WorldWideScience

Sample records for cavity-enhanced direct frequency

  1. Analysis of Trace Impurities in Semiconductor Gas via Cavity-Enhanced Direct Frequency Comb Spectroscopy

    OpenAIRE

    Cossel, Kevin C.; Adler, Florian; Bertness, Kris A.; Thorpe, Michael J.; Feng, Jun; Raynor, Mark W.; Ye, Jun

    2010-01-01

    Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) has demonstrated powerful potential for trace gas detection based on its unique combination of high bandwidth, rapid data acquisition, high sensitivity, and high resolution, which is unavailable with conventional systems. However, previous demonstrations have been limited to proof-of-principle experiments or studies of fundamental laboratory science. Here we present the development of CE-DFCS towards an industrial application -- mea...

  2. Frequency-feedback cavity enhanced spectrometer

    Science.gov (United States)

    Hovde, David Christian; Gomez, Anthony

    2015-08-18

    A spectrometer comprising an optical cavity, a light source capable of producing light at one or more wavelengths transmitted by the cavity and with the light directed at the cavity, a detector and optics positioned to collect light transmitted by the cavity, feedback electronics causing oscillation of amplitude of the optical signal on the detector at a frequency that depends on cavity losses, and a sensor measuring the oscillation frequency to determine the cavity losses.

  3. Cavity-enhanced optical frequency combspectroscopy

    DEFF Research Database (Denmark)

    Balslev-Clausen, David Morten; Thorpe, M. J.; Kirchner, M. S.;

    2008-01-01

    Broad-bandwidth, high-spectral-resolution optical detection of human breath has identified multiple important biomarkers correlated with specific diseases and metabolic processes. This optical-frequency-comb-based breath analysis system comes with excellent performance in all criteria: high...

  4. Continuous Vernier filtering of an optical frequency comb for broadband cavity-enhanced molecular spectroscopy

    CERN Document Server

    Rutkowski, Lucile

    2016-01-01

    We have recently introduced the Vernier-based Direct Frequency Comb Cavity-Enhanced Spectroscopy technique and we present the corresponding formalism for quantitative broadband spectroscopy. We achieve high sensitivity and broadband performance by acquiring spectra covering more than 2000 cm$^{-1}$ around 12600 cm$^{-1}$ (800 nm), resolving the 3$\

  5. a New Broadband Cavity Enhanced Frequency Comb Spectroscopy Technique Using GHz Vernier Filtering.

    Science.gov (United States)

    Morville, Jérôme; Rutkowski, Lucile; Dobrev, Georgi; Crozet, Patrick

    2015-06-01

    We present a new approach to Cavity Enhanced - Direct Frequency Comb Spectroscopy where the full emission bandwidth of a Titanium:Sapphire laser is exploited at GHz resolution. The technique is based on a low-resolution Vernier filtering obtained with an appreciable -actively stabilized- mismatch between the cavity Free Spectral Range and the laser repetition rate, using a diffraction grating and a split-photodiode. This particular approach provides an immunity to frequency-amplitude noise conversion, reaching an absorption baseline noise in the 10-9 cm-1 range with a cavity finesse of only 3000. Spectra covering 1800 cm-1 (˜ 55 THz) are acquired in recording times of about 1 second, providing an absorption figure of merit of a few 10-11 cm-1/√{Hz}. Initially tested with ambient air, we report progress in using the Vernier frequency comb method with a discharge source of small radicals. Rutkowski et al, Opt. Lett., 39(23)2014

  6. Cavity-Enhanced Frequency-Agile Rapid Scanning (fars) Spectroscopy: Measurement Principles

    Science.gov (United States)

    Hodges, Joseph T.; Long, David A.; Truong, Gar-Wing; Douglass, Kevin O.; Maxwell, Stephen E.; Zee, Roger Van; Plusquellic, David F.

    2013-06-01

    We present the principles of frequency-agile, rapid scanning (FARS) spectroscopy, a new technique for high-bandwidth, cavity-enhanced, laser absorption measurements. This method enables a visible or near-infrared probe laser beam to be frequency tuned over several tens of GHz using a microwave source, a waveguide phase modulator and a filter cavity. For the types of cavity-enhanced methods discussed here, the optical resonator itself is used to select a single sideband of the modulated laser spectrum, obviating the need for a separate filter cavity. FARS offers several important advantages over conventional cw laser tuning methods based on thermal or mechanical methods. These include, high speed tuning with sub-ms switching times, the ability to select arbitrary frequency steps or chirp rates, and the realization of a spectrum detuning axis with sub-kHz level precision. We discuss how FARS can be applied to cavity ring-down spectroscopy and other cavity-enhanced methods to enable rapid and accurate measurements of line parameters and to give noise-equivalent absorption coefficients at the 10^{-12} cm^{-1} Hz^{-1/2} level.

  7. Cavity-Enhanced Frequency-Agile Rapid Scanning (fars) Spectroscopy: Experimental Realizations and Measurement Results

    Science.gov (United States)

    Long, David A.; Truong, Gar-Wing; Zee, Roger Van; Plusquellic, David F.; Hodges, Joseph T.

    2013-06-01

    We present a series of experimental realizations of cavity-enhanced, frequency-agile rapid scanning (FARS) spectroscopy using distributed feedback diode lasers, external cavity diode lasers, and ultra-narrow linewidth fiber lasers. FARS offers a scanning rate which is limited only by the cavity response time itself as well as a microwave-level frequency axis. Finally, it allows for an absorption sensitivity which is one of the highest ever reported. These realizations offer a range of applications from low-cost field measurements of trace gases to laboratory-based metrology.

  8. Cavity-enhanced spectroscopies

    CERN Document Server

    van Zee, Roger

    2003-01-01

    ""Cavity-Enhanced Spectroscopy"" discusses the use of optical resonators and lasers to make sensitive spectroscopic measurements. This volume is written by the researcchers who pioneered these methods. The book reviews both the theory and practice behind these spectroscopic tools and discusses the scientific discoveries uncovered by these techniques. It begins with a chapter on the use of optical resonators for frequency stabilization of lasers, which is followed by in-depth chapters discussing cavity ring-down spectroscopy, frequency-modulated, cavity-enhanced spectroscopy, intracavity spectr

  9. Cavity-enhanced single frequency synthesis via DFG of mode-locked pulse trains

    OpenAIRE

    Ferrari, Gabriele; Carusotto, Iacopo

    2005-01-01

    We show how to synthesize a CW, single-frequency optical field from the frequency-dispersed, pulsed field of a mode-locked laser. This process, which relies on difference frequency generation in an optical cavity, is efficient and can be considered as an optical rectification. Quantitative estimates for the output power and amplitude noise properties of a realistic system are given. Possible applications to optical frequency synthesis and optical metrology are envisaged.

  10. Noise-immune cavity-enhanced optical frequency comb spectroscopy: A sensitive technique for high-resolution broadband molecular detection

    CERN Document Server

    Khodabakhsh, Amir; Foltynowicz, Aleksandra

    2014-01-01

    Noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS) is a recently developed technique that utilizes phase modulation to obtain immunity to frequency-to-amplitude noise conversion by the cavity modes and yields high absorption sensitivity over a broad spectral range. We describe the principles of the technique and discuss possible comb-cavity matching solutions. We present a theoretical description of NICE-OFCS signals detected with a Fourier transform spectrometer (FTS), and validate the model by comparing it to experimental CO2 spectra around 1575 nm. Our system is based on an Er:fiber femtosecond laser locked to a cavity and phase-modulated at a frequency equal to a multiple of the cavity free spectral range (FSR). The NICE-OFCS signal is detected by a fast-scanning FTS equipped with a high-bandwidth commercial detector. We demonstrate a simple method of passive locking of the modulation frequency to the cavity FSR that significantly improves the long term stability of the system, a...

  11. Human breath analysis via cavity-enhanced optical frequency comb spectroscopy

    CERN Document Server

    Thorpe, Michael J; Kirchner, Matthew S; Ye, Jun

    2007-01-01

    To date, researchers have identified over 1000 different compounds contained in human breath. These molecules have both endogenous and exogenous origins and provide information about physiological processes occurring in the body as well as environment-related ingestion or absorption of contaminants1,2. While the presence and concentration of many of these molecules are poorly understood, many 'biomarker' molecules have been correlated to specific diseases and metabolic processes. Such correlations can result in non-invasive methods of health screening for a wide variety of medical conditions. In this article we present human breath analysis using an optical-frequency-comb-based trace detection system with excellent performance in all criteria: detection sensitivity, ability to identify and distinguish a large number of biomarkers, and measurement time. We demonstrate a minimum detectable absorption of 8 x 10-10 cm-1, a spectral resolution of 800 MHz, and 200 nm of spectral coverage from 1.5 to 1.7 micron wher...

  12. Walk-off-induced modulation instability, temporal pattern formation, and frequency comb generation in cavity-enhanced second-harmonic generation

    CERN Document Server

    Leo, F; Ricciardi, I; De Rosa, M; Coen, S; Wabnitz, S; Erkintalo, M

    2016-01-01

    We derive a time-domain mean-field equation to model the full temporal and spectral dynamics of light in singly resonant cavity-enhanced second-harmonic generation systems. We show that the temporal walk-off between the fundamental and the second-harmonic fields plays a decisive role under realistic conditions, giving rise to rich, previously unidentified nonlinear behaviour. Through linear stability analysis and numerical simulations, we discover a new kind of quadratic modulation instability which leads to the formation of optical frequency combs and associated time-domain dissipative structures. Our numerical simulations show excellent agreement with recent experimental observations of frequency combs in quadratic nonlinear media [Phys. Rev. A 91, 063839 (2015)]. Thus, in addition to unveiling a new, experimentally accessible regime of nonlinear dynamics, our work enables predictive modeling of frequency comb generation in cavity-enhanced second-harmonic generation systems.

  13. Walk-Off-Induced Modulation Instability, Temporal Pattern Formation, and Frequency Comb Generation in Cavity-Enhanced Second-Harmonic Generation

    Science.gov (United States)

    Leo, F.; Hansson, T.; Ricciardi, I.; De Rosa, M.; Coen, S.; Wabnitz, S.; Erkintalo, M.

    2016-01-01

    We derive a time-domain mean-field equation to model the full temporal and spectral dynamics of light in singly resonant cavity-enhanced second-harmonic generation systems. We show that the temporal walk-off between the fundamental and the second-harmonic fields plays a decisive role under realistic conditions, giving rise to rich, previously unidentified nonlinear behavior. Through linear stability analysis and numerical simulations, we discover a new kind of quadratic modulation instability which leads to the formation of optical frequency combs and associated time-domain dissipative structures. Our numerical simulations show excellent agreement with recent experimental observations of frequency combs in quadratic nonlinear media [Phys. Rev. A 91, 063839 (2015)]. Thus, in addition to unveiling a new, experimentally accessible regime of nonlinear dynamics, our work enables predictive modeling of frequency comb generation in cavity-enhanced second-harmonic generation systems. We expect our findings to have wide impact on the study of temporal and spectral dynamics in a diverse range of dispersive, quadratically nonlinear resonators.

  14. Long Wave Infrared Cavity Enhanced Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Taubman, Matthew S.; Scott, David C.; Cannon, Bret D.; Myers, Tanya L.; Bonebrake, Christopher A.; Aker, Pam M.; Wojcik, Michael D.; Munley, John T.; Nguyen, Vinh T.; Schultz, John F.

    2004-10-01

    The principal goal of Pacific Northwest National Laboratory's (PNNL's) long wave infrared (LWIR) cavity enhanced sensor (CES) project is to explore ultra-sensitive spectroscopic techniques and apply them to the development of LWIR chemical sensors needed for detecting weapons proliferation. This includes detecting not only the weapons of mass destruction (WMDs) themselves, but also signatures of their production and/or detonation. The LWIR CES project is concerned exclusively with developing point sensors; other portions of PNNL's IR Sensors program address stand off detection. PNNL's LWIR CES research is distinguished from that done by others by the use quantum cascade lasers (QCLs) as the light source. QCLs are novel devices, and a significant fraction of our research has been devoted to developing the procedures and hardware required to implement them most effectively for chemical sensing. This report details the progress we have made on our LWIR CES sensor development. During FY02, PNNL investigated three LWIR CES implementations beginning with the easiest to implement, direct cavity-enhanced detection (simple CES), including a technique of intermediate difficulty, cavity-dithered phase-sensitive detection (FM recovery CES) through to the most complex technique, that of resonant sideband cavity-enhanced detection also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy, or NICE-OHMS.

  15. Molecular frequency reference at 1.56  μm using a 12C16O overtone transition with the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy method.

    Science.gov (United States)

    Saraf, Shailendhar; Berceau, Paul; Stochino, Alberto; Byer, Robert; Lipa, John

    2016-05-15

    We report on a molecular clock based on the interrogation of the 3ν rotational-vibrational combination band at 1563 nm of carbon monoxide C1612O. The laser stabilization scheme is based on the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique in frequency modulation (FM) saturation spectroscopy. We use a high-finesse ultra-low expansion (ULE) glass optical cavity with CO as the molecular reference for long-term stabilization of the cavity resonance. We report an Allan deviation of 1.8×10-12 at 1 s that improves to ∼3.5×10-14 with 1000 s of averaging. PMID:27176959

  16. Development of a cavity enhanced aerosol albedometer

    Directory of Open Access Journals (Sweden)

    W. Zhao

    2014-03-01

    Full Text Available We report on the development of a cavity enhanced aerosol single scattering albedometer incorporating incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS approach and an integrating sphere (IS for simultaneous in situ measurements of aerosol scattering and extinction coefficients in the exact same sample volume. The cavity enhanced albedometer employed a blue light-emitting diode (LED based IBBCEAS approach for the measurement of wavelength-resolved aerosol optical extinction over the spectral range of 445–480 nm. An integrating sphere nephelometer coupled to the IBBCEAS setup was used for the measurement of aerosol scattering. The scattering signal was measured with a single channel photomultiplier tube (PMT, providing an integrated value over a narrow bandwidth (FWHM ~ 9 nm in the spectral region of 465–474 nm. A scattering coefficient at a wavelength of 470 nm was deduced as an averaged scattering value and used for data analysis and instrumental performance comparison. Performance evaluation of the albedometer was carried out using laboratory-generated particles and ambient aerosol. The scattering and extinction measurements of monodisperse polystyrene latex (PSL spheres generated in laboratory proved excellent correlation between two channels of the albedometer. The retrieved refractive index (RI from the measured scattering and extinction efficiencies agreed well with the values reported in previously published papers. Aerosol light scattering and extinction coefficients, single scattering albedo (SSA and NO2 concentrations in an ambient sample were directly and simultaneously measured using the developed albedometer. The developed instrument was validated via an intercomparison of the measured aerosol scattering coefficient and NO2 trace concentration against a TSI 3563 integrating nephelometer and a chemiluminescence detector, respectively.

  17. Cavity-enhanced spectroscopy and sensing

    CERN Document Server

    Loock, Hans-Peter

    2014-01-01

    The book reviews the dramatic recent advances in the use of optical resonators for high sensitivity and high resolution molecular spectroscopy as well as for chemical, mechanical and physical sensing.  It encompasses a variety of cavities including those made of two or more mirrors, optical fiber loops, fiber gratings and spherical cavities. The book focuses on novel techniques and their applications. Each chapter is written by an expert and/or pioneer in the field. These experts also provide the theoretical background in optics and molecular physics where needed. Examples of recent breakthroughs include the use of frequency combs (Nobel prize 2005) for cavity enhanced sensing and spectroscopy, the use of novel cavity materials and geometries, the development of optical heterodyne detection techniques combined to active frequency-locking schemes. These methods allow the use and interrogation of optical resonators with a variety of coherent light sources for trace gas detection and sensing of strain, temperat...

  18. Development of a cavity enhanced aerosol albedometer

    OpenAIRE

    Zhao, W.; Xu, X.; Dong, M.; Chen, W.; X. Gu; Hu, C; Huang, Y.; Gao, X; Huang, W.; Zhang, W

    2014-01-01

    We report on the development of a cavity enhanced aerosol single scattering albedometer incorporating incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS) approach and an integrating sphere (IS) for simultaneous in situ measurements of aerosol scattering and extinction coefficients in the exact same sample volume. The cavity enhanced albedometer employed a blue light-emitting diode (LED) based IBBCEAS approach for the measurement of wavelength-resolv...

  19. Real-time multiplexed digital cavity-enhanced spectroscopy

    International Nuclear Information System (INIS)

    Cavity-enhanced spectroscopy is a sensitive optical absorption technique but one where the practical applications have been limited to studying small wavelength ranges. In addition, this Letter shows that wideband operation can be achieved by combining techniques usually reserved for the communications community with that of cavity-enhanced spectroscopy, producing a multiplexed real-time cavity-enhanced spectrometer. We use multiple collinear laser sources operating asynchronously and simultaneously while being detected on a single photodetector. This is synonymous with radio frequency (RF) cellular systems in which signals are detected on a single antenna but decoded uniquely. Here, we demonstrate results with spectra of methyl salicylate and show parts-per-billion per root hertz sensitivity measured in real-time

  20. Cavity-enhanced Raman Microscopy of Individual Carbon Nanotubes

    CERN Document Server

    Hümmer, Thomas; Hofmann, Matthias S; Hänsch, Theodor W; Högele, Alexander; Hunger, David

    2015-01-01

    Raman spectroscopy reveals chemically specific information, and combined with imaging provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here we use a tunable high-finesse optical microcavity to demonstrate Purcell enhancement of Raman scattering in combination with high-resolution scanning-cavity imaging. We detect cavity-enhanced Raman spectra of individual single-walled carbon nanotubes, expand the technique to hyperspectral imaging, and co-localize measurements with cavity-enhanced absorption microscopy. Direct comparison with confocal Raman microscopy yields a 550-times enhanced collectable Raman scattering spectral density and a 11-fold enhancement of the integrated count rate. The quantitative character, the inherent spectral filtering, and the absence of intrinsic background in cavity-vacuum stimulated Raman scattering renders our technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman tran...

  1. Cavity-enhanced frequency doubling from 795nm to 397.5nm ultra-violet coherent radiation with PPKTP crystals in the low pump power regime.

    Science.gov (United States)

    Wen, Xin; Han, Yashuai; Bai, Jiandong; He, Jun; Wang, Yanhua; Yang, Baodong; Wang, Junmin

    2014-12-29

    We demonstrate a simple, compact and cost-efficient diode laser pumped frequency doubling system at 795 nm in the low power regime. In two configurations, a bow-tie four-mirror ring enhancement cavity with a PPKTP crystal inside and a semi-monolithic PPKTP enhancement cavity, we obtain 397.5nm ultra-violet coherent radiation of 35mW and 47mW respectively with a mode-matched fundamental power of about 110mW, corresponding to a conversion efficiency of 32% and 41%. The low loss semi-monolithic cavity leads to the better results. The constructed ultra-violet coherent radiation has good power stability and beam quality, and the system has huge potential in quantum optics and cold atom physics. PMID:25607194

  2. Direct Frequency Comb Measurement of OD + CO -> DOCO Kinetics

    CERN Document Server

    Bjork, Bryce J; Heckl, Oliver H; Changala, P Bryan; Spaun, Ben; Heu, Paula; Follman, David; Deutsch, Christoph; Cole, Garrett D; Aspelmeyer, Markus; Okumura, Mitchio; Ye, Jun

    2016-01-01

    The kinetics of the OH + CO reaction, fundamental to both atmospheric and combustion chemistry, are complex due to the formation of the HOCO intermediate. Despite extensive studies on this reaction, HOCO has not been observed at thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observe OD + CO reaction kinetics with the detection of stabilized trans-DOCO, the deuterated analogue of trans-HOCO, and its yield. By simultaneously measuring the time-dependent concentrations of both trans-DOCO and OD species, we observe unambiguous low-pressure termolecular dependence on the reaction rate coefficients for both N2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield.

  3. Cavity-Enhanced Immunoassay Measurements in Microtiter Plates Using BBCEAS.

    Science.gov (United States)

    Bajuszova, Zuzana; Ali, Zulfiqur; Scott, Simon; Seetohul, L Nitin; Islam, Meez

    2016-05-17

    We report on the first detailed use of broadband cavity enhanced absorption spectroscopy (BBCEAS) as a detection system for immunoassay. A vertical R ≥ 0.99 optical cavity was integrated with a motorized XY stage, which functioned as a receptacle for 96-well microtiter plates. The custom-built cavity enhanced microplate reader was used to make measurements on a commercially available osteocalcin sandwich ELISA kit. A 30-fold increase in path length was obtained with a minimum detectable change in the absorption coefficient, αmin(t), of 5.3 × 10(-5) cm(-1) Hz(-1/2). This corresponded to a 39-fold increase in the sensitivity of measurement when directly compared to measurements in a conventional microplate reader. Separate measurements of a standard STREP-HRP colorimetric reaction in microtiter plates of differing optical quality produced an increase in sensitivity of up to 115-fold compared to a conventional microplate reader. The sensitivity of the developed setup compared favorably with previous liquid-phase cavity enhanced studies and approaches the sensitivity of typical fluorometric ELISAs. It could benefit any biochemical test which uses single pass absorption as a detection method, through either the label free detection of biologically important molecules at lower concentrations or the reduction in the amount of expensive biochemicals needed for a particular test, leading to cheaper tests. PMID:27089516

  4. High Frequency Trade Direction Prediction

    OpenAIRE

    Stav, Augustine Dexter

    2015-01-01

    High Frequency Trade Direction PredictionbyAugustine StavAbstract High frequency trading involves large volumes and rapid price changes. The Volume Synchronized Probability of Informed Trading (VPIN) metric characterizes order flow toxicity. This toxicity is the unbalance of order flow between informed traders who possess knowledge of future price directions and market makers who do not have this information. VPIN requires trades to be classified as buys or sells and works with volume as a pr...

  5. Cavity-enhanced ultrafast two-dimensional spectroscopy using higher-order modes

    CERN Document Server

    Allison, Thomas K

    2016-01-01

    We describe methods using frequency combs and optical resonators for recording two-dimensional (2D) ultrafast spectroscopy signals with high sensitivity. By coupling multiple frequency combs to higher-order modes of one or more optical cavities, background-free, cavity-enhanced 2D spectroscopy signals are naturally generated via phase cycling. As in cavity-enhanced ultrafast transient absorption spectroscopy (CE-TAS), the signal to noise is enhanced by a factor proportional to the cavity finesse squared, so even using cavities of modest finesse, a very high sensitivity is expected, enabling ultrafast 2D spectroscopy experiments in dilute molecular beams.

  6. Cavity-Enhanced Raman Spectroscopy of Natural Gas with Optical Feedback cw-Diode Lasers

    OpenAIRE

    Hippler, M

    2015-01-01

    We report on improvements made on our previously introduced technique of cavity-enhanced Raman spectroscopy (CERS) with optical feedback cw-diode lasers in the gas phase, including a new mode-matching procedure which keeps the laser in resonance with the optical cavity without inducing long-term frequency shifts of the laser, and using a new CCD camera with improved noise performance. With 10 mW of 636.2 nm diode laser excitation and 30 s integration time, cavity enhancement achieves noise-eq...

  7. Long Wave Infrared Cavity Enhanced Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Taubman, Matthew S.; Scott, David C.; Cannon, Bret D.; Myers, Tanya L.; Munley, John T.; Nguyen, Vinh T.; Schultz, John F.

    2005-12-01

    The principal goal of Pacific Northwest National Laboratory's (PNNL's) long wave infrared (LWIR) cavity enhanced sensor (CES) task is to explore ultra-sensitive spectroscopic chemical sensing techniques and apply them to detecting proliferation of weapons of mass destruction (WMD). Our primary application is detecting signatures of WMD production, but LWIR CES techniques are also capable of detecting chemical weapons. The LWIR CES task is concerned exclusively with developing novel point sensors; stand-off detection is addressed by other PNNL tasks and projects. PNNL's LWIR CES research is distinguished from that done by others by the use quantum cascade lasers (QCLs) as the light source. QCLs are novel devices, and a significant fraction of our research has been devoted to developing the procedures and hardware required to implement them most effectively for chemical sensing. This report details the progress we have made on LWIR CES sensor development.

  8. Cavity-Enhanced Ultrafast Transient Absorption Spectroscopy

    CERN Document Server

    Reber, Melanie A R; Allison, Thomas K

    2015-01-01

    We present a new technique using a frequency comb laser and optical cavities for performing ultrafast transient absorption spectroscopy with improved sensitivity. Resonantly enhancing the probe pulses, we demonstrate a sensitivity of $\\Delta$OD $ = 1 \\times 10^{-9}/\\sqrt{\\mbox{Hz}}$ for averaging times as long as 30 s per delay point ($\\Delta$OD$_{min} = 2 \\times 10^{-10}$). Resonantly enhancing the pump pulses allows us to produce a high excitation fraction at high repetition-rate, so that signals can be recorded from samples with optical densities as low as OD $\\approx 10^{-8}$, or column densities $< 10^{10}$ molecules/cm$^2$. This high sensitivity enables new directions for ultrafast spectroscopy.

  9. Optical-Feedback Cavity-Enhanced Absorption Spectroscopy with a Quantum Cascade Laser.

    OpenAIRE

    Maisons, G.; Gorrotxategi Carbajo, P.; Carras, M.; Romanini, D.

    2010-01-01

    Optical{feedback cavity{enhanced absorption spectroscopy is demonstrated in the mid{IR using a quantum cascade laser (emitting at 4.46 ¹m). The laser linewidth reduction and frequency locking by selective optical feedback from the resonant cavity ¯eld turns out to be particularly important in this spectral range: It allows strong cavity transmission which compensates for low light sensitivity, especially when using room temperature detectors. We obtain a noise equivalent absorption coe±cient ...

  10. Cavity-enhanced frequency up-conversion in rubidium vapour

    CERN Document Server

    Offer, Rachel F; Riis, Erling; Franke-Arnold, Sonja; Arnold, Aidan S

    2016-01-01

    We report the first use of a ring cavity to both enhance the output power and dramatically narrow the linewidth ($<1\\,$MHz) of blue light generated by four wave mixing in a rubidium vapour cell. We find that the high output power available in our cavity-free system leads to power broadening of the generated blue light linewidth. Our ring cavity removes this limitation, allowing high output power and narrow linewidth to be achieved concurrently. As the cavity blue light is widely tunable over the $^{85}$Rb 5S$_{1/2} \\,\\,F=3$ $\\rightarrow$ 6P$_{3/2}$ transition, this narrow linewidth light would be suitable for second-stage laser cooling, which could be valuable for efficient $^{85}$Rb BEC production.

  11. Pump-probe differencing technique for cavity-enhanced, noise-canceling saturation laser spectroscopy

    CERN Document Server

    De Vine, G; Close, J D; Gray, M B; Vine, Glenn de; Clelland, David E. Mc; Close, John D.; Gray, Malcolm B.

    2004-01-01

    We present an experimental technique enabling mechanical-noise free, cavity-enhanced frequency measurements of an atomic transition and its hyperfine structure. We employ the 532nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The cell is placed in a traveling-wave Fabry-Perot interferometer (FPI) with counter-propagating pump and probe beams. The FPI is locked using the Pound-Drever-Hall (PDH) technique. Mechanical noise is rejected by differencing pump and probe signals. In addition, this differenced error signal gives a sensitive measure of differential non-linearity within the FPI.

  12. Direct frequency comb spectroscopy of trapped ions

    CERN Document Server

    Wolf, A L; Ubachs, W; Eikema, K S E

    2008-01-01

    Direct frequency comb spectroscopy of trapped ions is demonstated for the first time. It is shown that the 4s^2S_(1/2)-4p^2P_(3/2) transition in calcium ions can be excited directly with a frequency comb laser that is upconverted to 393 nm. Detection of the transition is performed using a shelving scheme to suppress background signal from non-resonant comb modes. The measured transition frequency of f=761 905 012.7(0.5) MHz presents an improvement in accuracy of more than two orders of magnitude.

  13. New Developments of Broadband Cavity Enhanced Spectroscopic Techniques

    Science.gov (United States)

    Walsh, A.; Zhao, D.; Linnartz, H.; Ubachs, W.

    2013-06-01

    In recent years, cavity enhanced spectroscopic techniques, such as cavity ring-down spectroscopy (CRDS), cavity enhanced absorption spectroscopy (CEAS), and broadband cavity enhanced absorption spectroscopy (BBCEAS), have been widely employed as ultra-sensitive methods for the measurement of weak absorptions and in the real-time detection of trace species. In this contribution, we introduce two new cavity enhanced spectroscopic concepts: a) Optomechanical shutter modulated BBCEAS, a variant of BBCEAS capable of measuring optical absorption in pulsed systems with typically low duty cycles. In conventional BBCEAS applications, the latter substantially reduces the signal-to-noise ratio (S/N), consequently also reducing the detection sensitivity. To overcome this, we incorporate a fast optomechanical shutter as a time gate, modulating the detection scheme of BBCEAS and increasing the effective duty cycle reaches a value close to unity. This extends the applications of BBCEAS into pulsed samples and also in time-resolved studies. b) Cavity enhanced self-absorption spectroscopy (CESAS), a new spectroscopic concept capable of studying light emitting matter (plasma, flames, combustion samples) simultaneously in absorption and emission. In CESAS, a sample (plasma, flame or combustion source) is located in an optically stable cavity consisting of two high reflectivity mirrors, and here it acts both as light source and absorbing medium. A high detection sensitivity of weak absorption is reached without the need of an external light source, such as a laser or broadband lamp. The performance is illustrated by the first CESAS result on a supersonically expanding hydrocarbon plasma. We expect CESAS to become a generally applicable analytical tool for real time and in situ diagnostics. A. Walsh, D. Zhao, W. Ubachs, H. Linnartz, J. Phys. Chem. A, {dx.doi.org/10.1021/jp310392n}, in press, 2013. A. Walsh, D. Zhao, H. Linnartz Rev. Sci. Instrum. {84}(2), 021608 2013. A. Walsh, D. Zhao

  14. Formalization and experimental evaluation of cavity-enhanced holographic readout

    Science.gov (United States)

    Miller, Bo E.; Takashima, Yuzuru

    2014-09-01

    We formalize the theoretical effects of optical resonator enhancement on diffraction efficiency, read rate, and write rate of plane wave holograms, with a view toward page based holographic data storage. Trade-offs in cavity enhancement are also examined. Theory predicts ~160% of enhancement in diffraction efficiency is feasible when power loss of the hologram is ~8% and diffraction efficiency is ~8%. We report experimental verification of ~30% enhancement of diffraction efficiency for a hologram written in 0.03% Fe:LiNbO3 (Deltronic Crystal Industries, Inc.) with a 532 nm wavelength, pulsed, DPSS, Nd-YAG, laser and read by a red He-Ne laser. The Bragg selectivity width under the cavityenhanced readout is experimentally confirmed to be unaffected by cavity enhancement, and it agrees with theoretical prediction.

  15. Line-Parameter Measurements and Stringent Tests of Line-Shape Models Based on Cavity-Enhanced Absorption Spectroscopy

    Science.gov (United States)

    Bielska, Katarzyna; Fleisher, Adam J.; Hodges, Joseph T.; Lin, Hong; Long, David A.; Reed, Zachary D.; Sironneau, Vincent; Truong, Gar-Wing; Wójtewicz, Szymon

    2014-06-01

    Laser methods that are based on cavity-enhanced absorption spectroscopy (CEAS) are well-suited for measuring molecular line parameters under conditions of low optical density, and as such they are complementary to broadband Fourier-transform spectroscopy (FTS) techniques. Attributes of CEAS include relatively low detection limits, accurate and precise detuning axes and high fidelity measurements of line shape. In many cases these performance criteria are superior to those obtained using direct laser absorption spectroscopy and FTS-based systems. In this presentation we will survey several examples of frequency-stabilized cavity ring-down spectroscopy (FS-CRDS)1 measurements obtained with laser spectrometers developed at the National Institute of Standards and Technology (NIST) in Gaithersburg Maryland. These experiments, which are motivated by atmospheric monitoring and remote-sensing applications that require high-precision and accuracy, involve nearinfrared transitions of carbon dioxide, water, oxygen and methane. We discuss spectra with signal-to-noise ratios exceeding 106, frequency axes with absolute uncertainties in the 10 kHz to 100 kHz range and linked to a Cs clock, line parameters with relative uncertainties at the 0.2 % level and isotopic ratios measured with a precision of 0.03 %. We also present FS-CRDS measurements of CO2 line intensities which are measured at atmospheric concentration levels and linked to gravimetric standards for CO2 in air, and we quantify pressure-dependent deviations between various theoretical line profiles and measured line shapes. Finally we also present recent efforts to increase data throughput and spectral coverage in CEAS experiments. We describe three new high-bandwidth CEAS techniques including frequency-agile, rapid scanning spectroscopy (FARS)2, which enables continuous-wave measurements of cavity mode linewidth and acquisition of ringdown decays with no dead time during laser frequency tuning, heterodyne

  16. Hybrid III-V/SOI resonant cavity enhanced photodetector

    DEFF Research Database (Denmark)

    Learkthanakhachon, Supannee; Taghizadeh, Alireza; Park, Gyeong Cheol;

    2016-01-01

    as part of the HG reflector, enabling a very compact vertical cavity. Numerical investigations show that a quantum efficiency close to 100 % and a detection linewidth of about 1 nm can be achieved, which are desirable for wavelength division multiplexing applications. Based on these results, a hybrid......A hybrid III–V/SOI resonant-cavity-enhanced photodetector (RCE-PD) structure comprising a high-contrast grating (HCG) reflector, a hybrid grating (HG) reflector, and an air cavity between them, has been proposed and investigated. In the proposed structure, a light absorbing material is integrated...... RCE-PD sample has been fabricated by heterogeneously integrating an InP-based material onto a silicon-on-insulator wafer and has been characterized, which shows a clear enhancement in photo-current at the designed wavelength. This indicates that the HG reflector provides a field enhancement sufficient...

  17. Cavity-enhanced resonant tunneling photodetector at telecommunication wavelengths

    Energy Technology Data Exchange (ETDEWEB)

    Pfenning, Andreas, E-mail: Andreas.Pfenning@physik.uni-wuerzburg.de; Hartmann, Fabian; Langer, Fabian; Höfling, Sven; Kamp, Martin; Worschech, Lukas [Technische Physik, Physikalisches Institut, Universität Würzburg and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Am Hubland, D-97074 Würzburg (Germany)

    2014-03-10

    An AlGaAs/GaAs double barrier resonant tunneling diode (RTD) with a nearby lattice-matched GaInNAs absorption layer was integrated into an optical cavity consisting of five and seven GaAs/AlAs layers to demonstrate cavity enhanced photodetection at the telecommunication wavelength 1.3 μm. The samples were grown by molecular beam epitaxy and RTD-mesas with ring-shaped contacts were fabricated. Electrical and optical properties were investigated at room temperature. The detector shows maximum photocurrent for the optical resonance at a wavelength of 1.29 μm. At resonance a high sensitivity of 3.1×10{sup 4} A/W and a response up to several pA per photon at room temperature were found.

  18. Cavity-enhanced resonant tunneling photodetector at telecommunication wavelengths

    International Nuclear Information System (INIS)

    An AlGaAs/GaAs double barrier resonant tunneling diode (RTD) with a nearby lattice-matched GaInNAs absorption layer was integrated into an optical cavity consisting of five and seven GaAs/AlAs layers to demonstrate cavity enhanced photodetection at the telecommunication wavelength 1.3 μm. The samples were grown by molecular beam epitaxy and RTD-mesas with ring-shaped contacts were fabricated. Electrical and optical properties were investigated at room temperature. The detector shows maximum photocurrent for the optical resonance at a wavelength of 1.29 μm. At resonance a high sensitivity of 3.1×104 A/W and a response up to several pA per photon at room temperature were found

  19. Noise-immune cavity-enhanced analytical atomic spectrometry — NICE-AAS — A technique for detection of elements down to zeptogram amounts

    International Nuclear Information System (INIS)

    Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a powerful technique for detection of molecular compounds in gas phase that is based on a combination of two important concepts: frequency modulation spectroscopy (FMS) for reduction of noise, and cavity enhancement, for prolongation of the interaction length between the light and the sample. Due to its unique properties, it has demonstrated unparalleled detection sensitivity when it comes to detection of molecular constituents in the gas phase. However, despite these, it has so far not been used for detection of atoms, i.e. for elemental analysis. The present work presents an assessment of the expected performance of Doppler-broadened (Db) NICE-OHMS for analytical atomic spectrometry, then referred to as noise-immune cavity-enhanced analytical atomic spectrometry (NICE-AAS). After a description of the basic principles of Db-NICE-OHMS, the modulation and detection conditions for optimum performance are identified. Based on a previous demonstrated detection sensitivity of Db-NICE-OHMS of 5 × 10−12 cm−1 Hz−1∕2 (corresponding to a single-pass absorbance of 7 × 10−11 over 10 s), the expected limits of detection (LODs) of Hg and Na by NICE-AAS are estimated. Hg is assumed to be detected in gas phase directly while Na is considered to be atomized in a graphite furnace (GF) prior to detection. It is shown that in the absence of spectral interferences, contaminated sample compartments, and optical saturation, it should be feasible to detect Hg down to 10 zg/cm3 (10 fg/m3 or 10−5 ng/m3), which corresponds to 25 atoms/cm3, and Na down to 0.5 zg (zg = zeptogram = 10−21 g), representing 50 zg/mL (parts-per-sextillion, pps, 1:1021) in liquid solution (assuming a sample of 10 μL) or solely 15 atoms injected into the GF, respectively. These LODs are several orders of magnitude lower (better) than any previous laser-based absorption technique previously demonstrated under

  20. Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

    Energy Technology Data Exchange (ETDEWEB)

    Sheps, Leonid; Chandler, David W.

    2013-04-01

    Experimental measurements of elementary reaction rate coefficients and product branching ratios are essential to our understanding of many fundamentally important processes in Combustion Chemistry. However, such measurements are often impossible because of a lack of adequate detection techniques. Some of the largest gaps in our knowledge concern some of the most important radical species, because their short lifetimes and low steady-state concentrations make them particularly difficult to detect. To address this challenge, we propose a novel general detection method for gas-phase chemical kinetics: time-resolved broadband cavity-enhanced absorption spectroscopy (TR-BB-CEAS). This all-optical, non-intrusive, multiplexed method enables sensitive direct probing of transient reaction intermediates in a simple, inexpensive, and robust experimental package.

  1. Mid-Infrared Tunable Resonant Cavity Enhanced Detectors

    Directory of Open Access Journals (Sweden)

    Hans Zogg

    2008-09-01

    Full Text Available Mid-infrared detectors that are sensitive only in a tunable narrow spectral band are presented. They are based on the Resonant Cavity Enhanced Detector (RCED principle and employing a thin active region using IV-VI narrow gap semiconductor layers. A Fabry-Pérot cavity is formed by two mirrors. The active layer is grown onto one mirror, while the second mirror can be displaced. This changes the cavity length thus shifting the resonances where the detector is sensitive. Using electrostatically actuated MEMS micromirrors, a very compact tunable detector system has been fabricated. Mirror movements of more than 3 μm at 30V are obtained. With these mirrors, detectors with a wavelength tuning range of about 0.7 μm have been realized. Single detectors can be used in mid-infrared micro spectrometers, while a detector arrangement in an array makes it possible to realize Adaptive Focal Plane Arrays (AFPA.

  2. Ultra-Trace Chemical Sensing with Long-Wave Infrared Cavity-Enhanced Spectroscopic Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Taubman, Matthew S.; Myers, Tanya L.; Cannon, Bret D.; Williams, Richard M.; Schultz, John F.

    2003-02-20

    are offset by the superior performance, ma-turity, and robustness of SWIR lasers, detectors, and other components, while the reverse is true for the MWIR and LWIR bands. PNNL's research activities include identification of signature chemicals and quantification of their spectroscopy, exploration of novel sensing techniques, and experimental sensor system construction and testing. In FY02, experimental QC laser systems developed with DARPA funding were used to explore continuous-wave (cw) CES in various forms culminating in the NICE-OHMS technique [1-3] discussed below. In FY02 PNNL also built an SWIR sensor to validate utility of the SWIR spectral region for chemical sensing, and explore the science and engineering of CES in field environments. The remainder of this report is devoted to PNNL's LWIR CES research. During FY02 PNNL explored the performance and limitations of several detection tech-niques in the LWIR including direct cavity-enhanced absorption, cavity-dithered phase-sensitive detection and resonant sideband cavity-enhanced detection. This latter tech-nique is also known as NICE-OHMS, which stands for Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy. This technique, pioneered in the near infra-red (NIR) by Dr J. Hall and coworkers at the University of Colorado, is one of the most sensitive spectroscopic techniques currently known. In this report, the first demonstra-tion of this technique in the LWIR is presented.

  3. Optical re-injection in cavity-enhanced absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Leen, J. Brian, E-mail: b.leen@lgrinc.com; O’Keefe, Anthony [Los Gatos Research, 67 E. Evelyn Avenue, Suite 3, Mountain View, California 94041 (United States)

    2014-09-15

    Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10{sup −10} cm{sup −1}/√(Hz;) an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features.

  4. Optical re-injection in cavity-enhanced absorption spectroscopy

    Science.gov (United States)

    Leen, J. Brian; O’Keefe, Anthony

    2014-01-01

    Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10−10 cm−1/\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$\\sqrt {{\\rm Hz;}}$\\end{document} Hz ; an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features. PMID:25273701

  5. Direct frequency comb laser cooling and trapping

    CERN Document Server

    Jayich, A M; Campbell, W C

    2016-01-01

    Continuous wave (CW) lasers are the enabling technology for producing ultracold atoms and molecules through laser cooling and trapping. The resulting pristine samples of slow moving particles are the de facto starting point for both fundamental and applied science when a highly-controlled quantum system is required. Laser cooled atoms have recently led to major advances in quantum information, the search to understand dark energy, quantum chemistry, and quantum sensors. However, CW laser technology currently limits laser cooling and trapping to special types of elements that do not include highly abundant and chemically relevant atoms such as hydrogen, carbon, oxygen, and nitrogen. Here, we demonstrate that Doppler cooling and trapping by optical frequency combs may provide a route to trapped, ultracold atoms whose spectra are not amenable to CW lasers. We laser cool a gas of atoms by driving a two-photon transition with an optical frequency comb, an efficient process to which every comb tooth coherently cont...

  6. Directional Time-frequency Analysis via Continuous Frames

    DEFF Research Database (Denmark)

    Christensen, Ole; Forster, Birgitte; Massopust, Peter

    2015-01-01

    Grafakos and Sansing [‘Gabor frames and directional time–frequency analysis’, Appl. Comput. Harmon. Anal.25 (2008), 47–67] have shown how to obtain directionally sensitive time–frequency decompositions in L2(Rn) based on Gabor systems in L2(R). The key tool is the ‘ridge idea’, which lifts a...

  7. Directional Preconditioner for High Frequency Obstacle Scattering

    OpenAIRE

    Ying, Lexing

    2014-01-01

    The boundary integral method is an efficient approach for solving time-harmonic obstacle scattering problems by a bounded scatterer. This paper presents the directional preconditioner for the iterative solution of linear systems of the boundary integral method. This new preconditioner builds a data-sparse approximation of the integral operator, transforms it into a sparse linear system, and computes an approximate inverse with efficient sparse and hierarchical linear algebra algorithms. This ...

  8. Direct Current Contamination of Kilohertz Frequency Alternating Current Waveforms

    OpenAIRE

    Franke, Manfred; Bhadra, Niloy; Bhadra, Narendra; Kilgore, Kevin

    2014-01-01

    Kilohertz Frequency Alternating Current (KHFAC) waveforms are being evaluated in a variety of physiological settings because of their potential to modulate neural activity uniquely when compared to frequencies in the sub-kilohertz range. However, the use of waveforms in this frequency range presents some unique challenges regarding the generator output. In this study we explored the possibility of undesirable contamination of the KHFAC waveforms by direct current (DC). We evaluated current- a...

  9. Aspects of the Application of Cavity Enhanced Spectroscopy to Nitrogen Oxides Detection

    Directory of Open Access Journals (Sweden)

    Zbigniew Bielecki

    2013-06-01

    Full Text Available This article presents design issues of high-sensitive laser absorption spectroscopy systems for nitrogen oxides (NOx detection. Examples of our systems and their investigation results are also described. The constructed systems use one of the most sensitive methods, cavity enhanced absorption spectroscopy (CEAS. They operate at different wavelength ranges using a blue—violet laser diode (410 nm as well as quantum cascade lasers (5.27 µm and 4.53 µm. Each of them is configured as a one or two channel measurement device using, e.g., time division multiplexing and averaging. During the testing procedure, the main performance features such as detection limits and measurements uncertainties have been determined. The obtained results are 1 ppb NO2, 75 ppb NO and 45 ppb N2O. For all systems, the uncertainty of concentration measurements does not exceed a value of 13%. Some experiments with explosives are also discussed. A setup equipped with a concentrator of explosives vapours was used. The detection method is based either on the reaction of the sensors to the nitrogen oxides directly emitted by the explosives or on the reaction to the nitrogen oxides produced during thermal decomposition of explosive vapours. For TNT, PETN, RDX and HMX a detection limit better than 1 ng has been achieved.

  10. Directivity of low-frequency solar type 3 radio bursts

    International Nuclear Information System (INIS)

    The occurrence rate of type 3 solar bursts in the frequency range 4.9 MHz to 30 kHz was analyzed as a function of burst intensity and burst arrival direction. Results show that the occurrence rate of bursts falls off with increasing flux and the distribution of burst arrival directions at each frequency shows a significantly larger number of bursts observed west of the earth--sun line than east of it. This western excess in occurrence rate appears to be correlated with the direction of the average interplanetary magnetic field, and is interpreted as beaming of the observed burst radiation along the magnetic field direction

  11. Directivity and prediction of low frequency rotor noise

    Science.gov (United States)

    Burley, C. L.; Marcolini, M. A.; Jones, H. E.; Splettstoesser, W. R.

    1991-01-01

    Acoustic data obtained over a large horizontal plane under the model rotor and digitally filtered in order to determine the low-frequency content near the blade passage frequency is analyzed. Focus is placed on the directivity of low-frequency noise, and the changes in directivity as a function of the descent glide slope angle and advance ratio are presented and compared with predicted directivity results. The differences between the data and prediction are discussed for two observer positions, one below and on the rotor axis, and the other 60 degrees down from the horizontal. It is demonstrated that for the latter position, blade-vortex interaction noise is strong when it occurs, and the loading at the low frequencies is significantly affected during blade-vortex interactions.

  12. Experimental and theoretical investigation of direct frequency comb spectroscopy

    OpenAIRE

    Peters, Elisabeth

    2011-01-01

    This thesis reports on theoretical and experimental examination of two-photon direct frequency comb spectroscopy (DFCS) using atomic two-level systems. This method is a very promising tool to extend optical spectroscopy into the short wavelength region where only few cw laser sources exist. The high peak intensities of pulsed lasers facilitate efficient nonlinear conversion into frequency regions which are so far unexplored, for example by high harmonic generation (HHG). DFCS is based on...

  13. Directivity of low frequency solar type III radio bursts

    International Nuclear Information System (INIS)

    The occurrence rate of type III solar bursts in the frequency range 4.9 MHz to 30 kHz is analyzed as a function of burst intensity and burst arrival direction. It is found that (a) the occurrence rate of bursts falls off with increasing flux, S, according to the power law Ssup(-1.5), and (b) the distribution of burst arrival directions at each frequency shows a significantly larger number of bursts observed west of the Earth-Sun line than east of it. This western excess in occurrence rate appears to be correlated with the direction of the average interplanetary magnetic field, and is interpreted as beaming of the observed burst radiation along the magnetic field direction. (Auth.)

  14. Scaling properties of cavity-enhanced atom cooling

    CERN Document Server

    Horak, P; Horak, Peter; Ritsch, Helmut

    2001-01-01

    We extend an earlier semiclassical model to describe the dissipative motion of N atoms coupled to M modes inside a coherently driven high-finesse cavity. The description includes momentum diffusion via spontaneous emission and cavity decay. Simple analytical formulas for the steady-state temperature and the cooling time for a single atom are derived and show surprisingly good agreement with direct stochastic simulations of the semiclassical equations for N atoms with properly scaled parameters. A thorough comparison with standard free-space Doppler cooling is performed and yields a lower temperature and a cooling time enhancement by a factor of M times the square of the ratio of the atom-field coupling constant to the cavity decay rate. Finally it is shown that laser cooling with negligible spontaneous emission should indeed be possible, especially for relatively light particles in a strongly coupled field configuration.

  15. High sensitivity liquid phase measurements using broadband cavity enhanced absorption spectroscopy (BBCEAS) featuring a low cost webcam based prism spectrometer.

    Science.gov (United States)

    Qu, Zhechao; Engstrom, Julia; Wong, Donald; Islam, Meez; Kaminski, Clemens F

    2013-11-01

    Cavity enhanced techniques enable high sensitivity absorption measurements in the liquid phase but are typically more complex, and much more expensive, to perform than conventional absorption methods. The latter attributes have so far prevented a wide spread use of these methods in the analytical sciences. In this study we demonstrate a novel BBCEAS instrument that is sensitive, yet simple and economical to set up and operate. We use a prism spectrometer with a low cost webcam as the detector in conjunction with an optical cavity consisting of two R = 0.99 dielectric mirrors and a white light LED source for illumination. High sensitivity liquid phase measurements were made on samples contained in 1 cm quartz cuvettes placed at normal incidence to the light beam in the optical cavity. The cavity enhancement factor (CEF) with water as the solvent was determined directly by phase shift cavity ring down spectroscopy (PS-CRDS) and also by calibration with Rhodamine 6G solutions. Both methods yielded closely matching CEF values of ~60. The minimum detectable change in absorption (αmin) was determined to be 6.5 × 10(-5) cm(-1) at 527 nm and was limited only by the 8 bit resolution of the particular webcam detector used, thus offering scope for further improvement. The instrument was used to make representative measurements on dye solutions and in the determination of nitrite concentrations in a variation of the widely used Griess Assay. Limits of detection (LOD) were ~850 pM for Rhodamine 6G and 3.7 nM for nitrite, respectively. The sensitivity of the instrument compares favourably with previous cavity based liquid phase studies whilst being achieved at a small fraction of the cost hitherto reported, thus opening the door to widespread use in the community. Further means of improving sensitivity are discussed in the paper. PMID:24049768

  16. Plasmonic Metasurface for Directional and Frequency-Selective Thermal Emission

    OpenAIRE

    Costantini, D.; Lefebvre, Antoine; Coutrot, A.-L; Moldovan-Doyen, I; Hugonin, J. -P.; Boutami, S.; Marquier, F; Benisty, H; Greffet, J. -J.

    2015-01-01

    International audience Incandescent filaments and membranes are often used as infrared sources despite their low efficiency, broad angular emission, and lack of spectral selectivity. Here, we introduce a metasurface to control simultaneously the spectrum and the directivity of blackbody radiation. The plasmonic metasurface operates reliably at 600 °C with an emissivity higher than 0.85 in a narrow frequency band and in a narrow solid angle. This emitter paves the way for the development of...

  17. Direct Frequency Comb Spectroscopy in the Extreme Ultraviolet

    CERN Document Server

    Cingoz, Arman; Allison, Thomas K; Ruehl, Axel; Fermann, Martin E; Hartl, Ingmar; Ye, Jun

    2011-01-01

    Development of the optical frequency comb has revolutionised metrology and precision spectroscopy due to its ability to provide a precise and direct link between microwave and optical frequencies. A novel application of frequency comb technology that leverages both the ultrashort duration of each laser pulse and the exquisite phase coherence of a train of pulses is the generation of frequency combs in the extreme ultraviolet (XUV) via high harmonic generation (HHG) in a femtosecond enhancement cavity. Until now, this method has lacked sufficient average power for applications, which has also hampered efforts to observe phase coherence of the high-repetition rate pulse train produced in the extremely nonlinear HHG process. Hence, the existence of a frequency comb in the XUV has not been confirmed. We have overcome both challenges. Here, we present generation of >200 {\\mu}W per harmonic reaching 50 nm, and the observation of single-photon spectroscopy signals for both an argon transition at 82 nm and a neon tra...

  18. Environmental Chamber Study of Atmospheric Chemistry and Secondary Organic Aerosol Formation Using Cavity Enhanced Absorption Spectroscopy

    OpenAIRE

    Liu, Yingdi

    2011-01-01

    Air pollution and global climate change are important environmental issues that affect our society. Deeper understanding of atmospheric chemistry is required to understand these problems and to develop effective control strategies. Environmental chambers have been used for the past few decades to study atmospheric chemistry and investigate processes leading to secondary pollutant formation. This thesis work provides two different high sensitivity real time cavity enhance absorption spectrosco...

  19. Broadband cavity enhanced spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde

    OpenAIRE

    Washenfelder, R. A.; A. R. Attwood; Flores, J. M.; Rudich, Y.; S. S. Brown

    2015-01-01

    Formaldehyde (CH2O) is the most abundant aldehyde in the atmosphere, and strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH2O and nitrogen dioxide (NO2) using broadband cavity enhanced spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and ...

  20. Note: Directly measuring the direct digital synthesizer frequency chirp-rate for an atom interferometer

    Energy Technology Data Exchange (ETDEWEB)

    Tao, Juan-Juan; Zhou, Min-Kang, E-mail: zkhu@hust.edu.cn, E-mail: zmk@hust.edu.cn; Zhang, Qiao-Zhen; Cui, Jia-Feng; Duan, Xiao-Chun; Shao, Cheng-Gang; Hu, Zhong-Kun, E-mail: zkhu@hust.edu.cn, E-mail: zmk@hust.edu.cn [MOE Key Laboratory of Fundamental Physical Quantities Measurement, School of Physics, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan 430074 (China)

    2015-09-15

    During gravity measurements with Raman type atom interferometry, the frequency of the laser used to drive Raman transition is scanned by chirping the frequency of a direct digital synthesizer (DDS), and the local gravity is determined by precisely measuring the chip rate α of DDS. We present an effective method that can directly evaluate the frequency chirp rate stability of our DDS. By mixing a pair of synchronous linear sweeping signals, the chirp rate fluctuation is precisely measured with a frequency counter. The measurement result shows that the relative α instability can reach 5.7 × 10{sup −11} in 1 s, which is neglectable in a 10{sup −9} g level atom interferometry gravimeter.

  1. Direct Acceleration of Ions With Variable-frequency Lasers

    CERN Document Server

    Peano, F; Fonseca, R A; Mulas, R; Coppa, G; Silva, L O

    2008-01-01

    A method is proposed for producing monoergetic, high-quality ion beams in vacuum, via direct acceleration by the electromagnetic field of two counterpropagating, variable-frequency lasers: ions are trapped and accelerated by a beat-wave structure with variable phase velocity, allowing for fine control over the energy and the charge of the beam via tuning of the frequency variation. The physical mechanism is described with a one-dimensional theory, providing the general conditions for trapping and scaling laws for the relevant features of the ion beam. Two-dimensional, electromagnetic particle-in-cell simulations, in which hydrogen gas is considered as an ion source, confirm the validity and the robustness of the method.

  2. Cavity-Enhanced Gas Analyzer for In-Situ Sampling of Biogenic Gases and Their Isotopes Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project concerns the novel application of cavity-enhanced absorption spectroscopy to quantify biogenic gases (CH4,...

  3. An Improved Fixed Switching Frequency Direct Torque Control of Induction Motor Drives Fed by Direct Matrix Converter

    OpenAIRE

    Taib, Nabil; Rekioua, Toufik; Francois, Bruno

    2010-01-01

    A few papers have been interested by the fixed switching frequency direct torque control fed by direct matrix converters, where we can find just the use of direct torque controlled space vector modulated method. In this present paper, we present an improved method used for a fixed switching frequency direct torque control (DTC) using a direct matrix converter (DMC). This method is characterized by a simple structure, a fixed switching frequency which causes minimal torque ripple and a unity i...

  4. Linear cavity optical-feedback cavity-enhanced absorption spectroscopy with a quantum cascade laser.

    Science.gov (United States)

    Bergin, A G V; Hancock, G; Ritchie, G A D; Weidmann, D

    2013-07-15

    A cw distributed feedback quantum cascade laser (DFB-QCL) coupled to a two-mirror linear optical cavity has been used to successfully demonstrate optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) at 5.5 μm. The noise-equivalent absorption coefficient, α(min), was 2.4×10(-8) cm(-1) for 1 s averaging, limited by etalon-fringing. The temporal stability of the instrument allows NO detection down to 5 ppb in 2 s. PMID:23939085

  5. Optical feedback cavity-enhanced absorption spectroscopy with a 3.24 μm interband cascade laser

    Energy Technology Data Exchange (ETDEWEB)

    Manfred, K. M.; Ritchie, G. A. D. [Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Rd, Oxford OX1 3QZ (United Kingdom); Lang, N.; Röpcke, J.; Helden, J. H. van, E-mail: jean-pierre.vanhelden@inp-greifswald.de [Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, 17489 Greifswald (Germany)

    2015-06-01

    The development of interband cascade lasers (ICLs) has made the strong C-H transitions in the 3 μm spectral region increasingly accessible. We present the demonstration of a single mode distributed feedback ICL coupled to a V-shaped optical cavity in an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) experiment. We achieved a minimum detectable absorption coefficient, α{sub min}, of (7.1±0.2)×10{sup −8} cm{sup −1} for a spectrum of CH{sub 4} at 3.24 μm with a two second acquisition time (100 scans averaged). This corresponds to a detection limit of 3 ppb CH{sub 4} at atmospheric pressure, which is comparable to previously reported OF-CEAS instruments with diode lasers or quantum cascade lasers. The ability to frequency lock an ICL source in the important 3 μm region to an optical cavity holds great promise for future spectroscopic applications.

  6. Directional spatial frequency analysis of lipid distribution in atherosclerotic plaque

    Science.gov (United States)

    Korn, Clyde; Reese, Eric; Shi, Lingyan; Alfano, Robert; Russell, Stewart

    2016-04-01

    Atherosclerosis is characterized by the growth of fibrous plaques due to the retention of cholesterol and lipids within the artery wall, which can lead to vessel occlusion and cardiac events. One way to evaluate arterial disease is to quantify the amount of lipid present in these plaques, since a higher disease burden is characterized by a higher concentration of lipid. Although therapeutic stimulation of reverse cholesterol transport to reduce cholesterol deposits in plaque has not produced significant results, this may be due to current image analysis methods which use averaging techniques to calculate the total amount of lipid in the plaque without regard to spatial distribution, thereby discarding information that may have significance in marking response to therapy. Here we use Directional Fourier Spatial Frequency (DFSF) analysis to generate a characteristic spatial frequency spectrum for atherosclerotic plaques from C57 Black 6 mice both treated and untreated with a cholesterol scavenging nanoparticle. We then use the Cauchy product of these spectra to classify the images with a support vector machine (SVM). Our results indicate that treated plaque can be distinguished from untreated plaque using this method, where no difference is seen using the spatial averaging method. This work has the potential to increase the effectiveness of current in-vivo methods of plaque detection that also use averaging methods, such as laser speckle imaging and Raman spectroscopy.

  7. [Measurement of Trace C2H6 Based on Optical-Feedback Cavity-Enhanced Absorption Spectroscopy].

    Science.gov (United States)

    Wan, Fu; Chen, Wei-gen; Gu, Zhao-liang; Zou, Jing-xin; DU, Ling-Ling; Qi, Wei; Zhou, Qu

    2015-10-01

    Ethane is one of major fault characteristic gases dissolved in power transformer, the detection of Ethane with high accuracy and sensitivity is the key of dissolved gas analysis. In this paper, based on optical feedback theory and cavity-enhanced absorption spectroscopy, combined with quantum cascade laser, a detection system for dissolved gas C2 H6 in transformer oil was built up. Based on the symmetry of the individual cavity modes, the phase matching of returning light in resonance with the cavity was achieved through LabVIEW codes. The optical feedback effect that the emitted light return to the laser cavity after a small delay time and lock to the resonance frequency of cavity, even and odd modes effect that the higher modes and lower modes structure will build up alternatively, and threshold current lowering effect of about 1.2 mA were studied and achieved. By cavity ring-down spectroscopy, the effective reflectivity of 99.978% and cavity finesse of 7 138.4 is obtained respectively. The frequency selectivity is 0.005 2 cm(-1). With an acquisition time of 1s, this optical system allows detection for the PQ3 band of C2 H6 with high accuracy of 95.72% ± 0.17% and detection limit of (1.97 ± 0.06) x 10(-3) μL x L(-1) at atmospheric pressure and temperature of 20 degrees C, which lays a foundation for fault diagnose from dissolved gas analysis. PMID:26904820

  8. Broadband cavity enhanced spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde

    Science.gov (United States)

    Washenfelder, R. A.; Attwood, A. R.; Flores, J. M.; Rudich, Y.; Brown, S. S.

    2015-09-01

    Formaldehyde (CH2O) is the most abundant aldehyde in the atmosphere, and strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH2O and nitrogen dioxide (NO2) using broadband cavity enhanced spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99933 ± 0.00003 (670 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.49 km within the 1 m cell. We measure the cavity output over the 315-350 nm spectral region using a grating monochromator and charge-coupled device (CCD) array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH2O and NO2 concentrations. Independent measurements of NO2 standard additions by broadband cavity enhanced spectroscopy and cavity ringdown spectroscopy agree within 2 % (slope for linear fit = 0.98 ± 0.03 with r2 = 0.998). Standard additions of CH2O measured by broadband cavity enhanced spectroscopy and calculated based on flow dilution are also well-correlated, with r2 = 0.9998. During constant, mixed additions of NO2 and CH2O, the 30 s measurement precisions (1σ) of the current configuration were 140 and 210 pptv, respectively. The current 1-min detection limit for extinction measurements at 315-350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and ground-based field experiments. Additionally, the instrument provides highly accurate, spectroscopically-based trace gas detection that may complement higher precision techniques based on non-absolute detection methods. In addition to trace gases, this approach will be appropriate for

  9. Heating mechanism in direct current superposed single-frequency and dual-frequency capacitively coupled plasmas

    International Nuclear Information System (INIS)

    In this work particle-in-cell/Monte Carlo collision simulations are performed to study the heating mechanism and plasma characteristics in direct current (dc) superposed radio-frequency (RF) capacitively coupled plasmas, operated both in single-frequency (SF) and dual-frequency (DF) regimes. An RF (60/2 MHz) source is applied on the bottom electrode to sustain the discharge, and a dc source is fixed on the top electrode. The heating mechanism appears to be very different in dc superposed SF and DF discharges. When only a single source of 60 MHz is applied, the plasma bulk region is reduced by the dc source, thus the ionization rate and hence the electron density decrease with rising dc voltage. However, when a DF source of 60 and 2 MHz is applied, the electron density can increase upon addition of a dc voltage, depending on the gap length and applied dc voltage. This is explained from the spatiotemporal ionization rates in the DF discharge. In fact, a completely different behavior is observed for the ionization rate in the two half-periods of the LF source. In the first LF half-period, the situation resembles the dc superposed SF discharge, and the reduced plasma bulk region due to the negative dc bias results in a very small effective discharge area and a low ionization rate. On the other hand, in the second half-period, the negative dc bias is to some extent counteracted by the LF voltage, and the sheath close to the dc electrode becomes particularly thin. Consequently, the amplitude of the high-frequency sheath oscillations at the top electrode is largely enhanced, while the LF sheath at the bottom electrode is in its expanding phase and can thus well confine the high-energy electrons. Therefore, the ionization rate increases considerably in this second LF half-period. Furthermore, in addition to the comparison between SF and DF discharges and the effect of gap length and dc voltage, the effect of secondary electrons is examined. (paper)

  10. An Improved Fixed Switching Frequency Direct Torque Control of Induction Motor Drives Fed by Direct Matrix Converter

    CERN Document Server

    Taib, Nabil; Francois, Bruno

    2010-01-01

    A few papers have been interested by the fixed switching frequency direct torque control fed by direct matrix converters, where we can find just the use of direct torque controlled space vector modulated method. In this present paper, we present an improved method used for a fixed switching frequency direct torque control (DTC) using a direct matrix converter (DMC). This method is characterized by a simple structure, a fixed switching frequency which causes minimal torque ripple and a unity input power factor. Using this strategy, we combine the direct matrix converters advantages with those of direct torque control (DTC) schemes. The used technique for constant frequency is combined with the input current space vector to create the switching table of direct matrix converter (DMC). Simulation results clearly demonstrate a better dynamic and steady state performances of the proposed method.

  11. Interfacing whispering-gallery microresonators and free space light with cavity enhanced Rayleigh scattering

    CERN Document Server

    Zhu, Jiangang; Yilmaz, Huzeyfe; Peng, Bo; Dong, Mark; Tomes, Matthew; Carmon, Tal; Yang, Lan

    2014-01-01

    Whispering gallery mode resonators (WGMRs) take advantage of strong light confinement and long photon lifetime for applications in sensing, optomechanics, microlasers and quantum optics. However, their rotational symmetry and low radiation loss impede energy exchange between WGMs and the surrounding. As a result, free-space coupling of light into and from WGMRs is very challenging. In previous schemes, resonators are intentionally deformed to break circular symmetry to enable free-space coupling of carefully aligned focused light, which comes with bulky size and alignment issue that hinder the realization of compact WGMR applications. Here, we report a new class of nanocouplers based on cavity enhanced Rayleigh scattering from nano-scatterer(s) on resonator surface, and demonstrate whispering gallery microlaser by free-space optical pumping of an Ytterbium doped silica microtoroid via the scatterers. This new scheme will not only expand the range of applications enabled by WGMRs, but also provide a possible r...

  12. Cavity-enhanced spontaneous emission rates for rhodamine 6-G in levitated microdroplets

    International Nuclear Information System (INIS)

    Fluorescence decay kinetics of Rhodamine 6-G molecules in levitated glycerol microdroplets (4--20 microns in diameter) have been investigated to determine the effects of spherical cavity resonances on spontaneous emission rates. For droplet diameters greater than 10 microns, the fluorescence lifetime is essentially the same as in bulk glycerol. As the droplet diameter is decreased below 10 microns, bi-exponential decay behavior is observed with a slow component whose rate is similar to bulk glycerol, and a fast component whose rate is as much as a factor of 10 larger than the bulk decay rate. This fast component is attributed to cavity enhancement of the spontaneous emission rate and, within the weak coupling approximation, a value for the homogeneous linewidth at room temperature can be estimated from the fluorescence lifetime data

  13. Sensitive CH4 detection applying quantum cascade laser based optical feedback cavity-enhanced absorption spectroscopy.

    Science.gov (United States)

    Lang, N; Macherius, U; Wiese, M; Zimmermann, H; Röpcke, J; van Helden, J H

    2016-03-21

    We report on sensitive detection of atmospheric methane employing quantum cascade laser based optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS). An instrument has been built utilizing a continuous-wave distributed feedback quantum cascade laser (cw-QCL) with a V-shaped cavity, a common arrangement that reduces feedback to the laser from non-resonant reflections. The spectrometer has a noise equivalent absorption coefficient of 3.6 × 10-9 cm-1 Hz-1/2 for a spectral scan of CH4 at 7.39 μm. From an Allan-Werle analysis a detection limit of 39 parts per trillion of CH4 at atmospheric pressure within 50 s acquisition time was found. PMID:27136874

  14. Cavity-Enhanced Absorption Spectroscopy and Photoacoustic Spectroscopy for Human Breath Analysis

    Science.gov (United States)

    Wojtas, J.; Tittel, F. K.; Stacewicz, T.; Bielecki, Z.; Lewicki, R.; Mikolajczyk, J.; Nowakowski, M.; Szabra, D.; Stefanski, P.; Tarka, J.

    2014-12-01

    This paper describes two different optoelectronic detection techniques: cavity-enhanced absorption spectroscopy and photoacoustic spectroscopy. These techniques are designed to perform a sensitive analysis of trace gas species in exhaled human breath for medical applications. With such systems, the detection of pathogenic changes at the molecular level can be achieved. The presence of certain gases (biomarkers), at increased concentration levels, indicates numerous human diseases. Diagnosis of a disease in its early stage would significantly increase chances for effective therapy. Non-invasive, real-time measurements, and high sensitivity and selectivity, capable of minimum discomfort for patients, are the main advantages of human breath analysis. At present, monitoring of volatile biomarkers in breath is commonly useful for diagnostic screening, treatment for specific conditions, therapy monitoring, control of exogenous gases (such as bacterial and poisonous emissions), as well as for analysis of metabolic gases.

  15. Resonant cavity enhanced light harvesting in flexible thin-film organic solar cells

    KAUST Repository

    Sergeant, Nicholas P.

    2013-04-24

    Dielectric/metal/dielectric (DMD) electrodes have the potential to significantly increase the absorption efficiency and photocurrent in flexible organic solar cells. We demonstrate that this enhancement is attributed to a broadband cavity resonance. Silver-based semitransparent DMD electrodes with sheet resistances below 10 ohm/sq. are fabricated on flexible polyethylene terephthalate (PET) substrates in a high-throughput roll-to-roll sputtering tool. We carefully study the effect of the semitransparent DMD electrode (here composed of ZnxSnyOz/Ag/InxSn yOz) on the optical device performance of a copper phthalocyanine (CuPc)/fullerene (C60) bilayer cell and illustrate that a resonant cavity enhanced light trapping effect dominates the optical behavior of the device. © 2013 Optical Society of America.

  16. Center frequency shift and reduction of feedback in directly modulated external cavity lasers

    DEFF Research Database (Denmark)

    Schiellerup, G.; Pedersen, Rune Johan Skullerud; Olesen, H.;

    1989-01-01

    It is shown experimentally and theoretically that a center frequency shift occurs when an external cavity laser is directly modulated. The shift can be observed even when the frequency deviation is small compared to the roundtrip frequency of the external cavity and can qualitatively be explained...... by a reduction in the effective feedback level due to modulation. The frequency shift was measured as a function of modulation frequency and current, and frequency shifts up to 350 MHz were observed...

  17. Resonant cavity enhanced photodetectors for high-speed and polarization-sensing applications

    Science.gov (United States)

    Onat, Bora M.

    1998-08-01

    The performance of today's optical components utilized in communication systems have reached the conventional limitations and require innovations in device structures for further improvements. We employ the unique properties of the resonant cavity enhanced (RCE) photodetection scheme to increase the functionality and performance of semiconductor photodiodes. The operation principle of RCE photodetection is based on a new family of opto-electronic devices whose performance is enhanced by placing the active device structure inside a Fabry-Perot resonant microcavity. The RCE devices benefit from the wavelength sensitivity and the large increase of the resonant optical field introduced by the cavity. The increased optical field allows photodetectors to be made thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. The research effort implemented all aspects of the device development including simulation, design, fabrication and characterization of photodiodes for high-speed and polarization-sensing applications. We studied the performance of RCE photodiodes through simulations and experimentally demonstrated their high- speed operation. Our simulation results predict a three- fold increase in the bandwidth-efficiency product (BWE) for RCE photodiodes. We designed, fabricated and characterized RCE Schottky photodiodes where the semi- transparent metal contact also functions as the top reflector. The RCE Schottky photodiode design for 900 nm wavelength operation exhibited a 10 ps temporal pulse width, corresponding to an estimated device bandwidth of 100 GHz. A peak quantum efficiency of 20% was measured and the theoretical expected value is 70%. A similar RCE Schottky photodiode structure designed for 840 nm operation exhibited a quantum efficiency of 50%. High- speed characterization of these devices revealed an estimated 50 GHz bandwidth, corresponding to a BWE product of 25 GHz. To the best of our knowledge

  18. Increasing global crop harvest frequency: recent trends and future directions

    International Nuclear Information System (INIS)

    The world’s agricultural systems face the challenge of meeting the rising demands from population growth, changing dietary preferences, and expanding biofuel use. Previous studies have put forward strategies for meeting this growing demand by increasing global crop production, either expanding the area under cultivation or intensifying the crop yields of our existing agricultural lands. However, another possible means for increasing global crop production has received less attention: increasing the frequency of global cropland harvested each year. Historically, many of the world’s croplands were left fallow, or had failed harvests, each year, foregoing opportunities for delivering crop production. Furthermore, many regions, particularly in the tropics, may be capable of multiple harvests per year, often more than are harvested today. Here we analyze a global compilation of agricultural statistics to show how the world’s harvested cropland has changed. Between 2000 and 2011, harvested land area grew roughly 4 times faster than total standing cropland area. Using a metric of cropland harvest frequency (CHF)—the ratio of land harvested each year to the total standing cropland—and its recent trends, we identify countries that harvest their croplands more frequently, and those that have the potential to increase their cropland harvest frequency. We suggest that a possible ‘harvest gap’ may exist in many countries that represents an opportunity to increase crop production on existing agricultural lands. However, increasing the harvest frequency of existing croplands could have significant environmental and social impacts, which need careful evaluation. (letter)

  19. Incoherent broadband cavity enhanced absorption spectroscopy using supercontinuum and superluminescent diode sources.

    Science.gov (United States)

    Aalto, Antti; Genty, Goëry; Laurila, Toni; Toivonen, Juha

    2015-09-21

    We investigate incoherent broadband cavity enhanced absorption spectroscopy using a tailored supercontinuum source. By tailoring the supercontinuum spectrum to match the high reflectivity bandwidth of the mirrors, we achieve an unprecedented spectral brightness of more than 7 dBm/nm at wavelengths where the effective absorption path length in the cavity exceeds 40 km. We demonstrate the potential of the source in spectrally broadband measurement of weak overtone transitions of carbon dioxide and methane in the near-infrared 1590 nm - 1700 nm range and evaluate its performance against that of a typical superluminescent diode source. Minimum detectable absorption coefficients (3σ) of 2.2 × 10(-9) cm(-1) and 6.2 × 10(-9) cm(-1) are obtained with the supercontinuum and the superluminescent diode sources, respectively. We further develop a spectral fitting method based on differential optical absorption spectroscopy to fully and properly account for the combined effect of absorption line saturation and limited spectral resolution of the detection. The method allows to cope with high dynamic range of absorption features typical of real-world multi-component measurements. PMID:26406720

  20. Near infrared cavity enhanced absorption spectra of atmospherically relevant ether-1, 4-Dioxane

    Science.gov (United States)

    Chandran, Satheesh; Varma, Ravi

    2016-01-01

    1, 4-Dioxane (DX) is a commonly found ether in industrially polluted atmosphere. The near infrared absorption spectra of this compound has been recorded in the region 5900-8230 cm- 1 with a resolution of 0.08 cm- 1 using a novel Fourier transform incoherent broadband cavity-enhanced absorption spectrometer (FT-IBBCEAS). All recorded spectra were found to contain regions that are only weakly perturbed. The possible combinations of fundamental modes and their overtone bands corresponding to selected regions in the measured spectra are tabulated. Two interesting spectral regions were identified as 5900-6400 cm- 1 and 8100-8230 cm- 1. No significant spectral interference due to presence of water vapor was observed suggesting the suitability of these spectral signatures for spectroscopic in situ detection of DX. The technique employed here is much more sensitive than standard Fourier transform spectrometer measurements on account of long effective path length achieved. Hence significant enhancement of weaker absorption lines above the noise level was observed as demonstrated by comparison with an available measurement from database.

  1. Interfacing whispering-gallery microresonators and free space light with cavity enhanced Rayleigh scattering

    Science.gov (United States)

    Zhu, Jiangang; Özdemir, Şahin K.; Yilmaz, Huzeyfe; Peng, Bo; Dong, Mark; Tomes, Matthew; Carmon, Tal; Yang, Lan

    2014-09-01

    Whispering gallery mode resonators (WGMRs) take advantage of strong light confinement and long photon lifetime for applications in sensing, optomechanics, microlasers and quantum optics. However, their rotational symmetry and low radiation loss impede energy exchange between WGMs and the surrounding. As a result, free-space coupling of light into and from WGMRs is very challenging. In previous schemes, resonators are intentionally deformed to break circular symmetry to enable free-space coupling of carefully aligned focused light, which comes with bulky size and alignment issues that hinder the realization of compact WGMR applications. Here, we report a new class of nanocouplers based on cavity enhanced Rayleigh scattering from nano-scatterer(s) on resonator surface, and demonstrate whispering gallery microlaser by free-space optical pumping of an Ytterbium doped silica microtoroid via the scatterers. This new scheme will not only expand the range of applications enabled by WGMRs, but also provide a possible route to integrate them into solar powered green photonics.

  2. Cavity-enhanced parity-nonconserving optical rotation in metastable Xe and Hg.

    Science.gov (United States)

    Bougas, L; Katsoprinakis, G E; von Klitzing, W; Sapirstein, J; Rakitzis, T P

    2012-05-25

    We propose the measurement of cavity-enhanced parity-nonconserving (PNC) optical rotation in several transitions of metastable Xe and Hg, including Xe (2P(3/2)(o))6s(2)[3/2](2)(o)→(2P(1/2)(o))6s(2)[1/2](1)(o) and Hg 6s6p (3)P(2)(o)→6s6p (1)P(1)(o), with calculated amplitude ratios of E(1)(PNC)/M1=11×10(-8) and 10×10(-8), respectively. We demonstrate the use of a high-finesse bow-tie cavity with counterpropagating beams and a longitudinal magnetic field, which allows the absolute measurement of chiral optical rotation, with a path length enhancement of about 10(4), necessary for PNC measurement from available column densities of 10(14) cm(-2) for metastable Xe or Hg. Rapid PNC-signal reversal, allowing robust background subtraction, is achieved by shifting the cavity resonance to an opposite polarization mode or by inverting the magnetic field. The precise measurement of isotope and nuclear-spin dependent E(1)(PNC) amplitudes provides a sensitive low-energy test of the standard model. PMID:23003234

  3. Method of measuring the amplitude directivity pattern of parabolic mirrored antennas in the audio frequency range

    Directory of Open Access Journals (Sweden)

    Sadchenko A. V.

    2016-02-01

    Full Text Available Directivity pattern (DP or graphical representation of the dependence of gain factor (directivity gain of antennas on the direction of the antenna in the target plane is the main characteristic that describes its directional properties. Running DP measurements directly in the microwave range is very expensive. While generating and receiving devices for the acoustic frequency range are reasonably priced. In this paper, we propose a method for measuring the amplitude directivity pattern of parabolic mirrored antennas on the basis of sound equivalent, which is based on the identity of the numerical values of the directivity gain of microwave range, and at audio frequencies. The paper presents analytical expressions for the calculation of equivalent frequency and defines the requirements for the minimum size of the antenna. The paper contains a modified block diagram for an amplitude directivity pattern meter for parabolic mirrored antennas in the audio frequency range.

  4. Direct frequency comb two-photon laser cooling and trapping

    Science.gov (United States)

    Jayich, Andrew; Long, Xueping; Campbell, Wesley C.

    2016-05-01

    Generating and manipulating high energy photons for spectroscopy on electric dipole transitions of atoms and molecules with deeply bound valence electrons is difficult. Further, laser cooling of such species is even more challenging for lack of laser power. A possible solution is to drive two-photon transitions. This may alleviate the photon energy problem and open the door to cold, trapped samples of highly desirable species with tightly bound electrons. We perform a proof of principle experiment with rubidium by driving a two-photon transition with an optical frequency comb. We perform optical cooling and extend this technique to trapping, where we are able to make a magneto-optical trap in one dimension. This work is supported by the National Science Foundation CAREER program.

  5. Fundamentals of Cavity-Enhanced Polarimetry for Parity-Nonconserving Optical Rotation Measurements: Application to Xe, Hg and I

    CERN Document Server

    Bougas, L; von Klitzing, W; Rakitzis, T P

    2013-01-01

    We present the theoretical basis of a cavity-enhanced polarimetric scheme for the measurement of parity-nonconserving (PNC) optical rotation. We discuss the possibility of detecting PNC optical rotation in accessible transitions in metastable Xe and Hg, and ground state I. In particular, the physics of the PNC optical rotation is presented, and we explore the lineshape effects on the expected PNC optical rotation signals. Furthermore, we present an analysis of the eigenpolarizations of the cavity-enhanced polarimeter, which is necessary for understanding the measurement procedure and the ability of employing robust background subtraction procedures using two novel signal reversals. Using recent atomic structure theoretical calculations, we present simulations of the PNC optical rotation signals for all proposed transitions, assuming a range of experimentally feasible parameters. Finally, the possibility of performing sensitive measurements of the nuclear-spin-dependent PNC effects is investigated, for the odd...

  6. Cavity Enhanced Absorption Spectroscopy with a red LED source for NOx trace analysis

    Science.gov (United States)

    Ventrillard Courtillot, I.; Sciamma O'Brien, E.; Méjean, G.; Romanini, D.

    2009-04-01

    This study presents a high sensitivity absorption system using a red LED source emitting at 625 nm and a small CCD spectrometer as detector [1]. This system is based on IBB-CEAS (Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy). The expected application is the measurement of NO2 and NO3 in urban concentration (ppbv and ppmv levels). The IBB-CEAS was firstly developed with arc lamps and then with LED. Systems based on this technique are easy to use, highly sensitive, compact and robust. They also are inexpensive. Existent techniques to measure NO2 and NO3 are generally slow or not sensitive enough and need frequently calibrations (chemical luminescent) or are characterized by a low spatial resolution (Long Path Differential Optical Absorption Spectroscopy). Previous works based on diodes lasers emitting around 410 nm and coupled with High Finess Cavity proved a highest sensibility than ppbv and a time measurement of 0.1 s [2]. This sensibility is necessary for measurements in unpolluted environment but a more expensive and more complex system is needed. NO2 is chosen for testing as it is stable and available in calibrated diluted samples. An excellent agreement in the range from 610 nm to 630 nm was gotten between an absorption spectrum obtained by IBB-CEAS and a spectrum calculated using a reference NO2 absorption cross section by Voigt et al [3] (after convolution with a 2.05-nm FWHM Gaussian simulating our spectrometer response function). The reflectivity of the mirrors was determined with a commercial spectrophotometer and was used to deduce the absorption spectrum of NO2 from the transmission spectrum of the cavity. We obtained by estimating the sensitivity of our setup from the noise in a baseline measurement of absorption, (standard deviation = 2E-10 cm-1). This corresponds (under atmospheric conditions) to a sensitivity about 0.5 ppbv. NO3 cross-section absorption is 600 times higher than the NO2 (at 623 nm), so a detection limit of 1 pptv is

  7. Rapid prototyping of frequency selective surfaces by laser direct-write

    Science.gov (United States)

    Mathews, Scott A.; Mirotznik, Mark; Good, Brandon L.; Piqué, Alberto

    2007-02-01

    In this work we describe the use of laser direct-write for the rapid prototyping of frequency selective surfaces. Frequency selective surfaces are generally described by a periodic array of conducting or dielectric features (i.e. crosses, loops, grids, etc.) that when properly designed can pass or reject specific frequency bands of incoming electromagnetic radiation. While simple frequency selective surfaces are relatively straight forward to design and fabricate, operational demands, particularly military, have motivated the design and fabrication of much more complicated patterns. These new designs combine features of significantly different length scales, randomly dithered patterns and combinations of passive and active elements. We will demonstrate how laser direct-write is an ideal tool for the rapid prototyping of these new more complicated frequency selective surface designs. We will present experimental results for devices fabricated using several different laser direct-write processes.

  8. Direct CFD Predictions of Low Frequency Sounds Generated by Helicopter Main Rotors

    Science.gov (United States)

    Sim, Ben W.; Potsdam, Mark; Conner, Dave; Watts, Michael E.

    2010-01-01

    This proposed paper will highlight the application of a CSD/CFD methodology currently inuse by the US Army Aerfolightdynamics Directorate (AFDD) to assess the feasibility and fidelity of directly predicting low frequency sounds of helicopter rotors.

  9. Frequency Properties Research of Elevator Drive System with Direct Torque Control-Pulse with Modulation

    Directory of Open Access Journals (Sweden)

    A. S. Koval

    2008-01-01

    Full Text Available In the article problems of frequency properties research for electric drive system with direct torque control and pulse width modulator are described. The mathematical description of elevator is present. Simplified mathematical description of direct torque control - pulse width modulator electric drive system is shown. Transfer functions for torque and speed loops are determined. Logarithmic frequency characteristics are computed. Damping properties of elevator drive system are estimated.

  10. Frequency Properties Research of Elevator Drive System with Direct Torque Control-Pulse with Modulation

    OpenAIRE

    A. S. Koval; A. V. Shvayakov

    2014-01-01

    In the article problems of frequency properties research for electric drive system with direct torque control and pulse width modulator are described. The mathematical description of elevator is present. Simplified mathematical description of direct torque control - pulse width modulator electric drive system is shown. Transfer functions for torque and speed loops are determined. Logarithmic frequency characteristics are computed. Damping properties of elevator drive system are estimated.

  11. Frequency Modulation of Directly Imaged Exoplanets: Geometric Effect as a Probe of Planetary Obliquity

    CERN Document Server

    Kawahara, Hajime

    2016-01-01

    We consider the time-frequency analysis of a scattered light curve by a directly imaged exoplanet. We show that the geometric effect due to planetary obliquity and orbital inclination induce the frequency modulation of the apparent diurnal periodicity. We construct a model of the frequency modulation and compare with the instantaneous frequency extracted from the pseudo-Wigner distribution of the simulated light curves of a cloudless Earth. The model provides good agreement with the simulated modulation factor even for the light curve with Gaussian noise comparable to the signal. Notably, the shape of the instantaneous frequency is sensitive to the difference between prograde, retrograde, and pole-on spin rotations. Whereas our technique requires the static property of the albedo map, it does not need to solve the albedo map of the planet. The time-frequency analysis is complementary to other methods which utilize the amplitude modulation. This paper demonstrates the importance of the frequency domain of the ...

  12. QCL - Optical-Feedback Cavity Enhanced Absorption Spectroscopy For The Analysis Of Atmospheric 13CO2/12CO2 In Ice-Core Gas Bubbles

    Science.gov (United States)

    Gorrotxategi Carbajo, Paula; Romanini, Daniele; Maisons, Gregory; Carras, Mathieu; Chappellaz, Jerome; Kerstel, Erik

    2013-04-01

    In the context of a globally warming climate it is crucial to study the climate variability in the past and to understand the underlying mechanisms. The composition of gas stored in bubbles in polar ice presents a paleo-climate archive that provides a powerful means to study the exact mechanisms involved in the ~40% increase in the atmospheric CO2 concentration between glacial and interglacial climates. It is particularly important to understand such natural coupling between climate and the carbon cycle, as it will partly determine what natural feedback can be expected on the atmospheric CO2 concentration in a future warmer world. The source of the CO2 released into the atmosphere during previous deglaciations can be constrained from isotopic measurements by the fact that the different CO2 reservoirs (terrestrial biosphere, oceans) and associated mechanisms (biological or physical) have different isotopic signatures. Unfortunately, such isotope studies have been seriously hampered by the experimental difficulty of extracting the CO2 without contamination or fractionation, and measuring the isotope signal off-line on an isotope ratio mass spectrometer (IRMS). Here we present an alternative method that leverages the extreme sensitivity afforded by Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) in the Mid-Infrared [1]. This region of the spectrum is accessed by a custom-developed Quantum Cascade Laser operating near 4.35 µm. The feedback to the laser of light that has been spectrally filtered by a high-finesse, V-shaped enhancement cavity has the effect of spectrally narrowing the laser emission and to auto-lock the laser frequency to one of the cavity's longitudinal modes, with clear advantages in terms of acquisition time and signal-to-noise ratio of the measurement. The line strengths in this region are about 5 orders of magnitude higher than in the more easily accessible NIR region near 1.6 µm and about 1000 times higher than at 2 µm. The

  13. Enhancing the sensitivity of mid-IR quantum cascade laser-based cavity-enhanced absorption spectroscopy using RF current perturbation.

    Science.gov (United States)

    Manfred, Katherine M; Kirkbride, James M R; Ciaffoni, Luca; Peverall, Robert; Ritchie, Grant A D

    2014-12-15

    The sensitivity of mid-IR quantum cascade laser (QCL) off-axis cavity-enhanced absorption spectroscopy (CEAS), often limited by cavity mode structure and diffraction losses, was enhanced by applying a broadband RF noise to the laser current. A pump-probe measurement demonstrated that the addition of bandwidth-limited white noise effectively increased the laser linewidth, thereby reducing mode structure associated with CEAS. The broadband noise source offers a more sensitive, more robust alternative to applying single-frequency noise to the laser. Analysis of CEAS measurements of a CO(2) absorption feature at 1890  cm(-1) averaged over 100 ms yielded a minimum detectable absorption of 5.5×10(-3)  Hz(-1/2) in the presence of broadband RF perturbation, nearly a tenfold improvement over the unperturbed regime. The short acquisition time makes this technique suitable for breath applications requiring breath-by-breath gas concentration information. PMID:25503003

  14. Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane—Breath Biomarkers of Serious Diseases

    Directory of Open Access Journals (Sweden)

    Jacek Wojtas

    2015-06-01

    Full Text Available The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (<3 s were achieved. Absorption lines of reference samples of the selected volatile biomarkers were probed using a distributed feedback quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases.

  15. Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane--Breath Biomarkers of Serious Diseases.

    Science.gov (United States)

    Wojtas, Jacek

    2015-01-01

    The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases. PMID:26091398

  16. Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane—Breath Biomarkers of Serious Diseases

    Science.gov (United States)

    Wojtas, Jacek

    2015-01-01

    The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases. PMID:26091398

  17. SPECIES: a versatile spectrometer based on optical-feedback cavity-enhanced absorption for in situ balloon-borne and airborne measurements

    Science.gov (United States)

    Jacquet, Patrick; Catoire, Valery; Robert, Claude; Chartier, Michel; Huret, Nathalie; Desbois, Thibault; Marocco, Nicola; Kassi, Samir; Kerstel, Eric; Romanini, Daniele

    2015-04-01

    Over the last twenty years, thanks to significant technological advances in measurement techniques, our understanding of the chemistry and dynamics of the upper troposphere and stratosphere has progressed significantly. However some key questions remain unsolved, and new ones arise in the changing climate context. The full recovery of the ozone layer and the delay of recovery, the impact of the climate change on the stratosphere and the role of this one as a feedback are almost unknown. To address these challenges, one needs instruments able to measure a wide variety of trace gas species simultaneously with a wide vertical range. In this context, LPC2E and LIPHY are developing a new balloon-borne and airborne instrument: SPECIES (SPECtromètre Infrarouge à lasErs in Situ, i.e. in-Situ Infrared lasEr SPECtrometer). Based on the Optical Feedback Cavity Enhanced Spectroscopy technique, combined with mid-infrared quantum cascade lasers, this instrument will offer unprecedented performances in terms of the vertical extent of the measurements, from ground to the middle stratosphere, and the number of molecular species simultaneously measured with sub-ppb detection limits (among others: NO, N2O, HNO3, H2O2, HCl, HOCl, CH3Cl, COF2, HCHO, HCOOH, O3, NH3 NO2, H2O, OCS, SO2). Due to high frequency measurement (>0.5 Hz) it shall offer very high spatial resolution (a few meters).

  18. Unfolded Frequency Response and Model of a Multi-Tap Direct Sampling Mixer

    Institute of Scientific and Technical Information of China (English)

    PAN Yun; GE Ning; DONG Zaiwang

    2008-01-01

    A transform method was used to model a discrete time multi-tap direct sampling mixer. The method transforms the mixed filtering and down.sampling stages to separate cascade filtering and sampling stages to determine the unfolded frequency response which shows the anti-aliasing ability of the mixer. The transformation can also be applied to other mixed signal and multi-rate receiver systems to analyze their unfolded frequency responses. The transformed system architecture was used to calculate the unfolded frequency response of the multi-tap direct sampling mixer and compared with the mixer model without noise in the ad-vanced design system 2005A environment to further evaluate the frequency response. The simulations show that the -3 dB bandwidth is 3.0 MHz and the voltage gain is attenuated by 1.5 dB within a 1-MHz baseband bandwidth.

  19. On an Iterative Method for Direction of Arrival Estimation using Multiple Frequencies

    OpenAIRE

    Andersson, Fredrik; Carlsson, Marcus; Tourneret, Jean-Yves; Wendt, Herwig

    2013-01-01

    We develop a method for the estimation of the location of sources from measurements at multiple frequencies, including wideband measurements, recorded by a linear array of sensors. We employ interpolation matrices to address unequal sampling at different frequencies and make use of the Kronecker theorem to cast the nonlinear least squares problem associated with direction of arrival estimation into an optimization problem in the space of sequences generating Hankel matrices of fixed rank.We t...

  20. Direction of arrival estimation using array model in time-frequency domain

    Institute of Scientific and Technical Information of China (English)

    LIU Yun; LI Zhishun

    2004-01-01

    Time-frequency analysis is combined with array processing to develop a direction of arrival (DOA) estimation method. The array data model is constructed in time-frequency domain by cross time-frequency distribution between the output of a reference sensor and those of two symmetric sub-arrays. Accordingly a subspace method is presented based on the average of two sub-arrays' time-frequency data vector model instead of the conventional array model, to estimate DOAs of multiple signals. Because the array data is processed both in spatial domain and 2-D time-frequency domain, the proposed method has an ability to select the signal of interesting, and is suitable for non-stationary signal. Additionally, the method is robust to noise and holds an advantage of low computational load. Simulations are conducted to verify the efficiency of the method and comparision is made with other methods.

  1. Effect of Low Frequency Electromagnetic Field on Macrosegregation of Horizontal Direct Chill Casting Aluminum Alloys

    Institute of Scientific and Technical Information of China (English)

    Zhihao ZHAO; Jianzhong CUI; Jie DONG; Beijiang ZHANG

    2005-01-01

    The horizontal direct chill (HDC) casting process is a well-established production route for aluminum alloy ingot but the ingot may suffer from macrosegregation sometimes. In order to control the defect, a low frequency electromagnetic field has been applied in HDC casting process and the relevant influence has been studied. The results show that application of low frequency electromagnetic field can reduce macrosegregation in HDC casting process; and two main parameters of electromagnetic field density and frequency, have great influences on the solution distribution along the diameter of ingot. Moreover, the mechanisms of reduction of macrosegregation by electromagnetic field have been discussed.

  2. Frequency Modulation of Directly Imaged Exoplanets: Geometric Effect as a Probe of Planetary Obliquity

    Science.gov (United States)

    Kawahara, Hajime

    2016-05-01

    We consider the time–frequency analysis of a scattered light curve of a directly imaged exoplanet. We show that the geometric effect due to planetary obliquity and orbital inclination induce the frequency modulation of the apparent diurnal periodicity. We construct a model of the frequency modulation and compare it with the instantaneous frequency extracted from the pseudo-Wigner distribution of simulated light curves of a cloudless Earth. The model provides good agreement with the simulated modulation factor, even for the light curve with Gaussian noise comparable to the signal. Notably, the shape of the instantaneous frequency is sensitive to the difference between the prograde, retrograde, and pole-on spin rotations. While our technique requires the albedo map to be static, it does not need to solve the albedo map of the planet. The time–frequency analysis is complementary to other methods which utilize the amplitude modulation. This paper demonstrates the importance of the frequency domain of the photometric variability for the characterization of directly imaged exoplanets in future research.

  3. Broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde

    Science.gov (United States)

    Washenfelder, R. A.; Attwood, A. R.; Flores, J. M.; Zarzana, K. J.; Rudich, Y.; Brown, S. S.

    2016-01-01

    Formaldehyde (CH2O) is the most abundant aldehyde in the atmosphere, and it strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH2O and nitrogen dioxide (NO2) using broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99930 ± 0.00003 (1- reflectivity = 700 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.43 km within the 1 m cell. We measure the cavity output over the 315-350 nm spectral region using a grating monochromator and charge-coupled device array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH2O and NO2 concentrations. Independent measurements of NO2 standard additions by broadband cavity-enhanced absorption spectroscopy and cavity ring-down spectroscopy agree within 2 % (slope for linear fit = 1.02 ± 0.03 with r2 = 0.998). Standard additions of CH2O measured by broadband cavity-enhanced absorption spectroscopy and calculated based on flow dilution are also well correlated, with r2 = 0.9998. During constant mixed additions of NO2 and CH2O, the 30 s measurement precisions (1σ) of the current configuration were 140 and 210 pptv, respectively. The current 1 min detection limit for extinction measurements at 315-350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and ground-based field experiments. Additionally, the instrument provides highly accurate, spectroscopically based trace gas detection that may complement higher precision techniques based on non-absolute detection methods. In addition to

  4. Cavity-enhanced second harmonic generation via nonlinear-overlap optimization

    CERN Document Server

    Lin, Zin; Loncar, Marko; Johnson, Steven G; Rodriguez, Alejandro W

    2015-01-01

    We describe an approach based on topology optimization that enables automatic discovery of wavelength-scale photonic structures for achieving high-efficiency second-harmonic generation (SHG). A key distinction from previous formulation and designs that seek to maximize Purcell factors at individual frequencies is that our method not only aims to achieve frequency matching (across an entire octave) and large radiative lifetimes, but also optimizes the equally important nonlinear--coupling figure of merit $\\bar{\\beta}$, involving a complicated spatial overlap-integral between modes. We apply this method to the particular problem of optimizing micropost and grating-slab cavities (one-dimensional multilayered structures) and demonstrate that a variety of material platforms can support modes with the requisite frequencies, large lifetimes $Q \\gtrsim 10^3$, small modal volumes $\\sim (\\lambda/n)^3$, and extremely large $\\bar{\\beta} \\gtrsim 10^{-2}$, orders of magnitude larger than the state of the art.

  5. Direct CFD Predictions of Low Frequency Sounds Generated by a Helicopter Main Rotor

    Science.gov (United States)

    Sim, Ben W.; Potsdam, Mark A.; Conner, Dave A.; Conner, Dave A.; Watts, Michael E.

    2010-01-01

    The use of CFD to directly predict helicopter main rotor noise is shown to be quite promising as an alternative mean for low frequency source noise evaluation. Results using existing state-of-the-art grid structures and finite-difference schemes demonstrated that small perturbation pressures, associated with acoustics radiation, can be extracted with some degree of fidelity. Accuracy of the predictions are demonstrated via comparing to predictions from conventional acoustic analogy-based models, and with measurements obtained from wind tunnel and flight tests for the MD-902 helicopter at several operating conditions. Findings show that the direct CFD approach is quite successfully in yielding low frequency results due to thickness and steady loading noise mechanisms. Mid-to-high frequency contents, due to blade-vortex interactions, are not predicted due to CFD modeling and grid constraints.

  6. Human perception of air movement. Impact of frequency and airflow direction on draught sensation

    Energy Technology Data Exchange (ETDEWEB)

    Genhong Zhou

    1999-08-01

    calculates the air velocity and temperature field above and below the skin surface under steady and non-steady conditions. The model predicts the impulses from thermal receptors of skin. The simulation results had a good agreement with the experimental results on subject`s sensation of draught. (au) 130 refs.; covertitle: Human perception of air movement: Impact of frequency and airflow direction on sensation of draught

  7. A directly phase-modulated light source

    CERN Document Server

    Yuan, Z L; Lucamarini, M; Roberts, G L; Dynes, J F; Shields, A J

    2016-01-01

    The art of imparting information onto a light wave by optical signal modulation is fundamental to all forms of optical communication. Among many schemes, direct modulation of laser diodes stands out as a simple, robust, and cost effective method. However, the simultaneous changes in intensity, frequency and phase are a drawback which has prevented its application in the field of secure quantum communication. Here, we propose and experimentally demonstrate a directly phase-modulated light source which overcomes the main disadvantages associated with direct modulation and is suitable for diverse applications such as coherent communications and quantum cryptography. The source separates the tasks of phase preparation and pulse generation between a pair of semiconductor lasers leading to very pure phase states. Moreover, the cavity enhanced electro-optic effect enables the first example of sub-volt halfwave phase modulation at high signal rates. The source is compact, stable and versatile, and we show its potenti...

  8. A broadband cavity enhanced absorption spectrometer for aircraft measurements of glyoxal, methylglyoxal, nitrous acid, nitrogen dioxide, and water vapor

    Science.gov (United States)

    Min, K.-E.; Washenfelder, R. A.; Dubé, W. P.; Langford, A. O.; Edwards, P. M.; Zarzana, K. J.; Stutz, J.; Lu, K.; Rohrer, F.; Zhang, Y.; Brown, S. S.

    2016-02-01

    We describe a two-channel broadband cavity enhanced absorption spectrometer (BBCEAS) for aircraft measurements of glyoxal (CHOCHO), methylglyoxal (CH3COCHO), nitrous acid (HONO), nitrogen dioxide (NO2), and water (H2O). The instrument spans 361-389 and 438-468 nm, using two light-emitting diodes (LEDs) and a single grating spectrometer with a charge-coupled device (CCD) detector. Robust performance is achieved using a custom optical mounting system, high-power LEDs with electronic on/off modulation, high-reflectivity cavity mirrors, and materials that minimize analyte surface losses. We have successfully deployed this instrument during two aircraft and two ground-based field campaigns to date. The demonstrated precision (2σ) for retrievals of CHOCHO, HONO and NO2 are 34, 350, and 80 parts per trillion (pptv) in 5 s. The accuracy is 5.8, 9.0, and 5.0 %, limited mainly by the available absorption cross sections.

  9. A broadband cavity-enhanced spectrometer for measuring the extinction of aerosols at blue and near-UV wavelengths

    Science.gov (United States)

    Venables, Dean; Fullam, Donovan; Hoa Le, Phuoc; Chen, Jun; Böge, Olaf; Herrmann, Hartmut

    2016-04-01

    We describe a new broadband cavity-enhanced absorption spectrometer for sensitive extinction measurements of aerosols. The instrument is distinguished by its broad and continuous spectral coverage from the near-UV to blue wavelengths (ca. 320 to 450 nm). The short wavelength region has been little explored compared to visible wavelengths, but is important because (1) brown carbon (BrC) absorbs strongly in this wavelength region, and (2) absorption of near-UV radiation in the atmosphere alters the photolysis rate of the key atmospheric species O3, NO2, and HONO, with implications for air quality and atmospheric oxidation capacity. The instrument performance and the effect of a switchable in-line filter are characterised. Early results using the instrument in the TROPOS atmospheric simulation chamber are presented. These experiments include studies of secondary organic aerosol formation (SOA), and biomass burning experiments of rice and wheat straw, followed by experiments simulating particle aging under daytime and nighttime conditions.

  10. Intrinsic limitation of cavity-enhanced Faraday detection of spin noise in quantum wells and quantum dots

    Science.gov (United States)

    Scalbert, D.

    2016-04-01

    Spin noise spectroscopy is a quite attractive experimental tool for studying unperturbed spin dynamics and magnetic resonance in semiconductor nanostructures. However in some cases its practical interest maybe severely limited by the weakness of the spin noise signal to be detected. In this paper we examine by how much the detection of spin noise of magnetic atoms or of nuclei, in quantum wells or quantum dots, can be improved by making use of cavity-enhanced Faraday rotation. The conditions for optimized cavities are first determined. In reflection geometry it corresponds to tune the cavity to the critical point of impedance matching. It is shown that even for optimized cavities the enhancement in spin noise detection is intrinsically limited by absorption. It turns out that the cavity effect improves the spin noise detection only when the inhomogeneous broadening of the involved optical resonance is large compared to its radiative broadening.

  11. Very high finesse optical-feedback cavity-enhanced absorption spectrometer for low concentration water vapor isotope analyses.

    Science.gov (United States)

    Landsberg, J; Romanini, D; Kerstel, E

    2014-04-01

    So far, cavity-enhanced absorption spectroscopy (CEAS) has been based on optical cavities with a high finesse F that, however, has been limited by mirror reflectivity and by cavity transmission considerations to a few times 10,000. Here, we demonstrate a compact near-infrared optical-feedback CEAS instrument for water vapor isotope ratio measurements, with F>140,000. We show that this very high finesse can be effectively exploited to improve the detection sensitivity to the full extent predicted by the increased effective path length to reach a noise equivalent absorption sensitivity of 5.7×10(-11)  cm(-1) Hz(-1/2) for a full spectrum registration (including possible effects of interference fringes and fit model inadequacies). PMID:24686607

  12. Evanescent-wave and open-air chiral sensing via signal-reversing cavity-enhanced polarimetry

    CERN Document Server

    Sofikitis, Dimitris; Katsoprinakis, Georgios E; Spiliotis, Alexandros K; Loppinet, Benoit; Rakitzis, T Peter

    2014-01-01

    Sensing chirality is of fundamental importance to many fields, including analytical and biological chemistry, pharmacology, and fundamental physics. Recent developments have extended optical chiral sensing using microwaves, fs pulses, superchiral light, and photoionization. The most widely used methods are the traditional methods of circular dichroism and optical rotation (OR). However, chiral signals are typically very weak, and their measurement is limited by larger time-dependent backgrounds and by imperfect and slow subtraction procedures. Here, we demonstrate a pulsed-laser bowtie-cavity-enhanced polarimeter with counter-propagating beams, which solves these background problems: the chiral signals are enhanced by the number of cavity passes; the effects of linear birefringence are suppressed by a large induced intracavity Faraday rotation; and rapid signal reversals are effected by reversing the Faraday rotation and subtracting signals from the counter-propagating beams. These advantages allow measuremen...

  13. Theory study on a photonic-assisted radio frequency phase shifter with direct current voltage control

    International Nuclear Information System (INIS)

    A photonic-assisted radio frequency phase shifter with direct current voltage control is proposed using a polymer-based integrated Mach—Zehnder modulator. A closed-form expression of radio frequency (RF) signal power and phase is given. Theoretical calculation reveals that by carefully setting the bias voltages, RF signal power variation lower than 1-dB and phase accuracy less than 3° can be achieved and are not degraded by perturbation of modulation index once the bias voltage drift is kept within −3% ∼ 3%. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  14. Fundamental Frequency and Direction-of-Arrival Estimation for Multichannel Speech Enhancement

    DEFF Research Database (Denmark)

    Karimian-Azari, Sam

    2016-01-01

    array, the multichannel periodic signals may have different phases due to the time-differences-of-arrivals (TDOAs) which are related to the direction-of-arrival (DOA) of the impinging sound waves. Hence, the outputs of the array can be steered to the direction of the signal of interest in order to align......-varying fundamental frequency in the statistical methods in order to lessen the estimation error. We also propose a maximum likelihood DOA estimator concerning the noise statistics and the linear relationship between the TDOAs of the harmonics. The estimators have benefits compared to the state-of-the-art statistical...... multichannel speech signal enhancement by exploiting the estimated fundamental frequency and DOA of the signal of interest. This general framework is tailored to a number of beamformers concerning the spectral and spatial information of the periodic signals which are quasi-stationary in short intervals...

  15. Ocean dynamic noise energy flux directivity in the 400 Hz to 700 Hz frequency band

    Institute of Scientific and Technical Information of China (English)

    Vladimir A. Shchurov; Galina F. Ivanova; Marianna V. Kuyanova; Helen S. Tkachenko

    2007-01-01

    Results of field studies of underwater dynamic noise energy flux directivity at two wind speeds, 6 m/s and 12 m/s, in the 400 Hz to 700 Hz frequency band in the deep open ocean are presented. The measurements were made by a freely drifting telemetric combined system at 500 m depth. Statistical characteristics of the horizontal and vertical dynamic noise energy flux directivity are considered as functions of wind speed and direction. Correlation between the horizontal dynamic noise energy flux direction and that of the wind was determined; a mechanism of the horizontal dynamic noise energy flux generation is related to the initial noise field scattering on ocean surface waves.

  16. First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar

    OpenAIRE

    De Ruiter, Stacy Lynn; Southall, Brandon L.; Calambokidis, John; Zimmer, Walter M X; Sadykova, Dinara; Falcone, Erin A.; Friedlaender, Ari S.; John E. Joseph; Moretti, David; Schorr, Gregory S.; Thomas, Len; Tyack, Peter Lloyd

    2013-01-01

    Most marine mammal­ strandings coincident with naval sonar exercises have involved Cuvier's beaked whales (Ziphius cavirostris). We recorded animal movement and acoustic data on two tagged Ziphius and obtained the first direct measurements of behavioural responses of this species to mid-frequency active (MFA) sonar signals. Each recording included a 30-min playback (one 1.6-s simulated MFA sonar signal repeated every 25 s); one whale was also incidentally exposed to MFA sonar from distant nav...

  17. Stiff Load Cell With High Overload Capability and Direct Frequency Output

    OpenAIRE

    Yan, T.; Jones, B E; Rakowski, R.T.; Tudor, M J; Beeby, S. P.; White, N.M.

    2004-01-01

    This paper reports on the design, construction and characteristics of a novel load cell having stiffness and potential overload capability some 10 times that of a resistive strain gauge load cell. The experimental cell loaded up to 600 kg gives a direct output frequency change of 870 Hz (safety factor of 5). It uses recently developed metallic triple beam resonators with thick-film PZT drives and pickups.

  18. Direct Measurement of Time-Frequency Analogues of Sub-Planck Structures

    OpenAIRE

    Praxmeyer, Ludmila; Chen, Chih-Cheng; Yang, Popo; Yang, Shang-Da; Lee, Ray-Kuang

    2015-01-01

    Exploiting the correspondence between Wigner distribution function and a frequency-resolved optical gating (FROG) measurement, we experimentally demonstrate existence of the chessboard-like interference patterns with a time-bandwidth product smaller than that of a transform-limited pulse in the phase space representation of compass states. Using superpositions of four electric pulses as realization of compass states, we have shown via direct measurements that displacements leading to orthogon...

  19. 47 CFR 80.361 - Frequencies for narrow-band direct-printing (NBDP), radioprinter and data transmissions.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Frequencies for narrow-band direct-printing (NBDP), radioprinter and data transmissions. 80.361 Section 80.361 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES STATIONS IN THE MARITIME SERVICES Frequencies Radiotelegraphy § 80.361 Frequencies...

  20. Tunable cavity-enhanced photon pairs source in Hermite-Gaussian mode

    CERN Document Server

    Zhou, Zhi-Yuan; Ding, Dong-Sheng; Zhang, Wei; Shi, Shuai; Shi, Bao-Sen; Guo, Guang-Can

    2015-01-01

    The spatial modes of light have grasped great research interests because of its great potentials in optical communications, optical manipulation and trapping, optical metrology and quantum information processing. Here we report on generating of photon pairs in Hermite-Gaussian (HG) mode in a type-I optical parametric oscillator (OPO) operated far below threshold. The bandwidths of the photon pairs are 11.4 MHz and 20.8MHz for two different HG modes respectively, which is capable to be stored in cold Rubidium atomic ensembles. From correlation measurements, non-classical properties of HG modes in different directions are verified by tuning the cavity. Our study provides an effective way to generate photon pairs with narrow bandwidth in high order spatial modes for high dimensional quantum communication.

  1. Directional high-frequency protective relays for 100-750 kV transmission lines

    Energy Technology Data Exchange (ETDEWEB)

    Gel' fand, Ya.S.; Doni, N.A.; Leviush, A.I.; Naumov, A.M.; Rubinchik, V.A.; Yariz, N.A.

    1985-08-01

    From the standpoint of high-frequency protective relaying, all existing 100-750 kV transmission lines can be classified into the 110-330 kV group with negligible capacitive currents and the 500-750 kV group with appreciable capacitive currents, some 300 kV lines also belonging to the second group. Accordingly, the response time of protective relays may be as long as two 50 Hz periods for the first group but must not exceed one 50 Hz period for the second group. While differential phase protection has been installed for most 110-500 kV overhead lines, directional filter protection with high-frequency interlocking is found to be preferable for multi-terminal 110-330 kV lines. This type of protective relaying is now being developed for both groups of high-voltage lines, to meet present and future requirements, with either nondirectional or directional high-frequency starting of the transceiver. Design and performance analysis of both schemes indicates that combining them may be required, to ensure sensitivity and response to any short circuit, with possible addition of differential phase protection where necessary for single-phase automatic reclosure.

  2. Hardware Implementation of 32-Bit High-Speed Direct Digital Frequency Synthesizer

    Directory of Open Access Journals (Sweden)

    Salah Hasan Ibrahim

    2014-01-01

    Full Text Available The design and implementation of a high-speed direct digital frequency synthesizer are presented. A modified Brent-Kung parallel adder is combined with pipelining technique to improve the speed of the system. A gated clock technique is proposed to reduce the number of registers in the phase accumulator design. The quarter wave symmetry technique is used to store only one quarter of the sine wave. The ROM lookup table (LUT is partitioned into three 4-bit sub-ROMs based on angular decomposition technique and trigonometric identity. Exploiting the advantages of sine-cosine symmetrical attributes together with XOR logic gates, one sub-ROM block can be removed from the design. These techniques, compressed the ROM into 368 bits. The ROM compressed ratio is 534.2 : 1, with only two adders, two multipliers, and XOR-gates with high frequency resolution of 0.029 Hz. These techniques make the direct digital frequency synthesizer an attractive candidate for wireless communication applications.

  3. High Frequency Synchrony in the Cerebellar Cortex during Goal Directed Movements

    Directory of Open Access Journals (Sweden)

    Jonathan David Groth

    2015-07-01

    Full Text Available The cerebellum is involved in sensory-motor integration and cognitive functions. The origin and function of the field potential oscillations in the cerebellum, especially in the high frequencies, have not been explored sufficiently. The primary objective of this study was to investigate the spatio-temporal characteristics of high frequency field potentials (150-350Hz in the cerebellar cortex in a behavioral context. To this end, we recorded from the paramedian lobule in rats using micro electro-corticogram (µ-ECoG electrode arrays while the animal performed a lever press task using the forelimb. The phase synchrony analysis shows that the high frequency oscillations recorded at multiple points across the paramedian cortex episodically synchronize immediately before and desynchronize during the lever press. The electrode contacts were grouped according to their temporal course of phase synchrony around the time of lever press. Contact groups presented patches with slightly stronger synchrony values in the medio-lateral direction, and did not appear to form parasagittal zones. The size and location of these patches on the cortical surface are in agreement with the sensory evoked granular layer patches originally reported by Welker’s lab (Shambes, 1978. Spatiotemporal synchrony of high frequency field potentials has not been reported at such large-scales previously in the cerebellar cortex.

  4. Resonance ionization mass spectrometric analysis of thorium by external laser cavity enhancement techniques

    International Nuclear Information System (INIS)

    Over the last several years, extensive effort has been directed towards the demonstration of Resonance Ionization Mass Spectrometry (RIMS) as a generally-applicable isotopic analysis technique. The major problems in this task have been to achieve a high overall ionization efficiency as well as good sample utilization. Several aspects of these problems are apparent in the choice of the excitation and ionization sources for the selective RIMS process. Pulsed lasers have typically had low repetition rates, poor spectral and temporal behavior, and short pulse durations. These characteristics have limited the general utility of pulsed lasers because of the low duty cycle (low efficiency), pulse pile-up detection difficulties (limited dynamic range), and relatively poor stability (poor precision). In contrast, cw lasers offer 100% effective duty cycles, well-controlled laser profiles (spectrally, spatially and temporally), and excellent power stability. The main feature limiting the utility of cw lasers has been power. While sufficient intensity is available to saturate the resonant transition, efficient promotion of excited atoms to the ionization continuum is difficult. This last aspect is where the authors efforts have centered. Presently, they are pursuing an external cavity technique which will generate overall ionization efficiencies of tens of percent, as well as increase the available spectral range. Experimental aspects and process to date on thorium will be discussed in detail

  5. Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS – applicability and corrections

    Directory of Open Access Journals (Sweden)

    D. Pöhler

    2009-11-01

    Full Text Available Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broadband light sources, the broadband CEAS (BB-CEAS. BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light path by the trace gas absorption, since cavity losses due to absorption by gases reduce the quality (Q of the cavity. In fact, at wavelength, where the quality of the BB-CEAS cavity is dominated by the trace gas absorption (especially at very high mirror reflectivity, the average light path will vary nearly inversely with the trace gas concentration and the strength of the band will become only weakly dependent on the trace gas concentration c in the cavity, (the differential optical density being proportional to the logarithm of the trace gas concentration. Only in the limiting case where the mirror reflectivity determines Q at all wavelength, the strength of the band as seen by the CE-DOAS instrument becomes directly proportional to the concentration c. We investigate these relationships in detail and present methods to correct for the cases between the two above extremes, which are of course the important ones in practice.

  6. Effects of low-frequency magnetic field on grain boundary segregation in horizontal direct chill casting of 2024 aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Effects of low frequency electromagnetic field on grain boundary segregation in horizontal direct chill (HDC)casting process was investigated experimentally. The grain boundary segregation and microstructures of the ingots,which manufactured by conventional HDC casting and low frequency electromagnetic HDC casting were compared.Results show that low frequency electromagnetic field significantly refines the microstructures and reduces grain boundary segregation. Decreasing electromagnetic frequency or increasing electromagnetic intensity has great effects in reducing grain boundary segregation. Meanwhile, the governing mechanisms were discussed.

  7. Effect of low frequency electromagnetic field on microstructures and macrosegregation of horizontal direct chill casting aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    赵志浩; 崔建忠; 董杰; 张海涛; 张北江

    2004-01-01

    The influences of low frequency electromagnetic field on cast surface, microstructures and macrosegregation in horizontal direct chill(HDC) casting process were investigated experimentally. The cast surfaces, microstructures and macrosegregation of the ingots manufactured by conventional HDC and low frequency electromagnetic HDC casting were compared. The results show that low frequency electromagnetic field significantly improves the surface quality, refines the microstructures and reduces macrosegregation. Further more, increasing electromagnetic intensity or decreasing frequency is beneficial to the improvement. In the range of ampere-turns and frequency employed in the experiments, the optimum ampere-turns is found to be 10 000 A · turn and the frequency to be 30 Hz.

  8. Directional algorithms for the frequency isolation problem in undamped vibrational systems

    Science.gov (United States)

    Moro, Julio; Egaña, Juan C.

    2016-06-01

    A new algorithm is presented to solve the frequency isolation problem for vibrational systems with no damping: given an undamped mass-spring system with resonant eigenvalues, the system must be re-designed, finding some close-by non-resonant system at a reasonable cost. Our approach relies on modifying masses and stiffnesses along directions in parameter space which produce a maximal variation in the resonant eigenvalues, provided the non-resonant ones do not undergo large variations. The algorithm is derived from first principles, implemented, and numerically tested. The numerical experiments show that the new algorithms are considerably faster and more robust than previous algorithms solving the same problem.

  9. Frequency dependence of arrival direction and polarization of low-latitude whistlers and their ducted propagation

    International Nuclear Information System (INIS)

    The combined use of digital recorders and a fast Fourier transform analyzer made it possible for them to carry out wideband field analysis direction finding measurements of whistlers at low latitude (geomagnetic latitude 25 degree N). It is found that there is a negligibly small frequency dependence of the ionospheric exit point and polarization of daytime whistlers during each occurrence peak with duration of about 2 hours, which lends further support to their propagation in a field-aligned duct in the magnetosphere for each occurrence peak

  10. Particle simulation for direct plasma injection in a radio frequency quadrupole matching section

    International Nuclear Information System (INIS)

    We have been investigating direct plasma injection scheme (DPIS) for high-intensity heavy-ion beam acceleration. In the DPIS, laser-produced plasma is directly injected into a radio frequency quadrupole (RFQ) linac. To study the beam dynamics of the ion injection in the DPIS, we tracked particle motions in the RFQ matching section using three-dimensional particle-in-cell method. As a result of the numerical simulation, we found that the electrostatic field generated by the extraction electrode reduces the transmission efficiency. To avoid the radially defocusing force, the input beam into the RFQ has to be initially convergent. In the DPIS, further optimization of the plasma density is required for better matching.

  11. Chemical Sensing Using Infrared Cavity Enhanced Spectroscopy: Short Wave Infrared Cavity Ring Down Spectroscopy (SWIR CRDS) Sensor

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Richard M.; Harper, Warren W.; Aker, Pam M.; Thompson, Jason S.; Stewart, Timothy L.

    2003-10-01

    The principal goal of Pacific Northwest National Laboratory's (PNNL's) Remote Spectroscopy Project is to explore and develop the science and technology behind point and stand off infrared (IR) spectroscopic chemical sensors that are needed for detecting weapons proliferation activity and countering terrorism. Missions addressed include detecting chemical, biological, and nuclear weapons and their production; counter terrorism measures that involve screening luggage, personnel, and shipping containers for explosives, firearms, narcotics, chemical weapons and/or their residues; and mapping of contaminated areas. The science and technology developed in this program is dual use in that it additionally supports progress in a diverse set of agendas that include chemical weapons defense programs, air operations activities, emissions monitoring, law enforcement, and medical diagnostics. Sensors for these missions require extremely low limits of detection because many of the targeted signature species are either present in low concentrations or have extremely low vapor pressures. The sensors also need to be highly selective as the environments that they will be operated in will contain a variety of interferent species and false positive detection is not an option. PNNL has been working on developing a class of sensors that draw vapor into optical cavities and use laser-based spectroscopy to identify and quantify the vapor chemical content. The cavity enhanced spectroscopies (CES) afford extreme sensitivity, excellent selectivity, noise immunity, and rapid, real-time, in-situ chemical characterization. PNNL's CES program is currently focused on developing two types of sensors. The first one, which is based on cavity ring down spectroscopy (CRDS), uses short wave infrared (SWIR) lasers to interrogate species. The second sensor, which is based on noise immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE OHMS), uses long wave infrared (LWIR

  12. Using a fourth-generation cavity enhanced spectrometer to isotopically investigate nitrous oxide emissions from biochar amended soils.

    Science.gov (United States)

    Grabenhofer, Jutta; Dercon, Gerd; Heiling, Maria; Mayr, Leo; Resch, Christian; Hood-Nowotny, Rebecca

    2016-04-01

    Research into the impacts of biochar on key processes in the nitrogen cycle is important to understand biochar's potential role in sustainable agriculture. There is conflicting evidence that biochar can reduce globally significant greenhouse gas emissions, especially N2O, one of the most important greenhouse gases in agriculture. However to date there is little information on the mechanisms involved. The source of N2O is dependent on the physical, chemical and biological status of the soil at a microbial scale and we need to understand how biochar influences it. Using the 15N2O gas flux method combined with gross rate measurements of nitrification and modelling, it should be possible to determine the parameters which drive N2O emissions and to evaluate the specific impact of biochar on these important N loss processes. To date the scope of isotopic studies on nitrous oxide emissions have been limited, due in part to technical and infrastructural access to complex and expensive mass spectrometry. With the advent of laser based systems these logistical and analytical constraints could be overcome and allow for a deeper and geographically more representative, understanding and assessment of the role of biochar in reducing nitrous oxide emissions from soil. In this study we have developed a simple method for investigated nitrous oxide emissions from soils amended with biochar, employing state of the art stable isotope techniques, using a fourth-generation cavity enhanced absorption technique a variant of conventional Cavity Ringdown Spectroscopy (CRDS) for measurement of isotopes of nitrous oxide. We will present methodologies used and results from these experiments, techniques that should path the way for a greater global understand nitrous oxide emissions from soils.

  13. Different Mode of Afferents Determines the Frequency Range of High Frequency Activities in the Human Brain: Direct Electrocorticographic Comparison between Peripheral Nerve and Direct Cortical Stimulation.

    Directory of Open Access Journals (Sweden)

    Katsuya Kobayashi

    Full Text Available Physiological high frequency activities (HFA are related to various brain functions. Factors, however, regulating its frequency have not been well elucidated in humans. To validate the hypothesis that different propagation modes (thalamo-cortical vs. cortico-coritcal projections, or different terminal layers (layer IV vs. layer II/III affect its frequency, we, in the primary somatosensory cortex (SI, compared HFAs induced by median nerve stimulation with those induced by electrical stimulation of the cortex connecting to SI. We employed 6 patients who underwent chronic subdural electrode implantation for presurgical evaluation. We evaluated the HFA power values in reference to the baseline overriding N20 (earliest cortical response and N80 (late response of somatosensory evoked potentials (HFA(SEP(N20 and HFA(SEP(N80 and compared those overriding N1 and N2 (first and second responses of cortico-cortical evoked potentials (HFA(CCEP(N1 and HFA(CCEP(N2. HFA(SEP(N20 showed the power peak in the frequency above 200 Hz, while HFA(CCEP(N1 had its power peak in the frequency below 200 Hz. Different propagation modes and/or different terminal layers seemed to determine HFA frequency. Since HFA(CCEP(N1 and HFA induced during various brain functions share a similar broadband profile of the power spectrum, cortico-coritcal horizontal propagation seems to represent common mode of neural transmission for processing these functions.

  14. Resonant cavity enhanced InGaAs photodiodes for high speed detection of 1.55 μm infrared radiation

    Science.gov (United States)

    Kaniewski, J.; Muszalski, J.; Pawluczyk, J.; Piotrowski, J.

    2005-05-01

    Resonant cavity enhanced photodetectors are promising candidates for applications in high-speed optical communications due to their high quantum efficiency and large bandwidth. This is a consequence of placing the thin absorber of the photodetector inside a Fabry-Perot microcavity so the absorption could be enhanced by recycling the photons with resonance wavelength. The performance of uncooled resonant cavity enhanced InGaAs/InAlAs photovoltaic devices operating near 1.55 μm has been studied both theoretically and experimentally. The analyses include two different types of structures with cavity end mirrors made of semiconducting and metallic reflectors as well as semiconducting and hybrid (dielectric Si3N4/SiO2 + metal) Bragg reflectors. Optimization of the device design includes: absorption layer thickness, position of absorption layer within the cavity and number of layers in distributed Bragg reflectors. Dependence of absorption on wavelength and incidence angle are discussed. Various issues related to applications of resonance cavity enhanced photodiodes in optical systems are considered. Practical devices with metallic and hybrid mirrors were fabricated by molecular beam epitaxy and by microwave-compatible processing. A properly designed device of this type has potential for subpicosecond response time.

  15. Cyclic stress at mHz frequencies aligns fibroblasts in direction of zero strain.

    Directory of Open Access Journals (Sweden)

    Uta Faust

    Full Text Available Recognition of external mechanical signals is vital for mammalian cells. Cyclic stretch, e.g. around blood vessels, is one such signal that induces cell reorientation from parallel to almost perpendicular to the direction of stretch. Here, we present quantitative analyses of both, cell and cytoskeletal reorientation of umbilical cord fibroblasts. Cyclic strain of preset amplitudes was applied at mHz frequencies. Elastomeric chambers were specifically designed and characterized to distinguish between zero strain and minimal stress directions and to allow accurate theoretical modeling. Reorientation was only induced when the applied stretch exceeded a specific amplitude, suggesting a non-linear response. However, on very soft substrates no mechanoresponse occurs even for high strain. For all stretch amplitudes, the angular distributions of reoriented cells are in very good agreement with a theory modeling stretched cells as active force dipoles. Cyclic stretch increases the number of stress fibers and the coupling to adhesions. We show that changes in cell shape follow cytoskeletal reorientation with a significant temporal delay. Our data identify the importance of environmental stiffness for cell reorientation, here in direction of zero strain. These in vitro experiments on cultured cells argue for the necessity of rather stiff environmental conditions to induce cellular reorientation in mammalian tissues.

  16. Directly modulated laser-based optical radio frequency self-interference cancellation system

    Science.gov (United States)

    Zhang, Shaojie; Xiao, Shilin; Zhang, Yunhao; Feng, Hanlin; Zhang, Lu; Zhou, Zhao

    2016-02-01

    We propose a microwave photonics system for radio frequency self-interference cancellation using optical techniques. With a simple structure, this system employs two low-cost directly modulated lasers and a balanced photodetector to subtract the strong self-interference signal from a corrupted received signal. For commonly used wireless applications, 40-dB cancellation within 900-MHz band and 33-dB cancellation within 2.4-GHz band are experimentally obtained, both over 400-MHz bandwidth. Moreover, for ultra-wideband cancellation, this system achieves more than 27-dB cancellation over 6-GHz bandwidth. The experimental results show good recovery of the weak signal of interest buried by strong self-interference after the cancellation.

  17. Bi-directional conversion between microwave and optical frequencies in a piezoelectric optomechanical device

    Science.gov (United States)

    Vainsencher, Amit; Satzinger, K. J.; Peairs, G. A.; Cleland, A. N.

    2016-07-01

    We describe the principles of design, fabrication, and operation of a piezoelectric optomechanical crystal with which we demonstrate bi-directional conversion of energy between microwave and optical frequencies. The optomechanical crystal has an optical mode at 1523 nm co-located with a mechanical breathing mode at 3.8 GHz, with a measured optomechanical coupling strength gom/2π of 115 kHz. The breathing mode is driven and detected by curved interdigitated transducers that couple to a Lamb mode in suspended membranes on either end of the optomechanical crystal, allowing the external piezoelectric modulation of the optical signal as well as the converse, the detection of microwave electrical signals generated by a modulated optical signal. We compare measurements to theory where appropriate.

  18. Direct Measurement of Time-Frequency Analogues of Sub-Planck Structures

    CERN Document Server

    Praxmeyer, Ludmila; Yang, Popo; Yang, Shang-Da; Lee, Ray-Kuang

    2015-01-01

    Exploiting the correspondence between Wigner distribution function and a frequency-resolved optical gating (FROG) measurement, we experimentally demonstrate existence of the chessboard-like interference patterns with a time-bandwidth product smaller than that of a transform-limited pulse in the phase space representation of compass states. Using superpositions of four electric pulses as realization of compass states, we have shown via direct measurements that displacements leading to orthogonal states can be smaller than limits set by uncertainty relations. In the experiment we observe an exactly chronocyclic correspondence to the sub-Planck structure in the interference pattern appearing for superposition of two Sch\\"{o}dinger-cat-like states in a position-momentum phase space.

  19. Direct measurement of time-frequency analogs of sub-Planck structures

    Science.gov (United States)

    Praxmeyer, Ludmila; Chen, Chih-Cheng; Yang, Popo; Yang, Shang-Da; Lee, Ray-Kuang

    2016-05-01

    Exploiting the correspondence between the Wigner distribution function and the frequency-resolved optical gating (FROG) measurement, we experimentally demonstrate the existence of chessboardlike interference patterns with a time-bandwidth product smaller than that of a transform-limited pulse in the phase-space representation of compass states. Using superpositions of four electric pulses as the realization of compass states, we have shown via direct measurements that displacements leading to orthogonal states can be smaller than limits set by uncertainty relations. In the experiment we observe an exactly chronocyclic correspondence to the sub-Planck structure in the interference pattern appearing for the superposition of two Schrödinger-cat-like states in a position-momentum phase space.

  20. A high speed direct digital frequency synthesizer based on multi-channel structure

    Science.gov (United States)

    Ling, Yuan; Qiang, Zhang; Yin, Shi

    2015-06-01

    This paper presents a direct digital frequency synthesizer (DDFS) for high speed application based on multi-channel structure. This DDFS has phase resolution of 32 bits and magnitude resolution of 12 bits. In order to ensure the high speed and high resolution at the same time, the multi-channel sampling technique is used and a 12 bits linear digital-to-analog converter is implemented. The chip is fabricated in TSMC 130 nm CMOS technology with active area of 0.89 × 0.98 mm2 and total power consumption of 300 mW at a single 1.2 V supply voltage. The maximum operating speed is up to 2.0 GHz at room temperature.

  1. DIRECT FREQUENCY CONVERTER WITH ARTIFICIAL AND NATURAL COMMUTATION FOR BRUSHLESS ASYNCHRONIZED MACHINES

    Directory of Open Access Journals (Sweden)

    А.М. Galynovskiy

    2015-11-01

    Full Text Available The comparative analysis of direct frequency converters with artificial and natural- switching term of the cyclical control algorithm is presented; the recommendations for their using in brushless asynchronized machines with three-phase winding are developed. Converters with a limited number of full-controlled valves have large losses in safety circuits of gates, they can be used in system of automatic excitation control. The best quality of voltage and current load are provided by converters with natural commutation using modulated input voltage, the combined potential compounds windings supply and the combined method of thyristor controlling. When the load is divided into two three-phase groups, an even number of phases of the power supply for single phase of the load are applied the bridge converter circuit. Regulation of the load current is carried out by the excitation current of field exciters and by the control angle of thyristor. Converters can be used in high-power asynchronized motors and generators. In asynchronized compensators it is possible to use diode-thyristor converters without transmitting the control signals to the rotating part. The frequency converters without modulation of input voltage have the smallest increase in rated capacity of power supply. However, they have a low quality form of the output voltage at high power factor of load.

  2. First direct two-sided bound on the B0(s) oscillation frequency

    Energy Technology Data Exchange (ETDEWEB)

    Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T.; Agelou, M.; Agram, J.-L.; Ahn, S.H.; Ahsan, M.; Alexeev, G.D.; /Buenos Aires U. /Rio de

    2006-03-01

    The authors report the first direct two-sided bound on the B{sub s}{sup 0} oscillation frequency using a large sample of B{sub s}{sup 0} semileptonic decays corresponding to approximately 1 fb{sup -1} of integrated luminosity collected by the D0 experiment in 2002-2006 during Run II of the Fermilab Tevatron Collider. The flavor (i.e., B{sub s}{sup 0} or B{sub s}{sup 0}) of the B{sub s}{sup 0} meson at the time of production was found using an opposite-side tagging technique, and the flavor at the time of decay was determined from the charge of the muon in the partially reconstructed decay B{sub s}{sup 0} {yields} {mu}{sup +} D{sub s}{sup -}X, D{sub s}{sup -} {yields} {phi}{pi}{sup -}, {phi} {yields} K{sup +}K{sup -}. A likelihood scan over the oscillation frequency, {Delta}m{sub s}, gives a most probable value of 19 ps{sup -1} and a range of 17 < {Delta}m{sub s} < 21 ps{sup -1} at the 90% C.L. At {Delta}m{sub s} = 19 ps{sup -1}, the amplitude method yields a result that deviates from the hypothesis of an oscillation amplitude of zero by 2.5 standard deviations, corresponding to a two-sided C.L. of 1%.

  3. A multiphysics and multiscale model for low frequency electromagnetic direct-chill casting

    Science.gov (United States)

    Košnik, N.; Guštin, A. Z.; Mavrič, B.; Šarler, B.

    2016-03-01

    Simulation and control of macrosegregation, deformation and grain size in low frequency electromagnetic (EM) direct-chill casting (LFEMC) is important for downstream processing. Respectively, a multiphysics and multiscale model is developed for solution of Lorentz force, temperature, velocity, concentration, deformation and grain structure of LFEMC processed aluminum alloys, with focus on axisymmetric billets. The mixture equations with lever rule, linearized phase diagram, and stationary thermoelastic solid phase are assumed, together with EM induction equation for the field imposed by the coil. Explicit diffuse approximate meshless solution procedure [1] is used for solving the EM field, and the explicit local radial basis function collocation method [2] is used for solving the coupled transport phenomena and thermomechanics fields. Pressure-velocity coupling is performed by the fractional step method [3]. The point automata method with modified KGT model is used to estimate the grain structure [4] in a post-processing mode. Thermal, mechanical, EM and grain structure outcomes of the model are demonstrated. A systematic study of the complicated influences of the process parameters can be investigated by the model, including intensity and frequency of the electromagnetic field. The meshless solution framework, with the implemented simplest physical models, will be further extended by including more sophisticated microsegregation and grain structure models, as well as a more realistic solid and solid-liquid phase rheology.

  4. First Direct Two-Sided Bound on the B_s^0 Oscillation Frequency

    CERN Document Server

    Abazov, V M; Abolins, M; Acharya, B S; Adams, M; Adams, T; Agelou, M; Agram, J L; Ahn, S H; Ahsan, M; Alexeev, G D; Alkhazov, G; Alton, A; Alverson, G; Alves, G A; Anastasoaie, M; Andeen, T; Anderson, S; Andrieu, B; Anzelc, M S; Arnoud, Y; Arov, M; Askew, A; Åsman, B; Assis-Jesus, A C S; Atramentov, O; Autermann, C; Avila, C; Ay, C; Badaud, F; Baden, A; Bagby, L; Baldin, B; Bandurin, D V; Banerjee, P; Banerjee, S; Barberis, E; Bargassa, P; Baringer, P; Barnes, C; Barreto, J; Bartlett, J F; Bassler, U; Bauer, D; Bean, A; Begalli, M; Begel, M; Belanger-Champagne, C; Bellavance, A; Benítez, J A; Beri, S B; Bernardi, G; Bernhard, R; Berntzon, L; Bertram, I; Besançon, M; Beuselinck, R; Bezzubov, V A; Bhat, P C; Bhatnagar, V; Binder, M; Biscarat, C; Black, K M; Blackler, I; Blazey, G; Blekman, F; Blessing, S; Bloch, D; Bloom, K; Blumenschein, U; Böhnlein, A; Boeriu, O; Bolton, T A; Borcherding, F; Borissov, G; Bos, K; Bose, T; Brandt, A; Brock, R; Brooijmans, G; Bross, A; Brown, D; Buchanan, N J; Buchholz, D; Bühler, M; Büscher, V; Burdin, S; Burke, S; Burnett, T H; Busato, E; Buszello, C P; Butler, J M; Calvet, S; Cammin, J; Caron, S; Carvalho, W; Casey, B C K; Cason, N M; Castilla-Valdez, H; Chakrabarti, S; Chakraborty, D; Chan, K M; Chandra, A; Chapin, D; Charles, F; Cheu, E; Chevallier, F; Cho, D K; Choi, S; Choudhary, B; Christofek, L; Claes, D; Clement, B; Clément, C; Coadou, Y; Cooke, M; Cooper, W E; Coppage, D; Corcoran, M; Cousinou, M C; Cox, B; Crepe-Renaudin, S; Cutts, D; Cwiok, M; Da Motta, H; Das, A; Das, M; Davies, B; Davies, G; Davis, G A; De, K; de Jong, P; De Jong, S J; De La Cruz-Burelo, E; De Oliveira Martins, C; Degenhardt, J D; Déliot, F; Demarteau, M; Demina, R; Demine, P; Denisov, D; Denisov, S P; Desai, S; Diehl, H T; Diesburg, M; Doidge, M; Dominguez, A; Dong, H; Dudko, L V; Duflot, L; Dugad, S R; Duperrin, A; Dyer, J; Dyshkant, A; Eads, M; Edmunds, D; Edwards, T; Ellison, J; Elmsheuser, J; Elvira, V D; Eno, S; Ermolov, P; Estrada, J; Evans, H; Evdokimov, A; Evdokimov, V N; Fatakia, S N; Feligioni, L; Ferapontov, A V; Ferbel, T; Fiedler, F; Filthaut, F; Fisher, W; Fisk, H E; Fleck, I; Ford, M; Fortner, M; Fox, H; Fu, S; Fuess, S; Gadfort, T; Galea, C F; Gallas, E; Galyaev, E; García, C; García-Bellido, A; Gardner, J; Gavrilov, V; Gay, A; Gay, P; Gelé, D; Gelhaus, R; Gerber, C E; Gershtein, Yu; Gillberg, D; Ginther, G; Gollub, N; Gómez, B; Gounder, K; Goussiou, A; Grannis, P D; Greenlee, H; Greenwood, Z D; Gregores, E M; Grenier, G; Gris, P; Grivaz, J F; Grünendahl, S; Grünewald, M W; Guo, F; Guo, J; Gutíerrez, G; Gutíerrez, P; Haas, A; Hadley, N J; Haefner, P; Hagopian, S; Haley, J; Hall, I; Hall, R E; Han, L; Hanagaki, K; Harder, K; Harel, A; Harrington, R; Hauptman, J M; Hauser, R; Hays, J; Hebbeker, T; Hedin, D; Hegeman, J G; Heinmiller, J M; Heinson, A P; Heintz, U; Hensel, C; Hesketh, G; Hildreth, M D; Hirosky, R; Hobbs, J D; Hoeneisen, B; Hohlfeld, M; Hong, S J; Hooper, R; Houben, P; Hu, Y; Hynek, V; Iashvili, I; Illingworth, R; Ito, A S; Jabeen, S; Jaffré, M; Jain, S; Jain, V; Jakobs, K; Jarvis, C; Jenkins, A; Jesik, R; Johns, K; Johnson, C; Johnson, M; Jonckheere, A; Jonsson, P; Juste, A; Käfer, D; Kahn, S; Kajfasz, E; Kalinin, A M; Kalk, J M; Kalk, J R; Kappler, S; Karmanov, D; Kasper, J; Katsanos, I; Kau, D; Kaur, R; Kehoe, R; Kermiche, S; Kesisoglou, S; Khanov, A; Kharchilava, A I; Kharzheev, Yu M; Khatidze, D; Kim, H; Kim, T J; Kirby, M H; Klima, B; Kohli, J M; Konrath, J P; Kopal, M; Korablev, V M; Kotcher, J; Kothari, B; Koubarovsky, A; Kozelov, A V; Kozminski, J; Kryemadhi, A; Krzywdzinski, S; Kühl, T; Kumar, A; Kunori, S; Kupco, A; Kurca, T; Kvita, J; Lager, S; Lammers, S; Landsberg, G L; Lazoflores, J; Le Bihan, A C; Lebrun, P; Lee, W M; Leflat, A; Lehner, F; Leonidopoulos, C; Lesne, V; Lévêque, J; Lewis, P; Li, J; Li, Q Z; Lima, J G R; Lincoln, D; Linnemann, J; Lipaev, V V; Lipton, R; Liu, Z; Lobo, L; Lobodenko, A; Lokajícek, M; Lounis, A; Love, P; Lubatti, H J; Lynker, M; Lyon, A L; Maciel, A K A; Madaras, R J; Mättig, P; Magass, C; Magerkurth, A; Magnan, A M; Makovec, N; Mal, P K; Malbouisson, H B; Malik, S; Malyshev, V L; Mao, H S; Maravin, Y; Martens, M; Mattingly, S E K; McCarthy, R; McCroskey, R; Meder, D; Melnitchouk, A; Mendes, A; Mendoza, L; Merkin, M; Merritt, K W; Meyer, A; Meyer, J; Michaut, M; Miettinen, H; Millet, T; Mitrevski, J; Molina, J; Mondal, N K; Monk, J; Moore, R W; Moulik, T; Muanza, G S; Mulders, M; Mulhearn, M; Mundim, L; Mutaf, Y D; Nagy, E; Naimuddin, M; Narain, M; Naumann, N A; Neal, H A; Negret, J P; Nelson, S; Neustroev, P; Nöding, C; Nomerotski, A; Novaes, S F; Nunnemann, T; O'Dell, V; O'Neil, D C; Obrant, G; Oguri, V; Oliveira, N; Oshima, N; Otec, R; Oteroy-Garzon, G J; Owen, M; Padley, P; Parashar, N; Park, S J; Park, S K; Parsons, J; Partridge, R; Parua, N; Patwa, A; Pawloski, G; Perea, P M; Pérez, E; Peters, K; Petroff, P; Petteni, M; Piegaia, R; Pleier, M A; Podesta-Lerma, P L M; Podstavkov, V M; Pogorelov, Y; Pol, M E; Pompos, A; Pope, B G; Popov, A V; Prado da Silva, W L; Prosper, H B; Protopopescu, S D; Qian, J; Quadt, A; Quinn, B; Rani, K J; Ranjan, K; Rapidis, P A; Ratoff, P N; Renkel, P; Reucroft, S; Rijssenbeek, M; Ripp-Baudot, I; Rizatdinova, F K; Robinson, S; Rodrigues, R F; Royon, C; Rubinov, P; Ruchti, R; Rud, V I; Sajot, G; Sánchez-Hernández, A; Sanders, M P; Santoro, A F S; Savage, G; Sawyer, L; Scanlon, T; Schaile, A D; Schamberger, R D; Scheglov, Y; Schellman, H; Schieferdecker, P; Schmitt, C; Schwanenberger, C; Schwartzman, A; Schwienhorst, R; Sen-Gupta, S; Severini, H; Shabalina, E; Shamim, M; Shary, V; Shchukin, A A; Shephard, W D; Shivpuri, R K; Shpakov, D; Siccardi, V; Sidwell, R A; Simák, V; Sirotenko, V I; Skubic, P L; Slattery, P F; Smith, R P; Snow, G R; Snow, J; Snyder, S; Söldner-Rembold, S; Song, X; Sonnenschein, L; Sopczak, A; Sosebee, M; Soustruznik, K; Souza, M; Spurlock, B; Stark, J; Steele, J; Stevenson, K; Stolin, V; Stone, A; Stoyanova, D A; Strandberg, J; Strang, M A; Strauss, M; Ströhmer, R; Strom, D; Strovink, M; Stutte, L; Sumowidagdo, S; Sznajder, A; Talby, M; Tamburello, P; Taylor, W; Telford, P; Temple, J; Tiller, B; Titov, M; Tokmenin, V V; Tomoto, M; Toole, T; Torchiani, I; Towers, S; Trefzger, T; Trincaz-Duvoid, S; Tsybychev, D; Tuchming, B; Tully, C; Turcot, A S; Tuts, P M; Unalan, R; Uvarov, L; Uvarov, S; Uzunyan, S; Vachon, B; Vanden Berg, P J; Van Kooten, R; Van Leeuwen, W M; Varelas, N; Varnes, E W; Vartapetian, A H; Vasilyev, I A; Vaupel, M; Verdier, P; Vertogradov, L S; Verzocchi, M; Villeneuve-Séguier, F; Vint, P; Vlimant, J R; Von Törne, E; Voutilainen, M; Vreeswijk, M; Wahl, H D; Wang, L; Warchol, J; Watts, G; Wayne, M; Weber, M; Weerts, H; Wermes, N; Wetstein, M; White, A; Wicke, D; Wilson, G W; Wimpenny, S J; Wobisch, M; Womersley, J; Wood, D R; Wyatt, T R; Xie, Y; Xuan, N; Yacoob, S; Yamada, R; Yan, M; Yasuda, T; Yatsunenko, Y A; Yip, K; Yoo, H D; Youn, S W; Yu, C; Yu, J; Yurkewicz, A; Zatserklyaniy, A; Zeitnitz, C; Zhang, D; Zhao, T; Zhao, Z; Zhou, B; Zhu, J; Zielinski, M; Zieminska, D; Zieminski, A; Zutshi, V

    2006-01-01

    We report the first direct two-sided bound on the $B^0_s$ oscillation frequency using a large sample of $B^0_s$ semileptonic decays corresponding to approximately 1 fb$^{-1}$ of integrated luminosity collected by the \\dzer\\ experiment in 2002--2006 during Run II of the Fermilab Tevatron Collider. The flavor (i.e., $B^0_s$ or $\\bar{B}^0_s$) of the \\bs meson at the time of production was found using an opposite-side tagging technique, and the flavor at the time of decay was determined from the charge of the muon in the partially reconstructed decay $\\bs\\to \\mu^{+}D_{s}^{-}X$, $D_{s}^{-}\\to \\phi \\pi^{-}$, $\\phi\\to K^{+}K^{-}$. A likelihood scan over the oscillation frequency, $\\Delta m_s$, gives a most probable value of 19 ps$^{-1}$ and a range of $17 < \\Delta m_s < 21$ ps$^{-1}$ at the 90% C.L. At $\\Delta m_s=19$ ps$^{-1}$, the amplitude method yields a result that deviates from the hypothesis of an oscillation amplitude of zero by 2.5 standard deviations, corresponding to a two-sided C.L. of 1%.

  5. Direct measurements of in-stream nitrate uptake with automated high frequency sensors

    Science.gov (United States)

    Kunz, Julia Vanessa; Hensley, Robert; Brase, Lisa; Borchardt, Dietrich; Rode, Michael

    2016-04-01

    Decades of nutrient studies have unveiled the importance of river networks in nutrient cycling. Still, direct methods to quantify instream removal in defined reaches have so far been limited to small streams. In rivers, where isotope tracer additions have been impracticable, uptake rates could only very rarely be measured and therefore have been mostly modelled by upscaling. Recently, the expanding availability of high resolution stream solute signals from automated sensors offers new possibilities for uptake kinetic studies. Cohen et al (2012) assessed assimilation and denitrification rates based on daily nitrate amplitudes and longitudinal concentration gradients in spring- fed chemostatic rivers. In higher order streams, overlapping of network, onsite and upstream signals require additional conceptual and methodological adaptation. Here we present a new combined longitudinal lagrangian and mass balance approach with continuous measurements of nitrate uptake rates in the German lowland river Weiße Elster, to our knowledge the first direct measurement of nitrate kinetics with continues high frequency sensors. We used 10 minutes time step NO3-N, pH, specific conductivity, dissolved oxygen, temperature and chlorophyl-a measurements and supplementing low frequency 15N isotope manual sampling. Longitudinal lagrangian measurements were conducted during day and night. Our data from two morphologically highly contrasting reaches indicate that local, seasonal or even day to day changes in uptake kinetics can be of several orders of magnitude and that the disregard of intermediate storage and dispersion can lead to high errors. The natural river reach revealed considerably higher N uptake than the channelized river reach. Furthermore, river bottom related N-uptake rates were in the same order than those found in agricultural head water streams. Besides depicting prospects and limits, we also provide important considerations for the set-up of measurement stations and for

  6. Inversion to estimate ocean wave directional spectrum from high-frequency radar

    Science.gov (United States)

    Hisaki, Yukiharu

    2015-04-01

    An high-frequency (HF) radar observes ocean surface currents and waves by radiating HF radio waves to the sea surface and analyzing the backscattered signals. Ocean wave spectrum is estimated from the first- and the second-order scattering of Doppler spectra by the inversion. The estimation of ocean surface currents is robust, because the surface currents can be derived from the peak Doppler frequency of the first-order scattering in the Doppler spectrum. The method to estimate ocean wave spectra is complicated and the second-order scattering in the Doppler spectrum is fragile, which is affected by the noise in the Doppler spectrum. A new method to estimate ocean wave spectra from HF radar is developed. This method is the extension of Hisaki (1996, 2005, 2006, 2009, 2014). The new method can be applied to both the single radar and dual radar array case, while the previous methods can be applied only the single radar case (Hisaki, 2005, 2006, 2009, 2014) or dual radar case (Hisaki, 1996). Ocean wave spectra are estimated in the regular grid cells, while wave spectra are estimated on the polar grids points with the origin of the radar position in the previous method for single radar case. The governing equations for wave estimation are the integral equations which relate the wave spectrum to the Doppler spectrum, and the energy balance equation under the assumption of stationarity. The regularization constraints in the horizontal space and the wave frequency-direction space are also used for the estimation. The unknowns, which are spectral values, surface wind speeds and directions, are estimated by seeking the minimum of the objective function, which is defined as the sum of weighted squares of the equations. The signal to noise ratio in the Doppler spectrum for wave estimation must be high. We selected the Doppler spectra using the SOM (Self organization map ) analysis method. The method will be demonstrated by comparing with in-situ observed data, in which only

  7. Spatial hearing in Cope's gray treefrog: II. Frequency-dependent directionality in the amplitude and phase of tympanum vibrations.

    Science.gov (United States)

    Caldwell, Michael S; Lee, Norman; Schrode, Katrina M; Johns, Anastasia R; Christensen-Dalsgaard, Jakob; Bee, Mark A

    2014-04-01

    Anuran ears function as pressure difference receivers, and the amplitude and phase of tympanum vibrations are inherently directional, varying with sound incident angle. We quantified the nature of this directionality for Cope's gray treefrog, Hyla chrysoscelis. We presented subjects with pure tones, advertisement calls, and frequency-modulated sweeps to examine the influence of frequency, signal level, lung inflation, and sex on ear directionality. Interaural differences in the amplitude of tympanum vibrations were 1-4 dB greater than sound pressure differences adjacent to the two tympana, while interaural differences in the phase of tympanum vibration were similar to or smaller than those in sound phase. Directionality in the amplitude and phase of tympanum vibration were highly dependent on sound frequency, and directionality in amplitude varied slightly with signal level. Directionality in the amplitude and phase of tone- and call-evoked responses did not differ between sexes. Lung inflation strongly affected tympanum directionality over a narrow frequency range that, in females, included call frequencies. This study provides a foundation for further work on the biomechanics and neural mechanisms of spatial hearing in H. chrysoscelis, and lends valuable perspective to behavioral studies on the use of spatial information by this species and other frogs. PMID:24504183

  8. Prospects for precision measurements of atomic helium using direct frequency comb spectroscopy

    CERN Document Server

    Eyler, E E; Stowe, Matthew C; Thorpe, Michael J; Schibli, T R; Ye, Jun

    2007-01-01

    We analyze several possibilities for precisely measuring electronic transitions in atomic helium by the direct use of phase-stabilized femtosecond frequency combs. Because the comb is self-calibrating and can be shifted into the ultraviolet spectral region via harmonic generation, it offers the prospect of greatly improved accuracy for UV and far-UV transitions. To take advantage of this accuracy an ultracold helium sample is needed. For measurements of the triplet spectrum a magneto-optical trap (MOT) can be used to cool and trap metastable $2 ^3S$ state atoms. We analyze schemes for measuring the two-photon $2 ^3S \\to 4 ^3S$ interval, and for resonant two-photon excitation to high Rydberg states, $2 ^3S \\to 3 ^3P \\to n^3S,D$. We also analyze experiments on the singlet-state spectrum. To accomplish this we propose schemes for producing and trapping ultracold helium in the $1 ^1S$ or $2 ^1S$ state via intercombination transition. A particularly intriguing scenario is the possibility of direct singlet state sp...

  9. The International Deep Planet Survey II: The frequency of directly imaged giant exoplanets with stellar mass

    CERN Document Server

    Galicher, Raphael; Macintosh, Bruce; Zuckerman, Ben; Barman, Travis; Konopacky, Quinn; Song, Inseok; Patience, Jenny; Lafreniere, David; Doyon, Rene; Nielsen, Eric L

    2016-01-01

    Radial velocity and transit methods are effective for the study of short orbital period exoplanets but they hardly probe objects at large separations for which direct imaging can be used. We carried out the international deep planet survey of 292 young nearby stars to search for giant exoplanets and determine their frequency. We developed a pipeline for a uniform processing of all the data that we have recorded with NIRC2/Keck II, NIRI/Gemini North, NICI/Gemini South, and NACO/VLT for 14 years. The pipeline first applies cosmetic corrections and then reduces the speckle intensity to enhance the contrast in the images. The main result of the international deep planet survey is the discovery of the HR 8799 exoplanets. We also detected 59 visual multiple systems including 16 new binary stars and 2 new triple stellar systems, as well as 2,279 point-like sources. We used Monte Carlo simulations and the Bayesian theorem to determine that 1.05[+2.80-0.70]% of stars harbor at least one giant planet between 0.5 and 14...

  10. First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar.

    Science.gov (United States)

    DeRuiter, Stacy L; Southall, Brandon L; Calambokidis, John; Zimmer, Walter M X; Sadykova, Dinara; Falcone, Erin A; Friedlaender, Ari S; Joseph, John E; Moretti, David; Schorr, Gregory S; Thomas, Len; Tyack, Peter L

    2013-08-23

    Most marine mammal- strandings coincident with naval sonar exercises have involved Cuvier's beaked whales (Ziphius cavirostris). We recorded animal movement and acoustic data on two tagged Ziphius and obtained the first direct measurements of behavioural responses of this species to mid-frequency active (MFA) sonar signals. Each recording included a 30-min playback (one 1.6-s simulated MFA sonar signal repeated every 25 s); one whale was also incidentally exposed to MFA sonar from distant naval exercises. Whales responded strongly to playbacks at low received levels (RLs; 89-127 dB re 1 µPa): after ceasing normal fluking and echolocation, they swam rapidly, silently away, extending both dive duration and subsequent non-foraging interval. Distant sonar exercises (78-106 dB re 1 µPa) did not elicit such responses, suggesting that context may moderate reactions. The observed responses to playback occurred at RLs well below current regulatory thresholds; equivalent responses to operational sonars could elevate stranding risk and reduce foraging efficiency. PMID:23825085

  11. A 4 GHz 32 bit direct digital frequency synthesizer based on a novel architecture

    International Nuclear Information System (INIS)

    This paper presents a novel direct digital frequency synthesizer (DDFS) architecture based on nonlinear DAC coarse quantization and the ROM-based piecewise approximation method, which has the advantages of high speed, low power and low hardware resources. By subdividing the sinusoid into a collection of phase segments, the same initial value of each segment is realized by a nonlinear DAC. The ROM is decomposed with a coarse ROM and fine ROM using the piecewise approximation method. Then, the coarse ROM stores the offsets between the initial value of the common segment and the initial value of each line in the same segment. Meanwhile, the fine ROM stores the differences between the line values and the initial value of each line. A ROM compression ratio of 32 can be achieved in the case of 11 bit phase and 9 bit amplitude. Based on the above method, a prototype chip was fabricated using 1.4 μm GaAs HBT technology. The measurement shows an average spurious-free dynamic range (SFDR) of 45 dBc, with the worst SFDR only 40.07 dBc at a 4.0 GHz clock. The chip area is 4.6 × 3.7 mm2 and it consumes 7 W from a −4.9 V power supply. (semiconductor integrated circuits)

  12. A 4 GHz 32 bit direct digital frequency synthesizer based on a novel architecture

    Science.gov (United States)

    Jin, Wu; Jianwu, Chen; Danyu, Wu; Lei, Zhou; Fan, Jiang; Zhi, Jin; Xinyu, Liu

    2013-11-01

    This paper presents a novel direct digital frequency synthesizer (DDFS) architecture based on nonlinear DAC coarse quantization and the ROM-based piecewise approximation method, which has the advantages of high speed, low power and low hardware resources. By subdividing the sinusoid into a collection of phase segments, the same initial value of each segment is realized by a nonlinear DAC. The ROM is decomposed with a coarse ROM and fine ROM using the piecewise approximation method. Then, the coarse ROM stores the offsets between the initial value of the common segment and the initial value of each line in the same segment. Meanwhile, the fine ROM stores the differences between the line values and the initial value of each line. A ROM compression ratio of 32 can be achieved in the case of 11 bit phase and 9 bit amplitude. Based on the above method, a prototype chip was fabricated using 1.4 μm GaAs HBT technology. The measurement shows an average spurious-free dynamic range (SFDR) of 45 dBc, with the worst SFDR only 40.07 dBc at a 4.0 GHz clock. The chip area is 4.6 × 3.7 mm2 and it consumes 7 W from a -4.9 V power supply.

  13. Improved ESPRIT Method for Joint Direction-of-Arrival and Frequency Estimation Using Multiple-Delay Output

    OpenAIRE

    Wang Xudong; Xiaofei Zhang; Jianfeng Li; Jinchao Bai

    2012-01-01

    An automatic pairing joint direction-of-arrival (DOA) and frequency estimation is presented to overcome the unsatisfactory performances of estimation of signal parameter via rotational invariance techniques- (ESPRIT-) like algorithm of Wang (2010), which requires an additional pairing. By using multiple-delay output of a uniform linear antenna arrays (ULA), the proposed algorithm can estimate joint angles and frequencies with an improved ESPRIT. Compared with Wang’s ESPRIT algorithm, the angl...

  14. Diminishing high-frequency directivity due to a source effect: Empirical evidence from small earthquakes in the Abruzzo region, Italy

    Science.gov (United States)

    Pacor, F.; Gallovič, F.; Puglia, R.; Luzi, L.; D'Amico, M.

    2016-05-01

    The aim of this study is to investigate the directivity effects of ~250 aftershocks (magnitudes 3-5.5) of the Mw 6.1 2009 L'Aquila earthquake (central Italy). To this end, we estimate the apparent source spectra at each station removing path and site effects inferred by standard Generalized Inversion Technique. Then, we evaluate the residuals between the apparent source spectra and the event mean source spectrum at selected frequencies. We investigate azimuthal and frequency dependence of the residuals for 40 events with the best station coverage. For most of events with the strongest directivity effect (Mw 3.4-4.0), we observe a remarkable decrease of the directivity amplification at high frequencies, which has not yet been documented for such relatively small-magnitude events. Since there is negligible distance dependence, we ascribe this observation to a source phenomenon such as significant small-scale rupture propagation complexity.

  15. Sub-kHz linewidth narrowing of a mid-infrared OPO idler frequency by direct cavity stabilization

    CERN Document Server

    Ricciardi, I; Parisi, M; Maddaloni, P; Santamaria, L; De Natale, P; De Rosa, M

    2015-01-01

    We stabilize the idler frequency of a singly-resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-P\\'erot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10$^3$ Hz$^2$/Hz is reached, with a Gaussian linewidth of 920 Hz over 100 ms, which demonstrates the potential for reaching spectral purity down to the Hz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance.

  16. Zipf’s word frequency law in natural language: A critical review and future directions

    OpenAIRE

    Piantadosi, Steven T.

    2014-01-01

    The frequency distribution of words has been a key object of study in statistical linguistics for the past 70 years. This distribution approximately follows a simple mathematical form known as Zipf ’ s law. This article first shows that human language has a highly complex, reliable structure in the frequency distribution over and above this classic law, although prior data visualization methods have obscured this fact. A number of empirical phenomena related to word frequencies are then revie...

  17. A direct frequency comb for two-photon transition spectroscopy in a cesium vapor

    Institute of Scientific and Technical Information of China (English)

    Zhang Yi-Chi; Wu Ji-Zhou; Li Yu-Qing; Jin Li; Ma Jie; Wang Li-Rong; Zhao Yan-Ting; Xiao Lian-Tuan; Jia Suo-Tang

    2012-01-01

    A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor.The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts,shaped in an original way,and focused into a room-temperature cesium vapor.We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb,and through absolute frequency measurements.

  18. Ancillary Frequency Control of Direct Drive Full-Scale Converter Based Wind Power Plants

    OpenAIRE

    Hu, Weihao; Su, Chi; Fang, Jiakun; Chen, Zhe; Hu, Yanting

    2013-01-01

    This paper presents a simulation model of a wind power plant based on a MW-level variable speed wind turbine with a full-scale back-to-back power converter developed in the simulation tool of DIgSILENT Power Factory. Three different kinds of ancillary frequency control strategies, namely inertia emulation, primary frequency control and secondary frequency control, are proposed in order to improve the frequency stability of power systems. The modified IEEE 39-bus test system with a large-scale...

  19. Prospects for precision measurements of atomic helium using direct frequency comb spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Eyler, E.E.; Chieda, D.E. [Connecticut Univ., Physics Dept., Storrs, CT (United States); Stowe, M.C.; Thorpe, M.J.; Schibli, T.R.; Ye, J. [Colorado Univ., Dept. of Physics, JILA, National Institute of Standards and Technology, Boulder, CO (United States)

    2008-06-15

    We analyze several possibilities for precisely measuring electronic transitions in atomic helium by the direct use of phase-stabilized femtosecond frequency combs. Because the comb is self-calibrating and can be shifted into the ultraviolet spectral region via harmonic generation, it offers the prospect of greatly improved accuracy for UV and far-UV transitions. To take advantage of this accuracy an ultracold helium sample is needed. For measurements of the triplet spectrum a magneto-optical trap (MOT) can be used to cool and trap metastable 2{sup 3}S state atoms. We analyze schemes for measuring the two-photon 2{sup 3}S {yields} 4{sup 3}S interval, and for resonant two-photon excitation to high Rydberg states, 2{sup 3}S {yields} 3{sup 3}P {yields} n{sup 3}S, D. We also analyze experiments on the singlet-state spectrum. To accomplish this we propose schemes for producing and trapping ultracold helium in the 1{sup 1}S or 2{sup 1}S state via intercombination transitions. A particularly intriguing scenario is the possibility of measuring the 1{sup 1}S {yields} 2{sup 1}S transition with extremely high accuracy by use of two-photon excitation in a magic wavelength trap that operates identically for both states. We predict a 'triple magic wavelength' at 412 nm that could facilitate numerous experiments on trapped helium atoms, because here the polarizabilities of the 1{sup 1}S, 2{sup 1}S and 2{sup 3}S states are all similar, small, and positive. (authors)

  20. Light emitting diode cavity enhanced differential optical absorption spectroscopy (LED-CE-DOAS): a novel technique for monitoring atmospheric trace gases

    Science.gov (United States)

    Thalman, Ryan M.; Volkamer, Rainer M.

    2009-08-01

    The combination of Cavity Enhanced Absorption Spectroscopy (CEAS) with broad-band light sources (e.g. Light- Emitting Diodes, LEDs) lends itself to the application of cavity enhanced DOAS (CE-DOAS) to perform sensitive and selective point measurements of multiple trace gases with a single instrument. In contrast to other broad-band CEAS techniques, CE-DOAS relies only on the measurement of relative intensity changes, i.e., does not require knowledge of the light intensity in the absence of trace gases and aerosols (I0). We have built a prototype LED-CE-DOAS instrument in the blue spectral range (420-490nm) to measure nitrogen dioxide (NO2), glyoxal (CHOCHO), iodine monoxide (IO), water (H2O) and oxygen dimers (O4). Aerosol extinction is retrieved at two wavelengths by means of observing water and O4 and measuring pressure, temperature and relative humidity independently. The instrument components are presented, and the approach to measure aerosol extinction is demonstrated by means of a set of experiments where laboratory generated monodisperse aerosols are added to the cavity. The aerosol extinction cross section agrees well with Mie calculations, demonstrating that our setup enables measurements of the above gases in open cavity mode.

  1. A Combination of Vocal Frequency Dynamic and Summary Features Discriminates between Three Pragmatic Categories of Infant-Directed Speech.

    Science.gov (United States)

    Katz, Gary S.; And Others

    1996-01-01

    Assessed the relative contribution of dynamic and summary features of vocal frequency to the discrimination of pragmatic categories in infant-directed speech. Forty-nine mothers were instructed to use their voice to get their infant's attention, show approval, and provide comfort. Findings suggest that both dynamic and summary features are…

  2. Design of smoothed multi-flared antenna for multi-frequency reception of direct transmission from meteorological satellites

    Science.gov (United States)

    Yasodha, Polisetti; Jayaraman, Achuthan; Kesarkar, Amit P.; Thawait, Prateek

    2016-07-01

    The direct radiance data assimilation is found to be advantageous for the numerical weather prediction over short and medium range. Therefore reception of satellite radiance in real time is important. Satellite earth station is the preferred choice for direct reception of this data, which is voluminous. High Rate Information being transmitted from these satellites operating in L, S, C and X bands needs to be received. A commercial wide band antenna is not preferred for such application, as it operates uniformly over the entire frequency range in these bands and may create interference over the unwanted frequencies. As the frequencies of interest occupy only a small portion of these bands, it is essential to design a horn antenna, which receives only specified frequencies and filter other frequencies. In this work, we have designed a multi-flare multi-frequency cylindrical horn antenna for reception of direct transmission from meteorological satellites. This earth station antenna tracks selected satellites working over specified frequency ranges, which are 1.694-1.703 GHz, 2.0-2.06 GHz, 4.5-4.6 GHz and 7.8-7.9 GHz in L, S, C and X bands respectively. Cylindrical waveguides for the frequencies, 1.6, 2, 4.5 and 8 GHz are designed and they are joined in the increasing order of radius with suitable conical shapes. The slope of the cones is adjusted experimentally. With this design, the return loss is simulated and found to be better than 20 dB upto 4.5 GHz and later it became poor. To overcome this difficulty, the abrupt transitions at the joints of the conical and cylindrical waveguides are made smoothen by increasing the diameter of one mouth of the cylinder and reducing the other mouth to match with the cylinders corresponding to next higher and lower frequency respectively. As a result, a smooth flared antenna is obtained and the simulated results are satisfactory. A parabolic reflector of 4 m diameter is designed and the smooth multi-flared antenna is kept at the

  3. Direct measurement of spatial electron density oscillations in a dual frequency capacitive plasma

    International Nuclear Information System (INIS)

    The spatio-temporal electron density oscillation in a narrow gap dual frequency (27.12 and 1.937 MHz) capacitive discharge has been measured for the first time by using a floating microwave hairpin resonance probe. By measuring the probe's resonance frequency in a space and phase-resolved manner, we observe significant oscillation in electron density at both drive frequencies throughout the region between the parallel plate electrodes. The observed phenomenon is attributed to the influence of presheath electric fields of the opposing electrodes in alternate fashion

  4. Self-referenced, accurate and sensitive optical frequency comb spectroscopy with a virtually imaged phased array spectrometer.

    Science.gov (United States)

    Kowzan, Grzegorz; Lee, Kevin F; Paradowska, Magdalena; Borkowski, Mateusz; Ablewski, Piotr; Wójtewicz, Szymon; Stec, Kamila; Lisak, Daniel; Fermann, Martin E; Trawiński, Ryszard S; Masłowski, Piotr

    2016-03-01

    We present a cavity-enhanced direct optical frequency comb spectroscopy system with a virtually imaged phased array (VIPA) spectrometer and either a dither or a Pound-Drever-Hall (PDH) locking scheme used for stable transmission of the comb through the cavity. A self-referenced scheme for frequency axis calibration is shown along with an analysis of its accuracy. A careful comparison between both locking schemes is performed based on near-IR measurements of the carbon monoxide ν=3←0 band P branch transitions in a gas sample with known composition. The noise-equivalent absorptions (NEA) for the PDH and dither schemes are 9.9×10-10  cm-1 and 5.3×10-9  cm-1, respectively. PMID:26974094

  5. Dielectric constants of multiwall carbon nanotubes from direct current to microwave frequencies.

    Science.gov (United States)

    Wang, Y C; Lue, J T; Pauw, K F

    2009-03-01

    A cylindrical rod constructed from a uniform mixture of multiwall carbon nanotubes and alumina powders dissolved in paraffin was inserted in the center of a radio frequency cavity. The real and imaginary dielectric constants of carbon tubes at various frequencies were measured, respectively, from the resonant frequencies and the quality factors, by a resistance-inductance-cacitance (RLC) meter and a microwave network analyzer. The dielectric rod benefits the protection of the sample from adsorbing moisture and preventing the rod from filling with air, thus making accurate measurments. A tunable probe specifically designed for the field pattern of a TM010 mode is delineated to improve the microwave coupling of the dielectric microwave resonator. This refined design is expected to facilitate the measurement yielding a significant manner. The real and imaginary parts of the dielectric constant of carbon nanotubes increase and decrease, respectively as frequencies increase satisfactorily in complying with the description from the free electron Drude model. PMID:19435033

  6. Direct Seeded Single Frequency mid-IR OPA all Passive Light Source

    DEFF Research Database (Denmark)

    Høgstedt, Lasse; Tidemand-Lichtenberg, Peter; Pedersen, Christian

    2013-01-01

    We present a two stage pulsed mid-infrared light source based on nonlinear downconversion of light. The light source is single frequency, tunable, all passive, single moded and build with standard optical components.......We present a two stage pulsed mid-infrared light source based on nonlinear downconversion of light. The light source is single frequency, tunable, all passive, single moded and build with standard optical components....

  7. Coupling and tuning of modal frequencies in direct current biased microelectromechanical systems arrays

    Energy Technology Data Exchange (ETDEWEB)

    Kambali, Prashant N.; Swain, Gyanadutta; Pandey, Ashok Kumar, E-mail: ashok@iith.ac.in [Department of Mechanical and Aerospace Engineering, IIT Hyderabad, Yeddumailaram 502205 (India); Buks, Eyal [Faculty of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Gottlieb, Oded [Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

    2015-08-10

    Understanding the coupling of different modal frequencies and their tuning mechanisms has become essential to design multi-frequency MEMS devices. In this work, we fabricate a MEMS beam with fixed boundaries separated from two side electrodes and a bottom electrode. Subsequently, we perform experiments to obtain the frequency variation of in-plane and out-of-plane mechanical modes of the microbeam with respect to both DC bias and laser heating. We show that the frequencies of the two modes coincide at a certain DC bias, which in turn can also be varied due to temperature. Subsequently, we develop a theoretical model to predict the variation of the two modes and their coupling due to a variable gap between the microbeam and electrodes, initial tension, and fringing field coefficients. Finally, we discuss the influence of frequency tuning parameters in arrays of 3, 33, and 40 microbeams, respectively. It is also found that the frequency bandwidth of a microbeam array can be increased to as high as 25 kHz for a 40 microbeam array with a DC bias of 80 V.

  8. Coupling and tuning of modal frequencies in direct current biased microelectromechanical systems arrays

    International Nuclear Information System (INIS)

    Understanding the coupling of different modal frequencies and their tuning mechanisms has become essential to design multi-frequency MEMS devices. In this work, we fabricate a MEMS beam with fixed boundaries separated from two side electrodes and a bottom electrode. Subsequently, we perform experiments to obtain the frequency variation of in-plane and out-of-plane mechanical modes of the microbeam with respect to both DC bias and laser heating. We show that the frequencies of the two modes coincide at a certain DC bias, which in turn can also be varied due to temperature. Subsequently, we develop a theoretical model to predict the variation of the two modes and their coupling due to a variable gap between the microbeam and electrodes, initial tension, and fringing field coefficients. Finally, we discuss the influence of frequency tuning parameters in arrays of 3, 33, and 40 microbeams, respectively. It is also found that the frequency bandwidth of a microbeam array can be increased to as high as 25 kHz for a 40 microbeam array with a DC bias of 80 V

  9. Magnetic Force Nanoprobe for Direct Observation of Audio Frequency Tonotopy of Hair Cells.

    Science.gov (United States)

    Kim, Ji-Wook; Lee, Jae-Hyun; Ma, Ji-Hyun; Chung, Eunna; Choi, Hongsuh; Bok, Jinwoong; Cheon, Jinwoo

    2016-06-01

    Sound perception via mechano-sensation is a remarkably sensitive and fast transmission process, converting sound as a mechanical input to neural signals in a living organism. Although knowledge of auditory hair cell functions has advanced over the past decades, challenges remain in understanding their biomechanics, partly because of their biophysical complexity and the lack of appropriate probing tools. Most current studies of hair cells have been conducted in a relatively low-frequency range (perception of 20 kHz or higher. Here, we demonstrate that the magnetic force nanoprobe (MFN) has superb spatiotemporal capabilities to mechanically stimulate spatially-targeted individual hair cells with a temporal resolution of up to 9 μs, which is equivalent to approximately 50 kHz; therefore, it is possible to investigate avian hair cell biomechanics at different tonotopic regions of the cochlea covering a full hearing frequency range of 50 to 5000 Hz. We found that the variation of the stimulation frequency and amplitude of hair bundles creates distinct mechanical responsive features along the tonotopic axis, where the kinetics of the hair bundle recovery motion exhibits unique frequency-dependent characteristics: basal, middle, and apical hair bundles can effectively respond at their respective ranges of frequency. We revealed that such recovery kinetics possesses two different time constants that are closely related to the passive and active motilities of hair cells. The use of MFN is critical for the kinetics study of free-standing hair cells in a spatiotemporally distinct tonotopic organization. PMID:27215487

  10. Coherent Photon Scattering and Direct Imaging of the Iso-frequency Contours in Large-area Photonic Crystal Slabs

    CERN Document Server

    Regan, Emma C; Zhen, Bo; Kaminer, Ido; Hsu, Chia Wei; Shen, Yichen; Joannopoulos, John D; Soljacic, Marin

    2015-01-01

    While the absorption of light can be enhanced using optical resonances in a photonic crystal slab, the characteristics of resonance-enhanced scattering are much less studied. Here, we present an analytical model of resonance-enhanced photon scattering from generic fabrication errors and surface roughness, which agrees well with our experimental results. This phenomenon provides a new method to measure the photonic band structure and to directly map the iso-frequency contours of large-area photonic crystal slabs. Additionally, the iso-frequency contours provide information about the characteristics of the disorder and serve as a feedback tool to improve fabrication processes.

  11. Estimation of the Doppler frequency and direction of arrival of the ionospherically propagated HF signals

    Science.gov (United States)

    Su, Hongtao; Liu, Hongwei; Shui, Penglang; Bao, Zheng

    2009-08-01

    High-frequency (HF) signals reflected from different points within each ionospheric layer may have slightly different Doppler frequencies and angles of arrival. The superposition of these signals leads to time varying and nonplanar wavefronts. Investigation of temporal and spatial characteristics of the ionospherically propagated HF signals plays an important role in designing the signal processing algorithms for the HF over-the-horizon radar (OTHR). A cost-efficient superresolution algorithm for simultaneously estimating the Doppler frequencies and angles of arrival of the ionospherically propagated HF signals is proposed in this paper. The effectiveness of the proposed algorithm is verified by the experimental data from a trial HF OTHR. Furthermore, the superposition model with the HF signal reflected by a smooth ionospheric layer consisting of a number of submode signals is also confirmed by the experimental data processing results.

  12. Continuous probe of cold complex molecules with infrared frequency comb spectroscopy

    CERN Document Server

    Spaun, Ben; Patterson, David; Bjork, Bryce J; Heckl, Oliver H; Doyle, John M; Ye, Jun

    2016-01-01

    Cavity-enhanced frequency comb spectroscopy for molecule detection in the mid-infrared powerfully combines high resolution, high sensitivity, and broad spectral coverage. However, this technique, and essentially all spectroscopic methods, is limited in application to relatively small, simple molecules. Here we integrate comb spectroscopy with continuous, cold samples of molecules produced via buffer gas cooling, thus enabling the study of significantly more complex molecules. We report simultaneous gains in resolution, sensitivity, and bandwidth and demonstrate this combined capability with the first rotationally resolved direct absorption spectra in the CH stretch region of several complex molecules. These include nitromethane (CH$_3$NO$_2$), a model system that presents challenging questions to the understanding of large amplitude vibrational motion, as well as several large organic molecules with fundamental spectroscopic and astrochemical relevance, including naphthalene (C$_{10}$H$_8$), adamantane (C$_{1...

  13. Feasibility of weaning and direct extubation from open lung high-frequency ventilation in preterm infants

    NARCIS (Netherlands)

    A. van Velzen; A. de Jaegere; J. van der Lee; A. van Kaam

    2009-01-01

    OBJECTIVE: High-frequency ventilation (HFV) is increasingly used in preterm infants, but data on weaning and extubation are limited. We aimed to establish if weaning the continuous distending pressure (CDP) below 8 cm H2O and the Fio2 below 0.30 is feasible in preterm infants on open lung HFV and if

  14. On the Directivity of Low-Frequency Type IV Radio Bursts

    CERN Document Server

    Gopalswamy, Nat; Mäkelä, Pertti; Yashiro, Seiji; Cairns, Iver H

    2016-01-01

    An intense type IV radio burst was observed by the STEREO Behind (STB) spacecraft located about 144 degres behind Earth. The burst was associated with a large solar eruption that occurred on the backside of the Sun (N05E151) close to the disk center in the STB view. The eruption was also observed by the STEREO Ahead (STA) spacecraft (located at 149 degrees ahead of Earth) as an eruption close to the west limb (N05W60) in that view. The type IV burst was complete in STB observations in that the envelope reached the lowest frequency and then receded to higher frequencies. The burst was partial viewed from STA, revealing only the edge coming down to the lowest frequency. The type IV burst was not observed at all near Earth because the source was 61 degrees behind the east limb. The eruption was associated with a low-frequency type II burst observed in all three views, although it was not very intense. Solar energetic particles were also observed at both STEREOs and at SOHO, suggesting that the shock was much ext...

  15. Extended exergy concept to facilitate designing and optimization of frequency-dependent direct energy conversion systems

    International Nuclear Information System (INIS)

    Highlights: • Proved exergy method is not adequate to optimize frequency-dependent energy conversion. • Exergy concept is modified to facilitate the thermoeconomic optimization of photocell. • The exergy of arbitrary radiation is used for a practical purpose. • The utility of the concept is illustrated using pragmatic examples. - Abstract: Providing the radiation within the acceptable (responsive) frequency range(s) is a common method to increase the efficiency of the frequency-dependent energy conversion systems, such as photovoltaic and nano-scale rectenna. Appropriately designed auxiliary items such as spectrally selective thermal emitters, optical filters, and lenses are used for this purpose. However any energy conversion method that utilizes auxiliary components to increase the efficiency of a system has to justify the potential cost incurred by those auxiliary components through the economic gain emerging from the increased system efficiency. Therefore much effort should be devoted to design innovative systems, effectively integrating the auxiliary items and to optimize the system with economic considerations. Exergy is the widely used method to design and optimize conventional energy conversion systems. Although the exergy concept is used to analyze photovoltaic systems, it has not been used effectively to design and optimize such systems. In this manuscript, we present a modified exergy method in order to effectively design and economically optimize frequency-dependent energy conversion systems. Also, we illustrate the utility of this concept using examples of thermophotovoltaic, Photovoltaic/Thermal and concentrated solar photovoltaic

  16. Ancillary Frequency Control of Direct Drive Full-Scale Converter Based Wind Power Plants

    DEFF Research Database (Denmark)

    Hu, Weihao; Su, Chi; Fang, Jiakun; Chen, Zhe; Hu, Yanting

    2013-01-01

    This paper presents a simulation model of a wind power plant based on a MW-level variable speed wind turbine with a full-scale back-to-back power converter developed in the simulation tool of DIgSILENT Power Factory. Three different kinds of ancillary frequency control strategies, namely inertia...

  17. Sub-kilohertz linewidth narrowing of a mid-infrared optical parametric oscillator idler frequency by direct cavity stabilization.

    Science.gov (United States)

    Ricciardi, I; Mosca, S; Parisi, M; Maddaloni, P; Santamaria, L; De Natale, P; De Rosa, M

    2015-10-15

    We stabilize the idler frequency of a singly resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-Perot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10(3)  Hz(2)/Hz is reached on average, with a Gaussian linewidth of 920 Hz over 100 ms, which reveals the potential for reaching spectral purity down to the hertz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance. PMID:26469609

  18. Absolute absorption and fluorescence measurements over a dynamic range of 10$^6$ with cavity-enhanced laser-induced fluorescence

    CERN Document Server

    Sanders, Scott E; Nahler, N Hendrik; Wrede, Eckart

    2013-01-01

    We describe a novel experimental setup that combines the advantages of both laser-induced fluorescence and cavity ring-down techniques. The simultaneous measurement of the ring-down and fluorescence signals from the same sample in a single laser beam delivers the calibration of the fluorescence measurement to gain absolute quantities: absorption cross section, sample density and fluorescence quantum yield. At the same time, the fluorescence measurement extends the dynamic range of a stand-alone cavity ring-down setup from typically three to at least six orders of magnitude. The methodology of this combined cavity-enhanced laser-induced fluorescence (CELIF) technique is developed and rigorously tested against the spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell.

  19. Experimental and theoretical analysis of THz-frequency, direction-dependent, phonon polariton modes in a subwavelength, anisotropic slab waveguide.

    Science.gov (United States)

    Yang, Chengliang; Wu, Qiang; Xu, Jingjun; Nelson, Keith A; Werley, Christopher A

    2010-12-01

    Femtosecond optical pulses were used to generate THz-frequency phonon polariton waves in a 50 micrometer lithium niobate slab, which acts as a subwavelength, anisotropic planar waveguide. The spatial and temporal electric field profiles of the THz waves were recorded for different propagation directions using a polarization gating imaging system, and experimental dispersion curves were determined via a two-dimensional Fourier transform. Dispersion relations for an anisotropic slab waveguide were derived via analytical analysis and found to be in excellent agreement with all observed experimental modes. From the dispersion relations, we analyze the propagation-direction-dependent behavior, effective refractive index values, and generation efficiencies for THz-frequency modes in the subwavelength, anisotropic slab waveguide. PMID:21164986

  20. Laser ion source: A direct plasma injection scheme for two-beam type interdigital-H radio frequency quadrupole linac

    International Nuclear Information System (INIS)

    We developed a laser ion source using a direct plasma injection scheme (DPIS) as an injection system for a two-beam type radio frequency quadrupole (RFQ) linac with an interdigital-H (IH) type cavity. The laser ion source in the DPIS is directly connected to the RFQ cavity without the low energy beam transport system. We achieved a high current C2+ beam above 60 mA per beam channel from the ion source. The beam will be injected to the two-beam type IH-RFQ linac, and the linac will generate a beam current of approximately 44 mA per beam channel.

  1. Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing.

    Science.gov (United States)

    Keiner, Robert; Herrmann, Martina; Küsel, Kirsten; Popp, Jürgen; Frosch, Torsten

    2015-03-15

    The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N2 and N2O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of (15)N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases ((14)N2, (14)N2O, O2, and CO2) and to trace the fate of (15)N-labeled nitrate substrate ((15)N2, (15)N2O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO2-bicarbonate equilibrium. Continuous pH monitoring - without the need to insert an electrode into solution - elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N2O, due to an inhibition of nitrous oxide reductase. Cavity enhanced Raman gas spectroscopy has a high potential for the assessment of denitrification processes and can contribute substantially to our understanding of nitrogen cycling in both natural and agricultural systems. PMID:25732425

  2. Cavity-enhanced AlGaAs/GaAs resonant tunneling photodetectors for telecommunication wavelength light detection at 1.3 μm

    Science.gov (United States)

    Pfenning, Andreas; Hartmann, Fabian; Langer, Fabian; Kamp, Martin; Höfling, Sven; Worschech, Lukas

    2015-09-01

    We demonstrate a cavity-enhanced photodetector at the telecommunication wavelength of λ = 1.3 μm based on a resonant tunneling diode (RTD). The cavity-enhanced RTD photodetector consists of three integral parts: First, a Ga0.89In0.11N0.04As0.96 absorption layer that can be grown lattice-matched on GaAs and which is light-active in the near infrared spectral region due to its reduced bandgap energy. Second, an Al0.6Ga0.4As/GaAs double barrier resonant tunneling structure (RTS) that serves as high gain internal amplifier of weak electric signals caused by photogenerated electron-hole pairs within the GaInNAs absorption layer. Third, an optical distributed Bragg reflector (DBR) cavity consisting of five top and seven bottom alternating GaAs/AlAs mirror pairs, which provides an enhanced quantum efficiency at the resonance wavelength. The samples were grown by molecular beam epitaxy. Electro-optical properties of the RTDs were studied at room temperature. From the reflection-spectrum the optical resonance at λ = 1.29 μm was extracted. The current-voltage characteristics were studied in the dark and under illumination and a wellpronounced photo-response was found and is attributed to accumulation of photogenerated holes in the vicinity of the RTS. The maximum photocurrent was found at the optical resonance of 1.29 μm. At resonance, a sensitivity of S = 3.97 × 104 A/W was observed. From the sensitivity, a noise equivalent power of NEP = 1.18 × 10-16 W/Hz1/2, and a specific detectivity of D∗ ≅ 6.74 × 1012 cm Hz1/2/W were calculated. For a single absorbed photon a photocurrent of ISP = 50 pA was determined.

  3. Metamaterial-based Fabry-Pérot leaky wave antennas: low profile, high directivity, frequency agility and beam steering

    International Nuclear Information System (INIS)

    The analysis and design of subwavelength metamaterial-based Fabry-Pérot (FP) leaky wave antennas (LWAs) are presented. The antennas under investigation are formed by embedding a feeding source in a cavity composed of a Perfect Electrical Conductor (PEC) surface and a metasurface reflector. Several configurations of such antennas are presented to achieve different desired performances such as: high directivity, frequency agility and beam steering.

  4. Deterministic frequency-wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array: Theory and methods

    Science.gov (United States)

    Goldstein, Peter; Archuleta, Ralph J.

    1991-04-01

    We present an approach for measuring the spatial extent, duration, directions and speeds of rupture propagation during an earthquake using array signal processing techniques. Unlike most previous approaches, no assumptions are made regarding the directions and speeds of propagation. The solution we obtain is unique, and its accuracy, precision and resolution can be estimated. We use preprocessing and coprocessing techniques that improve the accuracy/precision of existing frequency-wavenumber methods. Subarray spatial averaging modifies frequency-wavenumber techniques so that they are sensitive to multiple deterministic (transient) as well as stochastic (stationary) signals. This technique is also advantageous because it ensemble averages the cross spectral matrix and reduces the variance of the frequency-wavenumber spectrum. Seismogram alignment is a preprocessing procedure that accounts for nonplanar wavefronts due to lateral velocity variations beneath an array. This procedure also allows us to study signals of interest using much shorter time windows than has previously been possible. The use of short time windows is important for reducing uncertainty in estimates of arrival times of seismic phases. We tested subarray spatial averaging and seismogram alignment with a variety of frequency-wavenumber techniques and found that the multiple signal classification (MUSIC) method gave the best resolution of multiple signals. We also note that standard theoretical estimates of uncertainties in peak locations of frequency-wavenumber spectra are much smaller than those typically observed using seismic arrays and we present a different formula that more accurately describes observed uncertainties. Using synthetic P and S body-wave seismograms from extended earthquake sources we show that the above array signal processing techniques can be combined with ray theory to obtain accurate estimates of the locations and rupture times of an earthquake's high-frequency seismic

  5. Analysis of direct current signals measured at the Borssele reactor. Noise analysis from direct measured DC-signals, investigation at very low frequency region

    International Nuclear Information System (INIS)

    The direct current (DC) component of the plant signals from Borssele NPP in the Netherlands was analyzed to investigate the detailed reactor dynamics in the low frequency range, 0-0.5 Hz. A neutron-flux oscillation at 0.1 Hz was found and a correlation of this to thermohydraulic variables such as the cold-leg temperature in the primary loops. Signals from ex-core neutron detectors and core-exist thermocouples at various positions were used to examine space dependent behaviors inside the core. (orig.)

  6. Analysis of direct current signals measured at the Borssele reactor. Noise analysis from direct measured DC-signals, investigation at very low frequency region

    Energy Technology Data Exchange (ETDEWEB)

    Suzudo, T. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan); Tuerkcan, E. [Netherlands Energy Research Foundation (ECN), Petten (Netherlands); Verhoef, J.P. [Netherlands Energy Research Foundation (ECN), Petten (Netherlands)

    1996-09-01

    The direct current (DC) component of the plant signals from Borssele NPP in the Netherlands was analyzed to investigate the detailed reactor dynamics in the low frequency range, 0-0.5 Hz. A neutron-flux oscillation at 0.1 Hz was found and a correlation of this to thermohydraulic variables such as the cold-leg temperature in the primary loops. Signals from ex-core neutron detectors and core-exist thermocouples at various positions were used to examine space dependent behaviors inside the core. (orig.).

  7. Automatically determining the origin direction and propagation mode of high-frequency radar backscatter

    Science.gov (United States)

    Burrell, Angeline G.; Milan, Stephen E.; Perry, Gareth W.; Yeoman, Timothy K.; Lester, Mark

    2015-12-01

    Elevation angles of returned backscatter are calculated at Super Dual Auroral Radar Network radars using interferometric techniques. These elevation angles allow the altitude of the reflection point to be estimated, an essential piece of information for many ionospheric studies. The elevation angle calculation requires knowledge of the azimuthal return angle. This directional angle is usually assumed to lie along a narrow beam from the front of the radar, even though the signals are known to return from both in front of and behind the radar. If the wrong direction of return is assumed, large uncertainties will be introduced through the azimuthal return angle. This paper introduces a means of automatically determining the correct direction of arrival and the propagation mode of backscatter. The application of this method will improve the accuracy of backscatter elevation angle data and aid in the interpretation of both ionospheric and ground backscatter observations.

  8. High-frequency market-making with inventory constraints and directional bets

    OpenAIRE

    Fodra, Pietro; Labadie, Mauricio

    2012-01-01

    In this paper we extend the market-making models with inventory constraints of Avellaneda and Stoikov ("High-frequency trading in a limit-order book", Quantitative Finance Vol.8 No.3 2008) and Gueant, Lehalle and Fernandez-Tapia ("Dealing with inventory risk", Preprint 2011) to the case of a rather general class of mid-price processes, under either exponential or linear PNL utility functions, and we add an inventory-risk-aversion parameter that penalises the marker-maker if she finishes her d...

  9. High-directivity planar antenna using controllable photonic bandgap material at microwave frequencies

    International Nuclear Information System (INIS)

    In this letter, we experimentally demonstrate the capability of a controllable photonic bandgap (CPBG) material to conform the emitted radiation of a planar antenna at 12 GHz. The CPBG material is a variable conductance lattice fabricated with high-frequency PIN diodes soldered along metallic stripes on dielectric printed boards. Depending on the diode bias, the emitted radiation of the antenna can be either transmitted or totally reflected by the material. In the transmission state, the antenna radiation is spatially filtered by the CPBG material in a sharp beam perpendicular to the surface of the material. [copyright] 2001 American Institute of Physics

  10. [Manufacture of high frequency direct current dental X-ray machine].

    Science.gov (United States)

    Su, Jun-Jie; Chen, Hai-Hui; Zhang, Yang-De

    2008-11-01

    This paper introduces five dental X-ray machines which are manufactured with IGBT to realize high frequency, real-time sampling and PWM to ensure the closed-loop control for tube current and Anodes's high voltage. These five machines also use microcomputer and combined X-ray tube for precise control. The sets don't have high voltage outside. The error of tube voltage is less than 1% and exposure time is less than 3%. The photos of pulp cavity and surrounding tissue can be seen clearly. These sets surely meet the requirements of perspective use in clinical. PMID:19253581

  11. Direct and sustained intracellular delivery of exogenous molecules using acoustic-transfection with high frequency ultrasound

    Science.gov (United States)

    Yoon, Sangpil; Kim, Min Gon; Chiu, Chi Tat; Hwang, Jae Youn; Kim, Hyung Ham; Wang, Yingxiao; Shung, K. Kirk

    2016-02-01

    Controlling cell functions for research and therapeutic purposes may open new strategies for the treatment of many diseases. An efficient and safe introduction of membrane impermeable molecules into target cells will provide versatile means to modulate cell fate. We introduce a new transfection technique that utilizes high frequency ultrasound without any contrast agents such as microbubbles, bringing a single-cell level targeting and size-dependent intracellular delivery of macromolecules. The transfection apparatus consists of an ultrasonic transducer with the center frequency of over 150 MHz and an epi-fluorescence microscope, entitled acoustic-transfection system. Acoustic pulses, emitted from an ultrasonic transducer, perturb the lipid bilayer of the cell membrane of a targeted single-cell to induce intracellular delivery of exogenous molecules. Simultaneous live cell imaging using HeLa cells to investigate the intracellular concentration of Ca2+ and propidium iodide (PI) and the delivery of 3 kDa dextran labeled with Alexa 488 were demonstrated. Cytosolic delivery of 3 kDa dextran induced via acoustic-transfection was manifested by diffused fluorescence throughout whole cells. Short-term (6 hr) cell viability test and long-term (40 hr) cell tracking confirmed that the proposed approach has low cell cytotoxicity.

  12. Low frequency eardrum directionality in the barn owl induced by sound transmission through the interaural canal

    DEFF Research Database (Denmark)

    Kettler, Lutz; Christensen-Dalsgaard, Jakob; Larsen, Ole Næsbye;

    2016-01-01

    The middle ears of birds are typically connected by interaural cavities that form a cranial canal. Eardrums coupled in this manner may function as pressure difference receivers rather than pressure receivers. Hereby, the eardrum vibrations become inherently directional. The barn owl also has a la...

  13. Low frequency, electrodynamic simulation of kinetic plasmas with the DArwin Direct Implicit Particle-In-Cell (DADIPIC) method

    International Nuclear Information System (INIS)

    This dissertation describes a new algorithm for simulating low frequency, kinetic phenomena in plasmas. DArwin Direct Implicit Particle-in-Cell (DADIPIC), as its name implies, is a combination of the Darwin and direct implicit methods. One of the difficulties in simulating plasmas lies in the enormous disparity between the fundamental scale lengths of a plasma and the scale lengths of the phenomena of interest. The objective is to create models which can ignore the fundamental constraints without eliminating relevant plasma properties. Over the past twenty years several PIC methods have been investigated for overcoming the constraints on explicit electrodynamic PIC. These models eliminate selected high frequency plasma phenomena while retaining kinetic phenomena at low frequency. This dissertation shows that the combination of Darwin and Direct Implicit allows them to operate better than they have been shown to operate in the past. Through the Darwin method the hyperbolic Maxwell's equations are reformulated into a set of elliptic equations. Propagating light waves do not exist in the formulation so the Courant constraint on the time step is eliminated. The Direct Implicit method is applied only to the electrostatic field with the result that electrostatic plasma oscillations do not have to be resolved for stability. With the elimination of these constraints spatial and temporal discretization can be much larger than that possible with explicit, electrodynamic PIC. The code functions in a two dimensional Cartesian region and has been implemented with all components of the particle velocities, the E-field, and the B-field. Internal structures, conductors or dielectrics, may be placed in the simulation region, can be set at desired potentials, and driven with specified currents

  14. Low frequency, electrodynamic simulation of kinetic plasmas with the DArwin Direct Implicit Particle-In-Cell (DADIPIC) method

    Energy Technology Data Exchange (ETDEWEB)

    Gibbons, M.R.

    1995-06-01

    This dissertation describes a new algorithm for simulating low frequency, kinetic phenomena in plasmas. DArwin Direct Implicit Particle-in-Cell (DADIPIC), as its name implies, is a combination of the Darwin and direct implicit methods. One of the difficulties in simulating plasmas lies in the enormous disparity between the fundamental scale lengths of a plasma and the scale lengths of the phenomena of interest. The objective is to create models which can ignore the fundamental constraints without eliminating relevant plasma properties. Over the past twenty years several PIC methods have been investigated for overcoming the constraints on explicit electrodynamic PIC. These models eliminate selected high frequency plasma phenomena while retaining kinetic phenomena at low frequency. This dissertation shows that the combination of Darwin and Direct Implicit allows them to operate better than they have been shown to operate in the past. Through the Darwin method the hyperbolic Maxwell`s equations are reformulated into a set of elliptic equations. Propagating light waves do not exist in the formulation so the Courant constraint on the time step is eliminated. The Direct Implicit method is applied only to the electrostatic field with the result that electrostatic plasma oscillations do not have to be resolved for stability. With the elimination of these constraints spatial and temporal discretization can be much larger than that possible with explicit, electrodynamic PIC. The code functions in a two dimensional Cartesian region and has been implemented with all components of the particle velocities, the E-field, and the B-field. Internal structures, conductors or dielectrics, may be placed in the simulation region, can be set at desired potentials, and driven with specified currents.

  15. Construction of a High Frequency and High Reflectance Shutter for a Direct Write EUV Lithography System

    Directory of Open Access Journals (Sweden)

    Jyun-Yan Chuang

    2013-05-01

    Full Text Available Extreme ultraviolet lithography (EUVL is widely seen as a key technology for future semiconductor mass production. However, due to the short wavelength material properties of EUV, it is strongly absorbed by most materials. Thus if the shutter for a lithography system operates by means of absorption, one must consider the potential temperature rise due to the high energy radiation absorbed by the structure. In this paper, we propose using a high-reflectance shutter so as to resolve temperature-related precision problems in lithography systems. A single-layer molybdenum film is used to greatly reduce the quantity of absorbed radiation energy by the shutter structure (in line with Fresnel equation by increasing the incidence angle. A green laser is used as the light source to construct an automatic measuring system for reflectance and transmittance to verify the increase of material reflectance by the incidence angle of the photosource. The obtained incidence angle is also be fixed on the multilayered piezoelectric to serve as an actuator, so as to measure the high-frequency echoed signal of the laser photosource. Results show that, when the incidence angle is 83°, the optimum energy reflectance (50% is obtained and the switching frequency reaches a maximum of 19 kHz, verifying the feasibility of using the reflected energy as the photosource switch. Finally, experiments were conducted in Taiwan’s National Synchrotron Radiation Research Center (NSRRC using EUV as the photosource to measure the reflectance curves of single-layer molybdenum and aluminum films with different thicknesses under different incidence angles. Experimental results show that a high degree of reflection can be produced by the proposed single-layer film structure given a large incidence angle. The reflectance also increased significantly at an incidence angle of 60° for molybdenum while 70° for aluminum, and this relatively high reflection by molybdenum with a smaller

  16. Direct generation of low frequency single phase AC for the Railway in Norway and Sweden

    OpenAIRE

    Siles Blacutt, Carlos

    2009-01-01

    This thesis deals with direct generated electricity for the Swedish and Norwegian railway systems. The form of renewable energy sources that are presented in this thesis is hydropower and a small part is about wind power. Älvkarleby hydropower plant could give redundancy to the Swedish railway system and at the same time solve that problem of locations for static converters close to Stockholm since the land areas close to Stockholm are expensive [14]. A conversion of 50 Hz generators into 16....

  17. A New High Frequency Global-to-direct Irradiance Conversion Methodology

    OpenAIRE

    Fernández-Peruchena, Carlos M.; Bernardos, Ana; Monreal, Ana; Guisado, Maria V; Gastón, Martín; Pagola, Íñigo

    2012-01-01

    In order to accurately simulate the behavior of a solar thermal power plant, it is necessary to carry out an adequate evaluation of the available solar resource. To that end, it is important to know the cumulative Direct Normal solar Irradiation (DNI) values and their dynamic behavior. Only by knowing this information with accuracy, it will be possible to predict the solar thermal power plant behavior and to establish an adequate operation strategy. Sites with high cumulative DNI values are n...

  18. Low frequency radio observations of bi-directional electron beams in the solar corona

    CERN Document Server

    Carley, Eoin P; Vilmer, Nicole; Gallagher, Peter T

    2015-01-01

    The radio signature of a shock travelling through the solar corona is known as a type II solar radio burst. In rare cases these bursts can exhibit a fine structure known as `herringbones', which are a direct indicator of particle acceleration occurring at the shock front. However, few studies have been performed on herringbones and the details of the underlying particle acceleration processes are unknown. Here, we use an image processing technique known as the Hough transform to statistically analyse the herringbone fine structure in a radio burst at $\\sim$20-90 MHz observed from the Rosse Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual bursts which are signatures of bi-directional electron beams continuously accelerated to speeds of 0.16$_{-0.10}^{+0.11} c$. This occurs at a shock acceleration site initially at a constant altitude of $\\sim$0.6 R$_{\\odot}$ in the corona, followed by a shift to $\\sim$0.5 R$_{\\odot}$. The anti-sunward beams travel a distance of 170$_{-97}^{+174}$ ...

  19. Demonstration of displacement- and frequency-noise free laser interferometry using bi-directional Mach-Zehnder interferometers

    CERN Document Server

    Sato, S; Kawamura, S; Kokeyama, K; Pai, A; Somiya, K; Ward, R L; Chen, Yanbei; Kawamura, Seiji; Kokeyama, Keiko; Pai, Archana; Sato, Shuichi; Somiya, Kentaro; Ward, Robert L.

    2006-01-01

    We have demonstrated displacement- and frequency-noise free laser interferometry (DFI) by partially implementing a recently proposed optical configuration using bi-directional Mach-Zehnder interferometers (MZI). This partial implementation, the minimum necessary to be called DFI, has confirmed the essential feature of DFI: the combination of two MZI signals can be carried out in a way which cancels displacement noise of the mirrors while maintaining gravitational wave signals. The attained maximum displacement noise suppression allowed a simulated-SNR of 45dB.

  20. Spatial hearing in Cope’s gray treefrog: II. Frequency-dependent directionality in the amplitude and phase of tympanum vibrations

    OpenAIRE

    Caldwell, Michael S.; Lee, Norman; Schrode, Katrina M.; Johns, Anastasia R.; Christensen-Dalsgaard, Jakob; Bee, Mark A.

    2014-01-01

    Anuran ears function as pressure difference receivers, and the amplitude and phase of tympanum vibrations are inherently directional, varying with sound incident angle. We quantified the nature of this directionality for Cope’s gray treefrog, Hyla chrysoscelis. We presented subjects with pure tones, advertisement calls, and frequency-modulated sweeps to examine the influence of frequency, signal level, lung inflation, and sex on ear directionality. Interaural differences in the amplitude of t...

  1. Direct pumping of ultrashort Ti:sapphire lasers by a frequency doubled diode laser

    DEFF Research Database (Denmark)

    Müller, André; Jensen, Ole Bjarlin; Unterhuber, Angelika; Le, Tuan; Stingl, Andreas; Hasler, Karl-Heinz; Sumpf, Bernd; Erbert, Goetz; Andersen, Peter E.; Petersen, Paul Michael

    2011-01-01

    A simple and robust diode laser system emitting 1.28 W of green light suitable for pumping an ultrafast Ti:sapphire laser is presented. To classify our results, the diode laser is compared to a standard, commercially available diode pumped solid-state (DPSS) laser system pumping the same oscillator....... When using our diode laser system, the optical conversion efficiencies from green to near-infrared light reduces to 75 % of the values achieved with the commercial pump laser. Despite this reduction the overall efficiency of the Ti: sapphire laser is still increased by a factor > 2 due to the superior...... electro-optical efficiency of the diode laser. Autocorrelation measurements show that pulse widths of less than 20 fs can be expected with an average power of 52 mW when using our laser. These results indicate the high potential of direct diode laser pumped Ti: sapphire lasers to be used in applications...

  2. Feasibility of a Direct Sampling Dual-Frequency SDR Galileo Receiver for Civil Aviation

    OpenAIRE

    Blais, Antoine

    2014-01-01

    Cette thèse étudie l'intérêt des architectures SDR à échantillonnage direct pour des récepteurs Galileo dans le contexte particulier de l'Aviation Civile, caractérisé notamment par une exigence de robustesse à des interférences bien spécifiées, principalement les interférences causées par les signaux DME ou CW. Le concept de Software Defined Radio traduit la migration toujours plus grande, au sein des récepteurs, des procédés de démodulation d'une technologie analogique à du traitement numéri...

  3. Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing

    International Nuclear Information System (INIS)

    Highlights: • CERS is a versatile new analytical methodology. • Continuous online quantification of reduction of 15N-labelled nitrate by P. stutzeri was demonstrated. • The total nitrogen element budget was monitored online for the first time. • Sterile online acquisition of the pH changes in the P. stutzeri culture was demonstrated. • An increased slope of the pH value coincided with a temporary accumulation of N2O. - Abstract: The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N2 and N2O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of 15N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases (14N2, 14N2O, O2, and CO2) and to trace the fate of 15N-labeled nitrate substrate (15N2, 15N2O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO2-bicarbonate equilibrium. Continuous pH monitoring – without the need to insert an electrode into solution – elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N2O, due to an inhibition of nitrous oxide reductase. Cavity

  4. Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing

    Energy Technology Data Exchange (ETDEWEB)

    Keiner, Robert [Institute of Physical Chemistry, Friedrich Schiller University Jena, Jena 07743 (Germany); Leibniz Institute of Photonic Technology, Jena 07745 (Germany); Herrmann, Martina; Küsel, Kirsten [Institute of Ecology, Friedrich Schiller University Jena, Jena 07743 (Germany); German Centre for Integrative Biodiversity Research (iDiv) Halle–Jena–Leipzig, Leipzig 04103 (Germany); Popp, Jürgen [Institute of Physical Chemistry, Friedrich Schiller University Jena, Jena 07743 (Germany); Leibniz Institute of Photonic Technology, Jena 07745 (Germany); InfectoGnostics Forschungscampus, Zentrum für Angewandte Forschung, Jena 07743 (Germany); Abbe School of Photonics, Friedrich Schiller University, Jena (Germany); Frosch, Torsten, E-mail: torsten.frosch@uni-jena.de [Institute of Physical Chemistry, Friedrich Schiller University Jena, Jena 07743 (Germany); Leibniz Institute of Photonic Technology, Jena 07745 (Germany); InfectoGnostics Forschungscampus, Zentrum für Angewandte Forschung, Jena 07743 (Germany)

    2015-03-15

    Highlights: • CERS is a versatile new analytical methodology. • Continuous online quantification of reduction of {sup 15}N-labelled nitrate by P. stutzeri was demonstrated. • The total nitrogen element budget was monitored online for the first time. • Sterile online acquisition of the pH changes in the P. stutzeri culture was demonstrated. • An increased slope of the pH value coincided with a temporary accumulation of N{sub 2}O. - Abstract: The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N{sub 2} and N{sub 2}O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of {sup 15}N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases ({sup 14}N{sub 2}, {sup 14}N{sub 2}O, O{sub 2}, and CO{sub 2}) and to trace the fate of {sup 15}N-labeled nitrate substrate ({sup 15}N{sub 2}, {sup 15}N{sub 2}O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO{sub 2}-bicarbonate equilibrium. Continuous pH monitoring – without the need to insert an electrode into solution – elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in

  5. Letter to the Editor: First direct observations of the reduced striations at pump frequencies close to the electron gyroharmonics

    Directory of Open Access Journals (Sweden)

    M. T. Rietveld

    Full Text Available It is well known that the ionospheric plasma response to high-power HF radio waves changes drastically as the heater frequency approaches harmonics of the electron gyrofrequency. These include changes in the spectrum of the stimulated electromagnetic emission, reduction in the anomalous absorption of low-power diagnostic waves propagating through the heated volume, and reduction in the large scale F-region heating. Theoretical models as well as previous experimental evidence point towards the absence of small-scale field-aligned plasma density irregularities at pump frequencies close to electron gyroharmonics as the main cause of these changes. Results presented in this paper are the first direct observations of the reduced striations at the 3rd gyroharmonic made by the CUTLASS radar. In addition, simultaneous EISCAT observations have revealed that the "enhanced ion-line" usually present in the EISCAT ion-line spectrum during the first few seconds after heater switch on, persisted at varying strengths while the heater was transmitting at frequencies close to the 3rd electron gyroharmonics.Key words. Ionosphere (active experiments; ionospheric irregularities · Radio science (ionospheric physics

  6. Direct high-frequency modulation of VCSELs and applications in fibre optic RF and microwave links

    International Nuclear Information System (INIS)

    With the rapid development of wireless communication networks there is an increasing demand for efficient and cost-effective transmission and distribution of RF signals. Fibre optic RF links, employing directly modulated semiconductor lasers, provide many of the desired characteristics for such distribution systems and in the search for cost-effective solutions, the vertical cavity surface emitting laser (VCSEL) is of interest. It has therefore been the purpose of this work to investigate whether 850 nm VCSELs fulfil basic performance requirements for fibre optic RF links operating in the low-GHz range. The performance of single- and multimode oxide confined VCSELs has been compared, in order to pin-point limitations and to find the optimum design. Fibre optic RF links using VCSELs and multimode fibres have been assembled and evaluated with respect to performance characteristics of importance for wireless communication systems. We have found that optimized single-mode VCSELs provide the highest performance and that links using such VCSELs and high-bandwidth multimode fibres satisfy the requirements in a number of applications, including cellular systems for mobile communication and wireless local area networks

  7. Mechanical, tribological and corrosion properties of CrBN films deposited by combined direct current and radio frequency magnetron sputtering

    International Nuclear Information System (INIS)

    Cr–B–N films were deposited on stainless steel substrates by a combined direct current and radio frequency (RF) reactive unbalanced magnetron sputtering process using two elemental Cr and one compound BN targets. Boron content in the as-deposited films was qualitatively analyzed by time-of-flight secondary ion mass spectroscopy. Films' microstructure, mechanical and tribological properties were characterized by X-ray diffraction, nanoindentation and pin-on-disk tribometer experiments. Corrosion behavior of the Cr–B–N films was evaluated by electrochemical potentiodynamic polarization method in a 3 wt.% NaCl solution. All the films were crystallized into a NaCl-type cubic structure. At lower RF power applied on the BN target (≤ 600 W), films are relatively randomly oriented, and films' crystallinity increased with increasing RF power. With increasing RF power further (≥ 800 W), films became (200) preferentially oriented, and films' crystallinity decreased gradually. With incorporation of a small amount of boron atoms into the CrN films, hardness, wear- and corrosion-resistance were all improved evidently. The best wear and corrosion resistance was obtained for the film deposited with 600 W RF power applied on the BN target. - Highlights: • CrBN films deposited by direct current and radio frequency magnetron sputtering. • CrBN exhibited higher hardness, wear- and corrosion-resistance than pure CrN. • The best wear- and corrosion-resistant film was deposited with 600 W RF power

  8. Mechanical, tribological and corrosion properties of CrBN films deposited by combined direct current and radio frequency magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Jahodova, Vera [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, 638075 (Singapore); Koszalin University of Technology, Sniadeckich 2, 75-0453 Koszalin (Poland); Technical University of Liberec, Studentska 1402/2, 461 17 Liberec1 (Czech Republic); Ding, Xing-zhao, E-mail: xzding@SIMTech.a-star.edu.sg [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, 638075 (Singapore); Seng, Debbie H.L. [Institute of Materials Research and Engineering, 3 Research Link, 117602 (Singapore); Gulbinski, W. [Koszalin University of Technology, Sniadeckich 2, 75-0453 Koszalin (Poland); Louda, P. [Technical University of Liberec, Studentska 1402/2, 461 17 Liberec1 (Czech Republic)

    2013-10-01

    Cr–B–N films were deposited on stainless steel substrates by a combined direct current and radio frequency (RF) reactive unbalanced magnetron sputtering process using two elemental Cr and one compound BN targets. Boron content in the as-deposited films was qualitatively analyzed by time-of-flight secondary ion mass spectroscopy. Films' microstructure, mechanical and tribological properties were characterized by X-ray diffraction, nanoindentation and pin-on-disk tribometer experiments. Corrosion behavior of the Cr–B–N films was evaluated by electrochemical potentiodynamic polarization method in a 3 wt.% NaCl solution. All the films were crystallized into a NaCl-type cubic structure. At lower RF power applied on the BN target (≤ 600 W), films are relatively randomly oriented, and films' crystallinity increased with increasing RF power. With increasing RF power further (≥ 800 W), films became (200) preferentially oriented, and films' crystallinity decreased gradually. With incorporation of a small amount of boron atoms into the CrN films, hardness, wear- and corrosion-resistance were all improved evidently. The best wear and corrosion resistance was obtained for the film deposited with 600 W RF power applied on the BN target. - Highlights: • CrBN films deposited by direct current and radio frequency magnetron sputtering. • CrBN exhibited higher hardness, wear- and corrosion-resistance than pure CrN. • The best wear- and corrosion-resistant film was deposited with 600 W RF power.

  9. Pen-mate directed behaviour in ad libitum fed pigs given different quantities and frequencies of straw

    DEFF Research Database (Denmark)

    Amdi, C.; Lahrmann, H.P.; Oxholm, L.C.;

    2015-01-01

    is expensive. In addition, straw needs to remain fresh in order to have a degree of novelty. The aim of this study was to investigate pen-mate directed behaviour in pigs given different straw treatments. Pigs were assigned to one of five treatments testing either quantity or frequency of chopped......-mate directed behaviour were recorded. In addition, residual straw in the pens was assessed using four categories ranging from straw in a thin layer; little straw; few straws; and soiled straw. Pigs were active for about 30% of the registered time, but overall no differences in total pen-mate directed behaviour...... pigs were active for about 30% of the day corresponding to less than 5 h per day. Of the active time, an average of 17 min was spent on pen-mate directed behaviour. Only minor differences were found in the residual straw assessment, T25 had a higher percentage of little straw left compared to T50 and T...

  10. Radio-frequency electromagnetic field measurements for direct detection of electron Bernstein waves in a torus plasma.

    Science.gov (United States)

    Yatsuka, Eiichi; Kinjo, Kiyotake; Morikawa, Junji; Ogawa, Yuichi

    2009-02-01

    To identify the mode-converted electron Bernstein wave (EBW) in a torus plasma directly, we have developed an interferometry system, in which a diagnostic microwave injected outside of the plasma column was directly detected with the probing antenna inserted into the plasma. In this work, plasma production and heating are achieved with 2.45 GHz, 2.5 kW electron cyclotron heating (ECH), whereas diagnostics are carried out with a lower power (10 W) separate frequency (1-2.1 GHz) microwave. Three components, i.e., two electromagnetic (toroidal and poloidal directions) and an electrostatic (if refractive index is sufficiently higher than unity, it corresponds to radial component), of ECRF electric field are simultaneously measured with three probing antennas, which are inserted into plasma. Selectivities of each component signal were checked experimentally. Excitation antennas have quite high selectivity of direction of linear polarization. As probing antennas for detecting electromagnetic components, we employed a monopole antenna with a length of 35 mm, and the separation of the poloidal (O-wave) and toroidal (X-wave) components of ECRF electric field could be available with this antenna. To detect EBW, which is an electrostatic wave, a small tip (1 mm) antenna was used. As the preliminary results, we detected signals that have three characteristics of EBW, i.e., short wavelength, backward propagation, and electrostatic. PMID:19256646

  11. Radio-frequency electromagnetic field measurements for direct detection of electron Bernstein waves in a torus plasma

    International Nuclear Information System (INIS)

    To identify the mode-converted electron Bernstein wave (EBW) in a torus plasma directly, we have developed an interferometry system, in which a diagnostic microwave injected outside of the plasma column was directly detected with the probing antenna inserted into the plasma. In this work, plasma production and heating are achieved with 2.45 GHz, 2.5 kW electron cyclotron heating (ECH), whereas diagnostics are carried out with a lower power (10 W) separate frequency (1-2.1 GHz) microwave. Three components, i.e., two electromagnetic (toroidal and poloidal directions) and an electrostatic (if refractive index is sufficiently higher than unity, it corresponds to radial component), of ECRF electric field are simultaneously measured with three probing antennas, which are inserted into plasma. Selectivities of each component signal were checked experimentally. Excitation antennas have quite high selectivity of direction of linear polarization. As probing antennas for detecting electromagnetic components, we employed a monopole antenna with a length of 35 mm, and the separation of the poloidal (O-wave) and toroidal (X-wave) components of ECRF electric field could be available with this antenna. To detect EBW, which is an electrostatic wave, a small tip (1 mm) antenna was used. As the preliminary results, we detected signals that have three characteristics of EBW, i.e., short wavelength, backward propagation, and electrostatic.

  12. Adsorption of cytochrome c to silica surfaces studied using evanescent wave broadband cavity-enhanced absorption spectroscopy

    Science.gov (United States)

    Moore, L. J.; van der Sneppen, L.; Peverall, R.; Hancock, G.; Ritchie, G. A. D.

    2010-08-01

    The adsorption of cytochrome c (cyt c) to a silica surface has been studied by use of evanescent wave broadband cavityenhanced absorption spectroscopy (EW-BBCEAS). Visible radiation from a supercontinuum source is coupled into an optical cavity consisting of a pair of broadband high reflectivity mirrors, and a total internal reflection (TIR) event at the prism/water interface. Aqueous solutions of cyt c are placed onto the TIR footprint on the prism surface and the subsequent protein adsorption is probed by the resulting evanescent wave. The time integrated cavity output is directed into a spectrometer, where it is dispersed and analysed. The high spectral brilliance of the SC affords a baseline noise comparable to evanescent wave cavity ring-down spectroscopy (EW-CRDS), and the broadband nature of the source allows observation of a wide spectral range (ca 250 nm in the visible). The system is calibrated by measuring the absorption spectra of dyes of a known absorbance. Absorption spectra of cyt c are obtained for both S and P polarized radiation, allowing information about the orientation of the adsorbed protein to be extracted.

  13. Cavity-enhanced absorption spectroscopy with a ps-pulsed UV laser for sensitive, high-speed measurements in a shock tube.

    Science.gov (United States)

    Wang, Shengkai; Sun, Kai; Davidson, David F; Jeffries, Jay B; Hanson, Ronald K

    2016-01-11

    We report the first application of cavity-enhanced absorption spectroscopy (CEAS) with a ps-pulsed UV laser for sensitive and rapid gaseous species time-history measurements in a transient environment (in this study, a shock tube). The broadband nature of the ps pulses enabled instantaneous coupling of the laser beam into roughly a thousand cavity modes, which grants excellent immunity to laser-cavity coupling noise in environments with heavy vibrations, even with an on-axis alignment. In this proof-of-concept experiment, we demonstrated an absorption gain of 49, which improved the minimum detectable absorbance by ~20 compared to the conventional single-pass strategy at similar experimental conditions. For absorption measurements behind reflected shock waves, an effective time-resolution of ~2 μs was achieved, which enabled time-resolved observations of transient phenomena, such as the vibrational relaxation of O(2) demonstrated here. The substantial improvement in detection sensitivity, together with microsecond measurement resolution implies excellent potential for studies of transient physical and chemical processes in nonequilibrium situations, particularly via measurements of weak absorptions of trace species in dilute reactive systems. PMID:26832262

  14. GaInNAs/GaAs Multiple-Quantum Well Resonant-Cavity-Enhanced Photodetectors at 1.3μm

    Institute of Scientific and Technical Information of China (English)

    潘钟; 李联合; 徐应强; 张伟; 林耀望; 张瑞康; 钟源; 任晓敏

    2001-01-01

    A GaInNAs/GaAs multiple quantum well (MQW) resonant-cavity enhanced photodetector (RCE-PD) operated at a wavelength of 1.3μm with the full width at half maximum of 4nm has been demonstrated. The GaInNAs RCE-PD was grown by molecular beam epitaxy using a homemade ion-removed dc plasma cell as a nitrogen source. GaInNAs/GaAs MQW shows a strong exciton peak at room temperature, which is very beneficial for applications in long-wavelength absorption devices. For a 100μm diameter RCE-PD, the dark current is 20 and 32 pA at biases of 0 and 6 V, respectively, and the breakdown voltage is -18 V. The measured 3 dB bandwidth is 308 MHz, which is limited by the resistance of p-type distributed Bragg reflector mirror. The tunable wavelength in a range of 18nm with the angle of incident light was observed.

  15. Following interfacial kinetics in real time using broadband evanescent wave cavity-enhanced absorption spectroscopy: a comparison of light-emitting diodes and supercontinuum sources.

    Science.gov (United States)

    van der Sneppen, Lineke; Hancock, Gus; Kaminski, Clemens; Laurila, Toni; Mackenzie, Stuart R; Neil, Simon R T; Peverall, Robert; Ritchie, Grant A D; Schnippering, Mathias; Unwin, Patrick R

    2010-01-01

    A white light-emitting diode (LED) with emission between 420 and 700 nm and a supercontinuum (SC) source with emission between 450 and 2500 nm have been compared for use in evanescent wave broadband cavity-enhanced absorption spectroscopy (EW-BB-CEAS). The method is calibrated using a dye with known absorbance. While the LED is more economic as an excitation source, the SC source is superior both in terms of baseline noise (noise equivalent absorbances lower than 10(-5) compared to 10(-4) absorbance units (a.u.)) and accuracy of the measurement; these baseline noise levels are comparable to evanescent wave cavity ringdown spectroscopy (EW-CRDS) studies while the accessible spectral region of EW-BB-CEAS is much larger (420-750 nm in this study, compared to several tens of nanometres for EW-CRDS). The improvements afforded by the use of an SC source in combination with a high sensitivity detector are demonstrated in the broadband detection of electrogenerated Ir(IV) complexes in a thin-layer electrochemical cell arrangement. Excellent signal to noise is achieved with 10 micros signal accumulation times at a repetition rate of 600 Hz, easily fast enough to follow, in real time, solution kinetics and interfacial processes. PMID:20024193

  16. 谐振腔增强型光探测器的优化设计%Optimized Design of Resonant Cavity Enhanced Photo Detector

    Institute of Scientific and Technical Information of China (English)

    彭秀艳; 彭秀川; 吴利华; 徐倩

    2007-01-01

    在光通信系统中,量子效率和响应速率是光电探测器的2个重要的参数,要获得高的量子效率就必须增大吸收层的厚度,而增大吸收层的厚度将导致载流子渡越时间的延长,从而使响应速率下降.谐振腔增强型光探测器(Resonant Cavity Enhanced Photo Detector,简称REC)可以有效地解决量子效率与响应速率之间相互制约关系.笔者从实际的长波长RCE出发,充分考虑器件制备的工艺难度,综合分析其各方面因素,并对器件整体设计进行优化.

  17. Mid-infrared concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy of a continuous supersonic expansion discharge source

    Science.gov (United States)

    Talicska, Courtney N.; Porambo, Michael W.; Perry, Adam J.; McCall, Benjamin J.

    2016-06-01

    Concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is implemented for the first time on a continuous gas-flow pinhole supersonic expansion discharge source for the study of cooled molecular ions. The instrument utilizes a continuous-wave optical parametric oscillator easily tunable from 2.5 to 3.9 μm and demonstrates a noise equivalent absorption of ˜1 × 10-9 cm-1. The effectiveness of concentration-modulated NICE-OHMS is tested through the acquisition of transitions in the ν1 fundamental band of HN2+ centered near 3234 cm-1, with a signal-to-noise of ˜40 obtained for the strongest transitions. The technique is used to characterize the cooling abilities of the supersonic expansion discharge source itself, and a Boltzmann analysis determines a rotational temperature of ˜29 K for low rotational states of HN2+. Further improvements are discussed that will enable concentration-modulated NICE-OHMS to reach its full potential for the detection of molecular ions formed in supersonic expansion discharges.

  18. In-cylinder pressure-based direct techniques and time frequency analysis for combustion diagnostics in IC engines

    International Nuclear Information System (INIS)

    Highlights: • Direct pressure-based techniques have been applied successfully to spark-ignition engines. • The burned mass fraction of pressure-based techniques has been compared with that of 2- and 3-zone combustion models. • The time frequency analysis has been employed to simulate complex diesel combustion events. - Abstract: In-cylinder pressure measurement and analysis has historically been a key tool for off-line combustion diagnosis in internal combustion engines, but online applications for real-time condition monitoring and combustion management have recently become popular. The present investigation presents and compares different low computing-cost in-cylinder pressure based methods for the analyses of the main features of combustion, that is, the start of combustion, the end of combustion and the crankshaft angle that responds to half of the overall burned mass. The instantaneous pressure in the combustion chamber has been used as an input datum for the described analytical procedures and it has been measured by means of a standard piezoelectric transducer. Traditional pressure-based techniques have been shown to be able to predict the burned mass fraction time history more accurately in spark ignition engines than in diesel engines. The most suitable pressure-based techniques for both spark ignition and compression ignition engines have been chosen on the basis of the available experimental data. Time–frequency analysis has also been applied to the analysis of diesel combustion, which is richer in events than spark ignited combustion. Time frequency algorithms for the calculation of the mean instantaneous frequency are computationally efficient, allow the main events of the diesel combustion to be identified and provide the greatest benefits in the presence of multiple injection events. These algorithms can be optimized and applied to onboard diagnostics tools designed for real control, but can also be used as an advanced validation tool for

  19. Observation of Rb Two-Photon Absorption Directly Excited by an Erbium-Fiber-Laser-Based Optical Frequency Comb via Spectral Control

    OpenAIRE

    Wu, Jiutao; Hou, Dong; Dai, Xiaoliang; Qin, Zhengyu; Zhang, Zhigang; Zhao, Jianye

    2013-01-01

    We demonstrated the observation of Rb two-photon absorption directly excided by an optical frequency comb at fiber communication bands. A chain of comb spectral control is elaborately implemented to increase the power of the second harmonic optical frequency comb generation and the two-photon transition strength. A two-photon transition spectrum is obtained with clearly resolved transition lines. It provides a potential approach to realize the optical frequency comb or optical clock at ~1.5{\\...

  20. Direct observation of unstained biological specimens in water by the frequency transmission electric-field method using SEM.

    Directory of Open Access Journals (Sweden)

    Toshihiko Ogura

    Full Text Available Scanning electron microscopy (SEM is a powerful tool for the direct visualization of biological specimens at nanometre-scale resolution. However, images of unstained specimens in water using an atmospheric holder exhibit very poor contrast and heavy radiation damage. Here, we present a new form of microscopy, the frequency transmission electric-field (FTE method using SEM, that offers low radiation damage and high-contrast observation of unstained biological samples in water. The wet biological specimens are enclosed in two silicon nitride (SiN films. The metal-coated SiN film is irradiated using a focused modulation electron beam (EB at a low-accelerating voltage. A measurement terminal under the sample holder detects the electric-field frequency signal, which contains structural information relating to the biological specimens. Our results in very little radiation damage to the sample, and the observation image is similar to the transmission image, depending on the sample volume. Our developed method can easily be utilized for the observation of various biological specimens in water.

  1. Frequency domain near-infrared multiwavelength imager design using high-speed, direct analog-to-digital conversion

    Science.gov (United States)

    Zimmermann, Bernhard B.; Fang, Qianqian; Boas, David A.; Carp, Stefan A.

    2016-01-01

    Frequency domain near-infrared spectroscopy (FD-NIRS) has proven to be a reliable method for quantification of tissue absolute optical properties. We present a full-sampling direct analog-to-digital conversion FD-NIR imager. While we developed this instrument with a focus on high-speed optical breast tomographic imaging, the proposed design is suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed. Simultaneous dual wavelength operation at 685 and 830 nm is achieved by concurrent 67.5 and 75 MHz frequency modulation of each laser source, respectively, followed by digitization using a high-speed (180 MS/s) 16-bit A/D converter and hybrid FPGA-assisted demodulation. The instrument supports 25 source locations and features 20 concurrently operating detectors. The noise floor of the instrument was measured at Titration experiments consisting of 200 different absorption and scattering values were conducted to demonstrate accurate optical property quantification over the entire range of physiologically expected values.

  2. Online investigation of respiratory quotients in Pinus sylvestris and Picea abies during drought and shading by means of cavity-enhanced Raman multi-gas spectrometry.

    Science.gov (United States)

    Hanf, Stefan; Fischer, Sarah; Hartmann, Henrik; Keiner, Robert; Trumbore, Susan; Popp, Jürgen; Frosch, Torsten

    2015-07-01

    Photosynthesis and respiration are major components of the plant carbon balance. During stress, like drought, carbohydrate supply from photosynthesis is reduced and the Krebs cycle respiration must be fueled with other stored carbon compounds. However, the dynamics of storage use are still unknown. The respiratory quotient (RQ, CO2 released per O2 consumed during respiration) is an excellent indicator of the nature of the respiration substrate. In plant science, however, online RQ measurements have been challenging or even impossible so far due to very small gas exchange fluxes during respiration. Here we apply cavity-enhanced multi-gas Raman spectrometry (CERS) for online in situ RQ measurements in drought-tolerant pine (Pinus sylvestris [L.]) and drought-intolerant spruce (Picea abies [L. H. Karst]). Two different treatments, drought and shading, were applied to reduce photosynthesis and force dependency on stored substrates. Changes in respiration rates and RQ values were continuously monitored over periods of several days with low levels of variance. The results show that both species switched from COH-dominated respiration (RQ = 1.0) to a mixture of substrates during shading (RQ = 0.77-0.81), while during drought only pine did so (RQ = 0.75). The gas phase measurements were complemented by concentration measurements of non-structural carbohydrates and lipids. These first results suggest a physiological explanation for greater drought tolerance in pine. CERS was proven as powerful technique for non-consumptive and precise real-time monitoring of respiration rates and respirational quotients for the investigation of plant metabolism under drought stress conditions that are predicted to increase with future climate change. PMID:26016682

  3. An aircraft based three channel broadband cavity enhanced absorption spectrometer for simultaneous measurements of NO3, N2O5 and NO2

    Directory of Open Access Journals (Sweden)

    R. Nightingale

    2011-06-01

    Full Text Available A three channel broadband cavity enhanced absorption spectroscopy (BBCEAS instrument has been developed for airborne measurements of atmospheric trace gases involved in night-time oxidation chemistry and air quality. The instrument was deployed on board the Facility for Airborne Atmospheric Measurements BAe 146-301 atmospheric research aircraft during the Role of Nighttime Chemistry in Controlling the Oxidising Capacity of the Atmosphere (RONOCO measurement campaigns between December 2009 and January 2011. In its present configuration (i.e. specifications of the cavity optics and spectrometers the instrument is designed to measure NO3, N2O5 (by detection of NO3 after thermal dissociation of N2O5, H2O and NO2 by characterising the wavelength dependent optical attenuation within ambient samples by molecular absorption around 662 nm (NO3 and H2O and 445 nm (NO2. This paper reports novel advancements in BBCEAS instrumentation including a refined method for performing BBCEAS mirror reflectivity calibrations using measurements of the phase delay introduced by the optical cavities to amplitude modulated radiation. Furthermore, a new methodology is introduced for fitting the strong but unresolved transitions of water vapour, which is required for accurate retrieval of water absorption features from the 662 nm absorption band used to measure NO3 concentrations. The paper also details the first example of airborne measurements of NO3, N2O5 and NO2 over Europe from a flight over the North Sea and Thames Estuary on the night of the 20 July 2010, one of the most polluted days of the RONOCO summertime flying period. As part of this analysis, the performance of the BBCEAS instrument is assessed by comparing airborne NO2 measurements to those reported concurrently by a photolytic chemiluminescence based detector.

  4. Higher driver energy for fusion by lasers at the fundamental frequency using special smoothing for direct drive

    International Nuclear Information System (INIS)

    Instead of working with the 1.8 MJ blue laser pulse of National Ignition Facility, the 5 MJ red light at the fundamental frequency can be used for direct drive resulting in remarkably higher nuclear fusion gains. The necessary condition only is that the laser beam will receive the appropriate smoothing. Beginning with our numerical results of 1974 of changed is between mirror and phase reflection (due to self generated, nonlinear force produced density ripple in the coherent standing wave field), the 10 ps stochastic pulsation of laser-plasma interaction measured by Madderver and Luther-Davies can completely be understood numerically using the authors' genuine two-fluid hydro-code (H. Hora and M. Aydin, Phys. Rev. A45,6123(1992)). Incoherence by broad band laser or other smoothing can suppress the pulsation as was numerically show and as indicated by experiments of Obenschain, Schmitt et al. and others. Based on the authors' high gain volume ignition calculations, the fusion gain for the ideal direct drive can be increased by more than a factor fifteen above the present blue laser indirect drive

  5. Frequency Locking and Monitoring Based on Bi-directional Terahertz Radiation of a 3rd-Order Distributed Feedback Quantum Cascade Laser

    Science.gov (United States)

    van Marrewijk, N.; Mirzaei, B.; Hayton, D.; Gao, J. R.; Kao, T. Y.; Hu, Q.; Reno, J. L.

    2015-12-01

    We have performed frequency locking of a dual, forward reverse emitting third-order distributed feedback quantum cascade laser (QCL) at 3.5 THz. By using both directions of THz emission in combination with two gas cells and two power detectors, we can for the first time perform frequency stabilization, while monitor the frequency locking quality independently. We also characterize how the use of a less sensitive pyroelectric detector can influence the quality of frequency locking, illustrating experimentally that the sensitivity of the detectors is crucial. Using both directions of terahertz (THz) radiation has a particular advantage for the application of a QCL as a local oscillator, where radiation from one side can be used for frequency/phase stabilization, leaving the other side to be fully utilized as a local oscillator to pump a mixer.

  6. Effect of low-frequency gain and venting effects on the benefit derived from directionality and noise reduction in hearing aids.

    Science.gov (United States)

    Keidser, Gitte; Carter, Lyndal; Chalupper, Josef; Dillon, Harvey

    2007-10-01

    When the frequency range over which vent-transmitted sound dominates amplification increases, the potential benefit from directional microphones and noise reduction decreases. Fitted with clinically appropriate vent sizes, 23 aided listeners with varying low-frequency hearing thresholds evaluated six schemes comprising three levels of gain at 250 Hz (0, 6, and 12 dB) combined with two features (directional microphone and noise reduction) enabled or disabled in the field. The low-frequency gain was 0 dB for vent-dominated sound, while the higher gains were achieved by amplifier-dominated sounds. A majority of listeners preferred 0-dB gain at 250 Hz and the features enabled. While the amount of low-frequency gain had no significant effect on speech recognition in noise or horizontal localization, speech recognition and front/back discrimination were significantly improved when the features were enabled, even when vent-transmitted sound dominated the low frequencies. The clinical implication is that there is no need to increase low-frequency gain to compensate for vent effects to achieve benefit from directionality and noise reduction over a wider frequency range. PMID:17922345

  7. Single-sided deafness & directional hearing: contribution of spectral cues and high-frequency hearing loss in the hearing ear

    Directory of Open Access Journals (Sweden)

    Martijn Johannes Hermanus Agterberg

    2014-07-01

    Full Text Available Direction-specific interactions of sound waves with the head, torso and pinna provide unique spectral-shape cues that are used for the localization of sounds in the vertical plane, whereas horizontal sound localization is based primarily on the processing of binaural acoustic differences in arrival time (interaural time differences, or ITDs and sound level (interaural level differences, or ILDs. Because the binaural sound-localization cues are absent in listeners with total single-sided deafness (SSD, their ability to localize sound is heavily impaired. However, some studies have reported that SSD listeners are able, to some extent, to localize sound sources in azimuth, although the underlying mechanisms used for localization are unclear. To investigate whether SSD listeners rely on monaural pinna-induced spectral-shape cues of their hearing ear for directional hearing, we investigated localization performance for low-pass filtered (LP, 3 kHz and broadband (BB, 0.5 – 20 kHz noises in the two-dimensional frontal hemifield. We tested whether localization performance of SSD listeners further deteriorated when the pinna cavities of their hearing ear were filled with a mold that disrupted their spectral-shape cues. To remove the potential use of perceived sound level as an invalid azimuth cue, we randomly varied stimulus presentation levels over a broad range (45-65 dB SPL. Several listeners with SSD could localize HP and BB sound sources in the horizontal plane, but inter-subject variability was considerable. Localization performance of these listeners strongly reduced after diminishing of their spectral pinna-cues. We further show that inter-subject variability of SSD can be explained to a large extent by the severity of high-frequency hearing loss in their hearing ear.

  8. Preparation of novel Ni-Ir/γ-AlO3 catalyst via high-frequency cold plasma direct reduction process

    Institute of Scientific and Technical Information of China (English)

    Liqiong Huang; Wei Chu; Tao Zhang; Yongxiang Yin; Xumei Tao

    2009-01-01

    The novel Ni-Ir/γ-Al2O3 catalyst,denoted as NIA-E was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment,and the conventional sample,denoted as NIA-CR,was prepared by impregnation,thermal calcination,and then by H2 reduction method.The effects of reduction methods on the catalysts for ammonia decomposition were studied,and they were characterized by XRD,N2 adsorption,XPS,and H2-TPD.It was found that the plasma-reduced NIA-P sample showed a better catalytic performance,over which ammonia conversion was 68.9%,at T=450 ℃,P = 1 atm,and GHSV = 30,000 h-1.It was 31.7% higher than that of the conventional NIA-CR sample.XRD results showed that the crystallite size decreased for the sample with plasma reduction,and the dispersion of active components was improved.There were more active components on the surface of the NIA-P sample from the XPS results.This effect resulted in the higher activity for decomposition of ammonia.Meanwhile,the plasma process significantly decreased the time of preparing catalyst.

  9. Optimization and Implementation of Scaling-Free CORDIC-Based Direct Digital Frequency Synthesizer for Body Care Area Network Systems

    Directory of Open Access Journals (Sweden)

    Ying-Shen Juang

    2012-01-01

    Full Text Available Coordinate rotation digital computer (CORDIC is an efficient algorithm for computations of trigonometric functions. Scaling-free-CORDIC is one of the famous CORDIC implementations with advantages of speed and area. In this paper, a novel direct digital frequency synthesizer (DDFS based on scaling-free CORDIC is presented. The proposed multiplier-less architecture with small ROM and pipeline data path has advantages of high data rate, high precision, high performance, and less hardware cost. The design procedure with performance and hardware analysis for optimization has also been given. It is verified by Matlab simulations and then implemented with field programmable gate array (FPGA by Verilog. The spurious-free dynamic range (SFDR is over 86.85 dBc, and the signal-to-noise ratio (SNR is more than 81.12 dB. The scaling-free CORDIC-based architecture is suitable for VLSI implementations for the DDFS applications in terms of hardware cost, power consumption, SNR, and SFDR. The proposed DDFS is very suitable for medical instruments and body care area network systems.

  10. Observation of Rb Two-Photon Absorption Directly Excited by an Erbium-Fiber-Laser-Based Optical Frequency Comb via Spectral Control

    CERN Document Server

    Wu, Jiutao; Dai, Xiaoliang; Qin, Zhengyu; Zhang, Zhigang; Zhao, Jianye

    2013-01-01

    We demonstrated the observation of Rb two-photon absorption directly excided by an optical frequency comb at fiber communication bands. A chain of comb spectral control is elaborately implemented to increase the power of the second harmonic optical frequency comb generation and the two-photon transition strength. A two-photon transition spectrum is obtained with clearly resolved transition lines. It provides a potential approach to realize the optical frequency comb or optical clock at ~1.5{\\mu}m with high stability and accuracy.

  11. Comparison of the electrical and optical properties of direct current and radio frequency sputtered amorphous indium gallium zinc oxide films

    International Nuclear Information System (INIS)

    The electrical and optical properties of direct current and radio frequency (RF) sputtered amorphous indium gallium zinc oxide (a-IGZO) films are compared. It is found that the RF sputtered a-IGZO films have better stoichiometry (In:Ga:Zn:O = 1:1:1:2.5–3.0), lower electrical conductivity (σ < 8 S/cm), higher refractive index (n = 1.9–2.0) and larger band gap (Eg = 3.02–3.29 eV), and show less shift of Fermi level (△ EF ∼ 0.26 eV) and increased concentration of electrons (△ Ne ∼ 104) in the conduction band with the reduction concentration of oxygen vacancy (VO). Although a-IGZO has intensively been studied for a semiconductor channel material of thin film transistors in next-generation flat panel displays, its fundamental material parameters have not been thoroughly reported. In this work, the work function (φ) of a-IGZO films is tested with the ultraviolet photoelectron spectroscopy. It is found that the φ of a-IGZO films is in the range of 4.0–5.0 eV depending on the VO. - Highlights: ► Amorphous InGaZnO4 (a-IGZO) films were prepared with different sputtering modes. ► Electrical and optical properties of the different films were compared. ► Fermi level (△EF) shift in a-IGZO films were tested by X-ray photoelectron spectroscopy. ► The relation of △EF with the properties of a-IGZO films were discussed. ► Work function was tested by ultraviolet photoelectron spectroscopy

  12. Direct comparison of two cold-atom-based optical frequency standards by using a femtosecond-laser comb.

    Science.gov (United States)

    Vogel, K R; Diddams, S A; Oates, C W; Curtis, E A; Rafac, R J; Itano, W M; Bergquist, J C; Fox, R W; Lee, W D; Wells, J S; Hollberg, L

    2001-01-15

    With a fiber-broadened, femtosecond-laser frequency comb, the 76-THz interval between two laser-cooled optical frequency standards was measured with a statistical uncertainty of 2x10(-13) in 5 s , to our knowledge the best short-term instability thus far reported for an optical frequency measurement. One standard is based on the calcium intercombination line at 657 nm, and the other, on the mercury ion electric-quadrupole transition at 282 nm. By linking this measurement to the known Ca frequency, we report a new frequency value for the Hg(+) clock transition with an improvement in accuracy of ~10(5) compared with its best previous measurement. PMID:18033520

  13. Directions of arrival estimation for multicomponent frequency-hopping signals based on spatial time-frequency analysis%基于空时频分析的多分量跳频信号DOA估计

    Institute of Scientific and Technical Information of China (English)

    陈利虎

    2011-01-01

    An algorithm of directions of arrival estimation for multicomponet frequency-hopping signals based on spatial time-frequency analysis is proposed, which can realize direction-of-arrival (DOA) estimation in underdetermined condition. First, a clear time-frequency representation is gained by short-time-Fourier-transform (STFT) and smoothed-pseudo-Wigner-Ville distribution (SPWVD) synthesis method, which can obtain robust results with good time-frequency concentration and suppression cross-term interference performance. Then, effective hops are selected from the time-frequency distribution, and every hop's spatial time-frequency matrix is built. Finally, every hop's DOA is estimated by three methods: linear spatial time-frequency method, bilinear spatial time-frequency method, and root-MUSIC, The simulation results demonstrate that the estimation algorithm is effective.%提出了一种基于空时频分析的多跳频信号波达方向(direction of arrival,DOA)估计方法.该方法能够在欠定条件下(传感器数目小于信号数目)实现多个信号的测向.首先将信号的短时傅里叶变换(short time Fourier transform,STFT)与平滑伪魏格纳-威利分布(smoothed pseudo Wigner-Ville distribution,SPWVD)组合,利用STFT的无交叉项和SPWVD的时频聚焦性性能,得到了一种切实可行、时频图清晰稳健的分布;然后在时频域提取有效跳(hop),并建立该hop的空时频矩阵,最后分别运用线性空时频、二次空时频和root-MUSIC共三种方法估计每hop信号的DOA.仿真结果验证了方法的有效性.

  14. High intensity signal of the posterior pituitary. A study with horizontal direction of frequency-encoding and fat suppression MR techniques

    International Nuclear Information System (INIS)

    Purpose: To evaluate the consistency of fat in the high intensity signals of the normal neurohypophysis and to differentiate the high signal of posterior pituitary from that of dorsum sella. Sagittal SE T1-weighted images with frequency encoding in the horizontal direction were used in order to differentiate the high signal of posterior pituitary and dorsum sella by the vertically-oriented chemical shift artifact. Material and methods: The sellae of 46 normal volunteers were imaged with a commercially available fat suppression technique and SE sequences with frequency encoding in vertical (25 cases) and horizontal (21 cases) axes. Results: The high signal intensity was absent in 9% of the normal volunteers with no predilection to any specific age group. None of the cases with posterior pituitary high intensity signals showed suppression of the signal with fat suppression technique. A fat suppression technique was helpful in documenting the hyperintensity in 7% of normal volunteers. Nineteen of the 21 (90%) cases with high signal intensity were detected by routine SE T1-weighted images, whereas 18 of the 19 (95%) cases were detected by imaging with frequency encoding in the horizontal direction. Conclusion: The high signal does not indicate the presence of fat. Fat suppression technique and a horizontal direction of frequency encoding help in differentiating the high signal of the neurohypophysis from that of dorsum sella. (orig.)

  15. Design of a SiGe BiCMOS canceller for low frequency noise reduction in direct conversion receivers

    DEFF Research Database (Denmark)

    Squartecchia, Michele; Johansen, Tom Keinicke; Michaelsen, Rasmus Schandorph

    of the local oscillator (LO) toward the RF port of the mixer (Figure 1(a)). This causes the LO self-mixing phenomenon, which is responsible of a significant DC offset at the output of the receiver (Figure 1(b)). In turn, this DC offset gives rise to a high level of low frequency noise affecting the...

  16. Experimental demonstration of directive Si3N4 optical leaky wave antenna with semiconductor perturbations at near infrared frequencies

    CERN Document Server

    Zhao, Qiancheng; Huang, Yuewang; Campione, Salvatore; Capolino, Filippo; Boyraz, Ozdal

    2015-01-01

    Directive optical leaky wave antennas (OLWAs) with tunable radiation pattern are promising integrated optical modulation and scanning devices. OLWAs fabricated using CMOS-compatible semiconductor planar waveguide technology have the potential of providing high directivity with electrical tunability for modulation and switching capabilities. We experimentally demonstrate directive radiation from a silicon nitride ($Si_3N_4$) waveguide-based OLWA. The OLWA design comprises 50 crystalline Si perturbations buried inside the waveguide, with a period of 1 {\\mu}m, each with a length of 260 nm and a height of 150 nm, leading to a directive radiation pattern at telecom wavelengths. The measured far-field radiation pattern at the wavelength of 1540 nm is very directive, with the maximum intensity at the angle of 84.4{\\deg} relative to the waveguide axis and a half-power beam width around 6.2{\\deg}, which is consistent with our theoretical predictions. The use of semiconductor perturbations facilitates electronic radiat...

  17. Directional patterns of cross frequency phase and amplitude coupling within the resting state mimic patterns of fMRI functional connectivity.

    Science.gov (United States)

    Weaver, Kurt E; Wander, Jeremiah D; Ko, Andrew L; Casimo, Kaitlyn; Grabowski, Thomas J; Ojemann, Jeffrey G; Darvas, Felix

    2016-03-01

    Functional imaging investigations into the brain's resting state interactions have yielded a wealth of insight into the intrinsic and dynamic neural architecture supporting cognition and behavior. Electrophysiological studies however have highlighted the fact that synchrony across large-scale cortical systems is composed of spontaneous interactions occurring at timescales beyond the traditional resolution of fMRI, a feature that limits the capacity of fMRI to draw inference on the true directional relationship between network nodes. To approach the question of directionality in resting state signals, we recorded resting state functional MRI (rsfMRI) and electrocorticography (ECoG) from four human subjects undergoing invasive epilepsy monitoring. Using a seed-point based approach, we employed phase-amplitude coupling (PAC) and biPhase Locking Values (bPLV), two measures of cross-frequency coupling (CFC) to explore both outgoing and incoming connections between the seed and all non-seed, site electrodes. We observed robust PAC between a wide range of low-frequency phase and high frequency amplitude estimates. However, significant bPLV, a CFC measure of phase-phase synchrony, was only observed at specific narrow low and high frequency bandwidths. Furthermore, the spatial patterns of outgoing PAC connectivity were most closely associated with the rsfMRI connectivity maps. Our results support the hypothesis that PAC is relatively ubiquitous phenomenon serving as a mechanism for coordinating high-frequency amplitudes across distant neuronal assemblies even in absence of overt task structure. Additionally, we demonstrate that the spatial distribution of a seed-point rsfMRI sensorimotor network is strikingly similar to specific patterns of directional PAC. Specifically, the high frequency activities of distal patches of cortex owning membership in a rsfMRI sensorimotor network were most likely to be entrained to the phase of a low frequency rhythm engendered from the

  18. Direct torque control of the induction machine using field oriented method and time frequency transformation for speed estimation and parameter adaptation

    Energy Technology Data Exchange (ETDEWEB)

    Restrepo, J.A.; Aller, J.M.; Paga, T.; Guzman, V.M.; Bueno, A.; Gimenez, M.I. [Universidad Simon Bolivar, Grupo SIEP, Lab C, Caracas (Venezuela)

    2000-08-01

    In this paper, a Direct Torque Control (DTC) scheme for the induction machine is presented. The rotor speed estimation is performed using the field oriented model. Time frequency spectral methods are studied for accurate speed estimation, using the stator current information. Combining these estimation techniques a precise T{sub r} adaptation in real time is expected. The proposed method reduces controller dependence on the induction machine model parameters and removes the need for speed sensor in the mechanical shaft. (orig.)

  19. Effects of experience on the dimensions of intensity, direction and frequency of the competitive anxiety and self-confidence: A study in athletes of individual and team sports

    OpenAIRE

    Marcos Gimenes Fernandes; Sandra Adriana Neves Nunes; José Vasconcelos Raposo; Helder Miguel Fernandes

    2014-01-01

    The present study had the following objectives: i) to examine the inter-scale correlations between the three dimensions of responses (intensity, direction and frequency) of the CSAI-2R and its relationship with competitive experience, and ii) evaluate the effect of competitive experience anxiety (cognitive and somatic) and self-confidence in the total sample and for different types of modalities (individual vs. team). The sample consisted of 267 athletes (196 male and 71 female), of different...

  20. Direct generation of an optical vortex beam in a single-frequency Nd:YVO4 laser.

    Science.gov (United States)

    Kim, D J; Kim, J W

    2015-02-01

    A simple method for generating a Laguerre-Gaussian (LG) mode optical vortex beam with well-determined handedness in a single-frequency solid state laser end-pumped by a ring-shaped pump beam is reported. After investigating the intensity profile and the wavefront helicity of each longitudinal mode output to understand generation of the LG mode in a Nd:YVO4 laser resonator, selection of the wavefront handedness has been achieved simply by inserting and tilting an etalon in the resonator, which breaks the propagation symmetry of the Poynting vectors with opposite helicity. Simple calculation and the experimental results are discussed for supporting this selection mechanism. PMID:25680057

  1. Surface modification of carbon fiber by direct growth of zinc oxide nanowalls using a radio-frequency magnetron sputtering technique

    International Nuclear Information System (INIS)

    Zinc oxide nanowalls have been grown uniformly on a carbon fiber substrate at room temperature using a radio-frequency magnetron sputtering technique. The synthesis process involved two steps; application of catalyst using a solution process and subsequent radio-frequency sputter deposition of zinc oxide. The nanowalls were examined by field emission scanning electron microscopy for their microstructure and morphology while their nanostructure was studied by high resolution transmission electron microscopy. Both the X-ray and the electron diffraction techniques were used for crystallographic analysis of the produced nanowalls. Selected area electron diffraction and high resolution lattice image showed highly crystalline structure of the nanowalls. Photoluminescence analysis was carried out for the determination of their optical characteristics which showed a strong ultra violet peak at 393 nm and violet peak centered at 401 nm. The latter is a characteristic peak of zinc oxide which demonstrates oxygen rich composition of nanowalls. - Highlights: • Low temperature growth method • Zinc oxide nanowall growth on carbon fiber • Microstructural analysis using high resolution electron microscopy • X-ray and electron diffraction analysis • Photoluminescence characteristics

  2. Direct synthesis of nano-sized glass powders with spherical shape by RF (radio frequency) thermal plasma

    International Nuclear Information System (INIS)

    A new route for obtaining very small, spheroid glass powders is demonstrated using an RF (radio frequency) thermal plasma system. During the process, four kinds of chemicals, here SiO2, B2O3, BaCO3, and K2CO3, were mixed at pre-set weight ratios, spray-dried, calcined at 250 deg. C for 3 h, and crushed into fragments. Then, they were successfully reformed into nano-sized amorphous powders (< 200 nm) with spherical shape by injecting them along the centerline of an RF thermal plasma reactor at ∼ 24 kW. The as-synthesized powders show negligible (< 1%) composition changes when compared with the injected precursors of raw material compounds.

  3. Single-sided deafness & directional hearing: contribution of spectral cues and high-frequency hearing loss in the hearing ear

    OpenAIRE

    MartijnJohannes HermanusAgterberg; MyrtheK.S.Hol

    2014-01-01

    Direction-specific interactions of sound waves with the head, torso and pinna provide unique spectral-shape cues that are used for the localization of sounds in the vertical plane, whereas horizontal sound localization is based primarily on the processing of binaural acoustic differences in arrival time (interaural time differences, or ITDs) and sound level (interaural level differences, or ILDs). Because the binaural sound-localization cues are absent in listeners with total single-sided dea...

  4. Study of the lacustrine phytoplankton productivity dependence on solar radiation, on the basis of direct high-frequency measurements

    Science.gov (United States)

    Provenzale, Maria; Ojala, Anne; Heiskanen, Jouni; Erkkilä, Kukka-Maaria; Mammarella, Ivan; Hari, Pertti; Vesala, Timo

    2016-04-01

    One of the main components of the carbon cycle in lakes is phytoplankton. Its in situ photosynthesis and respiration are usually studied with traditional methods (dark and light bottle method, 14C labelling technique). These methods, relying on sampling and incubation, may lead to unrealistic results. They also have a poor temporal resolution, which does not allow the non-linear relationship between photosynthetically active solar radiation (PAR) and photosynthesis to be properly investigated. As a consequence, the phytoplankton net primary productivity (NPP) cannot be parameterised as a function of ambient variables. In 2008 an innovative free-water approach was proposed. It is based on non-dispersive infrared air CO2 probes that, by building an appropriate system, can be used to measure the CO2 concentration in the water at a high-frequency. At that time, the method was tested only on 3 days of data. Here, we deployed it on a boreal lake in Finland for four summers, in order to calculate the NPP and verify its dependence on PAR. The set-up was completed by an eddy-covariance system and water PAR and temperature sensors. In analogy with the procedure typically used in terrestrial ecology, we obtained the phytoplankton NPP computing the mass balance of CO2 in the mixed layer of the lake, i.e. the superficial layer where the conditions are homogeneous and most of the photosynthetic activity takes place. After calculating the NPP , we verified its dependence on PAR. The theoretical model we used was a saturating Michaelis-Menten curve, in which the variables are water temperature and PAR. The equation also contains parameters typical of the phytoplankton communities, which represent their maximum potential photosynthetic rate, their half-saturation constant and their basal respiration. These parameters allow the NPP to be parameterised as a function of T and PAR. For all the analysed year, we found a very good agreement between theory and data (R2 ranged from 0.80 to

  5. Radio frequency plasma transition caused by gas puffing and/or direct current biasing using multiturn internal antenna

    International Nuclear Information System (INIS)

    The transitions between capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) were investigated using chemical vapor deposition (CVD) plasma with the internal RF multiturn antenna. The typical electron densities of both 1015/m3 in CCP mode and 1017/m3 in ICP mode were measured, and the measured electron temperature profile was hollow in the CCP mode, which was in contrast to the broadened temperature profile in the ICP mode. Finally, we succeeded in controlling the RF plasma transition by changing the gas density and also by supplying the direct current (DC) voltage. (author)

  6. Experimental and kinetic simulation studies of radio-frequency and direct-current breakdown in synthetic air

    International Nuclear Information System (INIS)

    We report a combined experimental and modeling study of the breakdown of synthetic air under the influence of static (dc) and time-varying electric fields, up to radio-frequencies (RF). The simulations of the breakdown events are based on a simplified model that makes the problem computationally tractable: only electrons are traced by Monte Carlo simulation. In the dc case the simulation is used for the determination of the effective secondary electron emission coefficient, based on the measured dc Paschen curve. In the RF case we observe a transition between the modes (i) where reproduction of the charges takes place in the gas volume (at electron oscillation amplitudes smaller than the gap size) and (ii) where surface processes—secondary electron emission and electron reflection—play an important role, as most of the oscillating electrons reach the electrode surfaces. The RF (f = 13.56 MHz) simulations, assuming a constant effective secondary electron yield, reproduce well the breakdown curve obtained in the experiment. (paper)

  7. 3D frequency modeling of elastic seismic wave propagation via a structured massively parallel direct Helmholtz solver

    Science.gov (United States)

    Wang, S.; De Hoop, M. V.; Xia, J.; Li, X.

    2011-12-01

    We consider the modeling of elastic seismic wave propagation on a rectangular domain via the discretization and solution of the inhomogeneous coupled Helmholtz equation in 3D, by exploiting a parallel multifrontal sparse direct solver equipped with Hierarchically Semi-Separable (HSS) structure to reduce the computational complexity and storage. In particular, we are concerned with solving this equation on a large domain, for a large number of different forcing terms in the context of seismic problems in general, and modeling in particular. We resort to a parsimonious mixed grid finite differences scheme for discretizing the Helmholtz operator and Perfect Matched Layer boundaries, resulting in a non-Hermitian matrix. We make use of a nested dissection based domain decomposition, and introduce an approximate direct solver by developing a parallel HSS matrix compression, factorization, and solution approach. We cast our massive parallelization in the framework of the multifrontal method. The assembly tree is partitioned into local trees and a global tree. The local trees are eliminated independently in each processor, while the global tree is eliminated through massive communication. The solver for the inhomogeneous equation is a parallel hybrid between multifrontal and HSS structure. The computational complexity associated with the factorization is almost linear with the size of the Helmholtz matrix. Our numerical approach can be compared with the spectral element method in 3D seismic applications.

  8. A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

    KAUST Repository

    Zhang, Wei

    2015-05-05

    We present results of direct numerical simulations of a synthetic jet (SJ) based separation control of flow past a NACA-0018 (National Advisory Committee for Aeronautics) airfoil, at 10° angle of attack and Reynolds number 104 based on the airfoil chord length C and uniform inflow velocity U 0. The actuator of the SJ is modeled as a spanwise slot on the airfoil leeward surface and is placed just upstream of the leading edge separation position of the uncontrolled flow. The momentum coefficient of the SJ is chosen at a small value 2.13 × 10−4 normalized by that of the inflow. Three forcing frequencies are chosen for the present investigation: the low frequency (LF) F + = feC/U 0 = 0.5, the medium frequency (MF) F + = 1.0, and the high frequency (HF) F + = 4.0. We quantify the effects of forcing frequency for each case on the separation control and related vortex dynamics patterns. The simulations are performed using an energy conservative fourth-order parallel code. Numerical results reveal that the geometric variation introduced by the actuator has negligible effects on the mean flow field and the leading edge separation pattern; thus, the separation control effects are attributed to the SJ. The aerodynamic performances of the airfoil, characterized by lift and lift-to-drag ratio, are improved for all controlled cases, with the F + = 1.0 case being the optimal one. The flow in the shear layer close to the actuator is locked to the jet, while in the wake this lock-in is maintained for the MF case but suppressed by the increasing turbulent fluctuations in the LF and HF cases. The vortex evolution downstream of the actuator presents two modes depending on the frequency: the vortex fragmentation and merging mode in the LF case where the vortex formed due to the SJ breaks up into several vortices and the latter merge as convecting downstream; the discrete vortices mode in the HF case where discrete vortices form and convect downstream without any fragmentation and

  9. Constraining the Frequency of Free-Floating Planets from a Synthesis of Microlensing, Radial Velocity, and Direct Imaging Survey Results

    CERN Document Server

    Clanton, Christian

    2016-01-01

    A microlensing survey by Sumi et al. (2011) exhibits an overabundance of short-timescale events (STEs; t_E~10 AU) and free-floating planets. Assuming these STEs are indeed due to planetary-mass objects, we aim to constrain the fraction of these events that can be explained by bound but wide-separation planets. We fit the observed timescale distribution with a lens mass function comprised of brown dwarfs, main-sequence stars, and stellar remnants, finding and thus corroborating the initial identification of an excess of STEs. We then include a population of bound planets that are expected not to show signatures of the primary lens (host) in their microlensing light curves and that are also consistent with results from representative microlensing, radial velocity, and direct imaging surveys. We find that bound planets alone cannot explain the entire STE excess without violating the constraints from the surveys we consider and thus some fraction of these events must be due to free-floating planets, if our model ...

  10. Effects of experience on the dimensions of intensity, direction and frequency of the competitive anxiety and self-confidence: A study in athletes of individual and team sports

    Directory of Open Access Journals (Sweden)

    Marcos Gimenes Fernandes

    2014-06-01

    Full Text Available The present study had the following objectives: i to examine the inter-scale correlations between the three dimensions of responses (intensity, direction and frequency of the CSAI-2R and its relationship with competitive experience, and ii evaluate the effect of competitive experience anxiety (cognitive and somatic and self-confidence in the total sample and for different types of modalities (individual vs. team. The sample consisted of 267 athletes (196 male and 71 female, of different sports, aged between 18 and 40 years (M = 24.30, SD = 5.62. Athletes completed the Brazilian version of the CSAI-2, which included the addition of the dimensions of direction and frequency response. Spearman test and Manova were used for the data analysis. Overall, it was found that the competitive experience has a high multivariate and significant effect on the dimensions of competitive anxiety. Both individual and team athletes with low competitive experience showed a trend to report lower levels of self-confidence intensity, compared to counterparts with high competitive experience. These results were discussed in view of the theoretic framework and practical implications planning Sport Psychology intervention programs in local athletes with different backgrounds.

  11. Development of a New Class of Low Cost, High Frequency Link Direct DC to AC Converters for Solid Oxide Fuel Cells (SOFC)

    Energy Technology Data Exchange (ETDEWEB)

    Prasad Enjeti; J.W. Howze

    2003-12-01

    This project proposes to design and develop a new class of power converters (direct DC to AC) to drastically improve performance and optimize the cost, size, weight and volume of the DC to AC converter in SOFC systems. The proposed topologies employ a high frequency link; direct DC to AC conversion approach. The direct DC to AC conversion approach is more efficient and operates without an intermediate dc-link stage. The absence of the dc-link, results in the elimination of bulky, aluminum electrolytic capacitors, which in turn leads to a reduction in the cost, volume, size and weight of the power electronic converter. The feasibility of two direct DC to AC converter topologies and their suitability to meet SECA objectives will be investigated. Laboratory proto-type converters (3-5kW) will be designed and tested in Phase-1. A detailed design trade-off study along with the test results will be available in the form of a report for the evaluation of SECA Industrial partners. This project proposes to develop a new and innovative power converter technology suitable for Solid Oxide Fuel Cell (SOFC) power systems in accordance with SECA objectives. The proposed fuel cell inverter (FCI) employs state of the art power electronic devices configured in two unique topologies to achieve direct conversion of DC power (24-48V) available from a SOFC to AC power (120/240V, 60Hz) suitable for utility interface and powering stand alone loads. The primary objective is to realize cost effective fuel cell converter, which operates under a wide input voltage range, and output load swings with high efficiency and improved reliability.

  12. Continuous probing of cold complex molecules with infrared frequency comb spectroscopy

    Science.gov (United States)

    Spaun, Ben; Changala, P. Bryan; Patterson, David; Bjork, Bryce J.; Heckl, Oliver H.; Doyle, John M.; Ye, Jun

    2016-05-01

    For more than half a century, high-resolution infrared spectroscopy has played a crucial role in probing molecular structure and dynamics. Such studies have so far been largely restricted to relatively small and simple systems, because at room temperature even molecules of modest size already occupy many millions of rotational/vibrational states, yielding highly congested spectra that are difficult to assign. Targeting more complex molecules requires methods that can record broadband infrared spectra (that is, spanning multiple vibrational bands) with both high resolution and high sensitivity. However, infrared spectroscopic techniques have hitherto been limited either by narrow bandwidth and long acquisition time, or by low sensitivity and resolution. Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) combines the inherent broad bandwidth and high resolution of an optical frequency comb with the high detection sensitivity provided by a high-finesse enhancement cavity, but it still suffers from spectral congestion. Here we show that this problem can be overcome by using buffer gas cooling to produce continuous, cold samples of molecules that are then subjected to CE-DFCS. This integration allows us to acquire a rotationally resolved direct absorption spectrum in the C–H stretching region of nitromethane, a model system that challenges our understanding of large-amplitude vibrational motion. We have also used this technique on several large organic molecules that are of fundamental spectroscopic and astrochemical relevance, including naphthalene, adamantane and hexamethylenetetramine. These findings establish the value of our approach for studying much larger and more complex molecules than have been probed so far, enabling complex molecules and their kinetics to be studied with orders-of-magnitude improvements in efficiency, spectral resolution and specificity.

  13. Quantum non-Gaussianity of frequency up-converted single photons.

    Science.gov (United States)

    Baune, Christoph; Schönbeck, Axel; Samblowski, Aiko; Fiurášek, Jaromír; Schnabel, Roman

    2014-09-22

    Nonclassical states of light are an important resource in today's quantum communication and metrology protocols. Quantum up-conversion of nonclassical states is a promising approach to overcome frequency differences between disparate subsystems within a quantum information network. Here, we present the generation of heralded narrowband single photons at 1550 nm via cavity enhanced spontaneous parametric down-conversion (SPDC) and their subsequent up-conversion to 532 nm. Quantum non-Gaussianity (QNG), which is an important feature for applications in quantum information science, was experimentally certified for the first time in frequency up-converted states. PMID:25321750

  14. Hybrid radio-frequency/direct-current plasma-enhanced chemical vapor deposition system for deposition on inner surfaces of polyethylene terephthalate bottles

    International Nuclear Information System (INIS)

    A hybrid radio-frequency (rf)/direct-current (dc) system has been developed to control the biasing effects during deposition of diamondlike carbon (DLC) films onto the inner wall of polyethylene terephthalate (PET) bottles. An additional dc bias is coupled to the rf electrode to produce the effect of equivalent rf self-biasing. This allows more flexible control of the deposition of the DLC films which are intended to improve the gas barrier characteristics. The experimental results demonstrate that the additional dc bias improves the adhesion strength between the DLC film and PET, although the enhancement in the gas barrier properties is not significantly larger compared to the one without dc bias. The apparatus and methodology have practical importance in the food and beverage industry.

  15. High sensitivity measurement system for the direct-current, capacitance-voltage, and gate-drain low frequency noise characterization of field effect transistors

    Science.gov (United States)

    Giusi, G.; Giordano, O.; Scandurra, G.; Rapisarda, M.; Calvi, S.; Ciofi, C.

    2016-04-01

    Measurements of current fluctuations originating in electron devices have been largely used to understand the electrical properties of materials and ultimate device performances. In this work, we propose a high-sensitivity measurement setup topology suitable for the automatic and programmable Direct-Current (DC), Capacitance-Voltage (CV), and gate-drain low frequency noise characterization of field effect transistors at wafer level. Automatic and programmable operation is particularly useful when the device characteristics relax or degrade with time due to optical, bias, or temperature stress. The noise sensitivity of the proposed topology is in the order of fA/Hz1/2, while DC performances are limited only by the source and measurement units used to bias the device under test. DC, CV, and NOISE measurements, down to 1 pA of DC gate and drain bias currents, in organic thin film transistors are reported to demonstrate system operation and performances.

  16. Photonic generation of bipolar direct-sequence UWB signals based on optical spectral shaping and incoherent frequency-to-time conversion

    Science.gov (United States)

    Mu, Hongqian; Wang, Muguang; Ye, Jun; Jian, Shuisheng

    2016-06-01

    A novel technology to obtain binary phase-coded ultrawideband (UWB) signals for direct-sequence spread-spectrum communication systems is investigated by using a cost-effective incoherent source. The bipolar encoding is performed based on an all-fiber spectrum shaper composed of two FBG arrays to tailor the optical spectrum, and a section of single-mode fiber to achieve incoherent frequency-to-time conversion. We demonstrate a 1.325-Gb/s UWB encoding system by the use of binary spreading codes of 4-chip length via computer simulations. The proposed bipolar UWB encoding technology can be applied to high-speed UWB-over-fiber communication systems.

  17. Dynamic interference in the photoionization of He by coherent intense high-frequency laser pulses: Direct propagation of the two-electron wave packets on large spatial grids

    Science.gov (United States)

    Artemyev, Anton N.; Müller, Anne D.; Hochstuhl, David; Cederbaum, Lorenz S.; Demekhin, Philipp V.

    2016-04-01

    The direct ionization of the helium atom by intense coherent high-frequency short laser pulses is investigated theoretically from first principles. To this end, we solve numerically the time-dependent Schrödinger equation for the two-electron wave packet and its interaction with the linearly polarized pulse by the efficient time-dependent restricted-active-space configuration-interaction method (TD-RASCI). In particular, we consider photon energies which are nearly resonant for the 1 s →2 p excitation in the He+ ion. Thereby, we investigate the dynamic interference of the photoelectrons of the same kinetic energy emitted at different times along the pulse in the two-electron system. In order to enable observation of the dynamic interference in the computed spectrum, the electron wave packets were propagated on large spatial grids over long times. The computed photoionization spectra of He exhibit pronounced interference patterns the complexity of which increases with the decrease of the photon energy detuning and with the increase of the pulse intensity. Our numerical results pave the way for experimental verification of the dynamic interference effect at presently available high-frequency laser pulse sources.

  18. Influence of thickness on the structural properties of radio-frequency and direct-current magnetron sputtered TiO2 anatase thin films

    International Nuclear Information System (INIS)

    Thin films of TiO2 were deposited by reactive sputtering of a Ti target on unheated substrates and post-heated at 300 °C and 500 °C. They exhibit a granular structure. Direct current-sputtered films are amorphous as-deposited and crystallize (to pure anatase) only at 500 °C. Radio-frequency (rf)-sputtered films are already crystalline (pure anatase) as-deposited on unheated substrates. Above a thickness of 100 nm, the crystallite size, as deduced from the half-width of X-ray diffraction (XRD) peaks, is constant at 35 nm and decreases to zero when the thickness decreases to 25 nm. Below a thickness of 25 nm, the films are X-ray amorphous. Height and half-width of the XRD peaks of rf-sputtered films do not change upon post-heating at 300 or 500 °C. A larger lattice parameter ratio c/a is observed with respect to the bulk value that decreases with increasing film thickness and is about 1% larger for a film thickness larger than 100 nm. - Highlights: • Anatase films without the presence of rutile were grown on unheated substrates. • Radio-frequency sputtered films are crystalline as-deposited. • Direct-current sputtered films become crystalline only after annealing at 500 °C. • The crystallite size approaches zero when the film thickness approaches 25 nm. • There is an expansive strain in the crystallites along the c-axis

  19. Correction of phase velocity bias caused by strong directional noise sources in high-frequency ambient noise tomography: a case study in Karamay, China

    Science.gov (United States)

    Wang, Kai; Luo, Yinhe; Yang, Yingjie

    2016-05-01

    corrected interstation dispersion measurements are more consistent with results from geology surveys than those based on uncorrected data. As ambient noise in high-frequency band (>1 Hz) is mostly related to human activities or climate events, both of which have strong directivity, the iterative approach demonstrated here helps improve the accuracy and resolution of ANT in imaging shallow earth structures.

  20. Absolute frequency and isotope shift of the magnesium (3 s2) 1S0→(3 s 3 d ) 1D2 two-photon transition by direct frequency-comb spectroscopy

    Science.gov (United States)

    Peters, E.; Reinhardt, S.; Hänsch, Th. W.; Udem, Th.

    2015-12-01

    We use a picosecond frequency-doubled mode-locked titanium sapphire laser to generate a frequency comb at 431 nm in order to probe the (3 s2) 1S0 →(3 s 3 d ) 1D2 transition in atomic magnesium. Using a second, self-referenced femtosecond frequency comb, the absolute transition frequency and the 24Mg and 26Mg isotope shift is determined relative to a global-positioning-system-referenced hydrogen maser. Our result for the transition frequency of the main isotope 24Mg of 1 391 128 606.14 (12 ) MHz agrees with previous measurements and reduces its uncertainty by four orders of magnitude. For the isotope shift we find δ ν26 ,24=3915.13 (39 ) MHz. Accurate values for transition frequencies in Mg are relevant in astrophysics and to test atomic structure calculations.

  1. Cavity-enhanced absorption for optical refrigeration

    CERN Document Server

    Seletskiy, Denis V; Sheik-Bahae, Mansoor

    2009-01-01

    A 20-fold increase over the single path optical absorption is demonstrated with a low loss medium placed in a resonant cavity. This has been applied to laser cooling of Yb:ZBLAN glass resulting in 90% absorption of the incident pump light. A coupled-cavity scheme to achieve active optical impedance matching is analyzed.

  2. Cavity enhanced optical processes in microsphere resonators

    OpenAIRE

    Mazzei, Andrea

    2008-01-01

    Diese Arbeit beschreibt eine ausfŸhrliche Untersuchung der physikalischen Eigenschaften von Mikrokugelresonatoren aus Quarzglas. Diese Resonatoren unterstŸtzen sogennante whispering-gallery Moden (WGM), die GŸten so hoch bis 109 bieten. Als experimentelle Hilfsmittel wurden ein Nahfeld- und ein Konfokalmikroskop benutzt, um die Struktur der Moden bezŸglich der Topographie des Resonators eindeutig zu identifizieren, oder um einzelne Quantenemitter zu detektieren und anzuregen. Die resonante...

  3. Fast Flow Cavity Enhanced Ozone Monitor Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Naturally occurring in the stratosphere, ozone plays a significant role in many atmospheric reactions, cloud formation, and is the key player in shielding harmful...

  4. The direct injection of intense ion beams from a high field electron cyclotron resonance ion source into a radio frequency quadrupole

    International Nuclear Information System (INIS)

    The ion current achievable from high intensity ECR sources for highly charged ions is limited by the high space charge. This makes classical extraction systems for the transport and subsequent matching to a radio frequency quadrupole (RFQ) accelerator less efficient. The direct plasma injection (DPI) method developed originally for the laser ion source avoids these problems and uses the combined focusing of the gap between the ion source and the RFQ vanes (or rods) and the focusing of the rf fields from the RFQ penetrating into this gap. For high performance ECR sources that use superconducting solenoids, the stray magnetic field of the source in addition to the DPI scheme provides focusing against the space charge blow-up of the beam. A combined extraction/matching system has been designed for a high performance ECR ion source injecting into an RFQ, allowing a total beam current of 10 mA from the ion source for the production of highly charged 238U40+ (1.33 mA) to be injected at an ion source voltage of 60 kV. In this design, the features of IGUN have been used to take into account the rf-focusing of an RFQ channel (without modulation), the electrostatic field between ion source extraction and the RFQ vanes, the magnetic stray field of the ECR superconducting solenoid, and the defocusing space charge of an ion beam. The stray magnetic field is shown to be critical in the case of a matched beam

  5. The direct injection of intense ion beams from a high field electron cyclotron resonance ion source into a radio frequency quadrupole.

    Science.gov (United States)

    Rodrigues, G; Becker, R; Hamm, R W; Baskaran, R; Kanjilal, D; Roy, A

    2014-02-01

    The ion current achievable from high intensity ECR sources for highly charged ions is limited by the high space charge. This makes classical extraction systems for the transport and subsequent matching to a radio frequency quadrupole (RFQ) accelerator less efficient. The direct plasma injection (DPI) method developed originally for the laser ion source avoids these problems and uses the combined focusing of the gap between the ion source and the RFQ vanes (or rods) and the focusing of the rf fields from the RFQ penetrating into this gap. For high performance ECR sources that use superconducting solenoids, the stray magnetic field of the source in addition to the DPI scheme provides focusing against the space charge blow-up of the beam. A combined extraction/matching system has been designed for a high performance ECR ion source injecting into an RFQ, allowing a total beam current of 10 mA from the ion source for the production of highly charged (238)U(40+) (1.33 mA) to be injected at an ion source voltage of 60 kV. In this design, the features of IGUN have been used to take into account the rf-focusing of an RFQ channel (without modulation), the electrostatic field between ion source extraction and the RFQ vanes, the magnetic stray field of the ECR superconducting solenoid, and the defocusing space charge of an ion beam. The stray magnetic field is shown to be critical in the case of a matched beam. PMID:24593474

  6. The direct injection of intense ion beams from a high field electron cyclotron resonance ion source into a radio frequency quadrupole

    Science.gov (United States)

    Rodrigues, G.; Becker, R.; Hamm, R. W.; Baskaran, R.; Kanjilal, D.; Roy, A.

    2014-02-01

    The ion current achievable from high intensity ECR sources for highly charged ions is limited by the high space charge. This makes classical extraction systems for the transport and subsequent matching to a radio frequency quadrupole (RFQ) accelerator less efficient. The direct plasma injection (DPI) method developed originally for the laser ion source avoids these problems and uses the combined focusing of the gap between the ion source and the RFQ vanes (or rods) and the focusing of the rf fields from the RFQ penetrating into this gap. For high performance ECR sources that use superconducting solenoids, the stray magnetic field of the source in addition to the DPI scheme provides focusing against the space charge blow-up of the beam. A combined extraction/matching system has been designed for a high performance ECR ion source injecting into an RFQ, allowing a total beam current of 10 mA from the ion source for the production of highly charged 238U40+ (1.33 mA) to be injected at an ion source voltage of 60 kV. In this design, the features of IGUN have been used to take into account the rf-focusing of an RFQ channel (without modulation), the electrostatic field between ion source extraction and the RFQ vanes, the magnetic stray field of the ECR superconducting solenoid, and the defocusing space charge of an ion beam. The stray magnetic field is shown to be critical in the case of a matched beam.

  7. Low-temperature growth of low friction wear-resistant amorphous carbon nitride thin films by mid-frequency, high power impulse, and direct current magnetron sputtering

    International Nuclear Information System (INIS)

    The potential of different magnetron sputtering techniques for the synthesis of low friction and wear resistant amorphous carbon nitride (a-CNx) thin films onto temperature-sensitive AISI52100 bearing steel, but also Si(001) substrates was studied. Hence, a substrate temperature of 150 °C was chosen for the film synthesis. The a-CNx films were deposited using mid-frequency magnetron sputtering (MFMS) with an MF bias voltage, high power impulse magnetron sputtering (HiPIMS) with a synchronized HiPIMS bias voltage, and direct current magnetron sputtering (DCMS) with a DC bias voltage. The films were deposited using a N2/Ar flow ratio of 0.16 at the total pressure of 400 mPa. The negative bias voltage, Vs, was varied from 20 to 120 V in each of the three deposition modes. The microstructure of the films was characterized by high-resolution transmission electron microscopy and selected area electron diffraction, while the film morphology was investigated by scanning electron microscopy. All films possessed an amorphous microstructure, while the film morphology changed with the bias voltage. Layers grown applying the lowest substrate bias of 20 V exhibited pronounced intercolumnar porosity, independent of the sputter technique. Voids closed and dense films are formed at Vs ≥ 60 V, Vs ≥ 100 V, and Vs = 120 V for MFMS, DCMS, and HiPIMS, respectively. X-ray photoelectron spectroscopy revealed that the nitrogen-to-carbon ratio, N/C, of the films ranged between 0.2 and 0.24. Elastic recoil detection analysis showed that Ar content varied between 0 and 0.8 at. % and increased as a function of Vs for all deposition techniques. All films exhibited compressive residual stress, σ, which depends on the growth method; HiPIMS produces the least stressed films with values ranging between −0.4 and −1.2 GPa for all Vs, while CNx films deposited by MFMS showed residual stresses up to −4.2 GPa. Nanoindentation showed a significant increase in film

  8. Low-temperature growth of low friction wear-resistant amorphous carbon nitride thin films by mid-frequency, high power impulse, and direct current magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Bakoglidis, Konstantinos D., E-mail: konba@ifm.liu.se; Schmidt, Susann; Garbrecht, Magnus; Ivanov, Ivan G.; Jensen, Jens; Greczynski, Grzegorz; Hultman, Lars [Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden)

    2015-09-15

    The potential of different magnetron sputtering techniques for the synthesis of low friction and wear resistant amorphous carbon nitride (a-CN{sub x}) thin films onto temperature-sensitive AISI52100 bearing steel, but also Si(001) substrates was studied. Hence, a substrate temperature of 150 °C was chosen for the film synthesis. The a-CN{sub x} films were deposited using mid-frequency magnetron sputtering (MFMS) with an MF bias voltage, high power impulse magnetron sputtering (HiPIMS) with a synchronized HiPIMS bias voltage, and direct current magnetron sputtering (DCMS) with a DC bias voltage. The films were deposited using a N{sub 2}/Ar flow ratio of 0.16 at the total pressure of 400 mPa. The negative bias voltage, V{sub s}, was varied from 20 to 120 V in each of the three deposition modes. The microstructure of the films was characterized by high-resolution transmission electron microscopy and selected area electron diffraction, while the film morphology was investigated by scanning electron microscopy. All films possessed an amorphous microstructure, while the film morphology changed with the bias voltage. Layers grown applying the lowest substrate bias of 20 V exhibited pronounced intercolumnar porosity, independent of the sputter technique. Voids closed and dense films are formed at V{sub s} ≥ 60 V, V{sub s} ≥ 100 V, and V{sub s} = 120 V for MFMS, DCMS, and HiPIMS, respectively. X-ray photoelectron spectroscopy revealed that the nitrogen-to-carbon ratio, N/C, of the films ranged between 0.2 and 0.24. Elastic recoil detection analysis showed that Ar content varied between 0 and 0.8 at. % and increased as a function of V{sub s} for all deposition techniques. All films exhibited compressive residual stress, σ, which depends on the growth method; HiPIMS produces the least stressed films with values ranging between −0.4 and −1.2 GPa for all V{sub s}, while CN{sub x} films deposited by MFMS showed residual stresses up to −4.2

  9. Direct generation of 12.5-GHz-spaced optical frequency comb with ultrabroad coverage in near-infrared region by cascaded fiber configuration.

    Science.gov (United States)

    Kashiwagi, Ken; Kurokawa, Takashi; Okuyama, Yasushi; Mori, Takahiro; Tanaka, Yosuke; Yamamoto, Yoshinori; Hirano, Masaaki

    2016-04-18

    We generated a 12.5-GHz-spacing optical frequency comb that can be resolved over 100 THz, from 1040 to 1750 nm, without spectral mode filtering. To cover such a broad spectrum, we used electro-optic modulation of single frequency light and line-by-line pulse synthesis to produce a clear pulse train and subsequent spectral broadening in highly nonlinear fibers (HNLFs). We numerically and experimentally investigated a configuration of the HNLFs and find that a two-stage broadening through different HNLFs is required when using limited pulse energy at a high repetition rate. We designed and fabricated solid silica-based HNLFs with small zero-dispersion wavelengths to obtain strong spectral broadening, especially at the shorter wavelengths. The individual lines of the proposed frequency comb are resolvable with high contrast over the entire spectral range. The results described in this paper should lead to the development of multicarrier sources for wavelength-division-multiplexing communication and super-multi-point frequency calibration for spectrometers, especially in astrophysics. PMID:27137251

  10. Direct phase-locking of a 8.6-μm quantum cascade laser to a mid-IR optical frequency comb: application to precision spectroscopy of N2O.

    Science.gov (United States)

    Gambetta, Alessio; Cassinerio, Marco; Coluccelli, Nicola; Fasci, Eugenio; Castrillo, Antonio; Gianfrani, Livio; Gatti, Davide; Marangoni, Marco; Laporta, Paolo; Galzerano, Gianluca

    2015-02-01

    We developed a high-precision spectroscopic system at 8.6 μm based on direct heterodyne detection and phase-locking of a room-temperature quantum-cascade-laser against an harmonic, 250-MHz mid-IR frequency comb obtained by difference-frequency generation. The ∼30  dB signal-to-noise ratio of the detected beat-note together with the achieved closed-loop locking bandwidth of ∼500  kHz allows for a residual integrated phase noise of 0.78 rad (1 Hz-5 MHz), for an ultimate resolution of ∼21  kHz, limited by the measured linewidth of the mid-IR comb. The system was used to perform absolute measurement of line-center frequencies for the rotational components of the ν2 vibrational band of N2O, with a relative precision of 3×10(-10). PMID:25680033

  11. The Application of Auto-Disturbance Rejection Control Optimized by Least Squares Support Vector Machines Method and Time-Frequency Representation in Voltage Source Converter-High Voltage Direct Current System.

    Science.gov (United States)

    Liu, Ying-Pei; Liang, Hai-Ping; Gao, Zhong-Ke

    2015-01-01

    In order to improve the performance of voltage source converter-high voltage direct current (VSC-HVDC) system, we propose an improved auto-disturbance rejection control (ADRC) method based on least squares support vector machines (LSSVM) in the rectifier side. Firstly, we deduce the high frequency transient mathematical model of VSC-HVDC system. Then we investigate the ADRC and LSSVM principles. We ignore the tracking differentiator in the ADRC controller aiming to improve the system dynamic response speed. On this basis, we derive the mathematical model of ADRC controller optimized by LSSVM for direct current voltage loop. Finally we carry out simulations to verify the feasibility and effectiveness of our proposed control method. In addition, we employ the time-frequency representation methods, i.e., Wigner-Ville distribution (WVD) and adaptive optimal kernel (AOK) time-frequency representation, to demonstrate our proposed method performs better than the traditional method from the perspective of energy distribution in time and frequency plane. PMID:26098556

  12. The Application of Auto-Disturbance Rejection Control Optimized by Least Squares Support Vector Machines Method and Time-Frequency Representation in Voltage Source Converter-High Voltage Direct Current System.

    Directory of Open Access Journals (Sweden)

    Ying-Pei Liu

    Full Text Available In order to improve the performance of voltage source converter-high voltage direct current (VSC-HVDC system, we propose an improved auto-disturbance rejection control (ADRC method based on least squares support vector machines (LSSVM in the rectifier side. Firstly, we deduce the high frequency transient mathematical model of VSC-HVDC system. Then we investigate the ADRC and LSSVM principles. We ignore the tracking differentiator in the ADRC controller aiming to improve the system dynamic response speed. On this basis, we derive the mathematical model of ADRC controller optimized by LSSVM for direct current voltage loop. Finally we carry out simulations to verify the feasibility and effectiveness of our proposed control method. In addition, we employ the time-frequency representation methods, i.e., Wigner-Ville distribution (WVD and adaptive optimal kernel (AOK time-frequency representation, to demonstrate our proposed method performs better than the traditional method from the perspective of energy distribution in time and frequency plane.

  13. The Application of Auto-Disturbance Rejection Control Optimized by Least Squares Support Vector Machines Method and Time-Frequency Representation in Voltage Source Converter-High Voltage Direct Current System

    OpenAIRE

    Liu, Ying-Pei; Liang, Hai-Ping; Gao, Zhong-Ke

    2015-01-01

    In order to improve the performance of voltage source converter-high voltage direct current (VSC-HVDC) system, we propose an improved auto-disturbance rejection control (ADRC) method based on least squares support vector machines (LSSVM) in the rectifier side. Firstly, we deduce the high frequency transient mathematical model of VSC-HVDC system. Then we investigate the ADRC and LSSVM principles. We ignore the tracking differentiator in the ADRC controller aiming to improve the system dynamic ...

  14. Charge and frequency resolved isochronous mass spectrometry in storage rings: First direct mass measurement of the short-lived neutron-deficient $^{51}$Co nuclide

    CERN Document Server

    Shuai, P; Tu, X L; Zhang, Y H; Sun, B H; Litvinov, Yu A; Yan, X L; Blaum, K; Wang, M; Zhou, X H; He, J J; Sun, Y; Kaneko, K; Yuan, Y J; Xia, J W; Yang, J C; Audi, G; Chen, X C; Jia, G B; Hu, Z G; Ma, X W; Mao, R S; Mei, B; Sun, Z Y; Wang, S T; Xiao, G Q; Xu, X; Yamaguchi, T; Yamaguchi, Y; Zang, Y D; Zhao, H W; Zhao, T C; Zhang, W; Zhan, W L

    2014-01-01

    Revolution frequency measurements of individual ions in storage rings require sophisticated timing detectors. One of common approaches for such detectors is the detection of secondary electrons released from a thin foil due to penetration of the stored ions. A new method based on the analysis of intensities of secondary electrons was developed which enables determination of the charge of each ion simultaneously with the measurement of its revolution frequency. Although the mass-over-charge ratios of $^{51}$Co$^{27+}$ and $^{34}$Ar$^{18+}$ ions are almost identical, and therefore, the ions can not be resolved in a storage ring, by applying the new method the mass excess of the short-lived $^{51}$Co is determined for the first time to be ME($^{51}$Co)=-27342(48) keV. Shell-model calculations in the $fp$-shell nuclei compared to the new data indicate the need to include isospin-nonconserving forces.

  15. Coordinated primary frequency control among non-synchronous systems connected by a multi-terminal high-voltage direct current grid

    OpenAIRE

    Dai, Jing; Phulpin, Yannick; Sarlette, Alain; Ernst, Damien

    2012-01-01

    The authors consider a power system composed of several non-synchronous AC areas connected by a multiterminal high-voltage direct current (HVDC) grid. In this context, the authors propose a distributed control scheme that modifies the power injections from the different AC areas into the DC grid so as to make the system collectively react to load imbalances. This collective reaction allows each individual AC area to downscale its primary reserves. The scheme is inspired by algorithms for th...

  16. Single-sided deafness and directional hearing: contribution of spectral cues and high-frequency hearing loss in the hearing ear

    OpenAIRE

    Agterberg, Martijn J. H.; Hol, Myrthe K. S.; van Wanrooij, Marc M.; van Opstal, A. John; Snik, Ad F. M.

    2014-01-01

    Direction-specific interactions of sound waves with the head, torso, and pinna provide unique spectral-shape cues that are used for the localization of sounds in the vertical plane, whereas horizontal sound localization is based primarily on the processing of binaural acoustic differences in arrival time (interaural time differences, or ITDs) and sound level (interaural level differences, or ILDs). Because the binaural sound-localization cues are absent in listeners with total single-sided de...

  17. A Stable 22-W Low-Noise Continuous-Wave Single-Frequency Nd:YVO4 Laser at 1.06 μm Directly Pumped by a Laser Diode

    International Nuclear Information System (INIS)

    We report a low-noise continous-wave single-frequency Nd:YVO4 laser at 1.06 μm directly pumped by an 880-nm laser diode. A maximum output power of 22 W is achieved with an optical-to-optical conversion efficiency of 46.3%. The stability of the output is better than ±0.7% in the given four hours. The output beam is almost diffraction-limited with a measured beam quality of M2x = 1.05 and M2y = 1.02. The intensity noise and the phase noise of the laser reach the shot-noise limit at an analysis frequency of 5 MHz. (fundamental areas of phenomenology(including applications))

  18. Monolithically integrated absolute frequency comb laser system

    Energy Technology Data Exchange (ETDEWEB)

    Wanke, Michael C.

    2016-07-12

    Rather than down-convert optical frequencies, a QCL laser system directly generates a THz frequency comb in a compact monolithically integrated chip that can be locked to an absolute frequency without the need of a frequency-comb synthesizer. The monolithic, absolute frequency comb can provide a THz frequency reference and tool for high-resolution broad band spectroscopy.

  19. Photoionization of hydrogen atom by coherent intense high-frequency short laser pulses: Direct propagation of electron wave packets on enormous spatial grids

    CERN Document Server

    Demekhin, Philipp V; Cederbaum, Lorenz S

    2013-01-01

    The time-dependent Schr\\"{o}dinger equation for the hydrogen atom and its interaction with coherent intense high-frequency short laser pulses is solved numerically exactly by employing the code implemented for the multi-configurational time-dependent Hartree-Fock (MCTDHF) method. Thereby, the wavefunction is followed in space and time for times longer than the pulse duration. Results are explicitly shown for 3 and 10 fs pulses. Particular attention is paid to identifying the effect of dynamic interference of photoelectrons emitted with the same kinetic energy at different times during the rising and falling sides of the pulse predicted in [\\emph{Ph.V. Demekhin and L.S. Cederbaum}, Phys. Rev. Lett. \\textbf{108}, 253001 (2012)]. In order to be able to see the dynamic interference pattern in the computed electron spectra, the photoelectron wave packet has to be propagated over long distances. Clearly, complex absorption potentials often employed to compute spectra of emitted particles cannot be used to detect dy...

  20. Sputter crater formation in the case of microsecond pulsed glow discharge in a Grimm-type source. Comparison of direct current and radio frequency modes

    International Nuclear Information System (INIS)

    Depth profiling with pulsed glow discharge is a promising technique. The application of pulsed voltage for sputtering reduces the sputtering rate and thermal stress and hereby improves the analysis of thin layered and thermally fragile samples. However pulsed glow discharge is not well studied and this limits its practical use. The current work deals with the questions which usually arise when the pulsed mode is applied: Which duty cycle, frequency and pulse length must be chosen to get the optimal sputtering rate and crater shape? Are the well-known sputtering effects of the continuous mode valid also for the pulsed regime? Is there any difference between dc and rf pulsing in terms of sputtering? It is found that the pulse length is a crucial parameter for the crater shape and thermal effects. Sputtering with pulsed dc and rf modes is found to be similar. The observed sputtering effects at various pulsing parameters helped to interpret and optimize the depth resolution of GD OES depth profiles. - Highlights: ► The validity of the Boumans equation for pulsed rf and dc glow discharge is shown. ► The influence of the pulsing parameters on the sputter crater is ascertained. ► The dependence of the depth resolution on the pulsing parameters is shown. ► Rf and dc pulsed discharges are found to be similar in terms of sputtering.

  1. Frequency standards

    CERN Document Server

    Riehle, Fritz

    2006-01-01

    Of all measurement units, frequency is the one that may be determined with the highest degree of accuracy. It equally allows precise measurements of other physical and technical quantities, whenever they can be measured in terms of frequency.This volume covers the central methods and techniques relevant for frequency standards developed in physics, electronics, quantum electronics, and statistics. After a review of the basic principles, the book looks at the realisation of commonly used components. It then continues with the description and characterisation of important frequency standards

  2. Assessment of potential energy savings following the replacement of gear-motor-driven systems by frequency-converter-fed direct drives; Energiesparpotential bei Ersatz von Getriebemotoren durch FU-Antriebe. Potentialanalyse

    Energy Technology Data Exchange (ETDEWEB)

    Tanner, R.; Riesen, H. J.

    2007-03-15

    This project deals with the energy saving potential that can be achieved by replacing gear motor driven systems by frequency converter fed direct drives. Estimates have shown that due to the high percentage of gear motor installations, which amounts to approximately 10% of all motor driven systems, a significant amount of energy could be saved. However, several barriers impose major restrictions to the broad application of such actions: With the exception of worm gears that reach about 20% of all gear drives, todays' gears already offer a high efficiency of 97-98%. Gear motors are often included in OEM integrated solutions. Many processes require complex adaptations that can complicate replacements or make it even impractical. For low speed or high torque requirements, gear motors may have a dominant advantage concerning the compactness. Our investigations have shown, that in spite of such barriers the replacement of gear motors by direct motors can sum up to a significant amount of energy savings in many cases. Looking at the worm gear systems and the restricted speed and torque ranges that are covered by the direct drives from several suppliers we assume a total saving potential of about 78 GWh per year for Switzerland. (author)

  3. Theoretical study of direct-current and radio-frequency breakdown in GaN wurtzite- and zinc-blende-phase MESFETs (metal-semiconductor field-effect transistors)

    International Nuclear Information System (INIS)

    In this paper, we present a comparison of the direct-current (DC) and radio-frequency (RF) breakdown behaviours of representative wurtzite- and zinc-blende-phase GaN MESFET structures based on a theoretical analysis. The calculations are made using a full-band ensemble Monte Carlo simulation that includes a numerical formulation of the impact ionization transition rate. Calculations of both the DC and RF breakdown voltages are presented for submicron MESFET devices made from either wurtzite- or zinc-blende-phase GaN. The devices are otherwise identical. It is found that the DC breakdown voltage in the wurtzite-phase GaN MESFET is significantly larger than that in the zinc-blende-phase device. This is due to the fact that electron heating occurs more rapidly within the zinc-blende phase than the wurtzite phase of GaN. As a consequence, avalanche breakdown occurs at higher applied field strengths and voltages in the wurtzite phase than in the zinc-blende phase of GaN. It is further found that the RF breakdown voltage of the devices increases with increasing frequency of the applied large-signal RF excitation. (author)

  4. Frequency stability

    Czech Academy of Sciences Publication Activity Database

    Kroupa, Věnceslav František

    Bratislava: Department of Radio and Electronics, FEI STU, 2006 - (Píš, P.; Krajčušková, Z.), I.1-I.9 ISBN 80-227-2388-6. [ Radio elektronika 2006. Conference proceedings. Bratislava (SK), 25.04.2006-26.04.2006] R&D Projects: GA ČR(CZ) GA102/05/0852 Institutional research plan: CEZ:AV0Z20670512 Keywords : noise * frequency stability * frequency control Subject RIV: JW - Navigation, Links, Detection ; Counter-Measures

  5. High performance control of an synchronous engine without speed indicator by direct control of the torque: Kalman filtering: control of the inverter commutation frequency; Commande haute performance d'un moteur asynchrone sans capteur de vitesse par controle direct du couple: filtrage de Kalman etendu du vecteur d'etat: controle de la frequence de commutation de l'onduleur

    Energy Technology Data Exchange (ETDEWEB)

    El Hassan, Ismail

    1999-07-01

    This thesis describes the development of a direct control of the torque and flow without a speed indicator for an asynchronous motor. The power is supplied by a two level inverter. The lack of mechanical sensor leads to a non linear simulation. This study is applied to a prototype. The obtained results show good static and dynamic performance of the speed regulator and the control robustness for the whole speed range. (A.L.B.)

  6. A Novel Frequency Measurement Method Suitable for a Large Frequency Ratio Condition

    Institute of Scientific and Technical Information of China (English)

    ZHOU Wei; XUAN Zong-Qiang; YU Jian-Guo; WANG Hai; ZHOU Hui; LI Zhi-Qi

    2004-01-01

    @@ As for the obstacles to direct comparison between superhigh and lower frequencies, we accomplish the accurate comparison between low and microwave frequencies with the 105 ratios of the operating frequencies on the basis of phase comparison between the signals whose frequencies are related by an arbitrary integer. This method is simple and accurate, and will be widely used as a special frequency comparison approach.

  7. Research on Direct Power Control of Three-phase PWM Rectifier with Constant Switch Frequency%三相恒频PWM整流器的直接功率控制研究

    Institute of Scientific and Technical Information of China (English)

    唐雄民; 朱燕飞

    2011-01-01

    A predictive direct power control strategy for three-phase pulse width modulation rectifier was presented. Based on instantaneous active and reactive power theory, the rectifier s active and reactive power variations were predicted in the next sampling period and control vector of rectifier was directly calculated. With control vector of rectifier,space vector modulation was used to generate the required switch pulse of con verter in a constant switching frequency. The impact of sampling delay and online calculation delay on the accu racy of active and reactive power was analyzed,and the compensation method was achieved. Simulation results validate the control strategy and compensation method.%提出了一种基于功率预测模型的三相PWM整流器控制策略.控制策略利用瞬时功率理论预测下一个固定周期内电路的有功和无功变化,直接求取整流器交流侧的电压矢量,并采用空间矢量调制方法来保证整流器工作频率的恒定.还对由于采样、实时计算等原因引起的延时对电路有功和无功的影响进行探讨,并给出了补偿方法.仿真结果验证了控制策略和补偿方法的有效性.

  8. 基于谐振腔增强型石墨烯光电探测器的设计及性能分析∗%Design and p erformance analysis of micro cavity-enhanced graphene photo detector

    Institute of Scientific and Technical Information of China (English)

    梁振江; 刘海霞; 牛燕雄; 尹贻恒

    2016-01-01

    There is an increasing interest in grapheme photodetector for its applications, because graphene has rich optical and electronic properties, including zero band gap, high mobility and special optical absorption properties. A design of microcavity-enhanced photodetector based on ultra-thin graphene is proposed in this paper: detector absorption can be effectively improved by confining the light field in the microcavity. Through studying the light field resonant condition in the microcavity and enhanced mechanism of detector responsivity under resonant mode, the light absorption model of a microcavity-enhanced graphene photodetector under standing wave effect is established;it is analyzed that the influences of microcavity mirror reflectivity and length on detector performance are increased by light field. Further the optimal structure parameters and performance evaluations of microcavity-enhanced graphene photodetector at different incident wavelengths are demonstrated. Theoretical analysis shows that under the standing wave effect the effective absorption coefficient of monolayer graphene at the antinode is one multiple enlargement compared with no cavity;the microcavity length and topbottom mirror reflectivity directly affect the optical total phase during light folding back at one time in the microcavity, and the shift of the total optical phase changes the full width at half maximum (FWHM) of the responsivity of the microcavity-enhanced graphene photodetector. Through coordinating the relations among the microcavity length and reflectivities of two mirrors and the incident wavelength, it can be realized that the photodetector has a good characteristic of wavelength selectivity. At a nominal operating wavelength of 850 nm, the presented microcavity-enhanced graphene photodetector can reach a responsivity of 0.5 A/W, 32-fold increase compared with monolayer graphene photodetector with no cavity and FWHM can reach 10 nm, indicating that the designed photodetector

  9. Quantum Cascade Laser Frequency Combs

    OpenAIRE

    Faist, Jérôme; Villares, Gustavo; Scalari, Giacomo; Rösch, Markus; Bonzon, Christopher; Hugi, Andreas; Beck, Mattias

    2015-01-01

    It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100 mW and frequency coverage of 100 cm$^{-1}$ in the mid-infrared. In the THz range, 10 mW of average power and 600 GHz of frequency coverage are reported. As a result of th...

  10. Coherent cavity-enhanced dual-comb spectroscopy

    CERN Document Server

    Fleisher, Adam J; Reed, Zachary D; Hodges, Joseph T; Plusquellic, David F

    2016-01-01

    Dual-comb spectroscopy allows for the rapid, multiplexed acquisition of high-resolution spectra without the need for moving parts or low-resolution dispersive optics. This method of broadband spectroscopy is most often accomplished via tight phase locking of two mode-locked lasers, or via sophisticated signal processing algorithms, and therefore long integration times are difficult to achieve. Here we demonstrate an alternative approach to dual-comb spectroscopy using two phase modulator combs originating from a single continuous-wave laser capable of > 2 hours of coherent real-time averaging. The combs of > 250 teeth and 203 MHz spacing were generated by driving the phase modulators with step-recovery diodes, passive devices that provided low-phase-noise harmonics for efficient coupling into an enhancement cavity at picowatt optical powers. With this approach, we demonstrate the sensitivity to simultaneously monitor ambient levels of CO$_2$, CO, HDO, and H$_2$O at a maximum acquisition rate of 150 kHz. Robus...

  11. Cavity enhanced second-order nonlinear quantum photonic logic circuits

    CERN Document Server

    Trivedi, Rahul; Majumdar, Arka

    2015-01-01

    A large obstacle for realizing quantum photonic logic is the weak optical nonlinearity of available materials, which results in large power consumption. In this paper, we argue that second order ($\\chi^{(2)}$) nonlinear optical devices are more suitable for achieving low power photonic logic. We present the theoretical design of all-optical logic with $\\chi^{(2)}$ nonlinear bimodal cavities and their networks. Using semiclassical models derived from the Wigner quasi-probability distribution function, we analyze the power consumption of networks implementing an optical AND gate and an optical latch. Comparison between the second and third order $(\\chi^{(3)})$ optical logic reveals that the $\\chi^{(2)}$ design outperforms the corresponding $\\chi^{(3)}$ design in terms of the gate power consumption at high quality factors. Specifically, using realistic estimates for the $\\chi^{(2)}$ and $\\chi^{(3)}$ susceptibilities of available materials we show that at cavity quality factors $\\sim 10^4$, optical logic designed...

  12. Cavity-enhanced light emission from electrically driven carbon nanotubes

    Science.gov (United States)

    Pyatkov, Felix; Fütterling, Valentin; Khasminskaya, Svetlana; Flavel, Benjamin S.; Hennrich, Frank; Kappes, Manfred M.; Krupke, Ralph; Pernice, Wolfram H. P.

    2016-06-01

    An important advancement towards optical communication on a chip would be the development of integratable, nanoscale photonic emitters with tailored optical properties. Here we demonstrate the use of carbon nanotubes as electrically driven high-speed emitters in combination with a nanophotonic cavity that allows for exceptionally narrow linewidths. The one-dimensional photonic crystal cavities are shown to spectrally select desired emission wavelengths, enhance intensity and efficiently couple light into the underlying photonic network with high reproducibility. Under pulsed voltage excitation, we realize on-chip modulation rates in the GHz range, compatible with active photonic networks. Because the linewidth of the molecular emitter is determined by the quality factor of the photonic crystal, our approach effectively eliminates linewidth broadening due to temperature, surface interaction and hot-carrier injection.

  13. Artificial cavities enhance breeding bird densities in managed cottonwood forests

    Science.gov (United States)

    Twedt, D.J.; Henne-Kerr, J.L.

    2001-01-01

    The paucity of natural cavities within short-rotation hardwood agroforests restricts occupancy by cavity-nesting birds. However, providing 1.6 artificial nesting cavities (nest boxes)/ha within 3- to 10-year-old managed cottonwood forests in the Mississippi Alluvial Valley increased territory density of cavity-nesting birds. Differences in territory densities between forests with and without nest boxes increased as stands aged. Seven bird species initiated 38 nests in 173 boxes during 1997 and 39 nests in 172 boxes during 1998. Prothonotary warblers (Protonotaria citrea) and eastern bluebirds (Sialia sialis) accounted for 67% of nests; nearly all warbler nests were in 1.8-L, plastic-coated cardboard (paper) boxes, whereas bluebird nests were divided between paper boxes and 3.5-L wooden boxes. Larger-volume (16.5-L) wooden nest boxes were used by eastern screech owls (Otus asio) and great crested flycatchers (Myiarchus crinitus), but this box type often was usurped by honey bees (Apis mellifera). To enhance territory densities of cavity-nesting birds in cottonwood agroforests, we recommend placement of plastic-coated paper nest boxes, at a density of 0.5/ha, after trees are >4 years old but at least 2 years before anticipated timber harvest.

  14. Surface plasmon resonance optical cavity enhanced refractive index sensing

    Czech Academy of Sciences Publication Activity Database

    Giorgini, A.; Avino, S.; Malara, P.; Gagliardi, G.; Casalino, M.; Coppola, G.; Iodice, M.; Adam, Pavel; Chadt, Karel; Homola, Jiří; De Natale, P.

    2013-01-01

    Roč. 38, č. 11 (2013), s. 1951-1953. ISSN 0146-9592 R&D Projects: GA ČR GBP205/12/G118 Institutional support: RVO:67985882 Keywords : Resonators * Surface plasmon s * Optical sensing and sensors Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.179, year: 2013

  15. Cavity-Enhanced Second-Order Nonlinear Photonic Logic Circuits

    Science.gov (United States)

    Trivedi, Rahul; Khankhoje, Uday K.; Majumdar, Arka

    2016-05-01

    A large obstacle for realizing photonic logic is the weak optical nonlinearity of available materials, which results in large power consumption. In this paper, we present the theoretical design of all-optical logic with second-order (χ(2 )) nonlinear bimodal cavities and their networks. Using semiclassical models derived from the Wigner quasiprobability distribution function, we analyze the power consumption and signal-to-noise ratio (SNR) of networks implementing an optical and gate and an optical latch. A comparison between the second- and third-order (χ(3 )) optical logic reveals that, while the χ(3 ) design outperforms the χ(2 ) design in terms of the SNR for the same input power, employing the χ(3 ) nonlinearity necessitates the use of cavities with ultrahigh-quality factors (Q ˜106) to achieve a gate power consumption comparable to that of the χ(2 ) design at significantly smaller quality factors (Q ˜104). Using realistic estimates of the χ(2 ) and χ(3 ) nonlinear susceptibilities of available materials, we show that, at achievable quality factors (Q ˜104), the χ(2 ) design is an order of magnitude more energy efficient than the corresponding χ(3 ) design.

  16. Cavity-Enhanced Room-Temperature Broadband Raman Memory

    Science.gov (United States)

    Saunders, D. J.; Munns, J. H. D.; Champion, T. F. M.; Qiu, C.; Kaczmarek, K. T.; Poem, E.; Ledingham, P. M.; Walmsley, I. A.; Nunn, J.

    2016-03-01

    Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali-vapor Raman memories combine high-bandwidth storage, on-demand readout, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and have suffered from four-wave-mixing noise. Here, we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering antiresonance for the anti-Stokes field, we also suppress the four-wave-mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapor memory, (15 ±2 )×10-3 photons per pulse, with a total efficiency of (9.5 ±0.5 )%.

  17. Cavity-enhanced optical detection of carbon nanotube Brownian motion

    CERN Document Server

    Stapfner, S; Hunger, D; Weig, E M; Reichel, J; Favero, I

    2012-01-01

    Optical cavities with small mode volume are well-suited to detect the vibration of sub-wavelength sized objects. Here we employ a fiber-based, high-finesse optical microcavity to detect the Brownian motion of a freely suspended carbon nanotube at room temperature under vacuum. The optical detection resolves deflections of the oscillating tube down to 50pm/Hz^1/2. A full vibrational spectrum of the carbon nanotube is obtained and confirmed by characterization of the same device in a scanning electron microscope. Our work successfully extends the principles of high-sensitivity optomechanical detection to molecular scale nanomechanical systems.

  18. Research of Frequency Discriminator on Frequency Lock Loops

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Frequency lock loops (FLL) discriminating algorithms for direct-sequence spread-spectrum are discussed. The existing algorithms can't solve the problem of data bit reversal during one pre-detection integral period. And when the initial frequency offset is large, the frequency discriminator can't work normally. To solve these problems, a new FLL discriminating algorithm is introduced. The least-squares discriminator is used in this new algorithm. As the least-squares discriminator has a short process unit period, the corresponding frequency discriminating range is large. And the data bit reversal just influence one process unit period, so the least-squares discriminated result will not be affected. Compared with traditional frequency discriminator, the least-squares algorithm can effectively solve the problem of data bit reversal and can endure larger initial frequency offset.

  19. Frequency-locking and threshold current-lowering effects of a quantum cascade laser and an application in gas detection field

    International Nuclear Information System (INIS)

    In this paper, the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved. Combined with cavity-enhanced absorption spectroscopy, the noninvasive detection of H2 with a prepared concentration of 500 ppm in multiple dissolved gases is performed and evaluated. The high frequency selectivity of 0.0051 cm−1 at an acquisition time of 1 s allows the sensitive detection of the (1-0) S(1) band of H2 with a high accuracy of (96.53±0.29)% and shows that the detection limit to an absorption line of 4712.9046 cm−1 is approximately (17.26±0.63) ppm at an atmospheric pressure and a temperature of 20 °C. (paper)

  20. Wave directional spectrum from array measurements

    Digital Repository Service at National Institute of Oceanography (India)

    Fernandes, A.A; Sarma, Y.V.B.; Menon, H.B.

    Using the method of Esteva (1976, 1977), whcih assumes that at the frequency band the waves approach from just a single "mean" wave direction, wave direction has been consistently, accurately and unambiguously evaluated as a function of frequency...

  1. Precise frequency generators

    Czech Academy of Sciences Publication Activity Database

    Kroupa, Věnceslav František

    Brno: Institute of Radio Electronics, Brno University of Technology, 2005 - (Svačina, J.; Šebesta, V.; Kolka, Z.), s. 1-4 ISBN 80-214-2904-6. [International Czech-Slovak Scientific Conference Radio elektronika'2005 /15./. Brno (CZ), 03.05.2005-04.05.2005] R&D Projects: GA ČR(CZ) GA102/05/0852 Institutional research plan: CEZ:AV0Z20670512 Keywords : frequency stability * microwave oscilators * direct digital synthesis Subject RIV: BD - Theory of Information

  2. Frequency Standards and Metrology

    Science.gov (United States)

    Maleki, Lute

    2009-04-01

    over 172 KM of installed fiber / S. Crane -- pt. X. Miniature systems. Chip-scale atomic devices: precision atomic instruments based on MEMS (Invited) / J. Kitching ... [et al.]. CSAC - the chip-scale atomic clock (Invited) / R. Lutwak ... [et al.]. Reaching a few 10[symbol] stability level with a compact cold atom clock / F. X. Esnault ... [et al.]. Evaluation of Lin||Lin CPT for compact and high performance frequency standard / E. Breschi ... [et al.] -- pt. XI. Time scales. Atomic time scales TAI and TI(BIPM): present status and prospects (Invited) / G. Petit. Weight functions for biases in atomic frequency standards / J. H. Shirley -- pt. XII. Interferometers. Definition and construction of noise budget in atom interferometry (Invited) / E. D'Ambriosio. Characterization of a cold atom gyroscope (Invited) / A. Landragin ... [et al.]. A mobile atom interferometer for high precision measurements of local gravity / M. Schmidt ... [et al.]. Demonstration of atom interferometer comprised of geometric beam splitters / Hiromitsu Imai and Atsuo Morinaga -- pt. XIII. New directions. Active optical clocks (Invited) / J. Chen. Prospects for a nuclear optical frequency standard based on Thorium-229 (Invited) / E. Peik ... [et al.]. Whispering gallery mode oscillators and optical comb generators (Invited) / A. B. Matsko ... [et al.]. Frequency comparison using energy-time entangled photons / A. Stefanov -- List of participants.

  3. Laser Apparatus with Cascade of Nonlinear Frequency Mixers

    DEFF Research Database (Denmark)

    2015-01-01

    combine the first and second laser beams into a combined initial laser beam comprising at least a frequency component having the first frequency, and a frequency component having the second frequency one or more nonlinear frequency mixers operable to perform a frequency mixing process of a frequency...... component having the first frequency and a frequency component having the second frequency and resulting in at least a frequency component having a third frequency equal to a sum or difference of the first and second frequencies wherein the laser apparatus is configured to direct the combined initial laser......A laser apparatus comprising: a first laser source operable to generate a first laser beam having a least a beam component having a first frequency a second laser source operable to generate a second laser beam having a least a beam component having a second frequency a beam combiner operable to...

  4. Directed Polymer -- Directed Percolation Transition

    OpenAIRE

    Perlsman, Ehud; Havlin, Shlomo

    1999-01-01

    We study the relation between the directed polymer and the directed percolation models, for the case of a disordered energy landscape where the energies are taken from bimodal distribution. We find that at the critical concentration of the directed percolation, the directed polymer undergoes a transition from the directed polymer universality class to the directed percolation universality class. We also find that directed percolation clusters affect the characterisrics of the directed polymer...

  5. Frequency noise in frequency swept fiber laser

    DEFF Research Database (Denmark)

    Pedersen, Anders Tegtmeier; Rottwitt, Karsten

    2013-01-01

    This Letter presents a measurement of the spectral content of frequency shifted pulses generated by a lightwave synthesized frequency sweeper. We found that each pulse is shifted in frequency with very high accuracy. We also discovered that noise originating from light leaking through the acousto...

  6. FREQUENCY CONVERTERS WITH IMPROVED PERFORMANCE

    Directory of Open Access Journals (Sweden)

    Grigorash O. V.

    2016-01-01

    Full Text Available In the autonomous power supply systems there are widely used frequency converters that are able to simultaneously increase or decrease the frequency of the current and voltage stabilizing power supply. These positive properties of frequency converters can improve the operational and technical characteristics of the autonomous power supply system in the complex. The article suggests a functional diagram of a frequency converter performed on reversible rectifiers. We have presented timing diagrams illustrating the principle of its operation. The article also deals with two functional scheme of direct frequency converters executed on single-phase, threephase transformer with a rotating magnetic field. The principle of operation of these schemes has been also discussed in the timing diagrams. The proposed technical solutions for frequency converters contain a smaller amount of power electronic devices that make it possible, thereby reducing the level of electromagnetic interference, increase the efficiency and reliability of performance inverters. The considered scheme of frequency converters, can improve the technical characteristics of the autonomous power supply systems in the complex. We can significantly improve the performance of power systems through the use of modular aggregating principle of the basic functional units of an autonomous system

  7. Frequency of Financial Reports

    Directory of Open Access Journals (Sweden)

    Javad Izadi Zadeh Darjezi

    2013-08-01

    Full Text Available Interim reports are summary statements that are usually prepared in semi-annual format in the UK. Until theEU’s Transparency Directive was put into practice in the UK in 2007, there was no legal necessity forcompanies to provide interim financial reports. (Note 1 Instead such preparation was only a regulatoryrequirement of the London Stock Exchange. The responsibility on companies listed on the London StockExchange to provide these financial reports was first prepared as an suggestion in 1964, to meet therequirements for updates by financial analysts (May, 1971. In 1973, this advice to provide the market withinterim information became a requirement for the admission of stocks and securities to be listed on the stockExchange (Lunt, 1982. This study investigates the preparation of interim reports, and accounting standards forinterim reporting. Also, this study discusses the main purpose of interim reports, the methods of preparation andthe benefits of reporting frequency.

  8. 矿用卡轨车直接转矩四象限变频调速控制系统%Control System of Direct Torque Four Quadrant Frequency Converter for Mining Track

    Institute of Scientific and Technical Information of China (English)

    牛文斌

    2011-01-01

    结合山西潞宁煤业有限责任公司卡轨车四象限变频调速系统的设计与实施,介绍了控制系统的硬件组成、软件实现等内容。现场应用表明,该系统完全满足山西潞宁煤业有限责任公司卡轨车的控制要求,有一定的先进性,值得推广应用。%Based on the control system design and implementation of four quadrant frequency converter for tracks in Luning Coal Co., the hardware components and software realization are introduced. The field application shows that the system meets the control requirement and has certain advantages, which is worthwhile for extensive utilization.

  9. Reduced Frequencies and Activation of Regulatory T Cells After the Treatment of HIV-1-Infected Individuals with the CCR5 Antagonist Maraviroc Are Associated with a Reduction in Viral Loads Rather Than a Direct Effect of the Drug on Regulatory T Cells.

    Science.gov (United States)

    Joedicke, Jara J; Dirks, Miriam; Esser, Stefan; Verheyen, Jens; Dittmer, Ulf

    2016-04-01

    Regulatory T cells (Tregs) play an important role in the pathogenesis of HIV-1 infection and they frequently express the chemokine receptor CCR5. We therefore investigated whether antiretroviral treatment with the CCR5 antagonist Maraviroc affected Tregs in chronically HIV-1-infected individuals. HIV-1-infected patients with high viral loads had elevated frequencies of activated Tregs in the peripheral blood compared with healthy controls. In patients successfully treated with antiretroviral drugs (undetectable viral loads), the frequency and the activation status of Tregs were comparable with healthy controls without any specific effect related to the treatment with Maraviroc. These results indicate that the control of viral replication in general rather than a direct binding of Maraviroc to CCR5-positive Tregs influences Treg responses in successfully treated chronically HIV-1-infected individuals. PMID:27035639

  10. Frequency-Agile Differential Cavity Ring-Down Spectroscopy

    Science.gov (United States)

    Reed, Zachary; Hodges, Joseph

    2015-06-01

    The ultimate precision of highly sensitive cavity-enhanced spectroscopic measurements is often limited by interferences (etalons) caused by weak coupled-cavity effects. Differential measurements of ring-down decay constants have previously been demonstrated to largely cancel these effects, but the measurement acquisition rates were relatively low [1,2]. We have previously demonstrated the use of frequency agile rapid scanning cavity ring-down spectroscopy (FARS-CRDS) for acquisition of absorption spectra [3]. Here, the method of rapidly scanned, frequency-agile differential cavity ring-down spectroscopy (FADS-CRDS) is presented for reducing the effect of these interferences and other shot-to-shot statistical variations in measured decay times. To this end, an electro-optic phase modulator (EOM) with a bandwidth of 20 GHz is driven by a microwave source, generating pairs of sidebands on the probe laser. The optical resonator acts as a highly selective optical filter to all laser frequencies except for one tunable sideband. This sideband may be stepped arbitrarily from mode-to-mode of the ring-down cavity, at a rate limited only by the cavity buildup/decay time. The ability to probe any cavity mode across the EOM bandwidth enables a variety of methods for generating differential spectra. The differential mode spacing may be changed, and the effect of this method on suppressing the various coupled-cavity interactions present in the system is discussed. Alternatively, each mode may also be differentially referenced to a single point, providing immunity to temporal variations in the base losses of the cavity while allowing for conventional spectral fitting approaches. Differential measurements of absorption are acquired at 3.3 kHz and a minimum detectable absorption coefficient of 5 x10-12 cm-1 in 1 s averaging time is achieved. 1. J. Courtois, K. Bielska, and J.T Hodges J. Opt. Soc. Am. B, 30, 1486-1495, 2013 2. H.F. Huang and K.K. Lehmann App. Optics 49, 1378

  11. 阳煤集团煤层瓦斯抽采技术的现状分析%Control System of Direct Torque Four Quadrant Frequency Converter for Mining Track

    Institute of Scientific and Technical Information of China (English)

    樊利军

    2011-01-01

    为了提高阳煤集团本煤层瓦斯抽采效率,采用统计和对比分析方法,介绍了阳煤集团本煤层瓦斯抽采技术现状。分析表明,阳煤集团本煤层瓦斯年抽采量虽然已达1亿m^3但抽采效率还处于较低水平。需要进一步优化本煤层钻孔参数、提高钻孔封孔质量、强化抽采管路连接、搞好抽采系统日常维护,以使阳煤集团本煤层瓦斯抽采效率得到进一步提高。%Based on the control system design and implementation of four quadrant frequency converter for tracks in Luning Coal Co., the hardware components and software realization are introduced. The field application shows that the system meets the control requirement and has certain advantages, which is worthwhile for extensive utilization.

  12. The instantaneous frequency rate spectrogram

    Science.gov (United States)

    Czarnecki, Krzysztof

    2016-01-01

    An accelerogram of the instantaneous phase of signal components referred to as an instantaneous frequency rate spectrogram (IFRS) is presented as a joint time-frequency distribution. The distribution is directly obtained by processing the short-time Fourier transform (STFT) locally. A novel approach to amplitude demodulation based upon the reassignment method is introduced as a useful by-product. Additionally, an estimator of energy density versus the instantaneous frequency rate (IFR) is proposed and referred to as the IFR profile. The energy density is estimated based upon both the classical energy spectrogram and the IFRS smoothened by the median filter. Moreover, the impact of an analyzing window width, additive white Gaussian noise and observation time is tested. Finally, the introduced method is used for the analysis of the acoustic emission of an automotive engine. The recording of the engine of a Lamborghini Gallardo is analyzed as an example.

  13. Directed homology

    DEFF Research Database (Denmark)

    Fahrenberg, Uli

    2004-01-01

    We introduce a new notion of directed homology for semicubical sets. We show that it respects directed homotopy and is functorial, and that it appears to enjoy some good algebraic properties. Our work has applications to higher-dimensional automata.......We introduce a new notion of directed homology for semicubical sets. We show that it respects directed homotopy and is functorial, and that it appears to enjoy some good algebraic properties. Our work has applications to higher-dimensional automata....

  14. Frequency selectivity at very low centre frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado; Pedersen, Christian Sejer; Marquardt, Torsten

    2010-01-01

    measurements based on OAE suppression techniques and notched-noise masking data psychophysically measured for centre frequencies in the range 50-125 Hz, this study examines how individual differences in frequency selectivity, as well as in masking, may occur at very low CFs due to individual differences in the...... shape of the METFs, thought to be affected by the helicotrema impedance. Preliminary analysis indicates that individual differences in the METFs might underlay the observed individual differences in frequency selectivity. Main effects predicted by the calculations are a pronounced flattening off of the...

  15. Baffled Circular Loudspeaker Array With Broadband High Directivity

    OpenAIRE

    Kolundzija, Mihailo; Faller, Christof; Vetterli, Martin

    2010-01-01

    Super-directional loudspeaker arrays can be used to achieve high directivity in a limited low-frequency range. As opposed to microphone arrays, the distance between the loudspeakers has to be relatively large, resulting in aliasing starting at relatively low frequencies. On the other hand, mounting a loudspeaker on a rigid baffle (e.g., a rigid cylinder or sphere) increases its directivity with frequency. Using super-directional array techniques at low frequencies and leveraging loudspeakers'...

  16. Quantum Cascade Laser Frequency Combs

    Science.gov (United States)

    Faist, Jérôme; Villares, Gustavo; Scalari, Giacomo; Rösch, Markus; Bonzon, Christopher; Hugi, Andreas; Beck, Mattias

    2016-06-01

    It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100mW and frequency coverage of 100 cm-1 in the mid-infrared region. In the THz range, 10mW of average power and 600 GHz of frequency coverage are reported. As a result of the very short upper state lifetime of the gain medium, the mode proliferation in these sources arises from four-wave mixing rather than saturable absorption. As a result, their optical output is characterized by the tendency of small intensity modulation of the output power, and the relative phases of the modes to be similar to the ones of a frequency modulated laser. Recent results include the proof of comb operation down to a metrological level, the observation of a Schawlow-Townes broadened linewidth, as well as the first dual-comb spectroscopy measurements. The capability of the structure to integrate monothically nonlinear optical elements as well as to operate as a detector shows great promise for future chip integration of dual-comb systems.

  17. Quantum Cascade Laser Frequency Combs

    CERN Document Server

    Faist, Jérôme; Scalari, Giacomo; Rösch, Markus; Bonzon, Christopher; Hugi, Andreas; Beck, Mattias

    2015-01-01

    It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100 mW and frequency coverage of 100 cm$^{-1}$ in the mid-infrared. In the THz range, 10 mW of average power and 600 GHz of frequency coverage are reported. As a result of the very short upper state lifetime of the gain medium, the mode proliferation in these sources arises from four wave mixing rather than saturable absorption. As a result, their optical output is characterized by the tendency of small intensity modulation of the output power, and the relative phases of the modes to be similar to the ones of a frequency modulated laser. Recent results include the proof of comb operation down to a metrological level, the observation of a Schawlow-Townes broadened linewidth, as well as the fir...

  18. Dependence of synchronization frequency of Kuramoto oscillators on symmetry of intrinsic frequency in ring network

    Indian Academy of Sciences (India)

    Arindam Saha; R E Amritkar

    2014-12-01

    Kuramoto oscillators have been proposed earlier as a model for interacting systems that exhibit synchronization. In this article, we study the difference between networks with symmetric and asymmetric distribution of natural frequencies. We first indicate that synchronization frequency of oscillators in a completely connected network is always equal to the mean of the natural frequency distribution. In particular, shape of the natural frequency distribution does not affect the synchronization frequency in this case. Then, we analyse the case of oscillators in a directed ring network, where asymmetry in the natural frequency distribution is seen to shift the synchronization frequency of the network. We also present an estimate of the shift in the frequencies for slightly asymmetric distributions.

  19. Adjust or Synchronize LM2586/88 Switching Frequency

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    INTRODUCTIONSwitching frequency is a very important parameter in switchingpower converters. As the switching frequency increases, the physicalsize of magnetic elements and other components in the circuit reducesignificantly. Switching frequency also plays a great role incontrol loop gain and compensation design. Switching frequency determinesthe maximum allowable bandwidth of the control loop.Switching frequency is also important parameter for EMI and noiseissues. The EMI spectrum is a direct function of the switching fre-

  20. Cutoff frequency of toroidal plasma waveguide

    International Nuclear Information System (INIS)

    The cutoff frequencies of E and H-modes of empty and plasma filled toroidal waveguides are evaluated. The effects of space curvature and plasma density on cutoff frequencies for both modes are investigated. Using a suitable variable change, a scalar wave equation in the direction of propagation was obtained. The study indicates that the curvature in the direction of wave propagation in toroidal waveguide has an analogous effect as a straight waveguide filled with anisotropic media. The Rayleigh-Schrodinger perturbation method was employed to solve for cutoff frequencies in the first order of approximation. In the limit of small space curvature, the toroidal waveguide cutoff frequencies for both E and H-modes approach those of TM and TE modes of empty cylindrical waveguide with a radius equal to toroidal waveguide minor radius. The analysis shows that the curvature in the direction of propagation in toroidal waveguides leads to the removal of the degeneracy between E and H-modes

  1. Encoding voice fundamental frequency into vibrotactile frequency.

    Science.gov (United States)

    Rothenberg, M; Molitor, R D

    1979-10-01

    Measured in this study was the ability of eight hearing and five deaf subjects to identify the stress pattern in a short sentence from the variation in voice fundamental frequency (F0), when presented aurally (for hearing subjects) and when transformed into vibrotactile pulse frequency. Various transformations from F0 to pulse frequency were tested in an attempt to determine an optimum transformation, the amount of F0 information that could be transmitted, and what the limitations in the tactile channel might be. The results indicated that a one- or two-octave reduction of F0 vibrotactile frequency (transmitting every second or third glottal pulse) might result in a significant ability to discriminate the intonation patterns associated with moderate-to-strong patterns of sentence stress in English. However, accurate reception of the details of the intonation pattern may require a slower than normal pronounciation because of an apparent temporal indeterminacy of about 200 ms in the perception of variations in vibrotactile frequency. A performance deficit noted for the two prelingually, profoundly deaf subjects with marginally discriminable encodings offers some support for our previous hypothesis that there is a natural association between auditory pitch and perceived vibrotactile frequency. PMID:159917

  2. Static electromagnetic frequency changers

    CERN Document Server

    Rozhanskii, L L

    1963-01-01

    Static Electromagnetic Frequency Changers is about the theory, design, construction, and applications of static electromagnetic frequency changers, devices that used for multiplication or division of alternating current frequency. It is originally published in the Russian language. This book is organized into five chapters. The first three chapters introduce the readers to the principles of operation, the construction, and the potential applications of static electromagnetic frequency changers and to the principles of their design. The two concluding chapters use some hitherto unpublished work

  3. Modeling Frequency Comb Sources

    Directory of Open Access Journals (Sweden)

    Li Feng

    2016-06-01

    Full Text Available Frequency comb sources have revolutionized metrology and spectroscopy and found applications in many fields. Stable, low-cost, high-quality frequency comb sources are important to these applications. Modeling of the frequency comb sources will help the understanding of the operation mechanism and optimization of the design of such sources. In this paper,we review the theoretical models used and recent progress of the modeling of frequency comb sources.

  4. Direct Democracy

    DEFF Research Database (Denmark)

    Beramendi, Virginia; Ellis, Andrew; Kaufman, Bruno;

    While many books on direct democracy have a regional or national approach, or simply focus on one of the many mechanisms associated with direct democracy, this Handbook delves into a global comparison of direct democracy mechanisms, including referendums, citizens' initiatives, agenda initiatives...... included as a chapter in the Handbook are possible measures for best practices of implementation, designed for those who wish to tailor direct democracy instruments to their specific needs. In order to further complement the best practices, a variety of global case studies detail the practical uses of...... direct democracy mechanisms in specific contexts. These country case studies allow for in depth discussion of particular issues, including signature collection and voter participation, campaign financing, media coverage, national variations in the usage of direct democracy procedures and national lessons...

  5. Eastern Frequency Response Study

    Energy Technology Data Exchange (ETDEWEB)

    Miller, N.W.; Shao, M.; Pajic, S.; D' Aquila, R.

    2013-05-01

    This study was specifically designed to investigate the frequency response of the Eastern Interconnection that results from large loss-of-generation events of the type targeted by the North American Electric Reliability Corp. Standard BAL-003 Frequency Response and Frequency Bias Setting (NERC 2012a), under possible future system conditions with high levels of wind generation.

  6. Broadband frequency conversion

    DEFF Research Database (Denmark)

    Sanders, Nicolai Højer; Jensen, Ole Bjarlin; Dam, Jeppe Seidelin;

    We demonstrate a method for frequency conversion of broadly tunable or broad bandwidth light in a static, passive setup. Using simple optical components like lenses, mirrors and gratings and a BiBO crystal as the nonlinear material, we are able to frequency double a single-frequency, tunable...

  7. Quantum frequency downconversion experiment

    OpenAIRE

    Takesue, Hiroki

    2010-01-01

    We report the first quantum frequency downconversion experiment. Using the difference frequency generation process in a periodically poled lithium niobate waveguide, we successfully observed the phase-preserved frequency downconversion of a coherent pulse train with an average photon number per pulse of $

  8. Octave Spanning Frequency Comb on a Chip

    CERN Document Server

    Del'Haye, P; Gavartin, E; Holzwarth, R; Kippenberg, T J

    2009-01-01

    Optical frequency combs have revolutionized the field of frequency metrology within the last decade and have become enabling tools for atomic clocks, gas sensing and astrophysical spectrometer calibration. The rapidly increasing number of applications has heightened interest in more compact comb generators. Optical microresonator based comb generators bear promise in this regard. Critical to their future use as 'frequency markers', is however the absolute frequency stabilization of the optical comb spectrum. A powerful technique for this stabilization is self-referencing, which requires a spectrum that spans a full octave, i.e. a factor of two in frequency. In the case of mode locked lasers, overcoming the limited bandwidth has become possible only with the advent of photonic crystal fibres for supercontinuum generation. Here, we report for the first time the generation of an octave-spanning frequency comb directly from a toroidal microresonator on a silicon chip. The comb spectrum covers the wavelength range...

  9. Frequency discriminator/phase detector

    Science.gov (United States)

    Crow, R. B.

    1974-01-01

    Circuit provides dual function of frequency discriminator/phase detector which reduces frequency acquisition time without adding to circuit complexity. Both frequency discriminators, in evaluated frequency discriminator/phase detector circuits, are effective two decades above and below center frequency.

  10. Diophantine frequency synthesis.

    Science.gov (United States)

    Sotiriadis, Paul Peter

    2006-11-01

    A methodology for fine-step, fast-hopping, low-spurs phase-locked loop based frequency synthesis is presented. It uses mathematical properties of integer numbers and linear Diophantine equations to overcome the constraining relation between frequency step and phase-comparator frequency that is inherent in conventional phase-locked loop based frequency synthesis. The methodology leads to fine-step, fast-hopping, modular-structured frequency synthesizers with potentially very low spurs, especially in the vicinity of the carrier. The paper focuses on the mathematical principles of the new methodology and the related number theoretic algorithms. PMID:17091835

  11. Directing 101.

    Science.gov (United States)

    Pintoff, Ernest

    Providing an introduction to anyone considering directing as a field of study or career, this book takes a broad look at the process of directing and encourages students and professionals alike to look outside of the movie industry for inspiration. Chapters in the book discuss selecting and acquiring material; budgeting and financing; casting and…

  12. Radio frequency detection assembly and method for detecting radio frequencies

    Science.gov (United States)

    Cown, Steven H.; Derr, Kurt Warren

    2010-03-16

    A radio frequency detection assembly is described and which includes a radio frequency detector which detects a radio frequency emission produced by a radio frequency emitter from a given location which is remote relative to the radio frequency detector; a location assembly electrically coupled with the radio frequency detector and which is operable to estimate the location of the radio frequency emitter from the radio frequency emission which has been received; and a radio frequency transmitter electrically coupled with the radio frequency detector and the location assembly, and which transmits a radio frequency signal which reports the presence of the radio frequency emitter.

  13. Directing Creativity

    DEFF Research Database (Denmark)

    Darsø, Lotte; Ibbotson, Piers

    2008-01-01

    In this article we argue that leaders facing complex challenges can learn from the arts, specifically that leaders can learn by examining how theatre directors direct creativity through creative constraints. We suggest that perceiving creativity as a boundary phenomenon is helpful for directing it....... Like leaders, who are caught in paradoxical situations where they have to manage production and logistics simultaneously with making space for creativity and innovation, theatre directors need to find the delicate balance between on one hand renewal of perceptions, acting and interaction and on the...... other hand getting ready for the opening night. We conclude that the art of directing creativity is linked to developing competencies of conscious presence, attention and vigilance, whereas the craft of directing creativity concerns communication, framing and choice....

  14. LOW FREQUENCY DAMPER

    Directory of Open Access Journals (Sweden)

    Radu BOGATEANU

    2009-09-01

    Full Text Available The low frequency damper is an autonomous equipment for damping vibrations with the 1-20Hz range.Its autonomy enables the equipment to be located in various mechanical systems, without requiring special hydraulic installations.The low frequency damper was designed for damping the low frequency oscillations occurring in the circuit controls of the upgraded IAR-99 Aircraft.The low frequency damper is a novelty in the aerospace field ,with applicability in several areas as it can be built up in an appropriate range of dimensions meeting the requirements of different beneficiaries. On this line an equipment able to damp an extended frequency range was performed for damping oscillations in the pipes of the nuclear power plants.This damper, tested in INCAS laboratories matched the requirements of the beneficiary.The low frequency damper is patented – the patent no. 114583C1/2000 is held by INCAS.

  15. Breakfast frequency among adolescents

    DEFF Research Database (Denmark)

    Pedersen, Trine Pagh; Holstein, Bjørn E; Damsgaard, Mogens Trab;

    2016-01-01

    OBJECTIVE: To investigate (i) associations between adolescents' frequency of breakfast and family functioning (close relations to parents, quality of family communication and family support) and (ii) if any observed associations between breakfast frequency and family functioning vary by...... (n 3054) from a random sample of forty-one schools. RESULTS: Nearly one-quarter of the adolescents had low breakfast frequency. Low breakfast frequency was associated with low family functioning measured by three dimensions. The OR (95 % CI) of low breakfast frequency was 1·81 (1·40, 2·33) for...... adolescents who reported no close relations to parents, 2·28 (1·61, 3·22) for adolescents who reported low level of quality of family communication and 2·09 (1·39, 3·15) for adolescents who reported low level of family support. Joint effect analyses suggested that the odds of low breakfast frequency among...

  16. Word frequency affects hypermnesia.

    Science.gov (United States)

    Macie, K M; Larsen, J D

    1996-12-01

    Hypermnesia, the tendency of participants to recall more items from a list they have studied when they are asked to recall the list several times on a free-recall test, is enhanced by factors that lead to better performance on free-recall tests. This study tested the hypothesis that words which appear with high frequency in the English language would produce hypermnesia but that low frequency words would not. The activity the 57 participants were required to do between repeated recall tests was also manipulated but had no effect on the number of words recalled. High frequency words resulted in hypermnesia but low frequency words did not. PMID:9009796

  17. Frequency Response Analysis Tool

    Energy Technology Data Exchange (ETDEWEB)

    Etingov, Pavel V.; Kosterev, Dmitry; Dai, T.

    2014-12-31

    Frequency response has received a lot of attention in recent years at the national level, which culminated in the development and approval of North American Electricity Reliability Corporation (NERC) BAL-003-1 Frequency Response and Frequency Bias Setting Reliability Standard. This report is prepared to describe the details of the work conducted by Pacific Northwest National Laboratory (PNNL) in collaboration with the Bonneville Power Administration and Western Electricity Coordinating Council (WECC) Joint Synchronized Information Subcommittee (JSIS) to develop a frequency response analysis tool (FRAT). The document provides the details on the methodology and main features of the FRAT. The tool manages the database of under-frequency events and calculates the frequency response baseline. Frequency response calculations are consistent with frequency response measure (FRM) in NERC BAL-003-1 for an interconnection and balancing authority. The FRAT can use both phasor measurement unit (PMU) data, where available, and supervisory control and data acquisition (SCADA) data. The tool is also capable of automatically generating NERC Frequency Response Survey (FRS) forms required by BAL-003-1 Standard.

  18. Ionospheric very low frequency transmitter

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, Spencer P. [New York University-Polytechnic School of Engineering, 5 Metrotech Center, Brooklyn, New York 11201 (United States)

    2015-02-15

    The theme of this paper is to establish a reliable ionospheric very low frequency (VLF) transmitter, which is also broad band. Two approaches are studied that generate VLF waves in the ionosphere. The first, classic approach employs a ground-based HF heater to directly modulate the high latitude ionospheric, or auroral electrojet. In the classic approach, the intensity-modulated HF heater induces an alternating current in the electrojet, which serves as a virtual antenna to transmit VLF waves. The spatial and temporal variations of the electrojet impact the reliability of the classic approach. The second, beat-wave approach also employs a ground-based HF heater; however, in this approach, the heater operates in a continuous wave mode at two HF frequencies separated by the desired VLF frequency. Theories for both approaches are formulated, calculations performed with numerical model simulations, and the calculations are compared to experimental results. Theory for the classic approach shows that an HF heater wave, intensity-modulated at VLF, modulates the electron temperature dependent electrical conductivity of the ionospheric electrojet, which, in turn, induces an ac electrojet current. Thus, the electrojet becomes a virtual VLF antenna. The numerical results show that the radiation intensity of the modulated electrojet decreases with an increase in VLF radiation frequency. Theory for the beat wave approach shows that the VLF radiation intensity depends upon the HF heater intensity rather than the electrojet strength, and yet this approach can also modulate the electrojet when present. HF heater experiments were conducted for both the intensity modulated and beat wave approaches. VLF radiations were generated and the experimental results confirm the numerical simulations. Theory and experimental results both show that in the absence of the electrojet, VLF radiation from the F-region is generated via the beat wave approach. Additionally, the beat wave approach

  19. Frequency drift characterisation of directly modulated SGDBR tunable lasers

    OpenAIRE

    Maher, Robert D.; Anandarajah, Prince M.; Kaszubowska-Anandarajah, Aleksandra; Barry, Liam P.

    2007-01-01

    Tunable Lasers (TL) are rapidly becoming key components in Dense Wavelength Division Multiplexed (DWDM) systems, packet switched schemes and access networks. They are being introduced as alternatives to fixed wavelength sources to provide a greater degree of flexibility and to reduce large inventory [1]. The SGDBR laser is an ideal candidate due to its large tuning range (40 nm), high output power (10 dBm), large Side Mode Suppression Ratio (>30 dB) and its ability to be monolithically integr...

  20. Optical Orthogonal Frequency Division Systems with Direct Detection Receivers

    OpenAIRE

    Pérez Rosas, Juan Miguel

    2013-01-01

    Estudio y optimización de parámetros en sistemas de transmisión por fibra óptica usando modulación OFDM y detección directa. [ANGLÈS] The new generation of Pasive Optical Networks (PONs) to cover the last-mile to the user, is today a hot topic of research. Stringent performance requirements are both capacity and reach; these, together with reduced cost lead to consideration of a new paradigm. In this context, Optical OFDM (O-OFDM) is regarded as a promising candidate. From the many archite...

  1. Direct Taxation - Directions of Harmonization

    OpenAIRE

    Narcis Eduard MITU

    2008-01-01

    Most often, harmonization in the fiscal field concerned indirect taxation, and was aimed at assuring that national tax system do not interfere with the freedom of movement of goods, services, persons and capitals. There is no need to harmonize most part of direct taxation rules, as they are strictly enforceable the EU member states and they are thus an attribute of these states sovereignty. In the field of direct taxation, the community acquis mainly concerns the profit (company) tax and the ...

  2. Directed Replacement

    CERN Document Server

    Karttunen, L

    1996-01-01

    This paper introduces to the finite-state calculus a family of directed replace operators. In contrast to the simple replace expression, UPPER -> LOWER, defined in Karttunen (ACL-95), the new directed version, UPPER @-> LOWER, yields an unambiguous transducer if the lower language consists of a single string. It transduces the input string from left to right, making only the longest possible replacement at each point. A new type of replacement expression, UPPER @-> PREFIX ... SUFFIX, yields a transducer that inserts text around strings that are instances of UPPER. The symbol ... denotes the matching part of the input which itself remains unchanged. PREFIX and SUFFIX are regular expressions describing the insertions. Expressions of the type UPPER @-> PREFIX ... SUFFIX may be used to compose a deterministic parser for a ``local grammar'' in the sense of Gross (1989). Other useful applications of directed replacement include tokenization and filtering of text streams.

  3. A Novel Tunable Dual-frequency Laser with Large Frequency Difference

    Institute of Scientific and Technical Information of China (English)

    黄春宁; 郭辉; 李岩; 朱钧; 张书练

    2002-01-01

    This paper proposed a novel tunable dual frequency laser with large frequency difference,which used LD to pump the Nd∶YAG microchip in the end surface and put the liquid pressure on the radial direction of the crystal by a pressure-transporting thin film. As a result of the stress birefringence, there was a mode splitting phenomenon of the microchip laser longitudinal mode. Both theoretical analysis and experiments indicated that there is a directly proportional relation between the frequency difference and the pressure, so the tunable frequency difference could be obtained when the pressure was changed. A large frequency difference of about 3.4 GHz with linear tunable relation was achieved in the experiment,so it can be a practical light source for the absolute distance interferometry.

  4. Single frequency intracavity SRO

    DEFF Research Database (Denmark)

    Abitan, Haim; Buchhave, Preben

    2000-01-01

    Summary form only given. A single resonance optical parametric oscillator (SRO) is inserted intracavity to a CW high power, single frequency, and ring Nd:YVO4 laser. We obtain a stable single frequency CW SRO with output at 1.7-1.9 μm (idler) and a resonating signal at 2.3-2.6 μm. The behavior of...

  5. Frequency selective lens antenna

    OpenAIRE

    Thornton, J.; Haines, P.

    2007-01-01

    A variant of the hemispherical microwave lens antenna is reported where the ground plane region is modified through use of a frequency selective surface. This allows discrimination of frequencies by two closely spaced primary feeds. A scale model is reported operating at 12 and 30 GHz.

  6. Exploiting polarization using multi-frequency SAR data and multi-dimensional time-frequency techniques

    International Nuclear Information System (INIS)

    During recent years, Time-Frequency (TF) techniques have been introduced to characterize scene polarimetric behaviours using PolSAR data. In this paper, we apply a TF decomposition approach to the analysis of PolSAR data with different frequency bands and show some polarimetric TF behaviours of various scenes. The PolSAR data may be decomposed in azimuth direction, range direction only and in both directions. Two statistical descriptor, i.e., polarimetric TF stationarity and coherence indicators, are used to depict the features of the scene backscattering response. Their individual performance is assessed. The polarimetric TF features, extracted from the scenes of interest, can show some special relevant information compared to the original full resolution case. Moreover, with the availability of new multi-frequency full-polarization high resolution F-SAR data, the results of same site with respect to different frequency bands are exploited and compared with each other

  7. Microfabricated ion frequency standard

    Science.gov (United States)

    Schwindt, Peter; Biedermann, Grant; Blain, Matthew G.; Stick, Daniel L.; Serkland, Darwin K.; Olsson, III, Roy H.

    2010-12-28

    A microfabricated ion frequency standard (i.e. an ion clock) is disclosed with a permanently-sealed vacuum package containing a source of ytterbium (Yb) ions and an octupole ion trap. The source of Yb ions is a micro-hotplate which generates Yb atoms which are then ionized by a ultraviolet light-emitting diode or a field-emission electron source. The octupole ion trap, which confines the Yb ions, is formed from suspended electrodes on a number of stacked-up substrates. A microwave source excites a ground-state transition frequency of the Yb ions, with a frequency-doubled vertical-external-cavity laser (VECSEL) then exciting the Yb ions up to an excited state to produce fluorescent light which is used to tune the microwave source to the ground-state transition frequency, with the microwave source providing a precise frequency output for the ion clock.

  8. Investigation on porous frequency of regenerator of microminiature thermoacoustic refrigerator

    Institute of Scientific and Technical Information of China (English)

    LIU Yi-cai; ZHOU Jie-min; ZHOU Nai-jun; LIAO Sheng-ming

    2005-01-01

    A new method was proposed to directly measure the effective resistance and distinguish the porous frequency in the regenerator of the microminiature thermoacoustic refrigerator. Measured results were compared with the flux gain factor and transmission loss of the real system. The results show that the agreement between the range of the porous frequency and frequency of the system is good, the method can be used to predict the porous frequency of the regenerator in production.

  9. ISM band to U-NII band frequency transverter and method of frequency transversion

    Science.gov (United States)

    Stepp, Jeffrey David; Hensley, Dale

    2006-09-12

    A frequency transverter (10) and method for enabling bi-frequency dual-directional transfer of digitally encoded data on an RF carrier by translating between a crowded or otherwise undesirable first frequency band, such as the 2.4 GHz ISM band, and a less-crowded or otherwise desirable second frequency band, such as the 5.0 GHz 6.0 GHz U-NII band. In a preferred embodiment, the transverter (10) connects between an existing data radio (11) and its existing antenna (30), and comprises a bandswitch (12); an input RF isolating device (14); a transmuter (16); a converter (18); a dual output local oscillator (20); an output RF isolating device (22); and an antenna (24) tuned to the second frequency band. The bandswitch (12) allows for bypassing the transverter (10), thereby facilitating its use with legacy systems. The transmuter (14) and converter (16) are adapted to convert to and from, respectively, the second frequency band.

  10. Efficient 2(nd) and 4(th) harmonic generation of a single-frequency, continuous-wave fiber amplifier.

    Science.gov (United States)

    Sudmeyer, Thomas; Imai, Yutaka; Masuda, Hisashi; Eguchi, Naoya; Saito, Masaki; Kubota, Shigeo

    2008-02-01

    We demonstrate efficient cavity-enhanced second and fourth harmonic generation of an air-cooled, continuous-wave (cw), single-frequency 1064 nm fiber-amplifier system. The second harmonic generator achieves up to 88% total external conversion efficiency, generating more than 20-W power at 532 nm wavelength in a diffraction-limited beam (M(2) crystal operated at 25 degrees C. The fourth harmonic generator is based on an AR-coated, Czochralski-grown beta-BaB(2)O(4) (BBO) crystal optimized for low loss and high damage threshold. Up to 12.2 W of 266-nm deep-UV (DUV) output is obtained using a 6-mm long critically phase-matched BBO operated at 40 degrees C. This power level is more than two times higher than previously reported for cw 266-nm generation. The total external conversion efficiency from the fundamental at 1064 nm to the fourth harmonic at 266 nm is >50%. PMID:18542230

  11. Coupled Resonance Laser Frequency Stabilization

    Science.gov (United States)

    Burd, Shaun; Uys, Hermann; MAQClab Team

    2013-05-01

    We have demonstrated simultaneous laser frequency stabilization of a UV and IR laser, to the same photodiode signal derived from the UV laser only. For trapping and cooling Yb+ ions, a frequency stabilized laser is required at 369.9 nm to drive the S1/2-P1/2 cooling cycle. Since that cycle is not closed, a repump beam is needed at 935.18 nm to drive the D3/2-D[ 3 / 2 ] transition, which rapidly decays back to the S1/2 state. Our 369 nm laser is locked using Doppler free polarization spectroscopy of Yb+ ions, generated in a hollow cathode discharge lamp. Without pumping, the metastable D3/2 level is only sparsely populated, making direct absorption of 935 nm light difficult to detect. A resonant 369 nm pump laser can populate the D3/2 state, and fast repumping to the S1/2 ground state by on resonant 935 nm light, can be detected via the change in absorption of the 369 nm laser. This is accomplished using lock-in detection on the same photodiode signal to which the 369 nm laser is locked. In this way, simultaneous locking of two frequencies in very different spectral regimes is accomplished, while exploiting only the photodiode signal from one of the lasers. A rate equation model gives good qualitative agreement with experimental observation. This work was partially funded by the South African National Research Foundation.

  12. Digital Radio Frequency Memories

    Science.gov (United States)

    Hey-Shipton, Gregory L.

    The Digital RF Memory (DRFM) is gradually replacing the recirculating Frequency Memory Loop (FML). The shortcomings of the FML in the area of limited storage time, single signal processing, and limited ECM capabilities are overcome by the use of the DRFM. There are several architectures for the DRFM but all of them accomplish the same basic function: to convert an incoming RF signal to a low enough frequency to allow storage in a digital memory and subsequent upconversion to the original signal frequency. Multiple signal handling capabilities on a pulse by pulse basis and software controlled ECM generation make the DRFM a powerful addition to any ECM suite.

  13. Broadband frequency conversion

    DEFF Research Database (Denmark)

    Sanders, Nicolai; Jensen, Ole Bjarlin; Tidemand-Lichtenberg, Peter;

    We present a simple, passive and static setup for broadband frequency conversion. By using simple optical components like lenses, mirrors and gratings, we obtain the spectral angular dispersion to match the second harmonic generation phasematching angles in a nonlinear BiBO crystal. We are able to...... frequency double a single-frequency diode laser, tunable in the 1020-1090 nm range, with almost equal efficiency for all wavelengths. In the experimental setup, the width of the phasematch was increased with a factor of 50. The method can easily be extended to other wavelength ranges and nonlinear crystals...

  14. Broadband frequency conversion

    OpenAIRE

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

    2012-01-01

    We demonstrate a method for frequency conversion of broadly tunable or broad bandwidth light in a static, passive setup. Using simple optical components like lenses, mirrors and gratings and a BiBO crystal as the nonlinear material, we are able to frequency double a single-frequency, tunable, external cavity diode laser in the 1020-1090 nm range into the 510-545 nm range with almost equal efficiency for all wavelengths. Phase matching is obtained as follows; a diffraction grating is used to d...

  15. Broadband SHF Direction-Finder

    Directory of Open Access Journals (Sweden)

    S. Radionov

    2008-06-01

    Full Text Available The original design of the compact broadband direction-finder is presented in this paper. The cylindrical monopole antenna serves as a primary source of the reflector- type antenna. "Zero-amplitude" technique is used for bearing the SHF sources. The model experiments with the proposed direction-finder prototype in the frequency band 6 GHz - 11 GHz have been carried out.

  16. Microwave Radiometer - high frequency

    Data.gov (United States)

    Oak Ridge National Laboratory — The Microwave Radiometer-High Frequency (MWRHF) provides time-series measurements of brightness temperatures from two channels centered at 90 and 150 GHz. These two...

  17. Lunch frequency among adolescents

    DEFF Research Database (Denmark)

    Pedersen, Trine Pagh; Holstein, Bjørn E; Krølner, Rikke;

    2016-01-01

    OBJECTIVE: To investigate: (i) how lunch frequency of adolescents varies between schools and between classes within schools; (ii) the associations between frequency of lunch and individual sociodemographic factors and school characteristics; and (iii) if any observed associations between lunch...... frequency and school characteristics vary by gender and age groups. DESIGN: Cross-sectional study in which students and school headmasters completed self-administered questionnaires. Associations were estimated by multilevel multivariate logistic regression. SETTING: The Danish arm of the Health Behaviour...... in School-Aged Children study 2010. SUBJECTS: Students (n 4922) aged 11, 13 and 15 years attending a random sample of seventy-three schools. RESULTS: The school-level and class-level variations in low lunch frequency were small (intraclass correlation coefficient <2·1 %). At the individual level, low...

  18. High frequency beam protection

    International Nuclear Information System (INIS)

    This report describes the design and construction of a high-frequency beam protecting device. This apparatus controls a number of functions in a modulator. Furthermore it drives the phase shifter and the attenuator. (author). 6 figs

  19. Variable frequency photonic crystals

    CERN Document Server

    Wu, Xiang-Yao; Liu, Xiao-Jing; Yang, Jing-Hai; Li, Hong; Chen, Wan-Jin

    2015-01-01

    In this paper, we have firstly proposed a new one-dimensional variable frequency photonic crystals (VFPCs), and calculated the transmissivity and the electronic field distribution of VFPCs with and without defect layer, and considered the effect of defect layer and variable frequency function on the transmissivity and the electronic field distribution. We have obtained some new characteristics for the VFPCs, which should be help to design a new type optical devices.

  20. Uncertainty Measures of Regional Flood Frequency Estimators

    DEFF Research Database (Denmark)

    Rosbjerg, Dan; Madsen, Henrik

    1995-01-01

    Regional flood frequency models have different assumptions regarding homogeneity and inter-site independence. Thus, uncertainty measures of T-year event estimators are not directly comparable. However, having chosen a particular method, the reliability of the estimate should always be stated, e...

  1. Cooperative Frequency Control for Autonomous AC Microgrids

    DEFF Research Database (Denmark)

    Shafiee, Qobad; Quintero, Juan Carlos Vasquez; Guerrero, Josep M.; Nasirian, Vahidreza; Davoudi, Ali

    2015-01-01

    Distributed secondary control strategies have been recently studied for frequency regulation in droop-based AC Microgrids. Unlike centralized secondary control, the distributed one might fail to provide frequency synchronization and proportional active power sharing simultaneously, due to having...... different control parameters. This paper introduces a cooperative algorithm that regulates the system frequency while maintaining the power sharing properties of droop control. Dynamic consensus protocol is used to estimate the average of normalized active powers in the entire MG. This estimation is then...... added to primary control, compensating the frequency drop caused by the droop mechanism. The proposed controller is fully distributed, meaning that each source exchange information with only its direct neighbors through a sparse communication network. This controller has a unique feature that it does...

  2. Non-commutative time-frequency tomography

    CERN Document Server

    Man'ko, V I

    1999-01-01

    The characterization of non-stationary signals requires joint time and frequency information. However, time (t) and frequency (omega) being non-commuting variables there cannot be a joint probability density in the (t,omega) plane and the time-frequency distributions, that have been proposed, have difficult interpretation problems arising from negative or complex values and spurious components. As an alternative we propose to obtain time-frequency information by looking at the marginal distributions along rotated directions in the (t,omega) plane. The rigorous probability interpretation of the marginal distributions avoids all interpretation ambiguities. Applications to signal analysis and signal detection are discussed as well as an extension of the method to other pairs of non-commuting variables.

  3. Characteristics of Collision, Capacitive Radio Frequency Sheath

    Institute of Scientific and Technical Information of China (English)

    Zhang Yu; DingWanYu; Wang Wenchun; Liu JinYuan; Wang Xiaogang; Liu Yue

    2005-01-01

    A simple collisional radio frequency (rf) sheath fluid model, which is not restricted by the ratio of rf frequency to ion plasma frequency (β=ωrf/ωpi), was established and solved numerically. In the ion balance equation, the effect of the collision on the ion and the ion velocity is assumed to be a direct ratio to ion velocity. The ion energy distributions (IEDs) calculated in the model in comparison with the experimental data [M. A. Sobolewski, J. K. Olthoff, and Y.C. Wang, J. Appl. Phys. 85, 3966 (1999)], proved the validity of the model. And the effect of the collision on the sheath characteristic was obtained and discussed. This paper demonstrates that the collision frequency is another crucial parameter as well as the ratio β to determine the rf sheath characteristics and the shape of IE Ds.

  4. Orbit Steering and Central Frequency for LEP2 Energy Calibration

    CERN Document Server

    Wenninger, J

    2000-01-01

    "The central frequency is an important parameter of the LEP beam energy model. It is a direct measurementof the LEP circumference and is used to evaluate the contribution of the quadrupoles to field integral relevant forthe LEP beam ebergy. Its evolution over a run is tracked using direct frequency measurementscombined with radial beam position measurements in the LEP arcs.The influence of orbit corrections on the central frequency measurement techniques was evaluatedand a model allowing to correct for changes of corrector settings was developped.The central frequency data for the LEP2 runs between 1996 and 1999 was re-analysed to includecorrections due to the closed orbit steering."

  5. Initiating events frequency determination

    International Nuclear Information System (INIS)

    The paper describes work performed for the Nuclear Power Station (NPS). Work is related to the periodic initiating events frequency update for the Probabilistic Safety Assessment (PSA). Data for all relevant NPS initiating events (IE) were reviewed. The main focus was on events occurring during most recent operating history (i.e., last four years). The final IE frequencies were estimated by incorporating both NPS experience and nuclear industry experience. Each event was categorized according to NPS individual plant examination (IPE) initiating events grouping approach. For the majority of the IE groups, few, or no events have occurred at the NPS. For those IE groups with few or no NPS events, the final estimate was made by means of a Bayesian update with general nuclear industry values. Exceptions are rare loss-of-coolant-accidents (LOCA) events, where evaluation of engineering aspects is used in order to determine frequency.(author)

  6. High frequency energy measurements

    International Nuclear Information System (INIS)

    High-frequency (> 100 MHz) energy measurements present special problems to the experimenter. Environment or available electronics often limit the applicability of a given detector type. The physical properties of many detectors are frequency dependent and in some cases, the physical effect employed can be frequency dependent. State-of-the-art measurements generally involve a detection scheme in association with high-speed electronics and a method of data recording. Events can be single or repetitive shot requiring real time, sampling, or digitizing data recording. Potential modification of the pulse by the detector and the associated electronics should not be overlooked. This presentation will review typical applications, methods of choosing a detector, and high-speed detectors. Special considerations and limitations of some applications and devices will be described

  7. Observation of upper drift modes in radio frequency produced magnetized plasmas with frequency above ion cyclotron frequency

    International Nuclear Information System (INIS)

    In a RF produced magnetized argon plasma expanding into a larger expansion chamber, electrostatic modes propagating azimuthally in the direction of the electron diamagnetic drift and frequency greater than the ion cyclotron frequency are observed. In the radial direction, the mode amplitude peaks at a location where the radial density gradient is maximum. The modes are detected at axial locations up to 16 cm away from the entrance aperture. For fixed values of the neutral pressure and magnetic field, the mode frequency is found to be independent of the location at which it is measured. The modes exhibit drift wave characteristics revealing a radial structure with the azimuthal mode number m = 1 at the lower radial locations (r ∼ 3.0 cm) while the m = 2 mode is located in the outer region. Theoretical modeling using a local dispersion relation based on the fluid equations predicts destabilization of the modes with frequency greater than the ion-cyclotron frequency by electron-neutral collisions and exhibiting other drift wave features

  8. Modulation Frequency Optimization in Two-Colar Instruments

    Institute of Scientific and Technical Information of China (English)

    赵茂泰; 甘良才

    2003-01-01

    How to choose modulation frequency in the extra-high frequency geodimeter is directly related to a lot key matters such as distance sensitivity of instruments and degree of technological difficulty of modulation system. This paper analyzes and proves that choice range of modulation frequency can be from 800 MHz up to extra-high frequency with the basically same distance sensitivity. Therefore, in the developing of geodimeter, we can choose the modulation frequency in wide range according to practical situation. This is very convenient and useful in practice.

  9. Directional spread parameter at intermediate water depth

    Digital Repository Service at National Institute of Oceanography (India)

    SanilKumar, V.; Deo, M.C.; Anand, N.M.; AshokKumar, K.

    distribution of wave energies over various wave frequencies and directions. A number of methods are available to estimate directional spectrum from the measurements made by a moored buoy (Longuet-Higgins et al., 1963; Borgman, 1982; Isobe et al., 1984; Kobune.... These signals pertained to the vertical motion and two horizontal translations, viz., north–south and east–west motions of the buoy. Mitsuyasu et al. (1975) showed that maximum spreading parameter corresponding to the peak frequency of wave spectrum can...

  10. Direct cervicoplasty.

    Science.gov (United States)

    Jordan, J Randall; Yellin, Seth

    2014-08-01

    Rejuvenation of the aging neck is one of the common reasons for the patients presented to facial plastic surgeons. In the author's opinion, most of these patients will be best served by a full rhytidectomy approach with periauricular incisions, skin flap undermining, and platysmaplasty. There is a subset of patients, however, who presented with complaints limited to the so-called Turkey Gobbler deformity, and who do not wish to undergo a full rhytidectomy approach. These patients may be well served by a lesser procedure such as a direct cervicoplasty or submentoplasty. The advantages of this approach include shorter operative time, faster recovery, and lower complication rates. The primary disadvantage of these more limited approaches is that there is an anterior cervical scar that may be visible under some conditions. This article will review the multiple options for skin incisions as well as details of the technique that the authors have found may lead to a successful rejuvenation of the submental region. PMID:25076453

  11. Frequency scanning microstrip antennas

    DEFF Research Database (Denmark)

    Danielsen, Magnus; Jørgensen, Rolf

    1979-01-01

    The principles of using radiating microstrip resonators as elements in a frequency scanning antenna array are described. The resonators are cascade-coupled. This gives a scan of the main lobe due to the phase-shift in the resonator in addition to that created by the transmission line phase...

  12. Bag-of-frequencies

    DEFF Research Database (Denmark)

    Ciompi, Francesco; Jacobs, Colin; Scholten, Ernst Th;

    2015-01-01

    , obtaining a Bag-of-Frequencies, which is used to assign each spectra a label. The descriptor is obtained as the histogram of labels along all the spheres. Additional contributions are a technique to estimate the nodule size, based on the sampling strategy, as well as a technique to choose the most...

  13. High frequency electromagnetic dosimetry

    CERN Document Server

    Sánchez-Hernández, David A

    2009-01-01

    Along with the growth of RF and microwave technology applications, there is a mounting concern about the possible adverse effects over human health from electromagnetic radiation. Addressing this issue and putting it into perspective, this groundbreaking resource provides critical details on the latest advances in high frequency electromagnetic dosimetry.

  14. Extremely high frequency RF effects on electronics.

    Energy Technology Data Exchange (ETDEWEB)

    Loubriel, Guillermo Manuel; Vigliano, David; Coleman, Phillip Dale; Williams, Jeffery Thomas; Wouters, Gregg A.; Bacon, Larry Donald; Mar, Alan

    2012-01-01

    The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings.

  15. New families of optimal frequency hopping sequence sets

    OpenAIRE

    Bao, Jingjun; Ji, Lijun

    2015-01-01

    Frequency hopping sequences (FHSs) are employed to mitigate the interferences caused by the hits of frequencies in frequency hopping spread spectrum systems. In this paper, we present some new algebraic and combinatorial constructions for FHS sets, including an algebraic construction via the linear mapping, two direct constructions by using cyclotomic classes and recursive constructions based on cyclic difference matrices. By these constructions, a number of series of new FHS sets are then pr...

  16. FREQUENCY DETERMINATION OF HIGH-FREQUENCY LINK FOR PERCPECTIVE ELECTRIC ROLLING STOCK

    Directory of Open Access Journals (Sweden)

    D. O. Zabarylo

    2014-12-01

    Full Text Available Purpose. Total mileage of Ukrainian electric railways is distributed approximately equally between the areas of direct and alternating current. A double system of electric rolling stock is used to pass jointing places of different current kinds without train’s stop. Therefore introduction of such rolling stock of a new concept that is using an asynchronous traction drive is prospective for Ukrainian railways. Apart from advantages a rolling stock of similar concept has significant disadvantages, it is pulse energy consumption from the power supply, and it can affect the reliability of track automatic devices, and consequently, the train traffic safety. In addition the specific power of traction transformer is considerably inferior to the power density of other traction elements. The promising schemes using an intermediary link of increased frequency, which consist of a transformer and inverter, have been proposed for disadvantages amendments. The main task for the further introduction of prospective circuit is to determine the operating frequency for high frequency link. Methodology. The method of thermal parameters calculation of semiconductor devices has been used for determination switching transistors of maximum operating frequency. To obtain analytical expressions curves of energy, released during the IGBT (insulated-gate bipolar transistor switching from its current load approximation method is used. Findings. The permissible frequency of low-frequency link is determinated by load current of intermediate transformer. Operating frequency range of a link depending on load current has been determined. A comparative analysis of the switching characteristics of 65 class IGBT production by companies Infineon and ABB has been performed. Originality. The further determination method of the maximum operating frequency of intermediate link for circuit with high-frequency transformer has been developed. Practical value. The established operating

  17. PIC Simulations of the Ion Flow Induced by Radio Frequency Waves in Ion Cyclotron Frequency Range

    International Nuclear Information System (INIS)

    Full text: PIC simulations have been conducted to study the nonlinear interactions of plasmas and radio frequency wave in the ion cyclotron frequency range. It is found that in the presence of the mode conversion from an electromagnetic wave into an electrostatic wave (ion Bernstein wave), the ions near the lower hybrid resonance can be heated by nonlinear Landau damping via the parametric decay. As a result, the ion velocity distribution in the poloidal direction becomes asymmetric near the lower hybrid resonance and an ion poloidal flow is thus produced. The flow directions are opposite on both sides of the lower hybrid resonance. The poloidal flow is mainly produced by the nonlinear Reynolds stress and the electromagnetic force of the incident wave in the radial direction rather than poloidal direction predicted by the existing theories. (author)

  18. IQ Imbalance Estimation Scheme in the Presence of DC Offset and Frequency Offset in the Frequency Domain

    Science.gov (United States)

    Inamori, Mamiko; Takayama, Shuzo; Sanada, Yukitoshi

    Direct conversion receivers in orthogonal frequency division multiplexing (OFDM) systems suffer from direct current (DC) offset, frequency offset, and IQ imbalance. We have proposed an IQ imbalance estimation scheme in the presence of DC offset and frequency offset, which uses preamble signals in the time domain. In this scheme, the DC offset is eliminated by a differential filter. However, the accuracy of IQ imbalance estimation is deteriorated when the frequency offset is small. To overcome this problem, a new IQ imbalance estimation scheme in the frequency domain with the differential filter has been proposed in this paper. The IQ imbalance is estimated with pilot subcarriers. Numerical results obtained through computer simulation show that estimation accuracy and bit error rate (BER) performance can be improved even if the frequency offset is small.

  19. Recursive Time-Frequency Reassignment

    OpenAIRE

    Nilsen, Geir Kjetil

    2008-01-01

    A fast algorithm for producing time-frequency representations (TFRs) is proposed. The resulting TFRs have optional time-frequency resolution up to optimality. The algorithm is further extended with a method known as time-frequency reassignment. The main implication is that time-frequency reassignment now becomes well suited for real-time implementations.

  20. Frequency selective bolometers

    DEFF Research Database (Denmark)

    Kowitt, M.S.; Fixsen, D.J.; Goldin, A.;

    1996-01-01

    We propose a concept for radiometry in the millimeter, the submillimeter, and the far-IR spectral regions, the frequency selective bolometer (FSB). This system uses a bolometer as a coupled element of a tuned quasi-optical interference filter in which the absorption, the transmission, and the ref...... plane. An FSB system can be configured as a multiband, close-packed focal-plane array, permitting efficient use of the throughput of a telescope....

  1. Resonance frequency analysis

    OpenAIRE

    Rajiv K Gupta; Thallam V Padmanabhan

    2011-01-01

    Initial stability at the placement and development of osseointegration are two major issues for implant survival. Implant stability is a mechanical phenomenon which is related to the local bone quality and quantity, type of implant, and placement technique used. The application of a simple, clinically applicable, non-invasive test to assess implant stability and osseointegration is considered highly desirable. Resonance frequency analysis (RFA) is one of such techniques which is most frequent...

  2. Radio frequency ion source

    CERN Document Server

    Shen Guan Ren; Gao Fu; LiuNaiYi

    2001-01-01

    The study on Radio Frequency Ion Source is mainly introduced, which is used for CIAE 600kV ns Pulse Neutron Generator; and obtained result is also presented. The RF ion source consists of a diameter phi 25 mm, length 200 mm, coefficient of expansion =3.5 mA, beam current on target >=1.5 mA, beam spot =100 h.

  3. Increasing ferromagnetic resonance frequency using lamination and shape

    Science.gov (United States)

    El-Ghazaly, A.; White, R. M.; Wang, S. X.

    2015-05-01

    The magnetic permeability frequency spectrum is one of the most critical properties for the operation of high frequency magnetic devices in the gigahertz regime. Permeability is fairly constant up to the ferromagnetic resonance (FMR) frequency, at which point the relative permeability drops to unity. Extending FMR to higher frequencies is thus imperative for developing GHz-range magnetic devices. The simulation and experimental investigations presented in this paper demonstrate how stacking layers to form a laminated film increases the FMR frequency by allowing flux closure between layers along the induced easy-axis direction. This flux closure reduces the demagnetization factor along the easy-axis direction by two orders of magnitude. This effect, however, is only observable in patterned films where the shape anisotropy is enough to result in variation of the FMR frequency. Experiments using patterned magnetic cores were performed to illustrate this effect. Through detailed investigation of the permeability spectra of both single layer and laminated CoTaZr magnetic films patterned into 500 μm × L films (where L ranged from 200 μm to 1000 μm), the FMR frequency was extracted and proven to increase as a result of lamination. The degree to which the frequency is boosted by lamination increases exponentially as the length of the film is decreased. Through a combination of lamination and shape demagnetization, the effective anisotropy, which directly relates to FMR frequency, was shown to increase by about 100%.

  4. Rapid frequency scan EPR.

    Science.gov (United States)

    Tseitlin, Mark; Rinard, George A; Quine, Richard W; Eaton, Sandra S; Eaton, Gareth R

    2011-08-01

    In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x, y plane decays to baseline at the end of the scan, which typically is about 5T(2) after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5T(2). However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5T(2), even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B(1), periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation. PMID:21664848

  5. Orthogonal Frequency Division Multiplexing System with Frequency Offset Estimation

    Directory of Open Access Journals (Sweden)

    Meghashree D.Nimje

    2013-03-01

    Full Text Available Orthogonal Frequency Division Multiplexing (OFDM system, use a large number of parallel narrowband subcarriers instead of a single wide-band carrier to transport information. Orthogonal frequency division multiplexing is the modulation technique use in digital communication systems . Carrier frequency offset occurs due to Doppler effect or noise. Carrier frequency offsets (CFOs is the Offset between the transmitter and the receiver oscillators .CFO damages the orthogonality of the carries ,resulting in degradation of the systems performance. Carrier frequency offset estimation method is discussed in this paper. In this paper one complex training sequence use, which can effectively estimate carrier frequency offset in the time domain and frequency domain. Here fine and coarse frequency is estimated to improve the improve the system performance. This paper shows the estimation range for frequency offset can be improve to large extent..

  6. Frequency noise characterisation of narrow linewidth diode lasers

    Science.gov (United States)

    Turner, L. D.; Weber, K. P.; Hawthorn, C. J.; Scholten, R. E.

    2002-01-01

    We examine several approaches to laser frequency noise measurement in the frequency and time domains. Commonly employed methods such as optical frequency discrimination and the Allan variance are found to be complex, expensive, time-consuming, or incomplete. We describe a practical method of demodulating a laser beat note to measure a frequency noise spectrum, using a phase-locked loop frequency discriminator based on a single low-cost integrated circuit. This method measures the frequency noise spectrum of a laser directly and in detail and is insensitive to intensity fluctuations. The advantages of this scheme are demonstrated through measurement of the frequency noise spectrum for two external cavity diode lasers (ECDL), clearly distinguishing several common noise sources. These are isolated and removed, reducing the individual laser rms linewidth from 2 MHz to 450 kHz. The spectrum is used to calculate the Allan variance, which shows almost none of the important information.

  7. A non-commutative time-frequency tomography

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The characterization of non-stationary signal requires joint time and frequency information. However, time and frequency are a pair of non-commuting variables that cannot constitute a joint probability density in the time-frequency plane. The time-frequency distributions have difficult interpretation problems arising from negative and complex values or spurious components. In this paper, we get time-frequency information from the marginal distributions in rotated directions in the time-frequency plane. The rigorous probability interpretation of the marginal distributions is without any ambiguities. This time-frequency transformation is similar to the computerized axial tomography (CT or CAT) and is applied to signal analysis and signal detection and reveals a lot of advantages especially in the signal detection of the low signal/noise (S/N).

  8. Directional synthetic aperture flow imaging

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt; Nikolov, Svetoslav

    2004-01-01

    A method for flow estimation using synthetic aperture imaging and focusing along the flow direction is presented. The method can find the correct velocity magnitude for any flow angle and full color flow images can be measured using only 32 to 128 pulse emissions. The approach uses spherical wave...... emissions using a number of defocused elements and a linear frequency modulated pulse (chirp) to improve the signal-to-noise ratio. The received signals are dynamically focused along the flow direction and these signals are used in a cross-correlation estimator for finding the velocity magnitude. The flow...

  9. Quantifying Discipline Practices Using Absolute vs. Relative Frequencies: Clinical and Research Implications for Child Welfare

    OpenAIRE

    Lindhiem, Oliver; Shaffer, Anne; Kolko, David J.

    2013-01-01

    In the parent intervention outcome literatures, discipline practices are generally quantified as absolute frequencies or, less commonly, as relative frequencies. These differences in methodology warrant direct comparison as they have critical implications for study results and conclusions among treatments targeted at reducing parental aggression and harsh discipline. In this study, we directly compared the absolute frequency method and the relative frequency method for quantifying physically ...

  10. Revealing Carrier-Envelope Phase through Frequency Mixing and Interference in Frequency Resolved Optical Gating

    CERN Document Server

    Snedden, Edward W; Jamison, Steven P

    2015-01-01

    We demonstrate that full temporal characterisation of few-cycle electromagnetic pulses, including retrieval of the carrier envelope phase (CEP), can be directly obtained from Frequency Resolved Optical Gating (FROG) techniques in which the interference between non-linear frequency mixing processes is resolved. We derive a framework for this scheme, defined Real Domain-FROG (ReD-FROG), as applied to the cases of interference between sum and difference frequency components and between fundamental and sum/difference frequency components. A successful numerical demonstration of ReD-FROG as applied to the case of a self-referenced measurement is provided. A proof-of-principle experiment is performed in which the CEP of a single-cycle THz pulse is accurately obtained and demonstrates the possibility for THz detection beyond the bandwidth limitations of electro-optic sampling.

  11. Novel Doppler Frequency Extraction Method Based on Time-Frequency Analysis and Morphological Operation

    Institute of Scientific and Technical Information of China (English)

    HOU Shu-juan; WU Si-liang

    2006-01-01

    A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequency extraction becomes curve detection in the image-view. A set of morphological operations are used to implement curve detection. And a map fusion scheme is presented to eliminate the influence of strong direct current (DC) component of echo signal during curve detection. The radar real-life data are used to illustrate the performance of the new approach. Experimental results show that the proposed method can over come the shortcomings of piecewise-processing-based FFT method and can improve the measuring precision of miss distance.

  12. Frequency domain nonlinear optics

    Science.gov (United States)

    Legare, Francois

    2016-05-01

    The universal dilemma of gain narrowing occurring in fs amplifiers prevents ultra-high power lasers from delivering few-cycle pulses. This problem is overcome by a new amplification concept: Frequency domain Optical Parametric Amplification - FOPA. It enables simultaneous up-scaling of peak power and amplified spectral bandwidth and can be performed at any wavelength range of conventional amplification schemes, however, with the capability to amplify single cycles of light. The key idea for amplification of octave-spanning spectra without loss of spectral bandwidth is to amplify the broad spectrum ``slice by slice'' in the frequency domain, i.e. in the Fourier plane of a 4f-setup. The striking advantages of this scheme, are its capability to amplify (more than) one octave of bandwidth without shorting the corresponding pulse duration. This is because ultrabroadband phase matching is not defined by the properties of the nonlinear crystal employed but the number of crystals employed. In the same manner, to increase the output energy one simply has to increase the spectral extension in the Fourier plane and to add one more crystal. Thus, increasing pulse energy and shortening its duration accompany each other. A proof of principle experiment was carried out at ALLS on the sub-two cycle IR beam line and yielded record breaking performance in the field of few-cycle IR lasers. 100 μJ two-cycle pulses from a hollow core fibre compression setup were amplified to 1.43mJ without distorting spatial or temporal properties. Pulse duration at the input of FOPA and after FOPA remains the same. Recently, we have started upgrading this system to be pumped by 250 mJ to reach 40 mJ two-cycle IR few-cycle pulses and latest results will be presented at the conference. Furthermore, the extension of the concept of FOPA to other nonlinear optical processes will be discussed. Frequency domain nonlinear optics.

  13. Resonance frequency analysis

    Directory of Open Access Journals (Sweden)

    Rajiv K Gupta

    2011-01-01

    Full Text Available Initial stability at the placement and development of osseointegration are two major issues for implant survival. Implant stability is a mechanical phenomenon which is related to the local bone quality and quantity, type of implant, and placement technique used. The application of a simple, clinically applicable, non-invasive test to assess implant stability and osseointegration is considered highly desirable. Resonance frequency analysis (RFA is one of such techniques which is most frequently used now days. The aim of this paper was to review and analyze critically the current available literature in the field of RFA, and to also discuss based on scientific evidence, the prognostic value of RFA to detect implants at risk of failure. A search was made using the PubMed database to find all the literature published on "Resonance frequency analysis for implant stability" till date. Articles discussed in vivo or in vitro studies comparing RFA with other methods of implant stability measurement and articles discussing its reliability were thoroughly reviewed and discussed. A limited number of clinical reports were found. Various studies have demonstrated the feasibility and predictability of the technique. However, most of these articles are based on retrospective data or uncontrolled cases. Randomized, prospective, parallel-armed longitudinal human trials are based on short-term results and long-term follow up are still scarce in this field. Nonetheless, from available literature, it may be concluded that RFA technique evaluates implant stability as a function of stiffness of the implant bone interface and is influenced by factors such as bone type, exposed implant height above the alveolar crest. Resonance frequency analysis could serve as a non-invasive diagnostic tool for detecting the implant stability of dental implants during the healing stages and in subsequent routine follow up care after treatment. Future studies, preferably randomized

  14. Rapid Frequency Scan EPR

    OpenAIRE

    Tseitlin, Mark; Rinard, George A.; Quine, Richard W.; Eaton, Sandra S.; Eaton, Gareth R.

    2011-01-01

    In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x,y plane decays to baseline at the end of the scan, which typically is about 5 T2 after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5 T2. However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded...

  15. Microwave Frequency Polarizers

    Science.gov (United States)

    Ha, Vien The; Mirel, Paul; Kogut, Alan J.

    2013-01-01

    This article describes the fabrication and analysis of microwave frequency polarizing grids. The grids are designed to measure polarization from the cosmic microwave background. It is effective in the range of 500 to 1500 micron wavelength. It is cryogenic compatible and highly robust to high load impacts. Each grid is fabricated using an array of different assembly processes which vary in the types of tension mechanisms to the shape and size of the grids. We provide a comprehensive study on the analysis of the grids' wire heights, diameters, and spacing.

  16. High-frequency ventilation.

    Science.gov (United States)

    Crawford, M R

    1986-08-01

    Over the last six years high-frequency ventilation has been extensively evaluated both in the clinical and laboratory settings. It is now no longer the great mystery it once was, and it is now no longer believed (as many had hoped), that it will solve all the problems associated with mechanical pulmonary ventilation. Although the technique is safe and appears to cause no harm even in the long term, it has not yet been shown to offer any major advantages over conventional mechanical ventilation. PMID:3530042

  17. RADIO FREQUENCY ATTENUATOR

    Science.gov (United States)

    Giordano, S.

    1963-11-12

    A high peak power level r-f attenuator that is readily and easily insertable along a coaxial cable having an inner conductor and an outer annular conductor without breaking the ends thereof is presented. Spaced first and second flares in the outer conductor face each other with a slidable cylindrical outer conductor portion therebetween. Dielectric means, such as water, contact the cable between the flares to attenuate the radio-frequency energy received thereby. The cylindrical outer conductor portion is slidable to adjust the voltage standing wave ratio to a low level, and one of the flares is slidable to adjust the attenuation level. An integral dielectric container is also provided. (AFC)

  18. Optimized SQUID sensors for low frequency measurements

    International Nuclear Information System (INIS)

    We have fabricated and measured optimized SQUID sensors (superconducting quantum interference device) for low frequency measurements of magnetic field. We have also investigated the dependence of flux trapping field on the position of Josephson junctions with respect to the Ketchen-type washer. The sensors are measured using direct room temperature readout utilizing noise cancellation techniques based on negative and positive feedback. A superconducting magnesium diboride can is used to shield the sample in pulse-tube cryocooler measurements.

  19. Spurious in PLL-DDS frequency synthesizers

    Czech Academy of Sciences Publication Activity Database

    Kroupa, Věnceslav František; Štursa, Jarmil

    2002-01-01

    Roč. 2, č. 1 (2002), s. 48-51. ISSN 1335-8243. [Digital Signal Processing and Multimedia Communications DSP-MCOM 2001 /5./. Košice, 27.11.2001-29.11.2001] R&D Projects: GA ČR GA102/00/0958 Institutional research plan: CEZ:AV0Z2067918 Keywords : frequency synthesizers * phase locked loops * direct digital synthesis Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  20. Frequencies of inaudible high-frequency sounds differentially affect brain activity: positive and negative hypersonic effects.

    Directory of Open Access Journals (Sweden)

    Ariko Fukushima

    Full Text Available The hypersonic effect is a phenomenon in which sounds containing significant quantities of non-stationary high-frequency components (HFCs above the human audible range (max. 20 kHz activate the midbrain and diencephalon and evoke various physiological, psychological and behavioral responses. Yet important issues remain unverified, especially the relationship existing between the frequency of HFCs and the emergence of the hypersonic effect. In this study, to investigate the relationship between the hypersonic effect and HFC frequencies, we divided an HFC (above 16 kHz of recorded gamelan music into 12 band components and applied them to subjects along with an audible component (below 16 kHz to observe changes in the alpha2 frequency component (10-13 Hz of spontaneous EEGs measured from centro-parieto-occipital regions (Alpha-2 EEG, which we previously reported as an index of the hypersonic effect. Our results showed reciprocal directional changes in Alpha-2 EEGs depending on the frequency of the HFCs presented with audible low-frequency component (LFC. When an HFC above approximately 32 kHz was applied, Alpha-2 EEG increased significantly compared to when only audible sound was applied (positive hypersonic effect, while, when an HFC below approximately 32 kHz was applied, the Alpha-2 EEG decreased (negative hypersonic effect. These findings suggest that the emergence of the hypersonic effect depends on the frequencies of inaudible HFC.

  1. Behavioral estimates of human frequency selectivity at low frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado

    low sound frequencies. As a consequence of our lack of knowledge, we cannot accurately model our perception of complex low-frequency sound (such as that emitted by wind turbines or industrial processes, which can easily produce annoyance) nor make meaningful predictions of our perception based on...... physical sound measurements. In this PhD thesis a detailed description of frequency selectivity at low frequencies is given. Different experiments have been performed to determine the properties of human auditory filters. Besides, loudness perception of low-frequency sinusoidal signals has been evaluated....... In the analysis of results, factors that may influence our perception of low-frequency sound have been considered. It was found that the relative sharpness of auditory filters is poor at low frequencies. However, their bandwidth decreases with decreasing frequency down to about 80 Hz. Below this, a...

  2. RESEARCH OF BJMOSFET FREQUENCY CHARACTERISTICS

    Institute of Scientific and Technical Information of China (English)

    Zeng Yun; Yang Hongguan; Shang Yuquan; Li Xiaolei; Zhang Yan; Wu Yonghui

    2006-01-01

    The parasitic capacitance effect and its influence to the performance have been investigated in Bipolar Junction Metal-Oxide-Semiconductor Field-Effect Transistor (BJMOSFET). The frequency characteristic equivalent circuit and high frequency response model of BJMOSFET have been presented. The frequency characteristic of BJMOSFET is simulated using the multi-transient analytical method and PSPICE9 simulator.The conclusions that BJMOSFET owns less total capacitance, wider frequency band, better transient characteristic and better frequency responses are reached by comparing with the traditional MOSFET at the same structure parameters and bias conditions. BJMOSFET, as a novel promising high frequency device, would be desired to find application in future integrated circuit.

  3. Precision frequency measurement of visible intercombination lines of strontium

    OpenAIRE

    Ferrari, G; Cancio, P.; R. DRULLINGER; Giusfredi, G.; Poli, N.; Prevedelli, M.; Toninelli, C.; Tino, G. M.

    2003-01-01

    We report the direct frequency measurement of the visible 5s$^2$ $^1$S$_0$-5s 5p$^3$P$_1$ intercombination line of strontium that is considered a possible candidate for a future optical frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb-generator referenced to the SI second through a GPS signal. The $^{88}$Sr transition is measured to be at 434 829 121 311 (10) kHz. W...

  4. Infrared frequency-tunable coherent thermal sources

    Science.gov (United States)

    Wang, Hao; Yang, Yue; Wang, Liping

    2015-04-01

    In this work, we numerically demonstrate an infrared (IR) frequency-tunable selective thermal emitter made of graphene-covered silicon carbide (SiC) gratings. Rigorous coupled-wave analysis shows temporally-coherent emission peaks associated with magnetic polariton (MP), whose resonance frequency can be dynamically tuned within the phonon absorption band of SiC by varying graphene chemical potential. An analytical inductor-capacitor circuit model is introduced to quantitatively predict the resonance frequency and further elucidate the mechanism for the tunable emission peak. The effects of grating geometric parameters, such as grating height, groove width and grating period, on the selective emission peak are explored. The direction-independent behavior of MP and associated coherent emission are also demonstrated. Moreover, by depositing four layers of graphene sheets onto the SiC gratings, a large tunability of 8.5% in peak frequency can be obtained to yield the coherent emission covering a broad frequency range from 820 to 890 cm-1. The novel tunable metamaterial could pave the way to a new class of tunable thermal sources in the IR region.

  5. Reconfigurable ring filter with controllable frequency response.

    Science.gov (United States)

    Ab Wahab, Norfishah; Mohd Salleh, Mohd Khairul; Ismail Khan, Zuhani; Abd Rashid, Nur Emileen

    2014-01-01

    Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical length of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to determine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter design using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the center frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip technology, simulated, and measured to validate the proposed concept. The reconfigured filter using lumped elements is successfully reconfigured from 2 GHz to 984.4 MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured frequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10 GHz to 1.38 GHz spreading over 280 MHz frequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity. PMID:25121132

  6. High-frequency ECG

    Science.gov (United States)

    Tragardh, Elin; Schlegel, Todd T.

    2006-01-01

    The standard ECG is by convention limited to 0.05-150 Hz, but higher frequencies are also present in the ECG signal. With high-resolution technology, it is possible to record and analyze these higher frequencies. The highest amplitudes of the high-frequency components are found within the QRS complex. In past years, the term "high frequency", "high fidelity", and "wideband electrocardiography" have been used by several investigators to refer to the process of recording ECGs with an extended bandwidth of up to 1000 Hz. Several investigators have tried to analyze HF-QRS with the hope that additional features seen in the QRS complex would provide information enhancing the diagnostic value of the ECG. The development of computerized ECG-recording devices that made it possible to record ECG signals with high resolution in both time and amplitude, as well as better possibilities to store and process the signals digitally, offered new methods for analysis. Different techniques to extract the HF-QRS have been described. Several bandwidths and filter types have been applied for the extraction as well as different signal-averaging techniques for noise reduction. There is no standard method for acquiring and quantifying HF-QRS. The physiological mechanisms underlying HF-QRS are still not fully understood. One theory is that HF-QRS are related to the conduction velocity and the fragmentation of the depolarization wave in the myocardium. In a three-dimensional model of the ventricles with a fractal conduction system it was shown that high numbers of splitting branches are associated with HF-QRS. In this experiment, it was also shown that the changes seen in HF-QRS in patients with myocardial ischemia might be due to the slowing of the conduction velocity in the region of ischemia. This mechanism has been tested by Watanabe et al by infusing sodium channel blockers into the left anterior descending artery in dogs. In their study, 60 unipolar ECGs were recorded from the entire

  7. Time- vs. frequency-domain femtosecond surface sum frequency generation

    NARCIS (Netherlands)

    Roke, S.; Kleyn, A. W.; Bonn, M.

    2003-01-01

    We present an experimental and theoretical investigation into time- vs. frequency-domain ferntosecond sum frequency spectroscopy at the metal-liquid interface. Although frequency and time-domain measurements are theoretically equivalent it is demonstrated here experimentally that the two approaches

  8. Self-phase-locked frequency-by-two divider OPO with a residual fractional frequency instability of 8.1O(-18)

    OpenAIRE

    P. Gross; Klein, M.E.; Boller, K. -J.

    2004-01-01

    We directly measure the phase difference between the subharmonic waves of a self-phase-locked frequency by-2-divider OPO using a phase-sensitive detector scheme. The relative frequency instability of frequency division by 2 is measured to be 8.10(-18)

  9. Frequency modulation in nuclear magnetometer

    International Nuclear Information System (INIS)

    A version of the frequency-modulation magnetometer based on a particular design of the field-modulation nuclear magnetometer is proposed. Disadvantages of field modulation and advantages of frequency modulation are pointed out

  10. Frequency control : Pay for performance

    OpenAIRE

    Dahlborg, Elin

    2015-01-01

    The frequency control in the Nordic grid is to a large extent delivered by hydropower plants. The hydropower plants deliver frequency control of varying quality, meaning that a remuneration method based on more than just the static gain of the power plant is called for. This thesis has examined how three remuneration methods based on the hydropower plant output and the grid frequency deviation affects the grid stability. Using frequency data, the remunerated work along with the bandwidth and...

  11. Frequency mixer having ferromagnetic film

    Energy Technology Data Exchange (ETDEWEB)

    Khitun, Alexander; Roshchin, Igor V.; Galatsis, Kosmas; Bao, Mingqiang; Wang, Kang L.

    2016-03-29

    A frequency conversion device, which may include a radiofrequency (RF) mixer device, includes a substrate and a ferromagnetic film disposed over a surface of the substrate. An insulator is disposed over the ferromagnetic film and at least one microstrip antenna is disposed over the insulator. The ferromagnetic film provides a non-linear response to the frequency conversion device. The frequency conversion device may be used for signal mixing and amplification. The frequency conversion device may also be used in data encryption applications.

  12. Robust power system frequency control

    CERN Document Server

    Bevrani, Hassan

    2014-01-01

    This updated edition of the industry standard reference on power system frequency control provides practical, systematic and flexible algorithms for regulating load frequency, offering new solutions to the technical challenges introduced by the escalating role of distributed generation and renewable energy sources in smart electric grids. The author emphasizes the physical constraints and practical engineering issues related to frequency in a deregulated environment, while fostering a conceptual understanding of frequency regulation and robust control techniques. The resulting control strategi

  13. Time and frequency domain characteristics of detrending-operation-based scaling analysis: Exact DFA and DMA frequency responses

    Science.gov (United States)

    Kiyono, Ken; Tsujimoto, Yutaka

    2016-07-01

    We develop a general framework to study the time and frequency domain characteristics of detrending-operation-based scaling analysis methods, such as detrended fluctuation analysis (DFA) and detrending moving average (DMA) analysis. In this framework, using either the time or frequency domain approach, the frequency responses of detrending operations are calculated analytically. Although the frequency domain approach based on conventional linear analysis techniques is only applicable to linear detrending operations, the time domain approach presented here is applicable to both linear and nonlinear detrending operations. Furthermore, using the relationship between the time and frequency domain representations of the frequency responses, the frequency domain characteristics of nonlinear detrending operations can be obtained. Based on the calculated frequency responses, it is possible to establish a direct connection between the root-mean-square deviation of the detrending-operation-based scaling analysis and the power spectrum for linear stochastic processes. Here, by applying our methods to DFA and DMA, including higher-order cases, exact frequency responses are calculated. In addition, we analytically investigate the cutoff frequencies of DFA and DMA detrending operations and show that these frequencies are not optimally adjusted to coincide with the corresponding time scale.

  14. Robust power system frequency control

    CERN Document Server

    Bevrani, Hassan

    2008-01-01

    Emphasizes the physical and engineering aspects of the power system frequency control design problem while providing a conceptual understanding of frequency regulation and application of robust control techniques. This book summarizes the author's research outcomes, contributions and experiences with power system frequency regulation.

  15. Low-frequency-noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2008-01-01

    of the complainants are annoyed by a physical sound (20-180 Hz), while others suffer from low-frequency tinnitus (perceived frequency 40-100 Hz). Physical sound at frequencies below 20 Hz (infrasound) is not responsible for the annoyance - or at all audible - in any of the investigated cases, and none...

  16. Frequency of Financial Reports

    OpenAIRE

    Javad Izadi Zadeh Darjezi; Ehsan Khansalar

    2013-01-01

    Interim reports are summary statements that are usually prepared in semi-annual format in the UK. Until the EU’s Transparency Directive was put into practice in the UK in 2007, there was no legal necessity for companies to provide interim financial reports. (Note 1) Instead such preparation was only a regulatory requirement of the London Stock Exchange. The responsibility on companies listed on the London Stock Exchange to provide these financial reports was first prepared as an suggestion in...

  17. Directional dependence of binaural loudness

    DEFF Research Database (Denmark)

    Ellermeier, Wolfgang; Sivonen, Ville Pekka

    2006-01-01

    of experiments determining the effect of sound incidence angle on loudness[1,2,3,4]. The basic experiment to be reported on here was conducted in an anechoic chamber, in which loudspeakers were mounted to present sounds from a number of directions both in the horizontal, and median planes. The...... subject’s task was to produce a loudness match to a frontal reference location, and matches were obtained via a two-interval adaptive forced-choice procedure. Narrow-band noises were used, in order to investigate the frequency-specific effects of direction on loudness. Furthermore, individual HRTFs were...... measured for each incidence angle, in order to relate the changes in actual at-ear exposure to the observed changes in loudness as a function of sound incidence. Combining the listening-test data with the physical measurements, an attempt was made to model the binaural summation underlying the directional...

  18. TOPOLOGY OPTIMIZATION OF TRUSS STRUCTURE WITH FUNDAMENTAL FREQUENCY AND FREQUENCY DOMAIN DYNAMIC RESPONSE CONSTRAINTS

    Institute of Scientific and Technical Information of China (English)

    Pan Jin; Wang De-yu

    2006-01-01

    In this paper, adaptive genetic algorithm (AGA) is applied to topology optimization of truss structure with frequency domain excitations. The optimization constraints include fundamental frequency, displacement responses under force excitations and acceleration responses under foundation acceleration excitations. The roulette wheel selection operator, adaptive crossover and mutation operators are used as genetic operators. Some heuristic strategies are put forward to direct the deletion of the extra bars and nodes on truss structures. Three examples demonstrate that the proposed method can yield the optimum structure form and the lightest weight of the given ground structure while satisfying dynamic response constraints.

  19. A simple model for cavity-enhanced laser-driven ion acceleration from thin foil targets

    CERN Document Server

    Rączka, Piotr

    2012-01-01

    A scenario for the laser-driven ion acceleration off a solid target is considered, where the reflected laser pulse is redirected towards the target by reflection at the inner cavity wall, thus recycling to some extent the incident laser energy. This scenario is discussed in the context of sub-wavelength foil acceleration in the radiation pressure regime, when plasma dynamics is known to be reasonably well described by the laser-sail model. A semi-analytic extension of the 1D laser-sail model is constructed, which takes into account the effect of reflections at the inner cavity wall. The effect of cavity reflections on sub-wavelength foil acceleration is then illustrated with two concrete examples of intense laser pulses of picosecond and femtosecond duration.

  20. New resonant cavity-enhanced absorber structures for mid-infrared detector application

    OpenAIRE

    Zohar, Moshe; Auslender, Mark; Faraone, Lorenzo; Hava, Shlomo

    2012-01-01

    A new dielectric Fabry-Perot cavity was designed for a resonant enhancing optical absorption by a thin absorber layer embedded into the cavity. In this cavity, the front mirror is a subwavelength grating with $\\sim 100$% retroreflection. For a HgCdTe absorber in a matching cavity of the new type, the design is shown to meet the combined challenges of increasing the absorbing efficiency of the entire device up to $\\sim 100$% and reducing its size and overall complexity, compared to a conventio...

  1. Silicon photonic crystal cavity enhanced second-harmonic generation from monolayer WSe2

    CERN Document Server

    Fryett, Taylor K; Zheng, Jiajiu; Liu, Chang-Hua; Xu, Xiaodong; Majumdar, Arka

    2016-01-01

    Nano-resonator integrated with two-dimensional materials (e.g. transition metal dichalcogenides) have recently emerged as a promising nano-optoelectronic platform. Here we demonstrate resonatorenhanced second-harmonic generation (SHG) in tungsten diselenide using a silicon photonic crystal cavity. By pumping the device with the ultrafast laser pulses near the cavity mode at the telecommunication wavelength, we observe a near visible SHG with a narrow linewidth and near unity linear polarization, originated from the coupling of the pump photon to the cavity mode. The observed SHG is enhanced by factor of ~200 compared to a bare monolayer on silicon. Our results imply the efficacy of cavity integrated monolayer materials for nonlinear optics and the potential of building a silicon-compatible second-order nonlinear integrated photonic platform.

  2. Design of Transparent Anodes for Resonant Cavity Enhanced Light Harvesting in Organic Solar Cells

    KAUST Repository

    Sergeant, Nicholas P.

    2012-01-03

    The use of an ITO-free MoO 3/Ag/MoO 3 anode to control the photon harvesting in PCDTBT:PC 70BM solar cells is proposed. At first sight, the fact that these anodes possess reduced far-field transmission compared to ITO may seem to be a disadvantage. But, despite this, we show that by carefully tuning the resonant optical cavity we can enhance the external quantum efficiency close to the band edge of PCDTBT, resulting in high photocurrent and power conversion efficiency on par with ITO. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) – applicability and corrections

    OpenAIRE

    U. Platt; J. Meinen; D. Pöhler; T. Leisner

    2008-01-01

    Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broadband light sources, the broadband CEAS (BB-CEAS). BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light pa...

  4. Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS – applicability and corrections

    Directory of Open Access Journals (Sweden)

    D. Pöhler

    2008-12-01

    Full Text Available Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broad band light sources, the broad-band CEAS (BB-CEAS. BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light path by the trace gas absorption, since cavity losses due to absorption by gases reduce the quality (Q of the cavity. In fact, at wavelength, where the quality of the BB-CEAS cavity is dominated by the trace gas absorption (esp. at very high mirror reflectivity, the light path will vary inversely with the trace gas concentration and the strength of the band will become nearly independent of the trace gas concentration c in the cavity, rendering the CEAS Method useless for trace gas measurements. Only in the limiting case where the mirror reflectivity determines Q at all wavelength, the strength of the band as seen by the BB-CEAS instrument becomes proportional to the concentration c. We investigate these relationships in detail and present methods to correct for the cases between the two above extremes, which are of course the important ones in practice.

  5. PCF-Based Cavity Enhanced Spectroscopic Sensors for Simultaneous Multicomponent Trace Gas Analysis

    Directory of Open Access Journals (Sweden)

    Kamil Stelmaszczyk

    2011-01-01

    Full Text Available A multiwavelength, multicomponent CRDS gas sensor operating on the basis of a compact photonic crystal fibre supercontinuum light source has been constructed. It features a simple design encompassing one radiation source, one cavity and one detection unit (a spectrograph with a fitted ICCD camera that are common for all wavelengths. Multicomponent detection capability of the device is demonstrated by simultaneous measurements of the absorption spectra of molecular oxygen (spin-forbidden b-X branch and water vapor (polyads 4v, 4v + d in ambient atmospheric air. Issues related to multimodal cavity excitation, as well as to obtaining the best signal-to-noise ratio are discussed together with methods for their practical resolution based on operating the cavity in a “quasi continuum” mode and setting long camera gate widths, respectively. A comprehensive review of multiwavelength CRDS techniques is also given.

  6. Tunable cavity-enhanced photon pairs source in Hermite-Gaussian mode

    Science.gov (United States)

    Zhou, Zhi-Yuan; Li, Yan; Ding, Dong-Sheng; Zhang, Wei; Shi, Shuai; Shi, Bao-Sen; Guo, Guang-Can

    2016-02-01

    The spatial modes of light have grasped great research interests because of its great potentials in optical communications, optical manipulation and trapping, optical metrology and quantum information processing. Here we report on generating of photon pairs in Hermite-Gaussian (HG) mode in a type-I optical parametric oscillator operated far below threshold. The bandwidths of the photon pairs are 11.4 MHz and 20.8MHz for two different HG modes respectively, therefore the photons can be stored in cold Rubidium atomic ensembles. The non-classical properties of HG modes are clearly verified by the violation of Cauchy-Schwarz inequality. Our study provides an effective way to generate photon pairs with narrow bandwidth in high order spatial modes for high dimensional quantum communication.

  7. Tunable cavity-enhanced photon pairs source in Hermite-Gaussian mode

    Directory of Open Access Journals (Sweden)

    Zhi-Yuan Zhou

    2016-02-01

    Full Text Available The spatial modes of light have grasped great research interests because of its great potentials in optical communications, optical manipulation and trapping, optical metrology and quantum information processing. Here we report on generating of photon pairs in Hermite-Gaussian (HG mode in a type-I optical parametric oscillator operated far below threshold. The bandwidths of the photon pairs are 11.4 MHz and 20.8MHz for two different HG modes respectively, therefore the photons can be stored in cold Rubidium atomic ensembles. The non-classical properties of HG modes are clearly verified by the violation of Cauchy-Schwarz inequality. Our study provides an effective way to generate photon pairs with narrow bandwidth in high order spatial modes for high dimensional quantum communication.

  8. An electrically driven cavity-enhanced source of indistinguishable photons with 61% overall efficiency

    Science.gov (United States)

    Schlehahn, A.; Thoma, A.; Munnelly, P.; Kamp, M.; Höfling, S.; Heindel, T.; Schneider, C.; Reitzenstein, S.

    2016-04-01

    We report on an electrically driven efficient source of indistinguishable photons operated at pulse-repetition rates f up to 1.2 GHz. The quantum light source is based on a p-i-n-doped micropillar cavity with integrated self-organized quantum dots, which exploits cavity quantum electrodynamics effects in the weak coupling regime to enhance the emission of a single quantum emitter coupled to the cavity mode. We achieve an overall single-photon extraction efficiency of (61 ± 11) % for a device triggered electrically at f = 625 MHz. Analyzing the suppression of multi-photon emission events as a function of excitation repetition rate, we observe single-photon emission associated with g(2)HBT(0) values between 0.076 and 0.227 for f ranging from 373 MHz to 1.2 GHz. Hong-Ou-Mandel-type two-photon interference experiments under pulsed current injection at 487 MHz reveal a photon-indistinguishability of (41.1 ± 9.5) % at a single-photon emission rate of (92 ± 23) MHz.

  9. Cavity-enhanced surface-plasmon resonance sensing: Modeling and performance

    Czech Academy of Sciences Publication Activity Database

    Giorgini, A.; Avino, S.; Malara, P.; Zullo, R.; Gaglio, G.; Homola, Jiří; De Natale, P.

    2014-01-01

    Roč. 25, č. 1 (2014), 015205. ISSN 0957-0233 Institutional support: RVO:67985882 Keywords : optical resonators * optical sensor s * cavity ring-down spectroscopy Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.433, year: 2014

  10. Mid-infrared frequency combs

    CERN Document Server

    Schliesser, Albert; Hänsch, Theodor W

    2012-01-01

    Laser frequency combs are coherent light sources that emit a broad spectrum consisting of discrete, evenly spaced narrow lines, each having an absolute frequency measurable within the accuracy of an atomic clock. Their development, a decade ago, in the near-infrared and visible domains has revolutionized frequency metrology with numerous windfalls into other fields such as astronomy or attosecond science. Extension of frequency comb techniques to the mid-infrared spectral region is now under exploration. Versatile mid-infrared frequency comb generators, based on novel laser gain media, nonlinear frequency conversion or microresonators, promise to significantly expand the tree of applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the fingerprint region, with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may spark off new discoveries in the various fields relevant to molecular sciences.

  11. Two-photon experiments in the frequency domain

    Science.gov (United States)

    Mbodji, I.; Olislager, L.; Woodhead, E.; Galmes, B.; Cussey, J.; Furfaro, L.; Emplit, P.; Massar, S.; Phan Huy, K.; Merolla, J.-M.

    2012-06-01

    We report on the study of two-photon interference in the frequency domain. Bell and Hong-Ou-Mandel experiments are investigated. These experiments involve the manipulation of photons in the frequency domain, using off-the-shelf telecommunication components such as electro-optic phase modulators and narrow-band frequency filters. In the first experiment, photon pairs entangled in frequency are created and separated. Each photon is then directed through an independent electro-optic phase modulator. Variation of the radio-frequency parameters of the modulation gives rise to a well-controlled Bessel-shape two-photon interference pattern in the frequency domain. This is efficiently measured with narrow-band frequency filters and superconducting single photon detectors. Experimental measurements exhibit high visibilities (over 99 percent both for net and raw visibilities) and allow the (theoretically proven) optimal violation of a Bell inequality for our setup (by more than 18 standard deviations). The second experiment is a Hong-Ou-Mandel experiment in the frequency domain. We show that a grating (spatial domain) or a phase modulator (temporal domain) can be seen as a frequency beam splitter. A broadband spectrum of photon pairs is divided into two interleaved frequency combs, each one used as an independent input to this acting beam splitter. A theoretical calculation shows clear photon anti-bunching behavior.

  12. Launcher of high frequency heating device

    International Nuclear Information System (INIS)

    The present invention concerns a launcher of a high frequency heating device which emits high frequency electromagnetic waves to heat plasmas generated upon nuclear fusion by way of a bundle of waveguides. The rupture of the bundle of the waveguides due to electromagnetic force is prevented by preventing an induced large electric current in the bundle of the waveguides from flowing even if plasma disruption should occur. Namely, the launcher of the high frequency heating device transmits the high frequency electromagnetic waves by way of the bundle of the waveguides which distribute them in plurality and heat plasmas. In this case, a plurality of partitioning plates are disposed in parallel with each other each at an appropriate distance. The bundle of the waveguides is constituted by joining insulation spacers formed or coated with an electrical insulator between the opposing surfaces of the upper and the lower portions of each of the partitioning plate. With such a constitution, even if plasma disruption should occur, no large inducted current is caused in the bundle of the waveguide. In addition, the partitionings can be directly cooled to improve a cooling efficiency. (N.H.)

  13. A microresonator frequency comb optical clock

    CERN Document Server

    Papp, Scott B; DelHaye, Pascal; Quinlan, Franklyn; Lee, Hansuek; Vahala, Kerry J; Diddams, Scott A

    2013-01-01

    Optical-frequency combs enable measurement precision at the 20th digit, and accuracy entirely commensurate with their reference oscillator. A new direction in experiments is the creation of ultracompact frequency combs by way of nonlinear parametric optics in microresonators. We refer to these as microcombs, and here we report a silicon-chip-based microcomb optical clock that phase-coherently converts an optical-frequency reference to a microwave signal. A low-noise comb spectrum with 25 THz span is generated with a 2 mm diameter silica disk and broadening in nonlinear fiber. This spectrum is stabilized to rubidium frequency references separated by 3.5 THz by controlling two teeth 108 modes apart. The optical clocks output is the electronically countable 33 GHz microcomb line spacing, which features an absolute stability better than the rubidium transitions by the expected factor of 108. Our work demonstrates the comprehensive set of tools needed for interfacing microcombs to state-of-the-art optical clocks.

  14. Ionospheric modifications in high frequency heating experiments

    International Nuclear Information System (INIS)

    Featured observations in high-frequency (HF) heating experiments conducted at Arecibo, EISCAT, and high frequency active auroral research program are discussed. These phenomena appearing in the F region of the ionosphere include high-frequency heater enhanced plasma lines, airglow enhancement, energetic electron flux, artificial ionization layers, artificial spread-F, ionization enhancement, artificial cusp, wideband absorption, short-scale (meters) density irregularities, and stimulated electromagnetic emissions, which were observed when the O-mode HF heater waves with frequencies below foF2 were applied. The implication and associated physical mechanism of each observation are discussed and explained. It is shown that these phenomena caused by the HF heating are all ascribed directly or indirectly to the excitation of parametric instabilities which instigate anomalous heating. Formulation and analysis of parametric instabilities are presented. The results show that oscillating two stream instability and parametric decay instability can be excited by the O-mode HF heater waves, transmitted from all three heating facilities, in the regions near the HF reflection height and near the upper hybrid resonance layer. The excited Langmuir waves, upper hybrid waves, ion acoustic waves, lower hybrid waves, and field-aligned density irregularities set off subsequent wave-wave and wave-electron interactions, giving rise to the observed phenomena

  15. Ionospheric modifications in high frequency heating experiments

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, Spencer P. [Department of Electrical and Computer Engineering, Polytechnic School of Engineering, New York University, 5 MetroTech Center, Brooklyn, New York 11201 (United States)

    2015-01-15

    Featured observations in high-frequency (HF) heating experiments conducted at Arecibo, EISCAT, and high frequency active auroral research program are discussed. These phenomena appearing in the F region of the ionosphere include high-frequency heater enhanced plasma lines, airglow enhancement, energetic electron flux, artificial ionization layers, artificial spread-F, ionization enhancement, artificial cusp, wideband absorption, short-scale (meters) density irregularities, and stimulated electromagnetic emissions, which were observed when the O-mode HF heater waves with frequencies below foF2 were applied. The implication and associated physical mechanism of each observation are discussed and explained. It is shown that these phenomena caused by the HF heating are all ascribed directly or indirectly to the excitation of parametric instabilities which instigate anomalous heating. Formulation and analysis of parametric instabilities are presented. The results show that oscillating two stream instability and parametric decay instability can be excited by the O-mode HF heater waves, transmitted from all three heating facilities, in the regions near the HF reflection height and near the upper hybrid resonance layer. The excited Langmuir waves, upper hybrid waves, ion acoustic waves, lower hybrid waves, and field-aligned density irregularities set off subsequent wave-wave and wave-electron interactions, giving rise to the observed phenomena.

  16. Optical generation of radio-frequency power

    International Nuclear Information System (INIS)

    An optical technique for high-power radio-frequency (RF) signal generation is described. The technique uses a unique photodetector based on a traveling-wave design driven by an appropriately modulated light source. The traveling-wave photodetector (TWPD) exhibits simultaneously a theoretical quantum efficiency approaching 100 % and a very large electrical bandwidth. Additionally, it is capable of dissipating the high-power levels required for the RF generation technique. The modulated light source is formed by either the beating together of two lasers or by the direct modulation of a light source. A system example is given which predicts RF power levels of 100's of mW's at millimeter wave frequencies with a theoretical ''wall-plug'' efficiency approaching 34%

  17. Optimal System Realization in Frequency Domain

    Science.gov (United States)

    Juang, Jer-Nan; Maghami, Peiman G.

    1999-01-01

    Several approaches are presented to identify an experimental system model directly from frequency response data. The formulation begins with a matrix-fraction description as the model structure. Frequency weighting such as exponential weighting is introduced to solve a weighted least-squares problem to obtain the coefficient matrices for the matrix-fraction description. A multi-variable state-space model can then be formed using the coefficient matrices of the matrix-fraction description. An approach is introduced to fine-tune the model using non-linear programming methods to minimize the desired cost function. The method deals with the model in the real Schur or modal form and reassigns a subset of system poles using a nonlinear optimizer. At every optimization step, the input and output influence matrices are refined through least-squares procedures. The proposed approaches are used to identify an analytical model for a NASA testbed from experimental data.

  18. Frequency control of radiofrequency cavity

    OpenAIRE

    Menart, Jure

    2014-01-01

    This work describes the design, development and application of the system for frequency control of EMMA accelerator radiofrequency cavity. The problem with the radiofrequency cavities is, that because of various factors (change in the environmental temperature, mechanical stress, ...), they are continuously frequency detuning. The consequence of the frequency detuning is that electromagnetic field in the cavity is not optimal for the acceleration of the particles. For this reason the resonant...

  19. Counting Word Frequencies with Python

    OpenAIRE

    William J. Turkel; Adam Crymble

    2012-01-01

    Your list is now clean enough that you can begin analyzing its contents in meaningful ways. Counting the frequency of specific words in the list can provide illustrative data. Python has an easy way to count frequencies, but it requires the use of a new type of variable: the dictionary. Before you begin working with a dictionary, consider the processes used to calculate frequencies in a list.

  20. Counting Word Frequencies with Python

    Directory of Open Access Journals (Sweden)

    William J. Turkel

    2012-07-01

    Full Text Available Your list is now clean enough that you can begin analyzing its contents in meaningful ways. Counting the frequency of specific words in the list can provide illustrative data. Python has an easy way to count frequencies, but it requires the use of a new type of variable: the dictionary. Before you begin working with a dictionary, consider the processes used to calculate frequencies in a list.

  1. Seismic behavior of variable frequency pendulum isolator

    Institute of Scientific and Technical Information of China (English)

    V. R. Panchal; R. S. Jangid

    2008-01-01

    Earthquake performance of a flexible one-story building isolated with a variable frequency pendulum isolator(VFPI) under near-fault and far-field ground motions is investigated. The frictional forces mobilized at the interface of theVFPI are assumed to be velocity dependent. The interaction between frictional forces of the VFPI in two horizontal directionsis duly considered and coupled differential equations of motion of the isolated system in the incremental form are solvediteratively. The response of the system with bi-directional interaction is compared with those without interaction. In addition,the effects of velocity dependence on the response of the isolated system are also investigated. Moreover, a parametricstudy is carried out to critically examine the influence of important parameters on bi-directional interaction effects of thefrictional forces of the VFPI. These parameters are: the superstructure time period, frequency variation factor (FVF) andfriction coefficient of the VFPI. From the above investigations, it is observed that the dependence of the friction coefficienton relative velocity of the system does not have a noticeable effect on the peak response of the system isolated with VFPI, andthat the bi-directional interaction of frictional forces of the VFPI is important and if neglected, isolator displacements will beunderestimated and the superstructure acceleration and base shear will be overestimated.

  2. Mixed-frequency multivariate GARCH

    OpenAIRE

    DHAENE, Geert; Wu, Jianbin

    2016-01-01

    We introduce and evaluate mixed-frequency multivariate GARCH models for forecasting low-frequency (weekly or monthly) multivariate volatility based on high-frequency intra-day returns (at five-minute intervals) and on the overnight returns. The low-frequency conditional volatility matrix is modelled as a weighted sum of an intra-day and an overnight component, driven by the intra-day and the overnight returns, respectively. The components are specified as multivariate GARCH (1,1) models of th...

  3. Broadband antenna with frequency scanning

    Directory of Open Access Journals (Sweden)

    A. A. Shekaturin

    2014-06-01

    Full Text Available Relevance of this study. The main advantage of frequency scanning is simplicity of implementation. At this point, multifunctional usage of microwave modules is an urgent task, as well as their maximum simpler and cheaper. Antenna design and operation. The study is aimed at providing electric antenna with frequency scanning. It was based on the log-periodic antenna due to its wideband and negotiation capability over the entire operating frequency range. For this distribution line is bent in an arc of a circle in a plane blade while vibrators are arranged along the radius. Computer modeling of antennas with frequency scanning. Modeled with a non-mechanical motion antenna beam emitters representing system for receiving a radio frequency signal on mobile objects calculated for 1.8 GHz ... 4.2 GHz. The simulation was performed in a software environment for numerical modeling of electromagnetic «Feko 5.5». Analysis of the interaction of radiation is based on the method of moments. Findings. The result of this work is to propose a new design of the antenna with a frequency scanning method as agreed in a wide frequency range. In the studied technical solution provided by the rotation of NAM in the frequency range, and the matching of the antenna to the feed line is maintained. Application of this type of antennas on the proposed technical solution in communication systems will improve the communication reliability by maintaining coordination in the frequency range

  4. Numeracy, frequency, and Bayesian reasoning

    Directory of Open Access Journals (Sweden)

    Gretchen B. Chapman

    2009-02-01

    Full Text Available Previous research has demonstrated that Bayesian reasoning performance is improved if uncertainty information is presented as natural frequencies rather than single-event probabilities. A questionnaire study of 342 college students replicated this effect but also found that the performance-boosting benefits of the natural frequency presentation occurred primarily for participants who scored high in numeracy. This finding suggests that even comprehension and manipulation of natural frequencies requires a certain threshold of numeracy abilities, and that the beneficial effects of natural frequency presentation may not be as general as previously believed.

  5. Radio Frequency Anechoic Chamber Facility

    Data.gov (United States)

    Federal Laboratory Consortium — FUNCTION: Supports the design, manufacture, and test of antenna systems. The facility is also used as an electromagnetic compatibility/radio frequency interference...

  6. Demand as Frequency Controlled Reserve

    DEFF Research Database (Denmark)

    Xu, Zhao; Togeby, Mikael; Østergaard, Jacob

    This report summaries the research outcomes of the project ‘Demand as Frequency Controlled Reserve (DFR)’, which has received the support from Energinet.dk’s PSO program, Grant no. 2005-2-6380. The objective of this project is to investigate the technology of using electricity demands for providing...... frequency reserve to power systems. The project consists of five work packages, including: Background and perspective Dynamical simulation of chosen concepts Monitoring demand as frequency controlled reserve Strategy and practical implementation Conclusion and evaluation Within the project, the frequency...

  7. A contactless rotary frequency changer

    Science.gov (United States)

    Krasnoshapka, M. M.; Kovalenko, G. A.; Krasnoshapka, D. M.

    1984-10-01

    The design and the principle of operation of a contactless rotary frequency changer for converting commercial-frequency alternating current to stabilized three-phase current with a higher frequency (400 Hz or more) are presented. The frequency changer consists of a synchronous motor with a rotating rectifier and two asynchronous electric machines with phase rotors, one of which has an adjustable magnetic shunt in the stator. It is shown that the use of an adjustable magnetic shunt makes it possible to obtain a stable output voltage, while the use of toroidal three-phase windings reduces the amount of the winding wire as well as the dimensions and weight of the unit.

  8. An innovative MRE absorber with double natural frequencies for wide frequency bandwidth vibration absorption

    Science.gov (United States)

    Sun, Shuaishuai; Yang, Jian; Li, Weihua; Deng, Huaxia; Du, Haiping; Alici, Gursel; Yan, Tianhong

    2016-05-01

    A new design of adaptive tuned vibration absorber was proposed in this study for vibration reduction. The innovation of the new absorber is the adoption of the eccentric mass on the top of the multilayered magnetorheological elastomer (MRE) structure so that this proposed absorber has two vibration modes: one in the torsional direction and the other in translational direction. This property enables the absorber to expand its effective bandwidth and to be more capable of reducing the vibrations especially dealing with those vibrations with multi-frequencies. The innovative MRE absorber was designed and tested on a horizontal vibration table. The test results illustrate that the MRE absorber realized double natural frequencies, both of which are controllable. Inertia’s influence on the dynamic behavior of the absorber is also investigated in order to guide the design of the innovative MRE absorber. Additionally, the experimentally obtained natural frequencies coincide with the theoretical data, which sufficiently verifies the feasibility of this new design. The last part in terms of the vibration absorption ability also proves that both of these two natural frequencies play a great role in absorbing vibration energy.

  9. Wideband transmitter for low-frequency nuclear quadrupole resonance spectrometer

    International Nuclear Information System (INIS)

    A wideband transmitter for a nuclear quadrupole resonance spectrometer for study of light nuclei is described. The use of a digital shaper of radio-frequency pulses and a directly coupled two-stage power amplifier makes large number of wideband transformers and power supplies unnecessary. The output power of the radio-frequency pulses is 160 W in the range of 0.1-10 MHz

  10. Bianisotropy Picture of Higher Permeability at Higher Frequencies

    Institute of Scientific and Technical Information of China (English)

    XUE De-Sheng; LI Fa-Shen; FAN Xiao-Long; WEN Fu-Sheng

    2008-01-01

    With an effective bianisotropy picture, high-frequency behaviours of different magnetic materials can be reconciled, and the higher permeability and higher resonance frequencies are achieved even in the GHz range. The validity of the bianisotropy picture is quantitatively refilled by the in-plane anisotropic Fe34Co55Zr11 thin films.A prolate elliptical precession of the magnetization about its equilibrium direction is the key point, which can be induced by an artificial or an intrinsic bianisotropy system.

  11. High frequency single mode traveling wave structure for particle acceleration

    Science.gov (United States)

    Ivanyan, M. I.; Danielyan, V. A.; Grigoryan, B. A.; Grigoryan, A. H.; Tsakanian, A. V.; Tsakanov, V. M.; Vardanyan, A. S.; Zakaryan, S. V.

    2016-09-01

    The development of the new high frequency slow traveling wave structures is one of the promising directions in accomplishment of charged particles high acceleration gradient. The disc and dielectric loaded structures are the most known structures with slowly propagating modes. In this paper a large aperture high frequency metallic two-layer accelerating structure is studied. The electrodynamical properties of the slowly propagating TM01 mode in a metallic tube with internally coated low conductive thin layer are examined.

  12. Tailoring Carbon Nanostructure for High Frequency Supercapacitor Operation

    OpenAIRE

    Pritesh Hiralal; Gemma Rius; Piers Andrew; Masamichi Yoshimura; Amaratunga, Gehan A. J.

    2014-01-01

    The possibility of enhancing the frequency performance of electrochemical capacitors by tailoring the nanostructure of the carbon electrode to increase electrolyte permeability is demonstrated. Highly porous, vertically oriented carbon electrodes which are in direct electrical contact with the metallic current collector are produced via MPECVD growth on metal foils. The resulting structure has a capacitance and frequency performance between that of an electrolytic capacitor and an electrochem...

  13. Static and low frequency electric and magnetic fields

    International Nuclear Information System (INIS)

    The biological effects of exposure to low frequency electric and magnetic fields are reviewed with the objective of summarizing effects directly relevant to considerations of the health and safety of exposed people. Static and low frequency electric and magnetic fields may elicit biological reactions. Whether exposure to such fields may affect human health at field strengths present in everyday or occupational life is still unsettled. There is unsufficient knowledge to establish any dose concept relevant to health risk. 196 refs., 6 tabs

  14. Frequency doubling and memory effects in the Spin Hall Effect

    OpenAIRE

    Pershin, Yu. V.; Di Ventra, M.

    2008-01-01

    We predict that when an alternating voltage is applied to a semiconducting system with inhomogeneous electron density in the direction perpendicular to main current flow, the spin Hall effect results in a transverse voltage containing a double-frequency component. We also demonstrate that there is a phase shift between applied and transverse voltage oscillations, related to the general memristive behavior of semiconductor spintronic systems. A different method to achieve frequency doubling ba...

  15. INVESTIGATING THE LONGITUDINAL RELATION BETWEEN OFFENDING FREQUENCY AND OFFENDING VARIETY.

    Science.gov (United States)

    Monahan, Kathryn C; Piquero, Alex R

    2009-07-01

    Researchers interested in longitudinal patterns of criminal offending have paid close attention to several dimensions of criminal careers. Although it might be expected that several dimensions are strongly linked to one another, research has not explored their joint distribution. The study uses trajectory-based methodology to examine the joint relation between offending variety and offending frequency in a large sample of serious offenders from adolescence to early adulthood and also tests how several risk factors relate to the joint covariation between variety and frequency. Results indicate strong concordance between low and high rate variety and frequency trajectories but a more modest concordance among moderate rate variety and frequency trajectories. Criminal history, individual, parent, and peer characteristics predict differences in concordance between variety and frequency trajectories. Theoretical implications and directions for further research are outlined. PMID:20037667

  16. Design of high frequency integrated analogue filters

    CERN Document Server

    Sun, Yichuang

    2002-01-01

    This book brings together leading researchers to highlight recent advances and identify promising directions for future development. Motivated by the market for mobile and wireless communications, fully integrated analog filters for high-frequency applications are now receiving great interest world-wide. Chapters are dedicated to MOSFET-C and Gm-C filters, current-mode continuous-time filters, log-domain filters, switched-current filters, adaptive filters and on-chip automatic tuning. The topical nature of the book and caliber of the authors ensures that this book will be of wide interest to t

  17. Normal-dispersion microresonator Kerr frequency combs

    Directory of Open Access Journals (Sweden)

    Xue Xiaoxiao

    2016-06-01

    Full Text Available Optical microresonator-based Kerr frequency comb generation has developed into a hot research area in the past decade. Microresonator combs are promising for portable applications due to their potential for chip-level integration and low power consumption. According to the group velocity dispersion of the microresonator employed, research in this field may be classified into two categories: the anomalous dispersion regime and the normal dispersion regime. In this paper, we discuss the physics of Kerr comb generation in the normal dispersion regime and review recent experimental advances. The potential advantages and future directions of normal dispersion combs are also discussed.

  18. Electron heating mechanisms in dual-frequency capacitive discharges

    International Nuclear Information System (INIS)

    We discuss electron heating mechanisms in the sheath regions of dual-frequency capacitive discharges, with the twin aims of identifying the dominant mechanisms and supplying closed-form expressions from which the heating power can be estimated. We show that the heating effect produced by either Ohmic or collisionless heating is much larger when the discharge is excited by a superposition of currents at two frequencies than if either current had acted alone. This coupling effect occurs because the lower frequency current, while not directly heating the electrons to any great extent, strongly affects the spatial structure of the discharge in the sheath regions

  19. Lexical Frequency in Sign Languages

    Science.gov (United States)

    Johnston, Trevor

    2012-01-01

    Measures of lexical frequency presuppose the existence of corpora, but true machine-readable corpora of sign languages (SLs) are only now being created. Lexical frequency ratings for SLs are needed because there has been a heavy reliance on the interpretation of results of psycholinguistic and neurolinguistic experiments in the SL research…

  20. Frequency conversion of structured light.

    Science.gov (United States)

    Steinlechner, Fabian; Hermosa, Nathaniel; Pruneri, Valerio; Torres, Juan P

    2016-01-01

    Coherent frequency conversion of structured light, i.e. the ability to manipulate the carrier frequency of a wave front without distorting its spatial phase and intensity profile, provides the opportunity for numerous novel applications in photonic technology and fundamental science. In particular, frequency conversion of spatial modes carrying orbital angular momentum can be exploited in sub-wavelength resolution nano-optics and coherent imaging at a wavelength different from that used to illuminate an object. Moreover, coherent frequency conversion will be crucial for interfacing information stored in the high-dimensional spatial structure of single and entangled photons with various constituents of quantum networks. In this work, we demonstrate frequency conversion of structured light from the near infrared (803 nm) to the visible (527 nm). The conversion scheme is based on sum-frequency generation in a periodically poled lithium niobate crystal pumped with a 1540-nm Gaussian beam. We observe frequency-converted fields that exhibit a high degree of similarity with the input field and verify the coherence of the frequency-conversion process via mode projection measurements with a phase mask and a single-mode fiber. Our results demonstrate the suitability of exploiting the technique for applications in quantum information processing and coherent imaging. PMID:26875448

  1. Frequency dependence of quasiparticle mixers

    International Nuclear Information System (INIS)

    An analysis of the frequency dependence of superconductor-insulator-normal (SIN) and superconductor-insulator-superconductor (SIS) quasiparticle mixers is presented. Power-law expressions for conversion loss and mixer shot-noise temperature for the double-sideband SIN mixer are derived from the Tucker theory for the case of a source conductance which is small compared to the conductance of the junction. For an ideal SIN tunnel junction at T = 0 the mixer conversion efficiency is shown to decrease approximately linearly with frequency up to f = Δ/h. From f = Δ/h to 2Δ/h the conversion efficiency remains approximately constant, while above f = 2Δ/h it rolls off as the inverse square of the frequency. Expressions for the shot-noise contribution to the mixer noise temperature are also derived. At frequencies up to f = Δ/h the noise temperature rises as the square root of the frequency. From f = Δ/h to f = 2Δ/h the noise temperature of the mixer increases linearly with frequency, whereas above f = 2Δ/h it rises as the cube of the frequency. Conversion efficiency and noise temperature are also calculated numerically for the SIN mixer. Good agreement is found between the frequency dependencies calculated analytically in the limit of small local oscillator power and the numerical calculations for optimal pumping

  2. Tunable frequency 4-rod RFQ

    International Nuclear Information System (INIS)

    The frequency tunability of the 4-rod RFQ is investigated. By moving the shorting plate between the posts, which support the 4-rod electrodes, the resonant frequency can be varied almost twofold. Model studies and the calculation of the field uniformity, the variation of Q, and the shunt impedance are reported. (author)

  3. Frequency conversion of structured light

    Science.gov (United States)

    Steinlechner, Fabian; Hermosa, Nathaniel; Pruneri, Valerio; Torres, Juan P.

    2016-02-01

    Coherent frequency conversion of structured light, i.e. the ability to manipulate the carrier frequency of a wave front without distorting its spatial phase and intensity profile, provides the opportunity for numerous novel applications in photonic technology and fundamental science. In particular, frequency conversion of spatial modes carrying orbital angular momentum can be exploited in sub-wavelength resolution nano-optics and coherent imaging at a wavelength different from that used to illuminate an object. Moreover, coherent frequency conversion will be crucial for interfacing information stored in the high-dimensional spatial structure of single and entangled photons with various constituents of quantum networks. In this work, we demonstrate frequency conversion of structured light from the near infrared (803 nm) to the visible (527 nm). The conversion scheme is based on sum-frequency generation in a periodically poled lithium niobate crystal pumped with a 1540-nm Gaussian beam. We observe frequency-converted fields that exhibit a high degree of similarity with the input field and verify the coherence of the frequency-conversion process via mode projection measurements with a phase mask and a single-mode fiber. Our results demonstrate the suitability of exploiting the technique for applications in quantum information processing and coherent imaging.

  4. Gaming Frequency and Academic Performance

    Science.gov (United States)

    Ip, Barry; Jacobs, Gabriel; Watkins, Alan

    2008-01-01

    There are numerous claims that playing computer and video games may be educationally beneficial, but there has been little formal investigation into whether or not the frequency of exposure to such games actually affects academic performance. This paper explores the issue by analysing the relationships between gaming frequency--measured as the…

  5. A Survey of Advanced Microwave Frequency Measurement Techniques

    Directory of Open Access Journals (Sweden)

    Anand Swaroop Khare

    2012-06-01

    Full Text Available Microwaves are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. The science of photonics includes the generation, emission, modulation, signal processing, switching, transmission, amplification, detection and sensing of light. Microwave photonics has been introduced for achieving ultra broadband signal processing. Instantaneous Frequency Measurement (IFM receivers play an important role in electronic warfare. Technologies used for signal processing, include conventional direct Radio Frequency (RF techniques, digital techniques, intermediate frequency (IF techniques and photonic techniques. Direct RF techniques suffer an increased loss, high dispersion, and unwanted radiation problems in high frequencies. The systems that use traditional RF techniques can be bulky and often lack the agility required to perform advanced signal processing in rapidly changing environments. In this paper we discussed a survey of Microwave Frequency Measurement Techniques. The microwaves techniques are categorized based upon different approaches. This paper provides the major advancement in the Microwave Frequency MeasurementTechniques research; using these approaches the features and categories in the surveyed existing work.

  6. Island shadows in wave directional spectra

    Science.gov (United States)

    Pawka, S. S.

    1983-03-01

    Shadows of individual islands are observed in directional spectra sampled with a high resolution linear array at Torrey Pines Beach, California. A detailed investigation of the spectra indicates that the Channel Islands restrict the wave energy density to certain narrow directional sectors. A deep spectral trough, associated with San Clemente Island, is a predominant feature in the well resolved spectra (wave frequencies ˜0.06-0.15 Hz). Negligible values of energy density in the center of this directional `gap' were consistently observed in the range 0.082-0.114 Hz. Measurable but low gap energy density values are seen in the high and low frequency regimes. Generation of high frequency waves (f≥0.13 Hz) by local winds generally smears the island windowing effects and even creates a spectral peak in a directional sector which is blocked from deep ocean exposure. Several estimation techniques are used in the directional spectrum analysis. These include the Maximum Likelihood Method (MLM) and two methods developed in this work. The two new techniques show significant improvement over the MLM in the definition of gaps in the spectrum. Although none of these methods is considered an `Optimal' estimator for general use, each displays some superior merit in particular directional spectrum estimation problems.

  7. On directed interacting animals and directed percolation

    OpenAIRE

    Knezevic, Milan; Vannimenus, Jean

    2002-01-01

    We study the phase diagram of fully directed lattice animals with nearest-neighbour interactions on the square lattice. This model comprises several interesting ensembles (directed site and bond trees, bond animals, strongly embeddable animals) as special cases and its collapse transition is equivalent to a directed bond percolation threshold. Precise estimates for the animal size exponents in the different phases and for the critical fugacities of these special ensembles are obtained from a ...

  8. Direct Antiglobulin Test

    Science.gov (United States)

    ... this page helpful? Also known as: DAT; Direct Coombs Test; Direct Anti-human Globulin Test Formal name: ... antiglobulin test (DAT), also known as the direct Coombs test, is used primarily to help determine whether ...

  9. FOREIGN DIRECT INVESTMENT

    Directory of Open Access Journals (Sweden)

    Dr. Roshankumar M. Bhigania

    2012-06-01

    Full Text Available FOREIGN DIRECT INVESTMENT (FDI : Introduction – Importance of Foreign Capital – Types of Foreign Capital – Government Policy on Foreign Direct Investment –Role of Foreign Direct Investment in the inflow of Foreign Capital.

  10. Analysis of photonic crystal and multi-frequency terahertz microstrip patch antenna

    International Nuclear Information System (INIS)

    In this paper, two-dimensional photonic crystals working at terahertz (THz) frequency is analyzed, a multi-frequency terahertz microstrip patch antenna on photonic crystal substrate is presented and its electromagnetic wave propagation phenomenon is investigated. The proposed antenna can work at five frequency points' scope at terahertz frequency regions, and the radiation efficiency is as high as ∼96%. The photonic crystal structure of the substrate is used to enhance the gain, directivity and radiation efficiency of the antenna

  11. Analysis of photonic crystal and multi-frequency terahertz microstrip patch antenna

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Lechen, E-mail: yanglechen@163.com [The 41st Research Institute of CETC, Qingdao 266555, Shandong Province (China); Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu Province (China); Key Laboratory of Nanodevices and Applications, Chinese Academy of Science, Suzhou 215123, Jiangsu Province (China); Shi, Xueshun [The 41st Research Institute of CETC, Qingdao 266555, Shandong Province (China); Science and Technology on Electronic Test and Measurement Laboratory, Qingdao 266555, Shandong Province (China); Chen, Kunfeng [The 41st Research Institute of CETC, Qingdao 266555, Shandong Province (China); Fu, Kai; Zhang, Baoshun [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu Province (China); Key Laboratory of Nanodevices and Applications, Chinese Academy of Science, Suzhou 215123, Jiangsu Province (China)

    2013-12-15

    In this paper, two-dimensional photonic crystals working at terahertz (THz) frequency is analyzed, a multi-frequency terahertz microstrip patch antenna on photonic crystal substrate is presented and its electromagnetic wave propagation phenomenon is investigated. The proposed antenna can work at five frequency points' scope at terahertz frequency regions, and the radiation efficiency is as high as ∼96%. The photonic crystal structure of the substrate is used to enhance the gain, directivity and radiation efficiency of the antenna.

  12. Frequency-Locking in Coupled Chaotic Systems

    Institute of Scientific and Technical Information of China (English)

    HU Bam-Bi; LIU Zong-Hua; ZHENG Zhi-Gang

    2001-01-01

    A novel approach is presented for measuring the phase synchronization (frequency-locking) of coupled N nonidentical oscillators, which can characterize frequency-locking for chaotic systems without well-defined phase by measuring the mean frequency. Numerical simulations confirm the existence of frequency-locking. The relations between the mean frequency and the coupling strength and the frequency mismatch are given. For the coupled hyperchaotic systems, the frequency-locking can be better characterized by more than one mean frequency curves.

  13. Mutation direction by irradiation in rice

    International Nuclear Information System (INIS)

    The mutation directions of rice were studied. The results indicated that the mutation directions of rice induced by 14C were invert correlation to their genetic backgrounds of tested rice varieties, i.e. early mature and short stem varieties produced later mature and higher stem mutation; late mature and high stem varieties produced earlier mature and shorter stem mutation; the varieties of middle maturity and height produced both direction mutations of earlier and later maturity or shorter and higher stem. The mutation directions induced by 14C were also related to treated doses and stages. Frequency of earlier maturity mutation by protons treatment were higher than those induced by other mutagens. Frequency of later maturity by γ-rays were higher than those induced by other mutagens. Frequency of short stem mutation by synchronous irradiation (soft X-rays) were higher than those induced by other mutagens. Frequency of beneficial mutation induced by proton treatment were higher than those induced by γ-rays

  14. Approximating Document Frequency with Term Count Values

    CERN Document Server

    Klein, Martin

    2008-01-01

    For bounded datasets such as the TREC Web Track (WT10g) the computation of term frequency (TF) and inverse document frequency (IDF) is not difficult. However, when the corpus is the entire web, direct IDF calculation is impossible and values must instead be estimated. Most available datasets provide values for term count (TC) meaning the number of times a certain term occurs in the entire corpus. Intuitively this value is different from document frequency (DF), the number of documents (e.g., web pages) a certain term occurs in. We conduct a comparison study between TC and DF values within the Web as Corpus (WaC). We found a very strong correlation with Spearman's rho >0.8 (p<0.005) which makes us confident in claiming that for such recently created corpora the TC and DF values can be used interchangeably to compute IDF values. These results are useful for the generation of accurate lexical signatures based on the TF-IDF scheme.

  15. On directed interacting animals and directed percolation

    Science.gov (United States)

    Knezevic, Milan; Vannimenus, Jean

    2002-03-01

    We study the phase diagram of fully directed lattice animals with nearest-neighbour interactions on the square lattice. This model comprises several interesting ensembles (directed site and bond trees, bond animals, strongly embeddable animals) as special cases and its collapse transition is equivalent to a directed bond percolation threshold. Precise estimates for the animal size exponents in the different phases and for the critical fugacities of these special ensembles are obtained from a phenomenological renormalization group analysis of the correlation lengths for strips of width up to n = 17. The crossover region in the vicinity of the collapse transition is analysed in detail and the crossover exponent φ is determined directly from the singular part of the free energy. We show using scaling arguments and an exact relation due to Dhar that φ is equal to the Fisher exponent σ governing the size distribution of large directed percolation clusters.

  16. Blazars at Low Radio Frequencies

    Science.gov (United States)

    Trüstedt, J.; Kadler, M.; Brüggen, M.; Falcke, H.; Heald, G.; McKean, J.; Mueller, C.; Ros, E.; Schulz, R.; Wilms, J.

    We explore the low radio-frequency properties of the MOJAVE 1 blazar sample using the LOFAR Multi-Frequency Snapshot Sky Survey (MSSS). We find the characteristically flat blazar spectrum to extend down to the LOFAR bands, demonstrating that the emission at these low radio frequencies is still dominated by relativistically beamed emission. As most sources remain unresolved at the MSSS angular resolution, we are reimaging these data using LOFAR baselines beyond the standard MSSS uv-range resulting in an angular resolution of ~24 arcsec. We present first LOFAR images of MOJAVE sources from this project.

  17. Foundations for radio frequency engineering

    CERN Document Server

    Geyi, Wen

    2015-01-01

    The book provides a comprehensive coverage of the fundamental topics in microwave engineering, antennas and wave propagation, and electromagnetic compatibility, including electromagnetic boundary value problems, waveguide theory, microwave resonators, antennas and wave propagation, microwave circuits, principles of electromagnetic compatibility designs, information theory and systems. Deals systematically with fundamental problems in radio frequency engineering, this important volume provides an updated treatment of radio frequency theory and techniques. The book can be used as a one-semester course for senior and first-year graduate students or as a reference for radio frequency engineers and applied physicists.

  18. Self-referencing of an on-chip soliton Kerr frequency comb without external broadening

    CERN Document Server

    Brasch, Victor; Jost, John D; Geiselmann, Michael; Kippenberg, Tobias J

    2016-01-01

    Self-referencing turns pulsed laser systems into self-referenced frequency combs. Such frequency combs allow counting of optical frequencies and have a wide range of applications. The required optical bandwidth to implement self-referencing is typically obtained via nonlinear broadening in optical fibers. Recent advances in the field of Kerr frequency combs have provided a path towards the development of compact frequency comb sources that provide broadband frequency combs, exhibit microwave repetition rates and that are compatible with on-chip photonic integration. These devices have the potential to significantly expand the use of frequency combs. Yet to date self-referencing of such Kerr frequency combs has only been attained by applying conventional, fiber based broadening techniques. Here we demonstrate external broadening-free self-referencing of a Kerr frequency comb. An optical spectrum that spans two-thirds of an octave is directly synthesized from a continuous wave laser-driven silicon nitride micro...

  19. Radiation directivity rotation by acoustic metamaterials

    International Nuclear Information System (INIS)

    We use a metamaterial-based scheme to rotate the radiation directivity of sound radiated by a source surrounded by the structure. The rotation is demonstrated through both numerical simulations and experiments. The performance persists within a broadband and is entirely independent of the location and pattern of source inside, suggesting great potential in various practical scenarios where both the signal frequency and source position may vary significantly. We have also investigated the possibility to realize versatile controls of radiation direction by tailoring the structural parameters. Our design with special directivity-steering capability may open route to loudspeaker and auditorium acoustics designs and medical ultrasound applications

  20. Radiation directivity rotation by acoustic metamaterials

    Science.gov (United States)

    Jiang, Xue; Zhang, Likun; Liang, Bin; Zou, Xin-ye; Cheng, Jian-chun

    2015-08-01

    We use a metamaterial-based scheme to rotate the radiation directivity of sound radiated by a source surrounded by the structure. The rotation is demonstrated through both numerical simulations and experiments. The performance persists within a broadband and is entirely independent of the location and pattern of source inside, suggesting great potential in various practical scenarios where both the signal frequency and source position may vary significantly. We have also investigated the possibility to realize versatile controls of radiation direction by tailoring the structural parameters. Our design with special directivity-steering capability may open route to loudspeaker and auditorium acoustics designs and medical ultrasound applications.

  1. Implementation of virtual reality demonstrations with time-frequency-domain audio engine

    OpenAIRE

    Paasonen, Juhani

    2015-01-01

    Directional audio coding (DirAC) is a system originally developed for analyzing recordings of spatial audio and synthesizing them with arbitrary loudspeaker setups or headphones. It is based on knowledge of human hearing, psychoacoustics. In analysis, the input is divided to frequency bands. For each frequency band, the direction of arrival and the diffuseness of sound are estimated. In synthesis, the result is divided to diffuse and non-diffuse stream. The diffuse stream is non-directional, ...

  2. Optical frequency combs generated mechanically

    CERN Document Server

    Sumetsky, M

    2016-01-01

    It is shown that a highly equidistant optical frequency comb can be generated by the parametric excitation of an optical bottle microresonator with nanoscale effective radius variation by its natural mechanical vibrations.

  3. Frequency Steered Acoustic Transducer Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project is to develop, fabricate, and characterize a novel frequency steered acoustic transducer (FSAT) for the...

  4. Frequency Steered Acoustic Transducer Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This Small Business Innovation Research Phase II project is to fabricate, characterize, and verify performance of a new type of frequency steered acoustic...

  5. High Frequency Electronic Packaging Technology

    Science.gov (United States)

    Herman, M.; Lowry, L.; Lee, K.; Kolawa, E.; Tulintseff, A.; Shalkhauser, K.; Whitaker, J.; Piket-May, M.

    1994-01-01

    Commercial and government communication, radar, and information systems face the challenge of cost and mass reduction via the application of advanced packaging technology. A majority of both government and industry support has been focused on low frequency digital electronics.

  6. Dual-frequency microwave antenna

    Science.gov (United States)

    Bathker, D. A.; Brunstein, S. A.; Ludwig, A. C.; Potter, P. D.

    1980-01-01

    Single antenna using two feed horns (one for receiving and radiation X-band signals, and one for S-band signals), in conjunction with ellipsoid reflector and dichronic plate, can accommodate two different frequencies simultaneously.

  7. High-Frequency Rayleigh-Wave Method

    Institute of Scientific and Technical Information of China (English)

    Jianghai Xia; Richard D Millerg; Xu Yixian; Luo Yinhe; Chen Chao; Liu Jiangping; Julian Ivanov; Chong Zeng

    2009-01-01

    High-frequency (≥2 Hz) Rayleigh-wave data acquired with a multichannei recording sys-tem have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave tech-niques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a nou-iuvasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution.

  8. Low-Frequency Radioastronomy Basics

    Science.gov (United States)

    Zarka, P.

    2011-04-01

    With the many large instruments in construction or in project, the present epoch corresponds to a renewal of low-frequency radioastronomy. The field will attract new researchers and students not expert of the radioastronomy techniques. With this audience in mind, we present here a very brief introduction to radioastronomy basics, including propagation and polarization of low-frequency radio waves as well as instrumental aspects. Basic formulas are given. The references and internet links will allow the interested reader to go further.

  9. Multichannel frequency dividers using MSW

    OpenAIRE

    Zavislyak, I. V.; Romanyuk, V. F.; Stakhursky, L. L.

    1997-01-01

    Multichannel frequency dividers (multiplexers) are obligatory elements of many radar and communication systems. They are first of all used when signal processing in the real time is needed within the band of several GHz [1].The frequency dividers using magnetostatic waves (MSW) and resonances (MSR) are perspective devices in spite of the problems connected with low termostability of their electric characteristics. The use of the epitaxial films of yttrium-iron garnet (YIG), barium ferrite (BF...

  10. The radio-frequency quadrupole

    OpenAIRE

    Vretenar, Maurizio

    2013-01-01

    Radio-frequency quadrupole (RFQ) linear accelerators appeared on the accelerator scene in the late 1970s and have since revolutionized the domain of low-energy proton and ion acceleration. The RFQ makes the reliable production of unprecedented ion beam intensities possible within a compact radio-frequency (RF) resonator which concentrates the three main functions of the low-energy linac section: focusing, bunching and accelerating. Its sophisticated electrode structure and strict beam dynamic...

  11. Enhancement and quenching of high-intensity focused ultrasound cavitation activity via short frequency sweep gaps.

    Science.gov (United States)

    Hallez, Loïc; Lee, Judy; Touyeras, Francis; Nevers, Aymeric; Ashokkumar, Muthupandian; Hihn, Jean-Yves

    2016-03-01

    This letter reports on the use of frequency sweeps to probe acoustic cavitation activity generated by high-intensity focused ultrasound (HIFU). Unprecedented enhancement and quenching of HIFU cavitation activity were observed when short frequency sweep gaps were applied in negative and positive directions, respectively. It was revealed that irrespective of the frequency gap, it is the direction and frequency sweep rate that govern the cavitation activity. These effects are related to the response of bubbles generated by the starting frequency to the direction of the frequency sweep, and the influence of the sweep rate on growth and coalescence of bubbles, which in turn affects the active bubble population. These findings are relevant for the use of HIFU in chemical and therapeutic applications, where greater control of cavitation bubble population is critical. PMID:26584998

  12. Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

    Directory of Open Access Journals (Sweden)

    N. F. Blagoveshchenskaya

    2009-01-01

    Full Text Available Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency fH was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency was just below the third electron gyro harmonic frequency, while both the HF pump beam and UHF radar beam were directed towards the magnetic zenith (MZ. The HF pump-induced phenomena were diagnosed with several instruments: the bi-static HF radio scatter on the London-Tromsø-St. Petersburg path, the CUTLASS radar in Hankasalmi (Finland, the European Incoherent Scatter (EISCAT UHF radar at Tromsø and the Tromsø ionosonde (dynasonde. The results show thermal electron excitation of the HF-induced striations seen simultaneously from HF bi-static scatter and CUTLASS radar observations, accompanied by increases of electron temperature when the heater frequency was near and then above the critical frequency of the F2 layer by up to 0.4 MHz. An increase of the electron density up to 25% accompanied by strong HF-induced electron heating was observed, only when the heater frequency was near the critical frequency and just below the third electron gyro harmonic frequency. It is concluded that the combined effect of upper hybrid resonance and gyro resonance at the same altitude gives rise to strong electron heating, the excitation of striations, HF ray trapping and extension of HF waves to altitudes where they can excite Langmuir turbulence and fluxes of electrons accelerated to energies that produce ionization.

  13. Wave directional spreading at shallow and intermediate depth

    Digital Repository Service at National Institute of Oceanography (India)

    SanilKumar, V.; Deo, M.C.; Anand, N.M.

    for frequencies close to peak frequency. It is found that at both shallow and intermediate water depths, directional width is marginally more than the mean spreading angle. The estimated Fouries coefficient related parameters 's1' and 's2' are compared with each...

  14. DSWEIGHT: Stata module to generate direct standardization weights

    OpenAIRE

    Roger Newson

    2012-01-01

    dsweight generates direct standardization weights for input as pweights to estimation commands, standardizing the joint distribution of a list of standardization variables to a standard target population, possibly within groups defined by value combinations of a list of group variables. A direct standardization weight is defined as a ratio between the frequency of a combination of values of standardization variables in a target standard population and the frequency of the same combination of ...

  15. Outer hair cell piezoelectricity: Frequency response enhancement and resonance behavior

    Science.gov (United States)

    Weitzel, Erik K.; Tasker, Ron; Brownell, William E.

    2003-09-01

    Stretching or compressing an outer hair cell alters its membrane potential and, conversely, changing the electrical potential alters its length. This bi-directional energy conversion takes place in the cell's lateral wall and resembles the direct and converse piezoelectric effects both qualitatively and quantitatively. A piezoelectric model of the lateral wall has been developed that is based on the electrical and material parameters of the lateral wall. An equivalent circuit for the outer hair cell that includes piezoelectricity shows a greater admittance at high frequencies than one containing only membrane resistance and capacitance. The model also predicts resonance at ultrasonic frequencies that is inversely proportional to cell length. These features suggest all mammals use outer hair cell piezoelectricity to support the high-frequency receptor potentials that drive electromotility. It is also possible that members of some mammalian orders use outer hair cell piezoelectric resonance in detecting species-specific vocalizations.

  16. Resonance at the Rabi frequency in a superconducting flux qubit

    Energy Technology Data Exchange (ETDEWEB)

    Greenberg, Ya. S. [Novosibirsk State Technical University, Novosibirsk (Russian Federation); Il' ichev, E.; Oelsner, G. [common Leibniz Institute of Photonic Technology, Jena (Germany); Shevchenko, S. N. [B. Verkin Institute for Low Temperature Physics and Engineering, Kharkov, Ukraine and V. Karazin Kharkov National University, Kharkov (Ukraine)

    2014-10-15

    We analyze a system composed of a superconducting flux qubit coupled to a transmission-line resonator driven by two signals with frequencies close to the resonator's harmonics. The first strong signal is used for exciting the system to a high energetic state while a second weak signal is applied for probing effective eigenstates of the system. In the framework of doubly dressed states we showed the possibility of amplification and attenuation of the probe signal by direct transitions at the Rabi frequency. We present a brief review of theoretical and experimental works where a direct resonance at Rabi frequency have been investigated in superconducting flux qubits. The interaction of the qubit with photons of two harmonics has prospects to be used as a quantum amplifier (microwave laser) or an attenuator.

  17. Frequency Stepped Pulse Train Modulated Wind Sensing Lidar

    DEFF Research Database (Denmark)

    Olesen, Anders Sig; Pedersen, Anders Tegtmeier; Rottwitt, Karsten

    2011-01-01

    In this paper a wind sensing lidar utilizing a Frequency Stepped Pulse Train (FSPT) is demonstrated. One of the advantages in the FSTP lidar is that it enables direct measurement of wind speed as a function of distance from the lidar. Theoretically the FSPT lidar continuously produces measurements...

  18. Causality between the Amplitude and Frequency of Cardiac Oscillations

    Czech Academy of Sciences Publication Activity Database

    Paluš, Milan; Stefanovska, A.; Veber, M.

    2004-01-01

    Roč. 4, č. 2 (2004), s. 127-132. ISSN 1567-8822 Institutional research plan: CEZ:AV0Z1030915 Keywords : causality * cardiac frequency * systolic pressure * information theory * mutual information * synchronization * direction of driving Subject RIV: BB - Applied Statistics, Operational Research

  19. Demand as frequency controlled reserve

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Z.; Togeby, M.; OEstergaard, J.

    2008-09-15

    Using demand as frequency controlled reserve (DFR) is an emerging technology which allow demand to participate actively in maintaining the system operation without reducing the energy service delivered to the customer and without need of user interaction. The basic premise is that traditional frequency controlled reserves from power plants and interconnections with neighbouring systems can be costly, slow and not fulfil the need for future power grids with a high share of wind power and fewer central power plants, and an intention to perform flexible operation such as is landing. Electricity demands, on the other hand, have advantages as frequency reserve including fast activation speed, smooth linear activation, low expected costs, and well-dispersed in the distribution grid. The main challenge of DFR is new methods for monitoring the available capacity. This project has investigated the technology of using electricity demands for providing frequency reserve to power systems. Within the project the potential and economy of DFR compatible loads in Denmark has been investigated, control logic has been designed, power system impact has been investigated, potential business models has been evaluated and an implementation strategy has been suggested. The tasks and goals of the project have been successfully accomplished based on which the conclusion and future recommendation are made. This project has developed the DFR technology that enables electricity demands to autonomously disconnect or reconnect to the grid in response to system frequency variations. The developed DFR technology is proved to be a promising technology from several perspectives. Technically, using DFR is feasible to provide reserves and enhance power system frequency control, while fulfilling technical requirements such as linear activation (or reconnection) according to frequency (or time). Environmentally, the DFR technology is pollution free in contrast to traditional reserves from generation

  20. Invariants of directed spaces

    DEFF Research Database (Denmark)

    Raussen, Martin

    2007-01-01

    Directed spaces are the objects of study within directed algebraic topology. They are characterised by spaces of directed paths associated to a source and a target, both elements of an underlying topological space. The algebraic topology of these path spaces and their connections are studied from a...... categorical perspective. In particular, we study the preorder category associated to a directed space and various "quotient" categories arising from algebraic topological functors. Furthermore, we propose and study a new notion of directed homotopy equivalence between directed spaces....