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1

Surface Wave Chirp Transform Correlator.  

National Technical Information Service (NTIS)

The feasibility of developing a surface wave chirp transform correlator (CTC) is evaluated. A comprehensive characterization of chirp transform (CT) signal processing is presented. A computer model for simulating CT processors is described, with numerous ...

H. M. Gerard O. W. Otto

1976-01-01

2

Improved Chirp Transform Correlator.  

National Technical Information Service (NTIS)

This invention relates to a chirp transform correlator in which asynchronous operation is made possible by the use of a pair of paralleled signal processing channels to which the unknown signal to be correlated is applied. The two channels include sweepin...

H. M. Gerard

1983-01-01

3

The interlaced chirp Z transform  

Microsoft Academic Search

In this paper we introduce the Interlaced Chirp 2 Transform (Interlaced CZT). It is based on the computation of several carefully staggered Chirp Z transforms (CZT) that are progressively interlaced to result in a spectrum that has denser frequency samples where needed. This simple modification of the CZT is shown to result in significant computational savings over the regular CZT,

Indranil Sarkar; Adly T. Fam

2004-01-01

4

Temperature profile measurements within a chirped fiber Bragg grating using a Fourier transform technique  

NASA Astrophysics Data System (ADS)

The use of reflected power spectra arising from a chirped fiber Bragg grating (CFBG) to extract a nonuniform temperature distribution along the grating has been investigated. The technique uses a discrete Fourier transform (FFT) in which the measured spectrum of the CFBG due to a localised temperature change was simulated using the FFT grating design model. The model operated on the reference spectrum and hypothesis temperature distributions, T(z), to generate a spectrum representative of a localised temperature disturbance. The simulated spectrum was fitted to the measured spectrum using a three-parameter disturbance function operating on position, width and amplitude of temperature change. The rms deviation of the applied value for position of a localised temperature change was 0.14 mm.

Nand, Anbhawa; Kitcher, Daniel J.; Wade, Scott A.; Collins, Stephen F.; Baxter, Gregory W.

2005-05-01

5

Comparison of the Chirp z-Transform and Interpolation Techniques for Field-of-View Scaling  

Microsoft Academic Search

A version of a chirp z-transform (1) was programmed enabling phase-preserving FOV scaling for data sets with the zero of k-space in the middle. The method is important for all single-point imaging (SPI) sequences (2,3) such as SPRITE when used with multiple data acquisition for T2

J. B. Kaffanke; T. Dierkes; N. J. Shah

2004-01-01

6

Partitioned and modified chirp Z-transform: Signal processing technique for simultaneous multifrequency evaluation of the surface reradiated spectrum in slowly varying environments  

Microsoft Academic Search

The partitioned and modified chirp Z-transform (PAM-CZT) is a signal processing technique for computing the Z-transform of a sequence at equally spaced samples on a sector of the unit circle in the Z-plane. Unlike the computationally cumbersome classical technique (4), the PAM-CZT utilizes the fast Fourier transform (FFT) that allows real time implementation with state of the art minicomputers. Another

JAMES F. FERRIE; CARL W. NAWROCKI; G. CLIFFORD CARTER

1973-01-01

7

Determination of the position of a localized heat source within a chirped fibre Bragg grating using a Fourier transform technique  

NASA Astrophysics Data System (ADS)

The ability to determine the centre position of a localized temperature change within a chirped fibre Bragg grating (CFBG) has been investigated as a function of grating strength. The intragrating sensor is based on the analysis of reflected power spectra arising from a CFBG. The technique uses a discrete Fourier transform (FFT) in which the measured spectrum of the CFBG due to a localized temperature change (heat source) was simulated using a FFT grating design model. The model operated on the reference spectrum and hypothesis temperature distributions, T(z), to generate a spectrum of a CFBG subjected to a hypothesis temperature disturbance. The simulated spectrum was fitted to the measured spectrum using a three-parameter automatic disturbance function fitting algorithm operating on position, width and amplitude of temperature change. RMS deviations to within 0.03 mm of applied values of position have been obtained.

Nand, Anbhawa; Kitcher, Daniel J.; Wade, Scott A.; Nguyen, Thinh B.; Baxter, Greg W.; Jones, Rhys; Collins, Stephen F.

2006-06-01

8

Chirp Z transform based spectrum sensing via energy detection  

Microsoft Academic Search

In this study, the performance analysis of Fast Fourier Transform and Chirp Z transform based OFDM systems for cognitive radio networks with energy detector model for the spectrum sensing method is realized. Here, energy detection model for noncooperative spectrum sensing is investigated. On the other hand, the analysis is implemented by segmented Chirp z transform. In this study Chirp z

Mustafa Namdar; Baris Sahin; Haci Ilhan; Lutfiye Durak-Ata

2012-01-01

9

Spectral analysis using the CCD Chirp Z-transform  

Microsoft Academic Search

The charge coupled device (CCD) Chirp Z transformation (CZT) spectral analysis techniques were reviewed and results on state-of-the-art CCD CZT technology are presented. The CZT algorithm was examined and the advantages of CCD implementation are discussed. The sliding CZT which is useful in many spectral analysis applications is described, and the performance limitations of the CZT are studied.

W. L. Eversole; D. J. Mayer; P. W. Bosshart; M. Dewit; C. R. Howes; D. D. Buss

1978-01-01

10

Wideband Chirp-Transform Adaptive Filter.  

National Technical Information Service (NTIS)

A wideband chirp-transform adaptive-filter system is described that is capable of providing both spectral monitoring and the excision of multiple narrowband signals. The 80-MHz-bandwidth system processes a wideband continuous 300-MHz center-frequency inpu...

D. R. Arsenault

1985-01-01

11

Superconductive Chirp-Transform Spectrum Analyzer.  

National Technical Information Service (NTIS)

Spectral analysis over an instantaneous bandwidth of 2.4 GHz has been demonstrated utilizing superconductive dispersive delay lines in a chirp-transform configuration. Two-tone resolution of 43 MHz and + or - 1.2 dB amplitude uniformity was achieved.

R. S. Withers S. A. Reible

1985-01-01

12

The Chirp Z transform with CCD and SAW technology  

Microsoft Academic Search

The Chirp Z transform (CZT) is presented as an IF process that makes use of time compression and chirp pulse compression. This allows sampled signals to be stored in CCD memory for milliseconds or more, and Z transformed by the chirp filter in microseconds. A CZT spectrum analyzer therefore has extremely high throughput and the capability to process many channels

D. MacFall; J. Collins; Sclarretta; A. Cappon

1978-01-01

13

Transform domain adaptive filtering with the chirp Z transform  

Microsoft Academic Search

The use of the chirp Z transform (CZT) is proposed to improve the rate of convergence of transform domain adaptive output error algorithms. The use of the CZT is novel and is shown to possess advantages over the DFT. Other attempts at incorporating prior knowledge of input spectra use frequency sampling structures and their generalizations. Such structures require pole-zero cancellation,

Andrew W. Hull; W. Kenneth Jenkins

1990-01-01

14

The chirp-Z transform applied to adhesively bonded structures  

Microsoft Academic Search

A signal-processing technique based on the chirp-Z transform is presented to evaluate the echo signals of longitudinal ultrasonic transducers in contact with bonded materials. Both a simulated glass-glass interface of variable thickness and a realistic double lap bonded aluminum sample were tested. The observed frequency dips and peaks in the transducer spectrum from pulse-echo and through-transmission modes were recorded and

Vinod K. Nair; Reinhold Ludwig; Robert F. Anastasi

1991-01-01

15

The chirp z-transform - A CCD implementation  

Microsoft Academic Search

The chirp z-transform is a signal processing algorithm that can efficiently evaluate the z-transform of a time sampled signal when implemented using charge-coupled devices. The charge-coupled-device chirp z-transform realizes significant hardware savings over alternative approaches to perform spectral analysis and has the potential of greater signal-processing flexibility.

G. J. Mayer

1975-01-01

16

Chirp Transform in the Nonlinear Tracking Performance Analysis of the LMS Adaptive Predictors.  

National Technical Information Service (NTIS)

A chirp transform is defined for the A-step LMS adaptive predictors for linearly chirped signals embedded in additive white Gaussian noise. By converting the chirped signals to stationary baseband signals, this transform provides a different approach in a...

J. Han J. R. Zeidler W. H. Ku

2001-01-01

17

The chirp-Z transform applied to adhesively bonded structures  

NASA Astrophysics Data System (ADS)

A signal-processing technique based on the chirp-Z transform is presented to evaluate the echo signals of longitudinal ultrasonic transducers in contact with bonded materials. Both a simulated glass-glass interface of variable thickness and a realistic double lap bonded aluminum sample were tested. The observed frequency dips and peaks in the transducer spectrum from pulse-echo and through-transmission modes were recorded and related to the condition of zero reflection coefficient at the interfacial layer. Resulting thickness predictions for different transducer center frequencies ranging from 5-20 MHz are in excellent agreement with experimental measurements.

Nair, Vinod K.; Ludwig, Reinhold; Anastasi, Robert F.

1991-08-01

18

Applications of the partitioned and modified chirp z-transform to oceanographic measurements  

Microsoft Academic Search

The partitioned modified chirp Z-transform (PAM-CZT) is a signal processing technique which aids in the analysis of acoustically propagated ocean noises. The technique utilizes the fast Fourier transform (FFT) to allow real time computation in which long time data are processed in short-time-ordered sequences, thus providing spectral analysis to any frequency resolution.

JAMES F. FERRIE; CARL W. NAWROCKI; G. CLIFFORD CARTER

1975-01-01

19

Advanced digital techniques for high bandwidth chirp generation  

NASA Astrophysics Data System (ADS)

A brief summary of important digital chirp generation (DCG) techniques is provided, with emphasis on two complementary methods - systolic and parallel digital chirp generation. These techniques provide an order of magnitude improvement in performance when compared with conventional digital chirp generation techniques implemented on the same technology. When implemented on the same technology, the systolic DCG yields a threefold improvement in performance. If used in conjunction with the parallel DCG, an order of magnitude performance is readily achievable. Combining the systolic DCG with the parallel method and using the chirp generator FPGA devices with a video digital to analog converter enables sample rates of 160 MHZ to be produced.

Parkes, S. M.

20

A monolithic 512 point chirp Z transform processor  

Microsoft Academic Search

A monolithic analog 512 point chirp Z transform processor which calculates the discrete time Fourier transform will be described. A 6.1 × 5.5mm N-channel MOS chip includes premultiply, convolution and postmultiplication functions. Dynamic range of 63dB with operation from 1kHz to 1.5MHz has been measured.

Robert C. Pettengill; Patrick W. Bosshart; Michiel de Wit; C. Robert Hewes

1979-01-01

21

Error analysis of the chirp-z transform when implemented using waveform synthesizers and FFTs  

Microsoft Academic Search

This report analyzes the effects of finite-precision arithmetic on discrete Fourier transforms (DFTs) calculated using the chirp-z transform algorithm. An introduction to the chirp-z transform is given together with a description of how the chirp-z transform is implemented in hardware. Equations for the effects of chirp rate errors, starting frequency errors, and starting phase errors on the frequency spectrum of

Bielek

1990-01-01

22

An optimized SAW chirp -Z Transform for OFDM systems  

Microsoft Academic Search

The OFDM system that can use it combined to the Fourier transform to the OFDM signal for amount of wave of the inverse Fourier transform and received OFDM can have a definite advantage in power consumption, a super-high-speed operation processing performance be possessed, and the SAW chirp-Z transform be applied to high-speed wireless LAN and WAN. As for the SAW

Takaya Watanabe

2009-01-01

23

Real-time spectrum analysis using hardware Fourier and chirp-Z transformations  

Microsoft Academic Search

The paper emphasizes the wide variety of distinct block-schematic approaches to be adopted in analog implementations for real-time spectrum analysis by hardware Fourier and chirp-Z transformations. The discussion covers Fourier analysis by correlation, chirp-Z analysis by correlation, variants of chirp-Z correlation, chirp-Z analysis by matched filtering, matching the chirp waveform with a dispersive delay line, and some features common to

R. Benjamin

1979-01-01

24

Chirp Z-transform spectral zoom optimization with MATLAB  

Microsoft Academic Search

The MATLAB language has become a standard for rapid prototyping throughout all disciplines of engineering because the environment is easy to understand and use. Many of the basic functions included in MATLAB are those operations that are necessary to carry out larger algorithms such as the chirp z-transform spectral zoom. These functions include, but are not limited to mathematical operators,

Grant D

2005-01-01

25

High resolution Wigner distribution using chirp Z-transform analysis  

Microsoft Academic Search

The chirp Z-transform is used in the Wigner distribution for high resolution spectrum analysis. It has the capability to zoom onto the area of the signal of interest, which makes it a very useful spectral analysis tool for analyzing nonstationary time-varying signals. This capability results in a more reliable and accurate spectral analysis on the time-frequency plane

Soo-Chang Pei; Ing-Ing Yang

1991-01-01

26

Segmented chirp Z-transform and its applications  

Microsoft Academic Search

The segmented chirp Z-transform (SCZT) algorithm introduced, and its mathematical derivation is described. Only a small FFT is used to assist the implementation; hence, the algorithm can handle a very large amount of input data with very limited memory space. In an example of a frequency spectrum calculation the SCZT is able to handle 30K input data, whereas the regular

T. T. Wang

1989-01-01

27

Voltage Flicker Detection Based on Chirp-z Transform  

Microsoft Academic Search

Studying of the IEC flicker meter shows that the instantaneous flicker sensation level S can be calculated directly if the spectrums of fluctuating component of voltage are known. In this paper a novel flicker measurement method is proposed. First, the square demodulation is used to obtain the fluctuating component of voltage, and then the chirp-z transform (CZT) is used to

Kang Wei; Guo Jing; Li Heming; Yan Xiangwu

2010-01-01

28

A direct digital synthesis chirped pulse Fourier transform microwave spectrometer  

NASA Astrophysics Data System (ADS)

Chirped pulse Fourier transform microwave (CP-FTMW) spectrometers have become the instrument of choice for acquiring rotational spectra, due to their high sensitivity, fast acquisition rate, and large bandwidth. Here we present the design and capabilities of a recently constructed CP-FTMW spectrometer using direct digital synthesis (DDS) as a new method for chirped pulse generation, through both a suite of extensive microwave characterizations and deep averaging of the 10-14 GHz spectrum of jet-cooled acetone. The use of DDS is more suited for in situ applications of CP-FTMW spectroscopy, as it reduces the size, weight, and power consumption of the chirp generation segment of the spectrometer all by more than an order of magnitude, while matching the performance of traditional designs. The performance of the instrument was further improved by the use of a high speed digitizer with dedicated signal averaging electronics, which facilitates a data acquisition rate of 2.1 kHz.

Finneran, Ian A.; Holland, Daniel B.; Carroll, P. Brandon; Blake, Geoffrey A.

2013-08-01

29

Error analysis of the chirp-z transform when implemented using waveform synthesizers and FFTs  

SciTech Connect

This report analyzes the effects of finite-precision arithmetic on discrete Fourier transforms (DFTs) calculated using the chirp-z transform algorithm. An introduction to the chirp-z transform is given together with a description of how the chirp-z transform is implemented in hardware. Equations for the effects of chirp rate errors, starting frequency errors, and starting phase errors on the frequency spectrum of the chirp-z transform are derived. Finally, the maximum possible errors in the chirp rate, the starting frequencies, and starting phases are calculated and used to compute the worst case effects on the amplitude and phase spectrums of the chirp-z transform. 1 ref., 6 figs.

Bielek, T.P.

1990-11-01

30

The chirp z-transform algorithm  

Microsoft Academic Search

A computational algorithm for numerically evaluating thez-transform of a sequence ofNsamples is discussed. This algorithm has been named the chirpz-transform (CZT) algorithm. Using the CZT algorithm one can efficiently evaluate thez-transform atMpoints in thez-plane which lie on circular or spiral contours beginning at any arbitrary point in thez-plane. The angular spacing of the points is an arbitrary constant, andMandNare arbitrary

L. R. RABINER; R. Schafer; C. Rader

1969-01-01

31

Development and application of a SAW Chirp-Z transformer  

Microsoft Academic Search

A development is reported in which the Chirp-z transform algorithm is truncated to perform spectral amplitude analysis. The basic process is described in relation to a unit giving in excess of one hundred resolved spectral lines with a resolution of 50kHz and a total processing time of 50 microseconds per data set. The displayed spectrum covers a dynamic range in

M. B. N. Butler

1978-01-01

32

Application of the chirp z-transform to MRI data  

Microsoft Academic Search

A version of the chirp z-transform (CZT) enabling signal intensity and phase-preserving field-of-view scaling has been programmed. The algorithm is important for all single-point imaging sequences such as SPRITE when used with multiple data acquisition for T2? mapping or signal averaging. CZT has particular utility for SPRITE imaging of nuclei with short relaxation times such as sodium at high field.

J. Kaffanke; T. Dierkes; S. Romanzetti; M. Halse; J. Rioux; M. O. Leach; B. Balcom; N. J. Shah

2006-01-01

33

Application of the chirp z-transform to MRI data.  

PubMed

A version of the chirp z-transform (CZT) enabling signal intensity and phase-preserving field-of-view scaling has been programmed. The algorithm is important for all single-point imaging sequences such as SPRITE when used with multiple data acquisition for T2* mapping or signal averaging. CZT has particular utility for SPRITE imaging of nuclei with short relaxation times such as sodium at high field. Here, a complete theory of the properties of CZT is given. This method operates entirely in k-space. It is compared with a conventional interpolation approach that works in image space after the application of a fast Fourier transformation. PMID:16216539

Kaffanke, J; Dierkes, T; Romanzetti, S; Halse, M; Rioux, J; Leach, M O; Balcom, B; Shah, N J

2005-10-10

34

Application of the chirp z-transform to MRI data  

NASA Astrophysics Data System (ADS)

A version of the chirp z-transform (CZT) enabling signal intensity and phase-preserving field-of-view scaling has been programmed. The algorithm is important for all single-point imaging sequences such as SPRITE when used with multiple data acquisition for T2? mapping or signal averaging. CZT has particular utility for SPRITE imaging of nuclei with short relaxation times such as sodium at high field. Here, a complete theory of the properties of CZT is given. This method operates entirely in k-space. It is compared with a conventional interpolation approach that works in image space after the application of a fast Fourier transformation.

Kaffanke, J.; Dierkes, T.; Romanzetti, S.; Halse, M.; Rioux, J.; Leach, M. O.; Balcom, B.; Shah, N. J.

2006-01-01

35

The segmented chirp Z-transform and its application in spectrum analysis  

Microsoft Academic Search

The chirp Z-transform (CZT) algorithm is known to be more flexible than the fast Fourier transform in calculating the frequency spectrum. However, its mathematical implementation is complex, and additional memory space is required. A modified CZT algorithm called the segmented chirp Z transform (SCZT) is introduced. SCZT has the ability to handle a very large amount of input data with

T. T. Wang

1990-01-01

36

A completely integrated thirty-two-point chirp Z transform [CCD IC realisation  

Microsoft Academic Search

A monolithic 32-point DFT using the chirp Z transform (CZT) algorithm has been designed and fabricated using an n-channel two-level polysilicon coplanar electrode process. The detailed design and operation of this first fully integrated CCD chirp Z transform are discussed, and some spectral analysis applications for a CCD CZT are described.

WILLIAM L. EVERSOLE; DALE J. MAYER; PATRICK W. BOSSHART; M. De Wit; C. R. Hewes; D. D. Buss

1978-01-01

37

Real-time Fourier analysis of spread spectrum signals using surface-wave-implemented chirp-Z transformation  

Microsoft Academic Search

In many communication and radar applications, it is desirable to determine the spectral content of signals in real time. A technique employing dispersive surface-acoustic-wave devices to implement the chirp-Z transform is described. Experimental results obtained for a number of commonly used signals, including the maximal-length pseudonoise sequences, are presented, and agreement with theoretical prediction is discussed.

G. R. Nudd; O. W. Otto

1976-01-01

38

Real-Time Fourier Analysis of Spread Spectrum Signals Using Surface-Wave-Implemented Chirp-Z Transformation (Short Papers)  

Microsoft Academic Search

In many communication and RADAR applications it is desirable to determine the spectral content of signals in real time. A technique employing dispersive surface acoustic wave devices to implement the chirp-Z transform is described. The experimental results obtained for a number of commonly used signals, including the maximal-length pseudonoise sequences, are shown, and the agreement with theoretical prediction is discussed.

GRAHAM R. NUDD; OBERDAN W. OTTO

1976-01-01

39

Spotlight-Mode SAR Image Formation Utilizing the Chirp Z-Transform in Two Dimensions  

Microsoft Academic Search

A new spotlight-mode synthetic aperture radar im- age formation approach is presented that directly utilizes the reflected electromagnetic returns collected on a polar grid. This approach eliminates polar-to-rectangular grid interpolation by employing chirp z-transforms in two dimensions. Since the chirp z-transform can be implemented via fast Fourier transforms (FFTs), this image formation algorithm consists almost entirely of FFTs allowing it

David A. Yocky; Daniel E. Wahl; Charles V. Jakowatz

2006-01-01

40

A fully-integrated 32-point chirp Z-transform IC  

Microsoft Academic Search

An IC to perform a complete 32-point DFT with the chirp Z-transform algorithm has been developed, using a two-level polysilicon coplanar electrode process. Chip contains CCD filters, MDACs, ROM and clock logic.

William L. Eversole; D. Mayer; P. W. Bosshart; M. deWitt; C. R. Hewes; D. Buss

1978-01-01

41

Study of SAW Chirp Z transform for an enhancement of OFDM\\/OFDMA systems  

Microsoft Academic Search

The surface acoustic wave has a definite advantage in the Fourier transform for distribute of OFDM that is converted into the OFDM signal and received in power consumption and has a super-high-speed operation. The operation speed of the SAW Chirp-Z transform processor composed of SAW Down Chirp Filter of bandwidth 100 MHz and N=2,048 becomes 5.5GFLOPS. The condition that the

Takaya Watanabe

2009-01-01

42

Two-dimensional chirp z-transform and its application to zoom Wigner bispectrum  

Microsoft Academic Search

In this paper, we present the 2-D chirp z-transform as an extension of the 1-D chirp z-transform. It can be used as a powerful analytic tool to emphasize any region in either the (t-f)- or the (f1-f2) planes, covering a wide variety of multidimensional distributions ranging from two-dimensional filters to higher order moment spectra (HOMS) including the Wigner distribution and

J. A. Draidi; M. A. Khasawneh; J. M. Abu-Ghalune; N. M. Ghuneinii

1996-01-01

43

Study of a time-compression technique for TV transmission using a chirp filter and envelope detection  

NASA Astrophysics Data System (ADS)

A time-compression technique for possible application in communication signal processing is studied. The method uses a linear chirp, a linear dispersive filter realized by surface acoustic wave devices, and an envelope detector. This technique is heuristic and can be viewed as a quasi-stationary model of the FM wave involved. Numerical results show that excessive distortion is created, and its application to TV transmission is not suitable unless some kind of equalization is provided. One such form of equalization is the chirp transform processor which involves considerably more complexity. Simpler equalizations may be possible but do not seem to be straightforward.

Eng, K. Y.; Haskell, B. G.

1981-12-01

44

A high-speed processor for finely-spaced Fourier transform via chirp z-transform  

Microsoft Academic Search

This paper deals with the design of a processor for very-finely spaced spectral analysis over a narrow band of the available spectrum. The processor implements the chirp z-transform (CZT) algorithm, and exploits a fully-parallel architecture in order to address real-time applications with very-high throughput. The internal data-path is optimized as a trade-off between fixed-point accuracy and implementation complexity. The proposed

Giuseppe Gentile; Massimo Rovini; Luca Fanucci

2009-01-01

45

Wavelength-spacing-tunable multichannel filter incorporating a sampled chirped fiber Bragg grating based on a symmetrical chirp-tuning technique without center wavelength shift.  

PubMed

We propose and experimentally demonstrate a simple and flexible scheme for a wavelength-spacing-tunable multichannel filter exploiting a sampled chirped fiber Bragg grating based on a symmetrical modification of the chirp ratio. Symmetrical bending along a sampled chirped fiber Bragg grating attached to a flexible cantilever beam induces a variation of the chirp ratio and a reflection chirp bandwidth of the grating without a center wavelength shift. Accordingly, the wavelength spacing of a sampled chirped fiber Bragg grating is continuously controlled by the reflection chirp bandwidth variation of the grating corresponding to the bending direction, which allows for realization of an effective wavelength-spacing-tunable multichannel filter. Based on the proposed technique, we achieve the continuous tunability of the wavelength spacing in a range from 1.51 to 6.11 nm, depending on the bending direction of the cantilever beam. PMID:17130906

Han, Young-Geun; Dong, Xinyong; Lee, Ju Han; Lee, Sang Bae

2006-12-15

46

Application of inverse chirp-z transform in wideband radar  

Microsoft Academic Search

Pulse stepped frequency radar is a kind of wideband radar technique. It can obtain high range resolution by correct signal processing methods. One of most important methods is the inverse Fourier transform method. This method can realize pulse compression by the coherent sum of a series of echoes. Although the inverse Fourier transform method is very useful, the number of

Wang Yiding; Wu Yirong; Hong Jun

2001-01-01

47

Azimuth fractional transformation of the fractional chirp scaling algorithm (FrCSA)  

Microsoft Academic Search

The fractional chirp scaling algorithm (FrCSA) is based on the use of the fractional Fourier transform (FrFT) within the chirp scaling algorithm (CSA). In this paper, a closed-form expression for the azimuth FrFT of the FrCSA is mathematically derived and analyzed from the high-resolution synthetic aperture radar imaging point of view. The azimuth-FrFT expression of the FrCSA is compared to

Ahmed S. Amein; John J. Soraghan

2006-01-01

48

Rotation of NMR images using the 2D chirp-z transform.  

PubMed

A quick and accurate way to rotate and shift nuclear magnetic resonance (NMR) images using the two-dimensional chirp-z transform is presented. When the desired image grid is rotated and shifted from the original grid due to patient motion, the chirp-z transform can reconstruct NMR images directly onto the ultimate grid instead of reconstructing onto the original grid and then applying interpolation to get the final real-space image in the conventional way. The rotation angle and shift distances are embedded in the parameters of the chirp-z transform. The chirp-z transform implements discrete sinc interpolation to get values at grid points that are not exactly on the original grid when applying the inverse Fourier transform. Therefore, the chirp-z transform is more accurate than methods such as linear or bicubic interpolation and is more efficient than direct implementation of sinc interpolation because the sinc interpolation is implemented at the same time as reconstruction from k-space. PMID:10080271

Tong, R; Cox, R W

1999-02-01

49

Efficient Full Aperture Processing of TOPS Mode Data Using the Moving Band Chirp $Z$Transform  

Microsoft Academic Search

The main operational mode of the European Space Agency's upcoming Sentinel-1 operational satellite will be the Terrain Observation by Progressive Scans (TOPS) imaging mode. This paper presents a very efficient wavenumber domain pro- cessor for the processing of TOPS mode data. In particular, a novel signal transform, called a moving band chirp Z-transform, is introduced in order to allow the

Geir Engen; Yngvar Larsen

2011-01-01

50

Discrimination of Earthquakes and Explosions Using Chirp-Z Transform Spectrum Features  

Microsoft Academic Search

To discriminate between earthquakes and explosions, spectrum range selection and spectrum resolution are sensitive and important constraint factors for recognition rate. This paper proposes a feature extracting algorithm for seismic wave spectrum analysis by using Chirp-Z transform. Initially by Fourier transform (FFT), overall spectrum layout is acquired. Upon this overall layout, seismic signals, suitable frequency range in the spectrum which

Hanming Huang; Rui Li; Shijun Lu; Yin Ju Bian

2009-01-01

51

[Analysis of scatterer microstructure feature based on Chirp-Z transform cepstrum].  

PubMed

The fundamental research field of medical ultrasound has been the characterization of tissue scatterers. The signal processing method is widely used in this research field. A new method of Chirp-Z Transform Cepstrum for mean spacing estimation of tissue scatterers using ultrasonic scattered signals has been developed. By using this method together with conventional AR cepstrum method, we processed the backscattered signals of mimic tissue and pig liver in vitro. The results illustrated that the Chirp-Z Transform Cepstrum method is effective for signal analysis of ultrasonic scattering and characterization of tissue scatterers, and it can improve the resolution for mean spacing estimation of tissue scatterers. PMID:18232497

Guo, Jianzhong; Lin, Shuyu

2007-12-01

52

Using 2D Chirp z-Transforms for Near-field to Far-field Calculations  

Microsoft Academic Search

Phased arrays for radar applications are typically characterized in an instrumented near field range (NFR), and the far-field parameters are computed from these measurements. The advantages of using a 2D chirp z-transform for the far-field computations are considered

Peter J. Kajenski

2006-01-01

53

Incoherent optical two-dimensional Fourier transform using the chirp-z algorithm  

NASA Astrophysics Data System (ADS)

An incoherent optical method for computing two-dimensional complex-valued Fourier transforms is described. It is based on implementing the two-dimensional chirp-z algorithm with incoherent optical convolutions and indirect representation of complex-valued functions.

Glaser, I.; Katzir, Y.; Toschi, V.

1984-06-01

54

Segmented chirp Z-transform and multiple deep dip windows for electrical power system harmonic analysis  

Microsoft Academic Search

The combined use of the Segmented Chirp Z-Transform (SCZT) and of the Multiple Deep Dip (MDD) windows is proposed and applied to electrical power system harmonic analysis. The goal of increasing the resolvability of low magnitude non-harmonic tones close in frequency to higher magnitude harmonics and the detectability of very low magnitude high frequency harmonics is pursued. The SCZT allows

P. Daponte; D. Menniti; A. Testa

1996-01-01

55

A novel implementation of a chirp Z-transform using a CORDIC processor  

Microsoft Academic Search

An efficient implementation of the chirp Z transform (CZT) using a CORDIC (coordinate rotation digital computer) processor is presented. In particular, it is shown that a scaling operation in the CZT algorithm can be conveniently implemented with a norm correction (normalization) computation, which is often considered as an overhead in the CORDIC algorithm. Furthermore, since the desired frequencies of CZT

Y. H. Hu; S. Naganathan

1990-01-01

56

On using the chirp z-transform for radar image formation  

Microsoft Academic Search

The 'chirp z-transform' (CZT) approach to SAR signal processing has been the object of attention in virtue of allowing two separate signal-processing functions to be combined; it is presently noted, however, to be less computationally efficient than more conventional methods and to require the entire array of SAR data to be collected before the CZT can proceed. This requirement may

John W. Adams; Robert W. Bayma

1989-01-01

57

Using the inverse Chirp-Z transform for time-domain analysis of simulated radar signals  

Microsoft Academic Search

There exists a need to develop a method to locate underground voids, or caches. In the past, ground penetrating radar (GPR) operating in the time domain mode has been used. In this paper, we turn our attention to stepped frequency radar, capable of making frequency domain reflection coefficient measurements. We then apply the inverse Chirp-Z transform (ICZT) to this data,

Frickey

1995-01-01

58

An induction motor speed measurement based on current harmonic analysis with Chirp-Z Transform  

Microsoft Academic Search

The paper presents a new method to measure motor speed by means of frequency estimation of rotor slot harmonics present in the supply current of squirrel single cage induction motors. The novelty of the method is the use of Chirp-Z Transform as supply current harmonic analysis. The advantages are an improved spectral resolution and accuracy. Moreover a shorter sampling time

M. Aiello; A. Cataliotti; S. Nuccio

2001-01-01

59

A Chirp-z-Transform-Based Software Synchronization Method for Optical Performance Monitoring  

Microsoft Academic Search

A software synchronization method based on chirp-z transform is proposed for optical performance monitoring in this letter. In comparison with the previously reported software synchronization methods, the proposed method is shown to have higher spectral resolution and shorter calculation time. The accuracy of the sampling step size for eye diagram recovery is efficiently improved. The experimental results of the eye-diagram

Aiying Yang; Junsen Lai; Yu-nan Sun

2011-01-01

60

Efficient Implementation Of Chirp Z-Transform Using A Cordic Processor  

Microsoft Academic Search

In this paper, an efficient implementation of the Chirp Z Transform (CZT) using a CORDIC (Coordinate Rotation DIgital Computer) processor is presented. The proposed implementation is most effective when only a very few complex frequencies on the Z-plane is to be evaluated via CZT. In particular, it is shown that a scaling operation in the CZT algorithm can be conveniently

Yu Hen Hu; S. Naganathan

1988-01-01

61

Incoherent optical two-dimensional Fourier transform using the chirp-z algorithm.  

PubMed

An incoherent optical method for computing two-dimensional complex-valued Fourier transforms is described. It is based on implementing the two-dimensional chirp-z algorithm with incoherent optical convolutions and indirect representation of complex-valued functions. PMID:19721543

Glaser, I; Katzir, Y; Toschi, V

1984-06-01

62

Frequency Offset Estimation for Optical Coherent M-QAM Detection Using Chirp z-Transform  

Microsoft Academic Search

The chirp z-Transform (CZT) is introduced to replace the traditional gradient descent (GD) in frequency offset estimation for digital coherent quadrature amplitude modulation reception. Different from GD, CZT is not sensitive to the changes of the parameters and is free of uncertain latency that GD suffers. The implementation of frequency offset estimator based on CZT is presented and numeric simulations

Haijun Leng; Song Yu; Xin Li; Mingying Lan; Ping Liao; Tianyi Wang; Wanyi Gu

2012-01-01

63

On the modified chirp z transform for synthetic aperture radar systems  

Microsoft Academic Search

A modified chirp z-transform (MCZT) algorithm which has been proposed by Lawton (1988) to replace the conventional polar format interpolation in synthetic aperture radar systems is discussed. The key assumption used in the MCZT approach is that the spatial-frequency samples can be obtained on a concentric squares (CS) grid. The CS grid is briefly reviewed. The conventional approach to processing

John W. Adams; Robert W. Bayma; Michael E. Lawrence; Leon Petrosian

1991-01-01

64

Waveguide Chirped-Pulse Fourier Transform Microwave Spectroscopy of 2-ETHOXYETHANOL  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of 2-ethoxyethanol was recorded from 8.7 to 26.5 GHz at 250 K with a waveguide chirped-pulse Fourier transform microwave spectrometer. The full spectrum contains contributions from multiple vibrational states. Preliminary assignments have been made with a combination of ab initio calculations and an automated spectral fitting program that accelerates the initial fitting process.

Phillips, Maria A.; Shipman, Steven T.

2013-06-01

65

High-resolution NMR chemical-shift imaging with reconstruction by the chirp z-transform  

Microsoft Academic Search

A study of a novel nuclear magnetic resonance (NMR) chemical-shift image reconstruction method with a high chemical-shift resolution achieved by the chirp z-transform (CZT) is presented. Phase encoding is used for the spatial coordinates x and y, and the frequency coordinate is reserved especially for the chemical shift. The Fourier transform (FT) image reconstruction algorithm, which forms the basis of

TIE NAN MA; KUNIO TAKAYA

1990-01-01

66

Optical Fourier transform techniques for advanced Fourier spectroscopy systems.  

PubMed

A review of multichannel long integration time, optical Fourier transform techniques for advanced Fourier spectroscopy systems is followed by the description of a new multichannel time-integrating optical Fourier transform chirp-Z system and a discussion of its use in Fourier spectroscopy signal processing. PMID:20221177

Casasent, D; Psaltis, D

1980-06-15

67

2-D HARMONIC RETRIEVAL IN MULTIPLICATIVE AND ADDITIVE NOISE BASED ON CHIRP Z-TRANSFORM  

Microsoft Academic Search

The two-dimensional (2-D) harmonic retrieval method in multiplicative and additive noise based on 2-D chirp z-transform (CZT) is discussed in this paper. Unlike 2-D FFT, the 2-D CZT can improve the spectral resolution without increasing the size of the observation data and fine the spectra of 2-D harmonics in multiplicative and additive noise. Hence, the resolution and accuracy of the

Shiyong Yang; Hongwei Li; Cheng Wu; Zhiming Li

2006-01-01

68

Wideband spectral reconstruction via short-time modified chirp z-transform processing  

Microsoft Academic Search

In this paper the chirp z-transform is adapted for the spectral reconstruction of a wideband signal. Here, spectral reconstruction is based on the coherent and sequential processing of non-overlapping short-time segments. This approach eases hardware implementation in the presence of limited memory allocation and can provide savings in computational effort. In addition, it offers the flexibility of focusing the reconstruction

Ziad F. Hamed; Benjamin C. Flores

1997-01-01

69

An auditory spectral analysis model using the chirp z-transform  

Microsoft Academic Search

In this paper we discuss a new signal-processing approach to implementing an auditory processing model. The model is based on auditory physiology and psychophysics; it uses constant-bandwidth analysis below 500 Hz and constant-Q analysis above 500 Hz, with the analysis filters being implemented with multiple real poles. The constant-Q analysis is performed using the chirp z-transform (CZT). We review the

J. Kates

1983-01-01

70

On the modifier chirp z transform for synthetic aperture radar systems  

Microsoft Academic Search

A modified chirp z-transform (MCZT) algorithm which has been proposed by W. Lawton (IEEE Trans. Acoust., Speech, Signal Processing, vol.ASSP-36, p.931-3, June 1988) to replace the conventional polar format interpolation in synthetic aperture radar (SAR) systems is discussed. The key assumption used in the MCZT approach is that the spatial-frequency samples can be obtained on a concentric squares (CS) grid.

John W. Adams; Robert W. Bayma; Michael E. Lawrence; Leon Petrosian

1991-01-01

71

Wideband spectral reconstruction via short-time modified chirp z-transform processing  

NASA Astrophysics Data System (ADS)

In this paper the chirp z-transform is adapted for the spectral reconstruction of a wideband signal. Here, spectral reconstruction is based on the coherent and sequential processing of non-overlapping short-time segments. This approach eases hardware implementation in the presence of limited memory allocation and can provide savings in computational effort. In addition, it offers the flexibility of focusing the reconstruction of the spectrum on a narrow spectral band of interest.

Hamed, Ziad F.; Flores, Benjamin C.

1997-09-01

72

On the modified chirp z transform for synthetic aperture radar systems  

NASA Astrophysics Data System (ADS)

A modified chirp z-transform (MCZT) algorithm which has been proposed by Lawton (1988) to replace the conventional polar format interpolation in synthetic aperture radar systems is discussed. The key assumption used in the MCZT approach is that the spatial-frequency samples can be obtained on a concentric squares (CS) grid. The CS grid is briefly reviewed. The conventional approach to processing CS grid data is described. The MCZT is discussed, and its disadvantages are emphasized.

Adams, John W.; Bayma, Robert W.; Lawrence, Michael E.; Petrosian, Leon

1991-04-01

73

Application of the chirped Z-transform to processing frequency hopping spread spectrum signals  

Microsoft Academic Search

Charge coupled device\\/chirped Z transform (CCD\\/CZT) oriented detection schemes for a frequency-hopped spread spectrum (FHSS) signal in the presence of white Gaussian noise and radio frequency interference are derived. For the case when an FHSS signal is corrupted by white Gaussian noise, the frequency-hopped complex exponents representing a binary symbol are assumed to have partial coherence. The optimum receiver structures

S. Mahmood

1980-01-01

74

Constant-Q analysis using the chirp z-transform  

Microsoft Academic Search

Constant-Q spectral analysis can be performed by taking the Fourier transform of a windowed sequence where the window is a function of the product of time and frequency. If the window used is a decaying exponential whose argument is a constant times the product of time and frequency, the result is equivalent to evaluating the z-transform of the sequence along

J. Kates

1979-01-01

75

An algorithm for performing an inverse chirp z-transform  

Microsoft Academic Search

An efficient algorithm for the determination of the coefficients of a polynomial from evenly spaced sample values of that polynomial on a spiral contour in the complex plane is presented. It is useful for the determination of a sequence from evenly spaced values of its Fourier transform.

R. Mersereau

1974-01-01

76

Efficient computation of optical disk readout by use of the chirp z transform.  

PubMed

Computation of the readout signal of an optical disk involves Fourier transforms from the objective lens pupil to the disk and, after interaction with the disk, from the disk to the objective pupil. Traditionally, the complex two-dimensional Fourier transform is numerically evaluated as a two-dimensional fast Fourier transform. To obtain sufficient resolution in the involved planes, one must choose sampling grid sizes of typically 1,024 x 1,024 or higher, resulting in a substantial computation time if the calculation is to be repeated many times. Discussed is an alternative method for evaluating the Fourier transform, based on the chirp z transform, by which a considerable improvement in efficiency can be obtained without loss of accuracy. PMID:12197659

Bakx, Jan L

2002-08-10

77

Efficient Computation of Optical Disk Readout by use of the Chirp z Transform  

NASA Astrophysics Data System (ADS)

Computation of the readout signal of an optical disk involves Fourier transforms from the objective lens pupil to the disk and, after interaction with the disk, from the disk to the objective pupil. Traditionally, the complex two-dimensional Fourier transform is numerically evaluated as a two-dimensional fast Fourier transform. To obtain sufficient resolution in the involved planes, one must choose sampling grid sizes of typically 1024 x 1024 or higher, resulting in a substantial computation time if the calculation is to be repeated many times. Discussed is an alternative method for evaluating the Fourier transform, based on the chirp z transform, by which a considerable improvement in efficiency can be obtained without loss of accuracy.

Bakx, Jan L.

2002-08-01

78

A postprocessing method based on chirp Z transform for FDTD calculation of point defect states in two-dimensional phononic crystals  

Microsoft Academic Search

In this paper, a new postprocessing method for the finite difference time domain (FDTD) calculation of the point defect states in two-dimensional (2D) phononic crystals (PNCs) is developed based on the chirp Z transform (CZT), one of the frequency zooming techniques. The numerical results for the defect states in 2D solid\\/liquid PNCs with single or double point defects show that

Xiao-Xing Su; Yue-Sheng Wang

2010-01-01

79

A Chirp Z transform based synchronizer for power system measurements  

Microsoft Academic Search

Power system analyzers are required for performing an accurate evaluation of harmonic pollution, voltage and current synchronous sampling in order to limit leakage error and to assure reproducible results. Moreover, the increased interest about power and voltage quality, forced international working groups to define new standards for testing and measurement techniques. In particular, harmonic and interharmonic measurement and instrumentation standards

M. Aiello; A. Cataliotti; S. Nuccio

2002-01-01

80

On using the chirp z-transform for radar image formation  

NASA Astrophysics Data System (ADS)

The 'chirp z-transform' (CZT) approach to SAR signal processing has been the object of attention in virtue of allowing two separate signal-processing functions to be combined; it is presently noted, however, to be less computationally efficient than more conventional methods and to require the entire array of SAR data to be collected before the CZT can proceed. This requirement may further compromise processor throughput, and increase processor memory requirements. CZT is also judged to be unable to furnish the intermediate range bin data required for autofocusing.

Adams, John W.; Bayma, Robert W.

1989-08-01

81

Waveguide Chirped-Pulse Fourier Transform Microwave Spectroscopy of 1-PROPANETHIOL  

NASA Astrophysics Data System (ADS)

The rotational spectrum of 1-propanethiol was measured from 8.7 to 26.5 GHz at 250 K with a waveguide chirped-pulse Fourier transform microwave spectrometer. This thiol has a dense spectrum containing contributions from multiple conformers, excited vibrational states, and singly-substituted isotopomers (^{34}S and ^{13}C) in natural abundance. Further, the spectrum shows complications due to the presence of internal rotation. Despite this complexity, some progress has been made, and preliminary work on this molecule will be presented.

Gordon, Brittany P.; Shipman, Steven T.

2013-06-01

82

Broadband Chirped-Pulse Fourier Transform Microwave Spectroscopy and Molecular Structure of the ARGON-{ {(Z)}}-1-CHLORO-2-FLUOROETHYLENE Complex  

NASA Astrophysics Data System (ADS)

A chirped-pulse Fourier transform microwave spectrometer is used to obtain the 6--18 GHz rotational spectrum of the gas-phase complex formed between argon and (Z)-1-chloro-2-fluoroethylene. Both the 35Cl and 37Cl isotopologues are observed in natural abundance, and analysis of these spectra provides predictions for both singly-substituted 13C species with sufficient precision to allow their observation with minimal searching using the more sensitive narrow band Balle-Flygare cavity technique. The non-planar structure of the complex is similar to previously observed argon-fluoroethylene complexes with the argon atom closer to the fluorine than to the chlorine. In contrast to the argon-vinyl chloride and argon-cis-1,2-difluoroethylene complexes, tunneling of the argon atom between the two equivalent, non-planar geometries is not observed.

Marshall, Mark D.; Leung, Helen O.

2012-06-01

83

Bearing failure diagnosis in three-phase induction motor by chirp-Z transform and zoom-MUSIC  

Microsoft Academic Search

This paper introduces a new approach of the stator current spectral analysis, based on chirp-Z transform (CZT) and Zoom Multiple signal classification (ZMUSIC), for diagnosing the occurrence of bearing faults in three-phase induction motor. In contrast with traditional FFT, CZT and ZMUSIC are suitable when it is necessary to analyze a not stationary signal such as the current signal of

Xiangjun Wang; Fang Fang

2011-01-01

84

An induction motor speed measurement method based on current harmonic analysis with the chirp-Z transform  

Microsoft Academic Search

This paper presents a new method to measure motor speed by means of frequency estimation of rotor slot spectral components in the supply current of squirrel single-cage induction motors. The novelty of the method consists in the harmonic analysis of the supply current by means of the chirp-Z transform (CZT). The advantages are improved accuracy due to better spectral resolution

Massimo Aiello; Antonio Cataliotti; Salvatore Nuccio

2005-01-01

85

Train axle counters by Bragg and chirped grating techniques  

Microsoft Academic Search

Both sensing techniques, FBG wavelength shift and FCG intensity, were applied in a train axle counting system. Their structure and the process of changing strain data into accurate axle numbers are discussed.

Weilai Li; Ning Jiang; Jinshan Liu; Yefang Zhang

2008-01-01

86

Train axle counters by Bragg and chirped grating techniques  

NASA Astrophysics Data System (ADS)

Both sensing techniques, FBG wavelength shift and FCG intensity, were applied in a train axle counting system. Their structure and the process of changing strain data into accurate axle numbers are discussed.

Li, Weilai; Jiang, Ning; Liu, Jinshan; Zhang, Yefang

2008-06-01

87

Range Resampling in the Polar Format Algorithm for Spotlight SAR Image Formation Using the Chirp z-Transform  

Microsoft Academic Search

Besides an inverse two-dimensional (2-D) Fourier transform, the polar format algorithm (PFA) for the spotlight synthetic aperture radar (SAR) image formation can be normally divided into two cascaded processing stages, which are called the range and azimuth resampling, respectively. This paper focuses on a new implementation of the first stage, i.e., the range resampling, using the chirp z-transform (CZT). The

Daiyin Zhu; Zhaoda Zhu

2007-01-01

88

High-resolution NMR chemical-shift imaging with reconstruction by the chirp z-transform.  

PubMed

A study of a novel nuclear magnetic resonance (NMR) chemical-shift image reconstruction method with a high chemical-shift resolution achieved by the chirp z-transform (CZT) is presented. Phase encoding is used for the spatial coordinates x and y, and the frequency coordinate is reserved especially for the chemical shift. The Fourier transform (FT) image reconstruction algorithm, which forms the basis of the new CZT image reconstruction method, is introduced. The novel method, using the CZT instead of the FT to evaluate the chemical-shift spectrum at a much higher resolution, is studied. The chemical-shift resolutions, achieved by the FT and the CZT, are studied theoretically from the aspect of the peak height and the peak width of chemical-shift spectra. The chemical-shift spectra calculated at a selected point in the image plane, and the chemical shift-images reconstructed by this method, are shown for a simple phantom containing ethanol and methanol at different locations. The results obtained by this method and by the FT method are compared and discussed. The experimental results have shown that a chemical-shift as small as 39 Hz, relative to the proton resonance frequency of 21.34 MHz, can be resolved successfully by this method without improvements in magnetic field homogeneity. PMID:18222764

Ma, T N; Takaya, K

1990-01-01

89

Utilization of chirp-z transform to improve the performance of target number detection of low resolution radar  

Microsoft Academic Search

Although it is difficult to resolve formation flight targets for low resolution radar, several signal processing methods are proposed to solve the problem. All these methods need to first obtain the I\\/Q data of the range gate containing the formation targets. In this paper, chirp-z transform (CZT) is proposed to be used in obtaining peak I\\/Q data of range gate,

Wang Yang; Jin Lin; Liu Zhong

2006-01-01

90

The gas phase characterization of perfluorobutyryl chloride, C 3F 7COCl, using chirped pulse Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

A chirped pulse Fourier transform microwave spectrometer has been used to record the pure rotational spectrum of perfluorobutyryl chloride seeded in a pulsed supersonic expansion of argon gas. Only one conformer of the title molecule was observed. For the 35Cl species a total of 236 spectral transitions were recorded. Quantum chemical calculations together with the spectral constants obtained indicate that the observed conformer has the CCCCOCl centers contained within the ab plane with a dihedral angle ?CCCO = 0°.

Grubbs, G. S., II; Cooke, S. A.

2009-11-01

91

Probing Chemical Dynamics with High Resolution Spectroscopy: Chirped-Pulse Fourier-Transform Microwave Spectroscopy Coupled with a Hyperthermal Source  

NASA Astrophysics Data System (ADS)

Chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy has proven to be a well-suited technique for the rapid study and spectral identification of molecular species due to its ultra-broadband capability and excellent specificity to molecular structure from high-resolution rotational transitions. This talk will describe initial results from combining CP-FTMW detection with a hyperthermal nozzle source. This source has the advantage of producing traditionally high thermal product densities in a pulsed supersonic expansion with a short contact time compared to conventional pyrolysis. Used in tandem, CP-FTMW spectroscopy and the hyperthermal nozzle in a supersonic expansion is a powerful method that can produce and detect changes in conformation and isomer populations, and characterize important intermediates on the reaction surface of a precursor. In particular, we show its utility to provide insight into the unimolecular decomposition pathways of model lignin compounds and alternative biofuels. Preliminary results will be discussed including spectroscopic evidence for formation of cyclopentadienone in the pyrolysis of a lignin derivative guaiacol (o-methoxyphenol).

Kidwell, Nathanael M.; Vara, Vanesa Vaquero; Mehta-Hurt, Deepali N.; Korn, Joseph A.; Dian, Brian C.; Zwier, Timothy S.

2013-06-01

92

Using the inverse Chirp-Z transform for time-domain analysis of simulated radar signals  

SciTech Connect

There exists a need to develop a method to locate underground voids, or caches. In the past, ground penetrating radar (GPR) operating in the time domain mode has been used. In this paper, we turn our attention to stepped frequency radar, capable of making frequency domain reflection coefficient measurements. We then apply the inverse Chirp-Z transform (ICZT) to this data, generating a time domain response. The scenario under consideration is that of an airborne radar passing over the surface of the earth. The radar is directed toward the surface and is capable of measuring the reflection coefficient, seen looking toward the earth, as a function of frequency. The frequency domain -data in this work is simulated and is generated from a transmission line model of the problem. Using the ICZT we convert this frequency domain data to the time domain. Once in the time domain, reflections due to discontinuities appear at times indicating their relative distance from the source. The discontinuities occurring beyond the surface of the earth could be indicative of underground structures. The ICZT allows a person to zoom in on the time span of interest by specifying the starting time, the time resolution, and the number of time steps.

Frickey, D.A.

1995-01-01

93

Modular System for Performing the Discrete Fourier Transform via the Chirp-Z Transform.  

National Technical Information Service (NTIS)

The patent provides apparatus, useful for signal processing operations which involve taking a transform of an input signal, which can be implemented in modular form. The apparatus can be implemented either with a parallel output or a serial output, depend...

J. M. Speiser H. J. Whitehouse

1976-01-01

94

A postprocessing method based on chirp Z transform for FDTD calculation of point defect states in two-dimensional phononic crystals  

NASA Astrophysics Data System (ADS)

In this paper, a new postprocessing method for the finite difference time domain (FDTD) calculation of the point defect states in two-dimensional (2D) phononic crystals (PNCs) is developed based on the chirp Z transform (CZT), one of the frequency zooming techniques. The numerical results for the defect states in 2D solid/liquid PNCs with single or double point defects show that compared with the fast Fourier transform (FFT)-based postprocessing method, the method can improve the estimation accuracy of the eigenfrequencies of the point defect states significantly when the FDTD calculation is run with relatively few iterations; and furthermore it can yield the point defect bands without calculating all eigenfrequencies outside the band gaps. The efficiency and accuracy of the FDTD method can be improved significantly with this new postprocessing method.

Su, Xiao-Xing; Wang, Yue-Sheng

2010-09-01

95

Fibre Bragg grating interrogation technique based on a chirped grating written in an erbium-doped fibre  

Microsoft Academic Search

A fibre Bragg grating interrogation technique with tunable sensitivity is reported. It relies on the utilization of the edge filtering concept applied to a chirped fibre Bragg grating (CFBG) written in an erbium-doped fibre as the processing element. Through the combination of the optical gain properties of the erbium-doped fibre and of the distributed wavelength reflection characteristics of the CFBG,

R. Romero; O. Frazão; P. V. S. Marques; H. M. Salgado; J. L. Santos

2003-01-01

96

Techniques for High-Bandwidth (?30 GHz) Chirped-Pulse Submillimeter-Wave Spectroscopy  

NASA Astrophysics Data System (ADS)

Due to the increased availability of active multiplier chains for converting microwave pulses into the millimeter/submillimeter with reasonably high power (?1 mW), chirped pulses with high phase stability and complete arbitrary waveform generator (AWG) frequency agility can be created and employed for high-sensitivity molecular spectroscopy, as demonstrated at the Symposium in the past few years. The bandwidths of multiplier chains, however, can exceed the current limitations on digitizer bandwidth. Therefore, in order to obtain ?30 GHz spectra in ~1 ms or less, techniques are being developed in which a two-channel AWG creates both the chirped pulses for molecular irradiation and a local oscillator pulse for heterodyne detection. These approaches reduce the digitizer bandwidths to 500 MHz or less to collect a high-bandwidth spectrum. A single instrument design can be used to measure both absorption and emission spectra, only requiring that the AWG pulses are changed. Due to the phase stability of the pulse generation and detection, coherent time-domain signal averaging can be performed to enhance sensitivity as desired. Preliminary results from prototype instruments designed at UVa and NIST will be presented, with sensitivity, frequency accuracy, and measurement speed comparisons to current millimeter/submillimeter-wave spectrometers. G.B. Park, A.H. Steeves, K. Kuyanov-Prozument, A.P. Colombo, R.W. Field, J.L. Neill, and B.H. Pate, RH07, 64th International Symposium on Molecular Spectroscopy (2009) K.O. Douglass, D.F. Plusquellic, and E. Gerecht, WH09, 65th International Symposium on Molecular Spectroscopy (2010).

Neill, Justin L.; Steber, Amanda L.; Harris, Brent J.; Pate, Brooks H.; Douglass, Kevin O.; Plusquellic, David F.; Gerecht, Eyal

2011-06-01

97

The Marriage of Spectroscopy and Dynamics: Chirped-Pulse Fourier-Transform Mm-Wave Cp-Ft Spectroscopy in Pulsed Uniform Supersonic Flows  

NASA Astrophysics Data System (ADS)

A new experimental scheme is presented that combines two powerful emerging technologies: chirped-pulse Fourier-transform mm-Wave spectroscopy and pulsed uniform supersonic flows. It promises a nearly universal detection method that can deliver quantitative isomer, conformer, and vibrational level specific detection, characterization of unstable reaction products and intermediates, and perform unique spectroscopic, kinetics, and dynamics measurements. Chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy, pioneered by Pate and coworkers, allows rapid acquisition of broadband microwave spectrum through advancements in waveform generation and oscilloscope technology. This revolutionary approach has successfully been adapted to higher frequencies by the Field group at MIT. Our new apparatus will exploit amplified chirped pulses in the range of 26-40 GHz, in combination with a pulsed uniform supersonic flow from a Laval nozzle. This nozzle source, pioneered by Rowe, Sims, and Smith for low temperature kinetics studies, produces thermalized reactants at high densities and low temperatures perfectly suitable for reaction dynamics experiments studied using the CP-mmW approach. This combination of techniques shall enhance the thousand-fold improvement in data acquisition rate achieved in the CP method by a further 2-3 orders of magnitude. A pulsed flow alleviates the challenges of continuous uniform flow, e.g. large gas loads and reactant consumption rates. In contrast to other pulsed Laval systems currently in use, we will use a fast piezo valve and small chambers to achieve the desired pressures while minimizing the gas load, so that a 10 Hz repetition rate can be achieved with one turbomolecular pump. The proposed technique will be suitable for many diverse fields, including fundamental studies in spectroscopy and reaction dynamics, reaction kinetics, combustion, atmospheric chemistry, and astrochemistry. We expect a significant advancement in the ability to detect absolute populations of complex reaction products under near-nascent conditions, providing the powerful method of reaction dynamics with a universal spectroscopic probe capable of capturing the details of complex chemistry for specific product isomers and conformers.

Abeysekera, Chamara; Oldham, James M.; Suits, Arthur G.; Park, G. Barratt; Field, Robert W.

2012-06-01

98

A novel sensor interrogation technique using chirped fiber grating based Sagnac loop  

Microsoft Academic Search

We demonstrate a novel and simple sensor interrogation scheme for fiber Bragg grating (FBG) based sensing systems. In this scheme, a chirped FBG based Sagnac loop is used as a wavelength-dependent receiver, and a stable and linear readout response is realised. It is a significant advantage of this scheme that the sensitivity and the measurement wavelength range can be easily

Donghui Zhao; Xuewen Shu; Lin Zhang; Ian Bennion

2002-01-01

99

A Study of Excitation Dynamics of LT-GaAs by Chirp-Controlled Pump-Probe Technique  

NASA Astrophysics Data System (ADS)

In this work, a home made chirp-controlled pump-probe measurement system has been developed and the chirp-controlled pump-probe measurement system with temporal resolution of around 100 femtosecond and chirp parameter tuning from --350 fs^2 to +650 fs^2 was demonstrated. Meanwhile, using chirp-controlled pump-probe measurement system, ultrafast dynamics of photogenerated carrier in low-temperature growth GaAs in different chirp by was characterized. The shorter relaxation time of low-temperature growth GaAs in positive chirp pump pulse was observed and the result was explained by the Pump-Dump process in negative chirp pump pulse and similar band-filling effect in positive chirp pump pulse.

Lee, Chao-Kuei; Huang, C. K.; Liao, L. Y.

2007-03-01

100

Efficient Computation of Optical Disk Readout by use of the Chirp z Transform  

Microsoft Academic Search

Computation of the readout signal of an optical disk involves Fourier transforms from the objective lens pupil to the disk and, after interaction with the disk, from the disk to the objective pupil. Traditionally, the complex two-dimensional Fourier transform is numerically evaluated as a two-dimensional fast Fourier transform. To obtain sufficient resolution in the involved planes, one must choose sampling

Jan L. Bakx

2002-01-01

101

Implementation of Chirp Z Discrete Fourier Transform (DFT) on Virtex II FPGA  

Microsoft Academic Search

The application of Fourier results in conversion in representation of a signal in time domain to frequency domain. Hence, it forms an important tool for frequency analysis. With advent of digital computers, we can perform frequency analysis faster and more efficiently. Thus discrete Fourier transform is important for frequency analysis of signal in discrete form.\\u000aDiscrete Fourier Transform (DFT) and

Hariharan Natarajan

2004-01-01

102

Chirped-Pulse and Cavity Based Fourier Transform Microwave Spectroscopy of the Methyl Lactate-Ammonia Adduct  

NASA Astrophysics Data System (ADS)

The hydrogen bonded complex of ammonia with methyl lactate, a chiral alpha-hydroxyester, has been studied using rotational spectroscopy and high level ab initio calculations. Previous studies showed that methyl lactate can exist in a number of conformers. However, only the most stable one which has an intramolecular hydrogen bonded ring formed with its alcoholic hydroxyl and its carbonyl oxygen atom was detected experimentally An extensive ab initio search has been performed to locate all possible low energy conformers of the methyl lactate-ammonia contact pair. Five lowest energy conformers have been identified at the MP2/6-311++G(d,p) level. The lowest energy conformer favors an insertion arrangement, where ammonia is inserted into the existing intramolecular hydrogen bonded ring in the most stable methyl lactate conformer. Broadband scans for the rotational spectra of possible binary conformers have been carried out using a chirped-pulse Fourier transform microwave (FTMW) instrument. The most stable binary adduct was identified and assigned. The final frequency measurements have been done with a cavity based FTMW instrument. The spectrum observed shows complicated fine and hyperfine splitting patterns, likely due to the internal rotations of the methyl groups of methyl lactate and that of ammonia, as well as the 14N quadrupolar nucleus. The binary adduct with 15NH3 has also been studied to simplify the splitting pattern and to aid the assignments of the extensive splittings. The isotopic data and the fine and hyperfine structures will be discussed in terms of internal rotation dynamics and geometry of the hydrogen bonded adduct.

Thomas, Javix; Sukhorukov, Oleksandr; Jaeger, Wolfgang; Xu, Yunjie

2012-06-01

103

COMPUTATION OF THE NETWORK HARMONIC IMPEDANCE WITH CHIRP-Z TRANSFORM  

Microsoft Academic Search

An innovative technique for power system harmonic impedance computation is presented in the paper. We present a brief introduction to harmonic impedance estimation problems as well as a detailed description of the proposed method. Frequency analysis with DFT is strongly affected by frequency leakage and picket fence errors. A number of methods was developed to reduce the impact of these

Krzysztof Duda; Dariusz Borkowski

104

Faster than the FFT: The chirp-z RAG-n Discrete Fast Fourier Transform  

Microsoft Academic Search

DFT and FFTs are important but resource intensive building blocks and have found many applica- tion in communication systems ranging from fast convolution to coding of OFDM signals. It has recently be shown that the n-Dimensional Reduced Adder Graph (RAG-n) technique is beneficially in many applications such as FIR or IIR filters, where multiplier can be grouped in multiplier blocks.

Uwe Meyer-Bäse; Hariharan Natarajan; Encarnación Castillo; Antonio García

105

A chirp-z transform-based synchronizer for power system measurements  

Microsoft Academic Search

In the last few years, increased interest in power and voltage quality has forced international working groups to standardize testing and measurement techniques. IEC 61000-4-30, which defines the characteristics of instrumentation for the measurement of power quality, refers to IEC 61000-4-7 for the evaluation of harmonics and interharmonics. This standard, revised in 2002, requires a synchronous sampling of voltage or

Massimo Aiello; Antonio Cataliotti; Salvatore Nuccio

2005-01-01

106

117Sn and 119Sn hyperfine structure in the rotational spectrum of tin monosulfide recorded using laser ablation-source equipped, chirped-pulse Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

Tin metal has been ablated with pulsed radiation from a Nd:YAG laser (?=1064 nm). Carbonyl sulfide, diluted in high pressure argon, has been pulsed into the resultant Sn plasma. One of the results of this experiment has been the production of SnS. These events have allowed a rotational spectrum of tin monosulfide to be studied using a chirped-pulse Fourier transform microwave spectrometer. The resolution of the spectrum obtained was sufficient to observe hyperfine structure from the 117Sn and 119Sn-containing SnS molecules. Tin nuclear spin-rotation hyperfine constants are reported for the first time.

Grubbs, G. S.; Cooke, S. A.

2010-02-01

107

Space transformation search: a new evolutionary technique  

Microsoft Academic Search

In this paper, a new evolutionary technique is proposed, namely space transformation search (STS), which transforms current search space to a new search space. By simultaneously evaluating solutions in current search space and transformed space, we can provide more chances to find solutions more closely to the global optimum and finally accelerate convergence speed. The proposed STS method can be

Hui Wang; Zhijian Wu; Yong Liu; Jing Wang; Dazhi Jiang; Lili Chen

2009-01-01

108

Chirp-modulated visual evoked potential as a generalization of steady state visual evoked potential  

NASA Astrophysics Data System (ADS)

Visual evoked potentials (VEPs) are of great concern in cognitive and clinical neuroscience as well as in the recent research field of brain-computer interfaces (BCIs). In this study, a chirp-modulated stimulation was employed to serve as a novel type of visual stimulus. Based on our empirical study, the chirp stimuli visual evoked potential (Chirp-VEP) preserved frequency features of the chirp stimulus analogous to the steady state evoked potential (SSVEP), and therefore it can be regarded as a generalization of SSVEP. Specifically, we first investigated the characteristics of the Chirp-VEP in the time-frequency domain and the fractional domain via fractional Fourier transform. We also proposed a group delay technique to derive the apparent latency from Chirp-VEP. Results on EEG data showed that our approach outperformed the traditional SSVEP-based method in efficiency and ease of apparent latency estimation. For the recruited six subjects, the average apparent latencies ranged from 100 to 130 ms. Finally, we implemented a BCI system with six targets to validate the feasibility of Chirp-VEP as a potential candidate in the field of BCIs.

Tu, Tao; Xin, Yi; Gao, Xiaorong; Gao, Shangkai

2012-02-01

109

Multiple-element photonic microwave true-time-delay beamforming incorporating a tunable chirped fiber Bragg grating with symmetrical bending technique.  

PubMed

We experimentally demonstrate a novel scheme for a multiple-element photonic microwave true-time-delay device with high tunability based on a tunable chirped fiber Bragg grating without center wavelength shift. We achieve the different true time delay by controlling the grating period of a chirped fiber Bragg grating based on the symmetrical bending technique as a multiwavelength signal source is applied to carry microwave signals. The proposed method does not require the complex structure of systems, wavelength tuning, and synchronization of optical devices such as tunable bandpass filters and optical input signals. We achieve the tunabilty of the time delay for a microwave signal carried over an optical signal in a range from 1 to 230 ps. PMID:17572753

Han, Young-Geun; Lee, Ju Han

2007-06-15

110

Techniques for Recovering Optical Spectral Features Using a CHirped Optical Field.  

National Technical Information Service (NTIS)

Techniques for recovering optical spectral features include receiving a detected time series that represents a temporally varying intensity of an optical signal. The optical signal is formed in response to an interaction between a target optical spectrum ...

K. Merkel M. Tian T. Chang W. R. Babbitt

2005-01-01

111

Measurement and analysis of the pure rotational spectra of tin monochloride, SnCl, using laser ablation equipped chirped pulse and cavity Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of tin monochloride, SnCl, has been measured and analyzed using chirped pulse and cavity Fourier transform microwave spectrometers equipped with a laser ablation source. SnCl, in its X2? electronic state, has been measured in the 8-17 GHz region. Rotational constants, centrifugal distortion constants, ?-doubling constants, magnetic hyperfine constants, and nuclear electric quadrupole coupling constants for multiple isotopologues have been determined and are reported. The bond length, nuclear magnetic and quadrupole constants have been analyzed and compared against the family of tetral halides. Analysis of the bond length and hyperfine interactions point to a Sn-Cl single bond which is largely ionic in nature.

Grubbs, G. S.; Frohman, Daniel J.; Novick, Stewart E.; Cooke, S. A.

2012-10-01

112

Development of a Reduced-Cost Chirped Pulse Microwave Spectrometer  

NASA Astrophysics Data System (ADS)

Chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy has become a ubiquitous technique in the high-resolution molecular spectroscopy community. Unfortunately, many components of CP-FTMW spectrometers are extremely expensive. Here we report of the development of an inexpensive microwave circuit and we present spectra of tetrahydrofuran and methanol collected between 8-16 GHz. Possible applications in remote sensing will also be discussed.

Finneran, Ian A.; Holland, Daniel B.; Carroll, P. Brandon; Blake, Geoffrey A.

2013-06-01

113

Integral Transform Technique for Monitoring Electrocardiograms.  

National Technical Information Service (NTIS)

The paper applies time domain and filtered integral transform domain pattern recognition techniques to the problem of locating and discriminating between QRS-complexes and premature ventricular contractions in electrocardiograms. The data set consists of ...

J. H. Reid

1973-01-01

114

Barley Transformation Using Agrobacterium-Mediated Techniques  

NASA Astrophysics Data System (ADS)

Methods for the transformation of barley using Agrobacterium-mediated techniques have been available for the past 10 years. Agrobacterium offers a number of advantages over biolistic-mediated techniques in terms of efficiency and the quality of the transformed plants produced. This chapter describes a simple system for the transformation of barley based on the infection of immature embryos with Agrobacterium tumefaciens followed by the selection of transgenic tissue on media containing the antibiotic hygromycin. The method can lead to the production of large numbers of fertile, independent transgenic lines. It is therefore ideal for studies of gene function in a cereal crop system.

Harwood, Wendy A.; Bartlett, Joanne G.; Alves, Silvia C.; Perry, Matthew; Smedley, Mark A.; Leyland, Nicola; Snape, John W.

115

Molecular structure of the argon-(Z)-1-chloro-2-fluoroethylene complex from chirped-pulse and narrow-band Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

Broadband chirped pulse, Fourier transform microwave spectra in the 6-18 GHz region are obtained for the 35Cl and 37Cl isotopomers of the complex formed between argon and (Z)-1-chloro-2-fluoroethylene. Analysis of the spectra provides predictions of rotational transition frequencies for the two singly substituted 13C isotopomers of Ar-35ClHCCHF sufficient to narrow the search range required for observation in a more sensitive, narrow band cavity Fourier transform instrument. Only a non-planar structure with the argon atom maximizing the number of its contacts with preferably heavy atoms is consistent with the rotational constants for all four isotopomers, and no evidence of tunneling between the two equivalent minima on either side of the ethylene plane is found. Rotational transitions for four isotopomers of (Z)-1-chloro-2-fluoroethylene itself, appearing in the broadband spectrum, are analyzed to determine the complete chlorine nuclear quadrupole coupling tensor for this molecule, and when these are combined with the hyperfine constants determined for the complex with argon, the sign ambiguity of the measured off-diagonal tensor components is removed.

Marshall, Mark D.; Leung, Helen O.; Calvert, Catherine E.

2012-10-01

116

a 480 MHz Chirped-Pulse Fourier-Transform Microwave Spectrometer: Construction and Measurement of the Rotational Spectra of Divinyl Silane and 3,3-DIFLUOROPENTANE  

NASA Astrophysics Data System (ADS)

A chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer based on the original Pate design has been constructed to allow analysis of any 480 MHz region in the 7 - 18 GHz range. A 1 ?s chirped-pulse (0 - 240 MHz) from an arbitrary function generator is mixed with output from a microwave synthesizer and used to polarize a supersonic gas expansion; the resulting free induction decay is collected over 20 ?s and Fourier-transformed on a 500 MHz oscilloscope to produce a rotational spectrum. A variety of molecules have now been studied with this instrument and results will be presented for numerous conformers of divinyl silane (predicted ?total = 0.6 - 0.7 D) and the more polar 3,3-difluoropentane (predicted ?total = 2.5 - 2.8 D). Two of the three possible conformers of divinyl silane were assigned (both having a C_1=C_2-Si-C_3 dihedral angle of -120° and a {C_2-Si-C_3=C_4} dihedral of either 0° (C_1 symmetry) or -120° (C_2 symmetry)). For 3,3-difluoropentane, three of the four possible {conformers} were identified: anti-gauche (C_1), gauche-gauche (C_2) and anti-anti (C2v). While rotational spectra for only the silicon isotopologues were observed for divinyl silane, measurement of the 13C spectra of 3,3-difluoropentane allowed heavy atom structure determinations for the anti-gauche and gauche-gauche conformers. Initial assignments of all spectra were made on the CP-FTMW {spectrometer}, and a Balle-Flygare FTMW spectrometer was used to compare frequencies of measured transitions and also to provide Stark effect data. Substitution (r_s) and inertial fit (r_0) structures will be compared with computational data and instrumental details will be presented. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S.T. Shipman, B.H. Pate, Rev. Sci. Instrum., 79, (2008), 053103.

Obenchain, Daniel A.; Steber, Amanda L.; Elliott, Ashley A.; Peebles, Rebecca A.; Peebles, Sean A.; Wurrey, Charles J.; Guirgis, Gamil A.

2010-06-01

117

Ultrasonic signal processing of adhesive bonding data employing Chirp-Z transform and adaptive filtering techniques  

Microsoft Academic Search

An account is given of a method for the precise measurement of thin adhesive layers on the basis of a deconvolution of bondline response. A physical model was developed for the thickness measurement; to this, a frequency-domain analysis is applied. In order to deconvolve the adhesive-layer response, a transfer-function model is developed on the basis of adaptive filters. Excellent agreement

V. K. Nair; R. Ludwig; J. M. Sullivan; D. Dai

1992-01-01

118

Ultrasonic signal processing of adhesive bonding data employing Chirp-Z transform and adaptive filtering techniques  

NASA Astrophysics Data System (ADS)

An account is given of a method for the precise measurement of thin adhesive layers on the basis of a deconvolution of bondline response. A physical model was developed for the thickness measurement; to this, a frequency-domain analysis is applied. In order to deconvolve the adhesive-layer response, a transfer-function model is developed on the basis of adaptive filters. Excellent agreement is obtained between the deconvolved bondline transfer function and experimentally recorded signals.

Nair, V. K.; Ludwig, R.; Sullivan, J. M.; Dai, D.

119

Simulation Model of Rapid TAE Chirping  

NASA Astrophysics Data System (ADS)

Spontaneous nonlinear coherent frequency chirping structures can arise due to the resonant interaction of energetic particles with a discrete toroidal Alfven eigenmode (TAE). The initial development of a coherent structure is quantitatively described by a now standard hole-clump chirping theory. However, it is still unclear what conditions are needed for the TAE chirping frequency to deviate far from the bulk plasma eigenfrequency and enter the Alfven continuum. In our model, the linear TAE controlling equation is derived from the Berk-Mett quadratic form. The interaction is studied with the linear wave with the nonlinear response of energetic particles. For the present study we simplify the wave to a single symmetric couplet while a two-dimensional distribution is used to describe the energetic particles. In order to resolve the fine structure in the phase space, the numerical scheme integrates the Vlasov equation in the Fourier transformed phase space using a method developed by Breizman and Petviashvili. The simulation results show the saturated wave amplitude and square root law of the initial chirping are in accord with previous theory. We have found conditions where the chirping signal enters the Alfven continuum and a larger amplitude and more rapidly chirping signal then develops. Plots of the phase space structure can reproduce the shape of the separatrix structure that partitions the trapped and passing particles. We attempt to relate the portrait of the phase space structure with the measured wave amplitude and chirping frequency.

Wang, Ge; Berk, H. L.

2010-11-01

120

Rotational spectroscopy of iodobenzene and iodobenzene-neon with a direct digital 2-8 GHz chirped-pulse Fourier transform microwave spectrometer  

NASA Astrophysics Data System (ADS)

The design of a chirped-pulse Fourier transform microwave spectrometer operating in the 2-8 GHz frequency range is presented. The linear frequency sweep is generated by an arbitrary waveform generator with a sampling rate of 20 GS/s. After amplification, the microwave pulse is broadcast into a vacuum chamber where it interacts with a supersonically expanded molecular sample. The resulting molecular free induction decay signal is amplified and digitized directly on a digital oscilloscope with a 20 GS/s sampling rate. No frequency mixing or multiplication is necessary in this spectrometer, which allows for very high pulse quality and phase stability. The performance of this spectrometer is demonstrated on the rotational spectrum of iodobenzene. All four distinct singly-substituted 13C isotopologues have been detected in natural abundance, as well as two isotopic species of a van der Waals cluster of iodobenzene with a neon atom. Spectroscopic constants and derived structural parameters for iodobenzene and for iodobenzene-Ne are reported. In addition, the use of microwave-microwave double-resonance experiments in this spectrometer to facilitate spectral assignments is presented.

Neill, Justin L.; Shipman, Steven T.; Alvarez-Valtierra, Leonardo; Lesarri, Alberto; Kisiel, Zbigniew; Pate, Brooks H.

2011-09-01

121

pathChirp: Efficient Available Bandwidth Estimation for Network Paths  

SciTech Connect

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing rate within each chirp, pathChirp obtains a rich set of information from which to dynamically estimate the available bandwidth. Since it uses only packet interarrival times for estimation, pathChirp does not require synchronous nor highly stable clocks at the sender and receiver. We test pathChirp with simulations and Internet experiments and find that it provides good estimates of the available bandwidth while using only a fraction of the number of probe bytes that current state-of-the-art techniques use.

Cottrell, Les

2003-04-30

122

Efficient approximation of continuous wavelet transforms  

NASA Astrophysics Data System (ADS)

An efficient algorithm is developed for computing the continuous wavelet transform or wideband ambiguity function on a grid whose samples are spaced uniformly in time but placed arbitrarily in scale. The method is based on the chirp z transform and requires the same order of computation as constant-bandwidth analysis techniques, such as the short-time Fourier transform and narrowband ambiguity function.

Jones, D. L.; Baraniuk, R. G.

1991-04-01

123

A new method for the compensation of the SAR range cell migration based on the chirp z-transform  

Microsoft Academic Search

Precision synthetic aperture radar (SAR) data processing requires the compensation of the range-dependent range cell migration (RDRCM) phenomenon. This paper describes a new method that permits the compensation of the RDRCM effect using a nonstandard Fourier transform (FT). This operation is applied, in the two-dimensional Fourier domain, to the range signal spectrum and allows the compensation of the azimuth frequency-dependent

Riccardo Lanari

1995-01-01

124

Transionospheric chirp event classifier  

SciTech Connect

In this paper we will discuss a project designed to provide computer recognition of the transionospheric chirps/pulses measured by the Blackbeard (BB) satellite, and expected to be measured by the upcoming FORTE satellite. The Blackbeard data has been perused by human means -- this has been satisfactory for the relatively small amount of data taken by Blackbeard. But with the advent of the FORTE system, which by some accounts might ``see`` thousands of events per day, it is important to provide a software/hardware method of accurately analyzing the data. In fact, we are providing an onboard DSP system for FORTE, which will test the usefulness of our Event Classifier techniques in situ. At present we are constrained to work with data from the Blackbeard satellite, and will discuss the progress made to date.

Argo, P.E.; Fitzgerald, T.J.; Freeman, M.J.

1995-09-01

125

Detection of a chirping electromagnetic signal  

SciTech Connect

A matched chirp transform (MCT) method for detecting a dispersive electromagnetic pulse is described. The unique feature of this transform is that it gives a distribution of signal amplitude over time rather than frequency, and thereby simplifies signal detection and identification in the case described here. In the MCT method, the incoming signal is matched to a set of signal segments that chirp in accordance with an expected model of the dispersive medium. The performance of the MCT method is compared with that of a standard periodogram method of frequency measurement. 6 refs., 5 figs.

Stearns, S.D.

1989-01-01

126

The Pure Rotational Spectra of Acetaldehyde and Glycolaldehyde Isotopologues Measured in Natural Abundance by Chirped-Pulse Fourier Transform Microwave Spectroscopy  

NASA Astrophysics Data System (ADS)

Complex organic molecules (COMs) such as glycolaldehyde (HOCH_2CHO) and acetaldehyde (CH_3CHO) have now been detected in numerous interstellar sources. Glycolaldehyde has been detected in two hot cores, Sgr B2(N) and G31.41+0.31. Acetaldehyde has been observed in various sources, including the translucent clouds CB 17 and CB 24, cold molecular clouds such as TMC-1 and L134N, and hot cores such as Sgr B2(N), NGC 6334F, and the Orion Compact Ridge. Such COMs are known to have rich and complex spectra that add to the line confusion problem faced in observations of molecule-rich sources. Laboratory studies of excited vibrational states and isotopologues for known COMs therefore provide important guidance for sorting out the interstellar line confusion problem. Detection of isotopologues and determination of their abundance relative to the main isotopic species would also provide important constraints on interstellar chemical models, as these isotopic ratios are dependent on the formation mechanism for each species. The isotopic ratios for 13C/12C, 18O/16O, and D/H are known in various interstellar environments for simple molecules, but remain relatively unexplored for more complex species such as glycolaldehyde and acetaldehyde. The rotational spectra of the main isotopologues for glycolaldehyde and acetaldehyde have been well-characterized through microwave, millimeter, and submillimeter laboratory spectroscopy. Here we present the laboratory characterization of the isotopologues of acetaldehyde and glycolaldehyde in natural abundance by chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). This spectroscopic information lays the groundwork for additional higher-frequency studies that can be directly applied to the interpretation of millimeter and submillimeter observations.

Carroll, P. Brandon; McGuire, Brett A.; Weaver, Susanna L. Widicus; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.

2011-06-01

127

Optimal Design of Power Transformer Using Simulated Annealing Technique  

Microsoft Academic Search

The power transformer is one of the most important equipment in a power system. Optimal design of transformer involves determination of design parameters of a power transformer when a chosen objective is optimized, simultaneously satisfying a set of constraints. In this paper simulated annealing (SA) technique is proposed for Optimization of three-phase power transformer design (OPTD). The initial cost of

S. Padma; R. Bhuvaneswari; S. Subramanian

2006-01-01

128

Transform domain techniques for efficient extraction of substrate parasitics  

Microsoft Academic Search

A semi-analytical technique for computation of the frequency- behavior of silicon substrates is demonstrated. The technique uses a boundary element approach, that utilizes the complex substrate Green Function and the two-dimensional Fast Fourier Transform. The resultant dense system matrix is sparsified by application of orthogonal transform operators on the matrix representing the system. Three transform operators are evaluated for this

Ranjit Gharpurey; Srinath Hosur

1997-01-01

129

Chirp on crickets: teaching compilers using an embedded robot controller  

Microsoft Academic Search

Traditionally, the topics of compiler construction and language processing have been taught as an elective course in Computer Science curricula. As such, students may graduate with little understanding or experience with the useful techniques embodied in modern compiler construction.In this paper, we present the design of Chirp, a language specification and compiler implementation. As a language, Chirp is based on

Li Xu; Fred G. Martin

2006-01-01

130

Chirp on crickets: teaching compilers using an embedded robot controller  

Microsoft Academic Search

Traditionally, the topics of compiler construction and lan- guage processing have been taught as an elective course in Computer Science curricula. As such, students may gradu- ate with little understanding or experience with the useful techniques embodied in modern compiler construction. In this paper, we present the design of Chirp, a language specification and compiler implementation. As a language, Chirp

Li Xu; Fred G. Martin

2006-01-01

131

Tuning of external-cavity semiconductor lasers with chirped diffraction gratings  

Microsoft Academic Search

We present a novel scheme of tunable semiconductor laser based on the use of a chirped grating in an external cavity. The chirped grating is fabricated using a simple holographic technique: two Gaussian beams having wavefronts with different radii of curvature are brought to interfere on a photoresist layer. The tuning properties of chirped gratings have been investigated with semiconductor

Marc Duval; Gilles Fortin; Michel Piché; Nathalie McCarthy

2005-01-01

132

Analysis of discrete techniques for image transformation  

NASA Astrophysics Data System (ADS)

Let an image be distorted by a nonlinear transformationT, and then be restored back to its original by the inverse transformationT-1. Such a cycle conversion,T-1T, of digital images can be facilitated by the combination (CSIM) given in [6] using the splitting-shooting method and the splitting-integrating method forT andT-1 respectively. Since there is no need to solve nonlinear equations, CSIM has been widely applied to specific areas of image processing and pattern recognition, even those with complicated transformations, e.g., the harmonic transformation [12]; however, no strict error analysis has been provided so far. In this paper, a priori error estimates and convergence rates are derived for pixel greyness obtained from CSIM; also the analytical results are extended to the harmonic transformation. Numerical and graphical experiments are provided to support the theoretical analysis.

Li, Zi

1996-02-01

133

Photodissociation of H+2 in intense chirped laser fields  

NASA Astrophysics Data System (ADS)

Regarding an experimental measurement of proton kinetic energy spectra of H+2 with a chirped pulse [L. J. Frasinski, J. H. Posthumus, J. Plumridge, and K. Colding, Phys. Rev. Lett. 83, 3625 (1999)], we present a nonperturbative, time-dependent calculation for the photodissociation of H+2 in intense laser fields by combining three numerical techniques. The results show a finer kinetic-energy distribution structure of a proton due to the intrapulse pump-dump mechanism between two electronic states as the pulse duration and intensity change. Higher-energy peaks are also suppressed by frequency chirping of the laser field. The dissociation probabilities show that a positively chirped pulse is always more efficient for population inversion than no chirping or negatively chirped pulses, and a slight coordinate shift of the initial state could result in a significant increase of dissociation probability.

Lin, J. T.; Jiang, T. F.

2001-01-01

134

CHIRP Doppler radar  

Microsoft Academic Search

The present investigation is concerned with the concept of a combination of the clinical procedure of reconstruction tomography with the radar processing for linear FM pulse compression. An approach based on such a combination is to be employed to map radar backscatter energy. Radar systems employing pulse compression of linear frequency modulated (CHIRP) pulses are considered along with the inversion

M. Bernfeld

1984-01-01

135

Efficient extension of conventional low frequency filter bank spectrometer by implementation of high resolution Chirp Z signal processing  

Microsoft Academic Search

The spectral analysis of any signal involves a signal-processing tool using Fourier processors. Chirp Z Transform (CZT) is a modern technique providing ideally any frequency resolution in the spectrum. The conventional filter bank type spectrometer provides low to moderate (few 100 kHz) frequency resolution and if its frequency resolution is to be increased further then the number of channels must be

Jayesh P. Pabari

2008-01-01

136

Using wavelet transform reassignment techniques for ECG characterisation  

Microsoft Academic Search

Reassignment, a technique which sharpens the time frequency information within the time-frequency plane, can be applied to the wavelet transform to produce a more succinct, highly focused, representation. In this paper this technique is applied to interrogate and represent heart rate variation recorded by means of temporary reprogramming of a volunteer's pacemakers. The work has shown that the reassignment technique

D. Clifton; P. S. Addison; M. K. Stiles; I. Romero Legarreta; N. Grubb; J. N. Watson; G. R. Clegg; C. E. Robertson

2003-01-01

137

Advanced Techniques for Fourier Transform Wavefront Reconstruction  

SciTech Connect

The performance of Fourier transform (FT) reconstructors in large adaptive optics systems with Shack-Hartmann sensors and a deformable mirror is analyzed. FT methods, which are derived for point-based geometries, are adapted for use on the continuous systems. Analysis and simulation show how to compensate for effects such as misalignment of the deformable mirror and wavefront sensor gain. Further filtering methods to reduce noise and improve performance are presented. All these modifications can be implemented at the filtering stage, preserving the speed of FT reconstruction. Simulation of a large system shows how compensated FT methods can have equivalent or better performance to slower vector-matrix-multiply reconstructions.

Poyneer, L A

2002-08-05

138

Transformation-Governed Heating Techniques in Thermal Analysis II  

Microsoft Academic Search

The described instrumental method makes it possible that the quasi-static heating technique, well applicable to thermogravimetric measurements, (see Part I of this paper) can be used in the case of DTA and DSC examinations, too. Based on the new type of curves the characteristic transformation temperatures, the whole course of the transformation in dependence of sample temperature, the extent of

F. Paulik; E. Bessenyey-Paulik; K. Walther-Paulik

1999-01-01

139

Improved Compression by Coupling of Coding Techniques and Redundant Transform  

Microsoft Academic Search

The techniques commonly used in image coding (JPEG, MPEG, …) have as the main objective to compress as much as possible while retaining most of the information. These methods are often based on the use of the discrete cosine transform (DCT) and the wavelet transform (WT). Our purpose is to consider the necessary redundancy to achieve a good reception in

A.-M. Poussard; C. Olivier; J. H. Wu; C. Chatellier

2000-01-01

140

Chirp and polarization control of femtosecond molecular fragmentation  

PubMed Central

We explore the simultaneous effect of chirp and polarization as the two control parameters for non-resonant photo-dissociation of n-propyl benzene. Experiments performed over a wide range of laser intensities show that these two control knobs behave mutually exclusively. Specifically, for the coherently enhanced fragments (C3H3+, C5H5+) with negatively chirped pulses and C6H5+ with positively chirped pulses, polarization effect is the same as compared to that in the case of transform-limited pulses. Though a change in polarization affects the overall fragmentation efficiency, the fragmentation pattern of n-propyl benzene molecule remains unaffected in contrast to the chirp case.

Goswami, T; Das, D K; Kumar, S K Karthick; Goswami, D

2013-01-01

141

Propagation of chirped laser pulses in a plasma channel  

SciTech Connect

Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.

Jha, Pallavi; Malviya, Amita; Upadhyay, Ajay K. [Department of Physics, University of Lucknow, Lucknow 226007 (India)

2009-06-15

142

Technique for the metrology calibration of a Fourier transform spectrometer  

SciTech Connect

A method is presented for using a Fourier transform spectrometer (FTS) to calibrate the metrology of a second FTS. This technique is particularly useful when the second FTS is inside a cryostat or otherwise inaccessible.

Spencer, Locke D.; Naylor, David A

2008-11-10

143

Quality of Arabic utterances transformed using different residual prediction techniques  

NASA Astrophysics Data System (ADS)

Voice conversion (VC) is a process which modifies the speech signal produced by one source speaker so that it sounds like another target speaker. In this paper the transformation is determined by using equal Arabic utterances from source and target speakers; these utterances are time-aligned using dynamic time warping algorithm. A conversion function based on Gaussian mixture model (GMM) is used for transforming the spectral envelope described by line spectral frequencies (LSF) and the residuals are converted using three residual prediction techniques. We also compare between these techniques in the conversion of some Arabic utterances. The quality of the transformed utterances is measured using subjective and objective evaluations.

Elmanfaloty, Rania; Korany, N.; Youssef, El-Sayed A.

2011-10-01

144

Recent EISCAT heating results using chirped ISR  

Microsoft Academic Search

The chirp technique has recently become fully operational on the EISCAT UHF radar system and has been used for daytime observations of the HF-modified ionosphere over Ramfjordmoen in November 1992 and March 1993. During certain periods the UHF observations show a difference in the frequencies of the photoelectron-enhanced plasma line and the HF-enhanced plasma line (HFPL) similar to the one

B. Isham; C. La Hoz; H. Kohl; T. Hagfors; T. B. Leyser; M. T. Rietveld

1996-01-01

145

Reduction of energy chirp by the wake of coherent synchrotron radiation  

NASA Astrophysics Data System (ADS)

When an energy-chirped bunch is undercompressed in a magnetic chicane, the compressed bunch also has an energy chirp. The chirp may be decreased by sending the bunch through bending magnets, since the largest energy loss from the wake of coherent synchrotron radiation occurs in the tail of a typical bunch. We obtain formulas for the dechirping of a rectangular bunch by short magnets, and apply this dechirping technique in a design for a free-electron laser.

Bosch, R. A.

2010-11-01

146

Robust chirped mirrors.  

PubMed

Optimized chirped mirrors may perform suboptimally, or completely fail to satisfy specifications, when manufacturing errors are encountered. We present a robust optimization method for designing these dispersion-compensating mirror systems that are used in ultrashort pulse lasers. Possible implementation errors in layer thickness are taken into account within an uncertainty set. The algorithm identifies worst-case scenarios with respect to reflectivity as well as group delay. An iterative update improves the robustness and warrants a high manufacturing yield, even when the encountered errors are larger than anticipated. PMID:18470259

Nohadani, Omid; Birge, Jonathan R; Kärtner, Franz X; Bertsimas, Dimitris J

2008-05-10

147

Time-frequency transform techniques for seabed and buried target classification  

NASA Astrophysics Data System (ADS)

An approach for processing sonar signals with the ultimate goal of ocean bottom sediment classification and underwater buried target classification is presented in this paper. Work reported for sediment classification is based on sonar data collected by one of the AN/AQS-20's sonars. Synthetic data, simulating data acquired by parametric sonar, is employed for target classification. The technique is based on the Fractional Fourier Transform (FrFT), which is better suited for sonar applications because FrFT uses linear chirps as basis functions. In the first stage of the algorithm, FrFT requires finding the optimum order of the transform that can be estimated based on the properties of the transmitted signal. Then, the magnitude of the Fractional Fourier transform for optimal order applied to the backscattered signal is computed in order to approximate the magnitude of the bottom impulse response. Joint time-frequency representations of the signal offer the possibility to determine the timefrequency configuration of the signal as its characteristic features for classification purposes. The classification is based on singular value decomposition of the time-frequency distributions applied to the impulse response. A set of the largest singular values provides the discriminant features in a reduced dimensional space. Various discriminant functions are employed and the performance of the classifiers is evaluated. Of particular interest for underwater under-sediment classification applications are long targets such as cables of various diameters, which need to be identified as different from other strong reflectors or point targets. Synthetic test data are used to exemplify and evaluate the proposed technique for target classification. The synthetic data simulates the impulse response of cylindrical targets buried in the seafloor sediments. Results are presented that illustrate the processing procedure. An important characteristic of this method is that good classification accuracy of an unknown target is achieved having only the response of a known target in the free field. The algorithm shows an accurate way to classify buried objects under various scenarios, with high probability of correct classification.

Barbu, Madalina; Kaminsky, Edit; Trahan, Russell E., Jr.

2007-04-01

148

Raster Transformation and Resampling Technique for Geodetic Applications  

Microsoft Academic Search

Paper presents methods and technique to effectively process raster data being received from satellites for geodetic applications. Method of morphing of raster geometry using radial basis functions (RBF) and subsequent resampling the obtained transformations onto rectangular grid to accelerate calculations is proposed.

RaufKh. Sadykhov; Leonid P. Podenok

2005-01-01

149

Image fusion in discrete cosine transform domain using masking techniques  

NASA Astrophysics Data System (ADS)

Image fusion is the process of combining two or more images of the same scene into a single image which is suitable for human perception and practical applications. This paper investigates the effect of use of different types of masks in discrete cosine transform (DCT) domain for image fusion applications. Here we have used different types of masks such as rectangular, triangular, strip and fan shaped mask. In the proposed scheme, the DCT of both the images are taken and mask and its complimentary mask are applied on two transformed images respectively. The masked images are then fused in the transform domain and inverse DCT is applied to obtain the fused image. Simulation results of the proposed technique are also presented and it is observed that fusion based on the fan shaped mask gives better quality of fused image than other masks consider in this paper as well as some of the methods existing in the literature.

Sharma, K. K.; Priti, K.

2013-01-01

150

Chirped pulse amplification of 300 fs pulses in an alexandrite regenerative amplifier  

Microsoft Academic Search

The amplification of fsec dye-laser pulses up to the 3.5-mJ level in an alexandrite regenerative amplifier is discussed. An expansion\\/compression system using different gratings allows chirped amplification techniques to be used to produce peak powers upwards of 1 GW. Limitations in the chirped pulse amplification of ultrashort pulses due to intracavity dispersive elements are discussued.

Maurice Pessot; Jeff Squier; Philippe Bado; Gerard Mourou; Donald J. Harter

1989-01-01

151

Control of laser induced molecular fragmentation of n-propyl benzene using chirped femtosecond laser pulses  

PubMed Central

We present the effect of chirping a femtosecond laser pulse on the fragmentation of n-propyl benzene. An enhancement of an order of magnitude for the relative yields of C3H3+ and C5H5+ in the case of negatively chirped pulses and C6H5+ in the case of positively chirped pulses with respect to the transform-limited pulse indicates that in some fragmentation channel, coherence of the laser field plays an important role. For the relative yield of all other heavier fragment ions, resulting from the interaction of the intense laser field with the molecule, there is no such enhancement effect with the sign of chirp, within experimental errors. The importance of the laser phase is further reinforced through a direct comparison of the fragmentation results with the second harmonic of the chirped laser pulse with identical bandwidth.

Goswami, Tapas; Karthick Kumar, S.K.; Dutta, Aveek; Goswami, Debabrata

2009-01-01

152

On Application of the Fourier Transform Band Pass Filtering Technique  

NASA Astrophysics Data System (ADS)

In this work theoretical aspects of the Fourier Transform Band Pass Filter (FTBPF) technique are investigated which show that such a procedure is applicable to extraction of irregular monochromatic oscillations with time-varying amplitudes from the analyzed signal data. Considerations concerning the boundary effects occurring in numerical implementation of the FTBPF are included which indicate that the filter transfer function smoothness influences boundary effects magnitude. The possibility of using the studied filtration technique for recognition of elliptical oscillation polarization is envisaged and an estimate of oscillation polarization classification error is derived.

Popi?ski, Waldemar

2009-01-01

153

Wavelet transformation based watermarking technique for human electrocardiogram (ECG).  

PubMed

Nowadays, watermarking has become a technology of choice for a broad range of multimedia copyright protection applications. Watermarks have also been used to embed prespecified data in biomedical signals. Thus, the watermarked biomedical signals being transmitted through communication are resistant to some attacks. This paper investigates discrete wavelet transform based watermarking technique for signal integrity verification in an Electrocardiogram (ECG) coming from four ECG classes for monitoring application of cardiovascular diseases. The proposed technique is evaluated under different noisy conditions for different wavelet functions. Daubechies (db2) wavelet function based technique performs better than those of Biorthogonal (bior5.5) wavelet function. For the beat-to-beat applications, all performance results belonging to four ECG classes are highly moderate. PMID:16235811

Engin, Mehmet; Cidam, O?uz; Engin, Erkan Zeki

2005-12-01

154

Chirp response of an active-controlled thickness-drive tunable transducer  

PubMed

The chirp response of a thickness-drive tunable transducer for wide range time-bandwidth and sweep rates chirp signals is demonstrated experimentally and computationally. The computational evaluation uses recursive digital-filter model based on the z-transform method. The model is limited to simple lossless structure with no front and backing layers. The model and experimental results show that there is no limit on the maximum sweep rate of the chirp signal but practically the limit is determined by the limitation of the circuit that generates the control voltage that simulates a variable electric load. PMID:10738791

Alwi; Carey; Smith

2000-03-01

155

Transforming Spatial Entanglement Using a Domain-Engineering Technique  

NASA Astrophysics Data System (ADS)

We study the spatial correlation of a two-photon entangled state produced in a multistripe periodically poled LiTaO3 crystal by spontaneous parametric down-conversion. The far-field diffraction-interference experiments reveal that the transverse modulation of domain patterns transforms the spatial mode function of the two-photon state. This result offers an approach to prepare a novel type of two-photon state with a unique spatial entanglement by using a domain-engineering technique.

Yu, X. Q.; Xu, P.; Xie, Z. D.; Wang, J. F.; Leng, H. Y.; Zhao, J. S.; Zhu, S. N.; Ming, N. B.

2008-12-01

156

Fourier Transform of Untransformable Signals Using Pattern Recognition Technique  

Microsoft Academic Search

In this paper we are highlighting the signals that are not Fourier transformable and give its Fourier transform using PCA (Principle Component Analysis), lDA (linear Discriminant Analysis). Such signals are step signal, signum, etc. Basically Fourier transform transforms time domain signal into frequency domain and after transformation describes what frequencies original signal have. Principle Component Analysis is a way of

Varun Gupta; G. Singh; M. Mittal; Sharvan Kumar Pahuja

2010-01-01

157

A Study of Mexican Free-Tailed Bat Chirp Syllables: Bayesian Functional Mixed Models for Nonstationary Acoustic Time Series  

PubMed Central

We describe a new approach to analyze chirp syllables of free-tailed bats from two regions of Texas in which they are predominant: Austin and College Station. Our goal is to characterize any systematic regional differences in the mating chirps and assess whether individual bats have signature chirps. The data are analyzed by modeling spectrograms of the chirps as responses in a Bayesian functional mixed model. Given the variable chirp lengths, we compute the spectrograms on a relative time scale interpretable as the relative chirp position, using a variable window overlap based on chirp length. We use 2D wavelet transforms to capture correlation within the spectrogram in our modeling and obtain adaptive regularization of the estimates and inference for the regions-specific spectrograms. Our model includes random effect spectrograms at the bat level to account for correlation among chirps from the same bat, and to assess relative variability in chirp spectrograms within and between bats. The modeling of spectrograms using functional mixed models is a general approach for the analysis of replicated nonstationary time series, such as our acoustical signals, to relate aspects of the signals to various predictors, while accounting for between-signal structure. This can be done on raw spectrograms when all signals are of the same length, and can be done using spectrograms defined on a relative time scale for signals of variable length in settings where the idea of defining correspondence across signals based on relative position is sensible.

MARTINEZ, Josue G.; BOHN, Kirsten M.; CARROLL, Raymond J.

2013-01-01

158

Binary joint transform correlation using error-diffusion techniques  

NASA Astrophysics Data System (ADS)

Optical pattern recognition techniques based on the optical joint transform correlator (JTC) scheme are attractive due to their simplicity. Recent improvements in spatial light modulators (SLM) increased the popularity of the JTC, providing means for real time operation. Using a binary SLM for the display of the Fourier spectrum, first requires binarization of the joint power spectrum distribution. Although hard-clipping is the simplest and most common binarization method used, we suggest to apply error-diffusion as an improved binarization technique. The performance of a binary JTC, whose input image is considered to contain additive zero-mean white Gaussian noise, is investigated. Various ways for nonlinearly modifying the joint power spectrum prior to the binarization step, which is based on either error-diffusion or hard-clipping techniques, are discussed. These nonlinear modifications aim at increasing the contrast of the interference fringes at the joint power spectrum plane, leading to better definition of the correlation signal. Mathematical analysis, computer simulations and experimental results are presented.

Inbar, Hanni; Marom, Emanuel; Konforti, Naim

1993-08-01

159

Linear frequency-modulated signal detection using Radon-ambiguity transform  

Microsoft Academic Search

A novel time-frequency technique for linear frequency modulated (LFM) signal detection is proposed. The design of the proposed detectors is based on the Radon transform of the modulus square or the envelope amplitude of the ambiguity function (AF) of the signal. A practical assumption is made that the chirp rate is the only parameter of interest. Since the AF of

Minsheng Wang; Andrew K. Chan; Charles K. Chui

1998-01-01

160

Chirped pulse amplification: Present and future  

SciTech Connect

Short pulses with ultrahigh peak powers have been generated in Nd: glass and Alexandrite using the Chirped Pulse Amplification (CPA) technique. This technique has been successful in producing picosecond terawatt pulses with a table-top laser system. In the near future, CPA will be applied to large laser systems such as NOVA to produce petawatt pulses (1 kJ in a 1 ps pulse) with focused intensities exceeding 10/sup /plus/21/ W/cm/sup 2/. These pulses will be associated with electric fields in excess of 100 e/a/sub o//sup 2/ and blackbody energy densities equivalent to 3 /times/ 10/sup 10/ J/cm/sup 3/. This petawatt source will have important applications in x-ray laser research and will lead to fundamentally new experiments in atomic, nuclear, solid-state, plasma, and high-energy density physics. A review of present and future designs are discussed. 17 refs., 5 figs.

Maine, P.; Strickland, D.; Pessot, M.; Squier, J.; Bado, P.; Mourou, G.; Harter, D.

1988-01-01

161

Bandwidth-Tunable Fiber Bragg Gratings Based on UV Glue Technique  

NASA Astrophysics Data System (ADS)

In this study, we have demonstrated that a uniform fiber Bragg grating (FBG) can be transformed into a chirped fiber grating by a simple UV glue adhesive technique without shifting the reflection band with respect to the center wavelength of the FBG. The technique is based on the induced strain of an FBG due to the UV glue adhesive force on the fiber surface that causes a grating period variation and an effective index change. This technique can provide a fast and simple method of obtaining the required chirp value of a grating for applications in the dispersion compensators, gain flattening in erbium-doped fiber amplifiers (EDFAs) or optical filters.

Fu, Ming-Yue; Liu, Wen-Feng; Chen, Hsin-Tsang; Chuang, Chia-Wei; Bor, Sheau-Shong; Tien, Chuen-Lin

2007-07-01

162

Improved Technique for Fault Detection Sensitivity in Transformer Maintenance Test  

Microsoft Academic Search

Transformer windings might be shifted because of short-circuit current, aging or impact during transportation. The shift modifies the dielectric space between the layers of the windings and may cause an insulation breakdown. Since transformers are expensive to replace, it is vital that their condition are determined accurately without having to dismantle the apparatus to inspect it visually. Generally, transformers test

Essam Al-Ammar; George G. Karady; Orlando P. Hevia

2007-01-01

163

Transform Coding Techniques for Lossy Hyperspectral Data Compression  

Microsoft Academic Search

Transform-based lossy compression has a huge potential for hyperspectral data reduction. Hyperspectral data are 3-D, and the nature of their correlation is different in each dimension. This calls for a careful design of the 3-D transform to be used for compression. In this paper, we investigate the transform design and rate allocation stage for lossy compression of hyperspectral data. First,

Barbara Penna; Tammam Tillo; Enrico Magli; Gabriella Olmo

2007-01-01

164

Frequency chirp stabilization in semiconductor distributed feedback lasers with external control  

NASA Astrophysics Data System (ADS)

It is well known that current modulation in diode lasers generates amplitude (AM) and optical frequency (FM) modulations. The frequency chirp under direct current modulation originates from variations in the carrier density and from the finite difference in carrier density between the laser on and off states. Modulation of the carrier density modulates the gain and the optical index causing the resonant mode to shift. This frequency chirp broadens the spectrum, which is a serious limitation for high-speed applications and optical fiber communications. At low frequencies, thermal effects also alter the frequency chirp. The aim of this paper is to show that the laser's frequency chirp can be modified using an external control technique. The chirp response is evaluated via the determination of the chirp-to-power ratio (CPR) through a Mach-Zehnder interferometer. Experiments demonstrate that when an external optical feedback is properly adjusted, the CPR can be severely decreased over a wide range of modulation frequencies as compared to the free-running case. These preliminary results obtained on quantum well distributed feedback lasers (QW DFB) with low normalized coupling coefficient (?L) demonstrate how to stabilize the CPR through the DFB facet phase effects or parameters such as the linewidth enhancement factor. In order to confirm this frequency chirp engineering, selfconsistent calculations based on the transfer matrix method are also presented.

Grillot, F.; Provost, J. G.; Kechaou, K.; Thedrez, B.; Erasme, D.

2012-02-01

165

Efficient computation of densely sampled wavelet transforms  

NASA Astrophysics Data System (ADS)

An efficient algorithm is presented for computing the continuous wavelet transform and the wideband ambiguity function on a sample grid with uniform time spacing but arbitrary sampling in scale. The method is based on the chirp z-transform and requires the same order of computation as constant-bandwidth analysis techniques, such as the short-time Fourier transform and the narrowband ambiguity function. An alternative spline approximation method which is more efficient when the number of scale samples is large is also described.

Jones, Douglas L.; Baraniuk, Richard G.

1991-12-01

166

SAR impulse response with residual chirps.  

SciTech Connect

A Linear Frequency-Modulated (LFM) chirp is a function with unit amplitude and quadratic phase characteristic. In a focused Synthetic Aperture Radar (SAR) image, a residual chirp is undesired for targets of interest, as it coarsens the manifested resolution. However, for undesired spurious signals, a residual chirp is often advantageous because it spreads the energy and thereby diminishes its peak value. In either case, a good understanding of the effects of a residual LFM chirp on a SAR Impulse Response (IPR) is required to facilitate system analysis and design. This report presents an analysis of the effects of a residual chirp on the IPR. As reference, there is a rich body of publications on various aspects of LFM chirps. A quick search reveals a plethora of articles, going back to the early 1950s. We mention here purely as trivia one of the earlier analysis papers on this waveform by Klauder, et al.

Doerry, Armin Walter

2009-06-01

167

Chirp reduction and on/off contrast enhancement via optical injection locking and coherent carrier manipulation  

NASA Astrophysics Data System (ADS)

The most cost-effective solution for modulating data onto an optical carrier is via direct modulation of a semiconductor laser. Unfortunately, this approach suffers from high chirp. The chirp can be reduced by reducing the on/off modulation contrast ratio (i.e. by keeping the signaling laser well above threshold when generating both logical `0' and `1' bits), but the low contrast ratio itself compromises performance. Other techniques can better suppress chirp, e,g., based on selfinjection or optical injection locking of the directly-modulated laser (slave) to another laser (master) that emits CW light. However, this technique although very efficient at eliminating chirp, also requires the slave laser be operated well above threshold. We show however that the issue of the limited on/off modulation contrast can be addressed in this instance by subtraction of the carrier using a component of the master beam and an interferometric arrangement.

Slavík, Radan; Kakande, Joseph; Phelan, Richard; O'Carroll, John; Kelly, Brian; Richardson, David J.

2013-05-01

168

Chirped pulse amplification of 300 fs pulses in an Alexandrite regenerative amplifier  

SciTech Connect

The authors demonstrate the amplification of femtosecond dye laser pulses up to the 3.5 mJ level in an alexandrite regenerative amplifier. An expansion/compression system using diffraction gratings allows chirped pulse amplification techniques to be used to produce peak powers upwards of 1 GW. Limitations in the chirped pulse amplification of ultrashort pulses due to intracavity dispersive elements are discussed.

Pessot, M.; Squier, J.; Bado, P.; Mourou, G. (Lab. for Laser Energetics, Univ. of Rochester, Rochester, NY (US)); Harter, D.J. (Allied Signal In., Corporate Technology, Morristown, NJ (US))

1989-01-01

169

Improved technique for one-way transformation of information  

DOEpatents

Method and apparatus are provided for one-way transformation of data according to multiplication and/or exponentiation modulo a prime number. An implementation of the invention permits the one way residue transformation, useful in encryption and similar applications, to be implemented by n-bit computers substantially with no increase in difficulty or complexity over a natural transformation thereby, using a modulus which is a power of two. 9 figs.

Cooper, J.A.

1987-05-11

170

Wide-band superconductive Chirp filters  

SciTech Connect

Chirp filters are described that consist of miniature tapped superconductive stripline. The stripline consists of 40-micron-wide niobium thin films in a spiral pattern on 125-micron-thick silicon wafers, and tapping is effected by backward-wave couplers between neighboring lines. Sophisticated fabrication and packaging techniques have led to a now mature technology. Devices with 2.6-GHz bandwidth and time-bandwidth products of 98 are routinely fabricated that exhibit amplitude errors within a few tenths of a decibel and phase errors within a fractions of a degree of theoretical. In pulse-compression tests, matched amplitude-weighted devices yield peak relative side-lobe levels of -32 dB.

DiIorio, M.S.; Withers, R.S.; Anderson, A.C.

1989-04-01

171

Tuning of external-cavity semiconductor lasers with chirped diffraction gratings  

NASA Astrophysics Data System (ADS)

We present a novel scheme of tunable semiconductor laser based on the use of a chirped grating in an external cavity. The chirped grating is fabricated using a simple holographic technique: two Gaussian beams having wavefronts with different radii of curvature are brought to interfere on a photoresist layer. The tuning properties of chirped gratings have been investigated with semiconductor lasers operated with an external cavity. With this type of grating positioned in Littrow configuration, the wavelength selection can be done by translating the grating without any need to rotate it. This cavity configuration provides a tunable output beam with an angle of propagation that is independent of the wavelength. The translation of chirped gratings was shown to tune a visible diode laser and an infrared diode laser over the same spectral band as the conventional tuning scheme where an unchirped grating is rotated.

Duval, Marc; Fortin, Gilles; Piché, Michel; McCarthy, Nathalie

2005-08-01

172

Detection and frequency tracking of chirping signals  

SciTech Connect

This paper discusses several methods to detect the presence of and track the frequency of a chirping signal in broadband noise. The dynamic behavior of each of the methods is described and tracking error bounds are investigated in terms of the chirp rate. Frequency tracking and behavior in the presence of varying levels of noise are illustrated in examples. 11 refs., 29 figs.

Elliott, G.R.; Stearns, S.D.

1990-08-01

173

Frequency chirp characteristics on WDM external modulation  

Microsoft Academic Search

The paper studies the effect of frequency chirping and the Extension Ratio (ER) on the performance of optical communication system. The characteristics are obtained from the simulation using OptiSystem 7.0 on the externally modulated experimental setup. The parameter known as alpha factor (a) is used to characterize the chirp behavior and the effects of ER on Bit Error Rate (BER.

Zaiton Binti Abdul Mutalip

2010-01-01

174

Raman forward scattering of chirped laser pulses  

SciTech Connect

Raman scattering of a high-intensity, short duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all regimes of forward scattering, it is shown that the growth rate increases (decreases) for positive (negative) frequency chirp. The effect of chirp on the growth rate is relatively minor, i.e., a few percent chirp yields few percent changes in the growth rates. Numerical solutions based on fully nonlinear cold Maxwell-fluid model are presented which confirm analytical predictions. Relation of these results to recent experiments is discussed.

Schroeder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

2002-12-05

175

Embedded wavelet packet transform technique for texture compression  

NASA Astrophysics Data System (ADS)

A highly efficient texture compression scheme is proposed in this research. With this scheme, energy compaction of texture images is first achieved by the wavelet packet transform, and an embedding approach is then adopted for the coding of the wavelet packet transform coefficients. By comparing the proposed algorithm with the JPEG standard, FBI wavelet/scalar quantization standard and the EZW scheme with extensive experimental results, we observe a significant improvement in the rate-distortion performance and visual quality.

Li, Jin; Cheng, Po-Yuen; Kuo, C.-C. J.

1995-09-01

176

Lossless Image Compression Using Burrows Wheeler Transform (Methods and Techniques)  

Microsoft Academic Search

The burrows-wheeler transform (BWT) is a combinatorial algorithm originally created for text compression such as bzip2, and that has been recently applied to image compression field. This paper focuses on the impact of compression scheme based on the combinatorial transform on high-level resolution medical images. It overviews the original scheme and some improvements that have been develop in post processing

Elfitrin Syahrul; Julien Dubois; Vincent Vajnovszki; Taoufik Saidani; Mohamed Atri

2008-01-01

177

Population inversion by chirped pulses  

SciTech Connect

In this paper, we analyze the condition for complete population inversion by a chirped pulse over a finite duration. The nonadiabatic transition probability is mapped in the two-dimensional parameter space of coupling strength and detuning amplitude. Asymptotic forms of the probability are derived by the interference of nonadiabatic transitions for sinusoidal and triangular pulses. The qualitative difference between the maps for the two types of pulses is accounted for. The map is used for the design of stable inversion pulses under specific accuracy thresholds.

Lu Tianshi [Department of Mathematics and Statistics, Wichita State University, Wichita, Kansas 67260-0033 (United States)

2011-09-15

178

Chirping the LCLS Electron Beam  

SciTech Connect

We explore scenarios for generating a linear time-correlated energy spread in the LCLS electron bunch, prior to the undulator, that is needed for optical (x-ray) pulse compression. The correlated energy spread (''chirp'') is formed by generating an energy gradient along the length of the electron bunch using RF phasing and/or longitudinal wakefields of the accelerating structures. The sign of the correlation is an important limitation. Excluding a complete re-design of the compression systems, the best possibility is to use ''over-compression'' to effect the required energy chirp. This is easily done with only a slight strength increase ({approx}10%) in the chicane bends of the second compressor. In this case, the bend-plane emittance dilution associated with the increased coherent synchrotron radiation (CSR) in the bunch compressor may, however, significantly compromise the electron beam density. The CSR calculations for the momentary extremely short ({approx}1 {micro}m) electron bunch during over-compression are quite subtle and an adequate confidence level may not be achievable. A practical limit in this short-pulse scenario may be to use spontaneous rather than FEL radiation. Ignoring the potential emittance growth, a FWHM electron energy spread of 2% is possible.

Emma, P.

2005-01-31

179

Versatile optical pulse shaping using a linearly chirped fibre Bragg grating and an amplitude mask  

NASA Astrophysics Data System (ADS)

Optical pulse shaping finds many important applications in the area of ultrafast photonics. For example, in ultrafast all-optical switching, temporal shaping of the control pulses can be used to create a wide flat-top switching window with sharp rise and fall times. Such switching windows are more jitter-tolerant than simple Gaussian windows, and can therefore achieve a lower bit-error rate. Previously reported pulse shaping methods using linearly chirped Fibre Bragg Gratings (FBGs) take advantage of the direct correspondence between the spatial distribution of the grating periods and the temporal distribution of the spectral contents of the grating impulse response (space-to-frequency-to-time mapping). However, they have two major drawbacks: first, they are only valid for high-dispersion gratings, and therefore are unsuitable for producing short pulses; second, due to the inherent impulse response assumption, the power conversion efficiency is very low since the grating bandwidth needs to be much smaller than that of the input pulse. The numerical conversion efficiency demonstrated for this method is about a few percent. We report a versatile technique for temporal pulse shaping using a simple linearly chirped FBG and an amplitude mask. Unlike previous pulse shaping methods, ours is also applicable for low-dispersion gratings with bandwidths comparable to that of the input pulse (i.e., taking into account of finite input pulse duration). The chirped grating is used to stretch the incoming pulses to the desirable temporal width, while the amplitude mask modifies the shape of the pulses. We developed a novel optimization algorithm to obtain an amplitude mask that significantly increases the conversion efficiency. Pulse shaping using linearly chirped FBGs in the low dispersion regime is simulated using two methods. For weak gratings, the direct relationship between the spatial grating profile and the grating impulse response was used in tandem with a forward-correction deconvolution algorithm to solve for the optimum amplitude mask. For strong gratings, an optimization algorithm based on the partial validity of space-time mapping, as well as the causal relationship between the reflected temporal response and the grating apodization profile was used to design the amplitude mask. We experimentally demonstrated the conversion of 1-ps transform-limited Gaussian pulses to 10-ps pulses with a target shape at a high conversion efficiency of ~20% (measured) using a 1.5-mm-long grating. The spectral width of the pulses is 3.5 nm, centered at 1.55?m. As the reflected pulse shape is controlled by the shape of the amplitude mask, our method can be easily adapted to produce any arbitrary temporal pulse shape by designing an appropriate amplitude mask. To our knowledge, this is the first demonstration of this technique of arbitrary pulse shaping using the combination of a linearly chirped fiber grating and an amplitude mask in the low-dispersion regime.

Neata, S. A.; Wong, A.; Qian, L.; Gu, X.; Smith, P. W. E.

2005-09-01

180

Persistent spectral hole-burning materials as pulse shapers: phase analysis of a chirped coherent filter  

Microsoft Academic Search

We apply Fourier-transform spectral interferometry to complete phase and intensity characterization of a chirped filter engraved in a persistent spectral hole-burning (PSHB) material. The conjugated transfer function of a grating pair compressor is stored in a PSHB material as an accumulated spectral hologram that behaves as a pulse stretcher. By directing the diffracted pulse back through the compressor, we verified

T. Chanelière; J.-L. Le Gouët; D. Ricard

2003-01-01

181

Chirped-Pulse Millimeter-Wave Spectroscopy of Rydberg-Rydberg Transitions  

NASA Astrophysics Data System (ADS)

Transitions between Rydberg states of Ca atoms, in a pulsed, supersonic atomic beam, are directly detected by chirped-pulse millimeter-wave spectroscopy. Broadband, high-resolution spectra with accurate relative intensities are recorded instantly. Free induction decay (FID) of atoms, polarized by the chirped pulse, at their Rydberg-Rydberg transition frequencies, is heterodyne detected, averaged in the time domain, and Fourier transformed into the frequency domain. Millimeter-wave transient nutations are observed, and the possibility of FID evolving to superradiance is discussed.

Prozument, Kirill; Colombo, Anthony P.; Zhou, Yan; Park, G. Barratt; Petrovi?, Vladimir S.; Coy, Stephen L.; Field, Robert W.

2011-09-01

182

Self-referenced characterization of femtosecond laser pulses by chirp scan.  

PubMed

We investigate a variant of the d-scan technique, an intuitive pulse characterization method for retrieving the spectral phase of ultrashort laser pulses. In this variant a ramp of quadratic spectral phases is applied to the input pulses and the second harmonic spectra of the resulting pulses are measured for each chirp value. We demonstrate that a given field envelope produces a unique and unequivocal chirp-scan map and that, under some asymptotic assumptions, both the spectral amplitude and phase of the measured pulse can be retrieved analytically from only two measurements. An iterative algorithm can exploit the redundancy of the information contained in the chirp-scan map to discard experimental noise, artifacts, calibration errors and improve the reconstruction of both the spectral intensity and phase. This technique is compared to two reference characterization techniques (FROG and SRSI). Finally, we perform d-scan measurements with a simple grating-pair compressor. PMID:24150331

Loriot, Vincent; Gitzinger, Gregory; Forget, Nicolas

2013-10-21

183

Motion Estimation Algorithm Using One-Bit-Transform with Smoothing and Preprocessing Technique  

Microsoft Academic Search

\\u000a A high performance 2D one-bit-transform (1BT) motion estimation algorithm with smoothing and preprocessing (S + P) is introduced\\u000a in this paper. The 1BT technique is used to transform an 8-bit image into a 1-bit representation image (1BT image). In the\\u000a 1BT motion estimation algorithm, the 8-bit current frame (c frame) and reference frame (p frame) are first transformed into their

Wai Chong Chia; Li Wern Chew; Li-Minn Ang; Kah Phooi Seng

184

Superconducting current transformer for testing Nb3Sn cable splicing technique  

SciTech Connect

To provide a quick feedback on different approaches to superconducting cable splicing design and assembly techniques, a superconducting current transformer that can deliver more than 20 kA for testing splice samples has been designed and fabricated. The existing infrastructure of the Short Sample Test Facility at Fermilab, including its cryostat, power supply, and data acquisition system, was used for housing and operating the transformer. This report presents the design features of the transformer and the main results of cable splice tests.

Nicolai Andreev et al.

2002-09-10

185

Terahertz surface plasmon on chirped groove grating  

Microsoft Academic Search

The excitation of terahertz surface plasmon on metallized chirped groove gratings is studied in time- and frequency-domain. These gratings have a potential to launch and decouple broadband terahertz surface plasmon necessary for integrated optical circuits.

M. Martl; J. Darmo; K. Unterrainer; E. Gornik

2008-01-01

186

A chirp modem incorporating interference excision  

NASA Astrophysics Data System (ADS)

The paper describes an experimental 75-baud chirp modem designed to operate at high frequency (HF), which is able to reject interference from other HF users by adaptive filtering at the receiver. It also has inherently good performance in multipath preparation and in white noise, and is thus capable of robust digital communication. The system has been tested over a 170 km point-to-point HF skywave link, in which short chirp messages (approximately 30 s duration) were alternated in time with frequency-exchange keyed (FEK) messages. The total duration of the tests was 72 hours, and included day and night operation. In these tests, the chirp system had an overall performance which was superior to that of FEK. FEK occasionally suffered from long periods (e.g., 1 hour) of severe failure, essentially due to interference, whereas the chirp modem achieved more continuous useful operation.

Darbyshire, E. P.; Gott, G. F.

1992-08-01

187

Accumulation of copper in Trichoderma reesei transformants, constructed with the modified Agrobacterium tumefaciens -mediated transformation technique  

Microsoft Academic Search

A modified Agrobacterium tumefaciens-mediated transformation method was established for the construction of mutants with improved copper tolerance and accumulation\\u000a capability in Trichoderma reesei. One transformant, AT01, exhibited the highest copper accumulation capability. With copper at 0.7 mM, AT01 removed 13 mg\\u000a copper\\/g biomass (removal rate of 96%), whereas the wild-type strain removed only 6 mg copper\\/g biomass (removal rate of 50%).\\u000a Optimal conditions

Kehe Fu; Lixing Liu; Lili Fan; Tong Liu; Jie Chen

2010-01-01

188

Chirp-managed directly modulated laser (CML)  

Microsoft Academic Search

We demonstrate a new highly dispersion tolerant modulation format using a chirp-managed directly modulated laser (CML) for uncompensated 10-Gb\\/s transmission over >200 km at 1.55 ?m. The CML consists of a distributed feedback (DFB) laser followed by an optical filter. We show that the combination of adiabatic chirp from the DFB and filter edge response produces high extinction ratio pulses

Yasuhiro Matsui; Daniel Mahgerefteh; Xueyan Zheng; Charlie Liao; Zhencan Frank Fan; Kevin McCallion; Parviz Tayebati

2006-01-01

189

Raman forward scattering of chirped laser pulses  

Microsoft Academic Search

Raman scattering of a high-intensity, short-duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatiotemporal regimes. This includes a previously undescribed regime of strongly coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all

C. B. Schroeder; E. Esarey; B. A. Shadwick; W. P. Leemans

2003-01-01

190

Raman forward scattering of chirped laser pulses  

Microsoft Academic Search

Raman scattering of a high-intensity, short duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all

C. B. Schroeder; E. Esarey; B. A. Shadwick; W. P. Leemans

2002-01-01

191

A Fuzzy-Neural Technique for Flashover Diagnosis of Winding Insulation in Transformers  

Microsoft Academic Search

A Fuzzy-Neural pattern recognition technique for insulation flashover diagnosis in oil filled power transformers has been\\u000a described in the paper. Determination of exact nature and location of internal insulation flashover during impulse testing\\u000a of power transformers is of practical importance to the manufacturer as well as designers. The presently available diagnostic\\u000a techniques more or less depend on expertise of the

Abhinandan De; Nirmalendu Chatterjee

2002-01-01

192

High-Fidelity Adiabatic Passage by Composite Sequences of Chirped Pulses  

SciTech Connect

We present a method for optimization of the technique of adiabatic passage between two quantum states by composite sequences of frequency-chirped pulses with specific relative phases: composite adiabatic passage (CAP). By choosing the composite phases appropriately the nonadiabatic losses can be canceled to any desired order with sufficiently long sequences, regardless of the nonadiabatic coupling. The values of the composite phases are universal for they do not depend on the pulse shapes and the chirp. The accuracy of the CAP technique and its robustness against parameter variations make CAP suitable for high-fidelity quantum information processing.

Torosov, Boyan T. [Department of Physics, Sofia University, 5 James Bourchier Boulevard, 1164 Sofia (Bulgaria); Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 5209, BP 47870, F-21078 Dijon (France); Guerin, Stephane [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 5209, BP 47870, F-21078 Dijon (France); Vitanov, Nikolay V. [Department of Physics, Sofia University, 5 James Bourchier Boulevard, 1164 Sofia (Bulgaria)

2011-06-10

193

Interplay of the Chirps and Chirped Pulse Compression in a High-gain Seeded Free-electron Laser  

SciTech Connect

In a seeded high-gain Free-electron Laser (FEL), where a coherent laser pulse interacts with an ultra-relativistic electron beam, the seed laser pulse can be frequency chirped, and the electron beam can be energy chirped. Besides these two chirps, the FEL interaction introduces an intrinsic frequency chirp in the FEL even if the above mentioned two chirps are absent. In this paper we examine the interplay of these three chirps. The problem is formulated as an initial value problem, and solved via a Green function approach. Besides the chirp evolution, we also give analytical expressions for the pulse duration and bandwidth of the FEL, which remains fully longitudinally coherent in the high gain exponential growth regime. Because the chirps are normally introduced for a final compression of the FEL pulse, some conceptual issues are discussed. We show that in order to get a short pulse duration, an energy chirp in the electron beam is necessary.

Wu, Juhao; /SLAC; Murphy, J.B.; /LBNL, ALS; Emma, P.J.; /SLAC; Wang, X.J.; Watanabe, T.; /LBNL, ALS; Zhong, Xinming; /Beijing Normal U.

2007-01-03

194

Continuous wavelet transform technique for fault signal diagnosis of internal combustion engines  

Microsoft Academic Search

A fault signal diagnosis technique for internal combustion engines that uses a continuous wavelet transform algorithm is presented in this paper. The use of mechanical vibration and acoustic emission signals for fault diagnosis in rotating machinery has grown significantly due to advances in the progress of digital signal processing algorithms and implementation techniques. The conventional diagnosis technology using acoustic and

Jian-Da Wu; Jien-Chen Chen

2006-01-01

195

SSII cancellation in an EAM-based OFDM-IMDD transmission system employing a novel dynamic chirp model.  

PubMed

We develop a novel subcarrier-to-subcarrier intermixing interference (SSII) cancellation technique to estimate and eliminate SSII. For the first time, the SSII cancellation technique is experimentally demonstrated in an electro-absorption modulator- (EAM-) based intensity-modulation-direct-detection (IMDD) multi-band OFDM transmission system. Since the characteristics of SSII are seriously affected by the chirp parameter, a simple constant chirp model, we found, cannot effectively remove the SSII. Therefore, assuming that the chirp parameter linearly depends on the optical power, a novel dynamic chirp model is developed to obtain better estimation and cancellation of SSII. Compared with 23.6% SSII cancellation by the constant chirp model, our experimental results show that incorporating the dynamic chirp model into the SSII cancellation technique can achieve up to 74.4% SSII cancellation and 2.8-dB sensitivity improvement in a 32.25-Gbps OFDM system over 100-km uncompensated standard single-mode fiber. PMID:23388947

Hsu, Dar-Zu; Wei, Chia-Chien; Chen, Hsing-Yu; Lu, Yi-Cheng; Song, Cih-Yuan; Yang, Chih-Chieh; Chen, Jyehong

2013-01-14

196

Coherent control of ultracold collisions with chirped light: Direction matters  

Microsoft Academic Search

We demonstrate the ability to coherently control ultracold atomic Rb\\u000acollisions using frequency-chirped light on the nanosecond time scale. For\\u000acertain center frequencies of the chirp, the rate of inelastic trap-loss\\u000acollisions induced by negatively chirped light is dramatically suppressed\\u000acompared to the case of a positive chirp. We attribute this to a fundamental\\u000aasymmetry in the system: an excited

M. J. Wright; J. A. Pechkis; J. L. Carini; S. Kallush; R. Kosloff; P. L. Gould

2007-01-01

197

Chirped pulse shadowgraphy for single shot time resolved plasma expansion measurements  

SciTech Connect

The dynamics of ultrashort laser plasmas demand single shot temporal measurements on fast time scales. We describe a method to record the plasma expansion on picosecond (ps) timescales continuously over hundreds of ps, in single shot. The method uses the chirp of a Ti:sapphire laser as a time-resolved optical diagnostic tool. Using this technique, the evolution of the plasma expansion had been recorded with ps time resolutions, by probing with a chirped laser pulse of 200 ps duration. A peak expansion velocity of 1.8x10{sup 7} cm/s is observed and its evolution in time is obtained for approx300 ps.

Prasad, Y. B. S. R.; Barnwal, S.; Naik, P. A.; Chakera, J. A.; Khan, R. A.; Gupta, P. D. [Laser Plasma Division, RRCAT, Indore, 452 013 Madhya Pradesh (India)

2010-05-31

198

High Resolution Pulse Compression Imaging Using Super Resolution FM-Chirp Correlation Method (SCM)  

NASA Astrophysics Data System (ADS)

This study addresses the issue of the super-resolution pulse compression technique (PCT) for ultrasound imaging. Time resolution of multiple ultrasonic echoes using the FM-Chirp PCT is limited by the bandwidth of the sweep-frequency. That is, the resolution depends on the sharpness of auto-correlation function. We propose the Super resolution FM-Chirp correlation Method (SCM) and evaluate its performance. This method is based on the multiple signal classification (MUSIC) algorithm. Our simulations were made for the model assuming multiple signals reflected from some scatterers. We confirmed that SCM detects time delay of complicated reflected signals successfully with high resolution.

Fujiwara, M.; Okubo, K.; Tagawa, N.

199

ANN and wavelet-based discrimination technique between discharge currents in transformer mineral oils  

NASA Astrophysics Data System (ADS)

This paper is aimed at the analysis of positive pre-breakdown currents triggered in mineral transformer oil submitted to 50 Hz alternating overvoltages. Different shapes of streamer currents and electrical discharges have been recorded to develop a discrimination technique based on an Artificial Neural Network (ANN) and Wavelet analysis of these currents. This enables us to address a complementary diagnosis tool that can serve as an online transformer monitoring and protection.

Aberkane, F.; Moulai, H.; Nacer, A.; Benyahia, F.; Beroual, A.

2012-05-01

200

Characterization of the chirp in semiconductor laser under modulation  

Microsoft Academic Search

In this paper we present, shortly, a study of the chirp induced in direct modulated DFB laser. Our description of the chirp is based, first on analytical resolution of the rate equations, and second on a simulation of a heterodyne system with the Optisystem software. This study enables us to visualize the chirp of a DFB laser in the RF

O. Boukari; L. Hassine; O. Latry; M. Ketata; H. Bouchriha

2008-01-01

201

A precision chirp scaling SAR processor extension to sub-aperture implementation on massively parallel supercomputers  

Microsoft Academic Search

A new concept in SAR raw data focusing algorithms is discussed. The so called “chirp scaling” (CS) technique has allowed the complete elimination of the interpolation step required in conventional ?-K wave domain processing algorithms. This drives to high performance the implementation of aberrationless 2D processors, both for SAR focusing and for analogue problems (seismic wave migration, tomography, etc.). Furthermore

Fabr izio Impagnatiello

1995-01-01

202

Chirp signal matching and signal power optimization in pulse-echo mode ultrasonic nondestructive testing  

Microsoft Academic Search

Chirp pulse compression is a signal correlation technique that uses frequency modulated pulses as transmitted signals. Usually, signals with linear frequency modulation are applied. They can be generated rather easily, but their spectra are not totally matched to the transfer function of ultrasonic systems. In pulse-echo mode operation, with signal duration and consequently the time-bandwidth product being critical parameters, waveforms

Martin Pollakowski; Helmut Ermert

1994-01-01

203

Chirped area coupled resonator optical waveguide gyroscope.  

PubMed

We study the transmission of an optical field through a rotating coupled resonator optical waveguide (CROW) in which the size of the ring resonators changes from one ring to the next. We focus on symmetric integer wavelength chirps of the circumference of the rings relative to the central ring in the array. The transfer matrix method is used to obtain the transmission as a function of the inertial rotation rate ? resulting from the Sagnac effect. Chirping increases the slope of the oscillations in the transmission as a function of ?, which can be exploited to further enhance the rotation sensitivity beyond that of a CROW with uniform resonators. PMID:21479036

Toland, John R E; Kaston, Zachary A; Sorrentino, Christopher; Search, Christopher P

2011-04-01

204

Thermodynamic Studies of the Alpha-to-Beta Phase Transformation in Zirconium Using a Subsecond Pulse Heating Technique.  

National Technical Information Service (NTIS)

Measurements of the temperature and energy of the Alpha-to Beta phase transformation, and the electrical resistivity near and at the transformation point of zirconium using a subsecond duration pulse heating technique are described. The results yield 1147...

A. Cezairliyan F. Righini

1974-01-01

205

On the potential applicability of auto-regressive spectral estimation to HF chirp sounders  

NASA Astrophysics Data System (ADS)

A major limitation of HF chirp sounders is the use of fast Fourier transform (FFT) analysis to resolve the different multipath components. To reduce the effects of spectral leakage associated with the FFT, the signal is usually weighted by a suitable window prior to spectral analysis. For negligible frequency dispersion, multipath resolution including the two magneto-ionic waves is determined by the width of the mainlobe of the window function whereas, for large frequency dispersion, the use of window functions improves the resolution of multipath. Modern spectral estimation techniques such as auto-regressive (AR) modelling offer higher resolution capabilities which are only limited by the signal to noise ratio. This paper discusses the required stages for both FFT analysis and AR analysis. The results of applying both techniques to ionospheric data obtained over a short skywave link in the U.K. are presented. These include distributions for the 6 dB width, group time delay and order of the AR model. The resolution advantage of the AR method is demonstrated by ionograms.

Salous, S.

1997-10-01

206

Fourier transform infrared spectroscopy techniques for the analysis of drugs of abuse  

Microsoft Academic Search

Cryogenic deposition techniques for Gas Chromatography\\/Fourier Transform Infrared (GC\\/FT-IR) can be successfully employed in urinalysis for drugs of abuse with detection limits comparable to those of the established Gas Chromatography\\/Mass Spectrometry (GC\\/MS) technique. The additional confidence of the data that infrared analysis can offer has been helpful in identifying ambiguous results, particularly, in the case of amphetamines where drugs of

Kathryn S. Kalasinsky; Barry K. Levine; Michael L. Smith; Joseph J. Magluilo; Teresa Schaefer

1994-01-01

207

Multiple color images encryption by triplets recombination combining the phase retrieval technique and Arnold transform  

NASA Astrophysics Data System (ADS)

We propose a new method for multiple color images encryption by using triplets recombination. In this proposed technique, triplet (R, G and B) components of the secret color image are recorded simultaneously as a real and positive gray image exploiting parallel multi-wavelength recording technology. Arnold transform and phase retrieval algorithm adapted to Fresnel transform domain are used to encode the parallel hybrid result. By using of the proposed technique, each color image is encrypted into a pure phase distribution and combined by superposition. Phase modulation is introduced to eliminate the cross-talk caused by multiple images superposition. The wavelength and transform parameters are provided as keys to enhance the system security. In addition, computer simulations are performed and numerical results are presented to show the validity and efficiency of the proposed method.

Shi, Xiaoyan; Zhao, Daomu; Huang, Yinbo; Pan, Jianjiang

2013-10-01

208

Digital simulation of scalar optical diffraction: revisiting chirp function sampling criteria and consequences.  

PubMed

Accurate simulation of scalar optical diffraction requires consideration of the sampling requirement for the phase chirp function that appears in the Fresnel diffraction expression. We describe three sampling regimes for FFT-based propagation approaches: ideally sampled, oversampled, and undersampled. Ideal sampling, where the chirp and its FFT both have values that match analytic chirp expressions, usually provides the most accurate results but can be difficult to realize in practical simulations. Under- or oversampling leads to a reduction in the available source plane support size, the available source bandwidth, or the available observation support size, depending on the approach and simulation scenario. We discuss three Fresnel propagation approaches: the impulse response/transfer function (angular spectrum) method, the single FFT (direct) method, and the two-step method. With illustrations and simulation examples we show the form of the sampled chirp functions and their discrete transforms, common relationships between the three methods under ideal sampling conditions, and define conditions and consequences to be considered when using nonideal sampling. The analysis is extended to describe the sampling limitations for the more exact Rayleigh-Sommerfeld diffraction solution. PMID:19904309

Voelz, David G; Roggemann, Michael C

2009-11-10

209

Extension of harmonic cutoff in a multicycle chirped pulse combined with a chirp-free pulse  

SciTech Connect

We demonstrate high-order harmonic generation in a wave form synthesized by a multicycle 800-nm chirped laser pulse and a chirp-free laser pulse. Compared with the case of using only a chirped pulse, both the harmonic cutoff and the extreme ultraviolet supercontinuum can be extended when a weak chirp-free pulse is combined with the chirped pulse. When chirp-free pulse intensity grows, the cutoff energy and bandwidth of the supercontinuum grow as well. It is found that the broad supercontinuum can be achieved for a driving pulse with long duration even though the driving pulse reaches 10 optical cycles. An isolated attosecond pulse with duration of about 59 as is obtained, and after appropriate phase compensation with a duration of about 11 as. In addition, by performing time-frequency analyses and the classical trajectory simulation, the difference in supercontinuum generation between the preceding wave form and a similar wave form synthesized by an 800-nm fundamental pulse and a 1600-nm subharmonic pulse is investigated.

Xu Junjie; Zeng Bin; Yu Yongli [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800 (China)

2010-11-15

210

Cr4+ : YAG chirped-pulse oscillator  

PubMed Central

We demonstrate chirped-pulse operation of a Cr : YAG passively mode-locked laser. Different operation regimes of the laser are extensively investigated in the vicinity of zero dispersion both experimentally and numerically. It is shown that for a given laser configuration, transition to the positive dispersion regime allows a 5-fold increase in the output pulse energy, which is otherwise limited by the onset of the multipulsing or ‘chaotic’ mode-locking. The output pulses have 1.4 ps duration and are compressible down to 120 fs in a 3 m piece of silica fiber, enabling supercontinuum generation in a nonlinear fiber. The spectrum shape and operation stability of the chirped-pulse regime depend strongly on the amount and shape of the intracavity dispersion. The numerical model predicts the existence of the minimum amount of the positive dispersion, above which the chirped-pulse regime can be realized. Once located, the chirped-pulse regime can be reliably reproduced and is sufficiently stable for applications.

Sorokin, Evgeni; Kalashnikov, Vladimir L; Mandon, Julien; Guelachvili, Guy; Picque, Nathalie; Sorokina, Irina T

2010-01-01

211

Clinical comparison of pulse and chirp excitation  

Microsoft Academic Search

Coded excitation (CE) using frequency modulated signals (chirps) combined with modified matched filtering has earlier been presented showing promising results in simulations and in-vitro. In this study an experimental ultrasound system is evaluated in a clinical setting, where image sequences are assessed by skilled medical doctors. The effect on penetration depth and image quality were measured. A modified clinical scanner

Morten H. Pedersen; Thanassis X. Misaridis; J. A. Jensen

2002-01-01

212

Real-time holographic reconstruction of NMR images in Fresnel transform imaging technique  

Microsoft Academic Search

A method of real-time holographic reconstruction of Nuclear Magnetic Resonance (NMR) images by making a hologram directly from the NMR signal is described. Since the signal obtained in the NMR Fresnel transform technique is given by an equation similar to that of the Fresnel diffraction equation in light, holographic reconstruction of NMR images is possible by recording the NMR signal

Satoshi ITO; Yoshifumi YAMADA; Yoshitsugu KAMIMURA

1997-01-01

213

A CCD chirp-Z FFT Doppler signal processor for laser velocimetry  

Microsoft Academic Search

A charge-coupled Chirp-Z fast Fourier transform device, which has been configured to obtain the frequency of peak spectral amplitude in signals from laser velocimeters, is described for use in oceanographic and other low laser power field applications where weak optical signals and frequent dropout are encountered. With sufficient bandwidth to resolve photon arrivals, and with a pulse-height discriminator, the processor

Y. C. Agrawal

1984-01-01

214

Chirp Z-driven split-step propagation algorithms for AOA analysis  

Microsoft Academic Search

Parabolic wave equation (PWE) algorithms are widely used to model electromagnetic wave propagation in diverse environments. In most applications only the amplitude of received field is of interest, but the computed fields also contain phase information, which can subsequently be used for evaluating the effectiveness of angle-of-arrival (AOA) algorithms. In this paper, we use the chirp Z-transform, which does interpolation

Peter J. Kajenski; Joseph Otto; Ramakrishna Janaswamy

2009-01-01

215

Transformations  

NSDL National Science Digital Library

In this webquest, fourth grade students will be learning how to transform geometric shapes. They will also learn to define transformation, translation, and reflection. Introduction You are going to become math detectives. You will try and solve what a transformation is and how you use it. When you are finished you will be able to perform many different transformations. You will be able to identify many different geometric ...

Foust, Mrs.

2005-10-31

216

Two-color chirped-pulse amplification in an ultrabroadband Ti:sapphire ring regenerative amplifier  

Microsoft Academic Search

We have developed a high-energy, ultrabroadband Ti:sapphire ring regenerative amplifier capable of producing in excess of 20-mJ output at a 10-Hz repetition rate. The technique of chirped-pulse amplification is used to generate two-color, time-synchronized pulses with central wavelength separations of up to ~120 nm and with a total energy of 10 mJ by use of a regenerative pulse-shaping technique. Mid-infrared

Koichi Yamakawa; C. P. J. Barty

2003-01-01

217

Measurement of sulfur dioxide with the differential optical absorption technique combined with Fourier transformation  

Microsoft Academic Search

The concentration of sulfur dioxide has been measured in the ultraviolet spectral range with a combination of the differential optical absorption technique and Fourier transformation. Measurements have been made with a pathlength of two meters and a measuring time of one minute. Sulfur dioxide levels of less than 0.1 ppm (volume) were assessed with a measurement uncertainty of [plus minus]0.03

L. Axelsson; A. Lauber

1992-01-01

218

Fabrication technologies for chirped refractive microlens arrays  

NASA Astrophysics Data System (ADS)

Conventional microlens arrays consist of a repetitive arrangement of a unit cell on a fixed pitch. In a chirped array, the inflexibility of a regular structure has been overcome. Here, the array consists of individually shaped lenses which are defined by a parametric description of the cells optical function. We propose different fabrication methods for chirped microlens arrays and present experimentally obtained data. Reflow of photoresist is an established technology for the fabrication of microlenses with superior optical performance. For the generation of a chirped microlens array the photolithographic mask for patterning the resist to be melted has to be chirped. We present an algorithm for mask generation with an example of an ultra-thin camera objective. Inherent to the reflow process stringent limitations to viable surfaces apply. For achieving more arbitrary surfaces, laser lithography and also 2-photon polymerization are employed. In both methods the structures are decomposed into pixels. In laser lithography the local height is converted into an intensity value for the exposure. This variable dose writing locally changes the solubility of the resist in the development process leading to the required surface profile. We propose a writing scheme enabling structure heights of several ten microns with sufficient height discretization. 2-photon polymerization is a rapid prototyping method. Here, a small volume of a UV-curing organic-inorganic co-polymer is hardened in the tight focus of the writing beam. The volume pixel to be exposed is addressed by piezoelectric translation stages. Experimentally obtained structures and performed tests of the optical quality are presented.

Wippermann, F. C.; Radtke, D.; Zeitner, U.; Duparré, J. W.; Tünnermann, A.; Amberg, M.; Sinzinger, S.; Reinhardt, C.; Ovsianikov, A.; Chichkov, B. N.

2006-08-01

219

pathChirp: Efficient Available Bandwidth Estimation for Network Paths  

Microsoft Academic Search

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing

Les

2003-01-01

220

Chirp-Z analysis for sol-gel transition monitoring.  

PubMed

Gelation is a complex reaction that transforms a liquid medium into a solid one: the gel. In gel state, some gel materials (DMAP) have the singular property to ring in an audible frequency range when a pulse is applied. Before the gelation point, there is no transmission of slow waves observed; after the gelation point, the speed of sound in the gel rapidly increases from 0.1 to 10 m/s. The time evolution of the speed of sound can be measured, in frequency domain, by following the frequency spacing of the resonance peaks from the Synchronous Detection (SD) measurement method. Unfortunately, due to a constant frequency sampling rate, the relative error for low speeds (0.1 m/s) is 100%. In order to maintain a low constant relative error, in the whole speed time evolution range, Chirp-Z Transform (CZT) is used. This operation transforms a time variant signal to a time invariant one using only a time dependant stretching factor (S). In the frequency domain, the CZT enables us to stretch each collected spectrum from time signals. The blind identification of the S factor gives us the complete time evolution law of the speed of sound. Moreover, this method proves that the frequency bandwidth follows the same time law. These results point out that the minimum wavelength stays constant and that it only depends on the gel. PMID:15047337

Martinez, Loïc; Caplain, Emmanuel; Serfaty, Stéphane; Griesmar, Pascal; Gouedard, Gérard; Gindre, Marcel

2004-04-01

221

Fast x-ray microdiffraction techniques for studying irreversible transformations in materials.  

SciTech Connect

A pair of techniques have been developed for performing time-resolved X-ray microdiffraction on irreversible phase transformations. In one technique capillary optics are used to focus a high-flux broad-spectrum X-ray beam to a 60 {micro}m spot size and a fast pixel array detector is used to achieve temporal resolution of 55 {micro}s. In the second technique the X-rays are focused with Kirkpatrick-Baez mirrors to achieve a spatial resolution better than 10 {micro}m and a fast shutter is used to provide temporal resolution better than 20 {micro}s while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils.

Kelly, S. T.; Trenkle, J. C.; Koerner, L. J.; Barron, S. C.; Walker, N.; Pouliquen, P. O.; Tate, M. W.; Gruner, S. M.; Dufresne, E. M.; Weihs, T. P.; Hufnagel, T. C. (X-Ray Science Division); (Johns Hopkins Univ.); (Cornell Univ.)

2011-05-01

222

Fast X-ray microdiffraction techniques for studying irreversible transformations in materials.  

PubMed

A pair of techniques have been developed for performing time-resolved X-ray microdiffraction on irreversible phase transformations. In one technique capillary optics are used to focus a high-flux broad-spectrum X-ray beam to a 60 µm spot size and a fast pixel array detector is used to achieve temporal resolution of 55 µs. In the second technique the X-rays are focused with Kirkpatrick-Baez mirrors to achieve a spatial resolution better than 10 µm and a fast shutter is used to provide temporal resolution better than 20 µs while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils. PMID:21525656

Kelly, Stephen T; Trenkle, Jonathan C; Koerner, Lucas J; Barron, Sara C; Walker, Nöel; Pouliquen, Philippe O; Tate, Mark W; Gruner, Sol M; Dufresne, Eric M; Weihs, Timothy P; Hufnagel, Todd C

2011-03-16

223

SAR processing with stepped chirps and phased array antennas.  

SciTech Connect

Wideband radar signals are problematic for phased array antennas. Wideband radar signals can be generated from series or groups of narrow-band signals centered at different frequencies. An equivalent wideband LFM chirp can be assembled from lesser-bandwidth chirp segments in the data processing. The chirp segments can be transmitted as separate narrow-band pulses, each with their own steering phase operation. This overcomes the problematic dilemma of steering wideband chirps with phase shifters alone, that is, without true time-delay elements.

Doerry, Armin Walter

2006-09-01

224

Chirped pulse amplification with a nonlinearly chirped fiber Bragg grating matched to the Treacy compressor.  

PubMed

We demonstrate a fiber chirped pulse amplification system that uses an engineered nonlinearly chirped fiber Bragg grating stretcher dispersion matched to the Treacy compressor. The seed pulses at 1558 nm are stretched to 720 ps, amplified by more than 50 dB to 6.5-microJ energy, and recompressed to 940 fs. After almost 1000 times compression the pulses are within 30% of the bandwidth limit and have a contrast ratio of better than 30 dB. PMID:15072356

Imeshev, G; Hartl, I; Fermann, M E

2004-04-01

225

Polarization averaged short-time Fourier transform technique for distributed fiber birefringence characterization using Brillouin gain.  

PubMed

A polarization averaged short-time Fourier transform (PASTFT) technique is developed for distributed fiber birefringence characterization based on counterpropagating stimulated Brillouin scattering (SBS) gain signal. This technique can be used for the birefringence characterization of the general elliptical birefringent fiber. A theoretical model on polarization matching of counterpropagating SBS process is established. The performance of the short-time Fourier transform (STFT) method and the PASTFT technique is analyzed by using the simulation of the theoretical model. Simulation results show that the process of polarization average could effectively reduce the birefringence characterization error caused by the polarization dependence of the local period of SBS gain. A less than 8% normalized root mean square error is achieved for the characterization of the length of the birefringence vector on elliptical birefringent fibers. The PASTFT technique is experimentally verified by the distributed measurement of beat length and differential group delay of a standard single-mode fiber via the Brillouin optical time domain analysis system. PMID:22772108

Xie, Shangran; Chen, Liang; Bao, Xiaoyi

2012-07-01

226

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

PubMed

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

Shen, Che-Chou; Chiu, Yi-Yuan

2009-10-01

227

TRANSFORMATION  

SciTech Connect

Transformation, which alters the genetic makeup of an individual, is a concept that intrigues the human imagination. In Streptococcus pneumoniae such transformation was first demonstrated. Perhaps our fascination with genetics derived from our ancestors observing their own progeny, with its retention and assortment of parental traits, but such interest must have been accelerated after the dawn of agriculture. It was in pea plants that Gregor Mendel in the late 1800s examined inherited traits and found them to be determined by physical elements, or genes, passed from parents to progeny. In our day, the material basis of these genetic determinants was revealed to be DNA by the lowly bacteria, in particular, the pneumococcus. For this species, transformation by free DNA is a sexual process that enables cells to sport new combinations of genes and traits. Genetic transformation of the type found in S. pneumoniae occurs naturally in many species of bacteria (70), but, initially only a few other transformable species were found, namely, Haemophilus influenzae, Neisseria meningitides, Neisseria gonorrheae, and Bacillus subtilis (96). Natural transformation, which requires a set of genes evolved for the purpose, contrasts with artificial transformation, which is accomplished by shocking cells either electrically, as in electroporation, or by ionic and temperature shifts. Although such artificial treatments can introduce very small amounts of DNA into virtually any type of cell, the amounts introduced by natural transformation are a million-fold greater, and S. pneumoniae can take up as much as 10% of its cellular DNA content (40).

LACKS,S.A.

2003-10-09

228

Magnetic and spontaneous Barkhausen noise techniques used in investigation of a martensitic transformation  

NASA Astrophysics Data System (ADS)

Magnetic Barkhausen noise (MBN) was used to characterize the progress of austenite to martensite phase transformation while cooling steel specimens, using a conventional Barkhausen noise emission setup stimulated by an alternating magnetic field. The phase transformation was also followed by electrical resistivity measurements and by optical and scanning electron microscopy. MBN measurements on a AISI D2 tool steel austenitized at 1473 K and cooled to liquid nitrogen temperature presented a clear change near 225 K during cooling, corresponding to the MS (martensite start) temperature, as confirmed by resistivity measurements. Analysis of the resulting signals suggested a novel experimental technique that measures spontaneous magnetic emission during transformation, in the absence of any external field. Spontaneous magnetic noise emission measurements were registered in situ while cooling an initially austenitic sample in liquid nitrogen, showing that local microstructural changes, corresponding to an avalanche or ``burst'' phenomena, could be detected. This spontaneous magnetic emission (SME) can thus be considered a new experimental tool for the study of martensite transformations in ferrous alloys, at the same level as acoustic emission.

Capò Sànchez, J.; Huallpa, E.; Farina, P.; Padovese, L. R.; Goldenstein, H.

2011-10-01

229

Seismic coherent and random noise attenuation using the undecimated discrete wavelet transform method with WDGA technique  

NASA Astrophysics Data System (ADS)

One of the most crucial challenges in seismic data processing is the reduction of the noise in the data or improving the signal-to-noise ratio. In this study, the 1D undecimated discrete wavelet transform (UDWT) has been acquired to attenuate random noise and ground roll. Wavelet domain ground roll analysis (WDGA) is applied to find the ground roll energy in the wavelet domain. The WDGA will be a substitute method for thresholding in seismic data processing. To compare the effectiveness of the WDGA method, we apply the 1D double density discrete wavelet transform (DDDWT) using soft thresholding in the random noise reduction and ground roll attenuation processes. Seismic signals intersect with ground roll in the time and frequency domains. Random noise and ground roll have many undesirable effects on pre-stack seismic data, and result in an inaccurate velocity analysis for NMO correction. In this paper, the UDWT by using the WDGA technique and DDDWT (using the soft thresholding technique) and the regular Fourier based method as f-k transform will be used and compared for seismic denoising.

Goudarzi, Alireza; Riahi, Mohammad Ali

2012-12-01

230

End effect analysis of linear induction motor based on the wavelet transform technique  

SciTech Connect

HSST (High Speed Surface Transport) is currently being developed for the railway systems of urban transportation in Japan. It is used in the electromagnetic suspension and short-stator Linear Induction Motor (LIM) for the HSST. The performance of LIM is degraded due to the influence of the end effects. LIM is analyzed using the Fourier series expansion to throw light on this problem. However, to obtain the high-accuracy in this technique, the number of times for calculating is increased. In case of the Wavelet transform technique, as the Wavelet coefficients converge rapidly to zero, this technique has been applied to analyze the end effects of LIM. In this paper, the authors investigated the method for determining of mother wavelet.

Mori, Yoshihiko; Torii, Susumu; Ebihara, Daiki

1999-09-01

231

640Gb\\/s\\/Channel Single-Polarization DPSK Transmission Over 525 km With Ultrafast Time-Domain Optical Fourier Transformation  

Microsoft Academic Search

A single-channel 640-Gb\\/s differential phase-shift-keying transmission over 525 km was successfully demonstrated in a single polarization. A new ultrafast time-domain optical Fourier transformation (OFT) circuit was developed, in which the strong chirp required for the OFT of a subpicosecond optical pulse was realized with a phase modulator operated in a round-trip configuration. By applying this technique to a 640-Gb\\/s transmission,

Toshiyuki Hirano; Pengyu Guan; Toshihiko Hirooka; Masataka Nakazawa

2010-01-01

232

Image encryption based on extended fractional Fourier transform and digital holography technique  

NASA Astrophysics Data System (ADS)

We present a new optical image encryption algorithm that is based on extended fractional Fourier transform (FRT) and digital holography technique. We can perform the encryption and decryption with more parameters compared with earlier similar methods in FRT domain. In the extended FRT encryption system, the input data to be encrypted is extended fractional Fourier transformed two times and random phase mask is placed at the output plane of the first extended FRT. By use of an interference with a wave from another random phase mask, the encrypted data is stored as a digital hologram. The data retrieval is operated by all-digital means. Computer simulations are presented to verify its validity and efficiency.

Wang, Xiaogang; Zhao, Daomu; Chen, Linfei

2006-04-01

233

TRANSFORMER  

DOEpatents

Transformers of a type adapted for use with extreme high power vacuum tubes where current requirements may be of the order of 2,000 to 200,000 amperes are described. The transformer casing has the form of a re-entrant section being extended through an opening in one end of the cylinder to form a coaxial terminal arrangement. A toroidal multi-turn primary winding is disposed within the casing in coaxial relationship therein. In a second embodiment, means are provided for forming the casing as a multi-turn secondary. The transformer is characterized by minimized resistance heating, minimized external magnetic flux, and an economical construction.

Baker, W.R.

1959-08-25

234

Transformation  

NSDL National Science Digital Library

This video clip demonstrates the process of transformation. When a bacterial cell dies, the DNA in the cell breaks into fragments. This free DNA can be taken up by certain bacteria and integrated into their DNA.

American Society For Microbiology;

2002-01-01

235

Demonstration of stable raman fibre laser with asymmetrical laser cavity including broadband chirped FBG  

NASA Astrophysics Data System (ADS)

We experimentally and theoretically demonstrated a novel technique to generate a stable multi-wavelength Raman fibre laser (RFL) based on an asymmetrical all-fibre Raman laser cavity by using a broadband chirped fibre Bragg grating (CFBG). The output power variations from detuning the center wavelength of in/out reflectors are studied with symmetrical and asymmetrical RFL cavities. The RFL output with asymmetrical cavity is more stable than that of symmetrical cavity.

Im, Young-Eun; Chun, Kyungwon; Kim, Hangeul; Hann, Swook; Kim, Dong-Hwan; Chung, Youngjoo; Park, Chang-Soo

2009-10-01

236

Performance scaling via passive pulse shaping in cavity-enhanced optical parametric chirped-pulse amplification.  

PubMed

We show that an enhancement cavity seeded at the full repetition rate of the pump laser can automatically reshape small-signal gain across the interacting pulses in an optical parametric chirped-pulse amplifier for close-to-optimal operation, significantly increasing both the gain bandwidth and the conversion efficiency, in addition to boosting gain for high-repetition-rate amplification. Applied to a degenerate amplifier, the technique can provide an octave-spanning gain bandwidth. PMID:20548342

Siddiqui, Aleem M; Moses, Jeffrey; Hong, Kyung-Han; Lai, Chien-Jen; Kärtner, Franz X

2010-06-15

237

Image restoration in chirp-pulse microwave CT (CP-MCT)  

Microsoft Academic Search

Chirp-pulse microwave computed tomography (CP-MCT) is a technique for imaging the distribution of temperature variations inside biological tissues. Even if resolution and contrast are adequate to this purpose, a further improvement of image quality is desirable. In this paper, we discuss the blur of CP-MCT images and we propose a method for estimating the corresponding point spread function (PSF). To

Mario Bertero; Michio Miyakawa; Patrizia Boccacci; Francesco Conte; Kentaroh Orikasa; Masatoshi Furutani

2000-01-01

238

The adaptive line enhancer applied to chirp detection  

NASA Astrophysics Data System (ADS)

This paper discusses the ability of an adaptive line enhancer (ALE) driven by the least-mean-squares (LMS) algorithm to track the frequency of a chirping signal in broadband noise. The dynamic behavior of the weights is described and a weight tracking error bound is derived in terms in chirp rate. Frequency tracking and weight behavior are illustrated in examples.

Elliott, Glenn R.; Stearns, Samuel D.

1990-02-01

239

Frequency-chirped readout of spatial-spectral absorption features  

SciTech Connect

This paper examines the physical mechanisms of reading out spatial-spectral absorption features in an inhomogeneously broadened medium using linear frequency-chirped electric fields. A Maxwell-Bloch model using numerical calculation for angled beams with arbitrary phase modulation is used to simulate the chirped field readout process. The simulation results indicate that any spatial-spectral absorption feature can be read out with a chirped field with the appropriate bandwidth, duration, and intensity. Mapping spectral absorption features into temporal intensity modulations depends on the chirp rate of the field. However, when probing a spatial-spectral grating with a chirped field, a beat signal representing the grating period can be created by interfering the emitted photon echo chirped field with a reference chirped field, regardless of the chirp rate. Comparisons are made between collinear and angled readout configurations. Readout signal strength and spurious signal distortions are investigated as functions of the grating strength and the Rabi frequency of the readout pulse. Using a collinear readout geometry, distortions from optical nutation on the transmitted field and higher-order harmonics are observed, both of which are avoided in an angled beam geometry.

Chang, Tiejun; Mohan, R. Krishna; Harris, Todd L.; Merkel, Kristian D. [Spectrum Laboratory, Montana State University, Bozeman, Montana 59717 (United States); Tian Mingzhen [Physics Department, Montana State University, Bozeman, Montana 59717 (United States); Babbitt, Wm. Randall [Spectrum Laboratory, Montana State University, Bozeman, Montana 59717 (United States); Physics Department, Montana State University, Bozeman, Montana 59717 (United States)

2004-12-01

240

Design of step-chirped fibre Bragg gratings  

Microsoft Academic Search

Unapodised and apodised 10 mm and 100 mm long step-chirped fibre Bragg gratings have been theoretically modeled as a function of the number of sections for the first time. It is shown that even with a relatively few sections, the reflectivity and dispersion characteristics approach that of a continuously chirped grating, improving dramatically with apodisation. Experimental results for a 200

Raman Kashyap

1997-01-01

241

On the group delay characteristics of chirped fibre Bragg gratings  

Microsoft Academic Search

It is shown for the first time that the group delay characteristics of chirped fibre Bragg gratings show a symmetry when measured from either direction. It is shown that the dispersion of a chirped grating cannot be completely compensated by another identical grating. This has implications on the quality of apodisation required for dispersion compensation.

Raman Kashyap; Monica de Lacerda Rocha

1998-01-01

242

Filter characteristics of a chirped volume holographic grating  

Microsoft Academic Search

We compare and analyze the filter properties of transmission-type volume holographic gratings, especially the dispersion characteristics for uniform and chirped gratings. It is theoretically and experimentally shown that the dispersion characteristics can be controlled by introducing one-dimensional chirping to the volume grating in a photorefractive crystal. The filter response including output power and dispersion comes from a combined effect of

Seunghoon Han; Bong-Ahn Yu; Seunghwan Chung; Hwi Kim; Jungwook Paek; Byoungho Lee

2004-01-01

243

Chirp: a practical global filesystem for cluster and Grid computing  

Microsoft Academic Search

Traditional distributed £lesystem technologies designed for local and campus area networks do not adapt well to wide area grid computing environments. To address this problem, we have designed the Chirp distributed £lesystem, which is designed from the ground up to meet the needs of grid computing. Chirp is easily deployed without special privileges, provides strong andexible security mechanisms, tunable consistency

Douglas Thain; Christopher Moretti; Jeffrey Hemmes

2009-01-01

244

Single image orthogonal fringe technique for resolution enhancement of the Fourier transform fringe analysis method  

NASA Astrophysics Data System (ADS)

Gradient range and spatial resolution in Fourier Transform Profilometry depend on the size of the filter window in reciprocal space. The proposed methods to date for the elimination of the fundamental frequency and enlargement of the filter window are either too computationally complex or depend on the possibility of using two frames, thus disabling the method's ability to cope with dynamic situations and subjecting the results to possible intensity changes between the two frame acquisitions. This article describes a simple method for using a single crossed fringe pattern to accomplish that objective, greatly improving the previously reported technique, whilst retaining its main advantages.

Tavares, Paulo J.; Vaz, Mário A. P.

2013-03-01

245

Raman forward scattering of high-intensity chirped laser pulses  

SciTech Connect

Raman forward scattering of a high-intensity, short-duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all regimes of forward scattering, it is shown that the growth rate increases (decreases) for positive (negative) frequency chirp. The effect of chirp on the growth rate is relatively minor, i.e., a few percent chirp yields few percent changes in the growth rates. Relation of these results to recent experiments is discussed.

Schroeder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

2002-06-23

246

CHIRPED PULSE AMPLIFICATION OF HGHG-FEL FACILITY AT BNL.  

SciTech Connect

The DUV-FEL facility has been in operation in High Gain Harmonic Generation (HGHG) mode for one year producing 266 nm output from 177 MeV electrons. In this paper we present preliminary results of the Chirped Pulse Amplification (CPA) of HGHG radiation. In the normal HGHG process, a 1 ps electron beam is seeded by chirped 9 ps long 800 nm Ti:Sapphire laser. The electron beam sees only a narrow fraction of the seed laser bandwidth. However, in the CPA case the seed laser pulse length is reduced to 1 ps, and the electron beam sees the full bandwidth. We introduce an energy chirp on electron beam to match the chirp of the seed pulse, enabling the resonant condition for the whole beam. We present measurements of the spectrum bandwidth for various chirp conditions.

DOYURAN,A.ET AL.

2003-09-08

247

Beam homogenizers based on chirped microlens arrays.  

PubMed

Lens array arrangements are commonly used for the homogenization of highly coherent laser beams. These fly's eye condenser configurations can be used to shape almost arbitrary input intensity distributions into a top hat. Due to the periodic structure of regular arrays the output intensity distribution is modulated by equidistant sharp intensity peaks which are disturbing the homogeneity. As a new approach we apply chirped microlens arrays to the beam shaping system. These are non-regular arrays consisting of individually shaped lenses defined by a parametric description which can be derived completely from analytical functions. The advantages of the new concept and design rules are presented. PMID:19546927

Wippermann, Frank; Zeitner, Uwe-D; Dannberg, Peter; Bräuer, Andreas; Sinzinger, Stefan

2007-05-14

248

Extended-range, low coherence dual wavelength interferometry using a superfluorescent fibre source and chirped fibre Bragg gratings  

Microsoft Academic Search

We describe an all-fibre, passive scheme for making extended range interferometric measurements based on the dual wavelength technique. The coherence tuned interferometer network is illuminated with a single superfluorescent fibre source at 1.55 ?m and the two wavelengths are synthesised at the output by means of chirped fibre Bragg gratings. We demonstrate an unambiguous sensing range of 270 ?m, with

G. P Brady; K. Kalli; D. J Webb; D. A Jackson; L. Zhang; I. Bennion

1997-01-01

249

Analytical transform techniques to retrieve non-spherical particle size distribution  

NASA Astrophysics Data System (ADS)

The measurement of particle size distribution (PSD) from the extinction spectra is a challenging problem, especially for non-spherical particles. In this work, the analytical transform techniques are developed to retrieve PSD from the measured scattering data for a variety of shapes of non-spherical particle including spheroids, cuboids, triangular prisms, hexagonal prisms and elliptical cylinders. In the retrieve calculation, all particles have aligned orientations and their extinction cross sections can be adequately calculated by using the anomalous diffraction theory (ADT). It is shown that for each type of the considered non-spherical particles, there exists an ADT transform pair between the size distribution and the extinction spectrum. The inverse formula of PSD from the related ADT transform is therefore established. This result provides a new approach to the solution of the inversion problem and has the potential to be used in finding solutions for more complicated particle shapes. It is found that the solution of inverse scattering for absorbing particles can be simplified to a particular solution in which the character of absorption becomes no longer present.

Zhao, Jian-Qi; Li, Jiangnan

2013-11-01

250

Fourier transform infrared spectroscopy techniques for the analysis of drugs of abuse  

NASA Astrophysics Data System (ADS)

Cryogenic deposition techniques for Gas Chromatography/Fourier Transform Infrared (GC/FT-IR) can be successfully employed in urinalysis for drugs of abuse with detection limits comparable to those of the established Gas Chromatography/Mass Spectrometry (GC/MS) technique. The additional confidence of the data that infrared analysis can offer has been helpful in identifying ambiguous results, particularly, in the case of amphetamines where drugs of abuse can be confused with over-the-counter medications or naturally occurring amines. Hair analysis has been important in drug testing when adulteration of urine samples has been a question. Functional group mapping can further assist the analysis and track drug use versus time.

Kalasinsky, Kathryn S.; Levine, Barry K.; Smith, Michael L.; Magluilo, Joseph J.; Schaefer, Teresa

1994-01-01

251

Analysis of tokamak data using a novel Hilbert transform based technique  

NASA Astrophysics Data System (ADS)

A novel data analysis technique based on the ``empirical mode decomposition'' and Hilbert transform is applied to the analysis of edge fluctuation data and Mirnov coil data from the ADITYA tokamak [S. B. Bhatt et al., Ind. J. Pure Appl. Phys. 27, 710 (1989)]. It is shown that the edge fluctuations can be well represented by a finite number of about 10 discrete modes. Their instantaneous energies show intermittent bursts and the high frequency modes are nonstationary. The technique is further developed to study three-mode interactions and employed to show that triplet interactions are statistically significant among high frequency modes of the fluctuation data. A general critique of the method is presented and its utility for the analysis of nonlinear phenomena in complex systems like plasma turbulence is highlighted.

Jha, R.; Raju, D.; Sen, A.

2006-08-01

252

Transformers  

NSDL National Science Digital Library

All About Circuits is a website that âÂÂprovides a series of online textbooks covering electricity and electronics.â Written by Tony R. Kuphaldt, the textbooks available here are wonderful resources for students, teachers, and anyone who is interested in learning more about electronics. This specific section, Transformers, is the ninth chapter in Volume II âÂÂAlternating Current (AC). A few of the topics covered in this chapter include: Mutual inductance and basic operation; Step-up and Step-down transformers; Electrical isolation; Phasing; Winding configurations; Voltage Regulation; and finally, Special transformers and applications.. Diagrams and detailed descriptions of concepts are included throughout the chapter to provide users with a comprehensive lesson. Visitors to the site are also encouraged to discuss concepts and topics using the All About Circuits discussion forums (registration with the site is required to post materials).

Kuphaldt, Tony R.

2008-07-03

253

Application of wavelet transformation techniques to detect cyanobacteria bloom using hyperspectral data  

NASA Astrophysics Data System (ADS)

The existence of algal blooms of cyanobacteria has been documented in Lake Erie which is biologically the most active lake among the Great Lakes of North America. Cyanobacteria are known to produce toxic substances that are detrimental to the lake's biodiversity. The early detection of harmful algal blooms in the Western Basin of Lake Erie (WBLE) requires a more efficient and accurate monitoring tool. Remote sensing is an efficient tool with high spatial and temporal coverage that can allow accurate and timely detection of cyanobacteria bloom. However, in optically complex environments, such as in the Western Basin of Lake Erie, the water contains multiple constituents including phytoplankton, suspended sediment, and dissolved organic carbon and the discrimination between the various constituents requires separation of the mostly overlapping scattering and absorption properties. Determining a single in-water constituent from satellite observations is complicated when working with mixed spectral signatures. This study focuses on improving the quantification of chlorophyll a and phycocyanin as proxies to detect cyanobacteria remotely, by applying signal decomposition to the reflectance data using spectra transformation. This study indicates that applying spectral transformation using wavelet analysis, results in increased accuracy as compared to using other feature extraction methods such as the principle component analysis of untransformed spectra and conventional spectral indices. The superior results of the wavelet technique in discriminating between the various water constituents and detecting cyanobacteria can be attributed to the frequency content retrieved by the wavelet technique combined with the localization property of wavelets.

Al, A.; Witter, D. L.; Ortiz, J. D.

2011-12-01

254

The state of art of chirp grating lenses on LiNbO3  

NASA Astrophysics Data System (ADS)

The fabrication and performance characteristics of chirp-grating lenses made on LiNbO3 substrate for integrated-optics applications are reviewed and illustrated. The principle of the chirp-grating lens is introduced, and the essential problem of index-perturbation requirements for relatively high-index substrates like LiNbO3 is considered: at an input wavelength of 830 nm, efficient Bragg-grating diffraction requires an index perturbation of about 0.03. It is shown that this cannot be achieved by etching alone. Techniques applied successfully include overlays of TiO2 or Nb2O5 film, double-diffusion-grating lenses made by benzoic-acid proton-ion exchange, and Ti:LiNbO3 lenses made by the latter process, on an experimental basis. Graphs and tables of performance parameters and drawings of configurations are included.

Yao, S. K.; Findakly, T.; Forouhar, S.; Warren, C.; Chang, W. S. C.

1983-01-01

255

Transformer \\  

Microsoft Academic Search

Reduction of size and weight in electronic type transformers to keep pace with miniaturization in other phases of electronic component designing has led directly to higher temperature operation. Temperatures in the region of 185°C require inorganic materials throughout, including where used, the dielectric coolant. Design details and materials performance in \\

L. F. Kilham; R. R. Ursch

1956-01-01

256

Transformers  

Microsoft Academic Search

Purpose – The aim of this paper is to examine the current and future outlook of smartphones and how they will transform the loyalty marketing landscape. Design\\/methodology\\/approach – The approoach takes the form of tapping big-name companies, like Nielsen, Ogilvy and Wells Fargo, to provide insight into how marketers are looking to utilize smartphones and to predict where the future

Sharon M. Goldman

2010-01-01

257

Influence of Laser Frequency Chirp on the Performance of Optical Communication Systems.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. This thesis is concerned with a detailed study of laser frequency chirp and of the implications for the performance of very high bit rate direct detection optical fibre communication systems. In view of the inaccuracy and limitations of previously reported estimates of the chirp-induced penalty, a considerable part of the study is dedicated to the development of modelling and analysis techniques suitable to evaluate the performance of practical systems. In order to take into account laser dynamics, a SPICE2 equivalent-circuit model based on a set of coupled single-mode rate equations is employed, including structure-dependent electrical parasitics. Two alternative methods are considered to model the interaction between chirp and fibre dispersion: an approximate time domain technique, and a more formally based frequency domain method using a complex envelope representation of the transmitted optical field. The latter provides a rigorous description of propagation in monomode fibre, taking into account the intrinsic modulation spectrum, and is used to obtain estimates of transmission bandwidth attainable. A new method for modelling pulse distortion in monomode fibre is also presented, using an expansion of the optical signal in terms of Hermite -Gaussian functions. Pseudo-random data sequences are used to estimate the performance degradation due to chirp and patterning. Allowing for filtering at the receiver of distorted optical power waveforms, system eye-diagrams and estimates of the average error probability are obtained, and equivalent power penalties are determined. Finally, it is shown how the strategy developed may be employed to investigate overall system performance implications and design constraints.

Almeida da Silva, Henrique Jose

1988-12-01

258

Evaluation of small-angle scattering data of charged particles using the generalized indirect Fourier transformation technique  

Microsoft Academic Search

Small-angle x-ray and neutron scattering are widely used techniques to study the structure of colloidal particles in the size range up to 100 nm. The indirect Fourier transformation technique is well established to obtain model free real space information, but the interpretation of the results is limited to cases where particle interaction can be neglected. The extended generalized indirect Fourier

G. Fritz; A. Bergmann; O. Glatter

2000-01-01

259

A technique of phase-shifting for 3-D measurement using spectral-transform  

NASA Astrophysics Data System (ADS)

This paper presents a phase-shifting approach for three-dimensional (3-D) shape measurement using spectral-transform. In this technique, a projection system, with a simple structure and without moving parts, is used to achieve high precision and high speed phase shifts. This projection system utilizes three different wavelengths of LEDs as projection light source. When three LEDs light up individually, the light beam is collimated and vertically passes through the sinusoidal grating and an optical phase shifter, and then the sinusoidal grating image is projected onto the surface of the measured object by projection lens. Because three sinusoidal grating images are translated after through the optical phase shifter, and different wavelength of light has different offset distance; the direction of the fringes is perpendicular to the direction of translation. Therefore, three fringe patterns with phase shift which 3-D shape measurement requires are generated. The speed of phase shift depends on the driving signal frequency of LEDs. The phase-shifted value of fringe patterns between each other is a fixed value after the projection system was assembled. This technique has high stability, high phase-shifted accuracy and high scanning speed. In this paper, some evaluation experiments have been carried out. Experiment results indicate that the proposed technique is valid.

Huo, Jincheng; Wu, Qingyang; Zeng, Xiangjun

2013-10-01

260

Characterization of Silicon Sulfides by Chirped-Pulse Rotational Spectroscopy  

NASA Astrophysics Data System (ADS)

Chirped-pulse Fourier transform microwave spectroscopy is used to characterize the electrical discharge products that are formed in a supersonic molecular beam through a dilute gas mixture of silane and hydrogen sulfide. The spectrum between 6 and 18 GHz is dominated by SiS: more than 175 transitions have been assigned to either its isotopic species, its vibrationally excited states, or both, on the basis of previous cavity measurements. Owing to the flat instrument response function and extensive vibrational excitation that has been observed, it is possible to derive a precise vibrational temperature for SiS, and determine the relative abundances of SiS, HSiS, and H_2SiS. Although rotational lines from more than 15 other silicon or sulfur molecules have been identified in the same discharge, more than 50% of lines that have been detected with a signal-to-noise ratio of three or greater are presently unassigned. Attempts to assign these many remaining lines, and efforts to benchmark the performance of our spectrometer will be highlighted as well.

McCarthy, Michael C.; Crabtree, Kyle N.; Martinez, Oscar; , Jr.

2013-06-01

261

Transform and embedded coding techniques for maximum efficiency and random accessibility in 3-D scalable compression.  

PubMed

This study investigates random accessibility and efficiency enhancements in highly scalable video and volumetric compression. With the advent of interactive multimedia technology, random accessibility has emerged as an increasingly important consideration in the design and optimization process. In this paper, we assess the impact that the transform, embedded coding components, and code-block configurations have on the compression efficiency and accessibility of a scalable codestream. We develop performance bounds on techniques which exploit temporal redundancy within the confines of a feed-forward compression system. We also examine their random access properties to argue the significance of motion-adaptive subband transforms. When information-theoretic measures are used to determine the potential benefits of three-dimensional (3-D) context coding, we find that most of the coding gain is attributed to code-block extension, rather than interslice context modeling itself. To gain further insight into the tradeoffs that the coding part has to offer, we run a series of simulations to determine code-block partitioning strategies which maximize reconstruction quality and space-time localization. The LIMAT framework and EBCOT coding paradigm have laid a solid foundation for further progress in the development of highly scalable 3-D compression systems. PMID:16238067

Leung, Raymond; Taubman, David

2005-10-01

262

Study of polymorphic transformation of ornidazole drug by differential scanning calorimetry and other complementary techniques.  

PubMed

Differential scanning calorimetric (DSC) curves recorded for ornidazole drug during heating and cooling showed that the drug which melted around 86.1 degrees C undercooled to well below ambient room temperature of 27 degrees C during the cooling cycle. The undercooled melt kept in the freezer at 0 degree C for 10 days duration also remained in the viscous liquid form. This liquid on taking out from the freezer after ten days and ageing at ambient room temperature of 27 degrees C for 12 h transformed into white powder. The DSC pattern recorded for this white powder consisted of two prominent endothermic peaks beginning at 73.2 and 85.9 degrees C, respectively, suggesting that the powder consisted of a mixture of more than one phase. The X-ray diffraction (XRD) pattern recorded for this powder showed it to be a mixture of semi-crystalline phase and the original compound. The semi-crystalline phase melted at 73.2 degrees C prior to the melting of original compound at 85.9 degrees C. This phase on further ageing for 7 days transforms almost completely to its original form. DSC observations were corroborated by XRD and scanning electron microscopy (SEM) techniques. PMID:19051580

Desai, Satish R; Dharwadkar, Sanjiv R

263

Spectral tissue strain: a new technique for imaging tissue strain using intravascular ultrasound.  

PubMed

Spectral tissue strain (STS) is a new technique for measuring and imaging tissue strain from a set of images using intravascular ultrasound. The technique is based on the Fourier scaling property and uses the chirp z-transform (CZT) to estimate strain within the vessel walls. Some preliminary results, both in vitro and in vivo, are described. A novel display technique has also been developed for encoding radial strain and displaying the resulting colour map as an overlay on the original image. PMID:7863565

Talhami, H E; Wilson, L S; Neale, M L

1994-01-01

264

Chirped-Pulsed Ftmw Spectrum of Valeric Acid and 5-AMINOVALERIC Acid. a Study of Amino Acid Mimics in the Gas Phase  

NASA Astrophysics Data System (ADS)

Microwave studies of the structural and dynamical properties of several organic acids and their water complexes have been described by a number of research groups. Here we continue this theme by the study of valeric acid and 5-aminovaleric acid, using chirped-pulsed Fourier transform microwave spectroscopy (CP-FTMW). The rotational spectrum from 6.5 to 18 GHz was collected using a compilation of 250 MHz chirped pulses and pieced together. Their structures and water complexes were determined and will be compared to other amino acids.

Bird, Ryan G.; Vaquero, Vanesa; Pratt, David W.; Neill, Justin L.; Pate, Brooks H.

2011-06-01

265

Yb-doped chirped pulse amplification system  

NASA Astrophysics Data System (ADS)

A very compact, all diode pumped chirped pulse amplification system was developed based on Yb-doped gain materials. A passively mode-locked Yb:KYW oscillator in combination with a photonic crystal fiber was used to seed two different regenerative amplifiers. Energies up to 10mJ at 20Hz were obtained for cryo-cooled Yb:YLF and 6.5mJ between 10Hz and 30Hz for Yb:YAG at cryogenic temperatures also. For Yb:YAG it was possible to blue shift the spectrum of the oscillator to match the wavelength of the amplifier and the seed beam without using the non-linear fiber. The entire system (oscillator-stretcher-amplifier) has a footprint of less than 2m^2. After compression it should be possible to obtain amplified pulse duration of <8ps.

Furch, Federico; Reagan, Brendan; Luther, Bradley; Rocca, Jorge

2007-10-01

266

Photon Counting Chirped AM Ladar: Concept, Simulation, and Experimental Results.  

National Technical Information Service (NTIS)

The operating principles and experimental results for the Army Research Laboratory's (ARL's) patented chirped amplitude modulation (AM) ladar using linear response detectors have been presented and published previously, and will be briefly summarized here...

B. Redman M. Giza W. Ruff

2006-01-01

267

Performance of an HDTV codec adopting transform and motion compensation techniques  

NASA Astrophysics Data System (ADS)

Digital techniques are widely adopted to process the video signal, and nowadays there is the necessity of transmitting conventional and high-definition television signals between different studios. In the near future it could be possible to deliver a digital signal to the consumer. To allow the use of the presently available digital networks and satellites, sophisticated compression techniques have been devised to limit the bit-rate requirements and to provide a high-quality and reliable service. A hybrid predictive/transform system has been devised and implemented in the framework of the European project EU 256. The main parameters of this system are in accordance with those being recommended by ETSI and CMTT for the transmission of conventional component TV. Codecs are available for the TV and HDTV formats presently in use and can operate with a wide range of transmission rates. The optimization of the system and the evaluation of its performance have been carried out on the basis of a large number of subjective tests in accordance with the user requirements specified by the standardization bodies. The codecs have been extensively tested on-field during experimental point-to-multipoint satellite transmission of HDTV signals on the occasion of soccer matches.

Barbero, Marzio; Cucchi, Silvio; Muratori, Mario

1991-12-01

268

Raman Forward Scattering of High-Intensity Chirped Laser Pulses  

Microsoft Academic Search

Raman forward scattering of a high-intensity, short-duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatiotemporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all

C. B. Schroeder; E. Esarey; B. A. Shadwick; W. P. Leemans

2002-01-01

269

Multivariation calibration techniques applied to NIRA (near infrared reflectance analysis) and FTIR (Fourier transform infrared) data  

NASA Astrophysics Data System (ADS)

Multivariate calibration techniques can reduce the time required for routine testing and can provide new methods of analysis. Multivariate calibration is commonly used with near infrared reflectance analysis (NIRA) and Fourier transform infrared (FTIR) spectroscopy. Two feasibility studies were performed to determine the capability of NIRA, using multivariate calibration techniques, to perform analyses on the types of samples that are routinely analyzed at this laboratory. The first study performed included a variety of samples and indicated that NIRA would be well-suited to perform analyses on selected materials properties such as water content and hydroxyl number on polyol samples, epoxy content on epoxy resins, water content of desiccants, and the amine values of various amine cure agents. A second study was performed to assess the capability of NIRA to perform quantitative analysis of hydroxyl numbers and water contents of hydroxyl-containing materials. Hydroxyl number and water content were selected for determination because these tests are frequently run on polyol materials and the hydroxyl number determination is time consuming. This study pointed out the necessity of obtaining calibration standards identical to the samples being analyzed for each type of polyol or other material being analyzed. Multivariate calibration techniques are frequently used with FTIR data to determine the composition of a large variety of complex mixtures. A literature search indicated many applications of multivariate calibration to FTIR data. Areas identified where quantitation by FTIR would provide a new capability are quantitation of components in epoxy and silicone resins, polychlorinated biphenyls (PCBs) in oils, and additives to polymers.

Long, C. L.

1991-02-01

270

Propagation effects of isolated attosecond pulse generation with a multicycle chirped and chirped-free two-color field  

SciTech Connect

We present a theoretical study of isolated attosecond pulse generation with a multicycle chirped and chirped-free two-color field. We show that the bandwidth of the extreme ultraviolet supercontinuum can be extended by combining a multicycle chirped pulse and a multicycle chirped-free pulse. Also, the broadband supercontinuum can still be generated when the macroscopic effects are included. Furthermore, the macroscopic effects can ameliorate the temporal characteristic of the broadband supercontinuum of the single atom, and eliminate the modulations of the broadband supercontinuum. Thus a very smooth broadband supercontinuum and a pure isolated 102-as pulse can be directly obtained. Moreover, the structure of the broadband supercontinuum can be steadily maintained for a relative long distance after a certain distance.

Du Hongchuan; Hu Bitao [School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000 (China)

2011-08-15

271

On scaling properties of fractional Fourier transform and its relation with other transforms  

NASA Astrophysics Data System (ADS)

Several properties of fractional Fourier transform (FRFT) have been studied recently and many are being investigated at present. In this article, scaling property of the FRFT is generalized and some of its applications are suggested. Some extensions of the sampling relations in the FRFT domain are also presented. The issues related to connections between the FRFT and other signal transforms such as scale transform, fractional Mellin transform, and chirp z-transform, are also investigated.

Sharma, K. K.; Joshi, S. D.

2006-01-01

272

Hyperspectral imaging with stimulated Raman scattering by chirped femtosecond lasers.  

PubMed

Raman microscopy is a quantitative, label-free, and noninvasive optical imaging technique for studying inhomogeneous systems. However, the feebleness of Raman scattering significantly limits the use of Raman microscopy to low time resolutions and primarily static samples. Recent developments in narrowband stimulated Raman scattering (SRS) microscopy have significantly increased the acquisition speed of Raman based label-free imaging by a few orders of magnitude, at the expense of reduced spectroscopic information. On the basis of a spectral focusing approach, we present a fast SRS hyperspectral imaging system using chirped femtosecond lasers to achieve rapid Raman spectra acquisition while retaining the full speed and image quality of narrowband SRS imaging. We demonstrate that quantitative concentration determination of cholesterol in the presence of interfering chemical species can be achieved with sensitivity down to 4 mM. For imaging purposes, hyperspectral imaging data in the C-H stretching region is obtained within a minute. We show that mammalian cell SRS hyperspectral imaging reveals the spatially inhomogeneous distribution of saturated lipids, unsaturated lipids, cholesterol, and protein. The combination of fast spectroscopy and label-free chemical imaging will enable new applications in studying biological systems and material systems. PMID:23256635

Fu, Dan; Holtom, Gary; Freudiger, Christian; Zhang, Xu; Xie, Xiaoliang Sunney

2013-01-18

273

FD-CHIRP: hosted payload system engineering lessons  

NASA Astrophysics Data System (ADS)

The Commercially Hosted Infrared Payload (CHIRP) Flight Demonstration (FD-CHIRP) launched 21 Sept 2011 was designated a "resounding success" as the first Wide Field-of-View (WFOV) staring infrared (IR) sensor flown in geostationary earth orbit (GEO) with a primary mission of Missile Warning (MW). FD-CHIRP was an Air Force research and development project initiated in July 2008 via an unsolicited industry proposal aimed to mature and reduce the risk of WFOV sensors and ground processing technologies. Unlike the Defense Support Program (DSP) and the Space Based Infrared System (SBIRS) which were acquired via traditional integrated sensor and satellite design, FDCHIRP was developed using the "commercially hosted" approach. The FD-CHIRP host spacecraft and sensor were independently designed, creating significant development risk to the industry proposer, especially under a Firm Fixed Price contract. Yet, within 39 months of contract initiation, FD-CHIRP was launched and successfully operated in GEO to 30 June 2012 at a total cost of 111M including the 82.9M CHIRP commercial-hosting contract and a $28M sensor upgrade. The commercial-hosting contract included sensor and spacecraft modifications, integration and test, design and development of secure Mission Operations and Analysis Centers, launch, and nearly a year of GEO operations with 70 Mbps secure data acquisition. The Air Force extended the contract for six months to continue operations through the end of calendar 2012. This paper outlines system engineering challenges FD-CHIRP overcame and key lessons to smooth development of future commercially hosted missions.

Schueler, Carl F.

2012-10-01

274

Fast Transient Fault-Current Detection Based on PQR Transformation Technique for a Solid-State Fault Current Limiter  

Microsoft Academic Search

This paper describes analysis, modeling and simulation of electrical transient fault-current detection in power systems. The proposed modeling is based on simple numerical integration only, which is able to efficiently handle some sophisticated calculation. The proposed fault detector methods are sliding root mean square (SRMS) and PQR transformation technique. In this paper, an abnormal condition is situated by simply adding

B. BORIBUN; T. KULWORAWANICHPONG

2007-01-01

275

Quantum fluctuations in the chirped pendulum  

NASA Astrophysics Data System (ADS)

Anharmonic oscillators, such as the pendulum, are widely used for precision measurement and to model nonlinear phenomena. Fluctuations-such as thermal or quantum mechanical noise-can excite random motion in the oscillator, ultimately imposing a bound on measurement sensitivity. In systems where equilibrium is established with the environment, noise-induced broadening scales with the intensity of fluctuations. But how does noise affect an out-of-equilibrium oscillator where the motion is varied faster than energy is exchanged with the environment? We create such a scenario by applying fast, frequency-chirped voltage pulses to a nonlinear superconducting resonator where the ring-down time is longer than the pulse duration. Under these conditions, the circuit oscillates with either small or large amplitude depending on whether the drive voltage is below or above a critical value. This phenomenon, known as autoresonance, is significant in planetary dynamics and plasmas, enables the excitation of particles in cyclotron accelerators and may even be used to detect the state of a quantum two-level system. Our results show that the amplitude of fluctuations determines the initial conditions of such a non-equilibrium oscillator and does not affect its time evolution.

Murch, K. W.; Vijay, R.; Barth, I.; Naaman, O.; Aumentado, J.; Friedland, L.; Siddiqi, I.

2011-02-01

276

Quantum dynamical calculations of ultracold collisions induced by nonlinearly chirped light  

NASA Astrophysics Data System (ADS)

We describe quantum dynamical calculations of ultracold 85Rb trap-loss collisions induced by pulses of light whose frequency is chirped on the nanosecond time scale. The chirped light excites the ground-state collisional wave function to the long-range attractive potential and escape from the trap is modeled by an absorbing boundary at short range. Both positive and negative chirps are considered and various chirp shapes and detunings are examined. For positive chirps, the loss rates are rather independent of the chirp shape. Negative chirps, on the other hand, show a dependence on chirp shape for detunings where collisional flux can be coherently returned to the ground state. These trends are consistent with the results of a recent experiment.

Carini, J. L.; Pechkis, J. A.; Rogers, C. E., III; Gould, P. L.; Kallush, S.; Kosloff, R.

2012-01-01

277

Self-compression controlled by the chirp of the input pulse.  

PubMed

Self-compressed (SC) pulses have been achieved through the filamentation process in air without any additional dispersion compensation, using the input pulse chirp as the control parameter. For any studied input pulse energy (3-5 mJ), we have found two opposite sign input group-delay dispersion values for which SC pulses can be achieved systematically. In addition, we have observed that the energy coupled into the inner core of the filament is always of the order of 20% of the total input pulse energy, which opens the way to a scalable technique to obtain intense short pulses directly from the filamentation process. PMID:21042379

Varela, O; Alonso, B; Sola, I J; San Román, J; Zaïr, A; Méndez, C; Roso, L

2010-11-01

278

Feature extraction by wavelet transforms to analyze the heart rate variability during two meditation technique  

Microsoft Academic Search

In this study we present the analysis of HRV signals by wavelet transform. HRV, described by the extraction of the physiological rhythms embedded within its signal, is the tool through which adaptations of activity of the ANS have been widely studied. The assessment of wavelet transform (WT) as a feature extraction method was used in representing the electrophysiological signals. The

Ben Messaoud

279

A Wavelet-Based Technique for Discrimination between Faults and Magnetising Inrush Currents in Transformers  

Microsoft Academic Search

This paper presents the development of a wavelet-based scheme for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast, and computationally efficient tool. The operating time of the scheme is less than half power frequency cycle (based on a 5 kHz sampling rate). In this work, the wavelet transform concept is presented.

O. A. S. Youssef

2002-01-01

280

Review of modern diagnostic techniques for assessing insulation condition in aged transformers  

Microsoft Academic Search

Cellulosic paper and oil insulation in a transformer degrade at higher operating temperatures. Degradation is accelerated in the presence of oxygen and moisture. Power transformers being expensive items need to be carefully monitored throughout their operation. Well established time-based maintenance and conservative replacement planning is not feasible in a current market driven electricity industry. Condition based maintenance and online monitoring

Tapan K. Saha

2003-01-01

281

Estimation of high-resolution brightness temperature from auxiliary remote sensing products using transformation techniques  

NASA Astrophysics Data System (ADS)

Passive microwave observations of brightness temperature (TB) at the L-band (1.4 GHz) are highly sensitive to near-surface soil moisture and have been widely used to retrieve them. The European Space Agency-Soil Moisture and Ocean Salinity (ESA-SMOS) and the near-future NASA-Soil Moisture Active Passive (SMAP) missions will provide global observations of TB at 1.4 GHz every 3 days at spatial resolutions in the order of 40-50 kilometers . These observations need to be downscaled to 1 km to merge them with hydrometeorological models for data assimilation and to study the effects of land surface heterogeneity such as dynamic vegetation conditions. However, downscaling is an ill-posed problem and additional information regarding TB is required at finer scales. In this study, we investigate two methodologies that provide this information by transforming auxiliary remote sensing (RS) products such as Land Surface Temperature (LST), Vegetation Water Content (VWC), and Land Cover (LC), which are readily available at 1km, into initial estimates of TB at 1km. In the first method, a non-parametric probabilistic technique based on Baye's rule was used to estimate TB by embedding its functional relationship to the RS products in terms of conditional probability density functions. In the second method, the principle of local correlation was used to estimate TB by extracting structural information between TB and the RS products within local neighborhoods. Field observations obtained during the intensive field experiments conducted over growing seasons of corn and cotton in North Central Florida were used to compare and analyze the performance of the two methodologies. The impacts of limited training data on the accuracy and reliability of the two methodologies were also investigated.

Cheney, T. H.; Nagarajan, K.; Judge, J.

2010-12-01

282

THE EFFECT OF ACOUSTIC SIGNALS ON THE CHIRP RHYTHM IN THE BUSH CRICKET PHOLIDOPTERA GRISEOAPTERA  

Microsoft Academic Search

SUMMARY The effect of acoustic signals on the control of chirp production has been investigated using the insect's own chirp to trigger artificial sound signals (100 msec, 7odB, 12 or 15 kHz) at predetermined phases of the chirp cycle. The signals appear to reset the phase of the chirp rhythm generator, and sig- nals given late in the cycle are

M. D. R. JONES

1974-01-01

283

New Genetic Techniques for Group B Streptococci: High-Efficiency Transformation, Maintenance of Temperature-Sensitive pWV01 Plasmids, and Mutagenesis with Tn917  

Microsoft Academic Search

Three techniques were developed to improve the genetic manipulation of group B streptococci (GBS). We first optimized a protocol for transformation of GBS by electroporation, which provided transformation efficiencies of 10 5 CFU\\/mg. Variables that influenced the transformation efficiency were the glycine content of the competent cell growth media, the electric field strength during electroporation, the electroporation buffer composition, the

PAUL E. FRAMSON; APHAKORN NITTAYAJARN; JULIA MERRY; PHILIP YOUNGMAN; CRAIG E. RUBENS

1997-01-01

284

Synchrony during acoustic interactions in the bushcricket Mecopoda ‘Chirper’ (Tettigoniidae:Orthoptera) is generated by a combination of chirp-by-chirp resetting and change in intrinsic chirp rate  

Microsoft Academic Search

In several bushcricket species, individual males synchronise their chirps during acoustic interactions. Synchrony is imperfect\\u000a with the chirps of one male leading or lagging the other by a few milliseconds. Imperfect synchrony is believed to have evolved\\u000a in response to female preferences for leading chirps. We investigated the mechanism underlying synchrony in the bushcricket\\u000a species Mecopoda ‘Chirper’ from Southern India

Vivek Nityananda; Rohini Balakrishnan

2007-01-01

285

Effects of collisions on energetic particle-driven chirping bursts  

NASA Astrophysics Data System (ADS)

In the presence of an energetic particle population in a dissipative plasma, self-trapped structures in phase-space (holes and clumps) emerge from nonlinear wave-particle interactions. Their dynamics can lead to a nonlinear continuous shifting of the wave frequency (chirping). The effects of collisions on chirping characteristics are investigated, with a one-dimensional kinetic model. Existing analytic theory is extended to account for Krook-like collisions, which quantitatively explains a significant departure from widely accepted square-root time dependency. Relaxation oscillations, associated with chirping bursts, are investigated in the presence of dynamical friction and velocity-diffusion. The period increases with decreasing drag and weakly increases with decreasing diffusion. The mechanism is clarified with a simple semi-analytic model of hole/clump pair, which satisfies a Fokker-Planck equation. The model shows that the linear growth rate cannot be obtained simply by fitting an exponential to the amplitude time-series.

Lesur, M.

2013-05-01

286

Chirped-cavity dispersion-compensation filter design  

NASA Astrophysics Data System (ADS)

A new basic structure of a dispersive-compensation filter, called a chirped-cavity dispersion-compensator (CCDC) filter, was designed to offer the advantages of small ripples in both reflectance and group-delay dispersion (GDD). This filter provides a high dispersion compensation, like the Gires-Tournois interferometer (GTI) filter, and a wide working bandwidth, like the chirped mirror (CM). The structure of the CCDC is a cavity-type Fabry-Perot filter with a spacer layer (2 mH or 2 mL) and a chirped high reflector. The CCDC filter can provide a negative GDD of -50 fs2 over a bandwidth of 56 THz with half the optical thickness of the CM or the GTI.

Li, Ya-Ping; Chen, Sheng-Hui; Lee, Cheng-Chung

2006-03-01

287

Rainbow trapping using chirped all-dielectric periodic structures  

NASA Astrophysics Data System (ADS)

We report a numerical investigation of rainbow trapping (light of different wavelengths) at different spatial locations in a newly designed two-dimensional photonic structure that is formed using chirping parameters in two-dimensional photonic crystals. Chirped parameters ensure trapping of certain light wavelengths inside these structures. To achieve broadband electromagnetic wave trapping, we properly adjust and chirp the position and dielectric filling factor of each unit cell within a photonic crystal structure. The low group velocity regions of the dielectric continuum bands at the Brillouin zone edge enable different wavelengths to be slowed and stopped along the propagation direction. The all-dielectric transparent material nature of the proposed structure realizes light trapping in different electromagnetic regions by spatially varying the effective refractive index of the structure.

Kurt, H.; Yilmaz, D.

2013-03-01

288

Chirped Gaussian laser beam parameters in paraxial approximation  

SciTech Connect

In this paper, new expressions for spot size, radius of curvature, and Rayleigh length of a linearly and negatively chirped Gaussian beam are presented in paraxial approximation self-consistently. It is shown that there is a slight modification in those relations in comparison to that of used in literatures. These modifications change the tailored parameters in some laser beam interactions such as laser electron vacuum acceleration. At propagation distances much grater than the Rayleigh length, the modifications indicate that the temporal shape of the chirped laser beam will be changed. This effect indicates an asymmetric pulse with a slowly increasing front part and a suddenly dropping tail. For propagation distances less than the Rayleigh length, the change in laser pulse shape is not considerable. Finally, the modifications are employed in modeling of a single electron acceleration by the chirped Gaussian laser pulse.

Sohbatzadeh, F.; Mirzanejhad, S.; Aku, H.; Ashouri, S. [Department of Physics, Science Faculty, Mazandaran University, Babolsar, Mazandaran 47416-1467 (Iran, Islamic Republic of)

2010-08-15

289

Chirped pulse inverse free-electron laser vacuum accelerator  

DOEpatents

A chirped pulse inverse free-electron laser (IFEL) vacuum accelerator for high gradient laser acceleration in vacuum. By the use of an ultrashort (femtosecond), ultrahigh intensity chirped laser pulse both the IFEL interaction bandwidth and accelerating gradient are increased, thus yielding large gains in a compact system. In addition, the IFEL resonance condition can be maintained throughout the interaction region by using a chirped drive laser wave. In addition, diffraction can be alleviated by taking advantage of the laser optical bandwidth with negative dispersion focusing optics to produce a chromatic line focus. The combination of these features results in a compact, efficient vacuum laser accelerator which finds many applications including high energy physics, compact table-top laser accelerator for medical imaging and therapy, material science, and basic physics.

Hartemann, Frederic V. (Dublin, CA); Baldis, Hector A. (Pleasanton, CA); Landahl, Eric C. (Walnut Creek, CA)

2002-01-01

290

Velocity measurements using a single transmitted linear frequency-modulated chirp.  

PubMed

Velocity measurement is a challenge for a variety of remote sensing systems such as ultrasonic and radar scanners. However, current Doppler-based techniques require a comparatively long data acquisition time. It has been suggested to use coded signals, such as linear frequency-modulated signals (chirp), for ultrasonic velocity estimation by extracting the needed information from a set of several sequential coded pulses. In this study, a method for velocity estimation using a single linear frequency-modulated chirp transmission is presented and implemented for ultrasonic measurements. The complex cross-correlation function between the transmitted and reflected signals is initially calculated. The velocity is then calculated from the phase of the peak of the envelope of this cross-correlation function. The suggested method was verified using computer simulations and experimental measurements in an ultrasonic system. Applying linear regression to the data has yielded very good correlation (r = 0.989). With the suggested technique, higher frame rates of velocity mapping can be potentially achieved relative to current techniques. Also, the same data can be utilized for both velocity mapping and image reconstruction. PMID:17412485

Levy, Yoav; Azhari, Haim

2007-04-06

291

Transformation of Resources to Reserves: Next Generation Heavy-Oil Recovery Techniques  

SciTech Connect

This final report and technical progress report describes work performed from October 1, 2004 through September 30, 2007 for the project 'Transformation of Resources to Reserves: Next Generation Heavy Oil Recovery Techniques', DE-FC26-04NT15526. Critical year 3 activities of this project were not undertaken because of reduced funding to the DOE Oil Program despite timely submission of a continuation package and progress on year 1 and 2 subtasks. A small amount of carried-over funds were used during June-August 2007 to complete some work in the area of foamed-gas mobility control. Completion of Year 3 activities and tasks would have led to a more thorough completion of the project and attainment of project goals. This progress report serves as a summary of activities and accomplishments for years 1 and 2. Experiments, theory development, and numerical modeling were employed to elucidate heavy-oil production mechanisms that provide the technical foundations for producing efficiently the abundant, discovered heavy-oil resources of the U.S. that are not accessible with current technology and recovery techniques. Work fell into two task areas: cold production of heavy oils and thermal recovery. Despite the emerging critical importance of the waterflooding of viscous oil in cold environments, work in this area was never sanctioned under this project. It is envisioned that heavy oil production is impacted by development of an understanding of the reservoir and reservoir fluid conditions leading to so-called foamy oil behavior, i.e, heavy-oil solution gas drive. This understanding should allow primary, cold production of heavy and viscous oils to be optimized. Accordingly, we evaluated the oil-phase chemistry of crude oil samples from Venezuela that give effective production by the heavy-oil solution gas drive mechanism. Laboratory-scale experiments show that recovery correlates with asphaltene contents as well as the so-called acid number (AN) and base number (BN) of the crude oil. A significant number of laboratory-scale tests were made to evaluate the solution gas drive potential of West Sak (AK) viscous oil. The West Sak sample has a low acid number, low asphaltene content, and does not appear foamy under laboratory conditions. Tests show primary recovery of about 22% of the original oil in place under a variety of conditions. The acid number of other Alaskan North Slope samples tests is greater, indicating a greater potential for recovery by heavy-oil solution gas drive. Effective cold production leads to reservoir pressure depletion that eases the implementation of thermal recovery processes. When viewed from a reservoir perspective, thermal recovery is the enhanced recovery method of choice for viscous and heavy oils because of the significant viscosity reduction that accompanies the heating of oil. One significant issue accompanying thermal recovery in cold environments is wellbore heat losses. Initial work on thermal recovery found that a technology base for delivering steam, other hot fluids, and electrical heat through cold subsurface environments, such as permafrost, was in place. No commercially available technologies are available, however. Nevertheless, the enabling technology of superinsulated wells appears to be realized. Thermal subtasks focused on a suite of enhanced recovery options tailored to various reservoir conditions. Generally, electrothermal, conventional steam-based, and thermal gravity drainage enhanced oil recovery techniques appear to be applicable to 'prime' Ugnu reservoir conditions to the extent that reservoir architecture and fluid conditions are modeled faithfully here. The extent of reservoir layering, vertical communication, and subsurface steam distribution are important factors affecting recovery. Distribution of steam throughout reservoir volume is a significant issue facing thermal recovery. Various activities addressed aspects of steam emplacement. Notably, hydraulic fracturing of horizontal steam injection wells and implementation of steam trap control that limits steam entry into hor

Stanford University; Department of Energy Resources Engineering Green Earth Sciences

2007-09-30

292

Composite-second-order improvement of 15 dB in an optically amplified 110-km AM-VSB CATV transport system using chirped fiber grating  

Microsoft Academic Search

To improve system composite-second-order (CSO) of an optically amplified AM-VSB CATV transport system, we investigate the system using chirped fiber grating (CFG) and dispersion-compensating fiber (DCF) separately. We find that the CFG technique is superior to the DCF one in both CSO and carrier-to-noise ratio with satisfied composite-triple-beat performance

J. H. Su; C. C. Lee; W. Y. Guo; F. Y. Tsai; C. S. Wang; Y. k. Tu; Y. K. Chen

1999-01-01

293

Feature extraction by wavelet transforms to analyze the heart rate variability during two meditation techniques  

Microsoft Academic Search

\\u000a In this chapter, we present the analysis of HRV signals by wavelet transform. HRV, described by the extraction of the physiological\\u000a rhythms embedded within its signal, is the tool through which adaptations of activity of the ANS have been widely studied.\\u000a The assessment of wavelet transform (WT) as a feature extraction method was used in representing the electrophysiological\\u000a signals. The

G. Kheder; A. Kachouri; R. Taleb; M. ben Messaoud; M. Samet

294

A wavelet-based technique for discrimination between faults and magnetizing inrush currents in transformers  

Microsoft Academic Search

This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast, and computationally efficient tool. The operating time of the scheme is less than half the power frequency cycle (based on a 5-kHz sampling rate). In this work, a wavelet transform concept is presented.

Omar A. S. Youssef

2003-01-01

295

Current-sharing control technique for interleaving VRMs using intercell transformers  

Microsoft Academic Search

Parallel converter architecture using intercell transformers is one of the most adapted architecture for low-voltage, high-current and fast transient power conversion applications. Interleaved buck converter with intercell transformers main interest is the current ripple reduction in each converter arms which is not the case with non-coupled inductor architectures. As a consequence, current constraints on switches and inductors are less severe

Mathieu Le Bolloch; Marc Cousineau; Thierry Meynard

2009-01-01

296

Monolithic optical parametric oscillator using chirped quasi-phase matching  

NASA Astrophysics Data System (ADS)

We describe a highly efficient monolithic, Q-switched, nanosecond optical parametric oscillator based on a magnesium-oxide-doped periodically poled lithium niobate crystal and containing multiple quasi-phase-matched gratings. The crystal consisted of a single unchirped grating and five gratings containing progressively increasing amounts of longitudinal chirp. The monolithic design makes the device highly compact, stable, and robust, and it demonstrated a pump-to-signal conversion efficiency of around 50%, generating 50 ?J pulses at 1.55 ?m with a spectral bandwidth of 20 nm. Sonogram traces are presented showing the effect of crystal chirp on the temporal and spectral performance.

Tillman, Karl A.; Reid, Derryck T.

2007-06-01

297

Chirped gratings for efficient coupling into nonlinear waveguides  

NASA Astrophysics Data System (ADS)

The efficiency of chirped gratings used as couplers for nonlinear optics interactions in waveguide geometries was demonstrated. A uniform periodicity grating with a chirp rate of about 0.004 over a 2-mm-long grating was fabricated using the procedure of Xu Mai et al. (1985). Coupling efficiency for this grating illuminated with a 2-mm-diam laser beam at a wavelength of 0.515 micron showed an optimum of about 29 percent (a large value even for a linear coupler) occurring near 1500 mW input power.

Moshrefzadeh, R.; Svensson, B.; Xu, Mai; Seaton, C. T.; Stegeman, G. I.

1987-08-01

298

Effects of frequency chirp on magnetron injection locking  

SciTech Connect

The injection locking of a magnetron is theoretically analyzed when either the free running oscillator or the drive signal has a frequency chirp. It is found that complete phase locking of the signal cannot be achieved in either case. However, as long as the locking condition of Adler is well-satisfied instantaneously, a high degree of locking occurs during a major duration of the frequency chirps. The expected output phase variation is computed in terms of the noise in the free-running magnetron oscillator for the case of constant drive frequency.

Pengvanich, P.; Lau, Y. Y.; Luginsland, J. W.; Gilgenbach, R. M.; Cruz, E. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Schamiloglu, E. [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

2008-07-15

299

Chirped-pulse amplification of laser pulses with dispersive mirrors.  

PubMed

We report a novel implementation of chirped-pulse amplification (CPA) by dominantly using dispersive multilayer mirrors for chirp control. Our prototyp dispersive-mirror (DMC) compressor has been designed for a kHz Ti:sapphire amplifier and yielded--in a proof-of-concept study--millijoule-energy, sub-20-fs, 790-nm laser pulses with an overall throughput of approximately 90% and unprecedented spatio-temporal quality. Dispersive-mirror-based CPA permits a dramatic simplification of high-power lasers and affords promise for their advancement to shorter pulse durations, higher peak powers, and higher average powers with user-friendly systems. PMID:20372657

Pervak, V; Ahmad, I; Trushin, S A; Major, Zs; Apolonski, A; Karsch, S; Krausz, F

2009-10-12

300

Nanostrain measurement using chirped Bragg grating Fabry-Perot interferometer  

NASA Astrophysics Data System (ADS)

A simple nanostrain direct current (DC) measurement system based on a chirped Bragg grating Fabry-Perot (FP) structure is presented. The FP cavity, formed between the chirped fiber Bragg grating (CFBG) and the fiber end face, presents an aperiodic behavior due to the CFBG. A laser located in the fringe pattern slope is used to interrogate the sensing head. The optical power parameter is analyzed when strain is applied, for long and short period fringe pattern wavelengths, and sensitivities of -2.87 ?W/?? and -5.48 ?W/?? are respectively obtained. This configuration presents a resolution of 70 n?.

Silva, Ricardo M.; Ferreira, Marta S.; Santos, José L.; Frazão, Orlando

2012-03-01

301

Analysis in the instantaneous frequency forms of a chirped laser pulse  

SciTech Connect

We analyze two forms of the instantaneous frequency of a linearly chirped laser pulse. Using a 3D test particle simulation, numerical results are presented for electrons accelerated by a chirped laser pulse with these two linearly chirped forms of the instantaneous frequency. We summarize that the linearly chirped frequency, {omega}(t)={omega}{sub 0}[1-{alpha}(t-z/c)] is reasonable, {omega}{sub 0} is laser frequency at z=0 and t=0, and {alpha} is the frequency chirp parameter.

Yuan, C. J.; Wu, X. Y.; Wang, P. X. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education, China and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); Wang, J. X. [State Key Laboratory of Precision Spectroscopy and Department of Physics, East China Normal University, Shanghai 200062 (China)

2011-10-15

302

SEASONAL AND DAILY CHIRPING CYCLES IN THE NORTHERN SPRING AND FALL FIELD CRICKETS, GRYLLUS VELETIS AND G. PENNSYLVANICU S1  

Microsoft Academic Search

In southeastern Michigan, Gryllus veletis chirps from mid-May until early August, barely or not at all overlapping with its sympatric sibling, G. pennsylvanicus, which chirps from early August until mid-November. When nights are warm, both species chirp chiefly at night; when nights are cold, they chirp solely by day. SEASONAL RELATIONSHIP OF ADULT POPULATIONS

RICHARD D. ALEXANDER; GERALD H. MERAL

303

A broadband Fourier-transform microwave spectrometer with laser ablation source: The rotational spectrum of nicotinic acid  

NASA Astrophysics Data System (ADS)

A chirped pulse Fourier transform microwave spectrometer (CP-FTMW) has been combined with a laser ablation source to investigate the broadband rotational spectra of solid biomolecules in the 6.0-18 GHz region. This technique has been successfully applied to the conformational study of nicotinic acid for which two conformers have been characterized for the first time in the gas phase. The quadrupole hyperfine structure originated by a 14N nucleus has been completely resolved for both rotamers using a LA-MB-FTMW spectrometer.

Mata, S.; Peña, I.; Cabezas, C.; López, J. C.; Alonso, J. L.

2012-10-01

304

Broadband absorption bleaching in chirped InGaAs quantum dot semiconductor optical amplifier operating at 1211-1285 nm  

NASA Astrophysics Data System (ADS)

We report on photoinduced absorption bleaching of InAs/InGaAs chirped quantum dot semiconductor optical amplifier (QD SOA) waveguide devices investigated by the traditional femtosecond pump-probe technique applied for a waveguide configuration. To gain broader spectra for the device a chirped QD structure including three groups of quantum dots each dedicated to a ground state transition at wavelength 1285, 1243 and 1211 nm was designed. Photoinduced transmission spectra consisting of ground state transition for the groups of QD's involved showed coincidence with the electroluminescence spectra and even more exceeded to longer wavelength. From photoinduced transmission kinetics absorption recovery in the range of picoseconds was considered. For comparison a device with typical high photoinduced absorption demonstrating large suppression of absorption bleaching was shown and interpreted.

Jelmakas, E.; Tomaši?nas, R.; Vengris, M.; Rafailov, E.; Krestnikov, I.

2013-10-01

305

Discrete techniques for 3D digital images and patterns under transformations  

NASA Astrophysics Data System (ADS)

Three dimensional (3-D) digital images and patterns under transformations are facilitated by the splitting-shooting method (SSM) and the splitting-integrating method (SIM). The combination (CSIM) of SSM and SIM and the combination (CIIM) of SIM and SIM are proposed for a cycle conversion T-1T, where T is a nonlinear transformation, and T-1 is its inverse transformation. This paper focuses on exploitation of accuracy of the obtained image greyness. In our discrete algorithms, let a 3-D pixel be split into N3 subpixels. The convergence rates of sequential errors can be denoted by O(1/Nk), k >= 1. High convergence rates indicate less CPU time needed. Both error bounds and computation of pixel greyness have shown the following important conclusions: (1) O(1/N) for CSIM; (2) O(1/N) or O(1/N2) for CIIM; (3) O(1/N3) for CIIM using quadratic B-spline functions in antialiasing images.

Li, Zi C.

1993-01-01

306

Discrete techniques for 3-D digital images and patterns under transformation.  

PubMed

Three-dimensional (3-D) digital images and patterns under transformations are facilitated by the splitting-shooting method (SSM) and the splitting-integration method (SIM). The combination (CSIM) of using both SSM and SIM and two combinations (CIIM) of using SIM only are proposed for a cycle conversion T(-1)T, where T is a nonlinear transformation, and T(-1) is its inverse transformation. This paper focuses on exploitation of accuracy of obtained image greyness. In our discrete algorithms, letting a 3-D pixel be split into N(3) subpixels, the convergence rates, O(1/N), O(1/N(2)), and O(1/N (3)), of sequential error can be achieved by the three combinations respectively. High convergence rates indicate less CPU time needed. Both error bounds and computation of pixel greyness have shown the significance of the proposed new algorithms. PMID:18256009

Li, Z C

1998-01-01

307

Study of optical phase change measurement using the Hilbert Transform and interferometric techniques  

NASA Astrophysics Data System (ADS)

Advances in the fields of optics and optical communications have created a demand for effectively measuring relative phase changes along an optical path or within an optical system. We present a method for obtaining these measurements using an interferometric setup with processing involving Empirical Mode Decomposition and the Hilbert Transform. In this work, the Hilbert Transform algorithm is justified by accurately measuring the phase changes in software generated signals. Progress and improvements are shown regarding the ongoing design and implementation of an experimental benchtop setup. This testbed will prove the method in applications such as measuring and recording phase changes caused by propagating light through a turbulent freespace channel.

Duperre, Joseph A., III; Font, Carlos O.; Gilbreath, G. Charmaine; Bonanno, David; Tarpara, Eshani; Golden, Alexander

2011-02-01

308

Electrochemical noise analysis of LY12-T3 in EXCO solution by discrete wavelet transform technique  

Microsoft Academic Search

Electrochemical noise technique coupled with SEM was used to study the corrosion process of LY12-T3 in the modulated EXCO test solution, and the EN data were analyzed by wavelet technique based on orthogonal db4 wavelet. The results show that, under the experimental conditions, the characteristics of energy distribution plot (EDP) obtained from wavelet analysis technique can be used as “fingerprints”

F. H Cao; Z. Zhang; J. X Su; Y. Y Shi; J. Q Zhang

2006-01-01

309

Influence of nonideal chirped fiber grating characteristics on dispersion cancellation  

Microsoft Academic Search

The effect of nonideal dispersion and reflection characteristics of chirped fiber gratings on the performance of 10-Gb\\/s nonreturn-to-zero-transmission systems operating over standard fiber is investigated. The system penalty for different amplitude and period ripples are quantified. Analyses of an experimental grating confirm that current fabrication technology can meet the requirements for <1-dB-penalty operation

K. Ennser; M. Ibsen; M. Durkin; M. N. Zervas; R. I. Laming

1998-01-01

310

Mechanism of inverted-chirp infrasonic radiation from sprites  

Microsoft Academic Search

Farges and Blanc (2010) reported inverted-chirp infrasonic signals with high frequencies arriving before low frequencies, possibly emitted by sprite discharges and observed on the ground at close range (<100 km) from the source. In the present work a parallel version of a 2-D FDTD model of infrasound propagation in a realistic atmosphere is applied to demonstrate that the observed morphology

Sebastien de Larquier; Victor P. Pasko

2010-01-01

311

Aggressive Signal in ``Courtship'' Chirps of a Gregarious Cricket  

Microsoft Academic Search

Unlike other known species of crickets, Amphiacusta maya in Central America mates in groups. Experimentally silenced males experience reduced mating success, not owing to decreased receptivity by females, but owing to increased time spent fighting with other males that persistently interrupt silent courtships. Thus, the data indicate that ``courtship'' chirping functions as a warning to other males, rather than as

Christine R. B. Boake; Robert R. Capranica

1982-01-01

312

Chirped fiber Bragg grating sensor based on phase delay  

Microsoft Academic Search

A novel design of linearly chirped fiber Bragg grating (LCFBG) based sensor, operating at a single optical wavelength and avoiding the complicated interrogation, is presented and demonstrated. The LCFBG exhibits a good linear relation between the group delay and the wavelength. When a pulsed optical signal goes through the LCFBG with a fixed wavelength within the grating bandwidth, it will

Qizhen Sun; Deming Liu; Hairong Liu; Li Xia; Ping Shum

2007-01-01

313

A Novel Chirp Slope Keying Modulation Scheme for Underwater Communication  

Microsoft Academic Search

A digital modulation method using Chirp-Slope Keying (CSK) is developed for coherent underwater acoustic communications. Effective signal detection is a critical stage in the implementation of any communications system; we will see that CSK solves some significant challenges to reliable detection. This thesis is primarily based on analyzing the effectiveness of CSK through simulations using Matlab's Simulink for underwater communications.

Lastri Simanjuntak

2004-01-01

314

Experience of using the Chirp distributed file system in ATLAS  

NASA Astrophysics Data System (ADS)

Chirp is a user-level file system specifically designed for the wide area network, and developed by the University of Notre Dame CCL group. We describe the design features making it particularly suited to the Grid environment, and to ATLAS use cases. The deployment and usage within ATLAS distributed computing are discussed, together with scaling tests and evaluation for the various use cases.

Walker, Rodney; Nilsson, Paul

2012-12-01

315

Analysis of the Rayleigh-Plesset equation with chirp excitation  

NASA Astrophysics Data System (ADS)

The case of a bubble being insonified by an ultrasonic excitation in the form of a linear chirp is considered here. The dynamical equation of the bubble's motion is solved analytically and compared to a numerical solution. The analytical solution is then used to investigate the problem of maximizing the amplitude of the second harmonic with respect to the various system and signal parameters.

Barlow, Euan; Mulholland, Anthony J.; Gachagan, Anthony; Nordon, Alison; MacPherson, Kenneth

2009-02-01

316

A frequency based encoding technique for transformation of categorical variables in mixed IVF dataset  

Microsoft Academic Search

Implantation prediction of in-vitro fertilization (IVF) embryos is critical for the success of the treatment. In this study, support vector machine (SVM) method has been used on an original IVF dataset for classification of embryos according to implantation potentials. The dataset we analyzed includes both categorical and continuous feature values. Transformation of categorical variables into numeric attributes is an important

Asli Uyar; Ayse Bener; H. Nadir Ciray; Mustafa Bahceci

2009-01-01

317

A wavelet-based technique for discrimination between faults and magnetising inrush currents in transformers  

Microsoft Academic Search

Summary form only given, as follows. This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast and computationally efficient tool. The operating time of the scheme is less than half power frequency cycle (based on 5 kHz sampling rate). In this work, a

O. A. S. Youssef

2002-01-01

318

A NEURO-FUZZY TECHNIQUE FOR DISCRIMINATION BETWEEN INTERNAL FAULTS AND MAGNETIZING INRUSH CURRENTS IN TRANSFORMERS  

Microsoft Academic Search

This paper presents the application of the fuzzy-neuro method to investigate transformer inrush current. Recently, the frequency environment of power systems has been made more complicated and the magnitude of the second harmonic in inrush current has been decreased because of the improvement of cast steel. Therefore, traditional approaches will likely mal-operate in the case of magnetizing inrush with low

H. KHORASHADI-ZADEH; M. R. AGHAEBRAHIMI

2005-01-01

319

A flow-through Hankel transform technique for rapid, accurate Green's function computation  

Microsoft Academic Search

Layered Earth Green's functions play a central role in modeling the electromagnetic (EM) response of mineral exploration targets, both as the implicit basis of distributed source field computations and for integral equation and hybrid three-dimensional (3-D) formulations. They are computed as the Hankel transforms of analytic kernels. Computational precision can depend upon the choice of algebraically equivalent forms by which

Art Raiche

1999-01-01

320

Electrochemical technique and copper-promoted transformations: selective hydroxylation and amination of arylboronic acids.  

PubMed

An efficient and selective electrosynthesis of phenols and anilines from arylboronic acids in aqueous ammonia is achieved in an undivided cell. By simply changing the concentration of aqueous ammonia and the anode potential, good yields of phenols and anilines can be obtained chemoselectively with high reaction rates. We propose that anodic oxidation could have played an important role in these transformations. PMID:23808633

Qi, Hong-Lin; Chen, Dong-Song; Ye, Jian-Shan; Huang, Jing-Mei

2013-07-11

321

Combining Source Transformation and Operator Overloading Techniques to Compute Derivatives for MATLAB Programs  

Microsoft Academic Search

Derivatives of mathematical functions play a key role in various areas of numerical and technical computing. Many of these computations are done in MATLAB, a popular environment for technical computing providing engineers and scientists with capabilities for mathematical computing, analysis, visualization, and algorithmic development. For functions written in the MATLAB language, a novel software tool is proposed to automatically transform

Christian H. Bischof; H. Martin Bücker; Bruno Lang; Arno Rasch; Andre Vehreschild

2002-01-01

322

High efficiency, monolithic fiber chirped pulse amplification system for high energy femtosecond pulse generation.  

PubMed

A novel monolithic fiber-optic chirped pulse amplification (CPA) system for high energy, femtosecond pulse generation is proposed and experimentally demonstrated. By employing a high gain amplifier comprising merely 20 cm of high efficiency media (HEM) gain fiber, an optimal balance of output pulse energy, optical efficiency, and B-integral is achieved. The HEM amplifier is fabricated from erbium-doped phosphate glass fiber and yields gain of 1.443 dB/cm with slope efficiency >45%. We experimentally demonstrate near diffraction-limited beam quality and near transform-limited femtosecond pulse quality at 1.55 µm wavelength. With pulse energy >100 µJ and pulse duration of 636 fs (FWHM), the peak power is estimated to be ~160 MW. NAVAIR Public Release Distribution Statement A-"Approved for Public release; distribution is unlimited". PMID:24150384

Peng, Xiang; Kim, Kyungbum; Mielke, Michael; Jennings, Stephen; Masor, Gordon; Stohl, Dave; Chavez-Pirson, Arturo; Nguyen, Dan T; Rhonehouse, Dan; Zong, Jie; Churin, Dmitriy; Peyghambarian, N

2013-10-21

323

Data reconstructing for windowing broom Fourier transform imaging spectrometers based on multi-core techniques  

NASA Astrophysics Data System (ADS)

The windowing broom Fourier transform imaging spectrometer, based on space-time modulation, has the characteristics of high luminous flux, static interference part etc. However, the large amount of raw data and the data reconstruction increase the difficulty of the whole data processing and extend the computing time. In this paper, a parallel calculation algorithm for reconstruction of raw data is proposed. The proposed algorithm is achieved by using Task Parallel Library (TPL), which is provided by .NET framework, and a visualized processing system is further established. A set of data collected from a windowing broom Fourier transform imaging spectrometer is processed using both the proposed method and the ordinary serial algorithm. The scalability of this presented algorithm is verified by employing it on computers with different number of cores. The experimental results show that, compared to the serial algorithm, the proposed method can greatly speed up the processing with the same hardware condition, and it also has ideal scalability with different hardware.

Dong, Zhi-gang; Liao, Ning-fang; Qu, Liang; Lv, Hang

2013-08-01

324

Phase transformations in methanol at high pressure measured by dielectric spectroscopy technique  

NASA Astrophysics Data System (ADS)

The dielectric response in methanol measured in wide pressure and temperature ranges (P < 6.0 GPa; 100 K < T < 360 K) reveals a series of anomalies which can be interpreted as a transformation between several solid phases of methanol including a hitherto unknown high-pressure low-temperature phase with the stability range P > 1.2 GPa and T < 270 K. In the intermediate P-T region P ~ 3.4-3.7 GPa, T ~ 260-280 K, a set of complicated structural transformations occurs involving four methanol crystalline structures. At higher pressures within the narrow range P ~ 4.3-4.5 GPa methanol can be obtained in the form of fragile glass (Tg ~ 200 K, mp ~ 80 at P = 4.5 GPa) by relatively slow cooling.

Kondrin, M. V.; Pronin, A. A.; Lebed, Y. B.; Brazhkin, V. V.

2013-08-01

325

Advanced diagnostic\\/prognostic reasoning and evidence transformation techniques for improved avionics maintenance  

Microsoft Academic Search

Techniques used in the design and implementation of modern avionics suggest an opportunity to re-examine the maintenance and repair process for current and future systems. The authors have developed a framework with automated evidence collection, data representation and storage, and, advanced automated reasoning techniques to implement within an avionics health management system. This paradigm shift approach utilizes advanced capture and

Carl S. Byington; P. W. Kalgren; Brian K. Dunkin; Bryan P. Donovan

2004-01-01

326

Comparison of SAR processing SPECAN techniques for efficient ScanSAR image generation  

NASA Astrophysics Data System (ADS)

Recently developed Scanning Synthetic Aperture Radar (ScanSAR) instruments require new algorithms for the processing stages because the classical approaches to SAR image generation are not well suited to ScanSAR data. Therefore, other techniques must be investigated. Spectral Analysis (SPECAN) is an efficient implementation of chirp de-correlation and it is specially well adapted to ScanSAR bursts of data. It consists of deramping and a spectral analysis stage that can be implemented by several techniques. One of them is Fast Fourier Transform (FFT) that is very efficient but presents some drawbacks concerning pixel spacing. A recently proposed method is the Chirp Z-Transform (CZT) SPECAN that obtains spectrum information at arbitrary positions. CZT can be efficiently implemented by FFTs and mixing operations and it provides the desired flexibility to the user. The main contribution of this study is the analysis of SPECAN techniques for processing ScanSAR data by comparing spectral estimation methods and new multilook strategies. The new CZT-SPECAN technique is compared with the classical SPECAN approach showing its advantages avoiding interpolation steps. The new multilook strategy implemented by SPECAN also reduces the scalloping effect. The results show that the new method is very promising for obtaining fast and simple ScanSAR image generation.

Vidal-Pantaleoni, Ana; Ferrando, Miguel

1998-11-01

327

The Development and Implementation of Chirped-Pulse Frequency Combs at Millimeter Wavelengths  

NASA Astrophysics Data System (ADS)

Technological advances in such areas as active multiplier chains and high-speed digital electronics are enabling the development of sensitive high-throughput spectroscopic instruments in the millimeter and submillimeter ranges. Recently there has been an effort to develop multiplexed direct absorption spectroscopy techniques that use frequency comb sources derived from phase-locked pulse trains (often created using ultrafast lasers). We have used a high-speed arbitrary waveform generator (AWG with 12 GHz sample rate) to create frequency combs at mm-wave wavelengths using a chirped pulse as the repeating waveform. This waveform has important advantages including 100% duty cycle for the light output and compatibility with the use of frequency multiplier chains that extend the bandwidth of the comb proportional to the frequency multiplication factor. A new spectrometer operating in the 260-290 GHz range using active multiplier chains has been constructed to test the capabilities of chirped-pulse frequency comb spectroscopy for molecular rotational spectroscopy. The spectral properties of the mm-wave combs generated following x24 frequency multiplication, methods for compressed bandwidth detection using a dual-comb approach, and frequency comb analogs of FM spectroscopy will be presented.

Steber, Amanda L.; Harris, Brent J.; Neill, Justin L.; Lehmann, Kevin K.; Pate, Brooks H.

2012-06-01

328

Frequency-domain ``single-shot'' ultrafast transient absorption spectroscopy using chirped laser pulses  

NASA Astrophysics Data System (ADS)

Single-shot ultrafast transient absorbance spectroscopy based on the frequency encoding of kinetics is demonstrated. The kinetics are sampled in the frequency domain using linearly chirped, amplified 33 fs pulses derived from a Ti:sapphire laser. A variable length grating pair compressor is used to achieve sampling of 512 channels with a 2-160 ps window with sensitivity>5×10-4. In terms of the acquisition time, frequency-domain ``single-shot'' (FDSS) spectroscopy has an advantage over pump-probe spectroscopy when ``noise'' is dominated by variations in the amplitude of the signal due to pump and flow instability. Unlike some other single-shot techniques, FDSS can be used for fluid samples flowing in a high-speed jet and for thin solid samples that exhibit interference fringes. Another advantage is that, due to interference of quasimonochromatic components of the chirped probe pulse, an oscillation pattern near the origin of the FDSS kinetics emerges. This pattern is unique and can be used to determine the complex dielectric function of photogenerated species. The advantages of FDSS are illustrated with the kinetics obtained in multiphoton ionization of aqueous iodide and one-photon excitation of polycrystalline ZnSe.

Shkrob, Ilya A.; Oulianov, Dmitri A.; Crowell, Robert A.; Pommeret, Stanislas

2004-07-01

329

Spin-wave storage using chirped control fields in atomic frequency comb-based quantum memory  

NASA Astrophysics Data System (ADS)

It has been shown that an inhomogeneously broadened optical transition shaped into an atomic frequency comb can store a large number of temporal modes of the electromagnetic field at the single-photon level without the need to increase the optical depth of the storage material. The readout of light modes is made efficient thanks to the rephasing of the optical-wavelength coherence similar to photon-echo-type techniques, and the reemission time is given by the comb structure. For on-demand readout and long storage times, two control fields are used to transfer the optical coherence back and forth into a spin wave. Here, we present a detailed analysis of the spin-wave storage based on chirped adiabatic control fields. In particular, we verify that chirped fields require significantly weaker intensities than ? pulses. The price to pay is a reduction of the multimode storage capacity that we quantify for realistic material parameters associated with solids doped with rare-earth-metal ions.

Miná?, Ji?í; Sangouard, Nicolas; Afzelius, Mikael; de Riedmatten, Hugues; Gisin, Nicolas

2010-10-01

330

Fractional Fourier transform based image multiplexing and encryption technique for four-color images using input images as keys  

NASA Astrophysics Data System (ADS)

A digital technique for multiplexing and encryption of four RGB images has been proposed using the fractional Fourier transform (FRT). The four input RGB images are first converted into their indexed image formats and subsequently multiplexed into a single image through elementary mathematical steps prior to the encryption. The encryption algorithm uses two random phase masks in the input- and the FRT domain, respectively. These random phase masks are especially designed using the input images. As the encryption is carried out through a single channel, the technique is more compact and faster as compared to the multichannel techniques. Different fractional orders, the random masks in input-, and FRT domain are the keys for decryption as well as de-multiplexing. The algorithms to implement the proposed multiplexing-, and encryption scheme are discussed, and results of digital simulation are presented. Simulation results show that the technique is free from cross-talk. The performance of the proposed technique has also been analyzed against occlusion, noise, and attacks using partial windows of the correct random phase keys. The robustness of the technique against known-, and chosen plain-text attacks has also been explained.

Joshi, Madhusudan; Shakher, Chandra; Singh, Kehar

2010-06-01

331

ISAR imaging of maneuvering targets based on the range centroid Doppler technique.  

PubMed

A new inverse synthetic aperture radar (ISAR) imaging approach is presented for application in situations where the maneuverability of noncooperative target is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial. The proposed algorithm is referred to as the range centroid Doppler (RCD) ISAR imaging technique and is based on the stretch Keystone-Wigner transform (SKWT). The SKWT introduces a stretch weight factor containing a range of chirp rate into the autocorrelation function of each cross-range profile and uses a 1-D interpolation of the phase history which we call stretch keystone formatting. The processing simultaneously eliminates the effects of linear frequency migration for all signal components regardless of their unknown chirp rate in time-frequency plane, but not for the noise or for the cross terms. By utilizing this novel technique, clear ISAR imaging can be achieved for maneuvering targets without an exhaustive search procedure for the motion parameters. Performance comparison is carried out to evaluate the improvement of the RCD technique versus other methods such as the conventional range Doppler (RD) technique, the range instantaneous Doppler (RID) technique, and adaptive joint time-frequency (AJTF) technique. Examples provided demonstrate the effectiveness of the RCD technique with both simulated and experimental ISAR data. PMID:19775968

Lv, Xiaolei; Xing, Mengdao; Wan, Chunru; Zhang, Shouhong

2010-01-01

332

Study of the Q Branch Structure of the 14N and 15N Isotopologues of the ?4 Band of Ammonia Using Frequency Chirped Quantum Cascade Lasers  

NASA Astrophysics Data System (ADS)

Intrapulse quantum cascade (QC) laser spectrometers are able to produce both saturation and molecular alignment of a gas sample owing to the rapid sweep of the radiation through the absorption features. In the QC lasers used to study the 14N and 15N isotopologues of the -4 band of ammonia centered near 1625 cm-1, the variation of the chirp rate during the scan is very large, from ca. 85 to ca. 15 MHz ns-1. In the rapid chirp zone the collisional interaction time of the laser radiation with the gas molecules is short, and large rapid passage effects are seen, whereas at the slow chirp end the line shape resembles that of a Doppler broadened line. The total scan range of the QC laser of ca. 10 cm-1 is sufficient to allow the spectra of both isotopologues to be recorded and the rapid and slow interactions with the laser radiation to be seen. The rapid passage effects are enhanced by the use of an off axis Herriott cell with an effective path length of 62 m, which allows a buildup of polarization to occur. The effective resolution of the chirped QC laser is ca. 0.012 cm-1 full width at half-maximum in the 1625 cm-1 region. The results of these experiments are compared with those of other studies of the -4 band of ammonia carried out using Fourier transform and Laser Stark spectroscopy. They also demonstrate the versatility of the down chirped QC laser for investigating collisional effects in low pressure gases using long absorbing path lengths.

Duxbury, Geoffrey; Wilson, David; Hay, Kenneth; Langford, Nigel

2013-10-01

333

Efficient quantum-state tomography for quantum-information processing using a two-dimensional Fourier-transform technique  

SciTech Connect

A method of quantum-state tomography for quantum-information processing is described. The method is based on the use of the Fourier-transform technique and involves detection of all the diagonal elements of the density matrix in a one-dimensional experiment and all the off-diagonal elements by a two-dimensional experiment. The method is efficient for a large number of qubits ({>=}5). The proposed method is outlined using a two-qubit system and demonstrated using simulations by tomographing arbitrary complex density matrices of two- and four-qubit systems.

Das, Ranabir; Mahesh, T.S. [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Kumar, Anil [Department of Physics, Indian Institute of Science, Bangalore 560012, (India); Sophisticated Instruments Facility, Indian Institute of Science, Bangalore 560012 (India)

2003-06-01

334

Fourier domain interpolation techniques for synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Spotlight-mode synthetic aperture radar (SAR) produces complex Fourier data points on a polar grid which is offset from dc in the frequency domain. To produce an image in the spatial domain, it is necessary to invert this sampled Fourier data prior to extracting magnitude information. However, the polar format of the data makes this difficult, since there is no known polar FFT. An alternative is to interpolate the complex polar data to a Cartesian grid and then perform the two-dimensional FFT. The magnitude of the resulting data array represents the magnitude of the complex ground reflectivity of the terrain under illumination. The interpolation process can be very computationally intense, with an order two to fifty times that of the FFT. Reducing the computation in the interpolation stage, while maintaining reconstruction quality is the focus of this work. Several 2D interpolation techniques are examined, including nearest neighbor, bilinear, inverse-distance to the nth power, weighted sinc, chirp z-transform, and the newest interpolation algorithm proposed for this problem: the cubic spline. It is found that separable interpolation schemes outperform the more commonly used nearest neighbor and inverse distance algorithms, and that the cubic spline is very competitive in the weighted since interpolator in computation requirements and reconstruction quality. The chirp z-transform is determined to be a good alternative to the classical interpolation-DFT approach.

Mather, B. C.

1986-08-01

335

Synchrony during acoustic interactions in the bushcricket Mecopoda 'Chirper' (Tettigoniidae:Orthoptera) is generated by a combination of chirp-by-chirp resetting and change in intrinsic chirp rate.  

PubMed

In several bushcricket species, individual males synchronise their chirps during acoustic interactions. Synchrony is imperfect with the chirps of one male leading or lagging the other by a few milliseconds. Imperfect synchrony is believed to have evolved in response to female preferences for leading chirps. We investigated the mechanism underlying synchrony in the bushcricket species Mecopoda 'Chirper' from Southern India using playback experiments and simulations of pairwise interactions. We also investigated whether intrinsic chirp period is a good predictor of leading probability during interactions between males. The mechanism underlying synchrony in this species differs from previously reported mechanisms in that it involves both a change in the oscillator's intrinsic rate and resetting on a chirp-by-chirp basis. The form of the phase response curve differs from those of previously reported firefly and bushcricket species including the closely related Malaysian species Mecopoda elongata. Simulations exploring oscillator properties showed that the outcome of pairwise interactions was independent of initial phase and alternation was not possible. Solo intrinsic chirp period was a relatively good predictor of leading probability. However, changing the intrinsic period during interactions could enable males with longer periods to lead during acoustic interactions. PMID:16983544

Nityananda, Vivek; Balakrishnan, Rohini

2006-09-16

336

The Shallow Fault structure of the Incline Village Fault, Lake Tahoe NV, From Offshore Ultra High Resolution CHIRP Profiling and Onshore Paleo-Seismic Trenching.  

NASA Astrophysics Data System (ADS)

The shallow fault structure of the Incline Village fault, Lake Tahoe NV, has been mapped using a combination of sub-meter resolution seismic CHIRP profiling, conventional paleo-seismic trenching on-shore, and shallow remotely operated vehicle (ROV) imagery. The pairing of these geophysical and geologic techniques has provided new insights into the fault history of the active Incline Village fault. These data, combined with previous off-shore surveys of the Stateline and West Tahoe faults, will help constrain the extensional history of the Tahoe Basin. Six new CHIRP dip profiles and three strike profiles were collected this past summer along a submerged, late Pleistocene (19.2 +/- 1.8ka) paleo-terrace just offshore of Incline Village, NV, and show a well-defined normal fault zone with >2m of vertical offset across the paleo-terrace. The sediment draped hanging wall shows evidence of at least one prominent colluvial wedge. A 6+ m paleo-seismic trench was also excavated at the Incline Village Elementary School, some 1000 m from the shoreline, which was sited based on a reconnaissance CHIRP profile collected in 2000. Trenching results are complementary with the chirp profiles and show three colluvial wedges with more than 2 meters of vertical offset for each of the events. These preliminary results have strong implications for understanding the evolution of the Walker Lane dextral shear-zone, which defines the western boundary of the Basin and Range.

Dingler, J. A.; Seitz, G.; Kent, G.; Babcock, J.; Brothers, D.; Karlin, B.; Driscoll, N.; Harding, A.

2004-12-01

337

ATOMIC AND MOLECULAR PHYSICS: Ionization of atoms by chirped attosecond pulses  

NASA Astrophysics Data System (ADS)

We investigate the ionization dynamics of atoms by chirped attosecond pulses using the strong field approximation method. The pulse parameters are carefully chosen in the regime where the strong field approximation method is valid. We analyse the effects of the chirp of attosecond pulses on the energy distributions and the corresponding left-right asymmetry of the ionized electrons. For a single chirped attosecond pulse, the ionized electrons can be redistributed and the left-right asymmetry shows oscillations because of the introduction of the chirp. For time-delayed double attosecond pulses at different intensities with the weaker one chirped, exchanging the order of the two pulses shows a relative shift of the energy spectra, which can be explained by the different effective time delays of different frequency components because of the chirp.

Tan, Fang; Peng, Liang-You; Gong, Qi-Huang

2009-11-01

338

Dense monoenergetic proton beams from chirped laser-plasma interaction.  

PubMed

Interaction of a frequency-chirped laser pulse with single protons and a hydrogen gas target is studied analytically and by means of particle-in-cell simulations, respectively. The feasibility of generating ultraintense (10(7) particles per bunch) and phase-space collimated beams of protons (energy spread of about 1%) is demonstrated. Phase synchronization of the protons and the laser field, guaranteed by the appropriate chirping of the laser pulse, allows the particles to gain sufficient kinetic energy (around 250 MeV) required for such applications as hadron cancer therapy, from state-of-the-art laser systems of intensities of the order of 10(21) W/cm(2). PMID:22107638

Galow, Benjamin J; Salamin, Yousef I; Liseykina, Tatyana V; Harman, Zoltán; Keitel, Christoph H

2011-10-27

339

Excitation of the Morse oscillator by an ultrashort chirped pulse  

SciTech Connect

The excitation of the classic Morse oscillator by an ultrashort electromagnetic pulse with a linear frequency chirp is studied theoretically. Formulas are derived for the oscillation amplitude and the radiation power averaged over a period as functions of the excitation energy for free oscillations of the Morse oscillator. Analytical expressions for describing the oscillator motion after the end of the pulse are obtained in the harmonic limit. In the general case of arbitrary parameters of the problem, the specific features of an excited Morse oscillator are analyzed numerically. Prominence is given to the effect of chirp on the excitation energy. The consideration is performed in terms of dimensionless variables, which makes it possible to apply the results obtained to a wide range of molecular systems and exciting-pulse parameters.

Astapenko, V. A., E-mail: astval@mail.ru; Romadanovskii, M. S. [Moscow Institute of Physics and Technology (Russian Federation)

2010-03-15

340

Interaction of strongly chirped pulses with two-level atoms  

SciTech Connect

We study the effect of ultrachirped pulses on the population inversion of two-level atoms. Ultrachirped pulses are defined as those for which the frequency chirp is of the order of the transition frequency of the two-level atom. When the chirp is large enough, the resonance may be crossed twice, for positive and negative frequencies. In fact the decomposition of the field into amplitude and phase factors, and the corresponding definition of the instantaneous frequency, are not unique. The interaction pictures for different decomposition are strictly equivalent, but only as long as approximations are not applied. The domain of validity of the formal rotating wave approximation is dramatically enhanced by a suitable choice, the so-called analytic signal representation.

Ibanez, S.; Peralta Conde, A.; Muga, J. G. [Departamento de Quimica Fisica, Universidad del Pais Vasco - Euskal Herriko Unibertsitatea, Apdo. 644, Bilbao (Spain); Guery-Odelin, D. [Laboratoire Collisions Agregats Reactivite, CNRS UMR 5589, IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F-31062 Toulouse CEDEX 4 (France)

2011-07-15

341

Study of chirped pulse amplification based on Raman backscattering  

NASA Astrophysics Data System (ADS)

Raman backscattering (RBS) in plasma is an attractive source of intense, ultrashort laser pulses, which has the potential asa basic for a new generation of laser amplifiers.1 Taking advantage of plasma, which can withstand extremely high power densities and can offer high efficiencies over short distances, Raman amplification in plasma could lead to significant reductions in both size and cost of high power laser systems. Chirped laser pulse amplification through RBS could be an effective way to transfer energy from a long pump pulse to a resonant counter propagating short probe pulse. The probe pulse is spectrally broadened in a controlled manner through self-phase modulation. Mechanism of chirped pulse Raman amplification has been studied, and features of supperradiant growth associated with the nonlinear stage are observed in the linear regime. Gain measurements are briefly summarized. The experimental measurements are in qualitative agreement with simulations and theoretical predictions.

Yang, X.; Vieux, G.; Lyachev, A.; Farmer, J.; Raj, G.; Ersfeld, B.; Brunetti, E.; Wiggins, M.; Issac, R.; Jaroszynski, D. A.

2009-05-01

342

Controlling the femtosecond laser-driven transformation of dicyclopentadiene into cyclopentadiene  

PubMed Central

Dynamics of the chemical transformation of dicyclopentadiene into cyclopentadiene in a supersonic molecular beam is elucidated using femtosecond time-resolved degenerate pump–probe mass spectrometry. Control of this ultrafast chemical reaction is achieved by using linearly chirped frequency modulated pulses. We show that negatively chirped femtosecond laser pulses enhance the cyclopentadiene photo-product yield by an order of magnitude as compared to that of the unmodulated or the positively chirped pulses. This demonstrates that the phase structure of femtosecond laser pulse plays an important role in determining the outcome of a chemical reaction.

Goswami, Tapas; Das, Dipak K.; Goswami, Debabrata

2013-01-01

343

Evaluation of small-angle scattering data of charged particles using the generalized indirect Fourier transformation technique  

NASA Astrophysics Data System (ADS)

Small-angle x-ray and neutron scattering are widely used techniques to study the structure of colloidal particles in the size range up to 100 nm. The indirect Fourier transformation technique is well established to obtain model free real space information, but the interpretation of the results is limited to cases where particle interaction can be neglected. The extended generalized indirect Fourier transform (GIFT) allows one to separate inter- and intraparticle effects, but needs models for the particle interaction. We present the application of three different models for the calculation of interaction effects of charged particles, represented by the structure factor. With this extension, useful real space information can be obtained by the GIFT method for solutions with volume fractions up to about 0.3 without any assumption for the shape of the particles. Only the interaction effects need a model assumption, and the parameters determined from this model can give some additional information. Simulations show that it is impossible to determine charge and ionic strength simultaneously. There exists another ambiguity between the parameter sets for charge, radius, and volume fraction, but we show how this problem can be overcome in most cases. The practical applicability of the method is demonstrated by means of the micellar system CTAB in different concentrations from 1% up to 20% and with varying amounts of added salt to screen the charges and change the particle shape.

Fritz, G.; Bergmann, A.; Glatter, O.

2000-12-01

344

Excitation of Rydberg wave packets with chirped laser pulses  

NASA Astrophysics Data System (ADS)

We study Rydberg wave packets produced by pairs of time separated femtosecond laser pulses. The time separation ranges from femtosecond to picosecond time scales. The wave packets consist predominantly of f states of principal quantum numbers n=22-32 in Li. With a direct analysis of the field ionization spectra the n-level-resolved classical orbit times are displayed. By chirping the second excitation pulse we demonstrate controlled amplitude oscillations of n-level amplitudes on femtosecond time scales.

Preclíková, J.; Kozák, M.; Fregenal, D.; Frette, Ø.; Hamre, B.; Hjertaker, B. T.; Hansen, J. P.; Kocbach, L.

2012-12-01

345

Multimillijoule chirped parametric amplification of few-cycle pulses  

Microsoft Academic Search

The concept of optical parametric chirped-pulse amplification is applied to attain pulses with energies up to 8 mJ and a bandwidth of more than 100 THz. Stretched broadband seed pulses from a Ti:sapphire oscillator are amplified in a multistage noncollinear type I phase-matched beta-barium borate parametric amplifier by use of an independent picosecond laser with lock-to-clock repetition rate synchronization. Partial

N. Ishii; L. Turi; V. S. Yakovlev; T. Fuji; F. Krausz; A. Baltuska; R. Butkus; G. Veitas; V. Smilgevicius; R. Danielius; A. Piskarskas

2005-01-01

346

Chirping a two-photon transition in a multistate ladder  

SciTech Connect

We consider a two-photon transition in a specific ladder system driven by a chirped laser pulse. In the weak field limit, we find that the excited state probability amplitude arises due to interference of multiple quantum paths which are weighted by quadratic phase factors. The excited state population has the form of a Gauss sum which plays a prominent role in number theory.

Merkel, Wolfgang; Mack, Holger; Schleich, Wolfgang P.; Lutz, Eric; Paulus, Gerhard G.; Girard, Bertrand [Institut fuer Quantenphysik, Universitaet Ulm, Albert-Einstein-Allee 11, D-89081 Ulm (Germany) and Department of Physics, Universitaet Augsburg, D-86135 Augsburg (Germany) and Department of Physics, Texas A and M University, College Station, Texas 77843 (United States) and Laboratoire de Collisions, Agregats et Reactivite - UMR 5589, CNRS-Universite Paul Sabatier Toulouse 3, IRSAMC, Toulouse (France)

2007-08-15

347

Research on Cascaded Chirp Fiber Bragg Grating in Quasi-linear Optical Transmission System  

NASA Astrophysics Data System (ADS)

A Cascaded chirp fiber Bragg grating has been theoretical analyzed by using coupled mode equations and transfer matrix method. As a dispersion compensator, a wide bandwidth, big dispersion value, and low delay ripple cascaded chirp fiber Bragg grating is designed for a 200 km 8 × 160 Gbit/s high speed quasi-linear optical transmission system. The system Q value of 7.15˜8.74 demonstrates the success of the design of the cascaded chirp fiber Bragg grating.

Cai, Ju; Bai, Qiujian; Su, Xin

2013-09-01

348

Advanced microtomography combined synchrotron x-ray diffraction techniques for phase transformation researches in amorphous materials under pressure  

NASA Astrophysics Data System (ADS)

Advanced tomographic and x-ray diffraction techniques have attracted more attentions in mineral physics community in these years. In a recent collaborative project in APS of Argonne National Laboratory, we discovered unexpected dynamics and volume expansion associated with pressure-induced crystallization of amorphous Se by using novel high-pressure diamond anvil cell microtomography and x-ray diffraction techniques. The unusual volume expansion phenomenon under pressure associated with the recrystallization of over-pressurization of a metastable phase was found, which may be more common than previously believed. Tuning relative densities and energetics of phases under pressure may provide a new route for creating new structures from highly metastable states. The new microtomographic technique could find widespread use in determinations of the equation of state of glasses and melts under pressures, which is crucial to many problems in earth sciences. The importance of using advanced time-resolved or spatially-resolved high-pressure x-ray diffraction and imaging techniques will be emphasized. This will improve our understanding of the kinetics of structural transformations in minerals under extreme conditions far from equilibrium.

Wang, L.; Liu, H.

2009-12-01

349

Chirped holographic grating used as the dispersive element in an optical spectrometer  

NASA Astrophysics Data System (ADS)

We have developed a new design of optical spectrometer based on the use of a chirped holographic grating inscribed on a flat substrate. This type of grating has a surface modulation with a spatially varying period. The ability of the chirped grating to focus a beam is exploited to reduce significantly the physical dimensions of the instrument. Wavelength selection is achieved by a pure translation of the chirped grating. The properties of the chirped grating spectrometer have been characterized with different lasers and arc lamps and compared with those of two commercial spectrometers. A performance parameter has been defined, enabling the various instruments to be compared.

Fortin, Gilles; McCarthy, Nathalie

2005-08-01

350

Modified isotope pairing technique to study N transformations in polluted aquatic systems: theory.  

PubMed

Denitrification of nitrate in sediments of polluted aquatic systems has the potential to release considerable nitrogen amounts into the atmosphere in the form of dinitrogen (N2) and/or nitrous oxide (N2O). Nitrate may diffuse into the anoxic sediment layer either from the oxic sediment layer (after being produced there by nitrifiers) or directly from the overlying water. Currently, the most common technique that explicitly distinguishes between the two main nitrate sources is the Isotope Pairing Technique (IPT). 15N-labeled nitrate is added to the water column, and formation of 15N labeled N2 molecules is subsequently monitored. The main shortcoming of the IPT is that the formation of N20 is ignored, thus resulting in an underestimation of sediment denitrification. Another limitation is the inability to account for a possible influx of nitrate through the hyporheic zone (e.g., nitrate-polluted groundwater) into the anoxic sediment layer. We have further developed and analyzed the theoretical basis of the original IPT. The two important factors that we took into account are the isotopic composition of N20 and the input of an external source of nitrate. We also examined the option of adding 15N-labeled ammonium to the water column to specifically adjustthe technique to field studies. The presented modified technique allows us to (i) improve the estimation of sediment denitrification capacity, (ii) gain an insight into the N20 formation mechanism(s) and fluxes, and (iii) assess inputs of nitrate-polluted water through the hyporheic zone. PMID:15819234

Master, Y; Shavit, U; Shaviv, A

2005-03-15

351

The use of the fractional Fourier transform with coded excitation in ultrasound imaging.  

PubMed

Medical ultrasound systems are limited by a tradeoff between axial resolution and the maximum imaging depth which may be achieved. The technique of coded excitation has been used extensively in the field of RADAR and SONAR for some time, but has only relatively recently been exploited in the area of medical ultrasound. This technique is attractive because allows the relationship between the pulse length and the maximum achievable spatial resolution to be changed. The work presented here explores the possibility of using the fractional Fourier transform as an effective means for the processing of signals received after the transmission of linear frequency modulated chirps. Results are presented which demonstrate that this technique is able to offer spatial resolutions similar to those obtained with a single cycle duration signal. PMID:16602583

Bennett, Michael J; McLaughlin, Steve; Anderson, Tom; McDicken, Norman

2006-04-01

352

Chirped femtosecond solitons and double-kink solitons in the cubic-quintic nonlinear Schroedinger equation with self-steepening and self-frequency shift  

SciTech Connect

We demonstrate that the competing cubic-quintic nonlinearity induces propagating solitonlike dark(bright) solitons and double-kink solitons in the nonlinear Schroedinger equation with self-steepening and self-frequency shift. Parameter domains are delineated in which these optical solitons exist. Also, fractional-transform solitons are explored for this model. It is shown that the nonlinear chirp associated with each of these optical pulses is directly proportional to the intensity of the wave and saturates at some finite value as the retarded time approaches its asymptotic value. We further show that the amplitude of the chirping can be controlled by varying the self-steepening term and self-frequency shift.

Alka,; Goyal, Amit; Gupta, Rama; Kumar, C. N.; Raju, Thokala Soloman [Department of Physics, Panjab University, Chandigarh 160 014 (India); Department of Physics, Karunya University, Coimbatore 641 114 (India)

2011-12-15

353

PI film property analysis in the application of infrared image transform technique  

NASA Astrophysics Data System (ADS)

Modern infrared focal plane arrays (IR FPA) with high dynamic range, and multiband versions are being deployed in fielded systems. It needs to develop advanced scene projection technology to operate both in laboratory testing for hardware-in-the-loop simulation and validation of fielded units immediately prior to mission use. One of the fiber array visible to infrared imaging transducer is introduced. Different from the fiber bundle, the fiber array is etched on the substrate material. The property of transducer is determined by the substrate material. Polyimide (PI) film has the property of high dynamic range for temperature resistant, electric insulating, radiation resistant, good thermosetting and thermomechanical effect. The heat diffusion property of PI film is analyzed by experimental study. For experimental study, samples of with sputtered graphite on surface and different thickness of PI film were made. Using the visible light irradiate on the film and a high speed infrared camera capture the temperature information. The time of raising temperature process and the max temperature were recorded. The different energy of visible light was tried for the max temperature for samples. The result show the PI film can be achieved to 600K and has high thermal efficiency. And the surface film with good absorptivity is also important for heat transforming. PI film can be used as one of the material in the Infrared imaging transducer for high dynamic range and multiband radiation.

Li, Yanhong; Zhang, Li; Li, Zhuo

2013-09-01

354

Chirped-pulsed FTMW spectra of valeric acid, 5-aminovaleric acid, and ?-valerolactam: A study of amino acid mimics in the gas phase  

NASA Astrophysics Data System (ADS)

The lowest energy conformations of valeric acid (VA) and ?-valerolactam (DVL) were determined using chirped-pulsed Fourier transform microwave spectroscopy. DVL was produced by heating 5-aminovaleric acid (AVA) in a metal nozzle. A study of the reaction pathway leading to DVL identified the preferred structure of AVA and demonstrated that an n ? ?\\midast interaction plays the key role in the transformation of reactant into product. An inverse kinetic isotope effect was detected for this process. Additionally, the spectra of single and double water complexes of DVL along with the 13C and 15N-substituted species (in natural abundance) were collected and analyzed.

Bird, Ryan G.; Vaquero-Vara, Vanesa; Zaleski, Daniel P.; Pate, Brooks H.; Pratt, David W.

2012-10-01

355

Chirped laser dispersion spectroscopy for remote open-path trace-gas sensing.  

PubMed

In this paper we present a prototype instrument for remote open-path detection of nitrous oxide. The sensor is based on a 4.53 ?m quantum cascade laser and uses the chirped laser dispersion spectroscopy (CLaDS) technique for molecular concentration measurements. To the best of our knowledge this is the first demonstration of open-path laser-based trace-gas detection using a molecular dispersion measurement. The prototype sensor achieves a detection limit down to the single-ppbv level and exhibits excellent stability and robustness. The instrument characterization, field deployment performance, and the advantages of applying dispersion sensing to sensitive trace-gas detection in a remote open-path configuration are presented. PMID:23443389

Nikodem, Michal; Wysocki, Gerard

2012-11-28

356

Chirped InGaAs quantum dot molecules for broadband applications  

PubMed Central

Lateral InGaAs quantum dot molecules (QDMs) formed by partial-cap and regrowth technique exhibit two ground-state (GS) peaks controllable via the thicknesses of InAs seed quantum dots (x), GaAs cap (y), and InAs regrowth (z). By adjusting x/y/z in a stacked QDM bilayer, the GS peaks from the two layers can be offset to straddle, stagger, or join up with each other, resulting in multi-GS or broadband spectra. A non-optimized QDM bilayer with a 170-meV full-width at half-maximum is demonstrated. The temperature dependencies of the emission peak energies and intensities from the chirped QDM bilayers are well explained by Varshni's equation and thermal activation of carriers out of constituent quantum dots.

2012-01-01

357

Extended delay of broadband signals in stimulated Brillouin scattering slow light using synthesized pump chirp  

NASA Astrophysics Data System (ADS)

Judicious chirping of a directly modulated pump laser is used to broaden the intrinsic linewidth of stimulated Brillouin scattering in an optical fiber. The modulation waveform is designed to obtain a spectrum with sharp edges, resulting in phase gradients stronger that those obtained for random pump modulation. The gain and phase frequency response of the slow light process are measured by a vector network analyzer, and the delays obtained for our tailored modulation are compared with the case of random direct modulation. For equal pump powers and gain bandwidths (FWHM), the tailored modulation waveform introduces 30-40% longer delays. Using this technique, pseudo random bit sequences of 5 Gb/s were successfully delayed by up to 120 ps (BER<10-5) and 80 ps (BER<10-9).

Zadok, Avi; Eyal, Avishay; Tur, Moshe

2006-09-01

358

Target diagnostics for commissioning the AWE HELEN Laser Facility 100 TW chirped pulse amplification beam  

SciTech Connect

The capability of the HELEN laser at the Atomic Weapons Establishment Aldermaston has been enhanced by the addition of a short-pulse laser beam to augment the twin opposing nanosecond time scale beams. The short-pulse beam utilizes the chirped pulse amplification (CPA) technique and is capable of delivering up to 60 J on target in a 500 fs pulse, around 100 TW, at the fundamental laser wavelength of 1.054 {mu}m. During the commissioning phase a number of diagnostic systems have been fielded, these include: x-ray pinhole imaging of the laser heated spot, charged particle time of flight, thermoluminescent dosimeter array, calibrated radiochromic film, and CR39 nuclear track detector. These diagnostic systems have been used to verify the performance of the CPA beam to achieve a focused intensity of around 10{sup 19} W cm{sup -2} and to underwrite the facility radiological safety system.

Eagleton, R. T.; Clark, E. L.; Davies, H. M.; Edwards, R. D.; Gales, S.; Girling, M. T.; Hoarty, D. J.; Hopps, N. W.; James, S. F.; Kopec, M. F.; Nolan, J. R.; Ryder, K. [AWE Aldermaston, Reading, Berks RG7 4PR (United Kingdom)

2006-10-15

359

Generating nonlinear FM chirp waveforms for radar.  

SciTech Connect

Nonlinear FM waveforms offer a radar matched filter output with inherently low range sidelobes. This yields a 1-2 dB advantage in Signal-to-Noise Ratio over the output of a Linear FM waveform with equivalent sidelobe filtering. This report presents design and implementation techniques for Nonlinear FM waveforms.

Doerry, Armin Walter

2006-09-01

360

Multifractal detrended fluctuation analysis of human EEG: preliminary investigation and comparison with the wavelet transform modulus maxima technique.  

PubMed

Recently, many lines of investigation in neuroscience and statistical physics have converged to raise the hypothesis that the underlying pattern of neuronal activation which results in electroencephalography (EEG) signals is nonlinear, with self-affine dynamics, while scalp-recorded EEG signals themselves are nonstationary. Therefore, traditional methods of EEG analysis may miss many properties inherent in such signals. Similarly, fractal analysis of EEG signals has shown scaling behaviors that may not be consistent with pure monofractal processes. In this study, we hypothesized that scalp-recorded human EEG signals may be better modeled as an underlying multifractal process. We utilized the Physionet online database, a publicly available database of human EEG signals as a standardized reference database for this study. Herein, we report the use of multifractal detrended fluctuation analysis on human EEG signals derived from waking and different sleep stages, and show evidence that supports the use of multifractal methods. Next, we compare multifractal detrended fluctuation analysis to a previously published multifractal technique, wavelet transform modulus maxima, using EEG signals from waking and sleep, and demonstrate that multifractal detrended fluctuation analysis has lower indices of variability. Finally, we report a preliminary investigation into the use of multifractal detrended fluctuation analysis as a pattern classification technique on human EEG signals from waking and different sleep stages, and demonstrate its potential utility for automatic classification of different states of consciousness. Therefore, multifractal detrended fluctuation analysis may be a useful pattern classification technique to distinguish among different states of brain function. PMID:23844189

Zorick, Todd; Mandelkern, Mark A

2013-07-03

361

Laser absorption spectrometer using frequency chirped intensity modulation at 1.57 ?m wavelength for CO2 measurement.  

PubMed

We have demonstrated the laser-absorption spectrometer system using frequency chirped intensity modulation at 1.57 ?m wavelength for measurement of CO(2) concentration. Using this technique, backscattered laser radiation from different ranges can be discriminated in the frequency domain of the electrical signal. We have reported the discrimination of two signals from the targets with different ranges. It is shown that stable measurements with short time fluctuation corresponding to 4 ppm (rms) were obtained with 32 s measurement intervals. Furthermore, there is qualitative good agreement on, at least, the diurnal changes between the results of the laser absorption spectrometer system and the in-situCO(2) sensor. PMID:22743496

Imaki, Masaharu; Kameyama, Shumpei; Hirano, Yoshihito; Ueno, Shinichi; Sakaizawa, Daisuke; Kawakami, Shuji; Nakajima, Masakatsu

2012-07-01

362

Nonlinear distortion free fiber-based chirped pulse amplification with self-phase modulation up to 2pi.  

PubMed

We demonstrate the removal of 2pi radians of self-phase modulation (SPM) in a fiber-based chirped pulse amplification (CPA) system. Compensation of SPM distortion is achieved in the time domain by using a LiNbO(3) electro-optic phase modulator to emulate a negative nonlinear index of refraction. By synthesizing the drive waveform to the phase modulators with two RF frequencies that are phase-locked to the repetition rate of the seed laser, we achieve large phase compensations using cost-effective narrow band electronics. Our technique is simple, robust and can be readily integrated into existing fiber CPA systems. PMID:19532489

Zhu, Guanghao; Edinberg, Joel; Xu, Chris

2007-03-01

363

A kurtosis-guided adaptive demodulation technique for bearing fault detection based on tunable-Q wavelet transform  

NASA Astrophysics Data System (ADS)

This paper presents an adaptive demodulation technique for bearing fault detection. It is implemented via the tunable-Q wavelet transform (TQWT). With the TQWT, the bearing vibration signal is decomposed into sub-signals corresponding to different band-pass filters of the TQWT. Kurtosis as an effective indicator of signal impulsiveness is adopted to guide the merging of the sub-signals leading to a signal component which contains information most relevant to the bearing fault. The purpose of the proposed approach is to adaptively search for the best filter for envelope demodulation analysis. In fact, the implementation of the proposed method can be interpreted as the process to obtain the optimal filter for the Hilbert demodulation analysis by two steps of merging of the band-pass filters of the TQWT. The effectiveness of the proposed method has been demonstrated by both simulation and experimental analyses.

Luo, Jiesi; Yu, Dejie; Liang, Ming

2013-05-01

364

A NEW TECHNIQUE FOR OBSERVING THE AMORPHOUS TO CRYSTALLINE TRANSFORMATION IN THIN SURFACE LAYERS ON SILICON WAFERS  

SciTech Connect

Thin amorphous ({alpha}) films of silicon created by ion-implantation have been studied in-situ while undergoing the amorphous to crystalline transformation in the electron microscope. The specimens were prepared in such a manner that the amorphous/crystalline interface was viewed edge-on and its advance during annealing was easily observed over distances of several microns. Growth rates and activation energies were measured. The active role that defects play during the regrowth process was also studied. An additional advantage of the technique was that in a single specimen different segments of the recrystallization front advanced along several different growth directions simultaneously, hence the effect of regrowth direction on the interface migration rate and defect formation was graphically displayed in a single specimen.

Drosd, B.; Washburn, J.

1980-02-01

365

Learning-based computing techniques in geoid modeling for precise height transformation  

NASA Astrophysics Data System (ADS)

Precise determination of local geoid is of particular importance for establishing height control in geodetic GNSS applications, since the classical leveling technique is too laborious. A geoid model can be accurately obtained employing properly distributed benchmarks having GNSS and leveling observations using an appropriate computing algorithm. Besides the classical multivariable polynomial regression equations (MPRE), this study attempts an evaluation of learning based computing algorithms: artificial neural networks (ANNs), adaptive network-based fuzzy inference system (ANFIS) and especially the wavelet neural networks (WNNs) approach in geoid surface approximation. These algorithms were developed parallel to advances in computer technologies and recently have been used for solving complex nonlinear problems of many applications. However, they are rather new in dealing with precise modeling problem of the Earth gravity field. In the scope of the study, these methods were applied to Istanbul GPS Triangulation Network data. The performances of the methods were assessed considering the validation results of the geoid models at the observation points. In conclusion the ANFIS and WNN revealed higher prediction accuracies compared to ANN and MPRE methods. Beside the prediction capabilities, these methods were also compared and discussed from the practical point of view in conclusions.

Erol, B.; Erol, S.

2013-03-01

366

Temperature-strain discrimination using a wavelength-division-multiplexed chirped in-fibre-Bragg-grating\\/extrinsic Fabry-Perot sensor system  

Microsoft Academic Search

In this letter, we present a novel sensor approach allowing fast measurement of temperature. It consists of a chirped fibre Bragg grating (CFBG) and an extrinsic Fabry-Perot interferometric sensor (EFPI) in series. Both EFPI and CFBG are well integrated to provide local strain and temperature information respectively, using wavelength-division-multiplexed (WDM) technique. As the wavelength-shift of the CFBG is detected via

Y. J. Rao; X. K. Zeng; Y. P. Wang; T. Zhu; Z. L. Ran; L. Zhang; I. Bennion

2002-01-01

367

Frequency chirping for resonance-enhanced electron energy during laser acceleration  

NASA Astrophysics Data System (ADS)

The model given by Singh-Tripathi [Phys. Plasmas 11, 743 (2004)] for laser electron acceleration in a magnetic wiggler is revisited by including the effect of laser frequency chirping. Laser frequency chirp helps to maintain the resonance condition longer, which increases the electron energy gain. A significant enhancement in electron energy gain during laser acceleration is observed.

Gupta, D. N.; Suk, H.

2006-04-01

368

Frequency chirping for resonance-enhanced electron energy during laser acceleration  

SciTech Connect

The model given by Singh-Tripathi [Phys. Plasmas 11, 743 (2004)] for laser electron acceleration in a magnetic wiggler is revisited by including the effect of laser frequency chirping. Laser frequency chirp helps to maintain the resonance condition longer, which increases the electron energy gain. A significant enhancement in electron energy gain during laser acceleration is observed.

Gupta, D.N.; Suk, H. [Center for Advanced Accelerators, Korea Electrotechnology Research Institute, Changwon 641-120 (Korea, Republic of)

2006-04-15

369

Spectral and synchrony differences in auditory brainstem responses evoked by chirps of varying durations.  

PubMed

The chirp-evoked ABR has been termed a more synchronous response, referring to the fact that rising-frequency chirp stimuli theoretically compensate for temporal dispersions down the basilar membrane. This compensation is made possible by delaying the higher frequency content of the stimulus until the lower frequency traveling waves are closer to the cochlea apex. However, it is not yet clear how sensitive this temporal compensation is to variation in the delay interval. This study analyzed chirp- and click-evoked ABRs at low intensity, using a variety of tools in the time, frequency, and phase domains, to measure synchrony in the response. Additionally, this study also examined the relationship between chirp sweep rate and response synchrony by varying the delay between high- and low-frequency portions of chirp stimuli. The results suggest that the chirp-evoked ABRs in this study exhibited more synchrony than the click-evoked ABRs and that slight gender-based differences exist in the synchrony of chirp-evoked ABRs. The study concludes that a tailoring of chirp parameters to gender may be beneficial in pathologies that severely affect neural synchrony, but that such a customization may not be necessary in routine clinical applications. PMID:20968361

Petoe, Matthew A; Bradley, Andrew P; Wilson, Wayne J

2010-10-01

370

Simple measurement of fiber dispersion and of chirp parameter of intensity modulated light emitter  

Microsoft Academic Search

We report a novel method to measure two important parameters for optical fiber intensity modulated transmission systems: dispersion of optical fibers and chirp parameter of modulated light emitters. The method is easy, quick, and accurate for chirp parameter in the -10-to-10 range

F. Devaux; Y. Sorel; J. F. Kerdiles

1993-01-01

371

Nonlinear Dynamics of Chirped Pulse Excitation and Dissociation of Diatomic Molecules  

Microsoft Academic Search

The classical dynamics of a diatomic molecule modeled by a Morse oscillator interacting with a chirped infrared laser pulse is studied. When the chirping rate is small, the system can be described approximately in the moving frame by a time-independent Hamiltonian, which produces single-node separtrices (buckets) in phase space. Systems trapped in the buckets undergo convection to dissociation. This route

Wing-Ki Liu; Binruo Wu; Jian-Min Yuan

1995-01-01

372

Manipulating femtosecond magnetization in ferromagnets and molecular magnets through laser chirp  

NASA Astrophysics Data System (ADS)

Laser chirp has found many applications in pulse shaping, high harmonic generation, and dynamical control of the vibrational excitation. Here, we show that the laser chirp can significantly affect the amount of the magnetic moment change in the laser-induced femtosecond magnetism. Under the same laser condition, an increase in the chirp from 0 to 0.04 rad/fs2 results in the magnetic moment change from 0.4% to 5% in ferromagnetic nickel. We find that the laser pulse duration has a direct effect on the effectiveness of the chirp. For a shorter pulse of duration 12 fs, the spin change with the chirp is small. We attribute this to a shorter interaction time and consequently a smaller instantaneous photon energy. We also investigate the effect of chirp on laser-induced local-spin-switching on molecular magnets consisting of two magnetic centers (Fe, Co, and Ni) bridged by Na atoms. We find that the effect of chirping differs depending on the original switching behavior of the atom. On Fe the chirp renders the process slightly less effective, on Ni it leads to a more dramatic loss of fidelity due to quantum interference, and for Co the effect lies in-between. Our study opens a new way to manipulate spin on femtosecond time scales.

Zhang, G. P.; Lefkidis, G.; Hübner, W.; Bai, Yihua

2012-04-01

373

Time domain synchronization using Newman chirp training sequences in AWGN channels  

Microsoft Academic Search

We propose a new time-domain simultaneous fractional frequency and sampling offsets estimation algorithm using the characteristics of down-sampled chirp training signals. The training sequence is composed of one up and one down chirp symbols. We also propose a new estimation algorithm to estimate the integer timing and frequency offsets in the time domain. The algorithms use the outputs of matched

Sandrine Boumard; Aarne Mammela

2005-01-01

374

Airborne SAR processing of highly squinted data using a chirp scaling approach with integrated motion compensation  

Microsoft Academic Search

Proposes a new approach for high-resolution airborne SAR data processing, which uses a modified chirp scaling algorithm to accommodate the correction of motion errors, as well as the variations of the Doppler centroid in range and azimuth. By introducing a cubic phase term in the chirp scaling phase, data acquired with a squint angle up to 30° can be processed

A. Moreira; Yonghong Huang

1994-01-01

375

Chirped Pulse Adiabatic Passage in CARS for Imaging of Biological Structure and Dynamics  

Microsoft Academic Search

We propose the adiabatic passage control scheme implementing chirped femtosecond laser pulses to maximize coherence in a predetermined molecular vibrational mode using two-photon Raman transitions. We investigate vibrational energy relaxation and coUisional dephasing as factors of coherence loss, and demonstrate the possibility for preventing decoherence by the chirped pulse train. The proposed method may be used to advance noninvasive biological

Svetlana A. Malinovskaya

2008-01-01

376

Phase-locking and coherent power combining of broadband linearly chirped optical waves.  

PubMed

We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ~ 60 kHz, and a residual phase error variance of < 0.01 rad(2) between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers-where a rapidly chirping seed laser reduces stimulated Brillouin scattering-and electronic beam steering of chirped optical waves. PMID:23187338

Satyan, Naresh; Vasilyev, Arseny; Rakuljic, George; White, Jeffrey O; Yariv, Amnon

2012-11-01

377

Chirped Fiber Grating Beamformer for Phased Array Antennas Field of the Invention.  

National Technical Information Service (NTIS)

A new fiber optic based beamforming architecture for a time steered phased array antenna based on chirped fiber gratings. All of the gratings are identical in length and period chirp so that they all have the same dispersion, thus at a given optical wavel...

J. E. Roman M. Y. Frankel R. D. Esman

1998-01-01

378

Analytical solutions for a two-level system driven by a class of chirped pulses  

SciTech Connect

We present analytical solutions for the problem of a two-level atom driven by a class of chirped pulses. The solutions are given in terms of Heun functions. By use of the appropriate chirping parameters, an enhancement of four orders of magnitude in the population transfer is obtained.

Jha, Pankaj K. [Institute for Quantum Science and Engineering and Department of Physics, Texas A and M University, College Station, Texas 77843 (United States); Rostovtsev, Yuri V. [Institute for Quantum Science and Engineering and Department of Physics, Texas A and M University, College Station, Texas 77843 (United States); Department of Physics, University of North Texas, 1155 Union Circle 311427, Denton, Texas 76203 (United States)

2010-07-15

379

Photoionization of hydrogen by a chirped, short X-ray pulse in the presence of a laser field  

NASA Astrophysics Data System (ADS)

The ionization of hydrogen by a chirped XUV pulse in the presence of a few cycle infrared laser pulse is investigated. It is found that the combined action of the chirped pulse and the laser field brings about asymmetries in the photoelectron momentum distribution that may be exploited for obtaining information on both the chirp and XUV pulse duration.

Bivona, S.; Bonanno, G.; Burlon, R.; Leone, C.

2012-11-01

380

Chirp excitation of ultrasonic probes and algorithm for filtering transit times in high-rangeability gas flow metering.  

PubMed

The signal processing used in an ultrasonic high-rangeability gas flow meter using times of flight is presented. The flow meter under discussion uses a combination of continuous wave and chirp signals to measure at low flow velocities, below 20 m/s, and chirp signals alone to measure high flow velocities, above 20 m/s. Because of the need for a pulse compression technique in the signal waveform design the technique of pulse compression and the choice of signal waveforms are discussed. The advantages and disadvantages of amplitude weighting vis-a-vis frequency domain manipulations of the waveforms are also discussed. To eliminate spurious times of flight, a special filtering technique is used, based on assessing the gradient of ascendingly ordered time series of time-of-flight measurements. A summary of user experience with high-rangeability gas flow meters in use on different offshore platforms and in refineries is given. Long-term tests that examined the accuracy of the high-rangeability flow meter are also described. PMID:18263174

Folkestad, T; Mylvaganam, K S

1993-01-01

381

Transverse-to-longitudinal Emittance-exchange with an Energy Chirped Beam  

SciTech Connect

Emittance exchange has been proposed to increase the performance of free electron lasers by tailoring the phase space of an electron beam. The principle of emittance exchange - where the transverse phase space of the electron beam is exchanged with the longitudinal phase space - has been demonstrated recently at the A0 photoinjector. The experiment used a low charge bunch (250 pC) with no energy chirp. Theory predicts an improvement in the emittance exchange scheme when the incoming beam has an energy chirp imparted on it. The energy chirp helps to overcome the thick lens effect of the deflecting mode cavity and other second order effects that might lead to an incomplete emittance exchange at higher charges. In this work, we report experimental and simulation results from operating the emittance exchange beam line using an energy chirped beam with higher charge (500 pC) at different RF-chirp settings.

Thangaraj, J.; Ruan, J.; Johnson, A.S.; Thurman-Keup, R.; Lumpkin, A.H.; Santucci, J.; Sun, Y.-E; Maxwell, T.; Edwards, H.; /Fermilab

2012-05-01

382

Female house crickets, Acheta domesticus, prefer the chirps of large males.  

PubMed

This study demonstrates that invertebrate acoustic signals can provide information about male phenotypic attributes, and that females can use this acoustic information in mate choice to select a phenotypically superior mate. I investigated the relationships between a male acoustic sexual signal, the phenotype of the signaller, and the female response to signal variation. I recorded and analysed the calling songs of male house crickets, Acheta domesticus. The analyses showed that chirps convey information about male size. With the exception of amplitude, the mean number of pulses per chirp was the best predictor of male size. I performed a laboratory tape-playback experiment to determine female preference during phonotaxis. Females preferred tapes playing the chirps of large males, specifically chirps with a greater number of pulses per chirp. Selection on the female preference is discussed.Copyright 1997 The Association for the Study of Animal Behaviour PMID:9794780

Gray

1997-12-01

383

Chirped self-similar solutions of a generalized nonlinear Schrödinger equation model.  

PubMed

Exact chirped self-similar solutions of the generalized nonlinear Schrödinger equation with varying dispersion, nonlinearity, gain or absorption, and nonlinear gain have been found. The stability of these nonlinearly chirped solutions is then demonstrated numerically by adding Gaussian white noise and by evolving from an initial chirped Gaussian pulse, respectively. It is reported that the pulse position of these chirped pulses can be precisely piloted by tailoring the dispersion profile, and that the sech-shaped solitary waves can propagate stably in the regime of beta(z)gamma(z) > 0 as well as the regime of beta(z)gamma(z) < 0 , according to the magnitude of the nonlinear chirp parameter. Our theoretical predictions are in excellent agreement with the numerical simulations. PMID:15697746

Chen, Shihua; Yi, Lin

2005-01-11

384

Directional bending sensor with temperature insensitivity using a sampled chirped fiber Bragg grating  

NASA Astrophysics Data System (ADS)

A simple and practical scheme for a directional bending sensor based on a sampled chirped fiber Bragg grating is proposed. The proposed sensing method has temperature insensitivity. The wavelength spacing in the reflection spectrum of a sampled chirped fiber Bragg grating is changed by bending because of the modification of the chirp ratio. As positive or negative bending is applied to the sampled chirped fiber Bragg grating embedded on a flexible cantilever beam, the wavelength spacing increases or decreases because of the induction of the tension and the compression strain gradient along the fiber grating. However, the wavelength spacing is not changed by the applied temperature. Since the effect of the temperature variation along the grating length remains the same, the chirp ratio is independent of the applied temperature change. Regardless of temperature change, it is therefore possible to measure the direction and the variation of bending.

Han, Young-Geun

2009-03-01

385

Perturbation-theory analysis of ionization by a chirped few-cycle attosecond pulse  

SciTech Connect

The angular distribution of electrons ionized from an atom by a chirped few-cycle attosecond pulse is analyzed using perturbation theory (PT), keeping terms in the transition amplitude up to second order in the pulse electric field. The dependence of the asymmetry in the ionized electron distributions on both the chirp and the carrier-envelope phase (CEP) of the pulse are explained using a simple analytical formula that approximates the exact PT result. This approximate formula (in which the chirp dependence is explicit) reproduces reasonably well the chirp-dependent oscillations of the electron angular distribution asymmetries found numerically by Peng et al. [Phys. Rev. A 80, 013407 (2009)]. It can also be used to determine the chirp rate of the attosecond pulse from the measured electron angular distribution asymmetry.

Pronin, E. A.; Starace, Anthony F.; Peng Liangyou [Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588-0299 (United States); State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871 (China)

2011-07-15

386

Quantum and classical chirps in an anharmonic oscillator.  

PubMed

We measure the state dynamics of a tunable anharmonic quantum system, the Josephson phase circuit, under the excitation of a frequency-chirped drive. At small anharmonicity, the state evolves like a wave packet-a characteristic response in classical oscillators; in this regime, we report exponentially enhanced lifetimes of highly excited states, held by the drive. At large anharmonicity, we observe sharp steps, corresponding to the excitation of discrete energy levels. The continuous transition between the two regimes is mapped by measuring the threshold of these two effects. PMID:22400784

Shalibo, Yoni; Rofe, Ya'ara; Barth, Ido; Friedland, Lazar; Bialczack, Radoslaw; Martinis, John M; Katz, Nadav

2012-01-19

387

Seed laser chirping for enhanced backward Raman amplification in plasmas.  

PubMed

Backward Raman compression in plasma enables pulse compression to intensities not available using material gratings. Mediating the compression with higher density plasma generally produces shorter and therefore more intense output pulses. However, very high density plasma, even if sufficiently tenuous to be transparent to the laser, also produces group velocity dispersion of the amplified pulse, deleteriously affecting the interaction. What is shown here is that, by chirping the seed pulse, the group velocity dispersion may in fact be used advantageously, achieving the maximum intensities over the shortest distances while minimizing unwanted effects. PMID:23002752

Toroker, Z; Malkin, V M; Fisch, N J

2012-08-22

388

Supercontinuum generation with a chirped-pulse oscillator.  

PubMed

We demonstrate the generation of a high power ultrabroadband supercontinuum by coupling the uncompressed pulses from a Ti:Sapphire Chirped-pulse oscillator into a photonic crystal fibre that exhibits a highly anomalous dispersion at the centre wavelength of the laser. Our simulations show that the pulses first undergo quasi-linear compression before the actual supercontinuum is generated by soliton fission dynamics. This two-step process results in an optical spectrum that is remarkably independent on the input pulse energy. Moreover, the reduced peak intensity at the input facet of the fibre mitigates damage problems and allows the generation of high power white-light radiation. PMID:19333361

Fuerbach, A; Miese, C; Koehler, W; Geissler, M

2009-03-30

389

Photonic Generation of Chirped Millimeter-Wave Pulses Based on Nonlinear Frequency-to-Time Mapping in a Nonlinearly Chirped Fiber Bragg Grating  

Microsoft Academic Search

A novel approach to optically generating chirped millimeter-wave pulses with tunable chirp rate based on spectral shaping and nonlinear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed approach, the optical power spectrum of an ultrashort pulse from a femtosecond pulsed laser is shaped by a two-tap Sagnac loop filter that has a sinusoidal frequency response. The spectrum-shaped optical

Chao Wang; Jianping Yao

2008-01-01

390

A novel inductance-based technique for discrimination of internal faults from magnetizing inrush currents in power transformers  

Microsoft Academic Search

This paper presents a new methodology for discrimination between inrush currents and internal faults for a three-phase power transformer. This algorithm is based on instantaneous inductance. First, this method calculates differential inductance of transformer phases from primary side view of transformer by using voltage and current signals. Then, the algorithm compares differential inductance with a threshold value. If the calculated

H. Abniki; H. Monsef; P. Khajavi; H. Dashti

2010-01-01

391

Hadamard transform spectrometry: A new analytical technique; Progress report, Second year, March 15, 1992--November 15, 1992  

SciTech Connect

The document is divided into 4 parts: Hadamard transform photoacoustic spectrometry and depth profiling; Hadamard transform imaging with a 2D Hadamard encoding mask (Raman image using pararosaniline hydrochloride); Hadamard transform Raman spectrometry; and work on the growth of VO{sub 2}(s) crystals for Hadamard masking material. 13 figs, refs.

Fateley, W.G.; Hammaker, R.M.

1992-11-15

392

Workplace and Environmental Air Contaminant Concentrations Measured by Open Path Fourier Transform Infrared Spectroscopy: A Statistical Process Control Technique to Detect Changes from Normal Operating Conditions  

Microsoft Academic Search

Open path Fourier transform infrared (OP-FTIR) spectroscopy is a new air monitoring technique that can be used to measure concentrations of air contaminants in real or near-real time. OP-FTIR spectroscopy has been used to monitor workplace gas and vapor exposures, emissions from hazardous waste sites, and to track emissions along fence lines. This paper discusses a statistical process control technique

Maureen Simonds Malachowski; Steven P. Levine; Gary Herrin; Robert C. Spear; Michael Yost; Zhou Yi

1994-01-01

393

Detecting the blockage of the sensing lines of a differential-pressure flow sensor in a dynamic process using wavelet transform techniques  

Microsoft Academic Search

The blockage of the sensing lines of a differentialpressure (DP) flow sensor has been found to be the main cause of a malfunction of a flow measurement system in many industrial applications. In this paper, the blockage of the sensing lines under dynamic process conditions is investigated using wavelet transform techniques. The results obtained show that the blockage in a

Jian Qiu Zhang; Yong Yan

2006-01-01

394

Chirped dissipative solitons of the complex cubic-quintic nonlinear Ginzburg-Landau equation.  

PubMed

Approximate analytical chirped solitary pulse (chirped dissipative soliton) solutions of the one-dimensional complex cubic-quintic nonlinear Ginzburg-Landau equation are obtained. These solutions are stable and highly accurate under condition of domination of a normal dispersion over a spectral dissipation. The parametric space of the solitons is three-dimensional, that makes theirs to be easily traceable within a whole range of the equation parameters. Scaling properties of the chirped dissipative solitons are highly interesting for applications in the field of high-energy ultrafast laser physics. PMID:19905470

Kalashnikov, V L

2009-10-15

395

Phase-preserving chirped-pulse optical parametric amplification to 17.3 fs directly from a Ti:sapphire oscillator  

Microsoft Academic Search

Phase-stabilized 12-fs, 1-nJ pulses from a commercial Ti:sapphire oscillator are directly amplified in a chirped-pulse optical parametric amplifier and recompressed to yield near-transform-limited 17.3-fs pulses. The amplification process is demonstrated to be phase preserving and leads to 85-µJ, carrier-envelope-offset phase-locked pulses at 1 kHz for 0.9 mJ of pump, corresponding to a single-pass gain of 8.5×10^4.

C. P. Hauri; P. Schlup; G. Arisholm; J. Biegert; U. Keller

2004-01-01

396

Sub-picosecond pulses at 100 W average power from a Yb:YLF chirped-pulse amplification system.  

PubMed

We present a high-repetition-frequency, diode-pumped, and chirped-pulse amplification system operating at 106 W average output power with excellent beam quality (M(2)=1.3), based on cryogenically cooled Yb:YLF. 1 nJ seed pulses, derived from a mode-locked Ti:sapphire laser, are first amplified to 1 mJ pulse energy at 10 kHz repetition frequency in a regenerative amplifier. The second-stage, multipass amplifier increases the pulse energy to 10.6 mJ, resulting in a spectral width of 2.2 nm. The pulses are compressed to 865 fs in duration, which is 1.26 times the transform limit. PMID:22743500

Miller, Daniel E; Zapata, Luis E; Ripin, Daniel J; Fan, Tso Yee

2012-07-01

397

Stark-chirped rapid adiabatic passage among degenerate-level manifolds  

SciTech Connect

We generalize Stark-chirped rapid adiabatic passage (SCRAP) to the case of two and three degenerate-level manifolds. The analysis of a degenerate-level system is facilitated by its subdivision into a set of smaller independently evolving subsystems corresponding to the minimal-sized invariant subspaces of the Hamiltonian. Population transfer from the starting to the final level is examined for different types of the invariant subspaces depending on the presence of dark states. It is shown that the complete transfer is feasible if the initial state is prepared into specific coherent superpositions. Our formalism is applicable to the general case of arbitrary numbers of degenerate states within each level and arbitrary couplings of the appropriate transitions. It represents a generalization of well-known Morris-Shore transformation to the case when the removed degeneracy of the sublevels leads to detuning from two-photon resonance. We give the application of the SCRAP formalism to the {sup 87}Rb atom.

Radonjic, M.; Jelenkovic, B. M. [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia)

2009-10-15

398

Wavenumber scanning-based Fourier transform white-light interferometry.  

PubMed

Fourier transform white-light interferometry recovers the optical path difference of an interferometer by measuring the phase change caused by scanning wavelength. However, the optical spectrum, obtained by wavelength scanning method (?-method), contains a chirp in period. The chirp would induce deviation and decrease the measurement accuracy. An improved method, the wavenumber scanning method (k-method), is proposed and experimentally demonstrated, in which there is no chirp in the optical spectrum. The measurement results using the k-method and the ?-method are compared experimentally. The experimental results show that the standard deviation of the measurement results decreases from 0.015 to 0.004 ?m, when an extrinsic Fabry-Perot interferometer with a cavity length of 387 ?m is interrogated. PMID:22859041

Wang, Zhen; Jiang, Yi

2012-08-01

399

Current transformers  

Microsoft Academic Search

Current transformers are used primarily to measure time varying currents under conditions where some degree of isolation from the primary circuit is desired. In this paper, the basic physics of current transformers is considered and several useful techniques for extending their performance are described. They can be used in an undergraduate laboratory as the basis for very interesting and illustrative

Rodney C. Cross

1986-01-01

400

Security Transformation.  

National Technical Information Service (NTIS)

For the past 5 years, the United States has sought to transform its defense capabilities to reflect ongoing changes in technology, management techniques, the American political and economic landscapes, and the global security environment. The terrorist at...

S. Metz

2003-01-01

401

Asymmetric light propagation in chirped photonic crystal waveguides.  

PubMed

We report numerical and experimental investigations of asymmetric light propagation in a newly designed photonic structure that is formed by creating a chirped photonic crystal (PC) waveguide. The use of a non-symmetric distribution of unit cells of PC ensures the obtaining of asymmetric light propagation. Properly designing the spatial modulation of a PC waveguide inherently modifies the band structure. That in turn induces asymmetry for the light's followed path. The investigation of the transmission characteristics of this structure reveals optical diode like transmission behavior. The amount of power collected at the output of the waveguide centerline is different for the forward and backward propagation directions in the designed configuration. The advantageous properties of the proposed approach are the linear optic concept, compact configuration and compatibility with the integrated photonics. These features are expected to hold great potential for implementing practical optical rectifier-type devices. PMID:23037111

Kurt, H; Yilmaz, D; Akosman, A E; Ozbay, E

2012-08-27

402

Seed laser chirping for enhanced backward Raman amplification in plasmas  

NASA Astrophysics Data System (ADS)

Backward Raman compression in plasma enables pulse compression to intensities not available using material gratings. Mediating the compression with higher density plasma (moderately undercritical plasmas) generally produces shorter and therefore more intense output pulses. However, very high density plasma, even if sufficiently tenuous to be transparent to the laser, also produces group velocity dispersion of the amplified pulse, deleteriously affecting the interaction. Nevertheless the seed dispersion can be used advantageously, by chirping the seed pulse, the length to reach the highest intensity is considerably reduced. The fact that the plasma length is reduced has considerable advantages: first, there is less distance over which deleterious instabilities can develop, such as forward Raman amplification; second, there is less radiative loss through inverse bremsstrahlung; and, third, less plasma is needed in the first place, requiring less input pump energy.

Toroker, Z.; Malkin, V. M.; Fisch, N. J.

2012-10-01

403

Chirped rectilinear core longitudinally-graded optical fibers  

NASA Astrophysics Data System (ADS)

Reported here is a straight-forward and flexible method to fabricate silica optical fibers of circular cladding cross-section and rectilinear cores whose aspect ratio and refractive index profile changes with position along the fiber in a deterministic way. Specifically, a modification to the process recently developed to produce longitudinally-graded optical fibers, LGFs [Opt. Express 20 (2012) 17394–17402], was employed. Herein reported are MCVD-derived germanosilicate fibers with rectangular cores where the aspect ratio changes by nearly 200% and the average refractive index changed by about 5%. Fiber losses were measured to be about 50 dB/km. Such rectangular core fibers are useful for a variety of telecommunication and biomedical applications and the dimensional and optical chirp provides a deterministic way to control further the modal properties of the fiber.

Evert, A.; Hawkins, T.; Stolen, R.; Dragic, P.; Rice, R.; Ballato, J.

2013-10-01

404

In situ examination of tin oxide atomic layer deposition using quartz crystal microbalance and Fourier transform infrared techniques  

NASA Astrophysics Data System (ADS)

The atomic layer deposition (ALD) of tin oxide thin films has been examined using in situ quartz crystal microbalance (QCM) and Fourier transform infrared (FTIR) techniques. The SnOx films were deposited using sequential exposures of SnCl4 and H2O2 at temperatures from 150 to 430 °C. The linear growth of the tin oxide ALD films was observed by both the mass gain during QCM measurements and the background infrared absorbance increase during FTIR investigations. The FTIR spectra revealed the loss and gain of the O-H stretching vibrations of the hydroxyl group for the SnCl4 and H2O2 exposures, respectively. The background infrared absorbance also oscillated after each SnCl4 and H2O2 exposure. The background absorbance increased after SnCl4 exposure and decreased after H2O2 exposure. QCM measurements were consistent with a tin oxide ALD growth rate of ~60 ng cm-2 per cycle. This mass change corresponds to a growth rate of ~0.7 A?/cycle at 325 °C assuming a SnO2 density of 6.9 g cm-3. Additional ex situ surface analysis using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) revealed that the SnOx films grown at 325 °C were defined by x<2. Atomic force microscope (AFM) results also showed that the SnOx ALD films deposited on Si(100) wafers have a very rough surface. Understanding and controlling the growth of tin oxide ALD films should be useful to enhance the sensitivity of SnOx gas sensors.

Du, X.; Du, Y.; George, S. M.

2005-07-01

405

Fast Hearing-Threshold Estimation Using Multiple Auditory Steady-State Responses with Narrow-Band Chirps and Adaptive Stimulus Patterns  

PubMed Central

This paper describes the estimation of hearing thresholds in normal-hearing and hearing-impaired subjects on the basis of multiple-frequency auditory steady-state responses (ASSRs). The ASSR was measured using two new techniques: (i) adaptive stimulus patterns and (ii) narrow-band chirp stimuli. ASSR thresholds in 16 normal-hearing and 16 hearing-impaired adults were obtained simultaneously at both ears at 500, 1000, 2000, and 4000?Hz, using a multiple-frequency stimulus built up of four one-octave-wide narrow-band chirps with a repetition rate of 40?Hz. A statistical test in the frequency domain was used to detect the response. The recording of the steady-state responses was controlled in eight independent recording channels with an adaptive, semiautomatic algorithm. The average differences between the behavioural hearing thresholds and the ASSR threshold estimate were 10, 8, 13, and 15?dB for test frequencies of 500, 1000, 2000, and 4000?Hz, respectively. The average overall test duration of 18.6 minutes for the threshold estimations at the four frequencies and both ears demonstrates the benefit of an adaptive recording algorithm and the efficiency of optimised narrow-band chirp stimuli.

Muhler, Roland; Mentzel, Katrin; Verhey, Jesko

2012-01-01

406

Few-cycle attosecond pulse chirp effects on asymmetries in ionized electron momentum distributions  

SciTech Connect

The momentum distributions of electrons ionized from H atoms by chirped few-cycle attosecond pulses are investigated by numerically solving the time-dependent Schroedinger equation. The central carrier frequency of the pulse is chosen to be 25 eV, which is well above the ionization threshold. The asymmetry (or difference) in the yield of electrons ionized along and opposite to the direction of linear laser polarization is found to be very sensitive to the pulse chirp (for pulses with fixed carrier-envelope phase), both for a fixed electron energy and for the energy-integrated yield. In particular, the larger the pulse chirp, the larger the number of times the asymmetry changes sign as a function of ionized electron energy. For a fixed chirp, the ionized electron asymmetry is found to be sensitive also to the carrier-envelope phase of the few-cycle pulse.

Peng Liangyou; Tan Fang; Gong Qihuang; Pronin, Evgeny A.; Starace, Anthony F. [Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871 (China); Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States)

2009-07-15

407

Pulse dynamic in a passively mode-locked chirped-pulse fiber laser  

Microsoft Academic Search

We report experimental and numerical results on the pulse dynamic of passively modelocked Yb-doped fiber laser operating in the chirped-pulse regime. A newly design cavity with a CFBG provides positive dispersion with negligible nonlinearity.

B. Ortac; M. Plotner; T. Schreiber; J. Limpert; A. Tunnermann

2008-01-01

408

Individual acoustic variation in Belding's ground squirrel alarm chirps in the High Sierra Nevada  

NASA Astrophysics Data System (ADS)

The acoustic structure of calls within call types can vary as function of individual identity, sex, and social group membership and is important in kin and social group recognition. Belding's ground squirrels (Spermophilus beldingi) produce alarm chirps that function in predator avoidance but little is known about the acoustic variability of these alarm chirps. The purpose of this preliminary study was to analyze the acoustic structure of alarm chirps with respect to individual differences (e.g., signature information) from eight Belding's ground squirrels from four different lakes in the High Sierra Nevada. Results demonstrate that alarm chirps are individually distinctive, and that acoustic similarity among individuals may correspond to genetic similarity and thus dispersal patterns in this species. These data suggest, on a preliminary basis, that the acoustic structure of calls might be used as a bioacoustic tool for tracking individuals, dispersal, and other population dynamics in Belding's ground squirrels, and perhaps other vocal species.

McCowan, Brenda; Hooper, Stacie L.

2002-03-01

409

Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects  

PubMed Central

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size.

Erpelding, Todd N.; Hollman, Kyle W.; O'Donnell, Matthew

2007-01-01

410

Highly Efficient Tabletop Optical Parametric Chirped Pulse Amplifier at 1 um(micro sign).  

National Technical Information Service (NTIS)

Optical parametric chirped pulse amplification (OPCPA) is a scalable technology, for ultrashort pulse amplification. Its major advantages include design simplicity, broad bandwidth, tunability, low B-integral, high contrast, and high beam quality. OPCPA i...

I. Jovanovic C. A. Ebbers B. J. Comaskey R. A. Bonner E. C. Morse

2001-01-01

411

Optical parametric chirped pulse amplifier at 1600 nm with all-optical synchronization  

NASA Astrophysics Data System (ADS)

We demonstrate the amplification of 1.6 ?m pulses by a KTA optical parametric chirped-pulse amplifier based on an all-optical synchronization scheme as a scalable approach to generation of high power tunable mid infrared.

Pelletier, Etienne; Leitenstorfer, Alfred; Miller, RJ Dwayne

2013-03-01

412

Longitudinal Coherence Preservation and Chirp Evolution in a High Gain Laser Seeded Free Electron Laser Amplifier  

SciTech Connect

In this letter we examine the start-up of a high gain free electron laser in which a frequency-chirped coherent seed laser pulse interacts with a relativistic electron beam. A Green function formalism is used to evaluate the initial value problem. We have fully characterized the startup and evolution through the exponential growth regime. We obtain explicit expressions for the pulse duration, bandwidth and chirp of the amplified light and show that the FEL light remains fully longitudinally coherent.

Murphy, J.B.; /BNL, NSLS; Wu, Juhao; /SLAC; Wang, X.J.; Watanabe, T.; /BNL, NSLS

2006-06-07

413

Pulse multi-pass stretcher using linear chirped fiber Bragg grating  

NASA Astrophysics Data System (ADS)

A pulse stretcher using chirped fiber Bragg grating is demonstrated. Pulses from a 1053nm mode-locked fiber seed oscillator are multi-stretched by a Linear chirped grating set in a fiber regenerative amplifier structure. We have the pulse stretched from 23.6ps to 378ps after it transmits 3 loops in the stretcher. The major factors which affect the stretched pulse shape are discussed.

Zhang, Chengtao; Wang, Xiaochao; Fan, Wei; Rao, Daxing; Lin, Zunqi

2013-09-01

414

Pulse dynamics in a passively mode-locked chirped-pulse fiber laser  

NASA Astrophysics Data System (ADS)

We report experimental and numerical results on the new pulse dynamics in a passively mode-locked ytterbium-doped fiber laser operating in the chirped-pulse regime. Due to the negligible nonlinearity of added highly-positive GVD segment in the purely-normal-dispersion regime, highly-positive chirped pulses can be formed through weak intra-cavity temporal and spectral breathing. Numerical simulations reveal intra-cavity pulse evolution with local temporal stretching phenomena and pulse shaping properties.

Ortaç, B.; Plötner, M.; Limpert, J.; Tünnermann, A.

2010-04-01

415

Toward Broad Bandwidth 2-D Electronic Spectroscopy: Correction of Chirp From a Continuum Probe  

Microsoft Academic Search

Recent implementations of 2-D spectroscopy in the pump–probe geometry using a pulse-shaper demonstrate the ease with which frequency-resolved pump–probe experiments can be readily adapted to 2-D methods. Many frequency-resolved pump–probe experiments employ continuum probes to observe a broad range of electronic transitions. These continuum probes are often chirped, leading to distortions that can be postcorrected by characterizing the chirp and

Patrick A. Tekavec; Kristin L. M. Lewis; Franklin D. Fuller; Jeffrey A. Myers; Jennifer P. Ogilvie

2012-01-01

416

Performance of hybrid chirp/DS signals under Doppler and pulsed jamming  

NASA Astrophysics Data System (ADS)

The bit-error probability is evaluated for a hybrid chirp/direct sequence (DS) spread-spectrum communication system. The received signal is received in Doppler; the channel is contaminated by a pulsed barrage jammer with a varying duty factor. Moreover, the DS correlation loss due to imperfect code synchronization is taken into account. The tradeoffs involved in dividing the total RF bandwidth into the DS and chirp bandwidths to combat both the jamming and the Doppler are discussed.

Elhakeem, A. K.; Targi, Ali

417

Holocene sedimentation in the Skagerrak interpreted from chirp sonar and core data  

Microsoft Academic Search

High-resolution chirp sonar profiling in the northeastern Skagerrak shows acoustically stratified sediments draping a rough-surfaced substratum. A 32 metre long sediment core retrieved from the survey area encompasses the entire Holocene and latest Pleistocene. The uppermost seismo-acoustic units in the chirp profiles represent Holocene marine sediments. The lowermost unit is interpreted as ice-proximal glacial-marine sediments rapidly deposited during the last

Richard Gyllencreutz; Martin Jakobsson; Jan Backman

2005-01-01

418

Demonstration of a continuously variable true-time delay beamformer using a multichannel chirped fiber grating  

Microsoft Academic Search

A continuously variable true-time delay beamformer based on a multichannel chirped fiber grating (MCFG) is demonstrated. The beamformer is capable of wide-band squint-free operation and demonstrates beam steering of a four-element array over ±40°. The use of an MCFG provides a significant reduction in the length of the chirped grating required, eliminates spurious signal transmission, and utilizes narrow-band tunable laser

David B. Hunter; Michael E. Parker; James L. Dexter

2006-01-01

419

Rydberg-atom population transfer by population trapping in a chirped microwave pulse  

SciTech Connect

We demonstrate that Rydberg atoms can be transferred to states of lower principal quantum number by exposing them to a frequency chirped microwave pulse. Specifically, we have transferred n=75 atoms to n=66 with a 400-ns pulse chirped from 7.8 to 11.8 GHz. In spite of the large number of coupled levels, using a simplified model we can describe the process reasonably well as a sequence of adiabatic rapid passages.

Lambert, J.; Gallagher, T.F. [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Noel, Michael W. [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Department of Physics, Bryn Mawr College, Bryn Mawr, Pennysylvania 19010 (United States)

2002-11-01

420

On chirp stimuli and neural synchrony in the suprathreshold auditory brainstem response.  

PubMed

The chirp-evoked ABR has been regarded as a more synchronous response than the click-evoked ABR, referring to the belief that the chirp stimulates lower-, mid-, and higher-frequency regions of the cochlea simultaneously. In this study a variety of tools were used to analyze the synchronicity of ABRs evoked by chirp- and click-stimuli at 40 dB HL in 32 normal hearing subjects aged 18 to 55 years (mean=24.8 years, SD=7.1 years). Compared to the click-evoked ABRs, the chirp-evoked ABRs showed larger wave V amplitudes, but an absence of earlier waves in the grand averages, larger wave V latency variance, smaller FFT magnitudes at the higher component frequencies, and larger phase variance at the higher component frequencies. These results strongly suggest that the chirp-evoked ABRs exhibited less synchrony than the click-evoked ABRs in this study. It is proposed that the temporal compensation offered by chirp stimuli is sufficient to increase neural recruitment (as measured by wave V amplitude), but that destructive phase interactions still exist along the cochlea partition, particularly in the low frequency portions of the cochlea where more latency jitter is expected. The clinical implications of these findings are discussed. PMID:20649219

Petoe, Matthew A; Bradley, Andrew P; Wilson, Wayne J

2010-07-01

421

Influence of turbulence on the spectrum of diffracted chirped Gaussian pulsed beams  

NASA Astrophysics Data System (ADS)

The influence of turbulence on the spectrum of diffracted chirped Gaussian pulsed beams is studied in detail. By using the quadratic approximation of the Rytov’s phase structure function and the finite expansion of the aperture function, the analytical expression for the spectrum of diffracted chirped Gaussian pulsed beams propagating through atmospheric turbulence is derived. It is shown that in free space there exist the on-axis and off-axis multi-spectral switch for diffracted chirped Gaussian pulsed beams. However, the turbulence results in a decrease of the spectral transition height, and the spectral switch even disappears when the turbulence is strong enough, which is very different from the behavior of undiffracted chirped Gaussian pulsed beams. Specially, with increasing the strength of turbulence, the higher-order spectral switch disappears firstly for on-axis case, while the lower-order spectral switch disappears firstly for off-axis case. In free space the on-axis spectrum is blue-shifted after a certain propagation distance, but the on-axis spectrum is red-shifted after a shorter propagation distance when the turbulence is strong enough. The spectral transition height increases with increasing the chirp parameter and decreasing the pulse duration, and the odd number order position without spectral shift is independent of the chirp parameter and pulse duration.

Ji, Xiaoling

2008-07-01

422

Hough Transform from the Radon Transform  

Microsoft Academic Search

An appropriate special case of a transform developed by J. Radon in 1917 is shown to have the major properties of the Hough transform which is useful for finding line segments in digital pictures. Such an observation may be useful in further efforts to generalize the Hough transform. Techniques for applying the Radon transform to lines and pixels are developed

Stanley R. Deans

1981-01-01

423

Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques  

SciTech Connect

In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.

Lemery, F.; Mihalcea, D.; Prokop, C.R.; /Northern Illinois U.; Piot, P.; /Northern Illinois U. /Fermilab

2012-07-08

424

Coherent control of ultracold {sup 85}Rb trap-loss collisions with nonlinearly frequency-chirped light  

SciTech Connect

We present results on coherent control of ultracold trap-loss collisions using 40-ns pulses of nonlinearly frequency-chirped light. The chirps, either positive or negative, sweep {approx}1 GHz in 100 ns and are centered at various detunings below the D{sub 2} line of {sup 85}Rb. At each center detuning, we compare the collisional rate constant {beta} for chirps that are linear in time, concave-down, and concave-up. For positive chirps, we find that {beta} generally depends very little on the shape of the chirp. For negative chirps, however, we find that {beta} can be enhanced by up to 50(20)% for the case of the concave-down shape. This occurs at detunings where the evolution of the wave packet is expected to be coherent. An enhancement at these detunings is also seen in quantum-mechanical simulations of the collisional process.

Pechkis, J. A. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Currently with the Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States); Carini, J. L.; Rogers, C. E. III; Gould, P. L. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Kallush, S. [Department of Physics and Optical Engineering, ORT Braude, P.O. Box 78, Karmiel (Israel); Kosloff, R. [Department of Physical Chemistry and the Fritz Haber Research Center for Molecular Dynamics, Hebrew University, IL-91094 Jerusalem (Israel)

2011-06-15

425

Nitroxide-controlled free radical copolymerization of styrene and acrylonitrile monitored by electron spin resonance and fourier transform infrared technique in situ  

Microsoft Academic Search

Nitroxide-mediated homopolymerization of styrene (St) and copolymerization of styrene and acrylonitrile (An) were monitored\\u000a respectively by electron spin resonance and Fourier transform infrared technique in situ, and the polymerization kinetics\\u000a was investigated in detail. Homopolymerization of St was well controlled in the presence of 4-hydroxyl-2,2,6,6-tetramethyl-l-piperidinyloxy\\u000a (HTEMPO, N*) at high temperature. The initiation reactions and polymerization rates were changed by varying

F. J. Hua; S. M. Chen; D. S. Lee; Y. L. Yang

2001-01-01

426

An Analytical Solution for the Transient Two-Dimensional Advection–Diffusion Equation with Non-Fickian Closure in Cartesian Geometry by the Generalized Integral Transform Technique  

Microsoft Academic Search

Analytical solutions of equations are of fundamental importance in understanding and describing physical phenomena, since\\u000a they are able to take into account all the parameters of a problem and investigate their influence. In a recent work, [Bus07]\\u000a reported an analytical solution for the stationary two-dimensional advection–diffusion equation with Fickian closure by the\\u000a Generalized Integral Laplace Transform Technique (GILTT). The main

D. Buske; M. T. Vilhena; D. Moreira; T. Tirabassi

427

A novel single-output Mach-Zehnder joint transform correlator with two-channel encoding technique based on HSV color space for color pattern recognition  

NASA Astrophysics Data System (ADS)

A novel two-channel single-output joint transform correlator system with the Mach-Zehnder configuration using encoding technique based on HSV color space for color pattern recognition is introduced. The large zero order term can be removed directly by the Stokes relations in only one step in this structure. By the image encoding technique, the size of the liquid crystal spatial light modulators will be smaller with interlaced rearrangement of hue and saturation color components. Furthermore, the utilization of Lagrange multipliers to synthesize the reference image for reducing the correlation sidelobes is also studied. The computer numerical results are presented to verify the performance of the proposed system.

Lee, Chungcheng; Chen, Chulung; Wang, Chunming

2008-03-01

428

Comparison of chirp scaling and wavenumber domain algorithms for airborne low-frequency SAR  

NASA Astrophysics Data System (ADS)

In recent years a new class of Synthetic Aperture Radar (SAR) systems, using low frequencies, have emerged. The combination of low frequencies with high bandwidths allows a variety of new applications. Several new fields arise in forestry, biomass estimation and in archaeological and geological exploration. The P-band SAR technology benefits from technological advances in antenna design, low noise amplifiers, band pass filters, digital receiver technology, as well as new processing algorithms. For all the new applications of an airborne P-band SAR system, the high-resolution imaging is an important parameter, but it cannot be easily achieved with conventional processing techniques. In this paper, the performance and limitations of the Extended Chirp Scaling (ECS) algorithm and wavenumber domain Omega-K processing algorithm are analysed and discussed. Additionally, modifications of both algorithms are proposed, which optimise the respective algorithm for processing low frequency, wide-beam and wide-band SAR data. Despite of the inherent limitations of the above mentioned processing algorithms, a deterministic phase error, called "digital phase error", due to digital signal processing characteristics is formulated and its effect to the processed SAR data is analytically described. The analysis is carried out, using simulated low frequency airborne SAR data.

Potsis, Athanasios; Reigber, Andreas; Alivizatos, Emmanouil; Moreira, Alberto; Uzunoglou, Nikolaos K.

2003-03-01

429

Fiber-based pulse stretcher for narrowband terahertz pulse generation with a chirped-pulse beating method  

NASA Astrophysics Data System (ADS)

We theoretically show that it is possible to generate chirp-free terahertz (THz) pulses with a chirped-pulse beating method by using an optical fiber as a pulse stretcher. Proper choices of the core radius and the dopant fraction of the core material of a step-index single-mode optical fiber eliminate the third-order spectral phase of the fiber, thus giving the pump laser pulse a purely linear chirp. We also show that even a standard commercial single-mode optical fiber can give THz pulses of lower chirp than the lower limit for a grating pair. We perform experiments to verify our theory.

Yoshida, Tetsuya; Kamada, Shohei; Murata, Shuhei; Aoki, Takao

2013-10-01

430

Tracing the photodissociation probability of H{sub 2}{sup +} in intense fields using chirped laser pulses  

SciTech Connect

The temporal evolution of the dissociation probabilities for various vibrational levels of H{sub 2}{sup +} is observed in terms of shifts in the kinetic energy release dissociation spectra, induced by linearly chirped intense laser pulses. In contrast to previous observations, in which no dependence on the chirp sign was observed, the energy spectrum reported here shows peak shifts, up for negative chirp and down for positive chirp. For some vibrational levels, dissociation takes place early on in the pulse; hence, care must be taken while interpreting the effect of pulse duration in photodissociation studies. This interpretation is supported by numerical solutions of the time-dependent Schroedinger equation.

Prabhudesai, Vaibhav S.; Natan, Adi; Bruner, Barry D.; Diner, Adi; Silberberg, Yaron [Department of Physics of Complex Systems, Weizmann Institute of Science, IL-76100 Rehovot (Israel); Lev, Uri; Heber, Oded; Zajfman, Daniel [Department of Particle Physics, Weizmann Institute of Science, IL-76100 Rehovot (Israel); Strasser, Daniel [Department of Particle Physics, Weizmann Institute of Science, IL-76100 Rehovot (Israel); Institute of Chemistry, Hebrew University, IL-91904 Jerusalem (Israel); Schwalm, D. [Department of Particle Physics, Weizmann Institute of Science, IL-76100 Rehovot (Israel); Max-Planck-Institut fuer Kernphysik, D-69117 Heidelberg (Germany); Ben-Itzhak, Itzik; Hua, J. J.; Esry, B. D. [J. R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506 (United States)

2010-02-15

431

Auditory brainstem responses with optimized chirp signals compensating basilar-membrane dispersion.  

PubMed

This study examines auditory brainstem responses (ABR) elicited by rising frequency chirps. The time course of frequency change for the chirp theoretically produces simultaneous displacement maxima by compensating for travel-time differences along the cochlear partition. This broadband chirp was derived on the basis of a linear cochlea model [de Boer, "Auditory physics. Physical principles in hearing theory I," Phys. Rep. 62, 87-174 (1980)]. Responses elicited by the broadband chirp show a larger wave-V amplitude than do click-evoked responses for most stimulation levels tested. This result is in contrast to the general hypothesis that the ABR is an electrophysiological event most effectively evoked by the onset or offset of an acoustic stimulus, and unaffected by further stimulation. The use of this rising frequency chirp enables the inclusion of activity from lower frequency regions, whereas with a click, synchrony is decreased in accordance with decreasing traveling velocity in the apical region. The use of a temporally reversed (falling) chirp leads to a further decrease in synchrony as reflected in ABR responses that are smaller than those from a click. These results are compatible with earlier experimental results from recordings of compound action potentials (CAP) [Shore and Nuttall, "High synchrony compound action potentials evoked by rising frequency-swept tonebursts," J. Acoust. Soc. Am. 78, 1286-1295 (1985)] reflecting activity at the level of the auditory nerve. Since the ABR components considered here presumably reflect neural response from the brainstem, the effect of an optimized synchronization at the peripheral level can also be observed at the brainstem level. The rising chirp may therefore be of clinical use in assessing the integrity of the entire peripheral organ and not just its basal end. PMID:10738807

Dau, T; Wegner, O; Mellert, V; Kollmeier, B

2000-03-01

432

Optimized control of Stark-shift-chirped rapid adiabatic passage in a {lambda}-type three-level system  

SciTech Connect

Inhomogeneous broadening of energy levels is one of the principal limiting factors for achieving 'slow' or 'stationary' light in solid-state media by means of electromagnetically induced transparency, a quantum version of stimulated Raman adiabatic passage (STIRAP). Stark-shift-chirped rapid adiabatic-passage (SCRAP) has been shown to be far less sensitive to inhomogeneous broadening than STIRAP, a population transfer technique to which it is closely related. We further optimize the pulses used in SCRAP to be even less sensitive to inhomogeneous broadening in a {lambda}-type three-level system. The optimized pulses perform at a higher fidelity than the standard Gaussian pulses for a wide range of detunings (i.e., large inhomogeneous broadening)

Schoenfeldt, Johann-Heinrich; Twamley, Jason; Rebic, Stojan [Centre for Quantum Computer Technology, Physics Department, Macquarie University, Sydney, New South Wales 2109 (Australia)

2009-10-15

433

An efficient technique for the time domain analysis of multi-conductor transmission lines using the Hilbert transform  

Microsoft Academic Search

It has been found that, in order to obtain an accurate causal response for a multiconductor transmission line, extremely accurate characterization of the complex dielectric permittivity is required. In the present work, the Hilbert transform was used to enforce the causality requirements on the time-dependent TEM (transverse electromagnetic) fields of the transmission line. It is shown that it is possible

Tawfik Rahal Arabi; Arthur T. Murphy; Tapan K. Sarkar

1991-01-01

434

Ultrafast control of the internuclear distance with parabolic chirped pulses.  

PubMed

Recently, control over the bond length of a diatomic molecule with the use of parabolic chirped pulses was predicted on the basis of numerical calculations [Chang; et al. Phys. Rev. A 2010, 82, 063414]. To achieve the required bond elongation, a laser scheme was proposed that implies population inversion and vibrational trapping in a dissociative state. In this work we identify two regimes where the scheme works, called the strong and the weak adiabatic regimes. We define appropriate parameters to identify the thresholds where the different regimes operate. The strong adiabatic regime is characterized by a quasi-static process that requires longer pulses. The molecule is stabilized at a bond distance and at a time directly controlled by the pulse in a time-symmetrical way. In this work we analyze the degree of control over the period and elongation of the bond as a function of the pulse bandwidth. The weak adiabatic regime implies dynamic deformation of the bond, which allows for larger bond stretch and the use of shorter pulses. The dynamics is anharmonic and not time-symmetrical and the final state is a wave packet in the ground potential. We show how the vibrational energy of the wave packet can be controlled by changing the pulse duration. PMID:22082170

Chang, Bo Y; Shin, Seokmin; Santamaria, Jesus; Sola, Ignacio R

2011-11-15

435

a Chirped Pulse Ftmw Study of the Structure of Phenol Dimer  

NASA Astrophysics Data System (ADS)

Phenol dimer has been studied extensively and is considered a benchmark molecular complex for ab initio theory due to a long range dispersion interaction between the rings as well as an intermolecular hydrogen bond. Previously, the structure had been determined using RCS and high resolution UV measurements; however, several assumptions were integrated into the structure because a full isotopically substituted structure could not be determined. In this study, the rotational spectrum of the dimer as well as 13C and 18O isotopologue spectra that were seen in natural abundance were obtained using chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). The structure was determined using both linear least squares fitting (r_0 structure) and the Kraitchman substitution analysis (r_s structure). Ab initio calculations were performed for the dimer using MP2/cc-pVTZ cp, B3LYP/6-31G(d,p), M06-2X/6-31G(d,p), and M06-2X/6-311++G(d,p), while CCSD calculations are currently under way. Changing the level of theory and the basis set dramatically changes the structure. The MP2 calculation underestimates the hinge angle (C-O-O-C dihedral angle), while the B3LYP overestimates it. The M06-2X calculations seem to give the best cost-to-benefit ratio when compared to the r_s structure, but they show poorer agreement with increasing basis set size. L. L. Connell, S. M. Ohline, P. W. Joireman, T. C. Corcoran, and P. M. Felker, J.Chem.Phys. 96, 2585 (1992) A. Weichert, C. Riehn, and B. Brutschy, J. Phys. Chem. A 105, 5679 (2001) M. Schmitt, M. Böhm, C. Ratzer, D. Krügler, K. Kleinermanns, I. Kalkman, G. Berden, and W. L. Meerts, Chem. Phys. Chem. 7, 1241 (2006) P. Jurecka, J. Sponer, J. Cerny, and P. Hobza, Phys. Chem. Chem. Phys. 8, 1985 (2006)

Steber, Amanda L.; Neill, Justin L.; Zaleski, Daniel P.; Pate, Brooks H.; Lesarri, Alberto

2011-06-01

436

DNA Transformation  

NSDL National Science Digital Library

Stanley Cohen and Herbert Boyer's historic experiment used techniques to cut and paste DNA to create the first custom-made organism containing recombined or 'recombinant' DNA. Cohen and Boyer inserted the recombinant DNA molecule they created into E. coli bacteria by means of a plasmid, thereby inducing the uptake and expression of a foreign DNA sequence known as 'transformation.' This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents DNA transformation through a series of illustrations of the processes involved.

2012-04-06

437

Noncollinear parametric fluorescence by chirped quasi-phase matching for monocycle temporal entanglement.  

PubMed

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle of light. Harris [Opt. Express 98, 063602 (2007)] suggested using ultrabroad parametric fluorescenc generated from a quasi-phase-matched (QPM) device whose poling period is chirped. In the Harris's original proposal, it is assumed that the photons are collinearly generated and then spatially separated by frequency filtering Here, we alternatively propose using noncollinearly generated SPDC. In our numerical calculation, to achieve 1.2 cycle temporal correlation for a 532 nm pump laser, only 10% -chirped device is sufficien when noncollinear condition is applied, while a largely chirped (50%) device is required in collinear condition. We also experimentally demonstrate an octave-spanning (790-1610 nm) noncollinear parametric fluorescenc from a 10% chirped MgSLT crystal using both a superconducting nanowire single-photon detector and photomultiplier tube as photon detectors. The observed SPDC bandwidth is 194 THz, which is the largest width achieved to date for a chirped QPM device. From this experimental result, our numerical analysis predicts that the bi-photon can be compressed to 1.2 cycles with appropriate phase compensation. PMID:23187339

Tanaka, Akira; Okamoto, Ryo; Lim, Hwan Hong; Subashchandran, Shanthi; Okano, Masayuki; Zhang, Labao; Kang, Lin; Chen, Jian; Wu, Peiheng; Hirohata, Toru; Kurimura, Sunao; Takeuchi, Shigeki

2012-11-01

438

A novel method for the demodulation of fiber Bragg grating sensing system based on chirp grating  

NASA Astrophysics Data System (ADS)

In this paper, we propose a novel method of the demodulation of FBG sensing system based on chirp grating and LPG edge filter in which chirp grating is used as band filter. The measurement speed is mainly determined by the response time of the photo-detector and the convert time of AD chips. So, it can highly improve the stability and scan speed of the sensing system. In the experiment system, we use fiber Bragg grating and adjust its bandwidth to get a chirp grating.. The center wavelength of chirp grating is 1551.60nm, and the pass-band wavelength is 7nm. The LPG is written on a standard single mode fiber with microlens array. The grating has a period of 440?m and a length of 3 cm. The center wavelength of LPG is 1558nm, and the falling edge of LPG is from 1540nm to 1555nm. We investigate light power by using a monitor magnify circuit, while the reflected wavelength of FBG by using optical spectrum analyzer. This system has high linear output and the linear fitting is 0.9918. The windage is due to the non-perfect square spectral profile of the reference chirp fiber grating.

Liu, Bo; Zeng, Jian; Xiao, Chun-Xian; Kai, Gui-Yun; Dong, Xiaoyi

2004-04-01

439

ONE-SHOT THREE-DIMENSIONAL SURFACE PROFILOMETRY USING DMD-BASED TWO-FREQUENCY MOIRÉ AND FOURIER TRANSFORM TECHNIQUE  

Microsoft Academic Search

This article presents an optical measurement method for acquiring rapidly accurate geometric 3-D surface morphology of objects. To achieve high-speed profilometry and avoid disturbance due to in-field vibration, one-shot Fourier transform profilometry (FTP) using two- wavelength digital moiré pattern was developed to detect the morphology of the measured object at a speed of up to 60 frames or more per

L. C. Chen; C. H. Cho; X. L. Nguyen

2009-01-01

440

DETECTION OF PARTIAL DISCHARGE IN CAST-RESIN DRY-TYPE TRANSFORMER BY USING ACOUSTIC EMISSION TECHNIQUE  

Microsoft Academic Search

With a view to providing a stable electric quality, it is very important for industry to maintain their electronic equipment and to predict and diagnose their failures. Cast-resin dry-type transformers are humidity-proof, low-noise, inflammable and not harmful to the environment, so they are widely used in hospitals, high-tech companies, MRT system and aircraft industry. In order to increase the transmission

Ching-Chau Su; Hsien-Cheng Liu; Yu-Jung Lin; Ching-Shun Yi; Jiann-Fuh Chen

441

Developing and Evaluating Techniques for Localizing Pollutant Emission Sources with Open-Path Fourier Transform Infrared Measurements and Wind Data  

Microsoft Academic Search

This paper presents the simulation and field evaluation results of two approaches to localize pollutant emission sources with open-path Fourier transform infrared (OPFTIR) spectroscopy. The first approach combined the plume’s peak location information reconstructed from the Smooth Basis Function Minimization (SBFM) algorithm and the wind direction data to calculate source projection lines. In the second approach, the plume’s peak location

Chang-Fu Wu; Ching-Hui Chen; Shih-Ying Chang; Pao-Erh Chang; Ruei-Hou Shie; Lung-Yu Sung; Jen-Chih Yang; Jen-Wei Su; Chang-Tang Chang; Chyow-San Chiou; Je-Lueng Shie; Yu-Min Chang; H. Frey; Kangwook Kim; Shih-Hao Pang; William Rasdorf; Phil Lewis; William Faulkner; Bryan Shaw; Tom Grosch; Rhona Julien; Jonathan Levy; Gary Adamkiewicz; Russ Hauser; John Spengler; Robert Canales; H. Hynes; Thomas Stock; Maria Morandi; Masoud Afshar; Kuenja Chung; Phirun Saiyasitpanich; Tim Keener; Mingming Lu; Fuyan Liang; Soon-Jai Khang; Kang-Shin Chen; Hsin-Kai Wang; Yen-Ping Peng; Wen-Cheng Wang; Chia-Hsiu Chen; Chia-Hsiang Lai; Eugene Kim; Philip Hopke; Le Nghiem; Nguyen Oanh; Michelle Bergin; Armistead Russell; Mehmet Odman; Daniel Cohan; William Chameides

2008-01-01

442

Laser plasma acceleration with a negatively chirped pulse: all-optical control over dark current in the blowout regime  

NASA Astrophysics Data System (ADS)

Recent?experiments?with?100 terawatt-class,?sub-50 femtosecond?laser pulses show that electrons self-injected into a laser-driven electron density bubble can be accelerated above 0.5 gigaelectronvolt energy in a sub-centimetre-length rarefied plasma. To reach this energy range, electrons must ultimately outrun the bubble and exit the accelerating phase; this, however, does not ensure high beam quality. Wake excitation increases the laser pulse bandwidth by red-shifting its head, keeping the tail unshifted. Anomalous group velocity dispersion of radiation in plasma slows down the red-shifted head, compressing the pulse into a few-cycle-long piston of relativistic intensity. Pulse transformation into a piston causes continuous expansion of the bubble, trapping copious numbers of unwanted electrons (dark current) and producing a poorly collimated, polychromatic energy tail, completely dominating the electron spectrum at the dephasing limit. The process of piston formation can be mitigated by using a broad-bandwidth (corresponding to a few-cycle transform-limited duration), negatively chirped pulse. Initial blue-shift of the pulse leading edge compensates for the nonlinear frequency red-shift and delays the piston formation, thus significantly suppressing the dark current, making the leading quasi-monoenergetic bunch the dominant feature of the electron spectrum near dephasing. This method of dark current control may be feasible for future experiments with ultrahigh-bandwidth, multi-joule laser pulses.

Kalmykov, S. Y.; Beck, A.; Davoine, X.; Lefebvre, E.; Shadwick, B. A.

2012-03-01

443

Chirped moire fiber gratings operating on two-wavelength channels for use as dual-channel dispersion compensators  

Microsoft Academic Search

Long continuously chirped moire fiber gratings are demonstrated. Clean, dual-channel operation with dispersion equivalent to 100 and 200 km of standard fiber is shown from gratings of lengths 35.1 cm and 1 m. The gratings show reflection and time-delay characteristics of the same high quality as previously reported in single-channel chirped gratings

Morten Ibsen; Michael K. Durkin; Richard I. Laming

1998-01-01

444

Chirped Steady pi-pulses of Light of an Arbitrary Duration in a Lossy, Exactly Resonant Inverted Medium  

Microsoft Academic Search

It is shown that the steady ? -pulses of light in a lossy, resonant inverted medium can have an arbitrary duration greater than a critical value and are in general chirped. The non-chirped ? -pulses of fixed duration (for a given population inversion) obtained by Arecchi and Bonifacio and by Lamb is a special case of our results when the

Hari Prakash; G. S. Bhatnagar

1979-01-01

445

Responses of Neurons in Cat Primary Auditory Cortex to Bird Chirps: Effects of Temporal and Spectral Context  

Microsoft Academic Search

The responses of neurons to natural sounds and simplified natural sounds were recorded in the primary auditory cortex (AI) of halothane-anesthetized cats. Bird chirps were used as the base natural stimuli. They were first presented within the orig- inal acoustic context (at least 250 msec of sounds before and after each chirp). The first simplification step consisted of ex- tracting

Omer Bar-Yosef; Yaron Rotman; Israel Nelken

446

UTILIZING A CHIRP SONAR TO ACCURATELY CHARACTERIZE NEWLY DEPOSITED MATERIAL AT THE CALCASIEU OCEAN DREDGED MATERIAL DISPOSAL SITE, LOUISIANA  

EPA Science Inventory

The distribution of dredged sediments is measured at the Calcasieu Ocean Dredged Material Disposal Site (ODMDS) using a chirp sonar immediately after disposal and two months later. ubbottom reflection data, generated by a chirp sonar transmitting a 4 to 20 kHz FM sweep, is proces...

447

Theoretical and Experimental Study of the Injection-Locked TEA COâ Laser Incorporating Electron-Plasma Prepulse Chirp Phenomena  

Microsoft Academic Search

Electron-plasma-induced chirping phenomena are incorporated into a quantitative theoretical treatment of an injection-locked compact TEA COâ laser. For the first time, inferred estimates of both the magnitude and sense of the single mode detuning range asymmetry about resonance are shown to agree with experimentally derived data. Conditions for chirp-free operation are discussed and demonstrated.

A. K. Kar; R. G. Harrison; N. R. Heckenberg; D. M. Tratt

1955-01-01

448

Extended chirp scaling algorithm for air- and spaceborne SAR data processing in stripmap and ScanSAR imaging modes  

Microsoft Academic Search

Presents a generalized formulation of the extended chirp scaling (ECS) approach for high precision processing of air- and spaceborne SAR data. Based on the original chirp scaling function, the ECS algorithm incorporates a new azimuth scaling function and a subaperture approach, which allow an effective phase-preserving processing of ScanSAR data without interpolation for azimuth geometric correction. The azimuth scaling can

A. Moreira; J. Mittermayer; R. Scheiber

1996-01-01

449

FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): An Ultra-Broadband Spatially Dispersed Regenerative Amplifier Free from Spatial Chirp  

NASA Astrophysics Data System (ADS)

An ultra-broadband Ti:sapphire regenerative amplifier based on spatially dispersed amplification is demonstrated experimentally Departing from previous reports, a new design of the cavity gets the amplified pulse free from spatial chirp. Utilizing this new regenerative amplifier, chirped pulses with bandwidth (FWHM) of about 80 nm are obtained, and the bandwidth is limited only by that of the incident seed pulses.

Li, Chuang; Leng, Yu-Xin; Zhang, Chun-Mei; Liang, Xiao-Yan; Li, Ru-Xin; Xu, Zhi-Zhan

2008-06-01

450

Flexible time domain averaging technique  

NASA Astrophysics Data System (ADS)

Time domain averaging(TDA) is essentially a comb filter, it cannot extract the specified harmonics which may be caused by some faults, such as gear eccentric. Meanwhile, TDA always suffers from period cutting error(PCE) to different extent. Several improved TDA methods have been proposed, however they cannot completely eliminate the waveform reconstruction error caused by PCE. In order to overcome the shortcomings of conventional methods, a flexible time domain averaging(FTDA) technique is established, which adapts to the analyzed signal through adjusting each harmonic of the comb filter. In this technique, the explicit form of FTDA is first constructed by frequency domain sampling. Subsequently, chirp Z-transform(CZT) is employed in the algorithm of FTDA, which can improve the calculating efficiency significantly. Since the signal is reconstructed in the continuous time domain, there is no PCE in the FTDA. To validate the effectiveness of FTDA in the signal de-noising, interpolation and harmonic reconstruction, a simulated multi-components periodic signal that corrupted by noise is processed by FTDA. The simulation results show that the FTDA is capable of recovering the periodic components from the background noise effectively. Moreover, it can improve the signal-to-noise ratio by 7.9 dB compared with conventional ones. Experiments are also carried out on gearbox test rigs with chipped tooth and eccentricity gear, respectively. It is shown that the FTDA can identify the direction and severity of the eccentricity gear, and further enhances the amplitudes of impulses by 35%. The proposed technique not only solves the problem of PCE, but also provides a useful tool for the fault symptom extraction of rotating machinery.

Zhao, Ming; Lin, Jing; Lei, Yaguo; Wang, Xiufeng

2013-09-01

451

High-energy, high-contrast, multiterawatt laser pulses by optical parametric chirped-pulse amplification.  

PubMed

We describe a compact, reliable, high-power, and high-contrast noncollinear optical parametric chirped-pulse amplifier system. With a broadband Ti:sapphire oscillator and grating-based stretching and compression, the chirped pulses are amplified from 0.1 nJ to 122 mJ in type I beta-barium borate optical parametric chirped-pulse amplifiers with a total gain of over 10(9) at 10 Hz repetition rate. Pulse compression down to 19-fs duration achieved after amplification indicates a peak power of 3.2 TW at an average power of 0.62 W. The prepulse contrast is measured to be less than 10(-8) on picosecond time scales. PMID:17700770

Kiriyama, Hiromitsu; Mori, Michiaki; Nakai, Yoshiki; Yamamoto, Yoichi; Tanoue, Manabu; Akutsu, Atsushi; Shimomura, Takuya; Kondo, Shuji; Kanazawa, Shuhei; Daido, Hiroyuki; Kimura, Toyoaki; Miyanaga, Noriaki

2007-08-15

452

Transformation 2 - Transformation Methods  

NSDL National Science Digital Library

This lesson explains the procedure of introducing a new gene into a plant cell (transformation). It discusses the main goals of the transformation process and describes the four main methods of transformation.

453

Generation of an isolated sub-40-as pulse using two-color laser pulses: Combined chirp effects  

SciTech Connect

In this paper, we theoretically discuss the combined chirp effects on the isolated attosecond generation when a model Ar is exposed to an intense 5-fs, 800-nm fundamental chirped pulse combined with a weak 10-fs, 1200-nm controlling chirped pulse. It shows that for the case of the chirp parameters {beta}{sub 1} = 6.1 (corresponding to the 800-nm field) and {beta}{sub 2} = 4.0 (corresponding to the 1200-nm field), both the harmonic cutoff energy and the supercontinuum can be remarkably extended resulting in a 663-eV bandwidth. Moreover, due to the introduction of the chirps, the short quantum path is selected to contribute to the harmonic spectrum. Finally, by superposing a properly selected harmonic spectrum in the supercontinuum region, an isolated pulse as short as 31 as (5 as) is generated without (with) phase compensation.

Feng, Liqiang [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Chu, Tianshu [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Institute for Computational Sciences and Engineering, Laboratory of New Fiber Materials and Modern Textile, the Growing Base for State Key Laboratory, Qingdao University, Qingdao, 266071 (China)

2011-11-15

454

A simple photonic generation of linearly chirped microwave pulse with large time-bandwidth product and high compression ratio.  

PubMed

Based on the heterodyne beating between the pre-chirped optical pulse and the continuous wave (CW) light in a wideband photodetector (PD), linearly chirped microwave pulse with time duration of 3.2ns and bandwidth of 33GHz, which yields a large time-bandwidth product (TBWP) of 106 and high compression ratio of 160, is generated in our experiment. Dispersion compensation fiber (DCF) with uniform response across broad bandwidth is used for providing the original linear chirp in our method, which shows the promise to generate linearly chirped microwave pulse with bandwidth of up to THz. The flexibility of the center frequency and the stability of the time-frequency performance are demonstrated by generating different types of linearly chirped microwave pulses. The range resolution of our generated microwave pulse is also verified by off-line processing. PMID:24104226

Gao, Hongbiao; Lei, Cheng; Chen, Minghua; Xing, Fangjian; Chen, Hongwei; Xie, Shizhong

2013-10-01

455

Karyotype analysis of tumorigenic human bronchial epithelial cells transformed by chrysolite asbestos using chemically induced premature chromosome condensation technique.  

PubMed

We examined karyotypic changes of tumorigenic human bronchial epithelial cell lines transformed by asbestos fibers. Using Calyculin A mediated premature chromosome condensation (PCC) assay and Giemsa-trypsin banding, we showed that the common changes of all tumorigenic cell lines were the loss of one or two copies of chromosome 5, the monosomy of chromosome 19 and the increased trisomy of chromosome 8. The results indicate that the karyotypic change of chromosome 5, 8 and 19 could play an important role in asbestos-induced tumorigenic conversion of human bronchial epithelial cells from an immortalized to tumorigenic state. PMID:11408947

Suzuki, M; Piao, C Q; Zhao, Y L; Hei, T K

2001-07-01

456

Best chirplet chain: Near-optimal detection of gravitational wave chirps  

SciTech Connect

The list of putative sources of gravitational waves possibly detected by the ongoing worldwide network of large scale interferometers has been continuously growing in the last years. For some of them, the detection is made difficult by the lack of a complete information about the expected signal. We concentrate on the case where the expected gravitational wave (GW) is a quasiperiodic frequency modulated signal i.e., a chirp. In this article, we address the question of detecting an a priori unknown GW chirp. We introduce a general chirp model and claim that it includes all physically realistic GW chirps. We produce a finite grid of template waveforms which samples the resulting set of possible chirps. If we follow the classical approach (used for the detection of inspiralling binary chirps, for instance), we would build a bank of quadrature matched filters comparing the data to each of the templates of this grid. The detection would then be achieved by thresholding the output, the maximum giving the individual which best fits the data. In the present case, this exhaustive search is not tractable because of the very large number of templates in the grid. We show that the exhaustive search can be reformulated (using approximations) as a pattern search in the time-frequency plane. This motivates an approximate but feasible alternative solution which is clearly linked to the optimal one. The time-frequency representation and pattern search algorithm are fully determined by the reformulation. This contrasts with the other time-frequency based methods presented in the literature for the same problem, where these choices are justified by 'ad hoc' arguments. In particular, the time-frequency representation has to be unitary. Finally, we assess the performance, robustness and computational cost of the proposed method with several benchmarks using simulated data.

Chassande-Mottin, Eric [CNRS, Observatoire de la Cote d'Azur, ARTEMIS, BP 4229 06304 Nice Cedex 4 (France); Pai, Archana [INFN, Sezione Roma 1-P.le Aldo Moro, 2 00185 Rome (Italy)

2006-02-15

457

Coherence and its estimation via the partitioned modified chirp-Z transform  

Microsoft Academic Search

The application of the coherence function between two wide-sense stationary random processes is considered, including methods for linear and nonlinear system analysis, measuring signal-to-noise ratio, and determining time delay. Examples of misleading results owing to improper model identification and biased estimation are presented. Estimation of coherence is studied with emphasis on how practical estimation errors such as bias can be

G. C. Carter; C. H. Knapp

1975-01-01

458

Application of the chirp-z transform to fractional interpolation in DMT modems  

Microsoft Academic Search

Sampling clock synchronization in multi carrier systems, such as discrete multitone (DMT) digital subscriber line modems, can be done with a phase locked loop. This requires expensive voltage-controlled oscillators (VCO). Alternatively, clock-offset compensation can be done completely in the digital domain, replacing the VCO with a cheaper free-running oscillator. This solution requires the signal of interest to be fractionally interpolated

Fabio Pisoni

2005-01-01

459

The Polar Format Imaging Algorithm Based on Double Chirp-Z Transforms  

Microsoft Academic Search

Spotlight mode offers finer azimuth resolution than that achievable in stripmap mode using the same physical antenna. The most popular spotlight synthetic aperture radar (SAR) reconstruction method is the classic polar format algorithm (PFA). However, PFA needs to perform range and azimuth interpolation operations during SAR imaging, which, in turn, affect the imaging precision and the computation efficiency. In this

Yu Tang; Meng-Dao Xing; Zheng Bao

2008-01-01

460

Adaptive evaluation of the Sommerfeld-type integral using the chirp z-transform  

Microsoft Academic Search

An adaptive integration algorithm for the computation of the Sommerfeld-type integral has been developed. The algorithm allows the user to specify the precise location of the desired range sample points and change the integration contour. In addition, the algorithm can be used to recompute the Sommerfeld-type integral with different range resolutions without recomputing the integrand. It is also shown how

Y. L. Li; C. H. Liu; S. J. Franke

1991-01-01

461

Application of Image Reconstruction by Means of Chirp z-Transform  

Microsoft Academic Search

The optical CT (Computerized Tomogra- phy), which utilises light transmitted through a semi-opaque object extends vision to the inside of objects. The projection profiles of the optical CT are smeared due to the scattering of light in a translucent medium. In the image reconstruc- tion for MRI (Magnetic Resonance Imaging), FID (Free Induction Decay) signals consisting of de- caying sinusoids

Kunio Takaya; Tie-nan Ma; Koichi Shimizu; Masataka Kitama; Tomohisa Mikami

1990-01-01

462

Two dimension chirp-Z transform for polar format imaging algorithm  

Microsoft Academic Search

Spotlight SAR is an efficiency way to obtain high resolution radar imagery. The classic polar format algorithm (PFA) is the widely used method for spotlight SAR imagery reconstruction, but PFA need two dimension interpolation operation in SAR imaging, which has influence on the imaging precision and computation efficiency. This paper presents a novel polar format Algorithm based on two dimension

Tang Yu; Xing Meng-dao

2007-01-01

463

Chirped pulses of microwave radiation as a light source in Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

With recent advances in digital-to-analog and analog-to-digital speeds the possibility of performing high resolution (< 100 kHz), broadband (> 2 GHz per acquisition event) pure rotational spectroscopy has been realized. We have constructed several spectrometers of this type and will demonstrate their benefits. Target systems include mixed halogenated systems, functionalized hydrocarbons, and heavy metal-containing systems. Information obtained relates to molecular geometric structures, group electronegativities, and molecular electronic structures.

Cooke, Stephen; Grubbs, Garry, II; Dewberry, Christopher

2010-03-01

464

Pulse dynamics in a passively mode-locked chirped-pulse fiber laser  

Microsoft Academic Search

We report experimental and numerical results on the new pulse dynamics in a passively mode-locked ytterbium-doped fiber laser\\u000a operating in the chirped-pulse regime. Due to the negligible nonlinearity of added highly-positive GVD segment in the purely-normal-dispersion\\u000a regime, highly-positive chirped pulses can be formed through weak intra-cavity temporal and spectral breathing. Numerical\\u000a simulations reveal intra-cavity pulse evolution with local temporal stretching

B. Ortaç; M. Plötner; J. Limpert; A. Tünnermann

2010-01-01

465

Injection-seeded optical parametric amplifier for generating chirped nanosecond pulses.  

PubMed

We constructed an optical parametric amplifier with BiBO crystals, which was injection seeded by a phase-modulated cw beam in the 1,040-1,070 nm region. Two-stage pre-amplification by Yb-doped fibers were implemented for stable injection to the OPA. The frequency chirp in the OPA pulse was actively controlled by adjusting the RF wave for the phase modulation and its synchronization to the OPA firing. Down/up chirps with up to 500 MHz shift were demonstrated. The output pulse energy was ~40 mJ, which is sufficient for future application of frequency conversion and coherent population transfer. PMID:23482098

Miyake, Shinichirou; Ohshima, Yasuhiro

2013-03-11

466

Prepulse suppression and optimization of backward Raman amplification with a chirped pump laser beam.  

PubMed

Two-dimensional particle-in-cell (PIC) simulations have been performed to demonstrate how chirping the pump laser beam can make the seed backward Raman amplification more efficient. The PIC code ocean is detailed and validated with theoretical analysis of the three-wave coupling. Particular attention is devoted to the impact of numerical noise on Raman scattering. Once the numerical parameters are set, one- and two-dimensional simulations exhibit the ability to suppress the pedestal pulse preceding the amplified seed laser beam and lower the spontaneous Raman scattering by appropriately choosing the pump chirp value. PMID:23679532

Nuter, R; Tikhonchuk, V

2013-04-22

467

Dynamics of surface solitons at the edge of chirped optical lattices  

SciTech Connect

We address soliton formation at the edge of chirped optical lattices imprinted in Kerr-type nonlinear media. We find families of power thresholdless surface waves that do not exist at other types of lattice interfaces. Such solitons form due to combined action of internal reflection at the interface, distributed Bragg-type reflection, and focusing nonlinearity. Remarkably, we discover that surfaces of chirped lattices are soliton attractors: Below an energy threshold, solitons launched well within the lattice self-bend toward the interface, and then stick to it.

Kartashov, Yaroslav V.; Torner, Lluis [ICFO-Institut de Ciencies Fotoniques, and Universitat Politecnica de Catalunya, Mediterranean Technology Park, 08860 Castelldefels (Barcelona) (Spain); Vysloukh, Victor A. [Departamento de Fisica y Matematicas, Universidad de las Americas - Puebla, Santa Catarina Martir, 72820, Puebla (Mexico)

2007-07-15

468

Optimal Bichromatic Two-Photon Excitation with Near-Resonant Chirped Pulses  

SciTech Connect

We investigate a method for creating complete population inversion in a three level system by using bichromatic two-photon coherent excitations with laser pulses, and study the dependence of the optimal population transfer on the chirp of the pulses. We observe that the population inversion does not monotonously decrease with increasing the time-bandwidth product, and that the excitation depends on the sign of the chirp of the individual pulses. Our results, which evidence a worthwhile strategy for coherent population transfer in three level systems, are particularized to the level structure of atomic sodium, with regard to applications in bichromatic mesospheric guide stars.

Serrat, Carles [DFEN-Universitat Politecnica de Catalunya, Colom 1, 08222 Terrassa, Barcelona (Spain); Biegert, Jens [ICREA and ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels, Barcelona (Spain)

2007-12-26

469

Prepulse suppression and optimization of backward Raman amplification with a chirped pump laser beam  

NASA Astrophysics Data System (ADS)

Two-dimensional particle-in-cell (PIC) simulations have been performed to demonstrate how chirping the pump laser beam can make the seed backward Raman amplification more efficient. The PIC code ocean is detailed and validated with theoretical analysis of the three-wave coupling. Particular attention is devoted to the impact of numerical noise on Raman scattering. Once the numerical parameters are set, one- and two-dimensional simulations exhibit the ability to suppress the pedestal pulse preceding the amplified seed laser beam and lower the spontaneous Raman scattering by appropriately choosing the pump chirp value.

Nuter, R.; Tikhonchuk, V.

2013-04-01

470

ATOMIC AND MOLECULAR PHYSICS: Lithium atom population transfer by population trapping in a chirped microwave pulse  

NASA Astrophysics Data System (ADS)

Using a time-dependent multilevel approach, we demonstrate that lithium atoms can be transferred to states of lower principle quantum number by exposing them to a frequency chirped microwave pulse. The population transfer from n = 79 to n = 70 states of lithium atoms with more than 80% efficiency is achieved by means of the sequential two-photon ?n = -1 transitions. It is shown that the coherent control of the population transfer can be accomplished by the optimization of the chirping parameters and microwave field strength. The calculation results agree well with the experimental ones and novel explanations have been given to understand the experimental results.

Jia, Guang-Rui; Zhang, Xian-Zhou; Ren, Zhen-Zhong; Wu, Su-Ling

2009-12-01

471

Reflectivity of linear and nonlinear gamma radiated apodized chirped Bragg grating under ocean  

SciTech Connect

In this paper, the effect Co{sup 60} gamma radiation is investigated on the effective refractive index of apodized chirped Bragg grating. Nine apodization profiles are considered. Comparison between the reflectivity of the gamma radiated and non radiated fiber Bragg grating has been carried out. The electric field of signals propagating through the apodized chirped fiber Bragg grating (ACFBG) is first calculated from which, new values for the refractive index are determined. The nonlinear effects appear on the ACFBG reflectivity. The effect of nonlinearity and undersea temperature and pressure on the grating is also studied.

Hamdalla, Taymour A. [Faculty of Science, Alexandria University, Alexandria (Egypt); Faculty of Science, Tabuk University, Tabuk (Saudi Arabia)

2012-09-06

472

Microjoule pulse energy from a chirped-pulse Ti:sapphire oscillator with cavity dumping.  

PubMed

We demonstrate a chirped-pulse Ti:sapphire laser oscillator with both Kerr-lens and semiconductor- saturable-absorber-mirror-assisted mode locking generating 1.1 microJ pulses at 1 MHz pulse repetition rate. The pulses are coupled out of the laser cavity by means of an acousto-optical cavity dumper, have a spectral width that supports a Fourier limit of 74 fs, and currently have a chirped-pulse duration of 5 ps. After compressing the pulses, this laser will be an ideal tool for efficient high-harmonic generation directly from a laser oscillator. PMID:19282917

Siegel, Martin; Pfullmann, Nils; Palmer, Guido; Rausch, Stefan; Binhammer, Thomas; Kovacev, Milutin; Morgner, Uwe

2009-03-15

473

Dual-Chirped Optical Parametric Amplification for Generating High-Power Infrared Pulses  

NASA Astrophysics Data System (ADS)

We propose and calculate a novel OPA method for obtaining an ultrafast high-power infrared pulse source, called dual-chirped OPA (DC-OPA), based on a Ti:sapphire laser system in a collinear configuration. By chirping both pump and seed pulses in an optimized way, high-energy pump pulses can be utilized for a DC-OPA process without exceeding the damage threshold of BBO crystals, and broadband signal and idler pulses can be generated with a total conversion efficiency approaching 40%. Furthermore, the few-cycle idler pulses with a passively stabilized carrier-envelope phase (CEP) can be generated by the difference frequency generation (DFG) process.

Zhang, Q.; Takahashi, E. J.; Mücke, O. D.; Lu, P.; Midorikawa, K.

474

Tunable chirped microwave photonic filter employing a dispersive Mach-Zehnder structure.  

PubMed

A Mach-Zehnder structure with modulation in one arm and dispersive time delay in the other is proposed to implement highly flexible single-bandpass chirped microwave photonic filters based on broadband optical sources. Both the amplitude response and the time delay slope can be fully reconfigured via control of the optical spectra and dispersion. The passband can also be widely tuned without changing the shape. A chirped filter with a bandwidth of ?4?GHz, a delay slope of ?-0.6?ns/GHz, and a tunability up to 40?GHz is demonstrated experimentally. PMID:21886263

Xue, Xiaoxiao; Zheng, Xiaoping; Zhang, Hanyi; Zhou, Bingkun

2011-09-01

475

Optimal water and waste-load allocations in rivers using a fuzzy transformation technique: a case study.  

PubMed

In this paper, a new methodology is developed for integrated allocation of water and waste-loads in river basins utilizing a fuzzy transformation method (FTM). The fuzzy transformation method is used to incorporate the existing uncertainties in model inputs. In the proposed methodology, the FTM, as a simulation model, is utilized in an optimization framework for constructing a fuzzy water and waste-loads allocation model. In addition, economic as well as environmental impacts of water allocation to different water users are considered. For equitable water and waste load allocation, all possible coalition of water users are considered and total benefit of each coalition, which is a fuzzy number, is reallocated to water users who are participating in the coalition. The fuzzy cost savings are reallocated using a fuzzy nucleolus cooperative game and the FTM. As a case study, the Dez River system in south-west of Iran is modeled and analyzed using the methodology developed here. The results show the effectiveness of the methodology in optimal water and waste-loads allocations under uncertainty. PMID:22773144

Nikoo, Mohammad Reza; Kerachian, Reza; Karimi, Akbar; Azadnia, Ali Asghar

2012-07-10

476

Fourier transform-infrared spectroscopy and Gas chromatography-mass spectroscopy: Reliable techniques for analysis of Parthenium mediated vermicompost  

NASA Astrophysics Data System (ADS)

Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectroscopy have been carried out to investigate the chemical composition of Parthenium mediated vermicompost. Four different concentrations of Parthenium and cow dung mixtures were vermicomposted using the earthworms (Eudrilus eugeniae). FT-IR spectra reveal the absence of Parthenin toxin (sesquiterpene lactone) and phenols in vermicompost which was obtained from high concentration of cow dung mixed treatments. GC-MS analysis shows no phenolic compounds and predominant level of intermediate metabolites such as 4,8,12,16-Tetramethylheptadecan-4-olide (7.61%), 2-Pentadecanone, 6,10,14-trimethyl- (5.29%) and Methyl 16-methyl-heptadecanoate (4.69%) during the vermicomposting process. Spectral results indicated that Parthenin toxin and phenols can be eradicated via vermicomposting if mixed with appropriate quantity of cow dung.

Rajiv, P.; Rajeshwari, Sivaraj; Venckatesh, Rajendran

477

Female giant panda (Ailuropoda melanoleuca) chirps advertise the caller's fertile phase.  

PubMed

Although female mammal vocal behaviour is known to advertise fertility, to date, no non-human mammal study has shown that the acoustic structure of female calls varies significantly around their fertile period. Here, we used a combination of hormone measurements and acoustic analyses to determine whether female giant panda chirps have the potential to signal the caller's precise oestrous stage (fertile versus pre-fertile). We then used playback experiments to examine the response of male giant pandas to female chirps produced during fertile versus pre-fertile phases of the caller's reproductive cycle. Our results show that the acoustic structure of female giant panda chirps differs between fertile and pre-fertile callers and that male giant pandas can perceive differences in female chirps that allow them to determine the exact timing of the female's fertile phase. These findings indicate that male giant pandas could use vocal cues to preferentially associate and copulate with females at the optimum time for insemination and reveal the likely importance of female vocal signals for coordinating reproductive efforts in this critically endangered species. PMID:19955154

Charlton, Benjamin D; Keating, Jennifer L; Rengui, Li; Huang, Yan; Swaisgood, Ronald R

2009-12-02

478

Control of molecular vibrational excitation and dissociation by chirped intense infrared laser pulses. Rotational effects  

Microsoft Academic Search

We extend our previous studies on control of dissociation and vibrational excitation of a diatomic molecule using chirped, intense, infrared laser pulses [Phys. Rev. Lett. 65, 2355 (1990)]. The present model includes molecular rotations and a realistic molecular dipole function. The results obtained from numerical integration of the time-dependent Schro¨dinger equation show a considerable sensitivity of dissociation probabilities to the

Szczepan Chelkowski; André D. Bandrauk

1993-01-01

479

FY07 LDRD Final Report Precision, Split Beam, Chirped-Pulse, Seed Laser Technology.  

National Technical Information Service (NTIS)

The goal of this LDRD ER was to develop a robust and reliable technology to seed high-energy laser systems with chirped pulses that can be amplified to kilo-Joule energies and recompressed to sub-picosecond pulse widths creating extremely high peak powers...

C. W. Siders J. K. Crane J. W. Dawson M. J. Messerly R. J. Beach

2009-01-01

480

Design, fabrication, and analysis of chirped multilayer mirrors for reflection of extreme-ultraviolet attosecond pulses  

SciTech Connect

Chirped Mo/Si multilayer coatings have been designed, fabricated, and characterized for use in extreme-ultraviolet attosecond experiments. By numerically simulating the reflection of the attosecond pulse from a multilayer mirror during the optimization procedure based on a genetic algorithm, we obtain optimized layer designs. We show that normal incidence chirped multilayer mirrors capable of reflecting pulses of approximately 100 attoseconds (as) duration can be designed by enhancing the reflectivity bandwidth and optimizing the phase-shift behavior. The chirped multilayer coatings have been fabricated by electron-beam evaporation in an ultrahigh vacuum in combination with ion-beam polishing of the interfaces and in situ reflectivity measurement for layer thickness control. To analyze the aperiodic layer structure by hard-x-ray reflectometry, we have developed an automatic fitting procedure that allows us to determine the individual layer thicknesses with an error of less than 0.05 nm. The fabricated chirped mirror may be used for production of 150-160 as pulses.

Wonisch, A.; Neuhaeusler, U.; Kabachnik, N. M.; Uphues, T.; Uiberacker, M.; Yakovlev, V.; Krausz, F.; Drescher, M.; Kleineberg, U.; Heinzmann, U

2006-06-10