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Sample records for cavity-enhanced direct frequency

  1. 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 detec...... and unique molecular fingerprints exist for many biomarkers. We present a series of breath measurements including stable isotope ratios of CO2, breath concentrations of CO, and the presence of trace concentrations of NH3 in high concentrations of H2O. Udgivelsesdato: 02.05...

  2. 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$\

  3. 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

  4. Signal line shapes of Fourier transform cavity-enhanced frequency modulation spectroscopy with optical frequency combs

    CERN Document Server

    Johansson, Alexandra C; Khodabakhsh, Amir; Foltynowicz, Aleksandra

    2016-01-01

    We present a thorough analysis of the signal line shapes of Fourier transform-based noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS). We discuss the signal dependence on the ratio of the modulation frequency, f${_m}$, to the molecular line width, {\\Gamma}. We compare a full model of the signals and a simplified absorption-like analytical model that has high accuracy for low f${_m}$/{\\Gamma} ratios and is much faster to compute. We verify the theory experimentally by measuring and fitting NICE-OFCS spectra of CO${_2}$ at 1575 nm using a system based on an Er:fiber femtosecond laser and a cavity with a finesse of ~11000.

  5. Noise-cancelled, cavity-enhanced saturation laser spectroscopy for laser frequency stabilisation

    Energy Technology Data Exchange (ETDEWEB)

    Vine, Glenn de; McClelland, David E; Gray, Malcolm B [Centre for Gravitational Physics, Faculty of Science, Australian National University, Canberra, ACT 0200 (Australia)

    2006-03-02

    We employ a relatively simple experimental technique enabling mechanical-noise free, cavityenhanced spectroscopic measurements of an atomic transition and its hyperfine structure. We demonstrate this technique with the 532 nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The resulting cavity-enhanced, noise-cancelled, iodine hyperfine error signal is used as a frequency reference with which we stabilise the frequency of the 1064nm Nd:YAG laser. Preliminary frequency stabilisation results are then presented.

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

    Science.gov (United States)

    Rutkowski, Lucile; Morville, Jérôme

    2017-01-01

    We have recently introduced the Vernier-based Direct Frequency Comb Cavity-Enhanced Spectroscopy technique which allows us to record broadband spectra at high sensitivity and GHz resolution (Rutkowski and Morville, 2014) [1]. We discuss here the effect of Vernier filtering on the observed lineshapes in the 3 ν + δ band of water vapor and the entire A-band of oxygen around 800 nm in ambient air. We derive expressions for the absorption profiles resulting from the continuous Vernier filtering method, testing them on spectra covering more than 2000 cm-1 around 12,500 cm-1. With 31,300 independent spectral elements acquired at the second time scale, an absorption baseline noise of 2 ×10-8cm-1 is obtained, providing a figure of merit of 1.1×10-10 cm-1/√{ Hz } per spectral element with a cavity finesse of 3000 and a cavity round-trip length around 3.3 m.

  7. 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

  8. 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...

  9. Characteristic analysis of the optical delay in frequency response of resonant cavity enhanced (RCE) photodetectors

    Institute of Scientific and Technical Information of China (English)

    Guo Jian-Chuan; Zuo Yu-Hua; Zhang Yun; Ding Wu-Chang; Cheng Bu-Wen; Yu Jin-Zhong; Wang Qi-Ming

    2009-01-01

    With consideration of the modulation frequency of the input lightwave itself, we present a new model to calculate the quantum efficiency of RCE p-i-n photodetectors (PD) by superimposition of multiple reflected lightwaves. For the first time, the optical delay, another important factor limiting the electrical bandwidth of RCE p-i-n PD excluding the transit time of the carriers and RCd response of the photodetector, is analyzed and discussed in detail. The optical delay dominates the bandwidth of RCE p-i-n PD when its active layer is thinner than several 10 nm. These three limiting factors must be considered exactly for design of ultra-high-speed RCE p-i-n PD.

  10. Realization of 1.5 W 780 nm single-frequency laser by using cavity-enhanced frequency doubling of an EDFA boosted 1560 nm diode laser

    Science.gov (United States)

    Ge, Yulong; Guo, Shanlong; Han, Yashuai; Wang, Junmin

    2015-01-01

    We demonstrated a continuous-wave (CW) 780 nm laser with Watt-level output power by using external-cavity-enhanced frequency doubling of an Erbium-doped fiber amplifier (EDFA) boosted 1560 nm diode laser in a periodically-poled magnesium-oxide-doped lithium niobate (PPMgO:LN) bulk crystal. A 780 nm laser with maximum output power of 1.5 W is obtained at an incident 1560 nm laser of 2.05 W, corresponding to a doubling efficiency of 73%. The typical fluctuation of 780 nm laser's power is 1.2% (rms) in about 30 min. This 780 nm laser can be potentially applied to laser cooling and manipulation of rubidium atoms, generating 1560 nm squeezed vacuum field as well as 1560 nm continuous-variable entanglement based on optical parametric oscillator if additional locking and noise suppression is applied.

  11. Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies.

    Science.gov (United States)

    Knight, S; Schöche, S; Darakchieva, V; Kühne, P; Carlin, J-F; Grandjean, N; Herzinger, C M; Schubert, M; Hofmann, T

    2015-06-15

    The effect of a tunable, externally coupled Fabry-Perot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a traditional Drude-like two-dimensional electron gas is shown and discussed in this Letter. As a result, the detection of optical Hall effect signatures at conveniently obtainable magnetic fields, for example, by neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high-electron mobility transistor structure grown on a sapphire substrate is used for the experiment. The optical Hall effect signatures and their dispersions, which are governed by the frequency and the reflectance minima and maxima of the externally coupled Fabry-Perot cavity, are presented and discussed. Tuning the externally coupled Fabry-Perot cavity strongly modifies the optical Hall effect signatures, which provides a new degree of freedom for optical Hall effect experiments in addition to frequency, angle of incidence, and magnetic field direction and strength.

  12. Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared - application to trace detection of H2O2

    CERN Document Server

    Foltynowicz, Aleksandra; Fleisher, Adam J; Bjork, Bryce; Ye, Jun

    2012-01-01

    We demonstrate the first cavity-enhanced optical frequency comb spectroscopy in the mid-infrared wavelength region and report the sensitive real-time trace detection of hydrogen peroxide in the presence of a large amount of water. The experimental apparatus is based on a mid-infrared optical parametric oscillator synchronously pumped by a high power Yb:fiber laser, a high finesse broadband cavity, and a fast-scanning Fourier transform spectrometer with autobalancing detection. The comb spectrum with a bandwidth of 200 nm centered around 3.75 {\\mu}m is simultaneously coupled to the cavity and both degrees of freedom of the comb, i.e., the repetition rate and carrier envelope offset frequency, are locked to the cavity to ensure stable transmission. The autobalancing detection scheme reduces the intensity noise by a factor of 300, and a sensitivity of 5.4 {\\times} 10^-9 cm^-1 Hz^-1/2 with a resolution of 800 MHz is achieved (corresponding to 6.9 {\\times} 10^-11 cm^-1 Hz^-1/2 per spectral element for 6000 resolve...

  13. Cavity enhanced atomic magnetometry

    CERN Document Server

    Crepaz, Herbert; Dumke, Rainer

    2015-01-01

    Atom sensing based on Faraday rotation is an indispensable method for precision measurements, universally suitable for both hot and cold atomic systems. Here we demonstrate an all-optical magnetometer where the optical cell for Faraday rotation spectroscopy is augmented with a low finesse cavity. Unlike in previous experiments, where specifically designed multipass cells had been employed, our scheme allows to use conventional, spherical vapour cells. Spherical shaped cells have the advantage that they can be effectively coated inside with a spin relaxation suppressing layer providing long spin coherence times without addition of a buffer gas. Cavity enhancement shows in an increase in optical polarization rotation and sensitivity compared to single-pass configurations.

  14. Cavity enhanced atomic magnetometry.

    Science.gov (United States)

    Crepaz, Herbert; Ley, Li Yuan; Dumke, Rainer

    2015-10-20

    Atom sensing based on Faraday rotation is an indispensable method for precision measurements, universally suitable for both hot and cold atomic systems. Here we demonstrate an all-optical magnetometer where the optical cell for Faraday rotation spectroscopy is augmented with a low finesse cavity. Unlike in previous experiments, where specifically designed multipass cells had been employed, our scheme allows to use conventional, spherical vapour cells. Spherical shaped cells have the advantage that they can be effectively coated inside with a spin relaxation suppressing layer providing long spin coherence times without addition of a buffer gas. Cavity enhancement shows in an increase in optical polarization rotation and sensitivity compared to single-pass configurations.

  15. 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.

  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. 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...

  19. Cavity-enhanced dual-comb spectroscopy

    CERN Document Server

    Bernhardt, Birgitta; Jacquet, Patrick; Jacquey, Marion; Kobayashi, Yohei; Udem, Thomas; Holzwarth, Ronald; Guelachvili, Guy; Hänsch, Theodor W; Picqué, Nathalie

    2009-01-01

    The sensitivity of molecular fingerprinting is dramatically improved when placing the absorbing sample in a high-finesse optical cavity, thanks to the large increase of the effective path-length. As demonstrated recently, when the equidistant lines from a laser frequency comb are simultaneously injected into the cavity over a large spectral range, multiple trace-gases may be identified within a few milliseconds. Analyzing efficiently the light transmitted through the cavity however still remains challenging. Here, a novel approach, cavity-enhanced frequency comb Fourier transform spectroscopy, fully overcomes this difficulty and measures ultrasensitive, broad-bandwidth, high-resolution spectra within a few tens of $\\mu$s. It could be implemented from the Terahertz to the ultraviolet regions without any need for detector arrays. We recorded, within 18 $\\mu$s, spectra of the 1.0 $\\mu$m overtone bands of ammonia spanning 20 nm with 4.5 GHz resolution and a noise-equivalent-absorption at one-second-averaging per ...

  20. Analysis of a four-mirror-cavity enhanced Michelson interferometer

    OpenAIRE

    Thüring, A.; Lück, H.; Danzmann, K.

    2005-01-01

    We investigate the shot noise limited sensitivity of a four-mirror cavity enhanced Michelson interferometer. The intention of this interferometer topology is the reduction of thermal lensing and the impact of the interferometers contrast although transmissive optics are used with high circulating powers. The analytical expressions describing the light fields and the frequency response are derived. Although the parameter space has 11 dimensions, a detailed analysis of the resonance feature giv...

  1. Analysis of a four-mirror-cavity enhanced Michelson interferometer.

    Science.gov (United States)

    Thüring, André; Lück, Harald; Danzmann, Karsten

    2005-12-01

    We investigate the shot-noise-limited sensitivity of a four-mirror-cavity enhanced Michelson interferometer. The intention of this interferometer topology is the reduction of thermal lensing and the impact of the interferometers contrast although transmissive optics are used with high circulating powers. The analytical expressions describing the light fields and the frequency response are derived. Although the parameter space has 11 dimensions, a detailed analysis of the resonance feature gives boundary conditions allowing systematic parameter studies.

  2. Differential cavity mode spectroscopy: A new cavity enhanced technique for the detection of weak transitions

    Energy Technology Data Exchange (ETDEWEB)

    Vine, Glenn de [Centre for Gravitational Physics, Faculty of Science, The Australian National University, Canberra ACT 0200 (Australia)], E-mail: glenn.devine@jpl.nasa.gov; McClelland, David E.; Gray, Malcolm B. [Centre for Gravitational Physics, Faculty of Science, The Australian National University, Canberra ACT 0200 (Australia)

    2008-06-16

    We present a new cavity enhanced, continuous wave spectroscopic technique for the detection of weak atomic and molecular transitions. Differential Cavity Mode Spectroscopy (DCMS) measures the difference in absorption between two adjacent cavity longitudinal modes to yield a highly sensitive, yet relatively simple, cavity enhanced spectroscopic technique. In addition this relative absorption measurement is, to first order, independent of both laser frequency noise and cavity acoustic noise. Here we present both a theoretical description of this new technique and an initial experimental demonstration.

  3. Direct frequency comb measurement of OD + CO → DOCO kinetics.

    Science.gov (United States)

    Bjork, B J; Bui, T Q; Heckl, O H; Changala, P B; Spaun, B; Heu, P; Follman, D; Deutsch, C; Cole, G D; Aspelmeyer, M; Okumura, M; Ye, J

    2016-10-28

    The kinetics of the hydroxyl radical (OH) + carbon monoxide (CO) reaction, which is fundamental to both atmospheric and combustion chemistry, are complex because of the formation of the hydrocarboxyl radical (HOCO) intermediate. Despite extensive studies of this reaction, HOCO has not been observed under thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observed deuteroxyl radical (OD) + CO reaction kinetics and detected stabilized trans-DOCO, the deuterated analog of trans-HOCO. By simultaneously measuring the time-dependent concentrations of the trans-DOCO and OD species, we observed unambiguous low-pressure termolecular dependence of the reaction rate coefficients for N2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield.

  4. 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.

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

    Science.gov (United States)

    Allison, Thomas K.

    2017-02-01

    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, 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 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.

  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. Shock-Tube Measurement of Acetone Dissociation Using Cavity-Enhanced Absorption Spectroscopy of CO.

    Science.gov (United States)

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

    2015-07-16

    A direct measurement for the rate constant of the acetone dissociation reaction (CH3COCH3 = CH3CO + CH3) was conducted behind reflected shock wave, utilizing a sub-ppm sensitivity CO diagnostic achieved by cavity-enhanced absorption spectroscopy (CEAS). The current experiment eliminated the influence from secondary reactions and temperature change by investigating the clean pyrolysis of shock-tube kinetics studies.

  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. Hybrid III-V/SOI resonant cavity enhanced photodetector

    DEFF Research Database (Denmark)

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

    2016-01-01

    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...

  13. Measurement of glyoxal using an incoherent broadband cavity enhanced absorption spectrometer

    Directory of Open Access Journals (Sweden)

    R. A. Washenfelder

    2008-12-01

    Full Text Available We describe an instrument for simultaneous measurements of glyoxal (CHOCHO and nitrogen dioxide (NO2 using cavity enhanced absorption spectroscopy with a broadband light source. The output of a Xenon arc lamp is coupled into a 1 m optical cavity, and the spectrum of light exiting the cavity is recorded by a grating spectrometer with a charge-coupled device (CCD array detector. The mirror reflectivity and effective path lengths are determined from the known Rayleigh scattering of He and dry zero air (N2+O2. Least-squares fitting, using published reference spectra, allow the simultaneous retrieval of CHOCHO, NO2, O4, and H2O in the 441 to 469 nm spectral range. For a 1-min sampling time, the precision (±1σ on signal for measurements of CHOCHO and NO2 is 29 pptv and 20 pptv, respectively. We directly compare measurements made with the incoherent broadband cavity enhanced absorption spectrometer with those from cavity ringdown instruments detecting CHOCHO and NO2 at 404 and 532 nm, respectively, and find linear agreement over a wide range of concentrations. The instrument has been tested in the laboratory with both synthetic and real air samples, and the demonstrated sensitivity and specificity suggest a strong potential for field measurements of both CHOCHO and NO2.

  14. Cavity-enhanced Raman microscopy of individual carbon nanotubes

    Science.gov (United States)

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

    2016-07-01

    Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here, we demonstrate Purcell enhancement of Raman scattering in a tunable high-finesse microcavity, and utilize it for molecular diagnostics by combined Raman and absorption imaging. Studying individual single-wall carbon nanotubes, we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross-section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60%. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman transitions involving localized excitons could potentially be used for gaining quantum control over nanomechanical motion and open a route for molecular cavity optomechanics.

  15. Design of cavity-enhanced absorption cell for reducing transit-time broadening.

    Science.gov (United States)

    Abe, Masashi; Iwakuni, Kana; Okubo, Sho; Sasada, Hiroyuki

    2014-09-15

    To reduce the linewidth of Lamb dips, we introduce a cavity-enhanced absorption cell (CEAC) coupled with a Gaussian beam with a 1.9-mm 1/e(2) radius at the beam waist for the reduction of transit-time broadening. We state that transit-time broadening depends only on the beam radius at the beam waist. This fact is useful for the design of the CEAC, and a pair of concave and convex mirrors is thereby employed. We have carried out sub-Doppler resolution spectroscopy of the ν(3) band of CH(4) and the ν(1) band of CH(3)D using a difference-frequency-generation source and the CEAC, and the recorded Lamb dips narrow to 80 kHz (HWHM).

  16. 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.

  17. Gas trace detection with cavity enhanced absorption spectroscopy: a review of its process in the field

    Science.gov (United States)

    Liu, Siqi; Luo, Zhifu; Tan, Zhongqi; Long, Xingwu

    2016-11-01

    Cavity-enhanced absorption spectroscopy (CEAS) is a technology in which the intracavity absorption is deduced from the intensity of light transmitted by the high finesse optical cavity. Then the samples' parameters, such as their species, concentration and absorption cross section, would be detection. It was first proposed and demonstrated by Engeln R. [1] and O'Keefe[2] in 1998. This technology has extraordinary detection sensitivity, high resolution and good practicability, so it is used in many fields , such as clinical medicine, gas detection and basic physics research. In this paper, we focus on the use of gas trace detection, including the advance of CEAS over the past twenty years, the newest research progresses, and the prediction of this technology's development direction in the future.

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

    Science.gov (United States)

    Axner, Ove; Ehlers, Patrick; Hausmaninger, Thomas; Silander, Isak; Ma, Weiguang

    2014-10-01

    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 atmospheric

  19. 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.

  20. Measurement of glyoxal using an incoherent broadband cavity enhanced absorption spectrometer

    Directory of Open Access Journals (Sweden)

    R. A. Washenfelder

    2008-08-01

    Full Text Available We describe an instrument for simultaneous measurements of glyoxal (CHOCHO and nitrogen dioxide (NO2 using cavity enhanced absorption spectroscopy with a broadband light source. The output of a Xenon arc lamp is coupled into a 1 m optical cavity, and the spectrum of light exiting the cavity is recorded by a grating spectrometer with a charge-coupled device (CCD array detector. The mirror reflectivity and effective path lengths are determined from the known Rayleigh scattering of He and dry zero air (N2+O2. Least-squares fitting, using published reference spectra, allow the simultaneous retrieval of CHOCHO, NO2, O4, and H2O in the 441 to 469 nm spectral range. For a 1-min sampling time, the minimum detectable absorption is 4×10−10 cm−1, and the precision (±1σ on signal for measurements of CHOCHO and NO2 is 29 pptv and 20 pptv, respectively. We directly compare the incoherent broadband cavity enhanced absorption spectrometer to 404 and 532 nm cavity ringdown instruments for CHOCHO and NO2 detection, and find linear agreement over a wide range of concentrations. The instrument has been tested in the laboratory with both synthetic and real air samples, and the demonstrated sensitivity and specificity suggest a strong potential for field measurements of both CHOCHO and NO2.

  1. 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.

  2. 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.

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

    Science.gov (United States)

    Leen, J Brian; O'Keefe, Anthony

    2014-09-01

    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)/√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. Direct Load Control by AC Frequency Modulation

    DEFF Research Database (Denmark)

    Douglass, Philip James; You, Shi

    2012-01-01

    Fine-grained under frequency load shedding called “demand as a frequency controlled reserve“ (DFCR) has been shown to be a promising method of providingfrequency regulation service from distributed loads [1]. Micro-grids with a large portion of intermittent renewable generation will benefit great...

  5. Frequency detuning effects for parametrically and directly excited elastic structures

    DEFF Research Database (Denmark)

    Neumeyer, Stefan; van Gastel, M. H. M.; Sorokin, Vladislav;

    2015-01-01

    This study investigates the frequency detuning effects of parametric and direct excitation for near-resonant nonlinear structural vibrations. Specifically, the detuning effects of a two-to-one frequency ratio between the parametric and direct excitation, and of a drift in natural frequency, are s...

  6. 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...

  7. Measurements of Iodine Monoxide Levels During the CAST Campaign Using Broadband Cavity Enhanced Absorption Spectroscopy

    Science.gov (United States)

    Harris, N. R. P.; Popoola, O. A.; McLeod, M.; Ouyang, B.; Jones, R. L.

    2014-12-01

    Iodine monoxide (IO) has been regarded as an important radical involved in the ozone destruction in the remote marine boundary layer. Here we presented the first in situ aircraft measurements of IO using broadband cavity enhanced absorption spectroscopy with 1s -sensitivity of ~1.5 ppt Hz-1/2 on the surface level during the Coordinated Airborne Studies in the Tropics (CAST) campaign between January - February 2014. IO was retrieved from analysis of absorption spectrum recorded between 415 nm - 452.5 nm. Instrument baseline corresponding to the "zero" signal of IO was obtained by injection of ~20 ppb of nitric oxide (NO) into the sample air at chosen frequency and period. No clear absorption feature was observable from the spectra by eye with up to 100 seconds averaging, pointing to very low mixing ratios (<~0.5 ppt) of IO over the sampled area. A small positive bias (~0.3 ppt) of IO (against the baseline signal during NO titration) was obtained in the statistical histogram of retrieved IO from average of each straight and level run, but little altitude dependence was noted. In summary, our observation appears to support the existence of IO in the remote marine boundary above the Pacific Ocean at sub ppt levels, but the limited sensitivity precludes us from quantifying spatial gradients more accurately.

  8. Cavity enhanced telecom heralded single photons for spin-wave solid state quantum memories

    Science.gov (United States)

    Rieländer, Daniel; Lenhard, Andreas; Mazzera, Margherita; de Riedmatten, Hugues

    2016-12-01

    We report on a source of heralded narrowband (≈ 3 MHz) single photons compatible with solid-state spin-wave quantum memories based on praseodymium doped crystals. Widely non-degenerate narrow-band photon pairs are generated using cavity enhanced down conversion. One photon from the pair is at telecom wavelengths and serves as heralding signal, while the heralded single photon is at 606 nm, resonant with an optical transition of Pr3+:Y2SiO5. The source offers a heralding efficiency of 28% and a generation rate exceeding 2000 pairs mW-1 in a single-mode. The single photon nature of the heralded field is confirmed by a direct antibunching measurement, with a measured antibunching parameter down to 0.010(4). Moreover, we investigate in detail photon cross- and autocorrelation functions proving non-classical correlations between the two photons. The results presented in this paper offer prospects for the demonstration of single photon spin-wave storage in an on-demand solid state quantum memory, heralded by a telecom photon.

  9. Isotopic gas analysis through Purcell cavity enhanced Raman scattering

    Science.gov (United States)

    Petrak, B.; Cooper, J.; Konthasinghe, K.; Peiris, M.; Djeu, N.; Hopkins, A. J.; Muller, A.

    2016-02-01

    Purcell enhanced Raman scattering (PERS) by means of a doubly resonant Fabry-Perot microcavity (mode volume ≈ 100 μm3 and finesse ≈ 30 000) has been investigated as a technique for isotopic ratio gas analysis. At the pump frequency, the resonant cavity supports a buildup of circulating power while simultaneously enabling Purcell spontaneous emission rate enhancement at the resonant Stokes frequency. The three most common isotopologues of CO2 gas were quantified, and a signal was obtained from 13C16O2 down to a partial pressure of 2 Torr. Due to its small size and low pump power needed (˜10 mW) PERS lends itself to miniaturization. Furthermore, since the cavity is resonant with the emission frequency, future improvements could allow it to serve as its own spectral analyzer and no separate spectroscopic device would be needed.

  10. Tunable Resonant-Cavity-Enhanced Photodetector with Double High-Index-Contrast Grating Mirrors

    DEFF Research Database (Denmark)

    Learkthanakhachon, Supannee; Yvind, Kresten; Chung, Il-Sug

    2013-01-01

    In this paper, we propose a broadband-tunable resonant-cavity-enhanced photodetector (RCE-PD) structure with double high-index-contrast grating (HCG) mirrors and numerically investigate its characteristics. The detector is designed to operate at 1550-nm wavelength. The detector structure consists...

  11. Cavity-Enhanced Ultrafast Spectroscopy: Ultrafast Meets Ultrasensitive

    Science.gov (United States)

    Allison, Thomas K.; Reber, Melanie Roberts; Chen, Yuning

    2016-06-01

    Ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and 2D-spectroscopy, are widely used across many disciplines. However, these techniques are typically restricted to optically thick samples, such as solids and liquid solutions. Using a frequency comb laser and optical cavities, we present a new technique for performing ultrafast optical spectroscopy with high sensitivity, enabling work in dilute gas-phase molecular beams. Resonantly enhancing the probe pulses, we demonstrate transient absorption measurements with a detection limit of ΔOD = 2 × 10-10 (1 × 10-9/√{Hz}). 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 ≈ 10-8, or column densities oise performance of CE-TAS. (a), Transient absorption measurements taken with reduced gas flow and perpendicular polarizations. The red dots represent the average of 60 consecutive scans taken over a 1 hour period. Black curves are every 10th scan from the data set. Inset: Zoom-in around 0.8 ps delay. Error bars represent the uncertainty in the mean. (b), The green squares show the average of the Allan deviations obtained independently for each delay point. Error bars here are the standard deviation (not the uncertainty in the mean) of this ensemble, to represent the spread in the data. The blue diamond is the average of the error bars of (a), along with their standard deviation. The grey line has a slope of -1/2 on the log-log plot, the expected slope for white noise performance

  12. Measurement of aerosol optical properties by cw cavity enhanced spectroscopy

    Science.gov (United States)

    Jie, Guo; Ye, Shan-Shan; Yang, Xiao; Han, Ye-Xing; Tang, Huai-Wu; Yu, Zhi-Wei

    2016-10-01

    The CAPS (Cavity Attenuated Phase shift Spectroscopy) system, which detects the extinction coefficients within a 10 nm bandpass centered at 532 nm, comprises a green LED with center wavelength in 532nm, a resonant optical cavity (36 cm length), a Photo Multiplier Tube detector, and a lock in amplifier. The square wave modulated light from the LED passes through the optical cavity and is detected as a distorted waveform which is characterized by a phase shift with respect to the initial modulation. Extinction coefficients are determined from changes in the phase shift of the distorted waveform of the square wave modulated LED light that is transmitted through the optical cavity. The performance of the CAPS system was evaluated by using measurements of the stability and response of the system. The minima ( 0.1 Mm-1) in the Allan plots show the optimum average time ( 100s) for optimum detection performance of the CAPS system. In the paper, it illustrates that extinction coefficient was correlated with PM2.5 mass (0.91). These figures indicate that this method has the potential to become one of the most sensitive on-line analytical techniques for extinction coefficient detection. This work aims to provide an initial validation of the CAPS extinction monitor in laboratory and field environments. Our initial results presented in this paper show that the CAPS extinction monitor is capable of providing state-of-the-art performance while dramatically reducing the complexity of optical instrumentation for directly measuring the extinction coefficients.

  13. A frequency selective acoustic transducer for directional Lamb wave sensing.

    Science.gov (United States)

    Senesi, Matteo; Ruzzene, Massimo

    2011-10-01

    A frequency selective acoustic transducer (FSAT) is proposed for directional sensing of guided waves. The considered FSAT design is characterized by a spiral configuration in wavenumber domain, which leads to a spatial arrangement of the sensing material producing output signals whose dominant frequency component is uniquely associated with the direction of incoming waves. The resulting spiral FSAT can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels. The analytical expression of the shape of the spiral FSAT is obtained through the theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. Testing is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The discrete array approximates the continuous spiral FSAT geometry, and provides the flexibility to test several configurations. The experimental results demonstrate the strong frequency dependent directionality of the spiral FSAT and suggest its application for frequency selective acoustic sensors, to be employed for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health.

  14. Quantum secure direct communication with frequency coding scheme

    Science.gov (United States)

    Zhao, Xue-Liang; Ruan, Dong

    2016-11-01

    Quantum secure direct communication (QSDC) is an important branch of quantum cryptography. It can transmit secret information directly without establishing a key first, unlike quantum key distribution which requires this precursive event. One of the most highlighted QSDC protocol is the Two-step protocol. This paper will focus on proposing a frequency coding scheme in the Two-step protocol, while retaining other contents of the QSDC protocol. This new coding scheme will significantly increase the protocol's ability against channel noise and loss, and provides an efficient protocol for secure direct quantum communication in a noisy environment. Besides, the frequency coding technology is also easy to understand and highly practical. After numerically simulating the performance of the protocol in a noisy channel, the results showed that the scheme was robust against channel noise and loss.

  15. Cavity-enhanced laser cooling of solid-state materials in a standing-wave cavity

    Institute of Scientific and Technical Information of China (English)

    Youhua Jia; Biao Zhong; Jianping Yin

    2008-01-01

    We propose a new method to cool the Yba+-doped ZBLANP glass in a standing-wave cavity. There are two advantages of this cavity-enhanced technique: the pumping power is greatly enhanced and the absorption of the cooling material is greatly increased. We introduce the basic principle of the cavity-enhanced laser cooling and discuss the cooling effect of a solid-state material in a cavity. From the theoretical study, it is found that the laser cooling effect is strongly dependent on the reflectivity of the cavity mirrors, the length of the solid material, the surface scattering of the material, and so on. Some optimal parameters for efficient laser cooling are obtained.

  16. 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,...

  17. Frequency comb velocity-modulation spectroscopy.

    Science.gov (United States)

    Sinclair, Laura C; Cossel, Kevin C; Coffey, Tyler; Ye, Jun; Cornell, Eric A

    2011-08-26

    We have demonstrated a new technique that provides massively parallel comb spectroscopy sensitive specifically to ions through the combination of cavity-enhanced direct frequency comb spectroscopy with velocity-modulation spectroscopy. Using this novel system, we have measured electronic transitions of HfF⁺ and achieved a fractional absorption sensitivity of 3×10⁻⁷ recorded over 1500 simultaneous channels spanning 150  cm⁻¹ around 800 nm with an absolute frequency accuracy of 30 MHz (0.001  cm⁻¹). A fully sampled spectrum consisting of interleaved measurements is acquired in 30 min.

  18. Frequency Comb Velocity-Modulation Spectroscopy

    CERN Document Server

    Sinclair, Laura C; Coffey, Tyler; Ye, Jun; Cornell, Eric A

    2011-01-01

    We have demonstrated a new technique that provides massively parallel comb spectroscopy sensitive specifically to ions through the combination of cavity-enhanced direct frequency comb spectroscopy with velocity modulation spectroscopy. Using this novel system, we have measured electronic transitions of HfF+ and achieved a fractional absorption sensitivity of 3 x 10-7 recorded over 1500 simultaneous channels spanning 150 cm-1 around 800 nm with an absolute frequency accuracy of 30 MHz (0.001 cm-1). A fully sampled spectrum consisting of interleaved measurements is acquired in 30 minutes.

  19. 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.

  20. [Near infrared Cavity enhanced absorption spectroscopy study of NO2O].

    Science.gov (United States)

    Wu, Zhi-wei; Dong, Yan-ting; Zhou, Wei-dong

    2014-08-01

    Using a tunable near infrared external cavity diode laser and a 650 mm long high finesse optical cavity consisting of two highly reflective (R=99.97% at 6561.39 cm(-1)) plan-concave mirrors of curvature radius approximately 1000 mm, a cavity enhanced absorption spectroscopy (CEAS) system was made. The absorption spectra centered at 6561.39 cm(-1) of pure N2O gas and gas mixtures of N2O and N2 were recorded. According to the absorption of N2O at 6561.39 cm(-1) in the cavity, the measured effective absorption path was about 1460 km. The spectra line intensity and line-width of N2O centered at 6561.39 cm(-1) were carefully studied. The relationship between the line-width of absorption spectra and the gas pressure was derived. The pressure broadening parameter of N2 gas for NO2O line centered at 6 561. 39 cm(-1) was deduced and given a value of approximately (0.114 +/- 0.004) cm(-1) x atm(-1). The possibility to detect trace N2O gas in mixture using this CEAS system was investigated. By recording the ab- sorption spectra of N2O gas mixtures at different concentration, the relationship between the line intensity and gas concentration was derived. The minimum detectable absorption was found to be 2.34 x 10(-7) cm(-1) using this cavity enhanced absorption spectroscopy system. And te measurement precision in terms of relative standard deviation (RSD) for N2O is approximately 1.73%, indicating the possibility of using the cavity enhanced absorption spectroscopy system for micro gas N2O analysis in the future.

  1. New resonant cavity-enhanced absorber structures for mid-infrared detector application

    CERN Document Server

    Zohar, Moshe; 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 conventional resonant cavity enhanced HgCdTe absorber, while maintaining a fairly good tolerance against the grating's fabrication errors.

  2. Modeling and Simulation of a Resonant-Cavity-Enhanced InGaAs/GaAs Quantum Dot Photodetector

    Directory of Open Access Journals (Sweden)

    W. W. Wang

    2015-01-01

    Full Text Available We simulated and analyzed a resonant-cavity-enhancedd InGaAs/GaAs quantum dot n-i-n photodiode using Crosslight Apsys package. The resonant cavity has a distributed Bragg reflector (DBR at one side. Comparing with the conventional photodetectors, the resonant-cavity-enhanced photodiode (RCE-PD showed higher detection efficiency, faster response speed, and better wavelength selectivity and spatial orientation selectivity. Our simulation results also showed that when an AlAs layer is inserted into the device structure as a blocking layer, ultralow dark current can be achieved, with dark current densities 0.0034 A/cm at 0 V and 0.026 A/cm at a reverse bias of 2 V. We discussed the mechanism producing the photocurrent at various reverse bias. A high quantum efficiency of 87.9% was achieved at resonant wavelength of 1030 nm with a FWHM of about 3 nm. We also simulated InAs QD RCE-PD to compare with InGaAs QD. At last, the photocapacitance characteristic of the model has been discussed under different frequencies.

  3. Time-Resolved Broadband Cavity-Enhanced Absorption Spectroscopy behind Shock Waves.

    Science.gov (United States)

    Matsugi, Akira; Shiina, Hiroumi; Oguchi, Tatsuo; Takahashi, Kazuo

    2016-04-07

    A fast and sensitive broadband absorption technique for measurements of high-temperature chemical kinetics and spectroscopy has been developed by applying broadband cavity-enhanced absorption spectroscopy (BBCEAS) in a shock tube. The developed method has effective absorption path lengths of 60-200 cm, or cavity enhancement factors of 12-40, over a wavelength range of 280-420 nm, and is capable of simultaneously recording absorption time profiles over an ∼32 nm spectral bandpass in a single experiment with temporal and spectral resolutions of 5 μs and 2 nm, respectively. The accuracy of the kinetic and spectroscopic measurements was examined by investigating high-temperature reactions and absorption spectra of formaldehyde behind reflected shock waves using 1,3,5-trioxane as a precursor. The rate constants obtained for the thermal decomposition reactions of 1,3,5-trioxane (to three formaldehyde molecules) and formaldehyde (to HCO + H) agreed well with the literature data. High-temperature absorption cross sections of formaldehyde between 280 and 410 nm have been determined at the post-reflected-shock temperatures of 955, 1265, and 1708 K. The results demonstrate the applicability of the BBCEAS technique to time- and wavelength-resolved sensitive absorption measurements at high temperatures.

  4. 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.

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

    Science.gov (United States)

    Sergeant, Nicholas P; Niesen, Bjoern; Liu, Albert S; Boman, Lee; Stoessel, Chris; Heremans, Paul; Peumans, Peter; Rand, Barry P; Fan, Shanhui

    2013-05-01

    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 Zn(x)Sn(y)O(z)/Ag/In(x)Sn(y)O(z)) 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.

  6. Dual-recycled cavity-enhanced Michelson interferometer for gravitational-wave detection.

    Science.gov (United States)

    Müller, Guido; Delker, Tom; Tanner, David B; Reitze, David

    2003-03-01

    The baseline design for an Advanced Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO) is a dual-recycled Michelson interferometer with cavities in each of the Michelson interferometer arms. We describe one possible length-sensing and control scheme for such a dual-recycled, cavity-enhanced Michelson interferometer. We discuss the principles of this scheme and derive the first-order sensing signals. We also present a successful experimental verification of our length-sensing system using a prototype tabletop interferometer. Our results demonstrate the robustness of the scheme against deviations from the idealized design. We also identify potential weaknesses and discuss possible improvements. These results as well as other benchtop experiments that we present form the basis for a sensing and control scheme for Advanced LIGO.

  7. Cavity-enhanced eigenmode and angular hybrid multiplexing in holographic data storage systems.

    Science.gov (United States)

    Miller, Bo E; Takashima, Yuzuru

    2016-12-26

    Resonant optical cavities have been demonstrated to improve energy efficiencies in Holographic Data Storage Systems (HDSS). The orthogonal reference beams supported as cavity eigenmodes can provide another multiplexing degree of freedom to push storage densities toward the limit of 3D optical data storage. While keeping the increased energy efficiency of a cavity enhanced reference arm, image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe:LiNbO3 medium with a 532 nm laser at two Bragg angles. We experimentally confirmed write rates are enhanced by an average factor of 1.1, and page crosstalk is about 2.5%. This hybrid multiplexing opens up a pathway to increase storage density while minimizing modification of current angular multiplexing HDSS.

  8. 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.

  9. Scalable high-precision tuning of photonic resonators by resonant cavity-enhanced photoelectrochemical etching

    Science.gov (United States)

    Gil-Santos, Eduardo; Baker, Christopher; Lemaître, Aristide; Gomez, Carmen; Leo, Giuseppe; Favero, Ivan

    2017-01-01

    Photonic lattices of mutually interacting indistinguishable cavities represent a cornerstone of collective phenomena in optics and could become important in advanced sensing or communication devices. The disorder induced by fabrication technologies has so far hindered the development of such resonant cavity architectures, while post-fabrication tuning methods have been limited by complexity and poor scalability. Here we present a new simple and scalable tuning method for ensembles of microphotonic and nanophotonic resonators, which enables their permanent collective spectral alignment. The method introduces an approach of cavity-enhanced photoelectrochemical etching in a fluid, a resonant process triggered by sub-bandgap light that allows for high selectivity and precision. The technique is presented on a gallium arsenide nanophotonic platform and illustrated by finely tuning one, two and up to five resonators. It opens the way to applications requiring large networks of identical resonators and their spectral referencing to external etalons.

  10. Near-infrared broad-band cavity enhanced absorption spectroscopy using a superluminescent light emitting diode.

    Science.gov (United States)

    Denzer, W; Hamilton, M L; Hancock, G; Islam, M; Langley, C E; Peverall, R; Ritchie, G A D

    2009-11-01

    A fibre coupled near-infrared superluminescent light emitting diode that emits approximately 10 mW of radiation between 1.62 and 1.7 microm is employed in combination with a broad-band cavity enhanced spectrometer consisting of a linear optical cavity with mirrors of reflectivity approximately 99.98% and either a dispersive near-infrared spectrometer or a Fourier transform interferometer. Results are presented on the absorption of 1,3-butadiene, and sensitivities are achieved of 6.1 x 10(-8) cm(-1) using the dispersive spectrometer in combination with phase-sensitive detection, and 1.5 x 10(-8) cm(-1) using the Fourier transform interferometer (expressed as a minimum detectable absorption coefficient) over several minutes of acquisition time.

  11. Cavity enhanced detection methods for probing the dynamics of spin correlated radical pairs in solution

    Science.gov (United States)

    Neil, Simon R. T.; Maeda, Kiminori; Henbest, Kevin B.; Goez, Martin; Hemmens, Robert; Timmel, Christiane R.; Mackenzie, Stuart R.

    2010-04-01

    Cavity enhanced absorption spectroscopy (CEAS) combined with phase-sensitive detection is employed to study the effects of static magnetic fields on radical recombination reactions. The chemical system comprises the photochemically generated thionine semiquinone radical and a 1,4-diazabicyclo[2.2.2]octane (DABCO) cationic radical in a micellar solution of sodium dodecyl sulphate. Data obtained using the modulated CEAS technique, describing the magnetic field effect (MFE) on reaction yields, are shown to be superior to those obtained using conventional transient absorption (TA) flash photolysis methods typically employed for these measurements. The high sensitivity afforded by modulated CEAS detection is discussed in terms of the new possibilities it offers such as the measurement of magnetic field effects in real biological systems which have hitherto been largely beyond the detection capabilities of existing techniques.

  12. Sensitive and rapid laser diagnostic for shock tube kinetics studies using cavity-enhanced absorption spectroscopy.

    Science.gov (United States)

    Sun, Kai; Wang, Shengkai; Sur, Ritobrata; Chao, Xing; Jeffries, Jay B; Hanson, Ronald K

    2014-04-21

    We report the first application of cavity-enhanced absorption spectroscopy (CEAS) using a coherent light source for sensitive and rapid gaseous species time-history measurements in a shock tube. Off-axis alignment and fast scanning of the laser wavelength were used to minimize coupling noise in a low-finesse cavity. An absorption gain factor of 83 with a measurement time resolution of 20 µs was demonstrated for C2H2 detection using a near-infrared transition near 1537 nm, corresponding to a noise-equivalent detection limit of 20 ppm at 296 K and 76 ppm at 906 K at 50 kHz. This substantial gain in signal, relative to conventional single-pass absorption, will enable ultra-sensitive species detection in shock tube kinetics studies, particularly useful for measurements of minor species and for studies of dilute reactive systems.

  13. Diagnosis of Multiple Gases Separated from Transformer Oil Using Cavity-Enhanced Raman Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Yun; XIA Yu-Xing; HUANG Ju-Ming; ZHAN Li

    2008-01-01

    The Raman signal of gas molecules is very weak due to its small scattering cross section. Here, a near-confocal cavity-enhanced Raman detection system is demonstrated. In the cavity, a high power light of 9 W is achieved by using a cw 200mW 532nm laser, which greatly enhances the detection sensitivity of gas species. A photomultiplier tube connected to a spectrometer is used as the detection system. The Raman spectra of the mixed gases separated from transformer oil has been observed. The relationship of absolute Raman intensity and gas pressure is also obtained. To our knowledge, this is the first Raman system to detect the gases separated from transformer oil.

  14. Cavity-enhanced Faraday rotation measurement with auto-balanced photodetection.

    Science.gov (United States)

    Chang, Chia-Yu; Shy, Jow-Tsong

    2015-10-01

    Optical cavity enhancement for a tiny Faraday rotation is demonstrated with auto-balanced photodetection. This configuration is analyzed using the Jones matrix formalism. The resonant rotation signal is amplified, and thus, the angular sensitivity is improved. In the experiment, the air Faraday rotation is measured with an auto-balanced photoreceiver in single-pass and cavity geometries. The result shows that the measured Faraday rotation in the single-pass geometry is enhanced by a factor of 85 in the cavity geometry, and the sensitivity is improved to 7.54×10(-10)  rad Hz(-1/2), which agrees well with the Jones matrix analysis. With this verification, we propose an AC magnetic sensor whose magnetic sensitivity is expected to achieve 10  pT Hz(-1/2).

  15. 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.

  16. 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.

  17. 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.

  18. Shock-tube measurements of excited oxygen atoms using cavity-enhanced absorption spectroscopy.

    Science.gov (United States)

    Nations, Marcel; Wang, Shengkai; Goldenstein, Christopher S; Sun, Kai; Davidson, David F; Jeffries, Jay B; Hanson, Ronald K

    2015-10-10

    We report the use of cavity-enhanced absorption spectroscopy (CEAS) using two distributed feedback diode lasers near 777.2 and 844.6 nm for sensitive, time-resolved, in situ measurements of excited-state populations of atomic oxygen in a shock tube. Here, a 1% O2/Ar mixture was shock-heated to 5400-8000 K behind reflected shock waves. The combined use of a low-finesse cavity, fast wavelength scanning of the lasers, and an off-axis alignment enabled measurements with 10 μs time response and low cavity noise. The CEAS absorption gain factors of 104 and 142 for the P35←S520 (777.2 nm) and P0,1,23←S310 (844.6 nm) atomic oxygen transitions, respectively, significantly improved the detection sensitivity over conventional single-pass measurements. This work demonstrates the potential of using CEAS to improve shock-tube studies of nonequilibrium electronic-excitation processes at high temperatures.

  19. Applications of broadband cavity enhanced spectroscopy for measurements of trace gases and aerosols

    Science.gov (United States)

    Washenfelder, R. A.; Attwood, A. R.; Brock, C. A.; Brown, S. S.; Dube, W. P.; Flores, J. M.; Langford, A. O.; Min, K. E.; Rudich, Y.; Stutz, J.; Wagner, N.; Young, C.; Zarzana, K. J.

    2015-12-01

    Broadband cavity enhanced spectroscopy (BBCES) uses a broadband light source, optical cavity, and multichannel detector to measure light extinction with high sensitivity. This method differs from cavity ringdown spectroscopy, because it uses an inexpensive, incoherent light source and allows optical extinction to be determined simultaneously across a broad wavelength region.Spectral fitting methods can be used to retrieve multiple absorbers across the observed wavelength region. We have successfully used this method to measure glyoxal (CHOCHO), nitrous acid (HONO), and nitrogen dioxide (NO2) from ground-based and aircraft-based sampling platforms. The detection limit (2-sigma) in 5 s for retrievals of CHOCHO, HONO and NO2 is 32, 250 and 80 parts per trillion (pptv).Alternatively, gas-phase absorbers can be chemically removed to allow the accurate determination of aerosol extinction. In the laboratory, we have used the aerosol extinction measurements to determine scattering and absorption as a function of wavelength. We have deployed a ground-based field instrument to measure aerosol extinction, with a detection limit of approximately 0.2 Mm-1 in 1 min.BBCES methods are most widely used in the near-ultraviolet and visible spectral region. Recently, we have demonstrated measurements at 315-350 nm for formaldehyde (CH2O) and NO2. Extending the technique further into the ultraviolet spectral region will allow important additional measurements of trace gas species and aerosol extinction.

  20. Pattern-Directed Attention in Uncertain Frequency Detection.

    Science.gov (United States)

    1983-10-14

    performance when compared to a single frequency condition even if the listeners are aware that more than one signal can occur ( Creelman , 1960; Green...be missed. On the-other hand, the multiple band approach, introduced by Green (1958) and modified by Creelman (1960), assumes that listeners base...multiple-band approaches ( Creelman , 1960; Green, 1961; Macmillan & Schwartz, 1975). In general, the two views are difficult to distinguish empirically, and

  1. High-Speed Widely-Tunable 90% Quantum-Efficiency Resonant Cavity Enhanced p-i-n Photodiodes

    Science.gov (United States)

    1998-12-01

    REPORT unclassified b . ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 8:45am - 9...00am WB2 High-Speed Widely-Tunable >90% Quantum-Efficiency Resonant Cavity Enhanced p-i-n Photodiodes Necmi Biyiklia. Ibrahim Kimukinb. Orhan ...Bilkent, Ankara 06533, Turkey. b Department of Physics, Bilkent University, Bilkent, Ankara 06533, Turkey. c Department of Electrical and Computer

  2. 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.

  3. An off Axis Cavity Enhanced Absorption Spectrometer and a Rapid Scan Spectrometer with a Room-Temperature External Cavity Quantum Cascade Laser

    Science.gov (United States)

    Liu, Xunchen; Kang, Cheolhwa; Xu, Yunjie

    2009-06-01

    Quantum cascade laser (QCL) is a new type of mid-infrared tunable diode lasers with superior output power and mode quality. Recent developments, such as room temperature operation, wide frequency tunability, and narrow line width, make QCLs an ideal light source for high resolution spectroscopy. Two slit jet infrared spectrometers, namely an off-axis cavity enhanced absorption (CEA) spectrometer and a rapid scan spectrometer with an astigmatic multi-pass cell assembly, have been coupled with a newly purchased room temperature tunable mod-hop-free QCL with a frequency coverage from 1592 cm^{-1} to 1698 cm^{-1} and a scan rate of 0.1 cm^{-1}/ms. Our aim is to utilize these two sensitive spectrometers, that are equipped with a molecular jet expansion, to investigate the chiral molecules-(water)_n clusters. To demonstrate the resolution and sensitivity achieved, the rovibrational transitions of the static N_2O gas and the bending rovibrational transitions of the Ar-water complex, a test system, at 1634 cm^{-1} have been measured. D. Hofstetter and J. Faist in High performance quantum cascade lasers and their applications, Vol.89 Springer-Verlag Berlin & Heidelberg, 2003, pp. 61-98. Y. Xu, X. Liu, Z. Su, R. M. Kulkarni, W. S. Tam, C. Kang, I. Leonov and L. D'Agostino, Proc. Spie, 2009, 722208 (1-11). M. J. Weida and D. J. Nesbitt, J. Chem. Phys. 1997, 106, 3078-3089.

  4. Unification of Frequency direction Pilot-symbol Aided Channel Estimation (PACE) for OFDM

    DEFF Research Database (Denmark)

    Rom, Christian; Manchón, Carles Navarro; Deneire, Luc

    2007-01-01

    Frequency direction Pilot-symbol Aided Channel Estimation (PACE) for Orthogonal Frequency Division Multiplexing (OFDM) is crucial in high-rate wireless systems. The choice of an estimator for upcoming standards, such as the Long Term Evolution (LTE) of UTRA, has to take into account their specifi......Frequency direction Pilot-symbol Aided Channel Estimation (PACE) for Orthogonal Frequency Division Multiplexing (OFDM) is crucial in high-rate wireless systems. The choice of an estimator for upcoming standards, such as the Long Term Evolution (LTE) of UTRA, has to take into account...

  5. Tracing part-per-billion line shifts with direct-frequency-comb Vernier spectroscopy

    Science.gov (United States)

    Siciliani de Cumis, M.; Eramo, R.; Coluccelli, N.; Cassinerio, M.; Galzerano, G.; Laporta, P.; De Natale, P.; Cancio Pastor, P.

    2015-01-01

    Accurate frequency measurements of molecular transitions around 2 μ m are performed by using a direct-frequency-comb spectroscopy approach that combines an Er+ frequency-comb oscillator at 1.5 μ m , a Tm-Ho fiber amplifier, and a Fabry-Perot-filter, high-resolution dispersive spectrometer optical multiplex-detection system. This apparatus has unique performances in terms of a wide dynamic range to integrate the intensity per comb mode, which allows one to measure molecular absorption profiles with high precision. Spectroscopic information about transition frequencies and linewidths is very accurately determined. Relative frequency uncertainties of the order of a few parts in 10-9 are achieved for rovibrational transitions of the CO2 molecule around 5100 cm-1. Moreover, tiny frequency shifts due to molecular collisions and interacting laser power using direct comb spectroscopy are investigated in a systematic way.

  6. Using active resonator impedance matching for shot-noise limited, cavity enhanced amplitude modulated laser absorption spectroscopy.

    Science.gov (United States)

    Chow, Jong H; Littler, Ian C M; Rabeling, David S; McClelland, David E; Gray, Malcolm B

    2008-05-26

    We introduce a closed-loop feedback technique to actively control the coupling condition of an optical cavity, by employing amplitude modulation of the interrogating laser. We show that active impedance matching of the cavity facilitates optimal shot-noise sensing performance in a cavity enhanced system, while its control error signal can be used for intra-cavity absorption or loss signal extraction. We present the first demonstration of this technique with a fiber ring cavity, and achieved shot-noise limited loss sensitivity. We also briefly discuss further use of impedance matching control as a tool for other applications.

  7. Tuning of Detection Wavelength in a Resonant-Cavity-Enhanced Quantum-Dot-Embedded Photodiode by Changing Detection Angle

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hao; ZHU Hui; ZHENG Hou-Zhi; XU Ping; PENG Hong-Ling; TAN Ping-Heng; YANG Fu-Hua; NI Hai-Qiao; ZENG Yu-Xin; GAN Hua-Dong

    2005-01-01

    @@ We have Fabricated a resonant-cavity-enhanced photodiode (RCE-PD) with InGaAs quantum dots (QDs) as an active medium. This sort of QD-embedded RCE-PD is capable of a peak external quantum efficiency of 32%and responsivity of 0.27 A/W at 1.058 μm with a full width at half maximum (FWHM) of 5nm. Angle-resolved photocurrent response eventually proves that with the detection angle changing from 0° to 60°, the peak-current wavelength shifts towards the short wavelength side by 37nm, while the quantum efficiency remains larger than 15%.

  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. 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.

  10. 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.

  11. Direct RF modulation transmitter, sampling clock frequency setting method for direct RF modulation transmitter

    NARCIS (Netherlands)

    Fukuda, Shuichi; Nauta, Bram

    2013-01-01

    PROBLEM TO BE SOLVED: To provide a direct RF modulation transmitter capable of satisfying a radiation level regulation even without providing a SAW filter. SOLUTION: A direct RF modulation transmitter includes: digital/RF converters 105, 106 to which an I digital baseband signal, a Q digital baseb

  12. 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 ...

  13. Cavity Enhanced Optical Vernier Spectroscopy, Broad Band, High Resolution, High Sensitivity

    CERN Document Server

    Gohle, Christoph; Schliesser, Albert; Udem, Thomas; Hänsch, Theodor W

    2007-01-01

    A femtosecond frequency comb provides a vast number of equidistantly spaced narrow band laser modes that can be simultaneously tuned and frequency calibrated with 15 digits accuracy. Our Vernier spectrometer utilizes all of theses modes in a massively parallel manner to rapidly record both absorption and dispersion spectra with a sensitivity that is provided by a high finesse broad band optical resonator and a resolution that is only limited by the frequency comb line width while keeping the required setup simple.

  14. Development of a broadband cavity enhanced UV-LED spectrometer for the detection of atmospheric HONO and NO2

    Science.gov (United States)

    Wu, Tao; Xia, Ruxiao; Chen, Weidong; He, Xingdao

    2016-10-01

    An incoherent broadband cavity enhanced UV-LED spectrometer (IBBCEAS) was developed to detect atmospheric HONO and NO2. Using a UV light emitting diode (LED) operating at 366 nm in combination with a high finesse optical cavity, HONO and NO2 were able to be simultaneously measured with high sensitivity. Detection limits (for SNR=1) of 0.3 ppbv for HONO and 1 ppbv for NO2 were achieved with an optimum acquisition time of 120 s. Stability of the developed cavity enhanced UV-LED spectrometer has been characterized by means of an Allan variance analysis. Daytime and nighttime concentrations of atmospheric HONO and NO2 were measured and compared with data from LOPAP for HONO and blue light converter-based NOx analyzer for NO2. The present work performed in a real atmospheric environment demonstrates the feasibility of using IBBCEAS technique for interference (chemical and spectral) free measurement of HONO. Experimental detail will be presented, the problems encountered during the real atmospheric measurement will be discussed.

  15. Bromine Explosions In Smog Chamber Experiments: A comparison of Cavity-Enhanced (CE) and White-cell DOAS

    Science.gov (United States)

    Buxmann, J.; Hoch, D. J.; Sihler, H.; Pöhler, D.; Platt, U.; Bleicher, S.; Balzer, N.; Zetzsch, C.

    2011-12-01

    Reactive halogen species (RHS), such as Cl, Br or BrO, can significantly influence chemical processes in the troposphere, including the destruction of ozone, change in the chemical balance of hydrogen radicals (OH, HO2), increased deposition of toxic compounds (like mercury) with potential consequences for the global climate. Previous studies have shown that salt lakes can be significant sources for gaseous RHS. Environmental conditions such as salt composition, relative humidity (RH), pH, and temperature (T) can strongly influence reactive bromine levels, but are difficult to quantify in the field. Therefore, we conducted laboratory experiments by exposing NaCl salt containing 0.33% (by weight) NaBr to simulated sunlight in a Teflon smog-chamber under various conditions of RH and ozone concentrations. BrO levels were observed by a Differential-Optical-Absorption-Spectrometer (DOAS) in combination with a multi-reflection cell (White-cell). The concentrations of OH- and Cl- radicals were quantified by the radical clock method. We present the first direct observation of BrO from the "Bromine Explosion" (auto catalytic release of reactive bromine from salt surfaces - key to ozone destruction) in the laboratory above a simulated salt pan. The maximum BrO mixing ratio of 6419±71 ppt at 60% RH was observed to be one order of magnitude higher than at 37% RH and 2% RH. The release of RHS from the salt pan is possibly controlled by the thickness of the quasi liquid layer, covering the reactive surface of the halide crystals, as the layer thickness strongly depends on RH. Furthermore, a new cavity enhanced DOAS (CE-DOAS) instrument was designed and successfully used in chamber experiments. For the first time, such an instrument uses a spectral interval in the UV - wavelength range (325-365 nm) to identify BrO. We show a comparison of the CE-DOAS and White-cell DOAS instrument in a series of experiments, where e.g. a peak BrO mixing ratio up to 380 ppt within the first

  16. Low frequency vibrations induce malformations in two aquatic species in a frequency-, waveform-, and direction-specific manner.

    Directory of Open Access Journals (Sweden)

    Laura N Vandenberg

    Full Text Available Environmental toxicants such as industrial wastes, air particulates from machinery and transportation vehicles, and pesticide run-offs, as well as many chemicals, have been widely studied for their effects on human and wildlife populations. Yet other potentially harmful environmental pollutants such as electromagnetic pulses, noise and vibrations have remained incompletely understood. Because developing embryos undergo complex morphological changes that can be affected detrimentally by alterations in physical forces, they may be particularly susceptible to exposure to these types of pollutants. We investigated the effects of low frequency vibrations on early embryonic development of two aquatic species, Xenopus laevis (frogs and Danio rerio (zebrafish, specifically focusing on the effects of varying frequencies, waveforms, and applied direction. We observed treatment-specific effects on the incidence of neural tube defects, left-right patterning defects and abnormal tail morphogenesis in Xenopus tadpoles. Additionally, we found that low frequency vibrations altered left-right patterning and tail morphogenesis, but did not induce neural tube defects, in zebrafish. The results of this study support the conclusion that low frequency vibrations are toxic to aquatic vertebrates, with detrimental effects observed in two important model species with very different embryonic architectures.

  17. Direct generation of optical frequency combs in $\\chi^{(2)}$ nonlinear cavities

    CERN Document Server

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

    2015-01-01

    Quadratic nonlinear processes are currently exploited for frequency comb transfer and extension from the visible and near infrared regions to other spectral ranges where direct comb generation cannot be accomplished. However, frequency comb generation has been directly observed in continuously-pumped quadratic nonlinear crystals placed inside an optical cavity. At the same time, an introductory theoretical description of the phenomenon has been provided, showing a remarkable analogy with the dynamics of third-order Kerr microresonators. Here, we give an overview of our recent work on $\\chi^{(2)}$ frequency comb generation. Furthermore, we generalize the preliminary three-wave spectral model to a many-mode comb and present a stability analysis of different cavity field regimes. Although at a very early stage, our work lays the groundwork for a novel class of highly efficient and versatile frequency comb synthesizers based on second-order nonlinear materials.

  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. Direct generation of optical frequency combs in χ(2 nonlinear cavities

    Directory of Open Access Journals (Sweden)

    Mosca Simona

    2016-06-01

    Full Text Available Quadratic nonlinear processes are currently exploited for frequency comb transfer and extension from the visible and near infrared regions to other spectral ranges where direct comb generation cannot be accomplished. However, frequency comb generation has been directly observed in continuously pumped quadratic nonlinear crystals placed inside an optical cavity. At the same time, an introductory theoretical description of the phenomenon has been provided, showing a remarkable analogy with the dynamics of third-order Kerr microresonators. Here, we give an overview of our recent work on χ(2 frequency comb generation. Furthermore, we generalize the preliminary three-wave spectral model to a many-mode comb and present a stability analysis of different cavity field regimes. Although our work is a very early stage, it lays the groundwork for a novel class of highly efficient and versatile frequency comb synthesizers based on second-order nonlinear materials.

  20. 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.

  1. 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.

  2. A direct digital frequency synthesizer with high-speed current-steering DAC

    Institute of Scientific and Technical Information of China (English)

    Yu Jinshan; Fu Dongbing; Li Ruzhang; Yao Yafeng; Yan Gang; Liu Jun; Zhang Ruitao; Yu Zhou; Li Tun

    2009-01-01

    A high-speed SiGe BiCMOS direct digital frequency synthesizer (DDS) is presented. The design in tegrates a high-speed digital DDS core, a high-speed differential current-steering mode 10-bit D/A converter, a serial/parallel interface, and clock control logic. The DDS design is processed in 0.35 μm SiGe BiCMOS standard process technology and worked at 1 GHz system frequency. The measured results show that the DDS is capable of generating a frequency-agile analog output sine wave up to 400+ MHz.

  3. 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.

  4. 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.

  5. 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.

  6. Detection of HO2 in an atmospheric pressure plasma jet using optical feedback cavity-enhanced absorption spectroscopy

    Science.gov (United States)

    Gianella, Michele; Reuter, Stephan; Lawry Aguila, Ana; Ritchie, Grant A. D.; van Helden, Jean-Pierre H.

    2016-11-01

    Cold non-equilibrium atmospheric pressure plasma jets are increasingly applied in material processing and plasma medicine. However, their small dimensions make diagnosing the fluxes of generated species a challenge. Here we report on the detection of the hydroperoxyl radical, HO2, in the effluent of a plasma jet by the use of optical feedback cavity-enhanced absorption spectroscopy. The spectrometer has a minimum detectable absorption coefficient {α }\\min of 2.25× {10}-10 cm-1 with a 100 second acquisition, equivalent to 5.5× {10}12 {{cm}}-3 of HO2 (under ideal conditions). Concentrations in the range of (3.1-7.8) × 1013 cm-3 were inferred in the 4 mm wide effluent of the plasma jet.

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

    Directory of Open Access Journals (Sweden)

    K.-E. Min

    2015-10-01

    Full Text Available 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 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, state-of-the-art 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 pptv in 5 s. The accuracy is 5.8, 9.0 and 5.0 % limited mainly by the available absorption cross sections.

  8. Experimental verification of directional liquid surface wave emission at band edge frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhenyu, E-mail: wzyu@zju.edu.cn; Zhang, Pei; Zhang, Yongqiang; Nie, Xiaofei

    2013-12-15

    Directional liquid surface wave emission at band edge frequencies is an interesting physical phenomenon and has already been studied in theoretical research. There has been no experimental validation of it to date, however. This paper has as its subject the experimental investigation of the emission effect when a point source is placed inside a finite square array of rigid cylinders standing vertically in liquid. Both the wave patterns and spatial intensities are obtained by experiment and compared with simulated results calculated by using the finite element method. We can see from this comparison that the two results correspond closely both at lower and upper band edge frequency. Obvious directional wave emission along a desired direction is observed in the source structures, confirming previous theoretical predictions. In the future, this method could serve as a directional liquid wave source in applications used in hydraulic and ocean engineering for the concentration of wave energy.

  9. 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...

  10. 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.

  11. Design and analysis of a new high frequency double-servo direct drive rotary valve

    Science.gov (United States)

    Zhu, Muzhi; Zhao, Shengdun; Li, Jingxiang

    2016-12-01

    Researchers have investigated direct drive valve for many years to solve problems, such as fluid force imbalance and switching frequency. The structure of the rotary valve has received considerable research interest because of its favorable dynamic properties and simple structure. This paper studied the high frequency doubleservo direct drive rotary valve (DDRV), and proposed a novel structure and drive method satisfying high reversing frequency and adequate quantity of flow. Servo motors are integrated into the valve by the innovative structure, which is designed to equilibrate the unbalanced radial fluid force with the symmetric distributed oil ports. Aside from the fast reversing function of the valve, the DDRV presented high performance in linearity of the flow quantity and valve opening as a result of the fan-shaped flow ports. In addition, a computational fluid dynamics (CFD) method based on Fluent was conducted to verify the flux regulation effect of the height change of the adjustable boss.

  12. A high-performance MUX-direct digital frequency synthesizer with quarter ROMs

    Institute of Scientific and Technical Information of China (English)

    Hao Zhikun; Zhang Qiang; Ni Weining; Shi Yin

    2012-01-01

    This paper presents a detailed description of a high-performance direct digital frequency synthesizer (DDFS) using optimized quarter ROMs.To improve the working frequency and spectral purity,an original quarter ROMs structure in 0.13 μm CMOS is brought forward and implemented.The working frequency is increased by 40% compared with Yuan Ling's method[1] of implementing a segmented DAC based DDFS.It has been implemented in 0.13 μm CMOS technology.The DDFS has a resolution of 10 bits with a measured SFDR 54 dBc.Its maximum operating frequency is 1.2 GHz by using six pipelining stages.Analytical investigation of improving spectral performances by using dual-slope approximation and pipeline is also presented.

  13. 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

  14. Defectoscopy of direct laser sintered metals by low transmission ultrasonic frequencies

    Directory of Open Access Journals (Sweden)

    Ebersold Zoran

    2012-01-01

    Full Text Available This paper focuses on the improvement of ultrasonic defectoscopy used for machine elements produced by direct laser metal sintering. The direct laser metal sintering process introduces the mixed metal powder and performs its subsequent laser consolidation in a single production step. Mechanical elements manufactured by laser sintering often contain many hollow cells due to weight reduction. The popular pulse echo defectoscopy method employing very high frequencies of several GHz is not successful on these samples. The aim of this paper is to present quadraphonic transmission ultrasound defectoscopy which uses low range frequencies of few tens of kHz. Therefore, the advantage of this method is that it enables defectoscopy for honeycombed materials manufactured by direct laser sintering. This paper presents the results of testing performed on AlSi12 sample. [Projekat Ministarstva nauke Republike Srbije, br. OI 172057

  15. CMOS Direct-Injection Divide-by-3 Injection-Locked Frequency Dividers

    Institute of Scientific and Technical Information of China (English)

    Chia-Wei; Chang; Jhin-Fang; Huang; Sheng-Lyang; Jang; Ying-Hsiang; Liao; Miin-Horng; Juang

    2010-01-01

    <正>This paper proposes CMOS LC-tank divide-by-3 injection locked frequency dividers(ILFDs)fabricated in 0.18μn and 90nm CMOS process and describes the circuit design,operation principle and measurement results of the ILFDs.The ILFDs use two injection series-MOSFETs across the LC resonator and a differential injection signal is applied to the gates of injection MOSFETs.The direct-injection divide-by-3 ILFDs are potential for radio-frequency application and can have wide locking range.

  16. Metrology with PT-Symmetric Cavities: Enhanced Sensitivity near the PT-Phase Transition.

    Science.gov (United States)

    Liu, Zhong-Peng; Zhang, Jing; Özdemir, Şahin Kaya; Peng, Bo; Jing, Hui; Lü, Xin-You; Li, Chun-Wen; Yang, Lan; Nori, Franco; Liu, Yu-Xi

    2016-09-09

    We propose and analyze a new approach based on parity-time (PT) symmetric microcavities with balanced gain and loss to enhance the performance of cavity-assisted metrology. We identify the conditions under which PT-symmetric microcavities allow us to improve sensitivity beyond what is achievable in loss-only systems. We discuss the application of PT-symmetric microcavities to the detection of mechanical motion, and show that the sensitivity is significantly enhanced near the transition point from unbroken- to broken-PT regimes. Our results open a new direction for PT-symmetric physical systems and it may find use in ultrahigh precision metrology and sensing.

  17. 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.

  18. The research of high-directive anisotropic magnetic metamaterial antenna loaded with frequency-selective surface

    Institute of Scientific and Technical Information of China (English)

    Sun Yong-Zhi; Ran Li-Xin; Peng Liang; Wang Wei-Guang; Li Ting; Zhao Xu; Chen Qiu-Lin

    2009-01-01

    This paper uses a Computer Simulation Technology microwave studio to simulate the performance of a new highdirectivity anisotropic magnetic metamaterial antenna loaded with a frequency-selective surface. Frequency-selective surface with cross-dipole element has a great effect on the directivity, radiation pattern, and gain of such an antenna. The experimental results show that frequency-selective surface (FSS) significantly improve the radiation performance of anisotropic magnetic metamaterial antenna. For example, as a single anisotropic magnetic metamaterial antenna, half power beam width is 4 degrees in the H planes, and the gain of this antenna is 19.5dBi at 10GHz, achieving a 2.1 degree increment in half power beam width, and a 7.3dB gain increment by loading with the FSS reflector. The simulating results are consistent with our experimental results.

  19. Low Complexity Direction and Doppler Frequency Estimation for Bistatic MIMO Radar in Spatial Colored Noise

    Directory of Open Access Journals (Sweden)

    Lingyun Xu

    2014-01-01

    Full Text Available We investigate the algorithm of direction and Doppler frequency estimation for bistatic multiple-input multiple-output (MIMO radar in spatial colored noise. A novel method of joint estimation of direction and Doppler frequency in spatial colored noise based on propagator method (PM for bistatic MIMO radar is discussed. Utilizing the cross-correlation matrix which is formed by the adjacent outputs of match filter in the time domain, the special matrix is constructed to eliminate the influence of spatial colored noise. The proposed algorithm provides lower computational complexity and has very close parameters estimation compared to estimation of signal parameters via rotational invariance technique (ESPRIT algorithm in high signal-to-noise ratio (SNR. It is applicable even if the transmitted waveforms are not orthogonal. The estimated parameters can be paired automatically and the Cramér-Rao Bound (CRB is given in spatial colored noise. Simulation results confirm the effectiveness of the proposed method.

  20. 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 large interaural canal, but its role in barn owl hearing and specifically in sound localization has been controversial so far. We discuss here existing data and the role of the interaural canal in this species and add a new dataset obtained by laser Doppler vibrometry in a free-field setting....... Significant sound transmission across the interaural canal occurred at low frequencies. The sound transmission induces considerable eardrum directionality in a narrow band from 1.5 to 3.5 kHz. This is below the frequency range used by the barn owl for locating prey, but may conceivably be used for locating...

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

    Science.gov (United States)

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

    2016-10-01

    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 large interaural canal, but its role in barn owl hearing and specifically in sound localization has been controversial so far. We discuss here existing data and the role of the interaural canal in this species and add a new dataset obtained by laser Doppler vibrometry in a free-field setting. Significant sound transmission across the interaural canal occurred at low frequencies. The sound transmission induces considerable eardrum directionality in a narrow band from 1.5 to 3.5 kHz. This is below the frequency range used by the barn owl for locating prey, but may conceivably be used for locating conspecific callers.

  2. Direct current effects on high-frequency properties of patterned permalloy thin films.

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H.; Hoffmann, A.; Divan, R.; Wang, P.; Clemson Univ.

    2009-12-01

    We have investigated experimentally direct current (dc) effects on high-frequency properties of two different permalloy (Py) submicrometer patterns of 0.24 mum and 0.55 mum width, 10 mum length, and 100 nm thickness. The natural ferromagnetic resonance (FMR) frequencies for the two samples are about 8.5 and 11.5 GHz. A 50 mA dc produces a FMR frequency reduction of about 1 GHz in both samples. We extracted susceptibility spectra for the samples from the measurement data. We studied inductance variations of Py embedded transmission lines for different dc levels. With 50 mA dc, the operational frequencies of the inductances decreased by 9% and 12.5%. We also tested effects of magnetic fields generated by external magnets on the submicrometer patterns for comparison. To obtain the same magnetization rotation angle, the external magnetic field needs to be about five times larger than the Ampere field created by the direct current. This behavior is unique and may be associated with the increased thermal energy from the Joule heating effects.

  3. Self-directed Mindfulness Training and Improvement in Blood Pressure, Migraine Frequency, and Quality of Life

    OpenAIRE

    Oberg, Erica B.; Rempe, Margaret; Bradley, Ryan

    2013-01-01

    Background: Interest in case studies has undergone a resurgence concurrent with increasing prioritization of illustrations of patient-centered care. However, substantial inclusion of the patient in these reports remains limited. Here, a doctor and patient collaborate to present her case report of self-directed mindfulness training and the subsequent changes in blood pressure, migraine frequency, and quality of life. Methods: After receiving encouragement from her naturopathic doctor, the pati...

  4. 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.

  5. Hardware implementation of 32-bit high-speed direct digital frequency synthesizer.

    Science.gov (United States)

    Ibrahim, Salah Hasan; Ali, Sawal Hamid Md; Islam, Md Shabiul

    2014-01-01

    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.

  6. Spectrally efficient polarization multiplexed direct-detection OFDM system without frequency gap.

    Science.gov (United States)

    Wei, Chia-Chien; Zeng, Wei-Siang; Lin, Chun-Ting

    2016-01-25

    We experimentally demonstrate a spectrally efficient direct-detection orthogonal frequency-division multiplexing (DD-OFDM) system. In addition to polarization-division multiplexing, removing the frequency gap further improves the spectral efficiency of the OFDM system. The frequency gap between a reference carrier and OFDM subcarriers avoids subcarrier-to-subcarrier beating interference (SSBI) in traditional DD-OFDM systems. Without dynamic polarization control, the resulting interference after square-law direct detection in the proposed gap-less system is polarization-dependent and composed of linear inter-carrier interference (ICI) and nonlinear SSBI. Thus, this work proposes an iterative multiple-input multiple-output detection scheme to remove the mixed polarization-dependent interference. Compared to the previous scheme, which only removes ICI, the proposed scheme can further eliminate SSBI to achieve the improvement of ∼ 7 dB in signal-to-noise ratio. Without the need for polarization control, we successfully utilize 7-GHz bandwidth to transmit a 39.5-Gbps polarization multiplexed OFDM signal over 100 km.

  7. 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.

  8. 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.

  9. Cavity enhanced atomic magnetometry

    OpenAIRE

    Herbert Crepaz; Li Yuan Ley; Rainer Dumke

    2015-01-01

    Atom sensing based on Faraday rotation is an indispensable method for precision measurements, universally suitable for both hot and cold atomic systems. Here we demonstrate an all-optical magnetometer where the optical cell for Faraday rotation spectroscopy is augmented with a low finesse cavity. Unlike in previous experiments, where specifically designed multipass cells had been employed, our scheme allows to use conventional, spherical vapour cells. Spherical shaped cells have the advantage...

  10. 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

  11. 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.

  12. Change in mean frequency of resting-state electroencephalography after transcranial direct current stimulation

    Directory of Open Access Journals (Sweden)

    Tjeerd W. Boonstra

    2016-06-01

    Full Text Available Transcranial direct current stimulation (tDCS is proposed as a tool to investigate cognitive functioning in healthy people and as a treatment for various neuropathological disorders. However, the underlying cortical mechanisms remain poorly understood. We aim to investigate whether resting-state electroencephalography (EEG can be used to monitor the effects of tDCS on cortical activity. To end we tested whether the spectral content of ongoing EEG activity is significantly different after a single session of active tDCS compared to sham stimulation. Twenty participants were tested in a sham-controlled, randomized, crossover design. Resting-state EEG was acquired before, during and after active tDCS to the left dorsolateral prefrontal cortex (15 min of 2mA tDCS and sham stimulation. Electrodes with a diameter of 3.14 cm2 were used for EEG and tDCS. Partial least squares (PLS analysis was used to examine differences in power spectral density and the EEG mean frequency to quantify the slowing of EEG activity after stimulation. PLS revealed a significant increase in spectral power at frequencies below 15 Hz and a decrease at frequencies above 15 Hz after active tDCS (P=0.001. The EEG mean frequency was significantly reduced after both active tDCS (P<0.0005 and sham tDCS (p=0.001, though the decrease in mean frequency was smaller after sham tDCS than after active tDCS (P=0.073. Anodal tDCS of the left DLPFC using a high current density bi-frontal electrode montage resulted in general slowing of resting-state EEG. The similar findings observed following sham stimulation question whether the standard sham protocol is an appropriate control condition for tDCS.

  13. Wavelet packet transform-based optical orthogonal frequency-division multiplexing transmission using direct detection

    Science.gov (United States)

    Zhang, Hongbo; Yi, Xingwen; Chen, Lei; Zhang, Jing; Deng, Mingliang; Qiu, Kun

    2012-10-01

    As an alternate to fast Fourier transform-based orthogonal frequency-division multiplexing (OFDM), wavelet packet transform (WPT)-based OFDM (WPT-OFDM) does not require cyclic prefix to avoid inter-symbol-interference. The wavelet has many varieties and therefore, it can provide more freedom for system design to suit different applications. We propose a real-valued WPT-OFDM that uses intensity modulation/direct detection. We also conduct an experiment to verify its performance through a 75-km standard single-mode fiber.

  14. Phase Determination Method to Directly Measure Intensity and Frequency of Temporal Profiles of Attosecond EUV Pulses

    Institute of Scientific and Technical Information of China (English)

    GE Yu-Cheng

    2005-01-01

    @@ A new method of phase determination is presented to directly measure the intensity and frequency temporalprofiles of attosecond EUV pulses. The profiles can be reconstructed from the photoelectron energy spectra measured with two different laser intensities at 0° and 180° with respect to the linear laser polarization using a cross correlation between the femtosecond laser and the attosecond EUV. The method has a temporal measurement range from a quarter to about half of a laser oscillation period. The time resolution depends on the jitter and control precision of laser and EUV pulses. This method improves the time resolution in measuring attosecond EUV pulses.

  15. Convective stability in the Rayleigh-Benard and directional solidification problems - High-frequency gravity modulation

    Science.gov (United States)

    Wheeler, A. A.; Mcfadden, G. B.; Murray, B. T.; Coriell, S. R.

    1991-01-01

    The effect of vertical, sinusoidal, time-dependent gravitational acceleration on the onset of solutal convection during directional solidification is analyzed in the limit of large modulation frequency. When the unmodulated state is unstable, the modulation amplitude required to stabilize the system is determined by the method of averaging. When the unmodulated state is stable, resonant modes of instability occur at large modulation amplitude. These are analyzed using matched asymptotic expansions to elucidate the boundary-layer structure for both the Rayleigh-Benard and directional solidification configurations. Based on these analyses, a thorough examination of the dependence of the stability criteria on the unmodulated Rayleigh number, Schmidt number, and distribution coefficient, is carried out.

  16. Determine electric field directions at semiconductor surfaces by femtosecond frequency domain interferometric second harmonic (FDISH) generation

    Science.gov (United States)

    Nelson, C. A.; Zhu, X.-Y.

    2016-10-01

    Optical excitations at semiconductor surfaces or interfaces are accompanied by transient interfacial electric fields due to charge redistribution or transfer. While such transient fields may be probed by time-resolved second harmonic generation (TR-SHG), it is difficult to determine the field direction, which is invaluable to unveiling the underlying physics. Here we apply a time-resolved frequency domain interferometric second harmonic (TR-FDISH) generation technique to determine the phase relationship between the SH field emitted from bulk GaAs(1 0 0) and the transient SH field from the space charge region. The interference between these two SH fields allow us to unambiguously determine the directions of transient electric fields. Since SH fields from a static bulk contribution and a changing electric field contribution are present at most semiconductor surfaces or interfaces under optical excitation, the TR-FDISH technique is of general significance to probing the dynamics of interfacial charge transfer/redistribution.

  17. Transcranial direct current stimulation improves ipsilateral selective muscle activation in a frequency dependent manner.

    Directory of Open Access Journals (Sweden)

    Kazumasa Uehara

    Full Text Available Failure to suppress antagonist muscles can lead to movement dysfunction, such as the abnormal muscle synergies often seen in the upper limb after stroke. A neurophysiological surrogate of upper limb synergies, the selectivity ratio (SR, can be determined from the ratio of biceps brachii (BB motor evoked potentials to transcranial magnetic stimulation prior to forearm pronation versus elbow flexion. Surprisingly, cathodal transcranial direct current stimulation (c-TDCS over ipsilateral primary motor cortex (M1 reduces (i.e. improves the SR in healthy adults, and chronic stroke patients. The ability to suppress antagonist muscles may be exacerbated at high movement rates. The aim of the present study was to investigate whether the selective muscle activation of the biceps brachii (BB is dependent on altering frequency demands, and whether the c-tDCS improvement of SR is dependent on task frequency. Seventeen healthy participants performed repetitive isometric elbow flexion and forearm pronation at three rates, before and after c-tDCS or sham delivered to ipsilateral left M1. Ipsilateral c-tDCS improved the SR in a frequency dependent manner by selectively suppressing BB antagonist excitability. Our findings confirm that c-tDCS is an effective tool for improving selective muscle activation, and provide novel evidence for its efficacy at rates of movement where it is most likely to benefit task performance.

  18. Compliance boundaries for multiple-frequency base station antennas in three directions.

    Science.gov (United States)

    Thielens, Arno; Vermeeren, Günter; Kurup, Divya; Joseph, Wout; Martens, Luc

    2013-09-01

    In this article, compliance boundaries and allowed output powers are determined for the front, back, and side of multiple-frequency base station antennas, based on the root-mean-squared electric field, the whole-body averaged specific absorption rate (SAR), and the 10 g averaged SAR in both the limbs and the head and trunk. For this purpose, the basic restrictions and reference levels defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for both the general public and occupational exposure are used. The antennas are designed for Global System for Mobile Communications around 900 MHz (GSM900), GSM1800, High Speed Packet Access (HSPA), and Long Term Evolution (LTE), and are operated with output powers at the individual frequencies up to 300 W. The compliance boundaries are estimated using finite-difference time-domain simulations with the Virtual Family Male and have been determined for three directions with respect to the antennas for 800, 900, 1800, and 2600 MHz. The reference levels are not always conservative when the radiating part of the antenna is small compared to the length of the body. Combined compliance distances, which ensure compliance with all reference levels and basic restrictions, have also been determined for each frequency. A method to determine a conservative estimation of compliance boundaries for multiple-frequency (cumulative) exposure is introduced. Using the errors on the estimated allowed powers, an uncertainty analysis is carried out for the compliance distances. Uncertainties on the compliance distances are found to be smaller than 122%.

  19. A new calibration system for lightweight, compact and mobile Cavity-Enhanced Differential Optical Absorption Spectroscopy instruments

    Science.gov (United States)

    Zielcke, Johannes; Horbanski, Martin; Pöhler, Denis; Frieß, Udo; Platt, Ulrich

    2013-04-01

    Absorption Spectroscopy has been employed for several decades now to study the earth's atmosphere. While the focus has been on remote sensing for a long time, lately there has been a renewed interest in in-situ methods, as point measurements allow an easier interpretation for highly inhomogeneous distributions of gases of interest compared to the integration approach of most remote sensing methods. One comparatively new method offering both advantages of in-situ measurements as well as being contactless is open-path Cavity-Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS). Broadband open-path CE-DOAS instruments have been used for ten years now, and in the meantime allow the measurement of numerous atmospheric trace gases (e.g. NO2, NO3, IO, CHOCHO, HCHO). While those instruments were bulky and not very mobile at first, recent developments resulted in relatively lightweight (< 30 kg) instruments with a relatively low power consumption allowing mobile open-path measurements at remote field locations. An important operational issue has been the path length calibration in the field, necessary for the determination of the concentration of measured gases. Until now, often calibration gases were used with different scattering properties than air or known concentrations. However this methods has several major shortcomings, being rather inconvenient and cumbersome in the field with the need for compressed gas cylinders, as well as time consuming, preventing a quick check of the state of the instrument in the field after changing measurement locations. Here we present a new wavelength-resolved method for broadband CE-DOAS path length calibration. A small, custom made ring-down system is employed with a pulsed LED as light source. The wavelength is then resolved by tilting a narrow band interference filter. The system not only allows quick, automated path length calibrations without physical interaction on the instrument, but also saves weight, space and the

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

    Science.gov (United States)

    Galicher, R.; Marois, C.; Macintosh, B.; Zuckerman, B.; Barman, T.; Konopacky, Q.; Song, I.; Patience, J.; Lafrenière, D.; Doyon, R.; Nielsen, E. L.

    2016-10-01

    Context. 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. Aims: We carried out the international deep planet survey of 292 young nearby stars to search for giant exoplanets and determine their frequency. Methods: 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 yr. The pipeline first applies cosmetic corrections and then reduces the speckle intensity to enhance the contrast in the images. Results: 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 2279 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 MJ and between 20 and 300 AU. This result is obtained assuming uniform distributions of planet masses and semi-major axes. If we consider power law distributions as measured for close-in planets instead, the derived frequency is 2.30+5.95-1.55%, recalling the strong impact of assumptions on Monte Carlo output distributions. We also find no evidence that the derived frequency depends on the mass of the hosting star, whereas it does for close-in planets. Conclusions: The international deep planet survey provides a database of confirmed background sources that may be useful for other exoplanet direct imaging surveys. It also puts new constraints on the number of stars with at least one giant planet reducing by a factor of two the frequencies derived by almost all previous works. Tables 11-15 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc

  1. 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.

  2. Detection of particle flow patterns in tumor by directional spatial frequency analysis

    Science.gov (United States)

    Russell, Stewart; Camara, Hawa; Shi, Lingyan; Hoopes, P. Jack; Kaufman, Peter; Pogue, Brian; Alfano, Robert

    2016-04-01

    Drug delivery to tumors is well known to be chaotic and limited, partly from dysfunctional vasculature, but also because of microscopic regional variations in composition. Modeling the of transport of nanoparticle therapeutics, therefore must include not only a description of vascular permeability, but also of the movement of the drug as suspended in tumor interstitial fluid (TIF) once it leaves the blood vessel. Understanding of this area is limited because we currently lack the tools and analytical methods to characterize it. We have previously shown that directional anisotropy of drug delivery can be detected using Directional Fourier Spatial Frequency (DFSF) Analysis. Here we extend this approach to generate flow line maps of nanoparticle transport in TIF relative to tumor ultrastructure, and show that features of tumor spatial heterogeneity can be identified that are directly related to local flow isometries. The identification of these regions of limited flow may be used as a metric for determining response to therapy, or for the optimization of adjuvant therapies such as radiation pre-treatment, or enzymatic degradation.

  3. 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.

  4. Cyclic Stress at mHz Frequencies Aligns Fibroblasts in Direction of Zero Strain

    Science.gov (United States)

    Rubner, Wolfgang; Kirchgeßner, Norbert; Safran, Sam; Hoffmann, Bernd; Merkel, Rudolf

    2011-01-01

    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. PMID:22194961

  5. Direct power-frequency electric field effects on mammalian endocrine tissue. [60-Hz

    Energy Technology Data Exchange (ETDEWEB)

    Lymangrover, J.R.; Keku, E.; Hsieh, S.T.; Dunlap, W.P.; Seto, Y.J.

    1987-06-01

    A number of studies have investigated the in vivo biological effects of power-frequency electric fields (EF). Direct effects of EF on mammalian tissues, however, have rarely been reported. They now report that a 60-Hz EF can directly enhance the steroidogenic response of superfused rat adrenocortical tissue. The EF did not influence basal steroidogenic activity, however the corticosterone response to 10 mU of ACTH was almost doubled by an unperturbed 1000 kV/m EF during the initial 2 hr of exposure and was enhanced fourfold by 5.5 to 7 hr of exposure with a 10 kV/m EF. Other EF intensities (e.g., 5 and 100 kV/m) were without effect at these times. Turning the 1000 kV/m EF on and off at 30-min intervals did not influence the initial enhanced steroidogenic response but did cause an additional two- to threefold elevation in the response following 5.5-7 hr of exposure. It is not clear what EF exposure parameters or mechanisms were primarily responsible for these bioeffects, but it appears that direct exposure of mammalian endocrine tissue to a 60-Hz EF is capable of significantly influencing important cellular processes.

  6. 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.

  7. 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.

  8. Frequency-doubled diode laser for direct pumping of Ti:sapphire lasers

    DEFF Research Database (Denmark)

    Müller, André; Jensen, Ole Bjarlin; Unterhuber, Angelika

    2012-01-01

    A single-pass frequency doubled high-power tapered diode laser emitting nearly 1.3 W of green light suitable for direct pumping of Ti:sapphire lasers generating ultrashort pulses is demonstrated. The pump efficiencies reached 75 % of the values achieved with a commercial solid-state pump laser....... However, the superior electro-optical efficiency of the diode laser improves the overall efficiency of the Ti:sapphire laser by a factor > 2. The optical spectrum emitted by the Ti:sapphire laser shows a spectral width of 112 nm (FWHM). Based on autocorrelation measurements, pulse widths of less than 20...... fs are measured. These results open the opportunity of establishing diode laser pumped Ti:sapphire lasers for e.g. biophotonic applications like retinal optical coherence tomography or pumping of photonic crystal fibers for CARS microscopy....

  9. A ROM-less direct digital frequency synthesizer based on hybrid polynomial approximation.

    Science.gov (United States)

    Omran, Qahtan Khalaf; Islam, Mohammad Tariqul; Misran, Norbahiah; Faruque, Mohammad Rashed Iqbal

    2014-01-01

    In this paper, a novel design approach for a phase to sinusoid amplitude converter (PSAC) has been investigated. Two segments have been used to approximate the first sine quadrant. A first linear segment is used to fit the region near the zero point, while a second fourth-order parabolic segment is used to approximate the rest of the sine curve. The phase sample, where the polynomial changed, was chosen in such a way as to achieve the maximum spurious free dynamic range (SFDR). The invented direct digital frequency synthesizer (DDFS) has been encoded in VHDL and post simulation was carried out. The synthesized architecture exhibits a promising result of 90 dBc SFDR. The targeted structure is expected to show advantages for perceptible reduction of hardware resources and power consumption as well as high clock speeds.

  10. Appropriate microwave frequency selection for biasing superconducting hot electron bolometers as terahertz direct detectors

    Science.gov (United States)

    Jiang, S. L.; Li, X. F.; Jia, X. Q.; Kang, L.; Jin, B. B.; Xu, W. W.; Chen, J.; Wu, P. H.

    2017-04-01

    Terahertz (THz) direct detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) and biased by a simple microwave (MW) source have been studied. The frequency and power of the MW are selected by measuring the MW responses of the current–voltage (I–V) curves and resistance–temperature (R–T) curves of the NbN HEBs. The non-uniform absorption theory is used to explain the current jumps in the I–V curves and the resistance jumps in the R–T curves. Compared to the thermal biasing, the MW biasing method can improve the sensitivity, make the readout system much easier and consumes less liquid helium, which is important for long lasting experiments. The noise equivalent power (NEP) of 1.6 pW Hz‑1/2 and the response time of 86 ps are obtained for the detectors working at 4.2 K and 0.65 THz.

  11. 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%.

  12. Frequency interleaving towards spectrally efficient directly detected optical OFDM for next-generation optical access networks.

    Science.gov (United States)

    Mehedy, Lenin; Bakaul, Masuduzzaman; Nirmalathas, Ampalavanapillai

    2010-10-25

    In this paper, we theoretically analyze and demonstrate that spectral efficiency of a conventional direct detection based optical OFDM system (DDO-OFDM) can be improved significantly using frequency interleaving of adjacent DDO-OFDM channels where OFDM signal band of one channel occupies the spectral gap of other channel and vice versa. We show that, at optimum operating condition, the proposed technique can effectively improve the spectral efficiency of the conventional DDO-OFDM system as much as 50%. We also show that such a frequency interleaved DDO-OFDM system, with a bit rate of 48 Gb/s within 25 GHz bandwidth, achieves sufficient power budget after transmission over 25 km single mode fiber to be used in next-generation time-division-multiplexed passive optical networks (TDM-PON). Moreover, by applying 64- quadrature amplitude modulation (QAM), the system can be further scaled up to 96 Gb/s with a power budget sufficient for 1:16 split TDM-PON.

  13. Frequency, types, and direct related costs of medication errors in an academic nephrology ward in Iran.

    Science.gov (United States)

    Gharekhani, Afshin; Kanani, Negin; Khalili, Hossein; Dashti-Khavidaki, Simin

    2014-09-01

    Medication errors are ongoing problems among hospitalized patients especially those with multiple co-morbidities and polypharmacy such as patients with renal diseases. This study evaluated the frequency, types and direct related cost of medication errors in nephrology ward and the role played by clinical pharmacists. During this study, clinical pharmacists detected, managed, and recorded the medication errors. Prescribing errors including inappropriate drug, dose, or treatment durations were gathered. To assess transcription errors, the equivalence of nursery charts and physician's orders were evaluated. Administration errors were assessed by observing drugs' preparation, storage, and administration by nurses. The changes in medications costs after implementing clinical pharmacists' interventions were compared with the calculated medications costs if the medication errors were continued up to patients' discharge time. More than 85% of patients experienced medication error. The rate of medication errors was 3.5 errors per patient and 0.18 errors per ordered medication. More than 95% of medication errors occurred at prescription nodes. Most common prescribing errors were omission (26.9%) or unauthorized drugs (18.3%) and low drug dosage or frequency (17.3%). Most of the medication errors happened on cardiovascular drugs (24%) followed by vitamins and electrolytes (22.1%) and antimicrobials (18.5%). The number of medication errors was correlated with the number of ordered medications and length of hospital stay. Clinical pharmacists' interventions decreased patients' direct medication costs by 4.3%. About 22% of medication errors led to patients' harm. In conclusion, clinical pharmacists' contributions in nephrology wards were of value to prevent medication errors and to reduce medications cost.

  14. 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

  15. A dual-frequency online PMP method with phase-shifting parallel to moving direction of measured object

    Science.gov (United States)

    Peng, Kuang; Cao, Yiping; Wu, Yingchun; Chen, Cheng; Wan, Yingying

    2017-01-01

    A dual-frequency online phase measurement profilometry (PMP) method with phase-shifting parallel to moving direction of measured object is proposed in this paper. The high-frequency fringe is used for the better modulation patterns in pixel matching and it is not modified by the measured object's surface. Based on the relative positive between the moving measured object and digital light processing (DLP), the high-frequency fringe in each dual-frequency deformed pattern after pixel matching is the same. As a result, the phase can be calculated directly by the improved Stoilov algorithm without filtering out the low-frequency component containing the measured object's height information. As there is no filtering process in phase calculation, the valid information loss can be avoided so that the accuracy of the proposed method can be guaranteed. Simulations and experiments prove the method's feasibility and precision.

  16. Sensitivity and resolution in frequency comb spectroscopy of buffer gas cooled polyatomic molecules

    Science.gov (United States)

    Changala, P. Bryan; Spaun, Ben; Patterson, David; Doyle, John M.; Ye, Jun

    2016-12-01

    We discuss the use of cavity-enhanced direct frequency comb spectroscopy in the mid-infrared region with buffer gas cooling of polyatomic molecules for high-precision rovibrational absorption spectroscopy. A frequency comb coupled to an optical enhancement cavity allows us to collect high-resolution, broad-bandwidth infrared spectra of translationally and rotationally cold (10-20 K) gas-phase molecules with high absorption sensitivity and fast acquisition times. The design and performance of the combined apparatus are discussed in detail. Recorded rovibrational spectra in the CH stretching region of several organic molecules, including vinyl bromide (CH_2CHBr), adamantane (C_{10}H_{16}), and diamantane (C_{14}H_{20}) demonstrate the resolution and sensitivity of this technique, as well as the intrinsic challenges faced in extending the frontier of high-resolution spectroscopy to large complex molecules.

  17. Design and Fabrication of 1.06 μm Resonant-Cavity Enhanced Reflective Modulator with GaInAs/GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    YANG Xiao-Hong; HAN Qin; NI Hai-Qiao; HUANG She-Song; DU Yun; PENG Hong-Ling; XIONG Yong-Hua; NIU Zhi-Chuan; WU Rong-Han

    2006-01-01

    A resonant-cavity enhanced reflective optical modulator is designed and fabricated, with three groups of three highly strained InGaAs/GaAs quantum wells in the cavity, for low voltage and high contrast ratio operation.The quantum wells are positioned in antinodes of the optical standing wave. The modulator is grown in a single growth step in an molecular beam epitaxy system, using GaAs/AlAs distributed Bragg reflectors as both the top and bottom mirrors. Results show that the reflection device has a modulation extinction of 3 dB at -4.5 V bias.

  18. Cavity enhanced absorption spectroscopy for N2O detection at 2.86μm using a continuous tunable color center laser

    Institute of Scientific and Technical Information of China (English)

    Shaocheng Li(李少成); Qingxu Yu(于清旭); Maarten van Herpen; Sacco te Lintel Hekkert; Frans J. M. Harren

    2003-01-01

    The cavity enhanced absorption technique is applied to N2O detection around 2.86 μm using a continuouswave color center laser. A high-finesse triangular ring cavity is used in this technology. Transmission through the cavity is obtained by jittering the cavity-length with a piezo on one of the cavity mirrors.A minimum detectable absorption coefficient of 2 × 10-6 cm-1 is achieved with a mirror reflectivity of 99.24%, corresponding to a N2O detection limit of 600 parts per billion.

  19. 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.

  20. 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...

  1. A Direct Assessment of the Role of Genetic Drift in Determining Allele Frequency Variation in Populations of EUPHYDRYAS EDITHA

    OpenAIRE

    Mueller, Laurence D.; Wilcox, Bruce A.; Ehrlich, Paul R.; David G Heckel; Murphy, Dennis D.

    1985-01-01

    Estimates of allele frequencies at six polymorphic loci were collected over eight generations in two populations of Euphydryas editha . We have estimated, in addition, the effective population size for each generation for both populations with results from mark-recapture and other field data. The variation in allele frequencies generated by random genetic drift was then studied using computer simulations and our direct estimates of effective population size. Substantial differences between ob...

  2. 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.

  3. 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.

  4. Direct Spectroscopy in Hollow Optical with Fiber-Based Optical Frequency Combs

    Science.gov (United States)

    2015-07-09

    stabilization To fully stabilize the comb, there are three servo loops, shown in Fig. 1, that lock the carrier offset frequency f0 to an RF synthesizer ...GPS-Rb oscillator serves as the external reference for all synthesizers and frequency counters. The filtering cavity is stabilized to a particular...filled frequency reference in a 10 m length. Since optimal single-modedness is expected at longer lengths (~10-30 m), a gas such as ammonia , with weaker

  5. 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.

  6. Spatial profiles of interelectrode electron density in direct current superposed dual-frequency capacitively coupled plasmas

    Science.gov (United States)

    Ohya, Yoshinobu; Ishikawa, Kenji; Komuro, Tatsuya; Yamaguchi, Tsuyoshi; Takeda, Keigo; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru

    2017-04-01

    We present experimentally determined spatial profiles of the interelectrode electron density (n e) in dual-frequency capacitively coupled plasmas in which the negative direct current (dc) bias voltage (V dc) is superposed; in the experiment, 13 MHz (P low) was applied to the lower electrode and 60 MHz (P high) to the upper electrode. The bulk n e increased substantially with increases in the external power, P high, P low, and with increases in V dc. When P low was insufficient, the bulk n e decreased as the V dc bias increased. The bulk n e increased due to its dependence on V dc, especially for |V dc|  >  500 V. This may correspond to the sheath voltages (V s) of the lower electrode. The n e values in front of the upper electrode were coupled with the V dc: the V dc dependence first decreased and then increased. The dc currents (I dc) of the upper electrode were collected when a large P low was applied. The value of I dc at the threshold value of V dc  ≈  V s (e.g.  ‑500 V) increased with an increase in n e. When |V dc| exceeded the threshold, the spatial n e profile and the I dc dependence were changed relative to the electrical characteristics of the dc superposition; this led to a change in the location of the maximum n e, the width of the area of n e depletion in front of the electrodes, and a transition in the electron heating modes.

  7. Decision-Directed Frequency Tracking Algorithm for OFDM System in Fast Fading Environments

    Institute of Scientific and Technical Information of China (English)

    HE Bo; LI Jun; LIN Jia-ru; WU Wei-ling

    2005-01-01

    This paper analyzed the structure of Orthogonal Frequency Division Multiplex (OFDM) system and presented a new Carrier Frequency Offset (CFO) tracking algorithm, which depends on comparability between the decision data and the original data to correct carrier frequency offset. Therefore it is robust during the normal communization process since the Bit Error Rate (BER) of the decision data is low. We can utilize pilot data in time domain for channel estimation to track CFO without reducing system efficient and to enhance the tracking scope largely. Simulation results denote the presented algorithm can track the frequency offset and control it under ±1% using only 1 frame if the original frequency offset is within ±8%.

  8. Stretchable Complementary Split Ring Resonator (CSRR-Based Radio Frequency (RF Sensor for Strain Direction and Level Detection

    Directory of Open Access Journals (Sweden)

    Seunghyun Eom

    2016-10-01

    Full Text Available In this paper, we proposed a stretchable radio frequency (RF sensor to detect strain direction and level. The stretchable sensor is composed of two complementary split ring resonators (CSRR with microfluidic channels. In order to achieve stretchability, liquid metal (eutectic gallium-indium, EGaIn and Ecoflex substrate are used. Microfluidic channels are built by Ecoflex elastomer and microfluidic channel frames. A three-dimensional (3D printer is used for fabrication of microfluidic channel frames. Two CSRR resonators are designed to resonate 2.03 GHz and 3.68 GHz. When the proposed sensor is stretched from 0 to 8 mm along the +x direction, the resonant frequency is shifted from 3.68 GHz to 3.13 GHz. When the proposed sensor is stretched from 0 to 8 mm along the −x direction, the resonant frequency is shifted from 2.03 GHz to 1.78 GHz. Therefore, we can detect stretched length and direction from independent variation of two resonant frequencies.

  9. 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

  10. Focusing transform-based direction-of-arrival method exploiting multi-cycle frequencies

    Institute of Scientific and Technical Information of China (English)

    HUANG Zhitao; JIANG Wenli; ZHOU Yiyu

    2005-01-01

    When single cycle frequency is employed, the existing spectral correlation-signal subspace fitting (SC-SSF) algorithms usually contain two disadvantages: those single-cycle estimators cannot reach the best performance; it is inconvenient to be applied in practice since the right cycle frequency has to be selected. Based on the Jacobi-Anger expansion and the idea of focusing transform, a new approach exploiting multi-cycle frequencies of cyclostationary signal is discussed in this paper. Simulation results demonstrate the effectiveness of the new method.

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

    Directory of Open Access Journals (Sweden)

    Wang Xudong

    2012-01-01

    Full Text Available 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 angle estimation performance of the proposed algorithm is greatly improved. The frequency estimation performance of the proposed algorithm is same with that of Wang’s ESPRIT algorithm. Furthermore, the proposed algorithm can obtain automatic pairing DOA and frequency parameters, and it has a comparative computational complexity in contrast to Wang’s ESPRIT algorithm. By the way, this proposed algorithm can also work well for nonuniform linear arrays. The useful behavior of this proposed algorithm is verified by simulations.

  12. Direction of information flow in large-scale resting-state networks is frequency-dependent

    NARCIS (Netherlands)

    Hillebrand, Arjan; Tewarie, Prejaas; Van Dellen, Edwin; Yu, Meichen; Carbo, Ellen W S; Douw, Linda; Gouw, Alida A.; Van Straaten, Elisabeth C W; Stam, Cornelis J.

    2016-01-01

    Normal brain function requires interactions between spatially separated, and functionally specialized, macroscopic regions, yet the directionality of these interactions in large-scale functional networks is unknown. Magnetoencephalography was used to determine the directionality of these interaction

  13. 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.

  14. Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OClO and CH20 in Cl-initiated Photooxidation Experiment

    Institute of Scientific and Technical Information of China (English)

    Mei-li Dong; Wei-xiong Zhao; Ming-qiang Huang; Wei-dong Chen; Chang-jin Hu; Xue-jun Gu; Shi-xin Pei

    2013-01-01

    Chlorine dioxide (OClO) is an important indicator for Cl-activation.The monitoring of OClO appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas.We report the development of a Xe arc lamp based near-ultraviolet (335-375 nm) incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) spectrometer for quantitative assessment of OClO in an atmospheric simulation chamber.The important intermediate compound CH2O,and other key atmospheric trace species (NO2) were also simultaneously measured.The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.

  15. 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.

  16. 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...

  17. Direct measurement of the poliovirus RNA polymerase error frequency in vitro

    Energy Technology Data Exchange (ETDEWEB)

    Ward, C.D.; Stokes, M.A.M.; Flanegan, J.B. (Univ. of Florida College of Medicine, Gainesville (USA))

    1988-02-01

    The fidelity of RNA replication by the poliovirus-RNA-dependent RNA polymerase was examined by copying homopolymeric RNA templates in vitro. The poliovirus RNA polymerase was extensively purified and used to copy poly(A), poly(C), or poly(I) templates with equimolar concentrations of noncomplementary and complementary ribonucleotides. The error frequency was expressed as the amount of a noncomplementary nucleotide incorporated divided by the total amount of complementary and noncomplementary nucleotide incorporated. The polymerase error frequencies were very high, depending on the specific reaction conditions. The activity of the polymerase on poly(U) and poly(G) was too low to measure error frequencies on these templates. A fivefold increase in the error frequency was observed when the reaction conditions were changed from 3.0 mM Mg{sup 2+} (pH 7.0) to 7.0 mM Mg{sup 2+} (pH 8.0). This increase in the error frequency correlates with an eightfold increase in the elongation rate that was observed under the same conditions in a previous study.

  18. Zipf's word frequency law in natural language: a critical review and future directions.

    Science.gov (United States)

    Piantadosi, Steven T

    2014-10-01

    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 reviewed. These facts are chosen to be informative about the mechanisms giving rise to Zipf's law and are then used to evaluate many of the theoretical explanations of Zipf's law in language. No prior account straightforwardly explains all the basic facts or is supported with independent evaluation of its underlying assumptions. To make progress at understanding why language obeys Zipf's law, studies must seek evidence beyond the law itself, testing assumptions and evaluating novel predictions with new, independent data.

  19. 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...

  20. Direct observation of female mating frequency using time-lapse photography

    NARCIS (Netherlands)

    Kuijper, Bram; Morrow, Edward H.

    2009-01-01

    One basic condition of postmating sexual selection is that females mate more than once before fertilizing their ova. Knowledge of the frequency and extent of multiple mating in a given population or species is therefore important in order to fully understand the potential for sexual selection, in th

  1. Direct Derivation of the Gravitational Red Shift (Einstein Shift) with the frequency dependent Gall metric

    Science.gov (United States)

    Gall, Clarence A.

    1999-05-01

    When an electromagnetic radiation (EMR) source is in uniform motion with respect to an observer, a spectral (Doppler) shift in frequency is seen (blue as it approaches, red as it recedes). Since special relativity is limited to coordinate systems in uniform relative motion, this theory should be subject to this condition. On the other hand, the gravitational red shift (Einstein; Relativity: The Special and the General Theory, Crown,(1961), p.129) claims that EMR frequency decreases as the gravitational field, where the source is located, increases. As a gravitational effect, one would expect its derivation from a solution of the general relativistic field equations (R_μσ=0). Up to now, it has only been possible to derive it indirectly, by comparing the gravitational field to a (centrifugal) field produced by coordinate systems in relative rotational motion as an approximation of special relativity. Since rotation implies acceleration, it does not meet the conditions of special relativity so this is unsatisfactory. This work shows that the problem lies in the Schwarzschild metric which is independent of EMR frequency. By contrast it is easy to deduce the gravitational red shift from the frequency dependent Gall metric (Gall in AIP Conference Proceedings 308, The Evolution of X-Ray Binaries,(1993), p. 87).

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

    DEFF Research Database (Denmark)

    Hu, Weihao; Su, Chi; Fang, Jiakun;

    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 ...

  3. The influence of task frequency and force direction on psychophysically acceptable forces in the context of the biomechanically weakest links.

    Science.gov (United States)

    Cudlip, Alan C; Fischer, Steven L; Wells, Richard; Dickerson, Clark R

    2013-06-01

    This study examined the influence of frequency and direction of force application on psychophysically acceptable forces for simulated work tasks. Fifteen male participants exerted psychophysically acceptable forces on a force transducer at 1, 3, or 5 repetitions per minute by performing both a downward press and a pull toward the body. These exertions were shown previously to be strength and balance limited, respectively. Workers chose acceptable forces at a lower percentage of their maximum voluntary force capacity during downward (strength-limited) exertions than during pulling (balance-limited) exertions at all frequencies (4% to 11%, P = .035). Frequency modulated acceptable hand force only during downward exertions, where forces at five repetitions per minute were 13% less (P = .005) than those at one exertion per minute. This study provides insight into the relationship between biomechanically limiting factors and the selection of acceptable forces for unilateral manual tasks.

  4. Recombination frequency in plasmid DNA containing direct repeats--predictive correlation with repeat and intervening sequence length.

    Science.gov (United States)

    Oliveira, Pedro H; Lemos, Francisco; Monteiro, Gabriel A; Prazeres, Duarte M F

    2008-09-01

    In this study, a simple non-linear mathematical function is proposed to accurately predict recombination frequencies in bacterial plasmid DNA harbouring directly repeated sequences. The mathematical function, which was developed on the basis of published data on deletion-formation in multicopy plasmids containing direct-repeats (14-856 bp) and intervening sequences (0-3872 bp), also accounts for the strain genotype in terms of its recA function. A bootstrap resampling technique was used to estimate confidence intervals for the correlation parameters. More than 92% of the predicted values were found to be within a pre-established +/-5-fold interval of deviation from experimental data. The correlation does not only provide a way to predict, with good accuracy, the recombination frequency, but also opens the way to improve insight into these processes.

  5. Directional velocity estimation using a spatio-temporal encoding technique based on frequency division for synthetic transmit aperture ultrasound

    DEFF Research Database (Denmark)

    Gran, Fredrik; Jensen, Jørgen Arendt

    2006-01-01

    This paper investigates the possibility of flow estimation using spatio-temporal encoding of the transmissions in synthetic transmit aperture imaging (STA). The spatial encoding is based on a frequency division approach. In STA, a major disadvantage is that only a single transmitter (denoting...... be increased. However, to focus the data properly, the signals originating from the different transmitters must be separated. To do so, the pass band of the transducer is divided into a number of subbands with disjoint spectral support. At every transmission, each transmitter is assigned one of the subbands...... in the flow direction, directional data were extracted and correlated. Hereby, the velocity of the blood was estimated. The pulse repetition frequency was 16 kHz. Three different setups were investigated with flow angles of 45, 60, and 75 degrees with respect to the acoustic axis. Four different velocities...

  6. Direct comparison of phase-sensitive vibrational sum frequency generation with maximum entropy method: case study of water.

    Science.gov (United States)

    de Beer, Alex G F; Samson, Jean-Sebastièn; Hua, Wei; Huang, Zishuai; Chen, Xiangke; Allen, Heather C; Roke, Sylvie

    2011-12-14

    We present a direct comparison of phase sensitive sum-frequency generation experiments with phase reconstruction obtained by the maximum entropy method. We show that both methods lead to the same complex spectrum. Furthermore, we discuss the strengths and weaknesses of each of these methods, analyzing possible sources of experimental and analytical errors. A simulation program for maximum entropy phase reconstruction is available at: http://lbp.epfl.ch/.

  7. Index and Bulk Parameters for Frequency-Direction Spectra Measured at CERC Field Research Facility, September 1991 to August 1992

    Science.gov (United States)

    1994-05-01

    Index and Bulk Parameters for Frequency- Direction Spectra Measured at CERC Field Research Facility, September 1991 to August 1992 Accion For by...Prepared for U.S. Army Corps of Engineers Washington, DC 20314-1000 Under Civil Works Research Work Unit 32484 M US Army Corps of Engineers Waterways...that affect coastal engineering pro- jects. This effort was authorized by Headquarters, U.S. Army Corps o.’ Engi- neers (HQUSACE), under Civil Works

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

    DEFF Research Database (Denmark)

    Karimian-Azari, Sam

    their time differences which eventually may further reduce the effects of noise. This thesis introduces a number of principles and methods to estimate periodic signals in noisy environments with application to multichannel speech enhancement. We propose model-based signal enhancement concerning the model......-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...... in 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...

  9. Study on forming directivity with constant beam width in low frequency based on small sensor

    Institute of Scientific and Technical Information of China (English)

    HUI Junying; LIU Hong; YU Huabing; LIANG Guolong

    2001-01-01

    Based on a combined sensor with the size of 10 cm, a narrow beam with a constant receiving beam width of 20 degree has been formed in low frequency from several Hz to thousands of Hz by using simple adaptive algorithm. The results of theoretical simulation,laboratory experiment and lake experiment with one-dimension and two-dimension combined sensors have been given.

  10. Target DNA sequence directly regulates the frequency of activation-induced deaminase-dependent mutations.

    Science.gov (United States)

    Chen, Zhangguo; Viboolsittiseri, Sawanee S; O'Connor, Brian P; Wang, Jing H

    2012-10-15

    Activation-induced deaminase (AID) catalyses class switch recombination (CSR) and somatic hypermutation (SHM) in B lymphocytes to enhance Ab diversity. CSR involves breaking and rejoining highly repetitive switch (S) regions in the IgH (Igh) locus. S regions appear to be preferential targets of AID. To determine whether S region sequence per se, independent of Igh cis regulatory elements, can influence AID targeting efficiency and mutation frequency, we established a knock-in mouse model by inserting a core Sγ1 region into the first intron of proto-oncogene Bcl6, which is a non-Ig target of SHM. We found that the mutation frequency of the inserted Sγ1 region was dramatically higher than that of the adjacent Bcl6 endogenous sequence. Mechanistically, S region-enhanced SHM was associated with increased recruitment of AID and RNA polymerase II, together with Spt5, albeit to a lesser extent. Our studies demonstrate that target DNA sequences influence mutation frequency via regulating AID recruitment. We propose that the nucleotide sequence preference may serve as an additional layer of AID regulation by restricting its mutagenic activity to specific sequences despite the observation that AID has the potential to access the genome widely.

  11. Polarization dependence of the direct two photon transitions of 87Rb atoms by erbium: Fiber laser frequency comb

    Science.gov (United States)

    Dai, Shaoyang; Xia, Wei; Zhang, Yin; Zhao, Jianye; Zhou, Dawei; Wang, Qing; Yu, Qi; Li, Kunqian; Qi, Xianghui; Chen, Xuzong

    2016-11-01

    The femtosecond fiber-based optical frequency combs have been proved to be powerful tools for investigating the energy levels of atoms and molecules. In this paper, an Er-doped fiber femtosecond optical frequency comb has been implemented for studying the polarization dependence of 5S-5D two-photon transitions in thermal gas of atomic rubidium 87 using an entirely symmetrical optical configuration. By changing the polarization states of the counter-propagating light beams, the polarization dependence of direct two photon transition spectrum is demonstrated, and a dramatic variation (up to 5.5 times) of the two-photon transitions strength has been observed. The theory for the polarization dependence of two photon transition based on the second-order perturbation was established, which is in good agreement with the experimental results. The measurement results indicate that the polarization state manipulation with the existing frequency comb is used for femtosecond optical frequency comb based two photon transition spectroscopic purposes, which will improve the precision measurement of the absolute transition frequency and related applications.

  12. Nanoscale resonant-cavity-enhanced germanium photodetectors with lithographically defined spectral response for improved performance at telecommunications wavelengths.

    Science.gov (United States)

    Balram, Krishna C; Audet, Ross M; Miller, David A B

    2013-04-22

    We demonstrate the use of a subwavelength planar metal-dielectric resonant cavity to enhance the absorption of germanium photodetectors at wavelengths beyond the material's direct absorption edge, enabling high responsivity across the entire telecommunications C and L bands. The resonant wavelength of the detectors can be tuned linearly by varying the width of the Ge fin, allowing multiple detectors, each resonant at a different wavelength, to be fabricated in a single-step process. This approach is promising for the development of CMOS-compatible devices suitable for integrated, high-speed, and energy-efficient photodetection at telecommunications wavelengths.

  13. Resonance Frequency of Optical Microbubble Resonators: Direct Measurements and Mitigation of Fluctuations

    Science.gov (United States)

    Cosci, Alessandro; Berneschi, Simone; Giannetti, Ambra; Farnesi, Daniele; Cosi, Franco; Baldini, Francesco; Nunzi Conti, Gualtiero; Soria, Silvia; Barucci, Andrea; Righini, Giancarlo; Pelli, Stefano

    2016-01-01

    This work shows the improvements in the sensing capabilities and precision of an Optical Microbubble Resonator due to the introduction of an encaging poly(methyl methacrylate) (PMMA) box. A frequency fluctuation parameter σ was defined as a score of resonance stability and was evaluated in the presence and absence of the encaging system and in the case of air- or water-filling of the cavity. Furthermore, the noise interference introduced by the peristaltic and the syringe pumping system was studied. The measurements showed a reduction of σ in the presence of the encaging PMMA box and when the syringe pump was used as flowing system. PMID:27589761

  14. Frequency-Modulated Microwave Photonic Links with Direct Detection: Review and Theory

    Science.gov (United States)

    2010-12-15

    approach for digital signals looks at an eye diagram and uses a Levenberg-Marquart optimization to maximize the eye opening. • LMSE / minimize ISI [56...FFT number o f po in t s etaMHz = param ( 3 ) ; % Frequency modulation e f f i c i e n c y in MHz/mA G = param ( 4 ) ; % RIM norma l i za t ion...in MHz/mA G = param ( 4 ) ; % RIM norma l i za t ion parameter PmW = param ( 5 ) ; % Opt i ca l power b e f o r e the f i l t e r s R = param ( 6

  15. Direct observation of low frequency confined acoustic phonons in silver nanoparticles: Terahertz time domain spectroscopy.

    Science.gov (United States)

    Kumar, Sunil; Kamaraju, N; Karthikeyan, B; Tondusson, M; Freysz, E; Sood, A K

    2010-07-01

    Terahertz time domain spectroscopy has been used to study low frequency confined acoustic phonons of silver nanoparticles embedded in poly(vinyl alcohol) matrix in the spectral range of 0.1-2.5 THz. The real and imaginary parts of the dielectric function show two bands at 0.60 and 2.12 THz attributed to the spheroidal and toroidal modes of silver nanoparticles, thus demonstrating the usefulness of terahertz time domain spectroscopy as a complementary technique to Raman spectroscopy in characterizing the nanoparticles.

  16. 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.

  17. 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

  18. 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.

  19. Manipulation of cell cycle progression can counteract the apparent loss of correction frequency following oligonucleotide-directed gene repair

    Directory of Open Access Journals (Sweden)

    Kmiec Eric B

    2007-02-01

    Full Text Available Abstract Background Single-stranded oligonucleotides (ssODN are used routinely to direct specific base alterations within mammalian genomes that result in the restoration of a functional gene. Despite success with the technique, recent studies have revealed that following repair events, correction frequencies decrease as a function of time, possibly due to a sustained activation of damage response signals in corrected cells that lead to a selective stalling. In this study, we use thymidine to slow down the replication rate to enhance repair frequency and to maintain substantial levels of correction over time. Results First, we utilized thymidine to arrest cells in G1 and released the cells into S phase, at which point specific ssODNs direct the highest level of correction. Next, we devised a protocol in which cells are maintained in thymidine following the repair reaction, in which the replication is slowed in both corrected and non-corrected cells and the initial correction frequency is retained. We also present evidence that cells enter a senescence state upon prolonged treatment with thymidine but this passage can be avoided by removing thymidine at 48 hours. Conclusion Taken together, we believe that thymidine may be used in a therapeutic fashion to enable the maintenance of high levels of treated cells bearing repaired genes.

  20. Nonstationary Interference Excision in Time-Frequency Domain Using Adaptive Hierarchical Lapped Orthogonal Transform for Direct Sequence Spread Spectrum Communications

    Directory of Open Access Journals (Sweden)

    Zhu Yi-Sheng

    2003-01-01

    Full Text Available An adaptive hierarchical lapped orthogonal transform (HLOT exciser is proposed for tracking, localizing, and rejecting the nonstationary interference in direct sequence spread spectrum (DSSS communications. The method is based on HLOT. It utilizes a fast dynamic programming algorithm to search for the best basis, which matches the interference structure best, in a library of lapped orthogonal bases. The adaptive HLOT differs from conventional block transform and the more advanced modulated lapped transform (MLT in that the former produces arbitrary time-frequency tiling, which can be adapted to the signal structure, while the latter yields fixed tilings. The time-frequency tiling of the adaptive HLOT can be time varying, so it is also able to track the variations of the signal time-frequency structure. Simulation results show that the proposed exciser brings significant performance improvement in the presence of nonstationary time-localized interference with or without instantaneous frequency (IF information compared with the existing block transform domain excisers. Also, the proposed exciser is effective in suppressing narrowband interference and combined narrowband and time-localized impulsive interference.

  1. Directly Phase-Modulated Light Source

    Science.gov (United States)

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

    2016-07-01

    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 have 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 subvolt half-wave phase modulation at high signal rates. The source is compact, stable, and versatile, and we show its potential to become the standard transmitter for future quantum communication networks based on attenuated laser pulses.

  2. Adaptive extraction of emotion-related EEG segments using multidimensional directed information in time-frequency domain.

    Science.gov (United States)

    Petrantonakis, Panagiotis C; Hadjileontiadis, Leontios J

    2010-01-01

    Emotion discrimination from electroencephalogram (EEG) has gained attention the last decade as a user-friendly and effective approach to EEG-based emotion recognition (EEG-ER) systems. Nevertheless, challenging issues regarding the emotion elicitation procedure, especially its effectiveness, raise. In this work, a novel method, which not only evaluates the degree of emotion elicitation but localizes the emotion information in the time-frequency domain, as well, is proposed. The latter, incorporates multidimensional directed information at the time-frequency EEG representation, extracted using empirical mode decomposition, and introduces an asymmetry index for adaptive emotion-related EEG segment selection. Experimental results derived from 16 subjects visually stimulated with pictures from the valence/arousal space drawn from the International Affective Picture System database, justify the effectiveness of the proposed approach and its potential contribution to the enhancement of EEG-ER systems.

  3. Performance characteristics of a passively locked cavity-enhanced absorption spectrometer with wideband-tunable multimode near-infrared light source

    Science.gov (United States)

    Someya, Ryuta; Imamura, Takeshi; Okamoto, Tetsushi; Hatano, Hiroshi; Toyoshima, Naoko; Tei, Kazuyoku; Yamaguchi, Shigeru

    2016-03-01

    A trace material detection system was developed on the basis of cavity-enhanced absorption spectroscopy (CEAS) using a fiber-coupled passively locked external cavity diode laser (PLEC-DL) in the near-infrared (NIR) wavelength region. The oscillation range of an antireflection-coated diode laser (AR-DL) coupled into an external cavity could be simply selected with a narrowband bandpass filter (1 nm), resulting in a stable wavelength oscillation in the wideband tunability between 1640 and 1680 nm. The external cavity acts as a trace material sensor that exhibits excellent flexibility because it is free from the DL source and is carefully designed with mirrors having reflectivities of ca. 99.995 and 99.99%. Trace-level detection was successfully demonstrated with the developed sensor having a minimum detectable absorption coefficient of 2.4 × 10-8 cm-1, which corresponds to 0.15 ppm for CH4 concentration without interference from H2O absorption lines under atmospheric pressure.

  4. High-resolution Fourier-transform cavity-enhanced absorption spectroscopy in the near-infrared using an incoherent broad-band light source.

    Science.gov (United States)

    Orphal, Johannes; Ruth, Albert A

    2008-11-10

    An incoherent broad-band cavity-enhanced absorption (IBB-CEA) set-up was used in combination with a Fourier-transform (FT) spectrometer in order to explore the potential of this technique for high-resolution molecular spectroscopy in the near-infrared region. Absorption spectra of overtone bands of CO2, OCS, and HD18O were measured between 5800 and 7000 cm(-1) using a small sampling volume (1100 cm3, based on a 90 cm cavity length). The quality of the spectra in this study is comparable to that obtained with Fourier transform spectrometers employing standard multi-pass reflection cells, which require substantially larger sampling volumes. High-resolution methods such as FT-IBB-CEAS also provide an elegant way to determine effective mirror reflectivities (R(eff), i.e. a measure of the inherent overall cavity loss) by using a calibration gas with well-known line strengths. For narrow absorption features and non-congested spectra this approach does not even require a zero-absorption measurement with the empty cavity. Absolute cross-sections or line strengths of a target species can also be determined in one single measurement, if gas mixtures with known partial pressures are used. This feature of FT-IBB-CEAS reduces systematic errors significantly; it is illustrated based on CO2 as calibration gas.

  5. Trace species detection in the near infrared using Fourier transform broadband cavity enhanced absorption spectroscopy: initial studies on potential breath analytes.

    Science.gov (United States)

    Denzer, W; Hancock, G; Islam, M; Langley, C E; Peverall, R; Ritchie, G A D; Taylor, D

    2011-02-21

    Cavity enhanced absorption measurements have been made of several species that absorb light between 1.5 and 1.7 µm using both a supercontinuum source and superluminescent light emitting diodes. A system based upon an optical enhancement cavity of relatively high finesse, consisting of mirrors of reflectivity ∼99.98%, and a Fourier transform spectrometer, is demonstrated. Spectra are recorded of isoprene, butadiene, acetone and methane, highlighting problems with spectral interference and unambiguous concentration determinations. Initial results are presented of acetone within a breath-like matrix indicating ppm precision at absorption coefficient of ∼4 × 10(-9) cm(-1) reported within a 4 min acquisition time. Finally, two superluminescent light emitting diodes are coupled together to increase the wavelength coverage, and measurements are made simultaneously on acetylene, CO(2), and butadiene. The absorption cross-sections for acetone and isoprene have been measured with an instrumental resolution of 4 cm(-1) and are found to be 1.3 ± 0.1 × 10(-21) cm(2) at a wavelength of 1671.9 nm and 3.6 ± 0.2 × 10(-21) cm(2) at 1624.7 nm, respectively.

  6. 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.

  7. Improved Shock Tube Measurement of the CH4 + Ar = CH3 + H + Ar Rate Constant using UV Cavity-Enhanced Absorption Spectroscopy of CH3.

    Science.gov (United States)

    Wang, Shengkai; Davidson, David F; Hanson, Ronald K

    2016-07-21

    We report an improved measurement for the rate constant of methane dissociation in argon (CH4 + Ar = CH3 + H + Ar) behind reflected shock waves. The experiment was conducted using a sub-parts per million sensitivity CH3 diagnostic recently developed in our laboratory based on ultraviolet cavity-enhanced absorption spectroscopy. The high sensitivity of this diagnostic allowed for measurements of quantitatively resolved CH3 time histories during the initial stage of CH4 pyrolysis, where the reaction system is clean and free from influences of secondary reactions and temperature change. This high sensitivity also allowed extension of our measurement range to much lower temperatures (shock measurements were performed at temperatures between 1487 and 1866 K and pressures near 1.7 atm, resulting in the following Arrhenius rate constant expression for the title reaction: k(1.7 atm) = 3.7 × 10(16) exp(-42 200 K/T) cm(3)/mol·s, with a 2σ uncertainty factor of 1.25. The current data are in good consensus with various theoretical and review studies, but at the low temperature end they suggest a slightly higher (up to 35%) rate constant compared to these previous results. A re-evaluation of previous and current experimental data in the falloff region was also performed, yielding updated expressions for both the low-pressure limit and the high-pressure limit rate constants and improved agreement with all existing data.

  8. Validation and application of cavity-enhanced, near-infrared tunable diode laser absorption spectrometry for measurements of methane carbon isotopes at ambient concentrations.

    Science.gov (United States)

    Mortazavi, Behzad; Wilson, Benjamin J; Dong, Feng; Gupta, Manish; Baer, Doug

    2013-10-15

    Methane is an effective greenhouse gas but has a short residence time in the atmosphere, and therefore, reductions in emissions can alleviate its greenhouse gas warming effect within a decadal time frame. Continuous and high temporal resolution measurements of methane concentrations and carbon isotopic ratios (δ(13)CH4) can inform on mechanisms of formation, provide constraints on emissions sources, and guide future mitigation efforts. We describe the development, validation, and deployment of a cavity-enhanced, near-infrared tunable diode laser absorption spectrometry system capable of quantifying δ(13)CH4 at ambient methane concentrations. Laboratory validation and testing show that the instrument is capable of operating over a wide dynamic range of methane concentration and provides a measurement precision for δ(13)CH4 of better than ± 0.5 ‰ (1σ) over 1000 s of data averaging at ambient methane concentrations. The analyzer is accurate to better than ± 0.5 ‰, as demonstrated by measurements of characterized methane/air samples with minimal dependence (methane concentration. Deployment of the instrument at a marsh over multiple days demonstrated how methane fluxes varied by an order of magnitude over 2 day deployment periods, and showed a 17 ‰ variability in δ(13)CH4 of the emitted methane during the growing season.

  9. 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.

  10. 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}$ ...

  11. A New Fixed Switching Frequency Direct Torque Controlled PMSM Drives with Low Ripple in Flux and Torque

    Directory of Open Access Journals (Sweden)

    Tole Sutikno

    2011-11-01

    Full Text Available Direct Torque Control (DTC has gained popularity for development of advanced motor control due to its simplicity and offers fast instantaneous torque and flux controls. However, the conventional DTC which is based on hysteresis controller has major drawbacks, namely high torque ripple and variable inverter switching frequency. This paper presents an improved switching strategy for reducing flux and torque ripples in DTC of PMSM drives; wherein the torque hysteresis controller and the look-up table used in the conventional DTC are replaced with a constant frequency torque controller (CFTC and an optimized look-up table, respectively. It can be shown that a constant switching frequency is established due to the use of the CFTC while the reduction of torque and flux ripples is achieved mainly because of the selection of optimized voltage vector (i.e. with an optimized look-up table. This paper also will explain the construction of DTC schemes implemented using MATLAB-Simulink blocks. Simulation results were shown that a significant reduction of flux and torque ripples which is about 90% can be achieved through the proposed DTC scheme.

  12. Increasing Accuracy: A New Design and Algorithm for Automatically Measuring Weights, Travel Direction and Radio Frequency Identification (RFID) of Penguins.

    Science.gov (United States)

    Afanasyev, Vsevolod; Buldyrev, Sergey V; Dunn, Michael J; Robst, Jeremy; Preston, Mark; Bremner, Steve F; Briggs, Dirk R; Brown, Ruth; Adlard, Stacey; Peat, Helen J

    2015-01-01

    A fully automated weighbridge using a new algorithm and mechanics integrated with a Radio Frequency Identification System is described. It is currently in use collecting data on Macaroni penguins (Eudyptes chrysolophus) at Bird Island, South Georgia. The technology allows researchers to collect very large, highly accurate datasets of both penguin weight and direction of their travel into or out of a breeding colony, providing important contributory information to help understand penguin breeding success, reproductive output and availability of prey. Reliable discrimination between single and multiple penguin crossings is demonstrated. Passive radio frequency tags implanted into penguins allow researchers to match weight and trip direction to individual birds. Low unit and operation costs, low maintenance needs, simple operator requirements and accurate time stamping of every record are all important features of this type of weighbridge, as is its proven ability to operate 24 hours a day throughout a breeding season, regardless of temperature or weather conditions. Users are able to define required levels of accuracy by adjusting filters and raw data are automatically recorded and stored allowing for a range of processing options. This paper presents the underlying principles, design specification and system description, provides evidence of the weighbridge's accurate performance and demonstrates how its design is a significant improvement on existing systems.

  13. Increasing Accuracy: A New Design and Algorithm for Automatically Measuring Weights, Travel Direction and Radio Frequency Identification (RFID of Penguins.

    Directory of Open Access Journals (Sweden)

    Vsevolod Afanasyev

    Full Text Available A fully automated weighbridge using a new algorithm and mechanics integrated with a Radio Frequency Identification System is described. It is currently in use collecting data on Macaroni penguins (Eudyptes chrysolophus at Bird Island, South Georgia. The technology allows researchers to collect very large, highly accurate datasets of both penguin weight and direction of their travel into or out of a breeding colony, providing important contributory information to help understand penguin breeding success, reproductive output and availability of prey. Reliable discrimination between single and multiple penguin crossings is demonstrated. Passive radio frequency tags implanted into penguins allow researchers to match weight and trip direction to individual birds. Low unit and operation costs, low maintenance needs, simple operator requirements and accurate time stamping of every record are all important features of this type of weighbridge, as is its proven ability to operate 24 hours a day throughout a breeding season, regardless of temperature or weather conditions. Users are able to define required levels of accuracy by adjusting filters and raw data are automatically recorded and stored allowing for a range of processing options. This paper presents the underlying principles, design specification and system description, provides evidence of the weighbridge's accurate performance and demonstrates how its design is a significant improvement on existing systems.

  14. 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.

  15. 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.

  16. Switching direction affects switching costs: Behavioral, ERP and time-frequency analyses of intra-sentential codeswitching.

    Science.gov (United States)

    Litcofsky, Kaitlyn A; Van Hell, Janet G

    2017-02-03

    Bilinguals have the unique ability to produce utterances that switch between languages. Most language switching research has focused on isolated, unrelated items, which emphasizes separation of the languages. Fewer studies examined the cognitive and neural mechanisms of switching languages in natural discourse. The present study examined the effect of codeswitching direction on the comprehension of intra-sentential codeswitching in Spanish-English bilinguals, using self-paced reading behavioral measurements (Experiment 1) and electroencephalography (EEG) measurements (Experiment 2), analyzed via both event-related potentials (ERPs) and time-frequency analysis (TFR). Reading times showed a significant switching cost for codeswitched sentences in both codeswitching directions, though switching costs were somewhat higher into the dominant language than into the weaker language. ERPs showed that codeswitched as compared to non-switched words elicited a late positivity, but only when switching from the dominant into the weaker language, not in the reverse direction. TFRs showed complementary and converging results: switches into the weaker language resulted in a power decrease in lower beta band while switches into the dominant language resulted in a power increase in theta band. These multi-method findings provide novel insights into neurocognitive resources engaged in the comprehension of intra-sentential codeswitches related to sentence-level restructuring processes to activate and access the weaker language.

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

    NARCIS (Netherlands)

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

    2015-01-01

    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 stabilizati

  18. The Fabrication of Flow Field Plates for Direct Methanol Fuel Cell Using Lithography and Radio Frequency Sputtering.

    Science.gov (United States)

    Chang, Ho; Kao, Mu-Jung; Chen, Chih-Hao; Cho, Kun-Ching; Hsu, Chun-Yao; Chen, Zhi-Lun

    2015-08-01

    This study uses lithography to etch flow fields on a single side of a printed circuit board (PCB) and combines a flow field plate with a collector plate to make innovative anode flow field plates and cathode flow field plates for a direct methanol fuel cell (DMFC). TiO2 thin film is also sputtered on the anode flow field plate using radio frequency (RF) sputtering. The experimental results show that the prepared DMFC has a better maximum power density of 11.928 mW/cm2. Furthermore, when a TiO2 thin film is sputtered on the flow field plate of the assembled DMFC, the maximum power density is 14.426 mW/cm2, which is actually 21% more than that for a DMFC with no TiO2 thin film coated on the flow field plate.

  19. 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.

  20. A computer analysis of a conical monopole for use at Naval High Frequency Direction Finding Receiving Sites, part 2

    Science.gov (United States)

    Lemos, Panayiotis P.

    1992-12-01

    The Naval Security Group (NSG) High Frequency Direction Finding (HFDF) sites use large circularly disposed antenna arrays (CDAA) with moderate to high gain beams. Omnidirectional coverage is presently obtained by combining 8 to 120 elements of the CDAA. Recent measurements of site performance reveal that most HFDF sites suffer from high noise levels. Much of the noise is generated in the RF distribution system. This noise contaminates the CDAA omni signals, greatly reducing their effectiveness. One proposed solution to the problem is to use a semi-remotely located broadband conical monopole (CM), which does not connect through the noisy RF distribution system. A proof-of-performance comparing the CM and CDAA omnis is commencing at NSG. In this thesis, the performance of the model 2012AA Conical Monopole Antenna is studied in the presence of finite ground using the Numerical Electromagnetics Code (NEC-3). Ground constants used in this study were obtained for two locations where the CM are installed; Northwest, VA, and Winter Harbor, ME. The performance of the combined antenna/ground system was simulated over a frequency range from 2 to 30 MHz (HF), for various ground constants, with particular emphasis on the elevation plane radiation patterns. Part 2 contains the thesis abstract and figures only.

  1. Brain oscillatory activity during motor preparation: Effect of directional uncertainty on beta, but not alpha, frequency band

    Directory of Open Access Journals (Sweden)

    Charidimos eTzagarakis

    2015-07-01

    Full Text Available In time-constraint activities, such as sports, it is advantageous to be prepared to act even before knowing precisely what action will be needed. Here, we studied the relation between neural oscillations during motor preparation and amount of uncertainty about the direction of the upcoming target. Ten right-handed volunteers participated in a cued center-out task. A brief visual cue identified the region of space in which the target would appear. Three cue sizes were used to vary the amount of information about the direction of the upcoming target. The target appeared at a random location within the region indicated by the cue, and the participants moved a joystick-controlled cursor towards it. Time-frequency analyses showed phasic increases of power in low (delta/theta: 30 Hz frequency-bands in relation to the onset of visual stimuli and of the motor response. More importantly in regard to motor preparation, there was a tonic reduction of power in the alpha (8-12 Hz and beta (14-30 Hz bands during the period between cue presentation and target onset. During motor preparation, the main source of change of power of the alpha band was localized over the contralateral sensorimotor region and both parietal cortices, whereas for the beta-band the main source was the contralateral sensorimotor region. During cue presentation, the reduction of power of the alpha-band in the occipital lobe showed a brief differentiation of condition: the wider the visual cue, the more the power of the alpha-band decreased. However during motor preparation, only the power of the beta-band was dependent on directional uncertainty: the less the directional uncertainty, the more the power of the beta-band decreased. In conclusion, the results indicate that the power in the alpha-band is associated briefly with cue size, but is otherwise an undifferentiated indication of neural activation, whereas the power of the beta-band reflects the level of motor preparation.

  2. 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.

  3. Direct generation of graphene plasmonic polaritons at THz frequencies via four wave mixing in the hybrid graphene sheets waveguides.

    Science.gov (United States)

    Sun, Yu; Qiao, Guofu; Sun, Guodong

    2014-11-17

    A compact waveguide incorporating a high-index nano-ridge sandwiched between graphene sheets is proposed for the direct generation of graphene plasmonic polaritons (GSPs) via four wave mixing (FWM). The proposed waveguide supports GSP modes at the THz frequencies and photonic modes at the infrared wavelengths. Due to the strong confinement of coupled graphene sheets, the GSP modes concentrate in the high-index nano-ridge far below the diffraction limit, which improves integral overlap with the photonic modes and greatly facilitates the FWM process. To cope with the ultra-high effective refractive of the GSP modes, an alternative energy conservation diagram is selected for the degenerated FWM, which corresponds to one pump photon transfers its energy to two signal photons and one GSP photon. The single mode condition of the generated symmetric GSP modes is analyzed by the effective index method to suppress the undesired conversion. Due to the unique tunability of GSPs, the phase matching condition can be satisfied by tuning the chemical potential of the graphene sheets employing external gates. The FWM pumped at 1,550 nm with a peak power of 1 kW is theoretically investigated by solving the modified coupled mode equations. The generated GSP power reaches its maximum up to 67 W at a propagation distance of only 43.7 μm. The proposed waveguide have a great potential for integrated chip-scale GSP source.

  4. Optimization and implementation of scaling-free CORDIC-based direct digital frequency synthesizer for body care area network systems.

    Science.gov (United States)

    Juang, Ying-Shen; Ko, Lu-Ting; Chen, Jwu-E; Sung, Tze-Yun; Hsin, Hsi-Chin

    2012-01-01

    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.

  5. 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.

  6. Directional spectra of ocean waves from microwave backscatter: A physical optics solution with application to the short-pulse and two-frequency measurement techniques

    Science.gov (United States)

    Jackson, F. C.

    1979-01-01

    Two simple microwave radar techniques that are potentially capable of providing routine satellite measurements of the directional spectrum of ocean waves were developed. One technique, the short pulse technique, makes use of very short pulses to resolve ocean surface wave contrast features in the range direction; the other technique, the two frequency correlation technique makes use of coherency in the transmitted waveform to detect the large ocean wave contrast modulation as a beat or mixing frequency in the power backscattered at two closely separated microwave frequencies. A frequency domain analysis of the short pulse and two frequency systems shows that the two measurement systems are essentially duals; they each operate on the generalized (three frequency) fourth-order statistical moment of the surface transfer function in different, but symmetrical ways, and they both measure the same directional contrast modulation spectrum. A three dimensional physical optics solution for the fourth-order moment was obtained for backscatter in the near vertical, specular regime, assuming Gaussian surface statistics.

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

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Jianke, E-mail: yaojk@pkusz.edu.cn [School of Computer and Information Engineering, Shenzhen Graduate School of Peking University, Shenzhen 518055 (China); Gong, Li [Instrumental Analysis and Research Center, Sun Yat-Sen University, Guangzhou 10275 (China); Xie, Lei [School of Computer and Information Engineering, Shenzhen Graduate School of Peking University, Shenzhen 518055 (China); Zhang, Shengdong, E-mail: zhangsd@pku.edu.cn [School of Computer and Information Engineering, Shenzhen Graduate School of Peking University, Shenzhen 518055 (China); Institute of Microelectronics, Peking University, Beijing 100871 (China)

    2013-01-01

    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 (E{sub g} = 3.02–3.29 eV), and show less shift of Fermi level (△ E{sub F} ∼ 0.26 eV) and increased concentration of electrons (△ N{sub e} ∼ 10{sup 4}) in the conduction band with the reduction concentration of oxygen vacancy (V{sub O}). 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 V{sub O}. - Highlights: ► Amorphous InGaZnO{sub 4} (a-IGZO) films were prepared with different sputtering modes. ► Electrical and optical properties of the different films were compared. ► Fermi level (△E{sub F}) shift in a-IGZO films were tested by X-ray photoelectron spectroscopy. ► The relation of △E{sub F} with the properties of a-IGZO films were discussed. ► Work function was tested by ultraviolet photoelectron spectroscopy.

  8. Alarmingly High Segregation Frequencies of Quinolone Resistance Alleles within Human and Animal Microbiomes Are Not Explained by Direct Clinical Antibiotic Exposure.

    Science.gov (United States)

    Field, Wesley; Hershberg, Ruth

    2015-05-26

    Antibiotic resistance poses a major threat to human health. It is therefore important to characterize the frequency of resistance within natural bacterial environments. Many studies have focused on characterizing the frequencies with which horizontally acquired resistance genes segregate within natural bacterial populations. Yet, very little is currently understood regarding the frequency of segregation of resistance alleles occurring within the housekeeping targets of antibiotics. We surveyed a large number of metagenomic datasets extracted from a large variety of host-associated and non host-associated environments for such alleles conferring resistance to three groups of broad spectrum antibiotics: streptomycin, rifamycins, and quinolones. We find notable segregation frequencies of resistance alleles occurring within the target genes of each of the three antibiotics, with quinolone resistance alleles being the most frequent and rifamycin resistance alleles being the least frequent. Resistance allele frequencies varied greatly between different phyla and as a function of environment. The frequency of quinolone resistance alleles was especially high within host-associated environments, where it averaged an alarming ∼ 40%. Within host-associated environments, resistance to quinolones was most often conferred by a specific resistance allele. High frequencies of quinolone resistance alleles were also found within hosts that were not directly treated with antibiotics. Therefore, the high segregation frequency of quinolone resistance alleles occurring within the housekeeping targets of antibiotics in host-associated environments does not seem to be the sole result of clinical antibiotic usage.

  9. Frequency comb generation in quadratic nonlinear media

    CERN Document Server

    Ricciardi, Iolanda; Parisi, Maria; Maddaloni, Pasquale; Santamaria, Luigi; De Natale, Paolo; De Rosa, Maurizio

    2014-01-01

    Optical frequency combs are nowadays routinely used tools in a wide range of scientific and technological applications. Different techniques have been developed for generating optical frequency combs, like mode-locking in lasers and third-order interactions in microresonators, or to extend their spectral capabilities, using frequency conversion processes in nonlinear materials. Here, we experimentally demonstrate and theoretically explain the onset of optical frequency combs in a simple cavity-enhanced second-harmonic-generation system, exploiting second-order nonlinear interactions. We develop an elemental model which provides a deep physical insight into the observed dynamics. Moreover, despite the different underlying physical mechanism, the proposed model is remarkably similar to the description of third-order effects in microresonators, revealing a potential variety of new effects to be explored. Finally, exploiting a nonlinearity intrinsically stronger than the third-order one, our work lays the groundw...

  10. Direct measurement of recombination frequency in interspecific hybrids between Hordeum vulgare and H. bulbosum using genomic in situ hybridization.

    Science.gov (United States)

    Zhang, L; Pickering, R; Murray, B

    1999-09-01

    Two different genotypes of diploid Hordeum vulgare x H. bulbosum hybrids, which differ in their pattern of meiotic metaphase pairing behaviour, were investigated at MI and AI by genomic in situ hybridization (GISH). One hybrid, 102C2, showed a high frequency of bivalents at metaphase I whereas the other, 103K5, showed a high frequency of univalents. The GISH analysis of both hybrids established that pairing occurred only between chromosomes of different parental genomes and revealed that pairing frequency greatly exceeded recombination. Hybrid 102C2 had a significantly higher recombination frequency than 103K5, but in both hybrids recombination involved only distal chromosome regions. However, an interesting finding is that the ratio of recombination to pairing frequency in 103K5 (1:8.9) is twice as high compared with 102C2 (1:17). The hybrids also differed in chromosome stability; little chromosome elimination occurred in 102C2 but 103K5 showed extensive chromosome loss. It appears that the high frequency of bound arms at MI favours retention of H. bulbosum chromosomes and maintains stability of chromosome numbers in PMCs. Various ideas are put forward to explain the discrepancy between meiotic pairing frequency and recombination in these hybrids.

  11. Freeze drying of red blood cells: the use of directional freezing and a new radio frequency lyophilization device.

    Science.gov (United States)

    Arav, Amir; Natan, Dity

    2012-08-01

    Red blood cell (RBC) units are administered routinely into patients expressing a wide range of acute and chronic conditions (e.g., anemia, traumatic bleeding, chronic diseases, and surgery). The modern blood banking system has been designed to answer this need and assure a continuous, high quality blood supply to patients. However, RBCs units can be stored under hypothermic conditions for only up to 42 days, which leads to periodic shortages. Cryopreservation can solve these shortages, but current freezing methods employ high glycerol concentrations, which need to be removed and the cells washed prior to transfusion, resulting in a long (more than 1 hour) and cumbersome washing step. Thus, frozen RBCs have limited use in acute and trauma situations. In addition, transportation of frozen samples is complicated and costly. Freeze drying (lyophilization) of RBCs has been suggested as a solution for these problems, since it will allow for a low weight sample to be stored at room temperature, but reaching this goal is not a simple task. We studied the effect of different solutions (IMT2 and IMT3) containing trehalose and antioxidants or trehalose and human serum albumin, respectively, on freezing/thawing and freeze drying of RBCs. In addition, we evaluated the effect of cells concentrations and cooling rates on the post thaw and post rehydration recoveries of the RBCs. Finally, we developed a new radio frequency (RF) lyophilization device for a more rapid and homogeneous sublimation process of the frozen RBCs samples. Recovery and free Hb were measured as well as oxygen association/dissociation and cell's deformability. We found that IMT3 (0.3 M trehalose and 10% HSA) solution that was directionally frozen at a rapid interface velocity of 1 mm/sec (resulting in a cooling rate of 150°C/min) yielded the best results (better than IMT2 solution and slow interface velocity). Freeze thawing gave 100% survival, while freeze drying followed by rehydration with 20% dextran-40k

  12. 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...

  13. A discussion of the bi-directional ranking of occurrence-frequency based non-interactive literature method for knowledge discovery

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Yunqiu; GUO; Kelei

    2009-01-01

    Based on the analysis of the existing ranking terminology or subject relevancy of documents methods through an intermediary collection as a catalyst(designated as Group B collection)for the purpose of of non-interactive literature-based discovery,this article proposes a bi-directional document occurrence frequency based ranking method according to the"concurrence theory"and the degree and extent of the subject relevancy.This method explores and further refines the ranking method that is based on the occurrence frequency of the usage of certain terminologies and documents and injects a new insightful perspective of the concurrence of appropriate terminologies/documents in the"low occurrence frequency component"of three non-interactive document collections.A preliminary experiment was conducted to analyze and to test the significance and viability of our newly designed operational method.

  14. Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

    Science.gov (United States)

    Lin, H. C.; Kim, S. K.; Chang, D.; Xuan, Y.; Mohammadi, S.; Ye, P. D.; Lu, G.; Facchetti, A.; Marks, T. J.

    2007-08-01

    Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors (MISFETs) with very thin self-assembled organic nanodielectrics (SANDs) are presented. The application of SAND on compound semiconductors offers unique opportunities for high-performance devices. Thus, 1μm gate-length depletion-mode n-channel SAND/GaAs MISFETs exhibit low gate leakage current densities of 10-2-10-5A/cm2, a maximum drain current of 260mA/mm at 2V forward gate bias, and a maximum intrinsic transconductance of 127mS/mm. These devices achieve a current cutoff frequency (fT) of 10.6GHz and a maximum oscillation frequency (fmax) of 6.9GHz. Nearly hysteresis-free Ids-Vgs characteristics and low flicker noise indicate that a high-quality SAND-GaAs interface is achieved.

  15. Non-reciprocal directional dichroism in the AFM phase of BiFeO3 at THz frequencies

    Science.gov (United States)

    Nagel, Urmas; Rõõm, T.; Farkas, D.; Szaller, D.; Bordács, S.; Kézsmárki, I.; Engelkamp, H.; Ozaki, Y.; Tomiaki, Y.; Ito, T.; Fishman, Randy S.

    We did THz absorption spectroscopy of BiFeO3 single crystals in the AFM phase, where the spin cycloid is destroyed in magnetic fields between 18 T and 32 T in Voigt geometry at 1.6 K. If B0 ∥ [ 1 1 0 ] , we see strong directional dichroism (DD) of absorption of the magnon mode with light propagating along the direction of the ferroelectric polarization k ∥ P ∥ [ 111 ] and eω ∥ [ 1 1 0 ] , bω ∥ [ 1 1 2 ] . The sign of DD can be reversed (i) by reversing the direction of B0 or (ii) by flipping the sample, thus reversing the propagation direction of light. The observed effect is caused by the strong magneto-electric coupling in the collinear AFM phase. Research sponsored by the Estonian Ministry of Education and Research (IUT23-3).

  16. Time-resolved in situ detection of CO in a shock tube using cavity-enhanced absorption spectroscopy with a quantum-cascade laser near 4.6 µm.

    Science.gov (United States)

    Sun, Kai; Wang, Shengkai; Sur, Ritobrata; Chao, Xing; Jeffries, Jay B; Hanson, Ronald K

    2014-10-06

    Cavity-enhanced absorption spectroscopy (CEAS) using a mid-infrared DFB quantum-cascade laser is reported for sensitive time-resolved (10 μs) in situ CO measurements in a shock tube. Off-axis alignment and fast scanning of the laser wavelength were used to minimize coupling noise in a low-finesse cavity. An absorption gain factor of 91 was demonstrated, which enabled sub-ppm detection sensitivity for gas temperatures of 1000-2100K in a 15 cm diameter shock tube. This substantial improvement in detection sensitivity compared to conventional single-pass absorption measurements, shows great potential for the study of reaction pathways of high-temperature combustion kinetics mechanisms in shock tubes.

  17. Demonstration of 2×ONU 80 Gbps direct detection colorless polarization division multiplexing frequency division multiplexing passive optical network uplink transmission

    Science.gov (United States)

    Wang, Zhixin; Xu, Yinfan; Wang, Yanyi; Wang, Yuanquan; Chi, Nan

    2016-04-01

    In this study, we propose and experimentally demonstrate a simple direct detection passive optical network (PON) uplink transmission scheme based on frequency division multiplexing and polarization division multiplexing. Two optical network units (ONUs) are assigned to two different frequency bands at two different orthogonal polarization directions. At the optical line terminal, both ONU signals can be simultaneously detected by a single photodiode without utilizing any polarization control, polarization selection, or complicated polarization demultiplexing algorithms. As a proof-of-concept, the 2×ONU 80 Gbps 32-ary quadrature amplitude modulation Nyquist single carrier signals are successfully transmitted over 2 km standard single mode fiber or 20 km large effective area fiber with the assistance of frequency domain equalization and decision-directed least-mean-square. The measured bit error rate can be below the 7% pre-forward error correction threshold of 3.8×10-3. Meanwhile, this scheme is compatible with the widely used wavelength-division multiplexed PON, which shows the promising potential and feasibility of this proposal.

  18. 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

    Direct-conversion receivers are increasingly employed in many applications, such as wireless communications and radars. Indeed, they represent an effective alternative to heterodyne receivers, as they allow a higher level of integration. However, performance limitations are imposed by the leakage...

  19. Direct current superconducting quantum interference device spectrometer for pulsed nuclear magnetic resonance and nuclear quadrupole resonance at frequencies up to 5 MHz

    Science.gov (United States)

    TonThat, Dinh M.; Clarke, John

    1996-08-01

    A spectrometer based on a dc superconducting quantum interference device (SQUID) has been developed for the direct detection of nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR) at frequencies up to 5 MHz. The sample is coupled to the input coil of the niobium-based SQUID via a nonresonant superconducting circuit. The flux locked loop involves the direct offset integration technique with additional positive feedback in which the output of the SQUID is coupled directly to a low-noise preamplifier. Precession of the nuclear quadrupole spins is induced by a magnetic field pulse with the feedback circuit disabled; subsequently, flux locked operation is restored and the SQUID amplifies the signal produced by the nuclear free induction signal. The spectrometer has been used to detect 27Al NQR signals in ruby (Al2O3[Cr3+]) at 359 and 714 kHz.

  20. Superconducting Quantum Interference Devices for the Detection of Magnetic Flux and Application to Airborne High Frequency Direction Finding

    Science.gov (United States)

    2015-03-26

    Faculty Department of Electrical and Computer Engineering Graduate School of Engineering and Management Air Force Institute of Technology Air...Clair Corbin [18]. Captain Corbin evaluated alternative direction of arrival (DOA) estimation techniques to improve azimuthal resolution and found...starts with finding the wave function of an elementary particle Ψ(x, t). The wave function describes a quantum object for all future time, given suitable

  1. High-precision molecular interrogation by direct referencing of a quantum-cascade-laser to a near-infrared frequency comb.

    Science.gov (United States)

    Gatti, D; Gambetta, A; Castrillo, A; Galzerano, G; Laporta, P; Gianfrani, L; Marangoni, M

    2011-08-29

    This work presents a very simple yet effective way to obtain direct referencing of a quantum-cascade-laser at 4.3 μm to a near-IR frequency-comb. Precise tuning of the comb repetition-rate allows the quantum-cascade-laser to be scanned across absorption lines of a CO2 gaseous sample and line profiles to be acquired with extreme reproducibility and accuracy. By averaging over 50 acquisitions, line-centre frequencies are retrieved with an uncertainty of 30 kHz in a linear interaction regime. The extension of this methodology to other lines and molecules, by the use of widely tunable extended-cavity quantum-cascade-lasers, paves the way to a wide availability of high-quality and traceable spectroscopic data in the most crucial region for molecular detection and interrogation.

  2. 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

  3. High frequency directivity effect for a Mw 4.1 earthquake (Barcelonnette event, 2012), widely felt by the population

    Science.gov (United States)

    Courboulex, Francoise; Dujardin, Alain; Vallée, Martin; Delouis, Bertrand; Deschamps, Anne; Sira, Christophe; Maron, Christophe

    2013-04-01

    Can the directivity effect of a rupture process be detected by the population 100 km away for a moderate size Mw 4.1 earthquake? The February 26th 2012, earthquake that occurred in the French Alps proved that it can ! During the night of February 26, 2012, the inhabitants and winter holidaymakers of the Vallée de l'Ubaye in the French Alps were woken by a brutal vibration due to an earthquake. This event that occurred at 8km depth was widely felt in the epicentral area and caused some light damage to houses (25 chimneys were broken, and a great deal of non-structural damage was detected). This event occurred in a mountainous area populated only by villages or small cities, the two largest cities (Grenoble and Nice) being both situated about 100 km from the epicenter. A rapid inspection of the macroseismic intensity values (collected by the BCSF) estimated in both cities immediately proved the fact that this event was much more felt in Nice and its surroundings than in Grenoble. This discrepancy is very well correlated with Peak Ground Acceleration (PGA) values measured on the 16 accelerograms of the RAP network (Réseau Accélérométrique Permanent Français) in the two cities, the values measured in Grenoble being in average 8 times smaller than the one measured in Nice (smaller PGA value in Nice/ smaller PGA value in Grenoble, on good rock sites). A factor 10 was also observed inside both cities due to site effects, which results in a variability that reaches a factor 60 between the smallest and the largest PGA values recorded at 100km. In order to explain these observations, we selected French and Italian broad band stations in different azimuths and deconvolved the mainshock velocity recordings by the one of an aftershock (Mw 2.3) taken as empirical Green's function. The apparent source time functions obtained clearly show that the Barcelonnette event had a strong directivity effect of its rupture process. We found, using a simple linear source model

  4. Experimental demonstration of half cycle 64-QAM Nyquist-SCM direct-detection optical communication system with data-aided estimation and overlap frequency-domain equalization

    Science.gov (United States)

    Li, Danyu; He, Jing; Tang, Jin; Chen, Ming; Chen, Lin

    2014-12-01

    A half cycle 64-quadrature amplitude modulation (QAM) Nyquist subcarrier modulation (SCM) polarization division multiplexing (PDM) intensity modulation direct detection optical communication system is experimentally demonstrated. At the receiver, training sequences-based channel estimation and an overlap frequency domain equalization method are proposed to enhance the system performance. The experimental results show that the half cycle 64-QAM Nyquist-SCM PDM signal can be transmitted over 43-km standard single-mode fibers with a bit error rate below the forward error coding threshold of 2.4×10-2.

  5. 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

  6. Physical modeling of direct current and radio frequency characteristics for InP-based InAlAs/InGaAs HEMTs

    Science.gov (United States)

    Sun, Shu-Xiang; Ji, Hui-Fang; Yao, Hui-Juan; Li, Sheng; Jin, Zhi; Ding, Peng; Zhong, Ying-Hui

    2016-10-01

    Direct current (DC) and radio frequency (RF) performances of InP-based high electron mobility transistors (HEMTs) are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley-Read-Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover, the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency (f max) of 385 GHz. Project supported by the National Natural Science Foundation of China (Grant Nos. 61404115 and 61434006), the Postdoctoral Science Foundation of Henan Province, China (Grant No. 2014006), and the Development Fund for Outstanding Young Teachers of Zhengzhou University (Grant No. 1521317004).

  7. 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 ...

  8. 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.

  9. The position of DNA cleavage by TALENs and cell synchronization influences the frequency of gene editing directed by single-stranded oligonucleotides.

    Directory of Open Access Journals (Sweden)

    Natalia Rivera-Torres

    Full Text Available With recent technological advances that enable DNA cleavage at specific sites in the human genome, it may now be possible to reverse inborn errors, thereby correcting a mutation, at levels that could have an impact in a clinical setting. We have been developing gene editing, using single-stranded DNA oligonucleotides (ssODNs, as a tool to direct site specific single base changes. Successful application of this technique has been demonstrated in many systems ranging from bacteria to human (ES and somatic cells. While the frequency of gene editing can vary widely, it is often at a level that does not enable clinical application. As such, a number of stimulatory factors such as double-stranded breaks are known to elevate the frequency significantly. The majority of these results have been discovered using a validated HCT116 mammalian cell model system where credible genetic and biochemical readouts are available. Here, we couple TAL-Effector Nucleases (TALENs that execute specific ds DNA breaks with ssODNs, designed specifically to repair a missense mutation, in an integrated single copy eGFP gene. We find that proximal cleavage, relative to the mutant base, is key for enabling high frequencies of editing. A directionality of correction is also observed with TALEN activity upstream from the target base being more effective in promoting gene editing than activity downstream. We also find that cells progressing through S phase are more amenable to combinatorial gene editing activity. Thus, we identify novel aspects of gene editing that will help in the design of more effective protocols for genome modification and gene therapy in natural genes.

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

    Science.gov (United States)

    Clanton, Christian; Gaudi, B. Scott

    2017-01-01

    A microlensing survey by Sumi et al. exhibits an overabundance of short-timescale events (STEs; tE < 2 days) relative to what is expected from known stellar populations and a smooth power-law extrapolation down to the brown dwarf regime. This excess has been interpreted as a population of approximately Jupiter-mass objects that outnumber main-sequence stars nearly twofold; however the microlensing data alone cannot distinguish between events due to wide-separation (a ≳ 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 for bound planets holds. We estimate a median fraction of STEs due to free-floating planets to be f = 0.67 (0.23 ≤ f ≤ 0.85 at 95% confidence) when assuming “hot-start” planet evolutionary models and f = 0.58 (0.14 ≤ f ≤ 0.83 at 95% confidence) for “cold-start” models. Assuming a delta-function distribution of free-floating planets of mass {m}p=2 {M}{Jup} yields a number of free-floating planets per main-sequence star of N = 1.4 (0.48 ≤ N ≤ 1.8 at 95% confidence) in the “hot-start” case and N = 1.2 (0.29 ≤ N ≤ 1.8 at 95% confidence) in the “cold-start” case.

  11. 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.

  12. 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.

  13. 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.

  14. An improved assessment model of variable frequency-driven direct expansion air-conditioning system in commercial buildings for Taiwan green building rating system

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Kuan-Hsiung [Department of Mechanical and Electro-mechanical Engineering, National Sun Yet-Sen University, 70 Lien-hai Rd., Kaohsiung 804 (China); Hwang, Ruey-Lung [Department of Safety and Health of Occupant, China Medical University, 91 Huseh-Shin Rd, Taichung, 404 (China)

    2007-10-15

    Because of the superior performance of the multi-unit variable frequency-driven (VFD) direct expansion (DX) air-conditioning system, installing this kind of system in rental commercial buildings, dwelling houses, and schools is becoming more and more popular in Taiwan. Even though the features and characteristics of the multi-unit VFD DX system are different from those of the central system, it is still assessed by the conventional method used for evaluating the efficiency of all air-conditioning systems, which is designed mainly for central systems. This article explains the problems that occur when the current assessment method is applied to the multi-unit VFD DX system. An alternative assessment method is proposed. (author)

  15. 直接数字频率合成器的FPGA设计与实现%Design and Implementation of Direct Digital Frequency Synthesizer Based on FPGA

    Institute of Scientific and Technical Information of China (English)

    郑浩; 饶远

    2012-01-01

    On the premise of reducing cost, in order to improve the main frequency and realize complex modulation function and a good practicability, and from the phase concept, the high-performance FPGA devices (ACEXEP1K50) is used to design Direct Digital Fraquency Synthesis(DDS) circuit which meets the performance specifications requirements to realize the direct digital frequency synthesizer design. The operation principle and circuit structure are introduced in detail, and the performance specifications are tested strictly. The optimization method is proposed to improve the performance specifications. The design achieves the desired effect and good performance specifications.%在节约成本的前提下,为了提高主频频率,实现复杂的调制功能并具有良好的实用性,由相位概念出发,利用高性能的现场可编程门阵列(FPGA)器件(ACEXEP1K50)设计符合自己性能指标的要求的直接数字频率合成(DDS)电路,实现直接数字频率合成器的设计。对设计工作原理、电路结构进行了详细介绍,对设计的性能指标进行严格测试,同时提出了优化方法更好的提高了性能指标。设计结果达到预期效果,性能指标优良。

  16. Sidebands alongside the diurnal frequencies of radon time series in a simulation experiment -- an indication for a direct association with the earth-sun system

    Science.gov (United States)

    Steinitz, Gideon; Sturrock, Peter A.; Piatibratova, Oksana; Kotlarsky, Peter

    2015-04-01

    A radon simulation experiment using a confined mode is operating at GSI since 2007 at a time resolution of 15-minutes [1]. The nuclear radiation from radon in the confined air is measured using internal alpha and gamma sensors, and external gamma sensors. Detailed analysis [1, 2] demonstrated that the variation patterns cannot be ascribed to local environmental influences. On the other hand the specific features and relation led to the suggestion that a component in solar radiation is driving the signals. Prominent periodicities dominate the variation in the annual and diurnal frequency bands. The primary periodicity in the diurnal band has a frequency of 1 CPD (S1). Significant multiples occur at 2 CPD (S2), 3 CPD (S3) and also at 4 CPD (S4). The S2 and S3 constituents are clearly observed in the time domain in addition to the primary S1 periodicity. The measured signal is detrended by removing the large annual variation. Spectral analysis (FFT) of the residual time series reveals sidebands (Sb) alongside and on both sides of the S1 frequency in the time series of the alpha and gamma sensors. The lower sideband (LSb) occurs at a frequency close to the astronomical sidereal frequency (0.9972696 CPD). The upper sideband (USb) occurs at a symmetric frequency relative to S1. The four sensors (alpha and gamma)exhibit the LSb, S1, and USb at the following frequencies (CPD): Gamma-C: 0.99739; 0.99989; 1.00275 Gamma-W: 0.99717; 0.99986; 1.00257 Alpha-H: 0.99710; 0.99992; 1.00269 Alpha-L: 0.99719; 0.99991 Multiples of LSb and USb are observed around the S1 periodicity. Similar features of Sb and multiples occur also around S2, S3, and S4. The development of the specific Sb around the diurnal periodicities may be attributed to a driver composed of two waveforms having periodicities of 1 day and 365.25 days, which interacts in a non-linear mode with radon inside the confined volume. The pattern of the alpha and gamma emission of the decaying radon is reflecting this non

  17. 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.

  18. Cavity-Enhanced Third Harmonic Generation

    Institute of Scientific and Technical Information of China (English)

    YANG Xiao-Xue; WU Ying

    2005-01-01

    We derive the analytical expression of microcavity-enhanced factor for third harmonic generation in terms of detunings, linewidths, and the Purcell factors of the relevant microcavity modes. It is suitable for microcavities with any dimensions and arbitrary geometric shapes.

  19. 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 UV...

  20. 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.

  1. Near Infrared Cavity Enhanced Absorption Spectroscopy Study of N2 O%N2 O的近红外腔增强吸收光谱技术研究

    Institute of Scientific and Technical Information of China (English)

    吴志伟; 董燕婷; 周卫东

    2014-01-01

    Using a tunable near infrared external cavity diode laser and a 650mm long high finesse optical cavity consisting of two highly reflective (R= 99. 97% at 6 561. 39 cm-1 )plan-concave mirrors of curvature radius ~1 000 mm,a cavity enhanced ab-sorption spectroscopy (CEAS)system was made.The absorption spectra centered at 6 561. 39 cm-1 of pure N2 O gas and gas mixtures of N2 O and N2 were recorded.According to the absorption of N2 O at 6 561. 39 cm-1 in the cavity,the measured effec-tive absorption path was about 1 460 km.The spectra line intensity and line-width of N2 O centered at 6 561. 39 cm-1 were care-fully studied.The relationship between the line-width of absorption spectra and the gas pressure was derived.The pressure broadening parameter of N2 gas for N2O line centered at 6 561. 39 cm-1 was deduced and given a value of ~(0. 114±0. 004) cm-1 ·atm-1 .The possibility to detect trace N2 O gas in mixture using this CEAS system was investigated.By recording the ab-sorption spectra of N2 O gas mixtures at different concentration,the relationship between the line intensity and gas concentration was derived.The minimum detectable absorption was found to be 2. 34×10-7 cm-1 using this cavity enhanced absorption spec-troscopy system.And te measurement precision in terms of relative standard deviation (RSD)for N2 O is ~1. 73%,indicating the possibility of using the cavity enhanced absorption spectroscopy system for micro gas N2 O analysis in the future.%以外腔式可调谐、窄线宽近红外半导体激光为光源,以一对曲率半径r=1000 mm 的宽带高反射率平凹镜(反射率R=99.97%)构成的腔长为650 mm的对称高精度光学稳定腔,建立了腔增强吸收光谱系统。详细研究了纯净 N2 O 气体、以及 N2 O 和 N2的混合气体在不同浓度和不同气压下、中心波长位于6561.39 cm-1的腔增强吸收光谱、光谱强度和谱线宽度,该腔增强吸收光谱系统的有效吸收光程可达1460 km。

  2. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, G., E-mail: gerosro@gmail.com; Kanjilal, D.; Roy, A. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi (India); Becker, R. [Institut fur Angewandte Physik der Universitaet, D-60054 Frankfurt/M (Germany); Hamm, R. W. [R and M Technical Enterprises, Inc., 4725 Arlene Place, Pleasanton, California 94566 (United States); Baskaran, R. [Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu (India)

    2014-02-15

    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 {sup 238}U{sup 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.

  4. A Study of the Frequency and Social Determinants of Exposure to Cancer-Related Direct-to-Consumer Advertising Among Breast, Prostate, and Colorectal Cancer Patients.

    Science.gov (United States)

    Tan, Andy S L

    2015-01-01

    Cancer-related direct-to-consumer advertising (DTCA) is controversial because cancer treatment is complex and entails more risks and costs than typical treatments that are advertised for other conditions. Drawing from the Structural Influence Model of Communication, this study explores communication inequalities in DTCA exposure across social determinants among a population-based sample of 2013 patients diagnosed with breast, prostate, or colorectal cancers. Three survey items assessed patients' frequency of encountering ads concerning treatment alternatives for cancer, dealing with side effects of treatment, and doctors or hospitals offering services for cancer following their diagnosis. The analysis showed that overall exposure to DTCA in this study population was modest (median was once per week). Breast cancer patients reported significantly higher exposure to all three ad categories and overall DTCA exposure than prostate and colorectal cancer patients. Older patients consistently reported lower overall exposure to DTCA across the three cancer types. Other significant correlates included ethnicity (higher exposures among African American prostate cancer patients vs. White; lower exposures in Hispanic colorectal cancer patients vs. White) and cancer stage (higher exposures in Stage IV prostate cancer patients vs. Stages 0-II). Education level did not predict patients' DTCA exposure. The implications of these observed inequalities in DTCA exposure on cancer outcomes are discussed.

  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.

  6. 1.3μm GaInNAs 量子阱RCE光探测器%1.3μm GaInNAs/GaAs QUANTUM WELL RESONANT CAVITY ENHANCED PHOTODETECTOR

    Institute of Scientific and Technical Information of China (English)

    张瑞康; 钟源; 徐应强; 张纬; 黄永清; 任晓敏; 潘钟; 林耀望

    2002-01-01

    采用配有dc-N plasma N源的分子束外延(MBE)技术在GaAs衬底上生长制作了工作波长为1,3μm的GaInNAs量子阱RCE探测器.采用传输矩阵法对器件结构进行优化.吸收区由三个GaInNAs量子阱构成,并用湿法刻蚀和聚酰亚胺对器件进行隔离.在零偏压下,器件最大的量子效率为12%,半峰值全宽(FWHM)为5.8nm,3dB带宽为30MHz,暗电流为2×10-11A.通过对MBE生长条件和器件结构的优化,将进一步提高该器件的性能.%A 1.3μm GaInNAs resonant cavity enhanced (RCE) photodetector (PD) has been grown by molecular beam epitaxy(MBE) monolithically on (100) GaAs substrate using a home-made ion-removed dc-plasma cell as nitrogen source.A transfer matrix method was used to optimize the device structure.The absorption region is composed of three GaInNAs quantum wells separated by GaAs layers.Devices were isolated by etching 130μm-diameter mesas and filling polyamide into grooves.The maximal quantum efficiency of the device is about 12% at 1.293μm.Full width at half maximum (FWHM) is 5.8nm and 3dB bandwidth is 304MHz.Dark current is 2×10-11A at zero bias voltage.Further improvement of the performance of the RCE PD can be obtained by optimizing of the structure design and MBE growth conditions.

  7. Development of Miniaturized Difference Frequency Generation, Fiber Optic, and Quantum Cascade Laser Systems in Conjunction With Integrated Electronics for Global Studies of Atmospheric Tracers Using UAVs.

    Science.gov (United States)

    Witinski, M. F.; Lapson, L. B.; Anderson, J. G.

    2007-12-01

    In order to harness the power of UAVs (Unmanned Aerial Vehicles) for in situ atmospheric monitoring of tracers such as CO2, N2O, CH4, and H2O, we have developed small, lightweight, single mode laser systems with co- developed integrated electronics. The laser sources are of various types including newly developed cavity- enhanced difference frequency generation (CE DFG), distributed feedback quantum cascade lasers (DFB QCLs), and new types of commercially available DFB diode lasers. All are continuous wave (cw) and thermo-electrically cooled, ensuring a high instrument duty cycle in a compact, low maintenance package. The light sources are collimated with miniature aspherical lenses and coupled into a home-built astigmatic Herriott cell for detection of the various targets using direct absorption. In parallel with the optical components, we have developed integrated electrical systems for laser control, data processing, and acquisition. A prototype instrument suite is described that illustrates the importance of parallel development of optical and electrical components in achieving an apparatus that is compact, fully automated, and highly capable scientifically. Although the emphasis here is on atmospheric tracers, this technology could be applied to spectroscopic measurements of other atmospheric species such as isotopes, free radicals, and reactive intermediates.

  8. Direct measurement of transition frequencies in isolated pHe+ atoms, and new CPT-violation limits on the antiproton charge and mass.

    Science.gov (United States)

    Hori, M; Eades, J; Hayano, R S; Ishikawa, T; Pirkl, W; Widmann, E; Yamaguchi, H; Torii, H A; Juhász, B; Horváth, D; Yamazaki, T

    2003-09-19

    A radio frequency quadrupole decelerator and achromatic momentum analyzer were used to decelerate antiprotons and produce p4He+ and p3He+ atoms in ultra-low-density targets, where collision-induced shifts of the atomic transition frequencies were negligible. The frequencies at near-vacuo conditions were measured by laser spectroscopy to fractional precisions of (6-19) x 10(-8). By comparing these with QED calculations and the antiproton cyclotron frequency, we set a new limit of 1 x 10(-8) on possible differences between the antiproton and proton charges and masses.

  9. 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

  10. Bibliography of the Radio Frequency Radiation Branch, Directed Energy Bioeffects Division, Human Effectiveness Directorate, Air Force Research Laboratory: 1997-2003

    Science.gov (United States)

    2004-02-01

    H. Merritt. Radio frequency fields and teratogenesis . Bioelectromagnetics Suppl. 6, S174-S186, 2003. 2 Adair, E. R., K. S. Mylacraine, and S...field on day 1 of gestation does not alter pregnancy recognition, implatation rate, or embryonic and fetal survival to term. 21st Annual Meeting of the

  11. Pulsing frequency induced change in optical constants and dispersion energy parameters of WO{sub 3} films grown by pulsed direct current magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Punitha, K. [Department of Physics, Alagappa University, Karaikudi 630 004 (India); Sivakumar, R., E-mail: krsivakumar1979@yahoo.com [Directorate of Distance Education, Alagappa University, Karaikudi 630 004 (India); Sanjeeviraja, C. [Department of Physics, Alagappa Chettiar College of Engineering and Technology, Karaikudi 630 004 (India)

    2014-03-21

    In this work, we present the pulsing frequency induced change in the structural, optical, vibrational, and luminescence properties of tungsten oxide (WO{sub 3}) thin films deposited on microscopic glass and fluorine doped tin oxide (SnO{sub 2}:F) coated glass substrates by pulsed dc magnetron sputtering technique. The WO{sub 3} films deposited on SnO{sub 2}:F substrate belongs to monoclinic phase. The pulsing frequency has a significant influence on the preferred orientation and crystallinity of WO{sub 3} film. The maximum optical transmittance of 85% was observed for the film and the slight shift in transmission threshold towards higher wavelength region with increasing pulsing frequency revealed the systematic reduction in optical energy band gap (3.78 to 3.13 eV) of the films. The refractive index (n) of films are found to decrease (1.832 to 1.333 at 550 nm) with increasing pulsing frequency and the average value of extinction coefficient (k) is in the order of 10{sup −3}. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, oscillator strength, and oscillator energy (E{sub o}) of WO{sub 3} films were calculated and reported for the first time due to variation in pulsing frequency during deposition by pulsed dc magnetron sputtering. The E{sub o} is change between 6.30 and 3.88 eV, while the E{sub d} varies from 25.81 to 7.88 eV, with pulsing frequency. The Raman peak observed at 1095 cm{sup −1} attributes the presence of W-O symmetric stretching vibration. The slight shift in photoluminescence band is attributed to the difference in excitons transition. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.

  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.

    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.

  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. Hyperfine phononic frequency comb

    CERN Document Server

    Ganesan, Adarsh; Seshia, Ashwin A

    2016-01-01

    Optical frequency combs [1-8] have resulted in significant advances in optical frequency metrology and found wide application to precise physical measurements [1-4, 9] and molecular fingerprinting [8]. A direct analogue of frequency combs in the phononic or acoustic domain has not been reported to date. In this letter, we report the first clear experimental evidence for a phononic frequency comb. In contrast to the Kerr nonlinearity [10] in optical frequency comb formation, the phononic frequency comb is generated through the intrinsic coupling of a driven phonon mode with an auto-parametrically excited sub-harmonic mode [16]. Through systematic experiments at different drive frequencies and amplitudes, we portray the well-connected process of phononic frequency comb formation and define attributes to control the features [17-18] associated with comb formation in such a system. Further, the interplay between these nonlinear resonances and the well-known Duffing phenomenon [12-14] is also observed. The present...

  16. Absolute frequency list of the ν3-band transitions of methane at a relative uncertainty level of 10(-11).

    Science.gov (United States)

    Okubo, Sho; Nakayama, Hirotaka; Iwakuni, Kana; Inaba, Hajime; Sasada, Hiroyuki

    2011-11-21

    We determine the absolute frequencies of 56 rotation-vibration transitions of the ν(3) band of CH(4) from 88.2 to 90.5 THz with a typical uncertainty of 2 kHz corresponding to a relative uncertainty of 2.2 × 10(-11) over an average time of a few hundred seconds. Saturated absorption lines are observed using a difference-frequency-generation source and a cavity-enhanced absorption cell, and the transition frequencies are measured with a fiber-laser-based optical frequency comb referenced to a rubidium atomic clock linked to the international atomic time. The determined value of the P(7) F(2)((2)) line is consistent with the International Committee for Weights and Measures recommendation within the uncertainty.

  17. An Improved nABD Direction Finding Algorithm for Frequency Reconfigurable UWB Antenna%一种用于频率可重构超宽带天线的改进的nABD测向算法

    Institute of Scientific and Technical Information of China (English)

    解志斌; 谭冠南; 田雨波; 陈锦富; 王旭

    2013-01-01

    Direction finding system has strict requirement for the band width, angle measurement accuracy and direction finding range. To solve this problem, the frequency response and impedance-bandwidth characteristic of receiving antenna are designed based on a reconfigurable technique, and the demand of wideband for the direction finding system is satisfied. And in this paper, the traditional n amplitude-comparison bearing discriminator (nABD) comparing amplitude direction finding algorithm is studied on the basis of the designed antenna pattern, and a dynamic adjustment method of antenna weighting coefficient is proposed to get the better accuracy and range of direction finding. The simulation results show that the designed antenna has wide frequency range and appropriate reconfigurable notched band, and the proposed algorithm can obtain better resolution and greater direction finding range.%测向系统对于频带宽度、测角精度及测向范围等方面有着较高的要求.针对这一问题,对于接收天线的频率响应、阻抗带宽特性进行了可重构设计,以达到测向系统对宽频带的要求.同时,在所设计天线元方向特性的基础上,对传统的比幅测向算法nABD进行研究,给出相应的天线元加权系数调整方法,以获得较优的测角精度和测向范围.由仿真结果可知,所设计天线具有较好的工作频率范围与可重构阻带特性,所提测向算法可以获得较高的角度分辨率和较大的测向范围.

  18. Frequency-doubled DBR-tapered diode laser for direct pumping of Ti:sapphire lasers generating sub-20 fs pulses.

    Science.gov (United States)

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

    2011-06-20

    For the first time a single-pass frequency doubled DBR-tapered diode laser suitable for pumping Ti:sapphire lasers generating ultrashort pulses is demonstrated. The maximum output powers achieved when pumping the Ti:sapphire laser are 110 mW (CW) and 82 mW (mode-locked) respectively at 1.2 W of pump power. This corresponds to a reduction in optical conversion efficiencies to 75% of the values achieved with a commercial diode pumped solid-state laser. However, the superior electro-optical efficiency of the diode laser improves the overall efficiency of the Ti:sapphire laser by a factor > 2. The optical spectrum emitted by the Ti:sapphire laser when pumped with our diode laser shows a spectral width of 112 nm (FWHM). Based on autocorrelation measurements, pulse widths of less than 20 fs can therefore be expected.

  19. A physical model for low-frequency electromagnetic induction in the near field based on direct interaction between transmitter and receiver electrons

    Science.gov (United States)

    Smith, Ray T.; Jjunju, Fred P. M.; Young, Iain S.; Taylor, Stephen; Maher, Simon

    2016-07-01

    A physical model of electromagnetic induction is developed which relates directly the forces between electrons in the transmitter and receiver windings of concentric coaxial finite coils in the near-field region. By applying the principle of superposition, the contributions from accelerating electrons in successive current loops are summed, allowing the peak-induced voltage in the receiver to be accurately predicted. Results show good agreement between theory and experiment for various receivers of different radii up to five times that of the transmitter. The limitations of the linear theory of electromagnetic induction are discussed in terms of the non-uniform current distribution caused by the skin effect. In particular, the explanation in terms of electromagnetic energy and Poynting's theorem is contrasted with a more direct explanation based on variable filament induction across the conductor cross section. As the direct physical model developed herein deals only with forces between discrete current elements, it can be readily adapted to suit different coil geometries and is widely applicable in various fields of research such as near-field communications, antenna design, wireless power transfer, sensor applications and beyond.

  20. A physical model for low-frequency electromagnetic induction in the near field based on direct interaction between transmitter and receiver electrons

    Science.gov (United States)

    Smith, Ray T.; Jjunju, Fred P. M.; Young, Iain S.; Taylor, Stephen

    2016-01-01

    A physical model of electromagnetic induction is developed which relates directly the forces between electrons in the transmitter and receiver windings of concentric coaxial finite coils in the near-field region. By applying the principle of superposition, the contributions from accelerating electrons in successive current loops are summed, allowing the peak-induced voltage in the receiver to be accurately predicted. Results show good agreement between theory and experiment for various receivers of different radii up to five times that of the transmitter. The limitations of the linear theory of electromagnetic induction are discussed in terms of the non-uniform current distribution caused by the skin effect. In particular, the explanation in terms of electromagnetic energy and Poynting’s theorem is contrasted with a more direct explanation based on variable filament induction across the conductor cross section. As the direct physical model developed herein deals only with forces between discrete current elements, it can be readily adapted to suit different coil geometries and is widely applicable in various fields of research such as near-field communications, antenna design, wireless power transfer, sensor applications and beyond. PMID:27493580

  1. 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...

  2. 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.

  3. Influence of impulse current frequency on evolution of directionally solidifying organization of Al-Cu alloy%脉冲电流频率对Al-Cu合金定向凝固组织演变的影响

    Institute of Scientific and Technical Information of China (English)

    李霞; 杨效田

    2013-01-01

    The directional solidification behavior of Al-Cu alloy was investigated with directional solidification device designed by ourselves and the evolution of the microstructure characteristics of Al-5 % Cu alloy was researched under the action of pulse current.The results showed that the solidifying organization form of A1-Cu alloy was obviously changed by the pulse current and the influence would be different if the frequency of pulse current was different:when the frequency was 100 Hz,the directional solidification characteristics of the alloy would be strengthened and the dendrite structure was not obvious,but the columnar crystal radius of directional solidifying organization increased.As the current frequency increased to 200 Hz,the secondary dendrite structure began to emerge,making the organization a dendritic structure.When the current frequency increased to 300 Hz,the organization structure would exhibit skeleton structure of neat rows.As the current frequency continued to increase to 400 Hz,the organization would change into minute dendritic structure and the organization was fine and uniformly distributed as a whole.However,the organization would be bulky,displaying the trend to isometric transformation due to the effect of 500 Hz high frequency current.%采用自行设计的定向凝固装置进行Al-Cu合金定向凝固行为研究,研究Al-5%Cu合金在脉冲电流作用下微观组织的演变特征.结果发现:脉冲电流的导入明显改变了定向凝固的A1-Cu合金凝固组织形态,不同频率的脉冲电流具有不同的影响效果,在100 Hz的小频率电流作用下,合金的定向凝固特征加强,枝晶结构不明显,但定向凝固形成的柱状晶半径加大,随着电流频率增大到200 Hz,二次枝晶结构开始显现,组织呈现树枝状结构特征,当300 Hz电流频率时,组织结构呈现排列整齐的的骨架结构,随着电流频率继续增加到400 Hz时,组织变为细小的树枝状结构特征,组织整体

  4. Equivalent magnetic noise reduction at high frequency range due to polarized direction optimization in Terfenol-D/Pb(Mg1/3Nb2/3)O3-PbTiO3 magnetoelectric laminate sensors

    Science.gov (United States)

    Fang, Cong; Ma, Jiashuai; Yao, Meng; Di, Wenning; Lin, Di; Xu, Haiqing; Wang, Wei; Luo, Haosu

    2017-02-01

    In this paper, we investigate the responsivities and output voltage noise power spectral densities of magnetoelectric (ME) laminate sensors, consisting of length magnetized Terfenol-D alloys and transverse/width poled Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) crystals (i.e. L-T mode and L-W mode respectively), which are directly integrated with custom-build low noise charge amplifier circuits. Both the theoretical analyses and experimental results prove that the L-W mode sensor with the optimized polarized direction of the PMNT plate possesses lower magnetic detection limit at the interested high frequency range of 10 kHz≤f≤50 kHz. The equivalent magnetic noise (EMN) of the L-W mode sensor is 0.78 pT/Hz1/2 at 30 kHz, which is about 1.7 times lower than the 1.35 pT/Hz1/2 for conventional L-T mode sensor. Furthermore, an effective method of using operational amplifiers with low equivalent input noise voltage and employing ME laminate composites with high voltage coefficient to reduce the EMNs of the ME laminate sensors at high frequency range has been established.

  5. 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

  6. Frequency synthesiser

    NARCIS (Netherlands)

    Drago, Salvatore; Sebastiano, Fabio; Leenaerts, Dominicus Martinus Wilhelmus; Breems, Lucien Johannes; Nauta, Bram

    2016-01-01

    A low power frequency synthesiser circuit (30) for a radio transceiver, the synthesiser circuit comprising: a digital controlled oscillator configured to generate an output signal having a frequency controlled by an input digital control word (DCW); a feedback loop connected between an output and an

  7. 三相电压型PWM整流器准定频直接功率控制%Novel Quasi Direct Power Control for Three-phase Voltage-source PWM Rectifiers With a Fixed Switching Frequency

    Institute of Scientific and Technical Information of China (English)

    杨达亮; 卢子广; 杭乃善; 李国进

    2011-01-01

    建立三相电压型脉宽调制(pulse width modulation,PWM)整流器在不同坐标系下的数学模型,分析直接功率控制(direct power control,DPC)的工作原理。针对直接功率控制中开关频率变化问题,通过对PWM整流器瞬时功率分析推导,提出一种内环直接采用电流控制的新型准定频直接功率控制策略。仿真验证了算法的可行性。采用PM300DVAl20智能功率模块,设计50kVA的三相电压型PWM整流器控制实验,在10kHz、5us的开关频率下获得良好的实验结果。实验结果表明,所提方法实现单位功率因数运行,与现行的DPC—SVM定频控制方法相比,具有更好的动静态响应性能。%This paper established the three-phase voltage-source pulse width modulation (PWM) rectifier mathematical models in different coordinate systems and analyzed the principle of direct power control (DPC). To alleviate the problem of variable switching frequency, a novel quasi DPC control strategy with current loop was represented through the analysis of PWM rectifier instantaneous power. The novel control strategy was proved feasible by the Matlab/Simulink simulation results. The 50kVA three-phase voltage-source PWM rectifier control experiment system was designed using PM300DVA120 intelligent power module (IPM), the excellent experiment results were given at the 10kHz switching frequency with 5μs dead time. The experimental results indicate that the PWM rectifier system achieves unity power factor operation and has better performance of dynamic and static response compared to the present space vector modulation (SVM) DPC fixed-frequency control method.

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

    Institute of Scientific and Technical Information of China (English)

    陈伟根; 万福; 邹经鑫; 顾朝亮; 周渠

    2015-01-01

    In this paper, the frequency-locking and threshold current-lowering effects of quantum cascade laser are studied and achieved. Combined with cavity-enhanced absorption spectroscopy, the noninvasive detection of H2 with a pre-pared 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 ac-curacy 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.

  9. Inhibitory projections from the ventral nucleus of the lateral lemniscus and superior paraolivary nucleus create directional selectivity of frequency modulations in the inferior colliculus: a comparison of bats with other mammals.

    Science.gov (United States)

    Pollak, George D; Gittelman, Joshua X; Li, Na; Xie, Ruili

    2011-03-01

    This review considers four auditory brainstem nuclear groups and shows how studies of both bats and other mammals have provided insights into their response properties and the impact of their convergence in the inferior colliculus (IC). The four groups are octopus cells in the cochlear nucleus, their connections with the ventral nucleus of the lateral lemniscus (VNLL) and the superior paraolivary nucleus (SPON), and the connections of the VNLL and SPON with the IC. The theme is that the response properties of neurons in the SPON and VNLL map closely onto the synaptic response features of a unique subpopulation of cells in the IC of bats whose inputs are dominated by inhibition. We propose that the convergence of VNLL and SPON inputs generates the tuning of these IC cells, their unique temporal responses to tones, and their directional selectivities for frequency modulated (FM) sweeps. Other IC neurons form directional properties in other ways, showing that selective response properties are formed in multiple ways. In the final section we discuss why multiple formations of common response properties could amplify differences in population activity patterns evoked by signals that have similar spectrotemporal features.

  10. THz谐振腔型石墨烯光电探测器的设计∗%Design and p erformance analysis of THz micro cavity-enhanced graphene photo detector

    Institute of Scientific and Technical Information of China (English)

    梁振江; 刘海霞; 牛燕雄; 刘凯铭; 尹贻恒

    2016-01-01

    Detection of the terahertz (THz) electromagnetic spectrum(wavelengths range 0.03–3 mm) is a promising technique for a large variety of strategic applications, such as biomedical diagnostics and process, quality control, homeland security, and environmental monitoring, etc. Graphene has been recognized internationally to have dominant advantages in photodetectors operating due to its high carrier mobility, gapless spectrum, and frequency-independent absorption coefficient. Graphene photodetector operating in the THz region has been extensively studied with great interests. A graphene microcavity photodetector with THz electromagnetic spectrum is demonstrated in this paper, and its responsivity and detectivity under THz electromagnetic spectrum are evaluated. In the designed device, we adopt a distributed bragger reflection (DBR) consisting of two semiconductor materials SiO2 and TiO2 to form an alternating cavity with high-finesse planar, sandwich the absorbing graphene layer between the cavity’s top and bottom layers, and design the DBR’s reflectivity by the optical transmission matrix method. The monolayer graphene’s optical absorption mechanism of the THz radiation spectrum is studied by the conductivity matrix and Maxwell’s equations with the electromagnetic boundary conditions. Graphene’s transfer matrix and absorption coefficient equation are further derived. It is found that at THz region, graphene’s conductivity plays an important role in its absorptionand its absorption is 9–22 times enhanced compared with that at the visible region. An optical absorption model of microcavity-enhanced graphene photodetector at THz region is established. The photodetector’s absorption rate and responsitivity are analyzed specifically. Theoretical analysis shows that absorption rate is symmetrical to the microcavity’s center position and changes periodically, and the shift of the microcavity length influences the period numbers. The maximum rate of the

  11. 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

  12. Frequency comb swept lasers.

    Science.gov (United States)

    Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C; Fujimoto, James G

    2009-11-09

    We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a approximately -1.2dB sensitivity roll off over approximately 3mm range, compared to conventional swept source and FDML lasers which have -10dB and -5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0-3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed.

  13. 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.

  14. Direct reading inductance meter

    Science.gov (United States)

    Kolby, R. B. (Inventor)

    1977-01-01

    A direct reading inductance meter comprised of a crystal oscillator and an LC tuned oscillator is presented. The oscillators function respectively to generate a reference frequency, f(r), and to generate an initial frequency, f(0), which when mixed produce a difference equal to zero. Upon connecting an inductor of small unknown value in the LC circuit to change its resonant frequency to f(x), a difference frequency (f(r)-f(x)) is produced that is very nearly a linear function of the inductance of the inductor. The difference frequency is measured and displayed on a linear scale in units of inductance.

  15. Frequency steerable acoustic transducers

    Science.gov (United States)

    Senesi, Matteo

    Structural health monitoring (SHM) is an active research area devoted to the assessment of the structural integrity of critical components of aerospace, civil and mechanical systems. Guided wave methods have been proposed for SHM of plate-like structures using permanently attached piezoelectric transducers, which generate and sense waves to evaluate the presence of damage. Effective interrogation of structural health is often facilitated by sensors and actuators with the ability to perform electronic, i.e. phased array, scanning. The objective of this research is to design an innovative directional piezoelectric transducer to be employed for the localization of broadband acoustic events, or for the generation of Lamb waves for active interrogation of structural health. The proposed Frequency Steerable Acoustic Transducers (FSATs) are characterized by a spatial arrangement of active material which leads to directional characteristics varying with frequency. Thus FSATs can be employed both for directional sensing and generation of guided waves without relying on phasing and control of a large number of channels. The analytical expression of the shape of the FSATs is obtained through a theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. The FSAT configurations analyzed in this work are a quadrilateral array and a geometry which corresponds to a spiral in the wavenumber domain. The quadrilateral array is experimentally validated, confirming the concept of frequency-dependent directionality. Its limited directivity is improved by the Wavenumber Spiral FSAT (WS-FSAT), which, instead, is characterized by a continuous frequency dependent directionality. Preliminary validations of the WS-FSAT, using a laser doppler vibrometer, are followed by the implementation of the WS-FSAT as a properly shaped piezo transducer. The prototype is first used for localization of acoustic broadband sources. Signal processing

  16. 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.

  17. Automation of measurement frequency SVCh kolebany

    Directory of Open Access Journals (Sweden)

    A. A. Parfenov

    1987-12-01

    Full Text Available The functional diagram of the frequency meter, comprising a microprocessor controller and commercially available devices. An algorithm for calculating the frequency of the microprocessor used in determining the frequency SVChgeneratora. In the range of 52-79 GHz frequency provides direct reading with an absolute error of less than 2 MHz.

  18. 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...

  19. 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.

  20. Cavity-Enhanced Measurements of Defect Spins in Silicon Carbide

    Science.gov (United States)

    Calusine, Greg; Politi, Alberto; Awschalom, David D.

    2016-07-01

    The identification of new solid-state defect-qubit candidates in widely used semiconductors has the potential to enable the use of nanofabricated devices for enhanced qubit measurement and control operations. In particular, the recent discovery of optically active spin states in silicon carbide thin films offers a scalable route for incorporating defect qubits into on-chip photonic devices. Here, we demonstrate the use of 3C silicon carbide photonic crystal cavities for enhanced excitation of color-center defect spin ensembles in order to increase measured photoluminescence signal count rates, optically detected magnetic-resonance signal intensities, and optical spin initialization rates. We observe an up to a factor of 30 increase in the photoluminescence and optically detected magnetic-resonance signals from Ky5 color centers excited by cavity-resonant excitation and increase the rate of ground-state spin initialization by approximately a factor of 2. Furthermore, we show that the 705-fold reduction in excitation mode volume and enhanced excitation and collection efficiencies provided by the structures can be used to overcome inhomogenous broadening in order to facilitate the study of defect-qubit subensemble properties. These results highlight some of the benefits that nanofabricated devices offer for engineering the local photonic environment of color-center defect qubits to enable applications in quantum information and sensing.

  1. 基于分段多项式的直接数字频率合成器设计%Design of direct digital frequency synthesizer based on piecewise - polynomial approximation

    Institute of Scientific and Technical Information of China (English)

    宋学良; 郭裕顺

    2011-01-01

    In order to enhance the performance of direct digital frequency synthesizer( DDS), a new technique to implement a DDS with the phase-to-amplitude conversion block using piecewise-polynomial approximation was presented. A design was presented to achieve in the popular field-programmable gate array( FPGA) platform. The hardware was tested, an Altera FPGA prototype implementation results were summarized , the performance and resource consumption were compared with the approach of the ROM lookup table architecture. The experimental results show that this approach achieves better performance, and it reduces the circuit area through avoiding huge loopup table.%为提高直接数字频率合成器( DDS)系统的性能,将分段多项式逼近算法应用于优化相幅转换电路中,实现了基于此结构的直接数字频率合成器设计.提出了适合在流行的现场可编程门阵列( FPGA)平台上实现的电路结构方案,进行了硬件实验,给出了在Altera Cyclone Ⅱ器件中的实现结果,并在性能和资源消耗方面与基于ROM查找表的方案作了比较.研究结果表明,由于避免了庞大的查找表,这一方案大大减小了电路面积,提高了系统性能.

  2. 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...

  3. 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.

  4. Resonance frequency in ferromagnetic superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Qiu Rongke; Huang Andong [School of Science, Shenyang University of Technology, Shenyang 110870 (China); Li Da; Zhang Zhidong, E-mail: rkqiu@163.com [Shenyang National Laboratory for Materials Science, Institute of Metal Research and International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China)

    2011-10-19

    The resonance frequency in two-layer and three-layer ferromagnetic superlattices is studied, using the Callen's Green function method, the Tyablikov decoupling approximation and the Anderson-Callen decoupling approximation. The effects of interlayer exchange coupling, anisotropy, external magnetic field and temperature on the resonance frequency are investigated. It is found that the resonance frequencies increase with increasing external magnetic field. In a parameter region of the asymmetric system, each sublayer corresponds to its own resonance frequency. The anisotropy of a sublayer affects only the resonance frequency corresponding to this sublayer. The stronger the anisotropy, the higher is the resonance frequency. The interlayer exchange coupling affects only the resonance frequencies belonging to the sublayers connected by it. The stronger the interlayer exchange coupling, the higher are the resonance frequencies. All the resonance frequencies decrease as the reduced temperature increases. The results direct the method to enhance and adjust the resonance frequency of magnetic multilayered materials with a wide band.

  5. 47 CFR 74.761 - Frequency tolerance.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Frequency tolerance. 74.761 Section 74.761... Booster Stations § 74.761 Frequency tolerance. The licensee of a low power TV, TV translator, or TV... tolerance of stations using direct frequency conversion of a received signal and not engaging in...

  6. Direct photonic coupling of a semiconductor quantum dot and a trapped ion

    CERN Document Server

    Meyer, H M; Steiner, M; Gall, C Le; Matthiesen, C; Clarke, E; Ludwig, A; Reichel, J; Atatüre, M; Köhl, M

    2014-01-01

    Coupling individual quantum systems lies at the heart of building scalable quantum networks. Here, we report the first direct photonic coupling between a semiconductor quantum dot and a trapped ion and we demonstrate that single photons generated by a quantum dot controllably change the internal state of an $\\textrm{Yb}^+$ ion. We ameliorate the effect of the sixty-fold mismatch of the radiative linewidths with coherent photon generation and a high-finesse fiber-based optical cavity enhancing the coupling between the single photon and the ion. The transfer of information presented here via the classical correlations between the $\\sigma_z$-projection of the quantum-dot spin and the internal state of the ion provides a promising step towards quantum state-transfer in a hybrid photonic network.

  7. Frequency dependent polarization analysis of high-frequency seismograms

    Science.gov (United States)

    Park, Jeffrey; Vernon, Frank L., III; Lindberg, Craig R.

    1987-11-01

    We present a multitaper algorithm to estimate the polarization of particle motion as a function of frequency from three-component seismic data. This algorithm is based on a singular value decomposition of a matrix of eigenspectra at a given frequency. The right complex eigenvector zˆ corresonding to the largest singular value of the matrix has the same direction as the dominant polarization of seismic motion at that frequency. The elements of the polarization vector zˆ specify the relative amplitudes and phases of motion measured along the recorded components within a chosen frequency band. The width of this frequency band is determined by the time-bandwidth product of the prolate spheroidal tapers used in the analysis. We manipulate the components of zˆ to determine the apparent azimuth and angle of incidence of seismic motion as a function of frequency. The orthogonality of the eigentapers allows one to calculate easily uncertainties in the estimated azimuth and angle of incidence. We apply this algorithm to data from the Anza Seismic Telemetered Array in the frequency band 0 ≤ ƒ ≤ 30 Hz. The polarization is not always a smooth function of frequency and can exhibit sharp jumps, suggesting the existence of scattered modes within the crustal waveguide and/or receiver site resonances.

  8. 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.

  9. LEP radio-frequency cavity

    CERN Multimedia

    1991-01-01

    One of the copper radio-frequency accelerating cavities installed for the first phase of LEP (1989-1995). Bunches of electrons and positrons circulated in LEP in opposite directions and were accelerated in eight different sets of 16 cavities (situated on either side of the four experiments), gaining 400 million volts of accelerating power per turn.

  10. Frequency noise in frequency swept fiber laser.

    Science.gov (United States)

    Pedersen, Anders Tegtmeier; Rottwitt, Karsten

    2013-04-01

    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- optical modulators and forward propagating Brillouin scattering appear in the spectrum.

  11. 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...

  12. Frequency selectivity at very low centre frequencies

    DEFF Research Database (Denmark)

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

    2010-01-01

    -3638 (2007)]. Recent experiments showed that the exact frequency varies from individual to individual. Besides, the helicotrema region in the METF has been found to highly influence frequency selectivity for centre frequencies (CFs) below 80 Hz (Jurado and Moore in prep). By using individual METF...

  13. Matsubara Frequency Sums

    CERN Document Server

    Kumar, Alok

    2010-01-01

    We cannot use directly the results of zero-temperature at finite temperature, for at finite temperature the average is to be carried over all highly degenerate excited states unlike zero-temperature average is only on unique ground state. One of the formal way to take into account the finite temperature into quantum field theory is due to Matsubara, to replace temporal component of eigenvalues $k_{4}$ by $\\omega_{n}=\\frac{2\\pi n}{\\beta}$ $(\\frac{2\\pi (n+{1/2})}{\\beta})$ with summation over all integer values of $n$. The summation is done with the infinite series expansion of $\\coth (\\pi y)$. With the chemical potential $\\mu$, $\\omega_{n}$ will be replaced by $\\omega_{n} - \\mu$ in the eigenvalues and the summation over $n$ cannot be done easily. Various methods exist to evaluate it. We use the infinite series expansion of $\\coth (\\pi y)$ to work operationally for such Matsubara frequency sums.

  14. 腔增强拉曼技术下的过饱和硫酸镁液滴蒸发动力学初探%Preliminary Assessment of Evaporating Supersaturated MgSO4 Droplet at Low Relative Humidity with Cavity Enhanced Raman Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    陈斯华; 蔡宸; 冷春波; 张韫宏

    2013-01-01

    This paper is aimed to study the response of a single MgSO4 droplet to the variation of relative humidity through the combination of single beam gradient force optical tweezers and Raman spectroscopy.The evaporation dynamic of a single MgSO4 droplet which is trapped by a single beam gradient force optical tweezers is investigated by varying the relative humidity in a stepwise manner.The measurements of the variation in equilibrium wet droplet size with relative humidity (RH) are made using cavity enhanced Raman scattering(CERS),where the stimulated Raman signals appear at wavelength commensurate to the Whispering Gallery Modes (WGMs) are applied to determine the size of droplet with high precision.This study demonstrates the real time monitoring of MgSO4 droplet size over a RH range that had not previously been explored with aerosol optical tweezers.The results show that the MgSO4 droplet radius variation gradually becomes smaller as the RH=~44% and is greatly depressed when RH lower than 40%,indicating that water evaporation rate of captured MgSO4 droplet is limited at high concentration.On the other hand,the deliquescence of shrinked MgSO4 droplet is not equivalent with the dehumidification process.The re-growth of MgSO4 droplet size is observed to be significantly slower in response to the increase of RH.It is suggested that mass transfer effect caused by the gel formation has contributed to the retardation of water mass transfer.%本文通过单光束梯度力光学镊子-拉曼光谱系统,对硫酸镁单液滴随着相对湿度变化的反应进行了探究.当硫酸镁单液滴被光镊捕获之后,通过相对湿度的梯度变化探究了捕获液滴的蒸发动力学变化.发生在与耳语回音模相称波长的受激拉曼散射可以用来准确地确定液滴半径,因此,可以通过腔增强拉曼散射得到在不同湿度下处于平衡的液滴半径信息.本研究通过光镊对硫酸镁单液滴的实时监测,阐述了在某个相对

  15. DOA estimation exploiting coprime frequencies

    Science.gov (United States)

    Qin, Si; Zhang, Yimin D.; Amin, Moeness G.

    2014-05-01

    Coprime array, which utilizes a coprime pair of uniform linear subarrays, is an attractive structure to achieve sparse array configurations. Alternatively, effective coprime array configurations can be implemented using a uniform linear array with two coprime sensing frequencies. This enables the integration of the coprime array and filter concepts to achieve high capabilities in meeting system performance and complexity constraints. This paper examines its performance for direction-of-arrival estimations. In particular, we analyze the number of detectable signals and the estimation accuracy as related to the array configurations and sensing frequencies.

  16. 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....

  17. Multi-frequency excitation

    KAUST Repository

    Younis, Mohammad I.

    2016-03-10

    Embodiments of multi-frequency excitation are described. In various embodiments, a natural frequency of a device may be determined. In turn, a first voltage amplitude and first fixed frequency of a first source of excitation can be selected for the device based on the natural frequency. Additionally, a second voltage amplitude of a second source of excitation can be selected for the device, and the first and second sources of excitation can be applied to the device. After applying the first and second sources of excitation, a frequency of the second source of excitation can be swept. Using the methods of multi- frequency excitation described herein, new operating frequencies, operating frequency ranges, resonance frequencies, resonance frequency ranges, and/or resonance responses can be achieved for devices and systems.

  18. 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.

  19. Application of Zeeman graphite furnace atomic absorption spectrometry with high-frequency modulation polarization for the direct determination of aluminum, beryllium, cadmium, chromium, mercury, manganese, nickel, lead, and thallium in human blood.

    Science.gov (United States)

    Ivanenko, Natalya B; Solovyev, Nikolay D; Ivanenko, Anatoly A; Ganeev, Alexander A

    2012-10-01

    Determination of aluminum (Al), beryllium (Be), cadmium (Cd), chromium (Cr), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and thallium (Tl) concentrations in human blood using high-frequency modulation polarization Zeeman graphite furnace atomic absorption spectrometry (GFAAS) was performed. No sample digestion was used in the current study. Blood samples were diluted with deionized water or 0.1 % (m/v) Triton X-100 solution for Tl. Dilution factors ranged from 1/5 per volume for Be and Tl to 1/20 per volume for Cd and Pb. For Tl, Cd, and Hg, noble metals (gold, platinum, rhodium, etc.) were applied as surface modifiers. To mitigate chloride interference, 2 % (m/v) solution of NH(4)NO(3) was used as matrix modifier for Tl and Ni assessment. The use of Pd(NO(3))(2) as oxidative modifier was necessary for blood Hg and Tl measurement. Validation of the methods was performed by analyzing two-level reference material Seronorm. The precision of the designed methods as relative SD was between 4 and 12 % (middle of a dynamic range) depending on the element. For additional validation, spiked blood samples were analyzed. Limits of detection (LoDs, 3σ, n = 10) for undiluted blood samples were 2.0 μg L(-1) for Al, 0.08 μg L(-1) for Be, 0.10 μg L(-1) for Cd, 2.2 μg L(-1) for Cr, 7 μg L(-1) for Hg, 0.4 μg L(-1) for Mn, 2.3 μg L(-1) for Ni, 3.4 μg L(-1) for Pb, and 0.5 μg L(-1) for Tl. The LoDs achieved allowed determination of Al, Cd, Cr, Mn, Ni, and Pb at both toxic and background levels. Be, Hg, and Tl could be reliably measured at toxic levels only. The methods developed are used for clinical diagnostics and biological monitoring of work-related exposure.

  20. 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...

  1. Fuzzy Proportional Plus-Derivative Control Based Frequency Regulation of Permanent Magnet Direct-Drive Wind Power Generation Unit%基于模糊比例-微分控制的永磁直驱风电机组频率调节

    Institute of Scientific and Technical Information of China (English)

    姚骏; 赵磊; 刘奥林; 周特; 曾欣

    2014-01-01

    On the basis of analyzing the impacts of different equivalent inertial and damping on power grid frequency, a fuzzy proportional differential (PD) control based frequency regulation and control strategy for direct-drive permanent magnet synchronous wind power generator equipped with a flywheel energy storage unit is proposed to dynamically adjust equivalent inertia and damping of power grid. A small signal stability model of power grid is established to determine the output universe of discourse of PD controller, and the correctness of theoretical analysis is validated by results of corresponding simulation. The simulation results of a direct-drive permanent magnet synchronous generator based wind power generation system with capacity of 2 MW, in which a flywheel energy storage unit is equipped with, show that the proposed control strategy can play an auxiliary control role in power grid frequency regulation and the post-disturbance power grid frequency fluctuation can be decreased, so it contributes to enhance the frequency stability of power grid.%在分析系统不同等效惯量和阻尼对电网频率影响的基础上,提出了基于模糊比例-微分(proportional differential, PD)控制的含飞轮储能单元的永磁直驱风电机组频率调节控制策略,以动态调节电网等效惯量和阻尼。建立了系统小信号稳定性模型,以确定模糊PD控制器的输出论域,并通过相应仿真验证了理论分析的正确性。通过对1台含飞轮储能单元的2 MW永磁直驱风电系统进行仿真研究表明,所提控制策略能辅助电网频率调节,减小电网受扰动后的频率波动,有助于增强电网的频率稳定性。

  2. 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...

  3. High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools

    Science.gov (United States)

    Li, Xinlong; Reber, Melanie A. R.; Corder, Christopher; Chen, Yuning; Zhao, Peng; Allison, Thomas K.

    2016-09-01

    We present a detailed description of the design, construction, and performance of high-power ultrafast Yb:fiber laser frequency combs in operation in our laboratory. We discuss two such laser systems: an 87 MHz, 9 W, 85 fs laser operating at 1060 nm and an 87 MHz, 80 W, 155 fs laser operating at 1035 nm. Both are constructed using low-cost, commercially available components, and can be assembled using only basic tools for cleaving and splicing single-mode fibers. We describe practical methods for achieving and characterizing low-noise single-pulse operation and long-term stability from Yb:fiber oscillators based on nonlinear polarization evolution. Stabilization of the combs using a variety of transducers, including a new method for tuning the carrier-envelope offset frequency, is discussed. High average power is achieved through chirped-pulse amplification in simple fiber amplifiers based on double-clad photonic crystal fibers. We describe the use of these combs in several applications, including ultrasensitive femtosecond time-resolved spectroscopy and cavity-enhanced high-order harmonic generation.

  4. Frequency of Natural Resistance within NS5a Replication Complex Domain in Hepatitis C Genotypes 1a, 1b: Possible Implication of Subtype-Specific Resistance Selection in Multiple Direct Acting Antivirals Drugs Combination Treatment

    Directory of Open Access Journals (Sweden)

    Sabrina Bagaglio

    2016-03-01

    Full Text Available Different HCV subtypes may naturally harbor different resistance selection to anti-NS5a inhibitors. 2761 sequences retrieved from the Los Alamos HCV database were analyzed in the NS5a domain 1, the target of NS5a inhibitors. The NS5a resistance-associated polymorphisms (RAPs were more frequently detected in HCV G1b compared to G1a. The prevalence of polymorphisms associated with cross-resistance to compounds in clinical use (daclatasvir, DCV, ledipasvir, LDV, ombitasvir, and OMV or scheduled to come into clinical use in the near future (IDX719, elbasvir, and ELV was higher in G1b compared to G1a (37/1552 (2.4% in 1b sequences and 15/1209 (1.2% in 1a isolates, p = 0.040. Interestingly, on the basis of the genotype-specific resistance pattern, 95 (6.1% G1b sequences had L31M RAP to DCV/IDX719, while 6 sequences of G1a (0.5% harbored L31M RAP, conferring resistance to DCV/LDV/IDX719/ELV (p < 0.0001. Finally, 28 (2.3% G1a and none of G1b isolates harbored M28V RAP to OMV (p < 0.0001. In conclusion, the pattern of subtype-specific resistance selection in the naturally occurring strains may guide the treatment option in association with direct acting antivirals (DAAs targeting different regions, particularly in patients that are difficult to cure, such as those with advanced liver disease or individuals who have failed previous DAAs.

  5. 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.

  6. 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-

  7. Full stabilization of a microresonator-based optical frequency comb.

    Science.gov (United States)

    Del'Haye, P; Arcizet, O; Schliesser, A; Holzwarth, R; Kippenberg, T J

    2008-08-01

    We demonstrate control and stabilization of an optical frequency comb generated by four-wave mixing in a monolithic microresonator with a mode spacing in the microwave regime (86 GHz). The comb parameters (mode spacing and offset frequency) are controlled via the power and the frequency of the pump laser, which constitutes one of the comb modes. Furthermore, generation of a microwave beat note at the comb's mode spacing frequency is demonstrated, enabling direct stabilization to a microwave frequency standard.

  8. Calcineurin A versus NS5A-TP2/HD domain containing 2: a case study of site-directed low-frequency random mutagenesis for dissecting target specificity of peptide aptamers.

    Science.gov (United States)

    Dibenedetto, Silvia; Cluet, David; Stebe, Pierre-Nicolas; Baumle, Véronique; Léault, Jérémie; Terreux, Raphaël; Bickle, Marc; Chassey, Benoit D E; Mikaelian, Ivan; Colas, Pierre; Spichty, Martin; Zoli, Michele; Rudkin, Brian B

    2013-07-01

    We previously identified a peptide aptamer (named R5G42) via functional selection for its capacity to slow cell proliferation. A yeast two-hybrid screen of human cDNA libraries, using R5G42 as "bait," allowed the identification of two binding proteins with very different functions: calcineurin A (CnA) (PP2B/PPP3CA), a protein phosphatase well characterized for its role in the immune response, and NS5A-TP2/HD domain containing 2, a much less studied protein induced subsequent to hepatitis C virus non-structural protein 5A expression in HepG2 hepatocellular carcinoma cells, with no known activity. Our objective in the present study was to dissect the dual target specificity of R5G42 in order to have tools with which to better characterize the actions of the peptide aptamers toward their individual targets. This was achieved through the selection of random mutants of the variable loop, derived from R5G42, evaluating their specificity toward CnA and NS5A-TP2 and analyzing their sequence. An interdisciplinary approach involving biomolecular computer simulations with integration of the sequence data and yeast two-hybrid binding phenotypes of these mutants yielded two structurally distinct conformers affording the potential molecular basis of the binding diversity of R5G42. Evaluation of the biological impact of CnA- versus NS5A-TP2-specific peptide aptamers indicated that although both contributed to the anti-proliferative effect of R5G42, CnA-binding was essential to stimulate the nuclear translocation of nuclear factor of activated T cells, indicative of the activation of endogenous CnA. By dissecting the target specificity of R5G42, we have generated novel tools with which to study each target individually. Apta-C8 is capable of directly activating CnA independent of binding to NS5A-TP2 and will be an important tool in studying the role of CnA activation in the regulation of different signaling pathways, whereas Apta-E1 will allow dissection of the function of NS5A

  9. 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

  10. 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.

  11. 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.

  12. Demodulated low frequency currents from electrosurgical procedures.

    Science.gov (United States)

    Tucker, R D; Schmitt, O H; Sievert, C E; Silvis, S E

    1984-07-01

    Low frequency currents produced incidental to electrosurgical procedures are usually only a minor threat unless they are coupled directly into the heart through a catheter or a thoracic surgical procedure. However, should the low frequency blocking capacitors in the electrosurgical generator fail in the conducting state, extremely dangerous low frequency currents of many milliamperes may flow into the patient. Even with properly functioning capacitors, low frequencies up to several milliamperes may be produced by some generators. The results of this study show that the coagulation mode of operation produces greater amounts of low frequency currents than the "pure cutting" mode at the same power setting. These results also demonstrate that the higher the generator power output, the higher the magnitude of the low frequency currents.

  13. Frequency selective infrared sensors

    Science.gov (United States)

    Davids, Paul; Peters, David W

    2013-05-28

    A frequency selective infrared (IR) photodetector having a predetermined frequency band. The exemplary frequency selective photodetector includes: a dielectric IR absorber having a first surface and a second surface substantially parallel to the first surface; an electrode electrically coupled to the first surface of the dielectric IR absorber; and a frequency selective surface plasmonic (FSSP) structure formed on the second surface of the dielectric IR absorber. The FSSP structure is designed to selectively transmit radiation in the predetermined frequency band that is incident on the FSSP structure substantially independent of the angle of incidence of the incident radiation on the FSSP structure.

  14. 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....

  15. Future directions.

    Science.gov (United States)

    Raffa, Robert B; Tallarida, Ronald J

    2010-01-01

    The chapters of this book summarize much of what has been done and reported regarding cancer chemotherapy-related cognitive impairment. In this chapter, we point out some future directions for investigation.

  16. 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.

  17. 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.

  18. Universal Optical Frequency Comb

    CERN Document Server

    Savchenkov, A A; Liang, W; Ilchenko, V S; Seidel, D; Maleki, L

    2010-01-01

    We demonstrate that whispering gallery mode resonators can be utilized to generate optical frequency combs based on four wave mixing process at virtually any frequency that lies in the transparency window of the resonator host material. We show theoretically how the morphology of the resonator can be engineered to produce a family of spectrally equidistant modes with anomalous group velocity dispersion appropriate for the comb generation. We present experimental results for a frequency comb centered at 794 nm to support our theoretical findings.

  19. Frequency Response Analysis Tool

    Energy Technology Data Exchange (ETDEWEB)

    Etingov, Pavel V. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Kosterev, Dmitry [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Dai, T. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2014-12-01

    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.

  20. 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.

  1. Optimization of frequency quantization

    CERN Document Server

    Tibabishev, V N

    2011-01-01

    We obtain the functional defining the price and quality of sample readings of the generalized velocities. It is shown that the optimal sampling frequency, in the sense of minimizing the functional quality and price depends on the sampling of the upper cutoff frequency of the analog signal of the order of the generalized velocities measured by the generalized coordinates, the frequency properties of the analog input filter and a maximum sampling rate for analog-digital converter (ADC). An example of calculating the frequency quantization for two-tier ADC with an input RC filter.

  2. Ultrasonic Atomization Amount for Different Frequencies

    Science.gov (United States)

    Yasuda, Keiji; Honma, Hiroyuki; Xu, Zheng; Asakura, Yoshiyuki; Koda, Shinobu

    2011-07-01

    The mass flow rate of ultrasonic atomization was estimated by measuring the vaporization amount from a bulk liquid with a fountain. The effects of ultrasonic frequency and intensity on the atomization characteristics were investigated when the directivities of the acoustic field from a transducer were almost the same. The sample was distillated water and the ultrasonic frequencies were 0.5, 1.0, and 2.4 MHz. The mass flow rate of ultrasonic atomization increased with increasing ultrasonic intensity and decreasing ultrasonic frequency. The fountain was formed at the liquid surface where the effective value of acoustic pressure was above atmospheric pressure. The fountain height was strongly governed by the acoustic pressure at the liquid surface of the transducer center. At the same ultrasonic intensity, the dependence of ultrasonic frequency on the number of atomized droplets was small. At the same apparent surface area of the fountain, the number of atomized droplets became larger as the ultrasonic frequency increased.

  3. Conical Double Frequency Emission by Femtosecond Laser Pulses from DKDP

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xi-Peng; JIANG Hong-Bing; TANG Shan-Chun; GONG Qi-Huang

    2009-01-01

    Conical double frequency emission is investigated by femtosecond laser pulses at a wavelength of 800nm in a DKDP crystal. It is demonstrated that the sum frequency of incident wave and its scattering wave accounts for the conical double frequency emission. The gaps on the conical rings are observed and they are very sensitive to the propagation direction, and thus could be used to detect the small angle deviation of surface direction.

  4. Direct ELISA.

    Science.gov (United States)

    Lin, Alice V

    2015-01-01

    First described by Engvall and Perlmann, the enzyme-linked immunosorbent assay (ELISA) is a rapid and sensitive method for detection and quantitation of an antigen using an enzyme-labeled antibody. Besides routine laboratory usage, ELISA has been utilized in medical field and food industry as diagnostic and quality control tools. Traditionally performed in 96-well or 384-well polystyrene plates, the technology has expanded to other platforms with increase in automation. Depending on the antigen epitope and availability of specific antibody, there are variations in ELISA setup. The four basic formats are direct, indirect, sandwich, and competitive ELISAs. Direct ELISA is the simplest format requiring an antigen and an enzyme-conjugated antibody specific to the antigen. This chapter describes the individual steps for detection of a plate-bound antigen using a horseradish peroxidase (HRP)-conjugated antibody and luminol-based enhanced chemiluminescence (ECL) substrate. The methodological approach to optimize the assay by chessboard titration is also provided.

  5. FET frequency discriminator

    Science.gov (United States)

    Mawhinney, F. D.

    1982-03-01

    The FET Frequency Discriminator is an experimental microwave frequency discriminator developed for use in a specialized set-on VCO frequency memory system. Additional development and evaluation work has been done during this program to more fully determine the applicability of the FET frequency discriminator as a low-cost, expendable receiver front-end for both surveillance and ECM systems. Various methods for adjusting the frequency-to-voltage characteristic of the discriminator as well as the effects of detector characteristics and ambient temperature changes were evaluated. A number of discriminators for use in the 7- to 11-GHz and the 11to 18-GHz bands were fabricated and tested. Interim breadboard and final packaged models were either delivered or installed in developmental frequency systems. The major limitations and deficiencies of the FET frequency discriminator that were reviewed during the program include the effects of temperature, input power level variations, nonlinearity, and component repeatability. Additional effort will be required to advance the developmental status of the FET frequency discriminator to the level necessary for inclusion in low-cost receiver systems, but the basic simplicity of the approach continues to show much promise.

  6. Directing Lives

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    YANG Yang is he director of China Television PlayCenter.Before the arrival of the series Holding Hands,she filmed television plays reflecting women and marriage.Examples of her work include Niu Yuqin and Her Trees and theMidnight Trolley.The artistry and sympathy towards women inthese programmes make it obvious that they were directed by awoman.Holding Hands especially cements this connection.

  7. 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%.

  8. 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.

  9. Breakfast frequency among adolescents

    DEFF Research Database (Denmark)

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

    2016-01-01

    , quality of family communication and family support. Further, analyses suggested that the associations were more pronounced among girls, immigrants and adolescents from other family structure than traditional. The study highlights the importance of the family setting in promoting regular breakfast......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...... (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...

  10. A center frequency adjustable narrow band filter for the detection of weak single frequency signal.

    Science.gov (United States)

    Xin, Yunhong; Xiang, ZhenMing; Dong, LeMing; Zhu, Bing; Cao, Hui; Fang, Yu

    2014-04-01

    We describe and implement a center frequency adjustable narrow band filter based on the crystal filter for the detection of weak single frequency signal. It is formed by a multiplier, a direct digital frequency synthesizer, a multi-stage crystal bandpass filter, and a micro control unit which is used to set the center frequency of the filter. A theoretical study is proposed and experimentally validated. The test results show that the 3 db and 20 db bandwidths are 0.84 Hz and 2.73 Hz, respectively, and the filter system can effectively detect the signal with amplitude below 1 μV and a frequency which ranges from 10 Hz to the frequency that is mainly limited by the components applied.

  11. Pragmatic circuits frequency domain

    CERN Document Server

    Eccles, William

    2006-01-01

    Pragmatic Circuits: Frequency Domain goes through the Laplace transform to get from the time domain to topics that include the s-plane, Bode diagrams, and the sinusoidal steady state. This second of three volumes ends with a-c power, which, although it is just a special case of the sinusoidal steady state, is an important topic with unique techniques and terminology. Pragmatic Circuits: Frequency Domain is focused on the frequency domain. In other words, time will no longer be the independent variable in our analysis. The two other volumes in the Pragmatic Circuits series include titles on DC

  12. Quantum frequency downconversion experiment

    CERN Document Server

    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 $<$1, from the 0.7-$\\mu$m visible wavelength band to the 1.3-$\\mu$m telecom band. We expect this technology to become an important tool for flexible photonic quantum networking, including the realization of quantum repeater systems over optical fiber using atom-photon entanglement sources for the visible wavelength bands.

  13. Broadband frequency conversion

    DEFF Research Database (Denmark)

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

    that ensures phase matching over a broad spectral range in the BBO crystal. Since the tuning mechanism relies on all-passive components with extremely short response times the proposed method is well suited for short pulse, broad bandwidth laser sources like mode-locked lasers or super-continuum sources......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...

  14. 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...

  15. Advance care directives

    Science.gov (United States)

    ... advance directive; Do-not-resuscitate - advance directive; Durable power of attorney - advance care directive; POA - advance care directive; Health care agent - advance care directive; Health care proxy - ...

  16. Direct optical to microwave conversion

    Science.gov (United States)

    Taylor, Henry F.

    1990-09-01

    Support of high frequency fiber optic links through development of innovative higher efficiency techniques to convert optical energy directly to RF Energy. Control of Phases Arrays by optical means in an area of expanding technology development. Fiber optics and other forms of optical waveguide can provide greater accuracy and true time delay in a phase delay network. Methods of improvement in transfer of optical energy to RF Energy are determined. Development of Direct Optical-to-RF-Direct Amplifiers will result in higher efficiency, low noise, optical receivers for fiber optic links with improved performance. This results in longer fiber optic links without repeaters and improved BER or shorter links.

  17. 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...

  18. 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.

  19. 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.

  20. Comments on Landau damping due to synchrotron frequency spread

    Energy Technology Data Exchange (ETDEWEB)

    Ng, K.Y.; /Fermilab

    2005-01-01

    An inductive/space-charge impedance shifts the synchrotron frequency downwards above/below transition, but it is often said that the coherent synchrotron frequency of the bunch is not shifted in the rigid-dipole mode. On the other hand, the incoherent synchrotron frequency due to the sinusoidal rf always spreads in the downward direction. This spread will therefore not be able to cover the coherent synchrotron frequency, implying that there will not be any Landau damping no matter how large the frequency spread is. By studying the dispersion relation, it is shown that the above argument is incorrect, and there will be Landau damping if there is sufficient frequency spread. The main reason is that the coherent frequency of the rigid-dipole mode will no longer remain unshifted in the presence of a synchrotron frequency spread.

  1. Phononic Frequency Comb via Intrinsic Three-Wave Mixing

    Science.gov (United States)

    Ganesan, Adarsh; Do, Cuong; Seshia, Ashwin

    2017-01-01

    Optical frequency combs have resulted in significant advances in optical frequency metrology and found wide applications in precise physical measurements and molecular fingerprinting. A direct analogue of frequency combs in the phononic or acoustic domain has not been reported to date. In this Letter, we report the first clear experimental evidence for a phononic frequency comb. We show that the phononic frequency comb is generated through the intrinsic coupling of a driven phonon mode with an autoparametrically excited subharmonic mode. The experiments depict the comb generation process evidenced by a spectral response consisting of equally spaced discrete and phase coherent comb lines. Through systematic experiments at different drive frequencies and amplitudes, we portray the well-connected process of phononic frequency comb formation and define the attributes to control the features associated with comb formation in such a system. In addition to the demonstration of frequency comb, the interplay between the nonlinear resonances and the well-known Duffing phenomenon is also observed.

  2. Mid-frequency readers

    OpenAIRE

    Nation, Ian Stephen Paul; Anthony, Laurence

    2013-01-01

    This article describes a new free extensive reading resource for learning the mid-frequency words of English and for reading well known texts with minor vocabulary adaptation. A gap exists between the end of graded readers at around 3,000 word families and the vocabulary size needed to read unsimplified texts at around 8,000 word families. Mid-frequency readers are designed to fill this gap. They consist of texts from Project Gutenberg adapted for learners with a vocabulary size of 4,000 word...

  3. HIGHER FREQUENCY ULTRASONIC LIGHT MODULATORS.

    Science.gov (United States)

    LIGHT), (* MODULATORS , (*ULTRASONIC RADIATION, MODULATORS ), OPTICAL COMMUNICATIONS, BANDWIDTH, TRANSDUCERS, HIGH FREQUENCY, VERY HIGH FREQUENCY, ATTENUATION, DATA PROCESSING, OPTICAL EQUIPMENT, ANALOG COMPUTERS, THEORY.

  4. 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.

  5. Frequency of orthodontic extraction

    Directory of Open Access Journals (Sweden)

    Camila de S. Dardengo

    2016-02-01

    Full Text Available Introduction: The option of dental extraction for orthodontic purposes has been debated for more than 100 years, including periods when it was widely used in treatment, including the present, during which other methods are used to avoid dental extractions. The objective was to analyze the frequency of tooth extraction treatment performed between 1980 and 2011 at the Orthodontic Clinic of Universidade Estadual do Rio de Janeiro (UERJ. Material and Methods: The clinical records of 1484 patients undergoing orthodontic treatment were evaluated. The frequency of extractions was evaluated with regard to sex, Angle's classification, the different combinations of extractions and the period when orthodontic treatment began. Chi-square test was used to determine correlations between variables, while the chi-square test for trends was used to assess the frequency of extractions over the years. Results: There was a reduction of approximately 20% in the frequency of cases treated with tooth extraction over the last 32 years. The most frequently extracted teeth were first premolars. Patients with Class I malocclusion showed fewer extractions, while Class II patients underwent a higher number of extraction treatment. There were no statistically significant differences with regard to sex. Conclusion: New features introduced into the orthodontic clinic and new esthetic concepts contributed to reducing the number of cases treated with dental extractions. However, dental extractions for orthodontic purposes are still well indicated in certain cases.

  6. 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...

  7. Multiple Frequency Parametric Sonar

    Science.gov (United States)

    2015-09-28

    300003 1 MULTIPLE FREQUENCY PARAMETRIC SONAR STATEMENT OF GOVERNMENT INTEREST [0001] The invention described herein may be manufactured and...beams. However, the multiple nonlinear interactions are not taken advantage of in order to generate additional efficiencies, bandwidth, and SNR...array. [0050] It will be understood that many additional changes in details, materials , steps, and arrangements of parts which have been described

  8. All-frequency reflectionlessness

    CERN Document Server

    Philbin, T G

    2016-01-01

    We derive planar permittivity profiles that do not reflect perpendicularly exiting radiation of any frequency. The materials obey the Kramers-Kronig relations and have no regions of gain. Reduction of the Casimir force by means of such materials is also discussed.

  9. Lunch frequency among adolescents

    DEFF Research Database (Denmark)

    Pedersen, Trine Pagh; Holstein, Bjørn E; Krølner, Rikke

    2016-01-01

    frequency was most common among students who were boys, 13- and 15-year-olds, from medium and low family social class, descendants of immigrants, living in a single-parent family and in a reconstructed family. School-level analyses suggested that having access to a canteen at school was associated with low...

  10. Multiband frequency selective surface

    Science.gov (United States)

    Wu, Te-Kao

    1998-10-01

    This paper addresses the similarity of microwave/millimeter wave frequency selective surfaces (FSS) to optical filters. Specifically, the design approaches of the 4-band FSSs developed for NASA's CASSINI high gain antenna are described in detail. Representative RF test results are given to demonstrate the validity of these designs. These design approaches are very general and can be applied to multiband optical filters.

  11. Microwave Frequency Multiplier

    Science.gov (United States)

    Velazco, J. E.

    2017-02-01

    High-power microwave radiation is used in the Deep Space Network (DSN) and Goldstone Solar System Radar (GSSR) for uplink communications with spacecraft and for monitoring asteroids and space debris, respectively. Intense X-band (7.1 to 8.6 GHz) microwave signals are produced for these applications via klystron and traveling-wave microwave vacuum tubes. In order to achieve higher data rate communications with spacecraft, the DSN is planning to gradually furnish several of its deep space stations with uplink systems that employ Ka-band (34-GHz) radiation. Also, the next generation of planetary radar, such as Ka-Band Objects Observation and Monitoring (KaBOOM), is considering frequencies in the Ka-band range (34 to 36 GHz) in order to achieve higher target resolution. Current commercial Ka-band sources are limited to power levels that range from hundreds of watts up to a kilowatt and, at the high-power end, tend to suffer from poor reliability. In either case, there is a clear need for stable Ka-band sources that can produce kilowatts of power with high reliability. In this article, we present a new concept for high-power, high-frequency generation (including Ka-band) that we refer to as the microwave frequency multiplier (MFM). The MFM is a two-cavity vacuum tube concept where low-frequency (2 to 8 GHz) power is fed into the input cavity to modulate and accelerate an electron beam. In the second cavity, the modulated electron beam excites and amplifies high-power microwaves at a frequency that is a multiple integer of the input cavity's frequency. Frequency multiplication factors in the 4 to 10 range are being considered for the current application, although higher multiplication factors are feasible. This novel beam-wave interaction allows the MFM to produce high-power, high-frequency radiation with high efficiency. A key feature of the MFM is that it uses significantly larger cavities than its klystron counterparts, thus greatly reducing power density and arcing

  12. 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.

  13. Voluntary attention increases perceived spatial frequency.

    Science.gov (United States)

    Abrams, Jared; Barbot, Antoine; Carrasco, Marisa

    2010-08-01

    Voluntary covert attention selects relevant sensory information for prioritized processing. The behavioral and neural consequences of such selection have been extensively documented, but its phenomenology has received little empirical investigation. Involuntary attention increases perceived spatial frequency (Gobell & Carrasco, 2005), but involuntary attention can differ from voluntary attention in its effects on performance in tasks mediated by spatial resolution (Yeshurun, Montagna, & Carrasco, 2008). Therefore, we ask whether voluntary attention affects the subjective appearance of spatial frequency--a fundamental dimension of visual perception underlying spatial resolution. We used a demanding rapid serial visual presentation task to direct voluntary attention and measured perceived spatial frequency at the attended and unattended locations. Attention increased the perceived spatial frequency of suprathreshold stimuli and also improved performance on a concurrent orientation discrimination task. In the control experiment, we ruled out response bias as an alternative account by using a lengthened interstimulus interval, which allows observers to disengage attention from the cued location. In contrast to the main experiment, the observers showed neither increased perceived spatial frequency nor improved orientation discrimination at the attended location. Thus, this study establishes that voluntary attention increases perceived spatial frequency. This phenomenological consequence links behavioral and neurophysiological studies on the effects of attention.

  14. FPGA Implementation of High Speed and High Precision Direct Digital Frequency Synthesizer Based on Parallel - CORDIC%基于 Parallel -CORDIC 的高精度高速度直接数字频率合成器的 FPGA 实现

    Institute of Scientific and Technical Information of China (English)

    2014-01-01

    本文提出了一种直接数字频率合成器(DDFS)的设计,以 Parallel_CORDIC(COrdinate Rotation Digital Com-puter)算法模块替代传统的查找表方式,实现了相位与幅度的一一对应,输出相位完全正交的正余弦波形;同时应用旋转角度预测及4:2的进位保存加法器(CSA)技术,将速度比传统 CORDIC 算法提高41.7%,精度提高到10-4.最后以Xilinx 的 FPGA 硬件实现整个设计.%The design of a direct digital frequency synthesizer (DDFS) is proposed in this paper .Parallel - CORDIC (Cordi-nate Rotation Digital Computer) algorithm module is used to replace the traditional look-up table method ,the phase and amplitude of a one-to-one correspondence is realized ,and outputs are sine and cosine waveforms that completely orthogonal in phase .The angle prediction and 4 :2 Carry Save Adder (CSA) technologies are also applied in the design ,the calculation speed is 41 .7% faster than the traditional CORDIC algorithm and the accuracy is improved to 10 - 4 .Finally ,the whole design is implemented based on Xilinx FPGA development board .

  15. Direct Broadcast Satellite: Radio Program

    Science.gov (United States)

    Hollansworth, James E.

    1992-01-01

    NASA is committed to providing technology development that leads to the introduction of new commercial applications for communications satellites. The Direct Broadcast Satellite-Radio (DBS-R) Program is a joint effort between The National Aeronautics and Space Administration (NASA) and The United States Information Agency/Voice of America (USIA/VOA) directed at this objective. The purpose of this program is to define the service and develop the technology for a direct-to-listener satellite sound broadcasting system. The DBS-R Program, as structured by NASA and VOA, is now a three-phase program designed to help the U.S. commercial communications satellite and receiver industry bring about this new communications service. Major efforts are being directed towards frequency planning hardware and service development, service demonstration, and experimentation with new satellite and receiver technology.

  16. 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......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...... plane. An FSB system can be configured as a multiband, close-packed focal-plane array, permitting efficient use of the throughput of a telescope....

  17. [Frequency dependance of compliance].

    Science.gov (United States)

    Gayrard, P

    1975-01-01

    Resistance of peripheral or "small" airways is only a small part of the total pulmonary resistance (Raw). Even considerable obstruction in these airways will have little effect on total resistance. Conversely this will lead to inequality in the time constants of units in parallel, and dynamic lung compliance (C dyn) shall fall as respiratory frequence increases. C dyn is measured from simultaneous recordings of transpulmonary pressure (esophageal balloon) and volume obtained from a volume displacement plethysmograph. If Raw and static compliance are found to be normal, the frequency dependance of compliance will result from peripheral airway obstruction only. Early stages of chronic airway obstruction can be established by this method. However this appear not suitable for wide-scale studies.

  18. 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.

  19. Directivity of a simplified aeroengine

    OpenAIRE

    Mattei, Pierre-Olivier

    2006-01-01

    International audience; This paper presents theoretical and numerical results on the high frequency directivity of an aeroengine under flight conditions. In this paper, two different theories, based on a Kirchhoff approximation for semi-infinite cylinders, are combined to obtain the far field sound pressure radiated into the whole surrounding space. Although the geometric description of the engine is simplified - in particular, the annular exhaust is not taken into account - it includes some ...

  20. Analysis of Time and Frequency Domain Pace Algorithms for OFDM with Virtual Subcarriers

    DEFF Research Database (Denmark)

    Rom, Christian; Manchón, Carles Navarro; Deneire, Luc

    2007-01-01

    This paper studies common linear frequency direction pilot-symbol aided channel estimation algorithms for orthogonal frequency division multiplexing in a UTRA long term evolution context. Three deterministic algorithms are analyzed: the maximum likelihood (ML) approach, the noise reduction algori...

  1. 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..

  2. Arbitrary optical frequency synthesis traced to an optical frequency comb

    Science.gov (United States)

    Cai, Zihang; Zhang, Weipeng; Yang, Honglei; Li, Yan; Wei, Haoyun

    2016-11-01

    An arbitrary optical frequency synthesizer with a broad tuning range and high frequency accuracy is presented. The system includes an external cavity diode laser (ECDL) as the output laser, an Erbium-doped optical frequency comb being a frequency reference, and a control module. The optical frequency from the synthesizer can be continuously tuned by the large-scale trans-tooth switch and the fine intra-tooth adjustment. Robust feedback control by regulating the current and PZT voltage enables the ECDL to phase-lock to the Erbium-doped optical frequency comb, therefore to keep stable frequency output. In the meanwhile, the absolute frequency of the synthesizer is determined by the repetition rate, the offset frequency and the beat frequency. All the phase lock loops in the system are traced back to a Rubidium clock. A powerful and friendly software is developed to make the operation convenient by integrating the functions of frequency setting, tuning, tracing, locking and measuring into a LabVIEW interface. The output frequency tuning span and the uncertainty of the system are evaluated as >6 THz and <3 kHz, respectively. The arbitrary optical frequency synthesizer will be a versatile tool in diverse applications, such as synthetic wavelength based absolute distance measurement and frequency-stabilized Cavity Ring-Down Spectroscopy.

  3. DEMODULATION OF FREQUENCY OR SPACE MODULATED LIGHT.

    Science.gov (United States)

    LIGHT , DEMODULATION), (*OPTICAL COMMUNICATIONS, FREQUENCY MODULATION), (*FREQUENCY MODULATION, LIGHT ), OPTICAL TRACKING, BEAMS(ELECTROMAGNETIC), DEFLECTION, MICROWAVE FREQUENCY, ELECTRON BEAMS, PHOTOCATHODES

  4. Reflex feed system for dual frequency antenna with frequency cutoff means

    Science.gov (United States)

    Hartop, R. W. (Inventor)

    1978-01-01

    A reflex feed system is described for a dual frequency antenna such as one which transmits and receives both S and X band signals. The dichroic plate, normally employed for directing X band radiation away from the X band horn, is replaced by a flange about the opening of the X band horn.

  5. Laser frequency combs for astronomical observations.

    Science.gov (United States)

    Steinmetz, Tilo; Wilken, Tobias; Araujo-Hauck, Constanza; Holzwarth, Ronald; Hänsch, Theodor W; Pasquini, Luca; Manescau, Antonio; D'Odorico, Sandro; Murphy, Michael T; Kentischer, Thomas; Schmidt, Wolfgang; Udem, Thomas

    2008-09-05

    A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require measurements of Doppler velocity drifts of approximately 1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrated the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of approximately 9 meters per second at approximately 1.5 micrometers-beyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration.

  6. Inequivalence of direct and converse magnetoelectric coupling at electromechanical resonance

    Science.gov (United States)

    Wu, Gaojian; Nan, Tianxiang; Zhang, Ru; Zhang, Ning; Li, Shandong; Sun, Nian X.

    2013-10-01

    Resonant direct and converse magnetoelectric (ME) effects have been investigated experimentally and theoretically in FeGa/PZT/FeGa sandwich laminate composites under the same electric and magnetic bias conditions. Resonant direct ME effect (DME) occurs at antiresonance frequency while resonant converse ME effect (CME) occurs at resonance frequency. The antiresonance and resonance frequencies have close but different values under identical bias conditions. The magnitudes of resonant effective ME coefficients for direct and converse ME effects are also not equal. A model was developed to describe the frequency response of DME and CME in laminate composite, which was in good agreement with experimental results.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. Frequency Dependent Attenuation Revisited

    CERN Document Server

    Richard, Kowar; Xavier, Bonnefond

    2009-01-01

    The work is inspired by thermo-and photoacoustic imaging, where recent efforts are devoted to take into account attenuation and varying wave speed parameters. In this paper we study causal equations describing propagation of attenuated pressure waves. We review standard models like frequency power laws and and the thermo-viscous equation. The lack of causality of standard models in the parameter range relevant for photoacoustic imaging requires to derive novel equations. The main ingredients for deriving causal equations are the Kramers-Kronig relation and the mathematical concept of linear system theory. The theoretical results of this work are underpined by numerical experiments.

  12. Cavity-Enhanced Single-Photon Source Based on the Silicon-Vacancy Center in Diamond

    Science.gov (United States)

    Benedikter, Julia; Kaupp, Hanno; Hümmer, Thomas; Liang, Yuejiang; Bommer, Alexander; Becher, Christoph; Krueger, Anke; Smith, Jason M.; Hänsch, Theodor W.; Hunger, David

    2017-02-01

    Single-photon sources are an integral part of various quantum technologies, and solid-state quantum emitters at room temperature appear to be a promising implementation. We couple the fluorescence of individual silicon-vacancy centers in nanodiamonds to a tunable optical microcavity to demonstrate a single-photon source with high efficiency, increased emission rate, and improved spectral purity compared to the intrinsic emitter properties. We use a fiber-based microcavity with a mode volume as small as 3.4 λ3 and a quality factor of 1.9 ×1 04 and observe an effective Purcell factor of up to 9.2. Furthermore, we study modifications of the internal rate dynamics and propose a rate model that closely agrees with the measurements. We observe lifetime changes of up to 31%, limited by the finite quantum efficiency of the emitters studied here. With improved materials, our achieved parameters predict single-photon rates beyond 1 GHz.

  13. Quantum Noise Limits in White-Light-Cavity-Enhanced Gravitational Wave Detectors

    CERN Document Server

    Zhou, Minchuan; Shahriar, Selim M

    2014-01-01

    Previously, we had proposed a gravitational wave detector that incorporates the white light cavity (WLC) effect using a compound cavity for signal recycling (CC-SR). Here, we first calculate the quantum noise (QN) limited sensitivity curves for this design, and find that the broadening of sensitivity predicted by the classical analysis is also present in these curves, but is somewhat reduced. Furthermore, we find that the curves always stay above the standard quantum limit (SQL). To circumvent this limitation, we modify the dispersion to compensate the non-linear phase variation produced by the opto-mechanical (OM) resonance effects by making use of the single sideband approximation (SSA). We find that the resonance dips in the resulting QN curves entails a 14 times higher sensitivity-bandwidth product compared to the highest sensitivity result presented by Bunanno and Chen. We also present a simpler scheme (WLC-SR) where a dispersion medium is inserted in the SR cavity. Compared to the highest sensitivity re...

  14. 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.

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

    Science.gov (United States)

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

    2010-06-15

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

  16. Silicon photonic crystal cavity enhanced second-harmonic generation from monolayer WSe2

    Science.gov (United States)

    Fryett, Taylor K.; Seyler, Kyle L.; Zheng, Jiajiu; Liu, Chang-Hua; Xu, Xiaodong; Majumdar, Arka

    2017-03-01

    Nano-resonators integrated with two-dimensional materials (e.g. transition metal dichalcogenides) have recently emerged as a promising nano-optoelectronic platform. Here we demonstrate resonator-enhanced second-harmonic generation (SHG) in tungsten diselenide using a silicon photonic crystal cavity. By pumping the device with 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.

  17. 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.

  18. Scaling laws of the cavity enhancement for NV centers in diamond

    CERN Document Server

    Kaupp, Hanno; Chang, Huan-Cheng; Reichel, Jakob; Hänsch, Theodor W; Hunger, David

    2013-01-01

    We employ a fiber-based optical microcavity with high Finesse to study the enhancement of fluorescence emission of NV centers in nanodiamonds. Harnessing the full tunability and open access of the resonator, we explicitly demonstrate the scaling laws of the Purcell enhancement by varying both the mode volume and the quality factor over a large range. While changes in the emission lifetime remain small in the regime of a broadband emitter, we observe an ideal Purcell factor of up to 450. Our results show a way for the realization of wavelength-tunable, narrow-band single-photon sources and demonstrate a system that has the potential to reach the strong coupling regime.

  19. 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.

  20. 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.

  1. Cavity-enhanced room-temperature high sensitivity optical Faraday magnetometry

    Science.gov (United States)

    Sun, Hui; Lei, Yaohua; Fan, Shuangli; Zhang, Qiaolin; Guo, Hong

    2017-01-01

    We propose a cavity QED system with two-photon Doppler-free configuration for weak magnetic field detection with high sensitivity at room temperature based on cavity electromagnetically induced transparency. Owing to the destructive interference induced by the control and driving fields, two transparency channels are opened. The Faraday rotation within two transparency channels can be used to detect weak magnetic field with high sensitivity at room temperature. The sensitivity with single photon and multiphoton probe inputs is analyzed. With single photon measurement, our numerical calculations demonstrate that the sensitivity with 3.8nT/√{Hz} and 6.4nT/√{Hz} could be achieved. When we measure the magnetic field with multiphoton input, the sensitivity can be improved to 7.7fT/√{Hz} and 25.6fT/√{Hz} under the realistic experimental conditions.

  2. 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.

  3. Advanced two-way satellite frequency transfer by carrier-phase and carrier-frequency measurements

    Science.gov (United States)

    Fujieda, Miho; Gotoh, Tadahiro; Amagai, Jun

    2016-06-01

    Carrier-phase measurement is one of the ways to improve the measurement resolution of two-way satellite frequency transfer. We introduce two possible methods for carrier-phase measurement: direct carrier-phase detection identified by Two-Way Carrier-Phase (TWCP) and the use of carrier-frequency information identified by Two-Way Carrier Frequency (TWCF). We performed the former using an arbitrary waveform generator and an analog-to-digital sampler and the latter using a conventional modem. The TWCF measurement using the modem had a resolution of 10-13 and the result agreed with that obtained by GPS carrier-phase frequency transfer in a 1500 km baseline. The measurement accuracy may have been limited by the poor frequency resolution of the modem; however, the TWCF measurement was able to improve the stability of conventional two-way satellite frequency transfer. Additionally, we show that the TWCP measurement system has the potential to achieve a frequency stability of 10-17.

  4. Frequencies of inaudible high-frequency sounds differentially affect brain activity: positive and negative hypersonic effects.

    Science.gov (United States)

    Fukushima, Ariko; Yagi, Reiko; Kawai, Norie; Honda, Manabu; Nishina, Emi; Oohashi, Tsutomu

    2014-01-01

    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.

  5. Multiple frequency atmospheric radar techniques

    Science.gov (United States)

    Stitt, Gary Richard

    The use of multiple frequency coding to improve the vertical resolution of pulsed-Doppler very high frequency atmospheric radars, especially with regards to the two-frequency techniques known as frequency domain interferometry (FDI), is presented. This technique consists of transmitting alternate pulses on two distinct carrier frequencies. The two resulting time series are used to evaluate the normalized cross-correlation function, whose magnitude and phase are related to the thickness and position of a scattering layer. These same time series are also used to evaluate cross-spectra, which yield magnitude and phase values for each Doppler frequency component of the return signal.

  6. Malaria haplotype frequency estimation.

    Science.gov (United States)

    Wigger, Leonore; Vogt, Julia E; Roth, Volker

    2013-09-20

    We present a Bayesian approach for estimating the relative frequencies of multi-single nucleotide polymorphism (SNP) haplotypes in populations of the malaria parasite Plasmodium falciparum by using microarray SNP data from human blood samples. Each sample comes from a malaria patient and contains one or several parasite clones that may genetically differ. Samples containing multiple parasite clones with different genetic markers pose a special challenge. The situation is comparable with a polyploid organism. The data from each blood sample indicates whether the parasites in the blood carry a mutant or a wildtype allele at various selected genomic positions. If both mutant and wildtype alleles are detected at a given position in a multiply infected sample, the data indicates the presence of both alleles, but the ratio is unknown. Thus, the data only partially reveals which specific combinations of genetic markers (i.e. haplotypes across the examined SNPs) occur in distinct parasite clones. In addition, SNP data may contain errors at non-negligible rates. We use a multinomial mixture model with partially missing observations to represent this data and a Markov chain Monte Carlo method to estimate the haplotype frequencies in a population. Our approach addresses both challenges, multiple infections and data errors.

  7. Frequency Population Growth Rate

    Directory of Open Access Journals (Sweden)

    Nouralah Salehi Asfiji

    2012-10-01

    Full Text Available The Solow growth model assumes that labor force grows exponentially. That is not a realistic assumption. In generalized logistic equations that describes more accurately population growth. Economic growth is not a smooth process. Real GDP has fluctuations in the growth rate. We call these fluctuations business cycles. Business cycle theory came about from the failures of classical economics in being able to illuminate on the causes of the Great Depression. The logistic growth model to explain changes in population growth rates are not. In this paper a new analysis of the population growth rate in the frequency space is described with mathematical logic and economic reasoning, so that, firstly, to a higher level of capital per capita, or at least equal to the Solow growth model reaches Second, the limits of saturation (Carrying-Capacity is not, and ultimately, population growth rates have an impact on long-term per capita amounts. The initial classic assumption is changed in this article based on the available frequencies in the population growth equation.

  8. 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

  9. 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

  10. High Frequency Measurements of Methane Concentrations and Carbon Isotopes at a Marsh and Landfill

    Science.gov (United States)

    Mortazavi, B.; Wilson, B.; Chanton, J.; Eller, K.; Dong, F.; Baer, D. S.; Gupta, M.; Dzwonkowski, B.

    2012-12-01

    High frequency measurements of methane concentrations and carbon isotopes can help constrain the source strengths of methane emitted to the atmosphere. We report here methane concentrations and 13C values measured at 0.5 Hz with cavity enhanced laser absorption spectrometers (Los Gatos Research) deployed at a saltmarsh in Alabama and a landfill in Florida. Methane concentrations and 13C at the saltmarsh were monitored over a 2.5 day time period at 2 m, 0.5 m above the ground as well as from the outflow of a flow-through (2 L) chamber placed on the Spartina alterniflora dominated marsh. A typical measurement cycle included regular samples from two tanks of known methane concentrations and isotopic values and from ambient air samples. Over the 2.5-day measurement period methane concentrations and isotopic ratios at 2 m averaged 1.85 ppm and -43.57‰ (±0.34, 1 SE), respectively. The concentration and isotopic values from the chamber outflow varied from 1.92 to 5.81 ppm and -38.5 to -59.3‰, respectively. Methane flux from the marsh ranged from undetectable to 3.6 mgC m-2hr-1, with high fluxes measured during low tide. The 13δCH4 of the emitted CH4 from the marsh, determined from a mass balance equation using the chamber inflow and outflow concentration and isotopic values ranged from -62.1 to -93.9‰ and averaged -77‰ (±1.25, 1SE). At the landfill ambient methane concentrations and 13C ratios measured over multiple days varied from 4.25 to 11.91 ppm and from -58.81 to -45.12‰, respectively. At higher methane concentrations the δ13C of CH4 was more depleted consistent with previously observed relationship at this site made by more traditional techniques. Over a 30-minute measurement period CH4 concentrations at the landfill could vary by as much as 15 ppm. The high frequency continuous optical measurements with field-deployed instruments provide us with an unprecedented temporal resolution of CH4 concentrations and isotopic ratios. These measurements will

  11. Application of the Frequency Spectrum to Spectral Similarity Measures

    Directory of Open Access Journals (Sweden)

    Ke Wang

    2016-04-01

    Full Text Available Several frequency-based spectral similarity measures, derived from commonly-used ones, are developed for hyperspectral image classification based on the frequency domain. Since the frequency spectrum (magnitude spectrum of the original signature for each pixel from hyperspectral data can clearly reflect the spectral features of different types of land covers, we replace the original spectral signature with its frequency spectrum for calculating the existing spectral similarity measure. The frequency spectrum is symmetrical around the direct current (DC component; thus, we take one-half of the frequency spectrum from the DC component to the highest frequency component as the input signature. Furthermore, considering the fact that the low frequencies include most of the frequency energy, we can optimize the classification result by choosing the ratio of the frequency spectrum (from the DC component to the highest frequency component involved in the calculation. In our paper, the frequency-based measures based on the spectral gradient angle (SAM, spectral information divergence (SID, spectral correlation mapper (SCM, Euclidean distance (ED, normalized Euclidean distance (NED and SID × sin(SAM (SsS measures are called the F-SAM, F-SID, F-SCM, F-ED, F-NED and F-SsS, respectively. In the experiment, three commonly-used hyperspectral remote sensing images are employed as test data. The frequency-based measures proposed here are compared to the corresponding existing ones in terms of classification accuracy. The classification results by parameter optimization are also analyzed. The results show that, although not all frequency-based spectral similarity measures are better than the original ones, some frequency-based measures, such as the F-SsS and F-SID, exhibit a relatively better performance and have more robust applications than the other spectral similarity measures.

  12. Product directivity models for parametric loudspeakers.

    Science.gov (United States)

    Shi, Chuang; Gan, Woon-Seng

    2012-03-01

    In a recent work, the beamsteering characteristics of parametric loudspeakers were validated in an experiment. It was shown that based on the product directivity model, the locations and amplitudes of the mainlobe and grating lobes could be predicted within acceptable errors. However, the measured amplitudes of sidelobes have not been able to match the theoretical results accurately. In this paper, the original theories behind the product directivity model are revisited, and three modified product directivity models are proposed: (i) the advanced product directivity model, (ii) the exponential product directivity model, and (iii) the combined product directivity model. The proposed product directivity models take the radii of equivalent Gaussian sources into account and obtain better predictions of sidelobes for the difference frequency waves. From the comparison between measurement results and numerical solutions, all the proposed models outperform the original product directivity model in terms of selected sidelobe predictions by about 10 dB.

  13. Microwave transistor oscillator frequency tripling

    OpenAIRE

    B. A. Kotserzhynskyi

    2010-01-01

    The frequency tripler state of the art is consided. The oscillator-frequency tripler design is now at the state of scientific research. Microwave companies release the devices of the such structure: oscillator, buffer, amplifier-tripler.

  14. Microwave transistor oscillator frequency tripling

    Directory of Open Access Journals (Sweden)

    B. A. Kotserzhynskyi

    2010-01-01

    Full Text Available The frequency tripler state of the art is consided. The oscillator-frequency tripler design is now at the state of scientific research. Microwave companies release the devices of the such structure: oscillator, buffer, amplifier-tripler.

  15. High Frequency Acoustics and Signal Processing for Weapons

    Science.gov (United States)

    2005-01-24

    frequency correlation prediction using linear systems theory matches the measurements quite well. 1 - 1,it _ I ..... I Measured - direct path 20kHz...right: 40kHz). Measured for direct path (green solid) and surface bounce path (green dashed); modeled using linear systems theory (black) and signal

  16. 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.

  17. 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

  18. High frequency nanotube oscillator

    Science.gov (United States)

    Peng, Haibing; Zettl, Alexander K.

    2012-02-21

    A tunable nanostructure such as a nanotube is used to make an electromechanical oscillator. The mechanically oscillating nanotube can be provided with inertial clamps in the form of metal beads. The metal beads serve to clamp the nanotube so that the fundamental resonance frequency is in the microwave range, i.e., greater than at least 1 GHz, and up to 4 GHz and beyond. An electric current can be run through the nanotube to cause the metal beads to move along the nanotube and changing the length of the intervening nanotube segments. The oscillator can operate at ambient temperature and in air without significant loss of resonance quality. The nanotube is can be fabricated in a semiconductor style process and the device can be provided with source, drain, and gate electrodes, which may be connected to appropriate circuitry for driving and measuring the oscillation. Novel driving and measuring circuits are also disclosed.

  19. Frequency mixing crystal

    Science.gov (United States)

    Ebbers, Christopher A.; Davis, Laura E.; Webb, Mark

    1992-01-01

    In a laser system for converting infrared laser light waves to visible light comprising a source of infrared laser light waves and means of harmoic generation associated therewith for production of light waves at integral multiples of the frequency of the original wave, the improvement of said means of harmonic generation comprising a crystal having the chemical formula X.sub.2 Y(NO.sub.3).sub.5 .multidot.2 nZ.sub.2 o wherein X is selected from the group consisting of Li, Na, K, Rb, Cs, and Tl; Y is selected from the group consisting of Sc, Y, La, Ce, Nd, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, and In; Z is selected from the group consisting of H and D; and n ranges from 0 to 4.

  20. Frequency doubling crystals

    Science.gov (United States)

    Wang, Francis; Velsko, Stephan P.

    1989-01-01

    A systematic approach to the production of frequency conversion crystals is described in which a chiral molecule has attached to it a "harmonic generating unit" which contributes to the noncentrosymmetry of the molecule. Certain preferred embodiments of such harmonic generating units include carboxylate, guanadyly and imidazolyl units. Certain preferred crystals include L-arginine fluoride, deuterated L-arginine fluoride, L-arginine chloride monohydrate, L-arginine acetate, dithallium tartrate, ammonium N-acetyl valine, N-acetyl tyrosine and N-acetyl hydroxyproline. Chemical modifications of the chiral molecule, such as deuteration, halogenation and controlled counterion substitution are available to adapt the dispersive properties of a crystal in a particular wavelength region.

  1. Instantaneous Frequency Attribute Comparison

    Science.gov (United States)

    Yedlin, M. J.; Margrave, G. F.; Ben Horin, Y.

    2013-12-01

    The instantaneous seismic data attribute provides a different means of seismic interpretation, for all types of seismic data. It first came to the fore in exploration seismology in the classic paper of Taner et al (1979), entitled " Complex seismic trace analysis". Subsequently a vast literature has been accumulated on the subject, which has been given an excellent review by Barnes (1992). In this research we will compare two different methods of computation of the instantaneous frequency. The first method is based on the original idea of Taner et al (1979) and utilizes the derivative of the instantaneous phase of the analytic signal. The second method is based on the computation of the power centroid of the time-frequency spectrum, obtained using either the Gabor Transform as computed by Margrave et al (2011) or the Stockwell Transform as described by Stockwell et al (1996). We will apply both methods to exploration seismic data and the DPRK events recorded in 2006 and 2013. In applying the classical analytic signal technique, which is known to be unstable, due to the division of the square of the envelope, we will incorporate the stabilization and smoothing method proposed in the two paper of Fomel (2007). This method employs linear inverse theory regularization coupled with the application of an appropriate data smoother. The centroid method application is straightforward and is based on the very complete theoretical analysis provided in elegant fashion by Cohen (1995). While the results of the two methods are very similar, noticeable differences are seen at the data edges. This is most likely due to the edge effects of the smoothing operator in the Fomel method, which is more computationally intensive, when an optimal search of the regularization parameter is done. An advantage of the centroid method is the intrinsic smoothing of the data, which is inherent in the sliding window application used in all Short-Time Fourier Transform methods. The Fomel technique

  2. 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.

  3. A novel blind deconvolution algorithm using single frequency bin

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Former frequency-domain blind devolution algorithms need to consider a large number of frequency bins and recover the sources in different orders and with different amplitudes in each frequency bin, so they suffer from permutation and amplitude indeterminacy troubles. Based on sliding discrete Fourier transform, the presented deconvolution algorithm can directly recover time-domain sources from frequency-domain convolutive model using single frequency bin. It only needs to execute blind separation of instantaneous mixture once there are no permutation and amplitude indeterminacy troubles. Compared with former algorithms, the algorithm greatly reduces the computation cost as only one frequency bin is considered. Its good and robust performance is demonstrated by simulations when the signal-to-noise-ratio is high.

  4. A deep-UV optical frequency comb at 205 nm.

    Science.gov (United States)

    Peters, E; Diddams, S A; Fendel, P; Reinhardt, S; Hänsch, T W; Udem, Th

    2009-05-25

    By frequency quadrupling a picosecond pulse train from a Ti:sapphire laser at 820 nm we generate a frequency comb at 205 nm with nearly bandwidth-limited pulses. The nonlinear frequency conversion is accomplished by two successive frequency doubling stages that take place in resonant cavities that are matched to the pulse repetition rate of 82 MHz. This allows for an overall efficiency of 4.5 % and produces an output power of up to 70 mW for a few minutes and 25 mW with continuous operation for hours. Such a deep UV frequency comb may be employed for direct frequency comb spectroscopy in cases where it is less efficient to convert to these short wavelengths with continuous wave lasers.

  5. 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.

  6. Geostrophic Turbulence in the Frequency-Wavenumber Domain: Eddy-Driven Low-Frequency Variability

    Science.gov (United States)

    2014-08-01

    snapshot is multiplied by a two-dimensional Tukey window having a ratio of taper to constant sections equal to 0.2 in each horizontal direction. To enforce... taper to constant sections.3 Because the QG model is doubly periodic, and because c1 has a zero time mean at each grid point, we do not employ any spatial...frequencies, the Neither curve has an unphysically sharp jump due to substantial energy in the (nominally) zero frequency. In the remainder of this paper, we

  7. New scheme of the microwave signal formation for quantum frequency standard on the atoms of caesium-133

    Science.gov (United States)

    Petrov, A. A.; Davydov, V. V.

    2016-11-01

    In present work several directions of quantum frequency standard modernization are considered. A new implementation of a frequency synthesizer and a magnetic field control unit are presented. Experimental study of a frequency synthesizer showed improvement parameters of a microwave-excitation signal, such as step frequency tuning, time frequency tuning, range of generating frequencies and spectral characteristics. Magnetic field control unit eliminates one of the most important perturbing factors affecting the long-term frequency stability. Daily frequency stability of quantum frequency standard improved on 15%.

  8. High spectral purity Kerr frequency comb radio frequency photonic oscillator.

    Science.gov (United States)

    Liang, W; Eliyahu, D; Ilchenko, V S; Savchenkov, A A; Matsko, A B; Seidel, D; Maleki, L

    2015-08-11

    Femtosecond laser-based generation of radio frequency signals has produced astonishing improvements in achievable spectral purity, one of the basic features characterizing the performance of an radio frequency oscillator. Kerr frequency combs hold promise for transforming these lab-scale oscillators to chip-scale level. In this work we demonstrate a miniature 10 GHz radio frequency photonic oscillator characterized with phase noise better than -60 dBc Hz(-1) at 10 Hz, -90 dBc Hz(-1) at 100 Hz and -170 dBc Hz(-1) at 10 MHz. The frequency stability of this device, as represented by Allan deviation measurements, is at the level of 10(-10) at 1-100 s integration time-orders of magnitude better than existing radio frequency photonic devices of similar size, weight and power consumption.

  9. Challenges and limitations in retrofitting facilities for low frequency noise

    Energy Technology Data Exchange (ETDEWEB)

    Wierzba, P. [ATCO Noise Management, Calgary, AB (Canada)

    2007-07-01

    The trend to revise and increase environmental regulations regarding low frequency noise emissions from oil and gas facilities was discussed. Noise related complaints can often be traced to low frequency noise, which is the unwanted sound with a frequency range falling within 31.5-Hz, 63-Hz, and 125-Hz octave bands. This paper also discussed the challenges and limitations of field retrofits of the facilities aimed at reducing low frequency noise. The main sources of low frequency noise associated with a compression facility are the radiator cooler, engine exhaust and the building envelope. Regulators are paying close attention not only to the overall noise exposure as measured by the A-weighted levels, but also to the quality of noise emitted by the particular frequency spectrum. The Alberta Energy and Utilities Board recently issued Noise Control Directive 38 and made it a requirement to perform low frequency noise impact assessment for permitting of all new energy facilities. Under Directive 38, the low frequency noise assessment is to be performed using the C-weighted scale as a measure in addition to the previously used A-weighted scale. Directive 38 recommends that in order to avoid low frequency noise problems the difference between the C-weighted and A-weighted levels at the residential locations should be lower than 20 dB. This implies that noise should be limited to 60 dBC for Category 1 residences of low dwelling density. Small upgrades and changes can be made to lower low frequency noise emissions. These may include upgrading building wall insulation, providing wall-to-skid isolation system, upgrading the fan blades, or reducing the rpm of the fans. It was concluded that these upgrades should be considered for facilities in close proximity to residential areas. 3 refs., 2 tabs., 7 figs.

  10. 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.

  11. Digital frequency control of satellite frequency standards. [Defense Navigation Satellites

    Science.gov (United States)

    Nichols, S. A.

    1973-01-01

    In the Frequency and Time Standard Development Program of the TIMATION System, a new miniaturized rubidium vapor frequency standard has been tested and analyzed for possible use on the TIMATION 3A launch, as part of the Defense Navigation Satellite Development Program. The design and construction of a digital frequency control was required to remotely control this rubidium vapor frequency standard as well as the quartz oscillator in current use. This control must be capable of accepting commands from a satellite telemetry system, verify that the correct commands have been sent and control the frequency to the requirements of the system. Several modifications must be performed to the rubidium vapor frequency standard to allow it to be compatible with the digital frequency control. These include the addition of a varactor to voltage tune the coarse range of the flywheel oscillator, and a modification to supply the C field current externally. The digital frequency control for the rubidium vapor frequency standard has been successfully tested in prototype form.

  12. Direct measurement of light waves.

    Science.gov (United States)

    Goulielmakis, E; Uiberacker, M; Kienberger, R; Baltuska, A; Yakovlev, V; Scrinzi, A; Westerwalbesloh, Th; Kleineberg, U; Heinzmann, U; Drescher, M; Krausz, F

    2004-08-27

    The electromagnetic field of visible light performs approximately 10(15) oscillations per second. Although many instruments are sensitive to the amplitude and frequency (or wavelength) of these oscillations, they cannot access the light field itself. We directly observed how the field built up and disappeared in a short, few-cycle pulse of visible laser light by probing the variation of the field strength with a 250-attosecond electron burst. Our apparatus allows complete characterization of few-cycle waves of visible, ultraviolet, and/or infrared light, thereby providing the possibility for controlled and reproducible synthesis of ultrabroadband light waveforms.

  13. High-current, high-frequency capacitors

    Science.gov (United States)

    Renz, D. D.

    1983-06-01

    The NASA Lewis high-current, high-frequency capacitor development program was conducted under a contract with Maxwell Laboratories, Inc., San Diego, California. The program was started to develop power components for space power systems. One of the components lacking was a high-power, high-frequency capacitor. Some of the technology developed in this program may be directly usable in an all-electric airplane. The materials used in the capacitor included the following: the film is polypropylene, the impregnant is monoisopropyl biphenyl, the conductive epoxy is Emerson and Cuming Stycast 2850 KT, the foil is aluminum, the case is stainless steel (304), and the electrode is a modified copper-ceramic.

  14. Design and Analysis of Bifurcated Twin Dielectric Slab Loaded Rectangular Waveguide. Dual Frequency Array Elements

    Science.gov (United States)

    1977-03-01

    K V 3 lobe free scan volume in the high frequency band. At scan conditions for which high frequency grating lobes are entering or present, the...immediately obvious from the figures is that the triangular grid provides a grating lobe free scan region for all directions in the plane at high frequency. One

  15. Dispersion of Own Frequency of Ion-Dipole by Supersonic Transverse Wave in Solid

    Directory of Open Access Journals (Sweden)

    Minasyan V.

    2010-10-01

    Full Text Available First, we predict an existence of transverse electromagnetic field formed by supersonic transverse wave in solid. This electromagnetic wave acquires frequency and speed of sound, and it propagates along of direction propagation of supersonic wave. We also show that own frequency of ion-dipole depends on frequency of supersonic transverse wave.

  16. Phased-Array Antenna Beam Squinting Related to Frequency Dependency of Delay Circuits

    NARCIS (Netherlands)

    Garakoui, S.K.; Klumperink, E.A.M.; Nauta, B.; Vliet, F.E. van

    2011-01-01

    Practical time delay circuits do not have a perfectly linear phase-frequency characteristic. When these delay circuits are applied in a phased-array system, this frequency dependency shows up as a frequency dependent beam direction (“beam squinting”). This paper quantifies beam squinting for a linea

  17. 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.

  18. Directional Wave Spectra Using Normal Spreading Function

    Science.gov (United States)

    1985-03-01

    energy spectral density function U. g. Army Engineer Waternays Experiment Station. Coastal Engineering Research Center P. 0. lox 631, Vicksburg...Z39-18 D(f,e) = spreading function E (f,(3) = directional spectral density function f = frequency in cycles per second 8 = direction in radians...of this assumption depends on the narrow bandedness of the energy spectral density function . For fairly narrow spectra (e.g., a swell train), the

  19. 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.

  20. 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...

  1. 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

  2. Lexical frequency and voice assimilation.

    Science.gov (United States)

    Ernestus, Mirjam; Lahey, Mybeth; Verhees, Femke; Baayen, R Harald

    2006-08-01

    Acoustic duration and degree of vowel reduction are known to correlate with a word's frequency of occurrence. The present study broadens the research on the role of frequency in speech production to voice assimilation. The test case was regressive voice assimilation in Dutch. Clusters from a corpus of read speech were more often perceived as unassimilated in lower-frequency words and as either completely voiced (regressive assimilation) or, unexpectedly, as completely voiceless (progressive assimilation) in higher-frequency words. Frequency did not predict the voice classifications over and above important acoustic cues to voicing, suggesting that the frequency effects on the classifications were carried exclusively by the acoustic signal. The duration of the cluster and the period of glottal vibration during the cluster decreased while the duration of the release noises increased with frequency. This indicates that speakers reduce articulatory effort for higher-frequency words, with some acoustic cues signaling more voicing and others less voicing. A higher frequency leads not only to acoustic reduction but also to more assimilation.

  3. 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.

  4. Mixed Frequency Ultrasound Phased Array

    Institute of Scientific and Technical Information of China (English)

    香勇; 霍健; 施克仁; 陈以方

    2004-01-01

    A mixed frequency ultrasonic phased array (MPA) was developed to improve the focus, in which the element excitation frequencies are not all the same as in a normal constant frequency phased array. A theoretical model of the mixed frequency phased array based on the interference principle was used to simulate the array's sound distribution. The pressure intensity in the array focal area was enhanced and the scanning area having effective contrast resolution was enlarged. The system is especially useful for high intensity focused ultrasound (HIFU) with more powerful energy and ultrasound imaging diagnostics with improved signal to noise ratios, improved beam forming and more uniform imaging quality.

  5. Automatic oscillator frequency control system

    Science.gov (United States)

    Smith, S. F. (Inventor)

    1985-01-01

    A frequency control system makes an initial correction of the frequency of its own timing circuit after comparison against a frequency of known accuracy and then sequentially checks and corrects the frequencies of several voltage controlled local oscillator circuits. The timing circuit initiates the machine cycles of a central processing unit which applies a frequency index to an input register in a modulo-sum frequency divider stage and enables a multiplexer to clock an accumulator register in the divider stage with a cyclical signal derived from the oscillator circuit being checked. Upon expiration of the interval, the processing unit compares the remainder held as the contents of the accumulator against a stored zero error constant and applies an appropriate correction word to a correction stage to shift the frequency of the oscillator being checked. A signal from the accumulator register may be used to drive a phase plane ROM and, with periodic shifts in the applied frequency index, to provide frequency shift keying of the resultant output signal. Interposition of a phase adder between the accumulator register and phase plane ROM permits phase shift keying of the output signal by periodic variation in the value of a phase index applied to one input of the phase adder.

  6. Frequency hopping millimeter wave reflectometer

    Science.gov (United States)

    Cupido, L.; Sánchez, J.; Estrada, T.

    2004-10-01

    Reflectometry techniques are employed to study density fluctuations in fusion plasmas either using one channel or two channels with slightly different frequencies, to probe simultaneously closely spaced plasma layers (for radial correlation studies). The present article describes a novel system with increasing measuring capability utilizing only one single frequency that can be hopped during the discharge. This broadband fast hopping mm-wave reflectometer (BFHR) has been developed for both ASDEX upgrade (Max Plank Institute-Garching-Germany) and TJ-II stellarator (CIEMAT-Spain). The BFHR incorporates frequency synthesizers at microwave frequencies multiplied into the millimeter-wave range and uses heterodyne detection for sensitive phase and amplitude measurements.

  7. Frequency Resonance in Stochastic Systems

    Institute of Scientific and Technical Information of China (English)

    钱敏; 张雪娟

    2003-01-01

    The phenomenon of frequency resonance, which is usually related to deterministic systems, is investigated in stochastic systems. We show that for those autonomous systems driven only by white noise, if the output power spectrum exhibits a nonzero peak frequency, then applying a periodic signel just on this noise-induced central frequency can also induce a resonance phenomenon, which we call the frequency stochastic resonance. The effect of such a resonance in a coupled stochastic system is shown to be much better than that in a single-oscillator system.

  8. Behavioral estimates of human frequency selectivity at low frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado

    A fundamental property of our hearing organ is its ability to break down sound into different spectral components, allowing us to make use of the richness in natural sound phenomena. Auditory filters, which conceptualize this property of the ear, however, have not been appropriately described at ...... frequencies or considering larger bandwidths), due to the much narrower absolute bandwidths observed at low frequencies. Besides, observed increases in filter shape variability suggest that individual differences in perception are likely to increase at very low frequencies....... at 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...

  9. High resolution DAS via sinusoidal frequency scan OFDR (SFS-OFDR).

    Science.gov (United States)

    Leviatan, Eyal; Eyal, Avishay

    2015-12-28

    There are many advantages to using direct frequency modulation for OFDR based DAS. However, achieving sufficiently linear scan via direct frequency modulation is challenging and poses limits on the scan parameters. A novel method for analyzing sinusoidal frequency modulated light is presented and demonstrated for both static and dynamic sensing. SFS-OFDR projects the measured signal onto appropriate sinusoidal phase terms to obtain spatial information. Thus, by using SFS-OFDR on sinusoidal modulated light it is possible to make use of the many advantages offered by direct frequency modulation without the limitations posed by the linearity requirement.

  10. Negative Feedback Governs Gonadotrope Frequency-Decoding of Gonadotropin Releasing Hormone Pulse-Frequency

    OpenAIRE

    2009-01-01

    The synthesis of the gonadotropin subunits is directed by pulsatile gonadotropin-releasing hormone (GnRH) from the hypothalamus, with the frequency of GnRH pulses governing the differential expression of the common alpha-subunit, luteinizing hormone beta-subunit (LHbeta) and follicle-stimulating hormone beta-subunit (FSHbeta). Three mitogen-activated protein kinases, (MAPKs), ERK1/2, JNK and p38, contribute uniquely and combinatorially to the expression of each of these subunit genes. In this...

  11. 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.

  12. Thermal heat-balance mode flow-to-frequency converter

    Science.gov (United States)

    Pawlowski, Eligiusz

    2016-11-01

    This paper presents new type of thermal flow converter with the pulse frequency output. The integrating properties of the temperature sensor have been used, which allowed for realization of pulse frequency modulator with thermal feedback loop, stabilizing temperature of sensor placed in the flowing medium. The system assures balancing of heat amount supplied in impulses to the sensor and heat given up by the sensor in a continuous way to the flowing medium. Therefore the frequency of output impulses is proportional to the heat transfer coefficient from sensor to environment. According to the King's law, the frequency of those impulses is a function of medium flow velocity around the sensor. The special feature of presented solution is total integration of thermal sensor with the measurement signal conditioning system. Sensor and conditioning system are not the separate elements of the measurement circuit, but constitute a whole in form of thermal heat-balance mode flow-to-frequency converter. The advantage of such system is easiness of converting the frequency signal to the digital form, without using any additional analogue-to-digital converters. The frequency signal from the converter may be directly connected to the microprocessor input, which with use of standard built-in counters may convert the frequency into numerical value of high precision. Moreover, the frequency signal has higher resistance to interference than the voltage signal and may be transmitted to remote locations without the information loss.

  13. Measuring Auditory Selective Attention using Frequency Tagging

    Directory of Open Access Journals (Sweden)

    Hari M Bharadwaj

    2014-02-01

    Full Text Available Frequency tagging of sensory inputs (presenting stimuli that fluctuate periodically at rates to which the cortex can phase lock has been used to study attentional modulation of neural responses to inputs in different sensory modalities. For visual inputs, the visual steady-state response (VSSR at the frequency modulating an attended object is enhanced, while the VSSR to a distracting object is suppressed. In contrast, the effect of attention on the auditory steady-state response (ASSR is inconsistent across studies. However, most auditory studies analyzed results at the sensor level or used only a small number of equivalent current dipoles to fit cortical responses. In addition, most studies of auditory spatial attention used dichotic stimuli (independent signals at the ears rather than more natural, binaural stimuli. Here, we asked whether these methodological choices help explain discrepant results. Listeners attended to one of two competing speech streams, one simulated from the left and one from the right, that were modulated at different frequencies. Using distributed source modeling of magnetoencephalography results, we estimate how spatially directed attention modulates the ASSR in neural regions across the whole brain. Attention enhances the ASSR power at the frequency of the attended stream in the contralateral auditory cortex. The attended-stream modulation frequency also drives phase-locked responses in the left (but not right precentral sulcus (lPCS, a region implicated in control of eye gaze and visual spatial attention. Importantly, this region shows no phase locking to the distracting stream suggesting that the lPCS in engaged in an attention-specific manner. Modeling results that take account of the geometry and phases of the cortical sources phase locked to the two streams (including hemispheric asymmetry of lPCS activity help partly explain why past ASSR studies of auditory spatial attention yield seemingly contradictory

  14. Laser frequency modulator for modulating a laser cavity

    Science.gov (United States)

    Erbert, Gaylen V.

    1992-01-01

    The present invention relates to a laser frequency modulator for modulating a laser cavity. It is known in the prior art to utilize a PZT (piezoelectric transducer) element in combination with a mirror to change the cavity length of a laser cavity (which changes the laser frequency). Using a PZT element to drive the mirror directly is adequate at frequencies below 10 kHz. However, in high frequency applications (100 kHz and higher) PZT elements alone do not provide a sufficient change in the cavity length. The present invention utilizes an ultrasonic concentrator with a PZT element and mirror to provide modulation of the laser cavity. With an ultrasonic concentrator, the mirror element at the end of a laser cavity can move at larger amplitudes and higher frequencies.

  15. Intracavity frequency-doubled degenerate laser

    CERN Document Server

    Liew, Seng Fatt; Weiler, Sascha; Monjardin-Lopez, Jesus Fernando; Ramme, Mark; Redding, Brandon; Choma, Michael A; Cao, Hui

    2016-01-01

    We develop a green light source with low spatial coherence via intracavity frequency doubling of a solid-state degenerate laser. The second harmonic emission supports many more transverse modes than the fundamental emission, and exhibit lower spatial coherence. A strong suppression of speckle formation is demonstrated for both fundamental and second harmonic beams. Using the green emission for fluorescence excitation, we show the coherent artifacts are removed from the full-field fluorescence images. The high power, low spatial coherence and good directionality makes the green degenerate laser an attractive illumination source for parallel imaging and projection display.

  16. Coherence properties of Kerr frequency combs

    CERN Document Server

    Erkintalo, Miro

    2014-01-01

    We use numerical simulations based on an extended Lugiato-Lefever equation (LLE) to investigate the stability properties of Kerr frequency combs generated in microresonators. In particular, we show that an ensemble average calculated over sequences of output fields separated by a fixed number of resonator roundtrips allows the coherence of Kerr combs to be quantified in terms of the complex-degree of first-order coherence. We identify different regimes of comb coherence, linked to the solutions of the LLE. Our approach provides a practical and unambiguous way of assessing the stability of Kerr combs that is directly connected to an accessible experimental quantity.

  17. Coherence properties of Kerr frequency combs.

    Science.gov (United States)

    Erkintalo, Miro; Coen, Stéphane

    2014-01-15

    We use numerical simulations based on an extended Lugiato-Lefever equation (LLE) to investigate the stability properties of Kerr frequency combs generated in microresonators. In particular, we show that an ensemble average calculated over sequences of output fields separated by a fixed number of resonator roundtrips allows the coherence of Kerr combs to be quantified in terms of the complex degree of first-order coherence. We identify different regimes of comb coherence, linked to the solutions of the LLE. Our approach provides a practical and unambiguous way of assessing the stability of Kerr combs that is directly connected to an accessible experimental quantity.

  18. Coaxial direct-detection lidar-system

    DEFF Research Database (Denmark)

    2014-01-01

    The invention relates to a coaxial direct-detection LIDAR system for measuring velocity, temperature and/or particulate density. The system comprises a laser source for emitting a laser light beam having a lasing center frequency along an emission path. The system further comprises an optical...

  19. Simulation of the low-frequency collimator impedance

    CERN Document Server

    Kroyer, T

    2008-01-01

    The low-frequency transverse collimator impedance constitutes a major part of the LHC impedance budget. In this paper numerical simulations for frequencies below 1 MHz using a commercial package are presented. From the 3D field solution of the two-wire simulations the transverse impedance is directly calculated. After a cross-check with theory for rotationally symmetric structures a geometry with two jaws and an LHC graphite collimator is examined. Furthermore, a simple physics picture that explains the principal characteristics of the impedance at high and low frequencies is given.

  20. 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.

  1. 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…

  2. Frequency conversion of structured light.

    Science.gov (United States)

    Steinlechner, Fabian; Hermosa, Nathaniel; Pruneri, Valerio; Torres, Juan P

    2016-02-15

    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.

  3. Low-frequency-noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2008-01-01

    From 203 cases of low-frequency complaints a random selection of twenty-one cases were investigated. The main aim of the investigation was to answer the question whether the annoyance is caused by an external physical sound or by a physically non-existing sound, i.e. low-frequency tinnitus. Noise...... 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...... of the complainants has extraordinary hearing sensitivity at low frequencies. For comparable cases of low-frequency noise complaints in general, it is anticipated that physical sound is responsible in a substantial part of the cases, while low-frequency tinnitus is responsible in another substantial part of the cases....

  4. 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…

  5. Frequency Sensitivity in Nervous Systems

    Institute of Scientific and Technical Information of China (English)

    LIU Feng; WANG Wei

    2001-01-01

    We first demonstrate how to quantify the information conveyed in temporal firing patterns of neurons. We then show that neurons are more sensitive to signals with frequencies within the range of 20 - 70 Hz in weak signal detection. Such frequency sensitivity is characterized by both the output signal-to-noise ratio and the information measures.

  6. A variable frequency semiconductor laser

    Energy Technology Data Exchange (ETDEWEB)

    Tosikhiro, F.; Khiromoto, S.

    1984-03-27

    A variable frequency, power stabilized semiconductor laser is patented. This laser includes, in addition to an active layer, a photoconducting channel layer and a layer made from a material manifesting a Pockels effect. A voltage is injected between these two layers to vary the emission frequency. The laser pumping voltage is stabilized.

  7. Frequency-controlled voltage regulator

    Science.gov (United States)

    Mclyman, W. T.

    1980-01-01

    Converting input ac to higher frequency reduce size and weight and makes possible unique kind of regulation. Since conversion frequency is above range of human hearing, supply generated on audible noise. It also exploits highfrequency conversion features to regulate its output voltage in novel way. Circuit is inherently short-circuit proof.

  8. Direct current modulation of a photomixing signal

    Science.gov (United States)

    Constantin, Florin L.

    2016-04-01

    Direct modulation of the bias voltage of a LTG-GaAs photomixer is exploited to modulate the signal generated at the frequency of the optical beat between two diode lasers at 820 nm. The photomixing signal is calculated from an expansion in power series of the amplitude of the modulation voltage and displays amplitude modulation sidebands equidistantly spaced to the frequency of the optical beat by integer multiples of the modulation frequency. Modulation at harmonics of the modulation frequency is allowed by the electrical nonlinear response of the photomixer, driven at low voltage by the saturation of the electron drift velocity. Coupling of an alternative voltage to the photomixer operated at zero-bias leads to bifrequency operation. Modulation of the photomixing signal and bifrequency operation of the photomixer are observed experimentally with an optical beat in the microwave regime.

  9. Frequency conversion of structured light

    CERN Document Server

    Steinlechner, Fabian; Pruneri, Valerio; Torres, Juan P

    2015-01-01

    We demonstrate the coherent frequency conversion of structured light, optical beams in which the phase varies in each point of the transverse plane, from the near infrared (803nm) to the visible (527nm). The frequency conversion process makes use of sum-frequency generation in a periodically poled lithium niobate (ppLN) crystal with the help of a 1540-nm Gaussian pump beam. We perform far-field intensity measurements of the frequency-converted field, and verify the sought-after transformation of the characteristic intensity and phase profiles for various input modes. The coherence of the frequency-conversion process is confirmed using a mode-projection technique with a phase mask and a single-mode fiber. The presented results could be of great relevance to novel applications in high-resolution microscopy and quantum information processing.

  10. 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...... of frequency shifts corresponding to a specific distance. The spatial resolution depends on the repetition rate of the pulses in the pulse train. Directional wind measurements are shown and compared to a CW lidar measurement. The carrier to noise ratio of the FSPT lidar compared to a CW lidar is discussed...

  11. 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.

  12. Acoustic resonance frequency locked photoacoustic spectrometer

    Science.gov (United States)

    Pilgrim, Jeffrey S.; Bomse, David S.; Silver, Joel A.

    2003-09-09

    A photoacoustic spectroscopy method and apparatus for maintaining an acoustic source frequency on a sample cell resonance frequency comprising: providing an acoustic source to the sample cell, the acoustic source having a source frequency; repeatedly and continuously sweeping the source frequency across the resonance frequency at a sweep rate; and employing an odd-harmonic of the source frequency sweep rate to maintain the source frequency sweep centered on the resonance frequency.

  13. Radiation directivity rotation by acoustic metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xue; Liang, Bin, E-mail: liangbin@nju.edu.cn, E-mail: jccheng@nju.edu.cn; Zou, Xin-ye; Cheng, Jian-chun, E-mail: liangbin@nju.edu.cn, E-mail: jccheng@nju.edu.cn [Key Laboratory of Modern Acoustics, MOE, Department of Physics, Institute of Acoustics, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); Zhang, Likun [Department of Physics and Center for Nonlinear Dynamics, University of Texas at Austin, Austin, Texas 78712 (United States)

    2015-08-31

    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.

  14. Research of Direct Digital Correlative-Interferometric Radio Direction Finder with Double Correlation-convolutional Processing

    Directory of Open Access Journals (Sweden)

    V. V. Tsyporenko

    2016-06-01

    Full Text Available Introduction. In this article the unsettled part of the general problem of the research of direct digital methods of correlative-interferometric direction-finding was solved. The purpose of the article is to optimize the direction-finding of the direct digital correlative-interferometric radio direction finder with double correlation-convolutional processing by its exactness. Fundamentals of researches. As a result of the conducted researches it was defined that the basic parameter of equalization of dispersion of error of estimation of direction on the source of radio radiation for the explored radio direction finder, which ought to be optimized, is the size of frequency converting change. Optimization. It was conducted the parametrical optimization of the direct digital correlative-interferometric radio direction finder with double correlation-convolutional processing by its exactness. As a result of the modelling the dependence of middle quadratic deflection of estimation of direction from the relation of signal/noise for the different possible values of circular frequency converting shift was obtained. Conclusions. The analytical calculations and the results of the modelling fully coincided, that confirmed the rightness of the researches and the authenticity of the results of optimization.

  15. Frequency domain processing of on-chip biphoton frequency comb

    CERN Document Server

    Jaramillo-Villegas, Jose A; Odele, Ogaga D; Leaird, Daniel E; Ou, Zhe-Yu; Qi, Minghao; Weiner, Andrew M

    2016-01-01

    Quantum information processing (QIP) promises to improve the security of our communications as well as to solve some algorithms with exponential complexity in polynomial time. Biphotons have been demonstrated as one of the most promising platforms for real implementations of QIP systems. In particular, time-bin entangled photons have been used for implementations of quantum gates which require highly stable interferometers. On the other hand, frequency-bin entanglement has been proposed to avoid the use of interferometers and the complexity of their stabilization, which potentially makes the implementation of quantum gates highly scalable. Through Fourier transform pulse shaping and electro-optic modulation, there has been a wide range of experiments that show control of entangled photons in the frequency domain. In addition, biphoton frequency combs (BFC) have also been generated using bulk optics and frequency filtering of broadband continuous biphoton spectra. However, on-chip entangled photon pair generat...

  16. Blind speech source separation via nonlinear time-frequency masking

    Institute of Scientific and Technical Information of China (English)

    XU Shun; CHEN Shaorong; LIU Yulin

    2008-01-01

    Aim at the underdetermined convolutive mixture model, a blind speech source separation method based on nonlinear time-frequency masking was proposed, where the approximate W-disjoint orthogonality (W-DO) property among independent speech signals in time-frequency domain is utilized. In this method, the observation mixture signal from multimicrophones is normalized to be independent of frequency in the time-frequency domain at first, then the dynamic clustering algorithm is adopted to obtain the active source information in each time-frequency slot, a nonlinear function via deflection angle from the cluster center is selected for time-frequency masking, finally the blind separation of mixture speech signals can be achieved by inverse STFT (short-time Fourier transformation). This method can not only solve the problem of frequency permutation which may be met in most classic frequency-domain blind separation techniques, but also suppress the spatial direction diffusion of the separation matrix. The simulation results demonstrate that the proposed separation method is better than the typical BLUES method, the signal-noise-ratio gain (SNRG) increases 1.58 dB averagely.

  17. High-frequency magnetic components

    CERN Document Server

    Kazimierczuk, Marian K

    2009-01-01

    If you are looking for a complete study of the fundamental concepts in magnetic theory, read this book. No other textbook covers magnetic components of inductors and transformers for high-frequency applications in detail. This unique text examines design techniques of the major types of inductors and transformers used for a wide variety of high-frequency applications including switching-mode power supplies (SMPS) and resonant circuits. It describes skin effect and proximity effect in detail to provide you with a sound understanding of high-frequency phenomena. As well as this, you will disco

  18. Frequency synthesizers concept to product

    CERN Document Server

    Chenakin, Alexander

    2011-01-01

    A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed oscillator. They are found in modern devices like radio receivers, mobile phones, and GPS systems. This comprehensive resource offers RF and microwave engineers a thorough overview of both well-established and recently developed frequency synthesizer design techniques. Professionals find expert guidance on all design aspects, including main architectures, key building blocks, and practical circuit implementation. Engineers learn the development process and gain a solid understanding

  19. Frequency Correction for MIRO Chirp Transformation Spectroscopy Spectrum

    Science.gov (United States)

    Lee, Seungwon

    2012-01-01

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

  20. 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...

  1. Analysis of Omni-directivity Error of Electromagnetic Field Probe using Isotropic Antenna

    Science.gov (United States)

    Hartansky, Rene

    2016-12-01

    This manuscript analyzes the omni-directivity error of an electromagnetic field (EM) probe and its dependence on frequency. The global directional characteristic of a whole EM probe consists of three independent directional characteristics of EM sensors - one for each coordinate. The shape of particular directional characteristics is frequency dependent and so is the shape of the whole EM probe's global directional characteristic. This results in systematic error induced in the measurement of EM fields. This manuscript also contains quantitative formulation of such errors caused by the shape change of directional characteristics for different types of sensors depending on frequency and their mutual arrangement.

  2. 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.

  3. Low-frequency ac electroporation shows strong frequency dependence and yields comparable transfection results to dc electroporation.

    Science.gov (United States)

    Zhan, Yihong; Cao, Zhenning; Bao, Ning; Li, Jianbo; Wang, Jun; Geng, Tao; Lin, Hao; Lu, Chang

    2012-06-28

    Conventional electroporation has been conducted by employing short direct current (dc) pulses for delivery of macromolecules such as DNA into cells. The use of alternating current (ac) field for electroporation has mostly been explored in the frequency range of 10kHz-1MHz. Based on Schwan equation, it was thought that with low ac frequencies (10Hz-10kHz), the transmembrane potential does not vary with the frequency. In this report, we utilized a flow-through electroporation technique that employed continuous 10Hz-10kHz ac field (based on either sine waves or square waves) for electroporation of cells with defined duration and intensity. Our results reveal that electropermeabilization becomes weaker with increased frequency in this range. In contrast, transfection efficiency with DNA reaches its maximum at medium frequencies (100-1000Hz) in the range. We postulate that the relationship between the transfection efficiency and the ac frequency is determined by combined effects from electrophoretic movement of DNA in the ac field, dependence of the DNA/membrane interaction on the ac frequency, and variation of transfection under different electropermeabilization intensities. The fact that ac electroporation in this frequency range yields high efficiency for transfection (up to ~71% for Chinese hamster ovary cells) and permeabilization suggests its potential for gene delivery.

  4. 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.

  5. 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...

  6. 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 transducer...

  7. Geographies of High Frequency Trading

    DEFF Research Database (Denmark)

    Grindsted, Thomas Skou

    2016-01-01

    This paper investigates the geographies of high frequency trading. Today shares shift hands within micro seconds, giving rise to a form of financial geographies termed algorithmic capitalism. This notion refers to the different spatio-temporalities produced by high frequency trading, under...... the valuation of time. As high frequency trading accelerates financial markets, the paper examines the spatio-temporalities of automated trading by the ways in which the speed of knowledge exploitation in financial markets is not only of interest, but also the expansion between different temporalities....... The paper demonstrates how the intensification of time-space compression produces radical new dynamics in the financial market and develops information rent in HFT as convertible to a time rent and a spatio-temporal rent. The final section discusses whether high frequency trading only responds to crises...

  8. Primary Frequency Standards at NIST

    Science.gov (United States)

    2001-11-01

    Mode-Locked Laser, ” Physical Review Letters , 82,3568-337 I. J. Reicher, M. Niering, R. Holzwarth, M. Weitz, T. Udem, and T. W. Hansch, 2000, “Phase...Coherent Vacuum- Ultraviolet to Radio Frequency Comparison with a Mode-Locked Laser, ’’ Physical Review Letters , 84,3232-3235. M. Niering, R...Measurement of the Hydrogen IS- 2s Transition Frequency by Phase Coherent Comparison with a Microwave Cesium Fountain Clock,” Physical Review Letters , 84

  9. 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

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Carlson, H. C.; Kornienko, V. A.; Borisova, T. D.; Rietveld, M. T.; Yeoman, T. K.; Brekke, A.

    2009-01-01

    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.

  10. 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.

  11. Forecasting Value-at-Risk Using High-Frequency Information

    Directory of Open Access Journals (Sweden)

    Huiyu Huang

    2013-06-01

    Full Text Available in the prediction of quantiles of daily Standard&Poor’s 500 (S&P 500 returns we consider how to use high-frequency 5-minute data. We examine methods that incorporate the high frequency information either indirectly, through combining forecasts (using forecasts generated from returns sampled at different intraday interval, or directly, through combining high frequency information into one model. We consider subsample averaging, bootstrap averaging, forecast averaging methods for the indirect case, and factor models with principal component approach, for both direct and indirect cases. We show that in forecasting the daily S&P 500 index return quantile (Value-at-Risk or VaR is simply the negative of it, using high-frequency information is beneficial, often substantially and particularly so, in forecasting downside risk. Our empirical results show that the averaging methods (subsample averaging, bootstrap averaging, forecast averaging, which serve as different ways of forming the ensemble average from using high-frequency intraday information, provide an excellent forecasting performance compared to using just low-frequency daily information.

  12. Analysis of Pulse Modulated Control Systems (Ⅲ) Stability of Systems with Pulse Frequency Modulation and Systems with Combined Pulse Frequency and Pulse Width Modulation

    OpenAIRE

    OI,Shigemitsu

    1993-01-01

    Sufficient conditions for finite pulse stability of interconnected systems with combined pulse frequency and pulse width modulation are developed in this paper using a direct method. The stability criteria established provide upper bounds on the number of pulses emitted by each modulator. The results are also applicable to those systems which contain a finite number of pulse frequency modulators and a finite number of combined pulse frequency and pulse width modulators

  13. 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...

  14. Magnetic frequency tuning of the microwave Gunn diode oscillator

    OpenAIRE

    Gorbatov, Sergey S.; A.A. Semenov; Usanov, Dmitry A.; Sorokin, A. N.; Kvasko, Vladimir Yu.

    2009-01-01

    It has been found experimentally that the oscillation frequency of a Gunn diode placed in the low-dimensional resonance system “metal pin–closely set short-circuiter” can be effectively controlled by magnetic field applied in the normal direction with respect to the waveguide wide wall.

  15. 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

  16. The impact of attention on judgments of frequency and duration.

    Directory of Open Access Journals (Sweden)

    Isabell Winkler

    Full Text Available Previous studies that examined human judgments of frequency and duration found an asymmetrical relationship: While frequency judgments were quite accurate and independent of stimulus duration, duration judgments were highly dependent upon stimulus frequency. A potential explanation for these findings is that the asymmetry is moderated by the amount of attention directed to the stimuli. In the current experiment, participants' attention was manipulated in two ways: (a intrinsically, by varying the type and arousal potential of the stimuli (names, low-arousal and high-arousal pictures, and (b extrinsically, by varying the physical effort participants expended during the stimulus presentation (by lifting a dumbbell vs. relaxing the arm. Participants processed stimuli with varying presentation frequencies and durations and were subsequently asked to estimate the frequency and duration of each stimulus. Sensitivity to duration increased for pictures in general, especially when processed under physical effort. A large effect of stimulus frequency on duration judgments was obtained for all experimental conditions, but a similar large effect of presentation duration on frequency judgments emerged only in the conditions that could be expected to draw high amounts of attention to the stimuli: when pictures were judged under high physical effort. Almost no difference in the mutual impact of frequency and duration was obtained for low-arousal or high-arousal pictures. The mechanisms underlying the simultaneous processing of frequency and duration are discussed with respect to existing models derived from animal research. Options for the extension of such models to human processing of frequency and duration are suggested.

  17. Roller Bearing Health Monitoring Using CPLE Frequency Analysis Method

    Science.gov (United States)

    Jong, Jen-Yi; Jones, Jess H.

    2007-01-01

    This paper describes a unique vibration signature analysis technique Coherence Phase Line Enhancer (CPLE) Frequency Analysis - for roller bearing health monitoring. Defects of roller bearing (e.g. wear, foreign debris, crack in bearing supporting structure, etc.) can cause small bearing characteristic frequency shifts due to minor changes in bearing geometry. Such frequency shifts are often too small to detect by the conventional Power Spectral Density (PSD) due to its frequency bandwidth limitation. This Coherent Phase Line Enhancer technology has been evolving over the last few years and has culminated in the introduction of a new and novel frequency spectrum which is fully described in this paper. This CPLE technology uses a "key phasor" or speed probe as a preprocessor for this analysis. With the aid of this key phasor, this CPLE technology can develop a two dimensional frequency spectrum that preserves both amplitude and phase that is not normally obtained using conventional frequency analysis. This two-dimensional frequency transformation results in several newly defined spectral functions; i. e. CPLE-PSD, CPLE-Coherence and the CPLE-Frequency. This paper uses this CPLE frequency analysis to detect subtle, low level bearing related signals in the High Pressure Fuel Pump (HPFP) of the Space Shuttle Main Engine (SSME). For many rotating machinery applications, a key phasor is an essential measurement that is used in the detection of bearing related signatures. There are times however, when a key phasor is not available; i. e. during flight of any of the SSME turbopumps or on the SSME High Pressure Oxygen Turbopump (HPOTP) where no speed probe is present. In this case, the CPLE analysis approach can still be achieved using a novel Pseudo Key Phasor (PKP) technique to reconstruct a 1/Rev PKP signal directly from external vibration measurements. This paper develops this Pseudo Key Phasor technique and applies it to the SSME vibration data.

  18. Determination of Electromagnetic Source Direction as an Eigenvalue Problem

    CERN Document Server

    Martínez-Oliveros, Juan C; Bale, Stuart D; Krucker, Säm

    2012-01-01

    Low-frequency solar and interplanetary radio bursts are generated at frequencies below the ionospheric plasma cutoff and must therefore be measured in space, with deployable antenna systems. The problem of measuring both the general direction and polarization of an electromagnetic source is commonly solved by iterative fitting methods such as linear regression that deal simultaneously with both directional and polarization parameters. We have developed a scheme that separates the problem of deriving the source direction from that of determining the polarization, avoiding iteration in a multi-dimensional manifold. The crux of the method is to first determine the source direction independently of concerns as to its polarization. Once the source direction is known, its direct characterization in terms of Stokes vectors in a single iteration if desired, is relatively simple. This study applies the source-direction determination to radio signatures of flares received by STEREO. We studied two previously analyzed r...

  19. Frequency weighted system identification and linear quadratic controller design

    Science.gov (United States)

    Horta, Lucas G.; Phan, Minh; Juang, Jer-Nan; Longman, Richard W.; Sulla, Jeffrey L.

    1991-01-01

    Application of filters for frequency weighting of Markov parameters (pulse response functions) is described in relation to system/observer identification. The time domain identification approach recovers a model which has a pulse response weighted according to frequency. The identified model is composed of the original system and filters. The augmented system is in a form which can be used directly for frequency weighted linear quadratic controller design. Data from either single or multiple experiments can be used to recover the Markov parameters. Measured acceleration signals from a truss structure are used for system identification and the model obtained is used for frequency weighted controller design. The procedure makes the identification and controler design complementary problems.

  20. Precision frequency measurement of visible intercombination lines of strontium.

    Science.gov (United States)

    Ferrari, G; Cancio, P; Drullinger, R; Giusfredi, G; Poli, N; Prevedelli, M; Toninelli, C; Tino, G M

    2003-12-12

    We report the direct frequency measurement of the visible 5s(2) 1S0-5s5p 3P1 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 global positioning system signal. The 88Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the 88Sr-86Sr isotope shift to be 163 817.4 (0.2) kHz.