frequency and vibrational levels for the X2?+ and A2 states of CN radical  

NASA Astrophysics Data System (ADS)

This paper calculates the equilibrium structure and the potential energy functions of the ground state (X2?+) and the low lying excited electronic state (A2II) of CN radical are calculated by using CASSCF method. The potential energy curves are obtained by a least square fitting to the modified Murrell-Sorbie function. On the basis of physical theory of potential energy function, harmonic frequency (?e) and other spectroscopic constants (?e?e, ?e and ?e) are calculated by employing the Rydberg-Klein-Rees method. The theoretical calculation results are in excellent agreement with the experimental and other complicated theoretical calculation data. In addition, the eigenvalues of vibrational levels have been calculated by solving the radial one-dimensional Schrödinger equation of nuclear motion using the algebraic method based on the analytical potential energy function.

Wang, Jian-Kun; Wu, Zhen-Sen

2008-08-01

374

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

375

Visible spatial frequency domain imaging with a digital light microprojector.  

PubMed

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

376

Femtosecond two-photon LIF imaging of atomic species using a frequency-quadrupled Ti:sapphire laser  

NASA Astrophysics Data System (ADS)

Femtosecond (fs)-duration laser pulses are well suited for two-photon laser-induced-fluorescence (TPLIF) imaging of key atomic species such as H, N, and O in gas-phase reacting flows. Ultrashort pulses enable efficient nonlinear excitation, while reducing interfering photochemical processes. Furthermore, amplified fs lasers enable high-repetition-rate imaging (typically 1-10 kHz) for capturing the dynamics of turbulent flow fields. However, two-dimensional (2D), single-laser-shot fs-TPLIF imaging of the above species is challenging in most practical flow fields because of the limited ultraviolet pulse energy available in commercial optical parametric amplifier (OPA)-based tunable laser sources. In this work, we report the development of an efficient, fs frequency-quadrupling unit [i.e., fourth-harmonic generator (FHG)] with overall conversion efficiency more than six times greater than that of commercial OPA-based systems. The development, characterization, and application of the fs-FHG system for 2D imaging of H atoms in flames are described in detail. The potential application of the same laser system for 2D imaging of N and O atoms is also discussed.

Kulatilaka, Waruna D.; Gord, James R.; Roy, Sukesh

2014-07-01

377

Femtosecond two-photon LIF imaging of atomic species using a frequency-quadrupled Ti:sapphire laser  

NASA Astrophysics Data System (ADS)

Femtosecond (fs)-duration laser pulses are well suited for two-photon laser-induced-fluorescence (TPLIF) imaging of key atomic species such as H, N, and O in gas-phase reacting flows. Ultrashort pulses enable efficient nonlinear excitation, while reducing interfering photochemical processes. Furthermore, amplified fs lasers enable high-repetition-rate imaging (typically 1-10 kHz) for capturing the dynamics of turbulent flow fields. However, two-dimensional (2D), single-laser-shot fs-TPLIF imaging of the above species is challenging in most practical flow fields because of the limited ultraviolet pulse energy available in commercial optical parametric amplifier (OPA)-based tunable laser sources. In this work, we report the development of an efficient, fs frequency-quadrupling unit [i.e., fourth-harmonic generator (FHG)] with overall conversion efficiency more than six times greater than that of commercial OPA-based systems. The development, characterization, and application of the fs-FHG system for 2D imaging of H atoms in flames are described in detail. The potential application of the same laser system for 2D imaging of N and O atoms is also discussed.

Kulatilaka, Waruna D.; Gord, James R.; Roy, Sukesh

2014-04-01

378

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.

379

Scaling factors for fundamental vibrational frequencies and zero-point energies obtained from HF, MP2, and DFT\\/DZP and TZP harmonic frequencies  

Microsoft Academic Search

Recently, segmented contracted basis sets of double, triple, and quadruple zeta valence quality plus polarization functions (XZP, X=D, T, and Q) for the atoms from H to Ar were presented by Jorge et al. Scaling factors for the fundamental vibrational frequencies, low-frequency vibrations, and zero-point vibrational energies (ZPVEs) evaluated at 14 levels of theory are reported. The ab initio Hartree–Fock

S. G. Andrade; Luísa C. S. Gonçalves; F. E. Jorge

2008-01-01

380

Infrared-based least-invasive third and second harmonic generation imaging of ocular tissues  

Microsoft Academic Search

Cornea functions as an outermost lens and plays an important role in vision. For cornea diagnosis and treatment, a microscopic imaging system with cellular resolution and high eye safety is strongly desired. Recently, the cell morphology of corneal epithelium and endothelium can be revealed by confocal or two-photon fluorescence microscopy, while the collagen fibers in the corneal stroma can be

Szu-Yu Chen; Han-Chieh Yu; I.-Jong Wang; Chi-Kuang Sun

2009-01-01

381

Evidence for Harmonic Relationships in the High-Frequency Quasi-periodic Oscillations of XTE J1550-564 and GRO J1655-40  

NASA Astrophysics Data System (ADS)

We continue to investigate the X-ray properties of the black hole binary XTE J1550-564. By grouping observations (1998-1999) according to the type of low-frequency quasiperiodic oscillation (LFQPO) identified in a previous paper, we show evidence that two high-frequency QPOs (HFQPOs) occur simultaneously near 184 and 276 Hz. We can model the QPO profiles while assuming that the central frequencies are related by a 3:2 ratio. In one group, there is some evidence of a broad feature at the fundamental frequency of 92 Hz. We also investigate the 2000 April outburst, and we confirm the suggestion of Miller et al. that a 270 Hz QPO is accompanied by a second feature near 180 Hz. The histogram for the 28 individual HFQPO detections in XTE J1550-564 shows two peaks near 184 and 276 Hz, while there is a notable exception in the 143 Hz QPO detected on 1998 October 15. Similarly, all of the 13 HFQPO detections in the black hole binary GRO J1655-40 occur at two frequencies that are related by a 3:2 ratio. We next investigate all of the energy spectra for XTE J1550-564, and we find a systematic increase in the strength of the power-law component as the stronger of the two HFQPOs shifts from 276 to 184 Hz. A strikingly similar result is seen in the spectra of GRO J1655-40 when the stronger HFQPO shifts from 450 to 300 Hz. The fundamental HFQPO frequencies for the two X-ray sources scale as M-1, which is consistent with the hypotheses that these HFQPOs represent some kind of oscillation rooted in general relativity (GR) and that the two black holes have similar values of the dimensionless spin parameter. We discuss physical mechanisms that may explain these HFQPOs. A resonance between orbital and radial coordinate frequencies is one possibility suggested by Abramowicz & Kluzniak. For XTE J1550-564, this would imply moderate values for the dimensionless spin parameter (0.1frequencies allows additional values for a* above 0.9. There remain serious uncertainties regarding the physical mechanism whereby resonances in coordinate frequencies may produce HFQPOs. We also discuss models for ``diskoseismic'' oscillations. In this case, the concept that the inner disk behaves as a resonance cavity in GR has certain attractions for explaining HFQPOs, but integral harmonics are not predicted for the three types of diskoseismic modes derived for adiabatic perturbations in a thin accretion disk.

Remillard, Ronald A.; Muno, Michael P.; McClintock, Jeffrey E.; Orosz, Jerome A.

2002-12-01

382

Imaging Slabs and Plumes with Finite-Frequency Inverted Transition Zone Thickness  

NASA Astrophysics Data System (ADS)

The long-wavelength (harmonic degree, l < 6) pattern of mantle transition zone thickness (WTZ) is well constrained globally by travel-time variations of stacked SS-precursors (underside reflections off the discontinuities at approximately 410 & 660 km depth). Other techniques (e.g. receiver functions) can image short-wavelength (< 500 km) variations in WTZ, but only for limited regions where data are available. The amplitudes of the discontinuity phases are low (often below the noise level), so stacking is necessary to obtain robust travel times and associated interface depths. Stacking effectively smooths/averages over short-wavelength variations. The large lateral extent of SS-precursor sensitivity kernels tends to further reduce the sensitivity to small-scale structure for traditional stacking methods. In this study we apply an adaptive stacking method that maximizes resolution where data are available. In addition to stacking the SS-precursor waveforms, we stack the associated finite-frequency Frechet kernels with sensitivity to discontinuity topography [Dahlen, 2005]. We then invert the stacked kernels with the travel times of the stacked waves for transition zone thickness. The method may be thought of as an additive algorithm analogous to the differencing algorithm of multi-channel cross-correlation. Data stability is ensured by the bootstrap error estimation. While the technique is computationally expensive relative to traditional stacking and inversion techniques, the results yield finer-scale resolution in regions with good data coverage. The resultant transition zone thickness models possess narrow curvilinear regions of anomalously thick WTZ down-dip of subduction zones and various different sized regions of thinned WTZ beneath hotspots. The curvilinear regions near subduction zones are larger in vertical extent and narrower in horizontal extent than the equivalent long-wavelength anomalies imaged by previous stacking methods. The observation of horizontally smaller subduction-related transition zone thickening effectively decreases the upper volumetric limit of cool oceanic lithosphere currently stored within the transition zone.

Lawrence, J. F.; Shearer, P. M.

2006-12-01

383

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

384

In vivo time-lapse imaging of skin burn wound healing using second-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Wound healing is a process to repair the damaged tissue caused by thermal burn, incised wound, or stab wound. Although the wound healing has many aspects, it is common for dynamics of collagen fiber, such as decomposition, production, or growth, to be closely related with wound healing. If such the healing process can be visualized as a timelapse image of the collagen fiber in the same subject, one may obtain new findings regarding biological repairing mechanisms in the healing process. In this article, to investigate the temporal modoification of dermal collagen fiber in the burn wound healing, we used second-harmonic-generation (SHG) microscopy, showing high selectivity and good image contrast to collagen molecules as well as high spatial resolution, optical three-dimensional sectioning, minimal invasiveness, deep penetration, the absence of interference from background light, and in vivo measurement without additional staining. Since SHG light arises from a non-centrosymmetric triple helix of three polypeptide chains in the collagen molecule, SHG intensity sensitively reflects the structure maturity of collagen molecule and its aggregates. A series of time-lapse SHG images during the wound healing process of 2 weeks clearly indicated that condensation and melting of dermal collagen fibers by the deep dermal burn, decomposition of the damaged collagen fibers in the inflammation phase, production of new collagen fibers in the proliferation phase, and the growth of the new collagen fibers in the remodeling phase. These results show a high potential of SHG microscopy for optical assessment of the wound healing process in vivo.

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

2014-02-01

385

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

386

X-Band Linear Frequency Modulated Radar for Dynamic Aircraft Imaging.  

National Technical Information Service (NTIS)

Inverse synthetic aperture radar (ISAR) images of dynamic targets can be generated using stepped frequency radars. However, a stepped frequency waveform requires many pulses transmitted over tens of milliseconds to achieve range resolution. This has the u...

J. Trischman S. Jones R. Bloomfield E. Nelson R. Dinger

1995-01-01

387

A phase detection method for harmonics and unbalanced voltage  

Microsoft Academic Search

This paper proposes a phase detection method for harmonics and unbalanced voltage conditions. The proposed method uses harmonics and unbalanced voltage compensation circuit in addition to basic PLL (Phase Locked Loop) circuit. In the harmonic compensation circuit, the harmonic voltage components are eliminated from the input voltages using specific harmonic detection method. Besides, frequency information of power system used in

Tomonobu Senjyu; Yuri Yonaha; Norihiro Nakasone; Atsushi Yona; Chul-Hwan Kim

2008-01-01

388

Advanced Reservoir Imaging Using Frequency-Dependent Seismic Attributes  

SciTech Connect

Our report concerning advanced imaging and interpretation technology includes the development of theory, the implementation of laboratory experiments and the verification of results using field data. We investigated a reflectivity model for porous fluid-saturated reservoirs and demonstrated that the frequency-dependent component of the reflection coefficient is asymptotically proportional to the reservoir fluid mobility. We also analyzed seismic data using different azimuths and offsets over physical models of fractures filled with air and water. By comparing our physical model synthetics to numerical data we have identified several diagnostic indicators for quantifying the fractures. Finally, we developed reflectivity transforms for predicting pore fluid and lithology using rock-property statistics from 500 reservoirs in both the shelf and deep-water Gulf of Mexico. With these transforms and seismic AVO gathers across the prospect and its down-dip water-equivalent reservoir, fluid saturation can be estimated without a calibration well that ties the seismic. Our research provides the important additional mechanisms to recognize, delineate, and validate new hydrocarbon reserves and assist in the development of producing fields.

Fred Hilterman; Tad Patzek; Gennady Goloshubin; Dmitriy Silin; Charlotte Sullivan; Valeri Korneev

2007-12-31

389

An efficiently phase-shift frequency domain method for super-resolution image processing  

Microsoft Academic Search

How to reconstruct a high resolution and quality from low resolution images captured from a digital camera is always the top target of any image processing system. Exploit the aliasing feature of sampled images, we propose a new technique to register exactly the motions between images, including rotations and shifts, by using only frequency domain phase-shift method. Based on registered

Cao Bui-Thu; T. Le-Tien; Tuan Do-Hong; H. Nguyen-Duc

2009-01-01

390

Time-frequency conversion, temporal filtering, and temporal imaging using graded-index time lenses.  

PubMed

We propose several applications of graded-index (GRIN) time lenses including time-frequency conversion (time-to-frequency conversion and frequency-to-time conversion simultaneously), temporal filtering, and temporal imaging. The evolution of the signal pulses in these systems is demonstrated. As two important parameters, the focal length and the time-frequency conversion factors of time-frequency conversion based on GRIN time lenses are evaluated. PMID:23027252

Li, Bo; Lou, Shuqin

2012-10-01

391

Frequency Diversity for Improving Synthetic Aperture Radar Imaging.  

National Technical Information Service (NTIS)

In this work, a novel theoretical framework is presented for using recent advances in frequency diversity arrays (FDAs). Unlike a conventional array, the FDA simultaneously transmits a unique frequency from each element in the array. As a result, special ...

J. Farooq

2009-01-01

392

Graphical User Interfaces for Digital-Image Frequency Analysis.  

National Technical Information Service (NTIS)

Frequency analysis plays an important role in the area of visual research. The application described in this technical memorandum provides a graphical user interface that simplifies loading, analyzing, and storing the results of common frequency analysis ...

C. Tai G. A. Geri J. P. Gaska

2006-01-01

393

Current Density Imaging Using Directly Measured Harmonic Bz Data in MREIT  

PubMed Central

Magnetic resonance electrical impedance tomography (MREIT) measures magnetic flux density signals through the use of a magnetic resonance imaging (MRI) in order to visualize the internal conductivity and/or current density. Understanding the reconstruction procedure for the internal current density, we directly measure the second derivative of Bz data from the measured k-space data, from which we can avoid a tedious phase unwrapping to obtain the phase signal of Bz. We determine optimal weighting factors to combine the derivatives of magnetic flux density data, ?2Bz, measured using the multi-echo train. The proposed method reconstructs the internal current density using the relationships between the induced internal current and the measured ?2Bz data. Results from a phantom experiment demonstrate that the proposed method reduces the scanning time and provides the internal current density, while suppressing the background field inhomogeneity. To implement the real experiment, we use a phantom with a saline solution including a balloon, which excludes other artifacts by any concentration gradient in the phantom.

Kwon, Oh In

2013-01-01

394

Low frequency radio synthesis imaging of the galactic center region  

Microsoft Academic Search

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

Michael Evans Nord

2005-01-01

395

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of EUX3 (E=N, P, CH; X=H, F, Cl).  

PubMed

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-L

Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

2014-12-10

396

Imaging in electrically conductive porous media without frequency encoding  

NASA Astrophysics Data System (ADS)

Understanding multi-phase fluid flow and transport processes under various pressure, temperature, and salinity conditions is a key feature in many remote monitoring applications, such as long-term storage of carbon dioxide (CO2) or nuclear waste in geological formations. We propose a low-field NMR tomographic method to non-invasively image the water-content distribution in electrically conductive formations in relatively large-scale experiments (˜1 m3 sample volumes). Operating in the weak magnetic field of Earth entails low Larmor frequencies at which electromagnetic fields can penetrate electrically conductive material. The low signal strengths associated with NMR in Earth's field are enhanced by pre-polarization before signal recording. To localize the origin of the NMR signal in the sample region we do not employ magnetic field gradients, as is done in conventional NMR imaging, because they can be difficult to control in the large sample volumes that we are concerned with, and may be biased by magnetic materials in the sample. Instead, we utilize the spatially dependent inhomogeneity of fields generated by surface coils that are installed around the sample volume. This relatively simple setup makes the instrument inexpensive and mobile (it can be potentially installed in remote locations outside of a laboratory), while allowing spatial resolution of the order of 10 cm. We demonstrate the general feasibility of our approach in a simulated CO2 injection experiment, where we locate and quantify the drop in water content following gas injection into a water-saturated cylindrical sample of 0.45 m radius and 0.9 m height. Our setup comprises four surface coils and an array consisting of three volume coils surrounding the sample. The proposed tomographic NMR methodology provides a more direct estimate of fluid content and properties than can be achieved with acoustic or electromagnetic methods alone. Therefore, we expect that our proposed method is relevant for geophysical applications, such as for monitoring CO2 injections in saline aquifers or detecting water leakage into nuclear waste deposit sites installed in electrically conductive formations.

Lehmann-Horn, J. A.; Walbrecker, J. O.

2012-07-01

397

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

SciTech Connect

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. [Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa (Portugal)] [Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa (Portugal); Collaboration: JET-EFDA Contributors

2013-08-15

398

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

399

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

400

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

401

Multipath effects in semi-anechoic chambers at low frequencies: a simplified prediction model based on image theory  

Microsoft Academic Search

The multipath effects due to radiating sources inside a shielded room can not be neglected when the frequency of the harmonic components of the electromagnetic field are below the frequency threshold of the absorber lined walls. This paper deals with the prediction of the total radiated field by an electric dipole source inside a shielded room, taking into account the

A. Orlandi

1996-01-01

402

Study of inspection on metal sheet with subsurface defects using linear frequency modulated ultrasound excitation thermal-wave imaging (LFM-UTWI)  

NASA Astrophysics Data System (ADS)

The linear frequency modulated ultrasound excitation thermal wave imaging (LFM-UTWI) was investigated on detection of subsurface defects of metal sheet. A numerical finite element analysis is carried out to calculate thermal wave signal dependence of time by linear frequency modulated ultrasonic wave excitation. Cross-correlation operation in time domain and frequency domain are used to extract the main peak value and the corresponding delay time, respectively. Fourier transform (FT) is applied to calculate the amplitude and phase angle of harmonic component of thermal wave. Experimental results show that various deep subsurface defects are readily detected using LFM-UTWI with once excitation, and LFM-UTWI has an advantage of better defect detectability compared to ultrasound lock-in thermography (ULIT).

Liu, Junyan; Gong, Jinlong; Qin, Lei; Wang, Huiming; Wang, Yang

2014-01-01

403

Extended range harmonic filter  

NASA Technical Reports Server (NTRS)

Two types of filters, leaky-wall and open-guide, are combined into single component. Combination gives 10 db or greater additional attenuation to fourth and higher harmonics, at expense of increasing loss of fundamental frequency by perhaps 0.05 to 0.08 db. Filter is applicable to all high power microwave transmitters, but is especially desirable for satellite transmitters.

Jankowski, H.; Geia, A. J.; Allen, C. C.

1973-01-01

404

Harmonic generation in clusters  

Microsoft Academic Search

A model is presented for the nonlinear response of a small cluster, with a size much smaller than the wavelength, at the third harmonic of the laser frequency. The model involves collective modes of a cold electron core confined within a positively charged ion background. The response of the electron core to the laser field is similar to that of

Mykhailo V. Fomyts’kyi; Boris N. Breizman; Alexey V. Arefiev; Charles Chiu

2004-01-01

405

Molecular imaging of cancer cells using plasmon-resonant-enhanced third-harmonic-generation microscopy with silver nanoparticles  

Microsoft Academic Search

We demonstrate molecular-specific third-harmonic-generation microscopy in cultured oral squamous cell carcinoma lines by using silver nano-particles as contrast agent. Through surface plasmon resonance enhancement, cancer cells are clearly identified with their molecular signature.

Shih-Peng Tai; Shi-Wei Chu; Tsung-Han Tsai; Szu-Yu Chen; Xuan-Yu Shi; Chien-Huei Chang; Yana Wu; Dar-Bin Shieh; Lung-Jin Chen; Muppa Ramakrishna Prasad; Kuan-Jiuh Lin; Chi-Kuang Sun

2005-01-01

406

Electron and ion Bernstein waves excited in the ionosphere by high power EM waves at the second harmonic of the electron cyclotron frequency  

Microsoft Academic Search

Second harmonic HF transmissions yield electron and ion Bernstein wavesPremise verified with both theory and measurements at HAARPStimulated Bernstein waves are indicators of strong ionospheric modification

P. A. Bernhardt; C. A. Selcher; S. Kowtha

2011-01-01

407

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