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1

Adaptive chirp-Fourier transform for chirp estimation with applications in ISAR imaging of maneuvering targets  

NASA Astrophysics Data System (ADS)

This paper first reviews some basic properties of the discrete chirp-Fourier transform and then present an adaptive chirp- Fourier transform, a generalization of the amplitude and phase estimation of sinusoids (APES) algorithm proposed by Li and Stoica for sinusoidal signals. We finally applied it to the ISAR imaging of maneuvering targets.

Xia, Xiang-Gen; Wang, Genyuan; Chen, Victor C.

2001-03-01

2

Chirp Z-transform spectral zoom optimization with MATLAB.  

SciTech Connect

The MATLAB language has become a standard for rapid prototyping throughout all disciplines of engineering because the environment is easy to understand and use. Many of the basic functions included in MATLAB are those operations that are necessary to carry out larger algorithms such as the chirp z-transform spectral zoom. These functions include, but are not limited to mathematical operators, logical operators, array indexing, and the Fast Fourier Transform (FFT). However, despite its ease of use, MATLAB's technical computing language is interpreted and thus is not always capable of the memory management and performance of a compiled language. There are however, several optimizations that can be made within the chirp z-transform spectral zoom algorithm itself, and also to the MATLAB implementation in order to take full advantage of the computing environment and lower processing time and improve memory usage. To that end, this document's purpose is two-fold. The first demonstrates how to perform a chirp z-transform spectral zoom as well as an optimization within the algorithm that improves performance and memory usage. The second demonstrates a minor MATLAB language usage technique that can reduce overhead memory costs and improve performance.

Martin, Grant D.

2005-11-01

3

Phase-shifted distributed feedback laser with linearly chirped grating fabricated by reconstruction equivalent chirp technique  

NASA Astrophysics Data System (ADS)

The phase-shifted distributed feedback (DFB) semiconductor laser with linearly chirped grating based on reconstruction equivalent chirp (REC) technique is theoretically analyzed and experimentally demonstrated for the first time. The asymmetric property of the lasing spectrum is analyzed according to the normalized threshold gain, and the different spectra from each facet of the laser are compared. Due to the low cost and fabrication flexibility, REC technique provides a promising way for the future practical applications of DFB lasers with chirped gratings.

Li, Lianyan; Lu, Linlin; Li, Simin; Guo, Renjia; Shi, Yuechun; Chen, Xiangfei

2014-09-01

4

Sinewave parameter estimation using the fast fan-chirp transform  

E-print Network

Sinewave analysis/synthesis has long been an important tool for audio analysis, modification and synthesis. The recently introduced fan-chirp Transform (FChT) [2,3] has been shown to improve the fidelity of sinewave parameter ...

Dunn, Robert B.

5

Optical chirp z-transform processor with a simplified architecture.  

PubMed

Using a simplified chirp z-transform (CZT) algorithm based on the discrete-time convolution method, this paper presents the synthesis of a simplified architecture of a reconfigurable optical chirp z-transform (OCZT) processor based on the silica-based planar lightwave circuit (PLC) technology. In the simplified architecture of the reconfigurable OCZT, the required number of optical components is small and there are no waveguide crossings which make fabrication easy. The design of a novel type of optical discrete Fourier transform (ODFT) processor as a special case of the synthesized OCZT is then presented to demonstrate its effectiveness. The designed ODFT can be potentially used as an optical demultiplexer at the receiver of an optical fiber orthogonal frequency division multiplexing (OFDM) transmission system. PMID:25607197

Ngo, Nam Quoc

2014-12-29

6

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

7

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

E-print Network

A Fractional Fourier Transform Analysis of a Bubble Excited by an Ultrasonic Chirp Euan Barlow. 2 #12;1 Introduction When a bubble is insonified by an ultrasonic signal it oscillates perturbation of the bubble's radius to show that using an ultrasonic chirp signal as the forcing function

Mottram, Nigel

8

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

9

Chirped-Pulse Fourier Transform Microwave Spectroscopy of 3-METHOXYPROPYLAMINE  

NASA Astrophysics Data System (ADS)

The rotational spectrum of 3-methoxypropylamine was collected from 8.0 to 18.5 GHz with the Coker College chirped-pulse FTMW molecular beam spectrometer. Ab initio predictions using the B3LYP-D3 dispersion-corrected density functional gave high quality starting geometries, enabling us to quickly assign the spectrum of the lowest energy conformer, which has a g'gt configuration (moving from the amine end to the methoxy end of the molecule). Attempts were also made to collect the spectrum of this molecule in the room-temperature waveguide instrument at New College, but these attempts were unsuccessful as the molecule rapidly reacts with the copper walls of the waveguide to produce ammonia.

McCabe, Morgan N.; Shipman, Steven; Arnold, Sean; Chewning, J. Chase; Smith, Miranda; Brown, Gordon

2014-06-01

10

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics  

E-print Network

This second paper in a series of two reports on the performance of a new instrument for studying chemical reaction dynamics and kinetics at low temperatures. Our approach employs chirped-pulse Fourier-transform microwave ...

Abeysekera, Chamara

11

a Chirped-Pulse Fourier Transform Spectrometer Operating from 110 TO 170 GHZ  

NASA Astrophysics Data System (ADS)

A chirped-pulse Fourier transform spectrometer operating from 110 - 170 GHz was constructed. The design of this spectrometer is directly adapted from that of the 260 - 295 GHz chirped-pulse spectrometer built by Steber and co-workers at the University of Virginia. In this instrument, an arbitrary waveform generator (AWG) produces a chirped pulse which is frequency shifted to a range between 9.2 and 14.1 GHz and then multiplied by a factor of 12 via an active multiplier chain to a range between 110 and 170 GHz. As in the Pate lab design, the AWG also serves as a local oscillator (LO) source; this LO is multiplied and used to downconvert the molecular emission, allowing it to be collected by a 40 GS/s digitizer. Benchmark measurements were taken for methanol at room temperature, and details of the instrument's performance will be discussed. A.L. Steber, B.J. Harris, J.L. Neill, and B.H. Pate, J. Mol. Spectrosc., 280, 3 (2012)

Bernier, Lauren E.; Shipman, Steven

2014-06-01

12

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics  

NASA Astrophysics Data System (ADS)

This second paper in a series of two reports on the performance of a new instrument for studying chemical reaction dynamics and kinetics at low temperatures. Our approach employs chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy to probe photolysis and bimolecular reaction products that are thermalized in pulsed uniform flows. Here we detail the development and testing of a new Ka-band CP-FTMW spectrometer in combination with the pulsed flow system described in Paper I [J. M. Oldham, C. Abeysekera, B. Joalland, L. N. Zack, K. Prozument, I. R. Sims, G. B. Park, R. W. Field, and A. G. Suits, J. Chem. Phys. 141, 154202 (2014)]. This combination delivers broadband spectra with MHz resolution and allows monitoring, on the ?s timescale, of the appearance of transient reaction products. Two benchmark reactive systems are used to illustrate and characterize the performance of this new apparatus: the photodissociation of SO2 at 193 nm, for which the vibrational populations of the SO product are monitored, and the reaction between CN and C2H2, for which the HCCCN product is detected in its vibrational ground state. The results show that the combination of these two well-matched techniques, which we refer to as chirped-pulse in uniform flow, also provides insight into the vibrational and rotational relaxation kinetics of the nascent reaction products. Future directions are discussed, with an emphasis on exploring the low temperature chemistry of complex polyatomic systems.

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

2014-12-01

13

Application research of keystone transform in weak high-speed target detection in low-PRF narrowband Chirp radar  

Microsoft Academic Search

Because of the high speed and the long repeat interval of the radar, there would be serious echo envelope migration while using low-PRF narrowband chirp radar to detect weak high speed targets. The coherent integration method of envelope migration compensation based on keystone transform is studied, the problem of Doppler ambiguity is analyzed, and the influence on the coherent integration

Sijie Yuan; Tao Wu; Mao Mao; Gaojie Mei; Xin Wei

2008-01-01

14

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

15

Microwave Frequency Transitions Requiring Laser Ablated Uranium Metal Discovered Using Chirp-Pulse Fourier Transform Spectroscopy  

NASA Astrophysics Data System (ADS)

A rod of depleted uranium metal (mp = 1,132° C) has been ablated with the fundamental operating frequency of a Nd:YAG laser. The resulting ablation plume of uranium was then mixed with argon gas and expanded between the transmit/receive horn antennae of a chirp-pulse Fourier transform microwave spectrometer. The recorded spectra show nine strong transitions which are not present when the laser is not used in the experimental procedure. A series of experiments in which the backing gas conditions were altered provides evidence that the nine observed transitions are carried by the same species. Should the transitions be from one species it is most likely an asymmetric top. The transitions persist even when ultra-pure argon is used as the sole backing gas. The oxide coating of the uranium metal likely provides a source of oxygen and, presently, the ``top" candidate for the unknown molecule is UO_3, which is known to have C_2v symmetry. Double resonance experiments are planned to aid transition assignments. A plausible explanation for an elusive assignment to date is the presence of pseudo-rotation.

Long, B. E.; Cooke, S. A.

2014-06-01

16

Perfluorobutyric Acid and its Monohydrate: a Chirped Pulse and Cavity Based Fourier Transform Microwave Spectroscopic Study  

NASA Astrophysics Data System (ADS)

Perfluorobutyric acid (PFBA) is highly soluble in water and is a molecule of environmental importance. Rotational spectra of PFBA and its monohydrate were studied using a broadband chirped pulse and a narrow band cavity based Fourier transform microwave spectrometers and high level ab initio calculations. Extensive conformational search was performed for both the acid and its monohydrate at the MP2/6-311++G(2d,p) level of theory. Two and three conformers were predicted for PFBA and its monohydrate, respectively. One set of rotational transitions of PFBA and its mono-hydrate in each case was observed and assigned. Based on the broadband spectra obtained, one can confidently conclude that only one dominate conformer exists in each case. The orientation of the hydroxyl group in PFBA was determined using isotopic analysis. Comparison of the observed transition intensities and the calculated electric dipole moment components allowed one to identify the most stable monohydrate conformation which takes on the insertion hydrogen-bonding topology. Comparison to the shorter chain analogues, i.e. trifluoroacetic acid, perfluoropropionic acid, and their monohydrates, was made to elucidate the general trend in their conformational preference and binding topologies.

Thomas, Javix; Serrato, Agapito, III; Lin, Wei; Jaeger, Wolfgang; Xu, Yunjie

2014-06-01

17

Chirped Pulse-Fourier Transform Microwave Spectroscopy of Ethyl 3-METHYL-3-PHENYLGLYCIDATE (strawberry Aldehyde)  

NASA Astrophysics Data System (ADS)

Strawberry aldehyde (C_{12} O_3 H_{14}), a common artificial flavoring compound, has two non-interconvertible conformational families defined by the relative stereochemistry around its epoxide carbons. In one family, referred to as the trans because the two large substituents (a phenyl ring and an ethyl ester) are on opposite sides of the epoxide ring, these two substituents are unable to interact with each other. However, in the cis family, there is a long-range interaction that is difficult to accurately capture in electronic structure calculations. Three trans and two cis conformations have been assigned by broadband chirped pulse Fourier transform microwave spectroscopy, along with the C-13 isotopomers in natural abundance for one conformer from each of the families. The agreement of the rotational constants, relative dipole moments, and relative energies between theory and experiment is excellent, even at relatively crude levels of theory, for the trans family, but is quite poor for the cis conformers. In addition, due to the reactivity of strawberry aldehyde and the high temperature to which it must be heated to yield a suitable vapor pressure, several decomposition products have been assigned, and more, as of yet unassigned, are likely to be present. This project demonstrates some of the challenges in performing large-molecule rotational spectroscopy.

Shipman, Steven T.; Neill, Justin L.; Muckle, Matt T.; Suenram, Richard D.; Pate, Brooks H.

2009-06-01

18

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

19

Barley Transformation Using Biolistic Techniques  

NASA Astrophysics Data System (ADS)

Microprojectile bombardment or biolistic techniques have been widely used for cereal transformation. These methods rely on the acceleration of gold particles, coated with plasmid DNA, into plant cells as a method of directly introducing the DNA. The first report of the generation of fertile, transgenic barley plants used biolistic techniques. However, more recently Agrobacterium-mediated transformation has been adopted as the method of choice for most cereals including barley. Biolistic procedures are still important for some barley transformation applications and also provide transient test systems for the rapid checking of constructs. This chapter describes methods for the transformation of barley using biolistic procedures and also highlights the use of the technology in transient assays.

Harwood, Wendy A.; Smedley, Mark A.

20

Experimental demonstration of the three phase shifted DFB semiconductor laser based on Reconstruction-Equivalent-Chirp technique.  

PubMed

A three phase shifted (3PS) distributed feedback (DFB) semiconductor laser based on Reconstruction-Equivalent-Chirp (REC) technique is experimentally demonstrated for the first time. The simulation results show that the performances of the equivalent 3PS DFB semiconductor laser are nearly the same as that of the true 3PS laser. However, it only changes the ?m-level sampling structures but the seed grating is uniform. So, its cost of fabrication is low. The measurement results exhibit its good single longitudinal mode (SLM) operation even at high bias current and surrounding temperature. PMID:23038289

Shi, Yuechun; Chen, Xiangfei; Zhou, Yating; Li, Simin; Li, Lianyan; Feng, Yijun

2012-07-30

21

Chirped-Pulse Fourier-Transform Microwave/pulsed Uniform Flow Spectrometer: the Low-Temperature Pulsed Uniform Supersonic Flow System  

NASA Astrophysics Data System (ADS)

Traditional techniques (e.g. REMPI, imaging, etc.) that are used to study reaction dynamics are able to provide a great deal of fundamental information about systems containing atoms and smaller molecules. However, as larger molecules and more complex systems are targeted, it becomes more of a challenge to determine isomer- and vibrational level-specific information and accurate branching ratios. In order to complement existing methods and obtain information about larger systems, a Ka-band (26-40 GHz) chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer has been has been constructed. The system integrates a pulsed uniform supersonic flow (PUSF) source to ensure that experimental conditions, such as temperature and density, are well-known and constant. This PUSF system is based around a high-throughput piezoelectric stack valve, a Laval nozzle, and simple pumping scheme. This system is able to produce cold, uniform flows with densities on the order of 1016 cm-3 that persist for up to 20 cm from the nozzle exit. A description of this system and its characterization will be presented.

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

2014-06-01

22

Comparison of optical single-sideband modulation and chirped fiber gratings as dispersion mitigating techniques in optical millimeter-wave multichannel systems  

Microsoft Academic Search

A comparative study between optical single-sideband (SSB) modulation and chirped fiber gratings (CFG) as dispersion equalization techniques is carried out. The simulation results show that the dispersion-induced distortion arising in optical millimeter-wave multichannel systems can not be compensated by employing the SSB modulation approach. Furthermore, we have demonstrated that the use of a CFG significantly reduces (nearly 25 dB) the

Francisco Ramos; J. Marti

1999-01-01

23

Barley Transformation Using Agrobacterium-Mediated Techniques  

NASA Astrophysics Data System (ADS)

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

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

24

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

25

Giving encouragement as a transformational leadership technique.  

PubMed

Giving encouragement is not generally stated as a high priority role of health care supervisors. Traditionally, technical skills and productivity on the job were aspects that received the supervisor's primary focus. However, there is a growing appreciation that encouragement is a transformational leadership technique that is related to productivity on the job and to quality work. Use of encouragement is a leadership technique that fits in today's people-oriented work climate. PMID:10165425

Davidhizar, R; Shearer, R

1997-03-01

26

Multiplexed chirp waveform synthesizer  

DOEpatents

A synthesizer for generating a desired chirp signal has M parallel channels, where M is an integer greater than 1, each channel including a chirp waveform synthesizer generating at an output a portion of a digital representation of the desired chirp signal; and a multiplexer for multiplexing the M outputs to create a digital representation of the desired chirp signal. Preferably, each channel receives input information that is a function of information representing the desired chirp signal.

Dudley, Peter A.; Tise, Bert L.

2003-09-02

27

Chirped-Pulse Fourier-Transform Microwave Spectroscopy of the Prototypical C-H\\cdots? Interaction: the BENZENE\\cdotsACETYLENE Weakly Bound Dimer  

NASA Astrophysics Data System (ADS)

The rotational spectrum of the CH\\cdots? bonded complex between benzene and acetylene has been measured in the 6-20 GHz range using chirped-pulse Fourier-transform microwave spectroscopy. The spectra for the normal isotopologue, three unique 13C substituted species, and the d_1-benzene\\cdotsHCCH species have allowed determination of the dimer structure. The spectrum is that of a symmetric top, with effective C6v symmetry, and a CH\\cdots? distance of 2.4921(1) Å. The dipole moment has been measured using the Stark effect, and is 0.438(11) D. In addition to the ground state spectrum, three additional sets of transitions corresponding to similar rotational constants have been observed, likely due to excitation of the three low energy intermolecular vibrational modes of the dimer. Analysis of these excited state transitions is in progress. Comparison of the binding energy and structure of the benzene\\cdotsHCCH dimer with other H\\cdots? complexes will be presented.

Ulrich, Nathan; Seifert, Nathan A.; Dorris, Rachel E.; Peebles, Rebecca A.; Peebles, Sean A.; Pate, Brooks

2014-06-01

28

Back-side-coated chirped mirrors with ultra-smooth broadband dispersion characteristics  

NASA Astrophysics Data System (ADS)

We demonstrate a new technique for the design of chirped mirrors with extremely smooth dispersion characteristics over an extended ultra-broadband wavelength range. Our approach suppresses spectral dispersion oscillations, which can lead to unwanted strong spectral modulations and limit the bandwidth of mode-locked laser pulses. Dispersion oscillations are significantly reduced by coating the chirped mirror structure on the back side of a substrate, providing ideal impedance matching between coating and ambient medium. An anti-reflection coating may be added on the front side of the substrate, geometrically separated from the chirped mirror. The chirped mirror structure and the anti-reflection coating are non-interfering and can be independently designed and optimized. The separation of both coating sections provides a much better solution for the impedance-matching problems than previous approaches to chirped mirror design. We show by a theoretical analysis and numerical simulations that minimum dispersion oscillations are achieved if the index of the substrate is identical to the index of one of the coating materials and if double-chirping is used for the chirped mirror structure. Based on this analysis, we design a mirror that supports a bandwidth of 220 THz with group delay dispersion oscillations of about 2 fs2 (rms), an order-of magnitude improvement compared to previous designs of similar bandwidth. In a first experimental demonstration of back-side-coated (BASIC) mirrors, we achieve nearly transform-limited and virtually unchirped pulses of 5.8 fs duration from a Kerr-lens mode-locked Ti:sapphire laser. BASIC mirrors are particularly suited for higher-order dispersion compensation schemes. They support the extremely broad spectra of few-cycle pulses and promise to provide clean pulse shapes in this regime.

Matuschek, N.; Gallmann, L.; Sutter, D. H.; Steinmeyer, G.; Keller, U.

29

Fourier Transform Heterodyne Techniques Applied To Astronomy  

NASA Astrophysics Data System (ADS)

Fourier Transform Heterodyne (FTH) is a detection process capable of directly imaging the transverse amplitude and phase of coherent electromagnetic fields. Based on coherent detection principles governing conventional heterodyned systems, Fourier Transform Heterodyne (FTH) incorporates transverse spatial encoding of the local oscillator for image capture. Appropriate selection of spatial encoding functions (basis set) allows image retrieval by way of classic Fourier manipulations. Of practical interest: 1) Imaging is accomplished on a single element detector/sensor requiring no additional scanning or moving components. 2) Because detection is governed by heterodyne principles, near quantum limited performance is achievable. 3) The concept is general with the applicable electromagnetic spectrum encompassing the RF through optical. Although FTH is currently in its infancy, we believe this technique will provide new tools and concepts important to the development of future astronomical systems. For example: 1) An FTH-based optical or infrared interferometer (whether ground-based or space-based) can operate in direct analogy to VLBI radio astronomy systems. 2) FTH may be capable of measuring the atmospheric distortions of a target star to guide adaptive optical correction systems. 3) FTH may be used to determine the adjustments required to align a deployed structure in space and can remove aberrations from slight residual misalignments during operation. The work to be presented will include a brief introduction of the underlying principles governing FTH imaging, followed by cursory description of a simple proof-of-concept experiment carried out using a HeNe laser, a 69 element spatial phase modulator, and a 36 term Zernike basis set. Finally, astronomical applications will be discussed.

Laubscher, B. E.; Cooke, B. J.; Edwards, B. C.

1998-12-01

30

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

31

Towards Solvation of a Chiral Alpha-Hydroxy Ester: Broadband Chirp and Narrow Band Cavity Fouirier Transform Microwave Spectroscopy of Methyl Lactate-Water Clusters  

NASA Astrophysics Data System (ADS)

Methyl lactate (ML), a chiral alpha-hydroxy ester, has attracted much attention as a prototype system in studies of chirality transfer,[1] solvation effects on chiroptical signatures,[2] and chirality recognition.[3] It has multiple functional groups which can serve both as a hydrogen donor and acceptor. By applying rotational spectroscopy and high level ab initio calculations, we examine the delicate competition between inter- and intramolecular hydrogen-bonding in the ML-water clusters. Broadband rotational spectra obtained with a chirp Fourier transform microwave (FTMW) spectrometer, reveal that the insertion conformations are the most favourable ones in the binary and ternary solvated complexes. In the insertion conformations, the water molecule(s) inserts itself (themselves) into the existing intramolecular hydrogen-bonded ring formed between the alcoholic hydroxyl group and the oxygen of the carbonyl group of ML. The final frequency measurements have been carried out using a cavity based FTMW instrument where internal rotation splittings due to the ester methyl group have also been detected. A number of insertion conformers with subtle structural differences for both the binary and ternary complexes have been identified theoretically. The interconversion dynamics of these conformers and the identification of the most favorable conformers will be discussed. 1. C. Merten, Y. Xu, Angew. Chem. Int. Ed., 2013, 52, 2073 -2076. 2. M. Losada, Y. Xu, Phys. Chem. Chem. Phys., 2007, 9, 3127-3135; Y. Liu, G. Yang, M. Losada, Y. Xu, J. Chem. Phys., 2010, 132, 234513/1-11. 3. A. Zehnacker, M. Suhm, Angew. Chem. Int. Ed. 2008, 47, 6970 - 6992.

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

2013-06-01

32

Transionospheric chirp event classifier  

SciTech Connect

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

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

1995-09-01

33

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics.  

PubMed

Superharmonic imaging improves the spatial resolution by using the higher order harmonics generated in tissue. The superharmonic component is formed by combining the third, fourth, and fifth harmonics, which have low energy content and therefore poor SNR. This study uses coded excitation to increase the excitation energy. The SNR improvement is achieved on the receiver side by performing pulse compression with harmonic matched filters. The use of coded signals also introduces new filtering capabilities that are not possible with pulsed excitation. This is especially important when using wideband signals. For narrowband signals, the spectral boundaries of the harmonics are clearly separated and thus easy to filter; however, the available imaging bandwidth is underused. Wideband excitation is preferable for harmonic imaging applications to preserve axial resolution, but it generates spectrally overlapping harmonics that are not possible to filter in time and frequency domains. After pulse compression, this overlap increases the range side lobes, which appear as imaging artifacts and reduce the Bmode image quality. In this study, the isolation of higher order harmonics was achieved in another domain by using the fan chirp transform (FChT). To show the effect of excitation bandwidth in superharmonic imaging, measurements were performed by using linear frequency modulated chirp excitation with varying bandwidths of 10% to 50%. Superharmonic imaging was performed on a wire phantom using a wideband chirp excitation. Results were presented with and without applying the FChT filtering technique by comparing the spatial resolution and side lobe levels. Wideband excitation signals achieved a better resolution as expected, however range side lobes as high as -23 dB were observed for the superharmonic component of chirp excitation with 50% fractional bandwidth. The proposed filtering technique achieved >50 dB range side lobe suppression and improved the image quality without affecting the axial resolution. PMID:25389159

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

2014-11-01

34

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

2014-12-01

35

Fourier Transform Heterodyne Techniques Applied To Astronomy  

Microsoft Academic Search

Fourier Transform Heterodyne (FTH) is a detection process capable of directly imaging the transverse amplitude and phase of coherent electromagnetic fields. Based on coherent detection principles governing conventional heterodyned systems, Fourier Transform Heterodyne (FTH) incorporates transverse spatial encoding of the local oscillator for image capture. Appropriate selection of spatial encoding functions (basis set) allows image retrieval by way of classic

B. E. Laubscher; B. J. Cooke; B. C. Edwards

1998-01-01

36

A Transformed Lagged Ensemble Forecasting Technique for Increasing Ensemble Size  

E-print Network

A Transformed Lagged Ensemble Forecasting Technique for Increasing Ensemble Size Andrew. R.Lawrence@ecmwf.int #12;Abstract An ensemble-based data assimilation approach is used to transform old en- semble. The impact of the transformations are propagated for- ward in time over the ensemble's forecast period

Hansens, Jim

37

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70-102 GHz region  

E-print Network

Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on ...

Park, Barratt

38

A wireless spread-spectrum communication system using SAW chirped delay lines  

Microsoft Academic Search

We report on the use of broad-band chirp signals for spread-spectrum communications in indoor and industrial environments. The well-known pulse compression technique associated with chirp signals is exploited to achieve a highly robust communication system. For the generation and compression of the chirp signals, surface acoustic wave delay lines fabricated from an LiTaO3-X112rotY substrate are used. Center frequency, bandwidth, chirp

Andreas Springer; Wolfgang Gugler; Mario Huemer; Rainer Koller; Robert Weigel

2001-01-01

39

Transverse electric scattering widths for strips-Fourier transform technique  

NASA Technical Reports Server (NTRS)

A technique which is based on Fourier transformations is introduced for predicting scattering widths. For a strip it is shown that explicit determination of the linear current density is not necessary for bistatic or monostatic scattering width calculations. Comparisons of the predictions of the technique are made with the integral equation technique predictions, which do not require explicit evaluations of linear current densities.

Cockrell, C. R.; Harrah, S. D.; Beck, F. B.

1991-01-01

40

Image watermarking technique based on the steerable pyramid transform  

E-print Network

Image watermarking technique based on the steerable pyramid transform Fadoua DRIRA, Florence DENIS@liris.cnrs.fr fdenis@liris.cnrs.fr atilla.baskurt@liris.cnrs.fr ABSTRACT The application of the steerable pyramid properties of steerable pyramid transform that are relevant for use in image watermarking; these properties

Baskurt, Atilla

41

A VSP transformation technique for the determination of subsurface structure  

E-print Network

A VSP TRANSFORMATION TECHNIQUE FOR THE DETERMINATION OF SUBSURFACE STRUCTURE A Thesis by JEFFREY EDWARD MALLOY Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE August 1985 Major Subject: Geophysics A VSP TRANSFORMATION TECHNIQUE FOR THE DETERMINATION OF SUBSURFACE STRUCTURE A Thesis JEFFREY EDWARD MALLOY Approved as to style and content by: Terry W. pencer (Ch rman) Nichele Caputo (Nember...

Malloy, Jeffrey Edward

1985-01-01

42

Chirped Pulse Microwave Spectroscopy in Pulsed Uniform Supersonic Flows  

NASA Astrophysics Data System (ADS)

We present preliminary results describing the development of a new instrument that combines two powerful techniques: Chirped Pulse-Fourier Transform MicroWave (CP-FTMW) 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. We have constructed a new high-power K_a-band, 26-40 GHz, chirped pulse spectrometer with sub-MHz resolution, analogous to the revolutionary CP-FTMW spectroscopic technique developed in the Pate group at University of Virginia. In order to study smaller molecules, the E-band, 60-90 GHz, CP capability was added to our spectrometer. A novel strategy for generating uniform supersonic flow through a Laval nozzle is introduced. High throughput pulsed piezo-valve is used to produce cold (30 K) uniform flow with large volumes of 150 cm^3 and densities of 1014 molecules/cm3 with modest pumping facilities. The uniform flow conditions for a variety of noble gases extend as far as 20 cm from the Laval nozzle and a single compound turbo-molecular pump maintains the operating pressure. Two competing design considerations are critical to the performance of the system: a low temperature flow is needed to maximize the population difference between rotational levels, and high gas number densities are needed to ensure rapid cooling to achieve the uniform flow conditions. At the same time, collision times shorter than the chirp duration will give inaccurate intensities and reduced signal levels due to collisional dephasing of free induction decay. Details of the instrument and future directions and challenges will be discussed.

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

2014-06-01

43

Monitoring and multiplexing technique for interferometric fiber optic sensors with a linearly chirped Er:fiber laser  

NASA Astrophysics Data System (ADS)

The monitoring of interferometer fiber optic sensors using a laser that is scanned over a wide frequency range is investigated. The interrogation technique is based on the principle that if the light-source frequency varies linearly with time, the optical signal reflected or transmitted is intensity modulated at a frequency that is proportional to the optical path difference (OPD) in the interferometer. Fourier components in the detected optical output signal then correspond to the OPDs of any interferometers that have contributed to this modulation. The temporal position of a peak in the power spectrum of this signal is proportional to the OPD of the interferometer that is responsible for that peak. A fine tuning of the OPD value is determined from the phase of the corresponding Fourier component. Experimentally, an Er:fiber laser scanned over a 46-nm range centered at 1540 nm was used to monitor intrinsic fiber Fabry-Perot interferometers (FFPIs). Variations in the laser scan rate were compensated with the optical signal modulated by a reference FFPI held at a constant temperature. The OPD measurement resolution was 3.6 nm, and the dynamic range was 1.3 x 107. The temperature was measured from 20 degC to 610 degC with a 0.02 degC resolution, and multiplexing of three of the sensors arranged in series was demonstrated.

Wan, Xiaoke; Taylor, Henry F.

2002-12-01

44

Monitoring and multiplexing technique for interferometric fiber optic sensors with a linearly chirped Er:fiber laser.  

PubMed

The monitoring of interferometer fiber optic sensors using a laser that is scanned over a wide frequency range is investigated. The interrogation technique is based on the principle that if the light-source frequency varies linearly with time, the optical signal reflected or transmitted is intensity modulated at a frequency that is proportional to the optical path difference (OPD) in the interferometer. Fourier components in the detected optical output signal then correspond to the OPDs of any interferometers that have contributed to this modulation. The temporal position of a peak in the power spectrum of this signal is proportional to the OPD of the interferometer that is responsible for that peak. A fine tuning of the OPD value is determined from the phase of the corresponding Fourier component. Experimentally, an Er:fiber laser scanned over a 48-nm range centered at 1540 nm was used to monitor intrinsic fiber Fabry-Perot interferometers (FFPIs). Variations in the laser scan rate were compensated with the optical signal modulated by a reference FFPI held at a constant temperature. The OPD measurement resolution was 3.6 nm, and the dynamic range was 1.3 x 10(7). The temperature was measured from 20 degrees C to 610 degrees C with a 0.02 degrees C resolution, and multiplexing of three of the sensors arranged in series was demonstrated. PMID:12510927

Wan, Xiaoke; Taylor, Henry F

2002-12-20

45

SAR image enhancement technique based on morphological wavelet transformation  

NASA Astrophysics Data System (ADS)

In this paper, a morphological wavelet principle and a SAR image enhancement technique are introduced, and the image enhancement technique performance based on morphological wavelet transformation is proceeded using SAR image data. In wavelet transformation domain, an image enhancement method of 2D Butterworth filter constructed is applied, good enhancement effects are obtained, and an extraction edge and texture study of applying prewitt operator is taken. Because of morphological wavelet transformation good performance, a high efficiency in image enhancement and texture obtaining is gotten. The research results show that the SAR data with Speckle and Pepper and Salt noise is enhanced very well by nonlinear enhancement processing in morphological wavelet domain, and the ocean target characteristics is clearer, such as ship, ship tail and interalwave.

Yan, Jingwen; Lu, Gang; Lu, Hanqing

2001-09-01

46

Summary Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underly-  

E-print Network

Summary Orthonormal wavelet transformation (OWT) is a computationally efficient technique those of the measurements. Fourier and wavelet transformation are sig- nal processing techniques used- tral properties of eddy-covariance (EC)-measured NEE using standard Fourier transformation (FT

47

CHIRP Doppler radar  

NASA Astrophysics Data System (ADS)

The present investigation is concerned with the concept of a combination of the clinical procedure of reconstruction tomography with the radar processing for linear FM pulse compression. An approach based on such a combination is to be employed to map radar backscatter energy. Radar systems employing pulse compression of linear frequency modulated (CHIRP) pulses are considered along with the inversion formula employed by reconstruction tomography. The conventional system enabling radar backscatter mapping is based on pulse-Doppler radar which basically incorporates range-gated spectrum analysis. CHIRP Doppler radar represents a potential alternative. Advantages are related to an absence of requirements to maintain coherence from pulse to pulse, and the suppression of interference due to second-time-around signals. Raabe (1976) has discussed an application involving the imaging of the wakes of reentering space vehicles.

Bernfeld, M.

1984-04-01

48

Frequency chirping in external modulators  

Microsoft Academic Search

A general formula is given that expresses frequency chirping in some types of external intensity modulators, such as the loss modulator, directional-coupler-type modulator, Mach-Zehnder interferometry-type modulator, and total-internal-reflection-type modulator. The chirping phenomenon treated is caused by the phase modulation due to an accompanied refractive index change. It is uniquely expressed in terms of an ?-parameter that contributes to frequency chirping

Fumio Koyama; KENICHI IGA

1988-01-01

49

Image fusion in discrete cosine transform domain using masking techniques  

NASA Astrophysics Data System (ADS)

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

Sharma, K. K.; Priti, K.

2013-01-01

50

Block Digital Filter Implementation Techniques and Transform Domain Processing  

NASA Astrophysics Data System (ADS)

This dissertation is concerned with block implementation techniques of digital filters and their application to transform domain processing. Block implementation of digital filters is useful for high throughput filtering due to inherent parallelism. Furthermore, more accurate computation is possible through proper allocation of computation resources in the block transform domain when input data are correlated. The performance improvement is closely related to block transform coding gain of the input signal. By extending scalar linear constant coefficient difference equation (LCCDE) to block LCCDE, we have shown various block filter structure implementation techniques, and investigated their finite precision coefficient quantization effects. Particularly, block lattice implementation of IIR and FIR filters is of interest due to their good numerical properties. In order to derive the block lattice structures, we have used block lossless bounded real (BLBR) functions; in the block IIR lattice implementation, a BLBR function derived from the denominator of the block transfer function is used, which parallels the Gray-Markel lattice for the scalar case, and in the block FIR lattice implementation, the block version of power complementary pair polynomials is derived and utilized. It has been demonstrated that these block lattice filter structures have better finite coefficient quantization characteristics than those of any other block filter structures. The block filter structures are directly applied to transform domain filtering without any modification of the block filter structures. The matrix coefficients only need to be changed to the transform domain coefficients. It has been shown that nonuniform coefficient quantization in the transform domain filtering improves the accuracy of filtering for finite given computational resources (for example, number of transistors in the VLSI implementation).

Jang, Youngbeom

1994-01-01

51

Practical Application of Hilbert Transform Techniques in Identifying Interarea Oscillations  

Microsoft Academic Search

\\u000a Disturbances in large power systems can exhibit nonlinear, time-varying behavior. Traditional modal identification from field\\u000a data is via techniques, such as Prony analysis, which assume data stationarity. The Hilbert transform and analytic function\\u000a can be used to analyze inter-area oscillatory behavior of power systems with the stationarity assumption relaxed. However,\\u000a reducing the data to simple numerical results can be achieved

T. J. Browne; V. Vittal; G. T. Heydt; Arturo Roman Messina

52

Light synthesis with linearly chirped fibre Bragg gratings (FBGs) for optical coherence tomography (OCT) applications  

Microsoft Academic Search

A simple technique of using a combination of linearly chirped fibre Bragg gratings (FBGs) to generate light to enhance depth resolution in optical coherence tomography (OCT) is introduced. A [3×3] fused fibre coupler was used to couple and redistribute super luminescent diode (SLD) light to linearly chirped FBGs connected to the fibre output arms of the coupler. Reflected and\\/or transmitted

Enock Jonathan

2005-01-01

53

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

Microsoft Academic Search

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

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

1989-01-01

54

The use of fast Fourier transform techniques in blasting analysis  

SciTech Connect

The US Bureau of Mines has developed computer software which uses fast Fourier transform (FFT) techniques to evaluate blasting data. The software is useful because it allows blasters to evaluate (1) the frequency content of ground vibration time history data; (2) the effects of initiator scatter on the frequency spectra of ground vibrations; and (3) the fragmentation distribution of rock muckpiles from photographs. A one-dimensional version of the software was used in the first two cases. Monte Carlo techniques were used to simulate the scatter of initiators. The results are shown in computer generated three-dimensional color contour plots. To determine the fragment size distribution using photographic and digital image processing techniques a two-dimensional FFT routine was written. The FFT of the digitized muckpile images are filtered to remove lower spatial frequencies. The higher spatial frequencies, which are associated with rock particle edges, are subsequently enhanced. The inverse two-dimensional FFT was used to reconstruct the digital image. Photographic images taken of rock muckpiles resulting from full scale blasts at a limestone quarry were digitized and evaluated using the new FFT techniques. The fragment size distributions determined from the photographs agree with the distributions determined by partial screening.

Rholl, S.A.; Stagg, M.S. [Bureau of Mines, Minneapolis, MN (United States). Twin Cities Research Center

1995-12-31

55

The performance of methods based on the fractional Fourier transform for detecting marine mammal vocalizations.  

PubMed

The analysis of cetacean vocalizations is considered using Fourier-based techniques that employ chirp functions in their decomposition. In particular, the paper considers a short-time methods based on the fractional Fourier transform for detecting frequency modulated narrow-band signals, such as dolphin whistles, and compares this to the classical short-time Fourier methods. The fractional Fourier technique explored computes transforms associated with a range of chirp rates and automatically selects the rate for the final analysis. This avoids the need for prior knowledge of signal's chirp rate. An analysis is presented that details the performance of both methods as signal detectors and allows one to determine their detection thresholds. These thresholds are then used to measure the detectability of synthetic signals. This principle is then extended to measure performance on a set of recordings of narrow-band vocalizations from a range of cetacean species. PMID:21973352

Locke, Jonathan; White, Paul R

2011-10-01

56

Transform Coding Techniques for Lossy Hyperspectral Data Compression  

Microsoft Academic Search

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

Barbara Penna; Tammam Tillo; Enrico Magli; Gabriella Olmo

2007-01-01

57

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

PubMed Central

We describe a new approach to analyze chirp syllables of free-tailed bats from two regions of Texas in which they are predominant: Austin and College Station. Our goal is to characterize any systematic regional differences in the mating chirps and assess whether individual bats have signature chirps. The data are analyzed by modeling spectrograms of the chirps as responses in a Bayesian functional mixed model. Given the variable chirp lengths, we compute the spectrograms on a relative time scale interpretable as the relative chirp position, using a variable window overlap based on chirp length. We use 2D wavelet transforms to capture correlation within the spectrogram in our modeling and obtain adaptive regularization of the estimates and inference for the regions-specific spectrograms. Our model includes random effect spectrograms at the bat level to account for correlation among chirps from the same bat, and to assess relative variability in chirp spectrograms within and between bats. The modeling of spectrograms using functional mixed models is a general approach for the analysis of replicated nonstationary time series, such as our acoustical signals, to relate aspects of the signals to various predictors, while accounting for between-signal structure. This can be done on raw spectrograms when all signals are of the same length, and can be done using spectrograms defined on a relative time scale for signals of variable length in settings where the idea of defining correspondence across signals based on relative position is sensible. PMID:23997376

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

2013-01-01

58

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

PubMed

We describe a new approach to analyze chirp syllables of free-tailed bats from two regions of Texas in which they are predominant: Austin and College Station. Our goal is to characterize any systematic regional differences in the mating chirps and assess whether individual bats have signature chirps. The data are analyzed by modeling spectrograms of the chirps as responses in a Bayesian functional mixed model. Given the variable chirp lengths, we compute the spectrograms on a relative time scale interpretable as the relative chirp position, using a variable window overlap based on chirp length. We use 2D wavelet transforms to capture correlation within the spectrogram in our modeling and obtain adaptive regularization of the estimates and inference for the regions-specific spectrograms. Our model includes random effect spectrograms at the bat level to account for correlation among chirps from the same bat, and to assess relative variability in chirp spectrograms within and between bats. The modeling of spectrograms using functional mixed models is a general approach for the analysis of replicated nonstationary time series, such as our acoustical signals, to relate aspects of the signals to various predictors, while accounting for between-signal structure. This can be done on raw spectrograms when all signals are of the same length, and can be done using spectrograms defined on a relative time scale for signals of variable length in settings where the idea of defining correspondence across signals based on relative position is sensible. PMID:23997376

Martinez, Josue G; Bohn, Kirsten M; Carroll, Raymond J; Morris, Jeffrey S

2013-06-01

59

Chirped-pulse millimeter-wave spectroscopy: Spectrum, dynamics, and manipulation of Rydberg–Rydberg 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 Rydberg–Rydberg transitions is that they have enormous electric dipole transition ...

Colombo, Anthony P.

2013-01-01

60

Strain-independent temperature measurements using a standard and a Chirped fibre Bragg Grating  

Microsoft Academic Search

Chirped fibre Bragg gratings (CFBGs) fabricated in hydrogenated plain telecom fibre have a temperature coefficient approximately 20% higher than standard FBGs with identical strain coefficients. Thus a simple technique for strain-independent temperature measurement is proposed.

Anbhawa Nand; Daniel J. Kitcher; Scott A. Wade; Greg W. Baxter; Rhys Jones; S. F. Collins

2006-01-01

61

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

62

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

63

Chirp generated acoustic wavefield images  

NASA Astrophysics Data System (ADS)

Guided waves are being considered for structural health monitoring (SHM) applications, and they can also be used to reduce subsequent inspection times once defects are detected. One proposed SHM method is to use an array of permanently attached piezoelectric transducers to generate and receive guided waves between the various transducer pairs. The interrogation can be done on a continuous or periodic basis to assess the health of the structure. Once defects are suspected in the structure, the traditional approach is to disassemble components for conventional nondestructive evaluation (NDE); however, this is an expensive and time consuming process. A less expensive alternative to conventional NDE is to record acoustic wavefield images of guided waves generated from the attached transducers. These images clearly show details of guided waves as they propagate outward from the source, reflect from structural discontinuities and specimen boundaries, and scatter from any damage sites within the structure. However, the recorded waves are typically narrowband to enable effective visualization of echoes that are relatively compact in time. In this paper, we consider wavefield images that are recorded from a chirp excitation, which offers the advantage of high quality broadband data from a single excitation. However, responses are not directly useful because the received echoes are too extended in time. Signals are post-processed to obtain multiple narrowband and broadband responses containing echoes that are more compact in time to enable visualization of guided waves interacting with structural features. This technique is demonstrated on an aluminum plate that contains attached stiffeners and glued-on piezoelectric disc transducers. Wavefield data are recorded using an air-coupled transducer scanned over the plate surface while one of the attached transducers acts as a guided wave source. Waves interacting with the stiffener and the inactive discs are analyzed via broadband and narrowband processing at multiple frequencies.

Michaels, Thomas E.; Michaels, Jennifer E.; Lee, Sang Jun; Chen, Xin

2011-04-01

64

Detection algorithm of big bandwidth chirp signals based on STFT  

NASA Astrophysics Data System (ADS)

Aiming at solving the problem of detecting the wideband chirp signals under low Signal-to-Noise Ratio (SNR) condition, an effective signal detection algorithm based on Short-Time-Fourier-Transform (STFT) is proposed. Considering the characteristic of dispersion of noise spectrum and concentration of chirp spectrum, STFT is performed on chirp signals with Gauss window by fixed step, and these frequencies of peak spectrum obtained from every STFT are in correspondence to the time of every stepped window. Then, the frequencies are binarized and the approach similar to mnk method in time domain is used to detect the chirp pulse signal and determine the coarse starting time and ending time. Finally, the data segments, where the former starting time and ending time locate, are subdivided into many segments evenly, on which the STFT is implemented respectively. By that, the precise starting and ending time are attained. Simulations shows that when the SNR is higher than -28dB, the detection probability is not less than 99% and false alarm probability is zero, and also good estimation accuracy of starting and ending time is acquired. The algorithm is easy to realize and surpasses FFT in computation when the width of STFT window and step length are selected properly, so the presented algorithm has good engineering value.

Wang, Jinzhen; Wu, Juhong; Su, Shaoying; Chen, Zengping

2014-10-01

65

Image coding by differential pulse code modulation and transform coding techniques, a comparative survey  

Microsoft Academic Search

Differential pulse code modulation (DPCM) and transform coding techniques for digital image transmission are described, and their relative advantages are compared. For high-quality video transmission, both DCPM and transform coding were found to need sufficient data protection. Initial experiments showed that in transform coding the decomposition of the image into blocks results in residual errors that do not impair picture

H.-J. Grallert; W. Tengler

1984-01-01

66

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

67

Effective temporal resolution in pump-probe spectroscopy with strongly chirped pulses  

SciTech Connect

This paper introduces a general theoretical description of femtosecond pump-probe spectroscopy with chirped pulses whose joint spectral and temporal profile is expressed by Wigner spectrograms. We demonstrate that the actual experimental time resolution intimately depends on the pulse-sample interaction and that the commonly used instrumental response function needs to be replaced by a sample-dependent effective response function. We also show that, using the proper configurations in excitation and/or detection, it is possible to overcome the temporal smearing of the measured dynamics due to chirp-induced pulse broadening and recover the temporal resolution that would be afforded by the transform-limited pulses. We verify these predictions with experiments using broadband chirped pump and probe pulses. Our results allow optimization of the temporal resolution in the common case when the chirp of the pump and/or probe pulse is not corrected and may be extended to a broad range of time-resolved experiments.

Polli, D.; Lanzani, G. [IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); CNST, Istituto Italiano di Tecnologia, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Brida, D.; Cerullo, G. [IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Mukamel, S. [Chemistry Department, University of California, Irvine, Irvine, California 92697-2025 (United States)

2010-11-15

68

Chirped pulse amplification: Present and future  

SciTech Connect

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

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

1988-01-01

69

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

SciTech Connect

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

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

1989-01-01

70

Hybrid chirped pulse amplification system  

DOEpatents

A hybrid chirped pulse amplification system wherein a short-pulse oscillator generates an oscillator pulse. The oscillator pulse is stretched to produce a stretched oscillator seed pulse. A pump laser generates a pump laser pulse. The stretched oscillator seed pulse and the pump laser pulse are directed into an optical parametric amplifier producing an optical parametric amplifier output amplified signal pulse and an optical parametric amplifier output unconverted pump pulse. The optical parametric amplifier output amplified signal pulse and the optical parametric amplifier output laser pulse are directed into a laser amplifier producing a laser amplifier output pulse. The laser amplifier output pulse is compressed to produce a recompressed hybrid chirped pulse amplification pulse.

Barty, Christopher P.; Jovanovic, Igor

2005-03-29

71

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

72

Sectional chirped volume Bragg grating compressors for high-power chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

Chirped Bragg Gratings (CBGs) recorded in photo-thermo-refractive (PTR) glass have been successfully used as ultrashort pulse stretchers and compressors in a variety of solid-state and fiber chirped pulse amplification (CPA) laser systems. Compared to traditional pairs of surface gratings, CBG-based stretchers and compressors offer significant advantage in compactness and robustness. They are insensitive to polarization, require virtually no alignment and can handle high average and peak power. At the current technology stage PTR-glass CBGs can provide up to 30 nm spectral bandwidth and up to 300 ps stretched pulse duration. In this paper we propose a concept of sectional CBGs, where multiple CBGs with different central wavelengths recorded in separate PTR-glass wafers are stacked and phased to form a single grating with effective thickness and bandwidth larger than each section. We present results of initial experiment in which pulses from a femtosecond oscillator centered at 1028 nm are stretched by a 32-mm thick CBG to about 160 ps and recompressed by a monolithic 32-mm CBG with 11 nm bandwidth and by a sectional CBG with two 16-mm thick sections each having ~ 5 nm bandwidth and offset central wavelengths: 1025.5 and 1031 nm. In both cases, compressed pulse duration of 350-400 fs, ~ 1.1 × transform-limit was obtained. These results allow CBG-based pulse stretchers and compressors with high stretch ratio and wide bandwidth to be constructed from multiple sections.

Andrusyak, Oleksiy; Canioni, Lionel; Cohanoshi, Ion; Delaigue, Martin; Rotari, Eugeniu; Smirnov, Vadim; Glebov, Leonid

2010-02-01

73

Fourier transform techniques for mode separation in piezocomposites  

Microsoft Academic Search

One and two dimensional real and complex fast fourier transform (FFT) algorithms were applied to the results of displacement phase and magnitude maps obtained from interferometric studies on a type 1-3 piezocomposite specimen electrically driven at a number of frequencies between 6 kHz and 1.0 MHz. Analysis was performed on experimental results for materials consisting of square cross section piezoelectric

Dianne M. Granata; William R. Scott; Martin J. Ryan

1993-01-01

74

Diagnostic ultrasound tooth imaging using fractional Fourier transform.  

PubMed

An ultrasound contact imaging method is proposed to measure the enamel thickness in the human tooth. A delay-line transducer with a working frequency of 15 MHz is chosen to achieve a minimum resolvable distance of 400 ?m in human enamel. To confirm the contact between the tooth and the transducer, a verification technique based on the phase shift upon reflection is used. Because of the high attenuation in human teeth, linear frequency-modulated chirp excitation and pulse compression are exploited to increase the penetration depth and improve the SNR. Preliminary measurements show that the enamel-dentin boundary creates numerous internal reflections, which cause the applied chirp signals to interfere arbitrarily. In this work, the fractional Fourier transform (FrFT) is employed for the first time in dental imaging to separate chirp signals overlapping in both time and frequency domains. The overlapped chirps are compressed using the FrFT and matched filter techniques. Micro-computed tomography is used for validation of the ultrasound measurements for both techniques. For a human molar, the thickness of the enamel layer is measured with an average error of 5.5% after compressing with the FrFT and 13.4% after compressing with the matched filter based on the average speed of sound in human teeth. PMID:21989873

Harput, Sevan; Evans, Tony; Bubb, Nigel; Freear, Steven

2011-10-01

75

Program Transformation Techniques for Host-based Intrusion Prevention  

E-print Network

and execute malicious programs such as viruses and worms. Sandboxing is a well- known technique to protect end when to sandbox an application iii #12;given that the application can operate both on local files (more derived from network inputs. Eventually, Aussum helps the underlying sandboxing system to sandbox tainted

Chiueh, Tzi-cker

76

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

77

Parallel Loop Transformation Technique for Efficient Rate Detection  

Microsoft Academic Search

Races might result in unintended nondeterministic ex- ecution of purallel programs and thus race detection is one of the critical issues to be resolved in debugging of shared-memory parallel progrums. On-the-fly race detec- tion techniques have been developed as one of approuches for the problem. However on-the-fly race detection tech- niques suffer from the huge run-time overhead because in which

Jeong-si Kim; Dong-soo Han; Chan-su Yu

2001-01-01

78

Chirp Measurements Of A Ten Joule Pulsed CO2 Oscillator  

NASA Astrophysics Data System (ADS)

Chirp measurements have been conducted on the pulsed output of an unstable resonator oscillating on the P20 line of the 10.6 micron band of an e-beam sustained CO2 gain medium. The mode volume was approximately 5 liters at a pressure between 1/3 and 1/2 atm. The measurements were conducted at pulse lengths of the order of 10 microseconds and are useful in characterizing the device for use in radar applications. A heterodyne technique was used, mixing the oscillator signal with a cw laser operating on the P20 line, but offset approximately 40 MHz in order to resolve uncertainties in the sense of the frequency deviation. Chirp values of less than 400 kHz are observed during the first 10 ?sec.

Hoag, Ethan D.

1989-12-01

79

Parallel Loop Transformation Technique for Efficient Race Detection JeongSi Kim  

E-print Network

Parallel Loop Transformation Technique for Efficient Race Detection Jeong­Si Kim Computer@icu.ac.kr Abstract Races might result in unintended nondeterministic ex­ ecution of parallel programs and thus race­the­fly race detec­ tion techniques have been developed as one of approaches for the problem. However on

Yu, Chansu

80

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

Microsoft Academic Search

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

Jian-Da Wu; Jien-Chen Chen

2006-01-01

81

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

PubMed

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

Loriot, Vincent; Gitzinger, Gregory; Forget, Nicolas

2013-10-21

82

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

83

Transionospheric signal detection with chirped wavelets  

SciTech Connect

Chirped wavelets are utilized to detect dispersed signals in the joint time scale domain. Specifically, pulses that become dispersed by transmission through the ionosphere and are received by satellites as nonlinear chirps are investigated. Since the dispersion greatly lowers the signal to noise ratios, it is difficult to isolate the signals in the time domain. Satellite data are examined with discrete wavelet expansions. Detection is accomplished via a template matching threshold scheme. Quantitative experimental results demonstrate that the chirped wavelet detection scheme is successful in detecting the transionospheric pulses at very low signal to noise ratios.

Doser, A.B.; Dunham, M.E.

1997-11-01

84

Chirped-pulse manipulated carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs  

SciTech Connect

Chirped pulse controlled carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs are investigated by degenerate pump-probe technique. Varying the chirped condition of excited pulse from negative to positive increases the carrier relaxation time so as to modify the dispersion and reshape current pulse in time domain. The spectral dependence of carrier dynamics is analytically derived and explained by Shockley-Read Hall model. This observation enables the new feasibility of controlling carrier dynamics in ultrafast optical devices via the chirped pulse excitations.

Lee, Chao-Kuei, E-mail: chuckcklee@yahoo.com [Department of Photonics, National Sun-Yat-Sen University, Kaohsiung 80400, Taiwan (China); Lin, Yuan-Yao [Department of Electrical Engineering, Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 30010, Taiwan (China); Lin, Sung-Hui [Department of Photonics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Lin, Gong-Ru [Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan (China); Pan, Ci-Ling [Department of Photonics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Department of Physics, National Tsing Hwa University, Hsinchu 30010, Taiwan (China)

2014-04-28

85

Kinetic view of chirped optical lattice gas heating  

NASA Astrophysics Data System (ADS)

With a focus on optical lattice gas heating, direct simulation Monte Carlo was used to investigate the interaction between molecular nitrogen, argon and methane, initially at 300 K and 0.8 atm, with pulsed, chirped optical lattices. Created from two 700 mJ, 532 nm, flattop laser pulses, the optical lattice parameters simulated are based on published optical lattice-based experiments, to ensure that pulse energies and durations do not exceed published optical breakdown (ionization) thresholds. Resultant translational gas temperatures, as well as induced bulk velocities, were used quantify energy and momentum deposition. To maximize available gas temperature changes achieved using the technique, laser pulses were linearly chirped to produce lattice velocities able to more effectively facilitate energy deposition throughout the pulse duration. From the initial conditions, the maximum, end pulse axial translational temperature obtained in nitrogen was approximately 755 K, at a lattice velocity of 400 m/s linearly chirped at 25 Gm/s2 over the 40 ns pulse duration. To date, this stands as the single largest, numerically-predicted temperature change from optical lattice gas heating under the numerical integration of real world energy and laser-based limitations.

Graul, J. S.; Gimelshein, S. F.; Lilly, T. C.

2014-12-01

86

Adaptive Chirp Beamforming for Direction-of-Arrival Estimation of Wideband Chirp Signals in Sensor Arrays  

NASA Astrophysics Data System (ADS)

An adaptive chirp beamforming method is proposed to solve the bias problem in the direction-of-arrival (DOA) estimation of wideband chirp signals that have identical time-frequency parameters yet emanate from different directions. The proposed method, based on the steered minimum variance (STMV) method, exploits the time-frequency structure of a chirp signal to improve the DOA estimation performance by effectively suppressing the wideband chirp interferences causing the bias. Simulations are performed to demonstrate the effectiveness of the proposed method.

Kim, Jeong-Soo; Choi, Byung-Woong; Bae, Eun-Hyon; Lee, Kyun-Kyung

87

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

88

Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges.  

PubMed

We present a simple and robust technique to retrieve the phase of ultrashort laser pulses, based on a chirped mirror and glass wedges compressor. It uses the compression system itself as a diagnostic tool, thereby making unnecessary the use of complementary diagnostic tools. We used this technique to compress and characterize 7.1 fs laser pulses from an ultrafast laser oscillator. PMID:22274393

Miranda, Miguel; Fordell, Thomas; Arnold, Cord; L'Huillier, Anne; Crespo, Helder

2012-01-01

89

Characteristics of nonlinear imaging of broadband laser stacked by chirped pulses  

NASA Astrophysics Data System (ADS)

Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.

Wang, Youwen; You, Kaiming; Chen, Liezun; Lu, Shizhuan; Dai, Zhiping; Ling, Xiaohui

2014-11-01

90

Optical chirped beam amplification and propagation  

DOEpatents

A short pulse laser system uses dispersive optics in a chirped-beam amplification architecture to produce high peak power pulses and high peak intensities without the potential for intensity dependent damage to downstream optical components after amplification.

Barty, Christopher P.

2004-10-12

91

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

Microsoft Academic Search

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

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

1994-01-01

92

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

93

Electric field in transformer oil measured with the Kerr-effect technique  

Microsoft Academic Search

The electric field distribution in transformer insulating oil was measured as a function of time, both after application of a DC step voltage and after polarity change of the DC voltage, using a highly sensitive advanced Kerr electro-optic technique. The lower limit of the applied electric field intensity was 100 V\\/cm in insulating oil with an electrode length of 8

Y. Nonaka; H. Sato; T. Maeno; T. Takada

1991-01-01

94

The Technique of Genetic Transformation Mediated by keV Ion Beam  

Microsoft Academic Search

The application of keV ion beam in life science started in China several decades ago. In 1986, researchers initially studied the mutagenic effect of ion beam, and successfully applied it to plant breeding. Nowadays, ion beam implantation technique has been extensively applied to many biological fields. This paper mainly introduces one of its important applications: Genetic transformation mediated by keV

Po Bian; Zengliang Yu

2005-01-01

95

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

96

Transformation Technique Research of the Improved Link-type Shape Shifting Modular Robot  

Microsoft Academic Search

The link-type shape shifting modular robot permits high mobility under unstructured environment for their continuously driving and redundancy. The objective of this work is to enhance the flexibility of the primary shape shifting robot through transformation technique improvement, especially in the robot's torque and current reduction. The improved prototype, a manually reconfigurable and shape changeable tracked robot named \\

Jinguo Liu; Yuechao Wang; Bin Li; Shugen Ma; Jing Wang; Huibin Cao

2006-01-01

97

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

SciTech Connect

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

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

2007-01-03

98

Multispectral image sharpening using wavelet transform techniques and spatial correlation of edges  

USGS Publications Warehouse

Several reported image fusion or sharpening techniques are based on the discrete wavelet transform (DWT). The technique described here uses a pixel-based maximum selection rule to combine respective transform coefficients of lower spatial resolution near-infrared (NIR) and higher spatial resolution panchromatic (pan) imagery to produce a sharpened NIR image. Sharpening assumes a radiometric correlation between the spectral band images. However, there can be poor correlation, including edge contrast reversals (e.g., at soil-vegetation boundaries), between the fused images and, consequently, degraded performance. To improve sharpening, a local area-based correlation technique originally reported for edge comparison with image pyramid fusion is modified for application with the DWT process. Further improvements are obtained by using redundant, shift-invariant implementation of the DWT. Example images demonstrate the improvements in NIR image sharpening with higher resolution pan imagery.

Lemeshewsky, George P.; Schowengerdt, Robert A.

2000-01-01

99

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

100

Attenuated total reflectance spectroscopy with chirped-pulse upconversion.  

PubMed

Chirped-pulse upconversion technique has been applied to attenuated total reflectance (ATR) infrared spectroscopy. An extremely broadband infrared pulse was sent to an ATR diamond prism and the reflected pulse was converted to the visible by using four-wave mixing in krypton gas. Absorption spectra of liquids in the range from 200 to 5500 cm(-1) were measured with a visible spectrometer on a single-shot basis. The system was applied to observe the dynamics of exchanging process of two solvents, water and acetone, which give clear vibrational spectral contrast. We observed that the exchange was finished within ? 10 ms. PMID:25606893

Shirai, Hideto; Duchesne, Constance; Furutani, Yuji; Fuji, Takao

2014-12-01

101

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

NASA Astrophysics Data System (ADS)

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

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

102

Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments.  

PubMed

We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target approximately 5 x 10(13) W/cm(2) to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps. PMID:11970183

Benuzzi-Mounaix, A; Koenig, M; Boudenne, J M; Hall, T A; Batani, D; Scianitti, F; Masini, A; Di Santo, D

1999-09-01

103

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

104

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

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

105

The analysis of furanic and non-furanic compounds as a transformer diagnostic technique  

SciTech Connect

Overheating of solid transformer insulation produces a multitude of degradation products. To date their detection and significance in transformer oil have been limited primarily to 2-furaldehyde and its derivatives. In laboratory experiments, heating of thermally upgraded Kraft paper, pressboard, and paper laminates in conjunction with insulating oil produced a variety of other volatile and oil soluble compounds of potential diagnostic significance. Of particular importance was the presence of sulfides and nitrogen-containing compounds. Their identification and analytical techniques needed to detect these compounds are briefly described. The merits of a 2-furaldehyde-in-oil screen test in conjunction with gas-in-oil analysis to identify equipment with paper degradation problems are discussed. An update on the correlation of faraldehydes in oil with the DP of paper from in-service transformers is also given.

Dominelli, N.; Landa, J.V.; Hassanali, S.J.; Hall, E.A. [Powertech Labs Inc., Surrey (Canada)

1996-03-01

106

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 ~2×104 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

107

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

Microsoft Academic Search

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

Martin Pollakowski; Helmut Ermert

1994-01-01

108

Cost-Optimal Design of a 3-Phase Core Type Transformer by Gradient Search Technique  

NASA Astrophysics Data System (ADS)

3-phase core type transformers are extensively used as power and distribution transformers in power system and their cost is a sizable proportion of the total system cost. Therefore they should be designed cost-optimally. The design methodology for reaching cost-optimality has been discussed in details by authors like Ramamoorty. It has also been discussed in brief in some of the text-books of electrical design. The paper gives a method for optimizing design, in presence of constraints specified by the customer and the regulatory authorities, through gradient search technique. The starting point has been chosen within the allowable parameter space the steepest decent path has been followed for convergence. The step length has been judiciously chosen and the program has been maneuvered to avoid local minimal points. The method appears to be best as its convergence is quickest amongst different optimizing techniques.

Basak, R.; Das, A.; Sensarma, A. K.; Sanyal, A. N.

2014-04-01

109

Color image encryption based on fractional Fourier transforms and pixel scrambling technique  

Microsoft Academic Search

Color image encryption based on fractional Fourier transform (FRT) and pixel scrambling technique is presented in this paper. In general, color (RGB) image cannot be directly encrypted using a traditional setup for optical information processing, because which is only adapted to process two-dimensional gray image. In the proposed method, a three-dimensional RGB image is decomposed to three two-dimensional gray images

Jianlin Zhao; Hongqiang Lu; Qi Fan

2007-01-01

110

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?µm spot size and a fast pixel array detector is used to achieve temporal resolution of 55?µs. In the second technique the X-rays are focused with Kirkpatrick–Baez mirrors to achieve a spatial resolution better than 10?µm and a fast shutter is used to provide temporal resolution better than 20?µs while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils. PMID:21525656

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

2011-01-01

111

Techniques for Handling Channeling in High Resolution Fourier Transform Spectra Recorded with Synchrotron Sources  

SciTech Connect

Seven different techniques in dealing the problem of channel spectra in Fourier transform Spectroscopy utilizing synchrotron source were examined and compared. Five of these techniques deal with the artifacts (spikes) in the recorded interferogram which in turn result in channel spectra within the spectral domain. Such interferogram editing method include replacing these spikes with zeros, straight line, fitted polynomial curve, rescaled spike and spike reduced with Gauss Function. Another two techniques try to target this issue in the spectral domain instead by either generating a synthetic background simulating the channels or measuring the channels parameters (amplitude, spacing and phase) to use in the spectral fitting program. Results showed spectral domain techniques produces higher quality results in terms of signal to noise and fitting residual. The effect of each method on the line parameters such as position, intensity are air broadening are also measured and discussed.

Ibrahim, Amr; PredoiCross, Adriana; Teillet, P. M. [Department of Physics and Astronomy, University of Lethbridge. 4401 University Dr. W., Lethbridge T1K 3M4, Alberta (Canada)

2010-10-29

112

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-García, V.; Picó, R.; Cebrecos, A.; Sánchez-Morcillo, V. J.; Staliunas, K.

2013-03-01

113

Dispersive propagation of a chirped laser pulse  

NASA Astrophysics Data System (ADS)

Dispersive effects on the phase of a chirped infrared CO2 laser pulse propagating vertically through the atmosphere are determined. The dispersion is modeled using a Voigt type of integral. The line strength and line broadening are calculated as functions of height using the McClatchey tables for their sea level values. Changes in phase over the chirp width are then found by numerical integration with respect to height for heights to 50 km for the CO2 P20 and P22 lines in the 1.4-micron band.

Hallidy, W. H.

114

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

115

Unraveling the nature of electric field- and stress- induced structural transformations in soft PZT by a new powder poling technique.  

PubMed

A 'powder-poling' technique was developed to study electric field induced structural transformations in ferroelectrics exhibiting a morphotropic phase boundary (MPB). The technique was employed on soft PZT exhibiting a large longitudinal piezoelectric response (d(33) ? 650 pC N(-1)). It was found that electric poling brings about a considerable degree of irreversible tetragonal to monoclinic transformation. The same transformation was achieved after subjecting the specimen to mechanical stress, which suggests an equivalence of stress and electric field with regard to the structural mechanism in MPB compositions. The electric field induced structural transformation was also found to be accompanied by a decrease in the spatial coherence of polarization. PMID:25629264

Kalyani, Ajay Kumar; V, Lalitha K; James, Ajit R; Fitch, Andy; Ranjan, Rajeev

2015-02-25

116

On the relationship between pump chirp and single-photon chirp in spontaneous parametric downconversion  

E-print Network

We study the chronocyclic character, i.e. the joint temporal and spectral properties, of the single-photon constituents of photon pairs generated by spontaneous parametric down conversion. In particular we study how single photon properties, including purity and single-photon chirp, depend on photon pair properties, including the type of signal-idler spectral and correlations and the level of pump chirp.

X. Sanchez-Lozano; A. B. U'Ren; J. L. Lucio

2012-06-04

117

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

118

Fractional Fourier plane image encryption technique using radial hilbert-, and Jigsaw transform  

NASA Astrophysics Data System (ADS)

A new method for image encryption using integral order radial Hilbert transform (RHT) filter in the fractional Fourier transform (FRT) domain has been proposed. The technique is implemented using the popular double random phase encoding method in the fractional Fourier domain. The random phase masks (RPMs), integral orders of the RHT, fractional orders of FRT, and indices of the Jigsaw transform (JT) have been used as keys for encryption and decryption. Simulation results have been presented and the schematic representation for optical implementation has been proposed. The mean-square-error and signal-to-noise ratio between the decrypted image and the input image have been calculated for the correct as well as incorrect orders of the RHT. Effect of occlusion and noise on the performance of the proposed scheme has also been studied. The robustness of the technique has been verified against attack using partial windows of the correct random phase masks. Similar investigations have also been carried out for the chosen-, and the known-plain-text attacks.

Joshi, Madhusudan; Shakher, Chandra; Singh, Kehar

2010-07-01

119

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

SciTech Connect

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

Mori, Yoshihiko; Torii, Susumu; Ebihara, Daiki

1999-09-01

120

Adaptive narrow-band interference rejection in a DS spread-spectrum intercept receiver using transform domain signal processing techniques  

NASA Technical Reports Server (NTRS)

An intercept receiver which uses a transform-domain-processing filter is described. This receiver detects direct-sequence BPSK spread-spectrum signals in the presence of narrowband interference by employing adaptive narrowband interference rejection techniques. The improvement in the system performance over that of conventional detection techniques is shown by presenting the results of experimental measurements of probability of detection versus false alarm for an enhanced total power detector. Also presented are certain results corresponding to detection of the spectral lines generated at twice the carrier frequency, wherein the goal is often not just signal detection, but also carrier frequency estimation. The receiver uses one of two transform-domain-processing techniques for adaptive narrowband interference rejection. In the first technique, the narrowband interference is detected and excised in the transform domain by using an adaptive notch filter. In the second technique, the interference is suppressed using soft-limiting in the transform domain.

Gevargiz, John; Das, Pankaj K.; Milstein, Laurence B.

1989-01-01

121

Simplified Homodyne Detection for FM Chirped Lidar  

E-print Network

................................................................4 CHAPTER 2 – RADAR AND LIDAR TOPICS....................................................................6 2.1 REVIEW OF EXISTING LIDAR SYSTEMS..............................................................6 Geoscience Laser Altimeter System (GLAS..............................................................................18 2.3 PULSE COMPRESSION........................................................................................19 A Basic Pulse Compression Method................................................................20 Linear FM Chirp with Analog Mixing...

Adany, Peter

2007-12-14

122

Self-imaging chirped holographic optical waveguides.  

PubMed

To manipulate light propagation in optical waveguides, we have studied holographic, chirped structures within the waveguide's core. The holographic structures were embedded along the wave propagation direction and extended throughout the entire guide. Various self-imaging guides have been analyzed and realized to demonstrate the effect of different structures. PMID:18264499

Grebel, H; Graziani, J L; Vijayalakshmi, S; Shacklette, L W; Stengel, K M; Eldada, L; Norwood, R; Yardley, J T

1997-12-20

123

Self-Imaging Chirped Holographic Optical Waveguides  

Microsoft Academic Search

To manipulate light propagation in optical waveguides, we have studied holographic, chirped structures within the waveguide s core. The holographic structures were embedded along the wave propagation direction and extended throughout the entire guide. Various self-imaging guides have been analyzed and realized to demonstrate the effect of different structures.

Haim Grebel; Jean-Luc Graziani; Sankaran Vijayalakshmi; Lawrence W. Shacklette; Kelly M. T. Stengel; Louay Eldada; Robert Norwood; James T. Yardley

1997-01-01

124

Unambiguous evaluation of a chirp measurement standard  

NASA Astrophysics Data System (ADS)

This article describes an automated evaluation method for the chirp standard. Chirp calibration standards provide a way to describe the transfer behavior of different spatial frequencies as they contain sinusoidal functions of varying wavelengths (Krüger-Sehm et al 2007 chirp calibration standards for surface measuring instruments Tech. Mess. tm 74 572–76 Pehnelt et al 2011 Comparative analysis of optical surface measuring systems with a chip calibration standard Tech. Mess. tm 78 457–62). By introducing a new, automated evaluation method, an improvement for the application of the chirp standard can be achieved. The data-preprocessing for topography and profile measurement data and the fit of the geometric elements are described. Automated evaluation can reduce the labor required to evaluate measured data and make it easier to compare different evaluations in the course of standardization. The algorithm can be used to characterize the so-called ‘small scale fidelity’ of an optical instrument. The term ‘small scale fidelity’ is currently discussed in the optical group of working group no. 16 of the ISO technical committee 213.

Seewig, Jörg; Eifler, Matthias; Wiora, Georg

2014-10-01

125

Pattern Transformation of Heat-Shrinkable Polymer by Three-Dimensional (3D) Printing Technique  

NASA Astrophysics Data System (ADS)

A significant challenge in conventional heat-shrinkable polymers is to produce controllable microstructures. Here we report that the polymer material fabricated by three-dimensional (3D) printing technique has a heat-shrinkable property, whose initial microstructure can undergo a spontaneous pattern transformation under heating. The underlying mechanism is revealed by evaluating internal strain of the printed polymer from its fabricating process. It is shown that a uniform internal strain is stored in the polymer during the printing process and can be released when heated above its glass transition temperature. Furthermore, the internal strain can be used to trigger the pattern transformation of the heat-shrinkable polymer in a controllable way. Our work provides insightful ideas to understand a novel mechanism on the heat-shrinkable effect of printed material, but also to present a simple approach to fabricate heat-shrinkable polymer with a controllable thermo-structural response.

Zhang, Quan; Yan, Dong; Zhang, Kai; Hu, Gengkai

2015-03-01

126

Pattern Transformation of Heat-Shrinkable Polymer by Three-Dimensional (3D) Printing Technique  

PubMed Central

A significant challenge in conventional heat-shrinkable polymers is to produce controllable microstructures. Here we report that the polymer material fabricated by three-dimensional (3D) printing technique has a heat-shrinkable property, whose initial microstructure can undergo a spontaneous pattern transformation under heating. The underlying mechanism is revealed by evaluating internal strain of the printed polymer from its fabricating process. It is shown that a uniform internal strain is stored in the polymer during the printing process and can be released when heated above its glass transition temperature. Furthermore, the internal strain can be used to trigger the pattern transformation of the heat-shrinkable polymer in a controllable way. Our work provides insightful ideas to understand a novel mechanism on the heat-shrinkable effect of printed material, but also to present a simple approach to fabricate heat-shrinkable polymer with a controllable thermo-structural response. PMID:25757881

Zhang, Quan; Yan, Dong; Zhang, Kai; Hu, Gengkai

2015-01-01

127

A fast Fourier transform accelerated Ewald summation technique for the vector electromagnetic rectangular cavity Green's function  

NASA Astrophysics Data System (ADS)

A fast Fourier transform accelerated Ewald method for the computation of the vector electromagnetic rectangular cavity Green's function in terms of the electric field due to electric currents is presented and used in a boundary integral formulation. The Ewald summation technique suffers from the high-frequency breakdown when it is applied to Green's functions of wave problems. In the case of the rectangular cavity Green's function, the number of necessary terms in the spectral series grows, therefore, cubically with frequency for a given accuracy. To counteract the high-frequency breakdown, the evaluation of the spectral series is accelerated with an inverse fast Fourier transform in this work. At high frequencies, a speed-up of up to four orders of magnitude is achieved. As an application example, a reverberation chamber containing a metallic enclosure and a mode-stirrer is modeled.

Gruber, M. E.; Koenen, C.; Eibert, T. F.

2015-01-01

128

Pattern Transformation of Heat-Shrinkable Polymer by Three-Dimensional (3D) Printing Technique.  

PubMed

A significant challenge in conventional heat-shrinkable polymers is to produce controllable microstructures. Here we report that the polymer material fabricated by three-dimensional (3D) printing technique has a heat-shrinkable property, whose initial microstructure can undergo a spontaneous pattern transformation under heating. The underlying mechanism is revealed by evaluating internal strain of the printed polymer from its fabricating process. It is shown that a uniform internal strain is stored in the polymer during the printing process and can be released when heated above its glass transition temperature. Furthermore, the internal strain can be used to trigger the pattern transformation of the heat-shrinkable polymer in a controllable way. Our work provides insightful ideas to understand a novel mechanism on the heat-shrinkable effect of printed material, but also to present a simple approach to fabricate heat-shrinkable polymer with a controllable thermo-structural response. PMID:25757881

Zhang, Quan; Yan, Dong; Zhang, Kai; Hu, Gengkai

2015-01-01

129

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

130

Efficient Quantum State Tomography for Quantum Information Processing using a two-dimensional Fourier Transform Technique  

E-print Network

A new method of quantum state tomography for quantum information processing is described. The method based on two-dimensional Fourier transform technique involves detection of all the off-diagonal elements of the density matrix in a two-dimensional experiment. All the diagonal elements are detected in another one-dimensional experiment. The method is efficient and applicable to a wide range of spin systems. The proposed method is explained using a 2 qubit system and demonstrated by tomographing arbitrary complex density matrices of 2 and 4 qubit systems using simulations.

Ranabir Das; T. S. Mahesh; Anil Kumar

2002-12-19

131

The Climate Hazards group InfraRed Precipitation (CHIRP) with Stations (CHIRPS): Development and Validation  

NASA Astrophysics Data System (ADS)

CHIRP and CHIRPS are new quasi-global precipitation products with daily to seasonal time scales, a 0.05° resolution, and a 1981 to near real-time period of record. Developed by the Climate Hazards Group at UCSB and scientists at the U.S. Geological Survey Earth Resources Observation and Science Center specifically for drought early warning and environmental monitoring, CHIRPS provides moderate latency precipitation estimates that place observed hydrologic extremes in their historic context. Three main types of information are used in the CHIRPS: (1) global 0.05° precipitation climatologies, (2) time-varying grids of satellite-based precipitation estimates, and (3) in situ precipitation observations. CHIRP: The global grids of long-term (1980-2009) average precipitation were estimated for each month based on station data, averaged satellite observations, and physiographic parameters. 1981-present time-varying grids of satellite precipitation were derived from spatially varying regression models based on pentadal cold cloud duration (CCD) values and TRMM V7 training data. The CCD time-series were derived from the CPC and NOAA B1 datasets. Pentadal CCD-percent anomaly values were multiplied by pentadal climatology fields to produce low bias pentadal precipitation estimates. CHIRPS: The CHG station blending procedure uses the satellite-observed spatial covariance structure to assign relative weights to neighboring stations and the CHIRP values. The CHIRPS blending procedure is based on the expected correlation between precipitation at a given target location and precipitation at the locations of the neighboring observation stations. These correlations are estimated using the CHIRP fields. The CHG has developed an extensive archive of in situ daily, pentadal and monthly precipitation totals. The CHG database has over half a billion daily rainfall observations since 1980 and another half billion before 1980. Most of these observations come from four sets of global climate observations: the monthly Global Historical Climate Network version 2 archive, the daily Global Historical Climate Network archive, the Global Summary of the Day dataset (GSOD), and the daily Global Telecommunication System (GTS) archive provided by NOAA's Climate Prediction Center (CPC). A screening procedure was developed to flag and remove potential false zeros from the daily data, since these potentially spurious data can artificially suppress rainfall totals. Validation: Our validation focused on precipitation products with global coverage, long periods of record and near real-time availability: CHIRP, CHIRPS, CPC-Unified, CFS Reanalysis and ECMWF datasets were compared to GPCC and high quality datasets from Uganda, Colombia and the Sahel. The CHIRP and CHIRPS are shown to have low systematic errors (bias) and low mean absolute errors. Analyses in Uganda, Colombia and the Sahel indicate that the ECMWF, CPC-Unified and CFS-Reanalysis have large inhomogeneities, making them unsuitable for drought monitoring. The CHIRPS performance appears quite similar to research quality products like the GPCC and GPCP, but with higher resolution and lower latency.

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

2013-12-01

132

Optical spatial heterodyne interferometric Fourier transform technique (OSHIFT) and a resulting interferometer  

NASA Astrophysics Data System (ADS)

This article reports on the novel patent pending Optical Spatial Heterodyne Interferometric Fourier Transform Technique (the OSHIFT technique), the resulting interferometer also referred to as OSHIFT, and its preliminary results. OSHIFT was borne out of the following requirements: wavefront sensitivity on the order of 1/100 waves, high-frequency wavefront spatial sampling, snapshot 100Hz operation, and the ability to deal with discontinuous wavefronts. The first two capabilities lend themselves to the use of traditional interferometric techniques; however, the last two prove difficult for standard techniques, e.g., phase shifting interferometry tends to take a time sequence of images and most interferometers require estimation of a center fringe across wavefront discontinuities. OSHIFT overcomes these challenges by employing a spatial heterodyning concept in the Fourier (image) plane of the optic-under-test. This concept, the mathematical theory, an autocorrelation view of operation, and the design with results of OSHIFT will be discussed. Also discussed will be future concepts such as a sensor that could interrogate an entire imaging system as well as a methodology to create innovative imaging systems that encode wavefront information onto the image. Certain techniques and systems described in this paper are the subject of a patent application currently pending in the United States Patent Office.

Georges, James A., III

2007-09-01

133

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

134

Fourier transform ultraviolet-visible spectrometer based on a beam-folding technique  

NASA Astrophysics Data System (ADS)

A beam-folding technique in optical interferometry, where the number of beam folds used can be very large, is reported. This technique can be used as a low-cost position-tracking method in a Fourier transform spectrometer (FTS) to cover the broad spectral range from UV to IR. The main advantage gained is the simple position-tracking algorithm used in sampling the interferogram. We have developed a UV-visible FTS, whose wavelength coverage is limited only by the optical elements (350 nm-1 ?m with off-the-shelf components). Preliminary results show that it can achieve a resolution of ˜4 cm-1 even with a ball-bearing translation stage.

Chan, Robert K.; Lim, P. K.; Wang, Xuzhu; Chan, M. H.

2006-04-01

135

Dilatometric technique for evaluation of the kinetics of solid-state transformation of maraging steel  

SciTech Connect

Solid-state transformation kinetics of a 350 grad commercial maraging steel were investigated using a nonisothermal dilatometric technique. Two solid-state reactions -- namely, precipitation of intermetallic phases from supersaturated martensite and reversion of martensite to austenite -- were identified. Determination was made of the temperatures at which the rates of these reactions reached a maximum at different heating rates. The kinetics of the individual reactions in terms of activation energy were analyzed by simplified procedures based on the Kissinger equation. An estimated activation energy of 145 {+-} 4 kJ/mol for the precipitation of intermetallic phase was in good agreement with reported results based on the isothermal hardness measurement technique. Martensite to austenite reversion was associated with an activation energy of 224 {+-} 4 kJ/mol, which is very close to the activation energy for diffusion of substitutional elements in ferrite. Results were supplemented with microstructural analysis.

Viswanathan, U.K.; Kutty, T.R.G.; Ganguly, C. [Bhabha Atomic Research Centre, Bombay (India). Radiometallurgy Div.

1993-12-01

136

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

137

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

138

Design constraints of optical parametric chirped pulse amplification based on chirped quasi-phase-matching gratings.  

PubMed

Chirped quasi-phase-matching (QPM) gratings offer efficient, ultra-broadband optical parametric chirped pulse amplification (OPCPA) in the mid-infrared as well as other spectral regions. Only recently, however, has this potential begun to be realized [1]. In this paper, we study the design of chirped QPM-based OPCPA in detail, revealing several important constraints which must be accounted for in order to obtain broad-band, high-quality amplification. We determine these constraints in terms of the underlying saturated nonlinear processes, and explain how they were met when designing our mid-IR OPCPA system. The issues considered include gain and saturation based on the basic three-wave mixing equations; suppression of unwanted non-collinear gain-guided modes; minimizing and characterizing nonlinear losses associated with random duty cycle errors in the QPM grating; avoiding coincidentally-phase-matched nonlinear processes; and controlling the temporal/spectral characteristics of the saturated nonlinear interaction in order to maintain the chirped-pulse structure required for OPCPA. The issues considered place constraints both on the QPM devices as well as the OPCPA system. The resulting experimental guidelines are detailed. Our results represent the first comprehensive discussion of chirped QPM devices operated in strongly nonlinear regimes, and provide a roadmap for advancing and experimentally implementing OPCPA systems based on these devices. PMID:24787850

Phillips, C R; Mayer, B W; Gallmann, L; Fejer, M M; Keller, U

2014-04-21

139

Mechanism of electron acceleration by chirped laser pulse  

SciTech Connect

We studied the mechanism of electron acceleration by a chirped laser pulse. We found that, because of the chirp effect, a region exists where the laser wave phase experienced by the electron varies slowly, so that the electron can be accelerated for a long time. The mechanism of chirped laser acceleration is different to that of the capture and acceleration scenario, although both of them have a main acceleration stage in which the electrons are trapped for long periods.

Wu, X. Y.; Wang, P. X. [Department of Nuclear Science and Technology, Institute of Modern Physics, Fudan University, Shanghai 200433, China and Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education (China); Kawata, S. [Department of Advanced Interdisciplinary Science, Center for Optical Research and Education, Graduate School of Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan)

2012-05-28

140

Prepreg cure monitoring using diffuse reflectance-FTIR. [Fourier Transform Infrared Technique  

NASA Technical Reports Server (NTRS)

An in situ diffuse reflectance-Fourier transform infrared technique was developed to determine infrared spectra of graphite fiber prepregs as they were being cured. A bismaleimide, an epoxy, and addition polyimide matrix resin prepregs were studied. An experimental polyimide adhesive was also examined. Samples were positioned on a small heater at the focal point of diffuse reflectance optics and programmed at 15 F/min while FTIR spectra were being scanned, averaged, and stored. An analysis of the resulting spectra provided basic insights into changes in matrix resin molecular structure which accompanied reactions such as imidization and crosslinking. An endo-exothermal isomerization involving reactive end-caps was confirmed for the addition polyimide prepregs. The results of this study contribute to a fundamental understanding of the processing of composites and adhesives. Such understanding will promote the development of more efficient cure cycles.

Young, P. R.; Chang, A. C.

1984-01-01

141

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

142

Measurements of solar magnetic fields by Fourier transform techniques. II - Saturated and blended lines  

NASA Technical Reports Server (NTRS)

Fourier techniques have been exhaustively calibrated using Unno's (1956) results for the absorption profile of a simple Zeeman triplet. If a simple transformation is applied to the normalized line depths, then magnetic-field strengths and inclination angles can be measured very accurately from noisy saturated line profiles. Systematic errors caused by saturation effects can be estimated and reduced by varying one parameter. When a significant fraction of the line profile is unsplit and unpolarized, large errors may be made in measurements of low fields, unless the line is sufficiently weak. For a weak line, a vertical field of 1600 gauss can be measured to 10% accuracy even when 70% of the line profile is stray light. These stray-light errors are troublesome in measuring fields of gaps and pores but not sunspots. Numerical results of the error analysis are presented graphically.

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

1976-01-01

143

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

144

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

PubMed

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

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

2010-06-15

145

A 32x32 pixel focal plane array ladar system using chirped amplitude modulation  

Microsoft Academic Search

The Army Research Laboratory is researching system architectures and components required to build a 32x32 pixel scannerless ladar breadboard. The 32x32 pixel architecture achieves ranging based on a frequency modulation\\/continuous wave (FM\\/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (RF) subcarrier that is linearly frequency modulated (i.e. chirped amplitude modulation). The backscattered

Barry L. Stann; Keith Aliberti; Daniel Carothers; John Dammann; Gerard Dang; Mark M. Giza; William B. Lawler; Brian C. Redman; Deborah R. Simon

2004-01-01

146

Studies on Nephrite and Jadeite Jades by Fourier Transform Infrared (ftir) and Raman Spectroscopic Techniques  

NASA Astrophysics Data System (ADS)

The mineralogical properties of black nephrite jade from Western Australia are studied by Fourier transform infrared (FTIR) spectroscopy using both transmission and specular reflectance techniques in the 4000-400 cm-1 wavenumber region. The infrared absorption peaks in the 3700-3600 cm-1 region which are due to the O-H stretching mode provides a quantitative analysis of the Fe/(Fe+Mg) ratio in the mineral composition of jade samples. The Fe/(Fe+Mg) percentage in black nephrite is found to be higher than that in green nephrite, but comparable to that of actinolite (iron-rich nephrite). This implies that the mineralogy of black nephrite is closer to actinolite than tremolite. The jade is also characterized using Raman spectroscopy in the 1200-200 cm-1 region. Results from FTIR and Raman spectroscopic data of black nephrite jade are compared with those of green nephrite jade from New Zealand and jadeite jade from Myanmar. Black nephrite appears to have a slightly different chemical composition from green nephrite. Spectra from FTIR and Raman spectroscopic techniques were found to be useful in differentiating black nephrite, green nephrite, and green jadeite jades. Furthermore, data on refractive index, specific gravity, and hardness of black nephrite jade are measured and compared with those of green nephrite and of jadeite jade.

Tan, T. L.; Ng, L. L.; Lim, L. C.

2013-10-01

147

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

148

Chirp characteristics of silicon Mach-Zehnder modulators  

Microsoft Academic Search

Chirp characteristics of silicon based Mach-Zehnder-interferometer (MZI) modulators with PIN diode and PN diode are fully analyzed, respectively. Simulation result shows that the chirp parameter is negative and influenced by the carrier absorption effect, the amplitude and frequency of applied sinusoidal modulating signals

Yuxin Wei; Yong Zhao; Guoyi Li; Jianyi Yang; Minghua Wang; Xiaoqing Jiang

2010-01-01

149

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

150

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

151

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

152

Chirp: a practical global filesystem for cluster and Grid computing  

Microsoft Academic Search

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

Douglas Thain; Christopher Moretti; Jeffrey Hemmes

2009-01-01

153

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

154

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

SciTech Connect

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.

Kaprálová-Ž?ánská, Petra Ruth, E-mail: kapralova@jh-inst.cas.cz [Department of Radiation and Chemical Physics, Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic); J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8 (Czech Republic); Moiseyev, Nimrod, E-mail: nimrod@tx.technion.ac.il [Schulich Faculty of Chemistry and Faculty of Physics, Technion – Israel Institute of Technology, Haifa 32000 (Israel)

2014-07-07

155

Temporal compression and shaping of chirped biphotons using Fresnel-inspired binary phase shaping  

NASA Astrophysics Data System (ADS)

Chirped biphotons generated via spontaneous parametric down-conversion in chirped quasi-phase-matched nonlinear crystals have ultrabroadband frequency spectra, while their correlation times are not ultranarrow, due to the nonlinear frequency dependence of the phase factor. Based on the idea of Fresnel zone lenses, we propose a Fresnel-inspired binary phase-shaping scheme for tailoring broadband biphoton spectra. By applying binary phase masks to the biphoton spectrum, a Fresnel zone lens was produced in the frequency domain, compressing the broadband temporal wave packets of the chirped biphotons to the Fourier-transform limit due to the effective removal of the quadratic phase. Furthermore, biphoton correlation trains can also be generated by properly shaping the biphoton spectrum with this scheme. This provides a method for biphoton compression and shaping, which avoids the length dependence and the impact of higher-order dispersion in a dispersive medium by using the phase compensation method. Our results could prove useful in quantum metrology, lithography, and coding of entangled photons.

Li, Baihong; Xu, Yonggang; Zhu, Haifei; Lin, Fukun; Li, Yongfang

2015-02-01

156

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

157

Characterization of strong fiber Bragg gratings using an applied thermal chirp and iterative algorithm.  

PubMed

Coupling coefficients of various grating types and strengths are calculated from measurements of the complex reflectivity using an applied thermal chirp and optical frequency domain reflectometry (OFDR). The complex reflectivity is then utilized by a layer peeling algorithm to determine the coupling coefficient of the thermally chirped grating. A guess of the temperature profile enables the coupling coefficient of the unchirped grating to be estimated. An iterative algorithm is then used to converge on the exact coupling coefficient, employing an error minimization method applied to the reflectivity spectra. This technique removes the need for a reference grating while preserving the spatial resolution obtained with the initial OFDR measurement. Successful reconstruction of gratings with integrated |?|L ~ 9.0 are demonstrated with a spatial resolution of less than 100 ?m. PMID:22193191

Miller, Gary A; Peele, John R; Askins, Charles G; Cranch, Geoffrey A

2011-12-20

158

Fast classification and compositional analysis of cornstover fractions using Fourier transform near-infrared techniques.  

PubMed

The objectives of this research were to determine the variation of chemical composition across botanical fractions of cornstover, and to probe the potential of Fourier transform near-infrared (FT-NIR) techniques in qualitatively classifying separated cornstover fractions and in quantitatively analyzing chemical compositions of cornstover by developing calibration models to predict chemical compositions of cornstover based on FT-NIR spectra. Large variations of cornstover chemical composition for wide calibration ranges, which is required by a reliable calibration model, were achieved by manually separating the cornstover samples into six botanical fractions, and their chemical compositions were determined by conventional wet chemical analyses, which proved that chemical composition varies significantly among different botanical fractions of cornstover. Different botanic fractions, having total saccharide content in descending order, are husk, sheath, pith, rind, leaf, and node. Based on FT-NIR spectra acquired on the biomass, classification by Soft Independent Modeling of Class Analogy (SIMCA) was employed to conduct qualitative classification of cornstover fractions, and partial least square (PLS) regression was used for quantitative chemical composition analysis. SIMCA was successfully demonstrated in classifying botanical fractions of cornstover. The developed PLS model yielded root mean square error of prediction (RMSEP %w/w) of 0.92, 1.03, 0.17, 0.27, 0.21, 1.12, and 0.57 for glucan, xylan, galactan, arabinan, mannan, lignin, and ash, respectively. The results showed the potential of FT-NIR techniques in combination with multivariate analysis to be utilized by biomass feedstock suppliers, bioethanol manufacturers, and bio-power producers in order to better manage bioenergy feedstocks and enhance bioconversion. PMID:18249535

Philip Ye, X; Liu, Lu; Hayes, Douglas; Womac, Alvin; Hong, Kunlun; Sokhansanj, Shahab

2008-10-01

159

Color image encryption based on fractional Fourier transforms and pixel scrambling technique  

NASA Astrophysics Data System (ADS)

Color image encryption based on fractional Fourier transform (FRT) and pixel scrambling technique is presented in this paper. In general, color (RGB) image cannot be directly encrypted using a traditional setup for optical information processing, because which is only adapted to process two-dimensional gray image. In the proposed method, a three-dimensional RGB image is decomposed to three two-dimensional gray images (R, G and B values of the color image), and the encryption operation will be done on each two-dimensional gray image, then the encoded color image is available by composing the three two-dimensional encrypted images. The decryption process is an inverse of the encryption. The optical encrypting systems based on the presented method is proposed and simulated. Some results of computer simulation are presented to verify the flexibility and the reliability of this method. The quality of decrypted images would be debased with the difference of the fractional order. The frustrated decryption of monochromic image will affect the color of decrypted image. At the end of this paper, an all-optical and photoelectric encryption/decryption systems solution are presented, and the principle of selecting optical devices are also given.

Zhao, Jianlin; Lu, Hongqiang; Fan, Qi

2007-01-01

160

Characterization of Transformation Temperatures with the Bend and Free Recovery Technique: Parameters and Effects  

NASA Astrophysics Data System (ADS)

This study was conducted to investigate factors such as the deformation strain, straining temperature, and the number of testing cycles on the measurement of transformation temperatures using the bend and free recovery (BFR) technique. Ti-56.0%Ni wire with approximately 40% cold work and a 2 mm diameter was heat treated in an air furnace for 10 min at 490 °C to obtain an A f of approximately 21 °C. Wire specimens were deformed with one of two mandrels to apply an outer fiber strain of 2.4 or 5.8%. Deformation was performed at one of four straining temperatures: 0, -30, -50, or -65 °C. Specimens were tested ten times to investigate the effect of repeated testing. The resulting BFR curves were analyzed to determine the trends in the R-phase start ( R_{{text{s}}}^' ) and austenite finish ( A f) temperatures. For specimens strained at both 2.4 and 5.8% there was no detectable change in A f resulting from changes in the deformation temperature. Increasing the deformation strain from 2.4 to 5.8% tended to increase the measured A f by approximately 1 °C independent of deformation temperature. Repeat testing seemed to result in a slight increase in A f but the intrinsic scatter of the BFR data made it impossible to conclusively identify a trend.

Drexel, Masao; Proft, Jim; Russell, Scott

2009-08-01

161

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

162

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

163

Correlation Aware Technique for SQL to NoSQL Transformation Jen-Chun Hsu, Ching-Hsien Hsu  

E-print Network

and 2006 for distributed file system, parallel and distributed computing, and NoSQL database, respectively to NoSQL database. Sqoop becomes the top level project in 2012 which enable users to migrate large sizeCorrelation Aware Technique for SQL to NoSQL Transformation Jen-Chun Hsu, Ching-Hsien Hsu Dept

Chung, Yeh-Ching

164

Large-Mode-Area Erbium-Ytterbium-doped Photonic-Crystal Fiber Amplifier yielding 54kW Femtosecond Pulses without Chirped-Pulse Amplification  

Microsoft Academic Search

A high-energy femtosecond fiber amplifier using a large-mode-area single-mode erbium-ytterbium-codoped photonic-crystal fiber is presented. 700-fs pulses at 1557nm were amplified and compressed to near-transform-limited 100-fs, 7.4-nJ pulses with > 50-kW peak powers without chirped-pulse amplification.

A. Shirakawa; M. Musha; K. Ueda; J. R. Folkenberg; J. Broeng

2005-01-01

165

Improved nonlinear chirp scaling algorithm for dechirped missile-borne synthetic aperture radar  

NASA Astrophysics Data System (ADS)

An improved nonlinear chirp scaling (NLCS) algorithm for dechirped missile-borne synthetic aperture radar was proposed. The key step is to use an improved NLCS operation to equalize azimuth frequency modulation rate after linear range walk correction, secondary range compression, and range compression. By adopting a higher-order approximation, the image has better accuracy and less distortion. Validity of the algorithm is demonstrated using simulated and real datasets. Moreover, the whole procedure only consists of fast Fourier transform and complex multiplication, which means easier implementation and higher efficiency.

Chen, Si; Zhang, Shuning; Zhao, Huichang; Zhou, Xingang; Chen, Yong

2014-01-01

166

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

167

Chirped pulse amplification in single mode Tm:fiber using a chirped Bragg grating  

NASA Astrophysics Data System (ADS)

We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-?m fiber source as a pump for mid-IR supercontinuum generation.

Sims, R. Andrew; Kadwani, Pankaj; Ebendorff-Heideprem, Heike; Shah, Lawrence; Monro, Tanya M.; Richardson, Martin

2013-05-01

168

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

169

Multiterawatt laser system based on optical parametric chirped pulse amplification.  

PubMed

A compact multiterawatt laser system based on optical parametric chirped pulse amplification is demonstrated. Chirped pulses are amplified from 20 pJ to 900 mJ by two lithium triborate optical parametric preamplifiers and a final KDP optical parametric power amplifier with a pump energy of 5 J at 532 nm from Nd:YAG-Nd:glass hybrid amplifiers. After compression, we obtained a final output of 570-mJ-155-fs pulses with a peak power of 3.67 TW, which is the highest output power from an optical parametric chirped pulse amplification laser, to the best of our knowledge. PMID:18026385

Yang, Xiaodong; Xu, Zhi-Zhan; Leng, Yu-Xin; Lu, Hai-He; Lin, Li-Huang; Zhang, Zheng-Quan; Li, Ru-Xin; Zhang, Wen-Qi; Yin, Ding-Jun; Tang, Bing

2002-07-01

170

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

171

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

172

Chirped-Superlattice, Blocked-Intersubband QWIP  

NASA Technical Reports Server (NTRS)

An Al(x)Ga(1-x)As/GaAs quantum-well infrared photodetector (QWIP) of the blocked-intersubband-detector (BID) type, now undergoing development, features a chirped (that is, aperiodic) superlattice. The purpose of the chirped superlattice is to increase the quantum efficiency of the device. A somewhat lengthy background discussion is necessary to give meaning to a brief description of the present developmental QWIP. A BID QWIP was described in "MQW Based Block Intersubband Detector for Low-Background Operation" (NPO-21073), NASA Tech Briefs Vol. 25, No. 7 (July 2001), page 46. To recapitulate: The BID design was conceived in response to the deleterious effects of operation of a QWIP at low temperature under low background radiation. These effects can be summarized as a buildup of space charge and an associated high impedance and diminution of responsivity with increasing modulation frequency. The BID design, which reduces these deleterious effects, calls for a heavily doped multiple-quantum-well (MQW) emitter section with barriers that are thinner than in prior MQW devices. The thinning of the barriers results in a large overlap of sublevel wave functions, thereby creating a miniband. Because of sequential resonant quantum-mechanical tunneling of electrons from the negative ohmic contact to and between wells, any space charge is quickly neutralized. At the same time, what would otherwise be a large component of dark current attributable to tunneling current through the whole device is suppressed by placing a relatively thick, undoped, impurity-free AlxGa1 x As blocking barrier layer between the MQW emitter section and the positive ohmic contact. [This layer is similar to the thick, undoped Al(x)Ga(1-x)As layers used in photodetectors of the blocked-impurity-band (BIB) type.] Notwithstanding the aforementioned advantage afforded by the BID design, the responsivity of a BID QWIP is very low because of low collection efficiency, which, in turn, is a result of low electrostatic- potential drop across the superlattice emitter. Because the emitter must be electrically conductive to prevent the buildup of space charge in depleted quantum wells, most of the externally applied bias voltage drop occurs across the blocking-barrier layer. This completes the background discussion. In the developmental QWIP, the periodic superlattice of the prior BID design is to be replaced with the chirped superlattice, which is expected to provide a built-in electric field. As a result, the efficiency of collection of photoexcited charge carriers (and, hence, the net quantum efficiency and thus responsivity) should increase significantly.

Gunapala, Sarath; Ting, David; Bandara, Sumith

2004-01-01

173

Highly depth-resolved chirped pulse photothermal radar for bone diagnostics  

NASA Astrophysics Data System (ADS)

A novel chirped pulse photothermal (PT) radiometric radar with improved sensitivity over the conventional harmonically modulated thermal-wave radar technique and alternative pulsed laser photothermal radiometry is introduced for the diagnosis of biological samples, especially bones with tissue and skin overlayers. The constraints imposed by the laser safety (maximum permissible exposure) ceiling on pump laser energy and the strong attenuation of thermal-wave signals in tissues significantly limit the photothermally active depth in most biological specimens to a level which is normally insufficient for practical applications (a few mm below the skin surface). A theoretical approach for improvement of signal-to-noise ratio (SNR), minimizing the static (dc) component of the photothermal signal and making use of the photothermal radiometric nonlinearity has been introduced and verified by comparing the SNR of four distinct excitation wave forms (sine-wave, square-wave, constant-width and constant duty-cycle pulses) for chirping the pump laser, under constant exposure energy. At low frequencies fixed-pulsewidth chirps of large peak power were found to be superior to all other equal-energy modalities, with an SNR improvement up to two orders of magnitude. Distinct thickness-dependent characteristic delay times in a goat bone were obtained, establishing an active depth resolution range of ˜2.8 mm in a layered skin-fat-bone structure, a favorable result compared to the maximum reported pulsed photothermal radiometric depth resolution <1 mm in turbid biological media.

Kaiplavil, Sreekumar; Mandelis, Andreas

2011-07-01

174

Real-time tool condition monitoring using wavelet transforms and fuzzy techniques  

Microsoft Academic Search

In this paper, wavelet transforms and fuzzy tech- niques are used to monitor tool breakage and wear conditions in real time according to the measured spindle and feed motor currents, respectively. First, the continuous and discrete wavelet transforms are used to decompose the spindle and feed ac servo motor current signals to extract signal features so as to detect the

Xiaoli Li; Shiu Kit Tso; Jun Wang

2000-01-01

175

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

176

A technique to study Meloidogyne arenaria resistance in Agrobacterium rhizogenes-transformed peanut  

Technology Transfer Automated Retrieval System (TEKTRAN)

A reliable peanut root transformation system would be useful to study the functions of genes involved in root biology and disease resistance. The objective of this study was to establish an effective protocol to produce composite plants mediated by Agrobacterium rhizogenes transformation. More tha...

177

Dispersion compensation in chirped pulse amplification systems  

DOEpatents

A chirped pulse amplification system includes a laser source providing an input laser pulse along an optical path. The input laser pulse is characterized by a first temporal duration. The system also includes a multi-pass pulse stretcher disposed along the optical path. The multi-pass pulse stretcher includes a first set of mirrors operable to receive input light in a first plane and output light in a second plane parallel to the first plane and a first diffraction grating. The pulse stretcher also includes a second set of mirrors operable to receive light diffracted from the first diffraction grating and a second diffraction grating. The pulse stretcher further includes a reflective element operable to reflect light diffracted from the second diffraction grating. The system further includes an amplifier, a pulse compressor, and a passive dispersion compensator disposed along the optical path.

Bayramian, Andrew James; Molander, William A.

2014-07-15

178

Quantum Fluctuations in the Chirped Pendulum  

E-print Network

An anharmonic oscillator when driven with a fast, frequency chirped voltage pulse can oscillate with either small or large amplitude depending on whether the drive voltage is below or above a critical value-a well studied classical phenomenon known as autoresonance. Using a 6 GHz superconducting resonator embedded with a Josephson tunnel junction, we have studied for the first time the role of noise in this non-equilibrium system and find that the width of the threshold for capture into autoresonance decreases as the square root of T, and saturates below 150 mK due to zero point motion of the oscillator. This unique scaling results from the non-equilibrium excitation where fluctuations, both quantum and classical, only determine the initial oscillator motion and not its subsequent dynamics. We have investigated this paradigm in an electrical circuit but our findings are applicable to all out of equilibrium nonlinear oscillators.

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

2010-08-26

179

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

180

Iterative direction-of-arrival estimation with wideband chirp signals  

NASA Astrophysics Data System (ADS)

Amin et. al. recently developed a time-frequency MUSIC algorithm with narrow band models for the estimation of direction of arrival (DOA) when the source signals are chirps. In this research, we consider wideband models. The joint time-frequency analysis is first used to estimate the chirp rates of the source signals and then the DOA is estimated by the MUSIC algorithm with an iterative approach.

Wang, Genyuan; Xia, Xiang-Gen; Chen, Victor C.

1999-11-01

181

Applying image transformation and classification techniques to airborne hyperspectral imagery for mapping Ashe juniper infestations  

Technology Transfer Automated Retrieval System (TEKTRAN)

Ashe juniper (Juniperus ashei Buchholz), in excessive coverage, reduces forage production, interferes with livestock management, and degrades watersheds and wildlife habitat in infested rangelands. The objective of this study was to apply minimum noise fraction (MNF) transformation and different cla...

182

Development and Experimental Validation of a Numerical Tool for Structural Health and Usage Monitoring Systems Based on Chirped Grating Sensors  

PubMed Central

The interest of the aerospace industries in structural health and usage monitoring systems is continuously increasing. Among the techniques available in literature those based on Fibre Bragg Grating sensors are much promising thanks to their peculiarities. Different Chirped Bragg Grating sensor configurations have been investigated in this paper. Starting from a numerical model capable of simulating the spectral response of a grating subjected to a generic strain profile (direct problem), a new code has been developed, allowing strain reconstruction from the experimental validation of the program, carried out through different loading cases applied on a chirped grating. The wavelength of the reflection spectrum for a chirped FBG has a one-to-one correspondence to the position along the gauge section, thus allowing strain reconstruction over the entire sensor length. Tests conducted on chirped FBGs also evidenced their potential for SHM applications, if coupled with appropriate numerical strain reconstructions tools. Finally, a new class of sensors—Draw Tower Grating arrays—has been studied. These sensors are applicable to distributed sensing and load reconstruction over large structures, thanks to their greater length. Three configurations have been evaluated, having different spatial and spectral characteristics, in order to explore possible applications of such sensors to SHM systems. PMID:25587979

Bettini, Paolo; Guerreschi, Erika; Sala, Giuseppe

2015-01-01

183

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

184

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

185

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

DOE PAGESBeta

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

186

Time-Frequency Transform Techniques Applied to Ultra-wideband Ground-Penetrating Radar  

NASA Astrophysics Data System (ADS)

Background Recently, Dauvignac et al [1] utilized a ground penetrating radar unit consisting of an exponentially tapered slot antenna (ETSA) of the Vivaldi type, connected to an Agilent vector network analyzer to obtain a densely-sampled profile in the anti-blast tunnel of LSBB (Low-Noise inter-Disciplinary Underground Science & Technology Laboratory) located in Rustrel, France. The frequency data, from 150 MHz to 2 GHz, was inverse Fourier-transformed to obtain the time dependent data. Simultaneously, the same profile was obtained using a RAMAC 500 MHz ground-penetrating radar unit. Initial comparison of both data sets was done in the time-domain. Data obtained from the ETSA will be inverted using a constrained least squares algorithm, in order that the depth-dependent permittivity can be inferred. As a quality control, the RAMAC data will also be inverted. The resulting permittivity profiles obtained in both inversions will be used to image water content over a depth of several meters. Proposed Research It is well-known, qualitatively in the ground penetrating radar literature that high frequencies appear at early times, but generally are attenuated at later times, essentially due to the skin effect. However, a signal-processing verification of this well-known result is needed. We propose to use the Stockwell or S transform [2] to determine the temporal location of frequencies in both of the foregoing datasets. The S transform, a short-time Fourier transform with a frequency-dependent window, will be described and applied to synthetic data. Then the application of the S transform to the RAMAC and ETSA data will be presented, after each data set has undergone the same pre-processing. The S transform is completely linear and preserves the phase of the data, which allows for easy interpretation of the operations of filtering, due to the linear inverse of the forward S transform. Thus the S transform is ideal for comparing the temporal distribution of frequency in these two datasets. BIBLIOGRAPHY [1] DAUVIGNAC J.-Y., N. FORTINO, G. SENECHAL, A. CRESP, M. YEDLIN, S. GAFFET, D. ROUSSET, and C. PICHOT, "Ultra-Wideband GPR Imaging of the Vaucluse Karst Aquifer", American Geophysical Union, Fall Meeting 2008, Abstract #NS51A-08. [2] STOCKWELL R. G., L. MANSINHA, R. P. LOWE, "Localization of the complex spectrum: the S transform", IEEE Transactions on Signal Processing, vol.44, n°4, pp 998-1001, April 1996.

Yedlin, M.; Cresp, A.; Dauviganc, J. Y.; Gaffet, S.; Sénéchal, G.; Fortino, N.; Pichot, C.; Aliferis, I.

2009-04-01

187

Color image hiding based on the phase retrieval technique and Arnold transform.  

PubMed

A new (to our knowledge) method is proposed in this paper for color image hiding and extracting using the phase retrieval algorithm in the fractional Fourier transform (FRFT) domain and Arnold transform (ART). Based on a cascaded phase iterative FRFT algorithm, the three channels (R, G, and B) of the secret color image permuted by ART are encrypted. Then the encoded information is embedded in the blue channel (B channel) of the enlarged color host image. Using the security enhanced encryption method, not only the random phase mask and the wavelength but also the transform parameters of ART and FRFT are provided as additional keys for decryption. It is shown that the security of information hiding will be enhanced. Computer simulations are performed to show the hiding capacity of the proposed system. Numerical results are presented to verify the validity and efficiency of the proposed method. PMID:21556114

Shi, Xiaoyan; Zhao, Daomu

2011-05-10

188

Efficient prime factor algorithm and address generation techniques for the discrete cosine transform  

Microsoft Academic Search

Proposes an efficient prime factor algorithm for the discrete cosine transform. In the proposal, we formulate the decomposition directly, by using the proposed input and output mapping, a novel in-place address generation scheme for input index mapping is derived, while the formulations in the literature require a table to store the index mapping. The approach requires one output index mapping

Lap-Pui Chau; Daniel Pak-Kong Lun; Wan-Chi Siu

2001-01-01

189

Harmonic Analysis of a Short Stator Linear Induction Machine Using a Transformation Technique  

Microsoft Academic Search

An analysis method is introduced for the short stator linear induction machine with homogeneous conducting rotor. The method incorporates harmonic rotor currents and a coordinate transformation into a modified Lagrangian formulation of the equations of motion. These equations permit both excitation and ferromagnetic edge effects as well as skin effects to be accounted for.

G. G. North

1973-01-01

190

accepted for publication at EUSIPCO '94 An adaptive invariant transform using neural network techniques  

E-print Network

of the class CT as a neural network. The properties of the CT are combined with the adaptivity of the neuralaccepted for publication at EUSIPCO '94 An adaptive invariant transform using neural network digits of a dual representation of x i and x j . 3 A feedforward neural network The connection structure

191

FD-CHIRP: hosted payload system engineering lessons  

NASA Astrophysics Data System (ADS)

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

Schueler, Carl F.

2012-10-01

192

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?¹¹ temporal contrast at -20??ps and a carrier-envelope-phase drift of 240 mrad root mean square. PMID:24978734

Jullien, Aurélie; Ricci, Aurélien; Böhle, Frederik; Rousseau, Jean-Philippe; Grabielle, Stéphanie; Forget, Nicolas; Jacqmin, Hermance; Mercier, Brigitte; Lopez-Martens, Rodrigo

2014-07-01

193

A chirped photonic-crystal fibre  

NASA Astrophysics Data System (ADS)

Photonic crystals have widely increased the facility to guide and confine light at wavelengths close to the optical wavelength. Because they can include extremely sharp bends, photonic-crystal waveguides are a key element in future integrated optical devices. Moreover, they enable the manipulation of the spontaneous emission properties of luminescent devices, the localization of light in microcavities, and they may serve to generate negative refraction. A special class of these devices are the hollow-core photonic-crystal fibres, which confine the light by means of a periodic cladding, consisting of several layers of identical cells. This design resonantly decreases the transmission losses of such fibres to values of a few dB km-1 in a narrow wavelength range. However, the rather narrowband transmission bands and the detrimental third-order dispersion characteristics of this single-cell design generally render application of such hollow-core fibres difficult in the femtosecond range. Therefore, no fibre-based concept can currently provide guiding of sub-100 fs pulses over extended distances. By introducing a radial chirp into the photonic crystal, we here demonstrate a novel concept for photonic-crystal fibres that breaks with the paradigm of lattice homogeneity and enables a new degree of freedom in photonic-crystal-fibre design, eliminating much of the pulse duration restriction of earlier approaches.

Skibina, Julia S.; Iliew, Rumen; Bethge, Jens; Bock, Martin; Fischer, Dorit; Beloglasov, Valentin I.; Wedell, Reiner; Steinmeyer, Günter

2008-11-01

194

Asymptotic Properties of the Least Squares Estimators of the Parameters of the Chirp Signals  

E-print Network

of Technology Kanpur Kanpur, Pin 208016 India Abstract: Chirp signals are quite common in different areas rejection is important chirp signals provide a successful digital modulation scheme. For instance, consider

Kundu, Debasis

195

Noncontact determination of elastic moduli by two-dimensional Fourier transformation and laser ultrasonic technique  

NASA Astrophysics Data System (ADS)

A laboratory instrument that utilizes broadband laser ultrasonics and two-dimensional Fourier transformation for signal processing has been developed to characterize the properties of various foils and plates. Laser ultrasonics generation is achieved by using a pulsed laser which deposits pulsed laser energy on the surface of the specimen. The displacement of the resulting broadband ultrasonic modes is monitored using a two-wave mixing photorefractive interferometer. By means of the two-dimensional Fourier transformation of the detected spatial and temporal displacement wave forms, the image of density of state (DOS) for the excited ultrasound is obtained, and from it the materials properties are extracted. Results are presented for a 150?m thick paper sample, a 50?m stainless steel foil, and a 1.27mm thick aluminum plate. The DOS image demonstrates the ability to measure the properties of each generated ultrasonic modes and provides a direct, nondestructive, measure of elastic moduli of the tested specimens.

Zhang, Xinya; Jackson, Ted; Lafond, Emmanuel

2005-02-01

196

Discerning Some Tylenol Brands Using Attenuated Total Reflection Fourier Transform Infrared Data and Multivariate Analysis Techniques  

Microsoft Academic Search

Principal component anal. (PCA) and partial least squares discriminant anal. (PLS-DA) were used to classify acetaminophen-contg. medicines using their attenuated total reflection Fourier transform IR (ATR-FT-IR) spectra. Four formulations of Tylenol (Arthritis Pain Relief, Extra Strength Pain Relief, 8 H Pain Relief, and Extra Strength Pain Relief Rapid Release) along with 98% pure acetaminophen were selected for this study because

Huggins Z. Msimanga; Robert J. Ollis Jr.

2010-01-01

197

Enhancement of sound by soft reflections in exponentially chirped crystals  

NASA Astrophysics Data System (ADS)

The enhancement of sound inside a two dimensional exponentially chirped crystal during the soft reflections of waves is experimentally and theoretically explored in this work. The control of this enhancement is achieved by a gradual variation of the dispersion in the system by means of a chirp of the lattice constant. The sound enhancement is produced at some planes of the crystal in which the wave is softly reflected due to a progressive slowing down of the sound wave. We find that the character of the sound enhancement depends on the function of the variation of dispersion, i.e., on the function of the chirp. A simple coupled mode theory is proposed to find the analytical solutions of the sound wave enhancement in the exponentially chirped crystal. Harmonic and time domain numerical simulations are performed to interpret the concept of the soft reflections, and to check the analytically calculated field distributions both in good agreement with experiments. Specially we obtain stronger sound enhancement than in linearly chirped crystals. This sound enhancement could motivate applications in energy harvesting, e.g., to increase the efficiency of detectors and absorbers.

Cebrecos, A.; Picó, R.; Sánchez-Morcillo, V. J.; Staliunas, K.; Romero-García, V.; Garcia-Raffi, L. M.

2014-12-01

198

Technique for gray-scale visual light and infrared image fusion based on non-subsampled shearlet transform  

NASA Astrophysics Data System (ADS)

A novel image fusion technique based on NSST (non-subsampled shearlet transform) is presented, aiming at resolving the fusion problem of spatially gray-scale visual light and infrared images. NSST, as a new member of MGA (multi-scale geometric analysis) tools, possesses not only flexible direction features and optimal shift-invariance, but much better fusion performance and lower computational costs compared with several current popular MGA tools such as NSCT (non-subsampled contourlet transform). We specifically propose new rules for the fusion of low and high frequency sub-band coefficients of source images in the second step of the NSST-based image fusion algorithm. First, the source images are decomposed into different scales and directions using NSST. Then, the model of region average energy (RAE) is proposed and adopted to fuse the low frequency sub-band coefficients of the gray-scale visual light and infrared images. Third, the model of local directional contrast (LDC) is given and utilized to fuse the corresponding high frequency sub-band coefficients. Finally, the final fused image is obtained by using inverse NSST to all fused sub-images. In order to verify the effectiveness of the proposed technique, several current popular ones are compared over three different publicly available image sets using four evaluation metrics, and the experimental results demonstrate that the proposed technique performs better in both subjective and objective qualities.

Kong, Weiwei

2014-03-01

199

A robust ultra-broad-band wireless communication system using SAW chirped delay lines  

Microsoft Academic Search

Design and performance of a low-cost wireless communication system for indoor and industrial environments are presented. The system is based on chirp-signal transmission to achieve a robust communication link. For the chirp expansion and compression, surface acoustic wave chirped delay lines fabricated from LiTaO3-X112rotY are used. Center frequency, bandwidth, and chirp rate are 348.8 MHz, 80 MHz, and ±40 MHz\\/?s,

Andreas Springer; Mario Huemer; Leonhard Reindl; Clemens C. W. Ruppel; Alfred Pohl; Franz Seifert; Wolfgang Gugler; Robert Weigel

1998-01-01

200

Shifted-basis technique improves accuracy of peak position determination in Fourier transform mass spectrometry  

Microsoft Academic Search

The present paper suggests a new algorithm for estimation of peak positions in FTMS spectra. It is shown theoretically and\\u000a experimentally that the new technique yields superior results compared to the currently applied techniques, when the noise\\u000a level is high and\\/or the peaks are located close to each other. Cases are presented where the deviation from the true mass\\u000a could

Mikhail M. Savitski; Igor A. Ivonin; Michael L. Nielsen; Roman A. Zubarev; Youri O. Tsybin; Haåkansson Per Håkansson

2004-01-01

201

Experimental investigation of chirp properties induced by signal amplification in quantum-dot semiconductor optical amplifiers.  

PubMed

We experimentally show the dynamic frequency chirp properties induced by signal amplification in a quantum-dot semiconductor optical amplifier (QD-SOA) for the first time. We also compare the red and blue chirp peak values and temporal chirp changes while changing the gain and injected signal powers of the QD-SOA with those of a common SOA. PMID:25768145

Matsuura, Motoharu; Ohta, Hiroaki; Seki, Ryota

2015-03-15

202

The elimination of the temperature effect on a piezoelectric transformer in a backlight inverter based on the phase-locked loop technique  

Microsoft Academic Search

A new method is proposed in this paper to eliminate the temperature effect on a piezoelectric transformer (PT) residing inside a half-bridge backlight module which utilizes the phase-locked loop (PLL) technique. The PT is adopted to drive a cold cathode fluorescent lamp (CCFL) to eliminate the downside of a conventional transformer and to reduce the dimension, particularly the thickness, of

Chang-Hua Lin; Ying-Chi Chen; John Yanhao Chen; Fuh-Liang Wen

2005-01-01

203

Chirped pulse inverse free-electron laser vacuum accelerator  

DOEpatents

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

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

2002-01-01

204

Broadband-rejection filters using chirped and tilted fiber gratings  

NASA Astrophysics Data System (ADS)

Broadband-trimming 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 bandwidth (from 10 nm to 150 nm), together with a low transmission loss (less than 1 dB) 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 polarization of launch condition. 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.

Liu, Fu; Guo, Tuan; Guan, Bai-Ou

2014-11-01

205

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

206

A receptor model using a specific non-negative transformation technique for ambient aerosol  

NASA Astrophysics Data System (ADS)

Factor analysis receptor models attempt to estimate both the source composition and the source intensity from a series of observations. The factor analysis solution resulting from Principle Component Analysis (PCA) has no real physically interpretable meaning. Only an appropriate transformation enables a realistic interpretation. Any realistic transformation solution must obey certain natural and physical constraints, such as non-negative source elemental composition and non-negative source intensity, which are not explicitly examined in the existing receptor models. If these natural constraints are violated the results will be uninterpretable. All observed data sets contain more or less information about the sources. This paper presents a receptor model, which extracts source information from the observed data set to deduce the source profiles, and respects the important natural constraints. This receptor model was tested with a simulated test data set, which was generated with the source profiles and intensities used in the Quail Roost II Workshop. It has also been applied to an ambient data set sampled in Berlin (West) during January and February 1984.

Shen, J.; Israël, G. W.

207

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

208

Dense Monoenergetic Proton Beams from Chirped Laser-Plasma Interaction  

NASA Astrophysics Data System (ADS)

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 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 1021W/cm2.

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

2011-10-01

209

Non-diffracting chirped Bessel waves in optical antiguides  

E-print Network

Chirped Bessel waves are introduced as stable (non-diffracting) solutions of the paraxial wave equation in optical antiguides with a power-law radial variation in their index of refraction. Through numerical simulations, we investigate the propagation of apodized (finite-energy) versions of such waves, with or without vorticity, in antiguides with practical parameters. The new waves exhibit a remarkable resistance against the defocusing effect of the unstable index potentials, outperforming standard Gaussians with the same full width at half maximum. The chirped profile persists even under conditions of eccentric launching or antiguide bending and is also capable of self-healing like standard diffraction-free beams in free space.

Chremmos, Ioannis

2015-01-01

210

Spectral windowing with chirped magneto-optical Bragg gratings  

NASA Astrophysics Data System (ADS)

We present a theory on a novel class of magneto-optical devices operated by means of magneto-optically induced refractive-index perturbations in chirped Bragg gratings. The predicted effect of the introduced perturbation is an opening of a narrow transmission window in the band-blocking transmission of the chirped grating. The narrow transmission window is tunable in wavelength, and relative transmission and the effects of multiple, spatially separated perturbations can also be superimposed, hence allowing for tunable, magneto-optically operated, multichannel add-drop multiplexors suitable for modularization in integrated optics.

Jonsson, Fredrik; Flytzanis, Christos

2005-01-01

211

Chirped pulse excitation of two-atom Rydberg states  

E-print Network

We analyze excitation of two ground state atoms to a double Rydberg state by a two-photon chirped optical pulse in the regime of adiabatic rapid passage. For intermediate Rydberg-Rydberg interaction strengths, relevant for atoms separated by $\\sim$ten $\\mu$m, adiabatic excitation can be achieved at experimentally feasible Rabi frequencies and chirp rates of the pulses, resulting in high transfer efficiencies. We also study the adiabatic transfer between ground and Rydberg states as a means to realize a controlled phase gate between atomic qubits.

Kuznetsova, Elena

2015-01-01

212

Solidphase synthesis for beginners: Choice of tools and techniques for implementation of multistage transformations  

Microsoft Academic Search

Several mini-libraries were prepared by solid-phase synthesis: C,N-substituted glycines (1) and 2,5-diaminobenzoic acids (2)\\u000a using Wang resin as well as diarylthioureas (3) and diaryl-guanidines (4) using Rink resin. Comparative analysis of the instruments\\u000a and technique for these reactions was provided by applying glass vials with filters (BillBoard kit) to prepare the class (1),\\u000a the tea-bag technique for the class (2),

E. V. Babaev

2010-01-01

213

Advanced Techniques for In-Situ Monitoring of Phase Transformations During Welding Using Synchrotron-Based X-Ray Diffraction  

SciTech Connect

Understanding the evolution of microstructure in welds is an important goal of welding research because of the strong correlation between weld microstructure and weld properties. To achieve this goal it is important to develop a quantitative measure of phase transformations encountered during welding in order to ultimately develop methods for predicting weld microstructures from the characteristics of the welding process. To aid in this effort, synchrotron radiation methods have been developed at Lawrence Livermore National Laboratory (LLNL) for direct observation of microstructure evolution during welding. Using intense, highly collimated synchrotron radiation, the atomic structure of the weld heat affected and fusion zones can be probed in real time. Two synchrotron-based techniques, known as spatially resolved (SRXRD) and time resolved (TRXRD) x-ray diffraction, have been developed for these investigations. These techniques have now been used to investigate welding induced phase transformations in titanium alloys, low alloy steels, and stainless steel alloys. This paper will provide a brief overview of these methods and will discuss microstructural evolution during the welding of low carbon (AISI 1005) and medium carbon (AISI 1045) steels where the different levels of carbon influence the evolution of microstructures during welding.

Elmer, J W; Palmer, T A; Zhang, W; DebRoy, T

2005-06-05

214

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

2014-09-01

215

Techniques for computing the discrete Fourier transform using the quadratic residue Fermat number systems  

NASA Technical Reports Server (NTRS)

The complex integer multiplier and adder over the direct sum of two copies of finite field developed by Cozzens and Finkelstein (1985) is specialized to the direct sum of the rings of integers modulo Fermat numbers. Such multiplication over the rings of integers modulo Fermat numbers can be performed by means of two integer multiplications, whereas the complex integer multiplication requires three integer multiplications. Such multiplications and additions can be used in the implementation of a discrete Fourier transform (DFT) of a sequence of complex numbers. The advantage of the present approach is that the number of multiplications needed to compute a systolic array of the DFT can be reduced substantially. The architectural designs using this approach are regular, simple, expandable and, therefore, naturally suitable for VLSI implementation.

Truong, T. K.; Chang, J. J.; Hsu, I. S.; Pei, D. Y.; Reed, I. S.

1986-01-01

216

Analysis in the instantaneous frequency forms of a chirped laser pulse  

SciTech Connect

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

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

2011-10-15

217

Ultrafast chirped optical waveform recorder using referenced heterodyning and a time microscope  

DOEpatents

A new technique for capturing both the amplitude and phase of an optical waveform is presented. This technique can capture signals with many THz of bandwidths in a single shot (e.g., temporal resolution of about 44 fs), or be operated repetitively at a high rate. That is, each temporal window (or frame) is captured single shot, in real time, but the process may be run repeatedly or single-shot. This invention expands upon previous work in temporal imaging by adding heterodyning, which can be self-referenced for improved precision and stability, to convert frequency chirp (the second derivative of phase with respect to time) into a time varying intensity modulation. By also including a variety of possible demultiplexing techniques, this process is scalable to recoding continuous signals.

Bennett, Corey Vincent (Livermore, CA)

2011-11-22

218

Ultrafast chirped optical waveform recording using referenced heterodyning and a time microscope  

DOEpatents

A new technique for capturing both the amplitude and phase of an optical waveform is presented. This technique can capture signals with many THz of bandwidths in a single shot (e.g., temporal resolution of about 44 fs), or be operated repetitively at a high rate. That is, each temporal window (or frame) is captured single shot, in real time, but the process may be run repeatedly or single-shot. This invention expands upon previous work in temporal imaging by adding heterodyning, which can be self-referenced for improved precision and stability, to convert frequency chirp (the second derivative of phase with respect to time) into a time varying intensity modulation. By also including a variety of possible demultiplexing techniques, this process is scalable to recoding continuous signals.

Bennett, Corey Vincent

2010-06-15

219

Injection and acceleration of electron bunch in a plasma wakefield produced by a chirped laser pulse  

SciTech Connect

An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wakefield which can trap and accelerate charged particles up to GeV. One-dimensional analysis of electron injection, trapping, and acceleration by different chirped pulses propagating in plasma is investigated numerically. In this paper, we inject electron bunches in front of the chirped pulses. It is indicated that periodical chirped laser pulse can trap electrons earlier than other pulses. It is shown that periodical chirped laser pulses lead to decrease the minimum momentum necessary to trap the electrons. This is due to the fact that periodical chirped laser pulses are globally much efficient than nonchirped pulses in the wakefield generation. It is found that chirped laser pulses could lead to much larger electron energy than that of nonchirped pulses. Relative energy spread has a lower value in the case of periodical chirped laser pulses.

Afhami, Saeedeh; Eslami, Esmaeil, E-mail: eeslami@iust.ac.ir [Department of Physics, Iran University of Science and Technology (IUST), Narmak, Tehran 16846-13114 (Iran, Islamic Republic of)

2014-06-15

220

Cotton fiber quality characterization with light scattering and fourier transform infrared techniques.  

PubMed

Fiber quality measurement is critical to assessing the value of a bale of cotton for various textile purposes. An instrument that could measure numerous cotton quality properties by optical means could be made simpler and faster than current fiber quality measurement instruments, and it might be more amenable to on-line measurement at processing facilities. To that end, a laser system was used to investigate cotton fiber samples with respect to electromagnetic scattering at various wavelengths, polarization angles, and scattering angles. A Fourier transform infrared (FT-IR) instrument was also used to investigate the transmission of electromagnetic energy at various mid-infrared wavelengths. Cotton samples were selected to represent a wide range of micronaire values. Varying the wavelength of the laser at a fixed polarization resulted in little variation in scattered light among the cotton samples. However, varying the polarization at a fixed wavelength produced notable variation, indicating that polarization might be used to differentiate among cotton samples with respect to certain fiber properties. The FT-IR data in the 12 to 22 microm range produced relatively large differences in the amount of scattered light among all samples, and FT-IR data at certain combinations of fixed wavelengths were highly linearly related to certain measures of cotton quality including micronaire. PMID:19281648

Thomasson, J A; Manickavasagam, S; Mengüç, M P

2009-03-01

221

Electron heating enhancement by frequency-chirped laser pulses  

SciTech Connect

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 a{sub 0}?=?5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about n{sub e}???6n{sub c}, where n{sub c} 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.; Afarideh, H., E-mail: hafarideh@aut.ac.ir [Department of Energy Engineering and Physics, Amirkabir University of Technology, P.O. Box 15875-4413, Tehran (Iran, Islamic Republic of); Sadighi-Bonabi, R., E-mail: Sadighi@sharif.ir [Department of Physics, Sharif University of Technology, P.O. Box 11365-9567, Tehran (Iran, Islamic Republic of); Riazi, Z. [Physics and Accelerator School, Tehran (Iran, Islamic Republic of); Hora, H. [Department of Theoretical Physics, University of New South Wales, Sydney 2052 (Australia)

2014-09-14

222

Few-cycle chirped-pulse parametric amplification  

Microsoft Academic Search

We review progress in the development of kilohertz-repetition-rate few-cycle optical parametric chirped pulse amplifiers (OPCPA) in the near-IR (700-1000 nm) and IR (1700-2800 nm) spectral ranges. These sources hold promise for applications in extreme nonlinear optics and attosecond physics.

A. Baltuska; N. Ishii; T. Fuji; X. Gu; N. Forget; D. Kaplan; A. Galvanauskas; F. Krausz

2006-01-01

223

Pulse compression on the Mark III FEL using energy chirping  

Microsoft Academic Search

We have performed preliminary simulations of the optical-pulse formation in the Mark III FEL using electron micropulses which exhibit a linear energy dependence on time, and have demonstrated optical pulses whose frequency chirps agree fairly well with those obtained analytically by assuming that the resonance condition determines the lasing wavelength during the pulse. In a typical case, we project pulse

Eric B. Szarmes; Stephen V. Benson; John M. J. Madey

1990-01-01

224

Chirped frequency transfer: a tool for synchronization and time transfer.  

PubMed

We propose and demonstrate the phase-stabilized transfer of a chirped frequency as a tool for synchronization and time transfer. Technically, this is done by evaluating remote measurements of the transferred, chirped frequency. The gates of the frequency counters, here driven by a 10-MHz oscillation derived from a hydrogen maser, play a role analogous to the 1-pulse per second (PPS) signals usually employed for time transfer. In general, for time transfer, the gates consequently must be related to the external clock. Synchronizing observations based on frequency measurements, on the other hand, only requires a stable oscillator driving the frequency counters. In a proof of principle, we demonstrate the suppression of symmetrical delays, such as the geometrical path delay. We transfer an optical frequency chirped by around 240 kHz/s over a fiber link of around 149 km. We observe an accuracy and simultaneity, as well as a precision (Allan deviation, 18,000 s averaging interval) of the transferred frequency of around 2 × 10(-19). We apply chirped frequency transfer to remote measurements of the synchronization between two counters' gate intervals. Here, we find a precision of around 200 ps at an estimated overall uncertainty of around 500 ps. The measurement results agree with those obtained from reference measurements, being well within the uncertainty. In the present setup, timing offsets up to 4 min can be measured unambiguously. We indicate how this range can be extended further. PMID:24859656

Raupach, Sebastian M F; Grosche, Gesine

2014-06-01

225

Generating nonlinear FM chirp radar signals by multiple integrations  

SciTech Connect

A phase component of a nonlinear frequency modulated (NLFM) chirp radar pulse can be produced by performing digital integration operations over a time interval defined by the pulse width. Each digital integration operation includes applying to a respectively corresponding input parameter value a respectively corresponding number of instances of digital integration.

Doerry, Armin W. (Albuquerque, NM)

2011-02-01

226

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

227

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

228

Chirped-Pulse Broadband Microwave Spectra and Structures of the OCS Trimer and Tetramer  

NASA Astrophysics Data System (ADS)

Structure determination of weakly bound OCS clusters is a challenging problem due to many low energy isomers on the potential energy surface. The premier tool for studying these clusters is high-resolution infrared spectroscopy, as it can be used to analyze non-polar clusters. Following the analysis of high-resolution IR spectra of clusters formed in a molecular beam expansion of OCS there were some outstanding questions about the structures of the observed clusters. The chirped-pulse Fourier transform microwave spectrum in the 3-9 GHz frequency range was measured for a pulsed molecular beam of OCS in neon (1%). All 13C, 18O and 34S isotopologues of the previously detected OCS trimer have been observed in natural abundance in the 3-9 GHz band using chirped-pulse Fourier transform microwave spectroscopy. The structure of this trimer features a barrel-shaped structure with two aligned and one anti-aligned OCS monomers. A new OCS trimer is also observed for the first time, and its structure is consistent with a barrel-shaped structure with 3 aligned monomers. Using the infrared spectrum for guidance, a spectrum corresponding to a polar OCS tetramer has been assigned. This cluster has a similar barrel-like structure but with an additional tilted OCS monomer added to the top of the barrel. All 13C and 34S isotopologues have been assigned for the tetramer. However, due to sign ambiguities in Kraitchman's equations, and small rotational constant differences between aligned and anti-aligned combinations of OCS molecules in the trimer barrel, absolute structural assignment is indeterminate without additional constraints. Therefore a combinatoric approach was used to compute the most reasonable tetramer structure using distance and sign constraints between pairs of carbon and sulfur coordinates, assuming the experimental OCS monomer structure. Results of this approach will be presented, as well as a comparison of the experimental results with the most recent ab initio structures for the OCS tetramer.

Evangelisti, Luca; Perez, Cristobal; Seifert, Nathan A.; Pate, Brooks; Dehghany, Mehdi; Moazzen-Ahmadi, Nasser; McKellar, Bob

2014-06-01

229

Measuring the hypnotic depth of anaesthesia based on the EEG signal using combined wavelet transform, eigenvector and normalisation techniques.  

PubMed

This paper presents a new index to measure the hypnotic depth of anaesthesia (DoA) using EEG signals. This index is derived from applying combined Wavelet transform, eigenvector and normalisation techniques. The eigenvector method is first applied to build a feature function for six levels of coefficients in a discrete wavelet transform (DWT). The best Daubechies wavelet and their ranking value p are optimally determined to identify different states of anaesthesia. A statistic normalisation process is then carried out to re-scale data and compute the hypnotic depth of anaesthesia. Finally, a new function ZDoA is proposed to compute a DoA index which corresponds one of the five depths of anaesthesia states to very deep anaesthesia, deep anaesthesia, moderate anaesthesia, light anaesthesia and awake. Simulation results based on real anaesthetised EEGs demonstrate that the new index generally parallels the BIS index. In particular, the ZDoA index is often faster than the BIS index to react to the transition period between consciousness and unconsciousness for this data set. A Bland-Altman plot indicates a 95.23% agreement between the ZDoA and BIS indices. The ZDoA trend is responsive, and its movement is consistent with the clinically observed and recorded changes of the patients. PMID:22575174

Nguyen-Ky, Tai; Wen, Peng; Li, Yan; Malan, Mel

2012-06-01

230

Simultaneous 3D position sensing by means of large-scale spherical aberration of lens and Hough transform technique  

NASA Astrophysics Data System (ADS)

We demonstrate a real time 3D position sensing of multiple light sources by capturing their ring images that are transformed by the molecular lens system with large spherical aberration. The ring images change in diameter in accordance with the distance to the light sources, and the ring center positions determine the directions toward them. Therefore, the 3D positions of light sources are calculated by detecting the diameters and center positions of the circles. This time we succeeded to measure 3D positions of multiple light sources simultaneously in real time by extracting and tracking the circle patterns individually. Each circle is extracted by the Hough transform technique that uses not-closely-distributing three edge points to search the primal votes more than threshold, and is tracked by predicting the successive positions by Kalman filter. These processes make it possible to measure the 3D positions of light sources even in the case of overlapped plural circles. In the experiment, we could track several circle patterns measuring the center positions and diameters, namely, measuring the 3D positions of LEDs in real space. Measurement error of 3D positions for a LED was 6.8mm in average for 150 sampling points ranging from 450mm to 950mm in distance.

Seko, Yasuji; Saguchi, Yasuyuki; Yamaguchi, Yoshinori; Hotta, Hiroyuki; Murai, Kazumasa; Miyazaki, Jun; Koshimizu, Hiroyasu

2005-12-01

231

Imaging of human tooth using ultrasound based chirp-coded nonlinear time reversal acoustics.  

PubMed

Human tooth imaging sonography is investigated experimentally with an acousto-optic noncoupling set-up based on the chirp-coded nonlinear time reversal acoustic concept. The complexity of the tooth internal structure (enamel-dentine interface, cracks between internal tubules) is analyzed by adapting the nonlinear elastic wave spectroscopy (NEWS) with the objective of the tomography of damage. Optimization of excitations using intrinsic symmetries, such as time reversal (TR) invariance, reciprocity, correlation properties are then proposed and implemented experimentally. The proposed medical application of this TR-NEWS approach is implemented on a third molar human tooth and constitutes an alternative of noncoupling echodentography techniques. A 10 MHz bandwidth ultrasonic instrumentation has been developed including a laser vibrometer and a 20 MHz contact piezoelectric transducer. The calibrated chirp-coded TR-NEWS imaging of the tooth is obtained using symmetrized excitations, pre- and post-signal processing, and the highly sensitive 14 bit resolution TR-NEWS instrumentation previously calibrated. Nonlinear signature coming from the symmetry properties is observed experimentally in the tooth using this bi-modal TR-NEWS imaging after and before the focusing induced by the time-compression process. The TR-NEWS polar B-scan of the tooth is described and suggested as a potential application for modern echodentography. It constitutes the basis of the self-consistent harmonic imaging sonography for monitoring cracks propagation in the dentine, responsible of human tooth structural health. PMID:21371732

Dos Santos, Serge; Prevorovsky, Zdenek

2011-08-01

232

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

233

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

NASA Astrophysics Data System (ADS)

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

Erol, B.; Erol, S.

2013-03-01

234

Super-resolution technique for CW lidar using Fourier transform reordering and Richardson-Lucy deconvolution.  

PubMed

An interpolation method is described for range measurements of high precision altimetry with repeating intensity modulated continuous wave (IM-CW) lidar waveforms using binary phase shift keying (BPSK), where the range profile is determined by means of a cross-correlation between the digital form of the transmitted signal and the digitized return signal collected by the lidar receiver. This method uses reordering of the array elements in the frequency domain to convert a repeating synthetic pulse signal to single highly interpolated pulse. This is then enhanced further using Richardson-Lucy deconvolution to greatly enhance the resolution of the pulse. We show the sampling resolution and pulse width can be enhanced by about two orders of magnitude using the signal processing algorithms presented, thus breaking the fundamental resolution limit for BPSK modulation of a particular bandwidth and bit rate. We demonstrate the usefulness of this technique for determining cloud and tree canopy thicknesses far beyond this fundamental limit in a lidar not designed for this purpose. PMID:25503046

Campbell, Joel F; Lin, Bing; Nehrir, Amin R; Harrison, F Wallace; Obland, Michael D

2014-12-15

235

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

236

Design, fabrication and characterization of a specially apodized chirped grating for reciprocal second harmonic generation.  

PubMed

A specially-designed apodized chirped PPLN based on particular positioning of poled regions within the periods has been realized theoretically and experimentally to demonstrate the reciprocal response in the SHG spectra over a 30-nm bandwidth, for up-chirp and down-chirp directions. The simulation results are compared with another apodized chirped PPLN for which the placement of poled regions is deviated from optimum positions. The average power difference is less than 0.75 dB and the standard deviations of extrema on second harmonic power responses are 1.34 dB and 1.64 dB for two up-chirp and down-chirp directions respectively. PMID:25836551

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

2015-02-23

237

Pulse compression on the Mark III FEL using energy chirping  

NASA Astrophysics Data System (ADS)

We have performed preliminary simulations of the optical-pulse formation in the Mark III FEL using electron micropulses which exhibit a linear energy dependence on time, and have demonstrated optical pulses whose frequency chirps agree fairly well with those obtained analytically by assuming that the resonance condition determines the lasing wavelength during the pulse. In a typical case, we project pulse compression by a factor of 13.3, from an initial pulse width of 3.13 ps to a final pulse width of 236 fs, at a wavelength of 3.35 ?m and an electron energy chirp of +2% (energy increasing towards the back of the pulse). This represents an optical pulse less than half as short as the slippage length of 47 magnet periods for this wavelength.

Szarmes, Eric B.; Benson, Stephen V.; Madey, John M. J.

1990-10-01

238

Chirp Measurements Of A Ten Joule Pulsed CO2 Oscillator  

NASA Astrophysics Data System (ADS)

Chirp measurements have been conducted on the pulsed output of an unstable resonator oscillating on the P20 line of the 10.6 micron band of an e-beam sustained CO2 gain medium. A heterodyne method was used, mixing the oscillator signal with a cw laser operating on the same line. The mode volume was approximately 5 liters at a pressure between 1/3 and 1/2 atm. The measurements were conducted at pulse lengths of the order of 20 microseconds and are useful in characterizing the device for use in radar applications. Chirp values of less than 1 MHz are observed during the first 10 ? sec, in the remainder of the pulse, values of several MHz are observed, with decreasing frequency.

Hoag, Ethan D.

1989-07-01

239

Dense monoenergetic proton beams from chirped laser-plasma interaction.  

PubMed

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

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

2011-10-28

240

A robust ultra broadband wireless communication system using SAW chirped delay lines  

Microsoft Academic Search

Design and performance of SAW chirped delay lines on LiTaO3 -X112rotY for a wireless communication system are presented. Center frequency, bandwidth and chirp rate are 350 MHz, 80 MHz, and ±20 MHz\\/s, respectively. An optimized square-root weighting was chosen to reduce the sidelobes of the compressed pulse to -42 dB compared to the correlation peak. The chirp filters have been

A. Springer; A. Pohl; W. Gugler; M. Huemer; L. Reindl; C. C. W. Ruppel; F. Seifert; R. Weigel

1998-01-01

241

Pulse-shape effects on frequency chirping in single-frequency semiconductor lasers under current modulation  

Microsoft Academic Search

Directly modulated semiconductor lasers exhibit dynamic frequency shifts (chirping) due to gain-induced variations of the refractive index. Using the small-signal analysis of the single-mode rate equations, the effect of current-pulse shape on frequency chirping is analyzed, and the results are compared for the cases of sinusoidal and square-wave modulations. The chirp is generally larger for the square-wave case. However, its

T. Shen; G. Agrawal

1986-01-01

242

Multimillijoule chirped parametric amplification of few-cycle pulses  

Microsoft Academic Search

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

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

2005-01-01

243

Chirped multilayer coatings for increased x-ray throughput  

Microsoft Academic Search

Chirped Mo--Si multilayer coatings, where the multilayer period is systematically varied throughout the deposition process, exhibit an increased x-ray bandwidth at normal incidence with a corresponding increase in the integrated reflectance of as much as 20% at [lambda][similar to]13 nm. The increased bandwidth is accompanied by a slight reduction in peak reflectance. The relation between the integrated and peak reflectance

S. P. Vernon; D. G. Stearns; R. S. Rosen

1993-01-01

244

Excitation and control of chirped nonlinear ion-acoustic waves  

NASA Astrophysics Data System (ADS)

Large-amplitude ion acoustic waves are excited and controlled by a chirped frequency driving perturbation. The process involves capturing into autoresonance (a continuous nonlinear synchronization) with the drive by passage through the linear resonance in the problem. The transition to autoresonance has a sharp threshold on the driving amplitude. The theory of this transition is developed beyond the Korteweg-de Vries limit by using the Whitham's averaged variational principle within the water bag model and compared with Vlasov-Poisson simulations.

Friedland, L.; Shagalov, A. G.

2014-05-01

245

Chirping a two-photon transition in a multistate ladder  

SciTech Connect

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

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

2007-08-15

246

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

247

Hadamard transform spectrometry: A new analytical technique; Progress report, Second year, March 15, 1992--November 15, 1992  

SciTech Connect

The document is divided into 4 parts: Hadamard transform photoacoustic spectrometry and depth profiling; Hadamard transform imaging with a 2D Hadamard encoding mask (Raman image using pararosaniline hydrochloride); Hadamard transform Raman spectrometry; and work on the growth of VO{sub 2}(s) crystals for Hadamard masking material. 13 figs, refs.

Fateley, W.G.; Hammaker, R.M.

1992-11-15

248

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

249

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

250

Chirped InGaAs quantum dot molecules for broadband applications  

PubMed Central

Lateral InGaAs quantum dot molecules (QDMs) formed by partial-cap and regrowth technique exhibit two ground-state (GS) peaks controllable via the thicknesses of InAs seed quantum dots (x), GaAs cap (y), and InAs regrowth (z). By adjusting x/y/z in a stacked QDM bilayer, the GS peaks from the two layers can be offset to straddle, stagger, or join up with each other, resulting in multi-GS or broadband spectra. A non-optimized QDM bilayer with a 170-meV full-width at half-maximum is demonstrated. The temperature dependencies of the emission peak energies and intensities from the chirped QDM bilayers are well explained by Varshni's equation and thermal activation of carriers out of constituent quantum dots. PMID:22480323

2012-01-01

251

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

252

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

NASA Technical Reports Server (NTRS)

A set of co-aligned high resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) 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 quantitative description of sub visual 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-timeplots 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 which 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 the slow mode magneto-acoustic wave which seems to be the dominating wave mode in the studied loop structures. This result extends recent observations by Kiddie et al. (2012) to a more general class of fan loop systems not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

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

2013-01-01

253

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

254

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

255

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

256

Transient analysis of Kerr-like phase conjugators using frequency-domain techniques  

NASA Astrophysics Data System (ADS)

In this paper we develop the interrelationships between the steady-state and transient behavior for cw-pumped Kerr-like conjugators in which the optical Kerr effect is considered to respond instantaneously. We use Laplace-transform techniques to develop an expression for the conjugate response to input pulses of arbitrary form. For stable conjugator operation (in which the cw conjugate reflectivity is finite for all input frequencies), the expression reduces to an antilinear Fourier-transform relationship, which is readily adaptable to computer simulation. The cw filter function of Pepper and Abrams

[Opt. Lett. 3, 312 (1978)]
is found to play a central role. We show, both numerically and analytically, that our calculated delta-function response agrees with that previously published. We numerically demonstrate temporal spreading and reshaping when the conjugator transit time becomes equal to or longer than the duration of the input pulse, and we show numerically the perfect chirp reversal for sufficiently thin conjugators and the deviations from perfect chirp reversal upon increasing the thickness of the conjugator. These numerical results can be understood in terms of the bandwidth of the associated cw filter function.

Fisher, Robert A.; Suydam, B. R.; Feldman, B. J.

1981-06-01

257

A Novel Iron Loss Reduction Technique for Distribution Transformers Based on a Combined Genetic Algorithm - Neural Network Approach  

Microsoft Academic Search

This paper presents an effective method to reduce the iron losses of wound core distribution transformers based on a combined neural network - genetic algorithm approach. The originality of the work presented in this paper is that it tackles the iron loss reduction problem during the transformer production phase, while previous works were concentrated on the design phase. More specifically,

Palvos S. Georgilakis; Nikolaos D. Doulamis; Anastasios D. Doulamis; Nikos D. Hatziargyriou; Stefanos D. Kollias

2001-01-01

258

A novel iron loss reduction technique for distribution transformers based on a combined genetic algorithm - neural network approach  

Microsoft Academic Search

The paper presents an effective method to reduce the iron losses of wound core distribution transformers based on a combined neural network\\/genetic algorithm approach. The originality of the work presented is that it tackles the iron loss reduction problem during the transformer production phase, while previous works concentrated on the design phase. More specifically, neural networks effectively use measurements taken

Pavlos S. Georgilakis; Nikolaos D. Doulamis; Anastasios D. Doulamis; Nikos D. Hatziargyriou; Stefanos D. Kollias

2001-01-01

259

An equivalent instantaneous inductance-based technique for discrimination between inrush current and internal faults in power transformers  

Microsoft Academic Search

A novel equivalent instantaneous inductance (EII)-based scheme is proposed to distinguish the inrush current from internal faults in power transformers, which is derived from the inherent difference of the magnetic permeability, due to the saturation and unsaturation, in the transformer iron core between the inrush current and an internal fault. First, the EII that represents these differences is defined, and

Ge Baoming; Aníbal T. de Almeida; Zheng Qionglin; Wang Xiangheng

2005-01-01

260

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

PubMed

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

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

2012-11-01

261

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

262

Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers  

E-print Network

Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers Louis Daniault,1 femtosecond chirped- pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac amplifiers have great advantages to amplify ultrashort femtosecond pulses. Indeed, their geometry offers

Boyer, Edmond

263

Frequency chirp and pulse shape effects in self-modulated laser wakefield acceleratorsa...  

E-print Network

Frequency chirp and pulse shape effects in self-modulated laser wakefield acceleratorsa... C. B Received 7 November 2002; accepted 20 January 2003 The effect of asymmetric laser pulses on plasma wave of asymmetries in frequency chirp and tempo- ral pulse shape on the laser-excitation of plasma waves. Sec- tion

Geddes, Cameron Guy Robinson

264

Frequency chirp and pulse shape effects in self-modulated laser wakefield accelerators  

Microsoft Academic Search

The effect of asymmetric laser pulses on plasma wave excitation in a self-modulated laser wakefield accelerator is examined. Laser pulse shape and frequency chirp asymmetries, controlled experimentally in the laser system through a grating pair compressor, are shown to strongly enhance measured electron yields for certain asymmetries. It is shown analytically that a positive (negative) frequency chirp enhances (suppresses) the

C. B. Schroeder; E. Esarey; C. G. R. Geddes; Cs. Tóth; B. A. Shadwick; J. van Tilborg; J. Faure; W. P. Leemans

2003-01-01

265

Frequency chirp and pulse shape effects in self-modulated laser wakefield accelerators  

Microsoft Academic Search

The effect of asymmetric laser pulses on plasma wave excitation in a self-modulated laser wakefield accelerator is examined. Laser pulse shape and frequency chirp asymmetries, controlled experimentally in the laser system through a grating pair compressor, are shown to strongly enhance measured electron yields for certain asymmetries. It is shown analytically that a positive (negative) frequency chirp enhances (suppresses) the

C. B. Schroeder; E. Esarey; C. G. R. Geddes; Cs. Toth; B. A. Shadwick; J. van Tilborg; J. Faure; W. P. Leemans

2002-01-01

266

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

267

Anim. Behav., 1997, 54, 15531562 Female house crickets, Acheta domesticus, prefer the chirps of large males  

E-print Network

Anim. Behav., 1997, 54, 1553­1562 Female house crickets, Acheta domesticus, prefer the chirps and analysed the calling songs of male house crickets, Acheta domesticus. The analyses showed that chirps choice and sperm com- petition (Møller 1994). Many of these components can be separated in field crickets

Gray, David A.

268

Mono-bit digital chirp receiver using mono-bit IFM (instantaneous frequency measurement) receiver as a core  

Microsoft Academic Search

This paper describes the design and intricacies of a wideband digital chirp receiver utilizing a one-bit ADC (Analog to Digital Converter) to measure the carrier frequency and chirp rate of unknown received signals which have very high chip rates. The core of the chirp receiver is composed of monobit IFM receivers which are low cost and very accurate.

David M. Lin; Lihyeh L. Liou; Steve Benson; Henry Chen

2011-01-01

269

Superradiant Linear Raman Amplification in Plasma Using a Chirped Pump Pulse B. Ersfeld and D. A. Jaroszynski  

E-print Network

Superradiant Linear Raman Amplification in Plasma Using a Chirped Pump Pulse B. Ersfeld and D. A backscattering from a chirped pump pulse in plasma shows that an ultrashort probe pulse will grow superradiantly. Linear chirped pulse amplification in plasma could provide a very broad-bandwidth alternative to solid

Strathclyde, University of

270

3336 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 16, AUGUST 15, 2009 Chirped Microwave Pulse Generation Based on  

E-print Network

Generation Based on Optical Spectral Shaping and Wavelength-to-Time Mapping Using a Sagnac Loop Mirror and the chirp profile of the generated chirped microwave pulse can be controlled by simply tuning the time delay in the Sagnac loop mirror. A simple mathematical model to describe the chirped microwave pulse generation

Yao, Jianping

271

Multi-mode and multi-frequency guided wave imaging via chirp excitations  

NASA Astrophysics Data System (ADS)

Guided wave imaging has shown great potential for structural health monitoring applications by providing a way to visualize and characterize structural damage. For successful implementation of delay-and-sum and other elliptical imaging algorithms employing guided ultrasonic waves, some degree of mode purity is required because echoes from undesired modes cause imaging artifacts that obscure damage. But it is also desirable to utilize multiple modes because different modes may exhibit increased sensitivity to different types and orientations of defects. The well-known modetuning effect can be employed to use the same PZT transducers for generating and receiving multiple modes by exciting the transducers with narrowband tone bursts at different frequencies. However, this process is inconvenient and timeconsuming, particularly if extensive signal averaging is required to achieve a satisfactory signal-to-noise ratio. In addition, both acquisition time and data storage requirements may be prohibitive if signals from many narrowband tone burst excitations are measured. In this paper, we utilize a chirp excitation to excite PZT transducers over a broad frequency range to acquire multi-modal data with a single transmission, which can significantly reduce both the measurement time and the quantity of data. Each received signal from a chirp excitation is post-processed to obtain multiple signals corresponding to different narrowband frequency ranges. Narrowband signals with the best mode purity and echo shape are selected and then used to generate multiple images of damage in a target structure. The efficacy of the proposed technique is demonstrated experimentally using an aluminum plate instrumented with a spatially distributed array of piezoelectric sensors and with simulated damage.

Michaels, Jennifer E.; Lee, Sang Jun; Hall, James S.; Michaels, Thomas E.

2011-04-01

272

Experimental demonstration of a multi-wavelength distributed feedback semiconductor laser array with an equivalent chirped grating profile based on the equivalent chirp technology.  

PubMed

We report, to the best of our knowledge, the first realization of a multi-wavelength distributed feedback (DFB) semiconductor laser array with an equivalent chirped grating profile based on equivalent chirp technology. All the lasers in the laser array have an identical grating period with an equivalent chirped grating structure, which are realized by nonuniform sampling of the gratings. Different wavelengths are achieved by changing the sampling functions. A multi-wavelength DFB semiconductor laser array is fabricated and the lasing performance is evaluated. The results show that the equivalent chirp technology is an effective solution for monolithic integration of a multi-wavelength laser array with potential for large volume fabrication. PMID:24105542

Li, Wangzhe; Zhang, Xia; Yao, Jianping

2013-08-26

273

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

274

CE-Chirp® ABR in cerebellopontine angle surgery neuromonitoring: technical assessment in four cases.  

PubMed

Continuous monitoring of wave V of auditory brainstem response (ABR), also called brainstem auditory evoked potential (BAEP), is the most common method used in intraoperative neuromonitoring (IONM) functionality of cochlear nerve during surgery in cerebellopontine angle (CPA). CE-Chirp® ABR represents a recent development of classical ABR. CE-Chirp® is a new acoustic stimulus used in newborn hearing testing, designed to provide enhanced neural synchronicity and faster detection of larger amplitude wave V. In four cases, CE-Chirp® ABR was performed during cerebellopontine angle (CPA) surgery. CE-Chirp® ABR represented a safe and effective method in neuromonitoring functionality of vestibulocochlear nerve. A faster neuromonitoring feedback to surgical equipe was possible with CE-Chirp ABR®. PMID:25697141

Di Scipio, Ettore; Mastronardi, Luciano

2015-04-01

275

Backward Raman amplification in plasmas with chirped wideband pump and seed pulses  

NASA Astrophysics Data System (ADS)

Chirped wideband pump and seed pulses are usually considered for backward Raman amplification (BRA) in plasmas to achieve an extremely high-power laser pulse. However, current theoretical models only contain either a chirped pump or a chirped seed. In this paper, modified three-wave coupling equations are proposed for the BRA in the plasmas with both chirped wideband pump and seed. The simulation results can more precisely describe the experiments, such as the Princeton University experiment. The optimized chirp and bandwidth are determined based on the simulation to enhance the output intensity and efficiency. Project supported by the National Natural Science Foundation of China (Grant No. 11305157) and the Development Foundation of China Academy of Engineering Physics Laboratory (CAEPL) (Grant No. 2013A0401019).

Wu, Zhao-Hui; Wei, Xiao-Feng; Zuo, Yan-Lei; Liu, Lan-Qin; Zhang, Zhi-Meng; Li, Min; Zhou, Yu-Liang; Su, Jing-Qin

2015-01-01

276

Chirped laser dispersion spectroscopy with differential frequency generation source.  

PubMed

A feasibility study of open-path methane detection at 3.4 ?m using chirped laser dispersion spectroscopy (CLaDS) based on nonlinear differential frequency generation (DFG) laser source is performed. Application of a DFG source based on telecom laser sources and modulators allows mid-infrared CLaDS system to be optimized for measurements of gases at atmospheric conditions for which modulation in the GHz range is required. Excellent agreement between observed CLaDS signals and spectroscopic models has been observed. PMID:25078192

Nikodem, Michal; Krzempek, Karol; Karwat, Renata; Dudzik, Grzegorz; Abramski, Krzysztof; Wysocki, Gerard

2014-08-01

277

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

278

Robust Volume Assessment of Brain Tissues for 3-Dimensional Fourier Transformation MRI via a Novel Multispectral Technique  

PubMed Central

A new TRIO algorithm method integrating three different algorithms is proposed to perform brain MRI segmentation in the native coordinate space, with no need of transformation to a standard coordinate space or the probability maps for segmentation. The method is a simple voxel-based algorithm, derived from multispectral remote sensing techniques, and only requires minimal operator input to depict GM, WM, and CSF tissue clusters to complete classification of a 3D high-resolution multislice-multispectral MRI data. Results showed very high accuracy and reproducibility in classification of GM, WM, and CSF in multislice-multispectral synthetic MRI data. The similarity indexes, expressing overlap between classification results and the ground truth, were 0.951, 0.962, and 0.956 for GM, WM, and CSF classifications in the image data with 3% noise level and 0% non-uniformity intensity. The method particularly allows for classification of CSF with 0.994, 0.961 and 0.996 of accuracy, sensitivity and specificity in images data with 3% noise level and 0% non-uniformity intensity, which had seldom performed well in previous studies. As for clinical MRI data, the quantitative data of brain tissue volumes aligned closely with the brain morphometrics in three different study groups of young adults, elderly volunteers, and dementia patients. The results also showed very low rates of the intra- and extra-operator variability in measurements of the absolute volumes and volume fractions of cerebral GM, WM, and CSF in three different study groups. The mean coefficients of variation of GM, WM, and CSF volume measurements were in the range of 0.03% to 0.30% of intra-operator measurements and 0.06% to 0.45% of inter-operator measurements. In conclusion, the TRIO algorithm exhibits a remarkable ability in robust classification of multislice-multispectral brain MR images, which would be potentially applicable for clinical brain volumetric analysis and explicitly promising in cross-sectional and longitudinal studies of different subject groups. PMID:25710499

Chai, Jyh-Wen; Chen, Clayton C.; Wu, Yi-Ying; Chen, Hung-Chieh; Tsai, Yi-Hsin; Chen, Hsian-Min; Lan, Tsuo-Hung; Ouyang, Yen-Chieh; Lee, San-Kan

2015-01-01

279

Design of chirped fly's eye uniformizer for ArF lithography illumination system  

NASA Astrophysics Data System (ADS)

Fly's eye uniformizer is the key part of ArF lithography illumination system, whose main function is to illuminate the reticle uniformly. Due to the periodic structure of regular fly's eye uniformizer and the high coherence of the ArF laser, the output intensity distribution is modulated with equidistant sharp intensity peaks (interference speckle pattern) which disturbed the uniformity on the reticle. In this paper, we design a chirped fly's eye uniformizer which consists of chirped fly's eye and a condenser for illumination system in ArF lithography system. The chirped fly's eye consists of individually shaped micro-lenses defined by a parametric description which can be derived completely from analytical functions. The micro-lenses with different thicknesses in the chirped fly's eye have a function of delaying the optical path which reducing the laser coherence and speckle pattern on the reticle. Detailed design process of the chirped fly's eye uniformizer for numerical aperture (NA) 0.75 lithography illumination system is presented. Light intensity distribution on reticle produced by regular and chirped fly's eye uniformizer are analyzed and compared by the method of wave optics, and the results show that chirped can restrain sharp intensity peaks efficiently. Furthermore, the chirped fly's eye uniformizer has been traced in LightTools software under conventional and annual illumination modes, and the non-uniformity of the non-scan and scan direction on the reticle reached 0.75% and 1.24% respectively. The simulation results show that the chirped fly's eye uniformizer can provide high illumination uniformity and reduce the speckle pattern efficiently without additional elements.

Xiao, Lei; Li, Yanqiu; Wei, Lidong

2014-11-01

280

Peculiarities of laser phase behavior associated with the accelerated electron in a chirped laser pulse  

SciTech Connect

In this paper, we qualitatively analyzed peculiarities of laser phase behavior associated with the accelerated electron in a chirped laser pulse. We unveiled the relationship between the changes in the orientation of the electron trajectory and the cusps in magnitude of the phase velocity of the optical field along the electron trajectory in a chirped laser pulse. We also explained how the chirp effect induced the singular point of the phase velocity. Finally, we discussed the phase velocity and phase witnessed by the electron in the particle's moving instantaneous frame.

Song, Q.; Wu, X. Y. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); Wang, J. X. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); State Key Laboratory of Precision Spectroscopy and Department of Physics, East China Normal University, Shanghai 200062 (China); Kawata, S. [Center for Optical Research and Education, Department of Advanced Interdisciplinary Science, Graduate School of Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan); Wang, P. X., E-mail: wpx@fudan.edu.cn [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); Center for Optical Research and Education, Department of Advanced Interdisciplinary Science, Graduate School of Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan)

2014-05-15

281

Self-deflecting plasmonic lattice solitons and surface modes in chirped plasmonic arrays  

NASA Astrophysics Data System (ADS)

We show that chirped metal-dielectric waveguide arrays with focusing cubic nonlinearity can support plasmonic lattice solitons that undergo self-deflection in the transverse plane. Such lattice solitons are deeply-subwavelength self-sustained excitations, although they cover several periods of the array. Upon propagation,the excitations accelerate in the transverse plane and follow trajectories curved in the direction in which the separation between neighboring metallic layers decreases, a phenomenon that yields considerable deflection angles. The deflection angle can be controlled by varying the array chirp. We also reveal the existence of surface modes at the boundary of truncated plasmonic chirped arraythat form even in the absence of nonlinearity.

Li, Chunyan; Cui, Ran; Ye, Fangwei; Kartashov, Yaroslav V.; Torner, Lluis; Chen, Xianfeng

2015-03-01

282

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

283

Self-deflecting plasmonic lattice solitons and sur-face modes in chirped plasmonic arrays  

E-print Network

We show that chirped metal-dielectric waveguide arrays with focusing cubic nonlinearity can support plasmonic lattice solitons that undergo self-deflection in the transverse plane. Such lattice solitons are deeply-subwavelength self-sustained excitations, although they cover several periods of the array. Upon propagation,the excitations accelerate in the transverse plane and follow trajectories curved in the direction in which the separation between neighboring metallic layers decreases, a phenomenon that yields considerable deflection angles. The deflection angle can be controlled by varying the array chirp. We also reveal the existence of surface modes at the boundary of truncated plasmonic chirped arraythat form even in the absence of nonlinearity.

Li, Chunyan; Ye, Fangwei; Kartashov, Yaroslav V; Torner, Lluis; Chen, Xianfeng

2015-01-01

284

Automated Chirp Detection with Diffusion Entropy: Application to Infrasound from Sprites  

E-print Network

We study the performance of three different methods to automatically detect a chirp in background noise. (1) The standard deviation detector uses the computation of the signal to noise ratio. (2) The spectral covariance detector is based on the recognition of the chirp in the spectrogram. (3) The CASSANDRA detector uses diffusion entropy analysis to detect periodic patterns in noise. All three detectors are applied to an infrasound recording for detecting chirps produced by sprites. The CASSANDRA detector provides the best trade off between the false alarm rate and the detection efficiency.

Ignaccolo, M; Farges, T; Fullekrug, M

2005-01-01

285

Efficient prime factor decomposition algorithm and address generation techniques for the computation of discrete cosine transform [image compression  

Microsoft Academic Search

An efficient prime factor algorithm for the discrete cosine transform is introduced. In this approach, we formulate the decomposition directly, by using the proposed input and output mapping, and derive a novel in-place address generation scheme, whilst the formulations in the literature require multiple stages or have to be done via the DFT. This approach requires one output index mapping

Lap-Pui Chau; Daniel Pak-Kong LUN; Wan-Chi Siu

1998-01-01

286

Estimates of the Joint Statistics of Amplitudes and Periods of Ocean Waves Using an Integral Transform Technique  

Microsoft Academic Search

An integral transform method is used to obtain continuous time series of wave amplitude and period from ocean wave measurements. The joint statistics of these two variables are determined and directly compared with the theoretical probability densities predicted by Longuet-Higgins (1975, 1983). Good agreement is found for data from both calm and hurricane sea states. This method avoids the ambiguities

K. T. SI-IUM; W. K. Melville

1984-01-01

287

Analytical solution of the advection-diffusion transport equation using a change-of-variable and integral transform technique  

Technology Transfer Automated Retrieval System (TEKTRAN)

This paper presents a formal exact solution of the linear advection-diffusion transport equation with constant coefficients for both transient and steady-state regimes. A classical mathematical substitution transforms the original advection-diffusion equation into an exclusively diffusive equation. ...

288

Application of Laplace transform technique to the solution of certain third-order non-linear systems  

Microsoft Academic Search

The approach of Baycure (1968) for applying Laplace transforms to certain third-order nonlinear systems subjected to nonperiodic excitations is discussed. This approach is further extended to determine the pulse response of a gyrostabilized platform. Solutions are presented for a forcing function as a difference of two decaying functions, a suddenly applied force exponentially decaying, and an asymptotic step forcing function.

S. G. Joshi; P. Srinivasan

1978-01-01

289

Simultaneous etching of polysilicon materials with different doping types by low-damage transformer-coupled plasma technique  

Microsoft Academic Search

The feasibility of simultaneously etching n+, p+, and undoped polysilicon (poly-Si) materials by a commercial transformer coupled plasma (TCP) reactor has been investigated in this study. Response surface methodology (RSM) was used to optimize process parameters including pressure, TCP source power, bias power, and Cl2\\/HBr flow on the main etch step. Quantitative relationships between etching performance and process parameters were

Chi-Chao Hung; Horng-Chih Lin; Meng-Fan Wang; Tiao-Yuan Huang; Han-Chang Shih

2002-01-01

290

Robust poker image recognition scheme in playing card machine using Hotelling transform, DCT and run-length techniques  

Microsoft Academic Search

Poker is an interesting field for artificial intelligence research. It is a game of imperfect information and chance associated outcomes, where players deal with probability, risk assessment, and possible deception – just like real life decision-making. In our proposal, three strategies are used to organize a robust poker recognition scheme: (1) using Hotelling transform to place the object image in

Wen-Yuan Chen; Chin-Ho Chung

2010-01-01

291

Concepts, performance review, and prospects of table-top, few-cycle optical parametric chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

More than 20 years after the first presentation of optical parametric chirped-pulse amplification (OPCPA), the technology has matured as a powerful technique to produce high-intensity, few-cycle, and ultrashort laser pulses. The output characteristics of these systems cover a wide range of center wavelengths, pulse energies, and average powers. The current record performance of table-top, few-cycle OPCPA systems are 16 TW peak power and 22 W average power, which show that OPCPA is able to directly compete with Ti:sapphire chirped-pulse amplification-based systems as source for intense optical pulses. Here, we review the concepts of OPCPA and present the current state-of-the art performance level for several systems reported in the literature. To date, the performance of these systems is most generally limited by the employed pump laser. Thus, we present a comprehensive review on the recent progress in high-energy, high-average-power, picosecond laser systems, which provide improved performance relative to OPCPA pump lasers employed to date. From here, the impact of these novel pump lasers on table-top, few-cycle OPCPA is detailed and the prospects for next-generation OPCPA systems are discussed.

Vaupel, Andreas; Bodnar, Nathan; Webb, Benjamin; Shah, Lawrence; Richardson, Martin

2014-05-01

292

A 300 mV sub-threshold region 2.4 GHz voltage-controlled oscillator and frequency divider with transformer technique for ultralow power RF applications  

NASA Astrophysics Data System (ADS)

A new ultralow voltage 2.4 GHz voltage-controlled oscillator (VCO) and a divide-by-2 frequency divider circuits operating in a CMOS sub-threshold region using a transformer technique have been developed. In the sub-threshold region, the CMOS transistor high frequency performances are decreased to the point where oscillation and frequency division are challenging to achieve. The new proposed VCO uses the transformer feedback complementary VCO technique to improves VCO negative feedback gain. The circuits have been fabricated in a 65 nm standard CMOS process. The oscillation frequency is designed at 2.4 GHz under a 300 mV supply voltage. The total power consumption is 202 µW with noise performance of -96 dBc/Hz at 1 MHz offset. The new proposed frequency divider circuit consists of two stages master-slave D-type flip-flop (DFF). The DFF differential input is coupled to a transformer circuit instead of transistors to reduce the number of stacks. The minimum operating supply voltage is 300 mV with power consumption of 34 µW with a free-run frequency of 1.085 GHz.

Miyahara, Yasunori; Ishikawa, Keisuke; Kuroda, Tadahiro

2014-01-01

293

DNA Transformation  

NSDL National Science Digital Library

Stanley Cohen and Herbert Boyer's historic experiment used techniques to cut and paste DNA to create the first custom-made organism containing recombined or 'recombinant' DNA. Cohen and Boyer inserted the recombinant DNA molecule they created into E. coli bacteria by means of a plasmid, thereby inducing the uptake and expression of a foreign DNA sequence known as 'transformation.' This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents DNA transformation through a series of illustrations of the processes involved.

294

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

295

Emerging convergences of HCI techniques for graphical scalable visualization: Efficient filtration and location transparency of visual transformation  

Microsoft Academic Search

Human-Computer Interaction (HCI) techniques are important in visualization because a good combination of them can help users to design a good visualization system while optimizing its visualization effects. In order to incorporate different HCI techniques to 'work together' to achieve the synergy effects for optimizing graphical scalable visualization, three of them, i.e. goal, task and scenario analyses, are applied to

Doreen Ying Ying Sim; Ying Sim

2011-01-01

296

Variable-chirped microwave waveform generator based on reconfigurable microwave photonic filter  

NASA Astrophysics Data System (ADS)

An optical approach to generating chirped microwave signal using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response is proposed and demonstrated. In this scheme, a narrow band Gaussian pulse is used as the original signal. In order to eliminate the need for a wideband original microwave chirped-free signal, a mixer and a radio frequency signal are used to up-convert the spectrum of the original signal and the dispersion curve is tuned to minimize the attenuation caused by the fiber dispersion. Then the required frequency response can be reconstructed by a nonuniformly spaced PMDLF. Since the majority of the power of the original signal can bypass the filter, the power of the generated chirped microwave signal will be increased. A reconstruction example of a desired frequency response with a central frequency of 10 GHz is provided, and the generation of the corresponding chirped microwave signal is demonstrated by numerical simulations.

Chen, Dalei; Wang, Rong; Pu, Tao; Fang, Tao; Xiang, Peng; Zheng, Jiling; Wei, Zhihu; Xiong, Jintian

2014-09-01

297

Theoretical analysis of third order interferometric autocorrelation signals for enhanced sensitivity towards pulse chirp and asymmetry  

NASA Astrophysics Data System (ADS)

In this paper, we report theoretical analysis of third order interferometric autocorrelation to achieve enhanced sensitivity towards pulse chirp and asymmetry. The analysis is based on interferometric correlative envelope (ICE) functions and ICE difference signals derived from interferometric autocorrelation signals. The third order ICE signals are compared with second order ICE signals obtained from a second order interferometric autocorrelation signals. It is shown that one out of six third order ICED signals may be used to obtain simultaneous detection and measurement of pulse chirp as well as pulse asymmetry of the chirped ultrashort laser pulse. This is in contrast to use of two out of three second order ICED signals for simultaneous detection of pulse chirp and asymmetry.

Sharma, P. K.; Pandey, S. L.

2011-11-01

298

Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects  

PubMed Central

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size. PMID:17306697

Erpelding, Todd N.; Hollman, Kyle W.; O’Donnell, Matthew

2007-01-01

299

Controlled spatiotemporal plasmon excitation of silver nanoparticles with chirped optical pulses  

Microsoft Academic Search

Numerical studies of chirped optical pulses interacting with cone-shaped silver nanoparticles are discussed. We show how localized excitations on the nanoparticles can be generated and controlled in a spatiotemporal manner and discuss a potential application.

T.-W. Lee; S. K. Gray

2005-01-01

300

Effect of frequency chirp on supercontinuum generation in silicon waveguides with two zero-dispersion wavelengths  

NASA Astrophysics Data System (ADS)

The influence of initial chirp on supercontinuum generation in SOI rib waveguide with two zero-dispersion wavelengths was studied numerically, based on the generalized nonlinear Schrödinger equation (GNSE). The full-width at half-maximum (FWHM) and the peak power of the pre-chirped hyperbolic secant in the simulation are 50 fs and 50 W, respectively. The simulation results indicate that a positive initial chirp makes the energy transfer to the normal dispersion zone by affecting self-phase modulation (SPM) and four-wave mixing (FWM) processes, and therefore enhances the supercontinuum bandwidth as well as improves the spectral flatness. In particular, at the optimal initial chirp parameter of C=3, the bandwidth at -10 dB level increases to about 1620 nm (from 1140 to 2760 nm), exceeding an octave-spanning.

Cao, Yanmei; Zhang, Libin; Fei, Yonghao; Lei, Xun; Chen, Shaowu

2015-01-01

301

Evaluation of oxide layers formed during the decarburisation of grain-oriented electrical steel using a Fourier transform infrared (FTIR) technique  

NASA Astrophysics Data System (ADS)

Electrical steels are highly specialised, magnetically soft materials, used to form the cores that carry the magnetic flux in electrical machines such as motors, generators and transformers. During the production of GO electrical steel, the strip passes through a decarburisation furnace, which promotes the formation of a thin surface oxide layer consisting of predominantly fayalite (Fe 2SiO 4) and silica (SiO 2). During a subsequent high temperature anneal, this layer reacts with magnesia (MgO) to form a forsterite 'glass film' layer, which applies a tensile stress to the steel. This reduces the magnetic losses of the material on which the final product is routinely graded. Due to the effect that the oxide layer has on the quality of the final material, it would be beneficial to possess a technique that can rapidly assess its composition and/or morphology. This paper details the assessment of Fourier transform infrared (FTIR) and electrochemical potential (ECP) analysis, and a technique of combining the two. FTIR analysis of the decarburisation oxide layer exhibited evidence of just fayalite, with silica only being observed on the spectra following brief acid etching. To refine the etching process, samples were removed from the acid at various intervals based on the output of the ECP technique. It was established that there was a clear link between the position reached on the ECP profile and absorption bands observed on the corresponding FTIR spectra.

Poultney, Darren; Snell, David

302

The FAST technique: a simplified Agrobacterium-based transformation method for transient gene expression analysis in seedlings of Arabidopsis and other plant species  

PubMed Central

Background Plant genome sequencing has resulted in the identification of a large number of uncharacterized genes. To investigate these unknown gene functions, several transient transformation systems have been developed as quick and convenient alternatives to the lengthy transgenic assay. These transient assays include biolistic bombardment, protoplast transfection and Agrobacterium-mediated transient transformation, each having advantages and disadvantages depending on the research purposes. Results We present a novel transient assay based on cocultivation of young Arabidopsis (Arabidopsis thaliana) seedlings with Agrobacterium tumefaciens in the presence of a surfactant which does not require any dedicated equipment and can be carried out within one week from sowing seeds to protein analysis. This Fast Agro-mediated Seedling Transformation (FAST) was used successfully to express a wide variety of constructs driven by different promoters in Arabidopsis seedling cotyledons (but not roots) in diverse genetic backgrounds. Localizations of three previously uncharacterized proteins were identified by cotransformation with fluorescent organelle markers. The FAST procedure requires minimal handling of seedlings and was also adaptable for use in 96-well plates. The high transformation efficiency of the FAST procedure enabled protein detection from eight transformed seedlings by immunoblotting. Protein-protein interaction, in this case HY5 homodimerization, was readily detected in FAST-treated seedlings with Förster resonance energy transfer and bimolecular fluorescence complementation techniques. Initial tests demonstrated that the FAST procedure can also be applied to other dicot and monocot species, including tobacco, tomato, rice and switchgrass. Conclusion The FAST system provides a rapid, efficient and economical assay of gene function in intact plants with minimal manual handling and without dedicated device. This method is potentially ideal for future automated high-throughput analysis. PMID:19457242

Li, Jian-Feng; Park, Eunsook; von Arnim, Albrecht G; Nebenführ, Andreas

2009-01-01

303

Practical design of optical diagnostics for chirped-pulse free-electron lasers  

Microsoft Academic Search

In recent years there have been several proposals to operate rf-linac-driven FELs with chirped electron and optical micropulses for use in fast time-resolved experiments. We have been actively pursuing this application on the Mark-III infrared FEL at Duke University, and have designed and procured an apparatus to achieve broad-band compression of chirped optical pulses between roughly 2.5 mum and 4.1

Eric B. Szarmes; John M. J. Madey

1992-01-01

304

Stretching and compressing of short laser pulses by chirped volume Bragg gratings: analytic and numerical modeling  

NASA Astrophysics Data System (ADS)

The theory of stretching and compression of short light pulses by chirped volume Bragg gratings (CBGs) is reviewed based on spectral decomposition of short pulses and on wavelength-dependent coupled wave equations. Analytic theory of diffraction efficiency of CBG with constant chirp and approximate theory time-delay dispersion is presented. Comparison of approximate analytic results with exact numeric coupled-wave modeling shows excellent agreement for smooth heterogeneities of CBGs.

Kaim, Sergiy; Mokhov, Sergiy; Zeldovich, Boris Y.; Glebov, Leonid B.

2014-05-01

305

Multiplexed Chirped Pulse Quantum Cascade Laser Measurements of Ammonia and Other Small Molecules  

NASA Astrophysics Data System (ADS)

Spectrometers based on Quantum Cascade (QC) lasers can be run in either continuous or pulsed operation. Although the instrumentation based upon the most recent versions of continuously operating QC lasers can have higher resolution than chirped lasers, using chirped pulse QC lasers can give an advantage when rapid changes in gas composition occur. For example, when jet engines are being tested, a variety of temperature dependent effects on the trace gas concentrations of the plume may be observed. Most pulsed QC lasers are operated in the down chirped mode, in which the chirp rate slows during the pulse. In our spectrometer the changes in frequency are recorded using two Ge etalons, one with a free spectral range of 0.0495 cm-1, and the other with a fringe spacing of 0.0195 cm-1.They can also be deployed in multiplex schemes in which two or more down-chirped lasers are used. In this paper we wish to show examples of the use of multiplexed chirped pulse lasers to allow overlapping spectra to be recorded. The examples of multiplex methods used are taken partly from measurements of 14NH3 and 15NH3 in the region from 1630 to 1622 cm-1, and partly from the use of other chirped pulse lasers operating in the 8 ?m region. Among the effects seen are rapid passage effects caused by the rapid down-chirp, and the use of gases such as nitrogen to cause variation in the shape of the collisional broadened absorption lines.

Picken, Craig; Langford, Nigel; Duxbury, Geoffrey

2014-06-01

306

Chirp rate is independent of male condition in a synchronising bushcricket.  

PubMed

Males of the bushcricket Mecopoda elongata synchronise their chirps with neighbouring males, but because synchrony is imperfect, one male's chirp preceeds the other by some 50-200 ms. Since a male's intrinsic chirp rate is critical for the establishment of the leader role in a duet, and females prefer the leader in a choice situation, we investigated a possible condition dependence of this male trait. In a duet leader males are usually those calling at a higher intrinsic rate; therefore, we investigated whether calling at a higher rate indicates male condition. The calling metabolism was quantified in a respirometer; the factorial slope of males calling at a high rate was three times higher compared to males calling at lower rates. Males produce on average 3.4 singing bouts/per night, and there is a significant increase in chirp periods (CPs) with successive singing bouts. Call properties were investigated throughout a male's life; chirp period increases significantly with age. Two groups of males were reared on either a low- or a high-nutrition diet, and the influence of male condition on different song parameters was investigated. CPs in two feeding regimes did not differ significantly, although males of the low-nutrition diet group were significantly affected by nutrition with respect to mortality, a delayed last moult and reduced weight as adults. We therefore conclude that solo chirp rates do not reflect phenotypic male condition properly. PMID:16289569

Hartbauer, M; Kratzer, S; Römer, H

2006-03-01

307

Recovering strain readings from chirping fiber Bragg gratings in composite overwrapped pressure vessels  

NASA Astrophysics Data System (ADS)

This study reports on signal recovery of optical fiber Bragg gratings embedded in a carbon fiber composite overwrapped pressure vessel's (COPV) structure which have become chirped due to microcracks. COPVs are commonly used for the storage of high pressure liquids and gases. They utilize a thin metal liner to seal in contents, with a composite overwrap to strengthen the vessel with minimal additional mass. A COPV was instrumented with an array of surface mounted and embedded fiber Bragg gratings (FBGs) for structural health monitoring (SHM) via strain sensing of the material. FBGs have been studied as strain sensors for the last couple decades. Many of the embedded FBGs reflected a multi-peak, chirped response which was not able to be interpreted well by the current monitoring algorithm. Literature and this study found that the chirping correlated with microcracks. As loading increases, so does the number of chirped FBGs and microcracks. This study uses optical frequency domain reflectometry (OFDR) to demultiplex the array of FBGs, and then sub- divide individual FBGs. When a FBG is sub-divided using OFDR, the gratings' strain along its length is recovered. The sub-divided chirped FBGs have strain gradients along their length from microcracks. Applying this to all chirped gratings, nearly the entirety of the embedded sensors' readings can be recovered into a series of single peak responses, which show very large local strains throughout the structure. This study reports on this success in recovering embedded FBGs signal, and the strain gradient from microcracks.

Strutner, Scott M.; Pena, Frank; Piazza, Anthony; Parker, Allen R.; Richards, W. Lance; Carman, Gregory P.

2014-04-01

308

Photonic Technique for Radio Frequency Measurement  

Microsoft Academic Search

A novel photonic technique for radio frequency (RF) measurement utilising dispersion in a multichannel chirped fibre Bragg grating (MCFBG) is developed. The underlying principle for fast photonic RF measurement is based on amplitude comparison of the RF power fading functions of double sideband (DSB) modulated optical carriers propagating through a dispersive medium. In this paper, a demonstration of the photonic

L. V. T. Nguyen; D. B. Hunter; D. J. Borg

2005-01-01

309

A fully probe corrected near-field far-field transformation technique employing plane-wave synthesis  

NASA Astrophysics Data System (ADS)

The far-field behavior of an antenna under test (AUT) can be obtained by exciting the AUT with a plane wave. In a measurement, it is sufficient if the plane wave is artificially generated in the vicinity of the AUT. This can be achieved by using a virtual antenna array formed by a probe antenna which is sequentially sampling the radiating near-field of the AUT at different positions. For this purpose, an optimal filter for the virtual antenna array is computed in a preprocessing step. Applying this filter to the near-field measurements, the far-field of the AUT is obtained according to the propagation direction and polarization of the synthesized plane wave. This means that the near-field far-field transformation (NFFFT) is achieved simply by filtering the near-field measurement data. Taking the radiation characteristic of the probe antenna into account during the synthesis process, its influence on the NFFFT is compensated. The principle of the plane-wave synthesis and its application to the NFFFT is presented in detail in this paper. Furthermore, the method is verified by performing transformations of simulated near-field measurement data and of near-field data measured in an anechoic chamber.

Mauermayer, R. A. M.; Eibert, T. F.

2013-07-01

310

Statistical study of TIDs using HF radar ground backscatter data and chirp sounding network MUF data  

NASA Astrophysics Data System (ADS)

We present statistical characteristics of traveling ionospheric disturbances (TIDs) revealed from the data of ground mid-latitude high frequency (HF) facilities that cover a wide longitudinal sector. Firstly, we analyzed an extensive dataset collected by SuperDARN Hokkaido HF radar since the late 2006 until 2014. A technique based on the cross-correlation analysis of minimal group range variations was used. We discuss diurnal and seasonal dependencies of predominant TIDs azimuth and apparent horizontal velocity as well as its solar and geomagnetic activity dependence. Further, we compare these statistical results with the same obtained using the first Russian SuperDARN Ekaterinburg HF radar data during 2013. In addition, we analyzed maximum usable frequency (MUF) series obtained by Russian oblique chirp sounding network. The network includes transmitters in Magadan, Norilsk, Khabarovsk and receiver in Tory (Irkutsk) and allow us to reveal large-scale TIDs characteristics in 2010-2011. This work was done under financial support of the Russian Foundation for Basic Research (grants 14-05-00259-a, 12-05-00865-a and 14-05-00588-a).

Oinats, Alexey; Kurkin, Vladimir; Nishitani, Nozomu; Ratovsky, Konstantin; Ivanova, Vera; Berngardt, Oleg

311

Bimolecular Pyrolysis Reactions Studied by Chirped-Pulse Millimeter-Wave Spectroscopy  

NASA Astrophysics Data System (ADS)

The feasibility of using Chirped-Pulse Millimeter-Wave (CPmmW) spectroscopy for studies of pyrolysis reactions is demonstrated. The molecules under investigation were mixed with a source of H-atoms (methyl nitrite) and put through a heated silicon carbide micro-reactor (2 cm x 1 mm). More efficient paths of thermal cracking of (i) acetaldehyde and (ii) acetone are demonstrated when using, as a catalyst, the free H-atoms released from methyl nitrite compared to cracking of neat acetaldehyde or acetone. CPmmW spectra of (i) formaldehyde and (ii) acetaldehyde were observed, suggesting that the following bimolecular reactions took place in the micro-reactor: i) CH_3CHO + H ? CH_3 + CH_2O ii) CH_3COCH_3 + H ? CH_3 + CH_3CHO. The vibrational population distributions (VPDs) of the formaldehyde and acetaldehyde products of the pyrolysis reactions are measured using the broad bandwidth capability of the CPmmW technique. Although we found that the VPDs of the molecules convey little information about the pyrolysis reaction transition state(s), they provide insight to the vibrational collisional cooling mechanisms in different molecules. The relevance of the observed catalytic reactions to biomass decomposition is discussed and other bimolecular pyrolysis reactions are proposed for study by CPmmW spectroscopy. KP thanks the Petroleum Research Fund for support of this work.

Prozument, Kirill; Vasiliou, Angayle K.; Shaver, Rachel G.; Park, G. Barratt; Muenter, John S.; Stanton, John F.; Ellison, G. Barney; Field, Robert W.

2013-06-01

312

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

313

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems  

NASA Astrophysics Data System (ADS)

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10-3, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.

Mangone, Fall; He, Jing; Tang, Jin; Xiao, Jiangnan; Chen, Ming; Li, Fan; Chen, Lin

2014-08-01

314

Use of the Fourier transform infrared (FTIR) technique for determination of the composition of final phosphate coatings on grain-oriented electrical steel  

NASA Astrophysics Data System (ADS)

Electrical steels are highly specialised, magnetically soft materials, used to form the cores that carry the magnetic flux in electrical machines such as motors, generators and transformers. The steel strip is coated with a phosphate-based solution, which, on curing, provides an electrically insulating layer that also imparts a tension onto the strip. It has previously been shown that the magnetic losses of the material are affected by the ratio of phosphate and silica within the coating solution [O. Tanaka, H. Kobayashi, E. Minematsu, New insulating coating for grain-oriented electrical steel, J. Mater. Eng. 13 (1991) 161-168.]. It would therefore be highly beneficial to possess an analytical technique that can be used to accurately and rapidly determine the composition of this coating. This paper details the evaluation of the Fourier transform infrared (FTIR) technique for this purpose. Analysing each of the important constituents separately enabled their specific absorption bands to be identified, and laboratory trials produced spectra that exhibited a good agreement with theoretical predictions. Analysis of samples coated under production conditions was found to be more challenging due to the detection of an underlying forsterite layer. However, there is potential for FTIR analysis when using regions of the spectra that were unaffected by this compound.

Poultney, Darren; Snell, David

315

A privacy-preserving technique for Euclidean distance-based mining algorithms using Fourier-related transforms  

Microsoft Academic Search

Privacy preserving data mining has become increasingly popular because it allows sharing of privacy-sensitive data for analysis purposes. However, existing techniques such as random perturbation do not fare well for simple yet widely used and efficient Euclidean distance-based mining algorithms. Although original data distributions can be pretty accurately reconstructed from the perturbed data, distances between individual data points are not

Shibnath Mukherjee; Zhiyuan Chen; Aryya Gangopadhyay

2006-01-01

316

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

317

Chromatin isolation by RNA purification (ChIRP).  

PubMed

Long noncoding RNAs are key regulators of chromatin states for important biological processes such as dosage compensation, imprinting, and developmental gene expression (1,2,3,4,5,6,7). The recent discovery of thousands of lncRNAs in association with specific chromatin modification complexes, such as Polycomb Repressive Complex 2 (PRC2) that mediates histone H3 lysine 27 trimethylation (H3K27me3), suggests broad roles for numerous lncRNAs in managing chromatin states in a gene-specific fashion (8,9). While some lncRNAs are thought to work in cis on neighboring genes, other lncRNAs work in trans to regulate distantly located genes. For instance, Drosophila lncRNAs roX1 and roX2 bind numerous regions on the X chromosome of male cells, and are critical for dosage compensation (10,11). However, the exact locations of their binding sites are not known at high resolution. Similarly, human lncRNA HOTAIR can affect PRC2 occupancy on hundreds of genes genome-wide( 3,12,13), but how specificity is achieved is unclear. LncRNAs can also serve as modular scaffolds to recruit the assembly of multiple protein complexes. The classic trans-acting RNA scaffold is the TERC RNA that serves as the template and scaffold for the telomerase complex (14); HOTAIR can also serve as a scaffold for PRC2 and a H3K4 demethylase complex (13). Prior studies mapping RNA occupancy at chromatin have revealed substantial insights (15,16), but only at a single gene locus at a time. The occupancy sites of most lncRNAs are not known, and the roles of lncRNAs in chromatin regulation have been mostly inferred from the indirect effects of lncRNA perturbation. Just as chromatin immunoprecipitation followed by microarray or deep sequencing (ChIP-chip or ChIP-seq, respectively) has greatly improved our understanding of protein-DNA interactions on a genomic scale, here we illustrate a recently published strategy to map long RNA occupancy genome-wide at high resolution (17). This method, Chromatin Isolation by RNA Purification (ChIRP) (Figure 1), is based on affinity capture of target lncRNA:chromatin complex by tiling antisense-oligos, which then generates a map of genomic binding sites at a resolution of several hundred bases with high sensitivity and low background. ChIRP is applicable to many lncRNAs because the design of affinity-probes is straightforward given the RNA sequence and requires no knowledge of the RNA's structure or functional domains. PMID:22472705

Chu, Ci; Quinn, Jeffrey; Chang, Howard Y

2012-01-01

318

A 32x32 pixel focal plane array ladar system using chirped amplitude modulation  

NASA Astrophysics Data System (ADS)

The Army Research Laboratory is researching system architectures and components required to build a 32x32 pixel scannerless ladar breadboard. The 32x32 pixel architecture achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (RF) subcarrier that is linearly frequency modulated (i.e. chirped amplitude modulation). The backscattered light is focused onto an array of metal-semiconductor-metal (MSM) detectors where it is detected and mixed with a delayed replica of the laser modulation signal that modulates the responsivity of each detector. The output of each detector is an intermediate frequency (IF) signal (a product of the mixing process) whose frequency is proportional to the target range. Pixel read-out is achieved using code division multiple access techniques as opposed to the usual time-multiplexed techniques to attain high effective frame rates. The raw data is captured with analog-to-digital converters and fed into a PC to demux the pixel data, compute the target ranges, and display the imagery. Last year we demonstrated system proof-of-principle for the first time and displayed an image of a scene collected in the lab that was somewhat corrupted by pixel-to-pixel cross-talk. This year we report on system modifications that reduced pixel-to-pixel cross-talk and new hardware and display codes that enable near real-time stereo display of imagery on the ladar's control computer. The results of imaging tests in the laboratory will also be presented.

Stann, Barry L.; Aliberti, Keith; Carothers, Daniel; Dammann, John; Dang, Gerard; Giza, Mark M.; Lawler, William B.; Redman, Brian C.; Simon, Deborah R.

2004-09-01

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 information on molecular structure, chemical bondingandmolecularenvironment.Formanyyears,FTIR has been

Gerwert, Klaus

320

Time-domain measurement of a self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering  

SciTech Connect

We report, with an unequivocal time-domain measurement, that an appropriately chosen undulator taper can compensate for an electron beam longitudinal energy-chirp in a free-electron laser amplifier, leading to the generation of single-spike radiation close to the Fourier limit. The measurements were taken using the frequency-resolved optical gating technique by employing an advanced transient-grating diagnostic geometry. The reconstructed longitudinal radiation characteristics are compared in detail to prediction from time-dependent three-dimensional simulations.

Marcus, G.; Rosenzweig, J. B. [Particle Beam Physics Laboratory, Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095 (United States); Artioli, M.; Ciocci, F.; Del Franco, M.; Giannessi, L.; Petralia, A.; Quattromini, M. [ENEA C.R. Frascati, Via E. Fermi, 45 00044 Frascati, RM (Italy); Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Di Pirro, G.; Ferrario, M.; Filippetto, D.; Gatti, G.; Rossi, A. R. [INFN-LNF, Via E. Fermi, 40 00044 Frascati, RM (Italy); Cianchi, A. [INFN-Roma Tor Vergata and University of Rome Tor Vergata, Via della Ricerca Scientifica, 1-00133 Rome (Italy); Labat, M. [ENEA C.R. Frascati, Via E. Fermi, 45 00044 Frascati, RM (Italy); SOLEIL, L'Orme des Merisiers Saint-Aubin, BP 48 91192 GIF-sur-Yvette Cedex (France); Mostacci, A. [Universita degli Studi di Roma La Sapienza, P.le Aldo Moro 5, 00185 Roma (Italy); Petrillo, V. [Universita degli Studi di Milano and INFN-MI, Via Celoria, 16 20133 Milano (Italy); and others

2012-09-24

321

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

Microsoft Academic Search

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

Abbie L. Warrick; Pamela A. Delaney

1997-01-01

322

Assessment of nitrous oxide emission from cement plants: real data measured with both Fourier transform infrared and nondispersive infrared techniques.  

PubMed

Nitrous oxide (N2O) is the third most important greenhouse gas after carbon dioxide and methane, and contributes about 6% to the greenhouse effect. Nitrous oxide is a minor component of the atmosphere, and it is a thousand times less than carbon dioxide (CO2). Nevertheless, it is much more potent than CO2 and methane, owing to its long stay in the atmosphere of approximately 120 yr and the high global warmingpotential (GWP) of298 times that of CO2. Although greenhouse gases are natural in the atmosphere, human activities have changed the atmospheric concentrations. Most of the values of emission of nitrous oxide are still obtained by means ofemission factors and not actually measured; the lack ofreal data may result in an underestimation ofcurrent emissions. The emission factors used for the calculation of N2O can be obtained from the "Guidelines for the implementation of the national inventory of emissions" of the Intergovernmental Panel on Climate Change, which refer to all nations for the realization of their inventory. This study will present real data, measured in several Italian cement plants with different characteristics. The work also shows a comparison between N2O concentration measured with in situ-Fourier transform IR (FTIR) and the reference method EN ISO 21258 based on nondispersive IR (NDIR), in order to investigate the interfering compounds in the measurement with NDIR. PMID:25509548

Mosca, Silvia; Benedetti, Paolo; Guerriero, Ettore; Rotatori, Mauro

2014-11-01

323

Transforming traditional Tai Ji Quan techniques into integrative movement therapy-Tai Ji Quan: Moving for Better Balance.  

PubMed

Tai Ji Quan, developed as a martial art, has traditionally served multiple purposes, including self-defense, competition/performance, and health promotion. With respect to health, the benefits historically and anecdotally associated with Tai Ji Quan are now being supported by scientific and clinical research, with mounting evidence indicating its potential value in preventing and managing various diseases and improving well-being and quality of life in middle-aged and older adults. The research findings produced to date have both public health significance and clinical relevance. However, because of its roots in the martial arts, transforming traditional Tai Ji Quan movements and training approaches into contemporary therapeutic programs and functional applications is needed to maximize its ultimate utility. This paper addresses this issue by introducing Tai Ji Quan: Moving for Better Balance, a functional therapy that involves the use of Tai Ji Quan principles and Yang-style-based movements to form an innovative, contemporary therapeutic approach that integrates motor, sensory, and cognitive components to improve postural control, gait, and mobility for older adults and those who have neurodegenerative movement impairments. It provides a synergy of traditional and contemporary Tai Ji Quan practice with the ultimate goal of improving balance and gait, enhancing performance of daily functional tasks, and reducing incidence of falls among older adults. PMID:25126445

Li, Fuzhong

2014-03-01

324

Mismatch characteristics of optical parametric chirped pulse amplification  

NASA Astrophysics Data System (ADS)

The stability of an optical parametric chirped pulse amplifier (OPCPA) is influenced by time and the angular matching of the input beams. We derived the Gaussian dependence of the monochromatic signal gain on the small mismatch between the signal and pump beams. Gain characteristics were also calculated for polychromatic amplification and the impact of different beam mismatches and interaction geometries was explained. The asymmetry of the energy gain, and the square root dependence of the phase matched wavelength on beam angles were found. The predicted dependences were verified in a noncollinear OPCPA system with LBO and KDP crystal amplifying pulses of a Ti:sapphire laser around a central wavelength of 800 nm, pumped by the third harmonic frequency of an iodine gas laser at a wavelength of 438 nm. The widths of the gain curves in the dependence on both the pump–signal or the phase matching angles varied from several tenths to a few milliradians. The gain curve widths dependent on the pump–signal pulse delay were about two thirds of the pump pulse width for moderate pumping and about a half of the pump pulse width for pumping on the order of GW cm?2. A stable gain output is achieved if angular and temporal fluctuations are fractions of the measured gain curve widths, and when the signal direction is between the pump and the crystal principal axis (i.e. in the psz geometry).

Novák, O.; Tur?i?ová, H.; Divoký, M.; Huynh, J.; Straka, P.

2014-02-01

325

New image filtering technique combining a wavelet transform with a linear neural network: application to face recognition  

NASA Astrophysics Data System (ADS)

In order to improve the performance of a linear auto- associator (which is a neural network model), we explore the use of several pre-processing techniques. The gist of our approach is to represent each pattern by one or several pre- processed (i.e., filtered) versions of the original pattern (plus the original pattern). First, we compare the performance of several pre-processing techniques (a plain vanilla version of the auto-associator as a control, a Sobel operator, a Canny-Deriche operator, and a multiscale Canny- Deriche operator) and a Wiener filter on a pattern completion task using a noise degraded version of faces stored. We found that the multiscale Canny-Deriche operator gives the best performance of all models. Second, we compare the performance of the multiscale Canny-Deriche operator with the control condition of a pattern completion task of noise degraded versions (with several levels of noise) of learned faces and new faces of the same or another race than the learned faces. In all cases, the multiscale Canny- Deriche operator performs significantly better than the control.

Yang, Fan; Paindavoine, Michel; Abdi, Herve; Miteran, Johel

2000-11-01

326

Cynomolgus and rhesus monkey visual pigments. Application of Fourier transform smoothing and statistical techniques to the determination of spectral parameters  

PubMed Central

Microspectrophotometric measurements were performed on 217 photoreceptors from cynomolgus, Macaca fascicularis, and rhesus, M. mulatta, monkeys. The distributions of cell types, for rods and blue, green, and red cones were: 52, 12, 47, and 44, respectively, for the cynomolgus, and 22, 4, 13, and 13 for the rhesus. Visual cells were obtained fresh (unfixed), mounted in various media (some containing 11- cis-retinal), and then located visually under dim red (650 nm) illumination. Absolute absorbance (A), linear dichroism (LD), and bleaching difference (BD) absorbance spectra were recorded through the sides of outer segments. The spectra were subjected to rigorous selection criteria, followed by digital averaging and Fourier transform filtering. Statistical methods were also applied to the accepted samples in the estimation of population means and variances. The wavelength of mean peak absorbance (lambda max) and the standard error at 95% certainty of the rod and blue, green, and red cone pigments in cynomolgus were 499.7 +/- 2.5, 431.4 +/- 4.2, 533.9 +/- 2.4, and 565.9 +/- 2.8 nm, respectively. The rhesus pigments were statistically indistinguishable from the cynomolgus, having lambda max of approximately 500, 431, 534, and 566 nm. Statistical tests did not reveal the presence of a lambda max subpopulation (i.e., anomalous pigments). The bandwidth of each alpha-band was determined in two segments, giving rise to the longwave half-density (LWHDBW), shortwave half-density (SWHDBW), and total half-density (THDBW) bandwidths. The LWHDBW was found to have the smallest variance. Both the LWHDBW and the THDBW showed linear dependence on the peak wavenumber (lambda max)-1 for the four macaque pigments. PMID:3598558

1987-01-01

327

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

328

Laser plasma acceleration with a negatively chirped pulse: all-optical control over dark current in the blowout regime  

NASA Astrophysics Data System (ADS)

Recent?experiments?with?100 terawatt-class,?sub-50 femtosecond?laser pulses show that electrons self-injected into a laser-driven electron density bubble can be accelerated above 0.5 gigaelectronvolt energy in a sub-centimetre-length rarefied plasma. To reach this energy range, electrons must ultimately outrun the bubble and exit the accelerating phase; this, however, does not ensure high beam quality. Wake excitation increases the laser pulse bandwidth by red-shifting its head, keeping the tail unshifted. Anomalous group velocity dispersion of radiation in plasma slows down the red-shifted head, compressing the pulse into a few-cycle-long piston of relativistic intensity. Pulse transformation into a piston causes continuous expansion of the bubble, trapping copious numbers of unwanted electrons (dark current) and producing a poorly collimated, polychromatic energy tail, completely dominating the electron spectrum at the dephasing limit. The process of piston formation can be mitigated by using a broad-bandwidth (corresponding to a few-cycle transform-limited duration), negatively chirped pulse. Initial blue-shift of the pulse leading edge compensates for the nonlinear frequency red-shift and delays the piston formation, thus significantly suppressing the dark current, making the leading quasi-monoenergetic bunch the dominant feature of the electron spectrum near dephasing. This method of dark current control may be feasible for future experiments with ultrahigh-bandwidth, multi-joule laser pulses.

Kalmykov, S. Y.; Beck, A.; Davoine, X.; Lefebvre, E.; Shadwick, B. A.

2012-03-01

329

The Chirped Pulse and Cavity Fourier Transform Microwave Cp-Ftmw and Ftmw) Spectrum of Bromoperfluoroacetone  

NASA Astrophysics Data System (ADS)

The microwave spectrum of the molecule bromoperfluoroacetone has been measured on a newly constructed CP-FTMW spectrometer along with a FTMW spectrometer relocated from Oxford University to Missouri S&T. Rotational constants, centrifugal distortion parameters, and nuclear quadrupole coupling constants will be discussed. Comparisons to the previously studied halogen analogues perfluoroacetone and chloroperfluoroacetone will be discussed. J.-U. Grabow, N. Heineking, and W. Stahl, Z. Naturforsch. 46a (1991) 229. G. Kadiwar, C. T. Dewberry, G. S. Grubbs II and S. A. Cooke, Talk RH11, 65th International Symposium on Molecular Spectroscopy (2010).

Force, Nicholas; Gillcrist, David Joseph; Hurley, Cassandra C.; Marshall, Frank E.; Payton, Nicholas A.; Persinger, Thomas D.; Shreve, N. E.; Grubbs, G. S., II

2014-06-01

330

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...

331

Extension of high-order harmonic generation cutoff via coherent control of intense few-cycle chirped laser pulses  

E-print Network

We present an ab initio quantum investigation of the high-order harmonic generation (HHG) cutoff extension using intense few-cycle chirped laser pulses. For a few-cycle chirped driving laser pulse, it is shown that significant cutoff extension can...

Carrera, Juan J.; Chu, Shih-I

2007-03-16

332

First results of a deep tow CHIRP sonar seafloor imaging system  

USGS Publications Warehouse

The latest and most innovative technology has been applied towards the development of a full-ocean depth multi-sensor sonar system using linear swept-FM (Chirp) technology. The seafloor imaging system (SIS- 7000) described herein uses Chirp sidescan sonar to provide high resolution imagery at long range, and Chirp subbottom sonar to provide high resolution profiles in both the near bottom and deeper subbottom. The tow vehicle contains a suite of full-ocean depth instrumentation for measuring various oceanographic parameters and for monitoring vehicle status. Top side systems include a sonar display and data logging system as well as real-time sensor status display and tow vehicle control system. This paper will present an overview of this system, describe its technology and capabilities, and present some initial results. 

Parent, M.; Fang, Changle; O'Brien, Thomas F.; Danforth, William W.

1993-01-01

333

Self-deflecting plasmonic lattice solitons and surface modes in chirped plasmonic arrays.  

PubMed

We show that chirped metal-dielectric waveguide arrays with focusing cubic nonlinearity can support plasmonic lattice solitons that undergo self-deflection in the transverse plane. Such lattice solitons are deeply subwavelength self-sustained excitations, although they cover several periods of the array. Upon propagation, the excitations accelerate in the transverse plane and follow trajectories curved in the direction in which the separation between neighboring metallic layers decreases, a phenomenon that yields considerable deflection angles. The deflection angle can be controlled by varying the array chirp. We also reveal the existence of surface modes at the boundary of truncated plasmonic chirped array that form even in the absence of nonlinearity. PMID:25768141

Li, Chunyan; Cui, Ran; Ye, Fangwei; Kartashov, Yaroslav V; Torner, Lluis; Chen, Xianfeng

2015-03-15

334

Algorithm of matched filtering overcoming nonlinear chirp effect in synthetic aperture ladar  

NASA Astrophysics Data System (ADS)

Linear chirp laser signal is often employed as the transmitted signal of synthetic aperture laser radar (SAL). However, actual properties of frequency sweep of fiber laser always produces nonlinear terms such as quadratic and higher order terms. Existence of nonlinear terms of frequency produces phase errors during pulse time, leading to blurring of target in range direction and further reduces imaging resolution of range direction. It makes compensation of the nonlinear chirp from laser source a requirement. In this paper, we develop an algorithm of matched filtering in frequency spectrum to overcome the phase error from nonlinear chirp. The results of simulation show that the image in range direction can be well compressed. At the same time, we also analyze effects of signal compression in the range direction under different parameter situations such as reference channel length as well as ratio of nonlinear contribution.

Lu, Wei; Xu, Nan; Liu, Liren

2009-08-01

335

Predicting and testing the chirp rate of whistler-mode chorus  

NASA Astrophysics Data System (ADS)

Chorus emissions are a striking feature of the electromagnetic wave environment near Earth's radiation belts. These bursts of whistler-mode waves exhibit characteristic frequency sweeps (chirps) believed to result from nonlinear wave-particle interactions. Based on the theory of Omura [2008], we demonstrate how to predict the chirp rate of observed chorus elements. The predicted chirp rates are a function of the wave amplitude, and are calculated from available observations leaving no free parameters. We test these predictions against observations from the THEMIS satellites. The predictions agree well with the observations, both in terms of the absolute sweep rates and their relation to the wave amplitudes, lending strong support to the theory that these waves are the result of cyclotron-resonant wave-particle trapping.

Cully, C. M.

2010-12-01

336

Generation of an isolated sub-40-as pulse using two-color laser pulses: Combined chirp effects  

SciTech Connect

In this paper, we theoretically discuss the combined chirp effects on the isolated attosecond generation when a model Ar is exposed to an intense 5-fs, 800-nm fundamental chirped pulse combined with a weak 10-fs, 1200-nm controlling chirped pulse. It shows that for the case of the chirp parameters {beta}{sub 1} = 6.1 (corresponding to the 800-nm field) and {beta}{sub 2} = 4.0 (corresponding to the 1200-nm field), both the harmonic cutoff energy and the supercontinuum can be remarkably extended resulting in a 663-eV bandwidth. Moreover, due to the introduction of the chirps, the short quantum path is selected to contribute to the harmonic spectrum. Finally, by superposing a properly selected harmonic spectrum in the supercontinuum region, an isolated pulse as short as 31 as (5 as) is generated without (with) phase compensation.

Feng, Liqiang [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Chu, Tianshu [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Institute for Computational Sciences and Engineering, Laboratory of New Fiber Materials and Modern Textile, the Growing Base for State Key Laboratory, Qingdao University, Qingdao, 266071 (China)

2011-11-15

337

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

338

Robust Singular Spectrum Transform  

Microsoft Academic Search

Change Point Discovery is a basic algorithm needed in many time series mining applications including rule discovery, motif discovery, casual analysis, etc. Several techniques for change point discovery have been suggested including wavelet analysis, cosine transforms, CUMSUM, and Singular Spectrum Transform. Of these methods Singular Spectrum Transform (SST) have received much attention because of its generality and because it does

Yasser F. O. Mohammad; Toyoaki Nishida

2009-01-01

339

Chirped pulse Raman amplification in Ba(NO3)2 crystals  

NASA Astrophysics Data System (ADS)

In this study, 35.5% conversion efficiency is obtained at the first Stokes component frequency (873 nm) upon two-stage chirped pulse Raman amplification in a Ba(NO3)2 crystal by an 8 mJ, 620 ps, 800 nm pump laser. A maximum energy of 4.22 mJ with 3.82% rms stability at the first Stokes pulse can be obtained under 35 mJ pump energy. Moreover, the chirped first Stokes pulse can be compressed to 143 fs.

Guo, Xiaoyang; Lu, Jun; Li, Wenkai; Xu, Yi; Lu, Xiaoming; Leng, Yuxin; Li, Ruxin

2015-04-01

340

Microjoule pulse energy from a chirped-pulse Ti:sapphire oscillator with cavity dumping.  

PubMed

We demonstrate a chirped-pulse Ti:sapphire laser oscillator with both Kerr-lens and semiconductor- saturable-absorber-mirror-assisted mode locking generating 1.1 microJ pulses at 1 MHz pulse repetition rate. The pulses are coupled out of the laser cavity by means of an acousto-optical cavity dumper, have a spectral width that supports a Fourier limit of 74 fs, and currently have a chirped-pulse duration of 5 ps. After compressing the pulses, this laser will be an ideal tool for efficient high-harmonic generation directly from a laser oscillator. PMID:19282917

Siegel, Martin; Pfullmann, Nils; Palmer, Guido; Rausch, Stefan; Binhammer, Thomas; Kovacev, Milutin; Morgner, Uwe

2009-03-15

341

Practical design of optical diagnostics for chirped-pulse free-electron lasers  

NASA Astrophysics Data System (ADS)

In recent years there have been several proposals to operate rf-linac-driven FELs with chirped electron and optical micropulses for use in fast time-resolved experiments. We have been actively pursuing this application on the Mark-III infrared FEL at Duke University, and have designed and procured an apparatus to achieve broad-band compression of chirped optical pulses between roughly 2.5 ?m and 4.1 ?m, with subsequent measurement of pulse widths as short as 200 fs. The principles of design for this experiment will be reviewed, and extensions of the design to other wavelengths will be considered.

Szarmes, Eric B.; Madey, John M. J.

1992-07-01

342

Generation of a widely tunable linearly chirped microwave waveform based on spectral filtering and unbalanced dispersion.  

PubMed

We propose a method to generate a widely tunable linearly chirped microwave waveform based on spectral filtering and unbalanced dispersion. Heterodyne beating between two differently dispersed optical pulses in a photodetector produces the linearly chirped microwave waveform. Desired waveforms with flexible and independent control of the center frequency and sweep bandwidth can be obtained by simply tuning two optical filters. Simulation and experimental investigations are carried out, and the results are in good agreement. The measured microwave waveform has ?5.2-ns pulse duration and ?64-GHz sweep bandwidth, corresponding to a time-bandwidth product of ?166.4 and a compression ratio of ?248. PMID:25768188

Zhang, Hao; Zou, Weiwen; Chen, Jianping

2015-03-15

343

Noise filtering in parametric amplification by dressing the seed beam with spatial chirp.  

PubMed

We report a method for filtering out the noises produced in optical parametric chirped-pulse amplifiers by dressing the seed beam with spatial chirp. After dechirping the amplified signal with a compressor, the noises experience a spatiotemporal coupling, making themselves highly distinguishable from the compressed signal in space, and hence supporting noise filtering effectively and expediently in the spatial domain, which would otherwise not be possible. Numerical simulations performed for the proposed method show the capabilities of an order of magnitude reduction in the noise energy and several orders of magnitude enhancement in the temporal contrast. PMID:24979013

Wang, Jing; Ma, Jingui; Wang, Yongzhi; Yuan, Peng; Xie, Guoqiang; Qian, Liejia

2014-04-15

344

Reflectivity of linear and nonlinear gamma radiated apodized chirped Bragg grating under ocean  

SciTech Connect

In this paper, the effect Co{sup 60} gamma radiation is investigated on the effective refractive index of apodized chirped Bragg grating. Nine apodization profiles are considered. Comparison between the reflectivity of the gamma radiated and non radiated fiber Bragg grating has been carried out. The electric field of signals propagating through the apodized chirped fiber Bragg grating (ACFBG) is first calculated from which, new values for the refractive index are determined. The nonlinear effects appear on the ACFBG reflectivity. The effect of nonlinearity and undersea temperature and pressure on the grating is also studied.

Hamdalla, Taymour A. [Faculty of Science, Alexandria University, Alexandria (Egypt); Faculty of Science, Tabuk University, Tabuk (Saudi Arabia)

2012-09-06

345

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

346

Assessment of natural radioactivity and function of minerals in soils of Yelagiri hills, Tamilnadu, India by Gamma Ray spectroscopic and Fourier Transform Infrared (FTIR) techniques with statistical approach.  

PubMed

Gamma Ray and Fourier Transform Infrared (FTIR) spectroscopic techniques were used to evaluate the natural radioactivity due to natural radionuclides and mineralogical characterization in soils of Yelagiri hills, Tamilnadu, India. Various radiological parameters were calculated to assess the radiation hazards associated with the soil. The distribution pattern of activity due to natural radionuclides is explained by Kriging method of mapping. Using FTIR spectroscopic technique the minerals such as quartz, microcline feldspar, orthoclase feldspar, kaolinite, montmorillonite, illite, and organic carbon were identified and characterized. The extinction coefficient values were calculated to know the relative distribution of major minerals such as quartz, microcline feldspar, orthoclase feldspar and kaolinite. The calculated values indicate that the amount of quartz is higher than orthoclase feldspar, microcline feldspar and much higher than kaolinite. Crystallinity index was calculated to know the crystalline nature of quartz. The result indicates that the presence of disordered crystalline quartz in soils. The relation between minerals and radioactivity was assessed by multivariate statistical analysis (Pearson's correlation and cluster analysis). The statistical analysis confirms that the clay mineral kaolinite and non-clay mineral quartz is the major factor than other major minerals to induce the important radioactivity variables and concentrations of uranium and thorium. PMID:25467664

Chandrasekaran, A; Ravisankar, R; Rajalakshmi, A; Eswaran, P; Vijayagopal, P; Venkatraman, B

2014-10-28

347

Derivatization technique to increase the spectral selectivity of two-dimensional Fourier transform infrared focal plane array imaging: analysis of binder composition in aged oil and tempera paint.  

PubMed

The interpretation of standard Fourier transform infrared spectra (FT-IR) on oil-based paint samples often suffers from interfering bands of the different compounds, namely, binder, oxidative aging products, carboxylates formed during aging, and several pigments and fillers. The distinction of the aging products such as ketone and carboxylic acid functional groups pose the next problem, as these interfere with the triglyceride esters of the oil. A sample preparation and derivatization technique using gaseous sulfur tetrafluoride (SF4), was thus developed with the aim to discriminate overlapping signals and achieve a signal enhancement on superposed compounds. Of particular interest in this context is the signal elimination of the broad carboxylate bands of the typical reaction products developing during the aging processes in oil-based paints, as well as signal interference originating from several typical pigments in this spectral range. Furthermore, it is possible to distinguish the different carbonyl-containing functional groups upon selective alteration. The derivatization treatment can be applied to both microsamples and polished cross sections. It increases the selectivity of the infrared spectroscopy technique in a fundamental manner and permits the identification and two-dimensional (2D) localization of binder components in aged paint samples at the micrometer scale. The combination of SF4 derivatization with high-resolution 2D FT-IR focal plane array (FPA) imaging delivers considerable advances to the study of micro-morphological processes involving organic compounds. PMID:24694702

Zumbühl, Stefan; Scherrer, Nadim C; Eggenberger, Urs

2014-01-01

348

Assessment of natural radioactivity and function of minerals in soils of Yelagiri hills, Tamilnadu, India by Gamma Ray spectroscopic and Fourier Transform Infrared (FTIR) techniques with statistical approach  

NASA Astrophysics Data System (ADS)

Gamma Ray and Fourier Transform Infrared (FTIR) spectroscopic techniques were used to evaluate the natural radioactivity due to natural radionuclides and mineralogical characterization in soils of Yelagiri hills, Tamilnadu, India. Various radiological parameters were calculated to assess the radiation hazards associated with the soil. The distribution pattern of activity due to natural radionuclides is explained by Kriging method of mapping. Using FTIR spectroscopic technique the minerals such as quartz, microcline feldspar, orthoclase feldspar, kaolinite, montmorillonite, illite, and organic carbon were identified and characterized. The extinction coefficient values were calculated to know the relative distribution of major minerals such as quartz, microcline feldspar, orthoclase feldspar and kaolinite. The calculated values indicate that the amount of quartz is higher than orthoclase feldspar, microcline feldspar and much higher than kaolinite. Crystallinity index was calculated to know the crystalline nature of quartz. The result indicates that the presence of disordered crystalline quartz in soils. The relation between minerals and radioactivity was assessed by multivariate statistical analysis (Pearson's correlation and cluster analysis). The statistical analysis confirms that the clay mineral kaolinite and non-clay mineral quartz is the major factor than other major minerals to induce the important radioactivity variables and concentrations of uranium and thorium.

Chandrasekaran, A.; Ravisankar, R.; Rajalakshmi, A.; Eswaran, P.; Vijayagopal, P.; Venkatraman, B.

2015-02-01

349

Substitution Structures of Multiple Silicon-Containing Species by Chirped Pulse Ftmw Spectroscopy  

NASA Astrophysics Data System (ADS)

The structures of CH_{3}SiHF-NCO, 1-X-silacyclopropane (X = cyano, isocyanato), 1,1,3,3-tetrafluoro-1,3-disilacyclopentane and its hydrogen analogue (1,3-disilacyclopentane), and 1-isocyanato-silacyclohexane have been studied by chirped pulse FTMW spectroscopy in the 6-18 GHz band. Multiple conformers for some of the species were also detected: anti and gauche for both silacyclopropyl species, and axial and equatorial for the silacyclohexane. Heavy atom substitution structures were determined, with all possible single ^{13}C, ^{29}Si/^{30}Si and most ^{15}N isotopologues assigned in natural abundance. Nitrogen hyperfine and distortion parameters for all species have been determined, and the barrier for methyl internal rotation for CH_{3}SiHF-NCO has been determined as 481(20) cm^{-1}, close to the B3LYP/6-311++g(d,p) barrier of 450 cm^{-1}. A summary of the microwave and structural results for the aforementioned molecules will be presented. In addition, emphasis will be placed on the use of previously discussed automated fitting techniques as a means of efficient and fast assignment of isotopologues in spectra with increasingly large line densities. A. L. Steber, J. L. Neill, M. T. Muckle, B. H. Pate, D. F. Plusquellic, V. Lattanzi, S. Spezzano, M. C. McCarthy. 65th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2010, TC10. E. B. Kent, M. N. McCabe, M. A. Phillips, B. P. Gordon, S. T. Shipman. 66th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2011, RH01.

Seifert, Nathan A.; Lobsiger, Simon; Pate, Brooks H.; Guirgis, Gamil A.; Overby, Jason S.; Durig, James R.

2013-06-01

350

A LINEARIZATION METHOD FOR A UWB VCO-BASED CHIRP GENERATOR USING DUAL COMPENSATION  

E-print Network

of a VCO-based chirp generator with 6 GHz of bandwidth. The linearization system is composed of a Phase Lock Loop (PLL) and an external compensation added to the loop. The nonlinear behavior of the VCO was treated as added disturbances to the loop...

Gomez-Garcia Alvestegui, Daniel

2011-12-31

351

Extended Koch's model for chirp assessment in semiconductor singlemode lasers operating at high currents  

NASA Astrophysics Data System (ADS)

Semiconductor singlemode laser chirp models that discriminate the adiabatic and the transient frequency chirp components are very relevant and useful, as they allow evaluating per se the effects of both chirp components on directly modulated (DM) laser communication system performance. For this purpose, Koch's model has been extensively used, showing high accuracy for low and moderate laser current regimes. This paper aims at proposing an extended Koch's (e-Koch's) model that allows its accurate use in high current regimes for an arbitrary functional form of the laser nonlinear gain compression factor. High current regimes are commonly found in high bit-rate optical communication systems, in order to achieve sufficient laser intensity modulation bandwidth. Frequency chirping predictions by the proposed model, assessed by numerical simulation, show good agreement with the ones estimated by the laser rate equations, for both linear and logarithmic carrier density dependent laser gain models. It is also shown that e-Koch's model provides good estimates of the performance of 40 Gbit/s DM laser multi-span system.

Morgado, José A. P.; Cartaxo, Adolfo V. T.

2012-11-01

352

Fiber optical parametric chirped-pulse amplification in the femtosecond regime  

E-print Network

. Ishii, L. Turi, V. S. Yakovlev, T. Fuji, F. Krausz, A. Baltuska, R. Butkus, G. Veitas, V. Smilgevicius, R. Danielus, and A. Piskarskas, "Multimillijoule chirped parametric amplification of few. 30, 1974­1976 (2005). 3. I. Jovanovic, C. G. Brown, C. A. Ebbers, C. P. J. Barty, N. Forget, and C

Paris-Sud XI, Université de

353

Investigation of wavelength variations of fibre Bragg grating features using a chirped phase mask  

Microsoft Academic Search

A simple scheme, using a chirped phase mask, for studying the wavelength dependence of fibre Bragg grating (FBG) responses in the region of of the Bragg wavelength, which are due to the use of a non-ideal phase mask, is presented. Comparison of the FBG responses in the regions of of the Bragg wavelength (i.e. ?1030 nm) and the usual Bragg

Sui P Yam; D J Kitcher; S A Wade; G W Baxter; S F Collins

2008-01-01

354

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 membership and is important in kin and social group recognition. Belding's ground squirrels Spermophilus's ground squirrels from four different lakes in the High Sierra Nevada. Results demonstrate that alarm

Patricelli, Gail

355

Time Reversed Transmission with Chirp Signaling for UWB Communications and Its Application in  

E-print Network

for this purpose. Periodically modulated radar returns from jet engines can be modeled as a chirp [6]. This view. II. PULSE PROPAGATION IN RECTANGULAR METAL CAVITY The measurement is performed using frequency domain. The rectangular confined metal cavity in Fig. 1 measures 16 feet by 8 feet by 8 feet. The materials of the walls

Qiu, Robert Caiming

356

The monitoring and multiplexing of fiber optic sensors using chirped laser sources  

E-print Network

A wide band linearly chirped erbium-doped fiber laser has been developed. The erbium-doped fiber laser using a rotating mirror/grating combination as one of the reflectors in a Fabry-Perot laser cavity has been tuned over a 46 nm spectral range...

Wan, Xiaoke

2004-09-30

357

Evaluation and application of the linear variable differential transformer technique for the assessment of human dorsal hand vein alpha-receptor activity.  

PubMed

Diurnal, day-to-day, intrasubject, and intersubject variability of responsiveness of dorsal hand veins to norepinephrine has been investigated in healthy young subjects through the use of a novel technique in which a linear variable differential transformer (LVDT) is placed directly over the vein. Under constant operating conditions, control vein diameter remained consistent. There is a log dose responsiveness to norepinephrine infused directly into the hand vein. There was little diurnal, day-to-day, or intrasubject variability in the dose of norepinephrine required to induce 50% constriction of hand vein diameter. The responsiveness to norepinephrine of different veins in either hand was also consistent. However, there was wide intersubject variability, apparently unrelated to age, gender, or other subject characteristics. We conclude that the LVDT method is reproducible and reliable and offers a relatively noninvasive means of assessing the effects of disease and drugs on the human dorsal hand vein in vivo. The LVDT technique has been applied to study the rate of onset, magnitude of effect, dose responsiveness, and duration of action of intravenous dihydroergotamine, 0.1, 0.2, and 0.4 mg, on human dorsal hand veins. Despite systemic intravenous administration, there was an average delay in maximum response of 30 minutes to 1 hour. Venoconstriction was incomplete, with a maximum reduction of approximately 50% of vein diameter after each of the larger doses. There was no significant difference between the effects produced by 0.2 or 0.4 mg, which persisted for 6 hours after dosing. PMID:2996818

Alradi, A O; Carruthers, S G

1985-11-01

358

Effects of the initial chirp and fibre loss on the soliton mechanism of picosecond pulse compression in optical fibres  

SciTech Connect

The effect of the initial chirp and fibre loss on the efficiency of soliton-effect picosecond pulse compression are analysed by simulating numerically the transmission of picosecond pulse in fibres by the split-step Fourier method. Analysis of changes in the compression factor, the optimum fibre length, and the compression efficiency showed that the initial chirp and fibre loss affect the compression of a picosecond pulse in opposite ways. A further study revealed that an additional properly created initial chirp provides good pulse compression. (nonlinear optical phenomena)

Yang Xingyu; Yang Guangqiang [Department of Physics, Inner Mongolia University, Huhhot (China)

2001-08-31

359

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

360

Shape transformation for polyhedral objects  

Microsoft Academic Search

Techniques that transform one two-dimensionaf image into another have gained widespread use m recent yeara. Extending these tech- niques to transform pairs of 3D objects, as opposed to 2D images of the objects, providea several advsntagea, including the ability to sn- imate the objects independently of the transformation. This paper presents an algorithm for computing such transformations. The al- gorithm

James R. Kent; Wayne E. Carlson; Richard E. Parent

1992-01-01

361

A new high-frequency Agrobacterium-mediated transformation technique for Sesamum indicum L. using de-embryonated cotyledon as explant.  

PubMed

In spite of the economic importance of sesame (Sesamum indicum L.) and the recent availability of its genome sequence, a high-frequency transformation protocol is still not available. The only two existing Agrobacterium-mediated transformation protocols that are available have poor transformation efficiencies of less than 2%. In the present study, we report a high-frequency, simple, and reproducible transformation protocol for sesame. Transformation was done using de-embryonated cotyledons via somatic embryogenic stages. All the critical parameters of transformation, like incubation period of explants in pre-regeneration medium prior to infection by Agrobacterium tumefaciens, cocultivation period, concentrations of acetosyringone in cocultivation medium, kanamycin concentration, and concentration of plant hormones, including 6-benzylaminopurine, have been optimized. This protocol is superior to the two existing protocols in its high regeneration and transformation efficiencies. The transformed sesame lines have been tested by PCR, RT-PCR for neomycin phosphotransferase II gene expression, and ?-glucuronidase (GUS) assay. The regeneration frequency and transformation efficiency are 57.33 and 42.66%, respectively. T0 and T1 generation transgenic plants were analyzed, and several T1 plants homozygous for the transgenes were obtained. PMID:24590594

Chowdhury, Supriyo; Basu, Arpita; Kundu, Surekha

2014-09-01

362

Chirped-beam two-stage free-electron laser for high-power femtosecond x-ray pulse generation  

NASA Astrophysics Data System (ADS)

A method for generating femtosecond-duration x-ray pulses with a free-electron laser is presented. This method uses an energy-chirped electron beam propagating through an undulator to produce a frequency-chirped x-ray pulse by self-amplified spontaneous emission. A short temporal pulse is created by use of a monochromator to select a narrow radiation bandwidth. A second undulator is used to amplify the short-duration radiation. The radiation characteristics produced by a chirped-beam two-stage free-electron laser are calculated, and the performance of the chirped-beam two-stage option for the Linac Coherent Light Source is considered. 2002 Optical Society of America

Schroeder, Carl B.; Pellegrini, Claudio; Reiche, Sven; Arthur, John; Emma, Paul

2002-08-01

363

A new and efficient theoretical model to analyze chirped grating distributed feedback lasers  

NASA Astrophysics Data System (ADS)

Threshold conditions of a distributed feedback (DFB) laser with a linearly chirped grating are investigated using a new and efficient method. DFB laser with chirped grating is found to have significant effects on the lasing characteristics. The coupled wave equations for these lasers are derived and solved using a power series method to obtain the threshold condition. A Newton- Raphson routine is used to solve the threshold conditions numerically to obtain threshold gain and lasing wavelengths. To prove the validity of this model, it is applied to both conventional index-coupled and complex- coupled DFB lasers. The threshold gain margins are calculated as functions of the ratio of the gain coupling to index coupling (|?g|/|? n|), and the phase difference between the index and gain gratings. It was found that for coupling coefficient |?|l < 0.9, the laser shows a mode degeneracy at particular values of the ratio |? g|/|?n|, for cleaved facets. We found that at phase differences ?/2 and 3?/2, between the gain and index grating, for an AR-coated complex-coupled laser, the laser becomes multimode and a different mode starts to lase. We also studied the effect of the facet reflectivity (both magnitude and phase) on the gain margin of a complex- coupled DFB laser. Although, the gain margin varies slowly with the magnitude of the facet reflectivity, it shows large variations as a function of the phase. Spatial hole burning was found to be minimum at phase difference n?, n = 0, 1, ... and maximum at phase differences ?/2 and 3?/2. The single mode gain margin of an index-coupled linearly chirped CG-DFB is calculated for different chirping factors and coupling constants. We found that there is clearly an optimum chirping for which the single mode gain margin is maximum. The gain margins were calculated also for different positions of the cavity center. The effect of the facet reflectivities and their phases on the gain margin was investigated. We found the gain margin is maximum and the Spatial Hole Burning (SHB) is minimum for the cavity center at the middle of the laser cavity. Effect of chirping on the threshold gain, gain margin and spatial hole burning (SHB) for different parameters, such as the coupling coefficients, facet reflectivities, etc., of these lasers are studied. Single mode yield of these lasers are calculated and compared with that of a uniform grating DFB laser.

Arif, Muhammad

364

Simultaneous ranging and velocimetry of fast moving targets using oppositely chirped pulses from a mode-locked laser.  

PubMed

A lidar system based on the coherent detection of oppositely chirped pulses generated using a 20 MHz mode locked laser and chirped fiber Bragg gratings is presented. Sub millimeter resolution ranging is performed with > 25 dB signal to noise ratio. Simultaneous, range and Doppler velocity measurements are experimentally demonstrated using a target moving at > 330 km/h inside the laboratory. PMID:21716350

Piracha, Mohammad U; Nguyen, Dat; Ozdur, Ibrahim; Delfyett, Peter J

2011-06-01

365

Performance limitations of an optical RZ-DPSK transmission system affected by frequency chirp, chromatic dispersion and polarization mode dispersion  

Microsoft Academic Search

The performance limitations due to the combined effects of frequency chirp and CD or PMD in a 40 Gbit\\/s optical Return-to-Zero Differential Phase-Shift-Keying (RZDPSK) transmission system are numerically simulated. By means of numerical simulations, we optimize the bandwidths of the optical and electrical receiver’s filters. Then, the impact of the Chirp factor (C) on the Bit Error Rate (BER) performance

Lazhar Kassa-Baghdouche; Lotfy Mokhtar Simohamed

2011-01-01

366

Kinetics of electrochemically controlled surface reactions on bulk and thin film metals studied with Fourier transform impedance spectroscopy and surface plasmon resonance techniques  

NASA Astrophysics Data System (ADS)

In the work presented in this thesis, the surface sensitive electrochemical techniques of cyclic voltametry (CV), potential step (PS) and Fourier transform impedance spectroscopy (FT-EIS), as well as the optical technique of surface plasmon resonance (SPR), were used to probe a wide variety of surface processes at various metal/liquid interface. Three polycrystalline metals (Au, Ta and Cu) and a Cr-coated gold film were used for these studies in different aqueous environments. A combination of CV with FT-EIS and PS was used to investigate electronic and structural proprieties of a modified bulk electrode of Au. This experimental system involved under potential deposition (UPD) of Bi3+ on Au in a supporting aqueous electrolyte containing ClO-4 . UPD range of Bi3+ was determined, and adsorption kinetics of Bi3+ in the presence of coadsorbing anion, ClO-4 were quantified. Potentiodynamic growth of oxide films of Ta in the following electrolytes NaNO3, NaNO3 + 5wt% H2O2, NaOH and NaOH + 5wt% H2O2 had been investigated. The oxide films were grown in the range -0.1 ? +0.4V (high electric field) at a scan rate of 10 mV/s. Time resolved A.C. impedance spectroscopy measurements in the frequency range (0.1--20 KHz) were performed to characterize the surface reactions of oxide formation. The results are interpreted in terms of charge conductivity O2- through the oxide film, and disintegration of H2O2 into OH-. In a high pH medium (pH 12), dissociation of H2O2 was catalytically enhanced. This led to destabilization of the electrogenerated tantalum oxide surface film in the form of a soluble hexatantalate species. In contrast with the electrolytes, NaNO3, NaNO3 + 5wt% H2O2, NaOH, where only the oxide growth was observed, the A.C. impedance spectroscopy measurements in NaOH + 5wt% H 2O2 showed competition between oxide formation and its removal. These results are relevant for chemical slurry design in chemical mechanical polishing (CMP) of Ta. Further investigations were performed by studying potential galvanic corrosion effects that are susceptible to occur during planarization process in CMP technology. A combination of FT-EIS with potentiodynamic polarization and galvanic current measurements showed evidence of these effects when Cu (interconnected material in integrated circuits) and Ta (barrier material) were brought into electrical contact via abrasive-free polishing solutions. Quantitative analyses of kinetics of these effects were performed. Catalytic activity of a thin film Au (˜40 nm) toward methanol oxidation in alkaline medium for direct methanol fuel cell (DMFC) was carried out in this part of the work. A relatively unique combined technique of FT-EIS and SPR was used to perform this study. The FT-EIS data provided detailed kinetic parameters that characterize electro-oxidation of methanol. This led to a quantitative understanding of the mechanism of the probed surface reactions. At the same time, the SPR data provided with high accuracy the optical parameters and electronic characteristics of the thin film Au. The combined technique provided a complete understanding of the observed surface reactions, and showed consistency in data.

Assiongbon, Kankoe A.

2005-07-01

367

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

PubMed Central

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

Shekhar, Himanshu; Doyley, Marvin M.

2013-01-01

368

Low-chirp high-extinction-ratio modulator based on graphene-silicon waveguide.  

PubMed

We present a hybrid graphene-silicon waveguide, which consists of a lateral slot waveguide with three layers of graphene flakes inside. Through a theoretical analysis, an effective index variation for about 0.05 is found in the waveguide by applying a voltage on the graphene. We designed a Mach-Zehnder modulator based on this waveguide and demonstrated it can process signals nearly chirp-free. The calculation shows that the driving voltage is only 1 V even if the length of the arm is shortened to be 43.54 ?m. An extinction up to 34.7 dB and a minimum chirp parameter of -0.006 are obtained. Its insertion loss is roughly -1.37 dB. This modulator consumes low power and has a small footprint. It can potentially be ultrafast as well as CMOS compatible. PMID:23939097

Yang, Longzhi; Hu, Ting; Hao, Ran; Qiu, Chen; Xu, Chao; Yu, Hui; Xu, Yang; Jiang, Xiaoqing; Li, Yubo; Yang, Jianyi

2013-07-15

369

Ultrashort electron bunch generation by an energy chirping cell attached rf gun  

NASA Astrophysics Data System (ADS)

We present a new design for a rf electron gun to be used in ultrashort (˜1 ps) electron bunch generation. Using both simulation and measurement we evaluated the principle of this new type rf gun and were able to confirm an ultrashort bunch generation. During simulation, a bunch length of less than 100 fs(rms) with a 100 pC/bunch charge was confirmed at the optimum operating condition. The principle is to produce a linearly distributed longitudinal phase space by using an attached output cell specially designed for energy chirping. Such phase space distribution can be rotated by the velocity difference in the bunch. We already fabricated an energy chirping cell attached rf gun and successfully observed 0.2 THz coherent synchrotron radiation, which corresponds to less than 500 fs bunch. Such an electron gun can be used as a compact THz light source and a new electron injector with an ultrashort bunch.

Sakaue, K.; Koshiba, Y.; Mizugaki, M.; Washio, M.; Takatomi, T.; Urakawa, J.; Kuroda, R.

2014-02-01

370

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

371

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

372

Mode selection in a multimode SAW oscillator using FM chirp mixing signal injection.  

PubMed

Mode-selection control of a multimode surface-acoustic-wave (SAW) oscillator has been obtained using SAW linear FM chirp signal injection. The prototype 60-100-MHz SAW oscillator design employed a single-phase unidirectional transducer (SPUDT) low-loss comb filter in the feedback loop, with minimum insertion loss of approximately 3.7 dB. Mode selection was achieved using an injection signal derived from the mixed output of two 27.5-52.5-MHz up- and down-chirp SAW filters. Mode switching times of less, similar2 mus were obtained. The device could be useful as a local oscillator on frequency-agile radars, where hopping is required over a moderate number of frequencies. PMID:18290165

Saw, C B; Smith, P M; Edmonson, P J; Campbell, C K

1988-01-01

373

Self-injected semiconductor distributed feedback lasers for frequency chirp stabilization.  

PubMed

It is well known that semiconductor distributed feedback lasers (DFB) are key devices for optical communications. However direct modulation applications are limited by the frequency chirp induced by current modulation. We demonstrate that a proper external control laser operation leads to chirp-to-power ratio (CPR) stabilization over a wide range of modulation frequencies as compared to the free-running case. Under experimentally selected optical feedback conditions, the CPR decreases significantly in the adiabatic regime from about 650 MHz/mW in the solitary case down to 65 MHz/mW. Experimental results are also confirmed by numerical investigations based on the transfer matrix method. Simulations point out the possible optimization of the CPR in the adiabatic regime by considering a judicious cavity design in conjunction with a proper external control. These results demonstrate important routes for improving the transmission performance in optical telecommunication systems. PMID:23187422

Kechaou, Khalil; Grillot, Frédéric; Provost, Jean-Guy; Thedrez, Bruno; Erasme, Didier

2012-11-01

374

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, Clément; Crépin Kofané, Timoléon

2014-08-01

375

All optical quantum storage based on spatial chirp of the control field  

E-print Network

We suggest an all-optical quantum memory scheme which is based on the off-resonant Raman interaction of a signal quantum field and a strong control field in a three-level atomic medium in the case, when the control field has a spatially varying frequency across the beam, called a spatial chirp. We show that the effect of such a spatial chirp is analogous to the effect of a controllable reversible inhomogeneous broadening (CRIB) of the atomic transition used in the gradient echo memory (GEM) scheme. However, the proposed scheme does not require temporal modulation of the control field or the atomic levels, and can be realized without additional electric or magnetic fields. It means that materials demonstrating neither linear Stark nor Zeeman effects can be used and/or materials which are placed in specific external fields remain undisturbed.

Xiwen Zhang; Alexey Kalachev; Olga Kocharovskaya

2014-10-21

376

Efficient Quantum Transforms  

E-print Network

Quantum mechanics requires the operation of quantum computers to be unitary, and thus makes it important to have general techniques for developing fast quantum algorithms for computing unitary transforms. A quantum routine for computing a generalized Kronecker product is given. Applications include re-development of the networks for computing the Walsh-Hadamard and the quantum Fourier transform. New networks for two wavelet transforms are given. Quantum computation of Fourier transforms for non-Abelian groups is defined. A slightly relaxed definition is shown to simplify the analysis and the networks that computes the transforms. Efficient networks for computing such transforms for a class of metacyclic groups are introduced. A novel network for computing a Fourier transform for a group used in quantum error-correction is also given.

Peter Hoyer

1997-02-12

377

Chirp control of an electroabsorption modulator to be used for regeneration and wavelength conversion at 40 gbit\\/s in all-optical networking  

Microsoft Academic Search

Chirp control to produce low or negative values of chirp at the output of an electroabsorption modulator (EAM) is an important mechanism for reducing the signal degradation due to chromatic dispersion in high-speed transmission over standard single-mode fibre. An analytical model for the chirp performance of an EAM capable of optical regeneration and simultaneous wavelength conversion operating at 40 Gbit\\/s

M. Y. Jamro; J. M. Senior

2005-01-01

378

Deexcitation of high-Rydberg-state atoms with a chirped train of half-cycle pulses  

Microsoft Academic Search

Encouraged by the experiments on production of antihydrogen atoms in high Rydberg states we have calculated the effect of deexcitation towards lower states by a chirped train of identical unidirectional half-cycle pulses. The calculations exploit both the one-dimensional and impulse approximations providing convenient analytical formulas for the Rydberg-to-Rydberg transition amplitudes. The calculated deexcitation is shown in terms of the mean

T. Kopyciuk; R. Parzynski

2007-01-01

379

1.5 ?m MQW-DFB laser diode with low chirp and low threshold current  

Microsoft Academic Search

1.55-?m band InGaAs-InGaAsP multiple-quantum-well distributed feedback laser diodes have been successfully fabricated by metalorganic chemical vapor deposition. The threshold current is as low as 9 mA, and the slope efficiency is 0.2 mW\\/mA. A very low chirp of 3 Å at 2 Gbit\\/s NRZ modulation is obtained

K. Mizuguchi; N. Yoshida; T. Kimura; A. Takemoto; Y. Ohkura; M. Tsugami; T. Murotani

1989-01-01

380

Tunable optical delay line in SOI implemented with step chirped Bragg gratings and serial grating arrays  

NASA Astrophysics Data System (ADS)

Tunable optical delay devices have numerous applications in optical communications [1] and have been successfully implemented using slow light elements and fiber or waveguide gratings. There has been considerable interest in siliconon- insulator (SOI) as a technology platform for compact integration of optical signal processing systems. SOI-based delay lines have been realized using coupled ring resonators [2], photonic crystals [3], and various Bragg grating-based configurations including single or coupled chirped sidewall gratings [4,5] as well as tapered rib waveguide gratings [6]. By linearly chirping the period in sidewall gratings, relatively small delays (a few ps) over a bandwidth of tens of nm were demonstrated [4]; with tapered waveguides, significantly larger delays (300-500 ps) were obtained, albeit over a narrower bandwidth (< 2 nm) [6]. On the other hand, some signal processing applications may require large delays (e.g., tens to hundreds of ps) over large bandwidths (several to tens of nm). Several designs have been proposed to meet these requirements, e.g., a step-chirped rib waveguide grating providing 50 ps delay over 15 nm [7] or complementary apodized sidewall gratings providing up to 275 ps over 3 nm [8], however, they have not been realized experimentally. In this paper, we demonstrate discretely tunable optical delay lines that provide tens of ps delay (up to 65 ps) in steps of 15-32 ps over bandwidths of several tens of nm (35-70 nm). The devices are fabricated on SOI using electron beam lithography and implemented through two different approaches: serial sidewall Bragg grating arrays and the step-chirped sidewall Bragg gratings.

Spasojevic, Mina; Chen, Lawrence R.

2013-10-01

381

Theory and design of a photoinjector-driven chirped pulse free-electron maser  

Microsoft Academic Search

An overview of the design parameters of a compact high-gradient high-luminosity X-band (8.568 GHz) photoinjector is followed by a more detailed description of each of its major subsystems: X-band RF gun, GHz repetition rate synchronously modelocked AlGaAs quantum well laser oscillator, and eight-pass Ti:Al2O3 chirped pulse laser amplifier. The photoinjector uses a high quantum efficiency (~5%) Cs2Te photocathode, and is

Gregory P. Le Sage; Helena X. C. Feng; Lisa L. Laurent; F. V. Hartemann; S. N. Fochs; M. D. Perry; G. A. Westenskow; J. P. Heritage

1996-01-01

382

Microjoule pulse energy from a chirped-pulse Ti:sapphire oscillator with cavity-dumping  

Microsoft Academic Search

In this paper, we report for the first time to our knowledge on a chirped-pulse Ti:sapphire laser oscillator with acousto-optical cavity-dumping that reaches pulse energies in excess of 1 muJ at a repetition rate of 1 MHz and with a spectral width supporting pulse durations below 80 fs. After the laser, a CW-pumped, cryogenically cooled amplifier is used to further

M. Siegel; N. Pfullmann; G. Palmer; S. Rausch; T. Binhammer; U. Morgner

2009-01-01

383

160-gb\\/s adaptive dispersion equalization using an asynchronous dispersion-induced chirp monitor  

Microsoft Academic Search

This paper describes an adaptive dispersion equalizer (ADE) that uses an asynchronous dispersion-induced chirp monitor and the detailed study of the first demonstration of 160-Gb\\/s adaptive dispersion equalization. The device successfully equalized the dispersion change over a 40°C temperature range (from 5°C to 45°C) and the dispersion slope of an 80-km dispersion-shifted fiber (DSF). The ADE will enhance the feasibility

Tetsuro Inui; Tetsuro Komukai; Kunihiko Mori; Toshio Morioka

2005-01-01

384

Two and Three Beam Pumped Optical Parametric Amplifier of Chirped Pulses  

NASA Astrophysics Data System (ADS)

We present two and three beam pumped optical parametric amplifier of broadband chirped pulses. The seed pulses from Ti:sapphire oscillator were stretched and amplified in a non-collinear geometry pumping with up to three beams derived from independent laser amplifiers. The signal with ˜90 nm bandwidth was amplified up to 0.72 mJ. The conversion efficiency dependence on intersection angles of pump beams is also revealed.

Ališauskas, S.; Butkus, R.; Pyragait?, V.; Smilgevi?ius, V.; Stabinis, A.; Piskarskas, A.

2010-04-01

385

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

386

New stretcher scheme for a parametric amplifier of chirped pulses with frequency conversion  

SciTech Connect

The properties of hybrid prism-grating dispersion systems are studied. The scheme of a prism-grating stretcher matched to a standard compressor in the phase dispersion up to the fourth order inclusive is developed for a petawatt laser complex based on the optical parametric chirped-pulse amplification. The stretcher was used to obtain the {approx}200-TW peak power of laser radiation. (control of laser radiation parameters)

Freidman, Gennadii I; Yakovlev, I V [Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation)

2007-02-28

387

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

388

Chirped lasers dispersion spectroscopy implemented with single- and dual-sideband electro-optical modulators.  

PubMed

We report new approaches for signal generation in Chirped Laser Dispersion Spectroscopy (CLaDS). Two optical arrangements based on electro-optical modulators significantly reduce CLaDS system complexity and enable optimum performance when applied to detection of GHz-wide molecular transitions. Proof-of-principle experiments in the near-infrared spectral range are presented and potential strategies for application in the mid-infrared are discussed. PMID:23787653

Nikodem, Michal; Plant, Genevieve; Wang, Zhenxing; Prucnal, Paul; Wysocki, Gerard

2013-06-17

389

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.

390

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

391

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

392

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 1 dB) 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

393

Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification  

NASA Astrophysics Data System (ADS)

Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992, optical parametric chirped pulse amplification (OPCPA) became the most promising method for the amplification of broadband optical pulses. In the meantime, we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers. The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level. Meanwhile, the output pulse duration based on optical parametric amplification has entered the range of few-optical-cycle field. In this paper, we overview the basic principles, trends in development, and current state of the ultrashort and laser systems based on OPCPA, respectively. Project supported by the National Natural Science Foundation of China (Grant Nos. 61378030 and 11127901), the National Basic Research Program of China(Grant No. 2011CB808101), and the International S&T Cooperation Program of China (Grant No. 2011DFA11300).

Xu, Lu; Yu, Liang-Hong; Chu, Yu-Xi; Gan, Ze-Biao; Liang, Xiao-Yan; Li, Ru-Xin; Xu, Zhi-Zhan

2015-01-01

394

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Instrumentation and Methods for Structural Characterization of Trapped Biomolecular Ions: Innovative MS\\/MS Techniques, Gas-Phase Hudrogen\\/Deuterium Exchange, and Laser-Induced Fluoresnence  

Microsoft Academic Search

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has become a powerful tool for biomolecular structural characterization because of its superior mass resolving power and high mass accuracy. Of particular interest in this work is the optimization of the diverse range of fragmentation techniques available to FT-ICR MS\\/MS, including ion threshing, a novel form of collisionally activated dissociation (CAD),

Melinda A. McFarland

2004-01-01

395

Recognition of Sediments from Marine High Resolution Seismic Reflection (Chirp) Data  

NASA Astrophysics Data System (ADS)

Chirp sonar echo sounder is based on the frequency conversion of the transmission of electrical impulses, and it`s signal transmission frequency was gradually increased from the received signal being tackled by the original emitted signal to do each other comparison (correlation), to obtain high-resolution seabed sonar echo profile, use the amplitude and frequency conversion of the chirp features observed wave energy changes, shoot out and reflected wave energy to do comparison, get the change of the reflected energy change, different substrate will produce a different pass depletion, when a sound wave incident in the sea water to the seabed, the acoustic energy through the interface and transmitted by pressure waves and shear waves in the sea-bed, so different acoustic properties of the bottom material will produce different pass, the use of this nature to identify the substrate. the conditions in the water are quite large impact for acoustic detection, specifically, by the sound pass depletion performance, sound transfer loss will be affected by the hydrological environment, sediment characteristics, seabed topography, surface roughness and other factors, so chirp sonar data is the more complete the more accurate the more able to grasp the actual situation of the underwater acoustic transmission, and thus a comprehensive understanding of the actual situation of the background texture for the marine environment. Collect sediment data in two ways, one for the core sampling for sediment acoustic parameters of operational difficulties and only a little bit of information, and the second anti-algorithm, in theory, the chirp signal bandwidth is very wide, has a high SNR penetration ratio and substrate have different reactions for each frequency of the broadband rectifiable more accurate sediment attenuation coefficient (k) , In contrast, core sampling unable to obtain a wide range of information, and the sampling data is not enough depth, data variables and the results are not easy to control, use recognition of sediments from chirp data can get more comprehensive geological data, large amounts of data collated can provide Taiwan acoustic research help. The results showed that different sediments will have a different energy changes, the establishment of the collection into areas where the continuous variable frequency sonar data to do the calculation to obtain the acoustic attenuation coefficient in the sediment. Summarized a variety of sediment produced by the attenuation coefficient can be used to identify the bottom material, or can be used to exploration, search more information of the seabed.

Jiang, D.; Song, G.

2012-12-01

396

Modeling Transformation  

E-print Network

pGLO plasmids Bacterial chromosomal DNA Cell membrane #12;Heat-shock @ 42°C IncreasesModeling Transformation What does each step do? #12;Transformation Procedure #12;Transformation Procedure #12;Building Your Model Yarn = chromosomal DNA Beads

Rose, Michael R.

397

Ultrasound harmonic imaging using nonlinear chirp for cardiac imaging  

Microsoft Academic Search

Coded excitation techniques have been used to improve a signal-to-noise ratio (SNR) in tissue harmonic imaging. However, a poor separation between fundamental and target harmonic components causes the second harmonic signals to have a high level of range sidelobes after compression. In terms of the separation performance, pulse inversion (PI) is the best method and thus provides the lowest level

Hyun-jae Song; Jaehee Song; Jin Ho Chang; Tai-kyong Song

2010-01-01

398

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...

399

Periodic pulse train conformation based on the temporal Radon–Wigner transform  

Microsoft Academic Search

By using the Radon–Wigner transform (RWT), we analyze the temporal selfimaging or Talbot effect for producing well-conformed pulse trains with variable repetition rates and duty-cycles. The relationships linking the selfimaging conditions with the fractional orders of the RWT are first obtained for unchirped pulse trains. Then, we extend the analysis to chirped pulse sequences by deriving the conditions to be

Christian Cuadrado-Laborde; Pablo Costanzo-Caso; Ricardo Duchowicz; Enrique E. Sicre

2007-01-01

400

Nonlinear-optical spectral transformation of few-cycle laser pulses in photonic-crystal fibers  

Microsoft Academic Search

Photonic-crystal fibers with special dispersion profiles are shown to provide a high efficiency of spectral transformation of chirped sub- 6-fs Ti:sapphire laser pulses. With the wavelength of zero group-velocity dispersion of the fiber lying within the broad spectrum of the input few-cycle pulse, the output spectra feature well-resolved spectral peaks, indicative of soliton self-frequency shift, four-wave mixing, and Cherenkov emission

E. E. Serebryannikov; A. M. Zheltikov; N. Ishii; C. Y. Teisset; S. Köhler; T. Fuji; T. Metzger; F. Krausz; A. Baltuska

2005-01-01

401

Full-Field Spectroscopy at Megahertz-frame-rates: Application of Coherent Time-Stretch Transform  

NASA Astrophysics Data System (ADS)

Outliers or rogue events are found extensively in our world and have incredible effects. Also called rare events, they arise in the distribution of wealth (e.g., Pareto index), finance, network traffic, ocean waves, and e-commerce (selling less of more). Interest in rare optical events exploded after the sighting of optical rogue waves in laboratory experiments at UCLA. Detecting such tail events in fast streams of information necessitates real-time measurements. The Coherent Time-Stretch Transform chirps a pulsed source of radiation so that its temporal envelope matches its spectral profile (analogous to the far field regime of spatial diffraction), and the mapped spectral electric field is slow enough to be captured by a real-time digitizer. Combining this technique with spectral encoding, the time stretch technique has enabled a new class of ultra-high performance spectrometers and cameras (30+ MHz), and analog-to-digital converters that have led to the discovery of optical rogue waves and detection of cancer cells in blood with one in a million sensitivity. Conventionally, the Coherent Time-Stretch Transform maps the spectrum into the temporal electric field, but the time-dilation process along with inherent fiber losses results in reduction of peak power and loss of sensitivity, a problem exacerbated by extremely narrow molecular linewidths. The loss issue notwithstanding, in many cases the requisite dispersive optical device is not available. By extending the Coherent Time-Stretch Transform to the temporal near field, I have demonstrated, for the first time, phase-sensitive absorption spectroscopy of a gaseous sample at millions of frames per second. As the Coherent Time-Stretch Transform may capture both near and far field optical waves, it is a complete spectro-temporal optical characterization tool. This is manifested as an amplitude-dependent chirp, which implies the ability to measure the complex refractive index dispersion at megahertz frame rates. This technique is not only four orders of magnitude faster than even the fastest (kHz) spectrometers, but will also enable capture of real-time complex dielectric function dynamics of plasmas and chemical reactions (e.g. combustion). It also has applications in high-energy physics, biology, and monitoring fast high-throughput industrial processes. Adding an electro-optic modulator to the Time-Stretch Transform yields time-to-time mapping of electrical waveforms. Known as TiSER, it is an analog slow-motion processor that uses light to reduce the bandwidth of broadband RF signals for capture by high-sensitivity analog-to-digital converters (ADC). However, the electro-optic modulator limits the electrical bandwidth of TiSER. To solve this, I introduced Optical Sideband-only Amplification, wherein electro-optically generated modulation (containing the RF information) is amplified at the expense of the carrier, addressing the two most important problems plaguing electro-optic modulators: (1) low RF bandwidth and (2) high required RF drive voltages. I demonstrated drive voltage reductions of 5x at 10 GHz and 10x at 50 GHz, while simultaneously increasing the RF bandwidth.

DeVore, Peter Thomas Setsuda

402

Generalized Transforms and Special Functions  

E-print Network

We study the properties of different type of transforms by means of operational methods and discuss the relevant interplay with many families of special functions. We consider in particular the binomial transform and its generalizations. A general method, based on the use of the Fourier transform technique, is proposed for the study of the properties of functions of operators.

G. Dattoli; E. Sabia

2010-10-08

403

THE VERY FAST CURVELET TRANSFORM  

Microsoft Academic Search

The Digital Curvelet Transform provides near-optimal recon- struction of twice-continuously differentiable (C2) curves. Pre- vious implementations of the algorithm have not exploited newer technologies in modern processors, including the MMX and SSE instruction sets. Various optimization techniques were used on a form of the Digital Curvelet Transform re- sulting in the fastest Curvelet Transform currently available.

Brian Eriksson

404

Preliminary evaluation of techniques for transforming regional climate model output to the potential repository site in support of Yucca Mountain future climate synthesis  

SciTech Connect

The report describes a preliminary evaluation of models for transforming regional climate model output from a regional to a local scale for the Yucca Mountain area. Evaluation and analysis of both empirical and numerical modeling are discussed which is aimed at providing site-specific, climate-based information for use by interfacing activities. Two semiempirical approaches are recommended for further analysis.

Church, H.W.; Zak, B.D.; Behl, Y.K.

1995-06-01

405

New Seismic CHIRP evidence for Transpression and Transtension Beneath the Salton Sea, California  

NASA Astrophysics Data System (ADS)

The Salton Trough is a critical structure that separates spreading center dominated deformation in the Gulf of California and dextral strike-slip deformation along the San Andreas Fault (SAF) System. Geological and geophysical data suggest there is a transition within the Salton Trough near the town of Bombay Beach that separates transpression to the north from transtension in the south. To date, however, this transition remains poorly understood, in large part, due to a lack of geophysical subsurface data in the Salton Sea. We present preliminary analysis of > 350 line-km of high-resolution seismic CHIRP data acquired in 2006 and 2007 that imaged the different deformational styles beneath the Salton Sea, including several previously unidentified tectonic structures. The Extra Fault Zone (EFZ), which has been mapped onshore, is imaged in CHIRP profiles as an ~5 km wide deformation zone and can be traced offshore > 15 km along strike. Along the northern extent of the EFZ, ramp-flat deformation is observed with southward vergence. A marked angular unconformity between the Brawley and Cahuilla formations records fault-bend folding often predicted for ramp-flat thrust systems. Uplift and truncation of Pleistocene sediments along the northern edge of the EFZ is observed across the entire sea and appears to systematically increase towards the west. Onlapping sediments and growth folds in the Holocene Lake Cahuilla section to the north and south of the fault zone record ongoing uplift. Compression is also manifested in the bathymetry, with a mid-lake bathymetric high trending parallel the EFZ and separating southern and northern lake basins. The EFZ is interpreted to accommodate sinistral transpression related to clockwise- rotating crustal blocks. In contrast, at Bombay Beach the SAF takes an ~15 km releasing step towards the Imperial Fault, producing transtensional deformation through the Brawley Seismic Zone (BSZ). CHIRP profiles across the western margin of the BSZ image several down-to-the southeast, en echelon normal faults. Vertical offset of Lake Cahuilla sediments extends to within .5 m of the lake floor, suggesting recent deformation (possibly post-1905), and increases down-section to a maximum of ~6-8 m, thus providing evidence for several earthquakes during the past 1,300 - 1,500 years. The trend of these normal faults is approximately northeast, an orientation that is not aligned with the "ladder and rung" patterns in the relocated seismicity. Facies changes documented in ~15 m sediment cores collected by United Research Services (URS) allow us to identify at least four lake sequences. Semblance between coarse-grained materials in core logs and high-amplitude reflections in CHIRP data allow us to correlate strata throughout the basin and assign tentative ages. With an improved chronology for Lake Cahuilla sequences, the CHIRP data will allow us to constrain slip rates, paloeseismic event timing across the EFZ and faults in the BSZ, and to investigate relationships between events along the EFZ, SAF and San Jacinto Fault (SJF). The overall structure observed in CHIRP profiles might be a result of transrotation caused by strain interactions between the SAF and SJF and overprinted by regional transpression and transtension. Doming and uplift of LC sediments above the thrust ramp, as well as en echelon normal faults along the western edge of the BSZ suggest transpression and transtension are currently active and play an important role in the late Pleistocene- Holocene tectonic evolution of the Salton Trough.

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

2007-12-01

406

Photonic chirped radio-frequency generator with ultra-fast sweeping rate and ultra-wide sweeping range.  

PubMed

A high-performance photonic sweeping-frequency (chirped) radio-frequency (RF) generator has been demonstrated. By use of a novel wavelength sweeping distributed-feedback (DFB) laser, which is operated based on the linewidth enhancement effect, a fixed wavelength narrow-linewidth DFB laser, and a wideband (dc to 50 GHz) photodiode module for the hetero-dyne beating RF signal generation, a very clear chirped RF waveform can be captured by a fast real-time scope. A very-high frequency sweeping rate (10.3 GHz/?s) with an ultra-wide RF frequency sweeping range (~40 GHz) have been demonstrated. The high-repeatability (~97%) in sweeping frequency has been verified by analyzing tens of repetitive chirped waveforms. PMID:23670004

Wun, Jhih-Min; Wei, Chia-Chien; Chen, Jyehong; Goh, Chee Seong; Set, S Y; Shi, Jin-Wei

2013-05-01

407

Ultrafast single-electron transfer in coupled quantum dots driven by a few-cycle chirped pulse  

SciTech Connect

We theoretically study the ultrafast transfer of a single electron between the ground states of a coupled double quantum dot (QD) structure driven by a nonlinear chirped few-cycle laser pulse. A time-dependent Schrödinger equation without the rotating wave approximation is solved numerically. We demonstrate numerically the possibility to have a complete transfer of a single electron by choosing appropriate values of chirped rate parameters and the intensity of the pulse. Even in the presence of the spontaneous emission and dephasing processes of the QD system, high-efficiency coherent transfer of a single electron can be obtained in a wide range of the pulse parameters. Our results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through the nonlinear chirp parameter control, as well as a guidance in the design of experimental implementation.

Yang, Wen-Xing, E-mail: wenxingyang2@126.com [Department of Physics, Southeast University, Nanjing 210096 (China); Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China); Chen, Ai-Xi [Department of Applied Physics, School of Basic Science, East China Jiaotong University, Nanchang 330013 (China); Bai, Yanfeng [Department of Physics, Southeast University, Nanjing 210096 (China); Lee, Ray-Kuang [Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China)

2014-04-14

408

Generation of green frequency comb from chirped ?(2) nonlinear photonic crystals  

NASA Astrophysics Data System (ADS)

Spectrally broad frequency comb generation over 510-555 nm range was reported on chirped quasi-phase-matching (QPM) ?(2) nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 ?m to 7.1 ?m. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040 nm to 1090 nm wavelength range, the 520 nm to 545 nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted green frequency comb to have the same mode spacing of 450 GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (1020-1040 nm) and the idler (1090-1110 nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510-520 nm and the 545-555 nm spectral regime. Additional 530-535 nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ˜10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point.

Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.; Fu, S.-H.; Tsai, S.-T.; Hsu, C.-W.; Yu, N. E.; Boudrioua, A.; Kung, A. H.; Peng, L.-H.

2014-12-01

409

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

410

Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers.  

PubMed

Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal. PMID:24690803

Riedel, R; Stephanides, A; Prandolini, M J; Gronloh, B; Jungbluth, B; Mans, T; Tavella, F

2014-03-15

411

Spectral shaping of the amplified signal in optical parametric chirped pulse amplification  

NASA Astrophysics Data System (ADS)

A spectral shaping method during the optical parametric chirped pulse amplification is presented. The relationship between the temporal shape of the signal pulse and the pump pulse is analyzed theoretically, which shows that the temporal shape of the signal pulse can be modulated through modulation of the pump pulse. This is proven by our verification experiment. And we have successfully used this method in the pre-amplifier of the XG-III laser facility to modulate the signal spectrum to match the requirements of the main amplifier.

Wen, Jing; Zeng, Xiaoming; Zhou, Song; Zuo, Yanlei; Zhou, Kainan

2015-02-01

412

Two-photon adiabatic passage in ultracold Rb interacting with a single nanosecond, chirped pulse  

E-print Network

A semiclassical, four-level model of a nanosecond, chirped pulse interacting with all optically accessible hyperfine states in the ultracold Rb atom is analyzed aiming at population inversion within $5S_{1/2}$ electronic state. The nature of two-photon adiabatic passage performed by such a single pulse having a bandwidth smaller than the hyperfine splitting of $5S_{1/2}$ state is investigated in the framework of the dressed state picture. It is shown that two dressed states are involved in the adiabatic dynamics of population inversion. The excited state manifold appeared to play an important mediating role in the mechanism of population transfer.

Liu, Gengyuan

2015-01-01

413

High-Gain Regenerative Chirped-Pulse Amplifier Using Photonic Crystal Rod Fiber  

NASA Astrophysics Data System (ADS)

We have demonstrated a high-gain regenerative chirped-pulse amplifier (CPA) using an Yb-doped photonic crystal rod fiber of 100 µm core diameter. The input pulse energy is 150 nJ in a pulse width of 2.5 ns at a repetition rate of 1 kHz with a central wavelength of 1053 nm. At a pump power of 13.2 W, the amplified pulse energy is 0.26 mJ, yielding a gain of 1700.

Ogino, Jumpei; Sueda, Keiichi; Kurita, Takashi; Kawashima, Toshiyuki; Miyanaga, Noriaki

2013-12-01

414

Ultrashort laser-driven stable-buckling of blisters in chirped mirror  

NASA Astrophysics Data System (ADS)

Multilayer dielectric mirrors (niobium pentoxide/silica) were irradiated by single 800 nm-38fs laser pulses. A circular blister feature appeared in the chirped mirrors at a wide range of laser fluence, while only existed above a few percent of the damage threshold for the high-reflector. Absorptive source of laser energy can be determined by combining theoretical simulation with focused ion beam technology. Mechanical analysis with a linear-elastic buckling model reveals the blister evolution belonging to a stable-buckling process until the blister radius confined by limited laser spot size.

Li Chen, Shun; An Zhao, Yuan; Da Shao, Jian; Zhi Wang, Yan; Fang, Zhou; Feng Liu, Xiao; Hang Hu, Guo; Xin Leng, Yu; Xu, Yi

2013-02-01

415

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

416

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

417

Degenerated optical parametric chirped-pulse amplification with cesium lithium borate.  

PubMed

A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was approximately 6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO. PMID:16463743

Zhao, Baozhen; Liang, Xiaoyan; Leng, Yuxin; Jiang, Yongliang; Wang, Cheng; Lu, Haihe; Du, Juan; Xu, Zhizhan; Shen, Dezhong

2006-01-20

418

Degenerated optical parametric chirped-pulse amplification with cesium lithium borate  

NASA Astrophysics Data System (ADS)

A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was ˜6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO.

Zhao, Baozhen; Liang, Xiaoyan; Leng, Yuxin; Jiang, Yongliang; Wang, Cheng; Lu, Haihe; Du, Juan; Xu, Zhizhan; Shen, Dezhong

2006-01-01

419

Chirped laser dispersion spectroscopy using a directly modulated quantum cascade laser  

NASA Astrophysics Data System (ADS)

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; Spinner, Georg; Nikodem, Michal; Wysocki, Gerard

2013-11-01

420

10-MHz, Yb-fiber chirped-pulse amplifier system with large-scale transmission gratings.  

PubMed

Large-scale transmission gratings were produced for a stretcher and a compressor in the Yb-fiber chirped-pulse amplification system. A 23-W, 200-fs laser system with a 10-MHz repetition rate was demonstrated. Focused intensity as high as 10(14) W/cm(2) was achieved, which is high enough for multi-photon processes such as high-order harmonics generation and multi-photon ionization of neutral atoms. High-order harmonics up to 7th order were observed using Xe gas as a nonlinear medium. PMID:23736505

Kobayashi, Yohei; Hirayama, Nozomi; Ozawa, Akira; Sukegawa, Takashi; Seki, Takashi; Kuramoto, Yoshiyuki; Watanabe, Shuntaro

2013-05-20

421

RF-photonic chirp encoder and compressor for seamless analysis of information flow.  

PubMed

In this paper we realize an RF photonic chirp compression system that compresses a continuous stream of incoming RF data (modulated on top of an optical carrier) into a train of temporal short pulses. Each pulse in the train can be separated and treated individually while being sampled by low rate optical switch and without temporal loses of the incoming flow of information. Each such pulse can be filtered and analyzed differently. The main advantage of the proposed system is its capability of being able to handle, seamlessly, high rate information flow with all-optical means and with low rate optical switches. PMID:18545501

Zalevsky, Zeev; Shemer, Amir; Zach, Shlomo

2008-05-26

422

A stretcher fiber for use in fs chirped pulse Yb amplifiers.  

PubMed

A newly developed fiber for use in pulse stretchers for chirped pulse amplifiers working in the 1 mum wavelength range of Yb fiber amplifiers is reported. The fiber has a record high numerical third order to second order dispersion beta(3)/beta(2) ratio of -7.7 fs. The fiber has very good dispersion match to a grating compressor for second, third, and fourth order dispersion. By combining the stretcher fiber with an anomalous dispersion fiber working in a higher order mode, even higher beta(3)/beta(2) ratio of -16.8 fs is demonstrated. The combined module shows very good dispersion match to a grating compressor. PMID:20389387

Grüner-Nielsen, Lars; Jakobsen, Dan; Jespersen, Kim G; Pálsdóttir, Bera

2010-02-15

423

Spectrum bandwidth narrowing of Thomson scattering X-rays with energy chirped electron beams from laser wakefield acceleration  

SciTech Connect

We study incoherent Thomson scattering between an ultrashort laser pulse and an electron beam accelerated from a laser wakefield. The energy chirp effects of the accelerated electron beam on the final radiation spectrum bandwidth are investigated. It is found that the scattered X-ray radiation has the minimum spectrum width and highest intensity as electrons are accelerated up to around the dephasing point. Furthermore, it is proposed that the electron acceleration process inside the wakefield can be studied by use of 90° Thomson scattering. The dephasing position and beam energy chirp can be deduced from the intensity and bandwidth of the scattered radiation.

Xu, Tong; Chen, Min, E-mail: minchen@sjtu.edu.cn; Li, Fei-Yu; Yu, Lu-Le [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China)] [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Sheng, Zheng-Ming, E-mail: zmsheng@sjtu.edu.cn [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China) [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Zhang, Jie [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China) [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China)

2014-01-06

424

2-?m wavelength, high-energy Ho:YLF chirped-pulse amplifier for mid-infrared OPCPA.  

PubMed

A 2-?m wavelength laser delivering up to 39-mJ energy, ?10??ps duration pulses at 100-Hz repetition rate is reported. The system relies on chirped pulse amplification (CPA): a modelocked Er:Tm:Ho fiber-seeder is followed by a Ho:YLF-based regenerative amplifier and a cryogenically cooled Ho:YLF single pass amplifier. Stretching and compressing are performed with large aperture chirped volume Bragg gratings (CVBG). At a peak power of 3.3 GW, the stability was <1%??rms over 1 h, confirming high suitability for OPCPA and extreme nonlinear optics applications. PMID:25680122

Hemmer, M; Sánchez, D; Jelínek, M; Smirnov, Vadim; Jelinkova, H; Kube?ek, V; Biegert, J

2015-02-15

425

Processing advantages of linear chirped fiber Bragg gratings in the time domain realization of optical frequency-domain reflectometry.  

PubMed

The inclusion of a linear chirped fiber Bragg grating for short pulse dispersion is shown to enhance the time domain realization of optical frequency-domain reflectometry. A low resolution demonstrator is constructed with single surface scans containing 140 resolvable spots. The system dynamic range meets that shown in earlier demonstrations without digital post-processing for signal linearization. Using a conjugate pair of chirped pulses created by the fiber grating, ranging is performed with position and velocity information decoupled. Additionally, by probing the target with short pulses and introducing grating dispersion just before photodetection, velocity immune ranging is demonstrated. PMID:19550832

Saperstein, R E; Alic, N; Zamek, S; Ikeda, K; Slutsky, B; Fainman, Y

2007-11-12

426

One-way ranging technique for CSS-based indoor localization  

Microsoft Academic Search

In this paper we are seeking a real-time one-way ranging technique for the chirp spread spectrum (CSS) based indoor localization. The motivation of this research is to overcome some technical disadvantage inherent to the existing symmetric double side two way ranging (SDS-TWR) technique. It is our aim to establish a ranging technique that has the following features: (i) The mobile

Hyo-Sung Ahn; Hwan Hur; Wan-Sik Choi

2008-01-01

427

Electron beam energy chirp control with a rectangular corrugated structure at the Linac Coherent Light Source  

NASA Astrophysics Data System (ADS)

Electron beam energy chirp is an important parameter that affects the bandwidth and performance of a linac-based, free-electron laser. In this paper we study the wakefields generated by a beam passing between flat metallic plates with small corrugations, and then apply such a device as a passive dechirper for the Linac Coherent Light Source (LCLS) energy chirp control with a multi-GeV and femtosecond electron beam. Similar devices have been tested in several places at relatively low energies (˜100 MeV ) and with relatively long bunches (>1 ps ). In the parameter regime of the LCLS dechirper, with the corrugation size similar to the gap between the plates, the analytical solutions of the wakefields are no longer applicable, and we resort to a field matching program to obtain the wakes. Based on the numerical calculations, we fit the short-range, longitudinal wakes to simple formulas, valid over a large, useful parameter range. Finally, since the transverse wakefields—both dipole and quadrupole—are strong, we compute and include them in beam dynamics simulations to investigate the error tolerances when this device is introduced in the LCLS.

Zhang, Zhen; Bane, Karl; Ding, Yuantao; Huang, Zhirong; Iverson, Richard; Maxwell, Timothy; Stupakov, Gennady; Wang, Lanfa

2015-01-01

428

Electron Beam Energy Chirp Control with a Rectangular Corrugated Structure at the Linac Coherent Light Source  

DOE PAGESBeta

Electron beam energy chirp is an important parameter that affects the bandwidth and performance of a linac-based, free-electron laser. In this paper we study the wakefields generated by a beam passing between at metallic plates with small corrugations, and then apply such a device as a passive dechirper for the Linac Coherent Light Source (LCLS) energy chirp control with a multi-GeV and femtosecond electron beam. Similar devices have been tested in several places at relatively low energies (#24;100 MeV) and with relatively long bunches (> 1ps). In the parameter regime of the LCLS dechirper, with the corrugation size similar to the gap between the plates, the analytical solutions of the wakefields are no longer applicable, and we resort to a #12;field matching program to obtain the wakes. Based on the numerical calculations, we #12;fit the short-range, longitudinal wakes to simple formulas, valid over a large, useful parameter range. Finally, since the transverse wakefields - both dipole and quadrupole-are strong, we compute and include them in beam dynamics simulations to investigate the error tolerances when this device is introduced in the LCLS.

Zhang, Zhen; Bane, Karl; Ding, Yantao; Huang, Zhirong; Iverson, Richard; Maxwell, Timothy; Stupakov, Gennady; Wang, Lanfa

2015-01-30

429

Optical frequency comb generation based on chirping of Mach-Zehnder Modulators  

NASA Astrophysics Data System (ADS)

A new approach for the generation of an optical frequency comb, based on chirping of modulators, is proposed and numerically demonstrated. The setup includes two cascaded Mach-Zehnder Modulators (MZMs), a sinusoidal wave oscillator, and an electrical time delay. The first MZM is driven directly by a sinusoidal wave, while the second MZM is driven by a delayed replica of the sinusoidal wave. A mathematical model of the proposed system is formulated and modeled using the Matlab software. It is shown that the number of the frequency lines is directly proportional to the chirp factor. In order to achieve the highest number of frequency comb lines with the best flatness, the time delay between the driving voltages of the two MZMs is optimized. Our results reveal that at least 51 frequency lines can be observed at the output spectrum. In addition, 27 of these lines have power fluctuations of less than 1 dB. The performance of the proposed system is also simulated using a split-step numerical analysis. An optical frequency comb, with tunable frequency spacing ranging from 5 to 40 GHz, is successfully generated.

Hmood, Jassim K.; Emami, Siamak D.; Noordin, Kamarul A.; Ahmad, Harith; Harun, Sulaiman W.; Shalaby, Hossam M. H.

2015-06-01

430

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

SciTech Connect

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. (nonlinear optical phenomena)

Kim, G H; Yang, J; Kulik, A V; Sall, E G; Chizhov, S A; Kang, U [KERI, Russia Science Seuol, 612, DMC, Hi-Tech Industry Center, 1580 Sangam-dong, Mapo-gu, 121-835 Seoul (Korea, Republic of); Yashin, V E [Federal State Unitary Enterprise ' Scientific and Industrial Corporation 'Vavilov State Optical Institute', St. Petersburg (Russian Federation)

2013-08-31

431

Acetylene measurement in flames by chirp-based quantum cascade laser spectrometry.  

PubMed

We have designed and characterized a mid-IR spectrometer built around a pulsed distributed-feedback quantum cascade laser using the characteristic frequency down-chirp to scan through the spectral region 6.5 cm(-1) spectral region. The behavior of this chirp is extensively measured. The accuracy and detection limits of the system as an absorption spectrometer are demonstrated first by measuring spectra of acetylene through a single pass 16 cm absorption cell in real time at low concentrations and atmospheric pressure. The smallest detectable peak is measured to be approximately 1.5 x 10(-4) absorbance units, yielding a minimum detectable concentration length product of 2.4 parts per million meter at standard temperature and pressure. This system is then used to detect acetylene within an ethylene-air opposed flow flame. Measurements of acetylene content as a function of height above the fuel source are presented, as well as measurements of acetylene produced in fuel breakdown as a function of preinjection fuel temperature. PMID:19488121

Quine, Zachary R; McNesby, Kevin L

2009-06-01

432

Transformation Composition  

E-print Network

Proc. AGTIVE'99, to appear in LNCS Graph Transformation Modules and their Composition ? Frank,knirsch,kreo,kuskeg@informatik.uni-bremen.de Abstract. In this paper, we investigate the notion of transformation modules as a structuring principle. Based on the notion of transformation units, a concept that allows to specify binary relations on graphs

Drewes, Frank

433

transformations: representations  

E-print Network

Overview 1. Number transformations: from one base to another 2. Integer representations 3. Real rate, caches... #12; ECS 50, Discussion on 4/25 2 Integer Transformation: From Decimal to Binary Let, Discussion on 4/25 3 Integer Transformation: From Binary to Decimal Compute the weight of each digit position

Nguyen, Dat H.

434

Transformation Station  

NSDL National Science Digital Library

Shapes are all over the place in geometry. One way we can move these shapes is with transformations. Use these games to help you practice and identify the three types of transformations: reflections, translations, and rotations. Just as a refresher, watch this video about transformational geometry: Gingerbread Transformer! When you are ready...start playing the games!! Take it to the court for Basketball Geometry! Once you type in your name and choose a player, pay attention to the coach for a review on the three types of transformations. While you play, ...

Mrs. Stroud

2010-09-01

435

On a Chirplet Transform Based Method for Co-channel Voice Separation  

NASA Astrophysics Data System (ADS)

We use signal and image theory based algorithms to produce estimations of the number of wolves emitting howls or barks in a given field recording as an individuals counting alternative to the traditional trace collecting methodologies. We proceed in two steps. Firstly, we clean and enhance the signal by using PDE based image processing algorithms applied to the signal spectrogram. Secondly, assuming that the wolves chorus may be modelled as an addition of nonlinear chirps, we use the quadratic energy distribution corresponding to the Chirplet Transform of the signal to produce estimates of the corresponding instantaneous frequencies, chirp-rates and amplitudes at each instant of the recording. We finally establish suitable criteria to decide how such estimates are connected in time.

Dugnol, B.; Fernández, C.; Galiano, G.; Velasco, J.

436

Traceability for Mutation Analysis in Model Transformation  

E-print Network

, verification techniques have to be adapted to model transformation specificity to make profit from the modelTraceability for Mutation Analysis in Model Transformation Vincent Aranega1 , Jean-Marie Mottu2-marie.mottu@univ-nantes.fr Abstract. Model transformation can't be directly tested using program techniques. Those have to be adapted

Paris-Sud XI, Université de

437

Chirped-Beam Two-Stage SASE-FEL for High Power Femtosceond X-Ray Pulse Generation  

NASA Astrophysics Data System (ADS)

We present a method for generating femtosecond duration x-ray pulses using a single-pass free-electron laser (FEL). This method uses an energy-chirped electron beam to produce a frequency-chirped x-ray pulse through self-amplified spontaneous emission (SASE). After the undulator we consider passing the radiation through a monochromator. The frequency is correlated to the longitudinal position within the pulse, and therefore, by selecting a narrow bandwidth, a short temporal pulse will be transmitted. The short pulse radiation is used to seed a second undulator, where the radiation is amplified to saturation. In addition to short pulse generation, this scheme has the ability to control shot-to-shot fluctuations in the central wavelength due to electron beam energy jitter. We present calculations of the radiation characteristics produced by a chirped beam two-stage SASE-FEL, and consider the performance of the chirped-beam two-stage option for the Linac Coherent Light Source (LCLS).

Schroeder, C. B.; Pellegrini, C.; Reiche, S.; Arthur, J.; Emma, P.

2002-08-01

438

Chirped-beam two-stage SASE-FEL for high power femtosecond X-ray pulse generation  

NASA Astrophysics Data System (ADS)

A method for generating femtosecond duration X-ray pulses using a single-pass free-electron laser (FEL) is presented. This method uses an energy-chirped electron beam propagating through an undulator to produce a frequency-chirped X-ray pulse through self-amplified spontaneous emission (SASE). After the undulator, we consider passing the radiation through a monochromator. The frequency is correlated to the longitudinal position within the pulse; therefore, by selecting a narrow bandwidth, a short temporal pulse will be transmitted. The short pulse radiation is used to seed a second undulator, where the radiation is amplified to saturation. In addition to short pulse generation, this scheme has the ability to control shot-to-shot fluctuations in the central wavelength due to electron beam energy jitter. We present calculations of the radiation characteristics produced by a chirped-beam two-stage SASE-FEL, and consider the performance of the chirped-beam two-stage option for the Linac Coherent Light Source.

Schroeder, C. B.; Pellegrini, C.; Reiche, S.; Arthur, J.; Emma, P.

2002-05-01

439

JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 20, OCTOBER 15, 2014 3573 Generation of Linearly Chirped Microwave  

E-print Network

), in the order of 102 or 103 , is required. In the electrical domain, such an LCMW can be generated usingJOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 20, OCTOBER 15, 2014 3573 Generation of Linearly Chirped Microwave Waveform With an Increased Time-Bandwidth Product Based on a Tunable Optoelectronic

Yao, Jianping

440

FPGA Implementation of Low-Frequency GPR signal algorithm using Frequency Stepped Chirp Signals in the time domain  

E-print Network

FPGA Implementation of Low-Frequency GPR signal algorithm using Frequency Stepped Chirp Signals for mapping GPR signal- processing algorithms on real-time hardware systems, such as the one considered time of the algorithm etc. In [1], a Stepped-Frequency Processing in Low-frequency GPR was considered

Kuzmanov, Georgi

441

A wide temperature tunable fibre laser using a chirped grating and a type IIA fibre Bragg grating  

Microsoft Academic Search

A fibre laser sensor has been developed to operate over a wide temperature range from room temperature to 440 °C, where the laser cavity has been formed using a combination of a chirped grating and a type IIA fibre Bragg grating (FBG), enclosing a length of erbium doped fibre as the active gain medium. A FBG stabilized 1480 nm laser

Jharna Mandal; Tong Sun; Kenneth T. V. Grattan; Andreas T. Augousti; Scott A. Wade; Stephen F. Collins; Gregory W. Baxter; Bernard Dussardier; Gérard Monnom

2004-01-01

442

Use of conventional and chirped optical fibre Bragg gratings to detect matrix cracking damage in composite materials  

Microsoft Academic Search

A comparison is made between conventional (i.e. uniform) and chirped optical fibre Bragg gratings (FBGs) for the detection of matrix cracking damage in composite materials. Matrix cracking damage is generally the first type of visible damage to develop under load in the off-axis plies of laminated composites and is generally the precursor of more serious damage mechanisms, particularly delamination. The

J. Palaniappan; H. Wang; S. L. Ogin; A. Thorne; G. T. Reed; S. C. Tjin

2005-01-01

443

CONTROL OF LASER RADIATION PARAMETERS: New stretcher scheme for a parametric amplifier of chirped pulses with frequency conversion  

NASA Astrophysics Data System (ADS)

The properties of hybrid prism-grating dispersion systems are studied. The scheme of a prism-grating stretcher matched to a standard compressor in the phase dispersion up to the fourth order inclusive is developed for a petawatt laser complex based on the optical parametric chirped-pulse amplification. The stretcher was used to obtain the ~200-TW peak power of laser radiation.

Freidman, Gennadii I.; Yakovlev, I. V.

2007-02-01

444

PUBLISHED ONLINE: 19 DECEMBER 2010 | DOI: 10.1038/NPHYS1867 Quantum fluctuations in the chirped pendulum  

E-print Network

in the chirped pendulum K. W. Murch1 *, R. Vijay1 , I. Barth2 , O. Naaman1 , J. Aumentado3 , L. Friedland2 and I. Siddiqi1 Anharmonic oscillators, such as the pendulum, are widely used for precision measurement1 is the electron charge. This system is analogous to a mechanical pendulum with angular coordinate = (Fig. 1a

Loss, Daniel

445

Novel Applications of Chirp Managed Laser in Optical Fiber Communication Systems  

NASA Astrophysics Data System (ADS)

Nowadays, with the dramatically growing bandwidth requirement of Internet, the number of wavelength division multiplexing (WDM) channels of the optical fiber communication systems is increasing rapidly. Hence, optical transmitters with cost effectiveness, high power efficiency, and excellent transmission performance are necessary. Especially, for access and metropolitan applications, simple configuration is the essential factor. The conventional optical transmitter is composed of a laser as continuous-wave (CW) source and one or more external modulators for modulation. However, the high insertion loss, large driving voltage, and extra cost of external modulator make it relatively bulky and power-hungry. Chirp managed laser (CML), comprising a directly modulated semiconductor laser (DML) and a passive optical filter, is an alternative promising transmitter candidate. It has the merits of smaller device size, lower cost, less power consumption, and higher fiber chromatic dispersion (CD) tolerance, compared with that based on external modulator. In this thesis, we have investigated several novel applications of CML in optical fiber communication systems, taking advantage of its unique phase modulating and spectral reshaping properties. These topics include optical return-to-zero (RZ) pulses generation using CML, M-ary RZ differential phase-shift-keying (RZ-DPSK) signals generation using CML, and enhanced CD tolerance of CML with pre-emphasis. These CML-based designs consume low power for less electrical pre-coding, require reduced or no external modulator, and show notable transmission performances. Optical RZ pulses generation using CML: RZ pulses have been widely used in optical fiber communication systems together with on-off-keying (OOK) and DPSK modulation formats, for its high robustness towards inter symbol interference (ISI) and nonlinear distortions. In this thesis, we propose and experimentally demonstrate the technique of 10-Gb/s optical RZ pulses generation using CML. No external modulator is used for pulse carving. The frequency of the sinusoidal driving signal is half the output RZ pulse rate. 70-km and 50-km error-free SSMF transmissions have been achieved for the 10-Gb/s 33%-duty-cycle and 67%-duty-cycle CML-RZ- pulses based RZ-DPSK signals, respectively. Later, we extend to demonstrate the scheme of 20-Gb/s RZ pulses generation using CML driven at one-fourth the output pulse rate and investigate the transmission performance of the 20-Gb/s CML-RZ-pulses based RZ-OOK signal. M-ary RZ-DPSK signals generation using CML: M-ary RZ-DPSK is an attractive modulation format in optical fiber long-haul transmission systems, due to the advantages of high receiver sensitivity, increased spectral efficiency, and strong robustness against fiber nonlinearities. In this thesis, we propose and experimentally demonstrate the techniques of RZ-DPSK, ¾-RZ-DQPSK, and RZ-DQPSK signals generation using CML. First, we generate the 10-Gb/s RZ-DPSK signal using CML and pulse carver. It does not require any differential encoder or phase modulator (PM). The CML-based RZ-DPSK signal shows 3-dB higher receiver sensitivity after 70-km SSMF transmission without dispersion compensation and comparable nonlinear tolerance performance, compared with that generated by PM. Next, this proposal is generalized to generate the 10-Gbaud RZ-DQPSK signal using CML and pulse carver. Compared with the complex pre-coding required for the MZM-based RZ-DQPSK transmitter, only a simple exclusive-or (XOR) encoder is needed for that based on CML. Later, we demonstrate the scheme of 10-Gbaud ¾-RZ-DQPSK signal generation using single CML, without the need for external pulse carver. In this new signal format, the symbols with a differential phase shift of 0 remain non-return-to-zero (NRZ), while those with differential phase shifts of 0.5pi, pi, and 1.5pi are RZ. Error-free transmission is realized over 60-km SSMF without optical signal-noise-ratio (OSNR) penalty. Finally, we demonstrate the technique of 10.709-Gbaud RZ-DQPSK signal generation using single CML, w

Jia, Wei

446

A real-time chirp-coded imaging system with tissue attenuation compensation.  

PubMed

In ultrasound imaging, pulse compression methods based on the transmission (TX) of long coded pulses and matched receive filtering can be used to improve the penetration depth while preserving the axial resolution (coded-imaging). The performance of most of these methods is affected by the frequency dependent attenuation of tissue, which causes mismatch of the receiver filter. This, together with the involved additional computational load, has probably so far limited the implementation of pulse compression methods in real-time imaging systems. In this paper, a real-time low-computational-cost coded-imaging system operating on the beamformed and demodulated data received by a linear array probe is presented. The system has been implemented by extending the firmware and the software of the ULA-OP research platform. In particular, pulse compression is performed by exploiting the computational resources of a single digital signal processor. Each image line is produced in less than 20?s, so that, e.g., 192-line frames can be generated at up to 200fps. Although the system may work with a large class of codes, this paper has been focused on the test of linear frequency modulated chirps. The new system has been used to experimentally investigate the effects of tissue attenuation so that the design of the receive compression filter can be accordingly guided. Tests made with different chirp signals confirm that, although the attainable compression gain in attenuating media is lower than the theoretical value expected for a given TX Time-Bandwidth product (BT), good SNR gains can be obtained. For example, by using a chirp signal having BT=19, a 13dB compression gain has been measured. By adapting the frequency band of the receiver to the band of the received echo, the signal-to-noise ratio and the penetration depth have been further increased, as shown by real-time tests conducted on phantoms and in vivo. In particular, a 2.7dB SNR increase has been measured through a novel attenuation compensation scheme, which only requires to shift the demodulation frequency by 1MHz. The proposed method characterizes for its simplicity and easy implementation. PMID:25749529

Ramalli, A; Guidi, F; Boni, E; Tortoli, P

2015-07-01

447

Long-term stable passive synchronization of 50 µJ femtosecond Yb-doped fiber chirped-pulse amplifier with a mode-locked Ti:sapphire laser.  

PubMed

We report long-term stable passive synchronization of a femtosecond Yb-doped fiber chirped-pulse amplifier (CPA) with a mode-locked Ti:sapphire laser for pump-seed synchronization of an optical parametric chirped-pulse amplification (OPCPA) system. The fiber CPA system delivers pulses with a wavelength of 1035 nm, energy of 50 µJ, and duration of 690 fs at a repetition rate of 0.4 MHz. The seed fiber oscillator is passively synchronized with a mode-locked Ti:sapphire laser by injection of the Ti:sapphire laser pulses into the cavity of the fiber oscillator. The second harmonic (SH) output with a wavelength of 518 nm, energy of 18 µJ, and duration of 1.2 ps was prepared for the OPCPA pump. The measured timing jitter between the pump (fiber SH) and the seed (Ti:sapphire) was 42 ± 14 fs, while the jitter between two oscillator outputs was 1.4 ± 0.5 fs. The robust synchronization technique allows long-term stable operation over 8 h. PMID:21164950

Yoshitomi, Dai; Zhou, Xiangyu; Kobayashi, Yohei; Takada, Hideyuki; Torizuka, Kenji

2010-12-01

448

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.

2003-01-24

449

An approach to forward looking FMCW radar imaging based on two-dimensional Chirp-Z transform  

Microsoft Academic Search

Airborne forward looking radar imaging, which is an important work mode of imaging radar system, has many advantages combined\\u000a with frequency modulated continuous wave (FMCW) technology. This paper studies the configuration with one central antenna\\u000a element for signal transmitting and other antenna elements for signal receiving. According to its imaging geometry, the analytical\\u000a expression of the received signal for forward

Yi Liang; HongXian Wang; Long Zhang; Zheng Bao

2010-01-01

450

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 170°C. 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

451

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

452

Multiband cyclic wavelet transforms  

Microsoft Academic Search

Multiresolution analysis via decomposition into wavelets has been established as an important transform technique in signal processing. A wealth of results is available on this subject, the framework has been extended to treat finite length sequences of size 2n (for positive integers n) over finite fields. The paper extends this idea further to provide a framework for dealing with data

Sandip Sarkar; H. V. Poor

1996-01-01

453

Review article Genetic transformation  

E-print Network

Review article Genetic transformation: a short review of methods and their applications, results — This report reviews the state-of-the-art in plant genetic engineering, covering both di- rect and indirect gene transfer methods. The application of these techniques to forest trees has been discussed

Paris-Sud XI, Université de

454

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

455

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; Höppner, H; Tavella, F

2014-01-27

456

Complex, aperiodic random signal modulation on pulse-LFM chirp radar waveform  

NASA Astrophysics Data System (ADS)

In an effort to enhance the security of radar, the plausibility of using a complex, aperiodic random signal to modulate a pulse linear frequency modulation (LFM) or "chirp" radar waveform across both its fast-time and slow-time samples is investigated. A non-conventional threat is considered when illustrating the effectiveness of the proposed waveform as an electronic counter-countermeasure (ECCM). Results are derived using stretch processing and are assessed using the receiver cross-correlation function with a consideration for the unmodulated case as a basis for comparison. A tailored radar ambiguity function is also included in the analysis, and is used to demonstrate how the proposed waveform possesses an ideal characteristic suitable for combating today's electronic warfare (EW) threats while preserving its inherent functionality to detect targets.

Govoni, Mark A.; Li, Hongbin

2010-04-01

457

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; Höppner, H; Schulz, M; Teubner, U; Kränkel, C; Limpert, J; Tünnermann, A; Prandolini, M J; Tavella, F

2014-07-28

458

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

459

The Effective CSR Forces on an Energy-Chirped Bunch under Magnetic Compression  

SciTech Connect

Following our earlier formulation of the coherent synchrotron radiation (CSR) effect on bunch dynamics in magnetic bends, here we investigate the behavior of the effective CSR forces for an energy-chirped Gaussian bunch in the bending plane around full compression, with special care being taken in the incorporation of the retardation relation. Our results show clearly a delayed response of the CSR forces to the compression or lengthening of the bunch length. In addition, around full compression, our results reveal sensitivity of the effective CSR forces on the particles' transverse position, as a consequence of the geometry of particle interaction and retardation in this regime. These results can serve as benchmarks to the numerical simulation of the CSR effects.

Rui Li

2007-06-25

460

Linearization of an analog photonic link based on chirp modulation and fiber dispersion  

NASA Astrophysics Data System (ADS)

A simple and new method to linearize an analog photonic link is proposed and demonstrated. A dual-electrode Mach–Zehnder modulator is single-electrode driven by a radio frequency (RF) signal, with the other electrode left empty, to achieve a chirp modulation. Then a dispersive single mode fiber (SMF) is followed to introduce different phase shifts on different optical sidebands. By properly selecting the working point of the modulator and the fiber length, the third-order intermodulation distortion can be suppressed. Experimental results show that an improvement of 15.7 dB in the spurious-free dynamic range and 4.5 dB in the link gain is achieved after linearization. The scheme is simple, low cost, and the low-loss SMF can also act as a transmission medium to deliver the RF signal efficiently to a remote location.

Gao, Yongsheng; Wen, Aijun; Cao, Junjie; Chen, Yan; Zhang, Huixing

2015-03-01