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1

Gravitational Waves from Rotating Neutron Stars and Evaluation of fast Chirp Transform Techniques  

NASA Technical Reports Server (NTRS)

X-ray observations suggest that neutron stars in low mass X-ray binaries (LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are significantly less than the break-up rates for essentially all realistic neutron star equations of state, suggesting that some process may limit the spin frequencies of accreting neutron stars to this range. If the accretion induced spin up torque is in equilibrium with gravitational radiation losses, these objects could be interesting sources of gravitational waves. I present a brief summary of current measurements of neutron star spins in LMXBs based on the observations of high-Q oscillations during thermonuclear bursts (so called 'burst oscillations'). Further measurements of neutron star spins will be important in exploring the gravitational radiation hypothesis in more detail. To this end I also present a study of fast chirp transform (FCT) techniques as described by Jenet and Prince in the context of searching for the chirping signals observed during X-ray bursts.

Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

2000-01-01

2

The interlaced chirp Z transform  

Microsoft Academic Search

In this paper we introduce the interlaced chirp Z transform (Interlaced CZT). It is based on the computation of several carefully staggered 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, as well as

Indranil Sarkar; Adly T. Fam

2006-01-01

3

Spacevariant Fourier Analysis: the Exponential Chirp Transform  

E-print Network

of the fast exponential chirp algorithm on a data­base of images in a template matching task, and also­Variant Image Processing, Fourier Analysis, Non­Uniform Sampling, Real­Time Imaging, Warped Template Matching to the Mellin­ Transform) provides a fast exponential chirp transform. This provides size and rotation

Schwartz, Eric L.

4

Spectral analysis using the CCD Chirp Z-transform  

NASA Technical Reports Server (NTRS)

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.

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

1978-01-01

5

Project Summary MRI: Development of a Chirped-Pulse, Fourier-Transform mm-Wave Pulsed  

E-print Network

Project Summary MRI: Development of a Chirped-Pulse, Fourier-Transform mm-Wave Pulsed Uniform technologies: chirped-pulse Fourier-transform mm-wave spectroscopy and pulsed uniform supersonic flows: The instrument will leverage the ultra-broadband Chirped-pulse Fourier-transform Microwave (CP

Baskaran, Mark

6

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

7

Progress Towards Chirped-Pulse Fourier Transform Thz Spectroscopy  

NASA Astrophysics Data System (ADS)

New opportunities are provided by the development of higher power THz frequency multiplier sources, the development of a broadband Chirped-Pulse FTMW spectroscopy technique at microwave and mm Wave frequencies, and recently demonstrated heterodyne hot electron bolometer detection technology in the THz frequency region with near quantum noise-limited performance and high spectral resolution. Combining these three technologies and extending the chirped-pulse technique to 0.85 THz enables a host of new applications. NIST is currently pursing applications as a point sensor for greenhouse gases, volatile organic compounds, and potentially human breath. The generation and detection of phase stable chirped pulses at 850 GHz will be demonstrated. A description of the experimental setup and preliminary data will be presented for nitrous oxide. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S. Shipman and B.H. Pate, Rev.Sci.Instrum. 79 (2008) 053103. E. Gerecht, D. Gu, L. You, K.S. Yngvesson, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES. 56, (2008) 1083.

Douglass, Kevin O.; Plusquellic, David F.; Gerecht, Eyal

2010-06-01

8

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

9

Fourier Transforms of Finite Chirps Peter G. Casazza and Matthew Fickus  

E-print Network

is altered whenever the wave is emanating from or reflecting off a moving body. As such, chirps have-Fourier transform is introduced. Chirplets have been used in image processing for over a decade [5]. For that matter

Casazza, Pete

10

Frequency Correction for MIRO Chirp Transformation Spectroscopy Spectrum  

NASA Technical Reports Server (NTRS)

This software processes the flyby spectra of the Chirp Transform Spectrometer (CTS) of the Microwave Instrument for Rosetta Orbiter (MIRO). The tool corrects the effect of Doppler shift and local-oscillator (LO) frequency shift during the flyby mode of MIRO operations. The frequency correction for CTS flyby spectra is performed and is integrated with multiple spectra into a high signal-to-noise averaged spectrum at the rest-frame RF frequency. This innovation also generates the 8 molecular line spectra by dividing continuous 4,096-channel CTS spectra. The 8 line spectra can then be readily used for scientific investigations. A spectral line that is at its rest frequency in the frame of the Earth or an asteroid will be observed with a time-varying Doppler shift as seen by MIRO. The frequency shift is toward the higher RF frequencies on approach, and toward lower RF frequencies on departure. The magnitude of the shift depends on the flyby velocity. The result of time-varying Doppler shift is that of an observed spectral line will be seen to move from channel to channel in the CTS spectrometer. The direction (higher or lower frequency) in the spectrometer depends on the spectral line frequency under consideration. In order to analyze the flyby spectra, two steps are required. First, individual spectra must be corrected for the Doppler shift so that individual spectra can be superimposed at the same rest frequency for integration purposes. Second, a correction needs to be applied to the CTS spectra to account for the LO frequency shifts that are applied to asteroid mode.

Lee, Seungwon

2012-01-01

11

An Iterative Template Matching Algorithm Using the ChirpZ Transform for Digital Image Watermarking  

E-print Network

of the watermark. In the first part of the template matching process, the rotation and scale compensationAn Iterative Template Matching Algorithm Using the Chirp­Z Transform for Digital Image Watermarking to cropping, scaling and rotation, the idea of using an invisible template embedded in the DFT domain has also

Genève, Université de

12

Estimation of multiple accelerated motions using chirp-Fourier transform and clustering.  

PubMed

Motion estimation in the spatiotemporal domain has been extensively studied and many methodologies have been proposed, which, however, cannot handle both time-varying and multiple motions. Extending previously published ideas, we present an efficient method for estimating multiple, linearly time-varying motions. It is shown that the estimation of accelerated motions is equivalent to the parameter estimation of superpositioned chirp signals. From this viewpoint, one can exploit established signal processing tools such as the chirp-Fourier transform. It is shown that accelerated motion results in energy concentration along planes in the 4-D space: spatial frequencies-temporal frequency-chirp rate. Using fuzzy c-planes clustering, we estimate the plane/motion parameters. The effectiveness of our method is verified on both synthetic as well as real sequences and its advantages are highlighted. PMID:17283773

Alexiadis, Dimitrios S; Sergiadis, George D

2007-01-01

13

Estimation of phase derivatives using discrete chirp-Fourier-transform-based method.  

PubMed

Estimation of phase derivatives is an important task in many interferometric measurements in optical metrology. This Letter introduces a method based on discrete chirp-Fourier transform for accurate and direct estimation of phase derivatives, even in the presence of noise. The method is introduced in the context of the analysis of reconstructed interference fields in digital holographic interferometry. We present simulation and experimental results demonstrating the utility of the proposed method. PMID:19684794

Gorthi, Sai Siva; Rastogi, Pramod

2009-08-15

14

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave spectroscopy  

Microsoft Academic Search

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is presented. A new CP-FTMW spectrometer capable of measuring the entire 7.518.5GHz spectrum with a single polarizing pulse is described briefly. The CP-FTMW spectrometer takes advantage of recent advances in digital electronics by utilizing a 4.2GS\\/s arbitrary waveform generator as a frequency source and a 12GHz digital

Gordon G. Brown; Brian C. Dian; Kevin O. Douglass; Scott M. Geyer; Brooks H. Pate

2006-01-01

15

Technique for lymphocyte transformation  

PubMed Central

Current techniques for lymphocyte transformation are evaluated and criticised. A simple technique, designed to meet these criticisms, is described in detail, with particular reference to lymphocyte separation and scoring methods. PMID:5697050

Pentycross, C. R.

1968-01-01

16

Fourier-transform electron spin resonance with bandwidth-compensated chirp pulses.  

PubMed

Electron spin echo experiments using chirp pulses at X-band around 9GHz have been performed with a home-built spectrometer based on an arbitrary waveform generator. Primary echoes without phase dispersion were obtained by employing the Bhlen-Bodenhausen scheme with the refocusing pulse being half as long as the coherence-generating pulse. To account for physical bandwidth limitation by the resonator, the instantaneous sweep rate of the chirps was adapted to the spectrometer's frequency response function, which can be recorded from the sample under study within a few minutes. Such bandwidth-compensated chirp pulses are experimentally shown to achieve an almost uniform excitation bandwidth that exceeds the resonator bandwidth. This uniform excitation allows for computing frequency-domain spectra by Fourier-transformation (FT) of the echo signal. For a nitroxide in dilute solid solution with a spectral width of 200MHz, the FT EPR spectrum agrees remarkably well with a field-swept echo-detected EPR spectrum. The overall spectral perturbation for operation far beyond the resonator bandwidth was characterized by acquiring a 700MHz wide spectral range of a copper (II) EPR spectrum with nearly uniform amplitude with excitation and refocusing pulses of 200 and 100ns, respectively. Furthermore, peculiarities were observed in solid-state FT EPR spectra of disordered systems. To understand these peculiarities two-dimensional data sets were acquired that correlate the FT EPR spectrum to inversion recovery or nuclear modulation. The echo envelope modulation experiments reveal echo decay rates increased by enhanced instantaneous diffusion and passage-specific effects in the nuclear modulations. The latter effect can be suppressed by nuclear modulation averaging. Apparent longitudinal relaxation times for a given subset of orientations are influenced by nuclear modulation effects. Proper extraction of orientation-dependent relaxation times thus requires an experimental setup that minimizes the modulations. PMID:25063952

Doll, Andrin; Jeschke, Gunnar

2014-09-01

17

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

18

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

2008-04-01

19

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. Frazo; P. V. S. Marques; H. M. Salgado; J. L. Santos

2003-01-01

20

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

21

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

22

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. I. The low-temperature flow system  

NASA Astrophysics Data System (ADS)

We report the development of a new instrument that combines chirped-pulse microwave spectroscopy with a pulsed uniform supersonic flow. This combination promises a nearly universal detection method that can deliver isomer and conformer specific, quantitative detection and spectroscopic characterization of unstable reaction products and intermediates, product vibrational distributions, and molecular excited states. This first paper in a series of two presents a new pulsed-flow design, at the heart of which is a fast, high-throughput pulsed valve driven by a piezoelectric stack actuator. Uniform flows at temperatures as low as 20 K were readily achieved with only modest pumping requirements, as demonstrated by impact pressure measurements and pure rotational spectroscopy. The proposed technique will be suitable for application in diverse fields including fundamental studies in spectroscopy, kinetics, and reaction dynamics.

Oldham, James M.; Abeysekera, Chamara; Joalland, Baptiste; Zack, Lindsay N.; Prozument, Kirill; Sims, Ian R.; Park, G. Barratt; Field, Robert W.; Suits, Arthur G.

2014-10-01

23

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. I. The low-temperature flow system.  

PubMed

We report the development of a new instrument that combines chirped-pulse microwave spectroscopy with a pulsed uniform supersonic flow. This combination promises a nearly universal detection method that can deliver isomer and conformer specific, quantitative detection and spectroscopic characterization of unstable reaction products and intermediates, product vibrational distributions, and molecular excited states. This first paper in a series of two presents a new pulsed-flow design, at the heart of which is a fast, high-throughput pulsed valve driven by a piezoelectric stack actuator. Uniform flows at temperatures as low as 20 K were readily achieved with only modest pumping requirements, as demonstrated by impact pressure measurements and pure rotational spectroscopy. The proposed technique will be suitable for application in diverse fields including fundamental studies in spectroscopy, kinetics, and reaction dynamics. PMID:25338889

Oldham, James M; Abeysekera, Chamara; Joalland, Baptiste; Zack, Lindsay N; Prozument, Kirill; Sims, Ian R; Park, G Barratt; Field, Robert W; Suits, Arthur G

2014-10-21

24

High-spectral-resolution multiplex CARS spectroscopy using chirped pulses  

NASA Astrophysics Data System (ADS)

A novel technique for achieving high spectral resolution with a femtosecond laser system is presented. Transform-limited 800 nm, 90 femtosecond (fs) pulses pass off two gratings, stretching the pulse in time to a pulse width of several picoseconds due to an induced linear temporal chirp directly proportional to the grating separation. This chirped pulse is the degenerate pump (?P) and probe (?p) pulse for the CARS experiment. When overlapped in time with the 1050 nm, 90 fs transform-limited Stokes (?S) pulse, only a fraction of the chirped ?p pulse generates the CARS signal, thereby creating a temporal slit that defines the spectral resolution of the technique. Spectra for liquid methanol and liquid isooctane are presented, with ~6 cm-1 spectral resolution achieved for isooctane. Resonance enhancement and the mechanism of achieving high spectral resolution are shown by adjusting the ?S wavelength and ?p delay relative to the ?S pulse.

Knutsen, Kelly P.; Johnson, Justin C.; Miller, Abigail E.; Petersen, Poul B.; Saykally, Richard J.

2004-06-01

25

Methyl rotors in the gas phase: A study of o- and m-toluidine by chirped-pulse Fourier transform microwave spectroscopy  

Microsoft Academic Search

Microwave spectra of o- and m-toluidine were recorded in a pulsed supersonic jet using chirped pulse techniques. The spectra show both torsional and 14N quadrupole splittings at high resolution. From the torsional splittings, barrier heights were determined of 531 cm-1 and 2.0 cm-1 respectively. Using the quadrupole splittings, orbital occupancy numbers of the amino-nitrogen atoms were calculated. An apparent relationship

Ryan G. Bird; David W. Pratt

2011-01-01

26

Methyl rotors in the gas phase: A study of o- and m-toluidine by chirped-pulse Fourier transform microwave spectroscopy  

Microsoft Academic Search

Microwave spectra of o- and m-toluidine were recorded in a pulsed supersonic jet using chirped pulse techniques. The spectra show both torsional and 14N quadrupole splittings at high resolution. From the torsional splittings, barrier heights were determined of 531cm?1 and 2.0cm?1 respectively. Using the quadrupole splittings, orbital occupancy numbers of the amino-nitrogen atoms were calculated. An apparent relationship between these

Ryan G. Bird; David W. Pratt

2011-01-01

27

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

28

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

29

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

30

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

31

Transformer insulation monitoring by optical sensing techniques  

NASA Astrophysics Data System (ADS)

High voltage transformers use paper to insulate the electrical windings present in the core which is then subsequently immersed in oil. In service, the temperature of the windings will increase to typically 80 degrees C. If the transformer is loaded to beyond its design ratings, the temperature can exceed 100 degrees C causing the cellulose chains in the paper to cleave at an accelerated rate, resulting in the degradation of mechanical strength and performance of the insulation. If unchecked, this can lead to catastrophic failure of the transformed and accompanying disruption to electricity supply and large economic losses to the operating utility. Furfuraldehyde (FFA) is a chemical by-product which is released into the oil by the thermal degradation of the paper winding. The concentration of FFA within the oil has been directly related to the condition of the paper insulation. We have developed absorbance and fluorescence optical techniques incorporating a novel FFA- sensitive material which we have invested at our laboratories. This material has been incorporated into a prototype portable optoelectronic instrument for the measurement of FFA at the site of the transformer. Results of experiments will be presented, and the implication of these results for condition monitoring of HV transformer will be discussed.

Uttamchandani, Deepak G.; Blue, Robert; Farish, O.

1998-08-01

32

Chirped pulse enhancement of multiphoton absorption in molecular iodine Vladislav V. Yakovlev, Christopher J. Bardeen, Jianwe Che, Jianshu Cao,  

E-print Network

are observed for chirped pulses with respect to transform-limited, zero chirp pulses. Theoretical a negatively chirped pulse has the opposite ordering. A transform-limited pulse is of the shortest possible relative to the shortest, transform- limited pulse. Preliminary calculations suggest that this en

Cao, Jianshu

33

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

34

A Static Analysis Technique for Graph Transformation Systems  

E-print Network

A Static Analysis Technique for Graph Transformation Systems Paolo Baldan, Andrea Corradini,andrea,koenigb}@di.unipi.it Abstract. In this paper we introduce a static analysis technique for graph transformation systems. We in a direct and intuitive way. Graph Transformation Systems (GTSs) [18] add to the static description given

Baldan, Paolo

35

An improved processing sequence for uncorrelated Chirp sonar data  

NASA Astrophysics Data System (ADS)

Chirp sonar systems can be used to obtain high resolution seismic reflection images of the sub-seafloor during marine surveys. The exact knowledge of the Chirp signature allows the use of deterministic algorithms to process the data, similarly to that applied to Vibroseis data on land. Here, it is described an innovative processing sequence to be applied to uncorrelated Chirp data, which can improve vertical and lateral resolution compared to conventional methods. It includes application of a Wiener filter to transform a frequency-modulated sweep into a minimum-phase pulse sequence. In this way, the data become causal and can undergo predictive deconvolution to reduce ringing and enhance vertical resolution. Afterwards, FX-deconvolution and Stolt migration can be applied to obtain an improved imaging of the subsurface. The result of this procedure is a seismic reflection image with higher resolution than traditional ones, which are normally represented using the envelope function of the signal. This technique can be particularly useful for engineering-geotechnical surveys and archaeological investigations that require a fine detail imaging of the uppermost meters of the sub-seafloor.

Baradello, Luca

2014-03-01

36

Amplitude-modulation chirp imaging for contrast detection.  

PubMed

We propose an amplitude-modulation chirp imaging method for contrast detection with high-frequency ultrasound. Our proposed method detects microbubbles by extracting and then selectively compressing the component of the backscattered chirp signal modulated by changes in the radii of microbubbles at their resonance frequency. Microbubbles are sonicated simultaneously with a narrowband, low-frequency pumping signal at their resonance frequency and a wideband, high-frequency imaging chirp signal. Changes in the radii of the resonant microbubbles result in periodic changes in their acoustic cross section that modulate the amplitude of the backscattered imaging chirp signal, forming pumping and imaging frequency sum-and-difference chirp terms. The frequency-sum or -difference chirp component is then extracted by a bandpass filter (BPF). Because a long imaging pulse duration is required to obtain a sufficient modulation depth on the chirp for contrast detection and to facilitate frequency-sum-and-difference signal extraction with the BPF, a chirp with a longer-than-usual waveform is used so pulse compression of the extracted chirp signal can then be performed to maintain the axial resolution, and even further improve the signal-to-noise ratio and contrast-to-tissue ratio. Experiments performed on flow phantoms with and without a speckle-generating background were performed to demonstrate the efficacy of the proposed technique. These results indicate that our proposed method can potentially provide high-resolution contrast detection in the microvasculature. PMID:20800180

Li, Meng-Lin; Kuo, Yu-Chen; Yeh, Chih-Kuang

2010-09-01

37

A Static Analysis Technique for Graph Transformation Systems  

Microsoft Academic Search

In this paper we introduce a static analysis technique for graph transformation systems. We present an algorithm which, given a graph transformation system and a start graph, produces a nite struc- ture consisting of a hypergraph decorated with transitions (Petri graph) which can be seen as an approximation of the Winskel style unfolding of the graph transformation system. The fact

Paolo Baldan; Andrea Corradini; Barbara Knig

2001-01-01

38

Wavelet transform domain filters: a spatially selective noise filtration technique  

Microsoft Academic Search

Wavelet transforms are multiresolution decompositions that can be used to analyze signals and images. They describe a signal by the power at each scale and position. Edges can be located very effectively in the wavelet transform domain. A spatially selective noise filtration technique based on the direct spatial correlation of the wavelet transform at several adjacent scales is introduced. A

Yansun Xu; John B. Weaver; Dennis M. Healy Jr.; Jian Lu

1994-01-01

39

Compression of amplified chirped optical pulses  

Microsoft Academic Search

A system is reported which transposes a short-pulse amplification technique employed in radar to the optical regime and that, in principle, should be capable of producing short (1 pc or less) pulses with energies at the Joule level. The technique involves stretching a chirped optical pulse and then amplifying it before recompression. To date, 2-ps pulses with an energy of

D. Strickland; G. Mourou

1985-01-01

40

Fourier transform techniques for the inference of cloud motion  

NASA Technical Reports Server (NTRS)

The development and evaluation are reported of phase shift techniques based on the Fourier transform for the estimation of cloud motion from geosynchronous meteorological satellite photographs. An alternative approach to cloud motion estimation, involving thresholding, was proposed and studied.

Lo, R. C.; Rosenfeld, A.

1974-01-01

41

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

42

Weighted Fuzzy Interpolative Reasoning Based on Weighted Increment Transformation and Weighted Ratio Transformation Techniques  

Microsoft Academic Search

In this paper, we present a new weighted fuzzy interpolative reasoning method for sparse fuzzy rule-based systems. The proposed method uses weighted increment transformation and weighted ratio transformation techniques to handle weighted fuzzy interpolative reasoning in sparse fuzzy rule-based systems. It allows each variable that appears in the antecedent parts of fuzzy rules to associate with a weight between zero

Shyi-Ming Chen; Yaun-Kai Ko; Yu-Chuan Chang; Jeng-Shyang Pan

2009-01-01

43

Chirped pulse Raman amplifier  

NASA Astrophysics Data System (ADS)

All modern terawatt- and petawatt-class laser systems are based on the principle of chirped-pulse amplification (CPA). In this work, a compact subsystem that shifts a micro-joule portion of the chirped pulse energy to a new wavelength outside its original bandwidth, then amplifies it to millijoule energy without adding pump lasers, and without compromising the output of the fundamental CPA system in any significant way, has been developed and integrated into a standard terawatt-class CPA system. In this chirped pulse Raman amplifier sub-system, a 30 mJ portion of a chirped 800 nm fundamental pulse within the CPA system was split into two unequal portions, each of which impinged on a Raman-active barium nitrate, or Ba(NO3)2, crystal of length 5 cm. The weaker portion created a weak (15 J) first Stokes pulse (873 nm) by Stimulated Raman Scattering (SRS) in the first crystal, which then seeded a non-collinear four-wave-mixing process driven by the stronger portion of the split-off CPA pulse in the second crystal. The latter process amplified the first Stokes seed pulse to several millijoules with excellent beam quality. A study of Raman gain as a function of time delay between pump and Stokes pulse in the second crystal revealed a sharply peaked narrow interval (3 ps FWHM) of high gain and a wider interval (50 ps) of low gain. The amplified, chirped first Stokes pulse was successfully compressed to 100 fs duration using a grating pair of different line density than in the main CPA system, based on a comprehensive dispersion analysis of the optical path of the first Stokes pulse. The possibility of generating higher-order Stokes and anti-Stokes sidebands of the CPA pulse is also demonstrated. Further amplification of the sideband pulse by conventional methods, using an additional pump laser, appears straightforward. The chirped pulse Raman amplifier provides temporally synchronized fundamental and Raman sideband pulses for performing two-color, high-intensity laser experiments, some of which are briefly discussed. It can be integrated into any standard CPA system, and provides significant new versatility for high-intensity laser sources.

Grigsby, Franklin Bhogaraju

44

Real-Time Optical Hough Transform and Morphological Inspection Techniques.  

NASA Astrophysics Data System (ADS)

A real-time optical Hough transform inspection processor is described and applied to the industrial case study of the inspection of cigarette packages. The inspections are performed in real-time using a color Epson liquid crystal television as the input spatial light modulator. A new selective, real-time edge-enhancement technique is used to enhance edges only at the selected orientations which will Hough transform to peaks (this maximizes the signal to noise ratio in the Hough transform output). Several slices of the Hough transform are generated in parallel with a new computer generated hologram utilizing 1D modulated error diffusion. We benchmark our Hough transform processor with the inspection of 100 sample cigarette packages. Correct classification of all the packages (with defects that we intended to inspect for) was attained. We also discuss the confidence with which we can apply our laboratory sample set results to the industrial installation of our inspection processor. Extensions of the Hough transform are also described which generalize the Hough space to recognize shapes other than straight lines (e.g. circles, ellipses). We propose a new high speed acousto-optic architecture to implement these generalized Hough transforms. We also describe how the exact position of input lines can be extracted from Hough transform peak data. Typically, only the contour on which an input line resides is extracted from Hough data. Digital simulations illustrating both generalized Hough transformations and determination of input line position from Hough data are presented. Basic morphological transformations and their real-time optical implementation are discussed. We describe how morphological transformations are useful in inspection and show digital simulations and optical results of an inspection application (string detection in chopped tobacco) where morphological transformations are used.

Richards, Jeffrey Scott

45

Calibration of optical detectors using discrete Fourier transform techniques  

NASA Technical Reports Server (NTRS)

A method for determining the detector electrooptical transfer function (DEOTF) at different discrete frequencies simultaneously is presented. It involves simulation of the detector with a waveform of unknown frequency composition, such as a square wave or impulse function. The DEOTF is calculated as the ratio of the discrete Fourier transform of the detector output to the transform of the input waveform. This technique was successfully applied to Golay cell and bolometer detectors and can be used for other linear detector systems.

Hagopian, John G.; Eichhorn, William

1990-01-01

46

Control of Ultracold Collisions with Frequency-Chirped Light  

SciTech Connect

We report on ultracold atomic collision experiments utilizing frequency-chirped laser light. A rapid chirp below the atomic resonance results in adiabatic excitation to an attractive molecular potential over a wide range of internuclear separation. This leads to a transient inelastic collision rate which is large compared to that obtained with fixed-frequency excitation. The combination of high efficiency and temporal control demonstrates the benefit of applying the techniques of coherent control to the ultracold domain.

Wright, M.J.; Gould, P.L. [Department of Physics, U-3046, University of Connecticut, Storrs, Connecticut 06269 (United States); Gensemer, S.D. [Van der Waals-Zeeman Institut, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands); Vala, J. [Department of Chemistry and Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720 (United States); Kosloff, R. [Department of Physical Chemistry and the Fritz Haber Research Center for Molecular Dynamics, the Hebrew University, 91094 Jerusalem (Israel)

2005-08-05

47

New real time needle segmentation technique using grayscale Hough transformation  

NASA Astrophysics Data System (ADS)

Real-time needle segmentation and tracking is very important in image-guided surgery, biopsy, and therapy. In this paper, we described an automated technique to provide real-time needle segmentation from a sequence of 2-D ultrasound images for the use of guidance of a needle to the target in soft tissues. The Hough transform is used to find straight lines or analytic curves in binary image. Hough transform is applied usually to binary images. Hence one needs to convert, initially, the gray level image to a binary one (through thresholding, edge detection, or thinning) in order to apply the HT. While in the process of binarization, some information about line segments in the image may be lost when an inappropriate threshold is used. Gray-Scale Hough Transform can detect the line without binarization. Unfortunately, its high computational cost often prevents it from being applied in real-time applications without the help of specially designed hardware. In this paper, we proposed a needle segmentation technique based on a real-time gray-scale Hough transform. It is composed of an improved Gray Hough Transformation and a coarse-fine search strategy. Furthermore, the RTGHT (Real-Time Gray-Scale Hough Transform) technique is evaluated by patient breast biopsy images. Experiments with patient breast biopsy ultrasound (US) image sequences showed that our approach can segment the biopsy needle in real time (i.e., less than 60 ms) with the angular rms error of about 1 and the position rms error of about 0.5 mm an affordable PC computer without the help of specially designed hardware.

Qiu, Wu; Zhou, Hua; Ding, Mingyue; Zhang, Songgeng

2007-12-01

48

Chirped-pulse four-wave Raman mixing in molecular hydrogen  

NASA Astrophysics Data System (ADS)

Four-wave Raman mixing (FWRM) in molecular hydrogen was studied using chirped pump and Stokes pulses emitting at 802 and 1,203 nm, respectively. The group delay dispersion (GDD) of the anti-Stokes pulse was examined employing a frequency-resolved optical gating system at different GDDs of the pump and Stokes pulses (0 or 1,000 fs2). As a result, the energy and the sign of GDD for the anti-Stokes pulse remained unchanged, when the pump and Stokes pulses had the GDD with the same sign. When the sign was not the same, the energy decreased and only the portion useful for resonant FWRM was converted into a Raman emission. This technique has a potential for use in compensation of dispersion by passing the negatively chirped high-order Raman sidebands through the optics with positive chirps in the spectral region from the deep-ultraviolet to the near-infrared, to generate multiple transform-limited Raman pulses and then to produce an ultrashort optical pulse by a Fourier synthesis of these Raman emissions.

Shitamichi, Osamu; Kida, Yuichiro; Imasaka, Totaro

2014-07-01

49

Vibro-acoustic techniques to diagnose power transformers  

Microsoft Academic Search

This paper deals with new procedures based on vibro-acoustic techniques to diagnose power medium-voltage\\/low-voltage (MV\\/LV) transformers. The normal operating machines can be monitored and checked from a remote, dedicated diagnostic center where information is received directly from the field. The diagnostic method adopted and the experimental test results are reported. Tests have been performed either in the laboratory or directly

Cipriano Bartoletti; Maurizio Desiderio; D. Di Carlo; G. Fazio; F. Muzi; G. Sacerdoti; F. Salvatori

2004-01-01

50

High spectral resolution multiplex CARS spectroscopy using chirped pulses  

NASA Astrophysics Data System (ADS)

A simple technique for achieving high spectral resolution coherent anti-Stokes Raman scattering (CARS) spectra with a femtosecond laser system is presented. A linearly chirped and stretched (10 ps) pump pulse generates CARS signal only when overlapped in time with the Stokes pulse (90 fs), creating a `temporal slit' that defines the spectral resolution of the technique. Multiplex CARS spectra for liquid methanol and liquid isooctane are presented, demonstrating a spectral resolution of better than 5 cm -1. This new chirped (c-CARS) technique should prove useful for chemically-selective imaging applications, as it significantly reduces the non-resonant background contribution.

Knutsen, K. P.; Johnson, J. C.; Miller, A. E.; Petersen, P. B.; Saykally, R. J.

2004-04-01

51

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

SciTech Connect

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 collisional 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 imaging techniques.

Malinovskaya, Svetlana A. [Department of Physics and Engineering Physics, Stevens Institute of Technology Hoboken, NJ 07030 (United States)

2007-12-26

52

Tools and techniques for chloroplast transformation of Chlamydomonas.  

PubMed

The chloroplast organelle of plant and algal cells contains its own genetic system with a genome of a hundred or so genes. Stable transformation of the chloroplast was first achieved in 1988, using the newly developed biolistic method of DNA delivery to introduce cloned DNA into the genome of the green unicellular alga Chlamydomonas reinhardtii. Since that time there have been significant developments in chloroplast genetic engineering using this versatile organism, and it is probable that the next few years will see increasing interest in commercial applications whereby high-value therapeutic proteins and other recombinant products are synthesized in the Chlamydomonas chloroplast. In this chapter I review the basic methodology of chloroplast transformation, the current techniques and applications, and the future possibilities for using the Chlamydomonas chloroplast as a green organelle factory. PMID:18161489

Purton, Saul

2007-01-01

53

The Pure Rotational Spectrum of Perfluorooctanonitrile, C_7F15CN, Studied Using - and Chirped-Pulsed Fourier Transform Microwave Spectroscopies  

NASA Astrophysics Data System (ADS)

Fourier transform rotational spectroscopy has been used to collect the spectrum of perfluooctanonitrile. The spectrum was weak and only one conformer was observed. The assigned spectrum currently consists of both a- and b-type transitions spanning J = 8 to 40. The rotational constants are small, A = 681.37155(18) MHz, B = 126.116097(48) MHz, and C = 124.284824(49) MHz. The spectroscopic constants together with quantum chemical calculations have been used to identify the structure of the observed conformer. Notably the helical nature of the perfluoro alkyl chain is fully in evidence. Further calculations confirm that the nitrogen quadrupole coupling tensor is such that nitrogen hyperfine splitting will not be observable at the high J transitions recorded in our experiments. Spectroscopic constants and a discussion of the molecular structure will be presented.

Dewberry, C. T.; Grubbs, G. S. Grubbs, II; Cooke, S. A.; Bailey, W. C.

2011-06-01

54

Transforming spatial entanglement using a domain-engineering technique.  

PubMed

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. PMID:19113550

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

55

Frequency-chirped subwavelength nanoantennas.  

PubMed

Herein we propose, theoretically investigate, and numerically demonstrate the first use to our knowledge of frequency chirping to achieve broadband, efficient subwavelength vertical emission from a dielectric waveguide. We demonstrate this unique and effective approach in the telecom C band in a nanophotonic frequency-chirped dipole antenna. The structure utilizes a plasmonic antenna placed above an Si3N4 waveguide and a ground plane to enhance emission efficiency. Three-dimensional finite-difference time-domain simulations reveal up to 55% vertical emission efficiency, and a bandwidth of 500 nm is possible in a structure less than half a wavelength long. The design methodology and theoretical underpinnings of frequency-chirped nanophotonic antennas coupled to dielectric waveguides are presented. PMID:23202110

Yaacobi, Ami; Watts, Michael R

2012-12-01

56

The use of chirped pulse millimeter-wave spectroscopy in chemical dynamics and kinetics  

E-print Network

.Chirped-pulse millimeter wave (CPmmW) spectroscopy is a revolutionary technique that has taken advantage of advances in electronics to give high signal to noise broadband rotational spectra in a very short period of time ...

Shaver, Rachel Glyn

2013-01-01

57

Chirped-pulse millimeter-wave spectroscopy, dynamics, and manipulation of Rydberg-Rydberg Transitions  

E-print Network

The chirped-pulse millimeter-wave (CPmmW) technique is applied to transitions between Rydberg states, and calcium atoms are used as the initial test system. The unique feature of Rydberg{Rydberg transitions is that they ...

Colombo, Anthony P. (Anthony Paul)

2013-01-01

58

Chirped-pulse millimeter-wave spectroscopy: Spectrum, dynamics, and manipulation of RydbergRydberg transitions  

E-print Network

We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of RydbergRydberg transitions is that they have enormous electric dipole transition ...

Colombo, Anthony P.

2013-01-01

59

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

60

Image watermarking technique based on the steerable pyramid transform  

E-print Network

, invariance properties of the steerable pyramid transform may be exploited to counterattack geometrical attacks. Robustness is also obtained by the multiresolution aspect resulting from the application

Baskurt, Atilla

61

Compensation of high-order phase distortions in chirped-pulse amplification system  

NASA Astrophysics Data System (ADS)

Chirped-pulse amplification (CPA) technique has been widely used to generate ultra-intense femto-second pulses. In this scheme the seed pulses from an oscillator are stretched before amplification. The stretched pulses can support more energy extraction and effectively decrease the nonlinear effects in the gain media. The subsequent amplification in a CPA chain will result in a broadening of the output compressed pulses in temporal domain due to the gain narrowing and uncompensated phase distortions. In our experiment, using spectral modulation and phase pre-compensation system (Acoustic-Optics Programmable Dispersive Filter) between the oscillator and the stretcher, the effects of gain narrowing and high-order dispersions on the pulse duration in kHz chirped-pulse amplification system have been pre-compensated, and the spectral FWHM is expanded from 30nm to 50nm. The effects of GDD, TOD and FOD were investigated by scanning the four dispersion parameters respectively. By pre-compensating the high-order phase distortions with the phase measured by SPIDER, we successfully optimize the output duration from 51fs to 30fs, which is 1.07 times Fourier-transform-limitation.

Zhou, Bing; Jiang, Yong-Liang; Leng, Yu-xin; Chen, Xiao-Wei; Li, Ru-Xin; Xu, Zhi-Zhan

2007-01-01

62

Stable Genetic Transformation of a Beneficial Arthropod, Metaseiulus occidentalis (Acari: Phytoseiidae), by a Microinjection Technique  

Microsoft Academic Search

A microinjection technique has resulted in stable transformation of the western predatory mite Metaseiulus occidentalis. Early preblastoderm eggs within gravid females were microinjected. The needle was inserted through the cuticle of gravid females into the egg, or the tissue immediately surrounding the egg. This maternal injection method resulted in relatively high levels of survival and transformation. Transformation was achieved without

James K. Presnail; Marjorie A. Hoy

1992-01-01

63

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. Jay

1995-09-01

64

Interrogation Using Bandpass Filters with Chirped Fiber Bragg Gratings for Fiber Bragg Grating Sensor  

Microsoft Academic Search

Wavelength interrogation based on bandpass filters with an array of chirped fiber Bragg gratings has been investigated. Single-passband filters have been fabricated by the concatenation method with chirped fiber Bragg gratings. The reflected wavelength by a fiber Bragg grating sensor can be precisely interrogated by this system. This technique potentially offers a low-cost compact and high-performance solution for the interrogation

Kiyoshi Nakagawa

2008-01-01

65

A Novel Technique for the Metrology Calibration of a Fourier Transform  

E-print Network

A Novel Technique for the Metrology Calibration of a Fourier Transform Spectrometer Locke D transform spectrom- eter (FTS) to calibrate the metrology of a second FTS. This technique is particularly to verify the performance of the metrology system. The FTS of the Herschel/SPIRE spectrometer is one

Naylor, David A.

66

A deblocking technique for block-transform compressed image using wavelet transform modulus maxima.  

PubMed

In this work, we introduce a deblocking algorithm for Joint Photographic Experts Group (JPEG) decoded images using the wavelet transform modulus maxima (WTMM) representation. Under the WTMM representation, we can characterize the blocking effect of a JPEG decoded image as: 1) small modulus maxima at block boundaries oversmooth regions; 2) noise or irregular structures near strong edges; and 3) corrupted edges across block boundaries. The WTMM representation not only provides characterization of the blocking effect, but also enables simple and local operations to reduce the adverse effect due to this problem. The proposed algorithm first performs a segmentation on a JPEG decoded image to identify the texture regions by noting that their WTMM have small variation in regularity. We do not process the modulus maxima of these regions, to avoid the image texture being "oversmoothed"by the algorithm. Then, the singularities in the remaining regions of the blocky image and the small modulus maxima at block boundaries are removed. We link up the corrupted edges, and regularize the phase of modulus maxima as well as the magnitude of strong edges. Finally,the image is reconstructed using the projection onto convex set (POCS)technique on the processed WTMM of that JPEG decoded image.This simple algorithm improves the quality of a JPEG decoded image inthe senses of signal-to-noise ratio (SNR) as well as visual quality. We also compare the performance of our algorithm to the previous approaches,such as CLS and POCS methods. The most remarkable advantage of the WTMM deblocking algorithm is that we can directly process the edges and texture of an image using its WTMM representation. PMID:18276215

Hsung, T C; Pak-Kong Lun, D; Siu, W C

1998-01-01

67

Identification of biological tissue using chirped probe THz imaging  

Microsoft Academic Search

We consider the application of pulsed THz imaging systems in biomedical diagnostics and mail\\/packaging inspection. The sub-millimetre spectroscopic measurements obtained from T-ray systems contain a wealth of information about the sample under test. We demonstrate that different types of tissue can be classified based on their terahertz response measured with the chirped probe pulse technique. We demonstrate the performance of

B. Ferguson; S. Wang; D. Gray; D. Abbott; X.-C Zhang

2002-01-01

68

Linear FM chirp pulse compression ladar receiver operating characteristic  

Microsoft Academic Search

The linear frequency-modulation chirp pulse compression technique of classical microwave radar is examined in the context of coherent laser radar. A coherent CO2 laser radar may operate near 9.115 micrometers and 33,000 GHz. Because of this short wavelength, a large target Doppler-spread is realizable in a single ladar measurement. In addition, target surface roughness with respect to wavelength causes the

Douglas G. Youmans; David U. Fluckiger

1997-01-01

69

Frequency chirped differential absorption LIDAR  

NASA Astrophysics Data System (ADS)

We present a novel concept design of a differential absorption LIDAR for open path trace gas sensing in the atmosphere. To perform a range-resolved gas sensing we propose to arrange a set of retroreflectors in the laser beam path to measure a differential absorption in adjacent sections. In validation experiments we used a pulsed DFB quantum cascade laser fabricated by Alpes Lasers. The laser was excited with 200-ns current pulses with a repetition rate of 10 kHz. The frequency chirp rate was found to increase from 7.7 to 1.0 cm -1/?s as peak injection current was increased from 7.1, to 7.8 A. We utilized the frequency chirp at laser substrate temperature of 24.0 C to scan the 967.0 - 968.5 cm -1 spectral interval containing the absorption lines of CO II and NH3. We detected ~ 0.25 ppmv of NH 3 in nitrogen at atmospheric pressure using a double-pass gas cell with an effective absorption path of 2.4 m. Digital filtering of the spectra was shown to be effective in eliminating a high-frequency noise. To demonstrate range-resolved capabilities of the sensor we used two retroreflectors inserted into the laser beam. A differential absorption of CO II at 967.7 cm -1 was measured with the gas cell placed in one of the sections. Our experiments indicate that the frequency chirped LIDAR can be used for open path spectroscopy of NH 3 over the ranges up to ~ 1 km with a spatial resolution of ~ 30 m and detection limit of ~ 20 ppbv per a 30-m section.

Lytkine, A.; Jger, W.; Tulip, J.

2006-09-01

70

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

71

Synthesis of fiber Bragg grating for gain-narrowing compensation in high-power Nd: Glass chirped pulse amplification system  

NASA Astrophysics Data System (ADS)

We propose and analyze theoretically a method to compensate gain-narrowing effect by using the spectral shaping technology based on superstructure fiber Bragg grating (SSFBG) in high-power Nd:glass chirped pulse amplification system. The target spectrum is firstly calculated from hundreds joules amplified chirped Gaussian or super-Gaussian pulse by an inverse engineering operation. A genetic algorithm is used to design the SSFBG and obtain the index modulation distribution of grating which can transform the initial seed pulse to the target spectrum. The numerically simulations show that the spectral narrowing effect of chirped pulse amplification will be reduced largely and the ideal pulse spectrum (Gaussian or super-Gaussian) is also obtained. It is believed that this proposed method will provide a theoretical direction for the following experiment. Moreover, it will also be useful and flexible for the spectral transform in other chirped pulse application areas.

Liu, Qiong; Ye, Qing; Pan, Zhengqing; Luo, Aiping; Cai, Haiwen; Qu, Ronghui; Fang, Zujie

2011-05-01

72

Comparing Parameter Estimation Techniques for an Electrical Power Transformer Oil Temperature Prediction Model  

NASA Technical Reports Server (NTRS)

This paper examines various sources of error in MIT's improved top oil temperature rise over ambient temperature model and estimation process. The sources of error are the current parameter estimation technique, quantization noise, and post-processing of the transformer data. Results from this paper will show that an output error parameter estimation technique should be selected to replace the current least squares estimation technique. The output error technique obtained accurate predictions of transformer behavior, revealed the best error covariance, obtained consistent parameter estimates, and provided for valid and sensible parameters. This paper will also show that the output error technique should be used to minimize errors attributed to post-processing (decimation) of the transformer data. Models used in this paper are validated using data from a large transformer in service.

Morris, A. Terry

1999-01-01

73

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

74

A deblocking technique for block-transform compressed image using wavelet transform modulus maxima  

Microsoft Academic Search

In this work, we introduce a deblocking algorithm for Joint Photographic Experts Group (JPEG) decoded images using the wavelet transform modulus maxima (WTMM) representation. Under the WTMM representation, we can characterize the blocking effect of a JPEG decoded image as: 1) small modulus maxima at block boundaries over smooth regions; 2) noise or irregular structures near strong edges; and 3)

Tai-Chiu Hsung; Daniel Pak-kong Lun; Wan-Chi Siu

1998-01-01

75

Showing Full Semantics Preservation in Model Transformation - A Comparison of Techniques  

NASA Astrophysics Data System (ADS)

Model transformation is a prime technique in modern, model-driven software design. One of the most challenging issues is to show that the semantics of the models is not affected by the transformation. So far, there is hardly any research into this issue, in particular in those cases where the source and target languages are different.

Hlsbusch, Mathias; Knig, Barbara; Rensink, Arend; Semenyak, Maria; Soltenborn, Christian; Wehrheim, Heike

76

Novel Technique to Improve the Fault Detection Sensitivity in Transformer Impulse Test  

Microsoft Academic Search

Insulation is identified as one of the most important constructional rudiments of a transformer, and any weakness of insulation would lead to a transformer failure. To check the insulation integrity, a sensitive technique like the standard impulse test is used. Testing of winding insulation is performed by comparing the voltage and current waveforms of reduced and full test voltages, previously.

Essam Al-Ammar; George G. Karady; H. Jin Sim

2008-01-01

77

Transforming Student Health Services through Purpose-Driven Assessment Techniques  

ERIC Educational Resources Information Center

The University of Kansas Medical Center did a comprehensive review of the services provided in the Student Health Center (SHC). Using purpose-driven assessment techniques, areas needing improvement were identified. The results of the survey were presented to students and, with student support, student health fees were increased to fund desired

Knoll, Dorothy; Meiers, Chris; Honeck, Sara

2006-01-01

78

CHIRP  

Cancer.gov

Skip to Main Content Headlines Pediatric Oncology Branch Home > Pediatric Psycho-Oncology Professionals > Training Headline Title Pediatric Psycho-Oncology Professionals Pediatric Psychology Postdoctoral Fellowship University of Louisville School of

79

A new computational technique of magnetic nonlinear transients of a transformer  

Microsoft Academic Search

A technique to compute the magnetic nonlinear transients of a transformer is suggested. The technique is firstly composed of measuring the multiple L(i) characteristics represented by the relations of coil current and differential inductance corresponding to each part of the B-H curves of the transformer. Secondly, it is composed of subjecting each L(i) characteristic separately by current slope and current

M. Ogawa

2002-01-01

80

Chirps on finite cyclic groups Peter G. Casazzaa and Matthew Fickusb  

E-print Network

, the phenomenon by which the perceived frequency of a wave is altered whenever the wave is emanating from or reflecting off a moving body. As such, chirps have historically been of great interest in applications-Fourier transform,8 and chirplets have been used in image processing for over a decade.5 For that matter, discrete

Casazza, Pete

81

Chaotic chirped-pulse oscillators.  

PubMed

We present results of experimental investigation of the chaotic and quasi-periodic regime in the chirped-pulsed (dissipative soliton) Cr:ZnS and Cr:ZnSe mid-IR oscillators with significant third-order dispersion. The instability develops when the spectrum edge approaches resonance with a linear wave either due to power increase or by dispersion adjustment. In practice, this occurs when the spectrum edge reaches zero dispersion wavelength. The analysis suggests a three-oscillator chaos model, which is confirmed by numerical simulations. The regime is long-term stable and can be easily overlooked in similar systems. We show that chaotic regime is accompanied by a characteristic spectral shape and can be reliably recognized by using wavelength-skewed filters and by second-harmonic or two-photon absorption detectors. PMID:24514508

Sorokin, Evgeni; Tolstik, Nikolai; Kalashnikov, Vladimir L; Sorokina, Irina T

2013-12-01

82

Simplified Homodyne Detection for FM Chirped Lidar  

E-print Network

The investigation of global warming requires more sensitive altimeters to better map the global ice reserves. A homodyne detection scheme for FM chirped lidar is developed in which dechirping is performed in the optical domain, simplifying both...

Adany, Peter

2007-12-14

83

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

84

Chirp control of a single-mode, good beam quality, zigzag dye laser  

SciTech Connect

The authors report a substantial reduction of frequency chirp of a single-mode laser-pumped zigzag dye laser. A linear optical cavity using counterpropagating orthogonally polarized waves was injection-seeded at 568 nm and operated with a laser output of about 1 J. The chirp was controlled by an intracavity Pockels cell that was configured to add optical density at a rate which counterbalanced the decrease in optical density due to dye-solvent heating during the {approximately}1-{micro}s laser pulse. Heterodyne measurements were used to determine that the bandwidth was near the transform limit and chirp rate of {approximately}1 MHz/{micro}s. The beam quality of the laser was measured at 10 Hz as 1.7 XDL.

Mandl, A.; Zavriyev, A.; Klimek, D.E. [Textron Systems Div., Wilmington, MA (United States)] [Textron Systems Div., Wilmington, MA (United States)

1997-03-01

85

December 15, 1994 / Vol. 19, No. 24 / OPTICS LETTERS 2149 Self-phasemodulation in chirped-pulse amplification  

E-print Network

assume that the initial low-energy pulse is transform limited with a field distribution, Eo(z, t), and a Fourier transform, Eo(z, co- coo). This pulse is stretched by a grating-based stretcher with a phaseDecember 15, 1994 / Vol. 19, No. 24 / OPTICS LETTERS 2149 Self-phasemodulation in chirped-pulse

Ditmire, Todd

86

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

87

Agrobacterium -mediated transformation of cereals from technique development to its application  

Microsoft Academic Search

Agrobacterium tumefaciens is a very useful vector to transfer foreign genes into dicotyledonous cells. Monocotyledonous, especially cereals, were considered\\u000a outside the host range of the bacteria. The main, alternative technique of transformation developed for them was delivery\\u000a of naked DNA (e.g. microprojectile bombardment, electroporation of protoplasts). The results of Agrobacterium-mediated transformation of cereals accumulated during the last few years confirmed

Anna Nadolska-Orczyk; Wac?aw Orczyk; Anna Przetakiewicz

2000-01-01

88

Assessment of simple marker-free genetic transformation techniques in alfalfa  

Microsoft Academic Search

Methods to avoid the presence of selectable marker genes (SMG) in transgenic plants are available but not implemented in many\\u000a crop species. We assessed the efficiency of simple marker-free Agrobacterium-mediated transformation techniques in alfalfa: regeneration without selection, or marker-less, and co-transformation with\\u000a two vectors, one containing the SMG and one containing a non-selected gene. To easily estimate the efficiency of

Nicoletta Ferradini; Alessandro Nicolia; Stefano Capomaccio; Fabio Veronesi; Daniele Rosellini

89

Analytical chirped solutions to the (3 + 1)-dimensional Gross-Pitaevskii equation for various diffraction and potential functions.  

PubMed

Analytical solutions to the (3 + 1)-dimensional Gross-Pitaevskii equation in the presence of chirp and for different diffraction and potential functions are found. We utilize a method we formulated to solve the Riccati equation for the chirp function that arises when the F-expansion technique and the homogeneous balance principle are applied to the Gross-Pitaevskii equation. Three specific examples of physical interest are considered in some detail. PMID:21867333

Al Bastami, Anas; Beli?, Milivoj R; Milovi?, Daniela; Petrovi?, Nikola Z

2011-07-01

90

Spatial filtering of light by chirped photonic crystals  

SciTech Connect

We propose an efficient method for spatial filtering of light beams by propagating them through two-dimensional (also three dimensional) chirped photonic crystals, i.e., through the photonic structures with fixed transverse lattice period and with the longitudinal lattice period varying along the direction of the beam propagation. We prove the proposed idea by numerically solving the paraxial propagation equation in refraction-index-modulated media and we evaluate the efficiency of the process by harmonic-expansion analysis. The technique can be also applied for filtering (for cleaning) of the packages of atomic waves (Bose condensates), also to improve the directionality of acoustic and mechanical waves.

Staliunas, Kestutis [ICREA, Departament de Fisica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Colom 11, E-08222 Terrassa, Barcelona (Spain); Sanchez-Morcillo, Victor J. [Instituto de Investigacion para la Gestion Integrada de Zonas Costeras, Universidad Politecnica de Valencia, Ctra. Natzaret-Oliva S/N, 46730 Grao de Gandia (Spain)

2009-05-15

91

Optical cryptographic system employing multiple reference-based joint transform correlation technique  

NASA Astrophysics Data System (ADS)

An optical joint transform correlation-based cryptographic system is a used to feed multiple phase-shifted encryption keys into four parallel channels along with a to-be-encrypted signal in the form of an image. The resulting joint power spectra (JPS) signals are phase-shifted and then combined to yield a modified JPS signal. Inverse Fourier transformation of the modified JPS signal yields the secured encrypted image. For decryption purpose, the received encrypted signal is first Fourier transformed and multiplied by the encryption key used in encryption. The derived signal is then inverse Fourier transformed to generate the output signal. The proposed system offers a nonlinear encryption without the involvement of any complex mathematical operation on the encryption key otherwise required in similar encryption techniques and is invariant to noise. Computer simulation results are presented to show the effectiveness of the proposed scheme with binary, as well as gray images in both noise-free and noisy environment.

Islam, Mohammed Nazrul; Karim, Mohammad Ataul; Alam, Mohammad Showkat; Asari, K. Vijayan

2011-06-01

92

A reconstruction technique for three-dimensional porous media using image analysis and Fourier transforms  

Microsoft Academic Search

A truncated gaussian method based on Fourier transforms is proposed to generate periodic 3D porous structure from a 2D image of the sample. This technique improves a previous method developed by Quiblier [Quiblier, J.A., 1984. A new three-dimensional modeling technique for studying porous media. J. Colloid Interface Sci 98, 84102] and Adler et al. [Adler, P.M., Jacquin, C.G., Quiblier, J.A.,

Z. R. Liang; C. P. Fernandes; F. S. Magnani; P. C. Philippi

1998-01-01

93

Experimental demonstration of energy-chirp compensation by a tunable dielectric-based structure.  

PubMed

A tunable energy-chirp compensator was used to remove a correlated energy chirp from the 60-MeV beam at the Brookhaven National Laboratory Accelerator Test Facility. The compensator operates through the interaction of the wakefield of the electron bunch with itself and consists of a planar structure comprised of two alumina bars with copper-plated backs separated by an adjustable beam aperture. By changing the gap size, the correlated energy chirp of the electron bunch was completely removed. Calculations show that this device, properly scaled to account for the electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers. The experimental results are shown to be in good agreement with numerical simulations. Application of this technique can significantly simplify linac design and improve free-electron lasers performance. PMID:24702378

Antipov, S; Baturin, S; Jing, C; Fedurin, M; Kanareykin, A; Swinson, C; Schoessow, P; Gai, W; Zholents, A

2014-03-21

94

Control of chirped pulse trains: a speedway for free-optimization experiments  

NASA Astrophysics Data System (ADS)

Complex phase-only shaping of intense ultrashort laser pulses is applied to generate highly flexible pulse structures with regular envelopes. By incorporating the linear chirp as additional free parameter into the technique of colored pulses, trains of chirped pulses are produced, capable of independent and simultaneous modulation of relative intensity ratio, optical delay, and individual chirp. Such pulses might find applications in multi-parameter scans or closed-loop feedback measurements. For the latter, we demonstrate that with use of these tailored pulse trains, adaptive feedback control experiments quickly converge. They provide near-optimal solutions, already revealing key features of the system under study. Moreover, seeding standard free-optimization routines with these temporary solutions largely accelerates the search for the closest-possible optimum.

Truong, N. X.; Tiggesbumker, J.; Meiwes-Broer, K.-H.

2011-11-01

95

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

96

Sampled chirped fiber gratings as distributed pressure sensors  

Microsoft Academic Search

Fiber gratings have been studied for their applications in sensing and communications. Many sensing applications of the uniform fiber Bragg grating, chirped fiber grating and long period grating have been studied, proposed and commercialized. Sampled chirped gratings have been studied for multichannel dispersion compensation in DWDM systems. In this paper, we show that the sampled chirped fiber grating can be

Swee Chuan Tjin; Lipi Mohanty; Nam Quoc Ngo

2004-01-01

97

Chapter 55: Video-as-Data and Digital Video Manipulation Techniques for Transforming  

E-print Network

Chapter 55: Video-as-Data and Digital Video Manipulation Techniques for Transforming Learning and current progress of the Digital Interactive Video Exploration and Reflection (DIVER) Project at Stanford University. The DIVER Project aspires to accelerate cul- tural appropriation of video as a fluid expressive

Paris-Sud XI, Université de

98

A Transformation-Based Component Framework for a Generic Integerated Modeling Technique  

Microsoft Academic Search

This paper is based on two general ideas. The first one is the integration paradigm for data type and process modeling techniques developed by the first two authors within the last five years. The second one is a transformation-based component framework for system modeling presented at ETAPS 2002 in Grenoble. The aim of this paper is to join both ideas

Hartmut Ehrig; Fernando Orejas; Benjamin Braatz; Markus Klein; Martti Piirainen

2002-01-01

99

An accurate fault location technique for distribution lines with tapped loads using wavelet transform  

Microsoft Academic Search

This paper investigates the application of wavelet transform as an accurate fault location technique for power distribution lines with tapped loads. When a fault occurs, a transient wave travels from the fault point to substation busbars and load terminals. The time taken for the fault generated transient wave to arrive at busbars or load terminals depends on the distance traveled

Hassan Nouri; Chun Wang; Terry Davies

2001-01-01

100

Enhancement of sound in chirped sonic crystals  

NASA Astrophysics Data System (ADS)

We propose and experimentally demonstrate a mechanism of sound wave concentration based on soft reflections in chirped sonic crystals. The reported controlled field enhancement occurs at around particular (bright) planes in the crystal and is related to a progressive slowing down of the sound wave as it propagates along the material. At these bright planes, a substantial concentration of the energy (with a local increase up to 20 times) was obtained for a linear chirp and for frequencies around the first band gap. A simple couple mode theory is proposed that interprets and estimates the observed effects. Wave concentration energy can be applied to increase the efficiency of detectors and absorbers.

Romero-Garca, V.; Pic, R.; Cebrecos, A.; Snchez-Morcillo, V. J.; Staliunas, K.

2013-03-01

101

Powerful femtosecond pulse generation by chirped and stretched pulse parametric amplification in BBO crystal  

Microsoft Academic Search

Chirped pulses have been parametrically amplified by a factor of ~2104 without bandwidth limitation in BBO crystal. Pulses were compressed down to 70 fs, and ~0.9 GW output power has been obtained. A special technique to match temporal profiles of signal and pump pulses was used.

A. Dubietis; G. Jonusauskas; A. Piskarskas

1992-01-01

102

Harnessing modified manganin technique to study processes of explosive transformation in pyrotechnic compositions  

NASA Astrophysics Data System (ADS)

The paper reviews results of the experimental study of explosive transformation in pyrotechnic compositions with modified manganin technique. In particular, experimental data on pressure profiles recorded with tiny manganin sensors are cited to characterize the effect of parameters of the loading pulse, dispersion and density on peculiarities of explosive transformation in studied pyrotechnic pieces under shock-wave initiation. In the paper are shown the experimental pressure profiles, characteristic for processes of explosive transformation of extended delay. The experimental results prove the effect of density variation of the specimens under study on the process of the explosive transformation. It is felt that for given range of pressures of the incoming shock wave the difference of the explosive transformation history, at equal parameters of loading pulse, is caused also by different dispersion of the initial powder and final porosity of studied specimens. The experimental results provide support for possibility of use of tiny manganin and constantan sensors in studying processes of explosive transformation of pyrotechnic compositions under initiation by divergent shock waves of large curve front and slumping pressure profile.

Batalov, Sergei

2005-07-01

103

High Accuracy Evaluation of the Finite Fourier Transform Using Sampled Data  

NASA Technical Reports Server (NTRS)

Many system identification and signal processing procedures can be done advantageously in the frequency domain. A required preliminary step for this approach is the transformation of sampled time domain data into the frequency domain. The analytical tool used for this transformation is the finite Fourier transform. Inaccuracy in the transformation can degrade system identification and signal processing results. This work presents a method for evaluating the finite Fourier transform using cubic interpolation of sampled time domain data for high accuracy, and the chirp Zeta-transform for arbitrary frequency resolution. The accuracy of the technique is demonstrated in example cases where the transformation can be evaluated analytically. Arbitrary frequency resolution is shown to be important for capturing details of the data in the frequency domain. The technique is demonstrated using flight test data from a longitudinal maneuver of the F-18 High Alpha Research Vehicle.

Morelli, Eugene A.

1997-01-01

104

Application of a Fourier transform based filtering technique to improve signal-to-noise ratio in modulation spectroscopy experiments  

E-print Network

Application of a Fourier transform based filtering technique to improve signal-to-noise ratio of a fast Fourier transform FFT based simplified filtering procedure to improve S/N ratio, thereby enabling) is the Fourier transform of the above data. The frequency scale has been normalized with respect to the Nyquist

Ghosh, Sandip

105

Application of the transformation of variables technique for uncertainty mapping in nonlinear filtering  

NASA Astrophysics Data System (ADS)

This paper addresses the impact nonlinear observations of state variables have on uncertainty accuracy associated with state estimation algorithms. The transformation of variables technique is applied to exactly map probability density functions (PDFs) between domains completely spanned by different combinations of basis vectors. The technique allows for proper generation of the likelihood density when converting from measurement to state variable space and for association of a present state distribution with prior observation data. The exact mapping of probability distribution functions between domains and proper characterization of prior knowledge allows for Bayesian estimation to be appropriately carried out. A Bayes filter utilizing the technique is developed which uses the technique to map the uncertainty in time for generation of the prior density and in space for generation of the likelihood density. The filter is compared with conventional nonlinear filtering techniques in multiple scenarios to demonstrate the utility and insight offered for object tracking and parameter estimation applications.

Weisman, R. M.; Majji, M.; Alfriend, K. T.

2014-01-01

106

Feature extraction technique based on Hopfield neural network and joint transform correlation  

NASA Astrophysics Data System (ADS)

In this paper, a new Hopfield neural network based supervised filtering technique is proposed. The learnable filtering architecture has been developed by modifying the Hopfield network structure using 2D convolution instead of weight-matrix multiplications. This feature offers high speed learning and testing possibility for image feature extraction process. The learning property of the filtering technique is provided by using a recurrent learning algorithm. The proposed technique has been implemented using joint transform correlator. The requirement of non-negative data for optoelectronic implementation is provided by incorporating bias technique to convert the negative data to non-negative data. Simulation results for the proposed technique are reported for feature extraction problems such as edge detection, and vertical line extraction.

Bal, Abdullah; Alam, Mohammad S.

2004-10-01

107

The effect of different winding techniques on the stray capacitances of high frequency transformers used in flyback converters  

Microsoft Academic Search

In this paper, the effect of different winding techniques on the stray capacitances of high frequency transformers used in flyback converters has been studied. Since stray capacitances are affected by winding methods, all the typical kinds of winding techniques used for these transformers and their effects on the stray capacitances were analyzed. Furthermore, some modifications were applied to the typical

Sina Emrani Saravi; Abdolhossein Tahani; Firuz Zare; Reza Ahmadi Kordkheili

2008-01-01

108

Lineshape and polarization mode dispersion of waves diffracted by apodized and chirped fiber Bragg gratings in reflection  

Microsoft Academic Search

The amplitude and phase of a light wave propagating in an apodized and chirped Bragg grating is given by the superposition of two orthogonal coupled wave functions that are the solution of a non-linear Riccati equation. An analytical solution, in the form of an integral transform, that predicts the amplitude, phase, and intensity profile of the light diffracted by grating,

Vincent Ruddy; Aurelian Seugnet; Barry ONeill

2007-01-01

109

Fast-Fourier-transform spectral analysis techniques as a plasma fluctuation diagnostic tool  

Microsoft Academic Search

A review is given of the key ideas involved in computing power spectral density functions from fast-Fourier-transformed plasma fluctuation data. Next a model is described which enables one to determine, from the computer-generated power spectra, the amplitude, frequency, and wavenumber of each of several waves present in the plasma. The potential of digitally implemented spectral analysis techniques as a plasma

D. E. Smith; E. J. Powers; G. S. Caldwell

1974-01-01

110

Fast-Fourier-Transform Spectral-Analysis Techniques as a Plasma Fluctuation Diagnostic Tool  

Microsoft Academic Search

A review is given of the key ideas involved in computing power spectral density functions from fast-Fourier-transformed plasma fluctuation data. Next a model is described which enables one to determine, from the computer-generated power spectra, the amplitude, frequency, and wavenumber of each of several waves present in the plasma. The potential of digitally implemented spectral analysis techniques as a plasma

D. E. Smith; E. J. Powers; G. S. Caldwell

1974-01-01

111

A Hilbert transform method for parameter identification of time-varying structures with observer techniques  

Microsoft Academic Search

This paper presents a recursive Hilbert transform method for the time-varying property identification of large-scale shear-type buildings with limited sensor deployments. An observer technique is introduced to estimate the building responses from limited available measurements. For an n-story shear-type building with l measurements (l ? n), the responses of other stories without measurements can be estimated based on the first

Zuo-Cai Wang; Wei-Xin Ren; Gen-Da Chen

2012-01-01

112

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

113

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

PubMed Central

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?m spot size and a fast pixel array detector is used to achieve temporal resolution of 55?s. In the second technique the X-rays are focused with KirkpatrickBaez mirrors to achieve a spatial resolution better than 10?m and a fast shutter is used to provide temporal resolution better than 20?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. PMID:21525656

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

2011-01-01

114

Color enhancement of highly correlated images. II - Channel ratio and 'chromaticity' transformation techniques  

NASA Technical Reports Server (NTRS)

Two techniques for enhancing the color of multispectral images are described; both involve ratioing of data from different image channels. In the first technique, the ratioed data are assigned the primary color for display as color ratio pictures, and in the second method, image data are transformed to RGB chromaticity coordinates by ratioing the data acquired in three channels to the sum of their intensities. The two techniques are applied to a NASA Thermal-IR Multispectral Scanner (TIMS) image of Death Valley and to a Landsat MSS image of the Mojave Desert. The basic principles of ratioing are discussed, and the effects of atmospheric path radiances on the interpretation of ratioed images are investigated. It is observed that the color pictures produced using these two enhancement techniques are similar to the pictures enhanced by decorrelation and hue-saturation-intensity methods.

Gillespie, Alan R.; Kahle, Anne B.; Walker, Richard E.

1987-01-01

115

Chirped fiber Brillouin frequency-domain distributed sensing  

NASA Astrophysics Data System (ADS)

A frequency-domain distributed temperature/strain sensor based on a longitudinally graded optical fiber (LGF) is proposed and evaluated. In an LGF, the Brillouin scattering frequency, ?, changes (i.e., is chirped) lengthwise monotonically and thus every position along the fiber has a unique ?. Any change locally (at some position) in the fiber environment will result in a measurable change in the shape of the Brillouin gain spectrum (BGS) near the frequency component mapped to that position. This is demonstrated via measurements and modeling for an LGF with local heating. The LGF is one with 100 MHz Brillouin frequency gradient over 16.7 m, with 1.1 and 1.7 m segments heated up to 40 K above ambient. A measurement of the BGS can enable the determination of a thermal (or strain) distribution along a sensor fiber, thus rendering the system one that is in the frequency domain. A sensitivity analysis is also presented for both coherent and pump-probe BGS measurement schemes. The modeling results suggest that the frequency-domain systems based on fibers with a chirped Brillouin frequency are highly suited as inexpensive event sensors (alarms) and have the potential to reach submeter position determination with sub-1-K temperature accuracies at >1 kHz sampling rates. Limitations to the technique are discussed.

Dragic, Peter D.; Mangognia, Anthony; Ballato, John

2014-05-01

116

Slit Function Measurement of An Imaging Spectrograph Using Fourier Transform Techniques  

NASA Technical Reports Server (NTRS)

Knowledge of a spectrograph slit function is necessary to interpret the unresolved lines in an observed spectrum. A theoretical slit function can be calculated from the sizes of the entrance slit, the detector aperture when it functions as an exit slit, the dispersion characteristic of the disperser, and the point spread function of the spectrograph. A measured slit function is preferred to the theoretical one for the correct interpretation of the spectral data. In a scanning spectrometer with a single exit slit, the slit function is easily measured. In a fixed grating/or disperser spectrograph, illuminating the entrance slit with a near monochromatic light from a pre-monochrmator or a tunable laser and varying the wavelength of the incident light can measure the slit function. Even though the latter technique had been used successfully for the slit function measurements, it had been very laborious and it would be prohibitive to an imaging spectrograph or a multi-object spectrograph that has a large field of view. We explore an alternative technique that is manageable for the measurements. In the proposed technique, the imaging spectrograph is used as a detector of a Fourier transform spectrometer. This method can be applied not only to an IR spectrograph but also has a potential to a visible/UV spectrograph including a wedge filter spectrograph. This technique will require a blackbody source of known temperature and a bolometer to characterize the interferometer part of the Fourier Transform spectrometer. This pa?er will describe the alternative slit function measurement technique using a Fourier transform spectrometer.

Park, Hongwoo; Swimyard, Bruce; Jakobsen, Peter; Moseley, Harvey; Greenhouse, Matthew

2004-01-01

117

850 OPTICS LETTERS / Vol. 25, No. 11 / June 1, 2000 Chirp control in the direct space-to-time pulse shaper  

E-print Network

is manipulated. These properties are fundamentally different than in the well-known Fourier-transform pulse this geometry and the well- known Fourier-transform (FT) pulse-shaper geome- try4,5 is that the state of each850 OPTICS LETTERS / Vol. 25, No. 11 / June 1, 2000 Chirp control in the direct space-to-time pulse

Purdue University

118

Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique  

NASA Astrophysics Data System (ADS)

The parameters (temperature, activation energy) of the surface and volume glass transition (retrification process) in amorphous selenium produced by rapid quenching of the liquid phase have been determined using the EEE and DTA techniques. EEE is a surface effect connected with structural transformations in the surface layer whereas the DTA measurements give the information about the transformations occurring in the volume of the sample. It has been found that the surface retrification of selenium occurs with activation energy smaller than the volume retrification, both observed in the first heating run. The value of activation energy for the volume retrification measured in the second DTA heating run is higher compared with that measured in the first heating run. Irradiation with X-rays accelerates both the surface and volume retrification of amorphous selenium.

Grecki, Cz; Grecki, T.

2007-08-01

119

Effect of Data Transformations on Source Identification and Plume Delineation using Dimension Reduction Techniques  

NASA Astrophysics Data System (ADS)

Multivariate statistical approaches such as the Principal Component Analysis (PCA), Factor analysis and clustering algorithms are routinely employed for reducing the dimensionality of data and identifying chemical signatures and potential groupings for multi-species contaminant plumes. Although there are no general restrictions or specific guidelines for application of such approaches, it has been suggested (Aitchison, 1983) that dimensionality reduction techniques based on correlation structure of the analytical data (scaled but not transformed) may not be applicable to compositional data or data subject to equality constraint such as geochemical data. No restrictions have been identified for using such techniques with organic data such as chlorinated hydrocarbons. We examine real world and synthetic datasets that contain a combination of organic and inorganic data and test the impact of different data transformations on the results of PCA and other techniques. We are specifically interested in identifying clusters in the data for delineation of contaminant-specific plumes. We provide comparison with results obtained using traditional methods and evaluate against the known hydrogeological conditions.

Suribhatla, R. M.; Culkin, S. L.; Taraszki, M.

2013-12-01

120

High Sensitivity EMAT System using Chirp Pulse Compression and Its Application to Crater End Detection in Continuous Casting  

NASA Astrophysics Data System (ADS)

A high sensitivity EMAT system using chirp pulse compression technique was developed. The system uses a high power gated amplifier having 2kVpp output to transmit chirp waves. Pulse compression of the received signals are performed digitally in a PC after amplification and analog-to-digital conversion. A 20dB improvement of the signal-to-noise ratio was achieved by chirp pulse compression and synchronous averaging. A new surface cooling technique was also developed to improve the signal amplitude of the bulk shear wave with hot steel, and its effectiveness was demonstrated. An actual plant test of crater end detection by the developed EMAT system was conducted at a continuous caster, and clear detection by non-contact EMATs was achieved.

Iizuka, Y.; Awajiya, Y.

2014-06-01

121

Transformers  

NSDL National Science Digital Library

All About Circuits is a website that âprovides 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 âAlternating 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

122

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

123

A Hilbert transform method for parameter identification of time-varying structures with observer techniques  

NASA Astrophysics Data System (ADS)

This paper presents a recursive Hilbert transform method for the time-varying property identification of large-scale shear-type buildings with limited sensor deployments. An observer technique is introduced to estimate the building responses from limited available measurements. For an n-story shear-type building with l measurements (l ? n), the responses of other stories without measurements can be estimated based on the first r mode shapes (r ? l) as-built conditions and l measurements. Both the measured responses and evaluated responses and their Hilbert transforms are then used to track any variation of structural parameters of a multi-story building over time. Given floor masses, both the stiffness and damping coefficients of the building are identified one-by-one from the top to the bottom story. When variations of parameters are detected, a new developed branch-and-bound technique can be used to update the first r mode shapes with the identified parameters. A 60-story shear building with abruptly varying stiffness at different floors is simulated as an example. The numerical results indicate that the proposed method can detect variations of the parameters of large-scale shear-type buildings with limited sensor deployments at appropriate locations.

Wang, Zuo-Cai; Ren, Wei-Xin; Chen, Gen-Da

2012-10-01

124

Spatially adaptive wavelet transform speckle noise-smoothing technique for SAR images  

NASA Astrophysics Data System (ADS)

In this work we propose a new wavelet transform based speckle denoising algorithm for SAR images. The algorithm will explicitly account for the signal dependent nature of the noise by studying the variances of detail wavelet coefficients. The algorithm will use the analysis of variance ANOVA technique to check if variances are due to means belonging to the same population or not. If neighboring variances indicate belonging to the same population, then it's a smooth region and coefficient should be smoothed. If neighboring variances indicate the presence of two different populations, then coefficient is due to image feature and should be preserved. This approach will provide the flexibility of adjusting to region intensity level and thus no need for the fixed threshold concept. The algorithm will take advantage of the fact that wavelet transform creates three detail sub-images and a coarse sub-image. Each detail sub-image is associated with frequency contents due to certain edge location and orientation. The algorithm will also consider using cross-information from all three-detail sub-images to decide whether coefficients are due to a feature and thus should be preserved, or they are due to noise and should be smoothed. Simulations will show that our algorithm will provide better performance in terms of PSNR, ENL , and visually than currently existing techniques.

Hawwar, Yousef; Reza, Ali

2001-11-01

125

Chirped fiber Bragg grating sensor for pressure and position sensing  

Microsoft Academic Search

We present a chirped fiber Bragg grating sensor that should be suitable for esophageal motility studies. The device uses the time-dependent group delay response of a chirped fiber Bragg grating to measure the peristaltic pressure wave that propagates down the esophagus with the transport of a bolus to the stomach. In contrast to existing transducers that only measure at discrete

Pieter L. Swart; Beatrys M. Lacquet; Anatolii A. Chtcherbakov

2005-01-01

126

Chirped optical solitons in single-mode birefringent fibers  

NASA Astrophysics Data System (ADS)

The trapping behavior of two chirped solitons forming a bound state in a single-mode birefringent fiber is investigated on the basis of a model of coupled nonlinear Schroedinger equations. The positive initial chirp plays an important role in controlling the threshold amplitude for soliton trapping without causing excessive pulse broadening.

Mahmood, M. F.

1996-12-01

127

Distributed nonlinear fiber chirped-pulse amplifier system  

E-print Network

Distributed nonlinear fiber chirped-pulse amplifier system Marc Hanna,* Dimitris Papadopoulos-stage fiber-based femtosecond amplification system is presented, based on chirped-pulse amplification. 2009 Optical Society of America OCIS codes: (060.2320) Fiber optics amplifiers and oscillators; (140

Paris-Sud XI, Université de

128

Sampled chirped fiber gratings as distributed pressure sensors  

Microsoft Academic Search

Fiber gratings have been studied for their applications in sensing and communications. Many sensing applications of the uniform fiber Bragg grating, chirped fiber grating and long period grating have been studied, proposed and commercialized. Sampled chirped gratings have been studied for multichannel dispersion compensation in DWDM systems. In this paper, we show that the sampled chi rped fiber grating can

Swee Chuan Tjin; Lipi Mohanty; Nam Quoc Ngo

129

Chirp on Crickets: Teaching Compilers Using an Embedded Robot Controller  

E-print Network

Chirp on Crickets: Teaching Compilers Using an Embedded Robot Controller Li Xu Department into the simple yet versatile Handy Cricket educational robot con- troller. As a compiler, the Chirp design with code generation for the Cricket controller. They will test their work on both phys- ical Cricket

130

Hyperspectral Imaging with Stimulated Raman Scattering by Chirped Femtosecond Lasers  

E-print Network

Hyperspectral Imaging with Stimulated Raman Scattering by Chirped Femtosecond Lasers Dan Fu, Gary imaging system using chirped femtosecond lasers to achieve rapid Raman spectra acquisition while retaining laser beams with an energy difference tuned to the vibrational frequency of the molecule of interest

Xie, Xiaoliang Sunney

131

90 mJ parametric chirped pulse amplification of 10 fs pulses.  

PubMed

We demonstrate the amplification of broadband pulses from a Ti:Sapphire oscillator by non-collinear optical parametric chirped-pulse amplification technique in a type-I BBO crystal to energies of 90 mJ. Partial compression of the amplified pulses is demonstrated down to a 10 fs duration. These parameters come in combination with good spatial quality and focusability of the amplified beam. PMID:19532173

Tavella, Franz; Marcinkevicius, Andrius; Krausz, Ferenc

2006-12-25

132

Phase and intensity characterization of femtosecond pulses from a chirped-pulse amplifier by frequency-resolved optical gating  

SciTech Connect

Frequency-resolved optical gating (FROG) measurements were made to characterize pulses from a Ti:sapphire chirped-pulse amplified laser system. By characterizing both the pulse intensity and the phase, the FROG data provided the first direct observation to our knowledge of residual phase distortion in a chirped-pulse amplifier. The FROG technique was also used to measure the regenerative amplifier dispersion and to characterize an amplitude-shaped pulse. The data provide an experimental demonstration of the value of FROG for characterizing complex pulses, including tailored femtosecond pulses for quantum control.

Kohler, B.; Yakovlev, V.V.; Wilson, K.R. [Department of Chemistry, University of California, San Diego, La Jolla, California 92093-0339 (United States); Squier, J. [Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States); DeLong, K.W.; Trebino, R. [Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551 (United States)

1995-03-01

133

Decrease of pulse-contrast in nonlinear chirped-pulse amplification systems due to high-frequency spectral phase ripples.  

PubMed

It is analytically shown that weak initial spectral phase modulations cause a pulse-contrast degradation at the output of nonlinear chirped-pulse amplification systems. The Kerr-nonlinearity causes an energy-transfer from the main pulse to side-pulses during nonlinear amplification. The relative intensities of these side-pulses can be described in terms of Bessel-functions. It is shown that the intensities of the pulses are dependent on the magnitude of the accumulated nonlinear phase-shift (i.e., the B-integral), the depth and period of the initial spectral phase-modulation and the slope of the linear stretching chirp. The results are applicable to any type of laser amplifier that is based on the technique of chirped-pulse amplification. The analytical results presented in this paper are of particular importance for high peak-power laser applications requiring high pulse-contrasts, e.g. high field physics. PMID:18545600

Schimpf, Damian; Seise, Enrico; Limpert, Jens; Tnnermann, Andreas

2008-06-01

134

FY07 LDRD Final Report Precision, Split Beam, Chirped-Pulse, Seed Laser Technology  

SciTech Connect

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 suitable for petawatt class physics experiments. This LDRD project focused on the development of optical fiber laser technologies compatible with the current long pulse National Ignition Facility (NIF) seed laser. New technologies developed under this project include, high stability mode-locked fiber lasers, fiber based techniques for reduction of compressed pulse pedestals and prepulses, new compact stretchers based on chirped fiber Bragg gratings (CFBGs), new techniques for manipulation of chirped pulses prior to amplification and new high-energy fiber amplifiers. This project was highly successful and met virtually all of its goals. The National Ignition Campaign has found the results of this work to be very helpful. The LDRD developed system is being employed in experiments to engineer the Advanced Radiographic Capability (ARC) front end and the fully engineered version of the ARC Front End will employ much of the technology and techniques developed here.

Dawson, J W; Messerly, M J; Phan, H H; Crane, J K; Beach, R J; Siders, C W; Barty, C J

2009-11-12

135

Fast Fourier transform techniques for efficient simulation of Z-scan measurements  

NASA Astrophysics Data System (ADS)

Fast Fourier beam-propagation methods (BPM's) for simulating the roles of internal refractive effects and external propagation from nonlinear media are introduced. These techniques are applied to model picosecond Z-scan measurements for the induced absorber, the dye Chloro-Aluminum Phthalocyanine, at 532 nm. Within the thin-sample approximation an incident Gaussian beam is taken to experience a change in phase profile on propagation through the medium but remains of Gaussian amplitude profile. Outside this approximation one must determine both the phase and the amplitude profiles at the sample exit face that are due to the influence of nonlinear refraction (and nonlinear absorption) on the beam propagating through the medium. The BPM technique allows this to be achieved efficiently, and the external propagation technique enables a single discrete fast Fourier transform to be used to describe the subsequent external propagation of the non-Gaussian-shaped beams. The analysis is especially useful for such self-enhancing nonlinearities as one would wish to exploit in optical limiting. Copyright (c) 1995 Optical Society of America

Hughes, S.; Burzler, J. M.; Spruce, G.; Wherrett, B. S.

1995-10-01

136

Helium in chirped laser fields as a time-asymmetric atomic switch  

NASA Astrophysics Data System (ADS)

Tuning the laser parameters exceptional points in the spectrum of the dressed laser helium atom are obtained. The weak linearly polarized laser couples the ground state and the doubly excited P-states of helium. We show here that for specific chirped laser pulses that encircle an exceptional point one can get the time-asymmetric phenomenon, where for a negative chirped laser pulse the ground state is transformed into the doubly excited auto-ionization state, while for a positive chirped laser pulse the resonance state is not populated and the neutral helium atoms remains in the ground state as the laser pulse is turned off. Moreover, we show that the results are very sensitive to the closed contour we choose. This time-asymmetric state exchange phenomenon can be considered as a time-asymmetric atomic switch. The optimal time-asymmetric switch is obtained when the closed loop that encircles the exceptional point is large, while for the smallest loops, the time-asymmetric phenomenon does not take place. A systematic way for studying the effect of the chosen closed contour that encircles the exceptional point on the time-asymmetric phenomenon is proposed.

Kaprlov-nsk, Petra Ruth; Moiseyev, Nimrod

2014-07-01

137

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

2008-01-01

138

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

139

A noise filtration technique for fabric defects image using curvelet transform domain filters  

NASA Astrophysics Data System (ADS)

A noise filtration technique for fabric defects image using curvelet transform domain Filters is proposed in this paper. Firstly, we used FDCT_WARPING to decompose image into five scales curvelet coefficients. Secondly, the proposed algorithm distinguished major edges from noise background at the third scale. Thirdly, the possible lost edges in the procedure above were detected according to the decaying lever of the coefficients. Fourthly, the edges of the defect at the second scale were detected by four correlation coefficients in the two directions at the third scale. Fifthly, the curvelet coefficients at the fourth scale are filtered by the decaying lever. Sixthly, the curvelet coefficients at the fifth scale are filtered by hard threshing. Finally, the processed coefficients are reconstructed. The tests on the developed algorithms were performed with images from TILDA's Textile Texture Database, and suggest that the new approach outperforms wavelet methods in image denoising.

Luo, Jing; Ni, Jian-Yun; Lin, Shu-Zhong; Song, Li-Mei

2010-08-01

140

Accurate sizing of closed crack using nonlinear ultrasound of SPACE with high voltage transformer pulser technique  

NASA Astrophysics Data System (ADS)

As the improvement of the detectability of crack tip echo in ultrasonic inspection with low S/N ratio, we developed SPACE (Subharmonic Phased Array Crack Evaluation) as a subharmonic ultrasound imaging technique. Although the pulser of conventional SPACE could incident large displacement ultrasound to a crack, availability of the SPACE measurement was limited for only closed crack. In order to use the SPACE system for wider industrial inspection fields, we have been developed the larger displacement ultrasound incidence equipment considering the crack opening supposed to be several nm to sub- ?m in order. In this study, we developed new SPACE combining high voltage transformer to a low cost pulser. The availability of the developed system in ultrasonic inspection was investigated using several model cracks.

Mihara, Tsuyoshi; Konishi, Goki; Miura, Yusuke; Ishida, Hitoshi

2014-02-01

141

Chirped fiber Bragg grating detonation velocity sensing.  

PubMed

An all optical-fiber-based approach to measuring high explosive detonation front position and velocity is described. By measuring total light return using an incoherent light source reflected from a linearly chirped fiber Bragg grating sensor in contact with the explosive, dynamic mapping of the detonation front position and velocity versus time is obtained. We demonstrate two calibration procedures and provide several examples of detonation front measurements: PBX 9502 cylindrical rate stick, radial detonation front in PBX 9501, and PBX 9501 detonation along curved meridian line. In the cylindrical rate stick measurement, excellent agreement with complementary diagnostics (electrical pins and streak camera imaging) is achieved, demonstrating accuracy in the detonation front velocity to below the 0.3% level when compared to the results from the pin data. Finally, an estimate on the linear spatial and temporal resolution of the system shows that sub-mm and sub-?s levels are attainable with proper consideration of the recording speed, detection sensitivity, spectrum, and chirp properties of the grating. PMID:23387683

Rodriguez, G; Sandberg, R L; McCulloch, Q; Jackson, S I; Vincent, S W; Udd, E

2013-01-01

142

Chirped fiber Bragg grating detonation velocity sensing  

NASA Astrophysics Data System (ADS)

An all optical-fiber-based approach to measuring high explosive detonation front position and velocity is described. By measuring total light return using an incoherent light source reflected from a linearly chirped fiber Bragg grating sensor in contact with the explosive, dynamic mapping of the detonation front position and velocity versus time is obtained. We demonstrate two calibration procedures and provide several examples of detonation front measurements: PBX 9502 cylindrical rate stick, radial detonation front in PBX 9501, and PBX 9501 detonation along curved meridian line. In the cylindrical rate stick measurement, excellent agreement with complementary diagnostics (electrical pins and streak camera imaging) is achieved, demonstrating accuracy in the detonation front velocity to below the 0.3% level when compared to the results from the pin data. Finally, an estimate on the linear spatial and temporal resolution of the system shows that sub-mm and sub-?s levels are attainable with proper consideration of the recording speed, detection sensitivity, spectrum, and chirp properties of the grating.

Rodriguez, G.; Sandberg, R. L.; McCulloch, Q.; Jackson, S. I.; Vincent, S. W.; Udd, E.

2013-01-01

143

Impact of modulator chirp in 100 Gbps class optical discrete multi-tone transmission system  

NASA Astrophysics Data System (ADS)

Discrete multi-tone (DMT) technology is an attractive modulation technique for short reach optical transmission system. One of the main factors that limit the performance of the 1.5-?m band DMT system is the interplay between the chromatic dispersion of the transmission fiber and the chirp characteristic of the transmitter. We experimentally measured and compared the chirp characteristics of various modulator configurations, which are lithium-niobate Mach-Zehnder modulator, directly modulated laser, and electro-absorption modulator, by the frequency discriminator method using MZ interferometer. We also measured and compared the transmission characteristics of the transmitters using above-mentioned modulators and discuss the suitable transmitter configuration for DMT technology.

Nishihara, Masato; Tanaka, Toshiki; Takahara, Tomoo; Li, Lei; Tao, Zhenning; Rasmussen, Jens C.

2012-12-01

144

Frequency specificity of chirp-evoked auditory brainstem responses  

NASA Astrophysics Data System (ADS)

This study examines the usefulness of the upward chirp stimulus developed by Dau et al. [J. Acoust. Soc. Am. 107, 1530-1540 (2000)] for retrieving frequency-specific information. The chirp was designed to produce simultaneous displacement maxima along the cochlear partition by compensating for frequency-dependent traveling-time differences. In the first experiment, auditory brainstem responses (ABR) elicited by the click and the broadband chirp were obtained in the presence of high-pass masking noise, with cutoff frequencies of 0.5, 1, 2, 4, and 8 kHz. Results revealed a larger wave-V amplitude for chirp than for click stimulation in all masking conditions. Wave-V amplitude for the chirp increased continuously with increasing high-pass cutoff frequency while it remains nearly constant for the click for cutoff frequencies greater than 1 kHz. The same two stimuli were tested in the presence of a notched-noise masker with one-octave wide spectral notches corresponding to the cutoff frequencies used in the first experiment. The recordings were compared with derived responses, calculated offline, from the high-pass masking conditions. No significant difference in response amplitude between click and chirp stimulation was found for the notched-noise responses as well as for the derived responses. In the second experiment, responses were obtained using narrow-band stimuli. A low-frequency chirp and a 250-Hz tone pulse with comparable duration and magnitude spectrum were used as stimuli. The narrow-band chirp elicited a larger response amplitude than the tone pulse at low and medium stimulation levels. Overall, the results of the present study further demonstrate the importance of considering peripheral processing for the formation of ABR. The chirp might be of particular interest for assessing low-frequency information.

Wegner, Oliver; Dau, Torsten

2002-03-01

145

Three-Dimensional Analysis of Frequency-Chirped FELs  

SciTech Connect

Frequency-chirped free-electron lasers (FELs) are useful to generate a large photon bandwidth or a shorter x-ray pulse duration. In this paper, we present a three-dimensional analysis of a high-gain FEL driven by the energy-chirped electron beam. We show that the FEL eigenmode equation is the same for a frequency-chirped FEL as for an undulator-tapered FEL. We study the transverse effects of such FELs including mode properties and transverse coherence.

Huang, Z.

2010-09-14

146

Multiscale Transient Signal Detection: Localizing Transients in Geodetic Data Through Wavelet Transforms and Sparse Estimation Techniques  

NASA Astrophysics Data System (ADS)

Transients are a class of deformation signals on the Earth's surface that can be described as non-periodic accumulation of strain in the crust. Over seismically and volcanically active regions, these signals are often challenging to detect due to noise and other modes of deformation. Geodetic datasets that provide precise measurements of surface displacement over wide areas are ideal for exploiting both the spatial and temporal coherence of transient signals. We present an extension to the Multiscale InSAR Time Series (MInTS) approach for analyzing geodetic data by combining the localization benefits of wavelet transforms (localizing signals in space) with sparse optimization techniques (localizing signals in time). Our time parameterization approach allows us to reduce geodetic time series to sparse, compressible signals with very few non-zero coefficients corresponding to transient events. We first demonstrate the temporal transient detection by analyzing GPS data over the Long Valley caldera in California and along the San Andreas fault near Parkfield, CA. For Long Valley, we are able to resolve the documented 2002-2003 uplift event with greater temporal precision. Similarly for Parkfield, we model the postseismic deformation by specific integrated basis splines characterized by timescales that are largely consistent with postseismic relaxation times. We then apply our method to ERS and Envisat InSAR datasets consisting of over 200 interferograms for Long Valley and over 100 interferograms for Parkfield. The wavelet transforms reduce the impact of spatially correlated atmospheric noise common in InSAR data since the wavelet coefficients themselves are essentially uncorrelated. The spatial density and extended temporal coverage of the InSAR data allows us to effectively localize ground deformation events in both space and time with greater precision than has been previously accomplished.

Riel, B.; Simons, M.; Agram, P.

2012-12-01

147

Micro-Diffuse Reflectance And Matrix Isolation Fourier Transform Infrared Techniques For The Identification Of Tetrachlorodibenzodioxins  

NASA Astrophysics Data System (ADS)

Diffuse reflectance infrared Fourier transform (DRIFT) and matrix isolation gas chromatography Fourier transform infrared (MI/GC/FT-IR) spectra of the 22 tetrachloro dibenzodioxin (TCDD) isomers have been measured. The spectrum of each TCDD isomer is unique.

Gurka, Donald F.; Billets, Stephen; Brasch, Jimmie W.; Barnes, Russell H.; Riggle, Charles J.; Bourne, Sidney

1985-12-01

148

Transient water age distributions in environmental flow systems: The time-marching Laplace transform solution technique  

NASA Astrophysics Data System (ADS)

Environmental fluid circulations are very often characterized by analyzing the fate and behavior of natural and anthropogenic tracers. Among these tracers, age is taken as an ideal tracer which can yield interesting diagnoses, as for example the characterization of the mixing and renewal of water masses, of the fate and mixing of contaminants, or the calibration of hydrodispersive parameters used by numerical models. Such diagnoses are of great interest in atmospheric and ocean circulation sciences, as well in surface and subsurface hydrology. The temporal evolution of groundwater age and its frequency distributions can display important changes as flow regimes vary due to natural change in climate and hydrologic conditions and/or human induced pressures on the resource to satisfy the water demand. Groundwater age being nowadays frequently used to investigate reservoir properties and recharge conditions, special attention needs to be put on the way this property is characterized, would it be using isotopic methods or mathematical modeling. Steady state age frequency distributions can be modeled using standard numerical techniques since the general balance equation describing age transport under steady state flow conditions is exactly equivalent to a standard advection-dispersion equation. The time-dependent problem is however described by an extended transport operator that incorporates an additional coordinate for water age. The consequence is that numerical solutions can hardly be achieved, especially for real 3-D applications over large time periods of interest. A novel algorithm for solving the age distribution problem under time-varying flow regimes is presented and, for some specific configurations, extended to the problem of generalized component exposure time. The algorithm combines the Laplace transform technique applied to the age (or exposure time) coordinate with standard time-marching schemes. The method is validated and illustrated using analytical and numerical solutions considering 1-D, 2-D, and 3-D theoretical groundwater flow domains.

Cornaton, F. J.

2012-03-01

149

Low chirp observed in directly modulated quantum dot lasers  

Microsoft Academic Search

We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as

Hideaki Saito; Kenichi Nishi; Akio Kamei; Shigeo Sugou

2000-01-01

150

Dense Monoenergetic Proton Beams from Chirped Laser-Plasma Interaction  

Microsoft Academic Search

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 (107 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

Benjamin J. Galow; Yousef I. Salamin; Tatyana V. Liseykina; Zoltn Harman; Christoph H. Keitel

2011-01-01

151

Sampled chirped fiber gratings as distributed pressure sensors  

NASA Astrophysics Data System (ADS)

Fiber gratings have been studied for their applications in sensing and communications. Many sensing applications of the uniform fiber Bragg grating, chirped fiber grating and long period grating have been studied, proposed and commercialized. Sampled chirped gratings have been studied for multichannel dispersion compensation in DWDM systems. In this paper, we show that the sampled chirped fiber grating can be used as a distributed pressure sensor. The chirp provides ease of manufacture of many gratings. The sampling results in many small, uniform grating-like structures. This fact can be used to simulate a distributed sensor over the length of the sampled chirped grating. When a surface comes into contact with the sensor, the distribution of the pressure determines the shift in central wavelength of the various sub-gratings. The sub-grating that experiences the maximum pressure will show maximum wavelength shift whereas adjacent sub-gratings will show less shift. This can also give the location of the pressure. The sensor design comprises of a sampled chirped grating embedded in unidirectional fiber-reinforced composite prepreg. The prepreg enhances the mechanical strength and the unidirectional embedding reduces birefringence. The number of layers in the prepreg stack varies the sensitivity. Such distributed pressure sensors can be applied in robotics, ergonomics, and in the biomedical field.

Tjin, Swee Chuan; Mohanty, Lipi; Ngo, Nam Quoc

2004-09-01

152

A modified adaptive algorithm of dealing with the high chirp when chirped pulses propagating in optical fiber  

NASA Astrophysics Data System (ADS)

In this paper, we propose a modified adaptive algorithm (MAA) of dealing with the high chirp to efficiently simulate the propagation of chirped pulses along an optical fiber for the propagation distance shorter than the "temporal focal length". The basis of the MAA is that the chirp term of initial pulse is treated as the rapidly varying part by means of the idea of the slowly varying envelope approximation (SVEA). Numerical simulations show that the performance of the MAA is validated, and that the proposed method can decrease the number of sampling points by orders of magnitude. In addition, the computational efficiency of the MAA compared with the time-domain beam propagation method (BPM) can be enhanced with the increase of the chirp of initial pulse.

Wu, Lianglong; Fu, Xiquan; Guo, Xing

2013-03-01

153

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

154

Review of high-throughput techniques for detecting solid phase Transformation from material libraries produced by combinatorial methods  

NASA Technical Reports Server (NTRS)

High-throughput measurement techniques are reviewed for solid phase transformation from materials produced by combinatorial methods, which are highly efficient concepts to fabricate large variety of material libraries with different compositional gradients on a single wafer. Combinatorial methods hold high potential for reducing the time and costs associated with the development of new materials, as compared to time-consuming and labor-intensive conventional methods that test large batches of material, one- composition at a time. These high-throughput techniques can be automated to rapidly capture and analyze data, using the entire material library on a single wafer, thereby accelerating the pace of materials discovery and knowledge generation for solid phase transformations. The review covers experimental techniques that are applicable to inorganic materials such as shape memory alloys, graded materials, metal hydrides, ferric materials, semiconductors and industrial alloys.

Lee, Jonathan A.

2005-01-01

155

Slippage effect on energy modulation in seeded free-electron lasers with frequency chirped seed laser pulses  

Free-electron lasers (FELs) seeded with external lasers hold great promise for generating high power radiation with nearly transform-limited bandwidth in the soft x-ray region. However, it has been pointed out that the initial seed laser phase error will be amplified by the frequency up-conversion process, which may degrade the quality of the output radiation produced by a harmonic generation scheme. In this paper, theoretical and simulation studies on frequency chirp amplification in seeded FEL schemes with slippage effect taken into account are presented. It is found that the seed laser imperfection experienced by the electron beam can be significantly smoothed by the slippage effect in the modulator when the slippage length is comparable to the seed laser pulse length. This smoothing effect allows one to preserve the excellent temporal coherence of seeded FELs in the presence of large frequency chirp in the seed laser. Our studies show that the tolerance on frequency chirp in the seed laser for generating nearly transform-limited soft x-ray pulses in seeded FELs is much looser than previously thought and fully coherent radiation at nanometer wavelength may be reached with current technologies.

Feng, Chao; Deng, Haixiao; Wang, Guanglei; Wang, Dong; Zhao, Zhentang; Xiang, Dao

2013-06-01

156

Ultrashort pulses from an all-fiber ring laser incorporating a pair of chirped fiber Bragg gratings.  

PubMed

By incorporating two linearly chirped ultrabroadband fiber Bragg gratings of opposite dispersion in an all-fiber ring laser, we demonstrate a mode-locking regime in which a femtosecond pulse evolving in the normal dispersion gain segment is locally transformed into a highly chirped picosecond pulse that propagates in the remaining section of the cavity. By minimizing nonlinear effects and avoiding soliton pulse shaping in this anomalous-dispersion section, low repetition rate fiber lasers can be made to produce high-energy ultrashort pulses. Using this approach, 98 fs pulses with 0.96 nJ of energy are obtained from an erbium-doped fiber laser operated in the highly anomalous dispersion regime at a repetition rate of 9.4 MHz. PMID:24562259

Duval, Simon; Olivier, Michel; Bernier, Martin; Valle, Ral; Pich, Michel

2014-02-15

157

Direct generation of intense extreme ultraviolet supercontinuum with chirped 11-mJ pulses from a femtosecond laser amplifier  

E-print Network

We report on the generation of intense extreme ultraviolet (EUV) supercontinuum with photon energies spanning from 35 eV to 50 eV (i. e., supporting an isolated attosecond pulse with a duration of ~271 as) by loosely focusing 11-mJ chirped pulses from a femtosecond laser amplifier into a 10-mm long gas cell filled with krypton gas. We observe that when high-order harmonics are generated with transformed-limited ~35 fs pulses, only discrete harmonics can be produced; whereas for negatively chirped 188 fs pulses, EUV supercontinuum can be observed in single-shot harmonic spectrum. The dramatic change of spectral and temporal properties of the driver pulses after passing through the gas cell indicates that propagation effects play a significant role in promoting the generation of the EUV supercontinuum.

Zeng, Bin; Li, Guihua; Yao, Jinping; Ni, Jielei; Zhang, Haisu; Cheng, Ya; Xu, Zhizhan

2011-01-01

158

JOURNAL DE PHYSIQUE Colloque C 2, supplkment au no 3-4, Tome 28, mars-ravril1967, page C 2 -58 A FAST FOURIER TRANSFORM TECHNIQUE  

E-print Network

A FAST FOURIER TRANSFORM TECHNIQUE AND ITS APPLICATION TO FOURIER SPECTROSCOPY (I) Concord Radiance. Abstract. - A description of a new method for computing Fourier transforms is given ; it was originated. The problem of computing Fourier transforms on digital computers is of great concern to many people

Boyer, Edmond

159

A LABORATORY DEMONSTRATION OF HIGH-RESOLUTION HARD X-RAY AND GAMMA-RAY IMAGING USING FOURIER-TRANSFORM TECHNIQUES  

E-print Network

A LABORATORY DEMONSTRATION OF HIGH-RESOLUTION HARD X-RAY AND GAMMA-RAY IMAGING USING FOURIER-TRANSFORM A laboratory imaging system has been developed to study the use of Fourier-transform techniques in high. We discuss considerations for the design of a Fourier-transform imager and describe

Prince, Thomas A.

160

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

161

Optically tunable chirped fiber Bragg grating.  

PubMed

This work presents an optically tunable chirped fiber Bragg grating (CFBG). The CFBG is obtained by a side-polished fiber Bragg grating (SPFBG) whose thickness of the residual cladding layer in the polished area (D(RC)) varies with position along the length of the grating, which is coated with a photoresponsive liquid crystal (LC) overlay. The reflection spectrum of the CFBG is tuned by refractive index (RI) modulation, which comes from the phase transition of the overlaid photoresponsive LC under ultraviolet (UV) light irradiation. The broadening in the reflection spectrum and corresponding shift in the central wavelength are observed with UV light irradiation density of 0.64mW/mm. During the phase transition of the photoresponsive LC, the RI increase of the overlaid LC leads to the change of the CFBG reflection spectrum and the change is reversible and repeatable. The optically tunable CFBGs have potential use in optical DWDM system and an all-fiber telecommunication system. PMID:22565706

Li, Zhen; Chen, Zhe; Hsiao, V K S; Tang, Jie-Yuan; Zhao, Fuli; Jiang, Shao-Ji

2012-05-01

162

Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system.  

PubMed

We present the first carrier-envelope-phase stable chirped-pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including cross-polarized wave (XPW) filtering technique and a high-energy grism-based compressor. The 8 mJ, 22 fs pulses feature 10? temporal contrast at -20??ps and a carrier-envelope-phase drift of 240 mrad root mean square. PMID:24978734

Jullien, Aurlie; Ricci, Aurlien; Bhle, Frederik; Rousseau, Jean-Philippe; Grabielle, Stphanie; Forget, Nicolas; Jacqmin, Hermance; Mercier, Brigitte; Lopez-Martens, Rodrigo

2014-07-01

163

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 Romn, J; Zar, A; Mndez, C; Roso, L

2010-11-01

164

Fourier transform infrared spectroscopy as a suitable technique in the study of the materials used in waterproofing of archaeological amphorae  

Microsoft Academic Search

The resinous materials from the interior surfaces of two Roman and one Iberian amphora were studied with Fourier transform infrared (FTIR) spectroscopy. The results were then compared with those obtained by synchrotron radiation-FTIR, scanning electron microscopy (SEM), and gas chromatographymass spectrometry (GCMS).The FTIR spectra obtained by the technique of KBr micropellets, prepared directly with the materials scraped from the amphora

N. Salvad; S. But; J. Enrich

2007-01-01

165

Ultra-fast dynamic compression technique to study kinetics of phase transformations in Bismuth  

SciTech Connect

Pre-heated Bi was ramp compressed within 30 ns to a peak stress of {approx}11 GPa to explore structural phase transformation kinetics under dynamic loading conditions. Under these ultra-fast compression time-scales the equilibrium Bi I-II phase boundary is overpressurized by {Delta}P {approx} 0.8 GPa. {Delta}P is observed to increase logarithmically with strain rate, {var_epsilon}, above 10{sup 6} s{sup -1}. Estimates from a kinetics model predict that the Bi I phase is fully transformed within 3 ns.

Smith, R F; Kane, J O; Eggert, J H; Saculla, M D; Jankowski, A F; Bastea, M; Hicks, D G; Collins, G W

2007-12-28

166

Anti-ship missile tracking with a chirped AM ladar - Update: design, model predictions, and experimental results  

Microsoft Academic Search

Shipboard infrared search and track (IRST) systems can detect sea-skimming, anti-ship missiles at long ranges. Since IRST systems cannot measure range and line-of-sight (LOS) velocity, they have difficulty distinguishing missiles from false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a ladar based on the chirped amplitude modulation (AM) technique to provide range

Brian Redman; William Ruff; Barry Stann; Mark Giza; William Lawler; John Dammann; William Potter

2005-01-01

167

Single-shot detection of mid-infrared spectra by chirped-pulse upconversion with four-wave difference frequency generation in gases.  

PubMed

Single-shot detection of ultrabroadband mid-infrared spectra was demonstrated by using chirped-pulse upconversion technique with four-wave difference frequency generation in gases. Thanks to the low dispersion of the gas media, the bandwidth of the phase matching condition of the upconversion process becomes very broad and the entire mid-infrared spectrum spanning from 200 to 5500 cm(-1) was upconverted by using a 10 ps chirped pulse to visible wavelength radiation, which was detected with a conventional visible dispersive spectrometer. This method was demonstrated by the successful measurement of infrared absorption spectra of organic polymer films. PMID:23938695

Nomura, Y; Wang, Y-T; Kozai, T; Shirai, H; Yabushita, A; Luo, C-W; Nakanishi, S; Fuji, T

2013-07-29

168

Effects of collisions on energetic particle-driven chirping bursts  

SciTech Connect

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. [Itoh Research Center for Plasma Turbulence, Kyushu University, Kasuga, Kasuga Koen 6-1, Fukuoka 816-8580 (Japan)] [Itoh Research Center for Plasma Turbulence, Kyushu University, Kasuga, Kasuga Koen 6-1, Fukuoka 816-8580 (Japan)

2013-05-15

169

Beam energy chirp effects in seeded free-electron lasers  

NASA Astrophysics Data System (ADS)

Seeded free-electron lasers (FELs) hold great promise for generating high brilliance radiation pulses with a narrow bandwidth, which typically requires an electron bunch with relatively uniform energy distribution. However, it has been pointed out that the beam energy curvature generated in the acceleration process may degrade the output radiation pulse quality of seeded FELs. In this paper, we studied the beam energy chirp effects in various seeded FEL configurations. The theoretical and simulation results show that the performance degradation of high gain harmonic generation scheme is proportional to the beam energy chirp, while the advanced seeding schemes, e.g. echo-enabled harmonic generation and phase merging enhanced harmonic generation, are capable of eliminating the effect of the electron beam energy chirp.

Wang, Guanglei; Feng, Chao; Deng, Haixiao; Zhang, Tong; Wang, Dong

2014-07-01

170

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

171

Chirped Gaussian laser beam parameters in paraxial approximation  

NASA Astrophysics Data System (ADS)

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.

2010-08-01

172

Steganography Technique to Hide a Video into Another One via Discrete Wavelet Transform  

Microsoft Academic Search

In this work an algorithm is proposed to hide information, into an .avi video file. Such file is separated in audio and video. The video breaks down in its frames, in which we apply a discrete wavelet transform. Once the image has been separated in frequencies, zones are chosen where the information can be hidden. In this work the source

B E Carvajal-Gmez; J. Lpez-Bonilla

2009-01-01

173

APPLICATION OF MODERN TECHNIQUES FOR THE CONDITION ASSESSMENT OF POWER TRANSFORMERS  

Microsoft Academic Search

1. Summary The outstanding technical and economical importance of power transformers in the electrical transmission and distribution networks does not need to be discussed. The continuous awareness of the evolution of the conditions of the insulation system and of the internal mechanical sturdiness is of great value for the system operator as it allows to optimise the lifecycle management of

M. de Nigris; R. Passaglia; R. Berti; L. Bergonzi; R. Maggi

174

Cell Transformations and Physical Design Techniques for 3D Monolithic Integrated Circuits  

E-print Network

fine-grain (gate-level) partitioning of circuits. In this work we present three cell transformation of this work for personal or classroom use is granted without fee provided that copies are not made prior specific permission and/or a fee. Permissions may be requested from Publications Dept., ACM, Inc

De Micheli, Giovanni

175

A deblocking technique for JPEG decoded image using wavelet transform modulus maxima representation  

Microsoft Academic Search

In this paper, we introduce a local deblocking algorithm for JPEG decoded images using the wavelet transform modulus maxima (WTMM) representation. Under the WTMM representation, we can characterize the blocking effect as: 1) small modulus maxima at block boundaries over smooth regions; 2) noises or irregular structures near strong edges; 3) corrupted edges across block boundaries. The WTMM representation not

Tai-Chiu Hsung; Daniel Pak-Kong Lun; Wan-Chi Siu

1996-01-01

176

ANALYSIS OF POWER TRANSIENT DISTURBANCES USING WAVELET TRANSFORM MODULUS MAXIMA TECHNIQUE  

Microsoft Academic Search

Complex power quality disturbances are non-stationary and transient by nature and points of sharp variation such as singularities in transient signals usually carry the most important information about the disturbances. It is well known that wavelet transform modulus maxima (WTMM) of a signal using a wavelet that is the first derivative of a smoothing function, give a reliable multiscale representation

D T Nguyen; T A Hoang

177

Dynamic analysis of impact induced phase transformation in Shape Memory Alloys using numerical techniques  

E-print Network

by the numerical solution of initial boundary value problems of a semi- infinite, one-dimensional SMA rod subjected to impact loading. Special focus was placed on the initiation and propagation of material phase transformation due to the presence of stress waves...

Jimenez-Victory, Juan Carlos

2012-06-07

178

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

2013-08-01

179

Benchmarking techniques for evaluation of compression transform performance in ATR applications  

NASA Astrophysics Data System (ADS)

Image compression is increasingly employed in applications such as medical imaging, for reducing data storage requirement, and Internet video transmission, to effectively increase channel bandwidth. Similarly, military applications such as automated target recognition (ATR) often employ compression to achieve storage and communication efficiencies, particularly to enhance the effective bandwidth of communication channels whose throughput suffers, for example, from overhead due to error correction/detection or encryption. In the majority of cases, lossy compression is employed due the resultant low bit rates (high compression ratio). However, lossy compression produces artifacts in decompressed imagery that can confound ATR processes applied to such imagery, thereby reducing the probability of detection (Pd) and possibly increasing the rate or number of false alarms (Rfa or Nfa). In this paper, the authors' previous research in performance measurement of compression transforms is extended to include (a) benchmarking algorithms and software tools, (b) a suite of error exemplars that are designed to elicit compression transform behavior in an operationally relevant context, and (c) a posteriori analysis of performance data. The following transforms are applied to a suite of 64 error exemplars: Visual Pattern Image Coding (VPIC [1]), Vector Quantization with a fast codebook search algorithm (VQ [2,3]), JPEG and a preliminary implementation of JPEG 2000 [4,5], and EBLAST [6-8]. Compression ratios range from 2:1 to 200:1, and various noise levels and types are added to the error exemplars to produce a database of 7,680 synthetic test images. Several global and local (e.g., featural) distortion measures are applied to the decompressed test imagery to provide a basis for rate-distortion and rate-performance analysis as a function of noise and compression transform type.

Schmalz, Mark S.

2004-10-01

180

Elimination of spurious solutions from k.p theory with Fourier transform technique and Burt-Foreman operator ordering  

NASA Astrophysics Data System (ADS)

To eliminate spurious solutions in the multiple-band k.p theory, we developed the Fourier transform-based k.p approach through combining the Fourier transform technique with Burt-Foreman operator ordering. The performance is perfect for the six-band k.p calculation, and the spurious solutions in the conduction band met in the eight-band calculation can also be easily screened away in the inborn cut-off step in FTM, i.e., choosing a proper order of Fourier truncation. Truncating high-order terms of Fourier coefficients of the envelope function prevents the occurrence of a wild-spreading spectrum of the Fourier expansion coefficients, which can be taken as the signature of spurious solutions.

Zhao, Qiuji; Mei, Ting; Zhang, Dao Hua

2012-03-01

181

Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses  

NASA Astrophysics Data System (ADS)

The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom-dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems.

Munsch, Mathieu; Wst, Gunter; Kuhlmann, Andreas V.; Xue, Fei; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D.; Poggio, Martino; Warburton, Richard J.

2014-09-01

182

Comparative study of face recognition techniques that use joint transform correlation and principal component analysis  

NASA Astrophysics Data System (ADS)

Face recognition based on principal component analysis (PCA) that uses eigenfaces is popular in face recognition markets. We present a comparison between various optoelectronic face recognition techniques and a PCA-based technique for face recognition. Computer simulations are used to study the effectiveness of the PCA-based technique, especially for facial images with a high level of distortion. Results are then compared with various distortion-invariant optoelectronic face recognition algorithms such as synthetic discriminant functions (SDF), projection-slice SDF, optical-correlator-based neural networks, and pose-estimation-based correlation.

Alsamman, A.; Alam, Mohammad S.

2005-02-01

183

Ultra-wideband WDM transmission using cascaded chirped fiber gratings  

Microsoft Academic Search

We demonstrate 32 channel WDM transmission at a per-channel rate of 10 Gb\\/s over 375 km (five amplified fiber spans) of conventional fiber. Chirped-fiber-grating modules provide dispersion compensation over an 18-nm bandwidth, and a swept-frequency measurement confirms continuous good performance across the entire band

L. D. Garrett; A. H. Gnauck; R. W. Tkach; B. Agogliati; L. Arcangeli; D. Scarano; V. Gusmeroli; C. Tosetti; G. Di Maio; F. Forghieri

1999-01-01

184

High Squint SAR Processing Using Modified Extended Chirp Scaling  

Microsoft Academic Search

This paper proposes a novel approach for high squint missile borne SAR raw data processing using a modified extended chirp scaling algorithm to accommodate the condition of high squint and short wave wavelength. Compared with the tradition synthesis aperture radar (SAR), the missile borne SAR has important characteristics including high flight speed, non-straight movement with non-constant velocity and big squint

Duan Shizhong; Li Junxian

2006-01-01

185

Electron heating enhancement by frequency-chirped laser pulses  

NASA Astrophysics Data System (ADS)

Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2. Furthermore, it is noticed that for a chirped laser pulse with a0 = 5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about ne ? 6nc, where nc is plasma critical density. It shows 63% increase in the effective critical density compared to the relativistic induced transparency regime for an unchirped condition.

Yazdani, E.; Sadighi-Bonabi, R.; Afarideh, H.; Riazi, Z.; Hora, H.

2014-09-01

186

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

187

The Theta Laser A Low Noise Chirped Pulse Laser  

E-print Network

Coherence Tomography ( Medical ) Laser Ranging ( Millitary ) #12;6 Outline · Applications of frequency sweptThe Theta Laser A Low Noise Chirped Pulse Laser Dimitrios Mandridis dmandrid@creol.ucf.edu April 29, 2011 CREOL Affiliates Day 2011 #12;2 Objective: Frequency Swept (FM) Mode-locked Laser · Develop

Van Stryland, Eric

188

Coded multiple chirp spread spectrum system and overlay service  

NASA Astrophysics Data System (ADS)

An asynchronous spread-spectrum system called coded multiple chirp is proposed, and the possible spread-spectrum overlay over an analog FM-TV signal is investigated by computer simulation. Multiple single-sloped up and down chirps are encoded by a pseudonoise code and decoded by dechirpers (pulse-compression filters) followed by a digital code correlator. The performance of the proposed system, expressed in terms of in probability of bit error and code miss probability, is similar to that of FSK (frequency shift keying) using codewords if sufficient compression gain is used. When chirp is used to overlay an FM-TV channel, two chirp signals with data rate up to 25 kb/s could be overlaid in a 36-MHz satellite transponder without significant mutual interference. Performance estimates for a VSAT (very small aperture terminal) earth station operating at C-band show that a 2.4-m antenna and 300-mW transmitter could send a 2.4-kb/s signal to a large central earth station over an occupied channel.

Kim, Junghwan; Pratt, Timothy; Ha, Tri T.

189

Coded multiple chirp spread spectrum system and overlay service  

NASA Technical Reports Server (NTRS)

An asynchronous spread-spectrum system called coded multiple chirp is proposed, and the possible spread-spectrum overlay over an analog FM-TV signal is investigated by computer simulation. Multiple single-sloped up and down chirps are encoded by a pseudonoise code and decoded by dechirpers (pulse-compression filters) followed by a digital code correlator. The performance of the proposed system, expressed in terms of in probability of bit error and code miss probability, is similar to that of FSK (frequency shift keying) using codewords if sufficient compression gain is used. When chirp is used to overlay an FM-TV channel, two chirp signals with data rate up to 25 kb/s could be overlaid in a 36-MHz satellite transponder without significant mutual interference. Performance estimates for a VSAT (very small aperture terminal) earth station operating at C-band show that a 2.4-m antenna and 300-mW transmitter could send a 2.4-kb/s signal to a large central earth station over an occupied channel.

Kim, Junghwan; Pratt, Timothy; Ha, Tri T.

1988-01-01

190

Measurements of solar magnetic fields by Fourier transform techniques. I - Unsaturated lines  

NASA Technical Reports Server (NTRS)

If the basic profile shapes of the normal Zeeman triplet do not have zeros in their Fourier transform, the magnetic field splitting can be determined independent of the profile shape. When the ratio of the splitting of the components is greater than the intrinsic FWHM of the component profiles, the magnetic splitting can be determined with significantly greater accuracy than the measurement accuracy of the original profile. For Gaussian shaped components and a ratio of magnetic splitting to FWHM of 1.5, the noise reduction factor is 25.

Title, A. M.; Tarbell, T. D.

1975-01-01

191

Coherence rephasing combined with spin-wave storage using chirped control pulses  

NASA Astrophysics Data System (ADS)

Photon-echo based optical quantum memory schemes often employ intermediate steps to transform optical coherences to spin coherences for longer storage times. We analyze a scheme that uses three identical chirped control pulses for coherence rephasing in an inhomogeneously broadened ensemble of three-level ? systems. The pulses induce a cyclic permutation of the atomic populations in the adiabatic regime. Optical coherences created by a signal pulse are stored as spin coherences at an intermediate time interval, and are rephased for echo emission when the ensemble is returned to the initial state. Echo emission during a possible partial rephasing when the medium is inverted can be suppressed with an appropriate choice of control pulse wave vectors. We demonstrate that the scheme works in an optically dense ensemble, despite control pulse distortions during propagation. It integrates conveniently the spin-wave storage step into memory schemes based on a second rephasing of the atomic coherences.

Demeter, Gabor

2014-06-01

192

Focusing of tandem bistatic SAR data using the chirp-scaling algorithm  

NASA Astrophysics Data System (ADS)

Based on an exact analytical bistatic point target spectrum, an efficient chirp-scaling algorithm is proposed to correct the range cell migration of different range gates to the one of the reference range for tandem bistatic synthetic aperture radar data processing. The length of the baseline (baseline to range ratio) does not give a direct influence to the proposed algorithm, which can be applied to the processing of tandem bistatic data with a large baseline even when the baseline is equal to the range. No interpolation is needed during the entire processing, only fast Fourier transforms and phase multiplications are needed, which result in efficiency. The validity of the proposed algorithm has been verified by simulated experiments.

Chen, Shichao; Xing, Mengdao; Zhou, Song; Zhang, Lei; Bao, Zheng

2013-12-01

193

Coherence rephasing combined with spin-wave storage using chirped control pulses  

E-print Network

Photon-echo based optical quantum memory schemes often employ intermediate steps to transform optical coherences to spin coherences for longer storage times. We analyze a scheme that uses three identical chirped control pulses for coherence rephasing in an inhomogeneously broadened ensemble of three-level $\\Lambda$-systems. The pulses induce a cyclic permutation of the atomic populations in the adiabatic regime. Optical coherences created by a signal pulse are stored as spin coherences at an intermediate time interval, and are rephased for echo emission when the ensemble is returned to the initial state. Echo emission during a possible partial rephasing when the medium is inverted can be suppressed with an appropriate choice of control pulse wavevectors. We demonstrate that the scheme works in an optically dense ensemble, despite control pulse distortions during propagation. It integrates conveniently the spin-wave storage step into memory schemes based on a second rephasing of the atomic coherences.

Gabor Demeter

2014-03-19

194

Novel diagnosis technique of mass unbalance in rotor of induction motor by the analysis of motor starting current at no load through wavelet transform  

Microsoft Academic Search

This paper presents an improved technique for detection of mass unbalance in rotor of an induction motor by the analysis of transient stator current during starting period using both discrete wavelet transform (DWT) and continuous wavelet transform(CWT). The unbalanced magnetic pull due to centrifugal force developed for mass unbalance in rotor produces excessive vibration in the rotor as well as

S. K. Ahamed; Subrata Karmakar; M. Mitra; S. Sengupta

2010-01-01

195

Detection and evaluation of droplet and bubble fringe patterns in images of planar interferometric measurement techniques using the wavelet transform  

NASA Astrophysics Data System (ADS)

The acquired images of interferometric particle sizing techniques are characterized by intense fringe pattern overlapping in dense droplet and bubble areas, which hinders the image processing process and subsequent information extraction. Methods employed, such as thresholding and the Hough transform and template cross-correlation, exhibit weaknesses when processing such dense areas of interest. We investigate the viability of applying the wavelet transform (WT) for the detection of the fringe pattern centers and the evaluation of the particle size. We present the basics of the WT using the Mexican hat, which exhibits excellent localization properties and present two different alternatives routes in detecting the fringe patterns in the compressed and uncompressed fringe pattern cases. We found that in comparison to the most reported methods for image evaluation, such as intensity thresholding and plain cross-correlation, the WT is a very efficient tool for detecting the patterns, even in images with high-number fringe pattern areas. The usage of the WT for the sizing of the imaged droplets and bubbles is also examined, in comparison to the Fast Fourier Transform (FFT).

Hardalupas, Y.; Taylor, A. M. K. P.; Zarogoulidis, K.

2014-08-01

196

Study on adaptive thresholding technique of image denoising based on wavelet transform  

NASA Astrophysics Data System (ADS)

It is studied in the paper that an adaptive soft and hard thresholding image denoising method, in which image pyramid decomposing is realized by wavelet transform, and the mean value, mid-value and root mean square value of different sub bands are calculated as thresholding. The image is added into different kinds and different intensities noise, and processed by different wavelet decomposing levels and thresholding selected algorithms, the total 27 kinds of thresholding combination schemes are completed in the research process. The SNR (signal noise ratio) and PSNR (peak signal noise ratio) of denoised image are compared and analyzed and benefited results are achieved. Furthermore, the algorithm in reference is realized by MATLAB program, the results of reference are compared with that of the paper to demonstrate the significance and correctness of the results in the paper.

Zhu, Xi'an; Xie, Xiao

2010-12-01

197

Study on adaptive thresholding technique of image denoising based on wavelet transform  

NASA Astrophysics Data System (ADS)

It is studied in the paper that an adaptive soft and hard thresholding image denoising method, in which image pyramid decomposing is realized by wavelet transform, and the mean value, mid-value and root mean square value of different sub bands are calculated as thresholding. The image is added into different kinds and different intensities noise, and processed by different wavelet decomposing levels and thresholding selected algorithms, the total 27 kinds of thresholding combination schemes are completed in the research process. The SNR (signal noise ratio) and PSNR (peak signal noise ratio) of denoised image are compared and analyzed and benefited results are achieved. Furthermore, the algorithm in reference is realized by MATLAB program, the results of reference are compared with that of the paper to demonstrate the significance and correctness of the results in the paper.

Zhu, Xi'an; Xie, Xiao

2011-05-01

198

Spatial Registration of Multispectral and Multitemporal Digital Imagery Using Fast Fourier Transform Techniques  

Microsoft Academic Search

A system for spatial registration of digitized multispectral and multitemporal imagery is described. Multispectral imagery can be obtained from sources such as multilens cameras, multichannel optical-mechanical line scanners, or multiple vidicon systems which employ filters or other spectral separation techniques to sense selected portions of the spectrum. Spatial registration is required so that multidimensional analysis can be performed on contextually

PAUL E. ANUTA

1970-01-01

199

Radon transform technique for linear structures detection: Application to vessel detection in fluorescein angiography fundus images  

Microsoft Academic Search

In medical images linear patterns such as blood vessels are important structures for computer-aided diagnosis and follow-up of many diseases. Moreover, image processing techniques are required to extract suitable information about vascular tree and its alteration. Analyzing of retinal blood vessel is critical work for the investigation of some diseases. In this study, we present an automated method for detecting

M. Tavakoli; A. R. Mehdizadeh; R. Pourreza; H. R. Pourreza; T. Banaee; M. H. Bahreini Toosi

2011-01-01

200

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.

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

2010-10-01

201

Advanced burden level measurement radars using FFT signal processing techniques. [Fast Fourier Transform  

Microsoft Academic Search

Advanced design level-measuring radars have been developed and installed at Bethlehem Steel's Burns Harbor Plant to measure burden height in operating blast furnaces. Modern signal processing techniques are used in conjunction with a self-calibrating wideband swept-frequency dual-antenna radar to enhance measurement accuracy and better differentiate true surface returns from extraneous reflections. Provisions have been included to monitor and record critical

D. D. Mawhinney; A. Presser; T. G. Koselke

1993-01-01

202

High spatial resolution distributed strain sensor based on linear chirped fiber Bragg grating and fiber loop ringdown spectroscopy.  

PubMed

A simple sensor system for high spatial resolution distributed strain field measurement is proposed and demonstrated experimentally. The fiber loop ringdown technique combined with a linear chirped fiber Bragg grating is used to realize the high spatial resolution. A proof-of-concept distributed strain sensor with 2?mm spatial resolution is realized. The sensor network is also explored and researched experimentally. The proposed technique suggests a broad range of applications for real-time distributed physical parameter sensing, such as strain or temperature. PMID:21403715

Gan, Jiulin; Hao, Yunqi; Ye, Qing; Pan, Zhengqing; Cai, Haiwen; Qu, Ronghui; Fang, Zujie

2011-03-15

203

Single-shot chirped-pulse spectral interferometry used to measure the femtosecond ionization dynamics of air.  

PubMed

A novel interferometry technique is presented by which, in one shot, one can measure phase changes with a resolution of tens of femtoseconds while extending the measurement over picoseconds or even longer. The method is based on spectral (frequency-domain) interferometry with a pair of linearly chirped pules as probes. With this technique we obtained single-shot measurements of the rapid phase changes induced by optical field ionization of air. This allowed us to calculate the time profile of the electron density created by an intense short laser pulse. PMID:18064117

Chien, C Y; La Fontaine, B; Desparois, A; Jiang, Z; Johnston, T W; Kieffer, J C; Ppin, H; Vidal, F; Mercure, H P

2000-04-15

204

Controlling the femtosecond laser-driven transformation of dicyclopentadiene into cyclopentadiene  

NASA Astrophysics Data System (ADS)

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 photoproduct 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

2013-02-01

205

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 pumpprobe 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. PMID:24098059

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

2013-01-01

206

Partial discharge localization in power transformers based on the sequential quadratic programming-genetic algorithm adopting acoustic emission techniques  

NASA Astrophysics Data System (ADS)

Partial discharge (PD) in power transformers is one of the prime reasons resulting in insulation degradation and power faults. Hence, it is of great importance to study the techniques of the detection and localization of PD in theory and practice. The detection and localization of PD employing acoustic emission (AE) techniques, as a kind of non-destructive testing, plus due to the advantages of powerful capability of locating and high precision, have been paid more and more attention. The localization algorithm is the key factor to decide the localization accuracy in AE localization of PD. Many kinds of localization algorithms exist for the PD source localization adopting AE techniques including intelligent and non-intelligent algorithms. However, the existed algorithms possess some defects such as the premature convergence phenomenon, poor local optimization ability and unsuitability for the field applications. To overcome the poor local optimization ability and easily caused premature convergence phenomenon of the fundamental genetic algorithm (GA), a new kind of improved GA is proposed, namely the sequence quadratic programming-genetic algorithm (SQP-GA). For the hybrid optimization algorithm, SQP-GA, the sequence quadratic programming (SQP) algorithm which is used as a basic operator is integrated into the fundamental GA, so the local searching ability of the fundamental GA is improved effectively and the premature convergence phenomenon is overcome. Experimental results of the numerical simulations of benchmark functions show that the hybrid optimization algorithm, SQP-GA, is better than the fundamental GA in the convergence speed and optimization precision, and the proposed algorithm in this paper has outstanding optimization effect. At the same time, the presented SQP-GA in the paper is applied to solve the ultrasonic localization problem of PD in transformers, then the ultrasonic localization method of PD in transformers based on the SQP-GA is proposed. And localization results based on the SQP-GA are compared with some algorithms such as the GA, some other intelligent and non-intelligent algorithms. The results of calculating examples both stimulated and spot experiments demonstrate that the localization method based on the SQP-GA can effectively prevent the results from getting trapped into the local optimum values, and the localization method is of great feasibility and very suitable for the field applications, and the precision of localization is enhanced, and the effectiveness of localization is ideal and satisfactory.

Liu, Hua-Long; Liu, Hua-Dong

2014-10-01

207

Transient Water Age Distributions in Environmental Flow Systems: The Time-Marching Laplace Transform Solution Technique  

E-print Network

Environmental fluid circulations are very often characterized by analyzing the fate and behavior of natural and anthropogenic tracers. Among these tracers, age is taken as an ideal tracer which can yield interesting diagnoses, as for example the characterization of the mixing and renewal of water masses, of the fate and mixing of contaminants, or the calibration of hydro-dispersive parameters used by numerical models. Such diagnoses are of great interest in atmospheric and ocean circulation sciences, as well in surface and subsurface hydrology. The temporal evolution of groundwater age and its frequency distributions can display important changes as flow regimes vary due to natural change in climate and hydrologic conditions and/or human induced pressures on the resource to satisfy the water demand. Steady-state age frequency distributions can be modelled using standard numerical techniques, since the general balance equation describing age transport under steady-state flow conditions is exactly equivalent to...

Cornaton, F J

2011-01-01

208

River flow forecasting. Part 3. Applications of linear techniques in modelling rainfall-runoff transformations  

NASA Astrophysics Data System (ADS)

The Simple Linear Model (SLM) and the Linear Perturbation Model (LPM) are applied to 14 catchments chosen from various geographical locations in the world. These models are applied in non-parametric form as well as under the constraints of the gamma function impulse response. Parameter optimization is carried out by the method of ordinary least squares and by Rosenbrock's search technique for the non-parametric and parametric versions, respectively. The loss of generality associated with the constraint of the gamma function shape is found to be insignificant. For large catchments which exhibit seasonal behaviour, good results can be obtained with the Linear Perturbation Model which involves the assumption of a linear relationship between departures from seasonal expectations in the input and output series. For use in real-time forecasting, an autoregressive updating component obtained from the examination of the residuals is used.

Kachroo, R. K.; Sea, C. H.; Warsi, M. S.; Jemenez, H.; Saxena, R. P.

1992-04-01

209

Advanced burden level measurement radars using FFT signal processing techniques. [Fast Fourier Transform  

SciTech Connect

Advanced design level-measuring radars have been developed and installed at Bethlehem Steel's Burns Harbor Plant to measure burden height in operating blast furnaces. Modern signal processing techniques are used in conjunction with a self-calibrating wideband swept-frequency dual-antenna radar to enhance measurement accuracy and better differentiate true surface returns from extraneous reflections. Provisions have been included to monitor and record critical parameters of the radar and various installation accessories to improve maintainability and instrumentation accuracy. A ruggedized personal computer is used to perform the signal processing calculations, determine the distance in terms related to the furnace dimensions, sequence the remote monitoring elements, provide graphic displays of the real-time and historic burden height and monitor data, and operate the complete system from a basic keyboard.

Mawhinney, D.D. (MMTC, Inc., Princeton, NJ (United States)); Presser, A. (MMTC, Inc., Princeton, NJ (United States)); Koselke, T.G. (Bethlehem Steel Corp., Chesterton, IN (United States))

1993-01-01

210

Chirped-pulse terahertz spectroscopy for broadband trace gas sensing.  

PubMed

We report the first demonstration of a broadband trace gas sensor based on chirp-pulse terahertz spectroscopy. The advent of newly developed solid state sources and sensitive heterodyne detectors for the terahertz frequency range have made it possible to generate and detect precise arbitrary waveforms at THz frequencies with ultra-low phase noise. In order to maximize sensitivity, the sample gas is first polarized using sub-?s chirped THz pulses and the free inductive decays (FIDs) are then detected using a heterodyne receiver. This approach allows for a rapid broadband multi-component sensing with low parts in 10(9) (ppb) sensitivities and spectral frequency accuracy of <20 kHz in real-time. Such a system can be configured into a portable, easy to use, and relatively inexpensive sensing platform. PMID:21643150

Gerecht, Eyal; Douglass, Kevin O; Plusquellic, David F

2011-04-25

211

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

212

Dense monoenergetic proton beams from chirped laser-plasma interaction  

E-print Network

Interaction of a frequency-chirped laser pulse with single protons and a hydrogen plasma cell is studied analytically and by means of particle-in-cell simulations, respectively. Feasibility of generating ultra-intense (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.

Galow, Benjamin J; Liseykina, Tatyana V; Harman, Zoltan; Keitel, Christoph H

2011-01-01

213

Chirped fiber Bragg grating sensor for pressure and position sensing  

NASA Astrophysics Data System (ADS)

We present a chirped fiber Bragg grating sensor that should be suitable for esophageal motility studies. The device uses the time-dependent group delay response of a chirped fiber Bragg grating to measure the peristaltic pressure wave that propagates down the esophagus with the transport of a bolus to the stomach. In contrast to existing transducers that only measure at discrete points, the output of this device is a continuous function of length along the esophagus. This paper presents ex-vivo experimental results. There is a linear relation between the wavelength location of the maximum phase perturbation and the position along the sensor where the perturbation occurred. The maximum phase change itself is directly proportional to the magnitude of the applied load at a specific position.

Swart, Pieter L.; Lacquet, Beatrys M.; Chtcherbakov, Anatolii A.

2005-05-01

214

An adaptive algorithm for strongly chirped pulses propagating in optical fibers  

NASA Astrophysics Data System (ADS)

Chirp, especially strong chirp, can be used to control the pulses in optical fibers, but it makes numerical simulation difficult by using the time-domain beam propagation method (TD-BPM) because of more sampling data requirements. In this paper, we present a modified beam propagation method (M-BPM) to efficiently simulate the propagation of strongly chirped pulses along an optical fiber. The validity of the M-BPM is demonstrated both theoretically and numerically. Numerical simulations show that the number of samples in time necessary to simulate the chirped pulse propagation by the TD-BPM varies linearly with the initial chirp parameter, but that of the M-BPM is the same one would need to simulate the propagation of the envelope without the initial chirp. In addition, the closer the propagation distance is to the temporal focal length, the more efficient the M-BPM comparing with the TD-BPM is.

Wu, Lianglong; Fu, Xiquan; Guo, Xing; Li, Huai

2012-07-01

215

Multifractal Detrended Fluctuation Analysis of Human EEG: Preliminary Investigation and Comparison with the Wavelet Transform Modulus Maxima Technique  

PubMed Central

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.

2013-01-01

216

Hyper dispersion pulse compressor for chirped pulse amplification systems  

DOEpatents

A grating pulse compressor configuration is introduced for increasing the optical dispersion for a given footprint and to make practical the application for chirped pulse amplification (CPA) to quasi-narrow bandwidth materials, such as Nd:YAG. The grating configurations often use cascaded pairs of gratings to increase angular dispersion an order of magnitude or more. Increased angular dispersion allows for decreased grating separation and a smaller compressor footprint.

Barty, Christopher P. J. (Hayward, CA)

2011-11-29

217

Generalized chirp-like polyphase sequences with optimum correlation properties  

Microsoft Academic Search

A new general class of polyphase sequences with ideal periodic autocorrelation function is presented. The new class of sequences is based on the application of Zadoff-Chu polyphase sequences of length N=sm2, where s and m are any positive integers. It is shown that the generalized chirp-like sequences of odd length have the optimum crosscorrelation function under certain conditions. Finally, recently

Branislav M. Popovic

1992-01-01

218

Quantum Phenomena in a Chirped Parametric Anharmonic Oscillator  

NASA Astrophysics Data System (ADS)

Parametric ladder climbing and the quantum saturation of the threshold for the classical parametric autoresonance due to the zero point fluctuations at low temperatures are discussed. The probability for capture into the chirped parametric resonance is found by solving the Schrdinger equation in the energy basis and the associated resonant phase-space dynamics is illustrated via the Wigner distribution. The numerical threshold for capture into the resonance is compared with the classical and quantum theories in different parameter regimes.

Barth, I.; Friedland, L.

2014-07-01

219

Quantum phenomena in a chirped parametric anharmonic oscillator.  

PubMed

Parametric ladder climbing and the quantum saturation of the threshold for the classical parametric autoresonance due to the zero point fluctuations at low temperatures are discussed. The probability for capture into the chirped parametric resonance is found by solving the Schrdinger equation in the energy basis and the associated resonant phase-space dynamics is illustrated via the Wigner distribution. The numerical threshold for capture into the resonance is compared with the classical and quantum theories in different parameter regimes. PMID:25105601

Barth, I; Friedland, L

2014-07-25

220

Auditory brainstem responses to chirps delivered by different insert earphones.  

PubMed

The frequency response and sensitivity of the ER-3A and ER-2 insert earphones are measured in the occluded-ear simulator using three ear canal extensions. Compared to the other two extensions, the DB 0370 (Bru?el & Kjr), which is recommended by the international standards, introduces a significant resonance peak around 4500 Hz. The ER-3A has an amplitude response like a band-pass filter (1400 Hz, 6 dB/octave -4000 Hz, -36 dB/octave), and a group delay with "ripples" of up to 0.5 ms, while the ER-2 has an amplitude response, and a group delay which are flat and smooth up to above 10000 Hz. Both earphones are used to record auditory brainstem responses, ABRs, from 22 normal-hearing ears in response to two chirps and a click at levels from 20 to 80 dB nHL. While the click-ABRs are slightly larger for ER-2 than for ER-3A, the chirp-ABRs are much larger for ER-2 than for ER-3A at levels below 60 dB nHL. With a simulated amplitude response of the ER-3A and the smooth group delay of the ER-2 it is shown that the increased chirp-ABR amplitude with the ER-2 is caused by its broader amplitude response and not by its smoother group delay. PMID:22423705

Elberling, Claus; Kristensen, Sinnet G B; Don, Manuel

2012-03-01

221

Active stabilization of a rapidly chirped laser by an optoelectronic digital servo-loop control.  

PubMed

We propose and demonstrate a novel active stabilization scheme for wide and fast frequency chirps. The system measures the laser instantaneous frequency deviation from a perfectly linear chirp, thanks to a digital phase detection process, and provides an error signal that is used to servo-loop control the chirped laser. This way, the frequency errors affecting a laser scan over 10 GHz on the millisecond timescale are drastically reduced below 100 kHz. This active optoelectronic digital servo-loop control opens new and interesting perspectives in fields where rapidly chirped lasers are crucial. PMID:17392895

Gorju, G; Jucha, A; Jain, A; Crozatier, V; Lorger, I; Le Gout, J-L; Bretenaker, F; Colice, M

2007-03-01

222

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

SciTech Connect

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

2005-08-10

223

Reduction of damage threshold in dielectric materials induced by negatively chirped laser pulses  

SciTech Connect

The threshold fluence for laser induced damage in wide band gap dielectric materials, fused silica and MgF{sub 2}, is observed to be lower by up to 20% for negatively (down) chirped pulses than for positively (up) chirped, at pulse durations ranging from 60 fs to 1 ps. This behavior of the threshold fluence for damage on the chirp direction was not observed in semiconductors (silicon and GaAs). Based on a model including electron generation in the conduction band and Joule heating, it is suggested that the decrease in the damage threshold for negatively chirped pulse is related to the dominant role of multiphoton ionization in wide gap materials.

Louzon, E.; Henis, Z.; Pecker, S.; Ehrlich, Y.; Fisher, D.; Fraenkel, M.; Zigler, A. [Soreq NRC, Yavne 81800 (Israel); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)

2005-12-12

224

Detection of linear features using a localized radon transform with a wavelet filter  

SciTech Connect

One problem of interest to the oceanic engineering community is the detection and enhancement of internal wakes in open water synthetic aperture radar (SAR) images. Internal wakes, which occur when a ship travels in a stratified medium, have a V shape extending from the ship, and a chirp-like feature across each arm. The Radon transform has been applied to the detection and the enhancement problems in internal wake images to account for the linear features while the wavelet transform has been applied to the enhancement problem in internal wake images to account for the chirp-like features. In this paper, a new transform, a localized Radon transform with a wavelet filter (LRTWF), is developed which accounts for both the linear and the chirp-like features of the internal wake. This transform is then incorporated into optimal and sub-optimal detection schemes for images (with these features) which are contaminated by additive Gaussian noise.

Warrick, A L; Delaney, P A

1999-12-13

225

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

226

The Optoelectronic Swept-Frequency Laser and Its Applications in Ranging, Three-Dimensional Imaging, and Coherent Beam Combining of Chirped-Seed Amplifiers  

NASA Astrophysics Data System (ADS)

This thesis explores the design, construction, and applications of the optoelectronic swept-frequency laser (SFL). The optoelectronic SFL is a feedback loop designed around a swept-frequency (chirped) semiconductor laser (SCL) to control its instantaneous optical frequency, such that the chirp characteristics are determined solely by a reference electronic oscillator. The resultant system generates precisely controlled optical frequency sweeps. In particular, we focus on linear chirps because of their numerous applications. We demonstrate optoelectronic SFLs based on vertical-cavity surface-emitting lasers (VCSELs) and distributed-feedback lasers (DFBs) at wavelengths of 1550 nm and 1060 nm. We develop an iterative bias current predistortion procedure that enables SFL operation at very high chirp rates, up to 1016 Hz/sec. We describe commercialization efforts and implementation of the predistortion algorithm in a stand-alone embedded environment, undertaken as part of our collaboration with Telaris, Inc. We demonstrate frequency-modulated continuous-wave (FMCW) ranging and three-dimensional (3-D) imaging using a 1550 nm optoelectronic SFL. We develop the technique of multiple source FMCW (MS-FMCW) reflectometry, in which the frequency sweeps of multiple SFLs are "stitched" together in order to increase the optical bandwidth, and hence improve the axial resolution, of an FMCW ranging measurement. We demonstrate computer-aided stitching of DFB and VCSEL sweeps at 1550 nm. We also develop and demonstrate hardware stitching, which enables MS-FMCW ranging without additional signal processing. The culmination of this work is the hardware stitching of four VCSELs at 1550 nm for a total optical bandwidth of 2 THz, and a free-space axial resolution of 75 microns. We describe our work on the tomographic imaging camera (TomICam), a 3-D imaging system based on FMCW ranging that features non-mechanical acquisition of transverse pixels. Our approach uses a combination of electronically tuned optical sources and low-cost full-field detector arrays, completely eliminating the need for moving parts traditionally employed in 3-D imaging. We describe the basic TomICam principle, and demonstrate single-pixel TomICam ranging in a proof-of-concept experiment. We also discuss the application of compressive sensing (CS) to the TomICam platform, and perform a series of numerical simulations. These simulations show that tenfold compression is feasible in CS TomICam, which effectively improves the volume acquisition speed by a factor ten. We develop chirped-wave phase-locking techniques, and apply them to coherent beam combining (CBC) of chirped-seed amplifiers (CSAs) in a master oscillator power amplifier configuration. The precise chirp linearity of the optoelectronic SFL enables non-mechanical compensation of optical delays using acousto-optic frequency shifters, and its high chirp rate simultaneously increases the stimulated Brillouin scattering (SBS) threshold of the active fiber. We characterize a 1550 nm chirped-seed amplifier coherent-combining system. We use a chirp rate of 5*1014 Hz/sec to increase the amplifier SBS threshold threefold, when compared to a single-frequency seed. We demonstrate efficient phase-locking and electronic beam steering of two 3 W erbium-doped fiber amplifier channels, achieving temporal phase noise levels corresponding to interferometric fringe visibilities exceeding 98%.

Vasilyev, Arseny

227

Chirped Laser Dispersion Spectroscopy for Remote Open-Path Trace-Gas Sensing  

PubMed Central

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

2012-01-01

228

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

229

Experimental Demonstration of Energy Chirp Compensation by a Tunable Dielectric Based Structure  

E-print Network

A 60 MeV beam at the BNL Accelerator Test Facility (ATF) was manipulated by a planar tunable de-chirper made out of two 10 cm long dielectric slabs with copper plated backs. While the gap was changed from 5.8 mm to 1 mm, the correlated energy chirp of the low charge electron bunch was reduced from approximately 330 keV/mm to zero. This result is in agreement with simulations. Calculations show that similar devices, properly scaled to account for the expected electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers (FEL). Potentially, this technique could significantly simplify linac design and improve FEL performance.

Antipov, S; Jing, C; Fedurin, M; Kanareykin, A; Swinson, C; Schoessow, P; Gai, W; Zholents, A

2013-01-01

230

2-microm Doppler lidar transmitter with high frequency stability and low chirp.  

PubMed

A coherent Doppler lidar system was frequency stabilized in a master-slave configuration by a phase-modulation technique. The short-term frequency stability, ~0.2 MHz rms, was maintained in a vibrational environment on a ship during a field campaign in the tropical Pacific Ocean. The long-term frequency stability was <2.6 kHz/h. Thus, in many applications, shot-to-shot frequency correction can be disregarded, which will result in increased speed and simplicity of the data-acquisition system. A frequency chirp could not be detected. These properties permit Doppler wind measurements with high efficiency and duty cycles to be made, even on airborne and spaceborne platforms. PMID:18066175

Wulfmeyer, V; Randall, M; Brewer, A; Hardesty, R M

2000-09-01

231

Application of the windowed-Fourier-transform-based fringe analysis technique for investigating temperature and concentration fields in fluids.  

PubMed

The present work is concerned with the development and application of a novel fringe analysis technique based on the principles of the windowed-Fourier-transform (WFT) for the determination of temperature and concentration fields from interferometric images for a range of heat and mass transfer applications. Based on the extent of the noise level associated with the experimental data, the technique has been coupled with two different phase unwrapping methods: the Itoh algorithm and the quality guided phase unwrapping technique for phase extraction. In order to generate the experimental data, a range of experiments have been carried out which include cooling of a vertical flat plate in free convection conditions, combustion of mono-propellant flames, and growth of organic as well as inorganic crystals from their aqueous solutions. The flat plate and combustion experiments are modeled as heat transfer applications wherein the interest is to determine the whole-field temperature distribution. Aqueous-solution-based crystal growth experiments are performed to simulate the mass transfer phenomena and the interest is to determine the two-dimensional solute concentration field around the growing crystal. A Mach-Zehnder interferometer has been employed to record the path-integrated quantity of interest (temperature and/or concentration) in the form of interferometric images in the experiments. The potential of the WFT method has also been demonstrated on numerically simulated phase data for varying noise levels, and the accuracy in phase extraction have been quantified in terms of the root mean square errors. Three levels of noise, i.e., 0%, 10%, and 20% have been considered. Results of the present study show that the WFT technique allows an accurate extraction of phase values that can subsequently be converted into two-dimensional temperature and/or concentration distribution fields. Moreover, since WFT is a local processing technique, speckle patterns and the inherent noise in the interferometric data do not affect the resultant phase values. Brief comparisons of the accuracy of the WFT with other standard techniques such as conventional Fourier-filtering methods are also presented. PMID:24787402

Mohanan, Sharika; Srivastava, Atul

2014-04-10

232

Efficient broadband 400??nm noncollinear second-harmonic generation of chirped femtosecond laser pulses in BBO and LBO.  

PubMed

We report on 400 nm broadband type I frequency doubling in a noncollinear geometry with pulse-front-tilted and chirped femtosecond pulses (? =800??nm; Fourier transform limited pulse duration, 45 fs). With moderate power densities (2 to 10??GW/cm2) thus avoiding higher-order nonlinear phenomena, the energy conversion efficiency was up to 65%. Second-harmonic pulses of Fourier transform limited pulse duration shorter than the fundamental wave were generated, exhibiting good beam quality and no pulse-front tilt. High energy (20 mJ/pulse) was produced in a 40 mm diameter and 6 mm thick LBO crystal. To the best of our knowledge, this is the first demonstration of this optical configuration with sub-100-fs pulses. Good agreement between experimental results and simulations is obtained. PMID:24787591

Gobert, O; Mennerat, G; Maksimenka, R; Fedorov, N; Perdrix, M; Guillaumet, D; Ramond, C; Habib, J; Prigent, C; Vernhet, D; Oksenhendler, T; Comte, M

2014-04-20

233

Chirped fiber-optic Bragg grating interrogator in a multiplexed Bragg grating sensor configuration  

Microsoft Academic Search

This paper presents a chirped grating interrogator for fiber Bragg grating sensors. The interrogator uses the wavelength dependence of the phase group-delay response of a chirped fiber Bragg grating to determine the Bragg wavelength of the sensor. The sensitivity of the interrogator is determined by the selection of the grating length and the bandwidth. The experimental results demonstrated strain measurements

Anatoli A. Chtcherbakov; Pieter L. Swart

2004-01-01

234

Effects of Energy Chirp on Echo-Enabled Harmonic Generation Free-Electron Lasers  

SciTech Connect

We study effects of energy chirp on echo-enabled harmonic generation (EEHG). Analytical expressions are compared with numerical simulations for both harmonic and bunching factors. We also discuss the EEHG free-electron laser bandwidth increase due to an energy-modulated beam and its pulse length dependence on the electron energy chirp.

Huang, Z.; Ratner, D.; Stupakov, G.; Xiang, D.; /SLAC

2009-02-23

235

Analytical Expressions for Small-Signal and Saturation Processes of Optical Parametric Chirped-Pulse Amplification  

NASA Astrophysics Data System (ADS)

Analytical expressions corresponding to the small-signal and saturation processes of optical parametric chirped-pulse amplification are derived from the elliptic integration obtained by nonlinear-wave equations. The analytical expressions are simple and practical for the optimization of optical parametric chirped-pulse amplification even under the saturation process.

Harimoto, Tetsuo; Yamakawa, Koichi

2009-09-01

236

Design, fabrication, and analysis of chirped multilayer mirrors for reflection of extreme-ultraviolet attosecond pulses  

Microsoft Academic Search

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)

A. Wonisch; U. Neuhaeusler; N. M. Kabachnik; T. Uphues; M. Uiberacker; V. Yakovlev; F. Krausz; M. Drescher; U. Kleineberg; U. Heinzmann

2006-01-01

237

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

238

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

239

Helicopter-borne SAR Imaging Processing of Chirp-stepped Signal  

Microsoft Academic Search

In this paper, the processing algorithm of high resolution range profile of chirp-stepped signal is studied in the view of system, and the process of chirp-stepped signal SAR imaging on helicopter platform is analyzed. Furthermore, technology difficulties of helicopter-borne SAR imaging are showed, and imaging results are presented by experimental data

Hong Xiangru Zhang Tao; Du Zicheng

2006-01-01

240

JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 29, NO. 9, MAY 1, 2011 1239 Real-Time Interrogation of a Linearly Chirped  

E-print Network

of a Linearly Chirped Fiber Bragg Grating Sensor Based on Chirped Pulse Compression With Improved Resolution to interrogating in real time a lin- early chirped fiber Bragg grating (LCFBG) sensor based on spec- tral, fiber Bragg grating (FBG), wavelength-to-time mapping. I. INTRODUCTION F IBER BRAGG grating (FBG

Yao, Jianping

241

Spectral Characterizations of the Clouds and the Earth's Radiant Energy System (CERES) Thermistor Bolometers using Fourier Transform Spectrometer (FTS) Techniques  

NASA Technical Reports Server (NTRS)

Fourier Transform Spectrometer (FTS) techniques are being used to characterize the relative spectral response, or sensitivity, of scanning thermistor bolometers in the infrared (IR) region (2 - >= 100-micrometers). The bolometers are being used in the Clouds and the Earth's Radiant Energy System (CERES) program. The CERES measurements are designed to provide precise, long term monitoring of the Earth's atmospheric radiation energy budget. The CERES instrument houses three bolometric radiometers, a total wavelength (0.3- >= 150-micrometers) sensor, a shortwave (0.3-5-micrometers) sensor, and an atmospheric window (8-12-micrometers) sensor. Accurate spectral characterization is necessary for determining filtered radiances for longwave radiometric calibrations. The CERES bolometers spectral response's are measured in the TRW FTS Vacuum Chamber Facility (FTS - VCF), which uses a FTS as the source and a cavity pyroelectric trap detector as the reference. The CERES bolometers and the cavity detector are contained in a vacuum chamber, while the FTS source is housed in a GN2 purged chamber. Due to the thermal time constant of the CERES bolometers, the FTS must be operated in a step mode. Data are acquired in 6 IR spectral bands covering the entire longwave IR region. In this paper, the TRW spectral calibration facility design and data measurement techniques are described. Two approaches are presented which convert the total channel FTS data into the final CERES spectral characterizations, producing the same calibration coefficients (within 0.1 percent). The resulting spectral response curves are shown, along with error sources in the two procedures. Finally, the impact of each spectral response curve on CERES data validation will be examined through analysis of filtered radiance values from various typical scene types.

Thornhill, K. Lee; Bitting, Herbert; Lee, Robert B., III; Paden, Jack; Pandey, Dhirendra K.; Priestley, Kory J.; Thomas, Susan; Wilson, Robert S.

1998-01-01

242

Raman chirped adiabatic passage probed by X-ray spectroscopy.  

PubMed

We report a theoretical study of the selective vibrational excitation of a HCl molecule achieved by Raman chirped adiabatic passage (RCAP) and probed by X-ray photoelectron spectroscopy (XPS). It is demonstrated that HCl can be prepared in any vibrational level up to ? = 9 with nearly complete population inversion. We explore the effects of both the rotation of the molecule and of the temperature on the RCAP process, which is proved to be very robust. Furthermore, we emphasize that XPS spectra at the chlorine K-shell threshold show characteristic signatures of the populated vibrational level, allowing us to follow the RCAP process. PMID:23550700

Engin, Selma; Sisourat, Nicolas; Selles, Patricia; Taeb, Richard; Carniato, Stphane

2013-08-29

243

Fourier transform infrared spectroscopy as a suitable technique in the study of the materials used in waterproofing of archaeological amphorae.  

PubMed

The resinous materials from the interior surfaces of two Roman and one Iberian amphora were studied with Fourier transform infrared (FTIR) spectroscopy. The results were then compared with those obtained by synchrotron radiation-FTIR, scanning electron microscopy (SEM), and gas chromatography-mass spectrometry (GC-MS). The FTIR spectra obtained by the technique of KBr micropellets, prepared directly with the materials scraped from the amphora without any further sample preparation, provided enough information to establish their diterpenoic nature, and even to differentiate between the two main materials employed for waterproofing purposes, pitch and wood tar. Methyl dehydroabietic acid (DHAM) is the main chemical marker that allows a distinction to be made between these two materials. Pitch and wood tar were prepared in the laboratory heating pine resin and resinous pine wood, respectively. These resinous waterproofing materials were compared with the coatings extracted from the amphorae. The samples whose direct FTIR spectra showed a signal at approximately 1740 cm(-1), attributed to a carbonyl group of methyl ester, presented as well a peak of DHAM in the GC-MS chromatogram of the neutral fraction of their extract. Samples without this signal in their spectra did not present DHAM in their chromatogram. This work studies, for the first time, waterproofing of an amphora attributed to the Iberian culture. PMID:17693315

Font, J; Salvad, N; But, S; Enrich, J

2007-08-13

244

Oxidation of carbon monoxide at a platinum film electrode studied by Fourier transform infrared spectroscopy with attenuated total reflection technique  

SciTech Connect

Fourier transform infrared reflection absorption spectroscopy with the attenuated total reflection technique (ATR-FTIR), coupled with cyclic voltammetry (CV) measurement, is used to observe the oxidation process of adsorbed CO at Pt film sputtered on a silicon prism. The interesting bipolar shape of the linearly bonded CO band is observed at high coverage of CO, although no CO band is included in the reference spectrum. This asymmetric shape is ascribed to Fano resonance. In addition to a linear CO and bridged CO, a new absorption band presumably assigned to a carboxyl radical, was detected. This band may be formed by a heterogeneous reaction between adsorbed CO and H{sub 2}O on the Pt surface in the hydrogen adsorption potential region. The adsorbed carboxyl radical was oxidized at a less positive potential than the adsorbed CO, which can be ascribed to a presumable origin for the pre-peak that appeared in a CV reading prior to the oxidation of such a linear or bridged CO. This oxidation led to the rearrangement of CO ad-layers, especially at high coverage of CO. In the case of the low coverage of CO, the conversion from the bridged CO to the linear CO is ascribed to the potential induced electronic effects of the electrode surface on the adsorption states. A consumption of adsorbed H{sub 2}O and a production of CO{sub 2} were also clearly indicated by the spectroscopy when COOH of CO disappeared from the surface.

Zhu, Yimin; Uchida, Hiroyuki; Watanabe, Masahiro

1999-12-07

245

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

246

Effect of nonlinear chirped Gaussian laser pulse on plasma wake field generation  

NASA Astrophysics Data System (ADS)

An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wake field which can accelerate charged particles up to GeV energies within a compact space compared to the conventional accelerator devices. In this paper, the effect of different kinds of nonlinear chirped Gaussian laser pulse on wake field generation is investigated. The numerical analysis of our results depicts that the excitation of plasma wave with large and highly amplitude can be accomplished by nonlinear chirped pulses. The maximum amplitude of excited wake in nonlinear chirped pulse is approximately three times more than that of linear chirped pulse. In order to achieve high wake field generation, chirp parameters and functions should be set to optimal values.

Afhami, Saeedeh; Eslami, Esmaeil

2014-08-01

247

Use of time history speckle pattern and pulsed photoacoustic techniques to detect the self-accommodating transformation in a Cu-Al-Ni shape memory alloy  

SciTech Connect

Continuous and pulsed electromagnetic radiation was used to detect the self-accommodation mechanism on a polycrystalline Cu-13.83 wt.%Al-2.34 wt.%Ni shape memory alloy. Rectangular samples of this alloy were mechanically polished to observe the austenite and martensite phases. The samples were cooled in liquid nitrogen prior to the experiments to obtain the martensite phase. Using a dynamic speckle technique with a continuous wave laser we obtained the time history of the speckle pattern image and monitored the surface changes caused by the self-accommodation mechanism during the inverse (martensitic to austenitic) transformation. Using a photoacoustic technique based on a pulsed laser source it was also possible to detect the self-accommodation phenomena in a bulk sample. For comparison purposes, we used differential scanning calorimetry (DSC) to detect the critical temperatures of transformation and use these as reference to evaluate the performance of the optical and photoacoustical techniques. In all cases, the same range of temperature was obtained during the inverse transformation. From these results, we conclude that time history speckle pattern (THSP) and pulsed photoacoustic are complementary techniques; they are non-destructive and useful to detect surface and bulk martensitic transformation induced by a temperature change.

Sanchez-Arevalo, F.M., E-mail: fsanchez@iim.unam.mx [CCADET - Universidad Nacional Autonoma de Mexico, A.P. 70-186, Mexico D.F., C.P. 04510 (Mexico); Aldama-Reyna, W. [Departamento Academico de Fisica, Universidad Nacional de Trujillo, Trujillo (Peru); Lara-Rodriguez, A.G. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (Mexico); Garcia-Fernandez, T. [Universidad Autonoma de la Ciudad de Mexico (UACM), Prolongacion San Isidro 151, Col. San Lorenzo Tezonco, Mexico DF, C.P. 09790 (Mexico); Pulos, G. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (Mexico); Trivi, M. [Centro de Investigaciones Opticas, Universidad de la Plata (Argentina); Villagran-Muniz, M. [CCADET - Universidad Nacional Autonoma de Mexico, A.P. 70-186, Mexico D.F., C.P. 04510 (Mexico)

2010-05-15

248

Prediction technique for transformer oil breakdown voltage via multi-parameter correlation based on grey theory and BP neural network  

Microsoft Academic Search

Prediction of breakdown voltage of transformer oil has a great significance to the fault diagnosis and daily maintenance of transformer. Based on the correlation of performance parameters of transformer oil and the prominent fault-tolerance, non-linear approximation, and self-learning capabilities of BP neural network, this paper constructed a prediction method of breakdown voltage via multi-parameter correlation under the development environment of

Zhi Li; Jia-yuan Hu; Shun-an Cao; Jian-li Xie

2010-01-01

249

Fourier transform white-light interferometry based on nonlinear wavelength sampling  

NASA Astrophysics Data System (ADS)

Fourier transform white-light interferometry possesses high resolution and wide dynamic range for the absolute measurement of fiber optic interferometric sensors. However, the white-light optical spectrum distributed along wavelength is a chirp signal because the phase of the optical spectrum has a nonlinear relationship with the scanning wavelength. The chirped spectrum is considered as a constant period signal when it is Fourier transformed. The chirp in the period would bring errors into the phase shift and reduce the measurement resolution. A nonlinear wavelength sampling algorithm is proposed in this paper. The chirp characteristics of the white-light optical spectrum are considered, and the nonlinear wavelength sampling intervals vary with the wavelength. By using the nonlinear wavelength sampling algorithm, the errors in the phase shift can be reduced effectively, whereas the chirp characteristics of the signals can be retained entirely for filtering and extracting the chirped optical spectrum signals from the composite signal. The experimental results show that the standard deviation decreases from 0.016 to 0.005 ?m by using the nonlinear wavelength sampling, when a fiber optic extrinsic Fabry-Perot interferometric sensor with a cavity length of 1512.2 ?m is interrogated.

Wang, Zhen; Jiang, Yi; Ding, Wenhui; Gao, Ran

2013-10-01

250

Chirped CPMG for well-logging NMR applications.  

PubMed

In NMR well-logging, the measurement apparatus typically consists of a permanent magnet which is inserted into a bore, and the sample is the rock surrounding the borehole. When compared to the conditions of standard NMR experiments, this application is thus challenged by relatively weak and invariably inhomogeneous B0 and B1 fields. Chemical shift information is not generally obtained in these measurements. Instead, diffusivity, porosity and permeability information is collected from multi-echo decay measurements - most often using a Carr-Purcell Meiboom-Gill (CPMG) pulse sequence to enhance the experiment's limited sensitivity. In this work, we explore the consequences of replacing the hard square pulses used in a typical CPMG sequence with chirped pulses sweeping a range of frequencies. The greater bandwidths that for a maximum B1 level can be excited by chirped pulses translates into marked expansion of the detection volume, and thus significant signal-to-noise improvements when compared to standard CPMG acquisitions using hard pulses. This improvement, usually amounting to signal enhancements ?3, can be used to reduce the experimental time of NMR well-logging measurements, for measuring T2 even when B0 and B1 inhomogenieties complicate the measurements, and opening new opportunities in the determination of diffusional properties. PMID:24674888

Casabianca, Leah B; Mohr, Daniel; Mandal, Soumyajit; Song, Yi-Qiao; Frydman, Lucio

2014-05-01

251

1340 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 23, NO. 18, SEPTEMBER 15, 2011 Real-Time Interrogation of a Linearly Chirped Fiber  

E-print Network

of a Linearly Chirped Fiber Bragg Grating Sensor for Simultaneous Measurement of Strain and Temperature Weilin. Index Terms--Chirped fiber Bragg grating (CFBG), chirped mi- crowave pulse, interrogation, sensor-birefringence linearly chirped fiber Bragg grating (Hi-Bi LCFBG) for simultaneous measure- ment of strain and temperature

Yao, Jianping

252

Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques  

Microsoft Academic Search

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

F. Lemery; D. Mihalcea; C. R. Prokop; P. Piot

2012-01-01

253

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

254

Hadamard transform image coding  

Microsoft Academic Search

The introduction of the fast Fourier transform algorithm has led to the development of the Fourier transform image coding technique whereby the two-dimensional Fourier transform of an image is transmitted over a channel rather than the image itself. This devlopement has further led to a related image coding technique in which an image is transformed by a Hadamard matrix operator.

W. K. Pratt; J. Kane; H. C. Andrews

1969-01-01

255

Control of optical properties of hybrid materials with chirped femtosecond laser pulses under strong coupling conditions.  

PubMed

The interaction of chirped femtosecond laser pulses with hybrid materials--materials comprised of plasmon sustaining structures and resonant molecules--is scrutinized using a self-consistent model of coupled Maxwell-Bloch equations. The optical properties of such systems are examined with the example of periodic sinusoidal gratings. It is shown that under strong coupling conditions one can control light transmission using chirped pulses in a spatiotemporal manner. The temporal origin of control relies on chirps non-symmetric in time while the space control is achieved via spatial localization of electromagnetic energy due to plasmon resonances. PMID:25173035

Sukharev, Maxim

2014-08-28

256

Tunable optoelectronic oscillator based on a chirped Mach-Zehnder modulator  

NASA Astrophysics Data System (ADS)

Realization of a wideband tunable optoelectronic oscillator based on a chirped Mach-Zehnder modulator (MZM) and a chirped fiber Bragg grating is proposed and demonstrated. By simply adjusting the direct-current bias of the chirped MZM, the frequency of the oscillating signal is tuned. A theoretical model is established, then verified by an experiment. A high-purity microwave signal with a tunable frequency from 5.8 to 11.8 GHz is generated. The single-sideband phase noise of the generated signal is -112.6 dBc/Hz at a frequency offset of 10 kHz.

Wei, Zhihu; Pan, Shilong; Wang, Rong; Pu, Tao; Fang, Tao; Sun, Guodan; Zheng, Jilin

2013-05-01

257

A high performance control technique of power electronic transformers in medium voltage grid-connected PV plants  

Microsoft Academic Search

With reference to medium-voltage grid-connection of large photovoltaic (PV) plants, the paper proposes and analyses a high performance solution based on a power electronic transformer (PET). It Includes dc-links and multilevel converters either in low-voltage or in high-voltage side, and a medium-frequency (MF) transformer. Together with the very reduced sizes of the whole conversion apparatus, an important feature of the

G. Brando; A. Dannier; A. Del Pizzo; R. Rizzo

2010-01-01

258

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

259

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

260

Femtosecond Chirp-Free Transient Absorption Method And Apparatus  

DOEpatents

A method and apparatus for femtosecond transient absorption comprising phase-sensitive detection, spectral scanning and simultaneous controlling of a translation stage to obtain TA spectra information having at least a sensitivity two orders of magnitude higher than that for single-shot methods, with direct, simultaneous compensation for chirp as the data is acquired. The present invention includes a amplified delay translation stage which generates a splittable frequency-doubled laser signal at a predetermined frequency f, a controllable means for synchronously modulating one of the laser signals at a repetition rate of f/2, applying the laser signals to a material to be sample, and acquiring data from the excited sample while simultaneously controlling the controllable means for synchronously modulating.

McBranch, Duncan W. (Santa Fe, NM); Klimov, Victor I. (White Rock, NM)

2001-02-20

261

Large-scale symmetry-adapted perturbation theory computations via density fitting and Laplace transformation techniques: Investigating the fundamental forces of DNA-intercalator interactions  

Microsoft Academic Search

Symmetry-adapted perturbation theory (SAPT) provides a means of probing the fundamental nature of intermolecular interactions. Low-orders of SAPT (here, SAPT0) are especially attractive since they provide qualitative (sometimes quantitative) results while remaining tractable for large systems. The application of density fitting and Laplace transformation techniques to SAPT0 can significantly reduce the expense associated with these computations and make even larger

Edward G. Hohenstein; Robert M. Parrish; C. David Sherrill; Justin M. Turney; Henry F. Schaefer

2011-01-01

262

Effect of linear chirp on femtosecond two-photon processes in solution  

PubMed Central

Coherent control via linear chirping a femtosecond laser pulse holds the promise of a potent spectroscopic tool in the study of two-photon processes in condensed phase. Here, we show modulation in the two-photon absorption and fluorescence of several common dyes in solution by simple phase ordering of femtosecond laser pulse into a linearly frequency chirped pulse. However, the modulation is dependent on associated solvent properties as the coherence is lost rapidly in the solution phase. Also, systematic effects are mostly seen only over a limited range of chirp since it is an interplay of two opposing effects on two-photon processeslinear chirp enhancing it while the associated pulse broadening reducing it. PMID:24364002

Nag, Amit; Goswami, Debabrata

2013-01-01

263

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

264

Design of a 3D Chirp Sub-bottom Imaging System  

Microsoft Academic Search

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1-24 kHz) to produce decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and

Jonathan M. Bull; Martin Gutowski; Justin K. Dix; Timothy J. Henstock; Peter Hogarth; Timothy G. Leighton; Paul R. White

2005-01-01

265

3D CHIRP SUB-BOTTOM IMAGING SYSTEM: DESIGN AND FIRST 3D VOLUME  

Microsoft Academic Search

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1 - 24 kHz) to produce decimetre vertical resolution cross- sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning

Jonathan M. Bull; Martin Gutowski; Justin K. Dix; Timothy J. Henstock; Peter Hogarth; Timothy G. Leighton; Paul R. White

266

Generation and direct measurement of giant chirp in a passively mode-locked laser.  

PubMed

We evaluate the shape and chirp of nanosecond pulses from a fiber laser passively mode locked with a nanotube-based saturable absorber by using a synchronously scanning streak camera and a monochromator to directly measure the pulse spectrogram. We show that the stable sech(2) output pulse possesses a predominantly linear chirp, with a residual quartic phase and low noise. Comparison with analytical mode-locking theory shows a good quantitative agreement with the master equation mode-locking model. PMID:19927199

Kelleher, E J R; Travers, J C; Ippen, E P; Sun, Z; Ferrari, A C; Popov, S V; Taylor, J R

2009-11-15

267

Comparison of binaural auditory brainstem responses and the binaural dierence potential evoked by chirps and clicks  

E-print Network

auditory brainstem responses were recorded for clicks and chirps for levels from 10 to 60 dB nHL in steps and 40 dB nHL. Both the binaurally evoked potential and the binaural difference potential exhibit steeper growth functions for chirps than for clicks for levels up to 40 dB nHL. For higher stimulation levels

Oldenburg, Carl von Ossietzky, Universität

268

A New Approach of Extended Chirp Scaling Algorithm for High Squint Missile-Borne SAR Data Processing  

Microsoft Academic Search

In the traditional extended chirp scaling (ECS) algorithm, after RCMC in the range signal\\/Doppler domain, targets in the same range gate will have different FM rates for difference of the slant ranges. In the paper, a novel approach for high squint missile-borne SAR data processing using a modified extended chirp scaling algorithm is proposed. A non-linear chirp perturbation function (CPF)

Qiang Zhou; Changwen Qu; Feng Su; Ying Wang

2008-01-01

269

Structures of the Lowest Energy Nonamer and Decamer Water Clusters from Chirped-Pulse Rotational Spectroscopy  

NASA Astrophysics Data System (ADS)

In the breakthrough paper reporting observation and analysis of pure rotational spectra of the hexamer, heptamer and nonamer water clusters only one nonamer species was identified. The advances in this experiment, as described in the previous talk, allowed identification, among others, of five different nonamer, (H_2O)_9, conformers and of four different decamer, (H_2O)_{10}, conformers. Analysis of ^{18}O enriched spectra resulted in determination of oxygen framework geometries for three of the water nonamers and two of the water decamers. Determination of experimental geometries proved considerably more challenging than for the lighter clusters since isotopic changes to moments of inertia are proportionally smaller, and there are multiple instances of near-zero principal coordinates. There are also more indications of the effect of internal motions. These problems have been overcome by careful application of r_s and least-squares r_m techniques in concert with ab initio calculations so that it was possible to match the experimental and theoretical geometries unambiguously. The precise oxygen framework geometries obtained from chirped-pulse spectroscopy for water clusters ranging in size from the hexamer to the decamer allow, for the first time, to identify some common features of the underlying hydrogen bonding from direct experimental evidence. C. Perez, M. T. Muckle, D. P. Zaleski, N. A. Seifert, B. Temelso, G. C. Shields, Z. Kisiel, and B. H. Pate, Science {336}, 897 (2012).

Perez, Cristobal; Pate, Brooks H.; Kisiel, Zbigniew; Temelso, Berhane; Shields, George C.

2013-06-01

270

Application of the constant exposure time technique to transformation experiments with fission neutrons; failure to demonstrate dose-rate dependence  

Microsoft Academic Search

A direct comparison of the effectiveness of fission neutron at high or several low dose-rates was carried out under identical conditions. Monolayers of exponentially growing C3H\\/10T1\\/2 cells were exposed at 37 deg C to reactor-produced neutrons. Survival or transformation induction were studied at five doses from 10(exp 5) to 94 cGy. In low dose-rate irradiations, these doses were protracted over

E. K. Balcer-Kubiczek; G. H. Harrison; W. A. McCready

1994-01-01

271

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

2012-03-22

272

Comparison of chirp versus click and tone pip stimulation for cervical vestibular evoked myogenic potentials.  

PubMed

The current study explored differences among cervical vestibular evoked myogenic potentials (cVEMP) that were evoked by CE-chirp and click and tone pip in healthy controls, and tried to explain the differences of cVEMP between the three of them. Thirty normal volunteers were used as subjects for CE-chirp and click and tone-pip (Blackman pip) stimuli. The latency of P1, N1, peak-to-peak P1-N1 amplitude, and cVEMP interaural difference were obtained and analyzed. The response rates of cVEMP were 93% for click and 100% for both Blackman pip and CE-chirp, respectively. The P1 and N1 latencies of cVEMP evoked by CE-chirp were the shortest, followed by click, with Blackman pip the longest (F=6,686.852, P<0.001). All indices of cVEMP evoked by the three stimuli showed no significant difference between the left and right earsor between genders. cVEMP responses were significantly different between the three stimuli. Compared with the currently used stimulus, CE-chirp can evoke cVEMP with shorter latencies and demonstrates increased speed and reliability. PMID:24178551

Wang, Bo-Chen; Liang, Yong; Liu, Xiao-Long; Zhao, Jing; Liu, You-Li; Li, Yan-Fei; Zhang, Wei; Li, Qi

2014-12-01

273

Stimulated Brillouin scattering suppression with a chirped laser seed: comparison of dynamical model to experimental data  

NASA Astrophysics Data System (ADS)

When scaling CW single-mode fiber amplifiers to high power, the first nonlinear limitation that appears for narrowlinewidth seed lasers is stimulated Brillouin scattering (SBS). We present a dynamical simulation of Brillouin scattering in a Yb-doped fiber amplifier that numerically solves the differential equations in z and t describing the laser, Stokes and pump waves, the inversion, and the density fluctuations that seed the scattering process. We compare the model to experimental data, and show that a linearly chirped seed laser is an efficient form of SBS suppression; especially for long delivery fibers. The frequency chirp decreases the interaction length by chirping through the Brillouin resonance in a time that is short compared to the fiber transit time. The seed has a highly linear chirp of 1014 - 1016 Hz/s at 1064 nm which preserves a well-defined phase relationship in time. This method of SBS suppression retains a long effective coherence length for purposes of coherent combining, while at high chirps appears to the SBS as a large linewidth, increasing the threshold. An increase in fiber length increases the laser bandwidth as seen by the SBS, leading to a fiberlength- independent SBS threshold.

Petersen, Eliot; Yang, Zhi; White, Jeffrey O.; Rakuljic, George; Satyan, Naresh; Vasilyev, Arseny; Yariv, Amnon

2014-03-01

274

Landscapes of transformation  

E-print Network

This thesis aims to examine the cultural effect of transformation through the lens of procedural techniques applied to the human body and architecture. The body and architecture both operate as landscapes of transformation. ...

Ambs, Emily (Emily Kiersten)

2007-01-01

275

Phase retrieval with unknown sampling factors via the two-dimensional chirp z-transform  

E-print Network

error metric with respect to the sampling factor or the f -number that produced the measured point of the phase estimate. Computer simulation results show its effectiveness. � 2014 Optical Society of America of an optical system. In a laboratory environment this may be done using interferometry or wavefront sensing

Fienup, James R.

276

A Fractional Fourier Transform Analysis of a Bubble Excited by an Ultrasonic Chirp  

E-print Network

. If the pressure amplitude of the signal is relatively low the oscillations will be stable and lin- ear, a mathematical model which describes the dynamics of a bubble subjected to an external acoustic pressure. Oscillations of this type are denoted as stable cavitation. As the pressure increases the oscillations become

Mottram, Nigel

277

Fourier transform-infrared spectroscopy and Gas chromatography-mass spectroscopy: reliable techniques for analysis of Parthenium mediated vermicompost.  

PubMed

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. PMID:23998948

Rajiv, P; Rajeshwari, Sivaraj; Venckatesh, Rajendran

2013-12-01

278

Chirped-pulse millimeter-wave spectroscopy: Spectrum, dynamics, and manipulation of Rydberg-Rydberg transitions  

SciTech Connect

We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg-Rydberg transitions is that they have enormous electric dipole transition moments ({approx}5 kiloDebye at n*{approx} 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70-84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is {approx}100 kHz. Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed.

Colombo, Anthony P.; Zhou Yan; Prozument, Kirill; Coy, Stephen L.; Field, Robert W. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2013-01-07

279

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

280

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...

281

Evaluation of chirp reversal power modulation sequence for contrast agent imaging  

NASA Astrophysics Data System (ADS)

Over the last decade, significant research effort has been focused on the use of chirp for contrast agent imaging because chirps are known to significantly increase imaging contrast-to-noise ratio (CNR). New imaging schemes, such as chirp reversal (CR), have been developed to improve contrast detection by increasing non-linear microbubble responses. In this study we evaluated the contrast enhancement efficiency of various chirped imaging sequences in combination with well-established imaging schemes such as power modulation (PM) and pulse inversion (PI). The imaging schemes tested were implemented on a fully programmable open scanner and evaluated by ultrasonically scanning (excitation frequency of 2.5?MHz amplitude of 350?kPa) a tissue-mimicking flow phantom comprising a 4?mm diameter tube through which aqueous dispersions (dilution fraction of 1/2000) of the commercial ultrasound contrast agent, SonoVue were continuously circulated. The recovery of non-linear microbubble responses after chirp compression requires the development and the optimization of a specific filter. A compression filter was therefore designed and used to compress and extract several non-linear components from the received microbubble responses. The results showed that using chirps increased the image CNR by approximately 10?dB, as compared to conventional Gaussian apodized sine burst excitation but degraded the axial resolution by a factor of 1.4, at -3?dB. We demonstrated that the highest CNR and contrast-to-noise ratio (CTR) were achievable when CR was combined with PM as compared to other imaging schemes such as PI.

Novell, A.; Sennoga, CA; Escoffre, JM; Chaline, J.; Bouakaz, A.

2014-09-01

282

HfO2/SiO2 chirped mirrors manufactured by electron beam evaporation.  

PubMed

A HfO2/SiO2 chirped mirror was manufactured by electron beam evaporation to increase the laser resistance. The hybrid monitoring strategy utilizing both monochromatic monitoring and quartz crystal monitoring was applied to the deposition compared to the single optical monitoring method. The coatings were characterized by transmission spectrophotometer and white light interferometry, and the experimental results showed that the chirped mirror monitored with the hybrid strategy possessed high reflectivity (>99.7%) and tolerable group delay dispersion oscillation (-5020?fs2) in the spectra range of 740-860?nm. PMID:21460969

Jinlong, Zhang; Xinbin, Cheng; Zhanshan, Wang; Hongfei, Jiao; Tao, Ding

2011-03-20

283

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.; Mcke, O. D.; Lu, P.; Midorikawa, K.

284

Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water  

NASA Astrophysics Data System (ADS)

We analyze numerically and experimentally the effect of the input pulse chirp on the nonlinear energy deposition from $5\\ \\mu$J fs-pulses at $800$ nm to water. Numerical results are also shown for pulses at $400$ nm, where linear losses are minimized, and for different focusing geometries. Input chirp is found to have a big impact on the deposited energy and on the plasma distribution around focus, thus providing a simple and effective mechanism to tune the electron density and energy deposition. We identify three relevant ways in which plasma features may be tuned.

Milin, Carles; Jarnac, Amlie; Brelet, Yohann; Jukna, Vytautas; Houard, Aurlien; Mysyrowicz, Andr; Couairon, Arnaud

2014-11-01

285

Quasi-phase-matching high-harmonic radiation using chirped THz pulses  

E-print Network

High-order harmonic generation in the presence of a chirped THz pulse is investigated numerically with a complete 3D non-adiabatic model. The assisting THz pulse illuminates the HHG gas cell laterally inducing quasi-phase-matching. We demonstrate that it is possible to compensate the phase mismatch during propagation and extend the macroscopic cutoff of a propagated strong IR pulse to the single-dipole cutoff. We obtain two orders of magnitude increase in the harmonic efficiency of cutoff harmonics ($\\approx$170 eV) using a THz pulse of constant wavelength, and a further factor of 3 enhancement when a chirped THz pulse is used.

Kovcs, Katalin; Hebling, Jnos; Tosa, Valer; Varj, Katalin

2014-01-01

286

Design of a 3D Chirp Sub-bottom Imaging System  

Microsoft Academic Search

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (124kHz) to produce\\u000a decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp\\u000a system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and\\u000a precise positioning of sources and receivers.

Jonathan M. Bull; Martin Gutowski; Justin K. Dix; Timothy J. Henstock; Peter Hogarth; Timothy G. Leighton; Paul R. White

2005-01-01

287

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

2013-04-01

288

Chirped pulse formation dynamics in ultra-long mode-locked fiber lasers.  

PubMed

By modeling giant chirped pulse formation in ultra-long, normally dispersive, mode-locked fiber lasers, we verify convergence to a steady-state consisting of highly chirped and coherent, nanosecond-scale pulses, which is in good agreement with recent experimental results. Numerical investigation of the transient dynamics reveals the existence of dark soliton-like structures within the envelope of the initial noisy pulse structure. Quasi-stationary dark solitons can persist throughout a large part of the evolution from noise to a stable dissipative soliton solution of the mode-locked laser cavity. PMID:24690797

Kelleher, E J R; Travers, J C

2014-03-15

289

Two-photon ladder climbing and transition to autoresonance in a chirped oscillator  

NASA Astrophysics Data System (ADS)

The two-photon ladder climbing (successive two-photon Landau-Zener-type transitions) in a chirped quantum nonlinear oscillator and its classical limit (subharmonic autoresonance) are discussed. An isomorphism between the chirped one- and two-photon resonances in the system is used in calculating the threshold for the phase-locking transition in both the classical and quantum limits. The theory is tested by solving the Schrdinger equation in the energy basis and illustrated via the Wigner function in phase space.

Barth, I.; Friedland, L.

2013-05-01

290

Modelling chirp as a function of reflectivity in electroabsorption modulated lasers (EML)  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of the chirp caused by the reflection of light from the Electro-Absorption Modulator (EAM) facet back into the laser. The work is modelled on our Essex Distributed Time Domain Model (eDTDM) (S. P. Higgins and A. J. Vickers, Proc SPIE Phys. and Simulations of Opto-Electron. Devices X11, 5349, 435 (2004) [1]; A. J. Vickers and S. P. Higgins, A new model for complex dynamic laser modelling, IEEE J Quantum Electron., 2005, awaiting publication [2]). A novel method of determining the chirp within the simulation is presented.

Higgins, S. P.; Vickers, A. J.

2006-03-01

291

Dynamics of surface solitons at the edge of chirped optical lattices  

NASA Astrophysics Data System (ADS)

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.; Vysloukh, Victor A.; Torner, Lluis

2007-07-01

292

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

293

2.4-Joule chirped pulse operation by a laser-diode-pumped slab laser for pumping non-collinear OPCPA  

NASA Astrophysics Data System (ADS)

We present a diode-pumped chirped pulse amplification (CPA) system that generates multi-joule energy at a central wavelength of 1054 nm at a repetition rate of 10 Hz. The purpose of this laser is to serve as a pump source for non-collinear optical parametric chirped pulse amplification (NOPCPA). A Nd-doped glass slab with zigzag optical path was used as the gain medium of the main amplifier in this system to obtain multi-joule output with repeatable operation. The Nd:glass zigzag slab amplifier system consists of four-pass pre-amplification and four-pass power amplification. The seed pulse that is fed to the main amplifier was generated by a mode-locked fiber oscillator emitting at a 1053 nm central wavelength. The oscillator output was pulse-stretched to 2.7 ns duration with a 4.5 nm spectral bandwidth and amplified to 100 ?J by optical parametric amplification by use of type-I BBO crystals. After the main amplification, 2.4 J of energy in 3.7 nm of spectral bandwidth at 1 Hz repetition rate was obtained. This spectral bandwidth corresponds to a transform-limited pulse duration of 440 fs. This result indicates that our CPA laser is capable of delivering multi-joule pump light after pulse compression and frequency doubling for 30-TW NOPCPA system.

Kurita, T.; Sueda, K.; Sekine, T.; Kawashima, T.; Miyanaga, N.

2010-08-01

294

Time-to-frequency Fourier transformation with photon echoes.  

PubMed

We propose to use photon echoes in rare-earth-doped crystals to implement the Fourier-transform chirp algorithm. The process is considered for application to spectral analysis of fast radio-frequency signals. Compared with surface acoustic wave devices, the proposed scheme gives access to the larger bandwidths of rare-earth-doped crystals and greater flexibility. An experimental demonstration of the proposed process is reported. PMID:18049617

Mnager, L; Le Gout, J L; Lorger, I

2001-09-15

295

Transformational Learners: Transformational Teachers  

ERIC Educational Resources Information Center

Transformational learning, according to Mezirow (1981), involves transforming taken-for-granted frames of reference into more discriminating, flexible "habits of mind". In teacher education, transformative learning impacts on the development of students' action theories, self-efficacy and professional attributes. Although considered imperative to

Jones, Marguerite

2009-01-01

296

The Transformations of Transformations.  

ERIC Educational Resources Information Center

Harris's original idea of transformations has been changed several times in Chomsky's work. This article explicates these transformations, arguing that though their motivations are highly understandable, these transformations are not necessary for understanding the workings of natural languages. (Author/VWL)

Lin, Francis Y.

2000-01-01

297

Discrete Fourier Transform as applicable technique in electrochemical detection of hydrazine using multi-walled carbon nanotube/polyacrylonitrile ceramic fiber as working electrode.  

PubMed

Effect of "Discrete Fourier Transform" (DFT) is studied for electrochemical detection of some electroactive species using multi-walled carbon nanotube/polyacrylonitrile ceramic fiber as ultra micro electrode. Based on DFT theory, two independent phases i.e. the imaginary and real phases are evaluated during the oxidation/reduction of the quasi-reversible or irreversible electroactive species, revealing the independent components of imaginary (IImaginary) and real (IReal) currents. The results show that, in different electrochemical modes such as cyclic voltammetry (CV), the contribution of DFT to the electrochemical signals significantly improves the detection limit of the electrochemical technique. More sensitive signals are obtained at high scan rates according to the combination of electrochemical techniques with the DFT theory. The reliability of DFT algorithm was evaluated for rapid determination of trace amount of hydrazine (N2H4) at a scan rate up to 800 V s(-1). In this study, the amounts of phase and amplitude were estimated to 1.69 and 31.57, respectively. The detection limit of hydrazine was 4.1310(-9) M. The application of this technique was also evaluated for determination of hydrazine in different industrial wastewater samples. PMID:23498220

Doroodmand, Mohammad Mahdi

2013-05-01

298

Large-scale symmetry-adapted perturbation theory computations via density fitting and Laplace transformation techniques: Investigating the fundamental forces of DNA-intercalator interactions  

NASA Astrophysics Data System (ADS)

Symmetry-adapted perturbation theory (SAPT) provides a means of probing the fundamental nature of intermolecular interactions. Low-orders of SAPT (here, SAPT0) are especially attractive since they provide qualitative (sometimes quantitative) results while remaining tractable for large systems. The application of density fitting and Laplace transformation techniques to SAPT0 can significantly reduce the expense associated with these computations and make even larger systems accessible. We present new factorizations of the SAPT0 equations with density-fitted two-electron integrals and the first application of Laplace transformations of energy denominators to SAPT. The improved scalability of the DF-SAPT0 implementation allows it to be applied to systems with more than 200 atoms and 2800 basis functions. The Laplace-transformed energy denominators are compared to analogous partial Cholesky decompositions of the energy denominator tensor. Application of our new DF-SAPT0 program to the intercalation of DNA by proflavine has allowed us to determine the nature of the proflavine-DNA interaction. Overall, the proflavine-DNA interaction contains important contributions from both electrostatics and dispersion. The energetics of the intercalator interaction are are dominated by the stacking interactions (two-thirds of the total), but contain important contributions from the intercalator-backbone interactions. It is hypothesized that the geometry of the complex will be determined by the interactions of the intercalator with the backbone, because by shifting toward one side of the backbone, the intercalator can form two long hydrogen-bonding type interactions. The long-range interactions between the intercalator and the next-nearest base pairs appear to be negligible, justifying the use of truncated DNA models in computational studies of intercalation interaction energies.

Hohenstein, Edward G.; Parrish, Robert M.; Sherrill, C. David; Turney, Justin M.; Schaefer, Henry F.

2011-11-01

299

Order-disorder phase transformations in quaternary pyrochlore oxide system: Investigated by X-ray diffraction, transmission electron microscopy and Raman spectroscopic techniques  

NASA Astrophysics Data System (ADS)

Order-disorder transformations in a quaternary pyrochlore oxide system, Ca-Y-Zr-Ta-O, were studied by powder X-ray diffraction (XRD) method, transmission electron microscope (TEM) and FT-NIR Raman spectroscopic techniques. The solid solutions in different ratios, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, of CaTaO 3.5 and YZrO 3.5 were prepared by the conventional high temperature ceramic route. The XRD results and Rietveld analysis revealed that the crystal structure changed from an ordered pyrochlore structure to a disordered defect fluorite structure as the ratios of the solid solutions of CaTaO 3.5 and YZrO 3.5 were changed from 4:1 to 1:4. This structural transformation in the present system is attributed to the lowering of the average cation radius ratio, rA/ rB as a result of progressive and simultaneous substitution of larger cation Ca 2+ for Y 3+ at A sites and smaller cation Ta 5+ for Zr 4+ at B sites. Raman spectroscopy and TEM analysis corroborated the XRD results.

Radhakrishnan, A. N.; Prabhakar Rao, P.; Sibi, K. S.; Deepa, M.; Koshy, Peter

2009-08-01

300

Characterization of ancient glass excavated in Enez (Ancient Ainos) Turkey by combined Instrumental Neutron Activation Analysis and Fourier Transform Infrared spectrometry techniques  

NASA Astrophysics Data System (ADS)

Ancient glass fragments excavated in the archaeological district Enez (Ancient Ainos)-Turkey were investigated by combined Instrumental Neutron Activation Analysis (INAA) and Fourier Transform Infrared (FTIR) spectrometry techniques. Multi-elemental contents of 15 glass fragments that belong to Hellenistic, Roman, Byzantine, and Ottoman Periods, were determined by INAA. The concentrations of twenty six elements (Na, K, Ca, Sc, Cr, Mn, Fe, Co, Cu, Zn, As, Rb, Sr, Sb, Cs, Ba, Ce, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Au and Th), which might be present in the samples as flux, stabilizers, colorants or opacifiers, and impurities, were examined. Chemometric treatment of the INAA data was performed and principle component analysis revealed presence of 3 distinct groups. The thermal history of the glass samples was determined by FTIR spectrometry.

Akyuz, Sevim; Akyuz, Tanil; Mukhamedshina, Nuranya M.; Mirsagatova, A. Adiba; Basaran, Sait; Cakan, Banu

2012-05-01

301

Chirped-pulse Raman amplification for two-color high-intensity laser experiments  

NASA Astrophysics Data System (ADS)

We report generation and compression of millijoule-level first Stokes sideband (873nm) of 800nm TW pulses by inserting a multi-stage barium nitrate Raman shifter-amplifier into a conventional Ti:sapphire chirped pulse amplification system.

Dong, Peng; Grigsby, Franklin; Downer, Mike

302

Wideband and low dispersion slow light by chirped photonic crystal coupled waveguide  

E-print Network

Wideband and low dispersion slow light by chirped photonic crystal coupled waveguide Daisuke Mori coupled waveguide, which allows more robust slow light with lower loss. For this device, unique photonic, and J. Yonekura, "Observation of light propagation in photonic crystal optical waveguides with bends

Baba, Toshihiko

303

Individual acoustic variation in Belding's ground squirrel alarm chirps in the High Sierra Nevada (L)  

E-print Network

Individual acoustic variation in Belding's ground squirrel alarm chirps in the High Sierra Nevada (L) Brenda McCowan and Stacie L. Hooper Behavioral Biology Laboratory, Veterinary Medicine Teaching membership and is important in kin and social group recognition. Belding's ground squirrels Spermophilus

Patricelli, Gail

304

MATLAB simulation of a Distributed Feedback (DFB) laser with chirp effects  

NASA Astrophysics Data System (ADS)

A model of a distributed feedback (DFB) laser was implemented in MATLAB and SIMULINK. Using the laser rate equation, the model was simulated to obtain general characteristics of the chirp of the lasers frequency. The simulations were controlled by using different drive current waveforms, based on various bit patterns, data rates, and drive current values (threshold current and the extinction ratio). Once created, the laser drive current was passed to the SIMULINK DFB laser model. The output of a simulation provided frequency chirp, laser power emitted, photon density, and carrier density data. Two sets of simulations were conducted. The first set of simulations focused on the data rates and bit patterns. From these simulations it was determined that the transition from a ZERO bit to a ONE bit caused the greatest frequency excursions. Also, as the data rate increases the maximum frequency excursion increases. Finally, the first set of simulations revealed that the predictability of the chirp decreases as the data rate increases and as the complexity of the bit pattern increases. The second set of simulations examined the effect of the extinction ratio on frequency chirp. By plotting the maximum frequency excursion against its respective extinction ratio, it was determined that in some cases the maximum frequency excursions in a system could be minimized.

Espe, Burt L.

1994-12-01

305

Design, fabrication, and analysis of chirped multilayer mirrors for reflection of extreme-ultraviolet attosecond pulses.  

PubMed

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. PMID:16761058

Wonisch, A; Neuhusler, U; Kabachnik, N M; Uphues, T; Uiberacker, M; Yakovlev, V; Krausz, F; Drescher, M; Kleineberg, U; Heinzmann, U

2006-06-10

306

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

307

The effect of amplitude modulation on subharmonic imaging with chirp excitation.  

PubMed

Subharmonic generation from ultrasound contrast agents depends on the spectral and temporal properties of the excitation signal. The subharmonic response can be improved by using wideband and long-duration signals. However, for sinusoidal tone-burst excitation, the effective bandwidth of the signal is inversely proportional to the signal duration. Linear frequency-modulated (LFM) and nonlinear frequency-modulated (NLFM) chirp excitations allow independent control over the signal bandwidth and duration; therefore, in this study LFM and NLFM signals were used for the insonation of microbubble populations. The amplitude modulation of the excitation waveform was achieved by applying different window functions. A customized window was designed for the NLFM chirp excitation by focusing on reducing the spectral leakage at the subharmonic frequency and increasing the subharmonic generation from microbubbles. Subharmonic scattering from a microbubble population was measured for various excitation signals and window functions. At a peak negative pressure of 600 kPa, the generated subharmonic energy by ultrasound contrast agents was 15.4 dB more for NLFM chirp excitation with 40% fractional bandwidth when compared with tone-burst excitation. For this reason, the NLFM chirp with a customized window was used as an excitation signal to perform subharmonic imaging in an ultrasound flow phantom. Results showed that the NLFM waveform with a customized window improved the subharmonic contrast by 4.35 0.42 dB on average over a Hann-windowed LFM excitation. PMID:24297019

Harput, Sevan; Arif, Muhammad; McLaughlan, James; Cowell, David M J; Freear, Steven

2013-12-01

308

CHIRP SUB-BOTTOM PROFILER SOURCE SIGNATURE DESIGN AND FIELD TESTING  

E-print Network

signature. A 3D chirp system is currently being developed at the Southampton Oceanography Centre and as part@soc.soton.ac.uk § GeoAcoustics Ltd., Shuttleworth Close, Gapton Hall Industrial Estate, Great Yarmouth, Norfolk, NR31 0 of this development we developed and tested a number of alternative source sweeps to optimise the vertical resolution

National Oceanography Centre Southampton

309

Tunable dispersion using linearly chirped polymer optical fiber Bragg gratings with fixed center wavelength  

Microsoft Academic Search

We propose a new scheme for tunable dispersion using linearly chirped polymer optical fiber Bragg gratings made in fiber tapers. The simple tension and uniform heating to the fiber gratings act as the adjustment and control process. Dispersion is tuned by the applied tensile strain. Owing to the unusually large and negative thermooptic coefficient of polymer fiber, the center wavelength

Hongbo Liu; Huiyong Liu; Gangding Peng; Trevor W. Whitbread

2005-01-01

310

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.  

PubMed

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 that can be used with air monitoring data collected with an OP-FTIR spectrometer to detect departures from normal operating conditions in the workplace or along a fence line. Time series data, produced by plotting consecutive air sample concentrations in time, were analyzed. Autocorrelation in the time series data was removed by fitting dynamic models. Control charts were used with the residuals of the model fit data to determine if departures from defined normal operating conditions could be rapidly detected. Shewhart and exponentially weighted moving average (EWMA) control charts were evaluated for use with data collected under different room air flow and mixing conditions. Under rapidly changing conditions the Shewhart control chart was able to detect a leak in a simulated process area. The EWMA control chart was found to be more sensitive to drifts and slowly changing concentrations in air monitoring data. The time series and statistical process control techniques were also applied to data obtained during a field study at a chemical plant. A production area of an acrylonitrile, 1,3-butadiene, and styrene (ABS) polymer process was monitored in near-real time. Decision logics based on the time series and statistical process control technique introduced suggest several applications in workplace and environmental monitoring. These applications might include signaling of an alarm or warning, increasing levels of worker respiratory protection, or evacuation of a community, when gas and vapor concentrations are determined to be out-of-control. PMID:8012765

Malachowski, M S; Levine, S P; Herrin, G; Spear, R C; Yost, M; Yi, Z

1994-05-01

311

Building Climate Service Capacities in Eastern Africa with CHIRP and GeoCLIM  

NASA Astrophysics Data System (ADS)

In developing countries there is a great need for capacity building within national and regional climate agencies to develop and analyze historical and real time gridded rainfall datasets. These datasets are of key importance for monitoring climate and agricultural food production at decadal and seasonal time scales, and for informing local decision makers. The Famine Early Warning Systems Network (FEWS NET), working together with the U.S. Geological Survey (USGS) and the Climate Hazards Group (CHG) of the University of California Santa Barbara, has developed an integrated set of data products and tools to support the development of African climate services. The core data product is the Climate Hazards Group Infrared Precipitation (CHIRP) dataset. The CHIRP is a new rainfall dataset resulting from the blending of satellite estimated precipitation with high resolution precipitation climatology. The CHIRP depicts rainfall on five day totals at 5km spatial resolution from 1981 to present. The CHG is developing and deploying a standalone tool - the GeoCLIM - which will allow national and regional meteorological agencies to blend the CHIRP with station observations, run simple crop water balance models, and conduct climatological, trend, and time series analysis. Blending satellite estimates and gauge data helps overcome limited in situ observing networks. Furthermore, the GeoCLIM combines rainfall, soil, and evapotranspiration data with crop hydrological requirements to calculate agricultural water balance, presented as the Water Requirement Satisfaction Index (WRSI). The WRSI is a measurement of the degree in which a crop's hydrological requirements have been satisfied by rainfall. We present the results of a training session for personnel of the East African Intergovernmental Authority on Development Climate Prediction and Applications Center. The two week training program included the use of the GeoCLIM to improve CHIRP using station data, and to calculate and analyze trends in rainfall, WRSI, and drought frequency in the region.

Pedreros, D. H.; Magadzire, T.; Funk, C. C.; Verdin, J. P.; Peterson, P.; Landsfeld, M.; Husak, G. J.

2013-12-01

312

Relaxed dispersion requirement in the generation of chirped RF signals based on frequency-to-time mapping  

NASA Astrophysics Data System (ADS)

Photonic generation of chirped RF signal based on frequency-to-time mapping (FTM) is investigated in this paper. A new criterion on system parameters (dispersion amounts and pulse duration) for the generation of well-shaped linearly chirped signals is given, which is proved to be less restrictive than the currently known conditions. Therefore, requirement on the dispersion amount can be relaxed, which is highly desired in practical implementation of the FTM-based system. Theoretical results are presented, the correctness of which is verified by numerical and experimental results. The reported theory is a good guidance in designing the photonic system for the generation of chirped signals based on FTM.

Xu, Yuxiao; Shi, Zhiguo; Chi, Hao; Jin, Xiaofeng; Zheng, Shilie; Zhang, Xianmin

2014-11-01

313

The role of input chirp on phase shifters based on slow and fast light effects in semiconductor optical amplifiers.  

PubMed

We experimentally investigate the initial chirp dependence of slow and fast light effects in a semiconductor optical amplifier followed by an optical filter. It is shown that the enhancement of the phase shift due to optical filtering strongly depends on the chirp of the input optical signal. We demonstrate approximately 120 degrees phase delay as well as approximately 170 degrees phase advance at a microwave frequency of 19 GHz for different optimum values of the input chirp. The experimental results are shown to be in good agreement with numerical results based on a four-wave mixing model. Finally, a simple physical explanation based on an analytical perturbative approach is presented. PMID:19188968

Xue, Weiqi; Chen, Yaohui; Ohman, Filip; Mrk, Jesper

2009-02-01

314

Mathematical models for the reflection coefficients of lossy dielectric half-spaces with application to transient responses of chirped pulses  

NASA Technical Reports Server (NTRS)

Reflection coefficients are found at normal incidence for a large class of homogeneous lossy half-spaces with a one-dimensionally inhomogeneous or stratified lossy layer on top. Solutions are in terms of Hankel functions of complex argument to decrease cancellation error at high frequencies. One special case is that of layers on a homogeneous half-space where the dielectric constant in each layer may vary in a quite general manner. A Wronskian is used to insure the critical computations are correct. The reflection of chirped pulses is considered. Solutions are obtained by applying the fast Fourier transform. It is found that for a typical relatively long normalized 'long' pulse the power reflected as a function of time is essentially the power reflection coefficient for the frequencies swept out, whereas for a relatively short 'long' pulse, with the same relative change in frequency and the same number of oscillations there is only the uniform attenuation by the power reflection coefficient of the center frequency. By a 'long' pulse we mean a pulse whose spatial length is long compared to the thickness of the reflecting layer.

Evans, D. D.

1977-01-01

315

Development of a Fourier transform infrared spectroscopy coupled to UV-Visible analysis technique for aminosides and glycopeptides quantitation in antibiotic locks.  

PubMed

Antibiotic Lock technique maintains catheters' sterility in high-risk patients with long-term parenteral nutrition. In our institution, vancomycin, teicoplanin, amikacin and gentamicin locks are prepared in the pharmaceutical department. In order to insure patient safety and to comply to regulatory requirements, antibiotic locks are submitted to qualitative and quantitative assays prior to their release. The aim of this study was to develop an alternative quantitation technique for each of these 4 antibiotics, using a Fourier transform infrared (FTIR) coupled to UV-Visible spectroscopy and to compare results to HPLC or Immunochemistry assays. Prevalidation studies permitted to assess spectroscopic conditions used for antibiotic locks quantitation: FTIR/UV combinations were used for amikacin (1091-1115cm(-1) and 208-224nm), vancomycin (1222-1240cm(-1) and 276-280nm), and teicoplanin (1226-1230cm(-1) and 278-282nm). Gentamicin was quantified with FTIR only (1045-1169cm(-1) and 2715-2850cm(-1)) due to interferences in UV domain of parabens, preservatives present in the commercial brand used to prepare locks. For all AL, the method was linear (R(2)=0.996 to 0.999), accurate, repeatable (intraday RSD%: from 2.9 to 7.1% and inter-days RSD%: 2.9 to 5.1%) and precise. Compared to the reference methods, the FTIR/UV method appeared tightly correlated (Pearson factor: 97.4 to 99.9%) and did not show significant difference in recovery determinations. We developed a new simple reliable analysis technique for antibiotics quantitation in locks using an original association of FTIR and UV analysis, allowing a short time analysis to identify and quantify the studied antibiotics. PMID:24438668

Sayet, G; Sinegre, M; Ben Reguiga, M

2014-01-01

316

On decoding of Reed-Solomon codes over GF/32/ and GF/64/ using the transform techniques of Winograd. [based on cyclic convolution of Galois Field elements  

NASA Technical Reports Server (NTRS)

An algorithm based on the Winograd (1976) method is developed to compute a Fourier-like transform over Galois field GF(2 exp n) for n equal to 5 and 6. It is shown that this transform algorithm requires fewer multiplications than the more conventional fast transform algorithm described by Gentleman (1968). Such a transform can be used to encode and decode Reed-Solomon codes of length (2 exp n) -1.

Reed, I. S.; Truong, T. K.; Benjauthrit, B.

1978-01-01

317

Wavelet denoising for chirp-like signal in time-frequency domain and application to aircraft flight flutter testing  

Microsoft Academic Search

A novel denoising method for chirp-like signal that relies on the time-frequency analysis is described. Because the region of chirp signal in time-frequency (TF) map is well-concentrated relative to the widely distributed noise, the wavelet coefficients corresponding to the true signal can be extracted by a masking operation. And a new procedure is presented to design the mask and reconstruct

Wei Tang; Zhong-Ke Shi; Hong-Chao Li

2005-01-01

318

Measuring Temperature-dependent Propagating Disturbances in Coronal Fan Loops Using Multiple SDO/AIA Channels and the Surfing Transform Technique  

NASA Astrophysics Data System (ADS)

A set of co-aligned high-resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling a quantitative description of subvisual coronal motions with low signal-to-noise ratios of the order of 0.1%. The technique operates with a set of one-dimensional "surfing" signals extracted from position-time plots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency-velocity space that exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square-root dependence predicted for slow mode magneto-acoustic waves which seem to be the dominating wave mode in the loop structures studied. This result extends recent observations by Kiddie et al. to a more general class of fan loop system not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

Uritsky, Vadim M.; Davila, Joseph M.; Viall, Nicholeen M.; Ofman, Leon

2013-11-01

319

Fourier Transform Infrared (FTIR) Spectroscopy  

E-print Network

Fourier Transform Infrared (FTIR) Spectroscopy Klaus Gerwert, Lehrstuhl fu¨r Biophysik, Ruhr Transform IR by Johannes Orphal. Fourier transform infrared (FTIR) spectroscopy is an experimental technique. Introduction The underlying principle of a Fourier transform infrared (FTIR) spectrometer is the separation

Gerwert, Klaus

320

Detection performance improvement of chirped amplitude modulation ladar based on Gieger-mode avalanche photoelectric detector.  

PubMed

This paper presents an improved system structure of photon-counting chirped amplitude modulation (AM) ladar based on the Geiger-mode avalanche photoelectric detector (GmAPD). The error-pulse probability is investigated with statistical method. The research shows that most of the error pulses that are triggered by noise are distributed in the intensity troughs of the chirped AM waveform. The error-pulse probability is lowered with the sliding window and the threshold. With the average intensity of noise and signal being 0.3 count/sample and 1 count/sample, respectively, the probability of error pulses is reduced from 12% to 1.0%, and the SNR is improved by 2.2 dB in the improved system. PMID:22193131

Zhang, Zijing; Wu, Long; Zhang, Yu; Zhao, Yuan; Sun, Xiudong

2011-12-10

321

Making ultracold molecules in a two-color pump-dump photoassociation scheme using chirped pulses  

SciTech Connect

This theoretical paper investigates the formation of ground state molecules from ultracold cesium atoms in a two-color scheme. Following previous work on photoassociation with chirped picosecond pulses [Luc-Koenig et al., Phys. Rev. A, 70, 033414 (2004)], we investigate stabilization by a second (dump) pulse. By appropriately choosing the dump pulse parameters and time delay with respect to the photoassociation pulse, we show that a large number of deeply bound molecules are created in the ground triplet state. We discuss (i) broad-bandwidth dump pulses which maximize the probability to form molecules while creating a broad vibrational distribution as well as (ii) narrow-bandwidth pulses populating a single vibrational ground state level, bound by 113 cm{sup -1}. The use of chirped pulses makes the two-color scheme robust, simple, and efficient.

Koch, Christiane P. [Laboratoire Aime Cotton, CNRS, Bat. 505, Campus d'Orsay, 91405 Orsay Cedex (France); Department of Physical Chemistry and Fritz Haber Research Center, Hebrew University, Jerusalem 91904 (Israel); Luc-Koenig, Eliane; Masnou-Seeuws, Francoise [Laboratoire Aime Cotton, CNRS, Bat. 505, Campus d'Orsay, 91405 Orsay Cedex (France)

2006-03-15

322

FEMTOSECOND X-RAY PULSES FROM A FREQUENCY CHIRPED SASE FEL.  

SciTech Connect

We discuss the temporal and spectral properties of self-amplified spontaneous emission (SASE) utilizing an energy-chirped electron beam. A short temporal pulse is generated by using a monochromator to select a narrow radiation bandwidth from the frequency chirped SASE. For the filtered radiation, the minimum pulse length is limited by the intrinsic SASE bandwidth, while the number of modes and the energy fluctuation can be controlled through the monochromator bandwidth. Two cases are considered: (1) placing the monochromator at the end of a single long undulator; (2) placing the monochromator after an initial undulator and amplifying the short-duration output in a second undulator. We analyze these cases and show that tens of femtosecond x-ray pulses may be generated for the linac coherent light source.

KRINSKY,S.HUANG,Z.

2004-01-07

323

Power limitations and pulse distortions in an Yb : KGW chirped-pulse amplification laser system  

NASA Astrophysics Data System (ADS)

We have studied self-action effects (self-focusing and self-phase modulation) and stimulated Raman scattering in an Yb : KGW chirped-pulse amplification laser system. The results demonstrate that self-focusing in combination with thermal lensing may significantly limit the chirped pulse energy in this system (down to 200 ?J) even at a relatively long pulse duration (50 ps). Nonlinear lenses in the laser crystals in combination with thermal lenses bring the regenerative amplifier cavity in the laser system to the instability zone and limit the average output power at pulse repetition rates under 50 kHz. Self-phase modulation, a manifestation of self-action, may significantly distort a recompressed femtosecond pulse at energies near the self-focusing threshold. Stimulated Raman scattering in such a laser has a weaker effect on output parameters than do self-focusing and thermal lensing, and Raman spectra are only observed in the case of pulse energy instability.

Kim, G. H.; Yang, J.; Kulik, A. V.; Sall, E. G.; Chizhov, S. A.; Yashin, V. E.; Kang, U.

2013-08-01

324

Periodic compression of chirped femtosecond pulses in silicon waveguides under fourth-order dispersion  

NASA Astrophysics Data System (ADS)

We report the analysis of the compression mechanism for chirped femtosecond pulses in silicon-on-insulator waveguides under the effect of fourth-order dispersion (FOD) using the modified variational approach that involves Rayleigh's dissipation function (RDF). Our results show that the nonlinear compression in these waveguides is input pulse dependent. Moreover, this study leads to a nearly periodic-like dynamic induced by the interplay between self-phase modulation and FOD in a normal group-velocity dispersion. In addition, when large values of the initial chirp and absorption coefficients present in these waveguides are considered, the compression mechanism is completely destroyed, with the observation of at least one pulse amplification over a short distance of propagation prior to pulse broadening.

Mandeng Mandeng, Lucien; Ibraid Fewo, Serge; Tchawoua, Clment; Crpin Kofan, Timolon

2014-08-01

325

CSR Interaction for a 2D Energy-Chirped Bunch on a General Orbit  

SciTech Connect

When an electron bunch with initial linear energy chirp traverses a bunch compression chicane, the bunch interacts with itself via coherent synchrotron radiation (CSR) and space charge force. The effective longitudinal CSR force for such kind of 2D bunch on a circular orbit has been analyzed earlier [1]. In this paper, we present the analytical results of the effective longitudinal CSR force for a 2D energy-chirped bunch going through a general orbit, which includes the entrance and exit of a circular orbit. In particular, we will show the behavior of the force in the last bend of a chicane when the bunch is under extreme compression. This is the condition when bifurcation of bunch phase space occurs in many CSR measurements. [1] R. Li, Phys. Rev. ST Accel. Beams 11, 024401 (2008)

Rui Li

2009-05-01

326

Corn transformed  

SciTech Connect

Researchers have produced fertile corn transformed with a foreign gene that makes the plants resistant to the herbicide bialaphos. This achievement, is the first report of fertile transgenic corn in the reviewed literature, and it is the capstone of almost a decade's efforts to genetically engineer this country's most important crop. The only other major crop to be so manipulated is rice. The ability produce transgenic corn gives biologists a valuable tool to probe the whys and hows of gene expression and regulation. It may also give plant breeders a way to develop new corn varieties with a speed and predictability that would be impossible with classical breeding techniques.

Moffat, A.S.

1990-08-10

327

Ultrahigh contrast from a frequency-doubled chirped-pulse-amplification beamline.  

PubMed

This paper describes frequency-doubled operation of a high-energy chirped-pulse-amplification beamline. Efficient type-I second-harmonic generation was achieved using a 3 mm thick 320 mm aperture KDP crystal. Shots were fired at a range of energies achieving more than 100 J in a subpicosecond, 527 nm laser pulse with a power contrast of 10(14). PMID:23842168

Hillier, David; Danson, Colin; Duffield, Stuart; Egan, David; Elsmere, Stephen; Girling, Mark; Harvey, Ewan; Hopps, Nicholas; Norman, Michael; Parker, Stefan; Treadwell, Paul; Winter, David; Bett, Thomas

2013-06-20

328

Chirped AM ladar for anti-ship missile tracking and force protection 3D imaging: update  

Microsoft Academic Search

Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges. Since IRST systems cannot measure range and line-of-sight velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a chirped amplitude modulation ladar to provide range and velocity measurements for

Brian C. Redman; Barry Stann; William Lawler; Mark Giza; John Dammann; William Ruff; William Potter; Ronald G. Driggers; Jose Garcia; John Wilson; Keith Krapels

2006-01-01

329

Spectral broadening and self-compression of negatively chirped visible femtosecond pulses in fused silica  

SciTech Connect

This paper describes a new effect: spectral broadening and self-compression of negatively chirped visible femtosecond pulses as a result of nonlinear interaction of large-aperture beams with fused silica. We assume that the likely mechanism of the observed spectral broadening is the combined effect of self-phase modulation and four-wave mixing. (special issue devoted to the 90th anniversary of n.g. basov)

Aristov, A I; Grudtsyn, Ya V; Mikheev, L D; Polivin, A V; Stepanov, S G; Trofimov, V A; Yalovoi, V I

2012-12-31

330

Electro-optic measurement of THz field pulses with a chirped optical beam  

Microsoft Academic Search

Using a linearly chirped optical probe pulse in free-space electro-optic measurements, a temporal wave form of a co-propagating THz field is linearly encoded onto the frequency spectrum of the optical probe pulse, and then decoded by dispersing the probe beam from a grating to a detector array. We achieve acquisition of picosecond THz field pulses without using mechanical time-delay device.

Zhiping Jiang; X.-C. Zhang

1998-01-01

331

Modeling interface roughness scattering in a layered seabed for normal-incident chirp sonar signals.  

PubMed

Downward looking sonar, such as the chirp sonar, is widely used as a sediment survey tool in shallow water environments. Inversion of geo-acoustic parameters from such sonar data precedes the availability of forward models. An exact numerical model is developed to initiate the simulation of the acoustic field produced by such a sonar in the presence of multiple rough interfaces. The sediment layers are assumed to be fluid layers with non-intercepting rough interfaces. PMID:22502485

Tang, Dajun; Hefner, Brian T

2012-04-01

332

Non-collinear phase-matching geometries in optical parametric chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

This study presents a full three-dimensional nonlinear pulse propagation and amplification model that includes considerations for phase-matching, diffraction, and walk-off effects. By using this model, two types of type I non-collinear phase-matching geometries in BBO based optical parametric chirped-pulse amplification are investigated theoretically and experimentally. The simulation results agree well with the experimental findings.

Guo, Xiaoyang; Xu, Yi; Zou, Xiao; Lu, Xiaoming; Li, Yanyan; Wang, Cheng; Leng, Yuxin; Li, Ruxin

2014-11-01

333

Open-path sensor for atmospheric methane based on chirped laser dispersion spectroscopy  

NASA Astrophysics Data System (ADS)

The design and characterization of a near-IR Chirped Laser Dispersion Spectroscopy (CLaDS) sensor for atmospheric methane detection are reported. The near-IR CLaDS system exhibits the benefits of the prior mid-IR CLaDS systems implemented for open-path sensing while taking advantage of the robust fiber-optic components available in the near-IR. System noise, long-term stability, and comparison with existing technology for methane detection are presented.

Nikodem, Michal; Plant, Genevieve; Sonnenfroh, David; Wysocki, Gerard

2014-10-01

334

Cancellous bone analysis with modified least squares Prony's method and chirp filter: phantom experiments and simulation.  

PubMed

The presence of two longitudinal waves in porous media is predicted by Biot's theory and has been confirmed experimentally in cancellous bone. When cancellous bone samples are interrogated in through-transmission, these two waves can overlap in time. Previously, the Modified Least-Squares Prony's (MLSP) method was validated for estimation of amplitudes, attenuation coefficients, and phase velocities of fast and slow waves, but tended to overestimate phase velocities by up to about 5%. In the present paper, a pre-processing chirp filter to mitigate the phase velocity bias is derived. The MLSP/chirp filter (MLSPCF) method was tested for decomposition of a 500 kHz-center-frequency signal containing two overlapping components: one passing through a low-density-polyethylene plate (fast wave) and another passing through a cancellous-bone-mimicking phantom material (slow wave). The chirp filter reduced phase velocity bias from 100 m/s (5.1%) to 69 m/s (3.5%) (fast wave) and from 29 m/s (1.9%) to 10 m/s (0.7%) (slow wave). Similar improvements were found for 1) measurements in polycarbonate (fast wave) and a cancellous-bone-mimicking phantom (slow wave), and 2) a simulation based on parameters mimicking bovine cancellous bone. The MLSPCF method did not offer consistent improvement in estimates of attenuation coefficient or amplitude. PMID:20968389

Wear, Keith A

2010-10-01

335

Wideband-adjustable reflection-suppressed rejection filters using chirped and tilted fiber gratings.  

PubMed

Wideband-adjustable band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidths (from 10 nm to 150 nm), together with a low insertion loss (less than 1dB) and a negligible back-reflection (lower than -20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to the polarization state of the input light, as well as to temperature, axial strain and surrounding refractive index. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band-rejection filters, edge filters and gain equalizers. PMID:25322019

Liu, Fu; Guo, Tuan; Wu, Chuang; Guan, Bai-Ou; Lu, Chao; Tam, Hwa-Yaw; Albert, Jacques

2014-10-01

336

Anti-ship missile tracking with a chirped AM ladar - Update: design, model predictions, and experimental results  

NASA Astrophysics Data System (ADS)

Shipboard infrared search and track (IRST) systems can detect sea-skimming, anti-ship missiles at long ranges. Since IRST systems cannot measure range and line-of-sight (LOS) velocity, they have difficulty distinguishing missiles from false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a ladar based on the chirped amplitude modulation (AM) technique to provide range and velocity measurements of potential targets handed-over by the distributed aperture system - IRST (DAS-IRST) being developed by the Naval Research Laboratory (NRL) and sponsored by the Office of Naval Research (ONR). Using the ladar's range and velocity data, false alarms and clutter will be eliminated, and valid missile targets' tracks will be updated. By using an array receiver, ARL's ladar will also provide 3D imagery of potential threats for force protection/situational awareness. The concept of operation, the Phase I breadboard ladar design and performance model results, and the Phase I breadboard ladar development program were presented in paper 5413-16 at last year's symposium. This paper will present updated design and performance model results, as well as recent laboratory and field test results for the Phase I breadboard ladar. Implications of the Phase I program results on the design, development, and testing of the Phase II brassboard ladar will also be discussed.

Redman, Brian; Ruff, William; Stann, Barry; Giza, Mark; Lawler, William; Dammann, John; Potter, William

2005-05-01

337

Synthetic aperture acoustic imaging of canonical targets with a 2-15 kHz linear FM chirp  

NASA Astrophysics Data System (ADS)

Synthetic aperture image reconstruction applied to outdoor acoustic recordings is presented. Acoustic imaging is an alternate method having several military relevant advantages such as being immune to RF jamming, superior spatial resolution, capable of standoff side and forward-looking scanning, and relatively low cost, weight and size when compared to 0.5 - 3 GHz ground penetrating radar technologies. Synthetic aperture acoustic imaging is similar to synthetic aperture radar, but more akin to synthetic aperture sonar technologies owing to the nature of longitudinal or compressive wave propagation in the surrounding acoustic medium. The system's transceiver is a quasi mono-static microphone and audio speaker pair mounted on a rail 5meters in length. Received data sampling rate is 80 kHz with a 2- 15 kHz Linear Frequency Modulated (LFM) chirp, with a pulse repetition frequency (PRF) of 10 Hz and an inter-pulse period (IPP) of 50 milliseconds. Targets are positioned within the acoustic scene at slant range of two to ten meters on grass, dirt or gravel surfaces, and with and without intervening metallic chain link fencing. Acoustic image reconstruction results in means for literal interpretation and quantifiable analyses. A rudimentary technique characterizes acoustic scatter at the ground surfaces. Targets within the acoustic scene are first digitally spotlighted and further processed, providing frequency and aspect angle dependent signature information.

Vignola, Joseph F.; Judge, John A.; Good, Chelsea E.; Bishop, Steven S.; Gugino, Peter M.; Soumekh, Mehrdad

2011-06-01

338

Code synchronization based on lumped time-delay compensation scheme with a linearly chirped fiber Bragg grating in all-optical analog-to-digital conversion  

NASA Astrophysics Data System (ADS)

We propose a novel lumped time-delay compensation scheme for all-optical analog-to-digital conversion based on soliton self-frequency shift and optical interconnection techniques. A linearly chirped fiber Bragg grating is optimally designed and used to compensate for the entire time-delays of the quantized pulses precisely. Simulation results show that the compensated coding pulses are well synchronized with a time difference less than 3.3 ps, which can support a maximum sampling rate of 151.52 GSa/s. The proposed scheme can efficiently reduce the structure complexity and cost of all-optical analog-to-digital conversion compared to the previous schemes with multiple optical time-delay lines.

Wang, Tao; Kang, Zhe; Yuan, Jin-Hui; Tian, Ye; Yan, Bin-Bin; Sang, Xin-Zhu; Yu, Chong-Xiu

2014-10-01

339

Transform picture coding  

Microsoft Academic Search

Picture coding by first dividing the picture into sub-pictures and then performing a linear transformation on each sub-picture cud quantizing and coding the resulting coefficients is introduced from a heuristic point of view. Various transformation, quantization, and coding strategies are discussed. A survey of all known applications of these techniques to monochromatic image coding is presented along with a summary

P. A. Wintz

1972-01-01

340

Modeling Transformation  

E-print Network

Modeling Transformation What does each step do? #12;Transformation Procedure #12;Transformation Procedure #12;Building Your Model Yarn = chromosomal DNA Beads = ribosomes Black velcro = plasmid DNA Green velcro = GFP gene Pink velcro

Rose, Michael R.

341

Applying Improved Efficiency Transformers  

E-print Network

Today's business and energy conscious environment affords both producers and consumers of electric energy an opportunity to reduce costs and conserve energy through the use of improved efficiency transformers. Various design techniques...

Haggerty, N. K.; Malone, T. P.

342

Transformation inverse design  

E-print Network

We present a new technique for the design of transformation-optics devices based on large-scale optimization to achieve the optimal effective isotropic dielectric materials within prescribed index bounds, which is ...

Liu, David

343

Transform decoding of Reed-Solomon codes over GF(2 to the 2n power using the techniques of Winograd. [algorithms  

NASA Technical Reports Server (NTRS)

An algorithm for computing a Fourier-like transform over GF(2 to the (second power) to the n power), where n = 1,2,3,4,5, was developed to encode and decode and Reed-Solomon (RS) codes of length 2 to the (second power) to the n power. Such as RS detector is considerably faster than a decoder that uses the conventional fast transform over GF(2 to the (second power) to the n power).

Reed, I. S.; Truong, T. K.; Benjauthrit, B.

1978-01-01

344

Optical source transformations.  

PubMed

Transformation optics is a recently appreciated methodology for the design of complex media that control the propagation of electromagnetic and other types of waves. The transformation optical technique involves the use of coordinate transformations applied to some region of space, providing a conceptual means to redirect the flow of waves. Successfully designed devices to date have made use of transformations acting on passive space only; however, the technique can also be applied when source distributions (e.g., current and charge) are included within the space being transformed. In this paper we present examples of source transformations that illustrate the potential of these expanded transformation optical methods. In particular, using finite-element full-wave simulations, we confirm the restoration of dipole radiation patterns from both a distorted 'pin-wheel' antenna and a bent dipole partially occluded by a cylindrical scatterer. We propose the technique of source transformations as a powerful approach for antenna design, especially in relation to conformal antennas. PMID:19104551

Kundtz, N; Roberts, D A; Allen, J; Cummer, S; Smith, D R

2008-12-22

345

Effects of Detuning on Control of Intersubband Quantum Well Transitions with Chirped Electromagnetic Pulses  

SciTech Connect

We study the interaction of a chirped electromagnetic pulse with intersubband transitions of a double semiconductor quantum well. We specifically consider the interaction of the ground and first excited subbands with the electromagnetic field and use the nonlinear density matrix equations for the description of the system dynamics. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed with emphasis given to the effects of the detuning of the central frequency of the electromagnetic field from resonance.

Blekos, Konstantinos; Terzis, Andreas F. [Physics Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece); Simserides, Constantinos [Institute of Materials Science, National Center of Scientific Research Demokritos, 153 10 Athens (Greece); Paspalakis, Emmanuel [Materials Science Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece)

2010-11-10

346

Optical beam focusing by a single subwavelength metal slit surrounded by chirped dielectric surface gratings  

SciTech Connect

A method for optical beam focusing by a single subwavelength metal slit surrounded by surface gratings is proposed. In our proposed method, the period of each surface grating is chirped so that the radiation fields of surface plasmon polaritons can be controlled to make a beam spot at the desired focal length. Through our proposed method, it is numerically shown that we can make a beam spot which is located at the several times of wavelength distance from the slit, and its focal length can be controlled.

Kim, Seyoon; Lim, Yongjun; Kim, Hwi; Park, Junghyun; Lee, Byoungho [National Creative Research Center for Active Plasmonics Application Systems, Inter-University Semiconductor Research Center and School of Electrical Engineering, Seoul National University, Gwanak-Gu Sillim-Dong, Seoul 151-774 (Korea, Republic of)

2008-01-07

347

High-energy noncollinear optical parametric-chirped pulse amplification in LBO at 800 nm.  

PubMed

The optical parametric-chirped pulse amplification (OPCPA) based on large-aperture nonlinear optical crystals is promising for implementation of an ultrahigh peak-power laser system of 10 PW and beyond. We demonstrated the highest energy broadband OPCPA at 800 nm, to the best of our knowledge, by using an 80 mm in diameter LiB(3)O(5)(LBO) amplifier, with an output energy of 28.68 J, a bandwidth of 80 nm (FWHM), and conversion efficiency of 25.38%. After compression, a peak power of 0.61 PW with 33.8 fs pulse duration is produced. PMID:24322145

Xu, Lu; Yu, Lianghong; Liang, Xiaoyan; Chu, Yuxi; Hu, Zhanggui; Ma, Lin; Xu, Yi; Wang, Cheng; Lu, Xiaoming; Lu, Haihe; Yue, Yinchao; Zhao, Ying; Fan, Feidi; Tu, Heng; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan

2013-11-15

348

Chirped laser dispersion spectroscopy using a directly modulated quantum cascade laser  

SciTech Connect

Chirped laser dispersion spectroscopy (CLaDS) utilizing direct modulation of a quantum cascade laser (QCL) is presented. By controlling the laser bias nearly single- and dual-sideband CLaDS operation can be realized in an extremely simplified optical setup with no external optical modulators. Capability of direct single-sideband modulation is a unique feature of QCLs that exhibit a low linewidth enhancement factor. The developed analytical model shows excellent agreement with the experimental, directly modulated CLaDS spectra. This method overcomes major technical limitations of mid-infrared CLaDS systems by allowing significantly higher modulation frequencies and eliminating optical fringes introduced by external modulators.

Hangauer, Andreas, E-mail: hangauer@princeton.edu; Nikodem, Michal; Wysocki, Gerard, E-mail: gwysocki@princeton.edu [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States)] [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States); Spinner, Georg [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States) [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States); Institute for Quantum Electronics, ETH Zurich, 8093 Zurich (Switzerland)

2013-11-04

349

Experimental demonstration of distributed feedback semiconductor lasers based on reconstruction-equivalent-chirp technology.  

PubMed

In this paper we report, to the best of our knowledge, the first experimental realization of distributed feedback (DFB) semiconductor lasers based on reconstruction-equivalent-chirp (REC) technology. Lasers with different lasing wavelengths are achieved simultaneously on one chip, which shows a potential for the REC technology in combination with the photonic integrated circuits (PIC) technology to be a possible method for monolithic integration, in that its fabrication is as powerful as electron beam technology and the cost and time-consuming are almost the same as standard holographic technology. PMID:19333287

Li, Jingsi; Wang, Huan; Chen, Xiangfei; Yin, Zuowei; Shi, Yuechun; Lu, Yanqing; Dai, Yitang; Zhu, Hongliang

2009-03-30

350

Inducing changes in the bond length of diatomic molecules by time-symmetric chirped pulses  

SciTech Connect

We show numerically that it is possible to change the structure of a simple molecule, that is, a diatomic molecule, where the bond length is modified at a precise timing with symmetrically chirped laser pulses. In the adiabatic regime, the process is fully time reversible, making it possible to design slow vibrations with large bond elongations. The scheme relies on the preparation of a separable state of both nuclear and electronic degrees of freedom with predominant amplitude on the dissociative (antibonding) electronic wave function. Shorter laser pulses can be used to dynamically induce larger bond elongations, preparing a highly excited vibrational wave packet in the ground potential as the laser is switched off.

Chang, Bo Y.; Shin, Seokmin; Sola, Ignacio R. [School of Chemistry (BK21), Seoul National University, Seoul 151-747 (Korea, Republic of); Departamento de Quimica Fisica, Universidad Complutense, E-28040 Madrid (Spain)

2010-12-15

351

Population Transfer between Two Quantum States by Piecewise Chirping of Femtosecond Pulses: Theory and Experiment  

SciTech Connect

We propose and experimentally demonstrate the method of population transfer by piecewise adiabatic passage between two quantum states. Coherent excitation of a two-level system with a train of ultrashort laser pulses is shown to reproduce the effect of an adiabatic passage, conventionally achieved with a single frequency-chirped pulse. By properly adjusting the amplitudes and phases of the pulses in the excitation pulse train, we achieve complete and robust population transfer to the target state. The piecewise nature of the process suggests a possibility for the selective population transfer in complex quantum systems.

Zhdanovich, S. [Departments of Physics and Astronomy, University of British Columbia, Vancouver (Canada); Laboratory for Advanced Spectroscopy and Imaging Research (LASIR), University of British Columbia, Vancouver (Canada); Shapiro, E. A. [Chemistry, University of British Columbia, Vancouver (Canada); Shapiro, M.; Hepburn, J. W.; Milner, V. [Departments of Physics and Astronomy, University of British Columbia, Vancouver (Canada); Chemistry, University of British Columbia, Vancouver (Canada); Laboratory for Advanced Spectroscopy and Imaging Research (LASIR), University of British Columbia, Vancouver (Canada)

2008-03-14

352

Deriving Criteria-supporting Benchmark Values from Empirical Response Relationships: Comparison of Statistical Techniques and Effect of Log-transforming the Nutrient Variable  

EPA Science Inventory

In analyses supporting the development of numeric nutrient criteria, multiple statistical techniques can be used to extract critical values from stressor response relationships. However there is little guidance for choosing among techniques, and the extent to which log-transfor...

353

Dependence of spectrum on pump-signal angle in BBO-I noncollinear optical-parametric chirped-pulse amplification  

Microsoft Academic Search

. A BBO-I noncollinear optical-parametric chirped-pulse amplifier pumped by a Q-switched and frequency-doubled Nd:YAG laser\\u000a has been demonstrated. At an optimal pump-signal angle, the temporally stretched chirped signal pulses with bandwidth of 36nm\\u000a (FWHM) were amplified without any distortion in spectrum. The gain bandwidth was very sensitive to the pump-signal angle.\\u000a Variation of this angle by about 1.5mrad may significantly

X. Yang; Z. Xu; Z. Zhang; Y. Leng; J. Peng; J. Wang; S. Jin; W. Zhang; R. Li

2001-01-01

354

Transformer insulation life assessment  

Microsoft Academic Search

This paper presents novel techniques for life assessment of the insulation of the generator stepup units in power plants. Load and ambient temperatures are two important factors that influence the life of insulation in transformers. Hourly load and ambient temperatures obtained through condition monitoring are used to assess the operating profile of the equipment. Modeling techniques for estimating load factors

Kshira T. Muthanna; Abhinanda Sarkar; Kaushik Das; Kurt Waldner

2006-01-01

355

Utilizing infrared and power quality techniques to diagnose and recommission 33 old power, lighting & receptacles panels and distribution transformers at the New Jersey international & bulk mail center  

Microsoft Academic Search

This case study details electrical safety items and power quality assessment in conjunction with an IR survey of 285 panels and 85 transformers that was conducted in December 2004 and January 2005. The assessments were extremely useful in avoiding potential incidents and costly equipment shutdowns. This survey highlighted some of critical NEC deficiencies which were corrected immediately. Approximately 85 %

J. C. Pearson; D. A. Pandya

2007-01-01

356

Dual-chirped optical parametric amplification for generating few hundred mJ infrared pulses.  

PubMed

An ultrafast high-power infrared pulse source employing a dual-chirped optical parametric amplification (DC-OPA) scheme based on a Ti:sapphire pump laser system is theoretically investigated. 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 at 1.4 ?m and 1.87 ?m can be generated with a total conversion efficiency approaching 40%. Furthermore, few-cycle idler pulses with a passively stabilized carrier-envelope phase (CEP) can be generated by the difference frequency generation process in a collinear configuration. DC-OPA, a BBO-OPA scheme pumped by a Ti:sapphire laser, is efficient and scalable in output energy of the infrared pulses, which provides us with the design parameters of an ultrafast infrared laser system with an energy up to a few hundred mJ. PMID:21503032

Zhang, Qingbin; Takahashi, Eiji J; Mcke, Oliver D; Lu, Peixiang; Midorikawa, Katsumi

2011-04-11

357

Nonlinear transient chirp signal modeling of the aortic and pulmonary components of the second heart sound.  

PubMed

This paper describes a new approach based on the time-frequency representation of transient nonlinear chirp signals for modeling the aortic (A2) and the pulmonary (P2) components of the second heart sound (S2). It is demonstrated that each component is a narrow-band signal with decreasing instantaneous frequency defined by its instantaneous amplitude and its instantaneous phase. Each component is also a polynomial phase signal, the instantaneous phase of which can be accurately represented by a polynomial having an order of thirty. A dechirping approach is used to obtain the instantaneous amplitude of each component while reducing the effect of the background noise. The analysis-synthesis procedure is applied to 32 isolated A2 and 32 isolated P2 components recorded in four pigs with pulmonary hypertension. The mean +/- standard deviation of the normalized root-mean-squared error (NRMSE) and the correlation coefficient (rho) between the original and the synthesized signal components were: NRMSE = 2.1 +/- 0.3% and rho = 0.97 +/- 0.02 for A2 and NRMSE = 2.52 +/- 0.5% and rho = 0.96 +/- 0.02 for P2. These results confirm that each component can be modeled as mono-component nonlinear chirp signals of short duration with energy distributions concentrated along its decreasing instantaneous frequency. PMID:11059167

Xu, J; Durand, L G; Pibarot, P

2000-10-01

358

Study of chirping toroidicity-induced Alfvn eigenmodes in the National Spherical Torus Experiment  

NASA Astrophysics Data System (ADS)

Chirping toroidicity-induced Alfvn eigenmodes (TAEs) are destabilized during neutral beam injection on the National Spherical Torus Experiment (NSTX (Ono M. et al 2000 Nucl. Fusion 40 557)) by super-Alfvnic ions with velocities up to five times larger than the Alfvn velocity. TAEs exhibit repeated bursts in amplitude and down-chirps in frequency. Larger bursts, so-called TAE avalanches, are eventually observed and correlate with a loss of fast ions up to 30% over 1 ms. Frequency, amplitude and radial structure of TAEs are characterized via magnetic pickup coils and a multi-channel reflectometer system. The modes have a broad radial structure, which appears to be unaffected by the large frequency and amplitude variations. However, the large mode amplitude does impact the modes' dynamics by favouring the coupling among different modes. In addition, the coupling involves kink-like modes and can therefore degrade the thermal plasma confinement. In spite of the non-linear regime characterizing the TAE dynamics, the measured properties are found to be in reasonable agreement with solutions from the ideal MHD code NOVA.

Podest, M.; Bell, R. E.; Bortolon, A.; Crocker, N. A.; Darrow, D. S.; Diallo, A.; Fredrickson, E. D.; Fu, G.-Y.; Gorelenkov, N. N.; Heidbrink, W. W.; Kramer, G. J.; Kubota, S.; LeBlanc, B. P.; Medley, S. S.; Yuh, H.

2012-09-01

359

A strain sensing system using a novel optical fibre Bragg grating sensor and a synthetic heterodyne interrogation technique*A strain sensing system using a novel optical fibre Bragg grating sensor and a synthetic heterodyne interrogation technique  

Microsoft Academic Search

A potential low cost novel sensing scheme for monitoring absolute strain is demonstrated. The scheme utilizes a synthetic heterodyne interrogation technique working in conjunction with a linearly chirped, sinusoidally tapered, apodized Bragg grating sensor. The interrogation technique is relatively simple to implement in terms of the required optics and the peripheral electronics. This scheme generates an output signal that has

T. Allsop; K. Chisholm; I. Bennion; A. Malvern; R. Neal

2002-01-01

360

APPLICATION OF PULSE COMPRESSION SIGNAL PROCESSING TECHNIQUES TO ELECTROMAGNETIC ACOUSTIC TRANSDUCERS (EMATS) FOR NON-CONTACT THICKNESS MEASUREMENTS AND IMAGING  

Microsoft Academic Search

A pair of non-contact EMATs has been used for thickness measurements and imaging of metallic plates. This was performed using wide bandwidth EMATs and pulse- compression signal processing techniques, using chirp excitation. This gives a greatly improved Signal to Noise Ratio (SNR) for non-contact experiments, increasing the speed of data acquisition. A numerical simulation of the technique has confirmed the

T. H. Gan; K. S. Ho; D. A. Hutchins; D. R. Billson

361

Chirp Measurement of Multimode Q Switched Laser Diode Pulses by Use of a Streak Camera and a Grating Monochromator  

Microsoft Academic Search

We discuss spectrotemporal measurements of laser diode pulses performed with a streak camera and a grating monochromator to yield a precise evaluation of chirping effects in Q -switched multimode emissions. We experimentally illustrate several causes of errors, depending on the grating size and period as well as on the adjustment of the collimating lens at the monochromator output. An analytical

Alexandre Bresson; Nikola Stelmakh; Jean-Michel Lourtioz; Alexandre Shen; Claude Froehly

1998-01-01

362

Direct observation of ligand transfer and bond formation in cytochrome c oxidase using mid-infrared chirped-pulse upconversion  

NASA Astrophysics Data System (ADS)

We time resolved the CO ligand transfer process in the bimetallic active site of cytochrome c oxidase, using mid-infrared chirped-pulse upconversion to observe the full vibrational signature of Fe-CO bond breaking and CuB-CO bond formation.

Treuffet, Johanne; Kubarych, Kevin J.; Lambry, Jean-Christophe; Pilet, Eric; Masson, Jean-Baptiste; Martin, Jean-Louis; Vos, Marten H.; Joffre, Manuel; Alexandrou, Antigoni

363

Generation of high-energy 10-fs pulses by a new pulse compression technique  

Microsoft Academic Search

Summary form only given. In this work, we present a novel laser pulse compression technique for Ti:sapphire chirped pulse laser amplifiers, based on spectral broadening in a hollow cylindrical quartz fiber filled with noble gases at high pressure, which is suitable for high-energy pulses. Pulse recompression is then achieved using two conventional quartz prism pairs.

M. Nisoli; S. De Silvestri; O. Svelto

1996-01-01

364

Wavelet transforms versus Fourier transforms  

Microsoft Academic Search

This note is a very basic introduction to wavelets. It starts with an orthogonal basis of piecewise constant functions, constructed by dilation and translation. The ``wavelet transform'' maps each $f(x)$ to its coefficients with respect to this basis. The mathematics is simple and the transform is fast (faster than the Fast Fourier Transform, which we briefly explain), but approximation by

Gilbert Strang

1993-01-01

365

Drift-eliminating method of intensity demodulation on a chirped fiber grating strain sensor.  

PubMed

It is quite possible to detect the strain of a sample based on a chirped fiber grating (CFG) sensor, which has a wider bandwidth of light signal than a fiber Bragg grating. Usually, environmental factors play negative roles in the process of intensity demodulation. A drift-eliminating method of CFG intensity demodulation has been created and tested in our lab. Three CFG sensors were involved in this research. Two of them with close wavelength bands connected in series were used as a strain sensing unit; the third one was used as a referencing grating working within the reflective wavelength spectrum of the other two. It is shown that the signal ratio of the sensing unit and the referencing grating is a linear function of the loading strain. The linearity is as high as 99.79%. PMID:24921883

Pan, Jianjun; Li, Weilai; Liu, Jie

2014-05-01

366

Chirped arrays of refractive ellipsoidal microlenses for aberration correction under oblique incidence.  

PubMed

Improvements of the resolution homogeneity of an ultra-thin artificial apposition compound eye objective are accomplished by the use of a chirped array of ellipsoidal micro-lenses. The array contains 130x130 individually shaped ellipsoidal lenses for channel-wise correction of astigmastism and field curvature occurring under oblique incidence. We present an analytical approach for designing anamorphic micro-lenses for such purpose based on Gullstrands equations and experimentally validate the improvement. Considerations for the design of the photolithographical masks for the micro-lens array fabrication by melting of photoresist cylinders with ellipsoidal basis are presented. Measurements of the optically performance are proceed on first realized artificial compound eye prototypes showing a significant improvement of angular resolution homogeneity over the complete field of view of 64.3?. PMID:19503268

Duparr, Jacques; Wippermann, Frank; Dannberg, Peter; Reimann, Andreas

2005-12-26

367

Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp  

NASA Astrophysics Data System (ADS)

Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses.

Bouillard, J.-S.; Vilain, S.; Dickson, W.; Wurtz, G. A.; Zayats, A. V.

2012-11-01

368

High gain broadband amplification of ultraviolet pulses in optical parametric chirped pulse amplifier.  

PubMed

We report on a high gain amplification of broadband ultraviolet femtosecond pulses in an optical parametric chirped pulse amplifier. Broadband ultraviolet seed pulses were obtained by an achromatic frequency doubling of the output from a femtosecond Ti:Sapphire oscillator. Stretched seed pulses were amplified in a multipass parametric amplifier with a single BBO crystal pumped by a ns frequency quadrupled Nd:YAG laser. A noncollinear configuration was used for a broadband amplification. The total (after compression) amplification of 2.510(5) was achieved, with compressed pulse energy of 30 microJ and pulse duration of 24 fs. We found that the measured gain was limited by thermal effects induced by the absorption of the pump laser by color centers created in the BBO crystal. PMID:20588633

Wnuk, Pawe?; Stepanenko, Yuriy; Radzewicz, Czes?aw

2010-04-12

369

Design considerations for a high power, ultrabroadband optical parametric chirped-pulse amplifier.  

PubMed

A conceptual design of a high power, ultrabroadband optical parametric chirped-pulse amplifier (OPCPA) was carried out comparing nonlinear crystals (LBO and BBO) for 810 nm centered, sub-7.0 fs pulses with energies above 1 mJ. These amplifiers are only possible with a parallel development of kilowatt-level OPCPA-pump amplifiers. It is therefore important to know good strategies to use the available OPCPA-pump energy efficiently. Numerical simulations, including self- and cross-phase modulation, were used to investigate the critical parameters to achieve sufficient spectral and spatial quality. At high output powers, thermal absorption in the nonlinear crystals starts to degrade the output beam quality. Strategies to minimize thermal effects and limits to the maximum average power are discussed. PMID:24515165

Prandolini, M J; Riedel, R; Schulz, M; Hage, A; Hppner, H; Tavella, F

2014-01-27

370

Thermal properties of borate crystals for high power optical parametric chirped-pulse amplification.  

PubMed

The potential of borate crystals, BBO, LBO and BiBO, for high average power scaling of optical parametric chirped-pulse amplifiers is investigated. Up-to-date measurements of the absorption coefficients at 515 nm and the thermal conductivities are presented. The measured absorption coefficients are a factor of 10-100 lower than reported by the literature for BBO and LBO. For BBO, a large variation of the absorption coefficients was found between crystals from different manufacturers. The linear and nonlinear absorption coefficients at 515 nm as well as thermal conductivities were determined for the first time for BiBO. Further, different crystal cooling methods are presented. In addition, the limits to power scaling of OPCPAs are discussed. PMID:25089381

Riedel, R; Rothhardt, J; Beil, K; Gronloh, B; Klenke, A; Hppner, H; Schulz, M; Teubner, U; Krnkel, C; Limpert, J; Tnnermann, A; Prandolini, M J; Tavella, F

2014-07-28

371

Non-invasive monitoring of underground power cables using Gaussian-enveloped chirp reflectometry  

NASA Astrophysics Data System (ADS)

In this paper, we introduce non-invasive Gaussian-enveloped linear chirp (GELC) reflectometry for the diagnosis of live underground power cables. The GELC reflectometry system transmits the incident signal to live underground power cables via an inductive coupler. To improve the spatial resolution of the GELC reflectometry, we used the multiple signal classification method, which is a super-resolution method. An equalizer, which is based on Wiener filtering, is used to compensate for the signal distortion due to the propagation characteristics of underground power cables and inductive couplers. The proposed method makes it possible to detect impedance discontinuities in live underground power cables with high spatial resolution. Experiments to find the impedance discontinuity in a live underground power cable were conducted to verify the performance of the proposed method.

Lee, Chun Ku; Lee, Sin Ho; Chang, Seung Jin; Park, Jin Bae; Yoon, Tae Sung

2013-10-01

372

Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp  

PubMed Central

Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses. PMID:23170197

Bouillard, J.-S; Vilain, S.; Dickson, W.; Wurtz, G. A.; Zayats, A. V.

2012-01-01

373

Agile multicasting based on cascaded ?(2) nonlinearities in a step-chirped periodically poled lithium niobate.  

PubMed

We experimentally demonstrate the possibility of agile multicasting for wavelength division multiplexing (WDM) networks, of a single-channel to two and seven channels over the C band, also extendable to S and L bands. This is based on cascaded ?(2) nonlinear mixing processes, namely, second-harmonic generation (SHG)-sum-frequency generation (SFG) and difference-frequency generation (DFG) in a 20-mm-long step-chirped periodically poled lithium niobate crystal, specially designed and fabricated for a 28-nm-wide SH-SF bandwidth centered at around 1.55 ?m. The multiple idlers are simultaneously tuned by detuning the pump wavelengths within the broad SH-SF bandwidth. By selectively tuning the pump wavelengths over less than 10 and 6 nm, respectively, multicasting into two and seven idlers is successfully achieved across ~70 WDM channels within the 50 GHz International Telecommunication Union grid spacing. PMID:23903134

Ahlawat, Meenu; Bostani, Ameneh; Tehranchi, Amirhossein; Kashyap, Raman

2013-08-01

374

Impact of Mach-Zehnder Modulator Chirp on Radio over Fiber Links  

NASA Astrophysics Data System (ADS)

The impact of Mach-Zehnder modulator (MZM) chirp on single sideband (SSB) and carrier suppressed double sideband (CS-DSB) modulation radio over fiber (RoF) links are investigated and simulated. Finite extinction ratio and drive signal unbalanced ratio of non-ideal MZM are considered, power variation of target microwave signal and harmonic suppression are calculated and evaluated. Our results suggest that unbalanced ratio could be optimized to minimized the power variation owing to the finite extinction ratio and improve the harmonic suppress ratio in the two kinds of RoF links. However, harmonic suppression ratio declined rapidly with the decrease of extinction ratio in the CS-DSB RoF link. For a non-ideal modulator with low extinction ratio, high quality microwave signal could be obtained in the SSB RoF link while an additional filter is required to suppress the unwanted harmonic components in the CS-DSB RoF link.

Chen, Xiaogang; Feng, Shengqin; Huang, Dexiu

2009-07-01

375

Mechanical effect of retroreflected frequency-chirped laser pulses on two-level atoms  

SciTech Connect

We discuss the mechanical momentum transfer to two-level atoms by a pair of short, counterpropagating, frequency-chirped laser pulses, which partially overlap each other in the atomic medium. We show that such a pulse pair can induce a much greater change of momentum than pulses that do not overlap (interact separately with the atoms). The dispersive effect on the atomic velocity distribution is shown to be much smaller for the case of overlapping pulses. Furthermore, there are regimes where the method is not sensitive to the exact values of the pulse parameters or the initial velocity distribution. The interaction can be repeated for a cumulative effect, so a sequence of such pulse pairs can be used very effectively to manipulate the mechanical motion of atoms.

Demeter, G.; Djotyan, G. P.; Soerlei, Zs.; Bakos, J. S. [Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences, Konkoly-Thege Miklos ut 29-33, H-1121 Budapest (Hungary)

2006-07-15

376

Animating Transformations  

NSDL National Science Digital Library

In most introductory linear algebra courses, prominent applications of transformations or mappings are moving (rotating, reflecting, translating), resizing (contracting, expanding), changing the shape (shearing, projecting) objects in the plane. A typical problem in such courses is to write the matrix of a transformation that changes points in such prescribed ways. The goal of this demo is to help students more easily visualize such transformations on a wide class of plane objects.

Roberts, Lila F.; Hill, David R.

2003-01-24

377

Transformational Events  

ERIC Educational Resources Information Center

Transformational Events is a new pedagogic pattern that explains how innovations (and other transformations) happened. The pattern is three temporal stages: an interval of increasingly unsatisfactory ad hoc solutions to a persistent problem (the "mess"), an offer of an invention or of a new way of thinking, and a period of widespread adoption and

Denning, Peter J.; Hiles, John E.

2006-01-01

378

Generalized root-mean-square momentum method to describe chirped return-to-zero signal propagation in dispersion-managed fiber links  

Microsoft Academic Search

We present a generalized momentum method to describe evolution of the root-mean-square (rms) (averaged over time) optical pulse characteristics in dispersion-managed fiber lines. A closed system of the ordinary differential equations is derived for the rms pulse power, width, and chirp. The developed method can be useful for massive numerical simulations required to optimize wavelength-division-multiplexing dispersion-managed transmission using chirped return-to-zero

Sergei K. Turitsyn; T. Schafer; V. K. Mezentsev

1999-01-01

379

Transformation inverse design.  

PubMed

We present a new technique for the design of transformation-optics devices based on large-scale optimization to achieve the optimal effective isotropic dielectric materials within prescribed index bounds, which is computationally cheap because transformation optics circumvents the need to solve Maxwell's equations at each step. We apply this technique to the design of multimode waveguide bends (realized experimentally in a previous paper) and mode squeezers, in which all modes are transported equally without scattering. In addition to the optimization, a key point is the identification of the correct boundary conditions to ensure reflectionless coupling to untransformed regions while allowing maximum flexibility in the optimization. Many previous authors in transformation optics used a certain kind of quasiconformal map which overconstrained the problem by requiring that the entire boundary shape be specified a priori while at the same time underconstraining the problem by employing "slipping" boundary conditions that permit unwanted interface reflections. PMID:23787612

Liu, David; Gabrielli, Lucas H; Lipson, Michal; Johnson, Steven G

2013-06-17

380

Discrete Polynomial Transform for Digital Imagewatermarking Application  

Microsoft Academic Search

ABSTRACT In this study, we propose a new way to detect the image wa- termark messages,modulated,as linear chirp signals. The spread spectrum image watermarking,algorithm embeds,lin- ear chirps as watermark,messages. The phase of the chirp represents watermark,message,such that each phase corre- sponds to a different message. We extract the watermark,mes- sage using a phase detection algorithm based on Discrete Polynomial Phase

Lam Le; Sridhar Krishnan; Behnaz Ghoraani

2006-01-01

381

Optical Haar wavelet transform  

Microsoft Academic Search

An optical Haar mother wavelet is created with a SEMETEX 128 X 128 magneto-optic spatial light modulator. Two techniques for dilating the mother wavelet are explored: (1) aperture stopping and (2) operating the SLM in ternary phase-amplitude mode. Discrete resolution levels of a continuous wavelet transform are obtained by optically correlating a binarized image with multiple dilations of the mother

Thomas J. Burns; Kenneth H. Fielding; Steven K. Rogers; Steven D. Pinski; Dennis W. Ruck

1992-01-01

382

Application of multivariate chemometric techniques for simultaneous determination of five parameters of cottonseed oil by single bounce attenuated total reflectance Fourier transform infrared spectroscopy.  

PubMed

Single bounce attenuated total reflectance (SB-ATR) Fourier transform infrared (FTIR) spectroscopy in conjunction with chemometrics was used for accurate determination of free fatty acid (FFA), peroxide value (PV), iodine value (IV), conjugated diene (CD) and conjugated triene (CT) of cottonseed oil (CSO) during potato chips frying. Partial least square (PLS), stepwise multiple linear regression (SMLR), principal component regression (PCR) and simple Beer?s law (SBL) were applied to develop the calibrations for simultaneous evaluation of five stated parameters of cottonseed oil (CSO) during frying of French frozen potato chips at 170C. Good regression coefficients (R(2)) were achieved for FFA, PV, IV, CD and CT with value of >0.992 by PLS, SMLR, PCR, and SBL. Root mean square error of prediction (RMSEP) was found to be less than 1.95% for all determinations. Result of the study indicated that SB-ATR FTIR in combination with multivariate chemometrics could be used for accurate and simultaneous determination of different parameters during the frying process without using any toxic organic solvent. PMID:25127621

Talpur, M Younis; Kara, Huseyin; Sherazi, S T H; Ayyildiz, H Filiz; Topkafa, Mustafa; Arslan, Fatma Nur; Naz, Saba; Durmaz, Fatih; Sirajuddin

2014-11-01

383

Modeling of chirped pulse propagation through a mini-stop band in a two-dimensional photonic crystal waveguide  

NASA Astrophysics Data System (ADS)

The finite-difference time-domain (FDTD) and frequency-domain finite-element (FE) methods are used to study chirped pulse propagation in 2D photonic crystal (PhC) waveguides. Chirped pulse FDTD has been implemented, which allows the study of pulse propagation in a direct way. The carrier wavelength of the pulse is swept across the bandwidth of a mini-stop-band (MSB) feature, and pulse compression behavior is observed. Both round-hole and square-hole PhC waveguides are studied, with the latter giving increased pulse compression. A group-delay analysis is then used to understand the compression behavior, and this shows how the fast-light regime that occurs within the MSB plays an important role in the observed pulse compression.

Cao, Tun; Cryan, Martin J.; Ivanov, Pavel S.; Ho, Daniel; Ren, Bob; Craddock, Ian J.; Rorison, Judy M.; Railton, Chris J.

2007-07-01

384

Acoustic density measurements of consolidating cohesive sediment beds by means of a non-intrusive ``Micro-Chirp'' acoustic system  

NASA Astrophysics Data System (ADS)

A non-intrusive Micro-Chirp acoustic system and a signal-processing protocol have been developed to estimate the bulk density of consolidating cohesive sediment beds. Using high-frequency (300-700 kHz) Chirp acoustic waves, laboratory measurements were conducted with clay-water mixtures. Because acoustic echo strength is proportional to variations in acoustic impedance, and the speed of sound in the clay bed hardly changed during consolidation, the bulk density could be successfully estimated without disturbing the sediment bed. Based on acoustic signal analysis, this study demonstrates that the reflection coefficient and bulk density at the water-sediment interface increase with consolidation time, and that a single speed of sound value can be used for practical bulk density estimation in muddy environments.

Ha, Ho Kyung; Maa, Jerome P.-Y.; Holland, Charles W.

2010-12-01

385

Relativistic single-cycled short-wavelength laser pulse compressed from a chirped pulse induced by laser-foil interaction.  

PubMed

By particle-in-cell simulation and analysis, we propose a plasma approach to generate a relativistic chirped pulse based on a laser-foil interaction. When two counterpropagating circularly polarized pulses interact with an overdense foil, the driving pulse (with a larger laser field amplitude) will accelerate the whole foil to form a double-layer structure, and the scattered pulse (with a smaller laser field amplitude) is reflected by this flying layer. Because of the Doppler effect and the varying velocity of the layer, the reflected pulse is up-shifted for frequency and chirped; thus, it could be compressed to a nearly single-cycled relativistic laser pulse with a short wavelength. Simulations show that a nearly single-cycled subfemtosecond relativistic pulse can be generated with a wavelength of 0.2 ?m after dispersion compensation. PMID:20867711

Ji, L L; Shen, B F; Li, D X; Wang, D; Leng, Y X; Zhang, X M; Wen, M; Wang, W P; Xu, J C; Yu, Y H

2010-07-01

386

Chirped elliptically polarised cnoidal waves and polarisation 'chaos' in an isotropic medium with spatial dispersion of cubic nonlinearity  

SciTech Connect

It is found that chirped elliptically polarised cnoidal waves can propagate and aperiodic regimes, resembling polarisation chaos, can emerge in an isotropic medium with local and nonlocal components of cubic nonlinearity and second-order frequency dispersion. In the particular case of the formation of the waveguides of the same profile for two circularly polarised components of the light field relevant analytical solutions are derived and the frequencies of chirped components are shown to vary in concord with periodic changes of their intensities. In this case, the nature of the changes in the polarisation state during the light wave propagation depends on the values of nonlinear phase shifts of circularly polarised components of the field during the period and is sensitive to changes in the initial conditions. (nonlinear optical phenomena)

Makarov, Vladimir A; Petnikova, V M; Potravkin, N N; Shuvalov, Vladimir V

2012-12-31

387

Propagation of frequency-chirped laser pulses in a medium of atoms with a {lambda}-level scheme  

SciTech Connect

We study the propagation of frequency-chirped laser pulses in optically thick media. We consider a medium of atoms with a {lambda} level-scheme (Lambda atoms) and also, for comparison, a medium of two-level atoms. Frequency-chirped laser pulses that induce adiabatic population transfer between the atomic levels are considered. They induce transitions between the two lower (metastable) levels of the {lambda}-atoms and between the ground and excited states of the two-level atoms. We show that associated with this adiabatic population transfer in {lambda}-atoms, there is a regime of enhanced transparency of the medium--the pulses are distorted much less than in the medium of two-level atoms and retain their ability to transfer the atomic population much longer during propagation.

Demeter, G.; Dzsotjan, D.; Djotyan, G. P. [Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences, Konkoly-Thege Miklos ut 29-33, H-1121 Budapest (Hungary)

2007-08-15

388

Relativistic Single-Cycled Short-Wavelength Laser Pulse Compressed from a Chirped Pulse Induced by Laser-Foil Interaction  

SciTech Connect

By particle-in-cell simulation and analysis, we propose a plasma approach to generate a relativistic chirped pulse based on a laser-foil interaction. When two counterpropagating circularly polarized pulses interact with an overdense foil, the driving pulse (with a larger laser field amplitude) will accelerate the whole foil to form a double-layer structure, and the scattered pulse (with a smaller laser field amplitude) is reflected by this flying layer. Because of the Doppler effect and the varying velocity of the layer, the reflected pulse is up-shifted for frequency and chirped; thus, it could be compressed to a nearly single-cycled relativistic laser pulse with a short wavelength. Simulations show that a nearly single-cycled subfemtosecond relativistic pulse can be generated with a wavelength of 0.2 {mu}m after dispersion compensation.

Ji, L. L.; Shen, B. F.; Li, D. X.; Wang, D.; Leng, Y. X.; Zhang, X. M.; Wen, M.; Wang, W. P.; Xu, J. C.; Yu, Y. H. [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)

2010-07-09

389

High-power quantum-dot tapered tunable external-cavity lasers based on chirped and unchirped structures.  

PubMed

A high-power tunable external cavity laser configuration with a tapered quantum-dot semiconductor optical amplifier at its core is presented, enabling a record output power for a broadly tunable semiconductor laser source in the 1.2 - 1.3 m spectral region. Two distinct optical amplifiers are investigated, using either chirped or unchirped quantum-dot structures, and their merits are compared, considering the combination of tunability and high output power generation. At 1230 nm, the chirped quantum-dot laser achieved a maximum power of 0.62 W and demonstrated nearly 100-nm tunability. The unchirped laser enabled a tunability range of 32 nm and at 1254 nm generated a maximum power of 0.97 W, representing a 22-fold increase in output power compared with similar narrow-ridge external-cavity lasers at the same current density. PMID:25321756

Haggett, Stephanie; Krakowski, Michel; Montrosset, Ivo; Cataluna, Maria Ana

2014-09-22

390

Ultraviolet-enhanced supercontinuum generation in uniform photonic crystal fiber pumped by a giant-chirped fiber laser.  

PubMed

We report on an ultraviolet-enhanced supercontinuum generation in a uniform photonic crystal fiber pumped by a giant-chirped mode-locked Yb-doped fiber laser. We find theoretically and experimentally that the initial pluses with giant chirp leads more initial energy transferred to the dispersive waves in visible and ultraviolet wavelength. An extremely wide optical spectrum spanning from 370 nm to beyond 2400 nm with a broad 3 dB spectral bandwidth of 367 nm (from 431 nm to 798 nm) is obtained. Over 36% (350 mW) of the total output power locates in the visible and ultraviolet regime between 370 nm and 850 nm with a maximum spectral power density of 1.6 mW/nm at 550 nm. PMID:25322044

Gao, Shoufei; Wang, Yingying; Sun, Ruoyu; Li, Huihui; Tian, Cuiping; Jin, Dongchen; Wang, Pu

2014-10-01

391

All-fibre high-energy chirped-pulse laser in the 1 {mu}m range  

SciTech Connect

We report an all-fibre 1030-nm ultrashort (100 ps with the possibility of compression to 430 fs) chirped pulse laser configuration based on a seed oscillator that includes a semiconductor saturable absorber mirror, and demonstrate amplification of its pulses to an energy of 0.6 {mu}J, with the possibility of pulse compression to 650 fs. (extreme light fields and their applications)

Kotov, L V; Likhachev, M E; Bubnov, M M; Lipatov, D S; Gur'yanov, Aleksei N

2013-03-31

392

Improved transmission performance resulting from the reduced chirp of a semiconductor laser coupled to an external high-Q resonator  

Microsoft Academic Search

The improvement in the receiver sensitivity due to the reduced chirp is examined for NRZ and RZ intensity modulation, direct detection systems operating in the 1.55-?m wavelength region with conventional single-mode optical fiber. The methodology involves (a) solving modified rate equations numerically for the optical power and phase of the external resonator laser in response to an injected current waveform,

J. C. Cartledge

1990-01-01

393

Chirp reduction of directly modulated semiconductor lasers at 10 Gb\\/s by strong CW light injection  

Microsoft Academic Search

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb\\/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at

Stefan Mohrdiek; Herbert Burkhard; Herbert Walter

1994-01-01

394

Transforming California  

NSDL National Science Digital Library

Transforming California is a PowerPoint presentation of digital images (60.7 Mb) exploring the landforms found along the San Andreas Fault. Designed for classroom use, this slideshow provides a complementing narrative for each slide.

Mcguire, Thomas

2001-01-01

395

Transformative copy  

E-print Network

The ability to create an unlimited number of identical copies is a privilege of digital documents. What if that would not be the case, if each copy of a digital file would go along with some sort of transformation? This ...

Offenhuber, Dietmar

2008-01-01

396

Triple transformation  

NASA Astrophysics Data System (ADS)

A new business plan that enables policy transformation and resource mobilization at the national and international level, while improving access to resources, will allow the Green Climate Fund to integrate development goals and action on climate change.

Khan, Farrukh I.; Schinn, Dustin S.

2013-08-01

397

Covariant Transform  

NASA Astrophysics Data System (ADS)

Dedicated to the memory of Cora Sadosky The paper develops theory of covariant transform, which is inspired by the wavelet construction. It was observed that many interesting types of wavelets (or coherent states) arise from group representations which are not square integrable or vacuum vectors which are not admissible. Covariant transform extends an applicability of the popular wavelets construction to classic examples like the Hardy space H2, Banach spaces, covariant functional calculus and many others.

Kisil, Vladimir V.

2011-03-01

398

Cotton Transformation  

Microsoft Academic Search

Cotton has been cultured in vitro for 37 years, yet even today, some of the culture difficulties that were seen when it was\\u000a first cultured, namely, a very long culture time and a limited number of cultivars that can be cultured, continue to pose\\u000a problems. These inherent tissue culture limitations have made transforming cotton an arduous process. Transforming embryogenic\\u000a callus

D. R. Duncan

399

First Results Of The New Goldstone Delay-Doppler Radar Chirp Imaging System  

NASA Astrophysics Data System (ADS)

We report the first results of a new delay-Doppler radar chirp waveform system at Goldstone, which improves the range resolution by a factor of five from 18.75-m to 3.75-m. We successfully tested the new system on near-Earth asteroids (NEAs) 2010 AL30 and 2009 UN3 in January and February 2010. 2010 AL30 was a target-of-opportunity observed only three days after its discovery by LINEAR on January 10. During 2.3 hours of observations, 2010 AL30 moved between 1.0 to 0.8 lunar distances from Earth en route to a close approach of only 0.34 lunar distances. Due to this short round-trip light-travel time, the observations were bistatic with transmissions at the 70-m DSS-14 antenna and reception at the 34-m DSS-13 antenna. 2010 AL30 has a very faint absolute magnitude of 27.2, suggesting a diameter of less than 20 meters. We imaged 2010 AL30 at resolutions as high as 3.75-m, which reveal a somewhat elongated shape roughly 15-m in diameter, making 2010 AL30 the smallest NEA spatially resolved at Goldstone to date. The sequence of images shows obvious rotation that is consistent with the period of about 9 minutes reported by W. Ryan. (pers. comm.). 2009 UN3 was discovered in October 2009 by the Siding Spring Survey and approached within 0.037 AU (14 lunar distances) on February 9. We observed 2009 UN3 monostatically at Goldstone on February 8 and 9. Due to its moderate SNRs, we used chirp imaging at 15-m and 30-m resolutions, and binary-phase-coded imaging with 37.5-m resolution. The images reveal an irregular, elongated object close to 700-m in diameter. For future research, the new 3.75-m-resolution capability at Goldstone offers significant scientific potential to reveal much more detailed surface features than previously possible, to yield more detailed 3D shapes, and to substantially improve NEA orbits and long-term orbit prediction.

Slade, Martin A.; Lee, C. G.; Jao, J. S.; Benner, L. A. M.; Brozovic, M.; Giorgini, J. D.; Busch, M. W.

2010-10-01

400

Optical Haar wavelet transform  

NASA Astrophysics Data System (ADS)

An optical Haar mother wavelet is created with a SEMETEX 128 X 128 magneto-optic spatial light modulator. Two techniques for dilating the mother wavelet are explored: (1) aperture stopping and (2) operating the SLM in ternary phase-amplitude mode. Discrete resolution levels of a continuous wavelet transform are obtained by optically correlating a binarized image with multiple dilations of the mother wavelet. Frequency-plane masks for the correlation process are generated suing thermoplastic holography. Experimental results are compared with a digital simulation of the wavelet transform.

Burns, Thomas J.; Fielding, Kenneth H.; Rogers, Steven K.; Pinski, Steven D.; Ruck, Dennis W.

1992-09-01

401

DISCRETE POLYNOMIAL TRANSFORM FOR DIGITAL IMAGE WATERMARKING APPLICATION  

Microsoft Academic Search

In this study, we propose a new way to detect the image wa- termark messages modulated as linear chirp signals. The spread spectrum image watermarking algorithm embeds lin- ear chirps as watermark messages. The phase of the chirp represents watermark message such that each phase corre- sponds to a different message. We extract the watermark mes- sage using a phase

Lam Le; Sridhar Krishnan; Behnaz Ghoraani

402

The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds.  

PubMed

A diverse array of birds apparently make mechanical sounds (called sonations) with their feathers. Few studies have established that these sounds are non-vocal, and the mechanics of how these sounds are produced remains poorly studied. The loud, high-frequency chirp emitted by a male Anna's hummingbird (Calypte anna) during his display dive is a debated example. Production of the sound was originally attributed to the tail, but a more recent study argued that the sound is vocal. Here, we use high-speed video of diving birds, experimental manipulations on wild birds and laboratory experiments on individual feathers to show that the dive sound is made by tail feathers. High-speed video shows that fluttering of the trailing vane of the outermost tail feathers produces the sound. The mechanism is not a whistle, and we propose a flag model to explain the feather's fluttering and accompanying sound. The flag hypothesis predicts that subtle changes in feather shape will tune the frequency of sound produced by feathers. Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds. PMID:18230592

Clark, Christopher James; Feo, Teresa J

2008-04-22

403

Chirped pulse Raman amplifier for two-color high-intensity laser-plasma experiments  

NASA Astrophysics Data System (ADS)

The interactions of high-intensity lasers with a plasma are troubled by instabilities. A two-color laser pulse can be used to control these instabilities, but the intensities necessary to do this require that both colors have powers on the order of terawatts. Here, we present a scheme for generating terawatt, two-color laser pulses by using a three-stage amplifier system based on the stimulated Raman scattering of a chirped pulse. The first two stages consist of a Raman-shifter and a Raman-amplifier---two barium nitrate crystals---which works by first Stokes'-scattering a low-energy seed in the first crystal and then amplifying the seed via four-wave mixing to a few millijoules in the second crystal. The amplified first Stokes' pulse is then to be further amplified by a conventional Ti:Sapph crystal in a 6-pass bowtie configuration. The amplified beam has a peak wavelength of 873 nm and is to be compressed to the bandwidth limit (50 fs). It will then be re-combined with a conventionally generated TW laser centered at 800 nm and will be sent into the plasma.

Sanders, James Jc; Grigsby, Franklin; Zgadzaj, Rafal; Downer, Michael

2010-03-01

404

Thermal-dynamical analysis of blister formation in chirped mirror irradiated by single femtosecond lasers.  

PubMed

The laser-induced damage behaviors of chirped mirrors (CMs) are studied by single 800 nm, 38 fs lasers. The CMs provide group delay dispersion of around -60??fs and average reflectivity of about 99.4% with bandwidth range of 200-300 nm at a central wavelength of 800 nm. Interestingly, a circular blister feature appears in the CMs at a wide range of laser fluence. An optical microscope, atomic force microscope, scanning electron microscope, and surface profiler are applied to describe the blister characteristics. An adiabatic expansion model of ideal gas is adopted to illustrate the formation dynamics of blisters. The evolution of blisters can be explained by partial evaporation of the film and a subsequent gas expansion, driving the bulging of the film stack up to the stress limit, where the blister fractures. According to this model, the energy absorption ratio of blisters increases monotonously with increasing laser fluence before the occurrence of the focal spot confinement effect. PMID:24922225

Chen, Shunli; Gao, Pengpeng; Zhao, Yuanan; Wang, Yanzhi; Fang, Zhou; Leng, Yuxin; Shao, Jianda

2014-05-20

405

The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds  

PubMed Central

A diverse array of birds apparently make mechanical sounds (called sonations) with their feathers. Few studies have established that these sounds are non-vocal, and the mechanics of how these sounds are produced remains poorly studied. The loud, high-frequency chirp emitted by a male Anna's hummingbird (Calypte anna) during his display dive is a debated example. Production of the sound was originally attributed to the tail, but a more recent study argued that the sound is vocal. Here, we use high-speed video of diving birds, experimental manipulations on wild birds and laboratory experiments on individual feathers to show that the dive sound is made by tail feathers. High-speed video shows that fluttering of the trailing vane of the outermost tail feathers produces the sound. The mechanism is not a whistle, and we propose a flag model to explain the feather's fluttering and accompanying sound. The flag hypothesis predicts that subtle changes in feather shape will tune the frequency of sound produced by feathers. Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds. PMID:18230592

Clark, Christopher James; Feo, Teresa J

2008-01-01

406

Laser-generated proton bunches from chirped laser-plasma interaction  

NASA Astrophysics Data System (ADS)

Detailed single- and many-particle calculations are carried out for the acceleration of protons employing linearly-polarized plane-wave and tightly-focused chirped laser pulses of several ten to several hundred femtosecond durations, petawatt peak powers and relativistic peak intensities of the order of 10^21-10^22 W/cm^2 [1,2]. Analytic and numerical methods of calculation are used in the single-particle cases (in vacuum), and particle-in-cell (pic) simulations (under-dense plasma) are employed in the many-particle investigations, without and with electromagnetic particle-particle interactions, respectively. Feasibility of generating ultra-intense (10^7 particles per bunch) and phase-space collimated beams of protons is demonstrated. Interaction of the protons with the quasi-static part of the laser pulse allows the particles to gain sufficient kinetic energy (around 250 MeV) required for such applications as hadron cancer therapy.[4pt] [1] B. J. Galow, Y. I. Salamin, T. V. Liseykina, Z. Harman, and C. H. Keitel, Phys. Rev. Lett. 107, 185002 (2011)[0pt] [2] Y. I. Salamin, J.-X. Li, B. J. Galow, Z. Harman, and C. H. Keitel, submitted (2012)

Galow, Benjamin; Salamin, Yousef; Liseykina, Tatyana; Harman, Zoltan; Li, Jian-Xing; Keitel, Christoph

2012-06-01

407

Photon-counting chirped amplitude modulation lidar using a smart premixing method.  

PubMed

We proposed a new premixing method for photon-counting chirped amplitude modulation lidar (PCCAML). Earlier studies used the counting results of the returned signal detected by a Geiger mode avalanche photodiode detector (Gm-APD) to mix with the reference signal, called the postmixing method. We use an alternative method known as the premixing method, in which the reference signal is used to directly modulate the sampling gate width of the Gm-APD, and the mixing of the returned signal and the reference signal is completed before the Gm-APD. This premixing method is more flexible and may perform better than the postmixing method in terms of signal-to-noise ratio by cutting down a separated mixer commonly used in the postmixing lidar system. Furthermore, this premixing method lowers the demand for the sampling frequency of the Gm-APD. It allows the use of a much wider modulation bandwidth to improve the range accuracy and resolution. To the best of our knowledge, this is the first report to use the premixing method in the PCCAML system, which will benefit future lidar applications. PMID:24177101

Zhang, Zijing; Zhang, Jianlong; Wu, Long; Zhang, Yong; Zhao, Yuan; Su, Jianzhong

2013-11-01

408

Laser adiabatic manipulation of the bond length of diatomic molecules with a single chirped pulse.  

PubMed

We propose and test numerically a scheme for controlling the bond distance in a diatomic molecule that requires the use of a single chirped pulse. The laser prepares a superposition state of both nuclear and electronic degrees of freedom, where the main character of the electronic wave function is that of an excited dissociative state. The main limitation of the scheme is the need of ultra broadband pulses, where the bandwidth must be of the order of the dissociation energy to achieve large bond elongations. The scheme can be used to deform the bond during the laser excitation to an arbitrary large and constant value, or to allow slow time-dependent bond elongations. Additionally, the scheme can be used to prepare highly excited vibrational wave packets in the ground potential after the pulse is switched off, at the expense of losing some population that dissociates. These wave packets are initially localized at the outer well of the potential, at energies controllable by the excitation process. PMID:21495751

Chang, Bo Y; Shin, Seokmin; Santamaria, Jesus; Sola, Ignacio R

2011-04-14

409

Enhancement of EM-Ionosphere interaction through Plasma Lens and Frequency Chirping  

NASA Astrophysics Data System (ADS)

During ionospheric modification, both satellite beacons and sky maps from digital ionosonde measurements have detected large-density perturbation. This perturbation reaches a maximum when the incident HF matches the plasma frequency on the density plateau (or at f_oF2 layer). Experiments and theories are presented which describe how a plasma lens can be created at a lower altitude by pre-conditioning the ionosphere at a lower altitude; the lowering of plasma density at the center of the heated region causes a change in the index of refraction, thereby forming an equivalent ionospheric lens^1. Unlike earlier results obtained at Arecibo Observatory^2 using water molecules injected by a rocket, our concept is simpler and can be repeated many times. Another enhancement of interaction comes from the chirping of the heating frequency such that all the waves converge at the resonant layer at a particular time^3. Work supported by SDSU. ^1 A.Y. Wong, Proceedings of Ionsopheric Interactions Workshop, Santa Fe, NM, April, 2002. ^2 M. Sulzer, private communication. ^3 S. Cowley and E. Valeo, private communication.

Pau, J.; Wong, A. Y.; Rosenthal, G.; Koziar, K. E.; Stone, K.

2002-11-01

410

Time-resolved detection of the CF3 photofragment using chirped QCL radiation.  

PubMed

This paper demonstrates how a quantum cascade laser (QCL) in its intrapulse mode can provide a simple method for probing the products of a photolysis event. The system studied is the 266 nm photodissociation of CF3I with the CF3 fragments subsequently detected using radiation at approximately 1253 cm(-1) generated by a pulsed QCL. The tuning range provided by the frequency down-chirp of the QCL operated in its intrapulse mode allows a approximately 1 cm(-1) segment of the CF3 nu3 band to be measured following each photolysis laser pulse. Identification of features within this spectral region allows the CF3 ( v = 0) number density to be calculated as a function of pump-probe delay, and consequently the processes which populate and deplete this quantum state may be examined. Rate constants for the population cascade from higher vibrational levels into the v = 0 state, k 1, and for the recombination of the CF3 radicals to form C2F6, k2, are measured. The returned values of k1 = (2.3 +/- 0.34) x 10(-12) cm(3) molecule(-1) s(-1) and k2 = (3.9 +/- 0.34) x 10(-12) cm(3) molecule(-1) s(-1) are found to be in good agreement with reported literature values. PMID:18781727

Hancock, G; Horrocks, S J; Ritchie, G A D; Helden, J H van; Walker, R J

2008-10-01

411

Bayesian comparison of post-Newtonian approximations of gravitational wave chirp signals  

SciTech Connect

We estimate the probability of detecting a gravitational wave signal from coalescing compact binaries in simulated data from a ground-based interferometer detector of gravitational radiation using Bayesian model selection. The simulated wave form of the chirp signal is assumed to be a spinless post-Newtonian (PN) wave form of a given expansion order, while the searching template is assumed to be either of the same post-Newtonian family as the simulated signal or one level below its post-Newtonian expansion order. Within the Bayesian framework, and by applying a reversible jump Markov Chain Monte Carlo simulation algorithm, we compare PN1.5 vs PN2.0 and PN3.0 vs PN3.5 wave forms by deriving the detection probabilities, the statistical uncertainties due to noise as a function of the signal-to-noise ratio, and the posterior distributions of the parameters. Our analysis indicates that the detection probabilities are not compromised when simplified models are used for the comparison, while the accuracies in the determination of the parameters characterizing these signals can be significantly worsened, no matter what the considered post-Newtonian order expansion comparison is.

Umstaetter, Richard; Tinto, Massimo [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)

2008-04-15

412

The Community-based Healthy-lifestyle Intervention for Rural Preschools (CHIRP) Study: Design and Methods  

PubMed Central

The CHIRP Study is a two-arm, pilot randomized controlled trial assessing the effectiveness of a behavioral family weight management intervention in an important and at-risk population, overweight young children, 3 to 6 years of age, and their parents from underserved rural counties. Participants will include 96 parent-child dyads living in rural counties in north central Florida. Families will be randomized to one of two conditions: (a) Behavioral Family Based Intervention or (b) a Waitlist Control. Child and parent participants will be assessed at baseline (month 0), post-treatment (month 4), and follow-up (month 10). Assessments and intervention sessions will be held at the Cooperative Extension office in each participating rural county. The primary outcome measure is change in child body mass index (BMI) z-score. Additional key outcome measures include child dietary intake, physical activity, and parent BMI. This study is unique because (1) it is one of the few randomized controlled trails examining a behavioral family intervention to address healthy habits and improved weight status in young overweight and obese children, (2) addresses health promotion in rural settings, (3) examines intervention delivery in real world community settings through the Cooperative Extension Service offices. If successful, this research has potential implications for medically underserved rural communities and preventative health services for young children and their families. PMID:23183252

Janicke, David M.; Lim, Crystal S.; Mathews, Anne E.; Shelnutt, Karla P.; Boggs, Stephen R.; Silverstein, Janet H.; Brumback, Babette A.

2012-01-01

413

The community-based healthy-lifestyle intervention for rural preschools (CHIRP) study: design and methods.  

PubMed

The CHIRP study is a two-arm, pilot randomized controlled trial assessing the effectiveness of a behavioral family weight management intervention in an important and at-risk population, overweight young children, 3 to 6 years of age, and their parents from underserved rural counties. Participants will include 96 parent-child dyads living in rural counties in north central Florida. Families will be randomized to one of two conditions: (a) behavioral family based intervention or (b) a waitlist control. Child and parent participants will be assessed at baseline (month 0), post-treatment (month 4), and follow-up (month 10). Assessments and intervention sessions will be held at the Cooperative Extension office in each participating rural county. The primary outcome measure is change in child body mass index (BMI) z-score. Additional key outcome measures include child dietary intake, physical activity, and parent BMI. This study is unique because (1) it is one of the few randomized controlled trails examining a behavioral family intervention to address healthy habits and improved weight status in young overweight and obese children, (2) addresses health promotion in rural settings, and (3) examines intervention delivery in real world community settings through the Cooperative Extension Service offices. If successful, this research has potential implications for medically underserved rural communities and preventative health services for young children and their families. PMID:23183252

Janicke, David M; Lim, Crystal S; Mathews, Anne E; Shelnutt, Karla P; Boggs, Stephen R; Silverstein, Janet H; Brumback, Babette A

2013-03-01

414

Applications of some transformations for several variable-coefficient nonlinear evolution equations from plasma physics, arterial mechanics, nonlinear optics and Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

Variable-coefficient nonlinear evolution equations have occurred in such fields as plasma physics, arterial mechanics, nonlinear optics and Bose-Einstein condensates. This paper is devoted to giving some transformations to convert the original nonlinear evolution equations, e.g., the variable-coefficient nonlinear Schrdinger, generalized Gardner and variable-coefficient Sawada-Kotera equations to simpler ones or even constant-coefficient ones. Based on some constraints, we simplify the original equations and derive the associated chirp solitons, Lax pairs, and Bcklund transformations from the original equations by means of the aforementioned transformations.

Shan, Wen-Rui; Tian, Bo

2012-12-01

415

Validation of FBGs sensors C-PFM multiplexing and interrogation technique  

Microsoft Academic Search

In this paper, we propose an improvement of the Chirped-Pulsed Frequency Modulation (C-PFM) FBGs reading technique [8] as supported by new experimental results. The C-PFM technique, which was basically translated from its counterpart in the field of radar signal analysis, exploits the intensity modulation of the probe signal (the light traveling along the fiber in our case) by means of

L. Rossi; G. Breglio; A. Cusano; A. Irace; V. Pascazio; A. Cutolo

2007-01-01

416

SHARP transformation  

NASA Astrophysics Data System (ADS)

The U.S. Navy"s SHAred Reconnaissance Pod (SHARP) employs the Recon/Optical, Inc. (ROI) CA-279 dual spectral band (visible/IR) digital cameras operating from an F-18E/F aircraft to perform low-to-high altitude reconnaissance missions. SHARP has proven itself combat worthy, with a rapid transition from development to operational deployment culminating in a highly reliable and effective reconnaissance capability for joint forces operating in Operation Iraqi Freedom (OIF). The U.S. Navy"s intelligence, surveillance and reconnaissance (ISR) roadmap transforms the SHARP system from being solely an independent reconnaissance sensor to a node in the growing Joint ISR network. ROI and the U.S. Navy have combined their resources to ensure the system"s transformation continues to follow the ISR road map. Pre-planned product improvements (P3I) for the CA-270 camera systems will lead the way in that transformation.

Wyatt, Stephan

2004-08-01

417

Fourier Transform Pairs The Fourier transform transforms a function of  

E-print Network

Fourier Transform Pairs The Fourier transform transforms a function of time, f(t), into a function of frequency, F(s): F {f(t)}(s) = F(s) = Z - f(t)e- j2st dt. The inverse Fourier transform transforms a func. The inverse Fourier transform of the Fourier trans- form is the identity transform: f(t) = Z - Z - f()e- j2s

Masci, Frank

418

Exploring Transformations  

NSDL National Science Digital Library

In this activity, students will explore transformations of an absolute value function. Step by step instructions guide students in using graphing calculators to examine the effect that stretching and translating has on the coordinates of the graph. Teacher notes and a worksheet are also included to aid in teaching this lesson.

2011-11-25

419

Transformation & Metamorphosis  

ERIC Educational Resources Information Center

The sculptures of Canadian artist Brian Jungen are a great inspiration for a lesson on creating new forms. Jungen transforms found objects into unique creations without fully concealing their original form or purpose. Frank Stella's sculpture series, including "K.132,2007" made of stainless steel and spray paint, is another great example of

Lott, Debra

2009-01-01

420

Transforming Schools.  

ERIC Educational Resources Information Center

The authors in this book address the issues that relate to the crisis in American education and review some of the proposed solutions. To transform education, schools must be examined as social systems that are interrelated with families, communities, and the world of work. Following the introduction, section 1, "Conditions for Educational

Cookson, Peter W., Jr., Ed.; Schneider, Barbara, Ed.

421

Transformation Optics  

NASA Astrophysics Data System (ADS)

Transformation optics applies ideas from Einstein's general theory of relativity in optical and electrical engineering for designing devices that can do the (almost) impossible: invisibility cloaking, perfect imaging, levitation, and the creation of analogues of the event horizon. This chapter gives an introduction to this field requiring minimal prerequisites.

Leonhardt, Ulf

422

A Comparison of FTNMR and FTIR Techniques.  

ERIC Educational Resources Information Center

Nuclear magnetic resonance and infrared are two spectroscopic methods that commonly use the Fourier transform technique. Discussed are the similarities and differences in the use of the Fourier transform in these two spectroscopic techniques. (CW)

Ahn, Myong-Ku

1989-01-01

423

Study of lignification by noninvasive techniques in growing maize internodes. An investigation by Fourier transform infrared cross-polarization-magic angle spinning 13C-nuclear magnetic resonance spectroscopy and immunocytochemical transmission electron microscopy.  

PubMed Central

Noninvasive techniques were used for the study in situ of lignification in the maturing cell walls of the maize (Zea mays L.) stem. Within the longitudinal axis of a developing internode all of the stages of lignification can be found. The synthesis of the three types of lignins, p-hydroxyphenylpropane (H), guaiacyl (G), and syringyl (S), was investigated in situ by cross-polarization-magic angle spinning 13C-solid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, and immunocytochemical electron microscopy. The first lignin appearing in the parenchyma is of the G-type preceeding the incorporation of S nuclei in the later stages. However, in vascular bundles, typical absorption bands of S nuclei are visible in the Fourier transform infrared spectra at the earliest stage of lignification. Immunocytochemical determination of the three types of lignin in transmission electron microscopy was possible thanks to the use of antisera prepared against synthetic H, G, and the mixed GS dehydrogenative polymers (K. Ruel, O. Faix, J.P. Joseleau [1994] J Trace Microprobe Tech 12: 247-265). The specificity of the immunological probes demonstrated that there are differences in the relative temporal synthesis of the H, G, and GS lignins in the different tissues undergoing lignification. Considering the intermonomeric linkages predominating in the antigens used for the preparation of the immunological probes, the relative intensities of the labeling obtained provided, for the first time to our knowledge, information about the macromolecular nature of lignins (condensed versus noncondensed) in relation to their ultrastructural localization and development stage. PMID:9232887

Joseleau, J P; Ruel, K

1997-01-01

424

The IHS Transformations Based Image Fusion  

E-print Network

The IHS sharpening technique is one of the most commonly used techniques for sharpening. Different transformations have been developed to transfer a color image from the RGB space to the IHS space. Through literature, it appears that, various scientists proposed alternative IHS transformations and many papers have reported good results whereas others show bad ones as will as not those obtained which the formula of IHS transformation were used. In addition to that, many papers show different formulas of transformation matrix such as IHS transformation. This leads to confusion what is the exact formula of the IHS transformation?. Therefore, the main purpose of this work is to explore different IHS transformation techniques and experiment it as IHS based image fusion. The image fusion performance was evaluated, in this study, using various methods to estimate the quality and degree of information improvement of a fused image quantitatively.

Al-Wassai, Firouz Abdullah; Al-Zuky, Ali A

2011-01-01

425

Using a linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers  

NASA Astrophysics Data System (ADS)

When seeding a high power fiber amplifier with a frequency-chirped seed, the backward Brillouin scattering can be kept at the spontaneous level because the coherent laser/Stokes interaction is interrupted. Operating a conventional vertical cavity surface-emitting diode laser in an optoelectronic feedback loop can yield a linear frequency chirp of ~1016 Hz/s at a constant output power. The simple and deterministic variation of phase with time preserves temporal coherence, in the sense that it is straightforward to coherently combine multiple amplifiers despite a large length mismatch. The seed bandwidth as seen by the counter-propagating SBS is large, and also increases linearly with fiber length, resulting in a nearly-length-independent SBS threshold. Experimental results at the 600W level will be presented. The impact of a chirped seed on multimode instability is also addressed theoretically.

White, Jeffrey O.; Petersen, Eliot; Edgecumbe, J.; Rakuljic, George; Satyan, Naresh; Vasilyev, Arseny; Yariv, A.

2014-03-01

426

Flat-top picosecond pulses generated by chirped spectral modulation from a Nd:YLF regenerative amplifier for pumping few-cycle optical parametric amplifiers.  

PubMed

In this paper we present an optically synchronized Nd:YLF regenerative amplifier optimized for use as a preamplifier in a few-cycle optical parametric chirped pulse amplification pump laser. In the pump amplification process we employ a combination of spectral modulation and chirping in order to control and optimize the temporal shape of the pulses. We report on a comparative study of two methods for generating near-flat-top or custom real-time variable-shaped pump pulses using either controlled chirp and shaping of the spectrum of the pulses seeding a regenerative amplifier or intracavity spectral filtering to broaden the gain bandwidth of the system. We show that in addition to minimizing gain narrowing and B-integral, the efficiency of the cascaded nonlinear processes of the parametric amplifiers can be increased. PMID:24787185

Mecseki, Katalin; Bigourd, Damien; Patankar, Siddharth; Stuart, Nicholas H; Smith, Roland A

2014-04-01

427

Transformations Journal  

NSDL National Science Digital Library

Different forms of communication have always had a tendency to transform interactions and everyday life in ways that have surprised people from many different backgrounds. Academics have long been interested in such dynamic transformations, and this electronic journal represents one of the responses to such processes. As their site notes, this journal is "dedicated to the exploration of ideas, issues and debates emerging out of contemporary global culture." Visitors to the site can read the complete version of every issue on the site, and they will be pleased to find such intriguing titles as "Rethinking Regionality", "Accidental Environments", and "Fleeing the City". Interested parties can also consult the site to learn about the journal's editorial board, their calls for papers, submission guidelines, and related links.

428

Pulse transformers  

Microsoft Academic Search

Pulse transformers capable of transmitting substantially rectangular voltage pulses, with durations of less than one microsecond, were developed for radar applications during World War II. Their primary functions were to match the impedances of high-power microwave radio-frequency electron-tube generators to electronic pulse generators and coaxial transmission cables, and to provide polarity reversal and impedance matching functions within pulse generator circuitry.

H. Lord

1971-01-01

429

Fiber-optic chirped FBG for distributed thermal monitoring of ex-vivo radiofrequency ablation of liver.  

PubMed

A linearly chirped fiber Bragg grating (LCFBG) has been used as a temperature sensor for online monitoring of radiofrequency thermal ablation (RFTA). The LCFBG acts as a distributed sensor, with spatial resolution of 75 ?m. A white-light setup that records the LCFBG spectrum estimates the temperature profile in real time. Three RFTA experiments have been performed ex-vivo on porcine liver measuring the radial temperature distribution during the heating process. The analysis of thermal maps quantifies the spatial heat distribution along the measurement axis and determines the ablation efficiency. PMID:24940541

Tosi, Daniele; Macchi, Edoardo Gino; Gallati, Mario; Braschi, Giovanni; Cigada, Alfredo; Rossi, Sandro; Leen, Gabriel; Lewis, Elfed

2014-06-01

430

Near-infrared resonance-mediated chirp control of a coherently generated broadband deep-ultraviolet spectrum  

SciTech Connect

We investigate the use of shaped near-infrared (NIR) femtosecond pulses to control the generation of coherent broadband deep-ultraviolet (DUV) radiation in an atomic resonance-mediated (2+1) three-photon excitation to a broad far-from-resonance continuum. Previously, we have shown control over the total emitted DUV yield. Here, we experimentally demonstrate phase control over the spectral characteristics (central frequency and bandwidth) of the emitted broadband DUV radiation. It is achieved by tuning the linear chirp applied to the exciting NIR femtosecond pulse. The study is conducted with Na vapor.

Rybak, Leonid; Chuntonov, Lev; Gandman, Andrey; Shakour, Naser; Amitay, Zohar [Shirlee Jacobs Femtosecond Laser Research Laboratory, Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 32000 (Israel)

2011-09-15

431

Fiber-optic chirped FBG for distributed thermal monitoring of ex-vivo radiofrequency ablation of liver  

PubMed Central

A linearly chirped fiber Bragg grating (LCFBG) has been used as a temperature sensor for online monitoring of radiofrequency thermal ablation (RFTA). The LCFBG acts as a distributed sensor, with spatial resolution of 75 ?m. A white-light setup that records the LCFBG spectrum estimates the temperature profile in real time. Three RFTA experiments have been performed ex-vivo on porcine liver measuring the radial temperature distribution during the heating process. The analysis of thermal maps quantifies the spatial heat distribution along the measurement axis and determines the ablation efficiency. PMID:24940541

Tosi, Daniele; Macchi, Edoardo Gino; Gallati, Mario; Braschi, Giovanni; Cigada, Alfredo; Rossi, Sandro; Leen, Gabriel; Lewis, Elfed

2014-01-01

432

High peak-power monolithic femtosecond ytterbium fiber chirped pulse amplifier with a spliced-on hollow core fiber compressor.  

PubMed

We demonstrate a monolithic Yb-fiber chirped pulse amplifier that uses a dispersion matched fiber stretcher and a spliced-on hollow core photonic bandgap fiber compressor. For an output energy of 77 nJ, 220 fs pulses with 92% of the energy contained in the main pulse, can be obtained with minimal nonlinearities in the system. 135 nJ pulses are obtained with 226 fs duration and 82 percent of the energy in the main pulse. Due to the good dispersion match of the stretcher to the hollow core photonic bandgap fiber compressor, the duration of the output pulses is within 10% of the Fourier limited duration. PMID:25090494

Verhoef, A J; Jespersen, K; Andersen, T V; Grner-Nielsen, L; Flry, T; Zhu, L; Baltuka, A; Fernndez, A

2014-07-14

433

Rainbow Fourier Transform  

NASA Technical Reports Server (NTRS)

We present a novel technique for remote sensing of cloud droplet size distributions. Polarized reflectances in the scattering angle range between 135deg and 165deg exhibit a sharply defined rainbow structure, the shape of which is determined mostly by single scattering properties of cloud particles, and therefore, can be modeled using the Mie theory. Fitting the observed rainbow with such a model (computed for a parameterized family of particle size distributions) has been used for cloud droplet size retrievals. We discovered that the relationship between the rainbow structures and the corresponding particle size distributions is deeper than it had been commonly understood. In fact, the Mie theory-derived polarized reflectance as a function of reduced scattering angle (in the rainbow angular range) and the (monodisperse) particle radius appears to be a proxy to a kernel of an integral transform (similar to the sine Fourier transform on the positive semi-axis). This approach, called the rainbow Fourier transform (RFT), allows us to accurately retrieve the shape of the droplet size distribution by the application of the corresponding inverse transform to the observed polarized rainbow. While the basis functions of the proxy-transform are not exactly orthogonal in the finite angular range, this procedure needs to be complemented by a simple regression technique, which removes the retrieval artifacts. This non-parametric approach does not require any a priori knowledge of the droplet size distribution functional shape and is computationally fast (no look-up tables, no fitting, computations are the same as for the forward modeling).

Alexandrov, Mikhail D.; Cairns, Brian; Mishchenko, Michael I.

2012-01-01

434

COMPONENTS AND PARAMETERS OF LASER SYSTEMS: Use of nonlinear dynamic spectroscopy in determination of the chirp of picosecond pulses generated in a neodymium phosphate glass laser  

NASA Astrophysics Data System (ADS)

A nonlinear dynamic spectrograph with a time resolution of 0.1 psec and a spectral resolution of 0.02 nm was used to determine the chirp of picosecond pulses generated in a neodymium phosphate glass laser emitting at the wavelength of 1.054 . A time scan was obtained employing a nonlinear LiIO3 crystal together with conversion of the investigated radiation to the visible range, where dynamic spectrograms were recorded. It was established that the chirp amplitude increased at the end of a train of pulses to 1.5 nm/psec.

Gurzadyan, G. G.; Gyuzalyan, R. N.; Zakharkin, I. S.

1987-08-01

435

160-Gb/s all-optical phase-transparent wavelength conversion through cascaded SFG-DFG in a broadband linear-chirped PPLN waveguide.  

PubMed

We experimentally demonstrated ultra-fast phase-transparent wavelength conversion using cascaded sum- and difference-frequency generation (cSFG-DFG) in linear-chirped periodically poled lithium niobate (PPLN). Error-free wavelength conversion of a 160-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) signal was successfully achieved. Thanks to the enhanced conversion bandwidth in the PPLN with linear-chirped periods, no optical equalizer was required to compensate the spectrum distortion after conversion, unlike a previous demonstration of 160-Gb/s RZ on-off keying (OOK) using fixed-period PPLN. PMID:20389627

Lu, Guo-Wei; Shinada, Satoshi; Furukawa, Hideaki; Wada, Naoya; Miyazaki, Tetsuya; Ito, Hiromasa

2010-03-15

436

A Primer of Fourier Transform NMR.  

ERIC Educational Resources Information Center

Fourier transform nuclear magnetic resonance (NMR) is a new spectroscopic technique that is often omitted from undergraduate curricula because of lack of instructional materials. Therefore, information is provided to introduce students to the technique of data collection and transformation into the frequency domain. (JN)

Macomber, Roger S.

1985-01-01

437

Generalized fractional S-transform and its application to discriminate environmental background acoustic noise signals  

NASA Astrophysics Data System (ADS)

We propose a modification of S-transform (ST) by changing the kernel of Fourier transform (FT) with that of fractional Fourier transform (FRFT) and call it generalized fractional ST (GFST). The FRFT is a generalization of FT and it has been shown more useful than the FT for signals with changing frequencies such as chirp signals. The proposed GFST is applied to analyze and classify different environmental background sound mixed with speech signal in the form of additive noise. The simulation results demonstrate that Euclidean distance between the feature vectors computed from generalized fractional ST corresponding to different background noise is increased as compared to ST for the same set of feature vectors and signals.

Jhanwar, D.; Sharma, K. K.; Modani, S. G.

2014-07-01

438

Hamlet's Transformation.  

NASA Astrophysics Data System (ADS)

William Shakespeare's Hamlet has much evidence to suggest that the Bard was aware of the cosmological models of his time, specifically the geocentric bounded Ptolemaic and Tychonic models, and the infinite Diggesian. Moreover, Shakespeare describes how the Ptolemaic model is to be transformed to the Diggesian. Hamlet's "transformation" is the reason that Claudius, who personifies the Ptolemaic model, summons Rosencrantz and Guildenstern, who personify the Tychonic. Pantometria, written by Leonard Digges and his son Thomas in 1571, contains the first technical use of the word "transformation." At age thirty, Thomas Digges went on to propose his Perfit Description, as alluded to in Act Five where Hamlet's age is given as thirty. In Act Five as well, the words "bore" and "arms" refer to Thomas' vocation as muster-master and his scientific interest in ballistics. England's leading astronomer was also the father of the poet whose encomium introduced the First Folio of 1623. His oldest child Dudley became a member of the Virginia Company and facilitated the writing of The Tempest. Taken as a whole, such manifold connections to Thomas Digges support Hotson's contention that Shakespeare knew the Digges family. Rosencrantz and Guildenstern in Hamlet bear Danish names because they personify the Danish model, while the king's name is latinized like that of Claudius Ptolemaeus. The reason Shakespeare anglicized "Amleth" to "Hamlet" was because he saw a parallel between Book Three of Saxo Grammaticus and the eventual triumph of the Diggesian model. But Shakespeare eschewed Book Four, creating this particular ending from an infinity of other possibilities because it "suited his purpose," viz. to celebrate the concept of a boundless universe of stars like the Sun.

Usher, P. D.

1997-12-01

439

Rotary Transformer  

NASA Technical Reports Server (NTRS)

None given. From first Par: Many spacecraft (S/C) and surface rovers require the transfer of signals and power across rotating interfaces. Science instruments, antennas and solar arrays are elements needing rotary power transfer for certain (S/C) configurations. Delivery of signal and power has mainly been done by using the simplest means, the slip ring approach. This approach, although simple, leaves debris generating noise over a period of time...The rotary transformer is a good alternative to slip rings for signal and power transfer.

McLyman, Colonel Wm. T.

1996-01-01

440

Ultrabroadband optical parametric chirped-pulse amplifier using a fan-out periodically poled crystal with spectral spatial dispersion  

SciTech Connect

Based on the full two-dimensional characteristics of the quasi-phase-matched fan-out periodically poled crystal, a scalable and engineerable scheme for ultrabroadband optical parametric chirped-pulse amplification is proposed, which can significantly broaden the gain bandwidth by the spatial separation of different frequency components of the signal pulse and manipulation of the distribution of the pump beam along the fan-out direction of the crystal. The theoretical analysis shows that the signal pulse can be amplified with minimal spectrum narrowing, and the initial spectrum can be broadened considerably if needed. Based on this scheme, using a fan-out periodically poled 5% mol MgO-doped congruent lithium niobate with a configuration of 5x0.5x5 mm{sup 3} and two pump beams, the 3.3-{mu}m middle-infrared ultrabroadband optical parametric chirped-pulse amplifier is designed. The numerical computation results confirm that the -3 dB gain bandwidth of this amplifier exceeds 320 nm and can be further broadened.

Chen Liezun; Wang Youwen [Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, School of Information Science and Engineering, Hunan University, Changsha 410082 (China); Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008 (China); Wen Shuangchun; Fan Dianyuan [Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, School of Information Science and Engineering, Hunan University, Changsha 410082 (China); You Kaiming [Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008 (China); Qian Liejia [Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China)

2010-10-15

441

Chirp-managed lasers as cost-efficient transmitters for 10-Gbit/s WDM-PONs  

NASA Astrophysics Data System (ADS)

Chirp-managed lasers (CML) are demonstrated as simple low-cost transmitter with high tolerance to chromatic dispersion. This manuscript proposes the use of CML as cost-effective downstream (DS) transmitters for next generation access networks. The laser chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now used to generate differential phase-shift keying (DPSK) modulation format by direct modulation. The network architecture using CML as downstream DPSK transmitter is proposed. Bit error-rate measurement showed that an optical power budget of 36 dB could be obtained with direct phase-shift keying modulation ofCML which proves that the proposed solution is a strong candidate for future WDM-PONs. Budget-extended WDM-PON configuration is also demonstrated using Saturated Collision Amplifier, which is an amplification scheme that uses SOA saturation in order to maximize the output power and minimize the ASE noise and the polarization sensitivity. The extension scheme is demonstrated for four-wavelength 10 Gbit/s unidirectional downstream configuration with 60-dB maximum total optical budget for each wavelength.

Le, Quang Trung; Emsia, Ali; Briggmann, Dieter; Kppers, Franko

2013-01-01

442

Dynamics and structure of the vertical ionospheric disturbances caused by Tohoku earthquake according to Irkutsk bistatic CHIRP-sounding  

NASA Astrophysics Data System (ADS)

In the work we present results of observation of the mid-scale vertical ionospheric irregularities caused by Tohoku earthquake with 1 minute temporary resolution. Their spatial and temporary dynamics is also investigated. The main instrument used in the analysis is bistatic CHIRP-sounder of own development of ISTP SB RAS. The CHIRP-sounder provides frequency change speed up to 1000 kHz/sec, and provides 1 minute temporal resolution, comparable with SuperDARN radars and GPS receivers network. The receiver and the transmitter of the sounder are located close to Irkutsk (52N,104E) at distance 120 km between each other. Synchronization of time and frequency is provided by GPS. As showed the analysis of the experimental data, the main response of the ionosphere was observed at Irkutsk from 06:10 to 07:00UT. Short-term variations of the electron density profile were also observed from 06:00UT. This corresponds to the main horizontal speed of disturbances about 2500 m/s and below. The vertical scale of the irregularities was 10-20 km. Irregularities practically weren't observed at heights above 200km. The obtained data don't contradict the data obtained by other researchers. Work was done under financial support of IV.12.2 OFN Russian Academy of Sciences program.

Berngardt, Oleg; Kotovich, Galina; Podlesnyi, Alexey

443

Transforming vulnerability.  

PubMed

Asian American immigrant women engaged in filial caregiving are at special risk for health problems due to complex contextual factors related to immigration, cultural traditions, and role transition. This study examines the experience of two groups of immigrant Asian American women who are caring for older parents. A total of 41 women (22 Chinese American and 19 Filipino American) were interviewed in a study based on Strauss and Corbin's grounded theory methodology. The women were determined to be loyal to their traditional culture, which included strong filial values, while adapting to a new culture. Through the struggle of meeting role expectations and coping with paradox, the women mobilized personal and family resources to transform vulnerability into strength and well-being. PMID:14596182

Jones, Patricia S; Zhang, Xinwei Esther; Meleis, Afaf I

2003-11-01

444

Optical fiber temperature sensor using a gain-switched Fabry-Perot semiconductor laser self-seeded from a linearly chirped fiber Bragg grating  

NASA Astrophysics Data System (ADS)

We present a highly sensitive fiber temperature sensor based on a gain-switched Fabry-Perot semiconductor laser self-seeded from a linearly chirped fiber Bragg grating. A temperature resolution of better than 0.1 C was demonstrated. This sensor not only has the advantage of robustness against fluctuating light levels, but also obviates the need for fine wavelength discrimination.

Li, Shenping; Chan, K. T.

1998-12-01

445

Single-harmonic enhancement by controlling the chirp of the driving laser pulse during high-order harmonic generation from GaAs plasma  

SciTech Connect

We report a study of the enhancement of the intensity of the 27th-harmonic radiation produced during the high-order harmonic generation from the GaAs plasma by controlling the chirp of the fundamental Ti:sapphire laser radiation. The influence of Ga and As ions on the enhancement of the 27th-harmonic radiation is also studied.

Ganeev, Rashid A.; Singhal, Himanshu; Naik, Prasad Anant; Arora, Vipul; Chakravarty, Uday; Chakera, Juzer Ali; Khan, Riyaz Ahmed; Redkin, Pavel V.; Raghuramaiah, Manchi; Gupta, Parshotam Dass [Akadempribor Scientific Association, Academy of Sciences of Uzbekistan, Tashkent 700125 (Uzbekistan); Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Samarqand State University, Samarqand 703004 (Uzbekistan); Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

2006-12-15

446

Population inversion in hyperfine states of Rb with a single nanosecond chirped pulse in the framework of a four-level system  

NASA Astrophysics Data System (ADS)

We implement a four-level semiclassical model of a single pulse interacting with the hyperfine structure in ultracold rubidium aimed at control of population dynamics and quantum state preparation. We discuss a method based on pulse chirping to achieve population inversion between hyperfine states of the 5S shell. The results may prove useful for quantum operations with ultracold atoms.

Liu, G.; Zakharov, V.; Collins, T.; Gould, P.; Malinovskaya, S. A.

2014-04-01

447

EDITORIAL: Transformation optics Transformation optics  

NASA Astrophysics Data System (ADS)

Metamaterials are artificial materials with versatile properties that can be tailored to fit almost any practical need and thus go well beyond what can be obtained with `natural' materials. Recent progress in developing optical metamaterials allows unprecedented extreme control over the flow of light at both the nano- and macroscopic scales. The innovative field of transformation optics, which is enabled by metamaterials, inspired researchers to take a fresh look at the very foundations of optics and helped to create a new paradigm for the science of light. Similar to general relativity, where time and space are curved, transformation optics shows that the space for light can also be bent in an almost arbitrary way. Most importantly, the optical space can be designed and engineered, opening up the fascinating possibility of controlling the flow of light with nanometer spatial precision. This new paradigm enables a number of novel optical devices guiding how, using metamaterials, the space for light can be curved in a pre-designed and well-controlled way. Metamaterials which incorporate the innovative theories of transformation optics are pertinent to the important areas of optical cloaking, optical black holes, super-resolution imaging, and other sci-fi-like devices. One such exciting device is an electromagnetic cloak that can bend light around itself, similar to the flow of water around a stone, making invisible both the cloak and the object hidden inside. Another important application is a flat hyperlens that can magnify the nanometer-scale features of an object that cannot be resolved with conventional optics. This could revolutionize the field of optical imaging, for instance, because such a meta-lens could become a standard add-on tool for microscopes. By enabling nanoscale resolution in optical microscopy, metamaterial-based transformation optics could allow one to literally see extremely small objects with the eye, including biological cells, viruses, and possibly even DNA molecules. Light-concentrating devices, such as the optical black hole, can be used for efficient solar light collection in photovoltaic elements for renewable energy. With the dramatic advances in micro- and nanofabrication methods, we are presented with the opportunity to control light in a way that was not possible with the materials provided to us by nature. In an artificial pattern of sub-wavelength elements, the propagation of electromagnetic energy can be defined by an equivalent spatial and spectral dispersion of effective dielectric and magnetic properties. These synthetic structures, which can be fabricated with a desired spatial distribution of effective permittivity epsilon(r) and permeability ?(r), offer a unique potential to guide and control the flow of electromagnetic energy in such an engineered optical space. No longer are we constrained by the electromagnetic response of natural materials and their chemical compounds. Instead, we can tailor the shape and size of the structural units of the metamaterials, or tune their composition and morphology to provide new functionality.

Shalaev, Vladimir M.; Pendry, John

2011-02-01

448

Investigating molecular structures: Rapidly examining molecular fingerprints through fast passage broadband fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ?1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation off, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (?10 mus) than the molecular relaxation (?100 mus). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, and transient species may be studied with the spectrometer with high sensitivity, making it a viable option for many molecules wanting to be rotationally studied. The spectrometer has a relative correct intensity feature that, when coupled with theory, may ease the difficulty in transition assignment and facilitate dynamic chemical studies of the experiment. Molecules studied on this spectrometer have, in turn, been analyzed and assigned using common rotational spectroscopic analysis. Detailed theory on the analysis of these molecules has been provided. Structural parameters such as rotational constants and centrifugal distortion constants have been determined and reported for most molecules in the document. Where possible, comparisons have been made amongst groups of similar molecules to try and get insight into the nature of the bonds those molecules are forming. This has been achieved the the comparisons of nuclear electric quadrupole and nuclear magnetic coupling constants, and the results therein have been determined and reported.

Grubbs, Garry Smith Smitty, II

449

Analog signal isolation techniques  

SciTech Connect

This paper discusses several techniques for isolating analog signals in an accelerator environment. The techniques presented here encompass isolation amplifiers, voltage-to-frequency converters (VIFCs), transformers, optocouplers, discrete fiber optics, and commercial fiber optic links. Included within the presentation of each method are the design issues that must be considered when selecting the isolation method for a specific application.

Beadle, E.R.

1992-01-01

450

Analog signal isolation techniques  

SciTech Connect

This paper discusses several techniques for isolating analog signals in an accelerator environment. The techniques presented here encompass isolation amplifiers, voltage-to-frequency converters (VIFCs), transformers, optocouplers, discrete fiber optics, and commercial fiber optic links. Included within the presentation of each method are the design issues that must be considered when selecting the isolation method for a specific application.

Beadle, E.R.

1992-12-31

451

Transform coding for space applications  

NASA Technical Reports Server (NTRS)

Data compression coding requirements for aerospace applications differ somewhat from the compression requirements for entertainment systems. On the one hand, entertainment applications are bit rate driven with the goal of getting the best quality possible with a given bandwidth. Science applications are quality driven with the goal of getting the lowest bit rate for a given level of reconstruction quality. In the past, the required quality level has been nothing less than perfect allowing only the use of lossless compression methods (if that). With the advent of better, faster, cheaper missions, an opportunity has arisen for lossy data compression methods to find a use in science applications as requirements for perfect quality reconstruction runs into cost constraints. This paper presents a review of the data compression problem from the space application perspective. Transform coding techniques are described and some simple, integer transforms are presented. The application of these transforms to space-based data compression problems is discussed. Integer transforms have an advantage over conventional transforms in computational complexity. Space applications are different from broadcast or entertainment in that it is desirable to have a simple encoder (in space) and tolerate a more complicated decoder (on the ground) rather than vice versa. Energy compaction with new transforms are compared with the Walsh-Hadamard (WHT), Discrete Cosine (DCT), and Integer Cosine (ICT) transforms.

Glover, Daniel

1993-01-01

452

Optical parametric chirped pulse amplification and spectral shaping of a continuum generated in a photonic band gap fiber.  

PubMed

A chirped pulse, spectrally broadened in a photonic bandgap optical fiber by 120 fs Ti:Sapphire laser pulses, is parametrically amplified in a BBO crystal pumped by a frequency doubled nanosecond Nd:YAG laser pulse. Without changing the frequency of the Ti:Sapphire, a spectral tunability of the amplified pulses is demonstrated. The possibility to achieve broader spectral range amplification is confirmed for a non-collinear pump-signal interaction geometry. For optimal non-collinear interaction geometry, the pulse duration of the original and amplified pulse are similar. Finally, we demonstrate that the combination of two BBO crystals makes it possible to spectrally shape the amplified pulses. PMID:19475076

Hugonnot, E; Somekh, M; Villate, D; Salin, F; Freysz, E

2004-05-31

453

Theoretical study of the all-optical tunable rainbow-trapping-like effect in chirped plasmonic slot waveguides  

NASA Astrophysics Data System (ADS)

An all-optical tunable rainbow-trapping-like effect is realized theoretically in a plasmonic slot waveguide with a chirped nanograting, permeated with organic polymer made of poly(hexafluoropropylene oxide) doped with cholesteryl iodide. Gradually increasing the grating period ensures that the stop band edge of the surface plasmon polariton mode varies with position along the nanograting, which brings about the rainbow-trapping-like effect. The physical mechanism underlying the all-optical tunability of this effect is attributed to the variation in the dispersion relations of the surface plasmon polariton mode caused by the pump laser induced refractive index change of cholesteryl iodide. A shift of up to 17 ?m in the trapped position of the surface plasmon polariton mode is achieved under excitation of a 450 mJ cm-2 pump laser.

Zhu, Yu; Hu, Xiaoyong; Gong, Qihuang

2013-03-01

454

Theoretical study of Raman chirped adiabatic passage by X-ray absorption spectroscopy: highly excited electronic states and rotational effects.  

PubMed

Raman Chirped Adiabatic Passage (RCAP) is an efficient method to climb the vibrational ladder of molecules. It was shown on the example of fixed-in-space HCl molecule that selective vibrational excitation can thus be achieved by RCAP and that population transfer can be followed by X-ray Photoelectron spectroscopy [S. Engin, N. Sisourat, P. Selles, R. Taeb, and S. Carniato, Chem. Phys. Lett. 535, 192-195 (2012)]. Here, in a more detailed analysis of the process, we investigate the effects of highly excited electronic states and of molecular rotation on the efficiency of RCAP. Furthermore, we propose an alternative spectroscopic way to monitor the transfer by means of X-ray absorption spectra. PMID:24952537

Engin, Selma; Sisourat, Nicolas; Selles, Patricia; Taeb, Richard; Carniato, Stphane

2014-06-21

455

The impact of spectral modulations on the contrast of pulses of nonlinear chirped-pulse amplification systems.  

PubMed

A detrimental pulse distortion mechanism inherent to nonlinear chirped-pulse amplification systems is revealed and analyzed. When seeding the nonlinear amplification stage with pulses possessing weak side-pulses, the Kerr-nonlinearity causes a transfer of energy from the main pulse to side pulses. The resulting decrease in pulse contrast is determined by the accumulated nonlinear phase-shift (i.e., the B-integral) and the initial pulse-contrast. The energy transfer can be described by Bessel-functions. Thus, applications relying on a high pulse-contrast demand a low B-integral of the amplification system and a master-oscillator that exhibits an excellent pulse-contrast. In particular, nonlinear fiber CPA-systems operated at B-integrals far beyond pi have to be revised in this context. PMID:18607481

Schimpf, Damian N; Seise, Enrico; Limpert, Jens; Tnnermann, Andreas

2008-07-01

456

Programmable all-fiber structured waveshaper based on linearly chirped fiber Bragg grating and digital thermal controller  

NASA Astrophysics Data System (ADS)

We proposed and experimentally demonstrated an all-fiber structured programmable optical bandpass filter (waveshaper) based on a linearly chirped fiber Bragg grating and a digital-controlled thermal array. The key parameters of this filter such as the number of transmission channels, passing bandwidth per channel, central wavelength as well as the channel spacing can be reconfigured independently and flexibly by a program-controlled circuit. We have achieved in experiments the tunable passing bandwidth ranging from < 0.04 to 1.55 nm, adjustable central wavelength ranging from 1,547.16 to 1,558.64 nm, and a minimum wavelength spacing of 0.91 nm. The insertion loss of the whole device and the sideband rejection ratio are about 1.76 and 28 dB, respectively.

Zhang, Hailiang; Tang, Ming; Xie, Yiwei; Liao, Huiqi; Fu, Songnian; Shum, Perry Ping; Liu, Deming

2013-09-01

457

Chirping a two-photon transition in a multistate ladder RID C-2713-2008 RID A-7617-2010  

E-print Network

Chirping a two-photon transition in a multistate ladder Wolfgang Merkel, Holger Mack, and Wolfgang P. Schleich* Institut f?r Quantenphysik, Universit?t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany Eric Lutz Department of Physics... are M#1;=7, M =7, #4;=0.0225 fs?1, #6;=0.003 fs?1, #6;#3;=0.1525 fs?1, and em mg=1. MERKEL et al. PHYSICAL REVIEW A 76, 023417 #1;2007#2; 023417-2 E#1;t#2; = E0#3;e?i#3;0t f#1;t#2; + c.c.#4; #1;2#2; of amplitude E0, carrier frequency #3;0 and pulse...

Merkel, Wolfgang; Mack, Holger; Schleich, Wolfgang P.; Lutz, Eric; Paulus, Gerhard G.; Girard, Bertrand

2007-01-01

458

Chirp seismic-reflection data from the Baltimore, Washington, and Norfolk Canyons, U.S. mid-Atlantic margin  

USGS Publications Warehouse

A large number of high-resolution geophysical surveys between Cape Hatteras and Georges Bank have been conducted by federal, state, and academic institutions since the turn of the century. A major goal of these surveys is providing a continuous view of bathymetry and shallow stratigraphy at the shelf edge in order to assess levels of geological activity during the current sea level highstand. In 2012, chirp seismic-reflection data was collected by the U.S. Geologial Survey aboard the motor vessel Tiki XIV near three United States mid-Atlantic margin submarine canyons. These data can be used to further our understanding of passive continental margin processes during the Holocene, as well as providing valuable information regarding potential submarine geohazards.

Obelcz, Jeffrey B.; Brothers, Daniel S.; ten Brink, Uri S.; Chaytor, Jason D.; Worley, Charles R.; Moore, Eric M.

2014-01-01

459

Magnetothermoacoustics from magnetic nanoparticles by short bursting or frequency chirped alternating magnetic field: A theoretical feasibility analysis  

PubMed Central

Purpose: To propose an alternative method of thermoacoustic wave generation based on heating of magnetic nanoparticles (MNPs) using alternating magnetic field (AMF). Methods: The feasibility of thermoacoustic wave generation from MNPs by applying a short-burst of AMF or a frequency-modulated AMF is theoretically analyzed. As the relaxation of MNPs is strongly dependent upon the amplitude and frequency of AMF, either an amplitude modulated, fixed frequency AMF (termed time-domain AMF) or a frequency modulated, constant amplitude AMF (termed frequency-domain AMF) will result in time-varying heat dissipation from MNPs, which has the potential to generate thermoacoustic waves. Following Rosensweig's model of specific power loss of MNPs in a steady-state AMF, the time-resolved heat dissipations of MNPs of superparamagnetic size when exposed to a short bursting of AMF and/or to a linearly frequency chirped AMF are derived, and the resulted acoustic propagation is presented. Based on experimentally measured temperature-rise characteristics of a superparamagnetic iron-oxide nanoparticle (SPION) matrix in a steady-state AMF of various frequencies, the heat dissipations of the SPION under time-domain and frequency-domain AMF configurations that could have practical utility for thermoacoustic wave generation are estimated. Results: The initial rates of the temperature-rise of the SPION matrix were measured at an iron-weight concentration of 0.8 mg/ml and an AMF frequency of 88.8 kHz to 1.105 MHz. The measured initial rates of temperature-rise were modeled by Rosensweig's theory, and projected to 10 MHz AMF frequency, at which a 1 ?s bursting corresponding to a 1.55 mm axial resolution of acoustic detection could contain 10 complete cycles of AMF oscillation and the power dissipation is approximately 84 times of that at 1 MHz. Exposing the SPION matrix to a 1 ?s bursting of AMF at 10 MHz frequency and 100 Oe field intensity would produce a volumetric heat dissipation of 7.7 ?J/cm3 over the microsecond duration of the AMF burst. If the SPION matrix is exposed to a 1 ms long AMF train at 100 Oe field intensity that chirps linearly from 1 to 10 MHz, the volumetric heat dissipation produced over each 2? phase change of the AMF oscillation is estimated to increase from 0.15 to 1.1 ?J/cm3 within the millisecond duration of the chirping of AMF. Conclusions: The heat dissipations upon SPION (?1 mg/ml iron-weight concentration) by a 1 ?s bursting of 100 Oe AMF at 10 MHz and a 1 ms train of 100 Oe AMF that chirps linearly from 1 to 10 MHz were estimated to determine the potential of thermal-acoustic wave generation. Although thermoacoustic wave generation from MNPs by time- or frequency-domain AMF applications is predicted, the experimental generation of such a wave remains challenging. PMID:23718611

Piao, Daqing; Towner, Rheal A.; Smith, Nataliya; Chen, Wei R.

2013-01-01

460

Multikilohertz optical parametric chirped pulse amplification in periodically poled stoichiometric LiTaO3 at 1235 nm.  

PubMed

We demonstrate, for the first time to our knowledge, multikilohertz operation of a double-stage optical parametric chirped pulse amplifier with periodically poled stoichiometric LiTaO3 crystals, seeded by a homemade Cr:forsterite oscillator operating at 1235 nm. The repetition rate of the amplifier could easily be tuned without the use of electro-optic modulators by using a repetition-rate-tunable kilohertz pump laser operating at 532 nm and a time-synchronization unit. Amplified total (signal+idler) energies of 55.9 and 36.2 microJ were achieved at 1 and 5 kHz, respectively. After recompression, the pulse width of amplified idler pulses at 1235 nm amounted to 530 fs. PMID:17909587

Cho, W B; Kim, K; Lim, H; Lee, J; Kurimura, S; Rotermund, F

2007-10-01

461

Archive of digital Chirp subbottom profile data collected during USGS cruise 08CCT01, Mississippi Gulf Islands, July 2008  

USGS Publications Warehouse

In July of 2008, the U.S. Geological Survey (USGS) conducted geophysical surveys to investigate the geologic controls on island framework from Ship Island to Horn Island, Mississippi, for the Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazard Susceptibility project. Funding was provided through the Geologic Framework and Holocene Coastal Evolution of the Mississippi-Alabama Region Subtask (http://ngom.er.usgs.gov/task2_2/index.php); this project is also part of a broader USGS study on Coastal Change and Transport (CCT). This report serves as an archive of unprocessed digital Chirp seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) files, Field Activity Collection System (FACS) logs, observer's logbook, and formal Federal Geographic Data Committee (FGDC) metadata. Gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report.

Forde, Arnell S.; Dadisman, Shawn V.; Flocks, James G.; Worley, Charles R.

2011-01-01

462

Theoretical study of Raman chirped adiabatic passage by X-ray absorption spectroscopy: Highly excited electronic states and rotational effects  

NASA Astrophysics Data System (ADS)

Raman Chirped Adiabatic Passage (RCAP) is an efficient method to climb the vibrational ladder of molecules. It was shown on the example of fixed-in-space HCl molecule that selective vibrational excitation can thus be achieved by RCAP and that population transfer can be followed by X-ray Photoelectron spectroscopy [S. Engin, N. Sisourat, P. Selles, R. Taeb, and S. Carniato, Chem. Phys. Lett. 535, 192-195 (2012)]. Here, in a more detailed analysis of the process, we investigate the effects of highly excited electronic states and of molecular rotation on the efficiency of RCAP. Furthermore, we propose an alternative spectroscopic way to monitor the transfer by means of X-ray absorption spectra.

Engin, Selma; Sisourat, Nicolas; Selles, Patricia; Taeb, Richard; Carniato, Stphane

2014-06-01

463

Focusing wide bandwidth and wide swath synthetic aperture sonar data using modified nonlinear chirp-scaling imaging algorithm  

NASA Astrophysics Data System (ADS)

To solve the Synthetic Aperture Sonar (SAS) imaging problem with a wide bandwidth transmitted signal and a wide swath, a novel modified Nonlinear Chirp-Scaling (NCS) imaging algorithm is proposed. The first key step is to reduce the phase error by preserving the fourth order of the Taylor expansion for two-dimensional spectrum. To compensate the high order phase error sufficiently, the second key step is to derive a series of more exact relational parameters resulted from the third and fourth phase filtering and NCS operation by considering the change of linear and second nonlinear for equation frequency modulation slant rate. This operation increases the wide of swath for SAS with a wide bandwidth transmitted signal. The results of simulation show the accuracy and validity of the proposed modified NCS algorithm.

Tian, Zhen; Zhong, He-Ping; Tang, Jin-Song

2014-04-01

464

Chirped coherent anti-Stokes Raman scattering as a high-spectral-and spatial-resolution  

E-print Network

with a transform-limited broadband femtosecond Stokes pulse; both p